JP2000250286A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a good color image that color slipping, etc., are suppressed by providing a registration mark detection device that controls deviation in detection of a registration mark due to movement of a carrying belt and improves precision in detection. SOLUTION: This registration mark detection device has a pair of a light source J by which light irradiation of a registration mark M is carried out and an optical sensor I to detect reflected light IL from the registration mark M caused by irradiation of light from the light source J. Then, the pair of the optical sensor I and the light source J are arranged so that the registration mark M that is parallel to a line of intersection Q1 of a plane W including the reflected beam IL emitted from the light source J to the registration mark M for detection of the registration mark and a carrying belt BL plane where the registration mark M is formed, is detected, and the pair is in axial symmetry to a normal direction axis H1 of the carrying belt BL plane.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus having a plurality of image forming units, and for transferring and fixing a predetermined color toner image formed by the image forming units on a recording medium conveyed by a conveying belt. Detecting a registration mark formed on the recording medium or on the transport belt corresponding to each of the plurality of color toner images, in order to detect a positional shift of the multicolor toner image on the recording medium. A color image forming apparatus provided with a registration mark detecting device.

[0002]

2. Description of the Related Art In a color image forming apparatus such as a color laser printer, a plurality of image forming sections are provided so that toner images of predetermined colors different from each other can be formed for each image forming section. There is a color image forming apparatus in which a predetermined color toner image is transferred onto a recording medium conveyed by a conveying belt and transferred and fixed.

In the field of such a color image forming apparatus, in order to obtain a color image by superposing a plurality of color toner images on a recording medium, it is necessary to superimpose a predetermined color toner image formed in each image forming section. A problem arises in that misalignment between the toner images (images) of the respective colors due to the alignment occurs. In other words, when the position between the toner images (images) of each color is shifted, the image obtained on the recording medium undergoes a change in tint or a color shift, and the image quality is significantly reduced. For this reason, such a color image forming apparatus is provided with, for example, a registration mark formed on a conveyance belt corresponding to each of the multicolor toner images in order to detect a positional shift of the multicolor toner images. And a correction unit that corrects the position of a predetermined color toner image formed in each image forming unit according to the positional deviation amount of each color toner image detected by the detection device. Often have.

The registration mark detecting device for detecting a registration mark formed on the conveyor belt has the following problems. That is, if the belt flaps due to the movement of the surface of the transport belt, a detection error of the registration mark due to the flutter of the transport belt may occur. Further, if a good contrast between the conveyor belt and the registration marks of the respective colors formed thereon is not obtained, the detection accuracy tends to decrease.

Therefore, in such a registration mark detecting device, detection accuracy is ensured by suppressing the occurrence of detection errors due to the fluttering of the conveyor belt and obtaining a good contrast between the conveyor belt and the registration marks of each color. It is important to: In order to secure the detection accuracy by obtaining a good contrast between the conveyor belt and the registration mark of each color, for example, Japanese Patent Application Laid-Open No. Sho 63-3002
In Japanese Patent No. 62, a registration mark of each color formed in the registration mark formation region is detected by making the formation region of the registration mark on the color (for example, orange) transfer belt white achromatic. It is disclosed that the device can be easily identified.

Further, in order to suppress the occurrence of a detection error due to fluttering of the conveyor belt, for example, a light source and a detector for detecting reflected light reflected on a registration mark on the conveyor belt by light irradiation from the light source. A registration mark detection device including an optical sensor, and by arranging the direction of incidence of reflected light on the detection optical sensor and the normal direction of the surface of the conveyor belt to be aligned, the registration due to fluttering of the conveyor belt, etc. It has also been proposed to suppress the occurrence of mark detection errors.

[0007]

SUMMARY OF THE INVENTION However, Japanese Patent Application Laid-Open
In the registration mark detection taught by JP-A-300262, a white achromatic area must be formed in a part of a colored conveyor belt, which is disadvantageous in cost compared to using a uniform color conveyor belt. This is inevitable. Also, with the use of the conveyor belt, the registration mark forming area of the white achromatic portion becomes stained with time, which causes a problem that the contrast with the registration mark of each color is reduced and a registration mark detection error occurs. is there.

Further, in a registration mark detecting device in which a detection optical sensor is arranged so that the light incident direction on the detection sensor and the normal direction of the surface of the conveyor belt coincide with each other, the diffused light of the registration mark illumination is used. Therefore, the contrast of the detected registration mark of each color is low, and the detection accuracy tends to decrease. Therefore, the present invention provides a color image forming apparatus having a plurality of image forming units, wherein a predetermined color toner image formed by the image forming unit is transferred onto a recording medium conveyed by a conveyor belt and is fixed thereon. A registration mark detecting device for detecting registration marks formed on the recording medium or on the transport belt corresponding to the plurality of color toner images, respectively, in order to detect a positional shift of the multi-color toner image. A color image forming apparatus, wherein the registration mark detection error due to the fluttering of the conveyor belt can be suppressed to a small value, and a good contrast can be obtained even when the registration mark is detected on the conveyor belt of an arbitrary color. Equipped with a registration mark detection device that can be set high, thereby obtaining a good color image with suppressed color shift and the like. And to provide an image forming apparatus.

[0009]

SUMMARY OF THE INVENTION The present invention provides the following first and second color image forming apparatuses to solve the above-mentioned problems. (1) First Color Image Forming Apparatus A color image forming apparatus having a plurality of image forming units, in which a predetermined color toner image formed by the image forming unit is transferred onto a recording medium conveyed by a conveying belt, transferred and fixed. Detecting a registration mark formed on the recording medium or on the transport belt corresponding to each of the plurality of color toner images, in order to detect a positional shift of the multicolor toner image on the recording medium. A color image forming apparatus provided with a registration mark detection device, wherein the registration mark detection device includes at least one pair of a light source for irradiating the registration mark with light and reflection from the registration mark due to light irradiation from the light source. A light sensor for detecting light, wherein the paired light sensor and the light source are incident light beams from the light source to the registration mark for detecting the registration mark. Parallel to the intersection line between the plane including the reflected light beam from the registration mark toward the optical sensor and the recording medium surface or the conveyance belt surface on which the registration mark is formed (not only in the case of being completely parallel but also in the parallel state). (Including the case of being substantially parallel which may be regarded as being considered).
It is arranged axially symmetric with respect to the normal axis of the recording medium surface or the conveyance belt surface (including not only the case of complete axial symmetry but also the case of substantially axial symmetry that may be regarded as axial symmetry). A color image forming apparatus. (2) Second Color Image Forming Apparatus A color image forming apparatus having a plurality of image forming units, in which a predetermined color toner image formed by the image forming unit is overlaid on a recording medium conveyed by a conveying belt and fixed. Detecting a registration mark formed on the recording medium or on the transport belt corresponding to each of the plurality of color toner images, in order to detect a positional shift of the multicolor toner image on the recording medium. A color image forming apparatus including a registration mark detection device for detecting the registration mark, wherein the registration mark includes a V-shaped line composed of two lines crossing a conveyance direction of the recording medium by the conveyance belt. The apparatus comprises a pair of light sources for irradiating the registration mark with light and a light sensor for detecting reflected light from the registration mark due to light irradiation from the light source. The light sensor and the light source are formed with a plane including an incident light beam from the light source toward the registration mark and a reflected light beam from the registration mark toward the light sensor for the registration mark detection, and the registration mark is formed. The optical sensor and the light source corresponding to each other are such that the line of intersection with the recording medium surface or the conveyance belt surface falls within the acute angle range of two lines forming the V-shaped line in the registration mark. It is arranged axially symmetrical with respect to the normal axis of the recording medium surface or the conveying belt surface (including not only the case of complete axial symmetry but also the case of substantially axial symmetry which may be regarded as axial symmetry). A color image forming apparatus, comprising: According to the first and second color image forming apparatuses according to the present invention, it is possible to detect the registration marks formed on the recording medium or the conveyance belt corresponding to the multicolor toner images by the registration mark detection device. Based on this detection value, the displacement of the multicolor toner image can be obtained.

In the first and second color image forming apparatuses, a pair of the optical sensor and the light source in the registration mark detecting device are the normal axis of the recording medium surface or the conveyance belt surface, and The mark is axially symmetric with respect to a normal axis intersecting the normal passage of a predetermined portion of the mark. The pair of optical sensors and the light source arranged in this manner detect registration marks formed on the recording medium or the transport belt corresponding to the multicolor toner images, respectively.

That is, light is emitted from the light source to the resist mark. At this time, since the light sensor and the light source corresponding to each other are disposed axially symmetrically with respect to the normal direction axis, the incident light of light emitted from the light source to the registration mark and the light reflected by the registration mark are reflected. The light beam reflected toward the corresponding light sensor is axially symmetric with respect to the normal axis. Thus, the optical sensor can detect light that is regularly reflected on the registration mark by light irradiation from the corresponding light source. By arranging the optical sensor and the light source corresponding to each other in a regular reflection relationship with respect to the registration mark in this manner, it is possible to increase the SN ratio of a detection signal by the optical sensor, and Detection can be performed with a high contrast with the registration mark. This makes it possible to accurately detect a registration mark on a recording medium of an arbitrary color or on a transport belt of an arbitrary color.

Further, in the first color image forming apparatus according to the present invention, the light sensor and the light source forming a pair in the registration mark detecting device may include an incident light beam directed from the light source to the registration mark for detecting the registration mark. And a registration mark parallel to an intersection of the plane including the reflected light beam from the registration mark toward the optical sensor and the recording medium surface or the conveyance belt surface on which the registration mark is formed. I have.

[0013] In the second color image forming apparatus according to the present invention, the registration mark includes a V-shaped line composed of two lines crossing the conveying direction of the recording medium by the conveying belt. The pair of optical sensors and the light source in the registration mark detection device are a plane including an incident light beam from the light source toward the registration mark and a reflected light beam from the registration mark toward the optical sensor for detection of the registration mark, and the registration mark. The line of intersection with the surface of the recording medium or the surface of the transport belt to be formed may fall within an acute angle range of two lines forming a V-shaped line in the registration mark.

According to the arrangement of the light sensor and the light source with respect to the registration mark line, the first and second color image forming apparatuses of the present invention can reduce the registration mark position detection error due to the flutter of the conveyor belt. However, prior to the description, a pair of optical sensor and light source in the registration mark detection device may include an incident light beam from the light source to the registration mark and a reflected light beam from the registration mark to the optical sensor for the registration mark detection. To detect a registration mark line that is not parallel to the intersection line between the plane including the mark and the recording medium surface or the conveyance belt surface on which the registration mark is formed, and the axis of the recording medium surface or the conveyance belt surface in the normal direction. Are arranged axially symmetrically with respect to the normal direction axis intersecting the regular path of the predetermined portion of the registration mark line Occurrence of the registration mark detection error due to fluttering of the conveyor belt case will be described.

In this case, the transport belt flaps,
When the predetermined portion of the registration mark line passes through a position deviated from the normal path, the light emitting line from the light source to the predetermined portion or the light emitting line from the predetermined portion to the optical sensor passes through the normal path. It crosses earlier or later in time than when traveling, whereby the optical sensor detects the predetermined portion earlier or later than when it travels the regular path. This means that the registration mark position detected by the optical sensor differs due to the fluttering of the conveyor belt, and this appears as a registration mark position detection error.

The registration mark detection error is caused by a plane including an incident light beam from the light source toward the registration mark and a reflected light beam from the registration mark toward the optical sensor for detecting the registration mark, and the surface of the recording medium on which the registration mark is formed. Alternatively, it occurs due to the relationship between the direction of the line of intersection with the conveyor belt surface and the direction of the registration mark line. For example, when the direction of the intersection line is oblique to a direction orthogonal to the recording medium conveyance direction, and the direction of the registration mark line is orthogonal to the recording medium conveyance direction, Since the direction is not parallel to the direction perpendicular to the recording medium transport direction, when the transport belt flaps, the registration mark position detected by the optical sensor is different, and a registration mark detection error due to the transport belt flutter occurs. This will be specifically described below with reference to FIG.

Further, for example, when the direction of the intersection line is orthogonal to the recording medium transport direction and the direction of the registration mark line is oblique to the direction orthogonal to the recording medium transport direction, Since the direction of the registration mark line and the direction orthogonal to the recording medium conveyance direction are not parallel, when the conveyance belt flaps, the registration mark position detected by the optical sensor is different, and the registration mark detection by the conveyance belt flap is performed. An error occurs. This will be specifically described below with reference to FIG.

FIG. 2 illustrates the following. That is,
The paired optical sensor I and light source J are arranged axially symmetrically with respect to a normal axis H1 on the conveyance belt BL surface and a normal axis H1 intersecting a normal path of a predetermined portion of the registration mark line M. The direction of an intersecting line Q1 between a plane W including the incident light beam JL from the light source J toward the registration mark line M and the reflected light beam IL from the registration mark line M toward the optical sensor I and the surface of the conveyance belt BL is in the conveyance direction V. When the conveyor belt BL does not flutter (solid line in the figure) in a state where the registration mark line M is orthogonal to the conveyance direction V, the direction approaches the optical sensor I and the light source J. The detection state of the registration mark line M when fluttering over U (broken line in the figure) is shown.

FIG. 3 illustrates the following. That is,
The paired optical sensor I and light source J are arranged axially symmetrically with respect to a normal axis H1 on the conveyance belt BL surface and a normal axis H1 intersecting a normal path of a predetermined portion of the registration mark line M. The direction of an intersecting line Q1 between a plane W including the incident light beam JL from the light source J toward the registration mark line M and the reflected light beam IL from the registration mark line M toward the optical sensor I and the surface of the conveyance belt BL is in the conveyance direction V. When the conveyance belt BL does not flutter (solid line in the figure) in a state where the registration mark line M is oblique to the conveyance direction V, the direction approaches the optical sensor I and the light source J The detection state of the registration mark line M when fluttering over U (broken line in the figure) is shown.

The registration mark line M shown in FIGS. 2 and 3 indicates the same timing position when the conveyor belt BL is not fluttering (solid line in the drawing) and when it is fluttering (dashed line in the drawing). In the figure, IL ′ is a reflected light beam when the conveyor belt BL flutters, a solid line G0 (intersecting line Q1) is a chain line G1 when the conveyor belt BL does not flutter, and a chain line G1 is when the conveyor belt BL does not flutter. This is a registration mark detection line detected by the optical sensor I when fluttering. The chain line G0 'is a registration mark detection line to be detected when the transport belt BL is fluttering and is not fluttering.
Although the optical sensor I is shown small in the figure, it is actually large enough to detect the reflected light beam IL ′.

In the pair of the optical sensor I and the light source J shown in FIGS. 2 and 3, when the conveyor belt BL fluctuates, the registration mark line M is detected from the light source J to a predetermined portion of the registration mark line M. The light reflected at the intersection of the incident light beam JL and the surface of the conveyor belt BL (detected based on the light source side) with reference to the light projecting line (incident light beam JL), It is conceivable that the light reflected at the intersection of the reflected light beam IL and the surface of the conveyor belt BL is detected (detected based on the sensor side) based on the light projecting line (reflected light beam IL) to the sensor I.
Regarding the registration mark detection in FIGS. 2 and 3, in the case of detection based on the light source side reference and the case of detection based on the sensor side reference, it is determined whether the detection is earlier or later with respect to the direction of flutter of the conveyor belt BL. Only in the opposite case, both cases can be explained with substantially the same concept.
Therefore, in the following description, the case of detection based on the light source side reference will be described, and the description of the case of detection based on the sensor side reference will be omitted.

As shown in FIG. 2, when the conveyor belt BL is not fluttering (solid line in the figure), the registration mark line M is at the registration mark detection line G0 (intersection line Q1) detected by the optical sensor I. It is detected at the detection position R0. When the conveyor belt BL is fluttering in the U direction in the figure (broken line in the figure), the registration mark line M should be detected at the detection position R0 'on the registration mark detection line G0'. Line G0 '
Does not match the registration mark detection line G1,
The line G1 has already passed the position of the line G0 ', and when passing through the position of the line G0', it has been detected at the detection position R1 'on the line G1. Accordingly, the optical sensor I sets the line M to the detection position R1 and the detection position R when the conveyance belt BL is fluttering more than when the conveyance belt BL is not fluttering.
1 'is detected earlier by the distance (distance R in the figure) of the difference from 1'.
As a result, a detection error occurs due to the fluttering of the transport belt BL. Although not shown, even when the conveyor belt BL flutters in the direction away from the optical sensor I and the light source J, the registration mark detection line G0 'and the registration mark detection line G1 do not coincide with each other. Sensor I
When the conveyor belt BL is fluttering, the line M is detected later than when the conveyor belt BL is not fluttering, and in any case, a detection error due to the fluttering of the conveyor belt BL occurs.

Further, as shown in FIG.
When it does not flutter (solid line in the figure), the registration mark line M is detected at the detection position R0 on the registration mark detection line G0 (intersecting line Q1) detected by the optical sensor I. When the conveyor belt BL is fluttering in the U direction in the figure (broken line in the figure), the registration mark line M is inclined with respect to the direction orthogonal to the conveyance direction V. Mark detection line G1
Does not match the registration mark detection line G0 'to be detected when the conveyor belt BL is not fluttering, and the registration mark line M has not yet been detected by the optical sensor I at the detection position R0'. Thereafter, the line M advances in the transport direction V with the movement of the surface of the transport belt BL, and is detected at the detection position R1 on the registration mark detection line G1. Accordingly, the optical sensor I detects the line M when the transport belt BL is fluttering later by the difference distance (the distance R in the figure) between the detection position R1 and the detection position R0 ′ than when the conveyance belt BL is not fluttering. I do. As a result, a detection error occurs due to the fluttering of the transport belt BL. Although not shown, even when the conveyor belt BL flutters in the direction away from the optical sensor I and the light source J, the registration mark detection line G0 'and the registration mark detection line G1 do not coincide with each other. The sensor I detects the line M earlier when the transport belt BL is fluttering than when it is not fluttering, and in any case, a detection error occurs due to the fluttering of the transport belt BL.

Therefore, for example, a case where the direction of the intersection line and the direction of the registration mark line are parallel will be specifically described with reference to FIG. FIG. 1 illustrates the following. That is, the paired optical sensor I and light source J in the registration mark detecting device
The normal axis H1 of the L plane and the registration mark line M
Are arranged axially symmetrically with respect to the normal axis H1 intersecting the normal path of the predetermined portion of the predetermined portion, and the incident light beam JL from the light source J toward the registration mark line M and the registration mark line M
When the direction of the intersecting line Q1 between the plane W including the reflected light beam IL traveling toward the optical sensor I and the plane of the conveyor belt BL and the direction of the registration mark line M are parallel, the conveyor belt BL flaps. The detection state of the registration mark line M when there is no light (solid line in the figure) and when the light flutters in the direction U approaching the light sensor I and the light source J (dashed line in the figure) are shown.

In this example, the direction of the intersecting line Q1 and the direction of the registration mark line M are oblique to the transport direction V on the transport belt BL. The registration mark line M shown in FIG. 1 is when the conveyor belt BL is not fluttering (solid line in the figure) or when it is fluttering (dashed line in the figure).
Both show the same timing position. Also, IL ′ in the figure
Is a reflected light beam when the conveyor belt BL is fluttering, a solid line G0 (intersecting line Q1) is a reflected light beam when the conveyor belt BL is not fluttering, and a chain line G1 is a conveyor belt B when the conveyor belt BL is not fluttering.
This is a registration mark detection line detected by the optical sensor I when L flaps. The chain line G0 'is a registration mark detection line to be detected when the transport belt BL is fluttering and is not fluttering. Although the optical sensor I is shown small in the figure, it is actually large enough to detect the reflected light beam IL ′.

In the paired optical sensor I and light source J shown in FIG. 1, similarly to the optical sensor I and light source J shown in FIGS. Detects the light reflected at the intersection of the incident light beam JL and the surface of the conveyor belt BL with reference to the light projecting line (incident light beam JL) from the light source J to the registration mark line M (detected based on the light source side) ), The light reflected at the intersection of the reflected light beam IL and the surface of the conveyor belt BL is detected based on the light projecting line (reflected light beam IL) from the predetermined portion of the registration mark line M to the optical sensor I (sensor side). Detection based on a reference). Regarding the registration mark detection in FIG. 1, the detection position based on the light source side reference and the detection based on the sensor side reference differ only in the reflection position of the light from the light source J at a predetermined portion on the registration mark line M. Either case can be described with substantially the same concept. Therefore, in the following description, the case of detection based on the light source side reference will be described, and the description of the case of detection based on the sensor side reference will be omitted.

As shown in FIG. 1, when the conveyor belt BL is not fluttering (solid line in the figure), the registration mark line M is at the registration mark detection line G0 (intersection line Q1) detected by the optical sensor I. It is detected at the detection position R0. When the conveyor belt BL is fluttering in the U direction in the figure (broken line in the figure), the registration mark line M is
At the detection position R1 on the registration mark detection line G1. In this case, the registration mark detection line G1 and the registration mark detection line G0 'to be detected when the conveyor belt BL is not fluttering are at substantially the same position (both on the plane W). Accordingly, the optical sensor I detects the line M at the detection position R0 when the transport belt BL is not fluttering, and detects the line M at the detection position R1 when it is fluttering. Thereby, the position detection error due to the fluttering of the transport belt BL does not substantially occur. Although not shown, when the transport belt BL flutters in the direction away from the optical sensor I and the light source J,
The registration mark detection line G0 'and the registration mark detection line G1 are at substantially the same position (both on the plane W). Accordingly, also in this case, the optical sensor I detects the line M at substantially the same time regardless of whether the transport belt BL is fluttering or not, and in any case, the detection due to the fluttering of the transport belt BL. No error occurs substantially.

As described above, the paired optical sensor and the light source in the registration mark detecting device include the incident light beam from the light source toward the registration mark and the reflected light beam from the registration mark toward the optical sensor for detecting the registration mark. If the registration mark line is detected so as to be parallel to the intersection of the plane and the recording medium surface or the conveyance belt surface on which the registration mark is formed, the detection error due to the fluttering of the conveyance belt does not substantially occur.

In the first color image forming apparatus according to the present invention, as described above, the light sensor and the light source forming a pair are a plane including the incident light beam and the reflected light beam and the recording medium surface or the transport belt. The optical sensor is arranged so as to detect a registration mark line parallel to the line of intersection with the surface, so that the optical sensor detects the predetermined portion of the registration mark line, the transport belt does not flutter, and therefore the registration mark Either when the predetermined portion of the line is traveling along the regular path, or when the conveyor belt is fluttering and the predetermined portion of the registration mark passes through a position shifted from the regular passage, Regardless of the flutter, the registration mark detection error can be substantially eliminated. Strictly speaking, the optical path length of the paired optical sensor and the light source from the light source to the optical sensor fluctuates due to the flapping of the conveyor belt, and the light traveling time from the light source to the optical sensor fluctuates. The detection error due to this is extremely small and can be ignored.

In the above-described optical sensor and the light source, the intersection line between the plane including the incident light beam and the reflected light beam and the recording medium surface or the conveyance belt surface is not “completely parallel” to the registration mark line. As an example of the case where the photosensor is arranged so as to be “substantially parallel”, for example, the normal position of the registration mark position obtained by detecting the light reflected specularly by the registration mark line (the conveying belt is not fluttering) Case) is small (for example, on the order of microns). Further, the case may be within a range of a predetermined allowable detection error.

In any case, in the first color image forming apparatus, when detecting the image position shift in the recording medium conveyance direction, the plane including the incident light beam and the reflected light beam and the recording medium surface or the recording medium surface. The direction of the line of intersection with the conveying belt surface may be a direction that is not parallel to the conveying direction, that is, a direction that crosses the conveying direction (for example, a direction that is oblique to the conveying direction or a direction that is orthogonal to the conveying direction). That is,
The paired optical sensor and light source can be installed to detect the registration mark line that is not parallel to (transverses) the transport direction. In this case, the detection error of the image position shift in the transport direction can be suppressed small. Further, when detecting a displacement in a direction orthogonal to the recording medium transport direction, the direction of an intersection line between the plane including the incident light beam and the reflected light beam and the recording medium surface or the transport belt surface is determined in the transport direction. Can be parallel. That is, a pair of optical sensor and light source can be installed to detect the registration mark line parallel to the transport direction. In this case, the detection error of the image position shift in the direction orthogonal to the transport direction can be suppressed small.

When detecting the image position deviation in the recording medium transport direction, the amount of deviation of the detection position of the registration mark line of each color in the transport direction can be obtained by using a pair of optical sensors and light sources. For example, from a predetermined detection reference time (for example, when the light sensor starts emitting light from the light source before the light sensor performs a detection operation) to a time when the light sensor detects light reflected regularly on the registration mark line. The time is detected, and the difference between the detected time and the time when there is no displacement can be used to determine the displacement amount of each color registration mark line in the transport direction, and furthermore, the displacement amount between the color toner images. in this case,
Since the optical sensor and the light source detect a registration mark line that is not parallel to the recording medium conveyance direction, a detection error in the conveyance direction can be suppressed to a small value. Therefore, it is possible to accurately detect a displacement of the registration mark line in the conveyance direction. Can be.

When detecting the positional deviation in the direction perpendicular to the recording medium transport direction, the deviation of the detection position of the registration mark line of each color in the direction perpendicular to the transport direction is detected by a pair of optical sensor and light source. The quantity can be determined. For example, a line sensor (for example, a plurality of cells (detection elements) in which a registration mark line of each color is shifted in a direction orthogonal to the conveyance direction as a light sensor) (A multi-cell division type line sensor arranged in the same direction), the shift amount of the detection position of the registration mark line of each color in the direction orthogonal to the conveyance direction, and the shift amount between the toner images of each color can be obtained. In this case, since the paired optical sensor and the light source detect the registration mark line parallel to the recording medium conveyance direction, the detection error in the direction orthogonal to the conveyance direction can be suppressed to a small value. The displacement in the direction orthogonal to the direction can be accurately detected.

Therefore, in the first color image forming apparatus according to the present invention, the registration mark includes a line parallel to a direction of conveyance of the recording medium by the conveyance belt and a line parallel to a direction perpendicular to the conveyance direction. Wherein the registration mark detection device includes two pairs of optical sensors and a light source, and one pair of the two pairs of optical sensors and the light sources is parallel to a direction orthogonal to the transport direction. The case where the other pair is arranged to detect a line parallel to the transport direction so as to detect a line can be exemplified. In this case, it is possible to detect the positional deviation of the registration mark in the recording medium transport direction and to detect the positional deviation in the direction orthogonal to the recording medium transport direction.

In the second color image forming apparatus according to the present invention, as described above, the registration mark is a V-shaped line composed of two lines crossing the conveying direction of the recording medium by the conveying belt. Contains. And
The optical sensor and the light source are a plane including the incident light beam from the light source toward the registration mark and the reflected light beam from the registration mark toward the optical sensor for detecting the registration mark, and the recording medium surface on which the registration mark is formed. The line of intersection with the conveyor belt surface is V in the registration mark.
The two lines forming the character-shaped line are set so as to fall within the acute angle range, so that a pair of the optical sensor and the light source are a plane including the incident light beam and the reflected light beam and a surface of the recording medium. Alternatively, each line of the V-shaped line not parallel to the line of intersection with the conveyor belt surface is detected. Therefore, as described above (see FIG. 1 and the description thereof), it is not possible to eliminate registration mark detection errors due to the fluttering of the transport belt. However, each line of the V-shaped line can be brought as close as possible to a direction parallel to the intersection line, so that a registration mark detection error due to fluttering of the conveyor belt can be suppressed.

In the V-shaped line, one of the lines may be parallel to a direction orthogonal to the transport direction, and both lines are oblique to the transport direction. You may. In the second color image forming apparatus, the recording medium conveyance direction (sub-scanning direction) is determined based on the detection position information of both or any one of the two V-shaped lines that cross the recording medium conveyance direction. In the scanning direction), the amount of misregistration between the registration marks of the respective colors and the amount of misregistration between the toner images of the respective colors can be obtained. In addition, from the detection position information between the detection position of one of the V-shaped lines by the registration mark detection device and the detection position of the other line portion by the registration mark detection device, the recording medium conveyance is performed. The amount of displacement between the registration marks of each color in the direction (main scanning direction) orthogonal to the direction, and thus the amount of displacement between the toner images of each color, can be obtained. Therefore, if the acute angle of each line of the V-shaped line is too large, the registration mark detection error is likely to occur, and if it is too small, the positional deviation of the registration mark between the color registration marks in the direction orthogonal to the recording medium transport direction. A quantity error is likely to occur. The position at which the line of intersection between the plane including the incident light beam and the reflected light beam and the recording medium surface or the conveyance belt surface falls within the acute angle range of each line of the V-shaped line is the acute angle angle. Can be exemplified.

As described above, according to the first and second color image forming apparatuses according to the present invention, the registration mark detection error due to the fluttering of the conveyor belt can be suppressed to a small value, and the color mark on the conveyor belt of an arbitrary color can be suppressed. A good contrast can be obtained even in the registration mark detection, and a registration mark detection device capable of improving the detection accuracy is provided, whereby a good color image in which color shift and the like are suppressed can be obtained.

As a method of detecting the positional shift of each color toner image,
On a recording medium conveyance belt or on a recording medium conveyed by the conveyance belt, while forming a registration mark row composed of a plurality of registration marks of the same color displaced in a direction orthogonal to the recording medium conveyance direction, Such a registration mark row is sequentially formed by shifting the position in the recording medium conveyance direction for each color, and a registration mark detection device is formed in a direction orthogonal to the recording medium conveyance direction in correspondence with each registration mark in the registration mark row in the direction. By arranging and sequentially detecting the registration marks of each color arranged in the recording medium conveyance direction by each registration mark detection device, each registration mark in a direction (main scanning direction) orthogonal to the recording medium conveyance direction in an image finally obtained is obtained. The color shift in the recording medium transport direction (sub-scanning direction) at the portion and the color shift in the direction (main scanning direction) orthogonal to the recording medium transport direction. There is a method of detecting the respective deviation.

Therefore, in any of the first and second color image forming apparatuses according to the present invention, the position of the recording medium is shifted in the direction orthogonal to the direction of conveyance of the recording medium by the conveyance belt or on the recording medium or the conveyance medium. In order to detect a plurality of the registration marks formed on the belt,
The registration mark detection devices can be arranged in a direction perpendicular to the recording medium conveyance direction in correspondence with the respective registration marks.

In addition, the registration mark detection device detects the registration deviation between the registration marks of each color, for example, with reference to the registration mark of any color (for example, black), the amount of registration deviation between the registration marks of each color, and thus the toner of each color. This can be performed by detecting the amount of displacement between images. Based on this information, it is possible to correct the positional deviation of each color toner image.

[0041]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 4 is a side view showing a schematic configuration of an example of a full-color image forming apparatus provided with a registration mark detecting device according to an embodiment of the present invention. FIG. 5 is a laser scanning optical device in the image forming apparatus shown in FIG. 4,
FIG. 3 is an exploded perspective view of a photoconductor, a transfer / transport device, and a registration mark detection device as viewed from above a sheet discharge side.

The full-color image forming apparatus shown in FIG. 4 is an electrophotographic type image forming apparatus. They are arranged in order along a certain direction. Image forming unit 100
c to 100k are drum-shaped photoconductors 1c, 1c,
m, 1y, and 1k. The laser scanning optical device 3 is disposed above the photoconductors 1c to 1k.

Around each photoconductor 1c-1k,
Main charger 2c, 2m, 2y, 2k, developing device 4
c, 4m, 4y, 4k, transfer chargers 6c, 6m, 6
y, 6k, cleaning blades 7c, 7m, 7y, 7
k and the discharge lamps 8c, 8m, 8y, 8k are arranged in this order. The photoconductors 1c to 1k are respectively driven to rotate in the X direction in the drawing. Transfer charger 6c ~
6k face the photoconductors 1c to 1k, respectively, and form transfer sites Pc, Pm, Py, and Pk in the figure.

A transfer / conveyance device 600 is provided below the transfer sites Pc to Pk. The apparatus 600 includes transfer chargers 6c to 6k, a tension roller 62, a driving roller 63, a driven roller 61, and a transport belt 60 wound around these rollers.
It is constituted by. The transport belt 60 is driven in the V direction in the figure as the driving roller 63 rotates in the Y direction in the figure, and sequentially passes through the transfer portions Pc to Pk.

In the transfer device 600, the transfer chargers 6c to 6c
6k, power supplies PW3c, PW3m,
Transfer voltages can be applied from PW3y and PW3k, whereby the respective toner images on the photoconductors 1c to 1k can be overlaid and transferred onto the recording medium S conveyed by the conveyance belt 60. The recording medium S is held on the conveyor belt 60 by an electrostatic or mechanical holding device (not shown), and is conveyed in the direction V in the drawing. Further, a registration mark detection device 5 described later
In the detection of image misregistration by 1, 52, and 53, registration marks of a predetermined shape formed on each of the photoconductors 1c to 1k can be transferred onto the transport belt 60.

A timing roller pair 11 is provided on the right side of the transport device 600 in the figure, and a paper feeding unit (not shown) is provided. On the left side, registration mark detection devices 51 to 53 and a fixing roller pair 14 are sequentially provided, and a discharge roller pair and a paper discharge tray (not shown) are further provided. The registration mark detection device 51
4 are arranged at intervals in the direction V in the figure, downstream of the image forming unit 100k, above the conveyor belt 60, and in a direction perpendicular to the conveyance direction V as shown in FIG. I have.

The main chargers 2c to 2k can apply a high voltage from the power supplies PW1c, PW1m, PW1y, and PW1k, respectively, thereby charging the photoconductors 1c to 1k. The developing devices 4c to 4k include developing rollers 41c, 41m, 41y, and 41k, and a device case 4 respectively.
2c, 42m, 42y, and 42k, and the device cases 42c to 42k are respectively a cyan developer Dc, a magenta developer Dm, a yellow developer Dy, and a black developer Dk.
To accommodate. The developers Dc to Dk include cyan toner, magenta toner, yellow toner, and black toner, respectively. The developing rollers 41c to 41k are respectively driven to rotate, and the power sources PW2c, PW2m, PW2y, PW2
The developing bias voltage can be applied from k. Thereby, the electrostatic latent images on the photoconductors 1c to 1k can be developed.

As shown in FIG. 5, the laser scanning optical device 3 includes laser emitting units 310a and 310b and a laser deflecting unit 32.
0, laser imaging units 330a, 330b, laser reflecting unit 3
40a and 340b. Laser emitting unit 3
10a, laser imaging section 330a, laser reflection section 340a
Is located upstream of the laser deflecting unit 320 in the transport direction V of the recording medium S by the transport belt 60, and the laser emitting unit 310b, the laser imaging unit 330b, and the laser reflecting unit 340b are located downstream.

The laser beams Lc and Lm are emitted from the laser emitting section 3
After being emitted from the laser deflector 10a and entering the laser deflecting unit 320, the light is deflected by the deflecting unit 320 in the main scanning direction parallel to the direction orthogonal to the transport direction V, and is exposed through the laser imaging unit 330a and the laser reflecting unit 340a. An image is formed on the surface of the body 1c, 1m. Thereby, an electrostatic latent image can be formed on the photoconductors 1c and 1m. The laser beams Ly and Lk are emitted from the laser emitting unit 310b, are incident on the laser deflecting unit 320, are deflected in the main scanning direction by the deflecting unit 320, and are respectively transmitted through the laser imaging unit 330b and the laser reflecting unit 340b. An image is formed on the surfaces of the photoconductors 1y and 1k. Thus, an electrostatic latent image can be formed on the photoconductors 1y and 1k.

The laser deflection section 320 includes the deflector 30 and the deflection substrate 30 '. The deflector 30 is a rotary polygon mirror (here, a hexahedral polygon mirror), and is disposed on the substrate 30 'via a polygon motor (not shown).
The deflector 30 is rotated in the direction D in FIG. Thereby, the laser emitting unit 310
a, the laser beams Lc, Lm respectively emitted toward the laser imaging unit 330a, and the laser beams Ly, L respectively emitted from the laser emission unit 310b.
k can be deflected in the main scanning direction toward the laser imaging section 330b.

The laser emitting section 310a is connected to the laser light source 31.
c, 31m, collimator lenses 32c, 32m, a combining mirror 33a, and a cylindrical lens 34a. Here, the laser light sources 31c and 31m are laser diodes, and can emit laser beams Lc and Lm for forming electrostatic latent images corresponding to cyan and magenta images on the photoconductors 1c and 1m, respectively. The collimator lenses 32c and 32m can convert the laser beams Lc and Lm emitted from the laser light sources 31c and 31m into parallel light beams. The combining mirror 33a reflects the laser beam Lc passing through the collimator lens 32c and transmits the laser beam Lm. Thereby, the laser beams Lc and Lm can be incident on the cylindrical lens 34a. The cylindrical lens 34a can narrow the laser beams Lc and Lm from the combining mirror 33a to the polarizing section 320.

The laser imaging section 330a is provided with a scanning lens 35.
a, 35a ', 38c, and 38m. Lens 3
5a, 35a 'and 38c apply the laser beam Lc from the laser deflecting unit 320, and the lenses 35a, 35a' and 38m apply the laser beam Lm from the laser deflecting unit 320 to the photoconductors 1c and 1m via the laser reflecting unit 340a. I can form an image.

The laser reflecting section 340a is provided with the separating mirror 36.
a, folding mirrors 36a ', 36a ", 37a. The mirror 36a can reflect the laser beam Lm from the lens 35a' and guide it to the mirror 36a ',
The laser beam Lc can be transmitted. The mirror 36a 'can reflect the beam Lm from the mirror 36a and guide it to the mirror 36a ", and the mirror 36a" can reflect the beam Lm and guide it to the scanning lens 38m. Mirror 3
7a can reflect the laser beam Lc passing through the mirror 36a from the lens 35a 'and guide it to the scanning lens 38c.

Laser emitting section 310b, laser image forming section 33
0b and the laser reflecting unit 340b
10a, laser imaging section 330a, laser reflection section 340a
, And these components are symmetrically arranged with respect to the laser deflection unit 320. That is, the laser emitting unit 310b includes the laser light sources 31y and 31k, the collimator lens 32y,
32k, synthetic mirror 33b, cylindrical lens 34
b. The laser light sources 31y and 31k are composed of laser diodes, and can emit laser beams Ly and Lk for forming electrostatic latent images corresponding to yellow and black images on the photoconductors 1y and 1k, respectively. The collimator lenses 32y and 32k can convert the laser beams Ly and Lk into parallel light beams. The combining mirror 33b transmits the laser beam Ly and reflects the laser beam Lk. This allows the laser beams Ly and Lk to be incident on the cylindrical lens 34b. The cylindrical lens 34 b can narrow the laser beams Ly and Lk to the polarization section 320.

The laser imaging section 330b is provided with a scanning lens 35.
b, 35b ', 38y, and 38k. Lens 3
5b, 35b 'and 38y apply the laser beam Ly from the laser deflecting unit 320, and the lenses 35b, 35b' and 38k apply the laser beam Lk from the laser deflecting unit 320 to the photoconductors 1y and 1k via the laser reflecting unit 340b. I can form an image.

The laser reflecting section 340b is connected to the separation mirror 36.
b, folding mirrors 36b ', 36b "and 37b. The mirror 36b can reflect the laser beam Ly from the lens 35b' and guide it to the mirror 36b '.
The laser beam Lk can be transmitted. The mirror 36b 'can reflect the beam Ly from the mirror 36b and guide it to the mirror 36b ", and the mirror 36b" can reflect the beam Ly and guide it to the scanning lens 38y. Mirror 3
7b can reflect the laser beam Lk passing through the mirror 36b from the lens 35b 'and guide it to the scanning lens 38k.

As shown in FIG.
Each of c to 7k is a blade-shaped photosensitive member 1c.
Ｋ1k. Thereby, the photoconductors 1c to
The untransferred toner remaining on the recording medium S without being transferred onto the recording medium S can be removed. Lamp 8c for static elimination
8k can irradiate the photoconductors 1c to 1k with light, and thereby the electric charges on the photoconductors 1c to 1k can be removed by light.

In this image forming apparatus, the above-described registration mark detection for detecting the positional deviation of the multicolor toner images (cyan toner image, magenta toner image, yellow toner image, black toner image) on the recording medium S is performed. Devices 51, 52, 53
It has. FIG. 6 shows a state where the registration mark is transferred onto the conveyor belt 60 and an arrangement state of the registration mark detection devices 51, 52 and 53 in the image forming apparatus shown in FIG. , 1k
The figure which looked at from the top in the state where it removed is shown.

When detecting the misregistration of the multi-color toner image on the recording medium S, as shown in FIG.
0, three positions corresponding to the registration mark detection devices 51, 52, and 53 in a direction (main scanning direction) orthogonal to the transport direction V, and at predetermined intervals in the transport direction V (sub-scanning direction). The registration marks C1, C2, C3 corresponding to the cyan toner image, the registration marks M1, M2, M3 corresponding to the magenta toner image, and the registration marks Y1, Y2, Y3 corresponding to the yellow toner image correspond to the black toner image. Registration marks K1, K2, K3
Are formed by transfer.

The registration marks C1 to C3, M1 to M3,
Y1 to Y3 and K1 to K3 are patterns having the same shape and size, respectively. A line parallel to the direction perpendicular to the transport direction V (line perpendicular to the transport direction) and a line parallel to the transport direction V (parallel to the transport direction). L), which is an L-shaped resist mark composed of two lines (line). The registration mark detection device 51 detects registration marks C1 and M formed on the conveyance belt 60 corresponding to the multicolor toner images, respectively, in order to detect a positional shift of the multicolor toner images on the recording medium S.
1, Y1, and K1 are detected. Similarly, the registration mark detection device 52 detects the registration marks C2, M2, Y2, and K2,
The registration mark detection device 53 performs registration mark C3, M
3, Y3 and K3 are detected.

As described above, the registration mark detecting device 51,
By arranging 52 and 53, forming registration marks, and sequentially detecting registration marks of each color arranged in the recording medium conveyance direction by each registration mark detection device, in the recording medium conveyance direction in an image finally obtained. It is possible to detect a color shift in a recording medium transport direction (sub-scanning direction) and a color shift in a direction (main scanning direction) orthogonal to the recording medium transport direction in each area or portion in a direction (main scanning direction) perpendicular to the recording medium.

Next, registration mark detection devices 51 and 52,
The configuration and the like of the detection device 53 will be described.
Have substantially the same configuration, only the detection device 51 will be described here, and description of the detection devices 52 and 53 will be omitted. FIG. 7 shows a registration mark detection device 51.
FIG. 7A is a plan view of the registration mark K1 detected by the registration mark detection device 51, and FIG. 7B is a diagram showing the detection device 5 shown in FIG.
1, the detection state of the measurement system 510 'is indicated by an arrow 7 in the figure.
FIG. 7C shows a side view as viewed from the direction (B), and FIG.
FIG. 7A is a side view showing the detection state of the measurement system 510 in the detection device 51 shown in FIG.

As described above, the registration mark K1 shown in FIG. 7 has an L-shape including a transport direction orthogonal line K1y parallel to the transport direction V and a transport direction parallel line K1x parallel to the transport direction V. This is a registration mark. As shown in FIG. 7, the registration mark detection device 51 includes measurement systems 510 and 510 ′. The measurement system 510 includes a pair of optical sensor units 511 and a light source unit 512, and the measurement system 510 ′ includes a pair of optical sensor units 511 ′ and a light source unit 512 ′. The optical sensor unit 511 includes an optical sensor 511a and a condenser lens 511b. The optical sensor unit 511 ′ includes an optical sensor 511a ′ and a condenser lens 511b ′. Optical sensors 511a, 511
a ′ can convert the received light into an electric signal. The optical sensor 511a ′ is a multi-cell division type line sensor in which a plurality of cells (detection elements) are arranged in a direction orthogonal to the transport direction V, and is a direction orthogonal to the transport direction V of the registration mark K1 (line K1x). Can be detected.

The light source units 512 and 512 ′ are components that perform substantially the same function, and include the light sources 512 a and 512 a ′ and the projection lenses 512 b and 51, respectively.
2b '. Optical sensor unit 51 corresponding to each
1, light source unit 512, light sensor unit 511 ′ and light source unit 51
2 'is a normal axis H, H' of the surface of the conveyor belt 60 on which the registration mark K1 is formed, and a normal axis crossing the regular path of the predetermined portion N, N 'of the registration mark lines K1y, K1x. They are arranged axially symmetric with respect to H and H '. More specifically, the optical sensor unit 511 (51
1 ′) and the light source unit 512 (512 ′) are respectively incident light rays E1 (E1) from the light source unit 512 (512 ′) toward the line K1y (K1x) to detect the registration mark K1.
1 ′) and the line K1y (K1x) to the optical sensor unit 511
(511 ′) Conveying belt 60 on which a plane including reflected light beam E2 (E2 ′) and registration mark K1 are formed
Line K1y (K1x) parallel to intersection line Q (Q ') with the surface
Are arranged to detect

By irradiating light from the light sources 512a, 512a 'to the registration mark K1 via the projection lenses 512b, 512b', the sensors 511a, 51a
1a 'can detect specularly reflected light from a predetermined portion of the registration mark (the predetermined portions N and N' at the detection timing shown in FIG. 7) via the condenser lenses 511b and 511b '. The other registration mark detection devices 52 and 53 have the same configuration.

The image forming apparatus has a main control unit CONT for controlling the entire image forming apparatus as shown in FIG. The registration mark detection devices 51, 52, and 53 are connected to the main control unit CONT, respectively, and can send detection values detected by the optical sensors provided to the respective units to the main control unit CONT. The main control unit CONT is mainly composed of a computer, and calculates the amount of misregistration of each color registration mark based on the detection values of the registration mark detection devices 51, 52, 53, and forms an image for forming each color toner image. Parts 100c, 100m, 100y,
The position of each color toner image (image) at the time of normal image formation formed at 100k can be corrected. This correction is performed by a conventionally known method. The detection and correction of the positional deviation are performed at a predetermined time (for example, before normal image formation, after image formation is completed, at a predetermined number of times of image formation, and the like).

According to the above-described image forming apparatus, the photoconductors 1c, 1m, 1y, and 1k are driven to rotate at predetermined timings, and the main chargers 2c, 2m, and 2k are driven.
It is uniformly charged by y and 2k. As shown in FIG. 5, in the laser scanning optical device 3, the laser light sources 31c and 31c
Laser beams are emitted from m, 31y, and 31k at predetermined timings. Laser light sources 31c, 31m, 31
The laser beams y and 31k modulate the laser beams Lc, Lm, Ly and Lk based on image information of cyan, magenta, yellow and black sent from an image reading device or the like (not shown).

The laser light sources 31c, 31m, 31y, 31
k, laser beams Lc, Lm, L
y and Lk are collimator lenses 32c, 32m, 32y,
The light beams are made substantially parallel by 32k. The laser beams Lc and Lk are respectively combined with the combining mirrors 33a and 33b.
And is incident on a portion below the mirror surface of the deflector 30 via the cylindrical lenses 34a and 34b. The laser beams Lm and Ly pass through the combining mirrors 33a and 33b, respectively, and the portions above the mirror surface of the deflector 30 via the cylindrical lenses 34a and 34b, ie, the laser beam L
Light is incident above the incident positions of c and Lk.

The rotation of the deflector 30 deflects the laser beams Lc and Lm in the main scanning direction toward the scanning lenses 35a and 35a '. In addition, laser beams Ly, L
k is deflected in the main scanning direction toward the scanning lenses 35b and 35b '. The laser beam Lc passing through the scanning lenses 35a and 35a 'and the separation mirror 36a and the laser beam Lk passing through the scanning lenses 35b and 35b' and the separation mirror 36b are turned back mirrors 37a and 37b, respectively.
To the photoreceptor 1 via the scanning lenses 38c and 38k.
c, 1k. The laser beam Lm that has passed through the scanning lenses 35a and 35a 'is reflected by the separation mirror 36a and the return mirrors 36a' and 36a ",
The light is irradiated to the photoconductor 1m through 8m. The laser beam Ly passing through the scanning lenses 35b and 35b 'is reflected by the separation mirror 36b and the return mirrors 36b' and 36b ", and is irradiated on the photoreceptor 1y via the scanning lens 38y.

Thus, the photosensitive members 1c, 1m, 1y,
The charged area above 1k is exposed, and an electrostatic latent image is sequentially formed on each surface. Then, first, a cyan visible toner image is formed on the photoreceptor 1c in the formation transfer unit 100c. As shown in FIG. 4, the electrostatic latent image corresponding to the cyan image on the photoconductor 1c by the laser beam Lc from the laser scanning optical device 3 is rotated by the rotation of the photoconductor 1c to form the developing device 4c.
Move to

The developing device 4c supplies a cyan developer Dc to the electrostatic latent image formed on the photoreceptor 1c with the rotation of the developing roller 41c, and develops the latent image under application of a developing bias voltage. , A visible toner image T. The visible toner image T on the photoconductor 1c moves to the transfer portion Pc. The toner image T transferred to the transfer portion Pc is transferred to the recording medium S. The recording medium S is sent out from a paper supply tray (not shown) by a paper supply roller (not shown), and is sent to the timing roller pair 11. The timing roller pair 11 includes the photoconductor 1
The recording medium S is sent out in synchronization with the toner image T on c. The recording medium S is transported along with the rotation of the transport belt 60 of the transport device 600 and moves to the transfer section Pc.

In the transfer section Pc, the transfer charger 6c applies a voltage from the power supply PW3c to the recording medium S via the transport belt 60. Thereby, the toner image T on the photoconductor 1c is transferred to the recording medium S. The photoconductor 1c holds the residual toner that has not been transferred to the recording medium S, and the cleaning blade 7c removes the residual toner.
Thereafter, light is irradiated from the discharging lamp 8c to the photoconductor 1c, and the residual potential on the photoconductor 1c is removed. Then, the photoconductor 1c is prepared for the next image formation. The recording medium S further moves to the transfer portion Pm as the transport belt 60 moves.

In the same manner as described above, the formation transfer section 100m, 1
At 00y and 100k, laser beams Lm, Ly, and Lk are emitted from the laser scanning optical device 3, and the photoconductors 1m and 1m are irradiated.
After an electrostatic latent image corresponding to a magenta image, a yellow image, and a black image is formed on y and 1k and developed, a visible toner image of each color is sequentially formed and transferred to the recording medium S, and a visible toner image of each color is formed. Can be stacked.

After transferring the toner image at the transfer portion Pk, the recording medium S is conveyed to the fixing roller pair 14, where the toner image is fixed on the recording medium S. Thereafter, the sheet is discharged to a sheet discharge tray by a sheet discharge roller pair (not shown). At the time of detecting the registration mark, similar to the above-described normal image formation,
Each image forming unit 100c, 100m, 100y, 100k
Then, the registration marks for each color are transferred onto the conveyor belt 60 (see FIG. 6). Conveyor belt 60
Are driven by the driving roller 63 as shown in FIGS. 4 and 5, and the registration marks of each color move at a substantially constant speed in the direction of arrow V in the figure. The registration marks of each color sequentially conveyed on the conveyance belt are detected by a registration mark detecting device 5.
1, 52 and 53 are detected.

Each image forming unit 100c, 100m, 100
For y and 100k, actually, the main scan writing position shift, the sub-scan writing position shift, the main scanning magnification shift, the main scanning partial magnification shift, the main scanning direction bending shift, the sub-scanning direction bending shift, the main scanning direction tilt shift, Sub-scanning magnification deviation, sub-scanning partial magnification deviation, and the like occur in a complex manner, causing a deviation in the toner image (image) position of each color, and almost no registration mark of each color is formed at a predetermined position. In other words, the deviation of the toner image (image) position of each color appears as a deviation of the registration mark of each color from a predetermined position.

The detection of the displacement of the registration mark of each color is performed as follows.
This is performed by detecting the amount of deviation of the registration mark of another color from the registration mark of the reference color. Similarly, the misregistration correction of the toner image (image) of each color is also performed by matching the toner image (image) of the reference color. In this example, black is used as a reference in both the detection of the displacement of the registration mark of each color and the correction of the displacement of the toner image (image) of each color.

Each registration mark detection device 51, 52, 5
From the detected position information of the L-shaped registration mark perpendicular to the transport direction of the L-shaped registration mark, the amount of positional deviation between the color registration marks in the recording medium transport direction V (sub-scanning direction) and the amount of positional deviation between the color toner images are determined. be able to. In addition, when detecting the positional deviation between the registration marks of each color in the sub-scanning direction, each of the detection devices 51, 52, 53
A direction that is not parallel to the transport direction V, that is, a direction crossing the transport direction V, is the direction of the line of intersection of the plane including the incident light beam from the light source toward the registration mark and the reflected light beam from the registration mark toward the optical sensor and the surface of the transport belt 60 ( For example, the direction may be an oblique direction to the transport direction V or a direction orthogonal to the transport direction V. That is, the paired optical sensor and light source can be installed to detect a registration mark line that is not parallel to the transport direction V (crosses the transport direction V). Therefore,
Here, as described above, the optical sensor 511a and the light source 512a in the detection device 51 detect the transport direction orthogonal line K1y parallel to the direction orthogonal to the transport direction V (see FIG. 7).

Further, from the detected position information of the parallel line portion in the transport direction by the registration mark detecting device, the amount of positional deviation between the respective color registration marks in the direction (main scanning direction) orthogonal to the recording medium transport direction, and furthermore, the position between the respective color toner images. The shift amount can be obtained. Regarding the positional deviation of each color registration mark in the main scanning direction, specifically, the registration mark detection devices 51, 52, 53 arranged at three places in the main scanning direction are transported by the transport belt 60 in the sub scanning direction. A line sensor that can detect the position of a line parallel to the sub-scanning direction of the L-shaped registration mark even if the line moves in the main scanning direction,
The detection can be performed by detecting with the multi-cell division type line sensor 511a '(see FIG. 7) in the detection device 51 described above.

When there is no displacement, the registration mark detection output values for each color obtained from the three registration mark detection devices 51 to 53 are all the same. Therefore, the registration mark detection output value differs for each of the registration mark detection devices 51 to 53 and for each color. The amount of misregistration of the various images described above is calculated based on the detection results of the plurality of registration mark detection devices 51 to 53. The calculation method is known, and the description is omitted here. The registration mark detection of the present invention will be described in more detail.

Next, the registration mark detecting devices 51, 52,
The operation of the detection device 53 will be described. However, since the detection devices 51 to 53 shown in FIG. 5 are devices that perform substantially the same operation based on the same principle, only the detection device 51 will be described here. Description of 53 is omitted. Further, registration marks C1 to C3, M1 to M3, Y1 to Y3, K1 to K3 formed on the conveyor belt 60 are formed.
Are the same pattern, so only the detection of the registration mark K1 will be described here, and the description of the detection of other registration marks will be omitted.

The pair of optical sensors 511a shown in FIG.
And the light source 512a and the pair of optical sensors 511a 'and the light source 5
In 12a ', when the conveyor belt 60 flaps, the registration mark K1 is detected by detecting the light reflected at the intersection of the incident beams E1, E1' and the surface of the conveyor belt 60 with reference to the incident beams E1, E1 '. (Detected based on the light source side) and the reflected light E based on the reflected light E2 and E2 '.
2. It is conceivable that the light reflected at the intersection point between E2 'and the surface of the conveyor belt 60 is detected (detected based on the sensor side). Regarding the detection of the registration mark in FIG. 7, the light source 5 at a predetermined portion of the registration mark K1 is different between the detection based on the light source side reference and the detection based on the sensor side reference.
In any case, only the reflection position of the light from 12a, 512a 'is different, and in each case, the description can be made with substantially the same concept. Therefore, in the following description, the case of detection based on the light source side reference will be described, and the description of the case of detection based on the sensor side reference will be omitted.

As shown in FIG. 7, the registration mark detecting device 51 has a pair of corresponding light sensors 511a and a light source 512a and a pair of light sensors 511 as described above.
a 'and the light source 512a', and are arranged in the relationship described above. In detecting the registration mark K1, the light source 512a ′ moves from the light source 512a ′ to the conveyance belt 6 on the conveyance direction orthogonal line K1y on the conveyance belt 60.
Light is applied to each of the transport direction parallel lines K1x on 0.

At this time, the optical sensor 511a and the light source 51
2a, the optical sensor 511a 'and the light source 512a' are arranged axially symmetrically with respect to the normal direction axes H and H ', respectively. Predetermined part N,
The incident light rays E1 and E1 ′ of the light applied to N ′ and the light sensors 511a and 511 reflected by the registration mark K1
The reflected light rays E2 and E2 'directed to a' are normal axis H,
Each is axially symmetric with respect to H ′. As a result, the optical sensors 511a, 511a '
It is possible to detect light that is regularly reflected at the registration mark K1 by light irradiation from 512a '. Thus, the SN of the signal detected by the optical sensors 511a and 511a '
The ratio is high. Then, the transport belt 60
And the registration mark K1 can be detected with high contrast. As a result, a good contrast can be obtained even when a registration mark is detected on a transport belt of an arbitrary color.

The optical sensors 511a and 511a 'do not flutter the conveyor belt 60 when detecting the predetermined portions N and N' of the registration marks, and therefore, the predetermined portions N and N 'of the registration marks travel along a regular path. When
Specularly reflected light from predetermined portions N and N 'of the registration mark K1 due to light irradiation from the light sources 512a and 512a' is detected.

FIG. 7C shows the detection state of the line K1y by the optical sensor 511a and the light source 512a when the conveyor belt 60 is not fluttering. The detection state of the line K1y by the optical sensor 511a and the light source 512a (fluttering in the direction away from the optical sensor 511a and the light source 512a) is indicated by a broken line.

FIG. 7B shows the light sensor 511a 'and the light source 512 when the conveyor belt 60 is not fluttering.
The detection state of the line K1x by a ′ is indicated by a solid line, and the transport belt 60 fluctuates (in this example, the optical sensor 511).
The detection state of the line K1x by the optical sensor 511a 'and the light source 512a' when the light source a flutters in the direction away from the light source 512a 'is shown by a broken line.

In the detection state shown in FIG. 7C, when the transport belt 60 is not fluttering, the optical sensor 511a reads the position of the line K1y at A in the figure. When the belt 60 is fluttering, the sensor 511a reads the position. The position of the line K1y at B in the figure is read. As described above, the sensor 511a reads different positions of the line K1y due to the fluttering of the belt 60. However, the sensor 511a and the light source 5
Reference numeral 12a is arranged to detect a line K1y parallel to an intersection Q between the plane including the incident light beam E1 and the reflected light beam E2 and the surface of the belt 60, and the intersection line Q and the line K1y are orthogonal to the transport direction V. Is parallel to the scanning direction (main scanning direction), the reading position in the direction (main scanning direction) orthogonal to the transport direction V varies due to the fluttering of the belt 60, but the reading position in the transport direction V (sub-scanning direction) is substantially Since it does not fluctuate, there is substantially no detection error due to the flapping of the belt 60 in this direction (see FIG. 1 and its description).

Similarly, in the detection state of FIG.
When the conveyor belt 60 is not fluttering, the optical sensor 51
1a 'reads the position of A' in the figure of the line K1x, and when the belt 60 is fluttering, the sensor 511a 'reads the position of B' in the figure of the line K1x. As described above, the sensor 511a 'reads a different position of the line K1x due to the fluttering of the belt 60. However, the sensor 511a ′ and the light source 512a ′ have an intersection Q ′ between the plane including the incident light beam E1 ′ and the reflected light beam E2 ′ and the surface of the belt 60.
And the line K1x is parallel to the transport direction V (sub-scanning direction), so that the belt 60 flutters to read in the transport direction V (sub-scanning direction). Although the position fluctuates, the reading position in the direction (main scanning direction) orthogonal to the transport direction V does not substantially fluctuate, and therefore, a detection error due to the fluttering of the belt 60 in this direction does not substantially occur (FIG. 1 and its description). reference).

The registration mark lines K1y, K1
x direction, incident rays E1, E1 'and reflected rays E2, E
Intersecting lines Q and Q 'between the plane including 2' and the surface of the conveyor belt 60
Are not completely parallel to each other but are substantially parallel to each other, the optical sensor 511a, 511a ′ detects the regular reflection of the light E2, E2 ′ at the lines K1y, K1x, and the regularity of the registration mark position (conveyance belt 60). The amount of deviation from the position (if not fluttering) is small (for example,
(Micron order), and even if the transport belt 60 flaps in this state, it cannot be a level of a detection error to be regarded as a problem. In other words, the detection error is within an allowable range. Thereby, the registration mark detection error due to the fluttering of the transport belt can be suppressed to be small.

Of course, the other registration marks Y1, M1, C
1, K2, Y2, M2, C2, K3, Y3, M3, C3
Can be similarly detected in position, and similar advantages can be obtained. As described above, in the color image forming apparatus including the registration mark detection devices 51, 52, 53,
The detection accuracy of the registration mark can be increased.

Based on the detected values, the main control unit CONT shown in FIG. 4 can correct the position of each color image during normal image formation. The registration mark on the conveyor belt 60 after the detection of the image position shift is removed by a cleaning blade (not shown) arranged in contact with the conveyor belt 60.
Next, another example of registration mark detection by a color image forming apparatus including the registration mark detection device shown in FIGS. 4 and 5 will be described.

FIG. 8 shows a state in which a V-shaped registration mark is transferred onto the conveyor belt 60 in place of the L-shaped registration mark in the color image forming apparatus shown in FIGS. The state in which the registration mark detection devices 51 ', 52', 53 'are disposed in place of 52, 53 is referred to as the laser optical device 3 and each of the photosensitive members 1c, 1c.
FIG. 3 is a diagram viewed from above with m, 1y, and 1k removed.

An example of registration mark detection by the registration mark detection devices 51 ', 52', 53 'shown in FIG. 8 will be described below. When detecting the misregistration of the multicolor toner image on the recording medium S, the direction perpendicular to the transport direction V (main scanning direction) is placed on the transport belt 60 as shown in FIG.
, The registration mark detection devices 51 ', 52', 5
The registration marks C1 ', C2', C3 'corresponding to the cyan toner image and the registration marks corresponding to the magenta toner image are provided at three positions corresponding to 3', and at positions separated by a predetermined distance in the transport direction V (sub-scanning direction). Mark M1 ', M
2 ', M3', and registration marks Y1 ', Y2', and Y3 'corresponding to the yellow toner image, and registration marks K1', K2 ', and K3' corresponding to the black toner image, are formed.

Registration marks C1 'to C3', M1 'to
M3 ', Y1' to Y3 ', and K1' to K3 'are patterns having the same shape and size, respectively, and are V-shaped lines composed of two lines crossing the transport direction V. In these registration marks, one of the lines may be parallel to a direction orthogonal to the transport direction V, or both lines may be oblique to the transport direction V. Here, two lines, that is, a line orthogonal to the transport direction parallel to the direction perpendicular to the transport direction V, and an oblique line in which the distance between the line orthogonal to the transport direction at different positions in the direction orthogonal to the transport direction V gradually varies. V-shaped resist mark.

The registration mark detecting device 51 'detects registration marks C1 formed on the conveyor belt 60 corresponding to the multicolor toner images, respectively, in order to detect the displacement of the multicolor toner images on the recording medium S. ', M1', Y1 ', K
1 'is detected. Similarly, a registration mark detection device 52 '
Represents the registration marks C2 ', M2', Y2 ', K2',
The registration mark detection device 53 '
3 ′, M3 ′, Y3 ′, and K3 ′ are respectively detected.

Each of the registration mark detection devices 51 ', 5
Both or any one of the lines of the V-shaped line composed of two lines crossing the transport direction V by 2 ′ and 53 ′ (here, a line portion orthogonal to the transport direction)
From the detected position information, the amount of positional deviation between the registration marks of the respective colors in the transport direction V (sub-scanning direction), and the amount of positional deviation between the toner images of the respective colors can be obtained. In addition, the registration mark detection of the other line portion (here, diagonal line portion) from the detection position of one line portion (here, the line portion orthogonal to the transport direction) of the V-shaped line by the registration mark detection device. From the detected position information up to the position detected by the apparatus, the amount of positional deviation between the registration marks of each color in the direction (main scanning direction) orthogonal to the transport direction V, and the amount of positional deviation between the toner images of each color can be obtained.

More specifically, regarding the positional deviation of each color registration mark in the main scanning direction, the registration mark detection devices 51 ′, 52 ′,
53 ′ is V transported by the transport belt 60 in the sub-scanning direction.
This can be done by measuring the elapsed time between the detection of two lines of the character-shaped registration mark. Based on the detection results of the plurality of registration mark detection devices 51 ′ to 53 ′, the displacement amounts of the various images described above are calculated. The calculation method is known, and the description is omitted here. The registration mark detection of the present invention will be described in more detail.

Next, the registration mark detection devices 51 ', 5
The configuration and the like of 2 ′ and 53 ′ will be described.
Since 1 ′ to 53 ′ have substantially the same configuration, only the detection device 51 ′ will be described here.
The description of 2 ′ and 53 ′ is omitted. FIG. 9 is a diagram showing an arrangement state of the registration mark detecting device 51 '.
It is a top view of a 1 'detection state.

As described above, the registration mark K1 'shown in FIG. 9 has a transport direction orthogonal line K1y' parallel to the direction orthogonal to the transport direction V, and a transport direction orthogonal line at a different position in the direction orthogonal to the transport direction V. V consisting of two lines, an oblique line K1x 'with a gradually increasing distance from K1y'
It is a character-shaped resist mark. As shown in FIG. 9, the registration mark detecting device 51 'includes a pair of optical sensor units 511 ".
And a light source unit 512 ″.
1 "includes an optical sensor 511a" and a condenser lens 511b ". The optical sensor 511a" can convert the received light into an electric signal.

The light source unit 512 ″ includes a light source 512a ″ and a projection lens 512b ″. The corresponding light sensor unit 511 ″ and light source unit 512 ″ have a registration mark K
1 'is the normal axis H "of the surface of the conveyor belt 60 on which the registration mark lines K1y' and K1x 'correspond (corresponding to the predetermined portion N" on the conveyor belt 60 at the detection timing shown in FIG. 9). Are arranged axially symmetrically with respect to a normal axis H "intersecting the normal path of each line (a portion on each line). The optical sensor unit 511" and the light source unit 512 "are provided for detecting the registration mark K1 '. Incident light E from the light source unit 512 ″ to the registration mark K1 ′
1 "and a plane including the reflected light beam E2" traveling from the registration mark K1 'to the optical sensor portion 511 "and the registration mark K
A line of intersection Q ″ with the surface of the conveyor belt 60 on which 1 ′ is formed forms a V-shaped line in the registration mark K1 ′.
The lines K1y 'and K1x' are set so as to fall within the acute angle range.

Thus, from the light source 512a ″ to the projection lens 5
By irradiating the registration mark K1 'with light through the 12b ", the sensor 511a" can detect regular reflection light from a predetermined portion of the registration mark through the condenser lens 511b ". Another registration mark detection device 52' , 53 ′ have the same configuration.

The registration mark detecting devices 51 ', 5'
Reference numerals 2 'and 53' are connected to the main control unit CONT shown in FIG. 4, respectively, and can transmit the detection values detected by the optical sensors provided to the respective main control units CONT to the main control unit CONT. Next, registration mark detection devices 51 ', 52', 5
The operation of 3 ′ will be described. However, since the detection devices 51 ′ to 53 ′ shown in FIG. 8 are devices that perform substantially the same operation based on the same principle, only the detection device 51 ′ will be described here. The description of the detection devices 52 'and 53' is omitted. Further, registration marks C1 'to C3', M1 'to M3', Y
Since 1 'to Y3' and K1 'to K3' are all of the same pattern, only the detection of the registration mark K1 'will be described here, and the description of the detection of other registration marks will be omitted.

As shown in FIG. 9, as described above, the registration mark detecting device 51 'is provided with a pair of corresponding optical sensors 5'.
11a "and the light source 512a", and are arranged in the relationship described above. In detecting the registration mark K1 ', light is emitted from the light source 512a "to the transport direction orthogonal line K1y' and the oblique line K1x 'on the transport belt 60, respectively.

At this time, the optical sensor 511a ″ and the light source 5
12a "is arranged symmetrically with respect to the normal axis H", so that the light source 512a "
The incident light beam E1 ″ of light applied to a predetermined portion of y ′ and the reflected light beam E2 ″ reflected by the registration mark K1 ′ toward the optical sensor 511a ″ are axially symmetric with respect to the normal axis H ″. is there. As a result, the optical sensor 511a ″ emits the registration mark K
At 1 ′, light that has been specularly reflected can be detected. Thus, the SN of the detection signal by the optical sensor 511a ″ is obtained.
The ratio is high. Then, the transport belt 60
And the registration mark K1 'can be detected with high contrast. As a result, a good contrast can be obtained even when a registration mark is detected on a transport belt of an arbitrary color.

In detecting the predetermined portion of the registration mark, the optical sensor 511a ″ detects the light from the light source 512a ″ when the conveyor belt 60 is not fluttering and the predetermined portion of the registration mark is traveling along a regular path. Specularly reflected light from a predetermined portion of the registration mark K1 'due to the irradiation is detected. The optical sensor 511a ″ and the light source 512a ″
As described above, the intersection line Q "between the plane including the incident light beam E1" and the reflected light beam E2 "and the surface of the conveyor belt 60 is within the acute angle range between the line K1y 'in the transport direction and the oblique line K1x'. , The light sensor 511a ″ and the light source 512a ″.
Detects an orthogonal line K1y ′ in the transport direction and an oblique line K1x ′ in which the intersection line Q ″ between the plane including the incident ray E1 ″ and the reflected ray E2 ″ and the surface of the transport belt 60 is not parallel.
Therefore, it is not possible to substantially eliminate the registration mark detection error due to the fluttering of the conveyor belt 60 (FIG. 2, FIG.
(See FIG. 3 and its description). However, by making the transport direction orthogonal line K1y 'and the oblique line K1x' closer to the direction parallel to the intersection line Q ", it is possible to minimize the registration mark detection error due to the fluttering of the transport belt 60. If too large, registration mark K1 '
A detection error is likely to occur.
A detection error of a positional shift in a direction (main scanning direction) parallel to a direction orthogonal to the transport direction V of 1 ′ is likely to occur. The intersection line Q ″ between the plane including the incident light beam E1 ″ and the reflected light beam E2 ″ and the surface of the conveyance belt 60 is a line K1 orthogonal to the conveyance direction.
The position within the acute angle range between y ′ and the oblique line K1x ′ is の of the acute angle.

Of course, the other registration marks Y1 ', M
1 ', C1', K2 ', Y2', M2 ', C2', K
The positions of 3 ', Y3', M3 ', and C3' can be similarly detected, and similar advantages can be obtained. As described above, in the color image forming apparatus including the registration mark detection devices 51 ′, 52 ′, and 53 ′, the detection accuracy of the registration marks can be increased.

In the above-described example, the registration marks are transferred onto the conveyor belt 60 and the registration marks are detected by the registration mark detecting devices 51 to 53 and 51 'to 53'. It may be transferred onto S and detected by the registration mark detection device. Also,
In the example described above, the image forming units 100c to 100k employ an electrophotographic recording method in which a toner image based on image information is temporarily formed on the photoconductors 1c to 1k and indirectly recorded on the recording medium S. Without forming an electrostatic latent image
An image forming unit of a direct recording system for forming an image by directly flying toner on an appropriate image carrier or a recording medium based on image information may be employed.

[0108]

According to the present invention, there is provided a color image forming apparatus having a plurality of image forming sections, wherein a predetermined color toner image formed by the image forming sections is transferred onto a recording medium conveyed by a conveying belt, and is fixed thereon. Register for detecting registration marks formed on the recording medium or on the transport belt corresponding to the multicolor toner images, respectively, in order to detect a positional shift of the multicolor toner image on the recording medium. A color image forming apparatus provided with a mark detection device, wherein a registration mark detection error due to the fluttering of the transport belt can be suppressed to a small value, and a good contrast can be obtained even when register marks are detected on a transport belt of an arbitrary color. Equipped with a registration mark detection device that can increase the detection accuracy, enabling good color image formation with suppressed color misregistration It is possible to provide a color image forming apparatus.

[Brief description of the drawings]

FIG. 1 is a perspective view of a registration mark detecting device in which a pair of a photosensor and a light source are axially symmetric with respect to a normal axis of a conveyor belt surface and a normal axis intersecting a normal path of a predetermined portion of a registration mark line; FIG. 7 is a perspective view illustrating a state in which a direction of an intersecting line between a plane including incident light rays and reflected light rays and a conveying belt surface and a direction of a registration mark line are parallel to each other.

FIG. 2 is a perspective view showing an example for explaining a registration mark detection error due to a flutter of a conveyor belt.

FIG. 3 is a perspective view illustrating another example for explaining a registration mark detection error due to a fluttering of a conveyance belt.

FIG. 4 is a side view showing a schematic configuration of an example of a full-color image forming apparatus provided with a registration mark detecting device according to an embodiment of the present invention.

FIG. 5 is an exploded perspective view of the laser scanning optical device, the photoconductor, the transfer / transport device, and the registration mark detection device in the image forming apparatus shown in FIG.

FIG. 6 is a top view of the image forming apparatus shown in FIG. 5 in which a registration mark is transferred onto a conveyance belt and an arrangement of a registration mark detection device when the laser optical device and each photoconductor are removed; is there.

7A and 7B are views showing the arrangement of a part of the registration mark detection device shown in FIG. 5, wherein FIG. 7A is a plan view of the registration mark detection state by the registration mark detection device, and FIG. FIG. 7A is a side view showing the detection state of one measurement system in the detection device shown in FIG. 7A as viewed from the direction of arrow 7 (B) in the figure, and FIG. FIG. 7 is a side view of the detection state of FIG.

FIG. 8 is a top view of another example of registration mark detection by the color image forming apparatus including the registration mark detection device shown in FIGS. 4 and 5, with the laser optical device and each photoconductor removed. .

9 is a plan view showing a state of registration mark detection by the registration mark detection device, showing a part of the registration mark detection device shown in FIG. 8;

[Explanation of symbols]

BL transport belt G0, G0 ', G1 Registration mark detection line H1 Normal axis of transport belt BL surface I Optical sensor IL Reflected light beam from registration mark line M toward optical sensor IL' When transport belt BL flutters Reflected light J light source JL incident light beam from light source J toward registration mark line M registration mark line Q1 intersection line between plane W and conveyance belt BL surface R0 detection positions on registration mark detection line G0 R1, R1 'registration mark detection Detection position at line G1 U Direction approaching optical sensor I and light source J V Transport direction W Plane including incident light JL and reflected light IL 100c Image forming section for cyan visible toner image 100m Image forming section for magenta visible toner image 100y Yellow visible toner image forming unit 100k Black visible toner image Image forming unit 1c, 1m, 1y, 1k Photoconductor 2c, 2m, 2y, 2k Main charger 3 Laser scanning optical device 310a, 310b Laser emitting unit 31c, 31m, 31y, 31k Laser light source 32c, 32m, 32y, 32k Collimator lens 33a, 33b Synthetic mirrors 34a, 34b Cylindrical lens 320 Laser deflecting unit 30 Deflector 30 'Deflection substrate 330a, 330b Laser imaging unit 35a, 35a', 35b, 35b 'Scanning lens 340a, 340b Laser reflecting unit 36a, 36b Separating mirror 36a ', 36a ", 37a Folding mirror 36b', 36b", 37b Folding mirror 38c, 38m, 38y, 38k Scanning lens Lc, Lm, Ly, Lk Laser beam 4c, 4m, 4y, 4k Developing device 41c, 41m, 41y , 41k Developing rollers 42c, 42m, 42y, 42k Device case 51, 52, 53 Registration mark detecting device 510, 510 'Measuring system 511, 511', 511 "Optical sensor unit 512, 512 ', 512" Light source unit 511a, 511a " Optical sensor 511a 'Optical sensor (multi-cell split type line sensor) 511b, 511b', 511b "Condenser lens 512a, 512a ', 512a" Light source 512b, 512b', 512b "Projection lens 51 ', 52', 53 ' Registration mark detector 6c, 6m, 6y, 6k Transfer charger 7c, 7m, 7y, 7k Cleaning blade 8c, 8m, 8y, 8k Lamp for removing electricity 11 Timing roller pair 14 Fixing roller pair 600 Transfer transport device 60 Transport belt 61, 63 Drive roller 62 tension roller C1, C2, C3 Cyan registration mark M1, M2, M3 Magenta registration mark Y1, Y2, Y3 Yellow registration mark K1, K2, K3 Black registration mark C1 ', C2', C3 'Cyan registration mark M1', M2 ', M3' Magenta registration mark Y1 ', Y2', Y3 'Yellow registration mark K1', K2 ', K3' Black registration mark E1 Incident light beam irradiated on line K1y E1 'Irradiated on line K1x Incident light E2 reflected light reflected by the line K1y toward the optical sensor E2 ′ reflected light reflected by the line K1x toward the optical sensor E1 ″ incident light E2 ″ of light applied to the registration mark K1 ′ Reflected light rays H, H ', H "from the registration mark K1' toward the optical sensor Normal axis K1 of the surface of the conveyor belt 60 , K1y predetermined portion N of 'conveyance direction orthogonal lines K1x conveyance direction parallel lines K1x' diagonal line N the detected markline K1y 'predetermined portion N of the detected mark line K1x "the detected registration mark lines K1y', K1
Predetermined portion of x 'Dc Cyan developer Dm Magenta developer Dy Yellow developer Dk Black developer CONT Main control unit Pc, Pm, Py, Pk Transfer site PW1c, PW1m, PW1y, PW1k Power supply PW2c, PW2m, PW2y, PW2k Power supply PW3c, PW3m, PW3y, PW3k Power supply Q, Q ', Q "Intersecting line between the plane including the incident light beam and the reflected light beam and the conveyor belt surface S Recording medium T Visible toner image

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yasushi Nagasaka 2-13-13 Azuchicho, Chuo-ku, Osaka-shi Osaka International Building Minolta Co., Ltd. F-term (reference) 2C262 AA04 AA24 AA26 AB15 FA10 GA04 GA40 2H030 AA01 AB02 9A001 BB06 HH23 HH31 KK16 KK42

Claims (5)

[Claims] 1. A color image forming apparatus having a plurality of image forming units, wherein a predetermined color toner image formed by said image forming unit is transferred onto a recording medium conveyed by a conveying belt, and is fixed thereon. A registration mark detection device for detecting registration marks formed on the recording medium or on the transport belt corresponding to the plurality of color toner images, respectively, for detecting a positional shift of the multicolor toner image on the recording medium. Wherein the registration mark detection device detects at least one pair of a light source for irradiating the registration mark with light and light reflected from the registration mark due to light irradiation from the light source. The pair of optical sensors and the light source are an incident light beam from the light source toward the registration mark and a registration mark for detecting the registration mark. Detecting a registration mark line parallel to an intersection of a plane including a reflected light beam toward the optical sensor and the recording medium surface or the conveyance belt surface on which the registration mark is formed, and the recording medium surface Alternatively, the color image forming apparatus is arranged symmetrically with respect to an axis in a normal direction of the conveying belt surface. 2. The method according to claim 1, wherein the registration mark includes two lines: a line parallel to a conveyance direction of the recording medium by the conveyance belt and a line parallel to a direction orthogonal to the conveyance direction. The apparatus includes two pairs of optical sensors and a light source, and one pair of the two pairs of the optical sensors and the light sources detects a line parallel to a direction orthogonal to the transport direction, and the other pair in the transport direction. 2. The color image forming apparatus according to claim 1, wherein the color image forming apparatus is arranged to detect parallel lines. 3. A method for detecting a plurality of registration marks formed on the recording medium or the transport belt by displacing a position in a direction orthogonal to a transport direction of the recording medium by the transport belt. 3. The color image forming apparatus according to claim 1, wherein the registration mark detection devices are arranged in a direction orthogonal to a recording medium conveyance direction in correspondence with the registration marks. 4. A color image forming apparatus having a plurality of image forming units, wherein a toner image of a predetermined color formed by said image forming units is transferred onto a recording medium conveyed by a conveying belt, and fixed thereon. A registration mark detection device for detecting registration marks formed on the recording medium or on the transport belt corresponding to the plurality of color toner images, respectively, for detecting a positional shift of the multicolor toner image on the recording medium. Wherein the registration mark includes a V-shaped line composed of two lines crossing the conveyance direction of the recording medium by the conveyance belt, and the registration mark detection device includes a pair of registration marks. A light source for irradiating the resist mark with light, and an optical sensor for detecting reflected light from the resist mark due to the light irradiation from the light source; And a light source for detecting a registration mark, a plane including an incident light beam from the light source toward the registration mark and a reflected light beam from the registration mark toward the optical sensor, and the recording medium surface or the transport on which the registration mark is formed. The optical sensor and the light source corresponding to each other are set so that the line of intersection with the belt surface falls within the acute angle range of the two lines forming the V-shaped line in the registration mark, and A color image forming apparatus, which is arranged symmetrically with respect to a normal axis of a surface. 5. A method for detecting a plurality of registration marks formed on the recording medium or on the transport belt by shifting a position in a direction orthogonal to a transport direction of the recording medium by the transport belt. 5. The color image forming apparatus according to claim 4, wherein said registration mark detecting devices are arranged in a direction orthogonal to a recording medium conveyance direction in correspondence with said registration marks.