JPH0732656A - Image forming device - Google Patents

Abstract

PURPOSE:To form an excellent image with a little shear in color by providing a system for determining an image position measuring pattern by making sensors output by time sharing and synthesizing measured results of the image by respective sensors. CONSTITUTION:When a correction cycle starts, a positional shear measuring pattern is sent to an image forming device 105Y from an interface substrate 104Y and the formed positional shear measuring pattern is transferred on a transfer conveyor belt 8 as a transfer image of a symbol 108Y. After the positional shear measuring pattern to be outputted from the interface substrate 104Y at the image forming device 105Y is sent to the image forming device 105Y and after a fixed time pertinent to a difference in distance of transfer points between the image forming devices 105Y and 105M, a positional shear measuring pattern to be outputted from an interface substrate 104M at the image forming device 105M is sent to the image forming device 105M.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a laser beam copying machine or a printer, and more particularly to a multiple image forming apparatus having a plurality of image forming units.

[0002]

2. Description of the Related Art When sequentially transferring images formed by a plurality of image forming units onto a recording medium, if the transferred image position is deviated from the ideal position for each image forming unit, the tint may be different or the color misregistration may occur. It becomes a certain image, and good image quality cannot be obtained.

On the other hand, as described in JP-A-63-271275 and JP-A-1-281468, there are those which improve the image quality by using an image position detecting sensor. is there. This is because the image position detection sensor reads the image position measurement pattern on the transfer / conveying belt formed by each image forming apparatus, calculates the deviation amount of each color by the image position detection processing circuit, and then calculates the deviation amount. This is to obtain a good image with less color misregistration by performing correction in the image forming apparatus.

[0004]

However, if the apparatuses described in these publications are provided with a plurality of image reading means, the circuit scale of the image reading means and the image position detection processing means becomes large. Is unavoidable and leads to a rise in product prices.

For example, if the sensor of the image reading means is an image sensor, there are the following obstacles.

Generally, since the image pickup device has a plurality of outputs for high-speed driving, a difference occurs in the outputs of the plurality of systems due to the difference in the drive waveform of the output section, the difference in the internal capacitance coupling and the linearity of the amplifier. In order to correct such an output difference and obtain an appropriate output value, it is necessary to equip each output with an amplifier circuit and an offset adjustment circuit, which alone would be quite large and expensive. I will end up.

Further, in the case where a plurality of image reading means are provided, the circuit scale is increased by the number of image reading means,
It becomes more and more expensive.

Further, in the periphery of the image reading means, main parts constituting the electrophotographic process such as a discharging device, a heat roller, a developing device and a cleaner are arranged. For this reason,
The layout space is getting narrow and limited,
In many cases, the image position detection processing circuit cannot be arranged adjacent to the image reading means. Therefore, although a configuration of using a cable for electric transmission is adopted, a plurality of image reading means requires a plurality of electric transmission cables, and the image position detection processing circuit also has a large circuit scale and is very large. It becomes expensive.

The problem to be solved by the present invention is to provide an image forming apparatus in a multiplex image forming apparatus, which has a highly accurate, compact and inexpensive image position reading section and can form a good image with little color shift. is there.

[0010]

SUMMARY OF THE INVENTION The present invention provides a multiple image forming system for sequentially transferring and conveying images formed by a plurality of image forming portions onto one recording medium to obtain a color image, and a recording medium on the recording medium. In the image forming apparatus having a plurality of sensors for detecting the pattern for measuring the position of each image, the sensors are time-divided and output, and the image position measurement is performed by combining the image measurement results by the respective sensors. It is characterized by comprising a system for discriminating a usage pattern. The time division of the output of the sensor can be performed in the conveyance direction of the paper on which the image on the recording medium is transferred, or may be performed for each pixel.

Further, in the image forming apparatus having the reading means for detecting the pattern for measuring the position of the image in place of the sensor, the reading means is composed of two image pickup elements, and among the outputs in these image pickup elements. The position measurement pattern may be detected by the output of either one of them.

[0012]

By using a plurality of sensor outputs for detecting the image position measurement pattern in a time division manner, the gain and offset adjusting circuit, the A / D converter, the transmission cable, the image position detecting processing circuit and the like can be used by the plurality of sensors. Can be shared.

Further, by using only one side output of the odd-numbered and even-numbered outputs of the image pickup device used as the reading means, the image reading means can be constructed with half the circuit scale and space of the conventional one, and it is highly accurate, inexpensive, compact and reliable. It is possible to realize an image forming apparatus having an image position reading unit having high flexibility.

[0014]

FIG. 1 is a schematic diagram of the configuration of an image forming apparatus showing an embodiment of the present invention, and shows a color image forming apparatus of a multiple transfer system as an example.

In the figure, the image of the original 2 placed on the platen 1 is formed on the image pickup device 3 through the lens 16 and read as an electric signal, and temporarily stored in the storage means of the image processing unit 4.

The image processing section 4 outputs data of each color of yellow Y, magenta M, cyan C, and black K, and laser beam scanning devices 5Y, 5 of the image forming section.
M, 5C and 5K are used for the respective photosensitive drums 6Y,
An electrostatic latent image is formed on 6M, 6C, 6K, and further, a developing device 7
It is visualized by Y, 7M, 7C and 7K. At this time, a combination of the laser beam scanning devices 5Y, 5M, 5C, and 5K is one image forming unit, and in the present embodiment, 5Y, 6Y, and 7Y are devices that form, for example, a yellow color. 5M, 6M and 7M are magenta and 5
C, 6C and 7C are Sian, 5K, 6K and 7K are black,
These are the forming devices.

The paper 11 for recording the image of each of these colors is
It is supplied from the paper tray 12. The sheet 11 that has left the tray 12 is fed onto the transfer / conveying belt 8 by the feeding roller 13 at a predetermined timing. The transfer belt 8 is
A drive roller 9 connected to a dedicated motor (not shown) having an excellent constant speed drives the paper 11 in the direction of sending it to the discharge tray 15. A driven roller 10 is provided on the side facing the drive roller 9 and is supported so that a constant tension is applied to the transfer / conveyance belt 8.

The front end of the sheet 11 conveyed by the transfer / conveyance belt 8 and the front end of the image formed on the first photosensitive drum 6Y by the image forming apparatus are the photosensitive drum 6Y.
The paper feeding timing and the image writing timing are determined so that the transfer points at the lowest point of are coincident with each other.

The visible image on the photosensitive drum 6Y is transferred to the paper 11 which has reached the transfer point by a transfer corotron or the like, and further reaches a transfer point directly below the photosensitive drum 6M. The visible image on the photoconductor drum 6M is transferred to the paper 11 that has reached the transfer just below the photoconductor drum 6M, similarly to the case where it is transferred by the photoconductor drum 6Y. Similarly,
The sheet 11 that has undergone all the transfer of C and K is further conveyed by the transfer / conveying belt 8, and when it reaches the vicinity of the driven roller 10, the sheet 11 is separated by a corotron or a stripper for separating the sheet 11 from the transferring / conveying belt 8. 11 is separated from the transfer / transport belt 8. Then, it is fixed by the fixing device 14 and discharged onto the discharge tray 15.

FIG. 2 is a schematic diagram of a color misregistration correction system of a multi-transfer type color image forming apparatus.

In the figure, 101 is an image forming apparatus 105.
It is a sensor that reads a pattern image for image position measurement on the transfer conveyance belt 8 formed by Y, 05M, 105C, and 105K. In the illustrated example, these sensors 101 are arranged at both ends of the image area.

In 102, the sensor 101 is the transfer conveyance belt 8
It is a light source that creates the background light necessary for reading the above image, and can secure a sufficient amount of light as a light source of the sensor 101 such as an LED, a halogen lamp, or a fluorescent lamp.

104Y, 104M, 104C and 104
K is a laser beam scanning device 5Y in the image forming apparatus,
An interface board that sends image signals to 5M, 5C, and 5K, and 106 is a board that collectively handles the image position detection processing system. Reference numeral 109 denotes a substrate that collectively handles the memory and image processing, and 107 is a control substrate that manages the movements of all of these substrates and the entire apparatus.

Next, details of the color misregistration correction system will be described.

The positional deviation correction is executed by entering a dedicated correction cycle preset in the apparatus. The purpose of this device is to correct variations in parts and assembly,
It is intended to correct the color misregistration of each color caused by a minute positional deviation of the drum due to an external force or a temperature change or a timing change. Therefore, for example, the transfer condition of the transfer device after a paper jam has occurred, the temperature change in the device exceeds a certain amount, or the like may be the start condition for entering the correction cycle of the device.

When the correction cycle is started, each board 104Y, 104M, 104C, 10 is fed from the control board 107.
4K, 106, and 109 are instructed, and the interface boards 104Y, 104M, 104C, and 104K play the role of a pattern generator that outputs a pattern for measuring the positional deviation, and the image forming apparatuses 105Y and 105Y.
The misregistration measurement pattern is transmitted to M, 105C, and 105K, and the image position detection processing substrate 106 is transferred to the image forming apparatus 105.
Preparations are made to sample the displacement measurement patterns output by Y, 105M, 105C, and 105K. When the correction cycle starts, first, the interface board 104Y transmits the pattern for measuring the positional deviation to the image forming apparatus 105Y, and the pattern for measuring the positional deviation formed by the image forming apparatus 105Y is transferred onto the transfer conveyance belt 8. The image is transferred as a transfer image denoted by reference numeral 108Y. The pattern for measuring the positional deviation output from the interface board 104Y by the image forming apparatus 105Y is the image forming apparatus 10.
Image forming apparatus 105Y, 105M after being transmitted to 5Y.
Of the image forming apparatus 1 from the interface board 104M after a certain time corresponding to the difference in the distance of the transfer points of
The pattern for measuring the positional deviation output at 05M is transmitted to the image forming apparatus 105M. The transfer image 108M is transferred onto the transfer / conveying belt 8 by the pattern for measuring the positional deviation formed by the image forming apparatus 105M. At this time, the pattern of the transferred image 108M corresponds to the transferred image 10 that has already been transferred.
A pattern for measuring the positional deviation formed by the image forming apparatus 105M is additionally written on the 8Y.

Similarly, a transfer image 108C is formed,
A pattern in which the patterns for measuring the positional deviation formed by all the image forming apparatuses are overwritten is completed by the transfer image 108K on the transfer conveyance belt 8. The misregistration measurement pattern does not necessarily need to be overwritten.

The completed pattern transfer image 108K for measuring the positional deviation is further conveyed by the transfer / conveying belt 8 and reaches right below the sensor 101. Then, in the misregistration correction board 106 that samples the image data from the sensor 101, the interface boards 104Y, 104
At least one of the M, 104C, and 104K pattern output timings for measuring the positional deviation is monitored, and the time for the positional deviation measuring pattern to reach directly below the sensor 101 from the output timing of at least one of the interface boards. The sample start timing and sample necessary and sufficient to sample the pattern for measuring the positional deviation from the interval between the image forming apparatus for forming the pattern for measuring the positional deviation outputted from the interface board and the sensor 101 in advance. You can figure out the end timing.

The image position detection processing substrate 106 starts capturing the image signal from the sensor 101 into the high-speed memory at the sampling start timing, and ends the sampling at the sampling end timing.

At the same time as the end of the acquisition, before the end of the sampling of the pattern for measuring the next positional deviation, the image position is determined from the acquired data by, for example, the barycentric method, and the image position is determined, for example. Stored as address in main memory. By repeating this operation several times, several fixed image position addresses can be obtained for each image forming apparatus. Here, in order to improve the accuracy of the fixed image position address, these several fixed image position addresses are averaged for each image forming apparatus.

Next, in the image position detection processing substrate 106, some correction values for correcting the positional deviation between the image forming apparatuses are calculated by a predetermined algorithm from the image position address determined for each image forming apparatus. It is calculated for each position deviation correction parameter and for each image forming apparatus.
Some of the positional deviation correction parameters include, for example, the scanning start position of the laser beam scanning device, that is, the deviation in the main scanning direction, the transfer conveyance direction, that is, the deviation in the sub scanning direction, the deviation in the main scanning direction magnification, and the magnification in the sub scanning direction. There are deviations and angular deviations with respect to the main scanning direction. The calculated correction values are
From the image position detection processing substrate 106 to the image forming apparatus 105Y,
The correction cycle is completed by directly or indirectly setting to 105M, 105C, 105K and interface boards 104Y, 104M, 104C, 104K and the like.

After the completion of this correction cycle, a good image in which the amount of color misregistration between the image forming apparatuses is minimized can be obtained during the color image forming operation which is the original function of the image forming apparatus.

In order to minimize the color misregistration, it is meaningless if the misregistration amount cannot be grasped at a level finer than the permissible color misregistration amount at the portion detecting the misregistration amount. In addition, unless the product's maintainability and reliability are taken into consideration, a product that satisfies the user cannot be provided.

Therefore, the structure of the detecting portion which can solve such a problem will be described.

FIG. 3 is an exploded perspective view specifically showing the structure of the image reading means, and FIG. 4 is a longitudinal sectional view of the main part when viewed in the direction of arrow A in FIG.

In FIG. 3, a housing 200 concretely shows the sensor 101 of FIG. 2, and has studs 201a and 201b on the front side and studs 202a and 202b on the back side as viewed from the main body of the apparatus. ing. 203, 20
Reference numeral 4 is a frame of the image forming apparatus.

The housing 200 includes studs 202a, 202
Insert b in the holes 203a and 203b of the rear frame 203, insert the studs 201a and 201b into the holes 205a and 205b of the plate 205, and fix the plate 205 to the front frame with the fixing screws 206. . Holes 203a in the rear frame 203,
203b and holes 204a, 204b in the front frame
Is opened with controlled dimensions so that the distance from the transfer / transport belt 8 and the alignment between the two are within a specified value.

With this structure, the housing 200 can be easily attached to and detached from the frame of the image forming apparatus, and at that time, the positional relationship between the transfer belt and the studs on the housing falls within a certain standard value. It looks like this. Therefore, in addition to facilitating and shortening the assembly work and maintenance after installation, even if there is a work to replace due to a failure of the detection unit after installation, it can be dealt with only by replacing the main body, which is a troublesome and time-consuming adjustment. No work is required.

FIG. 5 is a vertical cross-sectional view of the internal structure of the casing 200 of the image reading means shown together with the transfer / transport belt 8, and FIG. 6 is a toner image on the sensor substrate 211, the short focus lens array 212 and the transfer / transport belt 8. It is a figure which shows the positional relationship of three-dimensionally.

In the figure, reference numeral 210 is an image pickup device,
Reference numeral 11 denotes a substrate on which a drive circuit of the sensor 210 and peripheral circuits are mounted. Reference numeral 212 is a short focus lens array,
Reference numeral 18 is a substrate on which the illumination light source 217 and its peripheral circuits are mounted.

Two pairs of the sensor substrate 211 and the short focus lens array 212 are arranged on the housing 200. By using two sensors, it is possible to adjust the color misregistration in all directions such as the deviation in the main scanning direction, the deviation in the sub scanning direction, the magnification error, and the angular deviation with respect to the main scanning direction. For example, if only the adjustment in the sub-scanning direction is performed, one sensor may be used, and if sensors are used for each color, four sensors may be used. Needless to say, any number of sensors may be used. May be.

Further, 213 is a short focus lens array 212.
It is a member for holding and is adjustable in the vertical direction with respect to the housing 200. Further, the sensor board 211 is provided in the housing 200.
It is adjustable with respect to the stud 214 fixed to the. By having such a mechanism, the housing 200
The positional relationship between the sensor 210 and the short-focus lens array 212 can be adjusted as desired, and the sensor 210 and the short-focus lens array 212 can be attached with desired accuracy in accordance with the required performance.

Here, a case where a CCD is used as the reading means in order to detect the image position with high accuracy will be described.

FIG. 7 shows the structure of a general CCD.

As shown in FIG. 7, the CCD line sensor has a photosensitive section, a transfer section and an output section, and the transfer section is provided with two columns of registers in order to increase the degree of integration and reduce the transfer loss. Then, the transfer of the signal charges of the odd-numbered pixel and the even-numbered pixel is carried out in each of the n pixels, and they are outputted to the outside as an odd output and an even output via the respective output parts.

However, due to the difference in the drive waveform of the output section, the difference in the internal capacitance coupling, the linearity of the amplifier, etc., a difference occurs in the outputs of the two systems. In the case of high-speed driving, an output difference will occur due to the delicate timing of sample hold during analog processing.

In order to correct such an output difference to obtain an appropriate output value, it is necessary to have an amplification circuit and an offset adjustment circuit for each of the odd number and the even number, and further two quantization circuits are required. is there.

FIG. 8 is a block diagram of a conventional CCD signal processing circuit.

There are gain and offset adjustment circuits for the odd and even outputs of the CCD, which are adjusted to the reference voltage for quantization. Multiple CCDs, eg two Cs
In the case of a CD, a gain / offset adjusting circuit and a quantizing circuit are required for four systems. If the offset adjustment circuit does not saturate during quantization, it adds it to either odd or even output and adds or subtracts a certain value to correct the relative difference between even and odd. Good.

The offset adjusting circuit may be added after quantization as shown in the block diagram of FIG.
It is possible even after combining odd or even numbers. Since the correction value varies depending on the CCD, it is better to be variable.

FIG. 10 shows a block diagram of a conventional reading unit using a plurality of CCDs and an image position detection processing circuit.

A CCD-A substrate and a CCD-B substrate are built in the image reading unit, and they are mounted in the direction perpendicular to the traveling direction of the transfer / conveying belt 8. If the interval is as wide as possible, the accuracy of detecting the inclination of the image region will be better, but the selection is made in consideration of the effects of dirt, bending, warpage, vibration, etc. And CCD
-A and CCD-B are adjusted in advance so that they are parallel to each other on the jig, and each has the above-mentioned signal processing circuit built therein, and four gain / offset adjustment circuits and four quantization circuits.

Since the CCD drive signal needs to be synchronized with the two CCDs, the same drive signal is sent to each CCD. Further, the CLK is also synchronized with the CLK of the laser beam scanning device, and the frequency is an integral multiple thereof. The read image signal of CCD-A is stored in the image memory A in the image position detection processing unit, and the image signal of CCD-B is stored in the image memory B in the image position detection processing unit. Made and recorded. Next, the signals of image memory A and image memory B are C
The light amount unevenness is corrected by the PU, the difference between the image positions of the respective colors is detected, the relative shift amount between the image positions of the CCD-A and CCD-B is detected, and the image transfer position of each color is controlled by the image forming device controller. Therefore, it is possible to obtain a good image with no color shift.

In this case, the inclination in the image area is as shown in FIG.
As shown in, the difference Δ between the centers of gravity of the images transferred to the sheet conveying belt at the same time from the image forming unit can be represented.

On the other hand, in the present invention, the following color misregistration is detected.

Consider the case where two CCDs are used. The CCD sensor is attached in the direction perpendicular to the direction of movement of the transfer / conveyance belt 8 in order to detect an image inclination and a magnification error in the image area. On the other hand,
As shown in FIG. 3, CCD-A and CCD-B can also be detected by using time division.

That is, if the magnification in the paper transport direction is obtained from the positional deviation measurement pattern interval X1 read in the same CCD, the normal positional deviation measurement pattern interval between CCD-A and CCD-B is determined. I can know. Then, if the difference between this pattern interval and the actual pattern displacement measurement pattern intervals X2 and X3 between CCD-A and CCD-B is taken, the inclination in the image area can be obtained.

In the measurement, it is preferable to take an average of some points. If the magnification in the paper transport direction is not shifted, the theoretical pattern interval and the actual value may be compared.

As shown in FIGS. 13A, 13B, and 13C, the CCD-A and the CCD-B are alternately switched at the cycle of the image position measurement pattern, and four circuits are conventionally required. Further, the gain and offset adjusting circuit and the quantizing circuit can be reduced to two half circuits as shown in FIG. Therefore, it is possible to reduce the electric components and the space, and the number of interface signals with the image position detection processing unit is halved. Therefore, the number of pins of cables and connectors can be reduced, the memory can be reduced, the data width of the image position detection processing unit can be reduced, and the circuit can be reduced, which can significantly reduce the cost and improve the reliability. You can

If a general-purpose device in which two circuits for gain and offset adjustment and a quantization / synthesis circuit are integrated into an LSI is used,
More space can be saved and reliability can be increased. In FIG. 12, the signal is time-divided immediately after CCD output, but it may be after quantization. Further, in FIG. 12, the CCD drive circuit is on the image position detection processing unit, but it may be on the image reading unit.

Discharge devices for charging and discharging the photosensitive drum, and transferring and peeling the sheet are arranged around the image position measuring pattern reading means on the transfer / conveying belt 8. Discharge at 1000V. On the other hand, the sensor output signal level in the reading means is several hundred mV, which is about 1/1000 of that, and when the CCD analog output signal is transmitted for a long time, if it is transmitted as it is, it will be affected by the noise of the discharge device. A / D
Even if it is amplified to the input voltage level of the converter, it is very small compared to the voltage level of the peripheral device and may be affected by noise.

When the sensors are separated from each other, it may be better to transmit the quantized data. The configuration shown in FIG. 14 is effective for such a condition.

That is, the CCD-A section and the CCD-B section are connected by a flexible substrate or cable so that they can be independently varied while maintaining parallelism, and individually adjusted to match the optimum focus position for image reading. To do.

In this case, although the gain / offset adjusting circuit and the quantizing / synthesizing circuit cannot be eliminated, the cable from the image reading unit to the image position processing section can be eliminated, and the cost can be reduced. Further, general-purpose elements integrated into an LSI may be used for the gain / offset adjustment and the quantization / synthesis circuit.

As another different time division method, as shown in FIG. 15, CCD-A output and CC are output not for each area but for each pixel.
A method in which the D-B output is combined and sent to the image position detection unit is also considered.

In this system, the video rate is doubled, but it is an advantage that the inclination in the image area can be detected by simultaneously comparing the CCD-A output and the CCD-B output. Therefore, it is suitable for a system having a slow video rate. Similar to the above-described time division, this method may be an analog synthesizing method after gain and offset adjustment or a digital synthesizing method.

Next, of the plurality of outputs of the reading image pickup device,
A method of reading an image and detecting a color shift by using only one of the outputs will be described.

FIG. 16 is a block diagram for this detection method.

Compared with the block diagram of FIG. 8, there is a difference in that the system in which the gain / offset adjusting circuit, the quantizing circuit and the synthesizing circuit for one channel are omitted.

As described with reference to FIG. 7, the CCD signal output is divided into the odd output and the even output to be output to the outside.
However, due to the difference in the drive waveform of the output section, the internal capacitive coupling, the difference in the linearity of the amplifier, etc., a difference occurs in the outputs of the two systems. In order to correct this and obtain an appropriate output value, it is necessary to have an amplifying circuit and an offset adjusting circuit for each of the odd number and the even number, and two quantizer circuits are required. Some CCDs have an output in which odd and even numbers are combined internally, but in the end, there is no difference in the output difference between odd and even numbers. The difference remains, and even if digital shading correction and dark correction are performed, an error may occur when detecting the image position, and the speed required for the video processing circuit is doubled. I will end up. There is also a CCD having a single transfer section and a single output, but the pixel size is large, the number of pixels is small, and the cost is high.

On the other hand, in the configuration of this embodiment,
Even if a general-purpose CCD is used, there is no difference because all the outputs pass through a common circuit, and the speed of the video processing circuit may be half that of the composite output. The effective pixels of the CCD are thinned out and used, but the size of one pixel being read does not change, so if the image position data has a uniform distribution on the left and right, it is the same as when pixels are not thinned out. The result is obtained. Even if the image position data has a non-uniform distribution on the left and right, by using an image position detection algorithm such as the center of gravity method, almost the same result as when the pixels are not thinned out is obtained, and one pixel is scanned by the light beam. It is an error that can be ignored if it is considerably small with respect to the control step of the device.

The image position detection accuracy can be further improved by increasing the number of data contained in the read image. That is, the accuracy is improved by reducing the reading pixel size of the sensor to increase the resolution or increasing the width of the read image. For example,
If you want to read the image position data with an accuracy of 14um,
It is sufficient to use a sensor of 7 μm, which is half the pixel size, and operate only one of the channels. In this case, CCD
Although the sensitivity decreases due to the smaller pixel size, the resolution of the short focus lens array cannot follow even if the CCD resolution becomes too small. Therefore, the reset signal is decimated to 1/2 of the normal value to reduce the exposure amount. There is also a method of doubling and using. The resolution does not deteriorate in the sub-scanning direction.

The above is shown in FIG. 17 by way of example.

As shown in FIG. 7A, in the case of image position data having a symmetrical distribution, the results are the same when there is no thinning of effective pixels, and the results are exactly the same. When the address of is calculated, the center of gravity becomes the position of address 5.

On the other hand, in the case of image position data having an asymmetrical distribution as shown in (b) of the same figure, if the address of the center of gravity of the image position is calculated up to 3 digits after the decimal point by the center of gravity method, no thinning is performed. The center of gravity address is 5.273
The center-of-gravity address when there is thinning out is 5.214, and the difference is 0.059. When a sensor with a pixel size of 14 μm is used, it is 0.8261 μm and 1 u.
The error is less than or equal to m and is a value that can be ignored.

Next, a method for mechanically scanning the reading means in the direction perpendicular to the sheet conveying direction will be described.

Instead of using a plurality of image reading means in a time-division manner, one image reading means is mechanically scanned in a direction perpendicular to the sheet conveying direction and moved to a required image reading position to obtain a plurality of images. It is possible to obtain the same performance as when the reading means is provided.

For example, in FIG. 13, after the section (a) of the positional deviation measuring pattern is read by the CCD-A,
Move CCD-A to the position where CCD-B should be,
The section (b) of the misregistration measurement pattern may be read, or the position of the CCD-A may be returned to read the section (c) of the misregistration measurement pattern. At this time, the output interval (X2) of the misregistration measurement pattern,
(X3) may be set longer than the time in which CCD-A moves to the position where CCD-B should be and is stationary and stable.

In this embodiment, the transmissive illumination type structure using the transparent transfer belt material has been described. However, if the belt material is opaque, the illumination lamp is also incorporated in the housing. Such an effect can be obtained.

[0080]

According to the present invention, a plurality of sensor outputs for detecting a pattern for measuring the position of an image are used in a time-sharing manner, so that a circuit related to the sensor, a transmission cable and the like can be shared. Therefore, it is possible to simplify the device and reduce the cost with a small number of parts and a simple circuit.

Further, by using only one side output of the odd-numbered and even-numbered outputs of the image pickup device used as the reading means, the image reading means can be constructed with half the circuit scale and space of the conventional one. Therefore, it is possible to read the position of an image that is small and highly accurate, and it is possible to provide a more compact image forming apparatus.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a schematic diagram of a color misregistration correction system of a multi-transfer type color image forming apparatus.

FIG. 3 is an exploded perspective view of essential parts showing a specific configuration example of a detection unit in FIG.

4 is a vertical cross-sectional view of the main part as seen in the direction of arrow A in FIG.

FIG. 5 is a vertical cross-sectional view of a reading unit shown together with a transfer / conveyance belt.

FIG. 6 is a schematic perspective view for explaining a positional relationship between a sensor substrate housed in a housing, a short focus lens array, and a toner image on a transfer belt.

FIG. 7 is a diagram showing a general configuration of a CCD.

FIG. 8 is a block diagram of a conventional CCD signal processing circuit.

FIG. 9 is a block diagram of a signal processing circuit including an offset adjusting circuit.

FIG. 10 is a block diagram of a conventional image position processing circuit using a plurality of CCDs.

FIG. 11 is a diagram of a conventional example showing a procedure for detecting an image position by a reading unit.

FIG. 12 is a block diagram of an image position processing circuit according to the present invention.

FIG. 13 is a diagram showing a procedure for detecting an image position of a reading unit according to the present invention.

FIG. 14 is a block diagram showing another example of the image position processing circuit in the present invention.

FIG. 15 is a diagram showing an example of a time division pattern.

FIG. 16 is a block diagram showing a method for detecting color shift using only one of the image pickup devices.

FIG. 17 is a diagram showing an example of a distribution pattern of image position data.

[Explanation of symbols]

1: Platen, 2: Original, 3: Image sensor, 4: Image processing unit, 5Y, 5M, 5C, 5K: Laser beam scanning device, 6Y, 6M, 6C, 6K: Photosensitive drum, 7Y, 7
M, 7C, 7K: developing device, 8: transfer conveyor belt, 9: drive roller, 10: driven roller, 11: paper, 12: paper tray, 14: fixing device, 15: discharge tray, 101:
Sensor, 102: Light source, 104Y, 104M, 104
C, 104K: Interface board, 105Y, 10
5M, 105C, 105K: image forming apparatus, 106: substrate, 107: control substrate, 109: substrate, 20
0: housing, 210: sensor, 211: substrate, 212: short focus lens array, 214: stud, 215: seal glass, 217: illumination light source, 218: substrate

Claims (4)

[Claims] 1. A multi-image forming system for sequentially transferring and conveying images formed by a plurality of image forming units onto one recording medium to obtain a color image, and a pattern for measuring the position of an image on the recording medium. In an image forming apparatus having a plurality of sensors for detecting, each of the sensors is time-divided and output, and a system for synthesizing image measurement results by the respective sensors to determine the image position measurement pattern is provided. Image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the time-division of the output of the sensor is a system that is performed in a conveying direction of a sheet onto which an image on the recording medium is transferred. 3. The image forming apparatus according to claim 1, wherein a time division of the output of the sensor is provided for each pixel. 4. A multiple image forming system for sequentially transferring and conveying images formed by a plurality of image forming sections onto one recording medium to obtain a color image, and a pattern for measuring the position of the image on the recording medium. In an image forming apparatus equipped with a reading means for detecting, the reading means is composed of two image pickup devices, and as a system for detecting the position measuring pattern by the output of any one of the outputs in these image pickup devices. Image forming device.