JP2008185848A - Image forming apparatus - Google Patents

Abstract

An image forming apparatus capable of obtaining a sensor output value with high accuracy by stabilizing an output waveform of a reflective optical sensor.
An optical sensor (1) is disposed so that a detected surface (4a) of a transfer belt (4a) is on a curvature surface of a driven roller (2), and the optical sensor (1) is attached to a bracket (8) having an L-shaped cross section. The bracket 8 is guided and supported so as to be movable on the holder 11 in the direction of the arrow L. An eccentric cam 10 is attached to the rotating shaft of the DC motor 9, and as the eccentric cam 10 rotates, an engagement hole 15 that engages with the outer surface of the eccentric cam 10 moves the bracket 8 in the left-right direction (arrow L direction). Move to. In this way, the optical sensor 1 is moved in the left-right direction with respect to the transfer belt 4, and the optical sensor 1 can be set at a desired position by stopping the rotation of the DC motor 9.
[Selection] Figure 3

Description

  The present invention provides a reflection type optical system that detects reflected light from a reference image on an endless transfer belt stretched around at least two rollers onto which a reference image of toner formed on a photoconductor is transferred. The present invention relates to an image forming apparatus that includes a sensor and controls image forming conditions by sensor output by reflected light from the reference image detected by the optical sensor.

Conventionally, in an image forming apparatus such as an electrophotographic copying machine or a laser beam printer, density detection is performed on an image carrier such as a photosensitive member or an intermediate transfer member in order to always obtain a stable image density. A toner reference image such as a toner patch is created, the patch density is detected by an optical detection means, and image forming conditions such as exposure intensity, charging bias, and developing bias are adjusted based on the detection result. It was.
As detection means for such a density detection patch, a light emitting element such as an LED (Light Emitting Diode) as a light emitting means and a light receiving element such as a photodiode (PD) or a phototransistor (PTr) as a light receiving means. In general, a reflection type optical sensor that irradiates a toner patch for density detection with light emitted from a light emitting element and receives the reflected light with a light receiving element to obtain a sensor output corresponding to the toner density is generally known. ing.
However, in a reflection-type optical sensor, if there is a variation in sensitivity between the light emitting and receiving elements, it is difficult to obtain an accurate sensor output corresponding to the toner concentration, and an accurate toner adhesion amount can be calculated. There are cases where it is not possible.
In order to improve such an indexing failure of the toner adhesion amount, the output level of diffuse reflection light is determined based on the sensor output value of specular reflection light obtained from the toner patch for density detection for specular reflection light. It has been proposed to make adjustments for this purpose (see, for example, Patent Document 1).
JP 2005-337749 A

However, in the invention described in Patent Document 1, it is possible to appropriately correct the sensor output level with respect to the sensitivity variation of each element. However, since the optical sensor is disposed on the plane portion of the intermediate transfer belt, The output waveform is likely to be unstable due to the vibration of the intermediate transfer belt.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an image forming apparatus capable of stabilizing the output waveform of a reflective optical sensor and obtaining a sensor output value with high accuracy.

In order to solve the above-mentioned problem, the invention described in claim 1 has an endless transfer belt stretched around at least two rollers, and the toner transferred from the transfer belt on the basis of a reference image. In an image forming apparatus that includes a reflective optical sensor that detects reflected light, and that controls image forming conditions based on an output of the optical sensor, the surface to be detected by the optical sensor is at least one of the rollers. The optical sensor is disposed so as to be on the roller, and moving means for adjusting the position of the optical sensor is provided.
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the moving means includes a drive motor, an eccentric cam attached to a rotation shaft of the drive motor, and an engagement with the eccentric cam. And a position of the optical sensor attached via the bracket is adjusted by rotation of the eccentric cam.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the optical sensor is disposed at a position where the output of the optical sensor is maximized.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, a plurality of the optical sensors are arranged, and the moving means is provided for each optical sensor. To do.

  According to the present invention, it is possible to provide an image forming apparatus capable of obtaining a sensor output value with high accuracy by stabilizing an output waveform of a reflective optical sensor.

In the present invention, since the detection surface of the optical sensor is set on the driving roller or the driven roller, it is difficult to be affected by the wave-like vibration of the transfer belt, and a stable output waveform of the optical sensor can be obtained. Become.
However, in this way, when detecting the reflected light by the optical sensor on the curved surface of the roller, the reflected light entering the light receiving element is reduced, and as a result, the output of the light receiving element is lowered. This is because there are fewer flat surfaces of the transfer belt than when the surface of the transfer belt is the surface to be detected. Further, the output of the light receiving element also decreases due to a change in glossiness of the transfer belt due to contamination of the transfer belt over time, contamination of the optical sensor with toner, and the like.
For this reason, by adjusting the light amount of the light emitting element such as increasing the light amount of the light emitting element corresponding to the decrease in the output of the light receiving element as described above at every predetermined use time interval, the light receiving element with respect to the detection surface of the transfer belt The output needs to be a predetermined output.
However, it is necessary to control the input current to the LED for increasing the amount of light emitted from the reflective optical sensor so as not to exceed the upper limit current allowed by the LED circuit. This is because the LED will be damaged if the upper limit current is exceeded. For this reason, it is necessary to make the input current value as small as possible in the initial stage in anticipation of an increase in the input current to the LED with the passage of time.

  FIG. 1 shows voltage change factors in the initial and time-dependent changes of a reflective optical sensor using LEDs, a voltage drop amount due to the factors, and an input current value necessary for voltage recovery. FIG. 1 shows the result when an LED circuit with an upper limit current of 40 mA is used and the reference voltage is 4 V when the planar portion of the transfer belt is the detected surface. Factors that cause voltage changes in the initial stage are (1) voltage drop when detecting reflected light on a 19 mm diameter roller, and (2) voltage drop due to mechanical variations such as variations in sensor mounting position. . In (1), the output is reduced by 0.76V to 3.24V with respect to the reference voltage Vsg = 4V when the flat surface between the rollers is used as the detection surface. In (2), it is decreased by 0.65V. The output is 2.71 V (3.24 × (4−0.65) / 4). In addition, over time, (3) the output of the intermediate transfer belt is lowered due to the lower limit product (initial), (4) the output is lowered due to the change in the gloss of the intermediate transfer belt over time, and (5) the toner adheres to the sensor. A decrease in output can be considered, and (6) a decrease in output due to current variation of the LED element at the time of shipment from a Gia sensor (reflective optical sensor manufactured by Ricoh Instruments) can be considered. For (3), the central value of the glossiness of the intermediate transfer belt is 85.0, whereas the glossiness of the lower limit product is 75.0, a voltage drop of 0.39 V occurs, and the output voltage is 2.45 V (2 .71 × (4−0.39) / 4). As for (4), in this test, the glossiness of the intermediate transfer belt increased with time, 75.0 in (3) increased to the center value 85.0, the output decrease was 0 V, and the output voltage Became 2.45V. Furthermore, about (5), since the cleaning mechanism of the sensor was attached, the output fall was suppressed and became 0V. Further, regarding (6), the LED current variation was 24 mA, and the total current of these LEDs was 39.4 mA, which was within the LED circuit current upper limit standard current of 40 mA.

  However, when the mechanical variation of (2) is large, the upper limit standard current of 40 mA is exceeded, so it is necessary to suppress the mechanical variation as much as possible. As the mechanical variation, as shown in FIG. 2, a roller that stretches the intermediate transfer belt, for example, a line connecting the center axis O of the driven roller 2 and the center of the optical sensor 1 is (A) There are positional deviation in the vertical direction (M direction in FIG. 2), (B) positional deviation in the horizontal direction (L direction in FIG. 2), (C) positional deviation in the rotational direction (θ direction in FIG. 2), and the like. The upper limit current of the LED is 40 mA, and in consideration of the decrease over time (belt gloss fluctuation and sensor toner contamination), the allowable range of positional deviation of the reflective optical sensor at the initial stage is about (A) Is ± 0.3 mm, (B) is ± 0.2 mm, and (C) is ± 1 degree. By adjusting the position of the optical sensor so that these positional deviations are within the allowable range, it is possible to set the current within the upper limit standard current value. In FIG. 2, 1 is a reflection type optical sensor, 2 is a follower roller for moving the intermediate transfer belt, and the intermediate transfer belt is omitted in the drawing.

However, it is very strict to maintain such positional accuracy, and it is difficult to ensure only by component accuracy. If such positional accuracy cannot be ensured, the initial LED current value will increase, and the sensor output will decrease due to transfer belt glossiness fluctuation and sensor contamination over time. The current value may exceed the upper limit value. If this happens, the LED of the light emitting element will fail, or if the device is set to detect an error with the upper limit current value of the LED, the device will be in a failed state. In addition, when the upper limit current value of the LED is a limiter, the LED current does not exceed the upper limit value, but the output of the light receiving element is reduced. In such a case, the detection output of the density detection pattern becomes unstable, and stable density control cannot be performed. Further, if the positional accuracy cannot be ensured, the output waveform is disturbed, so that the detection accuracy of the color matching pattern is deteriorated and an abnormal image in which the color is shifted is generated.
In the present invention, from the viewpoint of the above circumstances, the optical sensor is arranged at a position where the surface to be detected of the reflected light of the transfer belt by the optical sensor is on the roller over which the transfer belt is stretched. The position is adjusted.
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 3 is a diagram showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention. In FIG. 3, reference numeral 3 denotes a drum-shaped photoconductor, and Y, C, M, and BK denote yellow, cyan, magenta, and black photoconductors, respectively. An endless intermediate transfer belt 4 is stretched around the driving roller 5 and the driven roller 2 and is moved in the direction of arrow A by the rotation of the driving roller 5.
First, an image forming method using this image forming apparatus will be described. Each photoconductor 3 that rotates in the direction of the arrow includes a charging device 12 and a developing device 13. The surface of the photoconductor 3 is uniformly charged by the charging device 12, and the charged photoconductors are yellow, cyan. , Exposure is performed by laser light R based on image information corresponding to magenta and black, and an electrostatic latent image is formed. Subsequently, the electrostatic latent image is supplied with each color toner from the developing device 13 to form a visualized toner image. The toner image formed on the photoreceptor 3 is transferred to the intermediate transfer belt 4 by the primary transfer roller 6. The toner image formed on the intermediate transfer belt 4 is transferred onto the transfer paper S by the secondary transfer roller 7. The toner image transferred onto the transfer paper S is heated and pressed by the fixing device 14 to be fixed, and then discharged. In FIG. 3, the charging device 12 and the developing device 13 include any one of the C, M, and BK photoconductors 3, but only the Y photoconductor 3 is illustrated, and the other photoconductors 3 are omitted. ing.
In this way, a full color image is formed. When a toner image is formed on the photosensitive member 3, a reference image such as a density detection toner patch and a color matching pattern is formed on the photosensitive member 3, and the reference image is intermediate. The toner image is transferred to the transfer belt 4 and the density and color of the transferred reference image is detected by the reflective optical sensor 1 to detect the toner density and the like. Based on the detection result, the exposure intensity, the charging bias, and the development are detected. Image forming conditions such as bias are adjusted.

FIG. 4 is a diagram showing a schematic configuration of the reflective optical sensor 1. 1a is a light emitting element, 1b is a regular reflection light receiving element, and 1c is a diffuse reflection light receiving element. The light beam emitted from the light emitting element 1a is applied to the toner image of the transfer belt 4 (detected surface). Reflected light reflected from the toner image and the transfer belt surface is detected by a regular reflection light receiving element and a diffuse reflection light receiving element. The output voltage from these light receiving elements is detected to detect the toner density, and the above-mentioned image forming conditions are adjusted so as to obtain an appropriate toner density.
The present embodiment is characterized in that the reflective optical sensor 1 is set at a specific position and provided with a setting position adjusting means. As shown in FIG. 3, the optical sensor 1 is arranged so that the detected surface 4 a (see FIG. 4) of the transfer belt 4 is on the curved surface of the driven roller 2. It can move in the direction.

The optical sensor 1 is attached to a bracket 8 having an L-shaped cross section, and the bracket 8 is guided and supported so as to be movable on the holder 11 in the arrow L direction. An eccentric cam 10 is attached to the rotating shaft of the DC motor 9, and the eccentric cam 10 is engaged in a rectangular engagement hole 15 formed in a bent piece of the bracket 8, as shown in FIG. As the rotation shaft 9a of the DC motor 9 rotates, the center of the eccentric cam 10 rotates while being eccentric. As the eccentric cam 10 rotates, the engagement hole 15 that engages with the outer surface of the eccentric cam 10 moves the bracket 8 in the direction of arrow L. In this way, the optical sensor 1 is moved in the sub-scanning direction with respect to the transfer belt 4, and the optical sensor 1 can be set at a desired position by stopping the rotation of the DC motor 9. .
By observing the output voltage of the optical sensor 1, the optical sensor 1 can be set to an appropriate position in the L direction. FIG. 6 is a graph showing the relationship between the output voltage of the optical sensor 1 and the position (offset amount) in the L direction. As is apparent from this figure, the peak position P1 of the output voltage is the optimum position of the optical sensor 1 with respect to the detection surface. By obtaining the peak position P1 and stopping the rotation of the DC motor 9, the optical sensor 1 can be set at the optimum position.
In this way, in this embodiment, the eccentric cam 10 is used to adjust the position of the reflective optical sensor 1, so that fine adjustment is possible. Further, since only the DC motor 9 having an eccentric cam attached on the rotation shaft 9a needs to be installed in the image forming apparatus, the image forming apparatus can be easily installed in view of the layout of the image forming apparatus. As a result, the position of the optical sensor 1 can be automatically adjusted to the optimum position from the output of the reflective optical sensor 1, so that the initial LED current value is lowered, and the LED current becomes the upper limit over time. Therefore, it is possible to prevent the sensor from malfunctioning and to perform stable image density control.

  Although it is possible to install a plurality of reflective optical sensors, there are cases where these sensors are installed on a single substrate due to layout problems or cost problems. However, each of the optical sensors 1 has variations in sensitivity between the light emitting element and the light receiving element and variations in accuracy of the installation position on the substrate. It is difficult to make. Therefore, in this embodiment, as shown in FIG. 5, a DC motor 9 corresponding to each of the two optical sensors 1 is provided, and each sensor is adjusted independently. The optical sensor 1 is arranged so that the reference image 4b such as a color matching detection pattern formed at a plurality of positions such as both ends of the image is detected by the optical sensor 1 adjusted independently. In this way, reference images 4b are formed at a plurality of locations on the transfer belt 4, and corresponding optical sensors 1 are installed for these reference images 4b, and the plurality of optical sensors 1 can be adjusted independently. In this case, each optical sensor 1 can be adjusted to the optimum position, which is preferable. In this way, since the optical sensors 1 and 1 are individually adjusted in position in order to place all the installed optical sensors 1 in an optimal position, the initial LED current value is the lowest, In addition, it is possible to ensure the positional accuracy of the reflective optical sensor at a position where the output waveform is stable. As a result, the sensor 1 can be automatically adjusted to the optimum position from the output of the reflective optical sensor 1, so that the initial LED current value is lowered and the LED current is prevented from exceeding the upper limit value over time. Thus, it is possible to prevent the sensor 1 from being broken, and stable image density control can be performed.

As described above, in the image forming apparatus according to the present embodiment, the color matching detection pattern and the image density detection pattern 4 b on the transfer belt 4 are detected by the reflective optical sensor 1 on the curved surface of the driven roller 2. Since the optical sensor 1 is disposed in such a manner, an appropriate and stable output waveform can be obtained even when wave-like vibration of the transfer belt 4 occurs, the detection accuracy of the color matching pattern is good, and the color misregistration image can be obtained. Occurrence can also be prevented.
In the image forming apparatus according to the present embodiment, the position of the reflective optical sensor 1 can be adjusted by moving means such as a drive motor, and the position accuracy is ensured. As a result, the LED current does not exceed the upper limit value over time, the optical sensor 1 can be prevented from malfunctioning, and stable image density control can be performed.
In the above embodiment, the optical sensor 1 is disposed so that the detected surface 4a of the transfer belt 4 is on the driven roller 2. However, the optical sensor 1 is not limited to the driven roller 2, and may be on the driving roller 5. Alternatively, it may be on another roller on which the transfer belt 4 is stretched.
In the present embodiment, a full-color image forming apparatus has been described. However, a similar effect can be obtained even with a monochrome single-color image forming apparatus.

FIG. 7 shows a schematic configuration of the moving means of the optical sensor 1 according to another embodiment of the present invention. In this embodiment, the optical sensor 1 is attached to the driven roller 2 so as to be movable in the vertical direction (direction of arrow M). Also in this embodiment, the eccentric cam 10 is attached to the rotating shaft 9a of the DC motor 9, and the eccentric cam 10 is formed in a rectangular shape as shown in FIG. The bracket 8 is engaged in the engagement hole 15, and the bracket 8 moves up and down by the rotation of the eccentric cam 10. When the bracket 8 is moved up and down, the engagement holes 15 are arranged such that the long holes 15a are orthogonal to the position shown in FIG. Can be easily achieved.
In this way, the use of the eccentric cam enables automatic positioning of the optical sensor 1 in the vertical direction with a simple structure.

FIG. 8 shows a schematic configuration of the moving means of the optical sensor 1 according to another embodiment of the present invention. In this embodiment, an example in which the optical sensor 1 is attached to the driven roller 2 so as to be rotatable (rotation in the direction of the arrow θ) is shown. Also in this example, the eccentric cam 10 is attached to the rotating shaft 9a of the DC motor 9, and the eccentric cam 10 is engaged in the rectangular engaging hole 15 of the bracket 8 as shown in FIG. 8 is guided and supported so as to be rotated around a rotation fulcrum 11 a of the bracket 8 formed on the holder 11. Therefore, the bracket 8 is rotated in the θ direction about the rotation fulcrum 11a by the rotation of the eccentric cam 10, and the optical sensor 1 can be positioned at a desired angle by stopping the rotation of the DC motor 9.
Thus, the use of the eccentric cam enables the optical sensor 1 to be positioned at a position automatically rotated at a desired angle with a simple structure.
In the first to third embodiments, the movement direction of the optical sensor 1 is the single direction of the L direction, the M direction, and the θ direction, but a plurality of the L direction, the M direction, and the θ direction may be used as necessary. Needless to say, it can be adjusted in the direction or in all directions.

The figure which shows the relationship which shows the output reduction factor of LED, the total value of output voltage, and an electric current by a table | surface. Schematic which shows the attachment positional relationship of the optical sensor for demonstrating the required position accuracy of the reflection type optical sensor by this invention. 1 is a side view showing a schematic configuration of an image forming apparatus according to Embodiment 1 of the present invention. Sectional drawing which shows schematic structure of the optical sensor used in Example 1 by this invention. The top view which shows the engagement relationship of the bracket of Example 1 by this invention, and an eccentric cam. The graph which shows the relationship between the optical sensor position of Example 1 by this invention, and an output voltage. The schematic block diagram which shows the movement relationship of the optical sensor by the moving means of the optical sensor of Example 2 by this invention. The schematic block diagram which shows the movement relationship of the optical sensor by the moving means of the optical sensor of Example 3 by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Reflection type optical sensor, 1a ... Light emitting element, 1b ... Regular reflection light light receiving element, 1c ... Diffuse reflected light light receiving element, 2 ... Driven roller, 3 ... Photoconductor, 4 ... Transfer belt, 4a ... Detection surface, 5 DESCRIPTION OF SYMBOLS ... Drive roller, 8 ... Bracket, 9 ... DC motor, 9a ... Rotating shaft, 10 ... Eccentric cam, 11 ... Holder, 11a ... Rotation fulcrum, 12 ... Charging device, 13 ... Developing device, 14 ... Fixing device, 15 ... Hole

Claims (4)

Having an endless transfer belt stretched around at least two rollers;
A reflective optical sensor for detecting reflected light from a reference image of toner transferred onto the transfer belt;
In an image forming apparatus that controls image forming conditions based on the output of the optical sensor,
The optical sensor is disposed so that a surface to be detected of reflected light by the optical sensor is on at least one roller of the roller, and
An image forming apparatus comprising a moving means for adjusting the position of the optical sensor. The moving means is
A drive motor;
An eccentric cam attached to the rotating shaft of the drive motor;
A bracket having an engaging portion that engages with the eccentric cam;
The image forming apparatus according to claim 1, wherein the position of the optical sensor attached via the bracket is adjusted by rotation of the eccentric cam.   The image forming apparatus according to claim 1, wherein the optical sensor is arranged at a position where the output of the optical sensor is maximized. A plurality of the optical sensors are disposed,
The image forming apparatus according to claim 1, wherein the moving unit is provided for each optical sensor.

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