JPH08137168A - Color image forming device - Google Patents

Abstract

PURPOSE: To prevent the position detecting accuracy of a toner image carrier from being deteriorated even when the end of a reflection marker on the toner image carrier is turned up. CONSTITUTION: A position detecting means is constituted of the reflection marker 40 set out of an image area on an intermediate transfer belt 19 being the toner image carrier and a reflection type photosensor 50 detecting reflected light from the marker 40, and an area (detection area) 41 having different reflectance only at one part is formed on the reflection marker 40, and image data is started to be written with a laser beam on a photoreceptor by a laser write means synchronizing with a signal at the time of detecting the reflected light from the detection area 41 by the photosensor 50. It is conceivable that the detection area 41 is formed as an area having a line segment orthogonal with the rotating direction of the belt 19 or an area having the line segment and a line segment forming a specified angle to the line segment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an electrophotographic color image forming apparatus such as a digital color copying machine or a color laser printer.

[0002]

2. Description of the Related Art In a color image forming apparatus using an electrophotographic method such as a digital color copying machine, the surface of a rotating photoconductor is uniformly charged by a charging means, and a plurality of colors are colored by a laser writing means. After the image data is sequentially written with a laser beam to form an electrostatic latent image, toners of different colors are attached by a plurality of developing means to form a toner image for visualization, and each toner image is first transferred. There is one in which the toner image carrier such as the intermediate transfer belt or the intermediate transfer drum is sequentially transferred by means of the means and superposed, and then collectively transferred to the recording paper by the second transfer means.

In such a color image forming apparatus, since the positions of the toner images of the respective colors to be superposed on the toner image carrier must be accurately matched, the position for detecting the position of the toner image carrier in the circumferential direction is detected. A detection means is provided.

For example, a marker of a light reflector (hereinafter referred to as "reflection marker") is installed outside the image area on the toner image carrier, and a reflection type photosensor provided at a predetermined position so as to face the marker causes the reflection. By detecting the reflected light of the marker, the reference position in the circumferential direction of the toner image carrier is detected, and in synchronization with the detection signal, the writing of the image data by the laser light on the photoconductor by the laser writing means is started. I try to control the timing.

[0005]

However, even if the reflection marker is outside the image area in the circumferential direction of the toner image carrier, it is unavoidable that the marker is contaminated with time. Therefore, when cleaning the surface of the toner image bearing member with the cleaning unit, it is possible to clean the surface of the reflective marker, but the end of the reflective marker is turned up by the load of the rubber blade provided in the cleaning unit. This causes a problem that the toner image carrier rises, and the position detection accuracy of the toner image carrier deteriorates.

Further, when the toner image carrier is an intermediate transfer belt, there is a drawback that the repeated circumferential movement causes a positional deviation (belt of the belt) in a direction orthogonal to the circumferential direction of the belt itself. . That is, if the intermediate transfer belt is twisted due to repeated movements, a deviation with time occurs when the reflected light of the reflective marker is detected by the reflective photosensor. Further, if the belt is twisted during one image forming process, the toner images of the respective colors are misaligned when a superimposed image of a plurality of colors is formed on the intermediate transfer belt.

The present invention has been made in view of the above points, and prevents the accuracy of detecting the position of the toner image carrier from deteriorating even if the end of the reflection marker on the toner image carrier is turned up. With the goal. Further, when the toner image carrier is an intermediate transfer belt, it is also an object to be able to always detect the reference position of the intermediate transfer belt at a constant timing even if a twist occurs due to the repeated circumferential movement.

Further, when the toner image carrier is an intermediate transfer belt, it is also an object to prevent the toner images of the respective colors from being displaced when forming a superimposed image of a plurality of colors on the intermediate transfer belt. Still another object is to prevent the foreign matter from being erroneously detected even when the foreign matter adheres to a portion other than the reflection marker portion on the toner image carrier.

[0009]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the present invention provides a rotating photoconductor, a charging unit for uniformly charging the surface of the photoconductor, and a photoconductor charged by the unit. Laser writing means for sequentially writing image data of a plurality of colors on the surface by laser light to form an electrostatic latent image, and electrostatic latent images sequentially formed on the surface of the photoconductor by the means are formed by toner of different colors. A plurality of developing means for adhering to form a toner image for visualization, and a plurality of color toner images formed on the photoreceptor by the developing means, which circulates adjacent to the photoreceptor and are sequentially rotated, are superposed and held. Toner image carrier, first transfer means for transferring the toner image on the photoreceptor to the toner image carrier, second transfer means for transferring the toner image on the toner image carrier to recording paper, and toner image Detects the circumferential position on the carrier Color image forming apparatus including position detection means and optical writing start timing control means for controlling the timing of starting writing of image data by laser light onto the photoconductor by the laser writing means according to the detection result of the means In, the following is done.

That is, the position detecting means is composed of a reflection marker installed outside the image area on the toner image carrier and a reflection type photo sensor for detecting the reflected light, and only a part of the reflectance is provided on the reflection marker. A different area is provided, and the optical writing start timing control means is synchronized with a signal when the photosensor of the position detecting means detects the reflected light of the area having different reflectance on the reflection marker. This is a means for starting the writing of the image data on the upper side by the laser beam.

The regions having different reflectances on the reflection marker may be regions having line segments orthogonal to the circumferential direction of the toner image carrier. Alternatively, a region having a different reflectance on the reflection marker may be a first region that is orthogonal to the circumferential direction of the toner image carrier.
May be a region having a line segment of and a second line segment forming a certain angle with respect to the line segment.

In this case, the first line segment and the second line segment are detected based on the detection timings of the first line segment and the second line segment in the regions having different reflectances on the reflection marker by the photosensor of the position detection means. It is desirable to provide a measuring means for reading the distance to the line segment and measuring the variation amount in the direction orthogonal to the circumferential direction of the toner image carrier by the variation of the distance in each color superposition step.

Further, the optical writing start timing control means is provided with means for correcting the writing start timing of the image data by the laser light onto the photoconductor by the laser writing means in accordance with the fluctuation amount measured by the measuring means. It is good to provide. In addition, the area with different reflectance on the reflection marker,
The area may have a reflectance different from that of the toner image carrier.

[0014]

According to the color image forming apparatus of the present invention, the position detecting means is constituted by the reflection marker provided outside the image area on the toner image carrier and the reflection type photo sensor for detecting the reflected light, An area with a different reflectance is provided on the marker, and the optical writing start timing control means synchronizes with the signal when the photosensor of the position detection means detects the reflected light in the area with a different reflectance on the reflection marker. Then, the writing of the image data by the laser beam onto the photoconductor by the laser writing means is started, so that even if the edge of the reflection marker on the toner image carrier is turned up, good detection can be performed. The position detection accuracy of is not deteriorated.

If the areas having different reflectances on the reflection marker are areas having line segments orthogonal to the circumferential direction of the toner image carrier, when the toner image carrier is an intermediate transfer belt,
The position of the intermediate transfer belt can always be detected at a constant timing even if twisting occurs due to the repeated circumferential movement.

Alternatively, a region having different reflectance on the reflection marker is divided into a first line segment orthogonal to the circumferential direction of the toner image carrier and a second line segment forming a constant angle with respect to the line segment. And a second line segment of a region having different reflectance on the reflection marker by the photo sensor of the position detection means and the second line segment.
The first line segment and the second line segment based on the detection timing of the line segment of
The distance from the line segment of the toner image carrier is read, and the amount of fluctuation in the direction orthogonal to the circumferential direction of the toner image carrier is measured by the variation of the distance in each color superposition step. In the case of the intermediate transfer belt, it is possible to prevent the positional deviation of the toner images of the respective colors when forming a superimposed image of a plurality of colors on the intermediate transfer belt.

In this case, the optical writing start timing control means corrects the writing start timing of the image data by the laser light on the photoconductor by the laser writing means according to the variation amount measured by the measuring means. By doing so, even if a superposed image of a plurality of colors is formed on the intermediate transfer belt, it is possible to obtain a good color image without the positional deviation of the toner images of the respective colors.

Further, if a region having a different reflectance on the reflection marker is a region having a reflectance different from that of the toner image carrier, when foreign matter adheres to the toner image carrier other than the reflection marker portion. However, the foreign matter is not erroneously detected, and the position of the toner image carrier can always be detected accurately.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be specifically described below with reference to the drawings. FIG. 2 is a schematic configuration diagram showing a mechanical portion of a digital color copying machine according to an embodiment of the present invention, and FIG. 3 is a partially enlarged view around the photosensitive drum and the intermediate transfer belt shown in FIG.

The color scanner 1 illuminates the lower surface (color image) of the original 3 with the illumination lamp 4, and reflects the reflected light through the mirrors 5a, 5b, 5c and the lens 6 to CC.
By forming an image on the color line sensor 7 composed of D, the color image data of the original 3 is converted into R of the three primary colors of the additive method.
(Red), G (green), B (blue) are decomposed and read, and converted into an electric image signal.

Then, the R, G, B color image signals are subjected to color conversion processing by the image processing section, and the C of the three subtractive primary colors is used.
(Cyan), M (magenta), Y (yellow), and K (black) image data are obtained and once stored in the image memory, and then read out, and the color printer 2 reads the C, M, Y, and K toner images. It is formed and then overlapped to form a full-color image.

The color printer 2 has a photosensitive drum 9 inside, and a cleaning unit 10, a charge eliminating lamp 11, a charging charger 12, a potential sensor 13, and K around the photosensitive drum 9.
Developing device 14, C developing device 15, M developing device 16, Y developing device 1
7, a development density pattern detector 18, an intermediate transfer belt 19 and the like are provided.

In order to develop the electrostatic latent image, each of the developing devices 14 to 17 develops sleeves 14a to 17a which rotate so as to bring the toner into contact with the photosensitive drum 9, and developing paddles 14b to 17b which scoop up and agitate the toner. And toner concentration detection sensors 14c to 17c and the like. In this embodiment, the order of writing and developing with laser light (color image forming order) is K, C, M, Y.

When the copying operation is started, the color printer 2 orbits the photosensitive drum 9 in the direction of the arrow A, the surface of the photosensitive drum 9 is uniformly charged by the charging charger 12, and the color scanner 1 sends it. Image data of a plurality of colors corresponding to the color image of the original 3 is subjected to image processing, and then sequentially written by a laser beam by a laser writing unit 8 to form an electrostatic latent image.

In the laser writing unit 8, first, the leading end portion of the K latent image formed on the photosensitive drum 9 uniformly charged by the charging charger 12 according to the K image data is at the developing position of the K developing device 14. When K reaches, the K latent image begins to be developed with K toner by the rotating developing sleeve 14a, and K development ends when the rear end of the K latent image passes the developing position.

Then, the K formed on the photosensitive drum 9
The toner image is intermediately transferred onto the intermediate transfer belt 19 which rotates adjacent to the photosensitive drum 9. This intermediate transfer is performed by applying a predetermined bias voltage to the intermediate transfer bias roller 20 when the photosensitive drum 9 and the intermediate transfer belt 19 contact each other. Then, the photosensitive drum 9
The residual toner above is removed by the cleaning unit 10, the charge is removed by the charge removal lamp 11, and then the charging by the charging charger 12 is started again.
The cycle of development, intermediate transfer and cleaning is repeated.

As a result, the K, C, M, and Y toner images sequentially formed on the photoconductor drum 9 are sequentially aligned and transferred onto the intermediate transfer belt 19 to transfer the intermediate transfer image of four colors. Are formed and are collectively transferred onto a transfer paper. Therefore, when the K step of forming the K toner image on the intermediate transfer belt 19 is completed, the next intermediate transfer belt 19 is performed.
The process proceeds to the C step of forming the C toner image on the upper surface, but the C latent image is formed by the laser writing unit 8 so that the front end portion of the C toner image and the front end portion of the K toner image on the intermediate transfer belt 19 are aligned. The timing of starting writing by the laser light for use in the laser is adjusted.

Similarly, the M step and the Y step are carried out,
An intermediate transfer image of four colors is formed on the intermediate transfer belt 19. However, the image forming order is not limited to K, C, M, and Y, and the image forming order is predetermined according to the characteristics of the toner and the finishing effect of the color image finally formed on the transfer paper. To be done. The intermediate transfer belt 19 is stretched around an intermediate transfer bias roller 20, a drive roller 21, and a driven roller group, and is rotated in the direction of arrow B by a drive motor (not shown).

The belt cleaner 22 is a brush roller 22.
a, rubber blade 22b, and contact / separation mechanism 2 from the belt
2c and the like, which is in contact with the intermediate transfer belt 19 before the first intermediate transfer of the K toner image, but is separated from the belt surface by the contact / separation mechanism 22c when the intermediate transfer is started.

The paper transfer unit 23 is composed of a paper transfer bias roller 23a, a roller cleaning blade 23b, a belt contact / separation mechanism 23c and the like. The paper transfer bias roller 23a is normally the intermediate transfer belt 1
Although separated from 9, when the four-color superimposing intermediate transfer images formed on the intermediate transfer belt 19 are collectively transferred to the transfer paper,
The transfer paper 24 is pressed against the intermediate transfer belt 19 at a timing, and a predetermined bias voltage is applied to the roller 23a to transfer the intermediate transfer image to the transfer paper 24.

The transfer paper 24 is the paper feed roller 25.
And the registration roller pair 26, the intermediate transfer belt 1
The four-color superimposing intermediate transfer image of No. 9 is fed at the timing when the front end portion reaches the transfer position.

Here, the operation of forming an intermediate transfer image of four-color overlapping on the intermediate transfer belt 19 will be described in more detail. Outside the image area on the intermediate transfer belt 19, a reflection marker 40 is installed as shown in FIG.
Position detection in which a reflection type photo sensor (hereinafter, also simply referred to as “photo sensor”) 50 is provided at a predetermined position opposite to this, and the position of the intermediate transfer belt 19 in the circumferential direction is detected by the reflection marker 40 and the photo sensor 50. Constitutes a means. Further, on the reflection marker 40, as shown in an enlarged view in FIG. 4, a region (hereinafter also referred to as a “detection region”) 41 having a different reflectance is provided only partially (at the center).

The reflective photosensor 50 includes a light emitting element (L
ED), and the light reflected by the reflection marker 40 is received by the light receiving element (photodiode or phototransistor). Therefore, the control unit (which will be described later) of the color printer 2 detects the reflected light from the detection area 41 on the reflection marker 40 by the reflection type photo sensor 50, so that the reference position (the front end) of the intermediate transfer belt 19 in the circumferential direction (the front end). Position).

Then, in synchronization with the signal (reference position detection signal) when the reflection photosensor 50 detects the reflected light from the detection area 41, the laser writing unit 8 emits the laser light onto the photosensitive drum 9. The writing of the K image data is started, the intermediate transfer belt 19 makes one round, and the reflective photosensor 50 again causes an area 41 having a different reflectance.
When the reflected light from is detected, the writing of the C image data by the laser light onto the photosensitive drum 9 by the laser writing unit 8 is started in synchronization with the signal.

As a result, the C toner image formed on the photosensitive drum 9 is accurately aligned with the K toner image transferred on the intermediate transfer belt 19, and is transferred in a superposed manner. Then, after that, M, Y
Proceeding to the image process, an intermediate transfer image of four-color superimposition is formed on the intermediate transfer belt 19, and the intermediate transfer image of four-color superposition is collectively transferred to a transfer paper.

After that, the transfer paper on which the intermediate transfer images of four colors are transferred together from the intermediate transfer belt 19 is collectively conveyed to the conveyor belt 2.
At 7, the toner image is conveyed to the fixing unit 28, and the toner image is pressure-melted and fixed by the fixing roller 28a and the pressure roller 28b whose temperature is controlled to a predetermined temperature.

The surface of the photosensitive drum 9 after the belt transfer is cleaned by the cleaning unit 10 and uniformly discharged by the discharging lamp 11. Also, 4
When the color-superimposed intermediate transfer image starts to be transferred to the transfer paper, the belt cleaner 22 contacts the intermediate transfer belt 19 that has finished the paper transfer by the contact / separation mechanism 22c, and remains by the brush roller 22a and the rubber blade 22b. Cleaning is performed by collecting the toner.

By the way, at the time of repeat copying for obtaining a plurality of copies from the same original, the color scanner 1 operates only for the first original, and the stored color image data forms an image on the photosensitive drum 9. Is the first Y
Following the (fourth color) process, the process proceeds to the second K (first color) process at a predetermined timing. In addition, the intermediate transfer belt 19
The second K toner image is intermediately transferred to the area whose surface is cleaned by the belt cleaner 22, following the batch paper transfer of the first four-color superimposed intermediate transfer image to the transfer paper. After that, the operation is the same as that of the first sheet. Three
The second and subsequent sheets are the same as the second sheet.

The transfer sheet cassettes 30 to 33 store transfer sheets of various sizes, and the transfer sheet cassettes 30 to 33 are arranged at different timings from the cassettes that store transfer sheets of a size designated by an operation signal from an operation panel (not shown). It is fed to the pair of registration rollers 26. Reference numeral 34 is a manual paper feed tray for OHP paper or thick paper.

In the above, the case of the copy mode for obtaining four full colors has been described, but in the case of the three-color copy mode or the two-color copy mode, the same operation is performed for the designated color and the number of colors. In the single-color copy mode, only the developing device of the designated color is operated until the predetermined number of sheets are finished, and the intermediate transfer belt 19 is driven at a constant speed in the arrow B direction while being in contact with the photosensitive drum 9. Belt cleaner 2
2 also operates while being in contact with the intermediate transfer belt 19.

FIG. 5 is a perspective view showing a structural example of the laser writing unit 8 in the color printer 2 shown in FIG.
In this laser writing unit 8, the laser diode
The laser light emitted from the (LD) 61 is made into a parallel light flux by the collimator lens 62, and the aperture 6 having a slit corresponding to the size of the dot (pixel density) to be formed next.
By 3, the extra laser light is cut.

The parallel light flux shaped by the aperture 63 is condensed by the cylinder lens 64 so that the laser light for image formation in the main scanning direction becomes a predetermined size on the photosensitive drum 9, and the polygon motor 65 is used. The polygon mirror 66 that is rotated by is scanned in the main scanning direction (axial direction of the photoconductor drum 9) x. Then, the pair of Fθ lenses 6
7 makes the constant-angle motion a uniform velocity motion and corrects the field curvature.

The angle of the laser beam passing through the Fθ lens 67 is changed by the reflection mirror 68, and the cylinder lens 69
Thus, light is focused in the sub-scanning direction (rotational direction of the photosensitive drum 9) y, and an image is formed on the photosensitive drum 9 in a spot shape with a predetermined beam diameter.

The laser beam immediately before scanning on the photosensitive drum 9 is incident on the optical fiber 72 via the mirror 70 and the cylinder lens 71, and then the laser beam such as a photodiode provided in a control unit (not shown). It is detected by the synchronization detection sensor (light receiving element) 73. Then, the control unit uses the synchronization detection signal from the synchronization detection sensor 73 to control the emission start timing of the laser light (the writing start position of the image data by the laser light) for each scanning.

FIG. 6 is a block diagram showing the control system of the color printer 2. The control unit 80 uses a microcomputer and includes operation signals from the operation panel 81, the reflection type photo sensor 50 and the synchronization detection sensor 73. By inputting detection signals from various sensors and switches 82, as shown in FIG.
The laser writing unit 8, the charging charger 12, the developing devices 14 to 17, the copying process device 83 such as the paper transfer unit 23, and the sequence device 84 such as a motor, a solenoid, a clutch, and a fixing heater. Panel 8
The display information is sent to 1.

FIG. 7 is a flow chart showing the processing according to the present invention by the control unit 80 of FIG. This routine is executed when the image forming operation (copy operation) starts. First, the reflective photosensor 5 shown in FIG.
Intermediate transfer belt 1 which is rotating in the direction of arrow B by 0
By detecting the reflected light from the reflection marker 40 (the tip portion) on 9 and the reflected light from the detection region 41 provided in the center thereof, the intermediate transfer belt 19 is detected.
When the reference position of is detected, the following processing is performed.

That is, in synchronization with the signal when the detection area 41 is detected by the reflection type photosensor 50, the registration position, that is, the laser light of the image data by the laser writing unit 8 is synchronized with the writing system routine (not shown). After the writing start position is set and the writing is completed, only when writing the next color, the process returns to the first step and the same processing as described above is performed.

As described above, in the digital color copying machine of this embodiment, the position detecting means is constituted by the reflection marker 40 installed outside the image area of the intermediate transfer belt 19 and the reflection type photo sensor 50 for detecting the reflected light. Then, a detection area 41 is provided only partially (at the center thereof) on the reflection marker 40, and the photosensing by the laser writing unit 8 is performed in synchronization with the signal when the photosensor 50 detects the reflected light from the detection area 41. Since the writing of the image data on the body drum 9 by the laser beam is started, the following effects can be obtained.

That is, even when the end of the reflection marker 40 on the intermediate transfer belt 19 is turned up due to the load of the rubber blade 22b of the belt cleaner 22, as long as the position of the detection region 41 located at the center of the end of the reflection marker 40 does not shift. Since the reference position of the intermediate transfer belt 19 can be satisfactorily detected by detecting the reflected light from the detection area 41,
It is possible to prevent the deterioration of the position detection accuracy.

In this embodiment, the detection area 41 is provided at the center of the reflection marker 40. However, for example, as shown in FIG. 8, the detection area 41 is formed by a line segment orthogonal to the circumferential direction of the intermediate transfer belt 19. If the area is held, even if the intermediate transfer belt 19 is twisted due to repeated rotation, the reference position of the intermediate transfer belt 19 can be detected at a constant timing.

Further, the detection area 41 on the reflection marker 40
Is a region having a first line segment 41a orthogonal to the circumferential direction of the intermediate transfer belt 19 and a second line segment 41b forming a certain angle with respect to the circumferential direction of the intermediate transfer belt 19, as shown in FIG. 1st line segment 41a and 2nd line segment 41b by
The distance (pulse interval) between the respective line segments is read based on the detection timing of, and the fluctuation amount in the direction orthogonal to the circumferential direction of the intermediate transfer belt 19 is measured by the fluctuation of the distance in each color superposition process, When it is determined from the result that the belt is twisted during one image forming cycle, the image forming operation is interrupted and the operation panel 8 of FIG.
If an error display such as a serviceman call is displayed on the No. 1 display device, there is no possibility of causing misalignment of the toner images of the respective colors when forming a superimposed image of a plurality of colors on the intermediate transfer belt 19. .

In this case, if the writing start timing of the image data by the laser beam onto the photosensitive drum 9 by the laser writing unit 8 is corrected according to the above-mentioned variation amount, a plurality of colors on the intermediary transfer belt 19 can be obtained. Even if a superposed image is formed, it is possible to obtain a good color image without the positional deviation of the toner images of the respective colors.

This processing will be described in more detail with reference to the flow chart of FIG. 10. The reflection marker 40 (tip portion) on the intermediate transfer belt 19 which is rotating in the direction of the arrow B by the photosensor 50 as described above. Of the reflected light of the first detection area 41 provided on the first detection area 41.
When the reflected light of the line segment 41a is detected, the signal is synchronized with the signal, and when the second line segment 41b of the detection area 41 is detected, the distance between the line segments 41a and 41b is read, and the color superimposing step is performed every time. The variation amount in the direction orthogonal to the circumferential direction of the intermediate transfer belt 19 is measured by the variation in the above distance.

After that, the measured intermediate transfer belt 19
Based on the amount of fluctuation in the direction orthogonal to the orbiting direction, the writing start position of the image data by the laser writing unit 8 by the laser light is set in the writing routine, and after the writing is completed, Only when the writing of the color is performed, the process returns to the first step and the same processing as described above is performed.

For example, as shown in FIG. 11, when the intermediate transfer belt 19 is in the regular position, each line segment 41a,
Assuming that the distance between 41b is a regular distance y, when the distance (pulse interval) between the line segments 41a and 41b read by the photo sensor 50 is a distance y ₁ longer than the regular distance y, the intermediate transfer belt 19 is on the back side. Therefore, when the laser writing unit 8 scans from the back to the front to perform writing, the writing start timing is advanced. The preceding time (variation amount) ΔX ₁ is the measurement distance y
_It can be calculated by the formula 1 from ₁ and the regular distance y.

[0056]

[Formula 1] ΔX ₁ = (y−y ₁ ) tan (90 ° −θ)

Further, when the distance between the line segments 41a and 41b read by the photosensor 50 is the distance y ₂ which is shorter than the regular distance y, the intermediate transfer belt 19 is closer to the front side, and therefore the laser writing unit 8 is used. When writing is performed by scanning from the back to the front, the write start timing is delayed. Delay time (variation amount) Δ
X ₂ can be calculated from the measured distance y ₂ and the regular distance y by the equation 2.

[0058]

[Expression 2] ΔX ₂ = (y−y ₂ ) tan (90 ° −θ)

Further, the detection area 41 on the reflection marker 40
Is an area having a reflectance (detection level) different from the reflectance of the intermediate transfer belt 19 as shown in FIG.
Even if a foreign matter is attached to the area other than the reflection marker 40 on the intermediate transfer belt 19, the reflected light from the foreign matter is detected by the detection area 4
The reference position of the intermediate transfer belt 19 can always be detected accurately without being erroneously detected as the reflected light of No. 1.

The embodiment in which the present invention is applied to a digital color copying machine using an intermediate transfer belt has been described above, but the present invention is not limited to this, and another toner image carrier such as an intermediate transfer drum is used. It can be applied to various color image forming apparatuses such as digital color copying machines and color laser printers.

[0061]

As described above, according to the color image forming apparatus of the present invention, even if the end of the reflection marker on the toner image carrier is turned up, the accuracy of detecting the position of the toner image carrier is deteriorated. There is no such thing. Note that claim 2
According to the invention, in the case where the toner image carrier is the intermediate transfer belt, the reference position of the intermediate transfer belt can always be detected at a constant timing even if the twist occurs due to the repeated circumferential movement.

According to the third and fourth aspects of the invention, when the toner image carrier is an intermediate transfer belt, it is possible to prevent positional deviation of the toner images of the respective colors when forming a superimposed image of a plurality of colors on the intermediate transfer belt. You can According to the invention of claim 5, when the toner image carrier is an intermediate transfer belt, even if a superposed image of a plurality of colors is formed on the intermediate transfer belt, a good color image is obtained in which the toner images of the respective colors are not displaced. be able to.

According to the sixth aspect of the present invention, even if a foreign substance is attached to a portion other than the reflection marker portion on the toner image bearing member, the foreign substance is not erroneously detected, and the reference position on the toner image bearing member is always maintained. It can be detected accurately.

[Brief description of drawings]

FIG. 1 is a diagram showing a position detection unit including a reflection marker on the intermediate transfer belt shown in FIG. 2 and a reflection type photo sensor arranged opposite to the reflection marker.

FIG. 2 is a schematic configuration diagram showing a mechanical portion of a digital color copying machine which is an embodiment of the present invention.

FIG. 3 is a partially enlarged view around the photosensitive drum and the intermediate transfer belt in FIG.

FIG. 4 is a diagram showing a specific example of the reflection marker of FIG.

5 is a perspective view showing a configuration example of a laser writing unit in the color printer shown in FIG.

FIG. 6 is a block diagram showing a control system of the same color printer.

FIG. 7 is a flowchart showing a process according to the present invention by the control unit of FIG.

FIG. 8 is a diagram showing another specific example of the reflection marker of FIG.

FIG. 9 is a diagram showing yet another specific example of the reflection marker.

10 is a flowchart showing another processing according to the present invention by the control unit of FIG.

11 is an explanatory diagram related to the processing of FIG.

FIG. 12 shows reading (sensing) levels of the reflection type photosensor in the case where areas having different reflectances on the reflection marker of FIG. 1 are areas having reflectances (reflectances) different from the reflectance of the intermediate transfer belt. It is a timing diagram which shows the relationship with time.

[Explanation of symbols]

 1: Color Scanner 2: Color Printer 8: Laser Writing Unit 9: Photosensitive Drum 14 to 17: Developing Device 19: Intermediate Transfer Belt 20: Intermediate Transfer Bias Roller 21: Drive Roller 22: Belt Cleaner 40: Reflection Marker 41: Areas with different reflectances 50: Reflective photo sensor 61: Laser diode 73: Synchronous detection sensor 80: Control unit 81: Operation panel 82: Sensors / switches 83: Copy process equipment 84: Sequence equipment

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location G03G 21/14 (72) Inventor Mitsuhiro Kurama 1-3-6 Nakamagome, Ota-ku, Tokyo No. In Ricoh Co., Ltd. (72) Inventor Katsuhisa Tsuji 1-3-3 Nakamagome, Ota-ku, Tokyo In Ricoh Co., Ltd.

Claims (6)

[Claims] 1. A rotating photoconductor, charging means for uniformly charging the surface of the photoconductor, and image data of a plurality of colors are sequentially written by laser light on the surface of the photoconductor charged by the means. A laser writing means for forming an electrostatic latent image by means of a plurality of means, and a plurality of means for forming and visualizing a toner image by attaching toners of different colors to the electrostatic latent image sequentially formed on the surface of the photoconductor by the means. Developing means, a toner image carrier for rotating adjacent to the photosensitive member, and holding the toner images of a plurality of colors sequentially formed on the photosensitive member by the developing means in an overlapping manner, and the photosensitive member. A first transfer unit that transfers the toner image on the toner image carrier to the toner image carrier, a second transfer unit that transfers the toner image on the toner image carrier to recording paper, and a peripheral unit on the toner image carrier. Position detection means for detecting the position in the moving direction And an optical writing start timing control means for controlling a writing start timing of the image data by the laser light onto the photoconductor by the laser writing means according to a detection result of the means. The position detecting means is composed of a marker of a light reflector installed outside the image area on the toner image carrier and a reflection type photosensor for detecting the reflected light, and only part of the marker has a reflectance. Different areas are provided, and the optical writing start timing control means is synchronized with the signal when the photosensor of the position detecting means detects the reflected light of the areas having different reflectances on the marker to perform the laser writing. A color image forming apparatus, which is a means for starting writing of image data by laser light onto the photoconductor by the means. 2. A region of different reflectance on the marker is
The color image forming apparatus according to claim 1, wherein the area is a region having a line segment that is orthogonal to a circumferential direction of the toner image carrier. 3. A region of different reflectance on the marker is
2. An area having a first line segment orthogonal to the circumferential direction of the toner image bearing member and a second line segment forming a constant angle with respect to the line segment. Color image forming apparatus. 4. The color image forming apparatus according to claim 3, wherein the detection timing of the first line segment and the second line segment of the region of different reflectance on the marker by the photosensor of the position detection unit. The distance between the first line segment and the second line segment is read based on the variation, and the variation amount in the direction orthogonal to the circumferential direction of the toner image carrier is caused by the variation in the distance in each color superposition step. A color image forming apparatus comprising a measuring means for measuring 5. The color image forming apparatus according to claim 4, wherein the optical writing start timing control means controls the optical writing start timing control means on the photoconductor by the laser writing means according to a variation amount measured by the measuring means. A color image forming apparatus comprising means for correcting the timing of starting writing of image data by laser light. 6. The region of different reflectance on the marker is
The color image forming apparatus according to claim 1, wherein the area is a region having a reflectance different from that of the toner image carrier.