JP2000250281A - Multicolor image forming device - Google Patents

Abstract

(57) [Problem] To prevent a transfer position shift of a starting end of each color image due to a belt load fluctuation immediately after detecting a mark on an intermediate transfer belt which determines a starting end of each color image forming process. SOLUTION: A color image formation is started based on detection of a mark on a transfer belt and transferred to a transfer belt, and this process is repeated for each different color to obtain a color superimposed image. In obtaining a color image by collectively transferring onto a transfer sheet: first and second sensors S each detecting a mark
1, S2; a means 13 for measuring the timing difference Ai of these mark detections; and a means 13 for correcting the latent image formation start timing Bo by a deviation ΔA = Ai−Ao of the timing difference Ai with respect to the reference value Ao 13. To 16; (FIG. 3). Alternatively, the first and second marks MC1 and MC2 are provided on the transfer belt; each mark is detected by one sensor S, the timing difference Ai is measured, and the deviation ΔA = A
Bo is corrected to Bo + ΔAo by i-Ao (FIG. 5).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a photosensitive member and an intermediate transfer member, and sequentially transfers color toner images formed on the photosensitive member to an intermediate transfer member to form a superimposed transfer image.
The present invention relates to an image forming apparatus of a type in which this superimposed transfer image is collectively transferred onto transfer paper.

[0002]

2. Description of the Related Art A rotatable rotary member, for example, an endless belt-shaped, drum-shaped or roller-shaped photoreceptor, is disposed opposite to the photoreceptor and has the same circumference as the photoreceptor in contact with the photoreceptor. An endless belt-shaped or drum-shaped intermediate transfer body that rotates at a speed, a mark provided on a part of the intermediate transfer body, and a mark detection sensor provided in a pass area of the mark; A primary transfer unit that forms a state in contact with the primary transfer unit, and a charging unit at a charging position upstream of the contact position of the primary transfer unit in the rotation direction of the photoconductor. After a certain timing from the detection of the mark by the sensor during rotation of the intermediate transfer body, an image forming process is started, and light writing and light writing are performed on the charged area of the photosensitive body that has passed through the charging position and has been charged. Forming a toner image of an arbitrary color by an image, and then transferring the toner image of the arbitrary color to the intermediate transfer body by a primary transfer unit in the primary transfer unit, for each different color, 2. Description of the Related Art There is known an image forming apparatus which obtains a color superimposed toner image on an intermediate transfer member, and collectively transfers the superimposed toner image onto transfer paper to obtain a color image.

In such an image forming apparatus, the time from the mark detection to the start of the image forming process is kept constant for each color, and the position of the image of each color is kept constant on the intermediate transfer member, that is, no color shift occurs. Thus, between the mark detection and the start of the image forming process, the ON / OFF of the cleaning blade is performed.
For example, control has been generally performed to avoid a load fluctuation event that disturbs rotation and causes a time lag.

[0004]

However, in recent years, the demand for copy speed UP has been increasing day by day, and the above-mentioned control has a limit, so that it is necessary to accept a change in load in the middle. For this reason, it has become necessary to further dynamically adjust the displacement generated by the load fluctuation by using a motor having a servo function or the like. However, such devices are expensive and difficult to implement on low cost machines. An object of the present invention is to enable the above problems to be realized at low cost.

[0005]

(1) In the present invention, the intermediate transfer member (415) is rotated at a predetermined timing after the index (MC / MC1, MC2) of the rotating intermediate transfer member (415) reaches a predetermined position. Photoconductor (41
4) is charged and an electrostatic latent image is formed by exposure, developed and transferred to the intermediate transfer body (415), and this process is repeated for each different color to form a color image on the intermediate transfer body (415). In a multicolor image forming apparatus that obtains a superimposed image and collectively transfers the superimposed image onto transfer paper to obtain a color image: the index (MC / MC
1, MC2) and at least one (S / MC) of the means (S1, S2 / S) for detecting the arrival at the predetermined position are the first and second ones distributed in the moving direction of the intermediate transfer body (415). (S1, S2 / MC1, MC2); the apparatus comprises means (13) for measuring a timing difference (Ai) between the first and second arrival detections and the timing difference (Ai) with respect to a reference value (Ao). Means (13+) for correcting (Bo + ΔAo) the start timing (Bo) of the electrostatic latent image by the exposure with the deviation (ΔA = Ai−Ao)
16); (FIG. 3 / FIG. 5). In addition, in order to facilitate understanding, the reference numerals of the corresponding elements or the corresponding items of the embodiment shown in the drawings and described later are added in parentheses for reference.

According to this, during the period from the detection of the index (MC / MC1, MC2) to the start of the electrostatic latent image due to the exposure, if there is a load fluctuation, the movement amount of the intermediate transfer member (415) varies. Also,
Since the start timing (Bo) of the electrostatic latent image due to exposure is corrected (Bo + ΔAo) in accordance with the displacement (ΔA) of the movement amount, the displacement of the image start position between the colors on the intermediate transfer body (415) is corrected. Does not occur.

[0007] Since the displacement of the image start end on the intermediate transfer member (415) due to the variation in the amount of movement of the intermediate transfer member (415) due to the load fluctuation during the timing difference (Ai) is suppressed,
Timing of a load operation that may cause load fluctuations in the rotation drive system of the intermediate transfer member (415) and / or the photoconductor (414) or its power system, for example, ON / OFF of a cleaning blade, driving of a development sleeve. Set between the differences (Ai)
It is also possible to speed up image formation.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (2) Rotating intermediate transfer member (415)
At a certain time after the index (MC) reaches a predetermined position, the rotating photoconductor (414) is charged, an electrostatic latent image is formed by exposure, and it is developed to develop an intermediate transfer body (415). This process is repeated for each different color to obtain a multi-color image on the intermediate transfer member (415), and the multi-color image forming apparatus is configured to collectively transfer the multi-color image onto transfer paper to obtain a color image. In the first and second index detecting means (S1, S2) distributed in the moving direction of the intermediate transfer member (415) and detecting the index (MC) respectively; the first and second index detecting means (S1) , S2)
Means (13) for measuring the timing difference (Ai) of the detection of the index (MC); and the timing difference (A) with respect to the reference value (Ao).
means (13 to 16) for correcting (Bo + ΔAo) the start timing (Bo) of the electrostatic latent image by the exposure with the deviation (ΔA = Ai−Ao) of i);
And a multicolor image forming apparatus (FIG. 3). (3) At a certain time after the index (MC1, MC2) of the rotating intermediate transfer member (415) reaches a predetermined position, the rotating photosensitive member (414) is charged and an electrostatic latent image is formed by exposure. Formed, developed and transferred to the intermediate transfer body (415), this process is repeated for each different color to obtain a color superimposed image on the intermediate transfer body (415), and this superimposed image is printed on transfer paper. A multi-color image forming apparatus which collectively transfers color images to: an intermediate transfer member (415) having first and second indices (MC1, MC2) distributed in the direction of movement thereof; An index detecting means (S) for detecting arrival of each of the first and second indexes (MC1, MC2), a means (13) for measuring a timing difference (Ai) of arrival detection, and a reference value (Ao). The timing difference (A
i) a means (13 to 16) for correcting (Bo + ΔAo) the start timing (Bo) of the electrostatic latent image by the exposure with the deviation (ΔA = Ai−Ao); Image forming apparatus (FIG. 5). (4) a photoreceptor (414) composed of a rotating body, an intermediate transfer body (415) disposed opposite to the photoreceptor, and rotated in the same direction as the photoreceptor in contact with the photoreceptor; Means for detecting the rotational position of the body (MC + S1 / MC1 + S), the primary transfer unit (1) comprising the intermediate transfer body in contact with the photoconductor
Primary transfer means (416), the arrangement position of the primary transfer means (1)
A charging unit (419) at a charging position (2) upstream of the photoconductor in the rotation direction, and the rotation position detection unit (MC, MC) during the rotation of the photoconductor and the intermediate transfer body during image formation. After a certain timing (Bo) from the detection of the mark (MC / MC1) of the intermediate transfer member by (S), an image forming process (exposure of image light) is started, and the charged toner is charged through the charging position (2). A toner image of an arbitrary color is formed on the charged area of the photoreceptor by optical writing and development, and then the toner image of the arbitrary color is formed in the primary transfer unit (1) by the primary transfer unit (416). The step of transferring to a transfer body (415) is repeated for each different color to obtain a color superimposed image on the intermediate transfer body, and collectively transfer this superimposed toner image onto transfer paper to form a color image. In the apparatus, the intermediate transfer member (4
15) is a mark by the rotational position detecting means (MC + S1 / MC1 + S).
At an arbitrary position (Ao) between the detection (b) of (MC / MC1) and the start of the imaging process (d), a second position detection means (MC + S2 / MC2 + S),
Means for measuring the time (Ai) between the first rotational position detecting means (MC + S1 / MC1 + S) and the second rotational position detecting means (MC + S2 / MC2 + S)
(13), sampling means (15) for sampling the measured time (Ai), reference time (Ao) and the sampling time
(Ai) and means (13 to 16) for feeding back (Bo + ΔA) the difference (ΔA = Ai−Ao) to the timing (Bo) of the imaging process start (FIG. 3 / FIG. Five).

According to this, it is possible to adjust the phase shift (ΔA) (Bo + ΔA) due to the load fluctuation of (Bo) from the mark detection (b) to the start of the image forming process (d). There is no need to intentionally miss the timing of the operation to give. (5) The position detecting means (MC + S1 + S2) of the above (4) includes a plurality of sensors (S1, S2) on the apparatus body side (FIG. 3). According to this, only one mark (MC) is required for the intermediate transfer member, and the cost of consumables is not increased. (6) The position detecting means (MC1 + MC2 + S) of (4) includes a plurality of detected marks (MC1 + MC2) on the intermediate transfer member (FIG. 5). According to this, only one sensor (S) is required on the apparatus main body side, so that the cost of the apparatus is not increased, and the regulation on the size of the apparatus can be coped with.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment FIG. 1 shows an outline of a mechanism according to a first embodiment of the present invention. This embodiment is a digital full-color copying machine. Color image reading device (hereinafter referred to as color scanner) 200
Illuminates the image of the original 180 on the contact glass 202 with the illumination lamp 205 and the mirror groups 204A, 204B and 204.
C and the like, and the color sensor 20 via the lens 206.
7, the color image information of the original is read for each color separation light of blue (hereinafter, referred to as B), green (hereinafter, referred to as G), and red (hereinafter, referred to as R), and is electrically connected. Convert to image signal. Color sensor 207
In this example, B, G, R color separation filters and CCD
(Solid-state image pickup device), and is configured to read three colors simultaneously. Based on the B, G, and R color separation image signal intensity levels obtained by the color scanner 200, color conversion processing is performed by an image processing unit (not shown), and black (hereinafter, referred to as BK), cyan (hereinafter, referred to as BK) , C), magenta (hereinafter, referred to as M), and yellow (hereinafter, referred to as Y) are obtained.

A color image recording apparatus (hereinafter referred to as a color printer) described below using the color image data.
According to 400, the images of BK, C, M, and Y are overlaid on the intermediate transfer belt and transferred to a transfer paper. The color scanner 200 receives a scanner start signal that is timed with the operation of the color printer 400,
Illumination lamp 205 and mirror group 204A, 204B, 20
An illumination / mirror optical system composed of 4C or the like scans the document in the direction of the left arrow, and obtains one color image data for each scanning. Each time, while visualizing the images sequentially with the color printer 400, these are superimposed on the intermediate transfer belt, and
A full-color image of a color is formed.

A writing optical unit 401 as an exposure unit of the color printer 400 converts color image data from the color scanner 200 into an optical signal, performs optical writing corresponding to a document image, and
4, an electrostatic latent image is formed.

The optical writing optical unit 401 includes a laser light emitting device 441, a light emitting drive control unit (not shown) for driving the light emitting device, a polygon mirror 443, a rotating motor 444 for rotating the polygon mirror 443, an fθ lens 442, and a reflecting mirror 446. It is composed of Photoconductor drum 414
Rotates in the counterclockwise direction as indicated by the arrow. Around the photoconductor cleaning unit 421, a neutralization lamp 414M, a charger 419, a potential sensor 414D for detecting a latent image potential on the photoconductor drum, A selected developing device of the revolver developing device 420, a developing density pattern detector 414P, an intermediate transfer belt 415, and the like are arranged.

The revolver developing device 420 includes a BK developing device 420K, a C developing device 420C, an M developing device 420M, and a Y developing device 420Y, and a revolver rotary drive for rotating each developing device in a counterclockwise direction as indicated by an arrow. (Not shown). In order to visualize the electrostatic latent image, each of these developing devices rotates developing sleeves 420 KS and 420 which rotate by contacting the ears of the developer with the surface of the photosensitive drum 414.
Combine CS, 420MS, 420YS and developer
It is composed of a developing paddle that rotates for stirring. In the standby state, the revolver developing device 420 is set at a position where development is performed by the BK developing device 420, and when a copying operation is started, reading of BK image data is started at a predetermined timing by the color scanner 200. Optical writing / latent image formation by laser light starts based on the image data. Hereinafter, the electrostatic latent image based on the BK image data is referred to as a BK latent image. The same applies to each of the C, M, and Y image data. In order to enable development from the leading end of the BK latent image, before the leading end of the latent image reaches the developing position of the BK developing unit 420K, the rotation of the developing sleeve 420KS is started to develop the BK latent image with BK toner. . And after that,
The developing operation of the BK latent image area is continued, but the BK latent image
Immediately after passing the latent image position, the BK developing device 42
The revolver developing device 420 is driven to rotate from the development position at 0K to the development position at the next color developing unit. This rotation operation is completed at least before the leading end of the latent image based on the next image data arrives.

When the image forming cycle is started, the photosensitive drum 414 rotates counterclockwise as indicated by an arrow, and the intermediate transfer belt 415 is rotated clockwise by a drive motor (not shown). Move. Intermediate transfer belt 41
5, the BK toner image formation, the C toner image formation, the M toner image formation, and the Y toner image formation are sequentially performed, and finally, on the intermediate transfer belt 415 in the order of BK, C, M, and Y. , A toner image is formed. The formation of the BK image is performed as follows. That is, the charger 41
9 uniformly charges the photosensitive drum 414 with a negative charge to about -700 V by corona discharge. Subsequently, the laser diode 441 performs raster exposure based on the BK signal. When the raster image is exposed in this manner, in the initially exposed portion of the photosensitive drum 414 that is uniformly charged, the charge proportional to the amount of exposure light disappears, and an electrostatic latent image is formed. The toner in the revolver developing device 420 is negatively charged by stirring with the ferrite carrier, and the BK developing sleeve 420KS of the present developing device is charged.
Is biased by a power supply (not shown) with respect to the metal base layer of the photosensitive drum 414 to a potential at which a negative DC potential and an AC are superimposed. As a result, no toner adheres to the portion of the photosensitive drum 414 where the charge remains, and BK is applied to the portion having no charge, that is, the exposed portion.
The toner is attracted, and a BK visible image similar to the latent image is formed. The intermediate transfer belt 415 includes a driving roller 415D, a transfer facing roller 415T, and a cleaning facing roller 415.
C and a group of driven rollers, and is driven to rotate by a drive motor (not shown). Now, the photosensitive drum 4
The BK toner image formed on the surface of the intermediate transfer belt 415, which is driven at a constant speed in contact with the photoconductor, is transferred onto a belt transfer corona discharger (hereinafter, referred to as a belt transfer unit) 4.
16 transferred. Hereinafter, the transfer of the toner image from the photosensitive drum 414 to the intermediate transfer belt 415 is referred to as belt transfer. Some untransferred residual toner on the photoconductor drum 414 is cleaned by the photoconductor cleaning unit 421 in preparation for reuse of the photoconductor drum 414. The collected toner is stored in a waste toner tank (not shown) via a collection pipe.

On the intermediate transfer belt 415, the toner images of BK, C, M, and Y, which are sequentially formed on the photosensitive drum 414, are sequentially aligned on the same surface, and a four-color superimposed belt transfer image is formed. After that, batch transfer is performed on transfer paper by a corona discharge transfer device. By the way, the photosensitive drum 41
On the fourth side, the process proceeds to the C image forming process after the BK image forming process. At a predetermined timing, reading of the C image data by the color scanner 200 starts, and the C latent image is written by laser light writing based on the image data. An image is formed. The C developing device 420C has a
After the rear end of the BK latent image has passed and before the front end of the C latent image has arrived, the rotation operation of the revolver developing device is performed to develop the C latent image with C toner. Thereafter, the development of the C latent image area is continued, but when the rear end of the latent image has passed, the revolver developing device 420 is driven in the same manner as in the case of the BK developing device, and the C developing device 420C is sent out. Of the M developing device 420M is positioned at the developing position. This operation is also performed before the leading end of the next M latent image reaches the developing unit.
In the process of forming each of the M and Y images, the operations of reading image data, forming a latent image, and developing each image data are as follows.
The description is omitted because it is based on the above-described process of the BK image and the C image.

The belt cleaning device 415U includes an inlet seal, a rubber blade, a discharge coil, and a mechanism for contacting and separating the inlet seal and the rubber blade. 1
After the BK image of the color is transferred to the belt, while the images of the second, third, and fourth colors are transferred to the belt, the entrance seal and the rubber blade are separated from the intermediate transfer belt surface by the blade contact / separation mechanism. .

A paper transfer corona discharger (hereinafter, referred to as a paper transfer device) 417 uses an AC corona discharge method to transfer the superimposed toner image on the intermediate transfer belt 415 to transfer paper.
+ DC or a DC component is applied to the transfer paper and the intermediate transfer belt.

A transfer paper cassette 482 in the paper supply bank stores transfer papers of various sizes.
The sheet is fed and conveyed in the direction of the pair of registration rollers 418R by 83. Reference numeral 412B2 indicates a paper feed tray for manually feeding OHP paper, thick paper, and the like.

At the time when the image formation is started, the transfer paper is fed from one of the above-mentioned paper feed trays, and is waiting at the nip portion of the registration roller pair 418R. Then, when the leading end of the toner image on the intermediate transfer belt 415 approaches the paper transfer unit 417, the registration roller pair 418R is driven so that the leading end of the transfer paper coincides with the leading end of the image.
The paper and the image are aligned. In this way, the transfer paper is superimposed on the color superimposed image on the intermediate transfer belt, and passes over the paper transfer unit 417 connected to the positive potential. At this time,
The transfer paper is charged with a positive charge by the corona discharge current, and most of the toner image is transferred onto the transfer paper. Subsequently, when the transfer paper passes through a separation static eliminator by a static elimination brush (not shown) disposed on the left side of the paper transfer device 417, the transfer paper is discharged, separated from the intermediate transfer belt 415, and moved to the paper transport belt 422. The transfer paper on which the four-color superimposed toner image is collectively transferred from the intermediate transfer belt surface is conveyed to a fixing device 423 by a paper conveyance belt 422, and the fixing roller 4 is controlled to a predetermined temperature.
The toner image is melted and fixed at the nip portion between the pressure roller 23A and the pressure roller 423B, sent out of the main body by the discharge roll pair 424, and stacked face up on a copy tray (not shown).

The photosensitive drum 414 after belt transfer
Is cleaned by a photoreceptor cleaning unit 421 including a brush roller, a rubber blade, and the like.
Further, the charge is uniformly removed by the charge removing lamp 414M. Further, the intermediate transfer belt 415 after transferring the toner image to the transfer paper
Again, the blade is pressed by the blade contact / separation mechanism of the cleaning unit 415U to clean the surface.
In the case of the repeat copy, the operation of the color scanner and the image formation on the photoreceptor continue from the fourth-color image process on the first sheet and proceed to the first-color image process on the second sheet at a predetermined timing. In the intermediate transfer belt 415, the second BK toner image is belt-transferred to an area whose surface has been cleaned by a belt cleaning device, following a batch transfer process of the first four-color superimposed image onto transfer paper. So that Thereafter, the operation is the same as that of the first sheet.

The above is the description of the copy mode for obtaining a four-color full-color copy. However, in the case of the three-color copy mode and the two-color copy mode, the same operation as described above is performed for the designated color and the number of times. Will be done. In the case of the single color copy mode, until the predetermined number of sheets is completed,
Only the developing device of the predetermined color of the revolver developing device 420 is located at the developing position of the predetermined color to be in the developing operation state, and the copying operation is continuously performed while the blade of the belt cleaning device 415U is pressed against the belt.

In such an image forming apparatus, a mark for position detection is provided on the outer peripheral surface or the inner peripheral surface of the belt 415. However, on the outer peripheral surface side, it is necessary to devise a way to avoid the passage area of the belt cleaning device 415U, which may cause difficulty in arrangement. In this case, it is provided on the inner peripheral surface side. Although the optical sensor is not shown in FIG. 1, a driving roller 415D supporting the belt 415 is provided.
And a support roller 415F.

FIG. 2 is an enlarged view of main parts of the photosensitive drum 414 and the intermediate transfer belt 415 of the embodiment shown in FIG. The intermediate transfer belt 415 is driven to rotate by a roller 426. A reflection mark MC is affixed to the non-image surface of the intermediate transfer belt 415, and a process start signal a is issued when the intermediate transfer belt 415 passes the sensor S so that the photosensitive drum 414
(Charging) is started, and after a predetermined timing, an image formation (formation of an electrostatic latent image by image light) start signal d is issued, and the image light is transmitted to the photosensitive drum 414 via the reflection plate 446. Arrival, latent image is formed, developing roller 420C
The image is developed at S and transferred to the intermediate transfer belt 415 by the transfer charger 416. This step is repeated several times during multicolor image formation.

FIG. 3 shows the sensor S (S1 + S) shown in FIG.
2) shows a timing correction circuit connected thereto, and FIG. 4 shows electric signals of respective parts of the circuit. In the first embodiment,
One reflection mark MC is affixed to the intermediate transfer belt 415, and two reflection-type photo sensors S1 and S2 are disposed (fixed) along the movement locus. The movement of the intermediate transfer belt 415 first causes the first photo sensor S1
Detects the reflection mark MC, the waveform shaping circuit 11 generates a pulse b (high level H), and then, when the reflection mark MC moves L, the second photosensor S2 detects the reflection mark MC.
Upon detecting C, the waveform shaping circuit 12 generates a pulse c (high level H). Photoconductor drum 414 based on pulse b
And the other preparatory processes for image formation are started, and image formation (formation of an electrostatic latent image) is performed based on a pulse d (high level H) generated after a predetermined time (its reference value is Bo) after the pulse b. ) Is started.

The counter 13 of the timing correction circuit outputs a signal b indicating that the first photosensor S1 has detected the reflection mark MC.
Is a preset up counter which loads the set reference value Bo-Ao at the rising edge of the counter and then counts up the number of arrivals Ai of the clock pulse a. The count data output from the preset up counter is Bo + Ai-Ao. Show. Ai is a clock value (a value obtained by counting the clock pulse a).
This count data is stored in the latch 15 when the second photosensor S2 detects the reflection mark MC and the waveform shaping circuit 12 generates the pulse c.

Output (stored) data Bo + A of the latch 15
If Ai-Ao = .DELTA.A in i-Ao, the count data indicates Bo + .DELTA.A. Ao is a set value corresponding to the shortest time from when the first photosensor S1 detects the reflection mark MC to when the second photosensor S2 detects it when there is no load fluctuation in the intermediate transfer belt driving system. , The reference value. Bo is a speed L at which the reflection mark MC advances between the first and second photosensors S1 and S2 for a time Ao.
/ Ao is a timing reference value (elapsed time from the pulse b) at which exposure with image light (formation of an electrostatic latent image) is started when the intermediate transfer belt 415 moves at / Ao.

On the other hand, the up counter 14 clears (initializes to 0) the count data at the rising edge of the signal b in which the first photosensor S1 detects the reflection mark MC,
The count-up of the clock pulse a is started. The count data Bi is the output data Bo + ΔA of the latch 15.
When the above value is reached, the output d of the comparator 16 rises from the low level L to the high level H.

The signal b (H) that the first photosensor S1 has detected the reflection mark MC is a process start signal (preparation start signal) of one color, and the signal d (H) is the signal start signal.
A start signal for forming a color image (electrostatic latent image) is given to an image forming controller (not shown). The imaging controller starts a preparatory process for forming a single color image in response to the signal b (H), and forms the single color image (electrostatic latent image) in response to the pulse d (H). To start.

When the moving speed of the intermediate transfer belt 415 temporarily decreases due to a load change, the intermediate transfer belt 415
Since the upper image forming start position is shifted forward in the traveling direction from the reference position (the position corresponding to Bo), the image forming start timing is delayed by Bo + ΔA by the movement delay of the intermediate transfer belt 415 (corresponding to ΔA). Accordingly, even if the time Ai from when the first photosensor S1 detects the reflection mark MC to when the second photosensor S2 detects it has a variation ΔA that differs for each color (i), the intermediate transfer belt 41
No shift, ie, no color shift, occurs at the start end of each color image on the image 5. For example, when a control 460 (FIG. 4) that fluctuates when an image of an arbitrary color is formed, a speed change occurs, and the time Ai during which the reflection mark MC passes through the distance L also slightly changes. The timing value Bo is a set number and has no relation to the speed change or the movement delay of the intermediate transfer belt. If the shortest time for passing through the distance L when there is no load change is the reference value Ao, the time difference of ΔA = Ai−Ao is Therefore, the image formation started at the timing value Bo results in a positional shift corresponding to ΔA multiplied by the linear velocity. Therefore, in the present invention, an image (electrostatic latent image) is formed after adding Bo to ΔA calculated at the time when the reflection mark MC passes the sensor S2 and counting Bo + ΔA, that is, at the time of Bi = Bo + ΔA. , The color shift does not occur even if the control 460 (FIG. 4) is entered to cause a speed change.

Second Embodiment FIG. 5 shows a timing correction circuit according to a second embodiment of the present invention. The other parts are the same as in the first embodiment.
In the second embodiment, two reflection marks are used as indices and one reflection photosensor is used. 1
Two reflection marks MC1,
MC2 is detected, and a signal indicating detection of each of the two marks is converted into a first mark detection signal b and a second mark detection signal c by the flip-flop 17 and the AND gates 18 and 19. Distribute. The flip-flop 17 is reset by a power-on reset signal (not shown) and an image (electrostatic latent image) formation start pulse d (H). In this reset state, the Q output of the flip-flop 17 is L and the Q bar output is H. Therefore, when the reflection type photosensor S detects the first reflection mark MC1 and the waveform shaping circuit 11 generates the pulse H, This passes through the gate 18 and the preparation stage
The pulse is output to the counters 13 and 14 and an image forming controller (not shown) as a pulse b. The flip-flop 17 is set at the falling point of the pulse H (mark MC1 detection signal) generated first by the waveform shaping circuit 11, and its Q
The output is inverted to H and the Q output is inverted to L. Next, when the reflection type photosensor S detects the second reflection mark MC2 and the waveform shaping circuit 11 generates a pulse H, this is an AND gate.
The count data Bo + ΔA of the counter A at that time is stored in the latch 15 as a latch pulse c.

The signals b and c correspond to the first signals shown in FIGS.
The configuration and operation of the counter 13 to the comparator 16 in FIG. 5 are the same as those in the first embodiment shown in FIGS. 3 and 4. In the second embodiment, the signal b (H) that the photo sensor S has detected the first reflection mark MC1 is
The signal d (H) is used as a one-color process start signal (preparation start signal), and the one-color image (electrostatic latent image) forming start signal is used as an image forming controller (not shown). Given to. In response to the signal b (H), the imaging controller starts a preparatory process for forming an image of one color, and outputs a pulse d.
In response to (H), formation of the one-color image (electrostatic latent image) is started. If the moving speed of the intermediate transfer belt 415 is temporarily reduced due to a load change, the image formation start position on the intermediate transfer belt 415 is shifted forward in the traveling direction from the reference position (a position corresponding to Bo). By delaying the image formation start timing by the movement delay (equivalent to ΔA),
o + ΔA. Accordingly, even if the time Ai from when the photosensor S detects the first reflection mark MC1 to when the photosensor S detects the second reflection mark MC2 has a variation ΔA that differs for each color (i), the intermediate transfer belt There is no shift at the beginning of each color image on 415, that is, no color shift.

In any of the above embodiments,
The timing correction circuit is composed of a combination of discrete logic elements (FIG. 3: 13 to 16 / FIG. 5: 13 to 16 + 17 to 1).
8), but a CPU may be used instead. For example, when the first and second photo sensors S1 and S2 are used as shown in FIG.
The photosensor S1 starts timing in response to a signal b that detects the reflection mark MC, and the second photosensor S2 responds to the signal that detects the reflection mark MC to store the timing value at that time. And the clock continues, and the clock Bi changes to “Bo +
The signal d may be generated when the saved time value -Ao "is reached. As shown in FIG. 5, when the first and second marks MC1 and MC2 are used, the CPU detects the first mark MC1 as a signal b, and starts timing in response to the signal b. In response to the signal detecting the 2-mark MC2, the time value at that time is saved and the time measurement is continued, and the time value Bi becomes "B0 + the time value obtained by saving-
The signal d may be generated when Ao ”is reached.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an outline of a mechanism of a color image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is an enlarged vertical sectional view showing a photoconductor drum 414 and an intermediate transfer belt 415 shown in FIG. 1 and main elements around them.

FIG. 3 shows the configuration of the sensor S shown in FIG. 2 (S1 + S2).
And a block diagram showing a timing correction circuit connected thereto.

FIG. 4 is a time chart showing signals of the timing correction circuit shown in FIG. 3;

FIG. 5 is a block diagram of a timing correction circuit used in a second embodiment of the present invention.

[Explanation of symbols]

S, S1, S2: reflection type photo sensor MC, MC1, MC2: reflection mark 17: flip-flop 18, 19: AND gate 180: original 200: color scanner 202: contact glass 204A, 204
B, 204C: mirror group 205: illumination lamp 206: lens 207: color sensor 400: color printer 401: optical writing unit 414 photosensitive drum 414D: potential sensor 414M: static elimination lamp 414P: development density pattern detector 415: intermediate transfer Belt 415C: Cleaning opposed roller 415D: Driving roller 415F: Support roller 415T: Transfer opposed roller 415U: Belt cleaning device 416: Belt transfer corona discharger 417: Paper transfer corona discharger 418R: Registration roller pair 419: Charger 420: Revolver Developing devices 420K, 420C, 420M, 420Y: developing units 420KS, 420CS, 420MS, 420YS: developing sleeves 421: photoconductor cleaning unit 422: paper transport bell 423: fixing device 423A: fixing roller 423B: pressure roller 424: discharge roller pair 426: roller 441: laser emitting means 442: fθ lens 443: polygon mirror 444: rotation motor 446: reflection mirror 460: control 482: transfer paper Cassette 483: Paper feed roller

Claims (3)

[Claims] A timing is set after the index of the rotating intermediate transfer member reaches a predetermined position, the rotating photosensitive member is charged, an electrostatic latent image is formed by exposure, and the latent image is developed to develop an intermediate image. A multi-color image forming apparatus that transfers images to a transfer body, repeats this process for each different color, obtains a superimposed color image on an intermediate transfer body, and collectively transfers the superimposed image onto transfer paper to obtain a color image. : At least one of the index and the means for detecting its arrival at a predetermined position includes first and second ones distributed in the direction of movement of the intermediate transfer member; A multicolor image forming apparatus, comprising: means for measuring a timing difference; and means for correcting the start timing of the electrostatic latent image due to the exposure based on a deviation of the timing difference from a reference value. 2. A method according to claim 1, wherein the rotating photosensitive member is charged at a predetermined time after the index of the rotating intermediate transfer member reaches a predetermined position, an electrostatic latent image is formed by exposure, and the latent image is developed. A multi-color image forming apparatus that transfers images to a transfer body, repeats this process for each different color, obtains a superimposed color image on an intermediate transfer body, and collectively transfers the superimposed image onto transfer paper to obtain a color image. : First and second index detecting means distributed in the moving direction of the intermediate transfer member and each detecting the index; means for measuring a difference in timing of detection of the index by the first and second index detecting means; Means for correcting the start timing of the electrostatic latent image due to the exposure based on a deviation of the timing difference from a reference value. 3. A timing is measured after the index of the rotating intermediate transfer member reaches a predetermined position, the rotating photosensitive member is charged, an electrostatic latent image is formed by exposure, and the latent image is developed to develop the intermediate image. A multi-color image forming apparatus that transfers images to a transfer body, repeats this process for each different color, obtains a superimposed color image on an intermediate transfer body, and collectively transfers the superimposed image onto transfer paper to obtain a color image. : The intermediate transfer member has first and second indices distributed in the direction of its movement;
Index detection means for detecting the arrival of each of the first and second indexes, means for measuring the timing difference of the arrival detection, and correction of the start timing of the electrostatic latent image by the exposure based on a deviation of the timing difference from a reference value. A multicolor image forming apparatus.