JP2001117030A - Multicolor image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize improvement of quality of a multicolor image to be formed by superimposing images with plural colors with simple and low-cost structure. SOLUTION: Positions of light beams of each color to scan a sub-scanning position detection sensor are compared with an initial case (initial data) and fluctuation of positions in the sub-scanning direction of images of each color is detected (a step 232). When the direction of positional deviation of each of other colors against positional deviation (fluctuation) of a reference color is the same, page sync setting data to regulate starting time of writing image of the colors with quantity of color positional deviation >3/4 dot against the reference color is corrected by unit of one main scan for the colors (steps 240, 242). When the direction positional deviation of each of other colors against the reference color is in both directions, the page sync setting data to regulate the starting time of writing the image of the colors with the quantity of color positional deviation >=1/2 dot against the reference color is corrected by unit of one main scan for the colors (steps 236, 238).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-color image forming apparatus, and more particularly, to deflect a plurality of light beams by a deflecting means so as to perform main scanning on a photosensitive member and move the photosensitive member. The present invention relates to a multi-color image forming apparatus that forms a multi-color image by combining a plurality of single-color images formed on the photoconductor by performing sub-scanning as a single image.

[0002]

2. Description of the Related Art An image forming apparatus which forms an electrostatic latent image by scanning a light beam modulated in accordance with an image to be formed on a photosensitive member and forms an image on the photosensitive member has been conventionally used. Although used in devices such as printers and copiers, in recent years, with the digitization and colorization of devices in the future, image forming apparatuses having the above-described configuration have been widely used. In the formation of a color image, for example, images of the respective colors are sequentially formed on the photoconductor so that images of four different colors (for example, C, M, Y, and K) overlap on a single photoconductor. Although it can be realized, there is a problem that it takes time until a color image is finally formed.

For this reason, a plurality of photoconductors are simultaneously scanned and exposed by a plurality of light beams to form images of different colors on the photoconductors, and the images of the respective colors are transferred to the same transfer medium. 2. Description of the Related Art A tandem-type image forming apparatus that forms a color image by superimposing a color image thereon has been devised. Since the tandem type image forming apparatus forms images of each color at the same time, the time required for forming a color image can be greatly reduced.

However, in the tandem-type multicolor image forming apparatus, a positional shift is likely to occur when the images of the respective colors are superimposed due to variations in the optical characteristics of the light beams corresponding to the images of the respective colors. Since the positional deviation between the images of each color appears remarkably as a color deviation on the color image, it is essential to correct the positional deviation between the images of each color, that is, the color deviation, in order to obtain a high-quality image. In addition, even when the components of the apparatus are adjusted to eliminate the color misregistration during the production of the multicolor image forming apparatus, if the ambient environment such as temperature changes, the color misregistration due to a displacement of the arrangement position of the optical components or the like. Occurs.

Japanese Patent Publication No. 2748971 discloses a method of correcting color misregistration in a tandem type multicolor image forming apparatus.
Detecting means for detecting a beam position shift in the vicinity of each photosensitive drum is provided, and a beam position in the sub-scanning direction is detected to control a writing start timing in the sub-scanning direction, thereby correcting a color shift in the sub-scanning direction. The technology is disclosed.

In addition to the color misregistration correction technique, a pattern (for example, a "+" mark) for easily detecting color misregistration is formed on a photoreceptor, and the pattern is read by an image reading device. There is also known a technique for detecting a shift and correcting a color shift by moving a reflection mirror to change a beam position incident on the photosensitive drum or controlling a writing timing in a sub-scanning direction.

[0007]

However, in the technique described in Japanese Patent Publication No. 2748971, since the detecting means for detecting the amount of displacement in the sub-scanning direction is provided in correspondence with the photosensitive drum, the photosensitive member is provided. Adjustment between the photosensitive drum and the displacement detecting means is required when the drum unit is replaced or the like, and there is a problem that the replacement work of the photosensitive drum unit becomes complicated.

Further, in the case of detecting a color shift based on a pattern for detecting a color shift, since it is necessary to form a pattern for detecting a color shift on the photosensitive drum, the control becomes complicated. Further, an image reading device for reading the color misregistration detection pattern is expensive, so that the cost of the device is increased, and the size of the image forming device itself is increased in order to secure an arrangement space for the image reading device. There were also problems.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has a simple and low-cost structure, and can realize an improvement in the quality of a multicolor image formed by superimposing a plurality of color images. It is an object to provide an image forming apparatus.

[0010]

In order to achieve the above object, according to the first aspect of the present invention, a plurality of light beams are deflected by a deflecting means to perform main scanning on a photosensitive member, respectively. A multicolor image forming apparatus that forms a multicolor image by combining a plurality of single-color images formed on the photoconductor by performing sub-scanning by moving the photoconductor, A detecting means for detecting a position in the sub-scanning direction when the light beam is main-scanned on the photoconductor, based on a relative displacement amount in the sub-scanning direction of each color obtained from a detection result by the detecting means. Correction means for correcting the image writing time in units of one main scan.

According to the first aspect of the present invention, the correction means obtains a relative displacement amount of each color in the sub-scanning direction from the position of each light beam detected by the detection means in the sub-scanning direction.
Based on the relative displacement amount, the image writing time is corrected in units of one main scan. Thus, the misregistration (color misregistration) in the sub-scanning direction between the single-color images in the multicolor image can be corrected in one main scanning unit (1 dot unit), and a high-quality multicolor image with small color misregistration is obtained. be able to.

[0012] As described in claim 2,
Calculating means for calculating the relative displacement in the sub-scanning direction of each of the other colors with respect to a predetermined color based on the detection result by the detecting means; and the relative displacement in the sub-scanning direction of each of the other colors. And a judgment unit for judging whether or not it is necessary to correct the image writing time in units of one scan for each of the other colors, based on a predetermined maximum displacement amount. Therefore, it is preferable to correct the image writing time in units of one main scan for the color determined to require correction.

At this time, as described in claim 3, whether the maximum displacement amount used for the determination by the determination means is the same as the displacement direction of the relative displacement in the sub-scanning direction of each of the other colors It may be different depending on whether or not.
More preferably, as described in claim 4, when the displacement directions of the relative displacements of the other colors in the sub-scanning direction are all the same, 3/1/3 of one main scanning width. 4 when the displacement direction of the relative displacement in the sub-scanning direction of each of the other colors is different.
It is preferable that the displacement amount corresponds to a half of one main scanning width.

Further, as described in claim 5,
Only when the difference between the relative position of each color obtained from the previous detection result by the detection unit and the relative position of each color obtained from the current detection result by the detection unit is equal to or greater than a predetermined value, the correction unit performs the calculation. It is preferable that the apparatus further comprises a correction execution control means for performing the correction by performing the calculation by the means and the determination by the determination means.

Further, as described in claim 6,
It is preferable that the image forming apparatus further includes a setting unit that sets an initial value of the image writing time based on a formation result of the multicolor image.

[0016]

Next, an example of an embodiment according to the present invention will be described in detail with reference to the drawings.

(Overall Configuration) FIG. 1 shows a schematic configuration of a multicolor image forming apparatus according to the present invention. The multicolor image forming apparatus 10 includes three transport rollers 12A to 12C, an endless transfer belt 14 wound around the transport rollers 12A to 12C, and a transfer that is arranged to face the transport roller 12C with the transfer belt 14 interposed therebetween. And a roller 16.

Above the transfer belt 14, the transfer belt 1
The photosensitive drum 18K for forming a black (K) image and the photosensitive drum 18Y for forming a yellow (Y) image along the moving direction of the transfer belt 14 (the direction of arrow A in FIG. 1) when the roller 4 is driven to rotate. , A photosensitive drum 18M for forming a magenta (M) image and a photosensitive drum 18C for forming a cyan (C) image are arranged at substantially equal intervals. Each photoreceptor drum 18 is arranged such that the axis is orthogonal to the moving direction of the transfer belt 14.

In the following, for the portions provided for each of the colors K, Y, M, and C, the symbols of the respective portions are denoted by K in the same manner as described above.
It is distinguished by adding the symbol of / Y / M / C.

Around each photoreceptor drum 18, a charger 20 for charging the photoreceptor drum 18 is arranged. Above each of the photoreceptor drums 18, a charged each of the photoreceptor drums 18 is provided. A plurality of beam scanning devices 30 (details of which will be described later) for irradiating laser beams onto the photosensitive drums 18 to form electrostatic latent images on the respective photosensitive drums 18 are arranged.

Around the photosensitive drum 18, an electrostatic latent image formed on the photosensitive drum 18 is provided at a predetermined position downstream of the laser beam irradiation position along the rotation direction of the photosensitive drum 18. A developing unit 22 for developing a color (K or Y or M or C) toner to form a toner image; a transfer unit 24 for transferring the toner image formed on the photosensitive drum 18 to the transfer belt 14; Are sequentially disposed.

The toner images of different colors formed on the respective photosensitive drums 18 are respectively transferred to the transfer belt 14 so as to overlap each other on the belt surface of the transfer belt 14. Thus, a color toner image is formed on the transfer belt 14, and the formed color toner image is transferred to the transfer material 28 sent between the transport roller 12 </ b> C and the transfer roller 16. Then, the transfer material 28 is sent to a fixing device (not shown), and the transferred toner image is fixed. Thus, a color image (full color image) is formed on the transfer material 28.

(Optical Scanning Apparatus) Next, the multi-beam scanning apparatus 30 will be described with reference to FIGS. The multiple beam scanning device 30 includes a casing 3 having a substantially rectangular bottom surface.
2, and a rotating polygon mirror 34 that is rotated at a high speed by a motor (not shown) is disposed at a substantially central portion of the casing 32. A photosensitive drum 1 is attached to one end of the casing 32 along a direction perpendicular to the axis of the rotary polygon mirror 34.
Semiconductor laser 36 that emits laser light for irradiating 8K
K and an LD 36Y that emits a laser beam for irradiating the photosensitive drum 18Y are arranged near the corners.

A collimator lens 38K and a plane mirror 40 are sequentially arranged on the laser beam emission side of the LD 36K. The laser beam K emitted from the LD 36K is converted into a parallel light beam by the collimator lens 38K and is incident on the plane mirror 40. A collimator lens 38Y and a plane mirror 42 are arranged in this order on the laser beam emission side of the LD 36Y. The laser beam Y emitted from the LD 36Y is converted into a parallel light beam by the collimator lens 38Y and then reflected by the plane mirror 42. The plane mirror 40
Is incident on.

An fθ lens 44 is disposed between the plane mirror 40 and the rotary polygon mirror 34, and the laser beam K and the laser beam Y reflected by the plane mirror 40 are fθ
After passing through the lens 44 and entering the rotary polygon mirror 34 and being reflected and deflected by the rotary polygon mirror 34, the fθ lens 4
4 (a so-called double-pass configuration: see FIG. 1).

The LD 36K and LD 36Y are rotating polygon mirrors 34.
Are different in the axial direction (corresponding to the sub-scanning direction), and the laser beam K and the laser beam Y are respectively incident on the rotary polygon mirror 34 at different incident angles along the sub-scanning direction. The laser beams K and Y transmitted twice through the fθ lens 44 are incident on separate plane mirrors 46K and 46Y.

The laser beam K is applied to the plane mirror 46.
Due to K, the light is incident on a cylindrical mirror 48K disposed at a position corresponding to a position above the photosensitive drum 18K, is emitted from the cylindrical mirror 48K toward the photosensitive drum 18K, and is scanned on the peripheral surface of the photosensitive drum 18K. . Further, the laser beam Y is incident on the cylindrical mirror 48Y arranged at a position corresponding to the upper side of the photosensitive drum 18Y by the plane mirror 46Y, and is emitted from the cylindrical mirror 48Y toward the photosensitive drum 18Y. The peripheral surface of 18Y is scanned.

Incidentally, as shown in FIG.
Is entirely concealed by a lid 50. Lid 5
0, a rectangular opening 50A through which a laser beam passes is formed.
8K and 48Y are arranged on the upper surface of the lid 50 so as to straddle the opening 50A. On the other hand, an LD 36M for emitting a laser beam for irradiating the photosensitive drum 18M is provided at an end inside the casing 32 opposite to the position where the LDs 36K and LD 36Y are disposed with the rotating polygon mirror 34 interposed therebetween. 18
LDs 36C for emitting a laser beam for irradiating C are arranged near the corners, respectively. A collimator lens 38C and a plane mirror 52 are sequentially arranged on the laser light emission side of the LD 36C. The laser beam C emitted from the LD 36C is converted into a parallel light beam by the collimator lens 38C and is incident on the plane mirror 52. A collimator lens 38M and a plane mirror 54 are arranged in this order on the laser light emission side of the LD 36M. The laser beam M emitted from the LD 36M is converted into a parallel light beam by the collimator lens 38M, and then reflected by the plane mirror 54. The light enters the plane mirror 52.

An fθ lens 56 is disposed between the plane mirror 52 and the rotary polygon mirror 34, and the laser beam C and the laser beam M reflected by the plane mirror 52 are separated by fθ
After passing through the lens 56 and entering the rotary polygon mirror 34 and being reflected and deflected by the rotary polygon mirror 34, the fθ lens 5
6 is transmitted.

The LD 36C and the LD 36M are a rotating polygon mirror 34.
Are different from each other in the axial direction (corresponding to the sub-scanning direction), and the laser beam C and the laser beam M are respectively incident on the rotary polygon mirror 34 at different incident angles along the sub-scanning direction. The laser beams C and M transmitted twice through the fθ lens 56 are incident on separate plane mirrors 46C and 46M.

The laser beam C is applied to the plane mirror 46.
By C, the light is incident on a cylindrical mirror 48C disposed at a position corresponding to a position above the photosensitive drum 18C, is emitted from the cylindrical mirror 48C toward the photosensitive drum 18C, and is scanned on the peripheral surface of the photosensitive drum 18C. . The laser beam M is incident on a cylindrical mirror 48M disposed at a position corresponding to a position above the photosensitive drum 18M by a plane mirror 46M, and is emitted from the cylindrical mirror 48M toward the photosensitive drum 18M. It is scanned on the 18M peripheral surface.

As is clear from the above, since the laser beams K and Y and the laser beams C and M are incident on the opposite surfaces of the rotary polygon mirror 34, as shown by arrows in FIG. , Y and the laser beams C and M are scanned in opposite directions. The cylindrical mirrors 48C, 4C
As shown in FIG. 3, 8M is also arranged on the upper surface of the lid 50 so as to straddle an opening 50A formed in the lid 50 of the casing 32.

In the vicinity of the bottom of the casing 32, a pickup mirror (plane mirror) 5 is arranged so as to cross the scanning trajectories of the laser beams K, Y, M and C reflected by the cylindrical mirrors 48K, 48Y, 48M and 48C, respectively.
8 are arranged. The pickup mirror 58 is located near the scanning start side end (SOS: Start Of Scan) of the laser beams K and Y in the scanning locus of the laser beam, that is, the scanning end side end (EOS: End Of S) of the laser beams M and C.
can).

[0034] As shown in FIG.
An opening 50B is formed in the aperture 0 to allow each laser beam incident on and reflected by the pickup mirror 58 to pass therethrough. A sensor substrate 60 is disposed at a position where the laser beam that has passed through the opening 50B can be received. Have been. The sensor substrate 60 is mounted on the upper surface of the lid 50 via a bracket 62.

The laser beams K, Y, M, and C scan across the sensor substrate 60 as shown by dashed lines in FIG. 4, for example. A main scanning position detection sensor 64 and a sub-scanning position detection sensor 66 are arranged on the sensor substrate 60 along the scanning trajectory of each laser beam.

The main scanning position detecting sensor 64 outputs the level of the output signal when the laser beam passes through the light receiving portion (the rectangular portion shown in FIG. 4) formed on the sensor chip and when the laser beam does not pass. Are optical sensors that output different signals.

The sub-scanning position detection sensor 66 (PSD)
As shown in FIG. 5A, electrodes 66X are provided at both ends of the device.
66Y is provided and a bias voltage application terminal 66Z is connected. As shown in FIG. 5B, the equivalent circuit includes a current source 162 and a diode 164 with respect to a positioning resistor 160. , Junction capacity 16
6, a resistor 168 is connected in parallel (reference numeral 170 is a bias voltage).
With 0, the incident position of the light beam can be detected. That is, the sub-scanning position detection sensor 66 corresponds to the detection unit of the present invention.

In the following, the detection signal output from the main scanning position detection sensor 64K corresponding to the laser beam K will be referred to as "SOS (K)", and the detection signal output from the main scanning position detection sensor 64Y corresponding to the laser beam Y will be described. Change the signal to "SOS
(Y) ”, the detection signal output from the main scanning position detection sensor 64M corresponding to the laser beam M is referred to as“ EOS
(M) ”, the detection signal output from the main scanning position detection sensor 64C corresponding to the laser beam C is“ EOS (C) ”.
To distinguish them.

In the above description, the pickup mirror 58 and the sensor substrate 60 are integrally formed for each of the colors K, Y, M, and C. However, the present invention is not limited to this, and they may be individually provided for each color.

(Controller) Next, with reference to FIGS. 6 and 7, a configuration of a control system for controlling the operation of the multi-beam scanning device 30 including a circuit for controlling the driving of the LDs 36K, 36Y, 36M, and 36C will be described. . The main scanning position detection sensor 64 and the sub-scanning position detection sensor 66 are respectively connected to a control circuit 96 corresponding to the correction means of the present invention, and a writing timing control circuit 98 is connected to the control circuit 96.

As shown in FIG. 7, the control circuit 96
Is a main controller 100 including a microprocessor, a selector 102, an interval counter 10
4 and other peripheral circuits (other circuits are not shown). The main controller 100 includes a first storage unit 100A such as a ROM, and a non-volatile second storage unit 100B such as an EEPROM that can rewrite the storage contents. The image data of the test chart image is stored in the first storage unit 100A in advance. The second storage means stores various setting data (line sync setting data FDATA (K), FDATA (Y), FDATA (Y), which will be described later) that define the modulation timing of each laser beam.
(M), FDATA (C), page sync setting data SDATA (K), SDATA (Y), SDATA
(M), SDATA (C), etc.).

The control circuit 96 includes a control panel 10 including display means such as a liquid crystal display and information input means such as a numeric keypad and a touch panel.
6 are connected (see FIG. 6). Control circuit 9
6, a video clock generator 108 is connected. The video clock generator 108 includes a video clock generator 110 that generates a video clock signal that defines the timing of modulation of the laser beam for each dot, and is provided for each of K, Y, M, and C colors.

The write timing control circuit 98 comprises a synchronous clock generator 126, a line start control circuit 128, a page start control circuit 130, and four AND circuits 132. The synchronous clock generator 126 receives a video clock signal CLK (K) having a constant frequency from the video clock generator 110K and a detection signal SOS (K) from the main scanning position detection sensor 64K. The synchronous clock signal SYN based on the signal
-CLK (see FIG. 8B) is generated and output.

The line start control circuit 128 includes a counter circuit 134, an OR circuit 136, and a flip-flop circuit 1.
38 are provided corresponding to the four colors of K, Y, M, and C, and the detection signal SOS is provided.
(K), based on the synchronous clock signal SYN-CLK and the line sync setting data held in the main controller 100, each of the four laser beams emitted from each LD 36, the laser beam in one main scan Are generated for the four colors of K, Y, M, and C, respectively, which indicate the timing of starting the modulation.

That is, when the input detection signal SOS (K) goes low, the counter circuit 134 fetches line sync setting data from the main controller 100 as a count value, and outputs the synchronous clock signal SYNC-C.
The count value is decremented at a timing synchronized with LK. When the count value becomes 0, a pulse signal is output. This pulse signal is input to the flip-flop circuit 138 via the OR circuit 136, and the level of the output signal (line synchronization signal LS) from the flip-flop circuit 138 is switched by using the pulse signal as a trigger (FIG. 8).
(A)).

As described above, the timing at which the level of the line synchronization signal LS switches (corresponding to the timing at which laser beam modulation in one main scan is started) is determined by the line sync setting data (FIG. In FIG. 8 (B), it changes as indicated by the arrow in accordance with the value of FDATA. Then, the side registration position (the position in the main scanning direction) also changes according to the change in the timing.

Similarly to the line start control circuit 128, the circuit group including the counter circuit 140, the OR circuit 142, and the flip-flop circuit 144 corresponds to the four colors of K, Y, M, and C. Four sets are provided. The page start control circuit 130 receives a trigger signal TOP for determining the timing at which the transfer of the transfer material 28 to the transfer belt 14 is started.
Based on the OS (K), the trigger signal TOP, and the page sync setting data held in the main controller 100, each of the four laser beams emitted from each LD 36 is used to scan one page of the laser beam. A page synchronization signal PS indicating the timing of starting beam modulation is generated for each of the four colors K, Y, M, and C.

That is, when the trigger signal TOP becomes low level, the counter circuit 140 takes in the page sync setting data from the main controller 100 as a count value, and decrements the count value at a timing synchronized with the detection signal SOS (K). . When the count value becomes 0, a pulse signal is output. This pulse signal is supplied to the flip-flop circuit 144 via the OR circuit 142.
And the level of the output signal (page synchronization signal PS) from the flip-flop circuit 144 is switched using the pulse signal as a trigger (see FIG. 9A).

As described above, the timing at which the level of the page synchronization signal PS is switched (corresponding to the timing at which the modulation of the laser beam in the scanning of the laser beam for one page is started, ie, the image writing timing according to the present invention).
Changes in units of one line, as indicated by arrows in FIG. 9B, according to the value of the page sync setting data (denoted as SDATA in FIG. 9A) taken into the counter circuit 140. Then, the read registration position (the position in the sub-scanning direction) also changes according to the change in the timing.

The AND circuit 132 is a line start control circuit 1
28 and a page start control circuit 130, and outputs a synchronizing signal SYN corresponding to the logical product of the line synchronizing signal LS and the page synchronizing signal PS for each of the four colors K, Y, M, and C.

The write timing control circuit 98 has an LD
A modulation / drive circuit 146 is connected, and synchronization signals SYN (K), SYN (Y), SYN corresponding to each color are provided.
(M) and SYN (C) are input to the LD modulation / drive circuit 146. The LD modulation / drive circuit 146 is also connected to the video clock generator 108, and the video clock signals CLK (K), CLK (Y),
CLK (M) and CLK (C) are input. Further L
Color image data representing a color image to be formed on the transfer material 28 separated into four colors of K, Y, M, and C is input to the D modulation / drive circuit 146.

The LD modulation / drive circuit 146 includes the LD 36
Each of K, 36Y, 36M, and 36C corresponds to the same color at a timing synchronized with the video clock signal CLK corresponding to the same color within a period defined by the synchronization signal SYN corresponding to the same color. Each L is adjusted so that a laser beam modulated according to the image data is emitted.
The driving of D36 is controlled. As a result, laser beams are emitted from the respective LDs 36, and the emitted laser beams are deflected by the rotation of the rotary polygon mirror 34, and are scanned on the photosensitive drums 18K, 18Y, 18M, and 18C, respectively.

(Operation) Next, as an operation of the present embodiment, correction of color misregistration of a color image formed by the multicolor image forming apparatus 10 (correction of misregistration in the sub-scanning direction between images of each color in a multicolor image, so-called, (Lead registration correction) will be described. The color misregistration correction is performed when the multi-beam image forming apparatus 10 is equipped with the multiple beam scanning device 30.

The multicolor image forming apparatus 10 is set to a state where there is no color misregistration by the color misregistration initial correction process before shipment, and is shipped. After the shipment, the color misregistration automatic correction process automatically performs the color misregistration. Correction is made.
First, the color misregistration initial correction process will be described with reference to the flowchart shown in FIG.

(Color misregistration initial correction process) In the color misregistration initial correction process, as shown in FIG.
At 0, an evaluation test chart for evaluating the degree of color misregistration is created. When creating the evaluation test chart, the image data of the test chart image stored in advance in the first storage unit 100A is fetched,
Various setting data (line sync setting data FDATA (K), FDATA, etc.) that define the modulation timing of each laser beam stored in the second storage unit 100B.
(Y), FDATA (M), FDATA (C), page sync setting data SDATA (K), SDATA
(Y), SDATA (M), and SDATA (C)). At a predetermined timing according to the acquired setting data, each LD 36 is driven so that each laser beam is modulated according to the image data of the test chart image.

When the multi-beam image forming apparatus 10 is equipped with the multiple beam scanning device 30 and the process of step 200 is first performed, the second storage means 100 # stores default values and the like as the various setting data described above. Is set.

The four laser beams emitted from each LD 36 are deflected by a single rotating polygon mirror 34, and the corresponding laser beams are passed through optical components such as an Fθ lens 44 (or 56) and a cylindrical mirror 48. Body drum 1
8 is scanned over the circumference. The electrostatic latent image of the test chart image formed on the peripheral surface of the photosensitive drum 18 by the scanning of the laser beam is developed as toner images of different colors by the developing device 22, and the toner images of each color are transferred to the transfer belt. The color image (test chart) formed by overlapping on the belt surface of No. 14 is transferred to the transfer material 28. Then, the transfer material 28 onto which the test chart image has been transferred is discharged outside the multicolor image forming apparatus 10 through a fixing process.

In the next step 202, it is determined whether or not the image quality of the created test chart image is appropriate. Specifically, the operator (assembly operator) checks the discharged transfer material 2
8 to determine whether the K, Y, M, and C colors match in the sub-scanning direction, that is, whether color shift correction is unnecessary. Input via the control panel 106.
Based on the input result, it is determined whether the image quality of the test chart image is appropriate.

If the operator determines that correction is necessary, a negative determination is made in step 202, and
The process proceeds to step 204 to determine whether the setting data of the sub-scanning direction position (read register) needs to be corrected.

If it is determined in step 204 that the lead register setting data needs to be corrected,
The process proceeds to step 206, where a message requesting the operator to correct the setting data determined to require correction is displayed on the control panel 106 and the setting data is corrected by the operator.

When the operator operates the control panel 106 to correct the setting data, the next step 20
At 8, the setting data stored in the second storage means 100B is updated and stored to the setting data corrected by the operator. When the update and storage of the corrected setting data is completed, the process proceeds to the next step 210.

On the other hand, if it is determined in step 204 that the correction of the setting data of the lead register is not necessary, the process directly proceeds to step 210.

In step 210, it is determined whether or not the operation by the operator has been completed, and the process waits until the determination is affirmed. If the determination in step 210 is affirmative, the process returns to step 200. Until the determination in step 202 is affirmative, that is, until a test chart with proper image quality is obtained, the setting data is corrected and the evaluation test chart is re-read. Creation will be performed repeatedly.

If the determination in step 202 is affirmative, the process proceeds to step 212 in order to store the current state in which a test chart image of appropriate image quality has been obtained. In step 212, the sub-scanning position detection sensors 66K, 66Y, 6
The positions of the laser beams K, Y, M, and C in the sub-scanning direction are measured by 6M and 66C. Then, the next step 214
Then, the measurement results of the beam sub-scanning direction position (sub-scanning direction position measurement data PDATA (K), PDATA (Y), P
DATA (M), PDATA (C)) are stored in the second storage unit 100B as the initial value data, and the color misregistration initial correction processing ends.

After shipment of the multicolor image forming apparatus 10, various setting data for defining the modulation timing of each laser beam stored in the second storage means 100B, that is, a test chart image having an appropriate image quality can be obtained. By performing the image forming process based on the various setting data at the time of the setting, an image without color shift can be obtained.

However, due to a change in the ambient temperature of the multicolor image forming apparatus 10 and a rise in the temperature inside the multicolor image forming apparatus 10 due to the continuation of the operating state, the multiple beam scanning apparatus 3
The arrangement position of each optical component constituting 0 changes, the position of each laser beam in the sub-scanning direction is displaced, and a color shift occurs again. For this reason, in the multicolor image forming apparatus 10, for example, the color misregistration automatic correction processing is performed during a standby period during which the image forming is not in operation and the image forming is not performed, and the color misregistration correction is also performed in a normal state (during operation) after shipment. Is performed regularly. At this time, the lead registration correction is performed.

Hereinafter, the automatic color misregistration correction processing will be described with reference to FIG.
This will be described with reference to the flowchart shown in FIG.

(Color misregistration automatic correction processing) When the color misregistration automatic correction processing is started, first, in step 230, as in step 212 (see FIG. 10) of the color misregistration initial correction processing described above, the sub-scanning position detection is performed. Sensors 66K, 66Y,
The positions of the laser beams K, Y, M, and C in the sub-scanning direction are measured by 66M and 66C.

In the next step 232, step 230
The sub-scanning direction position of each laser beam measured in the sub-scanning direction represented by the sub-scanning direction position measurement data stored as initial data in the second storage unit 100B in step 214 (see FIG. 10) of the color misregistration initial correction process It is determined whether the position is displaced with respect to the position.

If the determination in step 232 is negative, the position of each laser beam in the sub-scanning direction has not been displaced since the time of performing the initial misregistration correction processing (at the time of initializing).
It is determined that there is no need to correct the color misregistration, and the automatic color misregistration correction process is terminated (see FIG. 12).

On the other hand, when the measured value of the position in the sub-scanning direction is displaced, there is a possibility that the lead registration of each color is shifted due to a change in the arrangement position of the optical components constituting the multiple beam scanning device 30. is there. Therefore, step 23
If the determination of No. 2 is affirmative, the page sync setting data SDATA (FIG. 10) is obtained based on the displacement of the sub-scanning direction position obtained from the sub-scanning direction position represented by the initial data and the sub-scanning direction position measured in step 230. 9)), the process proceeds to step 234.

In step 234, each laser beam Y,
It is determined whether the directions of displacement of M and C are the same direction or both directions. (See FIGS. 14 and 15). That is, the direction of displacement of the main scanning position of each color (Y, M, C) with respect to the reference color (K) in the sub-scanning direction (corresponding to the displacement direction of the relative displacement of the present invention) is the same direction or both directions. It is determined whether there is.

For example, the difference in displacement in the sub-scanning direction for each laser beam (the displacement in the sub-scanning direction of the scanning line of the laser beam K and the displacement in the sub-scanning direction of the scanning line of the predetermined color laser beam) Is calculated, and the direction of positional shift of each color with respect to the reference color (K) is determined from the sign of the result of the calculation.

If the direction of displacement of each color (Y, M, C) with respect to the reference color (K) is both + and-, the process proceeds to step 236.

In step 236, a laser beam of a predetermined color (Y, M, K) with respect to the scanning line of the laser beam K is determined based on the position of each laser beam K, Y, M, C measured in step 230 in the sub-scanning direction. Of the scanning line in the sub-scanning direction (corresponding to the relative displacement amount of the present invention, hereinafter referred to as “color deviation amount with respect to the reference color (K)”) is １ ／.
It is determined whether there is a color exceeding the value corresponding to dot. That is, it is determined whether or not there is a color that is shifted by 以上 dot or more in the sub-scanning direction with respect to the reference color (K). Note that one dot corresponds to the width of one main scanning line. In addition, the amount of color misregistration with respect to the reference color (K)
Is calculated by calculating the absolute value of the difference between the amount of displacement of the scanning line in the sub-scanning direction and the amount of displacement of the scanning line of the predetermined color laser beam in the sub-scanning direction.

The amount of color shift with respect to the reference color (K) is ｄd
If there is a color (laser beam) that is equal to or more than ot, the process proceeds to step 238, updates the page sync setting data SDATA of the color, and proceeds to step 244. Accordingly, the image writing time of the color is corrected, and the color shift of the color in the sub-scanning direction with respect to the reference color (K) on the color image is reduced.

If the amounts of color misregistration of the Y, M, and K colors with respect to the reference color (K) are all smaller than 1/2 dot, the determination is negative in step 236, and the color misregistration automatic correction process ends.

The reference color (K) of each color (Y, M, C)
If the direction of the positional deviation with respect to is the same direction (the same as either + or-), the process proceeds to step 240. In step 240, the color shift amount with respect to the reference color (K) is 3 /
It is determined whether there is a color exceeding 4 dots.

The amount of color shift with respect to the reference color (K) is 3 / 4d
If a color exceeding ot exists, the process proceeds to step 242, updates the page sync setting data SDATA of the color, and proceeds to step 244. Accordingly, the image writing time of the color is corrected, and the color shift of the color in the sub-scanning direction with respect to the reference color (K) on the color image is reduced.

If the amount of color misregistration of each of the Y, M, and K colors with respect to the reference color (K) is not more than 3/4 dot, step 24 is executed.
If the result is 0, the determination is negative, and the color misregistration automatic correction process ends.

When the page sync setting data is updated and the process proceeds to step 244, the updated page sync setting data is stored in the second storage unit 100B. afterwards,
The color shift automatic processing ends.

Here, the threshold value (corresponding to the maximum displacement amount of the present invention) for determining whether or not to perform the writing position correction will be described. In this embodiment, the writing position is corrected by one dot.
The scanning is performed every minute, that is, in one main scanning unit. Therefore, if the color shift amount for the reference color (K) is αdot and the writing position correction is performed, the color shift amount for the reference color (K) becomes (1−α) dot. The condition that the color shift amount after the writing start position correction is smaller than before the writing start position correction is as follows.
α ≧ 1−α, that is, α ≧ 1/2.

When the color misregistration direction of each color with respect to the reference color is in both directions, if the color misregistration amount of each color with respect to the reference color is reduced, the total color misregistration amount can be reduced. The same ｄdot is used.

Even when the direction of color shift of each color with respect to the reference color is the same, the amount of color shift with respect to the reference color (K) is βdot.
When the write start position of the color of (β ≧ １ ／) is corrected, the amount of color shift of the corrected color with respect to the reference color (K) is calculated as (1−β)
dot, but the color shift amount γdot (γ <1/2) of the color whose writing position has not been corrected remains.
｛(1−β) + γ｝ dot. Therefore, the condition that the color shift amount after the writing start position correction is smaller than that before the writing start position correction is as follows: β ≧ {(1−β) + γ}, γ <
1/2, that is, β> 3/4. Thus, ／ dot is used as the determination threshold.

Next, as a specific example, FIG.
3. The color misregistration automatic correction process will be described with reference to FIG. In each figure, (A) is a diagram showing a light beam position for scanning on the sub-scanning position detection sensor, where a solid line arrow indicates a current light beam scanning position, and a dotted line arrow indicates an initial value light beam scanning position (color shift). This is the light beam scanning position immediately after the execution of the initial correction process, and corresponds to the sub-scanning direction position represented by the initial data). Although the position of the light beam that scans on the sub-scanning position detection sensor is different for each color, the position correction in the sub-scanning direction is corrected based on the amount of deviation from the initial value (origin K, Y, M, C). Even if the position of the light beam that scans on the sub-scanning position detection sensor varies, there is no particular problem.

FIG. 11B is a diagram showing the color shift of each color predicted from the sub-scanning position detection sensor. In the case of the present invention, since the sub-scanning position detecting sensor is provided in the multi-beam scanning device 30, when the position of the multi-beam scanning device 30 and the photoconductor is shifted due to the temperature, each color expected from the sub-scanning position detecting sensor is obtained. Is different from the color shift of
By correcting the position of the beam emitted from 0, it is possible to correct the color shift of each color by a simple method.

FIG. 12 shows a case where the position of each laser beam in the sub-scanning direction has not been displaced immediately after the color misregistration initial correction process is performed or after the color misregistration initial correction process is performed. It can be seen that no occurrence has occurred.

FIG. 13 shows a case where the displacements of the laser beams M and C and the laser beam Y in the sub-scanning direction are opposite to each other based on the displacement of the laser beam K in the sub-scanning direction.
That is, a case is shown in which the misalignment direction of the reference color (K) in the sub-scanning direction with respect to the main scanning line is opposite between the M and C main scanning lines and the Y main scanning line. In FIG.
The color shift amounts of the M and C colors with respect to the reference color (K) correspond to 1/4 dot and 1/2 dot, respectively, and the color shift amounts with respect to the Y reference color (K) correspond to 5/8 dot.

In this case, in the color misregistration automatic correction processing, a color in which the color misregistration amount with respect to the reference color (K) is equal to or more than Ｙ dot, that is, the writing start position of Y which is displaced by ／ dot with respect to the reference color (K) In the direction of the reference color (K) by one dot, the page sync setting data SDATA (Y)
Is updated (corrected). As a result, as shown in (B) in the figure, the color shift amount is changed from 9/8 dot to 1/2 dot.
To be reduced.

FIG. 14 shows the case where the displacements of the laser beams Y, M and C in the sub-scanning direction are in the same direction based on the displacement of the laser beam K in the sub-scanning direction, that is, the main color of the reference color (K). This figure shows a case where the main scanning line of each color (Y, M, C) is displaced in the sub-scanning direction with respect to the scanning line in the same direction. In FIG. 14, the reference colors (K) of the Y, M, and C colors are shown.
Are ｄ dot and 7/8 d, respectively.
ot, 1/4 dot.

In this case, in the color misregistration automatic correction processing, the writing position of the color in which the color misregistration amount with respect to the reference color (K) is ３ dot or more, that is, M which is shifted by ／ dot with respect to the reference color (K) Of the page sync setting data SDATA (M) so as to be shifted by 1 dot in the direction of the reference color (K).
Is updated (corrected). As a result, as shown in (B) in the figure, the color shift amount is reduced from 7/8 dot to 5/8 dot.
To be reduced.

As described above, the position of the light beam of each color for scanning on the sub-scanning position detection sensor is compared with that at the time of the initialization, and the page sync setting data SD is determined based on the displacement of the positional relationship.
ATA, that is, the writing start timing of each image is corrected for each scanning line. This makes it possible to easily reduce the positional deviation in the sub-scanning direction between the images of each color, and to obtain a high-quality multicolor image with little color deviation. This eliminates the necessity of forming and reading a color misregistration detection pattern, which is required in the related art, so that the configuration can be simplified and the cost can be reduced.

Further, since the sub-scanning position detecting sensor as the positional deviation amount detecting means is provided not in the vicinity of the photosensitive drum but in the plural beam scanning device 30, the photosensitive member is replaced when the photosensitive drum unit is replaced. There is no need to adjust the drum and the displacement detection means, and the photosensitive drum unit can be easily replaced. Further, it is possible to prevent the displacement amount detecting means from being stained by dust or the like.

In the color misregistration automatic correction process, when the position of the other color in the sub-scanning direction is deviated from the reference color, the lead registration correction is performed. As shown in FIG. In the case where the positional shift amount is the same as that of the reference color and is shifted by the same amount, no color shift occurs when an image is printed by synthesizing the colors, so that no correction processing is performed. That is, since the correction is performed only when the relative position with respect to the reference color is shifted, the control can be simplified.

Normally, the color misregistration is corrected without any problem by the above correction. However, the installation environment of the multicolor image forming apparatus 10 is largely changed, or the photosensitive drums 18K, 18
In the case where the relative positions of Y, 18M, and 18C have significantly changed, the color misregistration cannot be sufficiently eliminated even by performing the color misregistration automatic correction processing, and image quality may deteriorate.
In such a case, it is preferable to return to the color misregistration initial correction processing shown in FIG. 9 and manually correct the color shift of each color. By performing such a color shift correction operation, the color shift can be corrected easily at low cost.

The image deterioration is determined based on the amount of displacement of each of the laser beams K, Y, M, and C from the initial position in the sub-scanning direction (when the amount of displacement of at least one laser beam is equal to or more than a predetermined value). In such a case, the determination may be made automatically, or the user may visually determine the multicolor image formed.

In the above description, each of the laser beams K, Y,
If the positions of the M and C sub-scanning directions are displaced from the initial state (see step 232 in FIG. 11), the position shift direction and the relative shift amount are determined, and the relative shift amount exceeds a predetermined value. In this case, the image writing position is corrected, but the present invention is not limited to this. In the case of performing the second or later automatic color shift correction processing after the color shift initial correction processing, the sub-scanning direction positions of the laser beams K, Y, M, and C are measured in the previous color shift automatic correction processing. In the case where the image is displaced from the position in the sub-scanning direction, the determination of the position shift direction and the determination of the relative shift amount are performed. Good.

That is, after performing the color misregistration initial correction process,
In the case of performing the second and subsequent color misregistration automatic correction processes, in step 232, the sub-scanning direction position acquired in the previous color misregistration automatic correction process in step 230 and the current color misregistration automatic correction process in step 230 are acquired. The position may be compared with the position in the sub-scanning direction.

In the above description, as a tandem type multicolor image forming apparatus, a multicolor image forming apparatus provided with a multi-beam scanning device for scanning a plurality of laser beams in opposite directions by using the reflecting surfaces 34A on both sides of the rotary polygon mirror 34 is used. Although the image forming apparatus (so-called spray paint method) has been described as an example, the present invention may be applied to other tandem type multicolor image forming apparatuses. For example, a multicolor image forming apparatus provided with a multiple beam scanning device that scans a plurality of laser beams using only one reflecting surface 34A of the rotating polygon mirror 34, or one laser beam is scanned by one rotating polygon mirror. The present invention can also be applied to a multicolor image forming apparatus provided with a plurality of optical scanning devices (a so-called quadruple tandem system).

[0100]

As described above, the present invention is superior in that the quality of a multicolor image formed by superimposing images of a plurality of colors can be improved with a simple and low-cost configuration. Has the effect.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a multicolor image forming apparatus (and a multiple beam scanning apparatus) according to an embodiment.

FIG. 2 is a schematic plan view of a multiple beam scanning device.

FIG. 3 is a perspective view of a multiple-beam scanning device showing a casing lid partially cut away.

FIG. 4 is a schematic plan view showing an arrangement of each sensor on a sensor substrate.

5A is a perspective view schematically showing a sub-scanning position detection sensor, FIG. 5B is an equivalent circuit, and FIG. 5C is a block diagram showing an example of a signal processing circuit.

FIG. 6 is a block diagram illustrating a schematic configuration of a control system that controls the operation of the multiple beam scanning device.

FIG. 7 is a block diagram showing a schematic configuration of a write timing control circuit.

FIGS. 8A and 8B are timing charts of a line synchronization signal and a signal related to its generation.

FIGS. 9A and 9B are timing charts of a page synchronization signal and a signal related to its generation.

FIG. 10 shows the contents of the color misregistration initial correction processing performed when a multi-beam image forming apparatus is equipped with a multi-beam scanning apparatus or when image quality deterioration is confirmed during operation of the multi-color image forming apparatus. FIG.

FIG. 11 is a flowchart illustrating the contents of a color misregistration automatic correction process performed during operation of the multicolor image forming apparatus.

FIG. 12A shows the sub-scanning position detection immediately after the color misregistration initial correction process is performed or when the position of each laser beam in the sub-scanning direction is not displaced from when the color misregistration initial correction process is performed. Light beam position scanning on the sensor, (B)
FIG. 3 is a conceptual diagram illustrating color misregistration of each color predicted from a sub-scanning position detection sensor.

FIG. 13A shows a case where the laser beam of each color (K, Y, M, C) is shifted in the sub-scanning direction in both directions.
(B) is a conceptual diagram showing a color shift of each color predicted from the sub-scanning position detection sensor.

FIG. 14A shows a case where the laser beams of each color (K, Y, M, C) are shifted in the same position in the sub-scanning direction.
Is a light beam position for scanning on the sub-scanning position detection sensor,
(B) is a conceptual diagram showing a color shift of each color predicted from the sub-scanning position detection sensor.

FIG. 15A shows a sub-scanning position detection sensor in the case where the laser beams of each color (K, Y, M, C) are shifted in the sub-scanning direction in the same direction and have the same shift amount. FIG. 7B is a conceptual diagram illustrating a color misregistration of each color predicted from the sub-scanning position detection sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Multicolor image forming apparatus 18 Photoreceptor drum 30 Multiple beam scanning device 32 Casing 34 Rotating polygon mirror 36 Semiconductor laser 64 Main scanning position detection sensor 66 Sub-scanning position detection sensor (detection means) 96 Control circuit (correction means) 98 Timing control Circuit 100 Main controller 100A First storage unit 100B Second storage unit 102 Selector 104 Interval counter 106 Control panel 108 Video clock generator 110 Video clock generator 126 Synchronous clock generator 128 Line start control circuit 130 Page start control circuit 146 Modulation / Drive circuit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) H04N 1/23 103 H04N 1/04 104A F term (Reference) 2H030 AA01 AB02 AD12 AD17 BB02 BB16 BB23 BB42 BB56 2H045 AA01 BA22 BA34 CA88 CA98 5C072 AA03 BA19 HA02 HA06 HA13 HB08 HB11 HB20 QA14 QA17 5C074 AA10 BB03 BB26 CC22 DD15 DD24 EE04 FF15 HH04

Claims (6)

[Claims] 1. A plurality of light beams formed on the photoconductor by performing main scanning on the photoconductor by deflecting a plurality of light beams by a deflecting unit and performing sub-scanning by moving the photoconductor. A multicolor image forming apparatus that forms a multicolor image by synthesizing a single color image as a single image, wherein a position in a sub-scanning direction when a plurality of light beams is main-scanned on the photoconductor is determined. Detecting means for detecting each, and correcting means for correcting the image writing timing in units of one main scan based on the relative displacement in the sub-scanning direction of each color obtained from the detection result by the detecting means. And a multicolor image forming apparatus. 2. A calculating unit for calculating a relative displacement amount of each of the other colors in a sub-scanning direction with respect to a predetermined color based on a detection result by the detecting unit, and a sub-scanning of each of the other colors. A determination unit for determining whether or not it is necessary to correct the image writing time in units of one scan for each of the other colors based on the relative displacement amount in the direction and the predetermined maximum displacement amount. 2. The multicolor image forming apparatus according to claim 1, wherein the image writing timing is corrected in units of one main scan for a color determined to require correction by the determination unit. . 3. The method according to claim 1, wherein the maximum displacement amount used for the determination by the determination unit is different depending on whether or not all the relative displacement directions of the other colors in the sub-scanning direction are the same. Item 3. A multicolor image forming apparatus according to Item 2. 4. The maximum displacement amount is a displacement amount corresponding to a displacement of ／ of one main scanning width when the displacement directions of relative displacements in the sub-scanning direction of the other colors are all the same. 4. The multicolor image according to claim 3, wherein when the displacement direction of the relative displacement in the sub-scanning direction of each of the other colors is different, the displacement amount corresponds to １ ／ of one main scanning width. Forming equipment. 5. Only when a difference between a relative position of each color obtained from a previous detection result by the detection means and a relative position of each color obtained from a current detection result by the detection means is a predetermined value or more, 5. The apparatus according to claim 2, further comprising: a correction execution control unit configured to cause the correction unit to perform the calculation by the calculation unit and the determination by the determination unit to perform the correction. 6. Color image forming apparatus. 6. The image processing apparatus according to claim 1, further comprising a setting unit configured to set an initial value of the image writing time based on a result of forming the multicolor image. The multicolor image forming apparatus as described in the above.