JPH11254757A - Multicolor image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To conform the respective color image drawing positions one another by the small correction amount. SOLUTION: Tone image patterns for sensing position shifts for respective color components are formed on an intermediate transfer body, and the positions of the toner image patterns are sensed by image position sensors 54S, 54C and 54E, and respective color component drawing positions are computed by an image position computation sections 56. Based on the drawing positions, the target values of respective color drawing positions are set as an intermediate value between the maximum value and the minimum value of color shifts by a CPU 60 and output to a correction control section 62. A laser beam source 14, a polygon motor 64 and a skew motor 66 are controlled by the correction control section 62 so that the target values conform to respective color drawing positions and correct the color shifts of respective colors.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a multicolor image forming apparatus for forming a multicolor image by sequentially transferring images of respective colors formed by a plurality of light beam scanning devices to a transfer member.

[0002]

2. Description of the Related Art Hitherto, a multicolor image forming apparatus which includes a plurality of light beam scanning devices for scanning with a light beam such as a laser beam and forms a color image has been known. As such a multicolor image forming apparatus, an optical scanning device, a photoconductor, and the like provided for each color (for example, black: K, cyan: C, magenta: M, yellow: Y) are arranged in series. There is a so-called tandem-type multicolor image forming apparatus in which a toner image of each color formed on a photoreceptor is sequentially superimposed and transferred onto a transfer belt, and then collectively transferred onto paper to obtain a multicolor image.

Such a multicolor image forming apparatus includes a laser light source for outputting a light beam, and outputs a light beam corresponding to image data. Then, the light beam output from the laser light source is collimated by a collimator lens, shaped by a slit, and then incident on a polygon mirror via an expander lens, a cylinder lens and the like. Thereafter, the light beam deflected by the polygon mirror has a constant scanning speed by the f · θ lens, and exposes the photoconductor charged by the charger.

[0004] The portion whose potential has been reduced by exposure is developed by a developing device and transferred onto a transfer belt. This process is performed for each color, and the images for four colors are sequentially transferred on the transfer belt in a superimposed manner, and then are collectively transferred onto the paper. Further, the toner images left on the photoconductor and the transfer belt are cleaned by a cleaner.

With this configuration, a full-color image can be formed at a high speed. Furthermore, even if the surface accuracy of the polygon mirror varies, a position corresponding to the end on the scanning start side in the entire scanning range of the light beam so that the printing position does not shift (jitter) in the main scanning direction. Is provided with an SOS (start of scan) sensor, which detects an SOS signal from the SOS sensor and controls printing so as to start printing after a lapse of a predetermined time from the detection of the SOS signal.

At this time, the positional deviation (registration deviation) of the image of each color may occur due to factors such as variations in the writing position of the image of each color, the position of the photoconductor, and a change in the speed of the transfer belt.

FIG. 7 shows typical types of misregistration. An arrow S direction in the figure is a direction in which the paper is conveyed (sub-scanning direction), and an arrow T direction in the figure is a direction in which the light beam is scanned (main scanning direction). In each registration shift, a solid line indicates a position where an image should be formed in a normal state, and a broken line indicates an image position when the registration shift occurs. The lead registration deviation is a state where the registration deviation occurs uniformly in the sub-scanning direction, the side registration deviation is a state where the registration deviation occurs uniformly in the main scanning direction, the magnification deviation is a state where the lengths in the main scanning direction are different, the skew. The shift indicates a state where the registration shift occurs obliquely, and the bow shift indicates a state where the registration shift occurs in an arc shape.

In order to correct such misregistration, predetermined patterns of predetermined colors are formed on the transfer belt at substantially equal intervals along a direction orthogonal to the traveling direction of the transfer belt. An image position detection sensor is provided at a position corresponding to the pattern. Then, a specific pattern is read by the image position detection sensor, and the amount of misregistration of the toner image of each color is relatively calculated with respect to the toner image of the reference color to measure the amount of registration misregistration. It is known that the registration deviation can be eliminated by changing the writing start position of the image of each color.

As shown in FIG. 14, the number of SOS signals is usually counted after the leading edge signal of the paper is generated, and the page start signal is generated at the count corresponding to the print start position, as shown in FIG. However, by changing the count number of the SOS signal according to the amount of misregistration, it is possible to perform correction in units of one scan. Further, by controlling the relative phase of the polygon mirror of each color, it is possible to correct the read registration in units of one scan or less.

As shown in FIG. 15, the number of image clocks is normally counted after the SOS signal is generated, and a line start signal is generated at the count corresponding to the print start position, as shown in FIG. The correction can be performed by changing the count number of the image clock according to the amount of registration deviation.

As shown in FIG. 16, the deviation of the magnification is corrected by changing the frequency (magnification) in the main scanning direction by changing the frequency of the image clock. Also, by changing the frequency of the image clock during scanning, a partial magnification shift can be corrected.

To prevent skew, one end of the cylinder mirror is fixed, and the other end is moved by a stepping motor or the like so as to form an angle with respect to the main scanning direction based on the amount of deviation. , Skew can be corrected. Also, skew can be corrected by tilting the entire light beam scanning device with respect to the rotation axis of the photoconductor.

The bow deviation can be corrected by bending the generating line of the cylinder mirror in an arc shape.

[0014]

In the conventional correction method as described above, a toner pattern image of a reference color is
The shift amount of the position of the toner pattern image of each color is relatively detected, and correction is performed so that the registration matches the reference color.
For example, when the skew is shifted as shown in FIG.
As shown in FIG. 9, correction is performed so that the image position matches cyan, which is the reference color. That is, in order to match the yellow image with the cyan image, the yellow image must be corrected by +0.4 mm. As described above, when the image position is largely corrected, particularly when the skew is corrected by moving the cylinder mirror, the ideal imaging state cannot be maintained, and the beam diameter and the exposure amount are adversely affected. Could have an effect. Further, since the correction amount becomes large, there is a problem that the mechanism becomes large and complicated, and the cost increases.

SUMMARY OF THE INVENTION An object of the present invention is to provide a multi-color image forming apparatus capable of making the image writing positions of respective colors coincide with each other with a small amount of correction in consideration of the above fact.

[0016]

According to a first aspect of the present invention, a latent image based on each color component of a color image is formed on a separate image carrier by a plurality of light beam scanning devices. A multicolor image forming apparatus that forms, forms and develops a latent image of each color component with a color toner, and transfers each color toner image formed by superimposing the color toner image on a transfer member sequentially to form a color image. A pattern forming unit for forming a toner image pattern for detecting a positional shift on the transfer member for each color component, and a position of the toner image pattern formed on the transfer member by the pattern forming unit is detected by an image position detection sensor A shift amount detecting unit that detects a shift amount of a writing position of each color component; and a shift amount of the writing position based on a shift amount of each color component detected by the shift amount detecting unit. Setting means for setting a target value, the writing position of each color component is characterized by having an adjustment means for adjusting so as to coincide with the target value.

According to the first aspect of the present invention, a toner image pattern for detecting misregistration is formed on the transfer member for each color component. Then, the position of the toner image pattern formed on the transfer member is detected by the image position detection sensor, and the shift amount of the writing position of each color component is detected. Based on this shift amount, a target value of the writing position of each color is set, and adjustment is performed so that the target value matches the writing position of each color.

Therefore, the invention according to claim 2 is characterized in that the target value is an intermediate value between the maximum value and the minimum value of the shift amount of each color component.

Further, the invention according to claim 3 is characterized in that the target value is an average value of the shift amounts of the respective color components.

The invention according to claim 4 is characterized in that the target value is a value of a color shift amount closest to the intermediate value or the average value.

Further, the invention according to claim 5 is characterized in that the target value is a reference position of the image position detecting sensor.

As described above, according to the present invention, the target value is set to an intermediate value between the maximum value and the minimum value of the shift amount of each color component, the average value of the shift amount of each color component, and the intermediate value. Since the value or the value closest to the average value is set to the reference position of the image position detection sensor, the amount of movement of the cylinder mirror can be small especially when the skew is corrected by moving the cylinder mirror. Therefore, the correction can be performed without deteriorating the optical characteristics of the light beam scanning device.

[0023]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 2 shows a schematic configuration of a multicolor image forming apparatus 10 according to the present invention. The multicolor image forming apparatus 10 includes a light beam scanning device 12 including a polygon mirror 28, a laser light source 14, a cylinder mirror 34, and the like for each color (yellow, magenta, cyan, and black), and a photoconductor as an image carrier. 36, a charger 42 for charging the photoconductor 36 is provided around each photoconductor 36, and a light beam is irradiated on the charged photoconductor 36 to form a portion where an electrostatic latent image is formed. Supplies toner to develop the electrostatic latent image,
A developing device 44 for forming a toner image on the photoconductor 36 and a cleaning device 46 for cleaning the toner remaining on the photoconductor 36 are arranged.

A transport roller 48 is provided below each photoconductor 36.
An endless transfer belt 50 is provided, which is wound around the transfer belt. The transfer charging roller for transferring from the photoconductor 36 to the transfer belt 50 is provided at a position opposed to each photoconductor 36 with the transfer belt 50 interposed therebetween. 52 are arranged. Photoconductor 3
6, the axis is the traveling direction of the transfer belt 50 (arrow A in FIG. 2).
Direction).

The monochromatic images of yellow, magenta, cyan, and black developed by each photoconductor 36 are transferred to the transfer belt 50.
All of them are superimposed and transferred on a single pass to form a multicolor toner image. Further, a charging roll 55 for transferring to a sheet 68 is disposed below the transfer belt 50, and is collectively transferred to the sheet 68 by the charging roll 55 to form a multicolor image on the sheet 68.

In the interval between sheets, for example, predetermined specific patterns of each color as shown in FIG. 6 are formed on the transfer belt 50 at substantially equal intervals in a direction orthogonal to the traveling direction A of the transfer belt 50. Formed. The specific pattern is read by the image position detection sensors 54S, 54C, 54E arranged on the downstream side in the traveling direction of the transfer belt 50 (see FIG. 3). The image position detection sensor 54 includes a photodetector or the like, and outputs the read specific pattern to the image position calculation unit 56 shown in FIG.

As shown in FIG. 1, the image position calculation unit 56
Via a bus 58, the CPU 60 is connected to a correction control unit 62 corresponding to each color. The laser light source 14, a polygon motor 64 for rotating and driving the polygon mirror 28, a skew motor 66 for moving the cylinder mirror 34, and the like are connected to the correction control unit 62.

The image position calculation unit 56 calculates the image position for each color from the data read by the image position detection sensors 54S, 54C and 54E. The CPU 60 calculates a correction target value for each color based on the calculated image position, and outputs correction data to the correction control unit 62. And
The correction control unit 62 for each color implements the timing of laser lighting in the lead registration direction and the side registration direction, setting of the image clock frequency for magnification correction, setting of the control clock phase of the polygon motor 64, and setting of the number of steps of the skew motor 66. , So that the image of each color matches the target value.

FIG. 5 shows the structure of the light beam scanning device 12. The light beam scanning device 12 is a laser light source 1
4 and the laser beam 1 of the laser light source 14.
5, the collimator lens 16, the slit 18,
An expander lens 20 is provided. A laser beam 15 emitted from a laser light source 14 is collimated by a collimator lens 16, the beam width is shaped by a slit 18, transmitted through an expander lens 20, and folded in a predetermined direction by a folding mirror 22. . Then, the light passes through the cylinder lens 24 and is returned in a predetermined direction by the return mirror 26.
The light passes through 0 and is incident on the reflection surface of the polygon mirror 28.

The polygon mirror 28 is a polygon motor 6
4 is rotated at a high speed, and the laser beam 15 reflected by the reflection surface of the polygon mirror 28 is
0 and 32 pass through again and enter the cylinder mirror 34,
It is folded in a predetermined direction and reaches the photoconductor 36. As shown in FIG. 4, the cylinder mirror 34 has one end fixed and the other end movable so as to form an angle with respect to the main scanning direction based on the amount of skew deviation. It moves by the driving force of the skew motor 66.

Laser beam 1 applied to photoreceptor 36
Reference numeral 5 is modulated according to each color component of an image to be formed, and scans the main surface of the photoconductor 36 along a direction parallel to the axis of the photoconductor 36 with the rotation of the polygon mirror 28 (main scanning). Then, an electrostatic latent image is formed on the photoconductor 36. Note that the sub-scan is performed by rotating the photoconductor 36.

A mirror 38 is arranged at a position corresponding to an end on the scanning start side in the entire scanning range of the laser beam 15, and the laser beam 15 reflected by the mirror 38 is incident on the SOS sensor 40. I do. The SOS signal output from the SOS sensor 40 is used to determine the timing of starting writing an image in each main scan.

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

As shown in FIG. 5, a laser beam 15 emitted from a laser light source 14 is collimated by a collimator lens 16.
Then, the beam width is shaped by the slit 18, transmitted through the expander lens 20, and turned back in a predetermined direction by the turning mirror 22. Then, the light passes through the cylinder lens 24, is turned in a predetermined direction by the turning mirror 26, passes through the fθ lenses 32 and 30, and is incident on the reflection surface of the polygon mirror 28.

The polygon mirror 28 is a polygon motor 64
Is rotated at a high speed, and the laser beam 15 reflected by the reflection surface of the polygon mirror 28 is
0 and 32 pass through again and enter the cylinder mirror 34,
The photoreceptor 36, which is folded in a predetermined direction and charged by the charger 42, is scanned to form an electrostatic latent image. A toner is supplied to the portion where the electrostatic latent image has been formed by the developing device 44 to develop the electrostatic latent image and form a toner image on the photoconductor 36.

As shown in FIG. 2, the toner image formed on the photoreceptor 36 is transferred to a transfer belt 50 by a transfer charging roll 52. The toner remaining on the photoreceptor 36 is cleaned by the cleaning device 46. In this manner, the single-color images of yellow, magenta, cyan, and black developed on each photoconductor 36 are all superimposed and transferred onto the transfer belt 50 in one pass to form a multicolor toner image. . Thereafter, the multi-color image is collectively transferred to the paper 68 by the charging roll 55 to form a multicolor image on the paper 68.

The specific patterns of each color formed at intervals between sheets as shown in FIG. 6 are read by the image position detection sensors 54S, 54C and 54E, respectively, and output to the image position calculation unit 56. In the image position calculation unit 56, the image position detection sensors 54S, 54C, 54E
The image position for each color is calculated from the data read in step (1). Then, based on the image position calculated by the CPU 60, a target value for correction of each color is determined, and the correction control unit 62
Output the correction data to Then, the correction control unit 6 for each color
2 sets the timing of laser lighting in the lead registration direction and the side registration direction, sets the image clock frequency for magnification correction, sets the control clock phase of the polygon motor 64, and sets the number of steps of the skew motor 66.
Control is performed so that the image of each color matches the target value. .

Next, a method of calculating a target value will be described with reference to an example of correcting a skew deviation.

FIG. 8 shows the skew state of the image of each color before correction. The direction of arrow A in FIG.
Is the direction of travel. The cyan image is skewed by +0.3 mm with respect to the reference position of the image position detection sensor 54, and similarly, magenta is −0.1 mm and yellow is −0.1 mm.
There is a skew of 0.1 mm and black is skewed by +0.2 mm.

First, a description will be given of a case in which a correction target value is set to an intermediate value between a color having a maximum color shift and a color having a minimum color shift at an image position of each color, corresponding to the second aspect of the present invention. I do. In this case, the target value is an intermediate value between cyan having the largest color shift and magenta or yellow having the smallest color shift. Therefore, the target value is calculated by the following equation.

(0.3 + (− 0.1)) / 2 = 0.1 Thus, the target value is 0.1 mm, and as shown in FIG. 10, the correction amount of cyan is −0.2 mm, and the correction value of magenta is The correction amount is +0.2 mm, the correction amount for yellow is +0.2 mm,
The black correction amount is -0.1 mm.

Next, a case will be described in which the average value of the color misregistration at the image position of each color is used as the correction target value, corresponding to the third aspect of the present invention. In this case, the target value is calculated by the following equation.

(0.3 + (− 0.1) + (− 0.1) +
0.2) /4=0.075 Thus, the target value is 0.075 mm, and as shown in FIG. 11, the correction amount for cyan is -0.225 mm, the correction amount for magenta is +0.175 mm, and the correction amount for yellow is The amount is +
0.175mm, black correction amount is -0.125mm
Becomes

Next, a case will be described in which a color close to the above-mentioned intermediate value or average value is set as a correction target value, corresponding to the fourth aspect of the present invention.

Since the color having the skew amount closest to the intermediate value of 0.1 mm is black, the black skew amount is 0.2 mm.
Is the target value. As shown in FIG. 12, the correction amount for cyan is -0.1 mm, the correction amount for magenta is +0.3 mm, the correction amount for yellow is +0.3 mm, and the correction amount is 0 mm because black is the reference color. It is.

Since the color whose skew amount is closest to the average value of 0.075 mm is also black, the correction amount of each color is the same as the case where the color whose skew amount is closest to the intermediate value is the target value.

Next, a case will be described in which the reference position of the image position detecting sensor 54 is used as a correction target value, corresponding to the invention described in claim 5 of the present invention.

In this case, since the reference position of the image position detection sensor 54 is the target value, 0 mm is the target value for correction, and the correction amount of cyan is -0.3 m as shown in FIG.
The correction amount for m and magenta is +0.1 mm, the correction amount for yellow is +0.1 mm, and the correction amount for black is -0.2 mm.

Further, the correction may be performed by combining a coarse adjustment in which a large correction amount is performed at a time and a fine adjustment in which a small correction is performed. It is also possible to carry out in a combination such as targeting a specific reference color.

The target value thus calculated is output to each correction control unit 62, and each correction control unit 62 sets the number of steps of each skew motor 66 corresponding to the specified target value. Then, each cylinder mirror 34 is moved by the designated number of steps by the skew motor 66, and the color shift is corrected.

Since the color misregistration is corrected as described above,
In comparison with the method of fixing the reference color and matching the image writing position of another color to the image writing position of this reference color,
The image writing position of each color can be matched with a small correction amount, and the color shift can be corrected without deteriorating the performance of the light beam scanning device 12.

The above-described correction is not limited to the interval between sheets, and may be performed when the image forming apparatus 10 starts up or when the temperature rise in the image forming apparatus 10 reaches a certain value.

Although the skew correction has been described in the present embodiment, it goes without saying that the present correction algorithm can be applied to any of the correction of the lead registration deviation, the correction of the side registration deviation, the correction of the magnification deviation, and the correction of the bow deviation. No.

[0055]

As described above, according to the present invention,
The position of the toner image pattern formed on the transfer member is detected by an image position detection sensor to calculate the shift amount of each color,
The target value of the writing position of each color is set based on the shift amount, and the target value and the writing position of each color are adjusted so as to match each other. Compared with the method of matching the image writing positions, it is possible to match the image writing positions of the respective colors with a small amount of correction, without causing the light beam profile to be disturbed due to the correction or increasing the size of the correction mechanism. It has an excellent effect that color misregistration can be effectively corrected.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically illustrating an image forming apparatus.

FIG. 2 is a side view illustrating a schematic configuration of the image forming apparatus.

FIG. 3 is a perspective view illustrating a part of the image forming apparatus.

FIG. 4 is a perspective view for explaining movement of a cylinder mirror.

FIG. 5 is a perspective view illustrating a configuration of a light beam scanning device.

FIG. 6 is a plan view illustrating a toner image pattern for image position detection formed on a transfer belt.

FIG. 7 is an explanatory diagram for explaining types of misregistration.

FIG. 8 is a diagram showing an image of each color before skew shift correction.

FIG. 9 is a diagram showing an image of each color after skew shift correction in the related art.

FIG. 10 is an image diagram showing an example of an image of each color after skew shift correction according to the present invention.

FIG. 11 is an image diagram showing an example of an image of each color after skew shift correction according to the present invention.

FIG. 12 is an image diagram showing an example of an image of each color after skew shift correction according to the present invention.

FIG. 13 is an image diagram showing an example of an image of each color after skew shift correction according to the present invention.

FIG. 14 is a timing chart for explaining a lead registration deviation correction method.

FIG. 15 is a timing chart for explaining a side registration deviation correction method.

FIG. 16 is a timing chart for explaining a magnification shift correction method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Light beam scanning device 14 Laser light source 36 Photoconductor 50 Transfer belt 54 Image position detection sensor 56 Image position calculation part 60 CPU 62 Correction control part 64 Polygon mirror 66 Skew motor

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI G03G 21/14 G03G 21/00 372 H04N 1/60 H04N 1/40 D 1/46 1/46 Z

Claims (5)

[Claims] A latent image based on each color component of a color image is formed on a separate image carrier by a plurality of light beam scanning devices, and the formed latent image of each color component is developed with a color toner. A multicolor image forming apparatus that sequentially transfers each color toner image onto a transfer member and forms a color image, wherein a toner image pattern for detecting a positional shift is formed on the transfer member for each color component. A pattern forming unit, a shift amount detecting unit that detects a position of the toner image pattern formed on the transfer member by the pattern forming unit with an image position detecting sensor, and detects a shift amount of a writing position of each color component; Setting means for setting a target value of the writing position based on the shift amount of each color component detected by the shift amount detecting means; Multi-color image forming apparatus including an adjusting unit that adjusts to match the target value. 2. The image forming apparatus according to claim 1, wherein the target value is an intermediate value between a maximum value and a minimum value of the shift amount of each color component. 3. The image forming apparatus according to claim 1, wherein the target value is an average value of a shift amount of each of the color components. 4. The method according to claim 1, wherein the target value is an intermediate value between a maximum value and a minimum value of the shift amounts of the respective color components or a value of a shift amount of the color closest to an average value of the shift amounts of the respective color components. The image forming apparatus according to claim 1. 5. The image forming apparatus according to claim 1, wherein the target value is a reference position of the image position detection sensor.