JPH04131872A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain a clear image free from color slippage by providing a means for analyzing read test pattern image information, deciding the cause of the displacement of registration on each image carrier, and carrying out a specific registration correction processing. CONSTITUTION:When the prescribed test patterns developed on image carriers 1Y, 1M, 1C, and 1BK by a pattern forming means are transferred to a transfer belt 6a, an image reading means 10 reads each test pattern transferred to the transfer belt 6a. A correcting means PCON analyzes the read image information and decides the cause of the displacement of registration on each image carrier to perform a specific registration correction. Thus, since the correcting means corrects the position where image writing is started in the moving direction of each image carrier, the color slippage caused by the phase difference of each image carrier based on speed variation can be prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention involves arranging a plurality of image carriers in parallel and sequentially transferring images formed on each image carrier to a recording medium conveyed by a transfer belt. The present invention relates to an image forming apparatus that can form images in multiple colors.

[Prior Art] Conventionally, a plurality of image carriers are arranged side by side, and images formed on each image carrier are sequentially transferred to a recording medium conveyed by a transfer belt to form a multi-color image. A forming device has been put into practical use.

FIG. 10 is a cross-sectional configuration diagram illustrating the configuration of this type of image forming apparatus, which is composed of a printer section P, a league section R, etc. It is configured to be able to form an image. As shown in the figure, the image forming station is composed of four image forming stations, and corresponds to an image forming apparatus that sequentially overlays and transfers yellow, magenta, cyan, and black developers to obtain a full-color image.

In the league portion R, the reading section 14 moves in the direction of the arrow and reads the document 0 on the document table glass 13. The reading unit 14 is
Illumination lamp 1431 reflecting mirror 142, optical element 141. C
It is composed of a light receiving element 144 such as a CD, etc., and is driven by a timing belt 18 . The document is scanned along the document ○ via the pulley 17.

The yellow image forming station of the printer section P is provided with a photosensitive drum IY, a charger 2Y, a laser scanning optical system 3Y, a developing device 4Y, and a cleaner 5Y, and a yellow toner image is formed by a well-known electrophotographic process. The transfer material S is directed by the transfer belt 6a, conveyed in the direction of arrow A, transferred by the transfer charger 6bY, and then conveyed to the next magenta image forming station.

The magenta image forming station of the printer section P is provided with a photosensitive drum 1M, a charger 2M, a laser scanning optical system 3M, a developer 4M, and a cleaner 5M, and a magenta toner image is formed by a well-known electrophotographic process. Transfer material S
is directed to the transfer belt 6a and conveyed in the direction of arrow A,
After being transferred by the transfer charger 6bM, it is transported to the next cyan image forming station.

The cyan image forming station of the printer section P includes a photosensitive drum IC, a charger 2C, a laser scanning optical system 3C, and a developer 4.
C and a cleaner 5C are provided, and a cyan toner image is formed by a well-known electrophotographic process. The transfer material S is directed by the transfer belt 6a, conveyed in the direction of arrow A, transferred by the transfer charger 6bC, and then conveyed to the next black image forming station.

The black image forming station of the printer section P includes a photosensitive drum IBK, a charger 2BK, and a laser scanning optical system 38.
A cleaner 58K is provided in the developing device 48, and a black toner image is formed by a well-known electrophotographic process. The transfer material S is directed by the transfer belt 6a, conveyed in six directions of arrows, transferred by a transfer charger 6bBK, fixed by a fixing device 8, and discharged onto a tray 9.

In an image forming apparatus in which a plurality of image forming stations are arranged side by side in this way, since images are transferred sequentially onto the same surface of the same transfer material S, if the transferred image position at each image forming station deviates from the ideal position, a difference in color tone may occur. In other words, color shift occurs and image quality is degraded.

FIG. 11 is a schematic diagram showing the causes of color misregistration in the image forming apparatus shown in Section 1○, in which the direction of arrow 6 is the conveyance direction of the transfer material S, and the direction of arrow B is the direction of the photosensitive drums IY, IM, I.
C, is the laser scanning direction for IBK.

For example, as shown in figure (a), if a positional shift occurs in the direction of arrow A (indicated by a broken line in the figure) from the normal writing start position (indicated by a solid line in the figure), a top margin shift that causes a mismatch in the top margin occurs. arise.

In addition, as shown in Figure (b), when a positional shift occurs in the direction of arrow B (indicated by a broken line in the figure) from the normal writing start position (indicated by a solid line in the figure), the left margin misalignment causes a mismatch in the left margin. occurs.

Furthermore, as shown in Figure (C), if the writing direction is tilted from the normal writing direction (shown by the solid line in the figure) to the diagonal direction shown by the broken line in the figure,
Tilt deviation occurs.

Further, as shown in FIG. 2D, a magnification error may occur as shown by the broken line in the figure from the normal writing direction (indicated by the solid line in the figure).

To compensate for these deviations, the scanning timing of the light beam must be electrically adjusted for the top margin and left margin, and the mirror of the scanning optical system must be moved and adjusted for diagonal tilt deviations and magnification errors. Proposals have already been made to resolve this issue.

That is, a reflector 24 that reflects the laser beam L emitted by the laser scanning optical systems 3Y, 3M, 3C, and 38.
By moving Y, 24M, 24C, and 248K in the a direction by linear actuators 27Y, 27M, 27C, and 27BK, the magnification error is corrected, and the reflector 24
Two linear actuators 28Y, 28M, 28C located 5 places in front of Y, 24M, 24C, 24BK
, 28BK correspond to reflectors 24Y, 24M, 24
By shifting C, 248K in the b direction, the tilt deviation in the diagonal direction is corrected.

In addition, in the above four types of misalignment detection processing, the registration correction mark written on the transfer belt 6a is detected by the detector 1.
0, and the reflector 24 is shifted based on it.

In this way, even after correcting the image shift, color unevenness 9
In order to suppress color shift, four photosensitive drums IY and IM are required.
, IC, and IBK, and measures such as keeping the moving speed of the transfer material S constant are required.

For this reason, conventionally, photosensitive drums IY and 1M have been used.

An encoder is directly connected to the IC, IBK, and the transfer roller drive motor, and the transfer roller drive motor is controlled to maintain a constant rotation using PLL control, and the four photosensitive drums IY
, IM, 1C, and IBK are matched, and the moving speed of the transfer material is kept constant.

[Problem to be Solved by the Invention 1] However, the photosensitive drums 1Y, IM, and IC may be damaged due to eccentric components of the necessary reduction gear train from the drive motor or meshing errors of the teeth of the gear train.

A driven object such as an IBK causes speed fluctuations.

This speed fluctuation results in a speed fluctuation on the surface of the photosensitive drums IY, IM, and ICIBK, and causes a positional shift in the image writing position during image formation by the laser scanning optical systems 3Y, 3M, 3C, and 38K serving as exposure means. This positional shift occurs in different ways depending on the drive system of the four photosensitive drums 1Y, 1M, IC, and IBK.
1C.

With conventional methods, it is very difficult to adjust the rotational speeds of all IBKs to a constant speed, so it is difficult to prevent color shift due to the positional shift.

Further, as in monochromatic image forming apparatuses using one photosensitive drum, there is a problem in that the image expands and contracts due to similar positional deviations due to eccentricity and meshing errors of the gear train for driving the photosensitive drum.

However, speed fluctuations due to eccentricity and gear meshing errors, which are causes of image misalignment (color shift) and expansion/contraction, can be avoided by using high-precision gears that minimize eccentricity and meshing errors, or by removing the motor's wow-flare. Furthermore, it is possible to make the installation smaller by increasing the precision, but this is a disadvantage in terms of cost.

We also attempted to reduce the influence of the gear train by installing a rotary encoder on the drum shaft and performing PLL control. : Requires a control circuit, which not only increases costs, but also
It is difficult to suppress speed fluctuations of the photosensitive drum due to delays in the transmission system from the motor.

This invention was made in order to solve the above-mentioned problems, and it reads and analyzes the registration correction image formed by each image carrier, and identifies the cause of registration deviation of each image carrier. By doing so, it is possible to obtain an image forming apparatus which can perform predetermined registration deviation correction processing to accurately correct the registration of each image carrier, and can sequentially transfer clear images without color deviation to a recording medium in an overlapping manner. With the goal.

[Means for Solving the Problems] An image forming apparatus according to the present invention includes a pattern forming device that develops a predetermined test pattern formed on each image carrier and transfers it to a transfer belt; An image reading means that reads each test pattern transferred to the transfer belt, and a specific registration correction process by analyzing the image information read by this image reading means to determine the cause of registration deviation on each image carrier. The correction means is configured to correct the image writing start position with respect to the moving direction of each image carrier.

Further, the test pattern is composed of a line pattern in which lines arranged at equal pitches in the direction of rotation of the image carrier intersect with lines perpendicular to the lines.

Furthermore, the correction means is configured to correct the top margin of each image carrier.

Further, the correction means is configured to correct the left margin of each image carrier.

Further, the correction means is configured to correct the tilt error of each image carrier.

Further, the correction means is configured to correct the magnification error of each image carrier.

[Effect]

In this invention, when the predetermined test pattern developed on each image carrier by the pattern forming means is transferred to the transfer belt, the image reading means reads each test pattern transferred to the transfer belt, and the correction means Analyzes the read image information, determines the causes of misregistration on each image carrier, executes specific registration correction processing, and responds to the causes of misregistration that occur on each image carrier. In particular, the correction means corrects the image writing start position with respect to the moving direction of each image carrier, and corrects the image writing start position with respect to the moving direction of each image carrier, and corrects the image writing start position due to the phase difference shift of each image carrier due to speed fluctuation. This makes it possible to prevent color shift.

In addition, the test pattern is composed of a line pattern in which lines arranged at equal pitches in the rotational direction of the image carrier intersect with lines perpendicular to each other. This makes it possible to understand the factors.

Furthermore, the correcting means corrects the top margin of each image carrier, making it possible to prevent color shift caused by deviation of the top margin of each image carrier.

Further, the correction means corrects the left margin of each image carrier, thereby making it possible to prevent color shift caused by left margin deviation of each image carrier.

Further, the correction means corrects the tilt error of each image carrier, and makes it possible to prevent color shift caused by the tilt error of each image carrier.

Further, the correction means corrects the magnification error of each image carrier, thereby making it possible to prevent color shift caused by the magnification error of each image carrier.

[Embodiment] FIG. 1 is a block diagram showing the main structure of an image forming apparatus according to an embodiment of the present invention, and the same parts as in FIG. 9 are given the same reference numerals.

In the figure, PCON is the printer controller and the 9th
CP for comprehensively controlling the printer section P shown in the figure
U100. RAM101. It is equipped with a ROM 102 and the like.

In the figure, stepping motors (STM) 22Y, 22M, 22C, and 228 connect the photosensitive drum 1Y via a reduction gear train 20 as described later.

It is configured to transmit rotational force to 1M, 1C, and IBK, and this reduction gear train 2o becomes a factor of speed fluctuation, causing the above-mentioned positional deviation. 33Y, 33M, 33C, 3
38 is a stepping motor drive circuit which drives the stepping motors 22Y, 22M, 22C, 228 based on the drive pulse train output from the printer controller PCON.
Drive K.

103 is a laser driver, and the laser scanning optical system 3Y, 3
Controls the driving of M, 3C, and 3BK semiconductor lasers.

In the image forming apparatus configured as described above, each image carrier (in this embodiment, the photosensitive drums 1Y, IM, IC, IBK) is
) The predetermined test pattern developed on the transfer belt 6
When the test patterns are transferred to the transfer belt 6a, the image reading means (detector 10 in this embodiment) reads each test pattern transferred to the transfer belt 6a, analyzes the read image information, and uses the pattern forming means to print each test pattern on each image carrier. When the predetermined test patterns developed thereon are transferred to the transfer belt 6a, the image reading means reads each test pattern transferred to the transfer belt, and the correction means (in this embodiment, the printer controller PCON) reads the test patterns. The image information is analyzed to determine the causes of misregistration on each image carrier, and a specific registration correction process is executed. Particularly, the correction means is characterized in that it executes a registration correction process.The correction means corrects the image writing start position with respect to the moving direction of each image carrier, and corrects color shift caused by phase difference shift of each image carrier due to speed fluctuation. This makes it possible to prevent

In addition, the test pattern is composed of a line pattern (see Fig. 5) in which lines arranged at equal pitches in the rotational direction of the image carrier intersect with lines perpendicular to each other, and each image carrier is This makes it possible to understand the causes of misregistration that occur.

Further, the correction means corrects the top margin of each image carrier (in this embodiment, corrects the laser irradiation timing for the image carrier), and prevents color shift caused by the top margin deviation of each image carrier. possible.

Further, the correction means corrects the left margin of each image carrier (in this embodiment, corrects the laser irradiation timing for the image carrier) to prevent color shift caused by left margin deviation of each image carrier. is possible.

Furthermore, the correction means corrects the tilt error of each image carrier (laser scanning optical system 3Y,
3M, 3C, and 3BK), thereby making it possible to prevent color shift caused by tilt errors of each image carrier.

Further, the correction means corrects the magnification error of each image carrier (laser scanning optical system 3Y,
3M, 3C, and 3BK and the respective image carriers), thereby making it possible to prevent color shift caused by magnification errors of the respective image carriers.

Hereinafter, registration correction processing caused by top margin deviation, left margin deviation, tilt deviation, 9 magnification deviation, etc. will be described with reference to FIGS. 2 and 3.

Figure 2 shows the laser scanning optical systems 3Y and 3M shown in Figure 1.
, 3C, and 3BK.

As can be seen from this figure, the detector 1o has detectors 10a and 10b arranged to face each other on the upstream and downstream sides in the laser scanning direction, and the detector 10a has image sensors 14 and 15°. Lamp 16.17. It is composed of condensing lenses 18, 19, etc., and is arranged so as to be able to read the test pattern image on the transfer belt 6a.

A blade 7 collects the developer transferred to the transfer belt 6a.

In this embodiment, the Y image pattern formed at the first image forming station is used as the reference station, and the M image pattern, C image pattern, and BK image pattern from the second image forming station onward are applied to the Y image pattern. Since the configuration is such that the shift is detected and corrected, the first image forming station is optically adjusted at the factory by non-rotation means, and the inclination of the scanning line with respect to the drum, scanning distance, etc. Adjustment has been completed. Therefore, if the image is matched with the image formed at the first image forming station, an image without distortion will be obtained.

Figure 3 shows the laser scanning optical systems 3Y and 3M shown in Section 2.
, 3C, and 38. FIG.

In the figure, reference numeral 20 denotes an fθ lens, which images a laser beam L emitted from a laser light source 22 and deflected by a polygon mirror 21 rotating at a constant speed onto, for example, a photosensitive drum 1C at a constant speed. 23 is an optical box, and the above-mentioned 20 to 22 are housed integrally.

Note that the laser beam L emitted from the laser light source 22 is emitted from the opening 23a via the fθ lens 20. 24a is a first reflecting mirror;
A second reflecting mirror 24b provided substantially perpendicularly to a.
Laser scanning optical systems 3Y, 3M, 3C, and 3BK are configured by these. Note that the laser beam emitted from the laser light source 22 is reflected by the first reflecting mirror 24a and the second reflecting mirror 2.
4b, for example, the photosensitive drums IY, IM.

It is configured to form an image on IC and IBK.

27 is a linear step actuator (actuator) composed of, for example, a stepping motor, and the reflector 24 is integrally supported with a first reflecting mirror 24a and a second reflecting mirror 24b according to the step amount output from the printer controller PCON. Move up and down in steps in direction a. Reference numerals 28 and 29 denote linear step actuators (actuators) composed of, for example, stepping motors, which move the first reflecting mirror 24a and the second reflecting mirror 24a according to the step amount output from the printer controller PCON.
The reflectors 24, on which the reflecting mirrors 24b are integrally supported, are horizontally moved independently in the b direction in the figure.

Based on the pattern reading results, Fig. 11(C), (
When the printer controller PCON recognizes that the tilt shift 1 magnification shift shown in d) has occurred, the amount of shift is calculated and the actuator 28.
By moving the reflector 24 in the direction indicated by the arrow 29, it is possible to correct the magnification deviation by moving the reflector 24 in the direction indicated by the arrow a by the actuator 27. .

In addition, in this embodiment, each actuator 27 to 2 corrects the tilt shift 7 magnification shift only for the reflector 24 of the second to fourth image forming stations other than the reference station.
9 are arranged as shown.

Furthermore, the top margin and left margin shown in FIGS. 11(a) and 11(b) may be corrected so as to match the scanning timing of the laser beam with the image of the reference station as described above. That is, for the top margin, the image writing timing of each image forming station is corrected, and for the left margin, the scanning start timing for one scanning line at each image forming station is corrected.

Hereinafter, a description will be given of the individual identification process of the cause of registration deviation by reading the image pattern by the detector 10.

First, the top margin shift is line a shown in the 5th section,
It is sufficient to detect the deviation of each color in the sub-scanning direction, and for the left margin deviation, it is sufficient to detect whether the intervals in the main scanning direction between line b1 and line b2 match for each color (also, for the tilt deviation What is necessary is to detect the inclination of line a1 with respect to the scanning line.

Regarding the phase shift, it is sufficient to read the lines a1 to a and detect a shift amount ΔI2 (described later) that indicates how much and in which direction each line is shifted from the normal position.

Hereinafter, the causes of the phase shift and the correction process thereof will be explained in detail.

FIG. 4 is a block diagram showing the drive mechanism of the stepping motor shown in FIG. 1, and the same components as in FIG. 1 are given the same reference numerals. For example, the case of magenta station is shown. Note that the other image forming stations have similar configurations, so the configuration and operation of the magenta station will be explained.

1M is a photosensitive drum serving as an image carrier, and 50 is a reduction gear train that reduces the rotation speed of the stepping motor 22M and transmits the rotation to the photosensitive drum FM. And these gears 50a to 50
Number of teeth in d: 7. The ratio of a, Zb + ZC+Zd is an integer ratio of 8:4:2:l, and the gear 50a at the final stage is directly connected to the photosensitive drum 1M by the photosensitive drum shaft, and the gear 50a is When the photosensitive drum 1M rotates, the photosensitive drum 1M also rotates once. This is configured so that each gear rotates an integral number of times during one rotation of the photosensitive drum 1M.
In this embodiment, the gear 50b rotates 2 times, and the gear 50c rotates 40 times.
The gear 50d rotates eight times.

33M is a stepping motor drive circuit that outputs excitation pulse signals to the stepping motors 2 and 1M based on the output of the stepping motor control circuit 32. Reference numeral 34 denotes a photosensitive drum home position signal generating section, which connects a disc 52 with a slit fixed to the drum shaft 1a to a photointerrupter 53.
A home position signal obtained by detection is output to the stepping motor control circuit 32.

With this configuration, when a pulse train of a constant interval (constant frequency) is applied to the stepping motor 21M and the motor is driven at a constant speed, the rotational speed variation ΔV of the drum shaft 1a of the photosensitive drum 1M is caused by the eccentricity of the gears 50a to 50d. Depending on the components, etc., it changes periodically as shown in the following equation (1).

Δv :3+C03(AJ +a2CO3((ωt/
2)+φI)+a, cos ((ωt/ 4)
+φ2 )+a4cos ((ωt/8)+φ3)
+F D) ・・・・・・(
1) Here, ω is the rotational angular velocity of the photosensitive drum.

Furthermore, F (t) is the rotational speed fluctuation component due to the gear meshing error, and if the number of teeth in the gear train is an integer ratio, the same teeth will always mesh with each other, so one rotation of the photosensitive drum is equal to 1 rotation.
It becomes a periodic function with a period. In other words, ΔV is a periodic function whose period is one rotation of the photosensitive drum. If the product R*△■ of the speed fluctuation △■ and the radius R of the photosensitive drum is integrated over time, this becomes the amount of positional deviation Δ℃ from the normal position of the photosensitive drum surface when rotating at a constant speed. .

When the stepping motor 22M is driven at a constant speed with this configuration, the characteristic of the positional deviation amount Δi as shown in FIG. 3 is obtained.

FIG. 5 is a plan view of a main part showing an example of a test pattern image in an image forming apparatus according to the present invention, in which straight lines a, -an extending in the main scanning direction are arranged at predetermined pitch intervals in the sub-scanning direction on an A3 size recording paper, for example. In this pattern, n lines are lined up, and a straight line bb2 extending in the sub-scanning direction orthogonally intersects the straight lines a1 to a.

For example, in the case of a printer with a process speed of 100 mm/sec and a scanner that rotates a 10-plane polygon mirror at 1200 rpm, it is possible to write lines at 0.05 mm intervals in the sub-scanning direction, and a laser beam is emitted every two rotations of the polygon mirror. If controlled so as to do so, it is possible to output a test pattern with a pitch of 1 mm in the sub-scanning direction as shown in FIG.

Such a test pattern image is generated on the photosensitive drums 1Y, IM, IC, and IB of each image forming station after the adjustment of the top margin of each image forming station is completed.
K, and is transferred onto a transfer belt 6a that is conveyed at a constant speed. The pattern images of each color transferred onto the transfer belt 6a in this manner are sequentially read by a detector 10 (disposed at a paper transport position relative to the black image forming station).

The process speed of the transfer belt 6a is 100 mm/sec.
Therefore, if there is no displacement of the line image, a line image is input to the detector 10 every 0.05 seconds.

Therefore, the image input to the detector 1o is 0.05
By calculating the differential time difference Δt, which indicates how much time varies with respect to each sec, correspondence can be established with the positional shift amount Δa of the image of each line of each color.

The registration correction process will be described below with reference to FIGS. 6 to 9.

Referring to FIG. 6, the operation of generating a driving pulse train for canceling image position deviation will be described.

FIG. 6 is a characteristic diagram showing the relative difference time between the pattern detection timing and the ideal detection timing by the detector 10 shown in FIG. 1, where the horizontal axis shows the line number of the test pattern line image and the vertical axis The relative difference time Δt is shown.

As can be seen from this figure, when the number of teeth in the gear train is an integer ratio, the same teeth always mesh with each other, so the relative difference time Δt becomes a periodic function with one rotation of the photosensitive drum as one period. Using the Fourier series, the following cylinder equations (2) to (5th
) can be approximated by the formula.

at(θ) =ao+ at CO8θ+a2 cos
2θ+...+an cosnθ+bo+ b+ CO
3θ+b2CO82θ+-+ bn cosnθ-
12) at(θ) = ao+C+ CO3(θ+δ1)
+C2C03(2θ+62) +cn cos (nθ+δn) (3), and when each constant a O and a ra 1bm1cm are calculated by the least squares method as the time shift Δtk of the k-th line pattern, the above (2) ) and equation (3), the constant 00 is as follows: Cm= am +bffi"tan 5m =-atw/b, ・(
It becomes s+.

In addition, in equation (3), the governing term with period 2π is CI
Since CO3(θ+δ1), tanδ, :a +
/ b + , and the phase angle δ1 can be calculated.

As a result, the phase angle δIY+ of each image forming station is
δLM, δIc, 61K are determined.

FIG. 7 is a characteristic diagram in which fluctuations in each relative time difference Δt of the photosensitive drum shown in FIG. 1 are approximated by a Fourier series, and the vertical axis indicates the difference time Δt.

In the figure, Δjy indicates the differential time variation of the Y image produced by the first image forming station, and at2 indicates the differential time variation of the M image produced by the second image forming station.

As can be seen from this figure, in order to eliminate the color shift between the two, the phase angle δ17. δ1. It is sufficient to make the images match. Note that each phase angle δ1 is the photosensitive drum IY, IM of each image forming station.

The angle from the reference point of IC and IBK is converted into the amount of driving pulses of the stepping motor and stored. Then, as shown in FIG. 4, a slit disk 52 is fixed to the drum shaft 1a, and its home position is detected by a photointerrupter 53, thereby determining the phase angle δ using this home position as a reference point.

FIG. 8 is a flowchart showing an example of the registration correction processing procedure of each image forming station in the image forming apparatus according to the present invention.

Note that (1) to (4) indicate each step.

First, the test pattern image read from the ROM 102 of the printer controller PCON is output onto the transfer belt 6a (1).Then, the test pattern image transferred to the transfer belt 6a is read by the detector 1o (2), and the above Top margin deviation amount, left margin deviation amount.

Tilt deviation amount 9 Calculate the magnification deviation amount and the positional deviation amount △ji of the test pattern output image (actually, the relative difference time △t of the test pattern image input to the detector 10) (3
) Next, the top margin shift, left margin shift, tilt shift, and single magnification shift are corrected (4), and the phase shift is corrected, and the process ends.

Regarding the phase shift, in each station after the second image forming station, the stepping motors 22M, 22C, and 228 are driven at the first image (after the home position signal of the image forming station is input, and the stepper motors 22M, 22C, and 228 are When starting, calculate whether the image writing angle at each station matches δIM, δIc, δl, and set the respective timings as Tsii, Ts., Tsa,
By starting the driving of the stepping motors 22M, 22C, and 22BK, it becomes possible to match the phase angle of each photosensitive drum 1M, IC, and IBK with the phase angle δ1Y of the photosensitive drum 1Y. Therefore, even if the stepping motors 22Y, 22M, 22C, and 22BK of each image forming station are driven at a constant drive frequency, the photosensitive drums 1Y, IM, IC,
The IBK image position shift changes approximately in phase,
Clear image formation without color shift becomes possible.

Note that the above correction process can be executed at any timing; for example, it may be configured to start when a correction start button (not shown) is pressed, or it may be executed after jam processing or after turning on the power switch. It may be configured to execute.

FIG. 9 is a flowchart showing an example of a phase shift correction processing procedure in the copying apparatus according to the present invention. In addition,(
1) to (5) indicate each step.

First, when an image forming star signal is input (1), the drum drive motor of each image forming station starts driving, and the drum rotates (2). Next, when the home position signal of the drum of each of the second to fourth image forming stations is input, the drum drive motors (stepping motors 22M, 22C, 228K) are stopped (3). The drum motor (stepping motor 22Y) continues to rotate, and when the input home position signal for the first image forming station becomes H level (4), an image is written on the photosensitive drum of the first image forming station. Paper feeding control is started at the timing when the start angle becomes 61Y, and at the second image forming station, the drum motor for the second image forming station is started at the timing Tsv when the image writing start angle on the photosensitive drum becomes δ. (Stepping motor 22M)
At the third image forming station, at the timing T, when the image writing start angle on the photosensitive drum becomes δIc. At this time, the drum motor (stepping motor 22C) for the third image forming station starts to be driven, and at the fourth image forming station,
The stepping motors 22Y and 22M start driving the drum motor (stepping motor 22BK) for the fourth image forming station at timing Tsa when the image writing start angle on the photosensitive drum reaches 61B.

Execute phase difference drive processing for 22C and 22BK (5),
Finish the process.

In addition, the above timing T 1llj + T 3°, Ts
The timing of ll is determined by counting a predetermined clock signal after the home position signal of the first image forming station is input.

[Effect of the Invention 1] As explained above, the present invention includes a pattern forming means for developing a predetermined test pattern formed on each image carrier and transferring it to the transfer belt, and a pattern forming means for developing a predetermined test pattern formed on each image carrier and transferring it to the transfer belt. an image reading means that reads each test pattern, and a correction that analyzes the image information read by the image reading means, determines the cause of registration deviation on each image carrier, and executes a specific registration correction process. Since the correcting means is configured to correct the image writing start position with respect to the moving direction of each image carrier, the cause of image position deviation of each image carrier can be identified simply by reading a predetermined test pattern. However, the registration correction process required for each image carrier can be executed with high precision.In particular, since the correction means corrects the image writing start position in the moving direction of each image carrier, It is possible to match the phases of fluctuations in positional displacement caused by variations in the rotational speed of the body, etc., and it is possible to suppress color shift as much as possible.

In addition, since the test pattern is composed of a line pattern in which lines arranged at equal pitches in the rotation direction of the image carrier intersect with lines perpendicular to each other, each image carrier can be read and processed just once. Possible causes of misalignment can be identified.

Furthermore, since the correction means is configured to correct the top margin of each image carrier, it is possible to make all the top margins of each image carrier coincide.

Further, since the correction means is configured to correct the left margin of each image carrier, it is possible to make all the left margins of each image carrier coincide.

Further, since the correcting means is configured to correct the tilt error of each image carrier, it is possible to match all the tilt errors of the image carriers.

Further, since the correction means is configured to correct the magnification error of each image carrier, it is possible to match all the magnification errors of each image carrier.

Therefore, registration deviations that may occur on each image carrier can be detected with high accuracy through test pattern reading processing, and the registration of each image carrier can be accurately corrected (corrected), and color images on each image carrier can be sequentially corrected with high accuracy. This makes it possible to transfer images overlappingly, and provides effects such as the ability to always provide four-color images that are synchronized and have no color shift and are of high quality.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of main parts of an image forming apparatus showing an embodiment of the present invention, FIG. 2 is an external perspective view showing the arrangement of the laser scanning optical system shown in FIG. 1, and FIG. The diagram is
FIG. 2 is a perspective view showing the main structure of the laser scanning optical system, FIG. 4 is a configuration diagram showing the driving mechanism of the stepping motor shown in FIG. 1, and FIG. 5 is an image forming system according to the present invention. FIG. 6 is a plan view of a main part showing an example of a test pattern image in the device. FIG. 6 is a characteristic diagram showing the relative difference time between the pattern detection timing and the ideal detection timing by the detector shown in FIG. 1. FIG. FIG. 1 is a variation characteristic diagram of each relative time difference of the photosensitive drum; FIG. 8 is a flowchart showing an example of the registration correction processing procedure of each image forming station in the image forming apparatus according to the present invention;
Section 9 is a flowchart showing an example of a phase shift correction processing procedure in a copying apparatus according to the present invention, FIG.
The figure is a schematic diagram showing factors of color shift in the image forming apparatus shown in FIG. 10. In the figure, IY, IM, 1C, and IBK are photosensitive drums, 6a transfer belt, 22Y, 22M, and 22C. 22BK is stepping motor, 100 is CPU, 10
1 is a RAM, and 102 is a ROM. Figure 3B (a) (b) (c) (d)

Claims (6)

[Claims] (1) Multiple image carriers driven by stepping motors are arranged side by side, and images formed on each image carrier are sequentially transferred to a recording medium conveyed by a transfer belt to form a multi-color image. An image forming apparatus includes a pattern forming means for developing a predetermined test pattern formed on each image carrier and transferring it to the transfer belt, and a pattern forming means for developing a predetermined test pattern formed on each image carrier and transferring the test pattern to the transfer belt. comprising an image reading means for reading, and a correction means for analyzing the image information read by the image reading means to determine the cause of registration deviation on each image carrier and execute a specific registration correction process, An image forming apparatus characterized in that the correction means corrects an image writing start position with respect to a moving direction of each image carrier. (2) The image forming apparatus according to claim (1), wherein the test pattern is composed of a line pattern in which lines orthogonal to lines arranged at equal pitches in the rotational direction of the image carrier intersect with each other. (3) The image forming apparatus according to claim 1, wherein the correction means corrects the top margin of each image carrier. (4) The image forming apparatus according to claim (1), wherein the correction means corrects the left margin of each image carrier. (5) The image forming apparatus according to claim (1), wherein the correction means corrects a tilt error of each image carrier. (6) The image forming apparatus according to claim (1), wherein the correction means corrects a magnification error of each image carrier.