JP2000284562A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device that toner is prevented from being uselessly consumed or the detecting time from being prolonged while maintaining accuracy of resist correction. SOLUTION: Relating to this image forming device, the dispersion quantity σ1 of positional information is obtained by repeating first resist pattern without receiving effect by the irregular travel of a transfer belt and the irregular rotation of a photoreceptor drum plural times (S1 to S3). Next, the dispersion quantity σ2 and σ3 are obtained by respectively repeating plural times of the second resist pattern without receiving the effect by the irregular rotation, and the third resist pattern without receiving the effect by the irregular travel (S4 to S9). When (σ2-σ1) and (σ3-σ1) are respectively beyond the prescribed value T1 and T2, a flag '1' is set for forming the first resist pattern in calculating misalignment (S12), and when they are respectively below T1 and T2, the flag '4' is set for forming the resist pattern to be affected by the irregular travel or the irregular rotation (S16).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming a color image by superposing a plurality of color images,
In particular, the present invention relates to an improvement in a technique for correcting a positional shift of an image of each color.

[0002]

2. Description of the Related Art In an image forming apparatus for a color image, generally, an image to be formed is separated into cyan (C), magenta (M), yellow (Y), and black (K) colors, and a toner is formed for each color. After forming the image, a color image is formed by multiple transfer of these. Therefore, if a shift in the writing position occurs between images formed in each color, color shift occurs and the image quality extremely deteriorates.

In particular, image forming units for each color are arranged in line along the transfer surface of the transfer belt, and the toner image formed on the peripheral surface of the photosensitive drum in each image forming unit is transferred by the transfer belt. In a so-called tandem type image forming apparatus in which a color image is obtained by sequentially superimposing and transferring on a transfer material, color misregistration is likely to occur. In order to prevent the occurrence of the color misregistration, a tandem type image forming apparatus has been conventionally used.
A reference pattern (resist pattern) is formed on a transfer belt by each image forming unit, and is detected by an optical sensor to acquire position information. A relative displacement amount is calculated from the acquired position information. In other words, so-called registration correction for correcting the image forming position is performed. In such registration correction, it is necessary to determine the amount of displacement of the registration pattern with high accuracy. However, in practice, the registration pattern formation position is not correct due to uneven running of the transfer belt or uneven rotation of the photosensitive drum. In some cases, the position information becomes stable, and the position information fluctuates, so that accurate position information that should be originally obtained cannot be obtained.

In order to perform accurate registration correction,
It is desirable not to cause such running unevenness and rotation unevenness at all, but due to problems in machining accuracy and cost and the members that drive them for rotation are worn over time, rotation unevenness is inevitably generated. Would. Therefore, conventionally, the influence of a factor (hereinafter, simply referred to as a “variation factor”) that fluctuates the positional information of each resist pattern in the registration correction, such as unevenness of the transfer belt or rotation of the photosensitive drum, is removed as much as possible. The resist pattern is formed by setting conditions such that a resist pattern can be formed.

[0005] For example, in order to eliminate the influence of unevenness of the transfer belt, the resist patterns of the respective colors are simultaneously transferred onto the transfer belt (hereinafter, the resist patterns of the respective colors are simultaneously transferred onto the transfer belt). Is referred to as “simultaneous transfer”). By performing the simultaneous transfer in this manner, even if the transfer position of the resist pattern of each color fluctuates due to running unevenness, the amount of the fluctuation occurs by the same amount for the corresponding resist pattern of each color. When the amount of positional deviation is calculated from the difference between the formation positions of the colors, the amount of variation due to the unevenness in both travels is subtracted, and the amount of positional deviation of each color can be accurately obtained.

In the case where rotation unevenness occurs on the photosensitive drum, if the occurrence is caused by eccentricity of the photosensitive drum, a resist pattern of each color is constituted by repeating a plurality of unit patterns. The formation range in the sub-scanning direction is set to be equal to the circumferential length of the photosensitive drum (this length is equivalent to one cycle of rotation unevenness caused by eccentricity). The position of each unit pattern detected with reference to a certain point fluctuates under the influence of rotation unevenness. However, the position information of each unit pattern is obtained for a range corresponding to exactly one cycle, and the average of them is obtained. In this case, the sum of the positive fluctuations and the sum of the negative fluctuations due to the rotation unevenness are exactly canceled out, and eventually, it is possible to obtain position information that is not significantly affected by the rotation unevenness.

[0007]

However, if the resist pattern is formed under the condition that is not affected by fluctuation factors as in the above-mentioned prior art, the displacement can be calculated with high accuracy. In any condition,
For example, even if the traveling unevenness of the transfer belt does not significantly affect the position information, the resist pattern is always formed under the above conditions.

However, if simultaneous transfer is performed to avoid the influence of the transfer belt running unevenness, the formation range of the resist pattern of all colors is at least the transfer position of the photosensitive drum on the most upstream side and the photosensitive drum on the most downstream side. , And it takes more time to detect the resist pattern of all colors, and the time required for one registration correction becomes longer. In particular, when registration correction is performed between successive copies, it is desired that the copy interruption time be short, so that even a slight delay may cause user discomfort.

On the other hand, in order to avoid the influence of the rotation unevenness of the photosensitive drum, the toner consumption is increased by forming a large number of unit patterns corresponding to the circumference of the photosensitive drum for each color. . Therefore,
In the state of the image forming apparatus, especially in the initial use period after adjustment at the time of shipment, the ideal resist pattern is always formed even though the rotation unevenness and the running unevenness are not so large. In addition, the registration correction time is unnecessarily prolonged, or the consumption of toner is increased, resulting in an undesirable situation for the user.

The present invention has been made in view of the above problems, and an image forming apparatus capable of eliminating unnecessary use of toner and prolonging the detection time while maintaining the accuracy of registration correction. The purpose is to provide.

[0011]

In order to achieve the above object, the present invention comprises a plurality of image carriers, and a pattern of each color written on each image carrier by an image writing means is transferred onto a predetermined transfer member. An image forming apparatus for forming a reference pattern by transferring the image data to the image carrier on the basis of position information obtained by detecting the reference pattern. A first control means for controlling each of the image writing means so as to form a first temporary reference pattern on the transfer body, and a second provisional reference pattern on the transfer body under the second condition. A second control means for controlling each of the image writing means, and a selection means for selecting any one of the first control means and the second control means, and is formed by the selected control means. Tentative reference pattern And turns, characterized in that the correction of the image writing position based on the position information.

The first condition is a condition in which the obtained position information is not affected by a specific fluctuation factor, and the second condition is all or one of the first conditions. The condition is that no section is provided.
Further, the selecting means sequentially controls the image writing means by the first and second control means to form first and second temporary reference patterns on the transfer body, respectively. And a variation amount acquiring unit for determining a variation amount of position information for each color in each pattern from the detection result of the second temporary reference pattern, and a variation amount acquisition unit for determining the variation amount of the position information of the corresponding color in the first and second patterns. The first or second control means is selected based on whether or not the difference in the amount of variation is equal to or greater than a predetermined value.

Further, the transfer member is a transfer belt, the specific fluctuation factor is uneven running of the transfer belt, and the first condition is a condition for transferring a pattern of each color to the transfer belt at the same timing. Wherein the second condition is a condition for transferring the pattern of each color to the transfer belt at a different timing. Also,
Each color pattern formed on each of the image carriers is composed of one or more unit patterns. The first condition is that the unit patterns are written at a fixed writing timing, and the unit pattern is written on the transfer body in the sub-scanning direction. Is a condition in which a plurality of transfer regions are formed such that the length of the transfer member is substantially equal to an integral multiple of the traveling distance during the passage of the generation cycle of the specific fluctuation factor. Is
The formation range in the sub-scanning direction of at least one unit pattern at a fixed writing timing is not equal to an integral multiple of the distance traveled by the transfer body during the passage of the generation cycle of the specific variation factor, and The condition is such that the formation range is shorter than the formation range under the first condition.

Further, each of the image carriers is a rotating body,
The specific fluctuation factor is uneven rotation of each image carrier. Further, the rotation unevenness is caused by the eccentricity of each image carrier, and the cycle of occurrence of the rotation unevenness is a rotation cycle of the image carrier. Further, the specific variation factor is a combination of a plurality of unit variation factors, and an occurrence cycle of the specific variation factor is a least common multiple of an occurrence cycle of each unit variation factor. .

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image forming apparatus according to the present invention will be described below using a tandem type digital color copying machine (hereinafter simply referred to as "copying machine") as an example. (1) Overall Configuration of Copying Machine FIG. 1 is a diagram showing an overall configuration of a copying machine according to the present embodiment. As shown in FIG. 1, the copying machine includes an image reader section 3 for reading a document image roughly divided, and a printer section 20 for printing the image read by the image reader section 3 on a recording sheet and reproducing it. Is done.

The image reader section 3 is a publicly known one that reads an original on a platen glass by a CCD color image sensor and obtains R, G, and B multi-valued electrical signals. The obtained electric signal is further converted into cyan (C), magenta (M), yellow (Y), and black (K) gradation data by the control unit 30 and then subjected to color correction to improve reproducibility. And so on.

The printer section 20 includes a printer head unit 40, an image forming system 60, and a transport system 70. A laser diode (not shown) for each color in the printer head unit 40 based on a signal output from the control unit 30
Is driven to emit a laser beam, and performs exposure scanning on the rotationally driven photosensitive drums 1C to 1K in the image forming system 60.

The photosensitive drums 1C to 1K are uniformly charged by the chargers 2C to 2K before receiving the exposure, and the exposure forms an electrostatic latent image. Each of the electrostatic latent images is developed by receiving each of the toners of cyan, magenta, yellow, and black by developing units 4C to 4K, and the developed toner images are transferred to transfer brushes 5C to 5C.
Receiving the transfer electric field from K, the transfer is performed in such a manner that the transfer electric field is superimposed on the transfer material conveyed by the transfer belt 10 which is driven to rotate by the drive roller 11.

The transfer material onto which the toner image has been transferred is separated from the transfer belt 10 and fixed by a fixing device 18. Thereafter, the transfer material is discharged onto the discharge tray 19. Here, the transfer belt 10 is made of a transparent material such as polyethylene terephthalate. An optical sensor unit 25 is provided at the most downstream position of the transport system 70 in the transfer material transport direction, and registration correction is performed using a detection value of the optical sensor unit 25. A transmission type optical sensor is used for the optical sensor unit 25, and an LED is used for a light emitting unit and a photodiode is used for a light receiving unit. When the transfer belt 10 is opaque, a reflection type optical sensor is used. (2) Configuration of Control Unit 30 Next, the configuration of the control unit 30 will be described with reference to FIG.

As shown in FIG. 1, the control unit 30 includes a CPU
31, an image processing unit 32, an image memory 33, a displacement correcting unit 34, a laser diode driving unit 35, a RAM 36, a ROM 37, and the like. Image processing unit 32
Converts the R, G, and B electrical signals obtained by scanning the original to generate image data composed of multi-level digital signals, and further performs shading correction and other corrections. Image data of the reproduced colors Y and K is generated and output to the image memory 33, and the image data is stored for each color.

The RAM 36 stores data σ1 of the variation amount calculated in a resist pattern optimizing process described later.
To σ3 and the pattern formation flag. The ROM 37 stores a control program for a scanning operation in the image reader unit 3 and an image forming operation in the printer unit 20, printing data for a resist pattern described later, a control program for executing a resist pattern optimizing process, and a resist pattern A program for calculating the amount of displacement and correcting the address of an image is stored.

The CPU 31 controls the ON / OFF operation of the optical sensor unit 25, samples the detection signal of the resist pattern of each color from the optical sensor unit 25 at regular time intervals, and performs A / D conversion. The sampling value is temporarily stored in the RAM 36, the formation position (position information) of the resist pattern is calculated from the waveform formed by the sampled signal, and the position shift amount of the resist pattern of each color is calculated based on the position information. This is sent to the displacement correcting unit 34.

In accordance with an instruction from the CPU 31, the displacement correcting section 34 changes the storage position (address) of each pixel of the image data of each color stored in the image memory 33 by an amount corresponding to the displacement amount. Generate an image (resist correction). The laser diode driving section 35 drives a laser diode based on the corrected image data to form a color image without color shift.

The CPU 31 reads a necessary program from the ROM 37 and performs data processing in the image processing unit 32 and writing / writing of image data in the image memory 33.
Read, and control the misregistration calculation operation of each color,
Alternatively, the operations of the image reader unit 3 and the printer unit 20 are controlled in a unified manner while taking timing, so that a smooth copying operation is executed.

As described above, in order to calculate the amount of positional deviation in the sub-scanning direction with higher accuracy, the resist pattern is not affected by the fluctuation of the positional information such as uneven running of the transfer belt 10 or the like. May be formed for each color, but if the ideal resist pattern is always formed regardless of the state of the apparatus, the toner is wastefully consumed or the detection time of the resist pattern becomes unnecessarily long. There is a problem such as becoming.

Therefore, in the present embodiment, the conditions for forming the resist pattern are determined according to the state of the apparatus, such as the unevenness of the transfer belt 10 and the photosensitive drums 1C to 1K.
The first condition that is not affected by both the rotation unevenness of the second condition, the second condition that is not affected only by the rotation unevenness due to the eccentricity of the photosensitive drums 1C to 1K, and that is not affected only by the running unevenness of the transfer belt 10 Third
Of the transfer belt 10 and the photosensitive drums 1C to 1K
(The resist pattern optimizing process).

Hereinafter, the resist pattern optimization process will be described after the specific configuration of the resist pattern of each color when the resist pattern is formed under the first to fourth conditions. FIG. 3 shows a first resist pattern 81 formed on the transfer belt 10 based on the first condition.
It is a figure showing the example of composition of K-81C.

In order not to be affected by the rotation unevenness due to the eccentricity of the photosensitive drums 1C to 1K, the formation range of the resist pattern of each color is set to the same length as the circumferential length m of the photosensitive drums 1C to 1K. A line segment of the color (a line segment parallel to the main scanning direction; hereinafter, referred to as a “unit pattern”) is formed at the timing of equally dividing the range in the sub-scanning direction. In the figure, for convenience, the unit pattern is formed so as to divide the circumference m equally into seven, and the formation position interval between adjacent unit patterns is m / 7 for each color when rotation unevenness does not occur. It is desirable that the number of unit patterns formed within the range of the circumference m be large in the sense that fluctuation components due to rotation unevenness and detection noise are likely to be canceled out. However, this increases the consumption of toner. An appropriate number is determined in consideration of the allowable range. Note that the right and left ends of the formation range of each color are the same on the peripheral surface of the photosensitive drums 1C to 1K. Therefore, it is not necessary to form a unit pattern on both sides. No pattern is formed. This is shown in FIG.
The same applies to the second resist patterns 82K to 82C shown in FIG.

Further, in order to prevent the transfer belt 10 from being affected by uneven running, unit patterns of respective colors are simultaneously formed on the transfer belt 10. That is, first, the unit patterns on the left end of each color are simultaneously transferred, and then the unit patterns on the right side are sequentially transferred simultaneously. Therefore, the interval between the corresponding unit patterns of each color is the same as the transfer position interval L of the photosensitive drums 1C to 1K.

When the driving unevenness of the transfer belt 10 is caused by the eccentricity of the drive roller 11, it is preferable to set the transfer position interval L to the same value as the circumference R of the drive roller 11. As a result, the unit pattern of each color transferred at the same time can be detected by the optical sensor unit 25 without being affected by the running unevenness. That is, since the running unevenness occurs periodically with one rotation of the drive roller 11 as one cycle, if the transfer position interval L is set to an integral multiple of the circumference of the drive roller 11, the arrangement of the optical sensor unit 25 is determined. This is because the unit pattern of each color can be detected at the set position in a state where the phases in the periodic change are matched, thereby eliminating the influence of running unevenness at the time of detection.

The first resist patterns 81K to 81C
The print data for forming the image data is stored in the ROM 37 in advance, and the printer head unit 40 and the image forming system 60 use the transfer belt 1 based on the print data.
The resist patterns 81K to 81C are formed on the “0”. Each unit pattern of the resist patterns 81K to 81C formed by being transferred onto the transfer belt 10 from the photosensitive drums 1C to 1K is detected by the optical sensor unit 25 on the detection line indicated by the broken line in FIG. Are detected at predetermined sampling intervals, and the detection signals are sent to the CPU 31.

The CPU 31 stores, for example, the sampling signal in the RAM 36, finds the position of the center of gravity of a waveform (sampling waveform) formed by the sampling value, and uses this as the position information of each unit pattern. This position information is represented, for example, as a clock count value from a predetermined reference time. Then, position information of the resist pattern is obtained from the position information of the seven unit patterns constituting one resist pattern, for example, as follows.

If the detected position information of the seven unit patterns is a1, a2,... A7 count in order from the left end, the second and subsequent unit patterns from the left end are formed later than the left end unit pattern. Further, values d2 to d7 are obtained by subtracting the clock count value corresponding to the delay from the position information of each unit pattern. For example, the second and subsequent unit patterns are sequentially counted by b from the pattern on the left (this is the distance m / 7 on the transfer belt 10).
If the second unit pattern is formed at a later timing, the second unit pattern is formed with a b count delay from the left end unit pattern, so that d2 = (a2−b) ), The third unit pattern on the right is formed 2b counts behind the leftmost unit pattern, so d3 = (a3-2b), and d7 = (a7-6b) in the last seventh unit pattern. Becomes

By performing such processing, all the positions to be formed in the state where there is no displacement of each unit pattern are all the same (that is, the positions where the unit patterns on the left end should be formed in the state where there is no displacement). Will be replaced by Using this position as a reference position, an average value d = (a1 + d2 + d3... + D7) / 7 is obtained, and this is set as position information of the resist pattern. Therefore, when the reference position is c count, the difference between c and d (count) is the displacement amount of the resist pattern, and the positional information d in the state where there is no displacement is c count. .

Based on the calculated position information of the resist patterns 81K to 81C, the CPU 31 calculates, for example, the relative positional shift amount in the sub-scanning direction with respect to other colors based on the black resist pattern 81K. Is calculated. In the case where the first resist patterns 81K to 81C are repeatedly formed on the transfer belt 10 a plurality of times, the first resist patterns 81K to 81C are firstly transferred in order to satisfy the condition of simultaneous transfer. Is formed on the photosensitive drum 1K of black color.
, The second and subsequent patterns are simultaneously transferred. Note that the resist pattern 81
K to 81C are not limited to being formed on the transfer belt 10, and may be formed on, for example, a transferred transfer material or another transfer body.

FIG. 4 is a diagram showing a configuration example of the second resist patterns 82K to 82C formed under the second condition. The second resist patterns 82K to 82C satisfy only the condition that is not affected by the rotation unevenness of each of the photosensitive drums 1C to 1K, excluding the condition that is not affected by the uneven running of the transfer belt 10 from the first condition. (In other words, it means that the transfer belt 10 is affected by uneven running), and like the first resist patterns 81K to 81C, the formation range of the resist pattern of each color is changed to the photosensitive drum 1C. The length is the same as the perimeter m of １1K, and seven unit patterns of the color are arranged at respective positions obtained by dividing the range into seven in the sub-scanning direction. Here, since it is not necessary to simultaneously form the unit patterns of each color on the transfer belt 10, the formation position interval of the unit patterns of each color is L1 (<L). Therefore, the detection time by the optical sensor unit 25 is shorter than that of the first resist patterns 81K to 81C. That is, if the second resist patterns 82C to 82K are used, the time required for the resist correction can be shorter than that of the first resist patterns 81K to 81C.

FIG. 5 is a diagram showing a configuration example of the third resist patterns 83K to 83C formed under the third condition. The third resist patterns 83K to 83C satisfy only the condition that is not affected by the running unevenness of the transfer belt 10 except the condition that is not affected by the rotation unevenness of each of the photosensitive drums 1C to 1K from the first condition. (That is, it is affected by the rotation unevenness of each of the photosensitive drums 1C to 1K), and the unit patterns of each color are simultaneously transferred, and the unit patterns of each color that are simultaneously transferred are The formation position interval is the same as the transfer position interval L.

Here, it is not necessary to form seven unit patterns for each color at equal intervals in the range of the circumferential length m of the photosensitive drums 1C to 1K.
The number of unit patterns to be formed can be reduced as compared with 1C, and toner consumption can be reduced. When the pattern is repeatedly formed on the transfer belt 10 a plurality of times, the same as the first resist patterns 81K to 81C,
The second and subsequent patterns are simultaneously transferred after the 83C formed the first time passes the transfer position of the black photosensitive drum 1K.

FIG. 6 is a diagram showing a configuration example of the fourth resist patterns 84K to 84C formed under the fourth condition. The fourth resist patterns 84K to 84C are obtained by removing both the first condition and the condition that are not affected by the rotation unevenness of each of the photoconductor drums 1C to 1K and the condition that is not affected by the running unevenness of the transfer belt 10. (Ie, both affected). Since there is no restriction on both conditions, the number of unit patterns of each color can be reduced (one color in each figure), and the interval between unit patterns of each color can be extremely narrow. That is, the first resist pattern 81K
~ 81C, both the toner consumption and the time required for registration correction can be greatly reduced.

FIG. 7 is a flowchart showing the contents of the resist pattern optimizing process. The resist pattern optimizing process is a process for determining which of the above-described first to fourth resist pattern forming conditions is most suitable when calculating the positional deviation amount. The CPU 31
First, the first resist patterns 81K to 81C are respectively formed on the transfer belt 10 by repeating a plurality of times (n times) on the transfer belt 10,
These are sequentially detected by the optical sensor unit 25 (steps S1 and S2).

Then, the individual first resist patterns 81
The position information is calculated for K to 81C, and from the result, the variation amount σ1 (σ1K, σ1Y, σ1) of the position information of each color is calculated.
M, σ1C) (step S3). Here, as an example, the variation amount σ1K of the position information for the black color
The method for obtaining the following will be described.

First, position information k1 (count) of the first formed resist pattern 81K of n times is calculated. This is, as described above, the position information (a1, d) of the seven unit patterns actually formed on the transfer belt 10.
2 to d7) are calculated by averaging. That is, k
1 = (a1 + d2 +... + D7) / 7. Then 2
The position information k2 of the first resist pattern 81K is calculated by the same method. This process is repeated until n
Position information k for all resist patterns 81K
1 to kn, and the absolute value of the difference between the maximum value kmax and the minimum value kmin among them is defined as the variation amount σ1K of the position information for the black color (σ1K = | kmax−k).
min |).

Since the first resist pattern 81K is formed under the first condition which is not affected by the rotation unevenness of the photosensitive drum 1K and the running unevenness of the transfer belt 10, the variation amount σ1K calculated here is obtained. Are those which do not include those fluctuation components, and mainly include each resist pattern 81K.
This is due to variations in the shape and density of the image.

Then, similarly, the variation amounts σ1Y, σ1 for the other colors, yellow, magenta, and cyan.
1M and σ1C are obtained. Hereinafter, the variation amount σ1
When K to σ1C are collectively referred to, a symbol indicating a color may be omitted and simply referred to as “σ1”. Also, σ2 and σ3 described below are described in a similar manner. Next, the CPU 31 sets the second resist patterns 82K to 82K
C is formed on the transfer belt 10 by repeating a plurality of times, and these are sequentially detected by the optical sensor unit 25.
By the same method as in step S3, the variation amount σ2K of each color for the second resist patterns 82K to 82C.
To σ2C (steps S4 to S6).

The second resist patterns 82K to 82C are
Although it is not affected by the rotation unevenness of the photoreceptor drums 1C to 1K, it is formed under the second condition affected by the running unevenness of the transfer belt 10, so that the variation amount σ2K
Σ2C mainly indicates the maximum fluctuation amount of the pattern formation position due to the uneven running of the transfer belt 10 for each color.

Further, the third resist patterns 83K to 83K
3C are formed on the transfer belt 10 a plurality of times, and they are sequentially detected by the optical sensor unit 25, and the third resist pattern 83 is formed in the same manner as in step S3.
Variation amount σ3K to σ3C of each color for K to 83C
(Steps S7 to S9). The third resist patterns 83K to 83C are formed under the third condition which is not affected by the uneven running of the transfer belt 10 but is affected by the uneven rotation of the photosensitive drums 1C to 1K. The amounts σ3K to σ3C mainly depend on the photosensitive drum 1C.
The maximum variation amount of the pattern formation position due to the rotation unevenness of up to 1K is shown for each color.

Here, the magnitude relation of σ1, σ2, σ3 is
For example, if the color is black, σ1K <σ2K, σ1K <
σ3K. This is because, compared to σ1K, σ2K and σ3K are calculated in a state in which a periodic fluctuation component of running unevenness and rotation unevenness is added, and are considered to be more scattered than σ1K. This is the same for other colors. In order to calculate these variations more accurately, it is desirable to increase the number n. However, there is a problem such as an increase in toner consumption. And the like are determined in advance by experimentation.

Then, the CPU 31 calculates the difference (σ2K−σ1K, σ2Y−σ1) between the variation amount σ2 and the variation amount σ1.
Y, σ2M-σ1M, σ2C-σ1C) are obtained for each color, and it is determined whether or not they are equal to or less than a predetermined value T1 (step S10). Here, the difference between σ1 and σ2 is determined by determining whether or not it is necessary to set a condition that is not affected by uneven running of the transfer belt 10 when forming a resist pattern in the positional deviation calculation process. That's why.

The fact that the difference is small means that the amount of variation when the resist pattern is affected by running unevenness is almost the same as when the resist pattern is not affected by running unevenness. This means that the position information will be substantially the same regardless of whether the information is formed under the same conditions. In such a case, it is not necessary to form the resist pattern under the condition not influenced by the running unevenness. Conversely, a large difference indicates that the variation due to the influence of the running unevenness is large, which indicates that the influence of the running unevenness on the position information is large. Therefore, unless the displacement amount is calculated under the unaffected condition, a periodic fluctuation component due to running unevenness will be added to the displacement amount as an error, and the registration correction will not be performed properly. .

Here, a predetermined value T1 is determined in advance by an experiment as an upper limit value of the difference between σ1 and σ2 within the range in which the registration correction is properly performed even if the difference is affected by running unevenness. When it is larger than this, a condition that is not affected by running unevenness is set as a condition for forming a resist pattern when the difference is smaller than this.

If all the differences between the colors are larger than the predetermined value T1 ("N" in step S10), then σ3 and σ3
1 (σ3K−σ1K, σ3Y−σ1Y, σ3M−
σ1M, σ3C-σ1C) (Step S1)
1). The difference between σ1 and σ3 is determined by the photosensitive drum 1
This is for determining whether or not it is necessary to form a resist pattern under the condition not affected by the rotation unevenness of C to 1K.

When the difference is equal to or less than the predetermined value T2, it is not necessary to form a resist pattern under the condition not affected by the rotation unevenness for the same reason as described above.
On the other hand, when the difference is larger than the predetermined value T2, the influence of the rotation unevenness on the position information is large unless the position shift amount is calculated under the condition not affected by the rotation unevenness, and the calculation accuracy is reduced. This predetermined value T2 is the value of the photosensitive drum 1
The upper limit value of the difference between σ1 and σ3 within the range where the registration correction is properly performed even when affected by the rotation unevenness of C to 1K is determined in advance by an experiment, and when the difference is larger than this. Is a condition that is not affected by uneven rotation.
If the difference is smaller than this, the affected condition is set as a resist pattern forming condition.

If all the differences between the colors are larger than the predetermined value T2 ("N" in step S11), a pattern formation flag "1" is set in the RAM 36 (step S1).
2), end the process. This pattern formation flag is referred to at the time of a position shift calculation process to be described later, and a value of “1” indicates that a resist pattern is formed under the first condition. This is because the resist pattern is formed under a condition that is not affected by the uneven running of the transfer belt 10 and the uneven rotation of the photosensitive drums 1C to 1K.

If the difference between σ3 and σ1 is equal to or less than the predetermined value T2 for each color (“Y” in step S11), a pattern formation flag “3” is set (step S1).
3), end the process. This is because the resist pattern may be formed under the third condition which may be affected by uneven rotation of the photosensitive drums 1C to 1K but is not affected by uneven running of the transfer belt 10.

On the other hand, all the differences between σ1 and σ2 are equal to a predetermined value T1.
(“Y” in step S10), σ1 and σ3
Are larger than the predetermined value T2 (step S2).
("N" in 14), the pattern formation flag "2" is set (step S15), and the process is terminated. The reason for this is that the resist pattern can be formed under the second condition which may be affected by the uneven running of the transfer belt 10 but is not affected by the uneven rotation of the photosensitive drums 1C to 1K.

Further, the difference between σ1 and σ2, and σ1 and σ
If the differences of all three are less than or equal to the predetermined values T1 and T2 for each color ("Y" in step S10, "Y" in step S14), a pattern formation flag "4" is set (step S16), and the processing is performed. To end. In this case, the resist pattern may be formed under the fourth condition that is affected by the uneven running of the transfer belt 10 and the uneven rotation of the photosensitive drums 1C to 1K.

FIG. 8 is a flowchart showing the contents of the processing for calculating the amount of displacement. The CPU 31 refers to the pattern formation flag stored in the RAM 36 and, if the flag “1” is set (“Y” in step S20), transfers the first resist patterns 81K to 81C to the transfer belt 10 (step S20). It is formed above (step S21). If the flag “2” is set (“N” in step S20 and “Y” in S22), the second resist pattern 82
K to 82C are formed on the transfer belt 10 (Step S23). If the flag “3” is set (“N” in step S22 and “Y” in S24), the third resist patterns 83K to 83C are formed on the transfer belt 10 (step S25), and the flag “4” is set. ("N" in step S24), the fourth resist pattern 84K-
84C is formed on the transfer belt 10 (step S2).
6). Then, any one of the formed first to fourth resist patterns is detected by the optical sensor unit 25, and their positional information is obtained by the above-described method, and the positional deviation amount is calculated from the positional information ( Steps S27 and S28),
The process ends.

The process of calculating the amount of misregistration is performed, for example, every time 10 color images are formed. May be performed every time 1000 sheets are formed. This is because a change in the amount of occurrence of the unevenness of the transfer belt 10 or the unevenness of the rotation of the photosensitive drums 1C to 1K is a very gradual change with time. Therefore, from a temporary standpoint, when the resist pattern optimizing process for forming the first to third resist patterns a plurality of times is performed, the toner consumption is increased and the time required for the resist correction is increased as compared with the related art. It seems that in the long term, in the calculation process of the misregistration amount, which is frequently performed, the reduction of the toner consumption etc. is surely performed each time, and as a result, the toner consumption etc. can be reduced as compared with the conventional case. It becomes.

As described above, in the present embodiment, the variations .sigma.1 to .sigma.3 of the formation positions of the resist patterns formed under the first to third conditions are obtained, and .sigma.1 and .sigma.2 are calculated.
When both the difference between σ1 and σ3 are equal to or smaller than a predetermined value, it is determined that the influence of the running unevenness of the transfer belt 10 and the rotation unevenness of the photosensitive drums 1C to 1K on the position information is small. The resist pattern is formed under the condition (fourth condition) affected by these, and when the differences are both larger than a predetermined value, it is determined that the effect on the position information is large, and the influence on the position information is determined. It is formed under conditions that are not present (first conditions). Further, the resist pattern can be formed under the second or third condition which is not affected by any one of the rotation unevenness and the running unevenness.

As described above, the resist pattern to be formed at the time of calculating the positional deviation is appropriately selected in accordance with the degree of the influence of the running unevenness and the rotation unevenness. Resist pattern 81K ~
As compared with the conventional case in which only 81C can be formed, there is an effect that there is no problem that the toner is wastefully consumed and the detection time of the resist pattern becomes unnecessarily long.

When the resist pattern is formed under the first condition depending on the diameters of the photosensitive drums 1C to 1K and the transfer position interval, the resist patterns of each color are divided into two pattern groups as shown in FIG. May not be obtained. This is the case where L <D, where D is the circumference of the photosensitive drums 1C to 1K, and L is the transfer position interval of each color. In this case, for example, when looking at the black color, a unit pattern is first formed in the range of x (x <L), a distance of 3D from the unit pattern located on the right end of the range, and then the range of y A unit pattern is formed on the substrate.
Since the distance is 3D, the right end of the range of x and y
Are located at the same position on the photosensitive drum 1K (therefore, the first resist pattern 81K).
The unit pattern may be formed only at any one of the positions, as in the case of -81C. ). Here, if the relation of x + y = D is satisfied, a black unit pattern is formed over one rotation of the photosensitive drum 1K. If the same relation is applied to the other color patterns, the unit patterns of the resist patterns 85K to 85C can be simultaneously transferred first, and then the unit patterns of 86K to 86C can be transferred simultaneously from the left end.

Conventionally, even with such a pattern in which the formation range in the sub-scanning direction is extremely long, this pattern is formed every time the positional deviation amount is calculated, so that toner is wasted or wasted. However, the problem that the detection time of the resist pattern becomes unnecessarily long has been remarkable. However, by applying the present invention, it is possible to eliminate such a problem without lowering the calculation accuracy of the displacement amount. Become. From this, it can be said that the present invention is extremely effective when a pattern as shown in FIG. 9 is formed.

(3) Modifications It goes without saying that the present invention is not limited to the above-described embodiment, and the following modifications can be considered. (3-1) In the above embodiment, the photosensitive drums 1C to 1C
As a condition that is not affected by the rotation unevenness of K, the length of the formation range of the resist pattern in the sub-scanning direction is set to be the same as the circumferential length of each of the photosensitive drums 1C to 1K. The reason for this is that the rotation cycle is the same as the rotation cycle of the photoconductor drums 1C to 1K, assuming that the rotation unevenness is caused by the eccentricity of the rotation shafts of the photoconductor drums 1C to 1K. However, the rotation unevenness may be generated separately from the eccentricity of the reduction gears in the drive system of the photoconductor drums 1C to 1K and vibrations generated when the reduction gears mesh with each other, for example.

Here, in order not to be affected by the rotation unevenness, the length of the formation range is set to a length that is an integral multiple of the distance that the peripheral surfaces of the photosensitive drums 1C to 1K move during one cycle of the rotation unevenness. For example, in order not to be affected by the vibration generated at the time of meshing, the vibration frequency is set to f
p, when the system speed (the transport speed of the transfer belt 10, which is also the peripheral speed of each of the photosensitive drums 1C to 1K) is v, the length of the forming range is an integer multiple of (v / fp). By doing so, it is possible to prevent the influence of uneven rotation due to meshing vibration.

Similarly, in order not to be affected by the eccentricity of the reduction gear, the length of the resist pattern formation range is set to (fg ·
v) can be an integral multiple of v). In order to avoid the influence of the rotation unevenness of the motor that drives the photosensitive drums 1C to 1K to rotate, the length of the resist pattern formation range is set to fm when the rotation period of the motor is set to fm. Can be an integer multiple of (fm · v).

Here, in order not to be affected by the plurality of rotation irregularities, the length of the formation range is set to the length of the least common multiple of the length of the formation range obtained for each factor. Good. For example, in order not to be affected by the eccentricity of the photosensitive drum and the meshing vibration of the reduction gear, the length of the formation range may be determined as follows. Assuming that the diameter of the photosensitive drum is Q, its circumference is (π · Q), so that the distance corresponding to one cycle of rotation unevenness due to eccentricity is (π · Q). On the other hand, if the reduction ratio of the reduction gear is (1 / N),
The distance corresponding to one cycle of the rotation unevenness due to the meshing vibration is (π · Q / N). Here, the least common multiple is (π · Q), which is the shortest formation range length.

At this time, the unit pattern interval is set to (π · Q /
N), that is, a length corresponding to one cycle of the meshing vibration having the shorter cycle. At this time, the number of unit patterns is N. In this way, individual unit patterns can be formed in a state where the phases within one cycle of the meshing vibration are matched, that is, in a state where the phase is not affected by the meshing vibration.

(3-2) In the above-described embodiment, conditions that are not affected by uneven running of the transfer belt 10 include:
The resist pattern of each color was transferred at the same time,
The following can be performed instead of the simultaneous transfer. When the driving unevenness is caused by the eccentricity of the driving roller 11, the range of the integral multiple of the circumference of the driving roller 11 is defined as the length of the formation range of the resist pattern of each color. A plurality of unit patterns are formed at equal intervals. If the average value is obtained for each color in the same manner as described above, the component of the rotation unevenness of the drive roller 11 can be offset, and the influence of the running unevenness can be prevented. That is, in order to avoid the influence of the running unevenness, the distance that the transfer belt 10 moves during one cycle of the running unevenness may be set to the length of the registration pattern forming range.

Further, the running unevenness is caused by, for example, the driving roller 11.
It may be caused by vibration generated at the time of eccentricity or meshing of the reduction gear of the drive system. For example, in order not to be affected by the vibration generated at the time of meshing, when the vibration frequency is fb, the length of the formation range is set to (v / f
By setting it to an integral multiple of b), it is possible to avoid the influence of running unevenness due to meshing vibration. Similarly, in order not to be affected by the eccentricity of the reduction gear, the length of the formation range is set to an integral multiple of (fh · v) when one rotation cycle of the gear is fh. Can be. In order to avoid the influence of the rotation unevenness of the motor that drives the drive roller 11, the length of the forming range is set to (fn ·
It can also be an integral multiple of v).

Further, the thickness of the transfer belt 10 may not be uniform in the sub-scanning direction, and uneven running may occur due to the uneven thickness. In order not to be affected by the thickness unevenness, the cycle of the travel unevenness is the cycle of the thickness unevenness, that is, one rotation cycle of the transfer belt 10. And it is sufficient. Also, as in the case of (3-1), in order to avoid the influence of the plurality of traveling unevenness, the length of the formation range is set to the least common multiple of the length of the formation range obtained for each factor. It should be length. In (3-1) and (3-2), if the least common multiple of the length of the obtained formation range is obtained, the resist pattern (the above-described first resist pattern and Under the same conditions).

(3-3) In the above embodiment, the optimum condition for forming the resist pattern to be formed at the time of calculating the displacement amount is determined by performing the resist pattern optimizing process. Without performing such processing, the registration pattern is formed under the fourth condition as an initial setting. For example, if the operator views the reproduced image and determines that the color misregistration is large, The operator may be able to select using a setting key or the like on an operation panel (not shown) so that the resist pattern can be formed in the order of the second, third, and first conditions.

Further, the predetermined value T in the above-mentioned optimization processing
1, T2 may be changed by the operator.
If the predetermined values T1 and T2 are changed, the range in which the pattern formation flags “1” to “4” are set changes.
This is because it is substantially the same as selecting the first to fourth conditions. (3-4) Steps S11 and S in the above embodiment
14, when the difference between σ3 and σ1 is larger than the predetermined value T2 for each color,
When it is determined that the rotation unevenness of C to 1K affects the position information for all the colors, the pattern formation flag “1” or “2” is set. Here, for example, the difference (σ3
If (C-σ1C) is larger than the predetermined value T2, but is equal to or smaller than the predetermined value T2 for other colors, a resist pattern is formed for the cyan color under the second condition that is not affected by rotation unevenness. Although it is necessary, the other colors do not need to satisfy the second condition.
In such a case, for colors other than cyan,
If the formation range is made shorter than the circumferential length of the photosensitive drums 1C to 1K and the number of formed toners is reduced except for the condition (1), the toner consumption is further reduced by the reduced number of formed toners compared to the above embodiment. It is also possible.

(3-5) First to Third Embodiments
The fourth resist pattern has a configuration in which unit patterns parallel to the main scanning direction are arranged at regular intervals in the sub-scanning direction in order to calculate the amount of displacement in the sub-scanning direction. It is also possible to form a line segment for calculating the amount of positional deviation at a different position from the unit pattern, and calculate the amount of positional deviation by a known method.

(3-6) In the above embodiment, a full-color tandem-type copying machine has been described.
By detecting a resist pattern formed on a transfer member such as the transfer belt 10, the position information of the resist pattern is obtained, and a function of correcting an image writing position on an image carrier such as a photosensitive drum is provided. Can be applied to all the image forming apparatuses.

[0075]

As described above, according to the present invention, the image writing position on each image carrier is corrected based on the position information obtained by detecting the reference pattern transferred on the transfer member. A first control unit for controlling each image writing unit so as to form a first temporary reference pattern on a transfer body under a first condition, and a second control unit for controlling an image writing unit on a transfer body under a second condition. Second control means for controlling each image writing means so as to form two temporary reference patterns;
And a selection means for selecting one of the second control means and the provisional reference pattern formed by the selected control means is used as the reference pattern. As described above, no matter what the state of the apparatus is, the reference pattern cannot be formed only under one condition, so that the toner is wastefully consumed and the detection time of the reference pattern becomes uselessly longer than in the related art. Such a thing disappears.

Further, since the second condition does not include all or a part of the first condition,
If the first condition is a condition that is not affected by a specific variation factor, for example, the unevenness of travel of the transfer body or the unevenness of rotation when each image carrier is a rotating body, the second condition is that the unevenness of travel is This excludes the condition that is not affected by either or any of the rotation unevenness. This makes it possible to at least shorten the formation range of the second temporary reference pattern or to reduce the number of patterns to be formed, as compared with the first temporary reference pattern. It is possible to reduce the toner consumption and the detection time of the reference pattern as compared with the case where the reference pattern is used.

Further, the selecting means controls the image writing means sequentially by the first and second control means,
First and second temporary reference patterns are respectively formed on the transfer body, and a variation amount of positional information for each color in each pattern is obtained from detection results of the formed first and second temporary reference patterns. A first variation control unit configured to determine whether the variation in the positional information of the corresponding color in the first and second patterns is greater than or equal to a predetermined value; Is selected, the labor of the operator is not required, and an extremely appropriate selection is made as compared with the case where the operator makes the selection.

The first condition is a condition for transferring the pattern of each color to the transfer belt at the same timing, and the second condition is a condition for transferring the pattern of each color to the transfer belt at a different timing. I have. As a result, when the second condition is selected, the formation range of the reference pattern can be made shorter than in the first condition, and the detection time is shorter than in the conventional case.

The first condition is that a unit pattern is written at a fixed writing timing, and the formation range on the transfer body in the sub-scanning direction is changed while the generation cycle of the specific fluctuation factor elapses. Is a condition for forming a plurality of patterns so as to be substantially equal to the length of an integral multiple of the traveling distance. The second condition is that at least one unit pattern is formed at a constant writing timing and its formation range in the sub-scanning direction is: The condition is such that the length is not equal to an integral multiple of the distance that the transfer body advances during the passage of the generation cycle of the specific fluctuation factor, and is shorter than the formation range under the first condition. Thus, when the second condition is selected, the number of unit patterns formed in the formation range of the reference pattern can be smaller than in the first condition, and the toner consumption can be reduced as compared with the related art. Will be.

Further, when the specific variation factor is a combination of a plurality of unit variation factors, the occurrence cycle of the specific variation factor is set to be the least common multiple of the occurrence cycle of each unit variation factor. , A reference pattern which is not affected by the variation factor can be formed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a tandem-type copying machine according to an embodiment of the present invention.

FIG. 2 is a block diagram of a control unit installed in the copying machine.

FIG. 3 is a diagram illustrating a configuration example of a first resist pattern formed on a transfer belt.

FIG. 4 is a diagram illustrating a configuration example of a second resist pattern formed on a transfer belt.

FIG. 5 is a diagram illustrating a configuration example of a third resist pattern formed on a transfer belt.

FIG. 6 is a diagram illustrating a configuration example of a fourth resist pattern formed on a transfer belt.

FIG. 7 is a flowchart showing the contents of a resist pattern optimizing process.

FIG. 8 is a flowchart illustrating the content of a calculation process of a displacement amount.

FIG. 9 is a diagram illustrating a configuration example of another first resist pattern formed on a transfer belt.

[Explanation of symbols]

1C-1K Photoconductor drum 10 Transfer belt 11 Drive roller 20 Printer unit 25 Optical sensor unit 30 Control unit 31 CPU 32 Image processing unit 33 Image memory 34 Position shift correction unit 35 Laser diode drive unit 36 RAM 37 ROM 81K-81C, 82K ~ 82C, 83K ~ 83C, 8
4K-84C, 85K-85C, 86K-86C
Resist pattern

Continued on the front page F term (reference) 2C262 AA05 AA17 AB15 FA06 FA08 FA09 FA10 FA12 GA03 GA04 GA36 GA40 GA42 GA43 GA47 GA54 2C362 BA52 BA71 BB35 BB47 BB48 BB49 CA22 CA23 CA39 CB59 CB73 CB80 DA47 2H027 DA17 EC04 ED06 ED24 EE02 EE07 EF09 2H030 AA01 AB02 AD12 AD17 BB02 BB16 BB23 BB44 BB56

Claims (8)

[Claims] A plurality of image carriers, wherein a pattern of each color written on each image carrier by an image writing means is transferred onto a predetermined transfer member to form a reference pattern, and the reference pattern is detected. An image forming apparatus that corrects an image writing position on each of the image carriers based on the position information obtained as described above, wherein a first temporary reference pattern is formed on a transfer body under a first condition. First control means for controlling each of the image writing means, and second control means for controlling each of the image writing means so as to form a second temporary reference pattern on the transfer body under a second condition. Selecting means for selecting one of the first control means and the second control means, a temporary reference pattern formed by the selected control means being the reference pattern, and Each of the above images An image forming apparatus characterized in that the correction of the write position. 2. The first condition is a condition in which the obtained position information is not affected by a specific variation factor, and the second condition is all or one of the first conditions. The image forming apparatus according to claim 1, wherein the condition is that no unit is provided. 3. The selecting unit controls the image writing unit sequentially by the first and second control units to form first and second temporary reference patterns on the transfer body, respectively. First and second
From the detection result of the provisional reference pattern, and a variation amount obtaining unit for determining the variation amount of the positional information for each color in each pattern, wherein the variation amount of the positional information of the corresponding colors in the first and second patterns is calculated. 3. The image forming apparatus according to claim 2, wherein the first or second control unit is selected based on whether the difference is equal to or greater than a predetermined value. 4. The transfer member is a transfer belt,
The specific variation factor is uneven running of the transfer belt, the first condition is a condition for transferring the pattern of each color to the transfer belt at the same timing, and the second condition is a condition for transferring the pattern of each color. 4. The image forming apparatus according to claim 2, wherein the conditions are such that the image is transferred to the transfer belt at different timings. 5. The pattern of each color formed on each of the image carriers is composed of one or more unit patterns, and the first condition is that the unit pattern is written at a fixed writing timing, and the sub-scanning is performed. A condition in which a plurality of forming ranges on the transfer body in the direction are formed so as to be substantially equal to an integral multiple of a distance traveled by the transfer body during the passage of the generation cycle of the specific variation factor; The second condition is that the formation range in the sub-scanning direction of at least one unit pattern at a fixed writing timing is an integral multiple of the distance the transfer body advances during the elapse of the generation cycle of the specific variation factor. Not equal to the length,
The image forming apparatus according to claim 2, wherein the image forming apparatus is configured to form the image so as to be shorter than the formation range under the first condition. 6. The image forming apparatus according to claim 5, wherein each of the image carriers is a rotating body, and the specific fluctuation factor is rotation unevenness of each of the image carriers. 7. The image forming apparatus according to claim 6, wherein the rotation unevenness is caused by eccentricity of each image carrier, and the rotation unevenness generation cycle is a rotation cycle of the image carrier. The image forming apparatus as described in the above. 8. The specific variation factor is a combination of a plurality of unit variation factors, and an occurrence cycle of the specific variation factor is a least common multiple of an occurrence cycle of each unit variation factor. The image forming apparatus according to claim 5, wherein: