JP2003280315A - Image forming device - Google Patents

Abstract

(57) [Problem] To provide an image forming apparatus capable of executing alignment mark detection processing by a single mark creation processing even when density fluctuation occurs. SOLUTION: A reference voltage Xm [V] stored in a non-volatile memory is compared with a detection output of a misregistration detection mark (Step S4). I don't know if it detected or noise. Therefore, the reference value is reset to a level at which the pattern can be clearly detected, and the newly set reference value is stored in the nonvolatile memory 48 each time (steps S6 and S7). That is, the reference value stored in the nonvolatile memory 48 is updated. The updated value is used as the reference voltage Xm in step S2 in the next displacement control.
[V].

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 and an image forming method for performing full color, preferably tandem, full color image forming means.

[0002]

2. Description of the Related Art As this type of technology, for example, (1) Japanese Patent Application Laid-Open No. 10-260567, and (2) Japanese Patent Application Laid-Open No. 11-84.
The inventions disclosed in Japanese Patent No. 811 and (3) Japanese Patent Laid-Open No. 2001-312116 are known.

In the above publication (1), the density of the misregistration detection mark is reduced or the density of the misregistration detection mark is uneven due to changes in the environment due to temperature and humidity fluctuations, changes over time, etc. If it is not formed, the density data of the misregistration detection mark is calculated in order to solve the problem that accurate mark detection cannot be performed and color misregistration correction cannot be performed normally. Discloses a technique for keeping the displacement pattern detection value above a certain value by changing the bias value for creating an image.

Further, in the above publication (2), when a color image is formed by a plurality of photoconductors, a pattern for detecting the position of the color image is formed on a transfer belt in a state where there are no other patterns or scratches. However, there is a technique for detecting this pattern to obtain a reference value, comparing the output value of the detection sensor with this reference value, determining the position detection pattern, and performing positional deviation correction control based on this determination result. It is disclosed.

Further, in the publication (3), a series of misregistration detection pattern images formed on the conveyor belt is read through a light sensor, and the misregistration amount between the color images is read based on the read image data. Is disclosed, and the position of the image of each image forming station other than the reference color is corrected based on the calculated positional deviation amount.

[0006]

However, according to this method, when the pattern density variation occurs, the positional deviation pattern creating process must be executed a plurality of times, and the positional deviation correction process takes time. There was a problem.

The present invention has been made in view of the circumstances of the prior art as described above, and an object thereof is to be able to execute alignment mark detection processing by one-time mark creation processing even when density fluctuation occurs. An object is to provide an image forming apparatus.

Another object of the present invention is to provide an image forming apparatus capable of obtaining an optimum reference value for detecting the alignment mark according to the state of use.

[0009]

In order to achieve the above object, the first means is to transfer images formed by a plurality of image forming portions arranged along a carrier one after another onto a recording medium. By doing so, in a color image forming apparatus that obtains a color image, means for forming a plurality of sets of positional deviation detection patterns for detecting positional deviation of each color of the superposed images on the conveyance body, and a preset reference value. It is characterized by further comprising means for comparing and detecting the misregistration detection pattern, and means for changing the reference value based on a detection result detected by the detecting means.

A second means is characterized in that, in the first means, the reference value is set to a level sufficient to discriminate a detection value from the detection pattern from other detection values. .

A third means is characterized in that, in the first or second means, the means for detecting comprises an optical sensor and the reference value is a voltage value photoelectrically converted.

A fourth means is characterized in that, in the first to third means, means for storing the reference value is provided.

In a fifth means, in the first to fourth means, the reference value stored in the storing means is updated every time the reference value is changed and used as a next reference value. It is characterized by

A sixth means, in the first to fifth means, corrects the positional deviation of the superposed images based on the detection result of the positional deviation detection pattern, and forms a preset number of images. And a means for forming the misregistration detection pattern and performing misregistration correction each time the above-mentioned operation is performed.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a schematic configuration of a tandem type color image forming apparatus according to an embodiment of the present invention. In FIG. 1, the color image forming apparatus is yellow (Y),
Four image forming units 1Y, 1M, 1C, 1 provided for each color of magenta (M), cyan (C), and black (K).
K (note that Y, M, C, and K added after the reference symbols respectively correspond to the constituent elements of the respective colors. Hereinafter, the symbols indicating the colors will be generally omitted and described). The colors are arranged in this order from the upstream side in the rotation direction along the recording paper transport belt 8 (hereinafter, transport belt).

Each image forming section 1 has a photosensitive drum 2 functioning as an image forming medium, and a charging unit 3, an exposure unit 4, a developing unit 5, a cleaning unit device 6, which are arranged around the photosensitive drum. And a static elimination unit (not shown). The conveyor belt 8 is rotationally driven in the direction of arrow A by a roller 9, one of which is a drive roller.

The surface of the photosensitive drum 2 is uniformly charged by the charging device 3 and then exposed by the exposure device 4 in a pattern corresponding to the image to be output, and an electrostatic latent image is formed on the surface of the photosensitive drum 2. Is formed. The electrostatic latent image formed on each photoconductor drum 2 is developed by the developing device 5 to form a toner image of each color as a visible image.

A recording paper 10 as a recording medium is sent out from a paper feed tray 11, passes sequentially through the image forming sections 1Y, 1M, 1C and 1K by a conveyor belt 8 and is transferred onto each photosensitive drum 2 at each transfer position 7. One color image is obtained on the transfer paper 10 by sequentially transferring the toner images of respective colors formed on the transfer paper 10 to the same position on the recording paper 10 by the transfer roller 13 and superposing them. Recording paper 1 onto which four color toner images have been transferred
0 is peeled off from the conveyance (transfer) belt 8, and the fixing device 12
Then, the sheet is fixed by and is discharged from the sheet discharge roller 12.

The toner remaining on the surface of the photoconductor drum 2 after the transfer of each color toner image formed on each photoconductor drum 2 is removed by the cleaning unit 6 to prepare for the next image forming cycle.

FIG. 2 is a perspective view showing the conveyor belt 8 and the photosensitive drums 2Y, 2M, 2C and 2K of the color image forming apparatus of FIG. An arrow B indicates a main scanning direction in a direction orthogonal to the moving direction of the conveyor belt 8, and an arrow C indicates a sub-scanning direction in a direction parallel to the moving direction of the conveyor belt 8.

FIG. 3 shows the positional deviation detection marks 201 and 203 transferred onto the conveyor belt 8 and the marks 20.
1, 203 is a perspective view showing the relationship with the detection devices 14 and 15 for detecting 1, 203, and FIG. 4 is a schematic view of a control circuit of a control device for performing writing alignment based on analog signals detected from the detection devices 14 and 15. It is a block diagram shown.

In this apparatus, as shown in FIG. 3, the positional deviation detecting marks 201 and 203 are detected by the detecting devices 14 and 15 which are light reflection type sensors having a light emitting portion and a light receiving portion, and the detected analog signals are detected. Is converted into a digital signal by the A / D converter 41 and input as a voltage value to the alignment controller 45 in the subsequent stage.

The alignment controller 45 calculates the positions of the misregistration detection marks 201 and 203 from the voltage values acquired by the A / D converter 41, and calculates the skew misregistration amount, the main scanning registration misregistration amount, and the main scanning magnification misregistration amount. , The sub-scanning registration deviation amount and the correction amount are calculated, and the set values of the control signals such as the write clock and the write timing are transmitted to the system controller 46. Then, the system controller 46
Then, each color is aligned by changing each timing to the transmitted set value. In addition, RO
A program executed by the alignment controller 45 and the system controller 46 is stored in the M43, and the alignment controller 45 and the system controller 4 are stored.
6 executes the program while using the RAM 44 as a work area. Further, a non-volatile memory (EPROM) 48 is connected to the alignment controller 45 via a bus and stores an updated reference voltage. Then, as will be described later, it is updated every time the reference voltage is changed, and the positional deviation pattern detection process is executed based on the updated reference voltage.

FIG. 5 is a plan view showing details of the positional deviation detection marks 201 and 203 formed on the conveyor belt 8 according to the embodiment of the present invention. Misalignment detection mark 20
As shown in FIG. 5, the misregistration detection patterns constituting Nos. 1 and 203 are 1 on the front side (operation side) and the rear side (back side) of the apparatus.
The first and second detection devices 14 and 15 are arranged in columns and are arranged at positions where these patterns can be detected. The misregistration detection patterns include black (k), yellow (y), cyan (c), and magenta (from the upstream side in the rotational direction) on the front surface side (shown as f on the front side) and the rear surface side (shown on the rear side as r). m) in parallel in order of 4 (Akf,
Ayf, Acf, Amf) and 4 lines (Bkf, Byf, Bcf, Bmf) are formed in the above order by inclining at an angle of 45 °, and a total of 8 lines are set as Mtf 1 to Mtf.
8 and 8 sets of Mtr1 to Mtr8 are formed. This image formation pattern is stored in the ROM 43, and an image is formed at a timing when an image is not formed on the recording paper 10 for each predetermined number of image formations, and the positional deviation correction control described below is executed. Further, the patterns Mst and Msr of the four colors in the main scanning direction x, which are formed on the downstream side of the first patterns Mtf1 and Mtr1 in the transfer belt transport direction, are patterns that trigger the start of pattern detection, and this pattern is detected. After that, the positional deviation correction control is started. In FIG. 5, d is four parallel lines (Akf, Ayf, Acf, Amf).
Between each pattern of 4 and tilted at an angle of 45 °
The spacing of each pattern of the book (Bkf, Byf, Bcf, Bmf) in the direction parallel to the transfer belt 8 conveyance direction is shown, and c is the spacing between the parallel pattern and the diagonal 45 ° putter,
A indicates a component in the direction parallel to the sheet conveyance direction of the pattern length of 45 ° diagonal.

The first and second detection devices 14 and 15 optically detect the positional deviation detection marks (positional deviation detection patterns) 201 and 203 formed as described above and the reflected light from the background portion of the conveyor belt 8. , And the A / D converter 41 converts the voltage value into a voltage value, and the two are compared. FIG. 6A shows the output values from the conveyor belt and the misregistration detection marks 201 and 201.
It is a figure which shows the output waveform of the output value from 03. The position of 5V is the output value from the background of the conveyor belt 8, and when the positional deviation detection marks 201 and 203 are detected, the output value changes from 5V to around 0V.

When the output drops from 5V to 0V in this way, the start trigger pattern M of the misalignment detection marks 201 and 203 is set to the first and second detection devices 14 and 15.
When it is determined that sf and Msr have passed, the mark position detection control is started.

The positional deviation adjustment is performed by the positional deviation detection mark 2
The peak value D of the output voltage of the first set of 01 patterns
The difference between [V] and the reference voltage X [V] is calculated, and the difference is S
When it is equal to or more than [V], the reference voltage X [V] is used as it is as the reference voltage for detection, and the detection of the misregistration detection marks of the second and subsequent sets is started. On the other hand, when the difference between the output voltage D [V] and the reference voltage X [V] is less than or equal to S [V], the value that makes the difference between the output voltage D [V] and S [V] becomes the new reference voltage Xs.
It is calculated as [V], and the detection of the misregistration detection mark is started using the new reference voltage Xs [V]. At that time, the reference voltage X [V] is rewritten with the new reference voltage Xs [V] to update the reference value.

When the alignment process is started, the reference voltage Xm stored in the non-volatile memory (EPROM) 48 is used.
[V] is read and comparison with the output voltage D [V] is started using the read value as a reference value. Compared difference is S [V]
When the new reference voltage Xs [V] is calculated to be smaller, Xm [V] stored in the nonvolatile memory (EPROM) 48 is rewritten to the new reference voltage Xs [V] as described above.

This processing is shown in the flowchart of FIG.
In this process, first, the positional deviation detection marks 201, 20
3, that is, the start trigger patterns Msf and Msr and the eight sets of patterns are formed on the front side and the rear side of the transfer belt 8 (step S1). Next, the reference voltage Xm [V] is read from the non-volatile memory 48 (step S2), and the output peak value D [V] of the first set (Mtf1, Mtr1) of the displacement pattern is acquired (step S3). Then, the acquired output peak value D [V] and the reference voltage Xm
The difference of [V] is calculated, and it is determined whether the difference is S [V] or more (step S4). In this determination, step S4
It is determined whether or not the difference calculated in step 3 is greater than or equal to the preset difference D [V]. The difference D [V] is 2.5 V (width of output value of mark detection signal) which is regarded as the width of the pattern when it decreases from 5 [V] to 0 [V] as shown in FIG. 6B. If ab Akrp (black pattern width) and cd Ayrp (yellow pattern width) corresponding to the above are equal to or more than the detectable values, the pattern can be detected without any error. Execution is performed (step S5), and the positional deviation correction process ends.

On the other hand, if the result of the difference calculated in step S4 is less than D [V], the width of the pattern (Ak
rp, Ayrp, etc.) cannot be reliably detected and cannot be discriminated from noise. Therefore, a reference voltage Xs [V] is calculated so that the width can be reliably detected (step S6), and the reference voltage Xm [] of the nonvolatile memory 48 is calculated. V] is the new reference voltage Xs
It is rewritten to [V] (step S7) and the positional deviation pattern detection process is executed (step S5).

As described above, in the processing shown in the flow chart of FIG. 7, when the difference with the reference value cannot be detected by comparison with the reference value, it is not known whether the pattern is actually detected or the noise is detected. Therefore, the reference value is set again to a level at which the pattern can be clearly detected, and the newly set reference value is applied to the nonvolatile memory (EPROM) 48 each time.
Store again. That is, the reference value stored in the non-volatile memory 48 is updated. The updated value becomes the reference voltage Xm [V] in step S2 in the next positional deviation control.

Such misregistration detection marks 201,2
As a result of detecting the detection of No. 03, when the misalignment of the optical writing position for each color is detected, the front and rear detection marks 201 and 203 are detected, and the front detection mark 201 and the rear detection mark 201 are detected. With respect to, the writing position is corrected until there is no positional deviation. As the correction processing of the writing position, known correction processing as disclosed in the above-mentioned known example is applied.

The correction processing of the writing position by writing the positional deviation detection marks 201 and 203 is performed every time when the preset number of images are formed. Therefore, the number-of-images-formed sheet is counted in advance by the print-sheet counter 47, and the system controller 46 causes the position-adjustment controller to finish after the job being executed at that time has passed the preset number of sheets. The positional deviation pattern detection process is executed for 45, and the writing position is corrected according to the amount of deviation.

In this embodiment, reflection type optical sensors are used as the first and second detecting devices 14 and 15, but if the transfer belt is a light transmitting type, a light transmitting type light sensor is used. Sensors can also be used.

As described above, according to the present embodiment, even if the density of the misregistration detection pattern fluctuates and the detection level from the pattern is lowered to make it difficult to discriminate the detection pattern from noise, the discrimination is performed. By changing the reference value for, it is only necessary to read the next detection pattern and execute the misalignment pattern detection process, so it is possible to detect the misalignment mark without executing the alignment process a plurality of times. Processing time can be shortened.

Further, by using the reference voltage that matches the environment of the machine (image forming apparatus), it is possible to reduce the recalculation process of the reference voltage and shorten the processing time.

[0038]

As described above, according to the present invention, based on the detection result detected by the means for detecting the misregistration detection pattern by comparing with a preset reference value. Since it is provided with a means for changing the reference value, by changing the reference value for detecting the misalignment pattern, even when density fluctuation occurs,
The registration mark detection process can be executed by performing the mark creation process once.

Further, according to the present invention, there is provided a means for storing the reference value, and the reference value stored in the storage means is updated every time the reference value is changed and used as the next reference value. Therefore, it is possible to obtain an optimum reference value for detecting the alignment mark according to the state of use, and efficient processing can be performed.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a tandem type color image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a conveyor belt and a photosensitive drum for each color of the color image forming apparatus of FIG.

FIG. 3 is a perspective view showing a relationship between a positional deviation detection mark transferred onto a conveyor belt and a detection device that detects the mark.

FIG. 4 is a block diagram illustrating an outline of a control circuit of a control device that performs write alignment based on an analog signal detected by a detection device of a tandem type color image forming apparatus according to an embodiment of the present invention.

FIG. 5 is a plan view showing details of misregistration detection marks formed on the conveyor belt according to the embodiment of the present invention.

FIG. 6 is a measurement diagram showing the relationship between the detection level of the detection means and the width of the detected pattern.

FIG. 7 is a flowchart showing a processing procedure for detecting a positional deviation pattern according to the embodiment of the present invention.

[Explanation of symbols]

8 conveyor belt 14,15 Detection device 41 A / D converter 45 Positioning controller 46 system controller 47 Print counter 48 Non-volatile memory (EPROM) 201, 203 Position shift detection mark

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H027 DA21 DA45 DE02 DE07 DE10                       EC03 EC06 ED04 EE07                 2H300 EB04 EB08 EB12 EF02 EF08                       EG02 EG05 EJ09 GG23 QQ10                       RR20 RR38 RR43 RR50 TT03                       TT04 TT05                 5C072 AA03 BA19 QA14 QA17 RA07                       UA11 UA13 UA18                 5C074 AA08 AA10 BB17 DD01 DD15                       DD16 DD24 DD28 EE04 EE12                       FF15

Claims (6)

[Claims] 1. A color image forming apparatus for obtaining a color image by sequentially superposing and transferring an image formed by a plurality of image forming units installed along a conveying body onto a recording medium. Means for forming a plurality of sets of position deviation detection patterns for detecting the position deviation of each color on the carrier, means for detecting the position deviation detection pattern by comparing with a preset reference value, and the detection And a means for changing the reference value based on a detection result detected by the means for performing the image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the reference value is set to a level sufficient to discriminate a detection value from the detection pattern and a detection value other than the detection value. 3. The image forming apparatus according to claim 1, wherein the detecting unit is an optical sensor, and the reference value is a photoelectrically converted voltage value. 4. The image forming apparatus according to claim 1, further comprising a unit that stores the reference value. 5. The reference value stored in the storing means is updated each time the reference value is changed, and is used as a next reference value. The image forming apparatus according to item 1. 6. A means for correcting the positional deviation of the superposed images based on the detection result of the positional deviation detecting pattern, and forming the positional deviation detecting pattern every time a preset number of images are formed. The image forming apparatus according to claim 1, further comprising: a unit configured to perform the positional deviation correction.