JP2002108041A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of surely preventing the occurrence of color slippage and missing of an image. SOLUTION: A main scanning synchronizing signal HSYNC is generated at every belt position of a transfer belt 20 by an image control signal generating part 40 based on the positional fluctuation R(N) at each belt position B(N). That is, the main scanning synchronizing signals HSYNC are continuously generated. Then, the occurrence of the color slippage is surely prevented. Besides, the main scanning synchronizing signal HSYNC is generated by the part 40 in an area other than the maximum plotting area, and also, in between the lower limit of a raster cycle and the upper limit of the raster cycle (within the variable raster cycle extent). Then, the missing of an image is prevented even in the case of continuously changing the cycle of the main scanning synchronizing signal HSYNC (a timing of writing an image).

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 full-color image by superimposing different color images. More specifically, the present invention relates to an image forming apparatus capable of preventing occurrence of image loss and color shift.

[0002]

2. Description of the Related Art In an image forming apparatus for forming a full-color image by superimposing different color images, it is necessary to accurately superimpose each image. Otherwise, color misregistration occurs and image quality is degraded. Such a color shift occurs because the image transfer position of the reference color and the image transfer position of another color are relatively shifted due to speed fluctuation of the transfer belt or the like.

In order to prevent this color shift, the following resist correction is generally performed. That is,
Before image formation, a plurality of resist patterns are formed on the transfer belt, and these are repeatedly sampled at predetermined timing by a resist detection sensor. Further, the amount of resist of another color (for example, cyan, magenta, and yellow) with respect to the reference color (for example, black) is detected from the sampling data thus obtained, and this is divided by the number of times of sampling to calculate the average amount of resist. Then, the resist correction is performed based on the average resist amount.

Further, a technique for improving the accuracy of the resist correction is disclosed in Japanese Patent Application Laid-Open No. 10-148992. In the non-image formation, first, a resist pattern is formed over the entire circumference of the transfer belt. Next, these patterns are repeatedly sampled by a resist detection sensor at a predetermined timing to detect the resist amount at each sampling timing and calculate a representative value of the resist amount. Then, difference data between the resist amount and the representative value at each sampling timing is calculated. On the other hand, at the time of image formation, first, a resist pattern is formed between image forming regions of the transfer belt. Next, these patterns are repeatedly sampled by a resist detection sensor at a predetermined timing to detect the resist amount at each sampling timing, and complement each resist amount with the corresponding difference data. Then, a representative value of the resist amount is calculated using the complemented data.

Thus, during image formation, the amount of change in the resist amount at each sampling timing is canceled by the corresponding difference data, so that even during image formation, the representative amount of the resist amount is at the same level as during non-image formation. The value can be calculated.

[0006]

However, in the technique disclosed in Japanese Patent Application Laid-Open No. H10-148992,
Since the amount of registration at the time of image formation is a representative value, it is not possible to cope with a position change of another color with respect to the reference color due to a speed change of the transfer belt at the image forming position. For this reason, in the sub-scanning direction (transfer belt feeding direction) of the image forming area, there is a problem that a change in magnification of another color with respect to the reference color may occur, causing a color shift.

In order to prevent this, it is necessary to change the image writing timing continuously during image formation. However, when the image writing timing, that is, the period of the main scanning synchronization signal is continuously changed,
There is a problem that it is very difficult to determine the change range. That is, if the period of the main scanning synchronization signal is too long, a deviation occurs in the first pixel of the next line. On the other hand, if the period of the main scanning synchronization signal is too short, image loss will occur.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has as its object to provide an image forming apparatus capable of reliably preventing the occurrence of color misregistration and image loss.

[0009]

According to the image forming apparatus of the present invention which has been made to solve the above-mentioned problems, a plurality of image forming means for forming images of different colors, and the plurality of image forming means are provided. Image control means for controlling the operation of
An endless image carrier for carrying a multicolor image obtained by sequentially superimposing images formed by the respective image forming devices based on the control by the image control device, and a reference position provided on the image carrier for the image carrier. Position detecting means for detecting each time the vehicle travels, and at a plurality of predetermined positions on the image carrier determined based on a detection signal detected by the position detecting means, a positional variation amount of another color with respect to a reference color at each of the predetermined positions. , A position change amount storage unit that stores the position change amount calculated by the position change calculation unit, and a position change at each predetermined position of the image carrier stored in the position change amount storage unit. Image control signal generating means for generating a write start signal of an image in each image forming means for each predetermined position based on the amount, the image control signal generating means, An image writing start signal is generated in each image forming unit within a range limited by the maximum value and the minimum value of the position variation stored in the moving amount storage unit and within a range outside the image forming area. It is characterized by doing.

In this image forming apparatus, a plurality of image forming means for forming images of different colors, an image control means for controlling the operation of the plurality of image forming means, and each image forming means based on the control by the image control means. And an endless image carrier that carries a multicolor image formed by sequentially superimposing images formed by the means, so that a multicolor image can be formed. Here, when the image carrier carries a multi-color image sequentially superimposed, it may be carried directly on the image carrier or indirectly via a recording body.

In order to form a multi-color image by superimposing images of different colors in this manner, the image forming apparatus performs the following control so that images of each color can be superimposed accurately. First, the reference position provided on the image carrier is detected by the position detecting means every time the image carrier makes one revolution. Then, at the time of non-image formation, at a plurality of predetermined positions on the image carrier determined based on the detection signal detected by the position detecting means by the position variation calculating means, the position of another color with respect to the reference color at each predetermined position. A variation is calculated. The position change amount calculated by the position change amount calculation means is stored in the position change amount storage means. Note that the non-image formation includes not only a state where image formation is not performed but also a state immediately after the power of the image forming apparatus is turned on.

Here, the position variation calculating means calculates the position variation at each predetermined position of the image carrier based on a resist pattern created over the entire circumference of the image carrier by the image forming means during non-image formation. What should I do?

At the time of image formation, the image control signal generating means generates an image writing start signal in each image forming means on the basis of the position fluctuation amount at each predetermined position of the image carrier stored in the position fluctuation amount storing means. It is generated for each predetermined position. That is, a write start signal after color shift correction is generated for each predetermined position. For this reason, color shift correction can be reliably prevented.

The image writing start signal generated by the image control signal generating means in each image forming means is within a range limited by the maximum value and the minimum value of the positional variation stored in the variation storing means. And is generated in a range outside the image forming area. Therefore,
Even if the image writing start signal is generated for each predetermined position, that is, continuously changed, no image loss occurs.

In the image forming apparatus according to the present invention, the image carrier may carry a recording body on which an image is recorded. That is, the present invention can be applied not only to an electrophotographic image forming apparatus but also to an image forming apparatus such as an ink jet method or a silver salt method. In the case of the electrophotographic system or the ink jet system, paper is mainly used as a recording body, and in the case of the silver halide system, photosensitive paper is mainly used as a recording body.

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a preferred embodiment of an image forming apparatus according to the present invention. As shown in FIG. 1, an image forming apparatus 10 according to the present embodiment includes image forming units 11Bk and 11Bk.
C, 11M, and 11Y, a transfer belt 20, an image control unit 30, an image control signal generation unit 40, a belt position detection sensor BS, and two registration detection sensors RS.

Image forming units 11Bk, 11C, 11M, 1
1Y forms an image (including a resist pattern) on the transfer belt 20. Each image forming unit 11Bk,
11C, 11M, and 11Y have write units 12Bk, 1
2C, 12M, 12Y, photosensitive drums 13Bk, 13
C, 13M, and 13Y, and peripheral devices (e.g., a charger, a developing device, a transfer charger, and a cleaner). Then, each image forming unit 11Bk, 11C, 1
1M and 11Y, each writing unit 12Bk, 12C, 1
Each photoconductor drum 13Bk, 13
The latent images written on the surfaces of C, 13M, and 13Y are visualized as toner images, and the toner images are transferred onto the transfer belt 20. At this time, the toner images of different colors are sequentially transferred by the image forming units 11Bk, 11C, 11M, and 11Y in a superimposed manner on the transfer belt 20 to form a multicolor image. Note that each of the writing units 12Bk, 12C, 12M, and 12Y has LE
A D array is used.

The transfer belt 20 travels in the direction of the arrow in FIG. 1 by the rotation of the drive roller 21, and is an endless belt wound around the drive roller 21 and two driven rollers 22 and 23. . On the traveling path of the transfer belt 20, one belt position detection sensor BS and two registration detection sensors RS are provided. The belt position detection sensor BS detects a reference position provided on the transfer belt 20 and outputs a pulse signal every time the transfer belt 20 makes one rotation. Further, the registration detection sensor RS is provided for each of the image forming units 11Bk, 11C, 11M, 11
Y detects a resist pattern formed on the transfer belt 20. Here, the two registration detection sensors RS are arranged in parallel in the main scanning direction (the direction orthogonal to the traveling direction (sub-scanning direction) of the transfer belt 20). That is, one is arranged at the front and one at the back of the paper. Thereby, the resist patterns RP formed on both ends of the transfer belt 20 as shown in FIG. 2A can be sampled.

The resist pattern RP is formed over the entire circumference of the transfer belt 20 by the image forming units 11Bk, 11C, 11M, and 11Y during non-image formation.
The total length when the transfer belt 20 is unfolded is about 960 mm
It is. The resist pattern RP has a pattern formed at regular intervals in the order of black (Bk), cyan (C), magenta (M), and yellow (Y) as shown in FIG. It is something that is repeated. In the present embodiment, the length of the repeating unit pattern (see FIG. 2B) in the resist pattern RP is about 16 mm. That is, the transfer belt 20 is configured so that an integral multiple of the unit pattern becomes the entire length of the transfer belt 20.

The image control section 30 is provided for each image forming section 11B.
k, 11C, 11M, and 11Y, an image signal of an image to be recorded on a recording medium is given, and each image forming unit 1
1Bk, 11C, 11M, and 11Y are controlled. For this reason, the image control unit 30
Is connected to the scanner 32 and the controller 33 via
An image signal or the like is obtained from these.

The image control unit 30 is connected to an image control signal generation unit 40 for generating a main scanning cycle signal for instructing a timing to start writing an image in each of the image forming units 11Bk, 11C, 11M and 11Y. . The image control unit 30 also plays a role of “position fluctuation amount calculating means” described in the claims. For this reason, the image control signal generation unit 40
3 includes a pixel counter 41, a comparator 42, an address counter 43, a calculator 44, a main scanning cycle signal generator 45, and a selector 46, as shown in FIG.

The pixel counter 41 has a pixel clock CLK.
Outputs a counter value DCT that is incremented by. Then, when the output signal LINE input to the terminal LD becomes “Low”, the counter value is reset. Here, the counter value DC
The minimum value of T is larger than the number of pixels in the maximum drawing area in the main scanning direction and larger than the minimum value of the variable main scanning cycle setting value PB that is changed based on the position variation information DAT. Also,
The maximum value of the counter value DCT is smaller than the maximum value of the variable main scanning cycle set value PB that is varied based on the position variation information DAT.

The comparator 42 determines whether or not a counter value DCT output from the pixel counter 41 matches a main scanning synchronization signal set value PD output from a selector 46 described later. Then, when the counter value DCT matches the main scanning synchronization signal set value PD, the output signal LINE is set to “Low”.

The address counter 43 outputs an address signal ADR which is incremented by the main scanning cycle signal HSYNC and reset by the belt position signal E. Note that the belt position signal E is a reference position pulse output from the belt position detection sensor BS. Then, the address signal ADR output from the address counter 43 is input to the position variation storage unit 47.

The computing unit 44 calculates a variable main scanning cycle set value PB by adding and subtracting the position variation information DAT to and from the main scanning cycle set value PA. Specifically, in the arithmetic unit 44, the variable main scanning cycle set value PB is set according to the flowchart shown in FIG. First, arithmetic unit 4
4 shows the main scanning period signal PA and the position fluctuation amount R (= DAT).
Is input (S1). Then, the first set value TP is calculated by equation (1) (S2). TP = PA + R (1)

Next, it is determined whether or not the position variation R input to the calculator 44 is positive (S3). If the position fluctuation amount R is positive (S3: YES), it is determined whether or not Expression (2) is satisfied (S4). TP ≧ PA + Ws (2) Here, Ws is a maximum drawing area start address, and indicates a start counter value of an effective drawing area from the fall of the main scanning cycle signal HSYNC.

If equation (2) holds, then (S
4: YES), the variable main scanning cycle set value PB is determined by equation (3). PB = PA + Ws-1 (3) On the other hand, if the equation (2) is not satisfied (S4: NO), the variable main scanning cycle set value PB is determined by the equation (4). PB = TP… (4)

If the position variation R input to the calculator 44 is negative (S3: NO), it is determined whether or not the equation (5) is satisfied (S7). TP ≦ We (5) Here, We is the maximum drawing area end address, and indicates the end counter value of the effective drawing area from the fall of the main scanning cycle signal HSYNC. .

If equation (5) holds, then (S
7: YES), the variable main scanning cycle set value PB is determined by equation (6) (S8). PB = We + 1 (6) On the other hand, if Expression (5) is not satisfied (S7: NO), the variable main scanning cycle set value PB is determined by Expression (4) (S7).
6). In this way, the calculator 44 calculates the variable main scanning cycle set value PB.

Returning to FIG. 3, the main scanning period signal generating section 45
Is a counter value DCT output from the pixel counter 41.
, The main scanning period signal HSYNC is continuously generated. For example, when the pixel counter DCT is “1”, the main scanning cycle signal generation unit 45 changes the main scanning cycle signal HSYNC from “High” to “Low”, and sets the counter value DCT to “register setting value (for example, "3
2 ")", the main scanning cycle signal HSYNC is set to "Lo".
What is necessary is just to comprise the flip-flop circuit which changes from "w" to "High".

Here, as described above, the counter value DC
T is larger than the number of pixels in the maximum drawing area in the main scanning direction and larger than the minimum value of the main scanning cycle set value PB. Also,
The maximum value of the counter value DCT is smaller than the maximum value of the main scanning cycle set value PB that is changed based on the position variation information DAT. Thus, the main scanning cycle signal generation unit 45 generates the main scanning cycle signal HSYNC in a range other than the drawing area and limited by the lower limit and the upper limit of the raster cycle.

The selector 46 has an image formation selection signal SEL.
, The main scanning cycle setting value PA preset based on the ideal machine system speed or the variable main scanning cycle setting value PB that is varied by the position variation information DAT is selected. Note that the image formation selection signal SEL is a signal indicating whether the image forming apparatus 10 is “at the time of non-image formation” or “at the time of image formation”. The value selected by the selector 46 is input to the terminal B of the comparator 42 as the main scanning cycle set value PD. Specifically, during non-image formation, PA is selected as the main scanning cycle set value PD. On the other hand, when an image is formed, PB is selected as the main scanning cycle set value PD.

Next, the operation of the image forming apparatus 10 configured as described above will be described. During non-image formation,
The resist pattern RP shown in FIG. 2A is formed (see FIG. 5A). Here, the interval of each color of the resist pattern RP is not always kept constant due to a speed variation of the transfer belt 20 or the like. That is, for example, FIG.
As shown in (b), when black (Bk) is used as a reference, a position change (position shift) occurs in cyan (C). Then, the resist pattern RP formed on the transfer belt 20 is repeatedly sampled at regular time intervals by the resist detection sensor RS. Thus, sampling data of each color is captured. Then,
The position variation amount R (N) with respect to the reference color is calculated by equation (7). R (N) = (d (i) −d0 (i)) − Rav (7) where d (i) is a distance calculated from sampling data at each belt position, and d0 (i) is This is the ideal distance at the belt position, and Rav is the average value of the amount of position variation over the entire circumference of the transfer belt 20.

As a result, as shown in FIG. 5A, the position fluctuation amount R at each belt position B (N): B (0) to B (N) is obtained.
(N): R (0) to R (N) are obtained. Then, as shown in FIG. 6, these position fluctuation amounts R (N) are calculated for each belt position B (N).
Are stored in the position fluctuation amount storage unit 47 in a state corresponding to. Note that each belt position B (N) corresponds to the address signal ADR, and the position variation R (N) corresponds to DAT. Also,
Here, the data is sampled only for one round of the transfer belt, but the accuracy of the position variation R (N) can be improved by sampling data for several rounds of the transfer belt. As a result, the accuracy of the resist correction (color shift correction) is also improved.

When the image forming apparatus 10 forms an image, the position change amount R stored in the position change amount
(N) is read out according to each belt position B (N), and the main scanning synchronization signal HSYNC is generated by the image control signal generation unit 40 based on the data. As a result, an electrostatic latent image is written on each of the photosensitive drums 13Bk, 13C, 13M, and 13Y so that color shift does not occur between the colors. Therefore, the toner images of the respective colors that are superimposed and transferred on the transfer belt 20 are accurately superimposed, and a high-quality multicolor image without color shift is formed.

Further, the main scanning synchronizing signal HSYNC is supplied from the image control signal generating section 40 to the main scanning cycle signal generating section 4.
5 is continuously generated based on the counter value DCT output from the pixel counter 41. Then, the pixel counter DCT is larger than the number of pixels in the maximum drawing area in the main scanning direction and larger than the minimum value of the variable main scanning cycle set value PB. Further, the maximum value of the counter value DCT is smaller than the maximum value of the variable main scanning cycle setting value PB. As a result, the main scanning cycle signal HSYNC generated by the main scanning cycle signal generation unit 45 is outside the maximum drawing area and between the lower limit of the raster cycle and the upper limit of the raster cycle (variable in the raster cycle), as shown in FIG. Within the range). Therefore, even if the period of the main scanning synchronization signal (image writing timing) is continuously changed, image loss does not occur.

As described above in detail, according to the image forming apparatus 10 according to the present embodiment, the image control signal generating section 40 performs the following for each belt position of the transfer belt 20.
The main scanning synchronization signal HSYNC is generated based on the position variation R (N) at each belt position B (N). That is, the main scanning synchronization signal HSYNC is continuously generated.
As a result, the occurrence of color shift is reliably prevented. Also,
The main scanning cycle signal HSYNC generated by the main scanning cycle signal generating section 40 is generated outside the maximum drawing area and between the lower limit of the raster cycle and the upper limit of the raster cycle (within the variable range of the raster cycle). Therefore, the main scanning synchronization signal HSYN
Even if the cycle of C (image writing timing) is continuously changed, no image loss occurs.

The present embodiment is merely an example, and does not limit the present invention. Therefore, of course, the present invention provides various improvements without departing from the gist thereof.
Deformation is possible. For example, in the above-described embodiment,
LE is applied to each of the writing units 12Bk, 12C, 12M, and 12Y.
Although a D array is used, a laser can also be used. However, when a laser is used, the linearity in the main scanning direction is inferior to that of the LED array. Therefore, it is desirable to arrange three or more resist detection sensors RS in the main scanning direction. Accordingly, the resist detection sensor R
Needless to say, it is necessary to create the same number of resist patterns RP as S.

The image forming unit 11 (color codes Bk, C,
M and Y are omitted), an image forming apparatus using an ink jet head (ink jet method), an image forming apparatus using a silver salt exposure head (silver salt method), or image forming using a photosensitive belt instead of a photosensitive drum In the device,
Of course, the present invention can be applied, and the above-described effects can be obtained.

[0040]

As described above, according to the present invention, there is provided an image forming apparatus capable of reliably preventing color misregistration and image defects.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment.

FIG. 2 is a diagram showing a shape of a resist pattern. FIG.
2A is a view showing the entire resist pattern, and FIG.
(B) is a diagram showing a repeating unit pattern.

FIG. 3 is a block diagram illustrating a configuration of an image control signal generation unit.

FIG. 4 is a flowchart illustrating a method of calculating a variable main scanning cycle set value in a computing unit.

FIG. 5 is a diagram illustrating an operation of detecting a position variation amount.

FIG. 6 is a diagram for explaining a data storage state in a position change storage unit.

FIG. 7 is a diagram for explaining a generation range of a main scanning cycle signal.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 image forming apparatus 11 image forming unit 12 writing unit (LED array) 13 photoreceptor drum 20 transfer belt 30 image control unit 40 image control signal generation unit 47 position fluctuation amount storage unit BS belt position detection sensor RS registration detection sensor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 21/14 F term (Reference) 2C162 AE04 AE12 AE19 AE28 AE47 AE69 AF13 AF54 AF62 AF69 AF82 AF92 FA17 FA50 2H027 DA21 DE07 DE10 EB04 EC03 EC06 EC07 ED04 EE02 EE07 EF06 EF09 ZA07 2H030 AA01 AB02 AD11 AD17 BB42 BB44 BB56

Claims (2)

[Claims] A plurality of image forming units for forming images of different colors; an image control unit for controlling operations of the plurality of image forming units; and a plurality of image forming units formed based on control by the image control units. An endless image carrier that carries a multicolor image in which images to be sequentially superimposed, and a position detection unit that detects a reference position provided on the image carrier for each rotation of the image carrier. At a plurality of predetermined positions on the image carrier determined based on the detection signal detected by the position detection unit, a position fluctuation amount calculation unit that calculates a position fluctuation amount of another color with respect to a reference color at each predetermined position, A position change amount storage means for storing the position change amount calculated by the position change calculation means; and a predetermined position of the image carrier stored in the position change amount storage means. Image control signal generating means for generating an image writing start signal in each of the image forming means for each of predetermined positions based on the amount of position fluctuation in the image forming means, wherein the image control signal generating means comprises: Generating an image writing start signal in each of the image forming units within a range limited by the maximum value and the minimum value of the positional variation amount stored in the image forming unit and outside the image forming area. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein the position variation calculating unit is configured to calculate the position variation based on a resist pattern created on the image carrier by the image forming unit during non-image formation. An image forming apparatus that calculates a position variation amount at each predetermined position.