JP2006220823A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for reducing color shift during forming color images (overlapping images). <P>SOLUTION: The image forming apparatus starts to perform delay of writing timing or beam selection so as to minimize a difference between an image formation start time for a mark reference of a second color and a image formation start time of a first color; finds an average start time tc1 of the image formation start time for the mark reference of the first color and the second color and starts to perform delay of writing timing or beam selection so as to minimize a difference between an image formation start time for a mark reference of a third color and the average image formation start time tc1; finds the image formation start time for the mark reference of the third color and an image formation start time tc2 with tc1 found precedently and starts to perform delay of writing timing or beam selection so as to minimize a difference between an image formation start time for a mark reference of a fourth color and the average image formation start time tc2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus, and more particularly to dot alignment in the sub-scanning direction of an image head in an image forming apparatus using an intermediate transfer member.

  Conventionally, in a color image forming apparatus, a process of forming an image on a scanned object by a scanning type writing unit and transferring the image onto an intermediate transfer body is repeated a plurality of times for each color, and the images are sequentially overlapped for each color. An image is formed (see FIG. 1).

  In the image forming apparatus shown in FIG. 1, a charging unit 2, a writing unit 3, a developing unit 4, a transfer unit 5, and a cleaning unit 6 are disposed around an image carrier 1 that is a scanned body. An intermediate transfer member 7 in the form of a belt or the like is disposed above the carrier 1. The intermediate transfer body 7 has a mark indicating the image formation start reference position.

Next, the operation of the image forming process of this image forming apparatus will be described.
The surface of the image carrier 1 rotating in the direction of the arrow is charged by the charging means 2. When the mark on the intermediate transfer member 7 is detected, the writing means 3 starts exposure based on the image data, and a latent image is formed on the image carrier 1. The latent image is visualized as a toner image by the developing unit 4 and transferred to the intermediate transfer member 7 by the transfer unit 5 at a contact point with the intermediate transfer member 7. After the transfer, the image carrier 1 is cleaned of residual toner by the cleaning means 6.

In the case of forming a color (multiple color) image, the above steps of developing with different colors are repeated for the required number of times by switching the developing means with the switching means, and the images of the respective colors are superimposed on the intermediate transfer member 7. .
The image superimposed on the intermediate transfer member 7 is transferred to a recording medium such as paper by another transfer means, and the fixed recording medium is discharged out of the apparatus.

  Here, the image formation of each color is started with reference to the mark on the intermediate transfer body 7, but when the writing means 3 is a scanning type using a laser scanning optical system, the mark detection and writing means on the intermediate transfer body 7 are used. Since the synchronization signal serving as the writing reference 3 is asynchronous, even if the image formation is started based on the mark reference of the intermediate transfer body 7, the superimposed images of the respective colors are displaced.

With respect to such a problem, in Patent Document 1, a means for generating a recording start signal in the sub-scanning direction, a means for receiving a light beam from the scanning means and generating a main scanning synchronization signal, and the main scanning. A means for detecting a time difference between the synchronization signal and the recording start signal, and a light source used for image recording of the first first line in accordance with the signal from the detection means, and a signal from the detection means Accordingly, the image recording of the first line is delayed. Accordingly, it is possible to reduce the vertical registration shift (color shift) generated between pages because the main scanning synchronization signal and the recording start signal for determining the recording start position in the sub-scanning direction are asynchronous.
Japanese Patent Laid-Open No. 11-212009

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that further reduces color misregistration when forming a color image (superimposed image).

  In order to solve the above-described problem, the invention described in claim 1 is provided with a plurality of beams arranged in the sub-scanning direction with a mark serving as an image formation start reference for each color provided on an intermediate transfer member, and based on the mark detection signal. A plurality of processes for each color to start image formation of each color by a scanning writing unit having a toner image, generate a toner image from a latent image formed on an image carrier by a developing unit, and transfer the toner image onto an intermediate transfer member In an image forming apparatus that forms a color image by repeatedly overlapping the toner images for each color, the difference between the image formation start time with respect to the mark reference for the second color and the image formation start time for the first color is minimized. As described above, the write timing is delayed or beam selection is started, and the average start time tc1 of the image formation start time with respect to the mark reference for the first and second colors is obtained. Is started by delaying the write timing or selecting a beam so that the time difference between the image formation start time with respect to the image and the average image formation start time tc1 is minimized. An average image formation start time tc2 with respect to the calculated tc1 is obtained, and a write timing delay or beam selection is performed so that the time difference between the image formation start time with respect to the fourth color mark reference and the average image formation start time tc2 is minimized. It is characterized by starting with.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, a write timing delay or beam selection is performed so that a time difference between the average image formation start time tc1 of the first color and the second color is minimized. When the image formation start time of the third color obtained by control deviates from the fluctuation (variation) width of the image formation start time with respect to the mark reference of the already formed first and second color images, the minimum or maximum value of the change width Assuming a start time that is advanced or delayed in the sub-scanning direction by a predetermined beam from the deviation from the above and the time obtained by the write timing delay or beam selection control, the minimum or maximum value of the fluctuation range at that time And the image formation start time with respect to the mark reference for the third color is started. The average image formation start time tc2 with respect to tc1 obtained in the above is obtained, and the image formation start time of the fourth color obtained by delaying the write timing or beam selection control so that the time difference with the average image formation start time tc2 is minimized. If the fluctuation range of the image formation start time with respect to the mark reference of the first to third color images that have already been formed deviates from the minimum value or the maximum value of the fluctuation range, the write timing is delayed or beam selection control is used. Assuming a start time that is advanced or delayed in the sub-scanning direction by a predetermined beam from the determined time, the deviation from the minimum value or maximum value of the fluctuation range at that time is compared, and the image formation start time when the deviation becomes smaller In this case, image formation is started.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, when the number of beams of the writing unit is n and the period of the write synchronization signal generated every time the writing unit scans is T, The first (first color) image formation is started after a time of (2n-1) T / 2n or more has elapsed with respect to the mark reference.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the first, second, or third aspect, the number of beams of the writing unit is n, and the period of the write synchronization signal generated every time the writing unit scans is T. In this case, the write timing is delayed when the difference from the previously formed image at the image start time with respect to the mark reference is (2n-1) T / 2n or more, and (2n-1) T / 2n is more than T / 2n. It is characterized in that the beam selection is performed when the number is less than.

  According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, when a beam is selected, a pseudo synchronization signal is set to obtain an image formation start time.

  According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the period T of the write synchronization signal used as a reference for obtaining the write start time is obtained by one rotation of the rotary polygon mirror. It is characterized in that it is an average of a plurality of synchronization signal periods.

  According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the writing used as a reference for obtaining the write start time by obtaining the period of the synchronization signal for each surface of the rotary polygon mirror The period T of the synchronization signal is set to a period corresponding to the surface used at the start of writing.

  According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, the image forming apparatus includes a plurality of image forming units arranged to face the moving surface of the intermediate transfer member. The image forming start signal of each image forming unit is generated at intervals equal to n equal to the time during which the intermediate transfer member moves the distance between the image forming units.

  According to the ninth aspect of the present invention, a mark serving as an image formation start reference for each color is provided on the intermediate transfer member, and each color is read by a scanning type writing unit having a plurality of beams arranged in the sub-scanning direction based on the mark detection signal. The toner image is generated from the latent image formed on the image bearing member by the developing means, and the process of transferring the toner image onto the intermediate transfer member is repeated a plurality of times for each color. In an image forming apparatus that forms a color image by superimposing each time sequentially, a mark detection unit that detects a mark on the intermediate transfer member, and an elapsed time after the mark detection is measured each time a mark that serves as an image formation start reference is detected In addition, the measurement unit that stops measurement during the image formation period of each color, initializes it, and waits for the measurement until the next color image formation instruction, and the writing unit after mark detection when the first color image is formed are generated. First storage means for storing and holding the measurement time of the measurement means up to the synchronization signal, and first determination means for comparing the value of the first reference value set in advance with the value of the first storage means and determining the magnitude thereof First synchronization means generated by the first addition means for adding and updating the first time obtained in advance to the first storage means based on the result of the first determination means and the writing means after mark detection when the second color image is formed Second storage means for storing and holding the measurement time of the measurement means up to the signal, and calculation means for obtaining a difference between the values of the updated first storage means and the second storage means reflecting the result of the first determination means And a second determination means for comparing the difference obtained by the computing means with a first reference value and a second reference value set in advance and determining the magnitude thereof, and either the first or the second obtained in advance Based on the result of the second determination means, the second memory Second addition means for adding and updating, first average storage means for obtaining and storing an average value of the updated first storage means and second storage means, and at the time of forming the third color image, after mark detection The third storage means for storing and holding the measurement time of the measurement means up to the first synchronization signal generated by the writing means, and the arithmetic means obtains the difference between the values of the third storage means and the first average storage means, and the difference Is determined by the second determining means, and based on the result, the third adding means is added and updated with the previously obtained value by the second adding means, and the first average storing means and the updated third A second average storage means for obtaining and storing an average value of the values of the storage means, and a second storage means for storing and holding the measurement time of the measurement means up to the first synchronization signal generated by the writing means after mark detection at the time of image formation for the fourth color 4 storage means and the arithmetic means for the fourth storage hand The difference between the values of the stage and the second average storage means is obtained, and the magnitude of the difference is judged by the second judgment means, and the write timing is determined based on the result of the first judgment means or the second judgment means. And a data selection output control means for selecting or switching the output of image data input from the outside based on the result of the second determination means, and for forming the first color image, As a result of 1 determination means, when the elapsed time is determined to be greater than the first reference value, it synchronizes with the synchronization signal of the writing means, and when the elapsed time is determined to be small, starts with the next synchronization signal, The image formation for the second and subsequent colors is started by delaying the write timing or selecting the beam according to the result of the second determination means. When the beam is selected, the data selection output control means selects the data. It is characterized by performing a switching output.

  According to a tenth aspect of the present invention, in the image forming apparatus according to the ninth aspect, at the time of image formation for the third and subsequent colors, the image formation has already been completed with the values of the first storage means, the second storage means and the third storage means. The start variation width detecting means for obtaining the fluctuation width of the recording start time from the minimum value and the maximum value, and the formation start time of the third color obtained by selecting the write timing delay or beam according to the result of the second determination means. A range determination unit that determines whether the value of the third storage unit corresponding to the fourth storage unit value corresponding to the formation start time of the fourth color is within the start variation range, or smaller or larger than the variation range A first difference calculating means for obtaining a difference between the value of the third storage means or the value of the fourth storage means and the time width obtained by the start fluctuation width detecting means; and the value of the third storage means or of the fourth storage means The range judgment to the value Addition / subtraction means for adding and subtracting a value obtained in advance based on the stage result to obtain a correction start time, and second difference calculation means for obtaining a difference from the time width obtained by the start fluctuation width detection means of the correction start time obtained by addition / subtraction And a third determination unit that determines the smaller of the results of the first difference calculation unit and the second difference calculation unit, and delays the writing timing in the image formation for the third and subsequent colors according to the result of the second determination unit. Alternatively, when the start time selected by the beam is out of the range obtained by the start fluctuation range detection means, image formation is started at either the image start time or the correction start time determined by the result of the second determination means according to the determination of the third determination means. It is characterized by doing.

  According to an eleventh aspect of the present invention, in the image forming apparatus according to the ninth or tenth aspect, the first time or the second time obtained in advance is a write synchronization signal used as a reference for obtaining a write start time. Is determined based on an average of a plurality of synchronization signal periods obtained by one rotation of the rotating polygon mirror or a period corresponding to the surface used at the start of writing by obtaining the period of the synchronization signal for each surface of the rotating polygon mirror. It is characterized by seeking.

  A twelfth aspect of the present invention is the image forming apparatus according to any one of the first to eleventh aspects, comprising a plurality of intermediate transfer members and a plurality of image forming means arranged facing the moving surface of the intermediate transfer member, The image forming means selectively selects one image carrier, one writing means, at least two developing means for developing the electrostatic latent image formed on the image carrier by the writing means, and the developing means. And switching means for driving.

According to the present invention, it is possible to further improve the color misregistration while improving the reliability of the head position misalignment (color misregistration) reduction control of the superimposed image.
Further, even a small, high-speed and low-cost image forming apparatus can form a high-quality image with reduced misalignment (color shift) of the superimposed image.

Hereinafter, preferred embodiments according to an image forming apparatus of the present invention will be described with reference to the drawings.
Each embodiment described below will be described as applied to the image forming apparatus shown in FIG.

<Embodiment 1>
FIG. 2 is an example of the relationship between the image formation start signal in the sub-scanning direction generated by detecting the mark on the intermediate transfer body 7 and the synchronization signal of the writing unit 3.
The time difference between the image formation start signal (A) and the synchronization signal is shifted by a maximum of the synchronization signal period T as shown in (B) and (C).
When the reference (first) image formation is performed with the synchronization signal p1 at the timing shown in FIG. 2B, the image formation timing outside the reference image (after the second color) starts with the synchronization signal p2 as shown in (C). If this happens, timing correction will not be performed, and a deviation of a maximum of one scan (Δt) will occur.

Therefore, first, the reference (first) image formation is performed from the synchronization signal after a certain time has elapsed after the detection of the image formation start signal.
FIG. 3 shows an example of dot formation positions when a plurality of beams are two beams (gray beam, white beam). The gray beam is the preceding (starting) side beam of the sub-scanning.

  In the first color (reference) image formation, after the image formation start (belt mark) signal in the sub-scanning direction is detected, the synchronization signal occurs after 3T / 4 (where T is the synchronization signal period) or more. First, image formation of the first color is started with the synchronization signal. In the case of FIG. 3, since t1> 3T / 4, the operation starts in synchronization with the first synchronization signal.

  As shown in the figure, in the second color, when the synchronization signal p1 is generated at the time t2 after the mark detection, the synchronization delayed by one scan so that the difference Δt (absolute value) from the writing start position of the first color is minimized. Image formation is started by the signal p2. The image formation start time from the belt mark signal at this time is t2 + T. Here, the average tc1 (centroid synchronization 1) of the image formation start times of the first and second colors is tc1 = (t1 + t2 + T) / 2.

In the third color, image formation is started by beam selection (white beam: L1) so that the time difference Δt between the average start time tc1 of the first and second colors and the start time of the third color is minimized. At this time, a pseudo synchronization signal (a dotted line between the gray beam (Du) and the white beam (L1) in FIG. 3) is assumed as the third color image formation start synchronization signal for the selected white beam L1. Therefore, the image formation start time with respect to the mark reference for the third color is t3 + T / 2.
The average tc2 (centroid synchronization 2) between tc1 and the image formation time of the third color is tc2 = (tc1 + t3 + T / 2) / 2.

  In the fourth color, the time difference Δt between the time t4 from the belt mark signal to the synchronization signal and the average image formation start time tc3 up to the third color is smaller than the time difference when delay or beam selection is performed. Therefore, image formation is started as it is.

The criteria for determining the write start position in the example of FIG. 3 are: when the time difference Δt is Δt ≧ 3T / 4, one scanning delay is selected. When T / 4 ≦ Δt <3T / 4, the beam (subsequent) is selected. Δt <T In the case of / 4, it remains as it is.

FIG. 4 is an example showing the difference in beam control between the prior art disclosed in Patent Document 1 and the present invention. In the same figure, when the time difference between the mark reference signal and the synchronization signal is less than T / 4 for the first color, T / 4 or more for the second color and less than 3T / 4 for the third color, and 3T / 4 or more for the fourth color. The beam head position is shown.
In the case of the prior art, gray is the head beam position, and the head beam variation range of each color is a dotted frame.
In the case of the first embodiment, unlike the prior art, the black circles are selected for the second and fourth image head beams, and the variation range can be reduced as shown by the solid line frame. That is, it is possible to reduce the start position shift (color shift) of the superimposed image.
In addition, when a beam is selected, an image formation start time that can reduce the leading color shift of the superimposed image can be easily obtained by setting a pseudo synchronization signal.

<Embodiment 2>
An example of the second embodiment that can further reduce the deviation of the head position of the superimposed image of the first embodiment will be described with reference to FIG.
The relationship between the initial sync signal of each color and the dot position with respect to the belt mark signal (top signal waveform) when the sync signal period T is 100 is shown. The time difference from the belt mark signal to the first synchronization signal is shown to the left of the dotted line indicating when the belt mark is generated, and the leading dot formation position (time) by the control method of Embodiment 1 described above is shown to the right of the dot. The image is formed in the order of C (cyan), Y (yellow), M (magenta), and K (black) from the top. FIG. 5 shows only the beam position that is the head of actual image formation out of the two beams for easy understanding. The black solid line is the boundary between the two beams (the preceding beam and the succeeding beam) that are scanned at one time and the dotted line is scanned at a time. Only M (magenta) of the third color indicates that the subsequent beam is selected.

Control will be described.
Since the time difference Δt between the second color (yellow) and the first color (cyan) is Δt = 98−76 = 22 (<T / 4 = 25), the second color (yellow) starts image formation as it is.

A time difference Δt = 87−57 = 30 (> T /) between the synchronization signal generation time (t3 = 57) of the third color (magenta) and the average start time tc1 = (76 + 98) / 2 = 87 between the first color and the second color 4) Therefore, the dot position (107 = 57 + T / 2) obtained by selecting the subsequent beam and delayed by one dot is obtained as the image formation start position.
Here, the beam selected position (107) is outside the range of the image formation start time (76 to 98) with respect to the previously formed cyan and yellow mark standards, but is a time one dot earlier than the beam selected position. Is 57, and the difference (19 = 76−57) from cyan 76 which is the minimum value of the image formation start time formed earlier is 98 and yellow which is the maximum value of the image formation start time. Therefore, the image formation is started at the beam selection time. At this time, the average start time tc2 of tc1 and magenta = (87 + 107) / 2 = 97.

  Since the time difference Δt between the fourth color (black) synchronization signal generation time (t4 = 20) and the average start time tc2 = 97 until the third color is Δt = 97−20 = 77 (> 3T / 4), one scan The dot position (120 = 20 + T) delayed by the minute is obtained as the image formation start position.

Here, the dot position (120) delayed by one scan is outside the range of the image formation start time (76 to 107) with respect to the previously formed cyan, yellow and magenta mark standards, and the maximum value of magenta is the maximum value. The difference from the start time 107 is 13.
However, the time that is one dot earlier from the dot position delayed by one scan (dotted white circle in the figure) is 70, and the difference from the cyan start time 76, which is the minimum value of the image formation start time, is 6. Since it is smaller than the difference between the dot position delayed by one scan and the maximum value of the image formation start time, image formation is started at the dotted white circle time of FIG.

Thus, the variation amount of the leading dot position can be reduced to 107−70 = 37.
(The variation amount of the leading dot position when black is formed at the dot position delayed by one scan is 120−76 = 44)
Thus, by controlling the leading dot position, the leading position deviation of the superimposed image can be further reduced as compared with the first embodiment.

<Embodiment 3>
Next, Embodiment 3 will be described.
The synchronization signal period T, which is the determination criterion of the above-described embodiment, is a period of a signal generated when the light beam deflected and scanned by the rotating polygon mirror scans the synchronization detector, and is determined by the surface of the rotating polygon mirror. Time is different. For example, when the rotary polygon mirror has six surfaces, strictly speaking, there are six synchronization signal periods.
Changing the synchronization signal period means changing the scanning time, so it seems that the scanning width in the sub-scanning direction changes, that is, the dot diameter formed in the sub-scanning direction changes over the main scanning width. be able to.

FIG. 6 schematically shows the relationship between the scanning time and the scanning width (dot diameter) in the sub-scanning direction. Arrow A is the main scanning direction, and arrow B is the belt movement (sub-scanning) direction.
When the scanning time is 1a, the belt movement amount during the scanning of the beam from the scanning start end S to the scanning end E is small, so the inclination of the scanning line becomes small. In addition, when the scanning time is 1b, the inclination of the scanning line increases.

  Considering the amount of belt movement from a certain scan start position to the next scan start position at the scan start end S as a dot line (diameter) formed by the scan beam, as shown in FIG. In this case, the dot diameter in the sub-scanning direction is small (thin), and in the case of scanning 1b with a long scanning time, the dot diameter can be regarded as large (thickening).

  In order to simplify the explanation, consider a case in which the synchronization signal cycle fluctuates between 96 and 104 with a two-beam writing means. Here, as shown in FIG. 7, when the synchronization signal of the second color is generated earlier by the time 25 with respect to the first dot position (gray) of the first color, the synchronization signal period T, which is a criterion, is assumed to be T = Assuming that 104 is set, T / 4 is 104/4 = 26, so that the beam A having a time difference Δt = 25 from the first color is valid as the head beam. At this time, if the synchronization signal period of the head of the second color is actually T = 96, the dot diameter can be regarded as 48, and the second color following beam B with the head dot (gray) of the first color can be considered. The deviation amount is 23, and the deviation amount can be reduced by selecting the subsequent beam B.

  Here, when the synchronization signal period serving as a determination reference is an average synchronization signal period 100, the determination reference is T / 4 = 25, and therefore the subsequent beam B is selected as the first beam of the second color. The amount of deviation can be reduced.

  As described above, the period T of the write synchronization signal used as a reference for obtaining the write start time is the average of a plurality of synchronization signal periods obtained by one rotation of the rotary polygon mirror, thereby improving the reliability of color misregistration reduction control. Can be increased.

<Embodiment 4>
An example of the fourth embodiment will be schematically described with reference to FIG.
The synchronization signal cycle is stored for each surface of the rotary polygon mirror, the surface that scans the leading line is determined at the start of image formation, and the synchronization signal cycle corresponding to that surface is used as a criterion.
When the synchronization signal of the second color is generated earlier by the time 25 than the first color, if the period T = 96 is used as a determination criterion from the determination result of the rotating polygon mirror, 1 of the beam selection determination criterion as shown in FIG. T / 4 is 96/4 = 24, and the subsequent beam B is selected as the head beam. The deviation amount from the first color when the beam B is selected is 23, and the deviation amount can be made smaller than when the preceding beam A is selected.

  In addition, when the period T = 104 is used as a determination criterion from the determination result of the rotating polygon mirror, T / 4, which is one of the beam selection determination criteria, becomes 104/4 = 26 as shown in FIG. 8B. The preceding beam A is selected as the leading beam. At this time, the shift amount from the first color is 25, and the shift amount can be made smaller than when the subsequent beam B is selected (the shift amount is 27).

  In this way, by obtaining the period of the synchronization signal for each surface of the rotary polygon mirror and setting the period T of the write synchronization signal used as a reference for obtaining the writing start time as the period corresponding to the surface used at the start of writing. Thus, the color shift can be further reduced.

In the above-described embodiment, it has been described that one mark is provided on an intermediate transfer member such as a belt. However, when a plurality of image forming units are provided, the distance between image forming units is set to n or the like on the intermediate transfer member. A plurality of marks are provided on the entire belt at the divided intervals, and are used as image formation start reference signals for the respective colors when the mark detector detects a number of marks corresponding to the distance between the image forming means.
Alternatively, a plurality of mark detectors may be provided at an interval obtained by dividing the distance between the image forming units by n, and the same mark may be detected n times to be used as an image formation start reference signal for each color.

  Thus, by generating the mark signal for each image forming unit, it is possible to form an image with reduced color misregistration regardless of the image size.

In the above-described embodiment, the number of beams of the writing unit is two. However, the present invention is not limited to this.
That is, assuming that the number of beams of the writing means is n and the period of the write synchronization signal generated every time the writing means scans is T, the first (first color) image formation is (2n-1) with respect to the mark reference. You may make it start after time more than T / 2n passes.
Further, when the difference from the previously formed image at the image start time with respect to the mark reference is (2n-1) T / 2n or more, the write timing is delayed, and when it is T / 2n or more, (2n-1) T / 2n You may make it perform beam selection when it is less than.

  In this way, it is possible to reduce the misalignment (color shift) of the head position of the superimposed image regardless of the number of beams.

Next, the configuration of the above-described embodiment will be described.
<Embodiment 5>
FIG. 9 is a block diagram illustrating a configuration of an image forming apparatus according to Embodiment 5 of the present invention. According to the figure, the image forming apparatus detects a mark on the intermediate transfer member 7 and generates an image formation start signal in the sub-scanning direction, and detects an image formation start signal in the sub-scanning direction when the first color image is formed. Thereafter, a measuring unit 12 that measures an elapsed time until the first synchronization signal that is generated, a first storage unit 13 that stores and holds the measurement time of the measuring unit 12, a first reference value 14 that is set in advance, and a first storage unit 13 1st determination means 15 for comparing the first reference value 14 with the first reference value 14, and first addition means for adding and updating the first time previously obtained in the first storage means 13 based on the result of the first determination means 15 16, a second storage means 23 for storing and holding the measurement time of the measurement means 12 for measuring the elapsed time from the detection of the image formation start signal in the sub-scanning direction when the second color image is formed to the first synchronization signal generated; Storage means 13 and the first The calculating means 20 for determining the difference between the values in the storage means 23, the second determining means 25 for determining the magnitude of the difference between the first reference value 14 and the second reference value 24 set in advance and the difference determined by the calculating means 20, second Based on the result of the determination means 25, the second addition means 26 for adding and updating the first time or the second time obtained in advance in the second storage means 23, the average of the values of the first storage means 13 and the second storage means 23 The first average storage means 27 for obtaining and storing the value stores the measurement time of the measurement means 12 for measuring the elapsed time from the detection of the image formation start signal in the sub-scanning direction when the third color image is formed to the first synchronization signal. The third storage means 33 to be held, the second average storage means 37 for obtaining and storing the average value of the values of the first average storage means 27 and the third storage means 33, and the image formation start signal in the sub-scanning direction when the fourth color image is formed. First synchronization after detection Timing delay means 40 for delaying the write timing based on the results of the fourth storage means 43 for storing and holding the measurement time of the measurement means 12 for measuring the elapsed time until the signal number, the first determination means 15 or the second determination means 25. The data selection output control means 50 performs selection or output switching of image data input from the outside based on the result of the second determination means 25 and the timing delay means 40.

Next, the operation of the fifth embodiment will be described.
When the first color image is formed, the first determination unit 15 determines the elapsed time from the mark detection to the generation of the synchronization detection signal. If the first reference value (3T / 4) or more has elapsed, image formation is started as it is. If not, the timing delay means 40 controls the image formation start time so as to start with a delay of one scan.
When the scanning is delayed by one scan, the first addition unit 16 adds and updates the first time T obtained in advance to the first storage unit 13.

When the image of the second color is formed, the value of the second storage means 23 that stores the elapsed time from the mark detection to the generation of the synchronization detection signal and the value of the first storage means 13 that is added and updated by the first addition means 16 as necessary. Is calculated by the calculation means 20 and determined by the second determination means 25.
At this time, if the difference is less than the second reference value (T / 4), image formation is started as it is, and if the difference is greater than or equal to the second reference value (T / 4) and less than the first reference value (3T / 4). The subsequent beam is selected to start image formation, and when it is equal to or greater than the first reference value (3T / 4), the timing delay means 40 controls the image formation start time so as to start with a delay of one scan.
At this time, when the beam is selected, the data selection / output control means 50 selects or switches the output of the image data input from the outside so that the subsequent beam forms the data of the first line of the image.

  Further, the second adding means 26 stores the first time T obtained in advance in the case of delaying one scanning, and the second time T / 2 obtained in advance in the case of selecting a beam in the second storage means 23. Add and update.

  The first average storage means 27 obtains and stores an average value of the values of the first storage means 13 and the second storage means 23 that are added and updated as necessary.

  When the image of the third color is formed, the difference between the value of the third storage means 33 storing the elapsed time from the mark detection to the generation of the synchronization detection signal and the value of the first average storage means 27 is obtained by the computing means 20, and the second determination means Judge at 25. According to the determination result, as in the second color, the timing delay unit 40 controls the image formation start timing, and the data selection / output control unit 50 performs image data selection or output switching to start image formation. Similarly, the second addition means 26 adds and updates the value in the third storage means 33. Further, the second average storage means 37 obtains and stores the average value of the third storage means 33 and the value of the first average storage means 27 that are added and updated as necessary.

  When the image of the fourth color is formed, the difference between the value of the fourth storage means 43 storing the elapsed time from the mark detection to the generation of the synchronization detection signal and the value of the second average storage means 37 is obtained by the computing means 20, and the second determination means Judge at 25. According to the determination result, as in the second and third colors, the timing delay unit 40 controls the image formation start timing, and the data selection / output control unit 50 performs image data selection or output switching to start image formation.

FIG. 10 shows a configuration example of the data selection output control means 50, and FIG. 11 shows the output control method.
The data selection output control means 50 includes an input stage data selection block, a ring buffer block composed of a plurality of line buffers, and an output stage output switching block.
Based on the result of the second determination means 25, the data selection block instructs the buffer for storing the input image data, and writes / reads the image data according to the timing delay means 40.

The output switching block switches the sequentially read buffers and outputs the image data to the next-stage LD drive control unit.
The plurality of line buffers are configured to switch between writing (reading) and reading (reading) image data for each scan.
When the writing means has two beams, as shown in FIG. 11 (C), image data input every two lines is normally stored in a buffer as shown in FIG. 11 (D) (when alignment control is not required). It is output at the next written scan (after one scan).

The upper stage of the image data shown in FIGS. 11C, 11D, and 11E is the preceding beam data, and the lower stage is the subsequent beam data.
When the beam is selected, as shown in FIG. 11E, Empty (dummy data) is output to the preceding beam of the first scan, and the line data is delayed by one beam and output to the subsequent LD drive control unit. Does not print with dummy data.

Here, FGate in FIG. 11A is an image formation start signal, and LSync in FIG. 11B is a synchronization signal.
Therefore, when the line delay is performed by the timing delay means 40, the FGate signal in FIG. 11A is input to the data selection output control means 50 with a delay of one scan from the normal time.

FIG. 12 shows a write / read sequence of image data to the line buffer by selecting two beams of data.
During normal (no alignment control), the first and second lines of image data of the formed image are written to the buffers A and B in the first scan. Here, data is not read (read). In the next (second) scan, the data in the buffers A and B are read, and the subsequent image line data 3 and 4 are written in the buffers C and D at the same time. In the next (third) scan, the data in the buffers C and D are read out, and the subsequent image line data 5 and 6 are written in the buffers E and A at the same time. This is repeated thereafter.

  When the beam is selected, the image data of 1 and 2 lines are written to the buffers B and C in the first scan. At this time, dummy data is written to the buffer A. In the next (second) scan, the data in the buffers A and B are read out, and the subsequent image line data 3 and 4 are written in the buffers D and E at the same time. Since the buffer A is dummy data, the preceding beam records data for the first line with the subsequent beam without recording data.

  In the next (third) scan, the data in the buffers C and D are read out, and the subsequent image line data 5 and 6 are written in the buffers A and B at the same time. This is repeated thereafter. In this way, the line buffer to which the image data is written is shifted by one.

  By outputting data with the above configuration, it is possible to reduce the top position shift (color shift) of the superimposed image.

<Embodiment 6>
FIG. 13 is a block diagram illustrating a configuration of an image forming apparatus according to Embodiment 6 of the present invention.
The sixth embodiment is the same as that of the fifth embodiment except that the fluctuation range detection for obtaining the fluctuation width of the image recording start time of the first storage unit 13, the second storage unit 23, and the third storage unit 33 that have already completed the image formation. It is determined whether the image formation start time of the third color and the fourth color, which is determined according to the results of the means 60 and the second determination means, is within the fluctuation width of the formation time of the already formed image, or longer or shorter than that. First difference means 81 for obtaining a time difference between the image formation start time of the third color and the fourth color determined from the results of the range determination means 70 and the second determination means and the fluctuation width of the formation start time of the already formed image. Addition / subtraction means 90 for adding / subtracting a preset value to the image formation start time of the third color and the fourth color according to the result of the range determination means 70 at the image formation start time of the third color and the fourth color determined according to the result of the second determination means. One of the results of the second difference means 82, the first difference means 81, and the second difference means 82 for obtaining a time difference from the fluctuation width between the start time added / subtracted by the addition / subtraction means 90 and the formation start time of the already formed image. The third determination unit 100 that determines the smaller one and outputs the determination result to the timing delay unit 40 and the data selection output control unit 50 is added.

Next, the operation of the sixth embodiment will be described.
At the time of forming the third color image, the fluctuation width detecting means 60 obtains the fluctuation width of the start time of the first and second color images.
Whether the image formation start time of the third color, which is added and updated as necessary by the second determination means 25, is within the fluctuation range obtained above, or is outside the fluctuation range and shorter than the shortest time or longer than the longest time Is determined by the range determination means 70, and the result is output to the timing delay means 40, the data selection output control means 50 and the addition / subtraction means 90.

  The timing delay unit 40 and the data selection output control unit 50 start image formation according to the result of the second determination unit 25 when the image formation start time of the third color is within the range, and when it is outside the range, According to the result of the determination means 100.

  The first difference unit 81 calculates a time difference from the shortest time or the longest time in the fluctuation range obtained by the fluctuation range detection unit 60 of the image formation start time of the third color, which is added and updated as necessary by the second determination unit 25. Ask.

  When the image formation start time for the third color is outside the fluctuation range obtained by the fluctuation range detection unit 60, the addition / subtraction unit 90 sets the previously obtained value to the image formation start time for the third color if it is shorter than the shortest time in the fluctuation range. If it is longer than the longest time in the fluctuation range, a value obtained in advance is subtracted from the image formation start time of the third color.

The second subtracting unit 82 determines whether the image forming start time of the third color added / subtracted by the adding / subtracting unit 90 according to the result of the range determining unit 70 from the shortest time or the longest time of the fluctuation range obtained by the fluctuation range detecting unit 60. Find the time difference. Here, a preset value to be added or subtracted is T / 2.
The third determination means 100 determines the smaller one from the results of the first difference means 81 and the second difference means 82. If the result of the first difference means 81 is small, the second determination means 100 follows the second determination means 25 as necessary. Image formation is started at the image formation start time of the third color updated by addition, and when the result of the second difference unit 82 is small, image formation is started at the image formation start time corrected by the addition / subtraction unit 90. The control signal is output to the timing delay means 40 and the data selection output control means 50.

  When the fourth color image is formed, the fluctuation width (variation) width of the start time of the first, second, and third color images is obtained by the fluctuation width detecting unit 60, and the fourth color image formation start time is obtained as described above. The range determination means 70 determines whether it is within the fluctuation range, shorter than the shortest time or longer than the longest time, and outputs the result to the timing delay means 40, the data selection output control means 50 and the addition / subtraction means 90. To do.

The first difference unit 81 obtains the time difference from the shortest time or the longest time in the fluctuation range obtained by the fluctuation range detection unit 60 of the image formation start time of the fourth color.
When the image formation start time for the fourth color is outside the fluctuation range obtained by the fluctuation range detection unit 60, the addition / subtraction unit 90 sets the previously obtained value to the image formation start time for the fourth color if it is shorter than the shortest time in the fluctuation range. If it is longer than the longest time in the fluctuation range, a value obtained in advance is subtracted from the image formation start time of the fourth color.

  The second difference means 82 adds the subtracting means 90 from the shortest time or the longest time of the fluctuation width obtained by the fluctuation width detecting means 60 of the image formation start time of the fourth color added or subtracted according to the result of the range determination means 70. Find the time difference.

  The third determination unit 100 determines the smaller one from the results of the first difference unit 81 and the second difference unit 82. If the result of the first difference unit 81 is small, the second determination unit 25 performs the fourth color image. The timing delay means 40 and the data selection so that the image formation is started at the formation start time, and when the result of the second difference means 82 is small, the image formation is started at the image formation start time corrected by the addition / subtraction means 90. A control signal is output to the output control means 50.

  With the above configuration, it is possible to further reduce the misalignment of the head position of the superimposed image as compared with the fifth embodiment. In addition, the reliability of color misregistration reduction control can be increased.

<Embodiment 7>
FIG. 14 shows an example in which the present invention is applied to an image forming apparatus called two stations, which has two image forming means (station 1 and station 2) below the intermediate transfer member 7.

  Each image forming means includes one image carrier 1a (1b), writing means 3a (3b), and at least two developing means for developing an electrostatic latent image formed by the writing means on the image carrier. 4a, 4b (4c, 4d), switching means (not shown) for selectively selecting and driving the developing means, charging means 2a (2b), primary transfer means 5a (5b), cleaning means 6a (6b), secondary transfer means 8, and intermediate transfer member cleaning means 9.

  Therefore, even in a small, high-speed and low-cost image forming apparatus, an image formation start signal for each image forming unit is generated by the mark detecting unit 11 and image formation in each image forming unit is started as described above. As a result, the tops of the images of a plurality of colors can be easily and accurately superimposed on the intermediate transfer member, and a high-quality full-color image forming apparatus can be realized.

An image forming apparatus for forming a color image by forming an image on a scanned body by a scanning type writing unit, transferring the image onto an intermediate transfer body a plurality of times for each color, and sequentially superimposing the images for each color. It is a figure which shows an example of a basic composition. FIG. 6 is a diagram for explaining a relationship between an image formation start signal in the sub-scanning direction generated by detecting a mark on an intermediate transfer member and a synchronization signal of a writing unit. It is a figure explaining the dot formation position at the time of using multiple beams as two beams. It is a figure explaining the difference of the beam control in a prior art and this invention. FIG. 6 is a diagram illustrating a relationship between a first synchronization signal of each color and a dot position with respect to a belt mark signal when the synchronization signal cycle T is 100; It is the figure which showed the relationship between scanning time and the scanning width (dot diameter) of a subscanning direction. FIG. 6 is a diagram for explaining a deviation of a first color first dot from a second color beam position when a second color synchronization signal is generated early with respect to the first color first dot position. It is a figure for demonstrating the period of the write synchronous signal used for the reference | standard for calculating | requiring write start time, when a synchronous signal period differs for every surface of a rotary polygon mirror. It is a block diagram which shows the structure of the image forming apparatus which concerns on Embodiment 5 of this invention. It is a block diagram which shows the structure of a data selection output control means. It is a figure for demonstrating the output control method of a data selection output control means. It is a figure which shows the write / read sequence to the line buffer of the image data by the data selection of 2 beams. It is a block diagram which shows the structure of the image forming apparatus which concerns on Embodiment 6 of this invention. This is an example in which the present invention is applied to an image forming apparatus called two stations.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,1a, 1b ... Image carrier, 2, 2a, 2b ... Charging means, 3, 3a, 3b ... Writing means, 4, 4a, 4b, 4c, 4d ... Developing means, 5, 5a, 5b ... Primary transfer Means 6, 6a, 6b ... Cleaning means 7 ... Intermediate transfer member 8 ... Secondary transfer means 9 ... Cleaning means 11 ... Mark detection means 12 ... Measurement means 13 ... First storage means 14 ... First 1 reference value, 15 ... first determination means, 16 ... first addition means, 20 ... calculation means, 23 ... second storage means, 24 ... second reference value, 25 ... second determination means, 26 ... second addition means , 27 ... first average storage means, 33 ... third storage means, 37 ... second average storage means, 40 ... timing delay means, 43 ... fourth storage means, 50 ... data selection output control means, 60 ... fluctuation range detection Means 70: Range determination means 81: First difference means 82: Second Difference means, 90 ... addition / subtraction means, 100 ... third determination means.

Claims (12)

  A mark serving as an image formation start reference for each color is provided on the intermediate transfer member, and image formation for each color is started by scanning type writing means having a plurality of beams arranged in the sub-scanning direction based on the mark detection signal. A toner image is generated from the latent image formed on the body by a developing means, and the process of transferring the toner image onto the intermediate transfer body is repeated a plurality of times for each color, and the toner images are sequentially superimposed for each color to form a color image. The image forming apparatus to be formed starts by delaying the writing timing or selecting a beam so that the difference between the image formation start time with respect to the mark reference for the second color and the image formation start time for the first color is minimized. The average start time tc1 of the image formation start time with respect to the color and second color mark standards is obtained, and the image formation start time with respect to the third color mark reference and the average image formation start time The write timing is delayed or beam selection is started so that the time difference from the interval tc1 is minimized, and an average image formation start time tc2 between the image formation start time with respect to the mark reference for the third color and the previously obtained tc1 is obtained. It is characterized in that it is started by delaying the write timing or selecting a beam so that the time difference between the image formation start time with respect to the mark reference for the fourth color and the average image formation start time tc2 is minimized. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the image formation of the third color obtained by delaying the write timing or beam selection control so that the time difference between the average image formation start time tc1 of the first color and the second color is minimized. If the start time deviates from the fluctuation (variation) width of the image formation start time with respect to the mark reference of the first and second color images that have already been formed, the deviation from the minimum or maximum value of the fluctuation width and the write timing Assuming a start time that is advanced or delayed in the sub-scanning direction by a predetermined beam from the time obtained by delay or beam selection control, the deviation from the minimum value or maximum value of the fluctuation range at that time is compared, and the deviation The image formation is started at the image formation start time when becomes smaller, and the average of the image formation start time with respect to the mark reference for the third color and the previously obtained tc1 The image formation start time tc2 is obtained, and the image formation start time of the fourth color obtained by delaying the write timing or by beam selection control is set so as to minimize the time difference from the average image formation start time tc2. If the fluctuation range of the image formation start time with respect to the mark reference of the image of the color is out of the fluctuation range of the image formation start time, the beam is determined in advance from the deviation from the minimum value or the maximum value of the fluctuation width and the time determined by the write timing delay or beam selection control Assuming a start time that is advanced or delayed in the sub-scanning direction, the deviation from the minimum value or maximum value of the fluctuation range at that time is compared, and image formation is started at an image formation start time at which the deviation becomes small. An image forming apparatus characterized by that.   3. The image forming apparatus according to claim 1, wherein n is the number of beams of the writing unit and T is a cycle of a writing synchronization signal generated every time the writing unit scans. The image forming apparatus is configured to start after a time of (2n-1) T / 2n or more with respect to the mark reference.   4. The image forming apparatus according to claim 1, wherein when the number of beams of the writing unit is n and the period of the write synchronization signal generated every time the writing unit scans is T, the image start time at the image reference time with respect to the mark reference. Write timing is delayed when the difference from the previously formed image is (2n-1) T / 2n or more, and beam selection is performed when T / 2n or more and less than (2n-1) T / 2n. An image forming apparatus.   5. The image forming apparatus according to claim 1, wherein when a beam is selected, a pseudo synchronization signal is set to obtain an image formation start time.   6. The image forming apparatus according to claim 1, wherein a period T of a write synchronization signal used as a reference for obtaining a write start time is an average of a plurality of synchronization signal periods obtained by one rotation of the rotary polygon mirror. An image forming apparatus.   6. The image forming apparatus according to claim 1, wherein the period of the synchronization signal is obtained for each surface of the rotary polygon mirror, and the period T of the write synchronization signal used as a reference for obtaining the writing start time is set as the writing start. An image forming apparatus having a period corresponding to a surface used sometimes.   8. The image forming apparatus according to claim 1, wherein the image forming apparatus includes a plurality of image forming units arranged to face the moving surface of the intermediate transfer member, and the image forming unit starts image forming. An image forming apparatus characterized in that the signal is generated at intervals equal to n equal to the time required for the intermediate transfer member to move the distance between the image forming means.   A mark serving as an image formation start reference for each color is provided on the intermediate transfer member, and image formation for each color is started by scanning type writing means having a plurality of beams arranged in the sub-scanning direction based on the mark detection signal. A toner image is generated from the latent image formed on the body by a developing means, and the process of transferring the toner image onto the intermediate transfer body is repeated a plurality of times for each color, and the toner images are sequentially superimposed for each color to form a color image. In the image forming apparatus to be formed, mark detection means for detecting a mark on the intermediate transfer member, and an elapsed time after the mark detection is measured every time a mark serving as an image formation start reference is detected, and during the image forming period of each color Measurement unit that stops measurement, initializes, and waits for measurement until the next color image formation instruction, and measurement unit up to the first synchronization signal generated by the writing unit after mark detection when the first color image is formed First storage means for storing and holding the measured time, first determination means for comparing the value of the first reference value set in advance with the value of the first storage means, and determining the magnitude thereof, and first obtained in advance First addition means for adding and updating time to the first storage means based on the result of the first determination means, and measurement by the measurement means up to the first synchronization signal generated by the writing means after mark detection when forming the second color image Second storage means for storing and holding time, calculation means for obtaining a difference between the values of the updated first storage means and second storage means reflecting the result of the first determination means, and calculation by the calculation means A second determination means for comparing the difference between the first reference value and the second reference value set in advance and determining the magnitude thereof; and the second determination means for determining either the first or second time obtained in advance. Based on the result of the second addition, the second addition means updates the second storage means. A first average storage means for obtaining and storing an average value of the updated values of the first storage means and the second storage means, and a first writing means generated after the mark detection at the time of forming the third color image. Third storage means for storing and holding the measurement time of the measurement means up to the synchronization signal, and a difference between the values of the third storage means and the first average storage means is obtained by the calculation means, and the magnitude of the difference is determined by the second determination means. Based on the result, the second addition means updates the third storage means with the previously obtained value, and calculates the average value of the values of the first average storage means and the updated third storage means. A second average storage means for obtaining and storing, a fourth storage means for storing and holding the measurement time of the measurement means up to the first synchronization signal generated by the writing means after mark detection when forming the image of the fourth color, and the arithmetic means The fourth storage means and the second average storage means And a timing delay unit for delaying a write timing based on a result of the first determination unit or the second determination unit, and determining the magnitude of the difference by the second determination unit. And a data selection output control means for selecting or switching the output of image data inputted from the outside based on the result of the second determination means, and forming the first color image by the result of the first determination means, When the elapsed time is determined to be greater than one reference value, it is synchronized with the synchronization signal of the writing means, and when the elapsed time is determined to be small, the next synchronization signal is started, and image formation for the second and subsequent colors is performed. Start by delaying the write timing or selecting the beam according to the result of the second determination means, and when the beam is selected, the data selection output control means performs data selection or output switching. An image forming apparatus comprising.   10. The image forming apparatus according to claim 9, wherein when forming an image for the third and subsequent colors, the minimum value and the maximum value among the values of the first storage unit, the second storage unit, and the third storage unit that have already been subjected to image formation. The value of the third storage means corresponding to the formation start time of the third color obtained by selecting the delay of the write timing or selecting the beam according to the result of the start variation width detecting means for obtaining the fluctuation width of the recording start time from the second determination means. Range determination means for determining whether the value of the fourth storage means corresponding to the formation start time of the fourth color is within the start fluctuation range, or smaller or larger than the fluctuation range, and the value of the third storage means or The first difference calculating means for obtaining a difference between the value of the fourth storage means and the time width obtained by the start fluctuation width detecting means, the value of the third storage means or the value of the fourth storage means, and the result of the range determining means Based on Addition / subtraction means for adding / subtracting the obtained value to obtain a correction start time, second difference calculation means for obtaining a difference from the time width obtained by the start fluctuation width detection means of the addition / subtraction correction start time, and the first difference calculation means And a third determination unit that determines the smaller of the results of the second difference calculation unit, and for the image formation for the third and subsequent colors, the write timing is delayed or the start time of the beam selection is started according to the result of the second determination unit Image formation is characterized in that, when outside the range determined by the fluctuation range detection means, image formation is started at either the image start time or the correction start time determined by the result of the second determination means in accordance with the determination of the third determination means. apparatus.   11. The image forming apparatus according to claim 9, wherein the first time or the second time obtained in advance is a period T of a write synchronization signal used as a reference for obtaining a write start time. Image formation characterized in that an average of a plurality of synchronization signal periods obtained by rotation or a period of a synchronization signal is obtained for each surface of a rotary polygon mirror and obtained based on a period corresponding to a surface used at the start of writing apparatus.   12. The image forming apparatus according to claim 1, further comprising: an intermediate transfer member; and a plurality of image forming units arranged to face the moving surface of the intermediate transfer member, wherein the image forming unit is a single image carrier. And one writing means, at least two developing means for developing an electrostatic latent image formed on the image carrier by the writing means, and a switching means for selectively driving the developing means. An image forming apparatus.