JP4245341B2 - Pixel clock generator having common means for generating a high-frequency clock, and image forming apparatus using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pixel clock generation unit and an image forming apparatus.
[0002]
[Prior art]
In the conventional color image forming apparatus, since the PLL is mounted for each of the plurality of light beams, the cost is increased. Since the frequency differs for each light beam, it is necessary to mount a PLL for each beam. However, an invention using a common PLL has not attracted attention. In addition, since the main scanning magnification correction is performed by changing the PLL frequency, when performing the main scanning magnification correction between pages, a certain amount of time is required, and the productivity of image formation is increased. Will be dropped.
Further, in the conventional image forming apparatus, pixels that are not the reference cycle are continuously sub-scanned, and in an extreme case, the image may appear as a vertical streak.
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-221431 [Patent Document 2]
JP 2000-221758 A [Patent Document 3]
JP 2002-160399 A [0004]
[Problems to be solved by the invention]
The present invention has been made in view of the above-described problems of the prior art, and is an image forming apparatus using a plurality of light beams, which reduces costs and performs main scanning magnification correction between pages. Even in such a case, an object is to provide an image forming apparatus that does not reduce the productivity of printing for image formation.
[0005]
[Means for Solving the Problems]
The pixel clock generation unit according to the first aspect of the invention includes means for modulating each of a plurality of light beams generated from a plurality of light sources by an image signal, and tip synchronization for generating a synchronization detection signal serving as a reference for a main scanning line. A detection unit and a rear end synchronization detection unit that detects the position of the rear end of one line, and irradiates the image on the photosensitive member by irradiating the plurality of light beams on the photosensitive member via a scanner optical system. A pixel clock generation unit of an image forming apparatus that measures a difference in detection time between a leading edge synchronization detection signal and a trailing edge synchronization detection signal, and performs main scanning magnification correction based on the obtained measurement result. a PLL for generating the high frequency clock according to the setting value, divides the high frequency clock generated from the PLL, as a pixel clock, dividing said high frequency clock by a predetermined value generated from the PLL Generated reference period, a period shorter than the reference period, and pixel clock generating means for specifying one of a clock period longer than the reference period, to the pixel clock generating unit, the specification information for each pixel And the PLL is common to the plurality of light beams, and the pixel clock control unit controls the number of pixels to be inserted with a pixel clock other than the reference period and the insertion interval by using a synchronization detection signal as a trigger. The image forming apparatus is characterized in that magnification correction in the main scanning direction is performed by control for adjusting the number and interval of pixel clocks that are not the reference period inserted into one line for each light beam .
[0006]
According to another aspect of the present invention, there is provided an image forming apparatus that modulates a plurality of light beams generated from a plurality of light sources by an image signal and a front end synchronization detection that generates a synchronization detection signal serving as a reference for a main scanning line. And a rear end synchronization detecting means for detecting the position of the rear end of one line, and forming an image on the photosensitive member by irradiating the photosensitive member with the plurality of light beams via a scanner optical system. In the image forming apparatus that measures the difference in detection time between the leading edge synchronization detection signal and the trailing edge synchronization detection signal and corrects the main scanning magnification based on the obtained measurement result, the high frequency clock corresponding to the set value is generated from the reference clock. a PLL for generating, divides the high frequency clock generated from the PLL, as a pixel clock, a reference cycle generated by dividing the high frequency clock generated by a predetermined value from the PLL, the reference Period shorter than the period, and the pixel clock generating means for specifying one of a clock period longer than the reference period, to the pixel clock generating means comprises means for controlling the designation information for each pixel, the PLL is shared by the plurality of light beams, the pixel clock controlling means, a trigger synchronization detection signal, the number of pixels to insert the pixel clock not the reference period, to control the insertion interval of the main scanning direction magnification correction, the number of pixels of the pixel clock not the reference period to be inserted in one line for each light beam, and performing control to adjust the spacing.
[0007]
According to a third aspect of the present invention, there is provided the image forming apparatus according to the second aspect, wherein the image forming apparatus further includes means for changing the main scanning control start position of the pixel clock control means for each line, and changes the position. The means is characterized in that pixels that are not in the reference period are not continuous in the sub-scanning direction.
[0008]
According to a fourth aspect of the present invention, there is provided the image forming apparatus according to the second or third aspect, wherein a clock for measuring an interval between the leading end synchronization detection signal and the trailing end synchronization detection signal is the high frequency clock.
[0009]
According to a fifth aspect of the present invention, the image forming apparatus according to the second or third aspect is characterized in that the high frequency clock frequency is adjusted with the reference color before the magnification correction in the main scanning direction is performed.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram illustrating an entire image forming apparatus according to an embodiment of the present invention.
Various types of image forming processes are known which are employed in an image forming apparatus that forms a color image by electrophotography. One of them is a method called a tandem type. This system includes a photoconductor for each color to be imaged and an image forming process element for the photoconductor, and these photoconductors and image forming process elements are arranged along the intermediate transfer body and the paper transport belt for each color. The formed image is superimposed on the intermediate transfer member and transferred onto a sheet for printing the superimposed full color image at once, or the sheet conveyed by the sheet conveying belt passes through the transfer process of each of the photosensitive members. Each time the color image formed on the photoconductor is transferred, it passes through all transfer stations to form a full color image.
[0012]
FIG. 1 shows the configuration of such a tandem type color image forming apparatus.
In the drawing, image forming units 100Y, 100M, 100C, and 100K that form images of different colors (yellow: Y, magenta: M, cyan: C, black: K), respectively, convey belt 2 that conveys transfer paper 1. Are arranged in a line on the upstream side in the transport direction.
The conveyor belt 2 is stretched between a driving roller, one of which is driven to rotate, and a conveying roller 3, 4 which is a driven roller, the other of which is driven to rotate. It is rotationally driven (in FIG. 1, it rotates counterclockwise).
A paper feed tray 5 in which the transfer paper 1 is stored is provided below the conveyance belt 2. The transfer sheet at the uppermost position among the stored transfer sheets 1 is fed at the time of image formation and is attracted onto the transport belt 2 by electrostatic attraction. The adsorbed transfer paper 1 is conveyed to the first image forming unit (yellow) 100Y, where yellow image formation is performed.
[0013]
The first image forming unit (yellow) includes a photosensitive drum 6Y, a charger 7Y, an exposure unit 8, a developing unit 9Y, and a photoconductor cleaner 10Y arranged around the photoconductor drum 6Y.
The surface of the photosensitive drum 6Y is uniformly charged by the charger 7Y, and then exposed by the exposure device 8 with the laser beam 11Y corresponding to the yellow image, thereby forming an electrostatic latent image. The electrostatic latent image formed on the photosensitive drum 6Y is developed by the developing unit 9Y, and a toner image is formed on the photosensitive drum 6Y. This toner image is transferred by the transfer device 12Y at a position (transfer position) where the photosensitive drum 6Y contacts the transfer paper 1 on the transport belt 2, and forms a single color (yellow) image on the transfer paper 1. After the transfer, the photoreceptor drum 6Y is cleaned with unnecessary toner remaining on the drum surface by the photoreceptor cleaner 10Y to prepare for the next image formation.
[0014]
The transfer sheet 1 having the single color (yellow) transferred by the first image forming unit (yellow) 100Y in this way is conveyed by the conveying belt 2 to the second image forming unit (magenta) 100M. Here again, the toner image (magenta) formed on the photosensitive drum 6M is transferred onto the transfer paper 1 in a similar manner. The transfer paper 1 is further conveyed to the third image forming unit (cyan) 100C and the fourth image forming unit (black) 100K, and similarly formed M, C, and K toner images are sequentially transferred to color. Form an image.
[0015]
The transfer paper 1 on which the color image is formed by passing through the fourth image forming unit 100K is peeled off from the conveying belt 2, fixed by the fixing device 13, and then discharged. In the following description, the image forming process elements of the second to fourth image forming units 100M, 100C, and 100K change the subscripts (M, C, and K) indicating colors from the first image forming unit 100Y. The description of each overlapping part is omitted.
[0016]
FIG. 2 is a schematic view of the optical unit constituting the exposure unit 8 as viewed from above.
In the figure, light beams from an LD unit BK16 (BK: black) and an LD unit Y17 (means for modulating a light beam with an image signal: the same applies to other LD units) pass through cylinder lenses CYL_BK18 and CYL_Y19 and are reflected by a mirror The light is incident on the lower surface of the polygon mirror 22 by the BK 20 and the reflection mirror Y21, and the polygon mirror 22 rotates to deflect the light beam, pass through the fθ lens BKC23 and the fθ lens YM24, and pass through the first mirror BK25 and first mirror Wrapped by Y26.
On the other hand, the light beams from the LD unit C27 and the LD unit M28 pass through CYL_C29 and CYL_M30, enter the upper surface of the polygon mirror 22, and the polygon mirror 22 rotates to deflect the light beam, and the fθ lens BKC23 and The light passes through the fθ lens YM24 and is folded by the first mirror C31 and the first mirror M32.
[0017]
Cylinder mirrors CYM_BKC33 and CYM_YM34 are provided upstream of the writing position in the main scanning direction, and sensors BKC35 and YM36 of the tip synchronization detecting means are provided. The light is reflected and condensed and is incident on the sensor BKC 35 and the sensor YM 36. These sensors BKC35 and YM36 are synchronization detection sensors for synchronizing in the main scanning direction. Further, on the downstream side of the image area in the main scanning direction, similarly to the upstream side, cylinder mirrors CYM_BKC37 and CYM_YM38, and sensors BKC39 and YM40 of rear end synchronization detection means are provided. The passing light beam is reflected and collected by CYM_BKC37 and CYM_YM38, and enters the sensor BKC39 and sensor YM40.
[0018]
In the light beams from the LD unit BK16 and the LD unit C27, the common CYM_BKC33 and the sensor BKC35 are used on the writing side, and the common CYM_BKC37 and the sensor BKC39 (rear end synchronization detecting means) are used on the end side. The same applies to the LD unit Y17 and the LD unit M28. Since light beams of two colors are incident on the same sensor, the timing at which each light beam is incident on each sensor can be changed by changing the incident angles of the polygon mirrors 22 for the light beams of the respective colors. It is output in series as a pulse train. As can be seen from the figure, the set of BK and C and the set of Y and M are scanned in the opposite directions.
[0019]
FIG. 10 shows a conventional pixel clock generator.
Each color has a PLL unit (51). In the PLL unit (51), a signal obtained by dividing the reference clock (REFCLK) by M and a signal obtained by dividing each color pixel clock (* _WCLK) by N are phase comparator + LPF + VCO. (53) to generate a high-frequency clock (* _PLLCLK) for each color. Based on each color synchronization detection signal (* _DETP_N) from the synchronization detection sensor, the high frequency clock is divided by K to generate the pixel clock (* _WCLK), and the internal synchronization signal (* _PSYNC_N) synchronized with the pixel clock is generated . Each color image forming unit operates with the pixel clock and the internal synchronization signal.
The pixel clock frequency (f _WCLK ) is f _WCLK = (f _REFCLK / M × N) / K
It becomes.
[0020]
When performing magnification correction for main scanning, the passing time of the two synchronization detection sensors is measured by counting with a pixel clock, and M is set so that the count value and a preset reference count value coincide with each other. And the value of N are adjusted to change the pixel clock frequency. In the present invention, this magnification correction point is the same.
In order to have a different frequency for each color, a separate PLL unit has been conventionally used, which causes a cost increase. In particular, when the multiplication factor is changed, it takes time for the PLL to stabilize the frequency. When magnification correction is performed between pages, it is necessary to ensure sufficient space between pages. Productivity will drop.
[0021]
Next, a pixel clock generation unit used in the image forming apparatus of the present invention will be described with reference to FIG.
In FIG. 3, a PLL unit 51 (means for generating a high-frequency clock) has the same configuration as a known PLL device, but the PLL unit 51 used in the present invention can be used in common for each color. it can.
The PWM clock generation unit 57 (pixel clock generation means) divides the high-frequency clock (PLLCLK) from the PLL unit 51 to generate the pixel clock (WCLK). The reference is determined according to the input data (PWMDAT). The frequency, the cycle shorter than the reference frequency, or the cycle longer than the reference frequency can be selected.
FIG. 4 is a timing chart showing an embodiment when generating a PWM clock.
[0022]
For example, if the reference frequency of the pixel clock (WCLK) is a clock obtained by dividing PLLCLK by 8, as shown in FIG. 4, the counter that generates the pixel clock operates with reference to the falling edge of DETP_N, but the input data ( If PWMDAT [1: 0]) is '0h (zero h)', divide by 8; if '1h', divide by 9 (1 division more than 0h); if '2h', 7 minutes (Refer to the portion of “−1/8 pixel clock” in FIG. 4). Since the laser is finally driven by this pixel clock (WCLK), the pixels to which “1h” is input are lengthened by 1/8 pixel clock, and the pixels to which “2h” is input are shortened by 1/8 pixel clock. Become.
[0023]
The internal synchronization signal generator 56 (means for generating a signal synchronized with the pixel clock) generates a main scanning synchronization detection signal (PSYNC_N) synchronized with the pixel clock. The PWM data control unit 58 (means for controlling designation information for each pixel) controls PWMDAT [1: 0]. FIG. 5 is a block diagram showing an embodiment of the PWM data control unit 58, and FIG. 7 is a timing chart of PWM data control.
The PWM data control unit 58 sets the number of pulses (A), the insertion interval (B), and the data (C) of pixels that are not the reference frequency as shown in FIG. 7 inserted in one line from the main CPU (not shown). It shall be possible. When the internal synchronization detection signal (PSYNC_N) is input, the period counter (60: tip synchronization detection means) counts WCLK, outputs DPPLS when it becomes equal to the insertion interval (B), the period counter resets, Count up (start counting) is performed again. The pulse number counter (61: rear end synchronization detecting means) counts DPPLS and stops when it becomes equal to the pulse number (A). The PWM data output unit 62 outputs data (C) as PWMDAT [1: 0] when DPPLS becomes “1”.
[0024]
In the conventional example, the passing time of the two synchronization detection sensors is counted by the pixel clock, but in the device of the present invention, the measurement is performed by counting with the high frequency clock (PLLCLK), and the count value and the preset reference count By reflecting the difference in values on A, B, and C, the magnification of main scanning can be corrected.
A flowchart of the main scanning magnification correction is shown in FIG. When magnification correction is performed, first, the interval between two synchronization detections is measured with PLLCLK using the reference color. When the reference color is black, the magnification is adjusted by changing the values of M and N so that the measured value of black matches the reference value.
Next, multi-color (magenta, cyan, yellow) synchronous detection measurement is performed. For example, when there are four magenta measurement values with respect to the reference value, the measurement is 4/8 pixels shorter than the reference. Therefore, if 4/8 pixels are increased, the magnification will be suitable, and A = 4 and C = 1 are set. As for the value of B, an optimum interval is set when four pixels are included in one line from the total number of pixels in one line. For example, when the total number of pixels is 10,000 pixels, B = 2500 is obtained because it is sufficient to insert them at 2500 pixels once. If this operation is also performed for cyan and yellow, the magnification of each color can be corrected.
[0025]
When correcting magnification between pages, changing the PLL frequency results in a longer page interval, so the high-frequency clock is not changed, and the values of A, B, and C are set for black as well as for multiple colors. adjust.
[0026]
Next, a second embodiment (Claim 3) will be described.
FIG. 6 is a block diagram illustrating an example of the PWM data control unit 58, and other configurations are the same as those of the image device of the first embodiment. FIG. 8 is a timing chart of PWM data control when the PWM data control unit 58 of FIG. 6 is used.
In the first embodiment (Claim 2), the positions where the pixels increased or decreased by 1/8 pixel are the same in each line, but in this embodiment, the vertical stripes are not noticeable depending on the image. Designed. For this reason, in this embodiment, the start position control unit 63 (means for varying for each line) is configured to vary the start position of the PWM data control so as not to be the same position for each line. From the main CPU, a shift width (D) and a shift upper limit (E) are set, and the start position is shifted by D pixels for each line. If the shift amount is added and E is exceeded, the difference is used as the start position.
[0027]
【The invention's effect】
Since the pixel clock generation unit of claim 1 uses a common means for generating a high-frequency clock, conventionally, a high-frequency clock generation circuit (for example, a PLL circuit) cannot be provided for each color because the frequency differs for each color. However, by making it common, it has become possible to provide a circuit used in an image forming apparatus that raises the problem of cost increase and increases the productivity of printing.
[0028]
In the image forming apparatus according to the second aspect, since the common PLL is used in the pixel clock generation units of the plurality of light beams, the cost can be reduced.
Moreover, when correcting the main scanning magnification between pages, it can be performed without changing the PLL frequency, so that printing can be performed at the same page interval as usual, and printing productivity (printing speed and image quality can be reduced). Including) is not dropped.
[0029]
In the image forming apparatus according to the third to sixth aspects, since the start position of the PWM data control is changed for each line, the image quality can be improved.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an overall configuration of an image forming apparatus according to the present invention.
FIG. 2 is a top view of the configuration of an optical unit constituting the exposure unit.
FIG. 3 is a diagram showing a configuration of a pixel clock generation unit that shares means (PLL circuit) for generating a high-frequency clock according to the present invention.
FIG. 4 is a timing chart showing an operation example of a pixel clock generation unit (first embodiment) of the present invention.
FIG. 5 is a diagram illustrating a configuration example of a unit (PWM data control unit) that controls designation information for each pixel used in the pixel clock generation unit of the present invention;
FIG. 6 is a diagram showing another configuration example (second embodiment) of means for controlling designation information for each pixel used in the pixel clock generation unit of the present invention.
FIG. 7 is a timing chart showing an operation example of means (PWM data control unit: used in the first embodiment) for controlling designation information for each pixel.
FIG. 8 is a timing chart showing an operation example of another unit (PWM data control unit: used in the second embodiment) for controlling designation information for each pixel.
FIG. 9 is a flowchart illustrating an example of an operation flow of the image forming apparatus of the present invention.
FIG. 10 is a diagram illustrating a configuration of a conventional pixel clock generation unit.
[Explanation of symbols]
16 LD unit BK (means for modulating a light beam with an image signal)
17 LD unit Y (means for modulating a light beam with an image signal)
27 LD unit C (means for modulating light beam with image signal)
28 LD unit M (means for modulating a light beam with an image signal)
35 sensor BKC (tip synchronization detection means)
36 Sensor YM (tip synchronization detection means)
39 sensor BKC (rear end synchronization detection means)
40 sensor YM (rear end synchronization detection means)
51 PLL section (means for generating a high-frequency clock)
56 Internal synchronization signal generator (means for generating a signal synchronized with the pixel clock)
57 PWM clock generator (pixel clock generator)
58 PWM data control unit (means for controlling designation information for each pixel)
60 period counter 61 pulse number counter 62 PWM data output unit 63 start position control unit

Claims (5)

Means for modulating a plurality of light beams generated from a plurality of light sources with image signals, front end synchronization detecting means for generating a synchronization detection signal serving as a reference for the main scanning line, and detecting the position of the rear end of one line A rear end synchronization detecting means, and irradiating the plurality of light beams onto the photosensitive member via a scanner optical system to form an image on the photosensitive member, and between the front end synchronizing detection signal and the rear end synchronization detecting signal; A pixel clock generation unit of an image forming apparatus that measures a difference in detection time and performs main scanning magnification correction according to the obtained measurement result,
A PLL that generates a high-frequency clock according to a set value from a reference clock;
A high frequency clock generated from the PLL is divided and a reference cycle generated by dividing the high frequency clock generated from the PLL by a predetermined value as a pixel clock, a cycle shorter than the reference cycle, a cycle longer than the reference cycle Pixel clock generation means capable of designating any one of the clocks;
Means for controlling designation information for each pixel with respect to the pixel clock generating means;
The PLL is common to the plurality of light beams;
The pixel clock control means controls the number of pixels to be inserted with a pixel clock that is not the reference period, the insertion interval, using a synchronization detection signal as a trigger,
Pixel clock generation, characterized in that the image forming apparatus performs magnification correction in the main scanning direction by controlling to adjust the number and interval of pixel clocks other than the reference period inserted into one line for each light beam Department. Means for modulating a plurality of light beams generated from a plurality of light sources with image signals, front end synchronization detecting means for generating a synchronization detection signal serving as a reference for the main scanning line, and detecting the position of the rear end of one line A rear end synchronization detecting means, and irradiating the plurality of light beams onto the photosensitive member via a scanner optical system to form an image on the photosensitive member, and between the front end synchronizing detection signal and the rear end synchronization detecting signal; In the image forming apparatus that measures the difference in the detection time of and performs main scanning magnification correction based on the obtained measurement result,
A PLL that generates a high-frequency clock according to a set value from a reference clock;
A high frequency clock generated from the PLL is divided and a reference cycle generated by dividing the high frequency clock generated from the PLL by a predetermined value as a pixel clock, a cycle shorter than the reference cycle, a cycle longer than the reference cycle Pixel clock generation means capable of designating any one of the clocks;
Means for controlling designation information for each pixel with respect to the pixel clock generating means;
The PLL is common to the plurality of light beams;
The pixel clock control means controls the number of pixels to be inserted with the pixel clock other than the reference period and the insertion interval by using a synchronization detection signal as a trigger, and magnification correction in the main scanning direction is inserted in one line for each light beam. An image forming apparatus that performs control to adjust the number and interval of pixels of a pixel clock that is not the reference period. The image forming apparatus according to claim 2, further comprising means for changing the main scanning control start position of the pixel clock control means for each line,
The image forming apparatus according to claim 1, wherein the changing means prevents pixels that are not in a reference period from continuing in the sub-scanning direction.   4. The image forming apparatus according to claim 2, wherein a clock for measuring an interval between the leading edge synchronization detection signal and the trailing edge synchronization detection signal is the high frequency clock. 4. The image forming apparatus according to claim 2, wherein the high-frequency clock frequency is adjusted with the reference color before performing magnification correction in the main scanning direction .

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