JP2014117910A - Image formation apparatus and image formation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-quality image formation apparatus by eliminating rotation irregularity of a rotary polygon mirror.SOLUTION: An image formation apparatus comprises: a light beam generator 104; a rotary polygon mirror 100 polarizing the light beam from the light beam generator 104 onto a photoreceptor 102; and a scanning beam detector 106 receiving the light beam that scans the photoreceptor 102, and outputting a synchronization signal indicating a drawing start position of the photoreceptor 102. A pixel clock generation device 107 generates a frequency correction value for correcting an error between a count of scanning intervals of a main scan one line and an Nref (ideal count), and generates a second pixel clock (image data modulation clock) obtained by correcting a first pixel clock with the frequency correction value on the basis of the error.

Description

  The present invention relates to an image forming apparatus and an image forming method.

In an image forming apparatus that scans a light beam with a rotating polygon mirror (polygon mirror) and exposes an image carrier, reducing the number of synchronization signals required for image forming operation and reducing the processing load of the video controller Is already known (see Patent Document 1).
In this conventional image forming apparatus in which the number of synchronization signals is reduced, a light beam is continuously detected twice by the tip synchronization sensor, the time interval is compared with a predetermined time interval, and the writing clock is controlled. .

  That is, in the image forming apparatus described in Patent Document 1, in order to perform main scanning magnification correction in main scanning writing in real time, the light beam is detected by the tip synchronization sensor, and the light beam is continuously transmitted by the tip synchronization sensor. The time interval detected twice is compared with a predetermined time interval, and the frequency of the reference write clock generated by the write clock generation circuit is changed according to the magnitude relationship and the magnitude of the difference. Variations in scanning magnification are corrected.

  The correction of the fluctuation of the main scanning magnification is similar to that of the present invention described below in that the time interval of the tip synchronization sensor is compared with a predetermined time interval. However, since the rotating polygon mirror has uneven rotation speed, the rotation unevenness of the rotating polygon mirror cannot be removed only by comparing the time intervals when the light beam is detected twice in succession. That is, this method cannot solve the problem of removing the rotation unevenness of the rotary polygon mirror.

  It is an object of the present invention to remove uneven rotation of a rotary polygon mirror and to form a high-quality image in an image forming apparatus.

  The present invention provides a light beam generating means, a rotating polygon mirror having a plurality of mirrors for scanning the light beam of the light beam generating means on the photosensitive member, and a write position of the photosensitive member by receiving the light beam. A scanning beam detecting means for outputting a synchronizing signal, a measuring means for measuring a scanning period of the light beam with a first pixel clock based on the synchronizing signal, and the measured measurement value. Is controlled and output from the frequency of the first pixel clock set so as to be the cycle of the target value, while controlling and outputting the frequency of the first pixel clock so as to be a predetermined target value. And a first pixel clock generation unit that outputs a change in frequency as a frequency correction value.

  According to the present invention, the rotation unevenness of the rotary polygon mirror can be removed in the image forming apparatus, and the error can be suppressed even with respect to the error of the light beam generating means. Can do.

1 is a diagram illustrating an entire image forming apparatus that suppresses rotation unevenness of a rotary polygon mirror according to a first embodiment of the present invention. FIG. It is a block diagram explaining the structure of the 1st pixel clock generation part of a pixel clock generation apparatus. It is a figure explaining a moving average calculator. It is a figure explaining operation | movement of the moving average calculator shown in FIG. It is a figure explaining the structure of a filter. It is a figure explaining control of a pixel clock. It is the figure which showed the state of the pixel clock before and behind control. It is a figure which shows the structure of a 2nd pixel clock production | generation part. FIG. 9 is an image forming apparatus according to a second embodiment, and is a view similar to FIG. 1 for explaining a case where the rotary polygon mirror 900 has six faces. It is a figure which shows the structure of the moving average calculating device which can respond | correspond to both the case of the rotation polygon mirror 4 surface, and the case of 6 surfaces. It is a figure explaining the whole image forming apparatus concerning other embodiments of the present invention. It is a figure explaining the whole image forming device concerning other embodiments of the present invention. FIG. 13 is a diagram illustrating a configuration example of a third pixel clock generation unit of the image forming apparatus illustrated in FIG. 12. It is the figure which showed the relationship between 1 dot width and scanning width. It is a timing chart of the 3rd pixel clock generation part.

  Hereinafter, in describing embodiments of the present invention, first, an image forming apparatus according to the present embodiment will be briefly described. In this embodiment, a scanning beam detector is disposed only on the writing start side to prevent rotational unevenness of the rotary polygon mirror. In this case, the time for one rotation of the rotary polygon mirror is converted into the time for one surface, and the write clock is generated so as to be equal to the ideal value compared with the ideal value.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating the entire image forming apparatus for suppressing the rotation unevenness of the rotary polygon mirror according to the first embodiment of the present invention, and the rotation unevenness of the rotation polygon mirror only by the scanning beam detector on the tip side. FIG. 2 is a diagram illustrating an entire image forming apparatus 113 that suppresses an image.
In the illustrated image forming apparatus 113, the rotating polygon mirror 100, the writing diode (light beam generator) 104, the photosensitive member 102, and the scanning beam detector 106 are assumed to be one, and the rotation unevenness of the rotating polygon mirror 100 is reduced. The entire image forming apparatus 113 to be suppressed will be described.

The image forming apparatus 113 includes an optical system portion and a control unit as a whole.
The optical system portion outputs a light beam generator 104 that outputs writing light, an incident mirror 103 that reflects incident light output from the light beam generator 104, and deflects incident light reflected by the incident mirror 103 to a scanning lens. A rotary polygon mirror 100 having four surfaces, a scanning lens 101 that increases the angle of incident light 105 so as to match the width of the photosensitive member 102, and a binary synchronization signal that is placed in the vicinity of the photosensitive member 102 and indicates an image writing position. And a scanning beam detector 106 for detecting.

Further, the control unit includes a pixel clock generation device 107, a modulation data generation unit 111 that generates modulation data synchronized with the pixel clock generated by the pixel clock generation device 107 based on the image data, and a modulation data based on the modulation data. The laser driving unit 112 generates data for determining whether the laser diode of the light beam generator 104 is turned on or off.
Here, this embodiment is particularly characterized by the pixel clock generation device 107.
An embodiment in which there are a plurality of laser driving units 112 will be described later.

  The pixel clock generator 107 is generated by a first pixel clock generator 108 that generates a pixel clock based on a scanning beam synchronization signal detected by the scanning beam detector 106, and a first pixel clock generator 108. A second pixel clock generation unit 110 that generates a second pixel clock with the synchronization signal based on the frequency correction value is provided.

  When the synchronization signal is input from the scanning beam detector 106, the first pixel clock generation unit 108 determines that the counter 201 (FIG. 2) is based on the interval at which the synchronization signal is asserted, that is, one rotation polygon mirror. The period or time interval at which one main scanning line is scanned is counted by the first pixel clock, and the average value of the number of counts corresponding to the number of surfaces of the rotary polygon mirror is Nref (target or ideal for one line (scan)) A first pixel clock having a controlled period per pixel so as to be equal to the clock count number). Note that the counter 201 is reset at the assertion timing of the synchronization signal.

The second pixel clock generation unit 110 outputs a second correction signal based on the input synchronization signal and the frequency correction value when the period per pixel output from the first pixel clock generation unit 108 is controlled. The pixel clock is output in phase synchronization with the synchronization signal.
When the second pixel clock is input, the modulation data generation unit 111 converts the image data into modulation data in synchronization with the second pixel clock, and the laser driving unit 112 generates a light beam based on the modulation data. Device 104 is driven.

Next, a procedure for controlling the clock cycle of the counter 201 will be described with reference to FIG. 2 showing the first pixel clock generation unit 108.
FIG. 2 is a block diagram schematically illustrating the configuration of the first pixel clock generation unit 108 of the pixel clock generation device 107.
The first pixel clock generation unit 108 includes a DPD (Digital Phase Detector) 200, a moving average calculator 203, a filter 204, a divider 205, a delay element 206, a register (REG) 207, as shown in the figure. , A digitally controlled oscillator (or digital clock oscillator) (DCO) 208.

The DPD 200 counts the time interval at which the synchronization signal is asserted by the counter 201 with the first pixel clock, compares the counted number with Nref (ideal count number), and outputs the difference to the moving average calculator 203. (How to determine Nref will be described later).
In the moving average calculator 203, in order to remove the inter-surface error of the rotation speed (or rotation time) of the rotary polygon mirror 100, the moving average of the difference (error) of the count number of the counter 201 for one rotation of the latest rotary polygon mirror 100 is obtained. Ask for. Next, the filter 204 removes noise from the output of the moving average calculator 203.

The divider 205 calculates an error of one pixel period from the smoothed moving average of the count number error and Nref.
The delay element 206 adds a correction value (control value) Δfc_now for eliminating the error of one pixel period obtained by the divider 205 to the control value so far, and obtains the total amount of control values (Σ correction value = Δfc). .

Next, a difference (subtraction value) between the frequency correction value Δfc, which is the total amount of control values, and the initial frequency (fclk_i) of the image forming apparatus set by the register 207 is obtained, and the digital control oscillator 208 calculates the first pixel. Generate a clock.
When the scanning time interval for one surface of the rotary polygon mirror is counted with the first pixel clock generated as described above, the count value is naturally equal to Nref, but the frequency correction value Δfc at that time is set to the first frequency clock. 2 to the pixel clock generation unit 110. Thereby, the influence of the rotation error of the rotary polygon mirror 100 on the main scanning magnification can be removed.
Since an ideal period for each scan is determined for each model of the image forming apparatus, the value of Nref and the initial frequency of the register 207 are determined by the model of the image forming apparatus, and the setting value of the register 207 is The frequency at which this ideal clock count is set is set as an initial value (initial frequency fclk_i).

  FIG. 14 is a diagram showing the relationship between the 1-dot width and the scanning width. SP1 and SP2 indicate the detection positions of the first synchronization signal, and La indicates the interval between SP1 and SP2. When the dot width of the image is Lp (first pixel clock cycle), La / Lp = Nref is the interval of the first synchronization signal, which is set as the reference value Nref, and is sent to the first pixel clock generation unit 108. give.

Next, each component of the first pixel clock generation unit 108 will be specifically described.
FIG. 3 is a diagram for explaining the moving average calculator 203.
The DPD 200 synchronizes and takes in the synchronization signal (asynchronous), measures the synchronization signal interval, and obtains a difference value between the measurement result and Nref. The difference or error err (i) output from the DPD 200 is delayed by the flip-flop 300 synchronized with the synchronization signal. In the present embodiment, since the rotary polygon mirror 100 has four surfaces, the moving average calculator 203 has three flip-flops 300 to 302 and three adders 304 to 306.

FIG. 4 is a diagram for explaining the operation of the moving average calculator 203 shown in FIG.
Note that the synchronization signal in FIG. 4 indicates a cycle per pixel of the synchronization signal.
The error (or difference); err (i) represents the i-th error input to the moving average calculator 203. Here, sum_err (i) (total error) at the time of err (i) = e (i + 3) will be described. Here, e indicates err and se indicates sum_err.
In the figure, error 308 (A) is err (i-1) in the first synchronization signal synchronization, so the error at the time of err (i) = e (i + 3) is e (i + 2). Since the error 309 (B) in err (i-2) in the first synchronization signal synchronization is e (i + 1), and the error 310 (C) is err (i-3) in the first synchronization signal synchronization, e (i), Since the error 311 (D) is err (i) + A, D (i + 3) = e (i + 3) + e (i + 2), and the error 312 (E) is D + B, so E (i + 3) = e (i + 3) + e (i + 2) + e (I + 1).
Since the total error sum_err (i) is E + C, se (i + 3) = e (i + 3) + e (i + 2) + e (i + 1) + e (i), and the total error (sum of errors) for the four surfaces can be obtained.
When the error err (i) = e (i + 4) is satisfied, the total error sum_err (i); se (i + 4) = e (i + 4) + e (i + 3) + e (i + 2) + e (i + 1) is obtained, so that the latest four planes are obtained. The sum of errors (total error) can be obtained.

FIG. 5 is a diagram for explaining the configuration of the filter 204.
The filter 204 is a moving average of the output value of the moving average calculator 203, that is, the count value of the counter 201 for the interval at which one main scanning line is scanned by one surface of the rotating polygon mirror. This is a filter circuit that smoothes the difference value from Nref. The filter 204 includes a multiplier 500 serving as a proportional circuit that outputs a proportional value by multiplying the sum of the difference values obtained by the moving average calculator 203 by a proportional constant Kp, and an integral constant for the integral value of the sum of the difference values. A filter value is output by a multiplier 504 that multiplies Ki and outputs an integral value, and an adder 501 that takes the sum of the proportional value and the integral value.
Specifically, the following calculation is performed on the sum of errors (total error) sum_err (i) calculated by the moving average calculator 203.
That is, the total error sum_err (i) is multiplied by the proportionality constant Kp. The delay element (inverse Z converter) 503 and the adder 502 take the sum of the total errors sum_err (i), and the multiplier 504 multiplies the integration constant Ki. The adder 501 calculates the sum of the results of the multiplier 500 and the multiplier 504 to obtain a filter value: lf_err (i) = Kp × err_sum (i) + Ki × Σerr_sum (i). As a result, a smoothed error is obtained.

Next, control of the pixel clock will be described again.
FIG. 6 is a diagram for explaining control of the pixel clock.
In the image forming apparatus, the frequency and the line period for each main scanning line are individually determined as shown in FIG. That is, the initial frequency fclk_i and the ideal count number Nref of the pixel clock are determined based on values determined for each model.
However, the scanning speed of one line is different from the ideal value due to fluctuations in the rotational speed of the rotary polygon mirror 100.

  That is, in the illustrated initial value clock (first pixel clock before control), the number of counts between the synchronization signals should be Nref, but in the illustrated example, synchronization is caused by the error of the rotational speed of the rotary polygon mirror. The number of counts between signals is greater than Nref. That is, it shows that a time error per one surface (delay of ΔT) occurs due to an error in rotational speed. On the other hand, the count number between the synchronization signals by the first pixel clock after the control is controlled to Nref (ideal count number) as illustrated.

This is expressed as follows.
The target synchronization signal time interval; Tspsp_target is determined as shown in FIG. That is, since Tspsp_target is determined, Nref and the initial frequency fclk_i are also uniquely determined for each model.
That is, Tspsp_target = Nref / fclk_i Equation 1
If the actual synchronization signal time interval is Tspsp, the time error per surface of the rotary polygon mirror 100 due to the scanning speed error is ΔT, and the frequency error (frequency correction value) due to the scanning speed error is Δfc,
ΣTspsp = num_f × Tspsp_target + ΣΔT Equation 2
ΣTspsp = num_f × Nref / fclk_i + ΣNref / Δfc Equation 3
It becomes.
“Num_f” is the number of surfaces of the rotating polygon mirror. Therefore, since “Σ” is not an average when added to num_f (number of faces) or more, it means that the sum of the number of faces is taken.
Here, from Equations 2 and 3, ΣΔT = ΣNref / Δfc is the rotational polygon mirror jitter.
Therefore, the average time error (ΔT_ave) per surface of the rotary polygon mirror 100 is
ΔT_ave = Nref / Δfc_ave,
The average frequency error (Δfc_ave) per surface of the rotary polygon mirror 100 is
Δfc_ave = 1 / num_f × Σ1 / Δfc
It becomes.

FIG. 7 is a diagram showing the state of the pixel clock before and after control.
The count value 1 / fclk_init at the initial value frequency fclk_init of the pixel clock before control, that is, Nref + 3 here, after the control, removes the influence of the rotation error of the rotary polygon mirror 100, and the count value of the frequency fclk_w of the counter 201 This indicates that 1 / fclk_w (= 1 / fclk_i + 1 / Δfc_ave) becomes Nref.

FIG. 8 is a diagram illustrating a configuration of the second pixel clock generation unit 110.
The second pixel clock generator 110 includes an initial frequency setter 800, an adder 801 that adds the frequency correction value and the output of the initial frequency setter 800, and a phase of the synchronization signal based on the calculation result of the adder 801. A digitally controlled oscillator (DCO) 802, which is a transmitter that generates a second pixel clock in synchronization, is included.
That is, in the second pixel clock generation unit 110, an initial value different from the set value of the first pixel clock generation unit 108 (register 207) set by the initial frequency setting unit 800 and the first pixel clock generation unit. The frequency correction value (Σ correction value, that is, Δfc_ave) generated in 108 is added and input to the digitally controlled oscillator 802 to generate a second pixel clock in phase synchronization with the synchronization signal.

Next, the operation of the second pixel clock generation unit 110 will be described.
In the image forming apparatus 113, factors that shift the writing end position include manufacturing errors in the curvature of the light beam generator 104 and the scanning lens, and errors in each scanning optical system caused by differences in the mounting positions of the optical systems. The second pixel clock generator 110 sets the initial value (initial frequency setting value) with the initial frequency setting unit 800, thereby suppressing the error for each laser diode of each light beam generator 104. can do.
Even when there are a plurality of laser diodes, an error can be suppressed for each laser diode by having a plurality of second pixel clock generation units 110. A method for setting the initial frequency setting value of the second pixel clock will be described later.

FIG. 9 is a diagram illustrating an image forming apparatus according to the second embodiment in which the rotary polygon mirror 900 has six surfaces.
That is, the rotary polygon mirror 100 of the first embodiment has four surfaces, whereas the rotary polygon mirror 900 has six surfaces in the present embodiment.
The scanning lens 101, the photosensitive member 102, the incident mirror 103, the light beam generator 104, and the scanning beam detector 106 other than the rotating polygon mirror 900 have the same configuration as that of the first embodiment, and the second pixel clock generation unit 110 and the modulation data. The generation unit 111 and the laser driving unit 112 have the same configuration as that of the first embodiment. Only the moving average calculator 203 of the first pixel clock generation unit 108 is different from that of the first embodiment.

FIG. 10 is a diagram showing a configuration of the moving average calculator 203 that can handle both the case of the rotating polygon mirror 4 and the case of 6 surfaces.
It is composed of five flip-flops 300 to 303 and 1000 and five adders 304 to 306, 1001 and 1002, which are synchronized with the first synchronization signal, and the switch 1007 causes either the node F313 or the node K1006 to be turned into the polygon mirror 900. Select together. That is, the node F 313 is selected by the selection signal sel for the four-sided rotary mirror and the node K 1006 for the six-sided mirror. G; 1003, H; 1004, J; 1006 indicate errors.

FIG. 11 is a diagram for explaining an entire image forming apparatus according to another embodiment of the present invention, and includes four photosensitive members, four scanning lenses, four incident mirrors, and four light beam generators. It is a figure which shows embodiment provided with the optical system which has.
That is, the image forming apparatus 113 according to the present embodiment includes one rotary polygon mirror 100, four photosensitive members 102 (1) to 102 (4), four scanning lenses 101 (1) to 101 (4), and four An optical system composed of incident mirrors 103 (1) to 103 (4), four light beam generators 104 (1) to 104 (4), and four scanning beam detectors 106 (1) to 106 (4); One first pixel clock generation unit 108, four second pixel clock generation units 110 (1) to 110 (4), four modulation data generation units 111 (1) to 111 (4), It is comprised by the control part which consists of four laser drive parts 112 (1) -112 (4).

Since the first pixel clock generation unit 108 is intended to control the rotation unevenness of the rotary polygon mirror 100, one pixel clock generation unit 108 is required for one rotary polygon mirror 100. Since the configuration of the first pixel clock generation unit 108 is the same as that of the first embodiment or the second embodiment, the description thereof is omitted.
One second pixel clock generator 110 is required for one light beam generator. In the present embodiment, since there are four light beam generators, the second pixel clock generation unit includes four second pixel clock generation units 110 (1) to 110 (4). One modulation data generation unit and one laser drive unit are required for each light beam generator. In this embodiment, since there are four light beam generators, four modulation data generation units and four laser drive units are provided. It consists of two modulation data generation units 111 (1) to 111 (4) and laser drive units 112 (1) to 112 (4). The configurations of the second pixel clock generation units 110 (1) to 110 (4), the modulation data generation units 111 (1) to 111 (4), and the laser driving units 112 (1) to 112 (4) themselves are implemented. The configuration is the same as in Embodiment 1 and Embodiment 2.

Hereinafter, a setting method of the initial frequency setting values of the plurality of second pixel clock generation units 110 (1) and 110 (2) will be described.
When there are a plurality of scanning optical systems, there is a problem that the writing end position is shifted for each scanning optical system. As a method for detecting the writing end position, a predetermined alignment mark used as a reference when combining the images of the photoconductors 102 (1) to 102 (4) as described in Patent Document 2 is aligned. A method of detecting based on a sensor and calculating a positional deviation amount is known. Based on the calculation result of the positional deviation amount, an initial setting value of the frequency is set. Since the writing end position changes with time, the problem of misalignment of the writing end position due to an error for each scanning optical system can be solved by appropriately setting an initial setting value of the frequency.

  According to the present embodiment, in addition to the advantages of the first embodiment, the control system is compactly integrated, so that there is an advantage that component costs can be suppressed, and power consumption and current can be reduced.

FIG. 12 is a diagram for explaining an entire image forming apparatus according to still another embodiment of the present invention. One rotating polygon mirror, two light beam generators, four photosensitive members, four incident mirrors, 1 is a configuration diagram of an image forming apparatus including an optical system including one scanning lens and four scanning beam detectors.
That is, the image forming apparatus includes one rotating polygon mirror 100, four photosensitive members 102 (1) to 102 (4), four scanning lenses 101 (1) to 101 (4), and four incident mirrors 103 (1). ) -103 (4), two light beam generators 104 (1), 104 (2), four scanning beam detectors 106 (1) -106 (4), and the laser from the light beam generator. An optical system composed of the same number of light beam splitting elements 1200 and 1201 as a light beam generator that generates polarized light beams for splitting in two directions and generating a light beam splitting laser for scanning corresponding photosensitive members. The first pixel clock generation unit 108, the two third pixel clock generation units 1202 (1) and 1202 (2), the two modulation data generation units 111 (1) and 111 (2), and two laser drives Part 112 (1), 1 Consists of the control unit consisting of two (2).

Since one first pixel clock generation unit 108 is required for one rotary polygon mirror 100, only one first pixel clock generation unit 108 is used in the present embodiment. However, the first pixel clock generation unit 108 measures the time interval using any one of the plurality of scanning beam detectors 106 (1) to 106 (4).
The third pixel clock generation unit 1202 (1), 1202 (2), the modulation data generation unit 111 (1), 111 (2), and the laser driving unit 112 (1), 112 (2) are included in the light beam generator 1. One for each. In the present embodiment, the light beam generators 104 (1) and 104 (2) are provided for each of the two photoconductors, that is, two, so that there are two each.
Since the third pixel clock generators 1202 (1) and 1202 (2) have two scanning beam detectors 106 (1) and 106 (2) corresponding to one light beam generator, respectively. It is necessary to have initial values corresponding to the scanning beam detectors 106 (1) and 106 (2).

FIG. 13 is a diagram illustrating a configuration example of the third pixel clock generation unit 1202 (1) and 1202 (2) of the image forming apparatus illustrated in FIG.
In FIG. 13, a third pixel clock generation unit 1202 (1) includes an initial frequency setting unit 1300 that sets an initial frequency of the third pixel clock during scanning of the photosensitive member 102 (1), and the photosensitive member 102 (3). An initial frequency setting unit 1301, an adder 801, a logical sum 803, a digital control oscillator (DCO) 802, a selector 804, and a side signal generation unit 805 for setting the initial frequency of the third pixel clock during scanning.
Here, the side signal is switched to H or L according to the x-th synchronization signal and the y-th synchronization signal. The initial frequency setting unit 1300 holds a first initial frequency setting value, and the initial frequency setting unit 1301 holds a third initial frequency setting value. The adder 801 adds one of the initial frequency setting values selected by the selector 804 and the frequency correction value generated by the first pixel clock generation unit 108. A digital control oscillator (DCO) 802 generates a third pixel clock in phase with the synchronization signal.
Details will be described below.

FIG. 15 shows a timing chart of the third pixel clock generation unit.
The x-th synchronization signal is asserted when incident light is detected by the PD (photodiode) 106 (1). The y-th synchronization signal is asserted when incident light is detected by the PD 106 (3). The side signal becomes H level when the y-th synchronization signal is asserted, and becomes L level when the x-th synchronization signal is asserted. The synchronization signal is a logical sum of the xth synchronization signal and the yth synchronization signal. The first initial frequency setting value and the second initial frequency setting value are values held in a register. Ma is a value obtained by selecting the value ma of the first initial frequency setting value or the value mb of the second initial frequency setting value by the side signal. When side is L, the value ma of the first initial frequency setting value is selected, and when side is H, the value mb of the second initial frequency setting value is selected. Mi is a frequency setting value of the pixel clock, and is determined by Ma + frequency correction value. Therefore, Mi = ma + Δfc or Mi = mb + Δfc depending on the side signal. The pixel clock is updated to Mi = ma + Δfc or mb + Δfc by a synchronization signal, and the third pixel clock is output by the digital control oscillator 802 in phase synchronization with the synchronization signal.

  In this manner, the third pixel clock generation unit 1202 (1), 1202 (2) receives two of the synchronization signals output from the plurality of scanning beam detectors 106 (1), 106 (2). The frequency correction value is added to or subtracted from the initial frequency value of the clock set by the initial frequency setting units 1300 and 1301, and a third pixel clock is output. The modulation data generation units 111 (1) and 111 (2) modulate the image data by the third pixel clock output from the third pixel clock generation unit 1202 (1) and 1202 (2), and the laser driving unit 112. In (1) and 112 (2), the laser diode is turned on and off based on the modulated image data.

  DESCRIPTION OF SYMBOLS 100 ... Rotary polygon mirror, 101, 101 (1) -101 (4) ... Scan lens, 102, 102 (1) -102 (4) ... Photoconductor, 103, 103 (1) -103 (4) ... Incident mirror, 104, 104 (1) to 104 (4) ... Light beam generator, 105 ... Incident light, 106, 106 (1) to 106 (4) ... Scanning Beam detector 107... Pixel clock generator 108... First pixel clock generator 110, 110 (1) to 110 (4) Second pixel clock generator 1202 (1 ) 1202 (2)... Third pixel clock generation unit 111, 111 (1) to 111 (4)... Modulation data generation unit 112, 112 (1) to 112 (4). Laser drive unit, 200 ... DPD, 201 ... first counter 203 ... Moving average calculator, 204 ... Filter, 205 ... Divider, 206 ... Delay element, 207 ... Register, 208, 802 ... DCO, 800 ... Initial frequency setting vessel.

JP 2011-197253 A Japanese Patent No. 3773384

Claims (8)

A light beam generating means, a rotating polygon mirror having a plurality of mirrors for scanning the light beam of the light beam generating means on the photosensitive member, and a synchronization signal indicating the writing position of the photosensitive member upon receiving the light beam; An image forming apparatus comprising:
Measuring means for measuring a scanning period of the light beam with a first pixel clock based on the synchronization signal;
The frequency of the first pixel clock that is set so as to be the scanning cycle of the target value while controlling and outputting the frequency of the first pixel clock so that the measured value becomes a predetermined target value. And a first pixel clock generator that outputs the controlled frequency change as a frequency correction value. The image forming apparatus according to claim 1,
The first pixel clock generation unit includes a moving average calculating means for calculating a moving average value of the difference in the scanning period corresponding to the number of surfaces of the rotary polygon mirror, a means for smoothing the moving average value, and a smoothing Means for calculating an error of one pixel period from the calculated moving average value and target value, means for generating a change in frequency based on the calculated error of one pixel period, and a period of the target value An image forming apparatus comprising: means for generating a first pixel clock obtained by correcting a set frequency value of the first pixel clock with the frequency correction value. The image forming apparatus according to claim 1 or 2,
A second pixel clock generation unit that outputs a second pixel clock having a frequency obtained by adding the frequency correction value and a predetermined initial frequency setting value in phase synchronization with the synchronization signal;
An image forming apparatus comprising: a modulation data generation unit that converts image data into modulation data in synchronization with the second pixel clock; and a light beam drive unit that drives a light beam generation unit based on the modulation data. The image forming apparatus according to claim 3.
The second pixel clock generation unit is phase-synchronized with the synchronization signal based on the added frequency, an initial frequency setting unit, a unit for adding the initial frequency setting value set in the initial frequency setting unit and the frequency correction value. An image forming apparatus having oscillation means for generating a second pixel clock. In the image forming apparatus according to claim 3 or 4,
A plurality of modulation data generation units provided corresponding to the one first pixel clock generation unit, the plurality of second pixel clock generation units, and the plurality of second pixel clock generation units, respectively. A light beam generating means, a photoconductor, a plurality of the scanning beam detection means provided corresponding to each photoconductor, and one rotating polygon mirror,
The first pixel clock generation unit receives any one of the plurality of scanning beam detection units as a synchronization signal,
The second pixel clock generation unit outputs an image of the second pixel clock when any one of the plurality of synchronization signals output from the plurality of scanning beam detection units is input. Forming equipment. The image forming apparatus according to any one of claims 1 to 5,
The rotating polygon mirror comprises a plurality of rotating polygon mirrors each having a different number of surfaces,
The moving average calculating unit is an image forming apparatus that calculates the moving average of each of the plurality of rotary polygon mirrors by switching. The image forming apparatus according to claim 1 or 2,
A plurality of modulation data generation units, a plurality of modulation data generation units provided corresponding to the one first pixel clock generation unit, the plurality of third pixel clock generation units, and the plurality of third pixel clock generation units, respectively. Beam generating means, beam splitting element, one rotating polygon mirror, a plurality of photoconductors that scan with the light beam split by the light velocity splitting element, and a plurality of scanning beam detections provided corresponding to each photoconductor Means, and
The first pixel clock generation unit receives any one of the plurality of scanning beam detection units as a synchronization signal,
The third pixel clock generation unit outputs the third pixel clock when any two of the plurality of synchronization signals output from the plurality of scanning beam detection units are input. apparatus. A light beam generating means, a rotating polygon mirror having a plurality of mirrors for scanning the light beam of the light beam generating means on the photosensitive member, and a synchronization signal indicating the writing position of the photosensitive member upon receiving the light beam; An image forming method in an image forming apparatus comprising:
A measuring step of measuring a scanning period of the light beam with a first pixel clock based on the synchronization signal;
The frequency of the first pixel clock that is set so as to be the scanning cycle of the target value while controlling and outputting the frequency of the first pixel clock so that the measured value becomes a predetermined target value. A first pixel clock generation step of outputting the controlled frequency change as a frequency correction value;
A second pixel clock generation step of outputting a second pixel clock having a frequency obtained by adding the frequency correction value and a predetermined initial frequency setting value in response to the input of the synchronization signal;
A modulation data generation step of converting image data into modulation data in synchronization with the second pixel clock;
A light beam driving step of driving the light beam generating means based on the modulation data;
An image forming method comprising:

Images