JP6565610B2 - Signal processing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a signal processing apparatus that performs signal processing based on image data and a technique that can eliminate a difference from an ideal value of an image forming signal in an image forming apparatus.

As an image forming apparatus, an image forming signal is generated according to image data, and an image is formed for one line or several lines in the main scanning direction using the image forming signal, and an image is formed for each line in the main scanning direction. Is known in which image formation for one page is performed by repeating the above in the sub-scanning direction.
As an example, in an electrophotographic image forming apparatus, an image forming signal (PWM signal by a PWM circuit) is generated from image data, and a laser beam modulated in accordance with the PWM signal is scanned in the main scanning direction. An image is formed by the laser beam on the image carrier that rotates in the sub-scanning direction.

By the way, the image formation signal such as the PWM signal varies due to various factors such as environmental factors such as temperature changes and individual differences of circuit elements, and becomes a value different from the originally planned value (ideal value). Sometimes. Due to the fluctuation of the image forming signal, it appears as an image density change.
The image formation in the main scanning direction according to the image data is positioned with reference to an image processing clock called “image processing clock” or “dot clock” which is a reference of the pixel to be formed.

  As a technique for correcting the density change in such an image forming apparatus, for example, it is described in the following patent documents.

JP 2006-150696 A JP 2013-45051 A JP-A-8-156330 Japanese Patent Laid-Open No. 9-200008 JP-A-8-265532 JP-A-8-337006

In the above Patent Documents 1-6, the target is to keep the image forming density at a predetermined value by measuring the pulse width and correcting the pulse width.
By the way, the inventor of the present application has verified the signal processing device used in the image forming apparatus. When a low-density dot is to be formed by the shortest pulse in each pixel, the laser beam is periodically emitted. It was confirmed that the phenomenon of light emission / no light emission occurred. For such light emission / non-light emission of the low-density dots, the PWM pulse width of the image forming signal is periodically subtle due to analog factors such as the influence of the circuit of the output stage of the PWM pulse generation unit. It turned out to be caused by the change. This cause may be a combination of various analog factors.

For example, as shown in FIG. 8, a subtle change in PWM pulse width may occur periodically in units of 4 dots, such as wide, wide, narrow, and narrow ((a1 in FIG. 8A). ), (A2), (a3), (a4)).
In this case, a periodic phenomenon such as light emission / light emission / non-light emission / non-light emission of the laser beam periodically occurs ((b1), (b2), (b3),. ). Here, (b3) corresponding to FIG. 8 (a3), which is narrow, shows a non-light-emitting state. Note that the next light emission timing of (b3) is also not lighted, although not shown.

When a low density is to be formed in this way, the laser beam is in a non-light emitting state, resulting in deterioration of gradation and graininess, resulting in a problem of deterioration of image quality.
Further, it has been found that when fine tilt correction of an image is performed, the periodic laser beam emission / non-emission becomes periodic unevenness in a direction that is slightly inclined in the sub-scanning direction. Such periodic unevenness may be easily visually recognized due to the spatial frequency even if the density change is subtle, which causes image quality degradation.

Note that the above problems are caused by various factors such as circuit compatibility between the circuit of the output stage of the PWM pulse generation unit and the laser drive unit of the exposure unit, the influence of fluctuations in the power supply voltage, and the like. It is difficult to specify.
In addition, it has been confirmed that the defect cycle varies depending on the relationship between the image processing clock and the PWM pulse, that is, how many PWM pulses are generated for one clock pulse. It is difficult to identify the cause.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to realize a signal processing apparatus and an image forming apparatus capable of improving an adverse effect on image quality due to a minute difference in pulse width. There is to do.

In order to achieve at least one of the above objects, a signal processing apparatus and an image forming apparatus reflecting one aspect of the present invention are configured as follows.
(1) This invention refers to an image processing clock corresponding to each pixel of image data and generates a pulse width modulated image forming signal for image formation in accordance with the image data, and the image The measurement clock that is asynchronous with the processing clock is supplied, the valid state and invalid state of the pulse of the imaging signal are counted over a predetermined period using the measurement clock, and the pulse included in the count result is high or low. the ratio, comprising: a measuring unit for measuring the pulse width of the imaging signal, and a control unit for controlling said said PWM processing unit measuring unit, wherein the control unit, in the measurement mode, the imaging signal When the pulse width of the signal changes to a plurality of states at a predetermined cycle, a plurality of image forming signals in a specific order in the predetermined cycle are continuously generated by the PWM processing unit, and the measurement unit is measured. Repeating the operation for each of the plurality of states to control the pulse width of the image forming signal, respectively, averaging the measurement values in the plurality of states, determining an average pulse width as a reference value, The PWM processing unit is controlled to determine a correction value that matches each pulse width of the image forming signals in a plurality of states with a reference value, and the correction value is used in the actual operation mode while the correction value is used. The PWM processing unit is controlled to generate an image forming signal.

  (2) In the above (1), the PWM processing unit refers to the measurement result of the measurement unit, determines the reference value of the pulse width in the predetermined cycle, and in which order the image forming signal is in the predetermined cycle. The correction value for correcting the pulse width to be the reference value is determined and applied depending on whether it exists.

In the signal processing apparatus and the image forming apparatus reflecting one aspect of the present invention, the following effects can be obtained.
(1) In the present invention, in the measurement mode, when the pulse width of the image forming signal changes to a plurality of states at a predetermined cycle, the PWM processing unit continuously generates a plurality of image forming signals in a specific order in the predetermined cycle. Control the measurement unit to measure each of the pulse widths of the image forming signal by repeating the measurement for each of the multiple states, average the measured values in the multiple states, determine the average pulse width as the reference value, The PWM processing unit is controlled to determine a correction value that matches each pulse width of the image formation signal in the state with the reference value, and in the actual operation mode, the image formation signal corresponding to the image data is generated while using the correction value. By controlling the PWM processing unit in this way, it is possible to improve the adverse effect on the image quality in the image forming apparatus due to a minute difference in pulse width.
Here, the measurement unit is supplied with a measurement clock that is asynchronous with the image processing clock, counts the valid state and invalid state of the pulse of the image forming signal over a predetermined period using the measurement clock, and is included in the count result. By measuring the pulse width based on the ratio of the pulse being high or low, the pulse width of the image forming signal can be accurately obtained.

  (2) In the above (1), referring to the measurement result, a reference value in a predetermined cycle of the pulse width is determined, and the pulse width becomes the reference value according to the order in which the imaging signal is in the predetermined cycle. By determining and applying the correction value to be corrected in this way, it is possible to reliably improve the adverse effect on the image quality in the image forming apparatus due to a minute difference in pulse width.

It is a block diagram which shows the structure of the signal processing apparatus of embodiment of this invention. It is a block diagram which shows the structure of the signal processing apparatus of embodiment of this invention. It is a block diagram which shows the structure of the signal processing apparatus of embodiment of this invention. It is a flowchart explaining operation | movement of embodiment of this invention. It is explanatory drawing which shows the mode of the signal processing of an image forming apparatus. It is explanatory drawing which shows the mode of the signal processing of an image forming apparatus. It is a block diagram which shows the other structure of the signal processing apparatus of embodiment of this invention. It is explanatory drawing which shows the state of the conventional signal processing and light emission.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments (embodiments) for implementing a signal processing apparatus and an image forming apparatus of the present invention will be described in detail with reference to the drawings.
[Configuration of Signal Processing Apparatus and Image Forming Apparatus (1)]
Here, the configuration of the signal processing apparatus 100 that can be used for image formation will be described in detail with reference to FIGS. Note that description of general parts that are known as the signal processing apparatus 100 and that are not directly related to the characteristic operation and control of the present embodiment is omitted.

  Further, here, as the signal processing device 100 used in the image forming apparatus, a clock generation unit 50 included in the image forming apparatus and an exposure unit that performs image formation exposure using an image forming signal generated by the signal processing apparatus 100. 210 is also illustrated. Note that a description of portions common to the image forming apparatus is omitted.

The clock generation unit 50 generates an image processing clock PXLCLK corresponding to dots generated by image formation and a measurement clock MSRCLK used for measurement because the phase and frequency of the image processing clock PXLCLK are asynchronous. ing.
The signal processing device 100 includes a control unit 101 that controls each unit of the signal processing device 100, an image processing unit 110 that performs various processes on the image data, and a PWM that generates a pulse signal for each pixel in accordance with the image data or measurement data. The processing unit 120, a buffer 130 that outputs the pulse signal generated by the PWM processing unit 120 as a signal waveform of a predetermined voltage, and a measurement unit 140 that measures the output of the PWM processing unit 120 or the output of the buffer 130 using the measurement clock MSRCLK , And is configured.

The PWM processing unit 120 includes a processing unit 121, a calculation unit 122, a frequency division unit 123, a delay element array 124, a timing adjustment unit 125, a synchronous calculation unit 126, and an output unit 128. It is configured.
Here, the processing unit 121 performs image processing necessary for PWM processing on image data during normal signal processing, generates measurement data during measurement, and outputs the measurement data to the calculation unit 122.

The calculation unit 122 calculates a necessary timing based on the image data or measurement data from the processing unit 121 and supplies the timing instruction value to the timing adjustment unit 125 and the output unit 128.
The delay element array 124 finely delays one cycle of the divided image processing clock PXLCLK ′ (two cycles of the image processing clock PXLCLK) obtained by dividing the image processing clock PXLCLK by the frequency dividing unit 123 into several hundred stages. As described above, the delay elements are connected in several hundreds of stages to output a delayed signal group. For example, in the delay element row 124, 512 stages of delay elements are connected so as to be finely delayed to about 400 to 500 stages for one period of the divided image processing clock PXLCLK ′.

The synchronization calculation unit 126 refers to the image processing clock PXLCLK, and calculates the delay time per delay element from the number of delay signal groups synchronized with one clock of the image processing clock PXLCLK.
As shown in FIGS. 2 to 3, the timing adjustment unit 125 includes a plurality of timing adjustment circuits 125 a to 125 e.

The plurality of timing adjustment circuits 125a to 125e respectively control the rising timing and the falling timing with respect to the pulse widths of the plurality of pulse signals that are to be image forming signals.
Here, assuming a case where a wide / narrow pulse width periodically occurs between two pulses of the first pulse and the second pulse, the rising timing adjustment of the first pulse, the falling timing adjustment of the first pulse, A total of five timing adjustment circuits are provided for the rise timing adjustment of the second pulse, the fall timing adjustment of the second pulse, and the timing switching. In addition, in the case where wide / narrow pulse widths periodically occur in the four pulses from the first pulse to the fourth pulse, a total of nine timing adjustment circuits are provided by the rise and fall of each four pulses and the timing switching. It only has to be provided. That is, in the case where the width of the pulse width is periodically increased / decreased by n pulses, a total of 2n + 1 timing adjustment circuits may be provided for the rise and fall of each n pulse and timing switching (described later). (See FIG. 7).

Note that each of the timing adjustment circuits 125a to 125e includes a selector 125_1, a delay train 125_2, and a selector 125_3, as shown in FIG.
Here, the selector 125_1 selects a pre-adjustment timing for the rise or fall of the pulse signal to be generated from the delay signal group from the delay element array 124 according to an instruction from the arithmetic unit 122. The delay string 125_2 includes a plurality of delay element strings, and generates timing signals having different delay times from the timing signal selected by the selector 125_1. Note that the delay train 125_2 is configured by connecting delay elements of about several tens of stages to the extent necessary for adjusting the rising or falling timing of a pulse signal to be an image forming signal. The selector 125_3 selects the timing after the fine adjustment of the rising edge or the falling edge of the pulse signal to be generated from the delay signals from the delay train 125_2 according to the instruction from the arithmetic unit 122.

The output unit 128 receives the rise and fall of each pulse generated by the timing adjustment unit 125, and generates and outputs a pulse signal having a finely adjusted pulse width.
[Operation]
Hereinafter, the operation of the signal processing device 100 and the operation of the image forming apparatus including the signal processing device 100 will be described with reference to the flowchart of FIG. 4 and the time charts of FIG.

[Measurement operation]
The control unit 101 checks whether or not the signal processing apparatus 100 is executing signal processing for image formation, and whether the signal processing apparatus 100 corresponds to a specific timing immediately after the power is turned on or after a certain period of signal processing execution has elapsed. (Step S100 in FIG. 2).

  When the signal processing is not being performed and the specific timing is met (YES in step S100 in FIG. 4), the control unit 101 sets the operation mode of the signal processing device 100 to the measurement mode (step S101 in FIG. 4). The control unit 101 supplies an operation mode signal for switching the operation mode to the processing unit 121, the calculation unit 122, the measurement unit 140, and the like.

Here, the control unit 101 controls the PWM processing unit 120 so as to continuously output pulses having a predetermined pulse width (step S102 in FIG. 4).
The predetermined pulse width is a first pulse width that forms a low-density image that starts to emit light in the exposure unit 210. Further, as the predetermined pulse width, a first pulse width that forms a low-density image that starts to emit light in the exposure unit 210 and a high-density image that emits light to the maximum in the exposure unit 210 are formed. The second pulse width may be two types.

  That is, the processing unit 121 set in the measurement mode from the control unit 101 generates measurement data for continuously outputting pulses having a predetermined pulse width and supplies the measurement data to the calculation unit 122. In the normal actual operation mode, the processing unit 121 processes the image data from the previous image processing unit 110 and supplies the processed image data to the calculation unit 122.

The arithmetic unit 122 selects an appropriate pulse rising timing and pulse falling timing in the timing adjustment unit 125 in order to generate a PWM signal having a predetermined pulse width according to the measurement mode data received from the processing unit 121. Give instructions for.
In response to the instruction from the arithmetic unit 122, the timing adjustment unit 125 selects a delay signal having a timing corresponding to rising and falling of a predetermined pulse width from the group of delay signals from the delay element array 124, and Output to the output unit 128. The output unit 128 generates a PWM signal having a predetermined pulse width by using the rising and falling edges of the delay signal output from the timing adjustment unit 125 and supplies the PWM signal to the buffer 130.

  Then, a PWM signal having a predetermined pulse width as described above is supplied from the output of the PWM processing unit 120 (output unit 128) or the output of the buffer 130 to the measurement unit 140, and there is a periodic difference in the pulse width. The measuring unit 140 measures whether or not it has occurred (step S103 in FIG. 4).

Here, the first pulse width as described above is continuously measured to check whether or not there is a difference in the pulse width, and then the second pulse width as described above is continuously measured and the difference in the pulse width is determined. The control unit 101 controls the PWM processing unit 120 so as to check whether the occurrence has occurred.
Actually, the width / width is narrowed for each pulse in a 2-pulse cycle, and the width / width / width / width is narrowed for every 2 pulses in a 4-pulse cycle. It is only necessary to measure about several hundred pulses to determine the occurrence / non-occurrence of wide / narrow and the generation cycle. The generation cycle in this case is such that when n pulses are generated for one pulse of the clock PXLCLK, the n pulses have a predetermined cycle (pulse width change generation cycle). Has been confirmed. Further, when the signal processing apparatus 100 has already been required to have a wide / narrow pulse width, this step can be omitted.

If there is no difference in the pulse width (NO in step S103 in FIG. 4), the measurement process is terminated (end in FIG. 4).
When the difference is periodically generated in the pulse width (YES in step S103 in FIG. 4), the control unit 101 executes the following processing. The control unit 101 processes the processing unit 121, the calculation unit 122, the timing adjustment unit 125, and the output unit 128 so as to continuously output the specific signal in the pulse width change generation cycle as a pulse having the above-described predetermined pulse width. Is controlled (step S104 in FIG. 4).

  Further, the pulse width output from the PWM processing unit 120 when the specific signal in the pulse width change generation period is continuously output is continuously measured by the measurement unit 140 (step S105 in FIG. 4). . Here, in order to reduce errors as necessary, the measurement results may be averaged after removing the maximum and minimum values.

  If the pulse width change generation cycle is two pulses, the first pulse in the two generation cycles is continuously output (step S104 in FIG. 4), and this pulse width is continuously measured (step in FIG. 4). S105), then (step S106 in FIG. 4), continuously output the second pulse of the remaining two pulses of the generation cycle (step S104 in FIG. 4), and continuously measure the pulse width (FIG. 4). Middle step S105).

  If the generation period of the pulse width change is four pulses, the first pulse in the four generation periods is continuously output (step S104 in FIG. 4), and this pulse width is continuously measured (step in FIG. 4). S105), and then (step S106 in FIG. 4), hereinafter, the continuous output of the second pulse in the four pulses and the continuous measurement, the continuous output of the third pulse in the four pulses, the continuous measurement, and the four of the four pulses Execute like continuous output and continuous measurement of the pulse.

  However, if the change in pulse width repeats the same state as wide, wide, narrow and narrow, the first pulse (wide) of the four generation cycles is output continuously and continuously measured (in FIG. 4 Steps S104 to S105) The third pulse (narrow) of the four pulses is continuously output and continuously measured (Steps S104 to S105 in FIG. 4). Output and measurement can be omitted (step S106 in FIG. 4).

That is, when a plurality of imaging signals are included for the same state in a plurality of states of the pulse width included in the pulse width change generation cycle, the pulse width is measured for at least one imaging signal for the same state. Also good.
Note that the measurement unit 140 is supplied with a measurement clock MSRCLK whose frequency and phase are asynchronous with the image processing clock PXLCLK from the clock generation unit 50. Then, the measurement unit 140 counts the valid state and invalid state of the measurement target pulse (pulse of the imaging signal) over a predetermined period using the measurement clock MSRCLK, and determines the valid state and invalid state included in the count result. Based on the ratio, the pulse width of the measurement target pulse (pulse of the image forming signal) is measured.

  The frequency f2 [Hz] of the measurement clock MSRCLK is preferably 0.5f1 <f2 <f1 when the frequency of the image processing clock PXLCLK is f1 [Hz]. In other words, asynchronous means that the frequency of the image processing clock and the frequency of the measurement clock are not in an integer ratio relationship. More preferably, it means that the frequency of the image processing clock and the frequency of the measurement clock are not in an integer ratio relationship and the rising and falling phases are not matched as much as possible.

  Here, sampling of whether the measurement target pulse is high or low (valid state or invalid state) is repeated a predetermined number of times, for example, 1000 times, at either the rising edge or falling edge of the measurement clock MSRCLK. . As a result, even if the measurement clock is at a lower frequency than the image processing clock, it is asynchronous and sampling of a random phase is possible. By further increasing the number of times, the error is reduced and the measurement target pulse (imaging signal) The pulse width of the second pulse can be measured.

  When the measurement of the pulse width for each pulse is completed as described above (YES in step S106 in FIG. 4), the control unit 101 that has obtained the measurement result from the measurement unit 140 determines the pulse width for the correction described later. A reference value is determined (step S107 in FIG. 4). The reference value is desirable because the entire density change does not occur by determining the reference value based on the average of the pulse width measurement results in the pulse width change generation period.

Then, the control unit 101 calculates, as an error time, the difference between the pulse width measurement result and the reference value described above for each pulse obtained as described above. This difference (error time) corresponds to the amount to be corrected.
Here, the control unit 101 supplies the error time, which is a difference from the reference value calculated for each pulse, to the calculation unit 122. The calculation unit 122 converts the error time for each pulse supplied from the control unit 101 into a correction value and stores it (step S108 in FIG. 4).

  The arithmetic unit 122 calculates a timing adjustment value (correction value) in the timing adjustment unit 125 from the error time supplied from the control unit 101 at the rise and fall of each pulse. This correction value is a value for fine adjustment of timing by selecting the delay time in the delay sequence 125_2 already described. That is, each timing adjustment value (correction value) is calculated and stored as necessary for each pulse in the pulse width change generation cycle.

  Then, with the timing adjustment values applied by the timing adjustment unit 125, the processes in steps S104 to S109 are repeated to check whether the difference in pulse width when a predetermined pulse width is generated is eliminated. (Step S110 in FIG. 4).

If the above-described difference in pulse width in the pulse width change generation period has been eliminated (YES in step S110 in FIG. 4), control unit 101 causes the measurement mode in the operation mode signal to end the above measurement operation. Is canceled (END in FIG. 4).
The operation waveforms of the respective units in the above-described measurement mode in the PWM processing unit 120 configured as shown in FIGS. 1 to 3 are as shown in FIG. Here, it is assumed that the pulse width change generation cycle has a difference in pulse width every two pulses.

Here, in the time chart of FIG. 5, FIG. 5A shows the measurement data generated by the processing unit 121 in the measurement mode, and the processing unit 121 processes the data input from the preceding image processing unit 110 in the actual operation mode. Image data.
5B1 shows the image processing clock PXLCLK supplied from the clock generation unit 50, and FIG. 5B2 shows the frequency-divided image processing clock PXLCLK ′ generated by dividing the image processing clock PXLCLK by 2 by the frequency division unit 123. It is. FIG. 5C shows a delay signal generated by being selected from the delay signal group in the timing adjustment circuit 125a, and is used as a switching signal for identifying the order of pulses in the pulse width change generation period. In order to identify the order of the pulses, it is also desirable to use an index signal (not shown) in addition to the switching signal as necessary.

  FIG. 5D is a delay signal generated by being selected from the delay signal group in the timing adjustment circuit 125b as the eleventh selector, and the rising timing of the first pulse in the pulse width change generation cycle (FIG. 5D). This is a delay signal used for t11) in 5 (h). FIG. 5E shows a delay signal selected and generated from the delay signal group in the timing adjustment circuit 125c as the twelfth selector, and the falling timing of the first pulse in the pulse width change generation cycle (FIG. 5). This is a delay signal used at t12) in 5 (h).

  FIG. 5F shows a delay signal generated by being selected from the delay signal group in the timing adjustment circuit 125d as the 21st selector, and the rising timing of the second pulse in the pulse width change generation cycle (FIG. 5F). This is a delay signal used at t21) in 5 (h). FIG. 5G shows a delay signal selected and generated from the delay signal group in the timing adjustment circuit 125e as the 22nd selector, and the falling timing of the second pulse in the pulse width change generation period (FIG. 5G). This is a delay signal used at t22) in 5 (h).

  FIG. 5H shows a predetermined pulse generated by the output unit 128 using the rising and falling edges of each delay signal output from the timing adjustment circuits 125a to 125e of the timing adjustment unit 125 described above. PWM signal of width. Since the odd / even pixels of the image processing clock PXLCLK are known by using the H level and the L level of the switching signal PXLCLK ′ (FIG. 5 (b2)), the first timing adjustment circuits 125a to 125e The selection of the use edge of the delay signal when generating the second pulse and the second pulse and the identification when generating the first pulse and the second pulse in the output unit 128 are performed.

  In FIG. 5, (c) to (g) have the same waveform, but only the timing of change is different. Here, signal rounding may differ between rising and falling of the delayed signal. Here, due to some cause, the rise is more sluggish than the fall. As a cause of such a phenomenon, a power supply voltage drop may occur in the delay train. Alternatively, the power supply voltage may periodically drop. Furthermore, the degree of power supply voltage drop may differ depending on the substrate, device, channel, delay line location, and the like. And these phenomena may occur in combination.

  Here, as the circuit configuration when generating the PWM signal, either the normal rotation signal or the inversion signal is used for the selector signal in which the rising edge is rounded, or the falling edge selector signal in which the rounding is not caused is used. Therefore, the pulse width of the PWM signal (t11 to t12, t21 to t22 in FIG. 5H) periodically changes. Here, every two pulses of the PWM signal, the width is periodically changed from narrow to wide to narrow to wide.

FIG. 6 shows the operation waveforms of the respective parts in the measurement mode when the pulse width change generation cycle has a difference in pulse width every four pulses. If the pulse width changes every four pulses in this way, as shown in FIG. 7, the timing adjustment circuit included in the timing adjustment unit 125 uses the timing for the switching signal and the rise timing for four pulses. A total of nine circuits, that is, an adjustment circuit and a timing adjustment circuit for falling timing for four pulses, are required.
Specifically, as shown in FIG. 7, timing adjustment circuits 125 a to 125 i are provided in the timing adjustment unit 125.

Here, in the time chart of FIG. 6, FIG. 6A shows the measurement data generated by the processing unit 121 in the measurement mode, and the processing unit 121 processes the data input from the preceding image processing unit 110 in the actual operation mode. Image data.
6B1 shows the image processing clock PXLCLK supplied from the clock generation unit 50, and FIG. 6B2 shows the divided image processing clock PXLCLK ′ generated by dividing the image processing clock PXLCLK by 2 by the dividing unit 123. It is. FIG. 6C shows a delay signal generated by being selected from the delay signal group in the timing adjustment circuit 125a, and is used as a switching signal for identifying the order of pulses in the pulse width change generation cycle. In order to identify the order of the pulses, it is also desirable to use an index signal (not shown) in addition to the switching signal as necessary.

  FIG. 6 (d1) is a delay signal selected and generated from the delay signal group in the timing adjustment circuit 125b as the eleventh selector, and the rising timing of the first pulse in the pulse width change generation cycle (FIG. 6). This is a delay signal used for t11) in 6 (h). FIG. 6 (d2) is a delay signal selected and generated from the delay signal group in the timing adjustment circuit 125c as the twelfth selector, and the falling timing of the first pulse in the pulse width change generation cycle (FIG. 6). This is a delay signal used at t12) in 6 (h).

  FIG. 6 (e1) is a delay signal selected and generated from the delay signal group in the timing adjustment circuit 125d as the 21st selector, and the rising timing of the second pulse during the pulse width change generation cycle (FIG. 6). This is a delay signal used at t21) in 6 (h). FIG. 6 (e2) is a delay signal generated by being selected from the delay signal group in the timing adjustment circuit 125e as the 22nd selector, and the fall timing of the second pulse in the pulse width change generation cycle (FIG. 6). This is a delay signal used for t22) in 6 (h).

  FIG. 6 (f1) is a delay signal selected and generated from the delay signal group in the timing adjustment circuit 125f as the 31st selector, and the rising timing of the third pulse in the pulse width change generation cycle (FIG. 6). This is a delay signal used at t31) in 6 (h). FIG. 6 (f2) is a delay signal generated by being selected from the delay signal group in the timing adjustment circuit 125g as the thirty-second selector, and the falling timing of the third pulse in the pulse width change generation cycle (FIG. This is a delay signal used at t32) in 6 (h).

  FIG. 6 (g1) is a delay signal selected and generated from the delay signal group in the timing adjustment circuit 125h as the 41st selector, and the rising timing of the fourth pulse in the pulse width change generation cycle (FIG. 6). This is a delay signal used at t41) in 6 (h). FIG. 6 (g2) is a delay signal generated by being selected from the delay signal group in the timing adjustment circuit 125i as the forty-second selector, and the falling timing of the fourth pulse in the pulse width change generation cycle (FIG. 6). 6 (h) is a delay signal used at t42).

  FIG. 6H illustrates a predetermined pulse generated by the output unit 128 using the rising and falling edges of each delay signal output from the timing adjustment circuits 125a to 125i of the timing adjustment unit 125 described above. PWM signal of width. Since the odd / even pixels of the image processing clock PXLCLK are known by using the H level and the L level of the switching signal PXLCLK ′ (FIG. 6 (b2)), the first timing adjustment circuits 125a to 125i The selection of the use edge of the delay signal when generating the 1st pulse to the 4th pulse and the identification when generating the 1st pulse to the 4th pulse in the output unit 128 are performed.

  In FIG. 6, (c) to (g2) have the same waveform, but only the timing of change is different. As described with reference to FIG. 5, the signal rounding may be different between the rising edge and the falling edge of the delay signal, and here, for some reason, the rounding of the rising edge is caused compared to the falling edge.

  Here, as the circuit configuration when generating the PWM signal, either the normal rotation signal or the inversion signal is used for the selector signal in which the rising edge is rounded, or the falling edge selector signal in which the rounding is not caused is used. Therefore, the pulse width of the PWM signal (t11 to t12, t21 to t22, t31 to t32, t41 to t42 in FIG. 6H) periodically changes. Here, every four pulses of the PWM signal, the width is periodically changed as narrow, narrow, wide, wide, narrow, narrow, wide, wide, and so on.

In practice, there is a possibility that the pulse width of the PWM signal periodically changes in various states other than those shown in FIGS. 5 and 6 based on various factors.
[Actual operation (signal processing for image formation)]
The control unit 101 checks whether or not the signal processing apparatus 100 is executing signal processing for image formation, and whether the signal processing apparatus 100 corresponds to a specific timing immediately after the power is turned on or after a certain period of signal processing execution has elapsed. (Step S100 in FIG. 2). When it does not correspond to the specific timing (NO in step S100 in FIG. 4), the control unit 101 sets the signal processing device 100 to the actual operation mode (step S111 in FIG. 4). The control unit 101 supplies an operation mode signal for switching the operation mode to the processing unit 121, the calculation unit 122, the measurement unit 140, and the like.

When an image processing instruction or image data input occurs (YES in step S112 in FIG. 4), the image data processed by the image processing unit 110 passes through the processing unit 121 and is supplied to the calculation unit 122. (Step S113 in FIG. 4).
The calculation unit 122 generates a PWM signal having a predetermined pulse width according to the image data while applying the correction value calculated in the measurement mode. Therefore, the timing adjustment unit 125 generates appropriate pulse rise timing and pulse fall time. An instruction for selecting the timing is given (step S114 in FIG. 4).

  In addition, as an application of the correction value calculated in the measurement mode, a method of correcting only with a pulse width corresponding to a low density such that light emission of the exposure unit 210 emits light / non-light emission in a predetermined cycle in an uncorrected state; Two types are conceivable: a method of correcting the pulse width of each density region using the measurement results measured at the low concentration and the high concentration.

  In response to the instruction from the arithmetic unit 122, the timing adjustment unit 125 selects a delay signal having a timing corresponding to rising and falling of a predetermined pulse width from the group of delay signals from the delay element array 124, and Output to the output unit 128. The output unit 128 generates a PWM signal having a predetermined pulse width by using the rising and falling edges of the delay signal output from the timing adjustment unit 125 and supplies the PWM signal to the buffer 130.

The buffer 130 supplies the PWM signal as an image forming signal to the exposure unit 210 (step S115 in FIG. 4). In addition, it is preferable to perform signal transmission between the buffer 130 and the exposure unit 210 by LVDS (Low Voltage Differential Signaling) or the like.
Upon receiving the image forming signal from the buffer 130, the exposure unit 210 performs exposure (image formation) by performing exposure on an image carrier such as a photosensitive drum (not shown) (step S116 in FIG. 4). Since various known methods can be used for image formation, specific examples are omitted.

  When the signal processing for image formation ends (end in FIG. 4), the control unit 101 returns to step S100, and whether the signal processing apparatus 100 is executing signal processing for image formation for image formation. Whether or not it corresponds to a specific timing immediately after the power is turned on or after a certain period of signal processing execution is checked, and the measurement mode (steps S101 to S101 in FIG. 4) is executed as necessary.

[Effect obtained by the embodiment]
In the above embodiments, in the measurement mode, when the pulse width of the image forming signal changes to a plurality of states at a predetermined cycle, the PWM processing unit continuously generates a plurality of image forming signals of a specific order in the predetermined cycle and performs measurement. Control to measure the pulse width of the image forming signal in each of the plurality of states by repeating the measurement in the plurality of states, and match the image forming signal to the predetermined pulse width based on the measurement result of the measuring unit. By controlling the PWM processing unit to determine the correction value and controlling the PWM processing unit so as to generate an image forming signal corresponding to the image data while using the correction value in the actual operation mode, the pulse width is very small. The adverse effect on the image quality in the image forming apparatus due to the difference can be improved.

  Also, referring to the measurement result, a reference value in a predetermined cycle of the pulse width is determined, and a correction value for correcting the pulse width to become the reference value according to the order in which the imaging signal is in the predetermined cycle. By defining and applying, it is possible to reliably improve the adverse effect on the image quality in the image forming apparatus due to a minute difference in pulse width.

In addition, by determining the reference value based on the average of the measurement results of the pulse width in a predetermined period, it is possible to improve the adverse effect on the image quality in the image forming apparatus due to a minute difference in pulse width, and the overall density after correction is also appropriate. Maintained at the value.
In addition, when a plurality of image forming signals are included for the same state among a plurality of states having a pulse width included in a predetermined cycle, the pulse width is measured by measuring the pulse width for at least one image forming signal for the same state. It is possible to reliably improve the adverse effect on the image quality in the image forming apparatus due to a minute difference without waste.

  In addition, the measurement unit receives a measurement clock that is asynchronous with the image processing clock, counts the valid state and invalid state of the pulse of the image forming signal over a predetermined period using the measurement clock, and includes the valid result included in the count result. By measuring the pulse width based on the ratio between the state and the invalid state, the pulse width of the image forming signal can be accurately obtained.

[Other operations (1)]
In the above embodiment, the specific example of “wide / narrow” is shown as the case where the pulse width of the image forming signal changes to a plurality of states at a predetermined cycle. However, the present invention is not limited to this. As a result of the measurement, there may be a state of “appropriate / narrow” or “appropriate / wide”. In this case, an appropriate pulse width may be determined as a reference value for correction.

[Other operations (2)]
Further, in the above embodiment, as the case where the pulse width of the image forming signal changes to a plurality of states at a predetermined cycle, two states of “wide / narrow” are shown as specific examples, but the present invention is not limited to this. . When the predetermined period is 3 pulses or more, there may be three states or four states. Even in such a case, the pulse width may be corrected by determining the reference value as in the above embodiment.

[Other operations (3)]
Further, in the problem or embodiment to be solved, a specific example is given of a case where the image quality deteriorates due to a state where the exposure part emits light or does not emit light due to a change in low-density pulse width, but this is limited to this phenomenon. It is not something.

For example, in the case of a pulse width corresponding to another density, if the periodic pulse width change occurs for some reason to affect the image quality, the above embodiment is applied to the pulse width affecting the image quality. By executing, it becomes possible to eliminate the influence on the image quality.
[Other operations (4)]
The image forming apparatus capable of using the signal processing apparatus 100 is assumed to be an electrophotographic image forming apparatus, but is not limited thereto. That is, it is possible to use the signal processing apparatus 100 of the above embodiment for various types of image forming apparatuses.

100 Signal Processing Device 101 Control Unit 105 Clock Generation Unit 110 Image Processing Unit 120 PWM Processing Unit 130 Buffer 140 Measurement Unit 210 Exposure Unit

Claims (3)

A PWM processing unit that generates an image forming signal that is pulse-width modulated for image formation in accordance with the image data with reference to an image processing clock corresponding to each pixel of the image data;
The measurement clock that is asynchronous with the image processing clock is supplied, the valid state and invalid state of the pulse of the image forming signal are counted over a predetermined period using the measurement clock, and the pulse included in the count result is high. A measurement unit for measuring the pulse width of the image forming signal according to a ratio of low ;
A control unit for controlling the PWM processing unit and the measurement unit,
The controller is
In the measurement mode, when the pulse width of the imaging signal changes to a plurality of states at a predetermined cycle, the PWM processing unit continuously generates a plurality of imaging signals in a specific order in the predetermined cycle, and the measurement unit Repeating the measurement for each of the plurality of states, and controlling to measure the pulse width of the image forming signal in the plurality of states, averaging the measured values in the plurality of states, and calculating the average pulse width Is defined as a reference value, and the PWM processing unit is controlled so as to determine a correction value that matches each pulse width of the imaging signals in the plurality of states with the reference value,
In the actual operation mode, the PWM processing unit is controlled to generate the image forming signal according to the image data while using the correction value.
A signal processing apparatus. The PWM processing unit refers to a measurement result of the measurement unit, determines a reference value of the pulse width in the predetermined cycle, and determines the pulse width according to the order in which the imaging signal is in the predetermined cycle. Determining and applying the correction value for correcting the reference value to the reference value,
The signal processing apparatus according to claim 1. A signal processing device according to any one of claims 1 to 2 , comprising:
Forming an image by the image forming signal generated by the signal processing device according to image data;
An image forming apparatus.