JP2018069656A - Pwm processing circuit and image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate a PWM signal for image formation in a proper cycle using a partial variable power clock.SOLUTION: A PWM processing circuit 140 to which a partial variable power clock having a different cycle at a position where the laser beam is scanned on a photoreceptor is input and which generates a PWM signal in accordance with the partial variable power clock and image data includes: a delay unit 141 which generates a plurality of delay signals with the different timings at a prescribed interval from a partial variable power clock signal; a state detection unit 142 which obtains a state detection result showing the fact that what stage of the plurality of delay signals is equivalent to the cycle of one pulse of the partial variable power clock signal during the image formation operation; a selection unit 144 which selects the delay signal equivalent to the timing of the start and end of the pulse of the PWM signal to be output in accordance with the state detection result and image data; and a pulse generation unit 145 which generates the PWM signal in accordance with the timing of the delay signal selected by the selection unit.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technique of a PWM processing circuit and an image forming apparatus capable of generating a PWM signal having an appropriate period when a partial scaling clock is used for image formation and forming a good image.

  As an image forming apparatus, a PWM signal is generated as an image forming signal in accordance with image data, and an image of one line or several lines in the main scanning direction is formed using the image forming signal, and each line in the main scanning direction is formed. It is known that image formation of one page is repeated in the sub-scanning direction to form an image for one page.

  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.

In an electrostatic image forming apparatus provided with this type of laser beam exposure apparatus, an electrostatic latent image formed on a photoconductor is sub-scanned with main scanning by the laser beam and movement (rotation) of the photoconductor. Formed by combining with scanning.
In this case, as shown in FIG. 9, the laser beam from the laser diode 151 is scanned in the main scanning direction by the polygon mirror 152, and an electrostatic latent image is formed on the rotating photoconductor 153. As shown here, the angle of the laser beam with respect to the photoconductor 153 differs between the central portion of the photoconductor 153 in the main scanning direction and the end portion in the main scanning direction. For this reason, even if the polygon mirror 152 rotates at a constant speed, the main scanning speed is higher at the end portion in the main scanning direction of the photoconductor 153 than in the vicinity of the central portion in the main scanning direction. That is, at the edge of the image, the size of one pixel extends in the main scanning direction from the center.

Note that an fθ lens or the like is arranged in the optical system in order to suppress such a phenomenon that the size of one pixel at the center and the end in the main scanning direction expands and contracts. However, it is difficult to completely solve the above phenomenon due to the displacement of the mounting position of each part.
Accordingly, in order to suppress the influence as described above, one line in the main scanning direction is divided into a plurality of arbitrary regions, and a process of electrically changing the cycle of the clock pulse for image processing in the region (hereinafter, “ Partial zoom processing ") is performed.

  Techniques for correction in such an image forming apparatus are described in the following patent documents, for example.

Japanese Patent No. 3812003

In the above prior art, a stable partial scaling clock (hereinafter referred to as “partial scaling clock”) can be generated in accordance with the correction coefficient.
However, in the above prior art, no consideration is given to the PWM processing circuit that generates the PWM for driving the laser diode. Therefore, depending on the accuracy of the components used in the PWM processing circuit, it is not always possible to generate a PWM signal in correspondence with the change in the period of the input partial scaling clock (change point of the partial scaling process). There's a problem.

Further, when a PWM signal is generated using a partial scaling clock, and the period of one dot changes suddenly at the changing point of the partial scaling process, the influence of the change is an image quality (for example, density) change. There is also a problem that it may appear as.
The present invention has been made in order to solve the above-described problems, and an object of the present invention is to generate a PWM signal having an appropriate period when a partial magnification clock is used for image formation, and to produce a good image. It is to realize a formable PWM processing circuit and an image forming apparatus.

In order to achieve at least one of the above objects, a PWM processing circuit and an image forming apparatus reflecting one aspect of the present invention are configured as follows.
(1) A PWM processing circuit reflecting one aspect of the present invention scans a laser beam emitted by a PWM signal modulated in accordance with image data by a polygon mirror rotating at a predetermined angular velocity on a photoconductor, and images And a partial magnification clock having a different period at a position where the laser beam is scanned on the photoconductor, and the partial magnification clock and the image data according to the image data. A PWM processing circuit that generates a PWM signal, a delay unit that generates a plurality of delay signals having different timings at a predetermined interval from the partial scaling clock signal; and how many stages of the plurality of delay signals are the partial variation A state detection unit that obtains a state detection result corresponding to one pulse period of the double clock signal during the image forming operation, and according to the state detection result and the image data A selection unit that selects a delay signal corresponding to the start and end timing of a pulse of the PWM signal to be output; a pulse generation unit that generates a PWM signal according to the timing of the delay signal selected by the selection unit; It is provided with.

  An image forming apparatus reflecting one aspect of the present invention includes a partial scaling clock generation unit that generates partial scaling clocks having different periods, and modulation according to image data in accordance with the timing of the partial scaling clock. A PWM processing circuit that generates the generated PWM signal, and an image forming unit that forms an image by scanning a laser beam emitted from the PWM signal with a polygon mirror that rotates at a predetermined angular velocity on the photosensitive member. It is characterized by that.

  (2) In the above (1), the selection unit is a case where the period of the partial scaling clock is set to change stepwise for each fixed section, and the period of the partial scaling clock is When a change is detected, the period after the change is maintained over a certain interval.

  (3) In the above (1)-(2), the selection unit is a case where the period of the partial scaling clock is set to change stepwise for each fixed section, and the partial scaling When a change in the clock period is detected, a period obtained by averaging a plurality of pulses after the change in the period of the partial magnification clock is maintained, and the period after the change is maintained over a certain period. Features.

  (4) In the above (1) to (5), the selection unit is a case where the period of the partial scaling clock is set to change stepwise for each fixed section, and the partial scaling When a change in the clock cycle is detected, a cycle obtained by averaging the pulse before the cycle change of the partial scaling clock and the pulse after the cycle change is used.

(5) In the above (4), the selection unit sets a period obtained by averaging a plurality of pulses before a period change of the partial scaling clock and a plurality of pulses after the period change. And
(6) In the above (4), the selection unit is a case in which the period of the partial scaling clock is set to change stepwise for each fixed section, and the period of the partial scaling clock is When a change is detected, the period is changed over a plurality of pulses so that the period change is smaller than the detection result between the pulse before the period change of the partial scaling clock and the pulse after the period change. It is characterized by that.

  (7) In the above (1), the selection unit is configured such that the period of the partial scaling clock is set to gradually change for each pulse, and the period difference between adjacent pulses is changed. When detected, the period obtained by averaging the pulse before the period change of the partial scaling clock and the pulse after the period change is used.

(8) In the above (7), the selection unit sets a period obtained by averaging a plurality of pulses before a period difference change and a plurality of pulses after a period change.
(9) In the above (8), the selection unit detects a change in the period difference between adjacent pulses, and averages the plurality of pulses according to the magnitude of the period difference. The range is changed.

  (10) In the above (1) to (9), the image forming apparatus performs image formation by repeating image formation in the main scanning direction in the sub-scanning direction. The period of each pulse of the previous partial scaling clock is held, and the period of each pulse being processed is the same position in the main scanning direction and the period preceding the sub-scanning direction and each period being processed The pulse period is averaged to obtain a period.

In the PWM processing circuit and the image forming apparatus reflecting one aspect of the present invention, the following effects can be obtained.
(1) In the PWM processing circuit and the image forming apparatus reflecting one aspect of the present invention, a partial magnification clock having a different period is input at a position where the laser beam is scanned on the photosensitive member. When generating a PWM signal according to the image data, a plurality of delay signals having different timings are generated from the partial scaling clock signal at a predetermined interval, and the number of stages of the plurality of delay signals is equal to the partial scaling clock signal. A state detection result corresponding to the period of one pulse is obtained during the image forming operation, and a delay signal corresponding to the start and end timing of the pulse of the PWM signal to be output is determined according to the state detection result and the image data. The PWM signal is generated according to the timing of the delay signal selected and selected by the selection unit.

For this reason, when a partial scaling clock is used for image formation, it is possible to generate a PWM signal with an appropriate period and form a good image.
(2) In the above (1), when the period of the partial scaling clock is set to change stepwise for every fixed section, and the change of the period of the partial scaling clock is detected By maintaining the period after change over a certain period, a PWM signal with an appropriate and stable period can be generated even when a partial scaling clock is used for image formation, and a good image can be formed. Is possible.

  (3) In the above (1)-(2), it is a case where the period of the partial scaling clock is set to change stepwise for every fixed section, and the change of the period of the partial scaling clock is detected. In such a case, the period obtained by averaging a plurality of pulses after the change of the period of the partial scaling clock is maintained, and the period after the change is maintained over a certain interval, so that the partial scaling clock is used for image formation. Even when the signal is used, it is possible to generate a PWM signal having an appropriate and stable period and form a good image.

  (4) In the above (1) to (5), it is a case where the period of the partial scaling clock is set to change stepwise for each fixed section, and the change of the period of the partial scaling clock is detected. In this case, the period obtained by averaging the pulse before the period change of the partial scaling clock and the pulse after the period change is used to suppress a sudden period change, and the partial scaling clock is used for image formation. Even when the signal is used, it is possible to generate a PWM signal having an appropriate and stable period and form a good image.

  (5) In the above (4), a rapid cycle change is suppressed by setting a cycle obtained by averaging a plurality of pulses before the cycle change of the partial magnification clock and a plurality of pulses after the cycle change. Even when a partial scaling clock is used for image formation, it is possible to generate a PWM signal with an appropriate and stable period and form a good image.

  (6) In the above (4), when the period of the partial scaling clock is set to change stepwise for every fixed section, and the change of the period of the partial scaling clock is detected , By changing the cycle over multiple pulses so that the cycle change is smaller than the detection result between the pulse before the cycle change of the partial scaling clock and the pulse after the cycle change, abrupt cycle change is suppressed In addition, even when a partial scaling clock is used for image formation, it is possible to generate a PWM signal having an appropriate and stable period and form a good image.

  (7) In the above (1), when the period of the partial scaling clock is set to gradually change for each pulse, and when a change is detected in the period difference between adjacent pulses, By setting the period obtained by averaging the pulse before and after the period change of the partial scaling clock to a period, a sudden period change is suppressed, and when the partial scaling clock is used for image formation In addition, a PWM signal having an appropriate and stable period can be generated and a good image can be formed.

  (8) In the above (7), by setting the period obtained by averaging the plurality of pulses before the period difference change and the plurality of pulses after the period change, the abrupt period change is suppressed, and for image formation Even when a partially variable clock is used, it is possible to generate a PWM signal with an appropriate and stable period and form a good image.

  (9) In the above (8), when a change is detected in the period difference between adjacent pulses, the range for averaging a plurality of pulses is changed according to the magnitude of the period difference, Abrupt changes in the period can be suppressed appropriately in a stable state, and a PWM signal with an appropriate and stable period can be generated even when a partial scaling clock is used for image formation, enabling a good image to be formed. Become.

  (10) In the above (1) to (9), the image forming apparatus repeats image formation in the main scanning direction in the sub-scanning direction, and executes image formation. The period of each pulse of the double clock is held, and the period of each pulse being processed is the average of the period before the sub-scanning direction and the period of each pulse being processed at the same position in the main scanning direction. By making the period obtained by the conversion, a rapid period change is appropriately suppressed in a stable state, and a PWM signal having an appropriate and stable period is generated even when a partial scaling clock is used for image formation, A good image can be formed.

It is a block diagram which shows the structure of the PWM processing circuit of embodiment of this invention. It is a block diagram which shows the structure of the partial scaling clock generation part 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 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 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 explanatory drawing which shows the basic principle of image formation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments (embodiments) for implementing a PWM processing circuit and an image forming apparatus of the present invention will be described below in detail with reference to the drawings.
[Configuration of PWM processing circuit and image forming apparatus]
Here, based on FIGS. 1 to 2, a PWM processing circuit and an image forming apparatus capable of generating a PWM signal with an appropriate period when a partial scaling clock is used for image formation and forming a good image. The configuration will be described in detail.

The image forming apparatus 100 includes a control unit 101, a basic clock generation unit 105, a partial scaling clock generation unit 110, an image data storage unit 120, an image processing unit 130, a PWM processing unit 140, a print And an engine 150.
Here, the control unit 101 controls each unit of the image forming apparatus 100 and supplies the scaling data to the partial scaling clock generation unit 110. The basic clock generation unit 105 generates a basic clock for each unit that is necessary for the image forming apparatus 100 to operate. The partial scaling clock generation unit 110 generates a partial scaling clock having a different period at a position where the laser beam is scanned on the photoconductor according to the scaling data. The image data storage unit 120 stores image data. The image processing unit 130 performs various image processes necessary for image formation on the image data to generate image forming image data. In the following description of the present specification, image forming image data is simply referred to as image data.

  The PWM processing unit 140 receives a partial magnification clock, and generates a PWM signal according to the partial magnification clock and the image data. When the PWM processing unit 140 generates a PWM signal, a plurality of delay signals having different timings from the partial magnification clock signal at predetermined intervals. The state detection result of how many stages of the plurality of delay signals correspond to the period of one pulse of the partial magnification clock signal is obtained during the image forming operation, and according to the state detection result and the image data, This is a PWM processing circuit that selects a delay signal corresponding to the start and end timing of a pulse of a PWM signal to be output and generates a PWM signal according to the timing of the delay signal selected by the selection unit. The print engine 150 is an image forming unit that forms an image on a photosensitive member and transfers the image to a sheet. The laser beam emitted by the PWM signal is scanned on the photosensitive member by a polygon mirror that rotates at a predetermined angular velocity to form an image. To do.

  Here, the delay element array unit 141 generates a plurality of delay signals having different timings at predetermined intervals from the partial scaling clock signal. This delay element array unit 141 outputs delay signal groups with hundreds of delay elements connected so as to be finely delayed to about several hundred stages for one to two cycles of the partial scaling clock. For example, in the delay element array 141, the delay elements are connected in 512 stages so as to be finely delayed to about 400 to 500 stages for one period of the partial magnification clock. The state detection unit 142 obtains a state detection result during the image forming operation as to how many stages of the plurality of delay signals correspond to the period of one pulse of the partial scaling clock signal. The memory 143 stores the state detection result, and the stored state detection result (the state detection result one pixel or several pixels before or the state detection result at the same position in the main scanning direction before one main scanning line). This is supplied to the selection unit 144. The selection unit 144 selects a delay signal corresponding to the start and end timing of the pulse of the PWM signal to be output, according to the state detection result and the image data. The pulse generation unit 145 generates a PWM signal according to the timing of the delay signal selected by the selection unit 144.

1 is configured as shown in FIG. 2, for example. Since the partial scaling clock generation unit 110 is described in detail in Japanese Patent No. 3812003 exemplified as the prior art, it will be briefly described here.
The partial scaling clock generation unit 110 includes, for example, a delay element array unit 111, a state detection unit 112, a scaling unit 113, a selection unit 114, and a pulse generation unit 115.

  Here, the delay element array unit 111 generates a plurality of delay signals having different timings at predetermined intervals from the basic clock signal. The delay element array unit 111 outputs delay signal groups having hundreds of delay elements connected so as to be delayed by a few hundred stages for one to two cycles of the basic clock. For example, in the delay element array 111, 512 delay elements are connected so as to be finely delayed by about 400 to 500 stages for one period of the basic clock. The state detection unit 112 obtains the state detection result of how many stages of the plurality of delay signals correspond to the period of one pulse of the basic clock signal during the image forming operation. The scaling unit 113 multiplies the state detection result by a scaling factor corresponding to the scaling data. The selection unit 114 selects a delay signal corresponding to the start and end timings of the partial scaling clock to be output, according to the state detection result multiplied by the scaling coefficient. The pulse generator 115 generates a partially scaled clock signal according to the timing of the delay signal selected by the selector 114. As a result, the partial scaling clock generation unit 110 generates a partial scaling clock signal that conforms to the scaling data.

[Operation]
Hereinafter, the operation of the image forming apparatus 100 of the present embodiment will be described focusing on the operation of the partial scaling clock generation unit 110 and the operation of the PWM processing unit 140.
[Operation of Partially Variable Clock Generation Unit 110]
The delay element array unit 111 outputs a delayed signal group that is finely delayed to about several hundred stages for one to two periods of the basic clock (FIG. 2A) supplied from the basic clock generation unit 105. (FIG. 2 (b)).

  The state control unit 112 obtains the number of synchronous delay stages as the state detection result of the delay element array unit 111. That is, the state control unit 112 compares the delay signal (FIG. 2B) with the basic clock signal (FIG. 2A), and the number of stages of the delay signal (synchronization delay) where a delay of exactly one clock has occurred. The number of stages) is output as the state detection result (FIG. 2C). In the delay element array unit 111, the delay time may change due to a change in temperature, a change in power supply voltage, or the like.

  Further, when image formation is performed, scaling data is supplied to the scaling unit 113 along with the main scanning direction position information based on the main scanning direction count result and the index signal indicating the end in the main scanning direction. Therefore, the scaling unit 113 refers to the number of synchronization delay stages as the state detection result, the scaling data, and the main scanning direction position information, and the scaling unit 113 performs scaling according to the main scanning direction position used at the time of exposure. The coefficient is multiplied to the state detection result, and the result is outputted as position scaling information in the main scanning direction (FIG. 2D).

  The selection unit 114 outputs a partial scaling clock to be output according to main scanning direction position scaling information (FIG. 2D) obtained by multiplying the state detection result by a scaling factor according to the main scanning direction position. A delay signal corresponding to the start timing and end timing of the first pulse is selected and output (FIG. 2E).

The pulse generator 115 generates a partially scaled clock signal in accordance with the timing of the delayed signal (FIG. 2 (e)) selected by the selector 114. As a result, the partial scaling clock generation unit 110 generates a partial scaling clock signal that conforms to the scaling data (FIG. 2 (f)).
In this case, even when the delay time of the delay element array unit 111 fluctuates for some reason, the state detection result (number of synchronization delay stages) at that time is accurately obtained using the basic clock. It is possible to accurately generate the rising timing and falling timing of the signal, and to generate an accurate partial scaling clock signal corresponding to the scaling coefficient corresponding to the position in the main scanning direction. The partial scaling clock generation unit 110 is an example, and may generate a partial scaling clock signal by another configuration or different operation.

[Operation of PWM processing unit 140]
The delay element array unit 141 includes a delay signal group that is finely delayed to about several hundred stages for one to two cycles of the partial scaling clock (FIG. 1A) supplied from the partial scaling clock generation unit 105. (FIG. 1 (b)).

  The state control unit 142 obtains the number of synchronous delay stages as the state detection result of the delay element array unit 141. That is, the state control unit 142 compares the delayed signal (FIG. 1B) with the partially scaled clock signal (FIG. 1A), and the number of stages of the delayed signal in which a delay of exactly one clock is generated ( (Synchronization delay stage number) is output as a state detection result (FIG. 1C). In the delay element array unit 141, the delay time may change due to a change in temperature, a change in power supply voltage, or the like. The state detection unit 142 also supplies the state detection result to the memory 143.

Note that the memory 143 displays the state detection history of the past state detection results for a plurality of pulses in the main scanning direction and the state detection result at the same position in the main scanning direction one line before in the sub-scanning direction (FIG. 1C ')) To the selection unit 144.
The selection unit 144 multiplies the state detection result (FIG. 1C) by the image data (FIG. 1D) from the image processing unit 130, and starts and ends the pulse of the PWM signal to be output. A delay signal corresponding to the timing is selected and output (FIG. 1 (e)). The state detection result (FIG. 1C) determines a delay signal corresponding to the start timing and end timing of the pulse of the PWM signal to be output in a state where the PWM signal is 100% duty. Further, delay signals corresponding to the start timing and end timing of the pulse of the PWM signal to be output are determined according to the duty of the PWM signal according to the signal value such as the density of the image data (FIG. 1D) ( FIG. 1 (e)).

  The pulse generator 145 generates a PWM signal in a state corresponding to the timing (pulse start timing and end timing) of the delay signal (FIG. 1 (e)) selected by the selector 144 (FIG. 1 (f)). . As a result, the partial scaling clock generation unit 140 generates a PWM signal corresponding to the image data using the partial scaling clock as a reference.

  In this case, even if the delay time of the delay element array unit 141 fluctuates for some reason, the state detection result (the number of synchronization delay stages) at that time is accurately obtained using the partial scaling clock, and therefore the partial variation The rising timing and falling timing of the PWM signal corresponding to the double clock signal can be accurately generated. For this reason, when a partial scaling clock is used for image formation, it is possible to generate a PWM signal with an appropriate period and form a good image.

  Since the PWM processing unit 140 uses the state detection result detected by the state detection unit 142 every time one pulse of the PWM signal is generated, the period of the partial scaling clock is within one main scanning line. Even if it changes, it becomes possible to generate a PWM signal having an accurate pulse width corresponding to the period change of the partial scaling clock and the signal value of the image data.

[Detailed Operation of PWM Processing Unit 140]
[Detailed operation (1)]
As shown in FIG. 3, the selection unit 144 is a case where the pulse period of the partial scaling clock (the reciprocal of the frequency f) is set to change stepwise for each fixed section. When a change in the period is detected, a predetermined interval (h0 to h1, h1 to h2, h2 to h3, h3 to h4, h4 to h5 in FIG. 3) until the state detection unit 142 detects the next change. The selection is performed so as to keep the period after the detected change.

As described above, the selection unit 114 maintains the cycle after the change over a certain interval, so that a PWM signal having an appropriate and stable cycle can be generated even when the partial scaling clock is used for image formation. Therefore, it is possible to form a good image.
Note that the selection unit 114 detects the change in the pulse cycle of the partially variable clock, that is, the current clock state detection result (FIG. 1C) and the previous clock state detection result (FIG. 1C ′). It is possible to determine whether or not the difference between the two exceeds a prescribed threshold value. It is also possible to know the change in the period by setting partial magnification.

Further, in this way, when the cycle changes for every fixed section, and it is determined that the cycle has changed, the selection unit 114 displays the state detection result held in the memory 143 in the next cycle. You may make it reflect to a change point.
Note that the selection unit 114 determines whether the frequency of the partial scaling clock is a stepwise change for each predetermined section or continuously changes gradually when setting the partial scaling. It is possible to determine whether or not the setting information of the partial magnification obtained from the above or whether the difference between the current clock cycle and the previous clock cycle exceeds a prescribed threshold value.

  In addition, the selection unit 114 is set so that the period of the partial scaling clock is set to change stepwise for each fixed section, and the change in the period of the partial scaling clock is detected as described above. In this case, by using a period obtained by averaging a plurality of pulses after changing the period of the partial scaling clock, and maintaining the period after the change over a certain interval, the partial scaling clock is used for image formation. In this case, it is possible to generate a PWM signal with an appropriate and stable period and form a good image.

[Detailed operation (2)]
In addition, the selection unit 114 is set so that the period of the partial scaling clock is set to change stepwise for each fixed section, and the change in the period of the partial scaling clock is detected as described above. In this case, it is also possible to create a section having a short period obtained by averaging the pulse before the period change of the partial scaling clock and the pulse after the period change.

  In FIG. 3, the period (frequency) of the partially variable clock is greatly changed at h1, which is a change point between the intervals h0 to h1 and the intervals h1 to h2. Therefore, as shown in FIG. 4, at the change point h1, the frequency f01 = (f0 + f1) / 2 between the frequency f0 of the intervals h0 to h1 and the frequency f1 of the intervals h1 to h2 (FIG. 4 (a)). ).

  Similarly, at the change point h2, an intermediate frequency f12 = (f1 + f2) / 2 between the frequency f1 of the intervals h1 to h2 and the frequency f2 of the intervals h2 to h3 (FIG. 4B) is provided. . At the change point h3, an intermediate frequency f23 = (f2 + f1) / 2 between the frequency f2 of the intervals h2 to h3 and the frequency f2 of the intervals h3 to h4 (FIG. 4C) is provided. At the change point h4, an intermediate frequency f01 = (f1 + f0) / 2 between the frequency f1 of the intervals h3 to h4 and the frequency f0 of the intervals h4 to h5 (FIG. 4 (d)) is provided.

In the above case, with respect to the changing point of the partially scaled clock, it is desirable to adjust the cycle as described above when the difference between the cycle of the current clock and the previous clock is larger than a prescribed threshold.
As a result, a sudden change in the frequency (frequency) of the partial scaling clock is suppressed at the change point, and a PWM signal having an appropriate and stable cycle is generated even when the partial scaling clock is used for image formation. It is possible to form a clear image.

  In this case, a period obtained by averaging one pulse before the period change of the partial scaling clock and one pulse after the period change may be used, or a plurality of pulses before the period change of the partial scaling clock may be used. It is good also as a period obtained by averaging a plurality of pulses after a period change. Averaging multiple pulses before and after the period change, the rapid period change is further suppressed more stably, and a PWM signal with an appropriate and stable period can be generated even when a partial scaling clock is used for image formation. Therefore, it is possible to form a good image.

  In addition, when the period of the partially scaled clock is set to change step by step in a certain interval, and the change of the period of the partially scaled clock is detected, the period change of the partially scaled clock is detected. It is also possible to gradually change the cycle over a plurality of pulses so that the cycle change is smaller than the detection result between the previous pulse and the pulse after the cycle change. This is shown in FIGS.

  In the example shown in FIG. 5, the period (frequency) changes at the changing points h1, h2, h3, h4, and h5 of the partially variable clock are adjusted so as to be smoother than in the case of FIG. doing. In the example shown in FIG. 6, the change in the period (frequency) at the changing points h1, h2, h3, h4, and h5 of the partial scaling clock is adjusted so as to be smoother than in FIG.

As a result, a sudden cycle change at the changing point of the partial scaling clock is suppressed, and a PWM signal with an appropriate and stable cycle is generated even when the partial scaling clock is used for image formation, thereby forming a good image. It becomes possible to do.
In the above case, with respect to the changing point of the partially scaled clock, it is desirable to adjust the cycle as described above when the difference between the cycle of the current clock and the previous clock is larger than a prescribed threshold.

[Detailed operation (3)]
In addition, the selection unit 114 is configured to change the partial scaling when the period of the partial scaling clock is set to gradually change for each pulse and a change is detected in the period difference between adjacent pulses. It is also possible to obtain a period obtained by averaging the pulses before the clock period change and the pulses after the period change.

  In FIG. 7, at the change points h1, h2, h3, h4, and h5 in the main scanning direction, the rate of change in the period (frequency) of the partial magnification clock changes. Therefore, as shown in FIG. 8, in the pulse immediately after each of the change points h1 to h5, the period obtained by averaging the pulse before the period change of the partial magnification clock and the pulse after the period change is set.

By adjusting the pulse period at the changing point of the partial scaling clock in this way, a sudden period change is suppressed, and a PWM signal having an appropriate and stable period can be obtained even when the partial scaling clock is used for image formation. And a good image can be formed.
If the period of the partial scaling clock is continuously changed in this way and the difference between the current clock and the previous clock is greater than a specified threshold, the difference in slope (the respective slopes before and after the change). (Difference) is also determined to be large, and the interval to be averaged is narrowed to an interval of several pixels. On the other hand, if the difference between the current clock and the previous clock is smaller than a predetermined threshold, it is determined that the slope is small, and a wide averaging interval is set. At this time, a plurality of threshold values may be prepared, and a plurality of sections to be averaged may be switched according to the threshold value.

  As described above, by changing the range in which a plurality of pulses are averaged according to the difference in inclination, that is, the magnitude of the period difference, abrupt period changes can be appropriately suppressed in a stable state, and image forming can be performed. Even when a partially variable clock is used, it is possible to generate a PWM signal with an appropriate and stable period and form a good image.

[Detailed operation (4)]
In the image forming apparatus 100 according to this embodiment, the print engine 150 serving as an image forming unit repeatedly performs image formation in the main scanning direction in the sub-scanning direction (see FIG. 9).

  Therefore, the memory 143 holds the period (state detection result) of each pulse of the partial magnification clock immediately before in the sub-scanning direction. Then, the selection unit 114 sets the cycle of each pulse being processed to the cycle obtained by averaging the cycle at the same position in the main scanning direction and the previous cycle in the sub-scanning direction and the cycle of each pulse being processed. To do. By doing so, a rapid cycle change is appropriately suppressed in a stable state, and a PWM signal having a proper and stable cycle is generated even when a partial scaling clock is used for image formation, and a good image is obtained. Can be formed.

In this case, in the case where the print engine 150 simultaneously performs exposure using a plurality of light beams in the main scanning direction, each light beam is obtained by averaging the PWM signals for the main scanning lines that are simultaneously exposed. It is possible to average and reduce the error between the two.
[Other operations (1)]
In the above embodiment, the PWM processing unit 140 has been described as using the state detection result detected by the state detection unit 142 every time one pulse of the PWM signal is generated. In this case, at least in the vicinity of the above change points, it is necessary to use the state detection result detected by the state detection unit 142 every time one pulse of the PWM signal is generated. Therefore, when the change point is known in advance from the information from the control unit 101, or when the change point is predicted from the previous state detection result, the frequency of state detection is set in the section excluding the vicinity of the change point. It can also be reduced.

[Other operations (2)]
The characteristics of the partially variable clock shown in FIGS. 3 to 8 are examples, and the present invention is not limited to these characteristics. It is possible to freely determine the characteristics of the partial scaling clock according to the characteristics required in the image forming apparatus 100.

[Other operations (3)]
The image forming apparatus 100 that can use the above PWM processing circuit 140 is assumed to be an electrophotographic image forming apparatus, but is not limited thereto. That is, it is possible to use the PWM processing unit 140 of the above-described embodiment also for various types of image forming apparatuses, printing apparatuses, etc., or multi-function peripherals incorporating the image forming apparatus.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 101 Control part 105 Basic clock generation part 110 Partial scaling clock generation part 120 Image data storage part 130 Image processing part 140 PWM processing part 150 Print engine (image formation part)

Claims (11)

Used in an image forming apparatus for forming an image by scanning a laser beam emitted by a PWM signal modulated according to image data with a polygon mirror rotating at a predetermined angular velocity on the photoconductor, and the laser beam is used for the photoconductor A PWM processing circuit that receives a partial scaling clock having a different period at a position scanned above and generates the PWM signal according to the partial scaling clock and the image data,
A delay unit that generates a plurality of delay signals having different timings at predetermined intervals from the partial scaling clock signal;
A state detection unit that obtains a state detection result during an image forming operation as to how many stages of the plurality of delay signals correspond to the period of one pulse of the partial scaling clock signal;
A selection unit that selects a delay signal corresponding to the start and end timing of the pulse of the PWM signal to be output according to the state detection result and the image data;
A pulse generator that generates a PWM signal according to the timing of the delayed signal selected by the selector;
A PWM processing circuit comprising: The selection unit is a case where the period of the partial scaling clock is set to change stepwise for each fixed section, and when the change of the period of the partial scaling clock is detected, the selection section Keep the cycle after change over time,
The PWM processing circuit according to claim 1. The selection unit is a case where the period of the partial scaling clock is set to change stepwise for each fixed section, and when the change of the period of the partial scaling clock is detected, the part With a period obtained by averaging a plurality of pulses after changing the period of the variable power clock, keeping the changed period over a certain interval,
The PWM processing circuit according to any one of claims 1-2. The selection unit is a case where the period of the partial scaling clock is set to change stepwise for each fixed section, and when the change of the period of the partial scaling clock is detected, the part The period obtained by averaging the pulse before the change of the period of the scaling clock and the pulse after the change of the period,
The PWM processing circuit according to any one of claims 1 to 5. The selection unit has a period obtained by averaging a plurality of pulses before a period change of the partial scaling clock and a plurality of pulses after the period change.
The PWM processing circuit according to claim 4. The selection unit is a case where the period of the partial scaling clock is set to change stepwise for each fixed section, and when the change of the period of the partial scaling clock is detected, the part The period is changed over a plurality of pulses so that the period change is smaller than the detection result between the pulse before the period change of the scaling clock and the pulse after the period change.
The PWM processing circuit according to claim 4. The selection unit is configured so that the period of the partial scaling clock is set to gradually change for each pulse, and when the change is detected in the period difference between adjacent pulses, the partial scaling is performed. The period obtained by averaging the pulse before the clock period change and the pulse after the period change,
The PWM processing circuit according to claim 1. The selection unit has a period obtained by averaging a plurality of pulses before a period difference change and a plurality of pulses after a period change.
The PWM processing circuit according to claim 7. The selection unit is a case where a change is detected in a period difference between adjacent pulses, and changes a range in which the plurality of pulses are averaged according to the magnitude of the period difference.
The PWM processing circuit according to claim 8. The image forming apparatus executes image formation by repeating image formation in the main scanning direction in the sub-scanning direction,
The selection unit holds the period of each pulse of the partial magnification clock immediately before in the sub-scanning direction,
The period of each pulse being processed is the same position in the main scanning direction and the period obtained by averaging the period of the previous pulse in the sub-scanning direction and the period of each pulse being processed,
The PWM processing circuit according to claim 1, wherein A partial scaling clock generator for generating partial scaling clocks having different periods;
A PWM processing circuit according to any one of claims 1 to 10, wherein the PWM processing circuit generates a PWM signal modulated in accordance with image data in accordance with a timing of a partial scaling clock;
An image forming unit that forms an image by scanning a laser beam emitted by the PWM signal with a polygon mirror that rotates at a predetermined angular velocity on a photosensitive member;
An image forming apparatus comprising:

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