JP2009178977A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a frequency modulating device which reduces a peak level of radiation noise of a specific frequency band that results from an image clock, and prevents decrease of an image quality. <P>SOLUTION: An image processing circuit identifies an image frequency and inputs it to a frequency control device. The frequency controlling device controls to output a frequency of a reference clock as the image clock when the image frequency is lower than a fixed value, and to output a frequency modulated in a fixed frequency range to the frequency of the reference clock as the image clock when the image frequency is higher than the fixed value. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a frequency modulation device that generates an image clock used for on / off control of a laser beam that scans an image carrier such as a photosensitive drum.

  In an electrophotographic image forming apparatus, in general, a laser beam emitted from a semiconductor laser is turned on and off, and this laser beam is scanned with a rotating polygon mirror (polygon mirror) and irradiated onto a photosensitive member, whereby a latent image is obtained. Image formation is performed.

  In such an image forming apparatus, an image clock having a constant frequency is used for on / off control of laser light. The reason is that if the frequency of the image clock is not constant, the on / off timing of the laser beam deviates from the normal timing, thereby causing the dot formation position of the electrostatic latent image formed on the photoreceptor to deviate slightly. As a result, image distortion, color shift, and color unevenness occur.

  Conventionally, an f-θ lens is provided between a rotary polygon mirror (polygon) and a photosensitive member, and has a distortion aberration that guarantees temporal linearity of scanning with respect to a deflected beam from the rotary polygon mirror. Make corrections. As a result, the light beam is scanned on the cylindrical photoconductor in the axial direction at a constant speed.

  FIG. 9 is a diagram illustrating the scanning speed of the laser beam on the surface of the photoconductor 11 when no f-θ lens is present. FIG. 10 is a diagram illustrating the scanning speed of the laser beam on the surface of the photoconductor 11 when the f-θ lens 34 is present.

  First, the case where the f-θ lens 34 is not present will be described.

  Since the rotating polygon mirror (polygon) 33 rotates at a constant angular velocity, the scanning speed is constant on an arc having the same radius (R1 to R5) around the laser beam reflection point on the surface of the polygon 33. θa, θb, θc, and θd are rotation angles per unit time (θa = θb = θc = θd).

At this time, when the scanning distances within the rotation angles (θa, θb, θc, θd) of the laser beam moving in the axial direction on the cylindrical photoconductor 11 are Xa, Xb, Xc, Xd,
Xa> Xb
Xd> Xc
It becomes the relationship. From this result, it can be seen that the scanning speed of the laser beam moving in the axial direction on the photoconductor 11 becomes “large” as it goes to the end in the axial direction of the photoconductor 11 and becomes “small” as it approaches the center. . For this reason, the size of the pixels in the latent image created on the photoconductor 11 by such laser beam scanning differs between the end portion and the center portion of the photoconductor 11 in the axial direction. That is, the pixel size increases from the center to the end.

Therefore, an f-θ lens 34 for correcting distortion is provided between the rotary polygon mirror (polygon) 33 and the photoconductor 11. by this,
Xa = Xb = Xc = Xd
And the size of the pixels in the latent image created on the photoconductor 11 is uniform at any position in the axial direction of the photoconductor 11.

  As described above, it is possible to form a pixel at a fixed position by always forming the pixel with a fixed image clock by the effect of the f-θ lens.

  However, when the image clock is always constant, radiation noise is generated in a transmission path for transmitting an on / off signal for controlling on / off of the laser light from the generation circuit to the laser driving circuit, and the radiation noise level is increased. Often exceeds the value specified in international radiation noise standards.

  In order to reduce the peak level of radiation noise in a specific frequency band caused by the image clock, at least a part of the image area on the main scanning line scanned with the laser beam on the image carrier and the other part And an image clock generation unit that generates image clocks having different frequencies, and the image clock generation unit performs frequency modulation so that the frequency of the image clock changes within a predetermined fluctuation range. Proposed.

Patent document 1 can be mention | raise | lifted as these prior art examples.
JP 2002-268504 A

  However, in the conventional example, there has been a problem that fluctuation of the pixel position leads to deterioration of image quality in a device that requires higher image quality.

  In order to achieve the above object, the present invention provides a frequency modulation device for use in an image forming apparatus having an image carrier scanned with a laser beam, wherein the frequency of an image in the main scanning direction is set from an image signal for image formation. It is characterized in that image quality degradation is suppressed to a minimum by performing frequency modulation of the image clock only when the image frequency is equal to or higher than a certain frequency.

  As described above, according to the present invention, the image frequency is identified from the image data, and the frequency modulation of the image clock is performed within a predetermined fluctuation range only when the image frequency having a relatively large radiation noise level is high. Thus, it is possible to reduce the peak level of radiation noise while preventing deterioration in image quality.

  Next, details of the present invention will be described in accordance with the description of the embodiments.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 11A shows a dither matrix growth method. In the figure, a glance of a thin line indicates one pixel. Ten pixels within the bold line represent one dither matrix. The practice arrows and numbers in the dither matrix indicate the order of growth of the dither matrix. That is, growth starts from the center of the dither matrix, and the growth pixels sequentially move to adjacent pixels. The sixth growth pixel has a duty of 50%, but is shifted to the right side in the pixel so as to be coupled to the fifth pixel after growth. This is because in electrophotography, it is possible to maintain a stable potential and density by combining a plurality of pixels rather than a single pixel. In the drawing, 5 pixels shown in gray and 1 pixel of 50% duty are printed in a 10-pixel dither matrix. FIG. 11-B shows the PWM signal at this time. One pixel is printed in the main scanning direction, but the ON / OFF cycle is 3 times / 10 pixels. For example, when the reference image clock is 30 MHz, the image frequency is 9 MHz.

  FIG. 12-A shows the dither matrix growth method. In the figure, a glance of a thin line indicates one pixel. Eleven pixels within the bold line represent one dither matrix. The practice arrows and numbers in the dither matrix indicate the order of growth of the dither matrix. In the same figure, the case where 3 pixels shown in gray and 1 pixel of 50% duty are printed in a dither matrix of 11 pixels is shown. FIG. 12-B shows the PWM signal at this time. One pixel is printed in the main scanning direction, but the ON / OFF cycle is 2 times / 11 pixels. For example, when the reference image clock is 30 MHz, the image frequency is 5.45 MHz.

  As described above, the maximum image frequency is determined by the dither matrix growth method. Even in an image forming apparatus capable of outputting a multi-valued image as described above, pixels having a duty are shifted to the left or right in the pixel and combined with the adjacent grown pixels to stabilize the image formation. In many cases, the frequency is sufficiently smaller than the image clock.

  At this time, if the image frequency is sufficiently low, the level of unnecessary radiation may be sufficiently low without using frequency modulation of the image clock. On the contrary, in such a case, there is a case where an image defect is caused due to a positional deviation of pixels formed by performing frequency modulation of the image clock. Therefore, in the present invention, it is possible to prevent image deterioration without increasing the level of unnecessary radiation by determining the image frequency from the image data and turning off the frequency modulation of the image clock according to the frequency or sufficiently lowering the modulation level.

  Next, a method of performing frequency modulation when the image frequency is high according to image data is shown below.

  FIG. 1 is a diagram schematically showing a configuration of an exposure unit of an image forming apparatus according to an embodiment of the present invention.

  As shown in FIG. 1, an electrophotographic image forming apparatus is an exposure unit that irradiates a photosensitive drum 15 with laser light so that a latent image corresponding to input image data is formed on the photosensitive drum 15. Is provided. The exposure unit includes a laser light source 1 that emits diffused laser light. The laser light emitted from the laser light source 1 is converted into parallel laser light L1 through the collimator lens 13, and this laser light L1 is irradiated to the polygon mirror 2 being rotationally driven by the scanner motor 3. Then, the laser beam L 1 irradiated to the polygon mirror 2 is reflected by the polygon mirror 2 and reaches the f-θ lens 14.

  The laser light that has passed through the f-θ lens 14 is combined and scanned on the photosensitive drum 15 at a constant speed in the main scanning direction, and a latent image 16 is formed on the photosensitive drum 15 by scanning of the laser light, that is, a scanning operation. The The start of the laser beam scanning operation is detected by a beam detect sensor (hereinafter referred to as a BD sensor) 17. The laser light source 1 is forcibly turned on at the time of starting the scan of the laser light with respect to the photosensitive drum 15, and the BD sensor 17 detects the laser light reflected and input by the polygon mirror 2 during the forced light-up period of the laser light source 1. A beam detect signal (hereinafter referred to as a BD signal) serving as a reference signal for image forming / writing timing for each scan is output.

  Next, the frequency modulation configuration of the image clock used for driving control of the laser light source 1 will be described with reference to FIG. FIG. 2 is a block diagram showing a frequency modulation configuration of an image clock used for driving control of the laser light source 1.

  The 51 image signal processing circuit obtains an image signal from a computer (PC) (not shown) or a scanner, converts it into multivalued image data suitable for the image forming apparatus, and writes the multivalued image data in the 52 FIFO memory. At the same time, the image frequency is identified from the image signal, and the image frequency identification signal is input to the 101 frequency controller.

  A reference clock generation means 104 for generating a reference clock, a memory 113, and a frequency control device 101 are provided. The frequency modulation setting parameter 106 is held in the memory 113, and the frequency modulation setting parameter 106 includes various setting values necessary for the image clock signal modulation operation of the frequency control apparatus 101. Specifically, an image area start position setting value 107, an image area end position setting value 108, and an image area frequency modulation setting value 110 are included.

  The image area start position setting 107 is a value for setting a period (time) from the input of the BD signal 29 from the BD sensor 17 to the image formation area start timing (image formation area start position) in the main scanning direction. The image area end position setting value 108 is a value for setting a period (time) from the input of the BD signal 29 to the image forming area end timing (image forming area end position) in the main scanning direction.

  The frequency modulation setting value 109 before the image area start is during a period (time) from the input of the BD signal 29 to the image area start timing (image formation area start position) set based on the image area start position setting value 107. This is a value for setting the frequency of the image clock generated by the frequency control device 101 in FIG. The image area frequency modulation setting value 110 is a frequency in an image area period (time) defined by the image area start timing and the image area end timing set by the image area start position setting value 107 and the image area end position setting value 108. This is a value for setting the frequency of the image clock generated by the control device 101 (a value for setting the fluctuation amount of the frequency of the image clock). After the end of the image area, the frequency modulation set value 111 is set by the frequency control apparatus 101 during the period (time) from the image area end timing set by the image area end position set value 108 to the input of the BD signal of the next main scanning line. This is a value for setting the frequency of the generated image clock. These various setting values are transferred to the frequency control device 101.

  The frequency control device 101 divides one line scanned in the main scanning direction into a plurality of segments composed of an arbitrary number of pixels, and an image for generating image clocks for the plurality of divided segments, respectively. Clock generation means 103. The image clock generation means 103 switches the image clock to be output according to the input image frequency identification signal. When the image frequency identification signal indicates that the image frequency is equal to or lower than a certain frequency, a reference clock synchronized with the BD signal 29 is output as an image clock, and the image frequency identification signal is equal to or higher than a certain frequency. If it indicates that there is, the reference clock 21 generated by the reference clock generation means 104 is frequency-modulated in synchronization with the BD signal 29 and based on the various set values, and an image clock is output.

  This image clock is input to the 52 FIFO memory and the 53 PWM circuit. The 52 FIFO memory corrects the operation timing of the 51 image signal processing circuit and the 53 PWM circuit, and supplies multi-value image data to the 53 PWM circuit. The 53PWM circuit converts the multivalued image data into a PWM signal and supplies it to the 112 laser drive circuit. In response to the input PWM signal, the 112 laser driving circuit performs flashing driving of one laser light source to expose the photosensitive member to form an electrostatic latent image.

  Next, an image clock having the above frequency modulation configuration will be described with reference to FIG. FIG. 3 is a graph showing the relationship between the frequency of the image clock generated by the frequency modulation circuit configuration of FIG. 2 and the main scanning position.

  As shown in FIG. 3, an image clock having a frequency greatly shifted from the frequency of the reference clock 21 is used as an image clock between the BD signal 29 and the image area start (image area start position). This is because the image is not formed on the photosensitive drum 15 in areas other than the image area, and therefore it is not necessary that the clock has a correct and constant frequency. In this way, it is effective to reduce the peak level of the radiation noise in the specific frequency band caused by the image clock by largely shifting the frequency of the section. Similarly, an image clock whose frequency is largely shifted from the reference clock is used from the image area end (END) until the next BD signal is input. This is for the same reason as that in the section from the BD signal 29 to the image area start (image area start position), and is effective in reducing the peak level of radiation noise in a specific frequency band caused by the image clock. .

  Next, frequency setting in the image area shown in FIG. 3 will be described.

  In the image area, when an image clock whose frequency is shifted more than necessary with respect to the reference clock 21 is used, a positional deviation occurs in which the image forming position on the photosensitive drum 15 is deviated from the normal position (ideal position). However, when there is almost no frequency fluctuation, there is no shift in the image forming position, but the peak level of radiation noise in a specific frequency band caused by the image clock cannot be reduced.

  Therefore, in the present embodiment, a method is used in which the image clock is generated by frequency-modulating the reference clock 21 so as to suppress image degradation due to a shift in the image formation position to 10 μm or less, which is difficult to confirm with the naked eye. In other words, the frequency of the image clock is set to the reference clock in order to reduce the radiation noise level caused by the image clock while suppressing the local image forming position shift due to frequency modulation more than necessary within the range where it is difficult to visually recognize. An image clock having fluctuations within a frequency range of ± 2% or less with respect to the 21 frequencies is generated. The fluctuation amount of the image clock is set for each segment divided by the segment dividing unit 102 based on the image area frequency modulation setting value 110.

  Further, as shown in FIG. 3, the fluctuation component is preferably set so as to cancel out the main scanning magnification fluctuation of the image due to the fluctuation component of the frequency between the image areas. Thereby, the main scanning magnification fluctuation of the entire image does not occur. However, although the writing position is slightly changed due to the fluctuation component between the image areas, this is a level that cannot be visually seen (not felt), and therefore does not cause image degradation.

  Here, an internal configuration of the frequency control apparatus 101 and an image clock generated thereby will be described with reference to FIGS. 4, 5, and 6. 4 is a block diagram showing the internal configuration of the frequency control apparatus 101 of FIG. 2, FIG. 5 is a graph showing the relationship between the segment and the period of the image clock 18 in the segment, and FIG. 6 is a graph showing the cycle of the image clock 18 in the segment. It is a graph which shows the relationship when making it change to a stage.

  As shown in FIG. 4, the frequency control device 101 includes a scaling factor setting register 22, an auxiliary pixel generation circuit 24, an initial period setting register 26, a modulation clock control circuit 30, a pixel number setting register 31, and a modulation. A clock generation circuit 28, and these circuits and registers constitute a segment division means 102 and an image clock generation means 103.

  The scaling factor setting register 22 stores a scaling factor 23 for changing the cycle ratio of the reference clock signal 21 generated from the reference clock generation means 104. The auxiliary pixel generation circuit 24 generates an auxiliary pixel period 25 based on the reference clock signal 21 and the scaling coefficient 23. With this auxiliary pixel period 25, the main scanning magnification is corrected. That is, the width or interval of main scanning dots on the photosensitive drum 15 is not uniform due to the optical system of the polygon mirror 2 and the f-θ lens 14 in FIG. The frequency of the image clock in one scanning section is corrected so that the width or the dot interval is uniform. For example, in the case of a rotational scanning system such as the polygon mirror 2, the scanning speed tends to increase at both ends in the main scanning direction of the photosensitive drum 15, and the scanning speed of the main scanning central portion of the photosensitive drum 15 is low. Therefore, the dot width or dot on the photosensitive drum 15 is corrected by increasing the frequency of the image clock in the vicinity of both ends of the photosensitive drum 15 and decreasing the frequency of the image clock in the central portion of the photosensitive drum 15. The interval can be made uniform.

  Here, the frequency control device 101 divides one main scanning line into a plurality of segments and generates a constant image clock 18 for each segment, and the frequency of the image clock in each divided segment. Either one of the second control methods for performing modulation can be executed.

First, a first control method for dividing one main scanning line into a plurality of segments and generating a constant image clock 18 for each segment will be described with reference to FIG.
For example, if the period of the reference clock signal 21 is τref, the magnification coefficient 23 is αk, and the period of the auxiliary pixel period 25 is Δτ, Δτ is expressed by the following equation (1).

Δτ = αk · τref (1)
Here, the scaling coefficient 23 (= αk) is set to a value such that the period Δτ is sufficiently shorter than the period of the image clock 18.

  The initial period setting register 26 stores an initial value 27 (τvdo) of the period of the image clock 18 output from the modulation clock generation circuit 28.

  The modulation clock control circuit 30 divides one line scanned in the main scanning direction into segments composed of an arbitrary number of pixels to form a plurality of segments. Based on the image area frequency modulation setting value 110, the modulation clock control circuit 30 manages the image clock period so as to have a predetermined range of fluctuation within each segment. The number of pixels in the segment is set by the pixel number setting value 32 in the pixel number setting register 31. The number of pixels between the segments may be the same or different.

  Here, details of the operation of the modulation clock control circuit 30 will be described. The modulation clock control circuit 30 generates a modulation clock control signal 33 for the first segment (segment 0) when a BD signal 29, which is a write reference signal output from the BD sensor 17, is input, and generates a modulation clock. It outputs to the circuit 28. Upon receiving this modulation clock control signal 33, the modulation clock generation circuit 28 outputs the image clock 18 having an initial period 27 (τvdo).

  For the next segment (segment 1), the modulation clock control circuit 30 generates a modulation clock control signal 33 for the next segment (segment 1) and outputs it to the modulation clock generation circuit 28. Upon receiving this modulation clock control signal 33, the modulation clock generation circuit 28 generates a modulation clock signal ΔT1 having a period represented by the following equation (2) based on the auxiliary pixel period 25 and the initial period 27 (τvdo) as an image clock. 18 is generated.

ΔT1 = τvdo + α · τref (2)
Here, α is a scaling factor for segment 1.

  Similarly, for a further next segment (segment 2), the modulation clock control circuit 30 outputs a modulation clock control signal 33 for the further next segment (segment 2) to the modulation clock generation circuit 28. The modulation clock generation circuit 28 that has received the modulation clock control signal 33 generates an image of the modulation clock signal ΔT2 having a period represented by the following equation (3) based on the auxiliary pixel period 25 and the initial period 27 (= τvdo). Generated as clock 18.

ΔT2 = τvdo + α · τref + β · ref (3)
Here, β is a scaling factor for segment 2.

  Also, when there are more segments after segment 2, a modulation clock signal for the segment is generated and output as an image clock 18 in the same procedure.

  As described above, the modulation clock generation circuit 28 outputs the image clock 18 having a plurality of cycles within one main scanning line under the control of the modulation clock control circuit 30.

  Next, a second control method for performing frequency modulation of the image clock in each segment will be described with reference to FIG.

  When the frequency of the image clock 18 is varied from the initial segment (segment 0), as shown in FIG. 6A, the initial period is τvdo, the number of pixels per segment is n, the modulation coefficient (segment 0) is α and When the reference clock period is τref, the period Δτa per pixel in the segment 0 and the total period ΔT0 of the segment 0 are expressed by the following equations (4) and (5).

初期セグメント（セグメント０）の画像クロック１８の周波数を固定し、以降のセグメントの画像クロック１８の周波数を可変する場合、図６（ｂ）に示すように、セグメント０の総周期をΔＴ０とすると、次の（６）式で表される。

When the frequency of the image clock 18 of the initial segment (segment 0) is fixed and the frequency of the image clock 18 of the subsequent segment is varied, as shown in FIG. 6B, if the total period of the segment 0 is ΔT0, It is represented by the following equation (6).

ΔT0 = n · τvdo (6)
On the other hand, for the next segment of the initial segment, that is, segment 1, if the modulation coefficient (segment 1) is β and the reference clock period is τref, the period Δτb per pixel in segment 1 and the total period ΔT1 of segment 1 Is expressed by the following equations (7) and (8).

そして、さらに以降の各セグメントに関しても、同様の式で１画素当りの周期Δτｂおよび各セグメントの総周期ΔＴｎ（ｎ≧２）を表すことができる。

Further, with respect to each subsequent segment, the period Δτb per pixel and the total period ΔTn (n ≧ 2) of each segment can be expressed by the same formula.

  Next, a change in the frequency of the image clock when the second control method is executed will be specifically described with reference to FIG. FIG. 7 is a graph showing changes in the frequency of the image clock when the second control method is executed. This figure is an enlarged view of a part of the image area so that the frequency setting in the image area can be easily understood.

  First, the image area frequency modulation setting value 110 in the memory 113 is sent to the frequency control apparatus 101. Here, the image area frequency modulation setting value 110 includes a frequency setting value for each segment, and the segment dividing unit 102 determines the image area according to the number of frequency setting values included in the image area frequency modulation setting value 110. Divide into multiple segments. In this example, a predetermined count section in which the image clock is set as a count value is used as one segment.

  As shown in FIG. 7, in the segment a, the image clock generation means 103 modulates and controls the frequency so that the frequency setting value b1 is connected to the frequency setting value b1 by a straight line. Subsequently, in the segment b, the image clock generation unit 103 modulates and controls the frequency so that the frequency setting value c1 and the frequency setting value c1 are connected by a straight line. Similar control is performed for the subsequent segments. In this way, by controlling the frequency for each segment, the image clock has fluctuations with respect to the reference clock. Therefore, the peak level of radiation noise in a specific frequency band caused by the image clock can be reduced.

  Next, a change in the frequency of the image clock when the first control method is executed will be specifically described with reference to FIG. FIG. 8 is a graph showing a change in the frequency of the image clock when the first control method is executed.

  In this example, the segments are set in the same way as in FIG. In this example, the frequency setting value in the segment is constant, but different frequencies are set between the segments so as to give fluctuations to the reference clock. Thereby, the peak level of the radiation noise in the specific frequency band resulting from the image clock can be reduced.

  Thus, in the present embodiment, frequency modulation is performed so that the frequency of the image clock changes within a predetermined fluctuation range, so that the peak level of radiation noise in a specific frequency band caused by the image clock can be reduced.

  In addition, the f-θ lens has such characteristics that it does not need to be frequency-modulated, the one-drum type color image forming apparatus that does not need to worry about color shift in the main scanning direction, and consideration for color shift. In a black-and-white image forming apparatus that does not need to be used, frequency modulation is rarely performed, and even in that case, the radiation noise level often exceeds the international radiation noise standard. By performing the frequency modulation of the image clock while minimizing the influence of the image position shift, it is possible to reduce the radiation noise level while minimizing image degradation.

  In addition, a configuration including all of the blocks constituting the frequency control device 101, including a part thereof, or a configuration including peripheral blocks thereof can be configured as an ASIC or other integrated circuit.

  Further, the same effect can be obtained when a method of selecting fluctuation levels of a plurality of image clocks according to the image frequency level is used.

1 is a diagram schematically showing a configuration of an exposure unit of an image forming apparatus according to an embodiment of the present invention. 3 is a block diagram showing a frequency modulation configuration of an image clock used for driving control of a laser light source 1; FIG. 3 is a graph showing the relationship between the frequency of an image clock generated by the frequency modulation circuit configuration of FIG. 2 and the main scanning position. It is a block diagram which shows the internal structure of the frequency control apparatus 101 of FIG. It is a graph which shows the relationship between a segment and the period of the image clock 18 in a segment. It is a graph which shows the relationship when changing the period of the image clock 18 in a segment in multiple steps. It is a graph which shows the change of the frequency of an image clock at the time of performing the 2nd control method. It is a graph which shows the change of the frequency of an image clock at the time of performing the 1st control method. It is a figure which shows the scanning speed of the laser beam in the surface of a photoreceptor in case an f-theta lens does not exist. It is a figure which shows the scanning speed of the laser beam in the surface of a photoreceptor in case an f-theta lens exists. It is a figure explaining the growth method of multi-value dither. It is a figure explaining the growth method of multi-value dither.

Claims (2)

In an image forming apparatus having an image carrier scanned with a laser beam,
Image frequency selection means for extracting the frequency of the laser beam blinking drive from the image data of the image to be formed;
A PWM circuit for generating a blinking signal of the laser beam in synchronization with an input image clock;
Image clock generating means for generating the image clock;
The image forming apparatus, comprising: an image signal processing device having different image clock generation modes and different output frequencies depending on the output of the image frequency identification signal. The image forming apparatus according to claim 1,
The scanning optical system used in the image forming apparatus has an f-θ lens,
When the image clock generation means indicates that the output of the image frequency identification signal is lower than a predetermined frequency, the image clock forms a pixel on the image carrier at a certain period during image formation. An image forming apparatus that generates a constant image frequency.

Images