JP3957646B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus configured such that a frequency spread width of a clock can be changed according to an image quality mode.
[0002]
[Prior art]
Conventionally, as a digital image forming apparatus (hereinafter referred to as an image forming apparatus) using an electrophotographic process, there are a digital copying machine and a facsimile. In recent years, along with technological innovation in the technical fields related to digital technology, image processing technology, image forming technology, etc., image formation that increases the resolution at the time of original reading and the resolution at the time of image formation to form an image faithful to the original The equipment is increasing. In addition, the output tends to be further increased with the resolution of the image.
[0003]
In the image forming apparatus as described above, an original is read by an image reading device, decomposed into innumerable minute pixels, subjected to image processing, and then exposed by an exposure device in accordance with the read pixels, and then on the photosensitive member. The formed electrostatic latent image is developed and visualized. A clock or timing pulse is supplied to an image processing circuit for reading and processing such an image.
[0004]
On the other hand, increasing the resolution means increasing the number of pixels per unit area, and increasing the output speed leads to an increase in the number of pixels processed per unit time. Therefore, in order to realize high resolution and high speed, it is necessary to make the clock and timing pulse supplied to the above-described image processing circuit faster and higher. As an adverse effect of clocks and timing pulses that increase speed, the level of radiation noise radiated from other circuits and devices to the circuit or device that generates or uses these clocks and timing pulses or to the outside increases, while other circuits and devices The device is easily affected by noise, which is a major factor that causes malfunction and failure of circuits and devices.
[0005]
Therefore, as a measure for reducing the level of this radiation noise, particularly its peak level, the frequency of the clock or timing pulse is periodically shifted (frequency spread) to modulate the frequency. Specifically, with the reference frequency of the reference clock as the center, the frequency is regularly changed by a predetermined modulation width toward the higher frequency, and then is regularly changed by the predetermined modulation width toward the lower frequency. Return to frequency. It is known that the level of radiation noise is lowered by periodically repeating this change.
[0006]
Further, if the modulation width (diffusion width) modulated from the reference frequency is increased, the waveform of the peak portion of the radiation noise is integrated, and the peak level can be further reduced. However, if the frequency of the clock is changed periodically, the timing pulse for control / drive generated based on the clock will have the same modulation, otherwise the generation of radiated noise will partly occur. Can only be reduced.
[0007]
On the other hand, the image reading and processing of the image forming apparatus includes a CCD that reads a document in units of pixels, an analog signal processing unit that converts information of a read pixel converted into a charge level by the CCD into an analog signal, and the analog signal. Are sequentially performed by an A / D converter that converts the signal into a digital signal and an image processing circuit that processes an image composed of the digital signal. These are all driven by timing pulses generated based on the clock. Therefore, if the frequency modulation width of the clock is increased in order to suppress the level of radiation noise from the clock, the timing pulse is similarly modulated, and the timing is shifted when transferring and detecting the charge of the pixel unit of the CCD, The charge level cannot be detected correctly. That is, the density level of each read pixel is disturbed, and side effects appear in the form of image noise mixing or disorder, and image quality degradation.
[0008]
According to Patent Document 1, the timing pulse generated based on the clock having the frequency spread by ± 0.5% or ± 1.0% as described above is generated by the analog signal processing unit, the A / D conversion unit, and the image processing. To reduce radiation noise of clocks and timing pulses. In this method, noise is mixed in the image as described above, but a diffusion period SYNC signal is output for each diffusion period of the clock to synchronize with the line period at the time of reading the charge level of the CCD, The apparent image noise is reduced by correcting the line shift.
[0009]
Further, according to Patent Document 2, a clock that does not spread the frequency is supplied to the CCD, the analog signal processing unit, and the A / D conversion unit in order to avoid the occurrence of image noise, and the timing shift due to the frequency spreading is an image. A timing pulse subjected to frequency spreading is supplied to an image processing unit that does not cause noise.
[0010]
Further, according to Patent Document 3, generation of radiation noise is suppressed by supplying timing pulses subjected to frequency spreading to all of the CCD, the analog signal processing unit, the A / D conversion unit, and the image processing unit. For this reason, a black offset level adjusting unit that suppresses the level fluctuation of the image signal caused by the frequency spread is newly provided, thereby suppressing the periodic level fluctuation (image noise) of the image signal.
[0011]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-281252
[Patent Document 2]
Japanese Patent Laid-Open No. 2002-33858
[Patent Document 3]
JP-A-2001-257881
[0012]
[Problems to be solved by the invention]
However, in the method according to Patent Document 1, since a timing pulse having a frequency spread is supplied to all the image reading and image processing circuits, a great effect can be expected in suppressing radiation noise. Since a synchronization circuit that generates a synchronization signal is required, and synchronization is performed for each line between the timing pulse for frequency spreading and the analog processing system, even if the image shift due to the line timing shift can be corrected, The difference in timing due to the frequency spread of the plurality of pixels is not taken into consideration, and there is a high possibility that the shading is disturbed in the line and image noise appears.
[0013]
In the method according to Patent Document 2, since a normal clock is supplied to an analog processing system in which the timing of each pixel may be shifted as a side effect of frequency spreading, generation of image noise is suppressed. However, since processing systems that supply timing pulses that have been subjected to frequency spreading are limited and clocks that have not been subjected to frequency spreading are also supplied, the generation of radiation noise cannot be significantly suppressed.
[0014]
Further, in the method according to Patent Document 3, as in the method according to Patent Document 1, timing pulses having a frequency spread are supplied to all processing systems related to image reading and processing, which is effective in suppressing radiation noise. However, black offset level adjusting means for suppressing the occurrence of image noise is newly required, the circuit configuration becomes complicated, and the cost increases.
[0015]
The present invention has been made in view of such a situation, and by adjusting the frequency diffusion width of the timing pulse according to the image quality mode, the influence of the image noise on the output image is suppressed while suppressing the generation of radiation noise. An object of the present invention is to provide an image forming apparatus capable of being suppressed.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, an image reading unit that is driven by a timing pulse to read an original, performs predetermined conversion and outputs the image signal, and an image reading unit that is driven by the timing pulse and based on the image signal. The timing pulse is a timing pulse that has been subjected to frequency spreading in which a reference frequency is continuously modulated at a predetermined period. The frequency spread width is changed according to the image quality mode.
[0017]
The image quality mode is a plurality of modes corresponding to the gradation of image formation, and the timing pulse has a frequency spread width corresponding to each of the plurality of image quality modes.
[0018]
The timing pulse is configured so that the frequency spread width is small when the gradation of the image quality mode is high and the frequency spread width is large when the gradation of the image quality mode is low.
[0019]
The width of the frequency spread of the timing pulse can be changed for each reading line when the original is read by the image reading unit.
[0020]
The image processing unit discriminates the image quality mode of a discrimination area composed of a plurality of continuous reading lines including the newest line read by the image reading unit, and is driven by a timing pulse having a frequency spread width corresponding to the image quality mode. Then, the next line is read.
[0021]
Alternatively, the image quality mode is a mode selected in advance by the user, or a mode that is automatically determined and selected by the image forming apparatus when the document is pre-scanned by the image reading unit.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the details of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a front sectional view showing an outline of a digital color copying machine (hereinafter referred to as a copying machine) equipped with an image reading unit and an image processing unit as an example of an image forming apparatus according to the present invention. In FIG. 1, a copying machine 1 is roughly composed of a scanner unit 2 that reads and processes an image of a document, and an output unit 10 that outputs the processed image onto a sheet.
[0023]
The scanner unit 2 includes an optical unit 30 including a lens, a mirror, or a prism (not shown), a CCD 31 on which light from the original enters through the optical unit 30 and forms an image, and each pixel of the formed image. An analog signal processing unit 32 that converts the charge level of each element of the corresponding CCD 31 into an analog signal, an A / D conversion unit 33 that converts the analog signal into a digital signal, and image processing that performs image processing on the digital signal of each pixel Part 34.
[0024]
The output unit 10 includes yellow, magenta, cyan, and black image forming units 3Y, 3M, 3C, and 3K, toner hoppers 4Y, 4M, 4C, and 4K corresponding to these colors, and a sheet P that is a recording medium. A paper feed cassette 5, a paper feed guide 6, a paper feed timing roller 7, a paper feed timing motor 7a that drives the paper feed timing roller 7, a transport belt 8, and a transport belt that drives the transport belt A roller 11, a conveyor belt motor 11a, a transfer roller 12, a fixing unit 13, paper discharge rollers 14 to 16, a paper discharge roller 18, a paper discharge unit 19, a control unit 20, and an input unit and a display unit (not shown). The operation unit 27 is provided.
[0025]
Further, the image forming units 3Y, 3M, 3C, and 3K for the respective colors include a developing unit 22, a photoconductor 23, a photoconductor motor 23a that drives the photoconductor, a charger 24, an exposure device 25, and a cleaning unit 26, respectively. It is configured.
[0026]
Next, a schematic operation of the copying machine 1 having the above configuration will be described. First, after setting a document on the scanner unit 2, when the operation unit 27 is operated to start copying, the optical unit 30 operates to scan the document. Light from the document is input to the image processing unit 34 as a digital signal image via the CCD 31, the analog signal processing unit 32, and the A / D conversion unit 33. The image processing unit 34 performs predetermined image processing such as shading correction and image processing according to the image quality mode, separates each color into yellow, magenta, cyan, and black, and then displays image data in accordance with an instruction from the control unit 20. Temporarily stored in a memory that is not used, or sent to the image forming units 3Y to 3K substantially in parallel with document scanning.
[0027]
On the other hand, the photosensitive member 23 charged by the charger 24 of each of the image forming units 3Y to 3K is exposed by the exposure device 25 in accordance with the image signal for each color separated as described above, and forms an electrostatic latent image on the surface thereof. . The photoreceptor 23 on which the electrostatic latent images of the respective colors are recorded in this way is developed with the corresponding color toner by the developing unit 22, and a visible image is formed on the surface thereof. Such an image forming process is performed for each color.
[0028]
The paper P fed from the paper feed cassette 5 is guided and sent out by the paper feed guide 6, but temporarily stops in a state where its leading end is sandwiched between the paper feed timing rollers 7. When the paper feed timing motor 7a is driven by a signal from the control unit 20 in synchronization with the image formation on the photosensitive member 23, the paper feed timing roller 7 transports the paper P and the transport belt motor 11a. The belt roller 11 conveys it to the upper surface of the conveyor belt 8 rotating counterclockwise. Then, the paper P is attracted to the upper surface of the transport belt 8 and when passing through the image forming units 3Y, 3M, 3C, and 3K for each color, the image for each color is transferred to the paper by the transfer roller 12 to which a transfer voltage is applied. Sequentially transferred to P.
[0029]
In this way, the four color toners that are superimposed on the paper P to form a full color image are fixed to the paper P by being heated and pressurized when the paper P passes through the fixing unit 13. Thereafter, the paper P is sequentially conveyed by the paper discharge rollers 14, 15, and 16 and is guided to the discharge unit 19 via the discharge roller 18.
[0030]
FIG. 2 is a diagram showing the relationship between the frequency and time of a timing pulse whose frequency is modulated (spread). The vertical axis represents frequency, the horizontal axis represents time, and the graph shows frequency-modulated timing pulses. The graph D1 (solid line) shows the timing pulse with the largest frequency spreading width, the graph D3 (dashed line) shows the timing pulse with the smallest frequency spreading width, and the graph D2 (dashed line) shows the middle of the two. Yes. Thus, the timing pulse used in the present invention has a frequency spread as in the conventional example.
[0031]
Next, a first embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a schematic block diagram of the first embodiment showing a main circuit portion of the copying machine 1 including a clock circuit. Light from the original enters the CCD 31 and charges are accumulated in elements corresponding to the pixels of the CCD 31. The analog signal processing unit 32 converts the charge level corresponding to each pixel into an analog signal, and the analog signal is converted into a digital signal by the A / D conversion unit 33. These processing systems constitute the image reading unit 31a. The image processing unit 34 processes a digital signal so that a predetermined image is formed, and outputs the digital signal as an image signal to the image forming units 3Y to 3K or a memory 41 described later.
[0032]
The control unit 20 controls the entire copying machine 1, and includes a main control circuit 40 and a memory 41. The control unit 20 controls the operation unit 27, the image forming units 3Y to 3K, the image processing unit 34, and control signals and data. We are exchanging. Further, a clock circuit 42 for generating timing pulses necessary for image reading and image processing by the scanner unit 2 is provided. The clock circuit 42 may be provided in the scanner unit 2.
[0033]
The clock circuit 42 is based on a reference clock generation circuit 43 that generates a reference clock, a frequency spread circuit 44 that performs frequency spread of a predetermined width using the frequency of the reference clock as a reference frequency, and the same frequency based on the frequency-spread clock. A timing pulse generation circuit 45 that generates a timing pulse having a reference frequency and a frequency spread width, and a spread width adjustment circuit 46 that outputs a parameter to the frequency spread circuit 44 to set the frequency spread width of the clock are provided. The timing pulse output from the timing pulse generation circuit 45 is supplied to the CCD 31, the analog signal processing unit 32, the A / D conversion unit 33, and the image processing unit 34. The parameter output from the diffusion width adjusting circuit 46 can be changed by an instruction from the main control circuit 40.
[0034]
Next, the image quality mode output from the copying machine 1 will be described. Usually, the digital copying machine performs image processing by the image processing unit 34 based on an output image quality mode, together with predetermined processing such as shading correction. Typical examples of such image quality modes include “character mode”, “photo mode”, and “character / photo mixed mode”.
[0035]
“Character mode” is a mode that is usually applied when outputting a document mainly composed of characters and lines. The document is read and processed in binary or low gradation and output in binary or low gradation. To do. Therefore, it is possible to obtain an output image with a short processing time, a sharp image, and a clear contrast. The “photo mode” is a mode applied to processing and output when a photograph or a printed matter on which a photograph is posted is a manuscript. The manuscript is read in multi-gradation such as 256 gradations, and multi-gradation processing is performed. Go and output. Therefore, it is possible to obtain an output image with fine texture and continuous light and shade. That is, this is a mode opposite to the “character mode” in terms of gradation. Also, in the “character / photo mixed mode”, which is used when text and photos are present at the same time in the original, the text is output in “text mode” and “photo mode” in order to output both text and photo images with satisfactory quality. ] Are processed with a substantially intermediate gradation, and output with a substantially intermediate gradation.
[0036]
In the copying machine 1, it is possible to switch such mode automatically or manually from the operation unit 27. When switching to manual mode, the user can further switch from the operation unit 27. It is necessary to select any one of “text mode”, “photo mode”, and “text / photo mixed mode”. When the mode is switched to automatic, all or part of the document is pre-scanned when the document is read, and the copying machine 1 recognizes and determines which mode image quality is closest to the document.
[0037]
As is clear from the description of the image quality mode described above, in the “character mode”, since a document with clear shading is output as such, even if a little image noise is mixed in the processing process in the image reading unit 31a. , It is difficult to appear in the output image, and even if it appears, it is difficult to recognize and not conspicuous. In the case of the “photo mode”, reproduction is performed with multiple gradations, that is, subtle changes in pixels. Therefore, if image noise is mixed, it is likely to appear in the output image and be easily recognized. The “character / photo mixed mode” is an intermediate level.
[0038]
In the present invention, by appropriately utilizing such image properties, radiation noise due to clocks and timing pulses can be reduced without impairing the image quality of the output image. That is, as described based on FIG. 2, the graph D1 is a timing pulse in which image noise is most likely to occur although radiation noise is least generated because the frequency spread width is the largest. The graph D3 is a timing pulse in which the emission noise is the largest but the image noise is least likely to occur because the frequency diffusion width is the smallest. The graph D2 is between these.
[0039]
The problem of the present invention can be solved by combining and controlling the image quality mode and the property of the frequency spread width of the timing pulse as described above. FIG. 4 shows a flowchart according to the first embodiment in which the frequency spreading width of the timing pulse is switched according to the image quality mode. For convenience of explanation, they are referred to as D1, D2, and D3 in descending order of frequency spreading width as shown in FIG.
[0040]
When copying is started, it is determined in S1 (step 1) whether the selection of the image quality mode is set to manual or automatic. In the case of manual operation, which image quality mode is set is read in S2, and the process proceeds to S5. If the automatic setting is set in S1, the process branches to S3, where a part or all of the original is pre-scanned, and in S4, the copying machine 1 automatically determines which image quality mode is optimal, and performs the processing. After determining the image quality mode to be performed, the process proceeds to S5. In S5, the process branches to processing according to the set or determined image quality mode. If the image quality mode is “text mode”, the process branches to S10. If the “text / photo mixed mode” is selected, the process branches to S20. If the image quality mode is “photo mode”, the process branches to S30.
[0041]
In S10, an instruction to set the frequency spread width of the clock to D1 (maximum) is output from the main control circuit 40 to the spread width adjustment circuit 46 according to the image quality mode. In response to this, the spread width adjusting circuit 46 outputs a parameter corresponding to D1 to the frequency spreading circuit 44 in S11. In S12, the frequency spread circuit 44 modulates the reference clock so that the spread width of the frequency becomes D1, and outputs the modulated clock to the timing pulse generation circuit 45 as a clock spread as the frequency D1. The adjustment process ends. S20 to S22 are the same as S10 to S12, and the frequency spread width is controlled to be set to D2. S30 to S32 are the same as S10 to S12, and the frequency spread width is controlled to be set to D3. In this way, the timing pulse generated by the timing pulse generation circuit 45 based on the frequency-spread clock is supplied to the CCD 31, analog signal processing unit 32, A / D conversion unit 33, and image processing unit 34. Image reading and image processing are performed.
[0042]
As described above, in the first embodiment of the present invention, the image quality mode is determined manually or automatically for each original, and the image reading unit 31a or the image is detected with the timing pulse having the frequency spread width corresponding to the image quality mode. The processing unit 34 is driven. Therefore, the circuit and the control are simplified, and at the same time, the radiation noise is reduced and the image noise becomes difficult to visually recognize on the output image. Although the example of automatically recognizing and discriminating the image quality mode of the entire document when performing the pre-scan in S3 of FIG. 4 has been described, a plurality of reading lines are in the process of sequentially pre-scanning from the beginning of the document. The image quality mode is automatically determined for each area composed of the area, the image quality mode corresponding to the area is stored, and the image quality mode is stored for each area stored when reading for image formation after the pre-scan is completed. It is also possible to change the frequency spread width according to the above. In order to perform finer control, there is a method of determining an image quality mode for each line, which will be described below.
[0043]
Next, a second embodiment of the present invention will be described with reference to FIGS. 1, 2, and 5 to 7. FIG. In the second embodiment, when the image quality mode is set to automatic, when determining the image quality mode of the document, the image quality mode is not determined by pre-scanning the document in advance as in the first embodiment. This is a method in which the image quality is determined for each predetermined area and the image quality mode is determined almost in parallel with reading the document for image formation, and the result is reflected when the next line is read. Therefore, the determination of the image quality mode is performed in almost real time for each region, that is, substantially for each reading line, the timing pulse is finely adjusted, and time is not wasted in pre-scanning.
[0044]
FIG. 5 is a schematic block diagram of the second embodiment showing a main circuit portion of the copying machine 1 including a clock circuit. In the figure, components having the same reference numerals as those in FIG. 3 represent the same components, and redundant description is omitted. 3 is different from that shown in FIG. 3 in that the image processing unit 34 includes an area discriminating circuit 50 for enabling the above-described real-time processing. As soon as the image quality mode for each area is determined, the information is the area discriminating circuit 50. The main control circuit 40 is configured to send a signal for designating the frequency spread width to the spread width adjusting circuit according to the information.
[0045]
FIG. 6 is a diagram in which numbers are assigned to lines on which the document is sub-scanned. Hereinafter, a schematic method in which the area determination circuit 50 determines the image quality mode for each area of the document will be described. The line from which the original is first read by the sub-scanning of the CCD 31 is L1, and sequentially L2, L3,..., Ln.
[0046]
FIG. 7 shows a flowchart according to the second embodiment for switching the frequency spreading width of the timing pulse in accordance with the image quality mode. For the convenience of the following explanation, as shown in FIG. 2, they are referred to as D1, D2, and D3 in descending order of the frequency pulse width. When copying is started, in S40, it is determined whether the selection of the image quality mode is set to manual or automatic. In the case of manual operation, which image quality mode is set is read in S41, and the process proceeds to S42. Since the flow after S42 is the same as S5 to S32 in FIG. 4, the description thereof is omitted.
[0047]
If the selection of the image quality mode is set to automatic in S40, the process branches to S50. In S50, a control signal is sent from the main control circuit 40 to the spread width adjustment circuit 46, and the frequency spread width of the timing pulse is initialized to D3 where the possibility of image noise is minimized. Thereafter, in S51, the lines L1, L2, and L3 are sequentially read by the CCD 31, and the line L1 + L2 + L3 is handled as a discrimination region by the region discrimination circuit 50 in S52. In S53, the area determination circuit 50 determines the image quality mode of the determination area. If the “character mode” is determined, control signals are sent from the area determination circuit 50 to the main control circuit 40 and the spread width adjustment circuit 46 in S54, and the frequency spread width of the timing pulse is set to D1. If “photo mode” is determined in S53, the process branches to S55, where control signals are sent from the region determination circuit 50 to the main control circuit 40 and the diffusion width adjustment circuit 46, respectively, and the frequency diffusion width of the timing pulse is D3. Set to
[0048]
Thereafter, in S56, it is determined whether or not the last read line is the last line of the document. If it is the last line, this flow is terminated and the normal operation is resumed. If it is not the last line, the next line Ln is read in S57. At this time, the frequency spread width of the timing pulse at the time of reading the line Ln is in accordance with the determination of the image quality mode in the determination area in S53. In other words, the frequency spread width at the time of reading the line Ln is based on the determination result of the image quality mode of the determination area composed of L (n−3), L (n−2), and L (n−1). It is a thing.
[0049]
When the reading of the line Ln is completed, the line L (n-3) is removed, and the lines L (n-2), L (n-1), and Ln constitute the next determination area. Thereafter, the process returns to S53, and the image quality mode of the new discrimination area is determined, and this repetition continues until the reading of the document is completed. Accordingly, the document reading for each line is performed for image formation, and at the same time, the image quality mode for each line is substantially determined.
[0050]
As described above, in the second embodiment, when the selection of the image quality mode is set to automatic, the image quality mode is substantially determined for each line, and the timing is set with an appropriate frequency spread width for each line. A pulse is set. Therefore, compared with the method according to the first embodiment in which the frequency spread width is set for each document according to the image quality, finer frequency spread control is possible, and the emission noise generated by the timing pulse is finely suppressed. Since it is controlled and the influence on image quality due to image noise, which is a side effect, is also controlled for each line, it is possible to obtain an efficient and highly effective result.
[0051]
In the above description of the second embodiment, the example in which the discrimination area is configured with three reading lines has been described. However, the number of reading lines that constitute the discrimination area is not limited to this example. In addition, the example in which the determination in S52 and S53 in FIG. 7 is either “character mode” or “photo mode” has been described, but it is also possible to provide an intermediate mode other than these two modes, for example. It is.
[0052]
In the first and second embodiments described above, two or three image quality modes have been described as examples. However, actual image quality modes are not limited to these examples. For example, various image quality modes may be provided, particularly in a color image forming apparatus, such as “line drawing / illustration mode” close to “character mode” and “printed material mode” close to photo mode. In that case, without being limited to three frequency spread widths, it is also possible to control with a spread width other than three by obtaining the correlation between the frequency spread width and the influence of image noise on the image quality, The size of the diffusion width may be set within a range where the side effect does not affect.
[0053]
【The invention's effect】
According to the present invention, it is possible to supply timing pulses that are uniformly frequency-spread to the image reading unit and the image processing unit, so that it is possible to greatly suppress the generation of radiation noise due to the timing pulses. In addition, since the frequency spread width is changed according to the image quality mode, there is an excellent effect that image noise caused by the frequency spread timing pulse hardly appears in the image and is not noticeable.
[0054]
In addition, if image quality is determined in parallel with document scanning, it is possible to control the appropriate image quality mode and frequency diffusion width of timing pulses for each scanning line of the document. The effect of reducing is also increased.
[0055]
Furthermore, in order to achieve both suppression of radiation noise and reduction of the effect of image noise on the output image, a complicated synchronization circuit and image noise suppression circuit are not required as in the prior art, and the cost is reduced. Can be realized with a simple configuration.
[Brief description of the drawings]
FIG. 1 is a front cross-sectional view schematically showing an image processing unit and a digital color copier equipped with the image processing unit as an example of an image forming apparatus according to the present invention.
FIG. 2 is a diagram illustrating the relationship between the frequency and time of a clock whose timing is modulated (spread) and a timing pulse.
FIG. 3 is a schematic block diagram of the first embodiment showing a main circuit portion of the copier 1 including a clock circuit.
FIG. 4 is a flowchart according to the first embodiment for switching the frequency spreading width of a timing pulse according to an image quality mode.
FIG. 5 is a schematic block diagram of a second embodiment showing a main circuit portion of the copier 1 including a clock circuit.
FIG. 6 is a diagram in which numbers are assigned to lines for sub-scanning a document.
FIG. 7 shows a flowchart according to a second embodiment for switching the frequency spread width of a timing pulse in accordance with the image quality mode.
[Explanation of symbols]
1 Copying machine
2 Scanner section
3Y-3K image forming unit
4Y-4K toner hopper
5 Paper cassette
6 Paper feed guide
7a Paper feed timing motor
7 Feeding timing roller
8 Conveyor belt
10 Output section
11 Conveyor belt roller
11a Conveyor belt motor
12 Transfer roller
13 Fixing part
14 to 16 discharge rollers
18 Discharge roller
19 Discharge section
20 Control unit
22 Developer
23 photoconductor
23a Photoconductor motor
24 Charger
25 Exposure equipment
26 Cleaning section
27 Operation unit
30 Optics
31 CCD
31a Image reading unit
32 Analog signal processor
33 A / D converter
34 Image processing unit
40 Main control circuit
41 memory
42 Clock circuit
43 Reference clock generation circuit
44 Frequency spread circuit
45 Timing pulse generator
46 Diffusion width adjustment circuit
50 area discrimination circuit

Claims (7)

An image reading unit that is driven by a timing pulse to read a document, performs predetermined conversion and outputs the image signal, and an image process that is driven by the timing pulse and performs image processing according to an image quality mode based on the image signal An image forming apparatus comprising:
The timing pulse is a timing pulse that has been subjected to frequency spreading in which a reference frequency is continuously modulated at a predetermined period, and is configured such that the width of the frequency spreading is changed according to the image quality mode. An image forming apparatus. 2. The image quality mode according to claim 1, wherein the image quality mode is a plurality of modes corresponding to gradation of image formation, and the timing pulse has a frequency spread width corresponding to each of the plurality of image quality modes. Image forming apparatus. The timing pulse is changed so that the frequency spread width is small when the gradation of the image quality mode is high and the frequency spread width is large when the gradation of the image quality mode is low. The image forming apparatus according to claim 1 or 2. 4. The image forming apparatus according to claim 1, wherein the frequency spreading width of the timing pulse is configured to be changeable for each reading line when the original is read by the image reading unit. 5. . The image processing unit determines an image quality mode of a determination region including a plurality of continuous reading lines including the newest line read by the image reading unit, and a timing pulse having a frequency spread width corresponding to the image quality mode 5. The image forming apparatus according to claim 1, wherein the next line is read by being driven by. 4. The image forming apparatus according to claim 1, wherein the image quality mode is a mode that is selected in advance by a user for each document. 4. The image quality mode according to claim 1, wherein the image quality mode is a mode in which a document is pre-scanned by the image reading unit and automatically determined and selected by the image forming apparatus. The image forming apparatus described in 1.

Images