JP2003072133A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate color variation in an image and to improve color representation by a method wherein a writing position in a sub-scanning direction can be controlled in a shift amount not greater than a width of one line, a shift amount in a main (beam) scanning direction is set based on the shift amount in the sub-scanning direction, and then an adequate condition of superposing colors is set. SOLUTION: Dots of different colors are placed such that the dots are not completely superposed and a part where the dots are not superposed is enlarged (shown in fig. 4). Therefore, a time difference of a sub-scanning reference signal (for determining a writing timing at a shift amount within a width of one line) with respect to a reference synchronizing signal is detected as a shift in a sub-scanning direction. A shift amount in the main scanning direction is calculated so as to shift a center of dot of each color by not less than one fourth of pixel (shown in fig. 4), and then a writing clock is delayed, thereby achieving a condition of predetermined and adequate superposing of colors.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copy which forms a color composite image by scanning / writing on an image carrier by a light beam from an LD (laser diode) or the like whose lighting is controlled by image data of a plurality of colors. For image forming devices such as printers, printers, facsimiles, plotters, printing machines, etc., the occurrence of color unevenness in a composite image is prevented by shifting the dots of each color forming the pixels formed on the image carrier surface in the main and sub directions. The present invention relates to the image forming apparatus having improved color reproducibility.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus such as a laser printer or a digital copying machine, an LD is controlled to be turned on in accordance with image data, and a light beam emitted from the LD causes the image carrier (photoconductor) surface to move. Sub-scanning (mainly line scanning with beam light, sub-scanning by relatively moving the image carrier in the direction intersecting with the main scanning line) is performed to write an image. At this time, it is necessary to write an image on the image carrier at a fixed timing for each main scanning line that is periodically scanned by the polygon mirror (optical deflector). Having a synchronous detection sensor to detect the beam,
It is common. The synchronization detection sensor detects the passage of the light beam scanned in the main scanning (line) direction, and starts image writing in the main scanning direction at a predetermined timing based on the generated synchronization signal. When a color image is formed by writing an image in this way,
For example, it is necessary to superimpose images of four color components such as yellow, magenta, cyan, and black, but it is known that color unevenness occurs depending on the superimposition state of the images of the respective colors. Conventionally, in order to prevent the occurrence of color unevenness in a low-density area due to such factors, a method of operating dot positions in the main scanning direction and the sub scanning direction has been proposed (see Japanese Patent Laid-Open No. 6-155815). In this conventional example, the solution is attempted by shifting the writing start position of each color component in the main scanning direction or in the sub scanning.

[0003]

However, in this conventional example, the deviation of the writing position in the sub-scanning direction is divided into front and rear lines for writing.
It is not possible to control the positional deviation within 1 line. Furthermore, the idea is adopted that the respective shift amounts are determined in consideration of the mutual relationship of the shift amounts in the main and sub-scanning directions of the respective color components written by being shifted in the preceding and following lines (sub-scanning direction) and the main scanning line direction. Since it does not exist (means for that purpose is not prepared), there is a problem that the color components cannot be set in the optimum superposition state. The present invention has been made in view of the above-mentioned problems of the conventional technology, and its purpose is to mainly apply to an image carrier by a light beam from a light source whose lighting is controlled by image data of a plurality of colors.
In an image forming apparatus (for example, a copying machine, a printer, a facsimile, a plotter, a printing machine, etc.) that performs image writing by sub-scanning and forms a color composite image, the writing position in the sub-scanning direction is controlled with a deviation amount within 1 line. It is possible to form an image in an appropriate color component superposition state, eliminate the occurrence of color unevenness in the formed image, improve color reproducibility, and adjust the amount of writing position deviation in the sub-scanning direction. By setting the shift amount of the writing position in the line scanning direction according to the above, an image is formed in an optimally superimposed state of color components, and further, the writing position control described above can be realized by a simpler means. Especially.

[0004]

According to a first aspect of the present invention, an image carrier is line-scanned by a light beam emitted by a light source whose lighting is controlled according to image data for a plurality of colors, and the image carrier is moved in a direction intersecting the scanning line. An image forming apparatus comprising means for writing an image on the surface of the image carrier for each color by relatively moving the image carrier, and writing control means for controlling the image writing start position, the writing control The means is an image forming apparatus characterized in that scanning lines of respective colors on the surface of the image carrier are shifted by a predetermined amount within one line width.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, there is provided a synchronization detection means for outputting a synchronization signal serving as a writing reference in the light beam scanning direction, and the writing control means for each color. The writing start position in the light beam scanning direction, which is determined based on the detected synchronization signal, is changed for each color according to the amount of deviation given to the scanning line.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the shift amount given to the scanning line for each color is obtained as a relative level value between the respective colors, and the light is output according to the obtained level value. It is characterized in that the control amount of the writing start position in the beam scanning direction is obtained.

According to a fourth aspect of the invention, in the image forming apparatus according to any one of the first to third aspects, the shift amount given to the scanning line for each color is set to the writing start position in the direction intersecting the scanning line. It is characterized in that it is obtained by a time difference of a predetermined timing signal with respect to the synchronizing signal.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the time difference indicating the amount of deviation given to the scan line for each color is the image writing clock, or an integral multiple or integer thereof. It is characterized in that the calculation is performed using a 1 × clock.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The image forming apparatus of the present invention will be described based on the following embodiments shown with reference to the accompanying drawings. First, an outline of a color laser printer as an image forming apparatus to which the present invention is applied will be described. Figure 1
3 illustrates an image writing unit using a laser beam in a printer. As shown in FIG. 1, under the control of a printer control unit 1 that controls the entire printer, an image writing control unit 10,
A polygon motor control unit 5 and a stepping motor control unit 3 are provided. According to the control operation of the printer control unit 1, the image writing control unit 10 controls the lighting of the LD 20 based on the captured image data. The light beam emitted from the LD 20 is deflected by the polygon motor control unit 5 by the polygon mirror 4 that rotates at a constant speed (see arrow A in FIG. 1), and then fθ
An image is formed on the photoconductor drum 2 as a light spot having a constant small diameter by the lens 8, and the surface of the photoconductor drum is subjected to main scanning at a constant speed (FIG. 1, arrow B) to perform light beam writing.

At this time, a sync signal is generated at a fixed position on the beam scanning line, and a write clock is generated at a timing corresponding to the write start position with the sync signal as a reference. The synchronization signal is generated by detecting a beam by the synchronization detection sensor 7 provided at a fixed position with respect to the photosensitive drum 2. In this way, the writing in the main line scanning direction is controlled for each line according to the start timing determined based on the synchronization signal for each color component. The details of the write control will be described later.
On the other hand, in the writing in the sub-scanning direction (arrow C in FIG. 1), the sub-scanning reference signal (timing signal) corresponding to the writing position determined for each color component based on the reference position in the drum rotation direction on the photosensitive drum 2 is used. ), The start of each page is controlled. Here, the printer control unit 1 generates a sub-scanning reference signal as a control signal that causes a writing position deviation within one line for each color, and controls the photosensitive drum 2 by this signal. The details of the write control will be described later.

As described above, an existing color laser printer is used as an image forming process for forming an image on the transfer paper by writing an image on the photosensitive drum 2 by controlling the writing start position for each color component. It can be implemented by applying the method adopted in. For example, it is possible to employ a method in which images of respective color components are sequentially written on the photoconductor drum, color composition is performed on the drum, and transfer to a transfer paper is performed. As another method, a method is used in which the image of each color component written on the photosensitive drum is transferred to the intermediate transfer member for each color, the intermediate transfer member performs color combination, and then the transfer is performed to the transfer paper. It is also possible.

Next, an embodiment relating to the image writing control section in FIG. 1 will be described in detail. In this embodiment, in order to form an image in an optimally superposed state of color components, control is performed to set the shift amount of the writing position in the line scanning direction according to the shift amount of the writing position in the sub-scanning direction. It is something to do. FIG. 2 is a block diagram showing in detail the image writing control unit 10 of this embodiment. In addition, FIG.
3 shows the mutual relationship of signals used in the write control operation of FIG. The configuration and operation of the image writing control unit 10 will be described with reference to FIGS. 2 and 3. Basic write clock generator 11
Is composed of an oscillator such as a crystal oscillator or a PLL circuit, and generates a basic clock used by the phase synchronization control unit 12 described below to generate a desired write clock (determines write timing in the main scanning direction). The basic clock is set to output N times the frequency of the write clock, and in the example shown in FIG. 3, the basic clock is N = 8, that is, 8 times the basic clock of the write clock (FIG. 3 (b)). A built-in clock (Fig. 3 (a)) is generated.

The phase synchronization control unit 12 has a function of generating a desired write clock from the basic write clock and a shift control amount in order to shift the write start position of the generated write clock in the main scanning direction described later. It has the function of delaying the clock phase. The write clock is generated by first generating a write clock group (FIG. 3B) having a cycle eight times that of the clock based on the basic write clock and changing the phases by the cycle of the clock. Further, the write clock to be used is generated by the operation of selecting the clock used for writing from the generated write clock group in accordance with the timing of the write operation. At this time, the timing of the writing operation is determined by the synchronization signal detected by the synchronization detection sensor 7. That is, the write clock (FIG. 3 (d)) is selected from the write clock group according to the input timing of the synchronization signal (FIG. 3 (c)) input to the phase synchronization control unit 12, and the write of the selected phase is performed. The clock is set. With this configuration, 1 / N (N:
(Integer) Synchronous alignment can be performed in pixel units.

Further, the phase synchronization control section 12 delays the phase of the write clock (FIG. 3 (d)) selected as described above by the control operation from the transfer delay control section 15.
This delay is performed as an operation for forming an image in an optimally superposed state of color components. The optimum superposition of the color components can be realized by controlling the write start position of each color component in the main / sub scanning direction. That is,
Corresponding to the writing start position set in the drum rotation direction (sub-scanning direction) on the photoconductor drum 2 for each color component, the writing start position in the line scanning direction (main scanning direction) that can achieve an optimum overlapping state is set. By setting and delay-controlling the phase of the write clock (FIG. 3 (d)) according to the setting, the write positions of the respective color components are optimized. Figure 4
Shows an example of an optimized superposition state of color components by controlling the writing start position in the main / sub-scanning direction. As shown in FIG. 4, the dot centers (that is, the writing start positions) of the respective color components are dispersed with an appropriate distance maintained, which is in the optimum state.

The phase delay control of the write clock for optimizing the write positions of the respective color components corresponding to the write start position in the sub-scanning direction will be described in detail. In order to control the phase delay of the write clock, first, it is necessary to detect the data indicating the write start position in the sub-scanning direction. The writing start position in the sub-scanning direction is set by the sub-scanning reference signal. The sub-scanning reference signal is a writing timing signal determined for each color component based on the reference position in the drum rotation direction on the photosensitive drum 2, and the drum rotation position at which writing is started is determined based on this signal. In this embodiment, the printer control unit 1 generates a sub-scanning reference signal for each color as a control signal so as to generate a writing position shift within one line width for each color, and inputs the sub-scanning reference signal to the image writing control unit 10. Image writing control unit 10
Determines the drum rotation position at which writing is started based on the input sub-scanning reference signal. At the same time, this signal is input to the line position determination unit 13 for use in phase delay control of the writing clock in the main scanning direction. It

The line position determination unit 13 detects data indicating the writing start position in the sub-scanning direction based on the input sub-scanning reference signal. The sub-scanning reference signal is a pulse signal generated at the timing corresponding to the writing start position in the sub-scanning direction given for each color component. Therefore, if the timing deviation of the pulses set for each color is seen, the writing start position Can be detected. This is always detected as a time width signal based on a synchronization signal generated at a fixed timing. FIG. 5 is a diagram showing the relationship between the synchronization signal and the sub-scanning reference signal, and is a diagram for explaining the line shift amount. The synchronization signal shown in FIG. 5 is a reference signal in the beam scanning direction detected by the synchronization detection sensor 7, and the sub-scanning reference signal is a reference signal in the sub-scanning direction (photosensitive member moving direction) intersecting the beam scanning direction. The synchronization signal and the sub-scanning reference signal are asynchronous with each other, and the time width signal (hereinafter referred to as "line deviation amount") representing the generation timing of the sub-scanning reference signal based on the synchronization signal is for each color component, that is, for each printing. , Can take different values.

The line position determination unit 13 detects the time width determined by the input synchronizing signal and the sub-scanning reference signal as the line shift amount. At this time, the detection of the time width representing the line shift amount is performed by counting the above-described writing clock, or an integral multiple or integral multiple thereof, in the period defined by the pulse of the synchronization signal and the sub-scanning reference signal,
This is done by calculating the count value. Since the write clock to be counted is synchronized with the synchronization signal, the line shift amount can be easily calculated by using this clock. Also here
For example, one line width is divided into levels at appropriate steps according to the amount of deviation, the amount of deviation within the width of one line is determined according to the level, and this is output to the delay amount calculation processing unit 14 in the subsequent stage.

The delay amount calculation processing unit 14, which has received the level data representing the line deviation amount, determines from the line deviation level that
In order to optimize the writing position of each color component, the necessary shift amount in the main scanning direction is calculated for each component according to the line shift level (shift amount in the sub-scanning direction), and it corresponds to the obtained shift amount. The delay amount of the write clock is calculated, and the delay amount is instructed to the phase delay control unit 15 in the subsequent stage. For this reason, the delay amount calculation processing unit 14 calculates the delay amount from the line shift level so as to obtain the optimum writing state, or
Alternatively, it is provided with means capable of obtaining the delay amount by referring to the reference table according to the line shift level. When the delay amount is set by the phase delay control unit 15, the phase synchronization control unit 12 causes the write clock selected from the write clock group (see FIG. 3) as described above.
The phase (d)) is delayed by the control operation from the phase delay controller 15. The phase delay of the write clock can be realized by operating the write clock group generated in the phase synchronization controller 12. FIG. 6 is a diagram for explaining the process of delaying the write clock by this operation. As shown in FIG. 6, in order to delay the phase of the write clock 1 (FIG. 6 (b)) selected from the write clock group by the period of the basic write clock (FIG. 6 (a)), it is delayed by the basic clock period. Write clock 2 (Fig. 6 (c))
And the write clock 2 is used to generate a desired delayed write clock 1 → 2 (FIG. 6 (d)). As described above, according to the means using the write clock group that changes in the cycle of the write clock, the delay can be performed in units of 1 / M (M: integer) pixels.

The write clock output from the phase synchronization control section 12 is input to the LD modulation section 16 and the LD 20 is turned on at the timing defined by the write clock. The modulation of the LD is determined by the image data output from the image processing unit (not shown) and input to the LD modulation unit 16. By using the image writing unit configured as described above, for example, an image formed by pixels in an optimum writing state in which dots of respective colors are not completely overlapped and a non-overlapped portion is large as shown in FIG. Can be formed. In a color image forming apparatus that forms each color component at the same time, the writing position of each color component in the sub-scanning direction is structurally determined, and the line shift amount is given in advance as an absolute amount. The position determination unit 13 (see FIG. 2) is unnecessary. At this time, the input / adjusted line shift amount is set in advance as an invariant and used.

Next, the delay amount calculation processing unit 14 of the above embodiment
A specific example of how to obtain the amount of deviation in the main scanning direction in is described.
Since the dots of each color component are arranged so that the dots of each color component do not completely overlap and the non-overlapping part becomes large (see FIG. 4), when the amount of deviation in the sub-scanning direction (line deviation amount) is small For this purpose, the amount of deviation in the main scanning direction is adjusted by adjusting the amount of deviation in the main scanning direction and the amount of deviation in the main scanning direction, and the calculated value is used. FIG. 7 is a diagram showing deviation amounts in the main / sub-scanning directions given to dots of four component colors. In the example shown here, the determination result of the line deviation amount in the sub-scanning direction is divided into eight levels A to H levels (vertical axis) as shown on the vertical axis of FIG. 7, and the horizontal axis indicates the deviation amount in the main scanning direction. I am taking it. Shown in Figure 7
Indicates the dot center values of the first to fourth colors, and the distance from the reference broken line represents the amount of deviation in the main scanning direction. In this embodiment, the dot shift amount between each color component is set to be 1/4 pixel or more in the total of main scanning and sub scanning. That is,
The maximum value of the line shift amount is equal to the size between synchronization detections (1 line width), that is, the size of 1 pixel, and in FIG. 7, 0 to 1/8 pixel (1 Since the position of (level) is misaligned, the dot position misalignment between each color
In order to have more than 1/4 pixel, 1 in the main scanning direction
It is necessary to delay by / 4 pixels. In addition, and, there is a positional deviation of 1/8 to 1/4 pixel in the sub-scanning direction, and there is a positional deviation of 1/4 pixel or more in the sub-scanning direction. Pixel delay. Considering in the same way, there is a positional deviation of 1/4 pixel or more in the sub-scanning direction, and a positional deviation of 1/8 to 1/4 pixel with respect to It must be delayed by 8 pixels.
However, since it has already been delayed, we advance 1/8 pixel to make no delay. (In order to simplify the circuit, 1/8 pixel delay is no problem). By performing such control, the desired writing state is obtained by shifting the overlap of the dots of the respective color components by 1/4 pixel or more.

[0021]

(1) Effects corresponding to the inventions of claims 1 and 2 Since the scanning lines of each component color on the surface of the image carrier can be displaced in the sub-scanning direction by a predetermined amount within one line width. It is possible to form a high-quality color composite image with no color unevenness by properly overlapping the dots of the respective component colors. Further, the writing start position in the light beam scanning direction, which is determined based on the detected synchronization signal, is changed for each component color according to the amount of deviation in the sub-scanning direction given to the scanning line for each component color. Therefore, the overlapping of the dots can be controlled to the optimum state, so that a higher quality color composite image can be formed. (2) Effect corresponding to the invention of claim 3 In addition to the effect of (1) above, the sub-scanning shift amount is obtained as a relative level value between each component color, and writing in the light beam scanning direction is performed by the obtained level value. Since the control amount of the start position is obtained, it is possible to easily implement the control. (3) Effects Corresponding to the Inventions of Claims 4 and 5 In addition to the effects of (1) and (2) above, sub-scanning is performed by the time difference with respect to the synchronization signal of the timing signal that determines the write start position in the direction intersecting the scanning line. To get the amount of deviation,
Since the time difference is calculated by using the image writing clock synchronized with the synchronization signal, or the integral multiple or integral multiple of the clock, the time difference can be realized with a simple circuit configuration.

[Brief description of drawings]

FIG. 1 illustrates an image writing unit using a laser beam in a printer that is an embodiment of the present invention.

FIG. 2 is a block diagram showing in detail an image writing control unit in the embodiment shown in FIG.

FIG. 3 shows a mutual relation of signals used in the write control operation of FIG.

FIG. 4 shows an example of a superposed state of optimized color components by controlling the write start position in the main / sub-scanning direction.

FIG. 5 is a signal line diagram showing a relationship between a synchronization signal and a sub-scanning reference signal, and a diagram for explaining a line shift amount.

FIG. 6 is a signal diagram for explaining a process of delaying a write clock.

FIG. 7 is a diagram showing a deviation amount in the main / sub-scanning direction given to dots of four component colors.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Printer control unit, 2 ... Photosensitive drum, 4 ... Polygon mirror, 10 ... Image writing control unit, 11 ... Basic writing clock generating unit, 12
... phase synchronization control unit, 13 ... line position determination unit,
14 ... Delay amount calculation processing unit, 15 ... Phase delay control unit,
16 ... LD modulator, 20 ... LD (laser diode).

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 1/23 103 H04N 1/04 104A F term (reference) 2C362 BB37 CA18 CA28 2H045 BA22 BA33 CA98 DA41 5C051 AA02 CA07 DB02 DB07 DB22 DB24 DB30 DC03 DE02 FA01 5C072 AA03 BA19 HA02 HA09 HA13 HB08 HB13 QA14 QA17 XA01 XA05 5C074 AA10 BB03 BB26 CC22 CC26 DD15 DD24 EE02 FF15 HH02

Claims (5)

[Claims] 1. An image carrier is line-scanned by a light beam emitted from a light source whose lighting is controlled in accordance with image data of a plurality of colors, and the image carrier is relatively moved in a direction intersecting the scanning line. An image forming apparatus comprising: a unit for writing an image on the surface of an image bearing member for each color; and a writing control unit for controlling an image writing start position, wherein the writing control unit scans each surface on the surface of the image bearing member. An image forming apparatus characterized in that lines are shifted by a predetermined amount within one line width. 2. The image forming apparatus according to claim 1, further comprising a synchronization detection unit that outputs a synchronization signal that serves as a writing reference in the light beam scanning direction, and the writing control unit provides the scanning line for each color. Depending on the amount of deviation,
An image forming apparatus characterized in that a writing start position in a light beam scanning direction, which is determined on the basis of a detected synchronization signal, is changed for each color. 3. The image forming apparatus according to claim 1, wherein the deviation amount given to the scanning line for each color is obtained as a relative level value between the colors, and the writing in the light beam scanning direction is performed according to the obtained level value. An image forming apparatus, characterized in that a control amount of an insertion start position is obtained. 4. The image forming apparatus according to claim 1, wherein the shift amount given to the scanning line for each color determines the writing start position in the direction intersecting the scanning line. An image forming apparatus characterized by being obtained by a time difference with respect to a synchronization signal. 5. The image forming apparatus according to claim 4, wherein the time difference indicating the amount of deviation given to the scanning line for each color is set using an image writing clock, or an integral multiple or integral multiple of that clock. An image forming apparatus characterized by being calculated by