JPH0575800A - Optical write controller - Google Patents

Abstract

PURPOSE:To control a timing of main scanning with the same count control even when a picture element density is changed by using an exclusive basic clock for main scanning control proportional to a scanning speed of a laser beam. CONSTITUTION:A frequency divider circuit 30 generates a picture element frequency under the control of a CPU 29 varying a frequency division ratio for each picture element density from a reference frequency of a reference frequency oscillator 25. The phase of the frequency signal is made equal to a phase of a main scanning write synchronizing signal LSYNC by a phase control circuit 32 to form a regular picture element frequency signal WCLK. On the other hand, a frequency divider circuit 31 generates an exclusive basic clock for main scanning control under the control of the CPU 29 from the reference frequency of the oscillator 25. The phase of the clock is made equal to that of a synchronization detection signal DETP by a phase control circuit 33 to generate the exclusive basic clock LCLK for main scanning control. When the signal DETP is inputted to a main scanning control circuit 28, the clock LCLK is counted and the generating timing of the synchronizing signal LSYNC is decided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical writing control device such as a laser printer or a copying machine using an electrophotographic process method, and particularly to adjusting the timing of generation of a main scanning writing synchronization signal when the pixel density is variable. Related to control.

[0002]

2. Description of the Related Art A laser printer is a printer device in which an image is formed by a large number of pixels arranged in a matrix, and a pixel is formed on a photosensitive drum by a scanning laser light modulated so as to be turned on and off according to information. A latent image is formed, a visible image is obtained by toner development, transferred to plain paper, and then fixed.

Since a laser printer is capable of high-speed modulation of laser light, high-speed and high-quality printing and graphic recording can be realized, and as a result, it is used as an output device for various data processing systems and image creating systems using computers. , Has a wide range of uses.

FIG. 3 is an example diagram showing a schematic configuration of a laser printer. This laser printer comprises a main body 10, a second paper feed unit 2, a third paper feed unit 3, and a double-sided machine 5. A standard paper feed unit 1, a manual paper feed unit 4, and a paper discharge tray 6 are mounted on the main body 10. The transport path 11 is indicated by a thick line. For example, the paper fed from the standard paper feed unit 1 is conveyed to the registration unit 7 and applied to the registration rollers to correct the skew (tilt) of the paper. The paper is conveyed to the photoconductor 8 and the toner developed on the photoconductor is transferred and the toner is fixed on the paper by the fixing unit 9.

The paper on which one side has been printed in this way enters the double-sided machine 5, reverses (switches back) the conveying direction, and is fed again to the main body to reach the resist section 7. At this time, the skew of the paper is corrected again. The surface on which the toner on the photoconductor is transferred is the reverse of the previous one, and is transferred to the back surface. The transferred paper is fixed by the fixing unit 9, and is discharged onto the paper discharge tray 6 to finish printing on both sides.

FIG. 4 is a schematic diagram showing an example of the optical writing section of the laser printer shown in FIG. In the operation of this optical writing unit, the laser light emitted from the laser diode (LD) 12 is collimated by the collimator lens 13. Excessive laser light is cut by the aperture 14 having a slit portion corresponding to the size of the dot (pixel density DPI) to be formed next.

[0007] are condensed to the image forming laser light in the main scanning by a cylinder lens # ₁ 15 has a predetermined size on the photoconductor 8, the main scanning direction by a polygon mirror 17 which is rotated by the polygon motor 16 (photosensitive Scanning is performed in the long axis direction x of the body 8. Then, the pair of Fθ lenses 18 make the uniform angular motion a uniform velocity motion and correct the field curvature.

[0008] Then the cylinder lens by changing the angle by the mirror # ₂ 19 # ₂ 20 by the sub-scanning direction (rotational direction of the photosensitive member)
The light of y is collected and irradiated onto the photoconductor 8.

Here, the laser light for synchronization detection is reflected by the polygon mirror 17, then enters the optical fiber 23 through the mirror # ₃ 21 and the cylinder lens # ₃ 22, and then the photodiode (PD) on the engine drive board. ) 24, the synchronous detection signal DETP in the main scanning direction is obtained, and the emission start timing of the image forming laser beam is controlled for each scanning.

By the way, there are various pixel densities DPI of image signals output from the host computer, and in order to print a normal image by receiving these outputs, the pixel density of the laser printer should be adjusted to match them. Must be variable. Further, it is necessary to change the pixel density of the laser printer in order to change the print size by using the character generator having the same pixel configuration.

In the laser printer capable of varying the pixel density, at least two of the photosensitive member linear velocity v, the polygon mirror rotation velocity Rm, and the pixel frequency (clock) W are not changed from the relation shown in the equation 1. Don't

[0012]

[Equation 1]

FIG. 5 shows an example of a conventional optical writing control circuit when the pixel density is variable, which controls the generation timing of the main scanning writing synchronization signal LSYNC.

In FIG. 5, reference numeral 25 is a reference frequency oscillator (O
SC), 26 is a frequency dividing circuit for the reference frequency, 27 is a phase control circuit for outputting the pixel frequency WCLK having a constant relationship with the phase of the synchronization detection signal DETP in the main scanning direction, and 28 is the synchronization detection signal for the main scanning direction. A main scanning control circuit that outputs a main scanning write synchronization signal LSYNC having a constant relationship with the phase of DETP, and 29 is a central processing unit (CPU) that controls the operations of the frequency dividing circuit 26 and the main scanning control circuit 28.

This is because the basic frequency WCLK0 (see the timing chart of FIG. 6, the same applies hereinafter) from the reference frequency oscillator 25, which is a crystal oscillator, is divided by the frequency dividing circuit 26 to become the basic pixel frequency for main scanning writing. Generate WCLK. The pixel frequency WCLK is made variable by the CPU 29 with respect to the frequency dividing ratio of the frequency dividing circuit 26 for each pixel density DPI.

Then, the polygon mirror described in FIG.
The laser beam scanned by 17 is the photodiode (P
D) Synchronous detection signal DE in the main scanning direction detected by 24
It becomes TP, and this DETP signal becomes the reference of the light emission start timing. Here, in order to keep the phases of the pixel frequency WCLK and the synchronization detection signal DETP constant, a phase control circuit
The regular pixel frequency WCLK is adjusted by 27. This will be described below with reference to FIGS. 7 and 8.

FIG. 7 shows an example of the phase control circuit 27 shown in FIG. 5, and its timing chart is shown in FIG. here,
When the image frequency WCLK before the phase control is WCLK0, WCLK0, WCLKB, ... In which the WCLK0 is slightly delayed by the delay circuit 27-1, are sequentially generated.
Input these pixel frequencies to the tap selector 27-2,
A phase close to the synchronization detection signal DETP in the main scanning direction, that is, the rising edge of the DETP signal and WCLK in the example of FIG.
At the falling edge of, WCLK is selected and output from the tap selector 27-2. That is, this is the normal pixel frequency WCLK
Becomes

Now, returning to FIG. 5, the main scanning control circuit 28 generates a main scanning writing synchronization signal LSYNC, and this signal controls the actual image writing position. That is, when the synchronization detection signal DETP is input to the synchronization signal LSYNC, the main scanning control circuit 28 counts the pixel frequency WCLK to determine the generation timing. This generation timing controls the count value from the CPU 29 and does not increase the counter. Therefore, as shown in FIG.
Is counted by 8 WCLK which is obtained by dividing 8 by.

Here, when it is desired to change the writing position in the main scanning direction, by increasing or decreasing the count value of the synchronization signal LSYNC generation, the generation timing of the synchronization signal LSYNC is shifted and the image writing position is moved.

[0020]

[Table 1]

Table 1 shows the synchronization signal LS described in FIG.
The YNC generation timing is controlled by 8 WCLK to show the horizontal scanning adjustment length (mm) for main scanning. In the example shown in Table 1, the image density DPI is switched between 240 DPI, 300 DPI and 40 DPI.
This is the case when there are three levels of 0 DPI. Also a polygon mirror
The laser beam scanning speed V _S (mm / sec) by 17, 1V _S, and 1.25V _S, and 1.67 V _S at 400DPI in 300DPI in 240 dpi, the linear velocity V of the photoreceptor 8 are kept constant.

Here, the pixel frequency WCLK is 1.56 MHz at 300 DPI and 2.78 at 400 DPI when 200 DPI is 1 MHz.
Being in MHz is proportional to the square of the pixel density DPI.

As can be seen from Table 1, the horizontal resist adjustment length differs depending on the number of adjustment steps depending on each pixel density DPI, and the higher the pixel density, the smaller the horizontal resist adjustment length.

[0024]

In the above laser printer, even if an image is written in a regular position on the photoconductor 8 as shown in FIG. If it shifts, the position of the image transferred on the sheet shifts, and the image quality deteriorates.

Therefore, conventionally, the position adjustment of the sheet feeding unit and the position adjustment of the double-sided machine 5 were adjusted with high accuracy. It becomes complicated and the adjustment time becomes long, which causes a cost increase of the laser printer.

In the case of the conventional optical writing control circuit (FIG. 5) when the pixel density is variable, the time from the detection of the synchronization detection signal DETP in the main scanning direction to the writing of the image is the pixel frequency WCLK. The main scanning control circuit 28 counts the
I am changing the (horizontal registration) to correct the misalignment, but
In a laser printer in which the pixel density DPI is variable, the unit time for correction changes according to the pixel density, so the lateral resist adjustment is performed according to the pixel density.
However, this also increases the adjustment time, which increases the cost of the laser printer.

Further, as described in Table 1, the pixel density DP
Depending on I, the horizontal resist adjustment length differs depending on the number of adjustment steps, and the higher the pixel density, the smaller the horizontal resist adjustment length, which makes adjustment difficult and takes a long time.

In view of the above situation, the present invention makes it easy for a laser printer having a variable pixel density, even if the pixel density is changed, to be an image writing position in the main scanning direction.
An object of the present invention is to provide an optical writing control device in which (horizontal resist) is changed to prevent misalignment.

[0029]

SUMMARY OF THE INVENTION According to the present invention, in a laser printer in which a laser beam is scanned to irradiate a photosensitive member and the rotation speed of a polygon mirror is changed to change the pixel density, a reference frequency is set to a pixel density. First and second frequency dividing circuits for varying the frequency dividing ratio for each, and a pixel frequency WCLK in which the phases of the output of the first frequency dividing circuit and the main scanning write synchronization signal LSYNC are made constant. No. 1 phase control circuit, and a second phase control circuit for outputting a dedicated basic clock LCLK for main scanning control in which the phases of the output of the second frequency dividing circuit and the synchronization detection signal DETP in the main scanning direction are made constant. And when the synchronization detection signal DETP in the main scanning direction is input, the dedicated basic clock LCL for main scanning control
K is counted and the main scanning write synchronization signal LSYNC is
And a central processing unit CPU for controlling the operations of the main scanning control circuit and the first and second frequency dividing circuits.

[0030]

According to the present invention, by using the dedicated basic clock for main scanning control which is proportional to the scanning speed of the laser beam, the main scanning timing can be controlled by the same count control even if the pixel density is changed. The accuracy of the writing position can be improved, and the writing position can be the same.

[0031]

FIG. 1 shows an optical writing control circuit according to an embodiment of the present invention, and FIG. 2 is a timing chart for explaining the operation of FIG.

In FIG. 1, reference numeral 30 is a first frequency dividing circuit, 31 is a second frequency dividing circuit, 32 is a first phase control circuit, and 33 is a second phase control circuit. Similarly, a reference frequency oscillator (OSC) 25, a main scanning control circuit 28, and a central processing unit (C
PU) 29.

The embodiment of the present invention is characterized in that a dedicated basic clock LCLK for main scanning control is generated. First, the reference frequency WCLK0 of the reference frequency oscillator 25 is generated by the first frequency dividing circuit 30 under the control of the CPU 29 that varies the frequency division ratio for each pixel density DPI. The normal phase of the pixel frequency WCL is set by the first phase control circuit 32 so that the pixel frequency WCLK becomes constant with the phase of the main scanning write cycle signal LSYNC.
Let K.

On the other hand, the reference frequency L of the reference frequency oscillator 25
The second frequency dividing circuit 31 generates a dedicated basic clock LCLK0 for main scanning control by the control of the CPU 29 which varies the frequency dividing ratio for each pixel density. In order to make the phases of the dedicated clock LCLK0 and the synchronization detection signal DETP constant, the second phase control circuit 33 generates a dedicated basic clock LCLK for regular main scanning control, which is output to the main scanning control circuit 28. To do.

The main-scanning control circuit 28 generates a main-scanning write sync signal LSYNC.
When the synchronization detection signal DETP is input to the main scanning control circuit 28, the NC supplies the dedicated basic clock LCL for the main scanning control.
K is counted to determine the timing of occurrence. At this generation timing, the CPU 29 controls the count value.

Therefore, when it is desired to change the writing position of the image in the main scanning direction, by increasing or decreasing the count value of the LSYNC signal generation, the generation timing of the LSYNC signal is shifted and the image writing position can be moved.

As the dedicated basic clock LCLK for main scanning control in the embodiment of the present invention, V _S / k = LCLK is used as the scanning speed V _S (mm / sec) and the constant k. That is, when the scanning speed becomes 1.56 times, LCLK also becomes 1.5 times and is proportional.

[0038]

[Table 2]

Table 2 shows the lateral resist adjustment length according to the present embodiment, and the pixel density DPI is set to 3 in the same manner as in Table 1 above.
Steps (240, 300, 400), scanning speed V _S in 3 steps (1, 1.2
5, 1.67), pixel frequency WCLK (MHz) in 3 steps (1, 1.5
6, 2.78).

Now, a dedicated basic clock L for main scanning control
Assuming that the frequency of CLK is V _S / k, the generation timing of the main scanning write cycle signal LSYNC is controlled by the LCLK as shown in FIG. 2, so the horizontal scanning resist adjustment in the main scanning is constant regardless of the pixel density. Becomes k.

As shown in Table 1 above, this is the pixel density DPI.
Depending on the number of adjustment steps, the lateral resist adjustment length does not differ, and the higher the pixel density, the smaller the lateral resist adjustment length, so the adjustment is easy.

[0042]

As described above, the optical writing control device of the present invention uses the dedicated basic clock for main scanning control which is proportional to the scanning speed of the laser beam, so that even if the pixel density is changed, the same. It is possible to control the generation timing of the main-scanning write synchronization signal by the count control, and improve the accuracy of the write position and make the same write position.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an optical writing control circuit according to an embodiment of the present invention.

FIG. 2 is a timing chart illustrating the operation of FIG.

FIG. 3 is a schematic configuration diagram of a laser printer as an example in which the present invention is implemented.

FIG. 4 is a schematic diagram showing an example of the optical writing unit in FIG.

FIG. 5 is a diagram showing an example of a conventional optical writing control circuit.

FIG. 6 is a timing chart illustrating the operation of FIG.

7 is a diagram showing an example of the phase control circuit of FIG.

FIG. 8 is a timing chart illustrating the operation of FIG.

[Explanation of symbols]

8 ... Photoconductor, 17 ... Polygon mirror, 24 ... Photodiode (PD), 25 ... Reference frequency oscillator (OSC), 28
... Main scanning control circuit, 29 ... Central processing unit (CPU), 30
... first frequency divider circuit, 31 ... second frequency divider circuit, 32 ... first
Phase control circuit 33, second phase control circuit, WCLK
... Pixel frequency, LCLK ... Dedicated basic clock for main scanning control, DETP ... Synchronous detection signal in the main scanning direction.

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display location H04N 1/23 103 Z 9186-5C 1/387 101 8839-5C

Claims (1)

[Claims] 1. In a laser printer in which a laser beam is scanned to irradiate it on a photosensitive member and the rotation speed of a polygon mirror is changed to make the pixel density variable, the reference frequency is made variable for each pixel density. The first and second frequency dividing circuits, and the pixel frequency WCL in which the phases of the output of the first frequency dividing circuit and the main scanning write synchronization signal LSYNC are made constant.
A first phase control circuit for outputting K, a dedicated basic clock LCL for main scanning control in which the phases of the output of the second frequency dividing circuit and the synchronization detection signal DETP in the main scanning direction are made constant.
A second phase control circuit for outputting K and a timing for generating the main scanning write synchronization signal LSYNC by counting the dedicated basic clock LCLK for main scanning control when the synchronization detection signal DETP in the main scanning direction is input. A main scanning control circuit for controlling, the main scanning control circuit, and the first
And a central processing unit CP for controlling the operation of the second frequency dividing circuit
An optical writing control device having U and.