JP2000263841A - Image-forming apparatus and image formation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct an exposure position deviation highly accurately in an image-forming apparatus having a plurality of exposure units. SOLUTION: A clock signal from an oscillator 10 is modulated in frequency and controlled in phase difference in a DDS circuit 1 to generate an image clock signal. To the DDS circuit 1 is connected an index sensor 24 for supplying an index signal, and a CPU 2 for supplying a synchronous phase setting data N to adjust a phase difference of a frequency setting data ΔF for controlling to modulate a frequency of the pixel clock signal, the pixel clock signal and the index signal. The DDS circuit 1 has a cumulative adder, a waveform data memory and a D/A converter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a laser copying machine, a laser printer, and a laser facsimile for scanning a photosensitive member with a light beam, and more particularly to a multicolor image forming apparatus having an exposure unit for each of a plurality of colors. Related to the device.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus such as a laser printer or a copying machine, a laser beam (light beam) modulated on the basis of image data scans over a photoconductor to lurch on the photoconductor. An image is formed. And
After the toner is applied to the photoconductor in accordance with the latent image, the toner is transferred and fused to the recording paper to form a desired image on the recording paper.

FIG. 6A is a schematic configuration diagram of a single exposure unit included in a monochrome image forming apparatus. FIG.
An exposure unit 30 shown in (a) includes a photoconductor 20, a laser diode 22 that outputs light according to an image signal,
A polygon mirror 21 for scanning the laser beam from the laser diode 22 toward the photoconductor 20, an fθ lens 26 for narrowing the beam diameter of the laser beam, and a CY lens 2
5, an index mirror 23, and an index sensor 24 for detecting a main scanning reference signal or a horizontal synchronizing signal (hereinafter, referred to as an “index (INDEX) signal”) in the laser beam. In the photoconductor 20, S1 (mm) is the length of an index area corresponding to S dots from the start point of the index signal in the horizontal scanning direction to the image formation start point (the point at which print data is output), and L1 (mm). Is the length of the image forming area corresponding to the L dot on which the image data is printed.

FIG. 7 is a block diagram for explaining signal processing of the exposure unit 30 shown in FIG. In FIG. 7, the oscillator 10 is controlled by a pixel clock (pixel CL).
K) Generate an original clock signal for generating a signal.
The index synchronization circuit 11 is a circuit for synchronizing a pixel clock signal generated from an original clock signal by a frequency divider (not shown) or the like with an index signal detected by the index sensor 24. Reference signal generator 1
Reference numeral 4 generates a sub-scanning area signal, a main scanning area signal, and a reading clock signal for reading image data from the image memory 15 based on the pixel clock signal output from the index synchronization circuit 11. In addition, the laser drive circuit 17 controls the laser diode 22 based on the pixel clock signal output from the index synchronization circuit 11 so as to emit light modulated in accordance with the image data read from the image memory 15. Generate a drive signal to control. FIG. 8 is a timing chart illustrating the operation of the image forming apparatus shown in FIGS. 6A and 7. In FIG. 8, the number of pixel dots corresponding to the index area from the time when the rising edge of the index signal is detected by the index sensor 24 to the start of image formation is S dots, and the number of pixel dots corresponding to the image formation area during the image formation period is S dots. Each is indicated by an L dot.

As shown in FIG. 8, a pixel clock signal is
In the index synchronizing circuit 11, synchronization is performed without a phase difference so that both rising edges are aligned with the index signal. Since one cycle of the pixel clock signal corresponds to one dot of the pixel, the image data read from the image memory 15 is transferred to the photosensitive member 2 in synchronization with the start point of the image forming area.
0 will be written as a latent image. in this way,
In a monochrome image forming apparatus, synchronization adjustment (main scanning shift) with an index signal in the main scanning direction is performed in units of one cycle of a pixel clock signal, that is, in units of one dot of a pixel, and the synchronous phase difference between the two is kept constant. It just needs to be done.

[0006]

On the other hand, in a color image forming apparatus having a plurality of (here, two) exposure units as shown in FIG. 6B, even if the same laser diode drive signal is used, For various reasons, the image forming positions on the photoconductor 20 by the respective exposure units 31 and 32 are different. That is, in the exposure unit 31, the length of the index area from the start point of the index signal to the image formation start point is S1 (mm), and the length of the image formation area is L1 (mm).
Assuming that the length of the index area in the exposure unit 32 is S ₂ (mm) and the length of the image forming area is L ₂ (mm), S 1 ≠ S 2 and L 1 ≠ L 2.
This is because each exposure unit has a different magnification in the main scanning direction (in other words, a different scanning speed). In order to correct the positional shift or color shift of the plurality of exposure units, it is necessary to make the pixel clock signal variable and delicately adjust it. For example, if L1 / L2 = 1.01, the frequency f2 of the pixel clock signal related to the exposure unit 32 is set to f2 = f1 / 1.01 in relation to the frequency f1 of the pixel clock signal related to the exposure unit 31. Frequency modulation control must be performed so as to satisfy the condition.

In a color image forming apparatus having a plurality of exposure units as shown in FIG. 6B, the distance (the length of the index area) up to the start of exposure differs for each of the exposure units 31 and 32. Therefore, it is necessary to finely control the number of dots of the pixel clock signal corresponding to the index area as being variable. That is, in a color image forming apparatus having a plurality of exposure units, it is necessary to variably control the phase relationship between the index signal and the pixel clock signal.

FIG. 5 is a diagram for explaining the above-described phase control, and is for explaining the operation of an image forming apparatus having a plurality of exposure units 31 and 32 as shown in FIG. 4 shows a timing chart. FIG.
In the case where the number of dots in the index area for a certain exposure unit is S + X / Y dots (X and Y are positive integers satisfying X <Y), the pixel clock signal of the exposure unit is calculated from the index signal and one dot. The phase is controlled so as to have a phase difference of small X / Y pixels. By performing such phase control for each of the exposure units 31 and 32, a latent image can be formed on the photoconductor 20 based on print data without causing an exposure position shift from the beginning of the image forming area.

As described above, in an image forming apparatus having a plurality of exposure units, in order to correct the exposure position shift of each exposure unit, the frequency modulation of the pixel clock signal and the position of the index signal and the pixel clock signal are performed. At the minimum, binary adjustment of phase difference control is required.

However, at present, no image forming apparatus having a plurality of exposure units realizes the above-described dual adjustment of the frequency modulation and the phase difference control by a single circuit. It was not satisfactory in terms of accuracy and cost.

SUMMARY OF THE INVENTION It is an object of the present invention to correct exposure position deviation by an image forming apparatus by enabling frequency modulation and phase difference control of an image forming apparatus having a plurality of exposure units to be performed by a single circuit. And to reduce the cost.

[0012]

In order to achieve the above object, an image forming apparatus according to the present invention comprises: an image storage unit for storing image data; and an image storage unit for storing image data read from the image storage unit. A plurality of exposure means for sequentially outputting light for scanning on the photoreceptor, a main scanning reference signal detecting means for detecting a main scanning reference signal included in an output from each of the plurality of exposure means, and the plurality of Frequency correction of a pixel clock signal used to drive the exposure unit and read image data from the image storage unit, and detect the main scanning reference signal detection unit to correct the exposure position shift by the exposure unit. Frequency / phase multiple adjusting means for controlling both the phase difference between the main scanning reference signal and the pixel clock signal.

Further, the frequency / phase multiple adjusting means includes:
A DDS circuit having an accumulator, a waveform data memory, and a D / A converter can be provided.

Further, according to the image forming method of the present invention, the light for scanning the photosensitive member based on the image data read from the image storage means using the pixel clock signal is sequentially output from the plurality of exposure means. In the image forming method for detecting a main scanning reference signal included in each of the outputs from the plurality of exposure units, the frequency modulation of the pixel clock signal and the main scanning reference signal are performed based on the frequency setting data and the synchronization phase setting data. An exposure position shift caused by the plurality of exposure units is corrected by using a frequency / phase multiple adjustment unit capable of performing both phase difference control with a pixel clock signal.

According to the image forming apparatus and the image forming method described above, since the frequency and phase multiple adjusting means for performing both the frequency control and the phase difference control with a single circuit are provided, the exposure position shift is performed. The correction can be performed with high accuracy, and the cost of the image forming apparatus can be reduced.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram for explaining signal processing of one exposure unit in an image forming apparatus having a plurality of exposure units according to the present embodiment. The schematic configuration of the exposure unit is the same as that shown in FIG. In FIG. 1, the same members as those in FIG. 7 are denoted by the same reference numerals, and the detailed description thereof will be omitted. The image forming apparatus according to the present embodiment is a color image forming apparatus such as a color laser copying machine. Each may have one exposure unit. However, in the following, in order to simplify the description, in principle, one exposure unit will be described as an example.

In addition, from the viewpoint of improving the accuracy of exposure position deviation correction, it is preferable that the oscillator 10 is not provided separately for each of the plurality of exposure units but is provided commonly for all the exposure units. However, a high-precision oscillator may be separately provided for each of the plurality of exposure units.

FIG. 1 is different from FIG. 7 in that a DDS (direct digital synthesizer) as frequency / phase multiple adjustment means is used.
r) The circuit 1 is arranged in place of the index synchronization circuit 11, and the DDS circuit 1 is connected to the CPU 2. One DDS circuit 1 is provided for each exposure unit including the laser drive circuit 17. The CPU 2 supplies the DDS circuit 1 with frequency setting data ΔF for modulating and controlling the frequency of the pixel clock signal and synchronous phase setting data N for adjusting the phase difference between the pixel clock signal and the index signal.

FIG. 4 is a block diagram showing the configuration of the DDS circuit 1. As shown in FIG. 4, the DDS circuit 1 has an accumulator 4, a waveform data memory 5, and a D / A converter 6. FIG. 2 is a timing chart for explaining a specific operation of the DDS circuit 1. FIG. 2 shows, from above, an index signal, a clock signal supplied from the oscillator 10 to the DDS circuit 1 via a frequency divider (not shown),
The output of the accumulator 4 and the output of the waveform data memory 5 are shown.

The accumulator 4 has an index sensor 24
, The frequency setting data ΔF and the synchronization phase setting data N
Is entered. The accumulator 4 is preset by detecting a rising edge of the index signal, and a signal (N, N + ΔF) in which the frequency setting data ΔF is sequentially added to the synchronous phase setting data N for each cycle of the clock signal from the oscillator 10. , N + ΔF × 2, N + ΔF ×
3, N + ΔF × 4,...).

The waveform data memory 5 receives the phase information output from the accumulator 4 as an address designation value, and outputs waveform data. The output of the waveform data memory 5 has a value represented by the following equation (1).

INT [2 ^K × [sin (2π × (cumulative adder output) / 2 ^M ) /2+0.5]] (1) (M: address length of waveform data memory 5, unit is bit , K: The peak value data length of the waveform data memory 5 is expressed in units of bits. However, this equation (1) indicates that the sine wave data (the time axis address length is M bits and the peak value data length is K bits) is stored in the waveform data memory 5. ) Are stored.

In FIG. 3, which is a graph with the rising edge of the index signal as the horizontal axis reference point, the actual waveform data output from the waveform data memory 5 is represented by a solid line 41.
It is a staircase wave of M steps as represented by. The output of the waveform data memory 5 is converted to a D / A
After the A conversion, a sine curve represented by a dotted line 42 as an envelope of a staircase wave as a solid line 41 is obtained as a pixel clock signal. Further, by binarizing the sine wave represented by the dotted line 42 by binarizing means (not shown), an actual pulse of the pixel clock signal as represented by the solid line 43 is obtained.

The frequency f of the pixel clock signal represented by the solid line 43 is the frequency f of the clock signal from the oscillator 10.
_If it is set to ₀ , it is modulated to a value represented by the following equation (2).

F = f ₀ × ΔF / 2 ^M (2) Accordingly, the frequency of the pixel clock signal is controlled by controlling the frequency setting data ΔF according to the equation (2) to obtain a frequency resolution f ₀ / Variable control is possible at ^2M .

From the equation (1), it can be seen that the synchronous phase difference adjustment between the pixel clock signal and the index signal represented by the solid line 43 is executed by controlling the synchronous phase setting data N. Then, since one cycle of the pixel clock signal corresponds to one dot, the control can be performed with a phase difference finer than one pixel.

As described above, in the image forming apparatus of the present embodiment, the pixel clock signal whose frequency and phase difference have been binary-adjusted is supplied to the laser drive circuit 17, so that in the related art, the writing timing control of each exposure unit is conventionally performed. Can be performed only in units of one dot, the main scanning shift can be performed with a phase difference finer than one dot of a pixel, and highly accurate exposure alignment can be performed.

Further, since the DDS circuit 1 is used,
Since the constituent circuits can be integrated into an IC, it is possible to achieve high precision and cost reduction of the image forming apparatus including the exposure unit.

[0029]

According to the image forming apparatus and the image forming method of the present invention, the exposure position deviation can be corrected with high accuracy, and the cost of the image forming apparatus can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram for explaining signal processing of one exposure unit in an image forming apparatus having a plurality of exposure units according to a preferred embodiment of the present invention.

FIG. 2 is a diagram showing a timing chart for explaining a specific operation of the DDS circuit of FIG. 1;

FIG. 3 is a graph for explaining how a pixel clock signal subjected to frequency modulation and phase difference control is obtained by the DDS circuit of FIG. 1;

FIG. 4 is a block diagram illustrating a configuration of the DDS circuit of FIG. 1;

FIG. 5 is a diagram illustrating a timing chart for explaining an operation of the image forming apparatus having a plurality of exposure units.

FIG. 6A is a schematic configuration diagram of a single exposure unit included in a monochrome image forming apparatus, and FIG. 6B is a schematic configuration diagram of two exposure units included in a color image forming apparatus. It is.

FIG. 7 is a block diagram for explaining signal processing of the exposure unit 30 shown in FIG.

FIG. 8 is a timing chart illustrating the operation of the image forming apparatus illustrated in FIGS. 6A and 7;

[Explanation of symbols]

 Reference Signs List 1 DDS circuit 2 CPU 10 Oscillator 11 Index synchronization circuit 14 Reference signal generation unit 15 Image memory 17 Laser drive circuit 24 Index sensor

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C262 AA05 AA17 AB15 FA02 FA03 GA21 GA22 GA23 GA26 GA36 GA40 GA47 2C362 BA52 BA53 BA68 BA70 BB31 BB32 BB37 BB38 CA22 CA39 DA09 2H027 DA50 EB04 EB06 EE01 EE02 HB07 ZA07 2030 BB23 5C074 AA10 BB03 DD15 DD16 EE02 EE04 EE06 FF15 GG02 GG09

Claims (3)

[Claims] An image storage unit for storing image data; a plurality of exposure units for sequentially outputting light for scanning on a photosensitive member based on the image data read from the image storage unit; Main scanning reference signal detecting means for detecting a main scanning reference signal included in the output from each of the exposing means, and driving the exposing means to correct an exposure position shift caused by the plurality of exposing means, and A frequency for performing both frequency modulation of a pixel clock signal used for reading image data from image storage means and control of a phase difference between the main scanning reference signal and the pixel clock signal detected by the main scanning reference signal detecting means. An image forming apparatus including a multi-phase adjusting unit; 2. The frequency / phase multi-adjustment means includes a cumulative adder, a waveform data memory, and a D / A converter.
The image forming apparatus according to claim 1, wherein the image forming apparatus is a DS circuit. 3. A plurality of exposure units sequentially output light for scanning on a photosensitive member based on image data read from an image storage unit using a pixel clock signal.
An image forming method for detecting a main scanning reference signal included in each of the outputs from the plurality of exposure units, wherein the frequency modulation of the pixel clock signal and the main scanning reference signal are performed based on the frequency setting data and the synchronization phase setting data. An image forming method, comprising: correcting an exposure position shift caused by the plurality of exposure units by using a frequency / phase multiple adjustment unit capable of performing both phase difference control with a pixel clock signal.