JP4504710B2 - Digital copier - Google Patents

Description

  The present invention relates to a digital copying machine that performs optical writing with a semiconductor laser on a photosensitive member, and adjusts the amount of light by varying the amount of light of the semiconductor laser within a main scanning line of the photosensitive member.

2. Description of the Related Art Conventionally, in a digital copying machine that performs optical writing on a photoconductor with a semiconductor laser (LD), develops a latent image by this optical writing, and transfers the image onto a transfer paper, it causes image density unevenness. There is a technique that stores data such as sensitivity unevenness, that is, shading data, and reflects the result in the PWM modulation width of multi-value data for optical writing control, thereby making the power on the photosensitive member constant. Proposed. In addition, a method has been proposed in which shading correction is performed by using a PWM modulation circuit and a smoothing circuit in optical writing control and changing the reference signal of the semiconductor laser emission power.
It should be noted that, among the above-mentioned prior art and the art described in paragraph [0003] below, none of the known literature related to the present invention is known by the applicant at the time of filing the application. There is no literature information.

By the way, in a digital copying machine using an optical writing device, the light intensity when writing a latent image on the photosensitive member varies with the main scanning position due to the characteristics of the writing optical system lens, and an error occurs. As a means to absorb this error, there is shading correction. However, since the transmittance of the optical lens decreases as the image height increases, the same intensity as the position of the image height ± 0 at any image height position. When it is desired to supply the amount of light to the photosensitive member, it is necessary to increase the amount of light of the LD in accordance with the image height.
This control is performed by shading correction. The light quantity of the LD is determined by an analog light intensity signal supplied to the LD control unit, and the shading correction operation is realized by adjusting the level of this analog signal according to the main scanning position.
As a method of determining the position in the main scanning direction and the LD light quantity, a position reference in the main scanning direction is set by a synchronization signal, the line cycle is divided into a plurality of areas from this position reference, and an analog signal is controlled for each area. Adopted. As an analog signal output means, a DAC setting value is changed for each area using a D / A converter (DAC). In this case, the amount of light varies at the boundary between the areas, so that a step occurs in the amount of light, and this light amount difference may affect the image. In particular, in a full-color machine, this variation appears as a different color, causing a problem.
It is possible to reduce the influence on the image by reducing the level difference between the areas, but in that case, it is necessary to increase the number of divided areas and to provide a DAC setting value for each area. In addition, the hardware configuration is greatly affected. In recent years, shading correction using a DAC has a large cost burden, and shading correction by PWM control using an I / O port has been proposed to reduce the cost.
The present invention provides a digital copying machine that can correct a PWM setting value in the vicinity of each square in each area even within each area, thereby minimizing a step between adjacent areas. With the goal.

In order to achieve the above object, the invention as set forth in claim 1 is directed to a detection signal of a light beam obtained by a light detector in a digital copying machine which adjusts the light amount by changing the light amount of a semiconductor laser in a main scanning line. The function of recognizing the main scanning position with reference to the above, the function of selecting a plurality of main scanning positions, and the intensity adjustment of the light beam at each selected main scanning position are performed by analog output level signals Function, function to realize analog output level signal by PWM operation, function to arbitrarily set multiple points of main scanning position and light intensity of each point, light at main scanning position between set points in PWM operation The intensity increases stepwise based on the difference between the light amount values set at adjacent front and rear points, the distance between adjacent points, and the main scanning position. Comprising a write control ASIC having the function of varying the PWM output width to small, said plurality of points and the light intensity of each point can be set by the measurement data obtained after the digital copying machine manufacturing The featured digital copier is the main feature.

  According to the present invention, in the PWM operation corresponding to the main scanning position in the main scanning line, the PWM output width corresponding to the main scanning position is finely set to control the light intensity setting value. Even if the conventional area is set, the step difference between the adjacent areas can be reduced as much as possible, and the light intensity can be changed gently.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic block diagram of a digital copying machine according to an embodiment of the present invention. In this digital copying machine, a scanner unit 1 that reads an original image has a VPU 2 that performs A / D conversion on the read signal to perform black offset correction, shading correction, and pixel position correction, and an IPU 3 that performs image processing. The printer unit 4 includes a writing control ASIC 5 that performs internal control, an LD control unit 6 that controls a semiconductor laser, and a semiconductor laser (LD) 7 that forms electrostatic latent image data on a photoconductor.
The digital copying machine also includes a CPU 8 that controls the entire apparatus, a ROM 9 that stores a control program, a RAM 10 that is temporarily used by the control program, an image memory 11 that stores a read image, and a user that gives instructions. An operation unit 12, an internal system bus 13 for exchanging data between the devices, and an interface 14 between the system bus 13 and the IPU 3 are provided.

FIG. 2 is a configuration diagram of the printer unit 4. In addition to the writing control ASIC 5, the LD controller 6, and the semiconductor laser 7, a deflector 21 composed of a rotating polygon mirror, an fθ lens 22, a photoconductor 23, and a photodetector 24 are provided.
The laser beam emitted forward from the semiconductor laser 7 is collimated by a collimator lens (not shown), deflected by a deflector 21, and imaged on a surface uniformly charged by a charger of a photosensitive member 23 by an fθ lens 22. Then, the image formation spot repeatedly moves in the axial direction (main scanning direction) of the photosensitive member 23 by the rotation of the deflector 21, and at the same time, the photosensitive member 23 rotates.
The photodetector 24 is provided outside the information writing area of the photoconductor 23, detects the laser beam deflected by the deflector 21, and generates a synchronization detection signal. The write control ASIC 5 applies an information signal from the scanner unit 1 (see FIG. 1) to the LD drive unit 28 in the LD control unit 6, and controls the timing by a synchronization signal from the photodetector 24. The LD driving unit 28 drives the semiconductor laser 7 by an information signal from the writing control ASIC 5 to form an electrostatic latent image on the photoconductor 23. This electrostatic latent image is developed by a developing device (not shown) and transferred to a transfer paper or the like by a transfer device (not shown).
A laser beam emitted backward from the light emitting unit 25 in the semiconductor laser 7 is incident on the light receiving unit 26, and a light reception signal is supplied to the APC control unit 27 in the LD control unit 6. The APC control unit 27 controls the LD drive unit 28 according to the output signal of the light receiving unit 26 and the light amount adjustment signal from the writing control ASIC 5 to control the output light amount of the semiconductor laser 7 to be constant (APC control). Specifically, the drive power supply of the light emitting unit 25 of the semiconductor laser is adjusted and held so that the output light amount is constant (line cycle interval).
The shading operation is to change the light amount according to the main scanning position by changing the voltage level of the light amount adjustment signal in the drive power supply information in the LD drive unit 28.
FIG. 3 is a block diagram of the write control ASIC. Memory block 31 that performs speed conversion and format conversion on image data from IPU 3, image processing unit 32 that performs image processing on image data from memory block 31, γ conversion on image data from image processing unit 32, P The output data control unit 33 performs processing such as sensor pattern application.

FIG. 4 is a block diagram of the output data control unit. A P pattern block 41 for giving a P sensor pattern, which is a toner of a certain density to be placed on the photoconductor 23 to acquire data for determining process conditions, is input to the data input from the image processing unit 32, and the data weight is set. A γ conversion block 42 to be changed, an APC block 43 that gives an image in synchronization with an APC operation timing for keeping the light quantity of the semiconductor laser 7 constant, an LD on / off block 44 that gives emission data for synchronization detection, A pixel count block 45 that measures the number of light-emitting dots of the semiconductor laser 7 and a gate signal generator 46 that has a main scanning counter that manages the main scanning position based on the synchronization signal and generates a gate signal in the main scanning direction according to the main scanning counter. PWM that receives area information from the gate signal generator 46 and adjusts the amount of light corresponding to each area Consisting PWM signal generating unit 47 to create an issue.
FIG. 5 is a diagram showing an example of a circuit for smoothing the PWM signal, and FIG. 6 is an output waveform diagram when PWM generation corresponding to the light intensity is performed for each area. In FIG. 5, a low-pass filter is provided for smoothing in (1), and in (2), a smoothing circuit is constituted by a resistor, a capacitor, and an amplifier.
Based on the area information by the gate signal generation unit 46 in FIG. 4, the PWM signal generation unit 47 continues to output the PWM output at the duty specified in each area according to the PWM signal so as to correspond to the light intensity. FIG. 6 shows the duty of 50% output and 75% output. For example, when it is desired to obtain a 2.475V light amount adjustment signal output in a certain area, if the output port H output is 3.3V, the PWM output is output with a duty of “2.475 ÷ 3.3 = 75%”. By doing so, the subsequent smoothing circuit is used, and as a result, 2.475 V is obtained.

FIG. 7 is a diagram showing a general light amount adjustment signal (DAC method). In FIG. 7, the main scanning lines are divided into 11 areas. The area position is recognized by a main scanning counter that is reset by a synchronization signal. When the counter operation is performed and the area position is reached, the light amount is changed by switching the set value of the D / A converter at any time and switching the DAC output. Area 0 is an area for determining a reference light amount, and the APC operation is performed in this area. A part of area 0 and areas 1 to 11 are effective image area ranges.
According to this method, switching of the DAC occurs at the boundary between the areas, so that a step of the DAC output is generated as a step of a light amount corresponding to 08 h, and a step is generated in the output image after image formation. Yes.
FIG. 8 is a diagram showing a general PWM control method. By changing the PWM width for each area, the PWM output is smoothed by a smoothing circuit and used as a light amount adjustment signal. In this example, the PWM width decreases in accordance with area 0 → area 6, and the PWM width increases in accordance with area 6 → area 11, thereby obtaining the same characteristics as in FIG. Since the PWM width in each area is always fixed and used, even in this case, a step occurs at the boundary between the areas as in FIG.
FIG. 9 is a timing chart of the control operation according to the present invention, and FIGS. 10 (1) and 10 (2) are flowcharts of the control operation according to the present invention. In this embodiment, each area is not divided and fixed PWM output is performed within the area, but an arbitrary point on the line cycle is selected, and the PWM width corresponding to the light quantity required at that position. The set value is set, and the write control ASIC 5 calculates the difference between the adjacent points, and while changing the PWM width in a direction to reduce the difference as needed when moving to the position of the next point, It will be moved. In FIG. 10 (1), a certain point is obtained (step S1), the difference X and the distance Y from this point to the next point are obtained (step S2), and then the amount of change in PWM duty is calculated for each clock. And store. (Step S3). In FIG. 10B, the clock is detected (step S11), and the PWM duty is added for each clock (step S12).
According to this method, it is possible to change at any time with a period of PWM width 100% (1 clock width) (several clocks are required when DAC is used), and the number of positions (points) in the main scanning direction to be set. Even when the PWM setting data has a large step, the step does not occur in the shading operation. In other words, since it is compensated by slight changes in the PWM waveform, there is no significant change at the area boundary, that is, no occurrence of a step.

The operation will be described below. The setting values of the PWM widths at points A and B are 80h (128/256) and 70h (112/256), respectively. Since the distance between point A and point B is 4 clock widths, the difference 112−128 = −16 between point A and point B is divided by 4. (−16 ÷ 4 = minus 4). That is, by reducing the PWM width by 4/256 each time one clock advances, the output level at point B is 70h (112/256). In the case of point E → point F, the difference is 96 (60h) -80 (50h) = 16.2. Since the level is changed using 8 clocks, the level can be increased by 2/256 minutes per clock when 16 ÷ 8 = 2. That's fine.
In this embodiment, each point position and the PWM value at that time are set in a special mode called SP mode, and the set data is set from the measurement data of each writing unit. .
According to the present invention, it is possible to divide the level difference by performing the above-described operation, thereby eliminating the influence of the level difference of the LD light quantity that affects the image. Further, in the process of shifting the semiconductor laser to a desired light amount, when the synchronization signal is detected twice, it is determined that the transition operation of the light source light amount is completed. The start-up operation can be performed without completing the transition operation. In addition, since the shading correction means is provided, the light amount can be adjusted in accordance with the lens characteristics, and the light amount on the surface of the photoreceptor can be accurately corrected based on the writing characteristics.
In another embodiment, how many clocks the difference between the adjacent area and the corresponding area is used is determined in advance in the SP mode. Thereafter, when the main scanning position enters the overview area, the difference between the areas can be calculated, and the PWM duty can be changed in a direction to reduce the difference as needed from the top of the area.

1 is a schematic block diagram of a digital copying machine according to an embodiment of the present invention. The block diagram of a printer part. The block diagram of write-control ASIC. The block diagram of an output data control part. The figure which shows the circuit example which smoothes a PWM signal. The output waveform figure at the time of performing PWM production | generation corresponding to light intensity for every area. The figure which shows the general light quantity adjustment signal (DAC system). The figure which shows the general PWM control method. The timing diagram of the control operation by this invention. The flowchart of the control action by this invention.

Explanation of symbols

1 Scanner unit 4 Printer unit 5 Write control ASIC
6 LD controller 7 Semiconductor laser (LD)

Claims (1)

A function for recognizing a main scanning position based on a detection signal of a light beam obtained by a photodetector in a digital copying machine that adjusts the amount of light of a semiconductor laser within a main scanning line, and a plurality of main scanning positions selecting a function, in performing control of the intensity of the light beam of each main scanning position where the selected function for the intensity adjustment of the light beam by the analog output level signal, the ability to realize the analog output level signal by P WM operation, the main A function for arbitrarily setting a plurality of points at the scanning position and the light intensity at each point. During the PWM operation, the light intensity at the main scanning position between the set points is the difference between the light intensity values set at adjacent front and rear points. , based on the distance and the main scanning position between adjacent points, having a function of varying the PWM output width to increase or decrease stepwise Comprising a write control ASIC,
The digital copying machine, wherein the plurality of points and the light intensity of each point can be set by measurement data obtained after manufacturing the digital copying machine.

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