JPH0266584A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent image deterioration to be caused by a difference between relative speeds by detecting scanning speed of a beam and rotating speed of a photosensitive drum, and correcting irradiation intensity of the beams based on speed information. CONSTITUTION:For instance assuming the linear velocity of the photosensitive body 2900 by a motor 2285 as VM, and the scanning speed of scanner laser light by a scanner motor 2300 as V1, laser light intensity is corrected to become larger when a subtracted result V1/VM is <=1. In contrast, laser light intensity is corrected to become smaller when the V1/VM is >=1. This process is controlled by latching the result subtracted by a substracter 2310 in a latching part 2312. In such a way, laser light intensity per unit time is corrected by the difference between the rotating speed of the photosensitive drum and the scanning speed of the laser light. Therefore, image deterioration such as density (or color) unevenness can be prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus that irradiates a photoreceptor such as a photoreceptor drum with a beam based on an image signal to form an image. be.

[Prior Art] Conventional devices of this kind, especially laser beam printers, have two motors: a motor that rotates a photosensitive drum, and a motor that rotates a polygon mirror that sweeps laser light onto the photosensitive drum (to distinguish, it is called a scanner). motor)
are each independently PLL (Phase 1ocked
1oop) circuit.

[Problems to be solved by the invention] However, in laser beam printers,
There may be a difference in the relative speed of rotation between the scanner motor that sweeps (scans) the laser beam and the motor that drives the photosensitive drum, resulting in uneven dot formation due to laser beam irradiation, resulting in uneven density (hereinafter referred to as Pitch unevenness) often occurs. This pitch unevenness appears conspicuously in halftone image reproduction, but it appears even more degraded in color images in which images are reproduced using three or four colors. In particular, it has been difficult to reproduce faithful images in achromatic areas such as gray.

The present invention has been made in view of such problems, and it is an object of the present invention to provide an image forming apparatus that can prevent image deterioration caused by the relative speed difference between the rotational speed of the photosensitive drum and the scanning speed of the beam. It is.

[Means for Solving the Problem] In order to solve this problem, the present invention includes the configuration shown below.

That is, in an image forming apparatus that irradiates a beam onto a photoreceptor to form an image based on an image signal, there is provided a first speed detection means for detecting the scanning speed of the beam irradiated onto the photoreceptor, and a forward bending photoreceptor. a second speed detection means for detecting the speed of the body; and a correction means for correcting the irradiation intensity of the beam based on the respective speed information detected by the second speed detection means.

[Operation] In the configuration of the present invention, the scanning speed of the beam and the rotational speed of the photosensitive drum are detected, and the irradiation intensity of the beam is corrected based on the detected speed information.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<Explanation of the configuration (Figures 1 and 2)> Figure 1 is a block diagram of the electric circuit system of the color copying machine of this embodiment (Figure 1 (a) is the reader section, Figure 1 (b) is the block diagram of the electric circuit system of the color copying machine of this embodiment). FIG. 2 shows a cross-sectional view of the structure of the color copying machine.

Hereinafter, each component unit and its contents will be explained in order.

In the figure, 1 is a synchronization signal processing section, and a printer section 200
Based on the signal from the 0 BD (beam detector) detector 2220, various timing signals are generated in synchronization with the horizontal synchronization signal 22 output from the gradation control circuit 2160. 2 is a Miwaka type CCD sensor block, which receives the reader horizontal synchronization signal (RH3YNC) generated by the synchronization signal processing section 1.
) and the drive signal 4, the original is read and the image signal is converted into an electrical signal and output. 3 is a signal processing section that performs waveform shaping processing to prevent high frequency components of the electrical signal 5 from attenuating. Reference numeral 6 denotes an image processing block, which is composed of an analog processing section 7, a connection memory 8, and an IPU 9.

The image signal from the signal processing section 3 is first input manually to the analog processing section 7. In the analog processing unit 7, the signal from the contact type CCD sensor block 2 is converted into cyan (C), cyan (C),
Since the configuration is such that green (G) and yellow (Y) signals are sequentially output, the signals are first divided into C, G, and Y colors. Next, each developer in the printer section 200 is yellow (Y), macenter (M).
) and cyan (C), the image signal is converted to red (R), green (G), and W (B) (No. 8).

This is CG=B.

This is performed by arithmetic processing according to the formula Y-G=H. In addition, since the output voltage of these signals separated into R, G, and B changes linearly with respect to 4 degrees, the A/D converter provided in the analog processing section 7 converts the 8-bit concentration into converted into a signal. The above processing is performed by the analog processing section 7.
is executed.

The image signals for each color digitized by the analog processing section 7 are divided into five channels, but since the video signals of each channel are not synchronized, they are divided into one image data by the connection memory 8. be synthesized. The image data synthesized by the connection memory 8 and converted into YMC signals is sent to an image processing unit (IPU) in synchronization for each color.
) sent to 9. In the IPU 9, a desired color signal is interpreted by the control unit 1o of the reader unit 100 through a shading process to correct the light distribution, and is sent from the IPU to the printer unit 200 through the 8-bit image data 11 that has been subjected to a predetermined color conversion process. will be sent to.

On the other hand, apart from the image signal 11, the control unit 1o drives a motor driver 13 for manipulating the original to control the rotation of the motor 12, and also controls the CVR to turn on the exposure lamp 14.
15 and an operation unit 1 for performing copy keys and other operations
It also controls the 6th class.

Although not shown, the operation section 16 has a switching mode switch for sharpening text and gradation for photographs.The control section 10 takes in the state of this switch and sends it to the printer section 2000. Send.

On the other hand, the control unit 2500 on the printer unit 2000 side controls a selector of a binarization circuit, which will be described later, using a signal from the CPU 2110.

Now, the image data 11 output from the reader section 100 is manually input to the gradation control circuit 2160 of the printer section 2000. Since the speeds of the image clock of the reader section 100 and the image clock of the printer section 2000 are different, this gradation control circuit 2160 has a function of synchronizing them and a function of making the image data correspond to the color reproduction density of the printer section 2000. have. Then, the output data from the gradation control circuit 2160 is inputted to the laser driver 2200 to drive the laser 2300 to form an image.

A control unit 2500 of the printer unit 2000 that communicates with the reader unit 100 via the communication control line 24 controls each control element of the printer unit 2000. The potential sensor 2700 is a potential measuring unit that converts the output from the potential sensor 2600 into a digital signal and manually inputs it to the control section 2500. The potential data input to the control unit 2500 is converted into digital data by the A/D conversion unit 2503 in the control unit 2500, and then input to the CPU 2110 and used to control the laser driver 2200 and the like. In addition, an I
A signal from the TOP 2800 is also taken into the control unit 2500 and used as the timing for image formation.

Further, a humidity sensor 2298 and a temperature sensor 2299 for correcting development characteristics are manually operated through the A/D converter 2503 of the controller 2500.

Now, referring to FIG. 2, an overview of the processing from image reading to image formation in the embodiment will be explained.

As shown, the copying system 80 is composed of a reader section 100 and a printer section 2000.

In the figure, reference numeral 83 denotes a document scanning unit, which moves and scans in the direction of arrow A to read the image of the document 84 on the document table. At this time, the exposure lamp 85 in the document scanning unit 83 is of course turned on. . The reflected light from the original is guided to a converging rod lens array 86, and is then directed to a contact type color CCD.
The light is focused on the sensor 87. Contact type color CCD sensor 8
7 is 1 pixel with 62.5 μm (1/16 mm)
Chips each having 0.24 pixels are arranged in 5 chips in a staggered pattern, and each pixel is divided into three parts of 15.5 μm x 62.5 μm, and C, G, and Y color filters are pasted on each pixel.

The optical image focused on this contact type color CCD sensor 87 is converted into an electrical signal for each color. These electrical signals are subjected to predetermined processing, which will be described later, by a processing block 88. The color separated image electrical signals formed by image processing block 88 are sent to printer 2000 for printing.

Now, the color image data from the reader unit 100 is PW
M (pulse width modulation) processing and the like are performed to finally drive the semiconductor laser 2223. The laser beam modulated in accordance with the image data is transmitted to a polygon mirror 22 that rotates at high speed.
89 and is reflected by a mirror 2290 to expose dots corresponding to an image on the surface of the photosensitive drum 2900.

One horizontal scan of the laser beam corresponds to one horizontal scan of the image,
In this example, f/! It is 6 mm wide.

On the other hand, since the photosensitive drum 2900 rotates at a constant speed in the direction of the arrow, a planar image is sequentially exposed by the aforementioned laser beam scanning in the main scanning direction and constant speed rotation of the photosensitive drum 2900 in the sub-scanning direction. become. Note that, prior to exposure, the photosensitive drum 2900 is uniformly charged with ii by a charger 2297.
A latent image is formed by exposing the F-electron to laser light. Then, one of the developers 2292 to 2295 is selected according to the corresponding color signal, and the image is visualized.

For example, considering the first original exposure scan in a color reader, a dot image of the yellow component of the original is first exposed onto the photosensitive drum 2900 and developed by the yellow developer 2292 .

Then, the yellow component toner visualized on the photosensitive drum 2900 is transferred and formed onto a sheet of paper wound on a transfer drum 2296 by a transfer charger 2298.

Thereafter, M (magenta), C (cyan), and BK (black) are repeatedly applied in the order of M (magenta), C (cyan), and BK (black) to the paper wound on the transfer drum 2296 to form a color image using four-color toners.

Description of pitch unevenness correction (FIGS. 3 to 5)> The principle of pitch unevenness correction processing according to the embodiment in the above-described configuration and processing outline will be described below.

FIG. 3 is a diagram showing the main configuration of the printer section 2000 in the embodiment.

Although the explanation will be complicated, the pitch unevenness is due to the difference in rotational speed between the motor 2300 that sweeps the laser beam and the motor that rotates the photosensitive drum 2900.

Now, the video signal outputted from the reader 100 via the signal line 11 is manually input to the image processing circuit 2160.
A laser driver 2200 generates a signal to drive a laser 2223.

In the figure, 2200-1 is a buffer for receiving signals;
200-2 is a transistor that receives the signal from the buffer 2200-1, 2200-3 is a resistor that drives the transistor 2200-2, 2200-4 is a transistor that is bare with 2200-2, and a laser 2223 is connected to the collector side of this transistor. (Razako occurs from here) is connected. In addition, 2200-5 is a constant current transistor, 22
00-6 is a constant current controller. 2200-7 is a D/A converter for controlling the constant current controller, and outputs a voltage level signal based on data latched in a latch section 2312 in the motor driver 2305, which will be described later, to the constant current flow controller 2206. . In other words, the electric current flowing through the laser 2223 is controlled by the potential of this voltage level signal, so by changing this value, the intensity of the laser light emitted from the laser 2223 can be controlled.

2289 is a polygon mirror for scanning the laser beam; 2300 is a scanner motor for rotating the polygon mirror; 2301 is an encoder attached to the scanner motor shaft; and 2302 is a scanner motor driver for rotating the scanner motor 2300. The signal output from the encoder 2301 is fed back to the motor driver 2305 as an encoder output signal after waveform shaping.

On the other hand, 2304 is an encoder attached to the rotating shaft of a motor 2285 that rotates the photosensitive drum 2900, and its detection signal is fed back to the motor driver 2305.

Now, the encoder 2 depends on the rotational speed of the scanner motor output from the scanner motor driver 2302.
The signal from 301 is frequency-divided by frequency divider 2308 so that it can be easily compared with the number of pulses of encoder 2304 attached to drive motor 2285 of photosensitive drum 2900.

Then, the frequency-divided signals of encoder 2301 and encoder 2304 are taken into a PLL circuit, and motor 2285 is driven by driver 2306.

Further, each signal output from these encoders is taken into counters 2309 and 2311 which are reset by a signal from ITOP 2801. Then, the mutual count values are subtracted by a subtracter 2310,
The subtraction result is latched in latch section 2312. Then, based on the speed difference of each motor, the current flowing to the laser 2223, that is, the laser 2223
Controls the intensity of the laser light generated from the

For example, the linear velocity of the photosensitive drum 2900 by the motor 2285 is set to V2. When the scanning speed of the scanner laser beam by the scan motor 2300 is VL, α・VL/VM
(α is a correction coefficient)" is larger than "1", it means that the rotational speed of the photosensitive drum 2900 is slow, so it can be seen that the amount of laser light exposure per hour is large. On the other hand, when this value is smaller than "1", the exposure amount of the laser beam is small.

Then, if normalization is performed using α·VL/VM=1 and the intensity of the laser light per unit time at that time is normalized as 1", an upward-sloping relationship as shown in FIG. 4 is obtained.

Therefore, as shown in Figure 5, the subtraction result is 1°.

In the following steps, as shown in the figure, the laser light intensity is corrected to increase, and conversely, when it is less than 1'°, the laser light intensity is corrected to decrease. Subtractor 231
The latch unit 231 stores the result of subtraction by 0 (including its sign).
This is to control the latching to 2.

As described above, according to this embodiment, by correcting the laser intensity per unit time based on the difference between the rotational speed of the photosensitive drum and the scanning speed of the laser beam, uneven density (or color), etc. It becomes possible to prevent image deterioration.

In the embodiment, a color copying machine has been described, but it goes without saying that a monochrome copying machine may be used. In addition, although the modeling system has been explained as a laser beam printer, LED printers and liquid crystal printers can also be used.
The present invention is not limited to this, since it is sufficient to provide a brightness control circuit for control.

[Effects of the Invention] As explained above, according to the present invention, in a printing system that forms an image by irradiating a photosensitive drum with a beam, the problem occurs due to the relative speed difference between the scanning speed of the beam and the rotational speed of the photosensitive drum. It becomes possible to suppress density unevenness and form a good output image.

[Brief explanation of the drawing]

FIG. 1(a) is a block diagram of the reader section in this embodiment, FIG. 1(b) is a block diagram of the printer section in this embodiment, FIG. 2 is a sectional view of the copying apparatus in the embodiment, and FIG. 3 FIG. 4 is a graph showing the relationship between the scanning speed ratio of the photosensitive drum and the laser beam and the irradiation intensity of the laser beam in the example. The figure is a graph showing a correction curve. In the figure, 2223...Laser, 2260...Laser driver, 2285...Motor, 2300...Scanner motor, 2301 and 2304...Encoder, 2
302...Scanner motor driver, 2305...
Motor driver, 2306...Driver, 2307.
... PLL circuit, 2308... Frequency divider, 2309 and 2311... Counter, 2310... Subtractor, 23
12-=-y Tsuchi part, 280.1 ・I To P
. 2900...Photosensitive drum, 2296...Transfer drum. Figure 4 Figure 5

Claims (1)

[Scope of Claims] An image forming apparatus that forms an image by irradiating a beam onto a photoreceptor based on an image signal, comprising: a first speed detection means for detecting a scanning speed of the beam irradiated onto the photoreceptor; , a second speed detection means for detecting the moving speed of the photoreceptor, and a correction means for correcting the irradiation intensity of the beam from the respective speed information detected by the first and second speed detection means. An image forming device characterized by: