JPS62287270A - Digital color copying machine - Google Patents

Abstract

PURPOSE:To accurately superpose plural images on one sheet of recording paper and to obtain a color image of good quality by controlling automatically the timing of laser beam exposure among plural image forming devices according to the speed variations of a photosensitive drum and a transfer belt. CONSTITUTION:So that the front end of an image on a drum 18y and the front end of an image transferred from a drum 18bk to recording paper are aligned with each other, the front end of a picture on recording paper should be at a point A when the drum 18y begins to be exposed to a laser beam. The point A is on the transfer belt 25 in the direction from the drum 18bk to the drum 18y and at distance ln from the transfer position of the drum 18bk. Other drums are also in said relation. The set value of a timer 5 corresponds to the number of pulses generated by a transfer belt encoder 203 during the movement of the transfer belt 25 by ln, the set value of a timer 6 corresponds to pulses during the movement of the transfer belt 25 by lm+ln, and the set value of a timer 7 correspond to pulses during the movement of the transfer belt 25 by 2lm+l.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (Technical Field) The present invention separates original illumination light into colors, and scans recorded color information obtained by this separation as a laser beam onto a photoreceptor drum dedicated to each color. The image forming process is performed on each photoreceptor drum, a developed image of each color is formed, and the developed image on the photoreceptor drum is transferred to recording paper conveyed on a transfer belt for 11 seconds.
The present invention relates to a digital color copying machine that obtains color images through 19-order overlapping transfer, and particularly relates to a timing control device for writing images onto each photoreceptor.

(Prior Art) In digital color copying machines, 1. Image data is exposed and written onto the photoreceptor using a laser beam. This writing system is equipped with one system each for cyan, magenta, yellow, and black, and images formed on each photoreceptor are sequentially transferred to recording paper placed on a transfer belt.
In a digital color copying machine that obtains color images, the generation timing of an image writing start signal must be given to the cyan, magenta, yellow, and black writing systems. Conventionally, when obtaining this timing, one method has been used: either by counting the pulses generated in response to the movement of the recording paper transport belt, or by counting the pulses generated in response to the movement of the photoreceptor. Met.

In this type of copying machine, it is necessary to keep the amount of deviation in the start timing of laser beam exposure as small as possible, so the influence of rotational speed fluctuations of the photoconductor and belt movement fluctuations are minimized to reduce the timing start signal. However, in the conventional method described above, if pulses due to belt movement are counted, the rotational speed fluctuation of the photoconductor is counted, and if pulses due to photoconductor movement are counted, the belt The movement fluctuations caused large shifts in the position of the leading edge of the image.

It is also known that the drive is distributed between the transfer belt and the photoreceptor from the same motor shaft via gears, etc., but even in this case, the intervening gears etc. can separate the drive between the transfer belt and the photoreceptor. Since speed fluctuations are constant, even if the start of writing by the image forming means is controlled by counting the pulses generated by one of the movements, the drawback remains that the timing will be off.

As mentioned above, unless the timing of the generation of the write start signal is controlled according to the fluctuations in the rotational speed of the photoreceptor and transfer belt, the cyan, magenta, yellow, and black images will not be aligned correctly on the recording paper. Color image quality deteriorates.

(Objective) The present invention eliminates the drawbacks of the conventional example described above, and generates the signal generation timing for image writing by minimizing the influence of rotational speed fluctuations of the photoreceptor and transfer belt, thereby cyan, cyan,
The purpose is to correctly overlap magenta, yellow, and black images.

(Structure) For this purpose, the present invention is characterized in that the image forming means is controlled by combining the pulse counting results of both the movement of the transfer belt and the movement of the photoreceptor drum.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the components of the mechanical section of one type of digital color copying machine embodying the present invention, and FIG. 2 shows the components of the electrical section.

First, referring to FIG. 1, an original 1 is placed on a platen (contact glass) 2, and fluorescent lamps 3r and 3 for illuminating the original are placed on a platen (contact glass) 2.
*, and the reflected light is reflected by the movable first mirror 41 + second mirror 4□ and third mirror 4, passes through the imaging lens 5, enters the guichroic prism 6, and there are three wavelength of light, red (R), green (
G) and blue (B). The separated light enters C0D7r, 7g, and 7b, which are solid-state imaging devices, respectively. That is, red light enters the CCD 7r, green light enters the COD 7g, and blue light enters the CCD 7b.

Fluorescent lamps 31, 3□ and first mirror 4. is the first carriage 8
The second mirror 4□ and the third mirror 4. is mounted on the second carriage 9, and by moving the second carriage 9 at the speed of the first carriage 8, the optical path length from the document 1 to the CCD is kept constant, and when reading the document image, the first and second The two carriages are scanned from right to left. The first carriage 8 is connected to a carriage drive wire 12 that is wound around a carriage drive pulley 11 fixed to the shaft of a carriage drive motor 10, and the wire 12 is wound around a movable pulley (not shown) on a second carriage 9. As a result, the first
The carriage 8 and the second carriage move forward (reading and scanning the original image) and backward (return), and the second carriage 9 scans the first
The carriage moves at a speed of 2 of 8.

When the first carriage 8 is at the home position shown in FIG. 1, the first carriage 8 is moved out by a home position sensor 39 which is a reflective photosensor. This detection B is shown in FIG. When the first carriage 8 is driven to the right during exposure scanning and moves away from the home position, the sensor 39 does not receive light (carriage non-detection). When the first carriage 8 returns to the home position, the sensor 39 receives light ( (carriage detection), and the carriage 8 is stopped when the state changes from non-light reception to light reception.

Referring now to FIG. 2, CCDs 7r and 7g.

The output of 7b is analog/digital converted and subjected to the necessary processing in the image processing unit 100 to obtain recording color information of black (BK), yellow (Y), magenta (M), and cyan (C), respectively. It is converted into a binary signal for recording activation. Each of the binary signals is transmitted by laser drivers 112bk, 112y, 112m and 112
C, and each laser driver outputs a semiconductor laser 43b.
k.

By energizing 43y, 43m, and 43C, laser light modulated with a recording color signal (binarized signal) is emitted.

Referring again to FIG. The emitted laser beams are rotated by rotating polygon IJt13bk, 13y, 13m and 1, respectively.
It is reflected by 3C and f-θ lens 14bk.

14y, 14m and 14C, the fourth mirror 15b
k, 1sy, 15m and 15C and 5th mirror 16
bk, IGy, reflected by 16m and 16C, polygonal mirror surface tilt correction cylindrical lens 17bk, 17y, 1
7m and 17c, photoreceptor drums 18bk and i'
ay, 18m and 13c are polygonal mirror drive motors 41b
The motors are fixed to rotating shafts of the motors k, 41y, 41m, and 41c, and each motor rotates at a constant speed to rotate the polygon mirror at a constant speed. Due to the rotation of the polygon mirror, the aforementioned laser beam is directed in a direction perpendicular to the direction of rotation of the photoreceptor drum (clockwise).
That is, it is scanned in the direction along the drum axis.

FIG. 4 shows the laser scanning system of the cyan color recording device in detail. 43c is a semiconductor laser. At one end of the laser scan (two-point ti line) in the direction along the axis of the photoreceptor drum 18c, a sensor 44c made of a photoelectric conversion element is arranged to receive the laser beam, and this sensor 44c receives the laser beam. The starting point of one line scan is detected at the time when the detection changes from detection to non-detection. That is, the laser light detection signal (pulse) from the sensor 44c is processed as a line synchronization pulse for laser scanning. magenta recording device,
The configuration of the yellow recording device and the black recording device is also the fourth one.
The configuration is exactly the same as that of the cyan recording apparatus shown in the figure.

Further, referring to FIG. 1, the surface of the photoreceptor drum is uniformly charged by charge scorotrons 19bk, 19)', 19m and 19c connected to a negative high voltage generator (not shown). When a laser beam modulated by a recording signal is irradiated onto the uniformly charged surface of the photoreceptor, the electric charge on the surface of the photoreceptor flows to the equipment ground of the drum body and disappears due to a photoconductive phenomenon. Here, the laser is not turned on in areas where the original density is high, and the laser is turned on in areas where the original density is low. As a result, the photoreceptor drum 18bk
, 18y, 18m, and 113c, the parts corresponding to the parts with high original density have a potential of -800V, and the parts corresponding to parts with low original density have a potential of about -100V.
An electrostatic latent image is formed corresponding to the density of the original.・This electrostatic latent image is transferred to a black developing unit 20bk,
Yellow developing unit 20y, magenta developing unit 2
-0m and cyan phenomenon unit 2-Oc, and the photosensitive drums 18b k, 18')', 1
Black, yellow, magenta and cyan toner images are formed on the 8'm and 18C surfaces, respectively.

The toner in the developing unit is positively charged by stirring, and the developing unit is biased to about -4'OOV by a developing bias generator (not shown), so that the surface potential of the photoreceptor is at a location higher than the developing bias. The toner image adheres to the original and forms a toner image corresponding to the original.

On the other hand, the recording paper stored in the transfer paper cassette 22 is fed by the feed operation of the feed roller 23, and is sent to the transfer belt 25 by the registration roller 24 at a predetermined timing. The recording paper placed on the transfer belt 25 is transferred to the photosensitive drums 18bk, 18 by the movement of the transfer belt 25.
y, 18m and 18C sequentially, and each photosensitive drum 18bk, 18y', 18m and 1'
8C, black, yellow, magenta, and white toner images are sequentially transferred onto the recording paper by the action of the transfer corotron at the lower part of the transfer belt.The transferred recording paper is then The toner is sent to a thermal fixing unit 36, where the toner is fixed onto a recording paper, and the recording paper is discharged onto a tray 37.

On the other hand, residual toner on the photoreceptor surface after transfer is removed by cleaner units 21bk, 21y, 21m, and 21C.

A cleaner unit 21bk and a black developing unit 20bk that collect black toner are connected to a toner collection pipe 4.
2, and the black toner collected by the cleaner unit 21bk is collected into the developing unit 20bk. Incidentally, yellow toner is collected by the cleaner units 21y, 21m, and 21c due to the reverse transfer of black toner from the recording paper during transfer onto the photoreceptor drum 18y.

The magenta and cyan toners are mixed with toners from different color developing devices in front of these units, so they are not collected for reuse.

The transfer belt 25 that feeds the recording paper is an idle roller 26.2
8.30, it is stretched around a drive roller 27, and is rotated counterclockwise by the drive roller 27.

The console board 300 is equipped with a copy start switch 301, various mode switches 32, other input key switches, a character display, indicator lights, and the like.

Figures 5 and 6 show the information that should be sent to the laser driver circuit.
FIG. 2 is a block diagram of a synchronization signal generation circuit that generates a horizontal synchronization signal and a vertical synchronization signal.

The horizontal synchronization signal shown in FIG. 5 gives a period for exposing the laser beam in the axial direction of the drum 18c in FIG. 4 in accordance with image data.

The vertical synchronizing signal shown in FIG. 6 provides a period during which scanning for laser beam exposure is completed while the horizontal synchronizing signal is being sent. Therefore, since the photoreceptor drum is rotating, an image of the rotating length of the photoreceptor drum is created while the vertical synchronization signal is being sent. These are shown in the timing chart of FIG.

First, the generation process of the horizontal synchronization signal will be explained. Figure 5 5 8A
Please refer to the figure.

The cyan horizontal synchronization signal generation circuit shown in FIG. 5 has the same circuit configuration as those for magenta, yellow, and black, so this cyan horizontal synchronization signal generation circuit will be explained below.
In FIG. 0, the others are omitted, the horizontal open 'uI detection sensor is the sensor 44c in FIG. 4, and when a laser beam is incident on this sensor, an output as shown in FIG. 8 is output from the synchronous position detection circuit 200. . Timer 1. Timer 2. timer 3
detects the falling edge of the signal input to the start (ST) input, raises the output (OUT), and starts the clock (
CLK) input, and as shown in Fig. 9, when the counted value falls short of the set value that can be changed using the rotary set digital switch 201, etc., the output (OUT) is turned off. This is a timer that has The above setting values are the time for timer 1 to start laser exposure after the horizontal synchronization position detection signal falls, and the time for timer 2 to finish laser exposure after the fall of the horizontal synchronization position detection signal. 3 is the time from when the horizontal synchronization position detection signal falls to when the laser should be turned on for horizontal synchronization detection (the laser beam is
4c, to ensure horizontal synchronization position detection).

Timer 1. Timer 2. The clock input to timer 3 is
In this embodiment, the output pulse of the crystal oscillator is frequency-divided.

When the timer set value is set as described above, the horizontal synchronizing signal generating circuit shown in FIG. 5 generates timing as shown in FIG. 8A. Then, the signal of the output of timer 2 passed through inverter IN and the output of timer 1 are passed through an OR circuit to obtain a horizontal synchronization signal.

Next, the process of generating the vertical synchronization signal will be explained. Please refer to Figure 2.

The CPU (Central Processing Unit) shown in Fig. 2 performs sequence control of the digital color copying machine according to the program in the ROM. Pass the bus at the timing of laser exposure start, ■
The exposure start signal of the vertical synchronization generating circuit shown in FIG. 6 among the synchronizing signal generating circuits is lowered through /○ (see FIG. 8B).

Please refer to FIGS. 6 and 8B.

Timers 4 to 11 of the vertical synchronization generation circuit in FIG. 6 are as follows:
It has the same function as the timer in the horizontal synchronization signal generation circuit. Timer 4 and timer 8 start counting when the exposure start signal falls. In FIG. 1, the setting value of the timer 4 is set to the time when the leading edge position of the image on the photosensitive drum 18C that is irradiated with the laser beam moves from the laser exposure position to the transfer position.
This is the number of pulses generated by 1.5 times the rotation of . The pulses generated in response to the rotation of the photosensitive drum i8c are those generated from the encoder 202 installed as shown in FIG. This encoder is attached to the photoreceptor drum shaft and a coupling.

Although FIG. 10 only shows the cyan drum 18c and the transfer belt 25, the other drums have similar configurations.

Since the timer 4 counts the pulses generated in response to the movement of the photoreceptor drum 18c, even if there are fluctuations in the rotational speed of the photoreceptor drum 18C, the leading edge of the image written on the cyan drum 18c is always at the transfer position. When the output is reached, the output is lowered. As the output of timer 4 falls, timer 5. Timer 6 and timer 7 start counting.

Here, the pulses to be counted are set on the photosensitive drum 18 of the timer 4.
From the encoder pulse of c, timer 5. The reason why the timer 6 and timer 7 are switched to encoder pulses by the transfer belt 25 is that the movement of the leading edge of the image on the cyan drum 18C is entrusted to the movement of the transfer belt 25.

Referring to FIG. 11, 42m is the distance between transfer positions between each drum, lπr is the half circumference length of the photosensitive drum, and in is 1m-
The length satisfies 1rcr. In order for the leading edge of the image on the drum 18y to overlap the leading edge of the image transferred to the recording paper by the drum 18bk, the leading edge of the image on the recording paper must be at point A when laser beam exposure is started on the drum 18y. Point A is a point on the transfer belt 25 at a distance of in from the transfer position of the drum 18bk in the direction from the drum 18bk to the drum 18y. This relationship is the same for the other drums in this embodiment. The setting value of the timer 5 indicates that the transfer belt 25 is j? This is the number of pulses generated from the transfer belt encoder 203 while moving by n. The setting value of the timer 6 is that the transfer belt 25 is βm+j! This is a pulse during n movement. The setting value of the Quimuff is that the transfer belt 25 is 21m.
+i! This is the number of pulses during n movement.

As mentioned above, timer 5. When the set values of timer 6 and timer 7 are determined, the output of timer 5 falls and timer 9 starts counting when the image by drum 18bk is transferred to the recording paper, moved by transfer belt 25, and reaches point A. At the time, 1
This is the time when the laser beam exposure of the 8y drum starts.

Similarly, the time when the output of timer 6 falls and timer 10 starts counting is the timing at which laser beam exposure of drum 18m should start, and the time when the output of timer 7 falls and timer 11 starts counting. is drum 1B'C
This is the timing to start laser beam exposure.

As mentioned above, the timing is determined by switching the pulses to be counted again from the transfer belt encoder pulses to the photoconductor drum encoder pulses. This is because it changes depending on the

By switching the pulses to be counted, the image produced by laser beam exposure always has a set length.

Timer 8. Timer 9. Timer 10. The set value of the timer II is the same value as the length of the image to be formed (the number of pulses of the photosensitive drum encoder generated while the 8-photo drum rotates).

When setting values are determined as above, timer 8. Timer 9.
Timer 10. When the output of timer 11 is passed through the inverter,
1st. Second. Third. A fourth vertical same-month signal is obtained.

(Effects) The present invention is as described above, and according to the present invention, the timing of laser beam exposure of a plurality of image forming devices is matched according to speed fluctuations of the photoreceptor drum and the transfer belt. The trailing edge of the image is automatically controlled so that the length of the image to be output does not change due to fluctuations in the speed of the photoreceptor drum. can be accurately superimposed on a single sheet of recording paper to obtain a high-quality color image.

[Brief explanation of the drawing]

Fig. 1 is a mechanical diagram of a digital color copying machine in which the present invention is implemented, Fig. 2 is a block diagram of the t-loading section, Fig. 3 is an external view showing a part of the scanner, and Fig. 4 shows the laser writing system. 5 is a horizontal synchronization signal generation circuit diagram, FIG. 6 is a vertical synchronization signal generation circuit diagram, FIG. 7 is a timing chart showing the relationship between the horizontal synchronization signal and vertical synchronization signal, and FIG. 8A is a horizontal synchronization signal generation circuit diagram. FIG. 8B is a timing chart of the vertical synchronization signal generation circuit, FIG. 9 is a circuit diagram of the variable setting value of the timer in FIG. 5, and FIG. 10 shows the photoreceptor drum and pulse generator. External view, 1st
FIG. 1 is a diagram for explaining the relationship between the image position on each photosensitive drum and the recording paper. Fig. 2 Fig. 3 M4 Fig. 5 Fig. 6 Fig. 7 Figure 88 TP14 Jukutsu Doho Signal

Claims (1)

[Claims] The document illumination light is separated into colors, and the recording color information obtained from this spectroscopy is scanned and exposed as a laser beam onto a photoreceptor drum dedicated to each color.The image forming process is executed on each photoreceptor drum to form a developed image of each color. In a digital color copying machine that obtains a color image by sequentially superimposing and transferring the developed image on the photoreceptor drum onto a recording paper that is conveyed on a transfer belt, pulses are generated in accordance with the movement of the photoreceptor. pulse generating means for generating pulses according to the movement of the recording paper; counting means for counting the two pulses; and control means for controlling the image forming means by combining the counting results. A digital color copying machine characterized by being equipped with.