JPH0778654B2 - Color image forming device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a color copying machine or a color printer to which electrophotography is applied.

2. Description of the Related Art In recent years, a color image forming apparatus has been popular in which a plurality of toner images of different colors are formed on a photoconductor by repeating charging, exposure, and development a plurality of times, and then the toner images are collectively transferred to paper to obtain a color image. Is being considered. An example of this type of color image forming apparatus is one proposed by the authors in Japanese Patent Application No. 62-95663. The drive part of the photoconductor of this comparative example will be described below.
It will be described with reference to the drawings.

FIG. 6 is a plan view of the driving portions of the photoconductor and the developing device, which are viewed from above, of a color image forming apparatus that forms a multicolored color image on the photoconductor and transfers it to a sheet of paper collectively to obtain a color image. . 161
Is a photoconductor and 162 is a developing device. The same developer as 162 is arranged around the photoconductor for each color of yellow, magenta, cyan, and black. The photoconductor 161 is driven by a gear 166 of a photoconductor drive motor 165 via a gear 164 engaged with a gear 163 integrally connected thereto. On the other hand, developing device 16
A gear 168 integrally connected to a developing roller 167 is driven by a gear 172 of a developing device drive motor 171 via a gear 170 rotatably supported by a shaft 169 of a photoconductor. Charging, exposure, and development are repeated on the photoconductor for each color, and the photoconductor rotates four times to form a color image on the photoconductor.

SUMMARY OF THE INVENTION It has been found that the color images developed on the photoconductor by this conventional method are likely to be misaligned with each other. It depends on the following causes. That is, the normal gear is inevitably unavoidable because there is a runout due to rotation in the single component or in the assembled state, a shape error for each tooth of the gear, a pitch error, or a slight fluctuation of the transmission speed due to the meshing state. Therefore, when developing by aligning the positions of the respective colors on the photoconductor, in general, when the latent image for each color is formed on the photoconductor, the photoconductor undergoes various speed fluctuations for each color.
A slight deviation is likely to occur between the positions of the colors.

SUMMARY OF THE INVENTION In view of the above points, an object of the present invention is to provide a color image forming apparatus in which a good image quality can be obtained in consideration of a method of driving a photoconductor in which the respective colors can be accurately aligned with each other.

Means for Solving the Problems The present invention is directed to a photoconductor that holds and rotates an electrostatic image, a charging unit that uniformly charges the photoconductor, and a latent image by performing line-scanning exposure on the photoconductor. A digital exposure means for forming a photoconductor, a photoconductor driving means for driving the photoconductor including a pulse motor and a reduction gear, and a plurality of developing devices for developing latent images on the photoconductor in different colors. Further, the reduction gear ratio of the reduction gear is selected so that the rotation amount of the photosensitive member rotated by one pulse input by the pulse motor is within one line pitch of scanning by the exposure unit on the outer periphery of the photosensitive member, and This is a color image forming apparatus in which the reduction ratio of the engaging teeth of the reduction gear is set to be an integer fraction.

Action The photoconductor is driven by a pulse motor, and its reduction ratio is
By selecting so that the amount of advance of the photosensitive member in one pulse is appropriate and the ratio of the teeth to be engaged is an integer, the same teeth are meshed at the same rotational position of the photosensitive member, no matter how many rotations the photosensitive member makes. In this way, the minute driving force fluctuations of the pulse motor are prevented from appearing in the final image. As a result, when the latent image of each color is formed, the same speed fluctuation occurs at the same position on the photoconductor, so that a color image of good quality can be formed in which the respective colors can be accurately aligned with each other.

Embodiment 1 FIG. 1 is a front view showing the overall construction of a digital color copying machine to which the present invention is applied. The configuration and operation will be described below.

Reference numeral 1 denotes a reading unit of a digital color copying machine, mainly a document table 2, a document illumination lamp 3, a lens 4, a color line sensor 5, a drive system 6 and an image processing circuit for moving these for scanning in the sub-scanning direction. (Not shown in the figure).

Reference numeral 10 is a writing unit of the digital color copying machine.

11 sensitized the sensitivity to laser light of wavelength 780 to 810 nm
It is a Se type photosensitive member and is rotatably supported in the direction of arrow A. Reference numeral 12 is a first charger for charging the surface of the photoconductor 11 to a positive predetermined potential, and 26 is a laser beam light.

Reference numeral 20 denotes a laser optical section, and laser beam light 26 is emitted from a laser oscillation block 21, and a polygon scanner 22 and a lens system 2 are provided.
3, configured to scan on the photoconductor 11 via the mirrors 24, 25. A part of the scanning light of the laser beam light 26 is reflected by the mirror 27 and is applied to the starting end detection sensor 28. There is a developing unit 30 on the right side of the photoreceptor 11, and along the periphery of the photoreceptor 11, a Y developing device 31 for yellow color development, an M developing device 32 for magenta color development, and a C development for cyan color development in order from the top. A device 33 (hereinafter collectively referred to as a color developing device) and a K developing device 34 for black developing are provided. The Y developing device 31, the M developing device 32, and the C developing device 33 are non-contact developing devices that use non-magnetic one-component toner, and can develop while letting the toner fly to the photoconductor 11 in a non-contact manner. It is a vessel. The K developing device 34 is a developing device that develops while contacting a developer using a two-component developer. Each developing device can take two positions, a position close to the photoconductor 11 and a position separated from it, and the Y developing device 31, the M developing device 32, and the C developing device are rotated by rotating the eccentric cams 35 to 38, respectively. The rear portion of the container 33 is pushed to move horizontally to approach the photoconductor, and the K developing device rotates counterclockwise about the shaft 39 to approach the photoconductor. FIG. 1 shows a case where only the M developing device 32 is in a developable state.

40 is an eccentric cam 35, 36, 37, 38 and a developing machine 31, 32, 33, 34.
Is a motor for driving.

Reference numeral 50 denotes a paper feeding unit, which can feed one sheet of paper from each of the cassettes 51 and 52 and the manual paper feeding unit 53. In this figure, the case where the paper 56 is fed from the cassette 51 is shown. There is. The sheet 56 is fed to the lower surface of the photoconductor 11 via the registration roller 54.

Reference numeral 60 denotes a transfer / transport unit, which has two states: a state in which a semiconductive belt 63 suspended by rollers 61 and 62 is lightly pressed against the photoconductor 11 and a state in which the belt 63 is separated from the photoconductor 11. In addition, it is possible to move in the direction of arrow B at the same speed as the outer peripheral surface of the photoconductor 11. This figure shows a state in which the photosensitive member 11 is separated from the photosensitive member 11. On the other hand, reference numeral 64 is a second charger for transfer, which gives a negative high potential to the back surface of the paper 56 fed between the belt 63 and the photoconductor 11 via the belt 63. Reference numeral 65 is a cleaning blade for the toner remaining on the belt, and a recovery box 66 is arranged below the cleaning blade. 69 is paper 56 is belt 63
Sprinkle a negative corona when separating from the third
It is a charger. Reference numeral 70 denotes a fixing discharge unit, in which a heat roller 72 heated by a fixing lamp 71 and a rubber roller 73 are rotatable while being in pressure contact with each other.
75 and a paper discharge tray 76 are provided.

Reference numeral 80 denotes a cleaner charge removing portion, which can be in two states, that is, a state where the fur brush 81 is lightly contacted with the photoconductor 11 and a state where the fur brush 81 is separated from the photoconductor 11, and can be rotated in the arrow D direction. This drawing shows a state in which the photosensitive member 11 is separated from the photosensitive member 11.
Further, a collection roller 82 is rotatably arranged in contact with the fur brush 81, and the fur brush 81 and the collection roller 82 are provided.
A negative voltage is applied to each of the photoconductors 11. A recovery screw 83 is installed below the recovery roller 82, and a pipe 84 is connected to the front end of the recovery screw 83 and is connected to a recovery box 85 through this. A fourth charger 84 for positively charging the toner on the photoconductor 11 and a discharge lamp 87 for discharging the photoconductor 11 are disposed at a position below the fur brush 81 and the like facing the photoconductor. There is.

Reference numerals 101 and 102 denote cooling fans for sucking air from the lower portion and the upper portion of the writing unit 10 and discharging the air to the outside of the apparatus.

The above is the outline of the overall configuration of the digital color copying machine to which the present invention is applied. Next, the operation will be described.

When the document is set on the document table 2 and the copy button is pressed, the document illumination lamp 3 is first turned on to project a line image of the document on the color line sensor 5, and the color line sensor 5 moves in the main scanning direction (paper surface). It is electrically and repeatedly scanned at high speed in the depth direction) and is moved in the sub-scanning direction (rightward on the paper surface) by the drive system 6. The color line sensor 5 outputs R, G, and B color signals at the same time, and the R, G, and B signals correspond to the respective points on the document by the above-described main scanning and sub-scanning. The time series is input to the image processing circuit.

In the image processing circuit, R, G and B signals corresponding to respective points of the original are used to develop black, yellow, magenta,
The signals for each color of cyan are calculated and output. In color copying, the sub-scanning of the original by the reading unit 1 is performed four times in one copy, and in the first sub-scanning, the black signal output from the image processing circuit is input to the laser transmission block 21 through the buffer memory and is exposed. The body 11 is irradiated with a laser beam light 26 which is modulated according to a black signal.

The photoconductor 11 is uniformly charged to + 850V by the first charger 12 while rotating in the direction of arrow A, and then the irradiated portion is discharged to about + 50V according to the intensity of the laser beam light 26.
The main scanning of the laser beam 26 on the photoconductor 11 is performed by the polygon scanner 22, and the sub-scanning is performed by the rotation of the photoconductor 11 in the arrow A direction. The main scanning repeating timing is made to correspond to the main scanning repeating timing of the color line sensor 5, and the signal read by the color line sensor is generated as a black signal after being delayed by the amount stored in the buffer memory through the image processing circuit. The laser beam light 26 corresponding to the black signal corresponding to each point of the document is irradiated on the photoconductor 11 to form a latent image of the document.

During the first sub-scan of the reading unit 1, the developing unit 30 is set to a black developing state, only the K developing unit 34 approaches the photoconductor 11 by the operation of the eccentric cam 38, and the other developing units are separated. Is in a state. Therefore, the latent image formed by the laser beam light 26 corresponding to the black signal is developed with black toner by the K developing device 34 and passes through without being affected by other developing devices. At this time, the K developing device 34 is controlled in the contact / separation timing so that the K developing device 34 performs a proximity operation before the photoconductor 11 is exposed to the laser beam 26 and is separated after the development. The image developed with black toner reaches the transfer / conveyance unit 60 as the photoconductor 11 rotates, but at this time, in the transfer / conveyance unit 60, the rollers 67 and 68 are slightly rotated counterclockwise around the axis of the roller 61. The belt 63 is separated from the surface of the photoconductor 11
The image passes undisturbed.

Furthermore, the fur brush 81 is in a state of being separated from the photoconductor 11 at a position slightly rotated counterclockwise around the axis of the recovery screw 83, and the black toner image passes therethrough without being disturbed, and the first charger is again provided. Pass under 12. The portion of the photoconductor 11 on which the black toner image is formed is recharged from above the toner by the first charger 12, the portion without toner is charged to + 850V, and the portion with toner is apparently charged to + 850V.

The tip of the black toner image is recharged and the laser beam light
In the reading unit 11, the drive system 6 is controlled so that the color line sensor 5 starts scanning again from the starting end of the original when the irradiation position of 1 is reached. In the second scanning of the reading unit 1, the yellow signal is input from the image processing circuit to the laser transmission block through the buffer memory, the laser beam light 26 is modulated according to the yellow signal, and the black toner image on the photoconductor 11 is exposed. To be done. Since the leading edge of the image is aligned and the scanning speed is also constant, the black toner image and the latent image formed by the yellow signal are formed in positional alignment. The latent image formed by the yellow signal is only developed by the yellow toner because the Y developing device 31 of the developing unit 30 is close to the photoconductor 11 and the other developing devices are separated from the photoconductor 11 this time. A yellow toner image is formed in addition to the black toner image. At this time, the Y developing device 31 has its contact / separation timing controlled so that the Y developing device 31 performs a proximity operation before the exposure of the photoconductor 11 by the laser beam 26 and separates after the development. Further, at this time, since the yellow development is performed in a non-contact manner, the previous black toner image is not disturbed. In the same manner, recharging, latent image formation by magenta signal, magenta development, recharging, latent image formation by cyan signal, and cyan development are repeated.

At this time, since the yellow toner and the magenta toner transmit the laser light, if necessary, that portion of the photoconductor is neutralized by exposing it to the yellow toner, magenta and cyan toner, and magenta toner. Cyan toner can be overlaid on. After the final cyan toner image is formed, immediately before the leading edge of the toner image reaches the transfer / transport unit 60,
The transfer conveyance unit 60 is brought into a state of being lightly pressed against the photoconductor 11, and the paper 56 enters between the photoconductor 11 and the belt 63 by the registration roller 54 at the timing when the front end of the toner image and the front end of the paper 56 coincide with each other. Is delivered as.

The toner image is formed on the paper by the electric field generated by the second charger 64.
While being transferred to the sheet 56, the sheet 56 is conveyed while being attached to the belt 63. However, since the roller 62 has a large curvature, the sheet 56 is separated from the belt 63 and enters the fixing and discharging section. At this time, in order to prevent the toner image on the sheet 56 from being disturbed by the peeling charge generated on the sheet 56 for separating from the belt,
Sprinkle the negative corona with the charger.

The toner image on the sheet 56 is fixed on the sheet 56 after passing through the fixing and discharging section and then stacked on the sheet discharge tray. On the other hand, the untransferred toner remaining on the photoconductor 11 is positively charged by the fourth charger 86 that starts to operate immediately before the tip of the fur brush moves, and at the same time, the fur brush moves into contact with the photoconductor 11. While being rubbed against 81, it moves to the fur brush 81 by the electric field applied between the fur brush 81 and the photoconductor 11. Further, the toner in the fur brush 81 is transferred to the collection roller 82 by the electric field applied between the collection roller 82 and the fur brush 81, dropped to the collection screw 83 portion, and stored in the collection box through the pipe 84.

As a result, the surface of the photoconductor 11 is cleaned and, at the same time, the charge is removed by the charge removal lamp 87, and the state is returned to the initial state to complete the preparation for the next copy.

On the other hand, the toner accumulated on the belt 63 of the transfer / conveyance unit 60 due to an operation error or minute amount is cleaned by the cleaning blade 65 and dropped to the collection box 66.

The above is the outline of the overall configuration and operation of the digital color copying machine to which the present invention is applied. Next, the structure and operation of the drive unit and the developing unit of the photoconductor of this digital color copying machine will be described in detail.

FIG. 2 is a diagram showing in detail the photoconductor 11 and the developing section 30 in FIG. 1, and in this figure, the K developing device 34 is in a developing state.

The developing devices 31, 32, 33, and 34 are housed in a developing rack 41, and this drawing shows a part of the developing device 41 in a sectional view. Reference numerals 131, 132, 133, and 134 denote developing rollers of the respective developing units, which are brought close to the photoconductor 11 while maintaining a predetermined minute gap in the developing state. The color developing devices 31, 32, 33 are returned to the positions shown in FIG. 2 in a free state in which no external force is applied to the color developing devices 31 and 32. Return springs (not shown) installed in the developing rack 41.
Is urged by. The K developing device 34 is an eccentric cam.
In the state where it is not pushed by 38, it rotates clockwise about the shaft 39 by its own weight and is in the position shown in FIG. The eccentric cams 35, 36, 37, 38 are installed in the main body of the copying machine, and the stored developing devices can be pressed from the rear via the leaf springs 44, 45, 46, 47, and every 180 degrees. By repeatedly stopping the rotation, the developing device can be pressed and separated. All developing devices are separated from the photoconductor, that is, the eccentric cam 38 in FIG.
In the state of being rotated by 0 degree, the developing rack 41 can be pulled out toward the front by using the rails 42 and 43 fixed to the main body of the copying machine as guides.

On the other hand, each developing device is provided with a gear 145 and a gear 1 rotatably supported about a shaft coaxially with the photoconductor connected to the motor 40.
Driven via 41, 142, 143, 144. Also eccentric cam 3
Each of 5, 36, 37, 38 is also connected to the motor 40 via a clutch (not shown) which can be disengaged.

Next, the photoconductor is connected to a photoconductor drive motor 148 which is a pulse motor through a gear 146 integrally fixed to the photoconductor and a two-stage gear 147 as shown in FIG. The gear 146 is a module 0.8 mm, the number of teeth is 182, and the small gear 147a is a two-stage gear 147.
Is a module 0.8 mm with 26 teeth and the reduction ratio is 1/7. The large gear 147b of the two-stage gear 147 is a module 0.6
75 teeth, photoconductor drive motor gear 149 is module 0.6
With 25 mm teeth, the reduction ratio is 1/3.

With such a configuration, a drive pulse having a constant cycle is applied to the motor to rotationally drive the photoconductor, and as a result of measuring the deviation of the actual rotational position of the photoconductor from the position of the photoconductor when rotated at a constant speed, The measurement result as shown in FIG. 4 (a) was obtained. In FIG. 4, the horizontal axis represents time, and the vertical axis represents the deviation of the rotation amount from the normal position when the photoconductor rotates at a constant speed.

In other words, the photoconductor rotates with a wave that deviates from the regular position in the cycle of one rotation, and also rotates with the positional fluctuation of the wave with a fine cycle of 1/21 of one rotation. I understand. It is clear that the former wave is due to the touch of the gear 146 of the photoconductor and the latter wave corresponds to the deflection of the gear 149 of the photoconductor drive motor. Further, if one of the waves of 1/21 of one rotation, that is, the scale of the horizontal axis of the portion B of FIG. 4 (a) is enlarged, it becomes as shown in FIG. 4 (b). That is, in the wave of 1/21 of one rotation, there is a minute wave position change of 1/182 of one rotation of the photoconductor, which is caused by the gear of the photoconductor or the small gear of the two-stage gear.
It can be seen that the position variation corresponds to one tooth of 7a.

Although the photoconductor rotates with a deviation from the normal position as described above, all of these deviations are repetitive waves of a positive fraction of one revolution of the photoconductor. The same shift occurs at the same position. That is, the waves appearing in FIGS. 4A and 4B are exactly overlapped with each rotation of the photosensitive member.

On the other hand, the relationship between the driving of the photoconductor and the exposure scanning will be described below. A control block diagram of the photoconductor drive motor 148 is shown in FIG. The pulses generated by the reference frequency generator 150 are frequency-divided by the frequency dividers 151 and 152 to the frequencies required for controlling the photoconductor drive motor 148 and the polygon scanner 22, respectively, and then passed through the respective control circuits 153 and 154. Drive the motor. Further, the photoconductor drive motor 148 is controlled by 720 pulses per rotation, so that one pulse input to the photoconductor drive motor 148 causes the photoconductor to rotate 1 / 15120th. The input pulse to the control circuit 154 is selected so that the polygon scanner 22 scans one line at 1/7560 rotation of the photosensitive member.
Therefore, the photoconductor moves by the input of two pulses to the photoconductor drive motor 149 while the exposure scanning of one line is performed.

Since the speed of the photosensitive member driving motor slightly changes in the cycle of the input pulse, the relationship between the input pulse to the photosensitive member driving motor and the exposure scanning cycle is 1
It is desirable that the rotation amount of rotation of the photosensitive member by the pulse is within one line of exposure scanning.

On the other hand, the exposure of each color signal is started by counting the number of line scans. That is, the exposure of the yellow signal is started when the line scanning is performed 7561 times after the black exposure is started. The same applies to magenta and cyan.

By configuring the relationship between the photoconductor and the exposure scanning as described above, an image of excellent quality can be obtained in which the front ends of the images of the respective colors are perfectly matched and the positions of the respective colors are surely matched with each other over the entire image. It is a thing.

EFFECTS OF THE INVENTION As described above, according to the present invention, even if there is a slight speed fluctuation factor in the photoconductor or the driving means for the photoconductor, good image quality in which the positions of the respective colors are completely excluded except for these influences It is possible to obtain a color image of.

[Brief description of drawings]

FIG. 1 is a front view showing the overall construction of a digital color copying machine to which the present invention is applied, FIG. 2 is a partial cross-sectional view of a developing section of an embodiment of the present invention, and FIG. 3 is a color image forming apparatus shown in FIG. 4 is a top view of the portion of the M developing device of FIG. 4, FIG. 4 is a characteristic diagram showing the deviation of the rotation amount, FIG. 5 is a schematic diagram of the drive unit of the photoconductor of the same apparatus, and FIG. Is. 1 ... reading section, 2 ... writing section, 11 ... photoreceptor,
30 ... Developer, 31 ... Y developer, 32 ... M developer, 33 ...
… C developing device, 34 …… K developing device, 35-38 …… Eccentric cam, 41
…… Development rack, 147 …… Two-stage gear, 148 …… Photoconductor drive motor.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hayato Kamata 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A 61-156162 (JP, A) JP-A 63-113478 (JP, A) JP 62-195686 (JP, A) JP 62-174160 (JP, A)

Claims (1)

[Claims] 1. A photoconductor that rotates while holding an electrostatic image, a charging unit that uniformly charges the photoconductor, and a digital exposure unit that forms a latent image by performing line-scanning exposure on the photoconductor. And a plurality of developing devices for developing a latent image on the photoconductor in different colors, the photoconductor drive means including a pulse motor and a reduction gear to drive the photoconductor, and the pulse. The reduction gear ratio of the reduction gear is selected so that the rotation amount of the photoreceptor rotated by one pulse of the motor becomes smaller than one line pitch of scanning by the exposure means on the outer periphery of the photoreceptor, and the reduction gear is engaged. A color image forming apparatus in which the speed reduction ratio between the teeth is reduced to an integer.