JPS6035063B2 - electrophotographic copying device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrostatic transfer type electrophotographic copying apparatus using a magnetic brush type developing device.

In a conventional electrophotographic copying apparatus of this type, the output is 30 to 50 kW to rotate the rotating sleeve of the developing device.
Synchronous motors or induction motors with an alternating current of about W have been used.

Normally, in order to rotate the rotary sleeve of a magnetic brush type developing device, a driving torque of approximately 3 to 6 k9 is required during rotation. This torque is mainly caused by the iron powder carriers in the developer being attracted to the permanent magnet in the rotating sleeve.
This is caused by the frictional force that causes the rotating sleeve to rotate while being pressed against the surface of the rotating sleeve.
In this case, as the rotating sleeve rotates, the developer is lifted upward, but this amount is not always constant and varies.
As a result, the drive torque required to rotate the rotating sleeve also varies.

Accordingly, when driving a rotating sleeve with an AC motor, the motor is synchronized with the power supply frequency, and after a certain amount of time, it should be rotating at a constant speed of, for example, 200 revolutions per minute. However, in reality, due to the torque fluctuations mentioned above, there were some speed fluctuations over a short period of time, and these speed fluctuations caused the harsh humming noise that is characteristic of magnetic brush development. . The present invention uses a constant speed control DC motor equipped with a rotational speed detection means (encoder), obtains a speed detection pulse signal of about 50 pulses per one rotation of the motor from the rotational speed detection means, and By driving the rotating sleeve of the developing device to rotate at a constant speed by controlling the current or voltage supplied to the armature so that the pulse interval is constant, uneven rotation caused by variations in the driving torque of the rotating sleeve can be eliminated. This has made it possible to realize a high-performance electrophotographic copying apparatus that minimizes the noise that is characteristic of secondary and magnetic brush type development.

The present invention will be explained below based on illustrated embodiments.

In FIG. 1, a cylindrical electrophotographic photoreceptor, ie, a photosensitive drum 12, having an electrophotographic photoreceptor layer is rotatably supported substantially in the center of a main body 11 of a copying apparatus.

Around the photosensitive drum 12, a charger 13, an exposure slit 14, a developer 15, a transfer charger 16, a paper charger 17, a photoreceptor charger 18, and a cleaner 19 are installed in that order. It is located. The charger 13 functions to uniformly charge the photosensitive drum 12.

When selenium is used as the photoreceptor of the photoreceptor drum 12, the charging wire of the charger 13 has a positive polarity of 5 to 5 V.
As the photosensitive drum 12 rotates in the direction of the arrow 20, the surface of the photosensitive drum 12 is uniformly charged as a result of corona discharge from the charging wire. Manuscript 24
The reflected light is projected onto the photosensitive drum 12 from the exposure slit 14 through mirrors 26, 26, 27, 28, 29, 30 and 31. The reflected light from the fixed original 24 is successively projected onto the rotating photosensitive drum 12 by an optical scanning mechanism including moving mirrors 25, 26, and 27. Therefore, a static exposure latent image corresponding to the original 24 is formed on the surface of the photosensitive drum 12.

The developing device 15 is constituted by a magnet roll in which a fixed magnetic pole group of permanent magnets 33 is provided inside a rotating sleeve 32 made of a non-magnetic material.

The developer consisting of toner and carrier is lifted by the magnetic force of the permanent magnet 33 as the rotating sleeve 32 rotates, forming a magnetic brush that lightly slides over the surface of the photosensitive drum 12.

As a result, the electrostatic port image on the photosensitive drum 12 is developed and visualized as a toner image. Note that a toner replenishing device 34 is provided above the developing device 15, and can sequentially replenish toner that has adhered to the photosensitive drum 12 as a toner image and has decreased. The transfer device includes a transfer charger 16, a paper neutralization charger 17, and a roller 35 for feeding the copy paper into the gap between the photosensitive drum 12 and the transfer charger 16. Copy sheets are fed into this transfer device one by one from a copy paper supply device 40 adjacent thereto. Toner developed by the developing device 15
When the photosensitive drum 12 carrying the image rotates and reaches the position of the transfer charger 16, the image is transferred onto the copy paper fed from the copy paper supply device.

In the embodiment of the present invention, a positive high voltage is applied to the transfer charger 16. Further, a high alternating current voltage is applied to a paper static elimination charger 17 provided adjacent to the paper static electricity removal charger 17. It is peeled off from the surface of the photosensitive drum 12 by the emitted alternating current corona. The copy paper peeled off from the photosensitive drum 12 is sent to a fixing device 41 provided adjacent to the transfer device.

The fixing device 41 includes a heating lamp 43 provided in a rotating roller 42.
The surface of the roller 42 is heated to about 200 qo by the heat.

The copy paper on which the toner image has been transferred is heated and pressed while being fed by rollers 42, and the toner image on the front side is fixed on the copy paper. The circumferential speed of the roller 42 is driven to be equal to the circumferential speed of the photosensitive drum 12. If there is a discrepancy between the peripheral speed of the roller 42 and the peripheral speed of the photosensitive drum 12, for example, if the peripheral speed of the fixing roller 42 is too fast,
This causes the copy paper being transferred to be stretched, causing the transferred image to shift and become an image that is more elongated than the original image. On the contrary, the fixing roller 42
If the circumferential speed is too slow, the transferred paper will be fed one after another, causing the copy paper to bend between the transfer position and the fixing roller 42, which will be described later. When it comes into contact with the bottom surface of the photoreceptor charger 18, the unfixed image will be rubbed and damaged.

For the above reasons, the peripheral speeds of the roller 42 and the photosensitive drum 12 are driven to match with high accuracy.

For the same reason, the copy paper feed roller 35 of the transfer device
The circumferential speed of the photosensitive drum 12 is also driven to match the circumferential speed of the photosensitive drum 12 .

After the copy paper is peeled off, the photosensitive drum 12 having residual toner on its surface is decharged by a photosensitive defrosting charger 18 .

A high AC voltage is applied to the photoconductor static elimination charger 18, and the photoconductor drum 1 is
The charge on the surface of 2 is neutralized. The photosensitive drum 12 then reaches the cleaner 19 as it rotates.

The cleaner 19 has a blade 4 made of polyurethane rubber or the like.
4, and the edge portion of this blade 44 is pressed against the surface of the photosensitive drum 12. As the photosensitive drum 12 rotates, the toner image remaining on the surface of the photosensitive drum 12 is scraped off by the edge of the blade 44 and collected into the toner container 45 of the cleaner 19. Next, the optical scanning mechanism will be explained.

The first movable mirror 25 moves in parallel with the surface of the original 24 from the left end to the right end of the original 24 together with the illumination lamp 50 .

The movable mirror 25 is inclined at an angle of 45° with respect to the original 24, and the light reflected from the original 24 is turned at right angles by the movable mirror 25 and directed to a mirror indicated by 26. Mirrors 26 and 27 are integrally held movable mirrors that are inclined at an angle of 450 degrees with respect to the surface of the original 24, and are opposed to each other at an angle of 90 degrees.

Therefore, the reflected light from the original 24 reflected by the movable mirror 25 is reflected by the mirrors 26 and 27 and is directed toward the lens 31.

The second movable mirrors 26 and 27 are mechanically coupled so that they move in the same direction as the moving direction of the movable mirror 25 at a speed ratio of 1/2 to the moving speed of the movable mirror 25. Therefore, while the first movable mirror 25 moves from the left end to the right end of the original 24, the distance from the original 24 to the lens 31 is kept constant. This distance is adjusted to be twice the focal length of the lens 31. The above is the optical scanning mechanism in the embodiment of the present invention, and the first and second movable mirrors 25, 2
When the scanning of the originals 24 No. 6 and 27 from left to right is completed, the scanning returns in the opposite direction and returns to the state before the start of scanning.

Note that the light that has passed through the lens 31 passes through the fixed mirrors 28 and 2.
9 and 30, and is projected onto the surface of the photosensitive drum 12 through the exposure slit 14.

The distance from the lens 31 to the photosensitive drum 12 is 31
The focal length of the lens is set to twice the focal length of the lens. Therefore, a light beam is projected onto the surface of the photosensitive drum 12 that is the same size as the image on the original document 24 and is a mirror image thereof. Further, the first movable mirror 25 is driven by a motor 60, which will be described later, so that the rightward movement speed is equal to the circumferential speed of the photosensitive drum 12.

Further, the second movable mirrors 26 and 27 are similarly driven by the motor 601 at a speed that is 1/2 of the circumferential speed of the photosensitive drum 12. Next, a mechanism for moving the first movable mirror 25 and the second movable mirrors 26 and 27 will be explained. As shown in FIG. 5, a wire 86, one end of which is fixed to the unit of the optical scanning mechanism at a position 85, is attached to a first movable pulley provided at one end of the movable support of the second movable mirrors 26, 27. 87, and then folded back again at a first fixed pulley 88 provided on the unit main body. This wire 86 is wound around the scanning pulley 89 several times and then folded back around the second fixed pulley 90.
It is folded back by a second movable pulley 91 provided on the support body 27 and fixed to the unit main body at a position 92. 1st
The support of the movable mirror 25 is fixed to the wire 86 at a position 93 intermediate between the second movable pulley 91 and the first fixed pulley 88. Therefore, when the scanning pulley 89 rotates clockwise in FIG. 5, the first
The second movable mirror 25 moves rightward at the circumferential speed of the scanning pulley 89, while the second movable mirrors 26 and 27 move at the circumferential speed of the scanning pulley 89.
It moves at a speed of 1'2 of the circumferential speed of . This scanning pulley 8
Reference numeral 9 is connected by a gear to the output shaft of an optical scanning mechanism drive motor 60, which will be described later, and is reversibly rotated by the rotation of the motor 60 in both forward and reverse directions. In Figure 1, it moves back and forth left and right at a specified speed.
The photosensitive drum 12, developing device 15, copy paper supply device 40, fixing device 41, cleaner 19, etc. are each formed into a unit, and are guided by a guide member so that they can be moved from the front of the main body 11 to a predetermined position in FIG. It will be inserted at the location. Further, the optical scanning mechanism including the first and second movable mirrors 25, 26, and 27 is loaded from the top of the main body 11.
In the embodiment of the present invention, the photosensitive drum 12, the fixing device 14,
The optical scanning mechanisms are each driven to rotate at a constant speed.

Next, this drive configuration will be explained. FIG. 2 is a perspective view of the main body of the apparatus seen from the back side of FIG. motor 60,
61 and 62 are fixed to the main body 11. The motor 60' is a motor for driving the optical scanning mechanism, and rotates in both forward and reverse directions. Further, the motor 61 is for driving the photosensitive drum 12, and the motor 62 is for driving the fixing device 41. Further, a motor 63 for rotating the rotating sleeve 32 of the developing device 15 is fixed to the main body 11.

As the above four motors 60 to 63, small flat type coreless DC motors with a thin armature made of disk-shaped windings and hardened with resin and having an output of about 20 W are used.

This motor has low armature inertia and is lightweight.
Moreover, since there is no iron core, the motor starts rotating quickly.
Suitable for the present invention. FIG. 3 shows a sectional view of a coreless type small DC motor with a built-in encoder used in an embodiment of the present invention.

In the figure, a shaft 65 rotatably supported by a bearing 66
A disk-shaped armature (molded coil) 68 made of a flat winding wound in a disk shape and hardened with resin is fixed to the armature, and this armature is held rotatably in the magnetic field by a circular permanent magnet 69. has been done. A commutator 80 and a brush 8 are attached to the winding of the armature 68.
A predetermined direct current is supplied through 1. Further, a slit disk 70 constituting rotational speed detection means is fixed to one end of the armature 68, and this is connected to the frame 71.
It is designed to rotate between a light emitting element 72 and a light receiving element 72 which are fixed to each other.

The slit disk 70 has five hard slits (
One rotation of the armature 68 generates 50 pulses as an output signal from the light receiving element 73.
Note that the motor frame 71 is fixed to the main body 11, and a gear 67 is fixed to the shaft 65. FIG. 4 shows a sectional view of the main body 11 from which units such as the photosensitive drum 12, the developing device 15, the fixing device 41, the cleaner 19, the copy paper supply device 40, and the optical scanning mechanism are removed.

That is, the figure shows a state in which the motors 60, 61, 62, and 63 are fixed to the main body 11, as viewed from the motor shaft 65 side. Gears 75, 76, 77, 78 corresponding to 67 in FIG. 3 are mounted on the shafts of the motors 60, 61, 62, 63, respectively.
is installed.

When the photosensitive drum 12 is loaded into the main body 11, a gear (not shown) attached to the rotating shaft of the photosensitive drum 12 meshes with a gear 76 attached to the shaft of the photosensitive drum drive motor 61, and driving force is transmitted. be done.

Similarly, in the rotating sleeve 32 of the developing unit 15, a gear 78 attached to the shaft of the motor 63 and a gear (not shown) attached to the rotating shaft of the rotating sleeve 32 mesh with each other to transmit driving force.

The fixing device 41 and the optical scanning mechanism are also equipped with a motor 62,
Driving force is transmitted from gears 77 and 75 of 60, respectively.

Note that an optical scanning mechanism, a photosensitive drum 12, a fixing roller 4
The reduction ratio between the gears 75, 76, and 77 for driving 2 and the gears on each unit side that mesh with them is 1/9. Therefore, each motor 60, 61, 62 operates at 42 m/min.
When rotating at 0 revolutions, the axis of rotation of the unit is 46.7 per minute.
rotate at the speed of rotation. Motor 63 for driving the developing device 15
In the embodiment of the present invention, the rotary sleeve 32 rotates at 1000 revolutions per minute, and the speed is reduced to 1/5 by the reduction gear mechanism, so that the rotating sleeve 32 rotates at 20 revolutions per minute.
Rotates 0.

Note that the copy paper feed roller 35 of the transfer device is provided with a gear that meshes with the gear 76 of the drum drive motor 61, and the roller 35 rotates at a circumferential speed equal to the circumferential speed of the photosensitive drum 12. Next, a method of controlling the rotational speed of each drive motor will be explained. There are 350
Equipped with HZ reference signal generator.

For example, when a current is applied to the motor 61 for driving the photosensitive drum, a pulse is generated from the light receiving element 73, which constitutes a rotational speed detecting means. In this case, the armature 6
Since 50 pulses are generated in one revolution of 8, when the armature 68 rotates at a speed of 420 revolutions per minute,
A signal of 350 pulses per second will be generated, so it can be used as the 350 HZ reference signal generator. The phase of the reference signal 350 days 2 from such a reference signal generator and the output pulse from the light receiving element 73 is compared, and if the motor rotation is too slow, the supply voltage to the motor is increased, and conversely, if the motor rotation is too fast, the voltage supplied to the motor is increased. In this case, the supply voltage is lowered, and a phase detection circuit is used for control so that the phase difference between the reference signal and the output pulse of the light receiving element 73 is always a constant value. Similarly, phase detection control is performed so that the number of rotations of the drive motor 60 during the forward motion of the optical scanning device and the number of rotations of the fixing device drive motor 62 rotate in synchronization with the reference signal from the reference signal generator. .

Since the developing device drive motor 63 needs to have a faster rotation speed than other motors, a separate reference signal generator generates a signal of 833 days 2, and a phase detection circuit of the same machine generates a constant rotation speed. It is controlled so that it rotates. Therefore, in the embodiment of the present invention, since the same reference signal and the output from the rotational speed detection means of each motor are controlled by phase detection, each motor is synchronized at the correct rotational speed even if a very short time interval is taken. This means that it is rotating.

Note that the developing unit driving motor 63 does not necessarily need to be controlled by the output of a separate reference signal generating device.
It goes without saying that the other three motors may be controlled using the same reference signal.

The larger the number of pulses generated per rotation from the motor rotational speed detection means, the more fine speed unevenness can be controlled, but in practice, as described above, sufficiently good results can be obtained with about 50 pulses.

Next, the actual copying operation in the embodiment of the present invention shown in FIGS. 1 to 5 will be explained. When copying the original 24, first the original 24 is placed at a predetermined position on the original layer table 10, and a start switch (not shown) is pressed.

Then, the photosensitive drum driving motor 61, the fixing device driving motor 62, and the developing device driving motor 63 begin to rotate, and the document illumination lamp 21 lights up. Further, high voltages are also applied to the charger 13, the transfer charger 16, the paper charger 17, and the photoreceptor defrost charger 18, respectively. After a period of time (0.4 seconds in the embodiment of the present invention) for the document illumination lamp 50 to reach a constant illuminance, the motor 60 for driving the optical scanning mechanism starts rotating, and the first and second movable mirrors 25
, 26, and 27 begin to move and scan the original 24.

At the same time, one sheet of copy paper is sent out from the copy paper supply device 40. The electrostatic image corresponding to the document 24 formed on the photosensitive drum 12 by the exposure slit 14 is developed into a toner image by the developing device 15, and is synchronized with the rotation of the photosensitive drum 12 at the position of the transfer charger 16. The toner image is transferred onto the copy paper that is fed in. The copy paper is removed from the surface of the photosensitive drum 12 after its electricity is removed by a charger 17 for paper electricity removal. The copy paper peeled off from the photosensitive drum 12 is then sent to a fixing device 41, the toner image is fixed on the copy paper, the copying is completed, and the copy paper is discharged outside the machine.

After the toner has been transferred to the photosensitive drum 12, residual charges are removed by a charger 18 for removing electricity from the photoreceptor, and residual toner images are removed by a cleaner 19.

The photosensitive drum 12 rotates at a constant speed while the optical scanning mechanism continues scanning the document 24. When the first movable mirror 25 reaches the left end of the original 24, the motor 6 begins to rotate in the opposite direction.

During the outward movement of the first movable mirror 25, the motor 6 rotates in synchronization with the rotation of the photosensitive drum 12;
During the return movement, the synchronization control is removed and there is no control, so the first movable mirror 25 returns to the movement start position at full speed. In the embodiment of the present invention, during the forward motion of the first movable mirror 25, the motors 60, 6
1 and 62 rotate, the first movable mirror 25 requires 1.5 seconds for its forward movement, while the return movement is completed in 0.4 seconds. The toner image on the photosensitive drum 12 is transferred to copy paper, and the copy paper is discharged from the fixing device 41 to the outside of the machine, completing one copying operation. Therefore, even after the optical scanning mechanism completes document scanning and the motor 60 stops, the motor 6
1, 62, and 63 will continue to rotate for a while. When copying two or more sheets in succession, the motors 61, 62, 6
3 continues to rotate at a constant speed, and the motor 60 that drives the optical scanning mechanism repeats forward and reverse rotation at intervals of 1.5 seconds and 0.4 seconds.

Note that the optical scanning mechanism, photosensitive drum 12, and fixing device 41
The rotors are rotated synchronously at a constant speed at very fine time intervals by the control circuit described earlier.

Therefore, the image corresponding to the original is copied onto the copy paper without being expanded or contracted. FIG. 6 shows a side sectional view of another embodiment of the invention.

In this embodiment, unlike the previous embodiment, the document counterfeit table 100 is moved back and forth linearly from side to side, and a light-concentrating glass fiber transmission body is used to make the apparatus more compact. That is, the embodiment shown in FIG. 6 differs from the previous document fixed type device in that the movable mirror for scanning the document is removed, and instead, the document layer table 100 can be moved back and forth linearly from side to side. The image of the original written thereon is projected onto the surface of the photosensitive drum 12 through the light-concentrating glass fiber transmission body 101. The light-concentrating glass fiber transmission body 101 is also called an optical fiber lens, and is made by arranging glass fibers each having a diameter of about 1 rib and having a light-concentrating property and having a length of about 3 fibers arranged by the width of the photosensitive drum. Each one of them acts as a lens.

A mirror image of the original is projected at a position away from the surface of the light-concentrating glass fiber transmission body 101. In the embodiment shown in FIG. 6, an optical scanning mechanism drive motor 60' has a gear attached to its shaft, and a rack (
(not shown), so that the document layer table 100 is reciprocated by rotation of the motor 60 in two directions, forward and reverse, as described above.

In this case, no special member is required as the exposure slit, and the glass fibers arranged in parallel themselves act as the slit.

The rest is essentially the same as the embodiment shown in FIG.

As is clear from the above description, in the present invention, the rotating sleeve of the magnetic brush developing device is driven to rotate at a constant speed by a motor equipped with a rotational speed detection means, in other words, a motor having a constant speed control function. , it is possible to eliminate uneven rotation caused by variations in the driving torque of the rotating sleeve. As a result, the generation of noise, which has heretofore been considered to be characteristic of magnetic brush development, can be minimized, and an extremely quiet electrophotographic copying apparatus can be realized. In particular, if a flat DC motor such as the one shown in the illustrated embodiment is used as the motor, the efficiency can be improved and the size can be reduced, which is extremely advantageous in making the copying apparatus itself more compact.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of a main part of an embodiment of the present invention, FIG. 2 is a perspective view of a main part of the same embodiment, and FIG. 3 is a side sectional view of a main part of an example of a drive motor used in the same embodiment. , FIG. 4 is a sectional view of a main part of the same embodiment, FIG. 5 is a configuration diagram of a main part of the drive system of an optical scanning device in the same embodiment, and FIG. 6 is a side view of another embodiment of the present invention. FIG. 10,100... Original calendar stand, 11... Copying device main body, 12... Photosensitive drum, 13... Charger, 14... Exposure slit, 15.・・・・・・
Developing device, 16...Transfer charger, 17...
・Charger for paper neutralization, 19 ・・Cleaner, 24
...Manuscript, 25...First movable mirror, 26,2
7...Second movable mirror, 31...Lens,
32... Rotating sleeve, 33... Permanent magnet, 34... Toner supply device, 40... Copy paper supply device, 41... Fixing device, 50... ...Lamp, 63...Developing device drive motor, 67,
78...Gear, 70...Slit disk, 7
2... Light emitting element, 73... Light receiving element. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Scope of Claims] 1. A rotatable photosensitive drum having an electrophotographic photoreceptor on its surface, a charging device that applies an electric charge to the surface of the electrophotographic photoreceptor, and an electrophotographic photoreceptor charged by the charging device. an optical scanning device that projects an optical image of a document to be copied onto its surface; and a developing device that uses toner to develop an electrostatic latent image formed on the surface of the electrophotographic photoreceptor by the optical scanning device. , an electrostatic transfer type electrophotographic copying apparatus comprising a transfer device for transferring the toner image developed by the developing device onto copy paper, and a fixing device for fixing the toner image transferred to the copy paper, The developing device uses a magnetic brush type that includes a rotating sleeve and a permanent magnet disposed inside the developing device, and the magnetic brush developing device is controlled at a constant speed and equipped with a rotational speed detection means. An electrophotographic copying apparatus characterized in that it is configured to be rotated at a constant speed by a DC motor. 2. The electrophotographic copying apparatus according to claim 1, wherein the DC motor is a flat type coreless DC motor that generates a speed detection pulse signal of approximately 50 pulses per rotation of the motor. Device.