JPH0934282A - Transfer brush device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transfer brush device capable of properly changing a transfer output in accordance with humidity, the material quality of paper, the thickness of the paper, etc., without installing any current control circuit. SOLUTION: The device is provided with the rotatably supported transfer brush 12 with many flexible conductive brush bristles which are so long to come into contact with the rear side of a transfer belt 20 planted on the circumferential surface of a conductive cylindrical body, a DC power source 29 for supplying a power to the brush bristles of the transfer brush 12, a cylindrical body rotary driving motor 26 which is connected to the shaft core of the cylindrical body, detecting means 32, 33 and 34 for detecting a physical quantity (humidity, etc.) which gives an influence to the decision of the transfer output, a storing means for storing the corresponding relation between the physical quantity and the rotating speed of the motor 26 for enabling the transfer output decided in accordance with the physical quantity, and a control means for reading the rotating speed corresponding to the detection result from the storing means and rotary-driving the motor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for transferring a toner image on an image carrier (eg, a photoconductor) to a transfer material such as paper by electrostatic attraction. Specifically, it relates to an apparatus using a transfer brush.

[0002]

2. Description of the Related Art A uniformly charged photoconductor is exposed to form an electrostatic latent image, the electrostatic latent image is developed with toner and visualized, and the toner image is electrostatically attracted onto a sheet. There is provided a so-called electrophotographic image forming apparatus (analog and digital copying machine, facsimile, printer) in which the image is transferred onto the sheet and then fixed by thermocompression.

In the above image forming apparatus, as a means for transferring toner onto a transfer material (paper) by electrostatic attraction, there is an apparatus utilizing corona discharge. However, a device using corona discharge has a problem of ozone generation. Therefore, as a countermeasure against ozone, a device for supplying electric charges using a transfer brush has been proposed or provided.

For example, in Japanese Laid-Open Patent Publication No. 59-30548, conductive brushes are planted at 90 ° intervals on the circumferential surface of a cylinder to form four rows of brush strips. An apparatus is disclosed in which the tip of the brush is brought into contact with a sheet or the like to supply an electric charge. In this device, by intermittently rotating the cylinder by 90 °, it is possible to avoid that the brush tips of the same brush band are kept in contact with the paper or the like for a long time. And hair loss is reduced.

[0005]

In the conventional transfer brush, since the effect of preventing the settling of the brush and the loss of bristles is incomplete, the pressure contact force at the tip of the brush changes over time, and the transfer output changes. There's a problem. In order to maintain the optimum transfer output of the transfer brush, for example, a mechanism for pressing the entire brush against the transfer material or the like (paper, transfer belt, transfer drum) is required. Increase complexity, size, and price. An object of the present invention is to provide a transfer brush device that can maintain an optimum transfer output for a long period of time without complicating the mechanism.

In the conventional transfer brush, even if the transfer output (the amount of charge supplied from the transfer brush to the transfer material etc.) is the same, the humidity changes or the material and thickness of the transfer material change. If this happens, the amount of toner electrostatically attracted will change, and there is the problem that an image of the desired image quality cannot be obtained.

For example, under high humidity, it is triboelectrically charged.
The charge amount of the toner in the component-based developer decreases. For this reason,
If the transfer output is controlled to be the same as in the case of standard humidity, the amount of toner electrostatically attracted will be smaller than in the case of standard humidity, and the image quality will be degraded. In addition, after the toner is transferred (primary transfer) to a transfer belt which is an intermediate transfer material, it is transferred (secondary transfer) from the transfer belt onto a sheet (example: JP-A 3-1).
In the configuration as disclosed in Japanese Patent No. 92279),
Under high humidity, the volume resistance of the belt is reduced, and the electric charge easily flows out. Therefore, if the transfer output is controlled to be the same as in the case of standard humidity, the amount of toner electrostatically attracted is smaller than in the case of standard humidity, and the image quality is degraded.

Further, the volume resistance of thick paper is larger than that of standard paper. Therefore, when the transfer output is controlled to be the same as in the case of the standard paper when the thick paper is fed as the transfer material, the charge amount held on the thick paper does not reach the desired value, and as a result,
The amount of toner that is electrostatically attracted decreases as compared with the case of standard humidity, and the image quality deteriorates.

In order to solve the above problems, it is necessary to appropriately change the transfer output according to the humidity, the material of the transfer material, the thickness of the transfer material, and the like. For that purpose, the amount of current supplied to the transfer brush may be appropriately controlled, but in that case, a circuit for current control is required, which complicates the circuit configuration. In particular, when trying to finely control the changing step of the transfer output, the degree of complication of the configuration increases.
The present invention provides a transfer brush device that can appropriately change the transfer output according to environmental changes such as humidity and the material and paper thickness of the paper to be fed without complicating the circuit configuration. The purpose is to

[0010]

According to the present invention, a large number of flexible conductive brush bristles are planted on the peripheral surface of a conductive cylindrical body, and the peripheral surface of the cylindrical body and the surface to which transfer charges are supplied are provided. Is rotatably supported at a position where the distance is shorter than the length of the brush bristles, a power source for supplying power to the bristles of the transfer bristles, and a shaft of the cylinder for rotating the cylinder. A motor, a detection unit that detects a physical quantity that influences the determination of the transfer output, and a storage unit that stores the correspondence relationship between the physical quantity and the rotation speed of the motor that realizes the transfer output that is determined corresponding to the physical quantity. A rotation speed corresponding to the detection result of the detection means, and a control means for driving the motor so that the rotation speed becomes the rotation speed, the toner obtained by toner-developing the charge latent image. The image is transferred by electrostatic attraction. A transfer brush device for transferring the wood.

When the rotation speed of the transfer brush becomes higher than the standard, the number of times of contact between the supply surface and the brush bristles increases more than the standard. As a result, the amount of electric charge per unit time supplied to the surface to be supplied via the brush bristles becomes larger than the standard amount. Therefore, by controlling the rotation speed of the motor, that is, the rotation speed of the transfer brush according to the detected value of the physical quantity, the transfer output is supplied so that the charge amount corresponding to the detected value is supplied to the transfer surface. It becomes possible to control.

Further, as the brush bristles, the tip ends hang down under its own weight when it is not rotated and does not come into contact with the transfer surface.
When a brush bristle having a material and a diameter that gradually rises due to centrifugal force and contacts the transfer surface during rotation is used, by controlling the rotation speed as described above, the unit time between the supply surface and the brush bristle is controlled. It is possible to control the number of contacts per hit and the amount of contact (contact length) per hit. Further, in this case, since the brush bristles do not come into contact with the surface to be transferred when the brush is not rotated, it is possible to completely prevent the brush bristles from being worn out when the brush is not operated.

Such brush bristles have, for example, 3 to 8d.
30d / 10f of fiber with pile width of about (denier)
(Filler) ~800d / 100f pile bundles of 10 ²
-10 ⁵ (f / inch ² ) with a pile density of 10-20
It can be realized by adjusting the pile length to about mm. If the stiffness of the waist is out of the above range, the tip of the brush is attracted to and comes into contact with the transfer surface due to electrostatic force. When the waist strength is out of the above range, the tips of the brush bristles come into contact with the transfer surface even when the brush is not rotated. It should be noted that about 10 ¹ to 10 ³ rpm is appropriate as the rotation speed of the transfer brush.

As the material of the brush bristles, it is possible to use, for example, a material in which conductive carbon is dispersed in nylon, rayon, acrylic, etc., and the resistance value is adjusted to about 10 ³ to 10 ⁵ Ω.

The physical quantity includes, for example, humidity, the thickness and material of the paper fed as the transfer material, and the total number of copies corresponding to the change over time. That is, when the humidity is higher than the standard, the charge amount of the toner in the two-component developer that is frictionally charged decreases, and it becomes difficult to transfer the toner. Therefore, it is necessary to change the rotational speed of the transfer brush in order to change the transfer output according to the humidity. Further, in the case of an intermediate transfer belt made of a material such that the volume resistance of the belt decreases and charges easily flow out when the humidity is higher than the standard as in the above-mentioned Japanese Patent Laid-Open No. 3-192279, the toner is high under high humidity. Becomes difficult to inhale. Therefore, it is necessary to change the rotational speed of the transfer brush in order to change the transfer output according to the humidity. Further, in the case of thick paper, the volume resistance thereof is larger than that of standard paper, so that it is difficult to receive electric charges, and thus it is difficult to suck toner. Therefore, it is necessary to change the rotation speed of the transfer brush in order to change the transfer output according to the thickness of the transfer material. This also applies to the case where the volume resistance differs depending on the material of the transfer material (whether it is plain paper, OHP sheet, etc.). In addition, when the brush bristles become worn due to aging, and it becomes more difficult for the tip to contact the transferred surface compared to the initial mounting, the rotational speed of the transfer brush should be adjusted to restore the contact state to the initial value. It is necessary to change. The physical quantity corresponding to the change over time includes, for example, the total number of copies, the total number of rotations (transfer brush, motor, transfer belt or transfer drum), and the like.

The supply surface to which the tips of the brush bristles are to be contacted is not only the back surface (inner surface) of the film of the transfer drum, the back surface of the transfer belt, the back surface of the paper to be fed, but also as an intermediate transfer member. There is the back side of the transfer belt.

The transfer belt device of the present invention can be mounted on an electrophotographic image forming apparatus. For example, it can be installed in an analog copying machine, a digital copying machine, an analog single color copying machine, a digital single color copying machine, an analog color copying machine, a digital color copying machine, a single color printer, a color printer, a single color facsimile, a color facsimile and the like.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION

(1) Overview of Image Forming Apparatus First, description will be given with reference to the copying machine of FIG. 1 equipped with the transfer brush device of the present invention. Further, if necessary, description will be made with reference to FIG. 2 showing a main part of FIG. In the copying machine shown in FIG. 1, the transfer belt 20 is electrostatically attracted to the transfer belt (the photosensitive drum 10
And a transfer brush 12). The transfer brush device 12 is provided so as to sandwich the belt 20 at a position facing the photoconductor drum 10.

Around the photosensitive drum 10 which can be rotated clockwise as indicated by an arrow in the drawing, a charger 15 for uniformly charging the surface of the photosensitive drum 10 and a latent charge image on the uniformly charged surface are provided. A print head 9 for exposing to form an image, a developing device for developing the visualized charge latent image with toner and visualizing it.
11, a transfer belt 20 that electrostatically attracts and conveys the paper 30 to transfer the visualized toner image onto the paper 30, a cleaner 13 that removes residual toner on the photoconductor drum 10, and a photoconductor drum
An eraser 14 is provided for exposing and removing 10 residual charges.

The print head 9 is, for example, an LED array that is turned on / off according to image data, but may be a laser head that performs laser exposure according to image data. Further, it may be an optical system that guides the reflected light of the original image as it is or by changing the magnification. In this copier, the image on the lower side of the original paper placed on the original glass is exposed by the exposure lamp 1,
First mirror 2, second mirror 3, third mirror 4, lens system
Exposure scanning is performed by a scanning optical system equipped with 5, etc., and the image reflected light is imaged on the image sensor 6 and converted into an electric signal, and this is subjected to LED exposure (or laser exposure) in the image processing circuit 7.
After the image data is converted into image data for use in the LED drive circuit (or laser drive circuit) 8 and the drive circuit 8 drives the print head 9, the image is evenly charged on the photosensitive drum 10. To form a latent charge image corresponding to.

The charge latent image formed in this manner is developed by a developing device.
Although it is visualized by developing toner with 11, the developing device 11 is not limited to a developing device for developing with black toner,
It may be developed with color toner. Further, a total of four developing devices containing cyan C, magenta M, yellow Y, and black Bk toners are prepared, and development is performed by any one developing device selected in order, and each toner image is developed. An apparatus configured as a so-called developing unit, which is configured to form a full-color image by superposing the above on the transfer belt 20, may be used.

The transfer belt 20 is stretched around a driving roller 16 and a driven roller 27. The transfer belt 20 is rotationally driven counterclockwise as indicated by an arrow in synchronization with the photoconductor drum 10. This drive is performed by the drive roller 16 rotated by a motor (not shown). In this example, the material of the transfer belt 20 is a semi-conductive rubber belt whose electric resistance is set to 10 ⁹ Ωcm by dispersing conductive carbon, but PVDF (polyvinylidene fluoride), PC (polycarbonate) or the like is used as the material. It is also possible to use a film type belt made of, or a rubber belt made of CR rubber, urethane rubber, or the like.

Inside the transfer belt 20, the photosensitive drum 10
There is provided a transfer brush 12 which supplies electric charges so as to electrostatically transfer the toner image of the above onto the sheet 30 conveyed by the transfer belt 20. The transfer brush 12 is driven by a motor 26 and rotated clockwise as indicated by an arrow in the figure. The transfer brush 12 will be described later in detail.

Further, in the vicinity of the transfer belt 20, a separation charger 17 for separating the paper 30 from the transfer belt 20, a belt cleaner 18 for cleaning the outer peripheral surface of the transfer belt 20, and static electricity removal for the inner and outer surfaces of the transfer belt 20. A pair of static eliminator chargers 19,
A driven roller 27 that is connected to a DC power source 28 and is applied with a voltage having the same polarity as or a polarity opposite to that of the toner on the photosensitive drum 10, and a grounded conductive counter guide 31 that is provided so as to face the driven roller 27. Etc. are provided. In addition, static elimination charger
19 can be omitted by adjusting the electric resistance of the transfer belt 20 to about 10 ⁸ Ωcm and taking measures such as keeping the driving roller 16 electrically conductive and grounded. Alternatively, it can be omitted by bringing a grounded metal plate or metal roller into contact with the transfer belt 20.

During the image forming operation, the paper 30 picked up by the paper feed roller from one of the paper trays 21 and 22 is guided to the timing roller by the guide and the conveyance roller,
After being synchronized with the photosensitive drum 10 by the timing roller, the transfer belt 20 is connected by the electrostatic attraction force from the driven roller 27 which is connected to the DC power source 28 and has a predetermined potential.
Is electrostatically adsorbed by.

When the sheet of paper 30 attracted to the transfer belt 20 and conveyed in the direction of the arrow in the drawing reaches the transfer position (between the transfer brush 12 and the photoconductor drum 10), the transfer brush 12 supplies electric charge to the transfer belt 20. To be done. The details will be described later. When electric charges are supplied to the transfer belt 20, the toner image visualized by developing the toner by the developing device 11 on the photosensitive drum 10 is statically transferred onto the paper 30 carried on the transfer belt 20. Electronically transferred.

After the toner image is transferred, the sheet 30 is conveyed to the left in the figure, the electrostatic attraction force is released by the separation charger 17, the sheet is separated from the transfer belt 20, and the sheet is sent to the fixing device 24 by the guide 23. After being subjected to image fixing processing by thermocompression bonding, the sheet is discharged onto the sheet discharge tray 25. Further, the transfer belt 20 after the paper 30 is peeled off is cleaned by the belt cleaner 18 on the outer peripheral surface thereof, and further, the neutralization charger 19 is used.
As a result, the residual charges on the inner and outer surfaces are eliminated, and the sheet is returned to the above-mentioned sheet suction position.

In FIG. 2, 32 is a humidity sensor that detects humidity and sends the detection result to the microcomputer 50 (see FIG. 8), and 33 is the humidity sensor that detects the thickness of the paper 30 and sends the detection result to the microcomputer 50. The paper thickness sensor for sending 34 is a counter for counting the number of papers on which the toner image is transferred by the transfer brush 12 and sending the count result to the microcomputer 50. The control using these will be described in detail later.

(2) Details of Transfer Brush 12 As described above, the transfer brush 12 is provided at a position facing the photoconductor drum 10 with the transfer belt 20 interposed therebetween, and is driven to rotate by the motor 26. There is. This transfer brush
As shown in FIG. 3, the reference numeral 12 is formed by implanting a large number of flexible conductive bristles on the peripheral surface of a conductive cylindrical body.

When the conductive brush bristles are planted in the tangential direction of the peripheral surface of the cylindrical body as shown in FIG. 3C, the brush bristles are transferred as shown in FIG. 3A when stopped. Belt 20
Although it does not come into contact with the back surface of the transfer belt 20, it gradually rises due to centrifugal force during rotation and comes into contact with the back surface of the transfer belt 20 as shown in FIG. Further, because of such a configuration, when the rotation speed is slow, only the tip portion of the brush bristles contacts the back surface of the transfer belt 20, and as the rotation speed increases, not only the tip portion of the brush bristles but also the tip. To a part of a certain length come into contact. That is, the contact amount changes according to the rotation speed. Further, in order to realize this function, that is, the function of changing the contact amount according to the rotation speed, the distance between the peripheral surface of the cylindrical body and the back surface of the transfer belt 20 is shortened to a certain extent smaller than the length of the brush bristles. Is provided.

On the other hand, when the conductive brush bristles are planted in a direction substantially perpendicular to the peripheral surface of the cylindrical body as shown in FIG. 3D, it is more than in the case of FIG. Also, by selecting soft brush bristles, it is possible to achieve the same function as in the case of FIG. That is, in the case of a soft brush bristle, the tip portion hangs down by its own weight when stopped, so that it does not contact the back surface of the transfer belt 20,
When rotating, the transfer belt gradually rises due to centrifugal force
It comes into contact with the back of 20. Further, also regarding the control of the contact amount by the rotation speed, it is possible to set the distance between the peripheral surface of the cylindrical body and the back surface of the transfer belt 20 as in the case of FIG. Is.

As described above, since the back surface of the transfer belt 20 does not come in contact with the transfer belt 20 when stopped, and the back surface of the transfer belt 20 comes into contact with the back surface of the transfer belt 20 gradually during rotation, the tip of the brush bristles stays in a non-operating state. It is possible to prevent creep and fatigue due to contact with the back surface of the transfer belt 20,
Brush life can be extended. In addition, since the bristle having weak stiffness can be used, the range of brush bristle selection can be expanded. Further, unlike the conventional configuration, the transfer brush is not pressed against the back surface of the transfer belt 20 by the force of a spring or the like,
Because it is configured to gradually contact by the centrifugal force of rotation,
There is no impact at the time of pressure contact by a spring or the like, and therefore, it is possible to prevent transfer defects such as hollowing out.

As such brush hair, nylon,
Conductive carbon is dispersed in rayon, acrylic or the like to adjust the resistance value to about 10 ³ to 10 ⁵ Ω.
Fiber with pile width of about d is 30d / 10f to 800d
/ 100f pile bundle, 10 ² to 10 ⁵ (f / inch
^With the pile density of ² ), the pile length adjusted to about 10 to 20 mm can be used. In addition, when the elasticity is outside the above range and the waist is weak, the bristle bristle cannot be adopted because the tip of the brush is attracted to and comes into contact with the transfer surface due to electrostatic force. Further, a brush bristle that is out of the above range and has a strong rigidity cannot be adopted because the tip of the brush bristle contacts the transfer surface even when the brush bristle is stopped.

Further, in this apparatus, the transfer brush is rotated in the direction of the arrow (clockwise) shown in the figure.
It is the same as the rotation direction of the photosensitive drum 10. Therefore, the charge density on the downstream side of the transfer position can be made higher than that on the upstream side, and a good transferred image without so-called pre-transfer can be obtained.

(3) Control of Transfer Output (Rotation Speed) As shown in FIGS. 4 to 6, the transfer brush 12 of the present invention is controlled according to humidity, paper thickness, and total copy count.
The rotation speed is changed. As a result, the optimum transfer output can always be performed regardless of the humidity, the thickness of the paper, and the change over time, and a transfer image with good image quality can be obtained.

First, the drive circuit 63 and the control circuit of the motor 26 capable of switching the rotation speed of the transfer brush 12 as described above will be described with reference to FIGS. 7 and 8. As shown in FIG. 7, the motor 26 is connected to the DC power supply E via four bridge-connected switching transistors Tr1 to Tr4.
Transistors Tr1 and Tr3 are turned on when the base voltage is "low", and transistors Tr2 and Tr4 are turned on when the base voltage is "high".・ It can be controlled to reverse and stop.

Diodes D1 to D4 are respectively connected in parallel to the transistors Tr1 to Tr4 to form a bypass when a counter electromotive voltage is generated.

At one input terminal B, a signal "b" which is either a "high level signal" which is a normal rotation signal or a "low level signal" which is a reverse rotation signal is supplied to the one-chip microcomputer 50 shown in FIG. Input from the output port 55 of. The input terminal B is connected to the input side of the AND gate AND1 and the base of the transistor Tr1. The input terminal B is connected to the input side of the AND gate AND2 and the base of the transistor Tr3 via an inverter. In the case of the device of the present invention, since the transfer brush 12 rotated by the motor 26 is rotated only in the direction of the arrow shown in the figure, the input terminal B receives only the “high level signal” which is the normal rotation signal. Is entered.

The other input terminal A has a P for energizing the motor.
The WM pulse a is the one-chip microcomputer of FIG.
Input from 50 PWM output ports 56. This PWM pulse a is a "high level signal" which is an energization ON signal,
It consists of a "low level signal" which is an energization off signal. The voltage determined by the ratio of the output times of these two signals is the motor
Supplied to 26. As a result, the motor 26 is rotationally controlled at a speed corresponding to the ratio of the output times of the two signals. That is, PWM control is performed.

In the case of this apparatus, the PWM pulse a for energizing the motor is set so that the rotation speed of the motor 26 becomes a speed (see FIGS. 4 to 6) which is determined according to humidity, paper thickness and copy count number. Is set. That is, the encoder 65 detects the rotation speed of the motor 26 as a frequency signal FG, the waveform shaping circuit 67 converts it into an encoder pulse c, and the encoder pulse c is taken into the timer unit. In the timer unit, based on the system clock fCLK supplied from the oscillation circuit 57 and the encoder pulse c, the CP
PWM pulse a corresponding to the set speed given by U51
Is generated and is output as a PWM pulse a from the PWM output port 56 to be input to the input terminal A of the motor drive circuit 63.

The input terminal A is connected to the input side of the AND gate AND1 and the input side of the AND gate AND2, respectively. That is, as described above, only the forward rotation signal is input in this device, but the rotation speed of the motor 26 is controlled by the PWM pulse a that is input while the forward rotation signal is being input.

In FIG. 8, the one-chip microcomputer 50 including the CPU 51 is dedicated to the rotation control of the motor 26, and is controlled by the master CPU 61 which controls the operation of the copying machine. The CPU 51 takes in humidity from the humidity sensor 32, paper thickness from the paper thickness sensor 33, and total copy count from the counter 34 via the input port 54, and stores the respective detected values in the ROM 54. By comparison with the tables of FIGS.
The rotation speed of the motor is set and this set value is given to the timer unit. In response to this, the timer unit generates and outputs the PWM pulse a corresponding to the set value as described above, and rotates the motor 26 to the set speed. In addition to the above table, the ROM 54
The control program is stored. The RAM 52 is also used for work.

FIG. 4 gives the relationship between humidity and the number of revolutions of the motor 26. That is, as described above, when the humidity is higher than the standard, the charge amount of the toner in the frictionally-charged two-component developer decreases and it becomes difficult to transfer the toner. Therefore, the transfer output is changed according to the humidity. That is, it is necessary to change the number of rotations of the transfer brush, and this relationship is given by FIG. As shown, when the detected humidity is 15% or less, the CPU 51 sets 2 × 10 ² rpm, and when the detected humidity is 85% or more, the CPU 51 sets 5 × 10 ² rpm. Further, when the detected humidity is 15% to 85%, the CPU 51 sets a value corresponding to the value. By controlling the rotation speed in this way, it is possible to compensate for the change in the toner charge amount due to humidity and obtain a good transferred image.

In FIG. 4, the influence of the change in volume resistance of the belt due to the change in humidity is neglected. That is, FIG. 4 is a characteristic table in consideration of the case where a belt having small environmental dependence is used.

FIG. 5 gives the relationship between the thickness of the fed paper and the rotation speed of the motor 26. That is, as described above, in the case of the paper thicker than the standard, the volume resistance is larger than the standard, so that it becomes difficult to receive the charge and it is difficult to suck the toner. For this reason, it is necessary to change the transfer output according to the thickness of the transfer material, and this relationship is given by FIG. As shown, 3.5 for standard paper thickness
Set × 10 ² rpm is the CPU 51, when the thickness of the paper is thin set 2 × 10 ² rpm is the CPU 51, when the thickness of the sheet is thick, 5 × 10 ² rpm the CPU
Set by 51. Here, the thickness of the paper is, for example,
The sheet can be sandwiched between the conductive rollers and a current can be applied to the front and back sides of the sheet to detect the current value. By controlling the rotation speed in this way, it is possible to compensate for the change in the toner suction force due to the thickness of the paper and obtain a good transferred image.

FIG. 6 gives the relationship between the total copy count number and the rotation number of the motor 26. That is, as mentioned above,
When it becomes more difficult for the tip of the brush bristles to come into contact with the transferred surface due to aging compared to the initial stage of mounting, it is necessary to change the rotational speed of the transfer brush in order to return the contact state to the same level as in the initial stage of mounting. , This relationship is given by FIG. As shown in the figure, 3 × 10 ² rpm at the beginning of mounting
Is set by the CPU 51, and the number of revolutions is increased stepwise as the copy count number increases. After the CPU 51 sets the rotation speed to 4 × 10 ² rpm, when the copy count reaches a certain value (10 ² k (km) times in the figure), it is considered that the life of the transfer brush 12 is reached. The above increase in the number of rotations is not performed. in this case,
The transfer brush 12 is instructed to be replaced. By controlling the rotation speed in this way, it is possible to compensate for a change in transfer output due to a change over time and obtain a good transferred image.

In the above description, the number of rotations of the motor 26 is controlled separately according to the humidity, the paper thickness, and the copy count, but they may be controlled in combination. Further, although the present invention has been described above in the context of a transfer belt type image forming apparatus, a transfer drum type image forming apparatus, an image forming apparatus using a transfer drum as an intermediate transfer member, and The present invention can of course be applied to an image forming apparatus of the type in which paper is directly fed between the photoconductor drum and the transfer belt.

In the above description, the rotation speed control of the present invention has been described in the context of a DC motor whose rotation speed is controlled by PWM control. However, in the present invention, the transfer brush 12 is set at the speed set by the CPU 51. It suffices if the drive motor for the vehicle can be rotationally controlled. Therefore, a stepping motor may be used in place of the DC motor 26, and the rotation speed may be controlled by the drive circuit for the stepping motor. Known circuits can be used as the stepping motor and its drive circuit.

[0049]

According to the present invention, the brush bristles and the surface to be transferred (film of the transfer drum) are controlled by controlling the rotational speed of the transfer brush in accordance with physical quantities such as humidity, thickness and material of transfer material, and degree of change over time. , The back surface of the transfer belt, the back surface of the paper, the back surface of the transfer belt as an intermediate transfer member) and the contact amount per unit time (length) are changed, The transfer output (supplied charge) is optimized. Therefore, the toner image can be appropriately transferred with the optimum electrostatic attraction force according to the physical quantity such as the detected humidity, so that the image with the optimum image quality can be obtained.

Further, since the transfer output is changed by changing the rotation speed of the motor for driving the transfer brush, it is not necessary to provide a complicated current control circuit for controlling the current supplied to the transfer brush, and the structure is improved. Is easy.

[Brief description of drawings]

FIG. 1 is a schematic view showing a mechanism of a copying machine equipped with a transfer brush device of the present invention.

FIG. 2 is a schematic diagram showing a main part of FIG. 1;

FIG. 3 is an explanatory view showing an example of a transfer brush of the present invention.

FIG. 4 is an explanatory diagram of a motor rotation speed controlled in accordance with humidity.

FIG. 5 is an explanatory diagram of a motor rotation speed that is controlled according to a sheet thickness.

FIG. 6 is an explanatory diagram of a motor rotation speed that is controlled according to the copy count number.

FIG. 7 is a circuit diagram showing a motor drive circuit.

FIG. 8 is a block diagram showing a control circuit of a motor.

[Explanation of symbols]

 12 Transfer brush 26 Motor 32 Humidity sensor 33 Paper thickness sensor 34 Paper detection sensor

Claims (1)

[Claims] 1. A large number of flexible conductive bristles are planted on the peripheral surface of a conductive cylindrical body, and the distance between the peripheral surface of the cylindrical body and the surface to which the transfer charge is supplied is the length of the brush bristles. A transfer brush rotatably supported at a shorter position, a power supply for supplying the brush bristles of the transfer brush, a motor connected to the shaft of the cylinder to rotate the cylinder, and a transfer output determination Detection means for detecting a physical quantity that affects the physical quantity, storage means for storing a correspondence relationship between the physical quantity and the rotation speed of the motor that realizes a transfer output determined in correspondence with the physical quantity, and a detection result of the detection means And a control means for driving the motor so that the rotation speed corresponding to the above is read from the storage means to the rotation speed, and the toner image obtained by toner-developing the charge latent image is electrostatically attracted. A transfer block that transfers to a transfer material Rashi device.