JP2000242059A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a miniaturized inexpensive image forming device making the color image being free from deviation in a developing position formed by respectively performing the attachment and detachment of the developing device with a photoreceptor belt, in a color image forming device making the color image formed by successively bringing plural image forming device into contact with a photoreceptor in an endless belt shape. SOLUTION: This image forming device is constituted so as to respectively hold developing device 10Y, 10M, 10C and 10B in contact and separation of the photoreceptor belt 1 by cam 19 respectively brought into press contact with and apart from the developing device, and so as to control the rotation of the rotary shaft 20 fixing the cam 19 by the drive of the motor. Moreover, the position control of the cam 19 is respectively performed by fixing a light shielding blade provided with plural slit respectively in different size and an optical transparent type sensor recognizing transmission light from the light shielding blade on a rotary shaft 20 of the cam.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used for a copying machine, a printer, a facsimile, and the like using an electrophotographic recording system.

[0002]

2. Description of the Related Art In a color image forming apparatus for forming a color image by an electrophotographic system, a plurality of developing devices containing toners of different colors are successively brought into contact with a photosensitive member to perform development. A color image is formed by superimposing toner images of the respective colors on top. In such a color image forming apparatus, as a method of sequentially switching a developing device for each color toner and bringing the developing device into contact with the photoreceptor belt, a plurality of developing devices are mechanically moved using a quarter-turn clutch, a solenoid, or the like. A method of performing switching is known. For example, the Journal of the Institute of Electrophotography, Vol. 28, No. 4, (1989)
On page 408, a method is described in which a plurality of developing devices are sequentially rotated by a rotary mechanism to abut on a photosensitive drum to form a toner image with toner of each color. Japanese Patent Application Laid-Open No. Hei 5-61339 has a separation / spring spring and a solenoid-type pressing device. Each developing device is moved horizontally to switch between a contact state and a separation state with respect to the photosensitive drum. A method of doing so is disclosed.

A color image forming apparatus has been put to practical use in many copying machines and laser printers and has been developed.
In recent years, a configuration has been developed in which a latent image formed on an endless belt-shaped photoconductor is developed with toner of each color, the formed toner images of each color are further combined on an intermediate transfer body, and then collectively transferred onto a recording medium. It has been used. A method of contacting the photosensitive belt with the developing device is disclosed in Japanese Patent Application Laid-Open No. 9-80.
As disclosed in Japanese Unexamined Patent Publication No. 860, four backup rollers movably supported within a predetermined range by a cam mechanism or the like are provided on an inner peripheral portion of a photoreceptor belt stretched around a rotating roller. In this technique, the photoconductor belt is moved in pairs for each developing device, and the photoconductor belt is sequentially contacted with each developing device by changing the running route while keeping the running length of the photoconductor belt constant. Have been.

[0004]

However, the above-mentioned prior art has the following problems. The method described in the Journal of the Electrophotographic Society, Vol. 28, No. 4, (1989), p. 408 and the method described in JP-A-5-61339, move the entire developing device filled with toner to the photoconductor side. In order to accurately position the developing device with respect to the photoconductor drum, the mechanism for switching the position of the developing device needs to have sufficient precision and rigidity to fit such a developing device. In addition, there is a problem that the size of the apparatus is increased and the manufacturing cost is increased.

In the method disclosed in Japanese Patent Laid-Open No. 9-80860, the developing device is fixed, and the photosensitive belt is brought into contact with the developing device by a small switching mechanism.
Although this is effective in reducing the size of the device, it cannot suppress an increase in manufacturing cost due to an increase in the number of components.

Accordingly, the present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a color image forming method in which a plurality of developing devices are sequentially brought into contact with an endless belt-shaped photosensitive member to form a color image. In the image forming apparatus, a small-sized image forming apparatus capable of forming a color image without a shift in the developing position is provided at a low cost by performing the contact between each developing device and the photosensitive belt at an accurate position. It is to be.

[0007]

In order to solve the above-mentioned problems, the present invention is directed to a color image forming apparatus for developing a latent image on a photoreceptor belt by a plurality of developing devices. A rotating shaft rotatably supported at a position facing the photoreceptor belt via a shaft, a cam eccentrically fixed to the rotating shaft, and a motor for rotating and driving the rotating shaft. Then, the cam is pressed against the developing device, and the developing device is displaced to provide a color image forming device that comes into pressure contact with the photosensitive belt. In such a color image forming apparatus, contact and switching between the developing device and the photoreceptor belt are performed by a simple mechanism that rotates individual rotating shafts to which the cams are attached by using only a motor without using a clutch or a solenoid. Therefore, the manufacturing cost can be reduced. In addition, since the individual components for switching the developing device are small, the size of the device can be reduced.

[0008] The invention described in claim 2 is the first invention.
In the image forming apparatus described in the above, a light blocking plate rotatably supported on a rotation axis of the cam, and having a plurality of slits having different sizes corresponding to the stop positions of the cam, and sandwiching the light blocking plate And a light transmission type sensor arranged at
A color image forming apparatus is provided in which the light transmission sensor identifies transmitted light transmitted through the slit of the light blocking plate based on an angle from the rotation axis, and determines the position of the cam.
In such a configuration, light transmitted from a plurality of slits of the light blocking plate is identified by one light transmission type sensor, thereby reducing manufacturing costs while achieving accurate control as well as mechanical control using a clutch or a solenoid. It is possible to stop the cam at a correct position by performing a proper position control.

Further, according to a third aspect of the present invention, in the image forming apparatus according to the second aspect, each slit of the light shielding plate includes two straight lines passing through a rotation center of the rotation shaft, and Provided is a color image forming apparatus which is formed in a fan shape surrounded by an arc connecting two linear ends.
Since the individual slits of such a light shielding plate are formed at a fixed angle by two straight lines passing through the center of the rotation axis, the light transmission type sensor can be moved at any distance from the rotation center of the light shielding plate. Even if it is mounted on the cam, it is possible to identify the individual slits, make a correct position determination, and perform accurate position control of the cam.

According to a fourth aspect of the present invention, in the image forming apparatus of the first, second or third aspect, the cam has a pressing area for pressing the developing device. And the arc of the cam in the pressing area is
An image forming apparatus that matches an arc of a circle around the rotation axis. As described above, the pressing of the developing device by the cam is performed by the pressing region formed on the cam, and the cam presses the developing device with a constant pressure in the pressing region. Even after the output is turned off, if the motor does not stop immediately due to the inertial force, the contact state between the developing device and the photoreceptor belt is kept constant as long as the cam is within the contact range with the developing device. Can be kept.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a color image forming apparatus according to the present invention will be described below with reference to the drawings. [First Embodiment] FIG. 1 is a schematic configuration diagram showing an embodiment of a color image forming apparatus according to the first, second and third aspects. This image forming apparatus is formed in an endless belt shape, and has a photoreceptor belt 1 laid over a driving roller 3 and a driven roller 4, and four developing devices 10Y, 10M,
The latent images formed on the photoreceptor belt 1 are developed by developing devices for the respective color toners.

The above four developing devices 10Y, 10M, 10M
C and 10B respectively contain yellow toner, magenta toner, cyan toner, and black toner, and perform development with the respective color toners, and face the photosensitive belt 1 stretched by the driving roller 3 and the driven roller 4. Are arranged along the rotation direction of the photoconductor belt 1 and are movably supported on the photoconductor belt 1 side. The developing devices 11Y, 10M, 10C, and 10B are provided at positions facing the photosensitive drum 1 with the developing rollers 11Y and 1Y.
1M, 11C and 11B are rotatably supported.

Each of the developing devices 10Y, 10M, 10M
A cam 19 is arranged close to the other ends of C and 10B. These cams 19 are respectively eccentrically inserted through the rotating shaft 20, and the rotating shaft 20 is fixed by the gear 22 and rotates simultaneously as shown in FIG. 4, so that the four cams 19 always have the same phase difference. Rotate. As shown in FIG. 5, the rotary shaft 20 of the cam has a position corresponding to the stop position of the cam 19.
A light shielding plate 23 provided with a slit 25 having a different size every two degrees is fixed.
The light transmission sensor 24 is supported at the position 5 with the light blocking plate 23 interposed therebetween. These are rotation control mechanisms for controlling the rotation of the cam 19, and rotate at the same speed as the rotation of the cam 19.

Next, the operation of the image forming apparatus will be described. When the image forming operation is stopped, as shown in FIG. 2, the cams 19 corresponding to the four developing devices 10Y, 10M, 10C, and 10B are stopped at a position where they are held in a non-contact state with the developing devices. In this state, 4
Each of the developing devices 10Y, 10M, 10C, and 10B is held at a position separated from the photosensitive belt 1 by a spring (not shown). An image forming operation is started, and after a latent image for a yellow component is formed on the photoreceptor belt 1 by an exposure unit (not shown), a rotation control mechanism of a cam 19 by a light blocking plate 23 and a light transmission type sensor 24 described later. Is operated, and the cam 19 driven by the motor is pressed against the developing device 10Y for yellow toner. Then, the yellow toner developing device 10Y moves in the direction of the photoconductor 1, and the developing roller 11Y and the photoconductor belt 1 come into contact.
The toner in the yellow toner developing device 10Y is transported by a transport unit (not shown), and is supplied to the surface of the developing roller 11Y. The toner on the developing roller 11Y rotates with the rotation of the developing roller 11Y, is frictionally charged by a toner regulating blade (not shown), is formed into a thin layer, and is conveyed to a position facing the photoreceptor belt 1. When a potential difference is applied between the developing roller 11Y and the photosensitive belt 1 at this position, the yellow toner adheres to the latent image formed on the photosensitive belt 1 and is visualized as a yellow toner image.
The visualized toner image is transferred onto the intermediate transfer belt 2 by the transfer roller 5 to which a voltage is applied. afterwards,
Similarly, magenta, cyan and black toner images are formed on the photoreceptor belt 1 and transferred so as to overlap on the intermediate transfer belt 2 to form a composite color toner image. This composite color toner image is transferred onto the recording medium 18 by the transfer roller 6 to which a voltage has been applied.
When the recording medium 18 onto which the synthetic toner image has been transferred passes between the heating roller 12 and the pressure roller 14, the toner is melted by the heating roller 12 whose surface temperature is controlled, and at the same time, It is pressed against the pressure roller 14 and is fixed on the recording medium 18.

(Mechanism for Controlling Contact of Developing Apparatus to Photoreceptor Belt) A mechanism for bringing the developing apparatus for each color toner into contact with the photoreceptor belt will be described. The four developing devices 10Y, 10M, 10C, and 10B containing the toners of each color are
As shown in FIG. 2 or FIG. These developing devices 10Y, 10Y
The positional relationship between M, 10C and 10B and the photoreceptor belt 1 is as follows.
There are a total of five types in a state where all the developing devices are separated from the photosensitive belt 1 as shown in FIG. 2 and a state where one of the four developing devices is in contact with the photosensitive belt 1 as shown in FIG. State is taken into account. Therefore, in order to perform a color image forming operation accurately and smoothly, it is necessary to control the switching between these five states. In this case, each of the developing devices 10Y, 10M, 10C, and 10B actually contacts and separates from the photoreceptor belt 1 by pressing by the cam 19 and returning by a spring (not shown).
The two cams 19 are eccentric so that a change between a state in which the developing device is pressed and a state in which the developing device is separated from the developing device occurs once while the fixed rotating shaft 20 makes one rotation. 20. The rotating shafts 20 of the four cams are fixed by gears 22 as shown in FIG. 4 and are configured to always rotate simultaneously. Therefore, in order to control the contact / separation between the developing devices 10Y, 10M, 10C, and 10B and the photoreceptor belt 1, the rotation of the cam rotation shaft 20 may be controlled.

As described above, the developing devices 10Y, 10M,
The positional relationship between the photoconductor belt 1 and the photoconductor belt 1 is 5
In order to switch between the two states, the stop positions of the opposed cams 19 are at five positions, and a reference is provided every time the rotation shaft 20 of the cams rotates 72 degrees corresponding to 1/5 rotation, and the motor is stopped. . As described above, a cam rotation control mechanism including the light blocking plate 23 and the light transmission type sensor 24 is fixed to the cam rotation shaft 20 as means for performing control every ５ rotation of the rotation shaft 20. . As shown in FIG. 5, a reference line 2 is provided on the light shielding plate 23 every 72 degrees around the rotation axis 20.
6 are formed, and fan-shaped slits 25 having different sizes are formed based on the reference line 26. This allows
The motor for driving the cam rotation shaft 20 is stopped for each reference line 26, and the five states are accurately determined by the light transmission type sensor 24. In addition, each slit 25 is
Since the light transmission type sensor 24 is formed in a sector shape including two straight lines passing through the center of rotation of 0 and an arc connecting the ends of these straight lines, the light transmission type sensor 24 may Regardless of the position of the sensor 23, the sensor 24 can obtain a constant on / off timing, and the position of the developing device and the photosensitive belt 1 can be accurately controlled based on the size of the slit 25.

Actually, the developing device 10
When the cam 19 is brought into contact with or separated from Y, 10M, 10C, and 10B, the output of the light transmission type sensor 24 is as shown in FIG. The output of the light transmission type sensor 24 is expressed as a low level signal at the time of light transmission, and it can be seen that the pulse width changes with the change of the slit 25 width. On this occasion,
The interval between the slits 25 can be obtained by measuring both the rising and falling edges of the output as interrupt inputs. For this purpose, the light transmission type sensor 24 passes through the inverting and non-inverting Schmitt trigger gates to remove noise as shown in FIG.
It is connected to an interrupt input of a control circuit such as U or ASIC. In each interrupt routine, FIG.
Processing as shown in FIGS. 9 and 10 is performed. In this embodiment, the time from the start to the end of the slit is measured by a 1 msec timer interrupt in order to measure the slit interval. Therefore, the position of the slit can be recognized with an accuracy of 1 msec.

On the other hand, the mounting positions of the four cams 19 on the rotary shaft 20 are displaced and fixed every 72 degrees as shown in FIGS. 2 and 3, so that the rotary shaft 20 rotates 72 degrees. The positional relationship between the developing device and the photoreceptor belt 1 is
All the developing devices 10Y, 10M, 10C and 10B are separated from the photoreceptor belt 1, only the yellow toner developing device 10Y is in contact with the photoreceptor belt 1, only the magenta toner developing device 10M is exposed. Developing device 10C for cyan toner in contact with body belt 1
Only the state in which only the photoconductor belt 1 is in contact with the photoreceptor belt 1 and the state in which only the black toner developing device 10B is in contact with the photoreceptor belt 1 are sequentially switched.

In FIG. 2, four cams 19 are connected to the rotating shaft 2 so that the upper cams 19 come into contact with the developing device in order.
0, but it is also possible to change the mounting position of the cam 19, thereby easily changing the order in which the developing devices 10Y, 10M, 10C, and 10B for each color are brought into contact with the photosensitive belt 1. be able to. Further, in the above-described embodiment, a configuration has been described in which four developing devices are provided and the corresponding cams are stopped at five positions in order to form an image using four color toners.
The image forming apparatus of the present invention is not limited to this, and the number of developing devices and the number of positions controlled by the cam are reduced with the decrease in the number of toner colors, or conversely, by the cam. When the number of positions to be controlled increases, for example, when a process of separating all the developing devices from the photoreceptor belt after the development of each color is added, the shape of the cam and the size and position of the slit of the light shielding plate are changed. It is possible to change the position according to the number of cam stop positions. In these cases, it is also possible to control the positions of the developing device and the photosensitive belt.

[Second Embodiment] Next, an image forming apparatus according to a fourth aspect will be described. This image forming apparatus has a configuration similar to that of the image forming apparatus shown in FIG. 1, and separately stores toners of four colors of yellow, magenta, cyan and black in a photoreceptor belt 1 formed in an endless belt shape. The four developing devices 10Y, 10M, 10C, and 10B are sequentially brought into contact with each other to form toner images of each color, and are superimposed on the intermediate transfer belt 2 to form a color image.
And fix it.

The four developing devices 10 of this image forming apparatus
Y, 10M, 10C, and 10B are arranged in the same manner as in FIGS. 2 and 3, and the contact with the photoreceptor belt 1 is performed by eccentrically pressing the cam 19 attached to the rotating shaft 20 against the developing device. Will be FIG. 11 shows the shape of a cam used in this image forming apparatus. As shown in FIG. 11, an area for pressing the developing device is provided on the outer peripheral portion of the cam. In this area, the arc of the cam coincides with the arc of a circle whose center of rotation is the center of rotation. Is formed. In general, when the cam is rotated by the motor, even if the power of the motor is turned off, the motor is slightly operated by the inertial force. Therefore, in a device without a forced stop mechanism such as a clutch, the device does not stop immediately. On the other hand, since the cam of the present embodiment has the above-described configuration, even if the cam is slightly shifted and stopped after the power of the motor is turned off, as long as the cam is within the area where the developing device is pressed. Since the developing device is pressed into contact with a constant pressing force, the position of the developing device with respect to the photoreceptor belt can be kept constant, and the developing device can always be stopped at a fixed position without depending on the operation accuracy. it can.

[0022]

As described above, in the image forming apparatus according to the present invention, a plurality of developing devices are arranged opposite to the photoreceptor belt, and the latent image formed on the photoreceptor belt is developed with toner of a plurality of colors. In a color image forming apparatus for forming an image, the developing device is brought into contact with and separated from the photoreceptor belt by pressing and separating a cam to and from the developing device, and the rotation of a rotation shaft fixing the cam is only driven by a motor. It is possible to reduce the manufacturing cost by adopting a configuration in which the control is performed by the control unit. Further, since the configuration is simple with small components, it is possible to reduce the occupied space and realize the miniaturization of the device. it can.

Further, a light shielding plate having a plurality of slits having different sizes on the rotation axis of the cam and a light transmission type sensor for recognizing light transmitted from the light shielding plate are fixed to control the position of the cam. By doing so, the cam can be stopped at the correct position while reducing the manufacturing cost, and a color image without a shift in the developing position can be formed.

Further, the slit is formed in a fan shape surrounded by two straight lines passing through the center of rotation of the rotating shaft and an arc connecting the ends of the two straight lines, so that the light blocking of the light transmission type sensor is achieved. The individual slits can be identified without depending on the mounting accuracy on the plate, and the position of the cam can be controlled based on the correct position determination.

Further, the cam is provided with a region for pressing the developing device, and the shape of the arc of the cam in this region is made to coincide with the arc of a circle centered on the rotation axis of the cam, thereby stopping the rotation shaft. Even if the position is slightly shifted, the pressing state of the developing device can be maintained within the pressing region, and the contact state between the developing device and the photosensitive belt can be maintained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to an embodiment of the invention.

FIG. 2 is a diagram showing a positional relationship among the cams, the developing device, and the photosensitive belt when all the cams are separated from the developing device in the image forming apparatus shown in FIG.

FIG. 3 is a diagram illustrating a positional relationship among the cam, the developing device, and the photosensitive belt when a part of the cam presses the developing device in the image forming apparatus illustrated in FIG. 1;

FIG. 4 is a diagram showing a cam position recognition mechanism shown in FIG. 1;

FIG. 5 is an enlarged view showing a structure of a light shielding plate shown in FIG.

FIG. 6 is a diagram illustrating a relationship between an output and an interrupt input by the light transmission type sensor illustrated in FIG. 4;

7 is a diagram showing connection of the light transmission type sensor shown in FIG. 4 to a control circuit.

FIG. 8 is a diagram showing a process performed at interrupt input 2 shown in FIG. 6;

FIG. 9 is a diagram showing a process performed at interrupt input 1 shown in FIG. 6;

FIG. 10 shows 1 msec to the output of the light transmission type sensor shown in FIG.
It is a figure showing processing of a c timer interruption routine.

FIG. 11 is a diagram showing a shape of a cam used in an embodiment of the image forming apparatus according to claim 4;

[Explanation of symbols]

 Reference Signs List 1 photoconductor belt 2 intermediate transfer belt 3, 7 drive roller 4, 8, 9 driven roller 5, 6 transfer roller 10Y developing device for yellow toner 10M developing device for magenta toner 10C developing device for cyan toner 10B developing device for black toner 11Y Yellow toner developing roller 11M Magenta toner developing roller 11C Cyan toner developing roller 11B Black toner developing roller 12 Heating roller 13 Heater 14 Pressure roller 15 Temperature detecting means 15a Temperature detector 16 Heater driver 17 Tension roller 18 Recording medium 19 Cam 20 Rotating shaft 21 Motor and reduction gear 22 Gear 23 Light blocking plate 24 Light transmission sensor 25 Slit 26 Reference line

Claims (4)

[Claims] 1. A color image forming apparatus for developing a latent image on a photoreceptor belt by a plurality of developing devices, comprising: a rotating shaft rotatably supported at a position facing the photoreceptor belt via the developing device; A cam that is eccentrically fixed to a rotating shaft, and a motor that drives the rotating shaft to rotate, by rotating the rotating shaft, pressing the cam against the developing device, displacing the developing device, A color image forming apparatus, which is in pressure contact with a photosensitive belt. 2. The image forming apparatus according to claim 1, wherein the light blocking plate is rotatably supported on a rotation axis of the cam, and has a plurality of slits having different sizes corresponding to stop positions of the cam. And a light-transmitting sensor disposed so as to sandwich the light-blocking plate. The light-transmitting sensor identifies transmitted light passing through a slit of the light-blocking plate by an angle from the rotation axis, and the cam A color image forming apparatus for determining a position of a color image. 3. The image forming apparatus according to claim 2, wherein each slit of the light blocking plate connects two straight lines passing through the center of rotation of the rotation shaft and ends of the two straight lines. A color image forming apparatus formed in a fan shape surrounded by an arc. 4. The image forming apparatus according to claim 1, wherein said cam has a pressing region for pressing said developing device, and said cam has an arc in said pressing region. The image forming apparatus is characterized in that the shape of the image coincides with the arc of a circle around the rotation axis.