JPH0926700A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent carrier from adhering to an image forming body even when a main switch is turned off suddenly in the midst of forming an image by providing a control circuit controlling the on/off of the output of plural high voltage power sources so that the control circuit may perform on/off control by holding the output by time in accordance with the holding characteristic of plural DC power sources. SOLUTION: This image forming device where development for an image forming body is performed by a contact reversal developing process is provided with the control circuit controlling the on/off of the output of the DC power sources A53 and B54 and the high voltage power source 55 having the different holding characteristic. An output control circuit 52 being one of the control circuit performs the on/off control by holding the output by the time in accordance with the holding characteristic of the power source B54. Thus, even when an area electrified before the main switch 56 is turned off reaches a developing area because the image forming body is rotated by its inertia when the main switch 56 is turned off, the carrier on a developer carrier is not transferred to the image forming body because developing bias voltage is impressed on the developer carrier.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for developing on an image forming body by a contact reversal developing process,
In particular, the present invention relates to an apparatus that prevents carrier adhesion to an image forming body that occurs when the power is turned off during image formation.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus, such as an electrophotographic copying machine, which develops on an image forming body by a contact reversal developing process, charges the image forming body to a zero potential by, for example, negatively charging it with a laser beam. A latent image is formed on the image forming body, and then the latent image on the image forming body is developed by a developer carrier to which a negative developing bias voltage having the same polarity as that of the image forming body is applied;
The process of separating, fixing, and forming an image is performed. A magnetic brush developing type developing device using a two-component developer is used in the image forming apparatus of the contact reversal developing process. This developing device has a cylindrical developer carrier (developing sleeve) rotatably supported by a magnet roll having a magnet body having a plurality of magnetic poles inside, and adheres toner particles to the surface of the developing sleeve. The magnetic carrier is held and conveyed to the developing area for development. It is relatively easy to control the triboelectric charging of the toner particles, the aggregation of the toner particles does not easily occur, and the magnetic brush has a good bristling, thus forming an image. It has characteristics such as excellent frictional property on the body surface and is often used in spite of the need to control the amount of toner particles with respect to carrier particles.

In the contact reversal developing system using the above-mentioned two-component developer, as shown in FIG. 5, the latent image portion 31b on the image forming body 31 or the uncharged area is applied with a developing bias voltage. When the developing sleeve 33A approaches the developing sleeve 33A, the toner 59 on the developing sleeve 33A adheres to the latent image 31b or the entire uncharged area due to the potential difference, and the charged area 31a has a developing bias voltage of 0V as shown in FIG. When approaching 33A, a phenomenon occurs in which the carrier 58 adheres from the developing sleeve 33A onto the charging area 31a of the image forming body 31. Therefore, it is generally necessary to perform strict timing control for controlling the bias voltage output unit.

Particularly, when the latter carrier adhesion occurs, the image, the image forming body, the cleaning blade and the like are damaged, which is a serious problem.

[0005]

FIG. 3 is a circuit diagram showing a control system of a conventional high-voltage power supply and a time chart showing an output state when the main switch of the high-voltage power supply is turned off. In the figure, 51 is a CPU of the control unit, 521 is a control circuit for controlling the output signal of the developing bias voltage of the high-voltage power supply 55, 52a is an inverter, 53 is a DC power supply A for supplying power to the control unit, the high-voltage power supply 55 and the like, 55 is a charger,
A high-voltage power supply for supplying a high-voltage bias voltage to the developer carrier, 55a is a charging output terminal connected to the charger of the high-voltage power supply 55, 55b is a development bias output terminal connected to the developing sleeve of the high-voltage power supply 55, and 56 Is the main switch, 5
7 is a commercial power supply, R ₁ is a resistor for pull-up, CPU5
1, the resistor R ₁ and the inverter 52a form a control circuit 521 which is a control unit for controlling the output signal of the developing bias voltage. As the DC power supply A53, a capacitor input type switching DC power supply is used.

In a normal image forming sequence, the sequence is controlled so that the above-mentioned carrier adhesion does not occur. However, the main switch 5 is abruptly caused by a power failure during image formation or an abnormal operation such as accidentally opening the front door.
When 6 is turned off, as shown in FIG.
The DC power supply A52, the bias output signal, the developing bias voltage output, the charging output, etc. are turned off all together after a delay of time t _{1 of} 0 ms or less. However, since the image forming body 31 continues to rotate due to inertia, the charged region 31a approaches the developing region G before the main switch 56 turns off, the main switch 56 turns off, and the developing bias voltage is not applied. 0V developing sleeve 33A to carrier 58
It has been difficult to avoid the phenomenon that the particles adhere to each other. In particular, in recent years, a flywheel is attached to increase the inertia of the image forming apparatus in order to prevent jitter (horizontal stripe density unevenness caused by uneven rotation of the image forming body) on the image. Therefore, the image forming body 31 continues to rotate due to inertia even after the main switch 56 is turned off,
Although a often reaches the development area G and carrier adhesion occurs, there is no suitable solution.

An object of the present invention is to solve the above problems and provide an image forming apparatus in which a carrier does not adhere to an image forming body even if the main switch is suddenly turned off during image formation.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a plurality of DC power supplies having different holding characteristics in an image forming apparatus which develops on an image forming body by a contact reversal development process.
A control circuit for controlling ON / OFF of a plurality of high-voltage power supply outputs is provided, and at least one of the control circuits performs ON / OFF control by holding for a time period according to a holding characteristic of the plurality of power supplies. It is achieved by the image forming apparatus.

Further, the control circuit is a control circuit for controlling the output signal of the output for the developing bias voltage of the high voltage power source, and CP
After the DC power supply A of the ON / OFF control circuit by U is turned OFF, the developing bias voltage output is held while the DC power supply B for supplying power to the high voltage power supply holds the output. Output for a period of time greater than twice the (distance from the charging means to the developing position) / (peripheral speed of the image forming body during the developing process) after the charging output of the high-voltage power supply is turned off. The image forming apparatus characterized in that it is held is a preferred embodiment.

[0010]

In the image forming apparatus according to the present invention, the holding characteristic of the DC power source for supplying power to the high voltage power source is lengthened, and an output signal for controlling the output of the developing bias voltage applied to the developer carrier of the high voltage power source is output. Since the developing bias voltage output of the DC power supply is held while it is held, the image forming body rotates due to its inertia after the main switch is turned off, and the charging is performed before the main switch is turned off. Even when the area reaches the developing area, the developer bias voltage is applied to the developer transport body, so that the carrier on the developer transport body does not transfer to the image forming body.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure and function of the image forming apparatus of the present invention will be described with reference to FIGS.

FIG. 2 is a schematic configuration diagram showing an example of the image forming apparatus of the present invention. This image forming apparatus comprises an automatic document feeder D, an image information reading section A, a laser writing section B, an image forming section H, a sheet feeding section 40 and the like.

At the top of the image forming apparatus, there are a document table 11 made of a transparent glass plate and an automatic document feeder D fixedly or detachably mounted on the document table 11. The automatic document feeder D includes an endless belt 71, belt pulleys 72a and 72b, rotary rollers 74a and 74.
b, a paper feed detector 75, stop levers 76 and 77, a document leading edge detector 78, a paper discharge detector 79, a document insertion port 83, discharge rollers 84a and 84b, and the like.
Reference numeral 5 is provided near the document insertion opening 83.

In the paper feed detector 75, a light source and a light receiving element are combined, the light source projects light at an incident angle of 45 degrees with respect to the document surface, and the light receiving element receives reflected light with a reflection angle of 45 degrees. It is like this. The belt pulleys 72a and 72b are rotated clockwise by a motor (not shown) together with the rotating roller 74a, and a plurality of endless belts 71 are stretched around the belt pulleys 72a and 72b. The endless belt 71 conveys the document 16 onto the document table 11 as the endless belt 71 rotates.

The document leading edge detector 78 comprises a light source and a light receiving element, detects the leading edge of the document on the document table 11 by reflected light,
It is detected whether or not the document is in the position where it is copied.

The front end of the stop lever 77 is located on the document path and prevents the document from advancing to the left side in the drawing, and regulates the position to copy the document. The tip of the stop lever 77 can be retracted from the document passage by the operation of a sheet discharge solenoid (not shown). The pair of paper discharge rollers 84a and 84b are always in a pressure contact state and discharge the document onto the document receiving tray 82 when the motor is operated.

The paper discharge detector 79 is composed of a light source and a light receiving element and detects the presence or absence of a document in the document path by reflected light.

When the original 16 is inserted into the original insertion port 83,
The document 16 is conveyed onto the document table 11 with the movement of the endless belt 71, and the leading end of the document hits the leading end of the stop lever 77 and stops, so that the document 16 is ready for copying. Tip detector 7
8 sends a tip detection signal to the controller.

In response to the leading edge detection signal, the image information reading section A, which will be described later, operates to read the image surface of the original 16.
By the control of the control unit for controlling the copying process after the reading is completed, the front end of the stop lever 77 is retracted from the document passage, and the endless belt 71 starts moving again.
The original 16 is conveyed to the left, and the next original 16 can be inserted.

On the other hand, the conveyed document 16 passes under the paper discharge detector 79 and is discharged onto the document receiving tray 82 by the paper discharge rollers 84a and 84b. Here, the paper discharge detector 7
Reference numeral 9 detects the passage of the end of the document and sends a paper discharge detection signal to the control section.

In response to the paper discharge detection signal, the paper discharge solenoid in operation is released and the motor is stopped to stop the endless belt 71, and then the operation of the image information reading section A described below is started.

Next, the image information reading section A will be described.

Below the document table 11 and inside the main body of the apparatus, an image reading section including a first mirror unit 12 and a second mirror unit 13, which are moving members, a main lens 14, an image pickup device 15 such as a CCD array, and the like. A is provided. The first mirror unit 12 includes a lighting lamp 12a and a first mirror unit 12a.
A mirror 12b is provided so as to be linearly movable in the left-right direction in the drawing in parallel with the document table 11, and is moved by a drive motor under the control of a control unit based on a leading edge detection signal from the leading edge detector 78. Optically scan the entire surface of. The second mirror unit 13 is the second mirror 12a.
Also, the third mirror 12b is integrally provided, and linearly moves in the same direction in the left and right directions at a speed half that of the first mirror unit 12 so as to always maintain a predetermined optical path length. Of course, the movement of the second mirror unit 13 is parallel to the document table 11 as in the case of the first mirror unit 12. The illumination lamp 12
The image of the document 16 on the document table 11 illuminated by a is
The main lens 14 allows the first mirror 12b and the second mirror 13
a, and an image is formed on the image sensor 15 via the third mirror 13b. When the scanning is completed, the first mirror unit 12 and the second mirror unit 13 return to their original initial positions, and in the case of continuous copying, the document scanning is restarted by the control of the control unit by the leading edge detection signal generated by the leading edge detector 78. However, if it is not continuous copying, it waits until the next image formation.

Image data, which is image information obtained by the image pickup device 15, is processed by an image signal processing unit (not shown) and is temporarily stored in a memory as an image signal. Next, the image signal is input to the laser writing section B.

In the image forming unit H, the image signal from the memory is controlled by the control unit so that the drive motor 21, the polygon mirror 22, the fθ lens 23, and the mirrors 24, 25, 2 are transmitted.
6 and an image recording operation is started when input to the laser writing section B which is an image exposure means including a semiconductor laser, a correction lens and the like (not shown).

That is, the photosensitive drum 3 which is an image forming body
Reference numeral 1 denotes a photosensitive layer formed by applying, for example, OPC, which is an organic photoconductor, onto a drum-shaped base body made of a conductor such as aluminum, and the base body is grounded and rotated clockwise at a constant speed. To be done. Along with this rotation, an electric charge is given by the charger 32, which is a charging means, and the surface of the drum is brought to a predetermined potential. The photosensitive drum 31, which is uniformly charged to a negative potential, is image-exposed by the laser beam L from the laser writing section B, and the absolute potential of the image-exposed portion is reduced to near zero to reduce the original document. An electrostatic latent image corresponding to 16 is formed. This electrostatic latent image is subjected to reversal development by the developer carried by the developing sleeve 33A to which a developing bias voltage having the same polarity as the charging potential of the developing device 33, which is the developing means, and a low potential is applied. The toner adheres to form a visible toner image.

On the other hand, the transfer paper P is unloaded one by one from the paper feed cassette 41 loaded in the paper feed section 40 by the unloading roller 42a, and is fed to the image transfer section via the unloading path 42. The transferred transfer paper P is used as the photosensitive drum 31.
It is sent onto the photosensitive drum 31 by the registration roller 44 which operates in synchronization with the above toner image. This transfer paper P
The toner image on the photoconductor drum 31 is transferred by the action of the transfer device 34, and is separated from the photoconductor drum 31 by the charge removal action of the separator 35.
After being sent to the fixing device 37 and melted and fixed by the heating roller 37a and the pressure roller 37b, the discharge roller 3
It is discharged to the tray 54 outside the apparatus by 8, 46.

The photosensitive drum 31 continues to rotate, and the toner remaining on the surface of the photosensitive drum 31 without being transferred is removed and cleaned by a cleaning blade 39a which is in pressure contact with a cleaning device 39 as a cleaning means. Then, the electric charge is applied, and the next image forming process starts.

FIG. 1A is a circuit diagram showing a control system of a high voltage power source of the present invention, and FIG. 1B is a DC power source of FIG. 1A when a main switch is turned off during image formation. A5
3 is a time chart showing the output states of the DC power supply B54 and the high voltage power supply 55. In FIG. 1, the same parts as those in FIG. 3 are designated by the same reference numerals, and detailed description thereof will be omitted. Reference numeral 52 is a control circuit for controlling the output signal of the developing bias voltage of the high voltage power supply 55, which is the inverter 5 of the conventional control circuit 521 shown in FIG.
A diode D is provided between the output end of 2a and the DC power supply A53.
₁ , a Zener diode ZD between the output terminal of the inverter 52a and the ground, a resistor R ₂ between the output terminal of the inverter 52a and the high voltage power supply 55, and between the high voltage power supply 55 side of the resistor R ₂ and the ground. A capacitor C ₁ is inserted into the capacitor for noise absorption. Reference numeral 54 denotes a DC power supply B of a capacitor input type switching system similar to the DC power supply A53. The capacity of the capacitor is set so that its output is held for about 600 ms (t ₂ ) after the main switch 56 is turned off. It has been set. In order to simplify the drawing, the control circuit for the output signal of the output other than the developing bias voltage of the high voltage power supply 55 uses the same circuit as 521 shown in FIG. 3, but the illustration is omitted.

With this configuration, the DC power source A is turned on after the main switch 56 is turned off as shown in FIG. 1 (b).
Although the output of 53 starts to decrease after t ₁ , the DC power supply B54
Output drops after t ₂ . The output signal of the developing bias voltage from the CPU 51 is not turned off by the diode D ₁ even when the DC power supply A53 is turned off, and the ON state is continued until the output of the DC power supply B54 decreases. Since the output signal of the charging voltage is output by the conventional output control circuit 521, it turns off after t ₁ .

In the embodiment of the image forming apparatus shown in FIG. 2, the peripheral speed (linear velocity) of the surface of the photosensitive drum 31 which is an image forming member at the time of image formation is 280 mm / sec, and the peripheral speed from the position of the charger 32 is changed. The distance to the developing area G in the rotation direction is about 80 mm
Therefore, if the drive motor of the photoconductor drum 31 is rotated by its inertia after it is turned off, and the circumference is rotated by 80 mm and then stopped, the time between them is 80 mm / linear velocity / 2.
= 80/280/2, which is about 150 ms. Since the drive motor is supplied with electric power from the DC power supply A53, it will rotate inertially after t _{1 has} elapsed after the main switch 56 was turned off. Therefore, the charging area 31a on the photoconductor drum 31 is 1 after the main switch 56 is turned off.
While 00 ms + 150 ms = 250 ms, the photoconductor charged by the charger 32 passes through the developing area G, but does not pass thereafter. On the other hand, the developing bias voltage applied to the developing sleeve 33A is t ₂ after the main switch is turned off.
= 600 ms, that is, the output for the developing bias voltage of the high-voltage power supply 55 is (distance from the charging means to the developing position) / (image formation during the developing process) after the charging output of the high-voltage power supply 55 is turned off. Since the toner is held until a time greater than twice the peripheral speed of the body), carrier adhesion does not occur on the photosensitive drum 31.

[0032]

As described above, the image forming apparatus of the present invention can prevent the carrier from adhering to the image forming body when the main switch is suddenly turned off during image formation with a simple structure. Has the effect. Moreover, recent image forming apparatuses require a power source for options such as a finisher for performing processing such as binding and binding the ADF and ejected copies all at once. So you can use
There is an advantage that it is only necessary to change the holding characteristic of the power supply, and it is not necessary to increase the power supply.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a control system of a high voltage power supply of the present invention and a time chart showing an output state of the high voltage power supply when a main switch is turned off.

FIG. 2 is a schematic configuration diagram illustrating an example of the image forming apparatus of the present invention.

FIG. 3 is a circuit diagram showing a control system of a conventional high-voltage power supply and a time chart showing an output state when the main switch of the high-voltage power supply is turned off.

FIG. 4 is a schematic diagram illustrating development with a two-component developer.

FIG. 5 is a schematic diagram illustrating carrier attachment by a two-component developer.

[Explanation of symbols]

31 Photoreceptor Drum (Image Forming Body) 31a Charging Area 33 Developing Device 33A Developing Sleeve (Developer Conveying Body) 51 CPU 52, 521 Output Control Circuit 53 DC Power Supply A 54 DC Power Supply B 55 High Voltage Power Supply 55a Charging Output Terminal 55b Development Bias output terminal 56 Main switch 57 Commercial power supply 58 Carrier 59 Toner A Image information reading section B Laser writing section D Automatic document feeding section G Development area H Image forming section D ₁ diode R ₁ , R ₂ resistance ZD Zener diode

Claims (3)

[Claims] 1. An image forming apparatus for developing on an image forming body by a contact reversal development process, comprising: a plurality of DC power supplies having different holding characteristics; and a control circuit for controlling ON / OFF of a plurality of high voltage power supply outputs. The image forming apparatus is characterized in that at least one of the control circuits holds for a time period corresponding to the holding characteristics of the plurality of power sources and performs ON / OFF control. 2. The control circuit is a control circuit for an output signal of a development bias voltage output of the high-voltage power supply, and supplies power to the high-voltage power supply after the DC power supply A of the ON / OFF control circuit by the CPU is turned off. The image forming apparatus according to claim 1, wherein the output for the developing bias voltage is held while the DC power supply B to be supplied holds the output. 3. The developing bias voltage output of the high-voltage power source after the charging output of the high-voltage power source is turned off (distance from the charging means to the developing position) / (circumference of the image forming body during the developing process). The image forming apparatus according to claim 2, wherein the image forming apparatus is held until a time larger than twice (speed) is elapsed.