JP2538594B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus using an electrophotographic method such as a copying machine.

(B) Summary of the Invention In summary, the image forming apparatus according to the present invention has a potential for forming an electrostatic latent image with respect to a non-image forming area on the surface of a photoconductor each time the image forming process is performed a predetermined number of times. Is to remove the defective toner in the developing device by driving the opposite polarity charging means for charging the opposite polarity potential.

(C) Conventional Technology An image forming apparatus using an electrophotographic method includes a developing device near the outer peripheral portion of a photoconductor, and a developer is stored in the developing device. The developing device supplies the developer housed inside to the surface of the photoconductor to visualize the electrostatic latent image previously formed on the surface of the photoconductor. In the case where a two-component developer composed of a toner of thermoplastic resin powder and a carrier of fine magnetic particles is used as the developer, the toner and the carrier are agitated in the developing device, and both are triboelectrified so that the carrier Toner is electrostatically adsorbed on the surface.

A magnet roller is exposed in a window portion facing the surface of the photoconductor of the developing device, and a carrier holding toner is magnetically attracted to the surface of the magnet roller. The developer consisting of toner and carrier forms a magnetic brush between the surface of the photoconductor and the surface of the magnet roller, and only the toner is adsorbed to the electrostatic latent image formed on the surface of the photoconductor. Since the potential for forming the electrostatic latent image charges the surface of the photoconductor by driving the charging charger, the polarity of the corona discharge of the charging charger is opposite to the polarity of the charging potential due to the frictional charging of the toner.

(D) Problems to be Solved by the Invention However, in the image forming apparatus using the conventional two-component developer, the charge amount of the toner in the developing apparatus becomes non-uniform due to deterioration over time, and the potential of the opposite polarity is generated. In some cases, it may become charged. Such defective toner adheres to a portion having no electrostatic latent image on the surface of the photoreceptor, that is, a portion having no image in the developing process. As a result, the toner adheres to the white background portion of the image formed on the paper, and the image quality deteriorates.

An object of the present invention is to provide an image forming apparatus capable of improving the quality of an image formed by adsorbing only the defective toner generated in the developing device to the surface of the photoconductor and removing the toner.

(E) Means for Solving the Problems In the image forming apparatus of the present invention, a reverse polarity charging means for charging the surface of the photoconductor to a potential opposite in polarity to the potential for forming an electrostatic latent image, and each image forming process. A counter that updates the count value after the start of and counts the number of executions of the image forming process,
During each image forming process, the count value of the updated counter is compared with a predetermined number of times, and when the count value of the counter matches the predetermined number of times, non-image formation on the surface of the photoconductor during the image forming process is performed. In the image forming process, the area is detected, the opposite polarity charging means is driven for the detected non-image forming area, and at least the surface of the photoconductor charged with the opposite polarity potential passes through the developing device and reaches the cleaning device. The feature is that the rotation of the photoconductor is continued.

(F) Operation In the present invention, the counter that counts the number of image formations is updated every time one image formation process is started, and when the updated count value matches the predetermined number, the image formation process is started. The non-image forming area on the surface of the photoconductor is detected, and the opposite polarity charging means is driven with respect to the detected non-image forming area. The opposite polarity charging means charges a potential having a polarity opposite to that of the potential for forming an electrostatic latent image on the surface of the photoconductor. The rotation of the photoconductor in the image forming process is continued until the oppositely charged portion passes through the developing device and reaches the cleaning device.

Therefore, if there is defective toner charged in the developing device with an electric potential having a polarity opposite to that of the normal toner, the defective toner is adsorbed to the non-image forming area on the surface of the photoconductor and removed from the inside of the developing device to remove the cleaning device. Will be collected. Further, the removal of the defective toner by the opposite polarity charging means is executed during the image forming process every predetermined number of times.

(G) Embodiment FIG. 1 is a schematic front cross-sectional view showing the configuration of the main part of an image forming apparatus according to an embodiment of the present invention.

The photoconductor drum 2 has a cylindrical shape and is rotatably supported. The rotation of the main motor (not shown) is transmitted to the photosensitive drum 2. A charging charger 3, a blank lamp 4, a developing device 5, a reverse polarity charger 1, a transfer charger 6, a peeling charger 7 and a cleaner 8 are provided near the outer peripheral portion of the photosensitive drum 2. The charging charger 3 performs corona discharge on the surface of the photosensitive drum 2 to charge it with a unipolar potential. Blank lamp 4
Irradiates light onto the non-image area on the surface of the photosensitive drum 2 that does not face the document.

In the image forming area on the surface of the photoconductor drum 2, the reflected light of the light emitted from the optical system device (not shown) to the document is distributed as shown by the alternate long and short dash line in the figure to form an electrostatic latent image.
A developer is supplied from the developing device 5 to the electrostatic latent image to visualize it. The developing device 5 has a magnet roller 5a inside.
And a stirring roller 5b. The stirring roller 5b stirs the two-component developer housed in the developing device 5 to frictionally charge the toner and the carrier. Rotational force is transmitted to the magnet roller 5a via the developing device clutch 5c. Magnetic poles are provided inside the magnet roller 5a, and when the magnet roller 5a rotates, a rotating magnetic field is formed on the outer peripheral portion thereof. Due to this rotating magnetic field, the carrier that electrostatically attracts toner is magnetically attracted to the surface of the magnet roller 5a. As a result, the toner and the carrier form a magnetic brush on the surface of the magnet roller 5a facing the photosensitive drum 2, and the toner is attracted to the electrostatic latent image on the surface of the photosensitive drum 2.

The toner image thus formed on the surface of the photosensitive drum 2 faces the transfer charger 6. The transfer charger 6 performs corona discharge of the same polarity as the charging charger 3 on the sheet conveyed by the timing roller 10,
Transfer the toner image to the surface of the paper. Peeling charger 7
Performs AC corona discharge on the paper on which the toner image is transferred, and relaxes the attraction force to the photoconductor drum 2. As a result, the paper separated from the surface of the photoconductor drum 2 is conveyed by the conveyor belt.
It is guided to a fixing device by 11 and is heated and pressed to melt and fix the toner image.

The surface of the photosensitive drum 2 that has completed the transfer process contacts the blade 8a of the cleaner 8. The blade 8a scrapes off the toner remaining on the surface of the photosensitive drum 2 and drops it downward. Further, the surface of the photoconductor drum 2 is irradiated with light by the charge eliminating lamp 9 to erase the remaining potential. A slit disk 12 is fixed to the rotary shaft of the photosensitive drum 2. The slit disk 12 has a plurality of slits with the same interval on the outer peripheral portion, and the photo interrupter 13 faces the slits. The photo interrupter 13 outputs a detection signal every time the slit passes.

FIG. 2 is a block diagram showing a part of the control unit of the image forming apparatus.

Each input / output device is connected to the CPU 21 via the I / O interface 24. The CPU 21 outputs control data to these input / output devices according to a program previously written in the ROM 22. Part of the memory area of the RAM 23 is assigned as a working area at this time. Also, RA
The memory area M1 of M23 is allocated to a counter C described later, and the memory area M2 is allocated to a counter K also described later. The I / O interface 24 is connected to a charger drive unit 25, a charge removal lamp drive unit 26, a clutch drive unit 27, a blank lamp drive unit 28, a counter 29, etc., and constitutes a part of the input / output device. I /
In addition to these components, the O interface 24 is connected to a motor driver that drives the main motor and a driving unit that drives each device of the image forming apparatus.

The charger drive unit 25 includes a charging charger 3, a transfer charger 6, a peeling charger 7 and a reverse polarity charger 1.
Is connected. The static elimination lamp 9 is connected to the static elimination lamp drive unit 26. The developing device clutch 5c is connected to the clutch driving unit 27. A blank lamp 24 is connected to the blank lamp drive unit 28. The counter 29 counts the detection signals output by the photo interrupter 13 and outputs a timing pulse to the CPU 21 when the count value reaches a preset value. When the timing pulse is output from the counter 29, the CPU 21 outputs data for controlling the device according to the timing. Therefore, each device provided in the image forming apparatus operates in synchronization with the rotation of the photosensitive drum 2.

FIG. 3 is a flowchart showing the operation of the image forming apparatus.

Warm-up is executed when the power is turned on (n1). When the warm-up is completed (n2), data input is accepted until the print switch is operated (n3, n4). When the print switch is operated, the main motor is turned on (n5) and the photosensitive drum 2 is rotated. At the same time, the charging charger 3, the developing device 5, the transfer charger 6, the peeling charger 7 and the power receiving lamp 8 are turned on (n6 to n8). After that, at a predetermined timing, the paper is fed from a paper feeding unit (not shown) (n9, n10), and the document is scanned by the optical system device (n11, n12). Further, the timing roller 10 is driven at a predetermined timing (n13, n14), and the blank lamp is turned on for the non-image forming area (n15, n1).
6). By the above steps n4 to n16, the reflected light of the light emitted from the optical system device to the original is distributed on the surface of the photosensitive drum, and an electrostatic latent image is formed. This electrostatic latent image is developed by the developing device 5.
To visualize the image, and a toner image is formed on the surface of the photosensitive drum 2. This toner image is transferred onto the paper by the transfer charger 6. Further, the blank lamp 4 irradiates a portion of the surface of the photosensitive drum 2 which does not correspond to the original area, with light to prevent unnecessary adhesion of toner.

After that, the content of the counter C assigned to the memory area M1 of the RAM 23 is read (n17). The counter C counts the number of executions of the image forming process. It is checked whether the contents of this counter C match the set value A (n1
8) If the content of the counter C does not match the set value A, the content of the counter C is incremented and the content of the counter K assigned to the memory area M2 is decremented (n22, n23). The counter K counts the number of copies in the data input in step n3. Until the content of this counter K becomes 0, step n5 ~
The operation of n23 is repeated (n24). When the content of the counter K becomes 0, that is, when the set number of image forming processes are executed, the main motor is turned off and the execution of the next image forming process is awaited (n25 → n3).

When the content of the counter C matches the set value A in step n18, the reverse polarity charger 1 is turned on at a predetermined timing (n19, n20). This timing is the timing at which the non-image forming area on the surface of the photosensitive drum 2 faces the opposite polarity charger 1. At the same time, the contents of the counter C are cleared (n21). As described above, when the content of the counter C matches the predetermined number A, the reverse polarity charger 1 is driven with respect to the non-image forming area on the surface of the photosensitive drum 2. The opposite polarity charger 1 performs a corona discharge having a polarity opposite to that of the charging charger 3. Therefore, the non-image forming area of the photoconductor drum 2 is charged with a potential having a polarity opposite to that of the potential for forming the electrostatic latent image, that is, a potential having the same polarity as the potential of normal toner adsorbed to the electrostatic latent image. To do. When the non-image forming area of the photoconductor drum 2 next faces the developing device 5, normal toner repels the surface of the photoconductor drum 2. On the other hand, defective toner charged with a potential having a polarity opposite to that of the normal toner is attracted to the non-image forming area of the photosensitive drum 2. After that, when the non-image forming area of the photoconductor drum 2 faces the cleaner 8, the defective toner adsorbed on the surface thereof is scraped off by the blade 8a and stored inside the cleaner 8.

As described above, every time the image forming process is completed a predetermined number of times, the non-image forming area of the photoconductor drum 2 is charged with the electric potential of the opposite polarity and the defective toner is removed from the developing device 5, as shown in FIG. A remarkable effect was obtained. That is, in the conventional image forming apparatus that does not remove the defective toner generated in the developing apparatus, as shown by the solid line in the figure, the background density of the sheet becomes darker as the number of image formed sheets increases. This is because defective toner adheres to a portion other than the electrostatic latent image on the surface of the photosensitive drum during the image forming process and is transferred onto the sheet. On the other hand, in the image forming apparatus embodying the present invention, as indicated by the broken line in the figure, the background density of the sheet remains substantially unchanged even if the number of image formed sheets increases. This is because, as a result of removing the defective toner in the developing device for each predetermined number of sheets, the defective toner does not adhere to the surface of the photosensitive drum during the image forming process. When the density of the background is unchanged in this way, the contrast between the image formed on the paper and the background becomes clear, and the formed image becomes clear. Further, the removal of the defective toner by driving the reverse polarity charger 1 is performed through the non-image forming area continuous with the image forming area on the surface of the photoconductor drum 2 during the image forming process every predetermined number of times. For this reason,
It is not necessary to provide a special operation state only for removing defective toner separately from the normal image forming process, and the operation control of the image forming apparatus can be facilitated.
There is no delay or interruption in the start of the imaging process.

In this embodiment, the reverse polarity charging means is composed of the reverse polarity charger, but the same effect can be obtained by changing the polarity of the power supply voltage applied to the charger at a predetermined timing. As a result, the reverse polarity charger can be eliminated and the cost can be reduced.

(H) Effect of the Invention According to the present invention, the defective toner in the developing device can be collected by the cleaning device through the non-image forming area of the photoconductor during the image forming process for each predetermined number of times, and the paper of the sheet can be collected. The image formed on the paper becomes clear and a high-quality image can be formed without soiling the base. In addition, it is not necessary to provide a special operation state only for removing the defective toner separately from the normal image forming process, the operation control of the image forming apparatus can be facilitated, and the image forming process can be started. There is no delay or interruption.

[Brief description of drawings]

FIG. 1 is a schematic front sectional view showing a part of an image forming apparatus according to an embodiment of the present invention, FIG. 2 is a block diagram showing a part of a control unit of the image forming apparatus, and FIG. It is a flow chart which shows operation of a device. FIG. 4 is a diagram showing the relationship between the number of images formed and the background density of the paper in the conventional image forming apparatus and the image forming apparatus according to the embodiment of the present invention. 1 ... Reverse polarity charger, 2 ... Photosensitive drum, 3 ...
Charger charger, 5 ... Developing device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Kinashi 22-22, Nagaikecho, Abeno-ku, Osaka 72) Inventor Teruhiko Noguchi 22-22 Nagaike-cho, Abeno-ku, Osaka City, Sharp Corporation (56) Reference JP 61-14674 (JP, A) JP 59-147372 (JP, A) JP Sho 58-111076 (JP, A)

Claims (1)

(57) [Claims] 1. A reverse polarity charging means for charging a surface of a photoconductor to a potential having a polarity opposite to that of a potential for forming an electrostatic latent image, and updating a count value after starting each image forming process to execute the image forming process. A counter that counts the number of times, and during each image forming process, compares the count value of the updated counter with a predetermined number of times, and when the count value of the counter matches the predetermined number of times, during the image forming process, The non-image forming area on the surface of the photoconductor is detected, and the opposite polarity charging means is driven for the detected non-image forming area, and the photoconductor surface charged with at least the opposite polarity potential passes through the developing device to the cleaning device. An image forming apparatus characterized by continuing rotation of a photosensitive member in the image forming process until reaching.