JPH04361284A - Image forming device - Google Patents

Abstract

PURPOSE:To clean a transfer roller by a cleaning bias impressing system without lowering an image forming speed, in other words, even when an interval between images formed on an electrostatic latent image carrier is short in an image forming device where a toner image formed on the electrostatic latent image carrier is transferred on a transfer paper by allowing the transfer paper to pass between the electrostatic latent image carrier and the transfer roller. CONSTITUTION:This image forming device where the toner image formed on a photosensitive drum 1 is transferred on the transfer paper S by allowing the transfer paper S to pass between the drum and the transfer roller 4 is provided with a bias power source S1 for transferring, a bias power source S2 for cleaning, and a high speed driving part 10 for driving and rotating the transfer roller when transfer is not performed at a higher speed than when the transfer is performed. When the transfer is performed, the bias power source S1 for transferring is connected to the transfer roller and when the transfer is not performed, the bias power source S2 for cleaning is connected to the transfer roller, and the transfer roller is driven at a high speed by the high speed driving part 10 in this device.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to copying, in which a toner image formed on an electrostatic latent image carrier is transferred onto the transfer paper by passing a transfer paper between the electrostatic latent image carrier and a transfer roller. The present invention relates to image forming devices such as machines and printers.

0002

2. Description of the Related Art In this type of image forming apparatus, when transferring a toner image onto a transfer paper, a transfer bias having a polarity substantially opposite to that of the toner is applied to a transfer roller. Therefore, some toner electrically adheres to the transfer roller and contaminates the roller. If such a phenomenon is left unaddressed, the toner adhering to the surface of the transfer roller may adhere to the back surface of the transfer paper, making it difficult to form an image on the back surface again.

[0003] Therefore, it has conventionally been proposed to return toner from the transfer roller to the electrostatic latent image carrier by applying a cleaning bias voltage to the transfer roller during non-transfer (see Japanese Patent Laid-Open No. 63-247781). ).

0004

[Problems to be Solved by the Invention] However, if the transfer roller is cleaned between the images formed on the electrostatic latent image carrier using this method, at least the amount of cleaning required for one rotation of the transfer roller is It is necessary to provide a period between images, which slows down the image forming speed accordingly. Therefore, the present invention provides an image forming apparatus that transfers a toner image formed on an electrostatic latent image carrier onto the transfer paper by passing a transfer paper between the electrostatic latent image carrier and a transfer roller. It is an object of the present invention to enable a transfer roller to be cleaned by a cleaning bias application method without requiring a reduction in image forming speed, in other words, even if the distance between images formed on an electrostatic latent image carrier is short.

[0005]

[Means for Solving the Problems] In accordance with the above-mentioned object, the present invention is directed to transferring a toner image formed on an electrostatic latent image carrier by passing a transfer paper between the electrostatic latent image carrier and a transfer roller. In an image forming device that transfers onto transfer paper, a transfer bias power source,
a cleaning bias power source, a means for driving and rotating the transfer roller at a higher speed than during transfer during non-transfer, and connecting the transfer bias power source to the transfer roller during transfer, and connecting the cleaning bias power source to the transfer roller during non-transfer. There is provided an image forming apparatus characterized in that the image forming apparatus is provided with a control means connected to the roller and for causing the high speed drive means to drive the transfer roller at high speed.

[0006]

According to the image forming apparatus of the present invention, at the time of toner image transfer, the transfer bias power source is connected to the transfer roller, and the toner image on the electrostatic latent image carrier is transferred onto the transfer paper. During non-transfer, a cleaning bias power source is connected to the transfer roller, and the transfer roller is rotated by its high-speed drive means at a higher speed than during transfer, thereby removing the toner adhering to the surface of the transfer roller. In other words, there is no need to reduce the image speed, in other words, the image can be quickly returned to the electrostatic latent image carrier even during short image intervals.

[0007]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an electrophotographic laser beam printer that is an embodiment of the present invention. This printer has a photosensitive drum 1 which is an electrostatic latent image carrier in the center.
A charging roller 2, a developing device 3, a transfer roller 4, and a cleaner 6 are sequentially arranged around the charging roller 2. A timing roller pair 7 is arranged on the upstream side of the transfer section A where the drum 1 and the transfer roller 4 come into contact, and further upstream there is a paper feed cassette (not shown) similar to conventional printers, a paper feed roller facing the cassette, A pair of transfer paper conveyance rollers and the like are arranged. Further, on the downstream side of the transfer section A, a conveyance guide plate, a fixing device, a paper ejection roller, and a paper ejection tray (not shown) are arranged as in conventional printers. Further, above the photosensitive drum 1, an optical system (not shown) is arranged which exposes the drum 1 to an image 8 using a laser beam modulated according to an image signal, similar to a conventional printer.

The transfer roller 4 has a sponge-like layer of silicon oxide mixed with an electrically conductive substance around a metal shaft 4a, and is electrically conductive as a whole. The drum 1 is driven by a driving means as shown in the figure.
It is rotated clockwise at a circumferential speed VA. The timing roller pair 7 and the like are also driven by the driving means. However, the timing roller pair 7 is driven via a clutch (not shown) so as to send the transfer paper to the transfer section A in synchronization with the toner image on the drum 1. Further, charging voltage is applied to the charging roller 2 by a power source (not shown), developing bias voltage is applied to the developing device 4 by a power source (not shown), and transfer bias power source S1 or cleaning bias power source S2 is switched to the transfer roller 4. Connection is made by operating the switch SW.

During transfer, when the transfer paper S passes through the transfer section A, the transfer roller 4 is moved in synchronization with the rotation of the photosensitive drum 1.
Although the photosensitive drum 1 rotates at a circumferential speed VA that is approximately the same as the circumferential speed of the photosensitive drum 1, in the non-transfer period when the transfer paper S is not present in the transfer section A between the images formed on the drum 1, the high-speed drive section 1
0, the photosensitive drum 1 is rotated at a peripheral speed VB higher than the peripheral speed of the photoreceptor drum 1. That is, the drive unit 10 drives the transfer roller 4
The shaft 4a is connected to the drive shaft of a motor M via a clutch CL.When not transferring, the clutch CL is connected and the transfer roller 4 is rotated at high speed by the motor M.Otherwise, the clutch CL is "disconnected". Make it.

[0010] Switching of the power sources S1 and S2 and switching of the rotation of the transfer roller are performed based on instructions from a control section 100 mainly composed of a microcomputer. That is, the control section 100 connects the power source S1 to the transfer roller 4 during transfer, and connects the power source S2 to the roller 4 during non-transfer, and uses the high-speed drive section 10 to drive the transfer roller 4.
switch SW and clutch CL to rotate at high speed.
is configured to operate.

According to the copying machine described above, the photosensitive drum 1 is driven to rotate clockwise in the figure, and the surface of the photosensitive drum 1 is uniformly charged by the charging roller 2. An image is exposed 8 to the charged area from an optical system (not shown), and an electrostatic latent image is formed. This latent image is developed by the developing device 3 with toner charged to the same polarity as the latent image, and becomes a toner image, which arrives at a transfer portion A formed at the nip portion between the drum 1 and the transfer roller 4. On the other hand, the transfer paper S is fed one by one from a paper feed cassette (not shown) and sent to the timing roller pair 7. The roller pair 7 feeds the transfer paper S to the transfer section A in synchronization with the toner image on the drum 1.

The transfer paper S sent to the transfer section A is transferred onto the transfer roller 4 by the action of the transfer roller 4, which is connected to the transfer power source S1 under the instruction of the control section 100 and biased to the opposite polarity to that of the toner. The toner image is transferred. The transfer paper S with the toner image transferred thereon then arrives at a fixing device (not shown), where the toner image is fixed, and then discharged outside the machine.

After the transfer, the photosensitive drum 1 continues to rotate clockwise in the figure, residual toner on its surface is scraped off by the cleaner 6, and its surface is charged again by the charging roller 2. Next, the relationship among the charging polarity of the photosensitive drum 1, the charging polarity of the toner, and the bias applied to the transfer roller will be explained with reference to FIG.

This embodiment employs a reversal development method in which toner is attached to the surface of the photosensitive drum irradiated with a laser beam. The photosensitive drum 1 is charged to a potential -V1 (-600V) by the charging roller 2, and the potential of the surface E2 of the photosensitive drum 1 irradiated with the laser beam is attenuated to -V2 (-80V). In order to attach the toner to this surface E2, the developing bias is set to -VD (-250V), and the negatively charged toner is transferred onto the photoreceptor drum 1 with a potential difference ΔV.

The bias of the transfer roller 4 is controlled by the control section 100.
At the time of transfer, by operating the switch SW based on the instruction,
This is obtained by applying a positive transfer voltage (+1.5 KV) from the power source S1. In addition, during non-transfer, a negative cleaning bias (-500 to -700V) is applied by the power source S2. Next, the timing of switching between the clutch CL and the transfer roller bias is shown in the timing chart of FIG. That is, at the time of transfer T2, the transfer roller 4 is rotated at approximately the same speed VA as the photoreceptor drum 1 due to the application of a transfer voltage having the opposite polarity to that of the toner. Toner is transferred. Furthermore, during non-transfer periods T1, T3, and T4, a transfer voltage of the same polarity as the toner is applied to the transfer roller 4, so that the toner adhering to the surface of the transfer roller 4 is transferred to the photoreceptor drum 1 and transferred. The surface of the roller 4 is cleaned, and at this time, the transfer roller 4 is removed from the photoreceptor drum 1.
Because it is rotated at a circumferential speed VB that is faster than the circumferential speed of
The time required for the transfer roller 4 to make one rotation is shortened, and the transfer roller 4 can be cleaned in a short interval between images.

In the figure, T1 is the period from when the transfer paper is fed to the transfer section A, and T3 is the period between the images (
Paper feeding interval) and T4 indicate the period from when the transfer paper passes through the transfer section until the image forming operation is completed, and both indicate the non-transfer time when there is no transfer paper in the transfer section. . It is preferable that the peripheral speed VB of the transfer roller 4 during non-transfer is set such that the transfer roller 4 rotates at least once during the period T3.

To show concrete numerical values, assuming that the system speed (peripheral speed of the photoreceptor drum) VA is 33 mm/sec,
For a printer that can print 6 sheets of A4 size paper per minute, the distance between images is 33 mm, that is, T
3 is 1 second. Therefore, the diameter of the transfer roller 4 is 1
If it is 6 mm, its circumference is 50.26 mm, so in order to make the transfer roller 4 rotate at least once in 1 second between images, the circumferential speed VB must be 50.26 mm/
It is necessary to rotate the transfer roller at a speed of sec or more.

In the above embodiment, the rotation direction of the transfer roller 4 during non-transfer is opposite to the rotation direction of the photosensitive drum 1, but it may be the same direction. Further, in the above embodiment, T1
Although the transfer roller 4 is cleaned at each of , T3, and T4, cleaning may be performed only for a portion of these periods depending on the degree of contamination.

[0019]

According to the present invention, the toner image formed on the electrostatic latent image carrier is transferred onto the transfer paper by passing the transfer paper between the electrostatic latent image carrier and the transfer roller. In the image device, there is no need to reduce the image forming speed, in other words, even if the distance between images formed on the electrostatic latent image carrier is short, the transfer roller can be cleaned by the cleaning bias application method.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a part particularly related to the present invention in an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the surface potential of a photoreceptor drum and the amount of light irradiated onto the drum from an optical system.

FIG. 3 is a timing chart showing the timing of switching between the clutch and transfer roller bias.

[Explanation of symbols]

1 Photoreceptor drum 4 Transfer roller S1 Transfer bias power supply S2　Cleaning bias power supply SW　Switch switch 10 High speed drive part CL Clutch M Motor 100 Control section A Transfer section S Transfer paper

Claims (1)

[Claims] 1. An image forming apparatus that transfers a toner image formed on an electrostatic latent image carrier onto the transfer paper by passing a transfer paper between the electrostatic latent image carrier and a transfer roller. a bias power source for cleaning, a means for driving and rotating the transfer roller at a higher speed than during transfer during non-transfer, and a means for connecting the transfer bias power to the transfer roller during transfer and the cleaning bias during non-transfer. An image forming apparatus comprising: a control means for connecting a power source to the transfer roller and causing the high-speed drive means to drive the transfer roller at high speed.