JPH0348870A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent an electrifying means from being deformed and deteriorated by permitting the electrifying means to abut on an image carrier at the prescribed pressure during a period of time that the electrifying means electrifies the image carrier, and permitting it to be separated from it or to come into contact with it at a pressure lower than the abutting pressure, at time other than that period. CONSTITUTION:When a solenoid 6 is turned on, an electrifying roller 2 abuts on the surface of a photosensitive drum 1 at the prescribed pressure by means of a spring 4, and the roller 2 turns accompanying the drum 1. A voltage is applied through an energizing terminal 5; thereby the surface of the drum 1 is uniformly electrified. When the solenoid 6 is turned off, an arm 7 turns to move the roller 2; consequently the roller 2 is caused to abut on the surface at a pressure lower than that in the condition where the solenoid is turned on, or to be completely separated from the surface. In this constitution, the roller 2 is not left abutting on the drum 1, and deformation of the electrifying roller 2 is prevented; additionally the occurrence of a residual image, which is formed by previous charges, is eliminated.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer, and more specifically to an image forming apparatus in which an image bearing member is uniformly charged by a contact charging member. Regarding.

(Prior Art) As is well known, an electrophotographic apparatus includes a process of uniformly charging the surface of a photoreceptor to a predetermined potential.

Most of the charging means currently in practical use are so-called corona dischargers. However, corona dischargers have the following problems.

(2) A high voltage of 4 to 8 KV must be applied to the wire of the corona discharger in order to bring the surface potential of the photoreceptor to 500 V to 700 ■.

■ Most of the discharge current from the wire flows through the shield, and the current used to charge the photoreceptor surface to a predetermined potential is only a few percent of the total discharge current.

■ Due to corona discharge, ozone is generated, which tends to cause oxidation of equipment components and deterioration of the surface of the photoreceptor due to ozone.In addition, in consideration of the effects of ozone on the human body, the ozone absorption/decomposition filter and the air flow to the filter are A fan is required as a means of generation.

■ Image unevenness is likely to occur due to wire dirt.

Therefore, recently, it has been considered to use contact charging means such as rollers, blades, brushes, etc., instead of using corona dischargers, which have many problems as described above. 'This is known, for example, from Japanese Patent Application Laid-open Nos. 57-t7a2s7, 58-40568, 5B-139156, and 58-150975.

[Problem that the invention is trying to solve]

However, these contact charging means need to be brought into contact with the photoreceptor with a certain degree of pressure in order to stably contact the photoreceptor and thereby obtain a good image without unevenness. Therefore, whether it is a charging roller, a charging brush, or a charging blade, a constant amount of pressure is constantly applied from the image carrier to the contact part. There is a problem that charging unevenness occurs in the roller pitch due to deformation and deterioration of parts, and charging unevenness occurs due to poor contact due to deformed parts of charging blades and brushes. In addition, due to long-term contact, charging means such as rollers and blades (
For example, plasticizers contained in conductive rubber (conductive rubber) that have a negative effect on the photoreceptor seep out into the contact area and adhere to the photoreceptor, resulting in drum memory or image deletion, resulting in poor images. There is also. Of course, there is a proposal to provide a protective layer on the surface of the charging roller (Japanese Patent Application Laid-Open No. 63-029814) to prevent this problem from occurring, but if the resistance value of the 1iFl is high (for example, 1012Ωc
m or more) The applied voltage is attenuated in the process of being applied to the contact portion with the photoreceptor, which has the disadvantage that a sufficient electric field necessary for charging is not formed. It is difficult to set the thickness of I to a value large enough to completely prevent plasticizer etc. from seeping out, so long-term contact may cause the plasticizer to pass through the protective layer and adversely affect the photoreceptor. be.

(Object of the Invention) The present invention has been made in view of the above points, and an object thereof is to prevent deformation and deterioration of the charging means that contacts the image carrier, and to prevent charging defects caused by the deformation and deterioration. be.

Another object of the present invention is to prevent charging memory of an image carrier and image deletion, and form a good image.

(Structure of the Invention) In order to achieve the above object, the present invention provides an image forming apparatus having a charging means that comes into contact with an image carrier and charges the surface of the image carrier, in which at least the charging means While the image bearing member is being charged, the charging means is brought into contact with the image bearing member at a predetermined pressure, and at other times, the charging means is not brought into contact with the image bearing member or the image being charged is It is characterized in that the carrier is moved so as to come into contact with the carrier with a pressure smaller than the contact pressure of the charging means with respect to the carrier.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

1 and 2 show a first embodiment of the present invention, and FIG. 1 is a schematic sectional view of the photosensitive drum and its surroundings of a copying machine that best represents the features of the present invention. Although this embodiment will be described using a copying machine, the present invention is not limited to copying machines, but can be applied to general image forming apparatuses that form images on image carriers, such as laser beam printers. Further, although a photosensitive drum is used for convenience, a belt-shaped photosensitive member may also be used.

In FIG. 1, 1 is a photosensitive drum which is an image carrier; 2 is a contact charging means; a charging roller made of conductive rubber; 3 is a conductive bearing that receives the core of the charging roller 2; 4 connects the charging roller 2 to the photosensitive drum 1
5 is a roller energizing terminal for supplying power to the charging roller 2; 6 is a charging roller solenoid for moving the position of the charging roller 2; 7 is charging when the solenoid 6 is turned ON-OFF. A solenoid arm for moving the roller, 8 a short focus imaging element for exposing the photosensitive drum 1, 9 a developing device, 10 a transfer guide, 11 a transfer roller, 12 a cleaning device, and 13 a conveyance guide. It is.

The operation will be explained according to FIG. The photosensitive drum 1 rotates at a constant speed in the direction of arrow A. The charging roller 2 is pressed against the photosensitive drum 1 with a predetermined pressure, and rotates as the photosensitive drum 1 rotates. The charging roller 2 will be explained in detail later. The photosensitive drum 1, whose surface has been uniformly charged by the charging roller 2, is exposed to image light by a short focus imaging element in an exposure section to form an electrostatic latent image. Thereafter, the electrostatic latent image formed on the photosensitive drum 1 is developed by the developing device 9, which uses toner from the developing device 9 to develop the image. The transfer roller 11 to which a voltage is applied transfers the image onto the transfer paper P, which is the transfer material that has been sent. The transfer paper P on which the toner image has been transferred passes through the conveyance guide 13 and is guided to a fixing device (not shown) where it is fixed. On the other hand, the surface of the photosensitive drum 1 on which the toner image has been transferred is cleaned of residual toner etc. by a cleaning device 12.
It is subjected to charging again.

Next, the charging process will be explained in detail. First, M3111 of the charging roller 2 will be explained. In the state shown in FIG. 1, the charging roller solenoid 6 is in an ON or pulled state. In this state, the f-electric roller 2 is in contact with the surface of the photosensitive drum 1 under a predetermined pressure (in this case, a pressure of I kg per 210 mm of A4 length) due to the pressing force of the roller pressure spring 4. Therefore, the charging roller 2 is driven by the frictional force between the surface of the photosensitive drum 1 and the surface of the charging roller 2 as the photosensitive drum 1 rotates.

In this state, if an appropriate voltage is applied to the charging roller 2 through the current terminal 5 from the power source, it becomes possible to charge the photosensitive drum 1 uniformly.

Next, when the charging roller solenoid 6 is turned off, the solenoid returns to its original state where it is not pulled, so the solenoid shaft moves as shown by the arrow a in the figure, the solenoid arm 7 rotates in the direction b, and the charging roller 2 move in the direction of C. Since the f-electric roller 2 is moved in the direction C, the pressure is at least lower than the pressure when the solenoid is in contact with the ON state (500 g per A4 vertical 210 mm).
(pressure below) or no contact at all. FIG. 2 shows a schematic sequence of the image forming apparatus of the present invention. Such sequence control is performed by the CPU. While the drum is stopped, the signal of the charging roller solenoid is OFF, so the charging roller 2 is not in contact with the surface of the photosensitive drum 1, or the pressure is lower than when it is in contact with the surface of the photosensitive drum 1. are in contact. The drum drive signal turns ON,
At the same time as the photosensitive drum 1 begins to rotate, the IF electric roller solenoid 6 is turned on, and as described above, the charging roller 2 comes into pressure contact with the photosensitive drum 1 with a predetermined pressure and begins to rotate. Even if the charging roller 2 is driven to rotate, the high-voltage power supply that applies voltage to the charging roller 2 is turned off at this point, so the photosensitive drum is not charged. Next, by turning on the high-voltage power supply output, a voltage is applied to the charging roller 2 through the roller passthrough 5, and uniform IF charging becomes possible on the photosensitive drum 1. Each process step such as image exposure and development is started after the primary charging is started. After a series of copying processes are completed, the drum drive is turned off.
FF, and at the same time charging roller solenoid 6 is also turned OFF.
Becomes FF. When the charging roller solenoid 6 is turned OFF, the charging roller 2 is brought into a state where it is not in contact with the photosensitive drum 1 again, or is brought into contact with the photosensitive drum 1 with a smaller pressure than when it is in contact with the photosensitive drum 1 in the ON state.

As explained above, during and outside the copying operation, the charging roller 2 is always in contact with the photosensitive drum 1 without contact or with a small pressure, so that the charging roller 2 and the photosensitive drum 1 stop and the roller 2 is deformed. Since the charging roller is not left in contact with the drum 1, there is no deformation of the charging roller, and before forming an image on the photosensitive drum, the previous charge cannot be completely removed by pre-exposure etc. An afterimage occurs. No memory is generated. Although the contact charging means has been described using a charging roller, it is not limited to the charging roller, and may of course be a charging blade or a charging brush.

FIG. 3 shows the configuration of a charging blade as an example of charging means. In FIG. 3, 1 is a photosensitive drum, 20 is a charging blade, and when a solenoid (not shown) is ON, as in the case of the charging roller, they are in contact with a predetermined pressure as shown by the solid line. When the is turned OFF, as shown by the dotted line, there is no contact with the photosensitive drum or the O
This brings about a state in which they come into contact with a smaller pressure than the state in which they were in contact in the N state. Therefore, during the copying operation and outside, the charging roller 2 is always in contact with the photosensitive drum 1 without contact or with a small pressure, so there is no deformation of the charging roller, and no memory is generated on the photosensitive drum.

In FIG. 1, a process cartridge system may be used in which the photosensitive tram 1 and other components (developing device or cleaning device) other than the charging roller are integrated and are detachable from the main body.

In the experiment, the photosensitive drum was φ60 opc, and the electric roller was a conductive EPDM (105 Ωcm) with a diameter of 1 mm whose surface was protected with carbon-dispersed nylon resin.
Using a 2mm roller, the voltage applied to the roller is 1
．． A good image was obtained by using an AC voltage with a peak-to-peak voltage of 8 KV and a DC voltage of -700 V superimposed thereon.

Next, another embodiment of the image forming apparatus of the present invention will be described.

This embodiment has a different sequence from the first embodiment in the apparatus shown in FIG. A timing chart of this embodiment is shown in FIG. FIG. 4 is a timing chart when the number of copies is two consecutive copies. The drum drive remains ON from the start to the end of copying.
There is no stopping between copying the first sheet and copying the second sheet. On the other hand, the charging roller solenoid is turned off during the amount of copying operation for the first and second sheets, and moves away from the surface of the photosensitive drum 1 (in this case, it is assumed that the contact pressure is not small). On the other hand, the high-voltage power supply output remains ON for the amount of copying operations for the first and second copies. Therefore, the voltage necessary for charging is applied to the charging roller 2 throughout the copying operation.

However, during the copying operation of the first and second sheets, the electric roller 2 is not brought into contact with the photosensitive drum 1.
The photosensitive drum 1 is not charged. By following the sequence explained above, ■Contact of charging roller, etc. 1! Since there is a time when the electric means is separated from the photosensitive drum 1 even during continuous copying operation, this is effective for preventing roller deformation and roller staining due to drum memory toner. ■Charging roller O
There is an advantage that the ON10FF of the high voltage power supply does not need to be controlled by the N10FF.

Further, FIG. 1 shows still another embodiment different from the above-mentioned embodiment in the apparatus.

A timing chart of this embodiment is shown in FIG. 5. In FIG. 5, the charging roller solenoid is turned on before the drum is driven. That is, while the photosensitive drum 1 is stopped, the charging roller 2 is pressurized. By turning on the charging roller solenoid before driving the drum, it is possible to prevent shocks that occur when applying pressure to bring the charging roller into contact with the drum while it is rotating. Damage to the charging roller can be prevented, and deformation of the charging roller 2 and memory of the photosensitive drum can also be prevented.

This embodiment also has a different sequence from the apparatus shown in FIG. A timing chart of this embodiment is shown in FIG. In FIG. 6, the high voltage bias output is turned on before the charging roller solenoid is turned on. That is, the sequence is such that first, a primary high voltage bias is applied to the charging roller 2, and then the charging roller 2 is brought into contact with the photosensitive drum 1.

By taking Sequence 2, the influence of the rise of the output voltage of the high voltage bias does not affect the photosensitive drum, and even if a rush current larger than usual occurs when the high voltage bias is turned on, the charging roller will come into contact with the photosensitive drum. Since they are not in contact with each other, the photosensitive drum will not be electrically damaged or destroyed.

Another embodiment is shown in FIG. 7. In FIG. 7, 1' is a seamed photosensitive drum, 2 is a charging roller, 3 is a roller bearing, and 4 is a pressure spring.

The photosensitive drum 1' has a seam part X.
A seam flange convex portion 18 is formed on the drum flange in an area completely including the drum flange. The seam flange convex portion 18 is provided at a longitudinal position in contact with the roller bearing 3. Therefore, in areas that are not convex, 1F
The electric roller 2 is in contact with the photosensitive drum 1', and when the seam flange convex part comes, the roller bearing 3 compresses the pressure spring 4 in the direction away from the photosensitive drum 1', and the charging roller moves along the convex part. 2 is spaced apart from the photosensitive drum 1'. Start position (stop position) of the image forming apparatus main body
By setting the charging roller 2 to the position shown in FIG. 7, the charging roller 2 can be kept separated from the photosensitive drum 1' when not in use. In addition, f'I is applied to the seam portion of the photosensitive drum 1'.
Since the t-roller 2 does not come into contact with the charging roller 2, no damage is caused to the charging roller 2.

Another embodiment is shown in FIG. FIG. 8 is a schematic cross-sectional view of a process cartridge section of an image forming process device in which a contact charging means (in the case of this embodiment, charging roller 2) is contained in a process cartridge frame 26 having a photosensitive drum 1, etc. . The process cartridge includes a photosensitive drum and at least one image forming process device (including a cleaning device), and is removably attached to the main body of an image forming apparatus (not shown) such as a copying machine. 1 is a photosensitive drum, 2
is a charging roller, 9 is a developing device, and 11 is a transfer roller.
12 is a cleaning device.

Since the image forming process is the same as in the embodiments described so far, the explanation will be omitted here, and the operation of the %Fm roller 2 will be explained in detail below.

The charging roller 2 is rotatably supported by a roller bearing 21, and a conductive material may be used as a means for supplying electricity to the charging roller 2. roller bearing 2
1 is a cartridge frame 26 by a roller release spring 22.
and fixed so that it can be moved. Under normal conditions, the charging roller 2 is released from the photosensitive drum 1 by the force of a roller release spring 22. That is, in normal cases, the charging roller 2 is in contact with the photosensitive drum 1 without contact or with light pressure (corresponding to the roller position indicated by the solid line in the figure). Now, from this state, image formation is started. To do this, when starting charging, the roller pressure solenoid 25 is turned on, that is, the solenoid 25 is pulled in the direction of arrow C in the figure. When the solenoid 25 is bent in the direction C, the solenoid lever 24 rotates as shown by the arrow d in the figure, and moves the roller pressure lever 23 as shown by the arrow e in the figure. Roller pressure lever 23
moves as shown by the arrow e in the figure, and moves the roller bearing 21 from the opening of the cartridge frame 26 as shown by the arrow f in the figure, against the force of the roller release spring 22. By moving the roller bearing 21 as shown by the arrow f, the charging roller 2 changes from being in contact with the photosensitive drum 1 or in contact with the photosensitive drum 1 with a light pressure to the photosensitive drum 1 with a pressure that provides a predetermined stable charging. be touched. When the charging sequence is completed, the roller pressure solenoid 25 is turned off, and the roller pressure lever 23 is separated from the roller bearing 21. At the same time as the roller pressure lever 23 separates from the roller bearing, the charging roller 2 and the roller bearing 21 are returned to their original states by the restoring force of the roller release spring 22, and the roller 2 is not in contact with the photosensitive drum 1 or the pressure at the time of charging is removed. It becomes a state of lighter pressure.

As explained above, even when the contact charging means is included in the process cartridge, as in the case where the contact charging means is included in the main body of the apparatus, the charging roller 2 is Since the charging roller 2 is always in contact with the photosensitive drum 1 without contact or with a small pressure, there is no deformation of the charging roller 2, and no memory is generated on the photosensitive drum. It goes without saying that the sequence shown in FIGS. 5 to 7 may be used, and the contact charging means is not limited to a roller shape, but may be a blade or a brush shape.

Furthermore, in the above embodiment, especially in the sequence shown in FIG. 2, the length of the photoreceptor in the 8th direction charged by the charging roller is
It is preferable that the length corresponds to the length of the transfer material in the moving direction. According to this, since electric charges are not applied to parts of the photoreceptor other than those corresponding to the transfer material, it is possible to prevent unnecessary electric charges and unnecessary toner from being applied to the photoreceptor.

[Effects of the Invention] As described above, according to the image forming apparatus of the present invention, the charging means is not in contact with the image bearing member or the charging means is not in contact with the image bearing member except when the contact charging means of the image bearing member is charging the image bearing member. Since it is moved so that it makes contact with a pressure smaller than the contact pressure during charging, it is possible to prevent deformation and deterioration of the charging means and prevent IF charging failures. Further, according to the image forming apparatus of the present invention, it is possible to prevent image deletion and charging memory of the image carrier and form a good image.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of a copying machine showing an embodiment of the image forming apparatus of the present invention. FIGS. 2 and 4 to 6 are timing charts showing the sequence of the image forming apparatus of the present invention. FIG. 3 is a schematic cross-sectional view of the vicinity of the charging blade when the charging blade is used as the charging means of the image forming apparatus of the present invention. FIG. 7 is a schematic cross-sectional view of the vicinity of the charging roller when a seamed photoreceptor is used as the image bearing member of the image forming apparatus of the present invention. FIG. 8 is a schematic sectional view of the vicinity of a process cartridge showing another embodiment of the image forming apparatus of the present invention. 1.1' is the photosensitive drum 2, the charging roller 3, the conductive bearing 4, the roller pressure spring 5, the roller energizing terminal 6, the charging roller solenoid 7, the solenoid arm 8, the short focus imaging element 9, the developing device 10, and the transfer roller. The guide 11 is the transfer roller 12, the cleaning device 13, the conveyance guide P, the transfer paper 18, the seam part, the flange, the convex part X, the seal part 20, the charging blade

Claims (1)

[Claims] In an image forming apparatus having a charging device that comes into contact with an image carrier to charge the surface of the image carrier, the charging device is held at a predetermined pressure at least while the charging device is charging the image carrier. During other times, the charging means is moved so as to be in contact with the image carrier without contact or with a pressure smaller than the contact pressure of the charging means against the image carrier during charging. An image forming apparatus characterized by: