JP5310349B2 - Charging device and image forming apparatus - Google Patents

Description

  The present invention relates to a charging device and an image forming apparatus.

  The charging device removes foreign matters that cause charging failure in the photoreceptor from the outer peripheral surface of the charging roll by bringing a cleaning roll that is a cylindrical cleaning means into contact with the surface of the charging roll that is a rotating charging means. . For example, Patent Document 1 discloses a technique in which a porous sponge layer formed using a silicone foam stabilizer is used on the outer periphery of a cleaning roll.

JP-A-8-062948

However, such a substance such as a silicone foam stabilizer may be transferred from the cleaning roll to the charging roll due to a phenomenon in which the additive dispersed inside the molded product called bleed-out rises on the surface.
An object of the present invention is to reduce poor charging of an image carrier caused by a substance transferred from a cleaning unit to a charging unit.

According to a first aspect of the present invention, there is provided a charging unit for charging an image holding member for holding an image, a cleaning unit for removing foreign matter attached to the charging unit and cleaning the charging unit, the charging unit, and the cleaning unit. A continuous contact time specifying means for specifying a continuous contact time, which is a time during which the region in contact with the surface does not change, a measuring means for measuring temperature or humidity, and the continuous contact time specified by the continuous contact time specifying means And changing the region where the charging unit and the cleaning unit are in contact with each other over a period corresponding to the temperature or humidity measured by the measuring unit, and between the charging unit and the image carrier. And a voltage applying unit that applies a voltage.
The invention according to claim 2 comprises the charging device according to claim 1 and an image transfer means for forming an image on an image holding member charged by the charging device and transferring the image onto a recording medium. The image forming apparatus.
According to a third aspect of the present invention, in the configuration according to the second aspect, when an operation for starting the supply of power to the device itself is performed, the voltage application unit includes the continuous contact time and the temperature or the humidity. An image forming apparatus, wherein a voltage is applied between the charging unit and the image holding member while changing a region where the charging unit and the cleaning unit are in contact with each other over a period of time It is.

According to the first aspect of the present invention, it is possible to reduce the charging failure of the image carrier caused by the substance transferred from the cleaning unit to the charging unit.
According to the second aspect of the present invention, it is possible to reduce defective charging of the image carrier caused by the substance transferred from the cleaning unit to the charging unit.
According to the third aspect of the present invention, it is possible to reduce defective charging of the image carrier caused by the substance transferred from the cleaning unit to the charging unit.

1 is a block diagram illustrating a configuration of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a structure of a photosensitive drum 161 and a charging unit 162 according to the same embodiment. It is a figure which compares the continuous contact time which concerns on the same embodiment, and white stripe generation | occurrence | production intensity | strength. It is a figure which compares the continuous contact time and refresh time which concern on the same embodiment. 4 is a flowchart illustrating a refresh operation according to the embodiment.

Embodiments of the present invention will be described below with reference to the drawings.
(1) Configuration FIG. 1 is a block diagram illustrating a configuration of the image forming apparatus 1.
The image forming apparatus 1 forms an image on a recording sheet that is an example of a recording medium using toner that is an example of a color material, and reads an image formed on the recording sheet, for example, printing or scanning. It is a device that integrates the functions. The image forming apparatus 1 includes a control unit 11, a storage unit 12, an operation unit 13, a display unit 14, an image reading unit 15, an image forming unit 16, and an environment sensor unit 17.

  The control unit 11 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory), and the CPU executes a program stored in the ROM or the storage unit 12. Thus, each part of the image forming apparatus 1 is controlled. The storage unit 12 is a non-volatile auxiliary storage device such as an HD (Hard Disk), and stores various programs and data. The operation unit 13 includes a power switch and a plurality of keys. The operation unit 13 receives a user operation and supplies a signal corresponding to the operation to the control unit 11. Further, the time when the power switch of the operation unit 13 is switched ON and OFF is stored in the power switch log 122 of the storage unit 12. The display unit 14 includes a VRAM (Video RAM), a liquid crystal display, and a liquid crystal drive circuit. Based on information supplied from the control unit 11, the display unit 14 displays the progress of processing, information for guiding operations to the user, and the like. To do. The image reading unit 15 includes an optical system member constituted by a CCD (Charge Coupled Device), reads an image formed on a recording sheet by the optical system member, and generates image data representing the read image.

  The environment sensor unit 17 is an example of a measurement unit, and includes a temperature measurement sensor 172 and a humidity measurement sensor 173. The temperature measurement sensor 172 is a member such as a thermistor and measures the temperature in the image forming apparatus 1. The humidity measuring sensor 173 measures the amount of water vapor contained in the atmosphere, and calculates the relative humidity (%) by dividing the measured amount by the saturated water vapor amount corresponding to the temperature measured by the temperature measuring sensor 172. .

  The image forming unit 16 includes a photosensitive drum 161, a charging unit 162, an exposure unit 163, a developing unit 164, a transfer unit 165, a fixing unit 166, and a voltage applying unit 167, and an image reading unit. 15 forms an image on recording paper based on the image data generated by the image data 15 and image data received by a communication unit (not shown) from an external system such as a host device. The photosensitive drum 161 is an example of an image holding body that holds an image. The charging unit 162 charges the photosensitive drum 161. At this time, the voltage application unit 167 applies a voltage obtained by superimposing the DC component and the AC component to the charging unit 162. The exposure unit 163 includes a laser and an LED, and irradiates the photosensitive drum 161 with light to form an electrostatic latent image. The developing unit 164 stores a developer in which toner and a carrier are mixed, and develops the electrostatic latent image with the developer. The transfer unit 165 is an example of an image transfer unit that applies a reverse polarity voltage to the developed image and transfers the image to a recording sheet. The fixing unit 166 includes a heating roll and a pressure roll, and fixes the transferred image on the recording paper by applying pressure and heating.

FIG. 2 is a diagram illustrating the structure of the photosensitive drum 161 and the charging unit 162.
The photosensitive drum 161 is a cylindrical member including a conductive drum base and a photoconductive film in which an OPC (Organic Photo Conductor) is formed on the surface of the drum base. The photosensitive drum 161 rotates at a predetermined peripheral speed in the direction of an arrow A in the drawing with the center of the drum base as a rotation axis while maintaining a state in contact with the intermediate transfer belt.
The charging unit 162 includes a charging roll 162a that is an example of a charging unit that charges the photosensitive drum 161, and a cleaning roll 162b that is an example of a cleaning unit that cleans the peripheral surface of the charging roll 162a. The charging roll 162a rotates in the direction of arrow B in the drawing while being in contact with the outer peripheral surface of the photosensitive drum 161 in a state where a voltage is applied from a voltage applying unit 167 which is an example of a voltage applying unit. Are uniformly charged to a certain potential. The cleaning roll 162b is a cylindrical rotating body whose outer periphery is formed of a porous sponge layer, and rotates with the rotation of the charging roll 162a while keeping the peripheral surface in contact with the peripheral surface of the charging roll 162a. The foreign matter adhering to the peripheral surface of the charging roll 162a is scraped off by the minute unevenness of the peripheral surface of the cleaning roll 162b. In addition, a large number of holes formed in the sponge layer of the cleaning roll 162b are aligned so that the size and density thereof are as uniform as possible by using a silicone foam stabilizer during the production thereof.

  By the way, due to the phenomenon such as bleed-out described above, the silicone foam stabilizer may be transferred and adhered from the sponge layer of the cleaning roll 162b to the surface of the charging roll 162a. On the surface of the charging roll 162a, the charging potential with respect to the photosensitive drum 161 is different between the adhesion region where the silicone foam stabilizer is adhered and the non-adhesion region where the silicone foam stabilizer is not adhered. Here, it will be described in detail how the adhesion area of the charging roll 162a affects the formation of an image on the recording paper.

  When the photosensitive drum 161 is charged by the charging roll 162a in which the adhesion area and the non-adhesion area are generated, a difference occurs in the charging potential. That is, the surface of the photosensitive drum 161 charged by the adhesion area of the charging roll 162a has a higher charging potential than the surface of the photosensitive drum 161 charged by the non-attachment area of the charging roll 162a. Hereinafter, the surface of the photosensitive drum 161 having a high charging potential is referred to as a high potential region of the photosensitive drum 161.

  The exposure unit 163 irradiates a laser beam modulated in accordance with image data serving as a document of an image to be formed while scanning the circumferential surface of the photosensitive drum 161. The potential of the portion irradiated with the laser light on the surface of the photosensitive drum 161 is lowered, thereby forming an electrostatic latent image. At this time, the potential of the portion irradiated with the laser light in the high potential region of the photosensitive drum 161 remains higher than the potential of the portion irradiated with the laser light in the region other than the high potential region of the photosensitive drum 161. .

  The developing unit 164 transfers the toner to the photosensitive drum 161 and develops the electrostatic latent image formed on the photosensitive drum 161. However, the electrostatic latent image formed in the high potential region of the photoconductive drum 161 has a high charging potential, so that the toner is difficult to transfer. Therefore, in the image formed on the recording paper, in the region corresponding to the high potential region of the photoconductive drum 161, a sufficient amount of toner is not supplied, and the image density becomes light. Hereinafter, the low density portion of the image is referred to as white streak.

  Next, the characteristics of the silicone foam stabilizer transferred from the sponge layer of the cleaning roll 162b when it adheres to the surface of the charging roll 162a will be described in detail.

  First, in a situation where the contact surface between the charging roll 162a and the cleaning roll 162b continuously changes, such as during image formation processing, the silicone foam stabilizer transferred from the cleaning roll 162b is applied to the surface of the charging roll 162a. Since it spreads uniformly, white streak is hard to occur. On the other hand, when the power is off, the contact surface between the charging roll 162a and the cleaning roll 162b does not change and the silicone foam stabilizer transferred from the cleaning roll 162b does not change when the contact surface remains in the same place. White streaks tend to be noticeable because they locally adhere on the surface of the charging roll 162a.

  FIG. 3 shows the white streaking intensity in terms of temperature, humidity, and time (continuous contact time) when the contact surface between the charging roll 162a and the cleaning roll 162b does not change. Here, the white streak generation strength means the degree of local adhesion of the silicone foam stabilizer to the surface of the charging roll 162a. Further, the continuous contact time indicates a time during which the surface where the charging roll 162a and the cleaning roll 162b are in contact does not change. The continuous contact time is the last time when the power of the image forming apparatus 1 read from the power switch log 122 by the control unit 11 as an example of the continuous contact time specifying unit is switched from ON to OFF, and from the power OFF. It is specified from the time of the difference from the last time switched to ON. In addition, below, normal temperature is used as the temperature of 5 degreeC or more and 35 degrees C or less determined by Japanese Industrial Standard. Similarly, normal humidity is used as a relative humidity of 45% or more and 85% or less as defined by Japanese Industrial Standards.

Series 31 in FIG. 3 shows measurement results in an environment of normal temperature and normal humidity. The series 32 is a result of measurement in an environment where the humidity is lower by a predetermined amount than the environment in which the series 31 is measured. Here, it can be seen that the series 32 has a higher white stripe generation intensity at the same continuous contact time than the series 31. In addition, the line located at the tip of the arrow C in the figure is measured in a lower humidity environment, indicating that the white stripe generation intensity is higher. In other words, the silicone foam stabilizer has a high degree of local adhesion (white stripe generation strength) on the surface of the charging roll 162a in an environment with low humidity.
The series 33 is a result of measurement in an environment where the temperature is lower by a predetermined amount than the environment in which the series 32 is measured. Here, it can be seen that the series 33 has a smaller increase rate of the white stripe occurrence intensity per unit time at the time of rising than the series 32. In addition, the series located at the tip of the arrow D in the figure is measured in a lower temperature environment, indicating that the rate of increase in white streak generation intensity per unit time at the start-up is smaller. ing. That is, the speed of the silicone foam stabilizer locally adhering to the surface of the charging roll 162a is slow in a low temperature environment.
The series 34 is a result of measurement in an environment in which the temperature and humidity are higher than the environment in which the series 31 is measured by a predetermined amount. Here, it can be seen that the series 34 has a larger increase rate of white stripe generation intensity per unit time at the time of rising than the series 31 and further attenuates the white stripe generation intensity after a predetermined continuous contact time. . That is, in a high temperature and humidity environment, the silicone foam stabilizer has a high rate of local adhesion to the surface of the charging roll 162a and diffuses to the surface of the charging roll 162a. Is attenuated.

  The white stripe generation intensity is gradually attenuated by repeatedly forming an image on a recording sheet. Further, the white streak generation intensity is greater than the case where an AC voltage or a DC voltage applied during image formation is applied when an AC voltage greater than the AC voltage applied during image formation is applied from the voltage application unit 167. Also decay in a short time. However, the charging roll 162a contains an ionic conductive agent that conducts ions, and when a high voltage is applied, the ionic conductive agent is consumed. Further, when the semiconductive property of the charging roll 162a decreases due to consumption of the ionic conductive agent, the electrical resistance increases and the charging property decreases, and various defects such as image unevenness and image defects occur in the formed image. It becomes easy. Therefore, the voltage application unit 167 may set the AC voltage applied to attenuate the white streak generation intensity to about 1.3 times the AC voltage applied during image formation. Hereinafter, an operation in which the voltage application unit 167 applies an AC voltage to the charging roll 162a in order to attenuate the white stripe generation intensity is referred to as a refresh operation. The time required for the refresh operation is referred to as refresh time. The refresh operation is performed when the charging roll 162a and the cleaning roll 162b are not changed from the state in which the contact surface between the charging roll 162a and the cleaning roll 162b does not change, such as the timing when the power of the image forming apparatus 1 is switched from OFF to ON and the timing when the image forming apparatus 1 is restored from the standby mode. This is performed at the timing when the contact surface with the cleaning roll 162b is changed.

FIG. 4 is a diagram comparing the continuous contact time and the refresh time.
The refresh time is proportional to the white stripe occurrence intensity. Therefore, the diagram comparing the continuous contact time and the refresh time in FIG. 4 is similar to the diagram comparing the continuous contact time and the white streak generation intensity in FIG. 4 is obtained by adding a to the code of the corresponding sequence in FIG. Also, the characteristics of each series in FIG. 4 are the same as the characteristics of each series in FIG. For example, if the continuous contact time is S1 in FIG. 4, the refresh time changes depending on the temperature and humidity, which are the remaining variables, particularly depending on the temperature. On the other hand, assuming that the continuous contact time is S2 in FIG. 4, the refresh time changes depending on the humidity among the remaining variables of temperature and humidity, in particular. Information for specifying these refresh times is described in the storage unit 12 as refresh information 121.

(2) Operation Next, FIG. 5 is a flowchart for explaining the refresh operation.
The user switches the power of the image forming apparatus 1 from OFF to ON by operating the power switch of the operation unit 13 of the image forming apparatus 1. Then, the control part 11 detects that it is a timing which starts a refresh operation | movement with the electric power supply from the power supply source which is not shown as a trigger (step S51; YES).

  Next, the control part 11 specifies temperature, humidity, and continuous contact time (step S52). First, the control unit 11 controls the temperature measurement sensor 172 to measure the temperature inside the image forming apparatus 1. Hereinafter, the temperature measured by the temperature measurement sensor 172 is referred to as the in-machine temperature. The control unit 11 also controls the humidity sensor 173 to calculate the relative humidity inside the image forming apparatus 1. Hereinafter, the humidity measured by the humidity sensor 173 is referred to as in-machine humidity. Further, the control unit 11 reads the last time when the power of the image forming apparatus 1 was switched from ON to OFF and the last time when the power was switched from OFF to ON from the power switching log 122, and the difference between them. Identify the time. The time of this difference is a continuous contact time indicating a time during which the contact surface between the charging roll 162a and the cleaning roll 162b does not change.

  Next, the control unit 11 specifies the refresh time corresponding to the in-machine temperature, the in-machine humidity, and the continuous contact time identified in Step S52 from the refresh information 121 stored in the storage unit 12 (Step S53). For example, it is assumed that the in-machine temperature and in-machine humidity specified in step S53 correspond to the series 31a of FIG. 4 which is a measurement result in a normal temperature and normal humidity environment, and the continuous contact time corresponds to S2. Then, the refresh time can be specified as S3 from the value of the series 31a when the continuous contact time is S2.

  The control unit 11 performs the refresh operation by controlling the voltage application unit 167 to apply the AC voltage to the charging roll 162a for the refresh time specified in step S53 (step S54). At this time, the voltage application unit 167 applies an AC voltage 1.3 times larger than the AC voltage applied during image formation to the charging roll 162a. Then, the white streak generation intensity of the charging roll 162a is attenuated by the electrical vibration of the AC voltage applied from the voltage application unit 167.

  When the refresh operation is completed, the image forming apparatus 1 is in a state where processing according to an operation from the user can be performed, and performs processing for forming an image on a recording sheet.

(3) Modification (3-1) Modification 1
In the above embodiment, the developing unit 164 may supply toner to the photosensitive drum 161 even during the refresh operation. The charging roll 162a and the photosensitive drum 161 rotate during the refresh operation. A cleaning blade (not shown) is in contact with the peripheral surface of the photosensitive drum 161 in order to clean the toner adhering to the peripheral surface of the photosensitive drum 161. The cleaning blade is a plate-like member having substantially the same depth width as the axial direction of the photosensitive drum 161. During the refresh operation, the peripheral surface of the photosensitive drum 161 where toner is not attached is continuously cleaned by the cleaning blade, and there is a risk of scratching due to friction. Therefore, the developing unit 164 reduces the scratches caused by friction on the photosensitive drum 161 by supplying the toner.

(3-2) Modification 2
In the above embodiment, the timing of performing the refresh operation changes the contact surface between the charging roll 162a and the cleaning roll 162b, such as the timing when the power of the image forming apparatus 1 is switched from OFF to ON, the timing when the image forming apparatus 1 is restored from the standby mode, etc. The timing at which the contact surface between the charging roll 162a and the cleaning roll 162b is changed from the state where the charging roll 162a is not changed is not limited to this.
For example, the user may operate the operation unit 13 to instruct the image forming apparatus 1 to perform a refresh operation when it is determined that white stripes are generated in the image formed by the image forming apparatus 1. That is, the refresh operation may be started at an arbitrary timing according to a user instruction and executed for an arbitrary time.
(3-3) Modification 3
In the above embodiment, the charging failure of the photosensitive drum 161 occurs when the silicone foam stabilizer adheres to the surface of the charging roll 162a. However, any substance that can be transferred from the cleaning roll 162b to the charging roll 162a and affects the charging potential of the photosensitive drum 161 by adhering to the surface of the charging roll 162a can be used as a silicone foam stabilizer. Not exclusively.
(3-4) Modification 4
In the above embodiment, the refresh time is specified from the refresh information 121 based on the values of the in-machine temperature, the in-machine humidity, and the continuous contact time. However, the refresh time is not necessarily specified from the three values of the in-machine temperature, the in-machine humidity, and the continuous contact time. For example, the refresh time may be specified from two values of the in-machine temperature and the in-machine humidity and the continuous contact time.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 11 ... Control part, 12 ... Memory | storage part, 121 ... Refresh information, 122 ... Power supply switching log, 13 ... Operation part, 14 ... Display part, 15 ... Image reading part, 16 ... Image forming part, 161 ... photosensitive drum, 162 ... charging unit, 162a ... charging roll, 162b ... cleaning roll, 163 ... exposure unit, 164 ... developing unit, 165 ... transfer unit, 166 ... fixing unit, 167 ... voltage applying unit, 17 ... environmental sensor Part, 172 ... temperature measuring sensor, 173 ... humidity measuring sensor.

Claims (3)

Charging means for charging an image holding body for holding an image;
A cleaning means for removing foreign matter adhering to the charging means and cleaning the charging means;
Continuous contact time specifying means for specifying a continuous contact time, which is a time during which the region where the charging means and the cleaning means are in contact does not change;
A measuring means for measuring temperature or humidity;
The region where the charging unit and the cleaning unit are in contact is changed over a period according to the continuous contact time specified by the continuous contact time specifying unit and the temperature or humidity measured by the measuring unit. A charging device comprising: a voltage applying unit that applies a voltage between the charging unit and the image carrier. A charging device according to claim 1;
An image forming apparatus comprising: an image transfer unit that forms an image on an image holding member charged by the charging device and transfers the image to a recording medium. When an operation for starting the supply of electric power to the apparatus is performed, the voltage applying unit is configured such that the charging unit and the cleaning unit are in contact with each other over a period according to the continuous contact time and the temperature or the humidity. The image forming apparatus according to claim 2, wherein a voltage is applied between the charging unit and the image holding member while changing a region in which the image forming unit changes.

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