JP2017068171A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation device capable of providing a good image with no concentration fluctuation, fogging, nor sticking of carrier on an image even if a resistance value of a charging roller fluctuates.SOLUTION: An image formation device includes an image carrier, a roll-like charging member which contacts to the image carrier, a power feeding member which contacts to the charging member, voltage application means capable of applying a voltage to each of the charging member and the power feeding member, a switch which makes the power feeding member come into a float state or a state being connected to the earth, and a current meter capable of detecting a current that flows the charging member or the power feeding member. The power feeding member is made to come into a state in which it is connected to the earth. When the charging member is applied with a predetermined voltage, a current that flows the charging member or the power feeding member is measured. Based on the measured current, a voltage that is applied at the time of image formation is decided.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus using an electrophotographic method, and particularly relates to cost reduction and image quality improvement.

  In the charging device, there is a technique for uniformly charging the surface of the photosensitive member by bringing a rubber roller (charging roller) into contact with the photosensitive drum and applying a voltage, and a DC charging method in which only a DC voltage is applied, and a DC voltage. An AC charging method or the like in which a voltage obtained by superimposing an AC voltage on the AC is known. Compared with the AC charging method, the DC charging method does not require an AC power supply, which is advantageous for downsizing and low cost of the apparatus.

  However, in the DC charging method, since the applied current is unidirectional, resistance fluctuation (so-called deterioration of energization) due to bias of the conductive material becomes a problem as compared with the AC charging method.

  In order to solve the above-described problem, a technology is disclosed in which a feeding roller that contacts a charging roller is provided, different voltages are applied, and current flow bias is reduced to suppress energization deterioration (Patent Document 1).

  Further, a technique for measuring and using the resistance of the charging roller in advance is disclosed (Patent Document 2).

US Pat. No. 7,298,993 JP 2002-296873 A

  However, even if the technique described in Patent Document 1 is used, it is inevitable that the resistance of the charging roller varies depending on the environment and usage conditions. In that case, in the case of the DC charging method, it is difficult to charge the photosensitive drum to a desired potential unless the applied voltage is changed depending on the resistance value of the charging roller.

  Further, if the technique of Patent Document 2 is used, micro chargeability such as horizontal stripes in an LL environment can be solved, but macro potential change of the photosensitive drum due to resistance change of the charging roller cannot be solved.

  Here, the Vd fluctuation, which is a problem of DC charging, will be described.

  In the DC charging method, when the difference between the surface potential of the charging roller 2a and the surface potential of the photosensitive drum 1 exceeds the discharge start voltage, discharging is performed between the charging roller 2a and the photosensitive drum 1, and the applied voltage increases. Along with this, the potential of the photosensitive drum 1 rises linearly. The surface potential of the charging roller 2a is determined by the resistance value of the charging roller 2a and the voltage applied to the charging roller 2a. However, since the resistance value of the charging roller 2a varies depending on manufacturing variations, environmental changes, and usage conditions, unless the voltage applied to the charging roller 2a is set to an appropriate value, the potential charged on the photosensitive drum 1 changes. As a result, density fluctuations on the image, a phenomenon in which the toner is developed in an unintended portion (fogging), and a phenomenon in which the carrier adheres occur.

In order to solve the above problems, an image forming apparatus according to the present invention includes:
A photosensitive drum; a roll-shaped charging member that contacts the photosensitive drum; a power supply member that contacts the charging member; a voltage applying unit that can apply a voltage to each of the charging member and the power supply member; and the power supply member. A switch to be in a float state or a state connected to the ground, and an ammeter capable of detecting a current flowing in the charging member or the power feeding member,
When the power supply member is connected to the ground and a predetermined voltage is applied to the charging member, the current flowing through the charging member or the power supply member is measured, and the measured current is applied during image formation. The voltage is determined.

  According to the image forming apparatus of the present invention, the resistance value of the charging roller can be known more accurately, and the photosensitive drum is uniformly charged to a desired potential by applying an appropriate voltage by the charging roller. Can do.

Schematic diagram of image forming apparatus Flow chart of the first embodiment Block circuit diagram of Embodiment 1 Applied voltage determination table Block circuit diagram of embodiment 2 Flow chart of embodiment 2 Environmental classification table Schematic diagram of Example 4

  DESCRIPTION OF EMBODIMENTS Embodiments for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic configuration model diagram of an example of an image forming apparatus according to the present invention. The image forming apparatus of this example is a laser beam printer using an electrophotographic process, a contact charging method, and a reversal development method.

  The image forming apparatus includes a rotatable drum-shaped electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1 as an image carrier, and also serves as a charging unit along the moving direction (clockwise) of the photosensitive drum 1. The charging unit 2, the latent image forming unit 3, the developing unit 4, the transfer unit 5, and the cleaning device 6 are disposed.

Further, a fixing unit 7 is installed on the downstream side of the transfer unit (the transfer direction of the transfer material P).
The photosensitive drum 1 is rotated in the arrow direction (clockwise) by a driving unit (not shown). The photosensitive drum 1 includes a subbing layer that suppresses light interference and improves the adhesiveness of the upper layer on the surface of a conductive base tube (in this embodiment, an aluminum cylindrical tube having a thickness of 0.8 mm), and photocharge generation. A layer and a charge transport layer are applied in order from the bottom. The resistance value of the photosensitive drum 1 is generally larger than 1E + 13 [Ω].

  The charging unit 2 includes a charging roller 2a disposed so as to contact the photosensitive drum 1, a power supply roller 2b disposed so as to contact the charging roller 2a, a power source S, a power source S and the charging roller 2a or the power supply roller 2b. The switch SW1 for switching the connection, the switch SW2 for switching the connection between the power supply roller 2b and the ground, and an ammeter A (not shown) that detects a current flowing in the circuit built in the power source S.

  In this embodiment, as the charging roller 2a, an elastic roller in which a SUS cored bar having a diameter of 6 mm is formed with a base layer having a thickness of 3 mm and a surface layer having a thickness of 10 μm is used. Any known technique can be used. Further, the resistance value of the charging roller 2a is generally about 1E + 05 to 1E + 08 [Ω]. When the voltage is lower than 1E + 05 [Ω], a phenomenon occurs in which current is concentrated at one point when a voltage is applied. When the voltage is higher than 1E + 08 [Ω], uniform discharge does not occur.

  As the power supply roller 2b, a round bar of SUS304 having a diameter of 8 mm, surface finish No. 2B was used. However, it is not limited to this, and any conductive roll-like member can be used. In that case, it is desirable to use a roller whose resistance value is sufficiently smaller than that of the charging roller.

  As the exposure apparatus 3, a laser scanner is used in this embodiment. A known technique can be used as long as it forms a latent image on the surface of the photosensitive drum 1.

  The developing unit 4 is a two-component magnetic brush developing system in the present embodiment, and the toner adheres to the exposed portion (bright portion) of the surface of the photosensitive drum 1 to reversely develop the electrostatic latent image. The developing section 4 is provided with a rotatable nonmagnetic developing sleeve 4a including a developing magnet 4b. The developer 10 in the developing container 4c is coated on the developing sleeve 4a in a thin layer with a regulating blade 4d. Then, it is conveyed to a portion facing the photosensitive drum 1. The developer 10 in the developing container 4c is conveyed to the developing sleeve 4a while being uniformly stirred by the rotation of a developer stirring member (not shown).

  A predetermined developing voltage is applied to the developing sleeve 4a from a power source (not shown). In this embodiment, the developing voltage applied to the developing sleeve during image formation is an oscillating voltage obtained by superimposing a rectangular wave AC voltage on a DC voltage. Further, the present invention is not limited to this, and only a DC voltage may be applied, or a known developing device may be used.

  The transfer unit 5 is a transfer unit that transfers the toner image on the surface of the photosensitive drum 1 to a transfer material P such as paper, and a sponge roller is disposed facing the photosensitive drum 1. Further, a voltage is applied to the sponge roller of the transfer unit 5 by a voltage applying means (not shown), and the transfer is performed electrically and mechanically. Further, the transfer technique is not limited to this, and a known transfer technique may be used.

  The cleaning device 6 rubs the surface of the photosensitive drum 1 after transferring the toner image onto the transfer material P with a cleaning blade, removes the transfer residual toner, and cleans the surface of the photosensitive drum 1. In this embodiment, a cleaning blade was used. The present invention is not limited to this, and any known technique can be used as long as the surface of the photosensitive drum 1 is cleaned.

  The fixing device 7 has a rotatable fixing roller and a pressure roller, and is transferred onto the surface of the transfer material P while nipping and conveying the transfer material P at a fixing nip portion between the fixing roller and the pressure roller. The toner image is heat-pressed and heat-fixed. In addition to the present embodiment, any known technique can be used as long as the toner transferred onto the surface of the transfer material P is fixed.

  Here, the resistance measurement method will be described with reference to the flowchart of FIG. 2, the block circuit diagram of FIG. 3, and Table 1 of FIG.

  FIG. 3 is a block circuit diagram.

  The CPU controls the power source S, changeover switches SW1 and SW2, and a motor (MTR) that drives the photosensitive drum 1. Further, the value measured by the ammeter A that detects the current flowing in the circuit is sent to the CPU.

  First, when the mode for measuring the resistance of the charging roller 2a is entered, the SW1 is switched to control the voltage to be applied to the charging roller 2a, and the SW2 is switched to connect the power supply roller 2b to the ground (F11). Next, the photosensitive drum 1 is rotated by a driving means (not shown), and the charging roller 2a and the power supply roller 2b are driven to rotate (F12). Then, the power source S is controlled to apply a voltage to the charging roller 2a (F13).

  In this embodiment, a DC voltage of 100 V is applied for a time during which the charging roller 2a rotates once. Further, the current value was measured for the time for which the charging roller 2a makes one rotation every 10 μs, and the resistance value of the charging roller 2a was calculated from the average value, and the resistance value was obtained as 4.5E + 06 [Ω] (F14). ).

  Next, the voltage applied at the time of image formation is determined according to the applied voltage determination table of FIG. 4 (F15). How many V the surface potential of the photosensitive drum 1 is set may be arbitrarily determined depending on, for example, the image density, the usage state of the photosensitive drum 1, the installed environment (temperature and humidity), and the like. In this embodiment, it was set to 600V. The resistance value is 1. E + 06 [Ω] or more Since it is less than E + 07 [Ω], the surface of the photosensitive drum 1 can be set to 600 V by applying 1200 V to the power supply roller 2b during image formation.

  Finally, the power supply S is controlled to stop the voltage application, the drive of the photosensitive drum 1 is stopped, the SW2 is switched to disconnect the power supply roller 2b from the ground, and the SW1 is switched to connect the power supply to the power supply roller 2b ( F16).

  By doing so, the surface potential of the photosensitive drum 1 can be accurately set to a desired potential at the time of image formation, and a good image without macro potential unevenness can be output.

  The second embodiment has substantially the same configuration as that of the first embodiment, and has an environmental sensor (not shown) that can measure the temperature and humidity of the place where it is installed. FIG. 5 is a block circuit diagram of the second embodiment, and the temperature and humidity measured by the environmental sensor are sent to the CPU.

  FIG. 6 is a flowchart of the second embodiment. FIG. 7 is a table showing the relationship between the environmental classification and the resistance correction value.

  First, as in the first embodiment, when the mode for measuring the resistance of the charging roller 2a is entered, the SW1 is switched to control the voltage to be applied to the charging roller 2a, and the SW2 is switched to connect the power supply roller 2b to the ground. To do. Next, the photosensitive drum 1 is rotated by a driving unit (not shown), and the charging roller 2a and the power supply roller 2b are driven to rotate. Then, the power source S is controlled to apply a voltage to the charging roller 2a. In this embodiment, a DC voltage of 100 V is applied for a time during which the charging roller 2a rotates once. Further, the current value is measured for the time for which the charging roller 2a makes one rotation every 10 μs (F21).

  Next, the value of an environmental sensor (not shown) is read (F22).

  Then, it is determined whether or not the measured resistance value is larger than 1E + 08 [Ω] (F23). When the measured resistance value is larger than 1E + 08 [Ω], the dirt discharge mode is executed (F231). First, the circuit is connected in the same manner as in normal image formation, and the photosensitive drum 1 is charged. In this embodiment, 1100 V was applied to the power supply roller. Next, when the photosensitive drum 1 goes around, the voltage applied to the power supply roller is lowered.

  In this example, it was set to 950V. By doing so, a potential difference between the photosensitive drum 1 and the charging roller 2a is generated, and the toner and external additives attached to the surface of the charging roller 2a move to the surface of the photosensitive drum 1. When the photosensitive drum 1 makes one round again, the voltage application to the power supply roller 2b is stopped.

  When the dirt discharge mode ends, the resistance value of the charging roller 2a is measured again (F232). The method of measuring the resistance value is the same as F21.

  When the resistance value is measured, it is determined whether or not the measured resistance value is greater than 1E + 08 [Ω] (F233).

If the measured resistance value is greater than 1E + 08 [Ω], it is determined whether the environmental classification has changed since the previous resistance measurement. If it has not changed, an error is displayed (F245).
If the environmental classification has changed, it is determined whether the environmental classification numerical value has increased (F235).

  If the environmental classification value becomes large, an error is displayed (F245).

  If the environmental category value is not increased, the environmental category change correction is performed (F236). 7 is multiplied by the correction value in accordance with the environmental classification values in Table 2.

  It is determined whether or not the resistance value after the environmental classification change correction is greater than 1E + 08 [Ω] (F237). When the resistance value is larger than 1E + 08 [Ω], an error is displayed.

  When the resistance value measured in F233 and F237 is not larger than 1E + 08 [Ω], it is determined whether or not the resistance value is smaller than 1E + 05 [Ω] (F24).

  When the measured resistance value is smaller than 1E + 05 [Ω], it is determined whether the environmental classification has changed since the previous resistance measurement. If it has not changed, an error is displayed (F245).

  If the environmental classification has changed, it is determined whether the environmental classification numerical value has increased (F242).

If the environmental classification value is not large, an error is displayed (F245).
If the environmental category numerical value is large, the environmental category change correction is performed (F243). 7 is multiplied by the correction value in accordance with the environmental classification values in Table 2.

  It is determined whether or not the resistance value after the environmental classification change correction is smaller than 1E + 05 [Ω] (F244). When the resistance value is smaller than 1E + 05 [Ω], an error is displayed.

  When the resistance value is not smaller than 1E + 05 [Ω] at F24 and F244, the voltage to be applied is determined according to the application voltage determination table of FIG.

  Finally, the power supply S is controlled to stop the voltage application, the driving of the photosensitive drum 1 is stopped, the SW2 is switched to disconnect the power supply roller 2b from the ground, and the SW1 is switched to connect the power supply to the power supply roller (F26). ).

  By doing so, the surface potential of the photosensitive drum 1 can be accurately set to a desired potential at the time of image formation, and a good image without macro potential unevenness can be output.

  When the film thickness of the photosensitive drum 1 changes, the surface potential of the photosensitive drum 1 changes even if the same voltage is applied depending on the film thickness. Therefore, it is necessary to change the voltage to be applied depending on the film thickness of the photosensitive drum 1. In this embodiment, every time the film thickness changes by 1 μm, the applied voltage is changed by 10V.

  First, the resistance value of the charging roller 2a is measured as in the first embodiment. Next, the film thickness of the photosensitive drum 1 is detected by a known method for measuring the film thickness of the photosensitive drum 1 (a method for detecting the current flowing through the photosensitive drum 1, an inference based on the number of sheets used).

Then, how much the film thickness of the photosensitive drum 1 has changed from the first time is obtained, and the applied voltage is changed according to the changed film thickness.
By doing so, the surface potential of the photosensitive drum 1 can be accurately set to a desired potential at the time of image formation, and a good image without macro potential unevenness can be output.

  The fourth embodiment has substantially the same configuration as that of the first embodiment. However, as shown in FIG. 8, the charging unit 2 is in contact with the charging roller 2a disposed so as to be in contact with the photosensitive drum 1 and the charging roller 2a. The power supply roller 2b disposed in the power supply S, the power supply S connected to the power supply roller 2b, the changeover switch SW2 for switching the connection between the charging roller 2a and the ground, and the current built in the power supply S to detect the current flowing through the circuit (not shown) A total of A.

  First, when the mode for measuring the resistance of the charging roller 2a is entered, the SW2 is switched to connect the charging roller 2a to the ground. Next, the photosensitive drum 1 is rotated by a driving unit (not shown), and the charging roller 2a and the power supply roller 2b are driven to rotate. Then, the power source S is controlled to apply a voltage to the power supply roller 2b. In this embodiment, a DC voltage of 100 V is applied for a time during which the charging roller 2a rotates once. Further, the current value was measured for the time that the charging roller 2a makes one rotation every 10 μs, and the resistance value of the charging roller 2a was calculated from the average value, and the resistance value was obtained as 4.5E + 06 [Ω].

  Next, the voltage applied at the time of image formation is determined according to the applied voltage determination table of FIG. How many V the surface potential of the photosensitive drum 1 is set may be arbitrarily determined depending on, for example, the image density, the usage state of the photosensitive drum 1, the installed environment (temperature and humidity), and the like. In this embodiment, it was set to 600V. The resistance value is 1. E + 06 [Ω] or more Since it is less than E + 07 [Ω], the surface of the photosensitive drum 1 can be set to 600 V by applying 1200 V to the power supply roller 2b during image formation.

  Finally, the power supply S is controlled to stop voltage application, drive of the photosensitive drum 1 is stopped, and SW2 is switched to disconnect the charging roller 2a from the ground.

  By doing so, the surface potential of the photosensitive drum 1 can be accurately set to a desired potential at the time of image formation, and a good image without macro potential unevenness can be output.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum, 2 Charging part, 2a Charging roller, 2b Feeding roller, 3 Exposure apparatus,
4 Developing unit, 5 Transfer unit, 6 Cleaning device, 7 Fixing device

Claims (14)

An image carrier, a roll-shaped charging member in contact with the image carrier, a power supply member in contact with the charging member, a voltage applying unit capable of applying a voltage to each of the charging member and the power supply member, and the power supply A switch that brings the member into a float state or a state connected to the ground, and an ammeter that can detect a current flowing through the charging member or the power feeding member,
When the power supply member is connected to the ground and a predetermined voltage is applied to the charging member, the current flowing through the charging member or the power supply member is measured, and the measured current is applied during image formation. An image forming apparatus that determines a voltage. The image forming apparatus according to claim 1, further comprising an environmental sensor that detects temperature and humidity where the apparatus is installed, and a predetermined voltage to be applied is changed according to an environmental value detected by the environmental sensor. The image forming apparatus according to claim 2, wherein the current value is corrected based on an environmental value when the current value is measured. 4. The image forming apparatus according to claim 1, wherein a predetermined operation is performed if the measured current value is larger than a predetermined value. 4. The image forming apparatus according to claim 1, wherein a predetermined operation is performed if the measured current value is smaller than a predetermined value. The image forming apparatus according to claim 4, wherein the predetermined operation sets the voltage and the potential to predetermined values so that a current flows from the image carrier to the charging member. The image forming apparatus according to claim 1, further comprising a detection unit configured to detect a film thickness of the image carrier and changing a voltage to be applied according to the film thickness of the image carrier. An image carrier, a roll-shaped charging member in contact with the image carrier, a power supply member in contact with the charging member, voltage applying means capable of applying a voltage to the power supply member, and the charging member in a float state or a ground A switch to be connected to a current meter and an ammeter capable of detecting a current flowing in the charging member or the power feeding member,
When the power supply member is connected to the ground and a predetermined voltage is applied to the charging member, the current flowing through the charging member or the power supply member is measured, and the measured current is applied during image formation. An image forming apparatus that determines a voltage. The image forming apparatus according to claim 8, further comprising an environmental sensor that detects temperature and humidity in which the apparatus is installed, and a predetermined voltage to be applied is changed according to an environmental value detected by the environmental sensor. The image forming apparatus according to claim 9, wherein the current value is corrected based on an environmental value when the current value is measured. 11. The image forming apparatus according to claim 8, wherein a predetermined operation is performed if the measured current value is larger than a predetermined value. 11. The image forming apparatus according to claim 8, wherein a predetermined operation is performed if the measured current value is smaller than a predetermined value. The image forming apparatus according to claim 11, wherein the predetermined operation sets the voltage and the potential to predetermined values so that a current flows from the image carrier to the charging member. The image forming apparatus according to claim 8, further comprising a detection unit configured to detect a film thickness of the image carrier and changing a voltage to be applied according to the film thickness of the image carrier.