JP2014119525A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing an increase in resistance of a charging member to avoid failure in charging, and reducing the amount of discharge from the charging member to avoid image defects.SOLUTION: A printer includes: a charging roller 25 that charges a photoreceptor drum 10 carrying toner images; and a charging bias supply unit 26 that supplies the charging roller 25, as a charging bias, with a superimposed voltage of a charging AC voltage having the magnitude equal to or less than half of a voltage difference between a discharge start voltage that is a charging bias of the charging roller 25 when the charging roller 25 starts discharge to the photoreceptor drum 10 and a control voltage that is a charging bias of the charging roller 25 when the surface potential of the photoreceptor drum 10 starts to be stabilized due to the discharge from the charging roller 25, and a charging DC voltage having the magnitude larger than that of the charging AC voltage.

Description

  The present invention relates to an image forming apparatus such as a printer, a copying machine, a facsimile machine, or a multifunction machine.

  2. Description of the Related Art Conventionally, an image forming apparatus includes an image forming unit for forming a toner image in an apparatus main body. In the image forming unit, after the surface of the image carrier such as a photosensitive drum is charged by a charging member such as a charging roller, the exposure device irradiates light corresponding to the image data to the image carrier. An electrostatic latent image is formed on the surface of the image carrier. Then, the electrostatic latent image is developed with a developer such as toner by a developing device, thereby forming a toner image on the image carrier. Thereafter, the toner image on the image carrier is transferred to a recording medium such as paper by the transfer unit. The transfer paper on which the toner image has been transferred is discharged to the outside of the image forming apparatus after the toner image is fixed to the transfer paper by the fixing unit.

  For example, a contact type or non-contact type charging roller as a charging member includes a conductive layer formed of an ion conductive material. When a charging bias is applied to the charging roller, the ionic conductive agent in the conductive layer is transmitted, and a predetermined electric field is generated between the charging roller and the image carrier to discharge the image carrier. To do. However, when the charging bias is a DC voltage, the voltage is applied only in one direction. Therefore, as the number of sheets used increases and the charging bias application time increases, the ionic conductive agent in the conductive layer has a DC voltage. Unevenly distributed in the application direction, the resistance value of the charging roller increases, and charging failure occurs.

  Therefore, in the control method of the image forming apparatus described in Patent Document 1, in order to avoid uneven distribution of the ionic conductive agent, when the charging member corresponds to the non-image forming area of the member to be charged, that is, other than during image formation. In this case, control is performed so that a DC voltage having a polarity opposite to that applied during image formation is applied to the charging member.

  Further, in the image forming apparatus described in Patent Document 2, the charging roller and the surface to be charged are brought into a non-contact state at times other than the time of image formation, and have a polarity opposite to the DC voltage applied to the charging roller at the time of image formation. A DC voltage is applied to the charging roller.

  Furthermore, the charging member described in Patent Document 3 applies a superimposed voltage of a DC voltage and an AC voltage having a peak-to-peak voltage that is at least twice the charging start voltage of the object to be charged when the DC voltage is applied. It is said. As described above, in the conventional method in which the superimposed voltage of the DC voltage and the AC voltage is applied to the charging member, the frequency of the AC voltage is often set to about 1.0 to 3.0 kHz in order to perform charging uniformly.

Japanese Patent Laid-Open No. 08-30073 JP 2002-328508 A Japanese Patent Application Laid-Open No. 08-22167

  However, in the control method of the image forming apparatus described in Patent Document 1, a positive direct current voltage is applied to the charging member during image formation, and a reverse polarity direct current voltage is applied to the charging member at times other than image formation. The applied voltage is switched. For this reason, there arises a problem that a continuous image forming operation cannot be promptly shifted.

  In addition, the image forming apparatus described in Patent Document 2 requires a moving operation for bringing the charging roller and the surface to be charged into a non-contact state at a time other than the time of image formation, resulting in a problem that the configuration becomes complicated. .

  Furthermore, in the charging member described in Patent Document 3, since a relatively high AC voltage that is twice or more the charging start voltage is applied, the amount of discharge increases, and many discharge products adhere to the photoreceptor. End up. For this reason, the image defect of a photoconductor arises, and the problem that deterioration of the cleaning blade which cleans a photoconductor becomes quick also arises.

  In view of the above circumstances, the present invention provides a technique capable of preventing charging failure by preventing an increase in resistance of a charging member and reducing an amount of discharge of the charging member to avoid image failure. With the goal.

  An image forming apparatus according to the present invention includes a charging member that charges an image carrier that carries a toner image, and a discharge start that is a charging voltage of the charging member when the charging member starts to discharge the image carrier. An AC voltage having a magnitude of ½ or less of a voltage difference between a voltage and a control voltage that is a charging voltage of the charging member when the surface potential of the image carrier starts to be stabilized by discharge from the charging member; And a charging voltage supply unit that supplies a superposed voltage with a DC voltage larger than the AC voltage as a charging voltage to the charging member.

  By adopting such a configuration, it is possible to prevent an increase in the resistance of the charging member and to suppress an increase in the amount of discharge generated by the AC voltage. As a result, an increase in discharge products adhering to the image carrier is suppressed, and damage to the cleaning blade for cleaning the image carrier and image defects on the image carrier due to excessive discharge products are generated. It becomes possible to prevent.

  The charging member may be a charging roller provided with a conductive layer containing an ionic conductive agent.

  By adopting such a configuration, the ionic conductive agent in the conductive layer of the charging roller is prevented from being unevenly distributed in one direction due to the DC voltage because the AC voltage is superimposed on the charging voltage. An increase in resistance of the charging member due to the uneven distribution of the conductive agent can be prevented.

  The charging member may be disposed in contact with or in a non-contact manner with the image carrier.

  By adopting such a configuration, regardless of the arrangement of the charging member and the image carrier, it is possible to prevent an increase in the resistance of the charging member and to suppress an increase in the amount of discharge generated by the AC voltage.

  The charging voltage supply unit may control so that at least one of the AC voltage and the DC voltage increases as the ambient humidity of the image forming apparatus decreases.

  By adopting such a configuration, even when the charging member becomes difficult to discharge to the image carrier due to a decrease in the humidity around the image forming apparatus, sufficient discharge can be achieved by increasing the charging voltage. .

  The charging voltage supply unit may perform control so that at least one of the AC voltage and the DC voltage increases as the ambient temperature of the image forming apparatus decreases.

  By adopting such a configuration, even when the resistance of the charging member increases due to a decrease in the ambient temperature of the image forming apparatus, sufficient discharge can be achieved by increasing the charging voltage.

  According to the present invention, it is possible to prevent an increase in the resistance of the charging member to avoid charging failure, and to reduce the amount of discharge of the charging member to avoid image failure.

1 is a schematic diagram illustrating an outline of a printer according to an embodiment of the present invention. FIG. 3 is a cross-sectional view illustrating a part of an image forming unit in the printer according to the embodiment of the invention. 6 is a graph showing a relationship between a charging bias of a charging roller and a surface potential of a photosensitive drum in a printer according to an embodiment of the present invention. It is a schematic diagram which shows the state before a charging bias is applied about the ionic conductive agent of a charging roller in the printer which concerns on one Embodiment of this invention. It is a schematic diagram which shows the state in which the direct-current charging bias was applied about the ionic conductive agent of the charging roller in the printer of a prior art. FIG. 4 is a schematic diagram illustrating a state in which a charging bias in which direct current and alternating current are superimposed is applied to an ionic conductive agent of a charging roller in a printer according to an embodiment of the present invention. 4 is a graph showing a relationship between energization time and resistance value for a charging roller in a printer according to an embodiment of the present invention.

  First, the overall configuration of a printer 1 as an image forming apparatus will be described with reference to FIG. FIG. 1 is a schematic diagram showing an outline of a printer according to an embodiment of the present invention. Hereinafter, the right side in FIG. 1 is the front side (front side) of the printer 1.

  The printer 1 includes a box-shaped printer main body 2. A paper feed cassette 3 that stores paper (not shown) is accommodated in a lower portion of the printer main body 2. A paper discharge tray 4 is disposed on the upper surface of the printer main body 2. Provided. An upper cover 5 is attached to the front of the paper discharge tray 4 so as to be openable and closable, and a toner container 6 as a toner container is stored below the upper cover 5.

  An exposure unit 7 having a laser scanning unit (LSU) is disposed below the paper discharge tray 4 above the printer body 2, and an image forming unit 8 is provided below the exposure unit 7. A photosensitive drum (image carrier) 10 that is an image carrier is rotatably provided in the image forming unit 8. Around the photosensitive drum 10, a charging device 11, a developing device 12, and a transfer roller 13 are provided. And the cleaning device 14 are arranged along the rotation direction of the photosensitive drum 10 (see arrow X in FIG. 1). Details of the image forming unit 8 will be described later.

  Inside the printer main body 2, a conveyance path 15 for the paper S (see FIG. 2) is provided. In the transport path 15, a paper feed unit 16 is provided at the upstream end, a transfer unit 17 including the photosensitive drum 10 and the transfer roller 13 is provided at the midstream portion, and a fixing device 18 is provided at the downstream portion. A paper discharge unit 20 is provided at the downstream end. A reverse path 21 for duplex printing is provided below the transport path 15. The fixing device 18 may be configured, for example, with the heating roller 22 and the pressure roller 23 facing each other's rotation surfaces (see FIG. 2).

  Next, an image forming operation of the printer 1 having such a configuration will be described.

  When the printer 1 is turned on, various parameters are initialized, and initial settings such as an applied voltage setting of the charging device 11 and a temperature setting of the fixing device 18 are executed. Then, when image data is input from a computer or the like connected to the printer 1 and an instruction to start printing is given, an image forming operation is executed as follows.

  First, after the surface of the photosensitive drum 10 is charged by the charging device 11, exposure corresponding to image data is performed on the photosensitive drum 10 by laser light from the exposure unit 7 (see the two-dot chain line P in FIG. 1). The electrostatic latent image is formed on the surface of the photosensitive drum 10. Next, the electrostatic latent image is developed by the developing device 12 into a toner image with toner.

  On the other hand, the paper S taken out from the paper feed cassette 3 by the paper feed unit 16 is conveyed to the transfer unit 17 in synchronization with the image forming operation described above, and the toner image on the photosensitive drum 10 is transferred to the transfer unit 17. Transferred onto the paper S. The sheet S to which the toner image has been transferred is conveyed downstream in the conveyance path 15 and enters the fixing device 18, where the toner image is fixed on the sheet S. The paper S on which the toner image is fixed is discharged from the paper discharge unit 20 to the paper discharge tray 4. The toner remaining on the photosensitive drum 10 is collected by the cleaning device 14.

  Next, the charging device 11 will be described in detail with reference to FIG. FIG. 2 is a cross-sectional view showing a part of the image forming unit in the printer according to the embodiment of the invention.

  As shown in FIG. 2, in the image forming unit 8, the photosensitive drum 10 is grounded. The photosensitive drum 10 is made of, for example, amorphous silicon and has a diameter of 30 mm.

  The charging device 11 includes a charging roller (charging member) 25 that can rotate within the case 24 in the vicinity of the photosensitive drum 10, and the charging roller 25 has a diameter of 12 mm and a thickness of 2 mm on the rotating surface, for example. A conductive layer 41 (see FIGS. 4 and 6) formed of an ion conductive material is provided. The charging roller 25 is a contact-type charging member that is in contact with the photosensitive drum 10, but is not limited to this configuration, and may be a non-contact type charging member that is spaced 50 to 100 μm from the photosensitive drum 10. The charging roller 25 is connected to a charging bias supply unit (charging voltage supply unit) 26, and the charging bias supply unit 26 includes a charging AC voltage from a charging AC power supply 27 and a charging DC from a charging DC power supply 28. A charging bias (charging voltage) that is a voltage superimposed on the voltage is supplied to the charging roller 25.

  The developing device 12 includes a developing roller 31 that can rotate within the case 30 in close proximity to the photoconductive drum 10. The development roller 31 is connected to a development bias supply unit 32, and the development bias supply unit 32 is a superimposed voltage of the development AC voltage from the development AC power source 33 and the development DC voltage from the development DC power source 34. A developing bias is supplied to the developing roller 31.

  The transfer roller 13 is disposed so as to constitute a transfer unit 17 in which a transfer nip is formed with the photosensitive drum 10, and the transfer unit 17 sends the paper S that has passed through the transfer nip to the fixing device 18. The transfer roller 13 is connected to a transfer bias supply unit 35, and the transfer bias supply unit 35 supplies the transfer DC voltage from the transfer DC power supply 36 to the transfer roller 13 as a transfer bias.

  The cleaning device 14 includes a cleaning blade 38 attached to the edge of the case 37 and disposed in contact with the rotating surface of the photosensitive drum 10, and a cleaning roller 40 that can rotate within the case 37.

  In FIG. 2, for the sake of convenience, the charging AC power source 27 and the developing AC power source 33 are separately illustrated. However, these are the AC voltage for charging and the developing from the AC voltage of the main body power source (not shown) of the printer 1. AC voltage may be obtained. Similarly, in FIG. 2, the charging DC power supply 28, the developing DC power supply 34, and the transfer DC power supply 36 are separately illustrated, but these charge the AC voltage obtained from the main body power supply of the printer 1. DC voltage for development, DC voltage for development, and DC voltage for transfer may be converted.

  The charging bias supply unit 26 connected to the charging roller 25 outputs, for example, a 500 V charging AC voltage from the charging AC power supply 27 and a 650 V charging DC voltage from the charging DC power supply 28. A charging bias that is a superimposed voltage of these is applied to the charging roller 25. That is, a DC voltage larger than the AC voltage becomes the main charging bias, and the charging roller 25 discharges due to this DC voltage. On the other hand, the AC voltage is 0.1 to 0.5 times as large as the voltage difference between the discharge start voltage of the charging roller 25 and the control voltage, that is, ½ or less. This AC voltage acts on the ionic conductive agent 42 (see FIGS. 4 and 6) in the conductive layer 41 of the charging roller 25 to prevent the ionic conductive agent 42 from being unevenly distributed in one direction due to the DC voltage, and is also sensitive to light. The voltage has a magnitude that does not contribute to charging of the body drum 10. When the AC voltage is smaller than 0.1 times the voltage difference, uneven distribution due to the DC voltage of the ionic conductive agent 42 cannot be prevented, and when it exceeds 0.5 times the voltage difference, the charging roller 25 Since the discharge amount increases and discharge products generated on the photosensitive drum 10 increase excessively, the charging AC voltage is preferably set as described above.

  Next, the discharge start voltage V1 and the control voltage V2 of the charging roller 25 will be described with reference to FIG. 3 together with the relationship between the charging bias of the charging roller 25 and the surface potential of the photosensitive drum 10 charged by this charging bias. To do. FIG. 3 is a graph showing the relationship between the charging bias of the charging roller and the surface potential of the photosensitive drum in the printer according to the embodiment of the present invention. In FIG. 3, the change in the charging bias of the charging roller 25 is shown on the horizontal axis, and the change in the surface potential of the photosensitive drum 10 is shown on the vertical axis.

  The discharge start voltage V1 is a charging bias when the charging roller 25 starts to discharge with the photosensitive drum 10, and the control voltage V2 is the surface potential of the photosensitive drum 10 stabilized by the discharge from the charging roller 25. This is the charging bias when starting to start. When the charging bias applied to the charging roller 25 reaches the discharge start voltage V1, discharge starts with the photosensitive drum 10, and the surface potential of the photosensitive drum 10 increases as the charging bias increases. . The change in the surface potential of the photosensitive drum 10 becomes gradual when the charging bias exceeds a predetermined amount, and then becomes stable. For example, the normal control voltage V2 is set slightly higher than the charging bias at the inflection point A where the surface potential change of the photosensitive drum 10 becomes gentle, for example, 1.1 to 1.2 times. The Therefore, the charging AC voltage output from the charging AC power supply 27 is set to (V2−V1) / 2 or less.

  Further, the state of the conductive layer 41 of the charging roller 25 that changes due to the application of the charging bias will be described with reference to FIGS. FIG. 4 is a schematic view showing a state before a charging bias is applied to the ionic conductive agent of the charging roller in the printer according to the embodiment of the present invention, and FIG. 5 is an ionic conductive agent of the charging roller in the conventional printer. FIG. 6 is a schematic diagram showing a state where a DC-only charging bias is applied, FIG. 6 is a state where a DC and AC charging bias is applied to an ionic conductive agent of a charging roller in a printer according to an embodiment of the present invention. It is a schematic diagram which shows.

  The conductive layer 41 of the charging roller 25 has a large number of uniform ionic conductive agents 42 so that charging failure does not occur. That is, the density of the ionic conductive agent 42 in the conductive layer 41 is any position of the conductive layer 41. It is uniform. For example, before the charging bias is applied, the ionic conductive agent 42 in the conductive layer 41 is uniform as shown in FIG.

When a charging bias consisting only of the DC voltage V _D1 according to the prior art is applied to the charging roller 25, the charging roller 25 discharges the photosensitive drum 10. However, as the charging bias energization time increases, as shown in FIG. 5, the ionic conductive agent 42 in the conductive layer 41 moves to the transmission direction of the DC voltage V _D1 , that is, to the surface side of the charging roller 25. Will be unevenly distributed. Further, since the ionic conductive agent 42 is unevenly distributed, the resistance of the charging roller 25 increases as the charging bias energization time increases.

On the other hand, when the superimposed voltage of the DC voltage V _D2 and the AC voltage _VA is applied as a charging bias to the charging roller 25 as in the present embodiment, even if the energization time of the charging bias increases, 6, the ionic conductive agent 42 in the conductive layer 41 is unevenly distributed on the surface side of the charging roller 25 by the action of the AC voltage _VA that is transmitted in the direction opposite to the direction in which the DC voltage V _D2 is transmitted. Is avoided. For this reason, the ion conductive agent 42 is made uniform in the conductive layer 41, and an increase in the resistance of the charging roller 25 accompanying an increase in the energization time of the charging bias is suppressed. Further, since this AC voltage _VA is less than half of the voltage difference between the discharge start voltage V1 of the charging roller 25 and the control voltage V2, the generation of extra discharge products in the photosensitive drum 10 occurs. It is suppressed.

Further, the relationship between the energization time of the charging bias of the charging roller 25 and the resistance of the charging roller 25 with respect to the charging bias will be described with reference to FIG. FIG. 7 is a graph showing the relationship between the energization time and the resistance value for the charging roller in the printer according to the embodiment of the present invention. In FIG. 7, the change in the electrification time of the charging bias is shown on the horizontal axis and the change in the resistance value of the charging roller 25 is shown on the vertical axis. Further, FIG. 7 shows a normal resistance limit value _RL at which charging failure occurs in the charging roller 25 and a normal guarantee time _TL for guaranteeing that there is no charging failure. That is, the energization time immediately before reaching the resistance limit value _RL is a guarantee time for guaranteeing that there is no charging failure.

  Here, the resistance value R1 of the charging roller 25 in the first control state in which only the DC voltage (800 V) according to the prior art is applied is indicated by a broken line, and the DC voltage (450 V) and the AC voltage (1000 V) according to the prior art are superimposed. In the second control state in which the voltage is applied, the resistance value R2 of the charging roller 25 is a two-dot chain line, and the third control for applying the superimposed voltage of the DC voltage (650 V) and the AC voltage (500 V) according to the present embodiment. The resistance value R3 of the charging roller 25 in the state is indicated by a solid line. That is, in the second control state according to the prior art, an AC voltage having a peak-to-peak voltage that is twice or more the charging start voltage is superimposed on the charging bias.

  In any control state, the same photosensitive drum 10 and charging roller 25 are used, the photosensitive drum 10 is made of amorphous silicon with a diameter of 30 mm, and the charging roller 25 has a diameter of 12 mm and is rotated. A conductive layer 41 formed of an ion conductive material having a thickness of 2 mm is provided on the surface. The linear velocity of the charging roller 25 is 300 mm / sec.

In the first control state, since the ionic conductive agent 42 is unevenly distributed due to the DC voltage, as shown in FIG. 7, the resistance value of the charging roller 25 is faster in the energization time than in the second and third control states. The resistance limit value _RL is reached, charging failure due to an increase in the resistance of the charging roller 25 is likely to occur, and the guarantee time cannot be set long.

On the other hand, in the third control state according to the present embodiment, the uneven distribution of the ionic conductive agent 42 is suppressed by the action of the AC voltage, so that the resistance value of the charging roller 25 is a resistance as shown in FIG. The energization time until the limit value R _L is reached has a sufficient margin as compared with the normal guarantee time _TL , charging failure due to the increase in resistance of the charging roller 25 hardly occurs, and the guarantee time may be set longer. it can.

  The surface dynamic friction coefficient of the photosensitive drum 10 when an image forming process including charging of the photosensitive drum 10 using the charging roller 25 is performed will be described.

  In this image forming process, toner having one magnetic component is used as a toner for developing the photosensitive drum 10. The surface dynamic friction coefficient of the photosensitive drum 10 is 0.18 μ before the image forming process, that is, in the unused state. The cleaning device 14 that cleans the photosensitive drum 10 includes a cleaning roller 40 that is an EPDM foaming roller, presses the cleaning roller 40 against the photosensitive drum 10 with a force of 18 N, and is linear with respect to the rotation of the photosensitive drum 10. Rotate at a speed ratio of 1.2. In this image forming process, 3000 sheets are continuously printed at a printing rate of 5%.

  When the photosensitive drum 10 is charged by the charging roller 25 in the first control state with only the DC voltage, the generation of discharge products is small because there is no AC voltage. After performing the above-described image forming process using this photosensitive drum 10, the surface dynamic friction coefficient of the photosensitive drum 10 is as low as 0.28 [mu] or 0.3 to 0.4 [mu], but as described above, the charging roller 25 There is a problem of poor charging due to an increase in resistance.

  When the photosensitive drum 10 is charged by the charging roller 25 in the second control state according to the prior art, the discharge voltage is generated because the AC voltage has a peak-to-peak voltage more than twice the charging start voltage and is relatively large. Increasing the generation of things. Therefore, after performing the above-described image forming process using this photosensitive drum 10, the surface dynamic friction coefficient of the photosensitive drum 10 increases to 0.5 to 0.7 μ, more specifically to 0.63 μ. As described above, when the surface dynamic friction coefficient exceeds 0.5, the cleaning blade 38 of the cleaning device 14 that cleans the photosensitive drum 10 is deteriorated such as squealing or damage regardless of the guarantee time of the charging roller 25. There is a high possibility that an image developed on the photosensitive drum 10 will be defective.

  On the other hand, when the photosensitive drum 10 is charged by the charging roller 25 in the third control state according to this embodiment, the AC voltage is ½ of the voltage difference between the discharge start voltage V1 and the control voltage V2. The occurrence of discharge products is suppressed due to the following small amount. After performing the above-described image forming process using this photosensitive drum 10, the surface dynamic friction coefficient of the photosensitive drum 10 is suppressed to 0.3 to 0.5 μ, more specifically 0.4 μ. Therefore, in the third control state, an increase in the surface dynamic friction coefficient of the photosensitive drum 10 is suppressed to be equal to that in the first control state, and the cleaning blade 38 that cleans the photosensitive drum 10 is deteriorated or developed by the photosensitive drum 10. The possibility of a malfunction of the displayed image is reduced.

As described above, in the third control state according to the present embodiment, the resistance increase of the charging roller 25 is suppressed compared to the first control state using only the DC voltage charging bias, charging failure is less likely to occur, and the resistance limit. There is sufficient margin for the warranty period up to the value _RL . Further, compared to the second control state in which a charging bias with a relatively large alternating voltage superimposed thereon is used, an increase in the surface dynamic friction coefficient of the photosensitive drum 10 is suppressed, and the cleaning blade 38 is deteriorated or developed on the photosensitive drum 10. This makes it difficult for image problems to occur.

  In the present embodiment, as described above, the charging bias applied to the charging roller 25 of the charging device 11 is for charging having a magnitude of 1/2 or less of the voltage difference between the discharge start voltage V1 of the charging roller 25 and the control voltage V2. By using a superimposed voltage of the AC voltage and a charging DC voltage larger than the charging AC voltage, uneven charging due to the DC voltage of the ionic conductive agent 42 in the conductive layer 41 of the charging roller 25 is prevented, and the charging roller Thus, an increase in the amount of discharge generated due to the AC voltage can be suppressed. Accordingly, it is possible to suppress an increase in discharge products adhering to the photosensitive drum 10 and prevent damage to the cleaning blade 38 due to excess discharge products and occurrence of image defects on the photosensitive drum 10.

  In the present embodiment, the charging bias applied to the charging roller 25 is a charging AC voltage having a magnitude of 1/2 or less of the voltage difference between the discharge start voltage V1 and the control voltage V2, and a charging larger than the charging AC voltage. The charging bias supply unit 26 changes the magnitude of the charging bias, that is, the charging AC voltage and the charging DC voltage according to the usage environment of the printer 1. You may control to do.

  For example, when the ambient humidity of the printer 1 is low as a use environment, the charging roller 25 is difficult to discharge. Therefore, the printer 1 includes a humidity sensor (not shown) and is configured to detect and monitor humidity. The charging bias supply unit 26 is set so that at least one of the charging AC voltage and the charging DC voltage increases as the humidity detected by the humidity sensor decreases. For example, in the case of low humidity, the charging AC Control may be performed so that at least one of the voltage and the DC voltage for charging is increased and at least one of the AC voltage for charging and the DC voltage for charging is decreased when the humidity is high. Therefore, even when the charging roller 25 becomes difficult to discharge to the photosensitive drum 10 due to a decrease in the humidity around the printer 1, sufficient discharge can be achieved by increasing the charging bias.

  Further, when the ambient temperature of the printer 1 is low as the use environment, the resistance of the charging roller 25 tends to increase, and when it is high, the resistance of the charging roller 25 tends to decrease. Therefore, the printer 1 includes a temperature sensor (not shown) and is configured to detect and monitor the temperature. The charging bias supply unit 26 is set so that at least one of the charging AC voltage and the charging DC voltage increases as the temperature detected by the temperature sensor decreases. For example, in the case of a low temperature, the charging AC The voltage and the DC voltage for charging may be increased, and control may be performed to decrease the AC voltage for charging and the DC voltage for charging when the temperature is high. Therefore, even when the resistance of the charging roller 25 increases due to a decrease in the ambient temperature of the printer 1, sufficient discharge can be achieved by increasing the charging bias.

  In the present embodiment, the case where the configuration of the present invention is applied to the printer 1 has been described. However, in another different embodiment, the configuration of the present invention may be applied to an image forming apparatus such as a copying machine, a facsimile, or a multifunction peripheral. Good.

1 Printer (image forming device)
10 Photosensitive drum (image carrier)
25 Charging roller (charging member)
26 Charging bias supply unit (charging voltage supply unit)

Claims (5)

A charging member for charging an image carrier that carries a toner image;
When the surface potential of the image carrier starts to stabilize due to the discharge start voltage, which is the charging voltage of the charging member when the charging member starts to discharge the image carrier, and the discharge from the charging member. Charging that supplies the charging member as a charging voltage with a superimposed voltage of an AC voltage having a magnitude of 1/2 or less of a voltage difference from a control voltage, which is a charging voltage of the charging member, and a DC voltage larger than the AC voltage. An image forming apparatus comprising: a voltage supply unit.   The image forming apparatus according to claim 1, wherein the charging member includes a charging roller including a conductive layer including an ionic conductive agent.   The image forming apparatus according to claim 1, wherein the charging member is disposed in contact with or close to the image carrier.   The image forming apparatus according to claim 1, wherein the charging voltage supply unit performs control so that at least one of the AC voltage and the DC voltage increases as the ambient humidity of the image forming apparatus decreases. apparatus. The image forming apparatus according to claim 1, wherein the charging voltage supply unit performs control so that at least one of the AC voltage and the DC voltage increases as the ambient temperature of the image forming apparatus decreases. apparatus.

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