JP4886484B2 - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of more effectively preventing image failure such as image blur or image deletion caused by a corona discharge product. <P>SOLUTION: The image forming apparatus 100 includes: a movable electrophotographic photoreceptor 1 whose surface an electrostatic image is formed on; and an electrifier 2 provided to be opposed to the surface of the electrophotographic photoreceptor 1 and performing electrifying or destaticizing action. The apparatus 100 has a sheet type heating means 20a arranged to contact with the surface of the electrophotographic photoreceptor 1, and heating the surface side of the electrophotographic photoreceptor 1 while coming into contact with the surface of the electrophotographic photoreceptor 1. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to an image forming apparatus such as a printer, a copying machine, and a facsimile using an electrophotographic system.

  In an image forming apparatus using an electrophotographic system, a corona charger (corotron, having a wire electrode and a shield plate as constituent members as a means for charging and neutralizing an electrophotographic photoreceptor (hereinafter also simply referred to as “photoreceptor”). Scorotron) is used. As the wire electrode, a metal wire such as a tungsten wire plated with gold having a diameter of 50 to 100 μm is used. A corona current generated by applying a high voltage (about 4 to 8 kv) to the wire electrode of the corona charger is applied to the surface of the photoconductor to charge and neutralize the surface of the photoconductor.

However, when a corona charger is used, ozone (O ₃ ) is generated with corona discharge. The generated ozone oxidizes nitrogen in the air to generate nitrogen oxides (NOx) and the like. Further, the generated nitrogen oxides react with moisture in the air to generate nitric acid and the like. Then, corona discharge products such as nitrogen oxide and nitric acid adhere to and accumulate on the photoreceptor. In particular, since the corona discharge product has a high hygroscopic property, the surface of the photoconductor is electrically reduced in resistance by absorption of the corona discharge product adhering to the surface in a high humidity environment, and the entire or partial surface of the photoconductor. In addition, the charge retention ability is substantially reduced. As a result, for example, a normal image as shown in FIG. 14B causes an image defect such as an image blur or an image flow as shown in FIG. 14A. This is because the charge on the surface of the photoreceptor leaks in the surface direction, and the electrostatic latent image pattern is broken or not formed as shown in FIG. 15B from a normal state as shown in FIG. It depends.

  Further, for example, a corona discharge product adhering to the inner surface of the shield plate of the corona charger is volatilized and released not only during the operation of the image forming apparatus but also during a long pause of the image forming apparatus such as at night. May adhere to the surface of the photoreceptor near the discharge opening. Further, the corona discharge product adhering to the photoreceptor absorbs moisture, and the surface of the photoreceptor is electrically reduced in resistance. For this reason, the first output image or the several tens of output images that are output first after the image forming apparatus is stopped for a long time are placed in a region corresponding to the discharge opening of the charger during the stop of the image forming apparatus. Image defects such as image blur and image flow are likely to occur. In the charging method, this phenomenon is remarkable in the case of a corona charger that performs AC charging (an AC voltage is applied as a discharging voltage) or negative charging (charges the target negatively).

In order to prevent the above-described problem of image flow, a method of heating the photosensitive member from the inside by a heating means such as a heat roller to raise the surface temperature of the photosensitive member (hereinafter referred to as “internal heating method”). Has been proposed (see Japanese Patent Application Laid-Open No. 07-104638).
Japanese Patent Application Laid-Open No. 07-104638

  However, in the internal heating method, it is necessary to heat the whole including the base material of the photoreceptor to a desired temperature (for example, about 40 ° C.), and there is a problem that energy consumption is wasted.

  Further, in the internal heating method, the heat energy from the internal heating means such as a heat roller is supplied from the back side to the front side of the photoconductor, so that the corona discharge product adhering to the surface of the photoconductor is uniformly dried, and It is difficult to keep the surface temperature of the photoreceptor uniform in a short time. Therefore, there is a problem that it takes time for such an operation.

  Accordingly, an object of the present invention is to provide an image forming apparatus that can more effectively prevent image defects such as image blur and image flow caused by corona discharge products.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides a rotatable photoreceptor, a charging means for charging the photoreceptor, an exposure means for exposing to form an electrostatic image on the photoreceptor, and formed on the photoreceptor. An image forming apparatus comprising: a developing unit that develops the electrostatic image formed with toner; and a transfer unit that transfers a toner image formed on the photoconductor to a transfer material, wherein the image forming apparatus is in contact with the photoconductor. A sheet-shaped heating member that heats the sheet, an adjustment unit that adjusts a contact area between the sheet-shaped heating member and the photoconductor, a detection unit that detects a surface temperature of the photoconductor, and a detection unit that detects the surface temperature. When the region higher than the predetermined temperature is heated by the heating member, the detection unit detects the contact area between the sheet-like heating member and the photoconductor so as to be the first contact area. Area below the specified temperature Control means for controlling the adjusting means so that the contact area between the sheet-like heating member and the photoconductor becomes a second contact area larger than the first contact area when heated by the heating member. And an image forming apparatus.

  According to the present invention, it is possible to more effectively prevent image defects such as image blur and image flow caused by corona discharge products.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
[Image forming apparatus]
First, the overall configuration of an image forming apparatus according to an embodiment of the present invention will be described.

  FIG. 1 schematically shows a schematic configuration of a main part of an image forming apparatus 100 of the present embodiment. The image forming apparatus 100 according to the present exemplary embodiment is an electrophotographic image forming apparatus.

  The image forming apparatus 100 includes a drum-type electrophotographic photosensitive member as an image carrier, that is, a photosensitive drum 1. The photosensitive drum 1 is supported by the image forming apparatus main body so as to be rotatable in the direction of the arrow R1 shown in the drawing. The photosensitive drum 1 as a photosensitive member includes a drum-shaped base and a photosensitive film formed on the outer surface thereof.

Around the photosensitive drum 1, there are a primary charger 2 as a primary charging means for supplying a charge onto the photosensitive film of the photosensitive drum 1, an exposure device 3 as an exposure means, and a photosensitive film of the photosensitive drum 1. A developing device 4 is disposed as a developing means for supplying toner as a developer. Further, around the photosensitive drum 1, a pre-transfer charger 5 as a transfer auxiliary unit (pre-transfer charging unit) for charging or discharging the toner on the photosensitive drum 1 and / or the photosensitive drum 1 is disposed. Has been. Further, around the photosensitive drum 1, a transfer charger 6 as a transfer unit for transferring the toner on the photosensitive drum 1 to a transfer material S that is a transfer target (transfer target material) , and the surface of the photosensitive drum 1. A separation charger 7 is disposed as separation means for separating the transfer material S from the toner. Further, around the photosensitive drum 1, a cleaning device 8 as a cleaning unit for removing the developer on the photosensitive film of the photosensitive drum 1 and a pre-exposure unit 9 as a discharging unit are arranged. Each of these means includes a primary charger 2, an exposure device 3, a developing device 4, a pre-transfer charger 5, a transfer charger 6, a separation charger 7, and a cleaning device 8 along the rotation direction R1 of the photosensitive drum 1. The pre-exposure devices 9 are arranged in this order. In this embodiment, the primary charger 2, the pre-transfer charger 5, the transfer charger 6, and the separation charger 7 are configured as corona chargers having wire electrodes and a shield plate.

  In this embodiment, as will be described in detail later, a heating device provided with a heating unit that heats the photosensitive drum 1 from the outside, that is, from the surface side, in contact with the photosensitive film on the surface of the photosensitive drum 1. A heater unit 20 is provided. In this embodiment, the heater unit 20 is configured so that the heating means can contact the photosensitive drum 1 between the cleaning device 8 and the primary charger 2 in the rotation direction (surface movement direction) R1 of the photosensitive drum 1. Has been placed. In particular, in this embodiment, the heater unit 20 is arranged so that the heating means can contact the photosensitive drum 1 between the cleaning device 8 and the pre-exposure device 9.

  Further, a fixing device 10 as a fixing unit is disposed in the passage portion of the transfer material S after the transfer. The fixing device 10 includes a fixing roller 10a having a built-in heat source, and a pressure roller 10b in pressure contact with the fixing roller 10a.

  At the time of image formation, the photosensitive drum 1 is rotationally driven at a predetermined rotational speed (peripheral speed, surface movement speed) in the direction of the arrow R1 in the figure by transmitting a rotational driving force from a driving motor 40 as a driving means. . In the present embodiment, the control means (controller) 50 can determine when the specific surface position of the photosensitive drum 1 is located at the opposed portion of the heater unit 20. In other words, in this embodiment, the control unit 50 outputs the number of output signals of the drive motor 40 necessary for one rotation of the photosensitive drum 1 and the output signal of the drive motor 40 from the power (main switch) on of the image forming apparatus 100. The above determination is made based on the number.

  In this embodiment, the photoconductor drum 1 includes a photoconductor film including an amorphous silicon layer (hereinafter referred to as “amorphous silicon photoconductor film”). This amorphous silicon photoreceptor film is formed by forming a blocking layer on the substrate to prevent charge injection from the drum-shaped substrate, and subsequently forming an amorphous silicon layer on the blocking layer, and finally the amorphous silicon film. It is formed by forming a surface protective layer on the silicon layer. Amorphous silicon is more hydrophilic than other inorganic photoreceptor materials. Therefore, even if the difference between the temperature inside the image forming apparatus and the room temperature is smaller than the temperature difference at which dew condensation occurs in the organic photoreceptor film or other inorganic photoreceptor films, a low resistance is formed on the amorphous silicon photoreceptor film. A film begins to form. As described above, the photosensitive member provided with the amorphous silicon photosensitive film is liable to cause image defects due to corona discharge products such as image blur and image flow.

  The image forming operation will be described. First, the surface of the photosensitive drum 1 is charged substantially uniformly (uniformly) to a predetermined potential of a predetermined polarity (negative polarity in this embodiment) by the primary charger 2. The surface of the photosensitive drum 1 after being charged is irradiated with light based on image information by the exposure device 3. As a result, the charge at the irradiated portion is removed, and an electrostatic image (latent image) is formed on the photosensitive drum 1. The electrostatic image is developed as a toner image by the toner attached by the developing device 4. As the developer, for example, a non-magnetic one-component developer can be used.

  The toner image formed on the photoconductive drum 1 is then controlled to a predetermined charge amount by the pre-transfer charger 5 and then transferred to the photoconductive drum 1 by the rotation of the photoconductive drum 1 in the direction indicated by the arrow R1. It reaches the transfer section with the container 6. A transfer material (for example, paper, transparent film) S is supplied to the transfer unit so as to be in time with the toner image. A transfer bias having a polarity opposite to the normal charging polarity of the toner (negative polarity in this embodiment) is applied to the transfer charger 6. As a result, the toner image on the photosensitive drum 1 is transferred to the transfer material S by the electrostatic force generated between the photosensitive drum 1 and the transfer charger 6.

  The transfer material S after the toner image is transferred is separated from the photosensitive drum 1 by applying a separation bias to the separation charger 7. The transfer material S separated from the photosensitive drum 1 is conveyed to the fixing device 10 by a conveyance belt 11 as a conveyance unit. The transfer material S conveyed to the fixing device 10 is heated and pressurized when passing between the fixing roller 10a and the pressure roller 10b, and the toner image is fixed on the surface. Thereafter, the transfer material S is discharged to the outside of the image forming apparatus 100.

  On the other hand, after the toner image is transferred to the transfer material S, the toner (transfer residual toner) remaining on the surface without being transferred to the transfer material S in the transfer process is removed by the cleaning device 8. Further, the charge remaining on the surface of the photosensitive drum 1 is removed by the pre-exposure device 9. Thus, the photosensitive drum 1 is used for the next image formation. The above is a series of image forming processes.

[Configuration of heater unit]
Next, the heater unit 20 as a heating device for the photosensitive drum 1 will be described.

  As described above, conventionally, when the internal heating method is used, it has been difficult to efficiently prevent image defects such as image blur and image flow due to corona discharge products in a low energy and in a short time.

  One of the objects of the present invention is to keep the surface temperature of the electrophotographic photosensitive member substantially uniform while drying the surface of the electrophotographic photosensitive member substantially uniformly with less energy.

  That is, one of the objects of the present invention is to provide an electrophotographic photosensitive member that can effectively eliminate image defects such as image blurring and image flow caused by corona discharge products, and more specifically, can reduce power consumption in a short time. It is providing the heating structure and control method of this.

  In the present embodiment, the heater unit 20 is an external heating means that employs a method of heating the photosensitive drum 1 from the outside (hereinafter referred to as “external heating method”), and is a flexible sheet (surface) as a high-efficiency heater. A PTC heater (a heating element using a PTC resistor) 20a.

  In this embodiment, the temperature of the photosensitive drum 1 is efficiently kept substantially uniform by using the checking means for checking the position of the photosensitive drum 1 in the rotation direction R1 and the high-efficiency heater. The photosensitive drum 1 is dried almost uniformly. In particular, the heater is directly brought into contact with the portion on the photosensitive drum 1 that is located at the opposite portion of the corona charger during a long period of rest of the image forming apparatus 100 such as at night so that heating can be performed.

  That is, when the part on the photosensitive drum 1 located at the opposite part of the corona charger reaches the opposite part to the heater at least during the long-time pause of the image forming apparatus 100 such as at night, the heater is removed from the photosensitive drum. It is made to contact the surface of 1.

  In particular, in this embodiment, when the part on the photosensitive drum 1 that is located at the opposite part of the corona charger reaches the opposite part to the heater while the image forming apparatus 100 is at rest for a long time, such as at night, The rotational speed of the body drum 1 is reduced. This will be described in detail below.

FIG. 3A is a transparent plan view of the heater unit 20 used in this embodiment. FIG. 3B is a side view of the heater unit 20. In the present embodiment, the heater unit 20 includes a PTC heater 20a which is a heat generating member (heating member) processed into an elastically deformable sheet shape as a heating means. Sheet-like (planar) heating elements (heating sheets) using PTC resistors (PTC elements) are disclosed in, for example, Japanese Patent Application Laid-Open Nos. 06-295780 and 2003-109803. Next, the PTC heater 20a will be described.

  When a voltage is applied to the PTC element, it self-heats due to Joule heat, and when the Curie temperature (Tc) is exceeded, its resistance value increases logarithmically. As the resistance value increases, the current decreases and the power (W) is suppressed, so the heat generation temperature decreases. Therefore, when the resistance value decreases, the current increases and the power (W) increases again, so that the heat generation temperature increases. By repeating this operation, it works as a constant temperature heating element having a self-control function. In this example, a PTC element processed into a sheet shape was used.

  FIG. 4 is a cross-sectional view showing a layer structure of a PTC nonwoven fabric heater as the PTC heater 20a used in this example. The heater electrode 19 and the stretchable PTC resistor 21 are printed on a nonwoven fabric. Moreover, the printed heater electrode 19 and the stretchable PTC resistor 21 can be covered with a stretchable coating (coating material). The PTC heater 20a uses a comb-shaped electrode (electrode pair) as the heater electrode 19 in order to minimize heat generation unevenness. The uppermost layer facing the photosensitive drum 1 is provided with a surface layer 26 (in this embodiment, a fluororesin layer) for reducing the friction coefficient on the surface of the nonwoven fabric.

  In this embodiment, the heater unit 20 is downstream of the cleaning device 8 and upstream of the primary charger 2 in the rotation direction R1 of the photosensitive drum 1 (in this embodiment, particularly downstream of the cleaning device 8 and upstream of the pre-exposure device 9). Is arranged.

  In this embodiment, the flexible sheet-like PTC heater 20a of the heater unit 20 is curved along its longitudinal direction so that the convex outer surface can be brought into contact with the surface of the photosensitive drum 1. It has become. In other words, the PTC heater 20a is convex toward the surface of the photosensitive drum 1, and is curved so that the cross section viewed along the axis in the direction intersecting the moving direction of the photosensitive drum 1 is substantially U-shaped. Arranged. Then, the outer surface of the convex portion is pressed against the surface of the photosensitive drum 1 to come into contact with the surface of the photosensitive drum 1.

  More specifically, in the PTC heater 20a, one end in the longitudinal direction on the side where the power supply connector 25 is provided is two fixed side plates (fixed side fixing means) 24 which are plate-like members as fixing means. It is fixed to the image forming apparatus main body (image forming unit) while being sandwiched. The connector 25 is electrically connected to a power source (not shown) for supplying power to the PTC heater 20a.

  The other end in the longitudinal direction of the PTC heater 20a is sandwiched between two movable plates (movable side fixing means) 23, which are plate-like members as the same fixing means. And the PTC heater 20a is arrange | positioned in the state folded in U shape (or U shape) so that the surface of the lower side in FIG.3 (b) might become an outer side. Further, the end portion of the PTC heater 20a sandwiched between the movable side plates 23 is attached to a solenoid drive actuator (hereinafter simply referred to as “solenoid”) SL constituting the moving means in this embodiment.

  In this embodiment, the solenoid SL causes the PTC heater (heater part) 20a to be separated from the photosensitive drum 1 within the heater unit 20 (FIG. 2 and FIG. 5A), and contact with the photosensitive drum 1. It is possible to move between the contact positions (FIG. 1 and FIG. 5B). At this time, the surface layer 26 of the PTC heater 20a is arranged on the photosensitive drum 1 side. In this embodiment, the PTC heater 20a is arranged at the contact position by moving the movable side plate 23 closer to the photosensitive drum 1 by the solenoid SL. Further, the PTC heater 20a is arranged at the separated position by moving the movable side plate 23 to a position farther from the photosensitive drum 1 by the solenoid SL.

  In this way, the PTC heater 20a curved in a U-shape moves at least one end in the longitudinal direction relative to the photosensitive drum 1 so that a contact position and a separation position with respect to the photosensitive drum 1 are obtained. It can be movable between.

  When the PTC heater 20a is folded in a U shape, the PTC heater 20a is in pressure contact with the photosensitive drum 1 by its own reaction force when located at the contact position. At this time, a nip (hereinafter referred to as “heater nip”) H is formed between the photosensitive drum 1 and the PTC heater 20a. Further, when the PTC heater 20a is located at the separation position, the PTC heater 20a can maintain the separation state from the photosensitive drum 1.

  Further, in this embodiment, a base for holding the PTC heater 20a on the lower side in the gravity direction of the PTC heater 20a so that the PTC heater 20a does not bend due to gravity, that is, does not hang down in the gravity direction. 27 is provided. The base 27 slidably holds the PTC heater 20a. That is, the PTC heater 20a is arranged so as to be convex in the direction intersecting the gravity direction, and the lower portion of the portion extending in the direction intersecting the gravity direction does not bend downward in the gravity direction. A foundation 27 is arranged. In this embodiment, the base 27 does not belong to the heater unit 20.

  Here, in order to prevent image defects caused by corona discharge products such as image blurring and image flow by heating, the surface of the photosensitive drum 1 is set to 40 ° C. or more, and the photosensitive drum 1 is dried. desired. Therefore, in this embodiment, the sheet-type PTC heater 20a is used by applying a voltage of 100V with a set temperature of 50 ° C.

  FIG. 6 shows changes in the surface temperature of the PTC heater 20a and the elapsed time of power consumption when a voltage of 100 V is applied in the PTC heater 20a used in this example. The surface temperature of the PTC heater 20a instantaneously exceeds 40 ° C. required for recovery of image defects such as image blur and image flow caused by corona discharge products, and then stabilizes at a set temperature of 50 ° C. Immediately after voltage application to the PTC element, inrush power is applied, but it stabilizes at constant power in a few seconds.

  Thus, in order to instantaneously raise the surface temperature of the PTC heater 20a to the target temperature or immediately stabilize it at a constant power, the configuration of the heater unit 20 in the present embodiment as described above is advantageous. That is, this is because the configuration of the heater unit 20 in the present embodiment has a characteristic that it is fast-heated, that is, has a small heat capacity. In order to maximize this characteristic, in this embodiment, the heater unit 20 does not use backup means or the like as means for pressing the heat generating member against the photosensitive drum 1. In this embodiment, the heat generating member itself does not employ a roller or the like having a large heat capacity. In other words, in the present embodiment, the heater unit 20 uses a sheet-like PTC heater 20a as a heat generating member, and the PTC heater 20a uses the repulsive force of the PTC heater 20a itself to surface the photosensitive drum 1. Pressed.

  For this reason, in this embodiment, the heater unit 20 is disposed downstream of the cleaning device 8 in the rotation direction R1 of the photosensitive drum 1 where toner is not substantially present on the photosensitive drum 1. However, for example, under the condition that the photosensitive drum 1 is not heated during image formation, the same effect can be obtained even if the heater unit 20 is disposed upstream of the cleaning device 8 in the rotation direction R1 of the photosensitive drum 1. .

  In addition, a heater having PTC characteristics has a property that heat is partially generated only when the temperature is lowered. Therefore, when the photosensitive drum 1 is heated by the PTC heater 20a, a portion where heat is consumed to dry the corona discharge product having absorbed moisture on the surface of the photosensitive drum, that is, a portion where the temperature of the PTC heater 20a is decreased It will quickly generate heat. Therefore, by using the PTC heater 20a, the surface of the photosensitive drum is divided into a portion where the corona discharge product is hardly attached and heat is hardly consumed, and a portion where the corona discharge product is much attached and heat is easily consumed. Difficult to generate temperature difference.

[Control of heater unit]
Next, control of the PTC heater 20a in the heater unit 20 will be described.

  In the present embodiment, the heating of the photosensitive drum 1 by the heater unit 20 is typically performed before shifting to the standby state when the main switch of the image forming apparatus 100 is turned on, as will be described in detail later. This is performed during the preparation operation (pre-multi-rotation operation). In this embodiment, the heating of the photosensitive drum 1 by the heater unit 20 is also performed when returning from the energy saving mode to the standby state.

  As described above, in this embodiment, the control means (controller) 50 can determine when the specific surface position of the photosensitive drum 1 is located at the opposed portion of the heater unit 20. In other words, in this embodiment, the control unit 50 outputs the number of output signals of the drive motor 40 necessary for one rotation of the photosensitive drum 1 and the output signal of the drive motor 40 from the power (main switch) on of the image forming apparatus 100. It functions as a photoreceptor surface position confirmation means for making the above determination from the number.

  In the present embodiment, the corona discharge product is accumulated most in the primary charger 2 having a corona charger in the rotation direction R1 of the photosensitive drum 1. In this embodiment, in the rotation direction R1 of the photosensitive drum 1, the angle from the central portion of the primary charger 2 to the central portion of the heater nip H between the PTC heater 20a of the heater unit 20 and the photosensitive drum 1 is It is 280 degrees with respect to the rotation center of the photosensitive drum 1. In this embodiment, the number of output signals of the drive motor 40 required for one rotation of the photosensitive drum 1 is 400. Therefore, in the rotation direction R1 of the photosensitive drum 1, the output of the drive motor 40 necessary for rotating the position on the photosensitive drum 1 facing the central portion of the primary charger 2 to the central portion of the heater nip H. The number of signals is 311.

  Similar to the primary charger 2, the positions of the pre-transfer charger 5, the transfer charger 6 and the separation charger 7 having a corona charger are also output from the drive motor 40 in the same manner as in the case of the primary charger 2. The position on the photosensitive drum 1 can be known from the number of signals.

  In this embodiment, the control means 50 functions as a speed changing means for controlling the rotational speed of the photosensitive drum 1 by controlling the drive motor 40. That is, in this embodiment, in order to dry the corona discharge product efficiently and in a short time using the PTC heater 20a having a small heat capacity, the rotational speed of the photosensitive drum 1 is set as follows at the time of image formation. Decreasing with respect to the rotational speed (hereinafter referred to as “process speed”).

  In other words, the control unit 50 determines that the photosensitive drum 1 when the portion on the photosensitive drum 1 facing the corona charger is opposed to the heater unit 20 during a long pause of the image forming apparatus such as at night. The rotation speed is made slower than the process speed. In this embodiment, the corona discharger is a primary charger 2, a pre-transfer charger 5, a transfer charger 6, and a separation charger 7.

  The photosensitive drum in the rotational direction of the photosensitive drum 1 passing through the portion facing the heater unit 20 when the rotational speed of the photosensitive drum 1 is decelerated from the process speed of the rotational speed of the photosensitive drum 1 and the photosensitive drum 1. The surface area of 1 was set as follows in this example. In this embodiment, the outer diameter of the photosensitive drum 1 is 80 mm.

  First, for the primary charger 2, the rotational speed of the photosensitive drum 1 during deceleration is 1/3 of the process speed. The surface area of the photosensitive drum 1 that passes through the heater nip H at the above speed is the area corresponding to the width of the discharge opening of the primary charger 2 (hereinafter simply referred to as “opening width”), and both upstream and downstream sides thereof. This is a region to which a region for 5 mm is added.

  For the pre-transfer charger 5, the rotational speed of the photosensitive drum 1 at the time of deceleration is a half of the process speed. The surface area of the photosensitive drum 1 that passes through the heater nip H at that speed is an area corresponding to the opening width of the pre-transfer charger 5.

  For the transfer charger 6 and the separation charger 7, the rotational speed of the photosensitive drum 1 at the time of deceleration is a half of the process speed. The surface area of the photosensitive drum 1 that passes through the heater nip H at that speed is an area obtained by adding an area corresponding to the opening width of each charger and an area corresponding to 5 mm on both the upstream and downstream sides.

  Incidentally, the amount of deceleration of the rotational speed of the photosensitive drum 1 as described above with respect to the process speed is obtained from the amount of corona discharge product deposited. Further, the area on the photosensitive drum 1 that passes through the portion facing the heater unit 20 when the speed is reduced is actually an image blur or image flow depending on the distance between the photosensitive drum 1 and each corona charger. An area in which image defects due to corona discharge products such as these are likely to occur is set. Accordingly, this value varies depending on the setting of each image forming apparatus. Preferably, the surface area of the photosensitive drum 1 that passes through the portion facing the heater unit 20 during the deceleration is at least the opening width area of the charger.

  Hereinafter, in this embodiment, for each corona charger, an area on the photosensitive drum 1 that passes through the opposing portion of the heater unit 20 when the speed of the photosensitive drum 1 is reduced with respect to the process speed is simply expressed as follows. This is called “deceleration area” for each corona charger.

  Further, in this embodiment, the control means 50 controls the solenoid SL to control the movement of the PTC heater 20a and also controls the energization to the PTC heater 20a.

  Next, the control in the present embodiment will be described in more detail with reference to the flowchart of FIG.

  When the main switch of the image forming apparatus 100 is turned on (S101), the PTC heater 20a of the heater unit 20 is moved to a contact position where it contacts the photosensitive drum 1 (S102). Thereafter, when the fixing device 10 is in a predetermined state while adjusting the temperature, the rotation of the photosensitive drum 1, the count of the output signal (rotation signal, drive signal) of the drive motor 40, and energization of the PTC heater 20a are performed. It starts simultaneously (S103). The photosensitive drum 1 starts rotating at the process speed.

  Next, the photosensitive drum 1 is rotated by a predetermined amount until the position on the photosensitive drum 1 facing the separation charger 7 when the photosensitive drum 1 is stopped reaches the facing portion of the heater unit 20 (S104). . Thereafter, the rotational speed of the photosensitive drum 1 is reduced to half of the process speed (S105). More specifically, the predetermined rotation amount of the photosensitive drum 1 here is the amount of time until the tip of the deceleration region for the separation charger 7 reaches the center position of the heater nip H in the rotation direction R1 of the photosensitive drum 1. This is the amount of rotation of the photosensitive drum 1 (the number of drive signals counted).

  In this embodiment, the separation charger 7 and the transfer charger 6 are adjacent to each other. Therefore, while the photosensitive drum 1 rotates by a predetermined amount until the position on the photosensitive drum 1 facing the transfer charger 6 when the photosensitive drum 1 stops passing through the facing portion of the heater unit 20, The rotational speed of the photosensitive drum 1 is set to half of the process speed (S106). Thereafter, the rotation speed of the photosensitive drum 1 is changed to the process speed (S107). More specifically, the predetermined amount of rotation of the photosensitive drum 1 here is the time until the rear end of the deceleration region for the transfer charger 6 passes through the center position of the heater nip H in the rotation direction R1 of the photosensitive drum 1. The amount of rotation of the photosensitive drum 1 (the number of drive signals counted).

  Next, the photosensitive drum 1 is rotated by a predetermined amount until the position on the photosensitive drum 1 facing the pre-transfer charger 5 when the photosensitive drum 1 is stopped reaches the facing portion of the heater unit 20 ( S108). Thereafter, the rotational speed of the photosensitive drum 1 is reduced to half of the process speed (S109). More specifically, the predetermined rotation amount of the photosensitive drum 1 here is determined until the front end of the deceleration region for the pre-transfer charger 5 reaches the center position of the heater nip H in the rotation direction R1 of the photosensitive drum 1. The amount of rotation of the photosensitive drum 1 (the number of drive signals counted).

  The photosensitive drum 1 is rotated by a predetermined amount until the position on the photosensitive drum 1 facing the pre-transfer charger 5 when the photosensitive drum 1 stops passing through the facing portion of the heater unit 20. The rotational speed of the photosensitive drum 1 is set to half of the process speed (S110). Thereafter, the rotational speed of the photosensitive drum 1 is changed to the process speed (S111). More specifically, the predetermined rotation amount of the photosensitive drum 1 here is such that the rear end of the deceleration region for the pre-transfer charger 5 passes through the center position of the heater nip H in the rotation direction R1 of the photosensitive drum 1. The amount of rotation of the photosensitive drum 1 up to this point (the number of drive signals counted).

  Next, the photosensitive drum 1 is rotated by a predetermined amount until the position on the photosensitive drum 1 facing the primary charger 2 when the photosensitive drum 1 is stopped reaches the facing portion of the heater unit 20 (S112). . Thereafter, the rotational speed of the photosensitive drum 1 is reduced to 1/3 of the process speed (S113). More specifically, the predetermined rotation amount of the photosensitive drum 1 here is the amount of time until the tip of the deceleration region for the primary charger 2 reaches the center position of the heater nip H in the rotation direction R1 of the photosensitive drum 1. This is the amount of rotation of the photosensitive drum 1 (the number of drive signals counted).

  While the photosensitive drum 1 is rotated by a predetermined amount until the position on the photosensitive drum 1 facing the primary charger 2 when the photosensitive drum 1 stops passing through the facing portion of the heater unit 20, the photosensitive drum 1 rotates. The rotational speed of the photosensitive drum 1 is set to 1/3 of the process speed (S114). Thereafter, the rotation speed of the photosensitive drum 1 is changed to the process speed (S115). More specifically, the predetermined rotation amount of the photosensitive drum 1 here is determined until the rear end of the deceleration region for the primary charger 2 passes through the center position of the heater nip H in the rotation direction R1 of the photosensitive drum 1. The amount of rotation of the photosensitive drum 1 (the number of drive signals counted). Thus, the photosensitive drum 1 is rotated once from the start of rotation.

  After this operation is repeated for a predetermined time (S116), the PTC heater 20a is moved to a separated position away from the photosensitive drum 1 (S117), and then the rotation of the photosensitive drum 1 is stopped (S118) to enter the standby state. (S119). In this embodiment, the predetermined time is 30 seconds. In this embodiment, the PTC heater 20a is moved to the separated position, and at the same time, the energization of the PTC heater 20a is stopped.

  In this embodiment, the standby state is an image formable state, and the time of image formation is a standby state including pre-rotation (preparation operation before image formation) and post-rotation (organization operation after image formation). It is an operation state until it returns to the state.

  The image forming apparatus 100 according to the present exemplary embodiment has an energy saving mode. In this embodiment, the energy saving mode is a state in which power is not supplied to the fixing device 10. In this embodiment, the surface temperature of the fixing roller 10a in the standby state is maintained at 200.degree. When the standby state exceeds the set time, it switches to the energy saving mode state. When switched to the energy saving mode state, the heater of the fixing roller 10a is turned off.

  In this embodiment, when returning from the energy saving mode, the heating operation of the photosensitive drum 1 by the heater unit 20 is performed in the same manner as when the main switch is turned on. That is, in this embodiment, when a signal for starting up from the energy saving mode to the image formable state is input, energization of the heater unit 20 is started together with the activation of the photosensitive drum 1. Then, while the photosensitive drum 1 rotates for 30 seconds, the same heating control of the photosensitive drum 1 is performed.

  As described above, according to the present embodiment, it is possible to obtain a good image with a short time and energy saving even when starting up after being left for a long time in a high humidity environment. In addition, the temperature of the photosensitive drum 1 can be kept substantially uniform, and the photosensitive drum 1 can be dried substantially uniformly.

  That is, according to the present embodiment, the highly efficient and flexible PTC heater 20a that directly heats the surface of the photosensitive drum 1 is brought into contact with the surface of the photosensitive drum 1 in a substantially U shape. Thereby, the corona discharge product adhering to the surface of the photosensitive drum 1 can be efficiently dried, and the start-up time can be shortened and the power can be reduced. Further, although the corona discharge product can be dried in a short time, it can be controlled so that the heat of the heater is efficiently applied to the portion on the photosensitive drum 1 where the corona charger is located. . For this reason, the temperature of the photoconductor can be kept substantially uniform and the photoconductor can be dried almost uniformly, so that a good image can be obtained from the beginning of the apparatus startup.

Example 2
Next, another embodiment according to the present invention will be described.

  FIG. 8 schematically shows a schematic configuration of a main part of the image forming apparatus of the present embodiment. The basic configuration of the image forming apparatus of this embodiment is the same as that of the first embodiment. Accordingly, elements having the same functions or configurations as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the first embodiment, in particular, in order to efficiently heat the region where the corona discharge products are accumulated on the photosensitive drum 1, the control motor 50 controls the driving motor 40 of the photosensitive drum 1 to control the photosensitive drum. The rotational speed of 1 was slowed down.

  On the other hand, in the present embodiment, the PTC heater 20a is applied to the surface portion of the photosensitive drum 1, that is, the deceleration region, in which the rotational speed of the photosensitive drum 1 is set slower than the process speed in the first embodiment. Increase the heating temperature. Therefore, in the present embodiment, a region on the photosensitive drum 1 corresponding to a region called “deceleration region” for each corona charger in the first embodiment is referred to as a “temperature increase region”.

  In particular, in this embodiment, when the part on the photosensitive drum 1 that is located at the facing part of the corona charger reaches the facing part of the heater during the long-time pause of the image forming apparatus 100 such as at night, the heater Is switched so that the high-output portion of the sensor contacts the photosensitive drum 1. This switching is performed by a temperature region changing unit described later.

  In the present embodiment, the temperature of the sheet-like PTC heater 20a of the heater unit 20 varies depending on the position in the plane. That is, the set temperature of the sheet-like PTC heater 20a used in this example is partially adjusted in the plane. As described above, since the PTC heater 20a operates as a constant temperature heating element having a self-control function, the temperature can be varied depending on the location of the PTC heater 20a. Thus, in the present embodiment, the PTC heater 20a has at least two different temperature regions (temperature positions). The PTC heater 20a can have the same layer configuration as that described in the first embodiment except that the set temperature of the PTC resistor is different in any temperature region. The at least two different temperature regions can be switched as appropriate to contact the photosensitive drum 1.

  More specifically, in the present embodiment, the heater unit 20 has a configuration similar to that of the first embodiment. However, in this embodiment, one end in the longitudinal direction of the PTC heater 20a on the side where the power feeding connector 25 is provided is fixed in the heater unit 20 while being sandwiched between two fixed plates 24. Yes.

  In the present embodiment, the other end in the longitudinal direction of the PTC heater 20a is sandwiched between the two movable plates 23, and the motor drive actuator (hereinafter referred to as “moving means”) in the present embodiment is used. It is simply attached to the MO. This moving motor MO performs the same operation as the solenoid SL in the first embodiment.

  In other words, in this embodiment, the moving motor MO causes the PTC heater 20a to be separated from the photosensitive drum 1 within the heater unit 20 (FIG. 9) and the contact position where the PTC heater 20a contacts the photosensitive drum 1 (FIG. 8). It is possible to move between. At this time, the surface layer 26 of the PTC heater 20a is arranged on the photosensitive drum 1 side.

  In this embodiment, the solenoid that moves the heater unit 20 itself between a first position closer to the photosensitive drum 1 and a second position farther from the photosensitive drum 1 than the first position. A drive actuator (solenoid) SL is provided. That is, when the heater unit 20 is moved to the first position by the solenoid SL, both ends of the PTC heater 20a fixed by the fixed plate 24 are closer to the photosensitive drum 1. Moved. Conversely, when the heater unit 20 is moved to the second position by the solenoid SL, both ends of the PTC heater 20a fixed by the fixed plate 24 are further away from the photosensitive drum 1. Moved to a different position. In this embodiment, the solenoid SL constitutes the temperature region changing means.

  In other words, at least two different temperature regions of the PTC heater 20a are selectively brought into contact with the photosensitive drum 1 by the moving motor MO and the solenoid SL, and the PTC heater 20a is brought into contact with or separated from the photosensitive drum 1. It can be made to. In other words, the relative position between the PTC heater 20a and the photosensitive drum 1 is set to the separated state and the contact state in the first temperature range by the switching means configured to include the solenoid SL and the moving motor MO. And the contact state in the second temperature region.

  The solenoid SL and the moving motor MO operate as follows when the first temperature region (first PTC resistor region) 21A in which the set temperature of the PTC heater 20a is lower is brought into contact with the photosensitive drum 1. That is, the heater unit 20 is moved to the first position by the solenoid SL, and the PTC heater 20a is moved to the contact position where it contacts the photosensitive drum 1 by the moving motor MO (FIG. 10A). In this embodiment, the set temperature in the first temperature region is 50 ° C.

  On the other hand, the solenoid SL and the moving motor MO operate as follows when the second temperature region (second PTC resistor region) 21B in which the set temperature of the PTC heater 20a is higher is brought into contact with the photosensitive drum 1. . That is, the heater unit 20 is moved to the second position by the solenoid SL, and the PTC heater 20a is moved to the contact position where it contacts the photosensitive drum 1 by the moving motor MO (FIG. 10B). In this embodiment, the set temperature in the second temperature region is 60 ° C.

  In this embodiment, the control means 50 controls the solenoid SL and the moving motor MO to control the movement of the PTC heater 20a and the heater unit 20, and also controls the energization of the PTC heater 20a.

  Further, as in the first embodiment, independent of the heater unit 20, a base 27 is provided to hold the sheet-like PTC heater 20a so as not to hang down due to gravity.

  Next, the control in the present embodiment will be described in more detail with reference to the flowchart of FIG.

  In this embodiment, similarly to the first embodiment, the heating of the photosensitive drum 1 by the heater unit 20 is typically performed until the standby state is entered when the main switch of the image forming apparatus 100 is turned on. Is performed during the preparatory operation (pre-multi-rotation operation). In addition, the photosensitive drum 1 is heated by the heater unit 20 when returning from the energy saving mode to the standby state.

  When the main switch of the image forming apparatus 100 is turned on (S201), the PTC heater 20a of the heater unit 20 is brought into contact with the photosensitive drum 1 in the first temperature region (low temperature position) 21A (S202). Thereafter, when the fixing device 10 is in a predetermined state while adjusting the temperature, the rotation of the photosensitive drum 1, the count of the output signal (rotation signal, drive signal) of the drive motor 40, and the energization to the PTC heater 20a are performed. It starts simultaneously (S203). That is, at this time, the heater unit 20 is moved to the first position closer to the photosensitive drum 1 by the solenoid SL, and the PTC heater 20a is moved to the contact position by the moving motor MO. As a result, the PTC heater 20a contacts the photosensitive drum 1 in the first temperature region (50 ° C. region) 21A as shown in FIG. The photosensitive drum 1 starts rotating at the process speed.

  Next, the photosensitive drum 1 is rotated by a predetermined amount until the position on the photosensitive drum 1 facing the separation charger 7 when the photosensitive drum 1 stops reaches the facing portion of the heater unit 20 (S204). . Thereafter, the PTC heater 20a is brought into contact with the photosensitive drum 1 in the second temperature region (high temperature position) 21B (S205). More specifically, the predetermined rotation amount of the photosensitive drum 1 here is determined until the leading end of the temperature rising region for the separation charger 7 reaches the center position of the heater nip H in the rotation direction R1 of the photosensitive drum 1. The amount of rotation of the photosensitive drum 1 (the number of drive signals counted). At this time, the heater unit 20 is moved to the second position further away from the photosensitive drum 1 by the solenoid SL, and the PTC heater 20a is moved to the contact position by the moving motor MO. As a result, the PTC heater 20a contacts the photosensitive drum 1 in the second temperature region (60 ° C. region) 21B as shown in FIG. 10B.

  In this embodiment, the separation charger 7 and the transfer charger 6 are adjacent to each other. Therefore, while the photosensitive drum 1 rotates by a predetermined amount until the position on the photosensitive drum 1 facing the transfer charger 6 when the photosensitive drum 1 stops passing through the facing portion of the heater unit 20, The contact state in the second temperature region 21B is maintained (S206). Thereafter, the PTC heater 20a is returned to the state in contact with the photosensitive drum 1 in the first temperature region (low temperature position) 21A (S207). More specifically, the predetermined rotation amount of the photosensitive drum 1 here is such that the rear end of the temperature rising region for the transfer charger 6 passes through the center position of the heater nip H in the rotation direction R1 of the photosensitive drum 1. The amount of rotation of the photosensitive drum 1 up to this point (the number of drive signals counted). At this time, the heater unit 20 is moved to the first position closer to the photosensitive drum 1 by the solenoid SL, and the PTC heater 20a is moved to the contact position by the moving motor MO. As a result, the PTC heater 20a contacts the photosensitive drum 1 in the first temperature region (50 ° C. region) 21A as shown in FIG.

  Thereafter, the photosensitive drum 1 is rotated by a predetermined amount until the position on the photosensitive drum 1 facing the pre-transfer charger 5 when the photosensitive drum 1 stops reaches the facing portion of the heater unit 20 (S208). ). Thereafter, the PTC heater 20a is brought into contact with the photosensitive drum 1 in the second temperature region (high temperature position) 21B (S209). More specifically, the predetermined rotation amount of the photosensitive drum 1 here is such that the front end of the temperature rising region for the pre-transfer charger 5 reaches the center position of the heater nip H in the rotation direction R1 of the photosensitive drum 1. The amount of rotation of the photosensitive drum 1 up to this point (the number of drive signals counted). At this time, the heater unit 20 is moved to the second position further away from the photosensitive drum 1 by the solenoid SL, and the PTC heater 20a is moved to the contact position by the moving motor MO. As a result, the PTC heater 20a contacts the photosensitive drum 1 in the second temperature region (60 ° C. region) 21B as shown in FIG. 10B.

  The photosensitive drum 1 is rotated by a predetermined amount until the position on the photosensitive drum 1 facing the pre-transfer charger 5 when the photosensitive drum 1 stops passing through the facing portion of the heater unit 20. The contact state in the second temperature region 21B is maintained (S210). Thereafter, the PTC heater 20a is returned to the state in contact with the photosensitive drum 1 in the first temperature region (low temperature position) 21A (S211). More specifically, the predetermined rotation amount of the photosensitive drum 1 here is such that the rear end of the temperature rising region of the pre-transfer charger 5 passes through the central position of the heater nip H in the rotation direction R1 of the photosensitive drum 1. This is the amount of rotation of the photosensitive drum 1 (the number of counts of drive signals) until it is completed. At this time, the heater unit 20 is moved to the first position closer to the photosensitive drum 1 by the solenoid SL, and the PTC heater 20a is moved to the contact position by the moving motor MO. As a result, the PTC heater 20a contacts the photosensitive drum 1 in the first temperature region (50 ° C. region) 21A as shown in FIG.

  Next, the photosensitive drum 1 is rotated by a predetermined amount until the position on the photosensitive drum 1 facing the primary charger 2 when the photosensitive drum 1 is stopped reaches the facing portion of the heater unit 20 (S212). ). Thereafter, the PTC heater 20a is brought into contact with the photosensitive drum 1 in the second temperature region (high temperature position) 21B (S213). More specifically, the predetermined rotation amount of the photosensitive drum 1 here is the time until the tip of the temperature rising region for the primary charger 2 reaches the center position of the heater nip H in the rotation direction R1 of the photosensitive drum 1. The amount of rotation of the photosensitive drum 1 (the number of drive signals counted). At this time, the heater unit 20 is moved to the second position further away from the photosensitive drum 1 by the solenoid SL, and the PTC heater 20a is moved to the contact position by the moving motor MO. As a result, the PTC heater 20a contacts the photosensitive drum 1 in the second temperature region (60 ° C. region) 21B as shown in FIG. 10B.

  While the photosensitive drum 1 is rotated by a predetermined amount until the position on the photosensitive drum 1 facing the primary charger 2 when the photosensitive drum 1 stops passing through the facing portion of the heater unit 20, the photosensitive drum 1 rotates. The contact state in the second temperature region 21B is maintained (S214). Thereafter, the PTC heater 20a is returned to the state in contact with the photosensitive drum 1 in the first temperature region (low temperature position) 21A (S215). More specifically, the predetermined rotation amount of the photosensitive drum 1 here is such that the rear end of the temperature rising region for the primary charger 2 passes through the center position of the heater nip H in the rotation direction R1 of the photosensitive drum 1. The amount of rotation of the photosensitive drum 1 up to this point (the number of drive signals counted). At this time, the heater unit 20 is moved to the first position closer to the photosensitive drum 1 by the solenoid SL, and the PTC heater 20a is moved to the contact position by the moving motor MO. As a result, the PTC heater 20a contacts the photosensitive drum 1 in the first temperature region (50 ° C. region) 21A as shown in FIG.

  After this operation is repeated for a predetermined time (S216), the PTC heater 20a is moved to a separated position away from the photosensitive drum 1 (S217), and then the rotation of the photosensitive drum 1 is stopped (S218) to enter a standby state. (S219). In this embodiment, the predetermined time is 30 seconds. In this embodiment, the PTC heater 20a is moved to the separated position, and at the same time, the energization of the PTC heater 20a is stopped.

  In the present embodiment, typically, the energization of the heater unit 20 as described above is performed until the standby state is entered when the main switch of the image forming apparatus 100 is turned on. Further, in this embodiment, when a signal for starting up from the energy saving mode to the image formable state is input when returning from the energy saving mode, the photosensitive drum 1 is started and the heater unit 20 is started. Is energized. Then, while the photosensitive drum 1 rotates for 30 seconds, the same heating control of the photosensitive drum 1 is performed. The standby state and the energy saving mode itself are as described in the first embodiment.

  As described above, according to the present embodiment, the same effects as those of the first embodiment can be obtained. That is, according to the present embodiment, for example, a good image can be obtained in a short time and with energy saving even when starting up after being left for a long time in a high humidity environment. In addition, the temperature of the photosensitive drum 1 can be kept substantially uniform, and the photosensitive drum 1 can be dried substantially uniformly.

  In this example, the moisture absorbed by the corona discharge product on the surface of the photosensitive drum 1 was evaporated by an external heating method. The energy by the external heating is used for moisture evaporation and is a short time, so that the temperature distribution of the photosensitive drum 1 is difficult to be uneven. However, the image forming apparatus 100 can be further provided with a temperature sensor 30 (FIGS. 8 and 9) as a photoconductor temperature detecting means for measuring the temperature of the surface of the photoconductor drum 1. When the surface temperature of the photosensitive drum 1 is high, the PTC heater 20a is brought into contact with the photosensitive drum 1 in the low temperature region (first temperature region) or moved to the separation position to separate from the photosensitive drum 1. Thus, the photosensitive drum 1 can be prevented from being heated. When the surface temperature of the photosensitive drum 1 is low, the PTC heater 20a is moved to the contact position, and at the low temperature region (first temperature region) or the high temperature region (second temperature region). Can be made to contact. Thereby, it is possible to recover from a state in which an image defect due to a corona discharge product such as image blur and image flow is likely to occur in an earlier time.

Example 3
Next, still another embodiment according to the present invention will be described. The basic configuration of the image forming apparatus of the present embodiment is the same as that of the first and second embodiments. Accordingly, elements having the same functions or configurations as those of the first and second embodiments are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the first embodiment, in particular, in order to efficiently heat the region where the corona discharge products are accumulated on the photosensitive drum 1, the rotational speed of the photosensitive drum 1 is controlled by controlling the driving motor 40 of the photosensitive drum 1. Slowed down. In the second embodiment, a plurality of different temperature regions are provided in the PTC heater 20a, and control is performed so that the plurality of temperature regions are properly used according to the position on the photosensitive drum 1 facing the heater unit 20.

  In contrast, in this embodiment, the contact area between the PTC heater 20a of the heater unit 20 and the photosensitive drum 1, that is, the nip amount (width) of the heater nip H is made variable. In the present embodiment, the nip amount is changed corresponding to the surface portion of the photosensitive drum 1, that is, the deceleration region, in which the rotational speed of the photosensitive drum 1 is slower than the process speed in the first embodiment. Therefore, in this embodiment, the area on the photosensitive drum 1 corresponding to the area called the “deceleration area” for each corona charger in the first embodiment is referred to as a “nip amount changing area”.

In particular, in this embodiment, when the part on the photosensitive drum 1 that is located at the facing part of the corona charger reaches the facing part of the heater during the long-time pause of the image forming apparatus 100 such as at night, the heater And the photosensitive drum 1 are widened (nip width, contact area, contact area). The switching of the contact area is performed by a contact area changing unit (adjusting unit) described later.

  More specifically, in the present embodiment, the heater unit 20 has a configuration similar to that of the first embodiment. That is, in the present embodiment, as in the first embodiment, one end in the longitudinal direction of the PTC heater 20a on the side where the power feeding connector 25 is provided is sandwiched between the two fixed-side plates 24. It is fixed in the unit 20.

  In this embodiment, the other end in the longitudinal direction of the PTC heater 20a is sandwiched between the two movable plates 23, and the motor drive actuator (moving motor) constituting the moving means in this embodiment is used. ) Mounted on MO. This moving motor MO performs the same operation as the solenoid SL in the first embodiment.

  In other words, in the present embodiment, the PTC heater 20a has a separation position in a state where the PTC heater 20a is separated from the photosensitive drum 1 within the heater unit 20 by the moving motor MO and a contact position in a state where the PTC heater 20a is in contact with the photosensitive drum 1. It is possible to move between. Furthermore, in the present embodiment, the PTC heater 20a has a first contact position (FIG. 12A) where the contact area with the photosensitive drum 1 becomes narrower as the contact position by the moving motor MO, and the contact area. It is possible to move between the second contact position (FIG. 12 (b)) where becomes wider. At this time, the surface layer 26 of the PTC heater 20a is arranged on the photosensitive drum 1 side. Thus, in this embodiment, the moving motor MO as the moving means has a function as the contact area changing means.

  In this embodiment, the nip amount (first nip amount) N1 of the heater nip H in the rotation direction of the photosensitive drum 1 when the PTC heater 20a is at the first contact position is about 7.5 mm, and the second The nip amount (second nip amount) N2 at the contact position was about 15 mm.

  In other words, the relative position between the PTC heater 20a and the photosensitive drum 1 is changed to the separated state, the contact state at the first contact position, and the second contact position by the switching unit constituted by the moving motor MO. Switch to one of the contact states at.

  In the present embodiment, the control means 50 controls the movement motor MO to control the movement of the PTC heater 20a, and also controls the energization of the PTC heater 20a.

  Further, as in the first embodiment, independent of the heater unit 20, a base 27 is provided to hold the sheet-like PTC heater 20a so as not to hang down due to gravity. The heater unit 20 itself is fixed to the image forming apparatus main body.

  Next, the control in the present embodiment will be described in more detail with reference to the flowchart of FIG.

  In this embodiment, similarly to the first embodiment, the heating of the photosensitive drum 1 by the heater unit 20 is typically performed until the standby state is entered when the main switch of the image forming apparatus 100 is turned on. Is performed during the preparatory operation (pre-multi-rotation operation). In addition, the photosensitive drum 1 is heated by the heater unit 20 when returning from the energy saving mode to the standby state.

  When the main switch of the image forming apparatus 100 is turned on (S301), the PTC heater 20a of the heater unit 20 is moved to the first contact position (FIG. 12 (a)), and the photosensitive drum is moved with the first nip amount N1. 1 (S302). Thereafter, when the fixing device 10 is in a predetermined state while adjusting the temperature, the rotation of the photosensitive drum 1, the count of the output signal (rotation signal, drive signal) of the drive motor 40, and energization of the PTC heater 20a are performed. It starts simultaneously (S303). The photosensitive drum 1 starts rotating at the process speed.

  Next, the photosensitive drum 1 is rotated by a predetermined amount until the position on the photosensitive drum 1 facing the separation charger 7 when the photosensitive drum 1 stops reaches the facing portion of the heater unit 20 (S304). . Thereafter, the PTC heater 20a is moved to the second contact position (FIG. 12B) by the moving motor MO, and contacts the photosensitive drum 1 with the second nip amount N2 (S305). More specifically, the predetermined rotation amount of the photosensitive drum 1 here is such that the tip of the nip amount changing region for the separation charger 7 reaches the center position of the heater nip H in the rotation direction R1 of the photosensitive drum 1. The amount of rotation of the photosensitive drum 1 up to this point (the number of drive signals counted).

  In this embodiment, the separation charger 7 and the transfer charger 6 are adjacent to each other. Therefore, while the photosensitive drum 1 rotates by a predetermined amount until the position on the photosensitive drum 1 facing the transfer charger 6 when the photosensitive drum 1 stops passing through the facing portion of the heater unit 20, The contact state at the second nip amount N2 is maintained (S306). Thereafter, the PTC heater 20a is moved to the first contact position by the moving motor MO and contacts the photosensitive drum 1 with the first nip amount N1 (S307). More specifically, the predetermined rotation amount of the photosensitive drum 1 here is such that the rear end of the nip amount changing region for the transfer charger 6 passes through the center position of the heater nip H in the rotation direction R1 of the photosensitive drum 1. This is the amount of rotation of the photosensitive drum 1 (the number of counts of drive signals) until it is completed.

  Thereafter, the photosensitive drum 1 is rotated by a predetermined amount until the position on the photosensitive drum 1 facing the pre-transfer charger 5 when the photosensitive drum 1 stops reaches the facing portion of the heater unit 20 (S308). ). Thereafter, the PTC heater 20a is moved to the second contact position by the moving motor MO and contacts the photosensitive drum 1 with the second nip amount N2 (S309). More specifically, the predetermined rotation amount of the photosensitive drum 1 here is such that the front end of the nip amount changing region for the pre-transfer charger 5 reaches the center position of the heater nip H in the rotation direction R1 of the photosensitive drum 1. This is the amount of rotation of the photosensitive drum 1 (the number of counts of drive signals) until it is completed.

  While the photosensitive drum 1 is rotated by a predetermined amount until the position on the photosensitive drum 1 facing the pre-transfer charger 5 finishes passing through the facing portion of the heater unit 20, the second nip amount is set. The contact state at N2 is maintained (S310). Thereafter, the PTC heater 20a is moved to the first contact position by the moving motor MO and contacts the photosensitive drum 1 with the first nip amount N1 (S311). More specifically, the predetermined rotation amount of the photosensitive drum 1 here is such that the rear end of the nip amount changing region for the pre-transfer charger 5 in the rotation direction R1 of the photosensitive drum 1 is the center position of the heater nip H. This is the amount of rotation of the photosensitive drum 1 until it passes (the number of drive signals counted).

  Next, the photosensitive drum 1 is rotated by a predetermined amount until the position on the photosensitive drum 1 facing the primary charger 2 when the photosensitive drum 1 stops reaches the facing portion of the heater unit 20 (S312). ). Thereafter, the PTC heater 20a is moved to the second contact position by the moving motor MO and contacts the photosensitive drum 1 with the second nip amount N2 (S313). More specifically, the predetermined rotation amount of the photosensitive drum 1 here is the time until the tip of the nip amount changing region reaches the center position of the heater nip H with respect to the primary charger 2 in the rotation direction R1 of the photosensitive drum 1. The amount of rotation of the photosensitive drum 1 (the number of drive signals counted).

  While the photosensitive drum 1 is rotated by a predetermined amount until the position on the photosensitive drum 1 facing the primary charger 2 when the photosensitive drum 1 stops passing through the facing portion of the heater unit 20, the photosensitive drum 1 rotates. The contact state at the second nip amount N2 is maintained (S314). Thereafter, the PTC heater 20a is moved to the first contact position by the moving motor MO, and contacts the photosensitive drum 1 with the first nip amount N1 (S315). More specifically, the predetermined rotation amount of the photosensitive drum 1 here is such that the rear end of the nip amount changing region for the primary charger 2 passes through the center position of the heater nip H in the rotation direction R1 of the photosensitive drum 1. This is the amount of rotation of the photosensitive drum 1 (the number of counts of drive signals) until it is completed.

  After this operation is repeated for a predetermined time (S316), the PTC heater 20a is moved to a separated position separated from the photosensitive drum 1 (S317), and then the rotation of the photosensitive drum 1 is stopped (S318) to enter a standby state. (S319). In this embodiment, the predetermined time is 30 seconds. In this embodiment, the PTC heater 20a is moved to the separated position, and at the same time, the energization of the PTC heater 20a is stopped.

  In the present embodiment, typically, the energization of the heater unit 20 as described above is performed until the standby state is entered when the main switch of the image forming apparatus 100 is turned on. In this embodiment, when returning from the energy saving mode, when a signal for starting up the image forming ready state from the energy saving mode is input, the heater unit 20 is activated together with the activation of the photosensitive drum 1. Is energized. Then, while the photosensitive drum 1 rotates for 30 seconds, the same heating control of the photosensitive drum 1 is performed. The standby state and the energy saving mode itself are as described in the first embodiment.

  As described above, according to this embodiment, the same effects as those of Embodiments 1 and 2 can be obtained. That is, according to the present embodiment, for example, a good image can be obtained in a short time and with energy saving even when starting up after being left for a long time in a high humidity environment. In addition, the temperature of the photosensitive drum 1 can be kept substantially uniform, and the photosensitive drum 1 can be dried substantially uniformly.

  In this example, the moisture absorbed by the corona discharge product on the surface of the photosensitive drum 1 was evaporated by an external heating method. The energy by the external heating is used for moisture evaporation and is a short time, so that the temperature distribution of the photosensitive drum 1 is difficult to be uneven. However, a temperature sensor can be further provided in the image forming apparatus 100 as a photosensitive member temperature detecting unit that measures the temperature of the surface of the photosensitive drum 1. When the surface temperature of the photosensitive drum 1 is high, the PTC heater 20a can be moved to the first contact position or moved to the separated position so that the photosensitive drum 1 is not heated. Further, when the surface temperature of the photosensitive drum 1 is low, the PTC heater 20a can be moved to the first contact position or the second contact position. Thereby, it is possible to recover from a state in which an image defect due to a corona discharge product such as image blur and image flow is likely to occur in an earlier time.

  As mentioned above, although this invention was demonstrated according to the specific Example, it should be understood that this invention is not limited to the above-mentioned embodiment.

  For example, in each of the above-described embodiments, the configuration using only the external heating means is adopted. It is possible to recover from a state in which an image defect is likely to occur.

  The heating control of the photosensitive drum 1 by the heater unit 20 described in each of the above embodiments can be arbitrarily combined. For example, the temperature region of the PTC heater 20a described in Embodiment 2 or 3 may be changed or the contact region may be changed, and the rotational speed of the photosensitive drum 1 may be decreased. Further, for example, a plurality of temperature regions may be provided in the PTC heater 20a, and the nip amount may be varied in each temperature region.

  In each of the above embodiments, the charger is described as a corona charger provided with a wire electrode and a shield plate. The present invention works extremely effectively in an image forming apparatus provided with a corona charger that is disposed opposite to such a photoconductor and performs a charging or discharging operation. However, the present invention is limited to such an embodiment. It is not something. Charger provided with a member that performs charging or discharging action when a high voltage is applied, such as a charging member or a transfer member (for example, a member that is placed in contact with a photosensitive member such as a roller or a brush and that has a charging or discharging action) If present, corona discharge products may adhere to the surface of the photoreceptor. Even in such an image forming apparatus, the same effects as described above can be obtained by applying the present invention.

1 is a schematic cross-sectional configuration diagram of an embodiment of an image forming apparatus according to the present invention (a state in which a heating unit is in contact with a photoreceptor). 1 is a schematic cross-sectional configuration diagram of an embodiment of an image forming apparatus according to the present invention (a state in which a heating unit is separated from a photoreceptor). (A) It is a general | schematic permeation | transmission top view of the sheet-like PTC heater comprised according to this invention, (b) It is a schematic side view of the PTC heater. It is a schematic sectional drawing for demonstrating the layer structure of the sheet-like PTC heater comprised according to this invention. It is a schematic sectional drawing for demonstrating an example of operation | movement of the PTC heater according to this invention. It is a graph for demonstrating the temperature rise of a PTC heater, and the time change of power consumption. It is a flowchart for demonstrating an example of control of the PTC heater according to this invention. FIG. 6 is a schematic cross-sectional configuration diagram of another embodiment of the image forming apparatus according to the present invention (a state where the heating unit is in contact with the photosensitive member). FIG. 6 is a schematic cross-sectional configuration diagram of another embodiment of the image forming apparatus according to the present invention (a state where the heating unit is separated from the photosensitive member). It is a schematic sectional drawing for demonstrating the other example of operation | movement of the PTC heater according to this invention. It is a flowchart for demonstrating the other example of control of the PTC heater according to this invention. It is a schematic sectional drawing for demonstrating the further another example of operation | movement of the PTC heater according to this invention. It is a flowchart for demonstrating the further another example of control of the PTC heater according to this invention. It is a schematic diagram for demonstrating the difference in the generation | occurrence | production state of the image defect resulting from a corona discharge product with the case where it does not provide with a heater. It is a schematic diagram of a latent image at the time of occurrence of an image defect caused by a corona discharge product.

Explanation of symbols

1 Photosensitive drum (electrophotographic photosensitive member)
2 Primary charger (corona charger)
4 Developing device 5 Pre-transfer charger (corona charger)
6 Transfer charger (Corona charger)
7 Separation charger (corona charger)
8 Cleaning device 19 Heater electrode 20 Heater unit 20a PTC heater (heating means)
27 Base 30 Temperature Sensor 40 Drive Unit 50 Control Unit

Claims (3)

A rotatable photoreceptor,
Charging means for charging the photoreceptor;
Exposure means for exposing to form an electrostatic image on the photoreceptor;
Developing means for developing the electrostatic image formed on the photoreceptor with toner;
Transfer means for transferring a toner image formed on the photoreceptor to a transfer material;
An image forming apparatus having
A sheet-like heating member for heating in contact with the photoreceptor;
An adjusting means for adjusting a contact area between the sheet-like heating member and the photosensitive member;
Detecting means for detecting the surface temperature of the photoreceptor;
When the region higher than the predetermined temperature detected by the detecting means is heated by the heating member, the contact area between the sheet-like heating member and the photoconductor becomes the first contact area. When the region lower than the predetermined temperature detected by the detection means is heated by the heating member, a second contact area between the sheet-like heating member and the photoconductor is larger than the first contact area. An image forming apparatus comprising: a control unit that controls the adjusting unit so as to have a contact area . The image forming apparatus according to claim 1 , wherein the adjusting unit adjusts a contact area between the sheet-like heating member and the photosensitive member by moving one end of the sheet-like heating member. Said adjusting means image forming apparatus according to claim 1 or 2, characterized in that it is spaced the photosensitive member and the sheet-like heating element.

Images