JP6402733B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device that melts and fixes unfixed toner on a recording medium onto a sheet, and an image forming apparatus such as a copying machine, a printer, and a facsimile machine including the fixing device.

  2. Description of the Related Art Conventionally, electrophotographic image forming apparatuses such as copying machines and printers include a fixing device that fixes a toner image onto a recording medium such as paper. A fixing device including a fixing member such as a fixing roller or a fixing belt and a pressure member such as a pressure roller is provided. The fixing device heats and fixes the toner transferred onto the paper while the paper passes through the nip between the fixing member and the pressure member.

  A pressure roller generally used in a fixing device is configured by providing an elastic layer such as silicon rubber around a core metal and further providing a release layer made of a fluororesin or the like on the outer periphery of the elastic layer. Since these elastic layers and release layers are insulative, the surface of the pressure roller is charged to a potential of minus several thousand volts by frictional charging of paper or the like. Further, since the unfixed toner on the paper is charged to a positive potential, it is held on the paper by applying a negative potential from the back side of the paper. Therefore, by charging the pressure roller to a negative potential, toner can be attracted to the paper, and a good image forming process can be performed.

  However, when the charging potential of the pressure roller becomes too high, discharge to the fixing member occurs, and the force to attract toner from the back side of the paper is weakened. For this reason, a part of the toner adheres to the fixing member, and the toner is transferred to the pressure roller, so that the printed matter may be stained due to electrostatic offset.

  In view of this, some fixing devices are provided with a neutralizing member such as a neutralizing sheet for neutralizing the surface charge of the pressure roller, at a position separated from the surface of the pressure roller by a predetermined distance along the axial direction of the pressure roller. is there. Moreover, the surface potential of the pressure roller is lowered to a predetermined potential by using a non-woven fabric coated with a conductive polymer as the charge eliminating sheet.

  For example, a fixing device disclosed in Patent Document 1 includes a heating roller (fixing member), a pressure roller (pressure member), a support member that rotatably supports the pressure roller, and the support member on the heating roller side. And a static elimination brush (static elimination member) attached to the support member. The tip of the brush portion of the static elimination brush is disposed so as to have a predetermined distance from the circumferential surface of the pressure roller.

  The fixing device disclosed in Patent Document 2 includes a heat roller (fixing member) and a pressure roller (pressure member) that contact each other to form a nip, and is grounded near the heat roller or the pressure roller. Conductive fibers (static elimination members) are arranged in a non-contact state with respect to the heat roller or pressure roller.

  Further, in the fixing device disclosed in Patent Document 3, a fixing roller (fixing member) including a heating element (heating member) and a pressure roller (pressure member) are pressed against each other, and the surface charge of the pressure roller is fixed. A static elimination sheet (static elimination member) that neutralizes the static electricity is provided along the axial direction of the pressure roller at a position separated from the surface of the pressure roller by a predetermined distance.

  Further, the heating device (fixing device) disclosed in Patent Document 4 is applied as a heating body (fixing member), a pressure rotating body (pressing member) pressed against the heating body, and a charge eliminating member for the pressure rotating body. And a plurality of conductive needle-like electrodes arranged in close contact with the pressure rotator in a non-contact manner with a predetermined gap. Then, the material to be heated is nipped and conveyed to the pressure nip formed between the heating body and the pressure rotating body, and the heat of the heating body is applied to the material to be heated. Further, the needle electrode has a projection area in the vertical direction smaller than a projection area in the direction orthogonal to the vertical direction.

JP 11-338282 A JP 2003-223073 A JP 2005-031402 A JP 2008-032818 A

  However, the neutralization member such as a neutralization sheet provided in the vicinity of the pressure member is pulled by the static electricity generated by the charging of the pressure member, and sometimes contacts. When the fibers of the static elimination member come into contact with the pressure member, the potential of the contact portion is extremely lowered, the force that attracts the toner to the paper is weakened, the toner adheres to the fixing member and the transfer to the pressure member occurs. It becomes easy to cause stains on the printed matter due to electrostatic offset. Further, in the contact portion between the charge removal member and the pressure member, the adhesion of the toner transferred to the pressure member, the growth (deposition) of the toner, and the separation of the grown toner (deposited toner) are repeated, so that the dirt expands. Such problems occur.

  SUMMARY OF THE INVENTION An object of the present invention is to prevent image defects due to toner contamination without bringing a charge eliminating member into contact with a pressure member during an image forming operation.

  The fixing device of the present invention includes a fixing member that is heated by a heating member, a pressure member that presses against the fixing member and forms a fixing nip between the fixing member, and a conductive non-woven fabric. A charge removing member for discharging charges charged on the surface of the pressure member, and a contact / separation mechanism for contacting / separating the pressure member and the charge removal member, wherein the contact / separation mechanism performs at least image formation. During the operation time to be performed, the pressure member and the charge removal member are spaced apart from each other with a predetermined interval, while the pressure member and the charge removal member are brought close to each other at a predetermined timing other than the operation time. Features.

  According to such a configuration, in the fixing device, the electrostatic potential can be prevented by lowering the surface potential of the pressure member to a predetermined potential by the static elimination member during the operation time during which image formation is performed such as during printing. it can. Further, in the fixing device, when the discharging member is pressed and brought into contact with the pressure member at a timing when printing is not performed except for the operation time, the fiber floating of the discharging member can be physically and thermally suppressed. For this reason, in the operation time after the next time, it is possible to prevent the occurrence of the problem of electrostatic offset due to the fibers coming into contact with the surface of the pressure member.

  The contact / separation mechanism may be configured to move the charge removal member relative to the pressure member.

  By adopting such a configuration, it is possible to realize the proximity function and the separation function between the pressure member and the charge removal member even when the pressure member cannot move.

  The contact / separation mechanism moves the pressure member relative to the fixing member to separate the pressure member from the charge removal member when the pressure member is brought close to the fixing member. The pressure member may be configured to be close to the charge removal member when the member is separated from the fixing member.

  By adopting such a configuration, the contact / separation mechanism can be realized by using a mechanism that moves the pressure member in order to prevent deformation due to continuation of the pressing state of the fixing member and the pressure member.

  The fixing device described above further includes a temperature detection unit that detects the temperature of the surface of the fixing member, and a control unit that calculates the predicted temperature of the pressure member based on the temperature of the surface of the fixing member, The contact / separation mechanism may use the predetermined timing when the predicted temperature of the pressure member is equal to or higher than a predetermined temperature in a time other than the operation time.

  The higher the temperature of the surface of the pressure member, the higher the effect of pressing the fibers of the static elimination member. Therefore, by adopting such a configuration, the effect of physically and thermally suppressing the floating of the fibers of the static elimination member is improved. Therefore, it is possible to further prevent the occurrence of the electrostatic offset problem due to the fibers coming into contact with the surface of the pressure member during the subsequent operation time. For example, a better effect can be obtained by continuing the rotation drive for a predetermined time after the printing is completed and performing the proximity function in a state where the temperature of the surface of the pressure member is raised.

  The contact / separation mechanism may set the predetermined timing when the fixing member and the pressure member are in a stationary state in which the fixing member and the pressure member are not rotating in a time other than the operation time.

  By adopting such a configuration, it is possible to physically and thermally efficiently suppress the floating of the fibers of the static elimination member without damaging the fibers of the static elimination member and the surface of the pressure member. Therefore, it becomes possible to further prevent the occurrence of the electrostatic offset problem due to the fibers coming into contact with the surface of the pressure member during the subsequent operation time.

  The contact / separation mechanism may use the predetermined timing when the fixing member and the pressing member are in a low speed state where the fixing member and the pressure member rotate at a low speed in a time other than the operation time.

  By adopting such a configuration, the static elimination state on the surface of the pressure member by the static elimination member is made uniform in the circumferential direction, so that the static elimination unevenness due to the static neutralization of the surface of the pressure member is avoided. be able to. Therefore, it is possible to avoid the occurrence of horizontal streak-like image defects due to electrostatic scattering, etc., and further prevent the occurrence of electrostatic offset problems due to the fibers coming into contact with the surface of the pressure member during the next operation time. It becomes possible to do.

  The image forming apparatus of the present invention includes any one of the fixing devices described above.

  According to the present invention, it is possible to prevent image defects due to toner contamination without bringing the charge removal member into contact with the pressure member during the image forming operation.

1 is a cross-sectional view illustrating a printer according to an embodiment of the present invention. 1 is a cross-sectional view illustrating a fixing device according to an embodiment of the present invention. FIG. 5 is a cross-sectional view illustrating a state in which a static elimination sheet is brought close to a pressure roller in a fixing device according to an embodiment of the present invention. 1 is a block diagram illustrating a control system for a fixing device according to an embodiment of the present invention. FIG. 6 is a cross-sectional view illustrating a state in which a pressure roller is brought close to a charge removal sheet in a fixing device according to another embodiment of the present invention.

  First, the overall configuration of a printer 1 (image forming apparatus) according to an embodiment of the present invention will be described with reference to FIG. Hereinafter, for convenience of explanation, the front side of the sheet in FIG.

  The printer 1 includes a box-shaped printer main body 2. A paper feed cassette 3 for storing paper (recording medium) is accommodated in the lower part of the printer main body 2, and a paper discharge tray 4 is provided on the upper surface of the printer main body 2. An upper cover 5 is attached to the upper surface of the printer main body 2 so as to be openable and closable on the side of the paper discharge tray 4, and a toner container 6 is stored below the upper cover 5.

  An exposure unit 7 composed of a laser scanning unit (LSU) is disposed below the discharge tray 4 above the printer body 2, and an image forming unit 8 is provided below the exposure unit 7. The image forming unit 8 is rotatably provided with a photosensitive drum 10 as an image carrier. Around the photosensitive drum 10, a charger 11, a developing device 12, a transfer roller 13, and a cleaning device 14 are provided. Are arranged along the rotation direction of the photosensitive drum 10 (see arrow X in FIG. 1).

  A paper transport path 15 is provided inside the printer body 2. A paper feed unit 16 is provided at the upstream end of the conveyance path 15, and a transfer unit 17 configured by the photosensitive drum 10 and the transfer roller 13 is provided at a middle portion of the conveyance path 15. Is provided with a fixing device 18, and a paper discharge unit 20 is provided at the downstream end of the conveyance path 15. A reverse path 21 for double-sided printing is provided below the transport path 15.

  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 setting such as temperature setting of the fixing device 18 is 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 charger 11, exposure corresponding to the image data is performed on the photosensitive drum 10 by laser light from the exposure device 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 sheet taken out from the sheet cassette 3 by the sheet feeding unit 16 is conveyed to the transfer unit 17 in synchronization with the above-described image forming operation, and the toner image on the photosensitive drum 10 is transferred to the sheet by the transfer unit 17. Is transcribed. The sheet on 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. The paper 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 fixing device 18 will be described with reference to FIGS.

  As shown in FIG. 2 and the like, the fixing device 18 includes a housing 23, a fixing roller 24 (fixing member), a pressure roller 25 (pressure member), a fixing heater 26 (heating member), and a guide portion 27. And a static elimination sheet 28 (static elimination member), a contact / separation mechanism 30, and a temperature detection unit 31.

  The housing 23 is formed in a substantially box shape that is long in the front-rear direction, and includes a paper feed port 23 a that is opened at a substantially vertical center of the right surface and a paper discharge port 23 b that is opened at a substantially vertical center of the left surface. The conveyance path 15 passes through the housing 23 through the paper supply port 23a and the paper discharge port 23b, and the paper introduced into the housing 23 through the paper supply port 23a passes through the paper discharge port 23b. It is discharged from the housing 23. Further, in the housing 23, the fixing roller 24 and the pressure roller 25 are respectively disposed on the upper side and the lower side with the conveyance path 15 interposed therebetween.

  The fixing roller 24 is formed in a cylindrical shape that is long in the front-rear direction and is rotatably supported in the housing 23. The rotation axis direction of the fixing roller 24 is the front-rear direction. The fixing roller 24 includes, for example, a cylindrical core material made of metal such as aluminum or iron, an elastic layer made of silicon rubber or the like provided around the core material, and a fluorine resin such as PFA covering the elastic layer. And a release layer.

  The pressure roller 25 is formed in a cylindrical shape that is long in the front-rear direction, and is rotatably supported in the housing 23. The rotation axis direction of the pressure roller 25 is the front-rear direction. The pressure roller 25 is pressed against the outer peripheral surface of the fixing roller 24, so that a fixing nip N is formed between the fixing roller 24 and the pressure roller 25. A driving gear (not shown) is attached to the rear end portion of the pressure roller 25. The pressure roller 25 is connected to a pressure roller drive source 42 (see FIG. 4) such as a motor via the drive gear, and is rotated by the pressure roller drive source 42.

  The pressure roller 25 includes, for example, a columnar core material, an elastic layer provided around the core material, and a release layer that covers the elastic layer. The core material of the pressure roller 25 is formed of, for example, a metal such as SUS or aluminum, and this core material serves as the rotating shaft of the pressure roller 25. The elastic layer of the pressure roller 25 is formed of, for example, silicon rubber, and the release layer of the pressure roller 25 is formed of, for example, PFA.

  The fixing heater 26 is a heat source configured by, for example, a halogen heater or a ceramic heater, and is provided in the internal space of the fixing roller 24. The fixing heater 26 is configured to generate heat by power supplied from a power source and to heat the fixing roller 24.

  The guide unit 27 is disposed on the upstream side of the fixing roller 24 and the pressure roller 25 in the conveyance path 15 and is configured to guide the sheet conveyed through the conveyance path 15 to the fixing nip N.

  The static elimination sheet 28 is comprised with the nonwoven fabric coat | covered with the conductive polymer, for example. The static elimination sheet 28 is formed so as to have a discharge surface 28a (tip of the nonwoven fabric fiber) that is long in the rotation axis direction of the pressure roller 25 and faces a part of the outer peripheral surface of the pressure roller 25.

  For example, the static elimination sheet 28 is provided on the right side (one side) of the pressure roller 25, the right end (one end) of the static elimination sheet 28 is attached to the holding member 32 of the contact / separation mechanism 30, and the left end (the other end) of the static elimination sheet 28. ) Constitutes the discharge surface 28a. The neutralization sheet 28 is arranged in a non-contact state having a gap of a predetermined distance facing a part of the outer peripheral surface of the pressure roller 25, thereby neutralizing the charge charged on the surface of the pressure roller 25.

  The contact / separation mechanism 30 has a function (separation function) for separating the pressure roller 25 and the charge removal sheet 28 at a predetermined interval at least during an operation time during which image formation is performed, and a predetermined time other than the operation time described above. It has a function (proximity function) for bringing the pressure roller 25 and the charge removal sheet 28 close to each other at the timing. For example, the contact / separation mechanism 30 is controlled by the following control unit 40 to switch between the separation function and the proximity function. In the present embodiment, the contact / separation mechanism 30 is configured to move the charge removal sheet 28 in the contact / separation direction (left-right direction) in which the charge removal sheet 28 approaches / separates the pressure roller 25.

  For example, the contact / separation mechanism 30 includes a holding member 32 that holds the charge removal sheet 28, a positioning frame 33, a moving shaft 34, a drive unit 35, and a coil spring 36. The holding member 32 is formed in a plate shape having a predetermined thickness in the left-right direction, and is arranged so that the left side surface of the holding member 32 faces a part of the outer peripheral surface of the pressure roller 25. A static elimination sheet 28 is attached to the surface. The positioning frame 33 is provided on the right side of the holding member 32 and restricts the movement of the holding member 32 to the right by a predetermined distance. The positioning frame 33 has, for example, a through hole 37 that penetrates in the left-right direction, and the area of the through hole 37 is set smaller than the area of the facing surface of the holding member 32.

  The moving shaft 34 is formed of a rod-like member that is long in the left-right direction, and is disposed through the through hole 37 of the positioning frame 33. The left end of the moving shaft 34 is attached to the right side surface of the holding member 32, and the right end of the moving shaft 34 is connected to the drive unit 35. The moving shaft 34 expands and contracts in the left-right direction according to the driving force of the driving unit 35. The drive unit 35 generates a drive force in the contact / separation direction (left / right direction), and transmits the drive force in the contact / separation direction to the moving shaft 34 connected to the drive unit 35. The drive part 35 is comprised by a solenoid actuator etc., for example. The coil spring 36 is provided so as to be wound around the moving shaft 34 and generates an urging force in the contact / separation direction (left / right direction), and is attached to the holding member 32 in the contact / separation direction. Transmit power.

  According to the configuration as described above, the contact / separation mechanism 30 separates the static elimination sheet 28 held by the holding member 32 from the pressure roller 25 by the driving force by the driving unit 35 and / or the urging force by the coil spring 36. Or can be brought into contact with the pressure roller 25. Note that the movement of the holding member 32 that moves in the separating direction is restricted by contacting the positioning frame 33.

  The temperature detector 31 is provided in the vicinity of the fixing roller 24, detects the surface temperature of the fixing roller 24, and notifies the control unit 40 of the detection result. The temperature detection unit 31 may be configured in a non-contact manner with respect to the fixing roller 24 or may be configured in a contact manner.

  Next, a control system of the fixing device 18 will be described with reference to FIG.

  The fixing device 18 is provided with a control unit 40 composed of a CPU or the like. The control unit 40 is connected to a storage unit 41 configured by a storage device such as a ROM or a RAM, and the control unit 40 controls the fixing device 18 based on a control program and control data stored in the storage unit 41. It is comprised so that each part may be controlled. The control system of the fixing device 18 may use a control unit (not shown) and a storage unit (not shown) that constitute the control system of the printer 1 instead of the control unit 40 and the storage unit 41. .

  The control unit 40 is connected to a pressure roller driving source 42 such as a motor that drives the pressure roller 25, and the pressure roller driving source 42 controls the pressure roller 25 based on a signal from the control unit 40. Rotate. When the pressure roller 25 rotates in this way, the fixing roller 24 in pressure contact with the pressure roller 25 is driven to rotate in the direction opposite to the pressure roller 25. At this time, a fixing nip N is formed between the fixing roller 24 and the pressure roller 25.

  The control unit 40 is connected to the fixing heater 26. The fixing heater 26 generates heat when electric power is supplied to the fixing heater 26 based on a signal from the control unit 40.

  The control unit 40 is connected to the drive unit 35 of the contact / separation mechanism 30. The control unit 40 controls the driving unit 35 of the contact / separation mechanism 30 so as to perform the separation function at least during an operation time during which image formation is performed, while at the predetermined timing other than the operation time described above. The drive unit 35 of the contact / separation mechanism 30 is controlled so as to perform the proximity function. For example, when the controller 40 does not drive the pressure roller 25 except for the operation time described above, that is, when the pressure roller 25 is in a stationary state where it does not rotate, the control unit 40 approaches the contact / separation mechanism 30. It is determined that it is a predetermined timing for performing the function.

  The control unit 40 is connected to the temperature detection unit 31. Then, the control unit 40 inputs the temperature detection result of the fixing roller 24 by the temperature detection unit 31. The control unit 40 predicts and calculates the temperature of the pressure roller 25 based on the temperature detection result of the fixing roller 24 and the driving time of the fixing roller 24 and the pressure roller 25. The control unit 40 determines whether the calculated predicted temperature of the pressure roller 25 is equal to or higher than a predetermined temperature, and performs the proximity function of the contact / separation mechanism 30 when the predicted temperature is equal to or higher than the predetermined temperature. It is determined that it is a predetermined timing.

  According to this embodiment, as described above, the fixing device 18 of the printer 1 (image forming apparatus) is in pressure contact with the fixing roller 24 (fixing member) heated by the fixing heater 26 (heating member) and the fixing roller 24. The pressure roller 25 (pressure member) that forms a fixing nip N with the fixing roller 24 and a non-woven fabric having conductivity are used to remove charges charged on the surface of the pressure roller 25. A neutralization sheet 28 (a neutralization member), and a contact / separation mechanism 30 that contacts and separates the pressure roller 25 and the neutralization sheet 28 are provided. The contact / separation mechanism 30 separates the pressure roller 25 and the charge removal sheet 28 at a predetermined interval at least during an operation time during which image formation is performed, while pressing the pressure roller at a predetermined timing other than the operation time. 25 and the static elimination sheet 28 are brought close to each other.

  As a result, the fixing device 18 can prevent electrostatic offset by lowering the surface potential of the pressure roller 25 to a predetermined potential by the charge eliminating sheet 28 during the operation time during which image formation is performed such as during printing. Further, the fixing device 18 can physically and thermally suppress the floating of the fibers of the charge removal sheet 28 by pressing and contacting the charge removal sheet 28 to the pressure roller 25 at a timing when printing is not performed except for the operation time. . For this reason, it becomes possible to prevent the occurrence of the problem of electrostatic offset due to the fibers coming into contact with the surface of the pressure roller 25 in the subsequent operation time.

  Further, according to the present embodiment, the contact / separation mechanism 30 is configured to move the charge removal sheet 28 relative to the pressure roller 25.

  Thereby, even if the pressure roller 25 cannot move, the proximity function and the separation function between the pressure roller 25 and the charge removal sheet 28 can be realized.

  Further, according to the present embodiment, the fixing device 18 calculates the predicted temperature of the pressure roller 25 based on the temperature detector 31 that detects the surface temperature of the fixing roller 24 and the surface temperature of the fixing roller 24. And a control unit 40. The contact / separation mechanism 30 sets the predetermined timing when the predicted temperature of the pressure roller 25 is equal to or higher than the predetermined temperature in a time other than the operation time.

  The higher the temperature of the surface of the pressure roller 25, the higher the effect of pressing the fibers of the static elimination sheet 28. Therefore, the effect of physically and thermally suppressing the floating of the fibers of the static elimination sheet 28 is improved. Therefore, it becomes possible to further prevent the occurrence of the electrostatic offset problem due to the fibers coming into contact with the surface of the pressure roller 25 during the next operation time. For example, a better effect can be obtained by performing the proximity function with the surface temperature of the pressure roller 25 increased by continuing the rotation drive for a predetermined time after the printing is completed.

  Further, according to the present embodiment, the contact / separation mechanism 30 sets the predetermined timing when the fixing roller 24 and the pressure roller 25 are in a stationary state that is not rotating in a time other than the operation time. .

  Thereby, the fiber floating of the static elimination sheet 28 can be physically and thermally efficiently suppressed without damaging the fibers of the static elimination sheet 28 or the surface of the pressure roller 25. Therefore, it becomes possible to further prevent the occurrence of the electrostatic offset problem due to the fibers coming into contact with the surface of the pressure roller 25 during the next operation time.

  In the present embodiment, the configuration of the contact / separation mechanism 30 that moves the static elimination sheet 28 relative to the pressure roller 25 has been described, but the configuration of the contact / separation mechanism 30 is not limited thereto. For example, in other embodiments, the static elimination sheet 28 may be fixedly disposed, and the contact / separation mechanism 30 may be configured to move the pressure roller 25 relative to the fixing roller 24. The contact / separation mechanism 30 separates the pressure roller 25 from the static elimination sheet 28 when the pressure roller 25 is brought close to the fixing roller 24, and pressurizes the pressure roller 25 when the pressure roller 25 is separated from the fixing roller 24. 25 is brought close to the charge removal sheet 28.

  The contact / separation mechanism 30 includes, for example, a swing plate 50, a cam 51, and an urging spring 52 as shown in FIG. The swing plate 50 has a shape that is long in the left-right direction, and supports the pressure roller 25 in a rotatable manner at the center in the left-right direction. A swing shaft 50a is provided at the right end of the swing plate 50, and the swing plate 50 is configured to swing around the swing shaft 50a. The cam 51 is disposed in contact with the upper surface of the left end of the swing plate 50 and is configured to be rotated by a drive unit (not shown). The biasing spring 52 is attached to the lower surface of the left end of the swing plate 50 and configured to bias the swing plate 50 upward.

  According to the configuration as described above, the contact / separation mechanism 30 moves the pressure roller 25 upward by moving the swing plate 50 upward by the rotation of the cam 51 and the biasing force of the biasing spring 52. In addition, it can be brought close to the fixing roller 24 and separated from the charge removal sheet 28. Further, as shown by a broken line in FIG. 5, the contact / separation mechanism 30 moves the pressure roller 25 downward by the rotation of the swing plate 50 by the rotation of the cam 51, and moves away from the fixing roller 24. And can be brought into close contact with the charge removal sheet 28.

  Thus, the contact / separation mechanism 30 can be realized by using a mechanism that moves the pressure roller 25 in order to prevent deformation due to the continuation of the pressing state of the fixing roller 24 and the pressure roller 25.

  In the present embodiment, an example is described in which the predetermined timing is the time when the fixing roller 24 and the pressure roller 25 are in a stationary state in which the contact / separation mechanism 30 is not rotating during a time other than the operation time during which image formation is performed. However, the predetermined timing at which the contact / separation mechanism 30 performs the separation function is not limited to this example. For example, in another embodiment, the contact / separation mechanism 30 may set a predetermined timing when the fixing member roller 24 and the pressure roller 25 are in a low speed state that rotates at a low speed in a time other than the above operation time. In this case, for example, the pressure roller 25 is controlled to rotate at a speed of about 200 mm / sec in a normal image forming operation, whereas in the above-described low speed state, the pressure roller 25 has a speed of about 50 to 60 mm / sec. Now it is controlled to rotate. The rotation of the pressure roller 25 in the low speed state may be performed, for example, for one rotation or more.

  Thereby, since the static elimination state of the surface of the pressure roller 25 by the static elimination sheet 28 is made uniform in the circumferential direction, it is possible to avoid unevenness in static elimination due to local neutralization of the surface of the pressure roller 25. Therefore, the occurrence of horizontal streak-like image defects due to electrostatic scattering or the like can be avoided, and the occurrence of electrostatic offset problems due to the fibers coming into contact with the surface of the pressure roller 25 during the subsequent operation time is further increased. It becomes possible to prevent. The rotational speed of the pressure roller 25 and the pressing force between the pressure roller 25 and the charge removal sheet 28 are set so that the charge removal sheet 28 is not peeled off or damaged.

  In this embodiment, the example in which the predicted temperature of the pressure roller 25 is calculated based on the detection result of the temperature detection unit 31 that detects the temperature of the surface of the fixing roller 24 has been described. You may provide the other temperature detection part which detects the temperature of the surface of the pressure roller 25. FIG.

  In the present embodiment, the case where the fixing roller 24 is used as a fixing member has been described. However, in another different embodiment, a fixing belt may be used as the fixing member. In the present embodiment, the case where the pressure roller 25 is used as the pressure member has been described. However, in another different embodiment, a pressure belt may be used as the pressure member.

  In this 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 is applied to other image forming apparatuses such as a copying machine, a facsimile machine, and a multifunction machine. It is also possible.

1 Printer (image forming device)
8 Image forming unit 15 Conveyance path 18 Fixing device 23 Housing 24 Fixing roller (fixing member)
25 Pressure roller (pressure member)
26 Fixing heater (heating member)
27 Guide part 28 Static elimination sheet (static elimination member)
28a Discharge surface 30 Contact / separation mechanism 31 Temperature detection unit 32 Holding member 33 Positioning frame 34 Moving shaft 35 Drive unit 36 Coil spring 37 Through hole 40 Control unit 41 Storage unit 42 Pressure roller drive source

Claims (7)

A fixing member heated by a heating member;
A pressure member that presses against the fixing member to form a fixing nip with the fixing member;
A neutralizing member that is composed of a non-woven fabric having conductivity, and neutralizes charges charged on the surface of the pressure member;
A contact / separation mechanism for contacting and separating the pressure member and the charge removal member;
With
The contact / separation mechanism separates the pressure member and the charge removal member at a predetermined interval at least during an operation time during which image formation is performed, while the pressure member at a predetermined timing other than the operation time. And a static eliminator.   The fixing device according to claim 1, wherein the contact / separation mechanism is configured to move the charge removal member relative to the pressure member.   The contact / separation mechanism moves the pressure member relative to the fixing member to separate the pressure member from the charge removal member when the pressure member is brought close to the fixing member. The fixing device according to claim 1, wherein the pressing member is configured to be close to the charge removal member when the member is separated from the fixing member. A temperature detector for detecting the temperature of the surface of the fixing member;
A controller that calculates a predicted temperature of the pressure member based on the temperature of the surface of the fixing member;
4. The contact timing mechanism according to any one of claims 1 to 3, wherein the predetermined timing is a time when the predicted temperature of the pressure member is equal to or higher than a predetermined temperature in a time other than the operation time. The fixing device according to claim 1.   2. The predetermined timing when the contact / separation mechanism is in a stationary state in which the fixing member and the pressure member are not rotating in a time other than the operation time. 4. The fixing device according to any one of 3 above.   2. The predetermined timing when the contact / separation mechanism is in a low speed state in which the fixing member and the pressure member rotate at a low speed in a time other than the operation time. 4. The fixing device according to any one of 3 above. An image forming apparatus comprising the fixing device according to claim 1.

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