Fixing apparatus and image forming apparatus

Abstract

This prevents the accumulation of electric charge in the fixed rotating body and pressurized rotating body over time. [Solution] The fixing belt 21 (fixing rotating body) has a conductive elastic layer 21b (conductive layer) that is conductive and an insulating surface layer 21c that is laminated directly or indirectly on the conductive elastic layer 21b and is insulating. The pressure roller 31 (pressure rotating body) has a nip portion that contacts the insulating surface layer 21c of the fixing belt 21 and is provided with a conductive surface layer 34 that is conductive and a conductive member 65 that is electrically connected to the conductive elastic layer 21b of the fixing belt 21 and is grounded. A conductive roller 66 is installed that contacts and is electrically connected to the conductive surface layer 34 and conductive member 65 of the pressure roller 31.

Description

Technical Field

[0001] The present invention relates to a fixing device that heats and fixes a toner image carried on the surface of a sheet, and an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine equipped with the same.

Background Art

[0002] Conventionally, in a fixing device installed in an image forming apparatus such as a copying machine or a printer, in order to prevent the occurrence of abnormal images such as electrostatic offset, a technique of discharging a fixing rotating body such as a fixing belt or a fixing roller and a pressing rotating body such as a pressing roller using a discharge brush is known (see, for example, Patent Documents 1 and 2).

Summary of the Invention

Problems to be Solved by the Invention

[0003] Conventional fixing devices suppress the accumulation of charges on the fixing rotating body and the pressing rotating body using a discharge brush, so an effect of reducing the occurrence of abnormal images such as electrostatic offset can be expected. However, over time, the brush hairs of the discharge brush fall out or become frayed, resulting in a reduction in the discharge effect. In addition, abnormal images may occur when the fallen brush hairs adhere to the fixed image.

[0004] The present invention has been made to solve the above-described problems, and an object thereof is to provide a fixing device and an image forming apparatus in which charges are less likely to accumulate on the fixing rotating body and the pressing rotating body even over time.

Means for Solving the Problems

[0005] The fixing device in this invention comprises a fixing rotating body heated by a heat source, and a pressurizing rotating body that forms a nip portion on which a sheet is conveyed by pressing it against the fixing rotating body, wherein the fixing rotating body comprises a conductive layer having conductivity and an insulating surface layer having insulating properties, which is directly or indirectly laminated on the conductive layer, and the pressurizing rotating body comprises a conductive surface layer having conductivity, which is in contact with the insulating surface layer of the fixing rotating body to form the nip portion, and a conductive member that is electrically connected to the conductive layer of the fixing rotating body and is grounded, and a conductive roller is installed that is in contact with the conductive surface layer of the pressurizing rotating body and the conductive member and is electrically connected. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide a fixing device and an image forming apparatus in which electric charge is less likely to accumulate on the fixing rotating body or the pressurizing rotating body over time. [Brief explanation of the drawing]

[0007] [Figure 1] This is an overall configuration diagram showing an image forming apparatus according to an embodiment of the present invention. [Figure 2] This is a diagram showing the configuration of the fixing device. [Figure 3] This is a top view of the fixing device as seen in the width direction. [Figure 4] This is a schematic side view showing the anchoring belt and guide member in the width direction. [Figure 5] This figure shows a fixing device in which a conductive roller is in contact with the target area. [Figure 6] This diagram shows a fixing device in which the conductive roller is separated from the target area. [Figure 7] This is a flowchart showing the contact and separation control of conductive rollers. [Figure 8] This flowchart shows the contact and separation control of a conductive roller as an example of modification 1. [Figure 9] This figure shows a fixing device in a modified form 2, where the conductive roller is in contact with the target area. [Modes for carrying out the invention]

[0008] Hereinafter, embodiments for carrying out this invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and redundant explanations will be simplified or omitted as appropriate.

[0009] First, Figure 1 will explain the overall configuration and operation of the image forming apparatus 100. In Figure 1, 100 represents a small printer as an image forming apparatus, 1 represents a photosensitive drum on which a toner image is formed, 6 represents a process cartridge that integrates the photosensitive drum 1, a charging roller 4, a developing device 5, and a cleaning device 2, and 7 represents an exposure device (writing unit) that irradiates the photosensitive drum 1 with exposure light L based on image information input from an input device such as a personal computer. Furthermore, 9 is a transfer roller that transfers the toner image supported on the surface of the photoreceptor drum 1 to the sheet P which is transported to the transfer nip section (transfer position), 12 is a paper feed device (paper feed cassette) in which the sheet P such as paper is stored, 16 is a register roller (timing roller) that transports the sheet P toward the transfer nip section where the photoreceptor drum 1 and the transfer roller 9 come into contact, and 20 is a fixing device that fixes the unfixed image on the sheet P.

[0010] Here, a charging roller 4, a developing device 5, a cleaning device 2, and other components are arranged around the photoreceptor drum 1. These components (photoreceptor drum 1, charging roller 4, developing device 5, and cleaning device 2) are integrated as a process cartridge 6 and are installed in a detachable (replaceable) manner on the image forming apparatus body 100 (apparatus body). The process cartridge 6 is mainly removed from the image forming apparatus body 100 by the user and replaced with a new one when it reaches a predetermined replacement cycle.

[0011] Referring to Figure 1, the operation of the image forming apparatus 100 during normal image forming will be described. First, when image information is transmitted from an input device such as a personal computer to the exposure device 7 of the image forming apparatus 100, the exposure device 7 emits exposure light L (laser light) based on that image information toward the surface of the photoreceptor drum 1. Meanwhile, the photoreceptor drum 1 is driven by a drive motor installed in the image forming apparatus body 100 and rotates in the direction of the arrow (clockwise). First, the surface of the photoreceptor drum 1 is uniformly charged at the position opposite the charging roller 4 (this is the charging process). In this way, a charge potential (approximately -900V) is formed on the photoreceptor drum 1. Subsequently, the charged surface of the photoreceptor drum 1 reaches the irradiation position of the exposure light L. Then, the potential of the part irradiated by the exposure light L becomes the latent image potential (approximately 0 to -100V), and an electrostatic latent image is formed on the surface of the photoreceptor drum 1 (this is the exposure process).

[0012] Subsequently, the surface of the photoreceptor drum 1, on which the electrostatic latent image has formed, reaches a position opposite the developing device 5. Then, toner is supplied from the developing device 5 onto the photoreceptor drum 1, and the latent image on the photoreceptor drum 1 is developed to form a toner image (this is the developing process). Subsequently, the surface of the photoreceptor drum 1 after the development process reaches the transfer nip (transfer position) with the transfer roller 9. At the transfer nip with the transfer roller 9, a transfer bias (a bias with a different polarity from the toner's polarity) is applied from the power supply unit to the transfer roller 9, thereby transferring the toner image formed on the photoreceptor drum 1 onto the sheet P conveyed by the register roller 16 (this is the transfer process).

[0013] Then, the surface of the photoreceptor drum 1 after the transfer process reaches a position facing the cleaning device 2. At this position, any untransferred toner remaining on the photoreceptor drum 1 is mechanically removed by the cleaning blade and collected in the cleaning device 2 (this is the cleaning process). Thus, the series of image-forming processes on the photoreceptor drum 1 are completed.

[0014] On one hand, the sheet P conveyed to the transfer nip between the photoreceptor drum 1 and the transfer roller 9 operates as follows. First, the uppermost sheet P stored in the paper feeding device 12 is fed by the paper feeding roller 15 toward the conveyance path. After that, the sheet P reaches the position of the registration roller 16. Then, the sheet P that has reached the position of the registration roller 16 is conveyed toward the transfer nip (the contact position between the transfer roller 9 and the photoreceptor drum 1) while synchronizing the timing to align with the image formed on the photoreceptor drum 1.

[0015] After passing through the position of the transfer nip (transfer roller 9), the sheet P after the transfer process reaches the fixing device 20 through the conveyance path. The sheet P that has reached the fixing device 20 is fed between the fixing belt 21 and the pressure roller 31, and the image is fixed by the heat received from the fixing belt 21 and the pressure received from both members 21 and 22 (this is the fixing process). After the sheet P with the image fixed is sent out from between the fixing belt 21 and the pressure roller 31 (the fixing nip), it is discharged from the image forming apparatus main body 100 and placed on the paper discharge tray. In this way, a series of image forming processes is completed.

[0016] Next, the configuration and operation of the fixing device 20 will be described using FIGS. 2 to 6 and the like. The fixing device 20 is a device that conveys the sheet P (a sheet carrying unfixed toner) while heating it. Referring to FIGS. 2 and the like, the fixing device 20 includes a fixing belt 21 as a fixing rotating body, a planar heater 24 as a heat source (heating means), a holder 23, a stay 30, a thermistor 40, a pressure roller 31 as a pressure rotating body, a conductive roller 66, a conductive member 65 (see FIGS. 3, 5, etc.), and the like.

[0017] Here, the fixing belt 21 as the fixing rotating body is an endless belt member that circumscribes the pressure roller 31 and rotates passively as the pressure roller 31 rotates. The fixing belt 21 is a thin and flexible endless belt that rotates (passively rotates) in the direction of the arrow in Fig. 2 (clockwise). Referring to Fig. 5 (not to scale), etc., from the inner peripheral surface side (the sliding contact surface with the planar heater 24), a base material layer 21a, a conductive elastic layer 21b as a conductive layer, and an insulating surface layer 21c (surface layer) of the fixing belt 21 are sequentially laminated, and the overall thickness thereof is set to 1 mm or less. The base material layer 21a of the fixing belt 2 is 30 to 50 μm in layer thickness and is formed of a metal material such as nickel or stainless steel or a resin material such as polyimide. The conductive elastic layer 21b of the fixing belt 21 is 100 to 300 μm in layer thickness and is obtained by dispersing carbon or the like in a rubber material such as silicone rubber, foamed silicone rubber, fluorine rubber, etc., and has conductivity. By providing the conductive elastic layer 21b, minute irregularities on the surface of the fixing belt 21 in the fixing nip are not formed, heat is uniformly transmitted to the toner image on the sheet P, and the generation of a smooth skin image is suppressed. s>The insulating surface layer 21c of the fixing belt 21 is 5 to 50 μm in layer thickness and is formed of an insulating material such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), polyimide, polyetherimide, PES (polyether sulfone), etc. By providing the insulating surface layer 21c, releasability (peelability) with respect to the toner (toner image) is ensured.

[0018] On the inner side (inner peripheral surface side) of the fixing belt 21, a planar heater 24, a holder 23, a stay 30, a thermistor 40, etc. are installed. Here, the planar heater 24 is arranged to extend in the width direction (the direction perpendicular to the plane of the paper in Figure 2, and the left-right direction in Figures 3 and 4). The planar heater 24 is pressed against the pressure roller 31 via the fixing belt 21 on the inside (inner circumferential surface side) of the fixing belt 21, forming a nip section (fixing nip) on which the sheet P is conveyed. That is, the planar heater 24 is installed so as to slide against the inner circumferential surface of the fixing belt 21. The planar heater 24 presses against the pressure roller 31 via the fixing belt 21, thereby forming a nip section on which the sheet P is conveyed. In this way, the planar heater 24 functions as a member that forms a nip section (fixing nip) (nip section forming member). In addition, to reduce sliding resistance with the fixing belt 21, the surface of the planar heater 24 can be covered with a sheet-like member made of a low-friction material such as PTFE or a surface layer can be provided on its surface. Furthermore, the planar heater 24 has a resistive pattern (heat-generating resistor) formed on the portion that slides against the inner circumferential surface of the fixing belt 21. Power is supplied to the resistive pattern from a power supply unit (not shown), and the resistive pattern generates heat due to its resistance, thereby heating the fixing belt 21. In this way, the planar heater 24 also functions as a heat source (heating means) for heating the fixing belt 21.

[0019] In this embodiment, the planar heater 24 is held by the holder 23 (holding member). The holder 23 has a recess formed therein, into which the planar heater 24 is fitted, thereby holding the planar heater 24 across its width. The holder 23 is held by the stay 30 while holding the planar heater 24. The stay 30, which holds the planar heater 24 and the holder 23, is held by the frame 60 of the fixing device 20 at both ends in the width direction via flange members 42 (see Figure 3, etc.).

[0020] In this way, the fuser belt 21 is directly heated by a planar heater 24 (resistor pattern) installed inside it. Then, heat is applied to the toner image on the sheet P from the surface of the heated fuser belt 21. Here, the output control of the planar heater 24 is performed based on the temperature detection result by the thermistor 40, which is in direct (or indirectly via another component) contact with the planar heater 24. In this embodiment, there is no temperature sensor that directly detects the surface temperature of the fixing belt 21. Instead, the temperature of the planar heater 24 is controlled by the thermistor 40, thereby indirectly controlling the surface temperature (fixing temperature) of the fixing belt 21 to reach a desired temperature.

[0021] Referring to Figure 4, the pair of flange members 42 guide both ends of the fixing belt 21 in the width direction from the inner circumferential surface side so that the fixing belt 21 maintains a substantially cylindrical position. More specifically, the two flange members 42 are made of a heat-resistant resin material or the like, and are held at both ends in the width direction of the frame 60 of the fixing device 20 so as to be slidable in the direction of forming a nip portion (fixing nip). The flange members 42 are provided with a guide portion 42a for holding the fixing belt 21 while maintaining the substantially cylindrical posture of the fixing belt 21, and a stopper portion for restricting the movement of the fixing belt 21 in the width direction (towards the belt), etc. Furthermore, in this embodiment, as shown in Figure 3, the fixing belt 21 (and the planar heater 24 and holder 23) are configured to be pressed against the pressure roller 31 by pressure applied by the pressure lever 52 (pressure mechanism 51) via the flange member 42. Furthermore, the flange members 42 are positioned at both ends in the width direction, within the circumferential range excluding the fixing nip, so as not to interfere with the formation of the fixing nip by the planar heater 24. Furthermore, in this embodiment, the only members that contact the inner circumferential surface of the fixing belt 21 are the flange members 42 that make loose contact at both ends in the width direction and the planar heater 24, and there are no other members (belt guides) that contact the inner circumferential surface and guide the rotation of the fixing belt 21.

[0022] In this embodiment, the stay 30 is installed inside the fixing belt 21 so as to contact the pressure roller 31 via the planar heater 24 (and holder 23) and the fixing belt 21. The stay 30 reinforces the strength of the planar heater 24 (and holder 23) that forms the fixing nip, and is installed on the frame 60 (or holder 23) by screw fastening or the like. Furthermore, the stay 30 contacts the pressure roller 31 via the planar heater 24 (and holder 23) and the fixing belt 21, thereby preventing the planar heater 24 (and holder 23) from deforming significantly in the fixing nip due to the pressure applied by the pressure roller 31. In order to satisfy the above-mentioned function, it is preferable that the stay 30 be made of a metal material with high mechanical strength, such as stainless steel or iron.

[0023] While resin materials and metal materials can be used to form the holder 23, a resin material (such as liquid crystal polymer (LCP), polyamide-imide (PAI), polyethersulfone (PES), polyphenylene sulfide (PPS), polyethernitrile (PEN), polyetheretherketone (PEEK), etc.) is preferred as it has sufficient rigidity to prevent excessive deflection even under pressure from the pressure roller 31, and possesses thermal and heat insulating properties. In this embodiment, liquid crystal polymer (LCP) is used as the material for the holder 23.

[0024] Referring to Figure 2, the pressure roller 31, which acts as a pressurizing rotating body, has an elastic layer 33 and a conductive surface layer 34 sequentially laminated on a core metal 32 (shaft portion), and is driven to rotate in a predetermined direction (counterclockwise in Figure 2) by a drive motor 95. The core metal 32 of the pressure roller 31 is a hollow structure made of a metal material (conductive material). The elastic layer 33 of the pressure roller 31 is made of an insulating material such as foamed silicone rubber, silicone rubber, or fluororubber. The conductive surface layer 34 of the pressure roller 31 is a thin surface layer (release layer) formed by dispersing carbon or the like in PFA, PTFE, etc., and is electrically conductive. The pressure roller 31 presses against the fixing belt 21 to form a desired nip (fixing nip) between the two components. Also, referring to Figure 3, a gear 45 that meshes with the drive gear of the drive motor is installed on the pressure roller 31, and the pressure roller 31 is rotated in the direction of the arrow in Figure 2 (counterclockwise). Furthermore, both ends of the pressure roller 31 in the width direction are rotatably supported on the frame 60 of the fixing device 20 via bearings. In this embodiment, the fixing device 20 is also equipped with conductive rollers 66 and conductive members 65, which will be explained in detail later.

[0025] The following briefly describes the normal operation of the fixing device 20 configured as described above. When the power switch of the main unit 100 is turned on, power is supplied to the planar heater 24, and the drive motor 95 starts rotating the pressure roller 31 in the direction of the arrow in Figure 2. As a result, the fixing belt 21 also rotates in the direction of the arrow in Figure 2 due to the frictional force between the fixing nip and the pressure roller 31. Subsequently, the sheet P is fed from the paper feeder 12, and the unfixed image is placed (transferred) onto the sheet P at the position of the transfer roller 9. The sheet P, on which the unfixed image (toner image) is placed, is guided by an entrance guide plate (not shown) and transported in the direction of arrow Y10 in Figure 2, and is fed into the nip section (fixing nip) of the fixing belt 21 and pressure roller 31, which are in a pressed state. Then, the toner image is fixed to the surface of the sheet P by heating from the fixing belt 21 heated by the planar heater 24, and by the pressing force between the planar heater 24 (and holder 23), reinforced by the stay 30, and the pressure roller 31. After that, the sheet P, which has been fed out from the fixing nip, is transported in the direction of arrow Y11 while being guided by an exit guide plate (not shown).

[0026] The configuration and operation of the characteristic fixing device 20 in the image forming apparatus 100 of this embodiment will be described in detail below. As explained earlier using Figures 2 and 5, the fixing belt 21, which serves as a fixing rotating body, is provided with a conductive elastic layer 21b, which is a conductive layer. Furthermore, an insulating surface layer 21c, which has insulating properties, is directly laminated on the conductive elastic layer 21b (conductive layer) of the fixing belt 21. In particular, in this embodiment, one end of the conductive elastic layer 21b in the width direction (the side on which the conductive member 65, described later, is installed, and which is the left side in Figure 5) is formed to protrude one end in the width direction from the insulating surface layer 21c. Furthermore, the pressure roller 31, which acts as a pressurizing rotating body, is provided with a conductive surface layer 34 (which has conductivity) that contacts the insulating surface layer 21c of the fixing belt 21 (fixing rotating body) to form a nip portion (fixing nip).

[0027] In this embodiment, the pressure roller 31 (pressure rotating body) of the fixing device 20 is equipped with a conductive member 65 that is electrically connected to the conductive elastic layer 21b (conductive layer) of the fixing belt 21 (fixing rotating body) and is also grounded. More specifically, as shown in Figure 5, the conductive member 65 is a donut-shaped (annular) member made of a conductive material, and is inserted into the core metal 32 (the part that functions as the shaft at the end) of the pressure roller 31 so as to contact the conductive elastic layer 21b (conductive layer) of the fixing belt 21. In this embodiment, the conductive member 65 is press-fitted into the core metal 32 in order to improve conductivity (electrical connectivity) with the core metal 32.

[0028] In particular, in this embodiment, the outer diameter of the conductive member 65 is approximately equal to or slightly larger than the outer diameter of the main roller portion of the pressure roller 31 (the portion on which the elastic layer 33 and conductive surface layer 34 are formed). The conductive member 65 is in contact with the conductive elastic layer 21b of the fixing belt 21 (the portion that protrudes to one end in the width direction). In this case, even if the outer diameter of the conductive member 65 is the same as the outer diameter of the main roller portion, the insulating surface layer 21 is extremely thin, and the pressure roller 31 presses against the fixing belt 21 in a way that it bites into it, so the conductive member 65 comes into contact with the conductive elastic layer 21b and becomes electrically conductive. Although not shown in Figure 5, the conductive elastic layer 21b comes into contact with the conductive member 6 by being sandwiched between the conductive member 65 and the flange member 42 (see Figures 3 and 4). Furthermore, the conductive member 65 is installed so that its end face is in close contact with the end face of the main roller portion of the pressure roller 31 (the portion on which the elastic layer 33 and conductive surface layer 34 are formed) without any gaps. This makes it possible to reduce the widthwise size without forming any gaps between the conductive member 65 and the main roller portion (elastic layer 33, conductive surface layer 34).

[0029] Furthermore, as shown in Figure 5, in this embodiment, the conductive member 65 is grounded via the core metal 32. More specifically, the core metal 32 is connected to the grounding wire (connected to the grounded frame 60) on which the resistor 68 (electrical resistance component) is installed. As a result, the conductive component 65 is properly grounded. Furthermore, the conductive member 65 is positioned outside the maximum paper-feeding area M of the fixing device 20 (the widthwise range through which the largest possible sheet P can be transported passes) (non-paper-feeding area). As a result, there is no influence from the conductive member 65 coming into contact with the fixed image.

[0030] Here, as shown in Figures 3 and 5, the fixing device 20 in this embodiment is equipped with a conductive roller 66 that contacts and conducts electricity with the conductive surface layer 34 of the pressure roller 31 (pressure rotating body) and the conductive member 65. More specifically, the conductive roller 66 has at least one surface made of a conductive material and is in contact with the conductive member 65 and the conductive surface layer 34 across its width. In other words, the conductive roller 66 is in contact with the outer circumferential surface of the main roller portion (conductive surface layer 34) of the pressure roller 31 and the outer circumferential surface of the conductive member 65. In this configuration, the conductive member 65 and the conductive surface layer 34 are electrically connected via the conductive roller 66. In particular, as explained earlier, the conductive member 65 is in close contact with the end face of the conductive surface layer 34, and although it is electrically connected through this contact, its conductivity is low because it is a thin layer. However, in this embodiment, the conductive roller 66 is in contact with the outer circumferential surfaces of both the conductive surface layer 34 and the conductive member 65, resulting in strong conductivity. Furthermore, the conductive member 65 is firmly electrically connected to the conductive elastic layer 21b (conductive layer) of the fixing belt 21 and is grounded via the core metal 32. Furthermore, the conductive roller 66 rotates along with (is driven to rotate by) the rotation of the pressure roller 31.

[0031] As described above, the fixing device 20 in this embodiment is equipped with a conductive member 65 and a conductive roller 66, which ensures that the conductive elastic layer 21b of the fixing belt 21 and the conductive surface layer 34 of the pressure roller 31 are well electrically connected to the grounded conductive member 65. Therefore, charge is less likely to accumulate on the fixing belt 21 and the pressure roller 31, and the occurrence of abnormal images such as electrostatic offset due to charge accumulation is reduced. In particular, in this embodiment, since the conductive roller 66 is installed so as to straddle the conductive member 65 and the conductive surface layer 34, problems such as a decrease in the static elimination effect or the occurrence of abnormal images due to shedding or wear of brush bristles, as can occur when using an electrostatic elimination brush, do not occur. In other words, charge is less likely to accumulate on the fixing belt 21 and the pressure roller 31 over time, and the occurrence of abnormal images such as electrostatic offset can be stably suppressed.

[0032] "Electrostatic offset" is a phenomenon that occurs during the fixing process when toner carried on the sheet P fed into the nip section (fixing nip) electrostatically transfers to and adheres to the surface of the fixing belt 21 (fixing rotating body), and this adhered toner then reattaches to the sheet P as the fixing belt 21 completes one rotation. This transfer of toner to the fuser belt 21 occurs because the surfaces of the fuser belt 21 and the pressure roller 31 each become electrically charged. In particular, the toner used in this embodiment has a negative polarity, and when the fuser belt 21 becomes positively charged and the pressure roller 31 becomes negatively charged, the toner receives an electrostatic repulsive force from the pressure roller 31 side and an electrostatic adsorption force from the fuser belt 21 side, causing it to adhere to the fuser belt 21. In response to this phenomenon, as described above, the fixing device 20 in this embodiment actively removes static electricity from the conductive elastic layer 21b of the fixing belt 21 and the conductive surface layer 34 of the pressure roller 31, so that the surfaces of the fixing belt 21 and the pressure roller 31 are less likely to become charged. Therefore, electrostatic offset is less likely to occur.

[0033] Referring to Figures 5 and 6, etc., in this embodiment, the conductive roller 66 is configured to be able to move toward and away from the conductive member 65 and the conductive surface layer 34. That is, the conductive roller 66 is configured to be able to move toward and away from the pressure roller 31. For details, please refer to Figure 2. The conductive roller 66 is connected to a contact / separation mechanism 96, which consists of a cam mechanism and the like, controlled by the control unit. During the fixing process (printing), the conductive roller 66 is controlled to be in contact with the conductive member 65 and the conductive surface layer 34, as shown in Figure 5, and to be separated from the conductive member 65 and the conductive surface layer 34, as shown in Figure 6, during the non-fixing process (non-printing).

[0034] For details, as shown in the flowchart in Figure 7, first, when the image forming apparatus 100 is stopped or during warm-up, the conductive roller 66 is in a separated state (the state in Figure 6) as its default state (step S1). Then, when it is determined whether it is time to print (step S2), and it is determined that printing has started, the contact / separation mechanism 96 is controlled to move the conductive roller 66 to a contact state (the state in Figure 5) (step S3). Then, when printing is finished, the contact / separation mechanism 96 is controlled to move the conductive roller 66 back to a separated state (the state in Figure 6) (step S4).

[0035] In this way, by bringing the conductive roller 66 into contact with the pressure roller 31 only during printing when electrostatic offset may occur, the amount of time the conductive roller 66 is unnecessarily in contact with the pressure roller 31 can be reduced. As a result, wear and deterioration of the conductive roller 66 and the pressure roller 31 can be reduced.

[0036] Here, as shown in Figure 5, in this embodiment, the conductive roller 66 is configured to contact the conductive member 65 and the conductive surface layer 34 at a position where it does not protrude outward in the width direction relative to the conductive member 65 (to the left in Figure 5). In other words, the conductive roller 66 (the roller portion that actually contacts the conductive member 65 and the conductive surface layer 34) was positioned within the range N shown in Figure 5. This configuration prevents problems such as the conductive roller 66 coming into contact with the edge of the conductive member 65, causing a gap to form nearby, and the roller surface becoming more susceptible to damage. In this embodiment, the conductive roller 66 (the roller portion that actually contacts the conductive member 65 and the conductive surface layer 34) is formed extending from one end in the width direction (the left side in Figure 5) to the other end in the width direction (the right side in Figure 5). This allows the contact pressure received by the pressure roller 31 to be made uniform across the width direction.

[0037] <Example 1> As shown in the flowchart of Figure 8, in the fixing device 20 of the modified example 1, the conductive roller 66 is controlled to contact the conductive member 65 and the conductive surface layer 34 as shown in Figure 5 when the number of sheets P conveyed per unit time exceeds a predetermined number A, when the number of sheets P conveyed per unit time does not exceed the predetermined number A, and to separate from the conductive member 65 and the conductive surface layer 34 as shown in Figure 6 when the number of sheets P conveyed per unit time does not exceed the predetermined number A. More specifically, as shown in Figure 8, first, when the image forming apparatus 100 is stopped or during warm-up, the conductive roller 66 is in a separated state (the state in Figure 6) as its default state (step S1). Then, it is determined whether continuous printing is occurring with a print count exceeding A sheets per unit time (step S10). If it is determined that continuous printing exceeding A sheets has begun, the contact / separation mechanism 96 is controlled to move the conductive roller 66 to a contact state (the state in Figure 5) (step S3). When printing is finished, the contact / separation mechanism 96 is controlled to move the conductive roller 66 back to a separated state (the state in Figure 6) (step S4). This type of control is implemented because electrostatic offset is likely to occur during continuous printing, especially when the number of printed pages per unit time is high. By bringing the conductive roller 66 into contact with the pressure roller 31 only when electrostatic offset is likely to occur, the amount of time the conductive roller 66 is unnecessarily in contact with the pressure roller 31 can be reduced. As a result, wear and deterioration of the conductive roller 66 and the pressure roller 31 can be reduced. Such control is useful when the device can vary the sheet transport speed (number of sheets printed per unit time) during continuous printing. For example, such a device may have a low-speed mode that allows continuous printing at a sheet transport speed slower than the normal sheet transport speed, so that the fixing temperature of the fixing belt 21 does not decrease easily during continuous printing.

[0038] <Modification 2> As shown in Figure 9, in the fixing device 20 of the modified example 2, the conductive roller 66 (the roller portion that actually contacts the conductive member 65 and the conductive surface layer 34) is shorter in width than the one shown in Figure 5 and is formed only on one end in the width direction (the left side in Figure 9), and is configured to contact the conductive member 65 and the conductive surface layer 34 outside the maximum paper feeding area M (non-paper feeding area). With this configuration, the conductive roller 66 does not come into contact with the maximum paper-feeding area M of the pressure roller 31 (conductive surface layer 34). Therefore, even if wear and deterioration occurs at the contact point between the pressure roller 31 and the conductive roller 66, this wear and deterioration will not affect the fixed image. As shown in Figure 9, in this embodiment as well, the conductive roller 66 is configured to contact the conductive member 65 and the conductive surface layer 34 at a position where it does not protrude outward in the width direction relative to the conductive member 65 (to the left in Figure 9). This configuration prevents problems such as the conductive roller 66 coming into contact with the edge of the conductive member 65, causing a gap to form nearby, and the roller surface becoming more susceptible to damage.

[0039] As described above, the fixing device 20 in this embodiment includes a fixing belt 21 (fixing rotating body) heated by a planar heater 24 (heat source), and a pressure roller 31 (pressure rotating body) that forms a nip portion on which the sheet P is conveyed by pressing it against the fixing belt 21. The fixing belt 21 has a conductive elastic layer 21b (conductive layer) that is conductive, and an insulating surface layer 21c that is laminated directly or indirectly on the conductive elastic layer 21b and is insulating. The pressure roller 31 is provided with a conductive surface layer 34 that is conductive and is electrically connected to the conductive elastic layer 21b of the fixing belt 21, and is grounded. A conductive roller 66 is installed that is electrically connected to the conductive surface layer 34 and the conductive member 65 of the pressure roller 31. This makes it less likely for electric charge to accumulate on the fixing belt 21 and pressure roller 31 over time.

[0040] In this embodiment, the present invention was applied to a fixing device 20 that uses a fixing belt 21 as the fixing rotating body, a pressure roller 31 as the pressure rotating body, and a planar heater 24 as the heat source. However, the fixing device to which the present invention is applied is not limited to this. For example, the present invention can also be applied to fixing devices that use a heater or electromagnetic induction coil as the heat source, fixing devices that use fixing rollers or fixing belts (stretched between multiple roller members) as the fixing rotating body, and fixing devices that use a pressure belt as the pressure rotating body. Furthermore, in this embodiment, a conductive elastic layer 21b was used as the conductive layer formed on the fixing belt 21 (fixing rotating body), but a conductive base layer 21a can also be used as the conductive layer formed on the fixing belt 21 (fixing rotating body). In such cases, it is also possible to use a fixing belt 21 in which an insulating surface layer is directly laminated on the base layer as the conductive layer, without forming an elastic layer on the fixing belt 21. Alternatively, a fixing belt 21 (fixing rotating body) can be used in which a non-conductive elastic layer and an insulating surface layer are sequentially laminated on a conductive base layer (in which the insulating surface layer is indirectly laminated on the base layer as the conductive layer). Furthermore, in this embodiment, a conductive donut-shaped member was used as the conductive member 65, but it is not limited to this as long as it is electrically connected to the conductive layer (conductive elastic layer 21b) of the fixing rotating body (fixing belt 21) and grounded. For example, a conductive gear or the like can be used as the conductive member 65. Furthermore, the same effects as those of this embodiment can be obtained in these cases as well.

[0041] It is clear that the present invention is not limited to this embodiment, and that this embodiment can be modified as appropriate within the scope of the technical concept of the present invention, in addition to what is suggested here. Furthermore, the number, position, shape, etc. of the constituent members are not limited to this embodiment, and can be set to a number, position, shape, etc. that is suitable for carrying out the present invention.

[0042] In this specification, the term "sheet" is defined to include not only paper but also all sheet-like recording media such as coated paper, label paper, OHP sheets, and film sheets that are transported. [Explanation of Symbols]

[0043] 20 Fixing device, 21 Fixing belt (fixing rotating body), 21a base material layer, 21b Conductive elastic layer (conductive layer), 21c insulating surface layer, 24-sided heater (heat source), 31 Pressure roller (pressure rotating body), 32 core metal, 33 Elastic layer, 34 conductive surface layer, 65 conductive member, 66 conductive rollers, 68 Resistors (electrical resistance components), 100 Image forming apparatus (image forming apparatus main unit), P-sheet (recording medium).

[0044] Furthermore, the embodiments of the present invention can also be, for example, combinations of appendices 1 to 8 as follows. (Note 1) A fixing rotating body heated by a heat source, A pressurizing rotating body that forms a nip section on which the sheet is conveyed by pressing it against the aforementioned fixing rotating body, Equipped with, The aforementioned fixing rotating body, A conductive layer having electrical conductivity, An insulating surface layer having insulating properties is directly or indirectly laminated on the conductive layer, It is equipped with, The aforementioned pressurized rotating body is The nip portion is formed by contacting the insulating surface layer of the fixing rotating body, and a conductive surface layer having conductivity, A conductive member that is electrically connected to the conductive layer of the fixing rotating body and is grounded, It is equipped with, A fixing device characterized in that a conductive roller is installed which contacts and conducts electricity with the conductive surface layer of the pressurized rotating body and the conductive member. (Note 2) The conductive member is in contact with the conductive layer and the conductive surface layer. The fixing device according to Appendix 1, characterized in that the conductive roller has at least one surface formed of a conductive material and is in contact with the conductive member and the conductive surface layer. (Note 3) The fixing device according to Appendix 1 or Appendix 2, characterized in that the conductive roller is configured to be able to move toward and away from the conductive member and the conductive surface layer. (Note 4) The fixing apparatus according to Appendix 3, characterized in that the conductive roller contacts the conductive member and the conductive surface layer during the fixing process and separates from the conductive member and the conductive surface layer during the non-fixing process. (Note 5) The fixing device according to Appendix 3, characterized in that when sheets are continuously conveyed to the nip portion and the number of sheets conveyed per unit time exceeds a predetermined number, the conductive roller comes into contact with the conductive member and the conductive surface layer, and when the number of sheets conveyed per unit time does not exceed the predetermined number, the conductive roller comes into contact with the conductive member and the conductive surface layer. (Note 6) The fixing device according to any one of the appendices 1 to 5, characterized in that the conductive roller contacts the conductive member and the conductive surface layer outside the area of ​​the maximum paper feeding region. (Note 7) The fixing device according to any one of the appendices 1 to 6, characterized in that the conductive roller contacts the conductive member and the conductive surface layer at a position where it does not protrude outward in the width direction relative to the conductive member. (Note 8) An image forming apparatus characterized by being equipped with a fixing device described in any of Appendix 1 to Appendix 7. [Prior art documents] [Patent Documents]

[0045] [Patent Document 1] Japanese Patent Publication No. 2009-93017 [Patent Document 2] Japanese Patent Publication No. 2023-102440

Claims

1. A fixing rotating body heated by a heat source, A pressurizing rotating body that forms a nip section on which the sheet is conveyed by pressing it against the aforementioned fixing rotating body, Equipped with, The aforementioned fixing rotating body, A conductive layer having electrical conductivity, An insulating surface layer having insulating properties is directly or indirectly laminated on the conductive layer, It is equipped with, The aforementioned pressurized rotating body is The nip portion is formed by contacting the insulating surface layer of the fixing rotating body, and a conductive surface layer having conductivity, A conductive member that is electrically connected to the conductive layer of the fixing rotating body and is grounded, It is equipped with, A fixing device characterized in that a conductive roller is installed which contacts and conducts electricity with the conductive surface layer of the pressurized rotating body and the conductive member.

2. The conductive member is in contact with the conductive layer and the conductive surface layer. The fixing device according to claim 1, characterized in that the conductive roller has at least one surface formed of a conductive material and contacts the conductive member and the conductive surface layer.

3. The fixing device according to claim 1 or 2, characterized in that the conductive roller is configured to be able to move toward and away from the conductive member and the conductive surface layer.

4. The fixing apparatus according to claim 3, characterized in that the conductive roller is in contact with the conductive member and the conductive surface layer during the fixing process and is separated from the conductive member and the conductive surface layer during the non-fixing process.

5. The fixing device according to claim 3, characterized in that the conductive roller comes into contact with the conductive member and the conductive surface layer when sheets are continuously conveyed to the nip portion and the number of sheets conveyed per unit time exceeds a predetermined number, and moves away from the conductive member and the conductive surface layer when the number of sheets conveyed per unit time does not exceed the predetermined number.

6. The fixing device according to claim 1 or 2, characterized in that the conductive roller contacts the conductive member and the conductive surface layer outside the area of ​​the maximum paper feeding region.

7. The fixing device according to claim 1 or 2, characterized in that the conductive roller contacts the conductive member and the conductive surface layer at a position where it does not protrude outward in the width direction relative to the conductive member.

8. An image forming apparatus characterized by comprising a fixing device according to claim 1 or claim 2.

Images