JP2009186691A - Fixing device and image forming apparatus provided with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of accurately detecting temperature by stabilizing the contact state of the temperature detecting section of a temperature detecting means with a heating rotation means, and to provide an image forming apparatus provided with the fixing device. <P>SOLUTION: The first energizing wire 37 connecting a thermal protector (temperature detecting section) 35 and an external power supply passes through the shaft center portion of a bearing section 31a being the rocking support point of a movable plate 33. The second energizing wire 41 connecting the thermal protector 35 and the heater of a heating roller passes through the shaft center portion of a bearing section 31b being the rocking support point of the movable plate 33. Even when the attitude of the movable plate 33 is changed, the lengths of the first energizing wire 37 and the second energizing wire 41 from the shaft center portions of the bearing sections 31a and 31b to the thermal protector 35 are not changed, so that in the first energizing wire 37 and the second energizing wire 41, elastic force due to deformation is hardly generated. Therefore, the thermal protector 35 can be stably pressed against the heating roller by the spring force of a spring member 34. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fixing device for fixing a toner image transferred on a sheet (copy paper, plastic film, etc.) to the sheet, and an electrophotographic image forming apparatus (copier, printer, facsimile apparatus, and the like) having the same. Multifunctional devices).

  FIG. 6 shows a conventionally known electrophotographic image forming apparatus 100. As shown in FIG. 6, the electrophotographic image forming apparatus 100 sends a sheet 102 from a paper feeding unit 101 to the image forming unit 103, and the toner image is transferred to the sheet 102 by the image forming unit 103. The sheet 102 on which the toner image is transferred is sent to the fixing device 104, the toner image is fixed to the sheet 102 by the fixing device 104, and the fixed sheet 102 is sent to the paper discharge tray 105 or a duplex printing unit (not shown). Yes.

  In the fixing device 104, the heating rotation unit 106 and the pressure rotation unit 107 are in contact with each other while rotating, and the contact portion forms a nip N that feeds the sheet 102 to the sheet conveyance path 108 on the downstream side in the sheet conveyance direction while sandwiching the sheet 102. It is like that. Then, the toner image is heated and pressurized by the nip N that is a contact portion between the heating rotation unit 106 and the pressure rotation unit 107, so that the toner image is welded to the sheet 102.

  In such a fixing device 104, a heater (not shown) is built in the heating rotation means 106, and the heating rotation means 106 is heated to a temperature suitable for fixing by the heater. Therefore, the fixing device 104 detects the surface temperature of the heating rotation unit 106 with the temperature detection unit 110, and the energization to the heater is controlled so that the heating rotation unit 106 does not overheat.

  The temperature detecting means 110 includes a non-contact type and a contact type. Among these, the non-contact temperature detecting means 110 is likely to cause a response delay because the heat of the surface of the heating rotation means 106 is transmitted through the air, and when quick and accurate temperature detection is required. Not suitable.

  Therefore, conventionally, as shown in FIG. 7 or FIG. 8, the temperature detection unit 111 is brought into direct contact with the surface of the heating roller 106 so that the heat of the surface of the heating rotation means (heating roller) 106 is directly transferred. Many types of temperature detecting means 110 are employed.

Among these, the temperature detection means 110 in FIG. 7 houses a metal temperature detection unit 111 slidably inside a cylindrical support 112, and this temperature detection unit 111 is attached to the surface of the heating roller 106 by a spring 113. It is designed to be pressed. However, as shown in FIG. 9, the temperature detection unit 110 is configured such that the temperature detection unit 111 is inclined in the support 112 due to the sliding resistance when the heating roller 106 rotates, and the corner portion 114 of the heating roller 106 is There is a risk that the surface of the heating roller 106 may be damaged by being pressed against the surface. In this respect, the temperature detection unit 110 shown in FIG. 8 has a temperature detection unit 111 attached to the tip side of a cantilevered plate spring 116 fixed to the frame 115, and the temperature detection unit 111 is heated by the plate spring 116. It is pressed against the surface of the roller 106, and there is no change in the attitude of the temperature detection unit 111 due to the sliding resistance with the heating roller 106, unlike the temperature detection unit 110 shown in FIGS. (See Patent Document 1).
Japanese Patent Laid-Open No. 5-107963

  However, the temperature detecting means 110 as shown in FIG. 8 is required to have heat resistance for the conductive wire 117 connected to the temperature detecting unit 111 because the temperature detecting unit 111 is in sliding contact with the surface of the heating roller 106 close to 200 ° C. In addition, a highly rigid conductive wire (for example, an electric wire having a diameter of 2.5 mm and a conductor such as a tin-plated annealed copper wire coated with silicon rubber as an insulator) 117 is used. As shown in FIGS. 8 and 10, one end side of the energization line 117 is connected to the temperature detection unit 111, and the other end side is held by an energization line restrainer 118 on the frame 115 side. The energization line 117 extends from the temperature detection unit 111 attached to the distal end side of the leaf spring 116 to the frame 115 side. The elastic deformation amount varies depending on the posture of the leaf spring 116, and the posture of the leaf spring 116 is increased. As a result, the elastic force acting on the temperature detector 111 also changes.

  As a result, the conventional fixing device 104 has a problem that the force for urging the temperature detection unit 111 toward the heating roller 106 is likely to vary due to the tension of the conductive wire 117. That is, if the elastic force of the energizing wire 117 acts so as to press the temperature detection unit 111 toward the pressure roller 106, the force pressing the temperature detection unit 111 toward the heating roller 106 becomes too large, and the surface of the heating roller 106 Wear tends to increase in a short time. On the other hand, if the elastic force of the conducting wire 117 acts in a direction that separates the temperature detection unit 111 from the heating roller 106 side, the contact state between the temperature detection unit 111 and the heating roller 106 becomes unstable, and accurate temperature detection may be difficult. There is.

  Therefore, the present invention suppresses variation in the contact pressure between the temperature detection unit of the temperature detection unit and the heating rotation unit due to the elastic force of the conducting wire, and stabilizes the contact state between the temperature detection unit of the temperature detection unit and the heating rotation unit. An object of the present invention is to provide a fixing device that enables accurate temperature detection and an image forming apparatus including the same.

  The invention of claim 1 provides (a). An endless fixing belt is stretched between the fixing roller and the heating roller, the fixing belt is heated by the heating roller, the fixing belt is rotated by the fixing roller, and the heating roller is driven via the fixing belt. Heating and rotating means adapted to rotate; (b). The fixing belt is urged toward the fixing roller, and the fixing belt is sandwiched between the fixing roller and a nip is formed between the fixing belt and the sheet on which the toner image is transferred at the nip. A pressure rotating means that presses and rotates in accordance with the rotation of the fixing belt; (c). And a temperature detecting means for detecting the temperature of the heating roller and shutting off the power supply to the heater built in the heating roller when the temperature of the outer peripheral surface of the heating roller rises to a predetermined temperature. It is. In the present invention, the temperature detecting means includes (1). It is installed in an internal space partitioned by an endless fixing belt stretched between the fixing roller and the heating roller, (2) -1. A frame fixed to a support member in a stationary state with respect to the rotating heating roller, along a direction in which the axis of the heating roller extends; (2) -2. A movable plate disposed on the surface side of the frame facing the heating roller, and supported so that shaft portions at both ends along the direction in which the axis of the heating roller extends can swing on the bearing portion of the frame; (2) -3. A temperature detector attached to the surface of the movable plate facing the heating roller and in contact with the outer peripheral surface of the heating roller; and (2) -4. A spring member that presses the temperature detection unit against the outer peripheral surface of the heating roller via the movable plate, (3). A first energization line connecting the temperature detection unit and an external power source penetrates one of the shaft portions at both ends and one shaft center portion of the bearing portion, and the temperature detection unit and the heating roller The second energization line connecting the heater is configured to pass through the other of the shaft portions at both ends and the other shaft center portion of the bearing portion.

  According to a second aspect of the present invention, there is provided a device for modifying the shapes of the first conductive line and the second conductive line of the fixing device according to the first aspect of the present invention. That is, in the present invention, the first conducting wire has (1) an inner portion on the bearing portion side, an outer portion on the external power source side, and a bent portion connecting the inner portion and the outer portion, (2) A boundary portion between the inner portion and the bent portion, and a boundary portion between the outer portion and the bent portion are shifted with respect to the extending direction of the inner portion. The second energization line includes (1) an inner portion on the bearing portion side, an outer portion on the heater side, and a bent portion connecting the inner portion and the outer portion, and (2) the inner portion The boundary portion between the portion and the bent portion, and the boundary portion between the outer portion and the bent portion are shifted with respect to the extending direction of the inner portion.

  A third aspect of the present invention relates to an image forming apparatus comprising: an image forming unit that forms a toner image on a sheet; and the fixing device according to the first or second aspect of the present invention.

  In the present invention, the first energization line connecting the temperature detection unit and the external power source passes through the shaft center portion of one of the bearing portions which is the swing fulcrum of the movable plate to which the temperature detection unit is attached. Since the second energization line connecting the temperature detection unit and the heater passes through the axial center portion of the other bearing unit, which is the swing fulcrum of the movable plate to which the temperature detection unit is attached, the position of the movable plate The length of the first energization line from the shaft center part of one bearing part to the temperature detection part, and the length of the second conduction line from the axis part of the other bearing part to the temperature detection part No change occurs, and the first conducting wire and the second conducting wire are unlikely to generate elastic force due to deformation. As a result, according to the present invention, the temperature detection unit can be stably pressed against the heating roller by the spring force of the spring member, and accurate temperature detection becomes possible.

  In the present invention, the first energization line and the second energization line are provided with bent portions, and the torsional stress acting on the first energization line and the second energization wire can be reduced by the bent portions. It is possible to suppress changes in the contact pressure between the temperature detection unit and the heating roller due to the twisting of the conduction wire and the second conduction wire, and to stabilize the contact state between the temperature detection unit and the heating roller. Detection is possible.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a structural diagram schematically showing an image forming apparatus 1 according to an embodiment of the present invention.

[Overall structure of image forming apparatus]
The image forming apparatus 1 shown in FIG. 1 is a sheet feeding unit that feeds sheets (sheet-shaped recording media such as copy sheets and plastic films) 2 having a square shape from a sheet feeding cassette 3 to a sheet conveying path 4 one by one. 5, a sheet conveying unit 6 that conveys the sheet 2 fed by the sheet feeding unit 5 along the sheet conveying path 4, and a registration roller that feeds the sheet 2 conveyed by the sheet conveying unit 6 to the image forming position P. 7, an image forming unit 8 that forms (transfers) a toner image on the sheet 2 fed by the registration roller 7, and a fixing that fixes the toner image transferred to the sheet 2 by the image forming unit 8 on the sheet 2. Apparatus 10, double-sided printing unit 11 that reverses the sheet 2 sent out from fixing apparatus 10 and sends the sheet 2 to registration roller 7 again, and fixing apparatus 10 A sheet discharge unit 13 that discharges the fed sheet 2 onto the sheet discharge tray 12, a sheet discharge tray 12 that can stack the sheet 2 fed out from the sheet discharge unit 13, and an upper portion of the apparatus main body 14. And an image reading unit 15 which is attached to the image reading unit and reads an image of a document or the like.

[Fixing device]
Hereinafter, the fixing device 10 according to the present embodiment will be described with reference to FIGS. 1 to 5. FIG. 2 is a structural diagram of the fixing device 10 according to the present embodiment. FIG. 3 is an external perspective view of the temperature detection means 16 used in the fixing device 10. 4 is a side view showing a part of the temperature detecting means 16 used in the fixing device 10 in a simplified manner so that the structure of the temperature detecting means 16 can be easily understood. FIG. 5 is a front view showing a part of the temperature detecting means 16 used in the fixing device 10 in a simplified manner so that it can be easily understood.

  The fixing device 10 shown in FIGS. 1 and 2 is housed in a substantially rectangular parallelepiped housing 18 having a space 17 therein so that a heating rotation means 20 and a pressure rotation means (pressure roller) 21 can rotate. ing. The housing 18 is formed of a heat-resistant resin (for example, liquid crystal polymer), and is formed with a sheet entrance 22 that allows the sheet 2 to enter and a sheet discharge port 23 that allows the sheet 2 to be discharged. ing.

(1. Heating rotation means)
The heating rotation unit 20 includes a heating roller 24, a fixing roller 25, and an endless fixing belt 26 that is stretched over the heating roller 24 and the fixing roller 25.

  Among these, the heating roller 24 has a coating layer of a resin (for example, a fluororesin) excellent in heat resistance on the surface of a metal cylindrical member such as aluminum (Al) or iron (Fe) excellent in thermal conductivity. A film is formed, and a heater (heat source) 27 for heating the fixing belt 26 is accommodated in the internal space of the metal cylindrical member. Both ends of the heating roller 24 are rotatably supported by bearings (not shown) of the housing 18.

  The fixing roller 25 includes a cored bar and a cylindrical elastic body layer (for example, silicon rubber or a sponge member (for example, foamed silicon rubber)) formed on the outer peripheral surface of the cored bar. ing. Both ends of the fixing roller 25 are rotatably supported by bearings (not shown) of the housing 18 and are driven to rotate by a motor (not shown).

  The fixing belt 26 has a 270 μm silicon rubber layer formed on the outer peripheral surface of an endless belt base material (for example, a nickel (Ni) 35 μm thin plate-like base material), and further the outer surface of the silicon rubber layer. In addition, a coating layer or film of a fluororesin of 30 μm is formed so that the molten toner is difficult to adhere.

  In such a heating rotation means 20, when the fixing roller 25 is rotationally driven by a motor (not shown), the heating roller 24 is rotated by a fixing belt 26 that rotates in the clockwise direction together with the fixing roller 25. (See FIG. 2).

(2. Pressure rotation means)
The pressure rotating means (pressure roller) 21 is formed by integrally forming a cylindrical elastic body (for example, silicon rubber) on the outer peripheral side of the core metal, and the melted toner hardly adheres to the outer peripheral surface thereof. It has become. Both ends of the pressure rotating unit 21 are rotatably supported by bearings (not shown) of the housing 18 and are pressed against the fixing roller 25 via a fixing belt 26 by a spring member (not shown). A nip N is formed at a contact portion with the fixing belt 26 constituting the heating rotation means 20, and a driven rotation (counterclockwise direction) is performed as the fixing roller 25 and the fixing belt 26 rotate (clockwise rotation). To rotate).

(3. Temperature detection means)
The temperature of the outer surface of the heating roller 24 is set in the inner space 28 partitioned by the endless fixing belt 26 spanned between the heating roller 24 and the fixing roller 25 and in the space near the heating roller 24. Temperature detecting means 16 for detecting is installed. When the temperature of the outer surface of the heating roller 24 rises to a predetermined temperature, the temperature detection means 16 cuts off the power supply to the heater 27 built in the heating roller 24.

  Hereinafter, details of the temperature detection means 16 will be described with reference to FIGS.

  The temperature detection means 16 shown in these drawings includes a frame 30 and a movable plate 33 supported by bearings 31a and 31b of the frame 30 so that shafts 32a and 32b at both ends in the longitudinal direction can swing. Spring members 34, 34 for urging the movable plate 33 in a direction away from the frame 30 are provided.

  The frame 30 has a pair of bearing portions 31 a and 31 b fixed along the longitudinal direction of the elongated metal plate, and the surface 30 a side to which the bearing portions 31 a and 31 b are fixed faces the outer peripheral surface of the heating roller 24. And it is fixed to the supporting member (not shown) of the housing 18 so that the axial center 24a of the heating roller 24 may extend. Here, since the bearing portions 31a and 31b are located in the vicinity of the high-temperature (180 ° C. to 250 ° C.) heating roller 24, they are made of the same material as the movable plate 33 in consideration of heat resistance and a coefficient of thermal expansion. Is preferred. That is, if the bearing portions 31a and 31b and the shaft portions 32a and 32b of the movable plate 33 are formed of the same material, a difference in thermal expansion hardly occurs, and the bearing portions 31a and 31b and the shaft portion 32a are not affected by temperature changes. , 32b can be kept substantially constant. Note that if the fitting gap between the bearing portions 31a and 31b and the shaft portions 32a and 32b takes into account the difference in thermal expansion, the bearing portions 31a and 31b and the shaft portions 32a and 32b can be separate members. For example, a part of the metal frame 30 may be cut and raised to form the bearing portions 31a and 31b.

  The movable plate 33 is an elongated plate-like body formed of a heat-resistant resin (for example, a liquid crystal polymer), and is arranged on the surface 30a side facing the heating roller 24 of the frame 30, and its longitudinal direction Shaft portions 32a and 32b are formed on one end side in the direction orthogonal to the longitudinal direction (the lower end side in FIG. 5), and the shaft portions 32a and 32b are supported by the bearing portions 31a and 31b of the frame 30. ing. The pair of shaft portions 32a and 32b of the movable plate 33 are arranged at symmetrical positions on both ends in the longitudinal direction of the movable plate 33, and are positioned along the direction in which the axis 24a of the heating roller 24 extends. It is supported by 30 bearing parts 31a and 31b.

  In addition, the movable plate 33 is provided with a thermal protector 35 as a temperature detector at a substantially central portion on the surface 33 a side facing the heating roller 24. The thermal protector 35 used in the present embodiment is arranged in the middle of the energization path connecting the external power source (not shown) and the heater 27 of the heating roller 24, and when the detected temperature rises to 250 ° C, The power supply from the external power source to the heater 27 is cut off. Here, in the thermal protector 35, the first terminal (terminal at the right end in FIG. 5) 36 is connected to an external power source via the first conducting wire 37, and the second terminal (terminal at the left end in FIG. 5) 40 is connected. It is connected to the heater 27 of the heating roller 24 through the second energization line 41. In the present embodiment, the first conducting wire 37 and the second conducting wire 41 are, for example, a wire diameter of 2.5 mm in consideration of heat resistance, and silicon rubber is an insulator for a conductor such as a tin-plated annealed copper wire. It is the electric wire formed by covering as.

  Further, one end side is supported by the frame 30 on both ends in the longitudinal direction of the movable plate 33 and on the other end side in the direction orthogonal to the longitudinal direction (a symmetric position on the upper end side in FIG. 5). Spring accommodating portions 42, 42 for accommodating the other end sides of the spring members (compression coil springs) 34, 34 are formed. The spring accommodating portions 42 and 42 are bottomed cylindrical portions projecting from the surface 33a facing the heating roller 24 of the movable plate 33, and are spaces for accommodating the other end sides of the compression coil springs 34 and 34 therein. 43 and 43 are formed so as to have a height that does not contact the heating roller 24 in a state where the thermal protector 35 is in contact with the outer surface of the heating roller 24 (see FIG. 4).

  As shown in FIGS. 3 and 5, the first conducting wire 37 extending from the first terminal 36 of the thermal protector 35 has a through hole 44 formed in the shaft center portion of the shaft portion 32 a through the shaft portion 32 a and the bearing portion 31 a. Passes along the direction in which the axis 45 extends, and is directly wired along the surface 30a of the frame 30 as it is, bent in the middle, and then further linearly along the surface 30a of the frame 30 Connected to an external power source. Here, in the first conducting wire 37, the linear portion on the bearing portion 31a side with the bent portion 37b as a boundary is referred to as an inner portion 37a, and the portion on the external power supply side with the bent portion 37b as a boundary is referred to as an outer portion 37c. In this case, the inner portion 37a and the outer portion 37c are displaced in parallel via the bent portion 37b. That is, in FIGS. 3 and 5, the inner portion 37 a of the first energization line 37 is disposed at a position close to the lower edge side of the movable plate 33, and the outer portion 37 c of the first energization line 37 is disposed on the upper edge side of the movable plate 33. The inner portion 37a and the outer portion 37c are connected to each other by a bent portion 37b that obliquely crosses the movable plate 33 from the lower edge side toward the upper edge side. As a result, the boundary portion between the outer portion 37c and the bent portion 37b of the first conductive wire 37 is orthogonal to the longitudinal direction of the movable plate 33 with respect to the boundary portion between the inner portion 37a and the bent portion 37b of the first conductive wire 37. It is shifted in the direction (shifted with respect to the extending direction of the inner portion 37a). The first conducting wire 37 is held at a predetermined position on the frame 30 by a first to third conducting wire restrainers 46 to 48 (held with a sufficient gap so that a slight displacement can be made). The bent portion 37 b is located between the second energization wire restraint 47 and the third energization wire restraint 48.

  As shown in FIGS. 3 and 5, the second conducting wire 41 extending from the second terminal 40 of the thermal protector 35 has a through hole 44 formed in the shaft center portion of the shaft portion 32 b as a shaft portion 32 b and a bearing portion. It passes along the direction in which the axial center 45 of 31b extends, and is wired as it is along the surface 30a of the frame 30 in a straight line as it is, bent in the middle, and then substantially straight along the surface 30a of the frame 30. And is connected to the heater 27 of the heating roller 24. Here, in the second conducting wire 41, the linear portion on the bearing portion 31b side with the bent portion 41b as a boundary is referred to as an inner portion 41a, and the portion on the heater 27 side of the heating roller 24 with the bent portion 41b as a boundary. In the case of the outer portion 41c, the inner portion 41a and the outer portion 41c are shifted in parallel via the bent portion 41b. That is, in FIGS. 3 and 5, the inner portion 41 a of the second energization line 41 is disposed at a position close to the lower edge side of the movable plate 33, and the outer portion 41 c of the second energization wire 41 is located on the upper edge side of the movable plate 33. The inner portion 41a and the outer portion 41c are connected by a bent portion 41b that obliquely crosses the movable plate 33 from the lower edge side toward the upper edge side. As a result, the boundary between the outer portion 41c and the bent portion 41b of the second conducting wire 41 is orthogonal to the longitudinal direction of the movable plate 33 with respect to the boundary portion between the inner portion 41a and the bent portion 41b of the second conducting wire 41. It is shifted in the direction (shifted with respect to the extending direction of the inner portion 41a). Note that the second conductive wire 41 is held at a predetermined position on the frame 30 by a fourth conductive wire restraint 50 disposed adjacent to the bearing portion 31b (with a sufficient gap to allow a slight displacement movement). The bent portion 41 b is located between the bearing portion 31 b and the fourth conductive wire restraint 50.

  As described above, in the temperature detection means 16 of the present embodiment, the first conducting wire 37 that connects the thermal protector 35 and the external power source is one bearing portion 31a that is the swing fulcrum of the movable plate 33 to which the thermal protector 35 is attached. The second energization line 41 connecting the thermal protector 35 and the heater 27 is the pivot point of the movable plate 33 to which the thermal protector 35 is attached. Since the axial center portion is penetrated, the posture change of the movable plate 33 is caused by an assembly error of the temperature detection unit 16 or a variation in the distance (position accuracy) between the temperature detection unit 16 and the heating roller 24. Even if it occurs (for example, even if the tilt angle (θ ± α) is different from the designed tilt angle θ), the thermal protector starts from the axial center of one of the bearing portions 31a. The length of the first power supply line 37 to 5, and never change the lengths of the second energization line 41 until the thermal protector 35 results from the axial center portion of the other bearing portion 31b. Therefore, even if the attitude | position of the movable plate 33 changes, the temperature detection means 26 of this embodiment is the elastic force (for example, the 1st conduction line 37 and the 1st conduction line 37 and the 2nd conduction line 41). (Tensile force generated when the two conductive wires 41 are stretched) is less likely to occur. As a result, the temperature detection means 16 of the present embodiment can stably press the thermal protector 35 against the heating roller 24 by the spring force of the spring member (compression coil spring) 34, thereby enabling accurate temperature detection. . In the conventional temperature detection means, when the posture of the leaf spring that presses the temperature detection portion against the heating roller changes, the length of the conductive wire changes, and the spring force of the leaf spring that presses the temperature detection portion against the heating roller is changed. Variation (increase / decrease), the contact state between the temperature detection unit and the heating roller becomes unstable, and accurate temperature detection becomes difficult as compared with the temperature detection means of the present invention.

  Further, the temperature detecting means 16 of the present embodiment is provided with bent portions 37b and 41b in the first conducting wire 37 and the second conducting wire 41 to bend the torsional stress acting on the first conducting wire 37 and the second conducting wire 41. Since the portions 37b and 41b can be reduced, a change in the contact pressure between the thermal protector 35 and the heating roller 24 caused by twisting of the first energizing wire 37 and the second energizing wire 41 can be suppressed. And 35 can stabilize the contact state of the heating roller 24 and enable accurate temperature detection.

(4. Separation means)
As shown in FIGS. 1 and 2, a sheet separating blade 51 as a separating unit is arranged downstream of the nip N between the heating rotating unit 20 and the pressure rotating unit 21 in the sheet conveying direction and in the vicinity of the nip N. ing. The sheet separating blade 51 is fixed to a blade fixing frame 52 having a base end 51 a side projecting into the space 17 inside the housing 18, and a leading end 51 b of the sheet separating blade 51 is positioned in the vicinity of the nip and is attached to the fixing belt 26 and wound up. The sheet 2 is separated from the fixing belt 26.

(5. Sheet detection means)
A sheet detection unit 53 is disposed downstream of the nip N between the heating rotation unit 20 and the pressure rotation unit 21 in the sheet conveyance direction and downstream of the sheet separation blade 51 in the sheet conveyance direction. The control controller (CPU) 54 to which the sheet detecting means 53 is connected, for example, when the sheet 2 is sent to the image forming position P side by the registration roller 7 (when the operation of the motor 55 of the registration roller 7 is started) is a reference time. From the reference time, the sheet detection means 53 is moved to the leading edge of the sheet 2 by a predetermined time (a time determined by the length of the sheet conveyance path 4 from the registration roller 7 to the sheet detection position by the sheet detection means 53, the sheet conveyance speed, etc.). If it is not detected, it is determined that a jam has occurred in the fixing device 10, a control signal for jam processing is output, and the operation of the fixing device 10 is stopped. At this time, energization of the heater 27 of the heating roller 24 is also cut off.

(Function and effect of fixing device)
The fixing device 10 of the present embodiment detects the temperature of the outer surface of the heating roller 24 by a temperature sensor (not shown), and the temperature of the outer surface of the fixing belt 26 becomes a temperature suitable for fixing (about 200 ° C.). The controller 54 controls on / off of energization to the heating roller 24. In such a fixing device 10, for example, when a temperature sensor (not shown) fails or the controller 54 for control fails and the heater 27 of the heating roller 24 is kept energized, the heating roller 24 is fixed. There is a possibility that the temperature becomes higher than a convenient temperature, the heating roller 24 and the fixing belt 26 are damaged by heat, and the function as the fixing device 10 cannot be exhibited. However, in the fixing device 10 of this embodiment, the temperature of the outer surface of the heating roller 24 is a predetermined temperature (250 ° C. in this embodiment) so that the heating roller 24 and the fixing belt 26 are not damaged by heat. When the temperature is raised to the temperature, the temperature detection means 16 functions as an excessive temperature rise prevention device, and the temperature detection means 16 cuts off the energization lines 37 and 41 that connect the external power source and the heater 27 of the heating roller 24. At this time, the fixing device 10 of the present embodiment accurately detects the temperature of the outer surface of the heating roller 24 because the contact state between the thermal protector 35 of the temperature detecting unit 16 and the outer surface of the heating roller 24 is stable. In addition, when the heating roller 24 abnormally rises in temperature, it is difficult to cause a delay in the timing of cutting off the energization of the heating roller 24 to the heater 27, and damage to the heating roller 24 and the fixing belt 26 due to heat can be reliably prevented. Here, in order to set the temperature of the outer surface of the fixing belt 26 to a temperature suitable for fixing (200 ° C.), the temperature of the outer surface of the heating roller 24 is 210 ° C. to 220 ° C. If a temperature detecting means with poor temperature detection accuracy is used, a temperature that serves as a reference for cutting off the power supply to the heater 27 of the heating roller 24 in order to prevent damage due to heat of the heating roller 24 and the fixing belt 26. Therefore, there is a possibility that the power supply to the heater 27 of the heating roller 24 may be interrupted even if the fixing temperature variation is normally allowed. However, the fixing device 10 of this embodiment does not cause such a problem.

  Note that the fixing device of the present embodiment can be used for both an image forming apparatus for monochrome printing and an image forming apparatus for color printing.

  Further, the fixing device according to the present exemplary embodiment is illustrated as being disposed in the sheet conveyance path extending in the horizontal direction, but is not limited thereto, and is disposed in the sheet conveyance path extending in the vertical direction (the direction perpendicular to the horizontal direction). Alternatively, it may be arranged on a sheet conveyance path extending in a direction inclined obliquely with respect to the horizontal direction.

1 is a structural diagram schematically showing an image forming apparatus according to an embodiment of the present invention. 1 is a structural diagram of a fixing device according to an embodiment of the present invention. FIG. 3 is an external perspective view of temperature detection means used in the fixing device of FIG. 2. FIG. 3 is a side view showing a part of a temperature detection unit used in the fixing device in a simplified manner so that the structure of the temperature detection unit can be easily understood. FIG. 3 is a front view showing a part of temperature detection means used in the fixing device in a simplified manner so that it can be easily understood. It is a structural diagram of a conventional image forming apparatus. FIG. 10 is a structural diagram showing, in a simplified manner, first temperature detection means used in a conventional fixing device. FIG. 10 is a structural diagram showing a simplified second temperature detecting means used in a conventional fixing device. It is a figure which shows the malfunction occurrence state of the 1st temperature detection means shown in FIG. It is a front view of the 2nd temperature detection means seen from the A direction of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Sheet, 8 ... Image forming part, 10 ... Fixing device, 16 ... Temperature detection means, 20 ... Heating rotation means, 21 ... Pressure roller (Pressure rotation means) ), 24... Heating roller, 25... Fixing roller, 26... Fixing belt, 27... Heater, 28 .. Internal space, 30 ... Frame, 30a ... Surface, 31a, 31b ... Bearing part, 32a 32b... Shaft portion 33... Movable plate 33a... Surface 34... Compression coil spring (spring member) 35... Thermal protector (temperature detection portion) 37. 41a: inner part, 37b, 41b ... bent part, 37c, 41c ... outer part, 41 ... second conducting wire, N ... nip

Claims (3)

An endless fixing belt is stretched between the fixing roller and the heating roller, the fixing belt is heated by the heating roller, the fixing belt is rotated by the fixing roller, and the heating roller is driven via the fixing belt. Heating and rotating means adapted to rotate;
The fixing belt is urged toward the fixing roller, and the fixing belt is sandwiched between the fixing roller and a nip is formed between the fixing belt and the sheet on which the toner image is transferred at the nip. Pressure rotating means that presses and rotates following the rotation of the fixing belt;
Detecting the temperature of the heating roller, and when the temperature of the outer peripheral surface of the heating roller rises to a predetermined temperature, temperature detection means for cutting off the power supply to the heater built in the heating roller;
In the fixing device provided with
The temperature detecting means includes
(1). Installed in an internal space partitioned by an endless fixing belt spanned between the fixing roller and the heating roller;
(2) -1. A frame fixed to a support member in a stationary state with respect to the rotating heating roller, along a direction in which the axis of the heating roller extends;
(2) -2. A movable plate disposed on the surface side of the frame facing the heating roller, and supported so that shaft portions at both ends along the direction in which the axis of the heating roller extends can swing on the bearing portion of the frame;
(2) -3. A temperature detector attached to the surface of the movable plate facing the heating roller, and in contact with the outer peripheral surface of the heating roller;
(2) -4. A spring member that presses the temperature detection unit against the outer peripheral surface of the heating roller via the movable plate,
(3). A first energization line connecting the temperature detection unit and an external power source penetrates one of the shaft portions at both ends and one shaft center portion of the bearing portion, and the temperature detection unit and the heating roller A second energization line connecting the heater penetrates the other shaft portion at both ends and the other shaft center portion of the bearing portion;
A fixing device. The first conducting wire is
(1) It has an inner part on the bearing part side, an outer part on the external power source side, and a bent part connecting these inner part and outer part,
(2) The boundary part between the inner part and the bent part, and the boundary part between the outer part and the bent part are shifted with respect to the extending direction of the inner part,
The second conducting wire is
(1) It has an inner part on the bearing part side, an outer part on the heater side, and a bent part connecting these inner part and outer part,
(2) The boundary portion between the inner portion and the bent portion, and the boundary portion between the outer portion and the bent portion are shifted with respect to the extending direction of the inner portion.
The fixing device according to claim 1.   An image forming apparatus comprising: an image forming unit that forms a toner image on a sheet; and the fixing device according to claim 1.

Images