Fixing device and image forming apparatus

Abstract

To provide a fixing device capable of detecting an abnormal temperature rise of a heater in a timely manner. [Solution] The fixing device 7 comprises a fixing belt that heats the toner on the paper as it rotates around its axis, a pressure roller that pressurizes the toner on the paper as it passes through a pressure area as it rotates around its axis, a heater 22 that contacts the inner surface of the fixing belt and heats the fixing belt, and a heat source temperature detection member 41 that detects the temperature of the heater 22. The heater 22 has a substrate 30 that extends in the axial direction of the fixing belt, and a heat generating section 31 that is formed on one side of the substrate 30 facing the pressure area across the fixing belt at a position shifted to one side from the axial center, and that generates heat when electricity is applied. The heater 22 is divided into a short region B1 on one side of the axial direction and a long region B2 on the other side of the axial direction, with the axial center of the heat generating section 31 as the boundary BL, and the heat source temperature detection member 41 is located in the short region B1 of the heater 22.

Description

[Technical Field]

[0001] The present invention relates to a fixing device that fixes a toner image on a medium and an image forming apparatus. [Background technology]

[0002] A fixing device is known that has a heater that heats paper and edge and center thermistors that detect the heater temperature (Patent Document 1). The heater has a base material and a resistance heating element, and has a large heat distribution area on one side of the resistance heating element's center position (reference position) in the direction perpendicular to the conveyance direction, and a small heat distribution area on the other side. The edge thermistors are located in the small heat distribution area and are said to detect the temperature inside the fixing device to prevent fixing failures. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-132101 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the fixing device described above, the temperature rise in the small heat distribution area lags behind that in the large heat distribution area, so the end thermistors provided in the small heat distribution area are sometimes unable to detect abnormal temperature rises in the heater in a timely manner, which can lead to the risk of failure of the fixing device due to excessive heating.

[0005] In consideration of the above circumstances, the present invention provides a fixing device and an image forming apparatus that can detect an abnormal temperature rise of a heater in a timely manner. [Means for solving the problem]

[0006] The fixing device of the present invention comprises a fixing belt formed in a cylindrical shape and rotating around its axis to heat toner on a medium; a pressure member that forms a pressure area between the fixing belt and the pressure member, and pressurizes the toner on the medium as it passes through the pressure area while rotating around its axis; a heater that contacts the inner surface of the fixing belt facing the pressure area and heats the fixing belt; and a heat source temperature detection member that detects the temperature of the heater.The heater has a substrate that extends in the axial direction of the fixing belt, and a heat generating portion that is formed on one side of the substrate facing the pressure area across the fixing belt at a position shifted to one side from the center of the axial direction and generates heat when electricity is applied, and the heater is divided into a short region on one side of the axial direction and a long region on the other side of the axial direction, with the axial center of the heat generating portion as the boundary, and the heat source temperature detection member is located in the short region of the heater.

[0007] In this case, it is preferable that the heater further includes a power cutoff member that is disposed in the longitudinal region of the heater and cuts off the power supplied to the heater when the heater reaches a predetermined temperature or higher.

[0008] In this case, it is preferable that the fixing device further includes a fixing temperature detection member that is disposed in correspondence with the short side region of the heater and detects the temperature of the fixing belt.

[0009] In this case, it is preferable that the device further includes a medium detection member that is disposed in correspondence with the longitudinal region of the heater and detects the medium entering the pressure region.

[0010] An image forming apparatus according to the present invention includes any one of the fixing devices described above. [Effects of the Invention]

[0011] According to the present invention, an abnormal temperature rise in the heater can be detected in a timely manner. [Brief explanation of the drawings]

[0012] [Figure 1]1 is a schematic diagram (side view) showing the internal structure of an image forming apparatus according to one embodiment of the present invention. [Figure 2] FIG. 1 is a perspective view showing a fixing device according to an embodiment of the present invention. [Figure 3] FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 2. [Figure 4] FIG. 2 is a bottom view showing a heater of a fixing device according to an embodiment of the present invention. [Figure 5] FIG. 2 is a block diagram showing a detection structure and the like of a fixing device according to an embodiment of the present invention. [Figure 6] 3A and 3B are explanatory diagrams showing a heater and a detection structure of a fixing device according to an embodiment of the present invention, and a temperature distribution of the heater. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In the drawings, Fr, Rr, L, R, U, and D indicate front, rear, left, right, top, and bottom. The front-to-back direction, left-to-right direction (axial direction), and top-to-bottom direction are perpendicular to one another. Terms indicating directions and positions are used in this specification, but these terms are used for convenience of explanation and do not limit the technical scope of the present invention. Furthermore, the terms "upstream," "downstream," and similar terms refer to "upstream" and "downstream" in the transport direction of paper P (medium) and similar concepts. In each drawing, the dimensions and angles of components are not accurate and are shown schematically for the purpose of explanation.

[0014] An image forming apparatus 1 according to this embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic diagram (side view) showing the image forming apparatus 1.

[0015] The image forming apparatus 1 is an electrophotographic printer. The image forming apparatus 1 has an apparatus main body 2 that has a substantially rectangular parallelepiped appearance. A paper feed cassette 3 that stores, for example, paper P (medium) is detachably provided at the bottom of the apparatus main body 2. A paper output tray 4 is provided on the top surface of the apparatus main body 2. Note that the paper P, which is an example of a medium, is not limited to being made of paper, and may be a resin sheet or the like.

[0016] The image forming apparatus 1 includes a paper feeder 5, an imaging device 6, and a fixing device 7. The paper feeder 5 is provided at the upstream end of a transport path 9A that extends from the paper feed cassette 3 to the paper output tray 4, and sends out paper P stored in the paper feed cassette 3 one sheet at a time to the transport path 9A. The imaging device 6 is provided in the middle of the transport path 9A, and forms a toner image on the transported paper P. The fixing device 7 is provided downstream of the transport path 9A, and thermally fixes the toner image to the paper P.

[0017] The conveying path 9A is provided with a pair of registration rollers 10A that temporarily block the conveyed paper P to correct (skew correct) the inclination of the paper P. Below the conveying path 9A, a reversing conveying path 9B is provided that branches off on the downstream side of the conveying path 9A and merges with the upstream side of the conveying path 9A. The reversing conveying path 9B is provided with a plurality of pairs of conveying rollers 10B that convey the paper P.

[0018] The image forming device 6 includes a toner container 11, a drum unit 12, and an optical scanning device 13. The toner container 11 is located at the upper front of the device main body 2 and contains, for example, black toner (developer). The drum unit 12 includes a photosensitive drum 14, a charging device 15, a developing device 16, and a transfer roller 17. The photosensitive drum 14 is formed in a substantially cylindrical shape and is driven to rotate about its axis by a motor (not shown). The charging device 15, the developing device 16, and the transfer roller 17 are arranged around the photosensitive drum 14 in the order of the image formation process. The transfer roller 17 contacts the photosensitive drum 14 from below to form a transfer nip. The optical scanning device 13 is located above the photosensitive drum 14 and emits scanning light toward the surface of the photosensitive drum 14.

[0019] The image forming apparatus 1 is provided with a control device 8 that controls the entire apparatus. The control device 8 may be configured with a processor, or may be configured with a logic circuit (hardware) formed in an integrated circuit or the like. When configured with a processor, the processor reads and executes programs stored in memory to perform various processes.

[0020] [Image formation processing] A control device 8 that controls the image forming apparatus 1 performs the following image forming process based on image data input from an external terminal.

[0021] The charging device 15 charges the surface of the photosensitive drum 14, and the optical scanning device 13 emits scanning light based on image data to form an electrostatic latent image on the photosensitive drum 14. The developing device 16 develops a toner image on the photosensitive drum 14 using toner supplied from the toner container 11. The paper feeder 5 feeds paper P one sheet at a time from the paper feed cassette 3 to the transport path 9A. The paper P is transported along the transport path 9A, skew-corrected by a pair of registration rollers 10A, and enters the transfer nip. The transfer roller 17 transfers the toner image on the photosensitive drum 14 to the surface of the paper P as it passes through the transfer nip. The fixing device 7 thermally fixes the toner image to the paper P. In the case of single-sided printing, the paper P that has passed through the fixing device 7 is discharged to the paper output tray 4.

[0022] In the case of double-sided printing, the paper P that has passed through the fixing device 7 switches back at the downstream end of the conveying path 9A and is sent to the reverse conveying path 9B. The paper P is conveyed by the conveying roller pair 10B, returned from the reverse conveying path 9B to the conveying path 9A again, and after skew correction by the registration roller pair 10A, is sent to the transfer nip. Thereafter, the toner image is transferred onto the paper P and thermally fixed, and the double-sided printed paper P is discharged onto the paper output tray 4.

[0023] [Fusing device] Next, the fixing device 7 will be described with reference to Figures 2 to 4. Figure 2 is a perspective view showing the fixing device 7. Figure 3 is a cross-sectional view taken along line III-III in Figure 2. Figure 4 is a bottom view showing the heater 22.

[0024] 2 and 3, the fixing device 7 includes a fixing belt 20, a pressure roller 21, and a heater 22. The fixing belt 20 and the pressure roller 21 are supported by a frame (not shown), and the frame is fixed to the device body 2.

[0025] <Fixing belt> The fixing belt 20 is an endless belt formed in a generally cylindrical shape that is long in the left-right direction (axial direction). The fixing belt 20 is made of a heat-resistant and flexible material (polymer resin, metal, or a combination of polymer resin and metal). A pair of holding members 24 (see FIG. 2) is inserted into both left and right ends of the fixing belt 20. The pair of holding members 24 guide the fixing belt 20 to rotate around its axis while maintaining its generally cylindrical shape. The fixing belt 20 is supported by a frame (not shown) via the pair of holding members 24.

[0026] As shown in FIG. 3, a bridge member 25 and a support member 26 are provided in the space surrounded by the fixing belt 20. The bridge member 25 is formed, for example, from a metal material such as stainless steel into a generally rectangular cylindrical shape that is elongated in the left-right direction (axial direction), and is bridged between the pair of holding members 24. The support member 26 is fixed to the lower part of the bridge member 25. The support member 26 is formed, for example, from a heat-resistant and abrasion-resistant synthetic resin into a generally semi-cylindrical shape that is elongated in the left-right direction. The support member 26 curves along the inner surface of the fixing belt 20 and contacts the lower side of the inner surface of the fixing belt 20 (the side of the pressure region N). A fitting portion 26A into which the heater 22 is fitted is recessed in the lower part of the support member 26.

[0027] <Pressure roller> As shown in FIGS. 2 and 3, pressure roller 21, an example of a pressure member, is formed in a generally cylindrical shape that is long in the left-right direction. Pressure roller 21 has a metal core 21A and an elastic layer 21B, such as a silicone sponge, laminated on the outer circumferential surface of the metal core 21A (see FIG. 3). A drive motor M is connected to the left end of core 21A via a gear train (not shown) (see FIG. 2). Pressure roller 21 contacts fixing belt 20 from below, forming a pressure region N between itself and fixing belt 20. A toner image is fixed onto paper P as it passes through pressure region N. Note that pressure region N refers to the region extending from an upstream position where the pressure is 0 Pa, through a position where pressure is applied, to a downstream position where the pressure returns to 0 Pa.

[0028] <Heater> 3, heater 22 is fitted into fitting portion 26A of support member 26. Heater 22 comes into contact with the inner surface of fixing belt 20 facing pressure region N, and heats fixing belt 20. As shown in FIG. 4, heater 22 has substrate 30 extending in the left-right direction (axial direction) of fixing belt 20, and heat generating portion 31 that generates heat when current is applied.

[0029] (substrate) The substrate 30 is made of an insulator (electrically insulating material) such as ceramic, and is formed in a generally rectangular plate shape that is long in the left-right direction (axial direction). The axial dimension of the substrate 30 (heater 22) is longer than the axial dimension of the fixing belt 20.

[0030] (heat generating part) The heat generating section 31 is provided on the underside (one surface) of the substrate 30 facing the pressure region N across the fixing belt 20. The heat generating section 31 is formed on the underside of the substrate 30 at a position shifted to one side (left in FIG. 4) from the center in the left-right direction (axial direction). The heater 22 is divided into a short region B1 on one side (left side) in the axial direction and a long region B2 on the other side (right side) in the axial direction, with the center of the heat generating section 31 as the boundary BL.

[0031] The heat generating section 31 has four first resistance heating elements 32A and four second resistance heating elements 32B. The first resistance heating elements 32A and the second resistance heating elements 32B are each formed in a substantially rectangular shape from a metal material with high electrical resistance. The four first resistance heating elements 32A and the four second resistance heating elements 32B are aligned in a line in the axial direction with a gap G sandwiched between them. The four first resistance heating elements 32A are disposed in the axial central region of the heat generating section 31, and the four second resistance heating elements 32B are disposed two on each side of the four first resistance heating elements 32A in the axial direction. The four first resistance heating elements 32A and the four second resistance heating elements 32B are arranged in line symmetry in the axial direction (left-right direction) with the boundary BL as the axis of symmetry. In this specification, when the four first resistance heating elements 32A and the four second resistance heating elements 32B are collectively described, they will be simply referred to as "resistance heating elements 32" and will be indicated by Arabic numerals only. Also, the gap G is set to an insulation distance (creepage distance) that can prevent creepage discharge between adjacent resistance heating elements 32.

[0032] In principle, the paper P is transported with the center of its width in the left-right direction roughly aligned with the center (boundary BL) in the left-right direction (axial direction) of the heat generating section 31. For this reason, the fixing belt 20 has a passing area A1 in the center in the axial direction that comes into contact with the paper P, and non-passing areas A2 on both sides in the axial direction that do not come into contact with the paper P (see FIG. 4). The axial dimension of the entire heat generating section 31 is shorter than the overall length of the fixing belt 20 in the left-right direction (axial direction), and is longer in the axial direction than the passing area A1 of the fixing belt 20.

[0033] The conveyed paper P always comes into contact with the vicinity of the axial center of the passing area A1, regardless of the size (left-right dimension) of the paper P. The four first resistance heating elements 32A correspond to the vicinity of the axial center of the passing area A1. Specifically, the four first resistance heating elements 32A correspond to the left-right width of a small-sized paper P (e.g., A5, B5, etc.). In contrast, a normal-sized paper P (e.g., A4 size) comes into contact with both sides of the passing area A1 in the axial direction, but a small-sized paper P does not come into contact with them. The four second resistance heating elements 32B correspond to both sides of the passing area A1 in the axial direction. All resistance heating elements 32 (heating sections 31) correspond to the entire passing area A1, and correspond to the left-right width of a normal-sized paper P.

[0034] A plurality of first wirings 33A, a plurality of second wirings 33B, a first terminal 34A, a second terminal 34B, and a common terminal 34C are formed on the underside of the substrate 30. In this specification, when the plurality of first wirings 33A and the plurality of second wirings 33B are collectively described, they will be simply referred to as "wirings 33" and will be marked with Arabic numerals only. When the first terminal 34A, the second terminal 34B, and the common terminal 34C are collectively described, they will be simply referred to as "terminals 34" and will be marked with Arabic numerals only.

[0035] The wiring 33 and the terminals 34 are formed, for example, from a metal material having a lower electrical resistance than the resistance heating element 32. The multiple first wirings 33A are connected to the upstream ends or downstream ends of axially adjacent first resistance heating elements 32A. The four first resistance heating elements 32A are connected in series by the multiple first wirings 33A. The multiple second wirings 33B are connected to the downstream ends of axially adjacent second resistance heating elements 32B, and are also connected to the upstream ends of two second resistance heating elements 32B that are axially spaced apart and sandwich the four first resistance heating elements 32A between them. The four second resistance heating elements 32B are connected in series by the multiple second wirings 33B.

[0036] The first terminal 34A and the second terminal 34B are arranged at the right end (longitudinal region B2) of the substrate 30, and the common terminal 34C is arranged at the left end (transverse region B1) of the substrate 30. The downstream end of the first resistance heating element 32A located at the right end is connected to the downstream end of the first terminal 34A via the first wiring 33A. The downstream end of the first resistance heating element 32A located at the left end is connected to the downstream end of the common terminal 34C via the first wiring 33A. The upstream end of the second resistance heating element 32B located at the right end is connected to the upstream end of the second terminal 34B via the second wiring 33B. The upstream end of the second resistance heating element 32B located at the left end is connected to the upstream end of the common terminal 34C via the second wiring 33B. The terminals 34 are electrically connected to devices such as a power source 35 (see FIG. 5, described later).

[0037] Heat generating portion 31, wiring 33, and terminals 34 are covered with a coating layer (not shown). Heater 22 is fitted into fitting portion 26A of support member 26, with the coating layer in contact with the inner surface of fixing belt 20. Heater 22 receives fixing belt 20 pressed against pressure roller 21, thereby forming a pressure region N at the contact point between fixing belt 20 and pressure roller 21 (see FIG. 3). Heater 22, drive motor M, etc. are electrically connected to control device 8, power source 35, etc., and are appropriately controlled by control device 8.

[0038] [Fixing process] Here, the operation (fixing process) of the fixing device 7 will be described. The control device 8 controls the drive motor M to rotate the pressure roller 21 around its axis. The fixing belt 20 rotates following the rotation of the pressure roller 21 (see the arrow in FIG. 3). The control device 8 also receives detection signals from a heat source temperature detection member 41 (described later) and controls the heater 22 (or power source 35) to maintain a desired temperature stored in advance in memory. The heater 22 (heat generating unit 31) generates heat when energized, and heats the fixing belt 20 (pressure region N).

[0039] At this time, the control device 8 changes the resistance heating elements 32 to be heated (energized) depending on the size of the paper P. For example, when a normal-sized paper P passes through the pressure region N, the control device 8 executes control to cause all of the resistance heating elements 32 to generate heat. On the other hand, when a small-sized paper P passes through the pressure region N, the control device 8 executes control to cause only the four first resistance heating elements 32A to generate heat. This makes it possible to heat only the necessary portions of the fixing belt 20 (pressure region N) in accordance with the size of the paper P. As a result, it is possible to minimize the amount of power used. It is also possible to prevent excessive (abnormal) temperature rise (overheating) at both ends of the fixing belt 20 in the axial direction.

[0040] When the fixing belt 20 (heater 22) reaches the target temperature, the control device 8 starts the image formation process already described. The paper P onto which the toner image has been transferred enters the pressure area N. The fixing belt 20 heats the toner (toner image) on the paper P as it passes through the pressure area N while rotating around its axis. The pressure roller 21 pressurizes the toner on the paper P as it passes through the pressure area N while rotating around its axis. The toner image is then fixed to the paper P, forming a fixed image on the paper P. The paper P with the fixed image is then discharged to the paper output tray 4.

[0041] Incidentally, in the fixing device 7, it is required to maintain the fixing belt 20 at a target temperature in order to perform a proper fixing process. Furthermore, in the fixing device 7, it is also required to prevent an excessive rise in temperature of the fixing belt 20, the heater 22, etc. when the heater 22, the control device 8, etc. do not operate normally due to a malfunction or the like. Therefore, the fixing device 7 according to this embodiment is provided with a detection structure 40 for preventing an excessive rise in temperature while ensuring a proper fixing process.

[0042] [Detection structure] The detection structure 40 will be described with reference to Figures 3, 5, and 6. Figure 5 is a block diagram showing the detection structure 40, etc. The upper part of Figure 6 is a plan view schematically showing the heater 22 and the detection structure 40, and the lower part of Figure 6 is a graph showing the temperature distribution of the heater 22.

[0043] 3, 5, and the upper part of Fig. 6, the detection structure 40 includes two heat source temperature detection members 41, two power cutoff members 42, two fixing temperature detection members 43, and a medium detection member 44. Note that the upper part of Fig. 6 shows the heat source temperature detection members 41, the power cutoff members 42, the fixing temperature detection members 43, and the medium detection member 44 in a schematic manner, and does not show their exact shapes or positions.

[0044] <Heat source temperature detection component> The heat source temperature detection member 41 is a temperature sensor such as a thermistor, and is provided in contact with the upper surface of the substrate 30 of the heater 22 (see FIG. 3). As shown in the upper part of FIG. 6, two heat source temperature detection members 41 correspond to the first and second resistive heating elements 32A and 32B, respectively, and are arranged in the short-side region B1 of the heater 22. Specifically, one heat source temperature detection member 41 is arranged on the substrate 30 facing the first resistive heating element 32A adjacent to the boundary BL in the short-side region B1. The other heat source temperature detection member 41 is arranged on the substrate 30 facing the second resistive heating element 32B, which is located at one end (left end) in the axial direction. The heat source temperature detection member 41 is electrically connected to the control device 8 via a control circuit or the like (not shown) (see FIG. 5). The heat source temperature detection member 41 detects the temperature of the heater 22 and transmits a detection signal to the control device 8.

[0045] <Power interruption component> The power interrupting member 42 is, for example, a thermo-sensitive element such as a ThermoCut, and is provided in contact with the upper surface of the heater 22 (substrate 30). As shown in the upper part of FIG. 6, two power interrupting members 42 correspond to the first and second resistive heating elements 32A and 32B, respectively, and are arranged in the longitudinal region B2 of the heater 22. Specifically, one power interrupting member 42 is arranged on the substrate 30 facing the first resistive heating element 32A adjacent to the boundary BL in the longitudinal region B2. The other power interrupting member 42 is arranged on the substrate 30 facing the second resistive heating element 32B located at the other end (right end) in the axial direction. The power interrupting member 42 is interposed in a control circuit connecting the heater 22 (heat generating unit 31) and the power source 35 (see FIG. 5), and interrupts the power supplied to the heater 22 when the heater 22 reaches or exceeds a predetermined temperature. The power interrupting member 42 operates independently, without being controlled by the control device 8.

[0046] If the power cut-off member 42 is activated and the power supply is cut off, the entire image forming apparatus 1 will stop operating. After that, a specialized worker will replace the power cut-off member 42 or perform other recovery work on the image forming apparatus 1, and the image forming apparatus 1 will return to a state where it can perform image formation processing again. In other words, once the power cut-off member 42 is activated, it cannot be restored by user operation, and the image forming apparatus 1 will be in a state where it cannot be used for a certain period of time.

[0047] <Fixing temperature detection member> The fixing temperature detection member 43 is, for example, a temperature sensor such as a thermistor, and is provided at the front of the internal space of the fixing belt 20 in contact with the inner surface of the fixing belt 20 (see FIG. 3). As shown in the upper part of FIG. 6, the two fixing temperature detection members 43 are arranged in the short-side region B1 of the heater 22 corresponding to the first resistance heating element 32A and the second resistance heating element 32B. Specifically, one fixing temperature detection member 43 is provided at approximately the same axial position as one heat source temperature detection member 41, and the other fixing temperature detection member 43 is provided at approximately the same axial position as the other heat source temperature detection member 41. The fixing temperature detection members 43 are electrically connected to the control device 8 via a control circuit or the like (see FIG. 5). The fixing temperature detection member 43 detects the temperature of the fixing belt 20 and transmits a detection signal to the control device 8.

[0048] <Media detection member> The medium detection member 44 is, for example, a reflective optical sensor, and is supported on the frame of the fixing device 7 upstream of the pressure region N (see FIG. 3). As shown in the upper part of FIG. 6, the medium detection member 44 is disposed in correspondence with the longitudinal region B2 of the heater 22. More specifically, the medium detection member 44 is provided in a position where it can detect the vicinity of the right edge of small-sized paper P from below. The medium detection member 44 is electrically connected to the control device 8 via a control circuit or the like (see FIG. 5). The medium detection member 44 detects paper P entering the pressure region N and sends a detection signal to the control device 8.

[0049] [Function of the detection structure] An example of the operation (temperature control method) of the above-mentioned detection structure 40 will be described. When the heat generating unit 31 starts to generate heat as the image forming process starts, the heat source temperature detection member 41 and the fixing temperature detection member 43 detect the temperatures of the resistance heating element 32 and the fixing belt 20, respectively, and transmit the detection results to the control device 8.

[0050] <Detection by heat source temperature detection element> The control device 8 determines whether the heater 22 (heat generating unit 31) is operating normally based on the detection result of the heat source temperature detection element 41. For example, the control device 8 determines whether the detection result of the heat source temperature detection element 41 is within a desired temperature range (target temperature) pre-stored in memory, and controls the heater 22 (or power supply 35) to maintain the target temperature. Furthermore, if the detection result of the heat source temperature detection element 41 exceeds the heat source upper limit temperature pre-stored in memory, the control device 8 determines that an abnormality has occurred in the heater 22, and performs control to stop the power supply to the heat generating unit 31.

[0051] <Detection by fixing temperature detection member> The temperature of the fixing belt 20 starts to rise with a delay after the temperature of the heater 22 rises. With the heater 22 maintained at the target temperature, the control device 8 determines whether the fixing belt 20 is within the desired temperature range (fixing temperature) based on the detection result of the fixing temperature detection member 43, and controls the heater 22 (or the power supply 35) to maintain the fixing temperature. Furthermore, if the detection result of the fixing temperature detection member 43 exceeds the upper fixing temperature limit stored in memory in advance, the control device 8 determines that an abnormality has occurred in the heater 22, and performs control to stop the power supply to the heat generating unit 31.

[0052] When the control device 8 executes the stop control of the heater 22, the control device 8 determines whether the detection results of the heat source temperature detection member 41 and the fixing temperature detection member 43 have dropped to a temperature at which the image formation process (fixing process) can be restarted (restartable temperature), and if it determines that the temperature has dropped to a restartable temperature, it allows the image formation process (fixing process) to be restarted. Although use of the image forming apparatus 1 is restricted until the temperature drops to a restartable temperature, the recovery time from the stop control by the control device 8 is extremely short compared to the recovery time from the activation of the power cutoff member 42, so there is little disadvantage to the user.

[0053] While the fixing belt 20 is maintained at the fixing temperature, the control device 8 executes the image forming process and the fixing process as described above. If an abnormality occurs in the heater 22 and the heater 22 reaches a predetermined temperature (for example, 250°C) or higher, the power cut-off member 42 forcibly cuts off the power supply to the heat generating unit 31.

[0054] As shown in the lower part of FIG. 6 , when the heat-generating portion 31 generates heat, the short-side region B1 of the heater 22 is more likely to become hotter than the long-side region B2. Furthermore, the short-side region B1 of the heater 22 is more likely to heat up before the long-side region B2. This is because the volume (heat capacity) of the substrate 30 is greater in the long-side region B2 than in the short-side region B1, so more heat is absorbed in the long-side region B2 than in the short-side region B1. If the power-cutting member 42 were located in the short-side region B1 of the heater 22, the power-cutting member 42 might activate before the heat source temperature detection member 41 or the fixing temperature detection member 43 detects an excessive (abnormal) temperature rise of the heater 22. As explained above, if the power-cutting member 42 were activated, a specialized operator would be required to restore the image forming apparatus 1, which would prolong the downtime and be detrimental to the user. Therefore, in the fixing device 7 according to this embodiment, the power cutoff member 42 is disposed in the longitudinal region B2, so that the heat source temperature detection member 41 and the fixing temperature detection member 43 detect an excessive temperature rise of the heater 22 before the power cutoff member 42 is activated. This enables the control device 8 to control the stopping of the heater 22, and the activation of the power cutoff member 42 is suppressed.

[0055] <Detection by media detection member> 6, in the fixing device 7 according to this embodiment, a heat source temperature detection member 41 and a fixing temperature detection member 43 are provided in the short side region B1 (left side) of the heater 22, making it possible to directly measure the temperatures of the heater 22 and the fixing belt 20. In contrast, in the long side region B2 (right side) of the heater 22, there are no members that directly measure the temperatures of the heater 22 and the fixing belt 20, making it difficult to determine an excessive temperature rise of the heater 22 to the extent that the power cut-off member 42 does not activate in the long side region B2. Therefore, in the fixing device 7 according to this embodiment, a medium detection member 44 arranged in the long side region B2 is used to predict an excessive temperature rise of the heater 22 in the long side region B2. This will be described in detail below.

[0056] The prediction of excessive temperature rise of the heater 22 using the medium detection member 44 is based on the phenomenon that when a sheet of paper P on which a toner image has been formed passes through the pressure region N, the sheet of paper P and the toner absorb heat from the fixing belt 20, lowering the temperatures of the fixing belt 20 and the heater 22. The medium detection member 44 detects the sheet of paper P entering the pressure region N and sends the detection result to the control device 8. The control device 8 determines that the sheet of paper P is being transported normally based on the detection result of the medium detection member 44, and predicts that excessive temperature rise of the fixing belt 20 and the heater 22 is being suppressed by the sheet of paper P passing through the pressure region N, etc.

[0057] In response to this, the control device 8 determines that a transport failure of the paper P has occurred if the medium detection member 44 cannot detect the paper P entering the pressure area N. Note that a "transport failure" of the paper P refers to the paper P getting jammed upstream of the transport path 9A, or the paper P being transported to a position shifted to the left (short side area B1), etc. If a transport failure of the paper P has occurred, it means that the paper P has not passed through the pressure area N in the long side area B2, and therefore the control device 8 predicts that an overheating of the fixing belt 20 and the heater 22 has occurred in the long side area B2 of the heater 22. For example, if the control device 8 detects a transport failure of the paper P multiple times, it performs control to stop the power supply to the heating unit 31.

[0058] In the fixing device 7 according to the present embodiment described above, the heat generating portion 31 of the heater 22 is formed on the underside of the substrate 30 at a position offset to one side (left) from the axial center, and the heat source temperature detection member 41 is disposed in the short region B1 of the heater 22 (see FIG. 6). With this configuration, the temperature rises in the short region B1 before the temperature rises in the long region B2, so that the heat source temperature detection member 41 disposed in the short region B1 can detect an abnormal temperature rise in the heater 22 in a timely manner. This makes it possible to control the stopping of the heater 22, thereby preventing breakdowns in the fixing device 7 due to excessive heating.

[0059] Furthermore, in the fixing device 7 according to this embodiment, the power cutoff member 42 is disposed in the long region B2 of the heater 22 (see FIG. 6). With this configuration, the temperature rises in the long region B2 later than in the short region B1, so it is possible to prevent the power cutoff member 42 from activating before the heat source temperature detection member 41 disposed in the short region B1 detects an excessive temperature rise in the heater 22. This eliminates the need for resetting the fixing device 7, such as replacing the power cutoff member 42, and makes it possible to shorten the time required to resume the fixing process.

[0060] Furthermore, in the fixing device 7 according to this embodiment, the fixing temperature detection member 43 is disposed in correspondence with the short side region B1 of the heater 22 (see FIG. 6). With this configuration, the fixing temperature detection member 43 provided in the short side region B1 can detect an excessive temperature rise of the fixing belt 20 in a timely manner. This enables control to stop the heater 22, thereby preventing damage to the fixing belt 20 due to excessive heating. Furthermore, control to maintain the fixing belt 20 at a desired temperature can be performed based on the detection result of the fixing temperature detection member 43, allowing the toner on the paper P to be properly thermally fixed. This allows for a good fixed image to be obtained.

[0061] Furthermore, in the fixing device 7 according to this embodiment, the medium detection member 44 is disposed in correspondence with the longitudinal region B2 of the heater 22 (see FIG. 6). With this configuration, for example, if the medium detection member 44 does not detect paper P, it is possible to predict that the temperature is rising in the longitudinal region B2. This allows for timely estimation of an excessive temperature rise of the heater 22 in the longitudinal region B2, making it possible to control the heater 22 to stop before the power cut-off member 42 is activated.

[0062] In the fixing device 7 according to this embodiment, the heat generating portion 31 is positioned on the underside of the substrate 30, shifted to the left from the axial center, but this is not limited to this and it may be formed in a position shifted to the right from the axial center (not shown).

[0063] Furthermore, in the fixing device 7 according to the present embodiment, the heat generating section 31 has four first resistance heating elements 32A and four second resistance heating elements 32B, but the present invention is not limited to this. It is sufficient for the heat generating section 31 to have at least one first resistance heating element 32A and at least one second resistance heating element 32B (not shown). Furthermore, in the fixing device 7 according to the present embodiment, the heat generating section 31 has two circuits, one for the first resistance heating element 32A and one for the second resistance heating element 32B, but the present invention is not limited to this. For example, the heat generating section 31 may have one circuit with only the first resistance heating element 32A, or may have three or more circuits by adding other resistance heating elements to the resistance heating element 32 (not shown). Furthermore, the positions and shapes of the wiring 33 and terminals 34 may be freely changed according to the number and positions of the resistance heating elements 32 (not shown).

[0064] In the fixing device 7 according to the present embodiment, two heat source temperature detecting members 41, two power cutoff members 42, and two fixing temperature detecting members 43 are provided, one for each of the first resistance heating element 32A and the second resistance heating element 32B, but the present invention is not limited to this. One or more heat source temperature detecting members 41, one power cutoff member 42, and one fixing temperature detecting member 43 may be provided, each corresponding to the number of circuits formed by the resistance heating element 32 (not shown).

[0065] Furthermore, in the fixing device 7 according to this embodiment, the detection structure 40 includes the heat source temperature detection member 41, the power cut-off member 42, the fixing temperature detection member 43, and the medium detection member 44, but the present invention is not limited to this. For example, as another detection structure, the medium detection member 44 may be omitted, or the fixing temperature detection member 43 and the medium detection member 44 may be omitted, or the power cut-off member 42, the fixing temperature detection member 43, and the medium detection member 44 may be omitted (all of these are not shown). In other words, it is sufficient for the detection structure to include at least the heat source temperature detection member 41 (not shown).

[0066] Furthermore, in the fixing device 7 according to this embodiment, the heat source temperature detection member 41 and the fixing temperature detection member 43 are thermistors, but they are not limited to this and may be other temperature sensors such as thermocouples or resistance temperature detectors. Furthermore, while the fixing temperature detection member 43 is in contact with the inner surface of the fixing belt 20, the present invention is not limited to this. For example, the fixing temperature detection member 43 may be in contact with the outer surface of the fixing belt 20 (not shown). Furthermore, the fixing temperature detection member 43 may be a non-contact temperature measuring device such as an infrared thermometer, and may be provided in a non-contact manner with respect to the inner or outer surface of the fixing belt 20 (not shown). Furthermore, while the medium detection member 44 is a reflective optical sensor, it is not limited to this and may be other sensors such as a transmissive optical sensor or a microswitch.

[0067] Furthermore, in the fixing device 7 according to this embodiment, the pressure roller 21 is driven to rotate and the fixing belt 20 is rotated accordingly, but this is not limited to this, and the fixing belt 20 may be driven to rotate and the pressure roller 21 may be rotated accordingly.

[0068] Furthermore, in the description of the above embodiment, the present invention has been applied to a monochrome image forming device 1 as an example, but this is not limiting and the present invention may also be applied to, for example, a color printer, a copier, a facsimile, or a multifunction device.

[0069] The above-described embodiment shows one aspect of the fixing device and image forming apparatus according to the present invention, and the technical scope of the present invention is not limited to the above-described embodiment. The present invention may be variously changed, substituted, or modified without departing from the spirit of the technical concept, and the claims include all embodiments that may fall within the scope of the technical concept. [Explanation of symbols]

[0070] 1. Image forming device 7 Fixing device 20 Fixing belt 21 Pressure roller (pressure member) 22 Heater 30 boards 31 Heat generating part 41 Heat source temperature detection member 42 Power interruption member 43 Fixing temperature detection member 44 Media detection member B1 short field B2 Longitudinal area BL boundary N pressure area P Paper (media)

Claims

1. a fixing belt formed in a cylindrical shape and rotating around its axis to heat the toner on the medium; a pressure member that forms a pressure region between itself and the fixing belt and that pressurizes the toner on the medium that passes through the pressure region while rotating around its axis; a heater that contacts the inner surface of the fixing belt facing the pressure area and heats the fixing belt; a heat source temperature detection member that detects the temperature of the heater, The heater is a substrate extending in an axial direction of the fixing belt; a heat generating portion that is formed on one surface of the substrate facing the pressure region across the fixing belt, the heat generating portion being shifted to one side from the center in the axial direction, and that generates heat when energized; the heater is divided into a short region on one side of the axial direction and a long region on the other side of the axial direction, with the center of the heat generating portion as a boundary; The fixing device is characterized in that the heat source temperature detection member is disposed in the short side region of the heater.

2. 2. The fixing device according to claim 1, further comprising a power cut-off member disposed in the longitudinal region of the heater, for cutting off power supplied to the heater when the heater reaches a predetermined temperature or higher.

3. 3. The fixing device according to claim 2, further comprising a fixing temperature detecting member disposed in correspondence with the short side region of the heater and detecting the temperature of the fixing belt.

4. 4. The fixing device according to claim 3, further comprising a medium detection member disposed in correspondence with the longitudinal region of the heater and detecting the medium entering the pressure region.

5. 5. An image forming apparatus comprising the fixing device according to claim 1.

Images