JP2018025743A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine a predetermined state, such as abnormality in heating means.SOLUTION: A fixing device 27 heats a recording material on which a toner is formed to fix the toner image to the recording material, and comprises: a heater 3 that performs heating with a heat element 32 generating heat upon supply of power; a first determination part 701a that determines a change in state of the resistance value of the heat element 32 when power is supplied to the heat element 32; and a second determination part 701b that determines that the heat element 32 is in a predetermined state on the basis of a result of determination performed by the first determination part 701a.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a fixing device for fixing a toner image on a recording material by heat and pressure, and an image forming apparatus such as a copying machine, a laser beam printer, or a facsimile machine including the fixing device.

  2. Description of the Related Art Conventionally, there is known a fixing device that fixes a toner image on a recording material by heating a recording material on which a toner image is formed with a heating member and pressing the recording material with a pressure member. In recent years, in order to increase the energy utilization efficiency, a fixing device that reduces the heat capacity of the heating member and reduces the energy (electric power) that raises the heating member to a temperature at which the fixing operation can be performed has been put into practical use.

  In such a fixing device, when a recording material having a width smaller than the recording material of the maximum width (hereinafter referred to as “small size recording material”) is passed, the temperature is higher than the temperature of the paper passing portion through which the recording material passes. The temperature of the non-sheet passing portion where the recording material is not passed tends to rise. The reason for this is that when a small-size recording material is passed through, the heat-passing part of the heating element is deprived of heat by the passage of paper, whereas the non-sheet passing part of the heating element is not deprived of heat by the passing of paper. Because. When such a phenomenon occurs, there is a possibility of causing image defects such as damage to parts such as a pressure roller and high temperature offset.

  Conventionally, in order to suppress the temperature rise in the non-sheet passing portion, the interval between passing the small-size recording material is longer than the interval between passing the recording material with the maximum width. A fixing device is known. However, in such a fixing device, there is a problem that when passing a small-size recording material, productivity is lowered because the paper passing interval is longer than when passing a recording material having the maximum width. .

  On the other hand, Patent Document 1 discloses a fixing device that suppresses an excessive temperature rise in a non-sheet passing portion by using a heater including a heating element having a large PTC characteristic. Here, the PTC characteristic refers to a characteristic that makes it difficult for a current to flow as the resistance value increases as the temperature increases. In the fixing device disclosed in Patent Document 1, the electric resistance of the non-sheet-passing portion increases as the temperature of the non-sheet-passing portion of the heating element increases, thereby making it difficult for current to flow through the non-sheet-passing portion. The temperature rise in the non-sheet passing portion can be suppressed.

  However, in Patent Document 1, even when the heater is broken due to thermal stress or mechanical stress at the time of abnormal temperature rise, the electrode portion and the heating resistor are connected and energized. When the path is secured, the heating resistor generates heat.

  Patent Document 2 discloses a fixing device that detects a resistance value of a heating resistor and determines that the heating resistor is abnormal when the detected resistance value is larger than a predetermined resistance value. In the fixing device disclosed in Japanese Patent Application Laid-Open No. 2004-260, heat is generated when an abnormality occurs in the heating resistor by detecting the abnormality of the heating resistor from the resistance value of the heating resistor and cutting off the power supply to the heating resistor. It is possible to prevent the resistor from generating heat.

JP 2009-103881 A Japanese Patent Laying-Open No. 2015-227917

  However, even when a small-size recording material is passed, the resistance value of the heating resistor increases as the temperature of the non-sheet passing portion increases. Therefore, Patent Document 2 has a problem that it is difficult to determine whether the cause of the increase in the resistance value of the heating resistor is the passage of a small-size recording material or the abnormality of the heater.

  An object of the present invention is to provide a fixing device and an image forming apparatus capable of determining a predetermined state such as abnormality of a heating unit.

  The fixing device according to the present invention is a fixing device that heats a recording material on which a toner image is formed and fixes the toner image on the recording material, and the recording is performed by a heating resistor that generates heat when supplied with electric power. Based on the determination result of the heating means for heating the material, the first determination means for determining the change state of the resistance value of the heating resistor when power is supplied to the heating resistor, and the first determination means And a second determination means for determining that the heating resistor is in a predetermined state.

  The fixing device according to the present invention is a fixing device that heats a recording material on which a toner image is formed and fixes the toner image on the recording material. The fixing device generates heat when supplied with electric power and exhibits PTC characteristics. The heating resistor, a substrate on which the heating resistor is formed along the longitudinal direction, and energization means for energizing the heating resistor in a short direction perpendicular to the longitudinal direction. Heating means for heating the recording material by the heating resistor energized by the means, temperature detection means for detecting the temperature of the heating resistor, and temperature detection means when power is supplied to the heating resistor. First determination means for determining a detected temperature change state; second determination means for determining that the heating resistor is in a predetermined state based on a determination result of the first determination means; Having And features.

  The fixing device according to the present invention is a fixing device that heats a recording material on which a toner image is formed to fix the toner image on the recording material, and includes a heating resistor that generates heat when supplied with power. Heating means for heating the recording material, and first determination means for determining a change state of the resistance value of the heating resistor and a change state of the temperature of the heating resistor when power is supplied to the heating resistor. And second determination means for determining that the heating resistor is in a predetermined state based on the determination result of the first determination means.

  The image forming apparatus according to the present invention includes an image forming unit that forms a toner image, a transfer unit that transfers the toner image to the recording material, and the toner image transferred to the recording material by the transfer unit. And a fixing device for fixing to a material.

  According to the present invention, it is possible to determine a predetermined state such as abnormality of the heating means.

1 is a cross-sectional view of an image forming apparatus according to Embodiment 1 of the present invention. 1 is a block diagram illustrating a configuration of an image forming apparatus according to Embodiment 1 of the present invention. 1 is a side view of a fixing device according to Embodiment 1 of the present invention. It is a top view of the heater which concerns on Embodiment 1 of this invention. 1 is a schematic diagram of a fixing device according to Embodiment 1 of the present invention. It is a flowchart which shows the state determination process which concerns on Embodiment 1 of this invention. FIG. 6 is a diagram showing a change in resistance value with time when a heater is not damaged when a large-size recording material according to Embodiment 1 of the present invention is passed. FIG. 6 is a diagram showing a change in resistance value with respect to time when a heater breaks when a large-size recording material according to Embodiment 1 of the present invention is passed. It is a top view of the heater which concerns on Embodiment 2 of this invention. FIG. 6 is a schematic diagram of a fixing device according to Embodiment 2 of the present invention. It is a figure which shows the change of the resistance value with respect to time passage when a heater breaks in the center when a large-sized recording material according to Embodiment 2 of the present invention is passed. It is a figure which shows the change of the resistance value with respect to time passage when a heater breaks in an edge part, when passing the large-sized recording material which concerns on Embodiment 2 of this invention. FIG. 10 is a diagram illustrating a change in resistance value with respect to time when a heater is not damaged when a small-size recording material according to Embodiment 2 of the present invention is passed. It is a figure which shows the change of the resistance value with respect to time passage when a heater breaks in the case of passing a small-sized recording material according to Embodiment 2 of the present invention. It is a block diagram which shows the structure of the image forming apparatus which concerns on Embodiment 3 of this invention. FIG. 6 is a schematic diagram of a fixing device according to Embodiment 3 of the present invention. It is a flowchart which shows the state determination process which concerns on Embodiment 3 of this invention. FIG. 10 is a diagram illustrating a change in resistance value with respect to time when a heater breaks when a small-size recording material according to Embodiment 3 of the present invention is passed. FIG. 10 is a diagram illustrating changes in temperature and power with time when a heater is not damaged when a small-size recording material according to Embodiment 3 of the present invention is passed. FIG. 10 is a diagram illustrating changes in temperature and power with time when a heater breaks when a small-size recording material according to Embodiment 3 of the present invention is passed. It is a block diagram which shows the structure of the image forming apparatus which concerns on Embodiment 4 of this invention. It is a flowchart which shows the state determination process which concerns on Embodiment 4 of this invention. It is a figure which shows the change of the temperature with respect to time passage, when a small-sized recording material which concerns on Embodiment 4 of this invention is passed, and a heater is not damaged. It is a figure which shows the change of the temperature with respect to time passage when a heater breaks in the case of passing a small-sized recording material according to Embodiment 4 of the present invention. It is a block diagram which shows the structure of the image forming apparatus which concerns on Embodiment 5 of this invention. It is a flowchart which shows the state determination process which concerns on Embodiment 5 of this invention. It is a figure which shows the change of the temperature and resistance value with respect to time passage when a heater does not break in the case of passing a small-sized recording material according to Embodiment 5 of the present invention. It is a figure which shows the change of the temperature and resistance value with respect to passage of time when a heater breaks in the case of passing a small-sized recording material according to Embodiment 5 of the present invention.

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

(Embodiment 1)
<Configuration of image forming apparatus>
The configuration of the image forming apparatus A according to the first embodiment of the present invention will be described in detail with reference to FIGS.

  The image forming apparatus A includes a charging high-voltage power supply 18, a charging roller 19, an image carrier 20, an exposure unit 21, a developing unit 22, a developing sleeve 23, a pre-transfer guide unit 24, and a transfer roller 25. A fixing nip inlet guide 26 and a fixing device 27. Further, the image forming apparatus A includes a cleaning blade 28, a waste toner storage unit 29, and a paper width sensor 30.

  Further, the image forming apparatus A includes an operation unit 100, an image processing unit 200, a pressure roller driving unit 300, a current / voltage supply unit 400, a current / voltage detector 500, an optical unit 600, and a control unit 700. And have. The fixing device 27 includes a thermistor 38, a pressure roller driving unit 300, a current / voltage supply unit 400, a current / voltage detector 500, and a control unit 700.

  The charging high-voltage power source 18, the charging roller 19, the image carrier 20, the exposure unit 21, the developing unit 22, and the developing sleeve 23 constitute an image forming unit.

  The charging high-voltage power supply 18 applies a bias voltage to the charging roller 19.

  The charging roller 19 charges the surface of the image carrier 20 by applying a bias voltage from the charging high-voltage power supply 18.

  The surface of the image carrier 20 is uniformly charged by the charging roller 19 by rotating in contact with the charging roller 19.

  The exposure unit 21 exposes the image carrier 20 to lower the image carrier 20 to a predetermined potential.

  The developing unit 22 contains toner.

  The developing sleeve 23 carries toner stored in the developing unit 22. The developing sleeve 23 uses the potential difference between the potential on the image carrier 20 lowered by the exposure unit 21 and the potential applied to the developing sleeve 23 to cause the carried toner to fly, thereby causing the developing sleeve 23 to move. A toner image is formed on the image carrier 20 by being attached to the surface.

  The pre-transfer guide unit 24 conveys a recording material such as a fed sheet toward a transfer area formed by the image carrier 20 and the transfer roller 25.

  The transfer roller 25 serving as a transfer unit transfers the toner image formed on the image carrier 20 onto the recording material conveyed by the pre-transfer guide unit 24. The transfer roller 25 conveys the recording material onto which the toner image has been transferred toward the fixing nip entrance guide 26.

  The fixing nip inlet guide 26 conveys the recording material conveyed by the transfer roller 25 toward the fixing device 27.

  The fixing device 27 fixes the toner image on the recording material by heating and pressurizing the recording material onto which the toner image conveyed from the fixing nip entrance guide 26 is transferred. The fixing device 27 conveys the recording material on which the toner image is fixed toward a discharge unit (not shown). The thermistor 38, the pressure roller driving unit 300, the current / voltage supply unit 400, the current / voltage detector 500, and the control unit 700 included in the fixing device 27 will be described later.

  The cleaning blade 28 scrapes off the toner that cannot be transferred and adheres to the image carrier 20 into the waste toner container 29.

  The waste toner storage unit 29 stores and collects toner scraped from the image carrier 20 by the cleaning blade 28.

  The paper width sensor 30 is provided at a paper feed port (not shown) and detects the width of the paper to be fed.

  The operation unit 100 outputs an electrical signal corresponding to an external operation to the control unit 700.

  Under the control of the control unit 700, the image processing unit 200 operates the exposure unit 21 and the developing sleeve 23 on the basis of image data output from a scanner unit (not shown) to form a toner image on a recording material.

  The optical unit 600 reads an image of a document by optical means, and outputs image data of the read image to the CPU 701.

  The I / F unit 702 is a device for connecting the CPU 701 and a network such as a LAN, and transmits and receives signals between the CPU 701 and an external device via the network. In particular, the I / F unit 702 receives a signal instructing execution of image formation transmitted from an external device and outputs the signal to the CPU 701. Here, the I / F unit 702 exemplifies a LAN card or a LAN board.

<Configuration of fixing device>
The configuration of the fixing device 27 according to the first embodiment of the present invention will be described in detail with reference to FIGS.

  The fixing device 27 includes a film unit 1, a pressure roller 2, an AC power supply 39, a pressure roller driving unit 300, a current / voltage supply unit 400, a current / voltage detector 500, and a control unit 700. Have.

  The film unit 1 heats the toner 9 on the recording material 8. The outer diameter of the film unit 1 illustrates 30 mm. Specifically, the film unit 1 includes a heater 3, a fixing film 4, a film guide 5, a T stay 6, and a thermistor 38.

  The heater 3 serving as a heating means is a ceramic heater and is included in the fixing film 4. The heater 3 generates heat in accordance with an AC voltage energization pattern controlled by the current / voltage supply unit 400. Here, the energization pattern is 9 half waves as one block pattern, and the electrode is switched every 10 msec of 1 half wave at 50 Hz.

  Specifically, the heater 3 includes a thermal fuse 31, a heating resistor 32, a substrate 33, an electrode 34, an electrode 35, a power feeding unit 36, and a power feeding unit 37. The heater 3 has a configuration of a longitudinal energization type that energizes in the longitudinal direction of the substrate 33.

  The thermal fuse 31 is inserted between the power supply unit 37 and the switch 42, and when the overcurrent flows, the connection between the power supply unit 37 and the switch 42 is disconnected and supplied from the AC power supply 39 to the heating resistor 32. Block AC current.

  Two heating resistors 32 are provided in parallel to each other along the longitudinal direction of the substrate 33 on the substrate 33. The heat generating resistor 32 is formed by applying a conductive paste (heat generating paste) containing a silver / palladium alloy uniformly on the substrate 33 in a film form by a screen printing method, or by baking, or by applying a nichrome wire or the like to the substrate. 33 is provided by bonding or the like. The heating resistor 32 is covered with an insulating coating layer (not shown) formed of an insulating material such as glass or resin. The heating resistor 32 has PTC characteristics.

  The thickness of the heating resistor 32 is exemplified here as 20 μm. The resistance value of the heating resistor 32 is exemplified here as 14Ω. When the resistance value of the heating resistor 32 is 14Ω, the power consumption of the heater 3 when a voltage of 120 V is applied to the heater 3 is 1029 W. The width of the heating resistor 32 is exemplified here as 1.5 mm. The distance between the two heating resistors 32 is exemplified here as 0.7 mm. The heating resistor 32 does not need to be directly formed on the substrate 33, and may be formed on the substrate 33 through a glaze layer that prevents diffusion of heat to the substrate 33, for example.

  The substrate 33 is formed of an insulating ceramic such as alumina or aluminum nitride, or is formed by providing an insulating layer such as a glass coat on a metal plate such as SUS. The thickness of the substrate 33 is exemplified here as 1.0 mm. When the substrate 33 is formed by the former, the thermal conductivity is higher than that when the substrate 33 is formed by the latter, so that the surface opposite to the surface provided with the heating resistor is brought into contact with the inner surface of the fixing film 4. It is configured as a backside heating type.

  The electrode 34 and the electrode 35 function as a contact for supplying power to the heating resistor 32. The electrode 34 and the electrode 35 are provided by performing baking after a silver paste is uniformly applied in a film shape on the substrate 33 by a screen printing method. The electrodes 34 and 35 are covered with an insulating coating layer (not shown) formed of an insulator such as glass or resin. The thickness of the electrode 34 and the electrode 35 is exemplified here as 20 μm.

  The electrode 34 connects one of the two heat generating resistors 32 and the power supply unit 36, and applies an AC voltage applied from the power supply unit 36 to the heat generating resistor 32.

  The electrode 35 connects the other of the two heating resistors 32 and the power supply unit 37, and applies an AC voltage applied from the power supply unit 37 to the heating resistor 32.

  The power feeding unit 36 applies the AC voltage applied from the AC power supply 39 to the electrode 34.

  The power feeding unit 37 applies the AC voltage applied from the AC power source 39 to the electrode 35.

  The fixing film 4 has a cylindrical shape and is formed of polyimide, and efficiently transfers heat from the heater 3 to the toner 9 on the recording material 8. The thickness of the fixing film 4 is about 70 μm.

  The film guide 5 includes a plurality of ribs (not shown) along the longitudinal direction, and the ribs assist the movement of the fixing film 4 while suppressing resistance to the fixing film 4.

  The T stay 6 is formed of a steel plate and applies a uniform pressure to the recording material 8.

  The thermistor 38 is provided on the back side of the ceramic substrate, detects the temperature, and outputs the detection result to the control unit 700.

  The thermistor 38 is provided on the surface opposite to the surface on which the heat generating resistor 32 of the substrate 33 is provided (the surface opposite to the surface on which the fixing nip 11 is formed). Although the illustration of the thermistor 38 is omitted, for example, a heat insulating layer is provided on the support, and the element of the chip thermistor is fixed on the heat insulating layer, and the element of the thermistor is added to the substrate 33 by the support. It is configured by pressurizing with pressure and making contact. The thermistor 38 detects the temperature of the substrate 33 and outputs an electrical signal corresponding to the detected temperature to the control unit 700. The thermistor 38 may be provided on the surface where the heating resistor 32 is provided.

The pressure roller 2 is formed by covering the cored bar 10 with conductive silicon rubber and further covering with an insulating tube. The outer diameter of the cored bar 10 is exemplified here as 20 mm. Here, the material of the cored bar 10 is exemplified by aluminum. Here, the volume resistivity of the conductive silicone rubber is exemplified as 1 × 10 ⁵ Ω · cm. The thickness of the insulating tube is exemplified here as 60 μm. The outer diameter of the pressure roller 2 is exemplified as 48 mm.

  The pressure roller 2 is pressed against the heater 3 with a predetermined pressure (nip pressure) with a fixing film 4 sandwiched by a spring (not shown) to form a fixing nip 11 with the film unit 1. Here, the length of the fixing nip 11 in the conveyance direction of the recording material 8 is exemplified as 5 to 8 mm.

  The pressure roller 2 is rotationally driven by the pressure roller driving unit 300 to rotate the fixing film 4 and conveys the recording material 8 conveyed to the fixing nip 11 in close contact with the fixing film 4. The unfixed toner image formed and supported on the recording material 8 conveyed to the fixing nip 11 is fixed by the heat of the heater 3 and the fixing nip pressure.

  The AC power supply 39 applies an AC voltage to the power supply unit 36 and the power supply unit 37.

  The pressure roller driving unit 300 drives the pressure roller 2 according to the control of the control unit 700.

  The current / voltage supply unit 400 supplies power to the heating resistor 32 of the heater 3 under the control of the control unit 700 to heat the heating resistor 32. Specifically, the current / voltage supply unit 400 includes a triac 41 and a switch 42.

  The triac 41 is composed of a semiconductor switching element having three terminals. The triac 41 is turned on by the control of the control unit 700 and starts energization from the AC power supply 39 to the heating resistor 32, or is turned off by the control of the control unit 700 and turned on. To the heating resistor 32 is stopped.

  The switch 42 switches between a state in which power is supplied from the AC power supply 39 to the power supply unit 36 and the power supply unit 37 and a state in which power supply from the AC power supply 39 to the power supply unit 36 and the power supply unit 37 is stopped under the control of the control unit 700. .

  The current / voltage detector 500 detects the current / voltage supplied to the heater 3 and outputs the detection result to the control unit 700.

  The control unit 700 operates by receiving power from a power source (not shown), and includes a CPU 701, an I / F unit 702, a RAM 703, and a ROM 704.

  The CPU 701 controls the operations of the image processing unit 200, the pressure roller driving unit 300, the current / voltage supply unit 400, and the optical unit 600 based on the electrical signal input from the operation unit 100 or the detection result of the current / voltage detector 500. To do.

  Specifically, the CPU 701 controls the driving of the pressure roller driving unit 300 by executing a pressure roller rotation control program 704 a read from the ROM 704. The CPU 701 controls the temperature of the fixing device 27 by executing a temperature control program 704 b read from the ROM 704 based on the detection result of the thermistor 38. The CPU 701 controls the power supplied from the current / voltage supply unit 400 to the fixing device 27 by executing the supply power control program 704 c read from the ROM 704.

  The CPU 701 controls the operation of the image processing unit 200 based on the image data input from the optical unit 600.

  A first determination unit 701 a that is a first determination unit of the CPU 701 executes a resistance change rate calculation program 704 d read from the ROM 704. The first determination unit 701a executes the resistance change rate calculation program 704d, converts the current voltage value indicated by the detection result input from the current voltage detector 500 into a resistance value, and sequentially records the resistance value in the RAM 703. The first determination unit 701 a of the CPU 701 determines the change state of the resistance value of the heating resistor 32 of the heater 3 using the resistance value recorded in the RAM 703. The change state of the resistance value is typically a resistance change rate for a predetermined time. The predetermined time is exemplified here as 10 msec.

  The second determination unit 701b, which is the second determination unit of the CPU 701, generates the heating resistance of the heater 3 based on the determination result of the change state of the resistance value of the heating resistor 32 of the heater 3 determined by the first determination unit 701a. It is determined that the body 32 is in a predetermined state, and control according to the determination result is performed. The predetermined state is typically an abnormality of the heater.

  The RAM 703 records information such as resistance values acquired by the CPU 701.

  The ROM 704 stores a program executed by the CPU 701 to control the image forming apparatus A. Specifically, the ROM 704 stores a pressure roller rotation control program 704a, a temperature control program 704b, a supply power control program 704c, and a resistance change rate calculation program 704d.

<Operation of fixing device>
The operation of the fixing device 27 according to Embodiment 1 of the present invention will be described in detail.

  The control unit 700 executes the supply power control program 704c read from the ROM 704 when receiving a print operation start signal. The control unit 700 executes the supply power control program 704c to control the current / voltage supply unit 400 to turn on the triac 41 and switch the switch 42 to a state in which the power supply unit 37 and the triac 41 are connected to each other. 3 is energized. As a result, the power supply unit 36 and the power supply unit 37 of the heater 3 are energized from the AC power supply 39 via a temperature detection type safety device (not shown).

  The heating resistor 32 of the heater 3 generates heat and rises in temperature by being energized from the power supply unit 36 through the electrode 34 and from the power supply unit 37 through the electrode 35.

  The thermistor 38 detects the temperature of the substrate 33 heated by the temperature rise of the heating resistor 32 and outputs an electric signal corresponding to the detection result to the control unit 700.

  Based on the electrical signal corresponding to the detection result input from the thermistor 38, the control unit 700 controls the current / voltage supply unit 400 to energize the heater 3 so that the temperature detected by the thermistor 38 becomes the target temperature. .

  When the temperature detected by the thermistor 38 reaches the target temperature, the control unit 700 controls the temperature of the heater 3 by controlling the power supplied to the heater 3 by phase control or frequency control. Specifically, the control unit 700 raises the temperature of the heating resistor 32 when the temperature detected by the thermistor 38 is lower than the target temperature, and the heater 3 when the temperature detected by the thermistor 38 is higher than the target temperature. The heater 3 is kept at the target temperature by controlling so as to lower the temperature.

  The control unit 700 executes state determination processing for determining that the heating resistor 32 is in a predetermined state.

<State determination processing>
The state determination process according to the first embodiment of the present invention will be described in detail with reference to FIG. FIG. 6 illustrates a case where the resistance change rate for a predetermined time is used as the resistance value change state. In FIG. 6, the case where the heating resistor 32 is abnormal will be described as the case where the heating resistor 32 is in a predetermined state.

  The first determination unit 701a of the CPU 701 has a resistance change rate per unit time (predetermined time) until the temperature detected by the thermistor 38 rises from a predetermined temperature to a fixable temperature when the heater 3 is first energized. Determine α0. The first determination unit 701a of the CPU 701 records the determined resistance change rate α0 in the RAM 703 in advance as a reference value (predetermined resistance change rate).

  The state determination process is started when a main power supply (not shown) of the image forming apparatus A is turned on.

  The CPU 701 acquires print information from the operation unit 100 or a host computer (not shown), and starts a print operation (S1).

  Next, the CPU 701 reads and executes the supply power control program 704c from the ROM 704, thereby controlling the current / voltage supply unit 400 to start energization of the heater 3 (S2).

  The current / voltage detector 500 detects the current value of the current supplied from the AC power supply 39 to the heating resistor 32. The first determination unit 701a of the CPU 701 reads the resistance change rate calculation program 704d from the ROM 704 and executes it, thereby converting the current voltage value detected by the current voltage detector 500 into a resistance value and recording it in the RAM 703. (S3).

  Next, the first determination unit 701a of the CPU 701 uses the resistance value R1 at the time T1 and the resistance value R2 at the time T2 recorded in the RAM 703 to calculate the resistance per unit time from the equation (1). The change rate α1 is determined (S4).

  α1 = (R2−R1) / (T2−T1) (1)

  The time from time T1 to time T2 is exemplified here as 10 msec.

  Next, the second determination unit 701b of the CPU 701 determines whether or not the determination result of the resistance change rate α1 determined by the first determination unit 701a is equal to or less than the reference value α0 (α1 ≦ α0) recorded in the RAM 703 ( S5).

  When the determination result of the resistance change rate α1 is equal to or less than the reference value α0 (S5: Yes), the CPU 701 reads and executes the pressure roller rotation control program 704a, the temperature control program 704b, and the supply power control program 704c from the ROM 704, respectively. Thereby, the CPU 701 performs a printing operation (S6).

  Next, the CPU 701 determines whether or not the printing operation is completed (S7).

  When the printing operation is finished (S7: Yes), the CPU 701 finishes the operation.

  On the other hand, if the printing operation has not ended (S7: No), the CPU 701 returns to the operation of S3.

  In addition, when the determination result of the resistance change rate α1 is larger than the reference value α0 (S5: No), the second determination unit 701b of the CPU 701 determines that the heating resistor 32 is abnormal and turns off the triac 41. The power supply to the heater 3 is turned off (S8). As an abnormality of the heat generating resistor 32, here, a state in which the heat generating resistor 32 is broken and broken is illustrated.

  Next, the CPU 701 displays an error on an operation panel (not shown) (S9) and ends the operation.

  FIG. 7 shows the change in resistance value over time when the heater 3 is not damaged when a large-sized recording material having a TCR (resistance temperature coefficient) of 8000 ppm / ° C. is passed through. The resistance change rate per unit time is a slope of a straight line indicating the relationship between the time and the resistance value shown in FIG.

  In the case of FIG. 7, the resistance value during the start-up period from the start-up to 5 seconds later changes from 2.73 Ω (30 ° C.) to 6.47 Ω (200 ° C.). From this, the resistance change rate per unit time in the start-up period is 0.748 Ω / sec.

  The first determination unit 701a of the CPU 701 records in advance in the RAM 703 the resistance change rate per unit time of 0.748 Ω / sec during the start-up period when power is first applied to the heater 3 as a reference value. The second determination unit 701b of the CPU 701 generates heat using the resistance change rate of 0.748 Ω / sec during the start-up period, which is the maximum value, as the reference value of the resistance change rate per unit time when the heater 3 is normal. The abnormality of the resistor 32 is determined.

  Thereafter, the second determination unit 701b of the CPU 701 has a resistance change rate of 0.748Ω / sec, which is a determination result of the first determination unit 701a, during the start-up period, which is equal to or less than the reference value 0.748Ω / sec. It is determined that the heating resistor 32 is normal.

  The resistance value during the copy period is maintained at 6.47Ω (200 ° C.). Thus, the resistance change rate per unit time in the copy period is 0Ω / sec. In the second determination unit 701b of the CPU 701, the resistance change rate 0Ω / sec, which is the determination result of the first determination unit 701a, is less than or equal to the reference value 0.748Ω / sec during the copy period. It is determined that

  The resistance value during the heater cooling period changes from 6.47Ω (200 ° C.) to 2.73Ω (30 ° C.). Thus, the resistance change rate per unit time in the heater cooling period is −0.748 Ω / sec. In the heater cooling period, the second determination unit 701b of the CPU 701 has a resistance change rate of −0.748Ω / sec, which is a determination result of the first determination unit 701a, which is equal to or less than the reference value 0.748Ω / sec. It is determined that the body 32 is normal.

  FIG. 8 shows the change in resistance value over time when the heating resistor 32 is damaged when a large-sized recording material having a TCR of 8000 ppm / ° C. is passed. The resistance change rate per unit time is a slope of a straight line indicating the relationship between the time and the resistance value shown in FIG.

  In the case of FIG. 8, the resistance value in the start-up period from the start-up to 5 seconds later is the same as in FIG.

  The resistance value during the copy period is maintained at 6.47Ω (200 ° C.), but changes from 6.47Ω to 2000Ω due to the breakage of the heating resistor 32. From this, the resistance change rate per unit time until the heating resistor 32 is damaged in the copy period is 0Ω / sec, but the resistance change rate per unit time after the heating resistor 32 is damaged in the copy period is 3987 Ω / sec.

  The second determination unit 701b of the CPU 701 determines that the resistance change rate 0Ω / sec as the determination result of the first determination unit 701a is the reference value 0.748Ω / sec until the heating resistor 32 in the copy period is damaged. Since it is below, it determines with the heating resistor 32 being normal. On the other hand, the second determination unit 701b of the CPU 701 has a resistance change rate of 3987Ω / sec, which is the determination result of the first determination unit 701a, after the heating resistor 32 is damaged during the copy period, and a reference value of 0.748Ω / sec. Therefore, it is determined that the heating resistor 32 is abnormal.

  As described above, according to the present embodiment, the abnormality of the heating resistor 32 is determined by comparing the resistance value with the reference value by determining the abnormality of the heating resistor 32 based on the resistance change rate. In comparison, the abnormality of the heating resistor 32 can be reliably determined early.

  Incidentally, conventionally, since the abnormality of the heating resistor is determined by comparing the resistance value and the threshold value, it is determined that the heating resistor is abnormal when the resistance value becomes larger than the threshold value 7.0Ω in the case of FIG. However, conventionally, since the resistance value becomes larger than the threshold value 7.0Ω even when the temperature of the heating resistor rises because a small-size recording material is passed, it is erroneously determined that the heating resistor is abnormal in this case. Will be.

  Thus, according to the present embodiment, the change state of the resistance value of the heating resistor 32 when power is supplied to the heating resistor 32 is determined, and the heating resistor 32 is determined based on the determination result. By determining that the heater is in the state, the abnormality of the heater can be determined.

  In addition, according to the present embodiment, since the resistance change rate can be obtained before the resistance value (threshold value) that becomes a reference for comparison with the conventional resistance value is exceeded, the heater state can be determined. Judgment can be made early. For example, while the heater abnormality is conventionally determined after 500 msec from the start-up start time, this embodiment can determine the heater abnormality after 20 msec from the start-up time.

  Further, according to the present embodiment, it is possible to minimize the influence on the peripheral members other than the heater due to the abnormality of the heater by determining the state of the heater at an early stage.

  In the present embodiment, the maximum value of the resistance change rate when the heater is normal is set as the reference value, but a value larger than the maximum value may be set as the reference value. That is, in the present embodiment, the maximum value or more of the resistance change rate when the heater is normal can be set as the reference value.

  In the present embodiment, the resistance change rate for a predetermined time is used as the resistance value change state, but a numerical value indicating the resistance value change state other than the resistance change rate for the predetermined time can be used.

(Embodiment 2)
Since the configuration of the image forming apparatus according to Embodiment 2 of the present invention is the same as that shown in FIGS. 1 and 2, the description thereof is omitted.

<Configuration of fixing device>
The configuration of the fixing device 327 according to the second embodiment of the present invention will be described in detail with reference to FIGS. 9 and 10.

  9 and 10, parts having the same configurations as those in FIGS. 2 to 5 are denoted by the same reference numerals, and description thereof is omitted.

  9 and 10 includes a pressure roller 2, an AC power source 39, a pressure roller driving unit 300, a current / voltage supply unit 400, a current / voltage detector 500, and a control unit 700. And a film unit 1000. The film unit 1000 includes a fixing film 4, a film guide 5, a T stay 6, a thermistor 38, and a heater 310. The heater 310 includes a thermal fuse 31, a substrate 33, a heating resistor 320, an electrode 340, an electrode 350, a power feeding unit 360, and a power feeding unit 370. The heater 310 has a short-direction energization type configuration that energizes in a short direction perpendicular to the longitudinal direction of the substrate 33.

  The thermal fuse 31 is inserted between the power supply unit 370 and the switch 42, and when an overcurrent flows, the connection between the power supply unit 370 and the switch 42 is disconnected and applied to the heating resistor 320 from the AC power supply 39. Block AC voltage.

  The heating resistor 320 is made of a material having a relatively high resistance value. After the heating resistor paste is screen-printed between the electrodes 340 and 350 along the longitudinal direction of the substrate 33, the heating resistor 320 is heated. It is formed by firing. The heating resistor 320 is covered with an insulating coating layer (not shown) formed of an insulating material such as glass or resin. The heating resistor 320 has PTC characteristics. Here, the material of the heating resistor 320 is exemplified by ruthenium oxide. The width of the heating resistor paste is exemplified here as about 7 mm. The resistance value of the heating resistor 320 is exemplified here as 10Ω. The thickness of the insulating coat layer that covers the heating resistor 320 is about 100 μm.

  The thickness of the substrate 33 is exemplified here as about 1.5 mm. The width in the longitudinal direction of the substrate 33 is exemplified here as about 300 mm. The width in the short direction of the substrate 33 is exemplified here as 15 mm. In addition, since the structure except the above in the board | substrate 33 is the same structure as the board | substrate 33 of the heater 3, the description is abbreviate | omitted.

  The electrode 340 and the electrode 350 function as contact points for supplying power to the heating resistor 320. The electrode 340 and the electrode 350 are provided by applying a silver paste uniformly on the substrate 33 in a film shape along the longitudinal direction of the substrate 33 by a screen printing method, and then performing baking. The electrodes 34 and 35 are covered with an insulating coating layer (not shown) formed of an insulator such as glass or resin.

  The electrode 340 connects one end of the heating resistor 320 in the short direction and the power feeding unit 360, and applies an AC voltage applied from the power feeding unit 360 to the heating resistor 320. The width of the electrode 340 is exemplified here as 2 mm.

  The electrode 350 is formed in parallel to the electrode 340 and connects the other end of the heat generating resistor 320 in the short direction and the power supply unit 370, and the AC voltage applied from the power supply unit 370 is applied to the heat generating resistor 320. Apply to. The width of the electrode 350 is exemplified here as 2 mm.

  The power feeding unit 360 is connected to one end of the electrode 340 in the longitudinal direction, and applies an AC voltage applied from the AC power supply 39 to the electrode 340. The width | variety of the electric power feeding part 360 illustrates 2 mm here.

  The power feeding unit 370 is connected to one end of the electrode 350 in the longitudinal direction, and applies the AC voltage applied from the AC power supply 39 to the electrode 350. The width | variety of the electric power feeding part 370 illustrates 2 mm here.

  The thermistor 38 is provided on the surface opposite to the surface on which the heating resistor 320 of the substrate 33 is provided (the surface on the opposite side of the surface on which the fixing nip 11 is formed). The thermistor 38 may be provided on the surface on which the heating resistor 320 is provided. In addition, since the configuration of the thermistor 38 other than the above is the same as the configuration of the thermistor 38 of the heater 3, the description thereof is omitted.

  The AC power supply 39 applies an AC voltage to the power supply unit 360 and the power supply unit 370.

  The triac 41 is composed of a semiconductor switching element having three terminals. The triac 41 is turned on by the control of the control unit 700 and starts energization from the AC power supply 39 to the heating resistor 320, or is turned off by the control of the control unit 700 and turned on. To the heating resistor 320 is stopped.

  The switch 42 switches between a state in which power is supplied from the AC power supply 39 to the power supply unit 360 and the power supply unit 370 and a state in which power supply from the AC power supply 39 to the power supply unit 360 and the power supply unit 370 is stopped under the control of the control unit 700. .

<Operation of fixing device>
The operation of the fixing device 327 according to the second embodiment of the present invention will be described in detail.

  When the control unit 700 receives the print operation start signal, the control unit 700 executes the supply power control program 704c read from the ROM 704 to control the current / voltage supply unit 400, thereby turning on the triac 41 to the heater 310. Start energizing. As a result, the power supply unit 360 and the power supply unit 370 of the heater 310 are energized from the AC power supply 39 via a temperature detection type safety device (not shown).

  The heating resistor 320 of the heater 310 heats up and rises in temperature by being energized from the power supply unit 360 through the electrode 340 and from the power supply unit 37 through the electrode 35.

  The thermistor 38 detects the temperature of the substrate 33 heated by the temperature rise of the heating resistor 32 and outputs an electric signal corresponding to the detection result to the control unit 700.

  The control unit 700 controls the current / voltage supply unit 400 to energize the heater 310 so that the temperature detected by the thermistor 38 becomes the target temperature based on the electrical signal corresponding to the detection result input from the thermistor 38. .

  When the temperature detected by the thermistor 38 reaches the target temperature, the control unit 700 controls the temperature of the heater 310 by controlling the power supplied to the heater 310 by phase control or frequency control. Specifically, the control unit 700 raises the temperature of the heating resistor 320 when the temperature detected by the thermistor 38 is lower than the target temperature, and the heater 310 when the temperature detected by the thermistor 38 is higher than the target temperature. Control to cool down. Thereby, the control unit 700 keeps the heater 310 at the target temperature.

  The control unit 700 executes a state determination process for determining that the heating resistor 320 is in a predetermined state.

<State determination processing>
The state determination process according to Embodiment 2 of the present invention will be described in detail.

  The state determination process according to the present embodiment is the process shown in FIG.

  FIG. 11 shows the change in resistance value over time when the heater 310 breaks in the center (position Z in FIGS. 9 and 10) when a large-size recording material having a TCR of 8000 ppm / ° C. is passed. Show. The rate of change in resistance per unit time is a slope of a straight line indicating the relationship between the time and the resistance value shown in FIG.

  In the case of FIG. 11, the resistance value in the start-up period from the start-up to 5 seconds later is the same as in FIG.

  The resistance value during the copy period is maintained at 6.47 Ω (200 ° C.), but changes from 6.47 Ω to 16.17 Ω due to breakage of the heating resistor 320. From this, the resistance change rate per unit time until the heating resistor 320 is damaged in the copy period is 0Ω / sec, but the resistance change rate per unit time after the heating resistor 320 is damaged in the copy period is 19.4Ω / sec.

  The second determination unit 701b of the CPU 701 determines that the resistance change rate determination result 0Ω / sec of the first determination unit 701a is equal to or less than the reference value 0.748Ω / sec until the heating resistor 320 in the copy period is damaged. Therefore, it is determined that the heating resistor 320 is normal. On the other hand, the second determination unit 701b of the CPU 701 determines that the determination result 19.4Ω / sec of the resistance change rate of the first determination unit 701a is 0.748Ω / sec after the heating resistor 320 in the copy period is damaged. Since it is longer than sec, it is determined that the heating resistor 320 is abnormal.

  In the present embodiment, the change in resistance value over time when the heating resistor 320 is not damaged is the same as that in FIG.

  FIG. 12 shows a resistance value with respect to the passage of time when the heating resistor 320 is damaged at the end portion (Y position in FIGS. 9 and 10) when a large-sized recording material having a TCR of 8000 ppm / ° C. is passed. Shows changes. The resistance change rate per unit time is a slope of a straight line indicating the relationship between the time and the resistance value shown in FIG.

  In the case of FIG. 12, the resistance value in the start-up period from the start-up to 5 seconds later is the same as in FIG.

  The resistance value during the copy period is maintained at 6.47 Ω (200 ° C.), but changes from 6.47 Ω to 7.17 Ω due to breakage of the heating resistor 320. From this, the resistance change rate per unit time until the heating resistor 320 is damaged in the copy period is 0Ω / sec, but the resistance change rate per unit time after the heating resistor 320 is damaged in the copy period is 1.4Ω / sec.

  The second determination unit 701b of the CPU 701 determines that the resistance change rate determination result 0Ω / sec of the first determination unit 701a is equal to or less than the reference value 0.748Ω / sec until the heating resistor 320 in the copy period is damaged. Therefore, it is determined that the heating resistor 320 is normal. On the other hand, the second determination unit 701b of the CPU 701 determines that the determination result 1.4Ω / sec of the resistance change rate of the first determination unit 701a after the heating resistor 320 in the copy period is damaged is the reference value 0.748Ω / sec. Since it is longer than sec, it is determined that the heating resistor 320 is abnormal.

  FIG. 13 shows a change in resistance value with time when the heating resistor 320 is not damaged when a small-sized recording material having a TCR of 8000 ppm / ° C. is passed. The rate of change in resistance per unit time is a slope of a straight line indicating the relationship between the time and the resistance value shown in FIG.

  In the case of FIG. 13, the resistance value during the start-up period from the start-up to 5 seconds later changes from 2.73Ω (30 ° C.) to 6.47Ω (200 ° C.). From this, the resistance change rate per unit time in the start-up period is 0.748 Ω / sec.

  The first determination unit 701a of the CPU 701 records in advance in the RAM 703 a resistance change rate of 0.748 Ω / sec per unit time during the start-up period when power is first applied to the heater 310 as a reference value for the resistance change rate. Keep it. The second determination unit 701b of the CPU 701 uses a resistance change rate of 0.748 Ω / sec during the start-up period, which is the maximum value, of the resistance change rate per unit time when the heating resistor 320 is normal as a reference value ( Abnormality of the heating resistor 320 is determined as a predetermined resistance change rate).

  After that, the second determination unit 701b of the CPU 701 has a resistance change rate of 0.748Ω / sec, which is a determination result of the first determination unit 700a, during the start-up period, which is equal to or less than the reference value 0.748Ω / sec. It is determined that the heating resistor 320 is normal.

  The resistance value in the copy period changes from 6.47Ω (200 ° C.) to 7.54Ω because the end of the heating resistor 320 is heated to 290 ° C. Accordingly, the resistance change rate per unit time in the copy period is 0.0178 Ω / sec. In the copy period, the second determination unit 701b of the CPU 701 has a resistance change rate of 0.0178Ω / sec, which is the determination result of the first determination unit 701a, which is equal to or less than the reference value 0.748Ω / sec. Is determined to be normal.

  The resistance value during the heater cooling period gradually decreases from 7.54Ω. From this, the resistance change rate per unit time in the heater cooling period is a reference value of 0.748 Ω / sec or less, and thus it is determined that the heater 310 is normal.

  On the other hand, conventionally, in the case of the heater 310 having the configuration of the short direction energization type, an abnormality due to breakage of the end portion of the heating resistor when the large-sized recording material shown in FIG. 12 is passed is determined. In order to do this, it is necessary to set the resistance value to 7.0Ω as the threshold value. However, when 7.0Ω is set as the threshold value, the resistance value during the copy period rises to 7.54Ω when the small-size recording material shown in FIG. Despite being present, it is erroneously determined to be abnormal.

  FIG. 14 shows the change in resistance value over time when the heating resistor 320 breaks when a small-sized recording material having a TCR of 8000 ppm / ° C. is passed. The resistance change rate per unit time is a slope of a straight line indicating the relationship between the time and the resistance value shown in FIG.

  In the case of FIG. 14, the resistance value in the start-up period from the start-up to 5 seconds later is the same as in FIG.

  The resistance value during the copy period changes from 6.47Ω (200 ° C.) to 7.20Ω because the end of the heating resistor 320 is heated to 290 ° C., but it is 7.20Ω due to damage to the heating resistor 320. To 7.79Ω. From this, the resistance change rate per unit time until the heating resistor 320 is damaged in the copy period is 0.017 Ω / sec, but the resistance change per unit time after the heating resistor 320 is damaged in the copy period. The rate is 1.18 Ω / sec.

  The second determination unit 701b of the CPU 701 determines that the resistance change rate determination result 0.017Ω / sec of the first determination unit 701a is the reference value 0.748Ω / sec until the heating resistor 320 in the copy period is damaged. Since it is below, it determines with the heating resistor 320 being normal. On the other hand, the second determination unit 701b of the CPU 701 has a resistance change rate of 1.18Ω / sec, which is the determination result of the first determination unit 701a, after the heating resistor 320 in the copy period is damaged. Since it is longer than sec, it is determined that the heating resistor 320 is abnormal.

  Thus, according to the present embodiment, the change state of the resistance value of the heating resistor 320 when power is supplied to the heating resistor 320 is determined, and the heating resistor 320 is determined based on the determination result. By determining that the heater is in the state, the abnormality of the heater can be determined.

  In the present embodiment, the maximum value of the resistance change rate when the heater is normal is set as the reference value, but a value larger than the maximum value may be set as the reference value. That is, in the present embodiment, the maximum value or more of the resistance change rate when the heater is normal can be set as the reference value.

  In the present embodiment, the resistance change rate for a predetermined time is used as the resistance value change state, but a numerical value indicating the resistance value change state other than the resistance change rate for the predetermined time can be used.

(Embodiment 3)
The configuration of the image forming apparatus according to Embodiment 3 of the present invention is the same as that shown in FIG.

<Configuration of fixing device>
The configuration of the fixing device 2327 according to the third embodiment of the present invention will be described in detail with reference to FIGS. 15 and 16.

  Note that a plan view of the fixing device 2327 according to this embodiment is the same as FIG. Further, in FIG. 15, parts having the same configuration as in FIG. Further, in FIG. 16, parts having the same configuration as in FIGS. 9 and 10 are denoted by the same reference numerals, and description thereof is omitted.

  The fixing device 2327 is provided in the image forming apparatus B, and includes a pressure roller 2, an AC power supply 39, a pressure roller driving unit 300, a current / voltage supply unit 400, a current / voltage detector 500, and a film unit 2000. And a control unit 2700.

  The film unit 2000 includes a fixing film 4, a film guide 5, a T stay 6, a thermistor 38 a, a thermistor 38 b, a thermistor 38 c, and a heater 310.

  The thermistor 38a, the thermistor 38b, and the thermistor 38c, which are temperature detecting means, are provided on the opposite surface of the substrate 33 to the surface on which the heating resistor 320 is provided (the surface opposite to the surface that forms the fixing nip 11). . The thermistor 38a, the thermistor 38b, and the thermistor 38c may be provided on the surface on which the heating resistor 320 is provided.

  The thermistor 38b is provided on the power supply side. The thermistor 38c is provided on the non-power feeding side. The thermistor 38a is provided between the thermistor 38b and the thermistor 38c. The thermistor 38a, the thermistor 38b, and the thermistor 38c detect the temperature of the position where each was provided. Note that the other configurations of the thermistor 38a, the thermistor 38b, and the thermistor 38c are the same as those of the thermistor 38, and the description thereof is omitted.

  The triac 41 is composed of a semiconductor switching element having three terminals. The triac 41 is turned on under the control of the control unit 2700 to start energization from the AC power supply 39 to the heating resistor 320, or is turned off under the control of the control unit 2700 to turn on the AC power supply 39. To the heating resistor 320 is stopped.

  The switch 42 switches between a state in which power is supplied from the AC power supply 39 to the power supply unit 360 and the power supply unit 370 and a state in which power supply from the AC power supply 39 to the power supply unit 360 and the power supply unit 370 is stopped under the control of the control unit 2700. .

  The pressure roller driving unit 300 drives the pressure roller 2 according to the control of the control unit 2700.

  The current / voltage supply unit 400 supplies power to the heating resistor 32 of the heater 3 under the control of the control unit 2700 to heat the heating resistor 32. The other configuration of the current / voltage supply unit 400 is the same as that of the current / voltage supply unit 400 in the first embodiment, and a description thereof will be omitted.

  The current / voltage detector 500 detects the current / voltage supplied to the heater 3 and outputs the detection result to the control unit 2700.

  The control unit 2700 operates by receiving power from a power source (not shown), and includes an I / F unit 702, a RAM 703, a CPU 2701, and a ROM 2704.

  The CPU 2701 controls the operations of the image processing unit 200, the pressure roller driving unit 300, the current / voltage supply unit 400, and the optical unit 600 based on the electrical signal input from the operation unit 100 or the detection result of the current / voltage detector 500. To do.

  Specifically, the CPU 2701 controls the driving of the pressure roller driving unit 300 by executing the pressure roller rotation control program 704a read from the ROM 2704. The CPU 2701 controls the temperature of the fixing device 2327 by executing the temperature control program 704b read from the ROM 704 based on the detection result of the thermistor 38a. The CPU 2701 controls the power supplied from the current / voltage supply unit 400 to the fixing device 2327 by executing the supply power control program 704 c read from the ROM 2704.

  The CPU 2701 controls the operation of the image processing unit 200 based on the image data input from the optical unit 600.

  The CPU 2701 executes state determination processing by the first determination unit 2701a as the first determination unit and the second determination unit 2701b as the second determination unit, and the heating resistor 320 is in a predetermined state. Determine.

  The first determination unit 2701a executes the temperature change rate calculation program 2704b read from the ROM 2704. The first determination unit 2701a executes the temperature change rate calculation program 2704b to sequentially record the detected temperature values detected by the thermistor 38c in the RAM 703 at predetermined time intervals. Here, the predetermined time is 10 msec. The first determination unit 2701 a determines the temperature change state of the heating resistor 320 of the heater 3 using the detected temperature value recorded in the RAM 703.

  The first determination unit 2701a executes the power calculation program 2704a read from the ROM 2704, thereby calculating and determining the power supplied from the current / voltage supply unit 400 to the fixing device 2327 every predetermined time.

  The second determination unit 2701b is based on the determination result of the temperature change state of the heating resistor 320 determined by the first determination unit 2701a and the calculation result of the power calculated by the first determination unit 2701a. It is determined that the body 320 is in a predetermined state. The second determination unit 2701b performs control according to the determination result that the heating resistor 320 is in a predetermined state. The predetermined state is typically an abnormality of the heater 310.

  The RAM 703 records temperature detection values and the like by the CPU 2701.

  The ROM 2704 stores a program executed by the CPU 2701 to control the image forming apparatus B. Specifically, the ROM 2704 stores a pressure roller rotation control program 704a, a temperature control program 704b, a supply power control program 704c, a power calculation program 2704a, and a temperature change rate calculation program 2704b.

  Since operations other than those related to the state determination process of the fixing device 2327 according to the present embodiment are the same as the operations of the fixing device 327 according to the second embodiment, description thereof is omitted.

<State determination processing>
The state determination process according to Embodiment 3 of the present invention will be described in detail with reference to FIG. In FIG. 15, the case where the heating resistor 320 is abnormal will be described as the case where the heating resistor 320 is in a predetermined state.

  The state determination process is started when a main power supply (not shown) of the image forming apparatus B is turned on.

  The CPU 2701 acquires print information from the operation unit 100 or a host computer (not shown), and starts a print operation (S11).

  Next, the CPU 2701 acquires the detected value of the temperature detected by the thermistor 38c (S12).

  Next, the CPU 2701 reads out and executes the supply power control program 704c from the ROM 2704, thereby controlling the current / voltage supply unit 400 to start energizing the heater 3 (S13).

  Next, the CPU 2701 reads out and executes the temperature control program 704b from the ROM 2704, thereby starting temperature control based on the detected temperature value detected by the thermistor 38a (S14).

  Next, the current / voltage detector 500 detects a current value and a voltage value supplied from the AC power supply 39 to the heating resistor 320. The first determination unit 2701a of the CPU 2701 acquires the current voltage value detected by the current voltage detector 500 at time T1 by reading and executing the power calculation program 2704a from the ROM 2704 (S15).

  Next, the first determination unit 2701a reads the temperature change rate calculation program 2704b from the ROM 2704 and executes it, thereby recording the detected value of the temperature detected by the thermistor 38c every predetermined time in the RAM 703. Then, the first determination unit 2701a uses the temperature detection value t1 at time T1 and the temperature detection value t2 at time T2 recorded in the RAM 703 to calculate the temperature change rate β1 per unit time from the equation (2). Calculate (S16).

  β1 = (t1-t2) / (T2-T1) (2)

  Next, the first determination unit 2701a calculates the power W1 at time T1 using the acquired current voltage value and records it in the RAM 703 (S17).

  Next, the second determination unit 2701b of the CPU 2701 determines whether or not the power W1 recorded in the RAM 703 is larger than a predetermined value recorded in the RAM 703 and whether or not the temperature change rate β1 is larger than a predetermined value. Determine (S18). The predetermined value to be compared with the power W1 is 600 W here. The predetermined value to be compared with the temperature change rate β1 is exemplified here as −3 ° C./sec.

  The second determination unit 2701b determines that the heating resistor 320 is abnormal when the power W1 is greater than the predetermined value and the temperature change rate α is greater than the predetermined value (S18: Yes), and turns off the triac 41. The power supply to the heater 3 is turned off (S19).

  Next, the CPU 2701 displays an error on an operation panel (not shown) (S20) and ends the operation.

  On the other hand, the second determination unit 2701b performs a printing operation when the temperature change rate α is equal to or lower than a predetermined value or when the power W1 is equal to or lower than a predetermined value (S28: No) (S21). Specifically, the second determination unit 2701b reads and executes the pressure roller rotation control program 704a, the temperature control program 704b, and the supply power control program 704c from the ROM 2704, respectively.

  Next, the CPU 2701 determines whether or not the printing operation is finished (S22).

  When the printing operation is finished (S22: Yes), the CPU 2701 finishes the operation.

  On the other hand, if the printing operation has not ended (S22: No), the CPU 2701 returns to the process of S12.

  When the small size recording material is passed and the heater 310 is broken, the rate of change in resistance per unit time is a slope of a straight line indicating the relationship between the time and the resistance value shown in FIG. The heater shown in FIG. 18 uses a TCR of 2000 ppm / ° C.

  Specifically, the resistance value during the rising period of 5 seconds changes from 10.66Ω (30 ° C.) to 14.28Ω (200 ° C.). The rate of change in resistance at this time is 0.724 Ω / sec. The resistance value for 55 seconds from the start of copying in the copying period changes from 14.28Ω (200 ° C.) to 15.6Ω as the heater temperature rises at the edge. The rate of change in resistance at this time is 0.024 Ω / sec.

  The heater 310 is damaged during the passage of the small-size recording material, and the resistance value for 500 msec from the time of the damage changes from 15.6Ω to 15.94Ω. The rate of change in resistance at this time is 0.68 Ω / sec. At this time, the largest resistance change rate of 0.724 Ω / sec out of the normal resistance change rate is larger than the resistance change rate of 0.68 Ω / sec when the heater is broken. I cannot judge whether or not.

  On the other hand, in the present embodiment, whether or not the heater is broken is determined even when a small-size recording material is passed by judging the breakage of the heater based on the temperature change rate and the transition of electric power. Can be judged.

  Specifically, when the heater 310 is not damaged when passing a small-size recording material, the temperature increase rate during the startup period of 5 seconds is 30 ° C. as shown in FIG. To a target temperature control temperature of 200 ° C., so that it becomes 34 ° C./sec. Further, the temperature increase rate for 60 seconds from the start of copying in the copy period of a small size recording material is 1.5 ° C./sec because it rises from 200 ° C. to 290 ° C. due to the temperature rise at the edge. Furthermore, the temperature decrease rate for 13 seconds from when the heater is turned off during the heater cooling period decreases from 290 ° C. to 200 ° C., and thus becomes −7 ° C./sec. Note that the heater shown in FIG. 19 uses a TCR of 2000 ppm / ° C.

  On the other hand, the temperature detected by the thermistor 38c installed at the end of the heater 310 on the non-power-feeding side during the start-up period and the copy period in which power is constantly supplied is 900 W as shown in FIG. It is constant.

  When the heater 310 is damaged when passing a small-size recording material, the temperature for 47 seconds from the start of copying in the copy period detected by the thermistor 38c until the heater 310 is damaged is shown in FIG. As shown in FIG. Further, when the heater 310 is damaged when a small-sized recording material is passed, the temperature for 13 seconds from the time of the failure of the heater 310 detected by the thermistor 38c is 270 as shown in FIG. Decrease from ℃ to 200 ℃. The heater shown in FIG. 20 uses a TCR of 2000 ppm / ° C.

  Accordingly, when the heater 310 is damaged when a small-size recording material is passed, the temperature increase rate for 47 seconds from the start of copying in the copy period until the heater 310 is damaged is 1.5 ° C./sec. Become. In addition, when the heater 310 is damaged when a small-size recording material is passed, the temperature decrease rate for 13 seconds from the time when the heater 310 is damaged is −7 ° C./sec. The temperature decrease rate when the heater is broken is the same as the temperature decrease rate during the heater cooling period.

  Therefore, the second determination unit 2701b can determine that the heater 310 is damaged when the temperature is decreased despite the constant power. Thus, the state of the heater 310 can be determined based on the power and the temperature change rate.

  As described above, according to the present embodiment, when the breakage of the heater 310 is determined based on the temperature change rate and the electric power, the breakage occurs within 10 mm from the end of the heating resistor 320 on the non-feeding side. In addition, the breakage of the heater 310 can be determined. On the other hand, in the above case, damage to the heater 310 cannot be determined based on the resistance change rate.

(Embodiment 4)
The configuration of the image forming apparatus according to Embodiment 4 of the present invention is the same as that shown in FIG.

<Configuration of fixing device>
The configuration of the fixing device 3327 according to the third embodiment of the present invention will be described in detail with reference to FIG.

  Note that a plan view of the fixing device 3327 according to the present embodiment is the same as FIG. Further, in FIG. 21, the same components as those in FIG. 15 are denoted by the same reference numerals, and description thereof is omitted.

  The fixing device 3327 is provided in the image forming apparatus C, and includes a pressure roller 2, an AC power supply 39, a pressure roller driving unit 300, a current / voltage supply unit 400, a current / voltage detector 500, and a film unit 2000. And a control unit 3700.

  The triac 41 is composed of a semiconductor switching element having three terminals. The triac 41 is turned on under the control of the control unit 3700 to start energization from the AC power supply 39 to the heating resistor 320, or is turned off under the control of the control unit 3700. To the heating resistor 320 is stopped.

  The switch 42 switches between a state in which power is supplied from the AC power supply 39 to the power supply unit 360 and the power supply unit 370 and a state in which power supply from the AC power supply 39 to the power supply unit 360 and the power supply unit 370 is stopped under the control of the control unit 3700. .

  The pressure roller driving unit 300 drives the pressure roller 2 under the control of the control unit 3700.

  The current / voltage supply unit 400 supplies power to the heating resistor 320 of the heater 310 under the control of the control unit 3700 to heat the heating resistor 32. The other configuration of the current / voltage supply unit 400 is the same as that of the current / voltage supply unit 400 in the first embodiment, and a description thereof will be omitted.

  The current / voltage detector 500 detects the current / voltage supplied to the heater 310 and outputs the detection result to the control unit 3700.

  The control unit 3700 operates by receiving power from a power source (not shown), and includes an I / F unit 702, a RAM 703, a CPU 3701, and a ROM 3704.

  The CPU 3701 controls the operations of the image processing unit 200, the pressure roller driving unit 300, the current / voltage supply unit 400, and the optical unit 600 based on the electrical signal input from the operation unit 100 or the detection result of the current / voltage detector 500. To do.

  Specifically, the CPU 3701 controls the driving of the pressure roller driving unit 300 by executing the pressure roller rotation control program 704a read from the ROM 3704. The CPU 3701 controls the temperature of the fixing device 3327 by executing the temperature control program 704b read from the ROM 704 based on the detection result of the thermistor 38a. The CPU 3701 controls the power supplied from the current / voltage supply unit 400 to the fixing device 3327 by executing the supply power control program 704 c read from the ROM 2704.

  The CPU 3701 controls the operation of the image processing unit 200 based on the image data input from the optical unit 600.

  The CPU 3701 executes state determination processing using the first determination unit 3701a as the first determination unit and the second determination unit 3701b as the second determination unit, and the heating resistor 320 is in a predetermined state. Determine.

  The first determination unit 3701a executes the temperature change rate calculation program 2704b read from the ROM 3704. The first determination unit 3701a executes the temperature change rate calculation program 3704b to sequentially record the detected values of the temperatures detected by the thermistor 38b and the thermistor 38c in the RAM 703 every predetermined time. Here, the predetermined time is 10 msec. The first determination unit 3701 a determines the temperature change state of the heating resistor 320 of the heater 310 using the detected temperature value recorded in the RAM 703.

  The second determination unit 3701b determines that the heating resistor 320 is in a predetermined state based on the determination result of the temperature change state of the heating resistor 320 determined by the first determination unit 3701a. The second determination unit 3701b performs control according to the determination result that the heating resistor 320 is in a predetermined state. The predetermined state is typically an abnormality of the heater 310.

  The RAM 703 records a temperature detection value acquired by the CPU 3701.

  The ROM 3704 stores a program executed by the CPU 3701 to control the image forming apparatus C. Specifically, the ROM 3704 stores a pressure roller rotation control program 704a, a temperature control program 704b, a supply power control program 704c, and a temperature change rate calculation program 3704a.

  Since operations other than those related to the state determination process of the fixing device 3327 according to the present embodiment are the same as the operations of the fixing device 327 according to the second embodiment, the description thereof is omitted.

<State determination processing>
The state determination process according to Embodiment 4 of the present invention will be described in detail with reference to FIG. In FIG. 22, the case where the heating resistor 320 is abnormal will be described as the case where the heating resistor 320 is in a predetermined state.

  The state determination process is started when a main power supply (not shown) of the image forming apparatus C is turned on.

  The CPU 3701 acquires print information from the operation unit 100 or a host computer (not shown), and starts a print operation (S31).

  Next, the CPU 3701 acquires the temperature detection value t11 detected by the thermistor 38c at time T11 and the temperature detection value t12 detected by the thermistor 38c at time T12, and stores them in the RAM 703 (S32).

  Next, the CPU 3701 acquires the temperature detection value t21 detected by the thermistor 38b at time T21 and the temperature detection value t22 detected by the thermistor 38b at time T22, and stores them in the RAM 703 (S33).

  Next, the CPU 3701 reads out and executes the supply power control program 704c from the ROM 3704, thereby controlling the current / voltage supply unit 400 to start energizing the heater 3 (S34).

  Next, the CPU 3701 reads out and executes the temperature control program 704b from the ROM 3704, thereby starting temperature control based on the detected value of the temperature detected by the thermistor 38a (S35).

  Next, the first determination unit 3701a of the CPU 3701 obtains the temperature change rate β2 per unit time of the temperature detected by the thermistor 38c by reading and executing the temperature change rate calculation program 3704a from the ROM 3704 (S36). Specifically, the first determination unit 3701a stores the detected value t11 of the temperature detected by the thermistor 38c at time T11 and the detected value t12 of the temperature detected by the thermistor 38c at time T12, which are stored in the RAM 703, (3) The temperature change rate β2 is obtained from the equation and.

  β2 = (t11−t12) / (T12−T11) (3)

  Next, the first determination unit 3701a obtains the temperature change rate β3 per unit time of the temperature detected by the thermistor 38b (S37). Specifically, the first determination unit 3701a stores the temperature detection value t21 detected by the thermistor 38b at time T21 and the temperature detection value t22 detected by the thermistor 38b at time T22, which are stored in the RAM 703, and (4). The temperature change rate β3 is obtained from the equation and.

  β3 = (t21−t22) / (T22−T21) (4)

  Next, the second determination unit 3701b of the CPU 3701 determines whether or not the temperature change rate β3 is equal to or higher than a predetermined value and the temperature change rate β2 is lower than a predetermined value (S38). The predetermined value to be compared with the temperature change rate β3 is exemplified here as 0 ° C./sec. The predetermined value to be compared with the temperature change rate β2 is exemplified here as −3 ° C./sec.

  When the temperature change rate β3 is equal to or higher than the predetermined value and the temperature change rate β2 is lower than the predetermined value (S38: Yes), the second determination unit 3701b determines that the heating resistor 320 is abnormal and turns off the triac 41. Then, the power supply to the heater 310 is turned off (S39).

  Next, the CPU 3701 displays an error on an operation panel (not shown) (S40) and ends the operation.

  On the other hand, the second determination unit 3701b performs a printing operation when the temperature change rate β3 is less than a predetermined value or when the temperature change rate β2 is greater than or equal to a predetermined value (S38: No) (S41). Specifically, the second determination unit 3701b reads and executes the pressure roller rotation control program 704a, the temperature control program 704b, and the supply power control program 704c from the ROM 3704, respectively.

  Next, the CPU 3701 determines whether or not the printing operation has been completed (S42).

  When the printing operation is finished (S42: Yes), the CPU 3701 turns off the triac 41, turns off the power to the heater 310 (S43), and finishes the operation.

  On the other hand, when the printing operation is not finished (S42: No), the CPU 3701 returns to the process of S32.

  As shown in FIG. 23 (a), the temperature during the startup period of 5 seconds detected by the thermistor 38c on the non-power supply side in a normal state where the heater 310 is not damaged when passing a small-size recording material is as shown in FIG. It rises from room temperature 30 ° C to target temperature control temperature 200 ° C. Accordingly, the temperature increase rate at this time is 34 ° C./sec. The heater shown in FIG. 23 uses a TCR of 2000 ppm / ° C.

  In addition, the temperature for 60 seconds from the start of copying in the copying period of the small-size recording material detected by the non-power-feeding thermistor 38c increases from 200 ° C. to 290 ° C. due to the temperature rise at the end. Therefore, the temperature increase rate at this time is 1.5 ° C./sec.

  Further, the temperature for 13 seconds from the heater OFF in the heater cooling period detected by the thermistor 38c on the non-power supply side decreases from 290 ° C. to 200 ° C. Accordingly, the temperature decrease rate at this time is −7 ° C./sec.

  Further, when the heater 310 is not damaged when passing a small size recording material, the temperature increase rate between the start-up period and the copy period detected by the power supply side thermistor 38b and the temperature decrease rate during the heater cooling period are as follows. As shown in FIG. 23B, this is the same as FIG.

  On the other hand, when the heater 310 is damaged when a small-size recording material is passed, the temperature for 47 seconds from the start of copying in the copy period detected by the thermistor 38c until the heater 310 is damaged is shown in FIG. As shown in a), the temperature rises from 200 ° C to 270 ° C. Further, when the heater 310 is damaged when the small-size recording material is passed, the temperature for 13 seconds from the time of the failure of the heater 310 detected by the thermistor 38c is 270 as shown in FIG. Decrease from ℃ to 200 ℃. The heater shown in FIG. 24 uses a TCR of 2000 ppm / ° C.

  As a result, the temperature increase rate for 47 seconds from the start of copying in the copy period until the heater 310 is damaged is 1.5 ° C./sec. Further, the temperature decrease rate for 13 seconds from the time when the heater 310 is damaged is −7 ° C./sec. The temperature decrease rate when the heater is broken is the same as the temperature decrease rate during the heater cooling period.

  Further, when the heater 310 is broken when passing a small-size recording material, the temperature increase rate between the start-up period and the copy period detected by the power supply side thermistor 38b and the temperature decrease rate during the heater cooling period are as follows. FIG. 24B is the same as FIG. 23B.

  The second determination unit 3701b has a temperature change rate of the temperature detected by the thermistor 38b of 1.5 ° C./sec and 0 ° C./sec or more, but the temperature change rate of the temperature detected by the thermistor 38c is −7 ° C./sec. Since it is less than −3 ° C./sec in sec, it is determined that the heater is abnormal.

  As described above, according to the present embodiment, the failure of the heater 3 is determined based on the temperature change rate on the non-feeding side and the feeding side, so that the end of the heating resistor 320 on the non-feeding side is within 10 mm. When the breakage occurs, the breakage of the heater 3 can be determined.

(Embodiment 5)
The configuration of the image forming apparatus according to Embodiment 5 of the present invention is the same as that shown in FIG.

<Configuration of fixing device>
The configuration of the fixing device 4327 according to the fifth embodiment of the present invention will be described in detail with reference to FIG.

  Note that a plan view of the fixing device 4327 according to the present embodiment is the same as FIG. In FIG. 25, parts having the same configuration as in FIG.

  The fixing device 4327 is provided in the image forming apparatus D, and includes a pressure roller 2, an AC power supply 39, a pressure roller driving unit 300, a current / voltage supply unit 400, a current / voltage detector 500, and a film unit 2000. And a control unit 4700.

  The triac 41 is composed of a semiconductor switching element having three terminals. The triac 41 is turned on under the control of the control unit 4700 and starts energization from the AC power supply 39 to the heating resistor 320 or is turned off under the control of the control unit 4700 to turn on the AC power supply 39. To the heating resistor 320 is stopped.

  The switch 42 switches between a state where power is supplied from the AC power supply 39 to the power supply unit 360 and the power supply unit 370 and a state where power supply from the AC power supply 39 to the power supply unit 360 and the power supply unit 370 is stopped under the control of the control unit 4700. .

  The pressure roller driving unit 300 drives the pressure roller 2 under the control of the control unit 4700.

  The current / voltage supply unit 400 supplies power to the heating resistor 320 of the heater 310 according to the control of the control unit 4700 to heat the heating resistor 320. The other configuration of the current / voltage supply unit 400 is the same as that of the current / voltage supply unit 400 in the first embodiment, and a description thereof will be omitted.

  The current / voltage detector 500 detects the current / voltage supplied to the heater 310 and outputs the detection result to the control unit 4700.

  The control unit 4700 operates by receiving power from a power source (not shown), and includes an I / F unit 702, a RAM 703, a CPU 4701, and a ROM 4704.

  The CPU 4701 controls the operation of the image processing unit 200, the pressure roller driving unit 300, the current / voltage supply unit 400, and the optical unit 600 based on the electrical signal input from the operation unit 100 or the detection result of the current / voltage detector 500. To do.

  Specifically, the CPU 4701 controls the driving of the pressure roller driving unit 300 by executing the pressure roller rotation control program 704a read from the ROM 4704. The CPU 4701 controls the temperature of the fixing device 4327 by executing the temperature control program 704b read from the ROM 704 based on the detection result of the thermistor 38a. The CPU 4701 controls the power supplied from the current / voltage supply unit 400 to the fixing device 4327 by executing the supply power control program 704 c read from the ROM 2704.

  The CPU 4701 controls the operation of the image processing unit 200 based on the image data input from the optical unit 600.

  The CPU 4701 executes state determination processing using the first determination unit 4701a serving as the first determination unit and the second determination unit 3401b serving as the second determination unit, and the heating resistor 320 is in a predetermined state. Determine.

  The first determination unit 4701a executes the resistance change rate calculation program 4704a read from the ROM 4704. The first determination unit 4701a executes the resistance change rate calculation program 4704a to convert the current / voltage value indicated by the detection result input from the current / voltage detector 500 into a resistance value and sequentially record it in the RAM 703. The first determination unit 4701 a determines the change state of the resistance value of the heating resistor 320 of the heater 310 using the resistance value recorded in the RAM 703. The change state of the resistance value is typically a resistance change rate for a predetermined time. The predetermined time is exemplified here as 10 msec.

  The first determination unit 4701a executes the temperature change rate calculation program 4704b read from the ROM 4704. The first determination unit 4701a executes the temperature change rate calculation program 4704b to sequentially record the detected temperature values detected by the thermistor 38c in the RAM 703 every predetermined time. Here, the predetermined time is 10 msec. The first determination unit 4701 a determines the temperature change state of the heating resistor 320 of the heater 310 using the detected temperature value recorded in the RAM 703.

  The second determination unit 4701b is based on the determination result of the resistance change state of the heating resistor 320 determined by the first determination unit 4701a and the determination result of the temperature change state of the heating resistor 320. Is determined to be in a predetermined state. The second determination unit 4701b performs control according to the determination result that the heating resistor 320 is in a predetermined state. The predetermined state is typically an abnormality of the heater.

  The RAM 703 records the resistance value and temperature detection value acquired by the CPU 4701.

  The ROM 4704 stores a program executed by the CPU 4701 to control the image forming apparatus D. Specifically, the ROM 4704 stores a pressure roller rotation control program 704a, a temperature control program 704b, a supply power control program 704c, a resistance change rate calculation program 4704a, and a temperature change rate calculation program 4704b. Yes.

  Since operations other than those related to the state determination process of the fixing device 4327 according to the present embodiment are the same as the operations of the fixing device 327 according to the second embodiment, description thereof is omitted.

<State determination processing>
The state determination process according to Embodiment 5 of the present invention will be described in detail with reference to FIG. In FIG. 26, the case where the heating resistor 320 is abnormal will be described as the case where the heating resistor 320 is in a predetermined state.

  The state determination process is started when a main power supply (not shown) of the image forming apparatus D is turned on.

  The CPU 4701 acquires print information from the operation unit 100 or a host computer (not shown), and starts a print operation (S51).

  Next, the CPU 4701 acquires the temperature detection value t21 detected by the thermistor 38c at time T21 and the temperature detection value t22 detected by the thermistor 38c at time T22, and stores them in the RAM 703 (S52).

  Next, the CPU 4701 reads the power supply control program 704c from the ROM 4704 and executes it to control the current / voltage supply unit 400 and start energizing the heater 310 (S53).

  Next, the CPU 4701 reads out and executes the temperature control program 704b from the ROM 4704, thereby starting temperature control based on the detected temperature value detected by the thermistor 38a (S54).

  Next, the current voltage detector 500 detects the current value of the current supplied from the AC power supply 39 to the heating resistor 320. The first determination unit 4701a of the CPU 4701 reads the resistance change rate calculation program 4704a from the ROM 4704 and executes it, thereby converting the current voltage value detected by the current voltage detector 500 into a resistance value and recording it in the RAM 703. (S55).

  Next, the first determination unit 4701a of the CPU 4701 obtains a temperature change rate β4 per unit time of the temperature detected by the thermistor 38c by reading and executing the temperature change rate calculation program 4704b from the ROM 4704 (S56). Specifically, the first determination unit 4701a stores the temperature detection value t21 detected by the thermistor 38c at time T21 and the temperature detection value t22 detected by the thermistor 38c at time T22, which are stored in the RAM 703, and (5). The temperature change rate β2 is obtained from the equation and.

  β4 = (t21−t22) / (T22−T21) (5)

  Next, the first determination unit 4701a of the CPU 401 uses the resistance value R11 at time T21 and the resistance value R12 at time T22 recorded in the RAM 703 to calculate the resistance per unit time from Equation (6). The change rate α2 is determined (S57).

  α2 = (R12−R11) / (T22−T21) (6)

  Here, the time from time T21 to time T22 is exemplified as 10 msec.

  Next, the second determination unit 4701b of the CPU 4701 determines whether or not the resistance change rate α2 is greater than a predetermined value and the temperature change rate β4 is less than a predetermined value (S58). The predetermined value to be compared with the resistance change rate α2 is exemplified here as 0Ω / sec. The predetermined value to be compared with the temperature change rate β4 is exemplified here as 0 ° C./sec.

  The second determination unit 4701b determines that the heating resistor 320 is abnormal when the resistance change rate α2 is greater than the predetermined value and the temperature change rate β4 is equal to or lower than the predetermined value (S58: Yes), and turns off the triac 41. Then, the power supply to the heater 310 is turned off (S59).

  Next, the CPU 4701 displays an error on an operation panel (not shown) (S60) and ends the operation.

  On the other hand, the second determination unit 4701b performs a printing operation when the resistance change rate α2 is equal to or smaller than the predetermined value or when the temperature change rate β4 is larger than the predetermined value (S58: No) (S61). Specifically, the second determination unit 4701b reads and executes the pressure roller rotation control program 704a, the temperature control program 704b, and the supply power control program 704c from the ROM 3404, respectively.

  Next, the CPU 4701 determines whether or not the printing operation is finished (S62).

  When the printing operation is finished (S62: Yes), the CPU 4701 turns off the triac 41 and turns off the power to the heater 310 (S63), and finishes the operation.

  On the other hand, if the printing operation has not ended (S62: No), the CPU 4701 returns to the process of S52.

  FIG. 27 shows a normal state in which the heater 310 is not damaged when a small-size recording material is passed through a fixing device 4327 including a heating resistor 320 having a resistance temperature coefficient (TCR) of 2000 ppm / ° C.

  In this embodiment, when the heater 310 is not damaged when a small-size recording material is passed, the temperature increase rate during the startup period of 5 seconds is room temperature 30 as shown in FIG. Since the temperature rises from 0 ° C. to the target temperature control temperature of 200 ° C., it becomes 34 ° C./sec. Further, the temperature increase rate for 60 seconds from the start of copying in the copy period of a small size recording material is 1.5 ° C./sec because it rises from 200 ° C. to 290 ° C. due to the temperature rise at the edge. Furthermore, the temperature decrease rate for 13 seconds from when the heater is turned off during the heater cooling period decreases from 290 ° C. to 200 ° C., and thus becomes −7 ° C./sec.

  Further, when the heater 310 is not damaged when passing a small size recording material, the resistance value during the start-up period of 5 seconds is changed from 10.66Ω (30 ° C.) to 14.28Ω (200 ° C.). To do. As a result, the rate of change in resistance per unit time during the start-up period is 0.724 Ω / sec. Further, the resistance value in the copy period of the small size recording material changes from 14.28Ω (200 ° C.) to 15.72Ω (290 ° C.) due to the temperature rise at the edge. Thus, the resistance change rate per unit time in the copy period is 0.024Ω / sec.

  FIG. 28 shows a case where the heater 310 is damaged when a small-size recording material is passed through a fixing device 4327 including a heating resistor 320 having a resistance temperature coefficient (TCR) of 2000 ppm / ° C.

  FIG. 28A shows the temperature for 55 seconds from the start of copying in the copy period detected by the thermistor 38c until the heater 310 is damaged when the heater 310 is damaged when passing a small-size recording material. As shown in FIG. Further, when the heater 310 is damaged when the small-size recording material is passed, the temperature for 11.8 seconds from the time of the failure of the heater 310 detected by the thermistor 38c is as shown in FIG. The temperature falls from 282.5 ° C. to 200 ° C.

  Accordingly, the temperature increase rate for 55 seconds from the start of copying in the copying period until the heater 310 is damaged is 1.5 ° C./sec. Further, the temperature decrease rate for 11.8 seconds from the time when the heater 310 is damaged is −7 ° C./sec. The temperature decrease rate when the heater is broken is the same as the temperature decrease rate during the heater cooling period.

  Further, when the heater 310 is damaged when a small-size recording material is passed, the resistance value for 55 seconds from the start of copying in the copy period until the heater 310 is damaged is as shown in FIG. In addition, the temperature is changed from 14.28Ω to 15.6Ω at the edge temperature rise. The rate of change in resistance at this time is 0.024 Ω / sec.

  The heater 310 is broken during the passage of the small-size recording material, and the resistance value for 500 msec from the time of breakage changes from 15.6Ω to 15.94Ω as shown in FIG. The rate of change in resistance at this time is 0.68 Ω / sec.

  Therefore, the second determination unit 4701b has a temperature change rate of −7 ° C./sec detected by the thermistor 38c on the non-feed side even though the resistance change rate is 0.68Ω / sec and larger than 0Ω / sec. Therefore, the heater 310 is determined to be abnormal.

  Usually, the heater 310 having the PTC characteristic has a characteristic that the resistance value increases as the temperature rises. When a part of the heater 310 is damaged, it is considered that the cross-sectional area A of the heater 310 is reduced, so that the resistance of the heater 310 as a whole increases from the equation (7).

R = ρ × L / A (7)
Where R is resistance
ρ is resistivity
L is full length

  On the other hand, the temperature of the portion where the thermistor 38c on the non-feed side of the heater 310 is installed is low due to a state in which an abnormality occurs and heat cannot be generated. As described above, when the temperature decreases despite the increase in the resistance value, the heater 310 can be determined to be abnormal.

  As described above, according to the present embodiment, the failure of the heater 3 is determined based on the temperature change rate and the resistance change rate on the non-power supply side, so that the heating resistor 320 is within 10 mm from the end on the non-power supply side. In the case where damage is caused by the above, the damage of the heater 310 can be determined. On the other hand, in the above case, damage to the heater 310 cannot be determined based on the resistance change rate.

  In the first to fifth embodiments, the second determination unit determines abnormality of the heating resistor, but the second determination unit determines that the heating resistor other than the abnormality of the heating resistor is in a predetermined state. May be determined, and control may be performed based on the determination result.

A image forming apparatus B image forming apparatus C image forming apparatus D image forming apparatus 1 film unit 2 pressure roller 3 heater 4 fixing film 5 film guide 6 stay 8 recording material 9 toner 10 cored bar 11 fixing nip 18 high voltage power supply 19 for charging 19 Charging roller 20 Image carrier 21 Exposure unit 22 Development unit 23 Development sleeve 24 Pre-transfer guide unit 25 Transfer roller 26 Fixing nip entrance guide 27 Fixing device 28 Cleaning blade 29 Waste toner storage unit 30 Paper width sensor 31 Thermal fuse 32 Heating resistor 33 Substrate 34 Electrode 35 Electrode 36 Power supply unit 37 Power supply unit 38 Thermistor 38a Thermistor 38b Thermistor 38c Thermistor 39 AC power supply 40 Current voltage detector 41 Triac 42 Switch 100 Operation unit 200 Image processing unit 300 Pressure roller drive unit 310 heater 320 heating resistors 327 fixing device 340 electrode 350 electrode 360 the feeding unit 370 feeding section 400 current-voltage supply unit 500 current-voltage detector 600 optical unit 700 control unit 701 CPU
701a First determination unit 701b Second determination unit 702 I / F unit 703 RAM
704 ROM
704a Pressure roller rotation control program 704b Temperature control program 704c Supply power control program 704d Resistance change rate calculation program 1000 Film unit 2000 Film unit 2327 Fixing device 2700 Control unit 2701 CPU
2701a First determination unit 2701b Second determination unit 2704a Power calculation program 2704b Temperature change rate calculation program 3327 Fixing device 3700 Control unit 3701 CPU
3701a First determination unit 3701b Second determination unit 3704a Temperature change rate calculation program 4327 Fixing device 4700 Control unit 4701 CPU
4701a First determination unit 4701b Second determination unit 4704a Resistance change rate calculation program 4704b Temperature change rate calculation program

Claims (11)

A fixing device that heats a recording material on which a toner image is formed and fixes the toner image on the recording material,
Heating means for heating the recording material with a heating resistor that generates heat upon receipt of electric power;
First determination means for determining a change state of a resistance value of the heating resistor when power is supplied to the heating resistor;
Second determination means for determining that the heating resistor is in a predetermined state based on a determination result of the first determination means;
A fixing device. The first determination means includes
The resistance change rate is determined as the change state of the resistance value,
The second determination means includes
When the determination result of the first determination means is larger than a predetermined resistance change rate, it is determined that the heating resistor is in the predetermined state, and energization to the heating resistor is cut off. The fixing device according to claim 1. The predetermined resistance change rate is:
It is the maximum value of the resistance change rate in a predetermined time when the heating means is normal.
The fixing device according to claim 2. The heating resistor is
Having PTC characteristics,
The fixing device according to any one of claims 1 to 3, wherein the fixing device is configured as described above. The heating means includes
A substrate on which the heating resistor is formed along the longitudinal direction;
Energization means for energizing the heating resistor in the longitudinal direction;
The fixing device according to any one of claims 1 to 4, further comprising: The heating means includes
A substrate on which the heating resistor is formed along the longitudinal direction;
Energization means for energizing the heating resistor in a short direction perpendicular to the longitudinal direction;
The fixing device according to any one of claims 1 to 4, further comprising: A fixing device that heats a recording material on which a toner image is formed and fixes the toner image on the recording material,
A heating resistor that generates heat upon receiving power supply and has PTC characteristics, a substrate on which the heating resistor is formed along the longitudinal direction, and a short direction perpendicular to the longitudinal direction with respect to the heating resistor Energizing means for energizing the recording medium, and heating means for heating the recording material by the heating resistor energized by the energizing means,
Temperature detecting means for detecting the temperature of the heating resistor;
First determination means for determining a temperature change state detected by the temperature detection means when power is supplied to the heating resistor;
Second determination means for determining that the heating resistor is in a predetermined state based on a determination result of the first determination means;
A fixing device. The first determination means includes
Determine the power supplied to the heating resistor,
The second determination means includes
Determining that the heating resistor is in a predetermined state based on the determination result of the power and the determination result of the temperature change state by the first determination means;
The fixing device according to claim 7. The temperature detecting means includes
Detecting the temperature of the non-feeding side and the feeding side of the heating resistor;
The first determination means includes
Determining the temperature change state of the non-power supply side and the temperature change state of the power supply side detected by the temperature detection means;
The fixing device according to claim 7. A fixing device that heats a recording material on which a toner image is formed and fixes the toner image on the recording material,
Heating means for heating the recording material with a heating resistor that generates heat upon receipt of electric power;
First determination means for determining a change state of the resistance value of the heating resistor and a change state of the temperature of the heating resistor when power is supplied to the heating resistor;
Second determination means for determining that the heating resistor is in a predetermined state based on a determination result of the first determination means;
A fixing device. Image forming means for forming a toner image;
Transfer means for transferring the toner image to the recording material;
The fixing device according to any one of claims 1 to 10, wherein the toner image transferred to the recording material by the transfer unit is fixed to the recording material.
An image forming apparatus comprising:

Images