JP2020115183A - Heating device, fixing device, and image forming apparatus - Google Patents

Abstract

To prevent a rapid increase in temperature of a heater while a fixing device has abnormality, while preventing an increase in cost and size of the device.SOLUTION: A heating device comprises: a heater 54 that has at least two or more plurality of heating elements including a heating element 54b1 having a first normal rated power and a heating element 54b2 having a second normal rated power lower than the first normal rated power; a relay 57a that switches connection of an AC power supply 55 between to the heating element 54b1 and to the heating element 54b2; a temperature fuse 107 that, when the temperature of the heater 54 is excessively increased, cuts off a power supply path between the AC power supply 55 and the heater 54 to cut off power supply; and an operational amplifier 207 that detects an excessive increase in temperature of the heater 54. When the excessive increase in temperature of the heater 54 is detected by the operational amplifier 207, the relay 57a connects the AC power supply 55 to the heating element 54b2.SELECTED DRAWING: Figure 4

Description

The present invention relates to a heating device, a fixing device, and an image forming apparatus, and relates to prevention of excessive temperature rise of a heating device for fixing a toner image formed by an electrophotographic process on a recording material.

2. Description of the Related Art In image forming apparatuses such as copying machines and printers that use an electrophotographic method, a fixing device that heats toner transferred onto a recording material to fix the toner image on the recording material is widely used. The fixing device includes a heating unit that is a heat source, a power supply that supplies electric power to the heating unit, a temperature detection unit that detects the temperature in the vicinity of the heating unit, and a control unit that controls the electric power supplied to the heating unit. In many cases.

If any one of the heating means, the temperature detection means, and the control means that configure the fixing device does not function normally, the fixing device cannot be controlled normally, and as a result, the heating element, which is the heating device, cannot be controlled. This may cause excessive temperature rise and may damage the fixing device. Therefore, generally, an excessive temperature rise prevention unit having an abnormality detection unit and a unit for cutting off the power supply is provided, and when the fixing device detects an abnormality leading to an excessive temperature rise, the electric power is not supplied to the heating unit. The operation of shutting off is executed.

By the way, as a method of improving the reliability of a fixing device having an excessive temperature rise prevention means, a configuration is provided in which the temperature rise when the heating means has an excessive temperature rise is moderated and the time until the excessive temperature rise prevention means operates is secured. Is proposed. For example, in Patent Document 1, when an abnormal temperature rise of a heater that is a heating unit is detected, the fixing nip in the fixing device is always brought into a contact state, and the heater is brought into contact with a pressure roller that is a heat dissipation member. A configuration has been proposed in which the temperature rise of the heater is moderated.

Patent No. 5528194

However, the above-mentioned conventional technique requires a contact/separation mechanism including a motor for contacting/separating the fixing nip portion, but many fixing devices do not have such a mechanism. Therefore, by newly providing such a contacting/separating mechanism in the fixing device, the cost of the fixing device is increased and a space for installing the contacting/separating mechanism is required, which causes a problem that the device is upsized.

The present invention has been made under such circumstances, and an object thereof is to suppress a rapid temperature rise of the heater when the fixing device is abnormal while suppressing the cost increase and the size increase of the device.

In order to solve the problems described above, the present invention has the following configurations.

(1) At least two or more heating elements including a first heating element having a first rated power and a second heating element having a second rated power lower than the first rated power And a switching unit for switching the connection between the first heating element or the second heating element and the power source, and the power source and the heater section when the heater section overheats. And an abnormality detecting unit for detecting an excessive temperature rise of the heater unit. The abnormality detecting unit prevents the excessive temperature rise of the heater unit. When detected, the switching unit connects the power source and the second heating element to each other.

(2) A first heating element in which the thermal stress to the heater becomes the first thermal stress during heat generation, and a second thermal stress in which the thermal stress to the heater during the heat generation becomes second thermal stress smaller than the first thermal stress. A heater section having at least two or more heating elements including a heating element; a switching section for switching connection between the first heating element or the second heating element and a power source; and the heater section. When the temperature rises excessively, a power supply path between the power source and the heater unit is cut off, a shutoff unit that shuts off the power supply, and an abnormality detection unit that detects an excessive temperature rise of the heater unit. The heating device, wherein the switching unit connects the power source and the second heating element when the abnormality detecting unit detects an excessive temperature rise in the heater unit.

(3) A fixing device for fixing an unfixed toner image carried on a recording material, the heating device according to (1) or (2), and a first rotation heated by the heating device. A fixing device comprising: a body; and a second rotating body that forms a nip portion together with the first rotating body.

(4) An image forming apparatus comprising: an image forming unit that forms an image on a recording material; and the fixing device described in (3) above.

According to the present invention, it is possible to suppress an abrupt temperature increase of the heater when the fixing device is abnormal, while suppressing an increase in cost and an increase in size of the device.

Overall configuration diagram of the image forming apparatus of Examples 1 to 3 Control block diagram of the image forming apparatus of Embodiments 1 to 3 Schematic cross-sectional view of the vicinity of the central portion in the longitudinal direction of the fixing device of Examples 1 to 3. 1 is an overall schematic diagram showing a circuit configuration of a fixing device of Embodiment 1, and a sectional view of a heater. FIG. 3 is a diagram showing a temperature profile when the fixing device of Example 1 is in an abnormal state. An overall schematic diagram showing a circuit configuration of a fixing device of Embodiment 2. FIG. 6 is a diagram showing a temperature profile when the fixing device of Example 2 is in an abnormal state. 3 is an overall schematic diagram showing a circuit configuration of a fixing device of Embodiment 3. FIG. FIG. 6 is a diagram showing a temperature profile and a thermal stress characteristic when the fixing device of Example 3 is abnormal. 3 is an overall schematic diagram showing a circuit configuration of a fixing device of Embodiment 3. FIG. An overall schematic diagram showing a circuit configuration of a fixing device of Embodiment 4. FIG. 8 is a diagram showing a temperature profile when the fixing device of Example 4 has an abnormality.

Embodiments of the present invention will be described below with reference to the drawings.

[overall structure]
FIG. 1 is a configuration diagram illustrating an in-line type color image forming apparatus, which is an example of an image forming apparatus including the fixing device according to the first exemplary embodiment. The operation of the electrophotographic color image forming apparatus will be described with reference to FIG. The first station is a station for forming a yellow (Y) toner image, and the second station is a station for forming a magenta (M) toner image. Further, the third station is a station for forming a cyan (C) color toner image, and the fourth station is a station for forming a black (K) color toner image.

In the first station, the photosensitive drum 1a which is the image carrier is an OPC photosensitive drum. The photosensitive drum 1a is formed by laminating a plurality of functional organic materials, such as a carrier generation layer that generates an electric charge upon exposure to light on a metal cylinder, a charge transport layer that transfers the generated electric charge, and the outermost layer is an electrical layer. It has low conductivity and is almost insulating. The charging roller 2a, which is a charging unit, is brought into contact with the photosensitive drum 1a, and is not driven to rotate as the photosensitive drum 1a rotates, so that the surface of the photosensitive drum 1a is uniformly charged. A voltage in which a DC voltage or an AC voltage is superimposed is applied to the charging roller 2a, and discharge is generated from a nip portion between the charging roller 2a and the surface of the photosensitive drum 1a in a minute air gap on the upstream side and the downstream side in the rotation direction. As a result, the photosensitive drum 1a is charged. The cleaning unit 3a is a unit that cleans the toner remaining on the photosensitive drum 1a after transfer, which will be described later. The developing unit 8a, which is a developing unit, includes a developing roller 4a, a non-magnetic one-component toner 5a, and a developer coating blade 7a. The photosensitive drum 1a, the charging roller 2a, the cleaning unit 3a, and the developing unit 8a are an integral type process cartridge 9a that is detachable from the image forming apparatus.

The exposure device 11a, which is an exposure unit, is composed of a scanner unit or an LED (light emitting diode) array for scanning a laser beam with a polygon mirror, and irradiates the photosensitive drum 1a with a scanning beam 12a modulated based on an image signal. Further, the charging roller 2a is connected to a charging high voltage power source 20a which is a means for supplying a voltage to the charging roller 2a. The developing roller 4a is connected to a developing high voltage power source 21a which is a voltage supplying means for the developing roller 4a. The primary transfer roller 10a is connected to a primary transfer high voltage power source 22a which is a voltage supply means for the primary transfer roller 10a. The above is the configuration of the first station, and the second, third, and fourth stations have the same configuration. With respect to the other stations, parts having the same functions as those of the first station are designated by the same reference numerals, and the suffixes of the reference numerals are denoted by b, c, d for each station. In the following description, the subscripts a, b, c, d will be omitted unless a specific station is described.

The intermediate transfer belt 13 is supported by three rollers of a secondary transfer counter roller 15, a tension roller 14, and an auxiliary roller 19 as a stretching member. Only the tension roller 14 is applied with a spring (not shown) in a direction to stretch the intermediate transfer belt 13, so that an appropriate tension force is maintained on the intermediate transfer belt 13. The secondary transfer counter roller 15 is rotated by receiving a rotational drive from a main motor (not shown), and the intermediate transfer belt 13 wound around the outer periphery is rotated. The intermediate transfer belt 13 moves at substantially the same speed in the forward direction (eg, clockwise direction in FIG. 1) with respect to the photosensitive drums 1a to 1d (eg, counterclockwise rotation in FIG. 1). Further, the intermediate transfer belt 13 rotates in the direction of the arrow (clockwise direction), and the primary transfer roller 10 is arranged on the opposite side of the photosensitive drum 1 with the intermediate transfer belt 13 interposed therebetween. Along with it, it rotates. A position where the photosensitive drum 1 and the primary transfer roller 10 are in contact with each other with the intermediate transfer belt 13 interposed therebetween is referred to as a primary transfer position. The auxiliary roller 19, the tension roller 14, and the secondary transfer counter roller 15 are electrically grounded. The primary transfer rollers 10b to 10d of the second to fourth stations have the same structure as the primary transfer roller 10a of the first station, and therefore the description thereof will be omitted.

Next, the image forming operation of the image forming apparatus of the first embodiment will be described. When the image forming apparatus receives the print command in the standby state, it starts the image forming operation. The photosensitive drum 1, the intermediate transfer belt 13 and the like start to rotate in the arrow direction at a predetermined process speed by a main motor (not shown). The photosensitive drum 1a is uniformly charged by the charging roller 2a to which a voltage is applied by the charging high-voltage power source 20a, and then an electrostatic latent image according to image information is formed by the scanning beam 12a emitted from the exposure device 11a. To be done. The toner 5a in the developing unit 8a is negatively charged by the developer coating blade 7a and is coated on the developing roller 4a. Then, a predetermined developing voltage is supplied to the developing roller 4a from the developing high voltage power source 21a. When the photosensitive drum 1a rotates and the electrostatic latent image formed on the photosensitive drum 1a reaches the developing roller 4a, the electrostatic latent image is visualized by the negative toner adhering to the photosensitive drum 1a. A toner image of the first color (for example, Y (yellow)) is formed. The other color M (magenta), C (cyan), and K (black) stations (process cartridges 9b to 9d) operate in the same manner. An electrostatic latent image by exposure is formed on each of the photosensitive drums 1a to 1d while delaying a writing signal from a controller (not shown) at a constant timing according to the distance between the primary transfer positions of the respective colors. A DC high voltage having a polarity opposite to that of the toner is applied to each of the primary transfer rollers 10a to 10d. Through the above steps, the toner images are sequentially transferred to the intermediate transfer belt 13 (hereinafter referred to as primary transfer), and a multiple toner image is formed on the intermediate transfer belt 13.

Thereafter, in accordance with the formation of the toner image, the paper P which is the recording material loaded in the cassette 16 is fed (picked up) by the paper feed roller 17 which is rotationally driven by a paper feed solenoid (not shown). .. The fed paper P is conveyed to a registration roller (hereinafter referred to as a registration roller) 18 by a conveyance roller. The sheet P is conveyed to the transfer nip portion, which is a contact portion between the intermediate transfer belt 13 and the secondary transfer roller 25, by the registration roller 18 in synchronization with the toner image on the intermediate transfer belt 13. A voltage having a polarity opposite to that of the toner is applied to the secondary transfer roller 25 by the secondary transfer high-voltage power supply 26, and the multicolor toner images of four colors carried on the intermediate transfer belt 13 are collectively printed on the paper P (recording). (On the material) (hereinafter referred to as secondary transfer). The member (for example, the photosensitive drum 1) that has contributed until the unfixed toner image is formed on the sheet P functions as an image forming unit. On the other hand, the toner remaining on the intermediate transfer belt 13 after the secondary transfer is finished is cleaned by the cleaning unit 27. After the secondary transfer is completed, the paper P is conveyed to a fixing device 50 that is a fixing unit, receives the fixing of the toner image, and is discharged to the discharge tray 30 as an image formed product (print, copy). The film 51, the nip forming member 52, the pressure roller 53, and the heater 54 of the fixing device 50 will be described later.

[Block diagram of image forming apparatus]
FIG. 2 is a block diagram for explaining the operation of the image forming apparatus, and the printing operation of the image forming apparatus will be described with reference to this figure. The PC 110, which is a host computer, is responsible for outputting a print command to the video controller 91 inside the image forming apparatus and transferring the image data of the print image to the video controller 91.

The video controller 91 converts the image data from the PC 110 into exposure data and transfers it to the exposure control device 93 in the engine controller 92. The exposure control device 93 is controlled by the CPU 94, and controls the exposure device 11 that turns on/off the laser light according to the exposure data. Upon receiving the print command, the CPU 94, which is the control means, starts the image forming sequence.

The engine controller 92 is equipped with a CPU 94, a memory 95, etc., and performs a preprogrammed operation. The high voltage power source 96 is composed of the charging high voltage power source 20, the developing high voltage power source 21, the primary transfer high voltage power source 22, and the secondary transfer high voltage power source 26 described above. Further, the power control unit 97 includes a bidirectional thyristor (hereinafter referred to as a triac) 56, a heating element switch 57 as a switching section that exclusively selects a heating element to supply power, and the like. The power control unit 97 selects a heating element that generates heat in the fixing device 50 and determines the amount of power to be supplied. The drive device 98 is composed of a main motor 99, a fixing motor 100 and the like. The sensor 101 includes a fixing temperature sensor 59 for detecting the temperature of the fixing device 50, a paper presence sensor 102 having a flag for detecting the presence or absence of the paper P, and the detection result of the sensor 101 is transmitted to the CPU 94. The CPU 94 acquires the detection result of the sensor 101 in the image forming apparatus, and controls the exposure device 11, the high-voltage power supply 96, the power control unit 97, and the drive device 98. As a result, the CPU 94 forms an electrostatic latent image, transfers the developed toner image, fixes the toner image on the paper P, and the like, and in the image forming process in which the exposure data is printed on the paper P as a toner image. Take control. The image forming apparatus to which the present invention is applied is not limited to the image forming apparatus having the configuration described with reference to FIG. 1, it is possible to print the paper P having different widths, and has the heater 54 described later. Any image forming apparatus including the fixing device 50 may be used.

[Configuration of fixing device]
Next, the configuration of the fixing device 50 according to the first exemplary embodiment that controls the heating device that heats the toner image on the sheet P by the heating element will be described with reference to FIG. Here, the longitudinal direction is a rotation axis direction of the pressure roller 53 that is substantially orthogonal to a conveyance direction of the sheet P described later. The length of the paper P in the direction (longitudinal direction) substantially orthogonal to the transport direction is called the width. FIG. 3 is a schematic sectional view of the fixing device 50. The sheet P holding the unfixed toner image Tn from the left side of FIG. 3 is heated while being conveyed from the left side to the right side in the figure in the fixing nip portion N, so that the toner image Tn is fixed to the sheet P. The fixing device 50 according to the first exemplary embodiment includes a cylindrical film 51, a nip forming member 52 that holds the film 51, a pressure roller 53 that forms a fixing nip portion N together with the film 51, and a sheet P for heating. And a heater 54.

The film 51 (first rotating body) is a fixing film as a heating rotating body. In Example 1, for example, polyimide is used as the base layer. An elastic layer made of silicone rubber and a release layer made of PFA are used on the base layer. In order to reduce the frictional force generated between the film 51 and the nip forming member 52 and the heater 54 due to the rotation of the film 51, grease is applied to the inner surface of the film 51.

The nip forming member 52 plays a role of guiding the film 51 from the inside and forming a fixing nip portion N between the film 51 and the pressure roller 53. The nip forming member 52 is a member having rigidity, heat resistance, and heat insulation, and is made of liquid crystal polymer or the like. The film 51 is fitted onto the nip forming member 52. The pressure roller 53 (second rotary body) is a roller as a pressure rotary body. The pressure roller 53 includes a core metal 53a, an elastic layer 53b, and a release layer 53c. The pressure roller 53 is rotatably held at both ends, and is rotationally driven by the fixing motor 100 (see FIG. 2). Further, the film 51 is driven to rotate by the rotation of the pressure roller 53. The heater 54, which is a heating member, is held by the nip forming member 52 and is in contact with the inner surface of the film 51. The heater 54 and the fixing temperature sensor 59 will be described later.

[Circuit configuration of fixing device]
FIG. 4 is a diagram showing an overall schematic view of the fixing device 50 of this embodiment. FIG. 4A is an overall schematic diagram showing the circuit configuration of the fixing device 50. The heater 54, which is a heating unit, receives power supplied from the AC power supply 55 and generates heat. The heater 54, which is a heater unit, mainly has heat generating elements 54b1 and 54b2, contacts 54d1, 54d3 and 54d4, and a protective glass layer 54e formed on a substrate 54a. The heating elements 54b1 and 54b2 are resistors that generate heat when power is supplied from the AC power supply 55. The protective glass layer 54e is provided to insulate the user from the heating elements 54b1 and 54b2 having substantially the same potential as the AC power supply 55. The heating element 54b1, which is the first heating element, is a heating element that is mainly used when fixing the toner on the sheet P having the maximum sheet width that can be passed through the fixing device 50. Therefore, the length of the heating element 54b1 in the longitudinal direction is set to be several mm longer than the LTR (letter) size paper width 215.9 mm. The heating element 54b2, which is the second heating element, is a heater mainly for heating the paper P having a width narrower than that of the heating element 54b1, and the length of the heating element 54b2 in the longitudinal direction is A4 size. The paper width is set to be several mm longer than 210 mm. The fixing device 50 mainly causes the heating element 54b1 to generate heat in order to raise the fixing device 50 from a cooled state to a predetermined temperature at the time of startup. Then, the fixing device 50 switches the heating element to be used to the heating element 54b1 or the heating element 54b2 in accordance with the paper width of the sheet of paper P to be used, when the fixing device 50 is in a steady state of rising to a predetermined temperature. The rated power of the heating element 54b1 is set to be higher than the rated power of the heating element 54b2.

The heating element 54b1 is a pair of heating elements having substantially the same length in the longitudinal direction (vertical direction in FIG. 4A). On the other hand, the heating element 54b2 is also a pair of heating elements having substantially the same length in the longitudinal direction, but the heating element 54b1 has a longer length in the longitudinal direction than the heating element 54b2. Further, the heat generating element 54b1, the heat generating element 54b2, the heat generating element 54b2, and the heat generating element 54b1 are arranged in this order in the lateral direction of the substrate 54a (from left to right in FIG. 4A).

FIG. 4B is a cross-sectional view showing a cross section of the heater 54 of the fixing device 50 taken along the line P-P′ shown in FIG. On the surface of the substrate 54a opposite to the surface on which the heating elements 54b1 and 54b2 are installed, a temperature fuse 107, which is an excessive temperature rise detection unit, is installed in a range where the paper P having the minimum paper width that can be passed through passes. Has been done. On the other hand, FIG. 4C is a cross-sectional view showing a cross section of the heater 54 of the fixing device 50 taken along the line Q-Q′ shown in FIG. On the surface of the substrate 54a opposite to the surface on which the heating elements 54b1 and 54b2 are installed, a fixing temperature sensor 59, which is a temperature detecting means, is installed in a range where the paper P having the minimum paper width that can be passed through passes. ing. In this embodiment, the fixing temperature sensor 59 uses a thermistor. As shown in FIGS. 4B and 4C, the temperature fuse 107 and the fixing temperature sensor 59 are installed in contact with the substrate 54a, and detect the temperatures of the heating elements 54b1 and 54b2 via the substrate 54a. The thermal fuse 107 electrically connects the AC power supply 55 and the heater 54. When the temperature of the thermal fuse 107 exceeds a predetermined temperature, the contacts inside the thermal fuse 107 are opened. As a result, the safety of the fixing device 50 is ensured by cutting off the power supply path from the AC power supply 55 to the heater 54 to cut off the power supply. The fixing temperature sensor 59 has one end connected to the DC voltage Vcc1 of 3.3V and the other end connected to the resistor 202. Then, the voltage V_TH obtained by dividing the DC voltage Vcc1 by the fixing temperature sensor 59 and the resistor 202 is input to the CPU 94.

The contact 54d1 to which the heating elements 54b1 and 54b2 are connected, the contact 54d3 to which the heating element 54b2 is connected, and the contact 54d4 to which the heating element 54b1 are connected are connected to the circuit that controls the fixing device 50 shown in FIG. 4A. ing. The contact 54d3 is connected to the contact 57a3 of the relay 57a having the c-contact structure, and the contact 54d4 is connected to the contact 57a4. The relay 57a, which is the heating element switching device 57, is a relay having a C contact structure, and has a coil portion 57a2 and contacts 57a1, 57a3, 57a4. The coil portion 57a2 has one terminal connected to the DC voltage Vcc2 of 24V and the other terminal connected to the collector terminal of the transistor 204. When the CPU 94 outputs the Drive2 signal of high level, the diode 206 becomes conductive, and the base current flows to the base terminal of the transistor 204 through the resistor 205. As a result, the voltage between the collector terminal and the emitter terminal of the transistor 204 becomes a saturation voltage of about 0.2 to 0.3 V, and the transistor 204 is turned on. When the transistor 204 is turned on, a collector current flows, a potential difference is generated across the coil portion 57a2, a current flows through the coil portion 57a2, and the magnetic force generated in the coil portion 57a2 connects the contact 57a1 to the contact 57a3. Hereinafter, this state is referred to as the ON state of the relay 57a.

On the other hand, when the CPU 94 outputs the low level Drive2 signal, the diode 206 is non-conductive, and the base current does not flow to the base terminal of the transistor 204. Therefore, the transistor 204 is not turned on, and no potential difference is generated across the coil portion 57a2. As a result, no current flows through the coil portion 57a2 and no magnetic force is generated, so that the contact 57a1 is connected to the contact 57a4. Hereinafter, this state is referred to as the OFF state of the relay 57a. That is, by the operation of the relay 57a having the c-contact structure, the contact 57a1 is connected to the contact 57a3 when the relay 57a is in the ON state, and power is supplied from the AC power supply 55 to the heating element 54b2 via the contact 54d3 and the contact 54d1. .. On the other hand, when the relay 57a is in the OFF state, the contact 57a1 is connected to the contact 57a4, and the AC power supply 55 supplies power to the heating element 54b1 via the contacts 54d4 and 54d1.

The CPU 94 controls the triac 56a, which is a supply control unit, so that the fixing temperature sensor 59 reaches a predetermined target temperature based on the input temperature information from the voltage V_TH of the fixing temperature sensor 59. Specifically, when the CPU 94 outputs a high level Drive1 signal, a base current flows to the base terminal of the transistor 225 via the current limiting resistor 226, whereby the transistor 225 turns on and a collector current flows. When the collector current of the transistor 225 flows, the light emitting diode of the phototriac coupler 221 becomes conductive, the current flows through the resistor 224, the light emitting diode emits light, and the light receiving portion of the phototriac coupler 221 becomes conductive. When the light receiving side of the phototriac coupler 221 becomes conductive, a gate trigger current flows between the T1 terminal and the G terminal of the triac 56a via the current limiting resistor 222, and the T1 terminal and T2 terminal of the triac 56a become conductive.

On the other hand, when the CPU 94 outputs the low level Drive1 signal, the base current does not flow to the base terminal of the transistor 225, and the transistor 225 does not turn on. As a result, the light emitting diode of the phototriac coupler 221 does not emit light, and the light receiving portion of the phototriac coupler 221 becomes non-conductive. Then, the gate trigger current of the triac 56a does not flow, and the T1 terminal and the T2 terminal of the triac 56a become non-conductive. The CPU 94 controls the relay 57a based on the paper width information of the paper P to switch the heating element to which power is supplied. Then, the CPU 94 controls the triac 56a based on the temperature information detected by the fixing temperature sensor 59 to control the temperature of the fixing device 50.

[Thermal fuse]
However, for example, when a failure such as a short circuit between the T1 terminal and the T2 terminal of the triac 56a occurs, the power supply from the AC power supply 55 to the heater 54 cannot be controlled. As a result, the temperature of the heater 54 cannot be controlled to the target temperature, resulting in a thermal runaway state. In such a case as well, the fixing device 50 is provided with an excessive temperature rise detection unit so that the fixing device 50 is not significantly damaged. In this embodiment, the temperature fuse 107 includes the excessive temperature rise detection unit. Becomes The temperature fuse 107, which also serves as a breaking unit, melts the internal pellets when the temperature rises above about 205° C., for example, and when a predetermined amount of pellets melts, the contacts inside the thermal fuse 107 change from the short-circuited state to the open state. As a result, the power supply from the AC power supply 55 to the heater 54 is cut off, and the thermal runaway state described above is eliminated.

[Abnormality detection part and route switching part]
By the way, in the process in which heat is transferred from the substrate 54a to the thermal fuse 107, it takes a certain amount of time for the temperature to be transferred to the pellets in the thermal fuse 107 due to the heat capacity of the thermal fuse 107. In addition, it takes a certain amount of time from the start of melting of the pellet to the melting of a predetermined amount. That is, even if the heater 54 overheats due to thermal runaway, the thermal fuse 107 operates immediately and the contacts are not opened. In order to ensure the safety of the fixing device 50 even if there is such a time lag, the fixing device 50 according to the present exemplary embodiment includes an operational amplifier 207 that is an abnormality detecting unit (also an abnormality detecting unit) and a path switching. It is equipped with a relay 57a as a part. In the operational amplifier 207, the voltage V_TH indicating the temperature detected by the fixing temperature sensor 59 is input to the non-inverting input terminal (+), and the reference voltage generated by the reference voltage generating unit 208 is input to the inverting input terminal (−). It Since the fixing temperature sensor 59 has an NTC characteristic in which the resistance value decreases as the temperature increases, the voltage V_TH input to the non-inverting input terminal (+) increases as the temperature detected by the fixing temperature sensor 59 increases. Get higher In this embodiment, the resistance value of the resistor 202 is selected so that the voltage V_TH becomes 2.5 V when the detection temperature of the fixing temperature sensor 59 is 180° C. The reference voltage generation unit 208 also generates a DC voltage of 2.5 V as a reference voltage. The voltage of the DC voltage Vcc2 of the operational amplifier 207 is DC hV. When the temperature of the fixing temperature sensor 59 is lower than 180° C., that is, when the voltage V_TH is lower than 2.5V, the output of the operational amplifier 207 is 0V which is substantially equal to the GND potential. In this case, the diode 209 is non-conducting and therefore the transistor 204 will be controlled only by the Drive2 signal. On the other hand, when the temperature of the fixing temperature sensor 59 is 180° C. or higher, that is, when the voltage V_TH is 2.5 V or higher, the output of the operational amplifier 207 is 24 V, which is substantially equal to the DC voltage Vcc2. In this case, the diode 209 becomes conductive, the base current flows through the resistor 210 to the base terminal of the transistor 204, and the relay 57a is turned on. Note that, when the output of the operational amplifier 207 outputs approximately 24 V by the diode 206, the base current is continuously supplied to the base terminal of the transistor 204 regardless of whether the Drive2 signal is at the high level or the low level. Therefore, when the temperature detected by the fixing temperature sensor 59 is 180° C. or higher (above a predetermined temperature), which is an abnormal temperature for the fixing device 50, the contact 57a1 of the relay 57a, which is a path switching unit, is connected to the contact 54a3 side. To be done.

[Temperature profile when the fixing device is abnormal]
FIG. 5 shows the temperature of the fixing temperature sensor 59 with the lapse of time until the fixing device 50 is in a thermal runaway state and the power supply from the AC power supply 55 to the heater 54 is cut off by the abnormality detection unit or the excessive temperature rise detection unit. It is a figure which shows a characteristic (temperature profile).

FIG. 5A is a diagram showing a temperature profile of the fixing temperature sensor 59 of the fixing device 50 of the present embodiment including the above-described abnormality detecting unit and path switching unit. In FIG. 5A, the horizontal axis represents time (unit: sec (second)), and the vertical axis represents the temperature detected by the fixing temperature sensor 59 (unit: °C). Further, t0 to t4 indicate time (timing).

In FIG. 5A, from time 0 to time t0, power is supplied from the AC power supply 55 to the heater 54 in the cooling state of the fixing device 50, and the fixing temperature is from 30° C. at room temperature to 160° C. which is the target temperature. It shows how the temperature detected by the sensor 59 rises. Next, during the period from time t0 to time t1, the temperature of the fixing temperature sensor 59 is controlled to 160° C. while controlling the power supply to the heating element 54b1. Time t1 is the timing at which a thermal runaway of the heater 54 has started due to a failure such as a short circuit between the T1 terminal and the T2 terminal of the triac 56a. When the thermal runaway of the heater 54 starts, the temperature of the fixing temperature sensor 59 rapidly rises. When the temperature detected by the fixing temperature sensor 59 reaches 180° C. at time t2, as described above, when the operational amplifier 207, which is the abnormality detecting unit, detects an abnormality in the temperature detected by the fixing temperature sensor 59, the relay 57a is turned on. Become. Then, the power supply destination from the AC power supply 55 is switched from the heating element 54b1 to the heating element 54b2. As described above, since the heating element 54b2 has a lower rated power than the heating element 54b1, the temperature rise at the time of thermal runaway becomes gentle. Time t3 is the timing when the pellet of the thermal fuse 107 starts melting. At time t4 after the period td_1 has elapsed from time t3 (after a predetermined time or more has elapsed), the contacts inside the thermal fuse 107 are opened, and the power supply from the AC power supply 55 to the heater 54 is cut off. As a result, the temperature of the heater 54 is gradually lowered, and the safety of the fixing device 50 is ensured.

For comparison with FIG. 5A, FIG. 5B is a diagram showing a temperature profile of the fixing temperature sensor 59 of the fixing device of the present embodiment which does not include the abnormality detecting unit and the path switching unit. is there. In FIG. 5B, the horizontal axis represents time (unit: sec (second)), and the vertical axis represents the temperature detected by the fixing temperature sensor 59 (unit: °C). Further, t0 to t2, t5, and t6 indicate time (timing).

5B, from time 0 to time t2, the temperature profile of the fixing temperature sensor 59 changes in the same manner as in FIG. 5A. At time t2 when the temperature detected by the fixing temperature sensor 59 reaches 180° C., the fixing device does not include the abnormality detecting unit and the path switching unit, and therefore the slope of the temperature rise does not become gentle. Therefore, at a time t5 earlier than the time t3 in FIG. 5A, the fixing temperature sensor 59 reaches 205° C., and the pellet of the thermal fuse 107 starts melting. Then, at time t6 when the period td_2 seconds has elapsed from time t5, the contacts inside the thermal fuse 107 are opened, and the power supply from the AC power supply 55 to the heater 54 is cut off. The thermal capacity of the temperature fuse 107 is sufficient for the temperature change from time t3 to time t4 (in the case of FIG. 5A) and the temperature change from time t5 to time t6 (in the case of FIG. 5B). Since they are large, the period td_1 and the period td_2 have substantially the same time width. At time t6, the contacts inside the thermal fuse 107 are opened, and after the power supply to the heater 54 is cut off, the temperature of the heater 54 gradually decreases, and the safety of the fixing device 50 is ensured. In the case of FIG. 5B, the temperature of the fixing temperature sensor 59 has reached 260° C. at time t6. On the other hand, in the case of FIG. 5A, the temperature of the fixing temperature sensor 59 is 220° C. at time t4. That is, the fixing device 50 of the present embodiment including the abnormality detecting unit and the path switching unit raises the temperature of the heater 54 by 40° C. (=260° C.) as compared with the case where the fixing device 50 does not include the abnormality detecting unit and the path switching unit. (−220° C.), the damage to the fixing device 50 can be reduced.

As described above, by using the fixing temperature sensor 59 and the relay 57a in order to detect the abnormality and switch the path, it is possible to minimize the cost increase and the size increase of the apparatus. Furthermore, when an abnormality is detected, the power supply destination is switched to the heating element having a low rated power, whereby the temperature rise of the heater is moderated and damage to the fixing device 50 at the time of excessive temperature rise can be minimized. .. The abnormality detection unit may be provided with a latch function or a hysteresis function so that the abnormality detection is not canceled even if the temperature of the fixing temperature sensor 59 is once detected to be lower than 180° C. after once exceeding the abnormality detection temperature. Good. Further, even if a component having the same function as the component of the present embodiment is used, such as a thermoswitch used in place of the temperature fuse 107 and a thermopile used in place of the thermistor used in the fixing temperature sensor 59, The effect of the embodiment does not change.

As described above, according to the present embodiment, it is possible to suppress an increase in the temperature of the heater when the fixing device is abnormal while suppressing an increase in cost and an increase in size of the device.

In the first embodiment, an example of a heater having two types of pair of heating elements has been described. In Example 2, an example of a heater having three types of heating elements will be described.

[Circuit configuration of fixing device]
FIG. 6 is an overall schematic diagram showing a circuit configuration of the fixing device 50. The heater 54 includes a heating element 54b1, a heating element 54b3, and a heating element 54b4. The heating element 54b1 which is the first heating element is a pair of main heating elements similar to the heating element used in the first embodiment, and the description thereof is omitted here. Both the heating element 54b3 and the heating element 54b4 are sub heating elements, and are heating elements that assist the function of the main heating element 54b1. The heating element 54b3, which is the second heating element, is a heating element suitable for fixing the sheet P having a sheet width of about B5. On the other hand, the heating element 54b4, which is the third heating element, is a heating element suitable for fixing the sheet P having a sheet width of about A5, and is mainly used for heating the sheet P having a sheet width smaller than A5. .. Similar to the first embodiment, the fixing device 50 mainly causes the heating element 54b1 to generate heat in order to raise the fixing device 50 from a cooled state to a predetermined temperature at startup. When the temperature rises to a predetermined temperature and reaches a steady state, the heating element to be used is switched to the heating element 54b1, the heating element 54b3, or the heating element 54b4 according to the paper width of the sheet P to be used. The rated power of the heating element 54b1 is set to be higher than the rated power of the heating elements 54b3 and 54b4.

The heating element 54b1 is a pair of heating elements having substantially the same length in the longitudinal direction (vertical direction in FIG. 6). Regarding the lengths in the longitudinal direction of the heating elements 54b1, 54b3, 54b4, the heating element 54b1 has the longest length, the heating element 54b3 has the longest length, and the heating element 54b4 has the shortest length. Further, the heat generating element 54b1, the heat generating element 54b4, the heat generating element 54b3, and the heat generating element 54b1 are arranged in this order in the lateral direction of the substrate 54a (from left to right in FIG. 6).

The contact point 54d1 to which the heating elements 54b1 and 54b3 are connected, the contact point 54d2 to which the heating element 54b4 is connected, the contact point 54d3 to which the heating element 54b3 is connected, and the contact point 54d4 to which the heating elements 54b1 and 54b4 are connected are the fixing elements shown in FIG. It is connected to the circuitry that controls the device 50. The contact 54d1 which is the first contact is connected to the contact 57b3 of the relay 57b having the c-contact structure, and the contact 54d2 which is the second contact is connected to the contact 57b4 of the relay 57b. On the other hand, the contact 54d3, which is the third contact, is connected to the contact 57a3 of the relay 57a having the c-contact structure, and the contact 54d4, which is the fourth contact, is connected to the contact 57a4 of the relay 57a.

The operation of the relay 57a, which is the first relay, controlled by the Drive2 signal output from the CPU 94 is the same as that in the first embodiment, and the description thereof is omitted here. The second relay 57b is a relay having a c-contact structure similar to that of the relay 57a, and has a coil portion 57b2 and contacts 57b1, 57b3, 57b4. The relays 57a and 57b are the heating element switch 57. The coil portion 57b2 has one terminal connected to the DC voltage Vcc2 of 24V and the other terminal connected to the collector terminal of the transistor 301. When the Drive3 signal output from the CPU 94 is at a low level, the diode 303 is in a non-conducting state, current does not flow to the base terminal of the transistor 301, and the transistor 301 is in an off state. Therefore, since no current flows through the coil portion 57b2, the contact 57b1 of the relay 57b is connected to the contact 57b3. Hereinafter, this state is referred to as an off state of the relay 57b. On the other hand, when the Drive3 signal output from the CPU 94 is at a high level, the diode 303 becomes conductive and a base current flows to the base terminal of the transistor 301 via the current limiting resistor 302. As a result, the collector-emitter voltage of the transistor 301 becomes a saturation voltage of about 0.2 to 0.3 V, and the transistor 301 is turned on. When the transistor 301 is turned on, a collector current flows, a potential difference is generated across the coil portion 57b2, and a current flows through the coil portion 57b2. When a current flows through the coil portion 57b2, the magnetic force generated in the coil portion 57b2 connects the contact 57b1 to the contact 57b4. Hereinafter, this state is referred to as the ON state of the relay 57b. In the initial setting of the fixing device 50, both the Drive2 signal and the Drive3 signal output from the CPU 94 are set to the low level, and the power supply path from the AC power supply 55 to the heating element 54b1 is selected.

In this way, the CPU 94 selects an appropriate heating element according to the sheet width based on the sheet width information of the sheet P, and the relay 57a, so that the selected heating element is supplied with power from the AC power supply 55. The relay 57b is controlled to switch the contact to be connected. The control of the fixing temperature sensor 59 and the triac 56a of the CPU 94, which is performed based on the temperature information of the fixing temperature sensor 59, is the same as that of the first embodiment, and the description thereof is omitted here.

[Power detector]
The power detection unit 400 includes a voltage detection unit 401, a current detection unit 402, and a power effective value calculation unit 403. The voltage detection unit 401 detects the AC voltage value input from the AC power supply 55 to the heater 54. The current detector 402 detects the value of the current supplied from the AC power supply 55 to the heater 54. The voltage value detected by the voltage detection unit 401 and the current value detected by the current detection unit 402 are output to the effective power value calculation unit 403. The power effective value calculation unit 403, which is the power value calculation unit, calculates the power effective value from the voltage value and the current value detected by the voltage detection unit 401 and the current detection unit 402, and calculates the calculated power effective value as the rms signal. It is transmitted to the CPU 94. When activating the fixing device 50, the CPU 94 controls the triac 56a based on the rms signal instead of the temperature information of the fixing temperature sensor 59 so that the power supplied to the heater 54 becomes a constant value. Even when the output voltage of the AC power supply 55 varies depending on the installation environment of the apparatus (for example, 100 V to 240 V), by performing such power control, there is little overshoot or undershoot, and a good fixing device. A startup characteristic of 50 can be realized.

[Thermo switch]
In the fixing device 50, for example, when the CPU 94 fails and the triac 56a is not controlled, the heater 54 cannot be controlled to a predetermined temperature. In particular, when the CPU 94 fails so as to detect the temperature of the heater 54 lower than it actually is, the heater 54 is in an excessive temperature rise state. Even in such a case, the fixing device 50 is provided with an excessive temperature rise detection unit so that the fixing device 50 is not significantly damaged. In this embodiment, the thermoswitch 227 serves as an excessive temperature rise detection unit. .. The thermoswitch 227, which is also a breaking means, operates at 270° C. or higher. The thermoswitch 227 is in a short state at a temperature lower than 270° C., connects the current detection unit 402 and the contact 57b1 of the relay 57b, and forms a power supply path from the AC power supply 55 to the heater 54. On the other hand, the thermoswitch 227 is in an open state at a temperature of 270° C. or higher, the connection between the current detection unit 402 and the contact 57b1 of the relay 57b is cut off, and the power supply from the AC power supply 55 to the heater 54 is cut off.

[Abnormality detection part and route switching part]
The fixing device 50 according to the present exemplary embodiment includes an operational amplifier 207, which is an abnormality detection unit, and a relay 57a and a relay 57b, which are path switching units, in addition to the thermoswitch 227 which is an excessive temperature rise detection unit. In the first embodiment, the voltage V_TH indicating the detection temperature of the fixing temperature sensor 59 is input to the non-inverting input terminal (+) of the operational amplifier 207, but in the present embodiment, the power effective value calculation unit of the power detection unit 400 is input. The difference is that the rms signal, which is the output of 403, is input. The other configuration of the operational amplifier 207 is the same as that of the first embodiment, and the description thereof is omitted here. When the power supplied to the fixing device 50 is larger than expected, the voltage of the rms signal input to the non-inverting input terminal (+) of the operational amplifier 207 becomes higher than the reference voltage of the reference voltage generation unit 208. As a result, the operational amplifier 207 outputs a high level abnormality detection signal.

When the operational amplifier 207 outputs a high-level abnormality detection signal, the diode 209 becomes conductive and a base current flows through the resistor 210 to the base terminal of the transistor 204. As a result, the transistor 204 is turned on, current flows through the coil portion 57a2, and the relay 57a is turned on. Further, when the operational amplifier 207 outputs a high-level abnormality detection signal, the diode 305 becomes conductive and a base current flows through the resistor 304 to the base terminal of the transistor 301. As a result, the transistor 301 is turned on, a current flows through the coil portion 57b2, and the relay 57b is turned on. As a result, the contact 57a1 of the relay 57a is connected to the contact 57a3, and the contact 57b1 of the relay 57b is connected to the contact 57b4. As a result, the AC power supply 55 is connected to a resistor in which three heating elements 54b4, 54b1 and 54b3 are connected in series to supply electric power.

[Temperature profile when the fixing device is abnormal]
FIG. 7 shows the fixing temperature sensor 59 with the lapse of time until the power supply from the AC power supply 55 to the heater 54 is shut off by the abnormality detection unit or the excessive temperature rise detection unit when the CPU 94 fails as described above. It is a figure which shows the temperature characteristic (temperature profile) of. FIG. 7A is a diagram showing a temperature profile of the fixing temperature sensor 59 of the fixing device 50 of the present exemplary embodiment including the above-described abnormality detecting unit and path switching unit. In FIG. 7A, the horizontal axis represents time (unit: sec (second)), and the vertical axis represents the temperature detected by the fixing temperature sensor 59 (unit: °C). Further, t7 to t10 indicate time (timing).

Time t7 in FIG. 7A is the timing at which the AC power supply 55 starts power supply to the heater 54 in the cooling state of the fixing device 50. In FIG. 7, at time t7, the CPU 94 has already failed to detect the temperature of the heater 54 lower than it actually is, and the fixing device 50 is in a thermal runaway state at the same time when power supply is started. And During the time period td_3 between time t7 and time t8, the operational amplifier 207, which is the abnormality detection unit, detects abnormal power based on the rms signal output by the effective power value calculation unit 403 of the power detection unit 400. For example, if the rated power of the fixing device 50 is 1000 W, the power that is determined to be abnormal is set to 1200 W. When the operational amplifier 207 detects that power of 1200 W or more (more than a predetermined power value) is supplied based on the rms signal, the operational amplifier 207 outputs a high-level abnormality detection signal. As a result, the relays 57a and 57b, which are the path switching units described above, operate to set the relays 57a and 57b to the ON state at time t8. Thus, after the time t8, the contacts are switched so that the electric power from the AC power supply 55 is supplied to the resistor formed by connecting the three heating elements 54b1, 54b3, and 54b4 in series, and the series connection is performed. The thermal runaway state of the connected resistor continues. Time t9 is the timing when the thermoswitch 227, which is the excessive temperature rise detection unit, starts reacting. When the temperature of the heater 54 formed of resistors connected in series reaches 270° C., which is the operating temperature of the thermoswitch 227, the thermoswitch 227 begins to react. After the lapse of the period td_4 seconds from the time t9, sufficient heat is applied to the thermosensitive part of the thermoswitch 227, the contact inside the thermoswitch 227 is opened, and the power supply from the AC power supply 55 to the heater 54 is cut off.

For comparison with FIG. 7A, FIG. 7B is a diagram showing a temperature profile of the fixing temperature sensor 59 of the fixing device of the present embodiment which does not include the abnormality detecting unit and the path switching unit. is there. In FIG. 7B, the horizontal axis represents time (unit: sec (second)), and the vertical axis represents the temperature detected by the fixing temperature sensor 59 (unit: °C). Moreover, t7, t8, t11, and t12 show time (timing).

In FIG. 7B, from time t7 to time t8, the temperature profile of the fixing temperature sensor 59 changes in the same manner as in FIG. 7A. At time t8 when the detection temperature of the fixing temperature sensor 59 reaches 150° C., the fixing device does not include the abnormality detecting unit and the path switching unit, and therefore the slope of the temperature rise does not become gentle. Therefore, the fixing temperature sensor 59 reaches 270° C. at a time t11 earlier than the time t9 in FIG. 7A, and the thermoswitch 227 starts to operate. Then, at the time t12 after the period td_5 seconds has elapsed from the time t11, the contact inside the thermoswitch 227 is opened, and the power supply from the AC power supply 55 to the heater 54 is cut off. The temperature detected by the fixing temperature sensor 59 at time t12 is 370°C. The heat capacity of the heat-sensitive part of the thermoswitch 227 is sufficient for the temperature change from time t9 to time t10 (in the case of FIG. 7A) or the temperature change from time t11 to time t12 (in the case of FIG. 7B). Since they are large, the period td_4 and the period td_5 have substantially the same time width. After the contact inside the thermoswitch 227 is opened at the time t12, the power supply to the heater 54 is cut off, so that the temperature of the heater 54 gradually decreases and the safety of the fixing device 50 is ensured. ..

In the case of FIG. 7B, the temperature of the fixing temperature sensor 59 reaches 370° C. at time t12. On the other hand, in the case of FIG. 7A, the temperature of the fixing temperature sensor 59 is 280° C. at time t10. That is, the fixing device 50 of the present exemplary embodiment including the abnormality detecting unit and the path switching unit raises the temperature of the heater 54 by 90° C. (=370° C.) as compared with the case where the fixing device 50 does not include the abnormality detecting unit and the path switching unit. (−280° C.), the damage to the fixing device 50 can be reduced.

As described above, in this embodiment, the operational amplifier 207, the power detection unit 400, and the relays 57a and 57b are used to perform abnormality detection and path switching. When the electric power supplied to the fixing device 50 is larger than expected, the temperature rise of the heater 54 due to excessive temperature rise is moderated by switching the connection of the heating element that supplies the electric power. Further, the path switching unit is operated at a temperature lower than the target temperature of the fixing temperature sensor 59 by providing an abnormality detecting unit that detects an abnormality of electric power which is a parameter different from the temperature of the fixing temperature sensor 59. As a result, it is possible to suppress damage to the fixing device 50 at the time of excessive temperature rise, while suppressing an increase in cost and an increase in size of the device. Even if a component having the same function as the component of this embodiment is used, for example, the temperature fuse 107 is used instead of the thermoswitch 227, or the thermopile is used instead of the thermistor used for the fixing temperature sensor 59. The effect of the example does not change.

As described above, according to the present embodiment, it is possible to suppress an increase in the temperature of the heater when the fixing device is abnormal while suppressing an increase in cost and an increase in size of the device.

In the third embodiment, in order to prevent the substrate having the heater from being damaged in the thermal runaway state of the heater, a configuration will be described in which an abnormality detection unit and a path switching unit are used to switch the heating element that supplies power during thermal runaway.

[Circuit configuration of fixing device]
FIG. 8 is an overall schematic diagram showing a circuit configuration of the fixing device 50. The heater 54 has a heating element 54b5 which is a first heating element and a heating element 54b6 which is a second heating element. If the thermal stress applied to the substrate 54a of the heater 54 during the heat generation of the heating elements 54b5 and 54b6 increases, the ceramic substrate 54a may be damaged. If the substrate 54a is damaged, the fixing device 50 will also be significantly damaged. The thermal stress applied to the substrate 54a of the heater 54 is caused by the temperature difference between the heating element 54b5, the heating element 54b6, and the portion without the heating element. The heater 54 of the present embodiment has a more uniform temperature distribution in the X-axis direction (shorter direction of the heater 54) when the heating element 54b5 generates heat than when the heating element 54b6 generates heat. high. Therefore, the thermal stress applied to the substrate 54a of the heater 54 is reduced, and the substrate 54a is less likely to be damaged. Therefore, in this embodiment, when the heating element 54b6 is in a thermal runaway state, the power supply path from the AC power supply 55 to the heater 54 is switched to supply power to the heating element 54b5. Thus, the uniformity of the temperature distribution in the X-axis direction is increased and the thermal stress applied to the substrate 54a is reduced, so that the substrate 54a of the heater 54 is less likely to be damaged when the temperature rises excessively.

The heating element 54b5 is a tapered heating element having a characteristic that the resistance value in the central portion is high and the resistance value gradually decreases toward the end portion in the longitudinal direction of the heater 54. On the other hand, the heating element 54b6 is a tapered heating element having a characteristic that the resistance value at the central portion is low and the resistance value gradually increases toward the ends in the longitudinal direction of the heater 54. Further, the heating element 54b5 and the heating element 54b6 are heating elements having a characteristic that the resistance value does not change with temperature and the resistance value is constant. Therefore, the heater 54 is designed such that the heat generating elements 54b5 and 54b6 are alternately heated or simultaneously heated, so that the heat generation in the Y-axis direction (longitudinal direction of the heater 54) in the drawing becomes uniform. It is a heater.

As shown in FIG. 8, the pair of heating elements 54b5 are arranged so as to sandwich the heating element 54b6 in the X-axis direction (short side direction of the heater 54) in the figure. The pair of heating elements 54b5 have substantially the same length in the Y-axis direction in the figure, and the heating elements 54b6 also have substantially the same length in the Y-axis direction in the figure. The contact 54d2 to which one end of the pair of heating elements 54b5 and one end of the heating element 54b6 are connected, the contact 54d3 to which the other end of the heating element 54b6 is connected, and the contact 54d4 to which the other end of the pair of heating elements 54b5 are connected are 8 is connected to a circuit for controlling the fixing device 50. The contact 54d2 is connected to the current detector 402 via a thermoswitch 227 which is an excessive temperature rise detector. The current detector 402 is connected to the AC power supply 55.

The contact 54d3 is connected to the triac 56b. The triac 56b which is the second switch is controlled to be conductive or non-conductive by the Drive2 signal output from the CPU 94. Specifically, when the CPU 94 outputs a high-level Drive2 signal, the diode 241 becomes conductive, a base current flows through the resistor 236 to the base terminal of the transistor 235, and the transistor 235 is turned on. When the transistor 235 is turned on, the light emitting diode of the phototriac coupler 231 becomes conductive, current flows through the resistor 234, the light emitting diode emits light, and the light receiving portion of the phototriac coupler 231 becomes conductive. When the light receiving side of the phototriac coupler 231 becomes conductive, a gate trigger current flows between the T1 terminal and G terminal of the triac 56b via the current limiting resistor 232, and the T1 terminal and T2 terminal of the triac 56b become conductive. On the other hand, when the CPU 94 outputs the low level Drive2 signal, the diode 241 becomes non-conductive, the base current does not flow to the base terminal of the transistor 235, and the transistor 235 does not turn on. As a result, the light emitting diode of the phototriac coupler 231 does not emit light, and the light receiving portion of the phototriac coupler 231 also becomes non-conductive. Then, the gate trigger current of the triac 56b does not flow, and the T1 terminal-T2 terminal of the triac 56b becomes non-conductive.

The contact 54d4 is connected to the triac 56a which is the first switch, and the triac 56a is controlled by the Drive1 signal output from the CPU 94 to be conductive or non-conductive. The circuit configuration for driving the triac 56a is the same as that of the first and second embodiments except that the diode 242 is added between the resistor 226 and the CPU 94, and the description thereof is omitted here. In this way, the CPU 94 controls the triacs 56a and 56b so that the temperature detected by the fixing temperature sensor 59 becomes the target temperature.

[Power detector]
As shown in FIG. 8, the power detection unit 400 includes a current detection unit 402, a storage unit 404, and a power effective value calculation unit 403. The storage unit 404 is an EEPROM, and stores the resistance value of the heating element 54b6 and the resistance value of the heating element 54b5 measured in advance at a predetermined room temperature (about 30° C.). The current detection unit 402 is the same as that in the second embodiment, and the description thereof is omitted here. The current detection unit 402 of the present embodiment outputs the detected current value to the CPU 94. The power effective value calculation unit 403 calculates the power effective value based on the resistance value stored in the storage unit and the current value detected by the current detection unit 402, and calculates the calculated power effective value as an rms signal. It outputs to the integrated electric power calculation part 501 in CPU94. The integrated power calculation unit 501 provided inside the CPU 94 calculates the integrated power supplied to the heater 54 based on the effective power value output from the effective power value calculation unit 403 as the rms signal and the power supply time to the heater 54. Calculate the value W_integ. The CPU 94 has a timer in order to measure the power supply time to the heater 54. Based on the current value detected by the current detection unit 402, the CPU 94 performs the following control when the detected current value is 15 A or more, which is a predetermined current value. That is, the CPU 94 controls the triacs 56a and 56b by the Drive1 signal and the Drive2 signal to cut off the power supply from the AC power supply 55 to the heater 54. In this way, the CPU 94 controls the triacs 56a and 56b so that the value of the current flowing from the AC power supply 55 to the heater 54 is less than 15A. In this embodiment, the excessive temperature rise detection unit uses the thermoswitch 227 as in the second embodiment. The operation of the thermoswitch 227 is similar to that of the second embodiment, and the description thereof is omitted here.

[Abnormality detection part and route switching part]
The fixing device 50 according to the present exemplary embodiment includes an operational amplifier 237, which is an abnormality detection unit, and triacs 56a and 56b, which are switching units that switch the power supply path to the heating element, in addition to the thermoswitch 227 that is the excessive temperature rise detection unit. I have it. The integrated power value W_integ supplied from the integrated power calculation unit 501 to the heater 54 is input to the non-inverting input terminal (+) of the operational amplifier 237. On the other hand, the reference voltage generated by the reference voltage generation unit 238 is input to the inverting input terminal (−) of the operational amplifier 237. The reference voltage generation unit 238 generates a DC voltage of 2.5V as a reference voltage. The voltage of the DC voltage Vcc2 of the operational amplifier 237 is the DC voltage 24V. When the voltage value of the integrated power value W_integ is higher than the reference voltage of the reference voltage generator 238, the operational amplifier 237 outputs a high level signal. When the operational amplifier 237 outputs a high level signal, the diode 239 becomes conductive, and a base current flows to the base terminal of the transistor 225 via the resistor 240. As a result, the T1 terminal and the T2 terminal of the triac 56a can be set in a conductive state regardless of whether the Drive1 signal is at the high level or the low level. For example, if the rated power of the fixing device 50 is 1000 W, 800 W is not abnormal power. However, if 800 W being continuously supplied to the heater 54 for 7 seconds is not a normal operation, a state of 800 W×7 seconds or more can be defined as an abnormal state. That is, the reference voltage generated by the reference voltage generation unit 238 is set to the voltage value corresponding to the integrated power value W_integ corresponding to “800 W×7 seconds”. As a result, when abnormal integrated power of “800 W×7 seconds” or more is supplied to the heater 54, the voltage value corresponding to the integrated power value W_integ becomes higher than the reference voltage of the reference voltage generation unit 238, and the operational amplifier 237 outputs a high level signal. Then, the operational amplifier 237 outputs a high-level signal, so that the T1 terminal and the T2 terminal of the triac 56a become conductive as described above, and power is supplied to the heating element 54b5.

[Temperature profile when the fixing device is abnormal]
Here, for example, assume a situation in which the triac 56b fails and the heater 54 overheats due to a failure in which the triac 56b is always in a conductive state. FIG. 9 shows a case where the supply of power from the AC power supply 55 to the heater 54 is shut off by the abnormality detection unit or the excessive temperature rise detection unit when the heater 54 is in an excessive temperature rise state due to a failure of the triac 56b. FIG. 9 is a diagram showing temperature characteristics and thermal stress characteristics of a fixing temperature sensor 59.

FIG. 9A is a diagram showing a temperature profile of the fixing temperature sensor 59 of the fixing device 50 of the present embodiment including the above-described abnormality detecting unit and path switching unit. In FIG. 9A, the horizontal axis represents time (unit: sec (second)), and the vertical axis represents the temperature detected by the fixing temperature sensor 59 (unit: °C). Further, t14 to t18 indicate time (timing).

9A, from time 0 to time t14, power is supplied from the AC power supply 55 to the heater 54 in the cooling state of the fixing device 50, and the fixing temperature is changed from 30° C. at room temperature to 200° C. which is the target temperature. It shows how the temperature detected by the sensor 59 rises. Next, during time t14 to time t15, the power supply to the heating elements 54b5 and 54b6 is normally controlled, and the temperature of the fixing temperature sensor 59 is controlled to 200°C. Time t15 is a timing at which the triac 56b fails and the triac 56b is always in the conductive state. From time t15 to time t16, electric power is constantly supplied from the AC power supply 55 to the heating element 54b6, and the heating element 54b6 is in a thermal runaway state. From time t15 to time t16, the integrated power calculation unit 501 of the CPU 94 includes the integrated power value W_integ supplied to the heater 54, including the power supplied to the heating element 54b6 in the period td_6 between time t15 and time t16. Is output. The operational amplifier 237, which is the abnormality detection unit, outputs a high-level signal when it determines that the abnormal integrated power is supplied to the heater 54 based on the integrated power value W_integ output from the integrated power calculation unit 501. As a result, at time t16, the T1 terminal and the T2 terminal of the triac 56a are always set in the conductive state. As a result, during the period from time t16 to time t17, both the heating element 54b5 and the heating element 54b6 are supplied with power from the AC power supply 55 and are in a heating state. Therefore, at time t17, when the temperature of the heater 54 detected by the fixing temperature sensor 59 reaches 270° C., the thermoswitch 227, which is an excessive temperature rise prevention unit, starts operating. Then, at time t18, the contact of the thermoswitch 227 is opened, and the power supply from the AC power supply 55 to the heater 54 is cut off.

FIG. 9B is a diagram showing a profile of thermal stress applied to the substrate 54a of the fixing device 50 of this embodiment including the above-described abnormality detecting unit and path switching unit. In FIG. 9B, the horizontal axis represents time [unit: sec (second)], and the vertical axis represents the maximum value of thermal stress [unit: MPa] on the long side of the substrate 54a. In FIG. 9A, the detected temperature of the fixing temperature sensor 59 in the period from time t16 to time t17 has a larger temperature rise than the detected temperature in the period from time t15 to time t16. On the other hand, in FIG. 9B, the increase in the thermal stress during the period from time t16 to time t18 is slower than that during the period from time t15 to time t16. This depends on the arrangement positions of the heating elements 54b5 and 54b6 on the substrate 54a shown in FIG. 8 of the present embodiment. That is, in order to reduce the thermal stress so that the heater 54 (the substrate 54a of the heater 54) is less likely to be damaged, power is forcibly supplied also to the heating element 54b5 in this embodiment, and the temperature rise of the heater 54 becomes large. Even if it does, the state where only the heating element 54b6 generates heat is avoided. In this way, by supplying power to the heating elements 54b5 and 54b6 at the same time to generate heat, uneven temperature distribution in the X direction (see FIG. 8) is reduced, thermal stress applied to the heater 54 is reduced, and the heater 54 is less likely to be damaged. By setting the state, damage to the fixing device 50 is suppressed.

As described above, in this embodiment, the power detection unit 400 and the integrated power calculation unit 501 are used to detect an abnormality, thereby suppressing the increase in cost and the increase in size of the apparatus, and fixing at the time of excessive temperature rise. Damage to the device 50 can be suppressed to a minimum.

[Other Examples]
FIG. 10 is an overall schematic diagram showing a circuit configuration of the fixing device in which a part of the configuration of the fixing device 50 described in FIG. 8 is changed. In FIG. 10, the power detection unit 400 includes a voltage detection unit 401, a storage unit 404 that stores the resistance values of the heating elements 54b5 and 54b6, and an effective power value calculation unit 403. It is different from the circuit configuration of 50. Other configurations are similar to those of the circuit configuration shown in FIG. 8, and description thereof is omitted here. In the fixing device 50 of FIG. 8 described above, the effective power value calculation unit 403 calculates the effective power value from the current value detected by the current detection unit 402 and the resistance value of the heating element stored in the storage unit 404. There is. On the other hand, in the fixing device shown in FIG. 10, the effective power value calculation unit 403 calculates the effective power value from the voltage value detected by the voltage detection unit 401 and the resistance value of the heating element stored in the storage unit 404. Although the configuration is adopted, the effective power value may be calculated by such a configuration. In addition, like the electric power detection part 400 of Example 2 mentioned above, the electric power effective value calculation part 403 may calculate an electric power effective value based on a voltage value and a current value. The configuration of the power detection unit 400 of the second embodiment may be the same as that of the power detection unit 400 of the third embodiment. Even if a component having the same function as the component of this embodiment is used, such as a temperature fuse being used instead of the thermoswitch 227 and a thermopile being used instead of the thermistor used for the fixing temperature sensor 59, this embodiment The effect of does not change.

As described above, according to the present embodiment, it is possible to suppress an increase in the temperature of the heater when the fixing device is abnormal while suppressing an increase in cost and an increase in size of the device.

In the fourth embodiment, a heater having three kinds of heating elements is driven as in the second embodiment, but a fixing device having a circuit configuration different from that of the second embodiment will be described.

[Circuit configuration of fixing device]
FIG. 11 is a diagram showing an overall schematic view of the fixing device 50 of this embodiment. The heater 54 receives power from the AC power supply 55 and generates heat. The heater 54 has heating elements 54b1, 54b2, 54b3 and contacts 54d1, 54d2, 54d3, 54d4 formed on the substrate 54a. The heating element 54b2 is different from the second embodiment in that it is connected to the contacts 54d2 and 54d3. The heating element 54b2 has a lower rated power than the heating element 54b3. The other configuration of the heater 54 is the same as that of the second embodiment, and the description thereof is omitted here.

The relay 58a, which is a switch unit, is a relay having an A contact structure and has a coil unit 58a3 and contacts 58a1 and 58a2. The coil portion 58a3 has one terminal connected to the DC voltage Vcc4 of 24V and the other terminal connected to the collector terminal of the transistor 245. In the initial setting of the fixing device 50, the Drive4 signal output from the CPU 94 is set to low level, whereby the transistor 245 is turned off, the relay 58a is turned off, and the power supply from the AC power supply 55 to the heating element 54 is cut off. Will be in a state of On the other hand, when the CPU 94 outputs a high level Drive4 signal, a base current flows through the resistor 246 to the base terminal of the transistor 245. As a result, the voltage between the collector terminal and the emitter terminal of the transistor 245 becomes a saturation voltage of about 0.2 to 0.3 V, and the transistor 245 is turned on. When the transistor 245 is turned on, a collector current flows through the transistor 245, a potential difference is generated across the coil portion 58a3, a current flows through the coil portion 58a3, and the magnetic force generated in the coil portion 58a3 connects the contact 58a1 to the contact 58a2. It Hereinafter, this state is referred to as the ON state of the relay 58a.

The thermal fuse 107 has one end connected to the DC voltage Vcc3 of 24V supplied from the outside and the other end connected to the DC voltage Vcc4. When the temperature of the thermal fuse 107 exceeds a predetermined temperature, the contacts inside the thermal fuse 107 are opened. When the contact inside the thermal fuse 107 is opened, the connection to the DC voltage Vcc3, which is 24V supplied from the outside, and the DC voltage Vcc4 is cut off, and the DC voltage Vcc4 becomes 0V. As a result, the DC voltage Vcc4 is not supplied to the coil portion 58a3 of the relay 58a, the relay 58a is turned off, the power supply path from the AC power supply 55 to the heater 54 is cut off, and the power supply is cut off. 50 safety is secured. The fixing temperature sensor 59 has the same configuration as that of the first embodiment, and the description thereof is omitted here.

A contact 54d1 to which one end of the heating element 54b1 and one end of the heating element 54b3 are connected and a contact 54d2 to which one end of the heating element 54b2 is connected are connected to a circuit that controls the fixing device 50 shown in FIG. Similarly, a contact 54d3 connected to the other end of the heating element 54b2 and the other end of the heating element 54b3, and a contact 54d4 connected to the other end of the heating element 54b1 are circuits for controlling the fixing device 50 shown in FIG. It is connected to the. The contact 54d1 which is the first contact is connected to the contact 58a2 of the relay 58a having the a-contact structure, and the contact 54d2 which is the second contact is connected to the contact 57a4, the resistor 232 and the triac 56b of the relay 57a having the c-contact structure. Has been done. On the other hand, the contact 54d3 which is the third contact is connected to the contact 57a1 of the relay 57a having the c-contact structure, and the contact 54d4 which is the fourth contact is connected to the triac 56a and the resistor 222.

The operation of the relay 57a controlled by the Drive3 signal output from the CPU 94 is similar to that of the relay 57a of FIG. 4 of the first embodiment, and the description thereof is omitted here. In the initial setting of the fixing device 50, the Drive3 signal output from the CPU 94 is set to the low level, whereby the contact 57a1 and the contact 57a4 of the relay 57a are connected, and the power supply path from the AC power supply 55 to the heating element 54b3. Is selected.

The operations of the triac 56a controlled by the Drive1 signal and the triac 56b controlled by the Drive2 signal are similar to those of the triac 56a of FIG. 4 of the first embodiment and FIG. 6 of the second embodiment, and the description thereof is omitted here. .. When the relay 58a is in the ON state, by controlling the triac 56a, electric power is supplied from the AC power supply 55 to the heating element 54b1 to heat the heater 54. Similarly, when the relay 58a is in the ON state and the c-contact relay 57a is in the ON state, by controlling the triac 56b, electric power is supplied from the AC power supply 55 to the heating element 54b2 to heat the heater 54. When the relay 58a is in the ON state and the c-contact relay 57a is in the OFF state, electric power is supplied from the AC power supply 55 to the heating element 54b3, and the heater 54 is heated. The relationship between the heater width and the paper is the same as that in the first embodiment, and the description is omitted here.

In this way, the CPU 94 selects the appropriate heating element according to the sheet width based on the sheet width information of the sheet P, and operates the relay 57a so that power is supplied from the AC power supply 55 to the selected heating element. Control and switch the contact to connect. The CPU 94 also controls the triacs 56a and 56b. The control of the fixing temperature sensor 59 and the triac 56a of the CPU 94, which is performed based on the temperature information of the fixing temperature sensor 59, is the same as that of the first embodiment, and the description thereof is omitted here.

[Thermal fuse]
However, if a failure such as a short circuit between the T1 terminal and the T2 terminal of the triac 56b and a short circuit between the collector and emitter of the transistor 245 occurs, the power supply from the AC power supply 55 to the heater 54 cannot be controlled. As a result, the temperature of the heater 54 cannot be controlled to the target temperature, resulting in a thermal runaway state. In such a case as well, the fixing device 50 is provided with an excessive temperature rise detection unit so that the fixing device 50 is not significantly damaged. In this embodiment, the temperature fuse 107 includes the excessive temperature rise detection unit. Becomes The temperature fuse 107, which also serves as a breaking unit, melts the internal pellets when the temperature rises above about 205° C., for example, and when a predetermined amount of pellets melts, the contacts inside the thermal fuse 107 change from the short-circuited state to the open state. As a result, the relay 58a is turned off, the power supply from the AC power supply 55 to the heater 54 is cut off, and the thermal runaway state described above is eliminated.

[Abnormality detection part and route switching part]
By the way, in the process in which heat is transferred from the substrate 54a to the thermal fuse 107, it takes a certain amount of time for the temperature to be transferred to the pellets in the thermal fuse 107 due to the heat capacity of the thermal fuse 107. In addition, it takes a certain amount of time from the start of melting of the pellet to the melting of a predetermined amount. That is, even if the heater 54 overheats due to thermal runaway, the thermal fuse 107 operates immediately and the contacts are not opened. In order to ensure the safety of the fixing device 50 even if there is such a time lag, the fixing device 50 according to the present exemplary embodiment includes an operational amplifier 207 that is an abnormality detecting unit (also an abnormality detecting unit) and a path switching. It is equipped with a relay 57a as a part. The operations of the operational amplifier 207 and the relay 57a are the same as those in the first embodiment, and the description thereof is omitted here.

[Temperature profile when the fixing device is abnormal]
FIG. 12A is a diagram showing a temperature profile of the fixing temperature sensor 59 of the fixing device 50 of this embodiment including the above-described abnormality detecting unit and path switching unit. In FIG. 12A, the horizontal axis represents time (unit: sec (second)), and the vertical axis represents the temperature detected by the fixing temperature sensor 59 (unit: °C). Also, t19 to t23 indicate time (timing).

12A, from time 0 to time t19, power is supplied from the AC power supply 55 to the heating element 54b3 to the heater 54 in the cooling state of the fixing device 50, and the target temperature is 160° C. from 30° C. at room temperature. Up to this point, it is shown that the detection temperature of the fixing temperature sensor 59 rises. At this time, the relay 58a is set to the ON state and the relay 57a is set to the OFF state, that is, the contact 57a1 and the contact 57a4 are connected. Further, the triac 56a is set to an off state (between the T1 terminal and the T2 terminal is open), and the triac 56b is set to an on state (a connecting state between the T1 terminal and the T2 terminal).

Next, during time t19 to time t20, the temperature of the fixing temperature sensor 59 is controlled to 160° C. while controlling the power supply to the heating element 54b3. Time t20 is a timing at which a thermal runaway of the heater 54 starts due to a failure such as a short circuit between the T1 terminal and the T2 terminal of the triac 56b or a short circuit between the collector and the emitter of the transistor 245. When the thermal runaway of the heater 54 starts, the temperature of the fixing temperature sensor 59 rapidly rises. When the temperature detected by the fixing temperature sensor 59 reaches 180° C. at time t21, the operational amplifier 207, which is the abnormality detecting unit, detects an abnormality in the temperature detected by the fixing temperature sensor 59, as described above. Then, the operational amplifier 207, which has detected the abnormality in the temperature detected by the fixing temperature sensor 59, outputs a high level to turn on the transistor 204 and turn on the relay 57a. Then, the power supply destination from the AC power supply 55 is switched from the heating element 54b3 to the heating element 54b2. As described above, since the heating element 54b2 has a lower rated power than the heating element 54b3, the temperature rise at the time of thermal runaway becomes gentle. Time t22 is the timing when the pellet of the thermal fuse 107 starts melting. At time t23 after the period td_7 has elapsed from time t22, the contacts inside the thermal fuse 107 are opened, and the power supply from the AC power supply 55 to the heater 54 is cut off. As a result, the temperature of the heater 54 is gradually lowered, and the safety of the fixing device 50 is ensured.

For comparison with FIG. 12A, FIG. 12B is a diagram showing a temperature profile of the fixing temperature sensor 59 of the fixing device which does not include the abnormality detecting unit and the path switching unit of the present embodiment. is there. In FIG. 12B, the horizontal axis represents time (unit: sec (second)), and the vertical axis represents the temperature detected by the fixing temperature sensor 59 (unit: °C). Further, t19 to t21, t24, and t25 indicate time (timing).

In FIG. 12B, from time t19 to time t21, the temperature profile of the fixing temperature sensor 59 changes in the same manner as in FIG. 12A. At time t21 when the temperature detected by the fixing temperature sensor 59 reaches 180° C., the fixing device does not include the abnormality detecting unit and the path switching unit, and therefore the slope of the temperature rise does not become gentle. Therefore, at a time t24 earlier than the time t22 in FIG. 12A, the fixing temperature sensor 59 reaches 205° C., and the pellet of the thermal fuse 107 starts melting. Then, at time t25 when the period td_8 seconds has elapsed from time t24, the contacts inside the thermal fuse 107 are opened, and the power supply from the AC power supply 55 to the heater 54 is cut off. The thermal capacity of the thermal fuse 107 is sufficient for the temperature change from time t22 to time t23 (in the case of FIG. 12A) and the temperature change from time t24 to time t25 (in the case of FIG. 12B). Since they are large, the period td_7 and the period td_8 have substantially the same time width. At time t25, the contacts inside the thermal fuse 107 are opened, and after the power supply to the heater 54 is cut off, the temperature of the heater 54 gradually decreases, and the safety of the fixing device 50 is ensured. In the case of FIG. 12B, the temperature of the fixing temperature sensor 59 has reached 260° C. at time t25. On the other hand, in the case of FIG. 12A, the temperature of the fixing temperature sensor 59 is 220° C. at time t23. That is, the fixing device 50 of the present embodiment including the abnormality detecting unit and the path switching unit raises the temperature of the heater 54 by 40° C. (=260° C.) as compared with the case where the fixing device 50 does not include the abnormality detecting unit and the path switching unit. (−220° C.), the damage to the fixing device 50 can be reduced.

The operation when the operational amplifier 207 detects an abnormality in the temperature detected by the fixing temperature sensor 59 while the heating element 54b3 is being supplied with power from the power supply 55 has been described above. If the operational amplifier 207 detects an abnormality in the temperature detected by the fixing temperature sensor 59 while the heating element 54b2 is being supplied with power from the power source 55, the power supply from the power source 55 to the heating element 54b2 is continued as it is. It When electric power is supplied from the power supply 55 to the heating element 54b1, the CPU 94 sets the relay 58a to the on state, the triac 56a to the on state, and the triac 56b to the off state. At this time, when the operational amplifier 207 detects an abnormality in the temperature detected by the fixing temperature sensor 59, the relay 57a is set to the ON state. Further, the temperature detected by the fixing temperature sensor 59 is also input to the CPU 94. When the CPU 94 determines that the temperature detected by the fixing temperature sensor 59 is abnormal, the output of the Drive signal 1 for controlling the on/off state of the triac 56a is switched from the high level to the low level, and the triac 56a is turned off. Set to state. As a result, the power supply from the power source 55 to the heater 54 is cut off. Here, when the abnormality in the temperature detected by the fixing temperature sensor 59 is detected, the CPU 94 sets the triac 56a to the off state. However, for example, the output of the operational amplifier 207 is output to the transistor 225 which controls the triac 56a. You may do it. Thus, when the temperature is abnormal, the triac 56a can be switched from the on state to the off state without the intervention of the CPU 94.

As described above, by using the fixing temperature sensor 59 and the relay 57a in order to detect the abnormality and switch the path, it is possible to minimize the cost increase and the size increase of the apparatus. Furthermore, when an abnormality is detected, the power supply destination is switched to the heating element having a low rated power, whereby the temperature rise of the heater is moderated and damage to the fixing device 50 at the time of excessive temperature rise can be minimized. .. The abnormality detection unit may be provided with a latch function or a hysteresis function so that the abnormality detection is not canceled even if the temperature of the fixing temperature sensor 59 is once detected to be lower than 180° C. after once exceeding the abnormality detection temperature. Good. Further, even if a component having the same function as the component of the present embodiment is used, such as a thermoswitch used in place of the temperature fuse 107 and a thermopile used in place of the thermistor used in the fixing temperature sensor 59, The effect of the embodiment does not change.

As described above, according to the present embodiment, it is possible to suppress an increase in the temperature of the heater when the fixing device is abnormal while suppressing an increase in cost and an increase in size of the device.

54 heaters 54b1 and 54b2 heating element 55 AC power supply 57a relay 107 temperature fuse 207 operational amplifier

Claims (29)

A heater having at least two or more heating elements including a first heating element having a first rated power and a second heating element having a second rated power lower than the first rated power. Department,
A switching unit that switches connection between the first heating element or the second heating element and a power source;
When the heater section has an excessive temperature rise, a power supply path between the power source and the heater section is disconnected, and a disconnection unit that disconnects the power supply,
Abnormality detecting means for detecting an excessive temperature rise of the heater part,
Equipped with
The heating device, wherein the switching unit connects the power source and the second heating element when the abnormal temperature detection unit detects an excessive temperature rise in the heater unit. When the abnormal temperature detection means detects an excessive temperature rise in the heater section, the switching section supplies the power source and the second heating element before the power supply to the heater section is cut off by the cutoff means. The heating device according to claim 1, wherein the heating device is switched so as to be connected to. A substrate having the heater section,
The first heating element is a pair of heating elements having substantially the same length in the longitudinal direction,
The second heating element is a pair of heating elements having a length in the longitudinal direction shorter than that of the first heating element and having substantially the same length,
The first heating element, the second heating element, the second heating element, and the first heating element are arranged in this order in the lateral direction of the substrate. The heating device described. A first contact to which one end of the first heating element and one end of the second heating element are electrically connected;
A second contact to which the other end of the second heating element is electrically connected,
The heating device according to claim 3, further comprising a third contact to which the other end of the first heating element is electrically connected. The switching unit has a relay,
The relay can switch connection between the power supply and the second contact, or connection between the power supply and the third contact,
The heating device according to claim 4, wherein the shut-off means is connected to the power source and the first contact. A temperature detecting means for detecting the temperature of the heater section,
The abnormality detection unit detects an excessive temperature rise of the heater unit and outputs a detection signal when the temperature of the heater unit detected by the temperature detection unit is equal to or higher than a predetermined temperature,
When the detection signal is input, the relay connects the power source and the second contact,
The heating device according to claim 5, wherein the power source is connected to the second heating element. A power supply path is provided between the power source and the relay, and a power supply control section that controls power supply to the heater section by connecting or disconnecting the power supply path is provided. Item 7. A heating device according to item 6. A substrate having the heater section,
The heater section further includes a third heating element having a third rated power lower than the first rated power,
The first heating element is a pair of heating elements having substantially the same length in the longitudinal direction,
The second heating element is a heating element having a longitudinal length shorter than that of the first heating element,
The third heating element is a heating element whose longitudinal length is shorter than that of the second heating element,
The first heating element, the third heating element, the second heating element, and the first heating element are arranged in this order in the lateral direction of the substrate. The heating device described. A first contact at which one end of the first heating element and one end of the second heating element are electrically connected;
A second contact to which one end of the third heating element is electrically connected;
A third contact to which the other end of the second heating element is electrically connected,
The heating device according to claim 8, further comprising: a fourth contact point at which the other end of the first heating element and the other end of the third heating element are electrically connected. The switching unit has a first relay and a second relay,
The first relay can switch connection between the power supply and the first contact, or connection between the power supply and the second contact,
The second relay is capable of switching connection between the power supply and the third contact, or connection between the power supply and the fourth contact,
The heating device according to claim 9, wherein the cutoff unit is provided in the power supply path between the power source and the first relay. A power detection unit for determining a power value supplied from the power source to the heater unit,
The abnormality detection means detects an excessive temperature rise of the heater section when the electric power value obtained by the electric power detection means is equal to or higher than a predetermined electric power value, and outputs a detection signal. The heating device according to claim 10. When the detection signal is input, the first relay connects the power supply and the second contact,
The second relay connects the power supply and the third contact when the detection signal is input,
The heating device according to claim 11, wherein the power source is connected to the third heating element, the first heating element, and the second heating element that are connected in series. A power supply control unit is provided in a power supply path between the power source and the second relay, and includes a supply control unit that controls power supply to the heater unit by connecting or disconnecting the power supply path. The heating device according to claim 12. A first contact to which one end of the first heating element and one end of the second heating element are electrically connected;
A second contact to which one end of the third heating element is electrically connected;
A third contact at which the other end of the second heating element and the other end of the third heating element are electrically connected,
The heating device according to claim 8, further comprising a fourth contact to which the other end of the first heating element is electrically connected. A switch unit provided in the power supply path between the power source and the first contact, for connecting or disconnecting the power supply path,
The heating device according to claim 14, wherein the switch unit is supplied with a voltage for driving the switch unit via the cutoff unit. The switching unit has a relay,
The relay can switch connection between the switch unit and the third contact, or connection between the power supply and the third contact,
The heating device according to claim 15, wherein the second contact and the fourth contact are connected to the power source. A temperature detecting means for detecting the temperature of the heater section,
The abnormality detection unit detects an excessive temperature rise of the heater unit and outputs a detection signal when the temperature of the heater unit detected by the temperature detection unit is equal to or higher than a predetermined temperature,
The relay connects the power supply and the third contact, and when the detection signal is input while power is being supplied from the power supply to the second heating element, the relay is connected to the switch unit. Switching to connection with the third contact,
The heating device according to claim 16, wherein the power source is connected to the third heating element. A power supply path between the power supply, the relay, and the second contact, and a power supply path between the power supply and the fourth contact are provided, and the power supply path is connected or disconnected. The heating device according to claim 17, further comprising: a supply control unit that controls electric power supply to the heater unit by performing the operation. A first heating element whose thermal stress on the heater becomes the first thermal stress when generating heat, and a second heating element whose thermal stress on the heater when generating heat becomes the second thermal stress smaller than the first thermal stress. A heater unit having at least two or more heating elements including
A switching unit that switches connection between the first heating element or the second heating element and a power source;
When the heater section has an excessive temperature rise, a power supply path between the power source and the heater section is disconnected, and a disconnection unit that disconnects the power supply,
Abnormality detecting means for detecting an excessive temperature rise of the heater part,
Equipped with
The heating device, wherein the switching unit connects the power source and the second heating element when the abnormal temperature detection unit detects an excessive temperature rise in the heater unit. The switching unit, when the abnormality detecting unit detects an excessive temperature rise of the heater unit, before the power supply to the heater unit is cut off by the cutoff unit, the power source and the first heating element. The heating device according to claim 19, wherein the heating device is switched so as to connect with. A substrate having the heater section,
The first heating element is a pair of heating elements having substantially the same length in the longitudinal direction, and has a characteristic that the resistance value decreases from the central portion toward the end portion in the longitudinal direction of the heater portion. ,
The second heating element is a heating element whose length in the longitudinal direction is substantially the same as that of the first heating element, and the resistance value increases from the central portion to the end portion in the longitudinal direction of the heater portion. Has the following characteristics:
The first heating element, the second heating element, and the first heating element are arranged in this order in the lateral direction of the substrate,
A first contact to which one end of the first heating element and one end of the second heating element are electrically connected;
A second contact to which the other end of the second heating element is electrically connected,
The heating device according to claim 20, further comprising: a third contact to which the other end of the first heating element is electrically connected. The switching unit is provided in a power supply path between the power supply and the third contact, and connects the power supply and the first heating element to or disconnects from each other; A second switch that is provided in a power supply path between the second contact and connects or disconnects the power source and the second heating element;
22. The heating device according to claim 21, wherein the cutoff unit is provided in the power supply path between the power source and the first contact. A power detection unit for calculating an integrated power value supplied from the power source to the heater unit,
The abnormality detecting unit detects an excessive temperature rise of the heater unit and outputs a detection signal when the integrated electric power value obtained by the electric power detecting unit is equal to or more than a predetermined electric power value. 23. The heating device according to claim 22. When the detection signal is input, the first switch is set to connect between the power supply and the third contact and supply power from the power supply to the first heating element. 24. The heating device according to claim 23, wherein: 25. The temperature cutoff unit is a thermal fuse or a thermoswitch whose contacts are opened when a temperature higher than a predetermined temperature continues for a predetermined time or longer. 25. Heating device. A fixing device for fixing an unfixed toner image carried on a recording material,
A heating device according to any one of claims 1 to 25,
A first rotating body heated by the heating device;
A second rotating body that forms a nip portion with the first rotating body;
A fixing device comprising: 27. The fixing device according to claim 26, wherein the first rotating body is a film. The heating device is provided so as to contact the inner surface of the film,
The fixing device according to claim 27, wherein the nip portion is formed by the heating device and the second rotating body via the film. An image forming means for forming an image on the recording material,
A fixing device according to any one of claims 26 to 28,
An image forming apparatus comprising: