JP2013238636A - Temperature control device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the temperature of a heating roller from being excessively increased when temperature control of the heating roller fails.SOLUTION: A first temperature sensor 31 and a second temperature sensor 32 detect temperature of a heating roller 26a that generates heat when powered, and output signals according to the detected temperature. A temperature control part 48 controls the temperature of the heating roller 26a on the basis of temperature according to the signals output from the first temperature sensor 31 and the second temperature sensor 32 and a preset target temperature. A relay 45 is connected to the heating roller 26a, and cuts off power to be supplied to the heating roller 26a when turned off. A high temperature detection circuit 44 compares an input current supplied from the first temperature sensor 31 with a reference current to determine whether the temperature of the heating roller 26a has exceeded an abnormal temperature T2, and turns off the relay 45 when the temperature of the heating roller 26a exceeds the abnormal temperature T2.

Description

  The present invention relates to a temperature control device and an image forming apparatus.

  In an electrophotographic image forming apparatus, a technique for detecting the temperature of a heating roller of a fixing device and controlling the temperature of the heating roller according to the detection result is known. For example, Patent Document 1 describes a technique for detecting the temperature of a heating roller using a center thermistor and a side thermistor and controlling the temperature so as to maintain a predetermined fixing temperature. Patent Document 1 describes that a thermostat is provided to prevent excessive heating of the heating roller.

JP 2010-224351 A

  An object of the present invention is to prevent the temperature of the heating roller from excessively rising even when the temperature control of the heating roller is not effective.

  A temperature control device according to claim 1 of the present invention detects a temperature of a heating roller that generates heat by energization, outputs a signal corresponding to the detected temperature, and responds to a signal output from the detection unit A temperature control unit that controls the temperature of the heating roller based on a predetermined temperature and a preset target temperature, a relay that is connected to the heating roller and shuts off the energization of the heating roller when turned off, and By comparing the signal output from the detection unit with a reference signal to determine whether the temperature of the heating roller exceeds a threshold value corresponding to the reference signal, and the temperature of the heating roller exceeds the threshold value Comprises a comparator for turning off the relay.

  The temperature control device according to a second aspect of the present invention is the temperature control device according to the first aspect, wherein the detection unit includes a first detection unit that detects a temperature of a region of the heating roller that contacts the recording medium. And the comparison unit compares the signal detected from the first detection unit with the reference signal.

  The temperature control device according to a third aspect of the present invention is the temperature control device according to the second aspect, wherein the detection unit detects a temperature of a region of the heating roller that does not contact the recording medium. And the temperature control unit controls the temperature of the heating roller based on a temperature corresponding to a signal output from the first detection unit and the second detection unit and the target temperature. It is characterized by.

  An image forming apparatus according to a fourth aspect of the present invention includes an image carrier, a charging unit that charges the image carrier, an exposure unit that exposes the charged image carrier to form a latent image, and the latent image. The image forming apparatus includes a developing unit that develops an image with toner to form a toner image, a transfer unit that transfers the toner image to a recording medium, a heating roller and a pressure roller, and records the toner image by heating and pressing. A fixing unit for fixing to a medium and the temperature control device according to any one of claims 1 to 3 are provided.

  An image forming apparatus according to a fifth aspect of the present invention is the image forming apparatus according to the fourth aspect, further comprising an operation prohibiting unit that prohibits the operation of the image forming apparatus when the relay is turned off. .

  An image forming apparatus according to claim 6 of the present invention is the image forming apparatus according to claim 4 or 5, wherein when the temperature of the heating roller reaches a predetermined temperature higher than the threshold value, It is characterized by including a shut-off portion for shutting off energization.

According to the first aspect of the present invention, it is possible to prevent the temperature of the heating roller from rising excessively even when the temperature control of the heating roller stops working.
According to the second aspect of the present invention, when the temperature of the area in contact with the recording medium in the heating roller exceeds the threshold value, the energization of the heating roller can be cut off.
According to the invention according to claim 3, compared to the case of controlling the temperature of the heating roller using only the temperature according to the signal output from either the first detection unit or the second detection unit, The accuracy of temperature control can be improved.
According to the invention which concerns on Claim 4, even when the temperature control of a heating roller stops working, it can prevent that the temperature of a heating roller rises excessively.
According to the fifth aspect of the present invention, the use of the image forming apparatus can be prohibited when the temperature of the heating roller exceeds the threshold value.
According to the sixth aspect of the present invention, it is possible to prevent the temperature of the heating roller from rising excessively even when both of the temperature control of the heating roller and the comparison unit do not work.

The figure which shows the structure of an image forming apparatus The figure which shows the structure of a 1st temperature sensor, a 2nd temperature sensor, and a temperature control circuit.

(Constitution)
FIG. 1 is a diagram illustrating a configuration of an image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 forms an image by electrophotography. The image forming apparatus 1 includes a photosensitive drum 21 (an example of an image carrier), a charger 22 (an example of a charging unit), an exposure device 23 (an example of an exposure unit), and a developing unit 24 (an example of a developing unit). And a transfer roller 25 (an example of a transfer unit) and a fixing device 26 (an example of a fixing unit). The photosensitive drum 21 is a cylindrical image holding member that rotates about an axis. A photoconductive film is formed on the surface of the photosensitive drum 21. The charger 22 charges the surface of the photosensitive drum 21 to a predetermined potential. The exposure device 23 exposes the charged photosensitive drum 21 based on the image signal to form an electrostatic latent image. The developing device 24 develops the electrostatic latent image formed on the photosensitive drum 21 with toner to form a toner image. The transfer roller 25 transfers the toner image formed on the photosensitive drum 21 to a recording medium P such as paper.

  The fixing device 26 includes a heating roller 26a and a pressure roller 26b. The recording medium P on which the toner image is formed is transported between the heating roller 26a and the pressure roller 26b after the position is adjusted so that the center of the recording medium P is aligned with the axial center of the heating roller 26a. The fixing device 26 fixes the toner image on the recording medium P by heating and pressing using the heating roller 26 a and the pressure roller 26 b. The sheet that has passed through the fixing device 26 is discharged from the discharge port of the image forming apparatus 1.

  The image forming apparatus 1 includes an operation panel used when a user operates the image forming apparatus 1 in addition to the configuration shown in FIG. The operation panel includes, for example, a plurality of buttons that accept user operations and a display that displays operation images and various messages.

  The image forming apparatus 1 includes a first temperature sensor 31, a second temperature sensor 32, and a temperature control circuit 40 in order to control the temperature of the heating roller 26a. FIG. 2 is a diagram illustrating the configuration of the first temperature sensor 31, the second temperature sensor 32, and the temperature control circuit 40.

  The heating roller 26a includes a metal core formed of a metal such as aluminum or iron. On the surface of the metal core, a resin layer is formed by a PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) tube. The heating roller 26a contacts the recording medium P in the paper passing area R. For example, when the maximum sheet size used in the image forming apparatus 1 is A3, the area that contacts the recording medium P of A3 in the heating roller 26a is the sheet passing area R. As described above, the position of the recording medium P is adjusted so that the center of the recording medium P coincides with the center of the heating roller 26a in the axial direction, and the recording medium P is conveyed between the heating roller 26a and the pressure roller 26b. ing. Accordingly, the central portion of the heating roller 26a comes into contact with the recording medium P regardless of the size of the recording medium P being conveyed.

  A heater 27 such as a halogen lamp is provided inside the metal core. The heater 27 generates heat when energized, and heats the heating roller 26a from the inside. The power supply circuit 29 supplies power supplied from the commercial power supply 30 to the heater 27. The safety device 28 (an example of a blocking unit) is disposed at a position that receives radiant heat from the heating roller 26a. The safety device 28 includes a bimetal thermostat. When the temperature of the heating roller 26a reaches a predetermined abnormal temperature T1 (eg, 320 degrees), the safety device 28 cuts off the power supply from the power supply circuit 29 to the heater 27.

  The first temperature sensor 31 (an example of a first detection unit) is disposed so as to contact the surface of the central portion of the heating roller 26a. The first temperature sensor 31 includes a thermistor element whose resistance decreases with increasing temperature. The 1st temperature sensor 31 detects the temperature of the center part of the heating roller 26a, and outputs the signal according to the detected temperature. The central portion of the heating roller 26a is in the above-described sheet passing region R. That is, the first temperature sensor 31 detects the temperature of the area in contact with the recording medium P in the heating roller 26a.

  The second temperature sensor 32 (an example of a second detection unit) is disposed so as to contact the surface of the end portion of the heating roller 26a. The second temperature sensor 32 includes a thermistor element whose resistance decreases with increasing temperature. The second temperature sensor 32 detects the temperature of the end portion of the heating roller 26a and outputs a signal corresponding to the detected temperature. The end of the heating roller 26a is outside the paper passing region R described above. That is, the second temperature sensor 32 detects the temperature of the area that does not contact the recording medium P in the heating roller 26a.

  The temperature control circuit 40 includes power terminals 41a and 41b, resistors 42a and 42b, A / D converters 43a, 43b and 43c, a high temperature detection circuit 44, a relay 45, and a CPU (Central Processing Unit) 46. And a memory 47. The CPU 46 functions as a temperature control unit 48 and an operation prohibition unit 49 by executing a program stored in the memory 47.

  The power supply terminal 41a is connected to the resistor 42a. The power supply terminal 41b is connected to the resistor 42b. Each of the power supply terminals 41a and 41b applies a reference voltage (for example, 3.3V). The resistor 42 a is connected in series to the second temperature sensor 32. The resistor 42 b is connected to the first temperature sensor 31 in series. The A / D converter 43a converts the signal (analog signal) output from the second temperature sensor 32 into a digital signal and outputs the digital signal. The A / D converter 43b converts the signal (analog signal) output from the first temperature sensor 31 into a digital signal and outputs the digital signal. The A / D converter 43c converts the signal (analog signal) output from the high temperature detection circuit 44 into a digital signal and outputs it.

  The temperature controller 48 controls the power supply circuit 29 so that the temperature of the heating roller 26a becomes a preset target temperature (for example, 170 degrees to 180 degrees). Specifically, the temperature control unit 48 acquires the temperatures of the end and center of the heating roller 26a based on signals output from the A / D converters 43a and 43b. When the acquired temperature is lower than the target temperature, the temperature control unit 48 controls the power supply circuit 29 to supply power to the heater 27. On the other hand, when the acquired temperature is higher than the target temperature, the temperature control unit 48 controls the power supply circuit 29 to cut off the power supply to the heater 27. Note that the temperature control unit 48 may determine, for example, whether both the temperature at the center and the temperature at the end of the heating roller 26a are higher or lower than the corresponding target temperature, or at the center of the heating roller 26a. It may be determined whether the higher one of the temperature and the end temperature is higher or lower than the target temperature.

  The high temperature detection circuit 44 (an example of a comparison unit) includes a comparator. An input current (an example of a signal) supplied from the first temperature sensor 31 and a reference current (an example of a reference signal) are input to the high temperature detection circuit 44. The high temperature detection circuit 44 determines whether or not the temperature detected by the first temperature sensor 31 has exceeded an abnormal temperature T2 (eg, 240 degrees) corresponding to the reference current by comparing the input current and the reference current. To do. In this embodiment, the abnormal temperature T2 is used as a threshold value according to the reference current. The abnormal temperature T2 is set to a temperature that is higher than the target temperature and lower than the abnormal temperature T1, for example.

  As described above, the resistance of the thermistor element of the first temperature sensor 31 decreases as the temperature of the heating roller 26a increases. Therefore, when the temperature of the heating roller 26a rises, the current supplied from the first temperature sensor 31 increases when the reference voltage is applied from the power supply terminal 41b. In the high temperature detection circuit 44, when the temperature detected by the first temperature sensor 31 exceeds the abnormal temperature T2, the input current becomes larger than the reference current. When the input current becomes larger than the reference current, the high temperature detection circuit 44 determines that the temperature detected by the first temperature sensor 31 has exceeded the abnormal temperature T2, and outputs a control signal S1 for turning off the relay 45. On the other hand, when the reference current becomes larger than the input current, the high temperature detection circuit 44 determines that the temperature detected by the first temperature sensor 31 is lower than the abnormal temperature T2, and outputs a control signal S2 for turning on the relay 45. .

  The relay 45 has one end connected to the heater 27 and the other end connected to the ground. The relay 45 operates according to a control signal output from the high temperature detection circuit 44. When the relay 45 is turned on, electric power is supplied from the power supply circuit 29 to the heater 27 so that the heater 27 is energized. On the other hand, when the relay 45 is turned off, the energization of the heater 27 is cut off. When the control signal S1 for turning off the relay 45 is output from the high temperature detection circuit 44, the operation prohibiting unit 49 prohibits the operation of the image forming apparatus 1. Specifically, the operation prohibiting unit 49 does not operate the image forming apparatus 1 even if an operation of turning off the main power supply of the image forming apparatus 1 and turning on the main power supply is performed.

(Operation)
When an operation for instructing image formation is performed by the user, the image forming apparatus 1 forms an image in accordance with this instruction. At this time, the temperature controller 48 controls the temperature of the heating roller 26a. While the temperature control unit 48 is controlling the temperature of the heating roller 26a, the temperature of the heating roller 26a does not exceed the abnormal temperature T2. Therefore, during this period, the control signal S2 for turning on the relay 45 is output from the high temperature detection circuit 44, and the relay 45 is in the on state. The temperature control unit 48 controls the power supply circuit 29 to supply power to the heater 27 until the temperature of the heating roller 26a reaches the target temperature. Thereby, the heater 27 generates heat and the heating roller 26a is heated. When the temperature of the heating roller 26 a becomes higher than the target temperature, the temperature control unit 48 controls the power supply circuit 29 to cut off the power supply to the heater 27. As a result, the temperature of the heating roller 26a decreases. As described above, the temperature controller 48 controls the power supply circuit 29, whereby the temperature of the heating roller 26a is kept constant.

  By the way, when a malfunction such as thermal runaway occurs in the CPU 46, the temperature control unit 48 may not work. When the temperature control unit 48 does not work, the temperature of the heating roller 26a is not controlled, so that the temperature of the heating roller 26a rises, which may cause smoke or fire. Therefore, in such a case, the high temperature detection circuit 44 works to stop the heating of the heating roller 26a. Specifically, when the temperature of the heating roller 26a exceeds the abnormal temperature T2, in the high temperature detection circuit 44, the input current supplied from the first temperature sensor 31 becomes larger than the reference current. In this case, the high temperature detection circuit 44 outputs a control signal S1 for turning off the relay 45. When the control signal S1 is output from the high temperature detection circuit 44, the relay 45 is driven and turned off. Thereby, the energization of the heater 27 is cut off, and the heating of the heating roller 26a is stopped.

  When a problem occurs in the CPU 46, the operation prohibiting unit 49 may be operable even if the temperature control unit 48 does not work as described above. In this case, when the control signal S1 is output from the high temperature detection circuit 44, the operation prohibiting unit 49 turns off the main power supply of the image forming apparatus 1 and prohibits the operation of the image forming apparatus 1. In this case, even if an operation for turning on the main power supply of the image forming apparatus 1 is performed, the image forming apparatus 1 does not operate. This is because if the temperature of the heating roller 26a exceeds the abnormal temperature T2, it is considered that it is preferable not to use the image forming apparatus 1 because it may cause some trouble. is there. For example, when a maintenance inspection is performed by a maintenance staff and a predetermined operation is performed, the operation prohibiting unit 49 may cancel the prohibition of the operation.

  It is also conceivable that a failure occurs in the CPU 46 and a failure also occurs in the high temperature detection circuit 44, and both the temperature control unit 48 and the high temperature detection circuit 44 do not work. In this case, even if the temperature of the heating roller 26a exceeds the abnormal temperature T2, the high temperature detection circuit 44 does not work, so that the temperature of the heating roller 26a rises, which may cause smoke or fire. Therefore, in such a case, the safety device 28 works to stop the heating of the heating roller 26a. Specifically, when the temperature of the heating roller 26a reaches the abnormal temperature T1, the safety device 28 cuts off the power supply from the power supply circuit 29 to the heater 27. Thereby, the energization of the heater 27 is cut off, and the heating of the heating roller 26a is stopped.

  In the embodiment described above, the first temperature sensor 31, the second temperature sensor 32, the high temperature detection circuit 44, the relay 45, the temperature control unit 48, and the operation prohibition unit 49 function as a temperature control device. According to this embodiment, even when the temperature control unit 48 stops working, heating of the heating roller 26a is stopped when the temperature of the heating roller 26a exceeds the abnormal temperature T2. This prevents the temperature of the heating roller 26a from rising excessively.

  Further, in the configuration using the high temperature detection circuit 44 as in the above-described embodiment, the change of the abnormal temperature T2 is realized only by changing the reference current. For example, the reference current may be increased to increase the abnormal temperature T2. On the other hand, in order to reduce the abnormal temperature T2, the reference current may be reduced. If a thermostat or a thermal fuse is used instead of the high temperature detection circuit 44, the detection temperature cannot be finely adjusted. For example, when the abnormal temperature T2 is desired to be changed in units of several degrees, it is possible to respond flexibly. I can't. On the other hand, in the above-described embodiment, since the high temperature detection circuit 44 is used, fine adjustment of the abnormal temperature T2 is easily realized.

  In the embodiment described above, the high temperature detection circuit 44 uses the temperature detected by the first temperature sensor 31 to determine whether or not the temperature of the heating roller 26a exceeds the abnormal temperature T2. This is due to the following reasons. As described above, the first temperature sensor 31 detects the temperature of the central portion of the heating roller 26a. For example, when both ends of the heating roller 26a are open, the end is brought into contact with the outside air and cooled, whereas heat is accumulated in the center, so the center of the heating roller 26a is closer to the end. The temperature is higher than that. In this case, in order to prevent accidents such as smoke and fire, it is preferable to stop heating of the heating roller 26a when the temperature of the central portion of the heating roller 26a exceeds the abnormal temperature. The recording medium P is in contact with the central portion of the heating roller 26a. Accidents such as smoke and fire are likely to occur when the recording medium P is in contact with the heating roller 26a. Therefore, in order to prevent such an accident, the heating roller 26a is heated when the temperature of the central portion of the heating roller 26a exceeds an abnormal temperature so as not to excessively increase the temperature of the area in contact with the recording medium P in the heating roller 26a. It is preferable to stop the heating of the roller 26a.

  In the embodiment described above, the temperature of the heating roller 26a is controlled using both the temperature detected by the first temperature sensor 31 and the temperature detected by the second temperature sensor 32. Thereby, for example, even when a failure occurs in the first temperature sensor 31 or the second temperature sensor 32, the temperature of the heating roller 26a is detected, so that the accuracy of temperature control of the heating roller 26a is improved.

(Modification)
The above-described embodiment is an example of the present invention. The present invention is not limited to the above-described embodiment, and may be modified. Moreover, you may implement combining the following modifications.

(1) Modification 1
In the embodiment described above, the high temperature detection circuit 44 uses the temperature detected by the first temperature sensor 31 to determine whether or not the temperature of the heating roller 26a exceeds the abnormal temperature T2. However, for example, when both ends of the heating roller 26a are closed, heat is removed from the central portion by contact with the recording medium P, whereas heat is accumulated at the end portion. In some cases, the temperature is higher than that in the central portion. In this case, in order to prevent accidents such as smoke and fire, it is preferable to stop the heating of the heating roller 26a when the temperature of the end of the heating roller 26a exceeds the abnormal temperature. Therefore, in such a case, the high temperature detection circuit 44 may use the temperature detected by the second temperature sensor 32 instead of the temperature detected by the first temperature sensor 31. In this case, an input current supplied from the second temperature sensor 32 is input to the high temperature detection circuit 44.

(2) Modification 2
In the embodiment described above, the first temperature sensor 31 and the second temperature sensor 32 detect the temperature of the heating roller 26a using a thermistor element. However, the means for detecting the temperature of the heating roller 26a is not limited to the thermistor element. For example, a non-contact temperature sensor that detects the temperature of the heating roller 26a using heat radiation may be used.

(3) Modification 3
In the embodiment described above, the first temperature sensor 31 and the second temperature sensor 32 are provided on the heating roller 26a. However, the number of temperature sensors is not limited to two. For example, three or more temperature sensors may be provided. In this case, the temperature control unit 48 may acquire the temperatures detected by all the temperature sensors and use them for the temperature control of the heating roller, or may acquire the temperatures detected by some of the temperature sensors for heating. You may utilize for the temperature control of a roller.

(4) Modification 4
In the embodiment described above, the safety device 28 cuts off the power supply from the power supply circuit 29 to the heater 27 using a bimetal thermostat. However, the means for cutting off the power supply from the power supply circuit 29 to the heater 27 is not limited to a bimetal thermostat. For example, a thermal fuse may be used. In this case, the temperature news cuts off the power supply from the power supply circuit 29 to the heater 27 when the temperature of the heating roller 26a becomes the abnormal temperature T1.

(5) Modification 5
The operation prohibition unit 49 is not necessarily provided. For example, depending on the abnormal temperature T2, the image forming apparatus 1 may operate normally even when the temperature of the heating roller 26a once exceeds the abnormal temperature T2. In such a case, the heating of the heating roller 26a is stopped by the action of the high temperature detecting circuit 44, and the image formation may be resumed when the temperature of the heating roller 26a falls below the abnormal temperature T2. Specifically, when the temperature of the heating roller 26a falls below the abnormal temperature T2, in the high temperature detection circuit 44, the reference current becomes larger than the input current. In this case, the high temperature detection circuit 44 outputs a control signal S2 for turning on the relay 45. When the control signal S2 is output from the high temperature detection circuit 44, the relay 45 is driven and turned on. The image forming apparatus 1 resumes image formation when the relay 45 is turned on and the temperature control unit 48 becomes operable. In this case, since the user does not have to stop using the image forming apparatus 1, the convenience for the user is improved.

(6) Modification 6
The abnormal temperature T2 may be changed dynamically. For example, accidents such as smoke and fire are likely to occur when the recording medium P is in contact with the heating roller 26a. Therefore, the image forming apparatus 1 includes a sensor that detects the recording medium P existing between the heating roller 26a and the pressure roller 26b. When the recording medium P is detected by this sensor, the abnormal temperature T2 is set. It may be lowered. Specifically, when the recording medium P is detected by the sensor, the reference current input to the high temperature detection circuit 44 is reduced. Thereby, when the recording medium P exists between the heating roller 26a and the pressure roller 26b, the high temperature detection circuit 44 works when the heating roller 26a exceeds an abnormal temperature T2 lower than normal. It is further prevented that the heating roller 26a becomes hot and accidents such as smoke and fire occur.

(7) Modification 7
In the embodiment described above, the high temperature detection circuit 44 determines whether or not the temperature detected by the first temperature sensor 31 exceeds the abnormal temperature T2 by comparing the currents. However, the high temperature detection circuit 44 may make this determination by comparing the voltages. In this case, the input voltage applied to the first temperature sensor 31 and the reference voltage are input to the high temperature detection circuit 44. The high temperature detection circuit 44 determines whether or not the temperature detected by the first temperature sensor 31 has exceeded the abnormal temperature T2 corresponding to the reference voltage by comparing the input voltage and the reference current. Also in this modification, fine adjustment of the abnormal temperature T2 can be easily realized only by changing the reference voltage.

(8) Modification 8
The configuration of the image forming apparatus 1 described in the above-described embodiment is merely an example, and the present invention is not limited to this. For example, the image forming apparatus 1 may be a color printer that forms a color image. Further, the image forming apparatus 1 may have a copy function and a facsimile function.
Moreover, the parameters (temperature, current value, voltage value, etc.) described in the above-described embodiment are merely examples, and the present invention is not limited to this.

(9) Modification 9
The program executed by the CPU 46 may be provided in a state where it is recorded on a recording medium such as a magnetic tape, a magnetic disk, a flexible disk, an optical disk, a magneto-optical disk, or a memory, and may be installed in the image forming apparatus 1. This program may be downloaded to the image forming apparatus 1 via a communication line such as the Internet.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 21 ... Photosensitive drum, 22 ... Charger, 23 ... Exposure device, 24 ... Developing device, 25 ... Transfer roller, 26 ... Fixing device, 26a ... Heating roller, 26b ... Pressure roller, 28 ... Safety device, 31 ... first temperature sensor, 32 ... second temperature sensor, 40 ... temperature control circuit, 44 ... high temperature detection circuit, 45 ... relay, 46 ... CPU, 47 ... memory, 48 ... temperature control unit, 49 ... Operation prohibited part

Claims (6)

A detection unit that detects the temperature of the heating roller that generates heat when energized and outputs a signal corresponding to the detected temperature;
A temperature control unit that controls the temperature of the heating roller based on a temperature corresponding to the signal output from the detection unit and a preset target temperature;
A relay that is connected to the heating roller and shuts off the energization of the heating roller when turned off;
By comparing the signal output from the detection unit with a reference signal, it is determined whether or not the temperature of the heating roller exceeds a threshold value corresponding to the reference signal, and the temperature of the heating roller exceeds the threshold value In this case, a temperature control device comprising: a comparison unit that turns off the relay. The detection unit includes a first detection unit that detects a temperature of a region in contact with the recording medium in the heating roller,
The temperature control device according to claim 1, wherein the comparison unit compares the signal detected from the first detection unit with the reference signal. The detection unit includes a second detection unit that detects a temperature of a region of the heating roller that does not contact the recording medium,
The temperature control unit controls the temperature of the heating roller based on a temperature corresponding to a signal output from the first detection unit and the second detection unit and the target temperature. The temperature control device according to claim 2. An image carrier,
A charging unit for charging the image carrier;
An exposure unit that exposes the charged image carrier to form a latent image;
A developing unit for developing the latent image with toner to form a toner image;
A transfer portion for transferring the toner image to a recording medium;
A fixing unit that includes a heating roller and a pressure roller, and fixes the toner image to the recording medium by heating and pressing;
An image forming apparatus comprising: the temperature control device according to claim 1. The image forming apparatus according to claim 4, further comprising an operation prohibiting unit that prohibits the operation of the image forming apparatus when the relay is turned off. 6. The image forming apparatus according to claim 4, further comprising: a blocking unit configured to block power supply to the heating roller when the temperature of the heating roller reaches a predetermined temperature higher than the threshold value.

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