JP2005201970A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which, occurrence of an abnormal state in CPUs that control the heating of a heating device, is surely detected and the supply of a high frequency current to an exciting coil is stopped. <P>SOLUTION: A fixing belt 22 which is brought into firm contact with a toner image is heated by electromagnetic induction. A high frequency current is supplied to an exciting coil 22c from the IH inverter circuit 113 of a power source unit 30. The IH inverter circuit is controlled by a drive signal outputted from the second CPU 111 of the IH control circuit. The IH control circuit has a runaway detection circuit 112 for the second CPU. When runaway is detected, a signal indicating the detection of the runaway is outputted to the control device 28. Based on the output of a temperature sensor 31, the first CPU 121 of the control device outputs an ON/OFF signal for the supply of power to the exciting coil. In addition, a runaway detection circuit 125 for the first CPU is provided, and the OFF signal for the supply of power is outputted when runaway is detected. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus that forms a toner image by adhering powder toner to a latent image due to a difference in electrostatic potential, and heat-melts the toner image to fix it on a recording sheet.

  In general, in an image forming apparatus using powdered toner, a step of fixing a toner image is performed by electrostatically transferring a toner image onto a recording sheet, and then a heating member and a pressure member having an endless peripheral surface. A method is widely used in which a recording sheet is sandwiched between the two and a toner image is heated and melted and pressed onto the recording sheet. Also known is an image forming apparatus that primarily transfers a toner image to an intermediate transfer member, then heats the toner image on the intermediate transfer member, and presses the toner image onto a recording sheet to simultaneously perform secondary transfer and fixing. It has been.

As means for heating the heating member or the intermediate transfer member, there is already known one in which a conductive layer is provided on the heating member or the intermediate transfer member and the conductive layer is heated by electromagnetic induction heating (Patent Documents 1 to 3). ).
The electromagnetic induction heating device includes an exciting coil arranged near a heated member such as a heating member or an intermediate transfer member, and a high-frequency generating circuit that supplies a high-frequency current to the exciting coil, and fluctuates near the heating member. Generate a magnetic field. This fluctuating magnetic field generates an induced current in the conductive layer of the heating member, and heats the heating member due to resistance loss.

  By using such an electromagnetic induction heating device, the heating member or the intermediate transfer body can be directly heated, and the temperature range becomes extremely limited, and the heating member can be heated in a very short time. it can. For this reason, even if preheating is not continued during standby of the apparatus, initial operation processing can be efficiently performed when the apparatus is started up or when the apparatus returns from the standby state, and power consumption can be reduced.

  In the image forming apparatus as described above, in order to heat the toner image at an appropriate temperature and perform good fixing, the temperature of the heating member or the intermediate transfer body is measured, and the temperature of the heated body is appropriately maintained. It is controlled so that In addition, the object to be heated is orbitally moved, and when the orbiting movement is not performed smoothly, a part of the object to be heated may be excessively heated and damaged at a high temperature. In addition to monitoring, control is performed to stop heating when the temperature of the object to be heated rises abnormally.

  In general, the temperature of the object to be heated is measured using a temperature sensor such as a thermistor or a thermocouple, a non-contact infrared sensor, or the like that measures the temperature by contacting the object to be measured. Further, in order to detect the circular movement of the heating member and the intermediate transfer member, a detection pattern made of a light-reflective material is provided, and a light sensor that detects the reflected light irradiated on the detection pattern is generally used. .

  Detection signals from these sensors are input to the CPU, and power supply to the excitation coil of the electromagnetic induction heating device is ON / OFF controlled. The high-frequency current supplied to the exciting coil is controlled in frequency and supplied power by a separately provided CPU. As described above, the image forming apparatus is generally controlled by using a plurality of CPUs, maintains appropriate fixing conditions, and performs an emergency stop when an abnormality occurs.

  However, the CPU may malfunction when the usage environment is poor or an error signal is input. When the CPU enters a so-called runaway state where it continues to output an error signal, the heating member or the intermediate transfer member may be excessively heated and burnt out. In order to solve such problems, Patent Document 4 proposes the following apparatus.

In this device, the heating roller is heated by electromagnetic induction, and the ON / OFF control of the exciting coil based on the detected temperature of the heating roller is performed by a hardware circuit. The output of this circuit and the main control of the fixing unit The ON signal output from the CPU that performs is output to the heating device side through an AND circuit. In such a configuration, since the ON / OFF signal of the exciting coil is controlled by the hardware circuit, the temperature of the heating roller is normally controlled even when the CPU runs out of control and continues to output an error signal. .
Japanese Patent Laid-Open No. 10-254263 JP-A-10-301415 Japanese Patent Application Laid-Open No. 11-152804 JP 2002-174982 A

However, the image forming apparatus has the following problems.
In the above apparatus, even if the CPU is in a runaway state and outputs an error signal, the control is performed by the hardware circuit and is driven without detecting any abnormality. For this reason, it is driven without being recognized by the operator that there is a CPU that outputs an abnormal signal. It is also difficult to specify the CPU that is outputting the abnormal signal.

  Furthermore, if the drive of the device is continued with such a CPU runaway, if the power setting for the runaway output is high, the temperature ripple may increase or the device may be heated abnormally by long-term drive. There is also. Also, if the power setting during runaway is low output, heating will be insufficient and fixing failure such as cold offset will occur.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to reliably detect the occurrence of a CPU abnormality and stop the supply of high-frequency current to the exciting coil. Is to provide.

  In order to solve the above-mentioned problems, the invention according to claim 1 is a recording medium in which a toner image is formed by attaching toner to a latent image due to a difference in electrostatic potential, and the toner image is heated and melted by a fixing device. An image forming apparatus to be fixed on a heating means for heating the toner image, a first control means for ON / OFF control of power supply to the heating means, and power supplied to the heating means Second control means for controlling the amount; and runaway detection means for detecting that the control means continues to output an error signal for each of the first control means and the second control means. An image forming apparatus is provided.

  In this image forming apparatus, since each of the first control means and the second control means is provided with a runaway detection means for detecting that these control means continue to output an error signal, the control means It is possible to immediately detect such an abnormality and take measures such as stopping the supply of high-frequency current to the exciting coil and displaying the occurrence of the abnormality.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the heating unit includes an exciting coil and a power source for supplying a high-frequency current to the exciting coil, and an eddy current is applied to the conductive layered member. The second control means controls at least one of a frequency of a current output from the power source, a current value, and a voltage value.

  In this image forming apparatus, a high frequency current is supplied to an exciting coil provided in the heating means, and the frequency, voltage, and the like of the high frequency current are adjusted by the second control means under conditions such as the temperature of the member to be heated. Properly controlled according to. When the second control means outputs an error signal, the second runaway detection means detects an abnormality and prevents an inappropriate control state from continuing.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, a signal from a first runaway detection unit that detects an error signal of the first control unit is input, and the first It is assumed that there is an emergency stop means for stopping the driving of the heating means when one control means outputs an error signal.

  In addition to the first control unit and the second control unit, the image forming apparatus includes an emergency stop unit that stops driving the heating unit when an abnormality is detected in the first control unit. Further, it is possible to reliably prevent the high frequency current from being supplied to the exciting coil by the ON / OFF signal.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the image forming apparatus further comprises a display unit whose display is controlled by the first control unit, and an error signal from the second control unit is generated. When the output of the second runaway detection means to be detected is input to the first control means, and the first control means receives a signal indicating that the second control means has output an error signal In addition, this fact is displayed on the display means.

  In this image forming apparatus, when the second control unit outputs an error signal, this is quickly displayed by the display unit. Therefore, the operator can accurately grasp and deal with the state of the apparatus.

  As described above, in the image forming apparatus according to the present invention, the runaway detection means provided for each of the plurality of control means continues to output an error signal, and the abnormality of the control means is detected. Is immediately detected, and measures such as stopping the heating means or displaying an abnormality are immediately taken. Accordingly, it is possible to effectively prevent the drive with excessive heating or abnormality from being continued, and a highly safe apparatus can be obtained.

Hereinafter, embodiments of the invention according to the present application will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to an embodiment of the present invention, and FIG. 2 is a schematic configuration diagram showing a fixing device used in the image forming apparatus shown in FIG.
The image forming apparatus includes a cylindrical photosensitive drum 1 on which a latent image due to a difference in electrostatic potential is formed by irradiating image light after uniform charging, and around the photosensitive drum 1. Further, a charging device 2 for uniformly charging the surface of the photosensitive drum 1, an exposure device 3 for irradiating the photosensitive drum 1 with image light to form a latent image on the surface, and a latent image on the photosensitive drum. A developing unit 4 that selectively transfers toner to form a toner image, an endless belt-shaped intermediate transfer member 5 that is opposed to the photosensitive drum 1 and is supported so as to be able to circulate around the photosensitive drum 1, and photosensitive after transfer of the toner image. A cleaning device 6 that removes toner remaining on the body drum 1 and a static elimination exposure device 7 that neutralizes the surface of the photosensitive drum 1 are provided.

  Further, inside the intermediate transfer member 5, a transfer charger 8 for primarily transferring the toner image formed on the photosensitive drum to the intermediate transfer member 5, two support rolls 9a and 9b, and secondary transfer are performed. A transfer counter roll 10 for carrying out is disposed, and the intermediate transfer body 5 is stretched around these rolls so as to be able to go around. A transfer roll 11 for transferring a toner image on the intermediate transfer body onto a recording sheet is disposed at a position facing the transfer opposing roll 10 via the intermediate transfer body 5. The transfer opposing roll 10 and the transfer roll The recording paper P is fed from a paper tray (not shown) into the pressure contact portion with the paper 11. Further, on the downstream side of the press contact portion, a fixing device 12 that heats and melts the toner image on the recording paper and press-bonds it to the recording paper, and removes the toner remaining on the intermediate transfer member at a position along the intermediate transfer member 5. A cleaning device 13 is provided.

  The photosensitive drum 1 has a metal drum surface with various inorganic photosensitive materials such as Se, a-Si, a-SiC, and Cds, organic photosensitive materials, amorphous selenium photosensitive materials, amorphous silicon photosensitive materials, and the like. What formed the layer can be used.

  The charging device 2 is obtained by coating a metal roll having conductivity such as stainless steel or aluminum with a coating of a high resistance material. The charging device 2 is in contact with the photosensitive drum 1 and is driven to rotate. When a predetermined voltage is applied, a continuous discharge is generated in a minute gap in the vicinity of the contact portion between the roll and the photosensitive drum 1, and the surface of the photosensitive drum 1 is charged almost uniformly. It is.

  The exposure device 3 generates blinking laser light based on the image signal, and scans this in the main scanning direction of the photosensitive drum 1 by a polygon mirror. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 1.

  In the developing unit 4, four developing devices 4a to 4d containing yellow, magenta, cyan, and black toners are rotatably supported, and the developing devices 4a to 4d are in close proximity to the photosensitive drum 1 in order. Oppositely, toner is transferred to a latent image corresponding to each color to form a visible image.

  The belt-like intermediate transfer member 5 has a two-layer structure of a base layer and a surface layer, and the base layer includes polyimide, polyamide, polyamideimide, etc. in consideration of heat resistance, strength, and surface smoothness. The surface layer is made of silicone rubber, fluorine rubber, or the like which has high heat resistance and high releasability from the toner.

The transfer charger 8 applies a voltage to the back surface of the intermediate transfer member 5 by applying a voltage so that the toner image on the photosensitive drum 1 is efficiently transferred to the intermediate transfer member 5.
The transfer roll 11 is made of a conductive or semiconductive roll-like member, and a toner image on the intermediate transfer body 5 is collectively transferred onto the recording paper P by applying a voltage between the transfer opposing roll 10. .

Next, the configuration of the fixing device 12 will be described with reference to FIG.
The fixing device 12 includes an endless fixing belt 21, an electromagnetic induction heating device 22 supported at a position facing the peripheral surface of the fixing belt 21, a pressure roll 23 pressed against the fixing belt 21, and a fixing belt. 21, a pressure facing member 24 that sandwiches the fixing belt 21 with the pressure roll 23, and a peeling supported near the pressure contact portion between the pressure roll 23 and the pressure facing member 24. Member 25. In addition, a temperature detection device 26 that measures the temperature of the inner peripheral surface of the fixing belt 21 is provided upstream of the pressure contact portion between the pressure roll 23 and the pressure facing member 24, and rotates around the outer peripheral surface of the fixing belt 21. A detection sensor 27 is provided.
And the power supply unit 30 which supplies electric power to the said electromagnetic induction heating apparatus 22, and the control apparatus 28 (1st control means) which controls the output of the control signal to this power supply unit 30, and the rotational drive of the pressurization roll 23 are included. The detection signals of the temperature detection device 26 and the rotation detection sensor 27 are input to the control device 28. The control device 28 may have a function of controlling the driving of the entire image forming apparatus.

  The fixing belt 21 is formed by using a sheet-like member having high heat resistance represented by polyimide, polyimide amide, etc. as a base layer, and laminating a conductive layer thereon, an elastic layer, and a surface release layer thereon. is there. The conductive layer is made of, for example, a magnetic metal such as iron, magnetic stainless steel, or nickel, or a main alloy thereof, a nonmagnetic metal such as nonmagnetic stainless steel, aluminum, or copper, or an alloy of these main bodies in a thickness of 5 μm to 50 μm. The formed material is used, and the material is selected so as to have a specific resistance value that allows sufficient heat generation by electromagnetic induction. The elastic layer adheres the surface of the fixing belt 21 to the toner image on the recording paper, has heat resistance, high thermal conductivity such as silicone rubber, fluorine rubber, fluorosilicone rubber, etc., and has a thickness of It is desirable that the hardness is 10 μm to 500 μm and the hardness is 600 (JIS-KA type tester) or less. As the surface release layer, one having a thickness of 1 μm to 100 μm, such as a fluororesin, a silicone resin, or the like, having high release properties and heat resistance can be used. Although not shown, the surface release layer is provided with one or more reflectors that reflect the light emitted from the rotation detection sensor 27.

  The pressure roll 23 has a metal cylindrical core 23a as a core material, and includes an elastic layer 23b such as sponge or rubber on the surface of the core 23a. The pressure roll 23 is rotationally driven by a drive motor (not shown), and the fixing belt 21 is driven to rotate accordingly.

  The electromagnetic induction heating device 22 is disposed so that the gap with the outer peripheral surface is 1 to 3 mm along the outer peripheral surface of the fixing belt 21 and heats the conductive layer of the fixing belt 21. . The electromagnetic induction heating device 22 includes a magnetic core 22b made of ferrite or the like supported on a pedestal 22a, and an excitation coil 22c wound around the magnetic core 22b.

  The pressure opposing member 24 includes an elastic member 24a having a contact surface curved in a shape along the peripheral surface of the pressure roll 23, and a support member 24b that supports the elastic member 24a and is fixedly supported at both ends. The main portion is constituted by a belt traveling guide (not shown) that is supported by the support member 24b, abuts against the inner peripheral surface at both ends in the width direction of the fixing belt 21, and regulates the position of the fixing belt 21. Yes.

  The release member 25 includes a support portion 25a whose one end is fixedly supported and a release sheet 25b supported by the support member 25a. The release member 25b is disposed so that the front end of the release sheet 25b approaches or contacts the fixing belt 21. As a result, the release sheet 25 b enters between the recording paper P that has passed through the press contact portion and the fixing belt 21, and the recording paper P is released from the fixing belt 21.

  The temperature detection device 26 contacts the fixing belt 21 to detect the temperature of the fixing belt 21, supports the temperature sensor 31, and elastically presses the temperature sensor 31 to the inner peripheral surface of the fixing belt 21. The temperature sensor 31 is brought into contact with the fixing belt 21 with a substantially constant contact pressure by the repulsive force of the elastic support member 32.

  The temperature sensor 31 measures the temperature in contact with the measurement object, and a thermocouple using the Seebeck effect, a thermistor using an element having a large temperature coefficient of resistance, or the like is used. The temperature sensor 31 may be one that detects temperature at a single location, but it is desirable to provide a plurality of temperature sensors so that temperatures are detected at a plurality of positions. Further, in place of the contact-type temperature sensor as described above, a non-contact type sensor such as an infrared sensor can be used.

FIG. 3 is a block diagram showing the configuration of the control device 28 and the power supply unit 30.
The control device 28 is provided on the circuit board on the main body side of the fixing device 12, and receives a signal from the temperature sensor 31a. From the first CPU 121 that processes these signals and the temperature sensor 31b for overheating detection. Overheat detection circuit 122 that outputs a warning signal at the time of overheating based on this signal, rotation detection circuit 126 that detects the rotation state of fixing belt 21 based on the signal from rotation detection sensor 27, and CPU 121 generates an error signal. And a first runaway detection circuit 125 that outputs a warning signal when the output is continued.

  The power supply unit 30 is provided on a circuit board on the side of the electromagnetic induction heating device 22, and includes an IH inverter circuit 113 that generates a high-frequency current, and the frequency and current value of the high-frequency current generated by the IH invert circuit 113. The IH control circuit 110 controls the voltage value, the ON duty width, and the like. The IH control circuit 110 includes a second CPU 111 and a second runaway detection circuit 112 that detects when the CPU 111 continues to output an error signal.

  Based on the signal from the temperature sensor 31a, the first CPU 121 provided in the control device 28 outputs a signal for turning off the power supply to the exciting coil 22c when the temperature becomes equal to or higher than the control upper limit value, and the detected temperature is the control lower limit. When the value is below the value, an ON signal is output. The overheat detection circuit 122 outputs a warning signal when the temperature sensor 31b for overheat detection detects a predetermined temperature, that is, an upper limit value of a temperature allowable by the apparatus. In this example, when an abnormality is detected, The H signal is output. The rotation detection circuit 126 monitors whether the fixing belt 21 is normally rotated based on the output from the rotation detection sensor 27, that is, the change in the output voltage due to the passage of the pattern on the fixing belt 21. Yes, a warning signal is output when the fixing belt 21 stops without being driven normally or when the speed becomes low, and an H signal is output when the fixing belt 21 stops or becomes low speed due to an abnormality. It has become. The first runaway detection circuit 125 detects whether or not the first CPU 121 is operating normally based on the clock signal, and outputs an H signal when detecting that the first CPU 121 is not operating normally. It is supposed to be.

  The output of the first CPU 121 detects that the temperature of the fixing belt 21 has fallen below the control lower limit value, and outputs an L signal when the power supply to the exciting coil 22c is turned on. The ON signal, the signal from the overheat detection circuit 122, and the signal from the rotation detection circuit 126 are input to the first OR circuit 123. At this time, if the temperature and rotation driving state of the fixing belt 21 are normal, the outputs from the overheat detection circuit 122 and the rotation detection circuit 126 are L signals, and the OR signal 123 outputs an L signal, that is, an ON signal. Is done. Further, when the temperature sensor 31a detects that the temperature of the fixing belt 21 has reached the control upper limit value, the output from the first CPU 121 becomes the H signal, and the output of the first OR circuit 123 becomes the H signal, that is, the exciting coil 22c. A signal for turning off the power supply to is output. When the fixing belt 21 is overheated or abnormal in rotation, the output of the overheat detection circuit 122 or the rotation detection circuit 126 becomes an H signal, and the output of the OR circuit 123 becomes an H signal (OFF signal). These signals are input to the IH control circuit 110 of the power supply unit 30.

  The first runaway detection circuit 125 outputs an H signal when an abnormality occurs in the first CPU 121 and runs out of control, and outputs an L signal when functioning normally. The output of the OR circuit 123 is input to the second OR circuit 124. Therefore, when the first CPU 121 runs away, the output of the second OR circuit 124 becomes an H signal (OFF signal) regardless of the output from the first OR circuit 123.

  On the other hand, the power supply unit 30 includes an AC rectifier circuit 119 supplied from a commercial AC power supply 117, and the IH inverter circuit 113 switches current based on a drive signal from the IH control circuit 110 to generate a high-frequency current. The excitation coil 22c is supplied. The IH control circuit 110 receives a signal for setting the amount of power from the first CPU 121, and the second CPU 111 supplies a high-frequency current supplied to the exciting coil 22c so that the amount of power corresponds to this signal. The ON duty width is controlled. The second CPU 111 can determine various errors in the power supply unit 30 and output an error signal to the first CPU 121. Depending on the type of error, the second CPU 111 stops outputting the drive signal. is there.

  The circuit that supplies the drive signal to the IH inverter circuit 113 is provided with a transistor 114 that controls ON / OFF of the drive signal. The output of the second OR circuit 124 included in the control device 28 is supplied to the base of the transistor 114. It is supposed to be entered. Therefore, when the H signal, that is, the OFF signal is output from the second OR circuit 124, the drive signal is cut off.

  The second runaway detection circuit 112 provided in the IH control circuit 110 outputs a signal indicating an abnormality when the second CPU 111 outputs an error signal and runs out of control. It is input to the CPU 121. Thus, the first CPU 121 detects that an abnormality has occurred in the second CPU 111, displays that fact on the display device 127, and outputs a signal for stopping the power supply to the exciting coil 22c.

  The power supply to the power supply unit 30 is performed via the thermistor 116 and the fuse 118, and the power supply is stopped when an abnormally high temperature or overcurrent of the fixing belt 21 occurs.

Next, operations of the image forming apparatus and the fixing device 12 will be described.
In this image forming apparatus, the toner image is formed by the following process.
First, the surface of the photosensitive drum 1 is charged almost uniformly by the charging device 2, and then image light is irradiated from the exposure device 3 to form a latent image on the surface of the photosensitive member 1 due to the difference in electrostatic potential. . Then, the photosensitive drum 1 is rotated to move to a position facing the one developing device 4a of the developing unit 4, and the first color toner is transferred from the developing device 4a to form a toner image. This toner image is conveyed to a position facing the intermediate transfer member 5 by the circumferential movement of the photosensitive drum 1 and is electrostatically primary-transferred onto the intermediate transfer member. On the other hand, the toner remaining on the photosensitive drum 1 after the primary transfer is removed by the cleaning device 6, and the surface of the photosensitive drum 1 is potentialally initialized by the static elimination exposure device 7, and again at a position facing the charging device 2. Moving.

  Thereafter, the three developing devices 4b, 4c, and 4d of the developing unit 4 sequentially move to positions facing the photosensitive drum 1, and similarly, second, third, and fourth color toner images are sequentially formed, and intermediate transfer is performed. It is transferred onto the body 5 in a superimposed manner. At this time, the transfer roll 11 for secondary transfer is retracted to a position where it does not come into contact with the intermediate transfer member 5.

  The toner image T superimposed on the intermediate transfer member 5 is conveyed to a position where the transfer roll 11 and the transfer counter roller 10 face each other by the circular movement of the intermediate transfer member 5, and contacts the recording paper P fed from the paper tray. Be touched. A transfer bias voltage is applied between the transfer roll 11 and the intermediate transfer member 5, and the toner image T is secondarily transferred onto the recording paper.

  The recording paper P carrying the unfixed toner image T is conveyed to the fixing device 12 and sent between the fixing belt 21 and the pressure roll 23 of the fixing device 12.

  In the fixing device 12, a high-frequency current is supplied from the IH inverter circuit 113 to the exciting coil 22 c almost simultaneously with or immediately after the pressing roll 23 starts driving and the fixing belt 21 is driven and starts rotating. The When a high frequency current is supplied to the exciting coil 22c, the magnetic flux indicated by the arrow H around the exciting coil 22c repeats generation and disappearance. Then, when this magnetic field H crosses the conductive layer of the fixing belt 21, an eddy current is generated in the conductive layer so as to prevent a change in the magnetic field, and the skin resistance and the conductive layer of the conductive layer are generated. It generates heat in proportion to the current flowing through it.

  The recording paper P sent to the fixing device is heated and pressed by the fixing belt 21 heated to a predetermined temperature by the electromagnetic induction heating device 22 and the pressure roll 23, and the toner image T is melt-pressed on the recording paper P. Is done. When the recording paper P is fed out from the pressure contact portion between the pressure roll 23 and the elastic member 24a, the recording paper P tends to move straight in the fed-out direction due to its rigidity, and is easily peeled off from the bent fixing belt 21. Further, it is peeled off from the fixing belt 21 by the peeling member 25.

  The fixing belt 21 needs to be maintained at an appropriate temperature for fixing the toner image, and the control of the temperature and the control for preventing the heating at the time of abnormality are based on the output of the temperature sensor 31 and the like. Is performed as follows.

  In the fixing device 12, for example, when the power switch is turned on, initial heating (warming up) is performed. An ON signal is output from the control device 28, and a high-frequency current is supplied from the power supply unit 30 to the exciting coil 22c. Is supplied. As a result, an eddy current is generated in the conductive layer of the fixing belt 21 to generate heat. At this time, the temperature of the fixing belt 21 is detected by the temperature sensor 31, and when the temperature reaches a predetermined temperature, the power supply to the exciting coil 22c is stopped.

  Thereafter, the fixing device 12 enters a standby state, and when an image forming operation is started, the fixing belt 21 is maintained at a predetermined temperature and pressed against a recording sheet carrying an unfixed toner image, and the toner image is heated under pressure. And fix. In these steps, the temperature of the fixing belt 21 is detected by the temperature sensor 31, and ON / OFF control of the electromagnetic induction heating device 22 is performed based on these outputs.

  When the temperature of the fixing belt 21 decreases due to heat transfer and heat radiation from the fixing belt 21 to the recording sheet P and the toner image and falls below a predetermined control lower limit value, the CPU 121 of the control device 28 turns on the electromagnetic induction heating device 22 ON signal ( Here, the L signal) is output. At this time, if the overheat detection circuit 122 and the rotation detection circuit 126 do not detect any abnormality, a heating permission signal (here, L signal) is output, and the first OR circuit 123 outputs an ON signal, that is, an L signal. Is output. When the first CPU 121 is functioning normally, the L signal is output from the first runaway detection circuit 125, and the output of the second OR circuit 124 is also the L signal, that is, the ON signal.

  The power supply unit 30 outputs a high-frequency current drive signal, that is, a signal for switching rectified direct current at high frequency to the IH inverter circuit 113 via the transistor 114 based on the ON signal from the control device 28 and the power setting signal. . At this time, the L signal is input from the second OR circuit 124 to the base of the transistor 114, and the transistor 114 is in a conductive state. As a result, a high frequency current is supplied from the IH inverter circuit 113 to the exciting coil 22c, and the fixing belt 21 is heated.

  When the temperature of the fixing belt 21 rises due to electromagnetic induction heating and the temperature detected by the thermistor 116 reaches the control upper limit value, the output of the first CPU 121 changes to an OFF signal (here, H signal), and the first OR circuit 123 and The output of the second OR circuit 124 becomes an H signal, that is, an OFF signal, and power supply to the exciting coil 22c is stopped.

  On the other hand, when the overheat detection circuit 122 or the rotation detection circuit 126 detects an abnormality, a warning signal, that is, an H signal is output from them. Therefore, even if any of these detects an abnormality, the output signal of the first OR circuit 123 becomes the H signal, and the power supply to the exciting coil 22c is stopped.

  Further, when the first CPU 121 becomes abnormal and runs out of control, the H signal is output from the first runaway detection circuit 125 and the output of the second OR circuit 124 becomes the H signal, and the power to the exciting coil 22c is also output. Supply is stopped.

  Further, when the second CPU 111 is in a runaway state, the second runaway detection circuit 112 detects this and outputs a signal to that effect to the first CPU 121. As a result, the first CPU 121 displays that effect on the display device 127 and outputs an OFF signal (H signal) to the first OR circuit 123. As a result, the signal supplied to the IH control circuit 110 and the transistor 114 becomes an OFF signal (H signal), and the drive signal is cut off by the transistor 114 even when the drive signal continues to be output due to the runaway of the second CPU 111. The power supply to the exciting coil 22c is stopped.

FIG. 4 is a schematic configuration diagram showing an image forming apparatus according to another embodiment of the present invention. In this figure, the same components as those in the image forming apparatus shown in FIG.
This image forming apparatus is substantially the same as the image forming apparatus shown in FIG. 1 with respect to the photosensitive drum 1, the charging device 2, the exposure device 3, the developing unit 4, the cleaning device 6, the static elimination exposure device 7, and the transfer device 8. Have the same thing. However, in the image forming apparatus of the present embodiment, the intermediate transfer member 5 has a conductive layer along an endless peripheral surface, and an electromagnetic that heats the toner image on the intermediate transfer member 5. An induction heating device 62 and a temperature detection device 63 for measuring the temperature of the intermediate transfer member 5 are provided along the peripheral surface of the intermediate transfer member 5.

  The intermediate transfer member 5 is composed of three layers: a base layer made of a sheet member having high heat resistance, a conductive layer laminated thereon, and a surface release layer that is the uppermost layer. The material is selected so that sufficient heat can be obtained by electromagnetic induction. The surface release layer is preferably a highly releasable sheet or coat layer. In consideration of electrostatic transfer properties of the toner image during primary transfer, a conductive material such as carbon black is dispersed to provide resistance. You may use the sheet | seat which adjusted.

  The temperature detection device 63 can be the same as the temperature detection device 26 included in the fixing device shown in FIG. 2, and the temperature sensor is pressed against the peripheral surface of the intermediate transfer member 5 by the elastic repulsion force of the elastic support portion. The temperature is to be detected.

  In this image forming apparatus, the toner image T transferred from the photosensitive drum 1 onto the intermediate transfer member 5 and overlaid with a plurality of colors is heated in a heating region facing the electromagnetic induction heating device 62 by the circumferential movement of the intermediate transfer member 5. Pass through. The toner image T is heated and melted on the intermediate transfer member, and is conveyed to the pressure contact portion between the transfer facing roll 10 and the pressure roll 11. The recording paper P is fed from a paper tray (not shown) between the intermediate transfer body 5 and the pressure roll 11 in time with this conveyance, and the toner image T is pressed against the recording paper P, and the transfer and fixing. Are performed simultaneously.

  At this time, the electric power supplied to the electromagnetic induction heating device 62 is controlled by the detection value of the temperature detection device 63 so that the surface temperature of the intermediate transfer member 5 maintains a desired temperature. As this control device, a device having the same configuration as that used in the image forming apparatus shown in FIG. 1 can be applied and controlled in the same manner.

1 is a schematic configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram illustrating a fixing device used in the image forming apparatus illustrated in FIG. 1. It is a block diagram which shows the structure of a control apparatus and a power supply unit. It is a schematic block diagram which shows the image forming apparatus which is other embodiment of this invention.

Explanation of symbols

1: Photosensitive drum, 2: Charging device, 3: Exposure device, 4: Development unit, 5: Intermediate transfer member, 6: Cleaning device, 7: Static elimination exposure device, 8: Transfer charger, 9: Support roll, 10 : Transfer counter roll, 11: transfer roll, 12: fixing device, 13: cleaning device, 21: fixing belt, 22, 62: electromagnetic induction heating device, 22c: exciting coil, 23: pressure roll, 24: pressure facing Member, 25: peeling member, 26, 63: temperature detection device, 27: rotation speed sensor, 28: control device (first control means), 31: temperature sensor, 32: elastic support member, 110: IH control circuit, 111: 2nd CPU, 112: 2nd runaway detection circuit, 113: IH inverter circuit, 114: Transistor, 31a, 31b: Temperature sensor, 116: Thermostat, 117: AC power supply, 118: fuse, 119: rectifier circuit, 28: control device, 121: first CPU, 122: overheat detection circuit, 123: first OR circuit, 124: second OR circuit, 125: First runaway detection circuit, 126: rotation detection circuit, 127: display panel

Claims (4)

An image forming apparatus that forms a toner image by attaching toner to a latent image due to a difference in electrostatic potential, heats and melts the toner image by a fixing device, and fixes the toner image on a recording medium
Heating means for heating the toner image;
First control means for ON / OFF control of power supply to the heating means;
Second control means for controlling the amount of power supplied to the heating means;
An image forming apparatus, comprising: a runaway detection unit that detects that the control unit continues to output an error signal for each of the first control unit and the second control unit. The heating means includes an exciting coil and a power source that supplies a high-frequency current to the exciting coil, and induces an eddy current in the conductive layered member,
The image according to claim 1, wherein the second control unit controls at least one of a frequency, a current value, and a voltage value of a current output from the power source. Forming equipment.   Emergency stop means for stopping the driving of the heating means when a signal from the first runaway detection means for detecting an error signal of the first control means is inputted and the first control means outputs an error signal The image forming apparatus according to claim 1, further comprising: Display means for controlling display by the first control means;
The output of the second runaway detection means for detecting an error signal of the second control means is input to the first control means,
The first control means, when a signal indicating that the second control means has output an error signal is inputted, displays that fact on the display means. Item 3. The image forming apparatus according to Item 2.

Images