JP5253370B2 - Induction heating apparatus and image forming apparatus - Google Patents

Description

  The present invention uses an induction heating device that heats an object to be heated by electromagnetic induction heating, and uses the induction heating device as a fixing device to fix the toner image on the recording medium by fusing and fixing the toner image on the recording medium. The present invention relates to an image forming apparatus.

  An image forming apparatus using an electrophotographic process, such as a copying machine, a facsimile machine, or a laser printer, includes a fixing device that melts and fixes a toner image formed on a sheet. Such a fixing device is configured such that a heating roller and a pressure roller are arranged to face each other. Then, the paper on which the toner image is formed is nipped and conveyed by a nip formed between the heating roller and the pressure roller, so that the toner image is heated while being pressed to melt and fix the toner image on the paper. It is supposed to be.

  As a heating device for a heating roller, an electromagnetic induction heating (IH) heating device is known. In such an electromagnetic induction heating type heating apparatus, an exciting coil is disposed inside a cylindrical heating roller body made of a conductive material. A high-frequency current flows through the exciting coil under the control of the IH control unit, an induced eddy current is generated in the heating roller body by the high-frequency magnetic field generated thereby, and Joule heat is generated by the resistance of the heating roller body.

  At this time, the power supplied to the heating roller, that is, the amount of heat generated by the heating roller, changes according to the frequency of the high-frequency current. Therefore, the IH control unit performs feedback control by adjusting the frequency of the high-frequency current so that the power supplied to the heating roller becomes a target value.

  In the induction heating apparatus, in order to protect the circuit in the apparatus, it is necessary to stop the current supply to the exciting coil when a temperature abnormality occurs in any circuit element. There are the following Patent Documents 1 to 3 as technical documents related to this point.

  In the following Patent Document 1, when the temperature detected by the control element that controls on / off of the current supply to the exciting coil and the sensor that detects the ambient temperature of the control element rises above a predetermined temperature, the control element is turned off, There is disclosed a fixing device including an induction heating control circuit for stopping supply of current to the exciting coil.

  Japanese Patent Application Laid-Open No. 2004-228561 discloses that an overheat prevention element is provided that cuts off the power supply to the coil when the fixing roller becomes abnormally hot.

  Patent Document 3 listed below includes a power cut-off means that cuts off power to the induction coil when the temperature of the induction coil exceeds a predetermined set temperature, and the power cut-off means is a thermal fuse or a comparator. And the point comprised by a relay is disclosed.

JP 2003-202772 A JP 09-197852 A JP 09-197854 A

  In order to reliably stop the current supply to the exciting coil when the abnormality occurs, only a circuit (hardware; hereinafter referred to as a protection circuit) that stops the current supply to the exciting coil as in Patent Documents 1 to 3 described above. Rather than stopping the current supply to the excitation coil, the configuration to stop the current supply to the excitation coil by the control (software) by the IH control unit, and the circuit to stop the current supply to the excitation coil (hardware; hereinafter protection) In some cases, a configuration that prevents the occurrence of a failure of the heating device may be employed.

  However, in this case, when any abnormality occurs, the IH control unit detects an abnormality based on a signal that has undergone a predetermined process. Delay. Therefore, the timing at which the IH control unit stops the current supply to the excitation coil is delayed from the timing at which the protection circuit stops the current supply to the excitation coil.

  Here, conventionally, since the IH control unit controls the frequency of the high-frequency current while this delay occurs, when the abnormality is resolved, the frequency when the protection circuit stops supplying the current to the exciting coil. Since the current is set to zero by the protection circuit while the delay is occurring, the feedback control is executed so as to increase the current value (supply power) to the target value. For this reason, the frequency of the high-frequency current is adjusted to a frequency corresponding to large power (current).

  As a result of controlling the frequency of the high-frequency current in this way, a situation may occur in which the frequency control of the high-frequency current starts from a frequency that is significantly different from the frequency when the protection circuit stops supplying the current to the exciting coil. In this case, the control of the IH control unit becomes unstable for a while.

  The present invention has been made in view of such circumstances, and includes a configuration in which an IH control unit and a protection circuit are provided to stop the supply of high-frequency current to the exciting coil when an abnormality occurs. And providing a technique for preventing frequency control by the IH control unit from becoming unstable due to the protection circuit detecting the abnormality before the IH control unit when an abnormality occurs. Objective.

  According to the first aspect of the present invention, there is provided an exciting coil that heats an object to be heated by electromagnetic induction, a high-frequency current generating unit that generates a high-frequency current to be supplied to the exciting coil, and power detection that detects power consumption of the exciting coil. A current generation control unit that feedback-controls the frequency of the high-frequency current generated by the high-frequency current generation unit so that the power consumption detected by the power detection unit becomes a predetermined target power, and a predetermined abnormality occurs. When it is detected that a first abnormality is detected using the current generation control unit, and when a predetermined abnormality is detected, it is detected that the current generation control unit is stopped. A second abnormality detection unit that stops supply of the high-frequency current to the exciting coil using the high-frequency current generation unit, and the current generation control unit includes the first abnormality detection unit and the first abnormality detection unit. When at least one of the second abnormality detection units detects that an abnormality has occurred in the predetermined circuit unit, the frequency of the high-frequency current supplied to the exciting coil remains the same as the current high-frequency current frequency. Induction heating device to maintain.

  According to the present invention, when the first abnormality detection unit detects that the predetermined abnormality has occurred, the first abnormality detection unit uses the current generation control unit to apply the current to the excitation coil. The supply of high-frequency current is stopped.

  On the other hand, when the second abnormality detector detects that the predetermined abnormality has occurred, the second abnormality detector supplies the high-frequency current to the exciting coil using the high-frequency current generator. Is stopped.

  When the current generation control unit detects that at least one of the first abnormality detection unit and the second abnormality detection unit has the predetermined abnormality, the high-frequency current supplied to the excitation coil Is maintained at the same frequency as the current high-frequency current.

  Accordingly, even if the timing at which the first abnormality detection unit detects the predetermined abnormality and the timing at which the second abnormality detection unit detects the predetermined abnormality are deviated, the second abnormality detection is performed. The current generation control unit is stopped from supplying the high-frequency current to the exciting coil even though the unit has stopped supplying the high-frequency current to the exciting coil using the high-frequency current generating unit. The situation in which the feedback control is performed is prevented, and the frequency of the high-frequency current when the predetermined abnormality is resolved is set so that the supply of the high-frequency current to the exciting coil is stopped by the second abnormality detection unit. Can be set to the current frequency.

  A second aspect of the present invention is the induction heating apparatus according to the first aspect, further comprising a heating state detection unit that detects a heating state of a predetermined circuit unit provided on the path of the high-frequency current. The abnormality detection unit detects whether there is an abnormality in the predetermined circuit unit based on the heating state of the predetermined circuit unit detected by the heating state detection unit, and detects that an abnormality has occurred in the predetermined circuit unit Then, the supply of high-frequency current to the exciting coil is stopped using the current generation control unit, and the second abnormality detection unit is configured to heat the predetermined circuit unit detected by the heating state detection unit. Based on the state, the presence or absence of an abnormality in the predetermined circuit unit is detected, and when the abnormality is generated in the predetermined circuit unit, the high-frequency current is supplied to the excitation coil using the high-frequency current generation unit. Stop Than is.

  According to this invention, the first and second abnormality detection units detect the presence / absence of an abnormality in the predetermined circuit unit based on the heating state of the predetermined circuit unit detected by the heating state detection unit. Even when the timing at which the first abnormality detection unit detects the predetermined abnormality and the timing at which the second abnormality detection unit detects the predetermined abnormality deviates, the second abnormality detection unit The current generation control unit is in a state where the supply of the high-frequency current to the excitation coil is stopped despite the supply of the high-frequency current to the excitation coil using the high-frequency current generation unit being stopped. The situation where the feedback control is performed is prevented, the frequency of the high-frequency current when the predetermined abnormality is resolved, and the supply of the high-frequency current to the exciting coil is stopped by the second abnormality detection unit. It can be set to a frequency of the time.

  According to a third aspect of the present invention, in the induction heating apparatus according to the second aspect, the high-frequency current generation unit turns on / off the supply of the high-frequency current to the exciting coil at a frequency set by the current generation control unit. The heating state detecting unit detects a temperature of the driving circuit as the predetermined circuit unit as a heating state of the exciting coil.

  According to this invention, the supply of the high-frequency current to the exciting coil can be stopped based on the temperature of the drive circuit.

  According to a fourth aspect of the present invention, in the induction heating apparatus according to the first aspect of the present invention, the induction heating device further includes a current detection unit that detects a current value of a current flowing through the excitation coil, and the first and second abnormality detection units The abnormality is detected based on the current value detected by the current detection unit.

  According to this invention, the first and second abnormality detection units detect the abnormality based on the current value detected by the current detection unit, and the first abnormality detection unit detects the predetermined abnormality. Even when the timing at which the second abnormality detection unit detects the predetermined abnormality deviates from the timing at which the second abnormality detection unit detects the predetermined abnormality, the second abnormality detection unit moves to the excitation coil using the high-frequency current generation unit. Although the supply of the high-frequency current is stopped, the current generation control unit prevents the situation where the feedback control is performed in a state where the supply of the high-frequency current to the exciting coil is stopped, The frequency of the high-frequency current when the predetermined abnormality is eliminated can be set to the frequency at the time when the supply of the high-frequency current to the exciting coil is stopped by the second abnormality detection unit.

  In the induction heating apparatus according to any one of claims 1 to 4, as in the invention according to claim 5, an abnormality determination criterion used when the first abnormality detection unit detects the predetermined abnormality. It is preferable that the value and the abnormality determination reference value used when the second abnormality detection unit detects the predetermined abnormality are the same.

  Invention of Claim 6 WHEREIN: In the induction heating apparatus as described in any one of Claims 1 thru | or 5, When the said 1st abnormality detection part detects that the said predetermined | prescribed abnormality has generate | occur | produced, An abnormality detection program execution unit that executes an abnormality detection program for stopping the supply of high-frequency current to the exciting coil using the current generation control unit, and the second abnormality detection unit generates the predetermined abnormality. When the detection is detected, the abnormality detection circuit stops the supply of the high-frequency current to the exciting coil using the high-frequency current generator.

  Timing when the first abnormality detection unit detects the predetermined abnormality when the first abnormality detection unit is the abnormality detection program execution unit and the second abnormality detection unit is the abnormality detection circuit. However, the second abnormality detection unit often deviates from the timing at which the predetermined abnormality is detected.

  Therefore, when the first abnormality detection unit is the abnormality detection program execution unit and the second abnormality detection unit is the abnormality detection circuit, as in the invention described in claim 6, the first abnormality detection unit is the abnormality detection circuit. Significance of adopting the invention described in any one of Items 5 to 5 is great.

According to a seventh aspect of the present invention, there is provided an image forming unit that forms an image on a recording medium using a developer, and a fixing unit that performs a fixing operation for fixing the image formed by the image forming unit to the recording medium. The fixing unit is an image forming apparatus including the induction heating device according to any one of claims 1 to 6 and performing the fixing operation using heat generated by the induction heating device.

  According to this invention, in the image forming apparatus, the effect of the invention according to any one of claims 1 to 6 can be obtained.

  According to the present invention, even if the timing at which the first abnormality detection unit detects the predetermined abnormality and the timing at which the second abnormality detection unit detects the predetermined abnormality deviates, The current generation control unit stops supplying the high-frequency current to the exciting coil even though the abnormality detection unit stops the supply of the high-frequency current to the exciting coil using the high-frequency current generating unit. The situation where the feedback control is performed in the state of being prevented is prevented, and the frequency of the high-frequency current when the predetermined abnormality is resolved is determined by supplying the high-frequency current to the excitation coil by the second abnormality detection unit. Can be set to the frequency at which it was stopped.

  Therefore, although the supply of the high-frequency current to the exciting coil using the high-frequency current generation unit by the second abnormality detection unit is stopped, the current generation control unit performs feedback of the frequency of the high-frequency current. By performing the control, the frequency of the high-frequency current when the predetermined abnormality is resolved is significantly different from the frequency at the time when the supply of the high-frequency current to the exciting coil is stopped by the second abnormality detection unit As a result, it is possible to prevent the frequency control of the high-frequency current supplied to the exciting coil from becoming unstable.

1 is a side view showing an internal configuration of an image forming apparatus. 2 is a functional block diagram of a fixing device. FIG. It is the graph which showed the relationship between the frequency of the high frequency current supplied to an exciting coil, and the power consumption of an exciting coil.

  Hereinafter, an embodiment of an image forming apparatus including an induction heating device according to the present invention will be described with reference to the drawings. FIG. 1 is a side view showing the internal configuration of the image forming apparatus 1 according to the present embodiment.

  As shown in FIG. 1, the image forming apparatus 1 includes a main body unit 2, a stack tray 3 disposed on the left side of the main body unit 2, a document reading unit 4 disposed on the top of the main body unit 2, and a document reading unit. 4 is provided with a document feeding section 5 disposed above 4.

  An input operation unit 6 is provided on the front part of the image forming apparatus 1. The input operation unit 6 displays a power key, a start key for a user to input a print execution instruction, a numeric keypad for inputting the number of copies to be printed, operation guide information for various copying operations, and the like. For example, the display unit 9 includes a liquid crystal display having a touch panel function.

  The document reading unit 4 includes an image sensor such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) and a scanner unit 13 including an exposure lamp, a document table 14 formed of a transparent member such as glass, and a document reading slit. 15. The scanner unit 13 is configured to be movable by a drive unit (not shown). When reading a document placed on the document table 14, the scanner unit 13 is moved along the document surface at a position facing the document table 14, and the document image is displayed. The image data acquired while scanning is output to the image forming unit 21. When reading the document fed by the document feeding unit 5, the document is moved to a position facing the document reading slit 15 and synchronized with the document feeding operation by the document feeding unit 5 via the document reading slit 15. The image of the original is acquired, and the image data is output to the image forming unit 21.

  The document feeder 5 includes a document placement unit 16 for placing a document, a document discharge unit 17 for discharging a document whose image has been read, and one document placed on the document placement unit 16. A document transport mechanism 18 including a paper feed roller, a transport roller (not shown), and the like for feeding the paper one by one to a position facing the document reading slit 15 and discharging it to the document discharge section 17 is provided.

  Further, the document feeding unit 5 is provided so as to be rotatable with respect to the main body unit 2 so that the front side thereof can move upward. By moving the front side of the document feeder 5 upward to open the upper surface of the document table 14, the user can place a read document, for example, a book in a spread state, on the upper surface of the document table 14. ing.

  The main body 2 includes a plurality of paper feed cassettes 19, a paper feed roller 20 that feeds the paper from the paper feed cassette 19 one by one and transports it to the image forming unit 21, and an image on the paper transported from the paper feed cassette 19. And an image forming unit 21 for forming the image.

  The image forming unit 21 outputs a laser beam or the like based on the image data acquired by the scanner unit 13 to expose the photosensitive drum 22, and forms an electrostatic latent image on the surface of the photosensitive drum 22. A developing unit 24 that forms a toner image by attaching toner to the surface of the photosensitive drum 22 on which the electrostatic latent image is formed; a transfer unit 25 that transfers the toner image on the photosensitive drum 22 to a sheet; A fixing device 28 having a heating roller 26 and a pressure roller 27 for heating and fixing the toner image on the sheet by heating the sheet on which the toner image is transferred, and a sheet conveying path in the image forming unit 21. Are provided with a pair of conveying rollers 30 and 31 for conveying the sheet to the stack tray 3 or the discharge tray 29.

  When images are formed on both sides of a sheet, the image forming unit 21 forms an image on one side of the sheet, and then the sheet is nipped between the pair of conveying rollers 30 on the discharge tray 29 side. In this state, the conveyance roller pair 30 is reversed to switch back the sheet, and the conveyance roller pairs 38 and 39 convey the sheet to the sheet conveyance path 32 and convey it again to the upstream area of the image forming unit 21. After the image is formed on the other side, the paper is discharged to the stack tray 3 or the discharge tray 29.

  FIG. 2 is a functional block diagram of the fixing device 28.

  As shown in FIG. 2, the fixing device 28 includes a heating roller 26, a pressure roller 27 (not shown in FIG. 2), an IH control unit 41, a drive circuit 42, an excitation coil 43, a temperature detection unit 44, and a power measuring device 45. , A protection circuit 46 and an AND circuit 47.

  The exciting coil 43 is disposed inside a cylindrical heating roller 26 made of a conductive material. The drive circuit 42 includes, for example, an IGBT (Insulated Gate Bipolar Transistor). The drive circuit 42 is turned on / off under the control of the IH control unit 41 to supply a high-frequency current to the excitation coil 43. An induction eddy current is generated in the main body of the heating roller 26 by the high-frequency magnetic field generated in the exciting coil 43 by this current supply, and the heating roller 26 generates heat. The drive circuit 42 corresponds to the high-frequency current generator in the claims.

  The temperature detection unit 44 measures the temperature of the heating roller 26 and the drive circuit 42 and outputs the measurement result to the IH control unit 41. The power measuring device 45 measures the power supplied to the exciting coil 43 and outputs the measurement result to the IH control unit 41. The temperature detection unit 44 is an example of the heating state detection unit.

  The IH control unit 41 reads a random access memory (RAM) having a function for temporarily storing data and a function as a work area, a read only memory (ROM) for storing a program in advance, and reading the program from the ROM. CPU (central processing unit) is executed.

  The IH control unit 41 is connected to the temperature detection unit 44 and the power measuring device 45, and based on the detected temperature of the temperature detection unit 44 and the measured power of the power measurement device 45, at a predetermined control cycle (for example, 40 msec). Drive control of the drive circuit 42 is performed, and functions as an abnormality detection unit 411 and a current generation control unit 412 by a control program stored in the ROM.

  The abnormality detection unit 411 performs processing such as noise removal processing on the detection signal output from the temperature detection unit 44, and the detection temperature indicated by the detection signal after this processing is equal to or higher than a predetermined threshold (for example, 100 ° C.). Whether or not there is an abnormality in at least one of the heating roller 26 and the drive circuit 42 is detected. The abnormality detection unit 411 corresponds to a first abnormality detection unit and an abnormality detection program execution unit in the claims.

  The current generation control unit 412 keeps the heating roller 26 and the drive circuit 42 at a predetermined temperature when the abnormality detection unit 411 determines that the temperature detected by the temperature detection unit 44 is not an abnormal value. Driving so that the target power supplied to the exciting coil 43 is calculated, and the temperature of the heating roller 26 is stably maintained based on the power (detected power) detected by the power meter 45 and the calculated target power. The amount of feedback related to the frequency of the high-frequency current output from the circuit 42, in other words, the frequency of the high-frequency current supplied to the exciting coil 43 in the next cycle with respect to the exciting coil 43 is obtained by PID control (feedback control). The PWM signal is output to the AND circuit 47.

  In addition, when the relationship between the frequency of the high frequency current supplied to the exciting coil 43 and the power consumption of the exciting coil 43 is represented by a graph, as shown in FIG. 3, a mountain shape having a peak at a certain frequency (hereinafter referred to as a peak frequency) is shown. In this embodiment, the power consumption of the exciting coil 43 decreases as the frequency of the high frequency current increases, that is, the frequency of the high frequency current decreases, and the excitation increases as the frequency of the high frequency current decreases. The current supply to the exciting coil 43 is controlled using a region where the power consumption of the coil 43 is high.

  When the abnormality detection unit 411 detects that the abnormality has occurred, the current generation control unit 412 sets the duty of the PWM signal to zero in order to stop the supply of the high-frequency current to the excitation coil 43. If the abnormality is not detected by the abnormality detection unit 411, the PID control of the drive circuit 42 is resumed.

  The protection circuit 46 is configured by a circuit independent of the IH control unit 41, and the detection temperature indicated by the detection signal output from the temperature detection unit 44 is a value equal to or higher than the predetermined threshold (hereinafter referred to as an abnormal value). Whether or not there is an abnormality in at least one of the heating roller 26 and the drive circuit 42, and an H (high) signal for turning the drive circuit 42 on and off according to the PWM signal is turned off. L (low) signal for output.

  That is, when the protection circuit 46 detects that an abnormality has occurred, the protection circuit 46 outputs an L (low) signal to the AND circuit 47 in order to stop supplying the PWM signal from the IH control unit 41 to the drive circuit 42. . The protection circuit 46 is communicably connected to the IH control unit 41, and outputs the L (low) signal to the IH control unit 41 when detecting that an abnormality has occurred.

  Further, when the protection circuit 46 no longer detects that an abnormality has occurred, the protection circuit 46 causes the AND circuit 47 and the drive circuit 42 to perform H to cancel the supply stop of the PWM signal from the IH control unit 41 to the drive circuit 42. (High) signal is output. The protection circuit 46 has a function as a second abnormality detection unit in the claims, and includes an abnormality detection circuit in the claims.

  The AND circuit 47 has an input terminal connected to the IH control unit 41 and the protection circuit 46, and an output terminal connected to the drive circuit 42. The AND circuit 47 outputs the PWM signal output from the IH control unit 41 to the drive circuit 42 only when the H (high) signal is output from the protection circuit 46, and in other cases, that is, from the protection circuit 46. When the L (low) signal is output, the PWM signal output from the IH control unit 41 is not output to the drive circuit 42.

  According to the above configuration, when the temperatures of the heating roller 26 and the drive circuit 42 are both normal, the PWM signal generated by the IH control unit 41 is output to the drive circuit 42 via the AND circuit 47. Then, the drive circuit 42 controls the on / off operation of the exciting coil 43 at the frequency of the PWM signal.

  On the other hand, when a temperature abnormality occurs in either the heating roller 26 or the drive circuit 42, the protection circuit 46 detects the abnormality before the abnormality detection unit 411 of the IH control unit 41. This is because the abnormality detection unit 411 of the IH control unit 41 performs processing such as noise removal processing on the detection signal output from the temperature detection unit 44, and detects an abnormality from the detection signal output from the temperature detection unit 44. This is because it takes time to determine the presence or absence.

  Therefore, the protection circuit 46 outputs the L (low) signal to the AND circuit 47 before the abnormality detection unit 411 of the IH control unit 41 detects the abnormality and sets the duty of the PWM signal (high frequency signal) to zero. . The protection circuit 46 outputs the L (low) signal to the AND circuit 47 and also outputs the L (low) signal to the current generation control unit 412 of the IH control unit 41.

  When receiving the L (low) signal, the current generation control unit 412 of the IH control unit 41 performs the following control as the frequency determination processing of the high-frequency current until the H (high) signal is received from the protection circuit 46. A process for setting the frequency in the cycle to the same frequency as the current frequency is performed.

  With this process, the current generation control unit 412 of the IH control unit 41 protects the current generation control unit 412 after receiving the L (low) signal until receiving the H (high) signal from the protection circuit 46. A PWM signal having a frequency in the control cycle of the IH control unit 41 when the L (low) signal is received from the circuit 46 is output to the AND circuit 47.

  Thereafter, when the supply of the high-frequency current by the protection circuit 46 is stopped and the temperature abnormality that has occurred in either the heating roller 26 or the drive circuit 42 is resolved and the normal state is restored, the protection circuit 46 is activated for the same reason as described above. The return to the normal state is detected prior to the abnormality detection unit 411 of the IH control unit 41.

  Therefore, the protection circuit 46 sends an H (high) signal to the AND circuit 47 before the abnormality detection unit 411 of the IH control unit 41 no longer detects an abnormality and the current generation control unit 412 resumes feedback control of the PWM signal. Output. Thereafter, the abnormality detection unit 411 of the IH control unit 41 detects the return to the normal state, and outputs a PWM signal based on feedback control to the AND circuit 47.

  Then, the current generation control unit 412 of the IH control unit 41 resumes the feedback control again. As described above, the feedback control means that the current generation control unit 412 of the IH control unit 41 calculates the target power to be supplied to the exciting coil 43 so that the heating roller 26 and the drive circuit 42 maintain a predetermined temperature. Based on the power (detected power) detected by the measuring device 45 and the calculated target power, the feedback amount related to the frequency of the high-frequency current output by the drive circuit 42 so that the temperature of the heating roller 26 is stably maintained. It is the control which calculates | requires.

  Here, until the current generation control unit 412 of the IH control unit 41 receives the H (high) signal from the protection circuit 46, a process of setting the frequency in the next control cycle to the same frequency as the current frequency is performed. Therefore, the frequency when the feedback control is resumed is the frequency in the control cycle of the IH control unit 41 when the protection circuit 46 outputs the L (low) signal to the IH control unit 41.

  As described above, in the present embodiment, only when the L (low) signal is not output from the protection circuit 46, the high-frequency current having the frequency determined by the current generation control unit 412 of the IH control unit 41 passes through the drive circuit 42. Is supplied to the excitation coil 43 (the frequency of the high-frequency current supplied to the excitation coil 43 is feedback controlled), and when the L (low) signal is output from the protection circuit 46, the IH control unit 41 The current generation control unit 412 is configured not to perform the feedback control.

  In addition, when the current generation control unit 412 of the IH control unit 41 receives the L (low) signal from the protection circuit 46, as a frequency determination process during a period until the H (high) signal is received from the protection circuit 46, The frequency in the next control cycle is set to the same frequency as the current frequency, and the protection circuit 46 eliminates the temperature abnormality that has occurred in either the heating roller 26 or the drive circuit 42 and returns to the normal state. When it was detected, feedback control was resumed.

  In the present embodiment, when the protection circuit 46 detects that the temperature abnormality that has occurred in either the heating roller 26 or the drive circuit 42 has been resolved and has returned to a normal state by such means, the protection circuit 46 The frequency control of the high-frequency current is performed from the frequency in the control cycle of the IH control unit 41 when the L (low) signal is output to the IH control unit 41.

  As a result, the timing at which the abnormality is detected by the abnormality detection unit 411 of the IH control unit 41 is delayed from the timing at which the abnormality is detected by the protection circuit 46 (when a time lag occurs). Although the supply of the high-frequency current to the excitation coil 43 is stopped, the current generation control unit 412 performs feedback control (the frequency of the PWM signal) to increase the high-frequency current during the time lag. Can be prevented from being performed.

  Therefore, the frequency of the high-frequency current to be set when the exciting coil 43 returns to the normal state by the feedback control during the time lag is output from the protection circuit 46 to the AND circuit 47 as an L (low) signal. Greatly deviates from the frequency at the point in time when the supply of the high-frequency current to the exciting coil 43 is stopped, so that the frequency control by the IH control unit 41 (current generation control unit 412) becomes unstable for a while. Can be prevented from occurring.

  In the embodiment, the temperature detection unit 44 detects the temperature of the excitation coil 43, and the IH control unit 41 and the protection circuit 46 determine whether the temperature of the excitation coil 43 is abnormal as described above. Although the operation is performed, the present invention is not limited to this, and an embodiment that operates as described above depending on whether there is an abnormality in the current flowing in the excitation coil 43 measured by the power measuring device 45 is also assumed.

  The image forming apparatus according to the present invention may be an image forming apparatus that employs the induction heating device according to the present invention as a fixing device that fixes a toner image transferred onto a sheet by pressing and heating.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 26 Heating roller 28 Fixing apparatus 41 IH control part 42 Drive circuit 43 Excitation coil 44 Temperature detection part 45 Power measuring device 411 Abnormality detection part 412 Current generation control part 46 Protection circuit 47 AND circuit

Claims (7)

An exciting coil for heating the object to be heated by electromagnetic induction;
A high-frequency current generator for generating a high-frequency current to be supplied to the exciting coil;
A power detector for detecting power consumption of the exciting coil;
A current generation control unit that feedback-controls the frequency of the high-frequency current generated by the high-frequency current generation unit so that the power consumption detected by the power detection unit becomes a predetermined target power;
A first abnormality detection unit that stops supply of a high-frequency current to the exciting coil using the current generation control unit when detecting that a predetermined abnormality has occurred;
A second abnormality detection unit that stops supply of the high-frequency current to the exciting coil using the high-frequency current generation unit when detecting that a predetermined abnormality has occurred;
With
When the current generation control unit detects that the predetermined abnormality has occurred in at least one of the first abnormality detection unit and the second abnormality detection unit, the frequency of the high-frequency current supplied to the excitation coil An induction heating device that maintains the same frequency as the current high frequency current. A heating state detection unit for detecting a heating state of a predetermined circuit unit provided on the path of the high-frequency current;
The first abnormality detection unit detects presence / absence of an abnormality in the predetermined circuit unit based on a heating state of the predetermined circuit unit detected by the heating state detection unit, and an abnormality occurs in the predetermined circuit unit. Is detected, the supply of high-frequency current to the exciting coil is stopped using the current generation control unit,
The second abnormality detection unit detects presence / absence of an abnormality in the predetermined circuit unit based on a heating state of the predetermined circuit unit detected by the heating state detection unit, and an abnormality occurs in the predetermined circuit unit. 2. The induction heating device according to claim 1, wherein when the detection is detected, supply of the high-frequency current to the exciting coil is stopped using the high-frequency current generation unit. The high-frequency current generation unit further includes a drive circuit that turns on and off the supply of the high-frequency current to the excitation coil at a frequency set by the current generation control unit,
The induction heating device according to claim 2, wherein the heating state detection unit detects a temperature of the drive circuit as the predetermined circuit unit as a heating state of the excitation coil. A current detection unit for detecting a current value of the current flowing through the excitation coil;
The induction heating device according to claim 1, wherein the first and second abnormality detection units detect the abnormality based on a current value detected by the current detection unit.   The abnormality determination reference value used when the first abnormality detection unit detects the predetermined abnormality is the same as the abnormality determination reference value used when the second abnormality detection unit detects the predetermined abnormality. The induction heating device according to any one of claims 1 to 4. When the first abnormality detection unit detects that the predetermined abnormality has occurred, the first abnormality detection unit executes an abnormality detection program that uses the current generation control unit to stop the supply of the high-frequency current to the exciting coil. A detection program execution unit,
The second abnormality detection unit is an abnormality detection circuit that stops supply of a high-frequency current to the exciting coil by using the high-frequency current generation unit when detecting that the predetermined abnormality has occurred. The induction heating device according to any one of 1 to 5. An image forming unit that forms an image on a recording medium using a developer;
A fixing unit that performs a fixing operation for fixing the image formed by the image forming unit to the recording medium,
The image forming apparatus, wherein the fixing unit includes the induction heating device according to any one of claims 1 to 6 and performs the fixing operation using heat generated by the induction heating device.

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