JP2019117280A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that can execute error processing at an early stage during abnormality in a heater.SOLUTION: A control unit 32 switches a heater control signal Sig4 to a low level (S9) after a time T1 elapses, even when determining that a heater temperature does not exceed a target temperature (S3: NO). When determining that a heater current flows (S11: YES), the control unit 32 executes error processing. This allows an image forming apparatus to execute the error processing at an early stage during abnormality in a heater, compared with a case where a control unit switches the heater control signal Sig4 to the low level in response to the heater temperature exceeding the target temperature, and determines if the heater current flows.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus.

  An electrophotographic image forming apparatus includes a heater for thermally fixing toner to a sheet. Conventionally, although the control unit does not output a signal instructing the energization of the heater, the energization current of the heater is detected to detect that an abnormality has occurred, and the energization of the heater is relayed by the relay. There is a technology to shut off (for example, Patent Document 1).

Unexamined-Japanese-Patent No. 04-287079

  However, in the above configuration, when the control unit continues to output the signal instructing the energization of the heater, the timing of detecting the abnormality is delayed, and the error processing such as interrupting the energization of the heater is performed. The problem was that it would be slow.

  The present application has been proposed in view of the above problems, and it is an object of the present invention to provide an image forming apparatus capable of executing an error process at an early stage when the heater is abnormal.

  This specification relates to a heater supplied with electric power from an AC power supply, a temperature sensor for outputting a temperature signal according to the temperature of the heater, a current sensor for outputting a current value signal according to the value of the current flowing through the heater, A switching element which is disposed in the path of the current flowing in the circuit, is turned on in response to the on signal, is turned off in response to the off signal, and includes a control unit. When the ON signal being output is switched to the OFF signal and the temperature of the heater is below the target temperature and the ON signal is being output for the first time In the period in which the off signal is continuously output for the second time and the off signal is continuously output for the second time, the error processing is performed when it is detected that the current value indicated by the current value signal is equal to or greater than the threshold. Characterized by performing Discloses that an image forming apparatus.

  According to the image processing apparatus according to the present application, the error processing is executed when it is detected that the current value is equal to or higher than the threshold before the temperature of the heater exceeds the target temperature. An image forming apparatus that can be implemented can be provided.

1 is a cross-sectional view of a laser printer according to a first embodiment. It is a circuit diagram of heating device 30 concerning a 1st embodiment. It is a flow chart of the 1st heater control processing concerning a 1st embodiment. It is a timing chart which shows the relation of the heater control signal of the period until it reaches the target temperature in the 1st heater control processing concerning a 1st embodiment, and heater current. It is a timing chart which shows the relation of the heater control signal of the period after reaching the target temperature in the 1st heater control processing concerning a 1st embodiment, and heater current. It is a timing chart which shows the relation between the heater control signal of a period until it reaches the target temperature in the 1st heater control processing concerning a 2nd embodiment, and a heater current. It is a timing chart which shows the relation between the heater control signal of the period after reaching the target temperature in the 1st heater control processing concerning a 2nd embodiment, and the heater current. It is a flow chart of the 2nd heater control processing concerning a 3rd embodiment. It is a timing chart which shows a relation of a heater control signal and a heater current concerning a 3rd embodiment.

First Embodiment Hereinafter, an embodiment of the present application will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a printer 1 which is a monochrome laser printer that is an embodiment of an image forming apparatus according to the present application. The printer 1 forms a toner image on the sheet supplied from the tray 4 disposed in the lower part in the main body casing 2 by the image forming unit 5, and then heats the toner image by the fixing unit 7 to fix it. Processing is performed, and finally, the sheet is discharged to the discharge tray 9 located at the upper part of the main body casing 2. In FIG. 1, the right side in the drawing is defined as the front side of the device, and the side coming to the left when the device is viewed from the front (the front side in the drawing) is defined as the left side. Do.

  The image forming unit 5 includes a scanner unit 11, a developing cartridge 13, a photosensitive drum 17, a charger 18, a transfer roller 19, and the like. The scanner unit 11 is disposed in the front of the main body casing 2, and the laser light emitted from the laser light emitting unit (not shown) is placed on the surface of the photosensitive drum 17 through a polygon mirror, a reflecting mirror, a lens and the like. Irradiate by high speed scanning.

  The developing cartridge 13 is configured to be attachable to and detachable from the main body of the printer 1 and accommodates toner therein. Further, at the toner supply port of the developing cartridge 13, the developing roller 21 and the supply roller 23 are provided in a state of facing each other. Further, the developing roller 21 is disposed in a state of facing the photosensitive drum 17. The toner in the developing cartridge 13 is supplied to the developing roller 21 by the rotation of the supply roller 23 and carried on the developing roller 21.

  A charger 18 is disposed above the front side of the photosensitive drum 17 at a distance. A transfer roller 19 is disposed behind the photosensitive drum 17 so as to face the photosensitive drum 17. The photosensitive drum 17 is charged with a uniform, for example, positive polarity by the charger 18 while rotating. Next, an electrostatic latent image is formed on the surface of the photosensitive drum 17 by the laser light from the scanner unit 11. Thereafter, the toner carried on the developing roller 21 rotating in contact with the photosensitive drum 17 is supplied to the electrostatic latent image on the surface of the photosensitive drum 17 and carried thereon, whereby the toner on the surface of the photosensitive drum 17 is produced. Forms a toner image. The formed toner image is transferred to the sheet by the transfer bias applied to the transfer roller 19 while the sheet passes between the photosensitive drum 17 and the transfer roller 19.

  The fixing unit 7 is disposed on the downstream side (upper side in the printer 1) in the sheet conveyance direction with respect to the image forming unit 5, and the fixing roller 27, the pressure roller 29 pressing the fixing roller 27, and the fixing roller 27 And a halogen heater 31 which heats the light. The fixing roller 27 is rotated in response to the driving of an electric motor (not shown) controlled by the control unit 32 shown in FIG. 2, and applies a conveying force to the sheet while heating the toner transferred to the sheet. On the other hand, the pressure roller 29 is driven to rotate while pressing the sheet to the fixing roller 27 side. The halogen heater 31 is controlled to be energized by the control unit 32 of the heating device 30 shown in FIG.

  As shown in FIG. 2, the heating device 30 includes a halogen heater 31, a control unit 32, an AC / DC converter 33, a DC / DC converter 34, a zero cross detection circuit 35, a current sensor 36, a temperature sensor 37, a relay 42, and a triac 43. , Photo triac coupler 46, resistors 44 and 45, and the like. For example, the control unit 32 may be mainly configured of a program operating on the CPU. Alternatively, the control unit 32 may be configured by dedicated hardware such as an ASIC, for example. In addition, the control unit 32 may be configured to operate by using, for example, both software processing and hardware processing. The control unit 32 also includes a memory 32A for storing information related to control and processing of the RAM, the ROM, the flash memory, and the like. The memory 32A stores programs such as a first heater control process and data such as times T1 and T2 used in the first heater control process. Further, the control unit 32 has a timer 32B. In addition, the printer 1 includes a display unit 61 on the front surface of the main body casing 2.

  The halogen heater 31 generates heat in response to energization of the AC power supply 101. The temperature sensor 37 provided in the vicinity of the halogen heater 31 includes, for example, a thermistor, and outputs a temperature signal Sig5, which is a signal corresponding to the detected temperature of the halogen heater 31, to the control unit 32. The AC / DC converter 33 converts, for example, an AC voltage of 100 V into a DC voltage of 24 V, and outputs the DC voltage to the DC / DC converter 34. The DC / DC converter 34 converts a DC voltage of 24 V into a DC voltage of 3.3 V and supplies the DC voltage to the control unit 32 and the like. The temperature sensor 37 outputs, to the control unit 32, a current value signal Sig1, which is a signal corresponding to the current value of the current flowing from the AC power supply 101 to the halogen heater 31. Since the consumption current of the halogen heater 31 is sufficiently large relative to the consumption current of the control unit 32 etc., the current value detected by the temperature sensor 37 is regarded as the current value flowing to the halogen heater 31 here. In the following description, the current flowing to the halogen heater 31 may be described as a heater current. Further, the temperature indicated by the temperature signal Sig5 may be described as a heater temperature. The relay 42 switches whether to electrically connect the AC power supply 101 and the halogen heater 31 in accordance with a relay control signal Sig2 output from the control unit 32.

  When the zero cross detection circuit 35 detects the zero cross timing of the AC power supply 101, the zero cross detection circuit 35 outputs a zero cross signal Sig3 which is a pulse signal to the control unit 32. Specifically, the zero cross detection circuit 35 includes a diode bridge 51, a photocoupler 52, resistors 53 and 54, and a transistor 55 which is an NPN bipolar transistor. The power of the AC power supply 101 is full-wave rectified by the diode bridge 51 and applied to the LED of the photocoupler 52. The collector terminal of the phototransistor of the photocoupler 52 is connected to a 24 V DC power supply via a resistor 53, and the emitter terminal is grounded. The base terminal of the transistor 55 is connected to the connection point between the resistor 53 and the phototransistor of the photocoupler 52, the collector terminal is connected to the control unit 32, and the emitter terminal is grounded. The wiring connecting the collector terminal of the transistor 55 and the control unit 32 is pulled up to the power supply voltage in the control unit 32. The LED of the photocoupler 52 emits light with an amount of light corresponding to the applied power. Therefore, when the voltage applied to the LED of the photocoupler 52 decreases, the on resistance of the phototransistor of the photocoupler 52 increases, and the base voltage of the transistor 55 increases. Then, when the base voltage of the transistor 55 exceeds the threshold value, the transistor 55 is turned on, and the zero cross signal Sig3 becomes low level. Therefore, the zero-crossing signal Sig3 output from the zero-crossing detection circuit 35 is, for example, a pulse signal which becomes low level for a predetermined time before and after the zero-crossing timing of the AC power supply 101 as shown in FIG. The control unit 32 detects the zero cross timing of the AC voltage flowing between the AC power supply 101 and the zero cross detection circuit 35 based on the input zero cross signal Sig3.

  In the TRIAC 43, the T2 terminal is connected to one pole of the AC power supply 101, and the T1 terminal is connected to the other pole of the AC power supply 101 via the halogen heater 31 and the relay. The gate terminal of the triac 43 and the T1 terminal are connected via a resistor 45. The T2 terminal of the TRIAC 43 and the gate terminal are connected via the TRIAC of the phototriac coupler 46 and the resistor 44. The heater control signal Sig4 output from the control unit 32 is input to the anode terminal of the LED of the phototriac coupler 46, and the cathode terminal is grounded.

  For example, when the power supply of the printer 1 is turned on, the control unit 32 starts energization of the halogen heater 31 so that the temperature of the halogen heater 31 becomes a target temperature. In addition, for example, in response to receiving a print job, the control unit 32 controls the image forming unit 5 to execute an image forming process for forming an image on a sheet.

The first heater control process according to the first embodiment will be described with reference to FIG.
In the first heater control according to the first embodiment, when the triac 43 is turned on, the control unit 32 performs wave number control to be turned on at the zero cross timing of the AC power supply 101.

  For example, when the power of the printer 1 is turned on and the print job is accepted, the control unit 32 starts the first heater control. Incidentally, in response to the power supply of the printer 1 being turned on, the control unit 32 sets the level of the relay control signal Sig2 to a level at which the contact of the relay 42 is closed.

  When the first heater control process is started, the control unit 32 switches the heater control signal Sig4 from the low level to the high level at the zero cross timing of the AC power supply 101 (S1). As a result, the triac 43 becomes conductive, and the electric power of the AC power supply 101 is supplied to the halogen heater 31 to generate heat. In step S1, the controller 32 causes the timer 32B to start counting. Next, the control unit 32 determines whether the temperature of the halogen heater 31 exceeds the target temperature based on the temperature signal Sig5 (S3). In response to the determination that the temperature does not exceed the target temperature (S3: NO), the control unit 32 determines whether to end the first heater control (S5). For example, the control unit 32 determines that the first heater control is ended when the image forming process is ended, and judges that the first heater control is not ended when the image forming process is not ended. In response to determining that the first heater control is ended (S5: YES), the control unit 32 switches the heater control signal Sig4 from the high level to the low level (S15). As a result, the photo triac of the photo triac coupler 46 is turned off, and the triac 43 is turned off in response to the polarity of the applied voltage being reversed at the zero cross timing of the AC power supply 101. Thereby, the conduction to the halogen heater 31 is cut off. After execution in step S15, the control unit 32 ends the first heater control process. In the following description, the triac 43 may describe the conductive state as the on state and the non-conductive state as the off state.

  On the other hand, in response to determining that the first heater control is not ended (S5: NO), the control unit 32 determines whether or not a time T1 or more has elapsed since step S1 is executed based on the time when the timer 32B elapses. It is determined (S7). If it is determined that the time T1 or more has not elapsed (S7: NO), the control unit 32 returns to step S3. On the other hand, when it is determined that the time T1 or more has elapsed (S7: YES), the control unit 32 switches the heater control signal Sig4 from the high level to the low level for abnormality detection (S9). Next, in accordance with the rising of the pulse of the zero cross signal Sig3, the control unit 32 determines whether or not the heater current flows above the threshold value, based on the current value signal Sig1 (S11). Further, the control unit 32 causes the timer 32B to start timing. Since it is an abnormal state in which the heater current flows despite the fact that the triac 43 is controlled to the off state according to the judgment that the heater current is flowing (S11: YES), the relay control signal Sig2 The contact point of the relay 42 is switched to the open level, and an error message is displayed on the display unit 61 to notify an error (S13). Thereby, the contact point of the relay 42 is opened, and the energization to the halogen heater 31 is interrupted. After executing step S13, the control unit 32 ends the first heater control process. On the other hand, since it is a normal state according to judging that heater current has not flowed (S11: NO), control part 32 performs time S2 after performing Step S11 based on time to which timer 32B passes. It is determined whether it has elapsed (S17). When it is determined that the time T2 has not elapsed (S17: NO), the control unit 32 returns to step S11, and repeatedly executes steps S11 and S17 until the time T2 elapses. When it is determined that the time T2 has elapsed and the time T2 has elapsed (S17: YES), the control unit 32 returns to step S1.

Here, the processes of steps S1 to S17 will be described with reference to FIG.
FIG. 4 shows each waveform when the control unit 32 executes step S7 and determines YES at time t1. The control unit 32 switches the heater control signal Sig4 to the low level in response to the determination of YES in step S7. When the photo triac of the photo triac coupler 46 is in the off state, the triac 43 is turned off in response to the polarity of the applied voltage being reversed at the zero cross timing immediately before time t2. Here, when normal, the heater current does not flow as shown by a solid line in FIG. 4, but when abnormal, the heater current flows as shown by a broken line in FIG. The control unit 32 executes step S11 at time t2 when the zero cross signal Sig3 rises, which is a timing after the zero cross timing. Here, the timing at which step S11 is performed is set to time t2 in order to determine whether the heater current is flowing with the triac 43 turned off with certainty. When the heater current does not flow, and the controller 32 determines NO in step S11, the heater control signal Sig4 is output at time t3 after time T2 from time t2 to turn on the triac 43 at the next zero cross timing. Switch from low level to high level. As a result, the triac 43 is turned on, and the heater current flows. On the other hand, when the heater current flows at time t2 and the controller 32 determines YES in step S11, the contact point of the relay 42 is opened to interrupt the energization of the halogen heater 31. As described above, even when the difference between the temperature of the halogen heater 31 and the target temperature is large and the energization of the halogen heater 31 is continued, the control unit 32 executes step S11 regardless of the temperature of the halogen heater 31. Therefore, abnormality detection can be performed early.

  Returning to FIG. 3, since the temperature of the halogen heater 31 exceeds the target temperature in response to the determination of YES in step S3, the control unit 32 sets the heater control signal Sig4 to turn the halogen heater 31 off. The high level is switched to the low level (S19). Next, the control unit 32 determines whether the temperature of the halogen heater 31 falls below the target temperature based on the temperature signal Sig5 (S21). In response to the determination that the temperature is below the target temperature (S21: YES), the control unit 32 returns to step S1. On the other hand, in response to the determination that the temperature is not lower than the target temperature (S21: NO), the control unit 32 determines whether to end the first heater control (S23), as in step S5. Since it is in the state where temperature of halogen heater 31 is higher than target temperature according to judging that 1st heater control is not ended (S23: NO), control part 32 returns to Step S21. On the other hand, in response to determining that the heater control is to be ended (S23: YES), the control unit 32 ends the first heater control process.

  Here, the process in the case where YES is determined in step S3 will be described with reference to FIG. In this case, the difference between the temperature of the halogen heater 31 and the target temperature is small, and switching of energization to the halogen heater 31 is performed in a short cycle. FIG. 5 shows each waveform when the control unit 32 determines that the step S3 is YES at time t11 and determines that the step S21 is YES at time t13. When the controller 32 determines that the step S3 is YES at time t11, the controller 32 switches the heater control signal Sig4 to the low level. In response to this, the triac 43 is turned off at the zero cross timing of time t12. Further, at time t13, the control unit 32 switches the heater control signal Sig4 to the high level, and the triac 43 is turned on.

Here, the printer 1 is an example of an image forming apparatus, the AC power supply 101 is an example of an AC power supply, the halogen heater 31 is an example of a heater, the temperature sensor 37 is an example of a temperature sensor, and the current sensor 36 is The triac 43 is an example of a switching element, and the control unit 32 is an example of a control unit. The zero cross detection circuit 35 is an example of a detection circuit, and the relay 42 is an example of a relay. The timer 32B is an example of a timer.
The high level heater control signal Sig4 is an example of the on signal, and the low level heater control signal Sig4 is an example of the off signal. The time T1 is an example of a first time, and the time from the time t1 to the time t3 is an example of a second time. Step S13 is an example of error processing. The process of determining YES in step S7 is an example when it is detected that the on-output state has continued for the first time. After the heater control signal Sig4 is switched to the low level in step S9, the processing for continuing the output of the heater control signal Sig4 at the low level until the heater control signal Sig4 is switched to the high level at step S1 is the off time for the second time. This is an example of continuous output.

According to the above-described first embodiment, the following effects can be obtained.
If the controller 32 determines NO in step S3 and determines that the time T1 has elapsed based on the time counted by the timer 32B (S7: YES), it switches the heater control signal Sig4 to the low level (S9). Then, the control unit 32 continues the output of the low level heater control signal Sig4 until the next zero cross timing until the time T2 elapses and the determination in the step S17 is YES. Further, in response to the determination of YES in step S11, control unit 32 executes step S13. As described above, even when the heater temperature does not exceed the target temperature, the control unit 32 outputs the low-level heater control signal Sig4 to execute step S11, and thus the heater temperature exceeds the target temperature. As compared with execution of step S13 when it is determined that the heater current is equal to or more than the threshold while the heater control signal Sig4 is being output, error processing when the heater is abnormal can be executed earlier.

  Further, the control unit 32 determines NO in step S11 in a period in which the low-level heater control signal Sig4 is output, and determines YES in step S17 when the heater control signal Sig4 is high in step S1. Switch to the level. As described above, when it is determined that the heater current is continuously less than the threshold during the period of time T2, the heater control signal Sig4 can be switched to the high level.

  Further, when detecting that the temperature of the halogen heater 31 exceeds the target temperature based on the temperature signal Sig5 in step S3, the control unit 32 switches the heater control signal Sig4 to low level in step S19. Thereby, the control unit 32 can switch the heater control signal Sig4 such that the temperature of the halogen heater 31 becomes the target temperature.

  In addition, the control unit 32 executes step S11 at time t2 when the zero cross signal Sig3 rises, which is a timing after the zero cross timing. Thus, it can be determined whether or not the heater current is flowing with the triac 43 turned off.

  Further, in step S13, the control unit 32 switches the relay control signal Sig2 to a level at which the contact point of the relay 42 is opened, and releases the electrical connection between the AC power supply 101 and the halogen heater 31. As a result, the current supply to the halogen heater 31 which is abnormal can be cut off with certainty.

Another Example of the First Embodiment After the execution of step S19, processing similar to that of steps S11 and S13 may be executed. Specifically, after execution of step S19, it is determined whether or not the heater current is flowing above the threshold value based on the current value signal Sig1, for example, at the rise timing of the zero cross signal Sig3, and the heater current is flowing In response to the determination, the same processing as step S13 is performed. On the other hand, it may be configured to proceed to step S21 according to judging that the heater current is not flowing.

Second Embodiment Next, a first heater control process according to a second embodiment will be described.
In the first heater control according to the second embodiment, when turning on the triac 43, the control unit 32 performs phase control to turn on at a timing according to the phase of the AC power supply 101. The timing at which the triac 43 is turned on includes the zero cross timing. The configuration of the printer 1 according to the second embodiment is the same as that of the first embodiment. Moreover, the control part 32 which concerns on 2nd Embodiment performs 1st heater control similarly to 1st Embodiment. However, the timings of executing steps S1 and S17 are different. This will be described using FIGS.

  FIG. 6 shows each waveform when the control unit 32 executes step S7 and determines YES at time t21. The controller 32 switches the heater control signal Sig4 from the high level to the low level in response to the determination of YES in step S7. When the photo triac of the photo triac coupler 46 is off, the triac 43 is turned off in response to the polarity of the applied voltage being reversed at the zero cross timing. Here, when normal, the heater current does not flow as shown by a solid line in FIG. 6, but when it is abnormal, the heater current flows as shown by a broken line in FIG. The control unit 32 executes step S11 at time t22 when the zero cross signal Sig3 rises, which is a timing after the zero cross timing. If the heater current does not flow more than the threshold and the controller 32 determines NO in step S11, the phase is switched according to the phase of the AC power supply 101 at time t23 after time T2 from time t22 to turn on the triac 43. Then, the heater control signal Sig4 is switched from the low level to the high level. As a result, the triac 43 is turned on, and the heater current flows.

  As compared with the first embodiment, in the second embodiment, the period during which the halogen heater 31 is deenergized is short. Therefore, even when the difference between the temperature of the halogen heater 31 and the target temperature is large and it is desired to quickly raise the temperature of the halogen heater 31, the inhibition of the temperature rise of the halogen heater 31 can be reduced.

  In the second embodiment, as shown in FIG. 7, the control unit 32 determines the ratio of the on period to the off period in the half cycle of the AC power supply 101 according to the determination of YES in step S3. Control to change and adjust according to the phase of. For example, step S19 is performed at the falling timing of the zero cross signal Sig3. As a result, the triac 43 is turned off at time t31 which is the zero cross timing of the AC power supply 101, and the heater current does not flow. Thereafter, at time t32 when the AC power supply 101 has a predetermined phase angle, the control unit 32 executes step S1. Thereby, the triac 43 is turned on and the heater current flows.

According to the above-described second embodiment, the following effects can be obtained.
When the controller 32 determines NO in step S3 and determines YES in step S7, the controller 32 switches the heater control signal Sig4 to the low level (S9). Then, the control unit 32 continues the output of the low level heater control signal Sig4 until the next zero cross timing until the time T2 elapses and the determination in the step S17 is YES. Further, in response to the determination of YES in step S11, control unit 32 executes step S13. As described above, even when the heater temperature does not exceed the target temperature, the control unit 32 outputs the low-level heater control signal Sig4 to execute step S11, so that the error processing when the heater becomes abnormal can be performed early. Can be performed. Further, since the duration of the low level of the heater control signal Sig4 is shorter than the time until the next zero cross timing, the time for which the halogen heater 31 is not energized can be reduced for a short time to reduce the inhibition of the temperature rise. it can.

Third Embodiment Next, a second heater control process according to a third embodiment will be described with reference to FIGS.
The configuration of the printer 1 according to the third embodiment is the same as that of the first embodiment.
For example, when the power of the printer 1 is turned on and the print job is accepted, the control unit 32 starts the second heater control. When the second heater control process is started, the control unit 32 starts phase control to turn on the triac 43 at a predetermined phase angle of the AC power supply 101, for example, to limit inrush current (S31). Note that the phase control here is control performed to limit the heater current and the like regardless of the heater temperature, and control whose purpose is different from that of the first heater control according to the second embodiment. Specifically, as shown in FIG. 9, the on / off of the heater control signal Sig4 is repeated every half cycle of the AC power supply 101. Thus, in the normal case, the heater current flows for a predetermined period of half cycle.

  Next, the control unit 32 determines whether to end the phase control process (S33 in FIG. 8). When the heater current is less than the predetermined current value, the controller 32 determines that the phase control process is to be ended because it is not necessary to limit the heater current, and ends the phase control process when the heater current is equal to or more than the predetermined current value. I will not judge. In response to determining that the phase control process is not completed (S33: NO), the control unit 32 determines whether the heater current is flowing at or above the threshold at the rising timing of the zero cross signal Sig3, as in step S11. It judges (S37). Since it is an abnormal state according to judging that the heater current is flowing (S37: YES), as in step S13, the contact of the relay 42 is opened to interrupt the energization to the halogen heater 31, and an error occurs. Informing (S39), the second control process is ended. On the other hand, when it is determined that the heater current does not flow (S37: NO), the control unit 32 returns to step S33 because it is in the normal state. On the other hand, in response to determining that the phase control process is to be ended (S33: YES), the control unit 32 shifts to the first heater control process described in the first embodiment (S35), and performs the second control process. finish.

  For example, when the control unit 32 executes step S37 at time t41 in FIG. 9, the heater current does not flow as shown by a solid line in FIG. 9 if normal, but if abnormal, FIG. The heater current flows as indicated by the broken line at. When the controller 32 determines that the heater current is flowing (S37: YES), step S39 is executed. On the other hand, when it is determined that the heater current is not flowing (S37: NO), the phase processing is continued, so the heater control signal Sig4 is switched to the high level at a predetermined phase angle in the next half cycle. Here, the half cycle of the AC power supply 101 is an example of a zero crossing cycle.

According to the above-described third embodiment, the following effects can be obtained.
Control part 32 performs step S39 according to judging that heater current has flowed more than a threshold in the OFF state of triac 43 in Step S37. As described above, the control unit 32 can determine whether the heater current flows more than the threshold when the TRIAC 43 is in the OFF state, and can perform error processing at the time of abnormality of the heater early.

The present invention is not limited to the above embodiment, and it goes without saying that various improvements and modifications can be made without departing from the spirit of the present invention.
For example, although it has been described above that the heater control signal Sig4 is switched to the low level in response to having determined that the time T1 has elapsed in step S7, the present invention is not limited thereto. The controller 32 may be configured to switch the heater control signal to the low level when it is detected that the number of times the zero cross timing has been detected after the controller 32 determines NO in step S3 has exceeded the predetermined number.

  Furthermore, although it has been described above that step S19 is performed in response to determining that the temperature of the halogen heater 31 has exceeded the target temperature in step S3, the present invention is not limited to this. For example, the heater control signal Sig4 is set to the low level in response to the elapsed time from the start of the first heater control process in which the timer 32B starts being exceeded the predetermined time (an example of the third time) longer than the time T1. It may be configured to switch to For example, the time from when the heater control signal Sig4 is switched to the high level to when the temperature approaches the target temperature can be estimated in advance. Therefore, in step S3, a comparison may be made with the estimated time. Further, instead of comparison with time, the number of times of detection of the zero cross timing from the start of the first heater control process may be compared with a predetermined number of times.

  Also, it has been described above that the time T1 stored in the memory 32A is used in step S7. The time T1 is not limited to one value, and the time T1 may be shortened as the temperature indicated by the temperature signal Sig5 is higher. As the time from the occurrence of an abnormality to the interruption of the energization to the halogen heater 31 becomes longer, the heater temperature further rises. Therefore, by shortening the time T1 as the heater temperature is higher, it is possible to suppress that the heater temperature greatly exceeds the target temperature even when an abnormality occurs. The correlation between the heater temperature and the time T1 is, for example, a table or a configuration to be stored in the memory 32A as a mathematical expression, and the time T1 is determined according to the temperature indicated by the temperature signal Sig5 in step S3. And the determined time T1 may be used.

  Further, although the timing at which step S11 is performed is described above as the timing of the rising edge of the pulse of the zero cross signal Sig3, the present invention is not limited to this. The timing may be any timing after detecting the zero cross timing after switching the heater control signal Sig4 to the low level. In the above description, it is described that the process returns to step S1 when the time T2 has elapsed after step S11 and the heater control signal Sig4 is switched to the high level. However, the present invention is not limited thereto. For example, the heater control signal Sig4 may be switched to the high level at the timing of the zero cross timing after step S11 is performed.

  In the third embodiment, the timing at which the heater control signal Sig4 is switched from the high level to the low level has been described as the falling timing of the zero cross signal Sig3. However, the present invention is not limited to this.

  In the above, as an example of the error processing, the relay control signal Sig2 is switched to the level at which the contact point of the relay 42 is opened, and the error message is displayed on the display unit 61 to notify an error. Only one of the switching of 42 and the error notification may be executed. Further, the error notification is not limited to displaying the error message on the display unit 61. For example, a display may be made using a display lamp instead of a message, and the error may be stored in the memory 32A as a log.

  In the above description, although the start condition of the first heater control process and the second heater control process is described as the power of the printer 1 being turned on and the print job being accepted, the present invention is not limited thereto. For example, when the power of the printer 1 is turned on, the control unit 32 may start the warm-up process regardless of the presence or absence of the print job. In this case, the start condition of the first heater control process and the second heater control process may be that the power supply of the printer 1 is turned on. Specifically, the control unit 32 starts energization of the halogen heater 31 so that the temperature of the fixing roller 27 becomes the target temperature. Here, the target temperature in the warm-up process is a temperature lower than the target temperature in the image forming process. The warm-up process is performed to warm the fixing roller 27 in advance in order to enable the image forming process to be promptly performed when a print job is received. In this case, if it is determined in step S5 of the first heater control process that the warm-up process is to be ended, it is determined that the first heater control is ended, and if it is determined that the warm-up process is not ended. The first heater control may be determined not to end.

  Moreover, although Triac was illustrated as an example of a switching element, it is not limited to this. For example, it may be realized by combining other semiconductor elements such as a thyristor, or may be realized not by an electronic element but by a mechanical element or the like.

DESCRIPTION OF SYMBOLS 1 printer 31 halogen heater 32 control part 36 current sensor 37 temperature sensor 42 relay 43 triac 101 AC power supply

Claims (12)

A heater powered by an AC power supply,
A temperature sensor that outputs a temperature signal according to the temperature of the heater;
A current sensor that outputs a current value signal according to the value of the current flowing through the heater;
A switching element disposed in a path of current flowing to the heater, turned on in response to an on signal, turned off, and turned off in response to an off signal;
And a control unit,
The control unit
When the temperature of the heater exceeds a target temperature, the on signal being output is switched to the off signal,
When the temperature of the heater is equal to or less than the target temperature and the on output state in which the on signal is output continues for a first time, the off signal is continuously output for a second time,
2. An image forming apparatus according to claim 1, wherein an error process is performed when it is detected that the current value indicated by the current value signal is equal to or greater than a threshold value in a period in which the off signal is continuously output for the second time. The control unit
The off signal that is being output is turned on when the current value indicated by the current value signal is continuously detected to be less than the threshold during the period in which the off signal is continuously output for the second time. The image forming apparatus according to claim 1, wherein the signal is switched to a signal. A detection circuit that outputs a signal according to a zero cross timing of an alternating voltage applied from the alternating current power supply,
The control unit
The OFF signal is continued for the second time when the temperature of the heater is equal to or less than the target temperature, and the number of times of detecting the zero cross timing exceeds a predetermined number of times while the ON output state continues. The image forming apparatus according to claim 1, wherein the image forming apparatus outputs the image. Equipped with a timer,
The control unit
Causing the timer to time the duration of the on output state,
The off signal is continuously output for the second time when the temperature of the heater is equal to or less than the target temperature and the time counted by the timer exceeds the first time. An image forming apparatus according to claim 1. The control unit
5. The on-signal being output is switched to the off-signal when it is detected that the temperature indicated by the temperature signal output by the temperature sensor exceeds the target temperature. The image forming apparatus according to any one of the above. Equipped with a timer,
The control unit
Causing the timer to count the time after the signal output to the switching element is switched from the off signal to the on signal,
5. The on-signal being output is switched to the off-signal when the time counted by the timer exceeds a third time which is longer than the first time. The image forming apparatus according to claim 1. A detection circuit that outputs a signal according to a zero cross timing of an alternating voltage applied from the alternating current power supply,
The control unit
The second time from the detection of the zero cross timing to the detection of the next zero cross timing when the temperature of the heater is equal to or less than the target temperature and the on-output state continues for the first time, The image forming apparatus according to any one of claims 1 to 6, wherein the off signal is continuously output. A detection circuit that outputs a signal according to a zero cross timing of an alternating voltage applied from the alternating current power supply,
The control unit
When the temperature of the heater is equal to or less than the target temperature, and the on-output state continues for the first time, the time shorter than the time from the detection of the zero cross timing to the detection of the next zero cross timing The image forming apparatus according to any one of claims 1 to 6, wherein the off signal is continuously output for a second time. The control unit
The image forming apparatus according to any one of claims 1 to 8, wherein the first time is shortened as the temperature indicated by the temperature sensor is higher. A heater powered by an AC power supply,
A temperature sensor that outputs a temperature signal according to the temperature of the heater;
A current sensor that outputs a current value signal according to the value of the current flowing through the heater;
A switching element disposed in a path of current flowing to the heater, turned on in response to an on signal, turned off, and turned off in response to an off signal;
A detection circuit that outputs a signal according to a zero cross timing of an alternating voltage applied from the alternating current power supply;
And a control unit,
The control unit
The conduction state of the switching element in the zero cross cycle is adjusted by adjusting the timing of switching from the off signal to the on signal in a zero cross cycle which is a period from detection of the zero cross timing to detection of the next zero cross timing. Adjust the ratio of the period of time to the period of non-conduction,
2. An image forming apparatus according to claim 1, wherein error processing is performed when it is detected that the current value indicated by the current value signal is equal to or greater than a threshold value in the non-conduction period. The switching element is a triac interposed between the AC power supply and the heater,
The control unit
When it is detected that the current value indicated by the current value signal is equal to or higher than the threshold value in the period from the detection of the zero cross timing to the switching of the on signal after the zero cross timing is detected in the state of outputting the off signal. The image forming apparatus according to claim 7, wherein the error processing is performed. A relay for switching whether or not the AC power supply and the heater are electrically connected;
The control unit
The image forming apparatus according to any one of claims 1 to 11, wherein in the error processing, the relay is disconnected.

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