JP2012133154A - Image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide means for detecting the occurrence of a failure in a short time when a failure of a fixing device, such as disconnection of a heater, occurs.SOLUTION: An image formation apparatus having a fixing device for heating a medium on which a developer image is formed and thereby thermally fixing the developer image on the medium, includes: heating means for heating the fixing device; temperature detection means for detecting the temperature of the fixing device; a current detection circuit for detecting a current flowing through the heating means; a temperature control part for controlling the temperature of the fixing device within a predetermined temperature range by controlling the energization to the heating means based on the detection result of the temperature detected by the temperature detection means; and a failure detection circuit for detecting a failure of the fixing device based on the detection result of the current detection circuit and a control signal from the temperature control part.

Description

  The present invention relates to an image forming apparatus such as a printer provided with a fixing device that heats a medium such as paper on which a developer image is formed and heat-fixes the developer image on the medium.

  Conventional printers equipped with a fixing device that heats the paper on which the developer image is formed and heat-fix the developer image on the paper are fixed by the heater when the fixing roller temperature of the fixing device is lower than the reference temperature. Heating of the roller is started, and the heater thermistor is detected by not detecting that the thermistor of the fixing device has reached the reference temperature after a lapse of a predetermined time after the heating is started, and the occurrence of the failure is notified (for example, , See Patent Document 1).

JP 2009-008744 A (mainly paragraphs 0039-0044, FIG. 6)

However, in the conventional technique described above, since the presence or absence of the heater breakage is detected based on the detected temperature of the thermistor after the elapse of a predetermined time after the heating of the fixing roller starts, the failure of the fixing device such as the heater breakage occurs. There is a problem that it takes time to detect the failure and the failure confirmation by the operator is delayed.
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide means for detecting occurrence of a failure in a fixing device such as a broken heater in a short time.

  In order to solve the above problems, the present invention provides an image forming apparatus including a fixing unit that heats a medium on which a developer image is formed and thermally fixes the developer image on the medium, and heats the fixing unit. Heating means, a temperature detection means for detecting the temperature of the fixing device, a current detection circuit for detecting a current flowing through the heating means, and a temperature detection result detected by the temperature detection means, to the heating means. A temperature control unit that controls the energization of the fixing unit to control the temperature of the fixing unit to a predetermined temperature range, and detects a failure of the fixing unit based on a detection result of the current detection circuit and a control signal of the temperature control unit And a failure detection circuit.

  Accordingly, the present invention can detect the occurrence of a failure in a short time by constantly monitoring the state of the heating means or the like by the failure detection circuit, shortening the time until the detection of the occurrence of the failure and making the occurrence of the failure early. The effect that it can be discovered is obtained.

Explanatory drawing which shows schematic structure of the printer of Example 1. FIG. Explanatory drawing which shows the circuit structure of the printer of Example 1. FIG. Explanatory drawing which shows the structure of the fixing temperature control part of the fixing temperature control circuit of Example 1. FIG. Explanatory drawing which shows the effect | action of failure detection of Example 1. Explanatory drawing which shows the structure of the low voltage power supply part and process control part of Example 2.

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the drawings.

  In FIG. 1, reference numeral 1 denotes a printer as an image forming apparatus. The printer 1 of the present embodiment is an electrophotographic color printer, and is connected to a host device 3 such as a personal computer that generates print information using an application such as drawing software via an interface 5. Yes.

When a user transmits print information to the printer 1 using the host device 3, the printer 1 uses a toner image as a developer image based on the print information for printing such as recycled paper, glossy paper or high-quality paper. An image based on printing information is formed on a sheet P as a medium, a toner image formed on the sheet P is fixed by a fixing device 6, and the sheet P on which the toner image is fixed is discharged outside the printer 1. Is provided to the user.
Such a printer 1 includes a control unit 8 that controls the operation of each unit constituting the printer 1, and a power supply unit 10 that supplies power acquired from the commercial power supply 9 to each unit including the control unit 8.

  The printer 1 also includes a paper tray 11 that stores the paper P, a hopping roller 13 that feeds the paper P stored in the paper tray 11 to a predetermined paper conveyance path 12 (path indicated by a thick broken line in FIG. 1), A transport belt 14 that transports the paper P fed on the paper transport path 12 by the hopping roller 13 further downstream.

  When the control unit 8 of the printer 1 receives the print information from the host device 3, the control unit 8 starts a printing operation based on the print information. At this time, the control unit 8 controls the hopping motor 13a that drives the hopping roller 13 to rotate the hopping roller 13, and the hopping roller 13 feeds the paper P stored in the paper tray 11 to the paper transport path 12. The paper P fed by the hopping roller 13 is transported to the transport belt 14 along the paper transport path 12.

  The conveyance belt 14 adsorbs the sheet P conveyed from the upstream side of the conveyance direction (referred to as a sheet conveyance direction) of the sheet P in the sheet conveyance path 12 onto the belt and reaches the lower part of the developing units 16c, 16m, 16y, and 16k. Transport. The conveyor belt 14 is driven by a driving force transmitted from a belt motor 14 a that is driven under the control of the control unit 8.

  Each of the developing units 16c, 16m, 16y, and 16k is based on a driving force supplied from a drum cartridge 17 such as a toner cartridge that stores toner as a developer or an induction motor that is driven under the control of the control unit 8. Photoconductor drums 18c, 18m, 18y, and 18k as image carriers for rotating the toner images of the respective colors. The printer 1 also includes exposure heads 19c, 19m, 19y, and 19k having a plurality of LEDs (Light Emitting Diodes) that expose the photosensitive drums 18c, 18m, 18y, and 18k based on print information.

  Then, the control unit 8 forms latent image images on the rotating photosensitive drums 18c, 18m, 18y, and 18k by the exposure heads 19c, 19m, 19y, and 19k based on the print information received from the host apparatus 3. The developing units 16c, 16m, 16y, and 16k develop toner images by developing the latent image carried on the photosensitive drums 18c, 18m, 18y, and 18k with toner by a developing unit (not shown). The toner image is transferred onto the paper P when the paper P passes below the photosensitive drums 18c, 18m, 18y, and 18k.

  On the downstream side of the sheet conveying path 12 of the conveying belt 14 in the sheet conveying direction, a fixing roller 20 that is rotationally driven by a fixing motor 20 a and a pressure roller 21 disposed at a position facing the fixing roller 20 are provided. A fixing device 6 is provided. Further, a heater 22 as a heating unit that generates heat by electric power supplied from the power supply unit 10 is disposed inside the fixing roller 20, and a surface temperature of the fixing roller 20 is detected near the upper portion of the fixing roller 20. A thermistor 23 is provided as temperature detecting means.

  When the paper P on which the toner image is transferred along the paper transport path 12 is transported to the fixing device 6, the fixing device 6 is provided to face the fixing roller 20 and the fixing roller 20 heated by the heater 22. The sheet P is sandwiched by the pressure roller 21 and is conveyed downstream in the sheet conveyance direction. At this time, the surface of the fixing roller 20 is heated by the heat of the heater 22 that generates heat based on the electric power supplied from the power supply unit 10, and the fixing roller 20 and the pressure roller 21 heated by the heater 22 form paper. When P is held and conveyed, the toner adhering to the paper P is dissolved, and the toner image is fixed on the paper P.

The paper P on which the toner image has been fixed is further transported through the paper transport path 12 to the downstream side in the paper transport direction by a transport roller (not shown) and discharged onto a stacker (not shown) provided outside the printer 1.
In this way, the printing process by the printer 1 of this embodiment is performed.

The circuit configuration of the printer 1 will be described in detail below with reference to FIG.
The control unit 8 is operated by the power acquired by the power supply unit 10 from the commercial power supply 9, and controls each unit when the printer 1 performs the above-described series of printing processes.

  Specifically, the control unit 8 controls the driving of the hopping motor 13 a to drive the hopping roller 13 and feed the paper P stored in the paper tray 11 to the paper transport path 12. Further, the control unit 8 supplies a signal based on the print information to the exposure heads 19c, 19m, 19y, and 19k at a predetermined timing, and drives the drum motor 17 and the belt motor 14a in accordance with the signals, thereby the paper P A toner image is formed based on the print information. Further, when the printer 1 starts a series of printing processes, the control unit 8 causes the heater 22 to generate heat and heats the fixing roller 20 by a method described later.

  As shown in FIG. 2, the control unit 8 and the power supply unit 10 are electrically connected by a first cable 25a, a second cable 25b, a third cable 25c, and a fourth cable 25d. Yes. The heater 22 is electrically connected to the power supply unit 10 by the fifth cable 25e and the sixth cable 25f.

  The fixing device 6 includes a heater 22 that generates heat based on the power supplied from the power supply unit 10, a temperature thermostat 27 that cuts off the power supplied to the heater 22 when the temperature of the fixing device 6 exceeds a predetermined temperature, And a thermistor 23 that detects the surface temperature of the fixing roller 20 heated by the heater 22.

  One end of the heater 22 is electrically connected to the power supply unit 10 via the fifth cable 25 e, and the other end of the heater 22 is electrically connected to one end of the temperature thermostat 27. The other end of the temperature thermostat 27 is electrically connected to the power supply unit 10 via the sixth cable 25f. For example, when electric power is supplied from the power supply unit 10 to the fixing device 6, the heater 22 generates heat by the electric power, and when the heater 22 generates heat, the surface of the fixing roller 20 is heated by the radiant heat. The surface temperature of the fixing roller 20 is detected by the thermistor 23.

  The power supply unit 10 includes a TRIAC 30 that controls the flow of power from the commercial power supply 9 to the heater 22, and a current having light emitting elements 31 a and 31 b and a phototransistor TR 2 for detecting the current supplied to the heater 22. A photo-coupler 31 as a detection circuit, and a waveform shaping circuit 34 for shaping the waveform of the output signal from the phototransistor TR2 in the photo-coupler 31 and the output signal from the fixing temperature control circuit 33 input via the fourth cable 25d. And a zero-cross circuit 35 that generates a reference signal that serves as a waveform shaping reference, and a failure detection circuit 36 that detects the occurrence of a failure in the heater 22 and the like of this embodiment. The output of the waveform shaping circuit 34 is a failure detection. The output of the fault detection circuit 36 is input to the process control unit 38 via the third cable 25c. . In addition, the power supply unit 10 includes a DC current generation unit 39 that generates a DC current to be supplied to the control unit 8 using electric power acquired from the commercial power supply 9.

The power acquired by the power supply unit 10 from the commercial power supply 9 is supplied to the fixing device 6 via the fifth cable 25e, the temperature thermostat 27, the sixth cable 25f, the triac 30 and the photocoupler 31.
The terminal T1 of the triac 30 is connected to the commercial power supply 9 through the resistor R13, the resistor R11 and the light emitting element 31a, and the resistor R14, the resistor R12 and the light emitting element 31b, and the terminal of the phototriac coupler 41 through the resistor R1. It is electrically connected to T3.

The terminal T2 of the triac 30 is electrically connected to the temperature thermostat 27 via the sixth cable 25f. When the heater 22 generates heat in such a circuit, the power of the commercial power supply 9 is supplied from the commercial power supply 9 to the heater 22 when the triac 30 is turned on.
Further, the terminal T2 of the triac 30 is electrically connected to the terminal T4 of the phototriac coupler 41 via the resistor R2, and is also electrically connected to one end of the capacitor 42. The terminal T4 of the phototriac coupler 41 is electrically connected to the other end of the capacitor 42 and also electrically connected to the gate terminal of the triac 30.

  The phototriac coupler 41 receives an LED element 41a as a heater control state output unit that outputs that an ON signal or an OFF signal of the heater 22 is output, and receives light emitted from the LED element 41a, and receives a terminal T3 and a terminal And a phototriac 41b that conducts to T4.

  That is, the phototriac coupler 41 is driven by a control current for controlling electric power supplied from the power supply unit 10 to the fixing device 6, which is output from a fixing control unit 44 as a temperature control unit to be described later. The gate terminal of the triac 30 is driven by 41, and the terminals T1 and T2 of the triac 30 are electrically connected.

  Specifically, an anode terminal as an input unit of the LED element 41a of the phototriac coupler 41 is electrically connected to a control current output terminal To that outputs a control current generated by the fixing control unit 44 via the first cable 25a. Connected. The cathode terminal as an output unit is electrically connected to a control current input terminal Ti that inputs a control current output from the cathode terminal to the fixing control unit 44 via the second cable 25b.

  When the control current is supplied from the fixing control unit 44 through the first cable 25a, the LED element 41a outputs the control current through the second cable 25b to emit light, and the light emitted from the LED element 41a is In contact with the gate portion of the phototriac 41b, the terminals T3 and T4 of the phototriac 41b are brought into conduction, and a drive current is supplied to the gate terminal of the triac 30.

  The control unit 8 forms an image by an electrophotographic printing process based on the image data generated by the fixing control unit 44, the image processing unit 46, and the image processing unit 46, so that charging, exposure, development, transfer, etc. A process control unit 38 for controlling each process and each mechanism unit is provided. The process control unit 38 is connected to a display unit 47 having a display screen such as an LCD (Liquid Crystal Display) via the seventh cable 25g.

  The fixing control unit 44 controls ON / OFF of the phototriac coupler 41 by supplying a control current to the phototriac coupler 41 based on the detection result of the thermistor 23, and turns on the power for supplying the temperature of the fixing device 6. Control by / OFF.

  Such a fixing control unit 44 controls the control current output from the control current output terminal To and the control current received from the control current input terminal Ti so as to keep the temperature of the fixing device 6 within a predetermined temperature range. As a fixing device protection control section that cuts off both the control current output terminal To and the control current input terminal Ti when the temperature of the fixing device 6 detected by the temperature control circuit 33 and the thermistor 23 is outside the predetermined temperature range. The fixing device protection circuit 49 is provided.

The fixing temperature control circuit 33 outputs a temperature control signal for controlling a control current at a normal temperature, and changes the impedance state on the output terminal side according to the output of the fixing temperature control unit 51. The open collector gate 52 is provided.
The output from the fixing temperature control unit 51 is input to the waveform shaping circuit 34 of the power supply unit 10 via the fourth cable 25d, and the output from the waveform shaping circuit 34 is input to the failure detection circuit 36.

  Further, as shown in FIG. 3, the fixing temperature control unit 51 latches the main control circuit 53 that generates the temperature control signal of the fixing device 6 based on the temperature detection signal of the thermistor 23, and the signal input to the input terminal IN. And an AND circuit 55 that outputs a logical product of the signal output from the main control circuit 53 and the signal output from the latch circuit 54.

  The main control circuit 53 includes an AD converter 53a that converts an analog signal input from the input terminal ADin into a digital signal, a CPU (Central Processing Unit) 53b, a RAM (Random Access Memory) 53c, and a ROM (Read only Memory). ) 53d and an IO port 53e that outputs a signal generated in the CPU 53b.

  In the ROM 53d, a program for controlling the heat generation of the heater 22 by generating a signal output from the output terminal OUT based on a digital signal indicating the temperature of the thermistor 23 read by the CPU 53b from the AD converter 53a; A program for notifying the user that the fixing roller 20 is abnormally heated based on the digital signal read from the converter 53a is stored.

Such a fixing temperature control unit 51 reads the temperature detection signal of the thermistor 23 input to the input terminal ADin, and keeps the temperature of the fixing device 6 within a predetermined fixable temperature range based on the temperature detection signal. Thus, the signal output from the output terminal OUT is controlled. The fixable temperature of the fixing device 6 is determined based on information relating to the type of paper P included in the print information received by the image processing unit 46.
The output terminal OUT of the fixing temperature control unit 51 is connected to the input terminal of the waveform shaping circuit 34 of the power supply unit 10 via the input terminal of the open collector gate 52 and the fourth cable 25d.

  The output terminal of the open collector gate 52 is connected to the base terminal of the transistor TR1, and when the open collector gate 52 is in the OFF state, the current output from the DC power supply Vcc is input to the base terminal of the transistor TR1 via the resistor R3. The transistor TR1 is turned on. When the transistor TR1 is turned on, a control current flows from the DC power source Vcc to the anode terminal of the LED element 41a through the first cable 25a, and the LED element 41a is turned on and emits light.

  Further, when the open collector gate 52 is in the ON state, the current from the DC power supply Vcc is not supplied to the base terminal of the transistor TR1, and the transistor TR1 is in the OFF state. When the transistor TR1 is turned off, the control current does not flow from the cathode terminal of the LED element 41a to the ground through the second cable 25b, so that the LED element 41a is turned off.

  The emitter terminal of the transistor TR1 is grounded, and the collector terminal is electrically connected to the cathode terminal of the LED element 41a via the second cable 25b. One end of the resistor R3 is electrically connected to the DC power source Vcc, and the other end is electrically connected to the base terminal of the transistor TR1. Furthermore, the anode terminal of the LED element 41a is electrically connected to one end of the resistor R4 via the first cable 25a, and the other end of the resistor R4 is electrically connected to the DC power source Vcc.

The fixing device protection circuit 49 compares the temperature detection signal of the thermistor 23 with a predetermined threshold value, and controls the flow of the control current supplied from the DC power source Vcc to the LED element 41a based on the comparison result.
Such a fixing device protection circuit 49 includes a DC power supply Vcc, a comparator 57, an open collector gate 58, an open collector gate 59, and the like. The negative terminal of the comparator 57 is electrically connected to one end of the thermistor 23 via the eighth cable 25h. The other end of the thermistor 23 is electrically connected to the DC power source Vcc via a ninth cable 25i.

The thermistor 23 is provided near the upper portion of the fixing roller 20, and its resistance value changes as the surface temperature of the fixing roller 20 changes. The voltage corresponding to the change in the resistance value of the thermistor 23 is the voltage of the comparator 57. Supplied to the negative terminal.
Further, one end of the thermistor 23 is electrically connected to the input terminal ADin of the fixing temperature control unit 51 via the eighth cable 25h, and the resistance value of the fixing temperature control unit 51 is similarly controlled from the thermistor 23. A voltage corresponding to the change is supplied.

  Furthermore, one end of the thermistor 23 is grounded through a resistor R6. One end of the resistor R7 is also connected to the ground, and the other end of the resistor R7 is electrically connected to the plus terminal of the comparator 57.

The plus terminal of the comparator 57 is electrically connected to the DC power supply Vcc via the resistor R8. The DC power source Vcc is electrically connected to the output terminal of the comparator 57, the input terminal IN of the fixing temperature control unit 51, the open collector gate 58, and the input terminals of the open collector gate 59 through the resistor R9.
Such a comparator 57 compares the reference voltage generated by the resistor R8, the resistor R7, and the DC power supply Vcc with the voltage at the minus terminal. This reference voltage is determined in consideration of the normal temperature range that the fixing roller 20 shows during printing.

  As a result of comparison by the comparator 57, when the voltage at the minus terminal is lower than the voltage at the plus terminal, that is, when the temperature of the fixing roller 20 detected by the thermistor 23 is within a normal temperature range, the output of the comparator 57 is output. The terminal is in a high impedance state. On the other hand, when the voltage at the negative terminal is higher than the voltage at the positive terminal, that is, when the temperature of the fixing roller 20 detected by the thermistor 23 is not within the normal temperature range, and the fixing roller 20 is abnormally heated. The output terminal of the comparator 57 is in a low impedance state.

  In the fixing controller 44 as described above, the direction of the control current flowing from the DC power supply Vcc to the LED element 41a via the resistor R4 varies depending on the impedance state of the output terminal of the open collector gate 59.

  Specifically, the control current flows in the direction of the output terminal of the open collector gate 59 depending on the impedance state of the output terminal of the open collector gate 59 or the LED element 41a through the first cable 25a. It is determined whether the current flows to the anode terminal. The fixing device protection circuit 49 controls whether the control current flows in the direction of the LED element 41 a or is drawn in the direction of the open collector gate 59 by controlling the impedance state of the output terminal of the open collector gate 59.

  For example, when the impedance state of the output terminal of the open collector gate 59 is set to a high impedance state by the fixing device protection circuit 49, the control current flows in the direction of the LED element 41a via the resistor R4. When the impedance state of the output terminal of the open collector gate 59 is set to a low impedance state by the fixing device protection circuit 49, the control current is drawn in the direction of the open collector gate 59 through the resistor R4, and the LED element 41a The control current is not supplied. That is, the flow of the control current output from the control current output terminal To to the anode terminal of the LED element 41a is controlled by the fixing device protection circuit 49.

  In addition, in order for the control current flowing from the DC power source Vcc to the resistor R4 to be input to the anode terminal of the LED element 41a and output from the cathode terminal, the emitter and collector of the transistor TR1 must be in a conductive state. Necessary. In order to make the emitter and collector of the transistor TR1 conductive, it is necessary to supply current from the DC power supply Vcc to the base terminal of the transistor TR1 via the resistor R3. In order to input a current to the base terminal of the transistor TR1 via the resistor R3, it is necessary to set the impedance state of the output terminals of the open collector gate 52 and the open collector gate 58 to a high impedance state.

  That is, when the fixing temperature control unit 51 of the fixing device protection circuit 49 sets the impedance state of at least one of the output terminal of the open collector gate 52 or the output terminal of the open collector gate 58 to a low impedance state, for example. The current supplied from the DC power source Vcc to the resistor R3 does not flow to the base terminal of the transistor TR1, but is drawn toward the output terminal of the open collector gate 52 or the open collector gate 58, and the LED element 41a does not emit light.

  On the other hand, when the impedance state of the output terminal of the open collector gate 52 and the output terminal of the open collector gate 58 is set to the high impedance state by the fixing temperature control unit 51 of the fixing device protection circuit 49, the DC power supply The current supplied from Vcc to the resistor R3 flows to the base terminal of the transistor TR1, and when the current is input to the base terminal of the transistor TR1, the emitter and collector of the transistor TR1 become conductive, and the emitter of the transistor TR1 When the collector becomes conductive, a control current can flow from the cathode terminal of the LED element 41a to the base terminal of the transistor TR1. That is, the flow of the control current received by the control current input terminal Ti is controlled by the fixing temperature control unit 51, the fixing device protection circuit 49, the open collector gates 52 and 58, and the transistor TR1.

Hereinafter, a series of operations of the fixing control unit 44, the power supply unit 10, and the fixing device 6 when the fixing roller 20 is heated will be described in detail.
When print information is transmitted from the host apparatus 3, the control unit 8 of the printer 1 starts a series of operations for heating the fixing roller 20. First, the operation of the printer 1 when the surface temperature of the fixing roller 20 is operating within the normal fixing possible temperature range will be described.

  In order to heat the fixing roller 20, the fixing temperature control unit 51 supplies a high level signal from the output terminal OUT to the input terminal of the open collector gate 52. When a high level signal is supplied to the input terminal of the open collector gate 52, the output terminal of the open collector gate 52 is in a high impedance state.

  When the output terminal of the open collector gate 52 is in a high impedance state, a current flows from the DC power supply Vcc to the base terminal of the transistor TR1 through the resistor R3. When a current flows from the DC power supply Vcc to the base terminal of the transistor TR1, the emitter terminal and the collector terminal of the transistor TR1 are electrically connected, so that the emitter of the transistor TR1 is connected from the cathode terminal of the LED element 41a via the second cable 25b. A current can be drawn in the direction of the terminal, a control current flows from the DC power supply Vcc to the LED element 41a via the resistor R4 and the first cable 25a, the LED element 41a emits light, and the ON signal of the heater 22 is turned on. Output what is being output.

  When the LED element 41a emits light, the phototriac 41b of the phototriac coupler 41 is turned on, and the terminals T1 and T2 are electrically connected. When the terminal T1 and the terminal T2 of the triac 30 are connected, the current flowing from the commercial power supply 9 to the power supply unit 10 is supplied to the heater 22 through the fifth cable 25e, and the current supplied to the heater 22 is the temperature thermostat 27. Then, the heater 22 generates heat and the fixing roller 20 is heated by the heater 22.

  At this time, the surface temperature of the fixing roller 20 is detected by the thermistor 23. For example, when the temperature of the surface of the fixing roller 20 increases, the resistance value of the thermistor 23 decreases. Conversely, when the surface temperature of the fixing roller 20 decreases, the resistance value of the thermistor 23 increases. That is, the fixing temperature control unit 51 monitors the surface temperature of the fixing roller 20 detected by the thermistor 23 based on the voltage determined by the thermistor 23, the resistor R6, and the DC power source Vcc.

  As a specific monitoring method, the fixing temperature control unit 51 converts the voltage determined by the resistance value of the thermistor 23 into a digital signal in the AD converter 53a, and the digital signal converted by the AD converter 53a is: Read by the CPU 53b, the CPU 53b detects a change in the surface temperature of the fixing roller 20 based on the digital signal, and controls the surface temperature of the fixing roller 20 in accordance with a program stored in the ROM 53d in advance.

  The temperature detection signal from the thermistor 23 is also supplied to the minus terminal of the comparator 57. When the surface temperature of the fixing roller 20 is in a normal state, the voltage at the minus terminal is lower than the voltage at the plus terminal. The output terminal 57 is in a high impedance state, and the signal input from the comparator 57 to the input terminal IN of the fixing temperature control unit 51 and the signal supplied to the open collector gate 58 and the open collector gate 59 are high level signals by the resistor R9. It becomes. When a high level signal is supplied to the open collector gate 58 and the open collector gate 59, the output terminals of the open collector gate 58 and the open collector gate 59 are in a high impedance state.

  In such a state, the current flowing from the DC power source Vcc to the resistor R4 flows toward the anode terminal of the LED element 41a, and the current flowing from the DC power source Vcc to the resistor R3 flows toward the base terminal of the transistor TR1. Become. That is, when the surface temperature of the fixing roller 20 is in a normal state, the fixing device protection circuit 49 continues to maintain such a state. The temperature can be controlled.

  When the series of printing processes is completed and the fixing temperature control unit 51 turns off the heater 22, the fixing temperature control unit 51 switches from the output terminal OUT to the open collector gate 52 through the IO port 53e. Supply signal. When a low level signal is supplied to the open collector gate 52, the output terminal of the open collector gate 52 is in a low impedance state, and when the output terminal of the open collector gate 52 is in a low impedance state, the base terminal of the transistor TR1 from the DC power supply Vcc. Is supplied in the direction of the output terminal of the open collector gate 52, and the transistor TR1 is turned off. When the transistor TR1 is turned off, the control current is no longer supplied to the LED element 41a, the LED element 41a is turned off and turned off, and an OFF signal of the heater 22 is output. When the LED element 41a is turned off, the phototriac 41b is also turned off, no current is supplied to the gate terminal of the triac 30, and the triac 30 is also turned off.

When the triac 30 is turned off, the terminal T1 and the terminal T2 of the triac 30 are in a non-conductive state, the electric power acquired from the commercial power supply 9 is not supplied to the heater 22, the heater 22 stops generating heat, When the heater 22 stops generating heat, the heating of the fixing roller 20 is also stopped.
Thus, when there is no abnormality in the heater 22, the temperature thermostat 27, the fifth cable 25e, and the sixth cable 25f, the printer 1 controls the temperature of the heater 22 using the fixing temperature control circuit 33 as described above. To do.

Next, the operation of the failure detection circuit 36 when the heater 22 or the like is disconnected will be described with reference to FIG. In the present description, the case where the outputs of the open collector gate 58 and the open collector gate 59 of the fixing device protection circuit 49 are in a high impedance state and operate within the fixing temperature range will be described as an example.
In order to heat the fixing roller 20, the fixing temperature control unit 51 supplies a high level signal from the output terminal OUT to the input terminal of the open collector gate 52. This high level signal is supplied as an input signal of the waveform shaping circuit 34 via the fourth cable 25d.

  When a high level signal is input to the open collector gate 52, the output becomes high impedance, current flows from the DC power source Vcc through the resistor R3, and TR1 becomes conductive, so that the LED element 41a emits light, and the heater The fact that the 22 ON signal is output is output. When the LED element 41a emits light, the phototriac 41b of the phototriac coupler 41 is turned on, and the terminals T3 and T4 are brought into conduction.

  At this time, if the heater 22 or the like is disconnected, no current flows through the light emitting elements 31a and 31b and no light is emitted. Therefore, the phototransistor TR2 is turned off, and the potential of the DC power supply Vcc passes through the resistor R15. A high level signal is supplied as an input signal to the waveform shaping circuit 34. The output signal (high level signal) from the phototransistor TR2 and the output signal (high level signal) from the fixing temperature control unit 51 are shaped by the reference signal output from the zero cross circuit 35, and the fault detection circuit. 36.

  In the failure detection circuit 36, the state of the input signal is confirmed, and the ON / OFF signal state of the heater 22 does not match the actual energization state of the heater 22 (in this case, the heater 22 is energized). Even though the ON signal to be output is output, the heater 22 is in a non-energized state (because of any disconnection of the power supply circuit including the heater 22), so that the occurrence of the failure is detected, and the failure notification information As a low level signal. This output signal is input to the process control unit 38 via the third cable 25c, and the process control unit 38 that has received this input notifies the occurrence of a failure due to the input via the seventh cable 25g. To notify the operator of the failure of the heater 22 and the like.

Next, detection when the heater 22 erroneously heats the fixing roller 20 due to a failure of the triac 30 or the like will be described.
When the triac 30 is in a state where the terminal T1 and the terminal T2 are kept in conduction for some reason, a current flows through the light emitting elements 31a and 31b to emit light, so that the phototransistor TR2 is turned on, and the low level signal Is supplied to the waveform shaping circuit 34.

  Further, since the fixing temperature control unit 51 does not heat the fixing roller 20, a low level signal is supplied from the output terminal OUT of the fixing temperature control unit 51 to the input terminal of the open collector gate 52. This low level signal is input as an input signal of the waveform shaping circuit 34 via the fourth cable 25d. The output signal (low level signal) from the fixing temperature control unit 51 and the output signal (low level signal) from the phototransistor TR2 are shaped by the reference signal output from the zero-cross circuit 35, and the fault detection circuit. 36.

  The failure detection circuit 36 confirms the state of the input signal, and the state of the ON / OFF signal of the heater 22 does not match the state of the actual energization of the heater 22 (in this case, the heater 22 is deenergized). The heater 22 is in an energized state (due to a failure of the triac 30 or the like even though an OFF signal to be output is output), and a failure is detected and a low level signal is output. Thus, the failure occurrence notification is output to the display unit 47 to notify the operator of the failure occurrence of the heater 22 and the like.

Hereinafter, the relationship between the failure detection time when the heater 22 in the prior art is disconnected and the failure detection time in this embodiment will be described with reference to FIG.
In the conventional fault detection, the surface temperature of the fixing roller 20 reaches the reference temperature F1 after a predetermined time has elapsed (time S1) from when the supply of power to the heater 22 of the fixing device 6 is started (time S0). If the temperature has not reached (temperature F2 shown in FIG. 4), a low temperature error due to disconnection of the heater 22 is detected, and a failure occurrence notification is made.

  On the other hand, in this embodiment, even when the surface temperature of the fixing roller 20 is controlled by turning on / off the power to the heater 22, the failure detection circuit 36 always uses the heater 22 and the like. When the current flowing through the heater 22 is not detected by the photocoupler 31 when the power to the heater 22 is controlled to be in the ON state, the failure detection circuit 36 does not wait for a predetermined time to elapse. In order to detect the occurrence of a failure due to the state mismatch confirmed in step S2 (time S2), it is possible to detect the occurrence of an early failure, and to detect the failure of the printer 1 early by reducing the time until the failure notification to the operator. It becomes possible to do.

  As described above, in this embodiment, in the printer, the thermistor for detecting the temperature of the fixing device, the photocoupler for detecting the current flowing through the heater of the fixing device, and the temperature detection result detected by the thermistor, By controlling the energization to the fuser, the fuser controller that controls the temperature of the fuser to a predetermined temperature range, and the fault detector that detects the trouble of the fuser based on the detection result of the photocoupler and the control signal of the fuser controller By providing the circuit, the failure detection circuit can always monitor the state of the heater and the like, and the occurrence of the failure can be detected early by reducing the time until the occurrence of the failure.

  Hereinafter, the printer of this embodiment will be described with reference to FIG. In addition, the same part as the said Example 1 attaches | subjects the same code | symbol, and abbreviate | omits the description.

  As shown in FIG. 5, the process control unit 38 according to the present embodiment includes a CPU 60, a RAM 61, a ROM 62, an EEPROM (Electrically Erasable and Programmable ROM) 63, and an IO that outputs a signal generated in the CPU 60. A low level signal as failure notification information, which is provided with a port 64 and a driver IC 65 and described in the first embodiment and detected and output by the failure detection circuit 36, passes through the third cable 25c ( 2) and input to the CPU 60 of the process control unit 38 of the present embodiment.

  The power supply unit 10 is provided with a low-voltage power supply unit 67. The low-voltage power supply unit 67 includes a primary side 68, a secondary side 69, a power supply control unit 70 for controlling the voltage on the secondary side 69, and the like. The electric power from the power source 9 is supplied to the primary side 68, and the voltage generated on the secondary side 69 is supplied to the process control unit 38 via the DC power source generation unit 39. The power supply control unit 70 controls the voltage on the secondary side 69 based on control information from the driver IC 65 of the process control unit 38.

  The low level signal output when the failure detection circuit 36 of this embodiment detects the occurrence of the failure is input to the CPU 60 of the process control unit 38 via the third cable 25c, and the failure occurrence notification generated there is Then, the data is output to the display unit 47 via the seventh cable 25g, and the operator is notified of the failure of the heater 22 and the like.

  After displaying the failure information notification on the display unit 47, the CPU 60 of this embodiment outputs a power OFF instruction signal to the IO port 64, and the IO port 64 supplies a low level to the enable signal of the driver IC 65. To do. By supplying a low level to the enable signal of the driver IC 65, the output of the driver IC 65 becomes a high impedance state, and the power supply control unit 70 detects this high impedance state and outputs it from the secondary side 69. The supply of DC voltage to the unit 38 is stopped. As a result, the printer 1 is turned off and the printer 1 is stopped.

As described above, in this embodiment, as in the first embodiment, the failure detection circuit always monitors the state of the heater and the like, and the printer can be automatically turned off by the power control unit when a failure occurs. Thus, in addition to the same effects as those of the first embodiment, the operation of the printer can be safely stopped.
In each of the above embodiments, the image forming apparatus is described as a printer. However, the image forming apparatus is not limited to the above, and may be a copying apparatus, a facsimile, or an MFP (Multi Function Printer).

DESCRIPTION OF SYMBOLS 1 Printer 3 Host apparatus 5 Interface 6 Fixing device 8 Control part 9 Commercial power supply 10 Power supply part 11 Paper tray 12 Paper conveyance path 13 Hopping roller 13a Hopping motor 14 Conveying belt 14a Belt motor 16c, 16m, 16y, 16k Developing unit 17 Drum motor 18c, 18m, 18y, 18k Photosensitive drum 19c, 19m, 19y, 19k Exposure head 20 Fixing roller 20a Fixing motor 21 Pressure roller 22 Heater 23 Thermistor 25a First cable 25b Second cable 25c Third cable 25d First 4 cable 25e 5th cable 25f 6th cable 25g 7th cable 25h 8th cable 25i 9th cable 27 Temperature thermostat 30 Triac 31 Photocoupler 3 a, 31b Light emitting element 33 Fixing temperature control circuit 34 Waveform shaping circuit 35 Zero cross circuit 36 Fault detection circuit 38 Process control unit 39 DC current generation unit 41 Phototriac coupler 41a LED element 41b Phototriac 42 Capacitor 44 Fixing control unit 46 Image processing unit 47 Display unit 49 Fixing device protection circuit 51 Fixing temperature control unit 52, 58, 59 Open collector gate 53 Main control circuit 53a AD converter 53b, 60 CPU
53c, 61 RAM
53d, 62 ROM
53e, 64 IO port 54 Latch circuit 55 AND circuit 57 Comparator 65 Driver IC
67 Low voltage power supply 68 Primary side 69 Secondary 70 Power supply control unit

Claims (2)

In an image forming apparatus including a fixing device that heats a medium on which a developer image is formed and heat-fixes the developer image on the medium.
Heating means for heating the fixing device;
Temperature detecting means for detecting the temperature of the fixing device;
A current detection circuit for detecting a current flowing through the heating means;
A temperature control unit that controls energization to the heating unit based on the temperature detection result detected by the temperature detection unit, and controls the temperature of the fixing device within a predetermined temperature range;
An image forming apparatus comprising: a failure detection circuit that detects a failure of the fixing device based on a detection result of the current detection circuit and a control signal of the temperature control unit. The image forming apparatus according to claim 1.
An image forming apparatus comprising: a power control unit that performs power control of the fixing device based on failure notification information detected by the failure detection circuit.

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