Image forming apparatus

Abstract

An image forming apparatus is disclosed. A switch is disposed between the external power source and the heater, and adjusts power supplied to the heater such that a temperature of the heater approaches a target temperature. The cutoff element is connected in series with the switch between the external power source and the heater, and cuts off the alternating current supplied from the external power source to the heater. The switch stops the supply of power to the heater when an end condition for the end of heating by the heater is satisfied. When the abnormal waveform is not detected when the end condition is satisfied, the motor stops. In a case where an abnormal waveform is detected when an end condition is satisfied, the motor stops after being delayed with respect to the heater.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an image forming apparatus. BACKGROUND

[0002] In an electrophotographic fixing device, a heater is heated by alternating current supplied from a commercial alternating current power supply, and toner is fixed to a sheet by the heater. When the fixing device continuously heats a sheet having a small size, the temperature of an end portion of the fixing device excessively increases. Therefore, when the temperature of the heater exceeds a temperature threshold, the power supply to the heater is cut off, and the fixing device is protected. Incidentally, when the waveform of the alternating current becomes an abnormal waveform, even if a gate signal of a bidirectional thyristor for supplying current to the heater is switched from an on signal to an off signal, the bidirectional thyristor can continue to be on (commutation failure). In this case, the temperature of the heater increases much more than expected. In Japanese Patent Application Publication No. 2016-136175, it is proposed to lower the temperature threshold during a period in which the abnormal waveform is occurring.

[0003] When the temperature threshold is lowered as in Japanese Patent Application Publication No. 2016-136175, the temperature of the heater tends to exceed the temperature threshold, and the frequency of warnings to the user increases. This can cause excessive anxiety to the user. In addition, it is also possible to perform printing in a print mode in which the target temperature of the heater is high. In this case, in order to reduce false detection of excessive temperature increase, it is necessary to lower the rotation speed of the pressurizing member, and therefore the productivity of the image forming apparatus decreases. SUMMARY

[0004] The present disclosure provides an image forming apparatus including: a first rotating body driven by a driving member and for rotation; a second rotating body disposed opposite the first rotating body and for cooperating with the first rotating body to form a nip; a heating member for heating the second rotating body by being supplied with alternating current from an external power source; a switching member disposed between the external power source and the heating member and for adjusting power supplied to the heating member so that a temperature of the heating member approaches a target temperature; a cutting member connected in series with the switching member between the external power source and the heating member and for cutting the alternating current supplied from the external power source to the heating member; and a waveform detecting member for detecting an abnormal waveform of the alternating current; wherein, in a case where an end condition of heating end of the heating member is satisfied, the switching member stops the supply of power to the heating member, in a case where the abnormal waveform is not detected when the end condition is satisfied, the driving member is stopped, and in a case where the abnormal waveform is detected when the end condition is satisfied, the driving member is stopped after being delayed with respect to the heating member.

[0005] The present disclosure provides an image forming apparatus including: a first rotating body driven by a driving member and for rotation; a second rotating body disposed opposite the first rotating body and for cooperating with the first rotating body to form a nip; a heating member for heating the second rotating body by being supplied with alternating current from an external power source; a switching member disposed between the external power source and the heating member and for adjusting power supplied to the heating member so that a temperature of the heating member approaches a target temperature; a cutting member connected in series with the switching member between the external power source and the heating member and for cutting the alternating current supplied from the external power source to the heating member; and a power failure detecting member arranged between the cutting member and the switching member and for detecting a power failure of the external power source; and a monitoring member for monitoring the temperature of the heating member; and wherein, in a case where an end condition of heating end of the heating member is satisfied, the switching member stops the supply of power to the heating member, in a case where a temperature abnormality of the heating member is not detected when the end condition is satisfied, the driving member is stopped, and in a case where a temperature abnormality of the heating member is detected when the end condition is satisfied, power supplied from the external power source to the heating member is cut by the cutting member for at least a predetermined period of time, and the driving member is stopped after being delayed with respect to the heating member.

[0006] This disclosure provides an image forming apparatus, comprising: a first rotating body driven by a driving member and used for rotation; a second rotating body disposed opposite to the first rotating body and used for cooperating with the first rotating body to form a clamping portion; a heating member used for heating the second rotating body by being supplied with alternating current from an external power source; a switching member disposed between the external power source and the heating member, and used for adjusting the power supplied to the heating member so that the temperature of the heating member is close to a target temperature; and a cutting-off member connected in series with the switching member between the external power source and the heating member and used for cutting off the power supplied from the external power source. The external power supply provides alternating current to the heating element; a waveform detection element is used to detect abnormal waveforms of the alternating current; and a control element is used to control the driving element, the switching element, and the cutting-off element. Specifically, when a termination condition for ending the heating of the heating element is met, the control element controls the switching element to stop supplying power to the heating element; if the abnormal waveform is not detected when the termination condition is met, the control element controls the driving element to stop; and if the abnormal waveform is detected when the termination condition is met, the control element delays the stopping timing of the driving element relative to the stopping timing of the heating element.

[0007] The features of this disclosure will become clear from the following description of embodiments with reference to the accompanying drawings. The following description of embodiments is by way of example. Attached Figure Description

[0008] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present disclosure and, together with the description, serve to illustrate the principles of the embodiments.

[0009] Figure 1 It is a cross-sectional view of the image forming apparatus.

[0010] Figure 2 It shows a cross-sectional view of the fixing equipment.

[0011] Figure 3 This is a circuit diagram illustrating the heater drive circuit.

[0012] Figure 4 This is a circuit diagram illustrating a detection circuit used to detect zero crossings.

[0013] Figure 5A and Figure 5B It is a diagram illustrating the waveforms of alternating current and zero-crossing signals.

[0014] Figure 6 It is a diagram used to illustrate the functions implemented by the CPU.

[0015] Figure 7 It is a flowchart illustrating the control method.

[0016] Figure 8 This is a circuit diagram illustrating another detection circuit.

[0017] Figure 9A and Figure 9B It is a diagram illustrating the waveforms of alternating current and zero-crossing signals.

[0018] Figure 10 It is a flowchart illustrating the control method.

[0019] Figure 11 It is a flowchart illustrating the control method.

[0020] Figure 12 It is a flowchart illustrating the control method. Detailed Implementation

[0021] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. It should be noted that the following embodiments are not intended to limit the scope of the claims. Several features are described in the embodiments, but not all such features are necessary, and multiple such features can be appropriately combined. Furthermore, in the drawings, the same reference numerals are given the same or similar configuration, and redundant descriptions are omitted.

[0022] First Embodiment

[0023] 1. Image forming apparatus

[0024] Figure 1 The image forming apparatus 100 shown is an electrophotographic printer. The sheet cassette 116 is a storage unit for storing and holding a large quantity of sheets P. The feed roller 102 is driven to rotate by a motor 118 and feeds the sheets P from the sheet cassette 116 onto the transport path. Transport rollers 103 and 104, located downstream of the feed roller 102 in the transport direction of the sheets P, transport the sheets P further downstream. A sheet sensor 120 detects the arrival and passage of the sheets P. The image forming apparatus 100 uses the timing of the detection of the leading edge of the sheets P as the start timing for the electrophotographic process.

[0025] Processing cartridge 109 includes a photosensitive drum 105, a charging roller 106, a developing roller 107, and a toner container 108. The photosensitive drum 105 is an image carrier driven and rotated by a motor 118. The charging roller 106 uniformly charges the surface of the photosensitive drum 105. A scanning optics device 110 illuminates the surface of the photosensitive drum 105 with light 111 corresponding to the image data to form an electrostatic latent image. The developing roller 107 develops the electrostatic latent image using toner contained in the toner container 108 to form a toner image. A transfer roller 112 transfers the toner image from the photosensitive drum 105 to the sheet P.

[0026] A fixing device 190 is deployed downstream of the transfer roller 112. The fixing device 190 includes a heating device 113 and a pressurizing device 114. The heating device 113 heats the sheet P and the toner image. The pressurizing device 114 pressurizes the sheet P and the toner image. Therefore, the toner image is fixed onto the sheet P. An ejector roller 115 is deployed downstream of the fixing device 190. The ejector roller 115 ejects the sheet P to the outside of the image forming apparatus 100.

[0027] Fan 117 is a cooling device used to reduce the temperature in the image forming apparatus 100. The temperature in the image forming apparatus 100 rises when the heating device 113 generates heat. When the internal temperature becomes too high, the toner in the toner container 108 adheres. Operation of fan 117 inhibits toner adhesion. Furthermore, it suppresses heat generation from electrical components such as power supply devices. Motor 118 is a drive source that applies driving force to multiple rotating bodies (such as the developing roller 107), including the pressurizing device 114. That is, the pressurizing device 114 and the processing cartridge 109 are driven by the same drive source. Although only one motor 118 is shown here, multiple motors 118 can be used.

[0028] The control board 130 includes a CPU 131, a heater drive circuit 132, etc. The CPU 131 controls the heater drive circuit 132 to control the temperature of the heating device 113. The CPU 131 also controls the motor 118.

[0029] 2. Heating and pressurizing equipment

[0030] Figure 2 The structure of heating device 113 and pressurizing device 114 are shown. Sheet P is conveyed along the conveying direction F. Heating device 113 includes a heating film 202 and a heater 200. Heating film 202 is a cylindrical rotating body. Heater 200 is a heating body that contacts the inner surface of heating film 202. The base layer of heating film 202 is made of a heat-resistant resin such as polyimide or a metal such as stainless steel.

[0031] The pressurizing device 114 includes a pressure roller 208. The pressure roller 208 is positioned to face the heating film 202. The pressure roller 208 cooperates with the heating film 202 and the heater 200 to form the fixing clamping section N.

[0032] The heater 200 is held by a heater support member 201 made of heat-resistant resin. The heater support member 201 also has a guiding function to guide the rotation of the heating film 202.

[0033] Metal bracket 204 is used to apply pressure from a spring (not shown) to heater support member 201. Metal bracket 204 has a U-shaped cross-section. Metal bracket 204 is a member extending in an axial direction parallel to the core metal 209. Metal bracket 204 increases the bending stiffness of heating device 113 and positions heater support member 201.

[0034] The heater 200 includes a heater substrate 203, a heating element 206, and a surface protective layer 205. For example, the heater substrate 203 is a ceramic substrate. The heating element 206 is a resistance heating element arranged on the heater substrate 203 along the longitudinal direction of the substrate. The surface protective layer 205 is an insulating member (e.g., glass) covering the heating element 206.

[0035] A thermistor 211 and a thermostat 212 are disposed on the upper surface of the heater 200. Thermistor 211 is a temperature sensor (temperature sensing element) that detects temperature related to the temperature of the heater 200. The thermostat 212 is a protective element that cuts off the power supply to the heater 200 when the temperature of the heater 200 becomes abnormally high. The thermostat 212 may have a thermal switch or a thermal fuse. Thermistor 211 and thermostat 212 may be pressed against the heater 200 by a leaf spring (not shown) or the like.

[0036] The pressure roller 208 includes a core metal 209 and an elastic layer 210. The core metal 209 is made of metal (e.g., iron, aluminum, etc.). The elastic layer 210 is made of silicone rubber, etc. The pressure roller 208 receives power from the motor 118 via a gear (not shown) connected to the core metal 209 of the pressure roller 208 and rotates in the direction of the arrow. When the pressure roller 208 rotates, the heating film 202 is driven to rotate relative to the pressure roller 208 (driven state). When no power is transmitted from the motor 118, the pressure roller 208 stops (stopped state). The sheet P carrying the unfixed toner image is conveyed while being clamped between the heating film 202 and the pressure roller 208 at the fixing clamping part N. Therefore, the toner image is fixed on the sheet P.

[0037] 3. Heater drive circuit

[0038] Figure 3The heater drive circuit 132 is shown. The external power supply 301 is an AC power supply connected to the image forming apparatus 100. For example, the external power supply 301 can be a commercial AC power supply. Power-on control of the heater 200 is performed by turning a triac 316 on and off. The triac 316 is a semiconductor switch positioned between the neutral side of the external power supply 301 and contacts C1 and C2 of the heater 200. Contact C1 is electrically connected to one end of the heating element 206. Contact C2 is electrically connected to the other end of the heating element 206. The hot side of the external power supply 301 is connected to contacts C1 and C2 of the heater 200 via a thermostat 212. In this way, the heater 200 is driven by AC power.

[0039] The detection circuit 308 detects zero crossings in the AC power supplied from the external power source 301. The detection circuit 308 generates a zero crossing signal "ZEROX" indicating that the AC voltage is equal to or below a certain threshold, and inputs the zero crossing signal ZEROX to the CPU 131.

[0040] One of the main terminals of the bidirectional thyristor 316 is connected to the neutral side of the external power supply 301 and one end of resistor R3. The other main terminal of the bidirectional thyristor 316 is connected to contact C1 and one end of resistor R7. The gate terminal of the bidirectional thyristor 316 is connected to the other end of resistor R3 and one end of the phototransistor (photoreceiving element) in the opto-bidirectional thyristor coupler 315. The other end of the phototransistor in the opto-bidirectional thyristor coupler 315 is connected to the other end of resistor R7. Here, resistors R3 and R7 are resistors used to drive the bidirectional thyristor 316. The opto-bidirectional thyristor coupler 315 is a semiconductor device used to ensure the creepage distance between the primary side circuit (AC side circuit) and the secondary side circuit (DC side circuit). Resistor R3 can be omitted. When the CPU 131 causes the LED (light-emitting element) of the opto-SCR 315 to emit light, the opto-SCR 315 is turned on, and the triac 316 is also turned on. When AC power is supplied, the LED of the opto-SCR 315 repeatedly turns on and off. Resistor R8 is connected between the power supply voltage Vcc and the anode of the LED of the opto-SCR 315. Resistor R8 is a limiting resistor used to limit the current flowing through the LED. The collector of transistor Tr1 is connected to the cathode of the LED of the opto-SCR 315. The emitter of transistor Tr1 is grounded. The base of transistor Tr1 is connected to the CPU 131. The CPU 131 turns the opto-SCR 315 on / off via transistor Tr1 by outputting a control signal "FUSER" to the base.

[0041] One end of the thermistor 211 is connected to the power supply voltage Vcc via resistor R1. The other end of the thermistor 211 is grounded. A detection signal TH is generated by dividing the power supply voltage Vcc using the internal resistance of the thermistor 211, which changes in response to temperature, and the resistance of resistor R1. The detection signal TH is input to CPU 131. CPU 131 controls the bidirectional thyristor 316 such that the detected temperature of the thermistor 211, indicated by the detection signal TH, is close to the set temperature (target temperature) of heater 200. Proportional-integral (PI) control can be used for this control. CPU 131 calculates the power to be supplied to heater 200 and calculates the corresponding phase angle (phase control) or wavenumber control level (wavenumber control). CPU 131 uses the control level with the edge of the zero-crossing signal ZEROX as a time reference to control the bidirectional thyristor 316.

[0042] Relay 302 is an electromagnetic relay deployed between external power supply 301 and bidirectional thyristor 316 and connected in series with bidirectional thyristor 316. CPU 131 supplies relay drive signal "RELAY" to relay 302 to control the state (off / on) of relay 302. When relay 302 is switched to the on state, external power supply 301 is supplied to heater 200.

[0043] Here, if a problem such as a short circuit in the bidirectional silicon controlled rectifier 316 occurs, the heating device 113 may be in a heated state exceeding the assumed steady-state in the design (abnormal temperature rise). In this case, the thermostat 212 cuts off the power supply to the heater 200. When the detected temperature of the thermistor 211, indicated by the detection signal TH, becomes equal to or higher than a predetermined threshold, the CPU 131 switches the relay 302 from the on state to the off state. Therefore, the power supply to the heater 200 is cut off. The operating temperature of the thermostat 212 is higher than the temperature threshold of the relay 302.

[0044] 4. Detection of abnormal waveforms

[0045] like Figure 4As shown, the hot-side potential of the external power supply 301 is connected to the anode of the light-emitting diode 401 of the optocoupler 404 via a current-limiting resistor R41. The cathode of the light-emitting diode 401 is connected to the neutral side of the external power supply 301. That is, the light-emitting diode 401 is connected in parallel with the external power supply 301. The optocoupler 404 is a semiconductor device used to ensure creepage distance. The collector of the phototransistor 402 of the optocoupler 404 is connected to the power supply voltage Vcc via a resistor R42. The resistor R42 is a current-limiting resistor that limits the current flowing through the phototransistor 402. The emitter of the phototransistor 402 is grounded. The capacitor C43 and the resistor R44 form a filter for noise reduction. The output signal (zero-crossing signal ZEROX) of the optocoupler 404 is input to the CPU 131 through the filter. In a low-noise environment, the capacitor C43 and the resistor R44 can be omitted.

[0046] exist Figure 4 In this example, the hot side of the external power supply 301 is connected to the anode of the LED 401. The neutral side of the external power supply 301 is connected to the cathode of the LED 401. However, this is merely an example. The hot side can be connected to the cathode of the LED 401, and the neutral side can be connected to the anode.

[0047] Figure 5A and Figure 5B The relationship between the input waveform from external power supply 301 and the waveform (pulse waveform) of the zero-crossing signal ZEROX is shown. The zero-crossing signal ZEROX is a pulse signal that repeats its rising and falling phases. Figure 5A As shown, the waveform of the AC power supplied from external power source 301 is a sine wave (normal condition). When the hot-side potential is higher than the neutral-side potential and the difference between them is higher than the threshold voltage Vz, the optocoupler 404 is turned on. Therefore, the zero-crossing signal ZEROX changes from high to low (falling). The threshold voltage Vz is determined by resistor R41. The hot-side potential can be lower than the neutral-side potential, or it can be lower than the threshold voltage Vz. In this case, the optocoupler 404 is turned off. Therefore, the zero-crossing signal ZEROX changes from low to high (rising). That is, the level of the zero-crossing signal ZEROX is switched according to whether the hot-side potential is higher than or greater than the threshold voltage Vz than the neutral-side potential. Therefore, a pulse waveform with an on-time Tsin1 that is wider than the on-time determined from the two actual zero-crossing points is output to CPU 131. Note that the on-time can be referred to as the on-duty cycle or the on-duty cycle width.

[0048] like Figure 5BAs shown, the AC waveform supplied from external power source 301 is a square wave. Because the voltage change rate at the zero-crossing timing is large, the square wave causes the bidirectional thyristor 316 to malfunction (commutation phenomenon). Therefore, the square wave is an abnormal waveform. The turn-on time of the square wave is the same as the turn-on time determined from the two actual zero-crossing points. That is, the turn-on time of the zero-crossing signal ZEROX when a square wave is input is Tsquare1, which is equal to the turn-on time of the square wave. Comparison Figure 5A and Figure 5B It can be seen that Tsquare1 of the square wave (abnormal waveform) is shorter than Tsin1 of the sine wave (normal waveform).

[0049] CPU 131 can monitor the on-time of the zero-crossing signal ZEROX to detect abnormal waveforms. For example, CPU 131 determines whether the on-time Ton of the zero-crossing signal ZEROX is less than a threshold (e.g., Tsin1). When Ton is less than Tsin1, CPU 131 determines that the input AC waveform is abnormal. The on-time Tsquare1 of the zero-crossing signal ZEROX for a square wave is less than Tsin1. Therefore, CPU 131 can detect a square wave. When Ton is not less than Tsin1, CPU 131 determines that the input AC waveform is normal.

[0050] 5. CPU Function

[0051] Figure 6 Various functions implemented by the CPU 131 executing the control program are shown. Some or all of these functions can be implemented using hardware circuitry such as an Application-Specific Integrated Circuit (ASIC) or a Field-Programmable Gate Array (FPGA). Memory 601 is a storage device that may include Random Access Memory (RAM), Read-Only Memory (ROM), Solid State Drive (SSD), Hard Disk Drive (HDD), etc. The ROM area of ​​memory 601 stores the control program. Timer 602 is a real-time clock or counter circuit. Heater control unit 603 controls the bidirectional thyristor 316 so that the temperature of heater 200, detected by the thermistor 211, approaches the target temperature. Motor control unit 604 generates a drive signal “DRV” and controls the rotation / stop of motor 118. Additionally, motor control unit 604 can also control the rotational speed of motor 118. That is, motor 118 can control the rotational speed of pressure roller 208. Relay control unit 605 generates a control signal RELAY for controlling the ON (conduction state) and OFF (off state) of relay 302 and supplies the control signal RELAY to relay 302.

[0052] Temperature monitoring unit 611 converts the detection signal TH output from the thermistor 211 into temperature, obtains a comparison result between the detected temperature and the threshold temperature, and outputs the comparison result to determination unit 620. Waveform detection unit 612 detects abnormal waveforms of AC power based on the zero-crossing signal ZEROX. Power fault detection unit 613 is optional and detects power faults in external power supply 301 based on the zero-crossing signal ZEROX. For example, if the zero-crossing signal ZEROX cannot be detected within a specified time, power fault detection unit 613 determines that a power fault has occurred. Note that image forming apparatus 100 has a backup power supply (e.g., a battery) that can supply power for a predetermined period of time even when external power supply 301 fails. Time monitoring unit 614 is optional and monitors the duration of abnormal waveforms and the forced cut-off time of relay 302.

[0053] The determining unit 620 determines whether the heating termination condition of the heater 200 is met based on print job information (e.g., number of pages printed). Furthermore, the determining unit 620 determines whether the power supply to the heater 200 should be stopped based on the comparison result of the temperature monitoring unit 611 (presence or absence of abnormal temperature rise). The determining unit 620 determines whether to delay and stop the motor 118 later than the heater 200 based on the detection result of the waveform detection unit 612. For example, at a first timing when the heating termination condition is met, the determining unit 620 outputs a stop command to the heater control unit 603. The heater control unit 603 switches the bidirectional thyristor 316 from on to off based on the stop command. At a second timing, the determining unit 620 outputs a stop command to the motor control unit 604. The motor control unit 604 stops the motor 118 according to the stop command. The second timing is a predetermined time later than the first timing. This predetermined time may be referred to as the rotation extension time or the stop extension time.

[0054] 6. Flowchart

[0055] Figure 7 The control method executed by CPU 131 according to the control program is shown. When a print job is input, CPU 131 performs the following processing: Determines the target temperature and conveyor speed of heater 200 based on the basis weight of sheet P specified by the print job.

[0056] In step S701, CPU 131 (heater control unit 603) starts heating the heater 200. The heater control unit 603 raises the temperature of the heater 200 to the target temperature and maintains the temperature of the heater 200 at the target temperature.

[0057] In step S702, CPU 131 (motor control unit 604) starts the rotation of pressure roller 208 via motor 118. Note that steps S701 and S702 can be executed simultaneously, or step S702 can be executed before step S701.

[0058] In step S703, CPU 131 (determining unit 620) determines whether the heating termination condition is met. For example, the heating termination condition may be that printing on the number of sheets P specified by the print job information has been completed. The heating termination condition may be that the temperature of heater 200 has reached the target temperature. When the heating termination condition is met, CPU 131 causes the process to proceed from step S703 to step S704.

[0059] In step S704, CPU 131 (heater control unit 603) changes the heater drive signal FUSER to turn off the bidirectional thyristor 316, thereby stopping the heating of heater 200. Motor control unit 604 continuously rotates pressure roller 208 via motor 118.

[0060] Note that problems may occur if the pressure roller 208 stops along with the heater 200. For example, if the AC waveform is a square wave, the bidirectional thyristor 316 remains on, and the heater 200 continues heating. In this case, when the motor 118 stops, a sudden temperature difference occurs between the fixing clamp N and other parts. This could cause malfunctions in the heating device 113 and the pressure device 114. Therefore, it is necessary to detect abnormal waveforms.

[0061] During the continuous driving period of the pressure roller 208 (rotation extension period), the driving speed (rotation speed) of the pressure roller 208 can be any speed, as long as it can suppress malfunctions. The rotation speed during the rotation extension period can be different from the rotation speed during the heat treatment.

[0062] In step S705, CPU 131 (waveform detection unit 612) acquires the detection result of the AC waveform based on the zero-crossing signal ZEROX. In waveform detection, for example, waveform detection unit 612 measures the time "ton" from the timing when the AC voltage becomes equal to or below a threshold voltage Vz to the timing when the AC voltage exceeds the threshold voltage Vz. In this way, waveform detection can be a measurement of time ton. Waveform detection does not need to be performed in step S705 and can be performed at other times. For example, it can be performed with... Figure 7 The processing shown is performed in parallel at regular measurement intervals. The waveform detection results can be stored in memory located inside or outside the CPU 131 and can be read out as needed.

[0063] In step S706, CPU 131 (determining unit 620) determines whether the AC waveform is a normal waveform. If ton is equal to or greater than a threshold (e.g., Tsin1), the AC waveform is a normal waveform. If ton is less than the threshold, the AC waveform is an abnormal waveform. When the detected waveform is a normal waveform, CPU 131 causes the processing to proceed from step S706 to step S707. If the detected waveform is an abnormal waveform, CPU 131 waits for the detected waveform to return to a normal waveform.

[0064] In step S707, CPU 131 (motor control unit 604) stops the rotation of pressure roller 208 via motor 118.

[0065] According to the first embodiment, when an abnormality occurs in the waveform of the alternating current, the pressurizing device 114 stops after issuing a stop command to the heating device 113 (this is called continuous rotation control or stop delay control). That is, the CPU 131 delays the stop timing of the motor 118 relative to the stop timing of the heater 200. Therefore, even if the bidirectional thyristor 316 is accidentally turned on due to an abnormal waveform, malfunctions of the pressurizing device 114 and the heating device 113 are unlikely to occur. This is because the rotation of the pressurizing device 114 continues, and the pressurizing device 114 stops after the temperature difference between the fixing clamp N and other parts decreases.

[0066] Motor 118 can be a shared drive source for both pressurizing device 114 and processing cartridge 109. In this case, considering factors such as the lifespan of photosensitive drum 105, CPU 131 can then cause the drive of pressurizing device 114 to stop earlier. That is, the rotation duration of motor 118 can be shortened. For example, the rotation duration can be shortened as the duration of use of photosensitive drum 105 increases.

[0067] Second Embodiment

[0068] In the second embodiment, a portion of the detection circuit 308 of the first embodiment is modified. Specifically, a transistor for improving the responsiveness of the zero-crossing signal ZEROX is added between the optocoupler 404 and the CPU 131. Furthermore, a constant voltage element (e.g., a Zener diode) can be added between the hot side of the external power supply 301 and the optocoupler 404, or between the neutral side of the external power supply 301 and the optocoupler 404. Descriptions of matters common to the first embodiment in the second embodiment will be omitted.

[0069] 1. Abnormal waveform detection circuit

[0070] Figure 8The detection circuit 308 of the second embodiment is shown. A Zener diode “ZD” is added between the current-limiting resistor R41 and the anode of the light-emitting diode 401 of the optocoupler 404 on the hot side of the external power supply 301. This helps adjust the threshold voltage Vz used to detect abnormal waveforms. Note that both resistor R41 and Zener diode ZD can be located between the hot side of the external power supply 301 and the optocoupler 404. Both resistor R41 and Zener diode ZD can be located between the neutral side of the external power supply 301 and the optocoupler 404. Here, the positions of the adjacent series-connected resistor R41 and Zener diode ZD can be reversed. Furthermore, resistor R41 can be located between the hot side of the external power supply 301 and the optocoupler 404, and Zener diode ZD can be located between the neutral side of the external power supply 301 and the optocoupler 404. In addition, the Zener diode ZD can be located between the hot side of the external power supply 301 and the optocoupler 404, and the resistor R41 can be located between the neutral side of the external power supply 301 and the optocoupler 404.

[0071] Resistor R71 is connected between the emitter of phototransistor 402 in optocoupler 404 and ground. Resistor R71 is a current-limiting resistor that limits the current flowing through phototransistor 402. Additionally, phototransistor 402 is connected to a filter. This filter is a noise reduction filter formed by resistor R72 and capacitor C75. One end of resistor R72 is connected to the emitter of phototransistor 402. The other end of resistor R72 is connected to the base of transistor Tr3. One end of capacitor C75 is connected to one end of resistor R72. The other end of capacitor C75 is grounded.

[0072] Resistor R74 is connected between the base and emitter of transistor Tr3. Resistor R74 is configured to prevent transistor Tr3 from malfunctioning. Resistor R76 is a current-limiting resistor for transistor Tr3. Resistor R76 is connected between the collector of transistor Tr3 and the power supply voltage Vcc. The zero-crossing signal ZEROX output from the collector of transistor Tr3 is input to CPU 131 via a filter. The filter is formed by capacitor C77 and resistor R78 to reduce noise.

[0073] exist Figure 8 In this example, the anode of the light-emitting diode 401 in the optocoupler 404 is connected to the hot side of the external power supply 301, and the cathode is connected to the neutral side. However, this is merely an example. The hot side can be connected to the cathode of the light-emitting diode 401, and the neutral side can be connected to the anode.

[0074] In low-noise environments, capacitor C75 and resistor R72 can be omitted. Similarly, capacitor C77 and resistor R78 can be omitted.

[0075] Figure 9A The diagram shows the zero-crossing signal ZEROX when the AC waveform is normal (sine wave). Note that the waveform of the zero-crossing signal ZEROX in the second embodiment is inverted compared to that in the first embodiment. This is due to the addition of transistor Tr3.

[0076] As described in the first embodiment, when the AC voltage is higher than the threshold voltage Vz, the optocoupler 404 is turned on, the transistor Tr3 is turned on, and the zero-crossing signal ZEROX is at a low level. When the AC voltage is lower than the threshold voltage Vz, the optocoupler 404 is turned off, the transistor Tr3 is also turned off, and the zero-crossing signal ZEROX becomes high.

[0077] In this way, the level of the zero-crossing signal ZEROX is switched based on whether the hot-side potential is higher than or greater than the neutral-side potential by a threshold voltage Vz. If the AC waveform is sinusoidal, a zero-crossing signal ZEROX with a turn-off time wider than the turn-off time determined from the two actual zero-crossing points is obtained. In this case, the turn-off time of the zero-crossing signal ZEROX is Tsin2. The turn-off time can be referred to as the turn-off duty cycle or the turn-off duty cycle width.

[0078] like Figure 9B As shown, the waveform of the alternating current supplied from the external power source 301 is a square wave. In this case, a zero-crossing signal ZEROX (pulse waveform) with a turn-off time Tsquare2 equal to the interval between the two true zero-crossing points is output to the CPU 131. The CPU 131 (waveform detection unit 612) measures the turn-off time "toff" of the zero-crossing signal ZEROX. When the turn-off time tooff is less than Tsin2, the CPU 131 (determination unit 620) determines that the waveform of the alternating current is an abnormal waveform. When the turn-off time tooff is not less than Tsin2, the CPU 131 (determination unit 620) determines that the waveform of the alternating current is a normal waveform.

[0079] like Figure 8 As shown, the output signal (zero-crossing signal ZEROX) of optocoupler 404 is output to CPU 131 via transistor Tr3. Therefore, when the potential generated by the output signal of optocoupler 404 and resistor R71 exceeds the base-emitter voltage of transistor Tr3, the logic of the zero-crossing signal ZEROX changes. Therefore, the responsiveness of the second embodiment is improved compared to the first embodiment. That is, the detection accuracy of normal waveforms and square waves (abnormal waveforms) is improved because the relationship indicated by the following formula Eq1 is satisfied.

[0080] (Tsin2-Tsquare2)>(Tsin1-Tsquare1)···Eq1

[0081] like Figure 8 As shown, the Zener diode ZD significantly increases the threshold voltage Vz of the optocoupler 404. That is, the turn-off time Tsin2 is relatively increased when a sine wave is input. Therefore, this further improves the detection accuracy of the square wave.

[0082] In the second embodiment, waveform detection does not need to be performed in step S705 and can be performed at other times. For example, it can be performed with... Figure 7 The processing shown is performed in parallel at regular measurement intervals. The waveform detection results can be stored in memory located inside or outside the CPU 131 and can be read out as needed.

[0083] Third Embodiment

[0084] The third embodiment is a variation of the first and second embodiments. Specifically, when an abnormal waveform is detected when the heating termination condition is met, the rotation termination condition of the pressure roller 208 is determined. For example, even if an abnormal waveform occurs, if the temperature of the heater 200 is normal, the pressure roller 208 can be stopped. Alternatively, if the temperature of the heater 200 returns to normal within a predetermined time, the pressure roller 208 can be stopped. Note that if the abnormal waveform and abnormal temperature persist even after the predetermined time has elapsed, the relay 302 can also forcibly stop the power supply to the heater 200. Descriptions of matters common to the first and second embodiments in the third embodiment will be omitted.

[0085] 1. Flowchart

[0086] Figure 10 A control method according to a third embodiment is shown. Here, modifications are made. Figure 7 The process from step S704 to step S707 is described in the figure. CPU 131 causes the process to proceed from step S704 to step S1001.

[0087] In step S1001, CPU 131 (time monitoring unit 614) starts monitoring the elapsed time using timer 602. Here, the elapsed time is the time elapsed since the timing of stopping the supply of power to heater 200 by turning off the bidirectional thyristor 316. Note that the elapsed time can be the period of time during which abnormal waveforms are detected after the bidirectional thyristor 316 has been turned off. Afterward, CPU 131 proceeds the process from step S1001 to step S705. In step S705, CPU 131 detects the waveform of the alternating current. When an abnormal waveform is detected in step S706, CPU 131 proceeds the process from step S706 to step S1002.

[0088] In step S1002, CPU 131 (temperature monitoring unit 611) uses thermistor 211 to detect the temperature of heater 200. In step S1003, CPU 131 (determination unit 620) determines whether the detected temperature of heater 200 is normal. If the temperature of heater 200 is normal, CPU 131 advances the process from step S1003 to step S707 and stops pressure roller 208. Since the power supply to heater 200 is stopped, heater 200 dissipates heat naturally, and the temperature of heater 200 gradually decreases. On the other hand, if heater 200 is not normal, CPU 131 advances the process from step S1003 to step S1004.

[0089] In step S1004, CPU 131 (determining unit 620) determines whether a predetermined time has elapsed based on the elapsed time obtained by time monitoring unit 614. If the predetermined time has not elapsed, CPU 131 proceeds the process from step S1004 to step S705. If the predetermined time has elapsed, CPU 131 proceeds the process from step S1004 to step S1005.

[0090] In step S1005, CPU 131 (relay control unit 605) turns off relay 302 (de-conducting state). This forcibly stops the power supply to heater 200. Additionally, CPU 131 disables image forming apparatus 100. That is, motor 118 also stops.

[0091] Several schemes exist for determining the normality of temperature. Temperature monitoring unit 611 uses thermistor 211 to acquire temperature T1 at a first timing interval and temperature T2 at a second timing interval. The second timing interval is a predetermined time t1 later than the first timing interval. Furthermore, temperature monitoring unit 611 calculates the difference ΔT (ΔT = T1 - T2) between temperature T1 and temperature T2. If temperature T2 is higher than temperature T1, ΔT is negative. When the difference ΔT is equal to or lower than a threshold Tth1, determination unit 620 determines that the temperature of heater 200 is abnormal. The threshold Tth1 is a positive value equal to or greater than 0. When the difference ΔT exceeds the threshold Tth1, determination unit 620 determines that the temperature of heater 200 is normal. Note that when ΔT is defined as ΔT = T2 - T1, the relationship between the difference ΔT and the threshold Tth1 is logically reversed.

[0092] Alternatively, the temperature monitoring unit 611 can obtain the temperature gradient G of the heater 200 by dividing the difference ΔT by a predetermined time t1. The determination unit 620 determines whether the gradient threshold G is equal to or lower than the gradient threshold Gth. If the temperature gradient G is equal to or lower than the gradient threshold Gth, the temperature of the heater 200 is determined to be normal. If the temperature gradient G exceeds the gradient threshold Gth, the temperature of the heater 200 is determined to be abnormal. The gradient threshold Gth is a positive value equal to or greater than 0. Note that when ΔT is defined as ΔT = T2 - T1, the relationship between the temperature gradient G and the gradient threshold Gth is logically reversed.

[0093] Alternatively, if temperature T2 is equal to or lower than the temperature threshold Tth2, the temperature of heater 200 can be determined to be normal. If temperature T2 exceeds the temperature threshold Tth2, the temperature of heater 200 is determined to be abnormal. The threshold Tth2 is a positive value equal to or greater than 0.

[0094] In the third embodiment, as in the first and second embodiments, the rotational speed of the pressure roller 208 during the rotation duration can be any speed capable of suppressing malfunctions of the heating device 113. The rotational speed applied during the rotation duration can differ from the rotational speed during the heat treatment.

[0095] In the first and second embodiments, when the temperature of the heater 200 becomes abnormal during the continuous rotation period, the thermostat 212 eventually switches from an on state to a non-on state, thereby stopping the image forming apparatus 100. Alternatively, the relay 302 switches from an on state to a non-on state before the thermostat 212 switches from an on state to a non-on state. In the first and second embodiments, the drive of the pressurizing device 114 continues when the AC waveform is abnormal. That is, the image forming apparatus 100 cannot perform the printing operation.

[0096] Even if an abnormal waveform is detected, the third embodiment is still useful when the bidirectional thyristor 316 is not consistently turned on. That is, in the third embodiment, even if an abnormal waveform is detected, the pressure roller 208 will immediately stop if the temperature of the heater 200 is normal. In other words, the image forming apparatus 100 can perform the following printing jobs, and the productivity of the image forming apparatus 100 is unlikely to decrease.

[0097] In the third embodiment, waveform detection does not need to be performed in step S705 and can be performed at other times. For example, it can be performed with... Figure 7 The processing shown is performed in parallel at regular measurement intervals. The waveform detection results can be stored in memory located inside or outside the CPU 131 and can be read out as needed.

[0098] Fourth embodiment

[0099] The fourth embodiment is a variation of the first or third embodiment. When an abnormal waveform is detected, the relay 302 is kept in the off state for at least a predetermined time period. Thereafter, the pressure roller 208 stops. Descriptions of aspects common to the first, second, or third embodiments in the fourth embodiment will be omitted.

[0100] 1. Flowchart

[0101] Figure 11 A control method according to the fourth embodiment is shown. When an abnormal waveform is detected in step S706, the pressure roller 208 continues to rotate. That is, the stopping of the pressure roller 208 is delayed, and the rotation duration (drive time) is extended. Furthermore, the CPU 131 causes the processing to proceed from step S706 to step S1101.

[0102] In step S1101, CPU 131 (relay control unit 605) turns off relay 302 (in a non-conducting state) for at least a predetermined time. Therefore, power supply to heater 200 is stopped. For example, the predetermined time can be equal to or greater than half a cycle of AC power. By stopping power supply to heater 200 for at least half a cycle, the square wave is cut off beyond the zero-crossing point, more reliably switching the bidirectional thyristor 316 from on to off. Therefore, even if the bidirectional thyristor 316 malfunctions due to abnormal waveforms such as the square wave, the image forming apparatus 100 is safely stopped.

[0103] like Figure 3As shown, since relay 302 is positioned between external power supply 301 and detection circuit 308, detection circuit 308 cannot detect abnormal waveforms when relay 302 is turned off. However, since the off-time of relay 302 is equal to or greater than half a cycle of AC power, the time period during which detection circuit 308 cannot perform waveform detection is short.

[0104] In the fourth embodiment, the pressure roller 208 stops after the relay 302 is turned off for at least a predetermined period of time, but this is merely an example. That is, the first period of rotation duration (drive time) of the pressure roller 208 can be longer than the second period of the relay 302 remaining off. In this case, the time monitoring unit 614 uses the timer 602 to monitor both the first and second periods. For example, the start point of the first period and the start point of the second period are determined by the timing of stopping the heating of the heater 200 in step S704 or by the timing of detecting an abnormal waveform in step S706. Note that the timing of detecting an abnormal temperature can be used as the start point. As described in the first embodiment, the rotation speed of the pressure roller 208 in the first period can be a rotation speed that can suppress the failure of the heating film 202. Furthermore, the timing of the relay 302 returning from the non-conducting state (OFF) to the conducting state (ON) can be after the pressure roller 208 stops.

[0105] In the fourth embodiment, compared to the first to third embodiments, the malfunction of the bidirectional thyristor 316 caused by abnormal waveforms can be eliminated in a shorter time. Therefore, the rotation duration of the pressure roller 208 can also be reduced. Consequently, the lifespan of the fixing equipment can be extended, and the power consumed by the image forming apparatus 100 can be reduced.

[0106] In the fourth embodiment, waveform detection does not need to be performed in step S705 and can be performed at other times. For example, it can be performed with... Figure 7 The processing shown is performed in parallel at regular measurement intervals. The waveform detection results can be stored in memory located inside or outside the CPU 131 and can be read out as needed.

[0107] Fifth embodiment

[0108] The fifth embodiment is a variation of the first embodiment, etc. In the first to fourth embodiments, at least abnormal waveforms of the alternating current are detected, but this is merely an example. For instance, if the temperature of the heater 200 is abnormal during the stop delay period of the pressure roller 208, the relay 302 can be shut off for a predetermined period of time as described in the fourth embodiment. Note that the zero-crossing signal ZEROX detected by the detection circuit 308 can be used by the power fault detection unit 613 to detect power faults in the external power supply 301.

[0109] 1. Power Fault Detection

[0110] The memory 601 may include a high-capacity non-volatile storage device (e.g., HDD, SSD). The RAM area of ​​the memory 601 may temporarily store printed image data transferred from a host computer, etc. When the memory 601 stores printed image data in its HDD, the external power supply 301 may fail, or the power cable connecting the external power supply 301 to the image forming apparatus 100 may be disconnected from the socket. Therefore, in the event of a power outage, the power supplied from the backup power supply located inside the image forming apparatus 100 can be gradually reduced. As a result, data corruption or inconsistency may occur in the HDD, and the CPU 131 may be unable to read data from the HDD.

[0111] Therefore, the power failure detection unit 613 detects power failures and unexpected power interruptions based on the zero-crossing signal ZEROX. The CPU 131 saves print image data from RAM to HDD from the moment a power failure occurs until the image forming apparatus 100 completely stops. Thus, the data is protected. For example, if no zero-crossing signal ZEROX is input for a predetermined time or longer, the power failure detection unit 613 determines that the external power supply 301 has failed. The power failure detection unit 613 can use timer 602 to measure the elapsed time "tp" from the edge of the zero-crossing signal ZEROX and determine whether the elapsed time tp exceeds a threshold time "tth". When the elapsed time tp exceeds the threshold time tth, the power failure detection unit 613 determines that a power failure has occurred. When the elapsed time tp does not exceed the threshold time tth, the power failure detection unit 613 determines that no power failure has occurred.

[0112] Whenever AC power is supplied from external power source 301, detection circuit 308 outputs a zero-crossing signal (ZEROX). Therefore, power failure detection unit 613 consumes power constantly. Since detection circuit 308 is connected between relay 302 and bidirectional thyristor 316, power consumption of power failure detection unit 613 decreases when relay 302 is turned off.

[0113] 2. Flowchart

[0114] Figure 12 A control method according to a fifth embodiment is shown. Figure 7 Steps S705 and S706 described herein have been replaced by steps S1201 to S1204. Therefore, steps S1201 to S1204 will be described in detail below. When heating of heater 200 stops in step S704, CPU 131 causes the process to proceed from step S704 to step S1201.

[0115] In step S1201, CPU 131 (temperature monitoring unit 611) uses thermistor 211 to detect the temperature of heater 200. In step S1202, CPU 131 (determination unit 620) determines whether the detected temperature of heater 200 is normal. The determination of normality is the same as the determination in step S1003. If the temperature of heater 200 is normal, CPU 131 advances the process from step S1202 to step S707. Therefore, pressure roller 208 stops. On the other hand, if the temperature of heater 200 is abnormal even when bidirectional thyristor 316 is turned off, CPU 131 advances the process from step S1202 to step S1203.

[0116] In step S1203, CPU 131 (relay control unit 605) shuts off relay 302 for at least a predetermined time period. This forcibly stops the supply of power to heater 200. Step S1203 is the same process as step S1101, and the predetermined time period can be equal to or greater than half a cycle of AC power. For example, CPU 131 (time monitoring unit 614) can use timer 602 to monitor the predetermined time period.

[0117] In step S1204, CPU 131 (relay control unit 605) returns relay 302 from the off (non-conducting state) to the on (conducting state). Afterward, CPU 131 proceeds the process from step S1204 to step S707. Therefore, motor 118 stops.

[0118] like Figure 3 As shown, since relay 302 is positioned between external power supply 301 and detection circuit 308, detection circuit 308 cannot detect the zero-crossing signal ZEROX when relay 302 is off. However, since the off-time of relay 302 is equal to or greater than half a cycle of AC power, the period during which detection circuit 308 cannot perform detection of the zero-crossing signal ZEROX is short. In other words, the period during which power fault detection unit 613 cannot perform power fault detection is also shortened.

[0119] In the fifth embodiment, the pressure roller 208 stops after the relay 302 has been turned off for at least a predetermined period of time, but this is merely an example. That is, the first period of rotation of the pressure roller 208 can be longer than the second period of the relay 302 remaining off. In this case, the time monitoring unit 614 uses the timer 602 to monitor both the first and second periods. For example, the start point of the first period and the start point of the second period are determined by the timing of stopping the heating of the heater 200 in step S704 or by the timing of detecting an abnormal temperature in step S1202. As described in the first embodiment, the rotation speed of the pressure roller 208 in the first period can be any rotation speed that can suppress the failure of the heating film 202. Furthermore, the timing of the relay 302 returning from the non-conducting state (OFF) to the conducting state (ON) can be after the pressure roller 208 has stopped.

[0120] In the fifth embodiment, when the temperature of the heater 200 becomes abnormal due to abnormal waveforms of the alternating current, the relay 302 cuts off the power supply to the heater 200. That is, the CPU 131 can estimate the occurrence of abnormal waveforms causing the abnormal temperature rise without directly detecting the waveform of the alternating current. When the CPU 131 detects an abnormal temperature rise, it shuts off the relay 302 for a predetermined period of time, thereby suppressing malfunctions in the heating device 113 and the pressurizing device 114. The period during which the power supply is forcibly cut off by the relay 302 is only at least half a cycle of the alternating current. Therefore, the period during which the power fault detection unit 613 cannot perform power fault detection is also shortened. Furthermore, the duration of rotation of the pressure roller 208 can also be shortened. Therefore, the lifespan of the fixing device 190 can be extended, and the power consumed by the image forming apparatus 100 can be reduced.

[0121] In the fifth embodiment, waveform detection does not need to be performed in step S705 and can be performed at other times. For example, it can be performed with... Figure 7 The processing shown is performed in parallel at regular measurement intervals. The waveform detection results can be stored in memory located inside or outside the CPU 131 and can be read out as needed.

[0122] Technical ideas derived from the embodiments

[0123] Motor 118 is an example of a drive unit and drive component. Pressure roller 208 is an example of a first rotating body. Heating film 202 is an example of a second rotating body. Heater 200 is an example of a heater. Bidirectional silicon controlled rectifier 316 and CPU 131 are examples of a switching unit and switching component. Relay 302 is an example of a cutting-off unit or cutting-off component. Detection circuit 308 and CPU 131 are examples of a waveform detection unit and waveform detection component. In this way, according to this embodiment, motor 118 stops with a delay relative to heater 200. Therefore, the temperature difference between the fixing clamp N and its surroundings is reduced, and the image forming apparatus 100 can be appropriately protected from heat.

[0124] If an abnormal waveform occurs, the bidirectional thyristor 316 may malfunction, and the heater 200 may generate heat. When the abnormal waveform persists, the motor 118 will continue to rotate, thereby suppressing the abnormal temperature rise of the heater 200 and the heating film 202. Therefore, this adequately protects the image forming apparatus 100 (especially the fixing device 190) from the effects of heat.

[0125] Thermistor 211 and CPU 131 are examples of temperature monitoring units and temperature monitoring components. CPU 131 is an example of a determining unit and determining component. Figure 10 As shown, when abnormal waveforms and abnormal temperatures occur simultaneously, motor 118 can maintain the rotation of pressure roller 208. Therefore, this effectively protects the image forming apparatus 100 from heat. Furthermore, even if abnormal waveforms occur, motor 118 can stop immediately if the temperature of heater 200 is normal. Therefore, this reduces the amount of time the image forming apparatus 100 is unable to perform printing and makes it difficult to reduce the productivity of the image forming apparatus 100.

[0126] For reference Figure 10 The starting point of the first time period (predetermined time) can be any of the three timings. The first time period can be referred to as a rotation duration period, a rotation extension period, or a stop delay period. When relay 302 cuts off the power supply path in step S1005, the power supply to motor 118 can also be cut off. Alternatively, power can be supplied to motor 118 from a DC power source unaffected by the on / off state of relay 302. In this case, CPU 131 stops motor 118 via motor control unit 604. Therefore, motor 118 can be stopped.

[0127] In this way, the motor 118 can stop when the temperature returns to normal. The amount of time that the image forming apparatus 100 cannot perform printing is further reduced, and this makes it difficult to reduce the productivity of the image forming apparatus 100.

[0128] As described in conjunction with step S1005, abnormal waveforms and temperatures can persist even after a predetermined time has elapsed. In this case, relay 302 can forcibly disconnect the power supply to heater 200. After this, CPU 131 can stop motor 118.

[0129] like Figure 11 As shown in the diagram, when an abnormal waveform is detected when the heating termination condition is met, the power supply to the heater 200 can be stopped by the relay 302 for a predetermined period of time.

[0130] Such as combination Figure 11 As described, relay 302 is in the off state for a predetermined period of time, but can then return to the on state. Furthermore, after relay 302 returns to the on state, motor 118 can stop. Therefore, this achieves both thermal protection of the image forming apparatus 100 and maintenance of its productivity.

[0131] The half-cycle of the alternating current can be measured by the detection circuit 308, or it can be the nominal half-cycle. Therefore, this can reduce the amount of time that the image forming apparatus 100 cannot form an image.

[0132] As described in the third embodiment, the normality of the temperature can be determined based on temperatures T1 and T2.

[0133] As described in the third embodiment, the normality of the temperature can be determined based on the temperature difference between temperatures T1 and T2.

[0134] As described in the third embodiment, the normality of the temperature can be determined based on the temperature gradient (e.g., G) and the gradient threshold (e.g., Gth).

[0135] As described in the third embodiment, the normality of the temperature can be determined based on temperature T2.

[0136] The detection circuit 308 is an example of a circuit that outputs a zero-crossing waveform.

[0137] As described in the first embodiment, the CPU 131 can detect abnormal waveforms based on the zero-crossing signal ZEROX.

[0138] As described in the first embodiment, the CPU 131 can detect abnormal waveforms based on the on-time (on-duty cycle) or off-time (off-duty cycle) of the zero-crossing signal ZEROX.

[0139] The detection circuit 308, prepared for power fault detection, can be used to detect abnormal waveforms in AC power.

[0140] The detection circuit 308 used in the power control of heater 200 can be used to detect abnormal waveforms of AC power.

[0141] As described in the first embodiment, the zero-crossing signal ZEROX can be output from the light-receiving element of optocoupler 404. As described in the second embodiment, the zero-crossing signal ZEROX can be output through phototransistor Tr3. In particular, in the second embodiment, the responsiveness of the zero-crossing signal ZEROX is improved.

[0142] The Zener diode ZD is an example of a constant voltage element. By employing a constant voltage element, the threshold voltage Vz of the light-emitting element in the optocoupler 404 used for emitting light is increased. Therefore, it is easy to distinguish abnormal waveforms from normal waveforms.

[0143] The detection circuit 308 can be deployed between the relay 302 and the external power supply 301. However, in this case, the detection circuit 308 always consumes power. Figure 3 As shown, the detection circuit 308 can be deployed between the relay 302 and the heater 200. In this case, when the relay 302 is turned off, the detection circuit 308 stops, thereby reducing the power consumption of the detection circuit 308.

[0144] Motor 118 can drive pressure roller 208, causing heating film 202 and pressure roller 208 to rotate at a speed at which they do not stick together. However, the rotational speed can be lower than the rotational speed during image formation.

[0145] Relay 302 can be an electromagnetic relay. The bidirectional thyristor 316 can be another type of semiconductor switch. Heater 200 can be a ceramic heater or a halogen lamp.

[0146] The pressure roller 208 and the processing box 109 for supplying toner can be driven by the same drive source. Therefore, the number of drive sources can be reduced.

[0147] As described in the fifth embodiment, monitoring or detection of abnormal waveforms is not required. When the heating termination condition is met and an abnormal temperature is detected, relay 302 can be turned off for a predetermined period of time. After this, relay 302 returns to the on state, and motor 118 can stop.

[0148] CPU 131 is an example of a control unit and control component. Delaying the stopping timing of motor 118 relative to the stopping timing of heater 200 corresponds to continuing the rotation of motor 118.

[0149] Other embodiments

[0150] The embodiments of this disclosure can also be implemented by a computer that reads and executes computer-executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be more fully referred to as a "non-transient computer-readable storage medium") to perform the functions of one or more embodiments described above and / or includes one or more circuits (e.g., application-specific integrated circuits (ASICs)) for performing the functions of one or more embodiments described above, and by a method executed by a computer of a system or device, for example, by reading and executing computer-executable instructions from a storage medium to perform the functions of one or more embodiments described above and / or controlling one or more circuits to perform the functions of one or more embodiments described above. The computer may include one or more processors (e.g., a central processing unit (CPU), a microprocessor unit (MPU)) and may include a network of separate computers or separate processors to read and execute the computer-executable instructions. The computer-executable instructions may be provided to the computer, for example, from a network or storage medium. Storage media may include one or more of the following: hard disk, random access memory (RAM), read-only memory (ROM), storage device for distributed computing systems, optical disc (such as compact disc (CD), digital versatile disc (DVD) or Blu-ray disc (BD)™), flash memory device, memory card, etc.

[0151] Other embodiments

[0152] Embodiments of the present invention can also be implemented by providing software (including computer program products of computer programs) that performs the functions of the above embodiments to a system or device via a network or various storage media, and the computer (central processing unit (CPU) or microprocessor unit (MPU) of the system or device) reads and executes the computer program.

[0153] While this disclosure has been described with reference to exemplary embodiments, it is to be understood that this disclosure is not limited to the disclosed exemplary embodiments. The scope of the appended claims shall be given the broadest interpretation to include all such modifications and equivalent structures and functions.

Claims

1. An image forming apparatus comprising: a first rotating body driven by a driving member and for rotation; a second rotating body disposed opposite to the first rotating body and for cooperation with the first rotating body to form a nip; a heating member for heating the second rotating body by being supplied with alternating current from an external power source; a switching member disposed between the external power source and the heating member and for adjusting electric power supplied to the heating member so that a temperature of the heating member approaches a target temperature; a cutting member connected in series with the switching member between the external power source and the heating member and for cutting the alternating current supplied from the external power source to the heating member; and a waveform detecting member for detecting an abnormal waveform of the alternating current; wherein the switching member stops the supply of electric power to the heating member in a case where an end condition in which heating of the heating member ends is satisfied, the driving member is stopped in a case where the abnormal waveform is not detected when the end condition is satisfied, and the driving member is stopped after being delayed with respect to the heating member in a case where the abnormal waveform is detected when the end condition is satisfied. The driving member is stopped when a waveform of the alternating current returns to a normal waveform from the abnormal waveform.

2. The image forming apparatus according to claim 1, wherein 3. The image forming apparatus according to claim 1, further comprising: a temperature monitoring member for monitoring a temperature of the heating member; and a determination member for determining whether the temperature is normal in the case where the abnormal waveform is detected when the end condition is satisfied; wherein the driving member is stopped when the temperature is normal, and the driving member continues a further operation when the temperature is not normal. The driving member is stopped when a first time period elapses from a timing at which the end condition is satisfied, a timing at which the abnormal waveform is detected, or a timing at which the temperature is detected to be not normal. The driving member is stopped when the temperature returns to normal before the first time period elapses.

4. The image forming apparatus according to claim 3, wherein In a case where the abnormal waveform is detected and the temperature is not normal even when the first time period elapses, the driving member is stopped after the cutting member forcibly cuts a connection of the heating member to the external power source.

5. The image forming apparatus according to claim 1, wherein In the case where the abnormal waveform is detected when the end condition is satisfied, the cutting member forcibly cuts the connection of the heating member to the external power source for a second time period, and the driving member is stopped when the second time period ends.

6. The image forming apparatus according to claim 4, wherein In the case where the abnormal waveform is detected when the end condition is satisfied, the cutting member forcibly cuts the connection of the heating member to the external power source for a second time period, and the cutting member returns from a cut state to an on state and the driving member is stopped when the second time period ends.

7. The image forming apparatus according to claim 1, wherein The second time period is a time period equal to or greater than half a cycle of the alternating current.

8. The image forming apparatus of claim 1, wherein, ​ 9. The image forming apparatus according to claim 7, wherein ​ 10. The image forming apparatus according to claim 3, wherein The determination component acquires a first temperature as a temperature of the heating component at a first timing, acquires a second temperature as a temperature of the heating component at a second timing after the first timing, and determines whether the temperature of the heating component is normal based on the first temperature and the second temperature.

11. The image forming apparatus according to claim 10, wherein The determination component determines whether the temperature of the heating component is normal based on a difference between the first temperature and the second temperature and a temperature threshold.

12. The image forming apparatus according to claim 10, wherein The determination component determines whether the temperature of the heating component is normal based on a temperature gradient between the first temperature and the second temperature and a gradient threshold.

13. The image forming apparatus of claim 3, wherein, The determination component determines whether the temperature is normal based on a temperature threshold and the temperature of the heating component.

14. The image forming apparatus according to claim 1, further comprising a detection component configured to output a pulse waveform that repeatedly rises and falls in response to zero crossings of the alternating current. 15.The image forming apparatus according to claim 14, wherein The waveform detection component detects the abnormal waveform based on the pulse waveform.

16. The image forming apparatus of claim 15, wherein, The waveform detection component detects the abnormal waveform based on a turn-on time or a turn-off time of the pulse waveform.

17. The image forming apparatus according to claim 14, further comprising a power failure detection component configured to detect a power failure of the external power source based on the pulse waveform.

18. The image forming apparatus according to claim 14, further comprising a control component configured to control power supplied to the heating component with respect to the pulse waveform.

19. An image forming apparatus comprising: a first rotating body driven by a driving component and configured to rotate; a second rotating body disposed opposite the first rotating body and configured to cooperate with the first rotating body to form a nip; a heating component configured to heat the second rotating body by being supplied with an alternating current from an external power source; a switching component disposed between the external power source and the heating component and configured to adjust power supplied to the heating component so that a temperature of the heating component approaches a target temperature; a cut-off component connected in series with the switching component between the external power source and the heating component and configured to cut off the alternating current supplied from the external power source to the heating component; and a power failure detection component disposed between the cut-off component and the switching component and configured to detect a power failure of the external power source; a monitoring component configured to monitor the temperature of the heating component; and wherein the switching component stops supply of power to the heating component in a case where an end condition in which heating of the heating component ends is satisfied, the driving component is stopped in a case where the temperature of the heating component is not detected to be abnormal when the end condition is satisfied, and ​ ​ ​ In a case where a temperature abnormality of the heating member is detected when the end condition is satisfied, the power supplied to the heating member from the external power source is cut off by the cut-off member for at least a predetermined period of time, and the drive member is stopped after being delayed with respect to the heating member.

20. The image forming apparatus of claim 19, wherein, The predetermined period of time is half a cycle of the alternating current.

21. The image forming apparatus of claim 19, wherein, In a case where a pulse waveform that repeats rising edges and falling edges in response to zero crossings of the alternating current cannot be detected within a prescribed time, the power failure detection member detects that the external power source has failed.

22. The image forming apparatus according to claim 19, further comprising a light emitting member for repeating turning on and off in response to the alternating current supplied from the external power source, and a light receiving member for generating a pulse waveform by receiving light output from the light emitting member, wherein The power failure detection member detects a power failure of the external power source using the pulse waveform output from the light emitting member.

23. The image forming apparatus of claim 19, wherein, The monitoring member acquires a first temperature that is a temperature of the heating member at a first timing, and acquires a second temperature that is a temperature of the heating member at a second timing after the first timing, and determines whether the temperature of the heating member is abnormal based on the first temperature and the second temperature.

24. The image forming apparatus of claim 23, wherein, The monitoring member determines whether the temperature of the heating member is abnormal based on a difference between the first temperature and the second temperature and a temperature threshold value.

25. The image forming apparatus of claim 23, wherein, The monitoring member determines whether the temperature of the heating member is abnormal based on a temperature gradient between the first temperature and the second temperature and a gradient threshold value.

26. The image forming apparatus of claim 19, wherein, The monitoring member determines whether the temperature is normal based on a temperature threshold value and the temperature of the heating member.

27. The image forming apparatus of claim 20, wherein, The drive time of the drive member is extended so that the drive member is stopped after the power supplied to the heating member from the external power source is cut off by the cut-off member for at least half a cycle of the alternating current.

28. An image forming apparatus comprising: a first rotating body driven by a drive member and for rotating; a second rotating body disposed opposite the first rotating body and for cooperating with the first rotating body to form a nip; a heating member for heating the second rotating body by being supplied with an alternating current from an external power source; a switching member disposed between the external power source and the heating member and for adjusting power supplied to the heating member so that a temperature of the heating member approaches a target temperature; a cut-off member connected in series with the switching member between the external power source and the heating member and for cutting off the alternating current supplied to the heating member from the external power source; and a waveform detection member for detecting an abnormal waveform of the alternating current, a control member for controlling the drive member, the switching member, and the cut-off member, wherein the control member when an end condition for ending heating of the heating member is satisfied, the switching member is controlled to stop supply of electric power to the heating member, when the end condition is satisfied and the abnormal waveform is not detected, the driving member is controlled to stop, and when the end condition is satisfied and the abnormal waveform is detected, the stop timing of the driving member is delayed with respect to the stop timing of the heating member.

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