Image forming apparatus

Abstract

To appropriately protect an image forming apparatus from heat.SOLUTION: The first rotating body is driven to rotate by the driving means. The second rotary member forms a nip portion in cooperation with the first rotary member. The heating means is supplied with an alternating current from an external power source to heat the second rotating body. The switch means is arranged between the external power supply and the heating means, and adjusts power supplied to the heating means. The interrupting unit is connected in series with the switching unit between the external power supply and the heating unit, and interrupts the alternating current supplied from the external power supply to the heating unit. When a termination condition for terminating the heating is satisfied, the switching means stops the supply of power to the heating means. If the abnormal waveform is not detected when the termination condition is satisfied, the driving means is stopped. If the abnormal waveform is detected when the termination condition is satisfied, the driving means stops later than the heating means.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] An electrophotographic fixing device uses AC power supplied from a commercial AC power source to heat a heater, which then fixes toner onto a sheet. When the fixing device continuously heats small sheets, the temperature at the edges of the fixing device rises excessively. Therefore, when the heater temperature exceeds a temperature threshold, the power supply to the heater is cut off to protect the fixing device. However, if the AC waveform becomes abnormal, the triac that supplies current to the heater may remain on even when its gate signal is switched from an on signal to an off signal (commutation failure). In this case, the heater temperature rises more than expected. Patent Document 1 proposes lowering the temperature threshold during periods when an abnormal waveform occurs. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-136175 Summary of the Invention [Problem to be solved by the invention]

[0004] Lowering the temperature threshold, as in Patent Document 1, makes it easier for the heater temperature to exceed the temperature threshold, increasing the frequency of warnings to the user. This can cause excessive anxiety to the user. Furthermore, printing may be performed in a print mode in which the heater's target temperature is high. In this case, it is necessary to reduce the rotation speed of the pressure member to reduce false detection of overheating, which reduces the productivity of the image forming apparatus. Therefore, an object of the present invention is to appropriately protect an image forming apparatus from heat. [Means for solving the problem]

[0005] The present invention is, for example, a first rotating body that is driven to rotate by a driving means; a second rotating body disposed opposite the first rotating body and cooperating with the first rotating body to form a nip portion; a heating means for receiving an AC current from an external power source and heating the second rotating body; a switch means disposed between the external power source and the heating means, for adjusting the power supplied to the heating means so that the temperature of the heating means approaches a target temperature; a cutoff means connected in series with the switch means between the external power source and the heating means, for cutting off the alternating current supplied from the external power source to the heating means; a waveform detection means for detecting an abnormal waveform of the AC current; When a termination condition for terminating heating by the heating means is satisfied, the switch means stops the supply of power to the heating means; If the abnormal waveform is not detected when the termination condition is satisfied, the driving means stops; If the abnormal waveform is detected when the termination condition is satisfied, the driving means stops later than the heating means. [Effects of the Invention]

[0006] According to the present invention, it is possible to appropriately protect an image forming apparatus from heat. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a cross-sectional view illustrating an image forming apparatus; [Figure 2] 1 is a cross-sectional view illustrating a fixing device; [Figure 3] Circuit diagram explaining the heater drive circuit [Figure 4] Circuit diagram explaining the zero-cross detection circuit [Figure 5] A diagram illustrating the waveform of an AC current and the waveform of a zero-cross signal. [Figure 6]A diagram explaining the functions realized by the CPU [Figure 7] Flowchart showing the control method [Figure 8] Circuit diagram illustrating another detection circuit [Figure 9] A diagram illustrating the waveform of an AC current and the waveform of a zero-cross signal. [Figure 10] Flowchart showing the control method [Figure 11] Flowchart showing the control method [Figure 12] Flowchart showing the control method DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention claimed. Although multiple features are described in the embodiments, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0009] First Embodiment 1. Image forming device The image forming apparatus 100 shown in FIG. 1 is an electrophotographic printer. A sheet cassette 116 is a storage container that stores and holds a large number of sheets P. A feed roller 102 is driven to rotate by a motor 118 and feeds the sheet P from the sheet cassette 116 to a conveyance path. Conveyance rollers 103 and 104, which are provided downstream of the feed roller 102 in the conveyance direction of the sheet P, convey the sheet P further downstream. A sheet sensor 120 detects the arrival and passage of the sheet P. The image forming apparatus 100 uses the timing when the leading edge of the sheet P is detected as the start timing for the electrophotographic process.

[0010] The process cartridge 109 has 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 that is driven to rotate by a motor 118. The charging roller 106 uniformly charges the surface of the photosensitive drum 105. The scanning optical device 110 irradiates the surface of the photosensitive drum 105 with light 111 corresponding to 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. The transfer roller 112 transfers the toner image from the photosensitive drum 105 to a sheet P.

[0011] A fixing device 190 is disposed downstream of the transfer roller 112. The fixing device 190 has a heating device 113 and a pressure device 114. The heating device 113 heats the sheet P and the toner image. The pressure device 114 pressurizes the toner image against the sheet P. This fixes the toner image onto the sheet P. A discharge roller 115 is disposed downstream of the fixing device 190. The discharge roller 115 discharges the sheet P to the outside of the image forming apparatus 100.

[0012] The fan 117 is a cooling device for lowering the temperature inside the image forming apparatus 100. Heat generated by the heating device 113 causes the temperature inside the image forming apparatus 100 to rise. If the internal temperature becomes too high, the toner in the toner container 108 will stick. Operating the fan 117 prevents the toner from sticking. Furthermore, heat generation from electrical components such as the power supply is also suppressed. The motor 118 is a drive source that provides driving force to multiple rotating bodies (such as the developing roller 197) including the pressure device 114. In other words, the pressure device 114 and the process cartridge 109 are driven by the same drive source. Although only one motor 118 is shown here, multiple motors 118 may be used.

[0013] The control board 130 includes a CPU 131 and a heater drive circuit 132. 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.

[0014] 2. Heating and pressure equipment 2 shows the structure of the heating device 113 and the structure of the pressure device 114. The sheet P is conveyed along the conveying direction F. The heating device 113 has a heating film 202 and a heater 200. The heating film 202 is a cylindrical rotating body. The heater 200 is a heating element that contacts the inner surface of the heating film 202. The material of the base layer of the heating film 202 is a heat-resistant resin such as polyimide, or a metal such as stainless steel.

[0015] The pressure device 114 has a pressure roller 208. The pressure roller 208 is disposed opposite the heating film 202. The pressure roller 208 forms a fixing nip N in cooperation with the heating film 202 and the heater 200.

[0016] The heater 200 is held by a heater support member 201 made of heat-resistant resin. The heater support member 201 also has a guide function for guiding the rotation of the heating film 202.

[0017] The metal stay 204 is a metal stay for applying pressure from a spring (not shown) to the heater support member 201. The cross section of the metal stay 204 is U-shaped. The metal stay 204 is a member that extends parallel to the axial direction of the core metal 209. The metal stay 204 increases the bending rigidity of the heating device 113 and positions the heater support member 201.

[0018] The heater 200 has a heater substrate 203, a heating element 206, and a surface protection layer 205. The heater substrate 203 is, for example, a ceramic substrate. The heating element 206 is a resistive heating element arranged on the heater substrate 203 along the longitudinal direction of the substrate. The surface protection layer 205 is an insulating member (for example, glass) that covers the heating element 206.

[0019] A thermistor 211 and a thermostat 212 are arranged on the upper surface of the heater 200. The thermistor 211 is a temperature sensor (temperature detection element) that detects a temperature correlated with the temperature of the heater 200. The thermostat 212 is a protection element that cuts off the power supply line to the heater 200 if the temperature of the heater 200 becomes abnormally high. The thermostat 212 may have a thermoswitch or a thermal fuse. The thermistor 211 and the thermostat 212 may be pressed against the heater 200 by a leaf spring (not shown) or the like.

[0020] The pressure roller 208 has 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 a 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. As the pressure roller 208 rotates, the heating film 202 rotates in conjunction with the pressure roller 208 (driven state). When power is not transmitted from the motor 118, the pressure roller 208 stops (stopped state). The sheet P carrying an unfixed toner image is conveyed while being sandwiched between the heating film 202 and the pressure roller 208 at the fixing nip N. As a result, the toner image is fixed on the sheet P.

[0021] 3. Heater drive circuit FIG. 3 shows the heater driving circuit 132. The external power supply 301 is an AC power supply connected to the image forming apparatus 100. The external power supply 301 may be, for example, a commercial AC power supply. The current supply to the heater 200 is controlled by turning on / off a triac 316. The triac 316 is a semiconductor switch disposed between the neutral side of the external power supply 301 and contacts C1 and C2 of the heater 200. The contact C1 is electrically connected to one end of the heating element 206. The 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 the contacts C1 and C2 of the heater 200 via a thermostat 212. In this manner, the heater 200 is driven by AC.

[0022] The detection circuit 308 detects the zero crossing of the AC voltage supplied from the external power supply 301. The detection circuit 308 generates a zero crossing signal ZEROX indicating that the AC voltage is equal to or lower than a certain threshold, and inputs the zero crossing signal ZEROX to the CPU 131.

[0023] One main terminal of the triac 316 is connected to the neutral side of the external power supply 301 and one end of a resistor R3. The other main terminal of the triac 316 is connected to a contact C1 and one end of a resistor R7. The gate terminal of the triac 316 is connected to the other end of the resistor R3 and one end of a phototriac (light-receiving element) in the phototriac coupler 315. The other end of the phototriac in the phototriac coupler 315 is connected to the other end of the resistor R7. Here, the resistors R3 and R7 are resistors for driving the triac 316. The phototriac coupler 315 is a semiconductor device for ensuring a creepage distance between the primary circuit (AC side circuit) and the secondary circuit (DC side circuit). The resistor R3 may be omitted. The CPU 131 causes the light-emitting diode (light-emitting element) of the phototriac coupler 315 to emit light, turning the phototriac coupler 315 on and further turning on the triac 316. The light-emitting diode of the phototriac coupler 315 repeatedly turns on and off when supplied with AC. Resistor R8 is connected between the power supply voltage Vcc and the anode of the light-emitting diode of the phototriac coupler 315. Resistor R8 is a limiting resistor that limits the current flowing through this light-emitting diode. The collector of transistor Tr1 is connected to the cathode of the light-emitting diode of the phototriac coupler 315. The emitter of transistor Tr1 is grounded. The base of transistor Tr1 is connected to the CPU 131. The CPU 131 outputs a control signal FUSER to the base to turn the phototriac coupler 315 on and off via transistor Tr1.

[0024] 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 by resistor R1 and the internal resistance of the thermistor 211, which changes depending on temperature. The detection signal TH is input to the CPU 131. The CPU 131 controls the triac 316 so that the temperature detected by the thermistor 211, indicated by the detection signal TH, approaches the set temperature (target temperature) of the heater 200. Proportional-integral (PI) control may be employed for this control. The CPU 131 calculates the power to be supplied to the heater 200 and calculates a control level for the phase angle (phase control) or wave number (wave number control) corresponding to this power. The CPU 131 controls the triac 316 using the control level, with the edge of the zero-cross signal ZEROX as a time reference.

[0025] The relay 302 is an electromagnetic relay that is disposed between the external power supply 301 and the triac 316 and is connected in series to the triac 316. The CPU 131 controls the state (on / off) of the relay 302 by supplying a relay drive signal RELAY to the relay 302. When the relay 302 switches to the on state, the external power supply 301 is supplied to the heater 200.

[0026] If some malfunction occurs, such as a short circuit in the triac 316, the heating device 113 may enter a heat generation state exceeding the steady state assumed 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 reaches or exceeds a predetermined threshold, the CPU 131 switches the relay 302 from a conductive state to a non-conductive state. This cuts off the power supply to the heater 200. The operating temperature of the thermostat 212 is higher than the temperature threshold of the relay 302.

[0027] 4. Detection of abnormal waveforms As shown in FIG. 4, the hot side potential of the external power supply 301 is connected to the anode of the light-emitting diode 401 of the photocoupler 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. In other words, the light-emitting diode 401 is connected in parallel to the external power supply 301. The photocoupler 404 is a semiconductor device for ensuring a creepage distance. The collector of the phototransistor 402 of the photocoupler 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 reducing noise. The output signal (zero-cross signal ZEROX) of the photocoupler 404 is input to the CPU 131 via this filter. In a low-noise environment, the capacitor C43 and the resistor R44 may be omitted.

[0028] 4, the hot side of the external power supply 301 is connected to the anode of the light-emitting diode 401. The neutral side of the external power supply 301 is connected to the cathode of the light-emitting diode 401. However, this is just one example. The hot side may be connected to the cathode of the light-emitting diode 401, and the neutral side may be connected to the anode.

[0029] 5A and 5B show the relationship between the input waveform from the external power supply 301 and the waveform (pulse waveform) of the zero-cross signal ZEROX. The zero-cross signal ZEROX is a pulse signal that repeatedly rises and falls. As shown in FIG. 5A, the AC waveform supplied by the external power supply 301 is a sine wave (normal). 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 photocoupler 404 turns on. As a result, the zero-cross signal ZEROX changes from high to low (falling). The threshold voltage Vz is determined by the resistor R41. There are also cases where the hot-side potential is lower than the neutral-side potential, or the hot-side potential is lower than the threshold voltage Vz. In these cases, the photocoupler 404 turns off. As a result, the zero-cross signal ZEROX changes from low to high (rising). That is, the level of the zero-cross signal ZEROX changes depending on whether the hot-side potential is higher than the neutral-side potential by at least the threshold voltage Vz. Therefore, a pulse waveform having an on-time Tsin1 that is wider than the on-time determined from the two true zero-crossing points is output to the CPU 131. The on-time may also be called an on-duty or an on-duty width.

[0030] As shown in FIG. 5(B), the AC waveform supplied from the external power supply 301 may be a square wave. A square wave has a large voltage change rate at the zero-crossing timing, which can cause the triac 316 to malfunction (commutation phenomenon). Therefore, a square wave is a type of abnormal waveform. The on-time of a square wave is the same as the on-time calculated from two true zero-crossing points. In other words, when a square wave is input, the on-time of the zero-crossing signal ZEROX is Tsqure1, which is equal to the on-time of the square wave. Comparing FIG. 5(A) and FIG. 5(B) reveals that Tsqure1 of the square wave (abnormal waveform) is shorter than Tsin1 of the sine wave (normal waveform).

[0031] The CPU 131 can detect an abnormal waveform by monitoring the on-time of this zero-cross signal ZEROX. For example, the CPU 131 determines whether the on-time Ton of the zero-cross signal ZEROX is less than a threshold value (e.g., Tsin1). If Ton is less than Tsin1, the CPU 131 determines that the input AC waveform is an abnormal waveform. For a square wave, the on-time Tsqure1 of the zero-cross signal ZEROX is less than Tsin1. Therefore, the CPU 131 can detect a square wave. On the other hand, if Ton is not less than Tsin1, the CPU 131 determines that the AC waveform is normal.

[0032] 5.CPU Functions FIG. 6 shows multiple functions realized by the CPU 131 executing a control program. Some or all of the multiple functions may be realized by hardware circuits such as an application-specific integrated circuit (ASIC) or a field-programmable gate array. The memory 601 is a storage device that may include a random-access memory (RAM), a read-only memory (ROM), a solid-state drive (SSD), a hard disk drive (HDD), etc. The ROM area of ​​the memory 601 stores the control program. The timer 602 is a real-time clock or a counter circuit, etc. The heater control unit 603 controls the triac 316 so that the temperature of the heater 200 detected by the thermistor 211 approaches the target temperature. The motor control unit 604 generates a drive signal DRV and controls the rotation and stopping of the motor 118. The motor control unit 604 can also control the rotation speed of the motor 118. That is, the motor 118 can control the rotation speed of the pressure roller 208. The relay control unit 605 generates a control signal RELAY for controlling the on (conducting state) / off (disconnecting state) of the relay 302 and supplies the control signal RELAY to the relay 302 .

[0033] The temperature monitoring unit 611 converts the detection signal TH output from the thermistor 211 into a temperature, compares the detected temperature with a threshold temperature, and outputs the comparison result to the determination unit 620. The waveform detection unit 612 detects an abnormal AC waveform based on the zero-cross signal ZEROX. The power outage detection unit 613 is optional and detects a power outage of the external power supply 301 based on the zero-cross signal ZEROX. For example, the power outage detection unit 613 determines that a power outage has occurred when it is unable to detect the zero-cross signal ZEROX for a specified period of time. Note that the image forming apparatus 100 is assumed to have a backup power source (e.g., a battery) that can supply power for a predetermined period of time even if the external power supply 301 fails. The time monitoring unit 614 is optional and monitors the duration of the abnormal waveform and the forced shutoff time of the relay 302.

[0034] The determination unit 620 determines whether the heating end condition for the heater 200 is satisfied based on print job information (e.g., the number of prints). Furthermore, the determination unit 620 determines whether to stop the power supply to the heater 200 based on the comparison result of the temperature monitoring unit 611 (presence or absence of an abnormal temperature rise). The determination unit 620 determines whether to stop the motor 118 later than the heater 200 based on the detection result of the waveform detection unit 612. For example, the determination unit 620 outputs a stop command to the heater control unit 603 at a first timing when the heating end condition is satisfied. Based on the stop command, the heater control unit 603 switches the triac 316 from on to off. The determination unit 620 outputs a stop command to the motor control unit 604 at a second timing. The motor control unit 604 stops the motor 118 in accordance with the stop command. The second timing is a predetermined time later than the first timing. This predetermined time may be called a rotation extension time or a stop postponement time.

[0035] 6. Flowchart 7 shows a control method executed by the CPU 131 in accordance with a control program. When a print job is input, the CPU 131 executes the following process: The target temperature of the heater 200 and the conveying speed are determined according to the basis weight of the sheet P specified by the print job.

[0036] In S701, the CPU 131 (heater control unit 603) starts heating the heater 200. The heater control unit 603 increases the temperature of the heater 200 to a target temperature and maintains the temperature of the heater 200 at the target temperature.

[0037] In S702, the CPU 131 (motor control unit 604) starts the rotation of the pressure roller 208 by the motor 118. Note that S701 and S702 may be executed simultaneously, or S702 may be executed before S701.

[0038] In S703, the CPU 131 (determination unit 620) determines whether a heating end condition is satisfied. The heating end condition may be, for example, that printing on the number of sheets P specified in the print job information has been completed. The heating end condition may also be that the temperature of the heater 200 has reached a target temperature. When the heating end condition is satisfied, the CPU 131 advances the process from S703 to S704.

[0039] In S704, the CPU 131 (heater control unit 603) changes the heater drive signal FUSER to turn off the triac 316, thereby stopping the heating of the heater 200. The motor control unit 604 causes the motor 118 to continue rotating the pressure roller 208.

[0040] However, stopping the pressure roller 208 along with the heater 200 can cause problems. For example, if the AC waveform is a square wave, the triac 316 remains on, causing the heater 200 to continue heating. If the motor 118 stops at this time, a sudden temperature difference occurs between the fixing nip N and other areas. This can cause failures in the heating device 113 and the pressure device 114. Therefore, it is necessary to detect abnormal waveforms.

[0041] During the period in which the pressure roller 208 continues to be driven (extended rotation period), the driving speed (rotation speed) of the pressure roller 208 may be any speed that can prevent breakdowns. The rotation speed during the extended rotation period may be different from the rotation speed during the heat treatment.

[0042] In S705, the CPU 131 (waveform detection unit 612) acquires the detection result of the AC waveform based on the zero-cross signal ZEROX. In the waveform detection, for example, the waveform detection unit 612 measures the time ton from the moment when the AC voltage becomes equal to or less than the threshold voltage Vz to the moment when the AC voltage exceeds the threshold voltage Vz. In this way, the waveform detection may be the measurement of the time ton. The waveform detection does not necessarily have to be performed in S705, and may be performed at other times. For example, it may be performed at regular measurement intervals in parallel with the processing shown in FIG. 7. The waveform detection result may be stored in a memory provided inside or outside the CPU 131 and read out as needed.

[0043] In S706, the CPU 131 (determination unit 620) determines whether the AC waveform is normal. If ton is equal to or greater than a threshold value (e.g., Tsin1), the AC waveform is normal. If ton is less than the threshold value, the AC waveform is abnormal. If the detected waveform is normal, the CPU 131 advances the process from S706 to S707. If the detected waveform is abnormal, the CPU 131 waits for the detected waveform to return to a normal waveform.

[0044] In S707, the CPU 131 (motor control unit 604) stops the rotation of the pressure roller 208 by the motor 118.

[0045] According to the first embodiment, when an abnormality occurs in the AC waveform, the pressure device 114 stops after issuing a stop command to the heating device 113 (rotation continuation control, stop delay control). In other words, the CPU 131 delays the stop timing of the motor 118 from the stop timing of the heater 200. This makes it less likely that the pressure device 114 and the heating device 113 will break down, even if the triac 316 is unintentionally turned on due to an abnormal waveform. This is because the pressure device 114 continues to rotate, and the pressure device 114 stops after the temperature difference between the fixing nip portion N and other parts becomes small.

[0046] The motor 118 may be a common drive source for the pressure device 114 and the process cartridge 109. In this case, the CPU 131 may accelerate the stopping of the pressure device 114 in consideration of the lifespan of the photosensitive drum 105 and the like. In other words, the rotation duration of the motor 118 may be shortened. For example, the rotation duration may be shortened as the period of use of the photosensitive drum 105 increases.

[0047] Second Embodiment The second embodiment is a partial modification of the detection circuit 308 of the first embodiment. Specifically, a transistor is added between the photocoupler 404 and the CPU 131 to improve the responsiveness of the zero-cross signal ZEROX. Furthermore, a constant voltage element (e.g., a Zener diode) may be added between the hot side of the external power supply 301 and the photocoupler 404, or between the neutral side of the external power supply 301 and the photocoupler 404. Descriptions of matters common to the first embodiment and the second embodiment will be omitted.

[0048] 1. Abnormal waveform detection circuit FIG. 8 shows a detection circuit 308 of a second embodiment. A Zener diode ZD is added between a current-limiting resistor R41 and the anode of the light-emitting diode 401 of the photocoupler 404 on the hot side of the external power supply 301. This helps adjust the threshold voltage Vz for detecting abnormal waveforms. Both the resistor R41 and the Zener diode ZD may be located between the hot side of the external power supply 301 and the photocoupler 404. Both the resistor R41 and the Zener diode ZD may be located between the neutral side of the external power supply 301 and the photocoupler 404. The positions of the resistor R41 and the Zener diode ZD, which are connected in series adjacent to each other, may be reversed. Furthermore, the resistor R41 may be located between the hot side of the external power supply 301 and the photocoupler 404, and the Zener diode ZD may be located between the neutral side of the external power supply 301 and the photocoupler 404. Alternatively, a Zener diode ZD may be provided between the hot side of the external power supply 301 and the photocoupler 404, and a resistor R41 may be provided between the neutral side of the external power supply 301 and the photocoupler 404.

[0049] A resistor R71 is connected between the emitter of the phototransistor 402 of the photocoupler 404 and ground potential. The resistor R71 is a current limiting resistor that limits the current flowing through the phototransistor 402. A filter is also connected to the phototransistor 402. This filter is a noise reduction filter formed by a resistor R72 and a capacitor C75. One end of the resistor R72 is connected to the emitter of the phototransistor 402. The other end of the resistor R72 is connected to the base of the transistor Tr3. One end of the capacitor C75 is connected to one end of the resistor R72. The other end of the capacitor C75 is grounded.

[0050] Resistor R74 is connected between the base and emitter of transistor Tr3. Resistor R74 is provided to prevent malfunction of transistor Tr3. Resistor R76 is a current limiting resistor for transistor Tr3. Resistor R76 is connected between the collector of transistor Tr3 and power supply voltage Vcc. The zero-cross signal ZEROX output from the collector of transistor Tr3 is input to the CPU 131 via a filter. This filter, formed by capacitor C77 and resistor R78, reduces noise.

[0051] 8, the anode of the light-emitting diode 401 of the photocoupler 404 is connected to the hot side of the external power supply 301, and the cathode is connected to the neutral side. This is just one example. The cathode of the light-emitting diode 401 may be connected to the hot side, and the anode may be connected to the neutral side.

[0052] In low noise environments, capacitor C75 and resistor R72 may be omitted, as may capacitor C77 and resistor R78.

[0053] 9A shows the zero-cross signal ZEROX when the AC waveform is normal (sine wave). Note that the waveform of the zero-cross signal ZEROX in the second embodiment is inverted compared to the waveform of the zero-cross signal ZEROX in the first embodiment. This is due to the addition of transistor Tr3.

[0054] As described in the first embodiment, when the AC voltage is higher than the threshold voltage Vz, the photocoupler 404 is turned on, the transistor Tr3 is turned on, and the zero-cross signal ZEROX is at a low level. When the AC voltage is lower than the threshold voltage Vz, the photocoupler 404 is turned off, the transistor Tr3 is also turned off, and the zero-cross signal ZEROX is at a high level.

[0055] In this way, the level of the zero-cross signal ZEROX changes depending on whether the hot-side potential is higher than the neutral-side potential by the threshold voltage Vz or more. When the AC waveform is a sine wave, the zero-cross signal ZEROX has an off-time that is wider than the off-time obtained from two true zero-cross points. In this case, the off-time of the zero-cross signal ZEROX is Tsin2. The off-time may also be called the off-duty or the off-duty width.

[0056] As shown in FIG. 9(B), the waveform of the AC supplied from the external power supply 301 may be a square wave. In this case, a zero-crossing signal ZEROX (pulse waveform) having an off-time Tsqure2 equal to the interval between two true zero-crossing points is output to the CPU 131. The CPU 131 (waveform detection unit 612) measures the off-time toff of the zero-crossing signal ZEROX. If the off-time toff is less than Tsin2, the CPU 131 (determination unit 620) determines that the AC waveform is abnormal. If the off-time toff is not less than Tsin2, the CPU 131 (determination unit 620) determines that the AC waveform is normal.

[0057] As shown in Figure 8, the output signal (zero-cross signal ZEROX) of the photocoupler 404 is output to the CPU 131 via transistor Tr3. Therefore, when the potential generated by the output signal of the photocoupler 404 and resistor R71 exceeds the base-emitter voltage of transistor Tr3, the logic of the zero-cross signal ZEROX changes. Therefore, the second embodiment has better responsiveness than the first embodiment. In other words, since the relationship shown in the following equation Eq1 holds, the detection accuracy of normal waveforms and square waves (abnormal waveforms) is improved. (Tsin2 - Tsqure2) > (Tsin1 - Tsqure1) ··· Eq1 8, the Zener diode ZD effectively increases the threshold voltage Vz of the photocoupler 404. In other words, the off-time Tsin2 when a sine wave is input increases relatively, which further improves the accuracy of detecting a square wave.

[0058] In the second embodiment, waveform detection does not necessarily have to be performed in S705, and may be performed at other timings. For example, it may be performed at regular measurement intervals in parallel with the processing shown in Fig. 7. The waveform detection results may be stored in a memory provided inside or outside CPU 131 and read out as needed.

[0059] Third Embodiment The third embodiment is a modification of the first and second embodiments. Specifically, if an abnormal waveform is detected while the heating end condition is satisfied, the rotation end condition of the pressure roller 208 is determined. For example, even if an abnormal waveform is generated, the pressure roller 208 may be stopped if the temperature of the heater 200 is normal. Alternatively, the pressure roller 208 may be stopped if the temperature of the heater 200 returns to normal within a predetermined time. Note that if the abnormal waveform and abnormal temperature continue even after the predetermined time has elapsed, the relay 302 may forcibly stop the supply of power to the heater 200. Descriptions of matters common to the first and second embodiments of the third embodiment will be omitted.

[0060] 1. Flowchart Fig. 10 shows a control method of the third embodiment. Here, the processes from S704 to S707 described with reference to Fig. 7 are modified. The CPU 131 advances the process from S704 to S1001.

[0061] In S1001, the CPU 131 (time monitoring unit 614) starts monitoring the elapsed time using the timer 602. Here, the elapsed time refers to the time elapsed from the timing when the supply of power to the heater 200 is stopped by turning off the triac 316. Note that the elapsed time may also be the time during which an abnormal waveform continues to be detected after the triac 316 is turned off. Thereafter, the CPU 131 advances the process from S1001 to S705. In S705, the CPU 131 detects the waveform of the AC current. When an abnormal waveform is detected in S706, the CPU 131 advances the process from S706 to S1002.

[0062] In S1002, the CPU 131 (temperature monitoring unit 611) detects the temperature of the heater 200 using the thermistor 211. In S1003, the CPU 131 (determination unit 620) determines whether the detected temperature of the heater 200 is normal. If the temperature of the heater 200 is normal, the CPU 131 advances the process from S1003 to S707 and stops the pressure roller 208. Because the supply of power to the heater 200 has been stopped, the heater 200 naturally dissipates heat, and the temperature of the heater 200 gradually decreases. On the other hand, if the temperature of the heater 200 is not normal, the CPU 131 advances the process from S1003 to S1004.

[0063] In S1004, the CPU 131 (determination unit 620) determines whether a predetermined time has elapsed based on the elapsed time acquired by the time monitoring unit 614. If the predetermined time has not yet elapsed, the CPU 131 advances the process from S1004 to S705. If the predetermined time has elapsed, the CPU 131 advances the process from S1004 to S1005.

[0064] In S1005, the CPU 131 (relay control unit 605) turns off the relay 302 (non-conductive state). This forcibly stops the supply of power to the heater 200. Furthermore, the CPU 131 stops the image forming apparatus 100. That is, the motor 118 also stops.

[0065] There are several methods for determining whether a temperature is normal. The temperature monitoring unit 611 uses the thermistor 211 to acquire a temperature T1 at a first timing and acquire a temperature T2 at a second timing. The second timing is a predetermined time t1 after the first timing. The temperature monitoring unit 611 then calculates a difference ΔT between the temperatures T1 and T2 (ΔT=T1-T2). If the temperature T2 is higher than the temperature T1, ΔT is a negative value. The determination unit 620 determines that the temperature of the heater 200 is abnormal if the difference ΔT is equal to or less than a threshold value Tth1. The threshold value Tth1 is a positive value equal to or greater than 0. The determination unit 620 determines that the temperature of the heater 200 is normal if the difference ΔT exceeds the threshold value Tth1. Note that when ΔT=T2-T1 is defined, the magnitude relationship between the difference ΔT and the threshold value Tth1 is logically inverted.

[0066] Alternatively, the temperature monitoring unit 611 may 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 temperature gradient G is equal to or less than the gradient threshold Gth. If the temperature gradient G is equal to or less 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 T2 - T1, the magnitude relationship between the temperature gradient G and the gradient threshold Gth is logically inverted.

[0067] Alternatively, if the temperature T2 is equal to or less than the temperature threshold value Tth2, the temperature of the heater 200 may be determined to be normal. If the temperature T2 exceeds the temperature threshold value Tth2, the temperature of the heater 200 may be determined to be abnormal. The threshold value Tth2 is a positive value.

[0068] In the third embodiment, similarly to the first and second embodiments, the rotation speed of the pressure roller 208 during the rotation continuation period may be a speed that can prevent breakdowns in the heating device 113. The rotation speed applied during this rotation continuation period may be different from the rotation speed during the heat treatment.

[0069] In the first and second embodiments, if the temperature of the heater 200 becomes abnormal during the continuous rotation period, the thermostat 212 eventually changes from a conductive state to a non-conductive state, and the image forming apparatus 100 is stopped. Alternatively, the relay 302 changes from a conductive state to a non-conductive state before the thermostat 212 changes from a conductive state to a non-conductive state. In the first and second embodiments, the pressure device 114 continues to be driven while the AC waveform is abnormal. In other words, the image forming apparatus 100 cannot perform a printing operation.

[0070] The third embodiment is useful in cases where the triac 316 is not fixed to ON even if an abnormal waveform is detected. That is, in the third embodiment, even if an abnormal waveform is detected, the pressure roller 208 is immediately stopped as long as the temperature of the heater 200 is normal. In other words, the image forming apparatus 100 can execute the next print job, and the productivity of the image forming apparatus 100 is less likely to decrease.

[0071] In the third embodiment, waveform detection does not necessarily have to be performed in S705, and may be performed at other timings. For example, it may be performed at regular measurement intervals in parallel with the processing shown in Fig. 7. The waveform detection results may be stored in a memory provided inside or outside the CPU 131 and read out as needed.

[0072] <Fourth embodiment> The fourth embodiment is a modification of the first or third embodiment. When an abnormal waveform is detected, the relay 302 is maintained in a cut-off state for at least a predetermined period of time. The pressure roller 208 then stops. In the fourth embodiment, a description of matters common to the first, second, or third embodiment will be omitted.

[0073] 1. Flowchart 11 shows a control method of the fourth embodiment. When an abnormal waveform is detected in S706, the pressure roller 208 continues to rotate. In other words, stopping the pressure roller 208 is postponed, and the rotation duration (drive time) is extended. Furthermore, the CPU 131 advances the process from S706 to S1101.

[0074] In S1001, the CPU 131 (relay control unit 605) turns off the relay 302 (non-conducting state) for at least a predetermined time. This stops the supply of power to the heater 200. For example, the predetermined time may be equal to or longer than a half cycle of the AC current. By stopping the supply of power to the heater 200 for at least a half cycle, the square wave is cut beyond the zero crossing point, and the triac 316 switches from on to off more reliably. Therefore, even if the triac 316 malfunctions due to an abnormal waveform such as a square wave, the image forming apparatus 100 is safely shut down.

[0075] 3, relay 302 is disposed between external power supply 301 and detection circuit 308, so when relay 302 is turned off, detection circuit 308 is unable to detect an abnormal waveform. However, because the off period of relay 302 is equal to or longer than half the cycle of the AC current, the period during which detection circuit 308 is unable to perform waveform detection is short.

[0076] In the fourth embodiment, the pressure roller 208 stops after the relay 302 is turned off for at least a predetermined period, but this is merely an example. That is, the first period, which is the rotation continuation period (drive time) of the pressure roller 208, only needs to be longer than the second period during which the relay 302 is maintained off. In this case, the time monitoring unit 614 monitors both the first period and the second period using the timer 602. The start points of the first period and the second period are, for example, the timing when the heater 200 stops heating in S704 or the timing when an abnormal waveform is detected in S706. The start points may also be the timing when an abnormal temperature is detected. As described in the first embodiment and other examples, the rotation speed of the pressure roller 208 during the first period may be any speed that can prevent failure of the heating film 202. Furthermore, the timing when the relay 302 returns from a non-conductive state (off) to a conductive state (on) may be after the pressure roller 208 has stopped.

[0077] In the fourth embodiment, a malfunction of the triac 316 caused by an abnormal waveform can be resolved in a shorter time than in the first to third embodiments. This also reduces the time that the pressure roller 208 continues to rotate. This can extend the life of the fixing device and reduce the power consumed by the image forming apparatus 100.

[0078] In the fourth embodiment, waveform detection does not necessarily have to be performed in S705, and may be performed at other timings. For example, it may be performed at regular measurement intervals in parallel with the processing shown in Fig. 7. The waveform detection results may be stored in a memory provided inside or outside the CPU 131 and read out as needed.

[0079] Fifth Embodiment The fifth embodiment is a modification of the first embodiment. In the first to fourth embodiments, at least an abnormal AC waveform is detected, but this is merely an example. For example, if the temperature of the heater 200 is abnormal during the delay period of the stop of the pressure roller 208, the relay 302 may be turned off for a predetermined period as described in the fourth embodiment. The zero-cross signal ZEROX detected by the detection circuit 308 may be used by the power outage detection unit 613 to detect a power outage of the external power source 301.

[0080] 1. Power outage detection The memory 601 may have a large-capacity, non-volatile storage device (e.g., HDD, SSD). The RAM area of ​​the memory 601 can temporarily store print image data transmitted from a host computer or the like. When the memory 601 stores the print image data in the HDD of the memory 601, the external power supply 301 may experience a power outage, or the power cable connecting the external power supply 301 and the image forming apparatus 100 may be unplugged from the outlet. If this causes a power outage, the power that can be supplied from the backup power supply provided inside the image forming apparatus 100 gradually decreases. As a result, data corruption or data inconsistency occurs in the HDD, and the CPU 131 becomes unable to read data from the HDD.

[0081] Therefore, the power outage detection unit 613 detects power outages and unintended power interruptions based on the zero-cross signal ZEROX. Between the time a power outage occurs and the time the image forming apparatus 100 completely shuts down, the CPU 131 saves print image data from RAM to the HDD. This protects the data. For example, if the input of the zero-cross signal ZEROX stops for a predetermined period of time or longer, the power outage detection unit 613 determines that the external power supply 301 has experienced a power outage. The power outage detection unit 613 may use the timer 602 to measure the elapsed time tp from the edge of the zero-cross signal ZEROX and determine whether the elapsed time tp exceeds a threshold time tth. If the elapsed time tp exceeds the threshold time tth, the power outage detection unit 613 determines that a power outage has occurred. If the elapsed time tp does not exceed the threshold time tth, the power outage detection unit 613 determines that a power outage has not occurred.

[0082] Detection circuit 308 constantly outputs zero-cross signal ZEROX while AC is being supplied from external power supply 301. Therefore, power failure detection unit 613 constantly consumes power. Because detection circuit 308 is connected between relay 302 and triac 316, when relay 302 is turned off, the power consumption of power failure detection unit 613 is reduced.

[0083] 2. Flowchart 12 shows a control method of the fifth embodiment. S705 and S706 described in FIG. 7 are replaced by S1201 to S1204. Therefore, the following description will mainly focus on S1201 to S1204. When heating by the heater 200 is stopped in S704, the CPU 131 advances the process from S704 to S1201.

[0084] In S1201, the CPU 131 (temperature monitoring unit 611) detects the temperature of the heater 200 using the thermistor 211. In S1202, the CPU 131 (determination unit 620) determines whether the temperature of the heater 200 is normal. This determination of normality is the same as that in S1003. If the temperature of the heater 200 is normal, the CPU 131 advances the process from S1202 to S707. This stops the pressure roller 208. On the other hand, if the temperature of the heater 200 is not normal even though the triac 316 has been turned off, the CPU 131 advances the process from S1202 to S1203.

[0085] In S1203, the CPU 131 (relay control unit 605) turns off the relay 302 for at least a predetermined period of time. This forcibly stops the supply of power to the heater 200. S1203 is the same process as S1101, and the predetermined period may be equal to or longer than a half cycle of the AC. For example, the CPU 131 (time monitoring unit 614) may monitor the predetermined period using the timer 602.

[0086] In S1204, the CPU 131 (relay control unit 605) returns the relay 302 from OFF (non-conductive state) to ON (conductive state). After that, the CPU 131 advances the process from S1204 to S707. As a result, the motor 118 stops.

[0087] 3, since relay 302 is disposed between external power supply 301 and detection circuit 308, when relay 302 is turned off, detection circuit 308 is unable to detect zero-cross signal ZEROX. However, because the off period of relay 302 is at least half a cycle of AC, the period during which detection circuit 308 is unable to detect zero-cross signal ZEROX is short. In other words, the period during which power outage detection unit 613 is unable to detect power outages is also short.

[0088] In the fifth embodiment, the pressure roller 208 stops after the relay 302 is turned off for at least a predetermined period, but this is merely an example. That is, the first period, during which the pressure roller 208 continues to rotate, may be longer than the second period during which the relay 302 is maintained off. In this case, the time monitoring unit 614 monitors both the first period and the second period using the timer 602. The start points of the first period and the second period are, for example, the timing when the heater 200 stops heating in S704 or the timing when an abnormal temperature is detected in S1202. As described in the first embodiment and the like, the rotation speed of the pressure roller 208 during the first period may be any rotation speed that can prevent breakdown of the heating film 202. Furthermore, the timing when the relay 302 returns from a non-conductive state (off) to a conductive state (on) may be after the pressure roller 208 has stopped.

[0089] In the fifth embodiment, if the temperature of the heater 200 becomes abnormal due to an abnormal AC waveform or the like, the relay 302 cuts off the power supply to the heater 200. In other words, the CPU 131 can infer the occurrence of an abnormal AC waveform that causes an abnormal temperature rise without directly detecting the AC waveform. Upon detecting an abnormal temperature rise, the CPU 131 turns off the relay 302 for a predetermined period, thereby preventing breakdowns in the heating device 113 and the pressure device 114. The period during which the relay 302 forcibly cuts off the power supply is at least a half cycle of the AC. Therefore, the period during which the power outage detection unit 613 cannot detect a power outage is shortened. Furthermore, the time during which the pressure roller 208 continues to rotate can be reduced. This can extend the life of the fixing device 190 and reduce the power consumed by the image forming apparatus 100.

[0090] In the fifth embodiment, waveform detection does not necessarily have to be performed in S705, but may be performed at other timings. For example, it may be performed at regular measurement intervals in parallel with the processing shown in Fig. 7. The waveform detection results may be stored in a memory provided inside or outside the CPU 131 and read out as needed.

[0091] <Technical concepts derived from the embodiments> (Item 1) a first rotating body that is driven to rotate by a driving means; a second rotating body disposed opposite the first rotating body and cooperating with the first rotating body to form a nip portion; a heating means for receiving an AC current from an external power source and heating the second rotating body; a switch means disposed between the external power source and the heating means, for adjusting the power supplied to the heating means so that the temperature of the heating means approaches a target temperature; a cutoff means connected in series with the switch means between the external power source and the heating means, for cutting off the alternating current supplied from the external power source to the heating means; a waveform detection means for detecting an abnormal waveform of the AC current; When a termination condition for terminating heating by the heating means is satisfied, the switch means stops the supply of power to the heating means; If the abnormal waveform is not detected when the termination condition is satisfied, the driving means stops; If the abnormal waveform is detected when the termination condition is satisfied, the driving means is stopped later than the heating means.

[0092] The motor 118 is an example of a driving means. The pressure roller 208 is an example of a first rotating body. The heating film 202 is an example of a second rotating body. The heater 200 is an example of a heating means. The triac 316 and the CPU 131 are examples of a switching means. The relay 302 is an example of a cut-off means. The detection circuit 308 and the CPU 131 are examples of a waveform detection means. As described above, according to this embodiment, the motor 118 stops with a delay relative to the heater 200. This reduces the temperature difference between the fixing nip portion N and its surroundings, making it possible to appropriately protect the image forming apparatus 100 from heat. (Item 2) 2. The image forming apparatus according to item 1, wherein the driving means stops when the waveform of the AC voltage returns from the abnormal waveform to a normal waveform.

[0093] When an abnormal waveform occurs, triac 316 may malfunction, causing heater 200 to overheat. While the abnormal waveform continues to occur, motor 118 continues to rotate, which will likely suppress abnormal temperature increases in heater 200 and heating film 202. This makes it possible to appropriately protect image forming apparatus 100 (particularly fixing device 190) from heat. (Item 3) a temperature monitoring means for monitoring the temperature of the heating means; and a determination means for determining whether the temperature is normal or not when the abnormal waveform is detected while the termination condition is satisfied, When the temperature is normal, the driving means stops; 2. The image forming apparatus according to claim 1, wherein the driving means continues to operate when the temperature is not normal.

[0094] Thermistor 211 and CPU 131 are an example of a temperature monitoring unit. CPU 131 is an example of a determination unit. As shown in FIG. 10, when an abnormal waveform and an abnormal temperature occur simultaneously, motor 118 may continue to rotate pressure roller 208. This makes it possible to appropriately protect image forming apparatus 100 from heat. Furthermore, even if an abnormal waveform occurs, motor 118 may immediately stop if the temperature of heater 200 is normal. This reduces the period during which image forming apparatus 100 cannot perform printing, and prevents a decrease in productivity of image forming apparatus 100. (Item 4) 4. The image forming apparatus according to item 3, wherein the driving means is stopped when a first period has elapsed from the time when the termination condition is satisfied, the time when the abnormal waveform is detected, or the time when it is detected that the temperature is not normal.

[0095] As described in relation to FIG. 10 , the start point of the first period (predetermined time) may be any of these three timings. The first period may also be called a rotation continuation period, a rotation extension period, or a stop postponement period. In S1005, the relay 302 may cut off the power supply path, thereby cutting off the power supply to the motor 118. Alternatively, the motor 118 may be supplied with power from a DC power source that is not affected by the conduction / cutoff of the relay 302. In this case, the CPU 131 stops the motor 118 via the motor control unit 604. This also stops the motor 118. (Item 5) 5. The image forming apparatus according to item 4, wherein if the temperature returns to normal before the first period has elapsed, the driving means stops.

[0096] When the temperature returns to normal in this way, motor 118 may be stopped. This further reduces the period during which image forming apparatus 100 cannot perform printing, and the productivity of image forming apparatus 100 is less likely to decrease. (Item 6) 5. The image forming apparatus according to item 4, wherein if the abnormal waveform is still detected and the temperature is not normal even after the first period has elapsed, the cutoff unit forcibly cuts off the connection between the external power source and the heating unit, and then the driving unit stops.

[0097] As described in relation to S1005, the abnormal waveform and abnormal temperature may continue even after the predetermined time has elapsed. In this case, the relay 302 may forcibly cut off the power supply path to the heater 200. Then, the CPU 131 may stop the motor 118. (Item 7) 2. The image forming apparatus according to item 1, wherein if the abnormal waveform is detected when the termination condition is satisfied, the cutoff unit forcibly cuts off the connection between the external power source and the heating unit for a second period, and when the second period ends, the drive unit stops.

[0098] As shown in FIG. 11, if an abnormal waveform is detected when the heating termination condition is satisfied, the relay 302 may stop the supply of power to the heater 200 for a predetermined period of time. (Item 8) 2. The image forming apparatus according to item 1, wherein if the abnormal waveform is detected when the termination condition is satisfied, the cutoff means forcibly cuts off the connection between the external power supply and the heating means for a second period, and when the second period ends, the cutoff means returns from the cutoff state to the conductive state and the driving means stops.

[0099] 11, the relay 302 may be in a disconnected state for a predetermined period of time, and then return to a conductive state. Furthermore, the motor 118 may be stopped after the relay 302 returns to a conductive state. This will achieve both protection of the image forming apparatus 100 from heat and maintaining the productivity of the image forming apparatus 100. (Item 9) Item 9. The image forming apparatus according to item 7 or 8, wherein the second period is a period of at least half a cycle of the AC current.

[0100] The half cycle of the AC may be measured via the sensing circuit 308 or may be the nominal half cycle, which will reduce the time that the image forming device 100 is unable to form an image. (Item 10) Item 4. The image forming apparatus according to item 3, wherein the determination unit acquires a first temperature, which is the temperature of the heating unit, at a first timing, and acquires a second temperature, which is the temperature of the heating unit, at a second timing that is later than the first timing, and determines whether the temperature of the heating unit is normal based on the first temperature and the second temperature.

[0101] As explained in the third embodiment, the normality of the temperature may be determined based on the temperatures T1 and T2. (Item 11) Item 11. The image forming apparatus according to item 10, wherein the determining unit determines whether the temperature of the heating unit is normal based on a difference between the first temperature and the second temperature and a temperature threshold value.

[0102] As explained in the third embodiment, the normality of the temperature may be determined based on the temperature difference between the temperatures T1 and T2. (Item 12) Item 11. The image forming apparatus according to item 10, wherein the determining unit determines whether the temperature of the heating unit is normal based on a temperature gradient between the first temperature and the second temperature and a gradient threshold value.

[0103] As described in the third embodiment, the normality of the temperature may be determined based on the temperature gradient (e.g., G) and the gradient threshold (e.g., Gth). (Item 13) 4. The image forming apparatus according to item 3, wherein the determining unit determines whether the temperature is normal based on the temperature of the heating unit and a threshold temperature.

[0104] As described in the third embodiment, the normality of the temperature may be determined based on the temperature T2. (Item 14) 14. The image forming apparatus according to any one of items 1 to 13, further comprising a detection circuit that outputs a pulse waveform that repeatedly rises and falls in response to zero crossings of the AC current.

[0105] The detection circuit 308 is an example of a circuit that outputs a zero-cross waveform. (Item 15) Item 15. The image forming apparatus according to item 14, wherein the waveform detection unit detects the abnormal waveform based on the pulse waveform.

[0106] As explained in the first embodiment, the CPU 131 may detect an abnormal waveform based on the zero-cross signal ZEROX. (Item 16) Item 16. The image forming apparatus according to item 15, wherein the waveform detection unit detects the abnormal waveform based on an on-time or an off-time of the pulse waveform.

[0107] As explained in the first embodiment, the CPU 131 may detect an abnormal waveform based on the on-time (on-duty) or off-time (off-duty) of the zero-cross signal ZEROX. (Item 17) 17. The image forming apparatus according to any one of items 14 to 16, further comprising a power outage detection unit that detects a power outage of the external power supply based on the pulse waveform.

[0108] The detection circuit 308 prepared for power outage detection may be used to detect abnormal AC waveforms. (Item 18) 18. An image forming apparatus according to any one of items 14 to 17, further comprising a control unit that controls the power supplied to the heating unit based on the pulse waveform.

[0109] The detection circuit 308 used for power control of the heater 200 may be diverted to detect abnormal AC waveforms. (Item 19) 19. The image forming apparatus according to any one of items 14 to 18, wherein the detection circuit includes a photocoupler that isolates a primary side circuit and a secondary side circuit in the image forming apparatus.

[0110] As described in the first embodiment, the zero-cross signal ZEROX may be output from the light-receiving element of the photocoupler 404. As described in the second embodiment, the zero-cross signal ZEROX may be output via the transistor Tr3. In particular, in the second embodiment, the responsiveness of the zero-cross signal ZEROX is improved. (Item 20) The photocoupler is a light-emitting element connected in parallel to the external power supply; a light-receiving element that receives light from the light-emitting element and outputs a detection signal; 20. The image forming apparatus according to item 19, wherein the light receiving element or a semiconductor switch connected to the light receiving element outputs the pulse waveform. (Item 21) 21. The image forming apparatus according to item 20, wherein the detection circuit further includes a constant voltage element connected in series to the light emitting element.

[0111] The Zener diode ZD is an example of a constant voltage element. By using a constant voltage element, the threshold voltage Vz at which the light emitting element of the photocoupler 404 emits light increases. This makes it easier to distinguish between abnormal waveforms and normal waveforms. (Item 22) 22. The image forming apparatus according to any one of items 19 to 21, wherein the detection circuit is provided between the cutoff means and the heating means.

[0112] The detection circuit 308 may be disposed between the relay 302 and the external power supply 301. However, in this case, the detection circuit 308 will always consume power. As shown in Fig. 3, the detection circuit 308 may be disposed 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. (Item 23) 22. The image forming apparatus according to any one of items 1 to 21, wherein during a period in which the driving means is continuously operating because the driving means stops later than the heating means, the driving means drives the first rotating body at a rotational speed at which the first rotating body and the second rotating body do not stick to each other.

[0113] The motor 118 may drive the pressure roller 208 so that the pressure roller 208 rotates at a rotation speed that prevents the heating film 202 from sticking to the pressure roller 208. However, this rotation speed may be lower than the rotation speed during image formation. (Item 24) the switch means is a triac, 23. The image forming apparatus according to any one of items 1 to 22, wherein the interrupting means is an electromagnetic relay.

[0114] The relay 302 may be an electromagnetic relay. The triac 316 may be another type of semiconductor switch. The heater 200 may be a ceramic heater or a halogen lamp. (Item 25) 17. The image forming apparatus according to any one of items 1 to 16, wherein the driving means includes the same driving source that drives the first rotating body and a cartridge that supplies toner.

[0115] The pressure roller 208 and the process cartridge 109 that supplies toner may be driven by the same driving source, thereby reducing the number of driving sources. (Item 26) a first rotating body that is driven to rotate by a driving means; a second rotating body disposed opposite the first rotating body and cooperating with the first rotating body to form a nip portion; a heating means for receiving an AC current from an external power source and heating the second rotating body; a switch means disposed between the external power source and the heating means, for adjusting the power supplied to the heating means so that the temperature of the heating means approaches a target temperature; a cutoff means connected in series with the switch means between the external power source and the heating means, for cutting off the alternating current supplied from the external power source to the heating means; a power failure detection means disposed between the cutoff means and the switch means and configured to detect a power failure of the external power supply; a monitoring means for monitoring the temperature of the heating means, When a termination condition for terminating heating by the heating means is satisfied, the switch means stops the supply of power to the heating means; If the temperature of the heating means is not detected to be abnormal when the termination condition is satisfied, the driving means is stopped, an image forming apparatus, wherein if an abnormal temperature of the heating means is detected when the termination condition is satisfied, the cut-off means cuts off the supply of power from the external power source to the heating means for at least a predetermined period of time, and the driving means stops later than the heating means.

[0116] As described in the fifth embodiment, monitoring or detecting an abnormal waveform is not required. If the heating termination condition is met and an abnormal temperature is detected, the relay 302 may be turned off for a predetermined period of time. Thereafter, the relay 302 may be turned back on, and the motor 118 may be stopped. (Item 27) 27. The image forming apparatus according to item 26, wherein the predetermined period is a half cycle of the AC current. (Item 28) 28. The image forming apparatus according to item 26 or 27, wherein the power outage detection means detects that the external power supply has experienced a power outage when a pulse waveform that repeatedly rises and falls in response to zero crossings of the AC cannot be detected for a specified time. (Item 29) a photocoupler including a light-emitting element that repeatedly turns on and off in response to the AC supplied from the external power source, and a light-receiving element that receives light output from the light-emitting element and generates a pulse waveform; 29. The image forming apparatus according to any one of items 26 to 28, wherein the power outage detection unit detects a power outage of the external power supply using the pulse waveform output from the photocoupler. (Item 30) 30. The image forming apparatus according to any one of items 26 to 29, wherein the monitoring unit acquires a first temperature, which is the temperature of the heating unit, at a first timing, and acquires a second temperature, which is the temperature of the heating unit, at a second timing that is later than the first timing, and determines whether the temperature of the heating unit is abnormal based on the first temperature and the second temperature. (Item 31) Item 31. The image forming apparatus according to item 30, wherein the monitoring means determines whether the temperature of the heating means is abnormal based on the difference between the first temperature and the second temperature and a temperature threshold value. (Item 32) Item 31. The image forming apparatus according to item 30, wherein the monitoring means determines whether the temperature of the heating means is abnormal based on a temperature gradient between the first temperature and the second temperature and a gradient threshold value. (Item 33) 2. The image forming apparatus according to claim 1, wherein the monitoring means determines whether the temperature of the heating means is normal based on the temperature of the heating means and a threshold temperature. (Item 34) 34. The image forming apparatus according to any one of items 27 to 33, wherein the drive time of the drive means is extended so that the drive means stops after the cutoff means cuts off the supply of power from the external power source to the heating means for at least half a cycle (a predetermined time) of the AC. (Item 35) 35. The image forming apparatus according to any one of items 26 to 34, wherein the driving means includes the same driving source that drives the first rotating body and a cartridge that supplies toner. (Item 36) 36. An image forming apparatus according to any one of items 26 to 35, wherein during a period in which the driving means is continuously operating because the driving means stops later than the heating means, the driving means drives the first rotating body at a rotational speed at which the first rotating body and the second rotating body do not stick to each other. (Item 37) a first rotating body that is driven to rotate by a driving means; a second rotating body disposed opposite the first rotating body and cooperating with the first rotating body to form a nip portion; a heating means for receiving an AC current from an external power source and heating the second rotating body; a switch means disposed between the external power source and the heating means, for adjusting the power supplied to the heating means so that the temperature of the heating means approaches a target temperature; a cutoff means connected in series with the switch means between the external power source and the heating means, for cutting off the alternating current supplied from the external power source to the heating means; a waveform detection means for detecting an abnormal waveform of the AC current; a control means for controlling the driving means, the switching means, and the interrupting means, The control means When a termination condition for terminating heating by the heating means is satisfied, the switch means is controlled to stop supplying power to the heating means; If the abnormal waveform is not detected when the termination condition is satisfied, the driving means is stopped; If the abnormal waveform is detected when the termination condition is satisfied, the image forming apparatus delays the stop timing of the driving means relative to the stop timing of the heating means.

[0117] The CPU 131 is an example of a control means. Note that delaying the timing at which the motor 118 stops relative to the timing at which the heater 200 stops corresponds to continuing the rotation of the motor 118.

[0118] The invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0119] 113. Heating device, 114. Pressure device, 200. Heater, 301. External power supply, 302. Relay, 308. Detection circuit, 316. Triac

Claims

1. a first rotating body that is driven to rotate by a driving means; a second rotating body disposed opposite the first rotating body and cooperating with the first rotating body to form a nip portion; a heating means for receiving an AC current from an external power source and heating the second rotating body; a switch means disposed between the external power source and the heating means, for adjusting the power supplied to the heating means so that the temperature of the heating means approaches a target temperature; a cutoff means connected in series with the switch means between the external power source and the heating means, for cutting off the AC supplied from the external power source to the heating means; a waveform detection means for detecting an abnormal waveform of the AC current; When a termination condition for terminating heating by the heating means is satisfied, the switch means stops the supply of power to the heating means; If the abnormal waveform is not detected when the termination condition is satisfied, the driving means stops; If the abnormal waveform is detected when the termination condition is satisfied, the driving means is stopped later than the heating means.

2. 2. The image forming apparatus according to claim 1, wherein the driving means stops when the waveform of the AC current returns from the abnormal waveform to a normal waveform.

3. a temperature monitoring means for monitoring the temperature of the heating means; and a determination means for determining whether the temperature is normal or not when the abnormal waveform is detected while the termination condition is satisfied, When the temperature is normal, the driving means stops; 2. The image forming apparatus according to claim 1, wherein said driving means continues to operate when said temperature is not normal.

4. 4. The image forming apparatus according to claim 3, wherein the driving means is stopped when a first period has elapsed from the time when the termination condition is satisfied, the time when the abnormal waveform is detected, or the time when it is detected that the temperature is not normal.

5. 5. The image forming apparatus according to claim 4, wherein the driving means is stopped when the temperature returns to normal before the first period has elapsed.

6. 5. The image forming apparatus according to claim 4, wherein if the abnormal waveform is still detected and the temperature is not normal even after the first period has elapsed, the cutoff means forcibly cuts off the connection between the external power source and the heating means, and then the driving means stops.

7. 2. The image forming apparatus according to claim 1, wherein if the abnormal waveform is detected when the termination condition is satisfied, the cutoff means forcibly cuts off the connection between the external power source and the heating means for a second period, and when the second period ends, the driving means stops.

8. 2. The image forming apparatus according to claim 1, wherein if the abnormal waveform is detected when the termination condition is satisfied, the cutoff means forcibly cuts off the connection between the external power source and the heating means for a second period, and when the second period ends, the cutoff means returns from the cutoff state to a conductive state and the driving means stops.

9. The image forming apparatus according to claim 7 , wherein the second period is a period equal to or longer than a half cycle of the AC current.

10. 4. The image forming apparatus according to claim 3, wherein the determination unit acquires a first temperature, which is the temperature of the heating unit, at a first timing, and acquires a second temperature, which is the temperature of the heating unit, at a second timing that is later than the first timing, and determines whether the temperature of the heating unit is normal based on the first temperature and the second temperature.

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

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

13. 4. The image forming apparatus according to claim 3, wherein the determining unit determines whether the temperature of the heating unit is normal based on the temperature of the heating unit and a threshold temperature.

14. 2. The image forming apparatus according to claim 1, further comprising a detection circuit that outputs a pulse waveform that repeatedly rises and falls in response to zero crossings of the AC current.

15. 15. The image forming apparatus according to claim 14, wherein the waveform detection unit detects the abnormal waveform based on the pulse waveform.

16. 16. The image forming apparatus according to claim 15, wherein the waveform detection unit detects the abnormal waveform based on an on-time or an off-time of the pulse waveform.

17. 17. The image forming apparatus according to claim 14, further comprising a power failure detection unit that detects a power failure in the external power supply based on the pulse waveform.

18. 17. The image forming apparatus according to claim 14, further comprising a control unit that controls the power supplied to said heating unit based on said pulse waveform.

19. 17. The image forming apparatus according to claim 14, wherein the detection circuit includes a photocoupler that isolates a primary side circuit from a secondary side circuit in the image forming apparatus.

20. The photocoupler is a light-emitting element connected in parallel to the external power supply; a light-receiving element that receives light from the light-emitting element and outputs a detection signal; 20. The image forming apparatus according to claim 19, wherein the pulse waveform is output by the light receiving element or a semiconductor switch connected to the light receiving element.

21. 21. The image forming apparatus according to claim 20, wherein the detection circuit further includes a constant voltage element connected in series to the light emitting element.

22. 20. The image forming apparatus according to claim 19, wherein the detection circuit is provided between the cutoff means and the heating means.

23. 17. An image forming apparatus according to claim 1, wherein during a period in which the driving means continues to operate because the driving means stops later than the heating means, the driving means drives the first rotating body at a rotational speed at which the first rotating body and the second rotating body do not stick to each other.

24. the switch means is a triac, 17. The image forming apparatus according to claim 1, wherein the interrupting means is an electromagnetic relay.

25. 17. The image forming apparatus according to claim 1, wherein the driving unit includes a same driving source that drives the first rotating body and a cartridge that supplies toner.

26. a first rotating body that is driven to rotate by a driving means; a second rotating body disposed opposite the first rotating body and cooperating with the first rotating body to form a nip portion; a heating means for receiving an AC current from an external power source and heating the second rotating body; a switch means disposed between the external power source and the heating means, for adjusting the power supplied to the heating means so that the temperature of the heating means approaches a target temperature; a cutoff means connected in series with the switch means between the external power source and the heating means, for cutting off the AC supplied from the external power source to the heating means; a power failure detection means disposed between the cutoff means and the switch means and configured to detect a power failure of the external power supply; a monitoring means for monitoring the temperature of the heating means, When a termination condition for terminating heating by the heating means is satisfied, the switch means stops the supply of power to the heating means; If the temperature of the heating means is not detected to be abnormal when the termination condition is satisfied, the driving means is stopped, an image forming apparatus, wherein if an abnormal temperature of the heating means is detected when the termination condition is satisfied, the cut-off means cuts off the supply of power from the external power source to the heating means for at least a predetermined period of time, and the driving means stops later than the heating means.

27. 27. The image forming apparatus according to claim 26, wherein the predetermined period is a half cycle of the AC current.

28. 27. The image forming apparatus according to claim 26, wherein said power failure detection means detects that said external power supply has experienced a power failure when a pulse waveform that repeatedly rises and falls in response to zero crossings of said AC current cannot be detected for a specified time.

29. a photocoupler including a light-emitting element that repeatedly turns on and off in response to the AC supplied from the external power source, and a light-receiving element that receives light output from the light-emitting element and generates a pulse waveform; 27. The image forming apparatus according to claim 26, wherein said power failure detection means detects a power failure in said external power supply by using said pulse waveform output from said photocoupler.

30. 27. The image forming apparatus of claim 26, wherein the monitoring means acquires a first temperature, which is the temperature of the heating means, at a first timing, and acquires a second temperature, which is the temperature of the heating means, at a second timing that is later than the first timing, and determines whether the temperature of the heating means is abnormal based on the first temperature and the second temperature.

31. 31. The image forming apparatus according to claim 30, wherein the monitoring unit determines whether the temperature of the heating unit is abnormal based on a difference between the first temperature and the second temperature and a temperature threshold value.

32. 31. The image forming apparatus according to claim 30, wherein the monitoring means determines whether the temperature of the heating means is abnormal based on a temperature gradient between the first temperature and the second temperature and a gradient threshold value.

33. 27. The image forming apparatus according to claim 26, wherein the monitoring means determines whether the temperature of the heating means is normal based on the temperature of the heating means and a threshold temperature.

34. 28. The image forming apparatus according to claim 27, wherein the driving time of the driving means is extended so that the driving means stops after the power supply from the external power source to the heating means is cut off by the cutting means for at least half a cycle of the AC.

35. 35. The image forming apparatus according to claim 26, wherein the driving means includes a same driving source that drives the first rotating body and a cartridge that supplies toner.

36. 35. An image forming apparatus according to claim 26, wherein during a period in which the driving means continues to operate because the driving means stops later than the heating means, the driving means drives the first rotating body at a rotational speed that does not cause the first rotating body and the second rotating body to stick to each other.

37. a first rotating body that is driven to rotate by a driving means; a second rotating body disposed opposite the first rotating body and cooperating with the first rotating body to form a nip portion; a heating means for receiving an AC current from an external power source and heating the second rotating body; a switch means disposed between the external power source and the heating means, for adjusting the power supplied to the heating means so that the temperature of the heating means approaches a target temperature; a cutoff means connected in series with the switch means between the external power source and the heating means, for cutting off the AC supplied from the external power source to the heating means; a waveform detection means for detecting an abnormal waveform of the AC current; a control means for controlling the driving means, the switching means, and the interrupting means, The control means When a termination condition for terminating heating by the heating means is satisfied, the switch means is controlled to stop supplying power to the heating means; If the abnormal waveform is not detected when the termination condition is satisfied, the driving means is stopped; If the abnormal waveform is detected when the termination condition is satisfied, the image forming apparatus delays the stop timing of the driving means relative to the stop timing of the heating means.

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