JP2017090784A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology capable of improving stability in operation of an image formation device at the time of occurrence of abnormality with a fixing device (fixing means).SOLUTION: An image formation device includes a latch circuit 503 which, when a temperature of a heater 203 detected with thermistors 205, 206 is at a first threshold value or higher, makes power supply from a commercial power source to the heater 203 into a shielded state, a latch circuit 504 which, when the temperature of the heater 203 detected with the thermistors 205, 206 is a second threshold value or higher, makes power supply from the commercial power source to the heater 203 into the shielded state, and a latch release circuit 540 which, during a state in which a pressure release mechanism 307 makes a press-contact state between a fixing film 201 and a pressurizing roller 202 into a pressurizing state, prevents the latch circuit 504 from forming such shielded state.SELECTED DRAWING: Figure 7

Description

  The present invention relates to an image forming apparatus including a fixing device.

  As a safety device for a fixing device provided in an image forming apparatus, a configuration is known in which a power supply to a heater is cut off when an abnormally high temperature of the fixing device is detected by detecting the temperature of the heater, and a cut-off state is latched, as disclosed in Patent Document 1. ing. Further, as disclosed in Patent Document 2, a configuration is proposed in which the abnormal temperature detection threshold is switched according to the pressure separation state between the fixing film and the pressure roller.

Japanese Patent No. 4817862 JP 2007-212868 A

  However, the release of the pressure state of the fixing film and the pressure roller may be performed manually by the user or automatically by shifting to the sleep mode, for example. When such pressure release is performed, even if the detected heater temperature is below the abnormal temperature detection threshold before the pressure release, a situation may occur in which the detected temperature exceeds the abnormal temperature detection threshold after the pressure release. . In other words, in spite of the fact that no abnormally high temperature has actually occurred, the system judgment is a situation in which an abnormally high temperature has occurred. In such a situation, in the configuration of Patent Document 2, the safety device shifts to a latched state, so that the system shifts to an operation at the time of occurrence of an abnormality, and no abnormally high temperature has occurred. It is possible that the system stops operating. In other words, the system operation may be unstable.

  An object of the present invention is to provide a technique capable of improving the stability of the operation of an image forming apparatus when an abnormality occurs in a fixing device (fixing unit).

In order to achieve the above object, an image forming apparatus of the present invention includes:
An image forming unit for forming a developer image on the recording material;
A heating member having a heater that generates heat by electric power supplied from a commercial power supply; and a pressure member that presses the heating member to form a nip portion. The developer image on the recording material is formed in the nip portion. Fixing means for heating and fixing the recording material;
A pressure switching means capable of switching a pressure contact state between the heating member and the pressure member to either a pressure state or a pressure release state;
Temperature detecting means for detecting the temperature of the heater;
When the temperature detected by the temperature detection means is equal to or higher than a first threshold, first power supply cutoff means for cutting off power supply from a commercial power source to the heater;
When the temperature detected by the temperature detection means is equal to or higher than a second threshold value smaller than the first threshold value, a second power supply cutoff means for cutting off the power supply from a commercial power source to the heater;
An interruption release means for preventing the second power supply interruption means from forming the interruption state while the pressure switching means is in the pressure contact state.
It is characterized by providing.

  According to the present invention, it is possible to improve the stability of the operation of the image forming apparatus when an abnormality occurs in the fixing device (fixing unit).

Configuration of an image forming apparatus in Embodiment 1 Sectional view of the fixing device in Embodiment 1 Configuration diagram of pressure release mechanism in embodiment 1 The figure which shows the drive circuit and control circuit of a heater in Example 1. FIG. Configuration diagram of safety circuit in embodiment 1 The graph which shows the temperature transition in Example 1 Configuration diagram of safety circuit in embodiment 2 The graph which shows the temperature transition in Example 2

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. That is, it is not intended to limit the scope of the present invention to the following embodiments.

[Example 1]
(Configuration of image formation measures)
FIG. 1 is a schematic cross-sectional view showing a configuration of an image forming apparatus 100 including a fixing device (fixing means) in an embodiment of the present invention. The image forming apparatus 100 forms an unfixed toner image on a recording paper (recording material) P by a series of processes of a known electrophotographic process. The image forming apparatus 100 includes a paper feed cassette 101 that stores recording paper (recording material) P, a paper presence / absence detection sensor 102 that detects the presence or absence of the recording paper P that is a recording material, and the size of the recording paper P. A paper size detection sensor 103 for detecting the above. The recording paper P loaded in the paper feed cassette 101 is fed out by the pickup roller 104 and then conveyed by one sheet by the paper feed roller 105 and the retard roller 106 disposed opposite to the paper feed roller 105. . Thereafter, the recording paper P is conveyed by a registration roller 107 at a predetermined timing to a transfer nip portion formed by a photosensitive drum 112 that is an electrophotographic photosensitive member and a transfer roller 117. The photosensitive drum 112 is integrated with a charging unit 109, a developing roller 110 as a developing unit, and a cleaner 111 as a cleaning unit as a part of a process cartridge 108 that can be attached to and detached from the apparatus main body of the image forming apparatus 100. .

The surface of the photosensitive drum 112 is uniformly charged by the charging unit 109, and then image exposure based on the image signal is performed by the scanner unit 113 which is an image exposure unit. Laser light emitted from the laser diode 114 in the scanner unit 113 is scanned in the main scanning direction through the rotating polygon mirror 115 and the reflecting mirror 116 and in the sub scanning direction by the rotation of the photosensitive drum 112. As a result, a two-dimensional latent image is formed on the surface of the photosensitive drum 112. The latent image on the photosensitive drum 112 is visualized as a toner image (developer image) by the developing roller 110, and the toner image is transferred onto the recording paper P conveyed from the registration roller 107 by the transfer roller 117. The above-described configuration relating to the formation of the toner image on the recording material corresponds to the image forming unit of the present invention. Subsequently, the recording paper P to which the toner image has been transferred is conveyed to the fixing device 118 and subjected to heat and pressure processing, and the unfixed toner image is fixed to the recording paper P. The recording paper P is further discharged out of the main body of the image forming apparatus 100 by the intermediate paper discharge roller 119 and the paper discharge roller 120, and a series of printing operations is completed. The pre-registration sensor 121, the fixing paper discharge sensor 122, and the paper discharge sensor 123 monitor the conveyance state of the recording paper P.

(Configuration of fixing device)
FIG. 2 is a diagram schematically showing a cross section (a cross section seen in the longitudinal direction) of the central portion in the heater longitudinal direction of the fixing device 118 that is the image heating apparatus in the embodiment of the present invention. A fixing film (fixing sleeve) 201 that is a moving body is a member that is heated by a ceramic heater 203 that is a heating body, and constitutes a heating member together with the ceramic heater 203. A fixing film 201 and a pressure roller 202 (pressure member) as a nip portion forming member are arranged to face each other to form a fixing nip portion 209 having a predetermined width, and the recording paper P applies pressure and heat to the fixing nip portion 209. Pass while receiving. A ceramic heater 203 is coated with a heating element 208 on a ceramic substrate 207 and covered with a glass protective layer 210. The fixing film 201 is a film made of a cylindrical heat-resistant material (a sleeve-like member having flexibility), and is externally fitted to a film guide 204 that supports a ceramic heater 203 on the lower surface side. A thermistor 205, which is a temperature detecting means, is in contact with the ceramic substrate 207 surface of the ceramic heater 203. In addition, a thermo switch (not shown) and a thermistor 206 for detecting the temperature of the end (shown in FIG. 4). ) Is also in contact. The thermistors 205 and 206 are temperature detecting elements and are not limited to contact type thermistors. The stay 208 is a rigid member whose longitudinal direction is the vertical direction of FIG. 2 and is disposed inside the film guide 204. In order to improve the slidability of the fixing film 201, slidable grease may be applied to the interface between the inner surface of the fixing film 201 and the ceramic heater 203. The fixing device 118 in the present embodiment is described with respect to the ceramic heater 203, but is not limited thereto. For example, even in a fixing device using a halogen heater, the same effect as in the first embodiment can be obtained.

(Pressure release mechanism (pressure switching means))
FIG. 3 is a pressure state switching means for switching the pressure contact state between the fixing film 201 and the pressure roller 202 of the fixing device 118 in the embodiment of the present invention to either the pressure state or the pressure release state. It is a block diagram of a certain pressure release mechanism 307. The pressure roller 202 is fixed to the fixing frame 301. Further, a pressure spring 303 is applied between the fixing frame 301 and the pressure frame 302, and the fixing film 201 is pressed against the pressure roller 202 via the film guide 204 and the ceramic heater 203. That is, the pressure of the pressure spring 303 becomes the pressure applied to the fixing nip portion 209. The pressure can be varied by the vertical movement of the pressure frame 302.

There are two methods for moving the pressure frame 302 up and down.
One is due to the rotation of the fixing motor 421 (described in FIG. 4). By controlling the rotation of the fixing motor 421 in the direction opposite to the feeding direction of the recording paper P, the pressure variable gear 304 is connected and driven. The pressurizing variable gear 304 switches between two or more types of pressures by changing the distance from the shaft to the outer periphery as shown in the figure. This function is to prevent deformation of the fixing film 201 and the pressure roller 202 that continue to be pressurized, and it is desirable to reduce the pressure as much as possible during periods other than the printing operation.

  Another method is manual pressure release by the user. The pressure frame 302 is connected to a lever or door (not shown) that is accessed by the user. Since the pressure frame 302 moves in the direction of decreasing the pressure of the fixing nip 209 (upward in FIG. 3) by the opening and closing operation of the door and lever by the user, the pressure of the fixing nip 209 is released. This manual pressure release by the user is for reducing the pressure so that the user can easily remove the jammed paper when the paper is jammed in the fixing nip 209 (hereinafter referred to as a jam). It is the mechanism provided in.

This pressure release state may be a state in which the fixing film 201 and the pressure roller 202 are completely separated, or a state in which the pressure is weakened when the fixing film 201 and the pressure roller 202 are in contact with each other. An effect is obtained. Further, there may be a plurality of types of pressures to be weakened (the strength and degree of pressure contact may be switched in a plurality of stages). In this embodiment, a state where a pressure necessary for image formation is applied will be described as a contact state (pressurized state), and a state where the pressure is weakened will be described as a pressure release state.

  The contact / pressure release state is determined by the pressure release sensor 306 detecting a pressure release detection flag 305 that moves in conjunction with the vertical movement of the pressure frame 302. In this embodiment, an optical photo sensor is used as the pressure release sensor 306, but the pressure release sensor 306 is not limited to the optical sensor. The pressure release mechanism 307 may be provided in the fixing device 118 or in the image forming apparatus 100. Further, the configuration is not limited to the above-described configuration, and other configurations may be used as long as the pressure is changed.

(Heater drive circuit and control circuit)
FIG. 4 shows a heater drive circuit and a control circuit in this embodiment. 401 in the figure is a commercial AC power supply, and is connected to the heating element 208 through the AC filter 402. The power supply to the heating element 208 is energized or interrupted by the triac 403. Reference numerals 404 and 405 denote bias resistors for driving the triac 403 as power supply means, and reference numeral 409 denotes a phototriac coupler for securing an insulation distance between the primary side and the secondary side. The triac 403 is turned on by energizing the light emitting diode of the phototriac coupler 409. Reference numeral 407 denotes a resistor for limiting the current of the phototriac coupler 409. A transistor 408 controls on / off of the phototriac coupler 409. The transistor 408 operates according to the FSRD signal from the engine controller 417 which is a control means via the resistor 406. The FSRD signal outputs a high level when the transistor 408 is turned on and the phototriac 409 is turned on, and a low level is outputted when the transistor 408 is turned off and the phototriac 409 is turned off. The high level is a voltage level of the port of the engine controller 417, and indicates a voltage level close to the voltage level supplied to the engine controller 417, and the “L” level indicates a voltage level close to the ground potential of the engine controller 417. Also, there may be a plurality of heating elements 208, and another set of components to be driven with the triac 403 may be prepared so that each heating element can be individually driven.

  Reference numeral 410 denotes a ZEROX (zero cross) detection circuit connected to the AC power supply 401 via the AC filter 402. The ZEROX (zero cross) detection circuit 410 notifies the engine controller 417 of the timing at which the voltage of the AC power supply 401 is zero voltage by replacing it with the edge of a pulse signal (hereinafter referred to as “ZEROX signal”). The engine controller 417 detects the edge of the pulse of the ZEROX signal and controls the triac 403 on / off by phase control or wave number control.

  The thermistor 205 is a thermistor (temperature detection means) for detecting the temperature of the ceramic heater 203, and is provided via an insulator having a dielectric strength voltage so as to ensure an insulation distance from the heating element 208 on the ceramic heater 203. Be placed. The thermistor 206 is a thermistor for detecting the temperature of the end portion of the ceramic heater 203, and is disposed via an insulator having an insulation withstand voltage so as to ensure an insulation distance from the heating element 208 in the same manner as the thermistor 205. Is done. The temperatures TH1 and TH2 detected by the thermistors 205 and 206 are detected as a partial pressure of the resistor 411 and the thermistor 205, and a partial pressure of the resistor 412 and the thermistor 206, and the TH1 signal and TH2 signal are A / D input to the engine controller 417. The The thermistors 205 and 206 are NTC thermistors, and have resistance characteristics with a negative slope as the temperature rises. Therefore, as the temperature rises, the resistance values of the thermistors 205 and 206 become smaller, and the divided voltages TH1 and TH2 also become smaller.

  The temperature of the ceramic heater 203 is monitored by the engine controller 417. The engine controller 417 compares the temperature set in the interior with the temperature detected by the thermistor to calculate the power supplied to the heating element 208, converts the supplied power into the output timing of the FSRD signal, The FSRD signal is transmitted to 408. Using this FSRD signal, the amount of power supplied to the heating element 208 is controlled.

  Reference numerals 413 and 414 denote AC / DC converters which are first DC voltage generating means (first DC generating means) and second DC voltage generating means (second DC generating means), respectively. This is converted into a DC voltage required by the image forming apparatus 100. In this embodiment, 24V and 3.3V are generated. These turn off unnecessary voltages in the sleep mode for the purpose of saving energy of the image forming apparatus 100. In this embodiment, the engine controller 417 transmits a 24 RMT signal to the AC / DC conversion unit 413 and turns off the 24V output.

  Reference numeral 415 is a relay (hereinafter referred to as a relay) in which the primary side and the secondary side are insulated, and the switch part of the relay is provided between the current supply path (power supply line) from the AC power supply 401 to the heating element 208. Be placed. A current is passed through the built-in coil connected to the secondary side of the relay 415 by the transistor 416, thereby exciting the coil and turning on / off the primary side switch unit. The transistor 416 is connected to the engine controller 417 via the resistors 422 and 418. The transistor 416 is turned on when the RLD signal sent from the engine controller 417 is at a high level, and the transistor 416 is turned off when the signal is at a low level. A diode 423 connected in parallel with the relay 415 is a diode for protecting the transistor 415 from the counter electromotive force of the coil of the relay 415.

  The engine controller 417 is mounted with a CPU and memory (not shown), and includes software such as monitoring the temperature of the thermistor and controlling power supplied to the heating element as described above. Reference numeral 421 denotes a motor for rotating the pressure roller. The engine controller 417 receives the speed signal pulse (FG) transmitted from the motor and reads the speed of the motor 421. The speed is controlled by an acceleration signal (ACC) and a deceleration signal (DEC). Further, the speed setting is switched according to conditions such as the paper conveyance speed and the paper size, and the motor rotation speed is changed.

  Safety circuits 419 and 420 as temperature monitoring means are abnormality detection means for detecting an abnormality of the fixing device 118 and forcibly stopping energization of the ceramic heater 203 (heating element 208). Compared with the threshold values of the TH1 and TH2 signals, when it is determined that the temperature of the ceramic heater 203 is abnormal, the relay 415 is turned off.

  As described with reference to FIG. 3, reference numeral 306 denotes a sensor that detects a pressurized state. When in the contact state, the High level is output, and when the pressure is released, the Low level is output. The detected PRESS signal is sent to the engine controller 417 and safety circuits 419 and 420.

(Safety circuit)
FIG. 5 shows the configuration of the safety circuit 419 in this embodiment. The safety circuit 419 is a safety circuit unit using the TH1 signal, and the safety circuit 420 is a safety circuit unit using the TH2 signal. Since the internal circuit configuration of the safety circuit 420 is the same as that of the safety circuit 419, description of the safety circuit 420 is omitted.

(Abnormality judgment detection unit)
Reference numerals 501 and 502 denote abnormality determination detection units.
Comparators 507 and 508 are connected to thermistor detection signal TH1 and predetermined voltages 505 and 50, respectively.
6 is compared. The predetermined voltages 505 and 506 are obtained by converting the temperature thresholds T1 and T2 that are determined to be abnormal in the fixing device 118 into voltages. In this case, a threshold voltage is applied to the inverting terminals of the comparators 507 and 508 by dividing the resistance. The temperature thresholds T1 and T2 are set to different temperatures. Since the amount of heat transferred from the ceramic heater 203 to the pressure roller 202 is smaller when the pressure is released than when the fixing nip 209 is in contact, the temperature of the ceramic heater 203 rises more quickly when there is an abnormality. Therefore, in order to stop the abnormal state earlier, the temperature threshold T2 (second threshold) in the pressure release state may be set lower than the temperature threshold T1 (first threshold) in the contact state. desired. Therefore, in this embodiment, the temperature threshold T1 in the contact state is 250 ° C., the temperature threshold T2 in the pressure release state is 150 ° C., and voltages corresponding to the temperatures are set to the predetermined voltages 505 and 506, respectively. As described above, when the temperature of the thermistors 205 and 206 is lower than the temperature thresholds T1 and T2, the outputs of the comparators 507 and 508 having the internal output circuit of the open collector become high impedance, and the high level is obtained by pulling up the resistors 510 and 525. It becomes. On the other hand, when the temperature of the thermistor is higher than the temperature thresholds T1 and T2 (when T1 and T2 or more), the comparators 507 and 508 output a low level.

(Latch circuit)
Next, the latch circuits 503 and 504 will be described.
When the operation outputs of the comparators 507 and 508 are at a high level, the transistors 513 and 528 are turned off. Therefore, the non-inverting terminals of the comparators 515 and 530 become the ground potential via the resistors 512 and 527, and the predetermined voltages 514 and 529 set to 2.0 V are higher, so that the comparators 515 and 530 are set to Low. Output. In this state, the transistors 519 and 534 are not turned on, and the SAFE signal is output High by the pull-up resistor 521. The diodes 522 and 523 are attached so as not to be affected by the individual operations of the latch circuits 503 and 504. 3.3 V is used for the pull-up resistors 516 and 531 connected to the output stages of the comparators 515 and 530. Resistors 517 and 532 are resistors for converting the input voltage into a current to stabilize the operation of the transistors 519 and 534. The resistors 518 and 533 are resistors for preventing malfunction of the transistors 519 and 534 by dropping leakage current or noise from the input side to the ground. Resistors 509 and 524 are resistors for converting the input voltage into a current to stabilize the operation of the transistors 513 and 528. The resistor 509 is built in as a part of the latch circuit 503, and the resistor 524 is a latch. The circuit 504 is built in as a part.

  On the other hand, when the operation outputs of the comparators 507 and 508 are at the low level, the transistors 513 and 528 are turned on. Then, the divided voltage of the resistors 511 and 512 and the divided voltage of the resistors 526 and 527 (when a transistor 539 described later is turned off) become 2.5 V, and the outputs of the comparators 515 and 530 become the high level. Accordingly, the transistors 519 and 534 are turned on, and the SAFE signal becomes a low level. In addition, the base voltages of the transistors 513 and 528 are set to the low level via the resistors 520 and 535 and are kept on. That is, this is equivalent to latching the SAFE signal at the Low level. As described above, when the thermistor detection temperature exceeds the temperature threshold value T1 or the temperature threshold value T2, the bases of the transistors 513 and 528 are fed back to the low level, thereby latching the SAFE signal to the low level. Since the transistor 416 is turned off, the relay 415 is turned off.

  As described above, the power supply from the commercial power supply to the heater 208 is cut off when the detected temperature of the thermistor in the safety circuit 419 is T1 or higher (first threshold or higher), such as the abnormality determination detection unit 501 and the latch circuit 503. The configuration for achieving this corresponds to the first power supply cutoff means of the present invention. Similarly, the power supply from the commercial power source to the heater 208 is cut off when the detected temperature of the thermistor of the safety circuit 419, such as the abnormality determination detection unit 502 and the latch circuit 504, is T2 or higher (second threshold or higher). The structure for this corresponds to the second power supply cutoff means of the present invention.

  Note that the relay 415 is not turned off only by the low level output operation of the comparators 507 and 508. This is because the SAFE signal has a potential of about 3.3 V due to the base-emitter voltage of the transistors 513 and 528 that are turned on and the anode-cathode voltage of the diodes 522 and 523, and does not go low. Therefore, as described above, the on operation of the transistors 519 and 534 causes the relay 415 to be turned off.

(Latch release circuit)
Here, the latch release circuit 540, which is a feature of this embodiment, will be described. The latch release circuit 540 is connected to a latch circuit 504 that latches at the lower temperature threshold T2. The latch release circuit 504 is energized together with the pressure release sensor 306 as a pressure release detection unit so that the second latch circuit 504 cannot perform a latch operation while the contact state between the fixing film 201 and the pressure roller 202 is the pressure release state. The shut-off release means for setting the state is configured.

  In the pressure release state, that is, when the PRESS signal of the pressure release sensor 306 is at the low level, the transistor 539 is turned off, and as described above, the non-inversion terminal of the comparator 530 becomes 2.5 V and the relay 415 is turned off at the time of abnormality.

  On the other hand, in the contact state, that is, when the PRESS signal is at a high level, the transistor 539 is turned on, and the non-inverting terminal of the comparator 530 becomes 0.5 V due to the voltage division of the resistors 526, 527, and 536. Thus, the comparator 530 always outputs a low level while maintaining the contact state, and does not perform a latch operation. That is, the contact state is equivalent to substantially stopping the function of the latch circuit 504. Further, by performing the pressure release → contact operation during the latch operation, the output of the comparator 530 is forcibly set to Low and the transistor 534 is turned off, so that the latch operation is reset and becomes a non-latch state. The resistor 537 is a resistor for stabilizing the operation of the transistor 539, and the resistor 538 is a resistor for preventing a malfunction of the transistor 539 by dropping a leakage current or noise from the input side to the ground.

  Note that the operating point for determining the transition between the latched state and the non-latched state is not limited to the voltage at the non-inverting terminal of the comparator 530. A power supply voltage (for example, operation switching between 0.5 V and 3.3 V) may be used as a driving source of the latch circuit 504. Alternatively, when the latch circuit 504 is configured by a logic IC, a voltage for operating a reset function attached to the logic IC may be used.

  In summary, since the latch circuit 504 does not operate in the contact state, the abnormality of the fixing device 118 is monitored with a temperature threshold of 250 ° C. On the other hand, in the pressure release state, monitoring is performed with a temperature threshold of 150 ° C.

In FIG. 6, the temperature transition at the time of operation | movement of a present Example is shown.
A section t1 is a start-up operation of the image forming apparatus 100. In the standby mode, the engine controller 417 releases the pressure at the fixing nip 209 and supplies power to the ceramic heater 203 in the pressure released state. The engine controller 417 heats up to a target temperature of 120 ° C. (T3) by detection of the pressure release sensor 306. Thereafter, the engine controller 417 performs a contact operation, and when the contact is completed, the target temperature is set to 200 ° C. (T4) and heated. Note that the engine controller 417 may perform the contact operation instruction and the start of power supply at the same time. In this section t1, the temperature threshold value in the safety circuits 419 and 420 is switched from 150 ° C. (T2) to 250 ° C. (T1) according to the output of the pressure release sensor 306.

In the section t2, a printing operation is performed. Since the fixing nip 209 is in contact, the temperature threshold is 250 ° C. (T1). Then, a jam occurs at a certain time t5 in the section t2, and the temperature control is stopped.
In a section t3, the user opens the door of the image forming apparatus 100 in order to remove the jammed paper due to the jam. At this time, manual pressure release is performed by opening the door, and the temperature threshold is switched from 250 ° C. (T2) to 150 ° C. (T1). As shown in the drawing, when the user releases the pressure when the temperature of the ceramic heater 203 is 150 ° C. (T1) or higher, the latch circuit 504 operates and the power stop state is latched. Since the fixing device 118 is not abnormal, it is necessary to be able to turn on the power again.

  In a section t4, the user's operation to remove jammed paper is finished, and the door is closed. Then, the image forming apparatus 100 performs a contact operation and performs self-diagnosis while turning on the power to check whether a paper jam remains. By this contact operation, the latch circuit 504 that has been latched can release the latch and reapply power. Thereafter, if there is no problem in the result of the self-diagnosis, it starts up again after the section t4 and performs a printing operation.

  As described above, there is a limited case in which the safety circuit operation works depending on the pressure release state of the user even if the fixing device 118 is not abnormal. In the system configuration of Patent Document 2, when the operation of the safety circuit shifts to the latch state, the operation shifts to the operation at the time of occurrence of an abnormality (stop of the image forming operation) as it is. On the other hand, in this embodiment, by using a safety circuit that can return to the non-latching state even after the latch circuit that monitors the temperature in the pressure release state once enters the latching state, the image forming operation is accidentally performed. A system that can avoid being disturbed can be constructed. That is, according to the present embodiment, since the latch operation is also released in accordance with the switching of the contact operation from the pressure release by the user, a system in which the accidental latch operation is not immediately connected to the device stop state is constructed. Can do. Therefore, according to the present embodiment, safety can be maintained without reducing usability.

[Example 2]
The configuration of the image forming apparatus 100, the configuration of the fixing device 118, the configuration of the pressure release device 307, the configuration of the heater drive circuit and the control circuit in Embodiment 2 of the present invention are substantially the same as those in Embodiment 1. In the second embodiment, the same components as those of the first embodiment are denoted by the same reference numerals and the description thereof is omitted.

  FIG. 7 shows a configuration of the safety circuit 419 according to the second embodiment of the present invention. In this embodiment, the latch circuit 701 has a feature compared to the first embodiment. 24 V is used for the pull-up resistor connected to the output stage of the comparator 530. As described with reference to FIG. 4, 24 V is a power source generated by the AC / DC conversion unit 413 (first DC generation unit), and power generation is turned on / off by a 24 RMT signal transmitted from the engine controller 417. Can be switched off. In this embodiment, for the purpose of energy saving in the sleep mode, the 24V output is turned off in the sleep mode. That is, when the latch circuit 701 is 24V off, the output of the comparator 530 does not become high level and the transistor 534 does not turn on regardless of the state of the input terminal of the comparator 530. Therefore, it is equivalent to the latch circuit 701 being in the operation stop state during the sleep mode. Further, by turning off 24V during the latch operation, the output of the comparator 530 is forcibly set to the Low level. If the thermistor temperature TH1 is lower than the temperature threshold T2 when the 24V is turned on again, the latch operation is reset and becomes a non-latching state.

  In summary, in the 24V off state, the latch circuit 701 is in a non-operating state. On the other hand, while 24V is activated, the latch circuit 701 is in an operable state. In addition, the latch state is released in conjunction with the 24V being turned off.

  In FIG. 8, the temperature transition at the time of operation | movement of a present Example is shown. A section t5 is a start-up operation of the image forming apparatus 100. Since the operation is the same as the section t1 described in the first embodiment, the description is omitted. A section t6 indicates a printing operation. When printing is completed, the mode shifts to the standby mode at a section t7. In order to save energy, it is necessary to shift to a sleep mode (a low-load operation for reducing the power consumption of the apparatus during non-image formation) that consumes less power than the standby mode. In preparation for shifting to the sleep mode, in order to prevent the pressure roller 202 from being deformed, the pressure at the fixing nip 209 abutted at a certain time t10 in the section t7 is released. At this time, the thermistor temperature TH1 may be equal to or higher than the temperature threshold T2, in which case the safety circuit 419 operates and the latch circuit 701 operates. The section t8 indicates the sleep mode and 24V is turned off. After that, when a trigger for returning from sleep is applied, 24V is activated at interval t9 to release the latch, and start-up control is started.

  By the way, although the latch circuit 701 is in a non-operating state, the relay 415 is also turned off while 24V is turned off, and the heating element 208 is not energized, so safety is not impaired. As described above, even if the fixing device 118 is not abnormal, there is a limited case in which the safety circuit operation is activated when the temperature of the fixing device 118 is high when shifting to the sleep mode. According to the present embodiment, in such a case, the latch is automatically released during a series of operations of shifting to and returning from the sleep mode. Therefore, safety can be maintained without reducing usability. Further, since the sleep mode can be entered without waiting for the temperature of the ceramic heater 203 to drop, power saving of the image forming apparatus 100 can be achieved.

  DESCRIPTION OF SYMBOLS 100 ... Image forming apparatus, 118 ... Fixing apparatus, 201 ... Fixing film, 202 ... Pressure roller, 203 ... Ceramic heater, 205, 206 ... Thermistor, 307 ... Pressure release mechanism, 413, 414 ... AC / DC conversion part, 419 , 420: Safety circuit, 503, 504 ... Latch circuit, 540 ... Latch release circuit

Claims (6)

An image forming unit for forming a developer image on the recording material;
A heating member having a heater that generates heat by electric power supplied from a commercial power supply; and a pressure member that presses the heating member to form a nip portion. The developer image on the recording material is formed in the nip portion. Fixing means for heating and fixing the recording material;
A pressure switching means capable of switching a pressure contact state between the heating member and the pressure member to either a pressure state or a pressure release state;
Temperature detecting means for detecting the temperature of the heater;
When the temperature detected by the temperature detection means is equal to or higher than a first threshold, first power supply cutoff means for cutting off power supply from a commercial power source to the heater;
When the temperature detected by the temperature detection means is equal to or higher than a second threshold value smaller than the first threshold value, a second power supply cutoff means for cutting off the power supply from a commercial power source to the heater;
An interruption release means for preventing the second power supply interruption means from forming the interruption state while the pressure switching means is in the pressure contact state.
An image forming apparatus comprising: The first power supply cutoff means is a first latch circuit that forms the cutoff state by latching a relay provided in a power supply line from a commercial power source to the heater in an off state,
The second power supply cutoff means is a second latch circuit that forms the cutoff state by latching a relay provided in a power supply line from a commercial power source to the heater in an off state,
The shut-off release means includes a pressure release detection means for detecting whether the pressure contact state is a pressure release state, and a latch operation for latching the second latch circuit when the pressure release detection means detects the pressure release state. The image forming apparatus according to claim 1, further comprising: an unlatching circuit that makes the power supply unexecutable.   The second power supply cutoff unit is in a state in which the cutoff state cannot be formed while a low-load operation for reducing power consumption of the apparatus is being performed during non-image formation. The image forming apparatus described in 1. A first DC generating means for generating a first magnitude DC voltage from power supplied from a commercial power supply, wherein the output of the first magnitude DC voltage is turned off in the low load operation; First DC generation means;
Second DC generation means for generating a second magnitude DC voltage from the power supplied from the commercial power source;
Further comprising
The said 2nd latch circuit is comprised so that it may be in the energization state which cannot perform a latch operation, when the said output of a said 1st DC production | generation means is turned off. The image forming apparatus described.   The image forming apparatus according to claim 4, wherein the relay is operated by a direct current voltage output from the second DC generation unit.   The heating member has a flexible fixing sleeve, the inner surface of the fixing sleeve and the heater are in contact with each other, and the pressure member presses against the fixing sleeve so as to sandwich the fixing sleeve together with the heater. The image forming apparatus according to claim 1, wherein the nip portion is formed.

Images