JP2009300944A - Heating unit and image forming apparatus - Google Patents

Abstract

A heating device in which an electromechanical relay such as an electromagnetic relay constituting a main circuit is not disconnected during energization and an image forming apparatus using the heating device are provided.
A heating element that generates heat by power supply, a power control circuit that controls ON / OFF of power supply to the heating element, an electromechanical switch 202 that turns ON / OFF a circuit from a power supply to the power control means, A switch control circuit for controlling the electromechanical switch, a control means for controlling the power control circuit, a voltage monitor circuit 206 for monitoring a voltage for driving the electromechanical switch, and a voltage value monitored by the voltage monitor circuit is a predetermined value. A heating device comprising: a circuit for forcibly stopping ON / OFF control by the power control means and setting it to an OFF state regardless of an instruction from the control means in the following cases.
[Selection] Figure 1

Description

  The present invention relates to a heating device and an image forming apparatus such as a copying machine, a facsimile, or a printer including the heating device, and more particularly to control of an electromechanical switch, for example, an electromagnetic relay, when operating the heating device.

A heating device in an image forming apparatus such as a copying machine, a facsimile machine, or a printer is for heat-fixing an unfixed toner image transferred onto a transfer material onto the transfer material with a heating roller or the like. The temperature of the heating element is controlled by a temperature detection element such as a thermistor provided in the vicinity of the heating element for heating the heating roller or the like so that the heating roller or the like has a temperature necessary for heat fixing.
The heating element, that is, the heater, is usually connected to a commercial power source via an electromechanical switch and a power control element. In the case of controlling the temperature of the heater, the electromechanical switch is first turned on, and the electric power supplied to the heater is controlled using the power control element so that the heater reaches the target temperature.

Here, the electromechanical switch is used to reliably stop the heater and physically insulate the heater from a commercial power source, and electromagnetic relays are widely used.
The power control element is an element capable of finely controlling the electric power supplied to the heater by phase control or wave number control, and usually a semiconductor element such as a bidirectional three-terminal thyristor or a solid state relay is widely used.

In general, in an image forming apparatus, a path for supplying power to a heater and a path to a low voltage power source for supplying power to a controller or the like for controlling the image forming apparatus are branched internally to turn on and off the low voltage power source. Another switching means is provided. An electromagnetic relay or the like is on a different path from the low-voltage power source.
The electromagnetic relay or the like can be turned on / off by a controller or the like. When an abnormality is detected in the heater control, for example, when the heater temperature exceeds a predetermined temperature, the controller determines that an abnormality has occurred, and stops the bidirectional three-terminal thyristor and the like, and turns off the electromagnetic relay and the like. This cuts off the power supply to the heater. Depending on the configuration, a comparator such as a comparator monitors the state of a temperature detection element such as a thermistor without using a controller, and when it is determined to be abnormal, it directly shuts off a bidirectional three-terminal thyristor or electromagnetic relay. There are also things.
In addition, to ensure the safety of the user when the user opens the door for internal access to remove jammed paper and replace consumables in the image forming apparatus, the bi-directional 3 terminal is forcibly In some cases, a thyristor, an electromagnetic relay, or the like is turned off.

Further, as documents showing related prior art, there are the following Patent Documents 1 to 3. Patent Document 1 shows an example in which welding of a relay contact is detected. Patent Document 2 shows an example in which time delay means is provided so that the relay is turned off after the switching element is turned off. Patent Document 3 shows an example of prevention of burn-in of the relay contact when the cover is opened. It is shown.
JP 2002-296955 A JP 7-319341 A Japanese Patent Laid-Open No. 10-63133

  However, in the above-described conventional example, before the power control element such as the bidirectional three-terminal thyristor is turned off during the heater temperature control, such as when the image forming apparatus main body is turned on / off, when the door is opened / closed, or when an abnormality occurs, Sometimes relays were cut off. That is, the electromagnetic relay contact may be opened during energization of the heater.

  When the image forming apparatus is powered off, the operation of the low-voltage power supply that supplies power to the controller is stopped first. The low-voltage power supply also supplies driving power such as an electromagnetic relay, and this voltage also decreases. As a result, the voltage of the electromagnetic relay or the like drops earlier, and the contact of the electromagnetic relay or the like may be cut first while the controller drives the power control element or the like.

  When the user opens the door to access the inside of the image forming device, that is, to remove jammed paper or replace consumables, in order to ensure the safety of the user, the power supply to the electromagnetic relay etc. is cut off. The controller is notified that the door has been opened. The controller immediately stops the power control element, etc., but the control of the controller is delayed, the drive voltage of the electromagnetic relay etc. decreases first, and before the power control element etc. stops, the contact of the electromagnetic relay etc. There was a case where it was cut.

  When an abnormality occurs, for example, when a temperature detection element such as a thermistor disposed in the vicinity of the heater detects abnormal heating of the heater, the controller immediately notifies the occurrence of the abnormality, stops the power control element, etc., and electromagnetic relays Etc. are performed. However, even in this case, the drive voltage of the electromagnetic relay or the like is lowered first, and the contact of the electromagnetic relay or the like may be cut first.

  In such a case, when the current for driving the heater flows through the electromagnetic relay contact, the act of forcibly separating the contact is performed, and a spark is generated, which may cause stress on the contact portion. In addition, a large electromagnetic field noise is generated by the spark generated at this time, and the circuit including the controller may malfunction due to the electromagnetic field noise. In addition, a malfunction may occur in a system connected to the outside, for example, a personal computer.

  The present invention has been made under such circumstances, and a heating device in which an electromechanical relay such as an electromagnetic relay constituting a main circuit is not disconnected during energization and the heating device are used. An object of the present invention is to provide an image forming apparatus.

  In order to solve the above problems, in the present invention, the heating device is configured as described in the following (1) to (3), and the image forming device is configured as described in the following (4).

(1) a heating element that generates heat by power supply;
A power control circuit for performing ON / OFF control of power supply to the heating element;
An electromechanical switch for turning on / off a circuit from a power source to the power control means;
A switch control circuit for controlling the electromechanical switch;
Control means for controlling the power control circuit;
A voltage monitor circuit for monitoring a voltage for driving the electromechanical switch;
A circuit for forcibly stopping ON / OFF control by the power control means to be in an OFF state regardless of an instruction from the control means when a voltage value monitored by the voltage monitor circuit is a predetermined value or less; ,
Heating device with.

(2) a heating element that generates heat by supplying power;
A power control circuit for performing ON / OFF control of power supply to the heating element;
An electromechanical switch for turning on / off a circuit from a power source to the power control means;
A capacitor connected to the electromechanical switch;
A first switch circuit connected to one end of the electromechanical switch via a first rectifying element and controlling the electromechanical switch;
A second switch circuit connected to the other end of the electromechanical switch via a second rectifying element and controlling the electromechanical switch;
Control means for controlling the power control circuit;
The electromechanical switch is controlled by a voltage between a common connection point of the first rectifier element and the first switch control circuit and a common connection point of the second rectifier element and the second switch circuit. A monitor circuit for monitoring the driving voltage;
A circuit for forcibly stopping ON / OFF control by the power control means to be in an OFF state regardless of an instruction from the control means when a voltage value monitored by the voltage monitor circuit is a predetermined value or less; ,
Heating device with.

(3) a heating element that generates heat by supplying power;
A power control circuit for performing ON / OFF control of power supply to the heating element;
A plurality of electromechanical switches having at least first and second electromechanical switches for turning on and off a circuit from a power source to the power control means;
A third switch control circuit for controlling the first electromechanical switch;
A fourth switch control circuit for controlling the second electromechanical switch;
Control means for controlling the power control circuit;
An energization detection circuit for detecting energization of the plurality of electromechanical switches;
With
When the fourth switch control circuit turns on the second electromechanical switch, the first electromechanical switch is always turned on by the third switch control circuit,
And when the second electromechanical switch is turned off by the fourth switch control circuit, the first electromechanical switch is turned on by the third switch control circuit,
The third switch control circuit monitors the drive signal of the second electromechanical switch and the signal from the current detection circuit, and the drive signal of the second electromechanical switch is turned off. Nevertheless, the heating device in which the third switch control circuit forcibly turns off the first electromechanical switch only when the energization detection circuit detects energization.

  (4) An image forming apparatus using the heating device according to any one of (1) to (3) as a heating device for a fixing device.

  According to the present invention, in any situation, the electromechanical switch is not disconnected during energization, so that it can operate more reliably and stably without damaging the electromechanical switch contact. It can be carried out.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to an embodiment of an image forming apparatus.

  FIG. 2 is a schematic configuration diagram of an “image forming apparatus” according to the first embodiment. This embodiment is an example of a laser beam printer.

  The image forming apparatus main body 101 (hereinafter referred to as the main body 101) has a paper feed cassette 102 for storing the recording paper S, and a cassette presence / absence sensor 103 for detecting whether or not the recording paper S is in the paper feed cassette 102 is provided. It has been. In addition, a cassette size sensor 104 (consisting of multiple micro switches) that detects the size of the recording paper S in the paper feeding cassette 102, a paper feeding roller 105a that feeds the recording paper S from the paper feeding cassette 102, and a transport roller Pairs 105b, 105c, 105d and the like are provided. A registration roller pair 106 that synchronously conveys the recording paper S is provided downstream of the paper feed roller 105a and the conveyance roller pairs 105b, 105c, and 105d.

  Further, a paper feed sensor 124 for detecting the leading edge and the trailing edge of the recording paper S and taking an image writing timing is provided downstream of the registration roller pair 106. Further, a process cartridge 108 for forming a toner image on the recording paper S based on the laser beam 118 from the laser scanner 107 is provided. Further, a fixing device 109 for thermally fixing the toner image formed on the recording paper S is provided downstream of the process cartridge 108. Downstream of the heat fixing unit in the fixing device 109, a paper discharge sensor 110 that detects the conveyance state of the paper discharge unit, a paper discharge roller pair 111 that conveys the recording paper S, and a face-up paper discharge roller that discharges the recording paper S. A stacking tray 112 on which the recording paper S for which recording has been completed is stacked is provided. The conveyance reference of the recording paper S is set so as to be centered with respect to the length of the recording paper S in the direction orthogonal to the conveyance direction of the image forming apparatus, that is, the width of the recording paper S.

  The paper discharge sensor 110 is provided inside the fixing device 109 and detects the timing at which the recording paper S has passed through the thermal fixing unit. The recording paper S passes through the paper discharge roller pair 111 and is then discharged to the stacking tray 112 via the face-up paper discharge roller pair 140. The full load detection sensor 142 provided in the paper discharge unit is a sensor that detects whether the recording paper S on the stacking tray 112 is full and detects the movement of the recording paper S in the paper discharge unit.

The laser scanner 107 emits a laser beam modulated based on an image signal (image signal / VDO) transmitted from an external device 131 (to be described later), and the laser light from the laser unit 113 is described later. It comprises a polygon mirror 114 for scanning on the photosensitive drum 117, an imaging lens 115, a folding mirror 116, and the like.
The process cartridge 108 includes a photosensitive drum 117, a primary charging roller 119, a developing device 120, a transfer roller 121, a cleaner 122, and the like necessary for a known electrophotographic process. The fixing device 109 includes a fixing film 109a, a pressure roller 109b, a ceramic heater 109c provided inside the fixing film, and a thermistor 109d that detects the surface temperature of the ceramic heater 109c.

The main motor 123 applies driving force to the paper feed roller 105a via the paper feed roller clutch 125, and to the transport roller pairs 105b, 105c, 105d and to the registration roller pair 106 via the registration roller clutch 129. Yes. Further, a driving force is applied to each unit of the process cartridge 108 including the photosensitive drum 117, the fixing device 109, the discharge roller pair 111, and the face-up discharge roller pair 140.
An engine controller 126 controls the electrophotographic process by the laser scanner 107, the process cartridge 108, and the fixing device 109, and controls the conveyance of the recording paper S in the main body 101.
Reference numeral 127 denotes a video controller, which is connected to an external device 131 such as a personal computer via a general-purpose interface 130 (Centronics, RS232C, USB, etc.). Further, the image information sent from the general-purpose interface 130 is developed into bit data, and the bit data is sent to the engine controller 126 as a / VDO signal.
A line 128 connecting the engine controller 126 and the video controller 127 includes a command / status signal line, a clock signal line, a / VDO signal line, a synchronization signal line, and the like between the controllers.

Next, a circuit from the commercial AC power source to the ceramic heater 109c in the fixing device 109 will be described with reference to a block diagram shown in FIG. The inlet 201 is connected to a commercial AC power source 200. The heater 201 is connected to the heater control circuit 203 (corresponding to the power control circuit in the claims) and the ceramic heater 109c through the electromagnetic relay 202 from the inlet 201.
The main switch 212 is a power switch of the main body 101, and supplies commercial AC power to the low-voltage power supply 210 by turning on the main switch 212.
The low-voltage power source 210 is activated by turning on the main switch 212 and supplies various power sources to the engine controller 126, the drive system in the main body 101, and all other units. For example, a relatively low voltage such as 3.3 V or 5 V is supplied to a control system circuit such as the engine controller 126, and a voltage for operating mainly a drive system such as an electromagnetic relay or a motor, such as 24 V, is compared. A high voltage is supplied to each drive system unit.

The door switch 209 is a switch attached to the door for accessing the inside of the main body 101. The door switch 209 notifies the engine controller 126 that the door is opened and closed, and turns on the 24V voltage for driving the electromagnetic relay 202. / OFF control is also performed. This is to ensure the safety of the user when the user accesses the inside of the main body 101, for example, when the recording paper S in which the above-mentioned jam occurs is removed or the consumables such as the process cartridge 108 are replaced. This is because. In some cases, the door switch 209 may also turn ON / OFF the 24V supplied to the high-voltage power supply 213 that generates various high voltages necessary for the electrophotographic process such as charging, development, and transfer. This is also to ensure the safety of the user by shutting off the power supply of various high-voltage power supplies when the door is open.
The transistor 207 and the transistor 208 (corresponding to the switch control circuit in the claims) supply 24V voltage for driving the electromagnetic relay 202 in accordance with an instruction from the engine controller 126, and the engine controller 126 turns on / off the electromagnetic relay 202. It can be turned off.
The capacitor 204 is connected in parallel with the drive coil of the electromagnetic relay 202, and delays the OFF operation of the electromagnetic relay 202 when the drive voltage supply to the drive coil is interrupted.
Here, although the example using the capacitor 204 is shown as the delay means, it is a matter of course that the same effect may be obtained by using another method. For example, the operation response time of the electromagnetic relay 202 is changed to a slower relay. Various methods that can obtain the same effect can be considered.

The diode 205 (corresponding to the rectifying element in the claims) is for preventing the charge stored in the capacitor 204 from flowing backward when the drive voltage to the drive coil of the electromagnetic relay 202 is cut off. . A comparator 206 (corresponding to a voltage monitor circuit in the claims), which will be described later, instantly detects a drive voltage supply interruption to the drive coil. A voltage is input from the anode of the diode 205 to the + terminal side of the comparator 206, and the anode side corresponds to the preceding stage of the rectifying element in the claims.
The comparator 206 monitors the drive voltage value supplied to the drive coil of the electromagnetic relay 202, and when the voltage is lower than the OFF voltage of the electromagnetic relay 202 (corresponding to a predetermined value or less in the claims), the AND circuit 211. An OFF signal is notified. The electromagnetic relay 202 normally has a hysteresis characteristic in the operating voltage, and the voltage when turning from ON to OFF is lower than the voltage when turning from OFF to ON. Therefore, the reference voltage for the comparator 206 to compare the voltage can be arbitrarily set. However, it is usually set to a voltage value when the electromagnetic relay 202 is turned off, or the electromagnetic relay 202 is turned on from off. It is better to make it higher than the voltage value. With such a setting, even when the voltage gradually decreases, it can be reliably detected before the electromagnetic relay 202 is turned off. In addition, the voltage may be set to be higher than the voltage when the electromagnetic relay 202 is turned on from OFF. In this case, it is easy to react by instantaneous 24 V drop including noise and the like, so care should be taken. Here, instead of the comparator 206, the same effect may be obtained by another method. As a matter of course, the voltage drop of the forward voltage of the diode 205 is set in consideration.

  The AND circuit 211 takes AND logic of the heater drive signals from the comparator 206 and the engine controller 126. Thus, when either the comparator 206 or the heater drive signal from the engine controller 126 is turned off, the drive signal to the heater control circuit 203 is turned off. In the present embodiment, the AND circuit 211 is used to forcibly turn off the heater drive signal, but it is needless to say that the same effect can be obtained by another method. For example, the power supply of the heater control circuit 203 may be cut off directly from the comparator.

  The heater control circuit 203 is composed of a switching element such as a solid state relay or a bidirectional three-terminal thyristor, and controls power supplied to the ceramic heater 109c by phase control or wave number control in accordance with an instruction from the engine controller 126. . Based on the temperature detection information from the thermistor 109d, the engine controller 126 controls the power duty value by changing the phase angle, wave number, and the like so that the ceramic heater 109c has a predetermined temperature. At this time, the heater control circuit 203 may be controlled so that constant power is supplied to the ceramic heater 109c.

Next, the operation will be described with reference to FIG. First, when the main switch 212 of the main body 101 is turned on, the low voltage power supply 210 is activated. Then, comparison of the voltage supplied to the engine controller 126, for example, a relatively low voltage such as 3.3V or 5V, and the voltage for operating the drive system such as an electromagnetic relay or a motor, for example, 24V, etc. Start high voltage. When the door switch 209 is closed, a 24V voltage is supplied to the transistor 207.
Then, the engine controller 126 is activated and starts a pre-multi-rotation operation for warming up the main body 101. First, the transistors 207 and 208 are turned on to supply 24V voltage to the drive coil of the electromagnetic relay 202. The 24V voltage supplied by the transistor 207 is supplied to the drive coil of the electromagnetic relay 202 and the capacitor 204 via the diode 205. The drive coil voltage of the electromagnetic relay 202 increases due to the charging of the capacitor 204, and eventually exceeds the ON voltage of the electromagnetic relay 202, and the electromagnetic relay 202 is turned on. The comparator 206 monitors the drive coil voltage of the electromagnetic relay 202 at that time, and outputs an ON signal to the AND circuit 211 when detecting that the ON voltage of the electromagnetic relay 202 has been exceeded.

  When the electromagnetic relay 202 is turned on, power is supplied to the heater control circuit 203. The engine controller 126 confirms that the door switch 209 is closed, and outputs a heater drive signal to the AND circuit 211. In the AND circuit 211, since the ON signal is output from the comparator 206, the drive signal is output to the heater control circuit 203 in accordance with the heater drive signal from the engine controller 126.

  The engine controller 126 controls the heater control circuit 203 to supply electric power to the ceramic heater 109c and perform predetermined preheating control. After the ceramic heater 109c is preheated, the main motor 123 is started to be driven by the engine controller 126. Further, each unit of the process cartridge 108 including the photosensitive drum 117, the fixing device 109, the paper discharge roller pair 111, and the face-up paper discharge roller pair 140 are rotationally driven. Further, the heater control circuit 203 is controlled, and the drive control of the ceramic heater 109c in the fixing device 109 is also performed, and a preparatory operation for a predetermined process device is executed.

The engine controller 126 then causes the ceramic heater 109c to reach a predetermined temperature, finishes the preparation operation of each process device, and enters a standby state.
At this time, the engine controller 126 stops the heater control circuit 203 and stops power supply to the ceramic heater 109c.

Next, the printing operation will be described.
When the engine controller 126 receives a print operation start command from the video controller 127, the engine controller 126 starts the print operation.
First, the transistors 207 and 208 are turned on to supply 24V voltage to the drive coil of the electromagnetic relay 202. The 24V voltage supplied by the transistor 207 is supplied to the drive coil of the electromagnetic relay 202 and the capacitor 204 via the diode 205. The drive coil voltage of the electromagnetic relay 202 increases due to the charging of the capacitor 204, and eventually exceeds the ON voltage of the electromagnetic relay 202, and the electromagnetic relay 202 is turned on. The comparator 206 monitors the drive coil voltage of the electromagnetic relay 202 at that time, and outputs an ON signal to the AND circuit 211 when detecting that the ON voltage of the electromagnetic relay 202 has been exceeded.
When the electromagnetic relay 202 is turned on, power is supplied to the heater control circuit 203. The engine controller 126 confirms that the door switch 209 is closed, and outputs a heater drive signal to the AND circuit 211. In the AND circuit 211, since the ON signal is output from the comparator 206, the drive signal is output to the heater control circuit 203 in accordance with the heater drive signal from the engine controller 126.

The engine controller 126 controls the heater control circuit 203 to supply electric power to the ceramic heater 109c and perform predetermined preheating control. After the ceramic heater 109c is preheated, the main motor 123 is driven, and the heater control circuit 203 is controlled to start up the ceramic heater 109c and start driving the polygon mirror 114. By driving the main motor 123, the photosensitive drum 117 and the transfer roller 121, the fixing film 109a and the pressure roller 109b of the fixing device 109, the paper discharge roller pair 111, and the face-up paper discharge roller pair 140 start to rotate. Thereafter, the engine controller 126 starts the light amount control of the laser unit 113 and sequentially performs high-voltage driving of the primary charging roller 119, the developing device 120, and the transfer roller 121. The engine controller 126 detects that the rotation of the polygon mirror 114 is in a steady state from the pulse interval of the / BD signal sent from the laser light detection sensor by a CPU (not shown). Then, the sheet feeding roller clutch 125 is turned on to drive the sheet feeding roller 105a, and the recording sheets S in the sheet feeding cassette 102 are fed out one by one. The paper feed roller clutch 125 is immediately turned off when one sheet of recording paper S is fed from the cassette. The fed recording sheet S is conveyed toward the registration roller pair 106 by the conveyance roller pairs 105b, 105c, and 105d rotated by the registration roller clutch 129 that is turned on together with the paper supply roller clutch 125. Then, the CPU detects that the recording paper S has reached the paper feed sensor 124, starts to output a synchronization signal to the video controller 127, turns off the registration roller clutch 129, and feeds the conveyance roller pairs 105b, 105c, 105d. The driving of the registration roller pair 106 is temporarily stopped.
At that time, the video controller 127 has started developing the image information into a dot image, and has completed preparations for starting the output of the / VDO signal. The video controller 127 receives the synchronization signal from the engine controller 126 and starts outputting the / VDO signal as image data for one page.

  On the other hand, the engine controller 126 turns on the registration roller clutch 129 again at the start of the output of the synchronization signal, and restarts the driving of the conveyance roller pairs 105b, 105c, 105d and the registration roller pair 106. The conveyance roller pairs 105 b, 105 c, 105 d and the registration roller pair 106 are driven until the trailing edge of the recording paper S passes the registration roller pair 106. During this time, the engine controller 126 drives the laser unit 113 according to the / VDO signal from the video controller 127. The laser beam 118 emitted from the laser unit 113 is converted into a linear scan by the rotation of the polygon mirror 114 of the laser scanner 107, and is irradiated onto the photosensitive drum 117 by the imaging lens 115 and the folding mirror 116.

  The photosensitive drum 117 is rotationally driven at a predetermined peripheral speed (process speed) in the clockwise direction in FIG. The photosensitive drum 117 is uniformly charged to a predetermined polarity and potential by a primary charging roller 119 as a charging means during the rotation process. Scanning exposure with a laser beam modulated and controlled (ON / OFF control) on the time-series electric digital pixel signal of the target image information output from the laser scanner 107 to the uniformly charged surface of the photosensitive drum 117 is performed. Made. As a result, an electrostatic latent image of target image information is formed on the surface of the photosensitive drum 117. The electrostatic latent image formed on the photosensitive drum 117 is developed with a developer (toner) and visualized by a developing device 120 as a developing unit.

On the other hand, the recording paper S fed out one by one is subjected to predetermined control to a transfer nip portion, which is a pressure contact portion between the photosensitive drum 117 and the transfer roller 121 as a transfer means, by the conveyance roller pairs 105b, 105c, 105d and the registration roller pair 106. It is fed at the timing. Then, the toner image on the surface of the photosensitive drum 117 is sequentially transferred onto the surface of the recording paper S. The recording sheet S exiting the transfer nip is sequentially separated from the surface of the photosensitive drum 117 during the rotation process, and is introduced into the fixing device 109 for fixing the toner image. Toner on the recording paper S is applied to the recording paper S passing between the fixing film 109a and the pressure roller 109b by applying heat from the ceramic heater 109c through the fixing film 109a and applying pressure by the pressure roller 109b. The image is heat-fixed. The recording paper S exiting the fixing device 109 is printed out on the stacking tray 112 by the paper discharge roller pair 111 and the face-up paper discharge roller pair 140.
The photosensitive drum 117 after the recording paper S is separated is cleaned by a cleaner 122 as a cleaning unit to remove adhered contaminants such as transfer residual toner, and the electrophotographic image is started repeatedly by charging. Served for formation.

  When the printing operation is finished, the engine controller 126 stops the heater control circuit 203 to stop the power supply to the ceramic heater 109c, and stops the main motor 123, the laser scanner 107, and other series of printing process processes.

  When a jam occurs, for example, when the recording paper S being transported is caught in the main body 101 during the printing operation, the engine controller 126 stops the heater control circuit 203 and stops the power supply to the ceramic heater 109c. . At the same time, the main motor 123, the laser scanner 107, and other series of print process processes are urgently stopped.

Further, when the user accesses the inside of the main body 101, for example, when the recording paper S in which the above-described jam has occurred is removed or a consumable such as a process cartridge is replaced, the door switch 209 of the main body 101 is turned off. Then, 24V supplied to the transistor 207 is stopped, and the drive voltage supply to the drive coil of the electromagnetic relay 202 is turned off. Since the comparator 206 immediately receives a voltage lower than the OFF voltage of the electromagnetic relay 202, an OFF signal is output from the comparator 206 to the AND circuit 211. The AND circuit 211 ignores the heater drive signal from the engine controller 126 and immediately turns off the drive signal to the heater control circuit 203.
At that time, the electromagnetic relay 202 is kept on for a while due to the electric charge stored in the capacitor 204 via the diode 205. The ON time of the electromagnetic relay 202 here is the time until the heater control circuit 203 completely stops the power supply to the heater 109c after the drive signal to the heater control circuit 203 is turned OFF, that is, the commercial AC voltage is A sufficiently long time is set with respect to the time until the zero cross point is reached and the elements such as the bidirectional three-terminal thyristor are turned off. However, if it is too long, it will deviate from the original purpose, so it must be turned off at least during the time when the user can access the aircraft. With this configuration, when the electromagnetic relay 202 is turned off, the heater control circuit 203 is reliably turned off to cut off the power supply to the heater 109c. There will be no separation and no sparks will occur.

This is because the temperature of the ceramic heater 109c is controlled by the engine controller 126 controlling the heater control circuit 203 during standby so that the ceramic heater 109c is kept at a predetermined temperature during standby and the waiting time at the start of printing is shortened. This control is effective when control is performed.
Depending on the configuration, as described above, 24V supplied to the high-voltage power source 213 that generates various high voltages necessary for the electrophotographic process may be supplied via the door switch 209. In some cases, the high-voltage power supply 213 has a relatively large capacity component. Even in this case, when the electromagnetic relay 202 is turned off, the heater control circuit 203 is reliably turned off to supply power to the heater 109c. Is shut off. Therefore, the contact point of the electromagnetic relay 202 does not leave during energization, and no spark is generated.

The engine controller 126 detects that the door switch 209 is turned off. However, before detecting that the door switch 209 is turned off, for example, when the contact of the door switch 209 generates chattering or the like, it is necessary to confirm that the door switch 209 is turned off in order to remove the chattering. take time. Further, it may take time to detect that the door switch 209 is turned off due to control of other units in the main body 101 by the engine controller 126 or the like. Therefore, even if the heater drive signal is turned off, the electromagnetic relay 202 is turned off first, and as a result, the electromagnetic relay 202 is turned off while power is being supplied to the heater 109c. If the contact of the electromagnetic relay 202 leaves during energization, a spark is generated, which not only damages the relay contact, but also causes malfunction of the engine controller 126 due to noise caused by the spark, not only inside the main body 101 but also around the main body 101. May cause damage to other external devices.
Further, for example, even when the engine controller 126 falls into an uncontrollable state such as a failure or the engine controller 126 goes out of control, it is detected that the temperature of the ceramic heater 109c has exceeded a predetermined temperature, and the thermistor does not pass through the engine controller 126. In some cases, the transistor 207 or the like is immediately controlled by information from a temperature detection circuit or the like so that the electromagnetic relay 202 can be turned off. In this case, since the comparator 206 immediately inputs a voltage lower than the OFF voltage of the electromagnetic relay 202, an OFF signal is output from the comparator 206 to the AND circuit 211. The AND circuit 211 ignores the heater drive signal from the engine controller 126 and immediately turns off the drive signal to the heater control circuit 203. Therefore, as described above, when the electromagnetic relay 202 is turned off, the heater control circuit 203 is reliably turned off to cut off the power supply to the heater 109c, so that the contact of the electromagnetic relay 202 is released during energization. There is nothing and no sparks.

When the heater control circuit 203 is controlled by the engine controller 126 and the temperature control of the heater 109c is performed, when the main switch 212 is turned off, a voltage such as 3.3V or 5V supplied to the engine controller 126 is supplied. Then, a voltage such as 24V for controlling the drive system is cut off, and the voltage gradually decreases. In general, the load on the unit or device to which 3.3V or 5V is supplied is relatively light, and the load on the drive system unit or device to which 24V is supplied is relatively heavy. It will decline. Since the engine controller 126 cannot detect the OFF of the main switch 212, the temperature control of the heater 109c is continued as it is even though the voltage of 24V is lowered. Even in such a case, the comparator 206 can detect a voltage lower than the OFF voltage of the electromagnetic relay 202 and output an OFF signal to the AND circuit 211. The AND circuit 211 ignores the heater drive signal from the engine controller 126 and immediately turns off the drive signal to the heater control circuit 203. Therefore, as described above, when the electromagnetic relay 202 is turned off, the heater control circuit 203 is reliably turned off to cut off the power supply to the heater 109c, so that the contact of the electromagnetic relay 202 is released during energization. There is nothing and no sparks.
In addition, even when 24 V drops for some reason or when the transistor 207 is turned off, the heater control circuit 203 is reliably turned off as described above, so that the contact of the electromagnetic relay 202 is separated during energization. There is nothing and no sparks occur.

  In this embodiment, a printer as an image forming apparatus is described. However, the present invention can be applied not only to a device including a heating device but also to a driving device such as a motor.

  As described above, according to the present embodiment, since the electromechanical switch is not disconnected during energization in any situation, the electromechanical switch contact is not damaged and more reliable. High and stable operation can be performed.

  An “image forming apparatus” that is Embodiment 2 will be described. Since the configuration and operation of the entire image forming apparatus are the same as those in the first embodiment, the description thereof is used and re-explanation is omitted here.

The circuit from the commercial AC power source to the ceramic heater 109c in the fixing device 109 is shown in FIG.
The configuration and operation will be described with reference to FIG. The transistor 301 and the transistor 302 supply a 24V voltage for driving the electromagnetic relay 202 in accordance with an instruction from the engine controller 126 so that the engine controller 126 can perform ON / OFF control of the electromagnetic relay 202.
The transistor 303 is a transistor controlled separately from the engine controller 126, and is assumed to be connected to, for example, information from the thermistor 109d, a current detection circuit (not shown), a motor rotation detection circuit, or the like. If an abnormality is found based on the information from these units, if the configuration is such that the transistor 303 is immediately turned off, the ceramic heater 109c can be stopped while avoiding danger. Usually, it is in the ON state.
The circuit of the transistor 301 and the transistor 302 is referred to in the claims as “a first switch control that is connected to one end of the electromechanical switch via a first rectifier and controls the electromechanical switch. Corresponds to "circuit". The circuit of the transistor 303 is referred to in the claims as “a second switch control circuit that is connected to the other end of the electromechanical switch via a second rectifier and controls the electromechanical switch”. It is equivalent to.

The capacitor 204 is connected in parallel with the drive coil of the electromagnetic relay 202, as in the first embodiment, and delays the OFF operation of the electromagnetic relay 202 when the supply of the drive voltage to the drive coil is interrupted. It is for making it happen.
The diode 304 and the diode 305 are for preventing the charge stored in the capacitor 204 from flowing backward when the drive voltage to the drive coil of the electromagnetic relay 202 is cut off. A comparator 206 (to be described later) is for detecting the interruption of the supply of drive voltage to the immediate drive coil.

  As shown in FIG. 4, the comparator 206 divides the drive voltage supplied by the transistor 301 by the resistor 306 and the resistor 307, and the voltage defined by the resistor 307 and the Zener diode 308 by turning ON the transistor 303. Are output based on the comparison result of these voltages. Note that the circuit of the comparator 206 is referred to in the claims as “a common connection point of the first rectifier element and the first switch control circuit, a common point of the second rectifier element and the second switch control circuit”. It corresponds to a monitor circuit that monitors the voltage that drives the electromechanical switch by the voltage between the connection points.

  When the drive voltage supplied by the transistor 301 is normal, the ON signal is output from the comparator 206 because the transistor 303 is turned on and is higher than the voltage defined by the resistor 307 and the Zener diode 308. When the driving voltage by the transistor 301 decreases, the voltage is lower than the voltage defined by the resistor 307 and the Zener diode 308, and therefore, an OFF signal is output from the comparator 206 as shown in FIG. As a result, the drive signal to the heater control circuit 203 is turned off as will be described later.

When the transistor 303 is turned off, the level pulled up by the resistor 307 to 24 V is input to the inverting terminal of the comparator 206. Therefore, the voltage at the inverting terminal exceeds the voltage divided by the resistors 306 and 307, and an OFF signal is output from the comparator 206 as shown in FIG. 5, and the drive signal to the heater control circuit 203 is described later. Is turned off.
Therefore, when the drive voltage value supplied to the drive coil of the electromagnetic relay 202 is equivalently monitored by the comparator 206 and falls below the OFF voltage of the electromagnetic relay 202, an OFF signal is notified to the AND circuit 211. The electromagnetic relay 202 normally has a hysteresis characteristic in the operating voltage, and the voltage when turning from ON to OFF is lower than the voltage when turning from OFF to ON. Therefore, the reference voltage for the comparator 206 to compare the voltage can be arbitrarily set. However, it is usually set to a voltage value when the electromagnetic relay 202 is turned off, or the electromagnetic relay 202 is turned on from off. It is better to make it higher than the voltage value. With such a setting, even when the voltage gradually decreases, it can be reliably detected before the electromagnetic relay 202 is turned off. In addition, the voltage may be set to be higher than the voltage when the electromagnetic relay 202 is turned on from OFF. In this case, it is easy to react by instantaneous 24 V drop including noise and the like, so care should be taken. These voltages can be arbitrarily set by a divided voltage set by the resistor 306 and the resistor 307 and a voltage set by the resistor 307 and the Zener diode 308. Here, instead of the comparator 206, the same effect may be obtained by another method. Of course, the forward voltage drop of the diodes 304 and 305 is set in consideration.

The AND circuit 211 takes AND logic of the heater drive signals from the comparator 206 and the engine controller 126. Therefore, if either the comparator 206 or the heater drive signal from the engine controller 126 is turned off, the drive signal to the heater control circuit 203 is turned off. In the present embodiment, the AND circuit 211 is used to forcibly turn off the heater drive signal, but it is needless to say that the same effect can be obtained by another method. For example, the power supply of the heater control circuit 203 may be cut off directly from the comparator.
Other configurations and operations are the same as those in the first embodiment.

As described above, according to the present embodiment, it is possible to cope with various circuits for driving the electromagnetic relay, accurately monitor the driving voltage of the electromagnetic relay, and appropriately stop the heater control circuit according to the driving voltage. be able to. Therefore, the contact of the electromagnetic relay does not leave during energization, and no spark is generated.
In this embodiment, a printer as an image forming apparatus is described. However, the present invention can be applied not only to a device including a heating device but also to a driving device such as a motor.

  An “image forming apparatus” that is Embodiment 3 will be described. Since the configuration and operation of the entire image forming apparatus are the same as those in the first embodiment, the description thereof is used and re-explanation is omitted here.

  A circuit from the commercial power source to the ceramic heater 109c in the fixing device 109 will be described with reference to a block diagram shown in FIG. The inlet 201 is connected to a commercial AC power source (not shown). The inlet 201 is connected to the heater control circuit 226 and the ceramic heater 109c via the electromagnetic relays 202, 223, and 224, through the Zerox / current detection circuit 225 (corresponding to the energization detection circuit in the claims).

  The relay drive circuit 228 controls the electromagnetic relays 223 and 224 and turns the electromagnetic relays 223 and 224 ON / OFF according to instructions from the engine controller 126. The Zerox / current detection circuit 225 monitors the value of the current flowing through the ceramic heater 109c and detects the zero cross timing of the AC voltage. The information is notified to the engine controller 126 as appropriate, and the relay drive circuit 229 is notified of the presence / absence of a current value or whether the zero-cross timing can be detected.

  The information notified to the relay drive circuit 229 by the Zerox / current detection circuit 225 may be only the presence / absence information of the current value, or may be only the information indicating whether or not the zero cross timing is detected, or both. It may be. Zero-cross timing detection can be detected when all the electromagnetic relays 202, 223, and 224 are energized. Therefore, it is possible to determine whether all the electromagnetic relays are energized based on the zero cross timing detection information. In addition, since all the electromagnetic relays 202, 223, and 224 are energized and the heater control circuit 226 is energized, a current flows through the ceramic heater 109c. Therefore, if it is current value presence / absence information, it can be determined whether or not all the electromagnetic relays 202, 223, and 224 are energized by detecting the current value presence / absence. The relay drive circuit 229 corresponds to the “third switch control circuit that controls the first electromechanical switch” in the claims, and the relay drive circuit 228 has the “the first switch” in the claims. This corresponds to the “fourth switch control circuit that controls the two electromechanical switches”.

  The heater control circuit 226 is composed of a switching element such as a solid state relay or a bidirectional three-terminal thyristor, and controls the power supplied to the ceramic heater 109c by phase control or wave number control in accordance with instructions from the engine controller 126. . Based on the zero cross timing information and current value from the Zerox / current detection circuit 225 and the temperature detection information from the thermistor 109d, the engine controller 126 adjusts the phase angle, wave number, etc. so that the ceramic heater 109c has a predetermined temperature. The power duty value is controlled by changing the power duty value. At this time, the heater control circuit 226 may be controlled so that constant power is supplied to the ceramic heater 109c.

  Relay drive circuit 229 is independent of engine controller 126 and operates according to the table shown in FIG. That is, the electromagnetic relay 202 is turned off when the Zerox / current detection circuit 225 detects energization even though the relay control signal from the relay drive circuit 228 is relay OFF. In other states, for example, when the relay control signal from the relay drive circuit 228 is ON, or when the relay control signal from the relay drive circuit 228 is OFF and the Zerox / current detection circuit 225 cannot detect energization, The relay drive circuit 229 turns on the electromagnetic relay 202. Here, even though the relay control signal from the relay drive circuit 228 is ON, the Zerox / current detection circuit 225 cannot detect energization, or the heater control circuit 226 performs energization control. In the case where no failure is detected, since some abnormality is recognized in the energization path to the ceramic heater 109c, the failure may be notified to the user.

  In addition, when the 24V power supply, which is the relay drive voltage, is suddenly stopped for some reason, such as when the power of the main body 101 is turned off while the ceramic heater 109c is energized, the electromagnetic relays 202, 223, 224 Regardless, it turns off. At that time, the electromagnetic relay 202 is connected with delay means for delaying the OFF operation (corresponding to the OFF operation delay means in the claims), for example, a capacitor 230 connected in parallel with the drive coil of the electromagnetic relay 202. The relays 223 and 224 are turned off after a predetermined time from turning off. Therefore, even when the relay drive voltage is stopped for some reason during energization of the ceramic heater 109c, only the electromagnetic relay 202 does not generate contact sparks.

  Here, although the example using the capacitor 230 is shown as the delay means, it is needless to say that the same effect may be obtained by using other methods. For example, only the electromagnetic relay 202 may be set to an electromagnetic relay in which the operating voltage of the drive coil is shifted from the other electromagnetic relays 223 and 224 and is turned on even at a lower voltage. As a result, when the relay drive voltage decreases, a mechanism can be adopted in which the electromagnetic relays 223 and 224 are disconnected first. In addition, various methods that can obtain the same effect, such as setting the operation response time of the electromagnetic relay 202 to a relay slower than the electromagnetic relays 223 and 224, can be considered.

  Next, the operation will be described. First, when a main power supply (not shown) of the main body 101 is turned on, a low voltage power supply (not shown) is activated. Then, comparison of the voltage supplied to the engine controller 126, for example, a relatively low voltage such as 3.3V or 5V, and the voltage for operating the drive system such as an electromagnetic relay or a motor, for example, 24V, etc. Start high voltage. When the 24 V voltage is activated, the relay drive circuit 229 detects that the relay control signal from the relay drive circuit 228 is relay OFF and the Zerox / current detection circuit 225 is not energized, and there is no contradiction between both signals. The electromagnetic relay 202 is immediately turned on. Then, the engine controller 126 is activated and starts a pre-multi-rotation operation for warming up the main body 101. First, the relay drive circuit 228 is controlled to turn on the electromagnetic relays 223 and 224 to supply power to the heater control circuit 226. The engine controller 126 controls the heater control circuit 226 based on a signal from the Zerox / current detection circuit 225, supplies electric power to the ceramic heater 109c, and performs predetermined preheating control. After the ceramic heater 109c is preheated, the main motor 123 is started to be driven by the engine controller 126, and each unit of the process cartridge 108 including the photosensitive drum 117, the fixing device 109, the discharge roller pair 111, and the face-up discharge roller pair 140. Is driven to rotate. Further, the heater control circuit 226 is controlled, and drive control of the ceramic heater 109c in the fixing device 109 is also performed, and a preparatory operation for a predetermined process device is executed.

The engine controller 126 then causes the ceramic heater 109c to reach a predetermined temperature, finishes the preparation operation of each process device, and enters a standby state.
At this time, the engine controller 126 stops the heater control circuit 226 and stops the power supply to the ceramic heater 109c. Thereafter, the engine controller 126 controls the relay drive circuit 228 to turn off the electromagnetic relays 223 and 224. By stopping the heater control circuit 226 and the electromagnetic relays 223 and 224 in this order, the current to the ceramic heater 109c is always stopped when the electromagnetic relays 223 and 224 are turned off. Consideration is given to prevent the relay from being turned off. Therefore, no spark is generated when the relay is OFF.

Next, the printing operation will be described.
When the engine controller 126 receives a print operation start command from the video controller 127, the engine controller 126 starts the print operation. First, the relay drive circuit 228 is controlled to turn on the electromagnetic relays 223 and 224 to supply power to the heater control circuit 226. The engine controller 126 controls the heater control circuit 226 based on a signal from the Zerox / current detection circuit 225, supplies electric power to the ceramic heater 109c, and performs predetermined preheating control. After the ceramic heater 109c is preheated, the main motor 123 is driven, and the heater control circuit 226 is controlled to start up the ceramic heater 109c and start driving the polygon mirror 114. By driving the main motor 123, the photosensitive drum 117 and the transfer roller 121, the fixing film 109a and the pressure roller 109b of the fixing device 109, the paper discharge roller pair 111, and the face-up paper discharge roller pair 140 start to rotate. Thereafter, the engine controller 126 starts the light amount control of the laser unit 113 and sequentially performs high-voltage driving of the primary charging roller 119, the developing device 120, and the transfer roller 121. When the engine controller 126 detects that the rotation of the polygon mirror 114 is in a steady state from the pulse interval of the / BD signal sent from the laser light detection sensor by a CPU (not shown), the engine controller 126 turns on the paper feed roller clutch 125. The paper feed roller 105a is driven to feed out the recording sheets S in the paper feed cassette 102 one by one. The paper feed roller clutch 125 is immediately turned off when one sheet of recording paper S is fed from the cassette. The fed recording sheet S is conveyed toward the registration roller pair 106 by the conveyance roller pairs 105b, 105c, and 105d rotated by the registration roller clutch 129 that is turned on together with the paper supply roller clutch 125. Then, the CPU detects that the recording paper S has reached the paper feed sensor 124, starts to output a synchronization signal to the video controller 127, turns off the registration roller clutch 129, and feeds the conveyance roller pairs 105b, 105c, 105d. The driving of the registration roller pair 106 is temporarily stopped.
At that time, the video controller 127 has started developing the image information into a dot image, and has completed preparations for starting the output of the / VDO signal. The video controller 127 receives the synchronization signal from the engine controller 126 and starts outputting the / VDO signal as image data for one page.

  On the other hand, the engine controller 126 turns on the registration roller clutch 129 again at the start of the output of the synchronization signal, and restarts the driving of the conveyance roller pairs 105b, 105c, 105d and the registration roller pair 106. The conveyance roller pairs 105 b, 105 c, 105 d and the registration roller pair 106 are driven until the trailing edge of the recording paper S passes the registration roller pair 106. During this time, the engine controller 126 drives the laser unit 113 according to the / VDO signal from the video controller 127. The laser beam 118 emitted from the laser unit 113 is converted into a linear scan by the rotation of the polygon mirror 114 of the laser scanner 107, and is irradiated onto the photosensitive drum 117 by the imaging lens 115 and the folding mirror 116.

  The photosensitive drum 117 is rotationally driven in the clockwise direction in FIG. 1 at a predetermined peripheral speed (process speed). The photosensitive drum 117 is uniformly charged to a predetermined polarity and potential by a primary charging roller 119 as a charging means during the rotation process. Scanning exposure with a laser beam modulated and controlled (ON / OFF control) on the time-series electric digital pixel signal of the target image information output from the laser scanner 107 to the uniformly charged surface of the photosensitive drum 117 is performed. Thus, an electrostatic latent image of target image information is formed on the surface of the photosensitive drum 117. The electrostatic latent image formed on the photosensitive drum 117 is developed with a developer (toner) and visualized by a developing device 120 as a developing unit.

  On the other hand, the recording paper S fed out one by one is subjected to predetermined control to a transfer nip portion, which is a pressure contact portion between the photosensitive drum 117 and the transfer roller 121 as a transfer means, by the conveyance roller pairs 105b, 105c, 105d and the registration roller pair 106. It is fed at the timing. Then, the toner image on the surface of the photosensitive drum 117 is sequentially transferred onto the surface of the recording paper S. The recording sheet S exiting the transfer nip is sequentially separated from the surface of the photosensitive drum 117 during the rotation process, and is introduced into the fixing device 109 for fixing the toner image. Toner on the recording paper S is applied to the recording paper S passing between the fixing film 109a and the pressure roller 109b by applying heat from the ceramic heater 109c through the fixing film 109a and applying pressure by the pressure roller 109b. The image is heat-fixed. The recording paper S exiting the fixing device 109 is printed out on the stacking tray 112 by the paper discharge roller pair 111 and the face-up paper discharge roller pair 140.

  The photosensitive drum 117 after the recording paper S is separated is cleaned by a cleaner 122 as a cleaning unit to remove adhered contaminants such as transfer residual toner, and the electrophotographic image is started repeatedly by charging. Served for formation.

  When the printing operation is finished, the engine controller 126 stops the heater control circuit 226 to stop the power supply to the ceramic heater 109c, and stops the main motor 123, the laser scanner 107, and other series of printing process processes. Thereafter, the engine controller 126 controls the relay drive circuit 228 to turn off the electromagnetic relays 223 and 224. As described above, the control is such that no spark is generated.

  When a jam occurs, for example, when the recording sheet S being transported is caught in the main body 101 during the printing operation, the engine controller 126 stops the heater control circuit 226 and stops the power supply to the ceramic heater 109c. . At the same time, the main motor 123, the laser scanner 107, and other series of print process processes are urgently stopped. Thereafter, the engine controller 126 controls the relay drive circuit 228 to turn off the electromagnetic relays 223 and 224. As described above, the control is such that no spark is generated.

  Further, when the user accesses the inside of the main body 101, for example, when removing the recording paper S in which the above-mentioned jam occurs or replacing consumables such as a process cartridge, the safety of the user is ensured. There is a need. For this reason, the engine controller 126 stops the heater control circuit 226 from the door open detection information (not shown), stops the power supply to the ceramic heater 109c, and then controls the relay drive circuit 228 so that the electromagnetic relays 223 and 224 are turned on. Turn off. This is because the temperature of the ceramic heater 109c is controlled by the engine controller 126 controlling the heater control circuit 226 during standby so that the ceramic heater 109c is maintained at a predetermined temperature during standby and the waiting time at the start of printing is shortened. This control is effective when control is performed.

  Further, for example, when a failure occurs in the heater control circuit 226 or the like and the temperature of the ceramic heater 109c exceeds a predetermined temperature, the thermistor temperature detection circuit or current detection circuit does not pass through the engine controller 126. In some cases, the relay drive circuit 228 is immediately controlled based on the above information, and the electromagnetic relays 223 and 224 can be turned off. Such a configuration is effective even when the engine controller 126 goes out of control such as runaway. In this case, since energization to the ceramic heater 109c is performed, when the electromagnetic relays 223 and 224 are turned off, sparks are generated at the contacts of the electromagnetic relays 223 and 224.

  As another method, the engine controller 126 may turn off the heater control circuit 226 and then turn off the relay drive circuit 228. However, since the heater control circuit 226 is out of order, the energization cannot be stopped even if the engine controller 126 turns off the heater control circuit 226. In this case as well, since the ceramic heater 109c is energized, when the electromagnetic relays 223 and 224 are turned off, sparks are generated at the contacts of the electromagnetic relays 223 and 224.

  As described above, when the electromagnetic relays 223 and 224 are turned off, the electromagnetic relay is turned off while the ceramic heater 109c is energized, so that spark is generated at the relay contact. When the spark is generated, the contact is damaged. When the spark is generated a plurality of times, there is a concern about the contact welding of the electromagnetic relays 223 and 224. However, when contact welding occurs in only one of the electromagnetic relays 223 and 224, the energization can be interrupted by turning off the relay drive circuit 228, so that the Zerox / current detection circuit 225 detects the energization. There is no. Thereafter, when contact welding occurs in both of the electromagnetic relays 223 and 224, the Zerox / current detection circuit 225 can detect that both relay contacts of the electromagnetic relays 223 and 224 are welded. It can be turned off. Further, the relay drive circuit 229 has a latch function, and maintains the OFF state of the relay 202 once generated unless the power source of the main body 101 is turned off, so that the electromagnetic relay 202 is not turned on again. Absent.

  In this embodiment, a printer as an image forming apparatus is described. However, the present invention can be applied not only to a device including a heating device but also to a driving device such as a motor.

  As described above, according to the present embodiment, in any situation, at least one electromagnetic relay is not disconnected during energization, and therefore, more reliable without damaging the electromagnetic relay contact. High and stable operation can be performed.

  An “image forming apparatus” that is Embodiment 4 will be described. Since the configuration and operation of the entire image forming apparatus are the same as those in the first embodiment, the description thereof is used and re-explanation is omitted here.

A circuit from the commercial power source to the ceramic heater 109c in the fixing device 109 will be described with reference to a block diagram shown in FIG.
In the present embodiment, when the situation where the relay stop circuit 409 turns off the electromagnetic relay 202 occurs, that is, the Zerox / current detection circuit 225 is energized even though the relay drive circuit 228 is turning off the relay drive signal. And the electromagnetic relay 202 is not turned on again even if the power of the main body 101 is turned off / on. It has become.

  In FIG. 8, one of the drive coils of the electromagnetic relay 202 is connected to 24V, which is a relay drive power supply, via a fuse 411 (corresponding to a non-returnable element in the claims), and the other is set to the Gnd level. is set up. The relay coil side of the fuse 411 is also connected to the transistor 410 as shown. The transistor 410 is connected to a relay stop circuit 409 and is turned on by a relay stop signal from the relay stop circuit 409.

Next, the operation will be described. When the power source of the main body 101 is turned on, the electromagnetic relay 202 is turned on at the same time when the 24V power source is activated. The subsequent operation and the like are the same as those in the first embodiment.
If the Zerox / current detection circuit 225 detects energization even though the relay control signal from the relay drive circuit 228 is turned off, the relay stop circuit 409 turns on the transistor 410. Then, when the transistor 410 is turned on, the fuse 411 is short-circuited from 24 V, which is the relay drive voltage, to Gnd, and the fuse 411 is blown by an overcurrent. By blowing the fuse 411, the voltage supply from the relay drive voltage 24V to the drive coil of the electromagnetic relay 202 is stopped, and the electromagnetic relay 202 is turned off. After that, even if the main body 101 is turned off / on, no voltage can be supplied from the relay drive voltage 24V to the electromagnetic relay 202, and the electromagnetic relay 202 continues to maintain the OFF state.

  In this embodiment, since no software is interposed, the reliability is higher. In this embodiment, a circuit using a fuse and utilizing the non-recoverability of the fuse is used as an example. However, it is a matter of course that the circuit is not limited to the fuse and is configured by a method using other non-recoverable devices. It is also possible. For example, using a non-volatile semiconductor memory element (corresponding to the non-volatile memory element in the claims), the fact that the electromagnetic relay 202 is once turned off is stored in the semiconductor memory element. It is also possible to adopt a configuration in which the relay stop circuit 409 does not turn on the electromagnetic relay 202 again. Of course, a non-volatile semiconductor memory element, for example, a memory may be used, or it may be included in the engine controller 126 and software may be interposed. In that case, a counter may be provided as appropriate, the number of times the electromagnetic relay 202 is turned off is counted, and the electromagnetic relay 202 may not be turned on when the count reaches a predetermined number.

  As described above, according to the present embodiment, when the electromagnetic relay is turned off due to an abnormality, the occurrence can be stored, and thereafter, the electromagnetic relay is never turned on again. Therefore, more reliable and stable operation can be performed without damaging the electromagnetic relay contact.

FIG. 3 is a block diagram illustrating a circuit around a fixing device according to the first exemplary embodiment. Sectional drawing which shows schematic structure of the image forming apparatus of Example 1. FIG. The time chart which shows the operation | movement of the principal part of Example 1. FIG. 6 is a block diagram showing a circuit around a fixing device in Embodiment 2. Time chart showing operation of main part of embodiment 2 FIG. 6 is a block diagram showing a circuit around a fixing device in Embodiment 3. Table showing operation of main parts of Example 3 FIG. 6 is a block diagram showing a circuit around a fixing device in Embodiment 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Image forming apparatus 109 Fixing device 109c Heater 126 Engine controller 200 Commercial AC power supply 202 Electromagnetic relay 203 Heater control circuit 206 Comparator 207, 208 Transistor 228 Relay drive circuit

Claims (10)

A heating element that generates heat by supplying power;
A power control circuit for performing ON / OFF control of power supply to the heating element;
An electromechanical switch for turning on / off a circuit from a power source to the power control means;
A switch control circuit for controlling the electromechanical switch;
Control means for controlling the power control circuit;
A voltage monitor circuit for monitoring a voltage for driving the electromechanical switch;
A circuit for forcibly stopping ON / OFF control by the power control means to be in an OFF state regardless of an instruction from the control means when a voltage value monitored by the voltage monitor circuit is a predetermined value or less; ,
A heating apparatus comprising: The heating device according to claim 1,
The electromechanical switch is connected to the switch control circuit via a rectifying element,
A capacitor is connected in parallel with the electromechanical switch;
The voltage monitor circuit monitors a voltage in a previous stage of the rectifying element. A heating element that generates heat by supplying power;
A power control circuit for performing ON / OFF control of power supply to the heating element;
An electromechanical switch for turning on / off a circuit from a power source to the power control means;
A capacitor connected to the electromechanical switch;
A first switch control circuit that is connected to one end of the electromechanical switch via a first rectifier and controls the electromechanical switch;
A second switch control circuit that is connected to the other end of the electromechanical switch via a second rectifier and controls the electromechanical switch;
Control means for controlling the power control circuit;
The electromechanical switch is driven by a voltage between a common connection point of the first rectifier element and the first switch control circuit and a common connection point of the second rectifier element and the second switch control circuit. A monitor circuit for monitoring the voltage for driving
A circuit for forcibly stopping ON / OFF control by the power control means to be in an OFF state regardless of an instruction from the control means when a voltage value monitored by the voltage monitor circuit is a predetermined value or less; ,
A heating apparatus comprising: A heating element that generates heat by supplying power;
A power control circuit for performing ON / OFF control of power supply to the heating element;
A plurality of electromechanical switches having at least first and second electromechanical switches for turning on and off a circuit from a power source to the power control means;
A third switch control circuit for controlling the first electromechanical switch;
A fourth switch control circuit for controlling the second electromechanical switch;
Control means for controlling the power control circuit;
An energization detection circuit for detecting energization of the plurality of electromechanical switches;
With
When the fourth switch control circuit turns on the second electromechanical switch, the first electromechanical switch is always turned on by the third switch control circuit,
And when the second electromechanical switch is turned off by the fourth switch control circuit, the first electromechanical switch is turned on by the third switch control circuit,
The third switch control circuit monitors the drive signal of the second electromechanical switch and the signal from the current detection circuit, and the drive signal of the second electromechanical switch is turned off. Nevertheless, only when the energization detection circuit detects energization, the third switch control circuit forcibly turns off the first electromechanical switch. The heating device according to claim 4, wherein
A heating apparatus comprising an OFF operation delay means for delaying an OFF operation of the first electromechanical switch. The heating device according to claim 4 or 5,
The third switch control circuit has storage means for storing that the first electromechanical switch is forcibly turned off. When the third switch control circuit is forcibly turned off a predetermined number of times, the third switch control circuit thereafter performs the third switch control circuit. The switch control circuit of the heating device is characterized in that the first electromechanical switch is not turned on. The heating apparatus according to claim 6, wherein
The heating device is characterized in that the storage means is a non-returnable element. The heating device according to claim 6, wherein
The heating device, wherein the storage means is a nonvolatile storage element. The heating device according to claim 6, wherein
The storage means has a counter, and when the predetermined count is reached, the third switch control circuit does not turn on the first electromechanical switch thereafter. Heating device.   An image forming apparatus using the heating device according to claim 1 as a heating device for a fixing device.

Images