JP2014077847A - Fixing temperature monitoring device and image forming apparatus - Google Patents

Abstract

High temperature heating is appropriately performed according to a conveyance state of a recording sheet by a fixing unit, and even when a control unit is not controllable, an excessive temperature rise when a recording sheet conveyance to the fixing unit is abnormal is prevented.
The fixing temperature monitoring apparatus 10 includes a temperature detection unit 13, a heater control unit 12, a control unit 11, a temperature setting resistor 141, and a heat roller temperature of the heat roller 51. If the comparator 142 that outputs a heater energization stop signal when the temperature is higher than the monitored temperature, the timer 153, the reset time setting resistor 151, and the timer 153 when the reset voltage is input, the timer 153 measures the elapsed time, the temperature setting A reset IC 152 that outputs an instruction to disconnect the resistor R5 to the switch SW1 of the resistor 141, and the control unit 11 outputs an instruction to connect the resistor R5 to the switch SW1 to output the second monitoring temperature voltage. A connection switching instruction for the resistor R2 is output to the switch SW2 of the reset time setting resistor 151.
[Selection] Figure 3

Description

  The present invention relates to a fixing temperature monitoring device and an image forming apparatus, and more particularly to temperature control of a heat roller of a fixing unit.

  The image forming apparatus includes a fixing device that fixes a toner image to a recording sheet by thermocompression bonding after the image formation. The fixing device includes a heat roller and a pressure roller, and a heater for heating the heat roller is provided in the heat roller. For example, a temperature detection unit having a thermistor for monitoring the temperature of the heat roller is provided in the fixing device. Furthermore, when the temperature detected by the temperature detection unit reaches the monitored temperature, even if the control unit including the CPU that controls the heater is not controllable due to runaway or the like, the control by the control unit There is also known an image forming apparatus provided with a protection circuit that can stop driving the heater with only a hardware configuration. Patent Documents 1 and 2 disclose an image forming apparatus having a configuration for controlling heater heating of a fixing unit as described above.

JP 2003-345165 A JP 2004-109661 A

  Today, there is a demand for an improvement in printing speed during continuous printing in which image formation is continuously performed on a plurality of recording sheets. At this time, in order to give a heat amount necessary for fixing to each recording sheet conveyed continuously, it is necessary to heat the heat roller to a higher temperature than before. For this reason, the temperature difference between the fixing temperature necessary for fixing the toner image on the recording paper and the monitoring temperature for preventing the excessive temperature rise is small. In this case, it is necessary to ensure the amount of heat necessary for toner welding at the fixing unit during continuous printing, and excessive heating at the fixing unit when the conveyance stops abnormally with a gap between recording papers during conveyance of continuous printing. In order to achieve both prevention and prevention, it is necessary to control the fixing temperature by accurately switching the heating control by the heater.

  Since the image forming apparatus disclosed in Patent Document 1 reduces power by switching the set temperature from the printing temperature to the low power temperature at the timing after the power is turned on and after warming up, this technique is applied to the fixing unit. It is difficult to apply to heater drive control according to the fixing temperature and the recording paper conveyance state required in (1). The image forming apparatus disclosed in Patent Document 2 switches the fixing temperature between the printing operation and the idle time. In this technique, the fixing temperature is switched by the control of the control unit. In the case where the control unit runs out of control and becomes uncontrollable, it is impossible to manage the fixing temperature.

  In the present invention, the heating roller required as the printing speed is increased is heated to a higher temperature than before, and the fixing is performed even when the control unit becomes uncontrollable while accurately performing according to the recording paper conveyance state. An object of the present invention is to make it possible to prevent an excessive temperature rise at the time of abnormality in conveyance of the recording paper to the section.

The invention according to claim 1 is a temperature detection unit that detects a temperature of a heat roller provided in the fixing unit;
A heater control unit for controlling energization of a heater for heating the heat roller;
A control unit that performs energization control of the heater for heating the heat roller to a target temperature according to the temperature detected by the temperature detection unit via the heater control unit,
A first resistor that is always connected; a second resistor that can be switched; and a first switch that switches the connection of the second resistor based on an instruction from the control unit. When the resistor is disconnected, the first resistor outputs a basic monitoring temperature voltage corresponding to a predetermined basic monitoring temperature, and the second resistor is connected by the first switch. A monitoring voltage output unit for outputting a second monitoring temperature voltage corresponding to a predetermined second monitoring temperature higher than the basic monitoring temperature by one resistor and a second resistor;
The voltage indicating the temperature of the heat roller input from the temperature detection unit is compared with the basic monitoring temperature voltage or the second monitoring temperature voltage input from the monitoring voltage output unit, and each of these voltages When it is shown that the roller temperature is higher than the basic monitoring temperature or the second monitoring temperature, an energization stop signal output unit for outputting an energization stop signal for stopping energization of the heater to the heater control unit; ,
A timer for measuring a preset time;
A second switch for switching the connection of the resistor based on an instruction from the control unit, and a predetermined basic voltage and a voltage value different from the basic voltage by switching the resistor by the second switch; A voltage output unit for outputting a reset voltage;
When the reset voltage is input from the voltage output unit, the timer starts measuring the predetermined time, and when the predetermined time is measured by the timer, the monitoring voltage output A switch switching unit that outputs an instruction to disconnect the second resistor from the first switch and outputs the basic monitoring temperature voltage;
When the control unit outputs an instruction to connect the second resistor to the first switch of the monitoring voltage output unit to output the second monitoring temperature voltage, the control unit outputs the second monitoring temperature voltage to the second switch of the voltage output unit. It is a fixing temperature monitoring device that outputs the reset voltage by outputting a connection switching instruction of the resistor.

  In the present invention, for example, if the second monitoring temperature is set to a temperature corresponding to a high fixing temperature required for continuous printing, the control unit performs the heating with the heater up to the high fixing temperature during continuous printing. By switching the first switch so as to generate the voltage for the second monitoring temperature corresponding to the second monitoring temperature, it becomes possible to manage the high-temperature fixing temperature necessary for the continuous printing in a timely manner.

  Further, after the control unit outputs an instruction to connect the resistor by the second switch to the voltage output unit and outputs the reset voltage, even if the control unit falls out of control, the switch switching unit is controlled by the timer. Based on the measurement, the monitoring voltage is returned to the basic monitoring temperature voltage, and the temperature of the heat roller is monitored at the basic monitoring temperature. Therefore, the temperature monitoring at the second high monitoring temperature is interrupted at this time. When the roller temperature is higher than the basic monitoring temperature at the time point, the energization stop signal output unit can stop the driving of the heater via the heater control unit.

  As a result, according to the present invention, the control unit is not controllable while accurately heating the heat roller required as the printing speed is increased to a higher temperature than ever, according to the recording paper conveyance state. Even in this case, it is possible to prevent an excessive temperature rise when the recording paper is conveyed abnormally to the fixing unit.

According to a second aspect of the present invention, there is provided the fixing temperature monitoring device according to the first aspect, wherein the recording medium to be fixed by the fixing unit detects that the recording medium has passed through the fixing unit. Further comprising
The preset time, which is a measurement target of the timer, is a predetermined conveyance required for the recording medium to be conveyed from the recording medium storage unit to the position where the recording medium is completed to pass through the fixing unit. And a total time of a predetermined temperature rise time required for the heater to raise the heat roller from the basic monitoring temperature to the second monitoring temperature by the heater,
The controller outputs the reset voltage by outputting a connection switching instruction of the resistor to the second switch of the voltage output unit every time the detection unit detects arrival of the recording medium. .

  According to this invention, every time the control unit detects the arrival of the recording medium by the detection unit, the voltage output unit outputs a reset connection voltage by outputting a resistor connection switching instruction using the second switch, The switch switching unit restarts the measurement of the predetermined time by the timer. Therefore, as long as the control unit outputs the connection switching instruction to the voltage output unit without falling into an uncontrollable state, the temperature monitoring at the second monitoring temperature is performed every time the connection switching instruction is output. After the time when the control unit becomes uncontrollable, the temperature monitoring at the second monitoring temperature is limited to the predetermined time, and after the predetermined time has elapsed, By switching to the temperature monitoring at the basic monitoring temperature, the heating control of the heater can be performed safely.

According to a third aspect of the present invention, there is provided the fixing temperature monitoring device according to the first or second aspect,
An image forming unit for forming an image on the recording medium;
An image forming apparatus including a fixing unit that fixes the recording medium after the image is formed by the image forming unit.

  According to this invention, it is possible to achieve the same operation as that of the invention described in claim 1 or claim 2.

  According to the present invention, the control unit becomes uncontrollable while accurately heating the heat roller of the fixing unit, which is required as the printing speed is increased, according to the recording paper conveyance state. In addition, it is possible to prevent overheating of the heat roller when the recording paper transport to the fixing unit is abnormal.

1 is a side view showing an image forming apparatus according to an embodiment of the present invention. 2 is a block diagram illustrating a fixing temperature monitoring device provided in the image forming apparatus. FIG. It is a figure which shows a protection circuit. 5 is a flowchart showing processing at the time of fixing temperature monitoring by a fixing temperature monitoring circuit.

  Hereinafter, a recording medium conveying apparatus and an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a side view showing an image forming apparatus 1 according to an embodiment of the present invention.

  The image forming apparatus 1 includes an image forming unit 2, a conveying unit 3, a paper feeding unit 4, a fixing unit 5, and a discharge tray 6. In the present embodiment, a case where the image forming apparatus 1 is a printer will be described as an example.

  The image forming unit 2 performs an image forming operation for forming a toner image on the recording paper P (an example of a recording medium) conveyed from the paper feeding unit 4 by the conveying unit 3. The image forming unit 2 includes a photosensitive drum 21, a charging unit 22, an exposure unit 23, a developing unit 24, and a transfer roller 25.

  The photosensitive drum 21 is provided with a photosensitive layer on the surface, and the surface potential is set to a predetermined value by charging by the charging unit 22.

  The charging unit 22 is provided at a position facing the surface of the photosensitive drum 21. The charging unit 22 charges the peripheral surface of the photosensitive drum 21 rotating in the direction of the arrow shown in FIG. 1 substantially uniformly to a predetermined charging potential.

  The exposure unit 23 is a position facing the surface of the photosensitive drum 21 and is provided downstream of the charging unit 22 in the rotational direction of the circumferential surface of the photosensitive drum 21. The exposure unit 23 applies laser light indicated by arrows in FIG. 1 corresponding to image data input from a computer (not shown) connected to the image forming apparatus 1 via a network to the photosensitive drum 21 after charging. Irradiating the circumferential surface, an electrostatic latent image corresponding to the image data is formed on the circumferential surface of the photosensitive drum 21 on the circumferential surface of the photosensitive drum 21. The exposure unit 23 is a laser exposure unit, and a laser light source (not shown) that outputs a laser beam, a polygon mirror (not shown) that reflects the laser beam toward the surface of the photosensitive drum 21, and a reflection by the polygon mirror. Optical components such as a lens (not shown) and a mirror (not shown) for guiding the laser beam to the photosensitive drum 21 are provided.

  The developing unit 24 supplies toner (not shown) to the electrostatic latent image formed by the exposure unit 23 on the surface of the photosensitive drum 21. By supplying the toner by the developing unit 24, the toner adheres to the portion exposed by the exposure unit 23 on the surface of the photosensitive drum 21, and a toner image corresponding to the electrostatic latent image is formed on the surface of the photosensitive drum 21. Form. To the developing unit 24, toner is supplied from a toner container (not shown).

  The transfer roller 25 is provided at a position facing the photosensitive drum 21 and on the downstream side of the developing unit 24 in the rotation direction of the photosensitive drum 21. A transfer bias having a polarity opposite to the charging polarity of the toner is applied to the transfer roller 25 by a transfer bias applying mechanism (not shown). As a result, the transfer roller 25 causes the toner image formed on the surface of the photosensitive drum 21 to pass through the nip portion of the photosensitive drum 21 and the transfer roller 25 (hereinafter referred to as a toner image transfer position N). Transfer is performed on the recording paper P conveyed between the surface of the photosensitive drum 21 and the surface of the transfer roller 25.

  The fixing unit 5 is disposed downstream of the toner image transfer position N onto the recording paper P by the image forming unit 2 in the conveyance direction of the recording paper P, and is transferred to the recording paper P that has passed through the image forming unit 2. The toner image is heat-pressed by the heat roller 51 and the pressure roller 52 and fixed on the recording paper P. The hot roller 51 is heated by heat supplied from a heater 511 (see FIG. 2) described later. Further, in the vicinity of the heat roller 51, a thermistor 13 (a part of the temperature detection unit) described later that detects the temperature of the heat roller 51 is provided.

  The sheet transport mechanism (transport unit) 3 includes a transport path 31, a plurality of transport roller pairs 32, a registration roller pair 33, and switchback roller pairs 341 and 342. The conveyance roller pair 32, the registration roller pair 33, and the switchback roller pair 341, 342 are rotationally driven by a rotational driving force supplied from a driving unit (not shown).

  The conveyance path 31 is a conveyance path through which the recording paper P is conveyed from the paper feeding unit 4 to the discharge tray 6 through the image forming unit 2 and the fixing unit 5. A conveyance roller pair 32 is provided at each position of the conveyance path 31, and the recording paper P is transferred from the paper feeding unit 4 to the image forming unit in the conveyance path 31 by the rotation of the roller pair forming the conveyance roller pair 32. 2. It is conveyed to the fixing unit 5 and the discharge tray 6.

  The conveyance path 31 includes a main conveyance path 311 and a reverse conveyance path 312. The main conveyance path 311 is a conveyance path that connects the paper feed unit 4 to the image forming unit 2, the fixing unit 5, and the discharge tray 6. The reverse conveyance path 312 is a conveyance path for conveying the recording paper P, on which image formation has been completed on one side of the recording paper P in the image forming unit 2, to the image forming unit 2 again for duplex printing. The reverse conveyance path 312 branches from the main conveyance path 311 on the downstream side in the conveyance direction of the recording paper P from the fixing unit 5 in the main conveyance path 311, and is downstream of the paper supply unit 4 in the conveyance direction of the recording paper P. In addition, it joins the main transport path 311 at a position upstream of the image forming unit 2.

  The switchback roller pairs 341 and 342 are disposed in the main conveyance path 311 between the fixing unit 5 and the downstream side in the conveyance direction of the recording paper P to the discharge tray 6. The switchback roller pairs 341 and 342 convey the recording paper P between the fixing unit 5 and the discharge tray 6 under the control of the control unit 11 (FIG. 3) described later. When the recording paper P that has passed through the image forming unit 2 and the fixing unit 5 is discharged to the discharge tray 6, the switchback roller pairs 341 and 342 switch back on the downstream side in the conveyance direction of the recording paper P. The recording paper P is conveyed toward the discharge tray 6 by the switchback roller pairs 341 and 342 until the roller pair 342 is separated.

  On the other hand, the switchback roller pair 341, 342 passes the fixing unit 5 when the recording paper P that has passed through the image forming unit 2 and the fixing unit 5 is conveyed again to the image forming unit 2 for duplex printing. The recording paper P is first transported toward the discharge tray 6 by the switchback roller pairs 341 and 342. The trailing edge of the recording paper P in the transport direction leaves the switchback roller pair 341 on the upstream side in the transport direction of the recording paper P, and the switchback roller pair 342 on the downstream side in the transport direction of the recording paper P. The switchback roller pair 341, 342 rotates reversely under the control of the control unit 11. At this time, the recording paper P is guided to the reverse conveyance path 312 by a conveyance path switching mechanism (not shown) provided at a branch point of the main conveyance path 311 and the reverse conveyance path 312.

  In this way, the recording paper P that is reversely fed through the main conveyance path 311 by the switchback roller pair 341 and 342 is guided by the reverse conveyance path 312 and is upstream of the image forming unit 2 in the conveyance direction of the recording paper P. It is conveyed to the main conveyance path 311 and is conveyed again from here to the image forming unit 2.

  At the time of re-conveying, the recording paper P is opposite to the surface on which the image has been previously formed by the reversing operation by the switchback roller pair 341 and 342 and the conveying operation of the recording paper P in the reversing conveying path 312. Since the surface faces the photosensitive drum 21, image formation is performed by the image forming unit 2 on the other surface different from the surface on which image formation has already been performed.

  The registration roller pair 33 is provided on the upstream side in the transport direction of the recording paper P with respect to the image forming unit 2 in the main transport path 311, and the recording paper P transported in the main transport path 311 is transferred to the photosensitive drum 21 and the transfer roller 25. Are adjusted, that is, the timing at which the toner is transferred to the transfer position N of the toner image by the image forming unit 2.

  The paper detection sensor 77 (detection unit) is provided downstream of the fixing unit 5 in the conveyance direction of the recording paper P and in the vicinity of the fixing unit 5.

  The control unit 11 determines a paper jam (a jam of the recording paper P) in the conveyance path 31 based on the paper presence signal (ON signal) and the paper non-signal (OFF signal) acquired from the paper detection sensor 77. For example, the control unit 11 detects the leading edge of the recording paper P based on the paper presence signal and the paper non-signal from the paper detection sensor 77, and then the control unit 11 detects the leading edge of the recording paper P (the recording paper by the transport roller pair 32). (Determined based on the conveyance speed of P and the length of the recording paper P in the conveyance direction of the recording paper P), and it is determined that a paper jam has occurred when the trailing edge of the recording paper P is not detected To do.

  The paper feed unit 4 is a mechanism that feeds the recording paper P to the transport path 31 and includes a paper feed cassette 40 and a paper feed roller 41. The paper feed cassette 40 stores a plurality of recording papers P in a stacked state. The paper feed roller 41 contacts the surface of the uppermost recording paper P among the recording paper P accommodated in the paper feeding cassette 40, and one sheet of recording paper P is fed from the uppermost portion by the rotation of the paper feeding roller 41. Pick up one by one and feed it to the conveyance path 31.

  FIG. 2 is a block diagram showing an electrical configuration of the fixing temperature monitoring device provided in the image forming apparatus 1. FIG. 2 mainly shows a configuration related to the present invention.

  The fixing temperature monitoring device 10 includes a control unit 11, a heater control unit 12, a temperature detection unit 13, and a protection circuit 100.

  The control unit 11 includes a CPU, controls the heating of the heater 511 via the heater control unit 12, and outputs a switch-on signal and a switch-off signal to various switches described later. For example, the control unit 11 controls the overall operation of the image forming apparatus 1 and is mainly used to control the image forming unit 2, a drum motor (not shown), and a conveyance roller.

  The heater control unit 12 controls the heater 511 that heats the heat roller 51 under the control of the control unit 11. The heater 511 is composed of, for example, a halogen lamp, and the heater control unit 12 controls switching between turning on and off of the halogen lamp.

  The temperature detection unit 13 detects the temperature of the heat roller 51 of the fixing unit 5. The temperature detection unit 13 includes a thermistor connected to a constant voltage source via a pull-up resistor. In the temperature detection unit 13, the thermistor is provided in the vicinity of the heat roller 51, and outputs a voltage Vth that changes according to a temperature change of the heat roller 51 to the control unit 11 and the protection circuit 100. That is, in this embodiment, an example is adopted in which an NTC thermistor whose resistance decreases proportionally as the temperature rises is employed, and the temperature detection unit 13 outputs a voltage that decreases as the temperature rises. Show.

  The protection circuit 100 is a circuit that monitors the temperature of the heat roller 51 at a plurality of predetermined monitoring temperatures. The protection circuit 100 monitors whether the temperature of the heat roller 51 is higher than the set monitoring temperature among the plurality of monitoring temperatures, and the temperature of the heat roller 51 is higher than the set monitoring temperature. The heater controller 12 outputs an energization stop signal for stopping energization of the heater 511.

  FIG. 3 is a diagram illustrating a configuration of the protection circuit 100. As shown in FIG. 3, the protection circuit 100 includes a temperature setting resistor 141, a comparator 142, and a timer unit 15.

  The temperature setting resistor (monitoring voltage output unit) 141 generates voltages corresponding to a plurality of monitoring temperatures and outputs the voltages to the comparator 142. In this embodiment, the temperature setting resistor 141 generates voltages Vd1 and Vd2 corresponding to two temperatures of the basic monitoring temperature 190 ° C. and the second monitoring temperature 250 ° C. as the temperatures corresponding to the two monitoring temperatures. To do.

  The temperature setting resistor 141 includes resistors R3, R4, and R5, and a switch SW1 (first switch). The resistors R3 and R4 are always connected in series between the power supply Vcc and the ground. The temperature setting resistor 141 outputs the voltage between the resistors R3 and R4 to the comparator 142 as the basic monitoring temperature voltage Vd1 corresponding to the basic monitoring temperature 190 ° C. The connection line side opposite to the comparator 142 is open.

  The resistor R5 is connected between the resistors R3 and R4 via the switch SW1. The switch SW1 switches whether or not the resistor R5 is connected between the resistors R3 and R4. Switching on or off of the switch SW1 is switched by the control unit 11.

  When the switch SW1 is turned on by the control unit 11, the resistor R5 is connected between the resistors R3 and R4, and the second monitoring temperature voltage Vd2 corresponding to the second monitoring temperature 250 ° C. is generated. Is output.

  Note that the basic monitoring temperature of 190 ° C. is such that the control unit 11 sets the target temperature of the heat roller 51 to 180 ° C. and energizes the heater 511 during heating standby or normal printing (not described below) in the image forming apparatus 1. ) Used to monitor the temperature of the heat roller 51 during control. The second monitoring temperature of 250 ° C. is the heating roller 51 when the heater 511 is energized when it is necessary to heat the heating roller 51 to a temperature higher than that during normal printing, as in continuous printing in the image forming apparatus 1. It is used for temperature monitoring. In the continuous printing, the image forming unit 2 forms an image continuously on a plurality of recording papers P, and the fixing unit 5 continuously fixes the toner on the plurality of recording papers P after the image formation. To do.

  The basic monitoring temperature voltage Vd1 generated by the temperature setting resistor 141, the second monitoring temperature voltage Vd2, and the voltage Vth generated by the temperature detection unit 13 are set to have the same voltage value relationship. Has been. For example, the voltage Vth output by the temperature detection unit 13 indicating that the detection temperature is 190 degrees and the basic monitoring temperature voltage Vd1 corresponding to the basic monitoring temperature 190 ° C. are set to the same voltage value, and are detected by the temperature detection unit 13. The voltage Vth output indicating that the temperature is 250 degrees and the second monitoring temperature voltage Vd2 corresponding to the second monitoring temperature 250 ° C. are set to the same voltage value.

  The comparator (energization stop signal output unit) 142 compares the basic monitoring temperature voltage Vd1 or the second monitoring temperature voltage Vd2 input from the temperature setting resistor 141 with the voltage Vth input from the temperature detection unit 13. When the basic monitoring temperature voltage Vd1 or the second monitoring temperature voltage Vd2 is higher than the voltage Vth input from the temperature detection unit 13, a high level voltage (hereinafter, H signal) is supplied to the heater 511. When the basic monitoring temperature voltage Vd1 or the second monitoring temperature voltage Vd2 is lower than the voltage Vth input from the temperature detector 13, the low-level voltage ( Hereinafter, L signal) is output.

  That is, when the temperature of the heat roller 51 detected by the temperature detection unit 13 is higher than the set monitoring temperature (either the basic monitoring temperature 190 ° C. or the second monitoring temperature 250 ° C.), the comparator 142 Then, an energization stop signal for instructing to stop energization of the heater 511 is output to the heater control unit 12.

  As shown in FIG. 3, the temperature detection unit 13 includes a thermistor 131 connected to a constant voltage source Vp via a pull-up resistor R. The thermistor 131 is disposed close to the heat roller 51. The temperature detection unit 13 outputs the voltage Vth between the thermistor 131 and the pull-up resistor R as a voltage indicating the temperature of the heat roller 51 to the comparator 142 of the protection circuit 100 and the control unit 11.

  The timer unit 15 includes a reset time setting resistor 151, a reset IC 152, and a timer 153.

  The reset time setting resistor (voltage output unit) 151 includes resistors R1 and R2 and a switch SW2 (second switch). The resistor R1 is always connected to the reset IC 152. The resistor R2 is connected to a connection line connected to the reset IC 152 in a state where the connection to the reset IC 152 can be switched via the switch SW2. The reset time setting resistor 151 generates a predetermined basic voltage Vt1 and outputs it to the reset IC 152 in a state where the resistor R1 of R1 and R2 is connected to the reset IC 152. The reset time setting resistor 151 generates a reset voltage Vt2 having a voltage value different from the basic voltage and outputs the reset voltage to the reset IC 152 in a state where both R1 and R2 are connected to the reset IC 152. Note that the connection line side opposite to the reset IC 152 is open.

  The switch SW2 switches on or off according to a switch on signal or a switch off signal from the control unit 11. That is, the switch SW2 switches the connection of the resistor R2 based on an instruction from the control unit 11.

  The timer 153 is built in the reset IC 152 and measures a predetermined time. This predetermined time is the time required for the heating roller 51 to rise from the target temperature 180 ° C. to the target temperature 230 ° C. by the heater 511, and one recording paper P is fed by the transport unit 3 according to the print job. This is the total time required for the sheet to be transported from the paper unit 4 (recording medium storage unit) and to pass through the fixing unit 5. In the present embodiment, the controller 11 is conveyed from the paper feed cassette 40 after the heat roller 51 reaches 230 ° C. from the time when the controller 11 starts energizing the heater 511 via the heater controller 12 at the target temperature 230 ° C. The time t1 until the control unit 11 receives a paper absence signal indicating that the trailing edge of the recording paper P has passed through the fixing unit 5 from the paper detection sensor 77 is determined in advance by the manufacturer of the image forming apparatus 1 or the like. A predetermined time is set in advance. For example, the time until the heat roller 51 reaches 230 ° C. after the heater 511 is energized, and the time until the trailing edge of the recording paper P started to be transported from the paper feed cassette 40 passes through the fixing unit 5 are as described above. Preset by a person or the like.

  When the reset voltage Vt2 is input from the reset time setting resistor 151, the reset IC (switch switching unit) 152 causes the timer 153 to start measuring the time t1. Then, the reset IC 152 is a switch-off signal that is an instruction to disconnect the resistor R5 (second resistor in the claims) from the switch SW1 of the temperature setting resistor 141 when the time t1 is measured by the timer 153. To output the voltage Vd1 corresponding to the basic monitoring temperature of 190 ° C. Note that the reset IC 152 does not output a switch-off signal to the switch SW1 when the basic voltage Vt1 is input from the reset time setting resistor 151.

  The control unit 11 outputs a switch-on signal instructing connection of the resistor R5 to the switch SW1 of the temperature setting resistor 141, and the voltage Vd2 corresponding to the second monitoring temperature 250 ° C. is output from the temperature setting resistor 141. When outputting, a switch-on signal instructing connection of the resistor R2 is output to the switch SW2 of the reset time setting resistor 151. Accordingly, the reset time setting resistor 151 outputs the reset voltage Vt2 generated by the resistors R1 and R2 to the reset IC 152. The reset IC 152 receives the reset voltage Vt2 and starts measurement by the timer 153.

  FIG. 4 is a flowchart showing processing at the time of monitoring the fixing temperature by the fixing temperature monitoring device 10.

  When the main power supply of the image forming apparatus 1 is turned on by the operation of the operation unit (not shown) by the operator (YES in S1), the control unit 11 sets the target temperature to 180 ° C. via the heater control unit 12. Energization to the heater 511 is started (S2). At this time, the control unit 11 acquires the temperature information of the heat roller 51 input as the voltage Vth from the temperature detection unit 13, and based on this temperature information, the temperature of the heat roller 51 reaches the target temperature of 180 ° C. The heater 511 is energized until such time.

  In the initial state when the main power is turned on, the switch SW1 in the protection circuit 100 of the fixing temperature monitoring device 10 is in the off state, and the resistor R5 is not connected between the resistors R3 and R4. The comparator 142 is in a state where the voltage Vd1 between the resistors R3 and R4, that is, the basic monitoring temperature voltage Vd1 corresponding to the basic monitoring temperature 190 ° C. is input from the temperature setting resistor 141.

  In this state, the temperature of the heat roller 51 is maintained at the target temperature 180 ° C. by the energization control of the heater 511 by the control unit 11, and the temperature of the heat roller 51 is monitored by the protection circuit 100 at the basic monitoring temperature 190 ° C. Is done. When the basic monitoring temperature voltage Vd1 exceeds the voltage Vth input from the temperature detection unit 13 (when the temperature of the heat roller 51 detected by the temperature detection unit 13 is higher than the basic monitoring temperature 190 ° C.). The comparator 142 outputs the energization stop signal that instructs the heater control unit 12 to stop energization of the heater 511. When the heater control unit 12 receives the energization stop signal, the heater control unit 12 stops energization of the heater 511.

  Here, the control unit 11 continues to control the heater at the target temperature of 180 ° C. until a print job indicating execution of continuous printing is received from a networked computer or the like (NO in S3, S2). Is received by the control unit 11 (YES in S3), the control unit 11 outputs a switch-on signal instructing connection of the resistor R2 to the switch SW2 of the reset time setting resistor 151 of the timer unit 15 (S4). ). Thereby, the reset time setting resistor 151 generates the reset voltage Vt2 by the resistors R1 and R2 and outputs the reset voltage Vt2 to the reset IC 152.

  The reset IC 152 receives the reset voltage Vt2, and causes the timer 153 to start measuring the predetermined time t1 (S5).

  At this time, the control unit 11 transmits a switch-on signal to the switch SW1 in the temperature setting resistor 141 of the protection circuit 100 (S6), and connects the resistor R5 between the resistors R3 and R4. As a result, the second monitoring temperature voltage Vd2 corresponding to the second monitoring temperature 250 ° C. is output from the temperature setting resistor 141 to the comparator 142. The comparator 142 receives the second monitoring temperature voltage Vd2 corresponding to the second monitoring temperature 250 ° C. and the voltage Vth indicating the temperature of the heat roller 51 from the temperature detection unit 13, and outputs the second monitoring temperature. The temperature of the heat roller 51 is monitored by comparing the working voltage Vd2 and the voltage Vth.

  When the control unit 11 should output the switch-on signal to the switches SW1 and SW2, if the control unit 11 is already in an uncontrollable state due to a phenomenon such as runaway, the control unit 11 switches on. Since no signal is output, the resistor R5 is not connected between the resistors R3 and R4, and the second monitoring temperature voltage Vd2 is not generated. That is, the monitoring temperature by the protection circuit 100 does not become the second monitoring temperature 250 ° C., but the basic monitoring temperature voltage Vd1 is generated by the resistors R3 and R4 that are always connected, and the basic monitoring temperature 190 ° C. is monitored. Is called.

  When the control part 11 is functioning normally, after S6, the control part 11 acquires the temperature information of the heat roller 51 inputted as the voltage Vth from the temperature detection part 13, and based on this temperature information. Thus, the heater 511 is energized until the temperature of the heat roller 51 reaches the target temperature 230 ° C. (NO in S7 and S8).

  When the temperature of the heat roller 51 indicated by the voltage Vth from the temperature detection unit 13 reaches 230 ° C. (YES in S8), the control unit 11 starts image formation and recording paper conveyance based on the print job, Conveyance and image formation are performed one by one from the first recording paper P (S9).

  At the time of execution of this print job, the temperature setting resistor 141 of the protection circuit 100 is in a state where the resistor R5 is connected between the resistors R3 and R4. Therefore, the temperature of the heat roller 51 is monitored at the second monitoring temperature 250 ° C. ing.

  Then, the control unit 11 determines that the recording paper P conveyed from the paper detection sensor 77 is in a state where the elapse of time t1 has not been measured by the timer 153 that has started measurement in S6 (NO in S10, NO in S14). When a paper-out signal indicating that the paper has passed through the fixing unit 5 is received (YES in S10), if the print job has not ended (NO in S11), the switch SW2 of the reset time setting resistor 151 of the timer unit 15 is set. Once the switch-off signal is output, the switch-on signal is output again (S13). Thereafter, the process returns to S5, and conveyance and image formation are performed for each subsequent recording sheet P1. As described above, when the process returns to S5 through the process of S13, the processes of S6 and S7 have already been started, and the monitoring of the temperature of the heat roller 51 at the second monitoring temperature of 250 ° C. and the heater The energization control to 511 is continued.

  Accordingly, the reset voltage Vt2 generated by the reset time setting resistor 151 is output to the reset IC 152, and the reset IC 152 that has received the reset voltage Vt2 starts measuring the predetermined time again by the timer 153. For this reason, monitoring of the temperature of the heat roller 51 at the second monitoring temperature 250 ° C. by the protection circuit 100 indicates that a further sheet of recording paper indicated by the predetermined time t1 is conveyed from the paper supply unit 4 and fixed. The time required for passing through the section 5 is extended. Then, the remaining recording paper P indicated by the print job is transported and an image is formed.

  In other words, as long as the control unit 11 is functioning normally, the control unit 11 receives a paper-out signal from the paper detection sensor 77, that is, every time one sheet of recording paper completes passing through the fixing unit 5. Since the switch-on signal is output to the switch SW2 of the reset time setting resistor 151 in S21, the recording unit is necessary for image formation of a print job indicating continuous printing, and the fixing unit is controlled by heater control at a target temperature of 230 ° C. The fixing operation according to 5 is continued.

  The control unit 11 continues the processes of S5 to S11 and S13 until there is no recording paper to be imaged according to the print job, completes image formation and recording paper conveyance indicated by the print job, and ends the print job. (YES in S11), a switch-off signal is transmitted to the switch SW1 of the temperature setting resistor 141 (S12), the resistor R5 is disconnected between the resistors R3 and R4, and the basic monitoring temperature 190 ° C. is set from the temperature setting resistor 141. The basic monitoring temperature voltage Vd1 corresponding to is output. At this time, the control unit 11 transmits a switch-off signal to the switch SW2.

  Thereafter, the control unit 11 again performs energization control to the heater 511 at the target temperature of 180 ° C. via the heater control unit 12. As a result, the temperature of the heat roller 51 is kept at 180 ° C., and the apparatus waits for input of the next print job.

  Note that during the execution of the processing from S5 to S14 according to the print job, the time until the control unit 11 receives the paper absence signal from the paper detection sensor 77 (NO in S10) is determined by the timer 153 that has started measurement in S6. When the elapsed time t1 is measured (YES in S14), the reset IC 152 outputs a switch-off signal that is an instruction to disconnect the resistor R5 from the switch SW1 of the temperature setting resistor 141 (S15). The voltage Vd1 corresponding to the monitoring temperature of 190 ° C is output. Thereafter, the process ends. When the conveyance of the recording paper P and the image formation based on the print job are resumed, for example, the processing is performed from the above S4.

  As a result, when the recording paper P is in an abnormal state in which the recording paper P does not pass through the fixing unit 5 within the time t1, the temperature monitoring returns to the basic monitoring temperature 190 ° C. When the conveyance of the recording paper P is interrupted in the fixing unit 5 while the recording paper P is sandwiched during the conveyance of continuous printing, the heater 511 is turned on when the temperature of the heat roller 51 exceeds the basic monitoring temperature 190 ° C. Since the control is stopped, overheating of the fixing unit 5 is prevented. In this case, the control unit 11 performs processing such as interrupting a print job as necessary.

  As described above, according to the protection circuit 100 according to the embodiment, when the control unit 11 switches the switch SW1 of the temperature setting resistor 141, the temperature setting resistor 141 has the voltage Vd1 corresponding to the basic monitoring temperature 190 ° C., Alternatively, when the voltage Vd2 corresponding to the second monitoring temperature 250 ° C. is output, the comparator 142 compares the voltage Vd1 or the voltage Vd2 with the voltage Vth indicating the temperature of the heat roller 51 input from the temperature detection unit 13. Will do. The comparator 142 outputs an energization stop signal to the heater 511 to the heater control unit 12 when it is indicated that the temperature of the heat roller 51 is higher than the basic monitoring temperature 190 ° C. or the second monitoring temperature 250 ° C. . For this reason, if the control unit 11 outputs a switch-on signal to the switch SW1 at the timing of executing, for example, continuous printing that requires a high fixing temperature, and connects the resistor R5 between the resistors R3 and R4, the control unit 11 The fixing temperature can be managed using the second monitoring temperature of 250 ° C. corresponding to the high fixing temperature.

  Further, the control unit 11 outputs a switch-on signal to the switch SW1 of the temperature setting resistor 141 and outputs a switch-on signal to the switch SW2 of the reset time setting resistor 151, so that the temperature is higher than the target temperature 180 ° C. The energization control of the heater 511 at the target temperature of 230 ° C. and the temperature monitoring at the second monitoring temperature of 250 ° C. are limited to the above time t1, and then the second monitoring temperature is switched to the basic monitoring temperature of 190 ° C. Thus, the temperature of the heat roller 51 can be monitored.

  Thereby, according to the fixing temperature monitoring apparatus 10 according to the present embodiment, the high temperature of the recording paper by the fixing unit 5 required as the printing speed is increased by switching the monitoring temperature according to the required fixing temperature. Heating can be accurately performed according to the recording paper conveyance state. Furthermore, according to the fixing temperature monitoring device 10, even when the control unit 11 becomes uncontrollable, as described above, monitoring is performed at the basic monitoring temperature of 190 ° C., so that recording is performed during conveyance of continuous printing. Even when the recording paper P abnormally stops in the nip portion between the fixing unit 5 or the heat roller 51 and the pressure roller 52 with the sheet P sandwiched, the fixing unit 5, the heat roller 51, or the recording paper P It becomes possible to prevent overheating.

  More preferably, the predetermined time measured by the timer 153 is the predetermined time t1 for the first recording paper P conveyed in accordance with the print job, and the second and subsequent recording papers. For the above, the time t2 from the time when one recording sheet P starts to be conveyed from the paper supply unit 4 by the conveying unit 3 to the time when it passes through the fixing unit 5 is set as the predetermined time. Since the temperature of the heat roller 51 has already reached the target temperature of 230 ° C. during the conveyance of the second and subsequent recording sheets P, the recording sheet P has started to be conveyed as described above for the predetermined time. By adopting the time t2 from the time point to the time point of passing through the fixing unit 5, it is possible to prevent overheating of the heat roller 51 with higher accuracy.

  The present invention is not limited to the configuration of the above embodiment, and various modifications can be made. For example, in the above-described embodiment, the temperature setting resistor 141 of the protection circuit 100 includes the resistor R5 that can be switched, and two monitoring temperatures are set by switching the connection of the resistor R5 by turning on and off the switch SW1. Although the voltage corresponding to the monitoring temperature of 190 ° C and the second monitoring temperature of 250 ° C is generated, the present invention is not limited to this. For example, there are a plurality of combinations of resistors capable of switching connections and switches for switching the connections of the resistors. The respective voltages corresponding to the monitored temperatures corresponding to the number of the combinations may be generated by switching the connection of the resistors by switching on and off the switches. According to this, the fixing temperature monitoring device 10 monitors the fixing temperature by changing the monitoring temperature as appropriate according to the conveyance status of the recording paper P, the image formation status, etc., using more monitoring temperatures. Is possible.

  In the above embodiment, a printer is used as an embodiment of the image forming apparatus according to the present invention. However, this is only an example, and other image forming apparatuses such as a multifunction peripheral and a copier are used. Other image forming apparatuses such as a facsimile machine may be used.

  Moreover, in the said embodiment, the structure and process which were shown by the said embodiment using FIG. 1 thru | or FIG. 4 are only one Embodiment of this invention, and are not the meaning which limits this invention to the said structure and process.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Image forming part 5 Fixing part 10 Fixing temperature monitoring apparatus 11 Control part 12 Heater control part 13 Temperature detection part 131 Thermistor 141 Temperature setting resistance 142 Comparator 15 Timer part 151 Reset time setting resistance 152 Reset IC
153 Timer 51 Heat roller 511 Heater 71 Paper detection sensor 77 Paper detection sensor 100 Protection circuit P Recording paper SW1, SW2 switch

Claims (3)

A temperature detection unit for detecting the temperature of a heat roller provided in the fixing unit;
A heater control unit for controlling energization of a heater for heating the heat roller;
A control unit that performs energization control of the heater for heating the heat roller to a target temperature according to the temperature detected by the temperature detection unit via the heater control unit,
A first resistor that is always connected; a second resistor that can be switched; and a first switch that switches the connection of the second resistor based on an instruction from the control unit. When the resistor is disconnected, the first resistor outputs a basic monitoring temperature voltage corresponding to a predetermined basic monitoring temperature, and the second resistor is connected by the first switch. A monitoring voltage output unit for outputting a second monitoring temperature voltage corresponding to a predetermined second monitoring temperature higher than the basic monitoring temperature by one resistor and a second resistor;
The voltage indicating the temperature of the heat roller input from the temperature detection unit is compared with the basic monitoring temperature voltage or the second monitoring temperature voltage input from the monitoring voltage output unit, and each of these voltages When it is shown that the roller temperature is higher than the basic monitoring temperature or the second monitoring temperature, an energization stop signal output unit for outputting an energization stop signal for stopping energization of the heater to the heater control unit; ,
A timer for measuring a preset time;
A second switch for switching the connection of the resistor based on an instruction from the control unit, and a predetermined basic voltage and a voltage value different from the basic voltage by switching the resistor by the second switch; A voltage output unit for outputting a reset voltage;
When the reset voltage is input from the voltage output unit, the timer starts measuring the predetermined time, and when the predetermined time is measured by the timer, the monitoring voltage output A switch switching unit that outputs an instruction to disconnect the second resistor from the first switch and outputs the basic monitoring temperature voltage;
When the control unit outputs an instruction to connect the second resistor to the first switch of the monitoring voltage output unit to output the second monitoring temperature voltage, the control unit outputs the second monitoring temperature voltage to the second switch of the voltage output unit. A fixing temperature monitoring device for outputting a reset voltage by outputting a connection switching instruction for the resistor. A detection unit for detecting that a recording medium to be fixed by the fixing unit has passed through the fixing unit;
The preset time, which is a measurement target of the timer, is a predetermined conveyance required for the recording medium to be conveyed from the recording medium storage unit to the position where the recording medium is completed to pass through the fixing unit. And a total time of a predetermined temperature rise time required for the heater to raise the heat roller from the basic monitoring temperature to the second monitoring temperature by the heater,
2. The control unit outputs a reset switching voltage by outputting a connection switching instruction of the resistor to the second switch of the voltage output unit every time the detection unit detects arrival of the recording medium. The fixing temperature monitoring device according to 1. The fixing temperature monitoring device according to claim 1 or 2,
An image forming unit for forming an image on the recording medium;
An image forming apparatus comprising: a fixing unit that fixes the recording medium after image formation by the image forming unit.