JP2006058684A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a fixing device with which the time required before the overheat on the surface of a heating roll is detected can be shortened and the safety of the fixing device can be assured. <P>SOLUTION: A microcomputer 69 captures the voltage from a first thermistor 77 via an A/D converter and captures the surface temperature T 1 of the paper pass portion of the heating roll. If the surface temperature T 1 is higher by the prescribed temperature ΔE than the temperature suitable for fixing processing, the microcomputer judges that the heating roll is in the overheated state and the microcomputer outputs a signal of a low level to an AND circuit 81 to turn a heater 41 off. An overheat detection circuit 71 outputs the signal of the low level to the AND circuit 81 to de-energize the heater 41 and to turn the heater 41 off if the surface temperature T 2 captured from a second thermistor 79 is higher by the prescribed temperature ΔE 2 than the temperature suitable for the fixing processing in a non-paper pass section of the heating roll. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fixing device, and more particularly, to a fixing device having a mechanism for preventing overheating of a heating roll incorporating a heater.

Conventionally, in order to prevent overheating of the heating roll of the fixing device of the image forming apparatus, a temperature sensor composed of a thermistor is disposed in contact with a non-sheet passing portion which is an end portion of the surface of the heating roll. It detects the surface temperature and controls the power supply to the heater built in the heating roll. In addition, a thermostat is disposed in a non-contact state on the paper passing portion of the surface of the heating roll, and this thermostat is connected in series to the heater, and the power supply is cut off when the heating roll is overheated to prevent overheating of the heating roll. ing.
JP2003-186330

  However, since the thermistor of the temperature sensor arranged in contact with the non-sheet passing portion as described above is in contact with the temperature sensor, it can detect the temperature with good followability to the temperature change. The temperature rise rate of the non-sheet passing part, which is the end of the heating roll, is slower than the temperature speed, so if the heating roll is heated at a large temperature rise rate, the thermistor cannot detect overheating of the outer surface of the center part of the heating roll. When the overheat state can be detected by the temperature of the non-sheet passing portion, the temperature of the central portion of the heating roll is greatly increased over the overheating temperature, which may cause thermal damage to the heating roll and its peripheral portion. was there.

  In addition, since the thermostat arranged in a non-contact state as described above has poor followability to temperature changes, it is constant until the thermostat is heated to the operating temperature after the outer surface of the heating roll exceeds a predetermined superheat temperature. Therefore, there is a problem that heat damage may occur in the heating roll and its peripheral portion during the delay time, as in the case of the thermistor.

  The present invention has been made to solve the above-described problems, and it takes a short time to detect that the temperature of the outer surface of the heating roll has been raised to the superheat temperature, and even if the fixing device is in an abnormal state. An object of the present invention is to provide a fixing device that ensures safety.

  In order to achieve the above object, a fixing device according to the present invention is configured so that a rotatable heating roll having a built-in heater faces a sheet passing portion on the surface of the heating roll and does not come into contact with the heating roll. A non-contact type sensor that includes a thermistor that is disposed and detects a surface temperature of the sheet passing portion of the heating roll; and a non-sheet passing portion of the heating roll that is disposed in contact with the non-sheet passing portion of the surface of the heating roll. When the surface of the heating roll is overheated based on the surface temperature detected by any one of the contact-type sensor and the non-contact-type sensor or the contact-type sensor, the power to the heater is detected. And a shut-off means for shutting off the supply.

  According to the present invention, a non-contact sensor including a thermistor that is disposed so as to face a sheet passing portion on the surface of a heating roll having a built-in heater and that does not come into contact with the heating roll includes: The surface temperature of the part is detected. Further, a contact type sensor arranged in contact with the non-sheet passing portion on the surface of the heating roll detects the surface temperature of the non-sheet passing portion of the heating roll. And the interruption | blocking means interrupts | blocks the electric power supply to a heater, when the surface of a heating roll overheats based on the surface temperature detected by either one of a non-contact type sensor and a contact type sensor.

  In the present invention, since the temperature of the sheet passing portion having the highest temperature when heated is detected using a thermistor that has good followability to temperature changes, the time required to detect overheating is short, and Since the overheat state is detected using the non-contact sensor and the contact sensor, the safety of the fixing device can be ensured more reliably.

  Here, the blocking means is detected by the first overheat determining means for determining whether or not the surface of the heating roll is overheated based on the surface temperature detected by the non-contact type sensor, and the contact type sensor. One of the second overheat determining means, the first overheat determining means and the second overheat determining means for determining whether or not the surface of the heating roll is in an overheated state based on the surface temperature Based on one determination, it can be configured to include a power cut-off means for cutting off the power supply to the heater when the surface of the heating roll is overheated.

  Further, the fixing device according to the present invention adjusts the power supply to the heater based on the surface temperature detected by the non-contact sensor so that the surface temperature of the sheet passing portion of the heating roll is within a predetermined range. It is possible to further include a power adjustment means.

  The power adjustment means includes a fixing temperature judgment means for judging whether or not the surface temperature of the sheet passing portion of the heating roll is equal to or higher than a predetermined temperature based on the surface temperature detected by the non-contact type sensor, and a fixing temperature judgment. And a power supply adjusting unit that adjusts the power supply to the heater so that the surface temperature of the sheet passing portion is in a predetermined range based on the determination of the unit.

  Further, the fixing device according to the present invention is disposed so as to face the paper passing portion on the surface of the heating roll and not to contact the heating roll, and is heated when radiated from the surface of the heating roll. The power supply stop means for stopping the power supply to the heater can be further included.

  According to this configuration, since the power supply stop unit can stop the power supply to the heater when the heating roll is overheated even if the shut-off unit fails, the safety of the fixing device can be ensured.

  As described above, according to the fixing device of the present invention, the temperature of the sheet passing portion having the highest temperature is detected when heated by using a thermistor having good followability to a temperature change. The time required to detect the toner is short, and since the overheat state is detected using the non-contact type sensor and the contact type sensor, the effect that the safety of the fixing device can be ensured more reliably is obtained. .

  Embodiments of the present invention will be described below with reference to the drawings.

  As shown in FIG. 1, a photosensitive drum 2 is rotatably disposed in a four-cycle full-color printer main body 1 at an upper right portion slightly from the center. As this photosensitive drum 2, for example, a drum made of a conductive cylinder having a diameter of about 47 mm and having a surface coated with a photosensitive layer made of OPC or the like is used. It is driven to rotate at a process speed of / sec. The surface of the photosensitive drum 2 is charged to a predetermined potential by a charging roll 3 disposed almost directly below the photosensitive drum 2 and then ROS (Raster) disposed at a position just below the photosensitive drum 2. An output scanner 4 performs image exposure with a laser beam (LB), and an electrostatic latent image corresponding to the image information is formed. The electrostatic latent image formed on the photosensitive drum 2 is a rotary development in which yellow, magenta, cyan, and black (YMCK) developing devices 5Y, 5M, 5C, and 5K are arranged along the circumferential direction. The image is developed by the apparatus 5 and becomes a toner image of a predetermined color.

  At this time, charging, exposure and development processes are repeated a predetermined number of times on the surface of the photosensitive drum 2 in accordance with the color of the image to be formed. In the rotary developing device 5, the corresponding color developing devices 5 </ b> Y, 5 </ b> M, 5 </ b> C, and 5 </ b> K move to a developing position facing the photosensitive drum 2. For example, when forming a full-color image, charging, exposure, and development processes are repeated four times on the surface of the photosensitive drum 2 corresponding to each color of YMCK. , YMCK toner images corresponding to the respective colors are sequentially formed.

  The YMCK toner images sequentially formed on the photosensitive drum 2 are transferred onto the intermediate transfer belt 6 at the primary transfer position where the intermediate transfer belt 6 as an intermediate transfer member is wound around the outer periphery of the photosensitive drum 2. Are primarily transferred by the primary transfer roll 7 while being superimposed on each other. The YMCK toner images transferred in multiple onto the intermediate transfer belt 6 are secondarily transferred collectively onto the recording paper 9 fed at a predetermined timing by the secondary transfer roll 8. The recording paper 9 is fed by a pickup roll 11 from a paper feed cassette 10 disposed at the lower part of the full-color printer main body 1, and is fed in a state where it is rolled one by one by a feed roll 12 and a retard roll 13. The roller 14 is conveyed to the secondary transfer position of the intermediate transfer belt 6 in synchronization with the toner image transferred onto the intermediate transfer belt 6.

  The intermediate transfer belt 6 is stretched by a plurality of rolls, and is driven as the photosensitive drum 2 rotates, for example, so as to circulate at a predetermined process speed (about 150 mm / sec).

  Further, the recording paper 9 onto which the toner image is transferred from the intermediate transfer belt 6 is conveyed to the fixing device 27 as shown in FIG. The fixing device 27 includes a heating roll 30, a pressure roll 31, and a discharge roll 28. The toner image is melted and fixed on the recording paper 9 by heat and pressure by the fixing device 27 and discharged onto a discharge tray 29 provided on the upper portion of the printer main body 1 by a discharge roll 28.

  As shown in FIG. 2, a heater 41 is disposed in a hollow portion formed along the axis of the heating roll 30 of the fixing device 27. Both ends of the heater 41 are connected to power supply wiring.

  A first temperature sensor 51 for detecting the surface temperature of the sheet passing portion 30A of the heating roll 30 heated by the heater 41 faces the sheet passing portion 30A of the heating roll 30 and is separated from the heating roll 30 by, for example, 5 mm. The thermostat 47 is also disposed so as to face the paper passing portion 30 </ b> A of the heating roll 30 and not to contact the heating roll 30. A second temperature sensor 53 for detecting the surface temperature of the non-sheet passing portion 30B of the heating roll 30 is disposed in the non-sheet passing portion 30B of the heating roll 30 in a contact state.

  The thermostat 47 is connected in series with an AC power supply (not shown). Here, the thermostat 47 has a predetermined operating temperature, and when a built-in bimetal (not shown) is heated to a predetermined operating temperature by radiant heat from the heating roll 30, a pair of metals constituting the bimetal is formed. The pieces are separated by thermal expansion and the power supply to the heater 41 is cut off.

  Next, a circuit configuration relating to heating control of the heating roll 30 will be described. As shown in FIG. 3, the circuit relating to the heating control includes a heater 41, an SSR (Solid State Relay) 61, a power save switch 83, an overheating relay 63, a transistor 65, and a first temperature sensor 51. And a second temperature sensor 53 and a control board 67 for controlling on / off of the SSR 61 and the overheating relay 63.

  The SSR 61 includes a diode 61A and a triac 61B, and the diode 61A is connected to, for example, a 5-volt DC power source. When a current flows from the DC power source to the diode 61A, the triac 61B is turned on.

  For example, when the power consumption of a plurality of DC power sources connected to the circuit of FIG. 3 exceeds a predetermined power, the power save switch 83 turns off the switch.

  The overheating relay 63 includes an exciting coil 63A and normally open contacts 63B and 63C. When a current flows through the exciting coil 63A, the normally open contacts 63B and 63C are turned on.

  One end of the heater 41 is connected to the triac 61B of the SSR 61 via the wiring 45, and the other end of the heater 41 is connected to the power save switch 83 via the wiring 43. The power save switch 83 is connected to the normally open contact 63 </ b> C of the overheating relay 63. The triac 61B is connected to the normally open contact 63B of the overheating relay 63, and either one of the normally open contacts 63B and 63C is connected to the AC power source, and the other is connected to the thermostat 47.

  One end of the exciting coil 63A of the overheating relay 63 is grounded, the other end is connected to the collector terminal of the transistor 65, and the emitter terminal of the transistor 65 is connected to a DC power source of, for example, 24 volts.

  The first temperature sensor 51 includes an infrared absorbing sheet (not shown) that converts infrared rays emitted from the surface of the heating roll 30 into heat, and a first thermistor 77 that detects the temperature of the infrared absorbing sheet. The second temperature sensor 53 includes a second thermistor 79.

  The control board 67 includes a microcomputer 69, an AND circuit 81, an overheat detection circuit 71 for detecting that the non-sheet passing portion 30B on the surface of the heating roll 30 has reached a predetermined overheat temperature, and a first thermistor 77. And an A / D converter (not shown) that converts an analog quantity indicating a temperature detection result into a digital value. The microcomputer 69 includes a CPU, a ROM, and a RAM. The overheat detection circuit 71 is configured by a comparator or the like.

  One end of each of the first thermistor 77 and the second thermistor 79 is connected to a DC power source of 5 volts, for example. The other end of the first thermistor 77 is connected to the overheat detection circuit, and the input terminal of the microcomputer 69 is connected to the other end of the second thermistor 79.

  One of the output terminals of the microcomputer 69 is connected to the diode 61 </ b> A of the SSR 61, and the other output terminal is connected to the input terminal of the AND circuit 81.

  The output terminal of the overheat detection circuit 71 is connected to the input terminal of the AND circuit 81. The output terminal of the AND circuit 81 is connected to the base terminal of the transistor 65.

  Hereinafter, the operation of the present embodiment will be described. When the power supply of the full color printer 1 is turned on, the microcomputer 69 of the control board 67 executes a heating control processing routine of the heating roll 30 shown in FIG.

  First, in step 100, a high level signal is output to the AND circuit 81. Here, if a high level signal is output from the overtemperature detection circuit 71 to the AND circuit 81, the AND circuit 81 outputs a high level signal to the transistor 65. In the transistor 65, a current flows from the emitter to the collector. Then, the exciting coil 63A of the overheating relay 63 is excited and the normally open contacts 63B and 63C are turned on. In the next step 102, the voltage from the first thermistor 77 is taken in via the A / D converter, and the surface temperature T1 of the paper passing portion 30A of the heating roll 30 is taken in by the voltage level. In the next step 104, it is determined whether or not fixing processing is in progress. If the determination is affirmative, the process proceeds to step 106, but the determination is denied and the process proceeds to step 108 if the fixing process is on standby.

  In step 108, the surface temperature T1 of the sheet passing portion 30A of the captured heating roll 30 is lower by a predetermined temperature ΔK (45 ° C. as an example) than the temperature suitable for the fixing process (= fixing temperature, 210 ° C. as an example) That is, it is determined whether or not the fixing temperature −ΔK = 165 ° C., hereinafter referred to as standby temperature).

  If the surface temperature T1 of the sheet passing portion 30A of the heating roll 30 is equal to or lower than the standby temperature, the determination in step 108 is affirmed, the process proceeds to step 110, and a low level signal is output to the diode 61A of the SSR 61. A current flows through the diode 61A of the SSR 61, the triac 61B is turned on, and the heater 41 is energized. Thereby, the heater 41 generates heat, and the surface temperature T1 of the paper passing portion 30A of the heating roll 30 rises due to this heat.

  If the surface temperature T1 of the sheet passing portion 30A of the heating roll 30 is equal to or higher than the standby temperature, the determination in step 108 is negative, and a high level signal is output to the diode 61A of the SSR 61 in step 112, whereby current is supplied to the diode 61A. The flow stops and the triac 61B is turned off. Then, the energization to the heater 41 is stopped and the heater 41 is turned off. Thereby, the heat generation of the heater 41 is stopped, and the surface temperature T1 of the sheet passing portion 30A of the heating roll 30 is lowered. In this way, the power supply to the heater 41 is adjusted so that the surface temperature of the sheet passing portion 30A of the heating roll 30 is within a predetermined range by controlling the SSR 61 on and off.

  Next, if the fixing process is in progress, the determination in step 104 is affirmed, and in step 106, whether or not the surface temperature T1 of the sheet passing portion 30A of the heating roll 30 taken in in step 102 has dropped below the fixing temperature. Determine. If the determination is affirmative, the process proceeds to step 110, a low level signal is output to the diode 61A of the SSR 61, and the heater 41 is energized. If the determination is negative, the process proceeds to step 112, to the diode 61A of the SSR 61. The high level signal is output, and the energization to the heater 41 is stopped.

  In the next step 114, heating is performed by determining whether or not the surface temperature T1 captured in step 102 is higher than a fixing temperature by a predetermined temperature ΔE (40 ° C. as an example) (ie, fixing temperature + ΔE = 250 ° C.). It is determined whether or not the roll 30 is in an overheated state. If the determination is negative, the process returns to step 102, but if the determination is affirmative, the process proceeds to step 116.

  If it is determined that the heating roll 30 is in an overheated state, in step 116, a low level signal is output to the AND circuit 81, and the AND circuit 81 outputs a low level signal to the transistor 65. In the transistor 65, the current from the emitter to the collector is stopped, the energization to the overheating relay 63 is stopped, and the normally open contacts 63B and 63C are turned off by the de-energized state, and the energization to the heater 41 is performed. Stop and turn off the heater 41. Thereby, the heat generation of the heater 41 is stopped, the surface temperature T1 of the heating roll 30 is lowered, and the process of FIG.

  Next, the operation of the overheat detection circuit 71 will be described.

  First, the surface temperature T2 of the non-sheet passing portion 30B of the heating roll 30 is a predetermined temperature ΔE2 (20 as an example) rather than a temperature suitable for the fixing process in the sheet passing portion 30B (= second fixing temperature, 180 ° C. as an example). The voltage (hereinafter referred to as a reference voltage) supplied from the second thermistor 79 when the temperature becomes higher by 2 ° C. (that is, the second fixing temperature + ΔE2 = 200 ° C., hereinafter referred to as overheating temperature) is excessive. The temperature detection circuit 71 is set. The overheat detection circuit 71 compares the supplied voltage with a reference voltage, and outputs a low level signal if it is higher than the reference voltage, and outputs a high level signal if it is lower than the reference voltage.

  When the voltage of the electric power supplied from the second thermistor 79 is lower than the reference voltage, the overtemperature detection circuit 71 outputs a high level signal to the AND circuit 81, and the AND circuit 81 also receives a high signal from the microcomputer 69. When a level signal is input, a high level signal is output to the transistor 65. As a result, the normally open contacts 63B and 63C of the overheating relay 63 are turned on, and the heater 41 is energized to turn on the heater 41.

  On the other hand, when the voltage of the power supplied from the second thermistor 79 is higher than the reference voltage, the overtemperature detection circuit 71 outputs a low level signal to the AND circuit 81, so that a low level signal is sent to the transistor 65. Output. As a result, the normally open contacts 63B and 63C of the overheating relay 63 are turned off, the energization to the heater 41 is stopped, and the heater 41 is turned off.

  As described above, according to the fixing device in the embodiment of the present invention, the surface of the heating roll 30 having the highest temperature when heated using the first thermistor 77 having good followability to temperature changes. By detecting the temperature of the sheet passing portion 30A, the time required to detect that the temperature of the surface of the heating roll 30 has been raised to the superheat temperature can be shortened.

  Even if the first temperature sensor 51 breaks down due to the winding of the recording paper, the second temperature sensor 53 can detect the overheating state, so that the safety of the fixing device can be ensured. Even if the microcomputer 69 or the SSR 61 breaks down, the power supply to the heater 41 can be controlled by the overheat detection circuit 71 and the overheat relay 63, and the safety of the fixing device can be ensured. Further, even if the overheat detection circuit 71 or the overheat relay 63 breaks down, the overheating state of the heating roll 30 is detected by the thermostat 47 or the power save switch 83, the power supply to the heater 41 is stopped, and the fixing device Safety can be ensured.

  In the microcomputer 69, the output time of the low level signal to the diode 61A of the SSR 61 is calculated as a countermeasure for the disconnection of the first temperature sensor 51. Alternatively, a low level signal may be output to the AND circuit 81 to turn off the normally open contacts 63B and 63C of the overheating relay 63.

1 is a configuration diagram showing a main part of a full-color printer in an embodiment of the present invention. 1 is a perspective configuration diagram illustrating a schematic configuration of a fixing device according to an embodiment of the present invention. It is a circuit diagram which shows the circuit which performs the heating control of the heating roll in embodiment of this invention. 6 is a flowchart showing an operation of a control board of the fixing device in the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Full color printer 30 Heating roll 31 Pressure roll 41 Heater 47 Thermostat 51 1st temperature sensor 53 2nd temperature sensor 67 Control board 77 1st thermistor 79 2nd thermistor

Claims (3)

A rotatable heating roll with a built-in heater;
A non-contact type sensor that includes a thermistor that is disposed so as to face the paper passing portion on the surface of the heating roll and not to contact the heating roll, and that detects the surface temperature of the paper passing portion of the heating roll;
A contact-type sensor that is disposed in contact with the non-sheet passing portion of the surface of the heating roll and detects the surface temperature of the non-sheet passing portion of the heating roll;
Based on the surface temperature detected by any one of the non-contact type sensor and the contact type sensor, when the surface of the heating roll is overheated, a cutoff unit that cuts off the power supply to the heater;
Including a fixing device.   Based on the surface temperature detected by the non-contact type sensor, further includes a power adjusting unit that adjusts the power supply to the heater so that the surface temperature of the paper passing portion of the heating roll is within a predetermined range. The fixing device according to claim 1, further comprising:   A power supply that is disposed so as to face the paper passing portion on the surface of the heating roll and not to contact the heating roll, and stops power supply to the heater when overheated by radiant heat from the surface of the heating roll. The fixing device according to claim 1, further comprising a stopping unit.

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