JP2010066614A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing temperature rise in such a state that a fixing roller is not rotated. <P>SOLUTION: The output of a comparator 54 and the on/off signals of a heater from an MPU (Micro Processing Unit) 1 are inputted to an AND gate circuit 55 and control is performed so that the detection temperature of a thermistor 18 is held for a preheating temperature, a fixing temperature or the like. Meanwhile, a motor off signal is inputted to a transistor Tr2, so that in such a state that the fixing roller is rotated, a threshold voltage Vth becomes high and in such a state that the fixing roller is not rotated, the threshold voltage Vth becomes low. When the temperature of a fixing unit rises and a voltage Va at the a-point is higher than the threshold voltage Vth, a triac 52 is turned off and the energization of the fixing unit is interrupted to prevent the overheating of the fixing unit. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus having a function of restricting energization to a heater of a fixing device.

  In an electrophotographic image forming apparatus in which toner adhered to a recording paper corresponding to print image information is fixed on the recording paper by heating at a fixing unit, the photosensitive member is modulated by light modulated based on the print image information. An electrostatic latent image is formed on the surface. Then, the toner is attached to the photosensitive member on which the electrostatic latent image is formed and developed. After the toner attached to the photosensitive member is transferred to the recording paper, the recording paper to which the toner is attached is heated by a fixing heater. The toner is fixed on the recording paper by a fixing roller.

  In an electrophotographic image forming apparatus having a thermal fixing unit used in such a facsimile machine or a copying machine, the temperature of the fixing device is detected using a thermistor or the like, and the temperature of the fixing device is a preheating temperature or a fixing temperature. And so on. That is, when the temperature of the fixing device is higher than the above temperature, the power supply to the heater is stopped by the system control, and when it becomes lower, the power supply is controlled to resume.

  If the heater of the fixing device is turned on at the start of recording, it takes time to be able to print, and the user is kept waiting. For this reason, the time from the start of recording until the fixing temperature is reached, that is, the fixing start-up time, is usually shortened by raising the temperature of the fixing device to the preheating temperature immediately after the power is turned on and setting the standby state.

In addition, when the temperature of the fixing device exceeds a certain temperature, the components constituting the fixing device are thermally deformed and deteriorated, so the temperature of the fixing device is slightly higher than the fixing temperature (safety temperature). When it becomes higher, the heater energization circuit is shut off (see, for example, Patent Document 1).
JP-A-4-320573

  In the image forming apparatus as described above, when the fixing speed is fast, that is, when the paper transport speed is fast, the amount of heat taken away from the fixing roller is increased, so that the fixing set temperature is increased. Further, in recent years, since it has been demanded to increase the number of printed sheets per minute (PPM), the fixing temperature is increasing.

  For this reason, as described above, even if the heater power is turned off when the temperature of the fixing device becomes higher than the safe temperature, if the fixing temperature becomes high and the difference from the safe temperature becomes small, the device Depending on the operation state, the temperature of the fixing device may exceed the safe temperature. For example, while the fixing roller is rotating, the heat removal is large and the possibility of exceeding the safe temperature is low, but if the fixing between print jobs is not fixed, that is, the fixing roller is not rotating, the heat removal is There is little possibility of exceeding the safe temperature.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of preventing a temperature rise in a state where a fixing roller is not rotating.

  In order to achieve the above-described object, the image forming apparatus of the present invention has a threshold temperature (safe temperature) for comparing the temperature of the fixing device between the state where the fixing roller is rotating and the state where the fixing roller is not rotating. It is characterized by switching between. That is, the threshold temperature to be compared with the temperature of the fixing device is increased when the fixing roller is rotating, and the threshold temperature is decreased when the fixing roller is not rotating.

  According to the image forming apparatus of the present invention, when the fixing roller is not rotating, the temperature is set to a lower safe temperature. Therefore, the heat of the fixing device is abnormally increased with little heat removal and the fixing roller not rotating. It is possible to prevent the thermal deformation and thermal alteration of the members constituting the fixing device.

Hereinafter, an embodiment in which the image forming apparatus of the present invention is applied to a digital multifunction machine having a copying function, a facsimile function, a printing function, a scanner function, and the like will be described.
FIG. 1 is a schematic block diagram showing the hardware configuration of a digital multi-function peripheral. As shown in the figure, the digital multi-function peripheral has an MPU (Micro Processing Unit) 1, ROM (Read Only Memory) 2, SRAM (Static Random Access Memory). 3) Memory controller 4, image memory 5, codec 6, modem 7, network control unit NCU8, scanner 9, operation panel 10, printer image processing circuit 11, printer mechanism control circuit 12, LAN interface (I / F) 13 Etc., and each part is connected via a bus 14.

  The MPU 1 controls each part of the hardware of the digital multifunction peripheral via the bus 14 and executes various programs based on the programs stored in the ROM 2. The ROM 2 stores various programs and operation messages necessary for the operation of the digital multi-function peripheral, and the SRAM 3 stores temporary data generated when the program is executed.

  The memory controller 4 controls writing and reading of image data to and from the image memory 5, and the image memory 5 is configured using an SDRAM or the like, and stores image data to be transmitted, received image data, or read image data. The codec 6 encodes and decodes in accordance with a predetermined encoding method. In order to transmit the image data of the read original, the codec 6 is encoded by the MH, MR, or MMR method, and the image data received from the outside is decoded. To do.

  The modem 7 is connected to the bus 14 and has a function as a fax modem capable of facsimile communication. The modem 7 is similarly connected to the NCU 8 connected to the bus 14. The NCU 8 is hardware for closing and opening an analog line, and connects the modem 7 to the public switched telephone network (PSTN) as necessary.

  The scanner 9 includes a reading document placing table such as an auto document feeder (ADF) or a flatbed scanner (FBS), reads a document using a CCD or the like, and outputs dot image data. In addition, the operation panel 10 includes a display unit that displays an operation state of the digital multi-function peripheral and an operation screen for various functions, and a plurality of keys for operating the digital multi-function peripheral.

  Further, the printer image processing circuit 11 processes the print image signal and inputs it to the printer engine 15, and the printer mechanism control circuit 12 controls the printer engine 15 to print out the received image data, copy original data, and the like. To do. The fixing device heater 16 of the printer engine 15 is heated by a commercial AC power supply AC via a heater on / off control switch 17, and the output of the thermistor 18 for detecting the temperature of the fixing device is input to the printer mechanism control circuit 12. .

  The LAN interface 13 is connected to the LAN and receives signals from the Internet, while transmitting signals and data to the LAN, and executes interface processing such as signal conversion or protocol conversion.

  The digital multi-function peripheral has the above-described configuration. When sending a facsimile, the image data of the original is read by the scanner 9, and the read image signal is compressed by the codec 6 and is sent to the image memory 5 via the memory controller 4. Accumulated in. The compressed image data is read from the image memory 5, modulated by the modem 7, and transmitted from the NCU 8 to the communication partner through the PSTN. At the time of facsimile reception, the received image data is demodulated by the modem 7 and stored in the image memory 5 via the memory controller 4. Thereafter, the image data stored in the image memory 5 is decoded by the codec 6, and printing is performed by supplying a print image signal to the printer engine 15 via the printer image processing circuit 11.

Next, details of the structure of the printer engine 15 will be described with reference to FIG.
The printer engine 15 includes a photosensitive drum 21 as an image carrier that is rotationally driven at a predetermined speed. Around the photosensitive drum 21, a transfer roller 22, a memory removal brush 23, a charging corona charger 24, an LED print head 25, and a developing device 27 are arranged in the rotation direction (the arrow direction in the drawing). A fixing device 28 is provided on the sheet discharge side of the photosensitive drum 21.

  The memory removal brush 23 removes residual toner, paper dust, and the like on the surface of the photosensitive drum 21 after each toner image transfer process is completed, and removes the charge to prepare for the next image forming process. The charging corona charger 24 is a charger that uniformly charges the surface of the photosensitive drum 21, and the LED print head 25 exposes an image on the surface of the photosensitive drum 21 to form an electrostatic latent image. It is.

  The developing device 27 includes a developing roller 29, a supply roller 30, and a stirring paddle 31. The supply roller 30 supplies toner to the developing roller 29, and the agitation paddle 31 stirs the developer made up of toner and carrier replenished from a toner replenishing unit (not shown) along the bottom of the developing roller 29. Supply to the surface.

  The transfer bias high voltage generator 32, the memory removal brush high voltage generator 33, the charging bias high voltage generator 34, and the development bias high voltage generator 35 are controlled by the printer mechanism control circuit 12 to generate a high voltage. And supply to each part. The current detection resistor 36 detects a current supplied to the charging corona charger 24 and inputs it to the printer mechanism control circuit 12.

On the other hand, the fixing device 28 includes a heat roller 37 and a nip roller 38 that is pressed against the heat roller 37 and rotates. A halogen lamp 39 as a heater is disposed on the central axis of the heat roller 37 and is turned on by a commercial AC power supply AC. . The thermistor 18, which is a temperature detection element provided in contact with the heat roller 37, detects the temperature of the heat roller 37. Based on the output of the thermistor 18, the MPU 1 controls the heater on / off control switch 17 via the printer mechanism control circuit 12 to control the temperature of the heat roller 37 to the standby temperature, the fixing temperature, and the like. .
The motor 40 is a motor for rotating each rotating part of the printer mechanism, and is controlled by the printer mechanism control circuit 12 via the motor driver 41.

  The printer engine is configured as described above. When an image is formed by this printer engine, the surface of the photosensitive drum 21 is uniformly charged by the charging corona charger 24. Next, an electrostatic latent image is formed by exposing the surface of the charged photosensitive drum 21 with light for image formation emitted from the LED print head 25 according to image data. The electrostatic latent image formed on the photosensitive drum 21 in this way is developed into a visible toner image by the developing device 27 with toner. These visible toner images are sequentially transferred onto the paper by the charging action of the transfer roller 22, and then the paper on which the toner image has been transferred is heated and pressed by the fixing device 28 to fix the toner image. It is discharged to a paper part (not shown).

Next, the configuration of the heater on / off control circuit in the printer mechanism control circuit 12 will be described with reference to FIG. As shown in the figure, the heater on / off control switch 17 includes a photocoupler 51 and a triac 52.
The voltage Va at the terminal a obtained by dividing the power supply voltage Vcc by the thermistor 18 and the resistor R1 is a voltage corresponding to the temperature. This voltage Va is converted into a digital value by the A / D converter 53 and sent to the MPU1. At the same time, it is input to the negative terminal of the comparator 54. The voltage obtained by dividing the power supply voltage Vcc by the resistors R2, R3, and R4, that is, the voltage at the point b is input to the + terminal of the comparator 54 as the threshold voltage Vth.

  The transistor Tr2 receives a motor off signal, that is, a signal that is turned on when the motor 40 is not driven by the motor driver 41. Therefore, when the motor 40 is driven by the motor driver 41, that is, when the heat roller 37 is rotating, the transistor Tr2 becomes non-conductive, so the threshold voltage Vth increases. On the other hand, when the motor 40 is not driven by the motor driver 41, that is, when the heat roller 37 is not rotating, the transistor Tr2 is turned on, so the threshold voltage Vth is low.

  The AND gate circuit 55 receives the output of the comparator 54 and the heater on / off signal from the MPU 1. The MPU 1 turns off the heater signal when the temperature is higher than the above temperature so that the temperature of the heat roller 37 from the A / D converter 53 is maintained at the preheating temperature or the fixing temperature, and outputs the heater signal when the temperature is lower. Execute control to turn on.

  The heater on / off control circuit is configured as described above. When the output of the comparator 54 is at the H level, the heater on / off signal from the MPU 1 is input to the transistor Tr1. Therefore, when the heater on signal is input from the MPU 1, the transistor Tr 1 is turned on, and the triac 52, that is, the heater on / off control switch 17 is turned on via the photocoupler 51. As a result, the commercial AC power supply AC is supplied to the halogen lamp 39 of the fixing device 28, so that the heat roller 37 is heated. When the heater off signal is input from the MPU 1, the transistor Tr1 is turned off, and the heater on / off control switch 17 is turned off.

  On the other hand, the thermistor 18 exhibits a low resistance value when the ambient temperature is high, and exhibits a high resistance value when the ambient temperature is low. Therefore, the voltage Va at the point a where the power supply voltage Vcc is divided by the thermistor 18 and the resistor R1 is a high voltage when the temperature of the fixing device 28 is high and a low voltage when the temperature is low. When the temperature of the fixing device 28 rises and the voltage Va at the point a becomes higher than the threshold voltage Vth, the output of the comparator 54 becomes L level, so that the output of the AND gate circuit 55 also becomes L level. For this reason, the triac 52, that is, the heater on / off control switch 17 is turned off, and the energization to the halogen lamp 39 is interrupted, so that overheating of the fixing device can be prevented.

  As described above, when the heat roller is not rotating, the threshold voltage Vth input to the comparator is set to a low value, so that the heat of the fixing device is reduced while the heat roller is not rotating and the heat roller is not rotating. Prevents abnormal rise.

In the above embodiment, the threshold voltage input to the comparator is switched according to whether the fixing device drive system rotates or not. However, the temperature of the fixing device is compared by two comparators having different threshold temperatures. You can also.
Hereinafter, the heater on / off control circuit including two comparators will be described with reference to FIG. 4. However, the hardware configuration of the digital multi-function peripheral and the structure of the printer engine are the same as those in FIGS. To do.

  The voltage Va at the terminal a obtained by dividing the power supply voltage Vcc by the thermistor 18 and the resistor R1 is converted into a digital value by the A / D converter 53 and sent to the MPU 1 and also input to the negative terminals of the comparators 56 and 57. The Among the two threshold voltages obtained by dividing the power supply voltage Vcc by the resistors R2, R3, and R4, the high threshold voltage Vth1 is input to the + terminal of the comparator 56, and the low threshold voltage Vth2 is input to the + terminal of the comparator 57. Is done.

  The outputs of these comparators 56 and 57 are input to a selector 58 to which a motor on / off signal is input. The selector 58 inputs the output of the comparator 56 to the AND gate circuit 55 when the motor on / off signal is on, and inputs the output of the comparator 57 to the AND gate circuit 55 when the motor on / off signal is off.

  On the other hand, the output of the selector 58 and the heater on / off signal from the MPU 1 are input to the AND gate circuit 55. When the output of the selector 58 is at the H level, the transistor Tr1 is controlled by the heater on / off signal from the MPU 1. Is done. Therefore, when the heater-on signal is input from the MPU 1, the transistor Tr1 is turned on, the triac 52 is turned on via the photocoupler 51, the commercial AC power supply AC is supplied to the halogen lamp 39, and the heat roller 37 is heated. .

  When the motor 40 is driven, since the output of the comparator 56 is selected by the selector 58, the temperature of the fixing device 28 rises, and the voltage Va at the point a becomes higher than the high threshold voltage Vth1. In this case, the output of the comparator 56 becomes L level. As a result, the output of the AND gate circuit 55 becomes L level, the triac 52 is turned off, and energization to the halogen lamp 39 is interrupted, so that overheating of the fixing device can be prevented.

  On the other hand, when the motor 40 is not driven, since the output of the comparator 57 is selected by the selector 58, the temperature of the fixing device 28 rises, and the voltage Va at the point a becomes higher than the low threshold voltage Vth2. In this case, the output of the comparator 57 becomes L level. As a result, the output of the AND gate circuit 55 becomes L level, the triac 52 is turned off, and the energization to the halogen lamp 39 is interrupted.

  As described above, by selecting the outputs of the two comparators having different threshold temperatures, the threshold voltage can be set lower when the heat roller is not rotating. Therefore, similarly to the above, it is possible to prevent the temperature of the fixing device from rising abnormally with little heat removal and the heat roller not rotating.

  In the above embodiment, the case where the image forming apparatus of the present invention is applied to a digital multi-function peripheral has been described. However, the image forming apparatus of the present invention is also applicable to other image forming apparatuses such as a facsimile machine and a copying machine. it can.

2 is a block diagram illustrating a hardware configuration of a digital multifunction peripheral. FIG. It is a figure which shows the detail of the structure of a printer engine. It is a figure which shows the on / off control circuit of a heater. It is a figure which shows the other Example of the on / off control circuit of a heater.

Explanation of symbols

18 Thermistor 51 Photocoupler 52 Triac 53 A / D Converter 54, 56, 57 Comparator 55 AND Gate Circuit 58 Selector

Claims (2)

  A temperature detecting means for detecting the temperature of the fixing device; a comparing means for comparing the temperature detected by the temperature detecting means with a threshold temperature; and the threshold temperature of the comparing means according to rotation or non-rotation of the fixing device driving system. An image forming apparatus comprising: a switching unit that switches; and a blocking unit that blocks supply of power to a heating element of the fixing device based on a comparison result of the comparison unit.   A temperature detecting means for detecting the temperature of the fixing device; a first comparing means for comparing the temperature detected by the temperature detecting means with a first threshold temperature; and a temperature detected by the temperature detecting means for a second A second comparison means for comparing with the threshold temperature, a selection means for selecting one of the first and second comparison means according to rotation or non-rotation of the fixing device drive system, and the selection means selected by the selection means An image forming apparatus comprising: a blocking unit configured to block power supply to a heating element of the fixing device based on an output of the comparison unit.

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