JP2008164973A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device capable of preventing breakage of a fixing unit even when on/off of a power source is repeated while shortening a warm-up time. <P>SOLUTION: The voltage of a terminal (a) voltage-divided by a thermistor 19 detecting the temperature of the fixing unit and a resistor R1 is converted into a digital value by an A/D convertor 51 to be transmitted to MPU. In addition, a switch 53 switches reference voltage 1 at the time of power source-on, reference voltage 2 in waiting, and reference voltage 3 in printing to be input to a comparator 52, and when the temperature of the fixing unit is high and the voltage at the (a) point is higher than the reference voltage of any one of positions 1-3 selected by the switch 53, the output of an AND gate circuit 54 in which a heater-on/off signal from MPU is input is at an L level since the output of the comparator 52 is at an L level. Since triac 56 i.e. a heater-on/off control switch is turned off, overheat of the fixing unit can be prevented. <P>COPYRIGHT: (C)2008,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 photosensitive member, and toner is attached to the photosensitive member on which the electrostatic latent image is formed and developed. After the toner adhering to the photosensitive member is transferred to the recording paper, the recording paper to which the toner is adhering is conveyed to a fixing roller heated by a fixing heater, and the toner is fixed on the recording paper by the fixing roller. .

  In the electrophotographic image forming apparatus having a heat fixing portion used for such a facsimile machine or a copying machine, in recent years, the demand for energy saving has been increased, and in particular, consumption in a standby state where image formation is not performed. Since there is a strong demand for power reduction, an energy saving mode is provided to save power in a standby state in which image formation is not performed. In this energy saving mode, power consumption is reduced by stopping the power supply to the fixing device.

On the other hand, in a conventional electrophotographic image forming apparatus, the temperature of the fixing device is detected by using a thermistor or the like, and the temperature of the fixing device can be higher than the above temperature so as to be maintained at the preheating temperature or the fixing temperature. For example, the system is controlled so that the power supply to the heater is stopped, and the power supply is restarted when the power is low.
Note that if the heater of the fixing unit is turned on at the start of recording, it takes time to be able to print, and the user is kept waiting. Therefore, the temperature of the fixing unit is usually set to the preheating temperature immediately after the power is turned on. By raising and setting the standby state, the time from the start of recording until the fixing temperature is reached, that is, the fixing start-up time is shortened.

As mentioned above, the temperature of the fuser is controlled by system control. However, if a situation occurs in which the heater cannot be controlled due to system runaway, etc., energization of the heater stops even if the temperature of the fuser becomes abnormally high. In addition to the control system, a comparator is provided in addition to the control system, and the temperature detection output of the fixing device and the reference voltage are compared by this comparator. When the temperature becomes abnormally high, energization to the heater is stopped by the output of the comparator (see, for example, Patent Document 1).
JP-A-8-262923

By the way, in the temperature control of the fixing device as described above, after the power is turned on and the system is started up, the heater of the fixing device, that is, the halogen lamp is turned on, and the fixing device is heated to the target temperature to enter the standby state. If it does so, the problem that warm-up time becomes long will arise.
To shorten the warm-up time, if the lamp is turned on and heated immediately after the power is turned on, the temperature cannot be controlled until the system starts up, so if the power is turned on / off repeatedly, the fuser will continue to heat up. If the software does not start up, the fixing unit may be damaged.

  On the other hand, as described above, in order to prevent the fixing unit from being damaged, a technique has been proposed in which an abnormal temperature rise of the fixing unit is detected by a comparator and the heater power is turned off. When the temperature exceeds + α, the heater power is turned off. For example, if the power is turned on / off repeatedly and the fixing device continues to be heated, the heater is turned on at the start of the system. Is not rotating, that is, when the heat roller or the nip roller is not rotating, there is a problem that the temperature becomes locally high and parts are deformed.

  The present invention has been made in view of the above-described problems, and shortens the warm-up time, and even when the power is repeatedly turned on / off immediately after the power is turned on (when the fixing lamp is forcibly lit), the soft control is not effective. An object of the present invention is to provide an image forming apparatus capable of preventing damage to a fixing device.

  In order to achieve the above object, an image forming apparatus according to a first aspect of the present invention includes a temperature detection unit that detects the temperature of the fixing device, a voltage comparison unit that compares the output of the temperature detection output stage with a reference voltage, In the image forming apparatus provided with a power-off means for turning off the power of the heater of the fixing device by the output of the voltage comparison means, a plurality of reference voltages can be set as the reference voltage input to the voltage comparison means, Selection means for selecting one of the plurality of reference voltages and inputting it to the voltage comparison means is provided.

  An image forming apparatus according to a second aspect of the present invention is the image forming apparatus according to the first aspect, wherein the plurality of reference voltages are a power-on reference voltage, a standby reference voltage, and a print reference. It is a voltage.

  According to the image forming apparatus of the first and second aspects of the present invention, since there are a plurality of reference voltages as the reference voltage of the voltage comparison means, that is, the comparator, it is possible to run out of control at the time of system startup or once after startup. On the other hand, the power supply of the fixing device heater can be shut off at an appropriate temperature according to the status of the apparatus, and damage such as thermal deformation of the mechanical parts can be prevented.

Specifically, at the time of system startup, by applying a relatively low power-on reference voltage as the comparator reference voltage, the abnormal temperature rise temperature at system startup can be suppressed to a low temperature, so the warm-up time The fuser lamp can be turned on immediately after the power is turned on, and the protection circuit works on the low temperature setting side even if the power is turned on / off repeatedly when the fixing lamp is forcibly lit when the soft control does not work. , Can prevent the fixing unit from being damaged.
Further, by applying the standby reference voltage and the printing reference voltage as the reference voltage of the comparator during standby and printing, it is possible to prevent the temperature from rising above the reference temperature corresponding to the situation.

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 signals 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, it 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 functions as a fax modem capable of facsimile communication. The modem 7 is also 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. The operation panel 10 includes a display unit that displays an operation state of the digital multifunction peripheral or displays an operation screen for various functions, and a plurality of keys for operating the digital multifunction 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 received data, copy original data, and the like. To do. The fuser heater 16 of the printer engine 15 is heated by a commercial AC power supply AC via a power switch 17 and a heater on / off control switch 18, and the output of a thermistor 19 that detects the temperature of the fuser is a printer mechanism control circuit. 12 is input.

  The LAN interface 13 is connected to a LAN (not shown) and receives signals from the Internet network, while transmitting signals and data to the LAN, and performs interface processing such as signal conversion and protocol conversion. Then, the power supply circuit 20 generates various DC voltages from the commercial AC power supply AC supplied via the power switch 17 and supplies it to each part of the digital multi-function peripheral.

  The digital multi-function peripheral has the above-described configuration. When transmitting 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 the image memory 5 is connected 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, stored in the image memory 5 via the memory controller 4, then decoded by the codec 6, and the printer image processing circuit 11 is printed on the printer engine 15. Printing is executed by supplying an image signal.

Next, the 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 serving as an image carrier that is rotationally driven at a predetermined speed. A transfer roll 22 and a photosensitive drum are sequentially arranged around the photosensitive drum 21 in the rotation direction (arrow direction in the figure). A memory removing brush 23 for removing the electric potential 20; a charging corona charger 24 which is a charger for uniformly charging the surface of the photosensitive drum 21; and an image for exposing the surface of the photosensitive drum 21 to form an electrostatic latent image. An LED print head 25 as an exposure device, a developing device 27 that develops the electrostatic latent image formed on the photosensitive drum 21 with toner, and a fixing device 28 are provided on the paper discharge side of the photosensitive drum 21. It has been.

The developing device 27 agitates a developer composed of a developing roller 29, a supply roller 30 for supplying toner to the developing roller 29, and a toner and a carrier replenished from a toner replenishing portion (not shown) along the bottom thereof. In addition, a stirring paddle 31 that supplies the surface of the developing roller 29 is provided.
Further, the transfer roller 22, the memory removal brush 23, the charging corona charger 24, and the transfer roller high voltage generator 32 for supplying a high voltage to the developing roller 29, the memory removal brush high voltage generator 33, and the charging bias high voltage, respectively. The generator 34 and the developing bias high voltage generator 35 are controlled by the printer mechanism control circuit 12 to generate respective high voltages, and the current detection resistor 36 detects the supply current to the charging corona charger 24 to detect the printer mechanism. Input to the 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 serving 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 MPU 1 controls the heater on / off control switch 18 via the printer mechanism control circuit 12 based on the output of the thermistor 19 which is a temperature detecting element provided in contact with the heat roller 37, The temperature of the heat roller 37 is controlled to a standby temperature, a fixing temperature, and the like.

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 electrification to prepare for the next image forming process. 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.
Further, the LED print head 25 collects the light beam emitted from each LED chip of the LED array by the corresponding microlens and forms an image on the outer peripheral surface of the photosensitive drum 21, whereby the LED print head 25 as a whole. As described above, the light beam can be irradiated with a predetermined resolution in the axial direction of the photosensitive drum 21.

  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, and then the charged photosensitive drum. An electrostatic latent image is formed by exposing the surface of 21 with image forming light 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. The paper is guided to be discharged by a paper portion (not shown).

Next, the configuration of the fixing unit overheat prevention circuit in the printer mechanism control circuit 12 will be described with reference to FIG.
The voltage at the terminal a obtained by dividing the power supply voltage Vcc by the thermistor 19 and the resistor R1 is a voltage corresponding to the temperature. This voltage is converted into a digital value by the A / D converter 51 and sent to the MPU1, The signal is input to the negative terminal of the comparator 52.

  The voltage divided by the resistors R2, R3, R4, and R5 that divide the power supply voltage Vcc is selected by the switch 53 and input to the + terminal of the comparator 52. The voltage at the switching position 1 is a reference voltage when the power is turned on, and the switching device 53 connects the switching terminal to this position 1 until the system starts up when the digital multifunction peripheral is turned off and when the power is turned on. is doing. The voltage at the switching position 2 is a reference voltage for standby, the voltage at the switching position 3 is a reference voltage for printing, and the switching terminal of the switch 53 is set to each switching position by the MPU 1 during standby and printing. Can be switched.

  On the other hand, the output of the comparator 52 and the heater on / off signal from the MPU 1 are input to the AND gate circuit 54. When the output of the comparator 52 is at the H level, the transistor Tr1 is controlled by the heater on / off signal from the MPU 1. When the heater on signal is input from the MPU 1, the transistor Tr 1 is turned on, the triac 56, that is, the heater on / off control switch 18 is turned on via the photocoupler 55, and the halogen lamp 39 of the fixing device 28 is turned on. Commercial AC power AC is supplied to heat the heat roller 37.

On the other hand, the thermistor 19 shows a low resistance value when the ambient temperature of the thermistor is high, and shows a high resistance value when the ambient temperature is low, so that the power supply voltage Vcc is divided by the thermistor 19 and the resistor R1. The voltage is high when the temperature of the fixing device 28 is high and low when the temperature is low.
When the temperature of the fixing device 28 rises and the voltage at the point a becomes higher than any of the reference voltages at positions 1 to 3 selected by the switch 53, the output of the comparator 52 becomes L level. The output of the gate circuit 54 also becomes L level, the triac 56, that is, the heater on / off control switch 18 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, the temperature control of the fixing device 28 is executed by the MPU 1. Hereinafter, the operation when the MPU 1 executes the temperature control of the fixing device will be described with reference to the flowchart of FIG.
When the power of the digital multi-function peripheral is turned on, the MPU 1 starts the program shown in the flowchart of FIG. 4 and executes system initialization processing (step 101).

  During the system initialization process, that is, when the system is not started up, the signal from the MPU 1 inputted to the AND gate circuit 54 is at the H level, so that the halogen lamp 39 of the fixing unit 28 is turned on immediately after the power is turned on. Although the light roller 37 is turned on and the heat roller 37 is heated, since the switching terminal of the switch 53 is connected to the position 1, a low reference voltage for power-on is input to the comparator 52. Therefore, even if the temperature of the heat roller 37 rises in a state where this soft control is not effective, the heater is turned off at a relatively low temperature, so that the fixing device can be prevented from being damaged.

  When the system initialization process ends, the MPU 1 starts a timer Ta that measures the time for shifting the fixing device to the energy saving mode (step 102), and then sets the switching terminal of the switching device 53 to position 2, that is, Then, the reference voltage is switched to the standby reference voltage (step 103). Next, the MPU 1 determines whether or not the temperature of the fixing device is higher than the standby temperature based on the digital value from the A / D converter 51 (step 104). The fixing device is heated with the off signal turned on (step 105), and if it is determined that the standby temperature has been reached, it is determined whether or not a print job has occurred (step 106).

If it is determined that a print job has not occurred, the MPU 1 determines whether or not the timer Ta has expired (step 107). If it is determined that the timer Ta has not expired, the process returns to step 104. It is determined again whether the temperature of the fixing device is higher than the standby temperature.
On the other hand, if it is determined in step 106 that a print job has occurred, the MPU 1 switches the switching terminal of the switch 53 to position 3, that is, the reference voltage for printing (step 108), and then the A / D converter. Based on the digital value from 51, it is determined whether or not the temperature of the fixing device is higher than the fixing temperature (step 109). If the fixing temperature has not been reached, the heater ON / OFF signal is turned on to heat the fixing device. If it is determined that the fixing temperature has been reached (step 110), print processing is executed (step 111).

When the printing process is completed, the MPU 1 restarts the timer Ta and starts a timer Tb that measures the time for shifting to the standby mode (step 112). Thereafter, the MPU 1 determines whether or not a print job has occurred (step 113). If it is determined that no print job has occurred, the MPU 1 determines whether or not the timer Tb has expired (step 114). . If it is determined that the timer Tb has not expired, the MPU 1 returns to step 113 and determines again whether a print job has occurred.
If it is determined in step 113 that a print job has occurred, the MPU 1 returns to step 109 to determine whether or not the temperature of the fixing device is higher than the fixing temperature, and performs processing for print execution.

  On the other hand, if it is determined in step 114 that the timer Tb has timed up, that is, the transition time to the standby mode has elapsed, the MPU 1 switches the switching terminal of the switch 53 to position 2 (step 115), and then A Based on the digital value from the / D converter 51, it is determined whether or not the temperature of the fixing device is higher than the standby temperature (step 116). If it is determined that the temperature is lower than the standby temperature, the heater on / off signal is turned on. The fixing device is heated (step 117), and if it is determined that the temperature is equal to or higher than the standby temperature, it is determined whether or not a print job has occurred (step 118).

If it is determined in step 118 that a print job has not occurred, the MPU 1 determines whether or not the timer Ta has expired (step 119), and if it is determined that the timer Ta has not expired, Returning to step 116, it is determined again whether the temperature of the fixing device is higher than the standby temperature.
If it is determined in step 118 that a print job has occurred, the MPU 1 returns to step 108 and switches the switch terminal of the switch 53 to position 3 to perform processing for print execution.

  On the other hand, if it is determined in step 119 or step 107 that the timer Ta has timed up, that is, the transition time to the energy saving mode has elapsed, the MPU 1 turns off the fixing device heater by always turning off the heater on / off signal. After (step 120), the switching terminal of the switch 53 is switched to position 1 (step 121). Thereafter, the MPU 1 always determines whether or not a print job has occurred (step 122). If it is determined that a print job has occurred, the MPU 1 returns to step 102 to start the timer Ta, and the same as above. To execute processing for print execution.

  As described above, by switching the switching terminal of the switch 53 according to the situation and applying a relatively low power-on reference voltage at the time of system startup, the abnormal temperature rise at the time of system startup is suppressed to a low temperature. By applying the standby reference voltage and the printing reference voltage during standby and printing, it is possible to prevent the temperature of the fixing unit from rising above the reference temperature according to the situation.

  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. can do.

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 structure of a fixing device overheat prevention circuit. It is a flowchart which shows an effect | action when performing temperature control of a fixing device.

Explanation of symbols

19 Thermistor 51 A / D Converter 52 Comparator 53 Switch 54 AND Gate Circuit 55 Photocoupler 56 Triac

Claims (2)

Temperature detection means for detecting the temperature of the fixing device, voltage comparison means for comparing the output of the temperature detection output stage with a reference voltage, and power off means for turning off the power of the heater of the fixing device by the output of the voltage comparison means; In an image forming apparatus comprising:
A plurality of reference voltages can be set as the reference voltage input to the voltage comparison means, and a selection means for selecting one of the plurality of reference voltages and inputting it to the voltage comparison means is provided. An image forming apparatus. The image forming apparatus according to claim 1,
The image forming apparatus, wherein the plurality of reference voltages are a power-on reference voltage, a standby reference voltage, and a printing reference voltage.

Images