JP2011232432A - Temperature control device, image forming apparatus using the same, control method for temperature control device, and control program for temperature control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature control device able to detect a fixing temperature highly accurately over the entire temperature range of a fixing device.SOLUTION: A temperature control device 450 includes: a partial pressure circuit with a thermistor 451 and a partial pressure resistor 453; a D/A converter 457; a first wire 461 and a second wire 463 connecting the partial pressure resistor 453 and the thermistor 451 to the D/A converter 457, respectively; and a CPU 470 connected between the thermistor 451 and the partial pressure resistor 453 via a temperature monitor line 471a. Based on the detection result of the fixing temperature, the CPU 470 controls the D/A converter 457, thereby the direction of a current flowing into the thermistor 451 is switched, and the thermistor 451 is switched between the pull-up side and the pull-down side in the partial pressure circuit 455. The detection range of temperature can be switched by increasing the current value not only when the temperature is low but also when it is high.

Description

  The present invention relates to a temperature control device, an image forming apparatus using the same, a control method for the temperature control device, and a control program for the temperature control device, and in particular, a temperature control device for controlling the temperature of the fixing device, and an image using the same. The present invention relates to a forming apparatus, a temperature control apparatus control method, and a temperature control apparatus control program.

  Used for electrophotographic image forming apparatus (scanner function, facsimile function, copying function, printer function, data communication function, and MFP (Multi Function Peripheral) having a server function, facsimile apparatus, copying machine, printer, etc.) The fixing device is controlled to an appropriate temperature to fix the toner. In a temperature control device that controls the temperature of the fixing device, in general, priority is given to increasing the temperature detection accuracy when the temperature of the fixing device is around 160 to 200 ° C. A sensor is determined. However, as a result, in a low temperature range such as 0 to 30 ° C., the resolution with respect to the temperature is reduced, and the temperature detection accuracy is lowered. With regard to such a problem, for example, a temperature control device that improves temperature detection accuracy on the low temperature side as described in Patent Document 1 below is known.

  Patent Document 1 below discloses a fixing control device that improves the temperature detection accuracy of the thermal fixing device by increasing the voltage of the power source of the voltage dividing circuit only at a low temperature. In this fixing control device, the disconnection detection accuracy of the thermistor is improved by switching the input voltage from 3.3 V to 24 V at a low temperature.

  Patent Document 2 below discloses a temperature control device using a voltage dividing switching circuit that switches a voltage dividing ratio of a voltage dividing circuit in order to accurately detect a fixing temperature even at a low temperature / high temperature. The voltage dividing switching circuit switches the magnitude of the voltage dividing resistor using a transistor or the like.

JP 2008-90110 A JP 2008-216376 A

  By the way, the fixing control device described in Patent Document 1 sets the temperature sensor to the pull-up side and raises the power supply at a low temperature. When the temperature is high, the input voltage cannot be switched and the temperature is detected appropriately. It may not be possible.

  In the temperature control device described in Patent Document 2, since a semiconductor (transistor) is used to switch the voltage dividing resistor, the operation of the semiconductor affects the size of the voltage dividing resistor. Therefore, there is another problem that the detection accuracy of the fixing temperature is lowered.

  The present invention has been made to solve such a problem, and a temperature control device capable of detecting a fixing temperature with high accuracy over the entire temperature range of the fixing device, an image forming apparatus using the same, It is an object of the present invention to provide a temperature control device control method and a temperature control device control program.

  In order to achieve the above object, according to one aspect of the present invention, the temperature control device is connected to the temperature sensor for detecting the temperature of the fixing member for fixing the toner formed on the paper to the paper, and the temperature sensor. The temperature of the fixing member is detected based on a voltage dividing resistor, a voltage dividing circuit having a temperature sensor and a voltage dividing resistor, a power supply unit that supplies power to the voltage dividing circuit, and an output voltage divided by the voltage dividing circuit. And a temperature control unit that controls the temperature of the fixing member based on the detection result of the detection unit, and a power supply unit that controls the temperature of the fixing member based on the detection result of the detection unit. And a switching unit that switches the direction of the current flowing through the temperature sensor.

  Preferably, the switching unit controls at least one of a current and a voltage supplied to the temperature sensor by controlling the power supply unit for each of a plurality of temperature ranges.

  Preferably, when the temperature of the fixing member is a temperature corresponding to a boundary portion between one temperature range and the other temperature range among the plurality of temperature ranges, at least the current and voltage supplied to the temperature sensor. Make one change.

  Preferably, the switching unit abruptly changes at least one of a current and a voltage supplied to the temperature sensor.

  Preferably, the change width of at least one of the current and voltage supplied to the temperature sensor can be freely set by the user.

  According to another aspect of the present invention, an image forming apparatus includes: a toner image forming unit that forms a toner image on a sheet; a fixing member that fixes toner formed on the sheet by the toner image forming unit; Any of the temperature control devices described above, and the temperature control device controls the temperature of the fixing member.

  According to still another aspect of the present invention, a temperature sensor that detects the temperature of a fixing member that fixes toner formed on a sheet to the sheet, a voltage dividing resistor connected to the temperature sensor, a temperature sensor, and a voltage dividing resistor And a power supply unit that supplies power to the voltage dividing circuit, the method for controlling the temperature control device detects the temperature of the fixing member based on the output voltage divided by the voltage dividing circuit A temperature control step for controlling the temperature of the fixing member based on the detection result of the step, the detection step, and a power source unit based on the detection result of the detection step, thereby controlling the temperature according to the temperature of the fixing member. A switching step of switching the direction of the current flowing through the sensor.

  According to still another aspect of the present invention, a temperature sensor that detects the temperature of a fixing member that fixes toner formed on a sheet to the sheet, a voltage dividing resistor connected to the temperature sensor, a temperature sensor, and a voltage dividing resistor A control program for a temperature control device including a voltage dividing circuit having a power supply and a power supply unit that supplies power to the voltage dividing circuit detects a temperature of a fixing member based on an output voltage divided by the voltage dividing circuit A temperature control step for controlling the temperature of the fixing member based on the detection result of the step, the detection step, and a power source unit based on the detection result of the detection step, thereby controlling the temperature according to the temperature of the fixing member. And causing the computer to execute a switching step of switching the direction of the current flowing through the sensor.

  According to these inventions, the power supply unit is controlled based on the detection result of the temperature of the fixing member, and the direction of the current flowing through the temperature sensor is switched according to the temperature of the fixing member. Accordingly, a temperature control device capable of detecting the fixing temperature with high accuracy over the entire temperature range of the fixing device, an image forming apparatus using the temperature control device, a control method for the temperature control device, and a control program for the temperature control device are provided. be able to.

1 is a side view illustrating a hardware configuration of an image forming apparatus according to one embodiment of the present invention. 1 is a block diagram illustrating a configuration of an image forming apparatus. It is a figure which shows the circuit structure of a temperature control apparatus. It is a graph which shows an example of the relationship between the fixing temperature and the voltage of a temperature monitor line when a D / A converter is set so that an electric current may flow out from a thermistor. It is a graph which shows an example of the relationship between the fixing temperature and the voltage of a temperature monitor line when the D / A converter is set so that a current flows into the thermistor. It is a graph which shows an example of the relationship between fixing temperature and the voltage of a temperature monitor line. It is a flowchart which shows operation | movement of CPU.

  Hereinafter, an image forming apparatus according to one embodiment of the present invention will be described.

  The image forming apparatus has a print function for transporting paper or the like by a roller and printing (printing) on the paper or the like by an electrophotographic method, a server function for saving document data or the like in an HDD (Hard Disk Drive), or the like. ing. The image forming apparatus includes a fixing device that fixes toner formed on a sheet to the sheet. The fixing device fixes the toner by, for example, heating a fixing roller and heating a sheet conveyed by the fixing roller. The fixing roller is controlled to an appropriate temperature by the temperature control device detecting the temperature of the fixing roller and performing control according to the detection result.

  The temperature control device detects the temperature of the fixing roller using a temperature sensor such as a thermistor and a voltage dividing circuit having a voltage dividing resistor. The temperature control device can detect the fixing temperature with high accuracy over the entire temperature range of the fixing roller by switching the direction of the current flowing through the temperature sensor.

  [Embodiment]

First, the overall configuration of the image forming apparatus according to the present embodiment will be described.
[Entire configuration of image forming apparatus]

  FIG. 1 is a side view showing a hardware configuration of an image forming apparatus according to one embodiment of the present invention.

  Referring to the figure, the image forming apparatus 1 includes a paper feed cassette 3, a paper discharge tray 5, and a printing unit 30.

  The paper feed cassette 3 is disposed in the lower part of the image forming apparatus 1 so as to be detachable from the housing of the image forming apparatus 1. The paper loaded in each paper feed cassette 3 is fed one by one from the paper feed cassette 3 and sent to the printing unit 30 at the time of printing. The number of paper feed cassettes 3 is not limited to one and may be larger.

  The paper discharge tray 5 is disposed above the housing of the image forming apparatus 1. A sheet on which an image is formed by the printing unit 30 is discharged from the inside of the housing to the discharge tray 5.

  The print unit 30 is disposed inside the housing of the image forming apparatus 1. The printing unit 30 roughly includes a paper transport unit 200, a toner image forming unit 300, a fixing device 400, and a driving unit (shown in FIG. 2) 500. The print unit 30 is configured to be able to form a color image on a sheet by synthesizing four color images of CMYK by a so-called tandem method.

  The paper transport unit 200 includes a paper feed roller 210, a transport roller 220, a paper discharge roller 230, and the like. The paper feed roller 210, the transport roller 220, and the paper discharge roller 230 each transport the paper by rotating the rollers while sandwiching the paper between two opposing rollers, for example. The paper feed roller 210 feeds paper one by one from the paper feed cassette 3. A sheet is fed into the housing of the image forming apparatus 1 by the sheet feeding roller 210. The transport roller 220 transports the paper fed by the paper feed roller 210 to the toner image forming unit 300. Further, the conveyance roller 220 conveys the sheet that has passed through the fixing device 400 to the paper discharge roller 230. The paper discharge roller 230 discharges the paper transported by the transport roller 220 to the outside of the casing of the image forming apparatus 1. In addition to these, the paper transport unit 200 may include rollers that are used to transport paper.

  The toner image forming unit 300 includes four color toner bottles 301Y, 301M, 301C, and 301K (hereinafter, collectively referred to as a toner bottle 301), an intermediate transfer belt 305, a transfer roller 307, and four sets. Development units 310Y, 310M, 310C, and 310K (hereinafter, these may be collectively referred to as development unit 310), a laser scan unit 320, and the like.

  The yellow toner bottle 301Y, the magenta toner bottle 301M, the cyan toner bottle 301C, and the black toner bottle 301K store CMYK toners of yellow (Y), magenta (M), cyan (C), and black (K), respectively. To do.

  The intermediate transfer belt 305 has an annular shape and is stretched between two rollers. The intermediate transfer belt 305 rotates in conjunction with the paper transport unit 200. The transfer roller 307 is disposed so as to face a portion of the intermediate transfer belt 305 that is in contact with one roller. The sheet is conveyed while being sandwiched between the intermediate transfer belt 305 and the transfer roller 307.

  The developing unit 310 includes a photosensitive member 311 (photosensitive members 311Y, 311M, 311C, and 311K are provided for each developing unit), a developing device, a cleaner, a charger, and the like. The yellow developing unit 310Y, the magenta developing unit 310M, the cyan developing unit 310C, and the black developing unit 310K are arranged to form Y, M, C, and K images, respectively. The developing unit 310 is juxtaposed directly below the intermediate transfer belt 305. The laser scan unit 320 is disposed on each photoconductor 311 so as to be able to scan with laser light.

  In the toner image forming unit 300, the laser scanning unit 320 forms a latent image on the photoreceptor 311 that is uniformly charged by the action of the charger based on the image data for each color of YMCK. The developing device forms a toner image for each color on each photoconductor 311. Each photoconductor 311 transfers the toner image to the intermediate transfer belt 305, and forms a mirror image of the toner image formed on the paper on the intermediate transfer belt 305 (primary transfer). Thereafter, the transfer roller 307 to which a high voltage is applied transfers the toner image formed on the intermediate transfer belt 305 to the sheet, and a toner image is formed on the sheet (secondary transfer).

  When the toner in the developing unit 310 decreases due to image formation, the toner stored in the toner bottle 301 of each color is supplied to the developing unit.

  The fixing device 400 includes a heating roller (an example of a fixing member) 401 and a pressure roller 403 that are heated by a heater (not shown). The fixing device 400 conveys the sheet on which the toner image is formed between the heating roller 401 and the pressure roller 403 while sandwiching the sheet, and heats and presses the sheet. As a result, the fixing device 400 melts the toner image formed by the toner image forming unit 300 and fixes it on the paper, thereby forming an image on the paper. That is, the fixing device 400 fixes the toner image on the paper using the heat generated by the heater. The sheet that has passed through the fixing device 400 is discharged from the casing of the image forming apparatus 1 to the discharge tray 5 by the discharge roller 230.

  The fixing device 400 is provided with a temperature control device 450. The temperature control device 450 controls the temperature of the heating roller 401. As a result, during printing, the heating roller 401 is heated to an appropriate temperature for fixing the toner on the paper.

  The drive unit 500 includes, for example, a main motor 501, a fixing motor 502, a black developing motor 503, a color developing motor 504, and a color photoreceptor motor 505 (hereinafter, these motors are simply referred to as motors 501 to 505, etc.). Sometimes called). The drive unit 500 is driven under the control of a CPU 21 (shown in FIG. 2) described later. The main motor 501 carries the paper from the paper feeding process to the transfer process and drives the intermediate transfer belt 305 and the black photoconductor 311K. The fixing motor 502 drives the fixing device 400. The black developing motor 503 drives the black developing unit 310K. A color developing motor 504 drives yellow, magenta, and cyan developing units 310Y, 310M, and 310C. The color photoconductor motor 505 drives the yellow, magenta, and cyan photoconductors 311Y, 311M, and 311C.

  When printing is instructed to the image forming apparatus 1, the sheets stored in the sheet feeding cassette 3 are taken out one by one by the sheet feeding roller 210. The paper is transported by the paper feed roller 210 and the transport roller 220. In parallel with the paper feeding, the charged photoreceptors 311Y, 311M, 311C, 311K are exposed by the laser scan unit 320 based on the image data. A toner image is formed on the photoreceptor 311 by developing with toner in the developing units 310Y, 310M, 310C, and 310K of the respective colors. The toner images formed on the photoreceptors 311 of the respective colors are transferred onto the intermediate transfer belt 305, and toner images for four colors are formed on the intermediate transfer belt 305. Next, a voltage is applied to the transfer roller 307 so that the toner image formed on the intermediate transfer belt 305 is transferred to the conveyed paper. The toner image formed on the paper is fixed on the paper when the paper passes through the fixing device 400 and heat and pressure are applied. The paper on which the toner image is fixed is discharged to the paper discharge tray 3 by the paper discharge roller 230.

  FIG. 2 is a block diagram illustrating a configuration of the image forming apparatus 1.

  Referring to the figure, image forming apparatus 1 further includes an operation unit 11, a control unit (CPU unit) 20, a nonvolatile memory 27, an interface unit 29, and a power supply device 600.

  The operation unit 11 is disposed in the casing of the image forming apparatus 1 so that it can be operated by a user. A display panel 13 is disposed on the operation unit 11. The display panel 13 is, for example, an LCD (Liquid Crystal Display) provided with a touch panel. The display panel 13 displays a guidance screen for the user or displays an operation button to accept a touch operation from the user. The display panel 13 performs display under the control of the CPU 21 of the control unit 20. When the user operates the display panel 13, operation buttons (not shown), or the like, the operation unit 11 transmits an operation signal or a predetermined command corresponding to the operation to the CPU 21. That is, the user can cause the image forming apparatus 1 to execute various operations by operating the operation unit 11.

  The control unit 20 includes a CPU 21, a ROM (Read Only Memory) 23, a RAM (Random Access Memory) 25, and the like. The control unit 20 is connected to the system bus together with the operation unit 11, the nonvolatile memory 27, the interface unit 29, the power supply device 600, and the like. Thereby, the control part 20 and each part of the image forming apparatus 1 are connected so that signals can be transmitted and received.

  The CPU 21 controls various operations of the image forming apparatus 1 by executing a control program 23 a or the like stored in the ROM 23, RAM 25, or nonvolatile memory 27. When an operation signal is sent from the operation unit 11 or an operation command is sent from a client PC or the like, the CPU 21 executes a control program 23a according to them. Thereby, the operation of the image forming apparatus 1 is performed according to the operation of the operation unit 11 by the user.

  The ROM 23 is, for example, a flash ROM (Flash Memory). The ROM 23 stores data used for operating the image forming apparatus 1. Further, the ROM 23 stores a control program (program) 23 a for performing various operations of the image forming apparatus 1. In addition, the ROM 23 may store function setting data of the image forming apparatus 1. The CPU 21 reads data from the ROM 23 and writes data to the ROM 23 by performing predetermined processing. The ROM 23 may be non-rewritable.

  The RAM 25 is a main memory of the CPU 21. The RAM 25 is used for storing data necessary when the CPU 21 executes the control program 23a.

  The nonvolatile memory 27 stores information that needs to be maintained even after the image forming apparatus 1 is turned off, such as information related to the life state such as the number of prints. The nonvolatile memory 27 stores, for example, job data sent from the outside via the interface unit 29. The nonvolatile memory 27 may be configured to store setting information of the image forming apparatus 1 and a control program for performing various operations of the image forming apparatus 1. The nonvolatile memory 27 can store a plurality of jobs transmitted from one client PC or a plurality of client PCs. The nonvolatile memory 27 is composed of, for example, an HDD (Hard Disk Drive), a flash ROM, or the like.

  The interface unit 29 is configured, for example, by combining a hardware unit such as a NIC (Network Interface Card) and a software unit that performs communication using a predetermined communication protocol. The interface unit 29 connects the image forming apparatus 1 to an external network such as a LAN. As a result, the image forming apparatus 1 can communicate with an external apparatus such as a client PC connected to the external network. The image forming apparatus 1 can receive a job from a client PC. Further, the image forming apparatus 1 can transmit the image data to the client PC or by E-mail via a mail server or the like.

  The interface unit 29 may be configured to be connectable to an external network by wireless communication. The interface unit 29 may be, for example, a USB (Universal Serial Bus) interface. In this case, the interface unit 29 enables communication between the external device connected via the communication cable and the image forming apparatus 1.

  The power supply device 600 is provided inside the housing of the image forming apparatus 1. The power supply device 600 is connected to a commercial power supply and supplies power to each unit of the image forming apparatus 1 based on the commercial power supply.

  The developing units 310Y, 310M, 310C, and 310K are provided with nonvolatile memories 319Y, 319M, 319C, and 319K, respectively. The toner bottles 301Y, 301M, 301C, and 301K are provided with nonvolatile memories 309Y, 309M, 309C, and 309K, respectively.

  Since the photoconductor 311 and the like included in the developing unit 310 deteriorate as printing is repeated, the developing unit 310 has a lifetime. Further, since the toner stored in the toner bottle 301 decreases as printing is repeated, the toner bottle 301 has a lifetime. That is, the developing unit 310 and the toner bottle 301 are consumables. The CPU 21 stores information such as the life state of each consumable in these nonvolatile memories 319Y to 319K and 309Y to 309K (hereinafter, these may be collectively referred to as the nonvolatile memory 719). Thereby, even when each consumable is removed and mounted on another image forming apparatus, the life state of the consumable can be reflected in the image forming apparatus of the transfer destination. Therefore, it is possible to reliably manage the life of each consumable and appropriately print an image.

  [Configuration of Temperature Controller 450]

  Next, the configuration of the temperature control device 450 will be described.

  FIG. 3 is a diagram showing a circuit configuration of the temperature control device 450.

  Referring to the figure, temperature control device 450 includes a thermistor (an example of a temperature sensor) 451 and a voltage dividing circuit 455 having a voltage dividing resistor 453, a D / A converter (an example of a power supply unit) 457, and a first wiring. (DA) 461 and second wiring (DA) 463, and a CPU (an example of a detection unit, an example of a temperature control unit, an example of a switching unit) 470.

  The thermistor 451 is disposed near the surface of the heating roller 401 in order to detect the temperature of the heating roller 401. The voltage dividing resistor 453 is connected to the thermistor 451 in series. That is, the thermistor 451 and the voltage dividing resistor 453 constitute a voltage dividing circuit 455.

  The first wiring 461 connects the D / A converter 457 and the voltage dividing resistor 453. The second wiring 463 connects the D / A converter 457 and the thermistor 451.

  The CPU 470 has an A / D converter 471 and a memory 473. The CPU 470 is connected to the D / A converter 457 and controls the D / A converter 457. The A / D converter 471 of the CPU 470 is connected between the thermistor 451 and the voltage dividing resistor 453 via a temperature monitor line 471a. The memory 473 is, for example, a nonvolatile memory, and stores a control program 473a.

  The CPU 470 is connected to the power supply VCC1 and the ground potential. The power supply VCC1 is a substantially constant voltage of 5V, for example. CPU 470 operates using power supplied from power supply VCC1.

  The D / A converter 457 is connected to the power supply VCC2 and the ground potential. The power supply VCC2 is a substantially constant voltage of 24V, for example. The D / A converter 457 generates power based on the signal sent from the CPU 470 using the power supplied from the power supply VCC2, and the thermistor via the first wiring 461 and the second wiring 463. 451 and a voltage dividing resistor 453 are supplied.

  The output voltage divided by the voltage dividing circuit 455 is input to the A / D converter 471 via the temperature monitor line 471a and converted into a digital value by analog-digital conversion. CPU 470 detects the temperature of heating roller 401 based on the digital value output from A / D converter 471.

  When the temperature of the heating roller 401 is detected, the CPU 470 controls the fixing device 400 based on the detection result. For example, the CPU 470 controls the heater so that the heating roller 401 has an appropriate temperature during printing. The heating roller 401 is maintained at an appropriate temperature by performing feedback control of the heater based on the temperature of the heating roller 401 detected by the CPU 470 using the thermistor 451.

  [Control over temperature detection range]

  Here, the CPU 470 controls the temperature detection range of the thermistor 451 by controlling the D / A converter 457 based on the temperature detection result of the heating roller 401. Hereinafter, this control will be described. The CPU 470 executes such control by executing, for example, the control program 473a.

  There is a limit to the voltage range input to the A / D converter 471, that is, the detection range of the thermistor 451. By switching the detection range of the thermistor 451 for each of several fixing temperature ranges so that the voltage of the temperature monitor line 471a falls within the voltage range that can be input to the A / D converter 471, the temperature of the heating roller 401, The fixing temperature can be detected in a wide temperature range.

  Switching of the detection range is performed by the CPU 470 changing the electric power supplied to the thermistor 451 by controlling the D / A converter 457 for each of a plurality of temperature ranges. The CPU 470 hardly changes the power supplied to the thermistor 451 when the fixing temperature is within the same temperature range.

  When the fixing temperature is a temperature corresponding to a boundary portion between one temperature region and another temperature region among a plurality of temperature regions, that is, the fixing temperature is a temperature at a boundary between adjacent temperature regions (boundary temperature). When at least one of the power, voltage and current supplied to the thermistor 451 is changed. At least one of power, voltage, and current is rapidly changed. That is, the detection range is switched by suddenly increasing / decreasing the current of the thermistor 451 or rapidly decreasing / rapidly increasing the voltage of the thermistor 451 when the fixing temperature is the boundary temperature. Here, the abrupt change means, for example, that the change is made almost instantaneously.

  In the present embodiment, the temperature control device 450 switches the direction of the current flowing through the thermistor 451 in accordance with the temperature level of the heating roller 401. That is, the voltage dividing circuit 455 switches whether the thermistor 451 is on the pull-up side or the pull-down side. The direction of the current is switched by the CPU 470 controlling the D / A converter 457 based on the detection result of the fixing temperature. By switching the direction of the current flowing through the thermistor 451, the relationship between the fixing temperature and the voltage of the temperature monitor line 471a changes.

  FIG. 4 is a graph showing an example of the relationship between the fixing temperature and the voltage of the temperature monitor line 471a when the D / A converter 457 is set so that current flows from the thermistor 451.

  Referring to the figure, when control is performed so that current flows from the thermistor 451, the voltage of the temperature monitor line 471a gradually increases as the fixing temperature increases.

  FIG. 5 is a graph showing an example of the relationship between the fixing temperature and the voltage of the temperature monitor line 471a when the D / A converter 457 is set so that current flows into the thermistor 451.

  Referring to the figure, when control is performed so that a current flows into the thermistor 451, the voltage of the temperature monitor line 471a also decreases as the fixing temperature increases.

  FIG. 6 is a graph showing an example of the relationship between the fixing temperature and the voltage of the temperature monitor line 471a.

  With reference to the drawing, for example, the temperature control device 450 can detect the fixing temperature in the range of 0 to 200 ° C. The CPU 470 switches the detection range of the thermistor 451 for each of four temperature ranges (first to fourth temperature ranges), and detects the fixing temperature. The first temperature range refers to a range where the fixing temperature is 0 ° C. to 50 ° C. The second temperature range refers to a range where the fixing temperature is 50 ° C to 100 ° C. The third temperature range refers to a range where the fixing temperature is 100 ° C to 150 ° C. The fourth temperature range refers to a range where the fixing temperature is 150 ° C. to 200 ° C. The fixing temperature serving as a boundary between the first temperature range and the second temperature range is 50 ° C. The fixing temperature serving as a boundary between the second temperature range and the third temperature range is 100 ° C. The fixing temperature that is the boundary between the third temperature range and the fourth temperature range is 150 ° C.

  The range of each temperature range is set so that the input level of the A / D converter 471 becomes substantially maximum when the fixing temperature reaches the upper limit or lower limit temperature. In other words, the CPU 470 controls the D / A converter 457 for the temperature range so that the input level of the A / D converter 471 becomes substantially maximum when the fixing temperature reaches the upper limit or lower limit temperature of each temperature range. Then, power is supplied to the thermistor 451.

  When the fixing temperature is in a relatively low temperature range, for example, the first temperature range or the second temperature range, the CPU 470 sets the voltage of the second wiring 463 to 0 V and the voltage of the first wiring 461 to the second temperature range. The voltage is higher than that of the wiring 463. As a result, the direction of current flows out of the thermistor 451, and the voltage input to the A / D converter 471 via the temperature monitor line 471a increases as the temperature of the heating roller 401 increases. By increasing the current of the thermistor 451, the temperature can be detected with relatively high accuracy by making maximum use of the input range of the A / D converter 471.

  When the input level of the A / D converter 471 approaches substantially maximum as the temperature of the heating roller 401 rises, the CPU 470 performs control to reduce the current of the thermistor 451. In this case, the control for reducing the current may be performed when the fixing temperature is at the boundary between one temperature range and the adjacent temperature range.

  For example, referring to the figure, the voltage of the temperature monitor line 471a is the maximum value of the input voltage range of the A / D converter 471 at the first branch point at the boundary between the first temperature range and the second temperature range. (This may be referred to as the maximum input voltage.), So that the current is reduced. Thereby, even if the fixing temperature further rises and enters the second temperature range, the fixing temperature can be detected with high accuracy within the input range of the A / D converter 471. By repeating the current adjustment sequence as the temperature rises as necessary, the temperature detection accuracy can be improved.

  On the other hand, when the fixing temperature is in a relatively high temperature range, for example, the third temperature range or the fourth temperature range, the CPU 470 sets the voltage of the first wiring 461 to 0 V and the voltage of the second wiring 463 to the first level. Higher than the voltage of the first wiring 461. As a result, the direction of current flows into the thermistor 451, and the voltage input to the A / D converter 471 via the temperature monitor line 471a decreases as the temperature of the heating roller 401 increases. In the present embodiment, the voltage of the temperature monitor line 471a becomes substantially equal to the maximum input voltage of the A / D converter 471 at the second branch point at the boundary between the second temperature range and the third temperature range. . At this time, the direction of the current is changed as described above under the control of the CPU 470.

  When the input level of the A / D converter 471 approaches a minimum as the temperature of the heating roller 401 rises, the CPU 470 performs control to increase the current of the thermistor 451. In this case, the control for increasing the current may be performed at the boundary between the temperature ranges where the fixing temperatures are adjacent to each other. For example, referring to the figure, the voltage of the temperature monitor line 471a is substantially equal to the maximum input voltage of the A / D converter 471 at the third branch point at the boundary between the third temperature range and the fourth temperature range. As a result, the current is increased. Thereby, even if the fixing temperature further rises and enters the fourth temperature range, the fixing temperature can be detected with high accuracy within the input range of the A / D converter 471. By repeating the current adjustment sequence as the temperature rises as necessary, the temperature detection accuracy can be improved.

  Note that when the fixing temperature shifts from the second temperature range to the first temperature range, the current of the thermistor 451 may be increased contrary to the above. Further, when the fixing temperature shifts from the third temperature range to the second temperature range, the control may be performed so that the direction of the current is reversed. When the fixing temperature shifts from the fourth temperature range to the third temperature range, the current of the thermistor 451 may be reduced.

  FIG. 7 is a flowchart showing the operation of the CPU 470.

  Referring to the figure, CPU 470 starts detecting the fixing temperature during printing or the like. In step S101, the CPU 470 controls the D / A converter (D / A) 457 so that current flows from the thermistor (temperature sensor) 451.

  When the fixing control is started in step S103, the CPU 470 continues to detect the fixing temperature.

  In step S105, the CPU 470 confirms whether the fixing temperature is in the first temperature range.

  If it is the first temperature range in step S105, in step S107, the CPU 470 performs control to reduce the current value when the fixing temperature reaches the first branch point (branch 1).

  If it is not the first temperature range in step S105, in step S109, the CPU 470 checks whether or not the fixing temperature is in the second temperature range.

  When it is in the second temperature range in step S105 and when the process of step S107 is completed, in step S111, the CPU 470 performs the following process. That is, the CPU 470 controls the D / A converter 457 so that a current flows into the thermistor 451 when the fixing temperature reaches the second branch point (branch 2). That is, the direction of the current flowing through the thermistor 451 is changed.

  If it is not the second temperature range in step S109, in step S113, the CPU 470 confirms whether or not the fixing temperature is in the third temperature range.

  When it is in the third temperature range in step S113 and when the processing of step S111 is completed, in step S115, the CPU 470 determines the current value when the fixing temperature reaches the third branch point (branch 3). Increase the control.

  In step S113, when it is not the third temperature range but the fourth temperature range, and when the process of step S115 is completed, the CPU 470 once ends the series of processes.

  Note that the processing by the CPU 470 may be repeatedly executed at the time of printing, for example.

  [Effects of the embodiment]

  As described above, there is an upper limit on the height of the input voltage of the A / D converter. Therefore, when the direction of the current flowing through the thermistor is fixed, it is difficult to improve the detection accuracy of the fixing temperature over the entire temperature range of the fixing temperature by changing the power flowing through the voltage dividing circuit. However, in the image forming apparatus configured as described above, the CPU switches the thermistor temperature detection range without switching the voltage dividing resistor. By switching the direction of the current and switching the thermistor from the pull-up side to the pull-down side, the temperature detection range can be switched by increasing or decreasing the current value not only at a low temperature but also at a high temperature. The fixing temperature can be accurately detected over the entire temperature range of the fixing unit without using a circuit such as a thermistor for amplifying the output of the temperature sensor or a circuit for switching the voltage dividing resistor to switch the detection range.

  [Others]

  The detection range of the thermistor may be switched by changing at least one of the current and voltage supplied to the thermistor or changing the power supplied to the thermistor.

  The temperature sensor is not limited to the thermistor. In addition to the temperature sensor and the voltage dividing resistor, other circuit elements may be provided in the voltage dividing circuit.

  The change width of the power supplied to the thermistor, that is, the change width of the current of the thermistor may be set by the user. Further, the current change width may be calculated and set by the CPU in accordance with characteristics such as a temperature sensor to be used and a voltage dividing resistor.

  The number of temperature ranges is not limited to four as in the above example, but may be two or three, or five or more.

  The image forming apparatus may be any of a monochrome / color copying machine, a printer, a facsimile machine, and the like. The image forming apparatus may be an MFP (Multi Function Peripheral) having a scanner function, a copying function, a printer function, a facsimile function, a data communication function, and a server function. In the scanner function, an image of a set original is read and stored in an HDD or the like. In the copying function, it is further printed (printed) on paper or the like. In the function as a printer, when a print instruction is received from an external terminal such as a PC, printing is performed on a sheet based on the instruction. In the facsimile function, facsimile data is received from an external facsimile machine or the like and stored in an HDD or the like. In the data communication function, data is transmitted / received to / from a connected external device. In the server function, a plurality of users can share data stored in the HDD or the like.

  The present invention can be widely applied to a temperature control device that performs temperature control of a fixing device.

  In addition, it should be thought that the said embodiment is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 300 Toner image forming part 400 Fixing apparatus 401 Heating roller (an example of a fixing member)
450 Temperature Controller 451 Thermistor (Example of Temperature Sensor)
453 Voltage Dividing Resistor 455 Voltage Dividing Circuit 457 D / A Converter (Example of Power Supply Unit)
470 CPU (an example of a detection unit, an example of a temperature control unit, an example of a switching unit)

Claims (8)

A temperature sensor for detecting the temperature of a fixing member for fixing the toner formed on the paper to the paper;
A voltage dividing resistor connected to the temperature sensor;
A voltage dividing circuit having the temperature sensor and the voltage dividing resistor;
A power supply for supplying power to the voltage divider circuit;
A detection unit that detects the temperature of the fixing member based on the output voltage divided by the voltage dividing circuit;
A temperature control unit that controls the temperature of the fixing member based on a detection result of the detection unit;
A temperature control apparatus comprising: a switching unit that switches a direction of a current flowing through the temperature sensor according to a level of the temperature of the fixing member by controlling the power supply unit based on a detection result of the detection unit.   The temperature control device according to claim 1, wherein the switching unit controls the power supply unit for each of a plurality of temperature ranges to change at least one of a current and a voltage supplied to the temperature sensor.   When the temperature of the fixing member is a temperature corresponding to a boundary portion between one temperature range and the other temperature range among the plurality of temperature ranges, the switching unit is configured to supply current and voltage supplied to the temperature sensor. The temperature control device according to claim 1 or 2, wherein at least one of them is changed.   The temperature control device according to claim 2 or 3, wherein the switching unit abruptly changes at least one of a current and a voltage supplied to the temperature sensor.   5. The temperature control device according to claim 2, wherein a change width of at least one of a current and a voltage supplied to the temperature sensor can be freely set by a user. A toner image forming unit that forms a toner image on paper;
A fixing member for fixing the toner formed on the paper by the toner image forming unit to the paper;
A temperature control device according to any one of claims 1 to 5,
The temperature control device is an image forming device that controls the temperature of the fixing member. A temperature sensor for detecting the temperature of a fixing member for fixing the toner formed on the paper to the paper;
A voltage dividing resistor connected to the temperature sensor;
A voltage dividing circuit having the temperature sensor and the voltage dividing resistor;
A temperature control device comprising a power supply unit that supplies power to the voltage dividing circuit,
A detection step of detecting the temperature of the fixing member based on the output voltage divided by the voltage dividing circuit;
A temperature control step for controlling the temperature of the fixing member based on the detection result of the detection step;
And a switching step of switching the direction of the current flowing through the temperature sensor in accordance with the temperature of the fixing member by controlling the power supply unit based on the detection result of the detection step. . A temperature sensor for detecting the temperature of a fixing member for fixing the toner formed on the paper to the paper;
A voltage dividing resistor connected to the temperature sensor;
A voltage dividing circuit having the temperature sensor and the voltage dividing resistor;
A control program for a temperature control device comprising a power supply for supplying power to the voltage dividing circuit,
A detection step of detecting the temperature of the fixing member based on the output voltage divided by the voltage dividing circuit;
A temperature control step for controlling the temperature of the fixing member based on the detection result of the detection step;
A temperature control device that causes the computer to execute a switching step of switching the direction of the current flowing through the temperature sensor in accordance with the level of the temperature of the fixing member by controlling the power supply unit based on the detection result of the detection step. Control program.