JP2017116781A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a flicker from occurring at a device connected to a commercial AC power source which is the same as that of an image forming device.SOLUTION: An AC voltage for the heater can be continuously applied to a heater for the temperature adjustment of a heating member without making any ON/OFF operations by providing a heater for heating a heating member for heating a medium, a temperature detection part for detecting a temperature of the heating member, an AC voltage generation part for a heater for generating an AC voltage for the heater based on the commercial AC voltage supplied from the commercial AC power source so as to be applied to the heater, and a control part for controlling the AC voltage generation part for the heater so that the AC voltage for the heater is changed into an effective value. As a result, a coefficient of fluctuation of the power source voltage value per unit hour in the commercial AC power source can be substantially suppressed, and the flicker generated in the device connected to the commercial AC power source same as that of the image forming device can be prevented.SELECTED DRAWING: Figure 11

Description

  The present invention relates to an image forming apparatus, and is suitably applied to, for example, a color electrophotographic printer (hereinafter also referred to as a color printer) provided with a heater for heating a medium for image formation.

  The conventional image forming apparatus is provided with first and second switch portions that apply an AC voltage from a commercial AC power source to a halogen lamp in response to being turned on by phase control of the triac. Then, when the halogen lamp generates heat, the image forming apparatus turns on the triac of the second switch unit, applies an AC voltage from the commercial AC power source to the halogen lamp via the thermistor, and continues to the first switch unit instead of the second switch unit. By turning on the triac of the switch unit and directly applying an AC voltage from a commercial AC power source to the halogen lamp, an inrush current flowing at the start of application of the AC voltage to the halogen lamp has been reduced (see, for example, Patent Document 1).

JP 2013-235107 A (pages 7 to 9, FIGS. 3 to 7)

  However, although the conventional image forming apparatus can reduce the inrush current flowing to the halogen lamp and reduce the fluctuation rate of the power supply voltage value of the commercial AC power source to some extent, the AC is supplied to the halogen lamp in response to turning on by the TRIAC phase control. Since a voltage is applied, it is still insufficient to reduce the fluctuation rate of the power supply voltage value. For this reason, when an AC voltage is applied to the halogen lamp, the image forming apparatus has a problem that flicker is generated in a device such as a lighting device or a display device connected to the same commercial AC power supply as the image forming device.

  The present invention has been made in consideration of the above points, and an object of the present invention is to propose an image forming apparatus capable of preventing flicker from occurring in a device connected to the same commercial AC power supply as the image forming apparatus.

  In order to solve this problem, in the present invention, a heater for heating a heating member for heating a medium, a temperature detection unit for detecting the temperature of the heating member, and a heater AC based on a commercial AC voltage supplied from a commercial AC power source A heater AC voltage generator that generates a voltage and applies it to the heater, and a heater AC that is applied to the heater while generating the AC voltage for the heater variable to an effective value corresponding to the temperature detected by the temperature detector And a control unit for controlling the AC voltage generating unit.

  Therefore, in the present invention, the AC voltage for the heater can be continuously applied to the heater for adjusting the temperature of the heating member without being turned on / off at all. Therefore, the fluctuation rate of the power supply voltage value per unit time in the commercial AC power supply Can be greatly suppressed.

  According to the present invention, a heater for heating a heating member for medium heating, a temperature detection unit for detecting the temperature of the heating member, and an AC voltage for the heater are generated based on the commercial AC voltage supplied from a commercial AC power source. An AC voltage generator for the heater to be applied to the heater, and an AC voltage generator for the heater so that the AC voltage for the heater is applied to the heater while being generated by varying the effective value according to the temperature detected by the temperature detector. Since the heater AC voltage can be continuously applied to the heater without being turned on / off for adjusting the temperature of the heating member, a control unit for controlling the The rate of fluctuation of the power supply voltage value of the image forming apparatus can be significantly suppressed, and thus an image forming apparatus that can prevent flicker from occurring in a device connected to the same commercial AC power supply as the image forming apparatus is realized. It is possible.

1 is a schematic side view showing an internal configuration of a color printer according to the present invention. 2 is a block diagram illustrating a circuit configuration of a color printer. FIG. It is a block diagram which shows the circuit structure of a low voltage power supply. It is a rough-line wiring diagram which shows the circuit structure of an AC-AC converter. It is a timing chart with which it uses for description of the production | generation of a 1st and 2nd switching control signal. It is a basic diagram with which it uses for description of the simultaneous logic "L" level period of a 1st and 2nd switching control signal. It is a timing chart with which it uses for description of the production | generation of the 1st thru | or 4th switching control signal in an initial state. It is a timing chart with which it uses for description of the production | generation of the 1st thru | or 4th switching control signal at the time of the alternating voltage generation for heaters. It is a basic diagram with which it uses for description of the duty ratio of a 3rd and 4th switching control signal, and a zero cross logic "L" level period. It is a timing chart with which it uses for description of the detection of the voltage value of the alternating voltage for heaters applied to a heater. It is a timing chart with which it uses for description of the fluctuation | variation rate of the power supply voltage value by the application of the heater alternating voltage to the heater of this Embodiment. It is a timing chart with which it uses for description of the fluctuation rate of the power supply voltage value by the application of the alternating voltage for heaters to the conventional heater.

The best mode for carrying out the invention (hereinafter, also referred to as an embodiment) will be described below with reference to the drawings. The description will be given in the following order.
(1) Embodiment (2) Other embodiments

(1) Embodiment (1-1) Internal Configuration of Color Printer In FIG. 1, 1 indicates a color printer according to the present invention as a whole. The color printer 1 has, for example, a substantially square box type printer housing 2 in which the right end surface in the figure is the housing front surface 2A and the left end surface in the drawing is the housing back surface 2B. The printer housing 2 is provided with a display unit 4 at the front end of the housing upper surface 2C. In the printer housing 2, an image forming unit 6 for forming a print image on the surface of a medium 5 such as recording paper or film is disposed at the center. In the printer housing 2, a feeding roller 8 that feeds the media 5 from the media cassette 7 one by one is disposed together with a media cassette 7 loaded with a plurality of media 5 at the lower end. Incidentally, the feeding roller 8 is connected to a feeding motor.

  The image forming unit 6 includes first to fourth image forming units 10 to 13, a transfer unit 14, and a fixing unit 15. The first to fourth image forming units 10 to 13 include first to fourth charging rollers 21 to 24 on the first to fourth photosensitive drums 17 to 20, and developing rollers of the first to fourth developing units 25 to 28, respectively. Is pressed. Further, in the first to fourth image forming units 10 to 13, first to fourth LED (Light Emitting Diode) heads 29 to 32 are arranged to face the first to fourth photosensitive drums 17 to 20.

  Incidentally, the first to fourth photosensitive drums 17 to 20 are connected to a drum motor. The first to fourth image forming units 10 to 13 use the toner as the developer of four colors of black (K), yellow (Y), magenta (M), and cyan (C) for the first color. A toner image as a developer image that forms the basis of a print image is formed on the surface of the first to fourth photosensitive drums 17 to 20, and is arranged in order from the front to the rear.

  The transfer unit 14 is disposed below the first to fourth image forming units 10 to 13, and an endless transfer belt 37 is stretched around the driving roller 35 and the driven roller 36. Further, the transfer unit 14 presses the first to fourth transfer rollers 38 to 41 against the first to fourth photosensitive drums 17 to 20 via the transfer belt 37. Incidentally, the drive roller 35 is connected to a belt motor. The transfer unit 14 transfers the four color toner images formed on the surfaces of the first to fourth photosensitive drums 17 to 20 to the surface of the medium 5.

  The fixing unit 15 is disposed after the transfer unit 14, and a pressure roller 44 is pressed against a hollow pipe-shaped heating roller 43. In the fixing unit 15, a heater 45, which is a halogen lamp for heating the heating roller 43, is disposed in the heating roller 43. Further, the fixing unit 15 is also provided with one or more thermistors as temperature sensors for detecting the temperature of the heating roller 43. Incidentally, the heating roller 43 is connected to a fixing motor. The fixing unit 15 fixes the four color toner images on the surface of the medium 5 as a print image.

  Further, on the housing front surface 2 </ b> A side in the printer housing 2, from the medium cassette 7 to the image forming unit 6 via supply conveyance paths including a plurality of pairs of conveyance rollers (not shown), a pair of registration rollers 46, and the like. A medium supply / conveyance unit 47 for conveying the medium 5 is provided. Further, the housing rear surface 2B side in the printer housing 2 is connected to the housing from the fixing unit 15 via a discharge conveyance path including a plurality of pairs of conveyance rollers (not shown) and a pair of discharge rollers (not shown). A medium discharging / conveying section 48 that conveys and discharges the medium 5 to the stacker 2CX on the body upper surface 2C is disposed.

  Incidentally, the pair of registration rollers 46 corrects the conveying posture of the medium 5 and controls the timing of conveying the medium 5 to the transfer unit 14 and is connected to a registration motor. The plural pairs of transport rollers and the pair of discharge rollers are connected to a transport motor (not shown). Further, between the pair of registration rollers 46 and the transfer unit 14, a medium detection sensor 49 that detects the presence or absence of passage of the conveyed medium 5 by contact or non-contact is disposed.

(1-2) Circuit Configuration of Color Printer Next, the circuit configuration of the color printer 1 will be described with reference to FIG. The color printer 1 includes, for example, a printer control unit 50 having a microprocessor configuration, a host interface unit 51, a command / image processing unit 52, and the like. The printer control unit 50 performs overall control of the entire color printer 1 according to various programs such as a basic program and an image formation processing program stored in advance in an internal memory, and executes predetermined arithmetic processing and various processing.

  As a result, when print data described in PDL (Page Description Language) is transmitted from an external host computer (not shown), the printer control unit 50 receives the print data by the host interface unit 51 and performs command / image processing. Incorporated into part 52. When the command / image processing unit 52 receives an image formation instruction command included in the print data, the printer control unit 50 executes print image formation processing.

  During the print image forming process, the printer control unit 50 operates the fixing motor 53 to rotate the heating roller 43 in one rotation direction, and in response to this, the pressure roller 44 rotates in the other rotation direction opposite to the one rotation direction. Rotate to Incidentally, one rotation direction is the clockwise direction when the color printer 1 is viewed from the left side as shown in FIG. 1, and the other rotation direction is the opposite direction when the color printer 1 is viewed from the left side as shown in FIG. Clockwise direction.

  Further, the printer control unit 50 detects the temperature of the heating roller 43 via the thermistor 54 and controls the low-voltage power supply 55 according to the detected temperature (hereinafter also referred to as a detected temperature). Therefore, the printer control unit 50 generates an AC voltage for heating the heater (hereinafter also referred to as heater AC voltage) by the low-voltage power supply 55 and applies it to the heater 45. As a result, the printer controller 50 causes the heater 45 to generate heat in the fixing unit 15 to heat the heating roller 43, thereby setting the heating roller 43 to a desired temperature.

  In this state, the printer control unit 50 operates the drum motor 57 to rotate the first to fourth photosensitive drums 17 to 20 in one rotation direction, and accordingly, the first to fourth charging rollers 21 to 24 and the The developing rollers of the first to fourth developing units 25 to 28 are rotated in the other rotation direction. Further, the printer control unit 50 operates the belt motor 58 to rotate the driving roller 35 in the other rotation direction, and accordingly, the transfer belt 37 together with the driven roller 36 is also rotated in the other rotation direction.

  Further, the printer control unit 50 generates high voltages of various positive and negative voltage values by the high voltage generation unit 59, and the first to fourth charging rollers 21 to 24, first to fourth corresponding to these various high voltages. The voltage is applied to the fourth developing units 25 to 28 and the first to fourth transfer rollers 38 to 41. In addition, the printer control unit 50 operates the transport motor to rotate the plurality of pairs of transport rollers and the pair of discharge rollers for medium transport, and operates the feed motor 60 to rotate the feed roller 8 in the other rotation direction. As a result, the printer control unit 50 feeds the media 5 from the media cassette 7 one by one by the feed roller 8 and transports the media 5 to the image forming unit 6 through the supply transport path.

  At this time, the printer control unit 50 converts the print data into bitmap data indicating a color image to be printed by the command / image processing unit 52. The printer control unit 50 generates first to fourth head control data corresponding to the color components of black, yellow, magenta, and cyan of the color image based on the bitmap data by the command / image processing unit 52, and the LED head interface. It is sent to the unit 62.

  Further, the printer control unit 50 abuts the medium 5 on the pair of registration rollers 46 whose rotation is stopped in the middle of conveyance to the image forming unit 6 to correct the conveyance posture, and then operates the registration motor 61. The pair of registration rollers 46 convey the image again to the image forming unit 6. Therefore, the printer control unit 50 corresponds to the first to fourth LED heads 29 to 29 corresponding to the first to fourth head control data from the LED head interface unit 62 according to the timing when the medium 5 starts to be conveyed again by the pair of registration rollers 46. 32 is sequentially sent to control the drive.

  Thus, the printer control unit 50 charges the surfaces of the first to fourth photosensitive drums 17 to 20 with the first to fourth charging rollers 21 to 24 in the first to fourth image forming units 10 to 13. In addition, the printer control unit 50 exposes the surfaces of the first to fourth photosensitive drums 17 to 20 with the first to fourth LED heads 29 to 32 to form an electrostatic latent image, and the electrostatic latent image is converted into the first electrostatic latent image. A toner image is formed by developing with toner by the fourth developing units 25 to 28.

  Further, the printer control unit 50 conveys the toner image on the surfaces of the first to fourth photosensitive drums 17 to 20 by the first to fourth transfer rollers 38 to 41 while conveying the medium 5 by the transfer belt 37 in the transfer unit 14. The image is transferred by being superimposed on the surface of the medium 5 in order. The printer control unit 50 heats and presses the medium 5 by the heating roller 43 and the pressure roller 44 in the fixing unit 15 to fix the four color toner images on the surface of the medium 5, thereby printing a color print image. After being formed, the sheet is conveyed through the discharge conveyance path and discharged to the stacker 2CX.

  As shown in FIG. 3, the low-voltage power supply 55 can be connected to any of various commercial AC power supplies 65 that supply a commercial AC voltage having a power supply voltage value in a range of 100 [V] to 230 [V], for example. Arbitrarily selected commercial AC power supply 65 is connected. The low-voltage power supply 55 takes in an AC voltage (hereinafter also referred to as a commercial AC voltage) supplied from the commercial AC power supply 65 into the AC-DC converter 66 and the AC-AC converter 67. The AC-DC converter 66 converts the commercial AC voltage into, for example, an operating voltage that is a DC voltage having a voltage value of 24 [V] and 5 [V], and the corresponding printer control unit 50, AC-AC converter 67, and the like described above. To the command / image processing unit 52 and the fixing motor 53.

  The AC-AC converter 67 is controlled according to the detected temperature detected by the printer control unit 50 via the thermistor 54 (that is, according to the temperature of the heating roller 43), thereby reducing the commercial AC voltage. AC voltage is generated and applied to the heater 45. Incidentally, the heater 45 has, for example, a rated power consumption value of 800 [W]. Therefore, for example, when the heater AC voltage having an effective value of 80 [V] is generated and applied by the AC-AC converter 67, the heater 45 generates heat by flowing an electric current having an effective value of 10 [A].

(1-3) Circuit Configuration of AC-AC Converter Next, the circuit configuration of the AC-AC converter 67 of the low-voltage power supply 55 will be described with reference to FIG. The AC-AC converter 67 includes a converter control unit 70, a first full-wave rectifier circuit 71, a second full-wave rectifier circuit 72, and the like. The converter control unit 70 is a logic integrated circuit such as a microcomputer, an application specific integrated circuit (ASIC), or a field-programmable gate array (FPGA).

  The first full-wave rectifier circuit 71 is configured by bridge-connecting four diodes 73 to 76, and a pair of terminals of the commercial AC power supply 65 is connected to a pair of AC terminals. In the first full-wave rectifier circuit 75, the input terminals of the input voltage detector 77 and the zero cross detector 78 are connected to the positive terminal, and the negative terminal is grounded. The input terminals of the input voltage detector 77 and the zero cross detector 78 are connected to the converter controller 70, respectively.

  The second full-wave rectifier circuit 72 includes two first and second diodes 80 and 81 connected in series, and first and second switching circuit units 82 and 83. In the first switching circuit unit 82, the converter control unit 70 is connected to the input terminal of the first gate drive circuit 85, and the first gallium nitride power device 86 that is a switching element is connected to the output terminal of the first gate drive circuit 85. The gate is connected. The drain of the first gallium nitride power device 86 is connected to the cathode of the first diode 80.

  The second switching circuit unit 83 is basically configured in the same manner as the first switching circuit unit 82 by the second gate drive circuit 87 and the second gallium nitride power device 88. However, the second gallium nitride power device 88 has a source connected to the anode of the second diode 81 and a drain connected to the source of the first gallium nitride power device 86.

  In the second full-wave rectifier circuit 72, the connection midpoint of the first and second diodes 80 and 81 (hereinafter also referred to as a diode connection midpoint) is one AC input terminal of the first full-wave rectifier circuit 71. Is connected to one terminal of the commercial AC power supply 65. The second full-wave rectifier circuit 72 has a connection midpoint between the source of the first gallium nitride power device 86 and the drain of the second gallium nitride power device 88 (hereinafter also referred to as a first connection midpoint). The other AC input terminal of the full wave rectifier circuit 71 is connected to the other terminal of the commercial AC power supply 65. Incidentally, in the second full-wave rectifier circuit 72, the source of the second gallium nitride power device 88 is grounded together with the anode of the second diode 81.

  In addition, the AC-AC converter 67 is also provided with third and fourth switching circuit portions 90 and 91 having the same configuration as the first and second switching circuit portions 82 and 83. That is, the third switching circuit unit 90 is configured in the same manner as the first switching circuit unit 82 by the third gate drive circuit 93 and the third gallium nitride power device 94. The drain of the third gallium nitride power device 94 is connected to the drain of the first gallium nitride power device 86.

  The fourth switching circuit unit 91 is configured by the fourth gate drive circuit 95 and the fourth gallium nitride power device 96 in the same manner as the second switching circuit unit 83. The fourth gallium nitride power device 96 has its source connected to the source of the second gallium nitride power device 88 and grounded, and its drain connected to the source of the third gallium nitride power device 94.

  Thus, the third and fourth switching circuit units 90 and 91 constitute a full bridge circuit 100 together with the first and second switching circuit units 82 and 83. Incidentally, in the AC-AC converter 67, the capacitor 101 is connected in parallel between the drain of the third gallium nitride power device 94 and the source of the fourth gallium nitride power device 96.

  The AC-AC converter 67 is provided with a pair of heater connection terminals 103 and 104 connected to a pair of terminals of the heater 45, and a smoothing circuit 105 which is an LC filter is connected to the pair of heater connection terminals 103 and 104. ing. Incidentally, the smoothing circuit 105 is formed of a capacitor 106 connected in parallel between the pair of heater connection terminals 103 and 104 and an inductor 107 connected to one end of the capacitor 106 on one heater connection terminal 103 side.

  In the AC-AC converter 67, the smoothing circuit 105 has a connection midpoint between the source of the third gallium nitride power device 94 and the drain of the fourth gallium nitride power device 96 (hereinafter also referred to as a second connection midpoint). Connected to the inductor 107. The AC-AC converter 67 has a second connection midpoint (that is, a connection midpoint between the source of the first gallium nitride power device 86 and the drain of the second gallium nitride power device 88) in addition to the capacitor 106 of the smoothing circuit 105. Connected to the end. In the AC-AC converter 67, a relay switch 108 serving as a heater protection circuit is provided between the inductor 107 of the smoothing circuit 105 and one heater connection terminal 103.

  Further, the AC-AC converter 67 is provided with an output voltage detection unit 109 for detecting a voltage between the pair of heater connection terminals 103 and 104 as an AC voltage for the heater. That is, in the output voltage detection unit 109, one input terminal is connected to a connection midpoint between the relay switch 108 and the inductor 107 of the smoothing circuit 105, and the other input terminal is the other heater connection terminal 104 and the capacitor 106 of the smoothing circuit 105. Connected to the midpoint of the connection. The output voltage detection unit 109 has an output terminal connected to the converter control unit 70.

  As shown in FIGS. 5A to 5E, the AC-AC converter 67 is connected to the commercial AC voltage V1 (FIG. 5A) supplied from the commercial AC power supply 65 while the color printer 1 is operating. Is full-wave rectified by the first full-wave rectifier circuit 71. The AC-AC converter 67 uses the voltage obtained by full-wave rectifying the commercial AC voltage V1 by the first full-wave rectifier circuit 71 (hereinafter also referred to as full-wave rectified voltage) as the input voltage detection unit 77 and This is applied to each input terminal of the zero cross detector 78.

  The zero-cross detection unit 78 generates a zero-cross detection signal S1 (FIG. 5B) that is a pulse signal synchronized with the zero-cross timing of the commercial AC voltage V1 based on the waveform of the full-wave rectified voltage, and sends it to the converter control unit 70. To do. Therefore, converter control unit 70 detects the zero-cross timing of commercial AC voltage V1 based on zero-cross detection signal S1. Depending on the circuit configuration of the zero-cross detector 78, there may be a delay in sending the zero-cross detection signal S1 from the zero-cross detector 78 to the converter controller 70 with respect to the zero-cross timing of the commercial AC voltage V1. In this case, in the present embodiment, converter controller 70 may correct the zero-cross timing of commercial AC voltage V1 detected based on zero-cross detection signal S1 using an internal counter or the like.

  The input voltage detection unit 77 steps down the full-wave rectified voltage and supplies the obtained step-down voltage V2 (FIG. 5C) to the converter control unit 70. The converter control unit 70 takes in the step-down voltage V2 into an internal A / D (Analog / Digital) converter, samples it at a predetermined sampling period, and sequentially detects the step-down voltage value. Based on the step-down voltage value, the converter control unit 70 The power supply voltage value that changes in real time in V1 is sequentially calculated. Further, converter control unit 70 calculates an average value for each AC cycle of commercial AC voltage V1 based on the sequentially detected power supply voltage value and the zero-cross timing of commercial AC voltage V1. Furthermore, converter control unit 70 calculates the effective value of commercial AC voltage V1 based on the average value for each AC cycle.

  In the present embodiment, the converter control unit 70 does not detect the power supply voltage value of the commercial AC voltage V1 to obtain the effective value, but the input voltage detection unit 77 or the converter control unit 70 uses a circuit composed of a resistor and a capacitor. A smoothed voltage is generated by smoothing the full-wave rectified voltage or the step-down voltage V2. In the present embodiment, the converter control unit 70 may detect the voltage value of the smoothed voltage, and calculate the effective value of the commercial AC voltage V1 based on the voltage value.

  In this state, when the converter control unit 70 detects that the step-down voltage value exceeds a predetermined threshold value (or the power supply voltage value exceeds a predetermined threshold value such as 85 [V]), the first and second The switching control signals S2 and S3 (FIGS. 5D and 5E) are generated and sent to the first and second gate drive circuits 85 and 87. As a result, the converter controller 70 transmits the first and second switching control signals S2 and S3 in the first and second gate drive circuits 85 and 87 via an insulated signal transmission circuit such as a photocoupler, and gate drive. Is supplied to the gates of the first and second gallium nitride power devices 86 and 88 as a voltage amplitude pulse for turning on / off.

  Here, the first and second switching control signals S2 and S3 are for determining the frequency of the heater AC voltage generated in the AC-AC converter 67 (that is, controlling the frequency of the heater AC voltage). Therefore, the converter control unit 70 converts the frequency of the commercial AC voltage V1 into the first and second switching control signals S2 and S3 based on the zero-cross timing of the commercial AC voltage V1 by a pulse width modulation (PWM) method. Are generated as a pair of inversion signals having a rectangular wave with the same frequency as that of the other waveform.

  Incidentally, the converter control unit 70 causes the first switching control signal S2 to fall to a logic “L” level in a ½ period that is a positive power supply voltage value of the commercial AC voltage V1, and to become a negative power supply voltage value. It rises to a logic “H” level in two cycles. In addition, converter control unit 70 raises second switching control signal S3 to a logic “H” level in a ½ cycle at which commercial AC voltage V1 is a positive power supply voltage value, and becomes a negative power supply voltage value. It falls to the logic “L” level in two cycles.

  In the following description, a 1/2 cycle at which the commercial AC voltage V1 is a positive power supply voltage value is also referred to as a positive 1/2 cycle, and a 1/2 cycle at which the commercial AC voltage V1 is a negative power supply voltage value. Is also called the negative half cycle of the commercial AC voltage V1. In the following description, the 1/2 cycle of the commercial AC voltage V1 is also simply referred to as a 1/2 cycle when it is not necessary to distinguish between the positive 1/2 cycle and the negative 1/2 cycle.

  As a result, the converter control unit 70 turns on and off the first and second gallium nitride power devices 86 and 88 alternately in a 1/2 cycle of the commercial AC voltage V1 and turns the commercial AC into the second full-wave rectifier circuit 72. The voltage V1 is full-wave rectified. Then, the converter control unit 70 converts the full-wave rectified voltage obtained by full-wave rectifying the commercial AC voltage V1 by the second full-wave rectifier circuit 72 into the drain of the third gallium nitride power device 94 and the fourth gallium nitride power device. Applied between 96 sources.

  Note that the converter control unit 70 accurately sets the period of the logic “H” level and the period of the logic “L” level of the first and second switching control signals S2 and S3 to be ½ period of the commercial AC voltage V1 accurately. If the other of the first and second switching control signals S2 and S3 is delayed, the first and second gallium nitride power devices 86 and 88 are simultaneously turned on by simultaneously changing to a logic "H" level. Time will occur.

  For this reason, as shown in FIG. 6 which is an enlarged view of the region surrounded by the broken line in FIG. 5, the converter control unit 70 has both logic levels at the switching points of the logic levels of the first and second switching control signals S2 and S3. A predetermined period (hereinafter also referred to as a simultaneous logic “L” level period) Td for falling to the “L” level is provided. As a result, the converter control unit 70 prevents the first and second gallium nitride power devices 86 and 88 from being turned on at the same time and causing a through current to flow.

  Then, when the converter control unit 70 starts driving (that is, on / off) of the first and second gallium nitride power devices 86 and 88, the converter control unit 70 synchronizes with the start of the driving and outputs the third and fourth gallium nitride power devices 94 and The driving of 96 is also started. That is, the converter control unit 70 generates the third and fourth switching control signals S4 and S5 for generating the heater AC voltage by controlling the amplitude (that is, by modulating the amplitude).

  Then, the converter control unit 70 sends the third and fourth switching control signals S4 and S5 to the third and fourth gate drive circuits 93 and 95. As a result, the converter control unit 70 controls the third and fourth switching control signals in the same manner as when the first and second gallium nitride power devices 86 and 88 are turned on / off by the first and second switching control signals S2 and S3. The third and fourth gallium nitride power devices 94 and 96 are turned on / off via the third and fourth gate drive circuits 93 and 95 by S4 and S5.

  However, as shown in FIGS. 7A to 7E, the converter control unit 70, for example, in the initial state before the print image forming process is started by the printer control unit 50, the commercial AC voltage V1 (FIG. A third switching control signal S4 (FIG. 7D) similar to the first switching control signal S2 (FIG. 7B) is generated by the pulse width modulation method based on the zero cross timing of A)). Further, the converter control unit 70 uses a pulse width modulation method based on the zero-cross timing of the commercial AC voltage V1 to generate a fourth switching control signal S5 (FIG. 7) similar to the second switching control signal S3 (FIG. 7C). (E)) is generated.

  Thereby, converter control unit 70 simultaneously turns on / off first and third gallium nitride power devices 86 and 94 in every half cycle of commercial AC voltage V1 in full bridge circuit 100. In addition, the converter control unit 70 shifts the commercial AC voltage V1 by a half period with respect to the on / off of the first and third gallium nitride power devices 86 and 94, and the second and fourth gallium nitride power devices 88 and 96. Are simultaneously turned on / off every half cycle. That is, the converter control unit 70 simultaneously controls on / off of the first and third switching circuit units 82 and 90 that are the high-side pair in the full-bridge circuit 100 in a 1/2 cycle of the commercial AC voltage V1, and the low-side pair. The second and fourth switching circuit units 83 and 91 are simultaneously turned on / off with a ½ cycle shift.

  However, the converter control unit 70 is configured such that the first and fourth switching control signals S2 and S5 are both at the logic “H” level, and the second and third switching control signals S3 and S4 are both at the logic “L” level. In addition, the full bridge circuit only when the second and third switching control signals S3 and S4 are both at the logic "H" level and both the first and fourth switching control signals S2 and S5 are at the "L" level. The heater AC voltage is generated at 100 and applied to the heater 45. Therefore, converter control unit 70 does not generate heater AC voltage by full bridge circuit 100 in the initial state, and therefore does not apply heater AC voltage to heater 45.

  In this state, when the print control forming process is started, the printer control unit 50 raises the heater-on signal S7 sent to the converter control unit 70 from the logic “L” level to the logic “H” level at a predetermined timing. In addition, the printer control unit 50 instructs the duty ratios of the third and fourth switching control signals S4 and S5 to the converter control unit 70 according to the detected temperature detected through the thermistor 54 during the execution of the print image forming process. To do.

  When the heater on signal S7 supplied from the printer control unit 50 rises from the logic “L” level to the logic “H” level, the converter control unit 70 turns on the relay switch 108 in response to the heater on signal S7. -Conductive with the AC converter 67. Then, as shown in FIGS. 8A to 8E, when the duty ratio is continuously instructed from the printer control unit 50, the converter control unit 70 performs the same first and second switching control signals S2 and S3 as described above. (FIGS. 8D and 8E) are generated and sent to the first and second gate drive circuits 85 and 87.

  Further, the converter control unit 70 applies the third and fourth switching control signals S4 and S5 (FIGS. 8B and 8C) to the frequency of the commercial AC voltage V1 (FIG. 8A) by the pulse width modulation method. And a rectangular wave with the same frequency higher than that and generated at a duty ratio instructed by the printer control unit 50. Then, the converter control unit 70 sends the third and fourth switching control signals S4 and S5 to the third and fourth gate drive circuits 93 and 95.

  However, in this case, the converter control unit 70 also outputs the third and fourth switching control signals S4 and S5 in order to avoid that the third and fourth gallium nitride power devices 94 and 96 are simultaneously turned on and a through current flows. One waveform is generated as a pair of inverted signals in which the other waveform is inverted. Further, converter control unit 70 provides a predetermined simultaneous logic “L” level period at both of the logic level switching locations of third and fourth switching control signals S4 and S5. The converter control unit 70 sets the duty ratio of the third switching control signal S4 to the duty ratio instructed from the printer control unit 50 in the positive half cycle of the commercial AC voltage V1. Further, the converter control unit 70 sets the duty ratio of the fourth switching control signal S5 to the duty ratio instructed from the printer control unit 50 in the negative half cycle of the commercial AC voltage V1.

  As a result, the converter control unit 70 turns off the first gallium nitride power device 86 by the first switching control signal S2 and the second nitriding by the second switching control signal S3 in the positive half cycle of the commercial AC voltage V1. The gallium power device 88 is turned on. In this state, when the third gallium nitride power device 94 is turned on by the third switching control signal S4, the converter control unit 70 supplies current from the commercial AC power supply 65 to the diode connection midpoint, the first diode 80, and the third gallium nitride. The power device 94, the second connection midpoint, the inductor 107 of the smoothing circuit 105, the relay switch 108, and one heater connection terminal 103 are sequentially passed to the heater 45. Converter control unit 70 then returns the current that has flowed to heater 45 at this time to commercial AC power supply 65 via the other heater connection terminal 104 and the first connection midpoint in sequence.

  Further, when the third gallium nitride power device 94 is turned off by the third switching control signal S4, the converter control unit 70 turns on the fourth gallium nitride power device 96 by the fourth switching control signal S5. As a result, the converter control unit 70 causes the reflux current flowing through the inductor 107 of the smoothing circuit 105 to flow to the heater 45 through the relay switch 108 and one heater connection terminal 103 in this order. Then, the converter control unit 70 uses the return current flowing through the heater 45 as the other heater connection terminal 104, the first connection midpoint, the second gallium nitride power device 88, the fourth gallium nitride power device 96, and the second connection midpoint. Are returned to the inductor 107 sequentially.

  In this way, the converter control unit 70 turns off the first gallium nitride power device 86 and keeps the second gallium nitride power device 88 on in the positive half cycle of the commercial AC voltage V1. The gallium nitride power devices 94 and 96 are sequentially turned on / off. As a result, the converter control unit 70 causes the current from the commercial AC power supply 65 and the reflux current flowing through the inductor 107 to flow alternately to the heater 45 in the direction from one heater connection terminal 103 to the other heater connection terminal 104.

  Further, the converter control unit 70 turns off the second gallium nitride power device 88 by the second switching control signal S3 and turns off the first gallium nitride by the first switching control signal S2 in the negative half cycle of the commercial AC voltage V1. The power device 86 is turned on. In this state, when the fourth gallium nitride power device 96 is turned on by the fourth switching control signal S5, the converter control unit 70 sequentially supplies the current from the commercial AC power supply 65, the first connection midpoint, and the other heater connection terminal 104. Through the heater 45. Then, the converter control unit 70 converts the current flowing to the heater 45 at this time into one heater connection terminal 103, the relay switch 108, the inductor 107 of the smoothing circuit 105, the second connection midpoint, the fourth gallium nitride power device 96, the first The two diodes 81 and the diode connection midpoint are sequentially returned to the commercial AC power supply 65.

  Further, when the fourth gallium nitride power device 96 is turned off by the fourth switching control signal S5, the converter control unit 70 turns on the third gallium nitride power device 94 by the third switching control signal S4. Thereby, the converter control unit 70 converts the return current flowing through the inductor 107 of the smoothing circuit 105 at this time to the second connection midpoint, the third gallium nitride power device 94, the first gallium nitride power device 86, the first connection midpoint, and The other heater connection terminal 104 is passed through the heater 45 sequentially. Then, converter control unit 70 returns the reflux current that has flowed to heater 45 to inductor 107 via one heater connection terminal 103 and relay switch 108 in sequence.

  In this way, the converter control unit 70 turns off the second gallium nitride power device 88 and keeps the first gallium nitride power device 86 on in the negative half cycle of the commercial AC voltage V1. The gallium nitride power devices 94 and 96 are sequentially turned on / off. As a result, the converter control unit 70 sequentially alternates the current from the commercial AC power supply 65 and the return current flowing through the inductor 107, and the other heater connection terminal that is opposite to the positive half cycle of the commercial AC voltage V1. Flow from 104 to the heater 45 in the direction of one heater connection terminal 103.

  In this way, the converter control unit 70 can switch the commercial AC voltage V1 in the full bridge circuit 100 to generate the heater AC voltage V3 (FIG. 8A) and apply it to the heater 45. The converter controller 70 applies the heater AC voltage V3 generated in the full bridge circuit 100 to the heater 45 after smoothing the smoothing circuit 105 by removing the high frequency component of the switching frequency component.

  As shown in FIG. 9 which is actually an enlarged view of the area surrounded by two broken lines in FIG. 8, the converter control unit 70 receives the third and fourth switching control signals S4 in response to an instruction from the printer control unit 50. When the duty ratio, which is the ratio of the logic “H” level period Th to one cycle Tt of S5, is set to 80 [%], for example, the commercial AC voltage V1 having an effective value of 100 [V] is supplied from the commercial AC power supply 65. If so, the heater AC voltage V3 having an effective value of 80 [V] is generated and applied to the heater 45.

  The converter control unit 70 generates the third and fourth switching control signals S4 and S5 at a frequency of about 100 [kHz] to 200 [kHz] by the pulse width modulation method. Then, the converter control unit 70, in each of the third and fourth switching control signals S 4 and S 5, at a position corresponding to the zero cross point of the commercial AC voltage V 1 for a predetermined period (hereinafter referred to as zero cross). Tz) (also referred to as a logic “L” level period). As a result, the converter control unit 70 can output the third and fourth gallium nitride powers even if a phase shift occurs in the third and fourth switching control signals S4 and S5 sent to the third and fourth gate drive circuits 93 and 95. The commercial AC voltage V1 is accurately switched every 1/2 cycle by the devices 94 and 96. Incidentally, the heater AC voltage V3 indicated by a broken line in FIG. 8A is 0 before and after the zero cross point for a time corresponding to the zero cross logic “L” level period Tz of each of the third and fourth switching control signals S4 and S5. [V].

  In this embodiment, the AC-AC converter 67 is provided with gallium nitride power devices (that is, the first to fourth gallium nitride power devices 86, 88, 94, 96) as switching elements for switching the commercial AC voltage V1. However, in this embodiment, the AC-AC converter 67 can be provided with devices such as IGBT (insulated gate bipolar transistor), SiFET, and SiCFET instead of the gallium nitride power device as a switching element. In this embodiment, since the gallium nitride power device is provided in the AC-AC converter 67, the switching frequency of the gallium nitride power device (that is, the frequency of the third and fourth switching control signals S4 and S5) is set to 100 [kHz]. Or about 200 [kHz]. However, in this embodiment, when an IGBT or the like is provided as a switching element in the AC-AC converter 67, if the switching frequency is too high, the switching loss increases. Therefore, depending on the type of the switching element, 20 [kHz] to 40 [ [kHz] or so.

  In addition, when the gate is turned on, the gallium nitride power device can pass current in either direction between the drain and source. However, when the gate is turned on, the IGBT can pass current only in one direction between the drain and source. Absent. Therefore, in the present embodiment, when an IGBT is provided in the AC-AC converter 67, the IGBT is a body diode built-in type, or a diode is connected in parallel between the drain and the source of the IGBT. In addition, the current can flow between the source and the source in any direction, and the heater AC voltage V3 can be generated as described above.

  By the way, as shown in FIGS. 10A to 10D, the output voltage detection unit 109 causes the heater 45 to generate the heater AC voltage V3 (FIG. 10B) generated from the commercial AC voltage V1 (FIG. 10A). )) Is applied, the voltage applied to one heater connection terminal 103 is taken in through the one input terminal as the first detection voltage V4 (FIG. 10C). The output voltage detection unit 109 takes in the voltage applied to the other heater connection terminal 104 as the second detection voltage V5 (FIG. 10D) via one input terminal. The output voltage detection unit 109 calculates the absolute value of the difference between the voltage value of the first detection voltage V4 and the voltage value of the second detection voltage V5, and steps down the difference voltage of the absolute value by a predetermined ratio. , And supplied to the converter control unit 70 via the output terminal.

  Therefore, converter control unit 70 takes in the differential voltage into the internal A / D converter and executes the same processing as that for detecting the effective value of commercial AC voltage V1 described above, and AC voltage V3 for the heater based on the differential voltage. The effective value of is detected. Then, converter control unit 70 compares the detected effective value of heater AC voltage V3 with the effective value of heater AC voltage V3 to be generated based on the duty ratio instructed from printer controller 50 at this time. Thereby, converter control unit 70 performs feedback control so as to appropriately increase or decrease the duty ratio instructed from printer control unit 50 at this time according to the comparison result.

  Here, regarding the feedback control performed by the converter control unit 70, the commercial AC voltage V1 having a duty ratio instructed by the printer control unit 50 of 80 [%] and an effective value of 100 [V] is supplied from the commercial AC power supply 65. The case will be specifically described. As described above, the converter control unit 70 generates the third and fourth switching control signals S4 and S5 with a duty ratio of, for example, 80 [%] and switches the commercial AC voltage V1 having an effective value of 100 [V]. The heater AC voltage V3 having an effective value of 80 [V] as the target value is generated and applied to the heater 45. However, in the full bridge circuit 100, when the commercial AC voltage V1 is switched, the loss of the full bridge circuit 100 changes depending on the current value and direction of the current flowing through the heater 45, and the effective value of the heater AC voltage deviates from the target value. V3 may be generated.

  Therefore, when the effective value of the heater AC voltage V3 is higher than the target value of 80 [V], the converter control unit 70 sets the duty ratio to be lower than 80 [%] and sets the third and fourth switching control signals S4. And S5. In addition, when the effective value of the heater AC voltage V3 is lower than the target value of 80 [V], the converter control unit 70 sets the duty ratio to be higher than 80 [%] and sets the third and fourth switching control signals S4 and S5 is generated. Thus, when the duty ratio instructed from the printer control unit 50 is 80 [%], the converter control unit 70 stably generates the heater AC voltage V3 whose effective value is the target value of 80 [V]. Can be applied to the heater 45.

  By the way, when the heater control signal S7 is raised to the logic “H” level as described above, the printer control unit 50 sets the duty ratio of the third and fourth switching control signals S4 and S5 to, for example, 0 [ %] To a maximum duty ratio such as 80 [%], for example, and gradually increasing (ie, stepwise or continuously) and instructing the converter control unit 70. Further, the printer control unit 50 can select one of various detection temperatures detected via the thermistor 54 and a minimum duty ratio (ie, 0 [%]) to a maximum duty ratio (eg, 80 [%]) corresponding to the detected temperature. A data table in which the duty ratios are described in association with each other is stored in advance. In the following description, the data table is also referred to as a duty ratio table.

  Accordingly, when the duty ratio instructed to the converter control section 70 is increased to the maximum duty ratio, the printer control section 50 thereafter passes the thermistor 54 based on the duty ratio table until the formation of the print image on the medium 5 is completed. A duty ratio corresponding to the detected temperature is detected. Then, the printer control unit 50 instructs the converter control unit 70 as the duty ratio of the third and fourth switching control signals S4 and S5. Further, when the formation of the print image on the medium 5 is completed, the printer control unit 50 sets the duty ratio of the third and fourth switching control signals S4 and S5 to the minimum duty in a predetermined time from the duty ratio instructed at that time. The converter control unit 70 is instructed while gradually decreasing (ie, stepwise or continuously) and changing the ratio (ie, 0 [%]).

  When the printer controller 50 finishes reducing the duty ratio instructed to the converter controller 70 to the minimum duty ratio, the heater-on signal S7 sent to the converter controller 70 is logically changed from the logic “H” level at a predetermined timing. After falling to the “L” level, the print image forming process is terminated. In this way, when the printer control unit 50 executes the print image forming process, the converter control unit 70 sends the third and fourth to the converter control unit 70 according to the execution state of the forming process and the detected temperature detected through the thermistor 54. Instructs the duty ratio of the switching control signals S4 and S5.

  Therefore, as shown in FIGS. 11A to 11D, the converter control unit 70 controls the printer after the relay switch 108 is turned on when the heater-on signal S7 (11 (A)) rises to the logic “H” level. When the duty ratio starts to be instructed from the unit 50, the third and fourth switching control signals S4 and S5 are started to be generated at the duty ratio accordingly. The converter control unit 70 then generates a commercial AC voltage based on the third and fourth switching control signals S4 and S5 generated while gradually increasing the duty ratio from the minimum duty ratio to the maximum duty ratio in accordance with an instruction from the printer control unit 50. V1 is switched.

  Thereby, the converter control unit 70 gradually increases the effective value of the heater AC voltage V3 (FIG. 11C) from 0 [V] which is the minimum effective value to the maximum effective value (that is, stepwise or continuously). And generated and applied to the heater 45. Therefore, the converter control unit 70 gradually increases the heat generation amount of the heater 45 and gradually increases the temperature of the heating roller 43 while causing the heater 45 to generate heat. Incidentally, the maximum effective value of the heater AC voltage V3 is the maximum duty ratio (that is, 80 [%]) as described above when the commercial AC voltage V1 having an effective value of 100 [V] is supplied from the commercial AC power supply 65. It corresponds to 80 [V].

  Further, after generating the heater AC voltage V3 whose effective value is the maximum effective value, the converter control unit 70 continues the duty ratio instructed from the printer control unit 50 according to the detected temperature Tk1 (FIG. 11B). The third and fourth switching control signals S4 and S5 are generated to switch the commercial AC voltage V1. Thus, converter control unit 70 generates heater AC voltage V3 as appropriate while adjusting the effective value below the maximum effective value, and applies the generated voltage to heater 45. Therefore, the converter control unit 70 adjusts the temperature of the heating roller 43 by appropriately increasing or decreasing the amount of heat generated by the heater 45 while causing the heater 45 to generate heat.

  That is, when the detected temperature Tk1 detected by the printer controller 50 via the thermistor 54 becomes higher than the target temperature Ts (FIG. 11B), the converter control unit 70 causes the heater AC voltage V3 to be more effective than the maximum effective value. The value is reduced and applied to the heater 45. Further, the converter control unit 70 reduces the effective value of the heater AC voltage V3 applied to the heater 45 below the maximum effective value, so that when the detected temperature Tk1 becomes lower than the target temperature Ts, the converter AC voltage V3 is maximized. The effective value is increased to the effective value or close to the effective value and applied to the heater 45.

  Thus, converter control unit 70 appropriately adjusts the amount of heat generated by heater 45 together with the effective value of heater AC voltage V3 so that detected temperature Tk1 becomes target temperature Ts. Therefore, the converter control unit 70 can form a print image on the medium 5 while keeping the heating roller 43 at a substantially desired temperature (that is, the target temperature Ts or a temperature corresponding to the target temperature Ts) via the heater 45. . When the formation of the print image on the medium 5 is completed, the converter control unit 70 generates the third and fourth switching control signals S4 generated while gradually decreasing the duty ratio to the minimum duty ratio in accordance with an instruction from the printer control unit 50. And commercial AC voltage V1 is switched based on S5.

  Thereby, the converter control unit 70 generates and applies the heater AC voltage V3 to the heater 45 while gradually decreasing the effective value higher than 0 [V] (that is, stepwise or continuously), and finally. The effective value is set to the minimum effective value (that is, 0 [V]), and the generation of the heater AC voltage V3 and the application to the heater 45 are finished. Therefore, the converter control unit 70 stops the heat generation of the heater 45 after gradually decreasing the heat generation amount of the heater 45. When the heater-on signal S7 supplied from the printer controller 50 falls from the logic “H” level to the logic “L” level, the converter controller 70 turns off the relay switch 108 in response to this, and the AC− The AC converter 67 and the heater 45 are disconnected.

  In this way, the converter controller 70 starts generating the heater AC voltage V3 prior to the formation of the print image on the medium 5 during the print image formation process, and thereafter, the formation of the print image on the medium 5 ends. Until this time, the heater AC voltage V3 is changed to an effective value corresponding to the detected temperature Tk1 and applied to the heater 45. That is, the converter controller 70 continuously applies the heater AC voltage V3 to the heater 45 without adjusting the heater 45 during the print image forming process. For this reason, the converter control unit 70 greatly suppresses the fluctuation rate DV1 (FIG. 11D) of the power supply voltage value per unit time in the commercial AC power supply 65 during the print image forming process.

  The converter control unit 70 gradually increases the effective value from the minimum effective value of 0 [V] to the maximum effective value at the start of application of the heater AC voltage V3 to the heater 45. For this reason, the converter controller 70 greatly reduces the inrush current that flows when the heater AC voltage V3 starts to be applied in the heater 45 even when the resistance value is relatively low, particularly when the heater 45 is a halogen lamp. Suppressed. As a result, when the converter control unit 70 starts to apply the heater AC voltage V3 to the heater 45, the converter control unit 70 gradually decreases the power supply voltage value in the commercial AC power supply 65, and sets the fluctuation rate DV1 of the power supply voltage value per unit time. It is greatly suppressed.

  Furthermore, when the application of the heater AC voltage V3 to the heater 45 is finished, the converter control unit 70 gradually increases the effective value from a value higher than the minimum effective value of 0 [V], such as the maximum effective value, to the minimum effective value. It is low. Therefore, when the converter control unit 70 finishes applying the heater AC voltage V3 to the heater 45, the converter AC unit 70 gradually increases the power supply voltage value in the commercial AC power supply 65, thereby greatly increasing the fluctuation rate DV1 of the power supply voltage value per unit time. Suppressed.

  Here, a method of applying the heater AC voltage to the heater by a conventional image forming apparatus (not shown) will be described. As shown in FIGS. 12A to 12D, the conventional image forming apparatus includes a switch for turning on / off application of the heater AC voltage V10 (FIG. 12C) to the heater in the power supply unit. A thermistor for detecting the temperature of the heating roller is provided. Therefore, in the conventional image forming apparatus, the control unit raises the heater on signal S10 (FIG. 12A) to the logic “H” level and turns on the switch during the print image forming process. Thus, in the conventional image forming apparatus, a heater AC voltage V10 having a predetermined effective value such as 80 [V] is applied to the heater from the commercial AC power source via the power source unit to generate heat, and the heating roller is heated. .

  In the conventional image forming apparatus, when the detected temperature Tk2 detected by the control unit via the thermistor reaches the target temperature Ts (FIG. 12B), the heater ON signal S10 is lowered to the logic “L” level and the switch is turned on. Turn off. Thereby, in the conventional image forming apparatus, application of the heater AC voltage V10 having a predetermined effective value to the heater is stopped. At this time, in the conventional image forming apparatus, the detected temperature Tk2 (that is, the temperature of the heating roller) once exceeds the target temperature Ts and increases to a certain extent, but the application of the heater AC voltage V10 to the heater is stopped. Thus, the detected temperature Tk2 is lowered so as to approach the detected temperature Tk2.

  Therefore, in the conventional image forming apparatus, when the detected temperature Tk2 detected by the control unit via the thermistor falls below or reaches the target temperature Ts, the heater-on signal S10 is raised to the logic “H” level again to turn on the switch. As a result, in the conventional image forming apparatus, the heater AC voltage V10 having a predetermined effective value is again applied to the heater from the commercial AC power source via the power source unit to generate heat, and the heating roller is heated. In the conventional image forming apparatus, when the detected temperature Tk2 detected by the control unit via the thermistor reaches or exceeds the target temperature Ts, the heater-on signal S10 is again lowered to the logic “L” level and the switch is turned off. Thereby, in the conventional image forming apparatus, application of the heater AC voltage V10 having a predetermined effective value to the heater is stopped.

  Thus, in the conventional image forming apparatus, during the execution of the print image forming process, the control unit controls the switch so that the detected temperature Tk2 becomes the target temperature Ts (that is, the heating roller 43 is a desired temperature). The heater AC voltage V10 having a predetermined effective value is intermittently applied to the heater. In the conventional image forming apparatus, when the formation of the print image on the medium is completed, the control unit lowers the heater ON signal S10 to the logic “L” level to turn off the switch, and the heater AC having a predetermined effective value for the heater is turned off. Application of voltage V10 is stopped.

  Thus, in the conventional image forming apparatus, since the heater AC voltage V10 having a predetermined effective value is intermittently applied to the heater, the fluctuation rate DV2 of the power supply voltage value per unit time in the commercial AC power supply (FIG. 12 (D )) Is relatively large. That is, in the conventional image forming apparatus, since the heater is cooled and the resistance value is relatively low at the start of the print image forming process, the heater AC voltage V10 having a predetermined effective value is applied to the heater. Large inrush current flows. For this reason, in the commercial AC power supply, the power supply voltage value rapidly decreases and the fluctuation rate DV2 becomes relatively high.

  The heater has a relatively high resistance value as the temperature of the heater itself rises while the heater AC voltage V10 having a predetermined effective value is being applied during execution of the print image forming process. While the application of the voltage V10 is stopped, the resistance value decreases as the temperature of the heater itself decreases. For this reason, each time the heater AC voltage V10 is intermittently applied to the heater during execution of the print image forming process, an inrush current flows when the application is resumed. Therefore, in the commercial AC power supply, whenever the heater AC voltage V10 is intermittently applied to the heater during execution of the print image forming process, the power supply voltage value rapidly decreases and the fluctuation rate at the time when the application is resumed. DV2 is relatively high.

  Further, the conventional image forming apparatus stops so as to cut off the application of the heater AC voltage V10 having a predetermined effective value to the heater during or at the end of the print image forming process. For this reason, in the commercial AC power supply, whenever the application of the heater AC voltage V10 to the heater is stopped during execution or at the end of the print image forming process, the power supply voltage value suddenly increases at the stop of the application. As a result, the fluctuation rate DV2 becomes relatively high.

  From the above, in the present embodiment, even when the heater AC voltage V3 is applied to the heater 45 during the print image forming process, the variation rate DV1 of the power supply voltage value is greatly increased as compared with the conventional image forming apparatus. Can be reduced. In this embodiment, the heater AC voltage V3 is not turned on / off in order to adjust the temperature of the heating roller 43, but the heater AC voltage V3 is effective according to the detected temperature Tk1. The value is changed and applied to the heater 45. Therefore, in this embodiment, the amount of heat generated by the heater 45 can be adjusted frequently according to the detected temperature Tk1, and the fixing property of the toner image to the medium 5 is improved by making the temperature of the heating roller 43 substantially constant. be able to.

  In the color printer 1, various commercial AC power supplies 65 that supply commercial AC voltages having different power supply voltage values can be connected to the low-voltage power supply 55 as described above. For this reason, in the color printer 1, for each commercial AC power supply 65, the maximum duty ratio is set to be smaller as the power supply voltage value of the commercial AC voltage is higher. That is, in the color printer 1, the maximum duty ratio for the commercial AC power supply 65 that supplies the commercial AC voltage V1 having a power supply voltage value of 100 [V] is set to, for example, 80 [%]. In the color printer 1, the maximum duty ratio for the commercial AC power supply 65 that supplies the commercial AC voltage V1 having a power supply voltage value of 230 [V] is set to a predetermined duty ratio smaller than 80 [%]. Therefore, the printer control unit 50 holds a duty ratio table generated for each commercial AC power supply 65 according to the maximum duty ratio for the commercial AC power supply 65.

  Accordingly, the printer control unit 50 first sets the minimum value of 0 [%] for a predetermined time to the converter control unit 70 in accordance with the commercial AC power supply 65 connected to the low voltage power supply 55 during the print image forming process. The instruction is given while gradually increasing from the duty ratio to the maximum duty ratio for the commercial AC power supply 65. Next, the printer control unit 50 detects the duty ratio corresponding to the detected temperature Tk1 detected via the thermistor 54 based on the duty ratio table for the commercial AC power supply 65, and instructs the converter control unit 70. When the print image formation is completed, the printer control unit 50 gradually decreases the duty ratio instructed at that time from the duty ratio instructed at that time to the minimum duty ratio (that is, 0 [%]) in a predetermined time. And change it. As a result, the converter control unit 70 is connected to the AC-AC converter 67 when the commercial AC power supply 65 supplying any commercial AC voltage V1 having a power supply voltage value of 100 [V] to 230 [V] is connected. In the print image forming process, the same process as shown in FIGS. 11A to 11D is executed to generate heat from the same heater 45 and to bring the heating roller 43 to a substantially equal desired temperature. can do.

  In addition, the printer control unit 50 and the converter control unit 70 are not limited to the print image formation process, and apply a heater AC voltage having a certain effective value to the heater 45 in order to quickly start the print image formation process. Even in the standby state, basically the same processing as that shown in FIGS. 11A to 11D is executed. However, in the standby state, the printer control unit 50 controls the converter control unit 70 based on the maximum duty ratio and the target temperature that are lower than those in the print image forming process described above. Therefore, in the standby state, converter control unit 70 applies AC voltage to heater 45 while generating an AC voltage for heater that has a lower effective value than during print image formation processing. As a result, the converter control unit 70 can suppress the fluctuation rate of the power supply voltage value per unit time in the commercial AC power supply 65 even in the standby state, similarly to the above-described print image forming process.

  In the present embodiment, the printer controller 50 detects the duty ratio via the thermistor 54 instead of instructing the converter controller 70 according to the detected temperature Tk1 detected by the printer controller 50 via the thermistor 54. The detected temperature Tk1 is notified to the converter control unit 70. In the present embodiment, the converter control unit 70 holds the duty ratio table for each commercial AC power supply 65 described above, and the third and fourth switching control signals S4 and S4 are based on the duty ratio table and the detected temperature Tk1. The duty ratio of S5 can also be set.

(1-4) Operation and Effect of Embodiment In the above configuration, in the color printer 1, the printer control unit 50 detects the temperature of the heating roller 43 via the thermistor 54 during print image formation processing or in a standby state. Then, the converter control unit 70 applied the heater AC voltage V3 to the heater 45 while generating the AC voltage V3 for the heater by changing it to an effective value corresponding to the temperature. According to the above configuration, the color printer 1 continues the heater AC voltage V <b> 3 without turning on / off the heater 45 for adjusting the temperature of the heating roller 43 during the print image forming process or in the standby state. Therefore, the fluctuation rate DV1 of the power supply voltage value per unit time in the commercial AC power supply 65 can be significantly suppressed. As a result, the color printer 1 can prevent the occurrence of flicker in other devices connected to the same commercial AC power supply 65 as the color printer 1.

  In the color printer 1, the converter control unit 70 sets the heater AC voltage V <b> 3 to 0 [V] by the AC-AC converter 67 at the start of print image formation processing or the application of the heater AC voltage V <b> 3 to the heater 45 in the standby state. ], The effective value was gradually increased from the minimum effective value to a predetermined maximum effective value and applied to the heater 45 while being generated. As a result, the color printer 1 can significantly suppress the inrush current that flows when the heater 45 starts applying the heater AC voltage V3. Therefore, when the color printer 1 starts to apply the heater AC voltage V3 to the heater 45, the color voltage of the commercial AC power supply 65 is gradually decreased to greatly increase the fluctuation rate DV1 of the power supply voltage value per unit time. Can be suppressed. Therefore, the color printer 1 prevents flicker from occurring in other devices connected to the same commercial AC power supply 65 as the color printer 1 even when continuous application of the heater AC voltage V3 to the heater 45 is started. be able to.

  Further, in the color printer 1, the converter control unit 70 sets the heater AC voltage V <b> 3 to 0 [V] by the AC-AC converter 67 at the end of the print image forming process or the application of the heater AC voltage V <b> 3 to the heater 45 in the standby state. ], An effective value higher than the minimum effective value is applied to the heater 45 while being gradually lowered to the minimum effective value. Accordingly, when the color printer 1 finishes applying the heater AC voltage V3 to the heater 45, the power supply voltage value is gradually increased in the commercial AC power supply 65, and the fluctuation rate DV1 of the power supply voltage value per unit time is greatly increased. Can be suppressed. Therefore, the color printer 1 prevents flicker from occurring in other devices connected to the same commercial AC power supply 65 as the color printer 1 even after the continuous application of the heater AC voltage V3 to the heater 45 is completed. be able to.

  Further, in the color printer 1, the commercial AC voltage V <b> 1 is switched by the AC-AC converter 67 to generate the heater AC voltage V <b> 3 and apply it to the heater 45. However, in the color printer 1, a switching duty ratio with respect to the commercial AC voltage V1 when the AC-AC converter 67 generates the heater AC voltage V3 according to the power supply voltage value of the commercial AC voltage V1 supplied from the commercial AC power supply 65. The maximum switching duty ratio (that is, the duty ratio of the third and fourth switching control signals S4 and S5 for switching the commercial AC voltage V1 by the third and fourth switching circuit units 90 and 91) was changed.

  Therefore, the color printer 1 has a heater AC voltage V3 that is less than or equal to the maximum effective value corresponding to the power supply voltage value, regardless of which of the various commercial AC power supplies 65 that supply the commercial AC voltage V1 having different power supply voltage values. And the same heater 45 generates heat, and the heating roller 43 can be brought to a desired temperature. In other words, the color printer 1 can be used without any change in the configuration of the low-voltage power supply 55 having the AC-AC converter 67 and the fixing unit 15 having the heater 45, and any of various commercial AC power supplies 65 can be connected. 43 can be set to a desired temperature, and user convenience can be improved.

(2) Other embodiments (2-1) Other embodiments 1
In the above-described embodiment, the case where the AC-AC converter 67 is provided with the full bridge circuit 100 and the converter control unit 70 and the converter control unit 70 controls the full bridge circuit 100 has been described. However, the present invention is not limited to this, and although the full bridge circuit 100 is provided in the AC-AC converter 67, the converter control unit 70 is not provided, and the printer control unit 50 performs the AC-AC similarly to the converter control unit 70. The full bridge circuit 100 of the converter 67 may be controlled. According to the present invention, the configuration of the AC-AC converter 67 can be simplified.

(2-2) Other embodiment 2
In the embodiment described above, the case where the image forming apparatus according to the present invention is applied to the color printer 1 described above with reference to FIGS. 1 to 11 has been described. However, the present invention is not limited to this, and various other configurations such as a monochrome electrophotographic printer (hereinafter also referred to as a monochrome printer), an MFP (Multi-Function Peripheral), a facsimile, a copying machine, and the like. The present invention can be widely applied to image forming apparatuses.

(2-3) Other Embodiment 3
Further, in the above-described embodiment, the case where the heating roller 43 described above with reference to FIGS. 1 to 11 is applied as the heating member for heating the medium has been described. However, the present invention is not limited to this, and various other heating members can be widely applied such as an endless belt for heating a medium, a pressure roller provided with a heater inside, and the like.

(2-4) Other Embodiment 4
Further, in the above-described embodiment, the case where the heater 45 which is the halogen lamp described above with reference to FIGS. 1 to 11 is applied as the heater for heating the heating member for heating the medium has been described. However, the present invention is not limited to this, and various other configurations of heaters such as at least one halogen lamp or ceramic heater can be widely applied.

(2-5) Other Embodiment 5
Furthermore, in the above-described embodiment, the case where the thermistor 54 and the printer control unit 50 described above with reference to FIGS. 1 to 11 are applied as the temperature detection unit that detects the temperature of the heating member has been described. However, the present invention is not limited to this, and various other temperature detectors such as a thermistor and a converter controller 70 that detects the temperature of the heating roller 43 via the thermistor can be widely applied. .

(2-6) Other embodiment 6
Furthermore, in the embodiment described above, the AC voltage generator for heater that generates the AC voltage for heater based on the commercial AC voltage supplied from the commercial AC power source and applies it to the heater is used as the AC described above with reference to FIGS. -The case where the AC converter 67 is applied has been described. However, the present invention is not limited to this, and a wide variety of heater AC voltage generators having various configurations such as an AC-AC converter controlled by the printer controller 50 without the converter controller 70 being provided. Can be applied.

(2-7) Other Embodiment 7
Further, in the above-described embodiment, the heater AC voltage generator is controlled so that the heater AC voltage is applied to the heater while being variably generated with an effective value corresponding to the temperature detected by the temperature detector. The case where the converter control unit 70 described above with reference to FIGS. 1 to 11 is applied as the control unit has been described. However, the present invention is not limited to this, and various other control units such as the printer control unit 50 can be widely applied.

  The present invention can be used in an image forming apparatus such as a color printer, a monochrome printer, an MFP, a facsimile machine, and a copying machine.

  DESCRIPTION OF SYMBOLS 1 ... Color printer, 5 ... Medium, 15 ... Fixing unit, 43 ... Heating roller, 45 ... Heater, 50 ... Printer control part, 54 ... Thermistor, 55 ... Low voltage power supply, 65 ... Commercial AC power supply, 67... AC-AC converter, 70... Converter control unit, 100... Full bridge circuit, 82... First switching circuit unit, 83. 91, fourth switching circuit, S1, first switching control signal, S2, second switching control signal, S3, third switching control signal, S4, fourth switching control signal, V1,. Commercial AC voltage, V3: AC voltage for heater.

Claims (4)

A heater for heating a heating member for heating the medium;
A temperature detector for detecting the temperature of the heating member;
A heater AC voltage generator that generates a heater AC voltage based on a commercial AC voltage supplied from a commercial AC power source and applies the heater AC voltage;
A control unit that controls the heater AC voltage generation unit so that the heater AC voltage is applied to the heater while being variably generated to an effective value corresponding to the temperature detected by the temperature detection unit. An image forming apparatus. The controller is
When the application of the heater AC voltage to the heater is started, the effective value is gradually increased from 0 [V] to a predetermined maximum effective value so that the heater AC voltage is generated and applied to the heater. The image forming apparatus according to claim 1, wherein the heater AC voltage generator is controlled. The controller is
At the end of application of the heater AC voltage to the heater, the effective value higher than 0 [V] is gradually lowered to 0 [V] and applied to the heater while generating the heater AC voltage. The image forming apparatus according to claim 1, wherein the heater AC voltage generator is controlled. The heater AC voltage generator is
Switching the commercial AC voltage supplied from the commercial AC power source to generate the heater AC voltage;
The controller is
The commercial AC voltage supplied from the commercial AC power supply is switched at a maximum switching duty ratio or less corresponding to the power supply voltage value of the commercial AC voltage to be applied to the heater while generating the heater AC voltage. The image forming apparatus according to claim 1, wherein the heater AC voltage generation unit is controlled.

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