JP2005251561A - Heater driving device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heater driving device which is of lower cost and smaller in size than conventional one and can prevent flicker phenomenon caused by rush current, and an image forming device having the driving device. <P>SOLUTION: The heater driving device is constructed of a constant voltage output circuit having a slowing-up function, a power supply circuit for supplying power to a heater by a route different from the constant voltage output circuit, and a switching means for switching over the above constant voltage output circuit and the power supply circuit. When slowing up the heater, the constant voltage output circuit and the heater is connected, and at normal lighting, the power supply circuit is connected to the heater. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a heater driving device and an image forming apparatus including the heater driving device.

  For example, in an electrophotographic image forming apparatus such as a copying machine or a laser beam printer, it is well known that there is a fixing step for fixing a toner image semi-permanently on a recording sheet by applying heat and pressure. In such an image forming apparatus, in order to keep the temperature of the fixing device constant, control for repeatedly switching between energization and interruption of the heating unit is often performed.

  In the fixing step, a halogen heater is widely used as a heating means. However, generally, the resistance value of the halogen heater has a positive temperature coefficient characteristic, and the moment when the energization of the halogen heater is started (temperature is The resistance value at the time of low) is very small compared to the resistance value at the time of normal energization (when the temperature is high). For this reason, when an overcurrent flows when the halogen heater is turned on and off, and there is a lighting fixture that is supplied with power from the same outlet to which this type of image forming apparatus is connected, it is caused by the overcurrent. Flicker phenomenon (flickering of lighting equipment) may occur.

  For this reason, in the invention described in Patent Document 1, when the energization of the heater is started, a constant time constant is given to gradually increase the voltage (hereinafter referred to as slow-up), and conversely, when the energization is interrupted, gradually. A constant voltage output circuit having a function of lowering the voltage (hereinafter referred to as slow-down) is provided to prevent a flicker phenomenon.

  The effect of the said invention is demonstrated using FIG.

  FIG. 7 shows waveforms of effective voltage and effective current applied to the heater. When power is directly supplied from the commercial power supply to the heater, the waveforms of the effective voltage and effective current at the on / off switching are as shown in FIG. The reason why the overshoot (inrush current) at the rise of the effective current is very large is that the electric resistance when the temperature of the heater is low is very small. On the other hand, when a predetermined voltage is applied with a constant time constant Ta using a constant voltage output circuit having a slow-up function, inrush current can be suppressed as shown in FIG.

In this way, the flicker phenomenon can be prevented.
JP-A-11-354254

  However, as described above, when the heater is driven by the constant voltage output circuit, if the power consumption of the heater is large, the specifications required for elements such as capacitors and inductors used in the constant voltage output circuit are increased. There was a problem that it led to an increase in cost and an increase in the size of the apparatus. In addition, it is desirable to provide a noise countermeasure filter such as a π-type filter on the input side of the constant voltage output circuit, but this also requires a high-cost element if the power consumption of the heater is large. was there.

  On the other hand, in a high-speed machine having a large number of printed sheets per minute, a halogen heater with high power consumption is necessary in order to give the fixing device a sufficient amount of heat.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a heater driving device that is smaller in size than the prior art and that prevents flickering due to inrush current, and the heater. An image forming apparatus including a driving device is provided.

  Therefore, the present invention intends to achieve the above object by providing the heater driving device and the image forming apparatus described in any of the following items (1) to (9).

  (1) A constant voltage output circuit for supplying a predetermined voltage to a heater as a heat generating means, a slow-up means for raising the output voltage of the constant voltage output circuit with a predetermined time constant, and a path different from the constant voltage output circuit A heater driving device comprising: a power supply circuit for supplying power to the heater; and switching means capable of freely switching between conduction and interruption between the heater and the power supply circuit.

  (2) The heater driving apparatus according to (1), further comprising slow-down means for lowering the output voltage of the constant voltage output circuit with a predetermined time constant.

  (3) Either of (1) and (2), wherein when the power is supplied to the heater by the power supply circuit, the output of the constant voltage output circuit is reduced or cut off. The heater drive device according to item.

  (4) The heater driving device according to any one of (1) to (3), further including a filter for removing noise on an input side of the constant voltage output circuit.

  (5) Further, a timer for measuring the passage of time is provided, and the switching means switches between conduction and interruption between the heater and the power supply circuit on condition that a predetermined time has elapsed from a predetermined timing. The heater driving device according to any one of (1) to (4).

  (6) Furthermore, it has voltage detection means for detecting the output voltage of the constant voltage output circuit, and the switching means is connected to the heater and the power supply circuit according to the voltage value detected by the voltage detection means. 6. The heater driving device according to any one of (1) to (5), wherein the shut-off is switched.

  (7) The heater driving apparatus according to any one of (1) to (6), wherein the heater is a halogen heater.

  (8) The heater driving device according to any one of (1) to (7), wherein the switching unit is a triac or an FET.

  (9) An image forming apparatus including a heat fixing unit and a heat fixing device which is heated by the heat generating unit and fixes a toner image onto a recording medium, and the heater driving unit of the heat fixing device (1) An image forming apparatus comprising the heater driving device according to any one of (8) to (8).

  According to the present invention, there is provided a heater driving device and an image forming apparatus that can achieve specification down of a constant voltage output circuit and its peripheral circuits, are smaller at a lower cost than conventional ones, and can prevent a flicker phenomenon due to an inrush current. Can be provided.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings by using a plurality of examples.

  A first embodiment will be described with reference to FIGS.

  First, an image forming apparatus according to the present invention will be described.

  In FIG. 1, reference numeral 101 denotes an electrophotographic laser beam printer as an image forming apparatus according to the present invention.

  102 is a deck, 103 is a deck sheet presence sensor, 104 is a sheet size detection sensor that detects the size of a recording sheet, 105 is a pickup roller, 106 is a deck feeding roller, 107 is a retard roller, and 108 is a feeding roller. 109, feeding roller pair, 110 a registration roller pair, 111 a pre-registration sensor, 112 a laser scanner unit, 113 a process cartridge, 114 a photosensitive drum, 115 a charging roller, 116 a developer, 117 Is a transfer roller, 118 is a static elimination needle, 119 is a conveyance guide, 120 is a fixing roller, 121 is a halogen heater, 122 is a pressure roller, 123 is a fixing device, 124 is a fixing discharge sensor, 125 is a double-sided flapper, and 126 is paper discharge. Sensor 127, paper discharge roller pair, 128 reverse roller pair, 129 reverse Sensor, 130 is a D-cut roller, 131 is a duplex sensor, 132 is a duplex conveying roller pair, 133 is a laser unit, 134 is a polygon mirror, 135 is a scanner motor, 136 is an imaging lens group, 137 is a folding mirror, and 138 is a main mirror Motor 139, high voltage power supply, 140 printer control unit, 141 display panel, 142 external device, 143 MPU, 144 interface, 145 storage device, P recording sheet.

  The laser beam printer 101 includes a deck 102 that stores recording sheets P, a deck sheet presence sensor 103 that detects the presence of recording sheets P in the deck 102, and a sheet that detects the size of the recording sheets P in the deck 102. The recording sheet P is paired with a size detection sensor 104, a pickup roller 105 that feeds the recording sheet P from the deck 102, a deck feeding roller 106 that transports the recording sheet P fed by the pickup roller 105, and the deck feeding roller 106. A retard roller 107 for preventing double feeding of P is provided.

  A feed sensor 108 that detects a feeding / conveying state is provided downstream of the deck feeding roller 106 in the sheet conveying direction (hereinafter simply referred to as “downstream”), and a feeding conveyance for conveying the recording sheet P further downstream. A roller 109, a registration roller pair 110 that conveys the recording sheet P in synchronization with the image forming operation, and a pre-registration sensor 111 that detects the conveyance state of the recording sheet P to the registration roller pair 110 are provided.

  Downstream of the registration roller pair 110, a process cartridge 113 constituting an image forming unit that forms a toner image on the photosensitive drum 114 based on laser light from a laser scanner unit 112, which will be described later, is attached to the apparatus main body. It is detachably attached.

  The process cartridge 113 is provided with a rotatable photosensitive drum 114, a charging roller 115 and a developing device 116 around the photosensitive drum 114, and a cleaning device (not shown). The latent image is uniformly charged and selectively exposed from the laser scanner unit 112 to form a latent image. The latent image is developed with toner by the developing device 116 to be visualized.

  Further, the process cartridge 113 is provided with a nonvolatile storage element 145, and a printer control unit 140 described later can write information into the storage element 145 in addition to reading information from the storage element 145.

  Then, by applying a transfer bias voltage to the transfer roller 117, the toner image is transferred to the conveyed recording sheet P to form an image.

  Disposed downstream of the transfer roller 117 are a static elimination needle 118 and a conveyance guide 119 for removing charges on the recording sheet P and promoting separation from the photosensitive drum 114.

  A fixing device 123 for thermally fixing the toner image transferred onto the recording paper sheet P is disposed further downstream of the conveyance guide 119. The fixing device 123 includes a fixing roller 120 having a halogen heater 121 for heating therein, a pressure roller 122 that comes into contact with the fixing roller 120 with a certain nip width, and a fixing paper discharge that detects a conveyance state from the fixing unit. The sensor 124 and temperature detection means (not shown) for detecting the temperature of the fixing roller 120 are used, and a toner image is recorded by heat from the halogen heater 121 and pressure between the fixing roller 120 and the pressure roller 122. Fix to the sheet P.

  A printer control unit 140, which will be described later, controls on / off of the halogen heater 121 so that the temperature of the fixing roller 120 becomes a predetermined value.

  Further downstream, a double-sided flapper 125 for switching the destination of the recording sheet P conveyed from the fixing device 123 to the paper discharge unit or the double-side reversing unit is disposed. A paper discharge sensor 126 that detects the paper conveyance state of the paper discharge unit and a paper discharge roller pair 127 that discharges the recording paper are provided.

  On the other hand, in order to print on both sides of the recording sheet P, the recording sheet P after the one-side printing is turned upside down, and the recording sheet P is fed to the double-side reversing part side for feeding again to the image forming part by forward / reverse rotation. The recording sheet P is transported from a pair of reversing rollers 128 for switching back, a reversing sensor 129 for detecting a paper transporting state to the reversing rollers 128, and a lateral registration portion (not shown) for aligning the lateral position of the recording sheet P. A D-cut roller 130 for detecting the recording sheet P in the double-side reversing unit, and a double-sided conveying roller pair 132 for conveying the recording sheet P from the double-side reversing unit to the paper feeding unit. Yes.

  The laser scanner unit 112 scans the photosensitive drum 114 with a laser unit 133 that emits a laser beam modulated based on an image signal transmitted from an external device 142, which will be described later, and the laser beam from the laser unit 133. A polygon mirror 134, a scanner motor 135, an imaging lens group 136, and a folding mirror 137.

  The main motor 138 supplies power to each part.

  In addition to the charging roller 115, the high-voltage power supply 139 has a high-voltage circuit that supplies a desired voltage to the developing device 116, the transfer roller 117, and the charge removal needle 118.

  The printer control unit 140 controls the laser printer 101 and includes an MPU including a RAM, a ROM, a timer, a digital input / output port, an A / D conversion port, a D / A conversion port (all not shown), and the like. (Microcomputer) 143 and various input / output control circuits (not shown).

  The display panel 141 displays the status of the laser beam printer 101 and conveys information to the user.

  The printer control unit 140 is connected to an external device 142 such as a personal computer via an interface 144.

  FIG. 2 shows a block diagram of a signal path of a heater driving circuit for supplying electric power to the halogen heater 121.

  In the figure, 201 is a commercial power source, 202 is a rectifier circuit, 203 is a triac, 205 is a π-type filter, 206 is a constant voltage output circuit, 207 to 209 are capacitors, 210 and 211 are inductors, 212 is a diode, 213 is an FET, 214 is a control IC, 215 is a voltage detection circuit, and 216 is a capacitor.

  The printer controller 140 switches on / off the halogen heater 121 by the heater drive circuit shown in FIG. 2 so that the temperature of the fixing roller 121 becomes a predetermined value.

  The AC voltage output from the commercial power supply 201 is full-wave rectified by the rectifier circuit 202. When the triac 203 is conducting, the output voltage of the rectifier circuit 202 is directly applied to the halogen heater 121. When the triac 204 is shut off, the output voltage of the rectifier circuit 202 is applied to the halogen heater 121 via the π filter 205 and the constant voltage output circuit 206. The conduction and interruption of the triac 203 are switched by a signal Tsel from the printer control unit 140.

  The π-type filter 205 includes a capacitor 207, a capacitor 208, and an inductor 210, and has a role of removing noise from the power supply line.

  The constant voltage output circuit 206 includes a step-down DC-DC converter including a chopping FET 213, an inductor 211, a capacitor 209, and a diode 212. The gate terminal of the FET 213 is connected to the Vout terminal of the control IC 214, and the control IC 214 can switch the FET 213 on and off.

  The output voltage of the constant voltage output circuit 206 is detected by the voltage detection circuit 215 and fed back to the Vref terminal of the control IC 214. The control IC 214 controls the on-duty of the FET 213 so that the feedback value becomes a predetermined value.

  The printer control unit 140 is connected to the control IC 214 and can control on / off of the constant voltage power source 206 by a enable signal. When the enable signal goes high, the control IC 214 drives the constant voltage power source 206. At this time, the control IC 214 performs slow-up and slow-down with a slow-up time constant Ta and a slow-down time constant Td corresponding to the capacity of the capacitor 216 connected to the SS terminal.

  A means for controlling the voltage or current of the halogen heater 121 via the π-type filter 205 and the constant voltage output circuit 206 to prevent the flicker phenomenon caused by the inrush current is described in JP-A-11-354254. It is publicly known.

  Next, FIG. 3 shows a timing chart (one cycle) of heater on / off control in this embodiment.

  In FIG. 3, (a) is a constant voltage circuit drive signal Enable, (b) is a triac drive signal Tsel, (c) is an effective voltage waveform applied to the heater, and (d) is an effective current waveform flowing through the heater.

  When the signal Enable output from the printer controller 140 becomes high, the output voltage of the constant voltage circuit 206 gradually increases with the slow-up time constant Ta, and becomes constant after reaching the voltage Vb. The voltage Vb is set lower than the rated voltage Va of the halogen heater 121.

  The printer control unit 140 sets the signal Tsel to high and makes the triac 203 conductive after a predetermined time Tsa has elapsed from the rise of the signal Enable. When the triac 203 is turned on, the voltage that has been full-wave rectified by the rectifier circuit 202 is directly applied to the halogen heater 121. The effective voltage value at this time is Va.

  When the triac is conducting, the signal Enable is set to low to stop the constant voltage circuit 206.

  When turning off the halogen heater 121, the constant voltage circuit 206 is driven for slowing down, and then the Tsel signal is set to low to cut off the triac. Thereby, the effective voltage value applied to the halogen heater 121 becomes Vb.

  When the signal Enable is made low after the time Tsd has elapsed, the constant voltage circuit 206 slows down with the slowdown time constant Td and stops.

  In the configuration as described above, the maximum output of the constant voltage circuit 206 may be a voltage Vb lower than the rated voltage Va of the heater, and the average current flowing through the FET 213, the diode 212, the inductor 211, and the capacitor 209 is less than that of the conventional one. Become. Accordingly, the heat loss in each of the above elements is reduced, and it is possible to use a component of a package that is smaller and less expensive than the conventional one.

  Similarly, the inductor 210 and the capacitors 207 and 208 constituting the π-type filter can be reduced in cost and reduced in size as compared with the prior art.

  As described above, in this embodiment, it is possible to achieve cost reduction and miniaturization of the heater driving circuit while suppressing a steep current fluctuation at the time of heater on / off switching.

  In this example, Tsa> Ta, but Tsa <Ta, that is, before the slow-up in the constant voltage circuit 206 is completely finished, the triac 203 may be turned on.

  Next, Example 2 will be described with reference to FIGS. 4 and 5.

  The hardware configuration of the present embodiment is different from that of the first embodiment in the heater driving circuit for supplying power to the halogen heater 121.

  FIG. 4 is a block diagram showing a signal path of the heater driving circuit in the present embodiment.

  In the figure, 401 is a commercial power supply, 402 is a rectifier circuit, 403 is a triac, 405 is a π-type filter, 406 is a constant voltage output circuit, 407 to 409 are capacitors, 410 and 411 are inductors, 412 is a diode, 413 is an FET, 414 is a PWM generation circuit, 415 and 416 are resistors.

  The description of the same configuration as in the first embodiment is omitted.

  The FET 413 in the constant voltage circuit 406 is chopped by a pulse generated by the PWM generation circuit 414. The PWM generation circuit 414 is connected to the printer control unit 140 by an 8-bit bus PW, and changes the on-duty of a pulse to be output with a resolution of 255 gradations according to a signal from the bus PW.

  The output voltage of the constant voltage circuit 406 is divided by resistors 415 and 416 and input to the Vsense terminal of the printer control unit 140. The Vsense terminal is an A / D conversion port, and the divided voltage is converted into a digital value. The printer control unit 140 outputs an 8-bit signal to the bus PW so that the output of the constant voltage circuit 406 becomes a desired value using the input of the Vsense terminal as a feedback value.

  FIG. 5 is a timing chart (one cycle) of heater on / off control in this embodiment.

  5, (a) is a target value of the output voltage of the constant voltage circuit, (b) is a triac drive signal Tsel, (c) is an effective voltage waveform applied to the heater, and (d) is an effective current waveform flowing through the heater. It is.

  The printer control unit 140 performs slow-up and slow-down by gradually changing the signal on the bus PW. The target output voltage value of the constant voltage circuit at this time is as shown in FIG.

  The normal energization voltage is Vb.

  As in the first embodiment, after the time Tsa has elapsed from the start of the slow-up, the printer control unit 140 sets the signal Tsel to high to make the triac 403 conductive. When the triac 403 is turned on, the voltage that has been full-wave rectified by the rectifier circuit 402 is directly applied to the halogen heater 121. The effective voltage value at this time is Va.

  When the triac is conducting, the constant voltage circuit 406 is stopped.

  When turning off the halogen heater 121, the output of the constant voltage circuit 406 is set to Vd, and then the Tsel signal is set to low to cut off the triac. Thereby, the effective voltage value applied to the halogen heater 121 becomes Vb.

  Further, after the time Tsd has elapsed, the output of the constant voltage circuit 406 is slowed down.

  With the configuration as described above, as in the first embodiment, the heat loss in the FET 413, the diode 412, the inductor 411, and the capacitor 409 can be made smaller than before, and the package parts that are smaller and less expensive than the conventional can be obtained. Can be used.

  In addition, the inductor 410 and the capacitors 407 and 408 constituting the π-type filter can use parts of a package that is smaller and less expensive than the conventional one.

  Next, Example 3 will be described with reference to FIG.

  The hardware configuration of this embodiment is the same as that of the second embodiment.

  FIG. 6 is a timing chart (one cycle) of heater on / off control in this embodiment.

  6, (a) is a measured value of the output voltage of the constant voltage circuit, (b) is a triac drive signal Tsel, (c) is an effective voltage waveform applied to the heater, and (d) is an effective current waveform flowing through the heater. It is.

  As in the second embodiment, the printer control unit 140 performs slow-up and slow-down by gradually changing the signal on the bus PW. The measured output voltage of the constant voltage circuit at this time is as shown in FIG. 6A. When the heater slows up, in Example 2, the timing when the triac drive signal Tsel becomes high starts slowing up. In this embodiment, the timing is when the output of the constant voltage circuit 406 detected by the A / D port Vsense reaches the threshold voltage Vth.

  On the contrary, when slowing down, the heater control unit 140 gradually increases the output of the constant voltage output circuit (the drive of the constant voltage output circuit is stopped during energization in a steady state), and the measured value reaches Vth. When this occurs, the triac is shut off and the output of the constant voltage output circuit 406 is slowed down.

  In the configuration as described above, the maximum output of the constant voltage circuit 406 may be the voltage Vth lower than the rated voltage Va of the heater, and the average current flowing through the FET 413, the diode 412, the inductor 411, and the capacitor 409 is less than that of the conventional one. Become. Accordingly, the heat loss in each of the above elements is reduced, and it is possible to use a component of a package that is smaller and less expensive than the conventional one.

  Similarly, the inductor 410 and the capacitors 407 and 408 constituting the π-type filter can be reduced in cost and size as compared with the conventional one.

  As described above, in this embodiment, it is possible to achieve cost reduction and miniaturization of the heater driving circuit while suppressing a steep current fluctuation at the time of heater on / off switching.

  In the above embodiment, only one halogen heater is provided. However, in an image forming apparatus having a plurality of halogen heaters (for example, an image forming apparatus having a heater in a pressure roller), each halogen is used. Applicable to heaters.

1 is a configuration diagram of an image forming apparatus according to a first embodiment. Signal path block diagram of heater driving circuit of embodiment 1 Timing chart of heater on / off control of embodiment 1 Signal path block diagram of heater driving circuit of embodiment 2 Timing chart of heater on / off control of embodiment 2 Timing chart of heater on / off control of embodiment 3 Illustration of prior art

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Laser beam printer 121 Halogen heater 123 Fixing apparatus 140 Printer control part 201 Commercial power supply 202 Rectifier circuit 203 Triac 205 Pi type filter 206 Constant voltage power supply 214 Control IC
406 Constant voltage power supply 414 PWM generation circuit

Claims (9)

  A constant voltage output circuit for supplying a predetermined voltage to the heater as the heat generating means, a slow-up means for starting up the output voltage of the constant voltage output circuit with a predetermined time constant, and a path different from the constant voltage output circuit to the heater A heater driving apparatus comprising: a power supply circuit that supplies electric power; and a switching unit that can freely switch between conduction and interruption between the heater and the power supply circuit.   2. The heater driving apparatus according to claim 1, further comprising slow-down means for lowering the output voltage of the constant voltage output circuit with a predetermined time constant.   The power supply circuit according to any one of claims 1 and 2, wherein when the power is supplied to the heater, the output of the constant voltage output circuit is reduced or cut off. Heater drive device.   The heater driving apparatus according to any one of claims 1 to 3, further comprising a filter for removing noise on an input side of the constant voltage output circuit.   Furthermore, it has a timer for measuring the passage of time, and the switching means switches on and off between the heater and the power supply circuit on the condition that a predetermined time has elapsed from a predetermined timing, The heater drive device according to any one of claims 1 to 4.   Furthermore, it has a voltage detection means which detects the output voltage of the said constant voltage output circuit, and the said switching means switches conduction | electrical_connection and interruption | blocking with the said heater and the said power supply circuit according to the voltage value which the said voltage detection means detected The heater driving device according to any one of claims 1 to 5, wherein the heater driving device is provided.   The heater driving device according to any one of claims 1 to 6, wherein the heater is a halogen heater.   The heater switching device according to any one of claims 1 to 7, wherein the switching means is a triac or an FET.   9. An image forming apparatus comprising a heat fixing device and a heat fixing device that heats the heat generating device and fixes a toner image on a recording medium, and serves as a heater driving device of the heat fixing device. An image forming apparatus comprising the heater driving device according to any one of the above.

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