JP2011096605A - Heater drive device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve diversification of a fixing heater in an image forming apparatus responding to DC feeding. <P>SOLUTION: The heater drive device that supplies AC power to a heater includes a switching circuit which converts DC power to AC power, a current detection circuit which detects an output current of the switching circuit, and a controller which controls the switching operation of the switching circuit. The controller discriminates, based on the current detected by the current detection circuit, which of predetermined two types of heaters a load connected to the switching circuit is, and controls the switching circuit so as to output power of a frequency preliminarily determined for each type of heaters according to the discrimination results. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a heater driving device that supplies AC power to a heater and an image forming apparatus that includes a fixing heater.

  An image forming apparatus that forms an image on a sheet by electrophotography includes a fixing heater that heats the sheet on which the toner image is transferred. The toner, which is a color material, is melted by heating and fixed on the paper. A halogen lamp is widely used as a fixing heater. There is also an image forming apparatus including a heater that generates heat by induction heating (IH). Induction heating heaters are more expensive than halogen lamps, but have excellent heat generation efficiency and responsiveness, and are useful for speeding up image formation.

  Regarding the driving of the halogen lamp, there is a technique in which commercial alternating current is rectified and then intermittently supplied by a switching means and supplied to the halogen lamp. The average value of the supply voltage can be made substantially constant by switching control. For an AC control device using this technology, it has been proposed to detect a load current and limit the conduction ratio when the load current is a predetermined value or more (Patent Document 1).

  Regarding the driving of the induction heating type heater, in the induction heating type fixing device in which a plurality of cores having different frequency characteristics of loss are arranged in the vicinity of the coil, the AC power supplied to the coil according to the width dimension of the transfer paper There is a technology to change the frequency. According to this, the core optimum for the width dimension of the transfer paper can contribute to the generation of the AC magnetic field, and the temperature distribution of the fixing roller can be made uniform regardless of the size of the transfer paper (Patent Document 2). ).

JP-A-9-218720 JP 2002-40872 A

  While energy saving is desired, direct current power supply, which converts direct current indoor power supply to households, offices, factories, stores, etc., has attracted attention. In order to adapt an image forming apparatus having a fixing heater to DC power feeding, a heater driving device that drives the fixing heater with electric power supplied from a DC power source is required. Drives both a lamp heater such as a halogen lamp suitable for AC power with a relatively low frequency of several kHz or less and an induction heater suitable for AC power with a relatively high frequency of about several tens of kHz. If there is a heater driving device that can be used, it is possible to reduce the manufacturing cost by using a common heater driving device when manufacturing a plurality of types of image forming apparatuses such as a popular type and a high-speed type.

  The present invention has been made in view of such circumstances, and an object thereof is to diversify fixing heaters in an image forming apparatus compatible with DC power supply.

  A heater driving device that achieves the above object is a heater driving device that supplies AC power to the heater, a switching circuit that converts DC power into AC power, a current detection circuit that detects an output current of the switching circuit, A controller for controlling a switching operation of the switching circuit. In the heater driving apparatus, the controller determines whether the load connected to the switching circuit is one of two predetermined heaters based on the current detected by the current detection circuit. According to the result, the switching circuit is controlled so as to output electric power having a predetermined frequency for each type of the heater.

  According to the first or second aspect of the present invention, it is possible to provide a heater driving device useful for diversifying fixing heaters in an image forming apparatus that supports direct current power supply.

  According to the third to fifth aspects of the present invention, it is possible to realize a DC power supply compatible image forming apparatus in which the induction heating type heater and the lamp type heater can be interchanged without replacing the heater driving device.

It is a figure which shows the structure of the heater drive device which concerns on embodiment of this invention. It is a signal waveform diagram which shows the outline | summary of switching control. It is a flowchart of the heater discrimination | determination process which a heater drive device performs. It is a graph which shows the electric current characteristic at the time of an energization start of a lamp type heater and an induction heating type heater. It is a wave form diagram which shows the change of the switching signal and output current in soft start control. 1 is a diagram illustrating an example of a configuration of an image forming apparatus. It is a figure which shows the modification of the switching circuit of a heater drive device.

  A heater driving apparatus according to an embodiment of the present invention is incorporated in an electrophotographic image forming apparatus compatible with DC power supply, and drives a fixing heater.

  As shown in FIG. 1, the heater driving device 1 includes a switching circuit 2 that converts, for example, 400 volt DC power supplied from a DC power supply 6 into AC power, and a current detection circuit 3 that detects an output current of the switching circuit 2. And a controller 4 that controls the switching operation of the switching circuit 2. A series circuit of a DC power source 6, a power switch 7 and a fuse 8 is connected to the power input terminals 11 and 12 of the heater driving device 1, and a fixing heater 9 incorporated in the fixing unit 90 is connected to the output terminals 13 and 14. Connected as a load.

  The switching circuit 2 includes two switching elements 21 and 22 connected in series between the power input terminals 11 and 12. The switching elements 21 and 22 are insulated gate bipolar transistors (IGBTs), MOS field effect transistors (MOS-FETs), or other voltage controlled elements. A connection point (middle point) of the switching elements 21 and 22 is connected to one output terminal 13. When the switching element 21 connected to the power input terminal 11 on the positive polarity side is in an on state, the DC power source 6 passes through the power switch 7, the fuse 8, the power input terminal 11, the switching element 21, and the output terminal 13 for fixing. A current flows to the heater 9. When the switching element 21 is off, the energization from the DC power source 6 to the fixing heater 9 is stopped. When the switching element 21 is in the off state and the other switching element 22 is in the on state, a loop through which a current generated by the inductance component of the fixing heater 9 flows is formed.

  The current detection circuit 3 includes a current detection resistor (shunt resistor) 31 inserted between the power input terminal 12 and the output terminal 14, and a conductive path 32 that connects the output terminal 14 and the controller 4. . The potential of the output terminal 14 is transmitted to the controller 4 by the current detection circuit 3. When a current flows through the resistor 31, a potential difference corresponding to the voltage drop of the resistor 31 is generated between the potential of the power input terminal 12 and the potential of the output terminal 14, which are a reference potential (for example, ground potential). This potential difference, that is, the voltage between the terminals of the resistor 31, corresponds to the current value of the electric power supplied to the fixing heater 9.

  The controller 4 outputs switching signals S21 and S22 that determine the on / off states of the switching elements 21 and 22. The switching signals S21 and S22 are basically voltage pulse train signals in which pulses appear at a predetermined cycle as shown in FIG. When the switching signals S21 and S22 are switched from the low level (L) to the high level (H), the corresponding switching elements 21 and 22 transition from the off state to the on state. Conversely, when the switching signals S21 and S22 are switched from the high level (H) to the low level (L), the corresponding switching elements 21 and 22 transition from the on state to the off state. The switching signal S21 and the switching signal S22 are alternately at a high level. In order to prevent a short circuit between the power input terminals 11 and 12, a dead time during which both the signals S21 and S22 are low is provided between the high level period of the switching signal S21 and the high level period of the switching signal S22.

  The driving frequency (frequency of AC power supplied to the fixing heater 9) determined by the switching signals S21 and S22 is switched according to the type of the fixing heater 9 connected to the output terminals 13 and 14. In the present embodiment, one of two types of heaters, a lamp type heater represented by a halogen lamp and an induction heating type heater, is connected to the output terminals 13 and 14. When a lamp heater is connected, the drive frequency is set to a value of about 0.1 to 1 kHz. On the other hand, when an induction heater is connected, the drive frequency is set to a value of about several tens of kHz.

  In order to determine the driving frequency, the controller 4 automatically determines the type of the fixing heater 9. The controller 4 includes a current measurement unit 41 and a heater determination unit 42 for this operation. The current measuring unit 41 and the heater discriminating unit 42 are functional elements realized by the controller 4 executing the heat discriminating process shown in the flowchart of FIG. 3 in accordance with a program stored in an internal memory.

  The heat determination process in FIG. 3 is executed as a part of the initial setting process corresponding to the power-on to the image forming apparatus when the power switch 7 is turned on, for example. When the heat determination process is activated, the current measuring unit 41 of the controller 4 turns on the positive-side switching element 21 (# 1). At this time, if a specific lamp heater or a specific induction heater is properly connected to the output terminals 13 and 14, a predetermined current flows through the output terminal 14. When a certain time described later has elapsed since the switching element 21 was turned on, the current measurement unit 41 measures the voltage across the terminals of the resistor 31 of the current detection circuit 3 (# 2, # 3). This measurement is essentially a measurement of the output current. The heater discriminating unit 42 discriminates the type of the fixing heater 9 by comparing the measured value obtained by the current measuring unit 41 corresponding to the output current value with a predetermined threshold value (4). If the measured value is greater than or equal to the threshold value, the heater determination unit 42 determines that the connected fixing heater 9 is a lamp heater (# 5), and sets the output mode of the heater driving device 1 to drive the lamp heater. Is set to “low frequency output” suitable for (# 6). On the other hand, if the measured value is not equal to or greater than the threshold value, the heater discriminating unit 42 discriminates that the connected fixing heater 9 is an induction heating type heater (# 7), and the output of the heater driving device 1 is determined. The mode is set to “high frequency output” suitable for driving the induction heater (# 8).

  For the automatic determination of the type of the fixing heater 9, the difference in the current rise characteristic (transient characteristic at the start of energization) between the lamp heater and the induction heater shown in FIG. 4 is used. In the case of a lamp heater, the current value changes so as to draw an overshoot waveform indicated by a curve A1 in FIG. On the other hand, in the case of the induction heating type heater, the current value changes so as to draw a gentle blunt waveform at the leading edge indicated by the curve A2 in FIG. Therefore, the current is measured at a time point t1 when a time T1 shorter than the time T2 until the current value in the lamp heater rises to the peak value and then falls to the saturation level has elapsed. The type of the fixing heater 9 can be determined by comparing the threshold value C1 set appropriately and the measured value. By setting a time constant τ (τ = L / R) determined by the inductance (L) and resistance (R) of the coil of the induction heating type heater or a value in the vicinity thereof as the time T1, an error due to saturation of the L component is set. Detection can be prevented. For example, when the L value is 27 μH and the R value is 1.2Ω, the time T1 may be 22 μs. Further, the threshold value C1 can be set to a value of about ¾ of the rated peak current of the induction heating type heater. For example, if the rated peak current is 60A, the threshold C1 is set to 45A.

  When the fixing heater 9 is determined to be a lamp heater by such automatic determination, the controller 4 performs slow start control in the subsequent driving of the fixing heater 9. Slow start control suppresses an excessive inrush current caused by a low cold resistance in a halogen lamp. FIG. 5 shows the leading edge (leading edge) of the first pulse of the pulse train signal as the switching signal S21 at the start of energization to shift from the pause operation that keeps the switching element 21 off to the energization operation that turns the switching element 21 on and off at a predetermined cycle. Relax as shown in (A). By operating the switching element 21 in the active region, the transition of the output current supplied to the fixing heater 9 is made gentle as shown in FIG.

  The heater driving device 1 described above is incorporated in the image forming apparatus 100 illustrated in FIG.

  As shown in FIG. 6, the image forming apparatus 100 is a color printer compatible with DC power supply having a power supply circuit 80 connected to the DC power supply 6. The configuration of the image forming apparatus 100 is basically an electrophotographic printer compatible with AC power supply, except that it is compatible with DC power supply and has a heater mounting portion 10 that allows the type of the fixing heater 9 to be changed. It is the same.

  The heater mounting unit 10 has a configuration in which the induction heating type heater and the lamp type heater can be interchanged by exchanging the fixing unit 90. The fixing unit 90 is a roller type fixing device including a heating roller 91 and a pressure roller 92. The fixing heater 9 is attached inside the heating roller 91.

  The outline of the operation of the image forming apparatus 100 is as follows. When the image forming apparatus 100 is instructed to print an image from a computer or other host device (not shown), the recording medium (paper) is stored one by one from the storage in the paper feed tray 40 by the paper feed roller 71, and the transport roller 73. , 74 are conveyed upward. In parallel with this paper feeding, the four photosensitive members 51, 52, 53, and 54 charged with the laser unit 50 are exposed based on the image data, and the four developing units 55, 56, 57, and 58 are respectively exposed. In this case, one color toner is attached to one corresponding photoconductor. The developed toner images on the four photoconductors are sequentially transferred onto the intermediate transfer belt 66 by applying a voltage. Next, by applying a voltage to the transfer roller 75, the toner image on the intermediate transfer belt 66 is transferred to the recording medium. The toner image formed on the recording medium is fixed on the recording medium by passing through a fixing unit 90 that applies heat and pressure. The recording medium on which the toner image is fixed is discharged to a paper discharge tray by a paper discharge roller 76.

  When the toner in the developing units 55, 56, 57, and 58 is reduced due to image formation, the toner stored in the toner bottles 61, 62, 63, and 64 is supplied to the developing units 55, 56, 57, and 58.

  The paper feed roller 71, the transport roller 74, the intermediate transfer belt 66, and the photosensitive member 54 related to black image formation are driven by a main motor 81. The heating roller 91 and the pressure roller 92 of the fixing unit 90 are driven by a fixing motor 85. The developing unit 58 for forming a black image is driven by a black developing motor 82. The developing units 55, 56, and 57 for forming yellow, magenta, and cyan images are driven by a color developing motor 83. The photoreceptors 51, 52, and 53 for forming yellow, magenta, and cyan images are driven by a color photoreceptor motor 84.

  According to the above embodiment, since the fixing heater 9 that is installed is automatically determined, for example, when replacing a unit that is equipped with an efficient induction heating type heater instead of a lamp type heater, the operation setting is performed. There is no need to do special work. Therefore, not only the service person but also the user of the image forming apparatus 100 can easily replace the unit.

  As a modification of the circuit configuration of the heater driving device 1, there is a switching circuit 2b of the heater driving device 1b shown in FIG. The switching circuit 2b in FIG. 7 is a circuit in which a resonant capacitor C1 is arranged in parallel between the controlled terminals of the switching element 22 in the switching circuit 2 in FIG. 1 (between the collector and emitter in the case of an IGBT). By forming the LC resonance circuit in which the inductance component of the load is involved, the conversion efficiency of power can be increased when the fixing heater 9 is an induction heating type.

DESCRIPTION OF SYMBOLS 1 Heater drive device 2, 2b Switching circuit 3 Current detection circuit 4 Controller 6 DC power supply 9 Fixing heater (heater)
DESCRIPTION OF SYMBOLS 10 Heater mounting part 11, 12 Power input terminal 100 Image forming apparatus

Claims (5)

A heater driving device for supplying AC power to the heater,
A switching circuit that converts DC power to AC power;
A current detection circuit for detecting an output current of the switching circuit;
A controller for controlling the switching operation of the switching circuit,
The controller determines whether the load connected to the switching circuit is a predetermined two types of heaters based on the current detected by the current detection circuit, and according to the determination result, The heater driving device, wherein the switching circuit is controlled so as to output electric power having a frequency determined in advance for each type of the heater. The heater driving apparatus according to claim 1, wherein the controller determines the type of the load based on a magnitude of a current value when a predetermined time has elapsed from the start of energization of the load by the switching circuit. An image forming apparatus for forming an image on a recording medium,
An induction heating type heater or a lamp type heater is mounted as a fixing heater for heating the color material, and a heater mounting portion capable of mutually replacing the induction heating type heater and the lamp type heater;
A power input terminal connected to a DC power supply;
A switching circuit that converts DC power supplied to the power input terminal into AC power supplied to a fixing heater mounted on the heater mounting portion;
A current detection circuit for detecting an output current of the switching circuit;
A controller for controlling the switching operation of the switching circuit,
The controller determines whether the fixing heater mounted on the heater mounting portion is the induction heating heater or the lamp heater based on the current detected by the current detection circuit. The image forming apparatus, wherein the switching circuit is controlled so as to output power having a frequency predetermined for each type of the fixing heater according to a result. In the controller, the current value at the time when a predetermined time determined based on the transient characteristics of the induction heating heater has elapsed from the start of energization of the load by the switching circuit corresponds to the saturation current of the lamp heater. The fixing heater mounted on the heater mounting portion is determined to be the lamp-type heater, and when the current value is smaller than the threshold, the fixing heater mounted on the heater mounting portion is determined. The image forming apparatus according to claim 3, wherein the heater is discriminated from the induction heating type heater. The controller performs soft-start control to moderate a current change at the start of energization of the switching circuit after determining the fixing heater mounted on the heater mounting portion as the lamp-type heater. 5. The image forming apparatus according to 4.

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