JP2005346475A - Power controller and heater controller and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate the malfunction of a zero cross signal even in countries or regions encountering the distorted voltage waveform of an AC power source; and to achieve an optimum on-off timing signal for a triac. <P>SOLUTION: Current-carrying control to a ceramic heater 701 conducts on-off switching for the triac after a first delay time (approximately 2 ms) with reference to the rise edge (a point changing off to on) of the zero cross signal when a positive voltage is input from the AC power source 901. Meanwhile, the current-carrying control conducts the on-off switching for the triac after a second delay time (approximately 4 ms) with reference to the tailing edge (a point changing on to off) of the zero cross signal when a negative voltage is input from the AC power source 901. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heater control device that controls a heater such as a ceramic heater that fixes a toner image on a transfer paper, for example, and an image forming device that has this heater control device and performs image formation using an electrophotographic process, and a heater control device The present invention relates to a power control device used for the above.

  2. Description of the Related Art An electrophotographic image forming apparatus such as a laser printer using an electrophotographic process has a thermal fixing device that thermally fixes a toner image on a sheet. This heat fixing device fixes an unfixed image (toner image) formed on a transfer paper by an image forming means such as an electrophotographic process on the transfer paper. As a type thereof, a heat roller using a halogen heater as a heat source A film heating type heat fixing device using a heat fixing device of a type and a ceramic surface heater as a heat source is known.

In general, the heater of the heat fixing unit as described above is connected to an AC power source such as a commercial power source via a switching control element such as a triac, and power is supplied from the AC power source. Further, the thermal fixing device is provided with a temperature detection element, for example, a thermistor temperature sensing element, and the temperature of the thermal fixing device is detected by this temperature detection element. Based on the detected temperature information, the engine controller turns on / off the switching element to turn on / off the power supply to the heater, and the temperature of the heat fixing device is controlled to a target constant temperature ( (See Patent Document 1). The heater on / off control is performed according to wave number control for controlling the wave number of alternating current that is energized per unit time or phase control for controlling the phase that is energized in each cycle. This wave number control or phase control includes a point at which the input AC power supply is switched from positive to negative or from negative to positive, and a signal for informing that the magnitude of the power supply voltage is below a certain threshold (hereinafter, This is based on “zero cross signal”).
JP-A-10-105254

  As described above, when the heater, which is a heat source of the heat fixing device, is driven and controlled by wave number control, the AC power supply voltage is “a voltage that is below a certain threshold and switches between positive and negative (zero cross) or a voltage near the zero cross” (Hereinafter generally referred to as zero crossing) needs to be detected. As a circuit for this purpose (zero-cross detection circuit), there is a full-wave rectification method in which a full-wave rectified AC voltage is compared with a predetermined threshold voltage, and a zero-cross signal is output when they coincide. However, in countries and regions where power supply conditions are poor, the power supply voltage waveform may be distorted as shown in FIG. 20, FIG. 16, or FIG. For such a distorted AC power source, the full-wave rectification type zero-cross detection circuit sometimes generates an erroneous zero-cross signal as shown in FIG. That is, as a result of full-wave rectification, such as when the voltage rises and falls at the original zero-cross point is steep, the voltage may be equal to or higher than the threshold voltage where the voltage should be zero. Further, in the vicinity of the zero cross point where the positive and negative are switched, when the zero cross signal is generated, chattering tends to occur at the edge portion. Therefore, it is necessary to remove chattering. The removal of chattering is realized by, for example, outputting the level as a zero-cross signal after removing chattering when the zero-cross signal is stabilized at a constant level for a certain period of time. Therefore, the zero cross signal after chattering removal is a signal delayed for a considerable time from the zero cross point of the power supply voltage. In wave number control, control is performed on the assumption that the phase of the zero-cross signal and the phase of the AC power supply are in a fixed relationship, but if the power supply frequency fluctuates, this phase relationship breaks down, and control that should be performed originally is not performed. It may not be done.

  The present invention has been made in view of the above-described conventional example, and uses a half-wave rectification method for zero-cross detection and switches on / off of the switching element at an optimal timing for each rising and falling edge of the zero-cross signal. An object of the present invention is to provide a power control device, a heater control device, and an image forming apparatus that can perform heater control satisfactorily.

  In order to achieve the above object, the present invention has the following configuration.

A zero cross detection circuit that compares the power supply voltage supplied from the AC power supply with the threshold value and outputs a signal of a level according to the comparison result as a zero cross signal;
A zero-crossing synchronous switching element that is arranged between the AC power supply and the load, and controls the energization / non-energization of the AC half-wave according to the level of the gate signal in synchronization with the positive / negative switching of the power supply voltage; ,
The gate signal is synchronized with the timing delayed by a first delay time from the rising edge of the zero-cross signal or the timing delayed by a second delay time from the falling edge of the zero-cross signal according to the power applied to the load. Power control means for switching the level of the output and outputting.

  More preferably, the zero-cross detection circuit outputs a high-level signal as the zero-cross signal when the power supply voltage is larger than the threshold, and a low-level signal when the power supply voltage is small. A rising edge or a falling edge of the gate signal falls within a half-cycle period, and a falling edge of the gate signal rising in the first half-cycle in a half-cycle immediately after the first half-cycle, Alternatively, a gate signal obtained by delaying the edge of the zero-cross signal is output so that the rising edge of the gate signal falling in the first half cycle is accommodated.

  More preferably, the zero cross detection circuit outputs a high level signal as the zero cross signal when the power supply voltage is greater than the threshold, and a low level signal when the power supply voltage is small, and the delay means switches the level of the gate signal. Output a gate signal obtained by delaying the edge of the zero cross signal so that the timing of the signal does not coincide with the zero cross point of the AC power source and the phase of the gate signal and the phase of the AC power source are constant regardless of time. .

  More preferably, the zero-cross detection circuit outputs a high-level signal as the zero-cross signal when the power supply voltage is larger than the threshold, and a low-level signal as the zero-cross signal when the power supply voltage is small. A gate signal in which the edge of the zero cross signal is delayed so that the relationship with the second delay time b is a <4 ms and 2 ms <b <7.7 ms and a <b is output.

  More preferably, the load is a heater, and the power control means controls the gate signal of the zero-crossing synchronous switching element to an on level so as to energize power corresponding to the temperature of the heater.

  Alternatively, the present invention resides in a heater control device that controls the temperature of the heater as the load by the power control device.

Alternatively, the present invention provides an image forming unit that forms a visible image corresponding to image data on a print medium with a color material;
A heater for thermally fixing the color material on the print medium;
An image forming apparatus comprising the heater control device according to claim 4 or 5 for controlling the heater.

  ADVANTAGE OF THE INVENTION According to this invention, even when the waveform of alternating current power supply voltage is distorted, favorable wave number control of a heater is attained. In addition, even if the power supply frequency fluctuates, the heater wave number can be controlled satisfactorily.

<Configuration and Operation of Image Forming Apparatus>
FIG. 1 is a schematic diagram showing an example of a full-color image forming apparatus (full-color printer) having an in-line type intermediate transfer belt (intermediate transfer means) in the electrophotographic system of the present invention.

  The image forming apparatus 1000 includes an image forming unit 1Y that forms a yellow image, an image forming unit 1M that forms a magenta image, an image forming unit 1C that forms a cyan image, and a black image. The four image forming units (image forming units) of the image forming unit 1Bk are formed, and these four image forming units 1Y, 1M, 1C, and 1Bk are arranged in a line at regular intervals.

  In each of the image forming units 1Y, 1M, 1C, and 1Bk, drum-type electrophotographic photosensitive members (hereinafter referred to as photosensitive drums) 2a, 2b, 2c, and 2d are installed as image carriers. Around each photosensitive drum 2a, 2b, 2c, 2d, there are primary chargers 3a, 3b, 3c, 3d, developing devices 4a, 4b, 4c, 4d, transfer rollers 5a, 5b, 5c, 5d as transfer means, Drum cleaner devices 6a, 6b, 6c, and 6d are disposed, respectively, and a laser exposure unit 7 is provided below the primary chargers 3a, 3b, 3c, and 3d and the developing devices 4a, 4b, 4c, and 4d. is set up.

  Each of the photosensitive drums 2a, 2b, 2c, and 2d is a negatively charged OPC (organic photoconductor) photosensitive member having a photoconductive layer on an aluminum drum base. It is rotated in the clockwise direction at a predetermined process speed.

  Primary chargers 3a, 3b, 3c, and 3d as primary charging means bring the surface of each photosensitive drum 2a, 2b, 2c, and 2d to a predetermined negative potential by a charging bias applied from a charging bias power source (not shown). Charge uniformly.

  Each developing device 4a, 4b, 4c, and 4d contains yellow toner, cyan toner, magenta toner, and black toner, respectively. The developing devices 4a, 4b, 4c, and 4d develop toner images by attaching toners of the respective colors to the electrostatic latent images formed on the photosensitive drums 2a, 2b, 2c, and 2d of the respective colors. )

  Transfer rollers 5a, 5b, 5c and 5d as primary transfer means are arranged so as to be in contact with the respective photosensitive drums 2a, 2b, 2c and 2d via the intermediate transfer belt 8 in the respective primary transfer portions 32a to 32d. Yes.

  The drum cleaners 6 a, 6 b, 6 c, and 6 d have a cleaning blade or the like for removing, from the photosensitive drum 2, transfer residual toner remaining on the photosensitive drum 2 during the primary transfer.

  The intermediate transfer belt 8 is made of a dielectric resin such as a polycarbonate, a polyethylene terephthalate resin film, a polyvinylidene fluoride resin film, or the like. The intermediate transfer belt 8 is disposed on the upper surface side of each of the photosensitive drums 2a, 2b, 2c, and 2d, and is stretched between the secondary transfer counter roller 10 and the tension roller 11, and the secondary transfer counter roller 10 Are arranged in the secondary transfer portion 34 so as to be in contact with the secondary transfer roller 12 via the intermediate transfer belt 8.

  The secondary transfer counter roller 10 is disposed so as to be in contact with the secondary transfer roller 12 via the intermediate transfer belt 8 at the secondary transfer unit 34. In addition, a belt cleaning device (not shown) that removes and collects transfer residual toner remaining on the surface of the intermediate transfer belt 8 is installed outside the endless intermediate transfer belt 8 and in the vicinity of the tension roller 11. ing. Further, a fixing device 16 having a fixing roller 16a and a pressure roller 16b is installed in a vertical path configuration downstream of the secondary transfer portion 34 in the transport direction of the transfer material P.

  The exposure unit 7 includes a laser light emitting unit such as a semiconductor laser that emits light corresponding to a time-series electric digital pixel signal of given image information, a polygon lens, a reflection mirror, and the like. Each photosensitive drum 2a, 2b, 2c, 2d is exposed by a laser beam modulated by an image signal, thereby being charged by each primary charger 3a, 3b, 3c, 3d. An electrostatic latent image for each color corresponding to image information is formed on the surface.

  FIG. 2 shows a top view of the exposure unit (laser scanner unit) 7. In FIG. 2, the BD sensor 214 is mounted on the laser driver 117 substrate and is attached to the scanning start side of the Bk photosensitive drum 2d.

  Laser exposure scanning other than the Bk photosensitive drum is also performed based on the beam detection signal from the BD sensor 214. When the laser light is irradiated from the same direction as shown in FIG. 2, the laser exposure scanning for the Y and M photoconductors is performed from the rear end side of the main scanning, and the C and Bk photoconductors are used. This is in the opposite direction to the exposure. In this case, it is common to place one line of video data for Y and M in a LIFO (Last In First Out) memory or the like to change the order of the images. Of course, if all the photosensitive members are irradiated from the head of the main scanning line, it is not necessary to use the LIFO.

  The image forming apparatus of the present embodiment is configured and operates as described above. However, the image forming mechanism is different from that of the present embodiment as long as the image forming apparatus includes a thermal fixing device for a color material such as toner. Even if it exists, this invention is applicable.

  Image formation by the image forming apparatus (electrophotographic printer) of FIG. 1 is performed as follows. When an image formation start signal is issued, the photosensitive drums 2a, 2b, 2c, and 2d of the image forming units 1Y, 1M, 1C, and 1Bk that are rotationally driven at a predetermined process speed are respectively connected to the primary chargers 3a, 3b, 3c and 3d are uniformly charged to negative polarity. Then, the exposure device 7 irradiates an image signal, which is color-separated from the outside, from the laser light emitting element, and passes each color on each photosensitive drum 2a, 2b, 2c, 2d via a polygon lens, a reflection mirror, or the like. An electrostatic latent image is formed.

  First, yellow toner is adhered to the electrostatic latent image formed on the photosensitive drum 2a by the developing device 4a to which a developing bias having the same polarity as the charging polarity (negative polarity) of the photosensitive drum 2a is applied. Visualize as an image. This yellow toner image is driven by a transfer roller 5a to which a primary transfer bias (a reverse polarity (positive polarity) to toner) is applied in a primary transfer portion 32a between the photosensitive drum 2a and the transfer roller 5a. Primary transfer is performed on the intermediate transfer belt 8.

  The intermediate transfer belt 8 onto which the yellow toner image has been transferred is moved to the image forming unit 1M side. Also in the image forming unit 1M, the magenta toner image formed on the photosensitive drum 2b is superimposed on the yellow toner image on the intermediate transfer belt 8 in the same manner as described above, and the primary transfer unit 32b. Transcribed. At this time, the transfer residual toner remaining on each photosensitive drum 2 is scraped off and collected by a cleaner blade or the like provided in the drum cleaner devices 6a, 6b, 6c, and 6d.

  Similarly, cyan and black toner images formed by the photosensitive drums 2c and 2d of the image forming units 1C and 1Bk on the yellow and magenta toner images superimposed and transferred on the intermediate transfer belt 8 are respectively transferred in the same manner. A full-color toner image is formed on the intermediate transfer belt 8 by sequentially superposing the portions 32a to 32d.

  Then, in accordance with the timing when the leading edge of the full color toner image on the intermediate transfer belt 8 is moved to the secondary transfer portion 34 between the secondary transfer counter roller 10 and the secondary transfer roller 12, the paper feed cassette 17 or the manual feed tray. The transfer material (paper) P selected from 20 and fed through the transport path 18 is transported to the secondary transfer section 34 by the registration roller 19. A full-color toner image is collectively transferred to the transfer material P conveyed to the secondary transfer unit 34 by the secondary transfer roller 12 to which a secondary transfer bias (polarity opposite to the toner (positive polarity)) is applied. Is done.

  The transfer material P on which the full-color toner image is formed is conveyed to the fixing device 16, and the full-color toner image is heated and pressed at the fixing nip portion between the fixing roller 16 a and the pressure roller 16 b to transfer the transfer material. After being thermally fixed on the surface of P, the paper is discharged onto a paper discharge tray 22 on the top surface of the main body by a paper discharge roller 21, and a series of image forming operations is completed.

<Configuration of controller unit>
FIG. 3 is a block diagram of the controller unit 150 and the image processing unit 300 in the conventional image forming apparatus 1000. When the image forming apparatus 1000 receives a print command in a predetermined format from a host device such as the computer 106, the image processing unit 300 analyzes the command, and generates bitmap image data corresponding to the gradation expression capability of the image forming apparatus. Generate etc. The generated image data is input to the controller unit 150 in accordance with a BD signal, a vertical synchronization signal, or the like input to the image processing unit 300 from the controller 150 in accordance with the synchronization signal. In the controller unit 150, first, the PWM unit 215 performs pulse width modulation on the image signal to generate a PWM signal that becomes a laser on / off signal by the laser unit 117, and inputs the PWM signal to the laser unit 117.

  In the controller unit 150, the CPU 201 controls the entire controller 150 including an engine unit constituted by devices connected to the I / O interface 206. The CPU 201 sequentially reads and executes a program from a read-only memory 203 (ROM) that stores a control procedure (control program) of the image forming apparatus 1000. The address bus and data bus of the CPU 201 are connected to each load through the bus driver circuit and address decoder circuit of 202. The RAM 204 is a random access memory that constitutes a main storage device used as input data storage, a working storage area, or the like.

  The I / O interface 206 is connected to various input / output devices. The input / output device includes a touch panel, a switch for an operator to operate, an operation panel 151 including a liquid crystal and an LED for displaying the state of the apparatus, and motors for driving a paper feed system, a transport system, and an optical system. 207, the loads of the image forming apparatus such as the clutches 208, the solenoids 209, and the paper detection sensors 210 for detecting the conveyed paper are included. In addition, a toner residual detection sensor 211 that detects the amount of toner in the developing device, a switch 212 for detecting the home position of each load, the open / closed state of the door, and the like, disposed in the developing device 118, a high voltage unit 213, A beam detection (BD) sensor 214 is also connected to the I / O port 206. The high voltage unit 213 outputs a high voltage to the primary charger 113, the developing device 118, the pre-transfer charger 121, the transfer charger 133, and the separation charger 134 in accordance with instructions from the CPU 201. An input signal of the temperature sensor 218 for measuring the heater temperature of the heat fixing device 16 is also input to the IO interface 206.

  A heater drive circuit 216 and a zero cross detection circuit 217 are connected to the CPU 201. An on-demand heater 701 is further connected to the heater driving circuit 216. In the present embodiment, the heater drive circuit 216 and the zero cross detection circuit 217 are directly connected to the CPU 201, but may be connected via an IO interface 206. The CPU 201 inputs a register setting value for removing chattering to the zero cross detection circuit 217. The zero-cross detection circuit 217 detects the zero-cross point of the power supply voltage, removes chattering according to the register setting, and inputs it to the CPU 201 as the zero-cross signal ZERO_OUT. A heater control signal for controlling energization / disconnection to the heater 701 is input from the CPU 201 to the heater drive circuit 216. The CPU 201 generates a heater control signal based on the input zero cross signal ZERO_OUT. The heater drive circuit 216 supplies the power supply voltage from the AC power supply 901 to the heater 701 when the heater drive signal is on.

  If the host device 106 is not a computer but an image scanner or the like, an image signal output from an image sensor such as a CCD unit is input to the image processing unit 300. The image processing unit 300 performs predetermined image processing and inputs it to the PWM unit 215. The PWM unit 215 outputs a control signal for the laser unit 117 according to the input image data. The laser light output from the laser unit 117 irradiates and exposes the photosensitive drum 110, and the light emission state is detected by the 214 beam detection sensor which is a light receiving sensor in the non-image region, and the output signal is output to the I / O port. It is input to 206. As described above, the signal serves as a reference signal for the synchronization signal input to the image processing unit 300.

<Image forming operation>
Next, the operation of the image forming apparatus will be described. When the image forming operation start signal is issued, the paper feeding operation is started from the paper feeding stage selected according to the selected paper size or the like. For example, a case where paper is fed from the upper paper feed stage will be described. First, the transfer material P is sent out one by one from the cassette by the paper feed roller. The transfer material P is guided between the paper feed guides 18 and conveyed to the registration rollers 19. At that time, the registration roller is stopped, and the leading edge of the paper hits the nip portion. Thereafter, the registration roller starts to rotate based on a timing signal at which the image forming unit starts image formation. The rotation timing is set so that the transfer material P and the toner image primarily transferred onto the intermediate transfer belt 8 from the image forming unit exactly coincide with each other in the secondary transfer region.

  On the other hand, in the image forming unit, when an image forming operation start signal is issued, an electrostatic latent image is formed on each color drum by the above-described operation. That is, the formation timing in the sub-scanning direction is determined and controlled in accordance with the distance between the image forming units in order from the photosensitive drum (Y in this embodiment) that is the most upstream in the rotation direction of the intermediate transfer belt 8. The Further, the writing timing of each drum in the main scanning direction is generated and controlled using a single BD sensor signal (arranged at Bk in this embodiment) by a circuit operation (not shown). The formed electrostatic latent image is developed by the process described above. The toner image formed on the most upstream photosensitive drum 2a is primarily transferred to the intermediate transfer belt 8 in the primary transfer region by the primary transfer charger 5a to which a high voltage is applied. The primarily transferred toner image is conveyed to the next primary transfer area. In this case, the image formation is delayed by the time during which the toner image is conveyed between the image forming portions by the timing signal described above, and the next toner image is transferred by aligning the resist on the previous image. It will be a thing. Thereafter, the same process is repeated, and eventually the four color toner images are primarily transferred onto the intermediate transfer belt 8.

  Thereafter, when the recording material P enters the secondary transfer area and contacts the intermediate transfer belt 8, a high voltage is applied to the secondary transfer roller 12 in accordance with the passing timing of the recording material P. Then, the four color toner images formed on the intermediate transfer belt by the process described above are transferred onto the surface of the recording material P. Thereafter, the recording material P is accurately guided to the fixing roller nip portion by the conveyance guide 34. The toner image is fixed on the paper surface by the heat of the roller pair 16a and 16b and the pressure of the nip. Thereafter, the paper is conveyed by the inner and outer paper discharge rollers 21 and the paper is discharged outside the apparatus.

  Next, the wave number control of the on-demand heater according to the present invention will be described with reference to FIG. FIG. 4 is a block diagram of the on-demand heater 16 of FIG. The on-demand heater 16 includes a ceramic heater 701, a fixing film 702, a pressure roller 703, a U-shaped sheet metal 711, a thermistor 712, a holder 713, and a self-bias circuit 714. The ceramic heater 701 is a heater in which a heat generation pattern is printed on ceramic, and is an extremely responsive heater that rises in temperature by about 50 ° C. in one second. The fixing film 702 uses a metal as a base material and is provided with a rubber layer of about 300 μm thereon, and is further subjected to a fluorine surface treatment. The heat capacity is extremely small, and the heat of the heater is transmitted only to the nip portion (contact portion). The pressure roller 703 is a roller having a hardness of about 60 degrees, and frictionally drives the fixing film 702. The U-shaped metal plate 711 presses the fixing film 702 against the pressure roller 703 from the inside, and the pressure is about 180N. The thermistor 712 detects the temperature of the heater 701. A main thermistor arranged in the center of the heater detects the temperature for controlling the fixing temperature. The sub-thermistor arranged at the end of the heater detects a temperature rise in the non-sheet passing portion when a small size paper is passed. The thermistor 712 constitutes a temperature sensor 218, and the output of the thermistor 712 is output from the temperature sensor 218 as a temperature signal converted into a digital signal by an AD converter, for example. FIG. 5 is a plan view of the heater 701 in FIG. In the figure, the heating element 704 generates heat by applying a voltage across the electrode 705.

<Heater drive circuit>
Next, a heater driving circuit 216 that drives and controls the ceramic heater 701 in the fixing device 16 will be described. FIG. 6 is a circuit diagram of a heater drive circuit for driving and controlling the ceramic heater 701 according to the present invention. As shown in FIG. 6, the heater drive circuit 216 includes an AC filter 902, a ceramic heater 701 connected to the AC power source 901 via the AC filter 902, and a triac 904 connected between the AC filter 902 and the ceramic heater 701. , Resistors 905, 906, a phototriac coupler 907 connected in series between the resistors 905, 906, a resistor 908 having one end connected to the phototriac coupler 907, a transistor 909 having a collector terminal connected to the phototriac coupler 907, A resistor 910 is connected to the base terminal of the transistor 909. The CPU 201 is connected to one end of the resistor 910.

  An AC power source 901 such as a commercial power source supplies the ceramic heater 701 with electric power via an AC filter 902 to cause the ceramic heater 701 to generate heat. The electric power supplied to the ceramic heater 701 is energized and interrupted by the triac 904. The resistors 905 and 906 are bias resistors for the triac 904, and the phototriac coupler 907 is a device for ensuring a creepage distance between the primary and the secondary. The phototriac coupler 7 constitutes a gate signal switch of the triac 904. When the light-emitting diode is energized, the light receiving element is turned on, and the gate signal of the triac 904 is turned on (conductive state). Is turned on.

  The resistor 908 is a resistor for limiting the current of the phototriac coupler 907, and is turned on (conducting state) / off (non-passing state) by the transistor 909. The transistor 909 operates in accordance with the heater control signal from the CPU 201 via the resistor 910. The transistor 909 is turned on when the heater control signal is on, and the light emitting diode of the phototriac coupler 7 is energized, and the triac 904 is turned on. If the heater control signal is off, the transistor 909 is also turned off and the triac 904 is also turned off.

  As described in the configuration diagram of FIG. 4, the thermal response of the heater is extremely fast. Therefore, on-demand heaters generally perform temperature control by performing wave number control for controlling the wave number of the AC waveform and phase control for controlling the on phase. In phase control, harmonics and terminal noise are severe and cost is high. Therefore, in this embodiment, wave number control advantageous in terms of cost and noise is used. However, the concept for zero crossing is the same in phase control.

  The wave number control of the heater will be described with reference to FIG. The triac 904 used in FIG. 6 is of the zero cross synchronization type, and if the ON signal is input from before the zero cross point of the AC input waveform, that is, if the gate signal is ON at the zero cross point, the next from the zero cross point. The half-wave current up to the zero-cross point of is conducted.

  As shown in FIG. 7, when the heater control signal is turned on at timing t1 and the level is maintained up to the zero cross point z1, the triac 904 conducts (turns on) the half-wave waveform W1 from the zero cross point z1 to the next zero cross point z2. . If the heater control signal remains on at the zero cross point z2, the half-wave waveform W2 is also energized. When the heater control signal is turned off at timing t2, the triac 904 becomes non-conductive (off) at the zero cross point z3. Next, when the heater control signal is turned on at timing t3 between the zero cross points z3 and z4, the half-wave waveform W3 is energized from the next zero cross point z4. As described above, when the AC half-wave is energized by the triac 904, it is necessary to switch on the heater control signal at a timing before the zero cross point and maintain the level at least at the zero cross point. On the other hand, when the triac 904 is turned off, it is necessary to switch the heater control signal off at a timing before the zero crossing point, which is the time when the triac 904 is turned off, and hold the level at least at the zero crossing point.

  Next, the level of wave number control will be described with reference to FIG. In this embodiment, the AC waveform applied to the on-demand heater has 15 half-waves as one block, and has a value of 15 levels depending on how much half-waves in one block are turned on. Level 1 turns on only one half of the 15 half-waves, Level 2 turns on two half-waves. Similarly, there are 15 levels depending on the number of half-waves that are turned on. Depending on the temperature detection result by the main thermistor described above, the temperature control level of FIG. In addition, since the ceramic heater of this embodiment has very high responsiveness with respect to the applied voltage, it is desirable to turn it on as uniformly as possible in one block. If the power supply is 50 Hz, the time corresponding to one half wave is 10 milliseconds, and if it is 60 Hz, it is 8.3 milliseconds. Therefore, when the power source is 50 Hz, the current having a waveform corresponding to each temperature control level shown in FIG. In addition, level 0 includes a non-energized state.

  The CPU 201 switches the heater control signal on and off in order to drive the heater at any one of these 15 levels. According to the present invention, the phase of the heater control signal and the phase of the power supply voltage have a fixed temporal relationship, which will be described later with reference to FIGS. 11, 12, 14, and 15 etc. . Apart from this phase relationship, there is a correspondence between the number of waves applied to the heater and the ON level of the heater control signal, and the heater temperature control is performed by controlling the ON / OFF switching of the heater control signal. . That is, the CPU 201 outputs a heater control signal in a pattern corresponding to each level in FIG. In the present embodiment, the temperature of the heater is detected by the temperature sensor 218, PID control is performed by the CPU 201 so that the heater 701 reaches the target temperature, and the temperature control level (shown in FIG. 8) is used properly. In the P control, when the temperature is lower than the target temperature, the temperature control level is increased and the number of waves to be supplied to the heater is increased. When the temperature is higher than the target temperature, the temperature adjustment level is decreased and the number of waves to be supplied to the heater is decreased. That is, feedback control is performed by giving a control output (wave number) proportional to the fluctuation of the heater temperature per certain time to the load. In the I control, the central level of the temperature control level used for temperature control is determined by the accumulated value of the temperature difference with respect to the target temperature. As a result, the steady deviation can be solved. It is D control that changes the center level when there is a sudden temperature change. Thus, it is possible to perform predictive control before a large deviation actually occurs.

  The heater control by the CPU 201 is, for example, the following control. Based on the temperature (temperature data) input from the temperature sensor 218, the CPU 201 changes the output pattern of the control signal so as to be one of level 0 to level 15 in FIG. 8 in order to maintain the ceramic heater at a predetermined set temperature. The heater control signal is switched on and off according to the output pattern. For example, in order to increase the temperature by turning on the heater at the start of printing, the CPU 201 first outputs a heater control signal in a pattern corresponding to a predetermined level, for example, level 15 which is the highest level. At level 15, the heater control signal is maintained at the on level for a time corresponding to 15 half-waves (hereinafter, the 15 half-wave is referred to as 1 cycle and the time corresponding to 15 half-waves is referred to as 1 cycle time). . This is repeated for a predetermined number of cycles while monitoring the temperature data at a predetermined sampling rate. Assuming that the heater 701 is heated at about 50 degrees / second, for example, if the target temperature is 150 degrees and the room temperature is 25 degrees, if the level 15 is repeated 250 cycles, the heater is heated up to about 125 degrees to reach the target temperature. . At that time, the CPU 201 shifts to a steady state, and the CPU 201 outputs a heater control signal according to a drive pattern of a predetermined center level (for example, determined in accordance with the room temperature at that time). The CPU 201 monitors the heater temperature every predetermined time, and outputs a heater drive signal in a pattern corresponding to a level corresponding to the lowered temperature if the heater temperature is lowered. Further, if the heater is overheated, a heater driving signal is output in a pattern corresponding to a level corresponding to the excess temperature. The correspondence between the changed temperature and the temperature control level is determined by PID control.

  In this embodiment, the heater drive signal is output in a pattern corresponding to each level. However, the pattern is not particularly defined, and the wave number may be driven in correspondence with each pattern.

<Zero cross detection circuit>
Next, a detailed circuit configuration of the zero cross detection circuit will be described. First, for comparison with the present invention, FIG. 18 shows a circuit diagram of a conventional zero-cross detection circuit. As shown in FIG. 18, the zero cross detection circuit includes a diode bridge 931 to which an AC power supply 901 is input via an AC filter 902, a protection resistor 932 connected to the output terminal of the diode bridge 931, and the protection resistor 932 A resistor 933, a capacitor 935 and a resistor 936 connected between the negative terminals of the diode bridge 31 and forming a loop with respect to the AC power supply 901, a transistor 937 connected in parallel to the circuit elements forming these loops, a resistor 938, and the transistor 937 The photocoupler 942 is driven through a resistor 938, and the photocoupler 942 is included. The AC power supply 901 is input to the diode bridge 931 via the AC filter 902. The AC signal that has been full-wave rectified by the diode bridge 931 passes through the resistance 932, the resistor 933, the capacitor 935, and the resistor 936, and is input to the negative terminal of the diode bridge 931. It is formed.

  The voltage of the AC power supply 901 and the voltage determined by the resistors 932 and 933, the capacitor 935, and the resistor 936 are input to the transistor 937. Here, if the voltage of the AC power supply 901 is not higher than the slice voltage Vth determined by the resistors 932, 933, the capacitor 935, the resistor 936, and the transistor 937, the transistor 937 is turned off, and if it is higher than the slice voltage Vth, it is turned on. It becomes. The output of the transistor 937 drives the photocoupler 942. The photocoupler 942 is a device for ensuring a creepage distance between the primary and secondary.

  In the zero cross detection circuit as described above, when the AC power source 901 is equal to or lower than the slice voltage Vth, the transistor 937 is turned off, the photocoupler 942 is turned on, and the output ZEROXA of the zero cross detection circuit is low. That is, the zero cross signal ZEROXA is a signal indicating that the voltage of the AC power supply 901 is within the slice voltage Vth up and down around zero volts, that is, a voltage value near the zero cross. Here, the switching speed of the transistor 937 is controlled by resistors 933 and 936 and a capacitor 935.

  FIG. 19 shows the state of the waveform in the circuit of FIG. The zero-cross detection circuit using the full-wave rectifier circuit of FIG. 18 generates a zero-cross signal in which a pulse appears only at a point near the zero-cross of the AC waveform, and generates an active-low zero-cross signal as shown in FIG. . When a zero-cross signal is generated by a full-wave rectifier circuit in the case of a distorted AC input sine wave as shown in FIG. 20, the waveform after rectification becomes a point waveform in FIG. 20a, and there is a portion that does not reach the threshold level of the transistor. May end up. As a result, the generated zero-cross signal is as shown in FIG. 20 ZEROXS, and the pulse of the dotted line portion that is originally desired is not output. When the wave number control of FIG. 8 is performed using such a zero cross signal, there may be a case where the target temperature cannot be converged as expected even if the PID control is used, or a ripple may be greatly generated.

<Zero Cross Detection Circuit According to the Present Invention>
FIG. 9 is a circuit diagram of a zero-cross detection circuit that performs zero-cross detection by half-wave rectification according to the present embodiment. This circuit can prevent malfunction when the AC input sine wave is distorted as shown in FIG. In the circuit shown in FIG. 9, an AC signal on the HOT terminal side is input to the diode 961 via an AC filter 902 (not shown) and half-wave rectified. The half-wave rectified signal is input to the negative terminal of the diode bridge 960 via the resistor 965, the capacitor 963, and the resistor 968, and forms a loop with respect to the AC power source 901. The output of the bridge 960 is supplied to each part of the image forming apparatus as a DC power source through a smoothing circuit and a step-down circuit.

  The photocoupler 966 is a device for ensuring a creepage distance between the primary and the secondary. The transistor 967 is turned on / off according to the threshold level determined by the resistors 962 and 964 in accordance with the signal from the photocoupler 966, and the waveform of ZEROX in FIG. 10 is obtained.

  FIG. 10 is a diagram for explaining the ZEROX signal transmitted by this circuit. As shown in FIG. 10, the threshold level determined by resistors 962 and 964 is compared with the half-wave rectified voltage, and a zero-cross signal that switches between the H level and the L level is generated for each half wave. In the circuit of FIG. 18, an active-low pulsed zero cross signal is generated at the zero cross point of the AC input sine wave. However, in the circuit of FIG. 9, the zero cross signal is switched at a duty of approximately half a wave of AC. The points are the rising and falling portions of the ZEROX signal.

  As shown in FIG. 21, the zero-cross detection circuit using the half-wave rectifier circuit of FIG. 9 outputs a zero-cross signal in which rising and falling at the zero-cross point are ensured. Therefore, for a distorted waveform, it is more advantageous to generate a zero cross signal by half-wave rectification.

  Although the present embodiment has been described with reference to FIG. 20 as the distortion waveform, the same effect can be obtained for other distortion waveforms as shown in FIGS. That is, even if the power supply waveform is distorted, the zero cross point can be reliably detected and output as the rising or falling edge of the zero cross signal.

  However, as shown in FIG. 11, chattering may occur in the threshold value portion of the b-point waveform. Since the zero-cross signal is generated from the rectified waveform at the threshold level of the transistor, the rising edge and the falling edge of the zero-cross signal are strictly shown in FIG. A little). In this embodiment, the threshold level is determined so that the delay time Tzs from the zero cross point to the zero cross signal fall and the delay time Tze from the zero cross signal rise to the zero cross point are from about 500 μs to 1 ms. The pulse width of the zero-cross signal ZEROXA in the conventional zero-cross circuit (FIG. 18) is about 500 μs to 1 ms. If it is shorter than that, the pulse will not be produced well or chattering will occur, and if it is too long, it will be affected by the harmonic component of the distorted wave, so the pulse width is set to approximately 500 μs to 1 ms. In this embodiment, Tzs and Tze are set to 500 μs to 1 ms, respectively, in order to prevent chattering that occurs in the zero-cross signal near the threshold level (threshold). Therefore, when the power supply frequency is 60 Hz, the H section of ZEROX is 7.333 ms to 6.333 ms. In general, the threshold value Vth for setting Tzs and Tze to d seconds is Vth = √2 · V · sin (2πfd) if the effective value of the ideal sine wave is V and the frequency is f. It becomes. That is, the threshold Vth for setting Tzs and Tze to 500 μs to 1 ms, respectively, is about 22.5 V to 44.5 V in the case of an AC power supply with an execution voltage of 100 V and a frequency of 50 Hz.

  In this embodiment, as a triac for supplying power to the heater, a zero cross-synchronized one that conducts from the zero cross point where the gate signal is on to the zero cross point where the gate signal is off is used, so the gate signal for turning on and off the triac is used. The timing of switching needs to be earlier than the zero cross detection point by triac. Therefore, in this embodiment, the problem of the zero cross point is solved by optimally setting the values of X and Y in FIG. In this embodiment, chattering removal is performed by a zero cross detection circuit. Of course, both are accompanied by a delay of the phase of the zero cross signal, and can be realized only by the zero cross detection circuit or only by the CPU.

  In the system of this embodiment, the zero cross detection circuit 217 includes a chattering removal circuit in addition to the circuit of FIG. That is, as shown in FIG. 12, the ZEROX signal of FIG. 9 is input to the ASIC 1201 to eliminate chattering, and the signal is output as an output zero cross signal ZEROX_OUT. Thus, the circuit of FIG. 9 and the circuit of FIG. 12 are integrated to form a zero cross detection circuit 217. The ASIC 1201 includes a register that can be set by the CPU, and has, for example, the following configuration. That is, the value set in the register is set to r, the input ZEROX signal is sampled at a constant period, and if the sampled value is the same level continuously r times, the level is output as the output zero cross signal ZEOX_OUT To do. In this way, when the ASIC 1201 receives the zero cross signal from the half-wave rectifier circuit as shown in FIG. 12 and the same level continues for the number of register values set by the CPU, a signal ZEROX_OUT indicating the level is obtained. Is output. Therefore, the phase of the output signal is delayed for a time corresponding to the number of samplings after the chattering converges.

  However, in practice, chattering hardly occurs due to a capacitance component in the zero-cross detection circuit, and the sampling number r by the CPU does not need to be a large value. In addition, since the sampling frequency of the CPU is sufficiently faster than the frequency of the zero cross signal, the time required for this chattering removal is very short and is not long enough to affect the delay times X and Y for generating the heater on / off signal. This sampling number r is a fixed value set at the time of shipment.

  The signal ZEROX_OUT is input to the CPU 201 and further delayed for a predetermined time to become a heater control signal. The delay by the CPU is performed by a method in which a desired time is measured by a built-in or external timer and output is delayed by the measured time. Note that the signal ZEROX_OUT has the same frequency (50 to 60 Hz) as the AC frequency of the commercial power supply, and is considerably lower than the frequency of the CPU synchronization signal (several MHz to several hundred MHz). Therefore, it will be practically sufficient if the CPU 201 monitors the level change at a constant period without generating an interrupt due to the fluctuation of the signal ZEROX_OUT. Of course, it may be an interrupt drive due to a change in the number ZEROX_OUT.

  The CPU 201 to which the signal ZEROX_OUT is input generates a heater control signal by delaying the rising edge and the falling edge by the set values X and Y, respectively (see FIG. 11). The values of X and Y are set to delay amounts that satisfy both the waveforms in FIGS. 14 shows a waveform at 45 Hz, and FIG. 15 shows a waveform at 65 Hz. Since the frequency of commercial power supply in Japan is usually 50 Hz or 60 Hz, it is practically sufficient to assume that the power supply frequency is 45 Hz to 65 Hz and to ensure normal operation within that range.

  In FIG. 14, the length of the half wave is 11.1 milliseconds. The zero-cross signal has a delay for chattering removal (not shown in FIG. 14). Furthermore, because of the edge shift due to the threshold level (1 ms to 2 ms in total, the length of the half-wave is shorter than the length of the half wave), the on-level length in FIG. It is about 10.1 milliseconds, and the duty ratio of the signal is smaller than 0.5. Therefore, in this state, depending on the delay amount of the ZEROX_OUT signal, the on level may be entirely contained between the adjacent zero cross points of the power supply voltage. In that case, even if the heater control signal is turned on / off in synchronization with the rising or falling edge of the ZEROX_OUT signal, the on / off level is not maintained at the zero cross point of the power supply voltage and may not be energized. . Therefore, in order to surely turn on / off the heater at the zero cross point, the heater control signal is not turned on / off in synchronization with the edge of the ZEROX_OUT signal, and the phase of the heater control signal and the phase of the power supply voltage are related to time. The phase of the heater control signal is shifted so as to be constant. For this purpose, the heater control signal rise / fall timing is delayed from the edge of the ZEROX_OUT signal by a predetermined time X and Y, thereby ensuring that the heater control signal is at a desired level at the zero cross point. The same applies to FIG. Specifically: In the following example, the value of the threshold value Vth of the zero cross signal is determined so that the deviation between the zero cross signal and the actual zero cross point is about 0.8 milliseconds to 1.8 milliseconds. This is to increase the detection accuracy of the zero cross point.

  In order to satisfy FIGS. 14 and 15, the higher frequency side may be considered. Point a is later than the AC half-wave rising zero-cross point, and point b is earlier than AC half-wave falling zero-cross point. Therefore, a relationship of Y> X is desirable. Note that X and Y include the time required for chattering removal by the ASIC 1201. Therefore, the relationship Y> X is not necessarily required. However, when Y <X, the trailing edge chattering removal time margin cannot be sufficiently obtained depending on the set time (time Y is the chattering removal by the ASIC 1201). The timing may come out.

  Further, in FIG. 15, the threshold value Vth is given so that the H portion of the zero cross signal is about 4 to 6 ms out of 7.7 ms, and the L portion is about 11.4 to 9.4 ms with respect to 7.7 ms. It has been. Since the delay amount X should not be delayed from the zero cross for the next triac-on, X <4 ms. That is, the time X is equal to or more than the minimum value obtained by subtracting the Tzs and Tze times from the half-wave period in FIG. 13 (in this case, the minimum value is 4 ms because the H portion of the zero cross signal is assumed to be about 4 to 6 ms). It must not be a value. If it takes more than 4ms, the triac detects zero crossing and turns on the power before the off signal for the next half wave (heater control signal is turned off) is output. End up.

  On the other hand, even if the time Y is the shortest, a time that passes the zero cross point of the triac (Y> Tze, that is, about 2 ms) is required, and the time until the next triac on is shorter than 7.7 ms (Y <7.7 ms). is required. In this case as well, if a value of 7.7 ms or more is set, it will be delayed from the detection of the next triac zero cross, and there is a possibility that energization will not be possible.

  The set values of X and Y may be determined from the above relationship. In the case of the present embodiment, if the time is about X = 2 ms and Y = 4 ms, it is possible to have a time margin for eliminating chattering, and a sufficient time for the zero cross point for triac-on is secured. In this embodiment, the CPU 201 delays the rising and falling edges of the zero-cross signal ZEROX_OUT by the time obtained by subtracting the delay time for chattering removal by the ASIC 1201 from X = 2 ms and Y = 4 ms. As a delay time for eliminating chattering, for example, a fixed value determined experimentally is given. Then, the CPU 201 switches between the on level and the off level of the heater control signal in accordance with the temperature control level determined as shown in FIG. 8 in accordance with the timing. For example, in the case of level 8, the heater control signal on level and off level are in a pattern of off, on, off, on, off, on, off, on, on, off, on, off, on, off, on. Switch. The switching timing is the timing of the heater control signal shown in FIGS.

  With such a configuration, the image forming apparatus according to the present embodiment can generate a zero-cross signal using a half-wave rectified wave, thereby enabling favorable heater wave number control even when the waveform of the AC power supply voltage is distorted. Become.

  Further, by keeping the delay time of the heater control signal with respect to the AC power supply waveform within a certain range, normal temperature control can be performed without performing dynamic control with respect to fluctuations in the power supply frequency.

  In the present embodiment, the value of Y is given so that the duty ratio of the heater control signal is approximately 0.5. Thus, if the value of X is determined so that one edge (for example, the rising edge) of the heater control signal becomes the timing between the adjacent zero cross points of the power supply, the other edge (for example, the falling edge) is also phased. This is the timing between adjacent zero cross points.

<Modification>
The present invention can be applied not only to heat fixing devices in electrophotographic image forming apparatuses but also to heater temperature control using an AC power supply in general. For example, in the ink jet system, in a technique for controlling the ink permeability by heating a sheet at the time of ink discharge or immediately after the discharge, the temperature can be controlled by applying the present invention to a heater for heating the sheet in that case.

Schematic sectional view of a color image forming apparatus according to the present invention Laser scanner top view of the present invention Configuration diagram of electrical system for controlling the present invention Configuration diagram of the on-demand heater unit of the present invention Top view of the ceramic heater of the present invention Diagram showing heater on / off control circuit Diagram showing heater energization waveform when using zero cross-synchronized triac The figure which shows the wave number control table which is used for heater temperature control Diagram showing half-wave rectification zero-cross detection circuit The figure which shows the mode of the waveform of the zero cross signal generation by the zero cross detection circuit of half wave rectification Diagram showing chattering of zero cross in half-wave rectifier circuit The block diagram in the case of delaying the zero cross signal of this invention and producing | generating a heater on / off signal Diagram explaining the deviation of the zero cross point when a zero cross signal is generated from the half-wave rectified waveform Diagram showing the relationship between the zero-cross signal and triac on / off signal at 45 Hz Diagram showing the relationship between zero cross signal and triac on / off signal at 65 Hz Diagram showing another distortion wave of AC voltage waveform Diagram showing another distortion wave of AC voltage waveform Diagram showing zero-cross detection circuit for full-wave rectification The figure which shows the mode of the waveform of the zero cross signal generation by the zero cross detection circuit of full wave rectification Figure showing zero-cross malfunction in case of distorted wave in full-wave rectifier circuit Diagram showing correct zero-cross signal generation for a distorted wave in a half-wave rectifier circuit

Explanation of symbols

150 DC controller unit 201 CPU
215 PWM unit 300 image processing unit 106 host computer 701 ceramic heater 702 fixing film 703 pressure roller 901 AC power source 902 noise filter 904 triac 904 phototriac coupler 931 diode bridge

Claims (7)

A zero cross detection circuit that compares the power supply voltage supplied from the AC power supply with the threshold value and outputs a signal of a level according to the comparison result as a zero cross signal;
A zero-crossing synchronous switching element that is arranged between the AC power supply and the load, and controls the energization / non-energization of the AC half-wave according to the level of the gate signal in synchronization with the positive / negative switching of the power supply voltage; ,
The gate signal is synchronized with the timing delayed by a first delay time from the rising edge of the zero-cross signal or the timing delayed by a second delay time from the falling edge of the zero-cross signal according to the power applied to the load. And a power control means for switching and outputting the level of the power control device.   The zero-cross detection circuit outputs a high-level signal as the zero-cross signal when the power supply voltage is larger than the threshold, and a low-level signal when the power supply voltage is small, and the delay means is a period of the first half cycle of the AC power supply. The rising edge or the falling edge of the gate signal is contained in the first half period, and the falling edge of the gate signal rising in the first half period, or the first edge 2. The power control apparatus according to claim 1, wherein a gate signal obtained by delaying an edge of the zero-cross signal is output so that a rising edge of the gate signal falling in a half cycle of the first half-cycle is accommodated.   The zero-cross detection circuit outputs a high-level signal as the zero-cross signal when the power supply voltage is greater than the threshold, and a low-level signal when the power supply voltage is small, and the delay means has a timing of switching the level of the gate signal as the timing A gate signal in which the edge of the zero cross signal is delayed so that the phase does not coincide with the zero cross point of the AC power source and the phase of the gate signal and the phase of the AC power source are constant regardless of time The power control apparatus according to claim 1.   The zero-cross detection circuit outputs a high-level signal as the zero-cross signal when the power supply voltage is larger than the threshold, and a low-level signal as the zero-cross signal when the power supply voltage is small. The delay means includes the first delay time a and the second The gate signal obtained by delaying the edge of the zero-cross signal so that the relationship with the delay time b is a <4 ms and 2 ms <b <7.7 ms and a <b is provided. Power control device.   5. The load according to claim 1, wherein the load is a heater, and the power control means controls the gate signal of the zero-crossing synchronous switching element to an on level so as to energize electric power according to the temperature of the heater. The power control apparatus according to any one of claims.   The heater control apparatus characterized by controlling the temperature using the heater as the load by the power control apparatus according to any one of claims 1 to 5. Image forming means for forming a visible image according to image data on a print medium with a color material;
A heater for thermally fixing the color material on the print medium;
An image forming apparatus comprising: the heater control device according to claim 5 or 6 for controlling the heater.

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