JP2012098529A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that accurately detects current without the effect of an error of a current transformer.SOLUTION: A fixing device provided to an image forming apparatus controls the phase of drive of a heater 204 at a designated phase angle in driving the heater 204 with AC voltage. A current detection circuit 212 detects current that flows through the heater using a current transformer 209, while correcting the detection value by the current detection circuit 212 according to a phase angle of a half-wave immediately before a target half-wave for current detection.

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer having a fixing device that heats and fixes a toner image transferred onto a recording medium.

  In such an image forming apparatus, in order to start printing after power is turned on, the temperature of the heater (fixing heater) of the fixing device must be increased to a predetermined value or more. In order to obtain a quick print output, it is necessary to rapidly raise the temperature of the fixing heater. For this purpose, it is necessary to increase the amount of current supplied to the fixing heater.

  However, according to the “Electrical Safety Law”, domestic outlets are regulated to a rated current of 15 A, and can only flow a current equal to or lower than the rated current.

  In order to supply a larger current within the rated current to the fixing heater, a technique using current detection means for directly detecting the current flowing through the fixing heater has been proposed (see Patent Document 1). In this technique, the current flowing through the fixing heater is converted into a voltage via a current transformer, and the obtained voltage is integrated by an integration circuit to detect the current.

JP 2007-333888 A

  However, the image forming apparatus using the current detection circuit as the current detection unit described above has the following problems.

  That is, when the current flowing through the fixing heater is detected by converting it into a voltage via a current transformer by a current detection circuit, a conversion error occurs due to the characteristics of the current transformer. This conversion error affects the integrated output of the integrating circuit, and an accurate current value cannot be detected.

  The present invention has been made in view of such a background, and provides an image forming apparatus capable of performing high-precision current detection without being affected by an error of a current transformer when detecting a current of a fixing heater. For the purpose.

  An image forming apparatus according to the present invention is an image forming apparatus having a fixing device that heats and fixes a toner image transferred onto a recording medium, the heater being provided in the fixing device and driven by an alternating voltage, and an instruction A phase control means for phase-controlling the driving of the heater at a phase angle, a current detection means for detecting a current flowing through the heater using a current transformer, and a detection value by the current detection means in accordance with the phase angle. And correction means for correcting.

  In the current detection means using the current transformer, the detected value of the current flowing through the heater includes an error corresponding to the phase angle for driving the heater, and thus the detected value is corrected according to the phase angle.

  The current detection means includes, for example, a voltage conversion means for converting a current flowing through the heater into an AC voltage, a half-wave rectification means for extracting a half-wave from the AC voltage obtained by the voltage conversion means, and the half-wave rectification means. And integrating means for integrating the half-wave extracted by.

  In this configuration, the correction unit corrects the detection value based on the integrated half wave according to the phase angle applied to the half wave immediately before the half wave integrated by the integration unit.

  The correction means may include an error correction table in which phase angles and error correction values are stored in association with each other. By referring to such an error correction table, an error correction value corresponding to an arbitrary phase angle can be obtained immediately.

  The image forming apparatus may further include a zero-cross detection unit that detects a zero-cross point of the AC voltage, and a reset unit that resets an integration output of the integration unit at a predetermined timing with reference to the zero-cross point. . By such reset means, it is possible to reliably capture the integral value of the entire half wave subjected to arbitrary phase angle control and to determine the timing for starting the integration operation of the next half wave.

  According to the present invention, the value of the current flowing through the fixing heater can be detected with high accuracy. As a result, the maximum current can be allowed to flow within the allowable range of the rated current regulation, and as a result, the fixing device can be quickly started up.

1 is a configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a configuration diagram of a fixing control unit that controls the fixing device shown in FIG. 1. FIG. 3 is a timing diagram illustrating waveforms of respective units of the fixing control unit in FIG. 2. It is the schematic diagram which showed the structure of the outline of the error correction table used by embodiment of this invention. 6 is a flowchart of processing for realizing an operation of a fixing control unit according to the embodiment of the present invention. It is a figure for demonstrating distortion of the signal waveform of the current transformer in embodiment of this invention.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings.

  FIG. 1 is a configuration diagram of an image forming apparatus 100 according to the present embodiment.

  The image forming apparatus 100 detects a size of the recording paper P in the deck 101, a deck 101 that stores recording paper P as a recording medium, a deck paper presence sensor 102 that detects the presence or absence of the recording paper P in the deck 101. A paper size detection sensor 103 is included. The image forming apparatus 100 also includes a pickup roller 104 that feeds the recording paper P from the deck 101, and a deck paper feeding roller 105 that transports the recording paper P fed by the pickup roller 104. Opposing to the deck paper feed roller 105, a read roller 106 is provided to pair with the deck paper feed roller 105 and prevent double feeding of the recording paper P. Further, a paper feed sensor 107 is provided downstream of the deck paper feed roller 105 to detect a paper feed conveyance state from a double-side reversing unit described later. Downstream of the paper feed sensor 107, a paper feed transport roller 108 for transporting the recording paper P further downstream, and a registration roller 109 for transporting the recording paper P in synchronization with the printing timing are provided. A pre-registration sensor 110 that detects the conveyance state of the recording paper P to the registration roller 109 is installed in the conveyance path between the sheet feeding conveyance roller 108 and the registration roller 109.

  A process cartridge 112 that forms a toner image on the photosensitive drum (image carrier) 1 based on the laser beam from the laser scanner unit 111 is provided downstream of the registration roller 109. In the process cartridge 112, a charging roller 112 a that uniformly charges the surface of the photosensitive drum 1, a developing device 112 b that develops the electrostatic latent image formed by the laser beam with toner, and the like are disposed around the photosensitive drum 1. Has been.

  Further, on the downstream side of the registration roller 109, a roller member 113 for transferring the toner image formed on the photosensitive drum 1 to the recording paper, and a charge for removing the charge on the recording paper to promote separation from the photosensitive drum 1. A static elimination needle 114 is installed. A conveyance guide 115, a fixing device 116, a fixing paper discharge sensor 119, and a double-sided flapper 120 are installed downstream of the static elimination needle 114.

  The fixing device 116 is means for thermally fixing the toner image transferred onto the recording paper. A fixing paper discharge sensor 119 is a detecting unit for detecting a conveyance state from the fixing device 116. The double-sided flapper 120 is a means for switching the destination of the recording paper conveyed from the fixing device 116 to the paper discharge unit or the double-side reversing unit.

  A predetermined high voltage is applied to the charging roller 112a, the developing device 112b, and the roller member 113 from a high voltage power supply 128 at a predetermined time point.

  A paper discharge sensor 121 that detects a paper conveyance state of the paper discharge unit and a paper discharge roller 122 that discharges the recording paper are installed on the downstream side of the paper discharge unit of the image forming apparatus 100.

  A reversing roller 123, a reversing sensor 124, a D-cut roller 125, a double-sided sensor 126, and a double-sided conveying roller 127 are installed in the double-sided reversing unit of the image forming apparatus 100. Here, in order to print on both sides of the recording paper, the double-side reversing unit side reverses the recording paper after the single-sided printing is finished, and feeds it again to the image forming unit. The reverse roller 123 switches back the recording paper by forward and reverse rotation. Further, the reverse sensor 124 detects the paper conveyance state to the reverse roller 123. The D-cut roller 125 conveys the recording paper from a lateral registration unit (not shown) for aligning the lateral position of the recording paper. The double-sided sensor 126 detects the recording paper conveyance state of the double-side reversing unit, and the double-sided conveyance roller 127 conveys the recording paper from the double-side reversing unit to the paper feeding unit. A motor M <b> 1 is provided as a drive source for recording paper conveyance mechanism, rotation of the photosensitive drum 1, and the like. A motor M2 is provided as a drive source for the fixing device 116.

  Each unit of the image forming apparatus 100 is controlled by the control unit 118.

  Note that double-sided printing is not an essential function of the present invention, and the elements related to double-sided printing described above may be omitted.

  FIG. 2 is a configuration diagram of a fixing control unit that controls the fixing device 116. The fixing control unit includes the control unit 118 shown in FIG.

  The fixing device 116 includes a heater 204 as a fixing heater for heating and fixing the toner image transferred onto the recording paper. The heater 204 is controlled by the heater drive circuit 205 under the control of the heater ON signal from the control unit 206. The control unit 206 is configured by a CPU or the like. The control unit 206 and the heater drive circuit 205 constitute the “phase control means” of the present invention. Electric power to the heater 204 is supplied from an alternating current (AC) power source 201 via a switch 202 and a relay 203. One end of the heater 204 is connected to the relay 203, and the other end is connected to the heater drive circuit 205 via the primary winding of the current transformer 209 in the current detection circuit 212. The current transformer 209 functions as a voltage conversion unit that converts the current flowing through the heater 204 into an AC voltage. The current detection circuit 212 includes a half-wave rectification circuit 210 connected to the secondary winding of the current transformer 209 and an integration circuit 211 that integrates this output. The integration circuit 211 outputs the integration output to the control unit 206 and receives a reset signal from the reset circuit (reset means) 208.

  The AC voltage is input to the zero-cross detection circuit 207 in the subsequent stage of the switch 202 and the relay 203 as a power switch. The zero cross detection circuit 207 constitutes zero cross detection means for detecting the zero cross point of the AC voltage. The zero cross detection signal output from the zero cross detection circuit 207 is input to the control unit 206. The control unit 206 controls the heater drive circuit 205 and the reset circuit 208 based on the output of a temperature sensor or the like (not shown) that detects the temperature of the heater in addition to the output of the zero cross detection circuit 207. The control unit 206 can control each unit of the image forming apparatus as well as the control of the fixing device 116.

  When the switch 202 is turned on after AC input from the AC power supply 201, the heater 204 is controlled by the heater drive circuit 205 in accordance with the heater ON signal output from the control unit 206 to the heater drive circuit 205. . Thereby, the relay 203 is connected and a current flows through the heater 204. In the present embodiment, the current flowing through the heater 204 is detected by the current detection circuit 212. The zero cross detection circuit 207 detects the zero cross point of the AC input. Based on this zero cross signal, the control unit 206 determines the time from the zero cross point to the heater ON start point in each half wave of the AC input for each cycle of the AC input, thereby controlling the phase of the positive and negative uniform pattern. Do.

  Here, the operation of the current detection circuit 212 in this embodiment will be described.

  First, the current transformer 209 converts the current flowing through the heater 204 (heater current) into an AC voltage and outputs it between both ends of the secondary winding. That is, the current transformer 209 outputs an AC voltage. A half-wave rectifier circuit 210 was used to convert this AC voltage into a DC voltage. As described above, in the present embodiment, the phase applied to the heater 204 is changed in units of AC 1 period, so that it is necessary to measure the waveform for each period in order to execute quick control. Therefore, in order to detect the amount of current per cycle, the integrating circuit 211 integrates the half-wave rectified output. A value obtained by integrating the DC voltage extracted by the half-wave rectifier circuit 210 by the integrating circuit 211 corresponds to the detected value of the heater current.

  Further, the output of the integrating circuit 211 needs to be reset at a predetermined timing. For this purpose, a reset signal is sent from the reset circuit 208 to the integration circuit 211 under the control of the control unit 206 to reset the integration waveform. The control unit 206 outputs a reset signal at a predetermined timing based on the detection output from the zero cross detection circuit 207.

  FIG. 3 is a timing chart showing waveforms of the respective units of the fixing control unit shown in FIG.

  The zero cross detection circuit 207 outputs a periodic pulsed zero cross detection signal every time the AC input voltage crosses the zero point. After the heater ON signal is output from the control unit 206, a phase-controlled AC current flows through the heater 204. That is, the heater 204 is turned on at a phase point that can be different for each cycle by the heater drive circuit 205, and a current flows until the AC input voltage reaches the zero cross point. The current waveform is as shown in the figure. A similar voltage waveform is generated at both ends of the secondary winding of the current transformer 209. The half-wave rectifier circuit 210 extracts and outputs a half-wave of one polarity (negative in this example). This half wave is integrated by the integrating circuit 211 to generate an integrated waveform. An integrated reset signal is output from the reset circuit 208 at a predetermined time after the control unit 206 reads the peak value after the integrated waveform reaches the peak. The integration circuit 211 resets the integration output in response to the integration reset signal (that is, returns to the initial value). Such reset timing can be set in advance with reference to the zero cross point.

  By the way, when the present invention detects the heater current subjected to phase control by the current detection circuit 212 using the current transformer 209, a conversion error occurs in the output voltage due to the characteristics of the current transformer 209 in which residual magnetism is generated. I noticed that current detection results are affected. As a result of scrutiny, it was found that the larger the phase angle of the half wave immediately before the half wave to be detected (ie, the previous wave), the greater the error. This is because, due to the influence of hysteresis, the next wave is affected by the residual magnetism that remains in the coil of the current transformer. As added in FIG. 6, when the signal waveform before conversion of the current transformer 209 (FIG. 6A) is compared with the half-wave rectified signal waveform after conversion (FIG. 6B), It can be seen that distortion has occurred (that is, the flat signal portion before conversion is distorted so that its level decreases after conversion). A conversion error occurs due to this distortion. Therefore, in this embodiment, a configuration is employed in which control is performed so as to cancel the conversion error using an error correction table.

  Therefore, an error correction table in which the magnitude of an error is experimentally determined in advance according to the phase angle of the previous wave and a correction value (error correction value) associated with the error is stored. 214 is provided in a storage unit (not shown) such as a nonvolatile memory. When the current value for each half wave is detected by the current detection circuit 212, the detected value (measured value) is corrected with an error correction value corresponding to the phase angle of the previous wave. Thereby, the error caused by the current transformer 209 can be canceled and the accuracy of the detected current can be improved. As a result, it is possible to flow the current flowing through the heater 204 to the maximum without exceeding the rated value. As a result, the fixing device 116 can be quickly started up.

  FIG. 4 is a schematic diagram showing a schematic configuration of the error correction table 214. In this example, an error correction value corresponding to the phase angle of the previous wave is set stepwise every 10%. For example, when the phase angle of the previous wave is 40%, the error correction value ΔI4 (A) is applied (added or subtracted) to the detected value. The range of each phase angle is not limited to 10%. The unit of the error correction value is not necessarily limited to A (ampere), and the unit of the finally detected current may be A.

  FIG. 5 shows a flowchart of processing for realizing the operation of the fixing control unit in the present embodiment. This process is realized by the control unit 206 executing a control program stored in the storage unit.

  When driving of the fixing device 116 is started (S11, Yes), driving of the heater, in this example, phase control is started (S12). Next, the current detection circuit 212 detects the current (S13). Next, it is checked whether there is a front wave with respect to this half wave (S14). That is, it is confirmed whether a half wave exists immediately before the half wave in which the current is detected. When the previous wave exists, the greater the phase angle of the previous wave, the greater the influence of hysteresis. As a result, the larger the phase angle of the previous wave, the larger the conversion error. Therefore, the correction value for this must also be increased (FIG. 4 ΔI1 <ΔI2 <ΔI3... <ΔI10). There is no pre-wave at the beginning of the heater drive. If there is no previous wave, no conversion error occurs, and the error correction table 214 need not be used. Therefore, the process proceeds to step S17 as it is.

  If a previous wave exists, the phase angle is confirmed (S15). Next, error correction is performed with reference to the error correction table 214 based on the confirmed phase angle (S16).

  Thereafter, when the heater is controlled in accordance with the current temperature and the target temperature of the heater, the detected current value (corrected current value) is reflected in the heater control as necessary (S17). For example, when an attempt is made to rapidly raise the temperature, the phase angle is set so as to approach the standard upper limit value if the current value is lower than the standard upper limit value.

  Until the driving of the fixing device 116 is completed (S18), the process returns to step S12 and the above processing is repeated. When the driving is completed, the phase control is stopped (S19), and the process returns to the first step S11.

  The preferred embodiments of the present invention have been described above, but various modifications and changes other than those mentioned above can be made.

DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum 100 ... Image forming apparatus 101 ... Deck 102 ... Deck paper presence sensor 103 ... Paper size detection sensor 104 ... Pickup roller 105 ... Deck paper feed roller 106 ... Lead roller 107 ... Paper feed sensor 108 ... Paper feed conveyance roller 109 ... Registration roller 110 ... Pre-registration sensor 111 ... Laser scanner 112 ... Process cartridge 112a ... Charging roller 112b ... Developer 113 ... Roller member 114 ... Static removal needle 115 ... Conveying guide 116 ... Fixing device (fixing device)
DESCRIPTION OF SYMBOLS 118 ... Control part 119 ... Fixing paper discharge sensor 120 ... Double-sided flapper 121 ... Paper discharge sensor 122 ... Paper discharge roller 123 ... Reverse roller 124 ... Reverse sensor 125 ... Cut roller 126 ... Double-sided sensor 127 ... Double-sided conveyance roller 128 ... High voltage power supply 201 ... alternating current (AC) power supply 202 ... switch 203 ... relay 204 ... heater (fixing heater)
205 ... Heater drive circuit 207 ... Zero cross detection circuit 208 ... Reset circuit 209 ... Current transformer 210 ... Half-wave rectification circuit 211 ... Integration circuit 212 ... Current detection circuit 214 ... Error correction table

Claims (5)

An image forming apparatus having a fixing device that heat-fixes a toner image transferred onto a recording medium,
A heater provided in the fixing device and driven by an AC voltage;
Phase control means for phase-controlling the driving of the heater at an instructed phase angle;
Current detecting means for detecting a current flowing through the heater using a current transformer;
An image forming apparatus comprising: a correction unit that corrects a detection value of the current detection unit according to the phase angle. The current detection means includes
Voltage conversion means for converting the current flowing through the heater into an AC voltage;
Half-wave rectification means for extracting a half-wave from the AC voltage obtained by the voltage conversion means;
The image forming apparatus according to claim 1, further comprising an integrating unit that integrates the half wave extracted by the half wave rectifying unit.   The image forming apparatus according to claim 2, wherein the correction unit corrects a detection value based on the integrated half wave according to a phase angle applied to the half wave immediately before the half wave integrated by the integration unit.   The image forming apparatus according to claim 1, wherein the correction unit includes an error correction table that stores a phase angle and an error correction value in association with each other. Zero-cross detection means for detecting a zero-cross point of the AC voltage;
The image forming apparatus according to claim 1, further comprising: a reset unit that resets an integration output of the integration unit at a predetermined timing with respect to the zero-cross point.