JP2008164644A - Power supply controller and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply controller capable of performing power supply control with rapid responsiveness to a control object, and further performing control so that power to be supplied to a heater may not be lower than necessary by calculating the upper limit value of a current to be supplied to a load within a range where power supplied by a commercial power supply does not exceed a predetermined upper limit current, and to provide an image forming apparatus. <P>SOLUTION: The power supply controller includes: triacs 204 and 213 for supplying AC power from the commercial power supply to the heater 109c and interrupting the power supply; a current detection circuit 228 detecting the current supplied from the commercial power supply; a current detection circuit 227 detecting the current flowing into the heater, and calculates the upper limit value of a current to be supplied to the heater based on the current values detected by the current detection circuits 228 and 227, and decides an upper limit power ratio for driving the triac based on a power ratio for driving the triac and the current detected by the current detection circuit 227. By driving the triac at the upper limit power ratio or under, the power supply to the heater is controlled. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a power supply control device that controls power supplied from a commercial power source to a load, and an image forming apparatus.

  An image forming apparatus (laser printer) using a general electrophotographic process will be described.

  Such a heat fixing device of the image forming apparatus fixes an unfixed image (toner image) formed on the transfer paper by image forming means such as an electrophotographic process on the transfer paper. As this heat fixing device, a heat roller type heat fixing device using a halogen heater as a heat source and a film heating type heat fixing device using a ceramic surface heater as a heat source are used (Patent Documents 1 and 2).

  The heater of this heat fixing device is generally connected to an AC power source via a switching element such as a triac, and power is supplied from this AC power source. In addition, a temperature detection element, for example, a thermistor temperature sensing element, is provided in a heat fixing device using a heater as a heat source. Based on the temperature information detected by the temperature detection element, the switching element is controlled to be turned on and off to Control is performed so that the temperature of the fixing device becomes a target temperature. Further, on / off control of the ceramic surface heater is usually performed by phase control or wave number control of the input commercial power supply.

Also, if the heater overheats due to a failure of a switching element such as a triac or a power control runaway, the temperature detection element detects an excessive temperature rise of the heater and shuts off the power supply from the AC power supply to the heater. Yes.
JP-A-63-313182 Japanese Patent Laid-Open No. 02-157878 JP 2004-226557 A

  When controlling the temperature of the heat fixing device, the sequence controller compares the temperature detected by the temperature detecting element with a preset target temperature to calculate the power ratio supplied to the heater. Then, the phase angle or wave number corresponding to the power ratio is determined, and the switching element driving the heater is turned on / off under the phase condition or wave number condition.

Here, the upper limit of the current supplied from the commercial power source to the image forming apparatus is determined by, for example, UL or the electric safety method. The AC power supply for supplying power to the heater has a wide voltage range such as 85V to 140V or 187V to 264V. In addition, the resistance value of the heater also has manufacturing variations. For example, when the resistance value accuracy of the heater is ± 10%, the current supplied to the heater when fully lit is approximately 2.1 times as large as 85V to 140V, and approximately 1.7 times as large as 187V to 264V. The current supplied from the commercial power source to the image forming apparatus is a combined current of the current supplied to the heater and the circuit excluding the heater. Even when the current flowing through the heater is constant, the value of the current supplied from the commercial power supply to the image forming apparatus varies depending on the power factor of the combined current and the power consumed by the circuit excluding the heater. As described above, the current value supplied from the commercial power source to the image forming apparatus changes. In any case, the current supplied from the commercial power source to the image forming apparatus should not exceed a predetermined upper limit current. When the upper limit of the power ratio supplied to the heater is set,
That is, the power that can be supplied to the heater may be reduced more than necessary.

  Therefore, as proposed in Patent Document 3, it is conceivable to detect the energization current to the heater and control the power supplied to the heater so as to be equal to or less than the maximum current that can be supplied. Here, in general, when temperature control is performed by supplying power to a ceramic surface heater having a high output, phase control is often performed in order to speed up control responsiveness.

  Thus, when the control responsiveness becomes faster, it becomes necessary to detect the current with a small cycle, and the difference between the current average value and the effective value also increases depending on the control phase angle. When controlling the power supplied to the heater, the maximum current that can be supplied is often specified by the effective value, so if the current is detected by the average value, the error converted to the effective value by the sequence controller is controlled. Will affect the accuracy.

  Further, as proposed in Patent Document 3, when the upper limit of the current supplied to the heater is set to a predetermined fixed value, the current value supplied from the commercial power source to the image forming apparatus varies as described above. In either case, it is necessary to set the upper limit value of the current supplied to the heater so that the current supplied from the commercial power source to the image forming apparatus does not exceed a predetermined upper limit current. That is, the power that can be supplied to the heater may be reduced more than necessary.

  An object of the present invention is to solve the above-mentioned problems of the prior art.

  A feature of the present invention is that, based on the result of detecting the effective value of the current supplied to the commercial power supply and the load, the power supplied to the load is within a range where the current supplied to the commercial power supply does not exceed a predetermined upper limit current. It is to provide the technology to control.

In order to achieve the above object, a power supply control apparatus according to one aspect of the present invention has the following configuration. That is,
A power supply control device for controlling power supplied from a commercial power source to a load,
Supplying AC power from the commercial power source to the load, and energization switching means for cutting off the power supply;
First current detection means for detecting current supplied from the commercial power supply;
Second current detection means for detecting current flowing into the load;
Calculating means for calculating an upper limit value of a current supplied to the load based on a current value detected by the first current detecting means and the second current detecting means and a power ratio for driving the energization switching means;
An upper limit power ratio for driving the energization switching means is determined based on the upper limit value calculated by the calculation means, the current detected by the second current detection means, and the power ratio for driving the energization switching means. Power supply duty determining means to perform,
Control means for driving the energization switching means within the upper limit power ratio to control power supply to the load;
It is characterized by having.

In order to achieve the above object, an image forming apparatus according to an aspect of the present invention has the following configuration. That is,
An image forming apparatus that performs image formation by controlling power supplied from a commercial power source to a heating element,
Supplying AC power from the commercial power source to the heating element, and energization switching means for cutting off the power supply;
First current detection means for detecting current supplied from the commercial power supply;
Second current detection means for detecting current flowing into the heating element;
Calculating means for calculating an upper limit value of the current supplied to the heating element based on a current value detected by the first current detecting means and the second current detecting means and a power ratio for driving the energization switching means;
An upper limit power ratio for driving the energization switching means is determined based on the upper limit value calculated by the calculation means, the current detected by the second current detection means, and the power ratio for driving the energization switching means. Power supply duty determining means to perform,
Control means for controlling the power supply to the heating element by driving the energization switching means within the upper limit power ratio;
It is characterized by having.

  According to the present invention, it is possible to perform power supply control with quick response to a control target. Furthermore, the upper limit value of the current supplied to the load is calculated within a range where the current supplied to the commercial power supply does not exceed the predetermined upper limit current, and control can be performed without reducing the power that can be supplied to the heater more than necessary. it can.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments do not limit the present invention according to the claims, and all combinations of features described in the present embodiments are essential to the solution means of the present invention. Not exclusively.

[Embodiment 1]
FIG. 1 is a schematic configuration diagram of an image forming apparatus (laser printer) using an electrophotographic process according to the present embodiment.

    A laser printer main body 101 (hereinafter referred to as the main body 101) can be loaded with a cassette 102 for storing a recording sheet S, and forms an image on the recording sheet S supplied from the cassette 102. Reference numeral 103 denotes a cassette presence sensor that detects the presence or absence of the recording sheet S in the cassette 102. Reference numeral 104 denotes a cassette size sensor that detects the size of the recording sheet S accommodated in the cassette 102, and is composed of, for example, a plurality of micro switches. Reference numeral 105 denotes a paper feed roller that picks up and conveys the recording sheet S from the cassette 102. A registration roller pair 106 that synchronously conveys the recording sheet S is provided downstream of the paper feed roller 105. Further, an image forming unit 108 that forms a toner image on the recording sheet S based on the laser beam from the laser scanner unit 107 is provided downstream of the registration roller pair 106. Further, a fixing device 109 that thermally fixes the toner image formed on the recording sheet S is provided downstream of the image forming unit 108. Downstream of the fixing device 109, a paper discharge sensor 110 that detects the conveyance state of the paper discharge unit, a paper discharge roller pair 111 that discharges the recording sheet S, and a recording sheet S on which an image is formed and fixed are displayed. A loading tray 112 for loading and storing is provided. Here, the conveyance reference of the recording sheet S is set to be approximately in the center with respect to the length in the direction orthogonal to the conveyance direction of the recording sheet S, that is, the width of the recording sheet S.

  The laser scanner unit 107 includes a laser unit 113 that emits a laser beam modulated based on an image signal (image signal VDO) transmitted from the external device 131. The laser beam from the laser unit 113 is reflected by a polygon mirror that is rotationally driven by a polygon motor 114, reflected by an imaging lens 115, a folding mirror 116, and the like, and scans on the photosensitive drum 117.

  The image forming unit 108 includes a photosensitive drum 117, a primary charging roller 119, a developing device 120, a transfer charging roller 121, a cleaner 122, and the like necessary for a known electrophotographic process. The fixing device 109 includes a fixing film 109a, a pressure roller 109b, a ceramic heater 109c provided in the fixing film 109a, and a thermistor 109d for detecting the surface temperature of the ceramic heater 109c.

  The main motor 123 applies a rotational force to the paper feed roller 105 via the paper feed roller clutch 124. Further, a rotational force is applied to the registration roller pair 106 via a registration roller clutch 125. Further, a driving force is applied to each unit of the image forming unit 108 including the photosensitive drum 117, the fixing device 109, and the paper discharge roller pair 111.

  An engine controller 126 controls the electrophotographic process by the laser scanner unit 107, the image forming unit 108, and the fixing unit 109, and controls the conveyance of the recording sheet S in the main body 101. Reference numeral 127 denotes a video controller, which is connected to an external device 131 such as a personal computer via a general-purpose interface (Centronics, RS232C, etc.) 130. The video controller 127 expands image information sent via the general-purpose interface 130 into bit data, and sends the bit data to the engine controller 126 as a VDO signal.

  FIG. 2 is a block diagram showing a configuration of a heater control circuit (power supply control circuit) that controls energization driving to the ceramic heater 109c in the embodiment of the present invention.

  Reference numeral 201 denotes an AC power source to which the image forming apparatus is connected. In this image forming apparatus, an AC power supply 201 is supplied to a heating element 203 and a heating element 220 of the ceramic heater 109 c via an AC filter 202, a current transformer 225 and a relay 241. As a result, the heating element 203 and the heating element 220 constituting the ceramic heater 109c generate heat. The supply of electric power to the heating element 203 is controlled by energization and interruption of the triac 204. The resistors 205 and 206 are bias resistors of the triac 204, and the phototriac coupler 207 is a device for ensuring a creepage distance between the primary and secondary. When the light emitting diode of the phototriac coupler 207 is energized, the triac 204 is turned on. The resistor 208 is a resistor for limiting the current flowing through the phototriac coupler 207, and the energization of the phototriac coupler 207 is turned on / off by the transistor 209. The transistor 209 operates in accordance with a signal (ON1) supplied from the engine controller 126 via the resistor 210.

  The supply of electric power to the heating element 220 is controlled by energization and interruption of the triac 213. The resistors 214 and 215 are bias resistors of the triac 213, and the phototriac coupler 216 is a device for ensuring a creepage distance between the primary and secondary. The triac 213 can be turned on by energizing the light emitting diode of the phototriac coupler 216. The resistor 217 is a resistor for limiting the current flowing through the phototriac coupler 216. The transistor 218 is turned on / off by the phototriac coupler 216 in accordance with a signal (ON2) supplied from the engine controller 126 via the resistor 219.

  The AC power supply 201 is input to the zero cross detection circuit 212 via the AC filter 202. The zero-cross detection circuit 212 notifies the engine controller 126 with a pulse signal that the commercial power supply voltage is equal to or lower than the threshold value. Hereinafter, the signal sent to the engine controller 126 is referred to as a ZEROX signal. The engine controller 126 detects the edge of the pulse of the ZEROX signal, and controls on / off of the triac 204 or 213 by phase control or wave number control.

  The heater current controlled by the triacs 204 and 213 and energized to the heating elements 203 and 220 is converted into a voltage by the current transformer 225 and input to the current detection circuit 227. This current detection circuit 27 converts the voltage-converted heater current waveform into an effective value or a square value thereof, and inputs it to the engine controller 126 as an HCRRT1 signal. The HCRRT1 signal thus input is A / D converted by the engine controller 126 and managed as a digital value.

  Further, the current from the AC power supply 201 input through the AC filter 202 is converted into a voltage by the current transformer 226 and input to the current detection circuit 228. The current detection circuit 228 converts the voltage-converted heater current waveform into an execution value or a square value thereof, and inputs it to the engine controller 126 as an HCRRT2 signal. The HCRRT2 signal thus input is A / D converted by the engine controller 126 and managed as a digital value.

  The thermistor 109d is, for example, a thermistor temperature sensing element for detecting the temperature of the ceramic heater 109c in which the heating elements 203 and 220 are formed. The thermistor 109d is disposed on the ceramic heater 109c via an insulator having a withstand voltage so that an insulation distance can be secured with respect to the heating elements 203 and 220. The temperature detected by the thermistor 109d is detected as a partial pressure between the resistor 222 and the thermistor 109d, and is input to the engine controller 126 as a TH signal. The TH signal input in this way is A / D converted by the engine controller 126 and managed as a digital value.

  The temperature of the ceramic heater 109c is monitored by the engine controller 126 as a TH signal. Then, by comparing with the set temperature of the ceramic heater 109c set by the engine controller 126, a power ratio to be supplied to the heating elements 203 and 220 constituting the ceramic heater 109c is calculated. Then, it is converted into a phase angle (phase control) or wave number (wave number control) corresponding to the supplied power ratio, and the engine controller 126 sends an ON1 signal to the transistor 209 or an ON2 signal to the transistor 218 according to the control conditions. . Thus, the temperature of the ceramic heater 109c is controlled. Here, when calculating the power ratio supplied to the heating elements 203, 220, the upper limit power ratio is accurately calculated based on the HCRRT1 signal and the HCRRT2 signal notified from the current detection circuit 227 and the current detection circuit 228, Control is performed so that power equal to or less than the upper limit power ratio is energized. For example, in the case of phase control, the following control table is provided in the engine controller 126, and control is performed based on this control table.

Further, when the heating element 203, 220 is brought into a thermal runaway due to a failure in a circuit for supplying power to the heating element 203, 220 to control it, as a means for preventing the excessive temperature rise, the excessive temperature rise prevention unit 223 is used. Is disposed in the ceramic heater 109c. The excessive temperature rise prevention unit 223 is, for example, a thermal fuse or a thermo switch. When the heating elements 203 and 220 are in a thermal runaway and the excessive temperature rise prevention unit 223 reaches a predetermined temperature or more, the excessive temperature rise prevention unit 223 is opened and the energization to the heating elements 203 and 220 is interrupted. .

  In order to control the temperature of the ceramic heater 109c monitored as a TH signal, an abnormal temperature value for detecting an abnormally high temperature is set by the engine controller 126 separately from the temperature control setting temperature. As a result, when the temperature information indicated by the TH signal becomes equal to or higher than the abnormal temperature value, the engine controller 126 sets the RLD signal to a low level. Accordingly, the transistor 242 is turned off and the relay 241 is opened. In this way, the power supply to the heating elements 203 and 220 is cut off. Normally, during temperature control, the engine controller 126 always outputs the RLD signal at a high level to turn on the transistor 242 and turn on the relay 241 (conducting state). The resistor 243 is a current limiting resistor, and the resistor 244 is a base-emitter bias resistor of the transistor 242. The diode 245 is an element for absorbing a counter electromotive force when the relay 241 is off.

  3A and 3B are diagrams for explaining the outline of the ceramic heater 109c according to the present embodiment. 3A is a cross-sectional view of the ceramic surface heater, 301 in FIG. 3B shows a surface on which the heating elements 203 and 220 are formed, and 302 in FIG. The surface which opposes the surface which is shown is shown (refer FIG. 3 (A)).

  The ceramic surface heater 109c includes a ceramic insulating substrate 331 such as SiC, AlN, and Al 2 O 3, heating elements 203 and 220 formed on the surface of the insulating substrate 331 by paste printing, and two heating elements. It is comprised from protective layers 334, such as glass which is protecting. On the protective layer 334, a thermistor 109d for detecting the temperature of the ceramic surface heater 109c and an excessive temperature rise prevention unit 223 are arranged. These are arranged at positions symmetrical to the recording sheet conveyance reference, that is, the center in the length direction of the heat generating sections 203a and 220a, and at a position inside the minimum recording sheet width capable of passing paper. .

  The heating element 203 includes a portion 203a that generates heat when electric power is supplied, electrode portions 203c and 203d to which electric power is supplied via a connector, and a conductive portion 203b that connects the electrode portions 203c and 203d and the heating element 203. And have. The heating element 220 includes a portion 220a that generates heat when power is supplied, electrode portions 203c and 220d to which power is supplied via a connector, and a conductive portion 220b connected to the electrode portions 203c and 220d. ing. The electrode portion 203c is connected in common to the two heating elements 203 and 220, and serves as a common electrode for the heating elements 203 and 220. In addition, a glass layer may be formed on the surface facing the insulating substrate 331 on which the heating elements 203 and 220 are printed in order to improve the slidability.

  The common electrode 203 c is connected from the HOT side terminal of the AC power supply 201 via the overheat prevention unit 223. The electrode portion 203 d is connected to a triac 204 that controls the heating element 203, and is connected to the Neutral terminal of the AC power supply 201. The electrode part 220 d is electrically connected to the triac 213 that controls the heating element 220, and is connected to the Neutral terminal of the AC power supply 201. The ceramic heater 109c is supported by a film guide 62 as shown in FIGS.

  4A and 4B are diagrams showing a schematic configuration of the thermal fixing device 109 according to the present embodiment. FIG. 4A shows the nip portion of the heating elements 203 and 220 with respect to the insulating substrate 331. 4B shows the case where the heating elements 203 and 220 are located on the nip portion side with respect to the insulating substrate 331. FIG.

  The fixing film 109a is a fixing film made of a cylindrical heat-resistant material, and is externally fitted to a film guide 62 that supports a ceramic heater 109c on the lower surface side. The ceramic heater 109c on the lower surface of the film guide 62 and the elastic pressure roller 109b as a pressure member are sandwiched between the fixing film 109a and have a predetermined pressure against the elasticity of the elastic pressure roller 109b. Press contact. Thus, a fixing nip portion having a predetermined width as a heating portion is formed. Further, an excessive temperature rise prevention unit 223, for example, a thermostat is in contact with the insulating substrate 331 surface of the ceramic heater 109c or the protective layer 334 surface. The position of the excessive temperature rise prevention unit 223 is corrected by the film guide 62, and the heat sensitive surface of the over temperature rise prevention unit 223 is in contact with the surface of the ceramic heater 109c. Although not shown, the thermistor 109d is also in contact with the surface of the ceramic heater 109c. Here, as shown in FIG. 4A, the ceramic heater 109c may have the heating elements 203 and 220 on the side opposite to the nip portion. Alternatively, as shown in FIG. It may be on the nip side. Further, in order to improve the slidability of the fixing film 109a, slidable grease may be applied to the interface between the fixing film 109a and the ceramic heater 109c.

  FIG. 5 is a block diagram for explaining the configuration of the current detection circuit 227 according to the present embodiment, and FIG. 7 is a waveform diagram for explaining the operation of the current detection circuit 227.

  In 601 of FIG. 7, when a current I1 flows through the heating element 203, the current transformer 225 converts the current waveform into a voltage on the secondary side. The voltage output of the current transformer 225 is rectified by diodes 51a and 53a, and resistors 52a and 54a are connected as load resistors. Reference numeral 603 denotes a waveform half-wave rectified by the diode 53a. This voltage waveform is input to the multiplier 56a via the resistor 55a. The multiplier 56 a outputs a squared voltage waveform as indicated by 604. This squared waveform is input to the negative terminal of the operational amplifier 59a through the resistor 57a. The reference voltage 84a is input to the + terminal of the operational amplifier 59a through the resistor 58a, and is inverted and amplified by the feedback resistor 60a. It is assumed that the operational amplifier 59a is supplied with power from a single power source.

  Reference numeral 605 denotes a waveform that is inverted and amplified with reference to the reference voltage 84a. The output of the operational amplifier 59a is input to the + terminal of the operational amplifier 72a. In the operational amplifier 72a, the transistor 73a is controlled so that the reference voltage 84a, the voltage difference between the waveforms input to its + terminal, and the current determined by the resistor 71a flow into the capacitor 74a. In this way, the capacitor 74a is charged with the reference voltage 84a and the current determined by the voltage difference between the waveform input to the + terminal and the resistor 71a.

  When the half-wave rectification section by the diode 53a ends, the charging current to the capacitor 74a disappears, and the voltage value is peak-held. Then, as shown at 606, the transistor 75a is turned on by the DIS signal during the half-wave rectification period of the diode 51a. Thereby, the charging voltage of the capacitor 74a is discharged. As indicated by 607, the transistor 75a is turned on / off by the DIS signal from the engine controller 126, and on / off control of the transistor 75a is performed based on the ZEROX signal indicated by 602. The DIS signal is turned on after a predetermined time Tdly from the rising edge of the ZEROX signal, and turned off at the same timing as or immediately before the falling edge of the ZEROX signal. Thus, the heater energization period, which is the half-wave rectification period of the diode 53a, can be controlled without interference.

  That is, the peak hold voltage V1f of the capacitor 74a is an integral value corresponding to a half cycle of the square value of the waveform obtained by converting the current waveform to the secondary side by the current transformer 225. The voltage value thus peak-held by the capacitor 74a is sent from the current detection circuit 227 to the engine controller 126 as an HCRRT1 signal.

  FIG. 6 is a block diagram for explaining the configuration of the current detection circuit 228 according to this embodiment, and FIG. 8 is a waveform diagram for explaining the operation of the current detection circuit 228.

  Reference numeral 701 denotes a power supply current I 2 supplied via the AC filter 202, and this current I 2 is voltage-converted on the secondary side by the current transformer 226. This power supply current I2 is the sum of the current I1 (601) flowing through the heater 109c (heating elements 203, 220) and the low-voltage power supply (LVPS) current I3.

  The voltage output from the current transformer 226 is rectified by diodes 51b and 53b, and 52b and 54b are connected as load resistors. Reference numeral 703 denotes a voltage waveform that is half-wave rectified by the diode 53b, and this waveform is input to the multiplier 56b via the resistor 55b. Reference numeral 704 denotes a waveform squared by the multiplier 56b. This squared voltage waveform is input to the negative terminal of the operational amplifier 59b through the resistor 57b. On the other hand, the reference voltage 84b is input to the + terminal of the operational amplifier 59b via the resistor 58b, and is inverted and amplified by the feedback resistor 60b. The operational amplifier 59b is supplied with a single power source. The waveform thus inverted and amplified with reference to the reference voltage 84b, that is, the output of the operational amplifier 59b is input to the + terminal of the operational amplifier 72b.

  The operational amplifier 72b controls the transistor 73b so that the reference voltage 84b and the voltage difference between the waveform input to the + terminal and the current determined by the resistor 71b flow into the capacitor 74b. As a result, the capacitor 74b is charged with the current determined by the voltage difference between the reference voltage 84b and the waveform input to the + terminal and the resistor 71b. When the half-wave rectification section by the diode 53b ends, the charging current to the capacitor 74b disappears, and the voltage value is peak-held. Here, by turning on the transistor 75b during the half-wave rectification period of the diode 51b, the voltage charged in the capacitor 74b is discharged. This transistor 75b is turned on / off by a DIS signal from the engine controller 126 indicated by 707, and controls the transistor 75b based on a ZEROX signal indicated by 702. The DIS signal is turned on after a predetermined time Tdly from the rising edge of the ZEROX signal, and is controlled without interfering with the heater current period of the half-wave rectification period of the diode 53b by turning off the falling edge of the ZEROX signal or immediately before. be able to.

  That is, the peak hold voltage V2f of the capacitor 74b is an integral value corresponding to a half cycle of the square value of the waveform obtained by converting the current waveform to the secondary side by the current transformer 226. In 706, the voltage of the capacitor 74 b is sent from the current detection circuit 228 to the engine controller 126 as an HCRRT2 signal indicated by 706.

  Next, a control sequence of the fixing device 109 in the present embodiment will be described.

  FIG. 9 is a flowchart for explaining control processing by the engine controller 126 of the image forming apparatus according to the first embodiment.

  First, in step S1, the engine controller 126 determines whether a request to start power supply to the ceramic heater 109c is generated. When the request is generated, the process proceeds to step S2, and the same predetermined value is applied to both the heating elements 203 and 220. Energized with a fixed duty D. Here, at the phase angle α corresponding to the fixed duty D, the ON pulses of the ON1 and ON2 signals are transmitted from the engine controller 126 using the ZEROX signal as a trigger. As a result, current is supplied to the heating elements 203 and 220 at the phase angle α.

In step S3, the load (motor or the like) of the low-voltage power supply is driven so that the current flowing through the low-voltage power supply (LVPS) becomes the maximum value during image formation.
If the load of the low-voltage power source is driven to detect a jam or failure before starting the image formation, the sequence may be used.

  Next, in step S4, the voltage V1f (corresponding to the current value I1f) is acquired from the HCRRT1 signal sent from the current detection circuit 227 while the load of the low-voltage power supply is driven by energizing with the fixed duty D. . As described above, this corresponds to the voltage value V1f peak-held by the capacitor 74a. That is, the peak hold value of the HCRRT1 signal shown in FIG. In this embodiment, the ZEROX signal is used as a trigger, and this value is acquired within a period of Tdly from the rising edge of the ZEROX signal until the DIS signal is transmitted. This period Tdly is set to a time sufficient for the engine controller 126 to detect the peak hold value V1f. The fixed duty D is set so as not to exceed the allowable current in consideration of the input voltage range assumed in advance, the resistance value of the heater, and the like. That is, the fixed duty D is set assuming that the input voltage is the maximum value, the resistance value is the minimum value, and the low voltage power supply (LVPS) current is the maximum value. In the description of the flowcharts of FIGS. 9 and 10, the current value is detected and the upper limit current value and the upper limit duty are calculated based on the current value. However, as described above, the peak hold is actually performed. The detected voltage value is detected. Then, a current value corresponding to this voltage value is obtained and calculation is performed.

  In step S5, the voltage value V2f (corresponding to the current value I2f) is acquired from the HCRRT2 signal in a state where the current of the low-voltage power supply is driven with the fixed duty D. This voltage value V2f is a voltage value obtained by passing the current of the commercial power supply 201 through the AC filter 202, and it is necessary to suppress this voltage value V2f (current value I2f) within a predetermined value.

Next, in step S6, the engine controller 126 uses the acquired voltage value V1f and voltage value V2f (current values I1f and I2f) to determine the upper limit of the current that can be applied to the heater 109c (heating elements 203 and 220). The current value Ilimit1 is calculated. Here, as described above, the voltage value V1f indicated by the HCRRT1 signal and the voltage value V2f indicated by the HCRRT2 signal are integrated values corresponding to a half cycle of the commercial frequency of the square waveform. Here, if the current value I3f is an integral value corresponding to a half cycle of the commercial frequency of the square waveform of the current flowing in all circuits (LVPS) excluding the heater 109c,
I2f = ∫ (I1 + I3) ² · dt
= ∫I1 (I1 + 2 × I3) · dt + I3f
Here, when I1 >> 2 × I3 holds,
I2f ≒ I1f + I3f
It becomes. In this state with the fixed duty D energized and driving the load of the low voltage power supply, the voltage value V1f (current value I1f) acquired from the HCRRT1 signal and the voltage value V2f (current value I2f) acquired from the HCRRT2 signal The current value I3f can be obtained. When the value of I3f is set as an intercept β, the current value I2f can be approximated by a linear expression of the current value I1f. That is,
I2f ≒ I1f + β
It can be expressed as.

  Here, the I2f value notified by the HCRRT2 signal is an integral value corresponding to a half cycle of the commercial frequency of the square waveform as described above. If the commercial frequency is set to a specific frequency, for example, 50 Hz in advance, the I2f value is a current value at 50 Hz.

The engine controller 126 can detect the commercial frequency by detecting the time interval T from the falling edge to the falling edge of the ZEROX signal. Therefore, assuming that the current value I1f converted to 50 Hz is I150, from the ZEROX cycle T,
I150 = I1f × (1 / T) / 50
Also, assuming that the current value I2f converted to 50 Hz is I250, from the ZEROX cycle T,
I250 = I2f × (1 / T) / 50
Can be expressed as

  In this way, the voltage value V1f (current value I1f) acquired from the HCRRT1 signal, the voltage value V2f (current value I2f) acquired from the HCRRT2 signal, and the ZEROX cycle in the state of energizing with the fixed duty D and driving the load of the low voltage power source Using the 50 Hz-converted current value I150 and I250 calculated from T, the following equation β can be calculated.

β ≒ I250−I150
Here, a preset current value Ilimit2 that can be energized is set as a current limit value at 50 Hz. The engine controller 126 can calculate the upper limit current value Ilimit1 of the current that can be passed through the heater 109c (heat generating elements 203, 220) by subtracting the intercept β obtained from the above equation from Ilimit2. Here, Ilimit1 is a current limit value at 50 Hz.

Ilimit1 ≒ Ilimit2-β
However, if the calculated current value of Ilimit1 is supplied to the heater 109c (heating elements 203, 220) and the rated power that can be supplied to the heater is exceeded, the upper limit current value Ilimit1 that can be supplied to the heater is supplied to the heater. Set it below the allowable current value.

  In step S7, the engine controller 126 calculates the current value I150 converted to 50 Hz calculated from the acquired voltage value V1f (current value I1f), the fixed duty D, and the upper limit current value Ilimit1 obtained in step S4. An upper limit power duty Dlimit that can be energized is calculated.

  Here, since the current value Ilimit1 that can be energized is a current limit value at 50 Hz, the upper limit duty Dlimit is obtained by the following equation.

Dlimit = (Ilimit1 / I150) × D
With this Dlimit as the upper limit duty, the process proceeds to step S8 to start the heater temperature control.

Here, based on the information from the TH signal, the power supplied to the heating elements 203 and 220 is controlled by PI control, for example, so that the predetermined temperature set in the engine controller 126 is obtained. The power duty to be supplied is determined from the difference between the target temperature information and the temperature information from the TH signal. However, when the calculated power duty exceeds the upper limit duty Dlimit, the power of the ratio of Dlimit is supplied as the upper limit value. That is, in step S8, the heater temperature control is performed with a duty equal to or less than the upper limit duty Dlimit. Phase control is performed at a phase angle equal to or smaller than the phase angle αlimit corresponding to the upper limit duty Dlimit.

Then, in step S9, control is performed with the calculated upper limit duty Dlimit or less until a request to end the heater temperature control is received.

  In the above description. Although the description has been given of the case where there are two heating elements 203 and 220 constituting the heater 109c, the present invention is not limited to this, and the same control is possible even when there is only one heating element.

As described above, according to the first embodiment, when the fixing device 109 is started up, power is supplied at a predetermined power ratio so that the current flowing through the low-voltage power supply (LVPS) becomes the maximum value in the print sequence. The upper limit power ratio is calculated based on the HCRRT1 signal and the HCRRT2 signal notified from the current detection circuit 227 and the current detection circuit 228 in a state where the load (motor or the like) of the low voltage power source is driven. And it can control so that the electric power below the upper limit electric power ratio may be supplied with electricity.
As a result, when the approximate condition “I1 >> 2 × I3” of the above approximate expression is satisfied, the power supplied to the load can be controlled in a range in which the current supplied to the commercial power supply does not exceed the predetermined upper limit current. it can.

  In addition, the square value of the effective value is detected to correct the frequency, and the upper limit current value of the current that can be passed through the heater 109c (heat generating elements 203 and 220) is calculated using an approximate expression, so that The upper limit current value that can be supplied can be accurately set with respect to the variation in voltage, power factor, heater resistance, and waveform rate. Therefore, the power performance can be maximized under each condition.

[Embodiment 2]
FIG. 10 is a flowchart illustrating a control sequence of fixing device 109 by engine controller 126 according to the second embodiment of the present invention. Since the apparatus configuration according to the second embodiment is the same as that of the first embodiment, the description thereof is omitted.

  In FIG. 10, the processing of steps S11 to S15 is the same as the processing of steps S1 to S5 of FIG. In step S16, the engine controller 126 calculates the upper limit current value Ilimit1 of the current that can be passed through the heater 109c based on the acquired voltage value V1f (current value I1f) and voltage value V2f (current value I2f). Here, the current value I1f_1 detected from the HCRRT1 signal and the current value I2f_1 detected from the HCRRT2 signal (current value converted to 50 Hz) and the current value I2f_1 detected from the HCRRT2 signal when energized with the fixed duty D_1 Is determined as I250_1), and the intercept β is determined by the ZEROX cycle T_1.

β ≒ I250_1−I150_1
The intercept β is subtracted from the upper limit value Ilimit2 of the current value I2f that is the input current from the commercial power supply 201, and the upper limit current value Ilimit1 is calculated by the engine controller 126. Here, Ilimit1 and Ilimit2 are current limit values at 50 Hz.

Ilimit1 ≒ Ilimit2-β
However, if the calculated current value of Ilimit1 is supplied to the heater 109c (heating elements 203, 220) and the rated power that can be supplied to the heater is exceeded, the upper limit current value Ilimit1 that can be supplied to the heater is supplied to the heater. Set it below the allowable current value.

  In step S17, the engine controller 126 calculates the upper limit power duty Dlimit_1 that can be energized from the detected current value I1f_1, fixed duty D_1, the upper limit current value Ilimit1 obtained in step S16, and the ZEROX cycle T_1. .

Dlimit_1 = (Ilimit1 / I150_1) × D_1
The power duty Dlimit_1 obtained by this calculation is set as the upper limit duty, and the process proceeds to step S18 to start the heater temperature control. Here, based on the information from the TH signal, the power supplied to the heating elements 203 and 220 is controlled by PI control, for example, so that the predetermined temperature set in the engine controller 126 is obtained. The power duty D_2 to be supplied is determined from the difference between the target temperature information and the temperature information from the TH signal. However, if the calculated power duty exceeds the upper limit duty Dlimit_1, power having a ratio of Dlimit_1 is supplied as the upper limit value. At this time, the value of D_2 coincides with Dlimit_1. That is, in step S8, the heater temperature control is performed with a duty equal to or less than the upper limit duty Dlimit_1. The phase control is performed at a phase angle equal to or smaller than the phase angle αlimit_1 corresponding to the upper limit duty Dlimit_1.

  In step S19, the heater temperature control is started, and after power is supplied at the ratio of D_2, the voltage value V1f_2 (current value I1f_2) and the ZEROX cycle T_2 are detected by the HCRRT1 signal, and the 50Hz converted value I150_2 of the current value I1f_2 is obtained. calculate.

I150_2 = I1f_2 × (1 / T_2) / 50
In step S20, the voltage value V2f_2 (current value I2f_2) and the ZEROX cycle T_2 are detected from the HCRRT2 signal, and a 50 Hz converted value I250_2 of the current value I2f_2 is calculated.

I250_2 = I2f_2 × (1 / T_2) / 50
In step S21, I250_2 acquired in step S20 is compared with a preset current value Ilimit2 that can be supplied from the commercial power supply 201. Ilimit2 is a current limit value at 50 Hz.

If the condition Ilimit2> I250_2 is satisfied, the process branches to step S23. If the condition Ilimit2 ≦ I250_2 is satisfied, the process branches to step S22.

  Step 22 is a case where the current value I250_2 is equal to or higher than the preset upper limit current value Ilimit2 in a state where current is applied at the duty D_2, and the voltage value V1f_2 (current value I1f_2) obtained from the HCRRT1 signal and the voltage obtained from the HCRRT2 signal. The current upper limit value Ilimit1 is calculated using the current value I150_2 converted to 50 Hz and I250_2 calculated from the value V2f_2 (current value I2f_2) and the ZEROX cycle T_2, and the value of the upper limit current value Ilimit1 of the current that can be supplied to the heater 109c. Update.

β ≒ I250_2−I150_2
Ilimit1 ≒ Ilimit2-β
However, if the calculated current value of Ilimit1 is supplied to the heater 109c (heating elements 203, 220) and the rated power that can be supplied to the heater is exceeded, the upper limit current value Ilimit1 that can be supplied to the heater is supplied to the heater. Set it below the allowable current value. The value of Ilimit1 obtained here is set as a new upper limit current value, and the process proceeds to the next step S23.

  In step S23, the engine controller 126 calculates an upper limit power duty Dlimit_2 that can be energized from the current value I150_2, the power duty D_2, and the upper limit current value Ilimit1.

Dlimit_2 = (Ilimit1 / I150_2) × D_2
The above processing is repeated at every commercial power supply cycle until the temperature control of the heater 109c is completed in step S24, and the engine controller 126 calculates the power duty supplied to the heating elements 203 and 220.

  That is, when temperature control of the heater is performed with a power duty D_n + 1 less than Dlimit_n (S18), the voltage value V1f_n + 1 (current value I1f_n + 1) is obtained from the HCRRT1 signal (S19), and the voltage value is obtained from the HCRRT2 signal. V2f_n + 1 (current value I2f_n + 1) is acquired (S20), and I150_n + 1 and I250_n + 1 are calculated from the ZEROX cycle T_n + 1 (S19, S20).

  When I250_n + 1 exceeds the preset upper limit value Ilimit2 in a state where current is applied at the duty D_n + 1 (S21), the upper limit current value Ilimit1 is calculated using an approximate expression (S22), and a new upper limit current is set. Set to value. The upper limit power duty Dlimit_n + 1 is calculated from I150_n, the power duty D_n, and the upper limit current value Ilimit1 (S23).

As described above, according to the second embodiment, the upper limit power duty Ilimit1 that can energize the heater is set using the above approximate expression.
When the current value I2f acquired from the HCRRT2 signal whose value is updated every commercial frequency period after the setting exceeds the upper limit value that can be energized from the commercial power supply 201 set in advance, the upper limit duty Ilimit1 And the upper limit power ratio is updated.
The upper limit value of the power duty is repeatedly calculated using the current values I1f and Ilimit1 values obtained from the HCRRT2 signal, the duty D, and the ZEROX cycle T, and is updated every commercial frequency cycle.
By doing this, even when the approximation condition “I1 >> 2 × I3” of the above approximate expression is not satisfied, the voltage, power factor, heater resistance value variation, and waveform rate of the waveform are accurately supplied. Possible upper limit can be set. Further, even when the voltage or frequency of the commercial power supply 201 during the printing operation varies, it is possible to prevent a current exceeding the allowable current from being supplied.
Thus, it is possible to maximize the power performance under each condition.

1 is a schematic configuration diagram of an image forming apparatus (laser printer) using an electrophotographic process according to the present embodiment. It is a block diagram which shows the structure of the heater control circuit which controls the electricity supply drive to a ceramic heater in embodiment of this invention. It is a figure explaining the outline of the ceramic heater which concerns on this Embodiment. It is a figure which shows schematic structure of the heat fixing device which concerns on this Embodiment. It is a block diagram explaining the structure of the current detection circuit 227 which concerns on this Embodiment. It is a block diagram explaining the structure of the current detection circuit 228 which concerns on this Embodiment. It is a wave form diagram for demonstrating operation | movement of the current detection circuit 227 which concerns on this Embodiment. It is a wave form diagram for demonstrating operation | movement of the current detection circuit 228 which concerns on this Embodiment. 4 is a flowchart for explaining control processing by an engine controller of the image forming apparatus according to the first embodiment. 10 is a flowchart illustrating a control process by an engine controller of the image forming apparatus according to the second embodiment.

Claims (8)

A power supply control device for controlling power supplied from a commercial power source to a load,
Supplying AC power from the commercial power source to the load, and energization switching means for cutting off the power supply;
First current detection means for detecting current supplied from the commercial power supply;
Second current detection means for detecting current flowing into the load;
Calculating means for calculating an upper limit value of the current supplied to the load based on a current value detected by the first current detecting means and the second current detecting means and a power ratio for driving the energization switching means;
Based on the upper limit value calculated by the calculation means, the current value detected by the second current detection means, and the power ratio for driving the energization switching means, an upper limit power ratio for driving the energization switching means is calculated. A power supply duty determining means for determining;
Control means for driving the energization switching means within the upper limit power ratio to control power supply to the load;
A power supply control device comprising: The first and second current detecting means are
A half-wave rectifier circuit that half-wave rectifies the secondary current generated by the current to be detected;
A square circuit for obtaining a square value of the voltage half-wave rectified by the half-wave rectifier circuit;
An amplifier circuit for amplifying the output of the square circuit;
An integrating circuit for integrating the voltage value amplified by the amplifier circuit;
A voltage holding circuit that holds the voltage value integrated by the integration circuit,
The power supply control device according to claim 1, wherein the voltage value output from the voltage holding circuit is output as a current value to be detected.   The power supply according to claim 1 or 2, further comprising temperature detection means for detecting a temperature of the load, wherein the control means further performs control according to the temperature detected by the temperature detection means. Control device.   Frequency detection means for detecting the frequency of the commercial power supply is further provided, and the upper limit power ratio is determined based on the detection results of the first current detection means and the second current detection means and the frequency detected by the frequency detection means. It correct | amends, The electric power supply control apparatus of any one of Claim 1 thru | or 3 characterized by the above-mentioned. An image forming apparatus that performs image formation by controlling power supplied from a commercial power source to a heating element,
Supplying AC power from the commercial power source to the heating element, and energization switching means for cutting off the power supply;
First current detection means for detecting current supplied from the commercial power supply;
Second current detection means for detecting current flowing into the heating element;
Calculation means for calculating an upper limit value of current supplied to the heating element based on a current value detected by the first current detection means and the second current detection means and a power ratio for driving the energization switching means;
An upper limit power ratio for driving the energization switching means is determined based on the upper limit value calculated by the calculation means, the current detected by the second current detection means, and the power ratio for driving the energization switching means. Power supply duty determining means to perform,
Control means for controlling the power supply to the heating element by driving the energization switching means within the upper limit power ratio;
An image forming apparatus comprising: The first and second current detecting means are
A half-wave rectifier circuit that half-wave rectifies the secondary current generated by the current to be detected;
A square circuit for obtaining a square value of the voltage half-wave rectified by the half-wave rectifier circuit;
An amplifier circuit for amplifying the output of the square circuit;
An integrating circuit for integrating the voltage value amplified by the amplifier circuit;
A voltage holding circuit that holds the voltage value integrated by the integration circuit,
6. The image forming apparatus according to claim 5, wherein the voltage value output from the voltage holding circuit is output as a current value to be detected.   The temperature detection means for detecting the temperature of the heating element is further provided, and the control means further controls the temperature detected by the temperature detection means to be within a predetermined temperature range. The image forming apparatus described in 1.   Frequency detection means for detecting the frequency of the commercial power supply is further provided, and the upper limit power ratio is determined based on the detection results of the first current detection means and the second current detection means, and the frequency detected by the frequency detection means. The image forming apparatus according to claim 5, wherein correction is performed.

Images