Heating unit, auxiliary power unit, fixing unit, and image forming apparatus

A main controller controls a capacitor charger to charge a capacitor as necessary. A sub-controller controls a power saving mode and stops a power supply to the main controller when shifting to the power saving mode. A charge control circuit compares a terminal voltage of the capacitor with a predetermined value by a comparator circuit. If the terminal voltage is lower than the reference value, an AND circuit takes a logical product of an output signal of the comparator circuit and a power saving signal indicating the shift to the power saving mode, and outputs a control signal indicating an instruction to charge the capacitor, to the capacitor charger.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present document incorporates by reference the entire contents of Japanese priority documents, 2003-409019 filed in Japan on Dec. 8, 2003, 2004-021043 filed in Japan on Jan. 29, 2004, and 2004-026680 filed in Japan on Feb. 3, 2004.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The present invention relates to a heating unit and a fixing unit that include a heating member that produces heat with charging of a capacitor, an auxiliary power unit and a fixing unit that include a plurality of capacitors serially connected to each other, and an image forming apparatus including the above fixing unit.

2) Description of the Related Art

Japanese Patent Application Laid Open No. 2000-315567, Japanese Patent Application Laid Open No. 2002-357966, and Japanese Patent Application Laid Open No. 2003-140484 disclose technologies for a heating member (fixing heater) of a fixing unit used in an electrophotographic image forming apparatus. This technology is such that in addition to a power supply from a commercial power supply, a chargeable auxiliary power supply that uses an electric double layer capacitor is used to allow fast rising of temperature and enhance effects of power saving.

Electrophotographic image forming apparatuses and other electronic devices including a power saving mode are known. In the power saving mode, when the electrophotographic image forming apparatus or the like is in a standby state and is not used for a fixed time, a power supply to power loads thereof is restricted and the power is supplied only to some circuits minimum required to allow power saving and energy saving. One of these is disclosed in Japanese Patent Application Laid Open No. 2002-304088.

In the electrophotographic image forming apparatus, if temperature of a fixing unit is made to rise quickly by the chargeable auxiliary power supply using the capacitor such as the electric double layer capacitor, the power of the capacitor if it is low cannot increase the fixing temperature quickly. Therefore, when the charging power of the capacitor decreases to a predetermined level or less, a specified controller needs to control a charger so as to charge the capacitor.

However, in such an image forming apparatus as explained above that includes the power saving mode, if a power supply to the controller (e.g. microcomputer) that controls the charger so as to charge the capacitor is also stopped when mode shifts to the power saving mode, the capacitor is not charged in the power saving mode. In this case, if the amount of charge in the capacitor decreases to a quite low level right before shifting to the power saving mode, or if the power saving mode is active for a long time and natural discharge of the capacitor occurs, the charge amount of the capacitor is insufficient by the time it is returned from the power saving mode, which makes it impossible to quickly increase the fixing temperature of the fixing unit.

In such a case, it is possible to rapidly increase the fixing temperature by maintaining the power supply to the controller even after the shift to the power saving mode. However, the controller also consumes power even in the power saving mode, which is quite difficult to achieve satisfactory power saving and energy saving.

In the technologies disclosed in Japanese Patent Application Laid Open No. 2000-315567, Japanese Patent Application Laid Open No. 2002-357966, and Japanese Patent Application Laid Open No. 2003-140484, by using the capacitor including the electric double layer capacitor (large capacitor) as an auxiliary power supply, degradation of fixability due to power failure can be prevented. That is because a large amount of current can be instantly supplied from the capacitor to the fixing unit when the power supply to the fixing unit from the commercial power supply is insufficient. However, the technologies have such inconvenience that the capacitor has to be charged at a predetermined timing after the capacitor discharges to supply power to the heating member. Moreover, since a large amount of power has to be supplied from the commercial power supply during the charging, a copying operation cannot concurrently be executed by a copying machine, which causes a down time to occur in the copying machine and the operability of a user to be reduced.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve at least the above problems in the conventional technology.

A heating unit according to one aspect of the present invention includes a capacitor; a charger that charges the capacitor; a heating member that produces heat with a supply of a charging power from the capacitor; a terminal-voltage detecting circuit that detects a terminal voltage of the capacitor; a control unit that controls the charger based on the terminal voltage detected to charge the capacitor; a power controller that stops, when a predetermined condition is satisfied, a power supply to a part of power loads of the heating unit including the control unit, and releases, when a predetermined condition is satisfied during a stop state of the power supply, the stop state; and a charge controller that controls, during the stop state of the power supply, the charger to charge the capacitor based on the terminal voltage detected.

A fixing unit according to another aspect of the present invention includes a fixing member that applies pressure and heat to a medium, on which a toner image is formed, to fix the toner image on the medium; a capacitor; a charger that charges the capacitor with a supply of power from a commercial power supply; a heating member that produces heat with a supply of charging power from the capacitor; a terminal-voltage detecting circuit that detects a terminal voltage of the capacitor; a control unit that controls the charger based on the terminal voltage detected to charge the capacitor; a power controller that stops, when a predetermined condition is satisfied, a power supply to a part of power loads of the heating unit including the control unit, and releases, when a predetermined condition is satisfied during a stop state of the power supply, the stop state; and a charge controller that controls, during the stop state of the power supply, the charger to charge the capacitor based on the terminal voltage detected.

An image forming apparatus according to still another aspect of the present invention, which forms an image on a medium using an electrophotographic method, includes a fixing unit including a fixing member that applies pressure and heat to a medium, on which a toner image is formed, to fix the toner image on the medium; a capacitor; a charger that charges the capacitor with a supply of power from a commercial power supply; a heating member that produces heat with a supply of charging power from the capacitor; a terminal-voltage detecting circuit that detects a terminal voltage of the capacitor; a control unit that controls the charger based on the terminal voltage detected to charge the capacitor; a power controller that stops, when a predetermined condition is satisfied, a power supply to a part of power loads of the heating unit including the control unit, and releases, when a predetermined condition is satisfied during a stop state of the power supply, the stop state; and a charge controller that controls, during the stop state of the power supply, the charger to charge the capacitor based on the terminal voltage detected.

A heating unit according to still another aspect of the present invention includes a capacitor; a charger that charges the capacitor; a heating member; a discharger that discharges charging power of the capacitor to the heating member to make the heating member produce heat; a first control unit that stops, when a predetermined condition is satisfied, a power supply to other power loads except for a part of power loads of the heating unit, and releases, when the predetermined condition is satisfied during a stop state of the power supply, the stop state; and a second control unit that is driven with a supply of power independently from the first control unit, and controls charging of the capacitor.

A fixing unit according to still another aspect of the present invention includes a fixing member that applies pressure and heat to a medium, on which a toner image is formed, to fix the toner image on the medium; a first heating member that produces heat with a supply of power from a commercial power supply, and heats the fixing member; a capacitor; a charger that charges the capacitor with a supply of power from the commercial power supply; a second heating member that produces heat with a supply of power from the capacitor, and heats the fixing member; a first control unit that stops, when a predetermined condition is satisfied, a power supply to other power loads except for a part of power loads of the heating unit, and releases, when the predetermined condition is satisfied during a stop state of the power supply, the stop state; and a second control unit that is driven with a supply of power independently from the first control unit, and controls charging of the capacitor.

An image forming apparatus according to still another aspect of the present invention, which forms an image on a medium using an electrophotographic method, includes a fixing unit including a fixing member that applies pressure and heat to a medium, on which a toner image is formed, to fix the toner image on the medium; a first heating member that produces heat with a supply of power from a commercial power supply, and heats the fixing member; a capacitor; a charger that charges the capacitor with a supply of power from the commercial power supply; a second heating member that produces heat with a supply of power from the capacitor, and heats the fixing member; a first control unit that stops, when a predetermined condition is satisfied, a power supply to other power loads except for a part of power loads of the heating unit, and releases, when the predetermined condition is satisfied during a stop state of the power supply, the stop state; and a second control unit that is driven with a supply of power independently from the first control unit, and controls charging of the capacitor.

An auxiliary power unit according to still another aspect of the present invention includes a first capacitor; a first charger that charges the first capacitor with a supply of power from the commercial power supply; a first terminal-voltage detection circuit that detects a terminal voltage of the first capacitor; a second capacitor serially connected to the first capacitor; a second charger that charges the second capacitor with a supply of power from the commercial power supply; a second terminal-voltage detection circuit that detects a terminal voltage of the second capacitor; and a control unit that switches a charging operation between the first charger and the second charger so that the terminal voltage reaches a final target voltage based on results of detection by the first terminal-voltage detection circuit and the second terminal-voltage detection circuit.

A fixing unit according to still another aspect of the present invention includes a fixing member that applies pressure and heat to a medium, on which a toner image is formed, to fix the toner image on the medium; first heating member that produces heat with a supply of power from a commercial power supply, and heats the fixing member; and a second heating member that produces heat with a supply of power from a first capacitor and a second capacitor in an auxiliary power unit. The auxiliary power unit includes the first capacitor; a first charger that charges the first capacitor with a supply of power from the commercial power supply; a first terminal-voltage detection circuit that detects a terminal voltage of the first capacitor; the second capacitor serially connected to the first capacitor; a second charger that charges the second capacitor with a supply of power from the commercial power supply; a second terminal-voltage detection circuit that detects a terminal voltage of the second capacitor; and a control unit that switches a charging operation between the first charger and the second charger so that the terminal voltage reaches a final target voltage based on results of detection by the first terminal-voltage detection circuit and the second terminal-voltage detection circuit.

An image forming apparatus according to still another aspect of the present invention, which forms an image on a medium using an electrophotographic method, includes a fixing unit including a fixing member that applies pressure and heat to a medium, on which a toner image is formed, to fix the toner image on the medium; first heating member that produces heat with a supply of power from a commercial power supply, and heats the fixing member; and a second heating member that produces heat with a supply of power from a first capacitor and a second capacitor in an auxiliary power unit. The auxiliary power unit includes the first capacitor; a first charger that charges the first capacitor with a supply of power from the commercial power supply; a first terminal-voltage detection circuit that detects a terminal voltage of the first capacitor; the second capacitor serially connected to the first capacitor; a second charger that charges the second capacitor with a supply of power from the commercial power supply; a second terminal-voltage detection circuit that detects a terminal voltage of the second capacitor; and a control unit that switches a charging operation between the first charger and the second charger so that the terminal voltage reaches a final target voltage based on results of detection by the first terminal-voltage detection circuit and the second terminal-voltage detection circuit.

DETAILED DESCRIPTION

Exemplary embodiments of a heating unit, an auxiliary power unit, a fixing unit, and an image forming apparatus according to the present invention are explained in detail lower than with reference to the accompanying drawings.

FIG. 1is a vertical cross section of a digital copying machine1(hereinafter, “copying machine1”) according to a first embodiment of the present invention. The copying machine1realizes the image forming apparatus according to the present invention, which is a multifunction product. More specifically, the copying machine1includes a copying function and other functions such as a printer function and a facsimile function. The copying function, the print function, and the facsimile function can be sequentially switched and selected through an operation of an application switch key provided in an operation unit (not shown). Based on the configuration, a mode is switched to a copying mode when the copying function is selected, it is switched to a print mode when the printer function is selected, and it is switched to a facsimile mode when the facsimile function is selected.

A schematic configuration of the copying machine1and an operation in the copying mode are explained lower than. As shown inFIG. 1, a document with the image face up is set on a document table102of an automatic document feeder (ADF)101. When a start key in the operation unit (not shown) is pressed, the document is fed by a paper feed roller103and a paper feed belt104to a fixed position on the document table102including a contact glass105. The ADF101has a counting function of counting the number of documents each time feeding of a sheet of document is completed. The document on the contact glass105is read by an image reader106to obtain image information for the document, and the document is discharged onto a paper discharge base108by the paper feed belt104and a discharge roller107.

If a document set detector109detects that the next document is present on the document table102, the lowest document on the document table102is fed to the contact glass105by the paper feed roller103and the paper feed belt104. The document on the contact glass105is read by the image reader106to obtain image formation for the document, and the document is discharged onto the sheet discharge base108by the paper feed belt104and the discharge roller107. The paper feed roller103, the paper feed belt104, and the discharge roller107are driven by a conveying motor.

The image reader106includes a light source128, mirrors129to131, a lens132, and a charge-coupled device (CCD)133.

Any of a first paper feed device110, a second paper feed device111, and a third paper feed device112selected feeds a transfer paper loaded thereon, and the transfer paper is conveyed by a vertical conveying unit116up to a position where it is in contact with a photosensitive element117. The photosensitive element117employs, for example, a photosensitive drum, and is made to rotate by a main motor (not shown).

The image data read from the document by the image reader106is subjected to predetermined image processing by an image processor (not shown), and is converted to optical information by a writing unit118. The photosensitive drum117is uniformly charged by a charger (not shown), and the photosensitive drum117charged is exposed with the optical information from the writing unit118and an electrostatic latent image is formed thereon. The electrostatic latent image on the photosensitive drum117is developed by a developing device119to be a toner image. The writing unit118, the photosensitive drum117, the developing device119, and other peripheral devices (not shown) around the photosensitive drum117constitute a printer engine that forms an image on a medium such as a sheet of paper using an electrophotographic method. It is noted that the writing unit118includes a laser writing device134and a reflecting mirror136.

A conveying belt120serves as a unit for paper conveyance and also as a unit for image transfer, and is applied with transfer bias from a power supply. The conveying belt120transfers a toner image on the photosensitive drum117to a transfer paper while conveying the transfer paper from the vertical conveying unit116at a speed equal to that of the photosensitive drum117. A fixing unit121fixes the toner image on the transfer paper, and a paper discharge unit122discharges the transfer paper onto a paper discharge tray123. After the toner image is transferred, toner remaining on the photosensitive drum117is cleaned by a cleaning device (not shown).

The operation so far is performed when an image is copied on one side of the paper in an ordinary copying mode. If images are copied on both sides of the transfer paper in a double-sided copying mode, a transfer paper is fed from any one of paper feed trays113to115, an image is formed on the surface of the transfer paper in the above manner. The path for the transfer paper with the image is switched so that it is conveyed not to the paper discharge tray123but to a paper feeding path124for double-sided copying. The transfer paper is switched back and turned upside down by a reversing unit125, and is conveyed to a paper conveying unit126for double-sided copying.

The transfer paper conveyed to the paper conveying unit126is conveyed by this paper conveying unit126to the vertical conveying unit116, and is conveyed by the vertical conveying unit116to a position where it is in contact with the photosensitive drum117. The toner image formed on the photosensitive drum117in the above manner is transferred to the rear surface of the transfer paper, and the toner image is fixed on the transfer paper by the fixing unit121to obtain double-sided copied paper. The double-sided copied paper is discharged to the paper discharge tray123by the paper discharge unit122.

If the transfer paper is to be reversely discharged, the reversing unit125switches back the transfer paper, and reverses it. The transfer paper reversed is conveyed not to the paper conveying unit126but is conveyed to a reversely-discharged-paper conveying path127, and is discharged to the paper discharge tray123by the paper discharge unit122.

In the print mode, instead of the image data from the image processor, image data from an external device is input to the writing unit118, and an image is formed on the transfer paper in the above manner.

In the facsimile mode, a facsimile transmitter/receiver (not shown) transmits image data from the image reader106to the other party and receives image data from the other party. The facsimile transmitter/receiver inputs the image data received to the writing unit118instead of the image data from the image processor, and an image is formed on the transfer paper in the above manner.

The copying machine1includes a large capacity tray (LCT) and a finisher (both of which are not shown), and an operation unit. The finisher performs sorting, punching, and stapling on sheets of paper copied. Set on the operation unit are a mode to read a document, a magnification of copying, a paper feed stage, and any post-process by the finisher, and a display for an operator is displayed thereon.

The configuration of the fixing unit121is explained lower than with reference toFIG. 2. The fixing unit121realizes the heating unit and the fixing unit according to the present invention. The fixing unit121includes a fixing roller301that is a target to be heated, and a pressing roller302that is formed of an elastic member such as silicone rubber and is pressed against the fixing roller301with a predetermined pressure force by a pressing unit (not shown). A fixing member and a pressing member are generally a roller, but either one or both of the members may be formed with an endless belt. A fixing heater HT1and a fixing heater HT2are provided in arbitrary locations of the fixing unit121. For example, the fixing heaters HT1and HT2are arranged inside the fixing roller301, and the fixing roller301is heated from the inside of the fixing roller301.

A drive mechanism (not shown) rotates the fixing roller301and the pressing roller302. A temperature sensor (e.g. thermistor) TH11is made in contact with the surface of the fixing roller301to detect a temperature (fixing temperature) of the surface of the fixing roller301. A sheet307is a medium such as a transfer paper that carries a toner image306. When the sheet307passes through a nip part between the fixing roller301and the pressing roller302, the toner image306is heated and pressed by the fixing roller301and the pressing roller302to be fixed on the sheet307.

The fixing heater HT2as a first heating member is a main heater that is turned on when the temperature of the fixing roller301does not reach a predetermined target temperature Tt as a reference and heats the fixing roller301. The fixing heater HT1as a second heating member is an auxiliary heater that is turned on when a main power to the copying machine1is turned on or during a rising period from returning from a power saving mode explained later to being ready for copying. In other words, the fixing heater HT1is turned on when the fixing unit121is warmed up and heats the fixing roller301.

FIG. 3is a diagram of a configuration of a power control system for the copying machine1mainly including the fixing unit121. The power control system includes a main power supply SW201that turns on/off a power supply from an alternating-current (AC) power supply (commercial AC power supply) PS, and a microcomputer. The power control system also includes a controller202functioning as a control unit that controls components of a power supply circuit200and other parts, a capacitor CP1that is an auxiliary power supply for the fixing heater HT1, and a capacitor charger203that serves as a charger for charging the capacitor CP1. The power control system further includes a direct-current (DC) power generation circuit204that generates DC power for the copying machine1, an AC-heater drive circuit205that supplies AC power to the fixing heater HT2, an input-current detection circuit206that detects whether a current is input from the AC power supply PS, an interlock switch207, and a capacitor charge-discharge circuit208that performs discharge of the capacitor CP1and supplies DC power to the fixing heater HT1.

The AC power supply PS supplies AC power to the AC-heater drive circuit205, the DC-power generation circuit204, the capacitor charger203through the main power supply SW201, and the input-current detection circuit206.

The controller202controls mainly the components of the power supply circuit200, and controls the operations of the capacitor charger203, the AC-heater drive circuit205, and the capacitor charge-discharge circuit208. More specifically, the controller202outputs a control signal S11to the capacitor charger203so as to control a charging operation to the capacitor CP1by the capacitor charger203. The controller202outputs a control signal S13and a control signal S14to the capacitor charge-discharge circuit208so as to control an on/off operation of the fixing heater HT1by the capacitor charge-discharge circuit208. The controller202outputs control signals S18and S19to the AC-heater drive circuit205to control an on/off operation of the fixing heater HT2by the AC-heater drive circuit205. Furthermore, the controller202estimates the number of sheets of documents set on the ADF101based on a detection signal input from a slit sensor160, and predicts a time required for a copy job per operation mode based on the number of sheets estimated, the number of sheets to be copied set in an operation unit150, and a time required for printing per sheet in each operation mode (fast mode, slow mode).

The input-current detection circuit206is provided between the main power supply SW201, the AC-heater drive circuit205, the DC-power generation circuit204, and the capacitor charger203. The input-current detection circuit206detects an input current of AC power input through the main power supply SW201, and outputs a current detection signal S17to the controller202. The input current fluctuates according to each operating status of the AC-heater drive circuit205, the DC-power generation circuit204, the capacitor charger203, and the image forming apparatus.

The DC-power generation circuit204generates power Vcc and power Vaa based on the AC power input through the main power supply SW201, and outputs the power Vcc and the power Vaa to the components. The power Vcc is used mainly for the control system of the image forming apparatus, and the power Vaa is used mainly for the drive system and high- and medium-voltage power supply.

The interlock switch207is a switch that is interlocked with a cover (not shown) or the like of the copying machine1to turn the power on/off. If the copying machine1includes a drive member and an application member for the high- and medium-voltage power that are able to be touched when the cover is opened, the power is cut off when the cover is opened so as to stop the operation of the drive member or to stop applying a voltage to the application member. A part of the power Vaa generated in the DC-power generation circuit204is input to the interlock switch207, and is input to the capacitor charge-discharge circuit208and the AC-heater drive circuit205through the interlock switch207.

The AC-heater drive circuit205turns on/off the fixing heater HT2according to the control signals S18and S19input from the controller202.

The capacitor charger203is connected to the capacitor CP1, and charges the capacitor CP1based on the control signal S11input from the controller202.

The capacitor CP1is formed with a capacitor with large capacity such as the electric double layer capacitor. The capacitor CP1is connected to the capacitor charger203and the capacitor charge-discharge circuit208. The capacitor CP1is charged by the capacitor charger203and the power charged is supplied to the fixing heater HT1under the on/off control of the capacitor charge-discharge circuit208.

The capacitor charge-discharge circuit208discharges the power accumulated in the capacitor CP1according to the control signals S13and S14input from the controller202, and turns on/off the fixing heater HT1.

The thermistor TH11is provided near the fixing roller301, and outputs a detection signal S16according to the surface temperature of the fixing roller301to the controller202. Since the resistance of the thermistor TH11changes according to temperature, the controller202detects the surface temperature of the fixing roller301from the detection signal S16obtained based on the change in the resistance due to temperature.

FIG. 4is a diagram of a configuration of the AC-heater drive circuit205ofFIG. 3. The AC-heater drive circuit205includes a filter FIL21that removes noise of the AC power input, a fixing relay RL21for safety to be turned on/off according to the control signal S19input from the controller202, a diode D21for preventing counter electromotive force of the fixing relay RL21, and a heater on/off circuit220that turns on/off the fixing heater HT2based on the control signal S18input from the controller202.

The AC power supply PS is connected to one end of the fixing heater HT2through the filter FIL21and the fixing relay RL21. The other end of the fixing heater HT2is connected to the heater on/off circuit220.

The heater on/off circuit220includes a triac TRI21for turning on/off the AC power, a photocoupler PC21for insulating a signal from the controller202that is a secondary side, and a transistor TR21for driving a light emitting diode (LED) on a light emission side of the photocoupler PC21. The heater on/off circuit220also includes a noise-absorption snubber circuit including a capacitor C21and a resistor R21, an inductance L21for noise absorption, a resistor R22that is a resistor for preventing a dynamic current, and resistors R23and R24that are resistors for restricting a current from the photocoupler PC21.

In the AC-heater drive circuit205configured as explained above, the fixing heater HT2is supplied with power and is lit when both the fixing relay RL21and the gates of the transistor TR21are on.

The controller202turns on/off the control signal S18to be supplied to the gate of the transistor TR21for the heater on/off circuit220in an on state of the control signal S19that is supplied to the fixing relay RL21, and controls switching on/off of the fixing heater HT2.

FIG. 5is a diagram of a configuration of the capacitor charger203ofFIG. 3. The capacitor charger203includes a noise filter (NF)211that removes noise of an AC voltage input, a rush-current prevention circuit212that prevents a rush current, a diode bridge DB that rectifies AC power from the AC power supply PS input through the rush-current prevention circuit212, and a capacitor C100that performs smoothing on the AC voltage rectified. The capacitor charger203also includes a field-effect transistor (FET) controller213that controls switching of a FET214and controls the charging operation of the capacitor CP1(seeFIG. 3), the FET214that turns on/off a trance T100, and the trance T100that boosts an input voltage. The capacitor charger203further includes a rectification-smoothing circuit215that performs rectification and smoothing on an output on the secondary side of the trance T100to be converted to a DC output, a current detector216that detects a current, a voltage detector217that detects a voltage, an overvoltage detector218that detects overvoltage so as not to apply overvoltage to the capacitor CP1, a diode D100for preventing a back flow from the capacitor CP1, and an insulating element219.

The AC voltage input from the AC power supply PS is noise-removed by the noise filter211, is rectified by the diode bridge DB through the rush-current prevention circuit212, and is subjected to smoothing by the capacitor C100to obtain a DC voltage to be input to a primary side of the trance T100. If the control signal S11input from the controller202(seeFIG. 3) is “on”, the FET controller213starts switching control of the FET214to charge the capacitor CP1. The FET controller213controls switching of the FET214based on the respective detection signals input from the current detector216, the voltage detector217, and the overvoltage detector218. The FET controller213performs constant current control, constant voltage control, or constant power control for charging the capacitor CP1. Generally, the capacitor CP1is desired to be charged with the constant current. However, the capacitor CP1is charged with the constant power controlled to allow reduction in the charging time.

The trance T100is turned on/off by the FET214, a primary-side input is boosted and is output from the secondary side. The secondary-side output of the trance T100is subjected to rectification and smoothing by the rectification-smoothing circuit215, and is output to the capacitor CP1through the diode D100. The current, the voltage, and the overvoltage of the secondary-side output of the trance T100after rectification and smoothing are detected by the current detector216, the voltage detector217, and the overvoltage detector218, respectively, and each detection signal is input to the FET controller213.

FIG. 6is a diagram of a configuration of the capacitor charge-discharge circuit208ofFIG. 3. The capacitor charge-discharge circuit208includes a charge-discharge switch231, a fixing relay RL11for safety, a diode D11for preventing counter electro-motive force of the fixing relay RL11, and a terminal voltage detection circuit232that detects a terminal voltage of the capacitor CP1.

Both ends of the capacitor CP1are connected with the charge-discharge switch231and the fixing relay RL11. The charge-discharge switch231is turned on/off by the control signal S13input from the controller202. Likewise, the fixing relay RL11is turned on/off by the control signal S14input from the controller202.

When both of the charge-discharge switch231and the fixing relay RL11are turned on, charges accumulated in the capacitor CP1are discharged to supply power to the fixing heater HT1.

The terminal voltage detection circuit232detects a terminal voltage of the capacitor CP1and outputs a voltage detection signal S15indicating the terminal voltage detected, to the controller202. The controller202always monitors the voltage detection signal S15, and monitors the charged state of the capacitor CP1.

FIG. 7is a diagram of a schematic configuration of the controller202ofFIG. 3. The controller202includes a central processing unit (CPU)241and a memory242.

The CPU241communicates with the memory242that stores a program to control the copying machine1and stores data, and controls the printer engine and the power supply circuit200based on the program stored in the memory242.

Input to the CPU241are the voltage detection signal (analog signal) S15, the detection signal (analog signal) S16, and the current detection signal (analog signal) S17through analog (AN) ports AN11and AN12. The voltage detection signal S15indicates the terminal voltage of the capacitor CP1detected by the terminal voltage detection circuit232of the capacitor charge-discharge circuit208. The detection signal S16indicates the voltage being divided by the resistance of the thermistor TH11for detecting the surface temperature of the fixing roller301and the resistance of a resistor R41. The current detection signal S17indicates an input current to the system detected by the input-current detecting circuit206. These signals are input to the CPU241.

The CPU241outputs the control signal S11, the control signal S13, the control signal S14, the control signal S18, and the control signal S19through input-output (IO) ports IO11to IO13. The control signal S11causes charging to the capacitor CP1to be turned on/off. The control signal S13causes the charge-discharge switch231to be turned on/off. The control signal S14causes the fixing relay RL11to be turned on/off. The control signal S18causes the heater on/off circuit220to be turned on/off, and the control signal S19causes the fixing relay RL21to be turned on/off (see alsoFIG. 3).

Furthermore, the CPU241controls the operation unit150, and monitors entry of data through KEY163provided on the operation unit150. DRV243is a driver that drives a liquid crystal display (LCD)161, and DRV244is a driver that drives LED162, both being controlled by the CPU241.

FIG. 8is a block diagram for explaining operations of the DC-power generation circuit204. When the main power supply SW201is turned on, the AC power is supplied to the DC-power generation circuit204, and DC power is generated by DC controllers (formed with a converter, etc.)251and252of the DC-power generation circuit204. The DC power output of the DC controller252is supplied to the controller (main controller)202, and the DC power output of the DC controller251is supplied to a sub-controller253(in addition, to the operation unit150and a charge control circuit10as explained later).

The sub-controller253is a control unit that includes a microcomputer and controls the power saving mode. In other words, the copying machine1includes a function of a so-called power saving mode. The copying machine1includes a function of achieving power saving and energy saving if a predetermined condition is satisfied, i.e., if a fixed time passes while the copying machine1is in a standby state in which it is not used. The function is realized by maintaining a power supply only to a part of power loads and stopping the power supply to almost all parts of the power loads including the main controller202. In this case, when the predetermined condition is satisfied after the power supply to the large parts of the power loads is stopped, or when the predetermined condition is satisfied in a case where the user touches an operation key of the operation unit150, the power supply to the power loads to which the power supply has been stopped is re-started.

In this example, if a fixed time passes in a standby state where the copying machine1is not used, that is, if certain conditions are ready for shifting the mode to the power saving mode, the sub-controller253outputs a power saving signal S3to stop a DC output of the DC controller252(power controller). The DC controller251that supplies DC power to the sub-controller253regularly outputs DC power thereto. With this output, the main controller202stops its operation, and the control signals S11, S13, S14, S18, and S19are not output. Accordingly, the loads such as various types of sensors, the capacitor charger203, and the AC-heater drive circuit205stop their operations. Thus, power saving and energy saving can be achieved. When the sub-controller253detects that a predetermined key switch of the operation unit150is operated by a power-key input detector254, the sub-controller253relieves the power saving signal S3and restarts the power supply to the main controller202(power controller). Therefore, it is possible to supply power to the loads required for performing original functions of the copying machine1. In addition, a return condition from the power saving mode may include detection of a document that is set on the document table102, detection of facsimile (FAX) reception when the copying machine1includes a FAX transmitting/receiving function, and detection of reception of a printer job.

As explained above, in the power saving mode of the copying machine1, after the shift to the power saving mode, the main controller202in particular with a large power consumption also stops, while only the sub-controller253that controls the power saving mode operates. Thus, the power-saving effect is significant.

However, if the power saving mode is not active, the main controller202controls the capacitor charger203so as to charge the capacitor CP1according to the control signal S11as necessary based on the voltage detection signal S15indicating the voltage detected by the terminal voltage detection circuit232. More specifically, if the voltage detection signal S15is lower than the predetermined value, the main controller202determines that the charge amount of the capacitor CP1is not enough, and causes the capacitor CP1to be charged.

However, when the main controller202is at rest, the control signal (charge signal) S11is not output. As a result, charging to the capacitor CP1after the shift to the power saving mode is not performed. If so, there occur some inconveniences. That is, if the charge amount of the capacitor CP1is insufficient upon shifting to the power saving mode, or if the power saving mode is continuous over a long time and natural discharge of the capacitor CP1occurs, even if the mode is returned from the power saving mode and an image is to be formed in the copying machine1, it is difficult to immediately heat the fixing roller301, and the start of the image formation is delayed. As a result, the user has to wait for starting of the image formation for a long time.

Therefore, it is necessary to continue charging the capacitor CP1by a required amount even if the power supply to the main controller202having a large power consumption is stopped after the shift to the power saving mode. Means for solving this problem are explained lower than.

FIG. 9is a circuit diagram of the charge control circuit10capable of charging the capacitor CP1by a necessary amount even if the power supply to the main controller202is stopped after the shift to the power saving mode.

The charge control circuit10is a circuit that realizes a charge controller and operates together with the sub-controller253by the DC power output from the DC controller251after the shift to the power saving mode. The charge control circuit10includes the terminal voltage detection circuit232that divides a terminal voltage (charging voltage) of the capacitor CP1by resistors R1and R2serially connected to each other and detects the voltage, and a comparator circuit3that compares the voltage detection signal S15from the terminal voltage detection circuit232, with a predetermined reference voltage S2obtained by dividing a predetermined supply voltage by resistors R3and R4. Based on the comparison, it is possible to determine whether the charging voltage of the capacitor CP1is so low that charging is needed.

If the charging voltage of the capacitor CP1is in such a low level that charging is needed, the comparator circuit3outputs a high (“H”) level signal (signal indicating that the level of the voltage detection signal S15is lower than the reference voltage S2) to an AND circuit4(first signal). The power saving signal S3(“H” level signal), that is, a signal (second signal) indicating the shift to the power saving mode is also input to the AND circuit4. If the power saving signal S3is in “H” level and the power saving mode is active, and if the output signal of the comparator circuit3is in “H” level and the charging voltage of the capacitor CP1is in such a low level that charging is needed, the AND circuit4takes the logical product of these two and outputs a control signal S5(“H” level signal) to an OR circuit5.

The OR circuit5takes the logical sum of the control signal S14and the control signal S5and outputs the control signal S11indicating an instruction to charge the capacitor CP1, to the capacitor charger203(InFIG. 3, the control signal S11is directly output from the main controller202to the capacitor charger203, but actually, the control signal S11is output through the OR circuit5.).

As explained above, even in the power saving mode in which the main controller202does not cause the capacitor CP1to be charged, the charge control circuit10performs charging to the capacitor CP1when the charging voltage of the capacitor CP1is too low. Therefore, after the return from the power saving mode, the fixing roller301can be heated so quickly at any time, which allows image formation to be started immediately. Therefore, the user can be free from waiting for the starting of image formation for a long time, and usability is improved. It is noted that a circuit (not shown) is provided in the capacitor charger203to be used when the charging is performed by the control signal S11. The circuit determines that the capacitor CP1reaches full charge when the voltage detection signal S15reaches a predetermined value, and stops charging the capacitor CP1.

FIG. 10is a circuit diagram of another configuration of the charge control circuit10. The circuit elements ofFIG. 10having the same reference signs as these ofFIG. 9have the same functions as these of the charge control circuit10ofFIG. 9, and detailed explanation thereof is omitted. A charge control circuit20ofFIG. 10is different from the charge control circuit10ofFIG. 9in that a permit/inhibit signal S7(third signal) is input to the AND circuit4. The permit/inhibit signal S7is output from the operation unit150generally as an “H” level signal, but the permit/inhibit signal S7is changed to a low (“L”) level signal when the user operates a predetermined key through the operation unit150. At this time, since the AND circuit4outputs the L-level signal, even if the charging voltage of the capacitor CP1decreases after the shift to the power saving mode, the capacitor charger203does not charge the capacitor CP1.

More specifically, when the copying machine1is not used for a long time in such cases as an weekend and a long vacation, charging the capacitor CP1is unnecessary even if the charging voltage of the capacitor CP1decreases in the power saving mode, and if the charging is performed in these cases, such charging leads to a waste of power. In this case, if the user performs a predetermined key operation on the operation unit150, then the charge control circuit20accepts an instruction as this key operation from the user to inhibit charging to the capacitor CP1(acceptance unit). The permit/inhibit signal S7is maintained in “L” level, and this signal becomes a signal indicating an instruction to inhibit charging to the capacitor CP1from the user. Therefore, charging to the capacitor CP1by the charge control circuit20is inhibited, and power saving is achieved. When the weekend or the long vacation is over, the user again performs a predetermined key operation on the operation unit150, the permit/inhibit signal S7returns to “H” level, and the capacitor CP1in the power saving mode can be charged.

FIG. 11is a circuit diagram of still another configuration of the charge control circuit10. The circuit elements ofFIG. 11having the same reference signs as these ofFIG. 10have the same functions as these of the charge control circuit20ofFIG. 10, and detailed explanation thereof is omitted. A charge control circuit30ofFIG. 11is different from the charge control circuit20ofFIG. 10in that the AND circuit4is provided in the downstream side of the OR circuit5. With this arrangement, if the permit/inhibit signal S7is in “L” level by the predetermined key operation by the user, charging to the capacitor CP1is inhibited also by the control signal S14output from the main controller202even not in the power saving mode. Therefore, the charging to the capacitor CP1is absolutely inhibited if necessary through the operation of the operation unit150by the user, and power saving becomes possible.

FIG. 12is a circuit diagram of still another configuration of the charge control circuit10. The circuit elements ofFIG. 12having the same reference signs as these ofFIG. 9have the same functions as these of the charge control circuit10ofFIG. 9, and detailed explanation thereof is omitted. A charge control circuit40ofFIG. 12is different from the charge control circuit10ofFIG. 9in that a timer signal S8instead of the permit/inhibit signal S7is input to the AND circuit4. The sub-controller253includes a clock function and a timer function, and generally outputs the timer signal S8as an “H” level signal, but changes the level of the timer signal S8to “L” level in a predetermined time window (time determining unit). In other words, the timer signal S8is changed to a signal indicating that the current time is in the predetermined time window. With this signal, during the predetermined time window (during night time), even if the charge of the capacitor CP1is insufficient after the shift to the power saving mode, charging to the capacitor CP1is inhibited. Wasteful charging is thereby prevented to allow power saving.

FIG. 13is a circuit diagram of still another configuration of the charge control circuit10. The circuit elements ofFIG. 13having the same reference signs as these ofFIG. 9have the same functions as these of the charge control circuit10ofFIG. 9, and detailed explanation thereof is omitted. A charge control circuit50ofFIG. 13is different from the charge control circuit10ofFIG. 9in that the resistor R2(or the resistor R1, or both the resistors R1and R2) forming the terminal voltage detection circuit232is formed with a variable resistor. With this arrangement, even under situations as follows, a service person can adjust a resistance of the variable resistor to adjust a value of the reference voltage S2(variable unit). The situations are such that the performance of the capacitor CP1changes according to changes with the passage of time, the time required for charging the capacitor CP1up to the same voltage level is prolonged, and thereby charging to the capacitor CP1has to be started earlier. Thus, it is possible to start charging the capacitor CP1at earlier time after the shift to the power saving mode. In addition, by providing a variable resistor for at least one of the resistors R3and R4, the magnitude of the reference voltage input to the comparator circuit3may be variable.

FIG. 14is a circuit diagram of still another configuration of the charge control circuit10. The circuit elements ofFIG. 14having the same reference signs as these ofFIG. 9have the same functions as these of the charge control circuit10ofFIG. 9, and detailed explanation thereof is omitted. A charge control circuit60ofFIG. 14is different from the charge control circuit10ofFIG. 9in that the control signal S11is also output to the operation unit150based on the output signal of the AND circuit4. With this arrangement, if the control signal S11is in “H” level, the operation unit150can inform the user of execution of charging to the capacitor CP1after the shift to the power saving mode using predetermined means such as lighting of a light emitting diode (LED) (informing unit).

As another embodiment, a case where the functions of the charge control circuits10to60are realized by processes performed by another local controller, i.e., the sub-controller253in this example, is explained lower than.FIG. 15is a block diagram of hardware in this case. In the following explanation, members having the same reference signs as these ofFIG. 8toFIG. 14are the circuit elements as explained above, and therefore, detailed explanation thereof is omitted.

In this example, the main controller202outputs the control signal S14to the sub-controller253, and the sub-controller253controls the capacitor charger203to control the capacitor CP1when the power saving mode is not active.

Furthermore, the voltage detection signal S15, the permit/inhibit signal S7, and the timer signal S8are also input to the sub-controller253. When the power saving mode is active, the sub-controller253performs processes as shown in the flowchart ofFIG. 16. The processes are performed to realize the charge controller. More specifically, if the power saving mode is active (Yes (Y) at step S1), the sub-controller253determines whether a voltage detection signal S15indicating a terminal voltage of the capacitor CP1is lower than a preset reference value S2(step S2). If the voltage detection signal S15is lower than the reference value S2(“Y” at step S2), it is determined whether the permit/inhibit signal S7and the timer signal S8(in this example, the timer signal S8is a signal in the sub-controller253) are in “L” level (steps S3, S4). If both of the signals are in “L” level (“Y” at step S3, “Y” at step S4) and if the control signal S14indicating an instruction to charge the capacitor CP1is output from the controller202(“Y” at step S5), the control signal S14is canceled (step S6), the control signal S11is output to the capacitor charger203, and the capacitor CP1is charged (step S7). At step S7, the control signal S11is also output to the operation unit150, where it is informed to the user that the capacitor CP1is charged, in the same manner as explained above with reference toFIG. 14(informing unit).

If it is determined that the voltage detection signal S15of the capacitor CP1is not less than the reference value S2(No (N) at step S2), or if both the permit/inhibit signal S7and the timer signal S8are in “H” level (“N” at step S3, “N” at step S4), charging at step S7is not performed.

FIG. 17is a flowchart of the process of setting the reference value S2executed by the sub-controller253. More specifically, if a predetermined value is specified as the reference value S2by operating a predetermined key in the operation unit150by a service person (“Y” at step S11), the sub-controller253sets the value as the reference value S2in a nonvolatile memory (not shown) (variable unit) (step S12). In the process ofFIG. 16, the determination at step S2is performed using the reference value S2set in the above manner.

By performing the processes, the local controller such as the sub-controller253can execute the functions of the charge control circuits10to60.

A digital copying machine according to a second embodiment of the present invention is explained lower than. The digital copying machine according to the second embodiment has basically the same configuration as that of the digital copying machine according to the first embodiment as shown inFIG. 1toFIG. 3. Therefore, only different portions are explained lower than.

FIG. 18is a circuit diagram of a power control system of the digital copying machine1mainly including the fixing unit121. The power control system as shown inFIG. 18includes a main power supply SW428that turns on/off the power supply from the AC power supply (commercial AC power supply). When the main power supply SW428is turned on, power supply circuits401,402, and403are supplied with power from the AC power supply PS, and generate control power required for the fixing unit121and the like, respectively. In other words, the power supply circuit401supplies power to an engine control circuit421including the fixing unit121. The power supply circuit402supplies power to a charger-discharger control circuit422. The power supply circuit403supplies power to a power-saving control circuit423.

In the second embodiment, a fixing heater HT1as the first heating member is a main heater that is turned on when the temperature of the fixing roller301does not reach a predetermined target temperature Tt as a reference, and that heats the fixing roller301. A fixing heater HT2as the second heating member is an auxiliary heater that is turned on when the main power of the copying machine1is turned on or during a rising period from returning from the power saving mode to being ready for copying. In other words, the fixing heater HT2is turned on when the fixing unit121is warmed up and heats the fixing roller301.

The engine control circuit421includes a microcomputer, and controls the whole of the printer engine including the fixing unit121of the copying machine1. A heater drive circuit424is supplied with power from the AC power supply PS, and supplies power to the fixing heater HT1. The power supply is controlled based on a heater drive signal output from the engine control circuit421. Based on the control, the fixing heater HT1is turned on when the temperature does not reach the predetermined target temperature Tt as the reference of the fixing roller301(the temperature of the fixing roller301is detected by the temperature sensor TH11), and heats the fixing roller301.

A capacitor C that is an electric double layer capacitor is charged by a charger425supplied with power from the AC power supply PS. A discharge circuit426that is a discharger discharges charging power of the capacitor C, supplies power to the fixing heater HT2, and heats it. The charger425and the discharge circuit426are controlled by a charge control signal and a discharge control signal output of the charger-discharger control circuit422that includes a microcomputer. With the control, the fixing heater HT2is energized when the main power to the copying machine1is turned on and during a rising period from returning from the power saving mode explained later to being ready for copying. In other words, the fixing heater HT2is turned on when the fixing unit121is warmed up.

The power-saving control circuit423serves as a first control unit and includes a microcomputer. In the copying machine1, the power-saving control circuit423manages controls of the power saving mode for the printer engine that includes the fixing unit121and for other loads. In other words, when predetermined conditions as explained lower than are continuous over a fixed time, a power supply to power loads is stopped, but some of the power loads such as the printer engine including the fixing unit121is continuously supplied with power. The conditions are such that an idling state, in which the main power supply SW428is on but image formation is not performed by the copying machine1, is continuous over a fixed time, or that the user turns on a sub-power supply SW427. If a predetermined condition is satisfied during the stop of the power supply, for example, if the user touches the operation panel (not shown) to operate the copying machine1, the stop is released. In other words, the power supply circuit401supplies power to a large part of the power loads such as the engine control circuit421and the printer engine including the fixing unit121. When receiving the power saving signal from the power-saving control circuit423, the power supply circuit401is turned off and stops the power supply to the engine control circuit421and the other power loads. The power supply circuit401is turned on by the power saving signal from the power-saving control circuit423, and restarts the power supply to the engine control circuit421and the other power loads.

In the above manner, even if the power supply circuit401is turned off by shifting to the power saving mode, the power-saving control circuit423can be supplied with power from the power supply circuit403separately from the power supply circuit401. Therefore, the power-saving control circuit423has no obstacle in performing the control so that the mode of the power supply circuit401is returned from the power saving mode.

Furthermore, even if the power supply circuit401is turned off by shifting to the power saving mode, the charger-discharger control circuit422that is a second control unit can be supplied with power from the power supply circuit402, separately from the power supply circuit401. Therefore, the charger-discharger control circuit422continues operating even in the power saving mode and can perform charging and discharging on the capacitor C.

The circuit configuration and the operation of the charger-discharger control circuit422are explained lower than.FIG. 19is a circuit diagram for explaining the circuit configuration of the charger-discharger control circuit422. The charger-discharger control circuit422includes a microcomputer431. The capacitor C includes a voltage sensor432that divides a voltage between both ends of the capacitor C by the resistors R1and R2and detects the voltage to output a detection signal. A comparator433compares the detection signal with a predetermined reference voltage Vref. If the detection signal of the voltage is lower than the reference voltage Vref, the charger-discharger control circuit422outputs an “L” level signal to a wake up terminal WK of the microcomputer431.

The contents of the control process executed by the charger-discharger control circuit422having the circuit configuration are explained lower than.

FIG. 20is a flowchart of the process executed by the microcomputer431based on a predetermined control program. More specifically, in the copying machine1, if an imaging operation of the printer engine is requested and the microcomputer431is about to stop charging (“Y” at step S101), the microcomputer431stops charging to the capacitor C by the charger425(step S102). When discharging is executed (“Y” at step S103), the discharge circuit426discharges the capacitor C (step S104). If discharging should not be performed (“N” at step S103), then the microcomputer431stops discharging of the capacitor C by the discharge circuit426(step S105).

If charging is not stopped (“N” at step S101), charging is continued (“N” at step S106, step S107) until charging to the capacitor C is completed (e.g. until the voltage detected by the voltage sensor432reaches a predetermined voltage value (the reference voltage Vref and so on) (“Y” at step S106). When charging is completed (“Y” at step S106), the microcomputer431shifts to the power saving mode (step S107), and basically stops the operation. In other words, the microcomputer431includes mode called power saving mode. In the power saving mode, if a predetermined condition is satisfied, in this example, if a charge control signal is not received (that is, when the imaging operation by the printer engine is not requested) and charging to the capacitor C is completed, a power supply to power loads is stopped, but the power supply to some of the power loads of the microcomputer431is continued. More specifically, the whole of the microcomputer431is stopped except for a part of the circuits including a circuit portion that receives an input to the wake up terminal.

Thereafter, if a predetermined condition is satisfied, i.e., if the terminal voltage of the capacitor C is lower than the reference voltage Vref because the state of power saving mode is continuous over a long time or natural discharge of the capacitor C occurs, the comparator433outputs the “L” level signal to the wake up terminal WK. By inputting the “L” level signal to the wake up terminal WK, a circuit portion of the microcomputer431that is operating even after the shift to the power saving mode activates the whole of the microcomputer431, and shifts it to a normal mode. Therefore, after the activation, the process with reference toFIG. 19is performed, and the capacitor C can be charged by the processes at step S107and step S108even if the terminal voltage of the capacitor C decreases caused by natural discharge of the capacitor C and so on.

FIG. 21is a timing chart for explaining the operation of the microcomputer431in this case. More specifically, if the mode of the microcomputer431is in the power saving mode ((c) ofFIG. 21) and a terminal voltage of the capacitor decreases to be lower than the reference value as shown in (a) ofFIG. 21, the level of a signal output from the comparator433changes from “H” level to “L” level ((b) ofFIG. 21). The mode of the microcomputer431is returned to the normal mode (see (c) ofFIG. 21) in which the whole of the microcomputer431is activated. Therefore, the terminal voltage of the capacitor C recovers to the reference value or more in a short time.

As explained above, the charger-discharger control circuit422can be supplied with power from the power supply circuit402, independently from the load of the printer engine that is turned off in the power saving mode managed by the power-saving control circuit423. Therefore, even in the power saving mode, it is possible to perform charging in the above manner if the terminal voltage of the capacitor C decreases, to sufficiently supply power from the capacitor C to the fixing heater HT2right after the return from the power saving mode, and to quickly heat the fixing roller301. Thus, the image formation can be started immediately even right after the return from the power saving mode without causing the user to wait.

In this case, in the charger-discharger control circuit422, the mode shifts to the power saving mode, if charging is unnecessary, by the processes ofFIG. 20. Therefore, the power is not used wastefully in the charger-discharger control circuit422, which allows further power saving. In this case also, if the terminal voltage of the capacitor C decreases as shown inFIG. 21, the mode of the charger-discharger control circuit422is returned to the normal mode, and the capacitor C can be charged immediately. This allows a sufficient power supply to the fixing heater HT2from the capacitor C even right after the return from the power saving mode, and therefore, the influence on the fixing heater HT2is also a little.

A digital copying machine according to a third embodiment of the present invention is explained lower than. The digital copying machine according to the third embodiment has basically the same configuration as that of the digital copying machine according to the first embodiment as shown inFIG. 1toFIG. 3, and only different portions are explained lower than.

FIG. 22is a diagram of a configuration of a power control system of the copying machine1mainly including the fixing unit121. The power control system includes the main power supply SW201that turns on/off a supply of power from the AC power supply (commercial power supply) PS, and the microcomputer. The power control system also includes a controller3202functioning also as a control unit that controls components of a power supply circuit3200and other parts, a capacitor CP that is an auxiliary power supply for the fixing heater HT1, and the capacitor charger203that serves as a charger for charging the capacitor CP. The power control system further includes the DC power generation circuit204that generates DC power for the copying machine1, the AC-heater drive circuit205that supplies AC power to the fixing heater HT2, an input-current detection circuit206that detects a current input from the AC power supply PS, an interlock switch207, and a capacitor charge-discharge circuit208that performs discharge of the capacitor CP and supplies DC power to the fixing heater HT1.

The AC power supply PS supplies AC power to the AC-heater drive circuit205, the DC-power generation circuit204, and the capacitor charger203through the main power supply SW201and the input-current detection circuit206.

The controller3202mainly controls the components of the power supply circuit3200, and controls the operations of the capacitor charger203, the AC-heater drive circuit205, and the capacitor charge-discharge circuit208. More specifically, the controller3202outputs the control signal S11to the capacitor charger203and controls the charging operation of the capacitor charger203to the capacitor CP. The controller3202outputs the control signals S13and S14to the capacitor charge-discharge circuit208and controls an on/off operation the capacitor charge-discharge circuit208to the fixing heater HT1. The controller3202also outputs the control signals S18and S19to the AC-heater drive circuit205and controls an on/off operation of the AC-heater drive circuit205to the fixing heater HT2.

The input-current detection circuit206is provided between the main power supply SW201, the AC-heater drive circuit205, the DC-power generation circuit204, and the capacitor charger203. The input-current detection circuit206detects an input current of AC power input through the main power supply SW201, and outputs a current detection signal S17to the controller3202. The input current fluctuates according to each operating status of the AC-heater drive circuit205, the DC-power generation circuit204, the capacitor charger203, and the image forming apparatus.

The DC-power generation circuit204generates power Vcc and power Vaa based on the AC power input through the main power supply SW201, and outputs the power Vcc and the power Vaa to the components. The power Vcc is used mainly for the control system of the copying machine1, and the power Vaa is used mainly for the drive system and high- and medium-voltage power supply.

The interlock switch207is a switch that is interlocked with a cover (not shown) or the like of the copying machine1to turn the power on/off. If the copying machine1includes a drive member and an application member for the high- and medium-voltage power that are able to be touched when the cover is opened, it is configured to cut off the power so as to stop the operation of the drive member or to stop applying a voltage to the application member when the cover is opened. A part of the power Vaa generated in the DC-power generation circuit204is input to the interlock switch207, and is input to the capacitor charge-discharge circuit208and the AC-heater drive circuit205through the interlock switch207.

The AC-heater drive circuit205turns on/off the fixing heater HT2according to the control signals S18and S19input from the controller3202.

The capacitor charger203is connected to the capacitor CP, and charges the capacitor CP based on the control signal S11input from the controller3202.

The capacitor CP is a capacitor with large capacity such as the electric double layer capacitor. The capacitor CP is connected to the capacitor charger203and the capacitor charge-discharge circuit208. The capacitor CP is charged by the capacitor charger203and the power charged is supplied to the fixing heater HT1under the on/off control of the capacitor charge-discharge circuit208.

The capacitor charge-discharge circuit208discharges the power accumulated in the capacitor CP according to the control signals S13and S14input from the controller3202, and turns on/off the fixing heater HT1.

The thermistor TH11is provided near the fixing roller301, and outputs the detection signal S16corresponding to the surface temperature of the fixing roller301, to the controller3202. Since the resistance of the thermistor TH11changes depending on temperature, the controller3202detects the surface temperature of the fixing roller301from the detection signal S16based on the temperature-dependent change of the resistance.

A configuration near the capacitor charger203, the capacitor CP, and the controller3202that form an auxiliary power unit according to the third embodiment is shown inFIG. 23. In the third embodiment, the capacitor CP is formed not with a single capacitor but with a capacitor CPa as a first capacitor and a capacitor CPb as a second capacitor that are serially connected to each other. Each of the capacitor CPa and the capacitor CPb also includes a plurality of capacitors that are serially connected to each other. Each charging capacity (the number of capacitor cells) of these capacitors CPa and CPb may be different from each other, but the same charging capacity is preferable. The capacitor charger203includes a capacitor charger203a(first charger) and a capacitor charger203b(second charger), which are individually provided, corresponding to the capacitor CPa and the capacitor CPb, respectively. The capacitor chargers203aand203bare supplied with AC power from the AC power supply PS to charge the corresponding capacitors CPa and CPb. The controller3202outputs a control signal S11aand a control signal S11bas the control signal S11to the capacitor chargers203aand203b, respectively, so as to enable individual control of the charging operation of the capacitor chargers203aand203bto the capacitors CPa and CPb.

Furthermore, a terminal voltage detection circuit (first terminal-voltage detection circuit)209aand a terminal voltage detection circuit (second terminal-voltage detection circuit)209bthat detect each terminal voltage thereof are connected to the capacitors CPa and CPb. These terminal voltage detection circuits209aand209boutput terminal voltages detected, as a voltage signal S20aand a voltage signal S20b, respectively, to the controller3202.

The AC-heater drive circuit205is explained lower than.FIG. 24is a diagram of the configuration of the AC-heater drive circuit205ofFIG. 22. The AC-heater drive circuit205includes the filter FIL21that removes noise of the AC power input, the fixing relay RL21for safety to be turned on/off according to the control signal S19input from the controller3202, the diode D21for preventing counter electro-motive force of the fixing relay RL21, and the heater on/off circuit220that turns on/off the fixing heater HT2based on the control signal S18input from the controller3202.

The AC power supply PS is connected to one end of the fixing heater HT2through the filter FIL21and the fixing relay RL21. The other end of the fixing heater HT2is connected to the heater on/off circuit220.

The heater on/off circuit220includes the triac TRI21for turning on/off the AC power, the photocoupler PC21for insulating a signal from the controller3202that is a secondary side, and the transistor TR21for driving the LED on the light emission side of the photocoupler PC21. The heater on/off circuit220also includes the noise-absorption snubber circuit including the capacitor C21and the resistor R21, the inductance L21for noise absorption, the resistor R22that is a resistor for preventing a dynamic current, and the resistors R23and R24that are resistors for restricting a current from the photocoupler PC21.

In the AC-heater drive circuit205configured as explained above, the fixing heater HT2is supplied with power and is lit when both the fixing relay RL21and the gate of the transistor TR21are on.

The controller3202turns on/off the control signal S18to be supplied to the gate of the transistor TR21for the heater on/off circuit220in an on state of the control signal S19that is supplied to the fixing relay RL21, and controls switching on/off of the fixing heater HT2.

FIG. 25is a diagram of the configuration of the capacitor charger203ofFIG. 22. Although the capacitor charger203includes the two capacitor chargers203aand203bas shown inFIG. 23, the two are shown in the figure in a shared form because they have the same configuration as each other. The capacitor charger203a(or203b) includes the noise filter (NF)211that removes noise of an AC voltage input, the rush-current prevention circuit212that prevents a rush current, the diode bridge DB that full-wave rectifies AC power from the AC power supply PS input through the rush-current prevention circuit212, and the capacitor C100that performs smoothing on the AC voltage full-wave rectified. The capacitor charger203a(or203b) also includes the FET controller213that controls switching of the FET214and controls the charging operation of the capacitor CPa (or CPb) (seeFIG. 23), the FET214that turns on/off the trance T100, and the trance T100that steps down a voltage input. The capacitor charger203a(or203b) further includes the rectification-smoothing circuit215that performs rectification and smoothing of an output on the secondary side of the trance T100to be converted to a DC output, the current detector216that detects a current, the voltage detector217that detects a voltage, the overvoltage detector218that detects an overvoltage so as not to apply the overvoltage to the capacitor CPa (or CPb), the diode D100for preventing a back flow from the capacitor CPa (or CPb), and the insulating element219.

The AC voltage input from the AC power supply PS is noise-removed by the NF211, is full-wave rectified by the diode bridge DB through the rush-current prevention circuit212, and is subjected to smoothing by the capacitor C100to obtain a DC voltage to be input to a primary side of the trance T100. If the control signal S11a(or S11b) input from the controller3202(seeFIG. 22,FIG. 23) is “on”, the FET controller213starts switching control of the FET214to charge the capacitor CPa (or CPb). The FET controller213controls switching of the FET214based on the respective detection signals input from the current detector216, the voltage detector217, and the overvoltage detector218. The FET controller213performs constant current control, constant voltage control, or constant power control for charging the capacitor CPa (or CPb). Generally, the capacitor CPa (or CPb) is desired to be charged with the constant current. However, the capacitor CPa (or CPb) is charged by the constant power control to allow reduction in the charging time.

The trance T100is turned on/off by the FET214, and steps down a primary-side input to be output from the secondary side thereof. The secondary-side output of the trance T100is subjected to rectification and smoothing in the rectification-smoothing circuit215, and is output to the capacitor CPa (or CPb) through the diode D100. The current, the voltage, and the overvoltage of the secondary-side output of the trance T100after rectification and smoothing are detected by the current detector216, the voltage detector217, and the overvoltage detector218, respectively, and each detection signal is input to the FET controller213.

FIG. 26is a diagram of the configuration of the capacitor charge-discharge circuit208ofFIG. 22. The capacitor charge-discharge circuit208includes the charge-discharge switch231, the fixing relay RL11for safety, the diode D11for preventing counter electro-motive force of the fixing relay RL11, and the terminal voltage detection circuit232that detects a terminal voltage of the whole capacitor CP.

Both ends of the capacitor CP are connected with the charge-discharge switch231and the fixing relay RL11. The charge-discharge switch231is turned on/off by the control signal S13input from the controller3202. Likewise, the fixing relay RL11is turned on/off by the control signal S14input from the controller3202.

When both of the charge-discharge switch231and the fixing relay RL11are turned on, charges accumulated in the capacitor CP are discharged to supply power to the fixing heater HT1.

The terminal voltage detection circuit232detects a terminal voltage of the capacitor CP and outputs the voltage detection signal S15indicating the terminal voltage detected, to the controller3202. The controller3202always monitors the voltage detection signal S15, and monitors how the capacitor CP is charged.

FIG. 27is a diagram of the schematic configuration of the controller3202ofFIG. 22. The controller3202includes a CPU3241and the memory242.

The CPU3241communicates with the memory242that stores a program to control the copying machine1and stores data, and controls the printer engine and the power supply circuit3200based on the program stored in the memory242.

Input to the CPU3241are the voltage detection signal (analog signal) S15indicating the terminal voltage of the capacitor CP detected by the terminal voltage detection circuit232of the capacitor charge-discharge circuit208, the detection signal (analog signal) S16indicating the voltage being divided by the resistance of the thermistor TH11for detecting the surface temperature of the fixing roller301and the resistance of the resistor R41, the current detection signal (analog signal) S17indicating an input current to the power supply circuit403detected by the input-current detecting circuit206, and a voltage signal S20aand a voltage signal S20bindicating each terminal voltage of the capacitors CPa and CPb detected by the terminal voltage detection circuits209aand209b, respectively. These signals are input to the CPU3241through AN ports AN11to AN15.

The CPU3241outputs, through10ports1011to1016, the control signal S11aand the control signal S11bfor causing charging of the capacitors CPa and CPb to be turned on/off, the control signal S13for causing the charge-discharge switch231to be turned on/off, the control signal S14for causing the fixing relay RL11to be turned on/off, the control signal S18for causing the heater on/off circuit220to be turned on/off, and the control signal S19for causing the fixing relay RL21to be turned on/off (see alsoFIG. 22,FIG. 23, andFIG. 25).

In the above configuration, basically, the fixing heater HT2is turned on when the temperature of the fixing roller301does not reach a predetermined target temperature Tt as a reference of the fixing roller301, and heats the fixing roller301. Furthermore, the fixing heater HT1that uses the capacitor CP as an auxiliary heater is also turned on when the main power to the copying machine1is turned on or during a rising period from returning from the power saving mode to being ready for copying. In other words, the fixing heater HT1is turned on when the fixing unit121is warmed up, and heats the fixing roller301. As explained above, by using the capacitor CP such as the electric double layer capacitor as the auxiliary power supply, even if the power supply from the AC power supply PS to the fixing unit121is insufficient, a large current can be instantly supplied to the fixing unit121. Therefore, it is possible to prevent deterioration of fixability due to insufficient power. However, after the capacitor CP discharges to supply power to the fixing roller301, it is necessary to charge the capacitor CP at a predetermined timing.

A control example of the charging operation to the capacitor CP (CPa, CPb) by the capacitor chargers203aand203baccording to the third embodiment is explained lower than with reference to a schematic flowchart ofFIG. 28. The charging operation is executed under the control of the CPU3241. Basically, the charging operation to the capacitor CP is executed when the terminal voltage of the whole capacitor CP decreases lower than a predetermined voltage. It is determined whether the capacitor CP needs charging by monitoring the voltage detection signal S15from the terminal voltage detection circuit232(step S301). If it is determined by the voltage detection signal S15that the terminal voltage of the capacitor CP is lower than the predetermined voltage and charging is needed (“Y” at step S301), it is compared whether the voltage signal S20ais greater than the voltage signal S20b(step S302). The voltage signals S20aand S20bare obtained from the terminal voltage detection circuits209aand209bthat detect each initial terminal voltage of the capacitors CPa and CPb upon the start of the charging operation. Here, the terminal voltage of the capacitor CPa is indicated by Vcpa and the terminal voltage of the capacitor CPb is indicated by Vcpb.

As a result of comparison, if Vcpa≧Vcpb (“Y” at step S302), the control signal S11bindicating that the charging operation is allowed to be on is output to the capacitor charger203bcorresponding to the capacitor CPb of which terminal voltage is lower, and the capacitor charger203bstarts charging the capacitor CPb (step S303). At this time, a target voltage during this charging operation is set to Vcpa+α. More specifically, the target voltage is a voltage that exceeds the terminal voltage Vcpa that is higher, i.e., a voltage that increases by an amount of a defined voltage α preset with respect to the terminal voltage Vcpa. At this time, the control signal S11aoutput to the capacitor charger203aindicates that the charging operation is off, and accordingly the capacitor charger203adoes not charge the capacitor CPa. During this charging operation, it is monitored whether the terminal voltage Vcpb detected by the terminal voltage detection circuit209bhas reached the final target voltage preset (e.g. 45 volts) (step S304). If it has not reached the final target voltage preset (“N” at step S304), it is checked whether it has reached this target voltage Vcpa+α (step S305). If it has reached the target voltage Vcpa+α (“Y” at step S305), then the process returns to step S302.

As a result of comparison, if Vcpa≧Vcpb is not satisfied (“N” at step S302), the control signal S11aindicating that the charging operation is allowed to be on is output to the capacitor charger203acorresponding to the capacitor CPa of which terminal voltage is lower, and the capacitor charger203astarts charging the capacitor CPa (step S306). A target voltage during the charging operation in this case is set to Vcpb+α. More specifically, the target voltage is a voltage that exceeds the terminal voltage Vcpb that is higher, i.e., a voltage that increases by an amount of a defined voltage α preset with respect to the terminal voltage Vcpb. At this time, the control signal S11boutput to the capacitor charger203bindicates that the charging operation is off, and accordingly the capacitor charger203bdoes not charge the capacitor CPb. During this charging operation, it is monitored whether the terminal voltage Vcpa detected by the terminal voltage detection circuit209ahas reached a final target voltage preset (e.g. 45 volts) (step S307). If it has not reached the final target voltage preset (“N” at step S307), it is checked whether it has reached this target voltage Vcpb+α (step S308). If it has reached the target voltage Vcpb+α (“Y” at step S308), then the process returns to step S302.

The operations thereafter are executed as follows. If “Y” at step S305, then the process returns to step S302, at which Vcpa≧Vcpb is not satisfied this time, and the process proceeds along the routine of the N side at step S302. If “Y” at step S308, the process returns to step S302, at which Vcpa≧Vcpb is satisfied this time, and the process proceeds along the routine of the Y side at step S302. If one of the voltages Vcpa and Vcpb has reached the final target voltage (“Y” at step S304, or “Y” at step S307), the process returns to step S301. If one of the voltages has not reached the final target voltage, the charging operation is still needed (“Y” at step S308), and the process is executed along either one of the routine on the Y side at step S302and the routine on the N side at step S302. The charging operation is finished finally at the point in time when the terminal voltages Vcpa and Vcpb have reached the final target voltages.

FIG. 29is a diagram for explaining an example of switching control for the charging operation of the capacitor chargers203aand203b. For initial terminal voltages, the Vcpa side is lower inFIG. 29.

In the third embodiment, during the charging operation to the capacitor CP, switching is controlled for the charging operation between the capacitor chargers203aand203bbased on the result of detection (voltage signals S20aand S20b) of the terminal voltage detection circuits209aand209bunder the control of the CPU3241. In the third embodiment in particular, the charging operation is started from the capacitor charger203aor203bcorresponding to a lower initial terminal voltage. With this configuration, the switching is controlled so that the charging operations are alternately performed between the capacitor charger203aand the capacitor charger203b. In this manner, a charging voltage (e.g. 90 volts) required as the capacitor CP can be ensured as a total charging voltage of the capacitors CPa and CPb. However, because the capacitors CPa and CPb have the capacitor chargers203aand203b, respectively, charging is performed by switching between the charging operations by the capacitor chargers203aand203b. This allows the charging operation to be performed by a smaller power supply as compared with that when a single 90V-capacitor is charged by a single charger. As a result, even if the power supplied from the AC power supply PS is limited during copying, the capacitor CP can be charged efficiently.

When switching is controlled so that the charging operations are alternately performed, it is controlled so that a lower terminal voltage increases by an amount of a defined voltage α with respect to a higher terminal voltage. Therefore, a big difference does not occur between the terminal voltages of the two capacitors CPa and CPb, and a well-balanced charging operation is performed. The defined voltage α in this case is set preferably to a voltage not more than a reverse breakdown voltage (normally, about 1.2 volts) per capacitor cell for the capacitors serially connected to each other forming each of the capacitors CPa and CPb. By using such a defined voltage α, a reverse voltage is not applied from one side to the other, which allows performance of extremely well-balanced charging operation in which voltages are balanced between the two capacitors CPa and CPb.

A fourth embodiment of the present invention is explained lower than with reference toFIG. 30. Portions ofFIG. 30corresponding to these of the third embodiment are assigned with the same reference signs as these of the third embodiment, and explanation thereof is omitted (the same goes for an embodiment explained later).

The charging operations of the capacitor chargers203aand203bin the fourth embodiment are controlled following the case of the first embodiment basically, but the time controlled by a timer is added to the first half of alternate switching control for the charging operation. A timer built in the CPU3241is used here.

FIG. 30is a schematic flowchart of an example of controlling the charging operation of the capacitor chargers203aand203baccording to the fourth embodiment. A temporary target voltage (e.g. 40 volts) is preset to a voltage lower than a final target voltage (e.g. 45 volts).

The charging operation to the capacitor CP is executed when the terminal voltage of the whole capacitor CP decreases lower than a predetermined voltage, and it is determined whether charging is needed by monitoring the voltage detection signal S15from the terminal voltage detection circuit232(step S301). If it is determined from the voltage detection signal S15that the terminal voltage of the capacitor CP is lower than the predetermined voltage and charging is needed (“Y” at step S301), then it is compared which is higher between an initial voltage signal S20a(Vcpa) and an initial voltage signal S20b(Vcpb) upon the start of the charging operation, the voltage signals being obtained from the terminal voltage detection circuits209aand209b, respectively (step S401).

As a result of comparison, if Vcpa≧Vcpb (“Y” at step S401), the control signal S11bindicating that the charging operation is allowed to be on is output to the capacitor charger203bcorresponding to the capacitor CPb of which terminal voltage is lower, and the capacitor charger203bstarts charging the capacitor CPb (step S402). At this time, a fixed time t for performing the charging operation is set in the timer. The fixed time t is desirably set so that the charging operation for the fixed time t allows the terminal voltage to exceed the higher terminal voltage Vcpa. At this time, the control signal S11aoutput to the capacitor charger203aindicates that the charging operation is off, and accordingly the capacitor charger203adoes not charge the capacitor CPa. During this charging operation, it is monitored whether the terminal voltage Vcpb detected by the terminal voltage detection circuit209bhas reached the temporary target voltage preset (e.g. 40 volts) (step S403). If it has not reached the temporary target voltage (“N” at step S403), it is checked whether this set time t has passed (step S404). If the set time t has passed (“Y” at step S404), then the process returns to step S401.

As a result of comparison, if Vcpa≧Vcpb is not satisfied (“N” at step S401), the control signal S11aindicating that the charging operation is allowed to be on is output to the capacitor charger203acorresponding to the capacitor CPa of which terminal voltage is lower, and the capacitor charger203astarts charging the capacitor CPa (step S405). A fixed time t for performing the charging operation is set in the timer. The fixed time t is desirably set so that the charging operation for the fixed time t allows the terminal voltage to exceed the higher terminal voltage Vcpb. At this time, the control signal S11boutput to the capacitor charger203bindicates that the charging operation is off, and accordingly the capacitor charger203bdoes not charge the capacitor CPb. During this charging operation, it is monitored whether the terminal voltage Vcpa detected by the terminal voltage detection circuit209ahas reached the temporary target voltage preset (e.g. 40 volts) (step S406). If it has not reached the temporary target voltage (“N” at step S406), it is checked whether this set time t has passed (step S407). If the set time t has passed (“Y” at step S407), then the process returns to step S401.

The operations thereafter are executed as follows. If “Y” at step S404, then the process returns to step S401at which Vcpa≧Vcpb is not satisfied this time, and the process proceeds along the routine of the N side at step S401. If “Y” at step S407, the process returns to step S401at which Vcpa≧Vcpb is satisfied this time, and the process proceeds along the routine of the Y side at step S401.

If one of the voltages Vcpa and Vcpb has reached the temporary target voltage (“Y” at step S403, or “Y” at step S406), the process returns to step S302as shown inFIG. 28, and the alternate switching control is executed in the above manner.

In the fourth embodiment, the switching control can be performed before the voltage has reached the temporary target voltage lower than the final target voltage so that the charging operation is alternately performed by the capacitor chargers203aand203bunder the control of the timer. Thus, high speed processing is achieved.

A fifth embodiment of the present invention is explained lower than with reference toFIG. 31. The fifth embodiment is an example applied to the copying machine1having the so-called power saving mode.

A copying machine1according to the fifth embodiment includes a function of the power saving mode. More specifically, the copying machine1includes a function of achieving power saving and energy saving if a predetermined condition is satisfied, i.e., if a fixed time passes while the copying machine1is in a standby state in which it is not used. The function is realized by maintaining a power supply only to a part of power loads and stopping the power supply to almost all parts of the power loads. This function is such that when the predetermined condition is satisfied after the stop of the power supply to the large parts of power loads, or when the predetermined condition is satisfied, that is, when the user touches an operation key of the operation unit (not shown), the power supply to the power loads to which the power supply has been stopped is re-started (power controller). However, this function is well known, and therefore, drawing and explanation thereof are omitted. A return condition, as another condition, from the power saving mode may include detection of a document that is set on the document table102, detection of FAX reception when the copying machine1includes the FAX transmitting/receiving function, and detection of reception of a printer job.

In such a power saving mode, there are cases where the charge amount of the capacitor CP is insufficient when shifting to the power saving mode or after the shift. More specifically, the cases are such that the charge amount of the capacitor CP is insufficient upon shifting to the power saving mode or the time for the power saving mode is continuous over a long time and natural discharge of the capacitor CP occurs. In such cases, even if the mode is returned from the power saving mode and an image is to be formed in the copying machine1, it is impossible to immediately heat the fixing roller301, and the start of the image formation is delayed. As a result, the user has to wait for starting of the image formation for a long time. Therefore, even in the power saving mode, the charging operation to the capacitor CP needs to be performed if charging is required.

The fifth embodiment is provided to explain the control example of the charging operation by the capacitor chargers203(203aand203b) when the copying machine1has the power saving mode. The schematic control example is shown in the flowchart ofFIG. 31.

The charging operation to the capacitor CP is executed in the above manner when the terminal voltage of the whole capacitor CP decreases lower than a predetermined voltage. It is determined whether the capacitor CP needs charging by monitoring the voltage detection signal S15from the terminal voltage detection circuit232(step S301). If it is determined by the voltage detection signal S15that the terminal voltage of the capacitor CP is lower than the predetermined voltage and charging is needed (“Y” at step S301), it is determined whether the copying machine1is in the power saving mode (step S502). If it is in any mode other than the power saving mode (“N” at step S501), the alternate switching control is executed (e.g. controls after step S302ofFIG. 28and after step S401ofFIG. 30).

On the other hand, if the copying machine1is in the power saving mode (“Y” at step S501), the control signals S11aand S11bindicating that the charging operation is allowed to be on are simultaneously output to the capacitor chargers203aand203b, and the capacitor chargers203aand203bstart charging the capacitors CPa and CPb, respectively (step S502). During this charging operation, it is monitored whether the terminal voltages Vcpa and Vcpb detected by the terminal voltage detection circuits209aand209bhave reached the final target voltages preset (e.g. 45 volts) (step S503). If they have not reached the final target voltages preset (“N” at step S503), the charging operations are continued until they have reached the final target voltages, and then the process returns to step S501.

In the fifth embodiment, the CPU3241controls switching so that the capacitor chargers203aand203bare allowed to concurrently perform the charging operations in the power saving mode, and that the capacitor chargers203aand203bare allowed to alternately perform the charging operation in any other mode.

The power saving mode is provided to achieve power saving effect in a standby state in which the copying machine1is not used, and even if an image is formed in the power saving mode, the operation is not affected by the power saving mode. Therefore, even if all the power supplied from the AC power supply PS is spent for the charging operation to the capacitor CP (CPa, CPb), no trouble occurs in terms of the power. Further, if the capacitor chargers203aand203bconcurrently perform the charging operations, the charging operations to the capacitors CPa and CPb can be finished in a short time. Thus, it is also possible to return any mode to the original power saving mode in a short time.

According to one aspect of the present invention, the power saving mode is controlled in the following manner. if a predetermined condition is satisfied, a power supply to a part of power loads of the power controller, including the control unit that controls charging to the capacitor, is stopped. If a predetermined condition is satisfied during the stop of the power supply, the stop is released. By executing the control, the capacitor can be charged even if the power is not supplied to the control unit. Therefore, even right after the return from the power saving mode, it is possible to immediately increase a heat temperature of the heating member using a sufficient charging power of the capacitor.

According to another aspect of the present invention, the power saving mode is controlled in the following manner. If a predetermined condition is satisfied, the power supply to power loads except for a part of the power loads of the heating unit is stopped. If a predetermined condition is satisfied during the stop of the power supply, the stop (e.g. the power saving mode) is released. Even if the control is executed, a power supply to the second control unit is maintained independently from the control. Therefore, it is possible to charge the capacitor even if the power loads of the heating unit is stopped by the control.

According to still another aspect of the present invention, the capacitor includes the first capacitor and the second capacitor serially connected to each other. A charging voltage required as the capacitor can be ensured as a total charging voltage of these capacitors. Moreover, because the first and the second capacitors include the first charger and the second charger, respectively, by switching between the charging operations by the first and the second chargers, the charging operation can be performed with a smaller amount of power supply as compared with the case where a single capacitor is charged by a single charger. Thus, it is possible to efficiently charge the capacitor even if power to be supplied from the commercial power supply is limited during copying operation.