Image forming apparatus

A total-current control unit is configured to add a fuser current of a fuser unit to a load current of the load to thereby obtain a total current to be supplied from a commercial power supply to the image forming apparatus, the total-current control unit being configured to control the total current to be at a predetermined limit value or less. An auxiliary power supply is configured to supply an auxiliary current to the load. The total-current control unit is further configured to provide first control to control the total current to be at the limit value or less and allow the auxiliary power supply to supply the auxiliary current to the load, thereby supplying, to the load, a current obtained by adding the auxiliary current to the load current, if an increase in the load current causes the total current to exceed the limit value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application relates to and claims priority rights from Japanese Patent Application No. 2013-201423, filed on Sep. 27, 2013, the entire disclosures of which are hereby incorporated by reference herein.

BACKGROUND

1. Field of the Present Disclosure

2. Description of the Related Art

Some image forming apparatuses are supplied with power from a commercial power supply, and further include an auxiliary power supply in order to improve the performance of the image forming apparatuses. For example, a fuser device in an image forming apparatus may include the following: a heater for use during operation and a heater for use during preheating, which are supplied with an electric current from a primary power supply that is a commercial power supply; a rechargeable battery serving as an auxiliary power supply; and an auxiliary DC heater which is supplied with an electric current from the rechargeable battery.

SUMMARY

An image forming apparatus according to an aspect of the present disclosure includes a fuser unit, a load, a total-current control unit, and an auxiliary power supply. The fuser unit is configured to fix, on a sheet, an image formed on the basis of image data. The load is to be used to execute a job in the image forming apparatus. The total-current control unit is configured to add a fuser current of the fuser unit to a load current of the load to thereby obtain a total current to be supplied from a commercial power supply to the image forming apparatus, the total-current control unit being configured to control the total current to be at a predetermined limit value or less. The auxiliary power supply is configured to supply an auxiliary current to the load. The total-current control unit is further configured to provide first control to control the total current to be at the limit value or less and allow the auxiliary power supply to supply the auxiliary current to the load, thereby supplying, to the load, a current obtained by adding the auxiliary current to the load current, if an increase in the load current causes the total current to exceed the limit value.

These and other objects, features and advantages of the present disclosure will become more apparent upon reading of the following detailed description along with the accompanied drawings.

DETAILED DESCRIPTION

Referring to the drawings, an embodiment of the present disclosure will be described in more detail.FIG. 1is a schematic view illustrating the internal structure of an image forming apparatus1according to the embodiment of the present disclosure. For example, the image forming apparatus1is a digital multi function peripheral which has functions as a copier, printer, scanner, and facsimile. The image forming apparatus1includes a main apparatus body100, a document read unit200disposed on top of the main apparatus body100, a document feed unit300disposed on top of the document read unit200, and a manipulation unit400disposed at an upper front portion of the main apparatus body100.

The document feed unit300, which serves as an automatic document feeder, feeds a plurality of documents placed on a document loading unit301so that the document read unit200can successively read the documents.

The document read unit200includes a carriage201equipped with an exposure lamp or the like, a document platen203made of a transparent member such as glass, a charge coupled device (CCD) sensor (not shown), and a document read slit205. To read a document placed on the document platen203, the CCD sensor reads the document while the carriage201is being traveled in the longitudinal direction of the document platen203. In contrast to this, to read a document fed from the document feed unit300, the carriage201is moved to face the document read slit205, so that the CCD sensor reads, through the document read slit205, the document fed from the document feed unit300. The CCD sensor outputs, as image data, the document that has been read.

The main apparatus body100includes a sheet storage unit101, an image forming unit103, and a fuser unit105. The sheet storage unit101is located at the lowermost part of the main apparatus body100and includes sheet trays107which can store a bundle of sheets. In the bundle of sheets stored in the sheet trays107, the uppermost sheet is sent out to a sheet transport path111by actuating a pickup roller109. The sheet is transported to the image forming unit103through the sheet transport path111.

The image forming unit103forms a toner image on the transported sheet. The image forming unit103includes a photosensitive drum113, an exposure unit115, a development unit117, and a transfer unit119. The exposure unit115generates light which is modulated so as to correspond to image data (for example, image data delivered from the document read unit200, image data transmitted from a personal computer, or image data received at a facsimile) and then irradiates the circumferential surface of the photosensitive drum113, which has been uniformly charged, with the resulting light. This allows an electrostatic latent image corresponding to the image data to be formed on the circumferential surface of the photosensitive drum113. In this state, the development unit117supplies toner to the circumferential surface of the photosensitive drum113, thereby allowing a toner image corresponding to the image data to be formed on the circumferential surface thereof. This toner image is transferred by the transfer unit119to a sheet transported from the sheet storage unit101as described above.

The sheet onto which the toner image has been transferred is fed to the fuser unit105. The fuser unit105applies heat and pressure to the toner image and the sheet, thereby causing the toner image to be fixed onto the sheet. The sheet is discharged to a stack tray121or an exit tray123.

The manipulation key unit401is provided with manipulation keys implemented by hard keys. More specifically, for example, provided are a start key405, ten-key pads407, a stop key409, a reset key411, and a function switching key413for switching between the copier, printer, scanner, and facsimile.

The start key405is used to start, for example, the operation of copying and facsimile transmission. The ten-key pads407are used to input numerical values such as the number of copies and facsimile numbers. For example, the stop key409is used to stop copying halfway. The reset key411is used to initialize the contents of settings.

The function switching key413, which includes, for example, a copy key and a transmission key, switches between the copy function and the transmission function. Manipulating the copy key will cause an initial copy screen to be displayed on the display unit403. Manipulating the transmission key will cause the initial screen for facsimile transmission and mail transmission to be displayed on the display unit403.

FIG. 2is a block diagram illustrating the configuration of the image forming apparatus1shown inFIG. 1. The image forming apparatus1is configured in a manner such that the main apparatus body100, the document read unit200, the document feed unit300, the manipulation unit400, a control unit500, and a communication unit600are connected to each other through a bus. The main apparatus body100, the document read unit200, the document feed unit300, and the manipulation unit400have already been described above and thus will not be described again.

The control unit500includes, for example, a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and an image memory. The CPU performs control required to operate the image forming apparatus1on the aforementioned components of the image forming apparatus1such as the main apparatus body100. The ROM is configured to store software required to control the operation of the image forming apparatus1. The RAM is used to temporarily store data generated during execution of software and to store application software. The image memory temporarily stores image data (for example, image data delivered from the document read unit200, image data transmitted from a personal computer, and image data received by a facsimile).

The communication unit600includes a facsimile communication unit601and a network I/F unit603. The facsimile communication unit601includes a network control unit (NCU) configured to control a telephone line connection to a facsimile on the other end and a modem circuit for modulating and demodulating facsimile communication signals. The facsimile communication unit601is connected to a telephone line605.

The network I/F unit603is connected to a local area network (LAN)607. The network I/F unit603serves as a communication interface circuit which executes communications with a terminal device such as a personal computer that is connected to the LAN607.

FIG. 3is a circuit diagram of a current control system included in the image forming apparatus1according to the embodiment. This system includes a power supply unit11, a load current measurement unit13, a total-current control unit25, an auxiliary power supply27, and an induction heating (IH) control unit29.

The image forming apparatus1forms an image on the basis of image data and then causes the fuser unit105to fix the image on a sheet for output.

The power supply unit11, which is an example of the load current generation unit, supplies a current from a commercial power supply AC as a load current to a load19that is used to execute a job in the image forming apparatus1. As used herein, the load refers to a load other than the fuser unit105, for example, a motor or solenoid which is used in a sheet transport system, a punching unit, or a stapling unit.

The configuration of the power supply unit11will be described in detail. The power supply unit11employs the AC voltage supplied from the commercial power supply AC to produce a supply voltage that is used to operate the image forming apparatus1. The image forming apparatus1includes a plurality of power supply units (a plurality of load current generation units) for producing DC voltages that are different from each other, one of the power supply units being illustrated inFIG. 3. The power supply unit11produces a supply voltage (in other words, the load current) for driving the load19of the stapling unit in the image forming apparatus1. Another power supply unit produces a supply voltage which drives, for example, a load to be used in the sheet transport system or a load to be used for punching.

The image forming apparatus1includes a power supply line17. The power supply line17connects the commercial power supply AC to a plurality of power supply units (including the power supply unit11) of the image forming apparatus1.

The power supply unit11includes a diode bridge D1, a diode D2, capacitors C1and C2, a transformer T, a transistor Q (switching element), resistors R1and R2, and a switching control unit21.

The AC voltage supplied from the commercial power supply AC through the power supply line17is rectified by the diode bridge D1and then smoothed by the capacitor C1. Then, the voltage across the ends of the capacitor C1is applied to the series circuit of the primary winding of the transformer T and the transistor Q.

The gate of the transistor Q is connected to the switching control unit21. Turning the transistor Q ON or OFF in response to a control signal from the switching control unit21will cause a high-frequency current to flow through the primary winding of the transformer T and thereby induce a high-frequency voltage on the secondary winding of the transformer T due to electromagnetic coupling. The high-frequency voltage induced on the secondary winding of the transformer T is rectified by the diode D2and then smoothed by the capacitor C2, so that a supply voltage Vd is produced. The supply voltage Vd is supplied to the load19.

The supply voltage Vd is divided by the series circuit of the resistors R1and R2. Then, the divided voltage is delivered to the switching control unit21, thereby providing the supply voltage Vd as feedback to the switching control unit21. The switching control unit21provides control so that the supply voltage Vd takes on a preset constant voltage by varying the duty ratio, at which the transistor Q is turned ON and OFF, so as to cause the feedback voltage to be at a preset target value.

The IH control unit29, which is an example of the fuser current generation unit, supplies a current from the commercial power supply AC as a fuser current to the fuser unit105. The fuser unit105is an IH fuser device which fixes an image on a sheet by electromagnetic induction heating. In the embodiment, the commercial power supply AC to which the power supply unit11and another power supply unit are connected and the commercial power supply AC to which the IH control unit29is connected are different from each other, but may also be the same. Note that as the fuser unit105, a halogen-lamp type fuser device may also be employed.

The load current measurement unit13measures the total current which is supplied from the commercial power supply AC to the power supply unit11and another power supply unit. That is, the load current measurement unit13measures a load current being supplied from the commercial power supply AC to the image forming apparatus1. The load current measurement unit13includes a current transformer CT, resistors R3and R4, a diode bridge D3, a capacitor C3, and an AD converter23.

The current transformer CT is connected to the power supply line17, and includes a primary winding and a secondary winding. Part of the power supply line17serves as the primary winding of the current transformer CT. The load current to be supplied to the image forming apparatus1flows through the power supply line17, and is converted into a microcurrent by the current transformer CT. The secondary winding of the current transformer CT through which the microcurrent flows is connected in parallel with each of the resistor R3, the diode bridge D3, the resistor R4, and the capacitor C3.

The resistor R3provides a voltage signal depending on the microcurrent. In this manner, the resistor R3serves as a current voltage converter which converts the current detected by the current transformer CT into a voltage signal for output. This voltage signal is full-wave rectified by the diode bridge D3, which is an example of the rectifier diode, and then smoothed by the capacitor C3, which is an example of the smoothing capacitor. The resistor R4, which is a discharge resistor for the capacitor C3, can be reduced to provide improved trackability of a voltage signal to a change in the total current.

The voltage signal smoothed by the capacitor C3is converted into a digital signal by the AD converter23. Thus, the AD converter23converts the voltage signal delivered from the resistor R3(a current voltage converter) into a digital signal.

This digital signal is sent to the total-current control unit25.

The total-current control unit25employs a current obtained by adding the fuser current to the load current as the total current that is supplied from the two commercial power supplies AC to the image forming apparatus1, and controls the total current to be at a predetermined limit value or less. The total-current control unit25employs, as the total current, the value that is obtained by adding a value of the fuser current for which the total-current control unit25commanded the IH control unit29to a value of the load current measured by the load current measurement unit13. The total-current control unit25is implemented by the CPU, the ROM, and the RAM which are included in the control unit500of the image forming apparatus1.

The auxiliary power supply27, which is formed of a capacitor, supplies an auxiliary current to the load19to which the load current is supplied. In place of the capacitor, it is also possible to employ a rechargeable battery as the auxiliary power supply27.

The auxiliary power supply27is connected to the load19to which the power supply unit11supplies power. Furthermore, the conductor connecting between one electrode of the auxiliary power supply27and the load19is connected in series with a diode D4, a second switch SW2, and an auxiliary current measurement unit31.

The auxiliary current measurement unit31measures the auxiliary current supplied from the auxiliary power supply27to the load19. The auxiliary current measurement unit31is constructed in the same manner as the load current measurement unit13. The second switch SW2is switched between ON and OFF by the control of the total-current control unit25. In an ON state of the second switch SW2, the capacitor serving as the auxiliary power supply27is discharged to supply the auxiliary current to the load19. In an OFF state of the second switch SW2, the auxiliary power supply27and the load19are disconnected from each other to supply no auxiliary current to the load19.

In an ON state of the second switch SW2, the diode D4serves to block the flow of the load current produced by the power supply unit11into the auxiliary power supply27.

Furthermore, the one electrode of the auxiliary power supply27is connected via a first switch SW1to a conductor connecting between the diode D2and the capacitor C2among those conductors that connect between the secondary winding of the transformer T, the diode D2, and the capacitor C2. As described above, the first switch SW1is provided on the conductor connecting between the auxiliary power supply27and the power supply unit11(the load current generation unit). The first switch SW1is switched between ON and OFF by the total-current control unit25. With the first switch SW1in an ON state, the load current from the power supply unit11is supplied to the auxiliary power supply27, thereby charging the auxiliary power supply27. With the first switch SW1in an OFF state, the power supply unit11and the auxiliary power supply27are disconnected from each other, thereby stopping charging of the auxiliary power supply27.

Now, a description will be made to the current control to be executed by the image forming apparatus1according to the embodiment.FIGS. 4 and 5are each a time chart illustrating this current control.FIG. 6is a flowchart illustrating this current control.FIG. 4illustrates the case where the current obtained by adding the auxiliary current to the load current is not enough to be supplied to the load19, and thus feedforward control is performed to reduce the fuser current.FIG. 5illustrates the case where the current obtained by adding the auxiliary current to the load current is enough to be supplied to the load19, and thus the feedforward control to reduce the fuser current is not performed.

It is assumed that the total current to be supplied from the commercial power supply AC to the image forming apparatus1has a limit value of 15.0 A; the fuser current has a target value of 10.0 A; and the fuser current is reduced by an amount of decrease of 1.0 A by the feedforward control.

Referring toFIGS. 4 and 5, the load current has a peak period t that occurs cyclically. The peak period t refers to the period of the load current in which the total current would exceed the limit value unless control is provided to supply the auxiliary current to the load19or feedforward control is performed on the fuser current. For example, the period of stapling is the peak period t when the image forming apparatus1prints a predetermined number of sheets and then executes the job for stapling the sheets. The peak period t occurs each time the job is executed.

The total-current control unit25determines whether the total current has exceeded the limit value of 15.0 A (step S1). The total-current control unit25has caused the IH control unit29to produce the target value, 10.0 A of the fuser current. Furthermore, up to time T1 shown inFIG. 4andFIG. 5, the load current measured by the load current measurement unit13is 5.0 A. Thus, since the total current is 15.0 A (=10.0 A+5.0 A) up to time T1, the total-current control unit25does not determine that the total current has exceeded 15.0 A (No in step S1), and the process returns to step S1to repeat the processing of step S1.

Since the load current measured by the load current measurement unit13starts to increase at time T1 from 5.0 A and reaches 5.2 A at time T2 shown inFIG. 4andFIG. 5, the total-current control unit25determines that the total current has exceeded the limit value of 15.0 A (Yes in step S1). By way of example, 5.2 A may be based to determine whether the total current has exceeded 15.0 A.

As shown inFIGS. 4 and 5, to eliminate the state where the total current has exceeded the limit value, the total-current control unit25causes the power supply unit11to execute control to reduce the load current down to 5.0 A, and in order to supply a current required for the load19, provides control so that the auxiliary power supply27supplies the auxiliary current to the load19(step S2). This allows the current obtained by adding the auxiliary current to the load current (5.0 A) to be supplied to the load19, with the total current reduced to the limit value of 15.0 A (from time T2 onward as shown inFIG. 4andFIG. 5).

Referring toFIG. 3, a description will be made more specifically to the control that is provided to supply the auxiliary current from the auxiliary power supply27to the load19. The total-current control unit25provides control to manipulate the first switch SW1and thereby disconnect the auxiliary power supply27and the power supply unit11from each other, and provides control to manipulate the second switch SW2and thereby connect between the auxiliary power supply27and the load19. This allows for stopping charging the auxiliary power supply27using the current from the power supply unit11(the load current generation unit) and supplying the auxiliary current from the auxiliary power supply27to the load19.

The total-current control unit25determines whether the current obtained by adding the auxiliary current to the load current is not enough to be supplied to the load19(step S3). In the embodiment, when the auxiliary current has reached a predetermined threshold value, it is determined that the current obtained by adding the auxiliary current to the load current is not enough to be supplied to the load19.FIG. 4shows that since the auxiliary current has reached the threshold value at time T3 during the peak period t, the current obtained by adding the auxiliary current to the load current is not enough to be supplied to the load19. In contrast to this,FIG. 5shows that since the auxiliary current has not yet reached the threshold value during the peak period t, the current obtained by adding the auxiliary current to the load current is enough to be supplied to the load19.

First, a description will be made to the case ofFIG. 4. The total-current control unit25determines that since the auxiliary current measured by the auxiliary current measurement unit31has reached the threshold value at time T3, the current obtained by adding the auxiliary current to the load current is not enough to be supplied to the load19(Yes in step S3).

Then, the total-current control unit25causes the IH control unit29to execute feedforward control for reducing the fuser current by 1.0 A and the power supply unit11to execute control for increasing the load current (step S4). Furthermore, the total-current control unit25provides control to manipulate the first switch SW1shown inFIG. 3so as to connect between the auxiliary power supply27and the power supply unit11, and provides control to manipulate the second switch SW2so as to disconnect the auxiliary power supply27and the load19from each other. This allows the current from the power supply unit11to charge the auxiliary power supply27and the supply of the auxiliary current from the auxiliary power supply27to the load19to be stopped.

Not feedback control but feedforward control is provided because the fuser current can be immediately reduced by a predetermined amount of decrease so as to prevent the total current from exceeding the limit value even in the presence of an increase in the load current.

Now, the feedforward control to be executed will be briefly described. The data that associates the processing, in which the peak period t occurs, with the amount of decrease in the fuser current assigned to the processing is stored in advance in a storage unit which is included in the IH control unit29. For example, an amount of decrease d1 in the fuser current is assigned to the stapling, and an amount of decrease d2 in the fuser current is assigned to the punching. The amount of decrease in the fuser current is specified so that the total current will not exceed the limit value even in the presence of an increase in the load current after the feedforward control. The IH control unit29provides control to reduce the fuser current by the amount of decrease (here, 1.0 A) that is assigned to the processing during which the peak period t occurs.

The IH control unit29provides feedforward control to reduce the fuser current, and after that, starts to control to increase the fuser current to the target value of 10.0 A (step S5: time T3). For this control, employed is feedback control like the proportional integral derivative (PID) control so as to prevent the total current from exceeding the limit value. As described above, when the IH control unit29supplies the current from the commercial power supply AC as the fuser current to the fuser unit105, so that the total current exceeds the limit value and thus the feedforward control is provided to reduce the fuser current by a predetermined amount of decrease, the IH control unit29provides feedback control to increase the fuser current to the target value.

The feedback control requires relatively long time to increase the fuser current to the target value. Thus, since the feedback control is provided to increase the fuser current to the target value after the feedforward control is provided to reduce the fuser current, there will occur a period in which the total current to be used cannot be raised to the limit value (period from time T3 to time T5).

Because from time T3 onward, the load current continues to increase and the fuser current is increased by the feedback control, the total current also continues to increase. However, since at time T3, the feedforward control is performed on the fuser current so as to reduce the total current (in this example, the amount of decrease in the total current is 1.0 A), the total current is reduced to 15.0 A or less.

The load current takes on the maximum value at time T4 and after that, is reduced to 5.0 A at time T5, and the peak period t is ended. Then, the process returns to step S1.

On the other hand, as shown inFIG. 5, the total-current control unit25determines that the current obtained by adding the auxiliary current to the load current is enough to be supplied to the load19unless the auxiliary current measured by the auxiliary current measurement unit31is determined to have reached the threshold value (No in step S3).

If No in step S3, the total-current control unit25determines whether the peak period t has ended (step S6). If the total current is determined to have exceeded the limit value (Yes in step S1), the total-current control unit25starts to measure the peak period t and determines whether the peak period t assigned in advance depending on the processing has elapsed. For example, a peak period t1 is set for the stapling and a peak period t2 is set for the punching, and those pieces of data are stored in advance in the storage unit of the total-current control unit25. The total-current control unit25determines that the peak period t has ended if the peak period t is determined to have elapsed.

If the total-current control unit25does not determine that the peak period t has ended (No in step S6), then the process returns to step S3. If the total-current control unit25determines that the peak period t has ended (Yes in step S6), then the process returns to step S1.

Now, a description will be made to current control according to a comparative example.FIG. 7is a time chart illustrating the current control according to the comparative example. In the comparative example, no auxiliary current is supplied to the load19. Thus, the amount of decrease (2.0 A) in the fuser current by the feedforward control is greater as compared with that of the embodiment. The limit value of the total current (15.0 A), the target value of the fuser current (10.0 A), and the length of the peak period t are the same as those of the embodiment.

Like the embodiment, the comparative example is configured such that the load current starts to increase from 5.0 A at time T1 and then reaches 5.2 A at time T2. Thus, in the comparative example, like the embodiment, it is determined that the total current has exceeded the limit value of 15.0 A at time T2.

In the comparative example, unlike the embodiment, no control is provided to supply the auxiliary current to the load19. Thus, when the total current is determined to have exceeded the limit value, feedforward control for the amount of decrease of 2.0 A is performed on the fuser current (time T2). The amount of decrease in the fuser current is specified so that the total current will not exceed the limit value even in the presence of an increase in the load current after the feedforward control. In the comparative example, a larger amount of decrease is set as compared with that of the embodiment because no auxiliary current is supplied to the load19(2.0 A).

The feedforward control reduces the total current from 15.2 A to 2.0 A, so that from time T2 onward, the total current can be reduced to the limit value or less even in the presence of an increase in the load current.

Considering the embodiment and the comparative example, the following conclusions can be reached. As shown inFIGS. 4 and 7, when feedback control for controlling the fuser current at a target value (hereafter, the feedback control) is provided after the feedforward control is performed on the fuser current, a relatively long time is required to increase the fuser current to the target value so that the total current will not exceed the limit value. During the period of the feedback control, the total current to be used cannot be raised up to the limit value. In the embodiment, the feedback control is provided during the period from time T3 to time T5 (in which the total current to be used cannot be raised to the limit value). In the comparative example, the feedback control is provided during the period from time T2 to time T6 (in which the total current to be used cannot be raised to the limit value).

The amount of decrease in the fuser current for the feedforward control in the comparative example (2.0 A) is greater than the amount of decrease in the embodiment (1.0 A). This is because no auxiliary current is supplied to the load19in the comparative example, and thus the total current would exceed the limit value due to an increase in the load current unless a larger amount of decrease in the fuser current is employed as compared with that of the embodiment. As compared with the comparative example, the embodiment employs a smaller amount of decrease in the fuser current for the feedforward control. Thus, the embodiment provides a shorter period of feedback control as compared with the comparative example.

Now, a description will be made to the main effects of the embodiment. In the embodiment, the total-current control unit25provides the following two types of control when the load current increases and thereby the total current exceeds the limit value. One is to control the total current to be at the limit value or less (step S2, time T2 ofFIGS. 4 and 5). This allows for preventing the total current being supplied from the commercial power supply AC to the image forming apparatus1from exceeding the limit value. The other is to provide control so that the auxiliary power supply27supplies the auxiliary current to the load19and then the current obtained by adding the auxiliary current to the load current is supplied to the load19(step S2, from time T2 onward inFIGS. 4 and 5). This allows for supplying a current of a required magnitude to the load19and thus preventing degradation of the performance of the image forming apparatus1.

Furthermore, as shown inFIG. 5, when the current obtained by adding the auxiliary current to the load current is enough to be supplied to the load19(No in step S3), the total-current control unit25does not cause the IH control unit29to execute the feedforward control for reducing the fuser current. Thus, since the feedback control for increasing the fuser current to the target value is not provided, it is possible to prevent the occurrence of the period in which the total current to be used cannot be raised to the limit value.

On the other hand, as shown inFIG. 4, when the current obtained by adding the auxiliary current to the load current is not enough to be supplied to the load19(Yes in step S3), the total-current control unit25causes the IH control unit29to execute the feedforward control for reducing the fuser current and the power supply unit11to execute control to increase the load current (from time T3 onward). This allows for preventing degradation in the performance of the load19while controlling the total current to be at the limit value or less. Since the auxiliary current is supplied to the load19in addition to the load current, the amount of decrease (the amount of drop) in the fuser current can be reduced. Thus, since the period required to increase the fuser current to the target value by the feedback control can be reduced, it is possible to shorten the period in which the total current to be used cannot be raised to the limit value.

According to the embodiment, the IH control unit29sets the amount of decrease (the amount of drop) in the fuser current and the auxiliary power supply27sets the value of the auxiliary current that can be supplied to the load19so that the feedback control on the fuser current can be ended during the peak period t of the load current illustrated from time T2 to time T5 inFIG. 4(for example, during the period of the punching or stapling). This allows for preventing the occurrence of the period after the peak period t onward in which the total current to be used cannot be raised to the limit value.

In contrast to this, as shown inFIG. 7, the comparative example shows that since the feedback control has not been ended in the peak period t (i.e., the fuser current has not reached the target value by the feedback control), there occurs a period after the peak period t in which the total current to be used cannot be raised to the limit value (the diagonally shaded area from time T5 to time T6.)

An increase in the value of the auxiliary current could reduce the amount of decrease in the fuser current. A decrease in the amount of decrease of the fuser current could shorten the period of the feedback control. It is thus possible to end the feedback control during the peak period t by appropriately setting each of the value of the auxiliary current and the amount of decrease in the fuser current.

According to the embodiment, in step S2, the total-current control unit25disconnects the auxiliary power supply27and the power supply unit11from each other by providing control to manipulate the first switch SW1, and connects between the auxiliary power supply27and the load19by providing control to manipulate the second switch SW2. This allows for stopping charging of the auxiliary power supply27and supplying the auxiliary current to the load19. Then, in step S4, the total-current control unit25provides control to manipulate the first switch SW1and thereby connect between the auxiliary power supply27and the power supply unit11, and provides control to manipulate the second switch SW2and thereby disconnect the auxiliary power supply27and the load19. This allows the current from the power supply unit11to charge the auxiliary power supply27and the supply of the auxiliary current to the load19to be stopped.

As described above, according to the embodiment, when an increase in the load current causes the total current to exceed the limit value, the auxiliary current is supplied to the load19(step S2). Then, when the feedforward control is provided to reduce the fuser current because the current obtained by adding the auxiliary current to the load current is not enough to be supplied to the load19(step S4), the current from the power supply unit11is used to charge the auxiliary power supply27. Thus, the cycle of discharging and charging can be repeated when the peak period t occurs cyclically.

Furthermore, according to the embodiment, as shown inFIG. 4, when the auxiliary current measured by the auxiliary current measurement unit31has increased to the predetermined threshold value in step5(time T3), the total-current control unit25determines that the current obtained by adding the auxiliary current to the load current is not enough to be supplied to the load19(step S3). The determination of whether the current obtained by adding the auxiliary current to the load current is enough to be supplied to the load19may be made when the capacitor or the auxiliary power supply27has been completely discharged. However, since it is not easy to determine when the capacitor has been completely discharged, the aforementioned determination is made when the auxiliary current has increased to the predetermined threshold value.

According to the embodiment, since it is determined whether the total current has exceeded the limit value due to an increase in the load current (step S1), it is necessary to specify the increase in the load current and to specify the value of the total current. As shown inFIG. 3, in the embodiment, the total-current control unit25determines, as the total current, the value that is obtained by adding a value of the fuser current for which the total-current control unit25commanded the IH control unit29to a value of the load current measured by the load current measurement unit13. This allows for specifying the increase in the load current and specifying the value of the total current.

The description has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited.