JP6131211B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to control of a total current input from a commercial power source to an image forming apparatus.

  In the case of a commercial power supply of AC 100V, for example, in Japan, the current regulation value is set to 15A, and a current exceeding 15A cannot be used. For this reason, a limit value of the total current input from the commercial power source to the image forming apparatus is set. The limit value is a regulation value, a value slightly lower than the regulation value, or a value slightly higher than the regulation value.

  As an image forming apparatus capable of suppressing the total current below a limit value, for example, a table in which each operation mode of the image forming apparatus is associated with an upper limit power that can be supplied to a fixing unit assigned according to each operation mode. For each operation mode, there has been proposed one in which the upper limit power allocated to the operation mode can be supplied to the fixing unit (for example, see Patent Document 1).

  When these functions are executed in an image forming apparatus having a stapling function and a punching function, the power required for the image forming apparatus increases. Therefore, as an image forming apparatus to which power is supplied from two outlets in order to secure necessary power, for example, a primary coil connected to the first AC cord and the second AC cord, a heater A device including a secondary coil connected to a drive unit and an AC-DC conversion unit has been proposed (see, for example, Patent Document 2). If two outlets are used (to be precise, if one system uses two power supplies of 15A or one power supply whose capacity has been increased to 20A), the total current in Japan may be up to 20A. It becomes possible.

JP 2005-122124 A JP 2007-150456 A

  If the electric power supplied to the fixing unit is small, it takes time to raise the fixing unit to the fixing temperature, and the printing speed decreases. On the other hand, the total current input to the image forming apparatus must not exceed the limit value.

  An object of the present invention is to provide an image forming apparatus capable of supplying power to a fixing unit to the maximum while suppressing the total current input from the commercial power source to the image forming apparatus from exceeding a limit value.

  An image forming apparatus according to the present invention that achieves the above object is an image forming apparatus that forms an image based on image data, and fixes and outputs the image on a sheet, and fixes the image on the sheet. A fixing unit; a load current measuring unit for measuring a load current supplied to a load other than the fixing unit used for execution of a job of the image forming apparatus; and a fixing current supplied to the fixing unit. A current obtained by adding the load current is defined as a total current supplied from the commercial power source to the image forming apparatus, and the load is controlled from the limit value to the load in order to control the total current to a predetermined limit value or less. An allowable current calculation unit for calculating an allowable current of the fixing unit, which is a value obtained by subtracting a current for fixing, a fixing voltage measuring unit for measuring a fixing voltage supplied to the fixing unit, the allowable current and the fixing Multiply with voltage for An allowable power calculation unit that calculates an allowable power of the fixing unit, and an instruction power calculation unit that calculates an instruction power to the fixing unit in order to set the temperature of the fixing unit to a predetermined temperature. If the command power is less than or equal to the allowable power, the command power is determined as a target power to be supplied to the fixing unit, and if the command power is greater than the power control, the power allowable is determined as the target power. A target power determination unit; and a fixing power control unit that controls the fixing power so that the fixing power supplied to the fixing unit reaches the target power determined by the target power determination unit; Is provided.

  In the present invention, a value obtained by subtracting the load current measured by the load current measuring unit from the limit value of the total current input to the image forming apparatus is set as the allowable current of the fixing unit, and the allowable current and the fixing voltage measuring unit A value obtained by multiplying the measured fixing voltage is used as the allowable power of the fixing unit.

  The indicated command power to be supplied to the fixing unit should be the target power of the fixing unit. However, since the load current is relatively large, if the command power is set to the target power, if the total current exceeds the limit value, the allowable power that is lower than the command power is set as the target power.

  That is, according to the present invention, if the command power is equal to or less than the allowable power, the total current does not exceed the limit value even if the command power is the target power, so the command power is determined as the target power. On the other hand, if the command power is larger than the allowable power, if the command power is set as the target power, the total current exceeds the limit value, so the allowable power is determined as the target power. In this case, the target power is lower than the command power. However, in the present invention, as described above, the value obtained by subtracting the load current from the limit value is used as the allowable current of the fixing unit, and the value obtained by multiplying the allowable current and the fixing voltage is used as the allowable power of the fixing unit. Accordingly, when the allowable power is determined as the target power, the total current input to the image forming apparatus can be used up to the limit value, and therefore the total current input from the commercial power source to the image forming apparatus exceeds the limit value. It is possible to supply power to the fixing unit to the maximum while suppressing this.

  The load is a load other than the fixing unit (a load different from the fixing unit), and means, for example, a motor, a solenoid, or the like used for a paper conveyance system, a punch processing unit, a staple processing unit, or the like.

  In the above configuration, the target power determined by the target power determination unit is reduced as compared with the target power previously determined by the target power determination unit, and the amount of decrease exceeds a predetermined value. Then, the fixing power control unit executes feedforward control as control of the fixing power, and if the decrease amount does not exceed the predetermined value, feedback control is performed as control of the fixing power. Execute.

  According to this configuration, if the target power determined by the target power determination unit is reduced compared to the target power previously determined by the target power determination unit, and the amount of decrease exceeds a predetermined value, The feedforward control is executed as the fixing power control. In feedback control, it takes a relatively long time to reach the target power. Therefore, when the decrease amount exceeds a predetermined value (that is, when the decrease amount is relatively large), in the feedback control, the total current exceeds the limit value during the period required to reach the target power. There is a possibility. On the other hand, according to the feedforward control, the fixing power can be immediately reduced below the target power, so that the total current does not exceed the limit value.

  On the other hand, if the reduction amount does not exceed a predetermined value, the fixing power control unit executes feedback control (for example, PID control) as control of the fixing power. If the amount of decrease does not exceed a predetermined value (i.e., if the amount of decrease is relatively small), the time required to reach the target power is short even in feedback control, so the total current is limited during that period. This is because the value is never exceeded. By performing feedback control, the fixing power supplied to the fixing unit can be accurately adjusted to the target power.

  In the above configuration, if the target power determined by the target power determination unit is increased compared to the target power determined last time by the target power determination unit, the fixing power control unit Feedback control is performed as power control.

  Thus, when the target current is increased, the total current can be prevented from exceeding the limit value.

  In the above configuration, the allowable power calculation unit calculates the allowable power at a cycle shorter than a cycle at which the command power calculation unit calculates the command power.

  Since the allowable power is a value obtained by multiplying the allowable current (= limit value−load current) and the fixing voltage, when the allowable power is determined as the target power, the total current obtained by adding the load current and the allowable current is the total. The total current becomes a limit value. For this reason, if the load current increases, the total current exceeds the limit value.

  According to this configuration, the cycle for calculating the allowable power is shorter than the cycle for calculating the command power. Therefore, when the instruction power is calculated and the load power increases until the next instruction power is calculated, the allowable power can be reduced when the allowable power that is the target power must be reduced. Can be prevented from exceeding the limit value.

  In the configuration described above, the first internal wiring that sends the load current supplied from the first power cord connectable to the first outlet to the load other than the fixing unit and the second outlet can be connected. And a second internal wiring for sending the fixing current supplied from the second power cord to the fixing unit.

  In this configuration, an outlet to which a fixing current is supplied is different from an outlet to which a load current is supplied, and the present invention is applied to an image forming apparatus that is supplied with power from two outlets.

  According to the present invention, it is possible to supply power to the fixing unit to the maximum while suppressing the total current input from the commercial power source to the image forming apparatus from exceeding the limit value.

1 is a diagram illustrating an outline of an internal structure of an image forming apparatus according to an embodiment. FIG. 2 is a block diagram illustrating a configuration of the image forming apparatus illustrated in FIG. 1. 1 is a circuit diagram of a current control system provided in an image forming apparatus according to an embodiment. It is a longitudinal cross-sectional view which shows the structure of a fixing part. 6 is a time chart showing current control executed by the image forming apparatus according to the embodiment. 5 is a flowchart showing current control executed by the image forming apparatus according to the present embodiment (part 1). 7 is a flowchart showing current control executed by the image forming apparatus according to the present embodiment (part 2). 5 is a graph showing an example of the relationship among total power, fixing power, and load power in the present embodiment when the target power is allowable power. In a comparative example, it is a graph which shows an example of the relationship between total electric power, fixing electric power, and load electric power.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing an outline of the internal structure of an image forming apparatus 1 according to an embodiment of the present invention. The image forming apparatus 1 can be applied to, for example, a digital multifunction machine having functions of a copy, a printer, a scanner, and a facsimile. The image forming apparatus 1 includes an apparatus main body 100, a document reading unit 200 disposed on the apparatus main body 100, a document feeding unit 300 disposed on the document reading unit 200, and an operation disposed on the upper front surface of the apparatus main body 100. Part 400 is provided.

  The document feeding unit 300 functions as an automatic document feeding device, and can feed a plurality of documents placed on the document placing unit 301 so that the document reading unit 200 can read them continuously.

  The document reading unit 200 includes a carriage 201 on which an exposure lamp and the like are mounted, a document table 203 made of a transparent member such as glass, a CCD (Charge Coupled Device) sensor (not shown), and a document reading slit 205. When reading a document placed on the document table 203, the document is read by the CCD sensor while moving the carriage 201 in the longitudinal direction of the document table 203. On the other hand, when reading a document fed from the document feeding unit 300, the carriage 201 is moved to a position facing the document reading slit 205, and the document fed from the document feeding unit 300 is scanned. Reading is performed by the CCD sensor through the reading slit 205. The CCD sensor outputs the read original as image data.

  The apparatus main body 100 includes a sheet storage unit 101, an image forming unit 103, and a fixing unit 105. The sheet storage unit 101 is disposed at the lowermost part of the apparatus main body 100 and includes a sheet tray 107 that can store a bundle of sheets. In the bundle of sheets stored in the sheet tray 107, the uppermost sheet is sent out toward the sheet conveyance path 111 by driving the pickup roller 109. The sheet is conveyed to the image forming unit 103 through the sheet conveyance path 111.

  The image forming unit 103 forms a toner image on the conveyed paper. The image forming unit 103 includes a photosensitive drum 113, an exposure unit 115, a developing unit 117, and a transfer unit 119. The exposure unit 115 generates modulated light corresponding to image data (image data output from the document reading unit 200, image data transmitted from a personal computer, image data received by facsimile, etc.), and is uniformly charged. Irradiate to the peripheral surface of the photosensitive drum 113. As a result, an electrostatic latent image corresponding to the image data is formed on the peripheral surface of the photosensitive drum 113. In this state, a toner image corresponding to image data is formed on the peripheral surface by supplying toner from the developing unit 117 to the peripheral surface of the photosensitive drum 113. This toner image is transferred by the transfer unit 119 to the sheet conveyed from the sheet storage unit 101 described above.

  The sheet on which the toner image is transferred is sent to the fixing unit 105. In the fixing unit 105, heat and pressure are applied to the toner image and the paper, and the toner image is fixed on the paper. The paper is discharged to the stack tray 121 or the paper discharge tray 123.

  The operation unit 400 includes an operation key unit 401 and a display unit 403. The display unit 403 has a touch panel function, and displays a screen including soft keys. The user operates the soft keys while viewing the screen to make settings necessary for executing functions such as copying.

  The operation key unit 401 is provided with operation keys including hard keys. Specifically, a start key 405, a numeric key 407, a stop key 409, a reset key 411, a function switching key 413 for switching between a copy, a printer, a scanner, and a facsimile are provided.

  A start key 405 is a key for starting operations such as copying and facsimile transmission. A numeric keypad 407 is a key for inputting numbers such as the number of copies and a facsimile number. A stop key 409 is a key for stopping a copying operation or the like halfway. A reset key 411 is a key for returning the set contents to the initial setting state.

  The function switching key 413 includes a copy key, a transmission key, and the like, and is a key for switching between a copy function and a transmission function. When the copy key is operated, an initial copy screen is displayed on the display unit 403. When the transmission key is operated, an initial screen for facsimile transmission and mail transmission is displayed on the display unit 403.

  FIG. 2 is a block diagram showing a configuration of the image forming apparatus 1 shown in FIG. The image forming apparatus 1 has a configuration in which an apparatus main body 100, a document reading unit 200, a document feeding unit 300, an operation unit 400, a control unit 500, and a communication unit 600 are connected to each other by a bus. Since the apparatus main body 100, the document reading unit 200, the document feeding unit 300, and the operation unit 400 have already been described, description thereof will be omitted.

  The control unit 500 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an image memory, and the like. The CPU executes control necessary for operating the image forming apparatus 1 on the above-described components of the image forming apparatus 1 such as the apparatus main body 100. The ROM stores software necessary for controlling the operation of the image forming apparatus 1. The RAM is used for temporary storage of data generated during execution of software, storage of application software, and the like. The image memory temporarily stores image data (image data output from the document reading unit 200, image data transmitted from a personal computer, image data received by facsimile, etc.).

  The communication unit 600 includes a facsimile communication unit 601 and a network I / F unit 603. The facsimile communication unit 601 includes an NCU (Network Control Unit) that controls connection of a telephone line with a destination facsimile, and a modulation / demodulation circuit that modulates / demodulates a signal for facsimile communication. The facsimile communication unit 601 is connected to the telephone line 605.

  A network I / F unit 603 is connected to a LAN (Local Area Network) 607. A network I / F unit 603 is a communication interface circuit for executing communication with a terminal device such as a personal computer connected to the LAN 607.

  FIG. 3 is a circuit diagram of a current control system provided in the image forming apparatus 1 according to the present embodiment. This system includes a power supply unit 11, a load current measurement unit 13, a total current control unit 25, and an IH (Induction Heating) control unit 27.

  The power supply unit 11 supplies the current from the commercial power supply AC as a load current to the load 19 used for job execution in the image forming apparatus 1. The load 19 referred to here is a load other than the fixing unit 105 (a load different from the fixing unit 105), and means, for example, a motor, a solenoid, or the like used for a paper transport system, a punch processing unit, a staple processing unit, and the like.

  The configuration of the power supply unit 11 will be described in detail. The power supply unit 11 generates a power supply voltage used for the operation of the image forming apparatus 1 using an AC voltage supplied from the commercial power supply AC. The image forming apparatus 1 includes a plurality of power supply units that generate direct currents having different voltages, one of which is shown in FIG. The power supply unit 11 generates a power supply voltage (in other words, a load current) that drives the load 19 of the staple processing unit of the image forming apparatus 1. The other power supply unit generates, for example, a power supply voltage that drives a load used for the paper conveyance system and a load used for punching.

  The image forming apparatus 1 includes a power line 17. The power supply line 17 connects a plurality of power supply units (including the power supply unit 11) of the image forming apparatus 1 to the commercial power supply AC.

  The power supply unit 11 includes a diode bridge D1, a diode D2, capacitors C1 and C2, a transformer T, a transistor Q (switching element), resistors R1 and R2, and a switching control unit 21.

  The AC voltage supplied from the commercial power supply AC through the power line 17 is rectified by the diode bridge D1, and then smoothed by the capacitor C1. The voltage across the capacitor C1 is 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 unit 21. When the transistor Q is turned on / off according to a control signal from the switching control unit 21, a high-frequency current flows through the primary winding of the transformer T, and a high-frequency voltage is induced in the secondary winding of the transformer T by electromagnetic coupling. The high frequency voltage induced in the secondary winding of the transformer T is rectified by the diode D2, and then smoothed by the capacitor C2, thereby generating the power supply voltage Vd. The power supply voltage Vd is supplied to the load 19.

  The power supply voltage Vd is divided by a series circuit of resistors R1 and R2. Then, the divided voltage is output to the switching control unit 21 to feed back the power supply voltage Vd to the switching control unit 21. The switching control unit 21 controls the power supply voltage Vd to be a predetermined constant voltage by changing a duty ratio for turning on and off the transistor Q so that the fed back voltage approaches a preset target value. doing.

  The load current measurement unit 13 measures the current supplied from the commercial power supply AC to the power supply unit 11 and other power supply units. That is, the load current measuring unit 13 measures the load current supplied to a load other than the fixing unit 105 used for executing the job of the image forming apparatus 1. The load current measurement unit 13 includes a current transformer CT, resistors R3 and R4, a diode bridge D3, a capacitor C3, and an analog / digital conversion unit 23. It should be noted that other current measuring means can be used in place of the current transformer CT.

  The current transformer CT is connected to the power supply line 17 and includes a primary winding and a secondary winding. A part of the power supply line 17 is a primary winding of the current transformer CT. A load current supplied to the image forming apparatus 1 flows through the power supply line 17, and the load current is converted into a minute current by the current transformer CT. A resistor R3, a diode bridge D3, a resistor R4, and a capacitor C3 are connected in parallel to the secondary winding of the current transformer CT through which a minute current flows.

  A voltage signal corresponding to a minute current is obtained by the resistor R3. Thus, the resistor R3 functions as a current-voltage converter that converts the current detected by the current transformer CT into a voltage signal and outputs the voltage signal. This voltage signal is full-wave rectified by a diode bridge D3, which is an example of a rectifier diode, and then smoothed by a capacitor C3, which is an example of a smoothing capacitor. The resistor R4 is a discharge resistor for the capacitor C3. By reducing the resistor R4, the followability of the voltage signal with respect to a change in the total current can be improved. Note that an effective value may be detected instead of smoothing by the capacitor C3.

  The voltage signal smoothed by the capacitor C3 is converted into a digital signal by the analog-to-digital converter 23. Therefore, the digital-analog converter 23 converts the voltage signal output from the resistor R3 (current-voltage converter) into a digital signal. This digital signal is sent to the total current control unit 25.

  The IH control unit 27 supplies the alternating current supplied from the commercial power supply AC through the power supply line 29 to the fixing unit 105 as a fixing current. The image forming apparatus 1 (FIG. 1) forms an image based on the image data, and the fixing unit 105 fixes the image on a sheet and outputs it. The fixing unit 105 is an IH fixing device that fixes an image on a sheet by electromagnetic induction heating. The fixing unit 105 will be described in detail. FIG. 4 is a longitudinal sectional view showing the structure of the fixing unit 105.

  The fixing unit 105 includes a heating roller 80, a heating belt 81, a fixing roller 82, a pressure roller 83, and an excitation coil 84. These extend in the direction perpendicular to the paper surface of FIG.

  An endless heating belt 81 is hung on the fixing roller 82 and the heating roller 80. Following the rotation of the fixing roller 82, the heating belt 81, the heating roller 80, and the pressure roller 83 rotate. A temperature detection element 85 is disposed in the vicinity of the fixing roller 82. The temperature detection element 85 measures the temperature of the fixing roller 82 (that is, the temperature of the fixing unit 105).

  The heating belt 81 includes a base material, a surface layer, and a release layer. The substrate includes a ferromagnetic material (eg, nickel). The surface layer is formed on the substrate and includes a thin elastic layer (for example, silicone rubber). The release layer coats the surface layer and includes, for example, PFA (polytetrafluoroethylene).

  The heating roller 80 includes a core material and a release layer (for example, PFA) formed around the core material. The core material includes a magnetic metal (for example, iron).

  The pressure roller 83 is disposed in contact with the fixing roller 82 via the heating belt 81. The paper P on which the toner image is formed is nipped by the rotating heating belt 81 and the pressure roller 83 and sent to the downstream side of the paper transport path. At the time of the nip, the paper P on which the toner image is formed is heated by the heating belt 81 and is pressed by the pressure roller 83 so that the toner image is fixed on the paper P.

  The exciting coil 84 is disposed with a predetermined gap from the portion of the heating belt 81 that is hung on the heating roller 80 and the heating roller 80.

  The induction heating in the fixing unit 105 will be briefly described. A magnetic field (alternating magnetic flux) is generated by the exciting coil 84 by passing a high-frequency current through the exciting coil 84. Due to this magnetic field, an eddy current flows through the heating roller 80 and the heating belt 81 to generate Joule heat, and the heating roller 80 and the heating belt 81 are induction-heated. Note that a halogen lamp type fixing device can also be used as the fixing unit 105.

  Returning to the description of FIG. The fixing current measuring unit 31 measures the fixing current supplied to the fixing unit 105 from the commercial power supply AC using the power line 29. The fixing voltage measuring unit 33 measures the fixing voltage supplied to the fixing unit 105 from the commercial power supply AC using the power line 29.

  In the present embodiment, the commercial power supply AC to which the power supply unit 11 and other power supply units are connected is different from the commercial power supply AC to which the IH control unit 27 is connected. For this reason, the image forming apparatus 1 uses the first internal wiring (power supply line 17 or the like) that sends the load current supplied from the first power cord connectable to the first outlet to the load other than the fixing unit 105. And a second internal wiring (power supply line 29 and the like) for sending a fixing current supplied from a second power cord connectable to the second outlet to the fixing unit 105. The maximum value of the load current is 8 A, for example, and the maximum value of the fixing current is 15 A, for example.

  Since power is supplied to the image forming apparatus 1 using two outlets, the total current input to the image forming apparatus 1 can be increased to 20 A in Japan. In the present embodiment, the current obtained by adding the fixing current and the load current is defined as the total current supplied from the commercial power supply AC to the image forming apparatus 1.

  As described above, in the present embodiment, the commercial power supply AC to which the power supply unit 11 and other power supply units are connected is different from the commercial power supply AC to which the IH control unit 27 is connected. Also good.

  The total current control unit 25 is realized by a microcomputer including a CPU, a ROM, and a RAM. The total current control unit 25 includes an allowable current calculation unit 35 and a command power calculation unit 37.

  The allowable current calculation unit 35 calculates the allowable current of the fixing unit 105, which is a value obtained by subtracting the load current from the limit value in order to control the total current below a predetermined limit value (for example, 20A). .

  The command power calculation unit 37 calculates command power to the fixing unit 105 in order to set the temperature of the fixing unit 105 to a predetermined temperature (for example, a fixing temperature). That is, the command power calculation unit 37 uses the temperature of the fixing roller 82 as the temperature of the fixing unit 105, and obtains the temperature of the fixing roller 82 from the signal indicating the temperature of the fixing roller 82 output from the temperature detection element 85. The command power calculation unit 37 calculates command power for setting the temperature to a predetermined temperature.

  The IH control unit 27 includes an allowable power calculation unit 39, a target power determination unit 41, and a fixing power control unit 43. The IH control unit 27 is realized by a microcomputer including a CPU, a ROM, and a RAM.

  The allowable power calculation unit 39 calculates the allowable power of the fixing unit 105 that is a value obtained by multiplying the allowable current calculated by the allowable current calculation unit 35 and the fixing voltage measured by the fixing voltage measurement unit 33.

  The target power determination unit 41 determines the command power as the target power to be supplied to the fixing unit 105 when the command power calculated by the command power calculation unit 37 is less than or equal to the allowable power calculated by the allowable power calculation unit 39. If the command power is larger than the allowable power, the allowable power is determined as the target power.

  The fixing power control unit 43 controls the fixing power so that the fixing power supplied to the fixing unit 105 reaches the target power determined by the target power determination unit 41.

  The current control executed by the image forming apparatus 1 according to the present embodiment will be described. FIG. 5 is a time chart showing this current control. 6 and 7 are flowcharts showing this current control.

  Referring to FIG. 5, a time chart (A) shows a change over time in the indicated power and a change over time in the allowable power, and a time chart (B) shows a change over time in the target power and the change over time in the fixing power. It shows. The time axis of the time chart (A) and the time axis of the time chart (B) are common. The interval between the alternate long and short dash lines indicates the PID control period.

  The command power is power for setting the temperature of the fixing unit 105 to a predetermined temperature (for example, a fixing temperature). The command power is calculated every predetermined first cycle (for example, 160 msec) by the command power calculation unit 37 (FIG. 3).

  The allowable power is a value obtained by multiplying the allowable current calculated by the allowable current calculating unit 35 (FIG. 3) and the fixing voltage measured by the fixing voltage measuring unit 33 (FIG. 3). The allowable current is a value obtained by subtracting the load current from the limit value in order to control the total current supplied to the image forming apparatus 1 below the limit value (for example, 20 A). The load current is a current supplied to a load other than the fixing unit 105 used for executing a job of the image forming apparatus 1.

  The allowable power is calculated by the allowable power calculation unit 39 every predetermined second period (for example, 80 msec). When the fixing power exceeds the allowable power, the total power (total current) input to the image forming apparatus 1 exceeds the limit value.

  The target power is target power supplied to the fixing unit 105. If the command power is equal to or less than the allowable power, the command power is determined as the target power, and if the command power is greater than the allowable power, the allowable power is determined as the target power.

  The fixing power is power that is actually supplied to the fixing unit 105. The fixing power control unit 43 calculates the fixing power using the fixing voltage measured by the fixing voltage measuring unit 33 and the fixing current measured by the fixing current measuring unit 31.

  The fixing power control unit 43 (FIG. 3) executes PID (proportional-integral-derivative) control and feedforward control, which are examples of feedback control, as control of the fixing current. In the PID control, the PID control period (that is, the period for calculating the PID value) is, for example, 40 msec. The fixing power control unit 43 performs PID control while setting the fixing voltage to the target voltage while comparing the fixing power with the target power.

  When executing PID control, two measures are taken in order to ensure the stability of PID control. First, as shown in (1) of the time chart (B), when the fixing power is increased to the target power after the feedforward control (time t2), the PID control is not immediately executed, but after a predetermined period has elapsed. PID control is started (for example, after the lapse of 3 × PID control cycle). The other is, as shown in (2), determining an upper limit value (for example, 300 W) of the increase amount of fixing power in one PID control cycle.

  However, as shown in (3), after the feedforward control (time t5) and before the predetermined period has elapsed (before the period of 3 × PID control cycle), in other words, the load current is reduced. If it rises, the feedforward control is immediately executed (time t6). This suppresses the total current from exceeding the limit value.

  A flow of current control executed by the image forming apparatus 1 according to the present embodiment will be described with reference to FIGS. 3, 5, and 6. The command power calculation unit 37 obtains the temperature of the fixing unit 105 from the signal indicating the temperature of the fixing unit 105 output from the temperature detection element 85. The command power calculation unit 37 calculates command power for setting the temperature to a predetermined temperature (for example, a fixing temperature) (step S1).

  On the other hand, the allowable current calculation unit 35 calculates the allowable current of the fixing unit 105 using the load current measured by the load current measurement unit 13 (step S2).

  The allowable power calculation unit 39 calculates the allowable power to the fixing unit 105, which is a value obtained by multiplying the allowable current calculated in step S2 by the fixing voltage measured by the fixing voltage measurement unit 33 (step S3). . The calculation cycle of the allowable power is the same as the second cycle (for example, 80 msec) that is the calculation cycle of the allowable current.

  The target power determination unit 41 determines whether the command power is less than or equal to the allowable power (step S4). If the target power determination unit 41 determines that the command power is equal to or less than the allowable power (Yes in step S4), the target power determination unit 41 determines the command power as the target power to be supplied to the fixing unit 105 (step S5). Referring to FIG. 5, for example, from time t0 to time t1, the command power is equal to or less than the allowable power, so command power (1300 W) is determined as the target power (1300 W).

  If the target power determination unit 41 determines that the command power is larger than the allowable power (No in step S4), the target power determination unit 41 determines the allowable power as the target power (step S6). Referring to FIG. 5, for example, from time t2 to time t3, the command power is larger than the allowable power, so that the allowable power (1100W) is determined as the target power (1100W). In steps S5 and S6, the target power is determined at the same cycle as the allowable power calculation cycle (80 msec).

  The fixing power control unit 43 controls the fixing power so that the fixing power supplied to the fixing unit 105 reaches the target power determined by the target power determination unit 41 (step S7).

  FIG. 7 is a flowchart showing control of fixing power. The fixing power control unit 43 determines whether or not the target power determined by the target power determination unit 41 is smaller than the target power previously determined by the target power determination unit 41 (step S11). The target power is determined in the same cycle as the allowable power calculation cycle (80 msec). Therefore, the target power determined last time means the target power determined 80 msec before.

  When the target power determined by the target power determination unit 41 is not decreased by the fixing power control unit 43 compared to the target power previously determined by the target power determination unit 41, that is, the same or increased. If determined (No in step S11), the fixing power control unit 43 executes PID control, which is an example of feedback control, as the fixing power control (step S12). Referring to FIG. 5, for example, since the target power increases from 1000 W to 1200 W at time t4, PID control is executed from time t4 as the fixing power control.

  If the fixing power control unit 43 determines that the target power determined by the target power determination unit 41 has decreased compared to the target power previously determined by the target power determination unit 41 (Yes in step S11). The process proceeds to step S13.

  In step S <b> 13, the fixing power control unit 43 determines whether or not the reduction amount of the target power exceeds a predetermined value (for example, 100 W).

  If the fixing power control unit 43 determines that the reduction amount of the target power exceeds the predetermined value (Yes in step S13), the fixing power control unit 43 executes feedforward control as the fixing power control (step S14). ). Referring to FIG. 5, for example, at time t5, the target power decreases from 1300 W to 1000 W. Therefore, as control of fixing power, feedforward control is executed at time t5, and fixing power is reduced to 900 W. Yes.

  If the fixing power control unit 43 determines that the reduction amount of the target power does not exceed a predetermined value (No in step S13), the fixing power control unit 43 executes PID control as the fixing power control (step S12). Referring to FIG. 5, for example, at time t3, the target power decreases from 1100 W to 1000 W, so PID control is executed from time t3 as the fixing power control.

  The main effects of this embodiment will be described. In this embodiment, a value obtained by subtracting the load current measured by the load current measuring unit 13 from the limit value (for example, 20 A) of the total current input to the image forming apparatus 1 is set as the allowable current of the fixing unit 105. A value obtained by multiplying the allowable current by the fixing voltage measured by the fixing voltage measuring unit 33 is used as the allowable power of the fixing unit 105.

  The instructed instruction power to be supplied to the fixing unit 105 by the instruction power calculating unit 37 should be the target power of the fixing unit 105. However, since the load current is relatively large, if the command power is set to the target power, if the total current exceeds the limit value, the allowable power that is lower than the command power is set as the target power.

  That is, according to the present embodiment, if the command power is equal to or less than the allowable power (Yes in step S4), the total power does not exceed the limit value even if the command power is the target power, so the command power is determined as the target power. (Step S5). On the other hand, if the command power is larger than the allowable power (No in step S4), if the command power is set as the target power, the total current exceeds the limit value, so the allowable power is determined as the target power (step S6).

  In this case, the target power is lower than the command power. However, in this embodiment, as described above, the value obtained by subtracting the load current from the limit value is used as the allowable current of the fixing unit 105, and the value obtained by multiplying the allowable current and the fixing voltage is used as the allowable power of the fixing unit 105. Yes. Accordingly, when the allowable power is determined as the target power, the total current input to the image forming apparatus 1 can be used up to the limit value, and therefore the total current input to the image forming apparatus 1 from the commercial power supply AC is limited. It is possible to supply power to the fixing unit 105 to the maximum while suppressing exceeding the value.

  This effect will be described with reference to FIGS. FIG. 8 is a graph showing an example of the relationship among total power, fixing power, and load power in the present embodiment when the target power is allowable power. FIG. 9 is a graph showing an example of the relationship between the total power, the fixing power, and the load power in the comparative example. 8 and 9, the horizontal axis indicates time, and the vertical axis indicates power. In both of the present embodiment and the comparative example, the limit value of the total power input to the image forming apparatus 1 is set to 1500 W.

  As shown in FIG. 9, in the comparative example, the fixing power is fixed, and the fixing power is set so that the total power does not exceed the limit value even if the load power increases. For this reason, as indicated by diagonal lines, there is a period in which the total power is not used up to the limit value.

  On the other hand, in this embodiment, as shown in FIG. 8, when the target power is allowable power, the fixing power is increased or decreased according to the increase or decrease of the load power so that the total power becomes the limit value. ing. Therefore, there is no period in which the total power is not used up to the limit value. As described above, according to this embodiment, it is possible to supply power to the fixing unit 105 to the maximum while suppressing the total power (total current) input from the commercial power supply AC to the image forming apparatus 1 from exceeding the limit value. Can be.

  Moreover, this embodiment has the following effects. The target power determined by the target power determination unit 41 is smaller than the target power previously determined by the target power determination unit 41 (Yes in step S11), and the amount of decrease exceeds a predetermined value. If so (Yes in step S13), feedforward control is executed as control of the fixing power (step S14). In feedback control such as PID control, it takes a relatively long time to reach the target power. Therefore, if the decrease amount exceeds a predetermined value (that is, if the decrease amount is relatively large), in PID control, the total current exceeds the limit value during the period required to reach the target power. There is a possibility. On the other hand, according to the feedforward control, the fixing power can be immediately reduced below the target power, so that the total current does not exceed the limit value.

  Note that feedback control can also be used instead of feedforward control. In this case, since it is necessary to consider the time required to control the fixing power to the target power by feedback control, the allowable current calculation unit 35 sets the limit value to a value lower than the regulation value (20A) (for example, 19. Set to 5A). This prevents the total current from exceeding the regulation value.

  On the other hand, if the amount of decrease does not exceed a predetermined value (No in step S13), PID control is executed as control of fixing power. When the amount of decrease does not exceed a predetermined value (that is, when the amount of decrease is relatively small), even in PID control, the period required to reach the target power is short, so the total current is limited during that period. This is because the value is never exceeded. By performing PID control, the fixing power supplied to the fixing unit 105 can be accurately adjusted to the target power.

  Further, according to the present embodiment, if the target power determined by the target power determination unit 41 is larger than the target power previously determined by the target power determination unit 41 (No in step S11), the fixing is performed. PID control is executed as power control (step S12). Thus, when the target current is increased, the total current can be prevented from exceeding the limit value.

  Since the allowable power is a value obtained by multiplying the allowable current (= limit value−load current) and the fixing voltage, when the allowable power is determined as the target power, the total current obtained by adding the load current and the allowable current is the total. The total current becomes a limit value. For this reason, if the load current increases, the total current exceeds the limit value.

  According to the present embodiment, as shown in FIG. 5, the allowable power calculation unit 39 calculates the allowable power in a cycle (80 msec) shorter than the cycle (160 msec) in which the command power calculation unit 37 calculates the command power. . Therefore, when the instruction power is calculated and the load power increases until the next instruction power is calculated, the allowable power can be reduced when the allowable power that is the target power must be reduced. Can be prevented from exceeding the limit value.

  Further, according to the present embodiment, a value obtained by subtracting the load current from the limit value of the total current is set as the fixing current. For this reason, since the total current can be set to the limit value, the printing speed of the image forming apparatus 1 can be improved and the warm-up time can be shortened.

  Further, according to the present embodiment, the fixing current is increased or decreased according to the increase or decrease of the load current so that the total current does not exceed the limit value. For this reason, (1) when the image forming apparatus 1 is mass-produced, it is possible to eliminate the need to secure a total current margin in consideration of the variation inherent in each part of the image forming apparatus 1, and (2) image formation. Even when an optional function (such as a staple function) is combined with the apparatus, the total current can be prevented from exceeding the limit value. (3) Robust design of the image forming apparatus 1 (operation mode and use of the image forming apparatus 1) Design that is not affected by the environment).

1 Image forming apparatus 17 power line (an example of first internal wiring)
29 Power line (example of second internal wiring)
AC commercial power

Claims (4)

An image forming apparatus that forms an image based on image data, fixes the image on a sheet, and outputs the image.
A fixing unit for fixing the image on the paper;
A load current measuring unit that measures a load current supplied to a load other than the fixing unit used for execution of a job of the image forming apparatus;
A current obtained by adding the fixing current supplied to the fixing unit and the load current is defined as a total current supplied from the commercial power source to the image forming apparatus, and the total current is equal to or less than a predetermined limit value. In order to control the allowable current calculation unit for calculating the allowable current of the fixing unit, which is a value obtained by subtracting the load current from the limit value;
A fixing voltage measuring unit for measuring a fixing voltage supplied to the fixing unit;
An allowable power calculation unit that calculates an allowable power of the fixing unit, which is a value obtained by multiplying the allowable current and the fixing voltage;
An instruction power calculation unit for calculating instruction power to the fixing unit in order to set the temperature of the fixing unit to a predetermined temperature;
If the command power is less than or equal to the allowable power, the target power is determined as a target power to be supplied to the fixing unit, and if the command power is greater than the allowable power, the target power is determined as the target power. A power determination unit;
A fixing power control unit that controls the fixing power so that the fixing power supplied to the fixing unit reaches the target power determined by the target power determination unit ,
The allowable power calculation unit is an image forming apparatus that calculates the allowable power in a cycle shorter than a cycle in which the command power calculation unit calculates the command power .   If the target power determined by the target power determination unit is reduced compared to the target power previously determined by the target power determination unit, and the amount of decrease exceeds a predetermined value, The fixing power control unit executes feedforward control as control of the fixing power, and executes feedback control as control of the fixing power if the reduction amount does not exceed the predetermined value. Item 2. The image forming apparatus according to Item 1.   If the target power determined by the target power determination unit is larger than the target power previously determined by the target power determination unit, the fixing power control unit controls the fixing power. The image forming apparatus according to claim 1, wherein feedback control is executed as A first internal wiring for sending the load current supplied from a first power cord connectable to a first outlet to a load other than the fixing unit;
Image according to any one of claims 1 to 3 having the the fixing current the fixing portion to send the second inner wire supplied from the second power cord connectable to the second outlet, the Forming equipment.

Images