Image forming device

Abstract

To provide an image forming apparatus that can supply the maximum power to a fixing device, while surely preventing a total current input to the image forming apparatus from exceeding a limit value.SOLUTION: An image forming apparatus comprises: image forming units; a fixing device; a power supply unit; and a control unit. The fixing device includes a heated rotating body and a pressure rotating body, a heating unit that heats the heated rotating body, and a temperature detection unit that detects a temperature of the heated rotating body. The power supply unit supplies power to the entire image forming apparatus including the fixing device. When an apparatus total current Im(n) exceeds a total current threshold Ithresh lower than a rated current Imax by a predetermined value α, the control unit sets a fixing upper limit current Q(n) through total current threshold control so that the apparatus total current Im(n) does not exceed the rated current Imax, and corrects the fixing upper limit current Q(n) in a plurality of steps on the basis of, a power margin of the image forming apparatus.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus equipped with a fixing device, such as a copying machine, a printer, a facsimile machine, or a combination machine thereof, and more particularly to a method for efficiently supplying power to the fixing device. [Background technology]

[0002] In order to fix a toner image on paper in an image forming apparatus, a fixing device equipped with a fixing member formed by pressing a fixing roller or fixing belt (a heated rotating body) and a pressure roller (a pressure rotating body) is widely used. In this fixing device, a recording material such as paper is passed through a fixing nip formed by a heating roller and a pressure roller, and heat and pressure are applied to the toner image to melt and fix the toner image on the recording material.

[0003] In response to the recent demand for power saving, it is important for the fixing device to be able to warm up in a short time. In addition, the fixing device needs to heat the fixing member by the heating section and further heat the recording material using the fixing member, so the proportion of the power consumption of the fixing device in the entire image forming apparatus becomes large.

[0004] On the other hand, image forming devices must be designed to operate within the rated power (rated current, rated voltage) as an electrical condition. For example, in the case of a 100V AC commercial power source, the regulated current value in Japan is set at 15A, and a current exceeding 15A cannot be used. For this reason, a limit is set on the total current that can be input from the commercial power source to the image forming device.

[0005] Therefore, in order to improve warm-up performance, fixing performance, and image formation efficiency (productivity), it is necessary to allocate as much power as possible to the fixing device, within a range in which the total current of the image forming apparatus does not exceed a limit value.

[0006] For example, Patent Document 1 discloses an image forming apparatus including a second current detection unit that detects a current value supplied to an excitation coil of an induction heating type fixing device, a fixing current calculation unit that feeds back the current value detected by the second current detection unit and calculates a current value to be supplied to the excitation coil with the rated current value of the commercial power source as a target value, an allowable current calculation unit that calculates a current value to be supplied to the excitation coil by subtracting the rated current value of the commercial power source from the total drive current value of the entire apparatus from the current value detected by the second current detection unit, an IH control unit that calculates a frequency corresponding to the current values ​​calculated by the fixing current calculation unit and the allowable current calculation unit, and a switching unit that switches whether to have the fixing current calculation unit or the allowable current calculation unit calculate the current value to be supplied to the excitation coil depending on the total drive current value.

[0007] Patent Document 2 discloses an image forming apparatus including an instruction power calculation unit that calculates an instruction power to the fixing unit to set the temperature of the fixing unit to a predetermined temperature; an allowable current calculation unit that calculates an allowable current for the fixing unit, which is the sum of the fixing current and the load current, as the total current input to the image forming apparatus from the commercial power source, and calculates the allowable current for the fixing unit, which is the limit value minus the load current, in order to control the total current to be equal to or less than the limit value; an allowable power calculation unit that calculates the allowable power, which is the multiplication of the allowable current and the fixing voltage; and a target power determination unit that determines the instruction power as a target power if the instruction power is equal to or less than the allowable power, and determines the allowable power as the target power if the instruction power is greater than the allowable power. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2012-173364 A [Patent Document 2] JP 2015-191134 A Summary of the Invention [Problem to be solved by the invention]

[0009] Even in cases where the fixing current is controlled by detecting the total current input to the image forming apparatus, the fixing current allocated to the fixing device, and the secondary current allocated to devices other than the fixing device, as in Patent Documents 1 and 2, the time-series load operation of the image forming apparatus is not always the same, so the control of the fixing current has an aspect of predictive control.

[0010] Therefore, when the total current input to the image forming device is close to the limit value and there is no room for improvement, if an attempt is made to allocate as much of the fixing current as possible to the fixing device, there is a risk that the total current will exceed the limit value in the short term depending on the load operation status other than that of the fixing device.

[0011] In view of the above problems, the present invention aims to provide an image forming apparatus that can supply maximum power to a fixing device while reliably preventing the total current input to the image forming apparatus from exceeding a limit value. [Means for solving the problem]

[0012] In order to achieve the above object, a first configuration of the present invention is an image forming apparatus including an image forming section, a fixing device, a power supply section, and a control section. The image forming section forms a toner image on a recording medium. The fixing device includes a heated rotating body, a pressure rotating body that is pressed against the heated rotating body at a predetermined fixing nip pressure to form a fixing nip section, a heating section that heats the heated rotating body, and a temperature detection section that detects the temperature of the heated rotating body, and performs a fixing process in which a toner image is fixed to the recording medium by heating and pressurizing the recording medium passing through the fixing nip section. The power supply section is connected to a commercial power source and supplies power to the entire image forming apparatus including the fixing device. The control section determines the fixing current Ifuser flowing through the heating section to be the current command value Iht(n) when the current command value Iht(n) determined based on the detection result of the temperature detection section is equal to or less than the fixing upper limit current Q(n), and determines the fixing current Ifuser to be the fixing upper limit current Q(n) when the current command value Iht(n) is greater than the fixing upper limit current Q(n). When the total device current Im(n) during image formation exceeds a total current threshold Ithresh that is lower than the rated current Imax of the image forming device by a predetermined value α, the control unit sets an upper fixing current Q(n) by total current threshold control so that the total device current Im(n) does not exceed the rated current Imax, and corrects the upper fixing current Q(n) in multiple stages based on the power margin of the image forming device. Effect of the Invention

[0013] According to the first aspect of the present invention, the correction amount in the total current threshold control when the total device current Im(n) exceeds the total current threshold Ithresh is set in multiple stages according to the power margin, thereby providing a power control system that keeps the current allocable to the fixing device as large as possible while preventing the total device current Im(n) from exceeding the rated current Imax. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an internal structure of an image forming apparatus 100 according to an embodiment of the present invention. [Diagram 2] A side cross-sectional view of a fixing device 13 mounted in an image forming apparatus 100. [Diagram 3] A block diagram showing an example of a control path of the image forming apparatus 100. [Figure 4] FIG. 1 is a block diagram showing an example of a power control system for an image forming apparatus according to a first embodiment of the present invention. [Diagram 5] 1 is a flowchart showing a first control example of current control executed in the image forming apparatus 100 according to the first embodiment; [Figure 6] FIG. 13 is a diagram showing the fixing current Ifuser and the secondary current Ieng(n) under conditions 1 to 5 in which the total device current Im(n) is different in the first control example. [Figure 7] 11 is a flowchart showing a second control example of the current control executed in the image forming apparatus 100 according to the first embodiment. [Figure 8] 11 is a flowchart showing a third example of the current control executed in the image forming apparatus 100 according to the first embodiment. [Figure 9] FIG. 13 is a diagram showing the fixing current Ifuser and the secondary current Ieng(n) under conditions 1 to 5 in which the total device current Im(n) is different in the third control example. [Figure 10] FIG. 11 is a block diagram showing an example of a power control system for an image forming apparatus 100 according to a second embodiment of the present invention. [Figure 11] 11 is a flowchart showing a fourth control example of the current control executed in the image forming apparatus 100 according to the second embodiment. [Figure 12] FIG. 12 is a diagram showing the fixing upper limit current Q(n) and the secondary side current Ieng(n) under conditions 1 to 4 in which the total device current Im(n) is different in the control example of FIG. 11. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a schematic cross-sectional view showing the internal structure of an image forming apparatus 100 according to one embodiment of the present invention. Inside the main body of the image forming apparatus 100 (here, a color printer), four image forming sections Pa, Pb, Pc, and Pd are arranged in order from the upstream side in the transport direction (the right side in Fig. 1). These image forming sections Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and sequentially form images of cyan, magenta, yellow, and black through the respective processes of charging, exposure, development, and transfer.

[0016] In these image forming units Pa to Pd, photoconductor drums (image carriers) 1a, 1b, 1c, and 1d that carry visible images (toner images) of each color are disposed. Furthermore, an intermediate transfer belt 8 that rotates in a clockwise direction in FIG. 1 is provided adjacent to each image forming unit Pa to Pd. The toner images formed on these photoconductor drums 1a to 1d are sequentially primarily transferred and superimposed on the intermediate transfer belt 8 that moves while abutting against each of the photoconductor drums 1a to 1d. Thereafter, the toner images primarily transferred onto the intermediate transfer belt 8 are secondarily transferred onto a sheet S, which is an example of a recording medium, by a secondary transfer roller 9. Furthermore, the sheet S onto which the toner image has been secondarily transferred is discharged from the main body of the image forming apparatus 100 after the toner image is fixed by a fixing device 13. An image forming process for each of the photoconductor drums 1a to 1d is performed while the photoconductor drums 1a to 1d are rotated counterclockwise in FIG. 1 by a main motor 40 (see FIG. 3).

[0017] The paper S onto which the toner image is secondarily transferred is stored in a paper cassette 16 arranged at the bottom of the main body of the image forming apparatus 100, and is transported to a nip between a secondary transfer roller 9 and a drive roller 11 of the intermediate transfer belt 8 via a paper feed roller 12a and a pair of registration rollers 12b. A sheet made of a dielectric resin is used for the intermediate transfer belt 8, and a seamless belt is mainly used. In addition, a blade-shaped belt cleaner 19 is arranged downstream of the secondary transfer roller 9 to remove toner and the like remaining on the surface of the intermediate transfer belt 8.

[0018] Next, the image forming units Pa to Pd will be described. Around and below the rotatably arranged photoconductor drums 1a to 1d, there are provided charging devices 2a, 2b, 2c, and 2d that charge the photoconductor drums 1a to 1d, an exposure device 5 that exposes image information onto each of the photoconductor drums 1a to 1d, developing devices 3a, 3b, 3c, and 3d that form toner images on the photoconductor drums 1a to 1d, and cleaning devices 7a, 7b, 7c, and 7d that remove developer (toner) and the like remaining on the photoconductor drums 1a to 1d.

[0019] When image data is input from a host device such as a personal computer, first, the surfaces of the photoconductor drums 1a-1d are uniformly charged by the charging devices 2a-2d. Next, the exposure device 5 irradiates light according to the image data, and electrostatic latent images corresponding to the image data are formed on the photoconductor drums 1a-1d. The developing devices 3a-3d are filled with a predetermined amount of two-component developer containing toner of each color of cyan, magenta, yellow, and black. When the ratio of toner in the two-component developer filled in each developing device 3a-3d falls below a specified value due to the formation of a toner image described later, toner is replenished from the toner containers 4a-4d to each developing device 3a-3d. The toner in the developer is supplied onto the photoconductor drums 1a-1d by the developing devices 3a-3d and electrostatically adheres to them. As a result, a toner image corresponding to the electrostatic latent image formed by exposure from the exposure device 5 is formed.

[0020] Then, an electric field is applied between the primary transfer rollers 6a-6d and the photoconductor drums 1a-1d by the primary transfer rollers 6a-6d at a predetermined transfer voltage, and the cyan, magenta, yellow and black toner images on the photoconductor drums 1a-1d are primarily transferred onto the intermediate transfer belt 8. These four color images are formed with a predetermined positional relationship for forming a predetermined full-color image. After that, in preparation for the subsequent formation of a new electrostatic latent image, the toner and the like remaining on the surfaces of the photoconductor drums 1a-1d after the primary transfer are removed by the cleaning devices 7a-7d.

[0021] The intermediate transfer belt 8 is stretched over a driven roller 10 on the upstream side and a driving roller 11 on the downstream side, and when the intermediate transfer belt 8 starts to rotate clockwise with the rotation of the driving roller 11 by a belt driving motor (not shown), the paper S is transported at a predetermined timing from the registration roller pair 12b to a nip portion (secondary transfer nip portion) between the driving roller 11 and a secondary transfer roller 9 provided adjacent thereto, and the full-color image on the intermediate transfer belt 8 is secondarily transferred onto the paper S. The paper S to which the toner image has been secondarily transferred is transported to a fixing device 13.

[0022] The paper S conveyed to the fixing device 13 is heated and pressurized by a fixing belt 21 and a pressure roller 22 (see FIG. 2) to fix the toner image onto the surface of the paper S, and a predetermined full-color image is formed. The paper S on which the full-color image has been formed is then redirected by a branching section 14 that branches into multiple directions, and is discharged directly to a discharge tray 17 by a pair of discharge rollers 15 (or after being sent to a double-sided conveying path 18 and having images formed on both sides).

[0023] Fig. 2 is a side cross-sectional view of fixing device 13 mounted on image forming apparatus 100. The upper side in Fig. 2 is the downstream side in the paper insertion direction (transport direction) relative to fixing device 13, and the lower side is the upstream side in the paper insertion direction relative to fixing device 13. As shown in Fig. 2, fixing device 13 includes fixing belt 21 (heated rotatable member), pressure roller 22 (pressurizing rotatable member), heating section 23, nip forming member 24, belt guide 25, and frame member 26.

[0024] Fixing belt 21 is supported rotatably about a horizontal axis by a housing (not shown) of fixing device 13. Fixing belt 21 is endless and configured in a cylindrical shape with an outer diameter of 20 mm to 50 mm, for example, and has approximately the same axial length (width direction length of paper S) as pressure roller 22. Fixing belt 21 rotates in the clockwise direction in FIG. 2 along the insertion direction of paper S, which is a recording medium.

[0025] The fixing belt 21 has a laminated structure in which an elastic layer and a release layer are laminated on the outer periphery of a heat generating layer, which is a base layer. The heat generating layer is made of a metal film such as nickel having a thickness of 30 μm to 50 μm, or a polyimide film having a thickness of 50 μm to 100 μm containing metal powder such as copper, silver, or aluminum. The elastic layer is made of silicone rubber having a thickness of 100 μm to 500 μm. The release layer is made of a fluorine-based resin such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) having a thickness of 30 μm to 50 μm.

[0026] Pressure roller 22 is supported on the housing of fixing device 13 so as to be rotatable about a horizontal axis. Pressure roller 22 is cylindrical, and has approximately the same axial length (widthwise length of paper S) as fixing belt 21. A predetermined pressure is applied to pressure roller 22 by pressure mechanism 30 (see FIG. 3) toward fixing belt 21. The outer circumferential surface of pressure roller 22 is pressed against the outer circumferential surface of fixing belt 21 by pressing nip forming member 24 through fixing belt 21, thereby forming fixing nip portion N.

[0027] The pressure roller 22 is connected to a fixing drive motor 45 (see FIG. 3) and rotates in a counterclockwise direction in FIG. 2. The pressure roller 22 contacts the outer peripheral surface of the fixing belt 21 and applies a rotational drive force to the fixing belt 21 in the clockwise direction.

[0028] The pressure roller 22 has a laminated structure in which an elastic layer 22b is laminated on the outer periphery of a core metal 22a, and a release layer (not shown) is laminated on the surface of the elastic layer 22b. The core metal 22a is made of a metal such as aluminum with a diameter of about 20 mm. The elastic layer 22b is made of silicone rubber with a thickness of about 8 mm. The release layer is made of a fluorine-based resin such as PFA with a thickness of about 10 μm to 50 μm.

[0029] Heating unit 23 is an induction heating (IH) type heater that generates heat in the heat generating layer of fixing belt 21 by induction heating, and is disposed facing the outer circumferential surface of fixing belt 21 across a predetermined gap in an area opposite to the side of fixing belt 21 where pressure roller 22 is disposed. Heating unit 23 extends slightly longer than fixing belt 21 along the axial direction of fixing belt 21 (the width direction of paper S, the direction perpendicular to the paper surface of FIG. 2). The temperature of fixing belt 21 is detected by a thermistor 47 (see FIG. 3).

[0030] The heating unit 23 heats the fixing belt 21. It includes an exciting coil 23a, a holding member, a core, etc. (not shown). The exciting coil 23a and the core are held in a predetermined position by the holding member. The exciting coil 23a is made of a Litz wire made of a bundle of multiple conductive wires, and is wound so as to extend along the axial direction of the fixing belt 21. The exciting coil 23a is configured in an arc shape along the outer circumferential surface of the fixing belt 21 in the circumferential direction of the fixing belt 21.

[0031] The nip forming member 24 is disposed on the inside of the fixing belt 21, facing the pressure roller 22 across the fixing belt 21. The nip forming member 24 contacts the inner circumferential surface of the fixing belt 21, and forms a fixing nip portion N between the fixing belt 21 and the pressure roller 22.

[0032] The nip forming member 24 has a generally rectangular parallelepiped shape that extends along the axial direction of the fixing belt 21 with substantially the same length as the fixing belt 21. The nip forming member 24 has a base material made of a metal such as aluminum or a heat-resistant resin such as a liquid crystal polymer.

[0033] The belt guide 25 is disposed on the inside of the fixing belt 21, facing the heating unit 23 across the fixing belt 21. The belt guide 25 contacts the inner peripheral surface of the fixing belt 21 except for the fixing nip portion N, and supports the fixing belt 21 from the inside. The belt guide 25 is made of a metal plate that extends along the axial direction of the fixing belt 21 and has substantially the same length as the fixing belt 21. The belt guide 25 is made of an elastic magnetic metal such as SUS430 having a thickness of 0.1 mm to 0.5 mm.

[0034] The frame member 26 is supported by a housing portion of the fixing device 13, and holds the nip forming member 24 and the belt guide 25. The frame member 26 is disposed at approximately the center in the radial direction of the fixing belt 21, between the belt guide 25 and the nip forming member 24. The frame member 26 extends slightly longer than the fixing belt 21 along the axial direction of the fixing belt 21.

[0035] A fixing entrance guide 27 is disposed upstream of the fixing nip N in the paper insertion direction (lower side in FIG. 2). The fixing entrance guide 27 guides the paper S that has passed through the secondary transfer nip (see FIG. 1) to the fixing nip N.

[0036] A separation claw 29 is disposed downstream of the fixing nip N in the paper insertion direction (upper side in FIG. 2). The separation claw 29 separates the paper S after fixing processing from the surface of the fixing belt 21. The separation claw 29 is disposed at a predetermined angle such that its tip faces upstream with respect to the rotation direction of the fixing belt 21 (counter direction) and its tip approaches the outer circumferential surface of the fixing belt 21.

[0037] 3 is a block diagram showing an example of a control path of the image forming apparatus 100. Since various controls are performed on each part of the image forming apparatus 100 when it is used, the following description will focus on the parts of the control path that are necessary for implementing the present invention. Also, the description of the parts that have already been described will be omitted.

[0038] The low-voltage power supply 52 is connected to the power supply unit 51, and distributes the power supplied from the power supply unit 51 to each unit of the device in response to an output signal from the control unit 90. Specifically, it distributes a part of the AC voltage supplied from the power supply unit 51 directly to a fixing power control board 53 (see FIG. 4). It also generates a predetermined DC voltage from the remaining AC voltage and distributes it to a secondary load 60 (see FIG. 4). The power control system of the image forming apparatus 100 including the power supply unit 51 and the low-voltage power supply 52 will be described later.

[0039] The image input unit 70 is a receiving unit that receives image data transmitted from a personal computer or the like to the image forming apparatus 100. The image signal input from the image input unit 70 is converted into a digital signal and then sent to the temporary storage unit 94.

[0040] The operation unit 80 is provided with a liquid crystal display unit 81 and LEDs 82 that indicate various states, and is configured to indicate the state of the image forming apparatus 100, the image formation status, and the number of copies to be printed. In addition, the type and size of the paper S can be input by specifying the paper cassette 16 or manual paper feed tray (not shown) from which the paper S is fed from the operation unit 80. Various settings of the image forming apparatus 100 are made from the printer driver of the personal computer.

[0041] The control unit 90 at least includes a CPU (Central Processing Unit) 91 as a central processing unit, a ROM (Read Only Memory) 92 which is a read-only memory unit, a RAM (Random Access Memory) 93 which is a readable and writable memory unit, a temporary memory unit 94 which temporarily stores image data, etc., a counter 95, and multiple (here, two) I / Fs (interfaces) 96 which send control signals to each device within the image forming apparatus 100 and receive input signals from the operation unit 70.

[0042] The ROM 92 stores data such as a control program for the image forming apparatus 100, numerical values ​​necessary for control, and data that will not be changed during use of the image forming apparatus 100. The RAM 93 stores necessary data generated during the control of the image forming apparatus 100, data temporarily required for the control of the image forming apparatus 100, and the like.

[0043] The temporary storage unit 94 temporarily stores the image signal that is input from the image input unit 60 and converted into a digital signal. The counter 95 cumulatively counts the number of printed sheets.

[0044] 4 is a block diagram showing an example of a power control system of the image forming apparatus 100 according to the first embodiment of the present invention. The power control system of the image forming apparatus 100 according to the first embodiment includes a power supply unit 51, a low-voltage power supply 52, a fixing power control board 53, a CT board 57, and a control unit 90.

[0045] The power supply unit 51 is connected to a commercial power source AC via an inlet (not shown), and supplies AC voltage from the commercial power source AC to the low-voltage power source 52. A power control circuit 50 is connected to the low-voltage power source 52. The low-voltage power source 52 distributes a part of the AC voltage supplied from the power supply unit 51 directly to a fixing power control board 53. In addition, the low-voltage power source 52 generates a predetermined DC voltage from the remaining AC voltage and distributes it to a secondary load 60.

[0046] The fixing power control board 53 includes a current detection circuit that detects the AC current input to the fixing power control board 53 from the low-voltage power supply 52, and controls the current (fixing current) flowing through the fixing device 13 (particularly the heating unit 23) based on the fixing power determined by the control unit 90. Specifically, when the heating unit 23 is of the induction heating (IH) type as shown in FIG. 2, the control unit 90 monitors the current detected by the CT board 57 and compares it with the current command value (Iht(n)) based on the temperature control by the thermistor 47 to determine the fixing power. The fixing power control board 53 changes the driving frequency of the AC current input to the excitation coil 23a so as to stably maintain the fixing power determined by the control unit 90. As the actually flowing fixing current (Ifuser), the smaller of the upper limit fixing current Q(n) and the current command value Iht(n) commanded by the temperature control is selected. In addition, when a CPU or the like is mounted on the fixing power control board 53, it is also possible to obtain only the power instruction value (Iht(n)) from the control unit 90 and monitor the fixing voltage and fixing current within the fixing power control board 53 to control the power.

[0047] Control unit 90 directly controls a current (secondary current) input to secondary load 60 used to execute a printing operation in image forming apparatus 100. Note that secondary load 60 here refers to a load other than fixing device 13 (a load different from fixing device 13), and means, for example, a motor, solenoid, etc. used to drive image forming units Pa to Pd, paper transport mechanism 61 from paper cassette 16 to discharge roller pair 15 (see FIG. 1), etc.

[0048] The CT (Current Transformer) board 57 detects the current (total device current Im(n)) supplied from the commercial power source AC via the power supply unit 51 to the low-voltage power source 52. That is, the CT board 57 functions as a total current detection unit that detects the total device current Im(n) used to drive the image forming apparatus 100. Note that instead of the CT board 57, another current detection mechanism may be used.

[0049] Next, a description will be given of the current control executed in the image forming apparatus 100 according to the first embodiment of the present invention. First, an example will be described in which an induction heating (IH) heater with a rated voltage of 100 V and a rated current of 15 A is used as the heating section 23 of the fixing device 13. In this configuration, the upper limit fixing current Q(n) is determined by two-stage control, that is, PID control (hereinafter referred to as total current PID control) and threshold control based on a threshold value of the device total current (total current threshold value).

[0050] When an induction heating (IH) heater is used, power control is based on PID control (hereinafter referred to as power PID control), but when the image forming apparatus 100 is started up, power table control is performed based on a power table of frequency-power characteristics, and then power PID control is performed. Specifically, PID control of the IH drive frequency is performed so that the specified IH power level is reached. On the other hand, when the total current threshold is exceeded by a large amount and the upper limit fixing current value Q(n) becomes smaller than the specified current value Iht(n), it is necessary to quickly reduce the fixing current to the Q(n) level.

[0051] In this case, if the IH power is varied by power PID control, the time response is slow, so by temporarily switching from power PID control to power table control, the fixing current and the total device current Im(n) can be quickly reduced. However, power table control has a lower control accuracy for the commanded IH power level than power PID control, and the difference between the final fixing current (Ifuser) and the current command value Iht(n) tends to be large.

[0052] Therefore, if power table control occurs frequently, the range of change in the fixing current and power per unit time increases, making the current control itself unstable. In addition, the amount of fluctuation in the total device current Im(n) also increases, and there are cases in which the target of (total current < rated current) cannot be achieved.

[0053] Therefore, in the first control example of this embodiment, the power control when using an induction heating (IH) heater is a two-stage control consisting of total current PID control and total current threshold control, thereby reducing the frequency of total current threshold control and reducing the number of times that IH power control switches to power table control, thereby preventing the power control from becoming unstable.

[0054] Hereinafter, a specific procedure for current control will be described when an induction heating (IH) heater is used as the heating unit 23. Fig. 5 is a flowchart showing a first control example of current control executed in the image forming apparatus 100 of the first embodiment. Fig. 6 is a diagram showing the fixing current and the secondary side current under conditions 1 to 5 in which the device total current Im(n) is different in the first control example.

[0055] As a premise for the current control described below, the detection of the total device current Im(n) by the CT board 57 is performed by detecting the current at a cycle of 2 to 2.5 msec and averaging the detected current value every 40 msec. Also, the variable instruction cycle of the fixing upper limit current Q(n) by the control unit 90 is set to 80 msec, and the cycle of the power control (power PID control, power table control) of the heating unit 23 is set to 40 msec.

[0056] Also, the maximum value Qmax of the fixing upper limit current is defined within a range that does not exceed the rated current Imax even when the secondary load 60 is operating at maximum with no option device attached to the image forming apparatus 100. And in the following current control, Qmax is used as the maximum current that can be supplied to the fixing device 13, and the fixing upper limit current Q(n) is corrected to decrease according to the excess current amount of the total device current Im(n) so as to ensure Im(n) < Imax.

[0057] As shown in FIG. 5, first, the CT substrate 57 detects the total device current Im(n) (step S1). Next, the control unit 90 determines whether Im(n) is less than or equal to the total current threshold Ithresh (step S2). Ithresh is a current value that is lower than the rated current Imax by a predetermined value α1 (total current threshold margin, α1 < γ).

[0058] When Im(n) ≤ Ithresh (Yes in step S2), the control unit 90 calculates Q(n) so that Im(n) becomes the target value Ipid of the total current in the total current PID control (step S3). Ipid is a current value that is lower than the rated current Imax by a predetermined value γ (total current target value margin), and Ithresh > Ipid.

[0059] Conditions 1 to 3 in FIG. 6 show the fixing current Ifuser (hatched area) and the secondary side current Ieng(n) (white area) when Im(n) ≤ Ithresh. As the actual fixing current Ifuser, the smaller value between the current instruction value Iht(n) and the fixing upper limit current Q(n) is selected. Condition 1 shows the case where Iht(n) is selected as Ifuser (Iht(n) < Q(n) = Qmax), and condition 2 shows the case where Q(n) is selected as Ifuser (Q(n) = Qmax).

[0060] Even when Im(n) exceeds Ipid as in the left graph of condition 3, PID calculation of Q(n) is performed with Ipid as the target value so that Im(n) approaches Ipid through total current PID control within the range of Im(n)≦Ithresh. In the right graph, Im(n) has fallen to Ipid. However, although the PID calculation has Ipid as the target, the calculation result does not necessarily become Ipid. In this way, when Im(n) is equal to or less than Ithresh, PID control is performed with Ipid as the target value to determine Q(n), which can significantly reduce the frequency with which Im(n) exceeds Ithresh.

[0061] If Im(n)>Ithresh (No in step S2), the total current PID control is switched to the total current threshold control. Specifically, the excess current value (Im(n)-Ithresh) from the total current threshold is calculated (step S4).

[0062] Then, a provisional upper limit value Q'(n) is calculated by subtracting the excess current value (Im(n)-Ithresh) from the immediately preceding upper limit fixing current Q(n-1) using the following formula (1) (step S5). Q′(n)=Q(n-1)-(Im(n)-Ithresh)...(1) In equation (1), the provisional upper limit value Q'(n) is calculated by correcting the immediately preceding Q(n-1) using the excess current value Im(n)-Ithresh as the basic correction amount.

[0063] Next, the control unit 90 determines Q(n) based on the calculated Q'(n) and the power margin. In this specification, the "power margin" refers to a state where Q(n)=Qmax(Im(n)≦Ithresh) is maintained, and Q(n)<Qmax(Im(n)> Ithresh) is a state where there is no power margin (small power shortage), and Q(n)<<Qmax(Im(n)> > Ithresh) is defined as no power margin (large shortage).

[0064] A specific power margin is determined using the excess current value (Im(n)-Ithresh) (steps S2 & S6). If (Im(n)-Ithresh)≦0 (Yes in step S2), it is determined that there is a power margin. If 0<(Im(n)-Ithresh)≦δ (Yes in step S6), it is determined that there is no power margin (small shortage). In this case, Q(n) is set to Q'(n) calculated in step S7 (step S7).

[0065] If (Im(n)-Ithresh)>δ (No in step S6), it is determined that there is no power margin (large shortage), and the value obtained by subtracting the correction value β1 from Q'(n) is set to Q(n) (step S8). The correction value β1 is set to 0.2 to 0.5 [A]. Furthermore, the threshold value δ of Im(n)-Ithresh when determining the power margin is set to about 0.3 to 0.6 [A].

[0066] Condition 4 in Figure 6 shows the fixing current Ifuser and secondary current Ieng(n) when Im(n) > Ithresh and (Im(n) - Ithresh) ≦ δ. As in the left graph of condition 4, Im(n) exceeds Ithresh, but if the excess amount is δ or less, Q(n) = Q'(n) and Im(n) is reduced to Ithresh as in the right graph.

[0067] Condition 5 in Fig. 6 shows the fixing current Ifuser and the secondary current Ieng(n) when Im(n) > Ithresh and (Im(n) - Ithresh) > δ. When Im(n) exceeds Ithresh as in the left graph of condition 5 and the excess amount is greater than δ, Q(n) = Q'(n) - β1, and Im(n) is reduced to a value lower than Ithresh as in the right graph.

[0068] Then, it is determined whether the set Q(n) exceeds Qmax (step S9), and if Q(n)>Qmax (Yes in step S9), Q(n)=Qmax is set (step S10).

[0069] As described above, according to the first control example of the present embodiment, the correction amount in the total current threshold control when the total device current Im(n) exceeds the total current threshold Ithresh is set in multiple stages according to the power margin. This provides a power control system that keeps the current allocable to the fixing device 13 as large as possible while preventing the total device current Im(n) from exceeding the rated current Imax.

[0070] Also, by focusing on the magnitude of the excess current value (Im(n)-Ithresh), when Im(n)-Ithresh is large, the correction value β1 is subtracted from Q'(n) to set Q(n). This allows a larger correction amount for the upper fixing current Q(n) when the total device current Im(n) exceeds the total current threshold Ithresh, and the difference from the rated current Imax becomes larger. Therefore, even if the operations of the secondary loads 60 overlap, the risk of the total device current Im(n) exceeding the rated current Imax can be reduced.

[0071] In the above control example, when there is no power margin (when (Im(n)-Ithresh)>δ), the value obtained by subtracting the correction value β1 from Q'(n) is used as Q(n), but the value obtained by multiplying the basic correction amount Im(n)-Ithresh by a correction coefficient β2 and subtracting it from Q(n-1) may be used as Q'(n). The correction coefficient β2 is set to 1.5 to 3.

[0072] Fig. 7 is a flowchart showing a second control example of the current control executed in the image forming apparatus 100 of the first embodiment. In the second control example shown in Fig. 7, when the total device current Im(n) exceeds the total current threshold Ithresh (No in step S2), the excess current value (Im(n)-Ithresh) is calculated (step S4), the excess current value (Im(n)-Ithresh) is subtracted from the immediately preceding upper limit fixing current Q(n-1) to calculate a tentative upper limit value Q'(n) (step S5), and then the power margin is determined with attention paid to the sequence timing (operating state) of the image forming apparatus 100, and a plurality of correction amount settings of the upper limit fixing current Q(n) are provided according to the power margin.

[0073] Specifically, after warm-up (WU) for increasing the fixing temperature to the standby temperature, it is determined whether a predetermined time has elapsed (step S6). If the predetermined time has elapsed (Yes in step S6), it is determined that there is no power margin (small power shortage), and Q'(n) calculated in step S5 is set to Q(n) (step S7).

[0074] On the other hand, if the predetermined time has not elapsed (No in step S6), it is determined that there is no power margin (large power shortage), and the value obtained by subtracting the correction value β1 from Q'(n) is set to Q(n) (step S8). The correction value β1 is set to 0.2 to 0.5 [A].

[0075] The detection period of the total device current Im(n) by the CT board 57, the variable instruction period of the upper limit fixing current Q(n) by the control unit 90, and the period of power control (power PID control, power table control) of the heating unit 23 are the same as in the first control example.

[0076] As described above, according to the second control example of the present embodiment, when a predetermined time has not elapsed after warm-up, the value Q(n) is set to the value obtained by subtracting the correction value β1 from Q'(n). As a result, during the period immediately after warm-up when the fixing belt 21 and the pressure roller 22 are not sufficiently heated and the amount of heat absorbed by the members until the entire fixing device 13 accumulates heat is large, that is, during the period when there is no power margin (large power shortage), the correction amount of the upper limit fixing current Q(n) can be set to a large value, and the difference from the rated current Imax becomes large. Therefore, even if the operations of the secondary loads 60 overlap, the risk of the total device current Im(n) exceeding the rated current Imax can be reduced.

[0077] In the second control example, instead of subtracting the correction value β1 from Q'(n) to obtain Q(n), the Q'(n) calculated by multiplying the basic correction amount Im(n)-Ithresh by the correction coefficient β2 may be subtracted from Q(n-1) to obtain Q'(n). The correction coefficient β2 is set to 1.5 to 3.

[0078] Fig. 8 is a flowchart showing a third control example of the current control executed in the image forming apparatus 100 of the first embodiment. Fig. 9 is a diagram showing the fixing current and the secondary side current under conditions 1 to 5 in which the device total current Im(n) is different in the third control example. In the third control example shown in Figs. 8 and 9, an example will be described in which a halogen heater is used as the heating section 23 of the fixing device 13. In this configuration, the fixing upper limit current Q(n) is determined by total current threshold control (one-stage control) based on the device total current threshold (total current threshold).

[0079] For example, in the case of a halogen heater with a rated voltage of 100V and a rated power of 1000W, when a full-wave AC waveform of 100V is input, it consumes 1000W of power and generates the corresponding amount of heat. When controlling the power of the halogen heater, the fixing power control board 53 detects the zero-cross timing of the AC waveform, rather than the full-wave AC waveform, and controls the energization duty by inputting a half-wave waveform (or a phase control waveform) with a predetermined cycle and duty, thereby driving the heater at the desired power. Therefore, there is basically no feedback in the power control of the halogen heater. In this way, with power control without a feedback system, when a power command is received, it is possible to operate at a power equivalent to the command power immediately without the delay of the feedback system.

[0080] In this type of power control, the upper fixing current Q(n) is calculated using the total current threshold control using the above formula (1). In formula (1), the responsiveness of the heater power affects the total current Im(n), but as previously mentioned, with a halogen heater, power control is possible without any control delay, so the power control itself can stably output the commanded power. A factor that can cause fluctuations in the power control of a halogen heater is the change in the upper fixing current Q(n) due to total current control, but with a halogen heater, there is no need to consider issues related to the use of total current PID control and total current threshold control, as in the first and second control examples assuming power control of an induction heating (IH) heater, and there is no risk of the threshold control becoming unstable.

[0081] As shown in FIG. 8, first, the CT substrate 57 detects the total device current Im(n) (step S1). Next, the control unit 90 calculates the overcurrent value Im(n) - Ithresh (step S2). Then, the calculated Im(n) - Ithresh is subtracted from the previous fixing upper limit current Q(n - 1) to calculate the temporary upper limit value Q'(n) (step S3).

[0082] Next, the control unit 90 determines Q(n) based on the calculated Q'(n) and the power margin. Specifically, for the power margin, it is determined whether (Im(n) - Ithresh) ≤ δ using the overcurrent value Im(n) - Ithresh calculated in step S2 (step S4).

[0083] Conditions 1 to 3 in FIG. 9 show the fixing current Ifuser (hatched area) and the secondary current Ieng(n) (white area) when Im(n) ≤ Ithresh. As the actual fixing current Ifuser, the smaller of the current indication value Iht(n) or the fixing upper limit current Q(n) is selected. Condition 1 shows the case where Iht(n) is selected as Ifuser (Iht(n) < Qmax), and conditions 2 and 3 show the cases where Q(n) (= Qmax) is selected as Ifuser.

[0084] If (Im(n) - Ithresh) ≤ δ (Yes in step S4), it is determined that there is a power margin or no power margin (small shortage amount), and Q(n) is set to Q'(n) calculated in step S3 (step S5).

[0085] Condition 4 in FIG. 9 shows the fixing current Ifuser and the secondary current Ieng(n) when (Im(n) - Ithresh) ≤ δ. As shown in the left graph of condition 4, although Im(n) exceeds Ithresh, when the excess amount is δ or less, Q(n) = Q'(n), and Im(n) is decreased to Ithresh as shown in the right graph.

[0086] On the other hand, if (Im(n)-Ithresh)>δ (No in step S4), it is determined that there is no power margin (large shortage), and the value obtained by subtracting the correction value β1 from Q'(n) is set as Q(n) (step S6). The correction value β1 is set to 0.2 to 0.5 [A]. Furthermore, the threshold value δ of Im(n)-Ithresh when determining the power margin is set to about 0.3 to 0.6 [A].

[0087] Condition 5 in Fig. 9 shows the fixing current Ifuser and the secondary current Ieng(n) when (Im(n) - Ithresh) > δ. When Im(n) exceeds Ithresh as shown in the left graph of condition 5 and the excess amount is greater than δ, Q(n) = Q'(n) - β1 is set and Im(n) is reduced to a value lower than Ithresh as shown in the right graph.

[0088] Then, it is determined whether the set Q(n) exceeds Qmax (step S7), and if Q(n)>Qmax (Yes in step S7), Q(n)=Qmax is set (step S8).

[0089] As described above, according to the third control example of the present embodiment, the correction amount in the total current threshold control when the total device current Im(n) exceeds the total current threshold Ithresh is set in multiple stages according to the power margin. This provides a power control system that keeps the current allocable to the fixing device 13 as large as possible while preventing the total device current Im(n) from exceeding the rated current Imax.

[0090] Also, similarly to the first control example, attention is paid to the magnitude of the excess current value (Im(n)-Ithresh), and when Im(n)-Ithresh is large, the value obtained by subtracting the correction value β1 from Q'(n) is set to Q(n). This allows a larger correction amount for the upper fixing current Q(n) when the total device current Im(n) exceeds the total current threshold Ithresh, and the difference with the rated current Imax becomes larger. Therefore, even if the operations of the secondary loads 60 overlap, the risk of the total device current Im(n) exceeding the rated current Imax can be reduced.

[0091] In the above control example, when there is no power margin (large shortage) (when δ<(Im(n)-Ithresh)), the value obtained by subtracting the correction value β1 from Q'(n) is used as Q(n), but the Q'(n) calculated by subtracting the value obtained by multiplying the excess current value (Im(n)-Ithresh) by the correction coefficient β2 from Q(n-1) may also be used as Q(n). The correction coefficient β2 is set to 1.5 to 3.

[0092] Furthermore, similarly to the second control example, the power margin can be determined with attention paid to the sequence timing (operating state) of the image forming apparatus 100, and multiple correction amount settings for the fixing upper limit current Q(n) can be provided according to the power margin.

[0093] 10 is a block diagram showing an example of a power control system of an image forming apparatus 100 according to a second embodiment of the present invention. The power control system of the image forming apparatus 100 according to the second embodiment includes a first power supply unit 51a and a second power supply unit 51b. The first power supply unit 51a is connected to a commercial power source AC via an inlet (not shown) and supplies an AC voltage from the commercial power source AC to a fixing power control board 53. The second power supply unit 51b is connected to the commercial power source AC via an inlet (not shown) different from that of the first power supply unit 51a and converts the AC voltage from the commercial power source AC into a DC voltage by a low-voltage power source 52, and then supplies the DC voltage to a secondary load 60.

[0094] The CT board 57 detects the current supplied from the commercial power source AC via the second power supply unit 51b to the low-voltage power source 52. That is, the CT board 57 functions as a secondary current detection unit that detects the input current (secondary current Ieng(n)) of the power supply system for the secondary load 60. Note that, instead of the CT board 57, another current detection mechanism may be used.

[0095] In this embodiment, the power supply system is divided into two systems: a power supply system connected from the first power supply unit 51a to the heating unit 23 of the fixing device 13 via the fixing power control board 53, and a power supply system connected from the second power supply unit 51b to the secondary load 60 via the low-voltage power supply 52. ​​For example, as shown in Fig. 10, a two-wire power cord may be used, with one connected to the first power supply unit 51a and used exclusively as a power supply for the heating unit 23 of the fixing device 13, and the other connected to the second power supply unit 51b and used as a power supply for the secondary load 60 (two-outlet configuration), or power supplied from one power cord may be branched to the first power supply unit 51a and the second power supply unit 51b (one-outlet configuration).

[0096] In this embodiment, the total device current Im(n) and the upper limit fixing current Q(n) are calculated by the following equations (2) and (3). Im(n)=Q(n-1)+Ieng(n) ···(2) Q(n)=Ithresh-Ieng(n) ···(3)

[0097] The advantage of detecting the secondary side current Ieng(n) as in this embodiment is that since the values ​​of the fixing current and power are not included in the calculation, in the process of determining the final fixing current (Ifuser) from the upper limit fixing current Q(n) and the current command value Iht(n) based on temperature control, Q(n) and Ifuser are independent parameters. Therefore, even if the total current control is performed only by the total current threshold control, the fixing current Ifuser and the total device current Im(n) do not become unstable, and the control configuration can be simplified.

[0098] However, because the device total current Im(n) is calculated, an error is likely to occur in the device total current, which is the opposite of the first embodiment in which the device total current Im(n) is detected by the CT board 57. For this reason, the total current threshold margin α2 used when setting the total current threshold Ithresh must be set larger than the total current threshold margin α1 of the first embodiment.

[0099] FIG. 11 is a flowchart showing an example of current control executed in the image forming apparatus 100 of the second embodiment. FIG. 12 is a diagram showing the fixing current and the secondary current under conditions 1 to 5 in which the total device current Im(n) is different in the control example of FIG. 11. In the control example shown in FIG. 11 and FIG. 12, a two-outlet configuration with a rated voltage of 100V and a rated current of 20A is used, and one 15A outlet is dedicated to the heating section 23 of the fixing device 13, and the other 15A outlet is allocated to the secondary load 60. Then, the total device current control is performed with a rated current of 20A for the two outlets in total. In this configuration, the fixing upper limit current Q(n) is determined by threshold control (one-stage control) based on the threshold value of the total device current (total current threshold value).

[0100] 11, first, the secondary current Ieng(n) is detected by the CT board 57 (step S1). The control unit 90 adds the previously set upper limit fixing current Q(n-1) to the detected secondary current Ieng(n) to calculate the total device current Im(n) (step S2).

[0101] Next, the control unit 90 calculates the excess current value Im(n)-Ithresh using Im(n) calculated in step S2 (step S3). Ithresh is a current value lower than the rated current Imax by a predetermined value α2 (total current threshold margin, α2>α1). In addition, the control unit 90 calculates the provisional upper limit value Q'(n) by subtracting Ieng(n) from Ithresh using the above-mentioned equation (3) (step S4).

[0102] Here, the relationship between formula (3) and formula (1) for calculating the provisional upper limit value Q'(n) in the first embodiment will be described. In formula (1), the provisional upper limit value Q'(n) is set by subtracting the excess current value Im(n)-Ithresh, which is the difference between the total device current Im(n) and Ithresh, from the previously set upper limit fixing current Q(n-1). Substituting formula (2), which is a parameter when detecting the secondary side current Ieng(n), into formula (1) and transforming it, we obtain Q′(n)=Q(n-1)-(Im(n)-Ithresh) =(Im(n) - Ieng(n)) - (Im(n) - Ithresh) = Ithresh - Ieng(n) This results in the derivation of Equation (3) for calculating Q′(n) in the second embodiment for detecting the secondary current. That is, the essential control of setting the fixing upper limit current Q(n) by comparing the total device current Im(n) with the total current threshold Ithresh is the same as in the first embodiment for detecting the total device current.

[0103] Next, the control unit 90 determines Q(n) based on the calculated Q′(n) and the power margin. Specifically, for the power margin, it is determined whether (Im(n) - Ithresh) ≤ δ using the overcurrent value Im(n) - Ithresh (step S5).

[0104] Conditions 1 and 2 in FIG. 12 show the fixing upper limit current Q(n) and the secondary current Ieng(n) when Im(n) ≤ Ithresh. Condition 1 shows the case when Im(n) < Ithresh, and Condition 2 shows the case when Im(n) = Ithresh. In this control example, since the actual fixing current Ifuser is allowed up to the fixing upper limit current Q(n), Im(n) is the sum of the secondary current Ieng(n) and the fixing upper limit current Q(n). Therefore, for example, the actual total device current Im(n) in Condition 1 is like the right graph combining Ifuser (hatched area) and the secondary current (white area).

[0105] If (Im(n) - Ithresh) ≤ δ (Yes in step S5), it is determined that there is a power margin or no power margin (small shortage amount), and Q(n) is set to Q′(n) calculated in step S4 (step S6). Condition 4 in FIG. 12 shows the fixing upper limit current Q(n) and the secondary current Ieng(n) when (Im(n) - Ithresh) ≤ δ. When Im(n) exceeds Ithresh but the excess amount is δ or less as in the left graph of Condition 4, Q(n) = Q′(n), and Im(n) is decreased to Ithresh as in the right graph.

[0106] On the other hand, if δ<(Im(n)-Ithresh) (No in step S5), it is determined that there is no power margin (large shortage), and the value obtained by subtracting the correction value β1 from Q'(n) is set to Q(n) (step S7). The correction value β1 is set to 0.2 to 0.5 [A]. Furthermore, the threshold value δ of Im(n)-Ithresh when determining the power margin is set to about 0.3 to 0.6 [A].

[0107] Condition 4 in Fig. 12 shows the fixing current Q(n) and secondary current Ieng(n) when (Im(n) - Ithresh) > δ. When Im(n) exceeds Ithresh as in the left graph of condition 5 and the excess amount is greater than δ, Q(n) = Q'(n) - β1 is set, and Im(n) is reduced to a value lower than Ithresh as in the right graph.

[0108] Then, it is determined whether the set Q(n) exceeds Qmax (step S8), and if Q(n)>Qmax (Yes in step S8), Q(n)=Qmax is set (step S9).

[0109] As described above, according to the current control example of the present embodiment, the correction amount in the total current threshold control when the total device current Im(n) exceeds the total current threshold Ithresh is set in multiple stages according to the power margin. This provides a power control system that keeps the current allocable to the fixing device 13 as large as possible while preventing the total device current Im(n) from exceeding the rated current Imax.

[0110] Also, by focusing on the magnitude of the excess current value (Im(n)-Ithresh), when Im(n)-Ithresh is large, the correction value β1 is subtracted from Q'(n) to set Q(n). This allows a larger correction amount for the upper fixing current Q(n) when the total device current Im(n) exceeds the total current threshold Ithresh, and the difference from the rated current Imax becomes larger. Therefore, even if the operations of the secondary loads 60 overlap, the risk of the total device current Im(n) exceeding the rated current Imax can be reduced.

[0111] In the above control example, when there is no power margin (large shortage) (when δ<(Im(n)-Ithresh)), the value obtained by subtracting the correction value β1 from Q'(n) is used as Q(n), but the Q'(n) calculated by subtracting the value obtained by multiplying the excess current value (Im(n)-Ithresh) by the correction coefficient β2 from Q(n-1) may also be used as Q(n). The correction coefficient β2 is set to 1.5 to 3.

[0112] In addition, in a configuration in which the secondary current Ieng is detected by the CT board 57 and the total device current Im(n) is calculated from the upper limit fixing current Q(n-1) and Ieng(n) using equation (2) as in this control example, the responsiveness of the fixing power control does not affect the measurement value of the CT board 57. Furthermore, the fixing power control does not affect Q(n) calculated using equation (3). Therefore, the correction of Q(n) using the above calculation does not cause the fixing power control or the total current control to become unstable. Therefore, whether the heating unit 23 is an induction heating (IH) heater or a halogen heater, it can be handled with just the same total current threshold control.

[0113] In this embodiment, as in the second control example of the first embodiment, the power margin can be determined by focusing on the sequence timing (operating state) of the image forming apparatus 100, and multiple correction amount settings for the fixing upper limit current Q(n) can be provided according to the power margin.

[0114] In addition, the present invention is not limited to the above-mentioned embodiments, and various modifications are possible within the scope of the present invention. For example, in the above-mentioned embodiments, when the heating unit 23 is a halogen heater, the power control is performed by controlling the current duty of the AC voltage, but the power control may be performed by incorporating a current detection circuit and a voltage detection circuit in the fixing power control board 53 and monitoring the current and voltage.

[0115] In addition, in each of the above embodiments, a sliding belt type fixing device 13 in which an endless fixing belt 21 slides against a nip forming member 24 as a heated rotating body has been exemplified. However, the present invention can be applied in exactly the same way to a fixing device of a uniaxial belt type in which the fixing belt 21 is wound around a fixing roller, a biaxial belt type in which the fixing belt 21 is stretched between a fixing roller and a heating roller, or a fixing device equipped with a heated rotating body other than the fixing belt 21.

[0116] Furthermore, image forming apparatus 100 is not limited to a tandem color printer as shown in FIG. 1, but can be applied to various image forming apparatuses equipped with a fixing device, such as monochrome copying machines, digital multifunction machines, facsimiles, and laser printers. [Industrial Applicability]

[0117] The present invention can be used in an image forming apparatus equipped with a fixing device that applies heat and pressure to a toner image by inserting the recording medium into a fixing nip formed by a heated rotating body and a pressure member to melt and fix the toner image on the recording medium. By using the present invention, it is possible to provide an image forming apparatus that can supply maximum power to the fixing device while reliably preventing the total current input to the image forming apparatus from exceeding a limit value. [Explanation of symbols]

[0118] Pa~Pd Image forming section 13 Fixing device 21 Fixing belt (heated rotating body) 22 Pressure roller (pressure rotating body) 23 Heating section 30 Pressurizing mechanism 47 Thermistor (temperature detection part) 50 Power control circuit 51 Power supply section 52 Low voltage power supply 51a 1st power supply section 51b 2nd power supply section 53 Fixing power control board 55 Secondary power control board 57 CT board 60 Secondary load 90 Control section 100 Image forming device N Fixing nip S Paper (recording medium)

Claims

1. an image forming unit that forms a toner image on a recording medium; A heated rotating body; a pressure rotating body that is pressed against the heated rotating body at a predetermined fixing nip pressure to form a fixing nip portion; A heating unit that heats the heated rotating body; A temperature detection unit that detects the temperature of the heated rotating body; a fixing device that performs a fixing process of fixing the toner image onto the recording medium by applying heat and pressure to the recording medium passing through the fixing nip portion; a power supply unit connected to a commercial power source and supplying power to the entire image forming apparatus including the fixing device; a control unit that, when a current command value Iht(n) determined based on a detection result of the temperature detection unit is equal to or smaller than an upper limit fixing current Q(n), determines a fixing current Ifuser flowing through the heating unit to be the current command value Iht(n), and, when the current command value Iht(n) is greater than the upper limit fixing current Q(n), determines the fixing current Ifuser to be the upper limit fixing current Q(n); In an image forming apparatus comprising: The control unit is when the total device current Im(n) exceeds a total current threshold Ithresh that is lower than a rated current Imax of the image forming device by a predetermined value α during image formation, the fixing upper limit current Q(n) is set by total current threshold control so that the total device current Im(n) does not exceed the rated current Imax, and the fixing upper limit current Q(n) is corrected in multiple stages based on a power margin of the image forming device; when the device total current Im(n) exceeds the total current threshold Ithresh, the control unit determines the power margin based on an excess current value Im(n)-Ithresh which is a difference between the device total current Im(n) and the total current threshold Ithresh, and calculates a tentative upper limit value Q'(n) by subtracting the excess current value Im(n)-Ithresh from the previous fixing upper limit current Q(n-1), an image forming apparatus, characterized in that, when the excess current value Im(n)-Ithresh is equal to or smaller than a predetermined value δ, the fixing upper limit current Q(n) is set to the tentative upper limit value Q'(n), and, when the excess current value Im(n)-Ithresh exceeds a predetermined value δ, the fixing upper limit current Q(n) is set to a value smaller than the tentative upper limit value Q'(n).

2. An image forming unit that forms a toner image on a recording medium; A heated rotating body; a pressure rotating body that is pressed against the heated rotating body at a predetermined fixing nip pressure to form a fixing nip portion; A heating unit that heats the heated rotating body; A temperature detection unit that detects the temperature of the heated rotating body; a fixing device that performs a fixing process of fixing the toner image onto the recording medium by applying heat and pressure to the recording medium passing through the fixing nip portion; a power supply unit connected to a commercial power source and supplying power to the entire image forming apparatus including the fixing device; a control unit that, when a current command value Iht(n) determined based on a detection result of the temperature detection unit is equal to or smaller than an upper limit fixing current Q(n), determines a fixing current Ifuser flowing through the heating unit to be the current command value Iht(n), and, when the current command value Iht(n) is greater than the upper limit fixing current Q(n), determines the fixing current Ifuser to be the upper limit fixing current Q(n); In an image forming apparatus comprising: The control unit is when the total device current Im(n) exceeds a total current threshold Ithresh that is lower than a rated current Imax of the image forming device by a predetermined value α during image formation, the fixing upper limit current Q(n) is set by total current threshold control so that the total device current Im(n) does not exceed the rated current Imax, and the fixing upper limit current Q(n) is corrected in multiple stages based on a power margin of the image forming device; when the device total current Im(n) exceeds the total current threshold Ithresh, the control unit calculates a provisional upper limit value Q'(n) by subtracting an excess current value Im(n)-Ithresh, which is a difference between the device total current Im(n) and the total current threshold Ithresh, from the previous fixing upper limit current Q(n-1); an image forming apparatus, characterized in that, when a predetermined time has elapsed after a warm-up for raising the temperature of a heated rotating body to a standby temperature, the fixing upper limit current Q(n) is set to the provisional upper limit value Q'(n), and, when the predetermined time has not elapsed after the warm-up, the fixing upper limit current Q(n) is set to a value smaller than the provisional upper limit value Q'(n).

3. An image forming apparatus as described in claim 1 or claim 2, further comprising a total current detection unit which detects the device total current Im(n) supplied from the power supply unit, and the control unit performs the total current threshold control which compares the device total current Im(n) detected by the total current detection unit with the total current threshold Ithresh to set the upper fixing current limit Q(n).

4. The image forming apparatus according to claim 3, wherein the control unit performs two-stage control to set the upper fixing current Q(n) by total current PID control when the total device current Im(n) is equal to or less than the total current threshold Ithresh, and to set the upper fixing current Q(n) by total current threshold control when the total device current Im(n) exceeds the total current threshold Ithresh.

5. The image forming apparatus described in Claim 4, characterized in that the heating section is an induction heating type heater that generates heat by induction heating the heat generating layer of the heated rotating body.

6. The power supply unit, a first power supply unit connected to the commercial power source and supplying power to the fixing device; a second power supply unit connected to the commercial power source and supplying power to a secondary load other than the fixing device; It is composed of a secondary current detection unit that detects a secondary current Ieng(n) supplied from the second power supply unit, 6. The image forming apparatus according to claim 1, wherein the control unit performs the total current threshold control to calculate the total device current Im(n) by adding a previously set upper limit fixing current Q(n-1) to the secondary side current Ieng(n) detected by the secondary side current detection unit, and to set the upper limit fixing current Q(n) by comparing the calculated total device current Im(n) with the total current threshold Ithresh.

7. An image forming apparatus as described in any one of claims 1 to 6, characterized in that when the excess current value Im(n) - Ithresh exceeds a predetermined value δ, or when a predetermined time has not elapsed after warm-up for raising the temperature of the heated rotating body to a standby temperature, the control unit sets the fixing upper limit current Q(n) to a value obtained by subtracting a correction amount β1 from the provisional upper limit value Q'(n).

8. 7. The image forming apparatus according to claim 1, wherein the control unit sets the fixing upper limit current Q(n) to the provisional upper limit value Q'(n) calculated by multiplying the excess current value Im(n)-Ithresh by a correction coefficient β2 and subtracting the value obtained by multiplying the excess current value Im(n)-Ithresh by a correction coefficient β2 from the previous fixing upper limit current Q(n-1), when the excess current value Im(n)-Ithresh exceeds a predetermined value δ or when a predetermined time has not elapsed after a warm-up for raising the temperature of the heated rotating body to a standby temperature.

Images