Image forming apparatus

Abstract

To provide a technique that can prevent application of overvoltage to a heating element.SOLUTION: When a peak voltage detection unit 460 detects that an overvoltage exceeding a rated value is applied from a commercial AC power supply 401, a CPU 410 controls a triac 440 so that a waveform pattern of a current flowing in a heater 300 becomes a waveform pattern in which the energization time for every half wave falls within a predetermined time. Further, when the overvoltage exceeding the rated value from the commercial AC power supply 401 continues for a predetermined period, the CPU 410 turns off the triac 440 to cut off energization to the heater 300. Consequently, an image forming apparatus can be provided which can prevent application of an overvoltage damaging a heating element 302 that forms the heater 300.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to an image forming apparatus such as a printer or a copier using an electrophotographic method or an electrostatic recording method. The present invention also relates to a fixing device mounted on the image forming apparatus and an image heating device such as a gloss imparting device that improves the glossiness of a toner image by reheating the toner image fixed on a recording material.

Background Art

[0002] Conventionally, in order to achieve both reduction of harmonics generated from the current applied from a commercial AC power supply and reduction of flicker in a fixing device as an image heating device, control of the waveform pattern of the current flowing through the heating element of the heater has been performed. For example, in Patent Document 1, control has been proposed in which phase control is employed for at least one half-wave in a control period that is an integer multiple of a half-wave of the commercial frequency, and frequency control in which full energization or non-energization is performed for each of the remaining half-waves is employed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When an abnormal overvoltage is applied to the image heating device mounted on the image forming apparatus, there is a possibility that the overvoltage is applied to the heating element inside the image heating device in the conventional control method of the heating element, and it has been necessary to take sufficient measures so that the heating element is not damaged.

[0005] An object of the present invention is to provide a technique capable of suppressing the application of an overvoltage to a heating element.

Means for Solving the Problems

[0006] To solve the above problems, an image forming apparatus according to the present invention an image forming unit that forms a toner image on a recording material; a heating unit that has a heating element that generates heat upon receiving power supply from a commercial AC power source and heats the toner image formed by the image forming unit; a temperature detection unit that detects the temperature of the heating unit; a power control unit that controls the power supply from the commercial AC power source to the heating element based on the temperature information detected by the temperature detection unit; a detection unit that detects whether or not an applied voltage applied from the commercial AC power source exceeds a rated value; in an image forming apparatus comprising: when the detection unit detects that the applied voltage exceeds the rated value, the power control unit controls the power supply such that the waveform pattern of the current flowing through the heating element becomes a waveform pattern in which the energization time to the heating element for each half-wave is within a predetermined time, and when the period during which the applied voltage exceeds the rated value continues for a predetermined period, the power supply from the commercial AC power source to the heating element is cut off.

Advantages of the Invention

[0007] As described above, according to the present invention, it is possible to suppress the application of an overvoltage to the heating element, and thus it is possible to avoid damaging the heating element.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

[0009] Hereinafter, with reference to the drawings, modes for carrying out this invention will be exemplarily and detailedly described based on examples. However, dimensions, materials, shapes, relative arrangements, etc. of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. That is, it is not intended to limit the scope of this invention to the following embodiments. Also, although a plurality of features are described in the embodiment, not all of these plurality of features are essential to the invention, and the plurality of features may be arbitrarily combined. Further, in the attached drawings, the same or similar configurations are given the same reference numerals, and duplicate explanations are omitted.

[0010] (Example 1) FIG. 1 is a schematic cross-sectional view of an image forming apparatus 100 according to an embodiment of the present invention using electrophotographic recording technology. Examples of image forming apparatuses to which the present invention is applicable include copiers, printers, etc. that use electrophotographic or electrostatic recording methods. Here, the case where it is applied to a laser printer that forms an image on a recording material P using the electrophotographic method will be described.

[0011] The image forming apparatus 100 includes a video controller 120 and a control unit 113. The video controller 120 receives and processes image information and a print instruction transmitted from an external device such as a personal computer as an acquisition unit that acquires information on an image to be formed on a recording material. The control unit 113 is connected to the video controller 120 and controls each unit constituting the image forming apparatus 100 according to an instruction from the video controller 120. When the video controller 120 receives a print instruction from an external device, image formation is executed by the following operations.

[0012] When the image forming apparatus main body 100 receives a print signal, the scanner unit 21 emits laser light modulated according to the image information, and scans the surface of the photosensitive drum 19 charged to a predetermined polarity by the charging roller 16. As a result, an electrostatic latent image is formed on the photosensitive drum 19. By supplying toner from the developing roller 17 to this electrostatic latent image, the electrostatic latent image on the photosensitive drum 19 is developed as a toner image (toner image).

[0013] On the other hand, the recording material (recording paper) P loaded in the paper feed cassette 11 is fed one by one by the pickup roller 12 and conveyed toward the registration roller pair 14 by the conveyance roller pair 13. Further, the recording material P is conveyed from the registration roller pair 14 to the transfer position in accordance with the timing when the toner image on the photosensitive drum 19 reaches the transfer position formed by the photosensitive drum 19 and the transfer roller 20. The toner image on the photosensitive drum 19 is transferred to the recording material P as the recording material P passes through the transfer position.

[0014] Thereafter, the recording material P is heated by a fixing device (fixing unit) 200 as an image heating device (image heating unit), and the toner image is heat-fixed to the recording material P. The recording material P carrying the fixed toner image is discharged to a tray above the image forming apparatus 100 by the conveyance roller pairs 26 and 27.

[0015] The drum cleaner 18 cleans the toner remaining on the photosensitive drum 19. The paper feed tray 28 (manual feed tray) is a pair of recording material regulating plates whose width can be adjusted according to the size of the recording material P, and is provided to accommodate recording materials P of sizes other than standard sizes. The pickup roller 29 feeds the recording material P from the paper feed tray 28. The image forming apparatus main body 100 has a motor 30 that drives the fixing device 200 and the like.

[0016] The control circuit (power supply circuit) 400 as the power control unit is connected to a commercial AC power supply 401 and supplies power to the fixing device 200.

[0017] The above-described photosensitive drum 19, charging roller 16, scanner unit 21, developing roller 17, and transfer roller 20 constitute an image forming unit that forms an unfixed image on the recording material P. Further, in this embodiment, the developing unit including the photosensitive drum 19, charging roller 16, and developing roller 17, and the cleaning unit including the drum cleaner 18 are configured to be detachable from the apparatus main body of the image forming apparatus 100 as the process cartridge 15.

[0018] The image forming apparatus 100 of this embodiment corresponds to a plurality of recording material sizes as the sizes of recording materials on which image formation is possible. In the paper feed cassette 11, Letter paper (about 216 mm × 279 mm), Legal paper (about 216 mm × 356 mm), A4 paper (210 mm × 297 mm), Executive paper (about 184 mm × 267 mm), JIS B5 paper (182 mm × 257 mm), and A5 paper (148 mm × 210 mm) can be set as recording materials. The image forming apparatus 100 of this embodiment is basically a laser printer that feeds the recording material longitudinally (feeds it so that the long side is parallel to the transport direction). Note that the configuration of the present proposal can be similarly applied to a printer that feeds the recording material laterally. Among the widths of the standard recording materials supported by the apparatus (the widths of the recording materials in the catalog), the recording materials having the largest (widest) width are Letter paper and Legal paper, and these widths are about 216 mm. In this embodiment, a recording material P having a paper width smaller than the maximum size supported by the apparatus is defined as a small-size paper.

[0019] FIG. 2(a) is a schematic cross-sectional view of a fixing device 200 as an image heating device according to the present embodiment. The fixing device 200 includes a fixing film 202 as an endless belt (hereinafter referred to as a film), a heater 300 that contacts the inner surface of the film 202, a pressure roller 208 that presses against the heater 300 via the film 202, and a metal stay 204. The pressure roller (nip portion forming member) 208 contacts the outer peripheral surface of the film 202 and forms a fixing nip portion N together with the heater 300.

[0020] The film 202 is a multilayer heat-resistant film formed in a cylindrical shape, and the material of the base layer is a heat-resistant resin such as polyimide or a metal such as stainless steel. Further, an elastic layer such as heat-resistant rubber may be provided on the surface layer of the film 202. A thermistor 211 as a temperature detection unit is in contact with the heater 300. Note that the temperature detection unit is not limited to a thermistor. The pressure roller 208 has a core metal 209 made of a material such as iron or aluminum and an elastic layer 210 made of a material such as silicone rubber. The heater 300 is held inside the film 202 by a holding member 201 made of a heat-resistant resin. The holding member 201 also has a guide function for guiding the rotation of the film 202. The metal stay 204 is configured to apply the pressure of a spring (not shown) to the holding member 201. These heater 300, holding member 201, and stay 204 constitute a heater unit 213. Note that other members such as a heat transfer member may be interposed between the film 202 and the heater 300. The pressure roller 208 receives power from a motor 30 and rotates in the direction of the arrow. When the pressure roller 208 rotates, the film 202 is driven to rotate. A recording material P carrying an unfixed toner image is heated and fixed while being sandwiched and conveyed at the fixing nip portion N.

[0021] The heater 300 is a heater that is heated by the resistance heating elements 302a and 302b provided on the side opposite to the surface (hereinafter defined as the back surface) that contacts the holding member 201 of the ceramic substrate 305. The surface protection layer 307 provided on the fixing nip portion N side is glass used to insulate the resistance heating elements 302a and 302b.

[0022] Also, the safety element 212 is provided so as to directly or indirectly contact the heater 300 via the holding member 201, and is configured to operate due to abnormal heating of the heater 300 and cut off the power supplied to the heater 300. The safety element 212 is, for example, a thermoswitch, a temperature fuse, or the like.

[0023] FIG. 2(b) shows an example of the heater 300, which is heated by the heating elements (heating resistors) 302a and 302b provided on a ceramic substrate. The power supplied from the connectors C1 and C2 of the control circuit 400 described later is supplied to the heating elements 302a and 302b via the electrodes E1 and E2 and the conductors 308 to 310 provided on the heater 300.

[0024] Similarly, FIG. 2(c) also shows an example of the heater 300. The heating elements 302a and 302b provided on the ceramic substrate are each divided into heating elements 302a-1 to 302a-7 and heating elements 302b-1 to 302b-7 in the longitudinal direction. Thereby, it is configured such that the heat generation zones of the respective heating elements can be controlled according to the paper size of the recording material P. E1-1 to E1-7 indicate the electrodes of the respective heating elements, and power is supplied to the heating elements by supplying power between the electrodes E2-1 and E2-2 via the conductors 308-1 to 308-7 and the conductors 309-1 to 309-2. The heating elements 302a-1 to 302a-7 and the heating elements 302b-1 to 302b-7 may be an aggregate of resistors formed in parallel in the longitudinal direction of the ceramic substrate in each zone.

[0025] FIG. 3 shows a control circuit 400 that controls the power supply from a commercial AC power supply 401 to a heater 300 in Example 1. Heating elements 302a and 302b configured on the heater 300 are electrically connected to the control circuit 400 via connectors C1 and C2 by electrodes E1 and E2 also provided on the heater 300. The image forming apparatus 100 is connected to the commercial AC power supply 401 and is driven by the power supply from the commercial AC power supply 401. The power supply voltage Vcc is a DC power supply generated by an AC / DC converter (not shown) connected to the commercial AC power supply 401. The commercial AC power supply 401 is connected to the heater 300 via a relay 430 and a triac 440. The triac 440 is turned on / off controlled by a control signal FUSERON from the CPU 410. The drive circuit of the triac 440 is omitted from the illustration. The zero-cross circuit 420 generates a ZEROX signal according to the zero-cross timing of the commercial AC power supply 401 and inputs it to the CPU 410. The zero-cross circuit 420 is insulated internally, and reinforced insulation is provided between the primary side circuit connected to the commercial AC power supply 401 and the secondary side circuit that outputs the ZEROX signal.

[0026] Next, the temperature detection circuit of the thermistor 211 will be described. The thermistor 211 is voltage-divided by a resistor 450 pulled up to Vcc. The voltage-divided voltage is detected by the CPU 410 as a VTh signal, and the temperature is detected by converting the voltage into temperature based on information set in advance in the internal memory of the CPU 410. The thermistor 211 is used as a temperature control thermistor, and in the internal processing of the CPU 410, the power to be supplied is calculated based on, for example, PI control, based on the set temperature and the detected temperature as temperature information by the thermistor 211. Ze Based on the zero-cross timing of the commercial AC power supply 401 by the zero-cross circuit 420, it is converted into a control level corresponding to the power to be supplied, and the triac 440 is controlled according to the control conditions. Thereby, the detected temperature of the thermistor 211 can be maintained at a preset set temperature.

[0027] The operation of relay 430 will be described. When the CPU 410 sets the RLON signal to the High state, the secondary coil (not shown) of relay 430 is energized from the power supply voltage Vcc, and the primary side contacts of relay 430 become on. When the RLON signal is set to the Low state, the current flowing from the power supply voltage Vcc to the secondary coil (not shown) of relay 430 is interrupted, and the primary side contacts of relay 430 become off.

[0028] The peak voltage detection unit 460 outputs information VIN of the peak voltage of the AC waveform of the commercial AC power supply 401 to the CPU 410.

[0029] When safety elements 212 such as a thermoswitch and a thermal fuse detect that the preset temperature has been exceeded, they cut off the power supply to the heater 300. When the CPU 410 becomes unable to control and even when the triac 440 continues to be on regardless of the detected temperature of the thermistor 211, the power supply to the heater 300 can be surely cut off. The set temperature is preferably set without operating the safety element 212 during normal control of the heater 300 and without exceeding the heat-resistant temperature of each member constituting the fixing device 200.

[0030] FIG. 4 shows a circuit diagram of the peak voltage detection unit 460. A part of a switching power supply device using an active clamp method is shown in an isolated converter using a flyback transformer, which converts AC power supplied from the commercial AC power supply 401 into DC power and supplies power to the image forming apparatus. The voltage rectified by the bridge diode 471, which is a full-wave rectifying means and is connected to the commercial AC power supply 401, is input to the switching power supply circuit 461. The smoothing capacitor 472 is used as a smoothing means for the rectified voltage, with the lower potential of the smoothing capacitor 403 being DCL and the higher potential being DCH.

[0031] The switching power supply circuit 461 is voltage-supplied to the isolated secondary side, smoothed by the diode 495 and the capacitor 496, and outputs a constant voltage V1. The switching power supply circuit 461 has an isolated transformer T1 with a primary winding P1 and an auxiliary winding P2 on the primary side and a secondary winding S1 on the secondary side. Energy is supplied from the primary winding P1 to the secondary winding S1 of the transformer T1 by the switching operations of the FET (field effect transistor) 473 and the FET 474 controlled by the primary side control unit 462. The voltage clamp capacitor 481 and the FET 473 connected in series are connected in parallel to the primary winding P1 of the transformer T1. The voltage resonance capacitor 475 connected in parallel to the FET 474 is provided to reduce the loss when the FET 473 and the FET 474 are switched off. The resistor 482 is a current detection resistor and inputs a voltage IA corresponding to the current load value to the primary side control unit 462.

[0032] The auxiliary winding P2 of the transformer T1 rectifies and smooths the forward voltage of the input peak voltage applied to the primary winding P1 with the diode 483, the resistor 484, and the capacitor 485, divides the voltage with the resistor 486 and the resistor 487, and inputs the voltage ACV smoothed by the capacitor 488 to the primary side control unit 462. This ACV is a voltage proportional to the input peak voltage.

[0033] The primary side control unit 462 outputs an ACVPWM which is a PWM signal obtained by converting the ACV into a pulse width, and inputs it to the gate of the FET 476 via the resistors 489 and 491. According to the switching of the FET 476, the photocoupler 477 is supplied with current via the resistor 490. The pulse signal transmitted to the secondary side by the photocoupler 477 is smoothed via the resistors 492, 494, and the capacitor 493, and input to the CPU 410 as the VIN signal.

[0034] As described above, the peak voltage detector 460 in the first embodiment converts a voltage proportional to the input peak voltage detected from the auxiliary winding P2, which is a part of the switching power supply circuit 461, into a pulse signal, propagates it to the secondary side, and smooths it with the resistor 494 and the capacitor 493, and then transmits it to the CPU 410 as the VIN signal. Therefore, the CPU 410 can grasp the input voltage value by converting the VIN signal into the input peak voltage.

[0035] FIG. 5 is a diagram showing the input power pattern supplied to the heater 300 when the CPU 410 in the first embodiment supplies the FUSERON signal to the triac 440. The input power pattern assumes an update of the power flowing to the heater 300 every 4 cycles (4 full waves) of the commercial AC power supply 401, and FIG. 5 represents the input power pattern when 4 full waves are set as one cycle control period as an example.

[0036] When the power supplied to the heater 300 is 0 to 25%, the input power pattern is that the first full wave is frequency control (OFF), the second full wave is phase control, the third full wave is frequency control (OFF), and the fourth full wave is frequency control (OFF), and the control waveform is a mixed control waveform of frequency control and phase control within 4 full waves. Similarly, when the power supplied to the heater 300 is 25 to 100%, the input power pattern is also a control waveform in which frequency control (ON / OFF) and phase control are mixed within 4 full waves. That is, in one control period, the power supply is in any of the waveform patterns of the frequency control waveform pattern, the phase control waveform pattern, or a control pattern combining frequency control and phase control. Hereinafter, such a control waveform in which frequency control and phase control are mixed is abbreviated as hybrid control.

[0037] In this embodiment, the normal temperature control method of the triac 440 via the FUSERON signal by the CPU 410 is characterized by being the hybrid control described in FIG. 5. The amount of heat applied to the fixing device 200 is calculated for each zero-crossing period detected by the zero-crossing circuit 420, with the temperature control target temperature and the detected temperature of the thermistor 211 below. In this embodiment, PI control, which is a type of feedback control system, is used. The calculation of the supply power using PI control is determined by the following equation (1).

[0038] Supply power ratio D = P control value + I control value ··· (1)

[0039] The P control value in Equation (1) is the control value of proportional control, and is calculated by multiplying the difference between the target temperature and the detected temperature by a gain set to an appropriate value according to the fixing specification. The I control value is the control value of integral control, and is the integral value of the difference between the target temperature and the detected temperature over a certain period, that is, it corrects the drift from the target temperature, and is applied as an offset to the supply power in P control.

[0040] FIG. 6(A) is a diagram showing the waveform transition of the VIN signal output by the peak voltage detection unit 460 described in FIG. 4 and the transition of the input power pattern characteristic of Example 1 when the input voltage changes from the normal voltage to an abnormal voltage (hereinafter referred to as overvoltage). FIG. 6(B) shows the control method of the input power pattern when the CPU 410, which is a detection unit for detecting whether the voltage applied from the commercial AC power supply 401 is an overvoltage exceeding the rated value, detects an overvoltage.

[0041] In FIG. 6(A), due to the application of an overvoltage exceeding the rated value from the commercial AC power supply 401 to the input voltage, the input voltage changes from the normal voltage to the overvoltage at point A. The VIN signal of the peak voltage detection unit 460 gradually changes from point A at a speed at which charge is accumulated in the smoothing capacitor 472. It increases, and as the charge of the smoothing capacitor 472 saturates, the voltage of the VIN signal saturates. When the VIN signal exceeds a certain predetermined voltage Vth as a predetermined threshold value, the CPU 410 determines that it is an overvoltage. In FIG. 6(A), the timing at which the VIN signal exceeds the threshold value Vth is the point B. Immediately from the point B where the CPU 410 determines that it is an overvoltage, the input power pattern described in FIG. 5 is changed from hybrid control to phase control only.

[0042] In FIG. 6(B), ±Vbreak indicates the voltage threshold for not damaging the resistance heating elements 302a and 302b. It is necessary to control so that a voltage higher than ±Vbreak is not applied to the heating elements 302a and 302b. Since the peak part of the sine wave voltage waveform applied from the commercial AC power supply 401 is the highest, tmax may be set so that the skirt part of the sine wave voltage waveform avoiding the peak part is applied. That is, the waveform pattern of the current flowing through the heating elements 302a and 302b due to the power supply from the commercial AC power supply 401 to the heater 300 is controlled to be a waveform pattern without a peak. More specifically, the energization to the heating elements 302a and 302b in each half-wave starts after passing the peak part of each half-wave.

[0043] tmax is set to a value calculated from the overvoltage range of the commercial AC power supply 401 assumed in the market and ±Vbreak. The CPU 410 stores tmax, which is a predetermined on-time at which the input power pattern does not exceed ±Vbreak in phase control, and controls the input power pattern so that the on-time of the FUSERON signal does not exceed the time of tmax.

[0044] Note that the input power pattern shown in FIG. 6(B) is an example of a phase control waveform pattern in which the energization time to the heater 300 for each half-wave is within a predetermined time, and is not limited to the waveform pattern shown here.

[0045] FIG. 7 shows a flowchart of the control in Example 1. In S1, when a printing request is received from the user, printing is started. In S2, if the VIN signal detected by the peak voltage detector 460 is greater than the threshold value Vth, the process proceeds to S3; if it is smaller, the process proceeds to S5. In S3, since it is determined that an overvoltage state exists, phase control is selected for temperature control and energization is started. When controlling the triac 440, the CPU 410 sets the time of tmax in FIG. 6(B) to 0 sec. That is, the energization to the triac 440 is in a stopped state. Since the heater 300 is not energized, the printing operation stops and ends (S4).

[0046] In S5, since it is determined that it is not in an overvoltage state, hybrid control is selected for temperature control and energization is started, and the normal printing operation is performed. In S6, it is determined whether a stop request has been received. If a stop request has been received, the process ends normally. If there is no stop request, in S7, it is determined whether the VIN signal detected by the peak voltage detector 460 is greater than the threshold value Vth. If the VIN signal is greater than the threshold value Vth, the process proceeds to S8. If the VIN signal is smaller than the threshold value Vth, the process returns to S6 to determine whether a stop request has been received.

[0047] When the process proceeds to S8, phase control is selected for temperature control and printing is continued. When controlling the triac 440, the CPU 410 sets the time of tmax to a value greater than 0 sec and continues temperature control below tmax. In S9, if the state of VIN > Vth continues for A sec, the process transitions to S10. In S10, when controlling the triac 440, the CPU 410 sets the time of tmax to 0 sec. That is, the energization to the triac 440 is stopped. That is, when the period during which the applied voltage from the commercial AC power supply 401 exceeds the rated value continues for a predetermined period, the power supply from the commercial AC power supply 401 to the heating elements 302a and 302b is cut off. Since the heater 300 is not energized, the printing operation stops and ends (S11).

[0048] In S9, when the state where VIN > Vth has not continued for A sec, at S12, it is determined whether the state where VIN < Vth has not continued for B sec. That is, it is detected whether the overvoltage state has been eliminated. If the state where VIN < Vth has continued for B sec, that is, if the overvoltage state has been eliminated, a transition is made to S13.

[0049] Here, Vth in S12 may be set to a lower value compared to Vth in S2, S7, and S9, and hysteresis may be provided for the voltage detected by the peak voltage detection unit 460. When Vth in S9 and Vth in S12 have the same value, when the state where VIN > Vth in S9 has not continued (continued for the first period) for A sec, the condition for continued B sec (continued for the second period) in S12 will be satisfied. By setting Vth of S12 (the second threshold value) to a lower value than Vth of S9 (the first threshold value), when the period during which the applied voltage exceeds the first threshold value does not continue for the first period and the period during which the applied voltage is lower than the second threshold value which is lower than the first threshold value continues for the second period, it is determined that the overvoltage state has been eliminated. By setting Vth of S9 to a stricter value than Vth of S12 in this way, it can be configured so that the determination of the elimination of the overcurrent state becomes more reliable.

[0050] In S13, the temperature control is returned from phase control to hybrid control, the power limit by tmax is released, the normal printing operation is executed, and then it returns to S6. Here, the relationship between time A and time B will be described. Time A (the first period) and time B (the second period) are set such that A > B, that is, time A is longer than time B. In this embodiment, A is set to 1 sec and B is set to 0.5 sec. This is in correspondence with the instantaneous fluctuations of the commercial AC power supply 401 in the market.

[0051] When the peak voltage detection unit 460 detects momentary overvoltage due to instantaneous fluctuations at S12, phase control is selected for the temperature control, and the temperature is controlled below tmax. However, the instantaneous fluctuations of the commercial AC power supply 401 are limited to a very short time, and then it returns to the normal voltage within the rating.

[0052] Since it is necessary to quickly detect at S12 that the voltage has returned to the normal voltage within the freeze frame and return to the normal printing operation at S13, time B is set shorter than time A. If the state of VIN < Vth has not continued for Bsec at S12, the process returns to S8 and the power limitation to the heater 300 continues.

[0053] According to this embodiment, with the above configuration, the following effects are obtained.

[0054] When an overvoltage is applied, the CPU 410 controls the triac 440 so as to suppress the voltage application near the peak voltage of the commercial AC power supply 401 applied to the heater 300. Thereby, it becomes possible to avoid damage to the resistance heating elements 302a and 302b forming the heater 300. Further, by providing control for continuing printing for a predetermined period while avoiding damage to the resistance heating elements 302a and 302b, it becomes possible to continue printing with almost no deterioration in printing quality against instantaneous fluctuations in the market.

[0055] (Embodiment 2) With reference to FIGS. 8 to 11, an image forming apparatus according to Embodiment 2 of the present invention will be described. The apparatus configuration in Embodiment 2 is the same as that in Embodiment 1, and the same reference numerals are given to the same constituent members, and the description thereof is omitted.

[0056] FIG. 8 shows a power supply circuit 500 for the heater 300 in Embodiment 2. An electric current detection mechanism is added to the configuration of Embodiment 1 shown in FIG. 3. The current flowing through the heater 300 is voltage-converted by the current transformer 510 and transmitted to the secondary side, and is input to the current detection unit 52 0. In the current detection unit 520, the voltage-converted primary-side current waveform is converted into an effective value or an average value and input to the CPU 410 as an HCRRT signal.

[0057] Next, the supply power when performing phase control in Example 2 will be described. The supply power to the heater 300 is based on the supply power ratio D described by Equation (1) of Example 1. The CPU 410 has a control table shown in FIG. 9, and performs control based on this control table during phase control execution. The supply power ratio D in this embodiment is controlled in 2.5% increments as the ratio to the power when energization is performed for all half-waves of the waveform pattern, but the number of divisions may be another predetermined number according to the fixing specification.

[0058] When calculating the supply power to the heater 300, the CPU 410 calculates the upper limit supply power from the HCRRT signal notified from the current detection unit 520, and controls so that the power below the upper limit supply power (hereinafter referred to as the maximum supplyable power ratio Dmax) is energized. The maximum supplyable power ratio Dmax is given by the following Equation (2) using the HCRRT signal, the supply power ratio D calculated by Equation (1), and the current limit value (Ilimit).

[0059] Dmax=(Ilimit / Irms) 2 ×D ··· (2)

[0060] The above current limit value (Ilimit) may be set as follows, for example. An allowable current value that can be supplied to the heater 300 obtained by subtracting the maximum current value supplied to the switching power supply circuit 461 from the rated current of the commercial AC power supply 401 may be set so that the rated current of the commercial AC power supply 401 can be used to the maximum extent possible when necessary.

[0061] When the supply power ratio D controlled based on the detected temperature of the thermistor 211 exceeds the maximum supplyable power ratio Dmax calculated by Equation (2), the maximum supplyable power ratio Dmax is prioritized, and the heater 300 is controlled with the maximum supplyable power ratio Dmax as the upper limit.

[0062] Also, the maximum supplyable power ratio Dmax is configured to be set to a desired value when the peak voltage detection unit 460 detects an overvoltage of the commercial AC power supply 401, separately from the calculation formula of Equation (2).

[0063] Fig. 10 shows the state of phase control. The upper waveform in Fig. 10 is the current waveform supplied to the heater 300. The middle waveform is the FUSERON signal of the drive signal input from the CPU 410 to the triac 440. When the FUSERON signal is input, the triac 440 is turned on, and the power supply to the heater 300 is started. The lower waveform is the ZEROX signal notified to the CPU 410 as a pulse signal from the zero-cross circuit 420 that determines whether the voltage of the commercial AC power supply 401 is below a certain threshold value.

[0064] The CPU 410 calculates the supply power ratio D according to Equation (1) based on the temperature detected by the thermistor 211, and converts the corresponding phase angle from the control table in Fig. 9. Then, using the rising or falling edge of the ZEROX signal as the synchronization timing, the FUSERON signal is sent to the triac 440 based on a predetermined time corresponding to the phase angle. Also, the CPU 410 calculates the maximum supplyable power ratio Dmax from Equation (2). The input of the supply power ratio D exceeding this maximum supplyable power ratio Dmax is prohibited. Therefore, the range of phase control is from 0% to the maximum supplyable power ratio Dmax.

[0065] Fig. 11 shows the flowchart of the control in the second embodiment. In S21, when a printing request is received from the user, printing is started. In S22, if the VIN signal detected by the peak voltage detector 460 is greater than the threshold value Vth described in Fig. 6, the process proceeds to S23; if it is smaller, the process proceeds to S25. In S23, since it is determined to be an overvoltage state, phase control for temperature control is selected and the power supply is started. When controlling the triac 440, the CPU 410 sets 0% to Dmax in Fig. 10. That is, the power supply to the triac 440 is in a stopped state. Since the power supply to the heater 300 is not performed, the printing operation is stopped and ends (S24).

[0066] In S25, since it is determined that the overvoltage state does not exist, hybrid control is selected for temperature control to start energization, and the normal printing operation is performed. In S26, it is determined whether a stop request has been received. If there is a stop request, normal termination occurs. If there is no stop request, in S27, it is determined whether the VIN signal detected by the peak voltage detector 460 is greater than the threshold value Vth. If the VIN signal is greater than the threshold value Vth, the process proceeds to S28. If the VIN signal is smaller than the threshold value Vth, the process returns to S26 to determine whether a stop request has been received. When the process proceeds to S28, phase control is selected for temperature control to continue printing. When controlling the triac 440, the CPU 410 sets C% for Dmax, and the maximum value of the supply power ratio D is C% or less to continue temperature control.

[0067] The C% set here is a value that does not exceed the voltage threshold ±Vbreak for preventing damage to the resistive heating elements 302a and 302b forming the heater 300 described in FIG. 6(B). Since the peak portion of the sine wave voltage waveform applied from the commercial AC power supply 401 is the highest, the value of C may be set so that the trailing portion of the sine wave voltage waveform avoiding the peak portion is applied. The value of C is set based on the overvoltage range of the commercial AC power supply 401 assumed in the market and the value calculated from ±Vbreak. Alternatively, the input voltage may be estimated by the peak voltage detector 460 and made variable according to the estimated input voltage.

[0068] In S29, when the state of VIN > Vth continues for Asec, the process proceeds to S30. In S30, when controlling the triac 440, the CPU 410 sets 0% for Dmax. That is, the energization of the triac 440 is stopped. Since the heater 300 is not energized, the printing operation is stopped and terminated (S31).

[0069] In S29, when the state where VIN > Vth has not continued for Asec, in S32, it is determined whether or not the state where VIN < Vth has not continued for Bsec. That is, it is detected whether or not the overvoltage state has been resolved. If the state where VIN < Vth has continued for Bsec, that is, if the overvoltage state has been resolved, the process proceeds to S33. The Vth in S32 may be set to a lower value compared to the Vth in S22, S27, and S29, and hysteresis may be provided to the voltage detected by the peak voltage detection unit 460. In S33, the temperature control is returned from the phase control to the hybrid control, the power limit set to C% of Dmax is released, the normal printing operation is executed, and the process returns to S26. The relationship between time A and time B and the basis thereof are the same as those described in the description of the flowchart of the first embodiment.

[0070] In S32, when the state where VIN < Vth has not continued for Bsec, the process returns to S28, and the power limit to the heater 300 is continued.

[0071] According to the present embodiment, with the above configuration, the following effects are obtained.

[0072] When an overvoltage is applied, the CPU 410 controls the triac 440 within the range of the supply power ratio D below the maximum supplyable power ratio Dmax so as to suppress the voltage application near the peak voltage of the commercial AC power supply 401 applied to the heater 300. By such control, it becomes possible to avoid damage to the heating elements 302a and 302b forming the heater 300. Further, by providing control for continuing printing for a predetermined period while avoiding damage to the heating elements 302a and 302b, it becomes possible to continue printing with almost no deterioration in printing quality with respect to instantaneous fluctuations in the market.

[0073] The above-described embodiments can be combined with each other in terms of their respective configurations.

[0074] The disclosure of the embodiments of the present invention includes the following configurations. (Configuration 1) An image forming unit that forms a toner image on a recording material, It has a heating element that generates heat by receiving power from a commercial AC power supply, and a heating unit that heats the toner image formed by the image forming unit, a temperature detection unit that detects the temperature of the heating unit, a power control unit that controls the power supply from the commercial AC power supply to the heating element based on the temperature information detected by the temperature detection unit, a detection unit that detects whether the applied voltage applied from the commercial AC power supply exceeds the rated value, In an image forming apparatus comprising: When the detection unit detects that the applied voltage exceeds the rated value, the power control unit controls the power supply so that the waveform pattern of the current flowing through the heating element becomes a waveform pattern in which the energization time to the heating element within each half-wave is within a predetermined time. When the period during which the applied voltage exceeds the rated value continues for a predetermined period, the power supply from the commercial AC power supply to the heating element is cut off. An image forming apparatus characterized by this. (Configuration 2) When the detection unit detects that the applied voltage does not exceed the rated value, the power control unit performs first power control to control the power supply so that the waveform pattern of the current to the heating element becomes any one of a waveform pattern of frequency control, a waveform pattern of phase control, or a waveform pattern combining frequency control and phase control in one control cycle. When the detection unit detects that the applied voltage exceeds the rated value, The power control unit performs second power control to control the power supply so that the waveform pattern of the current to the heating element becomes a waveform pattern of phase control in one control cycle. The image forming apparatus according to Configuration 1, characterized by this. (Configuration 3) During the period when the second power control is being performed, when the period during which the applied voltage exceeds the rated value does not continue for the predetermined period, The power control unit switches the control of the power supply from the second power control to the first power control. The image forming apparatus according to Configuration 1 or 2, characterized by this. (Configuration 4) While the second power control is being performed, if the period during which the applied voltage exceeds the first threshold value continues as a first period which is the predetermined period, the power control unit cuts off the power supply from the commercial AC power supply to the heating element, While the second power control is being performed, if the period during which the applied voltage exceeds the first threshold value does not continue for the first period and the period during which the applied voltage is lower than a second threshold value which is lower than the first threshold value continues for a second period, the power control unit switches the control of the power supply from the second power control to the first power control, and the image forming apparatus according to any one of Configurations 1 to 3. (Configuration 5) The image forming apparatus according to any one of Configurations 1 to 4, wherein the first period is longer than the second period. (Configuration 6) The waveform pattern in which the energization time to the heating element for each half-wave is within the predetermined time is a waveform pattern that does not include the peak of the applied voltage, and the image forming apparatus according to any one of Configurations 1 to 5. (Configuration 7) The waveform pattern in which the energization time to the heating element for each half-wave is within the predetermined time is a waveform pattern in which energization to the heating element is started after passing the peak of the applied voltage for each half-wave, and the image forming apparatus according to any one of Configurations 1 to 6. (Configuration 8) The power supply is controlled by controlling a power ratio which is a ratio of the power in the case of energizing all half-waves of the waveform pattern, a maximum supplyable power ratio which is the maximum power ratio that can be supplied to the heating element is set in the power ratio, the power control unit controls the power supply so that the power ratio does not exceed the maximum supplyable power ratio, and the image forming apparatus according to any one of Configurations 1 to 7. (Configuration 9) If the period during which the applied voltage exceeds the rated value does not continue for the predetermined period, The power control unit releases the control of the power supply so that the waveform pattern of the current flowing through the heating element becomes a waveform pattern in which the energization time to the heating element for each half-wave is within a predetermined time, in the image forming apparatus according to any one of Configurations 1 to 8. (Configuration 10) The heating unit includes a heater including the heating element and a cylindrical film in which the heater is disposed inside, and heats the toner image through the film, in the image forming apparatus according to any one of Configurations 1 to 9. (Configuration 11) The heating unit has a roller that contacts the outer peripheral surface of the film, and forms a fixing nip portion that sandwiches and conveys a recording material between the film and the roller by sandwiching the film between the heater and the roller, in the image forming apparatus according to Configuration 10.

Explanation of Signs

[0075] 100... Image forming apparatus, 200... Fixing device, 212... Thermistor, 300... Heater, 302... Heating element, 401... Commercial AC power supply, 410... CPU, 420... Zero-cross circuit, 430... Relay, 440... Triac, 460... Peak voltage detection unit, 510... Current transformer, 520... Current detection unit

Claims

1. An image forming unit that forms a toner image on a recording material; A heating unit that has a heating element that generates heat upon receiving power supply from a commercial AC power source and heats the toner image formed by the image forming unit; A temperature detection unit that detects the temperature of the heating unit; A power control unit that controls the power supply from the commercial AC power source to the heating element based on the temperature information detected by the temperature detection unit; A detection unit that detects whether the applied voltage applied from the commercial AC power source exceeds a rated value; In an image forming apparatus comprising: When the detection unit detects that the applied voltage exceeds the rated value, the power control unit controls the power supply such that the waveform pattern of the current flowing through the heating element becomes a waveform pattern in which the energization time to the heating element for each half-wave is within a predetermined time. When the period during which the applied voltage exceeds the rated value continues for a predetermined period, the power supply from the commercial AC power source to the heating element is cut off. An image forming apparatus characterized by this.

2. When the detection unit detects that the applied voltage does not exceed the rated value, The power control unit performs first power control to control the power supply such that the waveform pattern of the current to the heating element becomes any one of a waveform pattern of frequency control, a waveform pattern of phase control, or a waveform pattern combining frequency control and phase control in one control period. When the detection unit detects that the applied voltage exceeds the rated value, The power control unit performs second power control to control the power supply such that the waveform pattern of the current to the heating element becomes a waveform pattern of phase control in one control period. The image forming apparatus according to claim 1, characterized by this.

3. When, during the second power control, the period during which the applied voltage exceeds the rated value does not continue for the predetermined period, The power control unit switches the control of the power supply from the second power control to the first power control. The image forming apparatus according to claim 2, characterized by this.

4. When, during the second power control, the period during which the applied voltage exceeds a first threshold value continues for a first period as the predetermined period, The power control unit cuts off the power supply from the commercial AC power source to the heating element. While the second power control is being performed, if the period during which the applied voltage exceeds the first threshold does not continue for the first period, and the period during which the applied voltage falls below a second threshold lower than the first threshold continues for the second period, The image forming apparatus according to claim 2, wherein the power control unit switches the control of the power supply from the second power control to the first power control.

5. The image forming apparatus according to claim 4, wherein the first period is longer than the second period.

6. The image forming apparatus according to claim 1, wherein the waveform pattern in which the energization time to the heating element for each half-wave is within the predetermined time is a waveform pattern that does not include the peak of the applied voltage.

7. The waveform pattern in which the energization time to the heating element for each half-wave is within the predetermined time is such that energization to the heating element starts after passing the peak of the applied voltage for each half-wave, and is the waveform pattern of the image forming apparatus according to claim 1.

8. The power supply is controlled by controlling a power ratio which is a ratio of the power in the case of energizing all half-waves of the waveform pattern, The maximum supplyable power ratio which is the maximum power ratio that can be supplied to the heating element is set in the power ratio, The image forming apparatus according to claim 1, wherein the power control unit controls the power supply so that the power ratio does not exceed the maximum supplyable power ratio.

9. When the period during which the applied voltage exceeds the rated value does not continue for the predetermined period, The image forming apparatus according to claim 1, wherein the power control unit releases the control of the power supply so that the waveform pattern of the current flowing through the heating element becomes a waveform pattern in which the energization time to the heating element for each half-wave is within a predetermined time.

10. The heating unit according to claim 1, comprising a heater including the heating element and a cylindrical film in which the heater is disposed inside, and heating the toner image through the film.

11. The heating unit according to claim 10, further comprising a roller that contacts an outer peripheral surface of the film, and forms a fixing nip portion that sandwiches and conveys a recording material between the film and the roller by sandwiching the film between the heater and the roller.

Images