Image forming apparatus, heater control method, and image forming method

Abstract

To drive a heater while suppressing influence on other electric equipment connected to a commercial power supply.SOLUTION: When starting the supply of commercial power PW to a heater 43 of a fixing part 40, an image forming apparatus 1 performs phase control, then performs wave number control, and then starts full-wave supply. Therefore, the image forming apparatus 1 supplies a part of the commercial power PW to the heater 43 in the phase control, supplies a part of the commercial power PW by modulation in a cycle different from that of the phase control in the next wave number control, and then performs the full-wave supply. As a result, when the full-wave supply is started, the image forming apparatus 1 can suppress the occurrence of flicker without deteriorating the harmonics.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus, a heater control method, and an image forming method, and is suitable for application to, for example, an electrophotographic printer. [Background technology]

[0002] In recent years, there have been image forming devices that print images by, for example, forming a toner image using toner with a developing device, transferring it to paper (also called a medium), and then fixing the image to the paper by applying heat and pressure with a fixing device. Among these, the fixing device has, for example, rollers or annular belts arranged above and below the paper transport path, and sandwiches the paper in a nip formed between them to apply heat and pressure to the paper.

[0003] This fixing device has, for example, a heater that generates heat in response to the supply of power, and for reasons such as minimizing power consumption, it is known to control the device so that, for example, heating begins just before the fixing process is performed, and the degree of heating is reduced or heating is stopped once the desired temperature is reached.

[0004] However, since a relatively large amount of power is required to heat the heater, if a relatively large amount of power is suddenly consumed when heating begins in the fixing device, this may cause voltage fluctuations in the commercial power source, which is the power supply source, or may cause flicker in lighting fixtures, etc.

[0005] In view of this, an image forming apparatus has been proposed in which voltage fluctuations, flicker, and the like are suppressed by performing phase control or the like in relation to the control of power related to the heater (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2014-232247 (Fig. 5, etc.) Summary of the Invention [Problem to be solved by the invention]

[0007] In the image forming apparatus described above, a heater with relatively high power consumption is used to raise the temperature of the fixing device in a short period of time. In such an image forming apparatus, the occurrence of pulsating changes in temperature (so-called temperature ripple) can be suppressed by shortening the period during which the power supply to the heater is turned on or off.

[0008] However, in an image forming apparatus, if the period during which phase control is performed is made relatively long, the occurrence of flicker can be reduced but harmonics increase. Also, in an image forming apparatus, if the period during which phase control is performed is made relatively short, the occurrence of flicker increases but harmonics can be reduced. In other words, in an image forming apparatus, it is not possible to reduce both flicker and harmonics at the same time, which makes it difficult to drive the heater stably.

[0009] The present invention has been made in consideration of the above points, and aims to propose an image forming apparatus, a heater control method, and an image forming method that are capable of driving a heater while minimizing the impact on other electrical devices connected to a commercial power source. [Means for solving the problem]

[0010] In order to solve this problem, the image forming apparatus of the present invention is provided with a heater that generates heat using AC power supplied from an AC power source, a fixing member that is heated by the heater and fixes an image on a medium, and a control unit that controls the AC power supplied from the AC power source to the heater, and the control unit controls the phase of the AC power when the heater starts to generate heat, and then controls the AC power so that full-wave supply of the AC power is started.

[0011] Furthermore, in the heater control method of the present invention, in a heater control method for controlling AC power supplied from an AC power supply to a heater, when the heater starts to generate heat, the AC power is phase-controlled, and following the phase control of the AC power, the AC power is wave-number-controlled, and following the wave-number control of the AC power, full-wave supply of the AC power is started.

[0012] Furthermore, in the image forming method of the present invention, the phase control, wave number control, and full-wave supply of AC power are performed by the heater control method described above, and the duty ratio of the phase control is determined based on the temperature of the fixing member that is heated by the heater and fixes the image on the medium.

[0013] When starting heating of a heater, the present invention first supplies a portion of AC power to the heater using phase control, then supplies a portion of AC power to the heater using wave number control using a modulation method different from the phase control, and then starts full-wave supply. Therefore, when starting full-wave supply, the present invention can reduce harmonics while reducing flicker. [Effects of the Invention]

[0014] According to the present invention, it is possible to realize an image forming apparatus that can drive a heater while suppressing the influence on other electrical devices connected to a commercial power source. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus. [Figure 2] FIG. 2 is a schematic circuit diagram illustrating a circuit configuration of the image forming apparatus. [Figure 3] FIG. 2 is a schematic diagram showing a waveform of power. [Figure 4] 5A to 5C are schematic diagrams showing various waveforms in phase control. [Figure 5] FIG. 4 is a schematic diagram illustrating a phase control table. [Figure 6] 5A to 5C are schematic diagrams showing various waveforms in wave number control. [Figure 7]10A and 10B are schematic diagrams showing a start wave number control table and an end wave number control table; [Figure 8] 10 is a flowchart showing a heater control process procedure. [Figure 9] 10 is a flowchart showing a phase control process procedure. [Figure 10] 10 is a flowchart showing a wave number control process procedure. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

[0017] [1. Configuration of image forming device] 1, the image forming apparatus 1 according to this embodiment is an electrophotographic printer that can form, i.e., print, a color image on a medium M such as plain paper or coated paper. Incidentally, the image forming apparatus 1 does not have an image scanner function for reading a document or a communication function using a telephone line, and is a single-function SFP (Single Function Printer) that has only a printer function.

[0018] Various components are arranged inside a roughly box-shaped housing 2 of the image forming apparatus 1. In the following description, the right end portion in Fig. 1 is defined as the front of the image forming apparatus 1, and the up-down direction, left-right direction, and front-rear direction are defined when viewed from the front.

[0019] The image forming apparatus 1 is controlled as a whole by a control unit 3. This control unit 3 is connected to a host device such as a computer device (not shown), and when it receives a print instruction or print data from this host device, it executes an image forming process (also called a printing process) that forms a print image on the surface of the medium M.

[0020] An operation panel 4 that displays various information and accepts operational inputs is provided near the front of the top surface of the housing 2. The operation panel 4 has a touch panel that combines a display panel such as a liquid crystal panel with a touch sensor, LEDs (Light Emitting Diodes), etc., and displays various information under the control of the control unit 3 and also accepts operational inputs from the user.

[0021] A tray 5 for storing media M is provided at the bottom of the housing 2. This tray 5 is capable of storing media M up to A3 size with the short sides aligned in the left-right direction. A paper feed conveyance unit 10 is provided above and in front of the tray 5. The paper feed conveyance unit 10 forms a paper feed conveyance path W1, which is a route for conveying the media M, with conveyance guides 11 facing each other at a predetermined distance.

[0022] The paper feed conveying section 10 also includes a pickup roller 12, a paper feed roller 13, a separation roller 14, a registration roller 15, a pressure roller 16, and a pair of conveying rollers 17 arranged along the paper feed conveying path W1. Each roller is cylindrical with its central axis aligned in the left-right direction and is rotatably supported. Some of the rollers receive driving force from a paper feed motor (not shown). The pairs of conveying rollers 17 and 18 are arranged opposite each other across the paper feed conveying path W1.

[0023] The paper feed conveying unit 10 rotates each roller appropriately under the control of the control unit 3, thereby picking up and conveying the media M stored in a stacked state on the tray 5 one by one while separating them. Specifically, the pickup roller 12 pulls out the media M from the tray 5. The paper feed roller 13 advances the media M pulled out of the tray 5 by the pickup roller 12 along the paper feed conveying path W1. The separation roller 14 separates the uppermost medium M from the other media M when multiple media M are removed from the tray 5. If the medium M is skewed relative to the paper feed conveying path W1, the registration roller 15 and the pressure roller 16 correct its posture (the orientation of each side relative to the direction of advancement) to allow it to advance correctly. The conveying roller pair 17 conveys the medium M along the paper feed conveying path W1 and then sends it out diagonally upward and rearward.

[0024] A transfer unit 20 is disposed below and above the rear of the pair of transport rollers 17 in the paper feed transport unit 10, and four developing units 30 are disposed above the transfer unit 20. A linear transfer transport path W2 is formed between the transfer unit 20 and each developing unit 30, and is connected to the paper feed transport path W1 and extends diagonally upward and rearward.

[0025] The transfer unit 20 is composed of a drive roller 21, an idle roller 22, a transfer belt 23, and four transfer rollers 24. The drive roller 21, the idle roller 22, and each of the transfer rollers 24 are all formed in a cylindrical shape with their central axes aligned in the left-right direction, and are each rotatably supported.

[0026] The drive roller 21 is disposed relatively rearward and can be rotated by a driving force supplied from a driving force source (not shown). The idle roller 22 is disposed slightly spaced forward and below the drive roller 21, in the vicinity of the conveying roller pair 17. The transfer rollers 24 are discretely disposed between the drive roller 21 and the idle roller 22 at approximately equal intervals.

[0027] The transfer belt 23 is a flexible endless belt that is stretched around the drive roller 21, the idle roller 22, and each transfer roller 24. The upper portion of the transfer belt 23 is stretched linearly along the transfer conveying path W2. The upper ends of each transfer roller 24 are in contact with the inner periphery of the upper portion of the transfer belt 23. Therefore, in the transfer unit 20, when the drive roller 21 rotates counterclockwise in FIG. 1, the transfer belt 23 runs, which in turn rotates the idle roller 22 and each transfer roller 24. At this time, the upper portion of the transfer belt 23 runs diagonally upward and rearward along the transfer conveying path W2.

[0028] The four developing units 30 (30K, 30Y, 30M, and 30C), also called image forming units, are arranged above the transfer unit 20, aligned along the transfer transport path W2, i.e., along a diagonal direction from the lower front to the upper rear. Each developing unit 30 corresponds to a respective color, black (K), yellow (Y), magenta (M), and cyan (C), but the only difference is the color; all of them are configured similarly.

[0029] The developing section 30 is made up of a developing unit 31 and an exposure unit 32. The developing unit 31 includes a toner storage unit that stores toner as a developer, multiple rollers, and a photosensitive drum 34. Each of the rollers and the photosensitive drum 34 is rotatably configured as a columnar or cylindrical shape with its central axis aligned in the left-right direction. The photosensitive drum 34 is located at the lowest position in the developing unit 31 and abuts against the transfer belt 23, sandwiching the transfer belt 23 between itself and the transfer roller 24.

[0030] The exposure processing unit 32 has multiple LEDs aligned in the left-right direction above the photosensitive drum 34. The exposure processing unit 32 exposes the outer circumferential surface of the photosensitive drum 34 to light by appropriately emitting light from each LED under the control of the control unit 3, thereby forming an electrostatic latent image. In response to this, the development processing unit 31 adheres toner to the outer circumferential surface of the photosensitive drum 34, thereby forming a toner image (also called a developer image).

[0031] At this time, when the medium M is transported along the transfer transport path W2, the transfer unit 20 transfers the toner image from the photosensitive drum 34 to the medium M, causing the toner image to adhere to the surface of the medium M.

[0032] The fixing unit 40 is disposed behind the transfer unit 20, i.e., behind the rearmost developing unit 30C. The fixing unit 40 includes a fixing roller 41, a pressure roller 42, a heater 43, and a thermistor 44. The fixing roller 41 and the pressure roller 42 are rotatably supported at positions sandwiching the fixing conveyance path W3 from above and below. The pressure roller 42 is biased toward the fixing roller 41 by a predetermined biasing member.

[0033] Heater 43 is, for example, a halogen heater, which generates heat in response to the power supplied to it and heats fixing roller 41. A thermistor 44 serving as a temperature detector changes its resistance value in response to the temperature of fixing roller 41, generates a temperature detection signal ST in response to the resistance value, and supplies the signal to control unit 3. Control unit 3 recognizes the temperature of fixing roller 41 based on this temperature detection signal ST, and controls the power supplied to heater 43 in response to the recognized temperature.

[0034] When a printing process is to be performed, the fixing unit 40 first rotates the fixing roller 41 and the pressure roller 42 and generates heat from the heater 43. When the medium M is conveyed along the fixing conveying path W3, the fixing unit 40 clamps the medium M between the fixing roller 41 and the pressure roller 42 and applies heat and pressure to fix the toner to the medium M, and then sends the medium M diagonally upward and rearward.

[0035] A double-sided printing unit 50 is provided behind and below the fixing unit 40. The double-sided printing unit 50 includes a switch 51 provided behind the fixing unit 40, as well as a plurality of conveyance guides and a plurality of conveyance roller pairs, which form a circulating conveyance path W4, a temporary evacuation conveyance path W5, and the like. Of these, the circulating conveyance path W4 is formed to connect the switch 51 and the conveyance roller pair 17 of the paper feed conveyance unit 10.

[0036] When double-sided printing is performed, the double-sided printing unit 50 switches the switch 51 under the control of the control unit 3 to cause the medium M to advance to the temporary evacuation conveyance path W5. After the tail of the medium M passes the switch 51, the double-sided printing unit 50 reverses the direction of travel of the medium M and causes it to advance along the circulating conveyance path W4, merging with the paper feed conveyance path W1 of the paper feed conveyance unit 10 near the conveyance roller pair 17. As a result, the double-sided printing unit 50 reverses the medium M and causes it to advance again from the paper feed conveyance path W1 to the transfer conveyance path W2, thereby transferring an image to the back side of the medium M. Incidentally, when double-sided printing is not performed on the medium M, or when an image has been transferred to the back side of the medium M, the double-sided printing unit 50 advances the medium M diagonally upward and rearward.

[0037] A paper discharge conveyance section 60 is disposed behind or above the switch 51. The paper discharge conveyance section 60 has a configuration similar to a portion of the paper feed conveyance section 10, and comprises conveyance guides 61 opposed to each other at a predetermined distance to form a paper discharge conveyance path W6, which is a route for conveying the medium M, and a discharge outlet 62 at the end of the path. In the paper discharge conveyance section 60, conveyance roller pairs 63 and 64 and the like are disposed in sequence along the paper discharge conveyance path W6.

[0038] The paper discharge conveying unit 60 rotates the conveying roller pairs 63 and 64 in accordance with the control of the control unit 3, thereby conveying the medium M received from the fixing unit 40 via the switch 51 along the paper discharge conveying path W6 and discharging it from the discharge outlet 62, thereby placing it on the discharge tray 6 formed on the top surface of the housing 2.

[0039] In this way, the image forming device 1 can form an image, i.e., print, by sequentially transporting the medium M along each transport path W, transferring the toner image formed by the developing unit 30 to the medium M, and fixing it in the fixing unit 40.

[0040] Next, the circuit configuration of the image forming apparatus 1 will be described with reference to Fig. 2. The image forming apparatus 1 is provided with a power supply board 71 and a control board 72 as circuit boards on which various electronic components are mounted. The power supply board 71 is provided with a transformer 81, an AC (Alternating Current) zero-cross circuit 82, a heater circuit 83, a power supply control circuit 84, a DC (Direct Current)-DC converter 85, etc. The control board 72 is also provided with a control unit 3.

[0041] Image forming apparatus 1 is connected to a commercial power source 100 as an AC power source, and AC power is supplied from commercial power source 100 to transformer 81 of power supply board 71. This AC power has, for example, an effective voltage of 100 V and a frequency of 50 Hz. Other electrical devices arranged in the room in which image forming apparatus 1 is installed, such as lighting fixtures and computer equipment (neither of which are shown), are also connected to commercial power source 100.

[0042] The transformer 81 is connected to the commercial power supply 100, and converts the voltage of the AC power supplied from the commercial power supply 100 into a desired voltage (e.g., 24 V, etc.), rectifies it using a rectifier circuit (not shown), and supplies it to the control board 72 as DC power.

[0043] The AC zero-cross circuit 82 detects the timing when the voltage of the AC power becomes 0 [V], generates a zero-cross signal SZ whose value fluctuates in a pulse-like manner in accordance with the timing, and supplies this to the control unit 3. Therefore, the zero-cross signal SZ has a waveform in which pulses appear at a period corresponding to a half-wave of the AC power supplied from the commercial power source 100 (this will be described in detail later).

[0044] The heater circuit 83 is a circuit that supplies power to the heater 43 of the fixing unit 40, and has a circuit configuration using a triac as disclosed in, for example, Japanese Patent Application Laid-Open No. 2014-232247. The heater circuit 83 switches whether or not to supply current to the heater 43 in response to a heater-on signal supplied from the control unit 3.

[0045] The power supply control circuit 84 is connected between the commercial power supply 100 and the input terminal of the transformer 81, and is also connected to the output terminal of the transformer 81. The power supply control circuit 84 controls the power input to the transformer 81 by feedback control in accordance with the output voltage of the transformer 81, thereby maintaining the output voltage constant.

[0046] The DC-DC converter 85 is a circuit that converts the voltage of DC power into another voltage, and converts the voltage of the DC power generated by the transformer 81, for example, from 24 [V] to 5 [V] and supplies it to the control unit 3.

[0047] The control unit 3 has a central processing unit (CPU), random access memory (RAM), read only memory (ROM), application specific integrated circuit (ASIC), input / output interface, etc., all of which are connected to one another via a bus. The control unit 3 is also connected to the thermistor 44 of the fixing unit 40, and acquires a detection signal from the thermistor 44 indicating the detected temperature.

[0048] The control unit 3 is connected to a host computer (not shown) via an input / output interface, and when it receives a print job including image data etc. from the computer, it performs printing while appropriately controlling each unit. At this time, the control unit 3 controls the power supplied to the heater 43 of the fixing unit 40 by supplying a heater-on signal to the heater circuit 83 while appropriately controlling the signal.

[0049] [2. Heater control] Incidentally, in the image forming apparatus 1, the temperature of the fixing roller 41 and the like in the fixing unit 40 is controlled, for example, to a fixing temperature when a printing process is performed, and to a standby temperature when a standby printing process is in a standby state. The fixing temperature is a relatively high temperature that melts and fixes the toner transferred onto the medium M, and the standby temperature is a temperature that is lower than the fixing temperature but reaches the fixing temperature in a relatively short time by heating with the heater 43.

[0050] Furthermore, in the image forming apparatus 1, although a certain amount of heat is taken away by the medium M during fixing in the fixing unit 40 during printing processing, there is a desire to minimize the extent of the temperature drop at this time. For this reason, the fixing roller 41 and pressure roller 42 in the image forming apparatus 1 are made of materials with a relatively large heat capacity.

[0051] On the other hand, in order to minimize the waiting time from when the power is turned on until the printing process can start, the image forming apparatus 1 needs to heat the fixing roller 41 and the like to a predetermined temperature in the shortest possible time in the fixing unit 40. Accordingly, the fixing unit 40 of the image forming apparatus 1 employs a heater 43 that requires a relatively large amount of power.

[0052] However, since heater 43, which has a relatively large power supply, has a lower electrical resistance when the temperature is low, such as immediately after power is turned on, compared to when the temperature is high, resulting in an excessive inrush current. In this case, image forming apparatus 1 may cause voltage fluctuation flicker in other electrical devices, such as lighting fixtures, connected to commercial power supply 100.

[0053] Therefore, in the image forming apparatus 1, in order to suppress the occurrence of flicker, etc., it is conceivable to perform phase control using a predetermined duty ratio in controlling the power supplied to the heater 43, and then perform full-wave supply, which supplies all of the power obtained from the commercial power source 100.

[0054] In addition, in the image forming apparatus 1, with regard to the control of the heater 43, as shown in the schematic voltage waveforms in Fig. 3, phase control is performed in periods T1 and T2, wave number control is performed for a predetermined time in period T3, and then full wave supply is performed in period T4. The phase control and wave number control will be described below.

[0055] [2-1. Phase control] In the present embodiment, the phase control is performed by turning on the power for only a portion of each half-wave of a sine wave, as shown in periods T1 and T2 in FIG. 3, so that the time for which power is supplied is reduced to a predetermined ratio (corresponding to the so-called duty ratio) compared to the case of full-wave supply.

[0056] Specifically, in the image forming apparatus 1, when commercial power PW is supplied from the commercial power source 100 (FIG. 2) to the power supply board 71, the AC zero-cross circuit 82 detects the timing when the voltage of the commercial power PW becomes 0 [V], i.e., the zero-cross timing, and generates a zero-cross signal SZ and supplies it to the control unit 3.

[0057] 4A, the zero-cross signal SZ has a pulse-like portion that fluctuates in accordance with the zero-cross timing of the commercial power PW. Hereinafter, the time length of half of one cycle of the commercial power PW will be referred to as the half cycle HC or zero-cross cycle, and the time length of the pulse-like portion of the zero-cross signal SZ will be referred to as the zero-cross pulse width WZ.

[0058] When performing this phase control, the control unit 3 generates a heater signal SH that periodically fluctuates in a pulsed manner as shown in Fig. 4(B) and supplies this to the heater circuit 83. Hereinafter, the time length of the pulsed portion of the heater signal SH will be referred to as the heater pulse width WH.

[0059] As described above, a predetermined circuit (not shown) using a triac is configured inside the heater circuit 83. Therefore, when a pulse is generated in the heater signal SH, the heater circuit 83 supplies the commercial power PW to the heater 43 for the period from when the pulse is generated in the heater signal SH until the next zero crossing of the commercial power PW, as shown in FIG.

[0060] Here, the time from the zero cross point in the zero cross signal SZ to the time when the heater signal SH rises in a pulse shape is defined as the on-wait time TS, and the proportion of the time that the heater 43 is on in one half cycle HC is defined as the on-time proportion t%.

[0061] Specifically, the control unit 3 calculates the on-wait time TS based on the on-time ratio t, the half cycle HC, and the zero-cross pulse width WZ according to the following equation (1).

[0062]

number

[0063] Furthermore, in phase control, the control unit 3 can not only keep the on-time ratio t constant, but also change the on-time ratio t midway. For example, as shown in Fig. 3, the control unit 3 can set the duty ratio to a relatively low ratio (e.g., 30%) in the first half period T1 and set it to a higher ratio (e.g., 50%) in the second half period T2. Therefore, the control unit 3 stores a phase control table TBL1 as shown in Fig. 5 in advance in a ROM (not shown), and refers to this phase control table TBL1 during phase control.

[0064] This phase control table TBL1 stores four phase control settings CP1, CP2, CP3, and CP4. Each phase control setting CP has a "first period" that means the first period and a "second period" that means the second period, and stores an on-time ratio t and an on-count n for each. The on-count n not only indicates the number of times the switch is switched on, but also corresponds to the number of half cycles HC, so it also indicates the length of the period over which phase control is performed.

[0065] However, in some phase control settings CP, the on-time ratio t and the on-count n of the second period are both set to the value "0." This indicates that the second period is invalid in that phase control setting CP, that is, phase control ends only in the first period.

[0066] When performing printing processing, the control unit 3 selects one of the phase control settings CP (CP1, CP2, CP3, or CP4) according to the temperature detected by the thermistor 44. Next, the control unit 3 reads out the on-time ratio t and the on-count n for each of the first and second periods according to the selected phase control setting CP from the phase control table TBL1, and generates a heater signal SH based on this and supplies it to the heater circuit 83.

[0067] [2-2. Wave number control] In this embodiment, as shown in Fig. 3, wave number control is performed in period T3 immediately before the start of full-wave supply in period T4. In this wave number control, by switching on or off in units of half waves of a sine wave, the power supplied in a period corresponding to a plurality of sine waves is controlled to be reduced to a predetermined ratio (corresponding to the so-called duty ratio) compared to the case of full-wave supply.

[0068] Specifically, in the image forming apparatus 1, when commercial power PW is supplied from the commercial power source 100 (FIG. 2) to the power supply board 71, a zero-cross signal SZ similar to that in the case of phase control performed by the AC zero-cross circuit 82 is generated and supplied to the control unit 3, as shown in the schematic waveform of FIG. 6(A).

[0069] When performing this wave number control, the control unit 3 generates a heater signal SH that varies in pulse form only at the timings when the heater should be turned on in half-wave units, in accordance with the periodic timing at which the zero-cross signal SZ rises, as shown in Figure 6(B), and supplies this to the heater circuit 83.

[0070] As in the case of phase control, the heater circuit 83 supplies the commercial power PW to the heater 43 only during the period from when the pulse included in the heater signal SH rises to when the commercial power PW next crosses zero. As a result, the heater circuit 83 can switch the heater 43 (FIG. 2) on or off in half-wave units based on the heater signal SH, as shown in FIG. 6(C).

[0071] Furthermore, as a result of various experiments and verifications conducted on the image forming apparatus 1, it was found that sufficient effects in suppressing harmonics and flicker can be obtained by performing half-wave control for a period equivalent to 10 half-waves. Specifically, for example, if the cycle of commercial power PW is 50 [Hz], the period equivalent to 10 half-waves is 100 [ms].

[0072] Furthermore, when performing wave number control, the control unit 3 can switch the ON ratio between multiple patterns. Specifically, the control unit 3 stores a start-time wave number control table TBL2 shown in Fig. 7(A) in advance in a ROM (not shown), and refers to this start-time wave number control table TBL2 during wave number control.

[0073] This start wavenumber control table TBL2 stores six start wavenumber control settings CNS0, CNS1, CNS2, CNS3, CNS4, and CNS5. Each start wavenumber control setting CNS (CNS0 to CNS5) stores an on-ratio r and a pattern pt.

[0074] The on-ratio r is the percentage of half-waves that are on based on the total number of half-waves in the period, and varies from 0% to 80% depending on the start-up wave number control setting CNS. In other words, the on-ratio r is the percentage of the commercial power PW that is supplied to the heater 43, and is a value equivalent to the so-called duty ratio.

[0075] The pattern pt indicates whether each half wave in each order should be turned on (ON) or off (OFF) for a period equivalent to 10 half waves. The order x is an integer representing the ordinal number of each half wave in each pattern pt, and is a value between "0" and "9."

[0076] 3, the image forming apparatus 1 performs wave number control during period T3, and then switches to full-wave supply during the following period T4. If the last half-wave in the wave number control during period T3 is on, the half-wave and the full-wave supply during period T4 will form a continuous waveform, which effectively extends the full-wave supply, potentially making it impossible to sufficiently suppress flicker.

[0077] Therefore, in the image forming apparatus 1, for all patterns pt of the start wavenumber control settings CNS in the start wavenumber control table TBL2, the half-wave order x is set to "9," the last value. That is, when switching from wavenumber control to full-wave supply, the image forming apparatus 1 always inserts an off period in half-wave units, which allows for sufficient suppression of flicker. Hereinafter, this period of time when switching from wavenumber control to full-wave supply is turned off in fractional units is referred to as an off period. This off period is a period of at least one fractional unit, depending on the pattern pt.

[0078] Furthermore, the image forming apparatus 1 terminates the full-wave supply when a predetermined condition is met, such as when the temperature detected by thermistor 44 exceeds a predetermined upper limit temperature. At this time, the image forming apparatus 1 does not simply terminate the full-wave supply, but instead performs wave number control again and phase control for a predetermined period following the full-wave supply. In other words, when terminating the full-wave supply, the image forming apparatus 1 sequentially switches from full-wave supply to wave number control and phase control, in the reverse order of when the full-wave supply is started as shown in FIG. 3.

[0079] Regarding the wave number control performed after the end of this full wave supply, the control unit 3 stores in advance in a ROM (not shown) an end wave number control table TBL3 shown in FIG. 7(B) and refers to this end wave number control table TBL3.

[0080] Six types of end wavenumber control settings CNE0, CNE1, CNE2, CNE3, CNE4, and CNE5 are stored in this end wavenumber control table TBL3. As with the start wavenumber control table TBL2, each end wavenumber control setting CNE (CNE0 to CNE5) stores an on-ratio r and a pattern pt.

[0081] Among these, pattern pt is configured by arranging the patterns pt of each start wavenumber control setting CNS (CNS0 to CNS5) in start wavenumber control table TBL2 in reverse order. That is, in end wavenumber control table TBL3, in the patterns pt of all end wavenumber control settings CNE, the half-wave order x is turned off when it is the first "0". As a result, in image forming apparatus 1, when switching from full-wave supply to wavenumber control, an off period in half-wave units is always inserted, which makes it possible to sufficiently suppress the occurrence of flicker.

[0082] [3. Processing Procedure] Next, the process of controlling the heater 43 when performing printing processing in the image forming apparatus 1 will be described with reference to the flowcharts of FIGS. 8, 9, and 10. FIG.

[0083] [3-1. Heater control processing] When the power is turned on, the control unit 3 of the image forming apparatus 1 reads a heater control program from a ROM (not shown) and starts the heater control processing procedure RT1 shown in Fig. 8. Incidentally, the control unit 3 also executes this heater control processing procedure RT1 when, for example, the temperature of the fixing roller 41 or the like drops during printing processing or when the apparatus is started up from a sleep state.

[0084] When the control unit 3 proceeds to the first step SP1, it obtains the temperature of the fixing roller 41 etc. by detecting the resistance value of the thermistor 44, and then proceeds to the next step SP2. In step SP2, the control unit 3 selects the phase control setting CP for the phase control and the start wave number control setting CNS and end wave number control setting CNE for the wave number control based on the detected temperature, and then proceeds to the next step SP3.

[0085] At this time, the control unit 3 selects a phase control setting CP based on the acquired temperature, for example, and selects a start wavenumber control setting CNS having an on-ratio r close to the value of the on-time ratio t in the final period of the selected phase control setting CP (i.e., a close duty ratio).Furthermore, the control unit 3 selects an end wavenumber control setting CNE having an on-ratio r value that matches the selected start wavenumber control setting CNS.

[0086] In step SP3, the control unit 3 acquires the zero-cross signal SZ from the AC zero-cross circuit 82 and proceeds to the next step SP4. In step SP4, the control unit 3 measures the half period HC based on the acquired zero-cross signal SZ and proceeds to the next step SP5.

[0087] In step SP5, the control unit 3 executes a phase control process as a subroutine (described in detail later), thereby supplying power of a phase-controlled waveform to the heater 43 as in periods T1 and T2 in FIG. 3 and FIG. 4(C), etc., as the first process before full-wave supply, and then proceeds to the next step SP6.

[0088] In step SP6, the control unit 3 executes wave number control processing as a subroutine (described in detail later), thereby supplying power having a wave number controlled waveform as in period T3 in Fig. 3 or Fig. 6(C) to the heater 43 as processing immediately before full wave supply, and then proceeds to the next step SP7. At this time, the control unit 3 performs wave number control based on the start-time wave number control table TBL2 (Fig. 7(A)).

[0089] In step SP7, the control unit 3 starts the full-wave supply of power to the heater 43, as in the period T4 in FIG. 3, and then proceeds to the next step SP8.

[0090] In step SP8, the control unit 3 determines whether a supply termination condition is satisfied. This supply termination condition is a condition for terminating the full-wave supply of power to the heater 43, and is satisfied, for example, when a predetermined upper limit temperature is reached or when printing processing is completed. If a negative result is obtained here, the control unit 3 repeats step SP8 to continue the current full-wave supply.

[0091] On the other hand, if a positive result is obtained in step SP8, the control unit 3 proceeds to the next step SP9, where it ends the full-wave supply of power to the heater 43, and then proceeds to the next step SP10.

[0092] In step SP10, the control unit 3 executes wave number control processing as a subroutine, thereby supplying power of a wave number controlled waveform to the heater 43 as the first processing immediately after completing the full wave supply, and then proceeds to the next step SP11. At this time, the control unit 3 performs wave number control based on the end-time wave number control table TBL3 (FIG. 7(B)).

[0093] In step SP11, the control unit 3 executes a phase control process as a subroutine to supply power of a phase-controlled waveform to the heater 43 as the second process immediately after the end of full-wave supply, and then proceeds to the next step SP12. In step SP12, the control unit 3 ends the heater control process procedure RT1.

[0094] [3-2. Phase control processing] Next, the phase control process will be described. In step SP5 of the heater control process procedure RT1, the control unit 3 reads out a phase control program from a ROM (not shown) and executes it, thereby starting the phase control process procedure RT2 of Fig. 9 as a subroutine, and proceeds to the first step SP21.

[0095] Additionally, the control unit 3 sets the heater signal SH supplied to the heater circuit 83 (FIG. 2) to 0 [V] as an initial state. As a result, the heater circuit 83 does not supply power supplied from the commercial power source 100 to the heater 43, and the heater 43 is not generating heat.

[0096] In step SP21, the control unit 3 initializes the number of periods T, which is a variable for counting the number of periods during which phase control is being performed, to the value "1", and proceeds to the next step SP22. In step SP22, the control unit 3 reads out the on-time ratio t and the on-count n of the Tth period from the phase control table TBL1 (FIG. 5) for the phase control setting CP selected in step SP2 of the heater control processing procedure RT1, and proceeds to the next step SP23.

[0097] In step SP23, the control unit 3 calculates the on-wait time TS according to the above-mentioned formula (1), and proceeds to the next step SP24. In step SP24, the control unit 3 initializes the value of the order x, which is a variable for counting the number of half-waves for which phase control has been performed, to "0", and proceeds to the next step SP25.

[0098] In step SP25, the control unit 3 enables the zero-cross interrupt, and proceeds to the next step SP26. This zero-cross interrupt is a mechanism for monitoring the commercial power PW and generating an interrupt when the voltage of the commercial power PW crosses zero (0 [V]).

[0099] In step SP26, the control section 3 determines whether or not a zero-cross interrupt has occurred. If a negative result is obtained here, the control section 3 repeats step SP26 to wait for the occurrence of a zero-cross interrupt.

[0100] On the other hand, if a positive result is obtained in step SP26, this indicates that the commercial power PW has crossed zero and the voltage has become 0 [V]. In this case, the control unit 3 proceeds to the next step SP27, where it disables the zero-cross interrupt, and then proceeds to the next step SP28. In step SP28, the control unit 3 starts measuring the elapsed time from the time the zero-cross interrupt occurred, and then proceeds to the next step SP29.

[0101] In step SP29, the control unit 3 determines whether the elapsed time has reached the on-standby time TS. If a negative result is obtained here, the control unit 3 repeats step SP29 to continue waiting for the on-standby time TS to elapse.

[0102] On the other hand, if a positive result is obtained in step SP29, this means that the on-wait time TS has elapsed since the zero-cross interrupt occurred, and therefore power should be supplied to the heater 43 for the remaining period of the current half wave. In this case, the control unit 3 proceeds to the next step SP30.

[0103] In step SP30, the control unit 3 generates a pulse with a predetermined pulse width in the heater signal SH supplied to the heater circuit 83, as shown in Fig. 4(B), and proceeds to the next step SP31. As a result, the heater circuit 83 supplies power to the heater 43 from the time when the pulse appears in the heater signal SH until the next zero crossing, as shown in Fig. 4(C).

[0104] In step SP31, the control unit 3 adds the value "1" to the order x and proceeds to the next step SP32. In step SP32, the control unit 3 determines whether the order x has reached the number of on-times n, that is, whether power equivalent to the on-time ratio t of the half wave has been supplied for the number of on-times n of phase control. If a negative result is obtained here, the control unit 3 returns to step SP25 and repeats the series of processes.

[0105] On the other hand, if a positive result is obtained in step SP32, this indicates that power has been supplied for n on-counts in period T, and therefore phase control for period T should be terminated. In this case, the control unit 3 proceeds to the next step SP33. In step SP33, the control unit 3 adds the value "1" to the number of periods T, and proceeds to the next step SP34.

[0106] In step SP34, the control unit 3 determines whether the Tth period is set in the set phase control setting CP, i.e., whether values ​​other than "0" are set for the on-time ratio t and the on-count n for the Tth period. If a positive result is obtained here, this indicates that phase control must also be performed for the Tth period. In this case, the control unit 3 returns to step SP22 and repeats the series of processes.

[0107] On the other hand, if a negative result is obtained in step SP34, this means that the Tth period is not set in the current phase control setting CP and phase control should be terminated within the (T-1)th period. In this case, the control unit 3 proceeds to the next step SP35, terminates the phase control processing procedure RT2, and returns to the original heater control processing procedure RT1 (FIG. 8).

[0108] [3-3. Wave number control processing] Next, the wave number control process will be described. In step SP6 of the heater control process procedure RT1, the control unit 3 reads out a wave number control program from a ROM (not shown) and executes it, thereby starting the wave number control process procedure RT3 of Fig. 10 as a subroutine, and proceeds to the first step SP41.

[0109] In step SP41, the control unit 3 reads out the pattern pt (i.e., information representing on or off in each order x) from the start wavenumber control table TBL2 (Figure 7(A)) for the start wavenumber control setting CNS selected in step SP2 of the heater control processing procedure RT1, and proceeds to the next step SP42.

[0110] In step SP42, the control unit 3 calculates the off-standby time TF, which is the standby time when one half wave is turned off, and proceeds to the next step SP43. This off-standby time TF is calculated using the following equation (2), and is the time obtained by excluding the portion corresponding to the zero-cross pulse width WZ from the half cycle HC of the commercial power PW (FIG. 6(A)).

[0111]

number

[0112] In step SP43, the control section 3 initializes the value of the order x, which is a variable indicating the order of half waves in the period in which phase control is performed, to "0", and then proceeds to the next step SP44.

[0113] In steps SP44, SP45 and SP46, the control unit 3 performs the same processes as steps SP25, SP26 and SP27 of the phase control processing procedure RT2 (FIG. 8), and proceeds to the next step SP47 when the voltage of the commercial power PW becomes 0 [V].

[0114] In step SP47, the control unit 3 determines whether sequence x is ON in the pattern pt of the start-time wavenumber control setting CNS that has been set. If a positive result is obtained here, this indicates that the entire period of the current half wave should be ON. In this case, the control unit 3 proceeds to the next step SP48.

[0115] In step SP48, the control unit 3 generates a pulse with a predetermined pulse width in the heater signal SH supplied to the heater circuit 83, as shown in Fig. 6(B), and proceeds to the next step SP51. As a result, the heater circuit 83 supplies power to the heater 43 from the time when the pulse appears in the heater signal SH to the time of the next zero crossing, i.e., for the entire period of the half wave, as shown in Fig. 6(C).

[0116] On the other hand, if a negative result is obtained in step SP47, this indicates that the entire period of the current half wave should be turned off. In this case, the control unit 3 proceeds to the next step SP49. In step SP49, the control unit 3 sets the off-wait time TF to the wait time, and proceeds to the next step SP50.

[0117] In step SP50, the control unit 3 determines whether or not the standby time has elapsed since the pulse appeared in the heater signal SH. If a negative result is obtained here, the control unit 3 repeats step SP50 to wait for the standby time to elapse.

[0118] On the other hand, if a positive result is obtained in step SP50, this means that a time period corresponding to one half wave has elapsed and the next process for the order x should be performed. In this case, the control unit 3 proceeds to the next step SP51.

[0119] In step SP51, the control unit 3 adds the value "1" to the order x and proceeds to the next step SP52. In step SP52, the control unit 3 determines whether the order x has reached 10 times, that is, whether wave number control over a predetermined period has been completed. If a negative result is obtained here, the control unit 3 returns to step SP44 and repeats the series of processes.

[0120] On the other hand, if a positive result is obtained in step SP52, the control section 3 proceeds to the next step SP53, ends the wave number control processing procedure RT3, and returns to the original heater control processing procedure RT1 (FIG. 8).

[0121] Incidentally, the control unit 3 also executes the wave number control processing procedure RT3 (FIG. 10) as a subroutine in step SP10 of the heater control processing procedure RT1, but in this case, in step SP41, it reads out the pattern pt of the end wave number control setting CNE from the end wave number control table TBL3 (FIG. 7(B)), and performs wave number control based on this.

[0122] [4. Effects, etc.] In the above configuration, when the image forming apparatus 1 according to the present embodiment starts full-wave supply to the heater 43 of the fixing unit 40, it first performs phase control, then wave number control, and then starts the full-wave supply (FIGS. 3, 8, etc.).

[0123] Generally, the heater 43 of the fixing unit 40 has an electric resistance member that generates heat when supplied with power. This electric resistance member has a predetermined temperature coefficient, and has the property that the resistance value is relatively low when the temperature is relatively low, and the resistance value increases as the temperature rises.

[0124] That is, when heater 43 starts to generate heat, its temperature and resistance are relatively low, so a relatively large inrush current is likely to flow, which in turn makes it more likely to cause flicker. Generally, phase control is sometimes used to suppress the generation of such inrush current, but with this phase control, the heater is turned on at a position shifted toward the voltage peak from the zero-cross point of the voltage waveform, as compared to wave number control. Therefore, by repeatedly turning on the heater using this phase control, the influence of fluctuations per unit time increases, which can worsen harmonics.

[0125] Therefore, in the image forming apparatus 1 according to the present embodiment, wave number control is performed after phase control is completed and immediately before full-wave supply is started. That is, by performing wave number control that turns on near the zero-cross point, the image forming apparatus 1 can reduce the influence of fluctuations per unit time, and accordingly the influence of harmonics due to phase control. As a result, when full-wave supply is started, the image forming apparatus 1 can suppress the occurrence of flicker without worsening harmonics.

[0126] Furthermore, the image forming apparatus 1 stores a plurality of start wavenumber control settings CNS (CNS0 to CNS5) in advance in a start wavenumber control table TBL2 (FIG. 7A). Then, in step SP2 of the heater control processing procedure RT1 (FIG. 8), the image forming apparatus 1 selects the start wavenumber control setting CNS so that the on-time ratio t of the selected phase control setting CP and the on-rate r of the start wavenumber control setting CNS approach each other.

[0127] Therefore, when switching the control method from phase control to wave number control, the image forming apparatus 1 can roughly maintain the ratio of power supplied to the heater 43 based on the commercial power PW, i.e., the duty ratio. In other words, the image forming apparatus 1 can be considered to change the modulation period from a period equivalent to one half wave (e.g., FIG. 4C) to a period equivalent to multiple half waves (e.g., FIG. 6C) while roughly maintaining the duty ratio, and then switch to full-wave supply.

[0128] From another perspective, in this embodiment, the commercial power PW supplied to the image forming apparatus 1 has a constant period. Therefore, even if phase control, which is a type of modulation control, is performed, the period of the power supplied to the heater 43 is constant, making it difficult to suppress harmonics. On the other hand, wave number control, which is another type of modulation control, can be considered a modulation process in which the entire period (e.g., a period equivalent to 10 half waves) is considered to be one period. Therefore, performing wave number control after phase control can be considered a process in which the period is extended in modulation control to lower the frequency, thereby suppressing harmonics.

[0129] Furthermore, in the start wave number control table TBL2 (FIG. 7A), for all start wave number control settings CNS, the last half wave, for which the order x is "9," is set to off. Therefore, when switching from half wave control to full wave supply, the image forming apparatus 1 can clearly separate the period of half wave control from the period of full wave supply.

[0130] This allows the image forming device 1 to prevent the period of full-wave supply from being substantially extended and flicker and harmonics from being insufficiently suppressed, which can occur when the wave number control waveform and the full-wave supply waveform are connected.

[0131] In addition, the control unit 3 configures the heater circuit 83 (FIG. 2) using a triac, and in wave number control, generates a pulse in the heater signal SH immediately after the zero crossing at which the half wave to be turned on begins in the commercial power PW, thereby supplying power over the entire period of that half wave. Therefore, the image forming apparatus 1 can perform appropriate wave number control by simply adjusting the timing at which the pulse is generated in the heater signal SH while still utilizing the mechanisms of the heater circuit 83 and heater signal SH configured for phase control.

[0132] Furthermore, the image forming apparatus 1 is configured to perform wave number control even after the end of full-wave supply (Fig. 8). As a result, even when the full-wave supply ends and the supplied current decreases significantly, the image forming apparatus 1 can effectively suppress the occurrence of flicker and harmonics by switching to wave number control.

[0133] According to the above configuration, when starting to supply commercial power PW to heater 43 of fixing unit 40, image forming apparatus 1 performs phase control, then wave number control, and then starts full-wave supply. Therefore, image forming apparatus 1 supplies a portion of commercial power PW to heater 43 in phase control, then in wave number control supplies a portion of the commercial power PW by modulation at a cycle different from that of the phase control, and then starts full-wave supply. As a result, when starting full-wave supply, image forming apparatus 1 can suppress the occurrence of flicker without worsening harmonics.

[0134] 5. Other Embodiments In the above-described embodiment, a plurality of start wavenumber control settings CNS (CNS0 to CNS5) are stored in the start wavenumber control table TBL2 (FIG. 7A) in advance. Then, in step SP2 of the heater control processing procedure RT1 (FIG. 8), a start wavenumber control setting CNS is selected in which the value of the on-time ratio t and the value of the on-ratio r in the phase control setting CP are close to each other. However, the present invention is not limited to this. For example, a start wavenumber control setting CNS may be selected in which the value of the on-ratio r is greater than the value of the on-time ratio t in the phase control setting CP. Alternatively, a start wavenumber control setting CNS may be selected in accordance with the temperature acquired from the thermistor 44 at the time when phase control is completed. That is, the start wavenumber control setting CNS may be selected using various selection methods. Alternatively, for example, only one start wavenumber control setting CNS may be prepared in advance, and that start wavenumber control setting CNS may be adopted regardless of the selected phase control setting CP.

[0135] In the above-described embodiment, the start wavenumber control table TBL2 (FIG. 7A) stores the pattern pt of each start wavenumber control setting CNS as "on" or "off" for each order x. However, the present invention is not limited to this. For example, half-wave control may be performed by various methods, such as performing a calculation based on a predetermined function or formula with the on-ratio r as a variable, and switching the half-wave of each order on or off based on the obtained calculation results.

[0136] Furthermore, in the above-described embodiment, the last half wave in which the order x in the pattern pt of the start wave number control setting CNS is "9" is turned off (FIG. 7(A)). However, the present invention is not limited to this, and the last half wave may be turned on.

[0137] Furthermore, in the above-described embodiment, the length of the period during which wave number control is performed is described as 10 half-waves ( FIG. 7 ). However, the present invention is not limited to this. Any number of half-waves may be used as long as the harmonic content is satisfactory even when the effects of full-wave supply are taken into account. Specifically, for example, if preliminary experiments have shown that the time required for the effects of harmonics to decay to a certain extent corresponds to 8 half-waves and that the time required for temperature ripple to be minimal corresponds to 15 half-waves or less, the length of the period during which wave number control is performed may be set to any number of half-waves greater than or equal to 8 and less than or equal to 15. Alternatively, the range within which the effects of harmonics are minimally attenuated and the effects of temperature ripple are minimal may be limited by converting the time into the number of half-waves, such as 100 ms or 120 ms.

[0138] Furthermore, in the above-described embodiment, six start wavenumber control settings CNS are stored in the start wavenumber control table TBL2 (FIG. 7(A)). However, the present invention is not limited to this, and five or fewer or seven or more start wavenumber control settings CNS may be stored. The same applies to the end wavenumber control table TBL3 (FIG. 7(B)). Furthermore, the phase control table TBL1 (FIG. 5) is not limited to a configuration in which the phase control settings CP are four, and may be three or fewer or five or more.

[0139] Furthermore, in the above-described embodiment, a start wavenumber control table TBL2 and an end wavenumber control table TBL3 (FIG. 7) are prepared, and the start wavenumber control table TBL2 is used for wavenumber control performed before the start of full-wave supply, and the end wavenumber control table TBL3 is used for wavenumber control performed after the end of full-wave supply. However, the present invention is not limited to this, and for example, only the start wavenumber control table TBL2 may be prepared, and the pattern pt may be read out in reverse order for wavenumber control performed after the end of full-wave supply.

[0140] Furthermore, in the above-described embodiment, a triac (not shown) is used to configure the heater circuit 83 (FIG. 2), and phase control and wave number control are each realized by adjusting the timing of pulses generated in the heater signal SH supplied from the control unit 3 to the heater circuit 83. However, the present invention is not limited to this, and phase control and wave number control may each be realized by using heater circuits having various circuit configurations and appropriately controlling the heater circuits from the control unit 3.

[0141] Furthermore, in the above-described embodiment, in the heater control processing procedure RT1 (FIG. 8), after the full-wave supply is completed in step SP9, wave number control processing is performed in step SP10, and then phase control processing is performed in step SP11. However, the present invention is not limited to this, and for example, the phase control processing in step SP11 may be omitted, and furthermore, the wave number control processing in step SP10 may be omitted.

[0142] Furthermore, in the above-described embodiment, the phase control table TBL1 (FIG. 5) stores the on-time ratio t and on-count n for each of two periods, i.e., the first period and the second period, and the phase control content is switched between up to two levels. However, the present invention is not limited to this. For example, the number of periods stored in the phase control table TBL1 may be three or more, and the phase control content may be switched between up to three or more levels. Alternatively, for example, the number of periods stored in the phase control table TBL1 may be one, and the phase control content may not be switched midway. Furthermore, the selection of the phase control setting CP in phase control is not limited to selection based on the temperature detected by the thermistor 44. For example, selection based on various other factors, such as the elapsed time since the last printing process, or a combination of these factors may also be used.

[0143] Furthermore, in the above-described embodiment, the image forming apparatus 1 is configured as a single-function printer. However, the present invention is not limited to this, and the image forming apparatus 1 may be configured as, for example, an MFP (Multi Function Peripheral) having the functions of a copier or facsimile machine.

[0144] Furthermore, the present invention is not limited to the above-described embodiments and other embodiments, and the scope of application of the present invention extends to embodiments in which the above-described embodiments and other embodiments are combined in part or in whole, or in which only a part of the above-described embodiments is extracted.

[0145] Furthermore, in the above-described embodiment, the image forming apparatus 1 is configured as an image forming apparatus by the heater 43 as a heater, the fixing roller 41 and the pressure roller 42 as fixing members, and the control unit 3 as a control unit. However, the present invention is not limited to this, and the image forming apparatus may be configured by heaters, fixing members, and control units having various other configurations. [Industrial Applicability]

[0146] The present invention can be used in, for example, electrophotographic printers. [Explanation of symbols]

[0147] 1...image forming apparatus, 3...control unit, 40...fuser unit, 41...fuser roller, 42...pressure roller, 43...heater, 44...thermistor, 71...power supply board, 72...control board, 82...AC zero cross circuit, 83...heater circuit, 84...power supply control circuit, 100...commercial power supply, CNE...end wave number control setting, CNS...start wave number control setting, CP...phase control setting, HC...half cycle, PC...commercial power, PWH...heater pulse width, PWZ...zero cross pulse width, SH...heater signal, ST...temperature detection signal, SZ...zero cross signal, TBL1...phase control table, TBL2...start wave number control table, TBL3...end wave number control table, TF...off wait time, TS...on wait time, n...number of on times, pt...pattern, r...on ratio, t...on time ratio, x...order.

Claims

1. a heater that generates heat by AC power supplied from an AC power source; a fixing member that is heated by the heater and fixes the image on the medium; a control unit that controls the AC power supplied from the AC power source to the heater; Equipped with The control unit controls the AC power so that, when the heater starts to generate heat, the AC power is phase-controlled, and then the AC power is wave-number-controlled, and then full-wave supply of the AC power is started. An image forming apparatus characterized by:

2. a temperature detection unit for detecting the temperature of the fixing member; Further comprising: The control unit changes a duty ratio in the wave number control in accordance with the temperature detected by the temperature detection unit.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. The control unit sets a duty ratio in the wave number control in accordance with the duty ratio in the phase control.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

4. The control unit controls the power supply to be temporarily turned off for a period when switching from the wave number control to the full wave supply.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

5. The control unit controls to switch to the wave number control when the full-wave supply of the AC power is terminated.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

6. When the wave number control is to be terminated after the full-wave supply of the AC power is terminated, the control unit controls to switch to the phase control.

6. The image forming apparatus according to claim 5,

7. A heater control method for controlling AC power supplied from an AC power supply to a heater, comprising: When starting to heat the heater, the AC power is phase-controlled, the AC power is wave-number-controlled following the phase control of the AC power, and full-wave supply of the AC power is started following the wave-number control of the AC power. A heater control method comprising:

8. When the heater starts to generate heat, the duty ratio of the wave number control is determined according to the duty ratio of the phase control.

8. The heater control method according to claim 7, wherein:

9. When the heater starts to generate heat, the wave number control includes an off period corresponding to at least half a cycle of the AC power immediately before the start of the full-wave supply of the AC power.

8. The heater control method according to claim 7, wherein:

10. The wave number control is a period of 8 to 15 half-waves of the AC power.

8. The heater control method according to claim 7, wherein:

11. When terminating the heat generation of the heater, immediately after the end of the full-wave supply of the AC power, the wave number control at the time of termination having an off period of at least half a cycle of the AC power is performed, and the phase control is performed after the wave number control at the time of termination, thereby terminating the heat generation of the heater.

8. The heater control method according to claim 7, wherein:

12. The heater control method according to claim 7 performs the phase control, the wave number control, and the full-wave supply of the AC power, The duty ratio of the phase control is determined based on the temperature of the fixing member that is heated by the heater and fixes the image on the medium. An image forming method comprising:

Images