Image forming apparatus, method for controlling heater, and control program for heater

Abstract

To reduce a harmonic noise without reducing the efficiency of power supply to a heater.SOLUTION: A heater control device controls an amount of power supplied to a heater in a control period including a predetermined number of periods of AC voltage, and comprises: a ratio determination section that determines a power ratio of the amount of power supplied to the heater to heat an object to be heated to a target temperature to the amount of power in the control period; and a voltage supply section that, in a pattern table, supplies voltage to the heater according to a voltage supply time indicated by time information corresponding to the power ratio determined by the ratio determination section. The pattern table stores, for every power ratio, time information indicating the time of voltage supply to the heater for each of a plurality of half-wave periods, and repeatedly includes a plurality of pattern groups containing first patterns in which all the time information in the plurality of half-wave periods indicate that voltage is supplied to the heater, and second patterns in which at least some of the time information in the plurality of half-wave periods indicate that the voltage is not supplied to the heater.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to Image forming apparatus a method for controlling a heater and a control program for the heater.

Background Art

[0002] In an electrophotographic image forming apparatus, for example, after a toner image formed on a photoreceptor is transferred to a recording sheet, the toner image is fixed to the recording sheet using a fixing roller heated by the heat of a fixing heater. A halogen lamp used for the fixing heater has a characteristic that its resistance decreases when the temperature is low, and an inrush current is generated at the start of energization. For this reason, a fluorescent lamp sharing the power supply with the halogen lamp may flicker due to a voltage drop of the power supply caused by the inrush current.

[0003] When the fixing heater is turned on, by performing phase control (soft start control) in which the conduction angle of the AC voltage supplied to the fixing heater is gradually increased in half-wave units, the inrush current is suppressed. However, in this case, harmonic currents (harmonic noise) are likely to be generated. In addition, among the phase control patterns for supplying an AC voltage to the heater using a plurality of half-waves, there are a pattern in which odd-order harmonic noise is likely to be generated and a pattern in which even-order harmonic noise is likely to be generated. Therefore, a method has been proposed in which by performing soft start control using a pattern that combines the characteristics of both patterns, it is possible to prevent the harmonics from exceeding the regulated value.

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when a pattern in which odd-order harmonic noise is likely to be generated and a pattern in which even-order harmonic noise is likely to be generated are combined, the number of half-waves included in the soft start control increases, and the period of the soft start control becomes longer. As a result, there is a problem that the efficiency of power supply to the heater decreases and the time required to raise the fixing roller to a desired temperature becomes longer.

[0005] The present invention has been made in view of the above problems, and an object thereof is to reduce harmonic noise without degrading the efficiency of power supply to a heater.

Means for Solving the Problems

[0006] To solve the above technical problems, one aspect of the present invention The image forming apparatus includes a fixing roller, a heater for heating the fixing roller, a temperature detection unit for detecting the temperature of the fixing roller, and a heater control device for controlling the amount of power supplied to the heater for each of a plurality of half-wave periods within a control period including a predetermined number of cycles of an AC voltage. The heater control device includes a ratio determination unit that determines a power ratio, which is a ratio of the amount of power supplied to the heater to make the fixing roller reach a target temperature, to the amount of power that can be supplied within the control period, based on the temperature detected by the temperature detection unit; a pattern table in which time information indicating the voltage supply time to the heater for each of the plurality of half-wave periods within the control period is stored for each power ratio; and a voltage supply unit that supplies a voltage to the heater according to the time information stored in the pattern table corresponding to the power ratio determined by the ratio determination unit. The pattern table repeatedly includes a plurality of pattern groups each including a predetermined number of first patterns indicating that the time information for all of the plurality of half-wave periods supplies a voltage to the heater, and a predetermined number of second patterns indicating that the time information for at least any one of the plurality of half-wave periods does not supply a voltage to the heater. The time information stored in the pattern table indicates a time ratio that is a ratio of the voltage supply time to the heater with respect to the half-wave period. In the pattern table, the sum of the time ratios of the plurality of half-wave periods within the control period in the first pattern is larger than the sum of the time ratios of the plurality of half-wave periods within the control period in the second pattern in which the power ratio is one larger than that of the first pattern. The power supplied to the heater increases as the power ratio increases.

Effects of the Invention

[0007] Harmonic noise can be reduced without degrading the efficiency of power supply to a heater.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments will be described with reference to the drawings. In each drawing, the same reference numerals are assigned to the same components, and redundant descriptions may be omitted.

[0010] FIG. 1 is a block diagram showing a schematic configuration of an image forming apparatus including a heater control device according to the present invention. The image forming apparatus 100 shown in FIG. 1 is, for example, an MFP (Multi-Function Peripheral), a printer, a copier, or a FAX, but is not limited thereto.

[0011] The image forming apparatus 100 includes a scanner unit 10, an engine unit 20, a paper feed tray 30 in which transfer paper is stored, and a fixing device 50. The engine unit 20 performs predetermined image processing on the image read by the scanner unit 10, and transfers a toner image corresponding to the processed image onto the transfer paper. The fixing device 50 fixes the toner image transferred onto the transfer paper by the engine unit 20. The heater control device according to the present invention is provided in the fixing device 50 as a heater control unit.

[0012] The scanner unit 10 converts an image or a document included in the document into an image signal by scanning and exposing the document, and outputs the converted image signal to the engine unit 20. The engine unit 20 performs image processing such as color conversion and gradation correction on the image signal output from the scanner unit 10. The engine unit 20 forms an electrostatic latent image on an image carrier (not shown) according to the image on which the image processing has been performed, attaches toner to the formed electrostatic latent image to form a toner image. Then, the engine unit 20 transfers the formed toner image onto the transfer paper conveyed from the paper feed tray 30 via the conveyance path 40, and sends out the transfer paper onto which the toner image has been transferred toward the fixing device 50 via the conveyance path 40.

[0013] The fixing device 50 fixes the toner image transferred onto the transfer paper sent out from the engine unit 20 via the conveyance path 40 onto the transfer paper by the heat from the cylindrical fixing roller 51a and the pressure from the pressure roller 51b, and discharges the paper toward a paper discharge tray (not shown). Here, the fixing roller 51a rotates in pressure contact with the pressure roller 51b to fix the toner image transferred onto the transfer paper onto the transfer paper. The fixing roller 51a is an example of an object to be heated.

[0014] FIG. 2 is a block diagram showing a mechanism portion for controlling the heating of the fixing roller 51a in the fixing device 50 of FIG. 1. For example, the fixing device 50 includes a heater 52 disposed inside the fixing roller 51a, a triac 53, a temperature sensor 54, a heater control unit 55, and a zero-cross detection unit 56. The heater control unit 55 and the triac 53 are an example of a heater control device.

[0015] The heater 52 heats the fixing roller 51a based on the electric power supplied from the AC power supply 200. Then, the toner image transferred onto the transfer paper melts by the heat of the fixing roller 51a and is embedded in the fibers of the transfer paper and fixed. For example, a halogen lamp or the like that is heated by the radiant heat generated when lit is used as the heater 52.

[0016] The AC power supply 200 outputs an AC voltage to be supplied to the heater 52. In the present embodiment, the AC power supply 200 is, for example, a commercial power supply, and supplies an AC voltage that changes in a sine wave shape over time to the heater 52 which is the load.

[0017] The triac 53 interrupts (turns on / off) the AC voltage supplied from the AC power supply 200 at the timing instructed by the heater control unit 55, and supplies the interrupted AC voltage to the heater 52. The heater 52 becomes energized and generates heat when the triac 53 is on, and becomes de-energized and stops generating heat when the triac 53 is off.

[0018] The temperature sensor 54 is an example of a temperature detection unit and measures the surface temperature of the fixing roller 51a. The temperature sensor 54 incorporates, for example, a thermistor whose resistance value changes according to temperature, and measures the surface temperature of the fixing roller 51a based on the resistance value of the thermistor. The surface temperature of the fixing roller 51a has a correlation with the temperature of the heater 52. Therefore, for example, the temperature of the heater 52 can be obtained by multiplying the temperature detected by the temperature sensor 54 by a predetermined coefficient. Note that the temperature sensor 54 may be incorporated in the fixing roller 51a.

[0019] The zero-cross detection unit 56 detects the zero-cross timing, which is the timing when the AC voltage supplied from the AC power supply 200 crosses 0 volts from the positive side to the negative side and the timing when it crosses from the negative side to the positive side. Then, when the zero-cross detection unit 56 detects the zero-cross timing, it outputs a zero-cross detection signal to the heater control unit 55.

[0020] The heater control unit 55 includes a ratio determination unit 551, a voltage supply unit 552, and a pattern table 553. The ratio determination unit 551 and the voltage supply unit 552 perform control to set the surface temperature of the fixing roller 51a to a predetermined target temperature when fixing the toner image on the transfer paper sent from the engine unit 20 to the transfer paper. The ratio determination unit 551 and the voltage supply unit 552 may be realized by a heater control program executed by a CPU (Central Processing Unit), not shown, provided in the fixing device 50 to realize the heater control method, or may be realized by hardware.

[0021] The ratio determination unit 551 determines the supply period of the AC voltage to the heater 52 (that is, the lighting period of the halogen lamp) for each control cycle of the AC voltage based on the surface temperature of the fixing roller 51a detected by the temperature sensor 54. For example, the control cycle of the AC voltage is two cycles (2T).

[0022] Hereinafter, the power supply amount PS supplied to the heater 52 for each control cycle and the power ratio, which is the ratio PS / Pmax of the maximum power amount Pmax that can be supplied in the control cycle, are referred to as the lighting duty ratio Do (0 ≦ Do ≦ 100%). For example, a lighting duty ratio Do = 50% means that AC voltage (power) is supplied to the heater 52 during a period corresponding to 50% of the area enclosed by the sine wave of the control cycle and 0V.

[0023] Based on the surface temperature of the fixing roller 51a, the ratio determination unit 551 determines the lighting duty ratio Do corresponding to the power supply amount to be supplied to the heater 52 in order to set the surface temperature of the fixing roller 51a to a predetermined target temperature. Then, the ratio determination unit 551 notifies the voltage supply unit 552 of the determined lighting duty ratio Do. Note that the ratio determination unit 551 may determine the lighting duty ratio Do from the surface temperature of the fixing roller 51a by referring to a table storing the relationship between the surface temperature of the fixing roller 51a and the lighting duty ratio Do.

[0024] The lighting duty ratio Do determined based on the surface temperature of the fixing roller 51a is used, for example, to turn on the heater 52 from the start to the end of the printing operation. For example, when the surface temperature of the fixing roller 51a is low, a relatively large lighting duty ratio Do is selected, so that the power supply amount increases and the surface temperature of the fixing roller 51a rises in a short time. Also, when the printing operation is repeated and the surface temperature of the fixing roller 51a has become high, a relatively small lighting duty ratio Do is selected, so that the power supply amount decreases.

[0025] The voltage supply unit 552 reads out the lighting pattern of the heater 52 corresponding to the determined lighting duty ratio Do from the pattern table 553, and outputs a timing signal for turning the triac 53 on or off according to the read lighting pattern to the triac 53. At this time, the voltage supply unit 552 outputs a timing signal to the triac 53 based on the zero-cross timing of the AC voltage detected by the zero-cross detection unit 56. Thereby, an AC current with a conduction angle corresponding to the lighting pattern read from the pattern table 553 is supplied to the heater 52.

[0026] In the pattern table 553, time information (lighting pattern) indicating the voltage supply time to the heater 52 in each of the four half-wave periods within the control period is stored for each lighting duty ratio Do. For example, the pattern table 553 is stored in a ROM (Read Only Memory), a RAM (Random Access Memory), etc. that can be read by the CPU provided in the fixing device 50.

[0027] The ROM and the RAM may be provided inside the fixing device 50, or may be provided outside the fixing device 50. When the ROM and the RAM are provided inside the fixing device 50, a heater control program executed by the CPU may be stored in the ROM and the RAM. An example of the pattern table 553 is shown in FIG. 4.

[0028] FIG. 3 is an explanatory diagram showing an example of the control period of the AC voltage supplied to the heater 52 in FIG. 2. As described in FIG. 2, the heater control unit 55 performs control to supply an AC voltage with a predetermined conduction angle to the heater 52 (halogen lamp) using two cycles (four half-waves) of the AC voltage supplied from the AC power supply 200 as the control period.

[0029] In FIG. 3, the voltage value e supplied from the AC power supply 200 to the heater 52 is represented by a sine wave with a peak value e0 and a period T. Hereinafter, in the control period (2T), four half-wave periods of the AC voltage that are continuous in time order are referred to as half-wave periods a, b, c, and d. That is, when the time is t, the half-wave period a represents the time range of 0 ≦ t < T / 2, the half-wave period b represents the time range of T / 2 ≦ t < T, the half-wave period c represents the time range of T ≦ t < 3T / 2, and the half-wave period d represents the time range of 3T / 2 ≦ t < 2T. When a 50 Hz commercial power supply is used as the AC power supply 200, the control period (2T) is 40 msec.

[0030] For example, under the control by the ratio determination unit 551 and the voltage supply unit 552 shown in FIG. 2, it is assumed that in the half-wave period a, power indicated by the shaded area R is supplied to the heater 52 during the period T / 10 from time t = 2T / 5 to T / 2. In this case, the alternating current is supplied to the heater 52 for a period of T / 10, which is 20% of the period T / 2 of the half-wave period a. In the half-wave periods a, b, c, and d, the ratio (time ratio) of the period during which the AC voltage is supplied to the heater 52 with respect to the period T / 2 is called the phase duty ratio Dp (0 ≦ Dp ≦ 100%). The phase duty ratio Dp corresponds to the conduction angle indicating the supply time of the AC voltage supplied to the heater 52. Therefore, the supply timing of the AC voltage supplied to the heater 52 may be specified by the phase angle of the AC voltage instead of the time.

[0031] The phase duty ratio Dp is set for each of the half-wave periods a, b, c, and d and is set as time information in the pattern table 553 of FIG. 2. Hereinafter, the phase duty ratio Dp set for the half-wave period a is referred to as the phase duty ratio Dpa, the phase duty ratio Dp set for the half-wave period b is referred to as the phase duty ratio Dpb, the phase duty ratio Dp set for the half-wave period c is referred to as the phase duty ratio Dpc, and the phase duty ratio Dp set for the half-wave period d is referred to as the phase duty ratio Dpd.

[0032] When supplying the alternating voltage shown in FIG. 3 to the heater 52, in the region of a predetermined lighting duty ratio Do of the pattern table 553, phase duty ratios Dpa = 20%, Dpb = 0%, Dpc = 0%, and Dpd = 0% are stored. Note that the control cycle is not limited to two cycles (2T) of the alternating voltage, and may be three or more cycles, or one cycle.

[0033] FIG. 4 is an explanatory diagram showing an example of a reference lighting pattern of the alternating voltage supplied to the heater 52 in a control cycle. In the waveforms of the alternating voltage of each lighting pattern PT1, PT2, PT3, and PT4, the shaded region indicates the period during which power is supplied to the heater 52, similar to FIG. 3. That is, at the timing corresponding to the shaded region, a timing signal is output from the voltage supply unit 552 of FIG. 2 to the triac.

[0034] Note that in the pattern table 553 shown in FIG. 2, instead of the reference lighting pattern shown in FIG. 4, a lighting pattern extracted from any of a plurality of reference lighting patterns is stored for each lighting duty ratio Do. The lighting pattern set in the pattern table 553 will be described with reference to FIG. 6. Note that FIG. 4 shows four reference lighting patterns, but the number of reference lighting patterns may be two or more, and the reference lighting pattern is not limited to the lighting pattern shown in FIG. 4.

[0035] In the lighting pattern PT1, in each half-wave period a, b, c, and d, as the lighting duty ratio Do increases, the phase duty ratios Dpa, Dpb, Dpc, and Dpd increase equally. Note that in order to adjust the amount of power supplied to the heater 52, the phase duty ratios Dpa, Dpb, Dpc, and Dpd do not have to be set to the same value for each lighting duty ratio Do.

[0036] In lighting pattern PT2, first, the phase duty ratios Dpa and Dpc of the half-wave periods a and c are sequentially increased as the lighting duty ratio Do increases. Then, when the phase duty ratios Dpa and Dpc reach 100%, with the phase duty ratios Dpa and Dpc maintained at 100%, the phase duty ratios Dpb and Dpd of the half-wave periods b and d are sequentially increased as the lighting duty ratio Do increases. Note that in order to adjust the amount of power supplied to the heater 52, at each lighting duty ratio Do, the phase duty ratios Dpa and Dpc do not have to be set to the same value, and the phase duty ratios Dpb and Dpd do not have to be set to the same value either.

[0037] In lighting pattern PT3, first, the phase duty ratios Dpa and Dpb of the half-wave periods a and b are sequentially increased as the lighting duty ratio Do increases. Then, after the phase duty ratios Dpa and Dpb reach 100%, with the phase duty ratios Dpa and Dpb maintained at 100%, the phase duty ratios Dpc and Dpd of the half-wave periods c and d are sequentially increased as the lighting duty ratio Do increases. Note that in order to adjust the amount of power supplied to the heater 52, at each lighting duty ratio Do, the phase duty ratios Dpa and Dpb do not have to be set to the same value, and the phase duty ratios Dpc and Dpd do not have to be set to the same value either.

[0038] In lighting pattern PT4, first, the phase duty ratio Dpa of the half-wave period a is sequentially increased as the lighting duty ratio Do increases. Then, after the phase duty ratio Dpa reaches 100%, with the phase duty ratio Dpa maintained at 100%, the phase duty ratio Dpb of the half-wave period b is sequentially increased as the lighting duty ratio Do increases.

[0039] Next, after the phase duty ratio Dpb reaches 100%, with the phase duty ratios Dpa and Dpb maintained at 100%, the phase duty ratio Dpc during the half-wave period c sequentially increases as the lighting duty ratio Do increases. Further, after the phase duty ratio Dpc reaches 100%, with the phase duty ratios Dpa, Dpb, and Dpc maintained at 100%, the phase duty ratio Dpd during the half-wave period d sequentially increases as the lighting duty ratio Do increases.

[0040] Generally, the larger the amount of power supplied to the load per unit time, the greater the inrush current, and thus the easier it is for the fluorescent lamp that receives power from the AC power supply 200 and lights up to flicker. Also, the more the AC voltage supplied to the load is dispersed in the time axis direction and the shorter and sharper the voltage supply time is, the easier it is for odd-order harmonic noise to occur. Further, the more the AC voltage supplied to the load is biased to the positive electrode side or the negative electrode side, the easier it is for even-order harmonic noise to occur, and the more the distribution of the AC voltage supplied to the load in the time axis direction is biased, the easier it is for even-order harmonic noise to occur.

[0041] From the above, summarizing the inrush current, even-order harmonic noise, and odd-order harmonic noise for the lighting patterns PT1 to PT4 is as follows.

[0042] The inrush current in the lighting pattern PT1 is less than that in the other lighting patterns PT2 to PT4. The odd-order harmonic noise in the lighting pattern PT1 is more likely to occur than in the other lighting patterns PT2 to PT4, and there is a possibility of not satisfying the regulation value of the odd-order harmonic current. The even-order harmonic noise in the lighting pattern PT1 is less likely to occur than in the other lighting patterns PT2 to PT4.

[0043] The inrush current in lighting pattern PT2 is larger than that in lighting pattern PT1, comparable to that in lighting pattern PT3, and smaller than that in lighting pattern PT4. The odd-order harmonic noise in lighting pattern PT2 is less likely to occur compared to the other lighting patterns PT1, PT3, and PT4. The even-order harmonic noise in lighting pattern PT2 is more likely to occur compared to the other lighting patterns PT1, PT3, and PT4.

[0044] Lighting pattern PT2 equalizes the power in two half-wave units, suppressing odd-order harmonic noise while suppressing flicker (flicker regulation value). However, due to the poor symmetry between the supply power of the upper (positive electrode side) half-wave and the supply power of the lower (negative electrode side) half-wave, the even-order harmonic noise tends to deteriorate. In particular, when the capacity of the heater 52 is large and the supply current to the heater 52 is large, there is a possibility of not satisfying the regulation value of the even-order harmonic current.

[0045] The inrush current in lighting pattern PT3 is larger than that in lighting pattern PT1, comparable to that in lighting pattern PT2, and smaller than that in lighting pattern PT4. The odd-order harmonic noise in lighting pattern PT3 is more likely to occur compared to lighting pattern PT2, comparable to that in lighting pattern PT4, and less likely to occur compared to lighting pattern PT1. The even-order harmonic noise in lighting pattern PT3 is more likely to occur compared to lighting pattern PT1, comparable to that in lighting pattern PT4, and less likely to occur compared to lighting pattern PT2.

[0046] Although the flicker (flicker regulation value) slightly deteriorates in lighting pattern PT3, it is easy to balance the flicker regulation value and the harmonic current regulation value. However, in lighting pattern PT3, when the lighting duty ratio Do is small, the even-order harmonic noise is likely to deteriorate. In particular, when the capacity of the heater 52 is large and the supply current to the heater 52 is large, there is a possibility of not satisfying the regulation value of the even-order harmonic current.

[0047] The inrush current in lighting pattern PT4 is larger than that in the other lighting patterns PT1 to PT3. The odd-order harmonic noise in lighting pattern PT4 is more likely to occur than in lighting pattern PT2, is at the same level as in lighting pattern PT3, and is less likely to occur than in lighting pattern PT1. The even-order harmonic noise in lighting pattern PT4 is more likely to occur than in lighting pattern PT1, is at the same level as in lighting pattern PT3, and is less likely to occur than in lighting pattern PT2.

[0048] From the above, the inrush current is the largest in lighting pattern PT4, is at the same level in lighting patterns PT2 and PT3, and is the smallest in lighting pattern PT1. Also, it can be said that in lighting pattern PT1, odd-order harmonic noise is likely to occur and even-order harmonic noise is less likely to occur. In lighting pattern PT2, odd-order harmonic noise is less likely to occur and even-order harmonic noise is likely to occur. In lighting patterns PT3 and PT4, the occurrence of odd-order and even-order harmonic noises is at the same level, but when the lighting duty ratio Do is low (generally 50% or less), even-order harmonic noise is more likely to occur.

[0049] FIG. 5 is an explanatory diagram showing an example of the change in the phase duty ratio Dp with respect to the lighting duty ratio Do in the reference lighting patterns PT1 to PT4 of FIG. 4.

[0050] As described with reference to FIG. 4, in lighting pattern PT1, as the lighting duty ratio Do increases, the phase duty ratios Dpa, Dpb, Dpc, and Dpd increase evenly. In lighting pattern PT2, as the lighting duty ratio Do increases, the phase duty ratios Dpa and Dpc increase to 100% and then the phase duty ratios Dpb and Dpd increase.

[0051] In lighting pattern PT3, as the lighting duty ratio Do increases, the phase duty ratios Dpa and Dpb increase to 100% and then the phase duty ratios Dpc and Dpd increase. In lighting pattern PT4, as the lighting duty ratio Do increases, the phase duty ratios Dpa, Dpb, Dpc, and Dpd increase sequentially to 100%.

[0052] Note that the lighting patterns PT1, PT2, PT3, and PT4 are created based on the measurement results of inrush current and harmonic noise, simulation results, or both the measurement results and the simulation results during the development of the image forming apparatus 100 or the fixing device 50. The lighting patterns PT1, PT2, PT3, and PT4 are not stored in the pattern table 553 shown in FIG. 2.

[0053] FIG. 6 is an explanatory diagram showing an example of the lighting pattern PTa stored in the pattern table 553 of FIG. 2. In this example, the lighting pattern PTa stored in the pattern table 553 is created by combining the lighting patterns PT1 and PT2 shown in FIGS. 4 and 5. Note that in FIG. 6, the phase duty ratios Dpa, Dpb, Dpc, and Dpd are set every 1% of the lighting duty ratio Do, but the increment of the lighting duty ratio Do may be other than 1%.

[0054] When creating the pattern table 553, for example, at three consecutive lighting duty ratios Do (for example, 34, 35, 36), the phase duty ratios Dpa to Dpd are selected from the lighting pattern PT2. Also, at the next lighting duty ratio Do (for example, 37) of the three consecutive lighting duty ratios Do, the phase duty ratios Dpa to Dpd are selected from the lighting pattern PT1. Then, by repeatedly selecting the phase duty ratios Dpa to Dpd of four consecutive lighting duty ratios Do, the lighting pattern PTa to be stored in the pattern table 553 is created.

[0055] In the lighting pattern PT1 used for the lighting pattern PTa, at each lighting duty ratio Do, all of the phase duty ratios Dpa, Dpb, Dpc, and Dpd are set to a predetermined ratio for supplying voltage to the heater 52. In the lighting pattern PT1, the phase duty ratios Dpa to Dpd of each lighting duty ratio Do used for the lighting pattern PTa are an example of a first pattern indicating that all of the phase duty ratios Dpa to Dpd supply voltage to the heater 52.

[0056] On the other hand, in the lighting pattern PT2 used for the lighting pattern PTa, until the lighting duty ratio Do exceeds a predetermined value (e.g., 58% in FIG. 5), the phase duty ratios Dpb and Dpd are set to 0% where no voltage is supplied to the heater 52. Also, the phase duty ratios Dpa and Dpc are set to predetermined values where voltage is supplied to the heater 52. In the lighting pattern PT2, the phase duty ratios Dpa to Dpd of each lighting duty ratio Do used for the lighting pattern PTa are an example of a second pattern indicating that at least one of the phase duty ratios Dpa to Dpd does not supply voltage to the heater 52.

[0057] The four patterns based on the phase duty ratios Dpa to Dpd of the selected four lighting duty ratios Do are an example of a pattern group. The pattern table 553 is created by repeatedly storing a plurality of pattern groups.

[0058] As shown in FIG. 5, until the lighting duty ratio Do reaches 58%, the phase duty ratios Dpb and Dpd are set to 0%, and when the lighting duty ratio Do exceeds 58%, all the phase duty ratios Dpa to Dpd are set to predetermined values.

[0059] Therefore, when the lighting duty ratio Do is greater than 58%, the reduction effect of odd - order and even - order harmonic noises by combining the lighting patterns PT1 and PT2 decreases. However, in the region where the lighting duty ratio Do is large, since the harmonic noise is originally small, the regulation value of the harmonic current is satisfied. In other words, in the region where the lighting duty ratio Do is small and it is difficult to satisfy the regulation value of the harmonic current, by combining the lighting patterns PT1 and PT2, the reduction effect of odd - order and even - order harmonic noises can be exerted.

[0060] In FIG. 6, the pattern table 553 is created by a plurality of pattern groups in which the phase duty ratios Dpa to Dpd are selected at a ratio of 1:3 from the lighting pattern PT1 and the lighting pattern PT2. However, the ratio of the lighting pattern PT1 to the lighting pattern PT2 included in each pattern group is not limited to 1:3, and may be 1:n or n:1 (n is an integer of 2 or more), and may be set to a ratio such as 2:5 or 3:7.

[0061] Also, the ratio of the lighting pattern PT1 to the lighting pattern PT2 included in each pattern group may be changed depending on whether the lighting duty ratio Do is large or small. For example, when the lighting duty ratio Do exceeds a predetermined value, the phase duty ratios Dpa to Dpd may be selected from only the lighting pattern PT1 or only the lighting pattern PT2 to create the pattern table 553. In other words, the pattern table 553 may be created by interweaving the lighting pattern PT1 and the lighting pattern PT2 only when the lighting duty ratio Do is equal to or less than a predetermined value.

[0062] The lighting patterns PT1 to PT4 shown in FIG. 5 and the lighting pattern PTa stored in the pattern table 553 are created, for example, during the development of the image forming apparatus 100 or the fixing device 50. For example, the lighting patterns PT1 to PT4 and PTa are created based on the measurement results of odd-order harmonic noise and even-order harmonic noise, simulation results, or both the measurement results and the simulation results. In other words, in the lighting pattern PTa, the ratio of the patterns taken from the lighting patterns PT1 and PT2 is determined so as to satisfy the regulation values of odd-order and even-order harmonic currents.

[0063] As described with reference to FIG. 4, in the lighting pattern PT1, odd-order harmonic noise is relatively likely to occur, and even-order harmonic noise is relatively unlikely to occur. In the lighting pattern PT2, odd-order harmonic noise is relatively unlikely to occur, and even-order harmonic noise is relatively likely to occur. Therefore, in a region where the lighting duty ratio Do is low, if only the lighting pattern PT1 is continuously selected, there is a possibility that the regulated value of the odd-order harmonic current may not be satisfied, and if only the lighting pattern PT2 is continuously selected, there is a possibility that the regulated value of the even-order harmonic current may not be satisfied.

[0064] The lighting pattern PTa is formed by extracting the phase duty ratios Dpa to Dpd corresponding to a predetermined number of consecutive lighting duty ratios Do from each of the lighting patterns PT1 and PT2 having opposite harmonic noise characteristics and arranging them as a pattern group. As a result, according to the change in the lighting duty ratio Do, the phase duty ratio Dp of the lighting pattern PT1 and the phase duty ratio Dp of the lighting pattern PT2 are selected, and an AC voltage is supplied to the heater 52 for a time corresponding to the selected phase duty ratio Dp.

[0065] Therefore, in the lighting pattern PTa, it is possible to prevent only one of the lighting patterns PT1 and PT2 from being continuously selected, and it is possible to smooth the even-order and odd-order harmonic noises. As a result, the regulated values of the even-order and odd-order harmonic currents can be satisfied.

[0066] Instead of the lighting pattern PT2, a lighting pattern PT3 or PT4 having harmonic noise characteristics similar to those of the lighting pattern PT1 may be used. That is, a lighting pattern Pta may be created by combining the lighting patterns PT1 and PT3 or by combining the lighting patterns PT1 and PT4. Similar to the lighting pattern PT2, the lighting patterns PT3 and PT4 are such that even-order harmonic noise is relatively likely to occur and odd-order harmonic noise is relatively unlikely to occur. Therefore, by combining the lighting pattern PT3 or PT4 with the lighting pattern PT1, both even-order harmonic noise and odd-order harmonic noise can be reduced in a well-balanced manner, and it becomes possible to satisfy the regulation values for both even-order harmonics and odd-order harmonics.

[0067] Note that in the lighting pattern Pta, the sum (= 132) of the phase duty ratios Dp with a lighting duty ratio Do = 33% is larger than the sum (= 89) of the phase duty ratios Dp with a lighting duty ratio Do = 34%. This is because the higher the temperature (resistance value) of the heater 52, the lower the inrush current, and it is necessary to increase the voltage required for temperature rise.

[0068] For example, when an AC voltage is supplied to the heater 52 (halogen lamp) during all half-cycle periods a to d, the temperature of the heater 52 is unlikely to drop within the control period, and the resistance of the heater 52 is maintained in a relatively high state. On the other hand, when an AC voltage is supplied to the heater 52 only during the half-cycle periods a and b, the temperature of the heater 52 drops during the half-cycle periods c and d, and the resistance value of the heater 52 becomes low.

[0069] Therefore, even when the magnitude relationship of the sum of the phase duty ratios Dp is reversed, the amount of current supplied to the heater 52 at a lighting duty ratio Do = 33% is smaller than the amount of current supplied to the heater 52 at a lighting duty ratio Do = 34%. Also, the amounts of current supplied to the heater 52 at lighting duty ratios Do = 32%, 33%, and 34% increase sequentially. That is, even when patterns with different change tendencies of the phase duty ratio Dp are arranged adjacent to each other in the order of the lighting duty ratio Do, the amount of current supplied to the heater 52 can be increased sequentially as the lighting duty ratio Do increases.

[0070] Also, at other lighting duty ratios Do, the sum of the phase duty ratios Dp is set so that the current (power) supplied to the heater 52 increases sequentially as the lighting duty ratio Do increases. In other words, even when patterns with different change tendencies of the phase duty ratio Dp are arranged in the order of the lighting duty ratio Do in the lighting pattern PTa, a current that increases as the lighting duty ratio Do increases can be supplied to the heater 52. Thereby, the amount of heat generated by the heater 52 can be increased as the lighting duty ratio Do increases.

[0071] As a result, the surface temperature of the fixing roller 51a can be quickly set to a desired temperature with a minimum control cycle. That is, based on the temperature acquired from the temperature sensor 54, the power responsiveness for supplying power to the heater 52 to set the surface temperature of the fixing roller 51a to a desired temperature can be improved compared to the conventional case.

[0072] FIG. 7 is an explanatory diagram showing the relationship between the surface temperature of the fixing roller 51a detected by the temperature sensor 54 and the lighting duty ratio Do.

[0073] When the temperature detected by the temperature sensor 54 is lower than the target temperature, the ratio determination unit 551 shown in FIG. 2 increases the lighting duty ratio Do. When the temperature detected by the temperature sensor 54 is higher than the target temperature, the ratio determination unit 551 decreases the lighting duty ratio Do. As a result, the surface temperature of the fixing roller 51a repeats fluctuations on the higher and lower sides of the target temperature around the target temperature. Due to the fluctuation of the surface temperature of the fixing roller 51a, the lighting duty ratio Do also always fluctuates. Therefore, in the pattern table 553 shown in FIG. 6, the phase duty ratio Dp corresponding to the same value of the lighting duty ratio Do is not continuously selected.

[0074] Therefore, in the pattern table 553, both of the phase duty ratios Dp corresponding to the lighting patterns PT1 and PT2 can be selected, and the even-order harmonic noise and the odd-order harmonic noise can be reduced well in balance. As a result, it becomes possible to satisfy the regulation values of both the even-order harmonics and the odd-order harmonics.

[0075] Note that the ratio of the lighting pattern PT1 and the lighting pattern PT2 included in the lighting pattern Pta is preferably set corresponding to the change range of the lighting duty ratio Do.

[0076] FIG. 8 is a flowchart showing an example of the operation of the heater control unit 55 in FIG. 2. The operation shown in FIG. 8 is implemented, for example, when a CPU provided in the fixing device 50 executes a heater control program for realizing the ratio determination unit 551 and the voltage supply unit 552. That is, FIG. 8 shows an example of a heater control method and a heater control program. The flow shown in FIG. 8 starts when heating the fixing roller 51a in order to perform a fixing operation for fixing the toner image transferred to the transfer paper in the engine unit 20.

[0077] First, in step S10, the CPU acquires the surface temperature of the fixing roller 51a from the temperature sensor 54. Next, in step S12, the CPU determines the lighting duty ratio Do based on the temperature acquired from the temperature sensor 54.

[0078] Next, in step S14, the CPU obtains the phase duty ratios Dpa to Dpd corresponding to the determined lighting duty ratio Do from the pattern table 553. Next, in step S16, the CPU outputs a timing signal corresponding to the phase duty ratios Dpa to Dpd obtained from the pattern table 553 to the triac 53. Thereby, an alternating voltage for bringing the temperature detected by the temperature sensor 54 closer to the target temperature is supplied to the heater 52.

[0079] Next, in step S18, the CPU determines whether the fixing operation has been completed. If the fixing operation has not been completed, the process returns to step S10. If the fixing operation has been completed, the process shown in FIG. 8 ends.

[0080] FIG. 9 is a block diagram showing an example of the hardware configuration of the fixing device 50 in FIG. 2. The fixing device 50 includes a CPU 501, a RAM 502, a ROM 503, an auxiliary storage device 504, and an input / output interface unit 505, and operates as a computer when these are interconnected by a bus 506.

[0081] The CPU 501 controls the operation of the fixing device 50 and realizes the operation shown in FIG. 8 by executing a heater control program stored in the RAM 502, the ROM 503, or the auxiliary storage device 504.

[0082] For example, the RAM 502 is used as a work area for the CPU 501. The ROM 503 stores various programs, parameters used in the various programs, etc., and also stores the pattern table 553 shown in FIG. 6.

[0083] The auxiliary storage device 504 is a storage device such as an SSD (Solid State Drive) or an HDD (Hard Disk Drive), and stores, for example, a control program such as an OS (Operating System) that controls the operation of the fixing device 50, and various data and files necessary for the operation of the fixing device 50. Note that the pattern table 553 shown in FIG. 6 may be stored in the auxiliary storage device 504. The input / output interface unit 505 includes a communication interface and the like for communicating with other functional units of the image forming apparatus 100.

[0084] As described above, in this embodiment, the pattern table 553 includes a predetermined number of patterns in which even-order harmonic noise is relatively likely to occur and a predetermined number of patterns in which odd-order harmonic noise is relatively likely to occur, corresponding to a predetermined number of consecutive lighting duty ratios Do. The voltage supply unit 552 reads the phase duty ratios Dpa to Dpd corresponding to the lighting duty ratio Do that changes depending on the temperature of the heater 52 from the pattern table 553, and supplies an alternating voltage to the heater 52 according to the read phase duty ratios Dpa to Dpd. Thereby, when supplying an alternating voltage to the heater 52, for example, it is possible to prevent only the patterns in which even-order harmonic noise is relatively likely to occur from being continuously selected. As a result, even-order and odd-order harmonic noises can be smoothed, and the regulation values of even-order and odd-order harmonic currents can be satisfied.

[0085] The sum of the phase duty ratios Dpa to Dpd set for each lighting duty ratio Do in the pattern table 553 is set in consideration of the temperature dependence of the resistance value of the heater 52. Thereby, even when arranging patterns with different change tendencies of the phase duty ratio Dp adjacent to each other in the order of the lighting duty ratio Do, the amount of current supplied to the heater 52 can be sequentially increased as the lighting duty ratio Do increases.

[0086] In the pattern table 553, by setting the phase duty ratios Dpa to Dpd for each lighting duty ratio Do associated with the temperature of the heater 52, the amount of power supplied to the heater 52 can be adjusted according to the temperature detected by the temperature sensor 54. For example, when the surface temperature of the fixing roller 51a is low, by selecting the phase duty ratios Dpa to Dpd corresponding to a relatively large lighting duty ratio Do, the temperature rise rate of the heater 52 can be increased.

[0087] As a result, the surface temperature of the fixing roller 51a can be quickly set to a desired temperature with a minimum control cycle. That is, based on the temperature acquired from the temperature sensor 54, the power responsiveness for supplying power to the heater 52 to set the surface temperature of the fixing roller 51a to a desired temperature can be improved compared to the conventional case.

[0088] As described above, the present invention has been described based on each embodiment, but the present invention is not limited to the requirements shown in the above embodiments. In this regard, it can be changed within the range not departing from the gist of the present invention, and can be appropriately determined according to its application form.

Explanation of Reference Numerals

[0089] 10 Scanner unit 20 Engine unit 30 Paper feed tray 40 Conveyor path 50 Fixing device 51a Fixing roller 51b Pressing roller 52 Heater 53 Triac 54 Temperature sensor 55 Heater control unit 56 Zero-cross detection unit 100 Image forming apparatus 200 AC power supply 501 CPU 502 RAM 503 ROM 504 Auxiliary storage device 505 Input / Output Interface Section 506 Bus 551 Ratio Determination Section 552 Voltage Supply Section 553 Pattern Table a, b, c, d Half - wave Periods Do Lighting Duty Ratio Dpa, Dpb, Dpc, Dpd Phase Duty Ratios PT1, PT2, PT3, PT4, PTa Lighting Patterns

Prior Art Documents

Patent Documents

[0090]

Patent Document 1

Claims

1. An image forming apparatus having a fixing roller, a heater for heating the fixing roller, a temperature detection unit for detecting the temperature of the fixing roller, and a heater control device for controlling the amount of power supplied to the heater for each of a plurality of half-wave periods within a control period including a predetermined number of cycles of an AC voltage, The heater control device includes: A ratio determination unit that determines a power ratio, which is a ratio of the amount of power supplied to the heater to make the fixing roller reach a target temperature, to the amount of power that can be supplied within the control period, based on the temperature detected by the temperature detection unit; A pattern table in which time information indicating the voltage supply time to the heater for each of a plurality of half-wave periods within the control period is stored for each power ratio; A voltage supply unit that supplies a voltage to the heater according to the time information stored in the pattern table corresponding to the power ratio determined by the ratio determination unit, The pattern table repeatedly includes a plurality of pattern groups including a predetermined number of first patterns indicating that all the time information of the plurality of half-wave periods supplies a voltage to the heater, and a predetermined number of second patterns indicating that the time information of at least any one of the plurality of half-wave periods does not supply a voltage to the heater, The time information stored in the pattern table indicates a time ratio that is a ratio of the voltage supply time to the heater with respect to the half-wave period, In the pattern table, the sum of the time ratios of the plurality of half-wave periods within the control period in the first pattern is larger than the sum of the time ratios of the plurality of half-wave periods within the control period in the second pattern in which the power ratio is one larger than that of the first pattern, An image forming apparatus in which the power supplied to the heater increases as the power ratio increases.

2. A heater control method for controlling the amount of power supplied to a heater for each of a plurality of half-wave periods within a control period including a predetermined number of cycles of an AC voltage, Based on the temperature of the object to be heated heated by the heater, determine a power ratio which is the ratio of the power supply amount to be supplied to the heater to make the object to be heated reach the target temperature, to the power amount that can be supplied in the control period, In a pattern table in which time information indicating the voltage supply time to the heater in each of a plurality of half-wave periods within the control period is stored for each power ratio, supply voltage to the heater according to the time information corresponding to the determined power ratio, The pattern table repeatedly includes a plurality of pattern groups including a predetermined number of first patterns in which all the time information of the plurality of half-wave periods indicates supplying voltage to the heater, and a predetermined number of second patterns in which at least any of the time information of the plurality of half-wave periods indicates not supplying voltage to the heater, The time information stored in the pattern table indicates a time ratio which is the ratio of the voltage supply time to the heater with respect to the half-wave period, In the pattern table, the sum of the time ratios of the plurality of half-wave periods within the control period in the first pattern is larger than the sum of the time ratios of the plurality of half-wave periods within the control period in the second pattern in which the power ratio is one larger than that of the first pattern, A heater control method in which the power supplied to the heater increases as the power ratio increases.

3. A heater control program for controlling the power supply amount to be supplied to a heater for each of a plurality of half-wave periods within a control period including a predetermined number of periods of an alternating voltage, causing a computer to Based on the temperature of the object to be heated heated by the heater, determine a power ratio which is the ratio of the power supply amount to be supplied to the heater to make the object to be heated reach the target temperature, to the power amount that can be supplied in the control period, In a pattern table in which time information indicating the voltage supply time to the heater in each of a plurality of half-wave periods within the control period is stored for each power ratio, supply voltage to the heater according to the time information corresponding to the determined power ratio, The pattern table repeatedly includes a plurality of pattern groups each including a predetermined number of first patterns indicating that the time information of all of the plurality of half-periods supplies voltage to the heater, and a predetermined number of second patterns indicating that the time information of at least any one of the plurality of half-periods does not supply voltage to the heater. The time information stored in the pattern table indicates a time ratio that is a ratio of the voltage supply time to the heater with respect to the half-period. In the pattern table, the sum of the time ratios of the plurality of half-periods within the control period in the first pattern is greater than the sum of the time ratios of the plurality of half-periods within the control period in the second pattern in which the power ratio is one greater than that of the first pattern. A heater control program in which the power supplied to the heater increases as the power ratio increases.

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