JP2012088444A - Fixing heater - Google Patents

Abstract

The present invention provides a fixing heating device capable of significantly suppressing harmonic current distortion in startup control of a fixing roller heating device of a heat roller system.
A heater 100 for fixing toner on a sheet, a triac 204 for energizing / cutting off power supplied from an AC power source 202 to the heater 100, a zero cross detection circuit 212 for detecting a zero cross of the AC power source, and a heater At the start of power supply, the control unit 203 performs phase control that changes the power supply ratio to the heater 100 stepwise by controlling the energization phase angle of the triac 204 using the detection result of the zero cross detection circuit 212. The control unit 203 performs phase control that maximizes the change in the power supply ratio in a period in which the power supply phase angle is changed stepwise from at least the power supply phase angle of 30% to the power supply phase angle of 70%. The fixing heating apparatus is characterized in that the triac 204 is controlled so as to include:
[Selection] Figure 2

Description

  The present invention relates to heater power control of a fixing heating device used in a copying machine, a printer device, a facsimile device, a multi-function device having a plurality of functions.

  2. Description of the Related Art Conventionally, in image forming apparatuses such as copying machines, printers, facsimiles, etc., there has been a fixing heating device that melts and fixes by heat in order to form an unfixed toner image formed on a recording material or a recording medium such as an OHP sheet as a fixed image. Is provided. In this fixing heating device, there is a fixing roller as a heating member having a built-in heat source, and a heat roller method in which a recording medium is nipped and conveyed while being heated and pressed by a pressure roller pressed against the fixing roller. . In addition, various systems and configurations such as a film fixing system are known. The heat roller type fixing heating device has a large heat capacity of the fixing roller as a heating member as compared with other methods, and is commonly used as a method for facilitating high speed and gloss.

  In general, a heat generating member (heater) such as a halogen lamp or a heat generating resistor is used as a heat source of the heat roller system. This heater is connected to an AC power supply via a switching control element such as a triac, and a temperature detecting element, for example, a thermistor temperature sensitive element, is provided in a fixing heating device to which electric power is supplied by this AC power supply. Based on the detected temperature information, the engine cotton roller of the device turns on / off the switching element to turn on / off the power supply to the heater and adjust the temperature of the fixing heating device to the target temperature. Is done.

  A heater such as a halogen lamp or a heat generating resistor as a heat source has a characteristic that the resistance characteristic with respect to temperature is positive. Therefore, when electric power is supplied to a heater having a low temperature, an excessive inrush current flows, and the AC power supply voltage connected to the apparatus is rapidly changed due to the influence of the internal impedance of the AC power supply or the impedance of the indoor power distribution network.

  In recent image forming apparatuses, full-color images are formed, and high-speed printing and high image quality are important. In addition, in order to frequently shift to the power saving mode due to recent power saving, it is required to shorten the return time from the power saving mode. For this reason, the fixing heating device in the image forming apparatus requires rapid heating start-up. Thus, the heat capacity of the heat roller in the fixing heating device tends to increase, in other words, the resistance value of the heater tends to decrease. As described above, the decrease in the resistance value of the heater means an increase in inrush current when the heater power is supplied, and this increase in inrush current causes further flicker. Flicker refers to a phenomenon in which peripheral equipment connected to the same AC power source as the fixing heating device, for example, lighting equipment flickers due to a rapid voltage fluctuation that occurs each time the heater is turned on / off. In order to suppress flicker due to inrush current when power is supplied to the heater, slow-up control by phase control is known. For example, the phase angle for turning on the heater is increased and changed so that the input current is constant (see, for example, Patent Document 1), and the phase angle is turned on at a predetermined phase angle (for example, see Patent Document 2), and phase control is performed. Slow-up control was performed to suppress sudden fluctuations in the power supply voltage of the AC power supply.

JP 09-106215 A JP-A-10-186842 JP-A-11-027932

  As described above, when flicker and harmonic current distortion increase, other devices on the power distribution network may malfunction or deteriorate the life, and the load on the power transmission and distribution equipment may increase. For this reason, flicker and harmonic current distortion are regulated by the EMC command low frequency EMC standard (IEC61000-3-2). In particular, regulations on power supply harmonic current distortion are strengthened for further efficient use of energy. That is, not only integer multiple harmonic current distortion of the fundamental frequency of the AC power source but also suppression of non-integer multiple harmonic current distortion (inter-order harmonic) is required, and heater slow-up control by conventional phase control is required. However, it has become difficult to respond. For example, the generation of harmonic distortion during slow-up control by phase control is higher than the conventional harmonic current distortion measurement method that does not include interharmonic harmonics. In the case of the strain measurement method, the number increases from about 1.5 times to 2 times. In the case of a heat roller type fixing heating device, heater control using phase control is not always performed, but only for a part of time, for example, during slow-up control. Therefore, in the conventional method for measuring harmonic current distortion that does not include harmonics between orders, the harmonic current distortion of each order is about 30% to about 50% with respect to the harmonic current distortion standard value. However, in the method of measuring harmonic current distortion including inter-order harmonics, the harmonic current distortion of each order is about 60% to about 100% with respect to the harmonic current distortion standard value. When the resistance value of the heater is further reduced to increase the printing speed, the harmonic current distortion measurement method including the harmonics between orders is higher than 100% of the harmonic current distortion standard value. Current distortion will occur.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and in the slow-up control when power is supplied to the heater of the fixing heating device used in the image forming apparatus, start-up control capable of suppressing harmonic current distortion is possible. It becomes.

  The present invention has the following configuration in order to solve the above problems.

  Fixing heating means for fixing a developer on a recording medium, electronic switch means for energizing / cutting off electric power supplied from an AC power source to the fixing heating means, zero cross detecting means for detecting a zero cross of the AC power source, and the fixing Phase control that changes the power supply ratio to the fixing heating unit stepwise by controlling the energization phase angle of the electronic switch unit using the detection result of the zero cross detection unit at the start of power supply to the heating unit The control means includes at least a power supply ratio in a period in which the energization phase angle is changed stepwise from at least an energization phase angle with a power supply ratio of 30% to an energization phase angle with a power supply ratio of 70%. A fixing heating apparatus characterized by controlling the electronic switch means so as to include a phase control in which the change is maximized.

  According to the present invention, in the slow-up control when power is supplied to the heater of the fixing heating device used in the image forming apparatus, it is possible to perform start-up control that can suppress harmonic current distortion.

1 is a schematic configuration diagram of a fixing heating device according to a first embodiment. Driving circuit diagram of the heater of the fixing heating device of Embodiment 1 Basic operation explanatory diagram of heater power control by phase control of embodiment 1 Operation explanatory diagram of heater power control by phase control of embodiment 1 Explanatory drawing of the harmonic current distortion of heater electric power control by phase control of Example 1 Chart of harmonic current distortion of heater power control by phase control of Example 1 Explanatory drawing of the average relative value calculation of the harmonic current distortion by phase control of Example 1 Chart of heater power control by phase control of embodiment 1 Explanatory drawing of heater electric power control by phase control of Example 1 Graph of heater power control by phase control of Example 1 Flowchart of heater power control by phase control of embodiment 1 Graph of heater power control by slow-down control of Example 1 Graph of heater power control by phase control of Example 2

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the embodiment described below, an example of an image forming apparatus having a fixing heating device using a halogen heater shown in FIG. 1 will be described. However, the present invention can be applied to all apparatuses using a heat roller type fixing heating apparatus, and is not particularly limited to an image forming apparatus. The technical scope of the present invention is defined by the claims, and is not limited by the following individual embodiments.

  In the present embodiment, an example of slow-up control when power is supplied to a heater capable of suppressing harmonic current distortion in an image forming apparatus having a heat roller type fixing heating device will be described.

[Fixing heating device]
A fixing heating device 100 shown in FIG. 1 is a heat roller type fixing device, and includes a fixing roller 101, a halogen heater (hereinafter referred to as a heater) 102, and a pressure roller 103. The fixing roller 101 has an elastic layer 105 made of silicon rubber or the like on the outer peripheral surface of a cylindrical metal core 104 made of a metal having good thermal conductivity such as aluminum, and further, an outer peripheral surface of the elastic layer is made of fluororesin or the like. The release layer 106 is formed. Both ends of the cylindrical metal core 104 are rotatably supported by a device frame (not shown) via bearings. A heater 102 is inserted into the cylindrical cored bar 104 of the fixing roller 101. Both ends of the heater 102 are supported by the apparatus frame via a heater holder (not shown). The pressure roller 103 has an elastic layer 108 made of silicon rubber or the like on the outer peripheral surface of a metal cylindrical cored bar 107, and further has a release layer 109 made of fluororesin or the like on the outer peripheral surface of the elastic layer. The pressure roller 103 is disposed below the fixing roller 101 in parallel with the fixing roller 101, and both ends of the cylindrical cored bar 107 are rotatably supported by a device frame (not shown) via a bearing. The pressure roller 103 forms a fixing nip portion 110 between the pressure roller 103 and the fixing roller by pressurizing both ends of the metal core to the fixing roller 101 by a pressure spring (not shown). The fixing roller is rotationally driven by a driving source such as a motor (not shown), and electric power is supplied to the heater 102 from the heater driving circuit 200 shown in FIG. The temperature of the fixing roller 101 heated by the heater 102 is detected by the thermistor 201 of the temperature detection element. The heater drive circuit 200 controls the power supply to the heater 102 based on the output signal of the thermistor 201, and maintains the temperature of the fixing roller 101 at the target temperature. Then, a sheet (recording medium) carrying an unfixed toner (developer) image is nipped and conveyed by the fixing nip portion 110. As a result, heat and pressure are applied to the unfixed toner image on the sheet surface, and gloss is imparted to the surface of the toner image while fixing the toner image on the sheet surface.

[Heater drive circuit]
FIG. 2 shows a heater drive circuit of the fixing heating apparatus according to this embodiment. A commercial AC power source 202 is connected to the fixing heating device 100, and the control unit 203 supplies the input voltage from the AC power source 202 to the heater 102 to cause the heater 102 to generate heat. Electric power is supplied to the heater 102 by energizing / cutting off the triac 204 (electronic switch). The resistors 205 and 206 are bias resistors for the triac 204, and the phototriac coupler 207 is a device for ensuring a creepage distance between the primary and secondary. Then, the triac 204 is turned on by energizing the light emitting diode 208 of the phototriac coupler 207. The resistor 209 is a resistor for limiting the current of the phototriac coupler 207, and turns on / off the phototriac coupler 207 by the transistor 210. The transistor 210 operates according to the heater drive signal from the control unit 203 via the resistor 211.

  The input power supply voltage from the AC power supply 202 is also input to the zero cross detection circuit 212 which is a voltage waveform detection circuit. The AC voltage from the AC power source 202 is half-wave rectified by the rectifiers 213 and 214. In this circuit, the neutral side is rectified. This half-wave rectified AC voltage is input to the base of the transistor 219 via the resistors 215 and 216, the capacitor 217, and the resistor 218. Thus, the transistor 219 is turned on when the neutral side potential is higher than the hot side potential, and the transistor 219 is turned off when the neutral side potential is lower than the hot side potential. The photocoupler 220 is an element for securing a creepage distance between the primary and secondary, and the resistors 221 and 222 are resistors for limiting the current flowing through the photocoupler 220. When the neutral side potential becomes higher than the hot side potential, the transistor 219 is turned on, so that the light emitting diode 223 in the photocoupler 220 is turned off, the phototransistor 224 is turned off, and the output voltage of the photocoupler 220 becomes high. On the other hand, when the neutral side potential becomes lower than the hot side potential, the transistor 219 is turned off, so that the light emitting diode 223 of the photocoupler 220 emits light, the phototransistor 224 is turned on, and the output voltage of the photocoupler 220 becomes low. The output of the photocoupler 220 is notified to the control unit 203 through the resistor 225 as a zero cross signal. The zero cross signal is a pulse signal having a signal period equal to the frequency of the AC power source 202, and the signal level changes according to the potential polarity of the AC power source 202. The control unit 203 detects the rising and falling edges of the zero-cross signal, and controls the power supply to the heater 102 by turning on / off the triac 204 at an arbitrary timing. The temperature detected by the thermistor 201 is detected as a partial pressure between the resistor 226 and the thermistor 201 and input to the A / D port as a TH signal to the control unit 203. In the above configuration, the temperature control of the fixing heating device 100 is performed as follows. That is, when the control unit 203 monitors the TH signal and reaches a target temperature at which the unfixed image can be heated and fixed as a fixed image, the heater 102 is deenergized using the heater drive signal. When the temperature falls below the target temperature, the temperature of the fixing heating device is kept constant by energizing the heater 102.

  Next, power control when the heater is energized will be described. The heater 102 is made of a material such as tungsten or molybdenum and has a characteristic that the resistance characteristic with respect to temperature is positive. Therefore, when the heater 102 having a low temperature is turned on, a large inrush current is generated because the resistance value is lower when the heater is on than when the heater is on. For example, even if the heater is turned on at the zero-cross timing with the lowest voltage in consideration of the impedance of the power supply or the circuit, an inrush current 7 to 10 times may occur. In this embodiment, heater slow-up control by phase control that suppresses harmonic current distortion will be described.

[Phase control]
Heater power control by phase control will be described with reference to FIG. The logic of the zero cross signal 3b is switched at a point where the AC power supply voltage waveform 3a is switched from positive to negative and from negative to positive. When the heater drive signal 3c is turned on after Ta time from the rising and falling edges, the heater is energized and supplied with power at the hatched portion of the heater applied voltage 3d. Since the heater is turned off at the next zero cross point after the heater is turned on, the same power is supplied to the heater in the next half-wave by turning on the heater drive signal again after time Ta from the edge of the zero cross signal. Is supplied. Further, when the heater driving signal is turned on after a time Tb different from the time Ta, the energization time to the heater changes, so that the power supplied to the heater can be changed. Thus, the power supplied to the heater can be controlled by changing the time for which the heater drive signal is turned on from the edge of the zero cross signal every half wave. When the frequency of the AC power source 202 is f and the time width for turning on the heater drive signal 3c is Tx (0 <= Tx <= 1 / f / 2), the heater supply power ratio Pr is expressed by the following equation.

  For example, in the AC power source 202 with f = 50 Hz, if Tx = 5 msec, Pr = 0.5. 5 msec means that the heater drive signal is turned on when the energization phase angle is 90 degrees, and power is supplied to the heater at a power ratio of 0.5 (50%) compared to the case where the heater is turned on for all half waves.

[Generation of harmonic current by phase control]
In the phase control, energization to the heater is turned on in the middle of the half wave of the AC power supply voltage waveform 3a, so that the current flowing through the heater suddenly rises and the harmonic current flows. Generation of harmonic current by phase control will be described with reference to FIGS. 4, 5, and 6.

  FIG. 4 shows the AC power supply voltage waveform 4a when the frequency of the AC power supply 202 is 50 Hz, and the heater applied voltage when the phase control is performed at a fixed phase angle with the heater supply power ratio Pr of 0.05 to 0.95. 4b to 4l). When the frequency of the AC power supply 202 is 50 Hz, the half-wave time of the AC power supply voltage waveform 4a is 10 ms. As shown in 4b to 4l of FIG. 4, the control unit 203 sets the heater drive signal timing for turning on the heater 102 to 7.97 ms to 2.03 ms from the zero cross point as shown in FIGS. Pr can be set to 0.05 to 0.95. Here, the same heater-on timing is used for two half waves of the positive cycle and the negative cycle of the continuous AC power supply 202.

  FIG. 5 shows a value obtained by dividing odd-order harmonic current distortion values from the second order to the 40th order under the conditions of a heater resistance value of 100Ω and an AC power supply of 230 V / 50 Hz by a harmonic current distortion standard (including harmonics between orders). The relationship of harmonic order is shown. As shown in FIG. 5, when Pr = 0.5, the harmonic current is maximized at almost all harmonic orders. Subsequently, Pr = 0.3, 0.7 is second, Pr = 0.2, 0.8 is third, Pr = 0.15, 0.85 is fourth, Pr = 0.1, 0.9 5 is the fifth, Pr = 0.05, and 0.95 is the sixth increase. Here, for example, Pr = 0.3 means a power supply ratio of 30%, and Pr = 0.7 means a power supply ratio of 70%. FIG. 6 shows the relative ratio obtained by dividing the total harmonic current distortion (including inter-order harmonics) by the total harmonic current distortion at Pr = 0.5. Also in the total harmonic current distortion, compared with Pr = 0.5, Pr = 0.3, 0.7 is 96%, Pr = 0.2, 0.8 is 86.7%, Pr = 0. 15 and 0.85 are reduced to 80.3%, Pr = 0.1 and 0.9 are reduced to 71.2%, Pr = 0.05 and 0.95 are decreased to 56.6%. It can be seen that Pr = 0.5 increases the harmonic current distortion most. Since Pr = 0 and 1 are ideally sine waves with no heater current waveform or no phase control, harmonic current distortion does not occur and is 0% here. That is, it can be seen that the harmonic current distortion tends to increase as the rising amount of current increases, and that Pr = 0.5 having the largest rising amount causes the highest harmonic current distortion. Therefore, for example, it can be said that reducing the number of times of phase control of the supply power ratio with a large amount of current rise, such as the supply power ratio Pr = 0.5, is effective in suppressing harmonic current distortion. Here, in the graph of FIG. 5, the harmonic order is omitted only for the odd order while the even order is omitted. This is because the heaters are turned on at the same timing for the two half-waves of the positive cycle and the negative cycle of successive AC power supplies, so that even-order components hardly appear when Fourier transform is performed. Actually, a heater-on timing shift occurs between the positive cycle and the negative cycle of the AC power source due to the error of the zero cross signal and the frequency fluctuation of the AC power source 202, so that even-order components are generated.

  As described above, in the case of a heat roller type fixing heating apparatus, heater control using phase control is not always performed, but is performed only for a part of time, for example, during slow-up control. Therefore, in the conventional method for measuring harmonic current distortion that does not include harmonics between orders, the harmonic current distortion of each order is about 30% to about 50% with respect to the harmonic current distortion standard value. However, in the method of measuring harmonic current distortion including inter-order harmonics, the harmonic current distortion of each order is about 60% to about 100% with respect to the harmonic current distortion standard value. Therefore, in order to satisfy the harmonic current distortion including the interharmonic harmonics with a margin with respect to the harmonic current distortion standard, at least 10% or more harmonic current distortion suppression is required. Therefore, a control for satisfying the harmonic current distortion including inter-order harmonics with a margin with respect to the harmonic current distortion standard will be described with reference to FIG. In FIG. 7, an example of suppressing more than 10% or exceeding 20% will be described.

[Calculation of average relative value of harmonic current distortion]
FIG. 7 shows the average relative value of the total harmonic current distortion corresponding to each heater power ratio Pr range, the number of times of control in the conventional example, the number of times of control in the reduction example exceeding 10%, and the number of control in the reduction example exceeding 20%. . A method of calculating the average relative value of the total harmonic current distortion will be described with reference to FIG. For example, as shown in FIG. 6, when Pr = 0.05 and 0.95, the relative value of the total harmonic current distortion is 56.6% with respect to the total harmonic current distortion of Pr = 0.5. When Pr = 0.1 and 0.9, the relative value of the total harmonic current distortion is 71.2% with respect to the total harmonic current distortion of Pr = 0.5. That is, the total harmonic current distortion in the range of Pr = 0.05 to 0.1 and 0.9 to 0.95 is 56.6% to 71.75 with respect to the total harmonic current distortion of Pr = 0.5. It can be seen that it is in the range of 2%. Here, the total relative harmonic current distortion in the range of Pr = 0.05 to 0.1, 0.9 to 0.95 is simply compared to the total harmonic current distortion of Pr = 0.5. The average is 63.9% (= (56.6% + 71.2%) / 2). In other ranges, the same calculation is performed using the chart of FIG. By this calculation, the average relative ratio of the total harmonic current distortion in the range of each heater power ratio Pr can be obtained.

  An example of the number of times of control (phase control time) in the conventional example, a reduction example exceeding 10%, and a reduction example exceeding 20% will be described. Here, the number of times of control in the conventional example, the reduction example exceeding 10%, and the reduction example exceeding 20% is set to 50 times of one phase control (one control cycle) required for slow-up. In the conventional example shown in FIG. 7, the degree of change in the heater supply power ratio is fixed uniformly. Therefore, the number of times of one phase control corresponding to each heater power ratio Pr range is, for example, Pr = 0 to 0.05, 0.95 to 1.00 (power supply ratio 5% or less and power supply ratio 95% or more), the number of times of control is 5 times, which is 10% of the total number of times of 50 times. Similarly, for example, in the range of Pr = 0 to 0.05 and 0.95 to 1.00 in a reduction example exceeding 10%, the number of one wave of phase control is 11, and the total number of slow-up control is 50 times. In contrast, the number of times of control is 22% (20% or more).

  Here, by using the average relative value of the total harmonic current distortion and the number of times of one phase control corresponding to the range of each heater power ratio Pr, the harmonic current distortion of the entire slow-up control shown in FIG. A method for obtaining the average relative value will be described. The average relative value is a value obtained by multiplying each heater power ratio Pr by multiplying the number of times of control. When the average relative value of the harmonic current distortion is calculated for each of the conventional example, the reduction example exceeding 10%, and the reduction example exceeding 20%, 8261.5 in the conventional example and 7035.0 in the reduction example exceeding 10%. In the reduction example exceeding 20%, it becomes 6282.4. That is, it can be seen that the reduction example of more than 10% and the reduction example of more than 20% are restrained by harmonic current distortion of about 85% and about 76%, respectively, as compared with the conventional example. The number of one phase of the phase control corresponding to the range of each heater power ratio Pr shown in the reduction example exceeding 10% and the reduction example exceeding 20% shown in FIG. 7 is merely an example, and is limited to the value shown in FIG. is not. Increasing the number of times of control in the range of Pr = 0 to 0.05, 0.95 to 1.00 and decreasing the number of times of control in the range of Pr = 0.3 to 0.7 reduces the harmonic current distortion most. It is effective to do. Then, increasing the number of times of control of Pr = 0 to 0.05 and 0.95 to 1.00 and decreasing the number of times of control of Pr = 0.3 to 0.7 inevitably results in Pr = 0.3. The change in the heater supply power ratio Pr in the range of .about.0.7 is maximum as compared with other heater power ratio Pr ranges.

[Specific heater control pattern and heater applied voltage change]
In the slow-up control using phase control for preventing inrush current when power is supplied to the heater of the fixing heating device, an example of heater control that suppresses harmonic current distortion that clearly represents the feature of this embodiment will be described.

  FIG. 8 shows a heater control pattern table at the time of supplying power to specific heaters created based on the reduction example exceeding 20% shown in FIG. When the heater slow-up control is started, the controller 203 changes the heater supply power ratio Pr for each wave in the order of wave number 1 to 50, and performs the heater slow-up control. In this pattern table, a heater control pattern of Pr = 0.3 to 0.7, which is a heater supply power ratio showing a total harmonic current distortion relative comparison of 96% or more shown in FIG. 20% or less). Further, as shown in FIG. 6, a heater control pattern of Pr = 0 to 0.05 or Pr = 0.95 to 1 showing a total harmonic current distortion relative comparison of about 56.6% or less is used for the entire heater slow-up control. The ratio is 36%. Then, control is performed that does not include the heater supply power ratio of Pr = 0.5 that causes the most harmonic current distortion. Further, the control is performed so that the change in the heater power supply ratio Pr is at a maximum at least before and after Pr = 0.5. In this embodiment, the change in the heater supply power ratio Pr between before and after Pr = 0.5 is 0.06.

  FIG. 9 shows changes in the heater applied voltage according to the heater control pattern table when the frequency of the AC power source 202 is 50 Hz. It can be seen that as the heater supply power ratio Pr 9b changes for each wave, the heater applied voltage (portion indicated by the hatched portion of 9c) changes. Then, the heater slow-up control ends at the wave number N = 50, and the heater supply power ratio Pr is set to 1 from the wave number N = 51 to perform the heater full lighting control.

[Comparison with the conventional heater supply power ratio]
FIG. 10 shows a graph of the heater control pattern shown in FIG. 8 and a graph of a conventional control example of a heater control pattern in which the degree of change in the heater supply power ratio is fixed uniformly. In the graph of an example of the present embodiment, compared to the graph of an example of the conventional control, the heater supply power ratio Pr is changed around Pr = 0.5 that changes the heater supply power ratio and generates the highest harmonic current distortion. Maximizes change. The number of control times of the heater control pattern in the range of Pr = 0.3 to Pr = 0.7 that can generate a large number of harmonic current distortions is 20 times in total in the conventional example, wave number numbers N = 16 to 35. In this embodiment, the number of wave numbers N = 22 to 29 is reduced to a total of 8 times. In addition, the number of times of control of the heater control pattern with Pr = 0.05 or less and Pr = 0.95 or more with relatively small harmonic current distortion is four times of wave number numbers N = 1, 2, 49, and 50 in the conventional example. On the other hand, in this embodiment, the wave number is increased to 18 times of N = 1 to 9 and N = 42 to 50.

[Slow-up control flow]
FIG. 11 shows a control flow of heater slow-up control at the start of power supply. The control unit 203 sets the wave number N to 1 (step (hereinafter, S) 1101), and the heater supply power ratio Pr corresponding to the wave number N is stored in a storage unit (not shown) in the control unit 203. A selection is made from a heater slow-up table (for example, FIG. 8) (S1102). Next, the control unit 203 updates the frequency detection result based on the zero cross signal (S1103), and calculates the time difference from the zero cross to the heater being turned on based on the heater supply power ratio Pr and the frequency detection result (S1104). At the ON timing of the calculated heater driving signal, the control unit 203 performs the two half-wave continuous phase control of the heater 102 (S1105). The wave number N is incremented by 1 (S1106), and repetitive control from S1102 to S1105 is performed. When the wave number N is updated to 51 (S1107, Y), the heater slow-up control is terminated, the heater supply power ratio Pr is set to 1, and the heater full lighting control is performed. If N is not updated to 51 (N in S1107), the process returns to S1102.

  Here, in the present embodiment, the control in which the maximum change in the heater supply power ratio Pr at around Pr = 0.5 is 0.06 has been described, but it is not necessarily limited to 0.06. An appropriate change in Pr may be set in consideration of the influence of flicker by the resistance value of the heater 102, the voltage value of the AC power source 202, and the like. When starting heater slow-up control with a low heater resistance value, a value that does not generate much harmonic current distortion (particularly, Pr = 0.05 or less) is used for the heater supply power ratio Pr if only harmonic current distortion is suppressed. There is also an effect of suppressing flicker. Therefore, at the time of starting the heater slow-up control, the heater supply power ratio Pr is set to a small value, and control not including the heater supply power ratio of Pr = 0.5 that causes the highest harmonic current distortion is performed. Further included is energization phase amount control in which the rate of change is maximized during a period in which the energization phase amount is changed from 30% energization phase amount control to 70% energization phase amount control. The energization phase amount control that maximizes the rate of change is control that maximizes the change in the heater supply power ratio Pr before and after Pr = 0.5. That is, for example, by performing the slow-up control shown in the present embodiment, it is possible to obtain a significant harmonic current distortion suppression effect compared to the conventional heater slow-up control in which the change in the heater supply power ratio is fixed uniformly. it can.

  Moreover, although this control demonstrated the heater control pattern in the case of slow-up control, it can be applied also to the slow-down control of a heater. When the heater is turned off, no inrush current is generated when the heater is turned off. However, sudden heater turn-off control causes a large change in the heater current before and after turning off, leading to an increase in flicker. Therefore, the heater slow-down control, which is the reverse of the heater slow-up control, may be performed even when the heater lighting is stopped. Although the heater slowdown control causes many harmonic current distortions due to phase control as in the case of the heater slowup control, the heater slowdown control shown in FIG. 12, for example, is applied by applying the heater slowup control described in this embodiment. Harmonic current distortion can be suppressed.

  Here, an example is shown in which the heater slow-up control is performed between the first wave and the 50th wave, and the heater power supply ratio is set to 1 from the 51st wave, but it is suppressed to a predetermined inrush current that can prevent malfunction of the apparatus. If necessary, the wave number required for the heater slow-up control can be adjusted as appropriate. The heater supply power ratio Pr for the first and last 50th waves of the heater slow-up control is 0.03 and 0.97, respectively. This is to prevent the heater 102 from being supplied with unintentionally greatly shifted power to the heater 102 due to a zero-cross signal error in the zero-cross detection circuit 212 or a malfunction due to a frequency variation of the AC power source 202. For example, when the heater power supply ratio Pr is set to 0.01 in the AC power source 202 with a frequency of 50 Hz, the control unit 203 turns on the heater drive signal after about 8.44 ms from the zero cross signal. For example, if the frequency fluctuation of the AC power supply greatly occurs and the heater drive signal ON timing exceeds the next zero cross, the heater supply power ratio Pr becomes from 0.1 to near 1.0, for example. On the other hand, when the heater supply power ratio Pr is set to 0.99, the control unit 203 turns on the heater drive signal approximately 1.56 ms after the zero cross signal is started. For example, if the frequency fluctuation of the AC power supply greatly occurs and the heater drive signal ON timing comes before the current zero cross, the heater supply power ratio Pr becomes close to 0 from 0.99. Such unexpected unintentional malfunctions greatly deviate the heater power control and lead to an increase in flicker and harmonic current distortion due to an increase in inrush current. Here, the minimum value of the heater supply power ratio Pr is set to 0.03 and the maximum value is set to 0.97. However, the heater supply power ratio Pr can be appropriately adjusted as long as the malfunction does not occur.

  As described above, according to the image forming apparatus of the present embodiment, in the slow-up control at the time of supplying power to the heater of the fixing heating device used in the image forming apparatus, the start-up control that can suppress the harmonic current distortion is performed. It becomes possible.

  In the second embodiment of the present invention, the heater configuration, phase control, and the like are the same as those in the first embodiment, and thus description thereof is omitted. In Example 1, the wave number NO. The heater supply power ratio Pr was changed for each wave in the order of 1 to 50. That is, for example, when the frequency of the AC power source 202 is 50 Hz, the heater slow-up control time is 1 second. Further, for example, when the frequency is 60 Hz, the heater slow-up control time is 0.83 seconds. That is, the time required for the heater slow-up control varies depending on the frequency of the AC power supply. In the present embodiment, in addition to the effects of the first embodiment, a control pattern in which optimum heater slow-up control can be performed even when the frequency of the AC power source 202 varies will be described.

  As described above, when the heater is turned on, the resistance value is lower than that in the steady state, so that a large inrush current, for example, 7 to 10 times the steady state current occurs. Therefore, for example, if the frequency of the AC power source 202 is increased and the heater slow-up time is shortened, the time for gradually heating the heater by the heater slow-up control is reduced as compared with the case where the frequency of the AC power source 202 is low. To do. FIG. 13 shows an example in which the frequency of the AC power source 202 is 50 Hz and 60 Hz. As shown in FIG. 13A, when the frequency of the AC power source 202 is 60 Hz, the wave number required for the heater slow-up control may be increased as compared with the case of 50 Hz. In this embodiment shown in FIG. 13A, for example, the wave number required for the heater slow-up control is set to 60 wave numbers, and the control is performed so that the control time of the heater slow-up control is the same as 50 Hz.

  Further, as shown in FIG. 13B, without changing the wave number of the heater slow-up control, the heater supply power ratio around Pr = 0.5 that causes the highest harmonic current distortion is moved to the latter half of the heater slow-up control. Also good. Here, compared with the case where the frequency of the AC power source 202 is 50 Hz, when the frequency is 60 Hz, it is delayed by 6 waves. However, even if the frequency changes, the integrated value of the heater power up to Pr = 0.5 or earlier It is desirable to delay so that there is almost no change. Further, as shown in FIG. 5, for example, the harmonic current distortion of Pr = 0.05 and Pr = 0.95 is the same. This is because the result of Fourier transform is the same for a waveform symmetric about a phase angle of 90 °, which is the center of the half wave. That is, even when the control timing of the heater supply power ratio of around Pr = 0.5 that causes the most harmonic current distortion is moved to the latter half of the heater slow-up control, Pr = 0.05 or less or Pr = 0.95 or more The ratio of the heater control pattern does not change. Therefore, it means that the harmonic current distortion does not change greatly.

  The wave number change control of the heater slow-up control due to the frequency fluctuation or the control to move the heater supply power ratio of Pr = 0.5 to the latter half of the heater slow-up control may be performed as follows. That is, one or two basic control patterns (for example, control patterns of 50 Hz and 60 Hz) are prepared in advance and stored in the storage unit in the control unit 203, and the control pattern is calculated based on the frequency detection result of the zero cross signal. Or perform interpolation.

  Both include energization phase amount control in which the rate of change is maximized during the period in which the energization phase amount is changed from 30% energization phase amount control to 70% energization phase amount control. The energization phase amount control that maximizes the rate of change is control that maximizes the change in the heater supply power ratio Pr before and after Pr = 0.5. Therefore, for example, even when the frequency of the AC power source 202 fluctuates, the harmonic current distortion is greatly reduced as compared with the conventional slow-up control such as the heater control pattern in which the degree of change in the heater power supply ratio is uniformly fixed. Can be suppressed.

  As described above, according to the image forming apparatus of the present embodiment, in the slow-up control at the time of supplying power to the heater of the fixing heating device used in the image forming apparatus, the start-up control that can suppress the harmonic current distortion is performed. It becomes possible.

DESCRIPTION OF SYMBOLS 100 Fixing heating apparatus 200 Heater drive circuit 202 AC power supply 203 Control part 212 Zero cross detection circuit

Claims (6)

Fixing heating means for fixing the developer to the recording medium;
Electronic switch means for energizing / cutting off the power supplied from the AC power source to the fixing heating means;
Zero-cross detecting means for detecting zero-cross of the AC power supply;
At the start of power supply to the fixing heating means, the power supply ratio to the fixing heating means is changed stepwise by controlling the energization phase angle of the electronic switch means using the detection result of the zero cross detection means. Having control means for performing phase control;
The control means performs phase control that maximizes the change in the power supply ratio in a period in which the power supply phase angle is changed stepwise from at least a power supply phase angle of 30% to a power supply phase angle of 70%. A fixing heating apparatus, wherein the electronic switch means is controlled so as to be included.   The phase control that maximizes the change in the power supply ratio means that the change in the power supply ratio is maximized when the energization phase angle is changed from an energization phase angle smaller than 90 degrees to an energization phase angle larger than 90 degrees. The fixing heating apparatus according to claim 1, wherein the phase control is as described above.   2. The fixing heating according to claim 1, wherein a phase control time of an energization phase angle from a power supply ratio of 30% to a power supply ratio of 70% by the control unit is 20% or less of one control cycle of the phase control. apparatus.   The phase control time of the energization phase angle with the power supply ratio of 5% or less and the power supply ratio of 95% or more by the control means is 20% or more of one control cycle of the phase control. Fixing and heating device.   The phase control time of the energization phase angle from the power supply ratio 30% by the control means to the power supply ratio 70% is 20% or less of one control cycle of the phase control and the power supply ratio 5% or less by the control means. 2. The fixing heating apparatus according to claim 1, wherein the phase control time of the energization phase angle with a power supply ratio of 95% or more is 20% or more of one control cycle of the phase control.   The fixing heating apparatus according to claim 1, wherein the control unit does not perform phase control of a power supply ratio of 50%.

Images