Patent Application
20100322657
1. Field of the Invention
The present invention relates to a fixing apparatus.
2. Description of the Related Art
Heretofore, heating apparatuses that drive a heater with phase control using an AC power supply as the drive source are known. With conventional phase control, there is a problem in that harmonic noise levels increase when power varies widely. For example, if power is supplied at a duty ratio of 50%, power supply is switched on/off at timings at which the sine wave peaks at phase angles of 90 and 270 degrees as shown in 11a in
In response, Japanese Patent Laid-Open No. 2006-73431 discloses a technique according to which on/off control of the heater is not performed at timings near the peaks of the sine wave indicating input power, in order to reduce sudden changes in power variation when performing phase control.
However, the following problem exists with the technique of Japanese Patent Laid-Open No. 2006-73431. When printing is performed continuously for an extended period of time, power input to the heater stabilizes to a substantially constant value due to the fixing apparatus warming up sufficiently. At this time, harmonic levels of specific order increase despite control being performed so as to avoid using heater current application start timings at which harmonic levels will be adversely affected, due to the same current application start timings being repeatedly used.
The present invention has been made in consideration of the problems with the above conventional technology, and provides a fixing apparatus that allows harmonic noise and flicker noise caused by alternating current to be reduced.
One aspect of the present invention provides a fixing apparatus comprising: a power supply unit that supplies AC power from a commercial power supply to a heater; a temperature detection element that detects a temperature of the heater; a setting unit that sets a power duty ratio for providing power to the heater such that the temperature detected by the temperature detection element maintains a target temperature; and a control unit that controls the power supply unit such that an average power duty ratio of a single cycle equals the power duty ratio based on the detected temperature, where a single cycle is three or more full waves of the commercial power supply, wherein there are three or more power duty ratios per one half wave of the commercial power supply in a single cycle.
The present invention enables provision of a fixing apparatus that allows for a reduction in harmonic noise and flicker noise caused by alternating current, for example.
Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).
Hereinafter, preferred embodiments of the present invention will be illustratively described in detail with reference to the drawings. The constituent elements described in the following embodiments are merely by way of example, and it is not intended to limit the technical scope of the present invention to these constituent elements. Not all combinations of features described in the embodiments are essential as a means of resolving of the present invention.
In a First Embodiment of the present invention, control is performed such that on/off control of a heater is not performed at timings near the peaks of a sine wave indicating input power, so that power does not vary widely, when performing phase control. In other words, supply of power is switched on and off while avoiding timings near the peaks. Specifically, in the case of power being supplied at a duty ratio of 50%, for example, an average duty ratio of 50% is realized by performing control for one wavelength at a duty ratio of 20% and subsequently performing control for one wavelength at a duty ratio of 80% as shown in 11b in
With control at a duty ratio of 20%, power is, for example, turned on at a phase angle of 144 degrees, off at 180 degrees, on at 324 degrees, and off at 360 degrees. With control at a duty ratio of 80%, power is, for example, turned on at a phase angle of 36 degrees, off at 180 degrees, on at 216 degrees, and off at 360 degrees. Wide variation in power can thereby be avoided, enabling noise to be reduced. A combination of duty ratios of 20% and 80% for realizing a duty ratio of 50% are represented using a (−30, +30) pattern, which will be referred to in the present specification as a “distribution pattern”. Note that the combination included in a distribution pattern is not limited to a combination of the differences from a target value of duty ratios relating to two full waves as described here, and may be a combination of three or more full waves. For example, in the First Embodiment, a combination of the differences from the target value of duty ratios relating to four full waves is used as a single distribution pattern, and four distribution patterns are defined.
Specifically, the numerical sequence “+2, −2, +3, −3” is defined as a distribution pattern 1, and the numerical sequence “+2, −2, +5, −5” is defined as a distribution pattern 2. Also, a numerical sequence “+30, −30, +33, −33” is defined as a distribution pattern 3, and a numerical sequence “+35, −35, +35, −35” is defined as a distribution pattern 4. Power supply for four full waves will be performed at duty ratios of 80%, 20%, 83% and 17% when distribution pattern 3 is used with a duty ratio of 50% as the target. In this case, variation in power can be suppressed and harmonic noise reduced, without switching supply of power on/off at timings in proximity to the peaks of the sine wave that occur at phase angles of 90 and 270 degrees.
Also, an increase in flicker due to power of similar shape being continuously applied to the heater can be readily prevented without increasing the load on the CPU by defining a plurality of distribution patterns.
Configuration
Also, the laser scanner portion 107 has a laser unit 113 that emits laser light modulated based on image signals (image signals VDO) sent by an external apparatus 131. The laser light from this laser unit 113 scans over a photosensitive drum 117 after being reflected by a polygon mirror rotationally driven by a motor 114, and by an imaging lens 115, a folding mirror 116 and the like.
The image forming portion 108 has the photosensitive drum 117, a primary charging roller 119, a developer 120, a transfer charging roller 121, a cleaner 122 and the like. The fixer 109 has a fixing film 109a, an elastic pressure roller 109b, a ceramic surface heater 109c provided inside the fixing film 109a, and a temperature detection element 109d (thermistor) that detects the surface temperature of the ceramic surface heater 109c. That is, toner is fixed on a recording sheet using the heat of the ceramic surface heater 109c.
A main motor 123 provides torque to the paper feed roller 105 via a paper feed roller clutch 124. The main motor 123 also provides torque to the pair of registration rollers 106 via a registration roller clutch 125. Further, the main motor 123 provides driving power to the various units of the image forming portion 108 including the photosensitive drum 117, as well as to the fixer 109, and the paper discharge rollers 111. Reference numeral 126 denotes an engine controller that controls the electrophotographic process by the laser scanner portion 107, the image forming portion 108 and the fixer 109, and the conveyance of recording sheets S in the laser printer 101. Reference numeral 127 denotes a video controller that is connected to an external apparatus 131 such as a personal computer via a general-purpose interface (Centronics interface, RS232C interface, etc.) 130. The video controller 127 converts image information received via this general-purpose interface 130 to bit data, and sends this bit data to the engine controller 126 as a VDO signal.
Reference numeral 201 denotes a commercial power supply (commercial AC power supply) to which the laser printer 101 is connected. The laser printer 101 supplies the AC power from the commercial AC power supply 201 to a heating element 203 of the ceramic surface heater 109c via an AC filter 202 and a relay 241. The heating element 203 constituting the ceramic surface heater 109c is thereby heated. Supply of power to this heating element 203 is controlled by applying and interrupting current to a triac 204. Resistors 205 and 206 are bias resistors of this triac 204, and a phototriac coupler 207 is a device for securing creepage distance between primary and secondary. The triac 204 is turned on by applying current to a light-emitting diode of this phototriac coupler 207. A resistor 208 is for regulating current flowing to the phototriac coupler 207, and current to the phototriac coupler 207 is turned on/off by a transistor 209. This transistor 209 operates in accordance with a signal (ON) provided by the engine controller 126 via a resistor 210. A resistor 211 is a bias resistor between the base and emitter of the transistor 209.
Output from the commercial AC power supply 201 is input to a zero cross detection circuit 212 via the AC filter 202. The zero cross detection circuit 212 detects that the voltage has dropped below a zero cross point at which the commercial power supply voltage alternates between positive and negative values, or a given threshold voltage that includes this zero cross point, and notifies the detection result to the engine controller 126 as a pulse signal. Hereinafter, this signal sent to the engine controller 126 will be called a ZEROX signal. The engine controller 126 detects the pulse edge of this ZEROX signal, and performs on/off control of the triac 204 by phase control or wave number control.
The temperature detection element 109d is a thermistor temperature-sensing element that detects the temperature of the ceramic surface heater 109c on which the heating element 203 is formed. This temperature detection element 109d is disposed on the ceramic surface heater 109c via an insulator with dielectric strength, so that an insulation distance can be secured with respect to the heating element 203. The temperature detected by this temperature detection element 109d is detected as partial voltages of a resistor 222 and the temperature detection element 109d, and is input to the engine controller 126 as a TH signal. The TH signal thus input is A/D converted by the engine controller 126, and managed with a digital value.
The temperature of the ceramic surface heater 109c is monitored as the TH signal by the engine controller 126. The engine controller 126 calculates the power duty ratio of AC power to be supplied to the heating element 203 constituting the ceramic surface heater 109c by comparing the temperature of the ceramic surface heater 109c and a set temperature of the ceramic surface heater 109c set by the engine controller 126. Further, the engine controller 126 converts the power duty ratio of AC power to be supplied to corresponding phase angles (phase control) or wave numbers (wave number control), and sends an ON signal to the transistor 209 depending on the control conditions. The temperature of the ceramic surface heater 109c is thus controlled. For example, in the case of phase control, a control table such as table 1 below is held in the engine controller 126. The engine controller 126 executes the above control based on this control table.
Further, an over-temperature protection portion 223 is disposed on the ceramic surface heater 109c as a means of protecting against an excessive rise in temperature in the case where the heating element 203 goes into thermal runaway due, for instance, to the failure of circuitry that supplies power to the heating element 203 and controls the heating element 203. This over-temperature protection portion 223 is, for example, a temperature fuse or a thermoswitch. When the over-temperature protection portion 223 reaches a prescribed temperature after the heating element 203 has gone into thermal runaway, the over-temperature protection portion 223 enters a released state, and the application of current to the heating element 203 is interrupted.
An abnormal temperature value for detecting abnormally high temperatures is set by the engine controller 126 separately to the set value for temperature control, in order to control the temperature of the ceramic surface heater 109c monitored as the TH signal. If the temperature of the ceramic surface heater 109c indicated by the TH signal reaches this abnormal temperature value, the engine controller 126 sets an RLD signal to low. A transistor 242 thereby enters an off state, and the relay 241 is released. Application of current to the heating element 203 is thus interrupted. Normally, when performing temperature control, the engine controller 126 turns on the transistor 242 by constantly outputting the RLD signal at a high level, turning the relay 241 on (conduction state). A resistor 243 is a current regulation resistor, and a resistor 244 is a bias resistor between the base and emitter of the transistor 242. A diode 245 is a back electromotive force absorption element for when the relay 241 is off.
This ceramic surface heater 109c includes an insulating substrate 331 made of ceramics such as SiC, AlN and Al2O3, the heating element 203 formed, for instance, by printing a paste on this insulating substrate 331, and a protective layer 334 made of glass or the like that protects the heating element. The temperature detection element 109d for detecting the temperature of the ceramic surface heater 109c and the over-temperature protection portion 223 are disposed on this protective layer 334. These components are disposed in positions that are bilaterally symmetrical with respect to a reference for conveying recording sheets, or in other words, the middle in the lengthwise direction of a heating portion 203a, and that are inside of the minimum acceptable recording sheet width.
The heating element 203 has the heating portion 203a that produces heat when supplied with power, electrode portions 203c and 203d to which power is supplied via a connector, and electrically conductive portions 203b and 203e connecting these electrode portions 203c and 203d with the heating portion 203a. A glass layer may also be formed on the surface facing the insulating substrate 331 on which the heating element 203 is printed, in order to improve slidability.
The electrode portion 203c is connected from a hot terminal of the commercial AC power supply 201 via the over-temperature protection portion 223. The electrode portion 203d is connected to the triac 204 that controls the heating element 203, and to a neutral terminal of the commercial AC power supply 201. The ceramic surface heater 109c is supported by a film guide 62, as shown in
The fixing film 109a is a cylindrical heat-resistant fixing film, and is fitted onto the film guide 62 supporting the ceramic surface heater 109c on the underside thereof. The ceramic surface heater 109c on the underside of this film guide 62 and the elastic pressure roller 109b serving as a pressure member are brought into contact across the fixing film 109a with a prescribed pressure against the elasticity of the elastic pressure roller 109b. A fixing nip portion of prescribed width serving as a heating portion is thus formed. The over-temperature protection portion 223 abuts on the surface of the insulating substrate 331 or the surface of the protective layer 334 of the ceramic surface heater 109c.
The position of this over-temperature protection portion 223 is corrected by the film guide 62, and a heat sensitive surface of the over-temperature protection portion 223 abuts on the surface of the ceramic surface heater 109c. Although not shown, the temperature detection element 109d also similarly abuts on the surface of this ceramic surface heater 109c. Here, with the ceramic surface heater 109c, the heating element 203 may be on the opposite side to the nip portion as shown in 4a in
Temperature Control
Next, temperature control by the engine controller 126 will be described based on
In other words, the engine controller 126 functions as a first determination portion that determines the first power duty ratio P for keeping the temperature of the ceramic surface heater 109c at a prescribed temperature. That is, the engine controller 126 sets the first power duty ratio P such that temperature detected by the temperature detection element 109d maintains a prescribed target temperature.
The calculation of the power duty ratio P is performed using PI (Proportional-Integral control) or PID control (Proportional-Integral-Differential control). The fixing apparatus whose heat source is the ceramic surface heater 109c calculates the duty ratio P (operation amount) of power to be supplied to the ceramic surface heater 109c, based on a PI or PID control equation, from the temperature difference between the temperature detected by the temperature detection element 109d and a preset target temperature. Corresponding phase angles or wave numbers are determined from this calculated power duty ratio, and on/off control of a switching element is performed with the determined phase angles or wave numbers to control the temperature of the fixing apparatus.
In the case of PI control, a calculated power duty ratio D is represented by the following equation:
D=Dp+Di(t)=Ap×(Tt−Tn)+Di(t−Δt)+ΔDi(t,Tt−Tn) (1)
where Dp is a power duty ratio (operation amount) corresponding to proportional control, Di(t) is a power duty ratio (operation amount) corresponding to integral control at time t, Tn is the temperature detected by the temperature detection element, Tt is the target temperature, and Δt is the control interval. Note that Ap is the proportional control coefficient, and ΔDi(t,Tt−Tn) is the increment in the power duty ratio Di(t) corresponding to the integral control at time t. The temperature of the fixing apparatus is controlled by performing on/off control of the switching element using the power duty ratio D thus calculated from the deviation of the detected temperature from the target temperature. The distribution pattern is determined depending on the value of the required power duty ratio P calculated by PI or PID control, and the power duty ratios D (second power duty ratios) of power that will actually be input to the ceramic surface heater 109c are determined. In other words, the engine controller 126 functions as a second determination portion that determines a second power duty ratio D for each of a predetermined number of full waves, such that average supplied power (average power duty ratio) for the predetermined number of full waves (here, four) equals the first power duty ratio P. For example, the engine controller 126 controls power supply, such that the average power duty ratio of a single cycle equals the first power duty ratio P, where three or more full waves of AC power supplied from a commercial power supply are set as a single cycle. Further, the engine controller 126 also functions as a control portion that controls the phase of supplied AC power, according to the second power duty ratios D.
Here, the engine controller 126 also functions as a selection portion that selects a numerical sequence for adjustment corresponding to the first power duty ratio P from the four patterns of numerical sequences for adjustment stored in the engine controller 126 serving as a storage portion. For example, in the case where the required power duty ratio P calculated by the engine controller 126 is judged to be larger than P5 (here, 37%) and less than or equal to P6 (here, 62%) (S1004), the power duty ratios D are determined based on the required power duty ratio P and the distribution pattern 3 of
W3 in
Next, in the case where, at S1004, P is not judged to be larger than P5 (37%) and less than or equal to P6 (62%), it is judged whether P is larger than P4 (32%) and less than or equal to P5 (37%), or larger than P6 (62%) and less than or equal to P7 (67%) (S1006). In the case where, at S1006, P is judged to be larger than P4 (32%) and less than or equal to P5 (37%), or larger than P6 (62%) and less than or equal to P7 (67%), the input power duty ratios D are determined based on the required power duty ratio P and the determination pattern 4 in
In the case where, at S1006, P is not judged to be larger than P4 (32%) and less than or equal to P5 (37%), or larger than P6 (62%) and less than or equal to P7 (67%), it is judged whether P is larger than P2 (9%) and less than or equal to P3 (20%), or larger than P8 (79%) and less than or equal to P9 (90%) (S1008). In the case where, at S1008, P is judged to be larger than P2 (9%) and less than or equal to P3 (20%), or larger than P8 (79%) and less than or equal to P9 (90%), the input power duty ratios D are determined based on the required power duty ratio P and the determination pattern 2 in
In the case where, at S1008, P is not judged to be larger than P2 (9%) and less than or equal to P3 (20%), or larger than P8 (79%) and less than or equal to P9 (90%), it is judged whether P is larger than 0% and less than or equal to P1 (4%), or larger than P10 (95%) and less than or equal to 100% (S1010). In the case where, at S1010, P is judged to be larger than 0% and less than or equal to P1 (4%), or larger than P10 (95%) and less than or equal to 100%, the input power duty ratio D is made the same as the required power duty ratio P, and distribution control is not performed (S1011).
In the case where, at S1010, P is not judged to be larger than 0% and less than or equal to P1 (4%), or larger than P10 (95%) and less than or equal to 100%, the input power duty ratios D are determined based on the required power duty ratio P and the distribution pattern 1 in
The drive start timings t of the triac 204 are calculated for four full waves, based on the application power duty ratios D thus determined (S1013). The calculation of t is performed using a table such as table 2. Table 2 is a table in the case where the frequency of the commercial power supply is 50 Hz. To address variations in the frequency of the commercial power supply, the frequency of the commercial power supply may be measured, and t may be calculated in accordance with the measurement result.
The triac 204 is driven for four full waves, based on t calculated at S1013 (S1014). Next, it is judged whether a heater ON request has occurred (S1015). If a heater ON request has occurred at S1015, the processing returns to the process of S1002, and the above control is repeated. If a heater ON request has not occurred at S1015, and application of current to the heater is turned OFF (S1016) and control is ended.
Performing control such as the above avoids application of current to the heater being started at timings that will cause a sudden variation in power in a short period of time. Also, an increase in harmonic levels of specific order can be prevented, even in the case where application of power to the heater stabilizes to a substantially constant value after the fixing apparatus has sufficiently warmed up as a result of printing being performed continuously for an extended period of time, since a plurality of current application start timings are used.
Next, a heating apparatus according to a Second Embodiment of the present invention and control in the case where this heating apparatus is applied to an image forming apparatus will be described.
Whereas, in the First Embodiment, four full waves of a commercial power supply were set as a single cycle, in the Second Embodiment, the timings at which current application to the heater is started within a single cycle when power is input are differentiated with eight full waves as a single cycle, with the aim of reducing harmonic and flicker levels. Since a larger number of current application start timings can be used than when four full waves are set as a single cycle as in the First Embodiment, an increase in harmonics of specific order can be prevented. Note that while the present embodiment will be described with eight full waves as a single cycle, the present invention is not limited to eight full waves. Here, updating of power for supply to the heater could be delayed when a single cycle is too long, increasing the temperature variation of the heater. For this reason, the length of a single heater control cycle needs to be set with consideration for heater temperature variation, harmonic levels and flicker levels.
However, the pattern of input power to the heater approximates the input power pattern of wave number control as a result of using given distribution patterns. For example, at W2-4 in
2-4′ in
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2009-147001, filed Jun. 19, 2009, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-147001 | Jun 2009 | JP | national |
