JP2000172108A - Fixing device/method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide fixing device/method for reducing a temperature ripple when a fixing temperature is controlled to a setting temperature and preventing the overshoot of the fixing temperature when the device is started at the time of thermally fixing a non-fixed toner image on recording paper. SOLUTION: The fixing device is provided with a fixing roller having a heat generator for thermal fixing and a power control circuit controlling power supplied to the heat generator by means of on/off-controlling AC voltage applied to the heat generator. The power control circuit makes a wave number which is turned on/off to be constant with one period of the wavelength of AC voltage as a unit and supplied power to the heat generator is changed to 0%, 25%, 50% and 100% with the control of the wave number for changing the wave number which is turned off/on.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device and a fixing method applicable to an image forming apparatus such as a copying machine and a printer.

[0002]

2. Description of the Related Art Conventionally, in a copying machine or the like, a latent image formed on a photosensitive drum by electrophotography is developed into a toner image,
After the developed toner image is transferred onto a recording sheet, the recording sheet on which the toner image has been formed is passed between a pair of heated fixing rollers of a fixing device to thermally fix the toner image. A heating element is disposed in the fixing roller, and the fixing temperature is controlled by controlling the power supply to the heating element. In the control of the power supply, the power supplied to the heating element is 100% output or 0% depending on the temperature detected by the fixing temperature sensor. Since the output is switched to the% output, the temperature ripple phenomenon that the temperature rises as it approaches the target control temperature and then decreases thereafter when the temperature is increased is likely to occur. At present, the heating element of the fixing roller is being changed from a halogen lamp to a resistance heating element having a quick response of temperature control. However, such a temperature ripple is more likely to occur. Further, if the power is turned off after the fixing temperature is reached at the time of starting the apparatus, a considerable overshoot occurs.

In order to reduce such a temperature ripple, for example, Japanese Patent Application Laid-Open No. 5-281865 discloses a method of controlling power supply to a heating element by outputting and non-outputting power within a unit time and supplying power at a ratio. There is disclosed a film heating type heating device which controls electric power and varies the unit time. This unit time varies between the start-up of the apparatus and the paper passing, but a control means for changing the unit time is required.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the temperature ripple when the fixing temperature is controlled to a set temperature during the thermal fixing of an unfixed toner image on a recording sheet, and to fix the fixing temperature at the time of starting up the apparatus. It is an object of the present invention to provide a fixing device and a fixing method capable of realizing overshoot prevention with a simple configuration.

[0005]

In order to achieve the above object, a fixing device according to the present invention includes a fixing unit having a heating unit for thermally fixing an unfixed developer carried on a recording medium; Power control means for controlling power supplied to the heat generating means by on / off control of an AC voltage applied to the heat generating means, wherein the power control means determines a wave number to be turned on in units of one cycle of the wavelength of the AC voltage. Keep it constant,
The power supply to the heating means is changed by wave number control for changing the wave number to be turned off.

Further, the fixing device of the present invention includes a fixing unit having a heating unit for thermally fixing an unfixed developer carried on a recording medium, and an on / off control of an AC voltage applied to the heating unit. Power control means for controlling the power supplied to the heat generating means, wherein the power control means makes the number of off waves constant in units of one cycle of the wavelength of the AC voltage, and controls the number of waves to be turned on by wave number control. The power supply to the heat generating means is changed.

According to the above two inventions, when power is supplied to the heating means, the ratio of supplied power to non-supplied power can be easily changed by changing the number of waves to be turned on or the number of waves to be turned off in the wave number control of the AC voltage. Power ratio) can be changed in a wide range step by step. For this reason, by changing the power ratio of the power supplied to the heating means in any number of steps, it is possible to finely control the temperature of the heating means, and reduce the temperature ripple when controlling the fixing temperature to the set temperature. In addition, it is possible to prevent overshooting of the fixing temperature at the time of starting up the apparatus and to reduce power consumption for fixing, thereby contributing to energy saving. Further, since this wave number is defined as a unit of one cycle of the wavelength of the AC voltage supplied to the heating means, control is easy, and a CPU for controlling a special frequency generating circuit is not required. Note that a heating element such as a halogen lamp, a resistance heating element, or a sheet heating element can be used as the heating means.

Further, the fixing device of the present invention includes a fixing unit having a heating unit for thermally fixing the unfixed developer carried on the recording medium, and an on / off control of an AC voltage applied to the heating unit. Power control means for controlling the power supplied to the heat generating means, wherein the power control means keeps the number of waves turned on in units of one cycle of the wavelength of the AC voltage and changes the number of waves to be turned off as a first wave number The power supplied to the heating means is changed by control and a second wave number control in which the number of waves to be turned off is made constant in units of one cycle of the wavelength of the AC voltage and the number of waves to be turned on is changed.

According to the present invention, the power ratio can be easily variably controlled by, for example, performing the wave number control with a constant on at a low power ratio and the wave number control with a constant off at a high power ratio. The fixing temperature can be controlled in accordance with the use condition of the apparatus.

The power control means performs the first wave number control when the heat generation amount of the heat generation means is relatively low, and performs the second wave number control when the heat generation amount is relatively high. And the second wave number control. Thus, for example, during a copy standby state in a copying machine or the like, the heat generation amount of the heat generation means may be kept low.
The first wave number control is performed at a low power ratio. For example, since a large amount of heat is required during copying, control can be performed at a high power ratio by the second wave number control. As a result, the power ratio can be easily variably controlled, so that the fixing temperature can be controlled according to the use state of the apparatus.

In addition, since the heating means includes a resistance heating element, the resistance heating element has excellent responsiveness to a change in supplied power as compared with a halogen lamp or the like.
The effects of the present invention, such as reduction of temperature ripple and prevention of overshoot, can be further exhibited.

Further, the fixing means includes a fixing member having a cylindrical base, and the resistance heating element is provided on an inner peripheral surface of the cylindrical base. Thus, since the resistance heating element is provided on the inner peripheral surface of the fixing roller or the like of the fixing unit, overshoot in the fixing unit can be more effectively prevented.

Further, the apparatus further comprises temperature detecting means for detecting the temperature of the heat generating means, wherein the number of waves to be turned on or the number of waves to be turned off in the wave number control is changed according to the detected temperature. Thereby, the fixing temperature can be easily controlled to the target temperature.

In the fixing method of the present invention, when the unfixed developer carried on the recording medium is thermally fixed by the heat generating means, the fixing method is turned on in units of one cycle of the wavelength of the AC voltage applied to the heat generating means. The number of waves to be turned off is kept constant, and the amount of power supplied to the heating means is changed by wave number control for changing the number of waves to be turned off to control the amount of heat generated from the heating means.

In the fixing method of the present invention, when the unfixed developer carried on the recording medium is thermally fixed by the heating means, the fixing method is turned off in units of one cycle of the wavelength of the AC voltage applied to the heating means. The number of waves to be turned on is kept constant, and the amount of power supplied to the heat generating means is changed by wave number control for changing the number of waves to be turned on to control the amount of heat generated from the heat generating means.

According to the above-described fixing methods of the present invention, when power is supplied to the heating means, the supplied power and the non-supplied power can be easily changed by changing the number of waves to be turned on or the number of waves to be turned off in the control of the number of waves of the AC voltage. (Power ratio) can be changed stepwise over a wide range. For this reason, by changing the power ratio of the power supplied to the heat generating means in any number of stages, it becomes possible to finely control the temperature of the heat generating means,
Temperature ripple when controlling the fixing temperature to the set temperature can be reduced, overshooting of the fixing temperature at the time of starting up the apparatus can be prevented, and power consumption for fixing can be reduced, contributing to energy saving. it can. Further, since this wave number is in units of one cycle of the wavelength of the AC voltage supplied to the heating means, control is easy, and no special frequency generating circuit or CPU for such control is required.

In the fixing method of the present invention, when the unfixed developer carried on the recording medium is heat-fixed by the heating means, the fixing method is turned on in units of one cycle of the wavelength of the AC voltage applied to the heating means. The first wave number control for changing the number of waves to be turned off and changing the number of waves to be turned off, and the second wave number control for changing the number of waves to be turned on while keeping the number of waves turned off in units of one cycle of the wavelength of the AC voltage. The amount of heat generated from the heat generating means is controlled by changing the power supplied to the heat generating means. In this case, the step of performing the first wave number control when the heat generation amount of the heating means is relatively low and the step of performing the second wave number control when the heat generation amount of the heat generation means is relatively high are switched. Is preferred. This makes it possible to easily control the power ratio variably by performing, for example, a wave number control with a constant on at a low power ratio and a constant wave at a high power ratio, and to control the fixing temperature by using the apparatus. Control can be performed according to the state such as the state.

Further, the temperature of the heat generating means is detected, and control can be performed so as to change the number of waves to be turned on or the number of waves to be turned off in the wave number control according to the detected temperature.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a fixing device according to an embodiment of the present invention, and FIG. 2 is an entire power control circuit for driving and controlling a heater disposed in a fixing roller of the fixing device of FIG. FIG. 3 is a block diagram showing the configuration, FIG. 3 is a diagram for explaining a specific circuit configuration and operation of the output determination circuit of FIG. 2, and FIG. 4 is an output waveform from the zero cross circuit and an output from the output waveform generation circuit of FIG. FIG. 5 is a diagram showing a waveform, FIG. 5 is a diagram showing an output waveform from the heater drive circuit of FIG. 2, and FIG. 6 is a diagram showing a modification.
FIGS. 7A to 7D are diagrams illustrating output waveforms from the heater drive circuit of FIG.

The fixing device according to the present embodiment is used in an image forming apparatus such as a copying machine, a printer or a facsimile for forming an image on a sheet-shaped recording medium by an electrophotographic method. As shown in FIG. 1, the fixing device includes a pair of fixing rollers 10 for conveying and thermally fixing the recording sheet S on which the toner image t is formed, and the fixing roller pair 10 includes a heater 11a as a resistance heating element. And a pressure roller 12 which is brought into contact with the heating roller 11 to form a nip 10a. The heater 11a of the resistance heating element is disposed on the inner peripheral surface of the base of the cylindrical heating roller 11 with an insulating layer interposed therebetween. Electric power is supplied to the resistance heating element by bringing a power supply brush into sliding contact with electrodes provided at both ends of the heating roller 11.

The fixing device shown in FIG.
A guide member 13 for guiding the recording sheet S conveyed from the nip portion 10a of the fixing roller pair 10, and a conveyance for pinching and further conveying the recording sheet S guided from the nip portion 10a and guided by the guide member 14a And a roller pair 14.

The power control circuit shown in FIG. 2 is for controlling and supplying power to the heater 11a shown in FIG. 1, and is arranged near the heating roller 11 shown in FIG. Thermistors 21 and 2 as detecting means
2, a control temperature setting circuit 23 for setting a control temperature of the fixing temperature, and an output for selecting and determining an output state based on a detected temperature signal from the thermistor 21 and a control signal from the control temperature setting circuit 23. A decision circuit 24, a zero-cross circuit 26 for counting the number of cycles of an alternating-current (AC) voltage input from a power supply and outputting a signal (zero-cross signal) synchronized with 0 V of the AC voltage, and a zero-cross signal based on the zero-cross signal An output waveform generation circuit 27 for generating a predetermined output waveform, and a waveform selection circuit 25 for selecting an output waveform generated by the output waveform generation circuit 27 based on a selection signal from the output determination circuit 24. A heater drive circuit 28 is provided for supplying power to and driving the heater 11a according to the selected output waveform.

The power control circuit shown in FIG. 2 includes an abnormality detection circuit 29 for detecting an abnormality such as when the temperature rises abnormally based on the temperature detected by the thermistor 22. The output from the drive circuit 28 is turned off.

As shown in FIG. 3A, the output decision circuit 2
Reference numeral 4 denotes an operational amplifier 31 which receives the detected temperature signal from the thermistor 21 and converts the voltage, and an operational amplifier 3 which converts the voltage into a voltage based on the variable resistor 23a of the control temperature setting circuit 23.
2, 33, and a reference voltage (Vtemp), which is an output voltage determined based on the detected temperature from the operational amplifier 31, and an input voltage (Vth1), which is an output voltage based on a set temperature from the operational amplifier 32, and selects a selection signal A ( selA), the selection signal A is supplied to the variable resistor 36 and the resistor 3
Assuming that the offset voltage to be fed back to the input side via 5a is Vth2 (= Vth2a + Vth2b), the input voltage ((Vth1 + Vth2a) or (Vth1-Vth2b) that differs depending on the result of the selection signal A and the reference voltage (Vtemp) from the operational amplifier 31 And outputs a selection signal B (selB).

As shown in FIG. 3B, the thermistor 21
The relationship between the temperature detected in step (1) and the input voltages in the comparators 34 and 35 is determined by comparing with the reference voltage (Vtemp).
And the values of the selection signals A and B (selA,
selB) is determined as shown in the figure. Then, as shown in FIG. 3 (c), the output from the output determination circuit 24 changes the output to 0, 25% by the value of the voltage (Vtemp) from the thermistor 21.
It is one of four stages of 50% and 100%. The voltage Vth1 is determined by the variable resistor 23a of the control temperature setting circuit 23, and the voltage Vth2 is determined by the variable resistor 36 and the resistor 35a.
Is determined by

Next, the operation of the power control circuit of FIG. 2 will be described with reference to FIGS. The zero cross circuit 26 of FIG.
Accordingly, a signal synchronized with 0 V of the alternating current (AC) voltage as shown in FIG. 4A supplied to the heater 11a is output to the output wave generation circuit 27 as a zero cross signal as shown in FIG. 4B. 4 (c), the 0% output waveform of FIG. 4 (d),
The 25% output waveform of FIG. 4E, the 50% output waveform of FIG. 4F, and the 100% output waveform of FIG. The zero-cross waveform doubles the wavelength of the zero-cross signal as shown in FIG.
Has the same wavelength as the AC voltage. When one of the waveforms in FIGS. 4D to 4G is selected by the waveform selection circuit 25 in FIG. 2 based on the output signal from the output determination circuit 24, the zero-cross waveform in FIG. (D) ~
(G) AND with output waveform selected from four types
A waveform is generated and input to the heater drive circuit 28,
Is output to the heater 11a.

That is, FIG. 5A shows a case where the power is 0% output, and the heater 11a is off. FIG. 5 (b)
Is the zero cross signal of FIG. 4 (c) and 25% of FIG. 4 (e).
FIG. 5 is based on the AND waveform of the output waveform.
(B), the first wave shown by the solid line is turned on, the three waves shown by the next broken line are turned off, and the next wave is turned on. Thus, 25% output power is supplied to the heater 11a. FIG. 5 (c)
Is the zero cross signal of FIG. 4 (c) and 50% of FIG. 4 (f).
FIG. 5 is based on the AND waveform of the output waveform.
(C), the first wave shown by the solid line is turned on, the next wave shown by the broken line is turned off, and the next wave is turned on. Thus, 50% output power is supplied to the heater 11a. FIG. 5D shows a case of 100% output, and 100% output power is supplied to the heater 11a.

As described above, the power control shown in FIG.
In the case of 25% and 50% output, the number of waves to be turned on is fixed to one wave, and the number of waves to be turned off is changed to three waves and one wave, respectively.
Thus, 0%, 25%, 50%, and 100% output power can be supplied to the heater 11a. For this reason, by changing the power ratio of the power supplied to the heater 11a to four stages from 100% to 0% in accordance with the temperature rise, the temperature control of the heater 11a is controlled by switching the output between 0% and 100%. It is possible to perform more finely than in the system, reduce the temperature ripple when controlling the fixing temperature to the set temperature, prevent the overshooting of the fixing temperature when starting up the image forming apparatus, etc. Since the power consumption can be reduced, it can also contribute to energy saving.

Next, a modified example in which the output pattern of the AC voltage output from the heater drive circuit 28 is changed will be described with reference to FIG. This example differs from the case of FIG.
A 75% output is realized instead of a% output. That is, the output waveform generation circuit 27 of FIG. 2 generates a 75% output waveform as shown in FIG. 6E in which the waveform of FIG. FIG. 6 (c) is based on the AND waveform of the zero-cross signal of FIG. 4 (c) and the 75% output waveform of FIG. 6 (e), and the first three waves indicated by solid lines in FIG. 6 (c) are on. The sequence of turning off one wave shown by the next broken line and turning on the next three waves is repeated. Thereby, 75% output power is supplied to the heater 11a. As shown in FIGS. 6A, 6B and 6D, 0%,
The outputs of 50% and 100% are the same as those in FIG.

As described above, the power control shown in FIG.
In the case of 50% and 75% output, the number of off waves is fixed to one wave, and the number of on waves is changed to one wave and three waves, respectively.
Thus, 0%, 50%, 75%, and 100% output power can be supplied to the heater 11a. Therefore, by changing the power ratio of the power supplied to the heater 11a to four levels, the same effect as in the case of FIG. 5 can be obtained.

As described above, in this embodiment, the wave number can be controlled by switching the heater 11a of the fixing device such as a copying machine in four stages with the output waveform pattern as shown in FIG. 5 (first wave number control). Wave number control can be performed by switching to four stages with an output waveform pattern as shown in FIG. 6 (second wave number control). The first and second wave number controls are performed by the first wave number control (FIG. 5), for example, when the copying machine or the like is in standby for operation, since the amount of heat is small. , And can be switched and used as in the second wave number control (FIG. 6). As a result, the fixing temperature can be controlled in accordance with the use state of the apparatus, without wasting power,
It can contribute to energy saving.

In the fixing device shown in FIG. 1, the recording sheet S on which the unfixed toner image t is formed is conveyed in the direction of the arrow a, passes through the nip portion 10a of the pair of fixing rollers 10, is thermally fixed, and is discharged in the direction of the arrow b. Paper. In this case, as described above, the temperature of the heating roller 11 including the heater 11a, which constitutes the fixing roller pair 10, can be finely controlled in four stages, so that the fixing temperature of the outer peripheral surface of the heating roller 11 is accurately controlled. ,
Moreover, since the temperature ripple can be reduced and the overshoot of the fixing temperature can be prevented, the thermal fixing of the toner image t on the recording sheet S is performed favorably. No offset phenomenon or the like occurs. Further, since the heater 11a is composed of a resistance heating element, the responsiveness of the temperature control is good and the heater 11a is more effective in reducing the temperature ripple.

Although the present invention has been described with reference to the embodiment, the present invention is not limited to this, and various modifications can be made within the technical idea of the present invention. For example, the wave number control can be performed in more steps by further increasing the number of steps. Further, as the heating element, it is needless to say that a known heating element such as a halogen lamp or a planar heating element can be used.

[0035]

According to the present invention, it is possible to reduce the temperature ripple when controlling the fixing temperature to the set temperature during the thermal fixing of the unfixed developer on the recording medium, and to reduce the fixing temperature when the apparatus is started up. It is possible to provide a fixing device and a fixing method capable of preventing overshoot and realizing these with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of a fixing device according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating an overall configuration of a power control circuit for driving and controlling a heater disposed in a fixing roller of the fixing device of FIG. 1;

FIG. 3 is a diagram for explaining a specific circuit configuration and operation of the output determination circuit of FIG. 2;

FIG. 4 is a diagram showing an output waveform from a zero cross circuit and an output waveform from an output waveform generation circuit of FIG. 2;

FIG. 5 is a diagram showing an output waveform from the heater drive circuit of FIG. 2;

6 is a diagram showing a modification, and is a diagram (a to d) showing output waveforms from the heater drive circuit of FIG. 2 and a diagram (e) showing an output waveform from the output waveform generation circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Fixing roller 11 Heating roller 11a Heater (resistance heating body) 21, 22 Thermistor (temperature detection means) 24 Output determination circuit 25 Waveform selection circuit 26 Zero cross circuit 27 Output waveform generation circuit 28 Heater drive circuit

Claims (12)

[Claims] 1. A fixing unit having a heating unit for thermally fixing an unfixed developer carried on a recording medium, and an AC voltage applied to the heating unit is supplied to the heating unit by on / off control. Power control means for controlling power, wherein the power control means keeps the number of waves turned on in units of one cycle of the wavelength of the AC voltage as a unit, and supplies power to the heating means by wave number control for changing the number of waves turned off. A fixing device characterized by changing the following. 2. A fixing unit having a heating unit for thermally fixing an unfixed developer carried on a recording medium, and an AC voltage applied to the heating unit is supplied to the heating unit by on / off control. Power control means for controlling power, wherein the power control means keeps the number of waves turned off in units of one wavelength of the AC voltage as a unit, and controls the power supplied to the heat generating means by controlling the number of waves to be turned on. A fixing device characterized by changing the following. 3. A fixing unit having a heating unit for thermally fixing an unfixed developer carried on a recording medium; and an AC voltage applied to the heating unit is supplied to the heating unit by on / off control. Power control means for controlling power, the power control means comprising: a first wave number control for changing a wave number to be turned off while keeping a wave number to be turned on in units of one wavelength of the AC voltage as a unit; The fixing device changes the power supplied to the heat generating means by performing a second wave number control that changes the number of waves to be turned on while keeping the number of waves to be turned off in units of one cycle of the wavelength. 4. The first power control means performs the first wave number control when the heat generation amount of the heat generation means is relatively low, and performs the second wave number control when the heat generation amount is relatively high. 4. The fixing device according to claim 3, wherein the control is switched between the wave number control and the second wave number control. 5. The fixing device according to claim 1, wherein said heating means includes a resistance heating element. 6. The fixing device according to claim 5, wherein the fixing unit includes a fixing member having a cylindrical base, and the resistance heating element is provided on an inner peripheral surface of the cylindrical base. apparatus. 7. The apparatus according to claim 1, further comprising a temperature detecting means for detecting a temperature of said heat generating means, wherein a wave number to be turned on or a wave number to be turned off in said wave number control is changed according to the detected temperature. 7. The fixing device according to 4, 5, or 6. 8. When the unfixed developer carried on the recording medium is thermally fixed by the heat generating means, the number of waves to be turned on is set to be constant in units of one cycle of the wavelength of the AC voltage applied to the heat generating means, and the power is turned off. A fixing method comprising: controlling the amount of heat generated from the heat generating means by changing power supplied to the heat generating means by wave number control for changing a wave number to be generated. 9. When the unfixed developer carried on the recording medium is heat-fixed by the heating means, the number of off-state waves is made constant in units of one cycle of the wavelength of the AC voltage applied to the heating means, and the on-state is kept on. A fixing method comprising: controlling the amount of heat generated from the heat generating means by changing power supplied to the heat generating means by wave number control for changing a wave number to be generated. 10. When the unfixed developer carried on a recording medium is heat-fixed by a heat generating means, a constant number of waves is turned on in units of one cycle of a wavelength of an AC voltage applied to the heat generating means, and off. The power supply to the heating means is changed by a first wave number control for changing the wave number to be turned on and a second wave number control for changing the wave number to be turned on while keeping the wave number to be turned off in units of one cycle of the wavelength of the AC voltage. The amount of heat generated by the heat generating means. 11. The step of performing the first wave number control when the heat generation amount of the heat generating means is relatively low, and the step of performing the second wave number control when the heat generation amount of the heat generation means is relatively high. , Is switched.
0 fixing method. 12. The method according to claim 8, wherein the temperature of the heat generating means is detected, and the number of waves to be turned on or the number of waves to be turned off in the wave number control is changed according to the detected temperature.
The fixing method according to 9, 10, or 11.