JP2840266B2 - Fixing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device that heats and fixes an image developed by a developing material on a recording material.

[Conventional technology]

Conventionally, a fixing device used in this type of apparatus forms an unfixed toner image by using a heating roller maintained at a predetermined temperature and a pressure roller having an elastic layer and pressing against the heating roller. A heat roller fixing system in which the transferred transfer material is heated while being nipped and conveyed is often used.

A belt fixing system described in US Pat. No. 3,578,797 is also known.

[Problems to be solved by the invention]

However, the above conventional example has the following disadvantages.

(1) Thermal Roll Fixing Method There is a so-called wait time in which the temperature is raised to a predetermined temperature and the image forming operation is prohibited.

Large electric power is required because heat capacity is required.

Since the roller temperature is high with the rotating roller, a heat-resistant special bearing is required.

The configuration is such that the hand touches the roller directly, which may be dangerous or require a protective member.

Transfer material is wrapped by constant temperature and curvature of roller JA
M.

(2) Belt fixing system Same as above The present invention has been made in view of the above points, and an object of the present invention is to provide an image forming apparatus which requires less power, has a shorter wait time, and has good fixability. It is in.

[Means (and action) for solving the problem]

The present invention provides a heating element that generates heat by energization, a fixing film that moves while being in contact with a recording material carrying an unfixed image on one surface while rubbing on one surface with the heating element, A fixing device comprising: a temperature detection element to be detected; and control means for controlling electric power supplied to the heating element so that the temperature detected by the temperature detection element maintains a set temperature, wherein the control means detects the temperature detection element. The higher the temperature, the smaller the energizing power is controlled to energize the heating element,
Among them, at least two types of energizing power are energized when the temperature detected by the temperature detecting element is higher than the set temperature.

Due to this feature, even if the detected temperature is higher than the set temperature, the temperature is lowered while energizing, so that a rapid temperature drop of the heating element can be prevented, and when there are at least two types of energized power when the temperature is higher than the set temperature, the temperature detecting element Even if the temperature detection is performed when the responsiveness of the heater is not sufficient and the temperature of the heating element is considerably higher than the set temperature, the temperature can be quickly lowered to around the set temperature because there is energizing power for cooling down corresponding to that temperature. it can.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

First, the schematic structure of the image forming apparatus of the present embodiment is described as a first example.
Referring to FIG. 1, reference numeral 1 denotes a document table made of a transparent material such as glass, which scans a document by reciprocating in the direction of arrow a. A short-focus small-diameter imaging element array 2 is disposed immediately below the document table, and an image of the document placed on the document table is illuminated by an illumination lamp 3, and a reflected light image is formed on the photosensitive drum by the array 2. 4 is subjected to slit exposure. The photosensitive drum 4 rotates in the direction of arrow b. Reference numeral 5 denotes a charger, which uniformly charges the photosensitive drum 4 covered with, for example, a zinc oxide photosensitive layer or an organic semiconductor photosensitive layer. Image exposure is performed by the element array 2 on the drum 4 uniformly charged by the charger 5 to form an electrostatic image. This electrostatic latent image is visualized by a developing device 6 using a toner made of a resin or the like which is softened and melted by heating. On the other hand, the sheet P stored in the cassette S
The sheet is fed onto the drum 4 by a pair of conveying rollers 8 which are rotated while being pressed against each other in a vertical direction at timing so as to synchronize with the feed roller 7 and the image on the photosensitive drum 4. Then, the toner image formed on the photosensitive drum 4 is transferred onto the sheet P by the transfer discharger 9. afterwards,
The sheet P is separated from the drum 4 by a known separation unit, guided to a fixing device 11 by a conveyance guide 10 and subjected to a heat fixing process, and then discharged onto a tray 13. After the transfer of the toner image, the residual toner on the drum 4 is removed by the cleaner 2.

 FIG. 2 is an enlarged view of the fixing device 11 of the present embodiment.

Reference numeral 21 denotes a fixedly supported low-heat-capacity linear heating element of the apparatus, which is a 1.0 mm-thick, 10 mm-wide, 240 mm-long alumina substrate 22 coated with a resistance material 23 to a 1.0 mm-wide width as an example.
Power is supplied from both ends in the longitudinal direction. Energization is DC100V cycle 20ms
A pulse corresponding to a desired temperature and energy release amount controlled by the temperature detecting element 24 with an ec pulse waveform is given by changing the pulse width. Approximate pulse width is 0.5msec-5
msec. The fixing film 25 moves in the direction of the arrow in FIG. As an example of this fixing film, a heat-resistant film having a thickness of 20 μm, for example, polyimide, polyetherimide, PE
An endless film in which a release layer obtained by adding a conductive material to a fluororesin such as PTFE or PAF to at least the image contacting surface side of S and PFA is coated at 10 μm. Generally, the total thickness is less than 100 μm, preferably less than 40 μm. The film drive moves without wrinkles in the direction of the arrow due to the drive by the drive roller 26 and the driven roller 27 and the tension.

Reference numeral 28 denotes a pressure roller having a rubber elastic layer of silicon rubber or the like with good releasability, which presses the heating element via the film at a total pressure of 4 to 7 kg and rotates by pressing against the film.

The unfixed toner T on the transfer material P is guided to a fixing unit by an entrance guide 29, and a fixed image is obtained by the above-described heating.

The case where the fixing film is an endless belt has been described above, but may be a film having an end as shown in FIG. 2 (b).

In addition, as an image forming apparatus, a copying machine, a printer, a fax,
This is applicable to all fixing devices that form an image using toner such as.

FIG. 3 shows a block circuit diagram relating to the temperature control of the present embodiment. The heater 23 made of a resistance material is energized by an energizing power supply 32 to generate heat. Then, the temperature of the heater 23 is measured by a temperature detecting element 24 by a thermistor placed close to the heater 23, and based on the temperature information, a temperature control circuit 31 is provided.
Controls the power supply 32 to control the amount of energy applied to the heater 23. Thereby, the temperature of the heater 23 is kept constant.

Next, a detailed method of controlling the heater to a constant temperature will be described.

First Embodiment First, an example of temperature control by pulse width control will be described.

FIG. 4 is a detailed view of a 32 power supply. 33 is a commercial Ac power source, rectifies the AC voltage in the diode static poke D1, it is smooth to DC voltage capacitor C _1. Temperature control circuit 31
The signal is inputted to Fuotokapura of Q _2. The power supply circuit, FETs Q ₁ is turned ON when the current flows through the light emitting diode Fuotokapura Q _2, are configured to be energized to the heater. R ₁ to R ₅ in Figure 4 resistor, Q ₃ is a transistor, C ₂ is a capacitor, Z _D1 is Zener diode. The temperature control circuit 31 controls the pulse width of the input current pulse to Q _2, is to control the energy applied to the heater 23.

Next, FIG. 6 (a) shows the relationship between the heater temperature for controlling the heater temperature, which is the basis for carrying out the first embodiment of the present invention, and the energy applied to the heater.
Now, the unfixed toner T on the transfer material P heated to melt, the heater temperature at the time of fixing without problems and T _0. Then, the effective energy applied to the heater controlled by the temperature control circuit 31 is W. The heater temperature is controlled by the temperature control circuit.
When less than T _0, the energy W ₁ above heat W ₀ to be deprived by the heat radiation path of the heater, also when the heater temperature is higher than T ₀ gives the amount of heat W ₀ is less than the energy W ₂ to the heater.

By switching in this way the applied energy to the boundary of the temperature T ₀ to W ₁ and W _2, it is possible to control the temperature of the heater 23 constant. The heater temperature as the FIG. 6 (a) is T ₀
By giving W ₀ is less than the energy W ₂ when higher, it is possible to suppress the lowering speed of the heater temperature, it is possible to reduce the temperature Ritsupuru occurring without response speed delay of the thermistor. FIG. 6B shows the relationship between the heater temperature and the output pulse of the temperature control circuit 31 at this time. As shown in FIG. 6 (b), the energy applied to the heater can be easily controlled by changing the energization time of the pulse energization.

FIG. 5 shows a detailed diagram of the temperature control circuit 31 for performing the above control. Q ₂ is in FIG. 5 is a Fuotokapura energizing power distributed to the heater when a current flows to the light emitting diodes as described above. Q ₇ is a current driving transistor of light emitting diodes of Fuotokapura Q _2. Q ₄ , Q ₅ and Q ₆ are OP amplifiers. OP amplifier Q ₄ are constitute a triangular wave generator, OP amplifier Q _5, Q ₆ constitute a comparator. R _{6 to} R ₁₅ are resistors, R
_TH is a thermistor, C ₃ is a capacitor, and D ₂ and D ₃ are diodes. Transistor Q ₇ is flow a current to the light emitting diode of Fuotokapura Q ₂ when the output D is "H" of the comparator Q _5. The operation of the temperature control P circuit will be described with reference to FIG.

FIG. 7 shows output waveforms at points A, B and D in FIG.
The waveform at the point A becomes a triangular wave as shown in FIG. 7, and when the voltage at the point B is higher than the voltage at the point A, the voltage at the point D becomes "H". Where the seventh
V _{1 in the} figure is a value determined by the resistors R ₈ and R ₉ , and V ₁ = R ₈ V / (R ₈ +
R ₉ ). The voltage at point B depends on the resistance of the thermistor _RTH . Now, when the temperature of the heater is low, the voltage at point C increases. Now the V _ref heater temperature is set equal to the voltage value of the point C at the time of T _0, the output V next to the comparator Q ₆ when the heater temperature T is TT _0, B point becomes OV. At this time, it is compared with the triangular wave at point A, and the pulse width t _{ON1 in} FIG.
Is output. And the heater temperature rises,
When the T> T _0, the voltage at point C becomes smaller than V _ref, the output of the comparator Q ₆ becomes -V. At this time, B
The voltage at the point becomes -V _2. The output waveform of the D point in this case is the output pulse is a pulse width of such t _ON1> t _ON2 of FIG. 7 of the D '.

By using the temperature control circuit described above, the sixth
The control shown in the figure can be performed, and the heater temperature can be controlled to be constant.

In FIG. 6A, the heater applied energy W may have a hysteresis characteristic with respect to the heater temperature T for the reason of stabilizing the operation (see FIG. 8). or,
In FIG. 6A, W ₂ may be 0. In this case, the control circuit configuration is simplified, but the heater temperature ripple increases, but if the thermistor response speed is increased, the increase in the ripple can be prevented.

Next, FIG. 9 shows the relationship between the heater temperature and the energy applied to the heater according to the first embodiment of the present invention. Temperature fluctuation of the heater temperature be changed the applied energy in a plurality of stages before and after the heater temperature T ₀ as shown in FIG. 9 is smaller than the view the 6 (a). Further, the energization pulse width of the output pulse of the temperature control circuit decreases as the number of stages increases. In particular, as shown in FIG. 9, at least two types of power are supplied when the detected temperature of the temperature detecting element is higher than the set temperature T ₀ , the response of the temperature detecting element is not sufficient, and the temperature of the heater becomes T _0. even the temperature was detected when more fairly high state, it is possible to lower the temperature in the vicinity of quick T ₀ because there are energizing power for cooling corresponding to the temperature.

Further, the applied energy may be continuously changed with respect to the heater temperature T (see FIG. 10).

In addition to these, with respect to the heater temperature T, in a TT ₀ WW ₀ T> T ₀ in W <may be controlled pulse width so as to become a relation of W _0.

Further, a micro computer (hereinafter, microcomputer) may be used as the temperature control circuit. In this case, FIGS.
The circuit configuration does not need to be changed for each control example shown in FIG. The detailed diagram and control flow chart at this time are shown in Chapter 11.
Fig. 12 and Fig. 12 show the results. Microcomputer Q ₁₀ is a one that has a built-in A / D converter, and input voltage divided by the resistors R ₁₀ and thermistor R _TH at its analog input port AD. Microcomputer Q ₁₀ converts the voltage inputted to the port AD in accordance with the control flow chart shown in FIG. 12 to the temperature data to determine the pulse width from the temperature data. The pulse signal is output from the output port OP ₁ and the driver Q ₁₁
The lights the light emitting diodes of Fuotokapura Q ₂ through.

Second Embodiment Next, an example in which the pulse period is controlled will be described.

The power supply 32 may have the same configuration as that of FIG. or,
Energization control circuit 31 controls the input current pulse period to Fuotokapura Q _2, and controls the energy applied to the heater.
FIG. 13 shows the relationship between the heater temperature T, the applied energy W, and the output pulse of the control circuit at that time.
As shown in Figure 13 as a basis for implementing the second embodiment of the present invention (b), the pulse width when the temperature is lower than T ₀
t _ON, the temperature of the pulse period tau ₁ outputs a pulse width t _ON, the period tau ₂ pulses when higher than T _0. By changing the pulse period in this way, the energy applied to the heater is given as shown in FIG. 13 (a). Thereby, the heater surface temperature is controlled to be constant.

FIG. 14 shows a detailed diagram of the current supply control circuit of this embodiment. No.
In FIG. 14, Q ₂ is a photocoupler of a power supply as in the previous embodiment, and when a current flows through the light emitting diode,
Turn on the heater. A power driver transistor when the same Fuotokapura Q ₂ of the light-emitting diode of Example transistor Q _7. Q ₂₁ , Q ₂₂ , Q ₂₃ are OP amplifiers,
Constitute a square wave generator at P amplifier Q _21, Q _22. The “H” time and “L” time of the square wave are
C _21, resistor R ₂₄ and C _21, determined by the resistance R ₂₅ · R _26. OP amplifier Q
₂₃ constitutes a comparator, R _{21 to} R ₃₁ are resistors, D _{21 to} D ₂₃
Diodes, K ₂₁ is a relay, Q ₂₄ is a transistor for driving the relay K _21. R _TH is a thermistor. The operation of this control circuit will be described with reference to FIG. FIG. 15 shows signal waveforms at points A, B and D in the circuit of FIG. Heater temperature is low, when the voltage at point C is greater than V _ref, D points to "H", the relay K ₂₁ is turn ON.
At this time, the waveforms at points A and B are as shown in the figure. Then, when the heater temperature increases, the voltage at point C decreases. Therefore
When the V _ref heater temperature T is set equal to the voltage value of the point C at the time of T _0, the relay K ₂₁ when the heater temperature T is higher than T ₀ is OFF. The waveforms at points A and B at that time are denoted by A ',
It is shown in B '. By changing the pulse period of the output pulse according to the heater temperature in this manner, the energy applied to the heater can be controlled, and the heater temperature can be kept constant.

In the second embodiment of the present invention, the energy applied to the heater is changed by changing the pulse period, and applied to the heater as shown in FIGS. 9 and 10 as in the first embodiment.

Further, a microcomputer may be used for the control circuit as in the first embodiment. In this case, the circuit configuration is the same as in FIG.

Third Embodiment Next, a description will be given of an embodiment in which the temperature is controlled by controlling both the pulse width and the pulse period.

The power supply 32 may have the same configuration as the circuit of FIG. Conduction control circuit 31 in this example controls both the pulse width and pulse period of the input current pulse to Fuotokapura Q _2, and controls the energy applied to the heater. FIG. 16 shows the relationship between the heater temperature T, the applied energy W, and the output pulse of the control circuit at that time. When the heater temperature as shown in Figure No. 16 (a) is lower than the controlled temperature T ₀ is, the amount of heat W ₀ or more energy deprived by the heat radiation path of the heater
The W _1, when the heater temperature is higher than T ₀ energizing W ₂ less than W ₀ to the heater. At this time, the pulse period tau ₂ pulse width t when the output pulse when the heater temperature is lower than T ₀ pulse period tau ₁ pulse width t _ON1, high conduction control circuit 31
Outputs _ON2 pulse. The period τ ₁ , τ ₂ , pulse width t
_ON1, t _ON2, the next there is a relationship between the applied energy W _1, W _2.

Where D _A And indicates the duty ratio of the pulse. In this case, the heater temperature when energizing of W ₁ to the heater rises, W ₂
The energy of the heater lowers the temperature of the heater. In accordance with the temperature of such a heater, a pulse period τ ₁ giving energy W ₁ , a pulse signal _having a pulse width t _ON1 , a pulse period τ ₂ giving energy W _2, and a pulse width t at the boundary of the regulated temperature T _0.
By inputting the _ON2 pulse signal to the power supply 32,
The temperature of the heater is controlled to be constant.

Next, the temperature control circuit 31 that performs the above control will be described in detail. In the present embodiment, an example using a microprocessor will be described. The detailed diagram of the control circuit 31 in this case is the same as FIG.

 FIG. 17 shows a control flowchart in this case.

Microcomputer Q ₁₀ reads from the analog input port AD as a divided pressure method voltage value voltage V and the resistance value of the thermistor R _TH at the resistor R ₁₀ and the thermistor R _TH. The microcomputer Q ₁₀ is to determine the value entered at an analog input port AD, which calculates the width and period of the energizing pulse output.

When T ≦ T ₀ in the present embodiment, the pulse period tau _1, a pulse signal having a pulse width t _ON1, T> when T _0, the pulse period tau _2, the microcomputer Q ₁₀ a pulse signal of pulse width t _ON2 output I do.

This control will be further described with reference to the flowchart of FIG.

When energization is started (101), the microcomputer Q ₁₀ reads the V _TH and digitizes the voltage value of the analog input port AD (102). Then, comparing the V _TH by the microcomputer Q _10, and V _ref which has a first data (103). Here V _ref is set equal to the voltage value read in the analog input ports when the heater temperature is T _0. V _TH
Is smaller than _Vref , that is, when the heater temperature is the regulated temperature T ₀
-Out lower, microcomputer Q ₁₀ is excisional reads tau _2, t _ON2 as the pulse data from the ROM (104), and outputs the pulse signal (106). Also, when V _TH is smaller than V _ref ,
That is, when the heater temperature is higher than the control temperature T _0, excisional (105) the reads τ _1, t _ON1 as pulse data outputs. This operation is repeated until the energization ends (107). In this way, the heater temperature is controlled to be constant.

In the third embodiment, the energy applied to the heater is changed by changing both the pulse width and the pulse period, and the energy is applied to the heater as shown in FIGS. 9 and 10 as in the first embodiment. According to the present embodiment, there is an advantage that the control power range can be widened as compared with the first and second embodiments.

Further, instead of controlling the pulse width and the pulse cycle by one control information (heater temperature) as in this embodiment, the pulse width and the pulse cycle may be controlled by two pieces of control information. In this case, since the pulse width and the pulse period can be controlled independently from each information, the control becomes easy. For example, the pulse width is controlled for the input voltage value, and the pulse cycle is controlled for the heater temperature. By doing so, it is possible to independently control the fluctuation correction of the input voltage value and the heater temperature adjustment.

(Example 4) Next, an example in which temperature control is performed by performing phase control of AC voltage application will be described. First, the phase control described in the present embodiment will be described.

FIG. 18 is a basic configuration diagram of a single-phase AC voltage control circuit.
Th ₁ and Th ₂ are thyristors, which are connected in reverse. or,
Instead of Th ₁ and Th ₂ , a triac may be used. The output AC voltage applied to the load R is controlled by changing the control angle α of the thermistors Th ₁ and Th ₂ . I ₂ , υ ₂ when R is pure resistance
19 is shown in FIG. When the phase angle α ₂₁₁ and the thyristor are controlled as shown in FIG.
Voltage is output up to. Then, the effective voltage applied to R is controlled by changing the control P phase angle α from 0 to π. Such control is called phase control in this embodiment. When the load is inductive, a voltage is output to the load up to the extinction angle β of the thyristor. In this case, the control range is from β to π.

The temperature control of the heater using such a phase control will be described. FIG. 20 is a block diagram of this embodiment.

In FIG. 20, BCR1 is a triac, and 41 is a trigger circuit for applying a gate voltage to the triac BCR1.
A voltage as shown in FIG. 19 is applied to the heater 23 according to the trigger phase of the trigger circuit 41. Reference numeral 43 denotes a zero-cross detection circuit of the commercial AC power supply voltage. The control circuit 42 outputs a control P signal to the trigger circuit 41 in synchronization with the zero-cross timing detected by the zero-cross detection circuit 43. Upon receiving the control signal, the trigger circuit 41 applies a gate voltage to the triac BCR1, thereby turning the triac BCR1 ON. Further, the control circuit 42 changes the control signal in accordance with the output value of the temperature detecting element 24 such as a thermistor, thereby changing the heater 23.
The heater temperature is controlled to be constant by changing the power applied to the heater.

FIG. 21 shows the relationship between the heater temperature, the heater applied power, and the heater applied voltage waveform at this time. In FIG. 21 (a),
T _0, W ₀ is the same as the described in the first embodiment, T ₀
Denotes the heater temperature adjustment temperature, W ₀ denotes the amount of heat deprived by the heat radiation of the heater. Then, the boundary of T ₀ as in FIG. 21, a large energy W ₁ than W ₀ of the heater applied energy W W ₀
By changing to a smaller energy W _2, it is possible to maintain the temperature of the heater constant at T _0. FIG. 21 (b) shows the waveform of the voltage applied to the heater at that time and the gate trigger timing of the triac. The control trigger signal for the triac is changed according to the heater temperature as shown in FIG. 21 (b). The phases α ₁ and α ₂ have a relationship of 0 <α ₁ <α ₂ <π.

Next, the control circuit 42 and the trigger circuit 41 in this embodiment
Will be described with reference to FIG.

R ₄₀ to R ₄₆ in FIG. 22 is the resistance, R _TH denotes a thermistor. Q ₄₀ ~Q ₄₂ in the OP amplifier, Q ₄₃ is the driver of the photo-Tri-Atsu-click Q ₄₄ for driving. Vc indicates the power supply voltage of the OP amplifier. In the trigger circuit 41, a current flows through the light emitting side of the photo-tri mediation click Q _44, photo-tri mediation click Q ₄₄ is in an ON state. In this case, through a resistor R _45, a trigger current flows to the gate terminal of Toraiatsuku BCR1, Toraiatsuku BCR1 is turned ON.

In the control circuit 42, the saw-tooth wave generation circuit 44 is a circuit that generates a saw-tooth wave based on the zero-cross timing of the AC power detected by the zero-cross detection circuit 43. The relationship between the AC voltage and the phase of the sawtooth wave at this time is a waveform as shown by D in FIG. OP amplifier Q ₄₀ and Q ₄₂ constitute a comparator, OP amplifier Q ₄₁ constitute an adder. When the heater temperature is low, (partial pressure value by R _TH and R ₄₀₎ voltage of the point A is small. As the heater temperature rises, the value at point A increases. Now, when the V _ref heater temperature is set equal to the voltage value at the point A when the T _0, the voltage of the point B becomes 0V when the heater temperature T TT _0, T> T ₀
It becomes Vc at the time of. The V ₁ and the sum of the voltage value at the point B (C
A voltage at the point), the comparator Q ₄₂ a sawtooth wave (voltage at point D)
When the voltage value at the point D is larger than the point C, the triac BCR1 is turned on. Note that the voltage V ₁ is
When 0V, voltage at point C is 0V (triac BCR1 is always ON
State). Further, this circuit by adjusting the voltage V ₁ and the variable resistor V _R40, and has a configuration capable of adjusting the phase angle for controlling the Toraiatsuku BCR1. In this control circuit 42,
FIG. 23 shows the relationship between points D and E and the waveform _VH of the voltage applied to the heater. The voltage at point C when the heater temperature T is lower than T ₀
C _L , and the voltage when the heater temperature T is higher than T ₀ is C _H. Voltage at point C is compared sawtooth wave and C _L when the C _L, the voltage waveform of E is output now. At this time, the voltage applied to the heater becomes _VH . Then, the heater temperature rises and becomes T> T _0, the voltage C _H next to the point C, the voltage and voltage applied to the heater at this time point E E ', V _H' becomes like.

With the control circuit as described above, the heater temperature is controlled to be constant by changing the heater applied energy according to the heater temperature. In the fourth embodiment, the energy applied to the heater was changed by phase control and applied to the heater as in FIGS. 9 and 10, as in the first embodiment. Further, a microprocessor may be used for the control circuit. In this case, various relationships between the heater temperature and the applied energy can be performed with a simple circuit configuration. The control circuit at this time is shown in FIG. The hardware configuration of the case, except that the zero-crossing signal from zero cross detection circuit 43 is inputted to the microcomputer Q _45, is substantially the same as a hence detailed description as in Figure 11 is omitted. Microcomputer Q ₄₅ converts the input voltage to the analog input port AD to temperature data, obtains the timer time corresponding to the conduction angle from the temperature data. When the signal is input from the zero-cross detection circuit 43 performs a timer operation to turn on the photo-tri mediation click Q ₄₄ through a timer time after driver Q ₄₃ corresponding to the conduction angle.

[Embodiment 5] Next, a description will be given of an embodiment in which the temperature control is performed by controlling the wave number of AC voltage application.

First, the wave number control described in the present embodiment will be described. FIGS. 25 (b) and 25 (c) show output waveforms when the input AC voltage and the phase control and the wave number control are performed so that the effective voltage applied to the load is halved. In the phase control, the load is energized from the control phase angles α to π to control the energy. In contrast, the wave number control is controlled by changing the number of basic power wavenumber in tau ₁ cycle during the conduction period T _2. Here, τ ₂ must always be an integral multiple of two times T ₁ . Further, τ _1/2 may be used as the basic power supply voltage waveform.

An embodiment for performing the above energy control will be described below. The block diagram of this embodiment is equivalent to FIG. As described above, the wave number control is performed by the control circuit 42 to control the heater applied energy with respect to the heater temperature as shown in FIG. 21 (a). Therefore, the operation of the control circuit 42 will be described below.

In this embodiment, a control circuit constituted by a microprocessor will be described. The configuration diagram of the control circuit is the same as FIG. In Figure 24, Q ₄₄ is a photo-tri mediation click of a trigger circuit, Q ₄₃ is a driver for driving the photo-tri mediation click Q _44. R _TH is a thermistor, and the resistance R
As divided voltage value of Vc by ₄₇ and the thermistor R _TH, read heater temperature. Microcomputer Q ₄₅ reads the value indicated by the thermistor R _TH by the analog input port AD, provides a signal to the driver Q ₄₃ in synchronization with the signal of the zero-crossing detection circuit.

The control algorithm at this time is shown in FIGS. 26 and 27.
FIG. 27 shows an interrupt processing routine in which an interrupt is issued at a zero crossing of the AC power supply voltage.

In the interrupt routine, subtract 1 from the value of COUNTER (21
5) If the value becomes 0 (216), the value of the output port OP is inverted. Then, in the main routine (Fig. 26), COUN
Each time the TER value becomes 0, a new COUNTER value is set (208, 213). As the COUNTER value, TRIAC BCR1
There are data T _ON corresponding to the _ON time and data T _OFF corresponding to the _OFF time, but T _ON and T _OFF need to be treated as one set. Therefore, in FIG. 26, the state of the output port OP is determined (202), and the state of the output port OP is changed from "H" (when the triac BCR1 is OFF) to COUNT.
Only when the value of ER becomes 0 (203), a new value of COUNTER is calculated. Then, the value of T _ON is put into COUNTER. When COUNTER from the state of the output port OP is "L" becomes 0 (212), placing the T _OFF as a previous T _ON paired to the value of COUNTER (213). In the calculation of the COUNTER value, the COUNTER values T _ON1 and T _{OFF1 at} which the heater applied energy becomes W ₁ when the heater temperature T is lower than T ₀ (205) according to the thermistor information from the analog input port AD (204). (206), when high give COUNTER value T _ON2, T _OFF2 become energy W ₂ (207). By repeating the above,
The temperature of the heater is controlled to be constant.

In the fifth embodiment, the energy applied to the heater is changed by wave number control, and the energy is applied to the heater in the same manner as in the first embodiment.
It was given to the heater as shown in FIG.

〔The invention's effect〕

As described above, according to the present invention, even if the detected temperature is higher than the set temperature, the temperature is lowered while energizing, so that a rapid temperature drop of the heating body can be prevented. Even if temperature detection is performed when the response of the temperature detection element is not sufficient and the temperature of the heating element is considerably higher than the set temperature, there is a power supply for cooling that corresponds to that temperature. There is an effect that the temperature can be lowered nearby.

[Brief description of the drawings]

1 is a sectional view of a copying machine to which the present invention is applied, FIGS. 2 (a) and 2 (b) are enlarged views of a fixing device, FIG. 3 is a block circuit diagram relating to temperature control, and FIG. FIG. 5 is a circuit diagram showing details of a power supply, FIG. 5 is a circuit diagram showing details of a temperature control circuit for performing pulse width control, FIG. 6 (a), FIG. 8 to FIG.
FIGS. 16 (a), 16 (a) and 21 (a) show the relationship between the heater temperature and the energy applied to the heater. FIGS. 6 (b), 13 (b) and 16 (B) and FIG. 21 (b)
FIG. 7 shows the relationship between the heater temperature and the output pulse of the temperature control circuit. FIG. 7 shows the voltage waveform at each point of the temperature control circuit shown in FIG. 5, and FIG. 11 shows the temperature control circuit using a micro computer. FIG. 12 is a control flowchart for temperature control by pulse width control, FIG. 14 is a diagram showing details of a temperature control circuit that performs pulse cycle control,
FIG. 15 is a diagram showing a signal waveform at each point of the temperature control circuit shown in FIG. 14, FIG. 17 is a control flow chart for temperature control by controlling both the pulse width and the pulse period, and FIG. FIG. 19 is a circuit diagram showing a basic configuration of a phase AC voltage control circuit,
The figure shows the current and voltage waveforms in the circuit of FIG. 18, FIG.
The figure is a block diagram showing a circuit configuration for performing phase control,
FIG. 22 is a circuit diagram showing details of FIG. 20, FIG. 23 is a voltage waveform diagram at each point of the circuit of FIG. 22, FIG. 24 is a diagram showing details of a control circuit using a micro computer, and FIG. The figures are voltage waveform diagrams for explaining wave number control, and FIGS. 26 and 27 are control flowcharts for wave number control. 11: Fixing device 21: Low heat capacity linear heating element 22: Alumina substrate 23: Resistive material 24: Temperature sensing element 25: Fixing film 26 to 28: Roller 31: Temperature control circuit 32: Electricity Power supply 41 Trigger circuit 42 Control circuit 43 Zero cross detection circuit

Claims (1)

(57) [Claims] 1. A heating element that generates heat when energized, a fixing film that moves while being in contact with a recording material bearing an unfixed image on one side while rubbing on one side with the heating element, and a temperature of the heating element. And a control means for controlling the power supplied to the heating element so that the temperature detected by the temperature detection element maintains the set temperature. The higher the detected temperature, the smaller the energizing power is controlled so as to energize the heating element, and at least two types of energizing power are energized when the detected temperature of the temperature detecting element is higher than the set temperature. Characteristic fixing device