JPH06214662A - Temperature controller - Google Patents

Abstract

PURPOSE:To provide a temperature controller constituted so as to supply fixed power to a heating element at all times. CONSTITUTION:At the time of starting temperature control, the enable signals of a first three-state buffer are energized so as to validate the output of a rush current control circuit 13 by the system of a microcomputer or the like for instance. Then, when the load current of a heater 15 changes to a prescribed value and when a rush current is generated for some reason or other, being inversely proportional to the amount of difference with an average load current IAV, the pulses of an AC voltage energizing time are outputted to a heater driving circuit 14. At this time, in order to prevent radio noise at the time of AC voltage energizing OFF to the heater 15, the pulses are outputted in synchronism with a zero cross switch.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature control device suitable for controlling the temperature of a fixing device of a recording device of an electrophotographic system such as a copying device or an optical printer device.

[0002]

2. Description of the Related Art Conventionally, a heat roller system has been most applied to a fixing device of an electrophotographic recording apparatus. Basically, a pair of a heating roller and a pressure roller that is in pressure contact with the heating roller is used to perform fixing by passing an unfixed image between the two. In order to improve the releasability of the developer and the heating roller, It is necessary to take measures against the so-called offset phenomenon such as providing a release layer of fluororesin on the surface or applying oil. In this method, the developer is liable to cause cohesive failure in the process in which the developer in a molten state heated and separated from the surface of the solid roller inevitably causes offset as a twist phenomenon.

Therefore, recently, as a new method, a method has been developed in which a heating element is pressed against a sheet via a film sheet or a belt to fix the sheet. According to this method,
Since a sheet having a small heat capacity is cooled by radiating heat immediately after passing through the heating element, it is possible to prevent offset by separating the developer in the solid state and the surface of the solid roller by interface destruction.

FIG. 6 is a view showing a cross section of such a fixing device, and the arrow in the drawing indicates the conveying direction of the recording paper 84. Here, it is assumed that the toner image has already been transferred onto the recording paper 84 by a known electrophotographic method.

The recording paper 84 conveyed in the direction of the arrow is heated and fixed by the heat-generating heater 4 via the film belt 85, which is given a proper tension by the driven roller 81, and at the same time, is driven by the drive roller 80 in the direction of the arrow. The belt 85 is conveyed and discharged. Heating heater 4
The temperature control is performed based on the resistance change of the thermistor 5.

Next, this temperature control will be described with reference to FIG.

In FIG. 7, reference numeral 535 is a subtracter, which is a voltage V _T (5) obtained by changing the resistance value of the thermistor 5.
1) and the control target voltage V _ref (52) voltage difference ΔV (5
3) is asked. Reference numerals 54 to 58 are comparators, which respectively have comparison voltages 59, 510 to 513 for the voltage difference ΔV. Reference numerals 514 to 517 are inverters. 518-52
An AND gate 1 outputs pulse-on signals 526 to 529 to pulse generation circuits 522 to 525, which will be described later, when a predetermined condition shown in the figure is satisfied. Reference numerals 522 to 523 denote pulse generation circuits, which generate a pulse having a predetermined pulse width in a predetermined cycle and output the pulse to the OR gate 526. The OR gate 526 inputs the heater driving signals 527-531.
Is output to the heater drive circuit 14.

Reference numeral 532 is a clock generation circuit, which outputs a reference pulse 533 to the pulse generation circuits 522 to 525. The cycle of the reference pulse 533 is equal to the cycle of the AC voltage applied to the heater 4. For example, the pulse width is t5, which will be described later, and is one half of AC100V, 50Hz.
It is 0 msec. Also, this pulse width is an integer multiple of this,
It may be 20 msec or 30 msec, and this value depends on the temperature characteristic of the heater 4.

FIG. 8 shows the above heater drive signals 527-.
531 is shown. Here, sections P1 to P5 indicate the period from the start of control in the temperature characteristic diagram shown in FIG. 9 to the temperature equilibrium state. Further, FIG. 10 shows the heater driving signals 527-
AC voltage 5 applied to the heater 4 obtained by 531
34 is shown.

Next, the operation will be described with reference to the flow chart shown in FIG. First, the subtractor 535 calculates the voltage difference ΔV between the target voltage V _ref and the measured voltage Vt (S20
0), the difference voltage ΔV is input to each of the comparators 54 to 58, and the following judgment is made. Here, the reference voltages V1 to V5 of the respective comparators
Is V1 <V2 <V3 <V4 <V5.

If ΔV ≦ 0 (S201), the heating heater 4 is turned off (S202). If 0 <ΔV ≦ 2 (S203), the heater 4 is turned on for the period t5 every t1 cycle (S204). V2 <△ V ＜ ≦ V
If it is 3 (S205), the heater 4 is turned on for the period t4 every t1 cycle (S206). V3 <△
If V <≤V4 (S207), turn on the heater 4 for the period t3.
The control to turn on only is performed every t1 cycle (S208).
If V4 <ΔV <≦ V5 (S209), control for turning on the heater 4 for the period t2 is performed every t1 cycle (S2).
10). If V5 <ΔV (S211), the heater 4 is constantly turned on (S212).

Returning to FIG. 9 again, the temperature characteristic of the heater 4 is shown. Here, ΔT5 is the control target temperature T in the section P1.
temperature difference from ref, V5 is voltage difference at this time, ΔT4 is temperature difference from control target temperature Tref in section P2, V
4 is the voltage difference at this time, ΔT3 is the temperature difference from the control target temperature Tref in section P3, V3 is the voltage difference at this time, ΔT2 is the temperature difference from the control target temperature Tref in section P4, and V2 is this time Voltage difference, ΔT2 is section P3
At the control target temperature Tref, V2 is the voltage difference at this time, ΔT1 is the overshoot amount from the temperature Tref, and V1 is the voltage difference at this time. As shown in the figure, in each section, the energization period to the heating heater is variable according to the difference between the control target temperature and the measured temperature,
There is little overshoot in the initial stage of control with respect to the control target temperature, and subsequent temperature fluctuations are also small.

[0013]

However, in the above-mentioned conventional temperature control method, a large amount of power is consumed and a large amount of power is consumed when an AC power source is applied to the heater by a mechanical switch or due to an excessive inrush current to the heater for some reason. There is a drawback that the heater is deteriorated and the safety is deteriorated due to the deterioration.

Therefore, in view of the above points, an object of the present invention is to provide a temperature control device configured to constantly supply a constant electric power to a heating element.

[0015]

In order to achieve the above object, the present invention provides a load current detecting means for detecting a load current flowing through a heater in a fixing device for driving an AC power source and controlling heating of the heater. A first drive means for alternating-currently driving the heater in inverse proportion to an integral value of the load current when a current larger than a predetermined value is detected by the load current detection means; When a small current is detected, the heater is provided with a second drive means for switching the AC drive of the heater by the zero cross of the AC power supply.

[0016]

According to the above configuration of the present invention, when a load current larger than a predetermined value is detected, the heater is AC-driven in inverse proportion to the integrated value of the load current, and the load current is smaller than the predetermined value. When the current is detected, the AC drive of the heater can be switched by the zero-cross of the AC power supply, so that the temperature of the heater can be controlled appropriately.

[0017]

Embodiment 1 FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, reference numeral 11 is a comparator for comparing the voltage difference between the voltage V _T obtained by the thermistor R _T and the set temperature V _ref . Reference numeral 12 is a pulse wave number control circuit, which outputs a predetermined pulse (described in detail later) to be supplied to the heater drive circuit 14 via the zero-cross switch circuit 17 in response to the voltage output from the comparator 11. . The zero-cross switch circuit 17 is a circuit that detects that the AC power supply 19 has become zero volt and turns it on and off. 20 is an OR gate, which is based on the output from the zero-cross switch circuit 17 or the output from the rush current control circuit 13,
Outputs a pulse to the heater driving circuit 14.

Numeral 13 is a rush current control circuit peculiar to this embodiment, which outputs a pulse to the heater driving circuit 14 when the AC voltage is applied to the heater 15 and when an overcurrent flows out at the time of an abnormality to suppress the rush current. Fulfill

Reference numeral 16 is a load current detection circuit for detecting the load current of the heater 15, and the detected load current is output to the rush current control circuit 13 and the load current comparison circuit 18. Reference numeral 18 denotes a load current comparison circuit, which determines whether or not the load current detected by the load current detection circuit 16 is larger than a specified value, and outputs an enable signal a if the load current is larger than the specified value. 13 is moved, and if it is smaller, the enable signal b is output to output the pulse wave number control circuit 1
Move 2

FIG. 2 shows a specific structure of the rush current control circuit 13 shown in FIG. In the figure, when the load current is larger than the specified value by the load current comparison circuit 18, the enable signal a is output and input to the AND gate 31. Reference numeral 21 is a current-voltage conversion circuit that converts the amount of current from the load current detection circuit 16 into a voltage amount. 22 is an integrating circuit.

Reference numeral 23 is an error amplifier, and V _Iref is applied to one input terminal in _advance . This V _Iref has a value obtained by converting the average current value in a steady state in which the load current is sufficiently stable into a voltage amount, and is determined in advance as a standard value. Further, the integrated load current amount V _r output from the integration circuit 22 is input to the other input terminal of the error amplifier 23. Therefore, the error amplifier 23 is compared with the standard value V _Iref, and when the integrated load current amount V _r is larger than V _Iref , the enable signal (enable 1) of the first three-state buffer 27 is activated to control the rush current. Enable the output of circuit 13.

Reference numeral 24 is a PWM circuit, and as shown in FIG. 3, the output from the error amplifier 23 and the standard triangular wave generation circuit 2
The pulse width modulation is performed so that a pulse proportional to the difference from the load current average value is generated by comparing the output of FIG. Here, the triangular wave frequency of the standard triangular wave generating circuit 25 is twice the frequency of the AC voltage applied to the heater 15.

Reference numeral 26 is a first inverter circuit, and when the pulse effective level output to the heater driving circuit 14 is a positive logic, the conduction time of the AC voltage applied to the heater 15, the load current (I _r ) and the average. This is for making the difference in the load current (I _AV ) inversely proportional.

Reference numeral 28 denotes a second three-state buffer, which is a load current (I
_{If r} ) is smaller than the average load current (I _AV ), the enable signal b is activated via the load current comparison circuit 18, and the pulse wave number control circuit 12 causes the zero-cross switch circuit 17 to operate.
To enable output to.

Next, the operation of this embodiment will be described with reference to FIG.

When the application of the AC voltage to the heater 15 is started, the temperature of the heater 15 starts to rise sharply as shown in FIG. 4 (d). Along with this, the load current also flows as shown in FIG. 4A, and a rush current is generated.

At the start of temperature control, the enable signal (enable 1) of the first three-state buffer 27 is activated so that the output of the rush current control circuit 13 becomes valid by a system such as a microcomputer. deep. Then, when the load current of the heater 15 changes as shown in FIG. 4A and when the rush current occurs due to some cause, the difference amount ΔI ₁ , ΔI ₂ , from the average load current I _AV , ΔI ₃ , ΔI ₄ , ΔI ₅
In inverse proportion to the AC voltage energization time t ₁ , t ₂ , t ₃ , t
The pulses of ₄ and t ₅ are output to the heater driving circuit 14. At this time, in order to prevent radio noise when AC voltage energization to the heater 15 is turned off, output is performed in synchronization with a zero cross switch (not shown).

When the load current reaches the average load current I _AV ,
The output of the error amplifier 23 is turned off to turn off the first three-state buffer 27, and the second three-state buffer 28 is turned on to output the output of the pulse wave number control circuit 12 to the heater drive circuit 14. FIG. 4C shows the generated pulse output from the pulse wave number control circuit 12.

Embodiment 2 In the above-mentioned first embodiment, the cycle of the pulse output from the rush current control circuit 13 to the heater drive circuit 14 is half the cycle of the applied AC voltage, but the heat capacity of the heater 15 is particularly large. When the rush current is significantly large, as shown in FIG. 5, a pulse having an integral multiple of the cycle of the applied AC voltage may be used.

In the example shown in FIG. 5, the pulse width modulation control is performed with the same period as that of the AC voltage. This case can be realized by setting the cycle of the triangular wave generation circuit in the rush current control circuit to T.

[0031]

As described above, according to the present invention, constant power is supplied as required even when an inrush current is generated when the power is turned on or when the load is short-circuited for some reason. As a result, it is possible to reduce the rated capacity of the mechanical switch, and to reduce the fusing surge current of the lamp filament.
It is possible to reduce radio noise interference caused by spike noise and the like.

[0032]

[Brief description of drawings]

FIG. 1 is a block diagram showing an entire embodiment of the present invention.

FIG. 2 is a detailed circuit configuration diagram of the rush current control circuit shown in FIG.

FIG. 3 is a waveform diagram showing the operation of FIG.

FIG. 4 is a waveform chart showing the operation of the embodiment shown in FIG.

FIG. 5 is an explanatory diagram of another embodiment of the present invention.

FIG. 6 is a cross-sectional configuration diagram of a fixing device included in an electrophotographic recording apparatus.

FIG. 7 is a diagram showing a conventionally known heater temperature control circuit.

FIG. 8 is an explanatory diagram of a heater driving signal shown in FIG.

9 is a temperature characteristic diagram of the heater 4 shown in FIG.

10 is an explanatory diagram of heater driving signals shown in FIG. 7. FIG.

11 is a flowchart showing the operation of FIG. 7. FIG.

[Explanation of symbols]

R _T thermistor 11 Comparator 12 Pulse wave number control circuit 13 Rush current control circuit 14 Heater drive circuit 15 Heater 16 Load current detection circuit

Claims (1)

[Claims] 1. A fixing device which drives an AC power source to control heating of a heater, wherein a load current detecting means for detecting a load current flowing through the heater and a current larger than a predetermined value are detected by the load current detecting means. At this time, first driving means for AC driving the heater in inverse proportion to the integral value of the load current, and AC driving of the heater when an electric current smaller than a predetermined value for the load current is detected. And a second drive means for switching by zero cross of the temperature control device.