JPH0333882A - Temperature control method for thermal fixing unit - Google Patents

Abstract

PURPOSE:To speedily raise a temperature to a prescribed target temperature by switching the setting of a reference temperature in response to the alteration of the action state of a thermal fixing unit and setting a temperature so that the reference temperature satisfies a specific relation. CONSTITUTION:Instead of setting a single proportional start point, proportional start set temperatures Ts1 and Ts2 at the time of weigh and a fixing action, respectively, just like control target temperatures (weight temperature Tal and a fixing temperature Ta2) are set. Together with the control target temperatures, the setting of the proportional start points is switched in response to the alteration of the action state of the thermal fixing unit. Simultaneously, respective reference temperatures are set so as to meet inequality I. Namely, the proportional start set temperatures Ts1 and Ts2 most suitable for actuating actions are set for each action state. Consequently, a current temperature is smoothly shifted to the control target temperatures Ta1 and Ta2 with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of controlling the temperature of a thermal fixing device used in copying machines, printers, other electrophotographic devices, etc. Proportional starting point (first reference temperature)
The present invention relates to a temperature control method for a thermal fixing device, in which the heating control of the heater is switched to a proportional control method after the temperature has been raised to a temperature of 100.degree.

``Prior Art'' For example, a thermal fixing device consisting of a combination of a fixing roller with a built-in heater and a pressure roller has been known, and the temperature control of this type of fixing device is generally based on the temperature required to perform the fixing operation. So-called 0N-OF, which controls the temperature by alternately supplying and de-energizing the heater across the reference temperature (fixing temperature).
The F control method and the so-called proportional control method (1983), in which the pulse width or pulse density of the pulse signal for controlling the heater energization are proportionally changed as the fixing temperature approaches the fixing temperature.
-50442, Japanese Patent Publication No. 61-1752, etc.), but in the former case, the startup speed is fast, but because the heating temperature gradient is linear, overshoot and undershoot are large, and in the latter case, Since the heating control is performed while maintaining thermal balance based on the density or width control of the pulse signal, it is easy to maintain the fixing temperature, but it has the disadvantage that the start-up speed is slow.

For this reason, conventionally a control method has been adopted in which the thermal fixing device is started up to the proportional start point by full energization heating of the heater, and then the temperature is shifted to and maintained at the fixing temperature required for the fixing operation while maintaining thermal balance through proportional control. ing. (Unexamined Japanese Patent Publication No. 58-420
No. 79 et al.) ``Problem to be Solved by the Invention'' Now, in the temperature control device of the heat fixing device, generally, in order to save power supply to the heater and shorten the transition time to the fixing temperature, each time the fixing operation is completed, , the temperature is controlled by lowering the fixing temperature to the weight temperature, but in an apparatus with such a configuration, the proportionality start point must be set below the weight temperature, in other words, the weight temperature cannot be lowered. Unless the weight is located in the proportional control temperature range above the proportional start point, accurate control of the weight temperature becomes impossible.

However, setting the proportional start point below the weight temperature will make the proportional control range from the proportional start point to the fixing temperature unnecessarily large when performing the fixing operation, resulting in a slow temperature rise rate. This leads to a decrease in printing speed, especially in recent years when printers using the above-mentioned fixing device are operated.
When used as part of Terminal A, the reduction in printing speed has been a major bottleneck in improving the efficiency of the entire system.

Now, as mentioned above, as printing speeds increase, the amount of heat absorbed per hour during printing (fixing) operations inevitably increases, and for this reason there is a large difference in the amount of heat absorbed during wait time. Despite that.

Since the accumulated heat capacity of the fixing roller itself, which acts as a cushion to maintain thermal balance with the heat source, has been significantly reduced in response to the miniaturization of the entire device, the above-mentioned pulse density etc. are simply changed proportionally. It is becoming increasingly difficult to perform accurate temperature control using only proportional control means.

SUMMARY OF THE INVENTION In view of the drawbacks of the prior art, it is an object of the present invention to provide a temperature control method for a thermal fixing device that can quickly raise the temperature to a predetermined target temperature during either fixing or waiting.

Another object of the present invention is to reduce the size of a fixing device with a built-in heater, so that even when its accumulated heat capacity is relatively reduced, there is a large difference in the amount of heat absorbed during fixing operation and wait operation. An object of the present invention is to provide a temperature control method for a heat fixing device that can accurately control the temperature of a heat fixing device.

"Means for Solving the Problems" The basic idea of the present invention is to improve the precision of temperature control by treating the weight state and fixing state as completely separate control states, rather than as a series, while at the same time improving the hardware configuration. The main control circuit side is configured to perform a common operation even when the two control states are changed, thereby avoiding complication of the configuration and control operation.

That is, in the invention described in claim 1), instead of providing a single proportional start point, the proportional start point is set at each time during the wait time and during the fixing operation, similarly to the control target temperature (wait temperature Tal and fixing temperature Ta2). Temperature Tsl, T
The first feature is that s2 is prepared and the set temperature of the proportionality start point is switched together with the control target temperature in response to a change in the operating state of the heat fixing device.

The second feature is that each reference temperature is set so as to satisfy the following relationship.

Tsl <Tal <Ta2 <Ta2 "Effect" According to this technical means, the most preferable proportional start set temperature Tsl for performing the start-up operation for each of the operation states.
Since Ta2 is set, each control target temperature Tal, T
In addition to being able to quickly and accurately shift to a2, in particular, because the proportional start point during fixing operation is set above the weight temperature, the transition from the weight temperature to the fixing temperature is always performed after full energization heating is performed using the proportional control method. Therefore, the transition to the fixing temperature Ta2 can be carried out more quickly, and it is possible to smoothly cope with the increase in the speed of the printer.

Furthermore, the present invention focuses on the fact that there is a large difference in the amount of heat absorbed between the printing (fixing) operation and the waiting time, and
The second and third aspects of the present invention are that the reference setting voltage for modulating the amount of heat is also different on the side that supplies the amount of heat.

In claim 2), in the control method for controlling pulse density, a reference frequency setting voltage of a frequency modulation circuit that performs frequency modulation of the pulse density signal is changed in response to a change in the operating state of the heat fixing device. On the other hand, in claim 3), in the control method for performing pulse width control, a time constant circuit whose charging potential is a reference voltage corresponding to the proportionality starting point is used to control the energization of the heater. It is characterized by performing width modulation of the pulse signal.

As a result, a heat balance is maintained between the amount of heat removed and the amount of heat supplied corresponding to each operating state, and temperature control can be performed smoothly and accurately even in an apparatus in which the storage heat capacity of the fixing device is reduced.

The frequency modulation means and the pulse width modulation circuit may be used alone or in combination as shown in the embodiments below.

"Embodiments" Hereinafter, preferred embodiments of the present invention will be described in detail by way of example with reference to the drawings. However, the dimensions, materials, shapes, relative positions, etc. of the components described in this example are unless otherwise specified.

This is not intended to limit the scope of the invention, but is merely an illustrative example.

FIG. 1 is a schematic block diagram showing a temperature control circuit of a heat fixing device according to an embodiment of the present invention. To briefly explain its configuration, lO is a heat roller consisting of a pressure roller and a fixing roller that rotate in synchronization with each other. Temperature detection means l for detecting the surface temperature of the thermal fixing device using a heater built into the fixing device (both not shown)
is placed close to its surface.

The temperature detection means l includes a fixed resistor R that divides the reference circuit voltage.
A frequency modulation circuit 3 (pulse position setting means, hereinafter referred to as VCO) and a pulse width modulation circuit 5 (hereinafter referred to as PWM) use the partial pressure output as a detection voltage Vl corresponding to the detected temperature T of the heat fixing device. ).

2 is a circuit for setting a reference voltage corresponding to the control target temperature, and the reference voltage Vat, Va proportional to the voltage dividing resistors R2, R3 is set.
A resistor R4 and a transistor Tri are connected between the voltage dividing resistors R2 and R3.
Since the voltage dividing resistor R3 and the resistor R4 are connected in parallel based on the switching signal from the CPU 7, the voltage dividing ratio is changed. In other words, the reference voltages Vat and Va2 output to the VCO 3 are weighted. control target temperature ↑at, Ta2 (e.g. 185.200℃
) is configured to be changeable.

The VCO 3 is a circuit that performs frequency modulation of the pulse density signal P outputted to the PWM 5, and is a circuit that performs frequency modulation of the pulse density signal P which is outputted to the PWM 5.
Input the reference voltage Va corresponding to a2 (hereinafter expressed as Ta or Va when indicating both the value at the time of wait and the time of printing), and calculate the pulse of the pulse density signal p based on the difference voltage. The interval is configured to change rapidly.

In other words, since the heat absorbed energy differs significantly between the printing operation and the waiting period, the weight is set at IHz as the reference frequency based on the difference voltage during the printing operation, corresponding to the control target temperature Ta during each operation. In some cases, the pulse density signal P of each reference frequency of 0.4 Hz is configured to be output, and when the detected temperature ↑ falls below the control target temperature Ta, the frequency is changed within the limit range of the saturation frequency. The frequency is set to suddenly decrease when the detected temperature T rises above the control target temperature Ta.

The VCO 3 is configured such that when the detected temperature ↑ is below the proportional starting point 〒S, a constant saturation voltage is input regardless of the differential voltage.

4 is a circuit for setting a reference voltage Vs corresponding to the proportional start point Ts for switching the heater 10 from full current heating to proportional control, and the reference voltage Vs is set by a resistor R5 and a capacitor C.
A switching circuit 9 consisting of a resistor R4 and a transistor Tri is connected between the two voltage dividing resistors R2 and R3, and a switching circuit 9 consisting of a resistor R4 and a transistor Tri is connected between the voltage dividing resistors R2 and R3, When the partial pressure ratio is changed, the proportional starting point 〒S In other words, the starting point of pulse width modulation during wait wait and printing (for example, 165, 180°C)
is configured to be switchable in accordance with the control target temperature Ta (185,200°C).

Also, changing the voltage division ratio is due to the charging potential V of capacitor C.
s will also be changed.

PWM5 uses the pulse density signal Pma from VCO3 as a trigger input, inputs the charging potential Vg of capacitor C corresponding to the proportionality start point Ts to the threshold input, and inputs the detection voltage Vl from the temperature detection means 1 to the threshold control input, respectively. By doing so, charging potential Vs>detection voltage v
In other words, when the detected temperature T is higher than the proportional start point Ts, the capacitor C is discharged and recharged at the falling edge of the pulse density signal P inputted to the trigger input,
The CPU outputs a control modulation pulse signal Pw corresponding to the pulse time formed when the detection voltage Vl crosses the discharge voltage curve.
It is possible to output to 7.

That is, by crossing the discharging and charging force curve of the time constant circuit 12 with the reference voltage corresponding to the proportionality starting point as the charging potential Vs at the detection voltage vl, an inverse correlation is obtained based on the difference signal between the detection voltage and the reference voltage. A modulated pulse signal with a pulse width can be obtained, and in this case, if the time constant is set so that the control target value is located at the shoulder of the discharging and charging force, it will be close to the saturation region. Since the detection voltage crosses the part, it effectively acts on the time constant error, and the output pulse width error can be set to be extremely small.

- If the detected temperature is lower than the force proportional start point Ts, the threshold input≦control holds, so the output level becomes old and the fully energized state can be maintained until the detected temperature T reaches the proportional start point Ts.

6 is a solid state relay SSR which inputs the energization signal corresponding to the modulated pulse signal Pw from the CPU 7, and when the 1 energization signal arrives, the output side is made conductive in synchronization with the built-in zero cross circuit, and is used for control from PWM 5. AC power corresponding to the pulse width of the pulse signal is applied to the heater IO.

Reference numeral 7 denotes a CPU which performs the various controls described above, and sends a predetermined switching signal W to a switching circuit 8.9 every time the operation of, for example, wait/print is switched.

11 is the control target temperature T during the double operation after the print command
This is a timer that stops paper feeding until the temperature changes from al (185° C.) to the control target temperature Ta2 (200° C.) during printing operation.

Next, the temperature control operation of the fixing device will be explained based on FIGS. 2 and 3.

First, when the power is turned on, the control circuit is initialized and various parts are checked for abnormalities (STEPI).
) Determine whether printing is possible or not, and if there is no print command, send the Lo times signal to each switching circuit 8.9 as a switching signal W from the CPU 7, and control the proportional start point Tsl (185°C) during wait operation. Target temperature Tel (
After setting the reference voltage Vat corresponding to (185°C)
TEP2) Enter temperature control operation.

In the temperature control operation (STEPIO), first, at the beginning of the wait operation transition, the detected temperature T is the proportional starting point T + 1 (165°C)
Because of the following, the output level of PWM 5 is independent of the pulse density signal p from VCO 3. Figure 2 (a) and (b) are distribution diagrams showing the temperature change state, and Figures 2 (a) and 2 (b) are flow charts showing the operating procedure. be. FIG. 4 is a schematic block diagram showing a temperature control circuit according to another embodiment.

Claims (1)

[Claims] 1) After raising the temperature of the fixing device to the first reference temperature by fully energizing the heater, the heating control of the heater is switched to a proportional control method to shift to the second reference temperature and thereafter. In the temperature control method of a thermal fixing device that aims to maintain the temperature, the second reference temperature is adjusted in response to a change in the operating state of the thermal fixing device from a wait state to a fixing state and from a fixing state to a wait state. A temperature control method for a thermal fixing device, characterized in that the set temperature of the first reference temperature is switched at the same time, and the temperature is set so that each of the reference temperatures satisfies the following relationship: Ts1<Ta1<Ts2< Ta2 Ts1: First reference temperature during wait Ta1: Second reference temperature during wait Ts2: First reference temperature during fixing operation Ta2: Second reference temperature during fixing operation
2) The temperature control method according to claim 1, wherein energization of the heater is controlled based on a frequency-modulated pulse density signal corresponding to the detected temperature of the heat fixing device. 3) Charging the reference voltage corresponding to the first reference temperature. The temperature control method according to claim 1), characterized in that the width modulation of a pulse signal for controlling the energization of the heater is performed using a time constant circuit that is set to a potential.