JPH0727419B2 - Temperature control method - Google Patents

Description

The present invention relates to a temperature control method effective for controlling the temperature of a heating roller of a copying machine, for example.

[Conventional technology]

Conventionally, as a method for controlling the temperature of a heating roller used in the fixing process of a copying machine, for example, a temperature detecting sensor including a temperature sensitive element such as a thermistor is held mechanically stable and brought into contact with the heating roller surface. It is known that the heater is turned on / off depending on whether the temperature detected by this sensor is higher or lower than the target control temperature of the surface of the heating roller to keep the surface temperature of the heating roller at a predetermined value.

[Problems to be Solved by the Invention]

However, in such a conventional temperature control method, especially when the heating roller as a heated object heated by the heat source has a high temperature rising rate, the response of the sensor for temperature detection is delayed at the start of control. A large overshoot occurs, which not only causes inconveniences such as the occurrence of offset and delay of warm-up time, but also a relatively large undershoot and overshoot after the large overshoot at the start of the control. Technical challenges arise.

As a method for solving such a technical problem, a target control temperature of the heating roller and a determination temperature lower than the target control temperature are provided, and the heater is heated by full energization up to the determination temperature, and then the heating amount is proportionally controlled. Has been provided so that the heater is gradually heated so as to gradually approach the target control temperature (for example, JP-A-58-209).
771 publication).

However, in this type, since the electric power supplied to the heater is controlled in phase, a special control circuit for controlling the phase becomes indispensable, and the device configuration becomes complicated accordingly. New technical challenges arise.

The present invention has been made to solve the above technical problems, and does not require a complicated device configuration and is for temperature detection that occurs at the start of control even if the rate of temperature rise of the object to be heated is high. It is possible to avoid a large overshoot due to the response delay of the sensor, and further, undershoot after that,
A temperature control method for effectively reducing overshoot is provided.

[Means for Solving the Problems]

That is, the present invention detects the temperature of a heated object heated by a heat source with a sensor, and turns on the heat source if the sensor detected temperature is lower than the control temperature, while the sensor detected temperature is equal to or higher than the control temperature. If there is a temperature control method that turns off the heat source and performs feedback control so that the temperature of the object to be heated becomes the control temperature, the temperature is higher than the target control temperature of the object to be heated according to the sensor detection temperature at the start of the control. A low initial control temperature is set as the control temperature, and when the sensor detected temperature reaches the initial control temperature, an intermediate control temperature located between the initial control temperature and the target control temperature is set as the control temperature. The intermediate control temperature is gradually made to approach the target control temperature with the passage of time.

[Action]

According to the technical means as described above, when the control is started, the initial control temperature lower than the target control temperature of the object to be heated is set according to the sensor detection temperature at the start of the control. Even if there is, the temperature of the object to be heated does not greatly exceed the target control temperature when the sensor detected temperature reaches the initial control temperature.

Further, when the sensor detected temperature reaches the initial control temperature, an intermediate control temperature positioned between the initial control temperature and the target control temperature is set, and the intermediate control temperature is gradually controlled over time. The temperature of the object to be heated gradually rises with each intermediate control temperature as a target, and finally reaches the target control temperature.

〔Example〕

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.

1 and 2 show an embodiment of the present invention.
The case where it is applied to the temperature control of the heating roller of the copying machine is shown.

In FIG. 1, (1) is a thermistor constituting a sensor for temperature detection, and a sensor having this thermistor (1) has a heater (2) as a heating device provided therein as shown in FIG. It is installed around the heating roller (3) for fixing. The thermistor (1) is inserted in series with the resistor R between the operating power source and the ground, and a voltage that changes according to the change of the resistance value of the thermistor (1) is taken out from both ends of the resistor R. In the illustrated example, the A / D converter (4) is used to A / D-convert the analog-to-digital converter, and then the central processing unit (CPU) of the microcomputer.
It is given to (5) as data indicating the sensor temperature. In the central processing unit (5), the sensor time constant and the roller temperature rising rate of the above-mentioned sensor and the heating roller (3) to be heated as well as the control target value of the temperature of the heating roller (3) are used in the central processing unit (5). Data is also given. Based on these data, the central processing unit (5) executes processing according to the program shown in the flowchart in FIG.
Heater (2) via solid state relay (6)
Turn on and off.

Next, referring also to FIGS. 3 and 4, the heating roller (3)
The operation of temperature control with respect to will be described.

In the drawings and the following description, T _CNT1 is a warm-up control target value, T _CNT2 is an idling control target value, T _ROLL (t) is a roller temperature, and T _SNR (t) is a control target value.
Is the sensor temperature, τ _SNR is the time constant of the sensor, a is the heating rate of the roller, and T _CNT is the control target value of the roller.

First, at the start of control, the control target is set to the value T _CNT1 (corresponding to the initial control temperature) obtained by the following equation (1), and this is controlled as the target value. That is, as the control temperature during warm-up However, t _RDY = (1 / a) (T _CNT -T _SNR (0)) is calculated.

In the above, T _SNR (0) is the sensor temperature at the start of control (t = 0), and a and τ _SNR are given as constants according to the heating roller (3) and sensor used as described above. It is a thing. Although T _CNT1 is represented by the equation (1), it may be a discrete value that can be approximated or another equation. Fig. 2 shows T _CNT1 because it uses the A / D converter (4).
This is an example when the value of is discrete.

Control is started in this way, and from the start of control, T
_{Period SNR} (t) is raised to a temperature of T _CNT1 obtained above (1), i.e., between T _SNR (t) <T _CNT1 is allowed to turn on the heater (2), which T _SNR (t) ≧ YES determination result in T _CNT1 judged whether or not the step is continued until leaving.

Next, when the sensor temperature T _SNR (t) reaches the above T _CNT1 and a YES determination result is obtained in the above determination step, T _CNT2 (t) (corresponding to the intermediate control temperature) is set as the subsequent control temperature. It is given by equation (2).

Note that t ′ _RDY is the time when T _SNR (t) ≧ T _CNT1 actually holds.

As described above, the above T _CNT2 (t) is obtained when the sensor temperature T _SNR (t) reaches the control temperature set by _obtaining T _CNT1 by the above equation (1) at the start of control (t =
After t ′ _RDY ), the control temperature is used as a starting point and the temperature gradually increases as time approaches the target temperature T _CNT of the heating roller (3). When t → ∞, it becomes equal to T _CNT. , This T _CNT is the end point. Further, this T _CNT2 (t) may also be a discrete value or another formula that can be approximated, and is discrete in this embodiment in which CPU calculation is performed.

At the stage after the time t ′ _{RDY when the} sensor temperature T _SNR (t) actually reaches T _CNT1 , the time-varying T changes as described above.
_CNT2 (t) is used as a control temperature, and T _SNR (t) is used as a reference.
It is determined whether or not ≧ T _CNT2 (t), the heater (2) is controlled, the T _CNT2 (t) is calculated again by the equation (2), and the heater (2) is controlled according to the result. The above cycle is repeated, and so on.

In this way, T _CNT1 , T given by the conditions of the above equations (1) and (2) according to each stage after the start of control.
When it is higher than _CNT2 (t), the heater (2) is turned off, and when it is lower than _CNT2 (t), the heater (2) is turned off.

In the apparatus of the above-described embodiment, when the temperature of the heating roller (3) is detected by the sensor and the temperature of the heating roller (3) is controlled by the feedback, the initial temperature lower than the target control temperature according to the temperature at the start of control. The control temperature is set, and further, after the sensor detected temperature reaches the initial control temperature, an intermediate control temperature located between the initial control temperature and the target control temperature of the heating roller (3) is set, This intermediate control temperature is gradually increased with the passage of time so as to approach the target control temperature.

That is, in this embodiment, the control temperature is not immediately set to the target value of the roller temperature from the start of the control, and even in the case of the control after the elapse of t ′ _RDY , it is not fixed to T _CNT but the above (2 ) The control is performed based on the control temperature that changes with time as shown in the equation.

Therefore, in the case of the control by the conventional method shown in FIG. 5, there is a large overshoot when the control is started, and the sensor temperature T _SNR (t) is the roller temperature T _ROLL (t from the control start time. ) Is equal to the constant target value of T _CNT when the roller temperature T _ROLL (t) is far above T _CNT and reaches a temperature near the peak of overshoot, and Even after that, considerable undershoot and overshoot occur, but as shown in FIG. 4, even if the heating rate a of the heating roller (3) is high, a small control of overshoot can be performed. . Even if the control start temperature changes, T _CNT1 is calculated from the temperature of the sensor after the start of control (this is also the temperature of the heating roller at that time), so when T _SNR (t) ≧ T _CNT1 The roller surface temperature of is almost in agreement with the control target of the roller, T _CNT ,
There is no risk of hot offset or unfixed. Moreover, after reaching T _CNT1 , the target control temperature is gradually increased and the control is performed based on T _CNT2 , so that the subsequent undershoot and overshoot can be greatly reduced as compared with the conventional case.

〔The invention's effect〕

As described above, according to the present invention, the initial control temperature that predicts the response delay of the sensor is set, and when the sensor detection temperature reaches the initial control temperature, the intermediate control temperature of the heated object is gradually increased. Since the temperature is close to the target control temperature, a large overshoot due to the response delay of the temperature detection sensor that occurs at the start of control can be avoided even if the rate of temperature rise of the heated object is fast, and the occurrence of offset and warm-up. Not only can the phenomenon of time delay be effectively prevented, but the overshoot at the start of control can be suppressed to a small extent, and the undershoot and overshoot after that can be greatly reduced.

Further, according to the present invention, since it is not necessary to control the phase of the electric power supplied to the heat source of the object to be heated, a special control circuit for performing the phase control is not required, and the device configuration becomes unnecessarily complicated. There is no concern.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a circuit configuration of an embodiment apparatus to which the present invention is applied, FIG. 2 is an external view of a heating roller portion whose temperature is detected by its sensor, and FIG. An example flowchart, FIG. 4 is a characteristic diagram showing changes in roller temperature, sensor temperature, and control target in that case,
FIG. 5 is a characteristic diagram of control by the conventional method. [Explanation of symbols] (1) ... Thermistor, (2) ... Heater (3) ... Heating roller, (5) ... Central processing unit

Claims (1)

[Claims] 1. A sensor detects the temperature of an object to be heated which is heated by a heat source. If the temperature detected by the sensor is lower than a control temperature, the heat source is turned on, while the temperature detected by the sensor is equal to or higher than the control temperature. For example, in the temperature control method of turning off the heat source and performing feedback control so that the temperature of the heated object becomes the control temperature, the temperature is lower than the target control temperature of the heated object according to the sensor detection temperature at the start of the control. The initial control temperature is set as the control temperature, and when the sensor detection temperature reaches the initial control temperature, the intermediate control temperature located between the initial control temperature and the target control temperature is set as the control temperature. A temperature control method characterized in that the intermediate control temperature is gradually made to approach the target control temperature with the passage of time.