JP6888202B2 - Temperature control device - Google Patents

Description

The present invention relates to a temperature control device capable of detecting an abnormality such as a disconnection of a controlled object. The “controlled object” refers to an object of temperature control (for example, resin in an injection molding machine, etc.), and in the following, a heater or the like for controlling the temperature of the controlled object is also included.

In temperature control using PID control or the like, anomalies such as a disconnection state of a heater or the like are detected from the viewpoint of accident prevention (hereinafter, also referred to as "disconnection alarm detection" or "abnormality alarm detection"). .. Hereinafter, as an example of the abnormality alarm, a disconnection alarm in the on / off control will be described as an example. Here, the disconnection alarm means that if the temperature control device outputs control on but no current is flowing through the heater or the like, it is determined that the wire is disconnected and the control is turned off. If a current is flowing through the heater or the like in spite of this, it indicates an alarm that determines that the operation device is out of order such as welding. Hereinafter, the case of disconnection will be described as an example.

The disconnection alarm is determined by capturing the value of the signal to be determined for a certain period of time. As described above, the disconnection is determined by whether or not the current value (which should be on) is off for a certain period of time. Therefore, when the current value to be determined is switched from on to off due to switching of the control cycle or the like, the current value during that period cannot be used for the output of the disconnection alarm.

Further, it is known that when the control output is switched, it takes a certain time (delay time) until the current to be determined is actually switched by the actuator or the like. Therefore, in order to determine the disconnection alarm, it is necessary to take in the current value after the above-mentioned delay time has elapsed.

The above delay time varies depending on the device configuration of the control system and the like. Therefore, in the actual operation of the temperature control device, in order to improve the generalization, the current value is taken in after a certain time has elapsed in the above delay time. Therefore, in order to judge the disconnection alarm, the above-mentioned delay time + fixed time + on-time for the period for determining the disconnection alarm is required (hereinafter, also referred to as "time required for determining the disconnection alarm"). ).

However, in recent years, in heater control of injection molding machines and the like, temperature control with a light load factor such as a large heater capacity and a low set temperature has been increasing. In the case of such a light load factor temperature control, the on time is shorter than that of the normal temperature control. Therefore, the time required for determining the disconnection alarm cannot be satisfied (the period during which the control is turned on is too short), and the disconnection alarm cannot be detected.

Such a case can be dealt with by extending the control cycle. By expanding the control cycle, if the on-time in the control cycle satisfies the time required for determining the disconnection alarm, the disconnection alarm can be detected. However, since unnecessary extension of the control cycle causes deterioration of controllability, it is desired to suppress the extension of the control cycle to the minimum necessary. However, as described above, it is difficult to minimize the period expansion because the time required for determining the disconnection alarm changes depending on the control system.

Under such a situation, in the actual operation of the temperature control device, after the auto-tuning of the PID parameter of the PID control is executed, first, it is verified whether or not the disconnection alarm can be detected manually. If the disconnection alarm cannot be detected, the control cycle is manually extended based on the empirical rule of the setter.
When constructing a control system incorporating a disconnection alarm, it is necessary to perform the setting manually in this way. Therefore, from the viewpoint of work complexity and controllability, automation of the setting is desired. In particular, it is desired that it is automatically set at the time of auto tuning.

As a general PID auto-tuning method, for example, Patent Document 1 can be mentioned.

Japanese Unexamined Patent Publication No. 04-291601

However, although Patent Document 1 describes that the PID parameter is automatically set by using the limit cycle method, the control cycle for enabling the detection of the disconnection alarm is automatically determined as described above. This point is not disclosed.

In view of the above points, it is an object of the present invention to provide a temperature control device capable of automatically determining a control cycle in which a disconnection alarm can be detected while maintaining controllability.

(Structure 1)
It is a temperature control device that controls the on / off control of the actuator based on the load factor and controls the temperature of the controlled object.
The lower limit of the control cycle in which the abnormality can be detected is calculated based on the value obtained by dividing the lower limit of the signal acquisition time required for detecting the abnormality of the control target by the load factor.
A temperature control device including a periodic calculation unit.

(Structure 2)
The periodic calculation unit
The configuration 1 is characterized in that the lower limit value of the control cycle in which the abnormality can be detected is calculated based on the value obtained by dividing the lower limit value of the signal acquisition time by the load factor and the delay time in the actuator. The temperature control device according to.

(Structure 3)
The periodic calculation unit
Configuration 1 or configuration 1, characterized in that the shorter of the on period and the off period in the preset control cycle is determined, and the lower limit value of the control cycle in which the abnormality can be detected is calculated based on the determination result. 2. The temperature control device according to 2.

(Structure 4)
The periodic calculation unit
The control cycle preset for the temperature control device is compared with the lower limit of the control cycle in which the abnormality can be detected.
When the control cycle is less than the lower limit of the control cycle in which the abnormality can be detected,
The temperature control device according to any one of configurations 1 to 3, wherein a value equal to or higher than the lower limit value of the control cycle for detecting the abnormality is set as a new control cycle.

According to the present invention, it is possible to automatically determine a control cycle in which a disconnection alarm can be detected while maintaining controllability.

It is a schematic block diagram which shows the temperature control apparatus of embodiment which concerns on this invention. It is a conceptual diagram which shows the relationship between an output state and a CT input value. It is a conceptual diagram which shows the relationship between an output state and a CT input value which shows an example of the case where a disconnection alarm cannot be detected. It is a flowchart explaining the operation of the temperature control apparatus of embodiment which concerns on this invention.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings.

<Embodiment>
FIG. 1 is a schematic configuration diagram showing a portion of a temperature controller according to an embodiment of the present invention according to the present invention.
The temperature control device 100 controls the on / off of the controller 120 based on the input value (PV), the target value (SV), and the PID parameter from the sensor (not shown) that measures the temperature of the control target 130, thereby controlling the control target. It is a device that controls the temperature of 130.

Further, the auto-tuning device 140 automatically sets PID parameters and the like based on the target control system (control target 130) and the preset target value (SV) before the start of control (at the time of initial operation, etc.) (hereinafter, "" It is also referred to as "AT").

The temperature control device 100 controls the temperature of the control target 130 based on the input PV so that the temperature of the control target 130 itself or the temperature of the target to be temperature controlled by the control target 130 becomes a set target value SV. It is configured to output an on / off control signal to the target device directly or via another device. Further, the temperature control device 100 includes a periodic calculation unit 110.

The cycle calculation unit 110 has a function of calculating a control cycle so that a disconnection alarm can be acquired based on the value of the load factor input at the time of AT, and resetting the control cycle according to the calculated control cycle. The periodic calculation unit 110 is composed of a microcomputer or the like.

The actuator 120 has a function of switching according to a control output from the periodic calculation unit 110, and is composed of an SSR and a mechanical relay. The control target 130 is a target for controlling the temperature based on the operation of the actuator 120, and is composed of a heater and the like. The signal acquisition for detecting an abnormality alarm such as a disconnection alarm is performed by a CT (current transformer, not shown) or the like arranged on the wiring of the control target 130.

FIG. 2 is a conceptual diagram showing the relationship between the output from the temperature control device 100 to the actuator 120 and the signal captured by the CT (current transformer). An example is shown in which CT acquisition is started after a delay time has elapsed from the start of the control cycle.
In the case of 1 in FIG. 2, since the control output is on, if the value taken from the CT is below the preset threshold value (when no current is flowing), the wire is broken. Is judged.
In the case of 2 in FIG. 2, since the control output is switched during the acquisition time, it cannot be used for the disconnection alarm.
In the case of 3 in FIG. 2, since the control output is off, when the value taken from the CT exceeds the preset threshold value (when current is flowing), the actuator, etc. It is judged that it is a failure of.

Note that FIG. 3 is a diagram showing an example of a control output at the time of a light load. In this case, since the on period during the control cycle is too short, the minimum acquisition time for detecting the disconnection alarm cannot be satisfied. Therefore, on / off switching always occurs during the capture time, and the disconnection alarm cannot be detected.

<Operation>
Next, the operation of the periodic calculation unit 110 in the embodiment will be described with reference to the flowchart of FIG.

First, in step S100, the auto-tuning device 140 inputs the PID parameter calculated based on the limit cycle method or the like to the temperature control device 100.

Next, in step S110, the control cycle (lower limit value) for calculating the disconnection alarm is calculated based on the input load factor. The operation in step S110 will be described below. First, the load factor (θ [%]) at the input target value is calculated by the following formula.

ここで、オン時間（オン期間）とは、制御周期のうち出力がオンとなっている時間を表す。なお、オフ時間（オフ期間）とは、制御周期のうち出力がオフとなっている時間を表す。

Here, the on-time (on-period) represents the time during which the output is on in the control cycle. The off time (off period) represents the time during which the output is off in the control cycle.

Then, the minimum current intake time required to detect the disconnection alarm, which is set in advance, is set to tmin. As described above, in order to detect the disconnection alarm, it is necessary that the target signal is continuously turned on for at least tmin.
In the on / off control, the above load factor represents the ratio of turning on during the control cycle, that is, the time of turning on. Therefore, in order to detect the disconnection alarm, it is sufficient that the signal is continuously turned on for at least tmin during the control cycle. Therefore, tmin and the minimum control cycle Tmin for detecting the disconnection alarm are required. The relationship with is expressed as follows.

In addition, in order to calculate the control cycle Tmin more accurately, the cycle calculation unit 110 may calculate the control cycle Tmin in consideration of the delay time td. The delay time is a fixed time that occurs until the switching operation of the actuator or the like is completed when the control output is switched and the current to be determined is actually switched.
When Tmin is calculated in consideration of the delay time td in this way, the minimum control cycle Tmin for detecting the disconnection alarm is calculated as follows.

このように、断線警報が検出可能となる制御周期の下限値であるＴminは、数２又は数３のように算出することができる。なお、遅れ時間を考慮してＴminを算出するかどうかは、温度制御装置１００に事前に設定されていてもよいし、スイッチ等により動作を切換えるように構成されていてもよい。

In this way, Tmin, which is the lower limit of the control cycle in which the disconnection alarm can be detected, can be calculated as in Equation 2 or Equation 3. Whether or not to calculate Tmin in consideration of the delay time may be set in advance in the temperature control device 100, or may be configured to switch the operation by a switch or the like.

Up to this point, the case of detecting a disconnection alarm has been described as an example, but the cycle calculation unit 110 is configured to calculate the lower limit value of the control cycle that enables detection of welding determination (malfunction of the operating device, etc.). You may. When making a welding judgment, it is judged that a failure such as welding has occurred when the signal that should have been turned off is on. Therefore, as with the disconnection alarm, a time required for the disconnection alarm to be continuously turned off for a certain period of time is required.
In this case, the control cycle Toffmin may be calculated in the same manner as in Equation 2 or 3 above, with the preset current take-in time required for detecting the welding determination as toffmin.
The threshold value for determining whether a current is flowing or not when making a disconnection determination or a welding determination may be set in advance or is input by an input device (not shown) or the like. It may be configured to be.

Further, the cycle calculation unit 110 determines the shorter of the on period and the off period of the control cycle from the value of the load factor θ and the like, and switches whether to calculate Tmin or Toffmin from the determination result. It may be configured as follows. If the on period is shorter, the minimum control cycle Tmin for detecting a disconnection alarm is calculated, and if the off period is shorter, the minimum control cycle Toffmin for detecting welding judgment is calculated. ..
The temperature control device 100 may be preset to calculate only Tmin, may be preset to calculate only Toffmin, or select Tmin and Toffmin according to the function. It may be set to calculate.
Hereinafter, the lower limit value of the control cycle calculated in step S110 is also referred to as a “calculated control cycle”.

In this way, in step S110, the lower limit value Tmin of the control cycle for detecting the disconnection alarm was calculated. Next, in step S120, the currently set (input) control cycle is compared with Tmin, which is the control cycle calculated in step S110, and the current control cycle is less than the calculated control cycle. If so, the process proceeds to step S130 (step S120: Yes → step S130). On the other hand, if the current control cycle is equal to or longer than the calculated control cycle, the process ends (step S120: No → end).

Finally, in step S130, the control cycle is set to the calculated control cycle, and the process (auto tuning) is completed. The control cycle newly set here may be a cycle equal to or longer than the control cycle calculated in step S110.

<Effect of each configuration>
As described above, according to the temperature control device 100 of the first embodiment, the cycle calculation unit 110 can automatically calculate the lower limit value of the control cycle in which the disconnection alarm can be detected. Therefore, it is possible to automatically determine the control cycle in which the disconnection alarm can be detected while maintaining the controllability.

Further, the cycle calculation unit 110 is configured to be able to calculate the lower limit value of the control cycle in which the disconnection alarm can be detected in consideration of the preset delay time. Therefore, it is possible to automatically determine the control cycle in which the disconnection alarm can be detected, which has higher controllability.

Further, the cycle calculation unit 110 is configured to be able to calculate the lower limit value of the control cycle in which the abnormality alarm can be detected based on the shorter of the on period and the off period obtained based on the load factor. Therefore, it is possible to automatically calculate the lower limit value of the control cycle in which both the disconnection alarm and the welding judgment can be detected in the control system.

Further, the cycle calculation unit 110 compares the current control cycle with the calculated control cycle, and if the current control cycle is less than the calculated control cycle, it is equal to or greater than the lower limit of the calculated control cycle. The value of is configured to be set as a new control cycle. Therefore, the control cycle in which the disconnection alarm can be detected can be automatically set.

In the present embodiment, an example in which the calculation of the control cycle capable of detecting the disconnection alarm and the resetting of the control cycle are performed during auto-tuning has been described, but it is configured to be performed separately from auto-tuning. You may.
Further, the cycle calculation unit 110 is configured to perform a disconnection alarm or a welding determination based on the shorter of the on period and the off period of the currently set control cycle, but the operation is set in advance. (Either a disconnection alarm or a welding judgment) may be performed.

It should be noted that each configuration in each of the above embodiments may be configured in hardware by a dedicated circuit or the like, or may be realized by software on a general-purpose circuit such as a microcomputer. Good.

Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above-described embodiments. Various changes that can be understood by those skilled in the art can be made to the structure and operation of the present invention without departing from the spirit of the present invention.

100 ... Temperature control device 110 ... Periodic calculation unit 120 ... Operator 130 ... Control target 140 ... Auto tuning device

Claims (2)

It is a temperature control device that controls the on / off control of the actuator based on the load factor and controls the temperature of the controlled object, and is equipped with a periodic calculation unit.
During the auto-tuning process that automatically sets PID parameters, etc.
The periodic calculation unit
When the temperature control device is not set to consider the delay time in the controller, the lower limit value of the signal acquisition time required to detect the abnormality of the control target is input from the auto-tuning device. The value divided by the load factor is set as the lower limit of the control cycle in which the abnormality can be detected, and the value is set.
When the temperature control device is set to take into account the delay time in the actuator, the value obtained by dividing the lower limit of the signal acquisition time by the load factor input from the auto-tuning device and the delay time. The value obtained by adding and is set as the lower limit value of the control cycle in which the abnormality can be detected .
The control cycle preset for the temperature control device is compared with the lower limit of the control cycle in which the abnormality can be detected.
When the control cycle is less than the lower limit of the control cycle in which the abnormality can be detected,
A temperature control device characterized in that a value equal to or higher than the lower limit value of the control cycle for detecting the abnormality is set as a new control cycle. The periodic calculation unit
Claim 1 is characterized in that the shorter of the on period and the off period in the preset control cycle is determined, and the lower limit value of the control cycle in which the abnormality can be detected is calculated based on the determination result. The temperature control device according to.

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