Patent Description:
In the related art, a method for detecting a failure in a feedback system on the basis of an actual temperature measurement value in a temperature control loop and a temperature prediction value predicted using a model has been proposed as a technology for detecting a failure in a heating device. For example, Patent Literature <NUM> discloses a method of determining a state of a control target with reference to a behavior in a control transient state, a representative example of which is a step response.

<CIT> discloses a heating device that includes a heater configured to heat an item to be heated, a temperature detection unit configured to detect a temperature of the item to be heated, and a temperature adjustment unit configured to control the heater on the basis of a detected value of the temperature detection unit and a target temperature so that the temperature of the item to be heated reaches the target temperature, the heating device comprising: a system gain rate calculation unit configured to obtain a temperature increase value of the item to be heated from the detected value of the temperature detection unit, and obtain a system gain, which is a ratio of the temperature increase value of the item to be heated with respect to electric power inputted to the heater.

According to a method for determining a state of a control target on the basis of a behavior of a feedback system when a transient state is caused to occur as disclosed in Patent Literature <NUM>, it is not possible to detect how much the respective changes related to heat-retaining properties of an item to be heated have occurred.

Thus, an objective of the invention is to provide a heating device and a failure detecting method of a heating device capable of detecting a change related to heat-retaining properties of an item to be heated.

As an example of the disclosure, there is provided a heating device that includes a heater configured to heat an item to be heated, a temperature detection unit configured to detect a temperature of the item to be heated, and a temperature adjustment unit configured to control the heater on the basis of a detected value of the temperature detection unit and a target temperature so that the temperature of the item to be heated reaches the target temperature, the heating device including; a system gain change rate calculation unit configured to obtain a temperature increase value of the item to be heated from the detected value of the temperature detection unit, obtain a system gain, which is a ratio of the temperature increase value of the item to be heated with respect to electric power inputted to the heater, and obtain, as a system gain change rate, a rate of change from an initial value of the system gain; and a heat-retaining property change rate calculation unit configured to obtain a rate of change in heat-retaining properties of the item to be heated from the system gain change rate.

With this configuration, it is possible to detect a change related to heat-retaining properties of the item to be heated.

Also, in the example of the disclosure, the heating device further includes: a heater resistance value change rate calculation unit configured to obtain a resistance value of the heater from a voltage and a current applied to the heater and obtain, as a heater resistance value change rate, a rate of change from an initial value of the resistance value, and the heat-retaining property change rate calculation unit obtains the rate of change in heat-retaining properties of the item to be heated from the system gain change rate and the heater resistance value change rate.

With this configuration. it is possible to detect deterioration of the heater in the heating device and a change related to heat-retaining properties of the item to be heated.

In addition, in the example of the disclosure, the heating device further includes: a heater voltage change rate calculation unit configured to obtain, as a heater voltage change rate, a rate of change from an initial value of a voltage applied to the heater, and the heat-retaining property change rate calculation unit obtains the rate of change in heat-retaining properties of the item to be heated from the system gain change rate and the heater voltage change rate.

With this configuration, it is possible to detect a variation in voltage applied to the heater and a change related to heat-retaining properties of the item to be heated.

Also, in the example of the disclosure, the heating device further includes: a heater voltage change rate calculation unit configured to obtain, as a heater voltage change rate, a rate of change from an initial value of a voltage applied to the heater, and the heat-retaining property change rate calculation unit obtains the rate of change in heat-retaining properties of the item to be heated from the system gain change rate, the heater resistance value change rate, and the heater voltage change rate.

With this configuration, it is possible to detect deterioration of the heater in the heating device, a variation in voltage applied to the heater, and a change related to heat-retaining properties of the item to be heated.

Also, in the example of the disclosure, the heating device further includes: a heat-retaining property failure detection unit configured to detect a failure in the heat-retaining properties by comparing the heat-retaining property change rate with a threshold for the heat-retaining property change rate. With this configuration, it is possible to detect a failure related to heat-retaining properties of the item to be heated.

Also, in the example of the disclosure, the heating device further includes: a heater resistance value failure detection unit configured to detect a failure in the resistance value of the heater by comparing the heater resistance value change rate with a threshold value for the heater resistance value change rate. With this configuration, it is possible to detect a failure in the resistance value of the heater.

Also, in the example of the disclosure, the heating device further includes: a heater voltage failure detection unit configured to detect a failure in the voltage applied to the heater by comparing the heater voltage change rate with a threshold value for the heater voltage change rate. With this configuration, it is possible to detect a failure in voltage applied to the heater.

Also, according to an example of the disclosure, there is provided a failure detecting method of a heating device that includes a heater configured to heat an item to be heated, a temperature detection unit configured to detect a temperature of the item to be heated, and a temperature adjustment unit configured to control the heater on the basis of a detected value of the temperature detection unit and a target temperature so that the temperature of the item to be heated reaches the target temperature, the failure detecting method including: obtaining a temperature increase value of the item to be heated from the detected value of the temperature detection unit, obtaining a system gain, which is a ratio of the temperature increase value of the item to be heated with respect to electric power inputted to the heater, and obtaining, as a system gain change rate, a rate of change from an initial value of the system gain; and obtaining a rate of change in heat-retaining properties of the item to be heated from the system gain change rate and detecting a failure in the heating device depending on whether or not the rate of change in heat-retaining properties exceeds a threshold value.

With this configuration, it is possible to detect a change related to heat-retaining properties of the item to be heated and a failure in heating device.

According to the invention, it is possible to detect a change related to heat-retaining properties of the item to be heated.

Hereinafter, an embodiment for carrying out the invention will be described with reference to some drawings.

First, an example to which the invention is applied will be described with reference to <FIG> is a diagram illustrating a configuration of a heating device <NUM> according to an embodiment of the invention.

As illustrated in <FIG>, the heating device <NUM> according to the embodiment includes a heater <NUM> configured to heat an item to be heated <NUM>, a temperature detection unit <NUM> configured to detect a temperature of the item to be heated <NUM>, and a temperature adjustment unit <NUM> configured to control the heater <NUM> such that the temperature of the item to be heated <NUM> reaches a target temperature on the basis of a detected value of the temperature detection unit <NUM> and the target temperature.

The temperature adjustment unit <NUM> includes a system gain change rate calculation unit, a heater resistance value change rate calculation unit, a heater voltage change rate calculation unit, and a heat-retaining property change rate calculation unit. The system gain change rate calculation unit obtains a temperature increase value of the item to be heated <NUM> from the detected value of the temperature detection unit <NUM>, obtains a system gain, which is a ratio of the temperature increase value of the item to be heated <NUM> with respect to electric power inputted to the heater <NUM>, and obtains a rate of change from an initial value of the system gain. The heater resistance value change rate calculation unit obtains a resistance value of the heater <NUM> from a voltage and a current applied to the heater <NUM> and obtains a rate of change from an initial value of the resistance value. The heater voltage change rate calculation unit obtains a rate of change in voltage applied to the heater <NUM> from an initial value thereof. Also, the heat-retaining property change rate calculation unit obtains a rate of change in heat-retaining properties of the item to be heated from the system gain change rate, the heater resistance value change rate, and the heater voltage change rate.

Next, a configuration of the heating device according to the embodiment of the invention will be described with reference to the drawing. As described above, <FIG> is a diagram illustrating a configuration of the heating device <NUM> according to the embodiment of the invention.

As represented in <FIG>, the heating device <NUM> includes the heater <NUM> configured to heat the item to be heated <NUM>, the temperature detection unit <NUM> configured to detect the temperature of the item to be heated <NUM>, the temperature adjustment unit <NUM> configured to control the heater <NUM> on the basis of the detected value of the temperature detection unit <NUM> and the target temperature, a solid state switch <NUM>, a heater power supply <NUM>, a voltage detection unit <NUM> configured to detect a voltage applied to the heater, and a current detection unit <NUM> configured to detect a current flowing through the heater <NUM>. The item to be heated <NUM> is a molded article of metal or the like. Since <FIG> is a block configuration diagram and the item to be heated <NUM> is conceptually illustrated, an actual shape thereof is appropriately defined.

The item to be heated <NUM> is a heating unit of a packaging machine configured to heat a resin and package an article, for example. The heater <NUM> and the temperature detection unit <NUM> are provided in the heating unit.

The temperature adjustment unit <NUM> includes a voltage-temperature conversion unit <NUM> configured to convert a voltage output from the temperature detection unit <NUM> into a temperature information signal, an operation amount-PWM conversion unit <NUM> configured to perform PWM control on the solid state switch <NUM>, and an operation amount conversion unit <NUM>. The operation amount conversion unit <NUM> is a PID controller and obtains the amount of operation through PID control on the basis of temperature information and target temperature information obtained by the voltage-temperature conversion unit <NUM>.

In addition, the operation amount conversion unit <NUM> performs an arithmetic operation as the system gain change rate calculation unit, an arithmetic operation as the heater resistance value change rate calculation unit, an arithmetic operation as the heater voltage change rate calculation unit, and an arithmetic operation as the heat-retaining property change rate calculation unit. These arithmetic operations will be described in detail below.

(A) of <FIG> is a sectional view illustrating a configuration inside the heater <NUM>. The heater <NUM> is configured of an insulating body 10i and a coil-shaped heat generating resistance wire 10r incorporated in the insulating body 10i. Although the heat generating resistance wire 10r is covered with the insulating body 10i in an initial state as illustrated in (B) of <FIG>, an oxide film 10f forms on the surface of the heat generating resistance wire 10r as illustrated in (C) of <FIG> due to aging, and a diameter of a power distribution part of the heat generating resistance wire 10r becomes thinner in accordance with the aging. If the oxide film 10f becomes thicker due to such aging, and the power distribution part of the heat generating resistance wire 10r becomes thinner, disconnection may eventually occur.

As illustrated in <FIG>, a heater resistance value of the heater <NUM> varies due to aging. In other words, a rate of change from an initial state gradually changes. In addition, the system gain also varies due to a change in resistance value of the heater <NUM>.

<FIG> are sectional views illustrating an example of "loosening" of the heater <NUM> and the like configured to heat the item to be heated <NUM>. In a normal situation, the heater (band heater) <NUM> is wound around an outer periphery of the item to be heated <NUM> in a close contact state as illustrated in (A) of <FIG>. Also, the outer periphery of the heater <NUM> is covered with a cover 10c that covers the heater <NUM>. (B) of <FIG> is an example of a failure in which a gap is generated between the outer periphery of the item to be heated <NUM> and the heater <NUM> and a gap is also generated between the heater <NUM> and the cover 10c.

In this manner, the system gain, which will be described later, varies due to a change "loosening" in an attachment state of the heater <NUM> and an attachment state of the cover. In other words, the system gain may vary from the initial state with utilization of the heating device.

<FIG> are sectional views illustrating an example of "loosening" of a sleeve that covers the temperature detection unit <NUM>. The temperature detection unit <NUM> is, for example, a thermocouple. In a normal situation, a leading end of the temperature detection unit <NUM> is in close contact with a sleeve <NUM> as illustrated in <FIG> is an example of a failure in which a gap is generated between the leading end of the temperature detection unit <NUM> and the sleeve <NUM>.

In this manner, the system gain, which will be described later, varies due to a change "loosening" in a state of an attachment portion of the temperature detection unit <NUM>. In other words, the system gain may vary from the initial state with utilization of the heating device.

<FIG> is a diagram illustrating an example of a change in temperature of the item to be heated <NUM>, and a change in the amount of operation of the heater <NUM> with elapse of time. The temperature of the item to be heated <NUM> rises from an ordinary temperature (initial temperature) to a target temperature (stable temperature) with elapse of time. Meanwhile, the amount of operation of the heater <NUM> starts from <NUM>%, decreases with elapse of time, and stabilizes at a stable amount of operation.

Here, if (the target temperature - ordinary temperature) is represented as ΔPV, and the stable amount of operation is represented as MV, a system gain K is represented by the following equation since the system gain is a ratio of the temperature increase value of the item to be heated <NUM> with respect to the electric power inputted to the heater <NUM>.

<FIG> is a block diagram illustrating details of an arithmetic operation performed as the system gain change rate calculation unit, an arithmetic operation performed as the heater resistance value change rate calculation unit, an arithmetic operation performed as the heater voltage change rate calculation unit, and an arithmetic operation performed as the heat-retaining property change rate calculation unit.

Here, if the gain related to a heat transmission coefficient between the item to be heated <NUM> and the temperature detection unit <NUM> is represented as B, the voltage applied to the heater <NUM> is represented as V, and the resistance value of the heater <NUM> is represented as R, the system gain K is also represented by the following equation.

The resistance value R of the heater <NUM> is obtained by <MAT> where the heater voltage is represented as V, and the heater current is represented as i.

If the system gain at a timing at which the system gain change rate is obtained is represented as K', the rate of change in gain related to the heat transmission coefficient between the item to be heated <NUM> and the temperature detection unit <NUM> is represented as a, the rate of change in heater voltage is represented as b, and the rate of change in heater resistance value is represented as c, the system gain K' after a variation is represented by the following equation.

Also, if the initial system gain is represented as K, and the system gain at the timing at which the system gain change rate is obtained is represented as K', the system gain change rate d is represented by the following equation.

In addition, it is possible to state that the rate of change a in the gain related to the heat transmission coefficient between the item to be heated <NUM> and the temperature detection unit <NUM> is a rate of change in heat-retaining properties of the item to be heated <NUM>. Therefore, it is possible to obtain the rate of change a in heat-retaining properties using the following equation.

An arithmetic operation performed by the operation amount conversion unit <NUM> illustrated in <FIG> as the heater resistance value change rate calculation unit is as follows.

If an initial resistance value of the heater <NUM> is represented as R, and a resistance value at a timing at which the heater resistance value change rate is obtained is represented as R', the heater resistance value change rate calculation unit obtains the heater resistance value change rate c using the following equation.

In addition, an arithmetic operation performed as the heater voltage change rate calculation unit is as follows.

If an initial voltage applied to the heater <NUM> is represented as V, and a voltage at the timing at which the heater voltage change rate is obtained is represented as V', the heater voltage change rate calculation unit obtains the heater voltage change rate b using the following equation.

In addition, the rate of change a in heat-retaining properties is obtained from the system gain change rate d, the heater resistance value change rate c, and the heater voltage change rate b.

As illustrated in <FIG>, it is possible to recognize that if d = <NUM>, c = <NUM>, and b = <NUM>, for example, the rate of change a in heat-retaining properties is <NUM>, that is, a state in which the heat-retaining properties have dropped by <NUM>% has been achieved.

<FIG> is a diagram illustrating a combination of abnormal states of the heating device <NUM>. Since there are three failures, namely a failure in the resistance value of the heater <NUM>, a failure in heater voltage, and a failure in heat-retaining properties of the item to be heated, in the heating device <NUM>, there are seven combinations of abnormal states.

The resistance value of the heater <NUM> is regarded as being "abnormal" in a state in which the heater resistance value change rate c exceeds a predetermined threshold. When c > <NUM>, for example, the heater resistance value is regarded as being abnormal.

Also, the heater voltage is regarded as being "abnormal" in a state in which the heater voltage change rate b exceeds a predetermined threshold value. For example, the heater voltage is regarded as being abnormal when b < <NUM> or b > <NUM>.

Also, the heat-retaining properties are regarded as being "abnormal" in a state in which the rate of change a in heat-retaining properties exceeds a predetermined threshold value. For example, the heat-retaining properties are regarded as being abnormal when a < <NUM>.

In this manner, any of the abnormal states can individually be detected.

Also, there is a concern that in a case in which properties (system gain) of the heating device, that is, the heater voltage, the heater resistance value, the heat-retaining properties, and the like have varied, temperature control performance may be degraded due to the variations. However, in a state in which the given heater voltage change rate, the heater resistance value change rate, and the rate of change in heat-retaining properties are small, it is possible to maintain the temperature control performance by calculating a proportional band (P in PID control) again from the new heater voltage, heater resistance value, and heat-retaining properties.

Claim 1:
A heating device (<NUM>) that includes a heater (<NUM>) configured to heat an item to be heated (<NUM>), a temperature detection unit (<NUM>) configured to detect a temperature of the item to be heated (<NUM>), and a temperature adjustment unit (<NUM>) configured to control the heater (<NUM>) on the basis of a detected value of the temperature detection unit (<NUM>) and a target temperature so that the temperature of the item to be heated (<NUM>) reaches the target temperature, the heating device (<NUM>) comprising:
a system gain change rate calculation unit configured to obtain a temperature increase value of the item to be heated (<NUM>) from the detected value of the temperature detection unit (<NUM>), obtain a system gain, which is a ratio of the temperature increase value of the item to be heated (<NUM>) with respect to electric power inputted to the heater (<NUM>), and obtain, as a system gain change rate, a rate of change from an initial value of the system gain;
a heater resistance value change rate calculation unit configured to obtain a resistance value of the heater (<NUM>) from a voltage and a current applied to the heater (<NUM>) and obtain, as a heater resistance value change rate "c", a rate of change from an initial value of the resistance value;
a heater voltage change rate calculation unit configured to obtain, as a heater voltage change rate "b", a rate of change from an initial value of a voltage applied to the heater (<NUM>); and
a heat-retaining property change rate calculation unit configured to obtain a rate of change rate "a" in heat-retaining properties of the item to be heated (<NUM>) from the system gain change rate "d", the heater resistance value change rate "c", and the heater voltage change rate "b", wherein the rate of change "a" in heat-retaining properties is obtained using the following equation: a=cd/b<NUM>.