Temperature control device and temperature control method

Abstract

The objective is to easily achieve temperature control that is suited to the thermal characteristics of the controlled object, without requiring the complex parameter settings of PID control. [Solution] The temperature control device includes an acquisition unit that acquires the measured temperature of the controlled object for each control cycle, a calculation unit that calculates an manipulated variable for each control cycle so that the measured temperature reaches the target temperature, and an operation unit that operates a heating device that heats the controlled object according to the manipulated variable. The calculation unit includes a set temperature determination unit that determines a set temperature to be set as the target value for each control cycle based on the measured temperature, and an manipulated variable calculation unit that calculates an manipulated variable based on the deviation between the measured temperature and the set temperature. The set temperature determination unit determines whether the measured temperature for the current control cycle belongs to a first temperature range or to a second temperature range that is closer to the target temperature than the first temperature range, and determines the set temperature for the current control cycle using a different algorithm according to the determination result.

Description

Technical Field

[0001] The present invention relates to a temperature control device and a temperature control method.

Background Art

[0002] For temperature control of an electric furnace or the like, mainly PID control (Proportional-Integral-Differential Controller) is adopted. PID control is a control method in which three types, proportional control, integral control, and differential control, are combined. The proportional control related to temperature control is, for example, setting a proportional band of a predetermined value with the target temperature as the center value, controlling the operation amount to be 100% until the measured temperature enters the proportional band, and when the measured temperature exceeds the temperature of the proportional band, controlling the operation amount to be 0% to make the measured temperature reach the target temperature. As a problem of the proportional control, if the proportional band is made too small, an overshoot occurs where the measured temperature becomes too high compared to the target temperature. If the proportional band is made too large, it takes time for the measured temperature to reach the target temperature. Further, even if the measured temperature stabilizes near the target temperature, at a temperature close to the target temperature, the operation amount becomes too small, the measured temperature does not reach the target temperature, and an offset occurs.

[0003] The control method for eliminating this offset is integral control. By combining proportional control and integral control, the offset can be eliminated. On the other hand, when a large temperature change occurs due to a disturbance or the like after the measured temperature has stabilized, there is a problem that it cannot be dealt with only by the combination of proportional control and integral control. The control method for suppressing the influence of the disturbance and stabilizing the measured temperature is differential control. By combining proportional control and integral control with differential control, temperature control capable of coping with disturbances such as rapid temperature changes can be performed.

[0004] As mentioned above, while PID control itself is an excellent control method, it cannot provide optimal temperature control in all situations. Specifically, for example, when controlling a large-volume electric furnace (such as a muffle furnace), such a controlled object has thermal characteristics in which the measured temperature changes non-linearly with respect to the output of heating devices such as heaters. Therefore, when controlling the temperature of such a controlled object using PID control, a large time lag occurs before the measured temperature changes, or if the PID control parameters (proportional gain, differential gain, and integral gain) are not optimized, overshoot, offset, or hunting may occur, making it impossible to maintain the measured temperature at the target temperature. Furthermore, optimizing the PID control parameters themselves for such controlled objects is not easy in the first place.

[0005] Patent Document 1 is known as a technology related to temperature control of a controlled object having such thermal characteristics. Patent Document 1 discloses a physical quantity control algorithm that combines a skunk cauliflower type control algorithm and a PID control algorithm and is adapted to a wide range of controlled objects. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2010-257436 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the technology disclosed in Patent Document 1 requires the adoption of a complex control algorithm called the Zazenso-type control algorithm, and still necessitates the setting of complex parameters for PID control.

[0008] This invention has been made in view of the above circumstances, and aims to easily realize temperature control in a manner that is suitable for the thermal characteristics of the controlled object, without requiring the complex parameter setting of PID control. [Means for solving the problem]

[0009] To solve the aforementioned problems, the temperature control device of the present invention comprises: an acquisition unit that acquires the measured temperature of a controlled object at predetermined control cycles; a calculation unit that calculates an operation variable at each control cycle so that the measured temperature acquired by the acquisition unit reaches a target temperature; and an operation unit that operates a heating device for heating the controlled object according to the operation variable calculated by the calculation unit. The calculation unit includes a set temperature determination unit that determines a set temperature to be set as a target value for each control cycle based on the measured temperature acquired by the acquisition unit; and an operation variable calculation unit that calculates the operation variable based on the deviation between the measured temperature acquired by the acquisition unit and the set temperature determined by the set temperature determination unit. The set temperature determination unit determines whether the measured temperature for the current control cycle belongs to a first temperature range which includes the initial measured temperature, or to a second temperature range which includes the target temperature and is closer to the target temperature than the first temperature range, and determines the set temperature for the current control cycle using a different algorithm according to the determination result. [Effects of the Invention]

[0010] According to the present invention, temperature control that is suited to the thermal characteristics of the controlled object can be easily achieved without requiring the complex parameter settings of PID control. [Brief explanation of the drawing]

[0011] [Figure 1] A diagram showing a temperature control device and an electric furnace that constitutes the object to be controlled by the first embodiment. [Figure 2] Figure 1 shows the functional configuration of the temperature control device. [Figure 3] Figure 2 illustrates the set temperature determination unit. [Figure 4] Another diagram illustrating the set temperature determination unit shown in Figure 2. [Figure 5] A flowchart illustrating the temperature control method of the first embodiment. [Figure 6] A flowchart showing the details of the set temperature determination process, as shown in Figure 5. [Figure 7] A flowchart showing the details of the operation process, as shown in Figure 5. [Figure 8] This figure compares the results of temperature control of an electric furnace with a target temperature of 200°C, performed using this embodiment and the prior art. [Figure 9] This figure compares the results of temperature control of an electric furnace with a target temperature of 300°C, performed using this embodiment and the prior art. [Figure 10] This figure compares the results of temperature control of an electric furnace with a target temperature of 400°C, performed using this embodiment and the prior art. [Figure 11] A diagram showing the temperature profile obtained by temperature control of the temperature control device of the second embodiment. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described below with reference to the drawings. Components denoted by the same reference numerals in each embodiment are similar in each embodiment unless otherwise specified, and their descriptions will be omitted.

[0013] [First Embodiment] A first embodiment of the present invention will be described using Figures 1 to 10. First, the temperature control device 200 of the first embodiment will be described using Figures 1 to 4. Figure 1 is a diagram showing the temperature control device 200 of the first embodiment and the electric furnace 100 that constitutes its controlled object.

[0014] The electric furnace 100 consists of a door part 110 and a main body part 120. The door part 110 and the main body part 120 mainly include a housing 121 and heat insulation layers 122 and 123. The main body part 120 further includes a heating device 124 and a temperature sensor 125. A handle 111 is provided on the front side of the door part 110. The door part 110 is opened and closed using the handle 111. When the door part 110 is closed, the inside of the electric furnace 100 is sealed.

[0015] Due to its nature, the inside of the electric furnace 100 needs to be well insulated. Therefore, a heat insulation layer 122 where air exists is provided inside the housing 121 of the electric furnace 100, and a heat insulation layer 123 made of a heat insulating material is provided inside the heat insulation layer 122. A heating device 124 made of a heater or the like is embedded inside the heat insulation layer 123. In the case of a normal electric furnace 100, the heating device 124 is provided so as to be exposed inside the furnace, and in the case where the electric furnace 100 is a muffler furnace, the heating device 124 is provided without being exposed inside the furnace.

[0016] The housing 121 is mainly formed of a metal material. However, the housing 121 may be formed of any material as long as it meets the performance and safety requirements of the electric furnace 100. The heat insulating material constituting the heat insulation layer 123 is mainly formed of ceramic fiber (for example, alumina fiber). However, the heat insulating material constituting the heat insulation layer 123 may be formed of any material as long as it meets the performance and safety requirements of the electric furnace 100.

[0017] The heating device 124 heats the air existing in the accommodation space of the electric furnace 100 where the object to be heated in the electric furnace 100 is accommodated. The heating device 124 is operated according to an operation signal from a temperature control device 200 provided outside the electric furnace 100. The temperature sensor 125 measures the temperature of the air in the accommodation space and transmits the measurement result to the temperature control device 200. The temperature sensor 125 is constituted by, for example, a thermocouple type temperature sensor and transmits an electromotive force signal as the measurement result to the temperature control device 200. The thermocouple constituting the temperature sensor 125 is, for example, a Type R thermocouple (a thermocouple of a platinum rhodium alloy), etc. However, as long as the temperature sensor 125 can accurately measure the temperature of the air in the accommodation space, it may be constituted by any temperature sensor.

[0018] The temperature control device 200 receives the electromotive force signal from the temperature sensor 125 and converts it into digital data called the measured temperature. In the present embodiment, the control target of the temperature control device 200 is the electric furnace 100. More precisely, in the present embodiment, the control target of the temperature control device 200 is the air existing in the accommodation space of the electric furnace 100. Details of the temperature control device 200 will be described later using FIGS. 2 to 10.

[0019] FIG. 2 is a diagram showing the functional configuration of the temperature control device 200 shown in FIG. 1. FIG. 3 is a diagram for explaining the set temperature determination unit 221 shown in FIG. 2. FIG. 4 is another diagram for explaining the set temperature determination unit 221 shown in FIG. 2.

[0020] The temperature control device 200 includes an acquisition unit 210 that acquires the measured temperature of the control target every predetermined control cycle (for example, 100 ms), a calculation unit 220 that calculates an operation amount every control cycle so that the measured temperature acquired by the acquisition unit 210 reaches the target temperature, and an operation unit 230 that operates the heating device 124 that heats the control target according to the operation amount calculated by the calculation unit 220.

[0021] The acquisition unit 210 is composed of an AD conversion circuit that converts the electromotive force signal from the temperature sensor 125 into a measured temperature. The operation unit 230 is composed of, for example, a voltage modulator that adjusts the voltage applied to the heating device 124. The operation unit 230, composed of the voltage modulator, adjusts the voltage according to the operation amount calculated by the calculation unit 220 and supplies the adjusted voltage as an operation signal to the heating device 124. In this way, the operation unit 230 can operate the heating device 124 according to the operation amount calculated by the calculation unit 220.

[0022] The calculation unit 220 is composed of a computer including a processor and memory. The calculation unit 220 realizes various functions by having the processor execute a program stored in memory. As such functions, the calculation unit 220 includes a set temperature determination unit 221 that determines a set temperature to be set as a target value for each control cycle based on the measured temperature acquired by the acquisition unit 210, and an manipulated variable calculation unit 222 that calculates a manipulated variable for each control cycle based on the deviation between the measured temperature acquired by the acquisition unit 210 and the set temperature determined by the set temperature determination unit 221.

[0023] In this embodiment, the target temperature is the final temperature of the controlled object that we want to reach. The set temperature is the temperature of the controlled object that we want to reach with each control cycle. The measured temperature is the temperature of the controlled object measured by the temperature sensor 125. In Figure 3, the measured temperature is shown by a thick solid line, the set temperature is shown by a thick dashed line, and the target temperature is shown by a thin solid line.

[0024] The manipulated variable calculation unit 222 calculates the manipulated variable for each control cycle using a PID control algorithm based on the deviation between the measured temperature and the set temperature. The PID control parameters (proportional gain, differential gain, and integral gain) are pre-set in the manipulated variable calculation unit 222. However, the PID control parameters do not need to be specially optimized for the electric furnace 100; they can be set using standard values.

[0025] The set temperature determination unit 221 determines whether the measured temperature acquired by the acquisition unit 210 during the current control cycle (hereinafter also referred to as "measured temperature for the current control cycle") belongs to the first temperature range or the second temperature range. Then, the set temperature determination unit 221 determines the set temperature for the current control cycle using different algorithms depending on the determination result.

[0026] As shown in Figure 3, the first temperature range includes the initial measurement temperature before heating (t0 in Figures 3 and 4). The second temperature range includes the target temperature and is closer to the target temperature than the first temperature range. For example, if the target temperature is 300°C, the first temperature range may be lower than 230°C, and the second temperature range may be higher than 230°C.

[0027] The set temperature determination unit 221 determines the set temperature for the current control cycle based on the temperature difference between the measured temperature for the current control cycle and the set temperature for the previous control cycle, if the measured temperature for the current control cycle falls within the first temperature range. The set temperature determination unit 221 determines the set temperature for the current control cycle based on the temperature difference between the measured temperature for the current control cycle and the target temperature, if the measured temperature for the current control cycle falls within the second temperature range.

[0028] As a result, in the first temperature range where the temperature difference between the measured temperature and the target temperature is large, the temperature control device 200 can determine the current set temperature by considering how much the current measured temperature has changed from the previously set target temperature. In other words, in the first temperature range, the temperature control device 200 can precisely determine the set temperature in accordance with the current temperature of the controlled object for each control cycle, thereby improving the tracking ability of the measured temperature to the set temperature. Therefore, the temperature control device 200 can suppress overshoot, which occurs when the amount of control applied to the heating device 124 becomes too large due to a large discrepancy between the set temperature and the measured temperature. Furthermore, in the second temperature range where the temperature difference between the measured temperature and the target temperature is small, the temperature control device 200 can determine the current set temperature based on the temperature difference between the target temperature and the measured temperature. In this way, the temperature control device 200 can dynamically change the set temperature according to the thermal characteristics of the controlled object and determine the set temperature for each control cycle, so the heating device 124 can be operated in a manner that is suitable for the thermal characteristics of the controlled object without optimizing the PID control parameters. Therefore, the temperature control device 200 can easily achieve temperature control that is suited to the thermal characteristics of the controlled object without requiring complex parameter settings for PID control.

[0029] Specifically, if the measured temperature for the current control cycle falls within the first temperature range, the set temperature determination unit 221 determines the set temperature for the current control cycle so that the set temperature changes (rises) at a predetermined rate, provided that the temperature difference between the measured temperature for the current control cycle and the set temperature for the previous control cycle is less than a predetermined value. On the other hand, if the temperature difference between the measured temperature for the current control cycle and the set temperature for the previous control cycle is greater than or equal to the predetermined value, the set temperature for the current control cycle is determined to be the measured temperature for the current control cycle plus the predetermined value.

[0030] For example, as shown in Figure 4 during the period t0 to t1, if the temperature difference between the measured temperature (shown by the thick solid line) and the set temperature (shown by the thick dashed line) is less than a predetermined value (e.g., 10°C), the set temperature determination unit 221 determines the set temperature for the current control cycle so that the set temperature changes (rises) at a predetermined rate (e.g., +2°C / second). This is to prevent the amount of control applied to the heating device 124 from becoming too large due to a large discrepancy between the set temperature and the measured temperature. In this embodiment, the set temperature determined to change at this predetermined rate is also called the "steady-state set temperature." As shown by the dashed line in Figure 4, if the rate of change (rise rate) of the steady-state set temperature remains fast, as shown by the double-dashed line in Figure 4, the measured temperature will have difficulty keeping up with the set temperature, and the discrepancy between the two will increase. As a result, the amount of control will gradually increase, and eventually the measured temperature will overtake the set temperature, making temperature control difficult. Therefore, as shown in Figure 4 for the period from t1 to t4, if the temperature difference between the measured temperature and the set temperature is greater than or equal to the predetermined value, the set temperature for the current control cycle is determined by adding the predetermined value to the measured temperature in order to keep the temperature difference constant.

[0031] As a result, the temperature control device 200 can further improve the tracking ability of the measured temperature to the set temperature in the first temperature range, thereby further suppressing overshoot caused by excessive manipulation. In particular, the temperature control device 200 determines the set temperature by adding a predetermined value to the measured temperature in order to maintain a constant temperature difference between the measured temperature and the set temperature. Therefore, even if the object heated by the electric furnace 100 is changed in various ways, or if the electric furnace 100 itself is changed, the temperature control device 200 can accurately determine the set temperature in a manner that suits the thermal characteristics of the controlled object, and obtain an appropriate manipulation amount that suits the thermal characteristics of the controlled object. Thus, the temperature control device 200 can easily and accurately achieve temperature control in a manner that suits the thermal characteristics of the controlled object without requiring complex parameter settings for PID control.

[0032] Furthermore, if the measured temperature for the current control cycle falls within the second temperature range, the set temperature determination unit 221 determines the set temperature for the current control cycle so that the set temperature changes according to an exponential function whose variable is the temperature difference between the measured temperature for the current control cycle and the target temperature.

[0033] For example, the set temperature determination unit 221 determines the set temperature for the current control cycle using an exponential function as shown in equation (1) below. y1 = y0 + a·exp(b·x) …(1)

[0034] In equation (1), y1 represents the set temperature for the current control cycle. y0 represents the set temperature for the previous control cycle. x represents the temperature difference between the measured temperature and the target temperature for the current control cycle. a and b represent predetermined parameters, which are fixed values. For example, the value of a may be 0.02 and the value of b may be 0.01.

[0035] As a result, the temperature control device 200 can change the measured temperature in the second temperature range while asymptotically bringing the measured temperature closer to the target temperature. Therefore, the temperature control device 200 can accurately bring the measured temperature to the target temperature while suppressing the occurrence of overshoot and offset. Thus, the temperature control device 200 can easily and accurately achieve temperature control that is suited to the thermal characteristics of the controlled object without requiring complex parameter settings for PID control.

[0036] Furthermore, if the determined set temperature for the current control cycle exceeds the target temperature, the set temperature determination unit 221 corrects the determined set temperature for the current control cycle to the target temperature. In other words, regardless of whether the measured temperature for the current control cycle belongs to the first temperature range or the second temperature range, the set temperature determination unit 221 sets the set temperature for the current control cycle so that the set temperature does not exceed the target temperature.

[0037] As a result, the temperature control device 200 can reliably suppress overshoot while bringing the measured temperature to the target temperature. Therefore, the temperature control device 200 can easily and reliably achieve temperature control that is suited to the thermal characteristics of the controlled object without requiring complex parameter settings for PID control.

[0038] Furthermore, the set temperature determination unit 221 determines whether the measured temperature for the current control cycle exceeds the measured temperature for the previous control cycle. If the measured temperature for the current control cycle exceeds the set temperature for the previous control cycle, the operation unit 230 restricts heating of the heating device 124. For example, as a heating restriction, the operation unit 230 may stop heating of the heating device 124 or limit the output of the heating device 124.

[0039] As a result, the temperature control device 200 can reach the target temperature while more reliably suppressing the occurrence of overshoot. Therefore, the temperature control device 200 can easily and reliably achieve temperature control that is suited to the thermal characteristics of the controlled object without requiring complex parameter settings for PID control.

[0040] The temperature control method 300 of the first embodiment will be explained using Figures 5 to 7. Figure 5 is a flowchart of the temperature control method 300 of the first embodiment.

[0041] As shown in Figure 5, the temperature control method 300 of this embodiment includes an acquisition step (step S310), a calculation step (step S320), and an operation step (step S370). The temperature control method 300 is realized by the temperature control device 200 executing a program that implements the functions of the acquisition unit 210, the calculation unit 220, and the operation unit 230. Specifically, the acquisition step is realized by the temperature control device 200 executing a program that implements the function of the acquisition unit 210. The calculation step is realized by the temperature control device 200 executing a program that implements the function of the calculation unit 220. The operation step is realized by the temperature control device 200 executing a program that implements the function of the operation unit 230.

[0042] In step S310, the temperature control device 200 performs an acquisition step to acquire the measured temperature of the controlled object at predetermined control cycles.

[0043] In step S320, the temperature control device 200 performs a calculation step to calculate a manipulated variable for each control cycle so that the measured temperature acquired in the acquisition step reaches the target temperature. In this calculation step, the temperature control device 200 performs a set temperature determination step (step S330) in which it determines a set temperature to be set as the target value for each control cycle based on the measured temperature acquired in the acquisition step, and a manipulated variable calculation step (step S360) in which it calculates a manipulated variable based on the deviation between the measured temperature acquired in the acquisition step and the set temperature determined in the set temperature determination step.

[0044] In step S370, the temperature control device 200 performs an operation step to operate the heating device that heats the controlled object according to the manipulated amount calculated in the calculation step. Thereafter, the temperature control device 200 repeats steps S310 to S370 each time a control cycle arrives.

[0045] Figure 6 is a flowchart showing the details of the set temperature determination process shown in Figure 5.

[0046] In step S331, the temperature control device 200 determines whether the measured temperature for the current control cycle exceeds the set temperature for the previous control cycle. If the measured temperature for the current control cycle exceeds the set temperature for the previous control cycle, the temperature control device 200 proceeds to step S332. If the measured temperature for the current control cycle does not exceed the set temperature for the previous control cycle, the temperature control device 200 proceeds to step S333.

[0047] In step S332, the temperature control device 200 decides to limit the heating of the heating device 124. Thereafter, the temperature control device 200 terminates the set temperature determination process.

[0048] In step S333, the temperature control device 200 determines whether the measured temperature for the current control cycle belongs to the first temperature range. If the measured temperature for the current control cycle belongs to the first temperature range, the temperature control device 200 proceeds to step S334. If the measured temperature for the current control cycle does not belong to the first temperature range, i.e., belongs to the second temperature range, the temperature control device 200 proceeds to step S337.

[0049] In step S334, the temperature control device 200 determines whether the temperature difference between the measured temperature of the current control cycle and the set temperature of the previous control cycle is less than a predetermined value. If the temperature difference between the measured temperature of the current control cycle and the set temperature of the previous control cycle is less than a predetermined value, the temperature control device 200 proceeds to step S335. If the temperature difference between the measured temperature of the current control cycle and the set temperature of the previous control cycle is greater than or equal to a predetermined value, the temperature control device 200 proceeds to step S336.

[0050] In step S335, the temperature control device 200 determines the set temperature for the current control cycle so that the set temperature changes (rises) at a predetermined rate. After that, the temperature control device 200 proceeds to step S338.

[0051] In step S336, the temperature control device 200 determines the set temperature for the current control cycle by adding a predetermined value to the measured temperature for the current control cycle. After that, the temperature control device 200 proceeds to step S338.

[0052] In step S337, the temperature control device 200 determines the set temperature for the current control cycle so that the set temperature changes according to an exponential function where the temperature difference between the measured temperature and the target temperature for the current control cycle is the variable. After that, the temperature control device 200 proceeds to step S338.

[0053] In step S338, the temperature control device 200 determines whether the set temperature for the current control cycle exceeds the target temperature. If the set temperature for the current control cycle exceeds the target temperature, the temperature control device 200 proceeds to step S339. If the set temperature for the current control cycle does not exceed the target temperature, the temperature control device 200 proceeds to step S340.

[0054] In step S339, the temperature control device 200 corrects the set temperature for the current control cycle to the target temperature. After that, the temperature control device 200 terminates the set temperature determination process.

[0055] In step S340, the temperature control device 200 determines that no correction is needed for the set temperature of the current control cycle. After that, the temperature control device 200 terminates the set temperature determination process.

[0056] Thus, in the set temperature determination process, the temperature control device 200 determines whether the measured temperature of the current control cycle belongs to a first temperature range, which includes the initial measured temperature, or to a second temperature range, which includes the target temperature and is closer to the target temperature than the first temperature range. Depending on the determination result, it uses a different algorithm to determine the set temperature of the current control cycle. Specifically, if the measured temperature of the current control cycle belongs to the first temperature range, the temperature control device 200 uses the algorithms in steps S334 to S336 to determine the set temperature of the current control cycle. If the measured temperature of the current control cycle belongs to the second temperature range, the temperature control device 200 uses the algorithm in step S337 to determine the set temperature of the current control cycle.

[0057] After the set temperature determination step, the temperature control device 200 calculates the difference between the measured temperature obtained in the acquisition step and the set temperature determined in the set temperature determination step, and performs an manipulated variable calculation step to calculate the manipulated variable based on the said difference.

[0058] Figure 7 is a flowchart detailing the operation process shown in Figure 5.

[0059] In step S371, the temperature control device 200 determines whether it was decided in the set temperature determination step to limit the heating of the heating device 124. If it was decided to limit the heating of the heating device 124, the temperature control device 200 proceeds to step S372. If it was not decided to limit the heating of the heating device 124, the temperature control device 200 proceeds to step S373.

[0060] In step S372, the temperature control device 200 sends an operation signal to the heating device 124 to stop the voltage application to the heating device 124, or sends an operation signal to the heating device 124 to limit the voltage applied to the heating device 124, in order to limit the heating of the heating device 124. After that, the temperature control device 200 ends the operation process.

[0061] In step S373, the temperature control device 200 adjusts the voltage applied to the heating device 124 according to the manipulated variable calculated in the manipulated variable calculation step, and supplies the adjusted voltage to the heating device 124 as an operation signal. After that, the temperature control device 200 terminates the operation step.

[0062] The results of verifying the temperature control device 200 and temperature control method 300 of the first embodiment will be explained using Figures 8 to 10. Figure 8 is a diagram comparing the results of temperature control of an electric furnace 100 with a target temperature of 200°C performed by this embodiment and the prior art. Figure 9 is a diagram comparing the results of temperature control of an electric furnace 100 with a target temperature of 300°C performed by this embodiment and the prior art. Figure 10 is a diagram comparing the results of temperature control of an electric furnace 100 with a target temperature of 400°C performed by this embodiment and the prior art.

[0063] In this verification experiment, a Yamato Scientific FO710 (internal volume 23.6L) was used as the electric furnace 100, and CompactRIO's analog main module was used as the hardware for the temperature control device in both the conventional technology and this embodiment. The PID control parameters were not optimized, but were set as appropriate.

[0064] In Figures 8 to 10, the horizontal axis represents time, and the vertical axis represents temperature. In Figures 8 to 10, the thick solid line represents the measured temperature, and the thick dashed line represents the set temperature. Conventional technology sets a target temperature as an initial setting, but does not dynamically determine the set temperature for each control cycle to control the temperature, as in this embodiment. Therefore, in the conventional technology shown in Figures 8 to 10, the thick dashed line is drawn as being equal to the target temperature and constant.

[0065] As shown in Figures 8 to 10, in the conventional technology, overshoot occurred in all cases of target temperatures from 200°C to 400°C, and offset also occurred, especially when the target temperature was 200°C and 300°C. In contrast, in the results of this embodiment, although there is a slight discrepancy between the set temperature and the measured temperature immediately after the start of temperature control, the overall tracking of the measured temperature to the set temperature is high, and no overshoot or offset occurs. Thus, in this embodiment, the set temperature can be determined while dynamically changing the set temperature in accordance with the current temperature of the controlled object, so the tracking of the measured temperature to the set temperature can be improved, and precise temperature control can be performed without causing overshoot or offset.

[0066] [Second Embodiment] A second embodiment of the present invention will be described using Figure 11. In the second embodiment, components similar to those in the first embodiment will not be described.

[0067] Figure 11 shows the temperature profile obtained by temperature control of the temperature control device 200 of the second embodiment.

[0068] The temperature control device 200 of the second embodiment controls the temperature of a cooling furnace that cools an object, rather than controlling the temperature of an electric furnace 100 that heats the object. The cooling furnace has a containment space for housing the object to be cooled, and a refrigerator and a heating device 124 are provided in this containment space. The refrigerator provided in the cooling furnace of this embodiment may be, for example, a GM (Gifford-McMahon) refrigerator. The temperature of this cooling furnace is controlled by heating the heating device 124 while the refrigerator itself is constantly operating to cool the object. Similarly, in a cooling furnace equipped with a compressor-type refrigerator, the compressor is constantly operating to cool the object while the temperature is controlled by heating the heating device 124.

[0069] Therefore, the temperature control device 200 of the second embodiment controls the air present in the containment space of the cooling furnace, or the cooling head in contact with the object to be cooled, and controls the temperature of the cooling furnace by operating the heating device 124 provided in the containment space. As a result, the temperature profile of the cooling furnace obtained by the temperature control of the temperature control device 200 of the second embodiment is a graph as shown in Figure 11. In Figure 11, the thick solid line shows the measured temperature, the thick dashed line shows the set temperature, and the dashed line shows the steady-state set temperature.

[0070] The temperature control device 200 of the second embodiment basically includes an acquisition unit 210, a set temperature determination unit 221, a calculation unit 220 including an manipulated variable calculation unit 222, and an operation unit 230, similar to the temperature control device 200 of the first embodiment. However, a part of the set temperature determination unit 221 of the second embodiment differs from that of the first embodiment. Specifically, if the temperature difference between the measured temperature of the current control cycle and the set temperature of the previous control cycle is less than a predetermined value, the temperature control device 200 of the second embodiment determines the set temperature of the current control cycle so that the set temperature changes (decreases) at a predetermined rate (for example, -2°C / second). Also, "a" in the exponential function of equation (1) becomes a negative value. Aside from these differences, the temperature control device 200 of the second embodiment is the same as that of the first embodiment. Aside from these differences, the temperature control method 300 of the second embodiment is the same as that of the first embodiment.

[0071] Thus, the temperature control device 200 of the second embodiment, like the first embodiment, can determine the set temperature while dynamically changing the set temperature in accordance with the current temperature of the controlled object. This improves the tracking ability of the measured temperature with respect to the set temperature, and enables precise temperature control without causing overshoot or offset.

[0072] Although embodiments of the present invention have been described in detail above, the present invention is not limited to each embodiment, and various modifications can be made without departing from the spirit of the invention. The present invention can be modified by adding components of one embodiment to components of another embodiment, replacing components of one embodiment with components of another embodiment, or deleting parts of components of one embodiment. [Explanation of Symbols]

[0073] 100...Electric furnace, 110...Door section, 111...Handle, 120...Main body section, 121...Housing, 122,123...Insulation layer, 124...Heating device, 125...Temperature sensor, 200...Temperature control device, 210...Acquisition unit, 220...Calculation unit, 221...Set temperature determination unit, 222...Operation variable calculation unit, 230...Operation unit, 300...Temperature control method

Claims

1. An acquisition unit that acquires the measured temperature of the controlled object at predetermined control cycles, A calculation unit calculates the manipulated variable at each control cycle so that the measured temperature acquired by the acquisition unit reaches the target temperature, The system includes an operating unit that operates a heating device for heating the controlled object according to the manipulated amount calculated by the calculation unit, The aforementioned arithmetic unit, A setting temperature determination unit determines a setting temperature to be set as a target value for each control cycle based on the measured temperature acquired by the acquisition unit, Includes an manipulated variable calculation unit that calculates the manipulated variable based on the deviation between the measured temperature acquired by the acquisition unit and the set temperature determined by the set temperature determination unit, The aforementioned set temperature determination unit is It is determined whether the measured temperature for the current control cycle belongs to a first temperature range which includes the initial measured temperature, or to a second temperature range which includes the target temperature and is closer to the target temperature than the first temperature range. Depending on the judgment result, a different algorithm is used to determine the set temperature for the current control cycle. A temperature control device characterized by the following features.

2. The aforementioned set temperature determination unit is If the measured temperature for the current control cycle falls within the first temperature range, the set temperature for the current control cycle is determined based on the temperature difference between the measured temperature for the current control cycle and the set temperature for the previous control cycle. If the measured temperature for the current control cycle falls within the second temperature range, the set temperature for the current control cycle is determined based on the temperature difference between the measured temperature for the current control cycle and the target temperature. The temperature control device according to claim 1.

3. If the measured temperature for the current control cycle falls within the first temperature range, the set temperature determination unit will If the temperature difference between the measured temperature in the current control cycle and the set temperature in the previous control cycle is less than a predetermined value, the set temperature for the current control cycle is determined so that the set temperature changes at a predetermined rate. If the temperature difference between the measured temperature for the current control cycle and the set temperature for the previous control cycle is greater than or equal to the predetermined value, the temperature obtained by adding the predetermined value to the measured temperature for the current control cycle is determined as the set temperature for the current control cycle. The temperature control device according to claim 2.

4. If the measured temperature for the current control cycle falls within the second temperature range, the set temperature determination unit determines the set temperature for the current control cycle such that the set temperature changes according to an exponential function whose variable is the temperature difference between the measured temperature and the target temperature for the current control cycle. The temperature control device according to claim 2.

5. The set temperature determination unit corrects the set temperature for the current control cycle to the target temperature if the determined set temperature for the current control cycle exceeds the target temperature. The temperature control device according to claim 2.

6. The set temperature determination unit determines whether the measured temperature for the current control cycle exceeds the set temperature for the previous control cycle. The operating unit limits heating of the heating device if the measured temperature for the current control cycle exceeds the set temperature for the previous control cycle. The temperature control device according to claim 2.

7. The manipulated variable calculation unit calculates the manipulated variable using a PID control algorithm. The temperature control device according to claim 2.

8. An acquisition step to acquire the measured temperature of the controlled object at predetermined control cycles, A calculation step which calculates the manipulated variable for each control cycle so that the measured temperature obtained by the acquisition step reaches the target temperature, The process includes an operation step of operating a heating device that heats the controlled object according to the operation amount calculated by the calculation step, The aforementioned calculation step is A setting temperature determination step, which determines a setting temperature to be set as a target value for each control cycle based on the measured temperature obtained in the acquisition step, The process includes a manipulated variable calculation step which calculates the manipulated variable based on the deviation between the measured temperature obtained by the acquisition step and the set temperature determined by the set temperature determination step, The above-mentioned setting temperature determination step is, It is determined whether the measured temperature for the current control cycle belongs to a first temperature range which includes the initial measured temperature, or to a second temperature range which includes the target temperature and is closer to the target temperature than the first temperature range. Depending on the judgment result, a different algorithm is used to determine the set temperature for the current control cycle. A temperature control method characterized by the following:

9. The above-mentioned setting temperature determination step is, If the measured temperature for the current control cycle falls within the first temperature range, the set temperature for the current control cycle is determined based on the temperature difference between the measured temperature for the current control cycle and the set temperature for the previous control cycle. If the measured temperature for the current control cycle falls within the second temperature range, the set temperature for the current control cycle is determined based on the temperature difference between the measured temperature for the current control cycle and the target temperature. The temperature control method according to feature 8.

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