Temperature controller of liquid cooling system

Abstract: There is disclosed a temperature controller for controlling a coolant temperature in a liquid cooling system comprising a liquid circulation circuit in which coolant for cooling a machine circulates and a refrigeration circuit for cooling the coolant. More specifically, when the operating capacity of a compressor of the refrigeration circuit is variably adjusted by an inverter and when the operating condition of the machine is changed, its frequency value is varied in accordance with the change, so that it is possible to immediately correspond to the change of a liquid temperature to be generated in the future. In addition, an appropriate control can be selected as a control varying the frequency in combination with a normal feedback control, wherein the liquid temperature may converge on a set value or it may be co-changed to a room temperature or the like.

Description: The present invention relates to a temperature controller of a liquid cooling system for holding the temperature of coolant in a machine such as a machine tool at a predetermined value using a refrigeration circuit and, more particularly, to an improvement in a control precision of the coolant temperature in consideration of the change of an operating condition, or a parameter relevant to the quantity of heat generated in a machine. Conventionally, as a temperature controller of a liquid cooling system for controlling a coolant temperature in a machine such as a machine tool at a predetermined value, a system has been well known in which coolant is cooled using a refrigeration circuit to hold the coolant temperature constant. For example, as disclosed by the Japanese Utility Model Publication Gazette No. 48- 27351, a temperature grade around a machine such as a machine tool is held constant in the course of operation and the heat strain of each part of the machine is restrained as much as possible by measuring the temperature of cooling oil in the machine and the temperature of the machine, and feedback-controlling the temperature difference between the cooling oil temperature and the machine temperature to hold it at a previously set value. In addition, as disclosed by the Japanese Patent Publication Gazette No. 46- 16216, it is known that the same effect as mentioned above can be obtained also by holding the temperature difference between the cooling oil temperature and the room temperature at a predetermined set value. In both cases, in order to hold the temperature difference at a set value, a compressor in a refrigeration circuit is turned ON and OFF in accordance with the difference between the temperature difference and the target set value for control. More specifically, as shown in Fig. 12, when the temperature difference reaches the set value from the high temperature side, the compressor is stopped (a1, a2, ···). On the other hand, when the temperature difference rises from the set value by a certain quantity, the compressor starts its operation (b1, b2, ···). Therefore, the cooling oil temperature changes considerably in accordance with the change of ON and OFF of and OFF of the compressor as shown by a solid line in that figure and the change of the machine temperature in accordance with the above-mentioned change is delayed, so that the hunting of the control could be generated. As disclosed by the Japanese Patent Laying Open Gazette No. 60- 131149 describing a temperature controller having the features of the preamble of Claim 1 it is considered that the change of the coolant temperature is smoothed and a temperature control precision of a machine can be improved by adjusting the operating capacity of a compressor in a refrigeration circuit with an inverter with a frequency variable. However, when the operating condition of the machine changes, for example, when the rotation frequency of a main shaft of the machine tool increases while the coolant temperature is feedback-controlled, it takes considerable time until the machine temperature, that is, the coolant temperature changes by the above-mentioned change. As a result, hunting due to the response delay of control could be generated resulting in the possibility that no stable control can be performed. A main object of the present invention is to improve temperature control precision, and to promptly correspond to the change of the coolant temperature that will happen in the future to prevent hunting, by detecting an operating condition of the machine and, when the very operating condition of the machine changes which could influence the coolant temperature, previously adjusting an operating frequency of the compressor in accordance with such a change. In order to attain the above object, a temperature controller of a liquid cooling system in accordance with the present invention has a liquid circulation circuit with the features of Claim 1 and a refrigeration circuit. As means for detecting the operating condition of the machine, there is a temperature sensor detecting the temperature of an operating part in the machine, a sensor detecting the mechanical strain of the operating part, a sensor detecting a load (for example, a current) of an actuator (for example, a motor) of the machine, a sensor detecting the rotation frequency of a main shaft in case where the machine is a machine tool and the like. With a temperature controller in accordance of the present invention the temperature as generated in the machine is accordingly detected as a prevailing measure for obtaining a feedforward-control for the frequency of the inverter by estimating the change of the temperature in the machine when the change of its operating condition is greater than a predetermined change value. When thusly the driving state of the machine such as for example the rotation frequency of a main shaft suddenly increases then the oil temperature will be controlled by this novel feedforward-control rather then by the more common feedback-control of the prior art temperature controller whereby the frequency of the inverter then increases by a necessary amount to become an estimated value where the oil temperature will be stable. In this case a relationship between the rotation frequency of the machine shaft and an appropriate increasing amount of the frequency of the inverter will be pre-calculated by an experiment. The frequency of the inverter will accordingly be compelled to change to a value which is near to the last stable value, and thereafter the feedforward-control will be shifted to the feedback-control for preventing any hunting state. It accordingly may be understood that with such normal feedback-control the frequency of the inverter increases in accordance with the rise of the oil temperature, and the oil temperature will be lowered for reaching any appropriate temperature where the frequency of the inverter will be higher than the appropriate value. In this case the time lag of the feedback-control causes a so-called overshoot which when repeated generates such a hunting state that is accordingly prevented with the incorporation of the feedforward-control in accordance with the present invention. The dependent claims refer to features of the inventive temperature controller that result in more advantageous specific improvements of the same as it will become apparent from the following description of preferred embodiments. The present invention is readily apparent from the following detailed description when considered with the accompanying drawings, in which: Fig. 1 is a block diagram, schematically showing a system as a whole; Fig. 2 is a front view of a switch panel; Fig. 3 is a view showing temperature zones of a multistage step control; Fig.4 is a capacity map showing the relation between an inverter frequency and an inlet oil temperature and a room temperature at the time of a starting control; Fig. 5 is a flowchart showing control contents when the system starts; Figs. 6a, 6b and 5c are flowcharts showing control contents of an FF mode operation; Figs. 7a, 7b and are flowcharts showing control contents of an FB mode operation; Fig. 8 is a flowchart showing control contents of an IF mode; Figs. 9a and 9b are flowcharts showing control contents by the FF mode when controlled so as to converge the temperature of coolant on a set value; Fig. 10 is a characteristic view showing the change of the temperature of cooling oil when a returned liquid from a machine is held constant; Fig. 11 is a characteristic view showing the change of the temperature of cooling oil when a feeding liquid to a machine is held constant; and Fig. 12 is a characteristic view showing the change of the temperature of cooling oil when the temperature of coolant is controlled by ON· OFF operation of the compressor. DESCRIPTION OF PREFERRED EMBODIMENTS Embodiments of the present invention will be explained below with reference to the accompanying drawings. In Fig. 1, reference numeral 1 designates a machine tool as a machine for performing a predetermined machine work and reference numeral 2 designates an oil conditioner as a liquid cooling system for cooling oil in the machine tool. The machine tool 1 comprises a main shaft 1a for mounting a cutting tool such as a milling cutter and a drill edge on a tip, an oil tube 1b for circulating the cooling oil which absorbs heat Q generated in the main shaft 1a with the machine work and the like to keep the temperature constant and a reservoir 1c for receiving the cooling oil. In addition, the above-mentioned oil conditioner 2 is connected to the machine tool 1 by the oil tube 1b such that oil may flow and has an oil circulation circuit 3 built-in as a liquid circulation circuit for circulating the cooling oil. A fixed delivery pump 4, driven for rotation by a motor M, for forcedly circulating the cooling oil is provided in the oil circulation circuit 3 in which the oil returned from the reservoir 1c of the machine tool 1 flows in through an inlet port 5 and flows out of an outlet port 6 toward the oil tube 1b of the machine tool 1 again. On the other hand, a refrigeration unit 7 is built in the oil conditioner 2 and the refrigeration unit 7 having a compressor 8 and a fan 9a comprises a condenser 9 for condensing refrigerant, a capillary 10 as a reducing valve for decompressing the refrigerant, an evaporator 11 for evaporating the refrigerant to cool the cooling oil in the oil circulation circuit 3 by the heat exchange with the refrigerant, and an accumulator 12 for isolating gas and liquid in the refrigerant which returns to the compressor 8. Those equipments 8 through 12 are connected by a refrigerant tube 13 such that the refrigerant can flow and there is constituted a refrigeration circuit 14 performing the so-called heat pump operation in which the cold obtained from the heat exchange with air in the condenser 9 is applied to the cooling oil of the oil circulation circuit 3 in the evaporator 11. More specifically, in the oil circulation circuit 3, the cooling oil whose temperature rose because it absorbed the heat Q at the main shaft 1a of the machine tool 1 is cooled in the evaporator 11 and then supplied to the machine tool 1 again, so that the temperature at the main shaft 1a of the machine tool 1 can be kept constant to control a dimensional change due to its temperature change to obtain a predetermined machining precision. As shown in the following table 1, reference numeral 15 is an inverter which variably adjusts and drives an operating frequency fn of the compressor 8 among 11 steps in total of n=0 (stop), n=1 (30Hz), n=2 (40Hz), n=3 (50Hz), n=4 (60Hz), ···, and n=10 (120Hz). Reference numeral 16 is a controller for controlling the operation of the whole system. The controller 16 comprises a main circuit 16a for controlling the oil conditioner and an interface circuit 16b inputting a predetermined external signal in accordance with the operating condition of the machine 1 and outputting it to the main circuit 16a. Both circuits 16a and 16b are connected by a signal line. Reference numeral Th1 represents an inlet oil thermistor mounted on the inlet side of the oil circulation circuit 3 in the oil conditioner 2, that is, an oil inlet joint of the pump 4 as liquid temperature detecting means for detecting the temperature of the coolant returning from the machine tool 1 to the oil conditioner 2, reference numeral Th2 represents a room temperature thermistor mounted on a panel of the controller 16 in the oil conditioner 2 as means for detecting a room temperature T A of a co-changing object to which the temperature of the cooling oil is to be co-changed, and reference numeral Th3 represents a main shaft thermistor mounted on the main shaft 1a of the machine tool 1 as operating condition detecting means for detecting a main shaft temperature H corresponding to the operating condition of the machine tool (machine). The controller 16 is connected to the inlet oil thermistor Th1, the room temperature thermistor Th2 and the inverter 15 directly and to the main shaft thermistor Th3 through a control unit 1d on the machine tool 1 side to be described later such that a signal can be input and output and the operation of the oil conditioner controlled by the controller 16. On the other hand, the control unit 1d for controlling the operation of the machine tool 1 can apply and receive a signal to and from the controller 16 and an external signal such as ON· OF of the main shaft 1a of the machine tool 1 can be input to the controller 16. The main shaft thermistor Th3 disposed on the main shaft 1a of the machine tool 1 is connected to the control circuit 1d such that a signal can be input. As a feature of the present invention, mode switches SW1 through SW3 for commanding three operation modes are mounted on a switch panel 17 of the controller 16 as shown in Fig. 2. The mode switches SW1 through SW3 correspond to an FB mode performing only a feedback control of the frequency of an inverter 15 in accordance with the signal of two thermistors Th1 and Th2, an FF mode performing the feedback control of the frequency in accordance with the signal of two thermistors Th1 and Th2, while switching to the control which changes the frequency in accordance with the main shaft temperature H when the change of the main shaft temperature H representing the operating condition of the machine tool (machine) 1 detected by the main shaft thermistor Th3 is a predetermined value or more, and an IF mode changing the frequency in accordance with the signal of the only main shaft thermistor Th3, respectively. More specifically, the mode switches SW1 though SW3 have the function as control mode selecting means for selecting the control mode of the frequency of the inverter 15 among the control mode (FB mode) performing only the feedback control, the control mode (FF mode) performing the feedback control, while switching to the control which changes the output frequency of the inverter 15 from the frequency value in the feedback control when the change of the operating condition of the machine 1 detected by the main shaft thermistor Th3 becomes a predetermined value or more. As shown in Fig. 3, referring to the temperature difference ΔT (= T o -T A ) between an inlet oil temperature T o and a room temperature T A detected by the inlet oil temperature thermistor Th1 and the room temperature respectively, multistage temperature zones are set at intervals of 0.5°C about predetermined set value Ts of its control target value in a memory unit (not shown) built in the controller 16. The region of change is divided into 10 multi stage steps in total which are arranged in the order of a temperature zone (3-U) within the range of ΔT > Ts + 1.5°C, a temperature zone (2-U) within the range of Ts + 1.5°C ≧ ΔT > Ts + 1.0°C, a temperature zone (1-U) within the range of Ts + 1.0°C ≧ ΔT > Ts + 0.5°C, a temperature zone (0-U) within the range of Ts + 0.5°C ≧ ΔT > Ts, a temperature zone (0-L) within the range of 0°C ≧ ΔT > Ts-0.5°C, a temperature zone (1-L) within the range of Ts-0.5°C ≧ ΔT > Ts- 1.0°C, and so forth until a temperature zone (5-L) within the range of ΔT ≦ Ts-2.0°C. More specifically, the frequency value f of the inverter 15 is feedback-controlled depending in which temperature zone the temperature difference ΔT between the inlet oil temperature T o and the air temperature T A detected by the inlet oil thermistor Th1 and the room temperature thermistor Th2 exists. In an individual input connector (not shown) having the allocation function of an eight-bit I/O signal in the interface circuit 16b, a six-bit signal arranged at addresses [2] through [7] thereof is used for control as shown in the following table 2. The two-bit signal arranged at the first two addresses [2] and [3] corresponds to a signal for switching the mode switches SW1 through SW3, in which the FB mode, the FF mode and the IF mode are selected at addresses (00), (01) and (10), respectively. The four-bit signal arranged at the addresses [4] through [7] is an external command signal (E. S.) classified by the kinds of the above-selected control modes and corresponding to a change value dH/dt of the main shaft temperature H detected by the main shaft thermistor Th3. In addition, a mark ┌-┘ means that it functions regardless of its value of ┌0┘ or ┌1┘ . More specifically, in the FB mode, a control command signal is (- - - -) which means that the feedback control in accordance with the inlet oil thermistor Th1 and the room temperature thermistor Th2 is performed regardless of the signal from the interface circuit 16b, that is, regardless of the signal of the main shaft thermistor Th3. In the FF mode, the present frequency fn of the inverter 15 controlled by the feedback control may be maintained as it is, that is, the feedback-control is performed only when the external command signal value is (0 0 0 0) (no external signal), which corresponds to a case in which there is almost no value of the main shaft temperature change dH/dt. In addition, when the external command signal value is (-1 -1), which corresponds to a case in which the main shaft change - dH/dt is a predetermined value or more (when excessively cooled), the compressor 1 is stopped. On the other hand, when the external command signal value is (0 0 0 1) through (1 1 0 0), the inverter frequency fn controlled by the feedback control is increased or decreased by predetermined steps. More specifically, when the value is (0 0 0 1) corresponding to the case where dH/dt = - ΔH₀ (for example, approximately ΔH₀ = 0.2°C/sec), the frequency is decreased by 2 steps and when the value is (0 0 1 0) corresponding to the case where dH/dt = - 2ΔH₀, the frequency is decreased by 3 steps. When the value is (0 0 1 1) corresponding to the case where dH/dt = - 3ΔH₀, the frequency is decreased by 4 steps and when the value is (0 1 0 0) corresponding to the case where dH/dt = ΔH₀, it is increased by 2 steps. In addition, when the value is (1 0 0 0) corresponding to the case where dH/dt = 2ΔH₀, it is increased by 3 steps and when the value is (1 1 0 0) corresponding to the case where dH/dt = 3ΔH₀, it is increased by 4 steps. On the other hand, in the IF mode, when the external. command signal value is (1 1 1 1) corresponding to the case where the main shaft temperature H is lower than a predetermined value, the compressor 1 is stopped and when the value is (0 0 0 0) corresponding to the case where there is almost no change dH/dt of the main shaft temperature H, the present frequency value fn is maintained as it is. When the value is (0 0 0 1) through (1 0 1 0) corresponding to the case where the main shaft temperature H is in temperature zones divided into 10 zones at the intervals of 0.5°C in the vicinity of a predetermined standard temperature, the inverter frequency value fn corresponds to a value in a steps of n = 1 through 11 shown in the above table 1. A description is given of control contents thereof in accordance with flowcharts in Fig.5 through Fig.7c. In Fig.5, when the operation of an oil conditioner starts, a power lamp (P. L.) turns on at a step R₂ after a step R₁ and when a main switch (not shown) for operation turns on at a step R₃, an operation lamp (O. L.) turns on at a step R₄. Then, it is determined whether a protection unit (P.U.) (not shown) is normal or not at a step R₅ and when it is normal, a monitor display (M. D.) is turned on at a step R₆ and a pump 4 for circulating oil is turned on at a step R₇ and then a connection condition of the mode switches SW1 through SW3 is determined at a step R₈. When the mode switch SW1 is on, the FB mode operation starts and when the mode switch SW2 is on, the FF mode operation starts and when the mode switch SW3 is on, the IF mode operation starts. When it is determined that the protection unit is not in the normal condition at the step R₅, an abnormal output is displayed (A.O.D.) at step R₉ and the operation of the system is stopped and reset at steps R₁₀ and R₁₁. Thereafter, the abnormal output display (A.O.D.) is turned off and then the flow returns to the step R₂ again. Since the FB mode operation is comprised in the FF mode operation, it will be described later. First, a description is given of the FF mode operation in reference to Figs. 6a, 6b and 6c. When the oil conditioner starts its operation, the inlet oil temperature T o and the room temperature T A detected by the inlet oil thermistor Th1 and the room temperature thermistor Th2 are input at a step S₁ and from those value, it is calculated that, in which area of A through F in a capacity map of the compressor 8 shown in Fig. 4, necessary capacity exists. Then, it is determined whether it corresponds to each area of A through F in the capacity map or not in order in steps S₂ through S₆ and the output frequency f of the inverter 15 is set at 100Hz, 80Hz,···, 30Hz in accordance with the area A through F from that result. Then, the temperature difference ΔT ( = T o -T A ) between the inlet oil temperature T o and the room temperature T A is calculated at a step S₁₃. It is determined that in which zone among the temperature zones (3-U) through (5-L) the calculated value exists at steps S₁₄ through S₂₂ and the output frequency f of the inverter 15 is increased or decreased by +30Hz, +20Hz, ... , -40Hz and -50Hz from the present frequency value corresponding to the temperature zones (3-U) through (5-L) at steps S₂₃ through S₃₂. The value of the output frequency f is maintained as it is at the temperature zones (0-U) and (0-L). When the multistage step control is completed as described above, it is determined whether the control condition is in a stable region or not. More specifically, it is determined whether the temperature difference ΔT between the inlet oil temperature T o and the room temperature T A is in a temperature zone (0-U) or (0- L) of the stable region or not at steps S₃₃. When it is in the stable region, the output frequency f of the inverter 15 is reset at the present frequency at a step S₃₄ but when it is not in the stable region, the number of times n this step has been performed is counted at a step S₃₅ and it is determined whether the number of times n is below 3 or not at step S₃₆. When the number of times n is 3 or less, it is determined that time has not passed sufficiently to change the operating condition yet and the output frequency f of the inverter 15 is maintained as it is at a step S₃₇. On the other hand, when the number of times n is more than 3, it is determined whether the change of the temperature difference ΔT is on the increased side of the frequency change or not at a step S₃₈. When it is on the increased side, it is reset that f = f + 10Hz at a step S₃₉ and when on the decreased side, it is reset that f = f - 10Hz at a step S₄₀. More specifically, even if the temperature difference ΔT between the inlet oil temperature T o and the room temperature T A change with the change of the operating condition and it is not in the temperature zones (0-U) and (0-L) of the stable region, the output frequency f of the inverter 15, that is, the operating frequency of the compressor 8 is not immediately changed and the temperature difference ΔT is not brought close to the temperature zones (0-U) and (0-L) by changing the frequency f until it is not in the stable region three times in succession. As described above, when the stable region control is completed, it is determined that the external signal (E. S.), that is, the information from the main shaft thermistor Th3 is input on the side of the machine tool 1 or not at a step S₄₁. When it is not input, then a next control will be performed. On the other hand, when the external signal is input, the information contents of the input signal is processed at a step S₄₂ and then the frequency f of the inverter 15 is set in accordance with the set value in the table 2 at a step S₄₃. More specifically, since the control is delayed in the multistage step control when the temperature H of the main shaft 1a rises in reference to time above a predetermined rate of change ΔHo, it is determined that it is necessary previously to increase cooling capacity of the refrigeration unit 7 and the output frequency f of the inverter 15 is increased from the control value of the above-stated multistage control. On the other hand, when the main shaft temperature H falls in reference to time above a predetermined rate of change -ΔHo, the inverter frequency f is decreased by a predetermined value so as to promptly reduce the cooling capacity. When the control in accordance with the external signal is completed, it is determined whether f ≦ 120Hz or not and whether f < 30Hz or not at steps S₄₄ and S₄₅, respectively. When both are YES, it is determined that the temperature difference ΔT reaches the temperature region in which the operation of the compressor 8 is to be stopped and the number of times of the determination m is counted at a step S₄₆. Then, it is determined whether the number m is below 3 or not at a step S₄₇. When the number m is 3 or less, the frequency f of the inverter 15 is forcedly maintained at 30Hz to avoid the stoppage of the compressor 8, but when it is determined that it reaches the region in which the operation is to be stopped more than 3 times at the steps S₄₄ and S₄₅ after several repetition of controls, the compressor 8 is stopped. On the other hand, it is determined that f > 120Hz, that is, the frequency f is higher than 120Hz at the step S₄₄, it is considered that the frequency f is too high and the frequency f is set at 120Hz at a step S₄₉. When it is determined that the frequency f is not less than 30 at the step S₄₉, frequency f is maintained as it is at a step S₅₀. Finally, the output frequency f of the inverter 15 set by the above control is output to the compressor 8 at a step S₅₁ and sampling time for 60 seconds is counted at a step S₅₃ and then the control of the FF mode operation is completed. The return of the control starts at the step S₁₃. In addition, the control of the FB mode operation at steps S₁′ through S₅₃′ shown in Figs. 7a through 7c almost correspond to the control contents of the FF mode operation in Figs. 6a through 6c. More specifically, the inverter frequency f is controlled by a part except for the steps S₄₁ through S₄₃ in Fig.6b, that is, the steps S₁′ through S₄₀′ and steps S₄₄′ through S₅₃′ having the same contents as those of the steps S₁ through S₄₀ and the steps S₄₄ through S₅₃. Then, a description is given of the IF control in accordance with a flowchart in Fig. 8. It is determined whether there is a external command signal at a step P₁ and when the external command signal is output, the output frequency f of the inverter is set in accordance with the above table 2 at a step P₂. Then, it is determined whether the command to stop the compressor 8 is output or not at a step P₃ and when the stoppage command is not output, the flow returns to the step R₂ in Fig. 5 after the lapse of 30 seconds at a step P₅. On the other hand, when it is determined that the external command signal is not output at the step P₁ and that the command to stop the compressor 8 is output at the step P₃. the operation of the compressor 8 is stopped at a step P₄ and then 30 seconds pass at the step P₅. Next, a description is given of a second embodiment in reference to a flowchart in Figs. 9a and 9b. In this embodiment, a description is given of the IF mode performing the feedback-control such that the liquid temperature T o may converge on a set value T S ′ regardless of the room temperature, while changing the operating frequency f of the compressor from the control value by the feedback control when the operating condition of the machine is changed. When the oil conditioner starts its operation, it is determined whether the operation is for the first or not at a step Q₁. When it is the first time, the control after a step Q₂ is performed and when it is not the first time, the control after a step Q₂₉ is performed. More specifically, 5 seconds pass at the step Q₂, a starting frequency of the compressor 8 is set at a step Q₃ and when the inlet oil temperature T o becomes the value reduced from the set temperature Ts′ by 0.3°C or more at a step Q₄, the compressor is started at a step Q₅. Then, 2 minutes pass at a step Q₆, the frequency f of the inverter 15 is set at a predetermined initial value fn at a step Q₇, 60 seconds pass at a step Q₈ and the inlet oil temperature T o is compared with the set temperature Ts′ at a step Q₉. When the inlet oil temperature To is equal to the set temperature Ts′ or more at the step Q₉, it is determined whether a differential value dTo/dt of the inlet oil temperature in reference to time is below zero or not, that is, whether the inlet oil temperature T o is falling or not at a step Q₁₀. When it is not falling, it is considered that cooling capacity has to be increased and the operating frequency f is increased by 1 step as fn = fn + 1 at step Q₁₁. On the other hand, when the inlet oil temperature T o is falling, it is determined that in which temperature zone of (3-U) through (5-L) the value exists and it is started to count how many times this determination is made at a step Q₁₂. The frequency fn of the inverter 15 is maintained as it is at a step Q₁₄ until it is determined that it is out of a reference zone (R.Z.) three times at a step Q₁₃. After the above-described control is repeated, when it is determined that it is out of the reference zone three times, the operating frequency fn is increased by 1 step at a step Q₁₁. On the other hand, when it is determined that the inlet oil temperature T o is less than the set temperature Ts′ at the step Q₉, control corresponding to the above steps Q₁₀ through Q₁₄ is performed at steps Q₁₅ through Q₁₉. More specifically, when the differential value dTo/dt of the inlet oil temperature T o is negative or when the differential value is zero or more and the determination that it is out of the reference zone is made three times, the frequency fn of the inverter 15 is decreased by 1 step. The frequency f is not changed in any case other than that. When the frequency fn of the inverter 15 finishes being set as described above, it is determined whether the frequency fn is lower than a lower limit value 30Hz of the frequency fn of the inverter 15 or not at a step Q₂₀. When it is lower, the stoppage avoiding (S. A.) operation of the compressor 8 which is the same as the steps S₄₇ and S₄₈ in the first embodiment is performed at a step Q₂₁ and then 60 seconds pass at a step Q₂₂. On the other hand, when it is not lower, 60 seconds pass at the step Q₂₂ directly after the step Q₂₀. Then, it is determined whether the inlet oil temperature T o is equal to the set temperature Ts′ or not at a step Q₂₃. The control at 'the steps Q₉ though Q₂₂ is repeated until To = Ts′ and when To = Ts′, it is determined whether the differential value dTo/dt of the inlet oil temperature T o is below zero or not at a step Q₂₄. When dTo/dt ≧ 0, it is set that fn = fn + 1 at a step Q₂₅ so as to increase cooling capacity because the temperature is rising. On the other hand, when dTo/dt < 0, it is set that fn = fn - 1 at a step Q₂₆ so as to reduce the cooling capacity because the temperature is falling. Then, operation which is the same as that at the steps Q₂₀ and Q₂₁ is performed at steps Q₂₇ and Q₂₈ and after 30 seconds pass at a step Q₂₉, it is determined whether an external command signal is input or not at a step Q₃₀. When the external command signal is input, control by the external command signal after a step Q₃₈ to be described later is performed and when the external command signal is not input, the feedback control after a step Q₃₁ is performed. More specifically, it is determined that in which temperature zone of (5-L) through (3-U) the present inlet oil temperature To exists from the signal of the inlet oil thermistor Th1 at a step Q₃₁ and it is determined whether the determined temperature zone is keep zones (0-U) and (0-L) or not at a step Q₃₂. When it is the keep zones (0-U) and (0-L), control is completed. On the other hand, when it is not the keep zones (0-U) and (0-L) and Ts′> To, the frequency fn is decreased by n steps in accordance with the temperature zone, but when Ts′ ≦ To, it is increased by n steps at steps Q₃₃ through Q₃₅. Then, stoppage avoiding control of the compressor 8 which is the same as that at the steps Q₂₀ and Q₂₁ is performed at steps Q₃₆ and Q₃₇ and then finished. On the other hand, when it is determined that the external command signal is input at the step Q₃₀, the frequency f is set in accordance with the external command signal value at a step Q₃₈. Then, it is determined whether the stoppage command of the compressor 8 is output or not at step Q₃₉. When it is not output, then control is completed but when it is output, the stoppage avoiding control is performed at the step Q₃₇ and then control is completed. The output frequency of the inverter 15 is controlled in accordance with a liquid temperature (or the temperature difference between the liquid temperature and co-changing temperature) by receiving the output of the thermistor Th1 (or the thermistors Th1 and Th2) at the steps S₁₄ through S₃₂ and S₁₄′ through S₃₂′ in Figs. 6a and 7a. In addition, the operating frequency of the inverter 15 is varied by receiving the output of the main shaft thermistor Th3 at the steps S₄₃ in Figs. 6b or the step P₂ in Fig. 8. Although the main shaft thermistor Th3 detecting the temperature of the main shaft 1a of the machine tool 1 is provided as means for detecting the operating condition of the machine 1 in the above embodiment, a strain gauge or an amperometer of a sensor for detecting a displacement V of the main shaft 1a or a current value 1 as a load of the main shaft motor (not shown) of the actuator are disposed and from the relation between the rate of change dV/dt of the displacement V or the rate of change dI/dt of the current I and a predetermined value ΔVo (for example, approximately ΔVo = 0.5%/sec) or ΔIo (for example, approximately ΔIo = 100mA), ΔHo in the table 2 is replaced with the ΔVo or ΔIo and the frequency f of the inverter 15 can be varied depending in which zone of the zones divided into 10 steps in the vicinity of a predetermined standard value the range of the displacement V or the current value I exists. When the machine 1 is a machine tool 1, the frequency f of the inverter 15 can be controlled in accordance with a rotation frequency A from the relation between the rate of change dA/dt and a predetermined value ΔAo (for example, approximately ΔAo = 1rpm) using a rotation counter for detecting the rotation frequency A of the main shaft as means for detecting the operating condition. As a result, in the above-described embodiment, a signal concerning the operating condition of the machine tool (machine) 1 is input by the operating condition detecting means and the output frequency f of the inverter 15 is finely varied for adjustment by changing the frequency in accordance with the value, so that control stable and immediately corresponding to the change of condition can be carried out without generating hunting due to the considerable change of temperature. While the feedback control is carried out such that a liquid temperature may converge on a set value, if the inverter frequency is changed from the control value by the feedback control only when the operating condition of the machine changes, the output frequency f of the inverter 15 is feedback-controlled in a multistaged manner such that the inlet oil temperature To of the cooling oil of the machine tool detected by the inlet oil thermistor Th1 may converge on the set value Ts′ and the operating frequency of the compressor 8 is adjusted in accordance with the value. As a result, the quantity of heat exchange between refrigerant and liquid of an evaporator 11 is adjusted so as to keep the liquid temperature constant. At that time, while the cooling oil temperature is held constant by such feedback control, if the operating condition of the main shaft rotation frequency A of the machine tool 1, the temperature H of the main shaft 1a, the displacement V of the main shaft 1a or the like is changed and its quantity of change exceeds the set value, it is not possible to immediately follow it with the adjustment of the frequency f of the inverter 15 by the feedback control only, so that a control delay or an unstable control condition could be generated. In the above-described embodiment, however, when such things happen, the inverter frequency by the feedback control means is changed for adjustment in accordance with the operating condition by changing the frequency by the change of the operating condition detected by the operating condition detecting means. As a result, the control delay due to the feedback control is not caused and it is possible to follow the change of the operating condition immediately, so that a control precision can be improved while the hunting is prevented effectively. When the room temperature T A to which the liquid temperature To is co-changed is detected by the room temperature thermistor Th2 and the same control as above is performed on the temperature difference ΔT (T o -T A ) between the cooling oil temperature T o and the room temperature T A instead of the cooling oil temperature T o , even if the room temperature T A is changed, the temperature difference between the liquid temperature and the room temperature is held within an appropriate range in accordance with the change. Therefore, a temperature control precision can be improved, following the change of the temperature of an co-changing object such as room air, that is, the change of atmosphere. In addition, in this case, the co-changing object is not limited to the room air and for example, the temperature of the machine tool 1 and the like may be used as the object. When the feedback control in accordance with the normal inlet oil thermistor Th1, the frequency changing control and the control switching the feedback control and the frequency changing control are selected in an alternative way by the mode switches SW1 through SW3, it is possible to control the operation of the oil conditioner (cooling system) 2 at a preferable control mode in accordance with the kind of machine, the kind of work in the machine tool 1 or the like. The same is true in the case where the feedback control by the feedback controlling means in accordance with the temperature difference (T o -T A ) between the inlet oil temperature T₀ and the room temperature T A , the control by frequency changing means and the control switching the feedback control and the frequency changing control are selected in an alternative way by the mode switch SW1 through SW3. When the main shaft thermistor Th3 in the above embodiment) is used as means for detecting the operating condition of the machine 1, the following effect can be obtained. That is, when the temperature of the machine 1 rises for some reason, there is usually a certain time delay until the temperature of the coolant is changed by the temperature rise, but in this case, since the change of the temperature of the machine 1 is promptly detected by the temperature thermistor Th3 and the refrigerating capacity of the refrigeration circuit 14 is previously changed, it is possible to immediately correspond to the change of the operating condition of the machine 1. When a sensor detecting the mechanical strain of an operating part on the machine 1 is used as means for detecting the operating condition, the strain generated by the change of applied force and the temperature of the operating part of the machine 1 is promptly detected. When a sensor detecting a load applied to the actuator of the machine 1 is used as means for detecting the operating condition, it is possible to know in advance the generation of the change of temperature, strain or the like in the operating part by an increase in the load of the machine 1. Similarly, when a sensor detecting the rotation frequency of the main shaft in the case where the machine is a machine tool, it is possible to know in advance the change of temperature or strain by the change of the rotation frequency of the main shaft. Although the mode switches SW1 through SW3 as means for selecting a control mode are switched by hand in the above embodiment, selection signals of the mode switches SW1 through SW3 may be programmed and the control may be selected by that signal when the changing pattern of the control mode has been already decided from an operation schedule of the machine tool 1 and the like. In that case, also when as an output external command signal in accordance with the operating condition of the machine 1, the change of the operating condition such as rotation frequency of the machine tool has been known from an operating pattern, a 4-bit signal in accordance with the table 2 can be directly input to the interface circuit 16b by having programmed a signal output timing into the interface circuit 16b. When the thermistor Th1 as means for detecting the coolant temperature is provided at the inlet of the oil conditioner 2 for cooling oil like in the above embodiment, especially there is an effect that the influence of the control temperature on the fluctuation of the heat due to the working and the like of the machine tool 1 can be restrained. When the heat on the machine tool 1 side is changed, an average temperature ϑ of a returned oil and a feeding oil is lowered due to an increase in the heat Q, so that the quantity of the change of component temperature ϑ is offset by this lowered quantity. For example, as shown in Fig. 10, the component temperature ϑ is raised to a temperature ϑ higher by the constant ratio corresponding to heat capacity in accordance with the average temperature of the return oil temperature and the feeding oil temperature. Therefore, when the heat Q of the machine tool 1 is increased from Q₁ to Q₂ (Q₁ < Q₂), the component temperature ϑ is accordingly increased from ϑ₁ to ϑ₂. At this time, as shown in Fig. 10, the change from ϑ₁ to ϑ₂ of the component temperature ϑ is restrained to be small by changing the average temperature ϑ o such that ϑ om1 > ϑ om2, that is, it may be lowered. Therefore, as shown in Fig. 11, it is possible to improve a temperature control precision without enlarging the temperature difference due to an increase in the heat Q of the machine tool 1. It is the same when the operating frequency of the compressor 8 is controlled such that the temperature difference ΔT between the inlet oil temperature T o and the room temperature T A may converge on the set value Ts. In addition, since the stable region control was carried out at the steps S₃₃ through S₄₀ in Fig. 6b and the change of the temperature condition is carefully determined by sampling three times until the change of the operating fr equency of the compressor 8 in the above embodiment, the temperature is prevented from changing frequently for a short time and stable control can be performed. The operating frequency f of the compressor 8 is forcedly controlled in accordance with the input of an external signal regardless of the signal of the thermistors Th1 and Th2 at the steps S₄₀ through S₄₃, so that the control can be carried out corresponding to the change of important external condition such as the change of the temperature of the main shaft 1a of the machine tool 1. In addition, as shown at the steps S₄₄ through S₅₀ or the steps Q₂₁, Q₂₈ and Q₃₇, there is provided a predetermined limit value at the operating frequency and no operation is performed above that limit value. Also, even when the command operating frequency is below the lowest controllable value, the operation is not stopped until determination is made by sampling three times. As a result, since the operating condition could recover for that time, the operation stoppage can be avoided as much as possible. Therefore, a trouble of the compressor because of frequent ON· OFF operation can be prevented. Consequently, the reliability of the compressor is improved. In addition, although its embodiment is dispensed with, as can be easily understood, the same effect can be obtained also in the case where the compressor is stopped when the stoppage command signal of the compressor is output over a predetermined time. In addition, it is needless to say that the machine 1 to be cooled in the present invention is not limited to the machine tool in the above embodiment and it can be applied to other kinds of industrial machines. Although oil is used as coolant in the above embodiment, the same effect can be obtained with other kinds of liquid such as water. The present invention can be applied not only to processing machines such as a lathe, a grinding machine, a press machine and an injection machine for plastic, but also to a cooling system for cooling coolant or lubricant in a machine having a heating part such as a general industrial machine used in a production line.

Claims: A temperature controller (16) of a liquid cooling system having a liquid circulation circuit (3) and a refrigeration circuit (14), said liquid circulation circuit (3) circulating coolant in a machine (1) having an operating part (la) for generating heat, and said refrigerating circuit (14) having a compressor (8), a condenser (9) and a reducing valve (10) for compressing, condensing and decompressing refrigerant, respectively, and an evaporator (11) for cooling the coolant in said liquid circulation circuit (3) by a heat exchange with refrigerant as sequentially connected by means of a refrigerant tube (13), said temperature controller (16) having inverter means (15) for variably adjusting the operating frequency of the compressor (18) relative to different temperature variables, means (Th1) for detecting the temperature (T o ) of the coolant and means (Th2; S14 - S32) for feedback-controlling the frequency of the inverter means (15) such that the temperature (T o ) of the coolant converges to a predetermined set value (T S ), characterized by operating condition detecting means (Th3) for detecting the temperature (H) relevant to the quantity of heat (Q) generated in the machine (I); and means (S42, S43) connected to said operating condition detecting means (Th3) for varying the frequency of the inverter means (15) from the frequency value as determined by the feedback-controlling means (Th2; S14 - S32) by a quantity corresponding to a change of the machine temperature (H) when the same becomes greater than a predetermined change value (ΔT). A temperature controller according to claim 1, wherein said frequency feedback-controlling means (Th2; S14 - S32) comprises means (Th2) for detecting a surrounding temperature (T A ) to which the temperature (T o ) of the coolant is to be changed to thereby feedback-control the frequency of the inverter means (15) such that a temperature difference (ΔT) between the temperature (T o ) of the coolant and the surrounding temperature (T A ) converges to the predetermined set value (T S ). A temperature controller according to claim 1 or claim 2, wherein said frequency varying means (S42, S43) comprises selection means (SW1, SW2, SW3) for selecting frequency control modes (FB, FF, IF) of the inverter means (15) in accordance with command signals as received only from the operating condition detecting means (Th3) or in common from the feedback-controlling means (Th2; S14 - S32) and the coolant temperature detecting means (Th1). A temperature controller according to any of the claims 1 to 3, wherein the coolant temperature detecting means (Th1) is connected to means (Q11, Q14, Q16, Q19, Q 25, Q26, Q34, Q35) for delivering a stoppage command signal for stopping operation of the compressor (8) when the temperature (T o ) of the coolant is within a previously set range, the compressor (8) being stopped when the stoppage command signal is delivered for a predetermined time period. A temperature controller according to claim 4, wherein the delivery means (Q11, Q14, Q16, Q19, Q 25, Q26, Q34, Q35) is further connected to the feedback-controlling means (Th2; S14 - S32) for stopping operation of the compressor (8) when a temperature difference (ΔT) between the temperature (T o ) of the coolant and the surrounding temperature (T A ) is within the previously set range. A temperature controller according to claim 4 or claim 5, wherein the compressor (8) is stopped when the stoppage command signal is successively delivered in a predetermined number of times. A temperature controller according to any of the claims 1 to 6, wherein the machine (1) comprises at least one of a grinding machine, a lathe, a press machine and an injection machine. A temperature controller according to any of the claims 1 to 7, wherein the operating condition detecting means (Th3) further comprises a sensor for detecting rotation frequency of a main shaft of the machine (1). A temperature controller according to any of the claims 1 to 8, wherein the operating condition detecting means (Th3) further comprises a sensor for detecting a mechanical strain of an operating part of the machine (1) and/or a sensor for detecting a power load of the machine (1). A temperature controller according to any of the claims 1 to 9, wherein the coolant temperature detecting means (Th1) detects the temperature (T o ) of the coolant when it is returned from the machine (1). A temperature controller according to any of the claims 1 to 10, wherein the operating condition detecting means (Th3) detects the surrounding room temperature (T A ) or the temperature of an operating part of the machine (1).

Inventors: FUKUNAGA OSAMU C O YODOGAWA-PL, TSUDA SHOZO C O YODOGAWA-PLANT, FUKUNAGA, OSAMU C/O YODOGAWA-PLANT DAIKIN IND.LTD., TSUDA, SHOZO C/O YODOGAWA-PLANT DAIKIN IND.LTD.
Applicants: DAIKIN IND LTD, DAIKIN INDUSTRIES, LIMITED
Application year: 1989
Main classification: G05D23
IPC codes: G05D23, F25B49, F25D17, B23Q11