Machine tool control with function to change operation according to motor temperature and amplifier temperature

Abstract

Machine tool control for controlling a spindle and a feed axis, comprising: a motor temperature detection unit (1) for obtaining the winding temperature of a spindle motor (50) and outputting the winding temperature as a motor temperature; an inverter temperature detection unit (2) for obtaining the temperature of an inverter (40) for driving the spindle motor and outputting the temperature as an inverter temperature; an engine temperature comparison unit (10) for comparing the output engine temperature with an overheat temperature for the engine; an inverter temperature comparison unit (20) for comparing the output inverter temperature with an overheat temperature for the inverter; and an overheat evaluation unit (4) for imposing a restriction on the output of the spindle motor according to the lower of the difference between the motor temperature and the overheat temperature for the motor and the difference between the inverter temperature and the overheat temperature for the inverter, wherein the motor temperature detection unit (1) comprises a motor temperature detector (11) for measuring the winding temperature of the spindle motor (50) and a motor temperature estimation unit (12) for estimating the winding temperature of the spindle motor from a current feedback detected at the inverter.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe present invention relates to a machine tool controller, and more particularly relates to a machine tool controller having the function of changing the operation according to a motor temperature and an booster temperature.2. Description of the Prior ArtIn machine tools having a spindle and a feed axis driven by motors, an increase in a motor temperature or an amplifier temperature may result in overheating of the motor or an amplifier due to processing conditions of the spindle, e.g., power cutting or a high frequency of acceleration and deceleration, an installation environment, and the like.As a method for preventing overheating, a servomotor control device is known which includes a temperature detector for detecting the temperature of a servomotor for driving a movable element, and a temperature responsive controller for controlling the servomotor so that an acceleration and deceleration time constant of the movable element is varied according to the detected temperature (for example, Japanese Unexamined Patent Application (Kokai) No. 2003-9563).As another method for preventing overheating, there is known a mechanical device control method in which a temperature data calculation unit estimates the temperature of a drive unit, e.g., a feed axis motor of a mechanical device, and generates temperature data, and an acceleration and deceleration time constant calculation unit compares the temperature data with allowable predetermined temperature data stored in advance in a data memory to vary an acceleration and deceleration time constant of a feed axis according to the comparison result (for example, Japanese Unexamined Patent Application (Kokai) No. 9-179623).As yet another method for preventing overheating, there is known a motor controller in which a torque monitoring unit monitors a torque as a load on a main motor for a predetermined period of time, and a temperature estimating circuit calculates a virtual motor temperature based on an average load torque, i.e., the monitoring result by the torque monitoring unit, and a protection circuit compares the virtual temperature with a predetermined allowable temperature. When the virtual temperature exceeds the allowable temperature, a speed reduction ratio is set to 0.9 to cause speed restriction. When the virtual temperature is recovered, the speed reduction ratio is reset to an initial value 1.0 (for example, Japanese Patent Publication No. 5160834).Further, as still another method for preventing overheating, there is known a method in which a temperature increase estimating unit is provided for estimating a temperature increase resulting from each of an acceleration and deceleration current and a quiescent current. According to the size relationship therebetween, when the temperature rise resulting from the acceleration and deceleration current is prevailing, the output of a spindle motor is reduced. When the temperature rise resulting from the quiescent current is prevalent, the speed of a feed axis is reduced (for example, Japanese Patent Publication No. 5727572).U.S. Pat. No. 9,093,946 B2 discloses a method for controlling an output voltage of an inverter driving an electric motor. The method may include the steps of: removing harmonic components of an output current output to the electric motor by using a low pass filter and obtaining a fundamental component of the output current; calculating a total harmonic current distortion using the fundamental component of the output current; comparing the current THD with a current reference THD; determining a pulse width modulation method to be changed from a first modulation method for reducing the harmonic components of the output current to a second modulation method for reducing a switching frequency of the inverter when the current THD is smaller than the current reference THD, the PWM method modulating a pulse width of a control pulse signal for controlling the output voltage of the inverter; and / or generating the control pulse signal based on the determined PWM method.U.S. Pat. No. 8,493,016 B2 discloses a semiconductor circuit device comprising a semiconductor circuit having a switching element, a temperature monitoring unit and a control unit. The temperature monitoring unit detects or estimates a temperature of a component connected to an inside or an outside of the semiconductor circuit. Here, the temperature of the component changes according to a frequency of a current flowing through the component, and the frequency of the current flowing through the component changes according to a switching frequency of the switching element. The control unit adjusts the switching frequency of the switching element such that the temperature of the device is equal to a target temperature.SUMMARY OF THE INVENTIONThe object of the present patent application is achieved by the independent patent claims. Advantageous embodiments are described in the dependent claims.SUMMARY OF THE INVENTIONSince the conventional anti-overheating measures do not consider heat generation by an amplifier for driving a motor, overheating cannot be prevented by imposing an output constraint in consideration of checking overheating of the amplifier, which becomes a problem in driving the motor.A controller according to an embodiment of the present invention is a machine tool controller for controlling a spindle and a feed axis. The controller includes a motor temperature acquisition unit for obtaining the winding temperature of a spindle motor and outputting the winding temperature as a motor temperature; an inverter temperature acquisition unit for obtaining the temperature of an inverter for driving the spindle motor and outputting the temperature as an inverter temperature; a motor temperature comparison unit for comparing the outputted motor temperature with an overheat temperature for the motor; an inverter temperature comparison unit for comparing the outputted inverter temperature with an overheat temperature for the inverter; and an overheat evaluation unit for imposing a limitation on the output of the spindle motor according to the lower one of the difference between the motor temperature and the overheat temperature for the motor and the difference between the inverter temperature and the overheat temperature for the inverter.A controller according to another embodiment of the present invention is a machine tool controller for controlling a spindle and a feed axis. The controller includes a motor temperature acquisition unit for obtaining the winding temperature of a spindle motor and outputting the winding temperature as a motor temperature; an inverter temperature acquisition unit for obtaining the temperature of an inverter for driving the spindle motor and outputting the temperature as an inverter temperature; a reactor temperature acquisition unit for obtaining the winding temperature of a reactor provided between the inverter and the spindle motor and outputting the winding temperature as a reactor temperature; a motor temperature comparison unit for comparing the outputted motor temperature with an over-heating temperature for the motor; an inverter temperature comparison unit for comparing the outputted inverter temperature with an over-heating temperature for the inverter; a reactor temperature comparing unit for comparing the output reactor temperature with an overheat temperature for the reactor, and an overheat evaluating unit for imposing a limitation on the output of the spindle motor according to the lowest one of the difference between the motor temperature and the overheat temperature for the motor, the difference between the inverter temperature and the overheat temperature for the inverter, and the difference between the reactor temperature and the overheat temperature for the reactor.BRIEF DESCRIPTION OF THE DRAWINGSThe objects, features and advantages of the present invention will become more apparent from the following description of embodiments taken in conjunction with the accompanying drawings, wherein: FIG. 1 is a block diagram showing the configuration of a control system including a machine tool controller according to a first embodiment of the present invention; FIG. 2 is a flowchart of the operation of the machine tool controller according to the first embodiment of the present invention; FIG. 3 is a flowchart of the operation of the machine tool controller according to a modification example of the first embodiment of the present invention; FIG. 4 is a block diagram showing the configuration of a control system including a machine tool controller according to a second embodiment of the present invention; FIG. 5 is a flowchart of the operation of the machine tool controller according to the second embodiment of the present invention; and FIG. 6 is a flowchart of the operation of the machine tool controller according to a modification example of the second embodiment of the present invention.DETAILED DESCRIPTION OF THE INVENTIONHereinafter, a machine tool controller according to the present invention will be described with reference to the drawings.[First Embodiment]First, a machine tool controller according to a first embodiment of the present invention will be described. FIG. 1 is a block diagram showing the configuration of a control system including the machine tool controller according to the first embodiment of the present invention. The control system includes a host controller 100, a spindle motor amplifier 40, a spindle motor 50, a feed axis motor amplifier 70, and a feed axis motor 80. A machine tool controller 101 according to the first embodiment of the present invention is provided within the spindle motor amplifier (hereinafter also referred to as an "inverter") 40. The machine tool controller 101 is a controller for a machine tool for controlling a spindle axis. The machine tool controller 101 includes a motor temperature detection unit 1, an inverter temperature detection unit 2, a motor temperature comparison unit 10, an inverter temperature comparison unit 20, and an overheat evaluation unit 4. The machine tool controller 101 controls the output of the inverter 40 in response to commands from the host controller 100.The motor temperature acquisition unit 1 acquires the winding temperature of the spindle motor 50 and outputs the winding temperature as a motor temperature to the motor temperature comparison unit 10. The motor temperature detection unit 1 includes at least one of a motor temperature detector 11 and a motor temperature estimation unit 12. the motor temperature detector 11 measures the winding temperature of the spindle motor 50 using a temperature sensor 52, e.g., a thermistor, provided in the spindle motor 50. The motor temperature estimation unit 12 estimates the winding temperature of the spindle motor 50 from current feedback detected at the spindle motor amplifier (inverter) 40, that is, current flowing through the spindle motor 50 and detected by a current sensor 5 provided in the spindle motor amplifier (inverter) 40. In an example illustrated in FIG. 1, the engine temperature detection unit 1 includes both the engine temperature detector 11 and the engine temperature estimation unit 12, but the engine temperature detection unit 1 may include, without being limited to this example, one of the engine temperature detector 11 and the engine temperature estimation unit 12.The meaning of observing both the measured temperature (actual temperature) and the estimated temperature using both the engine temperature detector 11 and the engine temperature estimation unit 12 of the engine temperature detection unit 1 is as follows. That is, sharp current variation causes a sudden rise in the temperature of a motor winding itself (with a short (fast) time constant), while causing a slower rise in the temperature of the temperature sensor, e.g., the thermistor, embedded in the motor winding (with a long (slow) time constant). Therefore, the estimated temperature is used to monitor the overheat with the short time constant, while the measured temperature (actual temperature) is used to monitor the overheat with the long time constant.The inverter temperature acquisition unit 2 acquires the temperature of the inverter 40 that drives the spindle motor 50, and outputs the temperature as an inverter temperature to the inverter temperature comparison unit 20. The inverter temperature detection unit 2 includes one of an inverter temperature detector 21 and an inverter temperature estimation unit 22. the inverter temperature detector 21 measures the temperature of the inverter 40 using a temperature sensor 42, e.g., a thermistor, provided in the spindle motor amplifier (inverter) 40. The inverter temperature estimation unit 22 estimates the temperature of the inverter 40 from current feedback detected at the inverter 40, that is, from current flowing through the inverter 40 and detected by the current sensor 5 provided in the inverter 40. In an example illustrated in FIG. 1, the inverter temperature detection unit 2 includes both the inverter temperature detector 21 and the inverter temperature estimation unit 22, but the inverter temperature detection unit 2 may include, without being limited to this example, one of the inverter temperature detector 21 and the inverter temperature estimation unit 22. The inverter 40 is, for example, a spindle motor amplifier having a function of converting DC voltage to AC voltage by a switching operation of a switching element provided therein.The meaning of observing both the measured temperature (actual temperature) and the estimated temperature using both the inverter temperature detector 21 and the inverter temperature estimation unit 22 of the inverter temperature detection unit 2 is as follows. That is, the temperature of the amplifier itself (a heat sink of the amplifier) and the temperature of a power device increase with different time constants. The amplifier has a long (slow) time constant, while the power device has a short (fast) time constant. Therefore, the measured temperature (actual temperature) is used to monitor the overheat with the long time constant, while the estimated temperature is used to monitor the overheat with the short time constant.The motor temperature comparing unit 10 compares the temperature output from the motor temperature detecting unit 1 with an overheat temperature for the motor. The overheat temperature for the motor, which refers to a temperature at which the spindle motor is overheated, is stored in advance in a memory (not shown).The inverter temperature comparison unit 20 compares the temperature output from the inverter temperature detection unit 2 with an over-heating temperature for the inverter. The overheat temperature for the inverter, which refers to a temperature at which the inverter is overheated, is stored in a memory (not illustrated) in advance.The overheat evaluation unit 4 places a constraint on the output of the spindle motor according to the lower one of the difference between the motor temperature and the overheat temperature for the motor and the difference between the inverter temperature and the overheat temperature for the inverter.As described above, the machine tool controller according to the first embodiment of the present invention imposes the restriction on the output of the spindle motor by focusing on the temperature closer to the overheat temperature among the measured temperatures and the estimated temperatures of the motor and the inverter. That is, the output limitation with respect to both the motor temperature and the inverter temperature (booster temperature) makes it possible to prevent an engine stop due to an overheat alarm.Next, the operation of the machine tool controller according to the first embodiment of the present invention will be described with reference to a flowchart illustrated in FIG. 2. First, in step S 101, the motor temperature acquisition unit 1 acquires the winding temperature of the spindle motor 50 and outputs the winding temperature as a motor temperature to the motor temperature comparison unit 10. As described above, the motor temperature acquisition unit 1 includes at least one of the motor temperature detector 11 and the motor temperature estimation unit 12. the motor temperature acquisition unit 1 outputs the temperature of the spindle motor measured by the motor temperature detector 11, the temperature of the spindle motor estimated by the motor temperature estimation unit 12, or both the measured temperature and the estimated temperature as the motor temperature to the motor temperature comparison unit 10.Next, in step S 102, the inverter temperature acquisition unit 2 obtains the temperature of the spindle motor amplifier, i.e., inverter 40, and outputs the temperature as an inverter temperature to the inverter temperature comparison unit 20. As described above, the inverter temperature detection unit 2 includes at least one of the inverter temperature detector 21 and the inverter temperature estimation unit 22. the inverter temperature detection unit 2 outputs the temperature of the inverter 40 measured by the inverter temperature detector 21, the temperature of the inverter 40 estimated by the inverter temperature estimation unit 22, or both the measured temperature and the estimated temperature as the temperature of the inverter (spindle motor amplifier) 40 to the inverter temperature comparison unit 20.Next, in step S 103, the motor temperature comparison unit 10 compares the motor temperature output from the motor temperature detection unit 1 with an overheat temperature for the motor. More specifically, the motor temperature comparison unit 10 calculates the difference between the motor temperature and the overheat temperature for the motor, and outputs the difference to the overheat evaluation unit 4. The difference between the motor temperature and the overheat temperature for the motor is calculated using the measured temperature, the estimated temperature, or both the measured temperature and the estimated temperature as the motor temperature.Next, in step S 104, the inverter temperature comparison unit 20 compares the inverter temperature obtained by the inverter temperature detection unit 2 with an over-heating temperature for the inverter. More specifically, the inverter temperature comparison unit 20 calculates the difference between the inverter temperature and the overheat temperature for the inverter, and outputs the difference to the overheat evaluation unit 4. The difference between the inverter temperature and the overheat temperature for the inverter is calculated using the measured temperature, the estimated temperature, or both the measured temperature and the estimated temperature as the inverter temperature.Next, in step S 105, the overheat evaluation unit 4 determines whether the difference between the motor temperature and the overheat temperature for the motor is larger than the difference between the inverter temperature and the overheat temperature for the inverter. When the difference between the motor temperature and the overheat temperature for the motor is equal to or less than the difference between the inverter temperature and the overheat temperature for the inverter, the spindle motor 50 has a temperature that is closer to the overheat temperature, and is therefore determined to be closer to an overheat state than the inverter 40.On the other hand, when the difference between the motor temperature and the overheat temperature for the motor is higher than the difference between the inverter temperature and the overheat temperature for the inverter, the inverter 40 has a temperature that is closer to the overheat temperature, and is therefore determined to be closer to an overheat state than the spindle motor 50. in this case, in step S 107, the machine tool controller 101 imposes a restriction on the output of the spindle motor 50 according to the difference between the inverter temperature and the overheat temperature for the inverter.Next, with reference to FIG. 3, the operation of the machine tool controller according to a modification example of the first embodiment of the present invention will be described. First, in step S201, the winding temperature of the spindle motor 50 is detected and compared with an overheat temperature for the winding temperature.Next, in step S 202, a change in winding temperature of the spindle motor 50 is estimated from current feedback and compared with an overheat temperature for the estimated value of winding temperature. For the spindle motor 50, one of the measured temperature and the estimated temperature or both may be used for determining an output constraint.Here, "the superheat temperature for the winding temperature" is preferably different from "the superheat temperature for the estimated value of the winding temperature". "the superheat temperature for the winding temperature" is a superheat temperature with respect to an actual temperature measured by the temperature sensor provided in a portion of the motor (or inverter). "The superheat temperature for the estimated value of the winding temperature", on the other hand, is a superheat temperature with respect to a winding temperature estimated from a flowing current. Since the actual temperature is the temperature of a location itself where the temperature sensor is provided, a protection temperature is directly indicated. However, a heat value is estimated for the estimated temperature from the current, and it is necessary to determine a protection temperature in consideration of the thermal conductivity of an object whose temperature is to be monitored. Therefore, the above two superheat temperatures preferably have different values. That an superheat temperature for an actual temperature is preferably different from a superheat temperature for an estimated temperature also applies to the inverter temperature and a reactor temperature to be described later.Next, in step S 203, the internal temperature of the inverter 40 is detected and compared with an overheat temperature for the internal temperature.Next, in step S 204, a change in the internal temperature of the inverter 40 is estimated from a current feedback and compared with an overheat temperature for the estimated value of the internal temperature. For the inverter 40, one of the measured temperature and the estimated temperature or both may be used to set an output constraint.Next, in step S 205, one of the detected winding temperature, the detected inverter temperature, the estimated winding temperature, and the estimated inverter temperature that is closest to the overheat temperature is selected.Next, in step S 206, it is determined whether the selected temperature closest to the superheat temperature is in the immediate vicinity of the superheat temperature.When the selected temperature closest to the superheat temperature is in the immediate vicinity of the superheat temperature, an output restriction value is calculated according to a distance with respect to the superheat temperature in step S207 to place a restriction on the output of the spindle motor.On the other hand, if the selected temperature closest to the superheat temperature is not in the immediate vicinity of the superheat temperature, no limitation is imposed on the output of the spindle motor in step S208.As described above, the machine tool controller according to the first embodiment of the present invention enables prevention of overheating by imposing an output constraint in consideration of checking overheating of both the spindle motor and the inverter (amplifier) which become a problem in driving the motor.[Second Embodiment]Next, a machine tool controller according to a second embodiment of the present invention will be described. FIG. 4 is a block diagram showing the configuration of a control system including the machine tool controller according to the second embodiment of the present invention. The control system includes a host controller 100, a spindle motor amplifier 40, a spindle motor 50, a feed axis motor amplifier 70, and a feed axis motor 80. The machine tool controller 102 is a controller for a machine tool for controlling a spindle axis. The machine tool controller 102 includes a motor temperature detection unit 1, an inverter temperature detection unit 2, a reactor temperature detection unit 3, a motor temperature comparison unit 10, an inverter temperature comparison unit 20, a reactor temperature comparison unit 30, and an overheat evaluation unit 4'. The difference between the machine tool controller 102 according to the second embodiment and the machine tool controller 101 according to the first embodiment is that the machine tool controller 102 further includes the reactor temperature detection unit 3 and the reactor temperature comparison unit 30, and the overheat evaluation unit 4' imposes a limitation on the output of the spindle motor according to the smallest one of the difference between a motor temperature and an overheat temperature for the motor, the difference between an inverter temperature and an overheat temperature for the inverter, and the difference between a reactor temperature and an overheat temperature for the reactor. The other configuration of the machine tool controller 102 according to the second embodiment is the same as that of the machine tool controller 101 according to the first embodiment, so detailed description is omitted.The reactor temperature detection unit 3 obtains the winding temperature of a reactor (reactor) 60 provided between the inverter 40 and the spindle motor 50, and outputs the winding temperature as the reactor temperature. The reactor temperature detection unit 3 includes at least one of a reactor temperature detector 31 and a reactor temperature estimation unit 32. the reactor temperature detector 31 measures the winding temperature of the reactor 60 using a temperature sensor 62, e.g., a thermistor, provided in the reactor 60. The reactor temperature estimation unit 32 estimates the winding temperature of the reactor 60 from a current feedback detected at the spindle motor amplifier 40, that is, from a current flowing through the reactor 60 and detected by a current sensor 5 provided in the spindle motor amplifier 40. In an example illustrated in FIG. 4, the reactor temperature detection unit 3 includes both the reactor temperature detector 31 and the reactor temperature estimation unit 32, without being limited to this example; the reactor temperature detection unit 3 may include one of the engine temperature detector 31 and the engine temperature estimation unit 32.The meaning of observing both the measured temperature (actual temperature) and the estimated temperature using both the reactor temperature detector 31 and the reactor temperature estimation unit 32 of the reactor temperature detection unit 3 is as follows. That is, sharp current variation causes a sudden rise in the temperature of a reactor winding itself (with a short (fast) time constant), while causing a slower rise in the temperature of the temperature sensor, e.g., the thermistor, embedded in the reactor winding (with a long (slow) time constant). Therefore, the estimated temperature is used to monitor the overheat with the short time constant, while the measured temperature (actual temperature) is used to monitor the overheat with the long time constant.The reactor temperature comparison unit 30 compares the reactor temperature output from the reactor temperature detection unit 3 with an superheat temperature for the reactor. The superheat temperature for the reactor, which refers to a temperature at which the reactor is superheatd, is stored in advance in a memory (not shown).The overheat evaluation unit 4' imposes a restriction on the output of the spindle motor 50 according to the lower one of the difference between the motor temperature and the overheat temperature for the motor, the difference between the inverter temperature and the overheat temperature for the inverter, and the difference between the reactor temperature and the overheat temperature for the reactor.As described above, the machine tool controller according to the second embodiment of the present invention imposes the restriction on the output of the spindle motor by focusing on the temperature closest to the overheat temperature from the measured temperatures and the estimated temperatures of the motor, the inverter, and the reactor. That is, the output restriction based on the three items of motor temperature, inverter temperature, and reactor temperature makes it possible to prevent engine stop due to overheat alarm.Next, the operation of the machine tool controller according to the second embodiment of the present invention will be described with reference to a flowchart illustrated in FIG. 5. First, in step S 301, the motor temperature acquisition unit 1 acquires the winding temperature of the spindle motor 50 and outputs the winding temperature as a motor temperature to the motor temperature comparison unit 10. As described above, the motor temperature acquisition unit 1 includes at least one of the motor temperature detector 11 and the motor temperature estimation unit 12. the motor temperature acquisition unit 1 outputs the temperature of the spindle motor measured by the motor temperature detector 11, the temperature of the spindle motor estimated by the motor temperature estimation unit 12, or both the measured temperature and the estimated temperature as the motor temperature to the motor temperature comparison unit 10.Next, in step S 302, the inverter temperature acquisition unit 2 obtains the temperature of the spindle motor amplifier, i.e., inverter 40, and outputs the temperature as an inverter temperature to the inverter temperature comparison unit 20. As described above, the inverter temperature detection unit 2 includes at least one of the inverter temperature detector 21 and the inverter temperature estimation unit 22. the inverter temperature detection unit 2 outputs the temperature of the inverter 40 measured by the inverter temperature detector 21, the temperature of the inverter 40 estimated by the inverter temperature estimation unit 22, or both the measured temperature and the estimated temperature as the temperature of the inverter (spindle motor amplifier) 40 to the inverter temperature comparison unit 20.Next, in step S 303, the reactor temperature acquisition unit 3 acquires the winding temperature of the reactor 60, and outputs the winding temperature as a reactor temperature to the reactor temperature comparison unit 30. As described above, the reactor temperature detection unit 3 includes at least one of the reactor temperature detector 31 and the reactor temperature estimation unit 32. the reactor temperature detection unit 3 outputs the temperature of the reactor measured by the reactor temperature detector 31, the temperature of the reactor estimated by the reactor temperature estimation unit 32, or both the measured temperature and the estimated temperature as the reactor temperature to the reactor temperature comparison unit 30.Next, in step S 304, the motor temperature comparison unit 10 compares the motor temperature output from the motor temperature detection unit 1 with an overheat temperature for the motor. More specifically, the motor temperature comparing unit 10 calculates the difference between the motor temperature and the overheat temperature for the motor, and outputs the difference to the overheat evaluating unit 4'. The difference between the motor temperature and the overheat temperature for the motor is calculated using the measured temperature, the estimated temperature, or both the measured temperature and the estimated temperature as the motor temperature.Next, in step S 305, the inverter temperature comparison unit 20 compares the inverter temperature obtained by the inverter temperature detection unit 2 with an over-heating temperature for the inverter. More specifically, the inverter temperature comparison unit 20 calculates the difference between the inverter temperature and the overheat temperature for the inverter, and outputs the difference to the overheat evaluation unit 4'. The difference between the inverter temperature and the overheat temperature for the inverter is calculated using the measured temperature, the estimated temperature, or both the measured temperature and the estimated temperature as the inverter temperature.Next, in step S 306, the reactor temperature comparison unit 30 compares the reactor temperature obtained by the reactor temperature detection unit 3 with an superheat temperature for the reactor. More specifically, the reactor temperature comparison unit 30 calculates the difference between the reactor temperature and the superheat temperature for the reactor, and outputs the difference to the superheat evaluation unit 4'. The difference between the reactor temperature and the superheat temperature for the reactor is calculated using the measured temperature, the estimated temperature, or both the measured temperature and the estimated temperature as the reactor temperature.Next, in step S 307, the overheat evaluation unit 4' determines which of the difference between the motor temperature and the overheat temperature for the motor, the difference between the inverter temperature and the overheat temperature for the inverter, and the difference between the reactor temperature and the overheat temperature for the reactor is the lowest.When the difference between the motor temperature and the overheat temperature for the motor is the lowest, the temperature of the spindle motor 50 is closest to the overheat temperature for the motor. Thus, among the three components of the spindle motor 50, inverter 40, and reactor 60, the spindle motor 50 is determined to be the closest to the overheated state. In this case, in step S 308, the machine tool controller 102 imposes a restriction on the output of the spindle motor 50 according to the difference between the motor temperature and the overheat temperature for the motor.On the other hand, when the difference between the inverter temperature and the overheat temperature for the inverter is the lowest, the temperature of the inverter 40 is closest to the overheat temperature for the inverter. Thus, among the three components of the spindle motor 50, the inverter 40, and the reactor 60, the inverter 40 is determined to be the closest to the overheated state. In this case, in step S 309, the machine tool controller 102 imposes a restriction on the output of the spindle motor 50 according to the difference between the inverter temperature and the overheat temperature for the inverter.On the other hand, when the difference between the reactor temperature and the superheat temperature for the reactor is the lowest, the temperature of the reactor 60 is closest to the superheat temperature for the reactor. Thus, among the three components of the spindle motor 50, the inverter 40, and the reactor 60, the reactor 60 is determined to be the closest to the overheated state. In this case, in step S 310, the machine tool controller 102 imposes a restriction on the output of the spindle motor 50 according to the difference between the reactor temperature and the superheat temperature for the reactor.Next, with reference to a flowchart of FIG. 6, the operation of the machine tool controller according to a modification example of the second embodiment of the present invention will be described. First, in step S 401, the winding temperature of the spindle motor 50 is detected and compared with an overheat temperature for the winding temperature.Next, in step S 402, a change in winding temperature of the spindle motor 50 is estimated from current feedback and compared with an overheat temperature for the estimated value of winding temperature. For the spindle motor 50, one of the measured temperature and the estimated temperature or both may be used for determining an output constraint.Next, in step S 403, the internal temperature of the inverter 40 is detected and compared with an overheat temperature for the internal temperature.Next, in step S 404, a change in the internal temperature of the inverter 40 is estimated from current feedback and compared with an overheat temperature for the estimated value of the internal temperature. For the inverter 40, one or both of the measured temperature and the estimated temperature may be used to determine an output constraint.Next, in step S 405 the winding temperature of the reactor 60 between the inverter 40 and the spindle motor 50 is detected and compared with an overheat temperature for the winding temperature.Next, in step S 406, a change in winding temperature of the reactor 60 is estimated from a current feedback and compared with an over-heating temperature for the estimated value of winding temperature. For the reactor 60, one or both of the measured temperature and the estimated temperature may be used to determine an output constraint.Next, in step S 407, from among the detected winding temperature, the detected inverter temperature, the detected reactor temperature, the estimated winding temperature, the estimated inverter temperature, and the estimated reactor temperature, the one closest to the superheat temperature is selected.Next, in step S 408, it is determined whether the selected temperature closest to the superheat temperature is in the immediate vicinity of the superheat temperature.When the selected temperature closest to the superheat temperature is in the immediate vicinity of the superheat temperature, an output restriction value is calculated according to a distance with respect to the superheat temperature in step S409 to place a restriction on the output of the spindle motor 50.On the other hand, if the selected temperature closest to the superheat temperature is not in the immediate vicinity of the superheat temperature, no limitation is imposed on the output of the spindle motor 50 in step S410.As described above, the machine tool controller according to the second embodiment of the present invention enables prevention of overheating by imposing the output constraint in consideration of checking overheating of the group of the spindle motor, the inverter (amplifier), and the reactor, which become a problem in driving the motor.The machine tool controllers according to the embodiments of the present invention enable prevention of overheating by imposing an output constraint in consideration of evaluation of overheating of the motor and the amplifier, which become a problem in driving the motor.

Claims

A machine tool controller for controlling a spindle and a feed axis, comprising: a motor temperature acquisition unit (1) for obtaining the winding temperature of a spindle motor (50) and outputting the winding temperature as a motor temperature; an inverter temperature acquisition unit (2) for obtaining the temperature of an inverter (40) for driving the spindle motor and outputting the temperature as an inverter temperature; a motor temperature comparison unit (10) for comparing the output motor temperature with an overheat temperature for the motor; an inverter temperature comparison unit (20) for comparing the output inverter temperature with an overheat temperature for the inverter; and an overheat judgment unit (4) for imposing a limitation on the output of the spindle motor according to the lower one of the difference between the motor temperature and the overheat temperature for the motor and the difference between the inverter temperature and the overheat temperature for the inverter, wherein the motor temperature detection unit (1) includes a motor temperature detector (11) for measuring the winding temperature of the spindle motor (50), and a motor temperature estimation unit (12) for estimating the winding temperature of the spindle motor from a current feedback detected at the inverter.A machine tool controller for controlling a spindle and a feed axis, comprising: a motor temperature acquisition unit (1) for obtaining the winding temperature of a spindle motor (50) and outputting the winding temperature as a motor temperature; an inverter temperature acquisition unit (2) for obtaining the temperature of an inverter (40) for driving the spindle motor and outputting the temperature as an inverter temperature; a motor temperature comparison unit (10) for comparing the output motor temperature with an overheat temperature for the motor; an inverter temperature comparison unit (20) for comparing the output inverter temperature with an overheat temperature for the inverter; and an overheat evaluation unit (4) for imposing a limitation on the output of the spindle motor according to the lower one of the difference between the motor temperature and the overheat temperature for the motor and the difference between the inverter temperature and the overheat temperature for the inverter, wherein the inverter temperature detection unit (2) includes an inverter temperature detector (21) for measuring the temperature of the inverter (40) and an inverter temperature estimation unit (22) for estimating the temperature of the inverter from a current feedback detected at the inverter.The machine tool controller according to claim 1, wherein the inverter temperature detection unit (2) comprises at least one of an inverter temperature detector (21) for measuring the temperature of the inverter (40) and an inverter temperature estimation unit (22) for estimating the temperature of the inverter from a current feedback detected at the inverter.A machine tool controller for controlling a spindle and a feed axis, comprising: a motor temperature acquisition unit (1) for obtaining the winding temperature of a spindle motor (50) and outputting the winding temperature as a motor temperature; an inverter temperature acquisition unit (2) for obtaining the temperature of an inverter (40) for driving the spindle motor and outputting the temperature as an inverter temperature; a reactor temperature acquisition unit (3) for obtaining the winding temperature of a reactor (60) provided between the inverter and the spindle motor and outputting the winding temperature as a reactor temperature; a motor temperature comparison unit (10) for comparing the outputted motor temperature with an overheat temperature for the motor; an inverter temperature comparison unit (20) for comparing the outputted inverter temperature with an overheat temperature for the inverter; a reactor temperature comparing unit (30) for comparing the output reactor temperature with an overheat temperature for the reactor; and an overheat evaluating unit (4') for imposing a limitation on the output of the spindle motor according to the lowest one of the difference between the motor temperature and the overheat temperature for the motor, the difference between the inverter temperature and the overheat temperature for the inverter, and the difference between the reactor temperature and the overheat temperature for the reactor, wherein the motor temperature detecting unit (1) includes a motor temperature detector (11) for measuring the winding temperature of the spindle motor (50), and a motor temperature estimating unit (12) for estimating the winding temperature of the spindle motor from a current feedback detected at the inverter.The machine tool controller according to claim 4, wherein the inverter temperature detection unit (2) comprises at least one of an inverter temperature detector (21) for measuring the temperature of the inverter (40) and an inverter temperature estimation unit (22) for estimating the temperature of the inverter from a current feedback detected at the inverter.The machine tool controller according to claim 4, wherein the reactor temperature detection unit (3) comprises at least one of a reactor temperature detector (31) for measuring the winding temperature of the reactor (60) and a reactor temperature estimation unit (32) for estimating the winding temperature of the reactor from a current feedback detected at the inverter.The machine tool controller according to claim 4, wherein the inverter temperature detection unit (2) comprises at least one of an inverter temperature detector (21) for measuring the temperature of the inverter (40) and an inverter temperature estimation unit (22) for estimating the temperature of the inverter from a current feedback detected at the inverter, and the reactor temperature detection unit (3) comprises at least one of a reactor temperature detector (31) for measuring the winding temperature of the reactor (60) and a reactor temperature estimation unit (32) for estimating the winding temperature of the reactor from a current feedback detected at the inverter.

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