Motor controller and machine tool

A motor controller comprises: a motor driver arranged at a housing attached to a machine support; fan motors and arranged in or outside the housing; and a control unit. The motor driver drives motors. The fan motors blow cooling air for cooling the interior of the housing. The CPU includes a machining mode selection unit allowing selection of at least either a first machining mode of machining a machining target finely or a second machining mode of machining the machining target more roughly than in the first machining mode. If the first machining mode is selected, the machining mode selection unit exerts control to change the rotation numbers of the fan motors and so as to reduce vibration to be transmitted from the housing to the support column.

This application is based on and claims the benefit of priority from Japanese Patent Application No. 2018-087348, filed on Apr. 27, 2018, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a motor controller and a machine tool including the motor controller.

Related Art

Many machine tools have the following independent (not integrated) structures: a machining unit with a spindle to which a machining member such as a drill is attachable; and a power magnetics cabinet with a motor driver for driving a motor for spindle rotation and a fan motor for cooling the motor driver.

By contrast, to achieve space saving, some machine tools have a configuration in which a power magnetics cabinet with a motor driver and a fan motor is attached to and integrated with a machining unit with a spindle. Patent document 1 discloses a machine tool having a configuration in which a fan motor for cooling a cooler is attached to and integrated with a body with a spindle through a back plate.

SUMMARY OF THE INVENTION

In the foregoing machine tool, however, the rotation of a fan of the fan motor may cause the vibration of the fan motor, and this vibration may be transmitted to the spindle through a support supporting the spindle. This may cause the vibration of a machining member attached to the spindle to reduce machine accuracy. In particular, if machine accuracy is reduced during finishing on a surface of a machining target, the quality of a machining surface may be reduced.

In view of the foregoing, the present invention is intended to provide a motor controller capable of suppressing transmission of the vibration of a fan motor to a machine support of a machine tool for machining on a machining target in a situation where machine accuracy is required, and a machine tool including the motor controller.

(1) The present invention relates to a motor controller (motor controller100described later, for example) comprising: a motor driver (motor driver65described later, for example) arranged at a housing (housing31described later, for example) attached to a machine support (support column21described later, for example) as a support of a machine tool (machine tool10described later, for example) for machining on a machining target (workpiece50described later, for example); a fan motor (fan motor33,34described later, for example) arranged in or outside the housing; and a control unit (CPU61described later, for example). The motor driver drives a motor (spindle motor24, X-axis motor124, Y-axis motor224, Z-axis motor324described later, for example) that generates power for the operation of the machine tool. The fan motor blows cooling air for cooling the interior of the housing. The control unit includes a machining mode selection unit (machining mode selection unit55described later, for example) allowing selection of a machining mode from at least a first machining mode of machining the machining target finely and a second machining mode of machining the machining target more roughly than in the first machining mode. If the first machining mode is selected, the machining mode selection unit exerts control to change the rotation number of the fan motor so as to reduce vibration to be transmitted from the housing to the machine support, compared to vibration to be transmitted in the second machining mode.

(2) The motor controller described in (1) may further comprise a load detector (temperature sensor71,72described later, for example) that detects load applied to the motor driver. If load detected by the load detector is determined to be equal to or less than a predetermined threshold, the control unit may exert control to change the rotation number of the fan motor so as to reduce vibration to be transmitted from the housing to the machine support, compared to vibration to be transmitted in the second machining mode.

(3) In the motor controller described in (2), if the load detected by the load detector is determined to be greater than the predetermined threshold after the rotation number of the fan motor is changed to a rotation number responsive to the first machining mode, the control unit may exert control to change the rotation number of the fan motor to the rotation number of the fan motor responsive to the second machining mode.

(4) The motor controller described in (2) or (3) may further comprise an alarm generator (alarm generator90described later, for example) that generates an alarm. If the load detected by the load detector is determined to be greater than the predetermined threshold, the control unit may control the alarm generator so as to make the alarm generator generate an alarm.

(5) In the motor controller described in any one of (1) to (4), changing the rotation number of the fan motor may mean that the rotation number of the fan motor is reduced so as to go out of the natural vibration frequency of the fan motor, or the fan motor is stopped.

(6) In the motor controller described in any one of (1) to (5), changing the rotation number of the fan motor may mean that the rotation number of the fan motor is increased so as to go out of the natural vibration frequency of the fan motor.

(7) The present invention may also be a machine tool comprising: the motor controller described in any one of (1) to (6); the machine support; and the motor.

According to the present invention, in a situation where machine accuracy is required, transmission of the vibration of a fan motor to a machine support of a machine tool for machining on a machining target can be suppressed.

DETAILED DESCRIPTION OF THE INVENTION

First Embodiment

[Overall Configuration of Machine Tool]

A motor controller according a first embodiment of the present invention and a machine tool including the motor controller will be described below by referring to the drawings.FIG. 1is a sectional view schematically showing a machine tool10including a motor controller100according to the first embodiment of the present invention.FIG. 2is a block diagram of the motor controller100provided in the machine tool10. Principal structures of the machine tool10of the first embodiment include a machining unit20, a drill26, a power magnetics cabinet30, and a controller60. Of these structures, the power magnetics cabinet30and the controller60form the motor controller100.

The machining unit20includes a support column21as a machine support, a spindle unit22, and a workpiece holder27.

The support column21forms a main body of the structure of the machine tool10, and mechanically supports structural elements of the machine tool10including the spindle unit22, the workpiece holder27, the power magnetics cabinet30, etc. In particular, the support column21supports the drill26provided at the spindle unit22and supports a workpiece50held by the workpiece holder27.

The support column21has a mechanism of adjusting the position of the drill26attached to the spindle unit22and the workpiece50fixed to the workpiece holder27relative to each other. The support column21includes a support member28. The support column21includes a moving mechanism (not shown) arranged in the support column21and for moving the support member28in an X-axis direction, a Y-axis direction, and a Z-axis direction. The support column21also includes an X-axis motor124, a Y-axis motor224, and a Z-axis motor324(seeFIG. 2) arranged in the support column21. The X-axis motor124, the Y-axis motor224, and the Z-axis motor324are motors that generate power for the operation of the machine tool10, particularly drive a moving mechanism for a guide (not shown) for moving the support member28in the X-axis direction, the Y-axis direction, and the Z-axis direction.

As the support member28moves in the X-axis direction, the Y-axis direction, and the Z-axis direction, the spindle unit22moves in the X-axis direction, the Y-axis direction, and the Z-axis direction.FIG. 1shows the X, Y, and Z axes, and the X axis extends from the front to the back of the plane of the sheet ofFIG. 1.

The support member28supports the spindle unit22. The support member28moves integrally with the spindle unit22.

The spindle unit22is a unit that holds the drill26as a machining member for machining on the workpiece50in a manner that allows attachment and detachment of the drill26. The spindle unit22includes a spindle housing23, a spindle motor24, a shaft25, and a rotation number detector80. The spindle motor24is a motor that generates power for the operation of the machine tool10, in particular, rotates the shaft25to which the drill26is attached. The rotation number detector80is a sensor that detects the rotation number of the spindle motor24.

The workpiece holder27is a member coupled to the support column21and for holding the workpiece50.

The drill26is attached to the shaft25of the spindle unit22so as to be detachable from the shaft25. The drill26rotate about the central axis of the shaft25.

The power magnetics cabinet30includes a housing31, a motor driver65, a heat sink32, a fan motor33and motor34, a temperature sensor71and72as load detectors, and an alarm generator90.

The housing31is attached to the support column21. Specifically, the housing31and the support column21are integrated. The motor driver65and the fan motors33and34are fixed directly or indirectly to the housing31. A relationship between these members in terms of vibration is as follows: When the fan motors33and34vibrate, the vibrations are transmitted to the housing31to cause the housing31to vibrate. When the housing31vibrates, resultant vibration W (seeFIG. 1) is transmitted to the support column21to cause the support column21to vibrate.

The motor driver65includes a spindle motor driver66, an X-axis motor driver67, a Y-axis motor driver68, and a Z-axis motor driver69. The spindle motor driver66is a device that drives the spindle motor24of the spindle unit22. The X-axis motor driver67is a device that drives the X-axis motor124. The Y-axis motor driver68is a device that drives the Y-axis motor224. The Z-axis motor driver69is a device that drives the Z-axis motor324. The motor driver65is a device that adjusts the speeds of the motors24,124,224, and324by means of motor voltage control or PWM control, for example.

The heat sink32is a member provided as a part of the configuration of the motor driver65and for releasing heat from the motor driver65. The heat sink32includes multiple fins.

The fan motor33is a part arranged to face the heat sink32and for blowing cooling air for cooling the heat sink32of the motor driver65in the housing31. The fan motor34is arranged on a bottom surface in the housing31. While blowing cooling air upwardly, the fan motor34diffuses air in the housing31.

The temperature sensor71is a sensor that measures a temperature at the motor driver65for detecting load applied to the motor driver65. The temperature sensor72is a sensor that measures a temperature in the housing31for detecting load applied to the motor driver65and an electronic part in the housing31other than the motor driver65.

The alarm generator90is an alarm unit that generates an alarm based on a result of detection by the temperature sensor71. The alarm to be generated is not particularly limited. For example, the alarm may be generated as sound, emitted light, vibration, or a message (character), for example.

The controller60includes a CPU61as a control unit, a ROM62, a RAM63, and an input/output interface64. The controller60is arranged in the power magnetics cabinet30and connected to the motor driver65.

The CPU61includes a machining mode selection unit55. The machining mode selection unit55is a part having a first machining mode and a second machining mode as machining modes, and having a function allowing selection of either the first machining mode or the second machining mode. The first machining mode is a mode of machining the workpiece50finely. For example, the first machining mode is a finishing mode of performing finishing on the workpiece50with the drill26. For example, the finishing is milling on a surface of the workpiece50. The second machining mode is a mode of machining the workpiece50more roughly than in the first machining mode. For example, the second machining mode is a normal machining mode of performing cutting or grinding on the workpiece50with the drill26.

The finishing mode may have stepwise machining modes such as a first machining mode (for example, precise finishing mode) and a second machining mode (for example, normal finishing mode). Further, a cutting mode (or grinding mode) may have stepwise machining modes such as a first machining mode (for example, precise cutting mode) and a second machining mode (for example, normal cutting mode). As described above, the first machining mode and the second machining mode may include any machining mode, as long as the first machining mode and the second machining mode are correlated to each other in such a manner that the first machining mode is a mode of machining a machining target finely and the second machining mode is a mode of machining the machining target more roughly than in the first machining mode.

If the first machining mode is selected, the machining mode selection unit55exerts control to change the rotation numbers of the fan motors33and34so as to reduce vibration to be transmitted from the housing31to the support column21, compared to vibration to be transmitted in the second machining mode.

Changing the rotation numbers of the fan motors33and34means reducing the rotation numbers of the fan motors33and34or stopping the fan motors33and34. Phenomena generally occurring in terms of a relationship between the rotation numbers of the fan motors33and34and a vibration frequency are such that, increasing the rotation numbers of the fan motors33and34causes the fan motors33and34to vibrate more, and reducing the rotation numbers of the fan motors33and34causes the fan motors33and34to vibrate less.

By making a transition from a state where the rotation numbers of the fan motors33and34are high to a state where the rotation numbers of the fan motors33and34are low, the vibrations of the fan motors33and34are reduced. Further, by making a transition from a state where the fan motors33and34are rotated to a state where the fan motors33and34are stopped, the vibrations of the fan motors33and34are stopped.

It is assumed, for example, that the machining mode selection unit55has a cutting mode and a finishing mode, the rotation numbers of the fan motors33and34are set high in the cutting mode, and the rotation numbers of the fan motors33and34are set low in the finishing mode. In this case, if the finishing mode is selected, the machining mode selection unit55exerts control so as to reduce the rotation numbers of the fan motors33and34from the high rotation numbers of the fan motors33and34responsive to the cutting mode to the low rotation numbers of the fan motors33and34responsive to the finishing mode.

In some machine configurations, the rotation frequencies of the fan motors33and34and the natural vibration frequency of peripheral equipment may agree with each other to cause resonance. In this case, the rotation numbers of the fan motors33and34may be increased or reduced so as to make the rotation frequencies of the fan motors33and34go out of the natural vibration frequency of the peripheral equipment. Vibration resulting from the resonance becomes larger as the rotation frequency of a fan motor gets closer and closer to the natural vibration frequency of peripheral equipment, and becomes smaller as the rotation frequency of the fan motor goes out of the natural vibration frequency of the peripheral equipment. In terms of a relationship between the rotation numbers of the fan motors33and34and a vibration frequency, there is a range where, as the rotation numbers of the fan motors33and34are increased from the rotation numbers of the fan motors33and34corresponding to the natural vibration frequency of the peripheral equipment, the vibration of the machine tool10as a whole is reduced. In this range, by making a transition from a state where the rotation numbers of the fan motors33and34are low to a state where the rotation numbers of the fan motors33and34are high, the vibrations of the fan motors33and34are reduced. Reducing the vibration frequency of the machine tool10as a whole by increasing the rotation numbers of the fan motors33and34is considered to be effective control where finishing at a high speed is intended after implementation of cutting.

It is assumed, for example, that the machining mode selection unit55has a cutting mode and a high-speed finishing mode, the rotation numbers of the fan motors33and34are set at predetermined values if a machining mode is the cutting mode, and the rotation numbers of the fan motors33and34are set at values greater than the predetermined values if a machining mode is the high-speed finishing mode. In this case, if the high-speed finishing mode is selected, the machining mode selection unit55exerts control so as to increase the rotation numbers of the fan motors33and34from the rotation numbers of the fan motors33and34at the predetermined values responsive to the cutting mode to the rotation numbers of the fan motors33and34greater than the predetermined values responsive to the high-speed finishing mode.

The CPU61changes the rotation numbers of the fan motors33and34by changing an input voltage to the fan motors33and34, for example. For example, the input voltage is set at 24 V in the second machining mode, the input voltage is set at 18 V in the first machining mode, and the input voltage is changed from 24 V to 18 V for changing a machining mode to the first machining mode. In this case, the input voltage is to be reduced stepwise, so that the rotation numbers of the fan motors33and34are to be reduced stepwise accordingly. This means that such stepwise change can be considered to be change in the rotations of the fan motors33and34from high-speed rotation, to middle-speed rotation, to low-speed rotation, and then to stop achieved by changing the input voltage as follows, for example: from a high voltage, to a middle voltage, to a low voltage, and then to 0 [V].

The CPU61may exert the foregoing control for voltage change under PWM control. In this case, the CPU61may transmit a PWM command to the fan motors33and34and change the rotation numbers of the fan motors33and34. In this way, the CPU61exerts voltage control by changing a pulse width with which a voltage is to become ON, thereby adjusting the rotation numbers of the fan motors33and34finely. To employ the PWM control, a fan motor responsive to the PWM control is required. An input voltage to the fan motors33and34is changed linearly by exerting the PWM control, thereby allowing the rotation speeds of the fan motors33and34to be changed linearly.

If load detected by the load detector is determined to be greater than a predetermined threshold, more specifically, if a temperature detected by the temperature sensor71is determined to be greater (higher) than the predetermined threshold after the rotation numbers of the fan motors33and34are changed to rotation numbers responsive to the first machining mode (finishing mode, for example), the CPU61exerts control to change the rotation numbers of the fan motors33and34to the rotation numbers of the fan motors33and34responsive to the second machining mode (normal grinding or cutting mode, for example).

If the temperature detected by the temperature sensor71is determined to be greater than the predetermined threshold, the CPU61controls the alarm generator90so as to make the alarm generator90generate an alarm.

The ROM62contains various types of control programs for controlling drive of the machine tool10based on a machining program, a display program for making a display95display various types of display information, a control program such as that shown inFIG. 3for changing the rotation numbers of the fan motors33and34, and others.

The RAM63contains multiple machining programs, etc. including rotation number information for controlling drive of the spindle motor24, the X-axis motor124, the Y-axis motor224, and the Z-axis motor324, position information, and tool information.

The rotation numbers of the fan motors33and34may be changed as follows: a user determines the rotation numbers of the fan motors33and34responsive to the first machining mode, a CNC gives a command for the determined rotation numbers of the fan motors33and34, and a motor driver (not shown) for the fan motors33and34gives a command for voltages at the fan motors33and34. In this case, the CNC corresponds to the machining mode selection unit55.

[Operation in First Embodiment]

The foregoing motor controller100of the machine tool10operates as follows.FIG. 3is a flowchart for the motor controller according to the first embodiment of the present invention. As shown inFIG. 3, in step S11, the CPU61receives a signal for turning on a power supply of the motor driver65. In step S12, the CPU61drives the fan motors33and34at rotation numbers responsive to the second machining mode. In step S13, the CPU61receives a machining command from a user input unit96(seeFIG. 2).

In step S14, the machining mode selection unit55of the CPU61determines whether a machining mode in the machining command is a finishing mode. If the machining mode is the finishing mode (step S14: YES), the CPU61brings the procedure to step S15, and changes the rotation numbers of the fan motors33and34to rotation numbers responsive to the first machining mode. Then, in step S16, the CPU61starts machining. Meanwhile, if the machining mode is determined not to be a finishing mode in step S14(step S14: NO), the CPU61brings the procedure to step S16. In this case, the fan motors33and34continue rotating without being changed in rotation number.

[Effect Achieved by First Embodiment]

The motor controller100of the first embodiment achieves the following effect, for example. The motor controller100of the first embodiment includes: the motor driver65arranged in the housing31attached to the support column21as a support of the machine tool10for machining on the workpiece50; the fan motors33and34arranged in the housing31; and the CPU61. The motor driver65drives the motors24,124,224, and324that generate power for the operation of the machine tool10. The fan motors33and34blow cooling air for cooling the interior of the housing31. The CPU61includes the machining mode selection unit55allowing selection of a machining mode from the first machining mode of machining the workpiece50finely and the second machining mode of machining the workpiece50more roughly than in the first machining mode. If the first machining mode is selected, the machining mode selection unit55exerts control to change the rotation numbers of the fan motors33and34so as to reduce vibration to be transmitted from the housing31to the support column21, compared to vibration to be transmitted in the second machining mode.

Thus, in a situation where machine accuracy is required (where a surface of the workpiece50is to be machined, for example), it becomes possible to suppress transmission of the vibrations of the fan motors33and34to the support column21of the machine tool for machining on the workpiece50.

In particular, cutting under low load is sufficient for finishing on the surface of the workpiece50, for example, thereby reducing generation of heat from the motor driver65, etc. In this case, even if the rotation numbers of the fan motors33and34are reduced or the fan motors33and34are stopped, trouble is unlikely to occur. Thus, it is unlikely that the vibrations of the fan motors33and34of the power magnetics cabinet30will be transmitted to the drill26of the machining unit20, thereby enhancing the quality of the machining surface of the workpiece50.

In the motor controller100of the first embodiment, changing the rotation numbers of the fan motors33and34means that the rotation numbers of the fan motors33and34are reduced so as to go out of the natural vibration frequencies of the fan motors33and34, or the fan motors33and34are stopped. Thus, the vibrations of the fan motors33and34are reduced to reduce the vibration of the machine tool, thereby enhancing the machine accuracy of a machining target.

In the motor controller100of the first embodiment, changing the rotation numbers of the fan motors33and34means that the rotation numbers of the fan motors33and34are increased so as to go out of the natural vibration frequencies of the fan motors33and34. Thus, the vibrations of the fan motors33and34are reduced to reduce the vibration of the machine tool, thereby enhancing the machine accuracy of the machining target.

Second Embodiment

FIG. 4is a flowchart for the motor controller100of the machine tool10according to a second embodiment. In the second embodiment, if a temperature at the motor driver65detected by the temperature sensor71or72is equal to or less than a predetermined threshold, the CPU61exerts control to change the rotation numbers of the fan motors33and34so as to reduce vibration to be transmitted from the housing31to the support column21, compared to vibration to be transmitted in the second machining mode (cutting mode, for example). More specifically, if a temperature at the motor driver65is low, the CPU61reduces the rotation numbers of the fan motors33and34, or stops driving the fan motors33and34. Unless there is specific explanation about the second embodiment, the explanation about the first embodiment will also be applied appropriately.

[Operation in Second Embodiment]

In step S21, the CPU61receives a signal for turning on the power supply of the motor driver65. In step S22, the CPU61drives the fan motors33and34at rotation numbers responsive to the second machining mode. In step S23, the CPU61receives a machining command from the user input unit96(seeFIG. 2).

In step S24, the machining mode selection unit55of the CPU61determines whether a machining mode in the machining command is a finishing mode. If the machining mode is the finishing mode (step S24: YES), the CPU61brings the procedure to step S25, and changes the rotation numbers of the fan motors33and34to rotation numbers responsive to the first machining mode. Then, in step S26, the CPU61starts machining. Meanwhile, if the machining mode is determined not to be a finishing mode in step S24(step S24: NO), the CPU61brings the procedure to step S26. In this case, the fan motors33and34continue rotating without being changed in rotation number.

In step S27, the machining mode selection unit55of the CPU61receives information about a temperature detected by the temperature sensor71or72. In step S28, the machining mode selection unit55of the CPU61determines whether the temperature detected by the temperature sensor71or72is equal to or less than a predetermined threshold. If the temperature detected by the temperature sensor71or72is equal to or less than the predetermined threshold (step S28: YES), the CPU61brings the procedure to step S29, and changes the rotation numbers of the fan motors33and34to rotation numbers responsive to the first machining mode. Meanwhile, if the temperature detected by the temperature sensor71or72is not equal to or less than the predetermined threshold (step S28: NO), the CPU61transmits a control signal to the alarm generator90to turn on the alarm generator90while driving the fan motors33and34at rotation numbers responsive to the second machining mode.

[Effect Achieved by Second Embodiment]

The motor controller100of the second embodiment achieves the following effect, for example. In the motor controller100of the second embodiment, the temperature sensor71is a temperature sensor that detects a temperature at the motor driver65. The temperature sensor72is a temperature sensor that detects a temperature in the housing31. If a temperature detected by the temperature sensor71(or temperature sensor72) is determined to be greater than a predetermined threshold after the rotation numbers of the fan motors33and34are changed to rotation numbers responsive to the first machining mode, the CPU61exerts control to change the rotation numbers of the fan motors33and34to the rotation numbers of the fan motors33and34responsive to the second machining mode. By doing so, even after the rotation numbers of the fan motors33and34are changed to rotation numbers responsive to the first machining mode, an equipment or a part such as the motor driver65in the housing31can be cooled with higher efficiency in response to application of high load to the equipment or the part such as the motor driver65.

The motor controller100of the second embodiment further includes the alarm generator90that generates an alarm. If load detected by the temperature sensor71is determined to be greater than a predetermined threshold, the CPU61controls the alarm generator90so as to make the alarm generator90generate an alarm. This allows an operator of the machine tool to be easily notified of abnormality, for example, occurring at the motor controller100.

The embodiments of the present invention have been described above. In the embodiments, the fan motor33is configured to be arranged at a position facing the heat sink32. Further, the fan motor34is configured to be arranged on the bottom surface in the housing31of the power magnetics cabinet30, and to blow air upwardly to diffuse air in the housing31. However, these configurations of the embodiments are not restrictive. The fan motor34may be configured to face the spindle motor24. Alternatively, the fan motors33and34may be configured to face other electronic parts in the housing31of the power magnetics cabinet30.

In the embodiments, the CPU61is configured to control the rotation numbers of the fan motors33and34by means of voltage control under PWM control. However, this configuration of the embodiments is not restrictive. The CPU61may be configured to include a programmable logic controller (PLC) or a motor control center (MCC) as a part of the CPU61, and to exert control so as to stop the fan motors33and34using the PLC or the MCC.

In the embodiments, the controller60is configured to be arranged in the housing31. However, this configuration of the embodiments is not restrictive. The controller60may be provided at the support column21. Alternatively, the controller60may be arranged at a position separated from the housing31of the power magnetics cabinet30and may be electrically connected to the motor driver65.

In the embodiments, the controller is configured as a combination including the computer numerical controller (CNC), the motor driver65, and the controller60. However, this configuration is not restrictive. The CNC may include the control unit, the motor driver65may include the control unit, a different part may include the control unit, or the control unit may be distributed to parts.

The motor controller100of the embodiments is configured to change the rotation numbers of the fan motors33and34in response to determination of the rotation numbers of the fan motors33and34made by a user, a command for the rotation numbers of the fan motors33and34given from the CNC, and a voltage command given from the motor driver65. However, this configuration is not restrictive.

(1) In one configuration, the rotation numbers of the fan motors33and34may be changed in response to determination of the rotation numbers of the fan motors33and34made by the CNC, and a command for the rotation numbers of the fan motors33and34and a voltage command given from the motor driver65.
(2) In one configuration, the rotation numbers of the fan motors33and34may be changed in response to determination of the rotation numbers of the fan motors33and34made by the CNC, a command for the rotation numbers of the fan motors33and34given from the CNC, and a voltage command given from the PLC.
(3) In one configuration, the rotation numbers of the fan motors33and34may be determined by a determining module (a standardized part for determining the rotation numbers of the fan motors33and34), a command for the rotation numbers of the fan motors33and34may be given from the CNC, and the rotation numbers of the fan motors33and34may be changed by a particular circuit in the motor driver65. In the foregoing cases (1) to (3), the function of determining the rotation numbers of the fan motors33and34and the function of giving a command for the rotation numbers correspond to the foregoing control by the machining mode selection unit55, and the function of giving a voltage command corresponds to control by a part of the CPU61other than the machining mode selection unit55.

In the embodiments, finishing is milling on a surface of the workpiece50. However, finishing is not limited to this milling but may be spring necked machining or polishing with a grinder, for example.

In the embodiments, the temperature sensor71is configured as a temperature sensor that detects a temperature at the motor driver65. Further, the CPU61is configured in such a manner that, if a temperature detected by the temperature sensor71is determined to be greater than a predetermined threshold after the rotation numbers of the fan motors33and34are changed to rotation numbers responsive to the first machining mode, the CPU61exerts control to change the rotation numbers of the fan motors33and34to the rotation numbers of the fan motors33and34responsive to the second machining mode. However, these configurations are not restrictive. The temperature sensor71may be replaced by the temperature sensor72that measures a temperature in the housing31. If a temperature detected by the temperature sensor72is determined to be greater than a predetermined threshold after the rotation numbers of the fan motors33and34are changed to rotation numbers responsive to the first machining mode, the CPU61may exert control to change the rotation numbers of the fan motors33and34to the rotation numbers of the fan motors33and34responsive to the second machining mode.

The motor controller100of the embodiments includes the temperature sensor71that detects load applied to the motor driver65. If a temperature detected by the temperature sensor71is determined to be equal to or less than a predetermined threshold, the CPU61exerts control to change the rotation numbers of the fan motors33and34so as to reduce vibration to be transmitted from the housing31to the support column21, compared to vibration to be transmitted in the second machining mode. However, this configuration is not restrictive.

(1) In one configuration, load applied to the motor driver65may be specified by an input current detector that detects an input current to be input to the motor driver65. If the input current is low, the rotation numbers of the fan motors33and34may be changed.
(2) In one configuration, load applied to the motor driver65may be specified by an output current detector that detects an output current to be output from the motor driver65to the motors24,124,224, and324. If the output current is low, the rotation numbers of the fan motors33and34may be changed.
(3) In one configuration, load applied to the motor driver65may be specified by a rotation number detector that detects the rotation numbers of the motors24,124,224, and324. If the rotation numbers are low, the rotation numbers of the fan motors33and34may be changed. This rotation number detector corresponds to the rotation number detector80for the spindle motor24shown inFIG. 1.
(4) In one configuration, load applied to the motor driver65may be specified by a load calculator that calculates the load based on machining information input to a machine tool. If the calculated load is low, the rotation numbers of the fan motors33and34may be changed.
(5) In one configuration, load applied to the motor driver65may be determined by a user based on actual machining and specified through the user input unit96for input of the load. If the input load is low, the rotation numbers of the fan motors33and34may be changed.
(6) The fan motor may be arranged outside the housing. In this case, the fan motor is arranged fixedly outside the housing, for example.
(7) The machining mode is not limited to the first machining mode and the second machining mode but may include a third machining mode or a fourth machining mode different from the first machining mode and the second machining mode.
(8) The motor driver may be arranged in the housing in its entirety, or may be arranged partially outside the housing. Alternatively, the motor driver may be arranged outside the housing in its entirety. In this case, the motor driver is arranged fixedly outside the housing, for example.

EXPLANATION OF REFERENCE NUMERALS