Motor control device and motor control method

Abstract

A motor control device 10 disclosed in the present invention comprises a motor 11, a heating command generation unit 13 that generates a heating command for heating the motor 11, a drive command generation unit 14 that generates a drive command for driving the motor 11, a current control unit 15 that controls a current supplied to the motor 11 on the basis of the heating command or the drive command, and a control switching unit 18 that switches a command inputted to the current control unit 15 between the heating command and the drive command. The control switching unit 18 inputs the heating command to the current control unit 15 until a prescribed time elapses from startup, and inputs the drive command to the current control unit 15 after the prescribed time has elapsed from startup. This makes it possible to reduce manufacturing cost.

Description

Motor control device and motor control method

[0001] The present disclosure relates to a motor control device and a motor control method.

[0002] Conventionally, there is known a technique for protecting a motor used in a low-temperature environment by heating it (for example, see Patent Document 1). The motor in Patent Document 1 includes a plurality of drive coils, a temperature sensor that detects the ambient temperature of the motor, and a non-drive heating current supply means that supplies a non-drive heating current to the drive coils that does not rotate the motor when the temperature detected by the temperature sensor is equal to or lower than a predetermined temperature, all of the drive coils are not energized, and the motor is stationary.

[0003] Japanese Patent Application Laid-Open No. 2001-359298

[0004] However, the motor of Patent Document 1 uses the temperature detected by a temperature sensor that detects the ambient temperature of the motor as a trigger for supplying a non-driving heating current. The provision of the temperature sensor increases the manufacturing cost of the motor. In this situation, one of the objectives of the present disclosure is to reduce manufacturing costs.

[0005] One aspect of the present disclosure relates to a motor control device including a motor, a heating command generation unit that generates a heating command for heating the motor, a drive command generation unit that generates a drive command for driving the motor, a current control unit that controls a current supplied to the motor based on the heating command or the drive command, and a control switching unit that switches a command input to the current control unit between the heating command and the drive command, wherein the control switching unit inputs the heating command to the current control unit until a predetermined time has elapsed since startup, and inputs the drive command to the current control unit after the predetermined time has elapsed since startup.

[0006] Another aspect of the present disclosure relates to a motor control method, the motor control method including: a heating step of supplying a heating current to a motor for a predetermined time period after startup to heat the motor; and a driving step of supplying a driving current to the motor after the heating step to drive the motor.

[0007] According to the present disclosure, manufacturing costs can be reduced.

[0008] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present application, will be better understood from the following detailed description taken in conjunction with the drawings.

[0009] 1 is a block diagram showing the configuration of a motor control device of embodiment 1. FIG. 2 is a graph showing the time changes of each parameter corresponding to the motor control method of embodiment 2, where (a) shows motor temperature, (b) shows load factor, and (c) shows the on / off state of the motor control device. FIG. 3 is a block diagram showing the configuration of a motor control device of embodiment 3. FIG. 4 is a graph showing the time changes of each parameter corresponding to the motor control method of embodiment 3, where (a) shows motor temperature, (b) shows load factor, and (c) shows the on / off state of the motor control device.

[0010] The following describes exemplary embodiments of a motor control device and a motor control method according to the present disclosure. However, the present disclosure is not limited to the exemplary embodiments described below. While the following description may use specific numerical values ​​and materials, other numerical values ​​and materials may be used as long as the effects of the present disclosure are achieved.

[0011] (Motor Control Device) A motor control device according to the present disclosure includes a motor, a heating command generation unit, a drive command generation unit, a current control unit, and a control switching unit. The motor control device according to the present disclosure does not need to include a temperature sensor that detects the ambient temperature of the motor (e.g., the temperature of the motor housing or the environmental temperature around the motor).

[0012] The motor may be a rotary motor or a linear motor. Examples of rotary motors include a three-phase synchronous motor, a squirrel-cage induction motor, and a stepping motor. The motor may include a stator having a coil, a rotor having a permanent magnet, and an output shaft fixed to the rotor. The motor may be configured so that the rotor rotates when a drive current is supplied to the stator coil. The rotation of the rotor also rotates the output shaft, which may rotate a member connected to the output shaft (e.g., the arm of a die bonder). The motor may be incorporated into equipment (e.g., a die bonder). In this specification, "motor" refers to an electric motor.

[0013] The heating command generator generates a heating command for heating the motor. The heating command may be a command for supplying a heating current (e.g., a so-called d-axis current in a three-phase synchronous motor) to a coil to heat the motor without rotating or linearly driving the motor. The heating command generator may be included in a controller (e.g., a microcomputer) included in the motor control device. The controller may include an arithmetic unit and a storage device storing a program executable by the arithmetic unit (e.g., a program for causing a computer to execute the motor control method according to the present disclosure).

[0014] The drive command generator generates a drive command for driving the motor. The drive command may be a command for supplying a drive current to a coil for rotational driving or linear driving of the motor. The drive command generator may be included in a controller provided in the motor control device.

[0015] The current control unit controls the current supplied to the motor based on a heating command or a drive command. The current control unit may control the current supplied to the motor by controlling a power supply device including an inverter circuit. The current control unit may control the power supply device to supply the heating current to the motor based on the heating command. The current control unit may control the power supply device to supply the drive current to the motor based on the drive command. The current control unit may be included in a controller provided in the motor control device.

[0016] The control switching unit switches the command to be input to the current control unit between a heating command and a drive command. When the control switching unit sets the command to be input to the current control unit to a heating command, the control switching unit may prohibit a drive command from being input to the current control unit. When the control switching unit sets the command to be input to the current control unit to a drive command, the control switching unit may prohibit a heating command from being input to the current control unit. The control switching unit may be included in a controller provided in the motor control device.

[0017] The control switching unit inputs a heating command to the current control unit until a predetermined time has elapsed since startup, and inputs a drive command to the current control unit after the predetermined time has elapsed since startup. In this specification, "starting" may mean, for example, inputting a signal from a control system of a device incorporating the motor to a motor control device to start supplying current to the motor, or inputting a signal from the control system to the motor control device to start drive control of the motor.

[0018] In this way, the motor control device according to the present disclosure is configured to supply a heating current to the motor for a predetermined period of time after startup to heat the motor without using a temperature sensor. Because no temperature sensor is required for the heating operation, the manufacturing costs of the motor control device can be reduced.

[0019] Furthermore, the motor control device according to the present disclosure can control the motor's output (torque or thrust) with high precision. Specifically, when drive control of a motor is initiated immediately after startup, the motor heats up due to the flow of drive current through the coil, causing its magnetic characteristics to change over time (a transient phenomenon). Changes in the motor's magnetic characteristics result in fluctuations in the motor's output. In contrast, the motor control device according to the present disclosure heats the motor with a heating current for a predetermined period of time before starting drive control. This allows drive control to be initiated with the motor's magnetic characteristics already changed, thereby suppressing the effects of the transient phenomenon on the motor's output and enabling high-precision control of the motor's output.

[0020] Furthermore, the motor control device according to the present disclosure enables highly accurate position control of equipment incorporating a motor. Specifically, when drive control of a motor is initiated immediately after startup, the motor heats up as described above, and the heat is transferred to the motor's output shaft and the components of the equipment connected to the output shaft (e.g., an arm), causing thermal expansion. Thermal expansion of the output shaft and the components of the equipment can result in errors in the position of the components of the equipment (e.g., the position of the tip of the arm). In contrast, the motor control device according to the present disclosure heats the motor with a heating current for a predetermined period of time before drive control begins. Therefore, drive control is initiated with thermal expansion of the output shaft and other components already occurring, preventing errors in the position of the components of the equipment and enabling highly accurate position control of the equipment.

[0021] The motor control device may further include a position detector that detects the position of the motor, and an abnormality determination unit that determines whether or not there is an abnormality in the motor based on the detection result of the position detector while a heating command is input to the current control unit. If the abnormality determination unit detects an abnormality in the motor, the control switching unit may stop inputting the heating command to the current control unit even before a predetermined time has elapsed since startup. The "motor position" may be the angular position of a rotor in a rotary motor, or the linear position of a mover in a linear motor. The position detector may be, for example, an encoder, resolver, or Hall sensor. A detection signal (position signal) from the position detector may be input to a controller included in the motor control device. The abnormality determination unit may determine that an abnormality has occurred in the motor if the detection value of the position detector fluctuates beyond a predetermined threshold while a heating command is input to the current control unit. The abnormality determination unit may determine that there is no abnormality in the motor if the fluctuation in the detection value of the position detector is equal to or less than a predetermined threshold while a heating command is input to the current control unit.

[0022] When the control switching unit stops inputting the heating command to the current control unit, it may start inputting the drive command to the current control unit. With this configuration, if an unintended large fluctuation occurs in the position of the motor, it is possible to return the motor to its normal position by stopping the supply of heating current to the motor and supplying a drive current. This makes it possible to suppress unintended fluctuations in the position of the device in which the motor is incorporated. When the input of the drive current to the current control unit suppresses fluctuations in the detection value of the position detector to a predetermined threshold or less, the control switching unit may resume inputting the heating command to the current control unit, or may continue inputting the drive command to the current control unit.

[0023] When the abnormality determination unit detects a motor abnormality, it may output an alarm signal to notify the user. The alarm signal may be input to a controller included in the motor control device or to a control system included in the equipment incorporating the motor. When this signal is input, the motor control device or the equipment may notify the user of the occurrence of a motor abnormality by some kind of alarm means (for example, a monitor, speaker, or lamp). This allows the user to quickly deal with the occurrence of a motor abnormality.

[0024] The heating command may include a temperature increase command to heat the motor to increase its temperature, and a warm-keeping command, generated after the temperature increase command, to heat the motor to keep it warm. The temperature increase command may be a command to supply a temperature increase current to the coil to increase the temperature of the motor. The warm-keeping command may be a command to supply a warm-keeping current to the coil to keep the motor warm. Here, the temperature increase current and the warm-keeping current are each a form of the heating current. The effective value of the temperature increase current may be greater than the effective value of the warm-keeping current. With this configuration, the motor is rapidly heated in response to the heating command, and then kept warm based on the warm-keeping command. For example, by making the effective value of the drive current supplied to the motor equal to or close to the effective value of the warm-keeping current, the difference between the motor's warm-keeping temperature and the motor temperature during operation can be reduced. In this case, the rapid heating of the motor shortens the time lag from startup to motor operation, and the keeping the motor warm reduces temperature changes during operation.

[0025] The heating command generator may continue generating the keep-warm command until the command input to the current controller is switched from a heating command to a drive command. In this case, the command input to the current controller is seamlessly switched from a keep-warm command to a drive command, thereby further enhancing the effect of keeping the motor warm.

[0026] The motor control device may further include a current determination unit that determines the magnitude of the current (keep-warm current) supplied to the motor in response to a keep-warm command based on the magnitude of the current (drive current) supplied to the motor in response to a drive command. For example, the current determination unit may determine the effective value of the keep-warm current based on the effective value of the drive current. In this case, the effective value of the keep-warm current may be, for example, 80% or more and 120% or less of the effective value of the drive current. The magnitude of the drive current may be determined by performing a predetermined motor control operation (e.g., an operation simulating a motor control operation when actually handling an object) and measuring the magnitude of the drive current during this predetermined motor control operation. This configuration makes it possible to appropriately reset the magnitude of the keep-warm current as needed. The current determination unit may be included in a controller provided in the motor control device.

[0027] When the motor control device is turned off after a predetermined time has elapsed since startup, the heating command generation unit may generate a warm-keeping command without generating a warm-up command at the next startup if the duration of the off state is shorter than a predetermined threshold time. In other words, when the motor control device is turned off after the motor has been heated once and then restarted within the predetermined threshold time, the heating command generation unit may keep the motor warm without rapidly heating the motor. In this configuration, if the duration of the motor control device's off state is short, i.e., if the motor temperature has not dropped significantly at the next startup, no warm-up current is supplied to the motor. Supplying a warm-up current to the motor can cause a temperature overshoot, but by avoiding such an overshoot, waste of electrical energy can be reduced.

[0028] (Motor Control Method) The motor control method according to the present disclosure can be executed, for example, in the motor control device described above, but may also be executed in other devices or systems. The motor control method according to the present disclosure includes a heating step and a driving step.

[0029] In the heating step, a heating current is supplied to the motor for a predetermined time after startup. The heating current may be a current that does not rotate or move the rotor or mover of the motor (for example, a so-called d-axis current in a three-phase synchronous motor). This heats the motor for a predetermined time after startup, pre-changing the magnetic properties of the motor and causing thermal expansion in the motor and the device in which it is incorporated.

[0030] In the driving step, after the heating step, a driving current for driving the motor is supplied to the motor. The driving current may be a current that rotates or moves the rotor or mover of the motor (for example, a current including a so-called q-axis component in a three-phase synchronous motor). In the heating step, drive control is started in a state in which the magnetic characteristics of the motor have changed and thermal expansion has occurred, so as described above, it is possible to control the motor output with high precision and to control the position of the device in which the motor is incorporated with high precision.

[0031] The motor control method may further include a measurement step of measuring a temperature change of an apparatus incorporating the motor while supplying a heating current to the motor before the heating step, and a time setting step of setting a predetermined time for the heating step based on the measured temperature change. In the measurement step, the temperature change of the apparatus may be measured to determine the time until the temperature of the apparatus reaches saturation (hereinafter also referred to as saturation time). In the time setting step, the predetermined time for the heating step (i.e., the time for supplying the heating current to the motor) may be set to 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, or 100% or more of the saturation time. The measurement step need only be performed once when the apparatus is installed, but may also be performed as needed. The temperature change of the apparatus incorporating the motor may be measured, for example, by measuring the temperature change of an arbitrary portion of the apparatus or the temperature change of an arbitrary portion of the motor.

[0032] The heating current may include a heating current that heats the motor to raise its temperature, and a warming current that is supplied to the motor after the heating current has been supplied and heats the motor to keep it warm. The effective value of the heating current may be greater than the effective value of the warming current. With this configuration, the motor is rapidly heated by the heating current, and then kept warm by the warming current.

[0033] During the heating step, the supply of a heat-retaining current to the motor may continue until the drive step is started. In this case, the supply of the heat-retaining current can be seamlessly switched to the supply of the drive current, which further enhances the effect of keeping the motor warm, i.e., the effect of suppressing fluctuations in the motor temperature during the drive step.

[0034] The motor control method may further include a current determination step of determining the magnitude of the warming current based on the magnitude of the drive current. For example, the current determination step may determine the effective value of the warming current based on the effective value of the drive current. In this case, the effective value of the warming current may be, for example, 80% or more and 120% or less of the effective value of the drive current. This configuration makes it possible to appropriately reset the magnitude of the warming current as needed.

[0035] The motor control method may further include a stopping step of stopping the supply of current to the motor (e.g., both the heating step and the drive current) after the driving step, and a reheating step of supplying a reheating current to the motor after the stopping step to reheat the motor. In the reheating step, if the duration of the stopping step is shorter than a predetermined threshold time, only a warming current may be supplied to the motor to keep the motor warm. In this configuration, if the time during which the current supply to the motor is stopped is short, i.e., if the motor temperature has not dropped significantly when the current supply is resumed, a warming current is not supplied to the motor. This prevents temperature overshoot and reduces waste of electrical energy. The reheating step may be initiated when the motor is restarted. Note that in the reheating step, if the duration of the stopping step is equal to or longer than a predetermined threshold time, a warming current may be supplied to the motor to heat the motor, followed by the warming current.

[0036] As described above, according to the present disclosure, since a temperature sensor is not used, the manufacturing cost of a motor control device can be reduced. Furthermore, according to the present disclosure, it is possible to control the output of a motor with high precision. Furthermore, according to the present disclosure, it is possible to control the position of a device incorporating a motor with high precision.

[0037] An example of a motor control device and a motor control method according to the present disclosure will be described in detail below with reference to the drawings. The components and steps described above can be applied to the components and steps of the example motor control device and motor control method described below. The components and steps of the example motor control device and motor control method described below can be modified based on the above description. Furthermore, the matters described below may be applied to the above embodiment. Of the components and steps of the example motor control device and motor control method described below, components and steps that are not essential to the motor control device and motor control method according to the present disclosure may be omitted. Note that the diagrams shown below are schematic and do not accurately reflect the shapes and numbers of actual components.

[0038] First Embodiment A first embodiment of the present disclosure will be described below. First, the configuration of a motor control device 10 of the present embodiment will be described, and then a motor control method of the present embodiment will be described.

[0039] 1, a motor control device 10 of this embodiment includes a motor 11, a position detector 12, a heating command generator 13, a drive command generator 14, a current controller 15, a power supply 16, a time counter 17, a control switch 18, and an abnormality determination unit 19. On the other hand, the motor control device 10 does not include a temperature sensor that detects the ambient temperature of the motor 11.

[0040] The motor 11 in this embodiment is a three-phase synchronous motor, but is not limited to this. The motor 11 has a stator with a coil, a rotor with a permanent magnet disposed inside the stator, and an output shaft fixed to the rotor (all not shown). The motor 11 may also have a current sensor (not shown) for feeding back information about the current I flowing through the coil to the current control unit 15.

[0041] The position detector 12 detects the position of the motor 11. Specifically, the position detector 12 is fixed to the motor 11 and detects the rotational angle position of the rotor (or output shaft) of the motor 11. The detection value of the position detector 12 is sent to the drive command generation unit 14 and the abnormality determination unit 19.

[0042] The heating command generator 13 generates a heating command for heating the motor 11. The heating command in this embodiment is a command for supplying a heating current (in this example, a so-called d-axis current) to the coil for heating the motor 11 without driving the motor 11 to rotate. The generated heating command is sent to the control switch 18.

[0043] The drive command generator 14 generates a drive command for driving the motor 11. The drive command in this embodiment is a command for supplying a drive current (in this example, a current including a so-called q-axis component) to the coil for rotationally driving the motor 11. The generated drive command is sent to the control switch 18.

[0044] Based on the heating command or the drive command, the current control unit 15 controls the current supplied to the motor 11. Specifically, the current control unit 15 controls the power supply unit 16 to control the current supplied to the motor 11. Based on the heating command, the current control unit 15 controls the power supply unit 16 to supply a heating current to the motor 11. Based on the drive command, the current control unit 15 controls the power supply unit 16 to supply a drive current to the motor 11.

[0045] The power supply unit 16 is controlled by the current control unit 15 and supplies a heating current or a drive current to the motor 11. The power supply unit 16 may include an inverter circuit (not shown) having a plurality of switching elements. The current supplied from the power supply unit 16 to the motor 11 can be controlled by the on / off operation of each switching element.

[0046] Time counter 17 receives a start signal (i.e., a signal indicating that power supply to motor 11 should be started) from a control system (not shown) that controls a device (e.g., a die bonder) in which motor 11 is incorporated, and counts the elapsed time from when the start signal was received. Time counter 17 may be included in a controller (not shown) provided in motor control device 10. The count information of time counter 17 is sent to control switch unit 18.

[0047] Control switching unit 18 switches the command to be input to current control unit 15 between a heating command and a drive command based on the count information of time counter 17. Specifically, control switching unit 18 inputs a heating command to current control unit 15 until a predetermined time has elapsed since startup, and inputs a drive command to current control unit 15 after the predetermined time has elapsed since startup. As a result, motor 11 is heated without being driven to rotate for a predetermined time after startup, and then rotation drive control of motor 11 is started from the heated state.

[0048] While a heating command is being input to the current control unit 15 (i.e., during a predetermined time period after startup), the abnormality determination unit 19 determines whether or not an abnormality has occurred in the motor 11 based on the detection result of the position detector 12. In this embodiment, the abnormality determination unit 19 determines that an abnormality has occurred in the motor 11 if the detection value of the position detector 12 fluctuates beyond a predetermined threshold while a heating command is being input to the current control unit 15 (i.e., while the motor 11 is not being driven).

[0049] When the abnormality determination unit 19 detects an abnormality in the motor 11, the control switching unit 18 stops inputting a heating command to the current control unit 15 even before a predetermined time has elapsed since startup. In this case, the control switching unit 18 may start inputting a drive command to the current control unit 15. Alternatively or in addition to this, when the abnormality determination unit 19 detects an abnormality in the motor 11, the abnormality determination unit 19 may output a notification signal to notify that fact.

[0050] (Motor Control Method) The motor control method of the present embodiment can be executed, for example, by the motor control device 10 of the present embodiment. The motor control method of the present embodiment includes a measuring step, a time setting step, a heating step, and a driving step. The measuring step and the time setting step can be executed by a user, while the heating step and the driving step can be executed by the motor control device 10 (or a controller included therein).

[0051] In the measurement process, a heating current (in this example, a so-called d-axis current) for heating the motor 11 is supplied to the motor 11, while measuring the temperature change of a device (e.g., a die bonder) incorporating the motor 11. Any type of temperature sensor may be used for this measurement. It is preferable to determine the time until the temperature of the device saturates (saturation time) based on the measured temperature change.

[0052] In the time setting step, a predetermined time in the heating step (i.e., the time for supplying a heating current to the motor 11) is set based on the temperature change measured in the measurement step. In this embodiment, the predetermined time is set to 90% or more and 110% or less of the saturation time, but is not limited to this.

[0053] In the heating step, a heating current is supplied to the motor 11 for a predetermined time (set in the time setting step, as described above) after startup. The heating current may be a current that can heat the motor 11 without driving the motor 11 to rotate. This causes the temperature of the device in which the motor 11 is incorporated to substantially saturate.

[0054] In the driving step, after the heating step, a driving current for driving the motor 11 is supplied to the motor 11. Because the motor 11 and the device in which it is incorporated are preheated in the heating step, the motor 11 can be driven without a large temperature change. In this case, since a thermal transient state does not substantially occur, it is possible to control the output (torque in this example) of the motor 11 with high precision and to control the position of the device in which the motor 11 is incorporated with high precision without performing any temperature compensation.

[0055] Second Embodiment A second embodiment of the present disclosure will be described. The motor control device 10 or motor control method of this embodiment differs from the first embodiment in the heating command generation unit 13 or the heating process. The following mainly describes the differences from the first embodiment.

[0056] The heating command generator 13 of the motor control device 10 of this embodiment generates a temperature increase command and a subsequent heat-keeping command as heating commands. The temperature increase command is a command to supply a temperature increase current (in this example, a relatively large d-axis current) to the coils to heat the motor 11 without rotating the motor 11, in order to increase the temperature of the motor 11. The heat-keeping command is a command generated after the temperature increase command, and is a command to supply a heat-keeping current (in this example, a relatively small d-axis current) to the coils to heat the motor 11 without rotating the motor 11, in order to keep the motor 11 warm. The generated temperature increase command and heat-keeping command are sent to the control switch 18.

[0057] In addition, the heating command generation unit 13 of this embodiment continues to generate a keep-warm command until the command input to the current control unit 15 is switched from a heating command (in this example, a temperature increase command or a keep-warm command) to a drive command.

[0058] Furthermore, in this embodiment, when the motor control device 10 is turned off after a predetermined time has elapsed since startup, if the duration of the off state is shorter than a predetermined threshold time t_th, the heating command generation unit 13 generates a keep-warm command without generating a temperature increase command at the next startup.

[0059] (Motor Control Method) In the heating step of the motor control method of this embodiment, a heating current and a heat-keeping current are supplied to the motor 11 as heating currents. The heating current is a current (in this example, a relatively large d-axis current) for heating the motor 11 without driving the motor 11 to rotate in order to raise the temperature of the motor 11. The heat-keeping current is a current (in this example, a relatively small d-axis current) supplied to the motor 11 after the heating current has been supplied, and is a current (in this example, a relatively small d-axis current) for heating the motor 11 without driving the motor 11 to rotate in order to keep the motor 11 warm.

[0060] In addition, in the heating step of this embodiment, the supply of the heat-retaining current to the motor 11 continues until the driving step is started.

[0061] Furthermore, the motor control method of this embodiment includes a stopping process and a reheating process. The stopping process is a process of stopping the supply of current to the motor 11 after the driving process. The reheating process is a process of supplying a reheating current (in this example, a so-called d-axis current) to the motor 11 to reheat the motor 11 after the stopping process. In this reheating process, when the duration of the stopping process is shorter than a predetermined threshold time t_th, only a heat-keeping current is supplied to the motor 11 to heat the motor 11 and keep it warm.

[0062] FIG. 2 is a graph showing the time evolution of each parameter corresponding to the motor control method of this embodiment. The load factor shown in FIG. 2(b) refers to the ratio of input power to the rated power of the motor 11 (input power / rated power). As shown in FIG. 2(b), at time t0, the motor control device 10 is turned on (or started), and the heating process is initiated. From time t0 to time t1, a heating current is supplied to the motor 11, and the temperature of the motor 11 rapidly rises to or slightly exceeds the target temperature Tg. In this example, the load factor is 0.9 or more and 1.1 or less, which is higher than the heat-retention load factor Lt and the target load factor Lg shown in the figure (the former is the load factor when the motor 11 is kept at the target temperature Tg, and the latter is the load factor when the motor 11 is driven while being kept at the target temperature Tg, with the former being slightly higher). From time t1 to time t2, a heat-retention current is supplied to the motor 11, and the temperature of the motor 11 is maintained at the target temperature Tg. At time t2, the heating process switches to the driving process, and a driving current is supplied to the motor 11 from time t2 to time t3. During this time, the temperature of the motor 11 hardly fluctuates. At time t3, the motor control device 10 is turned off (or stopped). The temperature of the motor 11 then drops, and at time t4, the motor control device 10 is turned on again (or restarted). Because the time from time t3 to time t4 (i.e., the duration of the stopping process) is shorter than the predetermined threshold time t_th shown in the figure, only a heat-retaining current is supplied to the motor 11 in the reheating process starting at time t4, and the temperature of the motor 11 reaches and is maintained at the target temperature Tg without overshooting.

[0063] Third Embodiment A third embodiment of the present disclosure will be described. The motor control device 10 or motor control method of this embodiment differs from the second embodiment in that it includes a current determination unit 21 or a current determination step. The following mainly describes the differences from the second embodiment.

[0064] As shown in FIG. 3 , the motor control device 10 of this embodiment includes a current determination unit 21 that determines the magnitude of the current (keep-warm current) to be supplied to the motor 11 in response to a keep-warm command based on the magnitude of the current (drive current) supplied to the motor 11 in response to a drive command. Information regarding the keep-warm current determined by the current determination unit 21 is sent to the heating command generation unit 13. The current determination unit 21 may receive information regarding the current I flowing through the driven motor 11 and determine the magnitude of the keep-warm current based on the received information. Alternatively, the current determination unit 21 may receive information regarding the magnitude of the drive current indirectly determined from the drive command and determine the magnitude of the keep-warm current based on the received information. Note that the flow of this information (or signals) is not shown in FIG. 3 .

[0065] (Motor Control Method) The motor control method of this embodiment includes a current determination step of determining the magnitude of the warming current based on the magnitude of the drive current. In this case, the magnitude of the warming current may be set to, for example, 80% or more and 120% or less of the magnitude of the drive current.

[0066] FIG. 4 is a graph showing the time evolution of each parameter corresponding to the motor control method of this embodiment. As shown in the figure, at time t0, the motor control device 10 is turned on (or started). From time t0 to time t1, a drive current is supplied to the motor 11, and the magnitude of the warming current to be supplied later is determined based on the magnitude of the drive current (current determination process). During this time, the temperature of the motor 11 increases due to the supply of the drive current. At time t1, a heating process is initiated. From time t1 to time t2, a warming current is supplied to the motor 11, and the temperature of the motor 11 rapidly increases to reach or slightly exceed the target temperature Tg. In this example, the load factor at this time is greater than or equal to 0.9 and less than or equal to 1.1, which is higher than the warming load factor Lt and the target load factor Lg shown in the figure. From time t2 to time t3, a warming current is supplied to the motor 11, and the temperature of the motor 11 is maintained at the target temperature Tg. At time t3, the heating process is switched to the driving process, and a driving current is supplied to the motor 11 from time t3 to time t4. During this time, the temperature of the motor 11 hardly changes. At time t4, the motor control device 10 is turned off (or stopped). Thereafter, the temperature of the motor 11 drops.

[0067] <<Additional Notes>> The above embodiments disclose the following technologies. (Technology 1) A motor control device comprising: a motor; a heating command generation unit that generates a heating command for heating the motor; a drive command generation unit that generates a drive command for driving the motor; a current control unit that controls a current supplied to the motor based on the heating command or the drive command; and a control switching unit that switches the command input to the current control unit between the heating command and the drive command, wherein the control switching unit inputs the heating command to the current control unit until a predetermined time has elapsed since startup, and inputs the drive command to the current control unit after the predetermined time has elapsed since startup. (Technology 2) A motor control device according to Technology 1, further comprising: a position detector that detects the position of the motor; and an abnormality determination unit that determines whether or not there is an abnormality in the motor based on the detection result of the position detector while the heating command is input to the current control unit, wherein the control switching unit stops inputting the heating command to the current control unit if the abnormality determination unit detects an abnormality in the motor, even before the predetermined time has elapsed since startup. (Technology 3) The motor control device according to Technology 2, wherein the control switching unit starts inputting the drive command to the current control unit when stopping input of the heating command to the current control unit. (Technology 4) The motor control device according to Technology 2 or 3, wherein the abnormality determination unit outputs a notification signal to notify the user of an abnormality in the motor when it detects an abnormality in the motor. (Technology 5) The motor control device according to any one of Technology 1 to 4, wherein the heating command includes: a temperature increase command for heating the motor to increase its temperature; and a keep-warm command, which is generated after the temperature increase command and heats the motor to keep it warm. (Technology 6) The motor control device according to Technology 5, wherein the heating command generation unit continues generating the keep-warm command until the command input to the current control unit is switched from the heating command to the drive command. (Technology 7) The motor control device according to Technology 5 or 6, further comprising a current determination unit that determines the magnitude of the current to be supplied to the motor in response to the keep-warm command, based on the magnitude of the current to be supplied to the motor in response to the drive command.(Technology 8) The motor control device according to any one of Technologies 5 to 7, wherein, when the motor control device is turned off after the predetermined time has elapsed since the start-up, the heating command generation unit generates the keep-warm command without generating the temperature increase command at the next start-up if the duration of the off state is shorter than a predetermined threshold time. (Technology 9) A motor control method comprising: a heating step of supplying a heating current to the motor for heating the motor for a predetermined time after start-up; and a driving step of supplying a drive current to the motor for driving the motor after the heating step. (Technology 10) The motor control method according to Technology 9, further comprising: a measuring step of measuring a temperature change in a device in which the motor is incorporated while supplying the heating current to the motor before the heating step; and a time setting step of setting the predetermined time for the heating step based on the measured temperature change. (Technology 11) The motor control method according to Technology 9 or 10, wherein the heating current includes: a temperature-raising current that heats the motor to raise the temperature of the motor; and a warm-keeping current that is supplied to the motor after the supply of the temperature-raising current and heats the motor to keep it warm. (Technology 12) The motor control method according to Technology 11, wherein in the heating step, the supply of the warm-keeping current to the motor continues until the driving step is started. (Technology 13) The motor control method according to Technology 11 or 12, further comprising a current determination step that determines the magnitude of the warm-keeping current based on the magnitude of the driving current. (Technology 14) The motor control method according to any one of Technology 9 to 13, further comprising: a stopping step that stops supply of current to the motor after the driving step; and a reheating step that supplies the motor with a reheating current to reheat the motor after the stopping step, wherein in the reheating step, only the warm-keeping current that heats the motor to keep it warm is supplied to the motor when the duration of the stopping step is shorter than a predetermined threshold time.

[0068] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0069] The present disclosure can be used in a motor control device and a motor control method.

[0070] 10: Motor control device 11: Motor 12: Position detector 13: Heating command generation unit 14: Drive command generation unit 15: Current control unit 16: Power supply unit 17: Time counter 18: Control switching unit 19: Abnormality determination unit 21: Current determination unit I: Motor current Lg: Target load factor Lt: Heat retention load factor Tg: Target temperature t_th: Threshold time

Claims

1. A motor control device comprising: a motor; a heating command generation unit that generates a heating command for heating the motor; a drive command generation unit that generates a drive command for driving the motor; a current control unit that controls a current supplied to the motor based on the heating command or the drive command; and a control switching unit that switches the command input to the current control unit between the heating command and the drive command, wherein the control switching unit inputs the heating command to the current control unit until a predetermined time has elapsed since startup, and inputs the drive command to the current control unit after the predetermined time has elapsed since startup.

2. A motor control device as described in claim 1, further comprising: a position detector which detects the position of the motor; and an abnormality judgment unit which judges whether or not there is an abnormality in the motor based on the detection result of the position detector while the heating command is being input to the current control unit, wherein if the abnormality judgment unit detects an abnormality in the motor, the control switching unit stops inputting the heating command to the current control unit even before the specified time has elapsed since the start-up.

3. The motor control device according to claim 2, wherein the control switching unit starts inputting the drive command to the current control unit when the input of the heating command to the current control unit is stopped.

4. A motor control device as claimed in claim 2 or 3, wherein the abnormality determination unit outputs an alarm signal to notify the driver when an abnormality in the motor is detected.

5. A motor control device as claimed in any one of claims 1 to 3, wherein the heating command includes: a temperature increase command for heating the motor in order to increase the temperature of the motor; and a heat-keep command, which is generated after the temperature increase command and for heating the motor in order to keep the motor warm.

6. The motor control device according to claim 5, wherein the heating command generating unit continues generating the keep warm command until the command input to the current control unit is switched from the heating command to the drive command.

7. The motor control device according to claim 5, further comprising a current determination unit that determines the magnitude of the current to be supplied to the motor in response to the keep-warm command, based on the magnitude of the current to be supplied to the motor in response to the drive command.

8. A motor control device as described in claim 5, wherein when the motor control device is turned off after the specified time has elapsed from the start-up, if the duration of the off state is shorter than a specified threshold time, the heating command generation unit generates the keep warm command without generating the temperature increase command at the next start-up.

9. A motor control method comprising: a heating step of supplying a heating current to the motor for a predetermined time after startup, for heating the motor; and a driving step of supplying a driving current to the motor for driving the motor after the heating step.

10. The motor control method according to claim 9, further comprising: a measurement step of measuring a temperature change in an equipment in which the motor is incorporated while supplying the heating current to the motor before the heating step; and a time setting step of setting the predetermined time in the heating step based on the measured temperature change.

11. A motor control method as described in claim 9 or 10, wherein the heating current includes: a temperature-raising current that heats the motor in order to raise the temperature of the motor; and a heat-retention current that is supplied to the motor after the supply of the temperature-raising current and that heats the motor in order to keep the motor warm.

12. The motor control method according to claim 11, wherein in the heating step, the supply of the heat-retention current to the motor is continued until the driving step is started.

13. The motor control method according to claim 11, further comprising a current determination step of determining the magnitude of the warming current based on the magnitude of the drive current.

14. A motor control method as claimed in claim 9 or 10, further comprising: a stopping step of stopping the supply of current to the motor after the driving step; and a reheating step of supplying a reheating current to the motor for reheating the motor after the stopping step, wherein in the reheating step, when the duration of the stopping step is shorter than a predetermined threshold time, only a heat-retention current for heating the motor in order to keep the motor warm is supplied to the motor.

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