Control device for electric motor

Abstract

This control device for controlling an electric motor for driving a drive shaft of an industrial machine is provided with a d-axis current control unit that, on the basis of an assumed processing region obtained by adding a margin that is necessary to start up a magnetic flux of the electric motor to an intensity necessary for actual processing in the periphery of an actual processing region of a workpiece, performs control to set a d-axis current in vector control to a value that is further reduced than an actual processing current value necessary for the actual processing in a region outside the assumed processing region, and set the d-axis current to the actual processing current value within the assumed processing region.

Description

Motor control device

[0001] The present disclosure relates to a control device for an electric motor.

[0002] For AC motors, such as induction motors and synchronous motors, a known method of controlling the current driving the motor is vector control, which separates and controls the q-axis component of the current that contributes to torque generation and the d-axis component of the current in the excitation direction. The dq coordinate axes are set so that the d-axis and q-axis are out of phase with each other by π / 2. Among AC motors, induction motors generate a rotating magnetic field by passing a primary current through the stator coil. This rotating magnetic field induces an electromotive force in the rotor, causing a secondary current to flow. The interaction between this secondary current and magnetic flux generates torque. Patent Document 1 describes an example configuration of a control device for an induction motor.

[0003] Among AC motors, in permanent magnet synchronous motors, the d-axis is defined as the direction of the magnetic flux of the permanent magnet, and the q-axis is defined as the direction that is π / 2 phase different from the d-axis. Various current control methods have been proposed for high-performance operation of permanent magnet synchronous motors. For example, Patent Document 2 describes a control method for a permanent magnet synchronous motor in which a current command vector, which is a composite vector of the q-axis current and the d-axis current, is set to eliminate voltage saturation. Patent Document 3 relates to a drive system for driving a three-phase synchronous motor and describes a configuration in which the rotor position is estimated based on the neutral point potential of the synchronous motor to control a pulse-width modulation inverter.

[0004] Such an AC motor is used, for example, in a control device for controlling the drive of a spindle of a machine tool. Patent Document 4 describes an example of the configuration of a machine tool (machining center) controlled by a numerical control device.

[0005] Japanese Patent Application Laid-Open No. 2017-46487 International Publication No. 2013 / 084461 International Publication No. 2012 / 157039 Japanese Patent Application Laid-Open No. 1-20954

[0006] When vector control is applied to AC motors, it is common to maintain a constant excitation current (d-axis current) above a certain level to ensure responsiveness to sudden load changes. However, for example, during the overall period in which a machine tool is machining a workpiece, there are periods in which the spindle is rotating without load. In these cases, the d-axis current flows more than necessary when the spindle, i.e., the motor, is rotating without load. Therefore, reducing the d-axis current during no-load operation of the motor is useful for power-saving operation. However, no method has been proposed to achieve this by appropriately distinguishing between the no-load operation state of the motor and the actual machining state. Therefore, there is a need for a technology that can appropriately distinguish between the no-load operation state of the motor and the actual machining state, thereby reducing the motor's power consumption.

[0007] One aspect of the present disclosure is a control device that controls an electric motor that drives a drive shaft of industrial machinery, and is equipped with a d-axis current control unit that controls, based on an expected machining area around the actual machining area of ​​the workpiece, to which a margin necessary for raising the magnetic flux of the electric motor to the strength required for actual machining is added, the d-axis current in vector control in areas outside the expected machining area is set to a value that is reduced from the actual machining current value required for actual machining, and the d-axis current within the expected machining area is set to the actual machining current value.

[0008] These and other objects, features and advantages of the present invention will become more apparent from the detailed description of exemplary embodiments of the invention illustrated in the accompanying drawings.

[0009] FIG. 1 is a block diagram showing the functional configuration of a control device for an electric motor according to an embodiment; FIG. 2 is a diagram showing the relationship between the q axis and the d axis in vector control; FIG. 3 is a diagram showing the configuration of a numerical control device and a machine tool; FIG. 4 is a diagram showing the configuration of a d-axis current control unit in the first embodiment and the second embodiment; FIG. 5 is a diagram for explaining an assumed machining area in the first embodiment and the second embodiment; FIG. 6 is a diagram for explaining an assumed machining area in the second embodiment; FIG. 7 is a diagram for explaining an assumed machining area in the second embodiment; FIG. 8 is a diagram for explaining an assumed machining area in the second embodiment; FIG. 9 is a diagram for explaining an assumed machining area in the third embodiment; FIG. 10 is a diagram for explaining an assumed machining area in the third embodiment; FIG. 11 is a diagram for explaining an assumed machining area in the third embodiment;

[0010] Next, embodiments of the present disclosure will be described with reference to the drawings. In the drawings, like components or functional parts are designated by like reference numerals. The scales of these drawings have been changed appropriately to facilitate understanding. Furthermore, the embodiment shown in the drawings is one example for implementing the present invention, and the present invention is not limited to the illustrated embodiment.

[0011] FIG. 1 is a block diagram showing the functional configuration of an electric motor control device 100 according to one embodiment. In the configuration shown in FIG. 1, the control device 100 controls an electric motor 1, which is an AC motor such as an induction motor or a synchronous motor, by vector control. In vector control, control is performed by separating the current into a q-axis component that contributes to torque generation and a d-axis component that corresponds to the excitation direction. FIG. 2 shows the relationship between the q-axis and d-axis in vector control. As shown in FIG. 2, in vector control, the q-axis is set in a direction that is π / 2 phase different from the d-axis, which corresponds to the excitation direction.

[0012] In the case of a synchronous motor, a q-axis current Iq corresponding to a target maximum torque is set in the q-axis direction on the qd coordinate axis in Figure 2. Circle C shows the locus of the motor current vector corresponding to this maximum torque. The q-axis current Iq alone cannot generate maximum torque due to the influence of back-EMF Iw and other factors caused by the rotor's magnetic flux acting on the rotor. Therefore, it is common to control the d-axis current Id to obtain a motor current vector I that generates maximum torque as a composite vector of the d-axis current Id and the q-axis current (the q-axis current Iq in Figure 2 minus the back-EMF Iw and other components). More specific vector control methods for synchronous motors include maximum torque control, which is based on the existence of a current phase that maximizes generated torque for a given current, and flux-weakening control, which maintains the motor terminal voltage below a limit value. Both of these control methods control the d-axis current for high-performance operation.

[0013] In an induction motor, the excitation current (d-axis current) is set in phase with the rotating magnetic field, and the secondary current (q-axis current) is set in phase with the secondary voltage that is generated in a direction that is π / 2 phase different from the excitation current, and the primary current that is the resultant vector of these current vectors is supplied to the motor. In the case of normal vector control of an induction motor, torque control is performed by setting the d-axis current.

[0014] As described above, normal control of an electric motor is generally performed by constantly setting the excitation current (d-axis current). That is, in vector control of an electric motor, control is generally performed to always flow a constant excitation current (d-axis current) in order to ensure responsiveness to suddenly applied loads. However, for example, during the entire machining operation of a workpiece using a machine tool, there may be a state in which the spindle is not machining the workpiece, i.e., a state in which the electric motor is rotating without load. As will be described in detail below, the control device 100 according to this embodiment is configured to prevent an excessive flow of d-axis current during the motor's rotation without load, thereby reducing the electric motor's power consumption.

[0015] As shown in FIG. 1, in the control device 100, a speed control unit 10 receives a speed command V ｃｍｄand the speed V of the electric motor 1 detected by the speed detector 50 based on the signal from the position detection sensor 2 of the electric motor 1. ｆｂ Based on the deviation from the reference value, a torque command (q-axis current command) is output in accordance with a predetermined control method such as proportional control.

[0016] The d-axis current control unit 20 outputs a d-axis current command, which is an excitation current. The d-axis current control unit 20 can apply various d-axis current controls as described above as controls during actual machining. The d-axis current control unit 20 according to this embodiment also provides a function to prevent the d-axis current from flowing more than necessary when the motor 1 is rotating without load. To achieve this function, the d-axis current control unit 20 is provided with a position feedback P ｆｂ Alternatively, the d-axis current control unit 20 may be configured to input the d-axis current signal, or to be connected to the processing load recording unit 214. The configuration for realizing the function of the d-axis current control unit 20 to prevent the d-axis current from flowing more than necessary when the electric motor 1 is rotating without load will be described later.

[0017] The dq converter 40 converts the three-phase current to the dq axis based on a signal from a current sensor 4 that detects the three-phase AC current that drives the motor 1, and outputs a q-axis current feedback Q ｆｂ and d-axis current feedback D ｆｂ The dq transform unit 30 outputs the q-axis current command and the q-axis current feedback Q ｆｂ and the deviation between the d-axis current command and the d-axis current feedback Q ｆｄ Based on the deviation from the dq axis, the inverter 3 performs conversion from the dq axis to three phases, and generates and outputs three-phase command voltages. Information representing the position (direction) of the magnetic flux of the electric motor 1, based on the output of the position detection sensor 2, is input to the dq conversion unit 30 and the dq conversion unit 40, and is used in the conversion calculation. The inverter 3 outputs a three-phase AC current for driving the electric motor 1 based on the three-phase command voltages.

[0018] These functions of the control device 100 may be configured by a microcomputer chip that integrates a processor, memory (ROM, RAM, non-volatile memory, etc.), input / output interface, etc.

[0019] As shown in FIG. 3 , the control device 100 may be incorporated into a CNC (numerical control device) 300 that controls a machine tool 400, and may drive and control a spindle motor 410 under the control of a processor 301 of the CNC 300. Alternatively, a control device having the same configuration as the control device 100 may be arranged within the CNC 300 to control a feed axis motor 420. The CNC 300 may be configured such that an operation unit 302, a display unit 303, the control device 100, and the like are connected to the processor 301. The machine tool 400 includes a spindle motor 410 and feed axis motors 420 (feed axis motors for the X-, Y-, and Z-axes). A tool is attached to the spindle motor 410. For example, the X- and Y-axis feed axis motors are driven to move the position of a table (not shown) on which a workpiece is placed in the X- and Y-axes, and the Z-axis feed axis motor is driven to move a spindle head carrying the spindle in the Z-axis direction. With this configuration, machine tool 400 performs cutting and other processing on the workpiece in accordance with a processing program under the control of CNC 300.

[0020] As described above, the control device 100 is configured to prevent the d-axis current from flowing more than necessary when the motor is rotating without load. The area where the workpiece is present—in other words, the area where the tool attached to the spindle driven by the motor 1 interferes with the workpiece and actually performs machining—is referred to as the actual machining area. The actual machining area may be expressed as a spatial area or a temporal area. Here, we consider a situation in which the tool enters the actual machining area from a state where the tool is outside the actual machining area and the motor is rotating without load. In an electric motor, it takes a certain amount of time for the magnetic flux to rise to the commanded strength in response to a d-axis current command. Therefore, if the d-axis current is raised to the current value required for machining when the tool enters the actual machining area, the delay in the rise of the magnetic flux may prevent the required performance from being achieved at the start of machining. In consideration of this, the control device 100 (d-axis current control unit 20) sets an expected machining area by adding a predetermined margin to the actual machining area based on information representing the spatial and temporal actual machining area of ​​the workpiece. This setting of the expected machining area allows the control device 100 (d-axis current control unit 20) to clearly distinguish between the no-load operation state of the motor and the actual machining state. The control device 100 (d-axis current control unit 20) then sets the d-axis current outside the expected machining area to a value that is lower than the actual machining current value required for actual machining.

[0021] Specifically, the control device 100 can execute the following controls (1) to (4) as controls for realizing a reduction in power consumption during no-load rotation of the electric motor 1. In these controls, it is assumed that the control device 100 is arranged in a CNC 300 that controls a machine tool 400, as shown in Fig. 3, and controls a spindle motor 410 of the machine tool 400.

[0022] Control (1): This control sets an expected machining area for the workpiece based on shape information of the workpiece, and reduces the value of the d-axis current outside the expected machining area to a value lower than the d-axis current required for actual machining. In this control (1), the expected machining area is an area surrounding the actual machining area corresponding to the size of the workpiece, plus a margin required for raising the magnetic flux before the tool comes into contact with the workpiece.

[0023] Control (2): In the above-mentioned control (1), the portion of the actual machining area through which the tool passes is removed from the workpiece during machining, and the shape of the workpiece changes. In this control (2), the assumed machining area is reset according to the portion removed from the workpiece by machining.

[0024] Control (3): In Control (3), the change in motor load over time when machining one workpiece is recorded. Then, when machining the same workpiece for the second or subsequent time, the timing of the start of the actual machining region is determined based on the recorded change in load over time. In Control (3), the d-axis current is switched based on the timing of the start of the actual machining region.

[0025] Control (4): In control (4), control is performed to reduce the d-axis current in a situation that is considered to be no-load rotation, based on the machining program.

[0026] Below, configurations for realizing the above-mentioned controls (1) to (4) will be described as first to fourth embodiments, respectively.

[0027] First Example The first example is a configuration example for implementing the above-described control (1). The d-axis current control unit for implementing the control (1) is denoted by the reference symbol 20A. FIG. 4 is a diagram showing the functional configuration of the d-axis current control unit 20A for implementing the control (1). In this example, the d-axis current control unit 20A holds workpiece information 211 including three-dimensional shape information of the workpiece. The workpiece information 211 may be stored in a storage unit, such as a nonvolatile memory, within the control device 100. The d-axis current control unit 20A may have a function for accepting input of the workpiece information 211 from an external device. For example, if the control device 100 is incorporated as a function within the CNC 300 or connected to the CNC 300 as shown in FIG. 3, the d-axis current control unit 20A may accept input of workpiece information (e.g., size information) of the workpiece from the processor 301 of the CNC 300, which serves as a higher-level device. The d-axis current control unit 20A may receive workpiece information (size information, etc.) input by the user via the operation unit 302 of the CNC 300.

[0028] The d-axis current control unit 20A includes an assumed machining region setting unit 212 and a selector 213.

[0029] The assumed machining area setting unit 212 has a function of calculating and saving the assumed machining area. The calculated assumed machining area may be stored in a memory unit within the control device 100. The assumed machining area setting unit 212 sets the assumed machining area as an area surrounding the actual machining area, plus an area (margin) necessary for the magnetic flux of the electric motor 1 to rise before the tool comes into contact with the workpiece. Specifically, as shown in FIG. 5 , the assumed machining area setting unit 212 sets the assumed machining area R1 as an area obtained by adding a predetermined margin M to the periphery of the actual machining area R0 corresponding to the outer shape of the workpiece W. The margin M is calculated, for example, using the following formula (1): (Margin M) = (Maximum tool diameter T) + (Magnetic flux rise time) × (Spindle feed rate) (1) In the above formula (1), the maximum tool diameter T is the maximum diameter of the tool 402 to be used. (Magnetic flux rise time) × (spindle feed rate) represents the distance (distance L in FIG. 5 ) required to ensure that the magnetic flux is in a rise state when the tool 402 or a control point set on the spindle 401 moving toward the actual machining region R0 enters the actual machining region R0. In reality, the tool 402 has a certain diameter, so the tool 402 interferes with the actual machining region R0 before the control point enters the actual machining region R0. Therefore, the maximum tool diameter T is added to the margin M. Note that, while an example has been described in which the margin M is determined by adding the maximum tool diameter to (magnetic flux rise time) × (spindle feed rate), there may also be an example in which the margin M is determined by adding a value based on the tool diameter (e.g., the tool radius) to (magnetic flux rise time) × (spindle feed rate).

[0030] The "flux rise time" refers to the response time required for the magnetic flux to rise to the commanded strength in response to an excitation command (d-axis current command). Since the "flux rise time" is considered to depend on the characteristics of the motor, an experimental value determined in advance through an experiment may be used as the "flux rise time." Such an experimental value may be stored in the memory unit of the control device 100. The "spindle feed rate" refers to the movement speed of the spindle 401, which is fed by driving the feed axis. Therefore, (flux rise time) x (spindle feed rate) represents the distance that must be secured around the actual machining region R0 to ensure that the magnetic flux rises to the commanded strength within the actual machining region R0. By setting the assumed machining region R1 in this manner, it is possible to ensure that the magnetic flux rises to the commanded strength in the actual machining region R0 when the tool 402 is used, thereby ensuring that appropriate machining is performed. The position feedback P input to the assumed machining region setting unit 212 ｆｂ includes a signal indicating the rotational position and speed of the feed axis motor 420, and the assumed machining area setting unit 212 can determine the feed speed of the spindle 401 (tool 402) based on the signal indicating the rotational position and speed of the feed axis motor 420.

[0031] The d-axis current control unit 20A (the assumed machining area setting unit 212) is configured to receive the position feedback P ｆｂ The position of the tool 402 (control point P0) can be grasped based on the signal (signal indicating the rotational position and speed of the feed axis). Therefore, the d-axis current control unit 20A can control the d-axis current to a value reduced from the current value required for actual machining when the tool 402 is outside the assumed machining region R1, and can control the d-axis current to a value required for actual machining when the tool 402 is inside the assumed machining region R1.

[0032] The d-axis current control unit 20A may be configured to control the selector 213 to select the minimum value of the d-axis current (reference numeral 26) as the d-axis current command outside the assumed machining region R1, and to select the d-axis current value during actual machining (reference numeral 25) as the d-axis current command inside the assumed machining region R1. Here, the minimum value of the d-axis current is the minimum current value required to rotate the motor while overcoming mechanical losses such as losses due to friction. Note that the d-axis current during actual machining is the d-axis current command value when normal vector control is executed, as described above.

[0033] By controlling the d-axis current as described above, it is possible to reduce the d-axis current to a minimum level outside the assumed machining region R1 where the spindle rotates without load, thereby realizing a reduction in power consumption. At the same time, it is possible to ensure that the magnetic flux reaches the commanded strength in the actual machining region, thereby ensuring that appropriate machining is performed.

[0034] Second Example The second example is a configuration example for realizing the above control (2). The functional block configuration in the second example is the same as the functional block diagram shown in Fig. 5. The second example will be described below with reference to Fig. 5 and Figs. 6A to 6C.

[0035] 6A , as the machining operation on the workpiece W progresses, a portion of the workpiece W is removed. In the second embodiment, the assumed machining area is also changed in accordance with changes in the shape of the workpiece as the machining progresses.

[0036] The left side of Fig. 6A shows the shape of the workpiece W before machining. As shown on the right side of Fig. 6A, it is assumed that the tool 402 moves along the path L1 and removes a part of the workpiece W. The assumed machining area setting unit 212 receives a feedback P ｆｂThe assumed machining area setting unit 212 can determine the path L1 of the tool 402 (control point P0) based on the information about the path L1 of the tool 402 and the information representing the position and size of the workpiece W. The assumed machining area setting unit 212 updates the workpiece information 211 (workpiece size information) according to the shape of the workpiece W in a state where a portion has been removed by machining, as shown on the right side of Fig. 6A. Then, the assumed machining area setting unit 212 updates the assumed machining area in the manner described in control (1) above, according to the updated workpiece information 211.

[0037] The left side of Fig. 6B shows the workpiece W and assumed machining area R1 before machining, as viewed from the direction of arrow A in Fig. 6A, and the right side of Fig. 6B shows the workpiece W and updated assumed machining area R2, as viewed from the direction of arrow A in Fig. 6A, when the shape of the workpiece W has changed due to machining as shown on the right side of Fig. 6A. The left side of Fig. 6C shows the workpiece W and assumed machining area R1 before machining, as viewed from the direction of arrow B in Fig. 6A, and the right side of Fig. 6C shows the workpiece W and assumed machining area R2, as viewed from the direction of arrow B in Fig. 6A, when the shape of the workpiece has changed due to machining as shown on the right side of Fig. 6A. Note that the assumed machining area R2 is also set as an area obtained by adding the above-mentioned margin M to the outer shape of the workpiece W whose shape has changed as shown on the right side of Fig. 6A.

[0038] In this way, by changing the expected machining area in accordance with changes in the shape of the workpiece as machining progresses, it is possible to more reliably capture the state in which the spindle is rotating without load, and more accurately reduce the power consumption when the spindle is rotating without load.

[0039] Third Example The third example is a configuration example for realizing the above-described control (3). The d-axis current control unit for realizing the control (3) is denoted by the reference symbol 20B. FIG. 7 is a diagram showing the functional configuration of the d-axis current control unit 20B for realizing the control (3). The d-axis current control unit 20B includes an assumed machining region setting unit 212B and a selector 213. In the control (3), the function of the machining load recording unit 214 is used.

[0040] In this embodiment, the machining load recording unit 214 records the load fluctuations of the electric motor 1 when machining is executed on one workpiece according to the machining program. Here, as an example, the q-axis current value output by the dq conversion unit 40 is input to the machining load recording unit 214 as machining load information representing the load on the electric motor 1 during machining. Since the q-axis current represents the state of torque control, the q-axis current value can be used as information representing the load on the electric motor 1 during machining. The machining load recording unit 214 stores data representing the load fluctuations in a memory unit within the control device 100, for example.

[0041] When the same workpiece whose machining load information is recorded by the machining load recording unit 214 is machined for the second or subsequent time, the assumed machining area setting unit 212B minimizes the d-axis current when the motor 1 is considered to be rotating without load, based on the recorded machining load information, and switches to a current command required for normal machining as the d-axis current in the actual machining area. FIG. 8 shows an example of load fluctuation indicated by the machining load information. Graph 230 represents the load fluctuation. In FIG. 8, it is assumed that the machining program is started at time t0. The load rises sharply at time t1 when the tool interferes with the actual machining area (i.e., when the tool comes into contact with the workpiece). Therefore, in FIG. 8, the area before time t1 can be considered the area outside the actual machining area, and the area after time t1 can be considered the temporal actual machining area.

[0042] Based on the recorded machining load information, the assumed machining area setting unit 212B determines the timing t1 at which the load increases after machining starts. As mentioned above, the magnetic flux of the motor has a rise time. Therefore, the assumed machining area setting unit 212B switches the d-axis current from the minimum value (reference numeral 26) to the d-axis current value (reference numeral 25) during actual machining at timing tc, which precedes timing t1 at which the actual machining area is entered by the rise time of the magnetic flux (Δt in FIG. 8). Δt = (rise time of the magnetic flux)

[0043] In setting Δt, which is the advance time for switching the d-axis current to the current value during actual machining prior to the timing of load increase based on the machining load record, it is not necessary to take into account the time required for the spindle (tool) to move the distance equivalent to the tool diameter, because the timing of load increase indicated by the machining load record represents the timing when the end of the tool actually comes into contact with the workpiece.

[0044] The d-axis current control unit 20B (expected machining area setting unit 212B) controls the selector 213 so that the minimum value of the d-axis current (symbol 26) is selected as the d-axis current command from the start of machining until timing tc, which precedes timing t1 at which the load increases by Δt, and at timing tc the d-axis current command is switched to the d-axis current value during actual machining (symbol 25).

[0045] With this configuration, even in the third embodiment, the assumed machining area setting unit 212B can reduce the d-axis current to a minimum level in the area where the spindle rotates without load, thereby realizing a reduction in power consumption, and at the same time, can ensure that the magnetic flux reaches the command value in the actual machining area, thereby ensuring that appropriate machining is performed.

[0046] In the configuration of the third embodiment, the period during which the load is increasing corresponds to the actual machining area, and the area on the time axis obtained by adding Δt to the period during which the load is increasing corresponds to the assumed machining area obtained by adding a margin to the actual machining area in Examples 1 and 2. Therefore, the configuration of the third embodiment can also be said to be a configuration that realizes, based on the machining load record of the workpiece, an operation equivalent to the operation of setting the assumed machining area based on shape information of the workpiece as in Examples 1 and 2.

[0047] Fourth Example The fourth example is a configuration example for realizing the above-described control (4). The d-axis current control unit for realizing the control (4) is denoted by the reference symbol 20C. FIG. 9 is a diagram showing the functional configuration of the d-axis current control unit 20C for realizing the control (4). The d-axis current control unit 20C includes an assumed machining region setting unit 212C and a selector 213.

[0048] In this embodiment, the d-axis current control unit 20C performs control to reduce the d-axis current when the motor is estimated to be rotating without load, based on the machining program 215. The machining program 215 may be stored in the storage unit of the control device 100.

[0049] In this embodiment, it is assumed that the control device 100 is used to control a spindle motor 410 of a machine tool 400 as shown in Fig. 3. The assumed machining area setting unit 212C cooperates with the processor 301 of the CNC 300 that is executing the machining program 215, thereby being able to grasp which step of the command in the machining program 215 the machine tool 400 is currently executing.

[0050] As shown in FIG. 10 , a machining program can be considered to have two basic building blocks: a rapid-forward command for rapid-forwarding the spindle (tool) to the machining start point Ps, and a cutting feed command for machining from the machining start point Ps. The rapid-forward command is a command for rapid-forwarding the spindle (tool) to the machining start position or approach position, and is a command that assumes that the tool will not contact the workpiece. The cutting feed command is a command for when the tool contacts the workpiece and performs cutting. The area after the machining start point Ps where the cutting feed command is executed can be considered the actual machining area. In this embodiment, the assumed machining area setting unit 212C sets the assumed machining area as an area that adds a predetermined margin M toward the non-machining area from the machining start point Ps where the cutting feed command starts, as shown in FIG. 10 . Similar to the first embodiment, in this embodiment, the margin M may also be set by multiplying the magnetic flux rise time by the spindle feed rate. The start point Ps can be obtained from the position coordinates specified in the rapid-forward command or cutting feed command. For example, the position coordinates specified in the cutting feed command may be used as the machining start point.

[0051] The d-axis current control unit 20C (assumed machining area setting unit 212C) controls the selector 213 so that the minimum value (reference numeral 26) is selected as the d-axis current up to a position Pm where a margin M is added to the non-machining area side of the machining start point Ps in a situation where the tool attached to the spindle is moving toward the machining start point Ps in accordance with a fast-forward command. Subsequently, the d-axis current control unit 20C (assumed machining area setting unit 212C) controls the selector 213 so that the d-axis current is switched to the current value (reference numeral 25) during actual machining at the position Pm. Note that such control is performed when the d-axis current control unit 20C (assumed machining area setting unit 212C) receives position feedback P ｆｂ This can be realized by calculating the position of the tool (control point) based on the rotational position of the feed axis shown in

[0052] With this configuration, even in the fourth embodiment, the d-axis current can be reduced to a minimum level in the region where the spindle rotates without load, thereby reducing power consumption, and at the same time, it is ensured that the magnetic flux reaches the command value in the actual machining region, ensuring that appropriate machining is performed.

[0053] The configuration of the fourth embodiment corresponds to a configuration in which it is determined based on the machining program whether the spindle (tool) is in the assumed machining area, and the d-axis current value is reduced below the current value during actual machining when the spindle is outside the assumed machining area. In other words, the configuration of the fourth embodiment can also be said to be a configuration in which the assumed machining area is estimated based on the machining program.

[0054] In addition, a fast-forward command may be used in a machining program to move the tool to a predetermined approach position. In such a case, the period during which the fast-forward command is executed may be considered to be a period during which the d-axis current can be set to a minimum value. In other words, the period during which the fast-forward command is executed may be considered to be a period during which the tool is outside the assumed machining area. Therefore, the assumed machining area setting unit 212C may consider the period during which the fast-forward command is executed in the machining program 215 as a time area outside the assumed machining area, and the period during which the fast-forward command is not executed as a time area within the assumed machining area. In other words, the d-axis current control unit 20C may control the selector 213 so that the minimum value (reference numeral 26) is selected as the d-axis current command during the period during which the fast-forward command is executed, and the d-axis current value during actual machining (reference numeral 25) is selected as the d-axis current command during the period during which the fast-forward command is not executed.

[0055] Even in the case of such a configuration, the d-axis current can be reduced to a minimum level in the area where the spindle rotates without load, thereby reducing power consumption, and at the same time, it is possible to ensure that the magnetic flux reaches the command value in the actual machining area, thereby ensuring that appropriate machining is performed.

[0056] As described above, according to this embodiment, by setting the assumed machining region as described above, it is possible to clearly distinguish between the state in which the motor is operating without load and the state in which it is actually machining. As a result, the d-axis current is reduced to a minimum in the region in which the motor is rotating without load, thereby reducing power consumption, and at the same time, it is ensured that the magnetic flux reaches the command value in the actual machining region, ensuring that appropriate machining is performed.

[0057] The configurations of the above-described embodiments can be applied to the control of electric motors that drive drive shafts to which tools are attached in various types of industrial machines that perform processing on workpieces. For example, the configurations of the above-described embodiments can also be applied to a control device for an electric motor that drives a wrist shaft or an additional shaft in a robot system configured to perform processing by attaching a tool to the wrist shaft or an additional shaft of a robot. In such a configuration, the position of the tool attached to the wrist shaft or the additional shaft can be calculated from rotational position information of each joint shaft of the robot.

[0058] The programs for executing the control methods described as motor control (1) to (4) in the above-mentioned embodiments can be recorded on various computer-readable recording media (e.g., semiconductor memories such as ROM, EEPROM, and flash memory, magnetic recording media, and optical disks such as CD-ROM and DVD-ROM).

[0059] Although the present disclosure has been described in detail, the present disclosure is not limited to the individual embodiments described above. Various additions, substitutions, modifications, partial deletions, etc. are possible in these embodiments without departing from the gist of the present disclosure or the spirit of the present disclosure derived from the content of the claims and their equivalents. These embodiments can also be implemented in combination. For example, in the above-described embodiments, the order of each operation and the order of each process are shown as examples and are not limited to these. The same applies when numerical values ​​or mathematical expressions are used in the description of the above-described embodiments.

[0060] The following supplementary notes are further provided with respect to the above-described embodiment and modified examples. (Supplementary Note 1) A control device (100) for controlling an electric motor that drives a drive shaft of an industrial machine, the control device (100) comprising: a d-axis current control unit (20) that performs control to set a d-axis current in vector control to a value that is reduced from an actual-machining current value required for actual machining in an area outside the expected machining area, based on an expected machining area around the actual machining area of ​​a workpiece, with a margin required for increasing the magnetic flux of the electric motor to the strength required for actual machining, and to set the d-axis current to the actual-machining current value within the expected machining area. (Supplementary Note 2) The control device (100) according to Supplementary Note 1, wherein the d-axis current control unit (20A) comprises an expected machining area setting unit (212) that sets the expected machining area using shape information representing the shape of the workpiece as information representing the actual machining area. (Supplementary Note 3) The control device (100) according to Supplementary Note 2, wherein the assumed machining area setting unit (212) sets the margin to a distance obtained by adding a value based on the maximum diameter of a tool attached to the drive shaft and a value obtained by multiplying a predetermined time required for starting up the magnetic flux of the electric motor by the moving speed of the tool. (Supplementary Note 4) The control device (100) according to Supplementary Note 2 or 3, wherein the assumed machining area setting unit (212) is configured to accept an external input or a user input of the shape information. (Supplementary Note 5) The control device (100) according to any one of Supplementary Notes 2 to 4, wherein the assumed machining area setting unit (212) calculates a portion removed from the workpiece by machining based on information representing a moving path of a tool attached to the drive shaft, and updates the assumed machining area according to the removed portion. (Supplementary Note 6) The control device (100) described in Supplementary Note 1 further comprises a machining load recording unit (214) that records machining load information that represents a change in load on the drive axis over time when machining one workpiece, and the d-axis current control unit (20B) comprises an assumed machining area setting unit (212B) that sets the assumed machining area using the recorded machining load information as information representing the actual machining area.(Supplementary Note 7) The control device (100) according to Supplementary Note 6, wherein the assumed machining area setting unit (212B) regards a region before a second timing, which precedes a first timing at which the load increases in the machining load information by a predetermined time required for the magnetic flux of the motor to rise, as a region outside the assumed machining area, and regards a region in time after the second timing as the assumed machining area, and the d-axis current control unit (20B) switches the d-axis current from the reduced value to the actual machining current value at the second timing. (Supplementary Note 8) The control device (100) according to Supplementary Note 1, wherein the d-axis current control unit includes an assumed machining area setting unit (212C) that sets the assumed machining area based on a machining program. (Supplementary Note 9) The control device (100) according to Supplementary Note 8, wherein the assumed machining area setting unit (212C) sets the assumed machining area based on a fast-forward command in the machining program. (Supplementary Note 10) The control device (100) according to Supplementary Note 8 or 9, wherein the assumed machining area setting unit (212C) sets the assumed machining area by adding, as the margin, a value obtained by multiplying a predetermined time required for starting up the magnetic flux of the electric motor by a moving speed of the tool, to a non-machining area side with respect to the actual machining area starting from a machining start point, based on a fast-forward command and a cutting feed command. (Supplementary Note 11) The control device (100) according to any one of Supplementary Notes 1 to 10, wherein the d-axis current control unit (20) reduces the d-axis current in an area outside the assumed machining area to a minimum current value required to overcome mechanical loss of the electric motor and rotate the electric motor.

[0061] REFERENCE SIGNS LIST 1 electric motor 2 position detection sensor 3 inverter 4 current sensor 10 speed control section 20, 20A, 20B, 20C d-axis current control section 30 dq conversion section 40 dq conversion section 50 speed detector 100 control device 212, 212B, 212C assumed machining area setting section 213 selector 214 machining load recording section 215 machining program 300 CNC 301 processor 302 operation section 303 display section 400 machine tool 401 spindle 402 tool 410 spindle motor 420 feed axis motor

Claims

1. A control device for controlling an electric motor that drives the drive shaft of industrial machinery, comprising a d-axis current control unit that performs control to set the d-axis current in vector control to a value that is reduced from the actual machining current value required for actual machining in areas outside the expected machining area, based on an expected machining area that is formed by adding a margin required to raise the magnetic flux of the electric motor to the strength required for actual machining around the actual machining area of ​​the workpiece, and to set the d-axis current to the actual machining current value within the expected machining area.

2. The control device according to claim 1, wherein the d-axis current control unit includes an assumed machining area setting unit that sets the assumed machining area using shape information representing the shape of the workpiece as information representing the actual machining area.

3. The control device according to claim 2, wherein the assumed machining area setting unit sets the margin to the distance obtained by adding together a value based on the maximum diameter of the tool attached to the drive shaft and a value obtained by multiplying the predetermined time required for the magnetic flux of the motor to rise by the moving speed of the tool.

4. The control device according to claim 2 or 3, wherein the assumed machining area setting unit is configured to accept external input or user input of the shape information.

5. A control device described in any one of claims 2 to 4, wherein the assumed machining area setting unit calculates the portion removed from the workpiece by machining based on information representing the movement path of a tool attached to the drive shaft, and updates the assumed machining area according to the removed portion.

6. The control device according to claim 1, further comprising a machining load recording unit that records machining load information that represents the change in load on the drive axis over time when machining one workpiece, and the d-axis current control unit comprises an assumed machining area setting unit that sets the assumed machining area using the recorded machining load information as information representing the actual machining area.

7. The control device described in claim 6, wherein the assumed machining area setting unit regards the area before a second timing that precedes a first timing at which the load increases in the machining load information by a predetermined time required for the magnetic flux of the motor to rise as an area outside the assumed machining area, and regards the area in terms of time after the second timing as the assumed machining area, and the d-axis current control unit switches the d-axis current from the reduced value to the actual machining current value at the second timing.

8. The control device according to claim 1, wherein the d-axis current control section includes an assumed machining area setting section that sets the assumed machining area based on a machining program.

9. The control device according to claim 8, wherein the assumed machining area setting unit sets the assumed machining area based on a fast-forward command in the machining program.

10. A control device as described in claim 8 or 9, wherein the expected machining area setting unit sets the expected machining area by adding, as the margin, a value obtained by multiplying the predetermined time required for the magnetic flux of the motor by the moving speed of the tool to the non-machining area side based on the actual machining area starting from the machining start point, based on a fast-forward command and a cutting feed command.

11. A control device as described in any one of claims 1 to 10, wherein the d-axis current control unit reduces the d-axis current in an area outside the expected machining area to the minimum current value required to overcome mechanical loss in the motor and rotate the motor.

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