Machine tool control device

Abstract

A machine tool control device according to one embodiment of the present disclosure controls a machine tool in which a main shaft is driven by an induction motor in accordance with a machining program, and is provided with: a load estimation unit that estimates the load of the machine tool by pre-reading the machining program; estimating whether the load state of the main shaft is an idle running that does not include a processing-induced load or an actual operation that includes the processing-induced load; and a current control unit that controls a d-axis current and a q-axis current of a spindle current supplied to the induction motor so that the rotational speed of the spindle matches the rotational speed in accordance with the machining program, and sets the d-axis current to a value greater than that in the case of the idle operation when the actual operation is estimated.

Description

Technical Field

[0001] This invention relates to machine tool control devices. Background Technology

[0002] Induction motors are used as various power sources. The speed of the induction motor is also controlled by supplying power to it from an inverter (see, for example, Patent Document 1). Specific speed control methods for induction motors include known V / f control, vector control, etc.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2018-57161 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] In machine tools, precise control of the motor speed is required. However, the load on the machine tool spindle varies drastically depending on the machining state, such as whether the tool is cutting the workpiece. For example, when transitioning from an idle state where the tool is not in contact with the workpiece to an actual operating state where the tool is cutting the workpiece, the output torque of the induction motor needs to be increased sharply. However, the rise of the secondary magnetic flux of the induction motor takes time, so in control based on feedback of the speed detection value, the deviation from the target speed sometimes becomes large. Therefore, a technology that can accurately control the speed of the spindle driven by the induction motor is desired.

[0008] Methods for solving problems

[0009] One aspect of this disclosure relates to a machine tool control device that controls a machine tool driven by an induction motor according to a machining program. It comprises: a load estimation unit that, by pre-reading the machining program, estimates whether the load state of the spindle is idling without machining load or actual operation including machining load; and a current control unit that controls the d-axis current and q-axis current supplied to the induction motor to make the spindle speed consistent with the speed according to the machining program, and, if actual operation is estimated, sets the d-axis current to a value greater than that estimated for idling. Attached Figure Description

[0010] Figure 1 This is a block diagram illustrating the structure of a machine tool equipped with a machine tool control device according to one embodiment of the present disclosure.

[0011] Figure 2 It is a graph representing the constant torque curve of an induction motor in the dq current coordinate system.

[0012] Figure 3 It is a timing diagram that shows the changes in the load on the spindle, the command value of the current control unit, and the state of the induction motor. Detailed Implementation

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. Figure 1 This is a block diagram showing the structure of the machine tool 1 according to the first embodiment of this disclosure.

[0014] Machine tool 1 includes: a machine tool control device 10, a spindle 20 that rotates a workpiece or tool, an induction motor 30 that drives the spindle 20, a spindle amplifier 40 that supplies spindle current to the induction motor 30 according to instructions from the machine tool control device 10, a positioning mechanism 50 that determines the relative position of the workpiece and the tool, multiple servo motors 60 that drive the positioning mechanism, and multiple servo amplifiers 70 that supply power to each servo motor 60 according to instructions from the machine tool control device 10. In machine tool 1, the induction motor 30, spindle amplifier 40, positioning mechanism 50, servo motors 60, and servo amplifiers 70 are known structures, therefore detailed descriptions are omitted.

[0015] The machine tool control device 10 is one embodiment of the machine tool control device of the present invention. The machine tool control device 10 includes, for example, a memory, a processor, an input / output interface, etc., and can be implemented by one or more computer devices that execute appropriate control programs. Typically, the machine tool control device 10 is configured as a numerical control device. The machine tool control device 10 includes a machining program storage unit 11, a load estimation unit 12, a current control unit 13, and a positioning control unit 14. Furthermore, these structural elements are derived from classifying the functions of the machine tool control device 10, and may not be structures that can be clearly distinguished in terms of physical and program structures.

[0016] The machining program storage unit 11 stores a machining program, which describes, for example, the relative movement path of the tool relative to the workpiece for cutting the workpiece to obtain the desired product using a predetermined language such as G-code.

[0017] The load estimation unit 12 estimates the load state of the spindle 20 by pre-reading the machining program. More specifically, the load estimation unit 12 reads and analyzes the machining program before the workpiece and tool actually move relative to each other, estimating whether the load state of the operating spindle 20 and, consequently, the induction motor 30 is idling without machining load or actual operation with machining load. Preferably, the load estimation unit 12 predicts the magnitude of the load during actual operation. As a result, the current control unit 13 can adjust the spindle current more appropriately based on the predicted load magnitude.

[0018] The load estimation unit 12 may determine whether a load caused by machining is included based on the type of command in the machining program, without confirming whether actual machining is performed. That is, the load estimation unit 12 determines whether the instruction statement in the machining program is an instruction statement for moving the workpiece and tool relative to each other for machining, or an instruction statement for moving the workpiece and tool to the starting position for machining, and estimates whether the action based on the instruction statement is idle or actually running.

[0019] The current control unit 13 controls the spindle current supplied to the induction motor 30 to match the spindle speed 20 according to the machining program. More specifically, the current control unit 13 determines the flux-forming component (d-axis current) and torque-generating component (q-axis current) of the spindle current based on the measured value of the spindle speed 20, and inputs a specified d-axis current command value and a specified q-axis current command value to the spindle amplifier 40 that supplies the spindle current to the induction motor 30. As a method to match the speed with the target value, the output torque can be varied by adjusting at least one of the slip frequency, the norm of the spindle current, the d-axis current, and the q-axis current.

[0020] When the spindle is expected to be in operation, the current control unit 13 sets the d-axis current of the spindle to a value larger than that expected for idling, preferably a larger value if the predicted load is higher. Conversely, when the spindle is expected to be in idling, the current control unit 13 sets the d-axis current of the spindle to a value smaller than that expected for actual operation. This suppresses power consumption of the d-axis current during idling with low load torque and generates sufficient secondary magnetic flux to produce torque balanced with the load during actual operation. The current control unit 13 can also switch to known control methods such as MTPA control after initially setting the d-axis current value for each machining operation. Even if the initial value of the d-axis current is determined solely based on the pre-reading results of the machining program, errors in the spindle speed 20 caused by variations in load torque can be suppressed. Therefore, by switching to control that optimizes the d-axis current value, power consumption can be further reduced. The current control unit 13 can also change the control mode between the expected operation and the idling operation.

[0021] Under the assumption of idling, the current control unit 13 preferably controls the d-axis current and q-axis current to the minimum value I of the norm of the current on the constant torque curve corresponding to the frictional torque of the spindle 20 during idling. min the following( Figure 2 (Within the range shown by the dashed line). Therefore, the current control unit 13 can be configured to pre-store the minimum value I of the norm of the current on the constant torque curve during idling. minFurthermore, the current control unit 13 can be configured to set the d-axis current to a preset value that satisfies the aforementioned conditions, and adjust the q-axis current through the aforementioned speed control. The frictional torque of the spindle 20 varies depending on the speed, but the variation in frictional torque within the practical speed range is sufficiently small compared to the torque generated by the load caused by machining. Therefore, the current control unit 13 can also be configured to output a constant d-axis current independent of the spindle 20's speed.

[0022] When idling is assumed, the current control unit 13 can control the spindle current so that the slip frequency of the induction motor 30 is consistent with the reciprocal of the second-order time constant of the induction motor 30. Furthermore, when idling is assumed, the current control unit 13 can also control the d-axis current and q-axis current to be equal values. Figure 2 Point A). Furthermore, "consistent with the reciprocal" means that the difference between it and the reciprocal is less than 10% of the reciprocal, preferably less than 5%, and "equal value" means that the difference between the two is less than 10% of the average value, preferably less than 5%.

[0023] During idling, since the magnetic flux is sufficiently small, voltage saturation is not a concern, and the output torque is also sufficiently small, so current limiting is not a concern. Therefore, the minimum spindle current relative to the required torque can be calculated using the following mathematical formulas (1) and (2). Hereinafter, the torque command value will be set to T. * [Nm], set the d-axis current to I 1d [A], Set the q-axis current to I. 1q [A], set the norm of the main shaft current to I[A], set the number of pole pairs to Pn, set the mutual inductance of the stator winding and the rotor winding to M[H], set the secondary self-inductance to L2[H], set the secondary resistance to R2[Ω], and set the slip frequency to ωs[rad / s].

[0024] [Formula 1]

[0025]

[0026] [Formula 2]

[0027]

[0028] If the d-axis current I 1d =Icosθ, q-axis current I 1q If = Isinθ, then the spindle current I can be minimized when θ = π / 4. The d-axis current command value I in this case is... * 1d and q-axis current command value I * 1q It can be represented by the following mathematical expressions (3) and (4).

[0029] [Formula 3]

[0030]

[0031] [Formula 4]

[0032]

[0033] In addition, the slip frequency ω s It can be represented by the following mathematical expression (5).

[0034] [Formula 5]

[0035]

[0036] If we substitute mathematical expressions (3) and (4) into mathematical expression (5), we get the following mathematical expression (6), from which we can know the slip frequency ω. s It becomes the reciprocal of the second-order time constant of the induction motor 30.

[0037] [Formula 6]

[0038]

[0039] Therefore, under the assumption of idling, the d-axis current I of the induction motor 30 will be... 1d and slip frequency ω s The values ​​are set to pre-stored optimal values, and the q-axis current I is used. 1q Fine-tuning maintains the spindle speed 20 at the target value, thereby suppressing the power consumption of the induction motor 30. Furthermore, under the assumption of idling, the d-axis current and q-axis current are initially set to pre-stored optimal values ​​that are equal to each other. By adjusting the d-axis current and q-axis current to be equal, the spindle speed 20 is maintained at the target value, which also suppresses the power consumption of the induction motor 30.

[0040] When the transition from idle to actual operation is assumed, the current control unit 13 preferably sets the d-axis current to a value larger than that during idle before the transition to actual operation. This increases the secondary magnetic flux before the transition to actual operation, allowing for a rapid increase in output torque when the load torque rises during the transition, thus suppressing speed fluctuations of the spindle 20 caused by the increase in load torque. To reliably suppress speed fluctuations, the d-axis current, set to a large value before the transition to actual operation, is maintained at least until the transition to actual operation. On the other hand, when the transition from actual operation to idle is assumed, it is not necessary to change the secondary magnetic flux beforehand, so the d-axis current value can be set to the aforementioned value at the instant the transition to idle is assumed. For example, in... Figure 2In the process, the spindle current is at point A when idling and at point B when actually running. When switching from idling to actual running, the d-axis current is increased in advance and the spindle runs at point C. However, when switching from actual running to idling, the spindle current moves directly from point B to point A.

[0041] The d-axis current value increases or decreases approximately without delay according to the commanded d-axis current value. However, the secondary flux of the induction motor 30 has a relatively large time constant, resulting in delays during its descent and ascent. The torque that the induction motor 30 can output is limited by the secondary flux; therefore, the delay in the descent of the secondary flux is not a problem, but the delay in the ascent of the secondary flux becomes a cause of insufficient output torque. In this embodiment, the current control unit 13 pre-increases the secondary flux by setting the d-axis current to a value larger than that during idling before transitioning from idle to actual operation. Therefore, it can instantaneously increase the output torque at the start of actual operation.

[0042] Figure 3 This indicates changes in the load on the spindle 20, the command value of the current control unit 13, and the state of the induction motor 30. More specifically... Figure 3 It is a timing diagram that shows the time changes of the load state estimated by the machining program, the expected load size, the command values ​​of the d-axis current and q-axis current, the slip frequency, and the flux number of the secondary magnetic flux.

[0043] As described above, when transitioning from actual operation to idling, the d-axis current is set to a relatively small value at the start of actual operation. Therefore, as a result of frequency maintenance control, the q-axis current decreases with almost no delay relative to the decrease in load torque, and the slip frequency increases with almost no delay, but the secondary flux decreases with a delay relative to the decrease in d-axis current. When transitioning from idling to actual operation, the d-axis current is set to a larger value before the start of actual operation. Therefore, as a result of frequency maintenance control, the slip frequency decreases with almost no delay from the decrease in d-axis current, and the secondary flux increases with a delay relative to the increase in d-axis current. Then, at the start of actual operation, if the secondary flux becomes sufficiently large, the q-axis current and slip frequency can increase with almost no delay. In the figure, it is intended that the larger the load, the larger the d-axis current will be set during actual operation; however, it is also possible to initially set it to a relatively large value and then switch to a known control such as MTPA control after the start of actual operation for further optimization.

[0044] The lower limit of the lead time from the moment the current control unit 13 sets the d-axis current to a value greater than that during idling until the estimated moment of transition to actual operation is preferably 4 times the secondary flux time constant of the induction motor 30, more preferably 6 times. On the other hand, the upper limit of the aforementioned lead time is preferably 10 times the secondary flux time constant of the induction motor 30, more preferably 8 times. By setting the aforementioned lead time above or above the aforementioned lower limit, the secondary flux can be sufficiently increased before transitioning to actual operation. In addition, by setting the aforementioned lead time below or below the aforementioned upper limit, the increase in power consumption during idling can be suppressed.

[0045] The positioning control unit 14 is a known structure that outputs a command value for specifying the drive current of the drive servo motor 60, so that the relative position of the workpiece and the tool can be determined according to the machining program.

[0046] As described above, the machine tool control device 10 of this embodiment sets the d-axis current and q-axis current to relatively small values ​​when the spindle 20 is idling, thereby suppressing the power consumption of the induction motor 30. Furthermore, by increasing the d-axis current before transitioning from idling to actual operation, the machine tool control device 10 pre-increases the secondary magnetic flux, thus preventing insufficient torque at the start of actual operation.

[0047] The following notes further disclose the above-described embodiments and variations.

[0048] (Note 1)

[0049] The machine tool control device (10) is a machine tool control device (1) that controls the spindle (20) driven by the induction motor (30) according to the machining program. It includes: a load estimation unit (12) that estimates the load state of the spindle (20) by pre-reading the machining program, whether it is idle running without machining load or actual operation with machining load; and a current control unit (13) that controls the spindle (20) current supplied to the induction motor (30) so that the spindle (20) speed is consistent with the speed according to the machining program, and when it is estimated to be actual operation, it sets the d-axis current of the spindle (20) current to a value larger than that when it is estimated to be idle running.

[0050] (Note 2)

[0051] Alternatively, in the machine tool control device (10) in Appendix (1), when it is assumed to be idling, the current control unit (13) controls the d-axis current and q-axis current in such a way that the norm of the current on the constant torque curve corresponding to the frictional torque of the spindle (20) during idling is less than or equal to the minimum value.

[0052] (Note 3)

[0053] Alternatively, in the machine tool control device (10) of Appendix (1) or (2), when it is assumed to be idling, the current control unit (13) controls the spindle (20) current in such a way that the slip frequency of the induction motor (30) is consistent with the reciprocal of the second time constant of the induction motor (30).

[0054] (Note 4)

[0055] Alternatively, in the machine tool control device (10) of Appendix (1) or (2), when it is assumed to be idling, the current control unit (13) controls the d-axis current and q-axis current by setting them to equal values.

[0056] (Note 5)

[0057] Alternatively, in any of the machine tool control devices (10) in notes (1) to (4), when it is assumed that the transition from idle to actual operation is to be made, the current control unit (13) sets the d-axis current to a value greater than that during idle operation before the transition to actual operation.

[0058] (Note 6)

[0059] Alternatively, in the machine tool control device (10) of Appendix (5), the lead time from the moment when the d-axis current is set to a value greater than that during idling to the moment when it is presumed to be transferred to actual operation is more than 4 times and less than 10 times the secondary flux time constant of the induction motor (30).

[0060] The present disclosure has been described in detail above, but it is not limited to the various embodiments described above. Various additions, substitutions, modifications, partial deletions, etc., can be made to these embodiments without departing from the spirit of the present disclosure, or without departing from the spirit of the present disclosure derived from the content described in the scope of the claimed patent protection and its equivalents.

[0061] Explanation of reference numerals in the attached figures

[0062] 1 machine tool

[0063] 10 Machine Tool Control Devices

[0064] 11. Processing Program Storage Department

[0065] 12 Load Estimation Section

[0066] 13 Current Control Section

[0067] 14 Positioning Control Department

[0068] 20 spindles

[0069] 30 Induction Motor

[0070] 40 spindle amplifier

[0071] 50 positioning mechanisms

[0072] 60 servo motors

[0073] 70 Servo Amplifier.

Claims

1. A machine tool control device that controls a machine tool with a spindle driven by an induction motor according to a machining program, characterized in that, The machine tool control device includes: The load estimation unit estimates the load state of the spindle by pre-reading the machining program, whether it is idling without machining load or actual operation with machining load. as well as The current control unit controls the d-axis current and q-axis current of the spindle current supplied to the induction motor so that the spindle speed is consistent with the speed according to the machining program, and sets the d-axis current to a larger value than the value of the idling situation when it is assumed to be actually running.

2. The machine tool control device according to claim 1, characterized in that, In the case of idling, the current control unit controls the d-axis current and the q-axis current in such a way that the norm of the current on the constant torque curve corresponding to the frictional torque of the spindle during idling is below the minimum value.

3. The machine tool control device according to claim 1 or 2, characterized in that, In the case of idling, the current control unit controls the spindle current in such a way that the slip frequency of the induction motor is consistent with the reciprocal of the second-order time constant of the induction motor.

4. The machine tool control device according to claim 1 or 2, characterized in that, In the case of idling, the current control unit controls the current by setting the d-axis current and the q-axis current to equal values.

5. The machine tool control device according to any one of claims 1 to 4, characterized in that, In cases where it is presumed that the operation is transitioning from idle to actual operation, the current control unit sets the d-axis current to a value greater than that during idle operation before transitioning to actual operation.

6. The machine tool control device according to claim 5, characterized in that, The lead time from the moment when the d-axis current is set to a value greater than that during idling to the moment when it is presumed to transition to the actual operation is more than 4 times and less than 10 times the secondary flux time constant of the induction motor.

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