Motor control device and motor control method

Abstract

The present invention provides a motor control device and motor control method capable of eliminating more asynchronous components than was conventionally possible and stabilizing a control system. The present invention includes: a position information acquisition unit 21 that acquires motor position information; a position deviation calculation unit 3 that calculates a position deviation that is a difference between the motor position information and repeated command position information; a frequency calculation unit 30 that calculates the frequency contained in the repeated commands; a filter constant determination unit 31 that determines a filter constant for controlling characteristics of a band limit filter 4 on the basis of the frequency; and a learning control unit 5 that derives a correction amount of the position deviation by passing the position deviation through the band limit filter 4 to which the filter constant is applied, the correction amount being added to the position deviation to control the motor.

Description

Motor control device and motor control method

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

[0002] Learning control is known as a method for improving machining accuracy when performing machining or the like using repeated commands of the same pattern. This learning control uses the time of a pattern operation, such as one rotation of the workpiece, as a learning cycle, rotates the workpiece multiple times, determines a position deviation for each predetermined control cycle, stores correction data in memory based on this position deviation, and attempts to converge the position deviation to zero by adding the correction data for the corresponding control cycle in the pattern cycle immediately preceding the one stored in memory to the position deviation for each control cycle of the pattern cycle. Techniques related to this type of learning are described in, for example, Patent Document 1 and Patent Document 2.

[0003] JP 2004-280772 A JP 4-362702 A

[0004] Here, repetitive control is a control that takes advantage of the repeatability of position error and commands, but if the position error and commands contain asynchronous components that are not repeatable, the control system may become unstable. As a countermeasure, conventional methods aim to stabilize the control system by removing asynchronous disturbances by passing the position error and repetitive commands through a low-pass filter. However, if the frequency of the asynchronous components is low, they may fall within the passband of the low-pass filter. As a result, the asynchronous components cannot be removed, and the control system may become unstable.

[0005] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a motor control device and a motor control method that can eliminate asynchronous components more than conventional devices and stabilize the control system.

[0006] One aspect of the present disclosure is a motor control device that issues a predetermined repeat command to a motor to perform machining while repeatedly moving a tool or workpiece, and that includes a position information acquisition unit that acquires position information of the motor, a position deviation calculation unit that calculates a position deviation that is the difference between the position information of the motor and the position information of the repeat command, a frequency calculation unit that calculates a frequency included in the repeat command, a filter constant determination unit that determines a filter constant that governs the characteristics of a band-limiting filter based on the frequency, and a learning control unit that derives a correction amount for the position deviation by passing the position deviation through the band-limiting filter to which the filter constant has been applied, and that adds the correction amount to the position deviation to control the motor.

[0007] One aspect of the present disclosure is a motor control method for providing a motor with a predetermined repeat command to perform machining while repeatedly moving a tool or workpiece, the motor control method comprising: position information acquisition means for acquiring position information of the motor; position deviation calculation means for calculating a position deviation which is the difference between the position information of the motor and the position information of the repeat command; frequency calculation means for calculating a frequency included in the repeat command; filter constant determination means for determining a filter constant that governs the characteristics of a band-limiting filter based on the frequency; and learning control means for deriving a correction amount for the position deviation by passing the position deviation through the band-limiting filter to which the filter constant has been applied, and adding the correction amount to the position deviation to control the motor.

[0008] FIG. 1 is a configuration diagram showing an overview of a motor control device; FIG. 2 is a configuration diagram of a band-limiting filter; FIG. 3 is an explanatory diagram of a state in which a specific frequency is passed by a band-limiting filter; FIG. 4 is a configuration diagram of a motor control device according to the present embodiment; FIG. 5 is a configuration diagram of a motor control device according to a modified example of the present embodiment; FIG. 6 is a configuration diagram of a motor control device according to a second modified example of the present embodiment; and FIG. 7 is a configuration diagram of a motor control device according to a third modified example of the present embodiment.

[0009] An example of an embodiment of the present invention will be described below.

[0010] 1 is a block diagram showing an overview of a motor control device 1. This motor control device 1, which is applicable to machine tools, industrial machinery, and the like, includes a subtractor 2 to which a motor movement command, which is a repetitive command, is input; a position deviation calculation unit 3 that calculates a position deviation, which is the difference between motor position information and the repetitive command; a band-limiting filter 4 that serves as a frequency filter that passes only predetermined frequencies included in the movement command; a learning controller 5 that serves as a learning control unit that learns the frequencies that have passed through the band-limiting filter 4; an adder 6 that receives an amount of learning correction derived by the learning controller 5; a motor speed and current control unit 7; and an encoder 8 that detects the motor and its position. The motor position information detected by the encoder is input to the subtractor 2 for feedback control.

[0011] Here, in machine tools and the like that operate with repetitive commands, the application of a repetitive controller can improve tracking ability and machining accuracy. For example, in oscillating cutting, oscillating operation is performed by superimposing a sine wave command of a certain frequency on a movement command specified by a machining program according to the machining conditions, and since the sine wave command has repeatability, repetitive control can be applied.

[0012] Repetitive control utilizes the repeatability of position deviations and commands, but if the position deviations and commands contain asynchronous components, the control system may become unstable. As a countermeasure to this, a known method is to pass the position deviation through a low-pass filter to remove high-frequency components before applying it to repetitive control.

[0013] However, if asynchronous components are mixed in at relatively low frequencies, particularly in the vicinity of the command frequency, the control system may not be stable even if a low-pass filter is used.

[0014] The motor control device and motor control method disclosed herein are characterized by the application of a bandpass filter to the band-limiting filter, focusing on the fact that, although it is usually difficult to predict in advance the frequency of the synchronous component of the position deviation, it is possible to calculate that frequency in advance when the application is limited to a control system that operates based on a specific repetitive command.

[0015] 2 is a configuration diagram of the band-limiting filter 4. For example, a finite impulse response (FIR) filter serving as a digital filter can be applied to the band-limiting filter 4. In the illustrated FIR filter, by changing the values ​​of a0, a1, a2, ..., an, it is possible to change the filter characteristics from a low-pass filter to a band-pass filter, for example. Note that the band-limiting filter 4 is not limited to an FIR filter, and an infinite impulse response (IIR) filter or the like may also be applied.

[0016] 3 is an explanatory diagram of a state in which a specific frequency is passed by the band-limiting filter 4. In this embodiment, by using the band-limiting filter 4 as a band-pass filter 12, it is possible to eliminate the asynchronous component 10 that exists in the vicinity of the synchronous component 11 on the lower frequency side. In control using the low-pass filter 13, this asynchronous component 10 would be input to the learning control unit 5 (see FIG. 1 ), which could cause the control system to become unstable. However, by using the band-pass filter 12 whose center frequency is the synchronous component 11 calculated in advance, only the synchronous component 11 is input to the learning control unit 5, making it possible to improve the stability of the control system.

[0017] 4 is a configuration diagram of a motor control device 1 according to this embodiment. The same reference numerals as those used above indicate the same or equivalent parts. The motor control device 1 includes a subtractor 2 to which a motor movement command is input, a position deviation calculation unit 3 that calculates a position deviation, which is the difference between the motor's position information and the repeat command, a band-limiting filter 4 as a band-limiting filter, a learning controller 5 as a learning control unit that learns the frequency that has passed through the band-limiting filter 4, an adder 6 to which a learning correction amount derived by the learning controller 5 is input, a motor position / speed control unit 20, and a position information acquisition unit 21 that acquires the motor and its position information.

[0018] Furthermore, the motor control device 1 includes a frequency calculation unit 30 that calculates the frequency as a synchronous component included in the movement command, and a filter constant determination unit 31 that determines a filter constant that governs the characteristics of the band-limiting filter 4 .

[0019] As a result, the motor control device 1, which issues a predetermined repeat command to a motor for machining while repeatedly moving a tool or workpiece, includes a position information acquisition unit 21 that acquires position information of the motor, a position deviation calculation unit 3 that calculates a position deviation, which is the difference between the motor's position information and the position information of the repeat command, a frequency calculation unit 30 that calculates a frequency included in the repeat command, a filter constant determination unit 31 that determines a filter constant that governs the characteristics of a band-limiting filter based on the frequency, and a learning control unit 5 that derives a correction amount for the position deviation by passing the position deviation through the band-limiting filter 4 to which the filter constant is applied, and controls the motor by adding the correction amount to the position deviation. As a result, it is possible to automatically set an appropriate band-limiting filter based on the frequency included in the repeat command and control the motor. This makes it possible to more effectively reject asynchronous components while retaining synchronous components that are desired to be input to the learning control unit that derives the correction amount, thereby improving the stability of the control system.

[0020] Furthermore, the filter constant determination unit 31 determines the filter constant so that the band-limiting filter 4 becomes a band-pass filter having the frequency calculated by the frequency calculation unit 30 as its center frequency. This makes it possible to automatically set a band-pass filter having the frequency included in the repeat command as its center frequency and perform motor control.

[0021] 5 is a configuration diagram of a motor control device 1a according to a modification of this embodiment. The same reference numerals as those used above indicate the same or equivalent parts. This modification is characterized in that a first band-limiting filter 40 and a second band-limiting filter 41, each with different characteristics, are provided in advance as band-limiting filters, and can be switched between by a selection unit 42 depending on the state of the control system. The first band-limiting filter 40 and the second band-limiting filter 41 can be, for example, a low-pass filter and a band-pass filter.

[0022] This makes it possible to obtain a motor control device in which the filter constant determination unit 31 determines the filter constant so that the band-limiting filter 4 becomes a band-pass filter whose center frequency is the frequency calculated by the frequency calculation unit 30, or determines the filter constant so that the band-limiting filter 4 becomes a low-pass filter that cuts off frequencies higher than the frequency calculated by the frequency calculation unit 30.

[0023] As a result, the band limiting filter can be switched between a band pass filter and a low pass filter, and motor control can be performed according to the state of the control system.

[0024] 6 is a configuration diagram of a motor control device 1b according to a second modification of this embodiment. The same reference numerals as those used above indicate the same or equivalent parts. This second modification includes a stability determination means 32 that determines the stability of the control system. The filter constant determination unit 31 determines the filter constant so that the band-limiting filter becomes a low-pass filter when the control system is determined to be stable, and determines the filter constant so that the band-limiting filter becomes a band-pass filter when the control system is determined to be unstable.

[0025] This makes it possible to control the motor by applying a low-pass filter when the control system is stable because the synchronous component contains a frequency different from the frequency contained in the repeat command, i.e., when the application of a low-pass filter is advantageous. On the other hand, when the control system is unstable because an asynchronous component is input to the learning control unit, the band-limiting filter can be used as a band-pass filter to stabilize the control system.

[0026] Furthermore, the stability determination means 32 can determine that the control system is stable when the position deviation is less than a predetermined threshold value, and can determine that the control system is unstable when the position deviation is equal to or greater than the predetermined threshold value, thereby making it possible to easily determine the degree of stability of the control system.

[0027] Furthermore, the stability determination means 32 can determine that the control system is stable when the position deviation is less than the amount of movement specified by the repeat command, and can determine that the control system is unstable when the position deviation is equal to or greater than the amount of movement specified by the repeat command, thereby making it possible to easily determine the degree of stability of the control system.

[0028] 7 is a block diagram of a motor control device 1c according to a third modification of this embodiment. The same reference numerals as those used above indicate the same or equivalent parts. This third modification is characterized by the inclusion of a filter characteristics designation means 33 that designates whether the band-limiting filter 4 is a low-pass filter or a band-pass filter. This makes it possible to easily switch between a low-pass filter and a band-pass filter depending on the degree of stability of the control system.

[0029] The motor control device can be configured with one or more control units and memory units. Here, the control unit is a processor such as a CPU (Central Processing Unit) that realizes various functions by executing programs stored in the memory unit. The memory unit is composed of a read-only memory (ROM) or random access memory (RAM) that stores an operating system (OS) and application programs, as well as a storage device such as a hard disk drive or solid-state drive (SSD) that stores various types of information.

[0030] According to the above motor control device, a motor control method can be obtained in which the position information acquisition unit 21 serves as a position information acquisition means, the position deviation calculation unit 3 serves as a position deviation calculation means, the frequency calculation unit 30 serves as a frequency calculation means, the filter constant determination unit 31 serves as a filter constant determination means, and the learning control unit 5 serves as a learning control means, and in which a correction amount is added to the position deviation to control the motor.

[0031] The motor control device and motor control method described above can be realized by hardware, software, or a combination of these. Here, "realized by software" means that the motor control device and motor control method are realized by a computer reading and executing a program.

[0032] The program can be stored and supplied to a computer using various types of non-transitory computer-readable media. Non-transitory computer-readable media include various types of tangible storage media. Examples of non-transitory computer-readable media include magnetic recording media (e.g., hard disk drives), magneto-optical recording media (e.g., magneto-optical disks), CD-ROMs (Read Only Memory), CD-Rs, CD-R / Ws, and semiconductor memories (e.g., mask ROMs, PROMs (Programmable ROMs), EPROMs (Erasable PROMs), flash ROMs, and RAMs (Random Access Memory)).

[0033] Furthermore, although the above-described embodiments are preferred embodiments of the present invention, the scope of the present invention is not limited to only the above-described embodiments, and the present invention can be implemented in various modified forms within the scope that does not deviate from the gist of the present invention.

[0034] 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.

[0035] The motor control device and motor control method disclosed herein can be applied to various control systems that operate based on repetitive commands, as well as to oscillating cutting and eccentric machining, which perform machining operations based on specific frequencies determined by machining conditions.

[0036] The following supplementary note is further disclosed regarding the above embodiment and modified examples: (Supplementary note 1) A motor control device (1) that issues a predetermined repeat command to a motor for machining while repeatedly moving a tool or workpiece, comprising: a position information acquisition unit (21) that acquires position information of the motor, a position deviation calculation unit (3) that calculates a position deviation that is a difference between the position information of the motor and the position information of the repeat command, a frequency calculation unit (30) that calculates a frequency included in the repeat command, a filter constant determination unit (31) that determines a filter constant that governs the characteristics of a band-limiting filter (4) based on the frequency, and a learning control unit (5) that derives a correction amount for the position deviation by passing the position deviation through the band-limiting filter (4) to which the filter constant has been applied, and controls the motor by adding the correction amount to the position deviation.

[0037] (Supplementary Note 2) In the above motor control device, the filter constant determination unit (31) determines the filter constant so that the band-limiting filter (4) becomes a band-pass filter having the frequency calculated by the frequency calculation unit (30) as its center frequency.

[0038] (Supplementary Note 3) In the above motor control device, the filter constant determination unit (31) determines the filter constant so that the band-limiting filter (4) becomes a band-pass filter having the frequency calculated by the frequency calculation unit (30) as its center frequency, or determines the filter constant so that the band-limiting filter (4) becomes a low-pass filter that cuts off frequencies higher than the frequency calculated by the frequency calculation unit (30).

[0039] (Supplementary Note 4) The motor control device includes a stability determination means (32) for determining the stability of a control system including learning control, and the filter constant determination unit (31) determines the filter constant so that the band-limiting filter (4) becomes a low-pass filter when it is determined that the control system is stable, and determines the filter constant so that the band-limiting filter (4) becomes a band-pass filter when it is determined that the control system is unstable.

[0040] (Supplementary Note 5) In the above motor control device, the stability determination means (32) determines that the control system is stable when the position deviation is less than a predetermined threshold value, and determines that the control system is unstable when the position deviation is equal to or greater than the predetermined threshold value.

[0041] (Supplementary Note 6) In the above motor control device, the stability determination means (32) determines that the control system is stable when the position deviation is less than the amount of movement of the repeat command, and determines that the control system is unstable when the position deviation is equal to or greater than the amount of movement of the repeat command.

[0042] (Supplementary Note 7) The motor control device described above comprises a filter characteristic designation means (33) for designating whether the band limiting filter (4) is the low pass filter or the band pass filter.

[0043] (Appendix 8) A motor control method for giving a predetermined repeat command to a motor in order to perform machining while repeatedly moving a tool or workpiece, the motor control method comprising: position information acquisition means (21) for acquiring position information of the motor; position deviation calculation means (3) for calculating a position deviation which is a difference between the position information of the motor and the position information of the repeat command; frequency calculation means (30) for calculating a frequency included in the repeat command; filter constant determination means (31) for determining a filter constant governing the characteristics of a band-limiting filter (4) based on the frequency; and learning control means (5) for deriving a correction amount for the position deviation by passing the position deviation through the band-limiting filter (4) to which the filter constant has been applied, and controlling the motor by adding the correction amount to the position deviation.

[0044] REFERENCE SIGNS LIST 1 Motor control device 1a Motor control device 1b Motor control device 1c Motor control device 3 Position deviation calculation unit 4 Band-limiting filter 5 Learning control unit 21 Position information acquisition unit 30 Frequency calculation unit 31 Filter constant determination unit 32 Stability determination means 33 Filter characteristic designation means

Claims

1. A motor control device that gives a predetermined repeat command to a motor for machining while repeatedly moving a tool or workpiece, comprising: a position information acquisition unit that acquires position information of the motor; a position deviation calculation unit that calculates a position deviation which is the difference between the position information of the motor and the position information of the repeat command; a frequency calculation unit that calculates a frequency included in the repeat command; a filter constant determination unit that determines a filter constant that governs the characteristics of a band-limiting filter based on the frequency; and a learning control unit that derives a correction amount for the position deviation by passing the position deviation through the band-limiting filter to which the filter constant has been applied, and controls the motor by adding the correction amount.

2. The motor control device according to claim 1, wherein the filter constant determination section determines the filter constant so that the band-limiting filter becomes a band-pass filter having a center frequency at the frequency calculated by the frequency calculation section.

3. A motor control device as described in claim 1, wherein the filter constant determination unit determines the filter constant so that the band-limiting filter becomes a band-pass filter having a center frequency of the frequency calculated by the frequency calculation unit, or determines the filter constant so that the band-limiting filter becomes a low-pass filter that cuts off frequencies higher than the frequency calculated by the frequency calculation unit.

4. A motor control device as described in claim 3, further comprising a stability determination means for determining the stability of a control system including learning control, wherein the filter constant determination unit determines the filter constant so that the band-limiting filter becomes a low-pass filter when the control system is determined to be stable, and determines the filter constant so that the band-limiting filter becomes a band-pass filter when the control system is determined to be unstable.

5. A motor control device as described in claim 4, wherein the stability determination means determines that the control system is stable when the position deviation is less than a predetermined threshold value, and determines that the control system is unstable when the position deviation is equal to or greater than a predetermined threshold value.

6. A motor control device as described in claim 4, wherein the stability determination means determines that the control system is stable when the position deviation is less than the amount of movement of the repeat command, and determines that the control system is unstable when the position deviation is equal to or greater than the amount of movement of the repeat command.

7. A motor control device according to any one of claims 3 to 6, further comprising filter characteristic designation means for designating whether said band limiting filter is to be said low pass filter or said band pass filter.

8. A motor control method for giving a predetermined repeat command to a motor for machining while repeatedly moving a tool or workpiece, comprising: position information acquisition means for acquiring position information of the motor; position deviation calculation means for calculating a position deviation which is the difference between the position information of the motor and the position information of the repeat command; frequency calculation means for calculating a frequency included in the repeat command; filter constant determination means for determining a filter constant governing the characteristics of a band-limiting filter based on the frequency; and learning control means for deriving a correction amount for the position deviation by passing the position deviation through the band-limiting filter to which the filter constant has been applied, and controlling the motor by adding the correction amount to the position deviation.

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