Machine tool control device

Abstract

The present invention provides a technology for a machine tool control device whereby inconsistent learning control can be avoided and consistent machining can be achieved. A machine tool control device 10 comprises: a position command generation unit 11 that generates a position command for driving a motor 1; a motor speed calculation unit 14 that calculates on the basis of the position command or position feedback regarding a driven object that is driven by the motor 1; a learning control unit 13 that acquires position information about the motor 1 synchronized with the driven object as a reference position and executes learning control that outputs a correction amount synchronized with the reference position to bring a position deviation, which is the difference between the position command and the actual position of the driven object driven by motor 1, close to zero on the basis of a prescribed learning control parameter; and a consistency estimation unit 15 that calculates an appropriate learning control parameter from a reference speed calculated by the motor speed calculation unit 14 during execution of the learning control, and compares the calculated learning control parameter to a preset learning control parameter to evaluate the consistency of the learning control.

Description

Machine tool control device

[0001] The present disclosure relates to a control device for a machine tool.

[0002] Conventionally, in a machine tool control device, a technique is known in which a correction amount is output so that the difference between a position command and the actual position of a driven body driven by a servo motor approaches zero (for example, Patent Documents 1 to 3).

[0003] Patent Document 1 describes a servo control device having a function for automatically adjusting a learning controller, which enables the selection of learning parameters that suit machine characteristics and operating conditions by visualizing the convergence of learning and disturbance response. Patent Document 2 describes a servo control device that includes an observer and calculates an estimated speed based on a torque command and a detected position value of the motor position. Patent Document 3 describes a servo motor control device that can achieve high accuracy by applying angle-synchronized learning control even when drilling holes with variable circle diameters or machining free-form closed curve shapes.

[0004] JP 2017-084104 A JP 2010-142020 A JP 2016-031735 A

[0005] For operations in which the same operation is repeated for a workpiece at predetermined intervals, learning control is effective, which associates the position deviation for one cycle with the motor angle and stores it in memory, and outputs correction data for each cycle so that the position deviation approaches 0. However, while learning control based on the motor angle is advantageous for following commands synchronized with the motor rotation and suppressing disturbances synchronized with the motor rotation, it has the disadvantage of being prone to becoming unstable by amplifying disturbances not synchronized with the motor rotation and high-frequency noise.

[0006] To address this issue, it is important to use a low-pass filter or adjust the division number (a parameter for the angular resolution of the memory) to moderately limit the response band of the learning control, which is essential for obtaining good machining results. These parameter adjustments are usually performed appropriately by those skilled in the art. However, depending on the machining, such as constant peripheral speed control, the motor rotation speed may change during operation. In such operations, the response band of the learning control changes in sync with the motor rotation speed, which can make the learning control unstable.

[0007] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a technique for avoiding unstable learning control in a machine tool control device and achieving stable machining.

[0008] The present disclosure relates to a control device for a machine tool that controls at least one motor, comprising: a position command generation unit that generates a position command for driving the motor; a motor speed calculation unit that calculates a reference speed that indicates the speed of the motor from the position command or position feedback of a driven body driven by the motor; a learning controller that acquires position information of the motor synchronized with the driven body as a reference position and performs learning control that outputs a correction amount synchronized with the reference position based on predetermined learning control parameters so as to bring a position error, which is the difference between the actual position of the driven body driven by the motor and the position command, closer to zero; and a stability estimation unit that calculates appropriate learning control parameters from the reference speed calculated by the motor speed calculation unit during execution of the learning control and compares the reference speed with preset learning control parameters to evaluate the stability of the learning control.

[0009] According to the present disclosure, it is possible to provide a technique for avoiding unstable learning control in a machine tool control device and realizing stable machining.

[0010] Fig. 1 is a functional block diagram of a control device for a machine tool according to a first embodiment; Fig. 2 is a graph showing an example of the relationship between the allowable range of the control band and the learning response band; Fig. 3 is a flowchart showing the flow of a stability estimation process; Fig. 4 is a graph showing an example of the relationship between an ideal reference speed and a reference speed during a machining operation; Fig. 5 is a functional block diagram of a control device for a machine tool according to a second embodiment; Fig. 6 is a functional block diagram of a control device for a machine tool according to a third embodiment;

[0011] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the description of the second and subsequent embodiments, the same reference numerals will be used to designate components common to the first and second embodiments, and the description thereof will be omitted as appropriate.

[0012] 1 is a functional block diagram of a control device 10 for a machine tool according to a first embodiment. The machine tool is, for example, a machining device or a robot that operates based on content specified in a machining program or content input by manual operation.

[0013] The control device 10 controls the operation of the machine tool by controlling at least one motor 1 that drives a driven object based on a machining program. The motor 1 that is the control target of the control device 10 is, for example, an electric motor such as a servo motor. The number of motors 1 that are the control target of the control device 10 may be one or more. For example, the machine tool that is the control target may also be a machine tool that further includes another motor (spindle motor) that operates in synchronization with the motor (servo motor).

[0014] The control device 10 of this embodiment includes a position command generating unit 11, an encoder 20, a subtractor 21, an adder 22, a position and speed control unit 12, a learning controller 13, a motor speed calculation unit 14, and a stability estimation unit 15.

[0015] The position command generator 11 generates a position command for operating the motor 1 based on the machining program or manually set contents. The position command is generated, for example, to change the pulse frequency in order to change the speed of the motor 1. The position command generator 11 is realized, for example, by a numerical control device (CNC: Computerized Numerical Control). The position command generator 11 outputs the generated position command to the subtractor 21. In this embodiment, the position command generator 11 also outputs the position command, which serves as a reference position, to the motor speed calculator 14.

[0016] The encoder 20 is a position detector that is disposed on the feed shaft of the motor 1 and detects the amount of rotation of the motor. The position information detected by the encoder 20 is output to the subtractor 21 as position feedback (actual position), and is also output to the learning controller 13 as a motor angle indicating the rotation angle of the motor 1.

[0017] The subtractor 21 is a position deviation acquisition unit that calculates a position deviation, which is the difference between the position command (movement command) created by the position command generation unit 11 and the position feedback from the motor 1. The subtractor 21 outputs the calculated position deviation to the adder 22 and also to the learning controller 13.

[0018] The adder 22 is a position deviation correction unit that generates a composite command by adding the position deviation output from the subtractor 21 and the correction amount calculated by the learning controller 13. The adder 22 outputs the generated composite command to the position and speed control unit 12.

[0019] The position and speed control unit 12 performs position control, speed control, and current control based on the command output from the adder 22 to drive and control the motor 1. This drive control drives the driven object via the motor 1. The motor 1 also outputs the motor angle to the learning controller 13.

[0020] The learning controller 13 stores the position deviation for a predetermined period (e.g., one revolution) in memory in association with a reference position (motor angle) based on a predetermined learning control parameter. The learning control parameter is, for example, a division number. The division number here refers to the angular resolution of the memory for storing the reference position and the position deviation in association with each other. The reference position may be any motor angle synchronized with the driven body, and may be, for example, information indicating the motor angle of a servo motor or the motor position of a spindle motor.

[0021] The learning controller 13 executes learning control to set a correction amount for each period based on the relationship between the position error and the reference position so as to bring the position error closer to zero. The learning controller 13 calculates a correction amount synchronized with the motor angle (reference position) input from the encoder 20. As described above, the correction amount calculated by the learning controller 13 is added to the position error by the adder 22. The learning controller 13 also outputs learning control parameters to the stability estimation unit 15, which will be described later.

[0022] The motor speed calculation unit 14 calculates a reference speed from the reference position. In this embodiment, the reference position is acquired from a position command before position feedback input from the position command generation unit 11. The motor speed calculation unit 14 calculates the reference speed during learning control by the learning controller 13 and outputs it to the stability estimation unit 15.

[0023] The stability estimation unit 15 evaluates the stability of the learning control based on the reference speed input from the motor speed calculation unit 14 and the learning control parameters input from the learning controller 13. The stability estimation unit 15 calculates an appropriate angular resolution from the reference speed, and compares it with the angular resolution (number of divisions), which is a preset learning control parameter of the learning controller 13, to evaluate the stability of the learning control.

[0024] Here, the evaluation criteria for stability will be explained. Fig. 2 is a graph showing an example of the relationship between the allowable range of the control band and the learning response band. Fig. 2 shows the relationship between the response band (actual band) of learning control when a machining program to be subjected to learning control is executed and the allowable band in which learning control is stably executed, in a graph with the horizontal axis representing machining time (s) and the vertical axis representing band (Hz).

[0025] The response band of learning control is correlated with the division number x motor speed of the reference axis. As shown in Figure 2, when the response band of learning control is within the allowable range of the control band, the position error is stabilized by the correction of learning control. On the other hand, when the response band of learning control is outside the allowable range of the control band, the position error increases.

[0026] The control band (actual band) in which learning control can efficiently suppress position deviation is calculated as shown in Equation 1. The number 60000 in Equation 1 is a value for converting RPM, which indicates the number of rotations per minute, into rotation speed per ms. The learning band in Equation 1 is the cutoff frequency of the LPF (Low Pass Filter), the division number is the angular resolution of the memory, and N is the rotation speed of the reference axis (reference speed) [min －１ The learning band and the number of divisions are both parameters that are set in advance.

[0027]

[0028] Equation 1 shows that when the number of divisions is constant, fluctuations in the reference speed, which is the motor speed of the reference axis motor, cause fluctuations in the actual band. Fluctuations in the actual band cause the amount of correction for the actual position output by the learning controller 13 to become inappropriate. For example, if the reference speed increases, the actual band also increases, resulting in excessive correction and unstable control. Conversely, if the reference speed decreases, the actual band also decreases, resulting in insufficient correction and reduced accuracy.

[0029] Solving Equation 1 for the division number results in Equation 2. In Equation 2, if it is assumed that the learning control parameter and the control band are the same as an ideal condition, Equation 2 can be simplified to Equation 3. If the reference speed is known from Equation 3, it is possible to calculate a learning control parameter (division number) that satisfies the condition.

[0030]

[0031]

[0032] In this embodiment, the stability estimation unit 15 compares the reference speed during operation with the allowable range of the calculated reference speed, and determines whether or not the state is such that learning control can be appropriately executed.

[0033] Next, the flow of the process of stability estimation based on the reference speed will be described with reference to Figures 3 and 4. Figure 3 is a flowchart showing the flow of the process of stability estimation. Figure 4 is a graph showing an example of the relationship between the ideal reference speed and the reference speed during machining operation. In the graph of Figure 4, the horizontal axis represents machining time [s] and the vertical axis represents reference speed [min －１ ]. Of these, the reference speed [min －１ 4 shows the relationship between the bandwidth and the processing time.

[0034] In step S1, an ideal value x of the reference speed is set based on a preset learning control parameter (number of divisions). The learning control parameter (number of divisions) is set by an operator using the machine tool. The ideal value x is calculated, for example, by Equation 3 based on the learning control parameter (number of divisions) set by the operator before the start of a machining operation. The calculation of the ideal value x may be performed by the control device 10, or the control device 10 may receive the calculated numerical value.

[0035] In step S2, an allowable range for the reference speed is set. The allowable range is set based on a predetermined value a that determines the monitoring level and an ideal value x. As shown in Fig. 4, in this example, the allowable range is set based on the maximum value obtained by adding a to the ideal value x and the minimum value obtained by subtracting a from the ideal value x.

[0036] In step S3, learning control is executed by the learning controller 13. As described above, in the learning control, the position deviation is corrected by a correction amount corresponding to the motor angle based on a preset learning control parameter (number of divisions).

[0037] In step S4, the stability estimation unit 15 performs stability estimation. The stability estimation unit 15 compares the reference speed during operation with the allowable range of the reference speed, and if it is outside the allowable range, evaluates that the stability condition is not satisfied. If the stability condition is satisfied (step S4; Yes) and machining has not yet ended, the stability monitoring continues (step S5; No). On the other hand, if the stability condition is satisfied (step S4; Yes) and machining has ended, this processing ends (step S5; Yes). If it is evaluated that the stability condition is not satisfied, the processing proceeds to step S6 (step S4; No).

[0038] In step S6, the stability estimation unit 15 outputs information indicating that the stability condition is not satisfied. In this embodiment, the stability estimation unit 15 outputs information instructing the learning control to be stopped or information instructing the division number to be changed to the learning controller 13 as information based on the evaluation result.

[0039] In step S7, the number of divisions is changed. In changing the number of divisions, the number of divisions is set so that the actual speed (reference speed) falls within an allowable range. The change in the number of divisions is set by the operator when information instructing the stopping of learning control is input in step S6. Furthermore, when a deterioration in the stability of learning control is determined in step S6 and information instructing a change in the number of divisions is input, the number of divisions is automatically calculated by the control device 10. For example, the number of divisions is recalculated so that the reference speed during the machining operation falls within the allowable range of the reference speed.

[0040] In the above embodiment, the stability of the learning control is evaluated by comparing the reference speed, which is the actual motor speed, with an allowable range based on an ideal reference speed corresponding to the division number preset in the learning controller 13. However, the present invention is not limited to this configuration. For example, an allowable range of the control band based on the division number preset in the learning controller 13 may be set, and if the division number calculated from the motor speed using Equation 3 or the like deviates from this allowable range, it may be evaluated that stability has deteriorated.

[0041] In the above embodiment, the learning control parameter is the division number, but this is not limiting. For example, since the actual band is made up of the learning band and the division number as shown in Equation 1, the learning control parameter can also be the learning band.

[0042] As described above, the control device 10 of the machine tool of this embodiment comprises a position command generation unit 11 that generates a position command for driving the motor 1; a motor speed calculation unit 14 that calculates a reference speed from the position command or position feedback of the driven body driven by the motor 1; a learning controller 13 that acquires position information of the motor 1 that is synchronized with the driven body as a reference position and executes learning control that outputs a correction amount synchronized with the reference position based on predetermined learning control parameters so as to bring the position error, which is the difference between the actual position of the driven body driven by the motor 1 and the position command, closer to zero; and a stability estimation unit 15 that calculates appropriate learning control parameters from the reference speed calculated by the motor speed calculation unit 14 during execution of the learning control and compares them with preset learning control parameters to evaluate the stability of the learning control.

[0043] This allows the rotation speed of the motor 1 during machining to be monitored in real time, and even if the current response band (actual band) becomes excessive or the correction amount becomes insufficient or excessive, the learning control can be automatically stopped and the learning control parameters (number of divisions) can be changed, or the operator can be notified that the stability of the learning control has deteriorated. This prevents the occurrence of situations where learning control is executed in an unstable state, and enables stable machining.

[0044] In this embodiment, the learning control parameter is the angular resolution of a memory for storing the reference position and the position deviation in association with each other, and the stability estimation unit 15 calculates an appropriate angular resolution from the reference velocity and compares it with a preset angular resolution to evaluate the stability of the learning control. This allows the angular resolution (number of divisions) to be used to evaluate the stability of the learning control in an appropriate and simple manner.

[0045] Furthermore, in this embodiment, when the stability estimation unit 15 determines that the stability of the learning control has deteriorated, it instructs the learning controller 13 to stop adding the correction amount. As a result, the learning control is automatically stopped when the stability has deteriorated, and it is possible to avoid a situation in which the position error is corrected with an excessive or insufficient correction amount.

[0046] Furthermore, in this embodiment, the stability estimation unit 15 instructs the learning controller 13 to change the learning control parameters based on the evaluated stability. As a result, when the stability deteriorates, the division number is automatically changed so that the actual band falls within the allowable range, thereby reliably preventing the position error from being corrected with an excessive or insufficient correction amount.

[0047] Second Embodiment Fig. 5 is a functional block diagram of a control device 10a for a machine tool according to a second embodiment. As shown in Fig. 5, in the second embodiment, a position command generator 11 does not output a position command to a motor speed calculator 14, but outputs a position command only to a subtractor 21. Instead, an encoder 20 outputs information indicating a reference position to the motor speed calculator 14 in addition to the subtractor 21 and the learning controller 13.

[0048] In this way, the motor speed calculation unit 14 of the second embodiment calculates the reference speed from the position feedback of the motor 1 instead of the position command input from the position command generation unit 11. Note that the configuration other than this is the same as that of the first embodiment. The configuration of this second embodiment can also achieve the same effects as the above embodiments.

[0049] [Third embodiment] Fig. 6 is a functional block diagram of a machine tool control device 10b according to a third embodiment. As shown in Fig. 6, the machine tool control device 10b further includes a screen display unit 25 in addition to the configuration of the first embodiment.

[0050] The screen display unit 25 is a display that displays various information as images. In this embodiment, the screen display unit 25 is disposed in a computer numerical control (CNC). The screen display unit 25 may have a speaker function that notifies various information by voice.

[0051] In the third embodiment, the stability estimation unit 15 outputs an instruction based on the evaluation result to the screen display unit 25, rather than to the learning controller 13. The instruction based on the evaluation result output by the stability estimation unit 15 is information for displaying a warning on the screen display unit 25 to notify the operator of a deterioration in the stability of the learning control.

[0052] As described above, the machine tool control device 10b of the third embodiment further includes the screen display unit 25, and when the stability estimation unit 15 determines that the stability of the learning control has deteriorated, it causes information indicating the deterioration in stability to be displayed on the screen display unit 25. The configuration of this third embodiment can also achieve the same effects as the above embodiments. Furthermore, in the third embodiment, the screen display unit 25 can be used to let the operator know that the stability of the learning control has deteriorated.

[0053] In the third embodiment, the stability estimation unit 15 is configured to output instructions based on the evaluation result only to the screen display unit 25, but may also be configured to output instructions based on the evaluation result to the learning controller 13. For example, the stability estimation unit 15 may output an instruction to the learning controller 13 to stop the execution of learning control, and may also instruct the screen display unit 25 to display information indicating that the execution of learning control has been stopped due to deterioration of stability. Alternatively, the stability estimation unit 15 may output an instruction to the learning controller 13 to change the number of divisions, and may also instruct the screen display unit 25 to display information indicating that the number of divisions has been changed.

[0054] The present disclosure is not limited to the above-described embodiments, and includes modifications and improvements within the scope of achieving the object of the present disclosure.

[0055] The following supplementary note is further disclosed regarding the above embodiment and modified examples: (Supplementary Note 1) A machine tool control device (10, 10a, 10b) for controlling at least one motor (1), comprising: a position command generation unit (11) that generates a position command for driving the motor (1), a motor speed calculation unit (14) that calculates a reference speed indicating the speed of the motor (1) from the position command or position feedback of a driven body driven by the motor (1), a learning controller (13) that acquires position information of the motor (1) synchronized with the driven body as a reference position and performs learning control that outputs a correction amount synchronized with the reference position based on predetermined learning control parameters so as to bring a position error, which is the difference between the actual position of the driven body driven by the motor (1) and the position command, closer to zero, and a stability estimation unit (15) that calculates appropriate learning control parameters from the reference speed calculated by the motor speed calculation unit during execution of the learning control, and evaluates the stability of the learning control by comparing the reference speed with the preset learning control parameters.

[0056] (Supplementary Note 2) In the above-mentioned machine tool control device (10, 10a, 10b), the learning control parameter is an angular resolution of a memory for storing the reference position and the position deviation in association with each other, and the stability estimation unit (15) calculates an appropriate angular resolution from the reference velocity and compares it with a preset angular resolution to evaluate the stability of the learning control.

[0057] (Supplementary Note 3) In the above-mentioned machine tool control device (10, 10a), the stability estimation unit (15) instructs the learning controller (13) to stop adding the correction amount when it determines that the stability of the learning control has deteriorated.

[0058] (Supplementary Note 4) In the above-described machine tool control device (10, 10a), the stability estimation unit (15) instructs the learning controller (13) to change the learning control parameters based on the evaluated stability.

[0059] (Supplementary Note 5) The above-mentioned machine tool control device (10b) further includes a screen display unit (20), and the stability estimation unit (15) causes the screen display unit (25) to display information indicating the stability degradation when it determines that the stability of the learning control has deteriorated.

[0060] 10, 10a, 10b Machine tool control device 11 Position command generation unit 12 Position and speed control unit 13 Learning controller 14 Motor speed calculation unit 15 Stability estimation unit 20 Encoder (position detection unit) 21 Subtractor (position deviation acquisition unit) 25 Screen display unit

Claims

1. A control device for a machine tool that controls at least one motor, comprising: a position command generation unit that generates a position command for driving the motor; a motor speed calculation unit that calculates a reference speed indicating the speed of the motor from the position command or the position feedback of the driven body driven by the motor; a learning controller that acquires the position information of the motor synchronized with the driven body as a reference position and outputs a correction amount synchronized with the reference position so as to bring the position deviation, which is the difference between the actual position of the driven body driven by the motor and the position command, close to zero based on a predetermined learning control parameter; and a stability estimation unit that calculates an appropriate learning control parameter from the reference speed calculated by the motor speed calculation unit during the execution of the learning control, and evaluates the stability of the learning control by comparing it with the preset learning control parameter.

2. The learning control parameter is the angular resolution of a memory for storing the reference position and the position deviation in association with each other, and the stability estimation unit calculates an appropriate angular resolution from the reference speed and evaluates the stability of the learning control by comparing it with the preset angular resolution. The control device for a machine tool according to claim 1.

3. The stability estimation unit instructs the learning controller to stop adding the correction amount when it determines that the stability of the learning control has deteriorated. The control device for a machine tool according to claim 1 or 2.

4. The stability estimation unit instructs the learning controller to change the learning control parameter based on the evaluated stability. The control device for a machine tool according to claim 1 or 2.

5. Further comprising a screen display unit, and the stability estimation unit causes the screen display unit to display information indicating a decrease in stability when it determines that the stability of the learning control has deteriorated. The control device for a machine tool according to claim 1 or 2.