JP7468157B2 - Numerical control devices and machine tools - Google Patents

Description

The present invention relates to a numerical control device and a machine tool.

Patent Document 1 discloses a numerical control device that performs feedforward control to improve tracking of a position command. The numerical control device calculates a command value to be used in the feedforward control based on values obtained by multiplying a constant with a value obtained by first differentiating a position command, a value obtained by second differentiating a position command, a value obtained by third differentiating a position command, and a value obtained by first differentiating a position command and further filtering the same.

JP 2011-113475 A

The feedforward control of the above-mentioned numerical control device does not take into account the first-order delay of the drive circuit that drives the motor. Therefore, when executing position commands with short cycles in particular, the first-order delay can cause a decrease in tracking ability.

The object of the present invention is to provide a numerical control device and a machine tool that have good tracking performance even when short-period position commands are executed.

A numerical control device according to a first aspect of the present invention is a numerical control device comprising: a position control unit that determines and outputs a speed command for controlling the speed of the motor by proportional control so that a position command for controlling the position of the motor coincides with a feedback signal of the position of the motor; a speed control unit that outputs a torque command for controlling the torque of the motor by proportional-integral control so that the speed command output by the position control unit coincides with the feedback signal of the speed of the motor; and a torque control unit that controls the torque of the motor based on the torque command output by the speed control unit, wherein the position control unit comprises a second average filter calculation unit that applies a second moving average filter to a second-order differential value obtained by second-order differentiation of the position command; The system is characterized by comprising a second lag filter calculation unit that applies a second lag filter, which is a first-order lag filter, to the calculation result obtained by applying the second moving average filter to the second-order differential value by the filter calculation unit; a third average filter calculation unit that applies a third moving average filter to a third-order differential value obtained by third-order differentiation of the position command; a third lag filter calculation unit that applies a third lag filter, which is a first-order lag filter, to the calculation result obtained by applying the third moving average filter to the third-order differential value by the third average filter calculation unit; and a feedforward calculation unit that multiplies the calculation results of the second lag filter calculation unit and the third lag filter calculation unit by a constant, adds them together, and adds the result to the speed command as a feedforward signal.

According to the first aspect, the second and third lag filters of the numerical control device can suppress the influence of the first-order lag of the position control unit. Therefore, the numerical control device can improve the motor's ability to follow the position command even when a position command with a short period is executed.

In the first aspect, the position control unit further includes a first lag filter calculation unit that applies a first lag filter, which is a first-order lag filter, to a first-order differential value obtained by first-order differentiation of the position command, and the feedforward calculation unit may multiply the calculation results of each of the first lag filter calculation unit, the second lag filter calculation unit, and the third lag filter calculation unit by a constant, add the result, and add the result to the speed command as the feedforward signal. In this case, the first to third lag filters can further suppress the influence of the first-order lag of the position control unit. Therefore, the numerical control device can further improve the motor's ability to follow the position command, even when a position command with a short period is executed.

In the first aspect, the second moving average filter and the third moving average filter may be moving average filters that remove noise from the differential value. Repeated differentiation of the position command in the position control unit may amplify discretization error, increasing noise and potentially reducing tracking ability. In response to this, the numerical control device can suppress the increase in noise caused by the amplification of discretization error using a moving average filter, thereby further improving the tracking ability of the motor to the position command.

In the first aspect, the device may further include a time constant setting unit that sets the time constants of the second lag filter and the third lag filter based on the integral time constant of the speed loop of the speed control unit. The numerical control device can further improve the motor's ability to follow a position command by optimizing the time constant of the first-order lag filter based on the integral time constant of the speed loop.

In the first aspect, the present invention may further include a time constant setting unit that sets the time constants of the second lag filter and the third lag filter based on the integral time constant of the speed loop of the speed control unit, the number of times the moving average filter is applied, and the time constant of the moving average filter. The numerical control device can further improve the motor's ability to follow a position command by optimizing the time constant of the first-order lag filter based on the integral time constant of the speed loop, the number of stages of the moving average filter, and the time constant of the moving average filter.

In the first aspect, the time constant setting unit may set the time constants of the second lag filter and the third lag filter in response to a change in the integral time constant. The numerical control device can improve the motor's ability to follow a position command even after the integral time constant is changed.

A machine tool according to a second aspect of the present invention includes the numerical control device according to the first aspect and the motor. According to the second aspect, the same effects as those of the first aspect can be obtained.

FIG. FIG. 2 is a block diagram showing the electrical configuration of the numerical control device 30 and the machine tool 1. FIG. 2 is a functional block diagram of a numerical control device 30. FIG. 2 is an explanatory diagram of a functional outline of a numerical control device 30. 1 is a flow chart of the main process. 5 is a graph showing the relationship between the speed and position deviation of the motor 50.

An embodiment of the present invention will be described. In the following description, the left/right, front/back, and up/down directions shown by arrows in the figures will be used. The left/right, front/back, and up/down directions of the machine tool 1 are the X-axis, Y-axis, and Z-axis directions of the machine tool 1, respectively. The machine tool 1 shown in Figure 1 is a machine that rotates a tool 4 attached to a spindle 9 and performs cutting on a workpiece 3 held on the upper surface of a table 13. A numerical control device 30 (see Figure 2) controls the operation of the machine tool 1.

<Structure of machine tool 1>
The structure of the machine tool 1 will be described with reference to FIG. 1. The machine tool 1 includes a base 2, a column 5, a spindle head 7, a spindle 9, a table device 10, a tool changer 20, a control box 6, an operation panel 15 (see FIG. 2), and the like. The base 2 is a metal base in the shape of a substantially rectangular parallelepiped. The column 5 is erected at the rear of the upper part of the base 2. The spindle head 7 is provided so as to be movable in the Z-axis direction along the front surface of the column 5. The spindle head 7 rotatably supports the spindle 9 inside. The spindle 9 has a mounting hole (not shown) at the bottom. The tool 4 is mounted in the mounting hole of the spindle 9, and the spindle 9 is rotated by the drive of a spindle motor 52 (see FIG. 2). The spindle motor 52 is provided on the spindle head 7. The spindle head 7 moves in the Z-axis direction by a Z-axis movement mechanism (not shown) provided in front of the column 5. The numerical control device 30 controls the drive of the Z-axis motor 51 (see FIG. 2) to control the movement of the spindle head 7 in the Z-axis direction.

The table device 10 includes a Y-axis movement mechanism (not shown), a Y-axis table 12, an X-axis movement mechanism (not shown), a table 13, etc. The Y-axis movement mechanism is provided on the front side of the upper surface of the base 2, and includes a Y-axis rail, a Y-axis ball screw, a Y-axis motor 54 (see FIG. 2), etc. The Y-axis rail and the Y-axis ball screw extend in the Y-axis direction. The Y-axis rail guides the Y-axis table 12 in the Y-axis direction on the upper surface. The Y-axis table 12 is formed in a roughly rectangular parallelepiped shape and includes a nut (not shown) on the bottom outer surface. The nut is screwed into the Y-axis ball screw. When the Y-axis motor 54 rotates the Y-axis ball screw, the Y-axis table 12 moves along the Y-axis rail together with the nut. Therefore, the Y-axis movement mechanism supports the Y-axis table 12 so that it can move in the Y-axis direction.

The X-axis movement mechanism is provided on the upper surface of the Y-axis table 12, and includes an X-axis rail (not shown), an X-axis ball screw (not shown), an X-axis motor 53 (see FIG. 2), etc. The X-axis rail and the X-axis ball screw extend in the X-axis direction. The table 13 is formed in a rectangular plate shape in a plan view, and is provided on the upper surface of the Y-axis table 12. The table 13 includes a nut (not shown) at the bottom. The nut is screwed into the X-axis ball screw. When the X-axis motor 53 rotates the X-axis ball screw, the table 13 moves along the X-axis rail together with the nut. Therefore, the X-axis movement mechanism supports the table 13 so that it can move in the X-axis direction. Therefore, the table 13 can move in the X-axis direction and the Y-axis direction on the base 2 by the Y-axis movement mechanism, the Y-axis table 12, and the X-axis movement mechanism.

The tool changer 20 is provided in front of the spindle head 7 and includes a disk-shaped tool magazine 21, a magazine motor 55 (see FIG. 2), etc. The tool magazine 21 holds multiple tools (not shown) radially on its outer periphery and positions the tool specified by a tool change command at the tool change position. The tool change command is issued by an NC program. The tool change position is the lowest position of the tool magazine 21. Driven by the magazine motor 55, the tool changer 20 swaps the tool 4 attached to the spindle 9 with the tool attached to the tool magazine 21 through a series of operations that lift the spindle head 7, rotate the tool magazine 21, and lower the spindle head 7.

The control box 6 houses a numerical control device 30 (see FIG. 2). The numerical control device 30 controls the Z-axis motor 51, spindle motor 52, X-axis motor 53, Y-axis motor 54, and magazine motor 55 (see FIG. 2) provided on the machine tool 1, and performs various types of machining on the workpiece 3 by moving the workpiece 3 held on the table 13 relative to the tool 4 attached to the spindle 9. The various types of machining include, for example, drilling using a drill or tap, side machining using an end mill or milling cutter, etc.

The operation panel 15 is provided, for example, on the outer wall of a cover (not shown) that covers the machine tool 1. The operation panel 15 includes an operation unit 16 and a display unit 17 (see FIG. 2). The operation unit 16 accepts inputs of various information, operation instructions, etc., and outputs them to the numerical control device 30, which will be described later. The display unit 17 displays various screens based on commands from the numerical control device 30, which will be described later.

<Electrical configuration>
The electrical configuration of the numerical control device 30 and the machine tool 1 will be described with reference to Figure 2. The numerical control device 30 comprises a CPU 31, a ROM 32, a RAM 33, a storage device 34, an input/output unit 35, drive circuits 51A-55A, etc. The ROM 32 stores various setting information. The RAM 33 temporarily stores various information. The storage device 34 is non-volatile, and stores an NC program and various information. The NC program is made up of multiple lines including various control commands, and controls various operations of the machine tool 1, including axis movement and tool replacement, on a line-by-line basis. The CPU 31 reads the commands of the NC program one by one and executes various operations.

Drive circuit 51A is connected to Z-axis motor 51 and encoder 51B of machine tool 1. Drive circuit 52A is connected to spindle motor 52 and encoder 52B of machine tool 1. Drive circuit 53A is connected to X-axis motor 53 and encoder 53B of machine tool 1. Drive circuit 54A is connected to Y-axis motor 54 and encoder 54B of machine tool 1. Drive circuit 55A is connected to magazine motor 55 and encoder 55B that drive tool magazine 21 of machine tool 1. Z-axis motor 51, spindle motor 52, X-axis motor 53, Y-axis motor 54, and magazine motor 55 are all servo motors. Drive circuits 51A, 52A, 53A, 54A, and 55A are collectively referred to as drive circuits 5A. Z-axis motor 51, spindle motor 52, X-axis motor 53, Y-axis motor 54, and magazine motor 55 are collectively referred to as motor 50. Encoders 51B, 52B, 53B, 54B, and 55B are collectively referred to as encoder 5B. Encoder 5B identifies the rotational position of the corresponding motor 50 (hereinafter referred to as the position of motor 50).

The drive circuit 5A receives commands from the CPU 31 and outputs drive currents to the corresponding motors 50. The drive circuit 5A receives a feedback signal indicating the position of the motors 50 from the encoder 5B and performs feedback control. The input/output unit 35 is connected to the operation unit 16 and the display unit 17 of the operation panel 15.

<Functional Overview of Numerical Control Device 30>
The following describes an outline of the functions of the numerical control device 30 with reference to Fig. 3. As shown in Fig. 3, a drive circuit 5A of the numerical control device 30 has, as functional blocks, a position control unit 6A, a speed control unit 7A, a torque control unit 8A, and a speed command input unit 9A.

The CPU 31 (see FIG. 2) reads the position command for controlling the position of the motor 50, one line at a time, from the NC program, and outputs it to the speed command input unit 9A. The speed command input unit 9A determines a speed command indicating the speed at which the motor 50 should be moved to the position indicated by the position command obtained from the CPU 31, by performing a first-order differential operation on the position command. The speed command input unit 9A outputs the determined speed command to the position control unit 6A, which will be described later.

The position control unit 6A determines a speed command that controls the speed of the motor 50 so that the feedback signal of the position of the motor 50 output by the encoder 5B matches the position command by correcting it using proportional control, and outputs it to the speed control unit 7A described below. The position control unit 6A has an acceleration calculation unit 61B, a jerk calculation unit 61C, a second average filter calculation unit 62B, a third average filter calculation unit 62C, a first lag filter calculation unit 63A, a second lag filter calculation unit 63B, a third lag filter calculation unit 63C, a first constant calculation unit 64A, a second constant calculation unit 64B, a third constant calculation unit 64C, a feedforward calculation unit (FF calculation unit) 65, a position command conversion unit 66, a position loop gain multiplication unit 67, and a subtractor 69A.

The first lag filter calculation unit 63A applies a first lag filter _E1 , which is a first-order lag filter with a time constant _T1 , to the speed command input from the speed command input unit 9A. That is, the first lag filter calculation unit 63A applies the first lag filter _E1 to the calculation result obtained by the speed command input unit 9A performing a first-order differential operation on the original position command. The value of the speed command generated by performing a first-order differential operation on the position command is called a first-order differential value. The first constant calculation unit 64A multiplies the calculation result obtained by applying the first lag filter _E1 to the first-order differential value by the first lag filter calculation unit 63A, by a constant _C1 .

The acceleration calculation unit 61B performs a first-order differential operation on the speed command input from the speed command input unit 9A. That is, the acceleration calculation unit 61B performs a second-order differential operation on the original position command to generate an acceleration command. The value of the acceleration command generated by the acceleration calculation unit 61B is called a second-order differential value. The second average filter calculation unit 62B applies a second moving average filter _F2 to the second-order differential value generated by the acceleration calculation unit 61B. The second lag filter calculation unit 63B applies a second lag filter E2, which is a first-order lag filter with a time constant _T2 , to the calculation result obtained by applying the second moving average filter _F2 to the second-order differential value by the second average filter calculation unit 62B. The second constant calculation unit 64B multiplies the calculation result obtained by applying _the second lag filter _E2 by a constant _C2 in the second lag filter calculation unit 63B.

The jerk calculation unit 61C performs a first-order differential calculation on the calculation result obtained by applying the second moving average filter _F2 to the second-order differential value by the second average filter calculation unit 62B. That is, the jerk calculation unit 61C performs a third-order differential calculation on the original position command to generate a jerk command. The value of the jerk command generated by the calculation performed by the jerk calculation unit 61C is called a third-order differential value. The third average filter calculation unit 62C applies a third moving average filter _F3 to the third-order differential value generated by the jerk calculation unit 61C. The third lag filter calculation unit 63C applies a third lag filter E3, which is a first-order lag filter with a time constant _T3 , to the calculation result obtained by applying the third moving average filter _F3 to the third-order differential value by the third average filter calculation unit _62C . The third constant calculation unit 64C multiplies the calculation result obtained by applying the third lag filter _E3 by a constant _C3 in the third lag filter calculation unit 63C.

In the above, the acceleration calculation unit 61B and the jerk calculation unit 61C are collectively referred to as the speed calculation unit 61. The second average filter calculation unit 62B and the third average filter calculation unit 62C are collectively referred to as the moving average filter calculation unit 62. The first lag filter calculation unit 63A, the second lag filter calculation unit 63B, and the third lag filter calculation unit 63C are collectively referred to as the first-order lag filter calculation unit 63. The first constant calculation unit 64A, the second constant calculation unit 64B, and the third constant calculation unit 64C are collectively referred to as the constant calculation unit 64.

The feedforward (FF) calculation unit 65 adds the sum of the calculation results of the first constant calculation unit 64A, the second constant calculation unit 64B, and the third constant calculation unit 64C as a feedforward signal to the speed command input from the speed command input unit 9A. The position control unit 6A outputs a signal indicating the calculation result by the FF calculation unit 65 to the speed control unit 7A described below as a corrected speed command. That is, the speed calculation unit 61, the moving average filter calculation unit 62, the first-order lag filter calculation unit 63, the constant calculation unit 64, and the FF calculation unit 65 correct and determine the speed command by proportional control, and output it to the speed control unit 7A.

In the above, the position command is differentiated by the speed command input unit 9A, differentiated by the acceleration calculation unit 61B, and differentiated by the jerk calculation unit 61C. Therefore, the discretization error of the position command may be amplified, and noise may increase. In response to this, the position control unit 6A applies a moving average filter F by the moving average filter calculation unit 62 to remove noise from each differential value in order to prevent the noise from adversely affecting the position deviation of the motor 50. Furthermore, the position control unit 6A is provided with multiple stages, including a second average filter calculation unit 62B that applies a second moving average filter _F2 to the second-order differential value and a third average filter calculation unit 62C that applies a third moving average filter _F3 to the third-order differential value, so that moving average filters F2 and _F3 (collectively referred to as moving average filters F ₎ are applied according to the number of stages of differentiation. This minimizes the influence of noise on the differential value. It is preferable that the time constant of each of the second moving average filter _F2 and the third moving average filter _F3 is twice the processing period of the position control section 6A.

In the above, a phase shift of one delay element may occur in the speed command output by the FF calculation unit 65. In response to this, the position control unit 6A applies the first delay filter _E1 to the third lag filter _E3 (collectively referred to as the first delay filter E) by the first-order lag filter calculation unit 63 to compensate for the position deviation of the motor 50. Furthermore, when the driving conditions of the motor 50 change, the numerical control device 30 calculates the time constants _T1 to _T3 (collectively referred to as the time constant T) of the first-order lag filter E by a calculation method described later, and switches the first-order lag filter E.

The position command conversion unit 66 performs first-order integration on the position command input from the speed command input unit 9A and converts it into the original position command. The subtractor 69A subtracts the feedback signal of the position of the motor 50 output by the encoder 5B from the value of the position command converted by the position command conversion unit 66, and calculates the difference (position deviation) between the actual position of the motor 50 and the position of the motor 50 indicated by the position command. The position loop gain multiplication unit 67 multiplies the calculation result of the subtractor 69A by the position loop gain Kp, and outputs it to the speed control unit 7A described below as a feedback signal of the speed of the motor 50 corresponding to the position deviation.

The speed control unit 7A outputs a torque command to control the torque of the motor 50 to the torque control unit 8A described later by proportional-integral control. More specifically, the speed control unit 7A outputs a torque command to the torque control unit 8A so that the feedback signal of the motor 50 speed output by the position loop gain multiplication unit 67 matches the speed command output by the FF calculation unit 65. The speed control unit 7A includes an adder 71. The adder 71 generates a torque command by adding the feedback signal of the motor 50 speed output by the position loop gain multiplication unit 67 and the speed command output by the FF calculation unit 65. The speed control unit 7A outputs the generated torque signal to the torque control unit 8A described later.

The gain of the above control by the speed control unit 7A is called the speed loop integral gain. The numerical control device 30 may switch the speed loop integral gain while the machine tool 1 is in operation, for example to suppress quadrant projections during axis reversal.

The torque control unit 8A drives the motor 50 based on the torque command output by the speed control unit 7A and controls the torque of the motor 50.

The relationship between the input value and the output value for the position control unit 6A will be described with reference to FIG. 4. However, the gain multiplication unit 81 multiplies the first-order differential value by a gain A. The gain multiplication unit 82 multiplies the second-order differential value by a gain B. The gain multiplication unit 83 multiplies the third-order differential value by a gain A. Note that the constant calculation unit 64 shown in FIG. 3 is omitted.

The output value Y[n] of a speed command output from the position control unit 6A to the speed control unit 7A (see FIG. 2) based on the nth (n is an integer) position command of the NC program can be expressed by the following formula (1-1): Y[n]=AX[n]+AX[n-1]-BY[n-1] (1-1) where X[n] indicates the input value of the nth position command.
Here, the gains A and B can be expressed by the formula (1-2).
A = 1/(1 + 2t _i ), B = (1 - 2t _i )/(1 + 2t _i ) (1 - 2)
t _i (i is an integer from 1 to 3) is defined as the first-order lag time constant of the i-th lag filter E _i and satisfies the relationship of equation (1-3), where T _i represents the time constant of the i-th lag filter E _i , and T _s represents the processing cycle of position control unit 6A.
t _i =T _i /T _s (1-3)

<Calculation method of time constant of first-order lag filter _Ei >
A method of calculating the time constant T _i of the first-order lag filter E _i will be described. The numerical control device 30 obtains the time constant T _i that minimizes the sum of square errors f _e (ω _c ) between the phase characteristic P and the first-order lag element Q in the low-frequency region. The phase characteristic P is the phase characteristic when a first-order lag filter (time constant T _i ) is applied after stacking (i-1) moving average filters with a time constant T _c that is twice the processing cycle of the position control unit 6A. The first-order lag element Q is a first-order lag element of the speed loop integral time constant T _VI . The speed loop integral time constant T _VI is the reciprocal of the speed loop integral gain of the speed control unit 7A (see FIG. 3). The low-frequency region refers to the main frequency band included in the waveform of a general position command for the motor 50, which is the object of control.

The numerical controller 30 appropriately determines the upper limit of the main frequency band as a parameter _ωc according to the control target. The numerical controller 30 obtains the time constant T _i that minimizes the sum of square errors f _e (ω _c ) of the phase characteristics in the region below ω=ω _c by an optimization calculation such as the quasi-Newton method.

即ち、数値制御装置３０は、速度ループ積分時定数Ｔ_ＶＩ、移動平均フィルタＦの適用回数ｉ、及び、移動平均フィルタＦの時定数Ｔｃに基づき、一次遅れフィルタＥの時定数Ｔを算出できる。 The sum of the squared errors in the low frequency region can be expressed by equation (2-1).

That is, the numerical control device 30 can calculate the time constant T of the first-order lag filter _E based on the velocity loop integral time constant TVI, the number of times i the moving average filter F is applied, and the time constant Tc of the moving average filter F.

ｆ_ｅ１（ω_ｃ）を最小化する為の第一遅れフィルタＥ_１の時定数Ｔ_１は、Ｔ_ＶＩとなる。 When i = 1, equation (2-1) can be expressed as equation (2-2).

The time constant _T1 of the first lag filter _E1 for minimizing f _e1 (ω _c ) is T _VI .

When i = 2, equation (2-1) can be expressed as equation (2-3).

数値制御装置３０は、ｆ_ｅ２（ω_ｃ）を最小化する為の第二遅れフィルタＥ_２の時定数Ｔ_２、及び、ｆ_ｅ３（ω_ｃ）を最小化する為の第三遅れフィルタＥ_３の時定数Ｔ_３を、夫々、最適化計算により算出する。 When i = 3, equation (2-1) can be expressed as equation (2-4).

The numerical control device 30 calculates, by optimization calculation, the time constant _T2 of the second lag filter _E2 for minimizing f _e2 (ω _c ), and the time constant _T3 of the third lag filter _E3 for minimizing f _e3 (ω _c ).

<Main processing>
The main process will be described with reference to FIG. 5. The drive circuit 5A of the numerical control device 30 executes the main process when the CPU 31 outputs a position command based on the NC program. The CPU 31 determines whether the main process is executed for the first time after the power supply to the machine tool 1 is turned on (S11). When the CPU 31 executes the main process for the first time (S11: YES), it initializes the first-order lag filters E (first lag filter E ₁ to third lag filter E ₃ ) (S13). The CPU 31 initializes the first-order lag filters E to those that satisfy the relationship when X[n-1] and Y[n-1] are both 0 in the formula (1-1). The CPU 31 advances the process to S17.

When the main process is not being executed for the first time after the machine tool 1 is powered on (S11: NO), the CPU 31 determines whether the speed loop integral gain has been changed (S15). When the speed loop integral gain has not been changed (S15: NO), the CPU 31 ends the main process. When the speed loop integral gain has been changed (S15: YES), the CPU 31 advances the process to S17 to set the time constant T of the first-order lag filter E.

The CPU 31 calculates the time constant _T1 of the first lag filter _E1 based on the formula (2-2), calculates the time constant _T2 of the second lag filter _E2 based on the formula (2-3), and calculates the time constant _T3 of the third lag filter _E3 based on the formula (2-4) (S17). The CPU 31 sets the calculated time constant T in the corresponding first-order lag filter E of the first-order lag filter calculation unit 63 (S19). The CPU 31 ends the main processing.

<Evaluation Results>
6 shows the change over time in the position deviation of the motor 50 before (A) and after (B) application of the present invention. The solid line shows the position deviation of the motor 50, and the dotted line shows the speed of the motor 50. It was found from the waveforms that application of the present invention reduces the position deviation when the speed change of the motor 50 is large (approximately 350 ms, approximately 1000 ms, approximately 1600 ms). Therefore, it was confirmed that application of the present invention can improve the follow-up ability of the motor 50 to the position command even when a position command with a short period is executed.

<Actions and Effects of the Present Embodiment>
The position control unit 6A of the numerical control device 30 has a first-order lag filter calculation unit 63 (first lag filter calculation unit 63A, second lag filter calculation unit 63B, third lag filter calculation unit 63C). The first-order lag filters E (first lag filter _E1 , second lag filter _E2 , third lag filter _E3 ) can suppress the influence of the first-order lag of the position control unit 6A. Therefore, the numerical control device 30 can improve the follow-up of the motor 50 to the position command even when a position command with a short period is executed. Furthermore, by providing a first-order lag filter calculation unit 63 for each moving average filter calculation unit 62, the numerical control device 30 can appropriately suppress the phase lag of the moving average filter F by the first-order lag filter E.

The position control unit 6A has a first lag filter calculation unit 63A in addition to a second lag filter calculation unit 63B and a third lag filter calculation unit 63C. At this time, the numerical control device 30 can further suppress the influence of not only the first-order lag of the second-order and third-order differential values of the position command, but also the first-order lag of the first-order differential value. Therefore, the numerical control device 30 can further improve the tracking ability of the motor 50 to the position command.

By repeatedly differentiating the position command in the position control unit 6A, the discretization error is amplified, the noise increases, and tracking performance may decrease. In response to this, the numerical control device 30 applies the moving average filter F by the second average filter calculation unit 62B and the third average filter calculation unit 62C to remove noise from the differential value. Therefore, the numerical control device 30 can suppress the increase in noise caused by the amplification of the discretization error by the moving average filter F, thereby further improving the tracking performance of the motor 50 to the position command.

The numerical controller 30 sets the time constant _T1 of the first lag filter _E1 , the time constant _T2 of the second lag filter _E2 , and the time constant _T3 of the third lag filter _E3 (S19) based on the speed loop integral time constant TVI of the speed control unit _7A , the number of applications i of the moving average filter F, and the time constant _Tc of the moving average filter F. Therefore, the numerical controller 30 can improve the tracking ability of the motor 50 to the position command even when the speed loop integral gain is switched during operation of the machine tool 1 for the purpose of suppressing quadrant projections during axis reversal, etc.

<Modification>
The present invention is not limited to the above embodiment. The jerk calculation unit 61C may calculate a third-order differential value by performing a second-order differential calculation on the velocity command. In this case, the third average filter calculation unit 62C may apply the moving average filter _F3 twice to the third-order differential value.

The position control unit 6A does not need to have the first lag filter calculation unit 63A. In this case, the position control unit 6A may have only the second lag filter calculation unit 63B and the third lag filter calculation unit 63C as the first-order lag filter calculation unit 63. In this case, the numerical control device 30 can reduce the possibility that the nonlinearity of the motor 50 will decrease by applying the first lag filter _E1 to the first-order differential value of the position command.

The time constant of the moving average filter F may be greater than the processing cycle of the position control unit 6 A. The time constant T of the first-order lag filter E may be constant regardless of the speed loop integral time constant T _VI of the speed control unit 7 A. In this case, the numerical control device 30 does not need to change the time constant T of the first-order lag filter E even when the speed loop integral gain is switched during operation of the machine tool 1.

The method for calculating the time constant T of the first-order lag filter E is not limited to the above method. For example, it may be calculated using the following method.

When tan ⁻¹ x is expanded by Maclaurin (that is, by Taylor expansion at x=0), it can be expressed as in equation (3-1).
tan ^-1 x = x - x ³ / 3 + x ⁵ / 5 - x ⁷ / 7 + ... (3-1)
By ignoring quadratic and higher terms in equation (3-1) and performing linear approximation, equation (3-2) can be derived.
tan ⁻¹ x = x (3-2)

式（３－３）＝０とした時のＴ_ｉについて解くと、式（３－４）のように表せる。

When formula (3-2) is satisfied, the phase error between the phase characteristic when a first-order lag filter (time constant T _i ) is applied after stacking (i-1) stages of moving average filters with time constant T _c and the first-order lag element of the speed loop integral time constant T _VI can be expressed as formula (3-3).

When equation (3-3)=0 is set, solving for T _i gives equation (3-4).

In formula (3-4), when i = 1, _T1 = _TVI , when i = 2, _T2 = _TVI - _Tc /2, when i = 3, and _T3 = _TVI - _Tc . Therefore, the drive circuit 5A may calculate the time constants _T1 , _T2 , and _T3 using this formula, and set them in the first-order lag filter E of the first-order lag filter calculation unit 63 in the process of S19 of the main process.

In the above modification, the numerical controller 30 sets the time constant T of the first-order lag filter E based on the speed loop integral time constant _TVI of the speed control unit 7A (S19). At this time, the numerical controller 30 can calculate the time constant T of the first-order lag filter E based on the speed loop integral time constant _TVI without using the application count i of the moving average filter F.

＜Other＞
The process of S19 is an example of the time constant setting unit of the present invention.

1: Machine tool 6A: Position control unit 7A: Speed control unit 8A: Torque control unit 9A: Speed command input unit 30: Numerical control device 31: CPU
62: Moving average filter calculation section 63: First-order lag filter calculation section 64: Constant calculation section 65: Feedforward calculation section E: First-order lag filter F: Moving average filter

Claims (7)

a position control unit that determines and outputs a speed command for controlling the speed of the motor by proportional control so that a position command for controlling a position of the motor coincides with a feedback signal of the position of the motor;
a speed control unit that outputs a torque command for controlling the torque of the motor by proportional-integral control so that the speed command output by the position control unit coincides with a feedback signal of the motor speed;
a torque control unit that controls the torque of the motor based on the torque command output by the speed control unit;
A numerical control device comprising:
The position control unit is
a second average filter calculation unit that applies a second moving average filter to a second-order differential value obtained by second-order differentiation of the position command;
a second lag filter calculation unit that applies a second lag filter, which is a first-order lag filter, to a calculation result obtained by applying the second moving average filter to the second-order differential value by the second average filter calculation unit;
a third average filter calculation unit that applies a third moving average filter to a third-order differential value obtained by third-order differentiation of the position command;
a third lag filter calculation unit that applies a third lag filter, which is a first-order lag filter, to a calculation result obtained by applying the third moving average filter to the third-order differential value by the third average filter calculation unit;
a feedforward calculation unit that multiplies the calculation results of the second lag filter calculation unit and the third lag filter calculation unit by a constant, adds the result, and adds the result to the speed command as a feedforward signal. The position control unit further includes:
a first lag filter calculation unit that applies a first lag filter, which is a first-order lag filter, to a first-order differential value obtained by first-order differentiation of the position command;
The feedforward calculation unit includes:
2. The numerical control device according to claim 1, wherein a sum obtained by multiplying the calculation results of each of the first lag filter calculation unit, the second lag filter calculation unit, and the third lag filter calculation unit by a constant and adding them together is added to the speed command as the feedforward signal. The numerical control device according to claim 1 or 2, characterized in that the second moving average filter and the third moving average filter are moving average filters that remove noise from the differential value. The numerical control device according to claim 3, further comprising a time constant setting unit that sets the time constants of the second lag filter and the third lag filter based on the integral time constant of the speed loop of the speed control unit. The numerical control device according to claim 3, further comprising a time constant setting unit that sets the time constants of the second lag filter and the third lag filter based on the integral time constant of the speed loop of the speed control unit, the number of times the moving average filter is applied, and the time constant of the moving average filter. The time constant setting unit is
6. The numerical control device according to claim 4, wherein the time constants of the second lag filter and the third lag filter are set in response to a change in the integral time constant. A numerical control device according to any one of claims 1 to 6,
A machine tool comprising the motor.

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