servo control unit

Abstract

Servo control unit (10) used for a machine tool (1) having a feed axis (2) driven by a servo motor (3), comprising: a unit (11) for generating a speed command, which generates a speed command value of the servo motor (3); a unit (12) for generating a torque command, which generates a torque command value of the servo motor (3); a unit (13) for detecting a rotational speed, which detects a rotational speed of the servomotor (3); a speed control loop (30) formed by the unit (11) for generating a speed command, the unit (12) for generating a torque command and the unit (13) for detecting a speed; a speed control amplification (14) which is a control amplification of the speed control loop (30); a unit (15) for inputting a sinusoidal disturbance variable, which performs a sinusoidal wobble on the speed control loop (30); a unit (16) for calculating actual frequency characteristics for estimating a gain and a phase of an input / output signal of the speed control loop based on an output of the speed control loop (30) when a sine wave has been input into the speed control loop (30); a unit (17) for changing reference parameters, which modifies a parameter formula that characterizes reference frequency parameters of the speed control loop (30); a unit (18) for calculating reference frequency parameters, which calculates reference frequency parameters for parameters assigned by the unit (17) for changing reference parameters; and a unit (19) for adjusting a control gain, which adjusts a speed control gain (14) based on an actual frequency response calculated by the unit (16) for calculating actual frequency characteristics and the reference frequency characteristics calculated by the unit (18) for calculating reference frequency characteristics, wherein the unit (15) for inputting a sinusoidal disturbance variable continuously changes a frequency, the unit (18) for calculating reference frequency characteristics continuously calculates the reference frequency characteristics for the characteristics assigned by the unit (17) for changing reference characteristics for respective frequencies, and the unit (16) for calculating actual frequency characteristics continuously calculates actual frequency characteristics of a control system for respective frequencies, and The unit (18) for calculating reference frequency characteristics stores the characteristic formula of the unit (17) for changing reference characteristics when the reference frequency characteristics and the actual frequency characteristics are closest to each other.

Description

BACKGROUND OF THE INVENTION Area of ​​the invention

[0001] The present invention relates to a servo control unit used for a machine tool with a feed axis driven by a servo motor. Related technology

[0002] Traditionally, a technology for automating a procedure for modeling machine parameters is known in connection with a servo control unit. This type of technology is disclosed, for example, in Patent Specification 1. Patent Specification 1 describes a model determination method in which, using a technology that provides a scheme for adapting machine parameters to an N-inertial system, a transfer function from a so-called test mode analysis is specified in advance, and a rigid body mode and several resonance modes are automatically determined. Many examples of technologies exist that involve a method for estimating such a transfer function.

[0003] Patent specification 1: Unexamined Japanese patent application, Publication No. 2003-79174

[0004] DE 10 2016 008 137 A1 discloses a servo control device comprising: a speed command generator; a torque command generator; a speed detection device; a speed control loop; a speed control loop gain adjustment unit; at least one filter for filtering a specific band of a torque command value; an input unit for a sinusoidal disturbance to perform a sinusoidal deflection on the speed control loop; a frequency characteristic calculator for assessing the gain and phase of the speed control loop input and output signals; a resonant frequency detection device; a filter adjustment device for adjusting the filter in accordance with a resonant frequency; and a gain adjustment device.A sequence control for the computer-dependent and automatic execution of the acquisition of the resonance frequency, the adjustment of the velocity control loop gain, and the filter setting; and a setting status display unit. The setting status display unit shows a stage and progress in the setting process by the sequence control.

[0005] The publication “Oliver Zirn, Sascha Weikert; Modeling and Simulation of Highly Dynamic Manufacturing Systems” - A practical introduction; Springer-Verlag Berlin Heidelberg 2006; pp. 271-274" reveals a consideration of elasticities in the speed control loop, whereby a transfer behavior of an elastic machine structure, for example a load inertia flexibly coupled via a tapered clamping device, is determined. SUMMARY OF THE INVENTION

[0006] Even when a servo control unit is set based on a reference model that represents the machine characteristics of a machine tool, the control parameters of the servo control unit can change before and after a change of the object clamped in the machine tool. In this respect, with the technology disclosed in Patent 1, it is difficult to determine the parameters for an open-loop control system by a sequential calculation within a control loop, even though curve fitting is performed on the frequency parameter with respect to the open-loop parameters. A modeling procedure in an open-loop control system is effective if a resonance avoidance filter and all control gains are set from their initial state. However, it is pointless to model all resonance and anti-resonance parameters with respect to a feed axis that has already undergone servo tuning.This is because, due to the limited computing capacity of a digital signal processor (DSP), a control unit only has a finite number of resonance avoidance filters, and the filters cannot handle all resonance modes with respect to such characteristics of a machine in which countless resonance modes are distributed.

[0007] It is an object of the present invention to provide a servo control unit in which a control gain is automatically adjusted so that the control parameters are maintained even when a clamped object is replaced and a machine configuration is changed.

[0008] The problem is solved by means of the servo control unit according to claim 1. Preferred embodiments are specified in the respective dependent claims. (1) A servo control unit according to the present invention is a servo control unit (for example, a servo control unit 10 to be described later) used for a machine tool (for example, a machine tool 1 to be described later) which has a feed axis (for example, a transport mechanism 2 to be described later) driven by a servo motor (for example, a servo motor 3 to be described later) and which comprises: a speed command generation unit (for example, a speed command generation unit 11 to be described later) which generates a speed command value of the servo motor; a torque command generation unit (for example, a torque command generation unit 12 to be described later).which generates a torque command value of the servo motor; a unit for sensing a rotational speed (for example, a unit 13 for sensing a rotational speed, to be described later), which senses a rotational speed of the servo motor; a speed control loop (for example, a speed control loop 30, to be described later), which is formed by the unit for generating a speed command, the unit for generating a torque command, and the unit for sensing a rotational speed; a speed control gain (for example, a speed control gain 14, to be described later), which is a control gain of the speed control loop; a unit for inputting a sinusoidal disturbance variable (for example, a unit 15 for inputting a sinusoidal disturbance variable, to be described later),which performs a sinusoidal wobble on the speed control loop; a unit for calculating actual frequency characteristics (for example, a unit 16 for calculating actual frequency characteristics, to be described later) for estimating a gain and a phase of an input / output signal of the speed control loop based on an output of the speed control loop when a sine wave has been input into the speed control loop; a unit for changing reference characteristics (for example, a unit 17 for changing reference characteristics, to be described later) that modifies a characteristic formula that characterizes reference frequency characteristics of the speed control loop; a unit for calculating reference frequency characteristics (for example, a unit 18 for calculating reference frequency characteristics, to be described later),the reference frequency characteristics for characteristics assigned by the unit for changing reference characteristics; and a unit for setting a control gain (for example, a unit 19 for setting a control gain to be described later) which sets a speed control gain on the basis of an actual frequency response calculated by the unit for calculating actual frequency characteristics and the reference frequency characteristics calculated by the unit for calculating reference frequency characteristics, wherein the unit for inputting a sinusoidal disturbance continuously changes a frequency, and the unit for calculating reference frequency characteristics continuously calculates the reference frequency characteristics for the characteristics assigned by the unit for changing reference characteristics for respective frequencies.and the unit for calculating actual frequency characteristics continuously calculates actual frequency characteristics of a control system for respective frequencies, and the unit for calculating reference frequency characteristics stores the unit's characteristic formula for changing reference characteristics when the reference frequency characteristics and the actual frequency characteristics are closest to each other. (2) In the servo control unit according to (1), the unit for calculating reference frequency characteristics can determine the characteristic formula of the reference frequency characteristics with respect to the actual frequency characteristics prior to setting the control gain by sequential calculation, wherein the characteristic formula is expressed as a rigid body mode and at least one 2-inertia mode.

[0009] With the servo control unit according to the present invention, it is possible to realize a configuration in which a control gain is automatically adjusted so that control parameters are maintained even when a clamped object is replaced and a machine configuration is changed. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Fig. Figure 1 is a block diagram showing a configuration of a servo control unit according to an embodiment of the present invention. Fig. Figure 2 is a flowchart showing the first half of a process for the self-generation of a reference model by a servo control unit according to the present embodiment. Fig. Figure 3 is a flowchart showing the second half of the process for the self-generation of a reference model by the servo control unit according to the present embodiment. Fig. Figure 4 is an explanatory diagram (a Bode diagram) showing frequency characteristics before an exchange of an object clamped in a machine tool to which the servo control unit according to the present embodiment is applied (before a change in control gain). Fig. Figure 5 is an explanatory diagram (a Bode diagram) showing how reference model parameters are determined based on a state prior to the replacement of an object clamped in a machine tool to which the servo control unit according to the present embodiment is applied. Fig. Figure 6 is an explanatory diagram (a Bode diagram) showing frequency characteristics in a state in which a readjustment of a control gain of a machine tool is initiated, to which the servo control unit according to the present embodiment is applied. Fig. Figure 7 is an explanatory diagram (a Bode diagram) showing frequency characteristics after replacing an object clamped in a machine tool to which the servo control unit according to the present embodiment is applied (after changing the control gain). Fig. Figure 8 is an explanatory diagram showing a 1-inertial system model using a first-order characteristic formula. Fig. Figure 9 is an explanatory diagram showing a 2-inertial system model using a second-order characteristic formula. Fig. Figure 10 is an explanatory diagram showing a 3-inertial system model using a third-order characteristic formula. Fig. Figure 11 is an explanatory diagram showing a 4-inertial system model using a fourth-order characteristic formula. DETAILED DESCRIPTION OF THE INVENTION

[0011] Below, with reference to the drawings, a servo control unit that controls a servo motor of a machine tool having a feed axis is described as a preferred embodiment of the present invention.

[0012] Fig. Figure 1 is a block diagram showing a configuration of a servo control unit 10 according to an embodiment of the present invention. The servo control unit 10 according to the present embodiment controls a servo motor 3, which actuates a (not shown) driver of a machine tool 1 via a gear mechanism (a feed axis) 2. The gear mechanism 2 is, for example, a ball screw, and the driver is a table actuated by the ball screw.

[0013] Next, a configuration of servo control unit 10 is described. As in Fig. As shown in Figure 1, the servo control unit 10 comprises a unit 11 for generating a speed command, a unit 12 for generating a torque command, a unit 13 for detecting a speed, a speed control loop 30, an adding device 20, a speed control gain 14, a unit 15 for inputting a sinusoidal disturbance, a unit 16 for calculating actual frequency characteristics, a unit 17 for changing reference characteristics, a unit 18 for calculating reference frequency characteristics, and a unit 19 for setting a control gain.

[0014] Unit 11 for generating a speed command generates a speed command value for controlling the servomotor 3. The speed command value generated by unit 11 for generating a speed command is output to the adding device 20.

[0015] The unit 12 for generating a torque command produces a torque command value for the servomotor 3. The servomotor 3 is driven on the basis of the torque command value generated by the unit 12 for generating a torque command.

[0016] Unit 13, used for sensing rotational speed, records the rotational speed of servomotor 3 as a rotational speed measurement value. This value is calculated, for example, based on a measured value obtained from a coding device integrated into servomotor 3.

[0017] The speed control loop 30 includes unit 11 for generating a speed command, unit 12 for generating a torque command and unit 13 for detecting a speed.

[0018] In the adding device 20, the speed detection value acquired by unit 13 for sensing a rotational speed is subtracted from the speed command value generated by unit 11 for generating a speed command, and a sinusoidal disturbance generated by unit 15 for inputting a sinusoidal disturbance, which performs a sinusoidal wobble on the speed control loop 30, is added. The frequency of unit 15 for inputting a sinusoidal disturbance is continuously varied.

[0019] The speed control gain 14 sets a control gain that is to be multiplied by the calculation result determined by the adding device 20. In the present embodiment, the torque command value of unit 12 is generated to produce a torque command based on the control gain set by the speed control gain 14 and the calculation result determined by the adding device 20.

[0020] The control gain of the speed control gain 14 is set by means of a setting value set by the control gain setting unit 19. The control gain setting unit 19 sets the setting value for the speed control gain 14 based on a calculation result determined by the actual frequency characteristics unit 16 and a calculation result determined by the reference frequency characteristics unit 18.

[0021] Unit 15 inputs a sinusoidal disturbance into Unit 16 for calculating actual frequency characteristics and Unit 18 for calculating reference frequency characteristics. Unit 16 for calculating actual frequency characteristics estimates the gain and phase of an input / output signal of the speed control loop 30 based on the output of the speed control loop 30 when the sinusoidal disturbance has been input into the speed control loop 30 of the servo control unit 10.Furthermore, unit 16, for calculating actual frequency characteristics, expresses the output of the speed control loop 30 using a Fourier series with a random number of terms, where the frequency of the disturbance input by unit 15 (a sinusoidal disturbance) is used as the fundamental frequency. It then calculates the amplitude and phase of a fundamental component of the Fourier series to calculate the frequency characteristics continuously. The frequency characteristics calculated by unit 16 are sent to unit 19 for setting a control gain.

[0022] Unit 17, used for changing reference parameters, modifies a parameter formula that characterizes the reference frequency parameters of the speed control loop 30. The parameter formula is set according to machine parameters or similar characteristics of the machine tool 1 (see the section to be described later). Fig. 8 to 11).

[0023] Unit 18, for calculating reference frequency characteristics, continuously calculates reference frequency characteristics for the characteristics assigned by Unit 17 for modifying reference characteristics at the respective frequencies. Unit 18 compares the actual frequency characteristics and reference frequency characteristics entered by Unit 16 for calculating actual frequency characteristics, and saves the characteristic formula from Unit 17 for modifying reference characteristics when the reference frequency characteristics and the actual frequency characteristics are closest to matching.

[0024] Unit 18 for calculating reference frequency characteristics includes a device for determining the characteristic formula of the reference frequency characteristics with respect to the actual frequency characteristics prior to setting the control gain by sequential calculation, wherein the characteristic formula is expressed as only a rigid body mode and at least one 2-inertia mode.

[0025] Next, a self-generation function for reference parameters of the servo control unit 10 according to the present embodiment is described. This self-generation function determines a reference model for automatic adjustment through concurrent sequential calculation. When a gain adjustment is performed with respect to the transport mechanism (a feed axis) 2 of the machine tool 1, on which a control adjustment has already been performed, the parameters prior to the gain adjustment are considered as reference parameters, and the gain adjustment is performed automatically. This gain adjustment is performed when a workpiece or clamping device is exchanged (a clamped object is replaced) or when a machine configuration is changed.

[0026] The Fig. 2 and Fig. Figure 3 are flowcharts showing a process for the self-generation of a reference model by the servo control unit 10 according to the present embodiment.

[0027] As in Fig. As shown in Figure 2, at the beginning of an automatic adjustment process, unit 15, for inputting a sinusoidal disturbance, updates the frequency of a sine wave (step S101) and inputs the sinusoidal disturbance with the updated frequency (step S102). Furthermore, unit 13, for sensing a rotational speed, acquires a rotational speed sensing value (step S103), and unit 12, for generating a torque command, executes a process to generate a torque command value based on the rotational speed command value and the rotational speed sensing value (step S104).

[0028] Unit 16 for calculating actual frequency characteristics calculates actual frequency characteristics at the frequency (step S105), and Unit 18 for calculating reference frequency characteristics calculates reference frequency characteristics at the frequency using a suitable reference model characteristic formula (step S106).

[0029] Following the process according to step S106, the servo control unit 10 determines whether a maximum sweep frequency has been reached (step S107). If the maximum sweep frequency is reached, the process continues with a procedure to determine whether all eligible reference model characteristic formulas have been searched (step S108). If step S107 determines that the maximum sweep frequency has not been reached, the process is reset to the process according to step S101, and the processes following step S101 are executed again.

[0030] If step S108 determines that not all eligible reference model characteristic formulas have been searched, the process continues with a step in which the unit modifying reference characteristics changes the characteristic formula of the reference model (step S109). Once the process according to step S109 is complete, the process reverts to the process according to step S101, and the processes following step S101 are executed again.

[0031] If, in step S108, it is determined that all possible reference model parameter formulas have been searched, the process continues with a procedure in which the unit 18 for calculating reference frequency parameters determines a reference model parameter formula for the current speed control gain 14 (step S110 according to Fig. 3) In the process according to step S110, a higher ranking is set to a lower-order characteristic formula.

[0032] Fig. Figure 4 is an explanatory diagram showing frequency characteristics before a change of an object clamped in the machine tool 1 for which the servo control unit 10 is used according to the present embodiment (before a change of a control gain). Fig. Figure 5 is an explanatory diagram showing how reference model parameters are determined based on a state prior to a change of an object clamped in the machine tool 1, to which the servo control unit 10 is applied according to the present embodiment. The parameter formula is set so that it corresponds to the parameters of a machine (for example, resonance parameters) prior to a change of a clamped object. The in Fig. 5 reference model shown, which is the one in Fig. The resonance shown in section 4, corresponding to the frequency parameters before the change of the clamped object, is determined, for example, using the relevant reference model parameter formulas. Fig. Figure 5 shows the frequency characteristics before the change in control gain, represented by a dashed line.

[0033] Following the process according to step S110, unit 19 for setting a control gain modifies the speed control gain 14 (step S111). After the speed control gain 14 has been modified by unit 19 for setting a control gain in the process according to step S111, unit 15 for inputting a sinusoidal disturbance updates the frequency of the sine wave (step S112) and inputs the sinusoidal disturbance with the frequency (step S113). Unit 13 for sensing a speed acquires a speed sensing value (step S114), and unit 12 for generating a torque command performs a process to generate a torque command value from the speed command value and the speed sensing value (step S115).

[0034] Fig. Figure 6 is an explanatory diagram showing frequency characteristics in a state where a readjustment of the control gain of the machine tool 1 begins, for which the servo control unit 10 is used according to the present embodiment. Following the process according to step S115, the unit 16 calculates the actual frequency characteristics at the frequency (step S116). For example, the in Fig. The 6 actual frequency characteristics shown were calculated.

[0035] Unit 18, used for calculating reference frequency parameters, calculates the reference frequency parameters at the specified frequency using the defined reference model parameter formula (step S117). Following step S117, servo control unit 10 determines whether the highest sweep frequency has been reached (step S118). If step S118 determines that the highest sweep frequency has not been reached, the sequence is reset to the process according to step S112, and the processes following step S112 are executed again.

[0036] If step S118 determines that the highest sweep frequency has been reached, it is then determined whether the difference between the reference frequency parameters and the actual frequency parameters has been minimized (S119). If step S119 determines that the difference between the reference frequency parameters and the actual frequency parameters has not been minimized, the process is reset to the procedure according to step S111, and the processes following step S111 are executed again.

[0037] Fig. Figure 7 is an explanatory diagram showing frequency characteristics after a change of an object clamped in the machine tool 1, for which the servo control unit 10 is used according to the present embodiment (after a change in control gain). If, in step S119, it is determined that the difference between the reference frequency characteristics and the actual frequency characteristics has been minimized, the control gain unit 19 determines the setpoint of the speed control gain 14 (step S120), and the process ends. As in Fig. As shown in Figure 7, the control gain is adjusted in a way that corresponds to the reference parameters, and thus the control parameters are maintained before and after the change of the clamped object.

[0038] Next, with reference to the Fig. Sections 8 to 11 describe an example of a formula for determining the reference parameters. Fig. In sections 8 to 11, the following symbols are used: S: Laplace operator; a0: constant term for the numerator polynomial; a1: primary coefficient of the numerator polynomial; a2: second-order coefficient of the numerator polynomial; a3: third-order coefficient of the numerator polynomial; a4: fourth-order coefficient of the numerator polynomial; b0: constant term for the denominator polynomial; b1: first-order coefficient of the denominator polynomial; b2: second-order coefficient of the denominator polynomial; b3: third-order coefficient of the denominator polynomial

[0039] Fig. Figure 8 is an explanatory diagram showing a 1-inertial system model using a first-order characteristic formula. Fig. Figure 8 shows a rigid body 5 of a rotating system. As in Fig. 8 in equation (1) is, in a so-called rigid body model, where it is assumed that the target object of the control is a rigid body, a characteristic formula is a first-order equation. Fig. Figure 9 is an explanatory diagram showing a 2-inertial system model using a second-order characteristic formula. Fig. Figure 9 shows a load 120 arranged between the rigid body 5 of a rotating system and a movable body 6 of a translation system. As in Fig. As represented in equation (2), in a 2-inertial system model, a characteristic formula is a second-order equation.

[0040] Fig. Figure 10 is an explanatory diagram showing a 3-inertial system model using a third-order characteristic formula. Fig. Figure 10 shows a servomotor 3, which is a drive source, a ball screw 7 driven by the servomotor, and a table 8 connected to the ball screw 7. Furthermore, a spring 121 is arranged as a load between the servomotor 3 and the ball screw 7, and a spring 122 is arranged as a load between the ball screw 7 and the table 8. As shown in Fig. As represented in equation (3), in a 3-inertial system model, a characteristic formula is a third-order equation. Fig. Figure 11 is an explanatory diagram showing a 4-inertial system model using a fourth-order characteristic formula. According to Fig. 11, is in addition to the configuration according to Fig. 10. A frame 9 is connected to the ball screw 7. Springs 123 and 124 are arranged as a load between the frame 9 and the ball screw 7. As in Fig. As represented in equation (4), a characteristic formula in a 4-inertial system model is a fourth-order equation.

[0041] As in the Fig. As shown in Figures 8 to 11, a characteristic formula of the reference model can generally be expressed as a linear N-inertia model. By adjusting the order of a characteristic formula based on a physical model according to the characteristics of a machine, it is possible to specify reference characteristics while considering control stability (resonance). Generally, a lower-order characteristic formula tends to be suitable for a small device configuration, while a higher-order formula is more suitable for a large device configuration with a large number of components. The formulas in the Fig. The characteristic formulas shown in Figures 8 to 11 are examples, and fifth-order or higher inertial system models can be included in the characteristic formulas in question.

[0042] In the present embodiment, the characteristic formula is applied under the rigid body mode and the one in Fig. The 2-inertia mode shown in Figure 8 is selected. The 2-inertia mode is expressed in such a way that the 2-inertia mode is used in the cases shown in Figure 8. Fig. 10 and Fig. 11 models shown, as well as the example of the one in Fig. The model shown in Figure 9 comprises two types of inertia.

[0043] The embodiment described above has the following configuration. A servo control unit 10 according to the embodiment comprises a unit 11 for generating a speed command, a unit 12 for generating a torque command, a unit 13 for sensing a speed, a speed control loop 30, a speed control gain 14, a unit 15 for inputting a sinusoidal disturbance, a unit 16 for calculating actual frequency parameters, a unit 17 for changing reference parameters, a unit 18 for calculating reference frequency parameters, and a unit 19 for setting a control gain.Unit 15 for inputting a sinusoidal disturbance variable continuously changes a frequency; Unit 18 for calculating reference frequency characteristics continuously calculates reference frequency characteristics for characteristics assigned by Unit 17 for changing reference characteristics for respective frequencies; Unit 16 for calculating actual frequency characteristics continuously calculates actual frequency characteristics of a control system for respective frequencies; and Unit 18 for calculating reference frequency characteristics stores a characteristic formula of the Unit for changing reference characteristics when the reference frequency characteristics and the actual frequency characteristics are closest to each other.

[0044] By comparing the reference parameters with the frequency parameters continuously calculated as the parameter pair of the reference model changes, it is possible to directly determine the parameters of a closed-loop control system through sequential calculation within the control loop. This is because the parameter pair that remains is the one with the smallest difference between the reference parameters and the actual parameters. This means that a parameter expression step is performed continuously (in real time) before changing a fixed object as the reference model, using a parameter formula. The criteria for automatically adjusting the gain are clearly defined, and an adjustment to change the control gain is performed continuously, so that the parameters of the actual response correspond to the reference parameters determined using the parameter formula.In this way, it is possible to automatically adjust the gain regardless of the configuration of a machine and a change of a clamped object, while maintaining the control parameters.

[0045] In the present embodiment, the unit 18 for calculating reference frequency parameters determines the parameter formula of the reference frequency parameters with respect to the actual frequency parameters before setting the control gain by sequential calculation, wherein the parameter formula is expressed as a rigid body mode and at least one 2-inertia mode.

[0046] In this way, the automatic adjustment of the gain can be limited to a rigid body mode and the most essential 2-inertia mode, and the reference model can be effectively generated in a form in which an insignificant resonance is ignored.

[0047] Although the preferred embodiment of the present invention has been described, the present invention is not limited to the embodiment described above and can be suitably modified. For example, the speed control loop 30 is shown as an example; the configuration of the speed control loop 30 as such is not essential, and the Fig. The part shown surrounded by a dashed line can be understood as a system with an input / output relationship. EXPLANATION OF REFERENCE SYMBOLS 1 machine tool 2 Gear mechanism (feed axis) 3 servo motors 10 Servo control unit 11 Unit for generating a speed command 12 Unit for generating a torque command 13 Unit for measuring rotational speed 14 Speed ​​control amplification 15 units for inputting a sinusoidal disturbance variable 16 Units for calculating actual frequency characteristics 17 Unit for changing reference parameters 18 Unit for calculating reference frequency parameters 19 Unit for adjusting a control gain 30 Speed ​​control circuit

Claims

[1] Servo control unit (10) used for a machine tool (1) having a feed axis (2) driven by a servo motor (3), and comprising: a speed command generation unit (11) that generates a speed command value of the servo motor (3); a torque command generation unit (12) that generates a torque command value of the servo motor (3); a speed detection unit (13) that detects a speed of the servo motor (3); a speed control loop (30) formed by the speed command generation unit (11), the torque command generation unit (12) and the speed detection unit (13); a speed control gain (14) which is a control gain of the speed control loop (30); a unit (15) for inputting a sinusoidal disturbance variable which performs a sinusoidal wobble on the speed control loop (30); an actual frequency characteristic calculation unit (16) for estimating a gain and a phase of an input / output signal of the speed control loop from an output of the speed control loop (30) when a sine wave has been input to the speed control loop (30); a reference characteristic changing unit (17) that changes a characteristic formula that indicates reference frequency characteristics of the speed control loop (30); a reference frequency characteristic calculation unit (18) that calculates reference frequency characteristics for characteristics assigned by the reference characteristic changing unit (17); and a control gain setting unit (19) that sets a speed control gain (14) based on an actual frequency response calculated by the actual frequency characteristic calculation unit (16) and the reference frequency characteristics calculated by the reference frequency characteristic calculation unit (18), wherein the sinusoidal disturbance input unit (15) continuously changes a frequency, the reference frequency characteristic calculation unit (18) continuously calculates the reference frequency characteristics for the characteristics assigned by the reference characteristic changing unit (17) for respective frequencies, and the actual frequency characteristic calculation unit (16) continuously calculates actual frequency characteristics of a control system for respective frequencies, and the reference frequency characteristic calculation unit (18) stores the characteristic formula of the reference characteristic changing unit (17) when the reference frequency characteristics and the actual frequency characteristics are closest to each other. [2] A servo control unit according to claim 1, wherein the reference frequency characteristic calculation unit (18) determines the characteristic formula of the reference frequency characteristics with respect to the actual frequency characteristics before adjustment of the control gain by sequential calculation, the characteristic formula being expressed as a rigid body mode and at least one 2-inertia mode.

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