JP2013219884A - Position controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a position/speed controller for synchronously driving one shaft such as a feed shaft or a main shaft of a machine tool by means of a plurality of motors, the controller stably operating a control object having a different resonance frequency for each work without causing mechanical vibration.SOLUTION: The position controller for controlling one shaft by means of a plurality of motors includes: a position controller for calculating a speed command value on the basis of a position command value and a position detection value of the motor; a speed controller for calculating a torque command value on the basis of the speed command value and a speed detection value calculated by the position detector; notch filters 8m and 8s for reducing a frequency component around a notch frequency from the torque command value; a position command error generator 15 for generating a position command error in the position command value; and a resonance frequency computing unit 16 for determining the notch frequency of the notch filter on the basis of the position command error, and each torque command value of the plurality of motors.

Description

  The present invention relates to a position control device that drives one axis synchronously with a plurality of motors.

  Various attempts have been made to operate a controlled object with high accuracy and to suppress machine vibration in a position control device that synchronously drives one axis of a feed axis and a main axis of a machine tool with a plurality of motors. By setting the gain of the control system large, it is possible to operate with high accuracy, but mechanical vibration is likely to occur. In order to suppress the mechanical vibration, the excitation force can be removed by adding a filter to the torque command and reducing the command component corresponding to the resonance frequency to be controlled. As a result, it is possible to control the controlled object while suppressing mechanical vibration. However, the torsional rigidity of the lathes facing each other varies depending on the workpiece, and depending on the machining shape, the torsional stiffness of the workpiece changes with machining, so that the resonance frequency of the controlled object changes, and the filter constant There is a problem that the resonance frequency shifts and mechanical vibration occurs.

  FIG. 3 shows a control block diagram of the prior art for suppressing mechanical vibration. Since the master side control system 20m and the slave side control system 20s in FIG. 3 are the same elements, the symbols m and s are added to the end of the symbols of the respective components, and the description of the configuration of the slave side control system 20s is omitted. The position command calculator 1 outputs synchronized position commands Pcm and Pcs to the respective position control systems. A deviation between the position command Pcm and the position detection value Pmm of the position detector 10m attached to the motor 11m is obtained by a subtractor 2m, and a position deviation Pdifm is output. The position deviation proportional calculator 3m multiplies the position deviation by the position loop gain Kp and outputs a speed command Vcm. The differentiator 13m differentiates the position detection value Pmm and outputs a motor speed detection value Vmm. A deviation between the speed command Vcm and the detected speed value Vmm of the motor is obtained by a subtractor 4m and output as a speed deviation. Based on the speed deviation, speed loop proportional gain Pv, and speed loop integral gain Iv, the speed deviation proportional calculator 5m and the speed deviation integral calculator 6m output a speed deviation proportional component and a speed deviation integral component, respectively, and an adder 7m The deviation proportional component and the speed deviation integral component are added to output a torque command Tcm. The notch filter 8m reduces a frequency component centered on the notch frequency ωN from the torque command Tcm. A symbol 9m in FIG. 3 indicates various filter units and a current control unit for filtering the torque command.

  When the workpiece 14 coupled by the main shaft 12m and the main shaft 12s vibrates at the resonance frequency ωr, the resonance frequency ωr appears in the torque command Tcm. The FFT calculator 17 receives the torque command Tcm, and outputs a frequency having the largest power spectrum as a resonance frequency ωr among frequency components included in the torque command Tcm by a known FFT process. The notch filter units 8m and 9m make the notch frequency ωN coincident with the resonance frequency ωr, thereby reducing the resonance frequency component included in the torque command Tcm and the torque command Tcs. As a result, the excitation force is reduced and the control is performed. The target mechanical vibration can be suppressed.

  In the prior art shown in FIG. 3, in order to obtain the resonance frequency component by the FFT calculator 17, it is necessary to sample the torque command Tcm for a certain period of time, so that the resonance of the controlled object is generated before the mechanical vibration occurs. The frequency cannot be set. If mechanical vibration occurred during workpiece machining, the workpiece could be damaged.

  A position control device according to the present invention is a position control device that controls a single axis in synchronization with a plurality of motors based on a position command value, the position command value and a position detection value of the motor detected by a position detector. A speed controller that calculates a speed command value, a speed controller that calculates a torque command value based on the speed command value and a speed detection value calculated from the position detector, and the torque A notch filter that reduces a frequency component centered on a notch frequency from the command value, a position command error generator that generates a position command error in the position command value, and each torque command value of the position command error and a plurality of motors And a resonance frequency calculator for determining a notch frequency of the notch filter.

When there are two motors, when the error of the position command of the two motors is ΔPc, the error of the torque command is ΔTc, and the inertia of the shaft driven by each motor is Jm, Js, the notch frequency ωN is


It is desirable to calculate based on the following formula.

  According to the position control apparatus of the present invention, the resonance frequency calculator varies the notch frequency of the notch filter that reduces the frequency component centered on the notch frequency before mechanical vibration occurs. As a result, the resonance frequency component included in the torque command is reduced, the excitation force is reduced, and vibration can be suppressed.

It is a block diagram which shows the structure of the position control apparatus which is an Example of this invention. It is a block diagram which shows the structure of a resonance frequency calculator. It is a block diagram which shows a prior art.

  A position control apparatus according to an embodiment of the present invention will be described. The same elements as those of the conventional example are denoted by the same reference numerals, and description thereof is omitted. A control block diagram of the position control device is shown in FIG. The position command calculator 1 outputs the position command Pcm to the position command error generator 15. The position command error generator 15 uses the position command Pcm output from the position command calculator 1 as the position commands Pcm and Pcs during a cutting operation in which the notch frequency ωN is not updated. And output to the slave side position control system 20s.

At the timing of updating the notch frequency ωN, specifically, at the timing of rapid feed not related to cutting, the position command error generator 15 outputs a position command including an error to the slave side position control system 20s. . Specifically, the position command error generator 15 outputs the position command Pcm output from the position command calculator 1 to the master side position control system 20m and the position command Pcm to the slave side position control system 20s. The position command Pcs of Expression 1 offset by the position command error ΔPc is output. The position command error ΔPc is a value that is empirically set in advance.
Pcs = Pcm−ΔPc (Formula 1)

  The resonance frequency calculator 16 is based on the master side position control system torque command value Tcm calculated by the master side control system 20m, the slave side position control system torque command value Tcs calculated by the slave side control system 20s, and the position error ΔPc. Then, the resonance frequency ωr of the workpiece 14 coupled by the main shaft 12m and the main shaft 12s is calculated, and the notch frequency ωN of the master side notch filter portion and the slave side notch filter portion is changed to the resonance frequency ωr.

Specifically, an example of the configuration of the resonance frequency calculator 16 is shown in FIG. The subtractor 161 calculates a torque command error ΔTc from the master side position control system torque command value Tcm and the slave side control system torque command value Tcs. Assuming that the main spindle opposed to the lathe is a rigid spring that is the value obtained by dividing the torque command error ΔTc by the position command error ΔPc, the master axis inertia Jm and the slave side inertia Js are combined. In this case, the resonance frequency ωr of the system is expressed by the following formula 2. The resonance frequency calculator 16 calculates the resonance frequency ωr based on Equation 2, and changes the notch frequency ωN of the master side notch filter and the slave side notch filter to the resonance frequency ωr. The calculation and the change of the notch frequency ωN are performed every time the workpiece, the master axis inertia Jm, and the slave side inertia Js change. Note that the shape of the workpiece changes with machining, and consequently the resonance frequency ωr changes. Therefore, it is desirable to update the notch frequency ωN during non-cutting operations such as when fast-forwarding is performed even while the same workpiece is being machined (even if the workpiece is not replaced).

  By changing the notch frequency ωN to a different resonance frequency ωr for each workpiece, the resonance frequency component included in the master side torque command Tcm and the slave side torque command Tcs is reduced, and as a result, the excitation force is reduced, Mechanical vibration to be controlled can be suppressed. Actually, even if the true value ωr ′ of the resonance frequency different for each workpiece and the notch frequency ωN set by the resonance frequency calculator 16 do not completely match, the notch filter unit also reduces the gain near the notch frequency. Therefore, vibration due to a change in resonance frequency can be suppressed.

  1 position command computing unit, 2m, 2s subtractor, 3m, 3s position deviation proportional computing unit, 4m, 4s subtractor, 5m, 5s speed loop proportional gain, 6m, 6s speed loop integral gain, 7m, 7s adder, 8m , 8s Notch filter unit, 9m, 9s Various filter units, Current control unit, 10m, 10s Motor position detector, 11m, 11s Motor, 12m, 12s Control target, 13m, 13s Differentiator, 14 Workpiece, 15 Position command error generation , 16 resonance frequency calculator, 161 subtractor, 162 divider, 163 constant, 164 multiplier, 165 square root calculator, 17 FFT calculator, 20m master side position control system, 20s slave side position control system.

Claims (2)

A position control device that controls one axis synchronously with a plurality of motors based on a position command value,
A position controller that calculates a speed command value based on the position command value and a position detection value of the motor detected by a position detector;
A speed controller that calculates a torque command value based on the speed command value and a speed detection value calculated from the position detector;
A notch filter that reduces a frequency component centered on a notch frequency from the torque command value;
A position command error generator for generating a position command error in the position command value;
A resonance frequency calculator for determining a notch frequency of the notch filter based on the position command error and a torque command value of each of a plurality of motors;
A position control device comprising: The position control device according to claim 1,
The number of the motors is two. When the error of the position command of the two motors is ΔPc, the error of the torque command is ΔTc, and the inertia of the shaft driven by each motor is Jm, Js.
The notch frequency ωN is


A position control device that is calculated based on the following formula.