JP2016140967A - Position control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a position control device which suppresses errors each of which may occur between a position specified by a position command value and an outputted position, by estimating vibration that occurs during cutting process without delay and compensating its impact.SOLUTION: A position control device calculates a gain characteristic and a phase characteristic in a cutting vibration frequency for a low-pass filter included in a disturbance observer. Then, the position control device performs a gain compensation and a phase compensation on an estimated disturbance value outputted from the disturbance observer, using an amplitude phase correcting unit 9, accurately estimates cutting vibration and compensates its impact.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a feed shaft position control device in a machine tool or the like, and more particularly to an improvement in a position control device that suppresses a position error caused by cutting vibration during machining.

  In the feed axis of a machine tool, for example, when milling is performed, a position error due to an increase in cutting load or cutting vibration accompanying the processing occurs. Disturbance observers are well known as a technique for suppressing position errors caused by these cutting disturbances.

  FIG. 3 is a block diagram showing the technique of Non-Patent Document 1 as an example of a conventional position control device. In FIG. 3, a controller 1 outputs an operation amount u0 from a position command value r and a position detection value from a host device (not shown), and is added to a compensation amount by an adder 2 to become a control input u. The control input u is input to the controlled object 4, but the substantial input becomes equal to the value obtained by subtracting the disturbance d from the control input u by the subtractor 3 due to the influence of the disturbance d. The control object 4 is controlled such that the position output y becomes equal to the position command value r when the control input u is given. Further, the position output y of the control object 4 is detected by a position detector or the like, but due to the influence of the observation noise ζ, the substantial position detection value y0 adds the observation noise ζ from the position output y. It is equal to the value added by the vessel 5.

On the other hand, the inverse system 6 of the nominal plant has a transfer characteristic of Pn ^{−1 which} is a reverse transfer characteristic with respect to the nominal characteristic Pn with respect to the transfer characteristic P of the controlled object 4. The inverse system 6 of the nominal plant estimates the substantial input of the controlled object 4 from the position detection value y0, and estimates the disturbance d acting on the controlled object 4 by taking the difference from the controlled input u by the subtractor 7. To do. However, since the inverse system 6 of the nominal plant is a non-proper function, the disturbance estimated value d ′ is substantially output through the low-pass filter 8. This disturbance estimated value d ′ is added as a compensation amount by the adder 2 with the manipulated variable u0 output from the controller 1.

Next, the operation principle will be described. The manipulated variable u0, the disturbance d, the position output y with respect to the observation noise ζ, and the control input u are expressed by Expression 1 and Expression 2, respectively.
y = P * Pn / {Pn * (1-L) + P * L} * u0
-P * Pn * (1-L) / {Pn * (1-L) + P * L} * d
−P × L / {Pn × (1−L) + P × L} × ζ Equation 1
u = Pn / {Pn * (1-L) + P * L} * u0
+ P * L / {Pn * (1-L) + P * L} * d
−L / {Pn × (1−L) + P × L} × ζ Expression 2

When the transfer characteristic L of the low-pass filter 8 is 1, Expression 1 is expressed by Expression 3, and the influence of the disturbance d can be eliminated.
y = Pn × u0−ζ Equation 3

On the other hand, Expression 2 is expressed by Expression 4, and it can be seen that the observation noise ζ is superimposed on the control input u in a state amplified by P− ¹ .
u = Pn / P × u0 + d−1 / P × ζ Equation 4

  That is, in order to suppress the influence of the disturbance d, it is preferable to set the cut-off frequency of the low-pass filter 8 as high as possible, but in order to prevent the generation of abnormal noise and high-frequency vibration due to the observation noise ζ, The fact is that it cannot be set too high.

  Here, taking the behavior during machining as an example, when the cutting load increases with machining, a steady load is applied as the disturbance d. However, since the low-pass filter 8 has a transfer characteristic L of 1 with respect to the DC component, the influence of the disturbance d is suppressed as described above, and the position output y is not affected. Similarly, even when cutting vibration is generated during processing, it is possible to suppress the influence under a situation where the vibration frequency is sufficiently lower than the cut-off frequency of the low-pass filter 8.

Koda Yamada et al., “Consideration on Higher Order and Robust Stability of Disturbance Observer”, T. IEEE Japan, Vol. 117 (1997) -C, No. 12, p. 1776-p. 1781

However, when cutting vibration acts as the disturbance d, it is difficult to increase the cutoff frequency of the low-pass filter 8 until the transfer characteristic L of the low-pass filter 8 at that vibration frequency becomes 1. In particular, a delay occurs in the phase characteristics of the low-pass filter 8 and hinders. Suppose that the transfer characteristic L of the low-pass filter 8 is determined as shown in Equation 5. Here, in Expression 5, ωc represents a cutoff angular frequency of the low-pass filter 8, and s represents a Laplace operator.
L = ωc / (s + ωc) Equation 5

  At this time, if the vibration angular frequency of the cutting vibration is half of the cutoff angular frequency ωc of the low-pass filter 8, that is, ωc / 2, the gain characteristic | L | of the low-pass filter 8 is 0.89 times, and the phase characteristic ∠L Becomes a delay of 26.6 deg. Furthermore, even if the vibration angular frequency of the cutting vibration is ωc / 5, | L | is 0.98 times and ∠L is 11.3 deg.

  FIG. 4 illustrates a time response characteristic when the transfer characteristic of the low-pass filter 8 is 1 (| L | = 1 ×, ∠L = 0 deg). Here, for simplicity, the manipulated variable u0 and the observation noise ζ are both zero. Since the transfer characteristic of the low-pass filter 8 is 1, the estimated disturbance value d 'coincides with the disturbance d, and the position output y is not affected by the disturbance d. That is, the position output y does not change even when cutting vibration is applied.

  On the other hand, FIG. 5 illustrates the time response characteristic when the transfer characteristic of the low-pass filter 8 is not 1, that is, when the gain characteristic is attenuated and the phase characteristic is delayed. The estimated disturbance value d ′ has a lower amplitude and a delayed phase than the disturbance d. At this time, the influence of the disturbance d cannot be canceled, and the influence of the disturbance d is superimposed on the position output y.

  In this way, when cutting vibration acts as the disturbance d, the transfer characteristic of the low-pass filter 8 with respect to the vibration frequency of the cutting vibration is not 1 (| L | = 1 ×, ∠L = 0 deg), and therefore the influence on the position output y is affected. There is a problem that it cannot be completely suppressed.

  The present invention has been made in view of the above problems, and estimates and compensates for cutting vibration generated during machining without delay, so that a position error generated between a position command value and a position output can be reduced. An object of the present invention is to provide a position control device that suppresses.

  In order to achieve the above object, a position control device according to the present invention is a position control that controls the position of a control target of a numerical control machine that drives a load using a servo motor in accordance with a position command value from a host device. In the apparatus, a controller that outputs an operation amount from the position command value and the position detection value of the control target obtained from a position detector, an adder that adds the operation amount and the compensation amount and outputs a control input; A means for driving a control object in accordance with the control input, and a difference between the control input and a value obtained by multiplying the position detection value by the inverse characteristic of the nominal value of the control object is input to a low-pass filter A disturbance observer that obtains an estimated value, and an amplitude phase corrector that calculates the compensation amount from the estimated disturbance value and the cutting vibration frequency, and the amplitude phase corrector includes the low pass at the cutting vibration frequency. A gain correction coefficient is calculated from the gain characteristic of the filter, a phase correction value is calculated from the phase characteristic of the low-pass filter at the cutting vibration frequency, and the estimated disturbance value is gain-corrected based on the gain correction coefficient and the phase correction value. And phase correction.

  In a preferred aspect, the cutting vibration frequency is calculated from a rotation speed of a main shaft provided in the numerical control machine and the number of blades of a tool attached to the main shaft.

  According to the position control device of the present invention, it is possible to estimate and compensate for the cutting vibration generated during machining without delay, and to suppress the position error generated between the position command value and the position output. it can.

It is a block diagram which shows the Example of this invention. It is a block diagram which shows the Example of this invention. It is a block diagram which shows a prior art. It is a time response characteristic figure when a disturbance can be estimated correctly. It is a time response characteristic figure when attenuation and a delay are included in a disturbance estimated value.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing a control block according to an embodiment of the present invention. The same elements as those of the conventional example are denoted by the same reference numerals, and description thereof is omitted. In the conventional example (FIG. 3), the output of the low-pass filter 8 is set to the disturbance estimated value d ′ and added to the manipulated variable u0. In contrast, in the present invention (FIG. 1), the output of the low-pass filter 8 is the amplitude phase corrector. 9 and the output is added to the manipulated variable u0 as a disturbance estimated value d '.

The amplitude / phase corrector 9 has the vibration frequency f as an input in addition to the output of the low-pass filter 8, and its transfer characteristic G is expressed as shown in Equation 6. Here, in Expression 6, K represents a gain correction coefficient, α represents a phase correction coefficient, s represents a Laplace operator, and the phase correction coefficient α is defined by Expression 7 using a phase correction value φ.
G = (K / √α) × (s + 2πf√α) / (s + 2πf / √α) Equation 6
α = (1−sinφ) / (1 + sinφ) Equation 7

The amplitude / phase corrector 9 has a transfer characteristic in which the gain characteristic | G | is K and the phase characteristic ∠G is the advance of φ at the vibration frequency f. On the other hand, the gain correction coefficient K and the phase correction value φ are set so as to have the relationship of Expression 8 and Expression 9 with respect to the transfer characteristic L of the low-pass filter 8 at the vibration frequency f.
K = 1 / | L |
φ = -∠L ... Equation 9

  That is, the vibration amplitude of the vibration frequency f attenuated by the low-pass filter 8 is amplified by the gain correction coefficient K, and the phase delay of the vibration frequency f generated by the low-pass filter 8 is advanced by the phase correction value φ. By the function of the amplitude phase corrector 9, the cutting vibration at the vibration frequency f can be accurately estimated without delay. Then, by adding the disturbance estimated value d ′ output from the amplitude phase corrector 9 as a compensation amount to the operation amount u0 output from the controller 1 by the adder 2, a position error caused by the influence of the cutting vibration is added. Can be suppressed.

  That is, since the transfer characteristic of the calculation unit including the low-pass filter 8 and the amplitude / phase corrector 9 is 1 with respect to the vibration frequency f, the disturbance estimated value d ′ and the disturbance as shown in the time response characteristic diagram shown in FIG. It is possible for d to match so that the position output y is not affected by the disturbance d.

  It is assumed that the vibration frequency f input to the amplitude / phase corrector 9 is given from the host device according to the processing conditions. For example, as shown in FIG. 2, it is possible to determine the vibration frequency f as the fundamental wave of the cutting vibration by multiplying the rotation speed S of the main shaft to which the tool is attached by the number of blades Z of the tool with a multiplier 10. It is also possible to vary the vibration frequency f handled by the amplitude phase corrector 9 in accordance with the change in the rotational speed S of the main shaft.

  Further, by adding the amplitude phase corrector 9, the disturbance estimated value d ′ is amplified K / √α times in a frequency band higher than the vibration frequency f, and the influence of the observation noise ζ is superimposed on the control input u. Is concerned. In this case, the problem can be avoided by configuring the low-pass filter 8 in advance with a high-order low-pass filter having excellent attenuation performance in a high frequency region.

  In the above-described embodiment, the case where the transfer characteristic L of the low-pass filter 8 is determined as shown in Expression 5 is described as an example, but the present invention is not limited to this transfer characteristic. For example, even if the transfer characteristic is a bandpass filter having a low-frequency cutoff characteristic in addition to a high-frequency cutoff characteristic, the estimated disturbance value obtained by appropriately correcting the gain and phase using the amplitude phase corrector 9 of the present invention d ′ can be calculated.

  As described above, according to the position control device of the present invention, it is possible to estimate and compensate for cutting vibration generated during machining without delay, and a position error generated between the position command value and the position output. Can be suppressed.

DESCRIPTION OF SYMBOLS 1 Controller, 2, 5 Adder, 3, 7 Subtractor, 4 Control object, 6 Nominal plant inverse system, 8 Low pass filter, 9 Amplitude phase corrector, 10 Multiplier.

Claims (2)

In a position control device that controls the position of a control target of a numerical control machine that drives a load using a servo motor according to a position command value from a host device,
A controller that outputs an operation amount from the position command value and the position detection value of the control target obtained from a position detector;
An adder that adds the operation amount and the compensation amount to output a control input;
Means for driving the controlled object in accordance with the control input;
A disturbance observer that obtains a disturbance estimated value by inputting a difference between a value obtained by multiplying the position detection value by a reverse characteristic of the nominal value of the control target and the control input to a low-pass filter,
An amplitude phase corrector for calculating the compensation amount from the disturbance estimated value and the cutting vibration frequency;
With
The amplitude phase corrector is
Calculate a gain correction coefficient from the gain characteristic of the low-pass filter at the cutting vibration frequency,
Calculate a phase correction value from the phase characteristics of the low-pass filter at the cutting vibration frequency,
Gain correction and phase correction of the disturbance estimated value based on the gain correction coefficient and the phase correction value;
A position control device characterized by that. The position control device according to claim 1,
The position control device characterized in that the cutting vibration frequency is calculated from a rotation speed of a main shaft provided in the numerical control machine and a number of blades of a tool attached to the main shaft.

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