CN101436053A - Control method of machine tool - Google Patents

Abstract

The invention discloses a method for controlling a machine tool, which is realized by the following steps: (1) a mathematical model of a cutting process is established; (2) a primary function is selected; (3) a force transducer of the machine tool is used to sample the actual cutting force F of the machine tool according to the sampling period; (4) the F is compared with Fm output in step (1) in each sampling period to obtain an error (e is equal to F-F), and the feedback compensation of the model is performed; (5) the model after the feedback compensation is substituted into a predictive functional control optimization algorithm; (6) the control quantity is output after the predictive functional controls optimization operation, and the machine tool performs the control according to u; (7) if e is not zero, the operation is returned to the step (3) to continue until the e is zero; and (8) if e is zero, the control quantity is a constant value U0, the U0 is the u determined in step (6), and the machine tool outputs a constant cutting force according to the U0. The method has good robustness and strong engineering practicability, and can meet the requirement of real-time control.

Description

The control method of lathe

Technical field

The present invention relates to the control technology field of numerically-controlled machine, specifically is a kind of control method of lathe.

Background technology

The feed rate of regulating numerically-controlled machine is the effective way that increases substantially numerically-controlled machine production efficiency with the self-adaptation constant force control that realizes working angles, also is the problem that numerous scholars concentrate on studies for many years always.Yet; in all kinds of self-adaptation constant force control algolithms that forefathers proposed; the parameter tuning of controller only depends on controlled system past and current dynamic behavior usually; and consider that control is imported and the influence of system's output prospect; and control procedure is not applied reasonable constraints; therefore; when because of cutting-in or cut wide sudden change and bring out cutting force when sudden change; it is excessive that PID control or other control methods can cause controlled system output overshoot or control to be imported usually, causes the performance of numerically-controlled machine not good.

Summary of the invention

The technical problem to be solved in the present invention is, overcomes the shortcoming of above prior art, provides that a kind of robustness is good, engineering practicability strong, can satisfy the control method of the lathe of requirement of real-time control.

Technical scheme of the present invention is, a kind of control method with lathe of following steps is provided, and its implementation is:

(1) sets up the mathematical model of cutting process, and this mathematical model is reduced to the pure lag model of first-order linear;

(2) selected basis function:, be basis function with the step function when setting value when variable quantity is less than or equal to threshold value a in controlled interval; When setting value when variable quantity is greater than threshold value b in controlled interval, with step function with ramp function is compound and function that come is a basis function;

(3) by the force cell of lathe actual cut power, remember that this actual cut power is F by sampling period sampling lathe;

(4) F that all the pure lag model of first-order linear described in F and the step (1) is exported in each sampling period _mCompare, obtain error, remember that this error is e, by expression formula e=F-F _mDetermine, and carry out the model feedback compensation;

(5) with the model substitution Predictive function control optimized Algorithm behind the feedback compensation;

(6) export controlled quentity controlled variable after Predictive function control is optimized computing, remember that this controlled quentity controlled variable is u, described lathe removes to control the servo-driver of lathe according to u;

(7), then forward the continuation of (3) step to, until e is zero if e is non-vanishing;

(8) if e is zero, then controlled quentity controlled variable is a steady state value, remembers that this steady state value is U ₀, this U ₀Value be this moment the sampling cycle in the determined u of step (6), described lathe is according to U ₀The servo-driver that goes to control lathe is exported a constant cutting force.

After adopting said method, the present invention compared with prior art, have following remarkable advantage and beneficial effect: because in the cutting process of lathe, adopt Predictive function control, the influence of counted the controlled system input, exporting prospect, so the control method of lathe of the present invention makes the stability of lathe and output performance good, robustness is good, and can satisfy the real-time requirement of numerical control cutting constant force control, and engineering practicability is strong.

Description of drawings

Accompanying drawing is the control flow synoptic diagram of the control method of lathe of the present invention.

Embodiment

The invention will be further described below in conjunction with the drawings and specific embodiments.

General numerically-controlled machine all comprises force cell, pfc controller and servo-driver.

Described pfc controller is built-in with Predictive function control optimized Algorithm software, and described Predictive function control optimized Algorithm is a prior art, and the control procedure of the control method of lathe of the present invention is as follows:

(1) set up the mathematical model of cutting process, and this mathematical model is reduced to the pure lag model of first-order linear, the cutting process of general lathe can be reduced to following mathematical model:

$\frac{F_m\left(s\right)}{u\left(s\right)}=\frac{K}{T_{1}s+1}{e}^{-\mathrm{\τs}}$

In this formula, K is the process full gain, K=60K _nK _sK _eAf ^M-1/ (pn), K wherein _nBe servo gain (mm/ (V.s)), K _sBe cutting specific force (N/mm ²), K _eBe ergometry instrument conversion coefficient, a is back engagement of the cutting edge (mm); F is the amount of feeding (mm/r), and m is index (general m＜1), and m depends on the workpiece material and the shape of tool; The number of teeth of cutter when p is milling, n is the speed of mainshaft (r/min).τ is a lag time constant.F _m(s) be the Laplace transform of cutting force F, u (s) is the Laplace transform of cutting force u, and s is a complex variable.T ₁Be the working angles time constant.

(2) set setting value variable quantity in controlled interval and be less than or equal to threshold value a, then selected basis function is a step function.

(3) by the force cell of lathe actual cut power, remember that this actual cut power is F by sampling period sampling lathe.

(4) mathematical model of the cutting force F that obtains of actual measurement and cutting process output F _mCompare, obtain error e (k)=F-F _m, and carry out the pure lag model feedback compensation of first-order linear, obtain F _m(k+P)+e (k), wherein F _m(k+P) be that the pure lag model of first-order linear is predicted cutting force when P goes on foot.

(5) model substitution Predictive function control optimized Algorithm behind the feedback compensation obtains following expression:

$u\left(k\right)=\frac{F_r(k+P)-{\mathrm{\β}}^P{F}_r\left(k\right)-F_{\mathrm{pav}}\left(k\right)(1-{\mathrm{\β}}^P)}{K(1-{\mathrm{\α}}_m^P)}+\frac{F_m\left(k\right)}{K}$

In this formula, F _r(k) be given cutting force, k is a current time, and P is prediction step number, F _rGiven cutting force when (k+P) prediction P goes on foot, $\mathrm{\β}=e^{({-T}_s/T_r)},$ T _rBe given signal time constant, F _Pav(k)=F (k)+F _m(k)-F _m(k-D), D is the hysteresis step number; ${\mathrm{\α}}_m=e^{({-T}_s/T_1)},$ T _sBe the sampling period

(6) export controlled quentity controlled variable after Predictive function control is optimized computing, remember that this controlled quentity controlled variable is u, described lathe removes to control the servo-driver of lathe according to u.

(7), then forward the continuation of (3) step to, until e (k) is zero if e (k) is non-vanishing.

(8) if e (k) is zero, then controlled quentity controlled variable is a steady state value, remembers that this steady state value is U ₀, this U ₀Value be this moment the sampling cycle in the determined u of step (6), described lathe is according to U ₀The servo-driver that goes to control lathe is exported a constant cutting force.

Claims (1)

1, a kind of control method of lathe is characterized in that,

Realize by following steps:

(1) sets up the mathematical model of cutting process, and this mathematical model is reduced to the pure lag model of first-order linear;

(2) selected basis function:, be basis function with the step function when setting value when variable quantity is less than or equal to threshold value a in controlled interval; When setting value when variable quantity is greater than threshold value b in controlled interval, with step function with ramp function is compound and function that come is a basis function;

(3) by the force cell of lathe actual cut power, remember that this actual cut power is F by sampling period sampling lathe;

(4) F that all the pure lag model of first-order linear described in F and the step (1) is exported in each sampling period _mCompare, obtain error, remember that this error is e, by expression formula e=F-F _mDetermine, and carry out the model feedback compensation;

(5) with the model substitution Predictive function control optimized Algorithm behind the feedback compensation;

(6) export controlled quentity controlled variable after Predictive function control is optimized computing, remember that this controlled quentity controlled variable is u, described lathe removes to control the servo-driver of lathe according to u;

(7), then forward the continuation of (3) step to, until e is zero if e is non-vanishing;

(8) if e is zero, then controlled quentity controlled variable is a steady state value, remembers that this steady state value is U ₀, this U ₀Value be this moment the sampling cycle in the determined u of step (6), described lathe is according to U ₀The servo-driver that goes to control lathe is exported a constant cutting force.

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