CN1258431C - Method for compensating error of numeric-contrlled machine and system - Google Patents

Abstract

The present invention relates to a numerical control machine tool error compensation method and a system thereof, which belongs to the technical field of numerical control machine tools. The present invention is characterized in that double position closed-loop control is realized by using semi-closed-loop position control mainly, using full-closed-loop position control additionally and using an inductosyn as a feedback element of a terminal actual position based on a real-time multitask RT-Linux operating system of a PC platform. At the same time, a closed-loop control system of a machine tool worktable position realizing the semi-closed-loop by using a servo motor and realizing the full-closed-loop by using the inductosyn is correspondingly proposed. The positioning accuracy and the path tracking precision of a feeding system of the numerical control machine tool controlled by the semi-closed-loop position are enhanced, when a positioning error of the numerical control machine tool changes along with time change, positioning error compensation energy can be updated and corrected in a real-time mode.

Description

NC machine tool error compensation process and system

Technical field

NC machine tool error compensation process and system belongs to the numerical control machine tool technique field.

Background technology

Mostly adopt the kind of drive of rotating servo motor+ball-screw at numerically controlled machine, include shaft coupling, ball-screw, pair of nut, bearing etc. in the mechanical drive train and owe stiffener, and also having manufacturing, alignment error and the drive gap of feed screw nut in the mechanical drive train, the existence of these factors seriously influences the positioning accuracy and the track following precision of system.

In position control systems such as lathe, generally be to utilize the feedback loop of the angular displacement information of servomotor, thereby constitute the position control system of a semiclosed loop as Position Control.In this control mode, factors such as the rigidity of driven mechanical part bring influence can for the stability of control system, thereby have than the advantage that is easier to the construction location control system.But owing to be driven the influence of factors such as elasticity that mechanical part exists, friction, non-linear and geometric error, realize relatively difficulty of the high position control accuracy of driven mechanical part, in addition, Digit Control Machine Tool adopts the feed screw nut auxiliary driving, owing in the process of leading screw and nut, unavoidably have mismachining tolerance, thereby cause the pitch error of Digit Control Machine Tool transmission process.

Because the existence of pitch error, when Digit Control Machine Tool adopts the semiclosed loop Position Control, even the angle of revolution displacement accuracy of servomotor is very high, but be when finally controlling target, in control procedure, will produce position error and track following error inevitably with the worktable displacement.Therefore, in most numerical control device,, all possesses the The compensation of pitch error function usually in order to compensate lathe position error and the track following error that pitch error causes.They are when carrying out The compensation of pitch error, by measuring the pitch error of screw pair transmission system in advance, then this pitch error and its corresponding coordinate position are stored in the numerical control device, when digital control system is carried out the reference axis motion control, the pitch error of machine coordinates position correspondence is added in the control instruction, realizes compensation pitch error.

In addition, the The compensation of pitch error function of traditional Digit Control Machine Tool semiclosed loop position control system, the coordinate position of The compensation of pitch error amount and platen is corresponding.In fact, in the screw pair transmission process of lathe, during Position Control because the difference of the direction of motion, the contact-making surface of leading screw and nut is also different, and the pitch error that the mismachining tolerance in the process of leading screw and nut causes, different these errors of the direction of motion are also inequality, even thereby on lathe identical position the position error of same point is not inequality yet because the direction of motion does not coexist.Therefore traditional The compensation of pitch error method is difficult to realize high-precision positioning accuracy.

And, if lathe is long-time use after, owing to mechanical wear, reason such as loosening, the position error of lathe and track following error also can change over time.Thereby after a period of time, the requirement that the error compensation value that records at first can not the adaline tool error compensation must remeasure the error compensation amount of lathe, revises the error compensation parameter of digital control system.

Relative therewith, if the feedback loop utilization is the positional information of driven mechanical part, then constituted the position control system of a full cut-off ring, in the position control system of full cut-off ring, even there is pitch error in system, because location feedback value directly is exactly to control the physical location of object, thereby in theory, the Full Closed-loop Position control system can not produce pitch error.In this control mode, when the rigidity of the mechanical part between servomotor and the position sensor is hanged down, the stability that is difficult to the retentive control system, though the gain that reduces control system can improve the stability of system, the control system gain lower time the positioning accuracy and the track following precision of lathe be difficult to again guarantee.

Melt semiclosed loop and full cut-off cyclization two closed loop position control systems, can remedy shortcoming separately, obtain higher position control accuracy and good position control system stability in one.Its essence is and utilized servomotor position and load (platen) position, for control system provides the control parameter.In this control scheme, with the half-closed loop control is basic control structure, additional one with the deviation of the position of the position of servo motor shaft and bearing axle control loop as the target location of load, come real-time Correction and Control desired value, thereby realize the physical location of bearing axle and the such control function of uniformity of target location.This control system structure has the stability identical with the half-closed loop control system, and has the position control accuracy of controlling effect with the full cut-off ring equally again under the lower situation of load rigidity.

Position detecting device commonly used comprises inductosyn, grating, magnetic grid, pulse coder, rotary transformer etc.Pulse coder and rotary transformer are commonly used for half-closed loop control, and grating and magnetic grid are as the feedback element of full cut-off ring control, and inductosyn is then done digital display control.

Grating and magnetic grid cost an arm and a leg, and working environment is required height, and the maintenance trouble will increase cost budgeting, and particularly for the large-size numerical control machine of long stroke, this is high expense.And inductosyn has low price, and is low to the working environment requirement, and installation and maintenance are all very convenient, and spreading is easy, is particularly suitable for big travel position and detects.

Inductosyn position probing principle is different with grating, magnetic grid etc., position detection signal is incompatible with it, and usually the acceptable feedback signal of digital control system all is the TTL square-wave signal of similar pulse coder, and therefore the inductosyn digitlization that is confined to machine tool position in the past shows.

In order to make full use of the advantage of inductosyn, it can be applied in digital control system as the position feedback element, must carry out corresponding conversion process to the detection signal of inductosyn, soon the detected alternation sine and cosine of inductosyn analog signal conversion is and the output compatible A of incremental optical-electricity encoder, B, Z signal.Signal after the conversion can be directly as the position feed back signal of the full cut-off ring of NC system.

The present invention is exactly the accuracy compensation problem at Digit Control Machine Tool, takes measures on control system hardware configuration and control algolithm, to improve the motion control precision of Digit Control Machine Tool.

Summary of the invention

The object of the present invention is to provide a kind of Digit Control Machine Tool error compensating method and system.

Error compensating method of the present invention is characterized in that: it is a kind of based on the semiclosed loop Position Control, and Full Closed-loop Position is controlled to be the error compensating method of auxilliary two-position closed-loop control, and it is realized according to following steps based on the PC platform:

(1) deposit PC after the following parameter of initialization in:

Platen theoretical error compensation weights ω: 0≤ω≤0.3;

The pulse equivalency δ of Digit Control Machine Tool control system;

The theoretical departure of platen is measured frequency n, chooses n between 10～20;

Platen departure measurement point number j generally determines measurement point number j with measurement point spacing 10～20mm;

The i time platen displacement control instruction value x based on the rotating servo motor angular displacement of j measurement point (i, j);

K control cycle is based on the platen straight-line displacement control instruction value Δ x of rotating servo motor angular displacement _m(k), the initial value ε (k of error precompensation _o);

(2) PC calculates according to following formula, the average Δ (j) of the actual displacement error of i measurement point machine coordinates axle:

$\mathrm{\Δ}\left(j\right)=\frac{1}{n}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}((x_s(i,j)-x(i,j))-(x_m(i,j)-x(i,j)))$

Wherein, x _s(i, j): j the platen physical location that measurement point is obtained by linear induction synchro measure on the platen for the i time;

x _m(i, j): the physical location of the platen that j measurement point the i time measured by incremental optical-electricity encoder on the rotating servo motor;

X (i, j): the i time control instruction value of j measurement point based on the platen of rotating servo motor angular displacement;

(3) Δ (j) value is deposited in the PC, whether repeating step (2) judges circulation measurement number of times greater than n again, if greater than n, n is that the theoretical departure of platen is measured number of times, then carries out following steps;

(4) PC is calculated as follows the theoretical displacement control instruction Δ x of k control cycle machine coordinates axle _s(k):

${\mathrm{\Δx}}_s\left(k\right)={\mathrm{\Δx}}_m\left(k\right)+\frac{\mathrm{\Δ}(j+1)-\mathrm{\Δ}\left(j\right)}{x(j+1)-x\left(j\right)}{\mathrm{\Δx}}_m\left(k\right)$

Wherein, Δ x _m(k): k control cycle is based on the platen straight-line displacement control instruction of rotating servo motor angular displacement;

Δ (j+1): the error of the actual value of j+1 measurement point machine coordinates axle;

Δ (j): the error of the actual value of j measurement point machine coordinates axle;

X (j+1): the physical location of j+1 measurement point lathe coordinate system;

X (j): the physical location of j measurement point lathe coordinate system;

(5) PC is calculated as follows the theoretical error ε of the corresponding platen displacement of k control cycle _n(k):

ε _n(k)＝Δx _m(k)-Δx _s(k)

(6) PC is calculated as follows the actual displacement control instruction Δ x (k) of the machine coordinates axle of k control cycle:

Δx(k)＝(Δx _m(k)+ω×ε _n(k))/δ

(7) PC is calculated as follows the actual error ε (k) of the corresponding platen displacement of k control cycle:

ε(k)＝x _s(k)+x _m(k)

Wherein, Δ x _s(k): k the platen actual displacement that control cycle is measured by linear inductosyn,

Δ x _m(k): k the platen actual displacement that the control cycle rotating servo motor measures from last incremental optical-electricity encoder,

(8) PC is calculated as follows the corresponding platen working control error pre-compensation value of k+1 control cycle

$\widehat{\mathrm{\ϵ}}(k+1)=\widehat{\mathrm{\ϵ}}\left(k\right)+w[\mathrm{\ϵ}\left(k\right)-\widehat{\mathrm{\ϵ}}\left(k\right)]$

Wherein,

The platen working control error compensation value of k control cycle;

ε (k): the actual error of the corresponding platen displacement of k control cycle;

(9) to be calculated as follows the machine tool position control instruction of k control cycle be SERVO CONTROL command value r to PC:

$r={\mathrm{\Δ}}_{n}x\left(k\right)=[{\mathrm{\Δx}}_m\left(k\right)+\mathrm{\ω}\×{\mathrm{\ϵ}}_n\left(k\right)+(1-\mathrm{\ω})\×\widehat{\mathrm{\ϵ}}\left(k\right)]/\mathrm{\δ}.$

The Digit Control Machine Tool error compensation system is characterized in that, it contains:

Industrial PC Computer, the servo-driver of embedded position control card, measurement interface card, Industrial PC Computer and servo-driver are interconnected with two interfaces of above-mentioned Position Control card respectively, and Industrial PC Computer links to each other with measurement interface output again;

The inductosyn post processing circuitry, it is connected in series by signal amplification circuit, shaping and filter circuit, signaling conversion circuit successively, and the output of signaling conversion circuit links to each other with above-mentioned measurement interface card input;

Incremental optical-electricity encoder, they link to each other with servo-driver is coaxial, and their outputs link to each other with above-mentioned servo-driver input;

Servomotor, it links to each other through leading screw-nut body with platen; Its input links to each other with above-mentioned servo-driver output;

Inductosyn, it is fixed on the platen, and its signal output part links to each other with signal amplification circuit input in the above-mentioned inductosyn treatment circuit.

Effect data

The control object is the motion platform of TSA200 type AC servo machinery driving, and parameter is:

Project	Numerical value	Unit
			Range	160	mm
Mesa dimensions
		90×90	mm
The leading screw helical pitch				4	mm
	Servomotor power	200	W
The servomotor maximum (top) speed				2000	Rpm
	Leading screw end play	＜100	Um
Encoder				2000	Groove
	Linear grating resolution ratio	1	Um
Control resolution				0.5	um

Track error measured curve such as Fig. 5 a;

With the same same distance of speed operation, compensation back track following error is 66.5um, and control accuracy has improved 100%, track following error measured curve such as Fig. 5 b;

Adopt U.S. Optodyne laser interferometer (accuracy of instrument: 0.00002 ± 1e-7mm) actual measurement, repetitive positioning accuracy 125um before the compensation, position error measured curve such as Fig. 5 c through China metering president degree measuring chamber;

Compensation back repetitive positioning accuracy is 16um, has improved about 8 times, resetting error measured curve such as Fig. 5 d.

Description of drawings

Fig. 1. the theory diagram of the Digit Control Machine Tool error compensation system of being invented.

Fig. 2. the theory diagram of the rearmounted treatment circuit of the signal of linear inductosyn.

Fig. 3. the error compensation control schematic diagram of the method for the invention.

Fig. 4. the computer programme flow diagram of the method for the invention.

Fig. 5. the effect data figure of the method for the invention: 5a, 5b, 5c, 5d.

The specific embodiment

Characteristics of the present invention are that the hardware of realizing is the two-position closed-loop control device of terminal physical location feedback element based on PC platform, software based on the RTLinux operating system of real-time multi-task, based on the semiclosed loop Position Control, with induction synchronous task device, solution is adopted with the contradiction between the control accuracy of the Digit Control Machine Tool of feed screw nut auxiliary driving or workbench, the stability of a system, the ratio of performance to price, mainly comprises following content.

1. adopt linear inductosyn as numerically controlled machine straight-line displacement measuring cell, have the numerical control device that two-position information detects.

In this numerical control device, the main body of Position Control is the semiclosed loop Position Control mode that is made of the servomotor incremental optical-electricity encoder, semiclosed loop is that the angle of revolution displacement of servomotor adopts traditional incremental optical-electricity encoder as measurement mechanism, and position full cut-off ring information measurement partly is that the straight-line displacement of platen adopts linear inductosyn as measurement mechanism.

2. numerical control device hardware is based on the Industrial PC platform, mainly be made up of Industrial PC, Position Control card and IO interface card, the rearmounted processing module of numerically controlled machine terminal induction synchronized, platen displacement measurement interface card, each control card is controlled and communication by the PC bus; Software is based on real-time multi-task operating system RT-Linux, the PLC control task of measuring task, outer shroud Position Control task and CNC system by CNC half-closed loop control task, based on the terminal location of inductosyn is formed, and each task is activated and dispatched by the CNC master control system.

In the device of this invention, the unique distinction of hardware configuration is in the numerical control device except general-purpose industrial PC and Position Control card, also added the numerically controlled machine actual displacement measurement mechanism and signal receiving device and the displacement measurement card that show unique characteristics, it is also inequality that this displacement measurement is stuck in the function and the effect of two closed loop position control systems that effect in the whole digital control system and other digital control system adopt.It is an auxiliary measurement means, and two tasks of the collection of its signal and compensate function are dispatched by software and realized.

3. the rearmounted treating apparatus of inductosyn that is used for platen coordinates of motion axle straight-line displacement digitized measurement.

This device is directly measured the actual displacement of platen rectilinear coordinates axle with linear inductosyn, convert to and the identical A of increment volume photoelectricity sign indicating number device output signal with the output signal of rearmounted treatment circuit then linear inductosyn, A, B, B, Z, Z standard Transistor-Transistor Logic level, handle by the numerically controlled machine displacement measurement interface card of the apparatus of the present invention in the summary of the invention 2 then, can generate the digital information of corresponding displacement.

4. in numerical control device of the present invention, by Digit Control Machine Tool full cut-off ring displacement error model and data that the data that adopt the detection of apparatus of the present invention measuring system to obtain generate, this model and data are used to compensate the positioning accuracy of semiclosed loop Digit Control Machine Tool.

The numerical control device of this invention, the Digit Control Machine Tool displacement signal of the correspondence by gathering the servomotor photoelectric encoder and the actual displacement signal of the numerically controlled machine that linear inductosyn measures, resolve the displacement error in the Digit Control Machine Tool motion process, through repeatedly duplicate measurements, measured Digit Control Machine Tool actual displacement error is carried out match, obtain the actual displacement error model in the Digit Control Machine Tool motion process, according to this error model, generate the theoretic full cut-off ring of Digit Control Machine Tool displacement error model and data then.Theoretical displacement model of the Digit Control Machine Tool full cut-off ring that generates and data are used for the generation of the numerically controlled machine situation theory error of summary of the invention 5.

Full cut-off ring displacement error model and data are not subjected to the restriction of other condition, can generate at any time and upgrade, and Digit Control Machine Tool is having the use that does not influence this function under load or the non-loaded situation.This is that the present invention compares and exclusive superiority with traditional machine tool error compensating measurement method, also is one of characteristic of the present invention.

Full cut-off ring displacement error model and data generating procedure are as follows:

$\mathrm{\Δ}\left(j\right)=\frac{1}{n}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}((x_s(i,j)-x(i,j))+(x_m(i,j)-x(i,j)))---\left(1\right)$

Δ (j)---the actual displacement error of j measurement point machine coordinates axle

x _s(i, j)---j the platen actual displacement that measurement point is measured by linear inductosyn for the i time

x _m(i, j)---j the platen actual displacement that measurement point is measured by incremental optical-electricity encoder for the i time

X (i, j)---the i time platen displacement control instruction value of j measurement point based on the rotating servo motor angular displacement

The theoretical departure of n---platen is measured number of times, chooses as required, is chosen as between 10～20

J---platen error measure point number is determined according to table stroke and digital control system servo period, can determine the measurement point number with measurement point spacing 10～20mm.

After platen actual displacement error measure finishes, these data are stored in the digital control system, are used to generate the theoretical displacement control instruction of machine coordinates axle.The theoretical displacement control instruction of machine coordinates axle adopts subordinate's method to generate:

${\mathrm{\Δx}}_s\left(k\right)={\mathrm{\Δx}}_m\left(k\right)+\frac{\mathrm{\Δ}(j+1)-\mathrm{\Δ}\left(j\right)}{x(j+1)-x\left(j\right)}{\mathrm{\Δx}}_m\left(k\right)---\left(2\right)$

Δ x _s(k)---the theoretical displacement control instruction of k control cycle machine coordinates axle

Δ x _m(k)---k control cycle is based on the platen straight-line displacement control instruction of rotating servo motor angular displacement

Δ (j+1)---the actual displacement error of j+1 measurement point machine coordinates axle

Δ (j)---the actual displacement error of j measurement point machine coordinates axle

X (j+1)---j+1 measurement point is based on the physical location of lathe coordinate system

X (j)---j measurement point is based on the physical location of lathe coordinate system

Adopt formula (2) when calculating, at first will judge Δ x _m(k) residing point position calculates then.

5. the platen situation theory error generation method that generates based on numerical control device inside corresponding to the platen straight-line displacement control instruction of rotating servo motor angular displacement and corresponding platen reference axis straight-line displacement instruction.

In the numerical control device of this invention, the NC code that will carry out according to Digit Control Machine Tool, the inner control instruction maker of device at first generates corresponding rotating servo motor angular displacement instruction, the factors such as gap, feed screw nut transmission stiffness, friction and pitch error of mechanical system are not considered in the platen reference axis straight-line displacement instruction of this angular displacement correspondence, only consider the angular displacement one straight-line displacement gearratio (leading screw helical pitch) of machinery, the generation of control instruction and corresponding control model are based on desirable semiclosed loop model.The control instruction maker also will directly generate platen reference axis straight-line displacement instruction simultaneously, the factors such as gap, feed screw nut transmission stiffness, friction and pitch error of mechanical system have been considered in this straight-line displacement instruction, and the generation of control instruction and corresponding control model are based on machine tool position full cut-off ring control model.

More than two kinds of differences in the displacement commands of same Position Control in the cycle, exactly by adopt in the inner machine tool position control procedure that generates automatically of controller between position semiclosed loop and the control of position full cut-off ring because the theoretical departure value that the control mode difference is produced.Theoretical departure value generation method is as follows:

ε _n(k)＝Δx _m(k)-Δx _s(k) (3)

Δ x _s(k)---the theoretical displacement control instruction of k control cycle machine coordinates axle

Δ x _m(k)---k control cycle is based on the platen straight-line displacement control instruction of rotating servo motor angular displacement

ε _n(k)---the platen theoretical error of the corresponding platen displacement of k control cycle

6. generate the actual displacement control instruction generation method of machine coordinates axle based on the platen straight-line displacement control instruction of rotating servo motor angular displacement.

Because the rectilinear motion of platen is the straight-line displacement that the servomotor angular displacement is converted into platen by the feed screw nut transmission, when adopting the feed screw nut auxiliary driving since exist in the system friction, elasticity, etc. link, if adopt simple conversion will produce the errors of principles, cause platen to produce position error.Therefore, in the control procedure of numerical control device, according to each specific platen, control algolithm by internal system, the displacement controlled quentity controlled variable that the NC code is determined is converted to the angular displacement instruction of rotating servo motor and corresponding platen reference axis straight-line displacement instruction respectively, compare the relation between these two displacements, determine the displacement control instruction of numerical control device reality.The displacement control instruction generation method of numerical control device reality is as follows:

Δx(k)＝(Δx _m(k)+ω×ε _n(k))/δ (4)

Δ x (k)---the actual displacement control instruction of k control cycle machine coordinates axle

Δ x _m(k)---k control cycle is based on the platen straight-line displacement control instruction of rotating servo motor angular displacement

ε _n(k)---the platen theoretical error of the corresponding platen displacement of k control cycle

δ---the pulse equivalency of Digit Control Machine Tool control system

ω---platen theoretical error compensation weights, 0≤ω≤1

7. based on generating that the externally measured element of numerical control device generates corresponding to the rotating servo motor actual displacement angle of NC code and the platen position actual error of the actual straight-line displacement of platen reference axis of correspondence.

In the numerical control device of this invention, control system is a position servo control in the cycle, produce the servomotor value of angular displacement by the photoelectric encoder that detects on the rotating servo motor, simultaneously by detecting the actual displacement of the additional numerically controlled machine that produces by linear inductosyn and rearmounted treatment circuit thereof on the numerically controlled machine.The former is the actual displacement of lathe under the half-closed loop control mode situation of position, and the latter is the actual displacement of platen under the full cut-off ring mode of position.

More than two kinds of differences in the actual displacement of same Position Control in the cycle, be exactly to adopt position semiclosed loop and the control of position full cut-off ring in the Digit Control Machine Tool working control process because the different actual displacement error amounts that produce of control mode.

ε(k)＝x _s(k)+x _m(k) (5)

x _s(k)---k the platen actual displacement that control cycle is measured by linear inductosyn

x _m(k)---k the platen actual displacement that control cycle is measured by incremental optical-electricity encoder

ε (k)---the platen actual error of the corresponding platen displacement of k control cycle

Actual displacement error ε (k) in the formula (5) is the error amount of current servo period, be to realize real-time error compensation, will observe and predicts error in each sampling period, obtains the error pre-compensation value of next instruction point.Employing is easy to calculate in real time and is easy to the exponential weighting smoothing prediction.This Forecasting Methodology need not modeling, directly utilizes the data of gathering to predict that the recursion calculating formula of exponential weighting smoothing prediction is:

$\widehat{\mathrm{\ϵ}}(k+1)=\widehat{\mathrm{\ϵ}}\left(k\right)+w[\mathrm{\ϵ}\left(k\right)-\widehat{\mathrm{\ϵ}}\left(k\right)]---\left(6\right)$

---k+1 control cycle platen working control error prediction value

---k control cycle platen working control error prediction value

ε (k)---the platen actual error of the corresponding platen displacement of k control cycle

W---weight coefficient is often got 0＜w＜=0.3 in the engineering, to guarantee to obtain higher forecast precision.

8. in numerical control device, based on the method for the physical location control instruction that generates the machine coordinates axle after the compensation corresponding to the site error value information that generates in the rotating servo motor angular displacement instruction of NC code and top the 5th summary of the invention and the 6th summary of the invention.

The numerical control device of this invention, the agent structure of Position Control remains the Position Control mode of semiclosed loop, so both can give full play to the advantage of semiclosed loop Position Control mode, and can all adopt this reality of semiclosed loop Position Control at present most Digit Control Machine Tool again simultaneously.The displacement control instruction that generates in the numerical control device is actually the angular displacement instruction at servomotor, just when this displacement commands generates, the displacement error information that has also added simultaneously summary of the invention 6 and summary of the invention 7, obtain the actual displacement control instruction of machine coordinates axle, improve the position control accuracy of Digit Control Machine Tool reference axis with this.

$r={\mathrm{\Δ}}_{n}x\left(k\right)=[{\mathrm{\Δx}}_m\left(k\right)+\mathrm{\ω}{\×\mathrm{\ϵ}}_n\left(k\right)+(1-\mathrm{\ω})\×\widehat{\mathrm{\ϵ}}\left(k\right)]/\mathrm{\δ}---\left(7\right)$

Δ x _n(k)---the actual displacement control instruction of k control cycle machine coordinates axle

Δ x _m(k)---k control cycle is based on the platen straight-line displacement control instruction of rotating servo motor angular displacement

ε _n(k)---the platen theoretical error of the corresponding platen displacement of k control cycle

δ---the pulse equivalency of Digit Control Machine Tool control system

ω---platen theoretical error compensation weights, 0≤ω≤1

---k control cycle platen working control error prediction value

The actual displacement control instruction (SERVO CONTROL command value) of r---k control cycle machine coordinates axle

9. in numerical control device,, be the position control method of major control object with the servomotor based on the machine tool position control instruction that generates in the summary of the invention 8.

Include the displacement error information that content 4 of the present invention and summary of the invention 5 are generated in the Position Control instruction that numerical control device generates, and the control of numerical control device reality is to liking servomotor, the target of control is the position control accuracy of numerically controlled machine reference axis, therefore the semiclosed loop positioner structure of semiclosed loop positioner structure of the present invention and algorithm and routine and algorithm are compared and are had specific characteristics, and do not comprise the control information of content 6 of the present invention and summary of the invention 7 in the conventional semiclosed loop Position Control instruction.

The structure of the present invention and the course of work such as Fig. 1～shown in Figure 4 below describe in conjunction with figure apparatus of the present invention embodiment.

Fig. 1 is a Digit Control Machine Tool error-compensating apparatus composition diagram of the present invention, and this numerical control device adopts Industrial PC Computer 1 as main control computer, based on the RT-Linux real-time multi-task operating system.The hardware of numerical control device 2 is by inserting the Position Control card 3 in the PC and measure interface card 4 and form, and realizes control and error compensation to Digit Control Machine Tool by supporting control software.The effect of Position Control card 3 is that the control signal that numerical control device software calculates is changed, deliver on the servo-driver, finish position servo function to lathe, it also will obtain the signal of servomotor incremental optical-electricity encoder 7 from servo-driver simultaneously, offers numerical control device 2 and makes feedback information.The measurement interface card 4 of numerical control device 2 resolves the actual position information of the platen 7 that inductosyn post processor 6 is brought, and supplies numerical control device as the error compensation information source.The control signal that servo-driver 5 is brought the Position Control card 3 of numerical control device 2 is handled, and finishes the half-closed loop control to Digit Control Machine Tool.

Fig. 2 is rearmounted 6 structure and the fundamental diagram handled of inductosyn among Fig. 1, the signal that signal amplifying apparatus 13 in the inductosyn post processor 6 is brought the linear inductosyn in apparatus of the present invention 9 amplifies, handle through shaping and filter 14 then, send into signal adapter 15 and carry out the signal conversion.Signal adapter 15 is sent shaping and filter 14 and inductosyn reference signal generator 16 to come signal and is resolved, and generates and the Transistor-Transistor Logic level signal of incremental optical-electricity encoder output signal compatibility.This signal offers the measurement interface card 4 of numerical control device 2 of the present invention, carries out resolving of signal by measuring interface card 4, obtains the actual displacement of numerically controlled machine 10, supplies numerical control device as the error compensation information source.

Fig. 3 is the error compensation control calcspar of numerical control device 2 of the present invention, also is one of the core of apparatus of the present invention and characteristic.The lathe deviations of actual position computing unit 20 of the semiclosed loop position control 17 of numerical control device 2 by obtaining numerical control device 2 and the control information of the lathe theoretical position error calculation unit 21 of numerical control device 2, calculate the actual displacement error compensation value of numerical control device 2 at the numerically controlled machine 10 in this position servo cycle, the semiclosed loop feedback information that Position Control instruction r that this offset and numerical control device 2 are received and the servomotor encoder 7 Position Control card feedback input interface 18 by Position Control card 3 obtains carries out position servo by semiclosed loop position control 17 to be regulated, the adjusting calculated result is delivered to servo-driver 5 by the Position Control card output interface 19 of Position Control card 3 and is carried out the adjusting of speed and electric current, finish position servo control, also finish semiclosed loop Position Control simultaneously Digit Control Machine Tool to servomotor 8.The information that includes the control of lathe full cut-off ring in the adjusting information in this semiclosed loop Position Control process, promptly by error compensating method of the present invention, utilize the theoretical error information and the actual error information of numerically controlled machine 10 motion processes, kinematic error to platen 10 is carried out real-time dynamic compensation, improves the kinematic accuracy of numerically controlled machine 10.

The program flow chart of computer is seen Fig. 4.

By the present invention, can improve positioning accuracy and track following precision with the NC machine tool feed system of semiclosed loop Position Control.And, when digital control machine tool positioning error changes in time, renewal and correction that the error compensation amount of position error can be real-time.

Claims (2)

1, the error compensating method of Digit Control Machine Tool is characterized in that, it is a kind of based on the semiclosed loop Position Control, and Full Closed-loop Position is controlled to be the error compensating method of auxilliary two-position closed-loop control, and it is realized according to following steps based on the PC platform:

(1) deposit PC after the following parameter of initialization in:

Platen theoretical error compensation weights ω: 0≤ω≤0.3;

The pulse equivalency δ of Digit Control Machine Tool control system;

The theoretical departure of platen is measured frequency n, chooses n between 10～20;

Platen departure measurement point number j generally determines measurement point number j with measurement point spacing 10～20mm;

The i time platen displacement control instruction value x based on the rotating servo motor angular displacement of j measurement point (i, j);

K control cycle is based on the platen straight-line displacement control instruction value Δ x of rotating servo motor angular displacement _m(k), the initial value ε (k of error precompensation ₀);

(2) PC calculates according to following formula, the average Δ (j) of the actual displacement error of i measurement point machine coordinates axle:

$\mathrm{\Δ}\left(j\right)=\frac{1}{n}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}((x_s(i,j)-x(i,j))-(x_m(i,j)-x(i,j)))$

Wherein,

x _s(i, j): j the platen physical location that measurement point is obtained by linear induction synchro measure on the platen for the i time;

x _m(i, j): the physical location of the platen that j measurement point the i time measured by incremental optical-electricity encoder on the rotating servo motor;

X (i, j): the i time control instruction value of j measurement point based on the platen of rotating servo motor angular displacement;

(3) Δ (j) value is deposited in the PC, whether repeating step (2) judges circulation measurement number of times greater than n again, if greater than n, n is that the theoretical departure of platen is measured number of times, then carries out following steps;

(4) PC is calculated as follows the theoretical displacement control instruction Δ x of k control cycle machine coordinates axle _s(k):

$\mathrm{\Δ}{x}_s\left(k\right)=\mathrm{\Δ}{x}_m\left(k\right)+\frac{\mathrm{\Δ}(j+1)-\mathrm{\Δ}\left(j\right)}{x(j+1)-x\left(j\right)}\mathrm{\Δ}{x}_m\left(k\right)$

Wherein,

Δ x _m(k): k control cycle is based on the platen straight-line displacement control instruction of rotating servo motor angular displacement;

Δ (j+1): the error of the actual value of j+1 measurement point machine coordinates axle;

Δ (j): the error of the actual value of j measurement point machine coordinates axle;

X (j+1): the physical location of j+1 measurement point lathe coordinate system;

X (j): the physical location of j measurement point lathe coordinate system;

(5) PC is calculated as follows the theoretical error ε of the corresponding platen displacement of k control cycle _n(k):

ε _n(k)＝Δx _m(k)-Δx _s(k)

(6) PC is calculated as follows the actual displacement control instruction Δ x (k) of the machine coordinates axle of k control cycle:

Δx(k)＝(Δx _m(k)+ω×ε _n(k))/δ

(7) PC is calculated as follows the actual error ε (k) of the corresponding platen displacement of k control cycle:

ε(k)＝x _s(k)+x _m(k)

Wherein,

Δ x _s(k): k the platen actual displacement that control cycle is measured by linear inductosyn,

Δ x _m(k): k the platen actual displacement that the control cycle rotating servo motor measures from last incremental optical-electricity encoder,

(8) PC is calculated as follows the corresponding platen working control error pre-compensation value of k+1 control cycle

$\widehat{\mathrm{\ϵ}}(k+1)=\widehat{\mathrm{\ϵ}}\left(k\right)+w[\mathrm{\ϵ}\left(k\right)-\widehat{\mathrm{\ϵ}}\left(k\right)]$

Wherein,

The platen working control error compensation value of k control cycle;

ε (k): the actual error of the corresponding platen displacement of k control cycle;

(9) to be calculated as follows the machine tool position control instruction of k control cycle be SERVO CONTROL command value r to PC:

$r={\mathrm{\Δ}}_{n}x\left(k\right)=[{\mathrm{\Δx}}_m\left(k\right)+\mathrm{\ω}\×{\mathrm{\ϵ}}_n\left(k\right)+(1-\mathrm{\ω})\×\widehat{\mathrm{\ϵ}}\left(k\right)]/\mathrm{\δ}---.$

2, the Digit Control Machine Tool error compensation system is characterized in that, it contains:

Industrial PC Computer, the servo-driver of embedded position control card, measurement interface card, Industrial PC Computer and servo-driver are interconnected with two interfaces of above-mentioned Position Control card respectively, and Industrial PC Computer links to each other with measurement interface output again;

The inductosyn post processing circuitry, it is connected in series by signal amplification circuit, shaping and filter circuit, signaling conversion circuit successively, and the output of signaling conversion circuit links to each other with above-mentioned measurement interface card input;

Incremental optical-electricity encoder, they link to each other with servo-driver is coaxial, and their outputs link to each other with above-mentioned servo-driver input;

Servomotor, it links to each other through leading screw-nut body with platen; Its input links to each other with above-mentioned servo-driver output;

Inductosyn, it is fixed on the platen, and its signal output part links to each other with signal amplification circuit input in the above-mentioned inductosyn treatment circuit.

Images