A method of eliminating contour error in NC machin

2022-08-06
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A method to eliminate contour error in NC machining

our factory has reformed a C6163 ordinary lathe with fanuc-0t NC system. When machining the workpiece shown in Figure 1, it is found that r10mm arc produces contour error. Before the experiment, the output control of the friction times required by the experimental specifications or set by the operator was piecemeal eliminated other reasons for the contour error. It was analyzed that it was caused by the lag of the electrical system. Fig. 1 and Fig. 2 show the trajectory error during circle cutting. Figure 2 contour (shape) error caused by radial lag of servo system during circle machining Δ R1 (unit: mm) is divided by Δ R1, profile error caused by deceleration after two axis interpolation Δ R2。 Δ R= Δ R1+ Δ R2 error calculation: when machining R10 arc, the cutting parameter s=100r/min; F=1mm/min, position gain 1/40, then figure 3 is the block diagram of servo system with feedforward function. Figure 3

vff - feedforward coefficient of speed loop α— Feedforward coefficient due to increase of feedforward control term α, Multiply the position error of the system by a factor (1- α), That is,

after the feedforward is added, the contour (shape) error caused by the radial hysteresis of the servo system except graphene during circle machining is assumed α When 0.8 is taken, Δ R1 will be reduced to 36% of the original error. Therefore, the feedforward setting in the phase error compression function of the application system can reduce the contour error

through the above analysis, when the feedforward is increased, the shape error caused by the lag of the servo system will be caused Δ R1 decrease, theoretically α= 1. The shape error should be 0. But because the torque of the motor is limited, α Cannot take 1, and cannot take too large, otherwise it will cause Δ R2 increase. Therefore, the parameters must be calculated and selected. The adjustment method is as follows

(1) set parameters to make PI control and feedforward function effective

set no.1808 parameter Pien (B3) =1

no.1833 parameter feed (B1) =1

(2) set feedforward coefficient No. 1961, take α= 0.8

(3) theoretical analysis of the feedforward coefficient of the speed loop of the set speed loop feedforward system α When taking 0.8, the shape error Δ R1 (mm) will be reduced to 36% of the original value. Feed speed f=1mm/min. R=10mm。 Position gain 1/40. At present, according to the actual inspection, the shape error is basically eliminated

the above is a basic function of the application system in the actual debugging to reduce the contour error during machining. To further reduce the contour error, FANUC system has several function settings that can be applied. ■ author unit: Guo Qingqi (Qiqihar No. 1 machine tool plant)

author profile: Guo Qingqi, design office of Qiqihar No. 1 machine tool plant, postal code: 161005 put improving performance and reducing cost in the first place reference: [1] chief editor of chenboshi Automatic control system Beijing: China Machine Press, 1981

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