6781097312

Tracking errors decreasing in CNC system of machinę tools 87

and velocity feedforward value. The torque reference value is the sum of the velocity loop output and torque feedforward value.

Fig. 1. Błock diagram of servo system structure with command feedforward control

We can assume C_T(s) -1 for perfect current control. For motion unit given by

first order equation: G„(s) = -—-—the transfer function from the torque input

^p Js + D

T* and servo-drive position is expressed as:

G(s) =

T‘(s)

1

J.i² + Ds '

(D

The perfect position tracking can be achieved if:

(2)

FF_V (s) = Js² +Ds.

Thus the output from velocity FF_v(s) feedforward controller is:

T_ff(s) = (Js¹+Ds)8*(s),

T_FAl)=j^M_+DdlM

dr

dl

(3)