Adjustable time constant control and method system for a servomotor

A method for determining an adjustable time constant for a servomotor, comprising the steps of:

• a) determining whether the servomotor will reach a commanded velocity V.sub.t, based on a movement distance X of the servomotor;
• b) setting the commanded velocity V.sub.t as a set velocity V if said step (a) determines that the servomotor will reach the commanded velocity V.sub.t ;
• c) determining a reaching velocity V.sub.u `(X.multidot.V.sub.max /.tau..sub.0).sup.1/2, V.sub.max being a maximum velocity of the servomotor and .tau..sub.0 being a time constant corresponding to the maximum velocity V.sub.max, if said step (a) determines that the servomotor will not reach the commanded velocity V.sub.t ;
• d) setting the reaching velocity V.sub.u as the set velocity V if said step (a) determines that the servomotor will not reach the commanded velocity V.sub.t ;
• e) determining a maximum torque T.sub.max based on a predetermined correspondence between velocity and torque of the servomotor, using the set velocity V;
• f) determining a current static load torque Tw.sub.n based on a current angular position P.sub.n of the servomotor;
• g) determining a current accelerating torque Ta.sub.n by subtracting the current static load torque Tw.sub.n from the maximum torque T.sub.max ;
• h) determining a current inertia I.sub.n of the servomotor based on the current angular position P.sub.n ;
• i) determining a current acceleration a.sub.n by dividing the current accelerating torque Ta.sub.n by the current inertia I.sub.n ;
• j) determining a target static load torque Tw.sub.n+1 based on a target angular position P.sub.n+1 of the servomotor;
• k) determining a target accelerating torque Ta.sub.n+1 by subtracting the target static load torque Tw.sub.n+1 from the maximum torque T.sub.max ;
• l) determining a target inertia I.sub.n+1 of the servomotor based on the target angular position P.sub.n+1 ;
• m) determining a target acceleration a.sub.n+1 by dividing the target accelerating torque Ta.sub.n+1 by the target inertia I.sub.n+1 ;
• n) determining a smallest one of the current acceleration a.sub.n and the target acceleration a.sub.n+1 ;
• o) determining the adjustable time constant by dividing the smallest one of the current acceleration a.sub.n and the target acceleration a.sub.n+1, by the set velocity V;
• and
• p) controlling the servomotor based on the adjustable time constant for the servomotor determined in said step (o).