Full digital joint motion controller for industrial robot and CNC machine tool

In this paper, a joint motion controller which drives the axes of motion of an industrial robot or a CNC machine tool by a digital control method is discussed. It is basically designed to provide acceleration/deceleration before interpolation and simultaneous control capability of current, speed, and position for two permanent magnet AC servomotors. The current controller consists of a nonlinear feedback controller compensating back EMF, a phase lead compensator, and a PI controller with gains varying according to motor speed. The final output of the current control algorithm is pulsewidth modulated through comparison with a digital triangular carrier signal to produce a PWM waveform. To obtain accurate estimation of the motor speed, a well-known speed observer is utilized in the speed control loop. Furthermore, a repetitive controller is applied in order to compensate errors in the position transducer. Acceleration/deceleration and interpolation techniques developed from the view point of enhancing machining accuracy are included in order to eliminate jerks or vibration at the transient state movement in the industrial robot and the CNC machine tool. To investigate the control performance, the proposed full digital joint motion controller based on digital signal processor TMS320C31 is applied to a milling center consisting of three axes and a spindle. The experimental results show that it can be effectively used in controlling industrial robots and CNC machine tools