Comparison of the Linear Position Control Algorithms for Direct Servo Drives
Direct servo drives are used in industrial installations that place high demands for the motion dynamic and precision characteristics. Proper control system design is the key factor in achieving the required servo drive accuracy and dynamic performance characteristics. Two basic linear control structures for controlling a precision servo drive's position are considered: the structure with a PID position controller and the structure with a P position controller and a nested speed loop with a PI controller. The structures were analyzed with taking into account the possibility of supplementing them with filters, observers, and predictors. The results of simulation and experiment carried out on the basis of a rotary precision servo drive have shown that the control structures are able to ensure commensurable motion accuracy provided that that the system parameters are known exactly. To this end, equations for recalculating the tunings from one structure to another are derived for analog and digital systems. With variable system parameters, the structure with a PID position controller ensures high tracking accuracy and requires the minimal computation effort, a circumstance that makes its use preferable in high-precision servo drive control systems. It is shown that commensurable performance characteristics in a subordinated control system can be achieved by using a Smith predictor.