On iterative learning control algorithm for industrial robots and CNC machine tools

A PID-type iterative learning controller is proposed for precise tracking control of industrial robots and CNC machine tools performing repetitive tasks. The convergence of the output error by the proposed PID-type learning controller is guaranteed under a certain condition even when system parameters are not known exactly and periodic disturbances exist. In actual implementation, the repeated execution of the proposed PID-type learning controller reduces the distance difference between the desired trajectory and the actual machined one, which is one of the most significant factors in evaluation of the control performance of industrial robots or CNC machine tools, in performing repetitive tasks. To investigate the performance, the proposed PID-type learning control algorithm is executed on the CNC system with a 32 bit CPU (Intel80486) and a 32 bit floating point digital signal processor (DSP) (TMS320C30) as the main processors. The experimental results demonstrate that the proposed PID-type learning controller can improve machining accuracy when the CNC machine tool machines circles on aluminum workpieces