A Review on Robust Control of Robot Manipulators for Future Manufacturing

Robots are used for many manufacturing tasks, and its prevalence in manufacturing is ever-increasing. Robots in future manufacturing are expected to be valuable and essential tools. It is difficult to control a robot to achieve assigned tasks because of the nonlinear time-varying coupled multi-input multi-output dynamics, nonlinear joint friction being difficult to estimate and compensate for, and variations in payload and in environmental dynamics. Further, from the manufacturing engineers’ point of view, the controller needs to be simple and intuitive to understand and implement in practice. One such controller is Time Delay Control, which has been used for more than three decades with many advances. The time-delay estimation allows us to estimate the unknown/uncertain robot dynamics and disturbances by just using the most recent past control torque and acceleration, alleviating the need to identify robot dynamics and/or its parameters for the design of the controller. Time Delay Control can be implemented in industrial controllers allowing only proportional-integral-derivative control thanks to the gain relationship between Time Delay Control and proportional-integral-derivative control; has built-in first-order low-pass filter reducing noise; can be equipped with a simple anti-windup scheme for increasing its stability. A brief comparison of Time Delay Control and Disturbance Observer is also provided for readers who are interested in various robust control. With the introduction and review of the Time Delay Control for a robot, it is expected that the readers’ understanding of this robust control is increased and the use of the Time Delay Control in manufacturing becomes prevalent.