Precise motion control of SCARA robot using combination of PWM signals and visual information

This paper proposes a pulse-width modulation method combined with visual information (VPWN) for precise motion control of a SCARA robot. In general, friction effects on joints are considerable and difficult problem for precise motion control of robotic arms. Various methods to overcome friction effects have been proposed, however it is still difficult to describe precise friction models and compensate the friction effects completely. This paper focuses on the minimum unit of angle on each joint which exceeds the static friction effects. We design the unit signal based on several preliminary experiments. In addition, based on the unit signal to generate minimum behavior, the control input like pulse-width modulation method is combined with visual information from cameras. VPWM changes the pulse-width based on the minimum inputs according to the deviation between current and desired position. In addition, the visual feedback is utilized to upgrade the performance of convergence of motion. In this paper, the new control method for SCARA robots is first proposed. The minimum pulse unit is defined by some preliminary experiments. Then, the proposed method using visual feedback and the pulse unit is described. Finally, two experiments to exemplify the usefulness of the method are conducted.