Multiple mode control of a compact wrist with application to door opening

This paper presents the multiple mode control system of a compact wrist, which can work in active mode with position or torque control, or passive mode with wrist-environment interactive force compensation. Passive mode is realized without using mechanical solutions such as a clutch, which not only saves weight and volume of the wrist, but also avoids losing track of the joints’ position while switching from passive mode to active mode. The objective is to make the wrist suitable for dexterous manipulation in unstructured environments, such as door opening. A robust adaptive controller is developed for tracking control of the wrist in active mode; and a new interactive force compensation technique is proposed based on force sensor measurement, to enable passive working mode of the compact wrist. A prototype wrist has been developed and experiments have been conducted to validate the proposed design and algorithms.