A. Experimental result of two arms locking and unlocking
We demonstrate the control of the robot arm to change its configuration from grasping mode to supporting mode. Both robot arms are closed and locked to form a firm handrail for walk assistance. In the transforming, dual arms first move to the buckle buffer point as shown in Fig. 9 (a).Then by tuning the joints to let buckle mechanism of two arms locked and combined, as shown in Fig. 9 (b)-(c). The two arms are locked by the buckle mechanism and configured as a handrail. To return to the grasping mode, the robot releases the locked buckle as shown in Fig.9 (d)-(f). A video clip of this experiment can be found in [12].