Grasp characteristics of an underactuated robot hand

An underactuated robot hand with three fingers has been developed to achieve planar pinch grasp and enveloping grasp. The grasp characteristics of the underactuated hand are studied. In planar pinch grasp, which depends on two or three distal phalanges to work together, the key factors to influence grasp stability are investigated, and the sufficient and necessary conditions for stable grasp are proposed with force-closure conception. The allowed maximum external wrench is calculated when the grasp can´t meet force-closure condition. In enveloping grasp, the phalanges driven by an actuator can´t be controlled independently and have local motion lead to unstable grasp. Based on the definition of grasp configuration and driving force, the relationship between grasp configuration and external wrench is studied. The transition difficulty of grasp configuration is employed to evaluate the stability of enveloping grasp. Finally, some cases of stimulation are given to validate the evaluation.