A planar geometric design approach for a large grasp range in underactuated hands

The performance of an underactuated hand is mainly determined by its mechanical design. However, the effect of the dimensions of the phalanges and palm and the torques applied to the phalanges by the actuation mechanism to the range of objects that can be successfully grasped is not known. The objective of this paper is to elaborate a method to dimension the main design parameters such that the hand grasps the desired range of objects. This method consists of three steps that calculate (1) boundary conditions to the length of the phalanges and the palm width such that the required object range is enveloped by the fingers; (2) boundary conditions to the torques that have to be applied to the phalanges to achieve equilibrium of the fingers and objects; (3) optimal dimensions of the phalanges, palm and actuation mechanism. It is concluded that the design steps – sustained by analytical equations and graphs to calculate and visualize the relation between the design parameters and the performance – constitute an effective method to design underactuated hands that grasp a large range of object sizes.