PASA Hand: A Novel Parallel and Self-Adaptive Underactuated Hand with Gear-Link Mechanisms

This paper proposes a novel underactuated robotic finger, called the PASA finger, which can perform parallel and self-adaptive (PASA) hybrid grasping modes. A PASA hand is developed with three PASA fingers and 8 degrees of freedom (DOFs). Each finger in the PASA hand has two joints, mainly consists of an actuator, an accelerative gear system, a spring, a parallel four-link mechanism and a mechanical limit. Two extra actuators in the palm of the PASA hand independently control the base rotation of two fingers. The PASA hand executes multiple grasping modes based on the dimensions, shapes and positions of objects: (1) a parallel pinching (PA) grasp for precision grasp like industrial grippers; (2) a self-adaptive (SA) enveloping grasp for power grasp like traditional self-adaptive hands; (3) a parallel and self-adaptive (PASA) grasping mode for hybrid grasp like human hands. The switch through different grasping modes is natural without any sensors and control. Kinematics and statics show the distribution of contact forces and the switch condition of PA, SA, and PASA grasping modes. Experimental results show the high stability of the grasps and the versatility of the PASA hand. The PASA hand has a wide range of applications.