Evaluation of grasp capability of a gripper driven by optimal spherical mechanism

Abstract

This paper evaluates grasp capability of a new three-fingered gripper driven by optimal spherical four-link mechanism design. The optimal mechanism provided a trajectory that is approximately a grate circle arc. Therefore, independently driven three fingers of prototype either surround or compress an object with only one degree of freedom for each finger. Thus, the gripper provided both force-closure and form-closure grasp. The force variation of fingertip along the trajectory was presented comparative to calculations for 32 static cases of grasped cylindrical objects. Regression analysis between calculated values and measured data showed %99 reliability. The mechanism provided contact force between 155-215 N along the trajectory. The lifting load capability of the gripper without slip on ceramic surface with low friction was measured by using a commercial single side rubber band on the fingertips. 9 +/- 0.05 kg lift capability for cylindrical objects without slip was observed. The prototype was tested for 11 grasp operations and 8 objects with various geometry. Each of the test showed success in the first grasp trial.