Development of Efficient Strategy for Square Peg-in-Hole Assembly Task

Abstract

In this paper, we present a dexterous gripper with an angle measurement system and efficient strategy for estimating a hole position from reaction force measurements in a square peg-in-hole task. The contact conditions between a square peg and hole have been analyzed to show that the redundancy in reaction force-moment relation around hole originated from contact conditions. In order to remove such redundancy in contact conditions, an angular error between a square peg and hole is first corrected with the help of the angle measurement system. Then, the positional error between them is identified by applying two clustering algorithms (K means algorithm and Gaussian Mixture Model (GMM) algorithm) to the reaction moment data obtained by the XY search. For grasping and manipulating a peg precisely, a 4-DOF dexterous gripper is designed, which consists of two fingers equipped with 6-axis force/torque sensor at fingertip. The extensive experiments using the proposed gripper with the angle measurement system demonstrate that during the square peg-in-hole task, the proposed strategy ensures the tact time of around 5 sec with the estimation accuracy of less than 0.35 mm and the deviation of less than 0.44 mm, respectively.