Autonomous alignment of peg and hole by force/torque measurement for robotic assembly

In the past years, many methods have been developed for robotic peg-hole-insertion to automate the assembly process. However, many of them are based on the assumption that the peg and hole are well aligned before insertion starts. In practice, if there is a large pose(position/orientation) misalignment, the peg and hole may suffer from a three-point contact condition where the traditional assembly methods cannot work. To deal with this problem, this paper proposes an autonomous alignment method by force/torque measurement before insertion phase. A three-point contact model is built up and the pose misalignment between the peg and hole is estimated by force and geometric analysis. With the estimated values, the robot can autonomously correct the misalignment before applying traditional assembly methods to perform insertions. A series of experiments on a FANUC industrial robot and a H7h7 tolerance peg-hole testbed validate the effectiveness of the proposed method. Experimental results show that the robot is able to perform peg-hole-insertion from three-point contact conditions with 96% success rate.