Robotic Peg-Hole Insertion Operations using a Six-Component Force Sensor

Peg-hole insertion is a widely used industrial robot process. For precise insertion it is common to use force sensors to obtain the deviation between the peg and the hole. In this paper, several examples of six-component force sensors, which are designed to measure the forces and torques in all directions, are reviewed. The problem of how to obtain the deviation between the peg and the hole from the measurement of the forces and the torques exerted on the sensors is then discussed. It is shown that the angle between the peg and the hole and the roughness of the contact surfaces (the end surface of the peg and the surface surrounding the hole) would significantly influence the identification of deviation, no matter how small they are. Two measures to address these phenomena are introduced. A novel strategy of the high-precision chamferless peg-hole insertion with a wrist force sensor is presented and verified experimentally. This strategy is constructed: to obtain the relationship between the peg and hole from the force sensor signal when angular misalignment and the defects of the contact surfaces are present to reduce the angular and lateral errors and to achieve precise chamferless robotic peg-hole insertion. In this paper, it is shown that the insertion can be effected with a reasonably large range of initial conditions. The principle is to move and rotate the peg from an area having many geometric uncertainties to a new area, where the deviation of the peg and hole can be obtained.