Reality-guided virtual assembly for contact-prohibited stepped shaft-in-hole task

Abstract

Contact-prohibited stepped Shaft in Hole (SSiH) task widely exists in structural docking mechanisms of aerospace equipment such as rockets or airplanes. However, the tight clearance, irregular deformation, large scale/volume/weight, and sensitivity to contacts, make it difficult to automate the assembly process. The answers to the questions of whether it can be assembled or not and what is the optimal installation posture are vital to the task. To address these problems, a reality-guided virtual assembly method is proposed to assess the clearance of the mating surfaces and ascertain their assembly feasibility before real installation. Firstly, the method takes 3D point clouds scanned from real parts as input and registers the shaft and hole point clouds to their corresponding CAD models, then a geometric-consistent registration algorithm is proposed to precisely align the shaft/hole point clouds. Secondly, by analyzing the geometric constraints, the original 6 DOF posture optimization problem is reduced to a 2 DOF one. To increase the calculation efficiency, a point cloud polarization and repair algorithm is proposed to convert the 3D stepped shaft model into a series of 2D polar models. The clearance/interference can be calculated by subtracting the polar radius. Finally, a two-staged grid search method is used to find the optimal installation posture by maximizing the minimum gap across all the shaft segments. Simulation and experimentation are performed to verify the effectiveness and reliability of this algorithm.