NA-OR:A path optimization method for manipulators via node attraction and obstacle repulsion

This paper is concerned with the issue of path optimization for manipulators in multi-obstacle environments.Aimed at overcoming the deficiencies of the sampling-based path planning algorithm with high path curvature and low safety margin,a path optimization method,named NA-OR,is proposed for manipulators,where the NA(node attraction)and OR(obstacle repulsion)functions are developed to refine the path by iterations.In the iterations of path optimization,the node attraction function is designed to pull the path nodes toward the center of their neighbor nodes,thereby reducing the path curvature and improving the smoothness.Also,the obstacle repulsion function is developed to push the path nodes out of the potentially unsafe region by generating a repulsive torque on the path nodes,thus improving the safety margin of the motion.By introducing the effect of NAOR,the optimized path has a significant improvement in path curvature and safety margin compared with the initial path planned by Bi-RRT,which meaningfully enhances the operation ability of manipulators for the applications that give a strong emphasis on security.Experimental results on a 6-DOF manipulator in 4 scenarios demonstrate the effectiveness and superiority of the proposed method in terms of the path cost,safety margin,and path smoothness.

Cutting force prediction for circular end milling process

A deduced cutting force prediction model for circular end milling process is presented in this paper. Traditional researches on cutting force model usually focus on linear milling process which does not meet other cutting conditions, especially for circular milling process. This paper presents an improved cutting force model for circular end milling process based on the typical linear milling force model. The curvature effects of tool path on chip thickness as well as entry and exit angles are analyzed, and the cutting force model of linear milling process is then corrected to fit circular end milling processes. Instantaneous cutting forces during circular end milling process are predicted according to the proposed model. The deduced cutting force model can be used for both linear and circular end milling processes. Finally, circular end milling experiments with constant and variable radial depth were carried out to verify the availability of the proposed method. Experiment results show that measured results and simulated results corresponds well with each other.