Yang Wenyu

Contact Force Modeling and Feasible Grasp Force Analysis of Power Grasp

Contact force modeling and grasp analysis methods of hyperstatic grasps with over-constraints are investigated,in order to obtain feasible grasp force and load condition in the capability design of manipulator and grip system. A general model to solve the constraint force in a grasp with friction contact is developed on the basis of Lagrange multiplier factor method and contact dynamic constraint condition. The indetermination of contact constraints in hyperstatic grasp is discussed. The feasible solution to constraint force of friction contact is characterized by an active internal force subspace,the basis wrenches of internal force subspace of object grasped is identified by double reciprocal of a pair of constraint force set at each two contacts. An explicit calculation of feasible contact force set is enabled under dynamic equilibrium condition. A method to solve the feasible grasp force and outside force balanced with dynamic load is performed.

Feedrate optimization of complex surfacemilling based on predictive model of cutting force

In terms of the low machining efficiency and bad surface quality using constant feedrate in complex surface milling, a feedrate optimization method is proposed based on cutting force model. Firstly, by the analysis and calculation of the tool path, the geometry of complex surface and tool, tool-workpiece engagement zone and uncut chip thickness, a cutting force model is derived in multi-axis maching of complex surface and the mapping relation is obtained between feedrate and cutting force. Then the objective function about the absolute value of difference between the reference cutting force and the maximum one calculated in each tool position is put forward. Then the method adopts Newton-Raphson iteration algorithm to alter the feedrate in the original tool path file, thus ensures the constant cutting forces and enhance steadiness of machining process. The experiment is carried out about model propeller, the results show that the proposed optimization method ensures the machining time of the blade reduced by more than 25%, the surface residual stresses and micro-hardness machining accuracy to be increased, which has a clear effect on increasing the machining efficiency and improving the machining surface quality of the blade. This thus validates the effectiveness of the proposed optimization method.

Projection on convex set and its application in testing force closure properties of robotic grasping

Force closure is one of the most fundamental properties for a multicontact robotic system to immobilize an object. Based on the projection of a point on a convex set, this paper presents an algorithm to compute the minimum distance from a point to a convex set in n-dimensional space. Further study of this projection algorithm, we found it can be used to test for closure properties of robotic grasping. Comparing with previous study, this method provides a clear physical interpretation and can be implemented very easily in practice. The superior efficiency and effectiveness of this algorithm are demonstrated by numerical examples.