Link-Based Performance Optimization of Spatial Mechanisms

In the design of spatial linkages, the finite-position kinematics is fully specified by the position of the joints in space. However, most of the tasks have additional requirements regarding motion smoothness, obstacle avoidance, force transmission or physical dimensions. Many of these additional performance requirements are independent of the finite-position kinematic task and can be solved using link optimization for an already defined set of joints.In this paper we develop a methodology to optimize spatial mechanisms after a first kinematic synthesis stage, by considering the links as anchored to sliding points of a given set of joint axes, which have to meet constraints including link dimension, restricted region of operation and force transmission. The optimization is performed using a hybrid algorithm, including a genetic algorithm (GA) and a gradient-based minimization solver.The methodology has been applied to a spatial CRR-RRR, one-degree-of-freedom closed linkage. The additional requirements in this example are used to control the position and size of the mechanism, and for reducing friction loads at the joints.The combination of the kinematic synthesis together with the link optimization developed in this paper allows interactive monitoring and control of the objectives and constraints, to yield practical solutions for realistic spatial mechanism design problems.Copyright © 2013 by ASME