An Obstacle Avoidance Trajectory Planning Scheme for Space ManipulatorsBased on Genetic Algorithm

Meeting a series of special needs of space manipulator systems, a trajectory planning method for space manipulator is put forward. It is assumed that there is an ideal trajectory in joint space, which can be described by two sections of high-order spline curve and satisfy all kinetic characteristics of space manipulator. Parameters of the connection point between the two spline trajectories can influence the distorted shape of the two trajectories in space. Consequently, the manipulator moves in accordance with the spline trajectories and in the same time avoids all the obstacles. Firstly, sectionalized functions of ideal trajectory are established. Unknown parameters in the functions are described using the parameters about the connection point of which the unknown parameters are extracted to be calculated. Thus the trajectory planning problem is transformed into a multi-objective optimization problem. Secondly, genetic algorithm (GA) is adopted to solve the problem. Based on the analysis on space manipulator control requirements and descriptions of obstacles in Cartesian space, a fitness function based on GA is defined by weighting coefficient method, with respect to the trajectory length of the end-effector in Cartesian space, the angles in joint space and the maximum torque during movement, the total movement time and the cases of interferences and collisions. At last, an ideal collision-free trajectory with short length and ideal movement time in the joint space is planned by using GA, and its dynamic features satisfies margin requirements. Additionally, the method proposed has wide expansibility. After decomposing trajectories and calculating connection points for many times, the manipulator can avoid obstacles in very complex circumstances. Simulation is accomplished on space manipulator simulation platform established by C language. And results show that the method is stable and effective, and the trajectory generated satisfies the special performance requirements of space manipulator.