Trajectory Planning of Two Cooperative Mobile Manipulators under Closed-chain and Differential Constraints

In this paper, we consider a new method for trajectory planning of two mobile manipulators for cooperative transportation of a rigid body. The method consists of constructing a graph on a portion of the configuration space that satisfies collision and closure constraints and searching the graph for the shortest possible path using an optimal graph search algorithm. Then, a sequence of time-optimal trajectories for movement between the consecutive points of the path is calculated. This approach allows for geometric constraints, such as joint limits and closed-chain constraints, along with differential constraints, such as nonholonomic velocity constraints and acceleration limits to be incorporated into the planning scheme. We also propose a heuristic method to keep the system from colliding with moving obstacles by adjusting a time scaling factor based on linear estimation of obstacles’ position. Simulation results illustrate the effectiveness of the proposed method.