Optimal Whole Body Trajectory Planning for Mobile Manipulators in Planetary Exploration and Construction

Space robotics poses unique challenges arising from the limitation of energy and computational resources, and the complexity of the environment and employed platforms. At the control center, offline motion planning is fundamental in the computation of optimized trajectories accounting for the system's constraints. Smooth movements, collision and forbidden areas avoidance, target visibility and energy consumption are all important factors to consider to be able to generate feasible and optimal plans. When mobile manipulators (terrestrial, aerial) are employed, the base and the arm movements are often separately planned, ultimately resulting in sub-optimal solutions. We propose an Optimal Whole Body Planner (OptiWB) based on Discrete Dynamic Programming (DDP) and optimal interpolation. Kinematic redundancy is exploited for collision and forbidden areas avoidance, and to improve target illumination and visibility from onboard cameras. The planner, implemented in ROS (Robot Operating System), interfaces 3DROCS, a mission planner used in several programs of the European Space Agency (ESA) to support planetary exploration surface missions and part of the ExoMars Rover's planning software. The proposed approach is exercised on a simplified version of the Analog-1 Interact rover by ESA, a 7-DOFs robotic arm mounted on a four wheels non-holonomic platform.

Planning of efficient trajectories in robotized assembly of aerostructures exploiting kinematic redundancy

Aerospace production volumes have increased over time and robotic solutions have been progressively introduced in the aeronautic assembly lines to achieve high-quality standards, high production rates, flexibility and cost reduction. Robotic workcells are sometimes characterized by robots mounted on slides to increase the robot workspace. The slide introduces an additional degree of freedom, making the system kinematically redundant, but this feature is rarely used to enhance performances. The paper proposes a new concept in trajectory planning, that exploits the redundancy to satisfy additional requirements. A dynamic programming technique is adopted, which computes optimized trajectories, minimizing or maximizing the performance indices of interest. The use case is defined on the LABOR (Lean robotized AssemBly and cOntrol of composite aeRostructures) project which adopts two cooperating six-axis robots mounted on linear axes to perform assembly operations on fuselage panels. Considering the needs of this workcell, unnecessary robot movements are minimized to increase safety, the mechanical stiffness is maximized to increase stability during the drilling operations, collisions are avoided, while joint limits and the available planning time are respected. Experiments are performed in a simulation environment, where the optimal trajectories are executed, highlighting the resulting performances and improvements with respect to non-optimized solutions.