Posture-Constrained Workspace Analysis and Flow-Constrained Actuator-Space Time–Jerk Trajectory Planning for Heavy-Duty Hydraulic Demolition Robots

Abstract

During high-speed multi-joint coordination, the nonlinear joint-to-cylinder mapping may increase the velocity and jerk peaks of the hydraulic cylinders, while simultaneous multi-cylinder motion may cause flow-peak superposition and increase the risk of exceeding the pump-flow limit. Addressing the limitations of traditional joint-space trajectory planning, which struggles to balance actuator-space smoothness, nonlinear inverse kinematics robustness, and multi-cylinder total-flow constraints, this paper proposes a multi-objective trajectory-planning method in the hydraulic-cylinder actuator space. First, a kinematic model is constructed based on the modified Denavit–Hartenberg method and hydraulic-cylinder closed-loop cosine mapping to evaluate effective moment arms and transmission sensitivity. Subsequently, a method combining Monte Carlo global search and Levenberg–Marquardt local iteration is adopted to solve inverse kinematics without explicitly computing the Moore–Penrose pseudoinverse of the Jacobian. On this basis, analytic quintic splines incorporating asymmetric perturbation terms are constructed, and a non-dominated sorting genetic algorithm II bi-objective optimization model for minimizing the motion time and the maximum absolute jerk in the actuator space is established, incorporating the total-flow hard constraint. Simulation results demonstrate that the motion time of the compromise solution is 7.71 s, the maximum absolute jerk in the actuator space is 22.94 mm/s3, and the total flow throughout the process is lower than 105 L/min. This method keeps the planned total-flow demand within the pump-flow capacity and reduces the risk that the planned actuator speeds cannot be maintained because of insufficient flow supply, providing a planning basis for the stable operation of heavy-duty hydraulic demolition robots.