Bridging Discrete Planning and Continuous Execution for Redundant Robot

TL;DR

This paper introduces a framework that enhances the transition from discrete voxel-grid path planning to smooth, stable continuous execution on 7-DoF robotic arms, significantly improving success rates and motion quality.

Contribution

It presents a novel bridging method combining step-normalized actions and a task-priority inverse kinematics layer to improve execution stability and efficiency.

Findings

Planning success in dense environments increased from 0.58 to 1.00.

Path length was reduced from 1.53 m to 1.10 m.

Peak joint accelerations decreased by over an order of magnitude.

Abstract

Voxel-grid reinforcement learning is widely adopted for path planning in redundant manipulators due to its simplicity and reproducibility. However, direct execution through point-wise numerical inverse kinematics on 7-DoF arms often yields step-size jitter, abrupt joint transitions, and instability near singular configurations. This work proposes a bridging framework between discrete planning and continuous execution without modifying the discrete planner itself. On the planning side, step-normalized 26-neighbor Cartesian actions and a geometric tie-breaking mechanism are introduced to suppress unnecessary turns and eliminate step-size oscillations. On the execution side, a task-priority damped least-squares (TP-DLS) inverse kinematics layer is implemented. This layer treats end-effector position as a primary task, while posture and joint centering are handled as subordinate tasks projected into the null space, combined with trust-region clipping and joint velocity constraints. On a 7-DoF manipulator in random sparse, medium, and dense environments, this bridge raises planning success in dense scenes from about 0.58 to 1.00, shortens representative path length from roughly 1.53 m to 1.10 m, and while keeping end-effector error below 1 mm, reduces peak joint accelerations by over an order of magnitude, substantially improving the continuous execution quality of voxel-based RL paths on redundant manipulators.