Efficient online motion planning method for the robotic arm to pick-up moving objects smoothly with temporal constraints

Abstract

This paper proposes a new efficient online motion planning method for the manipulator to grasp moving objects smoothly. The algorithm framework consists of front-end pathfinding and back-end nonlinear trajectory optimization. The sample-based pathfinding algorithm can predict the intersection location and find a safe initial path in the dynamic environment. The gradient-based continuous-time trajectory optimization method converts the Euclidean Signed Distance Field information into the joint space, uses the B-spline curve to represent the joint trajectories, optimizes the initial path using convex hull characteristics of B-spline, and generates a smooth and kinematics feasible trajectory in joint space. Finally, we use an adjustment method of iterative trajectory fragment length to guarantee kinodynamic feasibility. Simulation comparisons and real-world experiments verify our planning framework’s high performance.

Dynamic grasping of manipulator based on realtime smooth trajectory generation

“…The manipulator reaches the pregrasp pose, approaches the grasp pose, closes the gripper while tracking the target, and lifts it. Our previous algorithm framework 1 is the SPA system. The trajectory generation algorithm to reach the pregrasp position contains sampling-based path search and nonlinear trajectory optimization.…”

“…Assuming no obstacles, we need to calculate an optimal intersection trajectory to grasp the moving target. The total initial trajectory cost function J Σ of H + 1 dimensional joint space is defined as 1 :…”

“…This paper uses the method in Wei et al 1 to establish the approximate repulsive gradient field generated by obstacles in high-dimensional space. Thus, we establish the distance and gradient expressions between the path point and a single obstacle in joint space for the collision penalty.…”

“…(1) This paper makes the motion planner 1 suitable for multi-pregrasps real-time planning. After predicting the intersection time, we construct a joint space gradient field and use nonlinear optimization to calculate the joint trajectory quickly.…”

“…Finally, this paper simplified our earlier motion planning algorithm. 1 The trajectory planning module calculates the intersection time, use B-spline curves to represent joint trajectories, and generates smooth, collision-free and dynamically feasible trajectories after nonlinear optimization. The trajectory planner has good real-time performance and can be used in the whole grasping framework or alone.…”