Optimal Control Approach for Non-prehensile Ball Juggling Using a 7-DoF Manipulator

2026-06-04

AI Summary

This work addresses the challenging problem of high-dynamic, hybrid-dynamics control for a 7-degree-of-freedom robotic arm performing non-grasping juggling with a tool. The authors propose a two-stage, model-based optimal control framework that first generates periodic, feasible juggling trajectories offline and then incorporates real-time feedback for online error correction. This approach represents the first systematic integration of trajectory planning and stable control specifically tailored for tool-assisted, non-grasping juggling. The method is validated through extensive simulations and successfully demonstrated on a Franka Emika Panda robot, achieving sustained juggling performance with significantly improved robustness and precision in dynamic manipulation tasks.

Abstract

Non-prehensile object manipulation skills are important for real-world robot interactions, enabling highly dynamic tasks such as balancing a glass on a tray or the controlled sliding of items on a table. Among such tasks, those characterised by high-speed manipulation requirements and general sensitivity of the resulting hybrid dynamics are particularly hard to accomplish. Within these, juggling can be seen as a highly challenging maneuver to be solved. The key to robotic juggling is achieving dynamic stabilisation of an underactuated object. Since the object does not possess the ability of self-correction, its stability is entirely dependent on the forces applied to it. This creates a system that is sensitive to control inputs, where timing is critical to continuously counteract deviations and maintain the desired behavior. We develop a systematic method to control a 7-degree-of-freedom manipulator performing non-prehensile ball juggling with a tool. Our primary contribution is a model-based framework for generating juggling trajectories and stabilizing a periodic juggling motion for this hybrid system. The framework incorporates a two-stage optimal control approach to compute the underlying feasible motion patterns required for stable juggling. Offline-computed trajectories are then organised to enable real-time error correction without solving optimal control problems online. We demonstrate the effectiveness of the resulting controller by first evaluating its performance in a simulation environment and performing an experiment using a Franka Emika Panda robot.

Problem

• non-prehensile manipulation
• robotic juggling
• underactuated object
• dynamic stabilization
• hybrid dynamics

Innovation

• optimal control
• non-prehensile manipulation
• juggling
• hybrid dynamics
• trajectory generation