Simplified 3D Control of Magnetic Objects by a Triple-Coil Static Unit on a Robotic Arm
Luca Cinus, Jessé De Oliveira Santana Alves, Tamerlan Srymbetov, Marco Ferro, Claudio Pacchierotti, Arianna Menciassi, Veronica Iacovacci
AI summary
Problem
Mobile magnetic actuation systems struggle to balance dexterity and complexity: single-coil setups require cumbersome mechanical reorientation, while multi-coil arrays introduce bulky hardware and complex control. The paper addresses how to achieve full 3D magnetic steering without sacrificing system compactness or control simplicity.
Approach
The authors mount a fixed triple-coil electromagnetic unit on a 7-DOF robotic arm and use a hierarchical controller that decouples coarse global positioning (handled by the robot) from fine local field steering (handled by modulating coil currents).
Key results
- Design of a compact, fixed-configuration triple-coil end-effector decoupling local steering from global positioning
- Hierarchical QP-CLF control framework optimizing robot motion while regulating coil currents
- Experimental validation demonstrating highly repeatable open-loop steering of 1–3 mm magnetic spheres along complex 3D spiral trajectories in water and oil
- Demonstration of a compact system achieving a compelling balance of dexterity, simplicity, and control efficiency
Why it matters
Enables reliable, non-contact manipulation of milli-scale robots in constrained biomedical environments with a simpler, more compact system than traditional multi-coil setups.
Abstract
Magnetic actuation is a powerful, non-contact method for controlling milli-scale robots. However existing mobile magnetic field sources face a difficult trade-off. Single-coil end-effectors are simple but underactuated, forcing complex and inefficient robot motions to steer objects. Conversely, multi-coil systems improve dexterity but introduce significant mechanical and control complexity. To cope with this challenge, we present a compact, fixed-configuration triple-coil electromagnetic end- effector mounted on a 7-DOF robotic arm. Our innovation lies in a hierarchical control strategy that decouples global and local actuation. A Control Lyapunov Function-based Quadratic Programming (QP-CLF) controller guides the robotic arm for large-scale repositioning, extending the workspace and minimizing required currents. Simultaneously, modulating the currents through the three coils provides fine, high-bandwidth electrical control over the local magnetic field and gradient. We validated this approach by steering 1, 2, and 3 mm magnetic spheres along complex spiral trajectories inside fluid-filled phantoms (water and oil). Our system was teleoperated under operator vision and demonstrated highly repeatable path passing performance, proving that this synergistic robot-electromagnet control provides a compelling balance of dexterity, compactness, and simplicity for advanced magnetic manipulation tasks.