Magnetic Levitation for Haptic Interaction

Peter J. Berkelman, Michael Dzadovsky
Mechanical Engineering Department, University of Hawai'i at Manoa

Magnetic levitation systems are well suited for haptic and other human-machine interaction as they are highly backdrivable, contain only a single moving part, and are not subject to the friction, hysteresis and cogging present in motors, gear reductions, and linkage mechanisms. Furthermore, magnetic levitation devices have a high potential for precise positioning, fast dynamic responses, and very high achievable impedance ranges. The combination of these properties enables physical interaction with simulated environments with a degree of realism and detail unattainable by other means of actuation. Haptic interaction using magnetic levitation provides a particularly rich medium for human-computer interaction, distinct from graphical computer interfaces, in simulation application areas such as medical training and vehicle operation.

We are currently developing two magnetic levitation devices: (1) A hemispherical Lorentz force device for handheld, tool-based haptic interaction, with a novel design for twice the translation and over three times the rotation range of earlier hemispherical Lorentz force devices, and (2) a modular and scalable planar electromagnetic repulsion levitation device.

Testbed setup:

Current amplifiers are used for actuation of the electromagnetic coils, limited to 2.5 Amp to avoid overheating
Optotrak (Northern Digital Inc) rigid body motion tracker on rigid frame used position feedback at a 1000 Hz sample rate

(1) Hemispherical Lorentz Magnetic Levitation:


Single opening Lorentz maglev design	Double opening Lorentz maglev design

The levitated portion of this device or flotor consists of a thin hemispherical shell with 6 large coils wound around the outside surface (3 pairs, 2 layers) and a manipulation handle attached at the center. Currents in the 6 coils interact with magnetic fields from permanent NdFeb magnets on the fixed stator assembly to generate 3D forces and torques for levitation and haptic feedback. An optical motion tracking subsystem provides position sensing for closed-loop control. The handle has a motion range of 60 degrees in rotation and 50 mm in translation along any direction.

Lorentz Levitation System as Fabricated:


Levitating bowl with 2-layer straight wire coil pairs	Handle for haptic interaction

Preliminary motion results:

Vertical step response results

- The motion step response under simple PD control is currently underdamped due to the 1200 g levitated mass (reducible to 400-500 g by using aluminum coils), and the limited resolution and update rate of the motion tracking sensor.

(2) Planar Repulsion Magnetic Levitation:

The base of the magnetic levitation device concept contains an array of cylindrical electromagnet coils which generate repulsive forces and torques to levitate and manipulate a platform containing 4 disk magnets as pictured. Basic modules as shown will be able to scale to larger area coil arrays with multiple levitated platforms to support a human user and simulate arbitrary vehicles.

Planar Magnetic Levitation System as Fabricated:


Single disk magnet levitation, 5 DOF control	Two magnet levitation, 6 DOF control


Levitated PC mouse for haptic interaction	Motion stages and force/torque sensor for actuation model

Single magnet constant velocity trajectories for horizontal, vertical, and tilt motions

See publications for details

Video clips:    Single magnet constant velocity motions
                        Single magnet teleoperation
                           Narrated compilation

This project is supported by NSF grant #CNS-0551515 and a donation from Real Data Center, Inc.

Human-Robot Interaction Lab
356 Holmes Hall, 808-956-9421
University of Hawai'i at Manoa
Mechanical Engineering Department