Using Magnetic Levitation for Haptic Interaction

Magnetic levitation as a means of motion and force/torque control can provide many advantages for high-fidelity haptic interaction, as compared to motorized linkage and cable actuation. Impedance-based haptic interface devices function both as force display devices, generating forces and/or torques to be felt by the user, and as input devices, sensing the motions imparted by the user to the device. The realism of the haptic interaction is related to the performance of these two functions, which can be quantitatively measured by their position and force accuracy and response times. Magnetic levitation devices have been able to provide very high force & position control bandwidths, resolution, and impedance ranges for haptic interaction through a grasped tool handle. Only one moving part is required to provide precise, responsive, 6 degree-offreedom frictionless motion with force and torque feedback to interact with a simulated or remote environment. With no friction from contacts with actuation or sensing mechanisms, magnetic levitation devices are ideally backdriveable and dynamic nonlinearities such as cogging and backlash are eliminated. The small motion ranges of current tabletop magnetic levitation devices in translation and rotation have been a severe limitation on the size and type of interactive environments and tasks, however. Small motion ranges of magnetic levitation devices are due to a combination of narrow magnetic field gaps and linearized magnetic actuation models which are only valid in a neighborhood of a given setpoint. As a result, magnetic levitation haptic interfaces which have been previously developed focus on fingertip-scale motions, and provide variable indexing, rate control, and scaling methods through software to simulate interaction with larger environments. The mass and rotational inertia perceived by the user as the haptic interface device is manipulated affects the realism of haptic interaction, as well as the position control bandwidths of the device. The transparency of haptic interaction is improved when the encountered mass and inertia are minimized. We have developed two different magnetic levitation devices which provide unprecedented ranges of motion in both translation and rotation to a levitated handle to be used for toolbased haptic interaction. The first device levitates a handle attached to a thin spherical shell of flat coils suspended in permanent magnet fields using Lorentz forces. A novel coil type and magnet configuration provides double the translation and triple the rotation ranges of previous Lorentz levitation haptic devices. 2