Scientific experiments and manufacturing in many areas, such as materials and fluids, can benefit from the removal of vibrations and gravity-induced accelerations. Even in the free-fall or zero-g environments available to researchers, such as parabolic flights or orbital flights, trajectory errors (such as not executing a perfect flight parabola) and disturbances (such as crew-motion or thruster-induced structural vibrations) impose acceleration levels of over 10 millig to an experimental payload, resulting in a loss of performance for sensitive experiments. In a collaborative project with the Canadian Space Agency, two vibration isolation systems for zero-g environments have been developed - the Motion Isolation Mount (MIM) for orbital flights and the Large Motion Isolation Mount (LMIM) for parabolic flights.

The approach taken for MIM has been to develop a mechanism having two parts: a stator attached to the structure and a payload-carrying flotor, with the only coupling between the two components being a flexible umbilical carrying signals and power to the flotor. The flotor is actively magnetically levitated by a set of wide-gap voice coil actuators. Its position relative to the stator is sensed by an optical position sensor while its absolute acceleration is sensed by an inertial accelerometer system. A digital controller uses the sensed information to compute actuator currents based on a control law that regulates acceleration and steady-state position to zero. The weak coupling between stator and flotor and the insensitivity of actuator force with position makes such a system extremely effective for vibration isolation [Salcudean et al, 1992], [Hollis and Salcudean, 1993]. A prototype following our design has been built by MPB Technologies in Pointe Claire, Quebec, and is now flying on the Priroda module on MIR. A second prototype, MIM2, was constructed under contract by  the Canadian Space Agency and flown by astronaut Bjarni Tryggvason on shuttle flight STS-85.

 

Parabolic flights have residual acceleration errors of the order of 100 millig that correspond to aircraft trajectory errors of 1-2 meters. A system such as MIM could not accommodate such a large travel due to the limited size of the actuators. Therefore, we proposed a course-fine approach, or LMIM, in which the stator of the MIM device is transported by a large robot or motion stage. A one-degree-of-freedom prototype consisting of a motor-driven linear stage and the UBC maglev wrist has been built to demonstrate the feasibility of the approach. Photograph shows LMIM in a parabolic flight.

Work on control algorithms for the above or other active isolation systems is being carried out.