Microgravity test of a proof-mass actuator for active vibration control

The paper presents the results of an active structural control experiment performed under microgravity conditions. The test has been conducted during an ESA parabolic flight campaign, aboard a Caravelle aeroplane. The structure is a simple cantilevered steel beam with a proof-mass actuator located at the free end. The actuator is a voice-coil linear dc motor built in house with simple and readily available components. During the microgravity phase of the parabolic flight, the structure is given an initial tip displacement, and the consequent vibration is damped by the proof mass actuator. The actuator is a highly non-linear device due mostly to the non uniform magnetic field generated by the coil and to its limited stroke, which causes early saturation of the device. So, various control laws are tested to verify if the non-linearities can be overcome. All the control laws are based on incremental position control of the mass, but in some cases an on line identification of the effective magnetic field has been performed to linearize the behaviour of the actuator. To prevent undesirable saturation, the actuator is also switched off if the mass reaches its limit positions. Interesting results are obtained, which demonstrate the effectiveness of the actuator.