Two degrees of freedom miniaturized gyroscope based on active magnetic bearings

The introduction of the active blocking system, better known as ABS, into cars revealed the growing need for inertial sensing. Among other data, that permit to apprehend the movements of a vehicle, the measurement of the vehicle angular velocity describes the change rate of the vehicle attitude. This measurement has been called by Foucault in 1852 gyroscopic sensing (from the Greek words σκοπειν = observe and γυρος = rotation). The currently available gyroscopes are either very high precision instruments (hence very costly), used in planes, or cheaper products but with a lack of sensitivity to be used in vehicle navigation. Therefore, a real need for gyroscopes combining low cost and precision exists. This thesis proposes to develop a gyroscope based on miniaturized active magnetic bearings (AMB). The advantage of such a device is that the spun mass will be levitated what frees it from any mechanical link to the base of the instrument what render precise classical mechanical gyroscopes so expensive. This thesis presents two prototypes of AMB based gyroscopes. The first one relies on the ball orbit sensing method which is a new theory proposed in this work. Because of the uncertainties due to the nonlinearities inherent to active magnetic bearings, the position of the levitated mass is adaptively controlled. Measurements performed on the prototype have demonstrated the feasibility of this solution with a ball following either a circular or a vertical orbit. The second designed prototype relies on the Newton's second law of motion. Due to the AMB inherent uncertainties and to the force coupling present in the proposed prototype, it has been chosen to drive the levitated mass with a H∞ controller. Simulations are run to compare three different H∞ controllers with the quality of the angular velocity measurement as criterion. Finally, a feed forward H∞ controller showed the best performances in terms of angular velocity measurements during simulations run on the prototype developed during this thesis.

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