Abstract
Coriolis Vibratory Gyroscope (CVG) is an inertial rotation rate measurement sensor for inertial navigation applications. The rotation sensitive element is a hemispherical vibrating resonator, made of fused silica. It is forced to vibrate at a particular resonant mode with electrostatic forcing. As the resonator is a glass material its vibration amplitude is limited to the submicron level. An ultra-high vacuum environment is necessary for the resonator to sustain the vibration amplitude. Securing the required vacuum level is critical in sensor development. A detailed analysis has been carried out on the damping forces present at various ambiance conditions, the need for threshold vacuum level, threshold forcing voltage for the resonator, and different ways of degradation of the vacuum level in the sensor capsule. This paper presents an experimental study on the damping forces that appear on the resonator by measuring the Q factor at various vacuum levels, vacuum leak rate through weld joints, securing the vacuum environment, and remedial action to arrest vacuum in the sensor volume. Dedicated test setups have been established to carry out the experimental research work.
Highlights
A Gyroscope is an inertial rotation rate measurement sensor used in an inertial navigation system along with accelerometers for autonomous navigation [1], [2] for various platforms
The damping forces acting on the resonator from the ultra-high vacuum environment to the high vacuum environment have a degradation of Q factor which is less than 10 %
We have presented a detailed analysis of the damping forces that appear on the resonator at various vacuum levels by measuring the Q factor, threshold vacuum level, and the source of the vacuum degradation through the porous weld joints in the sensor capsule
Summary
A Gyroscope is an inertial rotation rate measurement sensor used in an inertial navigation system along with accelerometers for autonomous navigation [1], [2] for various platforms. The resonator is forced to vibrate at its mode 2 resonating standing wave [6] at a fixed amplitude by electrostatic excitation scheme. In the half-cycle, a similar deformation takes place but spatially shifts by 90° in azimuth This mode of vibration forms set of four anti-nodes (A, B, C, D) and four nodes (E, F, G, H) on the resonator. When the vibrating resonator rotates about a fixed axis with angular velocity (Ω), Coriolis forces act on the resonator generates a secondary standing wave on the resonator as shown, INFLUENCE OF VACUUM AND ITS DEGRADATION ON THE SENSING ELEMENT OF THE CORIOLIS VIBRATORY GYROSCOPE. The Primary requirement for the CVG is to maintain a fixed value of the amplitude and frequency of vibration on the resonator during the measurement of angular rotation [10]. A detailed study is carried out to identify a threshold vacuum level to the resonator for its satisfactory operation and practical vacuum level required for gyroscope life of a minimum of 5 years
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