A new Silicon axisymmetric Gyroscope for Aerospace Applications

For several years Thales has been developing silicon micro-machined tuning fork gyroscopes for military and civil applications, notably for the aerospace segment. Benefitting from this know-how, a brand new gyroscope based on an axisymmetric structure has been designed over the last few years.The technology is based on Deep Reactive Ion Etching (DRIE) on a Silicon On Insulator (SOI) wafer. Associated to an in-plane design, this technology allows the accurate realization of mechanical resonator and trimming elements within a unique active layer. The inherent simplicity of the gyro, composed of two masses vibrating in an anti-phase mode, combined with the defect cancelation capability obtained through electrostatic tuning, lead to a very high level of performance.Electrostatic trimming enables an excellent bias stability to be obtained by cancelling quadrature and frequency mismatch.The signal processing of the gyro is primarily digital and consists of four main closed loops dedicated to control the drive and the sense modes. An auxiliary loop is used for cancelling the quadrature bias and frequency mismatch.The gyro can operate in two modes: whole angle mode (WA) and force-to-rebalance mode (FTR or angle rate mode).The results obtained on a preliminary mock-up in the FTR mode are the following: · random walk =0.006°/√h, ·bias instability <; 0.01°/h · thermal bias instability <; 0.1°/h · thermal scale factor instability <; 50 ppm · Range: 375°/s (adjustable by the electronics)