Silicon MEMS by Safran - Navigation grade accelerometer ready for mass production

Abstract

Safran Electronics & Defense is a world leader in inertial navigation systems for both civilian and military applications. Capitalizing on its industrial heritage, Safran has achieved a major technological breakthrough in the past years by introducing the most CSWAP (Cost Size Weight and Power) navigation-grade INS technology based on HRG CrystalTM gyros.In line with past efforts to push back inertial navigation boundaries, Safran is increasing its technological and competitive edges through the development of new-generation accelerometers.Building on its daughter-company Safran Colibrys expertise and portfolio of tactical grade open loop accelerometers, Safran is indeed a leading player in Silicon MEMS accelerometers. As such, Safran’s choice was naturally steered towards silicon MEMS thanks to their unrivalled CSWAP, characteristics compared to the complex design of legacy pendulous torque-balanced servo-accelerometers.Closed-loop operation technology is indeed essential to reach the most demanding performance levels. For instance, ACSIL accelerometers, with their smart closed-loop operation design, have successfully been used for 30 years in high-grade commercial avionics AHRS.Taking advantage of their combined expertise, Safran Electronics & Defense and Safran Colibrys have brought the performance of closed loop pendulous MEMS accelerometers to an unprecedented level while keeping all the CSWaP benefits of the technology. This accelerometer is currently in production at low rate (LRIP) and is henceforth ready to enter mass-production phase as a component of HRG CrystalTM based INS for all applications including certified aerospace under DO-254 standards.This paper presents the key design choices of our navigation grade Si-MEMS accelerometer: the MEMS sensor architecture and its ∑Δ control electronics including innovative approach to reach very high measurement ranges.Actual product performances statistics from a few hundred-sample production batch are detailed. Navigation grade key characteristics are examined: bias, scale factor, misalignment temperature and ageing stability. Vibration susceptibility, a key performance for harsh environment capability and warm-up response, a key performance required by fast alignment time INS, are also discussed.Designed and matured under a rigorous process, Safran navigation grade MEMS accelerometer has proven a high level of inertial performances and its ability to operate as the ideal accelerometer to be associated to HRG CrystalTM to offer, by far, the best CSWAP INS on the market place.