IMU Architecture based on Functional Redundancy to improve Safety Features and Measurements Availability during Highly Dynamic Transients

Operations in high dynamic environments, in presence of strong vibrations and extreme mechanical shocks, may represent a big challenge for a high-performance Inertial Measurement Unit to maintain its accuracy, availability and continuity at the required level. When designing the IMU, several aspects must be considered and corresponding actions must be taken to avoid IMU unavailability, aimed to mitigate undesirable effects during high dynamic transients, such as sensor’s bias drifts due to rectification errors or saturations due to input forces out of specified sensors’ measurement range.In case of vibrations, typically damping systems are adopted to decrease the energy reaching the IMU sensors, however, sometime the proper design or selection of components can be definitely complex, and furthermore actions taken to mitigate vibration effects can even produce amplifications in case of mechanical shock pulses, depending on the frequency response of the employed dampers. In general, high accuracy accelerometers have limited dynamic range, so undesirable out-of-range effects can be experienced in certain high dynamic transients, limiting their usability in harsh high-g demanding operational scenarios.More sophisticated design techniques, like the adoption of a sensors’ skewed redundant architecture, can be used to overcome some of these limitations, however, they have some drawbacks: increase of costs, mechanical complexity, increased system dimensions, together with the need to adopt a more complex IMU calibration process.This paper proposes a simple technique and system architecture to extend the measurement range of high accuracy IMUs, when its accelerometers have to deal with both high vibration and high-g shock environments, reducing the overall effort in designing tasks and the overall IMU bill of materials cost, avoiding complex mechanical architectures and damping systems, and guaranteeing the continuity and availability of the IMU acceleration measurements even in presence of over-range conditions for the most accurate sensor devices. This goal is achieved by adopting a cost effective IMU architecture that employs hybrid redundant sensors of different technologies, and a data fusion technique of high-accuracy, limited-range sensors, together with less expensive, lower-accuracy and broad-dynamic-range sensors.