Module imu mod ISRAD

Overview

This module is designed for inertial still ranges detection. In other words, the module analyses gyroscopic velocities and translational accelerations to determine where the device is inertially still. This module is typically used for IMU earth self-alignment procedure for numerical integration initial conditions computation.

Module nomenclature

The module waits two physical streams that carry gyroscopic velocities and translational accelerations.

The module creates an integer unitary stream that stores final timestamp of the successive detected inertial still ranges. The initial timestamp is retrieved using the synchronization component. The first value of the unitary stream is used to store a copy of the longest detected inertial still range.

Module interface

This section gives a summary of the module interface in terms of streams and devices. The order of devices and streams is given as waited by the module. The devices interface is given by :

device( Physical ) IMU sensor

The stream input interface is :

stream( Physical | IMU ) Gyroscopic velocities
stream( Physical | IMU ) Translational accelerations

and the stream output interface is :

stream( Integer unitary | IMU ) Inertial still ranges definitions

The two input streams are attached.

Module operation

On the basis of the inertial measures coming from the IMU device, the algorithm parses the six components and accumulates them. The mean of each component is dynamically computed at each step. The immediate next values are compared to the dynamic means. If the difference reach the defined threshold, the range is considered as inertially non-still.

A additional constraint is added on mean computation. A minimum number of value have to be considered for mean computation to be able to trigger an inertial still range.