INITIALIZING AN INERTIAL SENSOR USING SOFT CONSTRAINTS AND PENALTY FUNCTIONS

摘要

An initialization method for an inertial sensor that estimates starting orientation and velocity without requiring the sensor to start at rest or in a well-known location or orientation. Initialization uses patterns of motion encoded as a set of soft constraints that are expected to hold approximately during an initialization period. Penalty metrics are defined to measure the deviation of calculated motion trajectories from the soft constraints. Differential equations of motion for an inertial sensor are solved with the initial conditions as variables; the initial conditions that minimize the penalty metrics are used as estimates for the actual initial conditions of the sensor. Soft constraints and penalty metrics for a specific application are chosen based on the types of motion patterns expected for this application. Illustrative cases include applications with relatively little movement during initialization, and applications with approximately periodic motion during initialization.

主权项

1. A method for determining an estimate of the initial orientation Q0 and initial velocity v0 of an inertial sensor, comprising the steps:
collecting sample data from an inertial sensor over a capture time interval [ti, tf] that includes an activity of interest, said sample data including accelerometer data s(t) and rate gyro data w(t); selecting an initialization interval [t0, tn]⊂[ti, tf] within said capture time interval; defining a set of soft constraints {Ci} on the position r(t) and velocity v(t) of said inertial sensor during said initialization interval, where each Ci⊂}r: [t0, tn]→3}×{v: [t0, tn]→3}, where said soft constraints represent approximations of typical patterns of position and velocity trajectories for said activity of interest during said initialization interval; defining penalty metrics mj(r(t), v(t)) to quantify the deviation of calculated trajectories of said position r(t) and said velocity v(t) from said soft constraints {Ci}; and calculating estimates of the initial orientation Q0=Q(t0) and initial velocity v0=v(t0) of said inertial sensor at the start of said initialization interval to minimize said penalty metrics when said initial orientation and initial velocity are used as initial conditions to integrate said sample data into orientation, position and velocity over said initialization interval via the coupled differential equation;Qt=Qωx,vt=Qs+g,rt=v.