Showing papers on "Inertial measurement unit published in 1975"

A Comparison of Two Approaches to Pure-Inertial and Doppler-Inertial Error Analysis

Abstract: Error equations for inertial navigation systems are derived using a perturbation (or true frame) approach and a psi angle (or computer frame) approach in a manner which shows the underlying as sumptions and allows direct comparison of the two methods. The comparison is general since the analysis is not associated with any particular mechanization. Different definitions of velocity errors and misalignment angles result from the two methods of error analysis, and, consequently, have significance in testing and analysis of pure-inertial systems, Doppler-inertial systems, and inertially aided weapon delivery systems. Examples and numerical results are presented for a local-level north-pointing mechanization.

Inertial free-sight system

Abstract: An inertial sighting system for slaving the axis of a craft mounted movable member such as an armament system, camera, spotlight or the like to the axis of a hand held sight including two sets of inertial sensors in the form of a pair of gyroscopes for each set. One pair of gyroscopes, fixed to the craft and responsive to changes in craft attitude, provides pitch, azimuth, and roll information regarding craft attitude. The other pair of gyroscopes, fixed to the sighting device and responsive to changes in sighting device attitude, provides pitch and azimuth information regarding sight device attitude. The spin axes of the gyroscopes are initially aligned by a caging mechanism provided on a sight stowing bracket mounted on the craft and a cooperating caging mechanism on the sight. Alignment of the axes establishes a reference system, and when the sight is removed from the bracket, at the start of a tracking mission, the gyroscopes are uncaged to provide azimuth and elevation information to slave the axis of the movable member to the sight member.

Self-Alignment Techniques for Inertial Measurement Units

Abstract: This paper presents the result of a study on self-alignment algorithms for inertial measurement units (IMU). The primary concern is the fine alignment of an inertial platform whose base is subject to vibration and whose sensors are subject to noise. The main contribution of the paper is a new self-alignment algorithm. The algorithm incorporates together the special property of platform kinematics and the concept of least square regression. Compared to the usual self-alignment algorithm, this algorithm gives a self-alignment which can be ten times more accurate and requires less computer time and memory. In addition, the new algorithm is less sensitive to erratic measurements and computational errors.

Failure Isolation for a Minimally Redundant Inertial Sensor System

Abstract: The application of two-degree-of-freedom inertial sensors in a minimally redundant strapdown configuration is considered. The potential improvement in reliability which can be achieved by exploiting the failure isolation capability unique to this configuration is evaluated. A unified, statistical approach to the detection and isolation of both hard and soft sensor failures is presented. The effectiveness of this unified approach to FDI in terms of the mean time to detection, the mean time between false alarms, and the accumulated attitude error prior to detection is indicated by simulation results.

Platform Alignment Using a Strapdown Stellar Sensor

Abstract: This paper examines the use of a body-mounted stellar-sighting device to align an aerospace vehicle's gimballed inertial measurement unit. The fundamental observability of not only platform misalignments but also timeinvariant sensor-mounting errors is demonstrated. The performance of an inflight estimation algorithm is shown to be a function of several environmental and navigation hardware parameters as well as the characteristics of the sighting device itself. Parametric case studies are presented for a sample system.

Advances in Inertial Navigation: Sensor Technology

Abstract: The purpose of this paper is to look at the nature of the advances being made in inertial navigation and in navigation displays. In avionics as a whole the advance from one generation of equipment to another can take different forms; sometimes, notably in flight control and instrumentation, the potential of new technologies is exploited almost immediately to provide more advanced operational facilities and systems become more complex. Alternatively, as in the application of solid state electronics to produce equipment for general aviation, the technology is exploited to reduce weight, volume and costs. Inertial navigation exhibits both trends but to a comparatively small degree; the basic system requirement is simple to define and has changed very little, one of the reasons being the particularly demanding nature of the technology and the very long development time scales involved.

Use of single star sightings in boost navigation

Abstract: Information obtained from a single inflight star sighting is used to calibrate a boost vehicle's IMU errors. Several error-inducing parameters, including initial alignment, accelerometers, and gyros are included in the estimation state vector. Although the problem studied is shown to be generally unobservable, suitable preflight alignment techniques can be used to induce observability. The resultant induced observability arises from correlations between initial alignment errors and platform gyros or accelerometer s used for initially aligning the platform. When the platform's initial misalignment is directly observable, the presence of correlations between the initial misalignment and formerly unobservable error sources permits estimation of the latter. Additional results and a sample problem demonstrate the effect of variations in initial conditions, dynamic effects, and observation noise as a function of relevant design parameters.

Space Tug laser gyro IMU

Abstract: A redundant inertial measuring unit (IMU) incorporating six strapdown laser gyros and six accelerometers, arranged so that sensitive axes are normal to the faces of a dodecahedron, provides enhanced reliability with reduced hardware weight. Software monitoring of sensor outputs senses failure of sensors and the system is designed for triple redundancy, with built-in test equipment. Attention is centered on redundancy and fail-safe features, and on the closed-path ring laser gyro arrangement.

Self-Alignment Techniques forInertial Measurement Units

Abstract: Thispaperpresents theresult ofastudy on self-alignment algorithms forinertial measurementunits (IMU).Theprimary concernisthe finealignment ofan inertial platform whosebaseissubject tovibrationandwhosesensorsaresubject tonoise. Themaincontribution ofthepaperisa new self-alignment algorithm. Thealgorithm incorporates together thespecial property ofplatform kinematics and theconceptofleast squareregression. Compared totheusual selfalignment algorithm, thisalgorithm gives aself-alignment whichcan betentimes more accurate andrequires less computertimeand memory. Inaddition, thenew algorithm isless sensitive toerratic measurements andcomputational errors.

Recent Results in Failure Detection and Isolation for the Space Shuttle IMU

Abstract: the requirement for a sensitive failure detection and isolation (FDI) capability for the space shuttle orbiter IMU system has been an important aspect of the development of the IMU for some time. In an earlier ION paper, a method for performing these functions for soft instrument failures in a 2-IMU environment was presented1, along with preliminary results. Additional studies of the performance capabilities of the technique for realistic shuttle trajectories followed and were published.2 The current paper addresses two areas which these earlier efforts showed to be potentially fruitful in improving the performance of the 2-IMU soft FDI approach. It is shown that improvement of the sensitivity of the skewed IMU FDI mechanization can be accomplished by (1) more accurate knowledge of cluster to cluster attitude and (2) appropriate selection of isolation geometry. Reduction of relative azimuth uncertainty due to gyro-compassing is shown to be possible by the use of the high accuracy gimbal angle readout devices to be used on the Space Shuttle IMU. Accelerometer FDI is shown in this paper to be significantly improved by the reduction of this error source. Additional improvement of the FDI capability is shown to be possible by careful selection of isolation geometry. It is shown that testing of the error vector against geometric spaces of various shapes changes the isolation probability, and that a very simply mechanized space has the attendant advantage of providing very high true isolation probabilities. Finally, data collected from Monte Carlo simulations of the FDI mechanization, applied to a Space Shuttle boost trajectory, are presented to demonstrate typical improvements which can be obtained through the application of these techniques.