Showing papers on "Inertial reference unit published in 1993"

Vehicle position determination system and method

Abstract: Systems and methods allow for the accurate determination of the terrestrial position of an autonomous vehicle in real time. A first position estimate of the vehicle 102 is derived from satellites of a global positioning system and/or a pseudolite(s). The pseudolite(s) may be used exclusively when the satellites are not in the view of the vehicle. A second position estimate is derived from an inertial reference unit and/or a vehicle odometer. The first and second position estimates are combined and filtered using novel techniques to derive a more accurate third position estimate of the vehicle's position. Accordingly, accurate autonomous navigation of the vehicle can be effectuated using the third position estimate.

Mobile robot attitude estimation by fusion of inertial data

Abstract: An attitude estimation system based on inertial measurements for a mobile robot is described. Five low-cost inertial sensors are used: two accelerometers and three gyros. The robot's attitude, represented by its roll and pitch angles, can be obtained using two different methods. The first method is based on accelerometric measurements of gravity. The second one proceeds by integration of the differential equation relating the robot's attitude and its instantaneous angular velocity which is measured by the gyrometers. The results of these two methods are fused, using an extended Kalman filter. Experimental results show that the resulting system is very sensitive and accurate. >

An inertial navigation system for a mobile robot

Abstract: A low-cost, solid-state inertial navigation system for robotics applications is described. Error models for the inertial sensors are generated and included in an extended Kalman filter (EKF) for estimating the position and orientation of a moving robot vehicle. A solid-state gyroscope and an accelerometer have been evaluated. Without error compensation, the error in orientation is between 5-15/spl deg//min but can be improved at least by a factor of five if an adequate error model is supplied. Similar error models have been developed for each axis of a solid-state triaxial accelerometer. Linear position estimation with accelerometers and tilt sensors is more susceptible to errors due to the double integration process involved in estimating position. WIth the system described here, the position drift rate is 1-8 cm/s, depending on the frequency of acceleration changes. The results show that with careful and detailed modeling of error sources, low cost inertial sensing systems can provide valuable position information.

Apparatus and method for autonomous satellite attitude sensing

Abstract: An attitude sensing system utilizing simplified techniques and apparatus includes a Kalman filter which receives signals from an inertial measurement unit, a GPS receiver, and an integrated optical assembly. The output vector of the filter includes estimates of attitude misalignments and estimates of gyro drifts corresponding to the axes of the inertial measurement unit. The optical assembly includes a sensor array providing signals to the filter representing detection of the Earth's horizon or the center of the Sun. More particularly, a local vertical vector, computed from fore and aft detections of the Earth's horizon, is used in combination with GPS received signals to initially determine attitude by means of gyrocompassing. This attitude information is thereafter maintained by the inertial measurement unit and azimuth error resulting from drift of the inertial measurement unit and the initial gyrocompassing error is corrected by detections of the Earth's horizon and the Sun. The integrated optical assembly, used to detect the locations of both the Sun and Earth relative to the satellite, eliminates a need for separate apparatus dedicated to each sensing function. Moreover, the GPS receiver eliminates the need for ground tracking apparatus by providing the satellite ephemerides (including orbital pitch rate used in gyrocompassing) for use by the filter, rendering the attitude sensing system substantially autonomous. Additionally, the GPS receiver, in combination with the Sun and Earth detections, eliminates the need for a complex star tracker by providing an accurate inertial frame of reference.

Inertial measurement unit providing linear and angular outputs using only fixed linear accelerometer sensors

Abstract: An inertial measurement unit is provided in which an arrangement of linear accelerometers in fixed positions measure angular acceleration and other inertial characteristics. Only linear acceleration readings are required for measurement of angular acceleration, and both expensive angular sensors and cyclically driven linear accelerometers are eliminated. A processor receives the linear accelerometer signals and calculates output values related to both the angular and linear motion of the body. In the preferred embodiment, the inertial measurement unit includes at least nine linear accelerometers, three disposed with their respective sensitive axes in substantially mutually orthogonal relationship defining first, second and third axes intersecting at a single origin point, and a pair of linear accelerometers disposed along each axis spaced at fixed distances from the origin point with their sensitive axes in substantially orthogonal relationship with each other and the axis. The present invention also includes a control system using the inertial measurement unit of the present invention to control the operation of a first component in response to angular motion of a second component connected thereto, and a method for inertial measurement of angular acceleration.

Method and apparatus for improving the accuracy of position estimates in a satellite based navigation system using velocity data from an inertial reference unit

Abstract: A method and apparatus for computing a precise position estimate for a receiver at or near the surface of the Earth uses a inertial reference unit associated with the receiver and a satellite-based navigation system. The satellite-based navigation system is used to determine a position estimate for the receiver at consecutive positions along its path of motion. The inertial reference unit is used to determine velocity vectors for the receiver. Each velocity vector corresponds to travel of the receiver between the consecutive positions. The velocity vectors from the inertial reference unit are used to refine the position estimates of the satellite-based navigation system to obtain precise position estimates.

Strapdown Stabilization for Imaging Seekers

Abstract: : In space constrained applications such as tactical missiles, locating the inertial sensors off the platform simplifies packaging and may allow existing missile autopilot gyros to be used for platform stabilization. In strapdown stabilization, inertial sensors are fixed to the base of the inertial platform rather than directly on the platform itself. Gimbal position sensor information is combined with body-fixed inertial rate sensor information to estimate the inertial rate of the platform. This estimate of platform rate is a key factor that determines the stabilization performance of the system. An initial assessment of the feasibility of strapdown stabilization for high-resolution imaging seekers was conducted. A linear state space model and a detailed nonlinear planar simulation were developed of a tactical high-resolution platform system. The simulation includes gimbal inertia, inertial sensors, position sensors, friction, mechanical alignment, compliances, and control loop compensation. The simulation was used to predict the platform stabilization performance. In addition, effects of stabilization performance on target signal strength for an imaging seeker were estimated.

Calibration of an internal sensor system

Abstract: A calibration device for establishing a 3-D reference frame for an inertial sensor system. A secondary mounting surface on the calibration device is used to provide a measurement of the reference line required for inertial system installation alignment. This device provides a means for establishing a highly accurate alignment of inertial system sensors relative to the output coordinates, called the "mounting frame", without a requirement for optics or a manual transfer of data. By rotating the inertial sensor system through use of a rate table into planes which are substantially perpendicular to each other, the mounting frame for the sensor system can be established.

Gyroscopic system for boresighting equipment by optically acquiring and transferring parallel and non-parallel lines

Abstract: A gyroscopic system and method is provided for translating parallel and non-parallel lines between a reference line and a device to be aligned with respect to the reference line A first inertial sensor (60) is provided that is configured to be substantially stationary This inertial sensor is boresighted with respect to the reference line and includes at least two gyroscopes and a mirror (61) having first and second nonplanar surfaces A second, portable inertial sensor (62) is provided that includes a gimbal, a gimbal drive system, an electronic energy beam generator, a collimator, and at least two gyroscopes One or more of the electronic beam generator, collimator, and gyroscopes can be optionally mounted on a platform that is mounted on the gimbal and adapted to move in accordance with signals from the gimbal drive system A control circuit (68) is provided that is operable to measure output signals generated by the first and second inertial sensor gyroscopes and to determine relative orientations of the inertial sensors

A fault-tolerant air data/inertial reference unit

Abstract: The fault-tolerant air data/inertial reference unit (ADIRU) described is a key part of a fault-tolerant air data/inertial reference system (ADIRS) designed to be the inertial and air data reference for the ARINC 651 Integrated Modular Avionics (IMA) distributed architecture. The ADIRU has been designed to meet the commercial aviation market demands for low life cycle cost and high integrity fault detection, fault isolation, and redundancy management. The ADIRU's internal redundant resources provide quad channel redundancy that is one level higher than conventional triple redundant systems, allowing it to provide deferred maintenance capability. Robust partitioning, simple serial internal interfaces, and simple voting planes ensure that internal redundant components are properly utilized to provide high integrity system outputs. This relieves systems using it from having to perform their own redundancy management of the air data and inertial outputs from multiple sources required by conventional systems. >

Integrated guidance system and method for providing guidance to a projectile on a trajectory

Abstract: An inertial measurement unit is provided which includes a core inertial measurement unit having accelerometers and gyroscopes aligned along x, y and z axes to provide signals to an onboard computer to determine position of the vehicle upon which they are mounted while in movement. A fourth accelerometer is pivoted perpendicular to the direction of the gravitational field for measuring the gravitational field about the axis upon which it is mounted to provide a reference set of data to an onboard computer prior to movement of the vehicle upon which the system is mounted.

The use of GPS for evaluating inertial measurement unit errors

Abstract: A trajectory reference system based on the Global Positioning System (GPS) can be used instead of conventional radars during missile flight tests. The high quality of the GPS-based trajectory reference makes it useful for evaluating the performance of the missiles' Inertial Measurement Units (IMUs). Such a system was installed and flight tested on two recently launched ballistic missiles. The GPS hardware configuration used on these flights is described. A Kalman filter approach is used to estimate individual IMU errors based on the GPS range and delta range data. The ability of the GPS-based system to identify IMU errors is compared to that of radar; GPS is found to provide superior estimates of the IMU errors.

Inertial rotation sensing apparatus and method

Abstract: An improved electro-mechanical inertial rotation sensor comprising a rotor which spins at substantially constant speed with respect to an inertial frame of reference. A pickoff generates a signal relating the rotational position of the rotor relative to the apparatus, as a function of time. A phase comparator compares this pickoff signal to a reference signal relating the rotational position of the rotor relative to a fixed orientation in an inertial frame of reference, as a function of time. Changes in phase between the two signals indicate changes in orientation of the apparatus with respect to the inertial frame of reference. In one embodiment, the rotor is driven through an Eddy current coupling and simultaneously braked by an Eddy current brake, in a matched torque drive. To generate an accurate reference signal, the rotations of the rotor with respect to the inertial frame of reference are accurately determined using parallel measurements from a similar rotor, used as a test rotor.

Standard compass/attitude and heading reference system (C/AHRS) utilizing fiber optic gyroscopes

Abstract: The requirement for replacement systems for in-service aircraft with aging compass and attitude heading reference systems was the basis for a joint U.S. Air Force/U.S. Navy program to develop, test, and acquire a standard low life-cycle-cost composite system. A single award was made to Smiths Industries in June 1991 to develop the C/AHRS, build fourteen prototypes, and support an extensive test program. The design approach chosen by Smiths included the use of fiber optic gyroscopes. In order to achieve the high reliability required for this replacement system, an Avionics Integrity Program (AVIP) has been implemented which includes extensive in-depth studies to determine actual environments which drive the design process. This paper presents a summary of the C/AHRS requirements and design approach. >

An inertial navigation system for robot measurement and control

Abstract: The present paper deals with application of inertial sensors in the field of robotics. Quite in contrast to conventional applications, short integration times and higher acceleration values are considered. Furthermore, when used as an dynamic augmentation of robot measurement and control, the static sensor offsets can be handled with much more ease. The author presents a gyroless inertial sensor head for the sensing of motion induced acceleration on robotic mechanisms. The sensor signals are used for real-time calculation of position and orientation changes of the mechanism. A discussion of error sources is included, and a simulation of a two dimensional sensor arrangement demonstrates the influence of sensor and mounting errors. Further more, the utilization of the system as a redundant signal source for measurement and control, as well as the possibility of robot vibration damping is analyzed. >

Integrated DGPS/Inertial TSPI for DOD Ranges: RAJPO Equipment Test Results

Abstract: The RAJPO at Eglin AFB has acquired a family of GPS based equipment to determine Time Space Position Information (TSPI) for the DOD test and training ranges. The High Dynamics Instrumentation System (HDIS), produced by Interstate Electronics Corporation (IEC), is a P-code receiver that can operate in a real-time differential mode with inertial reference unit (IRU) aiding. Recently, the Government conducted extensive flight tests with the F-15 and F-16 aircraft to demonstrate the accuracy specification compliance of the receiver under various dynamic scenarios. The receiver was evaluated under conditions of sustained high G’s (up to 8) and intermittent satellite visibility. Integrated differential GPS and IRU solutions were compared against the truth source involving a number of cinetheodolites, laser trackers, and the aircraft INS. This paper briefly describes the design features of the HDIS and the implementation of real-time differential corrections by using a data link. Next, the details of the test program covering the layout of the truth data sources, test scenario design, and the test data reduction methodology are discussed. Finally, the actual real-time test data statistics are presented showing the successful compliance with the required specifications.

NASA's first in-space optical gyroscope: A technology experiment on the X ray Timing Explorer spacecraft

Abstract: A technology experiment on the X-ray Timing Explorer spacecraft to determine the feasibility of Interferometric Fiber Optic Gyroscopes for space flight navigation is described. The experiment consists of placing a medium grade fiber optic gyroscope in parallel with the spacecraft's inertial reference unit. The performance of the fiber optic gyroscope will be monitored and compared to the primary mechanical gyroscope's performance throughout the two-year mission life.

Attitude control for the Pluto Fast Flyby spacecraft

Abstract: A conceptual attitude control subsystem design for the Pluto Fast Flyby spacecraft is described. Mass, cost, schedule and performance, approximately in that order, drove the mission, spacecraft, as well as the attitude control subsystem design. The paper discusses the key mission requirements impacting the attitude control subsystem design, as well as the important subsystem trades. The spacecraft is a three axis stabilized vehicle using cold gas jets for attitude control and hydrazine thrusters for trajectory correction maneuvers. Attitude determination relies heavily on a low mass star tracker capable of determining attitude by pointing anywhere in the celestial sphere. Tracking of planetary features with the star tracker may also be desirable. A small inertial reference unit and a sun sensor will accompany the tracker to complete the suite of components for attitude determination.

Simulation of a strapdown magnetic azimuth detector for wing tip mounted applications

Abstract: This paper addresses the instrument performance issues of a wing tip mounted solid state magnetic azimuth detector (MAD). The approach taken here dynamically tracks the wing tip deflections so that when used in conjunction with a fuselage mounted inertial reference unit (IRU), wing tip sensed magnetic measurements can be used to derive heading. Presented is a discussion of other strapdown approaches and their shortcomings with respect to wing mounted applications. This discussion is followed by a definition of the error sources associated with the new approach and a simulation illustrating the expected performance. >

The attitude accuracy consequences of on-orbit calibration of the Extreme Ultraviolet Explorer attitude sensors by the Flight Dynamics Facility at Goddard Space Flight Center

Abstract: The science mission of the Extreme Ultraviolet Explorer (EUVE) requires attitude solutions with uncertainties of 27, 16.7, 16.7 arcseconds (3 sigma) around the roll, pitch, and yaw axes, respectively. The primary input to the attitude determination process is provided by two NASA standard fixed-head star trackers (FHSTs) and a Teledyne dry rotor inertial reference unit (DRIRU) 2. The attitude determination requirements approach the limits attainable with the FHSTs and DRIRU. The Flight Dynamics Facility (FDF) at Goddard Space Flight Center (GSFC) designed and executed calibration procedures that far exceeded the extent and the data volume of any other FDF-supported mission. The techniques and results of this attempt to obtain attitude accuracies at the limit of sensor capability and the results of analysis of the factors that limit the attitude accuracy are the primary subjects of this paper. The success of the calibration effort is judged by the resulting measurement residuals and comparisons between ground- and onboard-determined attitudes. The FHST star position residuals have been reduced to less tha 4 arcsec per axis -- a value that appears to be limited by the sensor capabilities. The FDF ground system uses a batch least-squares estimator to determine attitude. The EUVE onboard computer (OBC) uses an extended Kalman filter. Currently, there are systematic differences between the two attitude solutions that occasionally exceed the mission requirements for 3 sigma attitude uncertainty. Attempts to understand and reduce these differences are continuing.

Inertial Platform Stabilization Using GPS Velocity Feedback

Abstract: To achieve a leveling accuracy of 2 arc seconds for airborne gravimetry, GPS velocity information is integrated into an inertial platform to damp Schuler oscillations of the platform leveling errors and, at the same time, maintain the Schuler characteristics of the platform system to avoid the influence of vehicle motions. GPS velocity errors using single point and double difference methods are analyzed in both the time and frequency domains. Simulations are done for the north leveling loop of an inertial platform. It is shown that single point (SA off or a cryptographic key is used) and double difference GPS velocities can be used for this application.

Conceptual design of the pointing and control subsystem of the space infrared telescope facility

Abstract: The Space Infrared Telescope Facility mission provides exciting pointing and control challenges. This paper describes the pointing and control subsystem (PCS) designed to meet these challenges. Cost, mass, performance and life-time drove the choice of the new solar orbit and the re-design of the telescope, spacecraft and the pointing and control subsystem. The PCS performs a number of key functions for the Observatory, including pointing to and holding inertial targets, tracking moving targets, performingprescribed motion patterns, maintaining pointing constraints and providing safe hold during failure. To attain the high precision demanded by the observatory, the PCS relies on a sub-arcsecond star tracker and a 0.001 arcsecond resolution inertial reference unit. An affordable PCS is realized by locating the fine guidance sensor externally, utilizing a simple fault protection strategy, and maximizing the commonality inthe use of hardware and in the development of flight software.