Showing papers on "Inertial measurement unit published in 1981"

Origins of inertial navigation

Abstract: Introduction A VIGNETTE* of the stages of development of inertial navigation at the M.I.T. Instrumentation Laboratory has been provided by the author. An earlier work provides a tutorial reference on the basic principles of the instruments and systems that were developed. Because this technology grew largely from classified programs, publication of the description of the technology for specific systems has often lagged by a decade or more, and sometimes has lacked coverage altogether. Also because of the author's responsibility for these classified programs, he was often constrained from publishing until after someone less intimately involved had already disclosed information on the programs of inertial navigation. Even at this late date, a description of the Mark 14 "Draper Sight" has not appeared in the open literature. It is the purpose of this treatise to describe some of the major systems that contributed to the evolution of inertial navigation, and to provide a record of the performance of some of these historically significant programs. An underlying theme is the continuity of gyroscopic sensor technology from the fire control systems of the Mark 14 vintage to the first successful inertial navigators. It is shown how the single degree of freedom gyroscopic element was adapted to perform simultaneously both the sensing and computation requirements for solving the fire control problem associated with close-in attacking aircraft. Refinements made to this gyroscopic element, including precise control of torques applied to the output gimbal, and eventual flotation led to the sensor technology that was eventually adapted to solving the inertial navigation problem.

Control, navigation, and guidance

Abstract: Self-contained systems providing control and navigation for vehicles of all kinds use gyroscopic elements to maintain reference directions with respect to inertial space. Sensors for resultant gravity field and inertial reaction forces along input axes determine the vertical and also linear velocities with respect to inertial space. These components divided by an equivalent Earth radius transfer the motion to Earth coordinates in which integration gives location. Corrections for Earth's rotation projected in and perpendicular to the horizontal plane are made as computed cosine and sine projections of Earth's angular velocity. Current systems result with the order of fractional miles per hour performance.

Ring laser gyroscope cluster for strapped down navigation

Abstract: An inertial measurement unit using body dithered ring laser gyroscopes in which the individual ring laser gyroscopes are firmly attached to a common dithered structure and provisions made to cancel the reaction moment from the dithered structure by a passive resonator. The stable element, to which both the dithered structure and the passive resonator are attached with torsion springs, also serves as a non-vibrating foundation for strapped down accelerometers. The resulting structure contains fewer parts, has lower fabricating cost and permits a smaller package size than a conventional inertial measurement unit with individually body dithered ring laser gyroscopes.

Failure detection and isolation analysis of a redundant strapdown inertial measurement unit

Abstract: The objective of this study was to define and develop techniques for failure detection and isolation (FDI) algorithms for a dual fail/operational redundant strapdown inertial navigation system are defined and developed. The FDI techniques chosen include provisions for hard and soft failure detection in the context of flight control and navigation. Analyses were done to determine error detection and switching levels for the inertial navigation system, which is intended for a conventional takeoff or landing (CTOL) operating environment. In addition, investigations of false alarms and missed alarms were included for the FDI techniques developed, along with the analyses of filters to be used in conjunction with FDI processing. Two specific FDI algorithms were compared: the generalized likelihood test and the edge vector test. A deterministic digital computer simulation was used to compare and evaluate the algorithms and FDI systems.

Missile azimuth aiming apparatus

Abstract: Apparatus for fast, accurate aiming of a missile from a launch vehicle. Thepparatus permits fast accurate aiming of a missile inertial measurement unit for cases in which the inertial measurement unit does not possess required performance capability for self-aiming. The apparatus involves no optical link and is not expended with the missile.

GPS aiding of ocean current determination

Abstract: The navigational accuracy of an oceangoing vessel using conventional GPS p-code data is examined. The GPS signal is transmitted over two carrier frequencies in the L-band at 1575.42 and 1227.6 MHz. Achievable navigational uncertainties of differenced positional estimates are presented as a function of the parameters of the problem, with particular attention given to the effect of sea-state, user equivalent range error, uncompensated antenna motion, varying delay intervals, and reduced data rate examined in the unaided mode. The unmodeled errors resulting from satellite ephemeris uncertainties are shown to be negligible for the GPS-NDS (Navigation Development) satellites. Requirements are met in relatively calm seas, but accuracy degradation by a factor of at least 2 must be anticipated in heavier sea states. The aided mode of operation is examined, and it is shown that requirements can be met by using an inertial measurement unit (IMU) to aid the GPS receiver operation. Since the use of an IMU would mean higher costs, direct Doppler from the GPS satellites is presented as a viable alternative.

A microprocessor-based data acquisition system for stall/spin research

Abstract: Accurate data are necessary for the identification of aerodynamic parameters at high angle of attack and in spinning flight. Modern sensors and microelectronic devices are employed in a stall/spin data acquisition system that will be tested in a Schweizer 2-32 sailplane. This instrumentation package will use a quaternion-based ?strapdown IMU? algorithm to derive vehicle attitude from angular rate data, and it will use fault-detection logic to identify inflight sensor failures. Details of the system and flight test program are presented, together with results of preflight digital simulation analysis.

Development and laboratory test of an integrated sensory system (iss) for advanced aircraft

Abstract: This paper presents the results of the second phase of an Integrated Sensory Subsystem (ISS) development effort performed by Grumman under contract to the Naval Air Development Center. The ISS is a combination of redundant inertial sensors, air data probes, transducers, and other flight control related sensors, interfaces, and the associated Data Handling System (DHS). The sensor data derived within the ISS meets the requirements (i.e., performance, redundancy, survivability, etc. ) for Digital Fly-By-Wire (DFBW) flight control systems. The key issue of this development phase was the synthesis and development of a DHS for dispersed arrays of flight control inertial sensors subjected to dissimilar motions due to body bending of the aircraft structure. The system design is described in terms of the hardware and Data Handling System synthesis, followed by a discussion of the methods utilized to verify system performance. I. Introduction Future aircraft design philosophy that incorporates relaxed static stability imposes increased demands for redundancy, reliability and survivability on the aircraft's flight control system. In order to meet these demands, while minimizing hardware proliferation, a new aircraft sensor configuration and data handling system concept was developed. The Integrated Sensory Subsystem attacks the problem of sensor proliferation by minimizing the quantity of each sensor type while maximizing the number of user systems in a manner that is consistent with the performance, reliability, redundancy, and survivability requirements. The ISS achieves these goals by using design techniques that:

Azimuth Determination Using a Low Noise Ring Laser Gyro Inertial Measurement Unit.

Abstract: : The performance requirements for a ring laser gyro inertial measurement system to achieve sub-arc second azimuth determination capability have been developed. Parallel theoretical studies link these requirements to identifiable laser gyro design parameters and indicate that a feasible design could be implemented within practical constraints. A feasibility system is being assembled which will consist of 3 Raytheon RB-25 multioscillator gyros and 3 Bell Aerospace Model XI accelerometers. The instrument cluster will be mounted on a single-degree-of-freedom rotary fixture. Rotation of the cluster will be used to washout long-term error contributors with a Kalman filter using a pseduo-velocity measurement technique.