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Showing papers on "Inertial measurement unit published in 1973"


Journal ArticleDOI
Stanley K. Jordan1
TL;DR: In this article, the steady-state rms errors that are excited in a damped inertial navigation system are analytically determined for four gravity uncertainty models and two vehicle maneuver models.
Abstract: Gravity uncertainties are an inexorable source of error in all inertial navigation systems and are particularly important in high-quality inertial navigation systems. In this paper the steady-state rms errors that are excited in a damped inertial navigation system are analytically determined for four gravity uncertainty models and two vehicle maneuver models. The statistical approach used in this paper is compared with an alternate scheme (?direct simulation?) that does not require statistical models for gravity uncertainties.

35 citations


Patent
17 Oct 1973
TL;DR: In this paper, a simplified inertial guidance system is provided for the cross track or inertial '''''' line-of-sight'' planar guidance of an unmanned tactical vehicle, or the like; wherein one of the attitude angles can be of large magnitude.
Abstract: A simplified strapdown inertial guidance system is provided for the cross track or inertial ''''line-of-sight'''' planar guidance of an unmanned tactical vehicle, or the like; wherein one of the attitude angles can be of large magnitude. The system includes three orthogonally-mounted accelerometers and two gyroscopes. The large attitude angle is accommodated by torquing the appropriate gyroscope in a capture loop. The system implements the body attitude angles to inertial attitude angles in two steps. First a transformation is made from body to gyroscope coordinates, and then a transformation is made from gyroscope to inertial coordinates.

16 citations


01 Jan 1973
TL;DR: An elementary understanding of the physical laws governing the spinning rotor 1S is necessary to grasp the essence and function of the various gyroscopic instruments found in to-day's aerospace and maritime vehicle control systems as discussed by the authors.
Abstract: An elementary understanding of the physical laws governing the spinning rotor 1S necessary to grasp the essence and function of the various gyroscopic instruments found in to-day's aerospace and maritime vehicle control systems. This report gives a brief exhibition of the very basic phenomena of gyro behaviour in a way that may especially appeal to the control engineer with a limited educational background in the field of mechanical engineering.

15 citations


Journal ArticleDOI
TL;DR: The formulation of the Strapdown system transfer alignment problem developed in this paper requires only three state variables which do not vary with time, and a good deal of the computer burden imposed by other recursive filter implementations is eliminated.
Abstract: Introduction I of Strapdown inertial systems requires determining the attitude (direction cosine) matrix which relates a vehicle-fixed set of axes to a reference or navigation coordinate frame. If the vehicle motion is measured in the reference frame by some auxiliary means such as another set of inertial sensors or doppler radar, transfer alignment can be accomplished by comparing similar quantities measured by the Strapdown system gyros and accelerometers. Several techniques to accomplish transfer alignment exist, including gyrocompassing and the use of Kalman-like (recursive) filters." Typically, alignment schemes employing the Kalman optimum technique involve many state variables to describe relative motion between the vehicle and reference axes. While such filters give generally better accuracy and faster alignment than gyrocompassing they impose a heavy computation burden on the alignment system. In particular, they require solution of a large number of simultaneous differential equations with coefficients dependent upon vehicle motion. The formulation of the Strapdown system transfer alignment problem developed in this paper requires only three state variables which do not vary with time. Consequently, a good deal of the computer burden imposed by other recursive filter implementations is eliminated.

8 citations


Journal ArticleDOI
TL;DR: In this article, three altitude damping mechanizations for a space-stable inertial navigation system are proposed, and the equivalent local-level mechanizations are then found by comparing error propagation equations in a common coordinate frame.
Abstract: In order to stabilize the altitude calculation in an inertial navigation system, an altimeter is commonly used. In a conventional local-level mechanization, this is generally accomplished by correcting the vertical channel integrators with the difference between the inertial system and altimeter indication of vertical position. However, in a space-stable system the procedure is not as clear since a vertical channel is not physically present. Three altitude damping mechanizations for a space-stable inertial navigation system are proposed. The equivalent local-level mechanizations are then found by comparing error propagation equations in a common coordinate frame.

7 citations


Journal ArticleDOI
TL;DR: In this paper, a Kalman filter approach is proposed for terrestrial inertial navigation, which is applicable to all of the above procedures, and presents numerical results to demonstrate its effectiveness. But, although the error dynamics are identical for the local-level and space-stable configurations, the dynamics of the sensor errors which drive these systems are quite different.
Abstract: Terrestrial inertial navigation is typically performed using an instrumented platform stabilized in a ?local-level? configuration for convenient generation of geographic navigation information. The local-level geographic reference must be maintained by torquing the system gyros, a requirement which may be incompatible with high-precision inertial sensors currently under development. Gyro torquing in a gimballed navigation system can be avoided by employing a ?space-stable? mechanization of the platform where an inertial, rather than geographic, reference is used for navigation calculations. The software design problems associated with this concept, especially those related to the application of Kalman filtering, are the principle focus of this paper. Although the space-stable configuration has been used extensively for spacecraft navigation and guidance, it has not been widely applied to terrestrial navigation, either for air or marine applications. The chief problem in this application is to perform navigation in local-level coordinates, using system outputs generated in an inertial reference frame. It can be demonstrated that, although the navigation system error dynamics are identical for the local-level and space-stable configurations, the dynamics of the sensor errors which drive these systems are quite different. These differences in sensor error propagation characteristics impose new requirements for the design of procedures to accomplish system calibration, alignment, and reset. This paper outlines a Kalman filtering approach which is applicable to all of the above procedures, and presents numerical results to demonstrate its effectiveness.

4 citations


Journal ArticleDOI
TL;DR: The heart of an inertial navigation system is the Inertial Measuring Unit (I.M.U.) as this carries out the fundamental tasks of measuring the vehicle acceleration and providing a spatial reference, and determines the system performance and accuracy.
Abstract: The heart of an inertial navigation system is the Inertial Measuring Unit (I.M.U.) as this carries out the fundamental tasks of measuring the vehicle acceleration and providing a spatial reference. The I.M.U. thus determines the system performance and accuracy; it also accounts for about two thirds of the initial cost of the system and is a major factor in the cost of ownership.Up to now the majority of IN systems have used a stable platform I.M.U. where the gyros and accelerometers are mounted on a gimbal suspended platform which is servo controlled from the gyros. This has greatly eased the task of developing suitable gyros of the required accuracy, as the gimbal stabilization system isolates the gyros from the angular motion of the vehicle and greatly simplifies the subsequent computation in terms of axis transformations; it provides a direct read out of the euler angles—heading, pitch and roll. However such a system is inevitably mechanically complex and its ultimate reliability is constrained by such components as slip rings, servo motors, synchros, resolvers, encoders, gimbal bearings &c.

3 citations


Proceedings ArticleDOI
01 Aug 1973
TL;DR: In this article, the authors present a real-time detection and isolation of hard and soft failures in real time by an airborne computer using skewed alignment of two redundant conventional inertial measuring units.
Abstract: Skewed alignment of two redundant conventional inertial measuring units permits nonambiguous detection and isolation of hard and soft failures in real time by an airborne computer. Accelerometer outputs and gimbal readouts are monitored periodically, and attitude rate and velocity error vectors are computed from these data. Magnitudes of these vectors provide failure detection, and projection of these error vectors onto the coordinate axes of the two clusters permits isolation. A detailed Monte Carlo simulation of one version of the mechanization as applied to Space Shuttle boost trajectories demonstrates effectiveness down to very low levels of inertial instrument performance failures. The results indicate that worst case overall navigation performance occurs when accelerometer failures are of the order of 20 sigma and gyro failures are about 100 sigma for conventional state-of-the-art IMU instruments.

3 citations


Proceedings ArticleDOI
Arthur J. Pejsa1
20 Aug 1973
TL;DR: In this article, the effect of gravity-dependent sensor errors and the generally reduced effect of azimuth errors on navigation accuracy significantly alter the situation and tend to decrease sensor elevation angles in an optimized system.
Abstract: The problem of proper placement of the inertial sensors to optimize system performance is important to system designers. This is especially true of redundant strapdown systems that employ more sensors than the conventional, mutually orthogonal sets of three. In systems designed for a free fall environment and with no preferred direction, such as for spacecraft attitude reference, the sensor input axes should divide the three-space equally, and can thus be viewed as being normal to the faces of regular polyhedra.' In Earth-bound inertial navigators, the effect of gravity-dependent sensor errors and the generally reduced effect of azimuth errors on navigation accuracy significantly alter the situation. Both effects tend to decrease sensor elevation angles in an optimized system. Formulas are derived and curves are drawn for optimum sensor elevation and azimuth angles vs a 0-sensitive sensor error parameter, and a mission relative azimuth error parameter. Tetrad, pentad, and hexad arrays are analyzed, affording a dramatic improvement in accuracy as well as autonomous fault isolation and/or detection capability.

1 citations