Showing papers on "Inertial measurement unit published in 1987"

Miniature inertial measurement unit

Abstract: A three axis inertial measurement unit (IMU) is shown with three pairs of accelerometers mounted upon a platform that is rotated about a single axis perpendicular to the plane of the platform. Each pair of accelerometers is mounted in parallel, at an angle to the platform and to the single axis and at the same distance from the axis. The rotational motion may be either an oscillation about a dither axis or spinning about a spin axis.

Method for determining the heading of an aircraft

Abstract: A method is disclosed for determining the heading of an aircraft which is equipped with both an inertial navigation system and a device capable of receiving navigation satellite signals and computing the aircraft's position, speed and acceleration therefrom. While the aircraft is still on the ground and before flight operations begin, an initial alignment of the inertial navigation system with an earth-fixed coordinate system is performed, and during this alignment, data corresponding to the initial attitude of an aircraft-fixed coordinate system relative to the earth-fixed coordinate system is also determined and stored. Thereafter, during flight operations, the acceleration vector of the aircraft relative to the aircraft-fixed coordinate system is measured by the inertial navigation system and then transposed into a coordinate system which has been horizontally aligned with the earth-fixed system using the initial attitude data. second acceleration vector, corresponding to the acceleration of the aircraft in the earth-fixed system, is computed using the navigation satellite system. The aircraft's heading is then determined by computing the difference, i.e., the angle between, the two acceleration vectors. The method is amenable to Kalman filtering techniques and, by eliminating the need for highly accurate gyroscopes or magnetic compasses, permits rapid and highly accurate heading determinations to be made at much less expense.

Ring Laser Gyro Marine INS

Abstract: Litton's Guidance and Control Systems Division has developed a ring laser gyro (RLG) marine inertial navigation system (INS) which provides improved performance and reliability compared to the-current Navy standard which uses a gimbaled inertial measuring unit (IMU) with gas bearing gyros. Since Litton has already provided over 1000 Navy -standard systems, the new RLG IMU was designed to be completely -compatible with the mechanical and electrical characteristics of the standard system enclosure. It can easily be retrofitted into existing shipboard installations without disturbing the enclosure mounting position. Appropriate engineering tradeoffs were made in the design of the RLG IMU to balance the sometimes conflicting factors of performance, reliability, cost, and environmental isolation. An engineering prototype of the system has been built and tested. Steps taken to isolate the instruments from environmental influences are described. The relationship between system design and reliability/maintainability is discussed.

Inertially Aided Navigation of Undersea Vehicles

Abstract: As the tasks to be performed by underwater vehicles become more sophisticated, the navigational requirements and positional-accuracy constraints become more rigorous. A number of proposed missions for manned and autonomous vehicles require that the position be accurately known at all times, independent of external navigational input data. A typical cruise duration might extend from several hours to several hundreds of hours. Inertial navigation systems have been proposed to assist in the solution to such underwater navigational problems. This paper will review the current state of development of inertial navigation systems (INSs) with respect to accuracy, power requirements, operational constraints, size and cost. Systems may be grouped into operation-specific categories as a result of these limitations. Recent technological developments, including ring-laser and fiberoptic gyros, will be briefly discussed along with their future applicability to undersea navigati on requirements.

Ring laser gyros

Abstract: Along with advanced digital computing a revolutionary new inertial sensor has changed the design of inertial navigation systems. This new sensor, the ring laser gyroscope, is discussed

A vector-based failure detection and isolation algorithm for a dual fail-operational redundant strapdown inertial measurement unit

Abstract: A vector-based failure detection and isolation technique for a skewed array of two degree-of-freedom inertial sensors is developed. Failure detection is based on comparison of parity equations with a threshold, and isolation is based on comparison of logic variables which are keyed to pass/fail results of the parity test. A multi-level approach to failure detection is used to ensure adequate coverage for the flight control, display, and navigation avionics functions. Sensor error models are introduced to expose the susceptibility of the parity equations to sensor errors and physical separation effects. The algorithm is evaluated in a simulation of a commercial transport operating in a range of light to severe turbulence environments. A bias-jump failure level of 0.2 deg/hr was detected and isolated properly in the light and moderate turbulence environments, but not detected in the extreme turbulence environment. An accelerometer bias-jump failure level of 1.5 milli-g was detected over all turbulence environments. For both types of inertial sensor, hard-over, and null type failures were detected in all environments without incident. The algorithm functioned without false alarm or isolation over all turbulence environments for the runs tested.