Showing papers on "Inertial measurement unit published in 1988"

Strapdown inertial measurement units for motion compensation for synthetic aperture radars

Abstract: It is shown that synthetic-aperture radar (SAR) motion can be compensated by using an antenna-mounted strapdown inertial measurement unit (IMU) as the motion sensing system, but sensor and system errors affect SAR image quality. A strapdown IMU consists of three accelerator channels and three gyro channels. Strapdown IMU errors include gyro-scale and accelerometer-scale factor and bias errors, velocity error, platform tilt, and errors induced by limited inertial sensor bandwidth. The effects of these errors on the SAR image quality are presented in terms of the SAR impulse response. IMU errors that cause low-frequency phase errors (less than one cycle per array time) are categorized in terms of quadratic and cubic phase errors. IMU errors that cause high-frequency phase errors (greater than one cycle per array time) are categorized in terms of the integrated sidelobe ratio and peak sidelobe ratio. A motion compensation system conceptualization is described wherein a strapdown IMU is attached to an antenna and transfer-aligns to the aircraft's master navigator. >

Sensor array dynamic position and orientation determination system

Abstract: A system, which uses inertial measurement units, is shown for determining the position and orientation of a towed array of sensors used for target detection. The system uses an onboard master inertial navigation system and a relative position determination mechanism to generate a first estimated position for each inertial measurement unit within the array. Each inertial measurement unit measures force and angular change information used by an onboard computer to create a second estimated position by known methods for each inertial sensor. An error signal represented by the difference between the two estimated positions for each inertial unit is processed over time by a Kalman filter to reduce the error in the heading and attitude determined for each inertial unit to establish an accurate location for each inertial unit and, thus, the towed array of such units.

Application of fixed point smoothing to the calibration, alignment and navigation data of inertial navigation systems

Abstract: The authors present an application of the fixed-point smoothing technique to calculate the relative azimuth of inertial measurement units (IMU), by postprocessing of calibration and alignment data. It is shown that the smoother performs best when the filter and smoother error covariances for gyro fixed-drift-rate parameters are increased. A test scenario was created with the calibration and alignment data from an IMU simulator. The data were postprocessed and the smoother estimated all but 0.1 arc seconds of the filter azimuth error. This is well within the expected accuracy for relative azimuth computation. >

Development of navigation guidance and control technology for Indian launch vehicles

Abstract: The orbital injection accuracy of any payload depends on the calibre of the inertial guidance system used on board the launch vehicle. This paper outlines the mission definition and the rationale for the selection of a proper guidance system to meet final mission objectives. The functions and the architecture of the navigation, guidance and control are discussed. The developmental aspects of the sophisticated inertial sensors, inertial systems, associated complex electronics, on-board computers, control actuators and systems are reported. The complexity of the on-board control and guidance software and the test and evaluation procedures used for their validation are included. The general scheme of the inertial guidance systems and the critical role played by them in the realization of Indian satellite launch vehicles SLV-3, ASLV and PSLV are presented in brief.

The design of SAR motion compensation systems incorporating strapdown inertial measurement units

Abstract: A discussion is presented of several important areas in the design of synthetic-aperture radar (SAR) motion compensation systems incorporating strapdown inertial measurement units (IMUs) as the motion-sensing system. A brief review of motion compensation for SAR is presented followed by a presentation of the effects of strapdown IMU sensor and system errors on SAR image quality. These errors include the following: gyro and accelerometer scale factor and bias errors, velocity error, and platform tilt, and errors induced by limited inertial sensor bandwidth. The effects of these errors on the SAR image quality are presented in terms of the SAR impulse response. A motion compensation system conceptualization is presented wherein a strapdown IMU is attached to an antenna and transfer-aligns to the aircraft's master navigator. >

Low cost high accuracy integrated GPS-inertial navigator for reconnaissance missions

Abstract: The authors affirm that the ability to deliver a reconnaisance payload over 300 miles from a launch point to better than 35 m can be achieved by using a tightly integrated GPS (global positioning system)-inertial system. This system provides navigation, guidance, airframe and payload management functions for an unmanned air vehicle (UAV). High accuracy is achieved by the integration of a 22-state Kalman filter for two low-cost sensors: a single-channel GPS receiver and a multisensor inertial measurement unit. The authors discusses various aspects of the UAV navigator functions and the hardware that will be used. The simulations run for a typical mission scenario, exclusive of satellite errors, demonstrated results well within specified accuracy. >

A ring laser gyro based navigator for space launch vehicle guidance

Abstract: The existing guidance and navigation system for the Centaur upper stage launch vehicle is being replaced with a single-package inertial navigation unit (INU) that includes updated electronics and inertial sensors in a strapped-down mechanization. The INU was adapted from an existing system based on a ring laser gyro (RLG) that was selected for its performance and adaptability to the space application. Adaptations were required to accommodate: space launch requirements, including qualification in accordance with MIL-STD-1540B; mission accuracies/performance requirements; and vehicle requirements. The adapted RLG INU features a proven electronic design, a single package (which includes inertial measurement and flight control subsystems), a large inertial sensor production base, and existing test facilities. >

Integrated Guidance and Control for Combined Command/Homing Guidance

Abstract: This paper describes an integrated design approach for a tactical missile which derives guidance commands from both a strapdown terminal homing seeker and a fixed-based radar system To deal with initial errors between the fixed-based radar and missile reference systems, a separate navigation filter is designed which estimates any misalignments using the fixed-based radar measurement of the missile position and outputs of the IMU on board the missile Simulation results indicate that small miss distances can be achieved without the need for accurate alignment of the missile prior to launch

Precision Pointing And Inertial Line-Of-Sight Stabilization Using Fine-Steering Mirrors, Star Trackers, And Accelerometers

Abstract: Many precision pointing systems for the coming decade will require subarcsecond stability in the presence of base motion. Satellite vibration data from various sources indicates that there is base motion between 30 and 150 urad in the frequency range from 1 to 300 Hz on most vehicles, and that there may be significant motion near 1000 Hz. In many applications, optical tracking sensor data is not available with sufficient band-width to allow rejection of base motion. Such line-of-sight (LOS) stabilization systems, therefore, require inertial sensors with signal noise levels in the submicroradian range and signal bandwidths of several hundred hertz. This paper discusses inertial LOS stabilization concepts having the potential for this accuracy. We present a configuration that illustrates the performance achievable using highly linear fine-steering mirrors (FSM), star trackers with high and long-term accuracy, and accelerometers with bandwidths approaching 1000 Hz. Simulation results are included for performance prediction.

Flight demonstration of redundancy management algorithms for a skewed array of inertial sensors

Abstract: Flight test results for two fault-tolerance algorithms developed for a redundant strapdown inertial measurement unit consisting of four 2-DOF gyros and accelerometers mounted on the faces of a semioctahedron are presented. Although both algorithms provided timely detection and isolation of flight control level failures, the generalized likelihood test algorithm provided more timely detection and isolation of low-level sensor failures than the edge vector test algorithm. The generalized likelihood test produced a false isolation for the case of a dual low-level failure applied to the sensitive axes of an accelerometer. Both of the algorithms were shown to provide dual fail-operational performance for the skewed array of inertial sensors.

Development of a tightly integrated ring laser gyro based navigation system

Abstract: The development of a small, tightly integrated GPS/inertial navigation system (INS) is being pursued following the development of a miniaturized GPS receiver and a compact multiaxis ring laser gyro The tradeoffs involved in achieving the present system architecture, along with a system description and performance summary, are presented A description of both the inertial hardware and the GPS receiver hardware, as well as a detailed implementation of both Kalman filters (inertial and receiver), is discussed Finally, the test program is presented >

Modular hybrid avionic system for precision tactical weapons

Abstract: A system architecture is described to tightly integrate the avionic functions of navigation, guidance, autopilot, and data link into a powerful, modular, high-reliability, cost-efficient solution to the expanding mission requirements of guided weapons. The system combines the navigation and secure data link attributes of the joint tactical information distribution system (JTIDS); GPS (global positioning system); an innovative low cost inertial measurement unit (IMU); a low-cost, lightweight Doppler; and software which combines data from JTIDS, GPS, IMU, target tracker, altimeter, and true airspeed sensor, to optimize navigation, guidance, and autopilot avionic functions. The intent of the system architecture is to form a network of cooperating battle elements, rather than rely exclusively on onboard measurements, to improve the weapon system capability. >

Morrison's QUBIK Inertial Measurement Unit

Abstract: A new inertial system, “the QUBIK IMU,” uses a single sensor to provide all six output signals (three linear and three angular). The sensor is a cubic design with parallel orthogonal linear arrays of capacitors and magnetic suspension elements arranged on a selected plane for each axis of motion. A corresponding set of capacitors and magnetic suspension elements is located on the interior surface of a cubic outer assembly. The IMU has six electronic servo control circuits that process outputs from variable capacitor elements and apply magnetic forces on certain locations on the cube to keep it “centralized” in the cubic cavity. When linear and/or angular motion occurs, the restoring signals maintain the cube's position in the cavity. The level and locations of the magnetic forces on the cube are processed by a computer using a Kalman filter. Working models of the QUBIK IMU have been built, tested, and analyzed to verify its envelope capabilities. Patent No. 4711125 was issued for this device by the U.S. Patent Office in December, 1987.

To the calibration. alignment and

Abstract: This paper presents an application of fixed point smoothing technique to calculate the relative azimuth of Inertial Measurement Units (IMU) via post processing of calibration and alignment data. between platform and computer frames about the local vertical axis. In many applications azimuth is a crucial parameter for a vehicle's accurate arrival to its destination. The smoothing algorithm has been implemented on an IBM computer and calibration and alignment data from an IMU simulator has been post processed. development and smoother post processing results are presented in this paper. Azimuth is the misalignment angle

Precision trajectory reconstruction

Abstract: A precision trajectory reconstruction technique based on photoscoring has been developed to evaluate the airborne accuracy performance of guidance and navigation systems The sensors include a reference inertial navigation system (INS) and a motion picture camera The camera is mounted in the aircraft at a known position and attitude with respect to the inertial system and is used to photograph marker panels placed at precisely surveyed locations on the ground The camera includes a time display device which is driven by a clock associated with the inertial data The image data from the camera are processed with a modern Kalman filter/smoother to estimate the inertial system errors The trajectory is then reconstructed by correcting the inertial system data with the estimated errors It is shown using covariance analysis that the precision photoscoring technique can be used to reconstruct the flight trajectory with a position error of 04 m under baseline conditions In addition, flight tests were used to evaluate the accuracy of the photoscoring process >

Integrated avionics reliability

Abstract: The integrated avionics reliability task is an effort to build credible reliability and/or performability models for multisensor integrated navigation and flight control. The research was initiated by the reliability analysis of a multisensor navigation system consisting of the Global Positioning System (GPS), the Long Range Navigation system (Loran C), and an inertial measurement unit (IMU). Markov reliability models were developed based on system failure rates and mission time.

Flight test results of a vector-based failure detection and isolation algorithm for a redundant strapdown inertial measurement unit

Abstract: Flight test results of a vector-based fault-tolerant algorithm for a redundant strapdown inertial measurement unit are presented. Because the inertial sensors provide flight-critical information for flight control and navigation, failure detection and isolation is developed in terms of a multi-level structure. Threshold compensation techniques for gyros and accelerometers, developed to enhance the sensitivity of the failure detection process to low-level failures, are presented. Four flight tests, conducted in a commercial transport type environment, were used to determine the ability of the failure detection and isolation algorithm to detect failure signals, such a hard-over, null, or bias shifts. The algorithm provided timely detection and correct isolation of flight control- and low-level failures. The flight tests of the vector-based algorithm demonstrated its capability to provide false alarm free dual fail-operational performance for the skewed array of inertial sensors.