Showing papers on "Inertial reference unit published in 2005"

Vision-Aided Inertial Navigation for Flight Control

Abstract: Published in the Journal of Aerospace Computing, Information, and Communication, Vol. 2, September 2005

An Overview of the Instrument Suite for the Deep Impact Mission

Abstract: A suite of three optical instruments has been developed to observe Comet 9P/Tempel 1, the impact of a dedicated impactor spacecraft, and the resulting crater formation for the Deep Impact mission. The high-resolution instrument (HRI) consists of an f/35 telescope with 10.5mfocal length, and a combined filtered CCD camera and IR spectrometer. The medium-resolution instrument (MRI) consists of an f/17.5 telescope with a 2.1 m focal length feeding a filtered CCD camera. The HRI and MRI are mounted on an instrument platform on the flyby spacecraft, along with the spacecraft star trackers and inertial reference unit. The third instrument is a simple unfiltered CCD camera with the same telescope as MRI, mounted within the impactor spacecraft. All three instruments use a Fairchild split-frame-transfer CCD with 1,024 × 1,024 active pixels. The IR spectrometer is a two-prism (CaF2 and ZnSe) imaging spectrometer imaged on a Rockwell HAWAII-1R HgCdTe MWIR array. The CCDs and IR FPA are read out and digitized to 14 bits by a set of dedicated instrument electronics, one set per instrument. Each electronics box is controlled by a radiation-hard TSC695F microprocessor. Software running on the microprocessor executes imaging commands from a sequence engine on the spacecraft. Commands and telemetry are transmitted via a MIL-STD-1553 interface, while image data are transmitted to the spacecraft via a low-voltage differential signaling (LVDS) interface standard. The instruments are used as the science instruments and are used for the optical navigation of both spacecraft. This paper presents an overview of the instrument suite designs, functionality, calibration and operational considerations.

Vision-aided inertial navigation for flight control

Abstract: Published in the Journal of Aerospace Computing, Information, and Communication, Vol. 2, September 2005

Navigation Error Analysis of Atom Interferometer Inertial Sensor

Abstract: The recent development of the atom interferometer and its demonstration as an inertial sensor of acceleration and rotation rate augur a new generation of inertial navigation systems that would rival today's satellite navigation accuracy at the few-meter level. This paper reviews the principles of inertial measurement using the atom interferometer from a rudimentary viewpoint to illustrate the fundamentals and to highlight some of the potential shortcomings with a particular type, the cold-atom interferometer. One of these shortcomings is the fact that this interferometer requires a finite period of time during which the atoms are prepared (cooled) before they enter the interferometer and respond to its dynamics relative to an inertial frame. This lapse in the measurement duty cycle could be supplemented with very precise conventional inertial measurement units (IMUs), or eliminated with multiple, interleaved atom interferometers. Error analyses show that cold-atom interferometric IMUs that capture 50 percent of the dynamics must be coupled with conventional IMUs that are 50 times more accurate than typical navigation-grade units to sustain a horizontal position error of under 5 m (root mean square) after 1 h.

A scheme for improving the performance of a gyroscope-free inertial measurement unit

Abstract: A gyroscope-free inertial measurement unit (GF-IMU) uses only accelerometers to compute specific force and angular rate. It is a low-cost inertial system, but its measurement error diverges at a rate that is an order faster than that of a conventional inertial system equipped with gyroscopes. In this paper, a redundant accelerometer-aided gyroscope-free IMU is designed to achieve a stable and bounded system. In this system, a three-axis accelerometer is used in addition to a set of six accelerometers that is typical in a conventional gyroscope-free IMU. The linear error dynamics of this aided gyroscope-free IMU is derived, and the effects of accelerometer errors are analyzed.

Integration of DGPS with a Low Cost MEMS - Based Inertial Measurement Unit (IMU) for Land Vehicle Navigation Application

Abstract: This paper focuses on evaluating the feasibility of using a low cost Micro Electro Mechanical System (MEMS) – based Inertial Measurement Unit (IMU) integrated with Differential Global Positioning System (DGPS), for land vehicle navigation. The main focus is on position accuracy analysis using a closed loop decentralized GPS/INS integration scheme. A Kalman filter is proposed for the IMU which models sensor scale factors and turn on biases. A performance comparative analysis of the MEMS Crista IMU with a tactical grade HG1700 IMU is presented. GPS outages are simulated in a clean data set collected in open sky conditions, by artificially omitting satellites during post-processing in order to asses the stand-alone performance of each IMU. Two different methods are investigated to prevent the errors from accumulating in the Inertial Navigation System (INS) in the absence of GPS. One is to use the constrained motion attributes of a land vehicle to bound the drift in the INS solution. This method is suitable for use in real-time applications. Another method is specifically a post processing scheme which involves the use of a Rauch Tung Streibel (RTS) smoother. Simultaneous field testing using DGPS and MEMS, tactical, and navigation-grade IMUs was conducted to allow for a direct comparison of their relative performance. The results show that in open sky conditions with MEMS IMU measurements and a pseudorange/Doppler derived DGPS solution, a positional accuracy better than 38 cm can be achieved. The use of vehicle movement constraints during GPS outages can prevent errors from accumulating, and can provide the improvement of up-to 80% in the position domain, whereas the corresponding improvements using the RTS smoother are about 99%.

Method and system for calibrating sports implement inertial motion sensing signals

Abstract: Techniques for calibrating club-like sports implement inertial motion sensing signals are disclosed. The disclosed method and system generate calibrated output of a motion sensing circuit, which circuit includes an inertial measurement unit and associates with a club-like sports implement. The method and system generate a plurality of calibration coefficients along a predetermined set of axes, said axes corresponding to the axes of movement for said club-like sports implement. The calibration coefficients are applied to a sensing program that operates in association with the inertial measurement unit. The method and system generate sensed motion data using the inertial measurement unit, which includes data relative to the predetermined set of axes. The data is in response to motion of the club-like sports implement. Furthermore, the method and system calibrate the sensed motion data using said plurality of calibration coefficients.

GPS/INS uses low-cost MEMS IMU

Abstract: A description of the design, operation, and test results of a miniature, low-cost, integrated GPS/inertial navigation system that uses commercial off-the-shelf micro-electro-mechanical system (MEMS) accelerometers and gyroscopes. The MEMS inertial measurement unit (EMU) is packaged in a small size and provides the raw EMU data through a serial interface to a processor board where the inertial navigation solution and integrated GPS/inertial Kalman filter is generated. The GPS/inertial software integration is performed using NAVSYS' modular InterNav software product. This allows integration with different low-cost GPS chip sets or receivers and also allows the integrated GPS/inertial navigation solution to be embedded as an application on a customer's host computer. This modular object-oriented architecture facilitates integration of the miniature MEMS GPS/INS navigation system for embedded navigation applications and is designed to handle the large errors characteristic of a low-grade MEMS IMU. Test results are presented showing the performance of the integrated MEMS GPS/inertial navigation system. Data is provided showing the position, velocity, and attitude accuracy when operating with GPS aiding and also for periods where GPS dropouts occur and alternative navigation update sources are used to bound the MEMS inertial navigation error growth.

In-use calibration of body-mounted gyroscopes for applications in gait analysis

Abstract: In this paper, we propose an in-use calibration procedure for gyroscopes. The case report is a simple inertial measurement unit (IMU), which is used in our current research on inertial motion-sensing for advanced footware. The IMU contains two biaxial accelerometers and one gyroscope; it is developed for being mounted on one subject's foot instep, with the aim to reconstruct the trajectory in the sagittal plane of the sensed anatomical point. Since the IMU sagittal displacements can be estimated by performing strapdown integration, they can also be compared with their true values. One movement, which corresponds to known (vertical) displacements, consists of foot placements from the ground level on to top of steps of known height (step climbing). Provided that the IMU accelerometers are calibrated separately by any standard calibration procedure, motion tracking during the stepping movement allows to estimate the gyroscope sensitivity. The experimental results we present in this paper demonstrate the proposed in-use calibration procedure.

Systems and methods for reducing vibration-induced errors in inertial sensors

Abstract: Systems and methods for reducing vibration-induced bias errors in inertial sensors are disclosed. A system for reducing bias errors in an inertial sensor operating within an environment may include a vibration detector for sensing vibration changes within the environment proximate to the inertial sensor, and a Kalman filter for computing an estimate of the navigational error produced by the inertial sensor due to a vibration-induced bias shift detected by the vibration detector. The vibration detector can be configured to measure an accelerometer output of the inertial sensor over a Kalman filter cycle, and then use the standard deviation of such output to obtain a statistical measure of the vibration within the environment. In some embodiments, the inertial sensor may include an inertial measurement unit (IMU) connected to an error compensation unit and strapdown navigator, each of which can be fed navigation corrections determined by the Kalman filter.

Traffic alert collision avoidance system (TCAS) devices and methods

Abstract: A device for determining the bearing of a vehicle using Inertial Reference Unit (IRU) and Traffic Alert Collision Avoidance System (TCAS) data. The device includes a means to communicate with the vehicle such as a transmitter, receiver, and antenna. The device also includes a processor configured to receive the IRU and TCAS data from the vehicle via the communication means and then generate a bearing value using the received data.

MEMS SoC: observer-based coplanar gyro-free inertial measurement unit

Abstract: This paper presents a novel design of a coplanar gyro-free inertial measurement unit (IMU) that consists of seven to nine single-axis linear accelerometers, and it can be utilized to perform the six DOF measurements for an object in motion. Unlike other gyro-fee IMUs, this design uses redundant accelerometers and state estimation techniques to facilitate the in situ and mass fabrication for the employed accelerometers. The alignment error from positioning accelerometers onto a measurement unit and the fabrication cost of an IMU can greatly be reduced. The outputs of the proposed design are three linear accelerations and three angular velocities. As compared to other gyro-free IMUs, the proposed design uses less integral operation and thus improves its sensing resolution and drifting problem. The sensing resolution of a gyro-free IMU depends on the sensing resolution of the employed accelerometers as well as the size of the measurement unit. Simulation results indicate that the sensing resolution of the proposed design is 2° s−1 for the angular velocity and 10 μg for the linear acceleration when nine single-axis accelerometers, each with 10 μg sensing resolution, are deployed on a 4 inch diameter disc. Also, thanks to the iterative EKF algorithm, the angle estimation error is within 10−3 deg at 2 s.

Inertial navigation system error correction

Abstract: Methods and apparatus for: (a) the correction of one or more elements determined from a first set of continuous gyro and accelerometer measurements comprising using a second set of discontinuously measured higher accuracy accelerometer measurements doubly integrated in an inertial coordinate system, (b) determining relative movement of a vehicle using a first set of acceleration measurements that do not include components of acceleration caused by the Earth's gravitational field, and a second set of acceleration measurements that do include components of acceleration caused by the Earth's gravitational field; and (c) correcting errors in an inertial navigation system positioned in a vehicle comprising using independently measured changes in position of the vehicle relative to an inertial coordinate frame.

Kinematic model aided inertial motion tracking of human upper limb

Abstract: A new motion tracking framework has been developed to estimate the position and orientation of human upper limb. This method fuses data from on-board accelerometers and gyroscopes, which are accommodated in a commercially available inertial sensor MT9. Human upper limb motion can be represented by a kinematic chain in which six joint variables are to be considered: three for the shoulder and three for the elbow. Based on measurements of the inertial sensor placed on the wrist, we then obtain the positions of the wrist and elbow. An extended Kalman filter then fuses the data from these sensors in order to reduce errors and noise in measurements. Preliminary results demonstrate the favorable performance of the proposed strategy.

A strapdown inertial system of minimum dimension : (A 3D oscillator as a complete inertial sensor)

Abstract: We discuss data acquisition and control algorithms for an isotropic 3D oscillator turning it into an inertial unit simultaneously combining a 3D angular orientation sensor and a 3D linear acceleration sensor.

Systems and methods for ultrasound imaging using an inertial reference unit

Abstract: Systems and methods for ultrasound imaging using an inertial reference unit are disclosed. In one embodiment, an ultrasound imaging system includes an ultrasound unit configured to ultrasonically scan at least one plane within a region of interest in a subject and generate imaging information from the scan. An inertial reference unit is provided that detects relative positions of the ultrasound unit as the ultrasound unit scans a plurality of plane. A processing unit is configured to receive the imaging information and the corresponding detected position and is operable to generate images of the region of interest.

Design and mechatronic implementation of an accelerometer-based, kinematically redundant inertial measurement unit

Abstract: This paper discusses the design, calibration, and simulation of a kinematically redundant inertial measurement unit which is based solely on accelerometers. The sensor unit comprises twelve accelerometers, two on each face of a cube. The location and direction of the sensors are determined so as to locally optimize the numerical conditioning of the system of governing kinematic equations. The orientational installation error of each sensor is identified by off-line iterative processing of the gravitational-acceleration measurements made at a number of known orientations of the unit. Furthermore, a novel procedure is developed through which the acceleration measurements can be used to directly determine the body angular velocity; this results in a major accuracy improvement over similar works whereby the angular velocity is obtained via integrating the angular acceleration. Numerical results are presented

Transfer Alignment for Space Vehicles Launched from a Moving Base

Abstract: Alignment of the inertial measurement unit (IMU) is a prerequisite for any space vehicle with self-contained navigation and guidance for any mission-critical application. Normally, inertial measurement unit is aligned through gyro-compassing using the stored data for heading. In case of launch from a moving base, it is essential to align the inertial measurement unit in the vehicle (slave unit) with that mounted on the moving platform (master unit). The master inertial navigation system is more accurate, stable, and calibrated wrt the slave unit. An error propagation system involving the misalignment between the master and the slave has been formulated involving the three misalignment angles, three velocity errors, and three positional errors. The manoeuvre of the moving base excites the sensors of both the master and the slave inertial navigation systems for the generation of data to be used in aligning the slave inertial measurement unit of the inertial navigation system (strapdown mode). The entire duration of manoeuvre has to be reduced to a minimum with minimum effort of manoeuvre. This involves the deployment of an adaptive estimator and a linear quadratic Gaussian regulator for alignment of the strapdown slave inertial navigation system.

Enhanced inertial system performance

Abstract: An inertial system is provided. The system includes at least one inertial sensor, a processing unit and a plurality of Kalman filters implemented in the processing unit. The Kalman filters receive information from the at least one inertial sensor, and at most one of the plurality of Kalman filters has processed zero velocity updates on the last cycle. The plurality of Kalman filters is used to optimize system response and performance during periods of intermittent motion.

Methods and systems for enhanced navigational performance

Abstract: Methods and systems for navigation are disclosed. In one embodiment, data from GPS satellites within a field of view of a ground station are retransmitted to LEO satellites, such as Iridium satellites, and cross-linked if necessary before being transmitted to a user. The user is then able to combine the fed-forward data with data received directly from GPS satellites in order to resolve errors due to interference or jamming. Alternately, a method includes receiving at least one carrier signal at a user device, each carrier signal being transmitted by a distinct LEO satellite. The user device processes the carrier signals to obtain a first carrier phase information. The user device recalls an inertial position fix derived at an inertial reference unit. The user device derives a position of the user device based on the inertial position fix and the first carrier phase information.

Accelerometers and an aircraft attitude evaluation

Abstract: The paper describes a method that enables a usage of low-cost inertial sensors, such as angular rate sensors and accelerometers, in a system of aircraft attitude evaluation. The method depicts a suitability of using accelerometers to restrict an influence of angular rates' integration on a precision of the attitude assessment. The method was verified with a simulation in MATLAB-Simulink environment and with various measurements. The method principles, simulation and measurement results are presented

Built in test for mems vibratory type inertial sensors

Abstract: The present invention provides a MEMS vibratory type inertial sensor that has some level of built in test to help improve the reliability by helping to identify erroneous or misleading data provided by the inertial sensor. A test signal is injected into one or more of the inputs of the MEMS vibratory type inertial sensor, where the test signal produces a test signal component at one or more of the MEMS vibratory type inertial sensor outputs. The test signal component is then monitored at one or more of the outputs. If the test signal component matches at least predetermined characteristics of the original test signal, it is more likely that the MEMS vibratory type inertial sensor is operating properly and not producing erroneous or misleading data. In some embodiments, the test signal is provided and monitored during the normal functional operate The present invention provides a MEMS vibratory type inertial sensor that has some level of built in test to help improve the reliability by helping to identify erroneous or misleading data provided by the inertial sensor. In one illustrative embodiment, a test signal is injected into one or more of the inputs of the MEMS vibratory type inertial sensor, where the test signal produces a test signal component at one or more of the MEMS vibratory type inertial sensor outputs. The test signal component is then monitored at one or more of the outputs. If the test signal component matches at least predetermined characteristics of the original test signal, it is more likely that the MEMS vibratory type inertial sensor is operating properly and not producing erroneous or misleading data. In some embodiments, the test signal is provided and monitored during the normal functional operation of the MEMS vibratory type inertial sensor, thereby providing on going built in test.

Hybrid inertial navigation system based on a kinematic model

Abstract: The invention concerns a method for improving determination of inertial navigation parameters (1) of a carrier (1) moving along modelizable kinematic movement components, the method including the following steps: (a) selecting, taking into account a kinematic model (13) of the carrier (1), at least one movement component whereby integration (11) of the inertial measurements (20) is assumed to give a predetermined value, (b) integrating (11) the inertial measurements (20) in accordance with the selected component(s), (c) determining (14) based on the component(s) a variation between the integration (11) obtained at step (b) and the predetermined value of step (a), (d) estimating on the basis of the variation(s) thus obtained a global inertial error resulting from inertial errors associated with said modelizable components, and values to be updated of variable parameters of the kinematic model (13), (e) correcting said inertial navigation based on the thus determined global inertial error. The invention also concerns an inertial navigation system for implementing said method.

Attitude Control System of the Wilkinson Microwave Anisotropy Probe

Abstract: The Wilkinson Microwave Anisotropy Probe mission produces a map of the cosmic microwave background radiation over the entire celestial sphere by executing a fast spin and a slow precession of its spin axis about the sun line to obtain a highly interconnected set of measurements. The attitude control system implements this spin-scan observing strategy while minimizing thermal and magnetic fluctuations, especially those synchronous with the spin period. The spacecraft attitude is sensed and controlled using an inertial reference unit, 2 star trackers, a dual-head digital sun sensor, 12 coarse sun sensors, 3 reaction wheel assemblies, and a propulsion system. Sufficient attitude knowledge is provided to yield instrument pointing to a standard deviation (1σ) of 1.3 arc-min per axis. The attitude control system also maintains the spacecraft attitude during orbit maneuvers, controls the spacecraft angular momentum, and provides for safety in the event of an anomaly. An overview of the design of the attitude control system to carry out this mission is presented, as well as some early flight experience.

Mass measurement system and method using inertial force and standard mass in gravity-free environment

Abstract: The mass measurement system includes a linear acceleration motion unit that is a linear motion driving source, a first load cell fastened to the linear acceleration motion unit to measure an inertial force of a sample caused by linearly accelerated motion of the 10 linear acceleration motion unit, a second load cell fastened to the linear acceleration motion unit while being spaced apart from the first load cell by a predetermined distance, the second load cell measuring an inertial force of a standard sample having a known standard mass caused by the linearly accelerated motion of the linear acceleration motion unit, and a main control unit for calculating and outputting mass of the sample through an arithmetic operation based on the inertial forces, measured by the first and second load cells, and the standard mass, and controlling an entire operation of the system.

Design of a nine-accelerometer non-gyro inertial measurement unit

Abstract: Non-gyro inertial measurement unit (NGIMU) uses only accelerometers replacing gyroscopes to compute the motion of a moving body. Use the traditional accelerometer configurations for reference, a novel nine-accelerometer configuration of NGIMU is proposed with its mathematic model constructed. This configuration can acquire the expressions of the angular accelerations directly and avoid calculating the differential poly-equation. To confirm the effectiveness of the design, the experiment system is set up and the DSP data processing circuit is also done. In addition, the experiments of the angle estimating are performed and the results show that the design can reflect the trend of the angle changing with high precision to some extend.

Flight Track Data Creation and Inertial Component Simulation the Strap-down INS

Abstract: Because we don’t receive easily comprehensive and actual flight track data and inertial component output parameters. But the capability testing of the software and hardware of the Strap-down inertial navigation systems need them. Therefor, the author bring forward the analytical idea of flight track data creation and inertial component simulation. The flight track data and the inertial component that been created by the idea have been applied successfully and gain better effect in system testing.

Method and device for measuring the orientation of an aircraft nose landing gear

Abstract: A device including an inertial reference station for measuring an aircraft heading. An inertial reference unit which is mountable on a wheel of a nose landing gear by a fixing system, and is used for measuring the heading of said landing gear in a non-steering position. A data processing unit includes a comparison unit for carrying out a comparison between the measured heading of the nose landing gear and the measured aircraft heading in such a way that the orientation of the nose landing gear is calculated with respect to the aircraft body.

Theoretical Summary on Non-gyro Inertial Measurement Unit

Abstract: Non-gyro inertial measurement unit (NGIMU) uses accelerometers instead of gyroscopes to compute the motion of a moving body Using the domestic and the international research achievements for reference, the origin and current status of NGIMU are summarized In addition, many kinds of accelerometer-configurations are analyzed, and then the advantages and the disadvantages of each mathematic model are reviewed, and the future research is expected

New Inertial Sensor Cluster for Vehicle Dynamic Systems

Abstract: The concept of Bosch’s new sensor cluster SC-MM3.x has been first presented at the AMAA conference in 2003 [21]. This sensor cluster will replace the current DRS-MM1.x, which was the first silicon micromachined angular velocity and lateral acceleration sensor for the Bosch ESP system. Start of series production will be in the spring of 2005.