Showing papers on "Inertial reference unit published in 2003"

Real-time integration of a tactical-grade IMU and GPS for high-accuracy positioning and navigation

Abstract: The integration of the Global Positioning System (GPS) and Inertial Navigation Systems (INSs) is often used to provide accurate positioning and navigation information. For applications requiring the highest accuracy, the quality of the inertial sensors required is usually assumed to be very high. This dissertation investigates the integration of GPS with a tactical-grade Inertial Measurement Unit (IMU) for centimetre-level navigation in real-time. Different GPS/INS integration strategies are investigated to assess their relative performance in terms of position and velocity accuracy during partial and complete data outages, carrier phase ambiguity resolution after such data outages, and the overall statistical reliability of the system. In terms of statistical reliability, the traditional equations used in dynamic systems are redeveloped in light of some practical considerations, including centralized and decentralized filter architectures, and sequential versus simultaneous measurement updating. Results show that the integrated solution outperforms the GPS-only approach in all areas. The difference between loose and tight integration strategies was most significant for ambiguity resolution and system reliability. The integrated solution is capable of providing decimetre-level accuracy or better for durations of about five or ten seconds when a complete or partial GPS outage is simulated. This level of accuracy, extended over longer time intervals, is shown to reduce the time required to resolve the L1 ambiguities by an average of about 50% or more for data outages as long as 30 seconds when using a tight integration strategy. More importantly, the reliability of the ambiguity resolution process is improved with the integrated

Design of all-accelerometer inertial measurement unit for tremor sensing in hand-held microsurgical instrument

Abstract: We present the design of an all-accelerometer inertial measurement unit (IMU). The IMU forms part of an intelligent hand-held microsurgical instrument that senses its own motion, distinguishes between hand tremor and intended motion, and compensates in real-time the erroneous motion. The new IMU design consists of three miniature dual-axis accelerometers, two of which are housed in a sensor suite at the distal end of the instrument handle, and one located at the proximal end close to the instrument tip. By taking the difference between the accelerometer readings, we decouple the inertial and gravitational accelerations from the rotation-induced (centripetal and tangential) accelerations, hence simplifies the kinematic computation of angular motions. We have shown that the error variance of the Euler orientation parameters /spl theta//sub x/, /spl theta//sub y/ and /spl theta//sub z/ is inversely proportional to the square of the distance between the three sensor locations. Comparing with a conventional three gyros and three accelerometers IMU, the proposed design reduces the standard deviation of the estimates of translational displacements by 29.3% in each principal axis and those of the Euler orientation parameters /spl theta//sub x/, /spl theta//sub y/ and /spl theta//sub z/ by 99.1%, 99.1% and 92.8% respectively.

Direct modification of DGPS information with inertial measurement data

Abstract: A global positioning system based navigation system for a ground vehicle, in particular an agricultural ground vehicle such as a tractor, combine, sprayer, or the like, includes an inertial compensation assembly that provides inertial augmentation to compensate global positioning system based navigation information such as position, course, and track spacing for errors caused by variation of ground vehicle attitude (i.e., roll and yaw) over non-level terrain.

Method and system for processing pulse signals within an inertial navigation system

Abstract: A method and system (100) for processing pulse signals within an inertial device is provided. The inertial device may have inertial sensors, such as accelerometers (110, 112, 114) and gyroscopes (104, 106, 108). The inertial sensors may output signals represen tative of a moving body's motion. The signals may require correction due to imperfections and other errors of the inertial sensors. The inertial device may receive signals from the inertial sensors and process the signals on a signal-by-signal basis so that when processing the signals, the inertial device at least recognizes which sensor output a signal and when the signal was output. The inertial device may then correlate signals that were output from the inertial sensors at selected times in order to transform the signals into desired navigational frame of reference.

Camera-Inertial Sensor modelling and alignment for Visual Navigation

Abstract: This article presents a technique for modeling and calibrating a camera with integrated low-cost iner- tial sensors, three gyros and three accelerometers for full 3D sensing. Inertial sensors attached to a camera can provide valuable data about camera pose and movement. In biological vision systems, inertial cues provided by the vestibular system, are fused with vision at an early processing stage. Vision systems in autonomous vehi- cles can also benefit by taking inertial cues into account. Camera calibration has been extensively studied, and standard techniques established. Inertial navigation systems, relying on high-end sensors, also have established techniques. Nevertheless, in order to use off-the-shelf inertial sensors attached to a camera, appropriate modeling and calibration techniques are required. For inertial sensor alignment, a pendulum instrumented with an encoded shaft is used to estimate the bias and scale factor of inertial measurements. For camera calibration, a standard and reliable camera calibration technique is used, based on images of a planar grid. Having both the camera and the inertial sensors calibrated and observing the vertical direction at different poses, the rigid rotation between the two frames of reference is estimated, using a mathematical model based on unit quaternions. The technique for this alignment and consequent results with simulated and real data are presented at the end of this article.

A new scheme of non-gyro inertial measurement unit for estimating angular velocity

Abstract: The non-gyro inertial measurement unit (NGIMU) uses only accelerometers replacing gyroscopes to compute the motion of a moving body. To alleviate the accumulation of angular velocity error attributed to accelerometers error, a novel design scheme for a NGIMU is proposed along with its mathematic model. Based on the conventional six-accelerometer cube configuration, this scheme employs a nine-accelerometer configuration scheme and obtains the correct sign by exploiting the redundant information of the accelerometers and integrating the angular acceleration value. The accurate angular velocity can be calculated as square root of the square expression of the angular velocity. Simulation results show that the computational accuracy of angular velocity can be improved and confirm the effectiveness and feasibility of the proposed design scheme.

Environmentally mitigated navigation system

Abstract: An environmentally mitigated navigation system includes a thermal isolating chamber, an inertial measurement unit that can include individual gyroscopes and accelerometers for making inertial measurements, and a temperature control system; the temperature control system includes a thermoelectric cooling system, which in a powered mode maintains the inertial measurement unit at a substantially predetermined temperature, and a phase change device for maintaining the inertial measurement unit or inertial sensors at substantially a predetermined temperature in an unpowered mode; the phase change device substantially maintains the predetermined temperature by changing phase to define a stable temperature window for the inertial measurement unit or individual sensors to make inertial measurements during the unpowered mode as well as during the powered mode.

Inertial reference unit with internal backup attitude heading reference system

Abstract: An inertial reference unit (IRU) is described which includes a processor programmed to provide inertial data from received inertial signals, a primary sensor unit providing the inertial signals to the processor, and an input/output (I/O) unit communicatively coupled to the processor The I/O unit provides signals, including inertial data, to an external interface of the IRU and routes signals to and from the processor The inertial reference unit also includes a secondary sensor unit separate from the primary sensor unit which provides inertial data independent of the inertial data provided by the processor

Vehicle model aided inertial navigation

Abstract: This paper studies the possibility of improving the accuracy of a low-cost strapdown inertial navigation system mounted on a land vehicle by using a vehicle kinematic model. The inertial navigation system is aided with virtual position measurements, which are predicted by a vehicle kinematic model along with virtual velocity measurements. This data is obtained from the non-holonomic constraints that govern land vehicle motion on a surface. Furthermore, the updated heading information obtained from the INS is used to refine the vehicle kinematic model. Analytic analysis and covariance simulation are carried out for the observability analysis of the aided inertial navigation system. Simulation results prove that the accuracy of the low-grade inertial navigation system aided by a vehicle kinematic model can be considerably improved. The strategies proposed in this paper can be used as a backup navigation loop during outages of GPS for an extended amount of time with the navigation error noticeably bounded. Finally, the redundancy and the integrity of the whole navigation system are also further enhanced.

Continuous Tuning and Calibration of Vibratory Gyroscopes

Abstract: A method of control and operation of an inertial reference unit (IRU) based on vibratory gyroscopes provides for continuously repeated cycles of tuning and calibration. The method is intended especially for application to an IRU containing vibratory gyroscopes that are integral parts of microelectromechanical systems (MEMS) and that have cloverleaf designs, as described in several previous NASA Tech Briefs articles. The method provides for minimization of several measures of spurious gyroscope output, including zero-rate offset (ZRO), angle random walk (ARW), and rate drift. These benefits are afforded both at startup and thereafter during continuing operation, in the presence of unknown rotation rates and changes in temperature. A vibratory gyroscope contains a precision mechanically resonant structure containing two normal modes of vibration nominally degenerate in frequency and strongly coupled via a Coriolis term. In the case of the cloverleaf design MEMS gyro, these normal modes of vibration are plate rocking modes. The rocking motion of the plate is described by giving two angles, theta(sub 1) and theta(sub 2). A proof mass consisting of a post orthogonal to the plate ensures a high degree of Coriolis coupling of vibratory energy from one mode into the other under inertial rotation. The plate is driven and sensed capacitively across a few-microns-wide gap, and the normal mode frequencies can be tuned electrostatically by DC voltages applied across this gap. In order to sense rotation, the resonator plate is caused to rock in the theta(sub 1) direction, then any small motions in the theta(sub 2) direction are sensed, rebalanced, and interpreted as inertial rotation. In this scenario, the "drive" has been assigned to the theta(sub 1) direction, and the "sense" has been assigned to the theta(sub 2) direction.

Operational Experience with Optimal Integration of Low-Cost Inertial Sensors and GPS for Flight Test Requirements

Abstract: This paper describes the development of, and operational flight test experience with, a real-time integrated navigation system that is based on a low-cost strapdown Inertial Measurement Unit (IMU) ...

Misalignment measuring method for inertial system

Abstract: PROBLEM TO BE SOLVED: To improve gyroscope misalignment estimation accuracy, and to estimate gyroscope misalignment of an inertial system extremely easily without requiring a dedicated device SOLUTION: The inertial system is placed on a triaxial rotary table, and alignment in the horizontal stationary state of the inertial system is performed (step S11) The attitude change of +90° around the X-axis, +90° around the Y-axis and -90° around the X-axis is applied successively to the inertial system (step S12) Similarly, attitude changes in steps S13-S15 are applied successively After the attitude of the inertial system is returned to the original state, the speed change calculated on the computer horizontal axis is measured as an acceleration error (step S16), and an error parameter of a gyroscope included in the inertial system is estimated and determined by using the acceleration error (step S17) COPYRIGHT: (C)2004,JPO&NCIPI

Present state and perspectives of micromachined inertial sensors

Abstract: A review is given to the present state of micromachined inertial sensor-micro-accelerometers and micro-gyro. These sensors have a number of significant advantages, such as lower cost, smaller form factor and lower power consumption. Their manufacturing process, transfer mechanism, control system and interface technique are described in detail.

Satellite tracking antenna control device

Abstract: PROBLEM TO BE SOLVED: To solve the problems that an airborne satellite tracking antenna, which is controlled on the basis of the position and attitude data measured by an inertial reference unit (IRU) installed in the front part of an airframe, is not accurately controlled owing to a bend and a twist in the airframe and that irregular response delay of the IRU causes inability to achieve accurate control SOLUTION: An angular velocity sensor 6 having higher-speed responsivity than the frequency of a bend or vibration of the airframe 1 is attached to an antenna support 3 installed in the airframe 1 In addition to the position and attitude data of an aircraft 1 measured by the IRU 2, angle data and angular velocity data are added to correct a control error caused by a bend and a twist in the airframe 1 An output of the IRU 2 is averaged in time to remove irregular response delay and is then corrected with the data of the angular velocity sensor 6 to be corrected to data having high-speed responsivity COPYRIGHT: (C)2005,JPO&NCIPI

Inertial Instrument Error Compensation Technology in Laser Gyro Strapdown Inertial Navigation System

Abstract: To improve the navigation precision of laser gyro strapdown inertial navigation system, an error compensation technology was presented, which has an effect on the navigation precision. The system errors mainly result from the inertial instrument errors, which must be eliminated in order to decrease the system errors. This paper emphasized the principle analysis of the inertial instrument errors, and built the exact mathematical models. And a new calibration approach was discussed, through which the models parameters can be exactly acquired. The procedure of the parameters analysis and solution was given. The results of the actual experiments demonstrate both the validity and highprecision of the new calibration approach, so the navigation precison can be improved.

Methods and apparatus for installation alignment of equipment

Abstract: A method for installation alignment of an inertial reference unit (IRU) (104) with vehicle axes (12, 14, 16) when the IRU is installed within the vehicle (10) is provided. The vehicle axes include roll, pitch, and yaw axes. The method includes recording (54) vehicle angular position data including roll and pitch, using an angular position measurement device with the vehicle being in a starting position, recording (56) IRU data including roll and pitch, receiving (62, 66) measured nose plunge data, computing (84) initial roll and pitch misalignment corrections, applying (86) initial roll and pitch misalignment corrections to measured nose plunge data. A nose plunge yaw misalignment is determined (88) using corrected nose plunge data and utilized to adjust (90) the assumed heading reference.

Method and apparatus to align auxiliary aircraft equipment attitude and heading

Abstract: Precision alignment of auxiliary equipment on an aircraft is accomplished by a locating tool for the aircraft inertial reference unit (IRU) attached to the auxiliary equipment mount. Aircraft attitude and heading are obtained using the IRU. The IRU is removed from its avionics tray in the aircraft and installed on the locating tool. The locating tool is connected for remote operation of the IRU and the IRU is operated to obtain attitude and heading. This attitude and heading is then compared to the IRU reading for the attitude and heading of the aircraft.

Towards automating spacecraft attitude sensor calibration

Abstract: With a view towards reducing cost and complexity for spacecraft early mission support at the NASA Goddard Space Flight Center (GSFC), efforts are being made to automate the attitude sensor calibration process. This paper addresses one of the major components needed by such a system. The beneficiaries of an improved calibration process are missions that demand moderate to high precision attitude knowledge or that need to perform accurate attitude slews. Improved slew accuracy reduces the time needed for re-acquisition of fine-pointing after each attitude maneuver, Rapid target acquisition can be very important for astronomical targeting or for off-nadir surface feature targeting by Earth-oriented spacecraft. The normal sequence of on-orbit calibration starts with alignment calibration of the star trackers and possibly the Sun sensor. Their relative alignment needs to be determined using a sufficiently large data set so their fields of view are adequately sampled. Next, the inertial reference unit (IRU) is calibrated for corrections to its alignment and scale factors. The IRU biases are estimated continuously by the onboard attitude control system, but the IRU alignment and scale factors are usually determined on the ground using a batch-processing method on a data set that includes several slews sufficient to give full observability of all the IRU calibration parameters. Finally, magnetometer biases, alignment, and its coupling to the magnetic torquers are determined in order io improve momentum management and occasionally for use in the attitude determination system. The detailed approach used for automating calibrations will depend on whether the automated system resides on the ground or on the spacecraft with an ultimate goal of autonomous calibration. Current efforts focus on a ground-based system driving subsystems that could run either on the ground or onboard. The distinction is that onboard calibration should process the data sequentially rather than in a single large batch since onboard computer data storage is limited. Very good batch- processing calibration utilities have been developed and used extensively at NASA/GSFC for mission support but no sequential calibration utilities are available. To meet this need, this paper presents the mathematical description of a sequential IRU calibration system. The system has been tested using flight data from the Rossi X-ray Timing Explorer (RXTE) during a series of attitude slews. The paper also discusses the current state of the overall automated system and describes plans for adding sequential alignment calibration and other additions that will reduce the amount of analyst time and input.

A Low-g Accelerometer for Inertial Measurement Units

Abstract: Inertial Measurement Units (IMU) for upcoming automotive chassis control systems require sensor clusters with multi-axial sensors for acceleration and angular rate. In this paper, we present a low-g accelerometer that fits the IMU requirements for advanced automotive applications and is capable of monolithic multiple-axes integration. For the target application a high offset stability and an overcritical damping of the sensing element are required. With simple design changes the squeezed-film damping of the sensor can be adjusted within a wide range (5Hz to 400Hz) using atmospheric pressure inside the cavity. Due to its symmetrical design and the differential readout principle, an offset drift of less than 50mg over the full temperature range (−40°C...120°C) was achieved. The sensor principle presented in this paper can be utilized to realize a sensitivity axis parallel to the wafer surface as well as perpendicular to the surface. Furthermore, monolithic integration into a two-axis (x/z) or a three-axis (x/y/z) sensing element is possible. The tri-axial element exhibits a four-mass design providing redundancy and thus an ongoing self-test capability.

Inertial reference system for an aircraft

Abstract: An inertial reference system for an aircraft includes two accelerometers and a gyrometer. One accelerometer is located at a front portion of the aircraft, the other is located at a rear portion of the aircraft. The gyrometer is located at a center portion of the aircraft. The system also includes a control computer linked to the accelerometers and to the gyrometer. The center portion can include the aircraft's center of gravity.

Covariance analysis of spacecraft attitude control system

Abstract: The covariance analysis is applied to the performance of spacecraft attitude control systems. Subsystem considered here are the spacecraft bus, attitude controller, reaction wheel assembly, star-tracker unit, inertial reference unit, and gyro drift estimator. The results computed by the covariance analysis are compared with the results computed by the Monte-Carlo simulation. The covariance analysis is shown to be useful for studying the effects of system parameters on attitude control performance.

Performance Analysis of MEMS-based Inertial Sensors for Positioning Applications

Abstract: The last two decades have shown an increasing trend in the use of positioning and navigation technologies in land vehicle applications. Cost and space constraints are currently driving manufacturers of vehicles to investigate the applicability of MEMS-based inertial sensors for the development of low cost and small size navigation and guidance systems. The aim of this paper is to investigate the performance of MEMS-based inertial sensors and to analyse their impact on the short-term positioning accuracy. In addition, this article suggests some real-time digital signal processing methods based on the wavelet techniques to improve the performance of these MEMS-based sensors.

Design of a pen-shaped input device using the low-cost inertial measurement units

Abstract: In this paper, we present a pen-shaped input device equipped with accelerometers and gyroscopes that measure inertial movements when a user writes on 2 or 3 dimensional space with the pen. The measurements from gyroscope are integrated once to find the attitude of the system and are used to compensate gravitational effect in the accelerations. Further, the compensated accelerations are integrated twice to yield the position of the system, whose basic concept stems from the field of inertial navigation. However, the accuracy of the position measurement significantly deteriorates with time due to the integrations involved in recovering the handwriting trajectory This problem is common in the inertial navigation system and is usually solved by the periodic or aperiodic calibration of the system with external reference sources or other information in the filed of inertial navigation. In the presented paper, the calibration of the position or velocity is performed on-line and off-line. In the on-line calibration stage, the complementary filter technique is used, where a Kalman filter plays an important role. In the off-line calibration stage, the constant component of the resultant navigational error of the system is removed using the velocity information and motion detection algorithm. The effectiveness and feasibility of the presented system is shown through the experimental results.

Inertial Sensors and Attitude Derivation

Abstract: Gyroscopes (hereafter abbreviated to gyros) and accelerometers are known as inertial sensors. This is because they exploit the property of inertia, namely the resistance to a change in momentum, to sense angular motion in the case of the gyro and changes in linear motion in the case of the accelerometer. They are fundamental to the control and guidance of an aircraft. For example, in a FBW aircraft the rate gyros and accelerometers provide the aircraftmotion feedback which enables amanoeuvre command control to be achieved and an aerodynamically unstable aircraft to be stabilised by the flight control system (as explained in Chapter 4).

Utilization of a Tactical Grade FOG-Based Inertial Measurement Unit in Real-Time Downhole Surveying

Abstract: Fiber optic gyroscopes (FOG) in an inertial navigation setup have been proposed as an alternative to magnetometer-based downhole surveying The aim of this work is to study the applicability of a tactical-grade FOG-based inertial measurement unit (IMU) as complete surveying sensor for measurement-while-drilling processes downhole Complete navigation solution for downhole applications was tested in laboratory conditions, indicating the usefulness of FOG-based IMUs as possible surveying sensors for directional drilling

Effect of Cross-coupling Coefficient of Accelerometer on Gyros-free Inertial Measurement Unit

Abstract: This paper researches the effect of the magnitude of the cross-coupling for accelerometers on the inertial measurement unit and gives the inertial navigating equation as the cross-coupling coefficient existed. We can know the influence of cross-coupling coefficient on the accuracy of the navigation and then test this effect by simulating. This research establishes the bases for practice application of gyros free inertial measurement unit and has some guidance for selecting the accelerometers.