Showing papers on "Gyroscope published in 2004"

A Step, Stride and Heading Determination for the Pedestrian Navigation System

Abstract: Recently, several simple and cost-effective pedestrian navigation systems (PNS) have been introduced. These systems utilized accelerometers and gyros in order to determine step, stride and heading. The performance of the PNS depends on not only the accuracy of the sensors but also the measurement processing methods. In most PNS, a vertical impact is measured to detect a step. A step is counted when the measured vertical impact is larger than the given threshold. The numbers of steps are miscounted sometimes since the vertical impacts are not correctly measured due to inclination of the foot. Because the stride is not constant and changes with speed, the step length parameter must be determined continuously during the walk in order to get the accurate travelled distance. Also, to get the accurate heading, it is required to overcome drawbacks of low grade gyro and magnetic compass. This paper proposes new step, stride and heading determination methods for the pedestrian navigation system: A new reliable step determination method based on pattern recognition is proposed from the analysis of the vertical and horizontal acceleration of the foot during one step of the walking. A simple and robust stride determination method is also obtained by analyzing the relationship between stride, step period and acceleration. Furthermore, a new integration method of gyroscope and magnetic compass gives a reliable heading. The walking test is preformed using the implemented system consists of a 1-axis accelerometer, a 1-axis gyroscope, a magnetic compass and 16-bit microprocessor. The results of walking test confirmed the proposed method.

Image orientation for endoscopic video displays

Abstract: An apparatus and technique for compensating the display of an image obtained from a video camera system associated with an endoscope as it is moved through various orientations are described. The received optical image is converted to an electrical signal with an image sensor that can be a CCD or a CMOS detector. The endoscope video camera system has an inertial sensor to sense rotations of the received image about the optical axis of the endoscope and the sensor's output signals are used to rotate either the image or the image sensor. In case of rotation of the image sensor the rotation sensor can be a gyroscope or a pair of accelerometers. In case of a rotation of the image obtained with the image sensor the inertial sensor, which can be an accelerometer or a gyroscope, the image is rotated within a microprocessor for subsequent viewing on a video display.

Wavelet de-noising for IMU alignment

Abstract: Inertial navigation system (INS) is presently used in several applications related to aerospace systems and land vehicle navigation. An INS determines the position, velocity, and attitude of a moving platform by processing the accelerations and angular velocity measurements of an inertial measurement unit (IMU). Accurate estimation of the initial attitude angles of an IMU is essential to ensure precise determination of the position and attitude of the moving platform. These initial attitude angles are usually estimated using alignment techniques. Due to the relatively low signal-to-noise ratio of the sensor measurement (especially for the gyroscopes), the initial attitude angles may not be computed accurately enough. In addition, the estimated initial attitude angles may have relatively large uncertainties that may affect the accuracy of other navigation parameters. This article suggests processing the gyro and accelerometer measurements with multiple levels of wavelet decomposition to remove the high frequency noise components. The proposed wavelet de-noising method was applied on a navigational grade inertial measurement unit (LTN90-100). The results showed that accurate alignment procedure and fast convergence of the estimation algorithm, in addition to reducing the estimation covariance of the three attitude angles, could be obtained.

Global Positioning System (GPS): A Low-Cost Velocity Sensor for Correcting Inertial Sensor Errors on Ground Vehicles

Abstract: This paper demonstrates the ability of a standard low-cost Global Positioning System (GPS) receiver to reduce errors inherent in low-cost accelerometers and rate gyroscopes used on ground vehicles. Specifically GPS velocity is used to obtain vehicle course, velocity, and road grade, as well as to correct inertial sensors errors, providing accurate longitudinal and lateral acceleration, and pitch, roll, and yaw angular velocities. Additionally, it is shown that transient changes in sideslip (or lateral velocity), roll, and pitch angles can be measured. The method utilizes GPS velocity measurements to determine the inertial sensor errors using a kinematic Kalman Filter estimator Simple models of the inertial sensors, which take into account the sensor noise and bias drift properties, are developed and used to design the estimator. Based on the characteristics of low-cost GPS receivers and IMU sensors, this paper presents the achievable performance of the combined system using the covariance analysis from the Kalman filter. Subsequent simulations and experiments validate both the error analysis and the methodology for utilizing GPS as a velocity sensor for correcting low-cost inertial sensor errors and providing critical vehicle state measurements.

X-y axis dual-mass tuning fork gyroscope with vertically integrated electronics and wafer-scale hermetic packaging

Abstract: An angular velocity sensor has two masses which are laterally disposed in an X-Y plane and indirectly connected to a frame. The two masses are linked together by a linkage such that they necessarily move in opposite directions along Z. Angular velocity of the sensor about the Y axis can be sensed by driving the two masses into Z-directed antiphase oscillation and measuring the angular oscillation amplitude thereby imparted to the frame. In a preferred embodiment, the angular velocity sensor is fabricated from a bulk MEMS gyroscope wafer, a cap wafer and a reference wafer. In a further preferred embodiment, this assembly of wafers provides a hermetic barrier between the masses and an ambient environment.

Performance Test Results of an Integrated GPS/MEMS Inertial Navigation Package

Abstract: This paper describes the design, operation and performance test results of a miniature, low cost integrated GPS/inertial navigation system (INS) designed for use in UAV or UGV guidance systems. The system integrates a miniaturized commercial GPS with a low grade Micro-Electro-Mechanical (MEMS) inertial measurement unit (IMU). The MEMS IMU is a small self-contained package (< 1 cu inch) and includes a triad of accelerometers and gyroscopes with additional sensors integrated for temperature compensation and baro pressure altitude aiding. The raw IMU data is provided 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 chips 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. Test results are presented in this paper showing the performance of the integrated MEMS GPS/INS navigation system when used to perform guidance for a small Unmanned Ground Vehicle (UGV). 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.

A quaternion-based orientation estimation algorithm using an inertial measurement unit

Abstract: This paper presents a real-time orientation estimation algorithm based on signals from a low-cost inertial measurement unit (IMU). The IMU consists of three MEMS accelerometers and three MEMS rate gyros. This approach is based on relationships between the quaternion representing the platform orientation, the measurement of gravity from the accelerometers, and the angular rate measurement from the gyros. Process and measurement models are developed, based on these relations, in order to implement them into an extended Kalman filter. The performance of each filter is evaluated in terms of the roll, pitch, and yaw angles. These are derived from the filter output since this orientation representation is more intuitive than the quaternion representation. Extensive testing of the filters with simulated and experimental data show that the filters perform very accurately in the roll and pitch angles, and even significantly corrects the yaw angle error drift.

A robust hybrid tracking system for outdoor augmented reality

Abstract: We present a real-time hybrid tracking system that integrates gyroscopes and line-based vision tracking technology. Gyroscope measurements are used to predict orientation and image line positions. Gyroscope drift is corrected by vision tracking. System robustness is achieved by using a heuristic control system to evaluate measurement quality and select measurements accordingly. Experiments show that the system achieves robust, accurate, and real-time performance for outdoor augmented reality.

Structural design and experimental characterization of torsional micromachined gyroscopes with non-resonant drive mode

Abstract: This paper reports a novel gimbal-type torsional micromachined gyroscope with a non-resonant actuation scheme. The design concept is based on employing a 2 degrees-of-freedom (2-DOF) drive-mode oscillator comprising a sensing plate suspended inside two gimbals. By utilizing dynamic amplification of torsional oscillations in the drive mode instead of resonance, large oscillation amplitudes of the sensing element are achieved with small actuation amplitudes, providing improved linearity and stability despite parallel-plate actuation. The device operates at resonance in the sense direction for improved sensitivity, while the drive direction amplitude is inherently constant within the same frequency band. Thus, the necessity to match drive and sense resonance modes is eliminated, leading to improved robustness against structural and thermal parameter fluctuations. In the paper, the structure, operation principle and a MEMS implementation of the design concept are presented. Detailed analysis of the mechanics and dynamics of the torsional system is covered, and the preliminary experimental results verifying the basic operational principles of the design concept are reported.

Direct measurement of diurnal polar motion by ring laser gyroscopes

Abstract: [1] We report the first direct measurements of the very small effect of forced diurnal polar motion, successfully observed on three of our large ring lasers, which now measure the instantaneous direction of Earth's rotation axis to a precision of 1 part in 108 when averaged over a time interval of several hours. Ring laser gyroscopes provide a new viable technique for directly and continuously measuring the position of the instantaneous rotation axis of the Earth and the amplitudes of the Oppolzer modes. In contrast, the space geodetic techniques (very long baseline interferometry, side looking radar, GPS, etc.) contain no information about the position of the instantaneous axis of rotation of the Earth but are sensitive to the complete transformation matrix between the Earth-fixed and inertial reference frame. Further improvements of gyroscopes will provide a powerful new tool for studying the Earth's interior.

Control of a Z-axis MEMS vibrational gyroscope

Abstract: This paper describes the design of the control loops in a z-axis, MEMS vibrational gyroscope operating in a vacuum enclosure. In this device, a silicon mass is driven through electrostatic actuator so that it has a sinusoidal linear motion, with a controlled speed. The design of a suitable controller, capable of maintaining the required speed and with prescribed restoring capabilities after shocks is briefly described in the paper. Attached to the driving mass, a second mass, free to move in the direction orthogonal to the motion of the first mass, is subjected to a Coriolis force, proportional to the product of the first mass speed by z-axis rotational speed. The sensing of the Coriolis force and, in turn, of the z-axis rotational speed, is performed in closed loop fashion, with a 1-bit quantized actuation. The restoring force that brings the motion of the second mass to zero is equivalent to the output bit stream of a band-pass sigma-delta converter and contains the information of the Coriolis force. The design of this second control loop and a detailed analysis on the signal-to-noise ratio achievable with the proposed design is reported.

Adaptive filter for a miniature MEMS based attitude and heading reference system

Abstract: A strapdown Inertial Navigation System (INS) can provide attitude and heading estimates after initialization and alignment. Many factors affect the accuracy and the performance of the system. They mainly are: sensor noise, bias, scale factor error, and alignment error. The Inertial Measurement Unit (IMU) based on the newly developed MEMS technology has wide applications due to its low-cost, small size, and low power consumption. However, the inertial MEMS sensors have large noise, bias and scale factor errors due to drift. The traditional strapdown algorithm using a low-cost MEMS sensor ONLY is difficultly satisfying the attitude and heading performance requirements. An extended Kalman filter with adaptive gain was used to build a miniature attitude and heading reference system based on a stochastic model. The adaptive filter has six states with a time variable transition matrix. The six states are three tilt angles of attitude and three bias errors for the gyroscopes. The filter uses the measurements of three accelerometers and a magnetic compass to drive the state update. When the system is in the non-acceleration mode, the accelerometer measurements of the gravity and the compass measurements of the heading have observability and yield good estimates of the states. When the system is in the high dynamic mode and the bias has converged to an accurate estimate, the attitude calculation will be maintained for a long interval of time. The adaptive filter tunes its gain automatically based on the system dynamics sensed by the accelerometers to yield optimal performance. The paper presents the methodology of the technique, performs the analysis, and gives the testing results of the system based on the adaptive filter. The whole system can be fitted within the size of 5cm /spl times/ 5cm /spl times/ 5cm with analog to digital conversion and digital signal processing boards.

A study on resonant frequency and Q factor tunings for MEMS vibratory gyroscopes

Abstract: A new approach for improving the performance of MEMS vibratory gyroscopes was developed. The methodology suggests a simple way of improving the performance such as the overshoot, settling time and shock immunity by tuning the resonant frequency and the quality factor. The difference in the resonant frequency in two modes (driving and sensing mode) and the quality factors were found to be key factors in determining the dynamics of the gyroscopes. The difference in the frequency could be easily controlled by the electrical stiffness but it was difficult to control the quality factor because it is determined by vacuum level and the shape of structure. An electrostatic feedback technique allowed the control of the quality factor of the micro-gyroscopes. The experimental results show that the magnitude of the resonant peak in the frequency response of the gyroscope is reduced by 58% when the equivalent quality factor of the sensing system is tuned from 264 to 100 at a 100 Hz frequency difference between the driving and sensing modes. The time domain estimation was an approximate 50% reduction in the overshoot and an approximate threefold shortening of the settling time in that case. The estimation in the time domain was based on the simulation because there is no method to measure the transient response of gyroscopes directly.

Portable absolute orientation estimation device with wireless network under accelerated situation

Abstract: In this paper, we develop an absolute orientation estimation device equipped with a wireless network. Accelerometers and magnetometers are used to measure the gravity and the geomagnetic field respectively. Gyroscope sensors are used to measure the local angular velocity. The geomagnetic field varies according to the environment. Therefore the device can obtain the information about the magnetic field through the wireless network. The orientation estimation task can be also requested to the other computers with the wireless network. By integrating the measured gravity and geomagnetic field with the local angular velocity using Sigma-Points Kalman Filters (SPKFs), the stability and the robustness of estimating the absolute orientation are improved over either sensor alone. We also propose an estimation method which excludes the effect of motion and magnetic disturbances for the accurate estimation.

Symmetrical and decoupled nickel microgyroscope on insulating substrate

Abstract: This paper presents a symmetrical and decoupled surface micromachined gyroscope fabricated by electroforming thick nickel on a glass substrate. The symmetric structure allows matched resonant frequencies for the drive and sense vibration modes for improved sensitivity, while the decoupled drive and sense oscillation modes prevents unstable operation due to mechanical coupling, resulting in a low zero-rate output drift. The use of a glass substrate instead of a silicon substrate reduces noise due to the parasitic signal coupling by two orders of magnitude, according to both simulation results in CoventorWare and measured results on fabricated devices. A capacitive interface circuit which is fabricated in a 0.8 μm CMOS process is hybrid connected to the gyroscope, where the circuit has an input capacitance lower than 50 fF and a sensitivity of 33 mV/fF, which are currently limited by the parasitic capacitances due to hybrid wirebonding. It has been identified that the amount of parasitic capacitances must be lower than or at least in the same order with the electrical equivalent capacitance of the gyroscope for clear mechanical resonance characteristics to be obtained. Fabricated gyroscopes have close resonant frequencies for the drive and sense modes, as 37.2 and 38.3 kHz, respectively. Calculations on measured resonance values suggest that the fabricated gyroscope with 16 μm-thick structural layer provides a Brownian noise floor of 7.3°/h/Hz 1/2 at vacuum. Currently, the overall rate sensitivity of the gyroscope is limited to 96°/h in 50 Hz bandwidth for matched-frequency operation, and it can be decreased down to 56°/h in 50 Hz bandwidth, by improving the quality of the electrodeposited nickel.

Toward a stellar gyroscope for spacecraft attitude determination

Abstract: A stellar gyroscope is a star tracker that can operate at high slew rates and high update rates. Stellar gyroscopes can potentially eliminate the need for conventional inertial gyros onboard a spacecraft and will eventually revolutionize attitude determination systems on all spacecraft. A conceptual design of a stellar gyroscope will be presented along with simulations of the stellar gyroscope performance. The simulations show that it is feasible to make spacecraft attitude determination relying exclusively on stellar gyroscopes. It is projected that the stellar gyroscope will be able to determine slew rates up to 420 deg/s and will be able to determine the absolute attitude at slew rates up to 50 deg/s.

Dynamic magnetic anomaly compensation

Abstract: An array of three-axis magnetometers used for dynamic magnetic anomaly compensation are located at the corners of a parallelopiped, with pairs of magnetometer outputs used to derive a magnetic anomaly gradient vector used to compensate a compass and/or the output of a gyroscope in an inertial management unit. The system may be used in a neutrally buoyant remotely operated vehicle to permit ascertaining of course and position in the absence of surface control signals.

Real-time data fusion on tracking camera pose for direct visual guidance

Abstract: To properly align objects in the real and virtual world in an augmented reality (AR) space, it is essential to keep tracking camera's exact 3D position and orientation, which is well known as the Registration problem. Traditional vision based or inertial sensor based solutions are mostly designed for well-structured environment, which is, however, unavailable for outdoor uncontrolled road navigation applications. This paper proposed a hybrid camera pose tracking system that combines vision, GPS and 3D inertial gyroscope technologies. The fusion approach is based on our PMM (parameterized model matching) algorithm, in which the road shape model is derived from the digital map referring to GPS absolute road position, and matches with road features extracted from the real image. Inertial data estimates the initial possible motion, and also serves as the relative tolerance to stabilize output. The algorithms proposed in this paper are validated with the experimental results of real road tests under different conditions and types of road.

Proposed IEEE inertial systems terminology standard and other inertial sensor standards

Abstract: A new inertial systems terminology standard is being developed by the IEEE/AESS Gyro and Accelerometer Panel for consideration by the IEEE Standards Board as IEEE Std 1559. It is intended to be a companion to IEEE Std 528-2001, IEEE Standard for Inertial Sensor Terminology. These two documents as well as IEEE standards that have been published for single- and two-degree-of-freedom spinning wheel gyros, laser gyros, interferometric fiber optic gyros, Coriolis vibratory gyros (including MEMS gyros), angular accelerometers, linear accelerometers, accelerometer centrifuge testing, and an inertial sensor test equipment and analysis document are discussed in this paper.

New Adaptive Mode of Operation for MEMS Gyroscopes

Abstract: This paper presents a new adaptive operation strategy that can identify and, in an adaptive fashion, compensate for most fabrication defects and perturbations affecting the behavior of a MEMS z-axis gyroscope. The convergence and resolution analysis presented in the paper shows that the proposed adaptive controlled scheme offers several advantages over conventional modes of operation. These advantages include a larger operational bandwidth, absence of zero-rate output, self-calibration and a large robustness to parameter variations, which are caused by fabrication defects and ambient conditions.

A high-Q in-plane SOI tuning fork gyroscope

Abstract: This paper presents the design and implementation of an in-plane solid-mass single-crystal silicon tuning fork gyro that has the potential of attaining sub-deg/hr rate resolutions. A design is devised to achieve high Q in the drive and sense resonant modes (Q/sub drive/=81,000 and Q/sub sense/=64,000) with effective mode decoupling. The gyroscope was fabricated on 40 /spl mu/m thick silicon-on-insulator (SOI) using a simple two-mask process. The drive and sense resonant modes were balanced electrostatically to within 0.07% of each other and the measured rate results show a sensitivity of 1.25 mV//spl deg//s in a bandwidth of 12 Hz.

A Head Tracking Method Using Bird's-Eye View Camera and Gyroscope

Abstract: This paper describes a new head tracking method utilizing a gyroscope mounted on a head-mounted display (HMD) and a bird's-eye view camera that observes the HMD from a fixed third-person viewpoint. Furthermore, we propose an extension of this method to hybrid registration, combining it with user's view cameras. The HMD is equipped with a gyroscope and a marker. The gyroscope measures the orientation of the user s view camera so that the number of pose parameters to be solved can be reduced. The other parameters are to be estimated by the bird's-eye view camera that observes the marker. This method is an improvement over the conventional outside-in-style vision-based tracker method, which only uses visual information. Hence, it can be thought of as an alternative to a physical head tracker such as a magnetic sensor and to an inside-out-style vision-based tracker. In addition to theoretical discussions, this paper demonstrates the effectiveness of our methods by experiments. We also propose methods for calibrating the gyroscope and the marker on HMD, which are essential in implementing the tracking method.

Measurement-while-drilling surveying of highly inclined and horizontal well sections utilizing single-axis gyro sensing system

Abstract: In the oil industry, when developing a plan for drilling horizontal wells, measurement-while-drilling (MWD) surveying becomes one of the important prerequisites for the successful completion of the drilling process. MWD surveying of horizontal wells determines the position and the orientation of the bottom hole assembly (BHA) in real-time during the drilling operation. The BHA orientation is determined by its inclination from the vertical direction as well as its azimuth. The present MWD surveying system incorporates three-axis accelerometers and three-axis magnetometers mounted in three mutually orthogonal directions. This magnetic surveying system suffers from the deviation of the magnetic field measurements due to the massive amount of steel around the drilling rig. A new method utilizing the fibre optic gyroscopes (FOG) technology was suggested to replace the magnetic surveying system. It was reported that a single FOG mounted inside the bearing assembly with its sensitive axis along the tool spin axis could be incorporated with three-axis accelerometers to continuously survey the near-vertical well section. This study aims at suggesting a surveying methodology for highly inclined and horizontal well sections utilizing FOG sensors. At each surveying station, the intrinsic uncertainties of the surveying sensors and the other vibration-induced noise are reduced using a transversal finite impulse response filter. The inclination is then computed by processing the accelerometer measurements, while the gyro measurement is utilized to determine the azimuth. In addition, optimal estimation techniques based on Kalman filtering are used to improve the azimuth accuracy and to limit the effect of the drift of the surveying sensors over time. This study indicates that gyroscopic surveying utilizing the FOG technology can be a reliable solution for MWD surveying of horizontal wells.

Inertial gps navigation system using injected alignment data for the inertial system

Abstract: An inertial ('INS')/GPS receiver uses injected alignment data to determine the alignment of the INS sub-system when the receiver is in motion during start-up. The alignment data is determined from parameterized surface information, measured GPS velocity, and a known or predetermined angular relationship between the vehicle on which the receiver is mounted and an inertial measurement reference, or body, frame associated with the accelerometers and gyroscopes of the inertial measuring unit ('IMU'). The parameterized surface information, which provides a constraint, may be the orientation of the surface over which the vehicle that houses the receiver is moving. The receiver uses the initial GPS position to determine the location of the vehicle on the parameterized surface, and thus, the known surface orientation. The receiver then determines the roll, pitch and heading of the vehicle on the surface using the associated GPS velocity vector. Thereafter, the receiver uses the calculated roll, pitch and heading of the vehicle and the known or predetermined angular relationship between the vehicle and the IMU body frame to determine a rotation matrix that relates the IMU body frame to a computation or referenced frame used by the receiver.

Gyroscopic steering tool using only a two-axis rate gyroscope and deriving the missing third axis

Abstract: A two-axis gyroscope used on a bottom hole assembly can be used for determining a rate of rotation about the rotational axis of a BHA. The method takes advantage of possible misalignment of at least one axis of the two axis gyroscope from orthogonality with respect to the rotational axis of the BHA, resulting in the misaligned gyro being sensitive to BHA rotation.

Analysis and compensation of errors in the input device based on inertial sensors

Abstract: Here, a pen-type input device is proposed to track trajectories in 3D space by using accelerometers and gyroscopes. Inertial navigation system (INS) theory, as an autonomous positioning technology widely adopted, is employed to track the users' handwriting motion without external reference sensors or signals. The INS-based positioning system, however, suffers from unbounded error, which grows with time due to the integration process involved. In order to solve this problem, the system error model is built to analyze the influence of error sources. Then efficient error compensation algorithm based on zero velocity compensation (ZVC) is developed to reduce the effect of identified errors. The experiments show the effectiveness and feasibility of the proposed method.

Integrated resonant micro-optical gyroscope and method of fabrication

Abstract: An integrated optic gyroscope is disclosed which is based on a photonic integrated circuit (PIC) having a bidirectional laser source, a pair of optical waveguide phase modulators and a pair of waveguide photodetectors. The PIC can be connected to a passive ring resonator formed either as a coil of optical fiber or as a coiled optical waveguide. The lasing output from each end of the bidirectional laser source is phase modulated and directed around the passive ring resonator in two counterpropagating directions, with a portion of the lasing output then being detected to determine a rotation rate for the integrated optical gyroscope. The coiled optical waveguide can be formed on a silicon, glass or quartz substrate with a silicon nitride core and a silica cladding, while the PIC includes a plurality of III–V compound semiconductor layers including one or more quantum well layers which are disordered in the phase modulators and to form passive optical waveguides.

Micromachined vibratory gyroscope and method with electronic coupling

Abstract: Micromachined vibratory gyroscope and method in which the vibrating masses are coupled electronically, e.g. by electronically adjusting the resonance frequency of one or more of the masses so that all of the masses have the same resonance frequency.