Showing papers on "Gyroscope published in 1997"

Precision Rotation Measurements with an Atom Interferometer Gyroscope

Abstract: We report the demonstration of a Sagnac-effect atom interferometer gyroscope which uses stimulated Raman transitions to coherently manipulate atomic wave packets. We have measured the Earth's rotation rate, and demonstrated a short-term sensitivity to rotations of $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}(\mathrm{rad}/\mathrm{s})/\sqrt{\mathrm{Hz}}$.

Micromachined vibratory rate gyroscope

Abstract: A microfabricated gyroscope (20) includes proof mass (22) connected to a frame or substrate (24) to measure rotation about an axis parallel to the surface of the substrate. The micromachined gyroscope includes a suspension system (30), a drive system (32) used to sustain oscillation of the proof mass (22) and a sensing system (34) used to detect deflections of the proof mass (22). The proof mass includes a plurality of electrode fingers (38). Voltage sources (120, 122, 124, 126) apply a voltage to sense fingers (74a-b, 76a-b) of sense electrodes (62a-b) to provide bias voltages to nullify quadrature error, select or adjust the resonant frequency of vibrations of the mass along the sense axis and cancel any centrifugal or other low-frequency forces.

Long-term unrestrained measurement of stride length and walking velocity utilizing a piezoelectric gyroscope

Abstract: Long-term monitoring of stride length and walking velocity is considered to provide useful information for making decisions on treatment of patients with gait disabilities. The purpose of this study was to develop a device with the following design criteria: lightweight, easy attachment, little hindrance to the natural gait pattern, sufficient memory to record for one day, and practicality in clinical use. The prototype consists of a piezoelectric gyroscope, which detects angular velocity of the thigh of one leg in the sagittal plane, and a microprocessor-based maximum/minimum detector/data logger of a cyclic analog signal associated with the gait cycle. The accuracy of the device was evaluated in 20 normal subjects, seven above-the-knee (A/K) amputees, and ten hemiplegic patients, and relative accuracy within /spl plusmn/15% was obtained, except for two special cases.

Dual axis operation of a micromachined rate gyroscope

Abstract: Since micromachining technology hs raised the prospect of fabricating high performance sensors without the associated high cost and large size, many researchers have investigated micromachined rate gyroscopes. The vast majority of research has focused on single input axis rate gyroscopes, but this paper presents work on a dual input axis micromachined rate gyroscope. The key to successful simultaneous dual axis operation is the quad symmetry of the circular oscillating rotor design. Untuned gyroscopes with mismatched modes yielded random walk as low as 10/spl deg///spl radic/(Hour) with cross axis sensitivity ranging from 3% to 16%. Subsequent mode frequency matching via electrostatic tuning allowed performance of 2/spl deg///spl radic/(Hour), but at the expense of excessive cross axis sensitivity.

Electronics for micromachined inertial sensors

Abstract: Capacitive interface circuits for micromachined sensors are described The focus is on the position sense electronics for accelerometers and gyroscopes Special attention is given to the characteristics of the interface between the sensor and electronic circuits, and on practical and fundamental noise mechanisms that limit the achievable resolution

Laterally oscillated and force-balanced micro vibratory rate gyroscope supported by fish hook shape springs

Abstract: A new concept micro vibratory rate gyroscope supported by fish hook shape springs, where the oscillating position sensing and force balancing take place on the wafer surface, has been developed. The gyroscope consists of: a grid-type planar mass; LT shape position sense electrodes for detecting the Coriolis motion; pairs of force-balancing electrodes to improve the linearity and dynamic range; prominence shape comb-drive electrodes to improve the resolution by increasing the oscillating displacement; fish hook shape springs to match the first and second modes with the mass oscillating and position sensing modes, respectively. Due to the relatively high stiffnesses of the proposed fish hook shape springs except in the desired directions, the gyroscope tends to be quite insensitive to the environmental vibrations or shocks, maintaining the electromechanical stability. It also features that the resonant frequencies associated with lateral vibration modes are not likely to be varied by the change in thickness of the poly-silicon structure, which guarantees the uniform sensitivity of products. Experimental results show that the gyroscope has the resolution of 0.1 degree per second at 2 Hz, the bandwidth of 100 Hz, and the dynamic range of 90 degree per second.

Extended Kalman filter for frequent local and infrequent global sensor data fusion

Abstract: In this paper we compare the performance of a dead-reckoning system for robot navigation to a system using an extended Kalman filter (EKF). Dead-reckoning systems are able to approximate position and orientation by feeding data (provided usually by local sensors) to the kinematic model of the vehicle. These systems are subject to many different sources of error. EKFs have the ability to combine the same information and compensate for most of these errors to yield a better estimate. Our simulation results using a simplified kinematic model of Rocky 7 [an experimental rover used in the Mars exploration program at Jet Propulsion Laboratory (JPL)] show that an improvement in performance up to 40% (position error) can be achieved. The local sensors used are: wheel encoders, steering angle potentiometer and gyroscope. Involvement of global sensor measurements can drastically increase the accuracy of the estimate. The lack of GPS or magnetic field on Mars narrows our choices for global localization. Landmarks, such as the sun can be used as natural beacons (reference point for absolute measuremnts). A sun sensor (SS) that measures the absolute orientation of the rover has been built by Lockheed Martin and now is part of the sensor suite of Rocky 7. The SS measurement is crucial for the estimation filter and we show that the accuracy of the estimation decreases exponentially as the frequency of the SS data fed to the EKF decreases.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Fundamentals of the interferometric fiber-optic gyroscope

Abstract: This paper reviews the basics of the interferometric fiber-optic gyroscope: fundamental principle based on Sagnac effect, importance of reciprocity and single-mode propagation, analysis of coherence and polarization problems, signal processing techniques. It also describes the technological progresses of guided-wave components (single-mode optical fiber, semi-conductor diode source, integrated optics, in-line fiber components). Finally, recent trends like multi-axis configurations and rare-earth doped fiber source are presented.

Survey apparatus and methods for directional wellbore wireline surveying

Abstract: A wellbore survey method and apparatus which includes a gyroscope, wherein the gyroscope has a spin axis, aligned with the instrument axis, and further having two sensitive axis orthogonally related to the spin axis and to each other. In addition, the wellbore survey apparatus contains a drive means, functionally connected with the gyroscope, to rotate the gyro about the instrument axis. The wellbore survey apparatus also contains a set of accelerometers, wherein the sensitive axis are aligned orthogonally to each other, and said drive means is functionally connected to the accelerometers to rotate the accelerometers about the instrument axis. Sensors determine the azimuthal direction of inclination of the wellbore at a first location therein and while traversing from said first location. Attitude references of the wellbore with regard to said first location are determined while the tool is continuously traversing through the wellbore.

Split electrode to minimize charge transients, motor amplitude mismatch errors, and sensitivity to vertical translation in tuning fork gyros and other devices

Abstract: A micromechanical tuning fork gyroscope having two center electrodes is disclosed. The two center electrodes are excited with bias potentials of opposite polarity. The oppositely biased center electrodes provide electrical symmetry across the gyroscope and thereby reduce charge transients and sensitivity to vertical translation. Currents injected directly into the proof masses are equal and opposite and thus cancel. Motor lift forces acting on the proof masses and interleaved electrodes are equal, and hence the proof masses move in pure translation, thereby reducing in-phase bias. Further, any pure translation normal to the plane of the gyroscope does effect sense axis output signals.

A surface-micromachined tunable vibratory gyroscope

Abstract: A tunable vibratory microgyroscope was fabricated by surface micromachining technology. The 7.5 /spl mu/m-thick polysilicon structural layer was deposited using LPCVD at 625/spl deg/C. The resonant frequency in the detection mode was higher than that in the driving mode so that gyroscope could be tuned to the resonant frequencies by applying the inter-plate DC bias. The gyroscope was driven in a resonant state by electrostatic force and detected the output due to a capacitance change between the plate and the polysilicon electrode. The resonant frequencies of gyroscope in the driving and detection direction were measured to be 10.48 kHz and 10.93 kHz, respectively. The resonant frequency in the detection direction could be shifted to 10.52 kHz by applying the tuning voltage of 4.0 V. The quality factor and resonant frequency of detection mode were significantly affected by ambient pressure and decreased as a function of ambient pressure. The noise equivalent rate of this device was about 0.1 deg/sec at 10/sup -2/Torr.

GPS compass: novel navigation equipment

Abstract: A GPS (Global Positioning System)-based compass is designed, which consists of three parts: the pointer, the sensor, and the controller. Using the carrier phase signals from GPS satellites, the 1 m long pointer equipped with two GPS receivers can aim to the desired direction with accuracy less than one degree. A baseline rotation method is proposed to resolve the problem of integer ambiguities. The classical antenna swap method is simply a special case of the rotation method. The rotating character of the compass provides a convenient environment for applying the turning technique. Such a compass may replace the traditional heading devices in navigation systems, such as the magnetic compasses or gyroscopes.

New designs of micromachined vibrating rate gyroscopes with decoupled oscillation modes

Abstract: This paper reports on new vibrating comb-drive rate gyroscope designs featuring decoupling of the actuation and the detection mode. Analytical calculations as well as FEM and system simulations are carried and the main drawbacks of these sensors are investigated which are especially the frequency mismatch of the two oscillation modes, the insufficient bandwidth and the effects of levitation. Concepts and simulations of electrostatically controlling both the resonance frequency and the bandwidth are presented. Within these concepts no mechanical balancing of the devices is required and thus calibration costs are reduced. Simulations of a new quasi-rotating rate gyroscope show, that a resolution of 0.1/spl deg//s is possible at a bandwidth of 50 Hz with 6 mm/sup 3/ sensor area only and that the effects of levitation are actually compensated.

Analysis of ceramic thickness shear piezoelectric gyroscopes

Abstract: Equations for linear piezoelectricity are formulated in a reference frame rotating at a constant angular velocity and are simplified by a perturbation procedure when the angular velocity of the reference frame is small The equations thus obtained are then employed in the analysis of a rectangular ceramic plate piezoelectric gyroscope operating with thickness shear modes Approximate analytical solutions to the equations resulted from the perturbation procedure are obtained based on Mindlin’s two-dimensional equations for a piezoelectric plate which are simplified by the thickness shear long wave approximation Free-vibration frequencies and mode shapes, as well as the condition for double resonance, are obtained Forced vibration is also studied which leads to a simple expression for the voltage sensitivity of the gyroscope The analysis is approximate and qualitative mainly with the purpose of exhibiting some most basic characteristics of the gyroscope Some of the results are compared with finite element numerical method

Accelerometer based gyro-free multi-sensor generic inertial device for automotive applications

Abstract: The importance of developing a unified inexpensive generic inertial device is substantiated in this paper based on the current situation in the automotive market. A gyro-free architecture of the generic inertial device is proposed as a solution. Exclusion of gyroscopes from the inertial system allows one to achieve an essential decrease in price, while the inertial system based on multiple accelerometers distributed inside the vehicle can still deliver data at sufficient accuracy for automotive inertially-aided systems. The paper also focuses on the choice of mathematical models as a Harwich of models evolving from the basic six sensor gyro free model, and shows the importance of optimization of parts of the design that permit formalization but involve tedious work. The original approach to the choice of optimal sequence of elementary operations is then described.

A high-stability fiber amplifier source for the fiber optic gyroscope

Abstract: We demonstrate an erbium-doped fiber amplifier (EDFA) source for the fiber gyroscope with an overall mean wavelength stability of four parts per million. This source, which amplifies the gyroscope signal before detection, is shown to be more stable than a similar single-pass source in a standard configuration. The effects of varying the fiber temperature, pump power, pump wavelength, gyroscope feedback power and signal polarization state on the output mean wavelength are individually explored. Experimental results are in excellent agreement with simulations.

Synthesized attitude and heading inertial reference

Abstract: An inertial reference system for determining the attitude and rate of change of attitude of a vehicle such as an aircraft is disclosed. Redundancy of the inertial reference system may be accomplished by replacement of one of the fiber optic gyroscopes of an otherwise dual fiber optic gyros installation with a low-cost reference IMU. Failure detection and isolation of a fiber optic gyroscope system may be accomplished with a low-cost reference IMU rather than with an additional fiber optic gyroscope. The information provided by the eliminated fiber optic gyroscope is synthesized from the output of the remaining fiber optic gyroscope and the output of the low-cost reference IMU.

Dead reckoning navigation for an autonomous mobile robot using a differential encoder and a gyroscope

Abstract: Dead reckoning navigation algorithm using a differential encoder and a gyroscope is proposed for an autonomous mobile robot (AMR). The indirect Kalman filter which feeds back the error estimates to the main navigation algorithm mutually compensates the differential encoder errors and the gyroscope errors. The experimental results show that the proposed AMR navigation algorithm provides the reliable position and heading of the AMR without any external positioning system.

Fiber optic gyroscope with deadband error reduction

Abstract: A deadband error reducer for a fiber optic gyroscope, which is an offset modulation signal that averages the deadband producing error over the range of the feedback modulation signal provided to the phase modulator. Although the offset modulation signal may be introduced at any of several points in the feedback loop, the offset modulation must approximate a critical amplitude at the phase modulator. If the offset modulation is a signal having segments that are linear with time, the critical amplitude of this signal will be 2π.

The navigation system of an autonomous underwater vehicle for Antarctic exploration

Abstract: In the context of the Italian Scientific Program for Antarctica an underwater vehicle is being developed that will be capable of operating autonomously for many hours under the Antarctic shelf or in sea areas covered by floating ice blocks. The vehicle must therefore carry a navigation system satisfying severe constraints on accuracy, size, and power consumption. During navigation the vehicle cannot use low-cost systems such as magnetic compasses (ineffective near the Earth poles), GPSs (which cannot be used underwater), or acoustic transponders (because of the long range of the missions). To estimate its own heading and position, the vehicle can only exploit measurements of acceleration, rotation rate, and velocity. The optimal integration of inertial and velocity measurements is accomplished by using a Kalman filter for correcting the effect of the biases of the inertial sensors (which would cause relevant long-term position errors) by exploiting a velocity measurement. Conceptually, the filter blends the high-frequency components of the inertial estimation with the low-frequency components of the velocity measurement, giving a long-term position estimation that is much more accurate than that obtainable using only accelerometers. A Doppler-dumped inertial navigation system has been developed using the recently available subsystems and implementing innovative signal processing techniques, obtaining a satisfactory trade-off between reliability, cost, accuracy, size, and power requirements. The inertial sensors (three accelerometers and three ring laser gyroscopes) are packaged in a small-size and relatively low cost, strap-down inertial unit. The velocimeter is a compact low-power Doppler sonar specifically designed for underwater vehicles. Signal processing is implemented on a general purpose computer having small space and power requirements. The performance of the Kalman filter was optimized by using the "indexing" technique, which consists of periodically rotating the inertial unit to increase the observability of the Kalman filter states and thus improve the correction of the biases of the inertial measurements. In the paper, the navigation system is described and its performance analyzed, showing the effectiveness of the indexing technique in improving the Kalman filter performance both in convergence speed and in estimation accuracy.

Optical signal noise reduction for fiber optic gyroscopses

Abstract: The RIN (random intensity noise) component of the random walk error of a fiber optic gyroscope can be reduced by utilizing an unpolarized light signal during processing. By depolarizing the light wave modulated by the fiber optic sensing coil or combining it with the unmodulated light wave of orthogonal polarization, a 3 db reduction in RIN can be achieved.

Initial calibration and alignment of an inertial navigation

Abstract: This work presents an efficient initial calibration and alignment algorithm for a six-degree of freedom inertial navigation unit. The individual error models for the gyros and accelerometers are presented with a study of its effects in trajectory prediction. A full error model is also presented to determine the sensors needed for full observability of the different perturbation parameters. Finally, dead reckoning experimental results are presented based on the initial alignment and calibration parameters. The results show that the algorithm proposed is able to obtain accurate position and velocity information for a significant period of time using an inertial measurement unit as the only sensor.

Simulation model for micromechanical angular rate sensor

Abstract: A simulation model for an angular rate sensor, a gyroscope, is presented. The device is based on a micromechanical dual torsional mass system which is actuated electrostatically and sensed capacitively. Model equations describing a dynamic, non-linear system are first presented and then realized as an electrical equivalent circuit. The vibrational modes of the system are modelled with coupled resonator circuits. The electrostatic and Coriolis forces as well as variable capacitances in the small air gaps are modelled with non-linear controlled current sources. External forces, torques and electrical actuation can act as inputs to the device. The model presented allows numerical sensor simulations concurrently with the interfacing electronics in the time and frequency domains. The model is verified by comparing its simulation results to measured frequency responses and capacitance-voltage characteristics.

Miniature box vibrating gyroscope

Abstract: An open top box structure is micromachined on a base, such as a crystalline silicon substrate, and drive and sensing devices are fabricated on the same substrate. Output transducers sense Coriolis force changes by processing signals representing force components at the corners of the vibrating box structure as it is rotated to yield angular rate measurement.

Fiber optic sensor coil including buffer regions

Abstract: A sensor coil for a fiber optic gyroscope. At least one dummy layer forms an integral structure with, and shares the thermal expansion characteristics of, a potted coil comprising a plurality of layers of windings of a first optical fiber. In a gyroscope, the potted coil is arranged to receive the output of a source of optical energy as a pair of beams that counter-propagate therein and to provide the resultant interference pattern, as gyro output, to a detector. The dummy layer displaces layers or windings of the potted coil from regions likely to contribute to Shupe bias effects.

Fiber optic gyroscope with reduced non-linearity at low angular rates

Abstract: The linearity of a fiber optic gyroscope can be improved by dithering the gyroscope's feedback signal. Any undesirable effects introduced by the dithering signal are removed by processing the gyroscope data over an entire cycle of the dithering signal. A further improvement in linearity can be achieved by introducing a compensation signal.

Fiber optic gyroscopes for vehicular use

Abstract: The measurement of rotational motion is an essential element of vehicle navigation and stabilization. Interferometric fiber optic gyroscopes (IFOG) are becoming affordable for many such applications. They offer the advantages of high reliability, resistance to shock and vibration, and repeatability over time and temperature. Based on the Sagnac effect, the IFOG has no moving parts, and consists of a fiber sensing coil, semiconductor light source, photodetector, polarizer, one or more directional couplers, and signal processing electronics. Only the "open-loop" signal processing approach is economic for land navigation use, with its simplified electronics and all-fiber optical circuit construction. It is now possible to produce an optical circuit using only one directional coupler, further simplifying the construction and reducing cost. Both types of open-loop gyro are in production. Performance data for bias and scale factor versus temperature as well as rate linearity, are presented.