Scale Factor Error Research Articles

Bounding the angular scale factor error for adaptive arrays

When compared with a conventional gimballed antenna a phased-array antenna conveys some important advantages to a tracking radar system, including inertialess beam-steering and the ability to modify the beam pattern to suppress interference. For successful tracking of a radar target the linearity of the antenna angular response must be carefully controlled. The effect of array calibration errors on the linearity of the response of an adaptive phased-array antenna is considered. Through analysis of the maximum likelihood estimate (MLE) of target angle, a lower bound is derived on the variance of the angular scale factor error achievable when tracking a target with an adaptive phased-array antenna in the presence of residual calibration errors and interference. It is shown that while the presence of a sidelobe interferer has little impact on the achievable variance, a strong mainbeam interferer can result in a very significant degradation.

Fault Detection with Sensor Errors

ABSTRACT A scheme for fault detection with sensor errors is discussed. Sensor output generally contains scale factor error and misalignment error as well as constant bias. In this paper the neural network is applied to compensate the residuals calculated by optimal parity vector method in order to remove the effect of sensor errors. And then compensated residuals are used to detect and isolate fault by analytic method and neural network. Thereby the accuracy of fault detection and isolation is improved

Parity Vector Compensation for Fault Diagnosis of Inertial Sensor Unit

A scheme based on neural network is presented to improve the fault detection and isolation (FDI) performance of a skewed redundant strapdown inertial measurement unit. The neural network is trained to eliminate the effects of input axis misalignment, scale factor errors and biases on parity vector. One advantage of the proposed technique over other compensation algorithm based on Kalman filter or bias separated estimation is that it does not require dynamic equation of error states and statistics of noise. The simulation results show that the proposed method can significantly improve the FDI performance of the skewed inertial sensor sets.

Estimation of Stability & Control Derivatives from Flight Test Data of Fighter Aircraft

Longitudinal stability and tontrol derivatives of a fightlfr aircraft are estimated by output error method for different types of input excitation. The uncertainties in the parameters are computed by cortfcting Cramer-Ra(j) bounds using fudge factor. In general, the step input response data is not usedfor estimating the derivatives. Therefore, step response time history trajectories were cross-validated using tIle estimated derivatives for standard inputs like doublet and 3211. This proves that the model parameters are estimated with high confidence. By appropriately choosing the mathematical modeland using the corrected flight data for bias and scale factor errors by compatability check for parameter estimation proves beyond doubt that such a procedure can be adopted for estimating stability and control derivatives of any aircraft.

Imperfect quarter-waveplate compensation in Sagnac interferometer-type current sensors

We analyze scale factor errors associated with integrating imperfect quarter-waveplates into loop and in-line Sagnac interferometer fiber-optic current sensors. We show that relatively large imperfections in the quarter-waveplates can be tolerated in the loop version when the birefringence axes of the two quarter-waveplates are oriented 45/spl deg/ with respect to each other. For the in-line version, we demonstrate an electronic signal processing scheme that desensitizes the scale factor to imperfections in the quarter-waveplate.

Elimination of birefringence induced scale factor errors in the in-line Sagnac interferometer current sensor

This paper presents theoretical and experimental results showing the effects of linear and circular birefringence on the sensing coil of an in-line Sagnac interferometer current sensor. Linear birefringence induces local scale factor variations along the length of the sensing coil which can be suppressed with circular birefringence. We show that by winding the sensing coil with tension in a helix configuration, these variations may be effectively reduced to zero for ordinary single mode fiber. In our opinion, this method of implementation overcomes the need to use annealed fiber in the sensing coil.

Signal distortion induced by Fresnel reflection in open-loop fiber-optic gyroscopes

The signal distortion that is due to Fresnel reflection in open-loop fiber-optic gyroscopes was theoretically analyzed to determine the relationship between the reflection ratio and the scale factor error of the gyroscopes. The analysis showed that the in-phase component of each Fourier harmonic of the gyroscope signal deviates from the true sinusoidal function, a quadrature-phase component appears, and the pi/2 rotation rates of harmonic components disagree. We evaluated the degree of scale factor degradation by defining the harmonic distortion ratio, which can be used as a measure for the reflectional quality of the gyroscopic optical system. The theory was verified by the response of an experimental gyroscope. The Fresnel reflection was eliminated by optical and electrical means, and the signal distortion of the experimental gyroscope was suppressed.

Development of high grade fiber-optic gyroscopes

Tokimec has been developing high grade interferometric fiber-optic gyroscopes (I-FOGs) for useful applications. The I-FOG consists of a sensing coil module, a light emitting module and an electronics circuits module. We achieved the bias stability of 0.003 deg/h and the angular random walk of 0.001 deg/√h and the scale factor error of 10 ppm (1σ). Then the azimuth error of the strapdown gyrocompass system with the high grade I-FOGs was less than ±0.05 s λ (deg) under the environmental temperature condition 23±5(°C).

Parity Vector Compensation Using Non-Linear Filtering

The performance of a failure detection and isolation(FDI) algorithm applied to a redundant strapdown inertial measurement unit (IMU) is limited by sensor errors such as input misalignments, scale factor errors, and biases. Non-linear filtering is proposed to estimate the combinations of sensor errors which affect the parity vector, the estimates are used to form a compensated parity vector. The compensated parity vector is used to make FDI decision for improving FDI performance. Simulation results prove that the FDI performance can be improved greatly by using the proposed method

Mine avoidance techniques for underwater vehicles

It is shown that by implementing certain mine avoidance techniques, an underwater vehicle equipped with an obstacle avoidance sonar (OAS) and a navigation system can safely navigate an unknown minefield. The mine avoidance techniques take into account the physical limitations of the sonar and the navigation system, the maneuverability constraints on the underwater vehicle, and the required safe standoff distance from all mines. Extensive computer simulations have verified the mine avoidance capability in more than 50 different minefields. In all 50 simulations the vehicle reached a predetermined end point and maintained at least the specified, minimum safe standoff distance from each mine. The simulation accurately models the major difficulties associated with the sonar, the navigation system, and the vehicle dynamics. The sonar model includes surface, bottom, and volume reverberation; thermal, ambient, and flow noises; actual receiver and projector beam patterns; and false alarms and missed detections. The navigation system model contains the effects of biases, random noises, and scale factor errors. The vehicle dynamic model simulates angular velocities and accelerations associated with underwater vehicles. >

A pseudo-heterodyne fiber optical gyro, using integrated optics

A hybrid fiber-optical gyro using a novel scheme for pseudo-heterodyne detection is presented. The large bandwidth of integrated optical phase modulators allows for the use of a triangular-wave for dynamical biasing of the interferometer, while still being able to choose the modulation frequency to be the eigenfrequency of the fiber-loop. It is shown that this, together with the use of a dual-channel approach, minimizes both bias and scale factor errors. It is proposed that the fourth harmonic can be used to keep the modulation index of the applied triangular-wave phase modulation at the correct height and thus guarantee a good scale factor linearity. >

Sliding-mode control system for the three-axis attitude control of rigid-body spacecraft with unknown dynamics parameters

Sliding-mode control is shown to be an advantageous new approach to the three-axis attitude control of rigid-body spacecraft in which accurate pre-launch estimation of the dynamics parameters is unnecessary. The control-system accuracy is shown to depend almost entirely on the attitude-measurement system, control-actuator misalignments and scale-factor errors being permitted. If the control actuators are operated in hot redundance, actuator failures are permitted while guaranteeing uninterrupted service from the control system. Extreme stiffness is also presented to disturbance torques. Continuous control actuators are assumed. Control smoothing integrators, introduced to facilitate continuous control action with negligible limit cycling, are treated as part of the controlled plant by including the three angular acceleration components in the state feedback. Closed-loop response independent of the dynamics parameters for a demanded attitude may be designed via pole assignment. The new ideal multivariate c...

Monolithic silicon accelerometer

A monolithic silicon micromechanical accelerometer, which is particularly well suited for integration with other mechanical and electrical components, and is about 0.75 mm 2 in area, is described. Four electrodes are built into the structure in the manner of buried layers and are used to effect a differential capacitance readout and electrostatic torquing for closed-loop operation. Current performance is less than 500 ppm scalefactor error. An important constraint was process compatibility with Draper Laboratory's micromechanical gyroscope, so that both can eventually be made on the same chip.

Alternating-current measurement and noninvasive data ring utilizing the Faraday effect in a closed-loop fiber magnetometer

A novel fiber-optic polarimetric configuration for a magnetometer utilizing the Faraday effect is described. The system is operated in a closed-loop mode using magneto-optic feedback through a simple current-driven solenoid to maintain the azimuth of the optical output from the polarimeter constant. In this mode of operation scale-factor errors due to changes in the Verdet constant of the fiber are effectively eliminated. The minimum detectable current was less than 1 mA, with linear operation up to several amperes. A multiplexed system was also demonstrated, with potential application as a multiaccess noninvasive data ring.

In-Flight Parity Vector Compensation for FDI

The performance of a failure detection and isolation (FDI) algorithm applied to a redundant strapdown inertial measurement unit (IMU) is limited by sensor errors such as input axis misalignment, scale factor errors, and biases. A techique is presented for improving the performance of FDI algorithms applied to redundant strapdown IMUs. A Kalman filter provides estimates of those linear combinations of sensor errors that affect the parity vector. These estimates are used to form a compensated parity vector which does not include the effects of sensor errors. The compensated parity vector is then used in place of the uncompensated parity vector to make FDI decisions. Simulation results are presented in which the algorithm is tested in a realistic flight environment that includes vehicle maneuvers, the effects of turbulence, and sensor failures. The results show that the algorithm can significantly improve FDI performance, especially during vehicle maneuvers.

Application of Model Following Control and Estimation Techniques to Attitude Control of Manoeuvring Spacecraft

The paper presents an approach to sampled data, on-board estimation and control of the attitude motion of manoeuvring spacecraft. Algorithms for a) estimation of gyroscope parameters (drift rate bias, scale factor error) and spacecraft state (attitude, angular velocity, disturbance torque), and b) model following control of attitude manoeuvres, are presented. The algorithms were validated in single-axis software simulations of an attitude control system of the type as used in the Infra Red Astronomical Satellite (IRAS). The considered control system comprises a strapdown rate-integrating gyro and a slit-type star sensor for optical - inertial attitude sensing, a reaction wheel actuator, and a 16-bit on-board computer.The estimation and control algorithms are described, design trade-offs are discussed, and simulation results are presented.

A Variational Technique for Smoothing Flight-Test and Accident Data

The problem of determining aircraft motions along a trajectory is solved using a variational algorithm that generates unmeasured states and forcing functions, and estimates instrument bias and scale-factor errors. The problem is formulated as a nonlinear fixed-interval smoothing problem, and is solved as a sequence or linear two-point boundary value problems, using a sweep method. The algorithm has been implemented for use in flight-test and accident analysis. Aircraft motions are assumed to be governed by a six-degree-of-freedom kinematic model; forcing functions consist of body accelerations and winds, and the measurement model includes aerodynamic and radar data. Examples of the determination of aircraft motions from typical flight-test and accident data are presented.

The double dual-slope multiplier: Elimination of offset

The double dual-slope multiplier is a multiplying analog-to-digital converter based on the dual-slope integrating converter. The ratio of the product of two unknown voltages to the square of a reference voltage is obtained in terms of the ratio of a measured time interval to a known time interval. Offset errors, which are the main source of error, are described and a modification which greatly reduces the error is proposed. The errors consist of scale factor, output, and linear feedthrough errors. The scale factor and output errors can be measured by a cycle consisting of two dual-slope measurements that use the reference voltage only. The feedthrough errors can be eliminated if the multiplying cycle is repeated with the order of the inputs reversed. The operation of the multiplier when the inputs are less than the offset is considered in detail. Since the decision making, memory, and calculations necessary for the control of the multiplier and the correction of the offset are considerable, the method is mainly applicable to precision instruments equipped with a microprocessor.

In-Flight Gyro Drift Rate Calibration on the Viking Orbiters

The drift rates of the attitude control gyros onboard the Viking Orbiters were calibrated several times during flight. The calibration was performed by engaging the gyro control of attitude for a six-hour period, recording the Viking Orbiter coordinates of the sun and the roll reference star as a function of time, and processing these data by a computer program. The computer program calculated drift rates for each data increment, and then smoothed the calculated rate versus the time function for all the data on the basis of a Gauss-Markov gyro-drift model. The effects of data noise were minimized by using a relatively long time constant in the Gauss-Markov model and by empirically determining a set of corrections for celestial inertial scale factor error differences. In this way the rms error of the data fit was lessened.

Analysis Strapdown Navigation Using Quaternions

A brief review of the theory of strapdown inertial navigation is presented in which the attitude of the sensor box with respect to inertial space is represented by the four-parameter quaternion vector. . A 4X4 matrix R is defined which aids in relating quaternions to direction cosines and facilitates interpretation of the equations for error propagation, which are also derived. In the interpretation, it is shown that the error in the quaternion vector causes aor-(correctable) scale factor error and an equivalent tilt vector error that propagates the same way as the platform tilt vector in a gimbaled system.