Abstract: A system and method for performing high performance quantizer processing of sensor data in a multiple-channel quantizer system. A reset prioritization scheme is provided for current sources connected to an integrator in the multiple-channel quantizer for preventing saturation of the various quantizer channels. The reset prioritization scheme determines the channels most in need of a reset to prevent saturation based upon predicted quantizer signals to appear on the channels during the next processing cycle of the quantizer system. This method of controlling the reset processing permits significantly higher acceleration capacity by preventing quantizer channel saturation in system utilizing accelerometers.

Abstract: A method for attitude alignment of a slave inertial measurement system connected to a rotationally mobile platform supported by a vehicle that is stationary relative to a reference navigation frame comprises the steps of mounting a master reference inertial measurement system on the rotationally mobile platform and determining a master reference system attitude using measurements of acceleration and angular rates of the master reference inertial measurement system relative to the reference navigation frame. A slave system attitude is determined using measurements of acceleration and angular rates of the slave inertial measurement system relative to a slave system navigation reference frame and comparing the slave system attitude to the master reference system attitude to determine an attitude difference. The attitude difference is processed to obtain a correction to the slave system attitude.

Abstract: The invention is a method and apparatus for improving the accuracy of an inertial navigation system. The method comprises (1) obtaining a measure of the angular velocity of a body frame of reference having a first axis, a second axis, and a third axis, (2) obtaining a measure of the acceleration of a first reference point in the direction of the first axis, a second reference point in the direction of the second axis, and a third reference point in the direction of the third axis, the first, second, and third reference points being fixed in the body frame, and (3) determining compensated acceleration values. A compensated acceleration value is the difference of the measure of acceleration of a reference point and a compensation quantity. A compensation quantity is an estimate of the portion of the acceleration of the reference point resulting from the rotation of the body frame. The method further comprises establishing the optimum navigation center based on a criterion of goodness.

Abstract: Multiple isolators are configured with respect to an assembly (101), such as a sensor assembly in an inertial navigation system or other system where cross-axis acceleration or rotation coupling is undesirable. The system utilizes a set of isolators (203, 209, 215, and 221; 305, 307, 311, 313, 317, 319, 323, 325; or 403, 405, 407, 411, 413, and 415) that are substantially matched to each other, but may have uncorrelated axial stiffness and radial stiffness. The system configuration does not introduce cross-axis coupling, such as cross-axis translational coupling and cross-axis rotational coupling.

Abstract: The invention is a method and apparatus for processing signals with frequencies fL and fR from a multioscillator ring laser gyro, the method being repeated at regular time intervals. The difference f&Dgr;&thgr;, of fL and fR is a measure of the angular rotation rate of the ring laser gyro and the sum fF of fL and fR divided by 2 is the Faraday bias frequency. The first step of the method comprises determining two or more of the values MLP, MRP, MFP, and M&Dgr;&thgr;P of a set of functions ML(fL), MR(fR), MF(fF), and M&Dgr;&thgr;(f&Dgr;&thgr;). The second step comprises storing two or more processed values MLS, MRS, MFS, and M&Dgr;&thgr;S of the functions ML(fL), MR(fR), MF(fF), and M&Dgr;&thgr;(f&Dgr;&thgr;) if the corresponding values of MLP, MRP, MFP, and M&Dgr;&thgr;P are valid. A processed value is derived from the value for the present time interval and zero or more processed values for prior time intervals.

Abstract: A closed loop gain circuit controls the gain of a variable gain amplifier and provides a stable AGC response irrespective of the actual gain level. The amplifier may be arranged to amplify electrical signals output from a fiber optic gyroscope. A perturbation injection circuit provides a perturbation signal ±d to a phase modulator connected to the fiber optic gyro. A perturbation compensation circuit applies perturbation compensation signals to signals output from the variable gain amplifier and produces a compensated signal by reducing the magnitude of the perturbation in the amplified signal output from the variable gain amplifier. A gain error circuit connected to the perturbation compensation circuit produces a gain error signal that indicates the magnitude of the perturbation signal remaining in the amplified signal after perturbation compensation. A feedback system provides a gain control signal to the variable gain amplifier to reduce the magnitude of the gain error signal.

Abstract: A closed loop gain circuit controls the gain of a variable gain amplifier and provides a stable AGC response irrespective of the actual gain level. The amplifier may be arranged to amplify electrical signals output from a fiber optic gyroscope. A perturbation injection circuit provides a perturbation signal ±d to a phase modulator connected to the fiber optic gyro. A perturbation compensation circuit applies perturbation compensation signals to signals output from the variable gain amplifier and produces a compensated signal by reducing the magnitude of the perturbation in the amplified signal output from the variable gain amplifier. A gain error circuit connected to the perturbation compensation circuit produces a gain error signal that indicates the magnitude of the perturbation signal remaining in the amplified signal after perturbation compensation. A feedback system provides a gain control signal to the variable gain amplifier to reduce the magnitude of the gain error signal.

Abstract: A phase and intensity modulated IFOG has a light source responsive to an intensity modulation signal for providing an intensity modulated light signal. A Sagnac interferometer has a fiber optic coil. The coil receives and circulates a clockwise and counter-clockwise beams. The Sagnac interferometer is responsive to an intensity modulated light signal at a first input port, and to a phase modulation signal at a phase modulation input terminal for outputting a non-reciprocal interference signal. A PSD detector system responds to the non-reciprocal interference signal and provides a demodulated bias signal. An intensity signal generator has an output that provides the intensity modulation signal. A phase signal generator provides the phase modulation signal to the phase modulation input terminal. The intensity signal generator and the phase signal generator have a common frequency.

Abstract: A system and method for controlling the cavity length of a ring laser gyroscope to properly tune the resonant wavelengths of the ring laser gyroscope during moments when experiencing sudden shocks or high g force accelerations. The system controls the position of a movable mirror in the laser cavity of the gyroscope to control the length of the laser cavity. The system measures the acceleration experienced by the laser cavity, wherein the position of the movable mirror is adjusted to counteract the effects of the acceleration on the movable mirror in a real-time response to the measured acceleration. By adjusting the position of the movable mirror, the resonant wavelengths propagating in the ring laser gyroscope will be maintained at their desired intensity and continue to lase even after experiencing this acceleration.

Abstract: A closed loop accelerometer includes apparatus within an associated digital rebalance loop for reducing the presence of low frequency moding noise in the accelerometer output. In one embodiment, the digitized corrective signal is applied to a moving average filter. In a second embodiment, the corrective signal is modulated with a random function and, in a third embodiment, the digitized corrective signal is both randomized and applied to a moving average filter. In each embodiment, the periodic moding noise that results from the analog-to-digital conversion within the rebalance loop is significantly reduced from that observed in prior art systems.

Abstract: The invention is a method and apparatus for repetitively executing a plurality of software packages at a plurality of rates utilizing a common set of computational resources. The method consists of counting contiguous time increments and executing a plurality of software packages. Each software package is executed during each time increment in one or more sequences of time increments. The time increments in each sequence recur at a predetermined rate, and the time increments assigned to one software package do not overlap the time increments assigned to any other of the plurality of software packages.

Abstract: A dithered Coriolis acceleration sensor system has a proof mass that is free of feedback in the accelerometer servo loop at the dither frequency by totally notching out all feedback torque at this frequency. The proof mass relative motion is then a direct measure of the rate because there is no feedback torque to alter the proof mass response to the acceleration. The feedback modulation system according to the invention captures the Coriolis-sensor output such that the phase and gain of the signal generated from the sensor are of no concern in maintaining good scale factor.

Abstract: The invention is a method and apparatus for generating a pseudorandom sequence of bits. The method comprises the steps of (1) selecting a “0” or a “1” as the next bit of the modified pseudorandom bit sequence if one or more criteria are satisfied, the criteria being based on the measured properties of a plurality of prior bits of the modified pseudorandom bit sequence; otherwise: (2) selecting the next bit of an initial pseudorandom bit sequence as the next bit of the modified pseudorandom bit sequence, the next bit of the initial pseudorandom bit sequence being a function of one or more prior bits of the initial pseudorandom bit sequence.

Abstract: The invention is a method and apparatus for generating a primary pseudorandom bit sequence consisting of a plurality of contiguous P subsequences. Each P subsequence consists of a start sequence of predetermined length followed by a sequence of trailing bits. The method comprises three steps. The first step consists of deriving a feedback bit from each generating sequence in a P subsequence in accordance with a specified rule where a generating sequence is any sequence of contiguous bits in the P subsequence having the same length as the start sequence. The bit that follows a generating sequence is called the trailing bit for that generating sequence. The second step of the method consists of determining a sequence of one or more modifier bits to be used in modifying the P subsequence. The third step of the method consists of modifying the P subsequence utilizing the one or more modifier bits.

Abstract: A system and method for improving the accuracy of altitude determinations in an inertial navigation system. The system utilizes pressure measurements which are taken by a barometric altimeter and converted into an estimated pressure altitude using any known pressure-to-altitude conversion. A pressure correction value is then generated using a correction value generating formula that is a function of altitude. The pressure correction value is then multiplied by a pressure offset value for the barometric altimeter to generate a pressure offset error for the barometric altimeter. This pressure offset error is used in the present invention to modify the pressure altitude estimation in order to generate an altitude determination having an improved accuracy. The present invention further determines an amount of observation noise in the barometric altimeter that is a function of pressure noise and altitude, where the altitude estimation is further modified to account for the observation noise.

Abstract: The invention is a method and apparatus for obtaining an accurate value x1c of a variable x1 based on an estimate x1e that is a function of K variables x1, x2, . . . , xk, . . . , xK. The method comprises the steps of (a) obtaining a plurality of estimates x1e, x2e, . . . , xke, . . . , xKe of the variables x1, x2, . . . , xk, . . . , xK over a method-execution time period, the values of the variables x1, x2, . . . , xk, . . . , xK changing or being changed during the method-execution time period; (b) obtaining from an external source the actual values x1a of x1 during the method-execution time period; (c) defining a compensation model &dgr;x1 that is a function of one or more of the estimates x1e, x2e, . . . , xke, . . . xKe of the variables x1, x2, . . . , xk, . . . , xK, the compensation model being further defined by I unknown constants a1, a2, . . . , ai, . . . , aI; (d) applying an operator G to the values of x1e−x1a and &dgr;x1; (e) determining the values of a1, a2, . . . , ai, . . .

Abstract: The invention is a method and apparatus for determining the fringe number for a fiber-optic gyro. The fiber-optic gyro comprises a light source feeding an interferometer which in turn feeds a detector. The detector output signal is a function of the fringe number and a plurality of controllable parameters. The method comprises the steps of (1) determining the values of the controllable parameters and (2) extracting the fringe number from the detector output signal utilizing the values of the controllable parameters.

Abstract: A system and method for improving the accuracy of altitude determinations in an inertial navigation system. Pressure measurements available to the inertial navigation system are used to initially calculate an estimated pressure altitude using the standard day model for the atmosphere. Temperature measurements are further utilized in the physical relationship between temperature, pressure, and altitude to compute a second computed altitude. A change between subsequent second computed altitudes is calculated and compared with a respective change in the computed pressure altitude in order to generate a correction value. The correction value is then used to modify the computed pressure altitude to generate a more accurate determination of the absolute altitude of the inertial navigation system.

Abstract: The invention is a method and apparatus for updating the attitude of a body by utilizing a plurality of gyros to measure as a function of time the angular rate vector or the integrated angular rate vector for the body. The method comprises the steps of (1) obtaining measured values of the angular rate vector at a plurality of readout intervals, (2) obtaining a smoothed value of each of one or more smoothed representations of the angular rate vector at the end of each of a plurality of smoothing intervals, and (3) obtaining the updated attitude of the body at the end of an update interval by utilizing the attitude at the beginning of the update interval and the smoothed values of the smoothed representations of the angular rate vector obtained during the update interval. A smoothed representation is a weighted sum of the measured values obtained during a smoothing interval.

Abstract: The invention is a method continuing over a plurality of time periods for compensating for the output error in each of one or more navigation instruments in a system comprising a plurality of navigation instruments after the system is introduced into its operating environment. The practice of the method begins with determining the values of one or more of a set of coordinates that specify the position, velocity, and orientation of the system in space together with the error in a compensated output for each of the one or more navigation instruments. The method continues with determining a compensation model for each of the one or more navigation instruments. A compensation model specifies for a current time period an adjustment in amplitude of the output of a navigation instrument as a function of time and temperature.