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Substantial efforts have gone into the development of sophisticated algorithms that reduce system drift errors in the presence of coning motion. Present-day algorithms form high-order coning correction terms using multiple incremental angle outputs from the gyros. These algorithms assume a at transfer function for the processing of the incremental angle outputs and are structured to yield very high-order responses. However, these algorithms do not address the issue of nonideal gyro frequency response or of ltered gyro data. Many gyros exhibit complex frequency responses and violate the assumptions used in deriving the previously developed coning algorithms. The mismatch between the assumed and actual frequency response of the gyro data leads to degradation of performance in a coning environment as well as ampli cation of pseudoconing errors. A method of deriving algorithms that are tailored to the frequency response of the particular type of gyrosused is presented. These algorithmscan be designed to arbitrarily high order and can also supply an extremely sharp high-frequency cutoff to minimize pseudo-coning errors. Additionally, this method can be used to design coning algorithms that are tuned to deliberately ltered gyro data. The technique developed equally applies to mechanical, ber-optic, and other types of gyros.

The research work evaluates the quality of the sensor to perform measurements and documents its effects on the performance of the system. It also evaluates if this performance changes due to the environments and other system parameters. These environments and parameters include vibration, system friction, structural resonance, and dynamic system input. The analysis is done by modeling a gimbal camera system that requires angular measurements from inertial sensors and gyros for stabilization. Overall, modeling includes models for four different types of gyros, the gimbal camera system, the drive motor, the motor rate control system, and the angle position control system. Models for friction, structural resonance, and vibration are analyzed, respectively. The system is simulated, for an ideal system, and then includes the more realistic environmental and system parameters. These simulations are run with each of the four types of gyros. The performance analysis depicts that for the ideal system; increasing gyro quality provides better system performance. However, when environmental and system parameters are introduced, this is no longer the case. There are even cases when lower quality sensors provide better performance than higher quality sensors.

Many inertial navigation systems of both platform and ring laser strapdown types are currently in service. This paper discusses the possibility and desirability of incorporating a small GPS receiver in these systems. Advances in technology such as microprocessors, gate arrays, and surface mount devices allow the existing INS electronics to be replaced in a reduced volume. The remaining space in many cases is sufficient to permit the insertion of a small GPS receiver. Locating the GPS receiver in an inertial navigation system (INS) solves many of the usual system integration problems. Tight coupling between the GPS and INS can be achieved since data latency is minimized and well controlled. In such a configuration, rate aiding of the GPS is easily achieved. This approach also leads to greater flexibility and enhanced overall performance since all GPS and INS data are simultaneously available. While not providing the ultimate in redundancy, the integrated INS/GPS approach does offer greater simplicity with enhanced performance. This discussion primarily focuses on military systems. Nevertheless, the proposed techniques also are applicable to commercial units.

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In the past, fiber optic gyros have generally been viewed as angular rate sensors. However, for inertial navigation purposes, a "rate integrating" gyro characteristic is desired. The distinction is subtle, but important. A rate gyro's output represents an estimate of instantaneous angular rate. The system attitude is determined by sampling the rate and integrating numerically to angular displacement. On the other hand, a rate integrating gyro provides the change in rotation angle rather than instantaneous rate. The system accumulates the angular increments obtained from the gyro to determine rotation angle and, hence, attitude. A ring laser gyro is a good example of a rate integrating sensor. Its output consists of pulses that represent fixed angle increments. It is shown that an interferometric fiber optic gyro can also be configured as a rate integrating gyro. The paper discusses the theory and application of this concept.

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