Use of a Three-Axis Monolithic Ring Laser Gyro and Digital Signal Processor in an Inertial Sensor Element

Donald J. Weber

Abstract:	Over the last decade the Ring Laser Gyro (RLG) has been introduced into various navigation applications. This technology continues to show performance growth relative to traditional "iron" gyros, while demonstrating greater reliability and lower power consumption. In order to realize the advantages of this technology, design considerations have included additional computational requirements, increased size;weight, and incorporation of mechanical gyro dither (to overcome the RLG lock-in phenomena). Coincident with advances in RLG technology to perform at levels consistent with those required for navigation systems has been the tremendous increase in computational capability of available processors. Initial configurations utilizing RLGs required special-purpose/dedicated processors to perform the "strapdown algorithm." This differed from traditional iron gyro inertial platform configurations, where electromechanical gimbals maintain the physical attitude of the inertial sensors. The advances in digital signal processor technology now permit an architecture that eliminates special-purpose processors and reduces the computational load on the general-purpose processor in the Inertial Navigation System (INS). The other issue of size and weight for a specified performance range is now yielding before the next generation of RLGs. In this vein, Kearfott has developed a Triple Laser Gyro (TRILAGTM ). The TRILAG is a three orthogonal axis monolithic RLG based on a design of nested optical cavities in Which 38 the mirrors are shared between the optical cavities. The six mirrors (visualized as the faces of a cube) form three square orthogonal gyros with each mirror shared by two gyros. This integrated approach provides the largest possible RLG path length in a given volume, provides increased alignment stability, and provides for a reduction in parts count which lowers manufacturing costs while increasing reliability. The current outlook indicates that inertial systems configured around this next generation sensor will find application in terrestrial, aircraft, and missile configurations. This forecast is now supported by laboratory and flight testing at both gyro and system level. This paper presents a configuration based upon a 24-cm path length TRILAG gyro, three miniature single-axis force rebalance accelerometers, and a digital signal processor. The resulting inertial sensor element provides navigation performance equal to a conventional medium-accuracy navigation system (0.4" to 1 nmh) with half the weight and volume of a traditional RLG configuration. Its application as a stand-alone inertial subsystem or as an will be discussed and performance- data presented. Companion development utilizing down-sized TRILAG gyros for tactical missile or sensor stabilization applications is also reviewed.
Published in:	Proceedings of the 43rd Annual Meeting of The Institute of Navigation (1987) June 23 - 25, 1987 Dayton, Ohio
Pages:	38 - 43
Cite this article:	Weber, Donald J., "Use of a Three-Axis Monolithic Ring Laser Gyro and Digital Signal Processor in an Inertial Sensor Element," Proceedings of the 43rd Annual Meeting of The Institute of Navigation (1987), Dayton, Ohio, June 1987, pp. 38-43.
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