Structural effects and techniques in precision pointing and tracking systems: a tutorial overview

Structural dynamics is one of the most important elements of a precision gimbal design which often dominates the system line-ofsight stabilization and pointing performance. Structural effects are manifested in these systems in several unrelated ways that the systems engineer, and other members of the design team, must understand in order to insure a successful design. Once the effects are clearly understood, analysis techniques, such as finite elements, can be applied to provide models to accurately predict the various interactions and evaluate potential designs. Measurement techniques such as modal analysis can also be used to obtain models of existing hardware and to verify the design. However, the successful and efficient application of the above process requires that the underlying principles and effects are well understood by all the members of the engineering design team. This usually includes, as a minimum, the control systems engineer, the structural analyst and the mechanical engineer but may involve other members of the design team as well. Appropriate transfer functions for the various interactions, for example, can be defined and provided by the structural analyst to the control system engineer to evaluate and performance predictions can be iterated as necessary until the entire system meets the required performance in the intended dynamic environment. Often, however, one or more members of the team do not have an appreciation for the effects or design process required and the result is a frustrated design effort and lower system performance that might have otherwise been easily achieved. While different systems can have vastly different requirements and configurations, the above effects and techniques are common to most and this paper is an attempt to provide a straightforward outline of the more common of these in order to improve communication among design team members so that they can all contribute at their maximum potential.