Direct Digital Control of Inertial Guidance Sensors

Abstract

This study is concerned with the theoretical design of rebalance control systems for inertial sensors using digital controllers. Specific attention is given to the case where a two-degree-of-freedom gyro is used as an attitude sensor in a strapdown inertial measurement system. Because of the similarity of the dynamical behaviour of gyros and accelerometers, the method can be extended to accelerometers without great difficulty. A new design method has been developed to yield control algorithms for the digital control elements. Control functions are synthesized to achieve a minimum settling time and eliminate interactions between the gyro control axes. It is shown that the method can be used when filters are included to remove pick-off noise, and can be adapted to take account of finite processing delay in the digital controller. Sensitivity of the system to control loop gain variations and mismatch in the controller elements is examined. Sensitivity analysis is exploited to allow overall compromise between response speed and the system sensitivity. The need for high frequency sampling in the control loops imposes restrictions on the execution time in the digital processor. Various methods of reducing the controller complexity are investigated with a view to reducing the computation time. A method of compensation for the effects of rounding coefficients in the control algorithm is developed for the specific problem involving the dry-tuned gyro. This consideration is extended to identify how the choice of processor is influenced for the gyro rebalancesystem.