Understanding an Inertial Platform

Abstract

with the coming advent of supersonic commercial transporation, inertial systems, with their high short term accuracies are destined to play a larger role than ever before in aircraft navigation. Present day equipment manufacturers are helping by an industry wide, concerted effort to produce low cost reliable gyros, accelerometers and other system components. The results should prove a stabilizing factor in an industry that in the past has depended solely on military usage. This article is an attempt to describe briefly the dynamics of inertial platforms using the major components and their transfer functions as the basic system building blocks. Single degree of freedom, rate integrating gyros are considered and for simplicity a three gimbal system will be used in this discussion. The principle of inertial navigation is based upon the double integration of accelerometer outputs and the addition of correction terms to give vehicle position. The accelerometer triad, however, must be maintained at a certain orientation and isolated from transient vehicle disturbances while sensing linear acceleration inputs. This then is the function of the inertial platform—proper isolation and orientation of the accelerometers. A typical 3 gimbal platform is depicted in Fig. 1. The gimbal system shown provides isolation from aircraft manuevers and other transient inputs for the inner cluster containring the gyro and accelerometer sensors. Fo-aircraft application, the cluster is usually controlled to follow the earth's contour through Schuler tuning and in addition may also be slaved in azimuth to north or a particular grid heading.