Design of a Gyro-stabilized Mirror Targeting System

Abstract

Electro-optical (E-O) sensors that are mounted on vehicles such as air craft, helicopter and tanks are subjected to vibrations introduced by these plat-forms. These vibrations cause the line-of-sight (LOS) of the E-O sensors to shift, resulting in serious degradation of the image quality (see for example [5]). This problem is even more pronounced in systems with high magnification property. One way of overcoming it is to use free gyro stabilization. A gyroscope or gyro is basically an axially symmetrical mass rotating at a high constant speed. With the magnitude of the angular inertia and the speed of rotation both kept constant, the momentum generated is also fixed. Bearing in mind that the momentum is a vector quantity, this implies that the directional orientation is maintained. Therefore, in the absence of large external forces, a gyro is capable of maintaining the orientation of its spin axis in the inertia space. By choosing an appropriate high value for the speed of rotation, the vibrational torque produced by the platforms can be made insignificant as compared to the momentum generated. The LOS can thus be stabilized by simply designing a system such that the LOS and the gyro spin axis are parallel in space. However, a spinning gyro has another property known as precession. This means that if a torque is applied to one axis, it will, contrary to the intuitions of mechanics, rotate in the direction of another axis [102]. Thus, to enable for changes in the space orientation of the LOS, a gyro with at least two degrees of freedom is needed. This property also poses a problem in controlling the LOS because movement about one axis will cause a coupled movement in the other. Therefore a controller has to be designed to provide the correct slewing (i.e., the application of a calculated torque to cause a desired precession).