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Proceedings Paper

Inertial Stabilization Of Periscopic Sights Band Driven Three Axle Gimbal
Author(s): Bruce Ellison; James Richi
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Paper Abstract

There are many applications for the use of optical instruments in vehicles, especially in the military. It is required that these instruments function while the vehicle is on the move, in rough terrain. Angular distrubances of the line-of-sight pointing vector can render these instruments useless as observation or pointing devices, due to image blurring. Instruments that must retain resolution in this environment are usually stabilized by means of gimbals. If the entire instrument (such as a large television camera) is to be stabilized, the problem becomes one of a simple stable platform, or, a single axle gimbal. If, however, the instrument is hard mounted to the vehicle and the image is instead to be stabilized by means of a compensating optical component, such as a periscope head mirror, the problem is a little more complex. In a periscopic sight the head mirror must be driven at half-speed to the line-of-sight disturbance to compensate for the angle doubling effect of the mirror. That is, in order to stabilize the line-of-sight, the mirror cannot be inertiallv stable, but must be coupled to a stable mass at a ratio of 1:2. In many applications it is necessary to transmit the elevation angle of the line-of-sight to a fire control system, or, to direct the lines-of-sight of other platforms. In order to do this, transducers are mounted on the "drive axle", (gyros, synchros, tachometers, potentiometers, motors), which detect and trasmit the angular position and rate of the elevation line-of-sight. This drive axle becomes the stable element and is coupled to the mirror axle, at a 2:1 ratio, by means of gears or metallic belts or bands. This is a double axle gimbal system. When subjected to a rotational disturbance such as boat or vehicle motion the inertias of the drive and mirror axles react with one-another to cause a displacement of the line-of-sight pointing vector. This disturbance is a dynamic coupling of inertias. It exists even in the absence of friction. The subject of this paper is a mechanism analysis of a band drive system with more than one axle and more than one inertia. It is concluded that in a 2:1 band drive system one should maximize the drive axle inertia and minimize the mirror axle inertia. When this is not adequate it is shown that it is possible to add a third axle parallel to the drive axle and mirror axle to cancel out the deleterious effects of the dynamic coupling between the first two inertias.

Paper Details

Date Published: 3 October 1983
PDF: 14 pages
Proc. SPIE 0389, Optical Systems Engineering III, (3 October 1983); doi: 10.1117/12.935041
Show Author Affiliations
Bruce Ellison, Kollmorgen Corporation (United States)
James Richi, Kollmorgen Corporation (United States)

Published in SPIE Proceedings Vol. 0389:
Optical Systems Engineering III
William H. Taylor, Editor(s)

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