Monitoring distance variations

Filing Information

• Patent Number: US4357104
• Application Number: US6217146
• Filing date: 12/16/1980
• Issue date: 11/02/1982
• Predicted expiration date: 12/16/2000

• U.S. Classifications: 356/4  · 250/201  ·
• International Classifications: G01C 308 ·
• International Classifications: 3564;1;28 ·
• Foreign Priority: GB7944134 - 12/21/1979 ·
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Abstract

An optical device for monitoring variations in the distance between an object and a datum is particularly useful for monitoring running clearances in the demanding environment of a gas turbine engine. The device depends upon the principle that an image focussed by an astigmatic lens system changes shape as it passes through the focus. To monitor variations, e.g., in the working clearance between a turbine blade tip and a turbine casing, light from a light source is projected through an astigmatic lens system, onto the blade tip. Reflected light from the astigmatic image on the blade tip is passed back through the lens system and re-projected onto an image shape monitor which includes photo-cells. The photo-cells may be mounted in the main optical assembly or probe, or they may be distant from the probe and fed by light guides. Signals from the cells are combined to produce a monitor signal, the magnitude of which is a measure of the shape of the image on the blade tip, and hence of the clearance.

Independent Claims | See all claims (21)

1. 1. An optical device for monitoring variations in the distance between an object and a datum, comprising:a light source;an astigmatic optical system for projecting an astigmatic image of said light source onto said object, said astigmatic optical system including said datum; andimage shape detector means for detecting changes of shape of said astigmatic image on said object due to said variations in the distance between said object and said datum, and for producing a monitor signal whose value is dependent on the shape of said astigmatic image on said object:said astigmatic optical system being arranged such that light reflected from said astigmatic image on said object passes back through said astigmatic optical system and is thereby projected onto a light-receiving surface of said image shape detector means as an astigmatic image of said astigmatic image on said object, said light-receiving surface of said image shape detector means being located in the proximity of said light source.