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R. Paris, T. Thurner, G. Schitter:
"Compensation Based Displacement Measurement Using Objective Laser Speckles";
Talk: 6th IFAC Symposium on Mechatronic Systems, Hangzhou, China; 04-10-2013 - 04-12-2013; in: "Proceedings of 6th IFAC Symposium on Mechatronic Systems", (2013), 264 - 270.

Objective laser speckles can be observed as intensity pattern from free space
propagation of coherent light that is diffracted from a technically rough surface. Utilizing this
pattern allows for very localized non-contacting measurement of surface displacement as well
as strain, and carries a high potential for miniaturization. Existing objective speckle techniques
suffer from decorrelation effects, dramatically decreasing the performance of such measurement
techniques. In this paper we present a compensation based displacement measurement scheme,
where we keep the measured speckle pattern displacement close to zero by actively following
the measuring objects movement in a feedback operation. This converts the image sensor into
a zero-detector, what considerably improves the speckle pattern correlation over a significantly
extended measurement range.

Compensating feedback, Displacement sensor, Objective laser speckles, Speckle decorrelation