Compact optical system for measuring linear and angular displacement of solid structures

We present a compact, low-cost optical method for detection of in-plane speckle translation, which e.g. could be a measure of in-plane translation or rotation of a solid structure. The speckles are produced by illuminating a non-specular target surface with coherent light. The scattered light propagates through free-space to the sensor inlet.

The sensor is based on a lenticular array, which implements a narrow spatial band-pass filter, acting on the translating speckle patterns. The sensor detects speckle translation, which for the given configuration can be caused to detect both translation and rotation of the target. The presented free space propagation design can provide a sensor with no direct sensitivity on the working distance.

The electrical signals from the sensor are processed with a digital algorithm, based on zero-crossings detection to provide real-time displacement measurements. The spatial filter of the sensor is characterized here, and the precision of the sensor, integrated with a processor, which applies zero-crossing detection to the signal, is considered. © 2004 COPYRIGHT SPIE--The International Society for Optical Engineering.

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