Patent ID: 8605291

Claim:
An image correlation displacement sensor for measuring a positional displacement relative to a target surface, the image correlation displacement sensor comprising: an illumination portion which emits illumination light to the target surface to produce a speckle field; an imaging portion including a detector, a first optical path that is used to capture a first plurality of images including the speckle fields produced on a first region of the target surface, and a second optical path that is used to capture a second plurality of images including the speckle fields produced on a second region of the target surface, wherein the first and second optical paths enter different parts of the detector; and a processing portion that measures a displacement including a rotation about a yaw axis of the target surface based on a first region translational displacement based on the first plurality of images captured along the first optical path and a second region translational displacement based on the second plurality of images captured along the second optical path, and a known separation between the first and second regions, wherein the image correlation displacement sensor has a measurement sample period and is configured to acquire at least one image of the first region and at least one image of the second region during a respective measurement sample period, and wherein the processing portion is configured to calculate at least the target surface rotation about the yaw axis during the respective measurement sample period.