Patent ID: 6937350

Claim:
An apparatus for monitoring thickness variations of an object having first and second opposing surfaces, the apparatus comprising: a first source positioned to project a first fringe pattern at a first location on the first surface; a second source positioned to project a second fringe pattern at a first location on the second surface; a first detector positioned to detect the first fringe pattern at the first location on the first surface, the first detector generating a first signal in response to the first fringe pattern at the first location; a second detector positioned to detect the second fringe pattern at the first location on the second surface, the second detector generating a second signal in response to the second fringe pattern at the first location; a processor adapted to calculate variations in the thickness of the object in response to the first and the second signals; and a control system locating the first and second fringe patterns to second locations on the first and second surfaces, respectively, the first and second detectors generating third and fourth signals, respectively in response to the first and second fringe patterns at the second locations, the processor adapted to calculate variations in the thickness of the object in response to the first, second, third and fourth signals.