Design and testing of a laser system developed for two-dimensional displacement detection

The paper presents a new instrument for three-dimensional displacement detection, consisting of two basic units: the first unit uses a laser-beam to detect the displacement of a point in two directions perpendicular to the beam itself; the second one employs a laser interferometer device in order to detect displacements in the third direction (i.e. the direction of the laser beam). In particular, the 2D unit is composed of a CCD camera facing a dark screen on which the incoming laser beam is focused. A filtered-through image on the CCD sensor is thus generated. The image is transmitted to a computer in order to calculate its centre of mass. When a significant image displacement is detected, a pair of computer-controlled step motors is used to reposition the system. The paper describes the entire system, composed of both 2D and 1D displacement-detection devices. A prototype of the 2D device is built and used to test the precision and reliability of the proposed solution. Results demonstrate that the device is highly sensitive and capable of detecting fractions of a millimetre of displacement in each direction. The subsequent computer-controlled repositioning is carried out with an error which is negligible with respect to the displacements the application understudy is characterized by