Study on Laser Speckle Correlation Method Applied in Triangulation Displacement Measurement

Laser triangulation displacement sensor is an important tool in non-contact displacement measurement; it is widely used in the measurement of 3D contour, thickness, width, position, and vibration. It uses diffuse reflection light as sensor signal, which is formed by laser scattering on object surface. The diffuse reflection light is converged to a light receiver on the focal plane by lens imaging principle, and then the image point is formed on the receiver. The receiver can be charge coupled device (CCD), or position sensitive device. The object moving or surface changing leads to the shooting spot of incident light moving along the optical axis, and the image point on the receiver moves correspondingly. The displacement of objects, or the vibration amplitude and frequency can be determined according to the size of phase shifting and structural parameters of the sensor. The principle of laser displacement sensor is shown in fig. 1. Take the direct-style triangulation method as an example, its light path is shown in fig. 1. In order to improve the accuracy, the scattering angle θ and the angle between CCD and normal plane of the lens φ must meet Scheimpflug [1] principle, in which the image plane, object plane and lens plane must intersect in a straight line, namely