Frequency-varying fringes projector based on acoustic grating

A new acoustic grating fringe projector (AGFP) was developed for solving the problems of the low speed, complex structure and hard on-line integration of the traditional structure light illuminator in three-dimensional (3-D) measurement. An acousto-optic deflector (AOD) driven by a beat frequency signal generated two overlap gratings inside the acousto-optic (AO) crystal and diffracted the incident laser beam into two first-order beams. The two first-order beams were brought together by a projection lens and the fringe pattern was generated by the interference of them. We established the math model of the fringe pattern and proposed a new method called 'phase freezing' to explain the changes of the spatial period and phase of fringes. The acousto-optic technique for producing fringe patterns provided a number of significant benefits, such as completely solid state, small scale, electronically control without any mechanical moving part, high precision and dynamic programmable ability. We obtained a precise phase map of a plaster statue with the device. The projection system is of great engineering value in high-accuracy three-dimensional non-contact complicated profile measurement.