High speed fringe projection for robot 3D vision system

The design, manufacture and test of a custom-made phase mask for use in a high-speed fringe projection system is presented. The mask produces a controlled anisotropic point spread function (PSF) that blurs binary fringes parallel to the fringe direction, to produce high quality greyscale patterns at up to the maximum projection rate, 22,000 frames s-1, of the DMD (Digital Micromirror Device)-based projector. The paper describes the numerical design method based on a binary scatter plate; a polychromatic Fourier optics model to predict the device’s optical performance; a method to design the fringe patterns; the manufacturing process, based on photolithography and reactive ion etching; and experimental validation of the phase mask performance. Noise in the computed height-encoding phase maps is found to be just 22% higher than for 8-bit greyscale fringe patterns produced by traditional temporal integration through a sequence of bit planes, but the projection rate is increased by over two orders of magnitude.