Jindong Tian

A flexible, simple telecentric three dimensional measurement system

Calibration which defines the relationship between the phase and depth data is the important part of the fringe projection profilometry. In practice, the inherently nonlinear and spatially variable relationship between the absolute phase of the projected fringe and the object surface depth without using telecentric lens make calibration problematic in the measurement of small object. In order to obtain this problem, a flexible, simple telecentric three dimensional measurement system is proposed. Because of the characteristic that the size of object will not change with depth in telecentric imaging, the absolute phase is linear with the depth and the process of calibration become simpler. The experiment result indicate that the standard deviation of calibration result at z coordinate is within 5 μm, while that at x and y coordinate is within 3 μm. Three-dimensional shape reconstruction of a coin value ¥1 and measurement of central circle points of the calibration target further verify the validity of the proposed calibration method.

Embedded 3D shape measurement system based on a novel spatio-temporal coding method

Structured light measurement has been wildly used since 1970s in industrial component detection, reverse engineering, 3D molding, robot navigation, medical and many other fields. In order to satisfy the demand for high speed, high precision and high resolution 3-D measurement for embedded system, a new patterns combining binary and gray coding principle in space are designed and projected onto the object surface orderly. Each pixel corresponds to the designed sequence of gray values in time – domain, which is treated as a feature vector. The unique gray vector is then dimensionally reduced to a scalar which could be used as characteristic information for binocular matching. In this method, the number of projected structured light patterns is reduced, and the time-consuming phase unwrapping in traditional phase shift methods is avoided. This algorithm is eventually implemented on DM3730 embedded system for 3-D measuring, which consists of an ARM and a DSP core and has a strong capability of digital signal processing. Experimental results demonstrated the feasibility of the proposed method.