Research On Embedded 3D Measurement System Based On Space-time Domain Coding

Structured light measurement is now the research hotspot of machine vision for its advantages of active and controllable projection, high speed, high precision, non-destruction, large measuring scale, real-time performance. It has been wildly used since 1970 s in industrial component detection, reverse engineering, 3D molding, robot navigation, medical and many other fields. With the continuous development of industry, the requirement of speed and precision for 3-D objects measurement is becoming more and more restrict for compact size, low power consumption, high stability, and strong adaptability for various industrial applications.In order to satisfy the demand for high speed, high precision and high resolution 3-D measurement, a research in spatio-temporal coding is carried out in this thesis. The number of projected structured light patterns is dramatically reduced; Phase unwrapping and triangulation operation in traditional coding method are avoided. This algorithm is eventually implemented on DSP embedded system for 3-D measuring. The main contents and achievements are as follows:1. Based on the analysis of the existing structured light coding and decoding method, the temporal binary codes and spatial grayscale linear codes are combined and the gray level vector modulating method presented by our research group is optimized. Regarding the nonlinear response of the measuring system, we proposed to raise the base value to solve the problem of matching error in low gray value region. In the decoding process, the coding periods are divided using the intersection points of forward and inverse gray code patterns, the algorithm stability and generality are then enhanced. Efficiency of stereo matching is improved through gray mapping method in which the code values are rearranged in monotonic increase form. The presented coding and decoding method is simulated in Matlab and the experimental result shows the correctness of this method. With same resolution, the number of projected patterns is dramatically reduced and the complicated operations of phase unwrapping and trigonometric functions solution are avoided compared to the traditional phase shifting method, which contribute to the effectiveness of algorithm speed.2. The programming of gray level vector modulating method on DM3730 embedded system is achieved. Building the embedded development environment, completing embedded system kernel cutting and transplantation, boot-loader transplantation, making root file system. Completing the building of Codec engine related modules. Packaging the gray level vector modulating method into x DM complaint algorithm which is appropriate for dual core communication. Creating the Codec Server and Codec Engine and generate the DSP side executable program. Writing the ARM side application program and realize the control of the projector and the camera and achieve the DSP algorithm call.3. An embedded 3D measurement system based on DM3730 embedded system is built up and the reconstruction of a 3D object is achieved. Projecting the designed coded patterns using research group self-developed high speed external trigger projector and control the camera to capture the modulated patterns with the ov2656 camera. ARM core and DSP core communication and coordination is realized by calling the DSP side algorithm on the ARM side. The 3D point cloud data is then acquired after raw data processing before transferring back to the ARM side. The correctness and feasibility of the presented gray level vector modulating method and the application on embedded system are proved by the practical measurement of 3-D objects.