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Wu J.,Tsinghua University | Wu J.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipment and Control | Zhang B.,University of Electronic Science and Technology of China | Wang L.,Tsinghua University | Wang L.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipment and Control
Solar Energy | Year: 2016

This paper proposes a novel U-3PSS two-axis sun-tracking mechanism with parallel mechanism. The tracker is energy saving due to most of the gravity of mobile platform and solar mirror/panel supported by the passive U chain. Two most important performance indices of a solar tracker, workspace and energy consumption are studied and the optimum design is investigated utilizing a complex method. Based on workspace and energy consumption, optimal configurations of the U-3PSS solar tracker and its nonredudnant counterpart are analyzed, respectively. By taking Beijing as a sample city where the tracker is placed, the trajectory planning of the tracker is investigated and the direction of two orthogonal axes of the U joint is studied. The power of the U-3PSS solar tracker and its nonredudnant counterpart with their optimal configurations in spring equinox, summer solstice, autumn equinox and winter solstice are compared. Furthermore, the workspace and consumed energy of two solar trackers are compared. The results show that the U-3PSS solar tracker has a bigger workspace and smaller energy consumption in one year than its counterpart - U-2PSS solar tracker. © 2016 Elsevier Ltd. Source


Chen R.,Tsinghua University | Chen R.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipment and Control | Xu J.,Tsinghua University | Xu J.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipment and Control | And 5 more authors.
Applied Optics | Year: 2016

The 3D measurement system based on fringe patterns is widely applied in diverse fields. The measurement accuracy is mainly determined by camera and projector calibration accuracy. In the existing methods, the system is calibrated by a dot calibration board with traditional image process algorithms. In this paper, an improved calibration method is proposed to increase camera and projector calibration accuracy simultaneously. To this end, first, a subpixel edge detection method is proposed to improve the detection accuracy of reference features for coarse calibration; second, an iterative compensation algorithm is developed to improve the detection accuracy of the reference feature centers for fine calibration. The experimental results demonstrate that the proposed calibration method can improve the calibration accuracy and measurement accuracy. © 2016 Optical Society of America. Source


Yu G.,Tsinghua University | Yu G.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipment and Control | Wu J.,Tsinghua University | Wu J.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipment and Control | And 2 more authors.
International Journal of Advanced Robotic Systems | Year: 2014

This paper investigates the stiffness modelling of a 3-DOF parallel manipulator with two additional legs. The stiffness model in six directions of the 3-DOF parallel manipulator with two additional legs is derived by performing condensation of DOFs for the joint connection and treatment of the fixed-end connections. Moreover, this modelling method is used to derive the stiffness model of the manipulator with zero/one additional legs. Two performance indices are given to compare the stiffness of the parallel manipulators with two additional legs with those of the manipulators with zero/one additional legs. The method not only can be used to derive the stiffness model of a redundant parallel manipulator, but also to model the stiffness of non-redundant parallel manipulators. © 2014 The Author(s). Source

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