Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipment and Control

Beijing, China

Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipment and Control

Beijing, China
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Liu Y.,Tsinghua University | Wu J.,Tsinghua University | Wu J.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipment and Control | Wang L.,Tsinghua University | And 3 more authors.
Industrial Robot | Year: 2017

Purpose - The purpose of this study is to develop a modified parameter identification method and a novel measurement method to calibrate a 3 degrees-of-freedom (3-DOF) parallel tool head. This parallel tool head is a parallel mechanism module in a five-axes hybrid machine tool. The proposed parameter identification method is named as the Modified Singular Value Decomposition (MSVD) method. It aims to overcome the difficulty of choosing the algorithm parameter in the regularization identification method. The novel measurement method is named as the vector projection (VP) method which is developed to expand the measurement range of self-made measurement implements. Design/methodology/approach - Newton Iterative Algorithm based on Least Square Method is analyzed by using the Singular Value Decomposition method. Based on the analysis result, the MSVD method is proposed. The VP method transforms the angle measurement into the displacement measurement by taking full advantage of the ability that the 3-DOF parallel tool head can move in the X - Y plane. Findings - The kinematic calibration approach is verified by calibration simulations, a Rotation Tool Center Point accuracy test and an experiment of machining an "S"-shaped test specimen. Originality/value - The kinematic calibration approach with the MSVD method and VP method could be successfully applied to the 3-DOF parallel tool head and other 3-DOF parallel mechanisms. © Emerald Publishing Limited.


Wu J.,Tsinghua University | Wu J.,Beijing Key Laboratory of Precision Ultra Precision Manufacturing Equipment and Control | Gao Y.,Tsinghua University | Gao Y.,Beijing Key Laboratory of Precision Ultra Precision Manufacturing Equipment and Control | And 4 more authors.
Robotics and Computer-Integrated Manufacturing | Year: 2017

The paper deals with the workspace and dynamic performance evaluation of the PRR–PRR parallel manipulator in spray-painting equipment. Functional workspace of planar fully parallel robots is often limited because of interference among their mechanical components. The proposed 3-DOF planar parallel manipulator with two kinematic chains connecting the moving platform to the base can reduce interference while still maintaining 3 DOFs. Based on the kinematics, four working modes are analyzed and singularity is studied. The workspace is investigated and the inverse dynamics is formulated using the virtual work principle. The dynamic performance evaluation indices are designed on the basis of maximum and minimum magnitude of acceleration vector of the moving platform produced by a unit actuated force. The index not only can evaluate the accelerating performance of a manipulator, but also can reflect the isotropy of accelerating performance. Workspace and dynamic performances of the four working modes are compared and the optimal working mode for the painting of a large object with conical surface is determined. © 2016 Elsevier Ltd


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.


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.


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).


PubMed | South University of Science and Technology of China, Shandong University and Beijing Key Laboratory of Precision Ultra Precision Manufacturing Equipment and Control
Type: | Journal: SpringerPlus | Year: 2016

The effects of strain rate and temperature on the dynamic behavior of Fe-based high temperature alloy was studied. The strain rates were 0.001-12,000s(-1), at temperatures ranging from room temperature to 800C. A phenomenological constitutive model (Power-Law constitutive model) was proposed considering adiabatic temperature rise and accurate material thermal physical properties. During which, the effects of the specific heat capacity on the adiabatic temperature rise was studied. The constitutive model was verified to be accurate by comparison between predicted and experimental results.

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