Guo Y.,Nankai University |
Sun M.,Nankai University |
Sun M.,State Key Laboratory of Robotics |
Garfinkel A.,University of California at Los Angeles |
And 2 more authors.
PLoS ONE | Year: 2014
Recent experimental work in lung morphogenesis has described an elegant pattern of branching phenomena. Two primary forms of branching have been identified: side branching and tip splitting. In our previous study of lung branching morphogenesis, we used a 4 variable partial differential equation (PDE), due to Meinhardt, as our mathematical model to describe the reaction and diffusion of morphogens creating those branched patterns. By altering key parameters in the model, we were able to reproduce all the branching styles and the switch between branching modes. Here, we attempt to explain the branching phenomena described above, as growing out of two fundamental instabilities, one in the longitudinal (growth) direction and the other in the transverse direction. We begin by decoupling the original branching process into two semi-independent sub-processes, 1) a classic activator/inhibitor system along the growing stalk, and 2) the spatial growth of the stalk. We then reduced the full branching model into an activator/inhibitor model that embeds growth of the stalk as a controllable parameter, to explore the mechanisms that determine different branching patterns. We found that, in this model, 1) side branching results from a pattern-formation instability of the activator/inhibitor subsystem in the longitudinal direction. This instability is far from equilibrium, requiring a large inhomogeneity in the initial conditions. It successively creates periodic activator peaks along the growing stalk, each of which later on migrates out and forms a side branch; 2) tip splitting is due to a Turing-style instability along the transversal direction, that creates the spatial splitting of the activator peak into 2 simultaneously-formed peaks at the growing tip, the occurrence of which requires the widening of the growing stalk. Tip splitting is abolished when transversal stalk widening is prevented; 3) when both instabilities are satisfied, tip bifurcation occurs together with side branching. © 2014 Guo et al.
Peng X.,South China Agricultural University |
Peng X.,State Key Laboratory of Robotics |
Zhang T.,South China Agricultural University |
Li J.,South China Agricultural University |
Yan G.,South China Agricultural University
Zhendong Ceshi Yu Zhenduan/Journal of Vibration, Measurement and Diagnosis | Year: 2014
The MEMS accelerometer has wide applications in object posture monitoring as a low-cost inertial measurement unit. According to the mathematical model of the three-axis digital MEMS accelerometer, the scale factor, zero bias, and error on the installation of the accelerometer are derived in detail. A simple six-position calibration method based on cuboids is proposed. In comparing the results with those of the three-axis turntable calibration, the six-position calibration method is shown to be simpler, more accurate, and easier for the MCU to achieve, which is suitable for places that lack a three-axis turntable. The six-position simple calibration method for the three-axis digital MEMS accelerometer thus demonstrates good universality.
Xiang S.,Northeastern University China |
Zhang Y.,Northeastern University China |
Zhang Y.,State Key Laboratory of Robotics |
Xia Z.,Northeastern University China |
And 2 more authors.
Journal of Computational Information Systems | Year: 2012
DV-Hop location algorithm is very suitable for the application of large-scale sensor network. But it requires the estimation of average hop distance, which lowers down the positioning accuracy. Current popular method is to improve the average hop distance and localization process for unknown nodes through Maximum Likelihood Estimation method or Least Square method. The positioning accuracy of these mentioned methods has been raised. However, it is easy for the position estimation to combine high residual error into the computing process, which will give rise to the localization error along with computational complexity. Considering existent problem, this paper employs Residual Weighting Algorithm to estimate the positions of unknown nodes by improving the calculating mode of average hop distance. For the position estimation with high residual error, we assign a relatively low weight to inhibit its influence. Thus the accuracy and computing process are effectively improved. The experimental results demonstrate that the proposed method can greatly improve the positioning accuracy of unknown nodes, reduce the computational complexity and boost the calculation efficiency. © 2012 Binary Information Press.
Wu L.-H.,Dalian Maritime University |
Wu L.-H.,State Key Laboratory of Robotics |
Ji D.-X.,State Key Laboratory of Robotics
Xitong Fangzhen Xuebao / Journal of System Simulation | Year: 2012
To solve the abnormal limitation boundary condition through AUV (Autonomous Underwater Vehicle) swim-out launching, a "define thin cuts method" was adopted to squeeze the mesh into narrow region between two walls, and y+ was calculated to mesh the boundary layer accurately according to scalable wall functions. Grid convergence study was performed for verification by refine mesh locally and globally. The numerical results were validated by grid convergence and compared with experiment, also the velocity and pressure distribution in narrow domain at quasi steady state were obtained. Further more, the relation between diameter ratio with total resistance, and the add-mass variation with AUV swimming-out were analyzed, which is helpful for design AUV power needed for swimming out from tube.
Wang B.,China Jiliang University |
Wang B.,State Key Laboratory of Robotics |
Yan D.,China Jiliang University |
Fang S.,China Jiliang University |
Jin Y.,China Jiliang University
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2012
In order to ascertain the affect of stiffness on slipping collision of flexible arm, the kinematics model was established by hybrid coordinate method, and flexible deformation was decoupled by using the assumed modes. Contact-impact model was established by using the Hertz impact theory and nonlinear spring-damper theory, collision dynamics of flexible arm was derived through Lagrange equations. The fourth-order Runge-Kutta numerical solution algorithm with variable step-size and precision was designed for solving dynamical equation. Simulation of the impact responses of flexible arm collision under different stiffness were completed, and curves of contact force, joint angle, angle velocity and elastic deformation were given. Based on comparative analysis, with bending stiffness increasing, contact force enlarged and the phase of peak force advanced, the flexible arm joint angle turned smaller, vibration of elastic deformation and angular velocity became lower. Material structural damping had obvious inhibition on the elastic deformation vibration. The model and solving algorithm of this paper are proved effective.
Wu L.-H.,Dalian Maritime University |
Wu L.-H.,State Key Laboratory of Robotics |
Xu W.-H.,Dalian Maritime University |
Wang L.-P.,Dalian Maritime University
Dalian Haishi Daxue Xuebao/Journal of Dalian Maritime University | Year: 2014
The autonomous underwater vehicle (AUV)underwater terminal docking guidance methods were introduced. With the characteristics of terminal underwater guidance sensors, a ultra short baseline (USBL) combining with a CCD camera was designed. A light source was arranged in dock centerline for vision co-target, with another center point for transponder of USBL. The image coordinates of the light source were obtained through image processing, and the dock position and pose were derived with the known distance between the transponder and the vision source, which can provide the foundation for AUV underwater docking.
Zhang Y.-Z.,Northeastern University China |
Zhang Y.-Z.,State Key Laboratory of Robotics |
Wu C.-D.,Northeastern University China |
Cheng L.,Northeastern University China |
Ji P.,Northeastern University China
Kongzhi yu Juece/Control and Decision | Year: 2010
The deployment of wireless sensor network in deterministic space with obstacles is researched. Sensor's detection models and coverage quality evaluation are set up. Based on the probabilistic detection model with false alarm rate, a new deployment method is proposed. Watershed algorithm is employed to choose the deploying sub-area. Then Delaunay triangulation is used to generate the candidate positions for new nodes. Thus, the placement of WSN nodes is realized orderly and efficiently. According to the simulation result, the proposed method can attain better detection probability and coverage uniformity compared with different methods such as random deployment, MAX_MIN_COV and MAX_AVG_COV.
Wang B.-R.,China Jiliang University |
Wang B.-R.,State Key Laboratory of Robotics |
Jin Y.-L.,China Jiliang University |
Wei D.,China Jiliang University
International Journal of Automation and Computing | Year: 2010
Pneumatic muscle (PM) of flexible actuators used in bionic robot is an active area of recent research. A novel PM with shape memory alloy (SMA) braided sleeve is proposed in this paper, and SMA is used to improve PM working characteristics. Based on the principle of virtual work, output force model of PM and relationship with braided wire inner-stress are established, and analysis of PM deformation has shown that braided wire length is the key factor of output force characteristic. Based on the crystal structure transitions, the relationship of temperature with wire shrinkage is derived. Then, the synthetic dynamics of novel PM is established. A physical prototype of PM with SMA braided sleeve is developed, and test platform that is built for the experiment. Experiment and simulation test of static isometric-length, static isobaric-pressure, and dynamic characteristics are done. The experimental results are compared with the simulation of theoretical model. Moreover, based on experiment, model of output force was improved by adding a correction factor to deal with the elastic force of rubber tube. The results analysis demonstrates that the established models are correct, and SMA wires can reinforce PM and make PM working characteristics adjustable. PM proposed in this paper has greater output force and is beneficial to achieve more accurate control that is useful for manipulating fragile things. © 2010 Institute of Automation, Chinese Academy of Sciences and Springer-Verlag Berlin Heidelberg.
Yu H.,Hunan University |
Yu H.,State Key Laboratory of Robotics |
Peng J.,Zhengzhou University |
Tang Y.,State Key Laboratory of Robotics
Mathematical Problems in Engineering | Year: 2014
Hammerstein model has been popularly applied to identify the nonlinear systems. In this paper, a Hammerstein-type neural network (HTNN) is derived to formulate the well-known Hammerstein model. The HTNN consists of a nonlinear static gain in cascade with a linear dynamic part. First, the Lipschitz criterion for order determination is derived. Second, the backpropagation algorithm for updating the network weights is presented, and the stability analysis is also drawn. Finally, simulation results show that HTNN identification approach demonstrated identification performances. © 2014 Hongshan Yu et al.
PubMed | Hunan University, State Key Laboratory of Robotics and University of Pittsburgh
Type: Journal Article | Journal: Sensors (Basel, Switzerland) | Year: 2014
Inspired by the human 3D visual perception system, we present an obstacle detection and classification method based on the use of Time-of-Flight (ToF) cameras for robotic navigation in unstructured environments. The ToF camera provides 3D sensing by capturing an image along with per-pixel 3D space information. Based on this valuable feature and human knowledge of navigation, the proposed method first removes irrelevant regions which do not affect robots movement from the scene. In the second step, regions of interest are detected and clustered as possible obstacles using both 3D information and intensity image obtained by the ToF camera. Consequently, a multiple relevance vector machine (RVM) classifier is designed to classify obstacles into four possible classes based on the terrain traversability and geometrical features of the obstacles. Finally, experimental results in various unstructured environments are presented to verify the robustness and performance of the proposed approach. We have found that, compared with the existing obstacle recognition methods, the new approach is more accurate and efficient.