Applied Mechanics and Materials Vols. 29-32

Abstract: It is well known that the friction force can lead to the analysis complexity of the contact constraint model. Based on Coulomb’s frictional model and unilateral constraint model, non-rigid bodies’ compliant dynamic model was established. Considering the whole motion of the assembly system and elastic contact deformation caused by assembly forces, the nearly rigid contact analysis is proposed. Jamming and wedging must be avoided for successful robot assembly operation. Based on the compliant dynamic model the conditions for jamming and wedging are provided in the formulations of the constrained dynamic system of peg-in-hole insertion.

Abstract: In order to overcome the system nonlinear instability and uncertainty inherent in magnetic bearing systems, two PID neural network controllers (BP-based and GA-based) are designed and trained to emulate the operation of a complete system. Through the theoretical deduction and simulation results, the principles for the parameters choice of two neural network controllers are given. The feasibility of using the neural network to control nonlinear magnetic bearing systems with un-known dynamics is demonstrated. The robust performance and reinforcement learning capability in controlling magnetic bearing systems are compared between two PID neural network controllers.

Abstract: The effects of the mechanical properties of Kevlar/PTFE fabric-reinforced polymer-based self-lubricating liners on the performance of the self-lubricating spherical plain bearings were investigated to improve the evaluation technology of the performance of the self-lubricating liners and the bearings. The mechanical experiments were carried out to study the mechanical properties of the liners with the use of Instron 5848 microtester. Based on these experimental data, several material models of liners were used to carry out the curve fitting, and the 3-terms Ogden form was chosen as an optimum model for the FEM numerical simulation of bearings with and without liners under the conditions of variable loads. These results show that: the mechanical properties of the liners has an important influence on the performance of the bearings; Owing to the elastic properties of the liners, the contact area is increased, and the contact stress between sliding faces are decreased, which improve the load capacity and service life of the bearings; An optimum elastic property of the liners is existed for the performance of the spherical plain bearings. The present study may provide evidence for the improvement of the evaluation technology of the liners and bearings, the further understanding of the role of the liners in the bearings, and the design of the fabric self-lubricating liners.

Abstract: This paper presents the use of a camera-based 3D motion analysis system for non-contact dynamic testing of a highly flexible spinning vertical shaft. The camera system uses high-resolution CMOS cameras to measure instant geometry of the shaft when visible red digital LED strobes are synchronized to work at a speed between 0.1 to 2000 frames per second. Dynamically deformed geometries are obtained by tracing the three-dimensional instantaneous coordinates of markers adhered to the shaft’s outside surface and triangulation techniques for identifying markers’ coordinates. Numerical simulation and experimental results show that the use of camera-based motion analysis systems is feasible and accurate enough for dynamic experiments. For dynamics characterization, we present the use of the Hilbert-Huang transform (HHT) for time frequency analysis of measured dynamic responses. The results show that the third-mode vibration has a cubic nonlinearity.

Abstract: LRB base isolation technology is different from the traditional continuous girder structure system, and shows good isolation performances. However, because fixed piers were canceled and all bearings were LRB, it is often considered that the reliability of structure might be reduced. Therefore, the reliability of LRB continuous girder bridges subject to seismic excitation was systematically studied from different indicators for the first time in this paper, the world's first double traffic double deck isolated continuous girder bridge – Dongjiang double-layer-pier isolated approach bridge in Dongguan of Guangdong province was adopted as study case. The results shows that, when the effect of pile-soil interaction is considered, LRB system still has a very good isolation performance; pounding subjected to seismic must be analyzed; dynamic stability needs checking when higher piers and larger earthquake displacement. Generally speaking, the reliability of LRB continuous girder bridges subject to seismic excitation won’t be reduced.

Abstract: Pocket corner in the high-speed milling (HSM) often occur under-cut, over-cut, vibration and other phenomena. This not only reduces tool life, seriously affected the work-piece machining accuracy and processing efficiency. In the paper, the impact of cutting speed on cutting forces is studied in the pocket corner based on the high-speed milling experiments. The results show that cutting force increased slightly with the increase in cutting speed, and that cutting force no significant change with the increase in radial depth of cut.

Abstract: Structural pounding under earthquakes has been recently extensively investigated by using different models of impact force. In this paper, reexamination into the Hertz contact model with nonlinear damping is made. Based upon this reexamination, the formula used to determine the damping constant in terms of the spring stiffness, the coefficient of restitution and relative approaching velocity of two colliding bodies is found to be wrong. In order to correct this error, a more accurate approximating formula for the damping constant is theoretically derived. The correctness of the derived analytical formula has been confirmed through numerical simulations.

Abstract: Mechanism of time effect on vertical ultimate bearing capacity (VUBC) of preformed concrete pile is analyzed. The effect strongly depends on seven parameters of pile engineering. Pile length, area of pile section, soil friction angle, soil consolidation coefficient, soil elastic module and time after pile installation and pile type are them. Considering time effect and soil consolidation, artificial neural network model to predict this time-dependent VUBC is established. Input layer includes seven parameters discussed above. Conjugate gradient method is adopted to train the net. Based on calculation of practical piles, results of the model are found to be in good agreement with field tests, and the efficiency of the present model is signalized.

Abstract: Children heart rate monitoring plays an important role among human health research field. In this paper, a synchronized intelligent sensor network was designed for children heart rate monitoring. The ECG sensor, MMA7261QT accelerometer sensor and CSR BC4 Bluetooth module were accepted for heart rate monitoring. The experimental data features were extracted by the bistable stochastic resonance data processing method. The signal-to-noise ratio (SNR) maximum value was used to judge the children action state. The experimental results showed that the designed system provided an effective method for a big scale children health monitoring.

Abstract: Linear matrix inequalities (LMI) method is proposed to design the robust controller for the servo-hydraulic actuator with parametric uncertainties. The pretreatments are adopted to convert the nonlinear dynamic models into linear state equations using the linear fractional transformation (LFT) approach, which facilitates conveniently utilizing the LMI method to calculate the state feedback controller. The supervising parameters, including the system output and special derivative output generated from the uncertain items, are proposed to model a state matrix equation for representing the dynamic system with the parameter variations and disturbances. LMI control base on the H∞ control schematic is finally employed to carry out the state feedback controller for the servo-hydraulic actuator with parametric uncertainties. The results demonstrate the efficiency of dynamical performance with small settling time and overshoot compared with the quantitative feedback theory (QFT) approach.