Robotic Systems and Applications
Not a member yet
20223 research outputs found
Sort by
Fault feature extraction of rolling element bearings based on short-time processing
Get PDFFault diagnosis of bearings is a crucial part of the maintenance process of the rotary machinery. Extracting the cyclic characteristics of the impact force is of significant importance for the bearing diagnosis. To highlight the fault features from signals combined with heavy background noise, a novel approach for bearing fault diagnosis based on the short-time processing is proposed. Fault signals are regarded as periodic impulse response signals. Firstly, a vibration signal is band-pass filtered with a subsequent spectral analysis. Then we integrate the energy of the filtered signal with a constant length, and the natural logarithm is considered to obtain the energy curve. The energy curve is a straight decaying curve, and its spectral energy is more concentrated on the fault characteristic frequency compared with envelope. Finally, the fault characteristic frequency of the bearing is found by the spectral analysis of the energy curve. The effectiveness of the proposed method is verified by simulation and experiments. The harmonics and sidebands in logarithmic energy spectrum are suppressed well, and the fault characteristic frequency is highlighted. Comparison of the proposed method with Hilbert envelope method shows that the proposed method can highlight the fault characteristic frequency
Experimental hysteretic behavior of high strength concrete columns confined by butt-welded closed composite stirrups
Get PDFSix specimens of high strength concrete columns with butt-welded closed composite stirrups were tested under cyclic lateral loads, to study the structural performance (deformation) and hysteretic characteristics of the columns. The influences of the axial compression ratio and the volume-stirrup ratio were considered. According to the regression analysis of the test results, it was determined that the unloading stiffness and strength degradation rate under repeated loading conditions are mainly dependent on the two parameters of the “displacement ductility factor” and “axial compression ratio”. According to the test results, the skeleton curves were determined by the section layer and the statistical regression analysis methods. By considering the influence of axial compression ratio and the volume-stirrup ratio to the hysteretic characteristics of high strength concrete columns confined by butt-welded closed composite stirrups, the shear force-lateral displacement restoring force model was established. The results show that the axial compression ratio has a great influence on the strength degradation of the columns. As the axial compression ratio increases, the strength degradation of the columns occurs faster. On the other hand, the volume-stirrup ratio has a reverse effect on the strength degradation of the columns, with the increase of the volume-stirrup, the strength degradation of the column is observed gradually and slowly. The stiffness degradation of the columns increases as the axial compression ratio increases while the volume-stirrup ratio decreases
Analysis of flow-induced vibration of cylinder with splitter plate based on overset grid method
Get PDFIn actual engineering, asymmetric flow often occurs, but rigid partitions are often installed in the direction of the flow field and are symmetric in the flow direction. This will result in a deflection angle between the dividing plate and the direction of the incoming flow. The research results show that when the declination angle is low, the partition plate has a limited impact on the system; when the deflection angle is about 10 degrees, the system vibration characteristics will have abrupt changes, the amplitude will decrease, and the vortex frequency will increase; at the deflection angle 10 degrees to 45 degrees As the declination angle increases, the amplitude increases, and the vortex frequency decreases; it can be seen from the motion trajectory that the declination angle changes suddenly after 10 degrees, and the system has a small amplitude between 10 degrees and 25 degrees. That is, in this declination interval, the partition plate has a better control effect on the vibration of the cylindrical system
Development of an underwater robotic arm using multibody dynamics approach
Get PDFUnderwater robotic arms are important devices that enables workers to carry out tasks remotely from a safe distance reducing or eliminating the risks that are involved with the task. The primary objective of the robotic manipulator is to perform maintenance and cleaning activities of the hull of a ship. However, the control of these devices underwater is quite complicated due to the numerous factors that make these systems unstable and non-linear. The aim of this study is to develop a multibody dynamic robotic manipulator model, integrated with a control strategy to optimize and obtain stable kinematics solutions. The hydrodynamic forces are integrated to the manipulator model considering buoyancy forces and surface drag forces. A basic algorithm is used to generate the joint angles using 7 geometrical parameters. The control of the manipulator was done to simply follow any path that represents the given coordinates. The P, I and D parameters are tuned individually to optimize the kinematic solution of the manipulator. 3-DOF articulated manipulator is the commonly used manipulator configuration. However, a 6-DOF manipulator configuration was selected in this study to allow for change in orientation using wrist motions
Experimental study on stress wave propagation in jointed rock coupling the effect of JMC & JRC
Get PDFThe objective of this study is to experimentally investigate how the rough joints effect the stress wave propagation through jointed rocks coupling the effect of the joint matching coefficient (JMC) and joint roughness coefficient (JRC). The Split Hopkinson Pressure Bar (SHPB) apparatus was adopted to conduct uniaxial compression experiments on jointed specimens. The joint matching coefficient (JMC) and joint roughness coefficient (JRC) are introduced as morphology parameters to estimate joint roughness. Based on SHPB experiments, we found out that the joint matching coefficient (JMC) has a greater influence on the transmission and reflection coefficient than the joint roughness coefficient (JRC). Jointed specimens with lower JMC and JRC make less energy transmitted through it and have a smaller transmission coefficient and bigger reflection coefficients. Also, the joint with lower JMC and JRC has less initial stiffness and greater maximum closure
Parametric studies on SEA parameters for coupled plates made of composite laminate
Get PDFStatistical Energy Analysis (SEA) has been used to compute velocity responses and Coupling Loss Factors (CLF) for two composite laminates joined in a 'L' junction configuration. Two case studies were carried on SEA. The effect of fibre orientation on SEA parameters was studied. The effects of internal damping were also determined. The computation of SEA parameters has been done using classical wave approach and Finite Element Method using Nastran/Patran. CLF determined using classical wave approach is independent of fibre orientation and internal damping factor. This study using FEM reveals that the SEA parameters vary in comparison with classical wave approach as fibre orientation and internal damping are also considered in the analysis. Also, by classical wave approach, the CLF varied linearly with the increase in frequency while there was some scatter in CLF determined by finite element method
Numerical convergence of the family of flux-continuous schemes with variable quadrature (qu1,qu2) for single phase flow in porous media
No full textFinite-volume schemes, which honor pressure and flux-continuity conditions, is developed using double quadrature (qu1,qu2), referred as double family scheme. The scheme is applicable to solve the elliptic pressure equation used in reservoir simulation. Schemes are applicable on both regular cartesian and unstructured triangular meshes. The scheme is defined over a control-volume distributed formulation. The scheme can be applied to both diagonal and full permeability tensor elliptic pressure equation with discontinuous coefficients. The scheme removes the first order errors, which are introduced by standard reservoir simulation schemes when applied to full tensor flow. The scheme is quantified with help of a quadrature rule. When the scheme is applied to highly heterogeneous and anisotropic porous media it does not honor maximum principle resulting in unstable solution with oscillatory behavior. The numerical solution is termed non-monotonicity for high anisotropy ratios with results showing oscillations in the numerical pressure solution. In this paper a double (qu1,qu2) quadrature flux continuous schemes is presented, which with specific choice of quadrature (qu1,qu2) helps in improved stability of the numerical solutions. Numerical convergence of the scheme is also demonstrated with help of a number of numerical test cases and schemes impact on monotonicity behavior is also demonstrated with numerical examples
Design and noise-reduction simulation of an acoustic metamaterial plate incorporating tunable shape memory cantilever absorbers
Get PDFMetamaterials are materials having artificially tailored internal structure and unusual physical and mechanical properties. Due to their unique characteristics, metamaterials possess great potential in engineering applications. This study proposes a tunable metamaterial for the applications in acoustic isolation. Therefore, a stopband in the dispersion curve can be created because of the energy gap. For the conventional metamaterial, the stopband is fixed. Although the metamaterial with tunable characteristics has been proposed in the literature to extend its working stopband, the efficacy is usually compromised. In this study, cantilevers of tunable shape memory materials (SMM) via controlled phase transformation are incorporated into the metamaterial plate. Its theoretical finite element formulation for determining the dynamic characteristics is established. The effect of the configuration of the SMM cantilever absorbers on the metamaterial plate for the desired stopband in wave propagation is simulated by using finite element model and a commercial multi-physics software. The result demonstrates the tunable capability on the stopband of the metamaterial plate under different activation controls of the SMM absorbers, and shows the ability to trap the vibration at the designed frequency and prevent vibration wave from propagating downstream in different absorber arrangements and alloy phases. It should be beneficial to precision machinery and defense industries which have desperate need in vibration and noise isolation
Occlusal plane parallel to camper plane: reality or fallacy? A tomographic study on human Sambaqui skeletal remains
Get PDFIntroduction: Since long time ago, dentists had used parallelism with Camper plane as a reference to establish a correct occlusal plane. However, in the literature, there are several different landmarks used to trace the occlusal plane and there are also many researchers questioning this parallelism. To evaluate it, we used ancient skulls from Human Sambaqui skeletal remains. The authors choose an ancient population because they were submitted to same environmental conditions, avoiding bias in craniofacial growth epigenetic stimuli. Methodology: For this work we analyzed tomographies of 27 well preserved adult skulls. The program used was Vista Dent Pro 2.1. Camper plane was determined according to the original points described by Peter Camper. We used the four occlusal planes more cited in the literature. Results: None of the occlusal planes evaluated on this study, showed parallelism with Camper plane. The occlusal plane determined by posterior teeth was the one that showed less divergence but still with a high SD and mediana. Conclusion: In Sambaqui ancient population, Camper plane was not a reliable reference to trace occlusal plane. It is necessary further investigations to find a better reference for prosthetic, orthodontic, functional orthopedics or orthognathic surgery purpose
Analysis of electromagnetic characteristic in the interior permanent magnet brushless DC motor
Get PDFThe motor vibration is mainly induced by the electromagnetic excitation. In order to improve the running performance of the permanent magnet brushless DC motor (BLDCM) within the rolling rotor compressor, this paper builds the predicted model of the electromagnetic excitation and analyzes the electromagnetic characteristic of the BLDCM. Firstly, the electromagnetic field is divided into four regions in 2D plane, including the magnet, air gap, stator slot, and slot-opening subdomains. Then, the relative equations of the electromagnetic field are constructed, and the vector magnetic potential is solved by the variable separation method. Thus, the magnetic flux density of the air gap is derived by the corresponding vector magnetic potential, which is used to describe the electromagnetic excitation. Based on the built model, the effects of the slot opening and air gap length on the electromagnetic characteristic are analyzed. The analysis results can provide a reference for the improvement of the electromagnetic characteristic of the BLDCM by structure optimization