Terms Of Rotation Angle Research Articles

Fiber-reinforced flexible joint actuator for soft arthropod robots

The flexible joints are the fundamental building blocks of modular soft robots. However, the investigation on flexible joints made entirely of soft material is still in its infancy, with complex structure, small rotation range and insufficient driving force output. Bio-inspired from the hydraulic joints of spider legs, a dexterous fiber-reinforced flexible joint actuator was proposed. For the irregular shape joint actuator with fiber-reinforced structure, its fabrication process and modeling method are discussed. And the advantages of fiber reinforcement are demonstrated in terms of rotation angle, driving torque and efficiency experiments. Compared with the joint actuator without fiber layer, the actuator with a fiber angle of 30° can increase the rotation angle by up to 36% and the driving efficiency by up to 19.6%. The maximum inflation pressure can reach 120 kPa, and the force density 3.56 mN/mm3, which demonstrates extremely high pressure tolerance capacity and force density, and shows the wide applicability of the fan-shaped flexible actuator to enable lightweight, mobile, multifunctional soft robots.

A novel GCN-based point cloud classification model robust to pose variances

Point cloud data can be produced by many depth sensors, such as Light Detection and Ranging (LIDAR) and RGB-D cameras, and they are widely used in broad applications of robotic navigation and remote-sensing for the understanding of environment. Hence, new techniques for object representation and classification based on 3D point cloud are becoming increasingly in high demand. Due to the irregularity of the object shape, the point cloud-based object recognition is a very challenging task, especially the pose variances of a point cloud will impose many difficulties. In this paper, we tackle the challenge of pose variances in object classification based on point cloud by developing a novel end-to-end pose robust graph convolutional network. Technically, we first represent the point cloud using the spherical system instead of the traditional Cartesian system for simplicity of computation and representation. Then a pose auxiliary network is constructed with an aim to estimate the pose changes in terms of rotation angles. Finally, a graph convolutional network is constructed for object classification against the pose variations of point cloud. The experimental results show the new model outperforms the existing approaches (such as PointNet and PointNet++) on the classification task when conducting experiments on both the ModelNet40 and the ShapeNetCore dataset with a series of random rotations of a 3D point cloud. Specifically, we obtain 73.02% accuracy for classification task on the ModelNet40 with delaunay triangulation algorithm, which is much better than the state of the art algorithms, such as PointNet and PointCNN.

Accurate analytical approximation to post-buckling of column with Ramberg−Osgood constitutive law

The post-buckling of a clamped column made of nonlinear elastic material and subject to axial compression is investigated in this paper. The Ramberg−Osgood type constitutive relation is adopted and it is expanded by using Taylor series. Based on Euler−Bernoulli beam theory, the exact governing equations are expressed in terms of rotation angle. Because the equations contain strongly nonlinear terms that are functions of the rotation angle, analytical solutions are virtually impossible. In this respect, this paper is focused on presenting an alternative method to construct concise yet accurate analytical approximate solutions for post-buckling of the Ramberg−Osgood column that is related to large rotation amplitude. The improved harmonic balance method is used to solve the nonlinear governing equations which are simplified via the Maclaurin series expansion and orthogonal Chebyshev polynomials. In addition, numerical solutions by applying the shooting method on the governing equations are obtained for comparison. The second-order analytical approximate solutions presented in this paper show excellent accuracy by comparing with numerical solutions. The analytical approximate method and numerical result presented in this paper can be applied as design guidelines for designing engineering structures that sustain large deformation, such as slender nonlinear compression of aluminum alloy columns, rods or braces.

Investigation on Texture Evolution Mechanism of NiTiFe Shape Memory Alloy Under Plane Strain Compression

Texture evolution of NiTiFe shape memory alloy (SMA) is investigated during plane strain compression based on crystal plasticity finite element method (CPFEM) and electron back-scatter diffraction (EBSD) experiment. The deformation textures of NiTiFe SMA are not influenced very considerably after experiencing recrystalline annealing at 600 °C for 1 h. Based on the results of CPFEM, the main activated slip systems of NiTiFe SMA are 〈100〉/{110} and 〈111〉/{110} ones during plane strain compression. According to the relationship between texture components and activated slip systems put forward in this study, 〈110〉 direction would rotate to rolling direction, whereas 〈100〉 and 〈111〉 directions would rotate to normal direction. These rotations contribute to the formation of γ-fibre texture and α-fibre texture in NiTiFe SMA. The deformation texture components predicted by CPFEM and determined by EBSD were compared with each other in detail. Due to the startup of the pencil glide and multiple slip in the refined microstructure, there are some differences between texture components predicted by CPFEM and texture components determined by EBSD. The deformation heterogeneity is discussed in terms of rotation angle at each integration point in the study.

Motion Periods of Planet Gear Fault Meshing Behavior.

Vibration sensors are, generally, fixed on the housing of planetary gearboxes for vibration monitoring. When a local fault occurred on the tooth of a planet gear, along with the system operating, the faulty tooth will mesh with the ring gear or sun gear at different positions referring to the fixed sensor. With consideration of the attenuation effect, the amplitudes of the fault-induced vibrations will be time-varying due to the time-varying transfer paths. These variations in signals are valuable information to identify the fault existence as well as the severity and types. However, the fault-meshing positions are time-varying and elusive due to the complicated kinematics or the compound motion behaviors of the internal rotating components. It is tough to accurately determine every fault meshing position though acquiring information from multi-sensors. However, there should exist some specific patterns of the fault meshing positions referring to the single sensor. To thoroughly investigate these motion patterns make effective fault diagnosis feasible merely by a single sensor. Unfortunately, so far few pieces of literature explicitly demonstrate these motion patterns in this regard. This article proposes a method to derive the motion periods of the fault-meshing positions with a faulty planet gear tooth, in which two conditions are considered: 1. The fault-meshing position initially occurs at the ring gear; 2. The fault-meshing position initially occurs at the sun gear. For each scenario, we derive the mathematical expression of the motion period in terms of rotational angles. These motion periods are, in essence, based on the teeth number of gears of a given planetary gearbox. Finally, the application of these motion periods for fault diagnosis is explored with experimental studies. The minimal required data length of a single sensor for effective fault diagnosis is revealed based on the motion periods.

Numerical method for vesicle movement analysis in a complex cytoskeleton network

The detection of the precise movement of a vesicle during transport in a live cell provides key information for the intracellular delivery process. Here we report a novel numerical method for analyzing three-dimensional vesicle movement. Since the vesicle moves along a linear cytoskeleton during the active transport, our method first detects the orientation and position of the cytoskeleton as a linear section based on angle correlation and linear regression, after noise reduction. Then, the precise vesicle movement is calculated using vector analysis, in terms of rotation angle and translational displacement. Using this method, various vesicle trajectories obtained via high spatiotemporal resolution microscopy can be understood..

Multi-objective optimization of stiffness and workspace for a parallel kinematic machine

This paper presents optimizations of a parallel kinematic manipulator used for a machine tool in terms of its workspace and stiffness. The system stiffness and workspace of the parallel manipulator are conducted in the paper. In order to locate the maximum system stiffness and workspace, single and multi-objective optimizations are performed in terms of rotation angles in x and y axes and translation displacement in z axis with genetic algorithms. By optimizing the design variables including geometric dimensions of the manipulator, the system stiffness and workspace of the proposed parallel kinematic manipulator has been greatly improved.

Stiffness optimization of a novel reconfigurable parallel kinematic manipulator

SUMMARYThis paper proposes a novel design of a reconfigurable parallel kinematic manipulator used for a machine tool. After investigating the displacement and inverse kinematics of the proposed manipulator, it is found that the parasitic motions along x-, y-, and θz-axes can be eliminated. The system stiffness of the parallel manipulator is conducted. In order to locate the highest system stiffness, single and multiobjective optimizations are performed in terms of rotation angles in x- and y-axes and translation displacement in z-axis. Finally, a case study of tool path planning is presented to demonstrate the application of stiffness mapping. Through this integrated design synthesis process, the system stiffness optimization is conducted with Genetic Algorithms. By optimizing the design variables including end-effector size, base platform size, the distance between base platform and middle moving platform, and the length of the active links, the system stiffness of the proposed parallel kinematic manipulator has been greatly improved.

Gyrator transform-based optical image encryption, using chaos

We propose a new method for image encryption, using gyrator transform and chaos theory. Random phase masks are generated using chaos functions and are called as chaotic random phase masks. In the proposed technique, the image is encrypted using gyrator transform and two chaotic random phase masks. Three types of chaos functions have been used to generate the chaotic random phase masks. These chaos functions are the logistic map, the tent map and the Kaplan-Yorke map. The computer simulations are presented to verify the validity of the proposed technique. The mean square errors have been calculated. The robustness of the proposed technique to blind decryption in terms of rotation angle and the seed values of the chaotic random phase mask have been evaluated. The optical implementation of the encryption and the decryption technique has been proposed.

Optimization of Backward Giant Circle Technique on the Asymmetric Bars

The release window for a given dismount from the asymmetric bars is the period of time within which release results in a successful dismount. Larger release windows are likely to be associated with more consistent performance because they allow a greater margin for error in timing the release. A computer simulation model was used to investigate optimum technique for maximizing release windows in asymmetric bars dismounts. The model comprised four rigid segments with the elastic properties of the gymnast and bar modeled using damped linear springs. Model parameters were optimized to obtain a close match between simulated and actual performances of three gymnasts in terms of rotation angle (1.5 degrees ), bar displacement (0.014 m), and release velocities (<1%). Three optimizations to maximize the release window were carried out for each gymnast involving no perturbations, 10-ms perturbations, and 20-ms perturbations in the timing of the shoulder and hip joint movements preceding release. It was found that the optimizations robust to 20-ms perturbations produced release windows similar to those of the actual performances whereas the windows for the unperturbed optimizations were up to twice as large. It is concluded that robustness considerations must be included in optimization studies in order to obtain realistic results and that elite performances are likely to be robust to timing perturbations of the order of 20 ms.

In vivo movement analysis of the patella using a three-dimensional computer model

We used three-dimensional movement analysis by computer modelling of knee flexion from 0 degrees to 50 degrees in 14 knees in 12 patients with recurrent patellar dislocation and in 15 knees in ten normal control subjects to compare the in vivo three-dimensional movement of the patella. Flexion, tilt and spin of the patella were described in terms of rotation angles from 0 degrees . The location of the patella and the tibial tubercle were evaluated using parameters expressed as percentage patellar shift and percentage tubercle shift. Patellar inclination to the femur was also measured and patellofemoral contact was qualitatively and quantitatively analysed. The patients had greater values of spin from 20 degrees to 50 degrees , while there were no statistically significant differences in flexion and tilt. The patients also had greater percentage patellar shift from 0 degrees to 50 degrees , percentage tubercle shift at 0 degrees and 10 degrees and patellar inclination from 0 degrees to 50 degrees with a smaller oval-shaped contact area from 20 degrees to 50 degrees moving downwards on the lateral facet. Patellar movement analysis using a three-dimensional computer model is useful to clearly demonstrate differences between patients with recurrent dislocation of the patella and normal control subjects.

Consistency of performances in the Tkatchev release and re-grasp on high bar

The Tkatchev on the high bar is a release and re-grasp skill in which the gymnast rotates in a direction during flight opposite to that of the preceding swing. Since the release window is defined as the time during which the gymnast has appropriate linear and angular momentum to ensure the bar can be re-grasped, it was speculated that the release windows for this skill would be smaller than for dismounts that are less constrained. One senior male gymnast competing at national standard performed 60 Tkatchev trials. A four-segment planar simulation model of the gymnast and high bar was used to determine the release windows in 10 successful and 10 unsuccessful performances of the Tkatchev recorded using a Vicon motion analysis system. Model parameters were optimized to obtain a close match between simulations and recorded performances in terms of rotation angle (1°), bar displacements (0.01 m), and release velocities (1%). Each matched simulation was used to determine the time window around the actual point of release for which the model had appropriate release parameters to complete the Tkatchev successfully. The release windows for the successful trials were small compared with those of dismounts. The unsuccessful trials were associated with later release and later timing of the actions at the shoulders and hips.

The Margin for Error When Releasing the Asymmetric Bars for Dismounts

It has previously been shown that male gymnasts using the "scooped" giant circling technique were able to flatten the path followed by their mass center, resulting in a larger margin for error when releasing the high bar (Hiley and Yeadon, 2003a). The circling technique prior to performing double layout somersault dismounts from the asymmetric bars in women's artistic gymnastics appears to be similar to the "traditional" technique used by some male gymnasts on the high bar. It was speculated that as a result the female gymnasts would have margins for error similar to those of male gymnasts who use the traditional technique. However, it is unclear how the technique of the female gymnasts is affected by the need to avoid the lower bar. A 4-segment planar simulation model of the gymnast and upper bar was used to determine the margins for error when releasing the bar for 9 double layout somersault dismounts at the Sydney 2000 Olympics. The elastic properties of the gymnast and bar were modeled using damped linear springs. Model parameters, primarily the inertia and spring parameters, were optimized to obtain a close match between simulated and actual performances in terms of rotation angle (1.2 degrees), bar displacement (0.011 m), and release velocities (<1%). Each matching simulation was used to determine the time window around the actual point of release for which the model had appropriate release parameters to complete the dismount successfully. The margins for error of the 9 female gymnasts (release window 43-102 ms) were comparable to those of the 3 male gymnasts using the traditional technique (release window 79-84 ms).

The margin for error when releasing the high bar for dismounts

In Men's Artistic Gymnastics the current trend in elite high bar dismounts is to perform two somersaults in an extended body shape with a number of twists. Two techniques have been identified in the backward giant circles leading up to release for these dismounts (J. Biomech. 32 (1999) 811). At the Sydney 2000 Olympic Games 95% of gymnasts used the “scooped” backward giant circle technique rather than the “traditional” technique. It was speculated that the advantage gained from the scooped technique was an increased margin for error when releasing the high bar. A four segment planar simulation model of the gymnast and high bar was used to determine the margin for error when releasing the bar in performances at the Sydney 2000 Olympic Games. The eight high bar finalists and the three gymnasts who used the traditional backward giant circle technique were chosen for analysis. Model parameters were optimised to obtain a close match between simulated and actual performances in terms of rotation angle (1.2°), bar displacements (0.014 m) and release velocities (2%). Each matching simulation was used to determine the time window around the actual point of release for which the model had appropriate release parameters to complete the dismount successfully. The scooped backward giant circle technique resulted in a greater margin for error (release window 88–157 ms) when releasing the bar compared to the traditional technique (release window 73–84 ms).

Diffusion induced recrystallization in single crystals of copper

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Solid State and Solution Conformation of Di-2-thienyl Telluride: X-Ray Structure and Dipole Moment Studies

The crystal and molecular structure of di-2-thienyl telluride was determined by X-ray analysis. Crystal (monoclinic) data were: a = 9.526(4), b = 6.252(4), c - 16.302(5) Å; β = 97.29(3)°, Z = 4, space group P21/c. Hydrogen bonds are absent and only van der Waals forces are determining crystal packing. The Cring-Te bond distances suggest little conjugation of Te atom with the rings. Comparisons with published structures for Car-X-Car (X = chalcogen) type molecules revealed that the C (l)-Te-C(5) angle takes the lowest value (95.6°) in the molecule understudy. The remaining bond lengths and angles are close to standard values. The molecular conformation found in the crystal is “butterfly-like” , with thienyl ring planes nearly perpendicular to the C(l)-Te-C(5) plane and the S atoms distal to each other. Dipole moment was measured for di-2-thienyl telluride in benzene solution (μ = 1.18 D at 30°). This value, which was interpreted via classical vector addition method in terms of rotation angles about C(l)-Te and C(5)-Te bonds, showed that the molecular conformation found in the crystalline state is retained in solution.