查看更多>>摘要：To further increase the adaptability and versatility of aerial vehicles, this paper presents a novel deployable quad-rotor enabled aerial gripper without integrating extra manipulators. In specific, the quad-rotor can morph/deploy in flight by actuating a simple but effective articulated rigid elements based morphing mechanism, and the function of the gripper can be simultaneously achieved by following the extension/contraction of the deployable articulated mechanism. The proposed mechanism not only endows the quad-rotor with mechanical advantages such as high stiffness but also forms a morph-driven aerial gripper, which helps materialize a novel, compact yet efficient, and dual functional aerial vehicle. In addition, in order to control the morphing quad-rotor system, a morph-independent dynamic model and the corresponding control strategy are developed and presented. Extensive simulations and experiments on the proposed inflight morphing mechanism and grasping functions of the gripper are performed. The results verify the effectiveness of the deployment/morphing mechanism and simultaneously enabled grasping functions, including handling different objects with various sizes, shapes, and textures. The results also validate that our deployment/morphing mechanism has less effect on flight behavior, but does own advantages of multi-maneuverability and morphological adaptation.
查看更多>>摘要：Although compliant mechanism design is a thoroughly studied field, surprisingly little information can be found in literature regarding selection of optimal materials. This paper is intended to fill this gap. Density-based, geometrically robust, stress constrained topology optimization based on a total Lagrangian FEM formulation is used for investigation of a compliant inverter and a compliant gripper example. Changes in handling of the projection parameters and the stress constraints are proposed for improved algorithmic stability and accurate representation of the stresses and material stiffness in topology optimization. Large-scale optimization studies are carried out, varying elastic modulus and allowable stress in a wide range. A comparison with an Ashby chart shows the characteristics of the best suited material. It is shown, that an optimal Young's modulus and a minimum required material strength (depending on the modulus) can be identified from the results. Altering critical optimization parameters, e.g. allowable volume fraction and the minimum length scale, their influence on the optimal material choice is investigated. Guidelines for compliant mechanism designers for efficient selection of suited materials are developed.
查看更多>>摘要：The asymmetrical dual-rotor can represent special fault cases of an aero-engine, such as cracked rotors or lost blades, and to understand characteristics of natural vibrations of the system are very important on the design or maintenance stages of the aero-engine. The novel asymmetrical dualrotor model is put forward based on special fault cases of the aero-engine. In the coupled dynamics model, equations of motion and natural vibration are derived by using Lagrange's equation and the harmonic balance algorithm, systematically. Natural vibration frequencies are studied by using equations of natural vibrations of the model, and coupled natural vibration frequencies between rotors are investigated too. Response curves of coupled phenomena of the model are analyzed in detail. Due to effects of an asymmetry and coupling actions between rotors, complex natural vibration phenomena, such as three unstable regions and two super harmonic resonances on the low pressure (LP) rotor, are firstly investigated on the proposed novel dualrotor model. In addition, solutions of theoretical analyses are good consistent with results of numerical simulations, and results of experiments can further illustrate natural vibration characteristics of the dynamics model. Research results prove the correctness of the proposed coupled dynamics model.
查看更多>>摘要：Data-driven fault diagnosis methods have become a research hotspot recently. However, the following two problems are still barring them from the application: (1) Most of the existing models rely deeply on sufficient labeled samples and neglect the high cost of labeled data collection in reality; (2) The existing models usually focus on the single-level attribute of the sample and ignore the latent hierarchical fault attributes. To address these issues, a novel semisupervised multi-layer non-negative matrix factorization (SMNMF) method is proposed in this study. The fault pattern and severity identification problems are converted into a hierarchical fault attribute representation task, which can reduce the complexity of the classification task and improve the fault diagnosis accuracy. The hierarchical attribute representations of different fault locations and sizes are learned from the time-frequency distribution (TFD) of signals by a newly constructed two-layer non-negative matrix factorization model. The graph-based semi-supervised learning method is adopted to lead the attributes of the hierarchy structure and carry out label propagation from labeled samples to unlabeled samples for more accurate fault diagnosis. The fault diagnosis experiments executed in the aeroengine bearings and a diesel engine demonstrated the feasibility and superiority of the proposed method.
查看更多>>摘要：The paper studies the tripod mechanisms that comprise novel spatial Cartesian flexible hinges and can be used in three-dimensional sensing/actuation applications. These hinges are formed of serially-connected straight- and circular-axis elastic segments that are located in planes parallel to the planes of a Cartesian reference frame. Two spatial flexible hinge designs are proposed and their compliance matrices are derived based on closed-form compliances of the basic segments. The hinge compliance matrices are utilized to formulate the stiffness matrix of tripod mechanisms that are parallel combinations of three identical hinges and a rigid link. The hinge analytical compliance model is confirmed through finite element code simulation while the tripod analytical stiffness is verified by both finite element analysis and experimental testing of fabricated specimens. Comprehensive simulation is subsequently performed to study the influence of the geometric parameter values on the hinge and tripod analytical compliance/stiffness.
查看更多>>摘要：A significant amount of research has been directed toward developing a more intuitive appreciation of spatial elastic behavior. Results of these analyses have often been described in terms of the elastic behavior (stiffness or compliance) centers. This paper investigates the properties of centers of stiffness and compliance and provides a fresh view of elastic center locations, specifically, the locus of centers associated with a given mechanism's topology and geometry. We show that the location of the center of stiffness (compliance) for a set of elastic components connected in parallel (in serial) can be described in terms similar to the location of the center of mass for a set of mass particles. This provides a physical interpretation of the centers associated with a compliant behavior, and a useful guide in the design of mechanisms that realize desirable compliant behaviors.
查看更多>>摘要：Rehabilitation medicine studies have indicated that occupational therapy has a positive effect on the recovery of hand function. However, few wearable hand exoskeletons can assist in performing the adduction and abduction exercises of occupational therapy. Therefore, the wearable index finger rehabilitation exoskeleton (WIFRE) is studied in this paper. First, a WIFRE is proposed to realize the index joint's independent actuation, including adduction and abduction movements. Second, the local/global kinematic and dynamic manipulability measures are proposed and analyzed to evaluate the performance of the WIFRE. The analysis results show that the dimensional parameters of the WIFRE have a significant effect on its global manipulability measures. The global kinematic and dynamic manipulability measures can be improved by 13%-15% compared with the corresponding minimums. Third, a multi-parameter multi-objective optimization method is proposed to simultaneously enhance the three global manipulability measures. Finally, experiments are performed to verify the effectiveness of the index finger exoskeleton and the global manipulability measures.
查看更多>>摘要：The stiffness of the Exechon hybrid manipulator is a crucial performance indicator as the manipulator is used as a 5-axis machine tool. Normally, the serial module of the Exechon is not included in the kinematic and stiffness analysis. In terms of kinematics, the parallel and serial modules are said to be decoupled, i.e. parallel module can be solved for position and the serial module can be used to compensate the parasitic orientation of the parallel platform. This is only possible when the serial module is a perfect spherical wrist. However, several models of Exechon technology have an offset wrist rather than a spherical one. Such an offset makes it impossible to obtain a kinematic decoupling. In all publications available in the literature, the Exechon is considered to have a perfect spherical wrist. Therefore, this paper presents the inverse kinematics and compliance model of Exechon manipulators with offset wrists. The unknown coefficients in the compliance model are determined by optimizing the model against experimental data. The resulting predictions are then compared against more experimental results to validate the model.
查看更多>>摘要：This paper presents a novel calculation method for dynamic excitation of the 3-D modified double-helical gear pair in consideration of actual contact state. The 3-D modification method combines tip, root, and axial modification. Firstly, the tooth surface equation of double-helical gear with 3-D modification is derived and the calculation method for time-varying mesh stiffness (TVMS) of the modified double-helical gear pair is proposed and the effects of modification parameters on TVMS are studied. Secondly, the tooth surface load distribution is analyzed on the basis of TVMS for the double-helical gear pair. Accounting the influence of modification parameters on tooth surface friction coefficient, the time-varying friction excitation (TVFE) of the modified double-helical gear pair is researched. Besides, combining approach mesh stiffness of the modified double-helical gear pair and impact dynamic model, the calculation formula of meshing impact force (MIF) is proposed, and the effects of helix angle and modification parameters on MIF are discussed. The calculation methods of TVMS, TVFE and MIF proposed in this paper will be useful for accurate prediction about vibration and noise of the double-helical gear system.
查看更多>>摘要：A four degrees-of-freedom (DOF) Parallel Manipulator (PM) with a 4PPa-2PaR configuration has been proposed to generate 3-DOF Translational and 1-DOF Rotational (3T1R) motions in our early work. It has the advantages of symmetric geometry, simple kinematics and infinite extension of translational workspace along its linear guide direction. However, its V-type assembly mode results in a long distance between its moving platform and the base, which makes its stiffness and accuracy lower. Besides, its the other two translational workspaces are limited due to its kinematic singularities. To overcome such limitations, the PM is modified by utilizing its M-type assembly mode and placing an offset angle to the last parallelogram mechanism. To simplify the displacement analysis, a geometrical projection method is employed, while a closed-loop vector approach is used for its instantaneous kinematic analysis. Both singularity and workspace issues are investigated. An optimization algorithm based on Genetic Algorithm is proposed to maximize the reachable workspace. The optimization result indicates that the workspace is significantly increased. A prototype of the M-type PM is fabricated to validate the effectiveness of the modified design.
NSTL
Elsevier