查看更多>>摘要：Compliant kaleidocycles exhibit continuous rotation and multistability. They have strong application prospects in the exploration of new spatial mechanisms. However, limited by the spatial structure of the kaleidocycle units, the design of compact and miniaturized kaleidocycles remains challenging. In this study, a corrugated flexure-based lamina emergent spatial (CFLES) joint is introduced for the design and analysis of symmetrical compliant kaleidocycles. First, the rotational compliance ratios are analyzed to set the degrees of freedom (DOFs) and the degrees of constraint (DOCs) of the CF-LES joint. Second, the parameters of the proposed joint are optimized for the compliant kaleidocycles. Third, the mechanical properties of the kaleidocycles based on the optimization result are evaluated by finite element analysis (FEA) and experiments. Finally, the potential applications of this mechanism are discussed, and a prototype is processed to determine the miniaturization capability of CF-LES joint-based symmetrical compliant kaleidocycles.
Gomez, Erik R.Sjostrand, JakobKari, LeifArteaga, Ines Lopez...
19页
查看更多>>摘要：A nonlinear centrifugal pendulum vibration absorber (CPVA) with normal-force dependant friction loss is investigated in a torsional model of a downspeeded powertrain of a heavy-truck. The engine model includes gas-pressure excitation and the existing pendulum model is extended to include a continuous formulation of end-stops at the end of the pendulum-path. Furthermore, the friction loss of the pendulum is experimentally determined. A pendulum-path parameter-study in the complete powertrain model is conducted to consider the effects of the system dynamics on the CPVA. It is shown that the performance of the CPVA is affected by the powertrain system-dynamics and thus important to consider in the design of the CPVA. Downspeeding of the engine by appropriate gearing of the driveline is a measure to decrease the CO2 emissions. However, downspeeding increases the torsional vibration and noise of the powertrain with conventional torsional vibration reduction methods. The CPVA can be used to reduce the torsional vibration and thus facilitate to reach environmental goals.
查看更多>>摘要：A novel method for eliminating isomorphism identification is proposed to improve synthesis efficiency and synthesize planar nonfractionated kinematic chain (KCs) automatically. This method is based on the vertex insertion of contracted graphs. First, similar edges of contracted graphs are divided into groups, in which the similar edges are found and their characteristic matrices are calculated. The edge types are divided based on whether or not isomerism occurs after vertices are inserted. Then, the vertices are inserted into contracted graphs according to the edge condition. In this process, all isomerism caused by the location and number of inserted vertices is reserved, and the property change of similar edges is checked. Lastly, the rigid subchains of remaining isomerism are distinguished. Contracted graphs with four independent loops and some of their inserted vertices are presented in appendix. A complete set of nonfractionated KCs with up to seven independent loops and three degrees of freedom is also provided. The veracity and efficiency of the method are confirmed by conducting a comparative analysis between this synthesis and other literature results.
查看更多>>摘要：This paper proposes a novel friction-actuated two degree-of-freedom positioning stage with large motion stroke, high resolution and low coupling rate. A parallelly decoupled driving unit and the serially configured sliders are utilized together to realize hybrid output decoupling, and a clamping unit is adopted to adjust the friction force between friction piece and moving platform, which can improve the output characteristic while reduce the amount of PZT stacks. In addition, the coarse-fine cooperatively actuation principle is developed to realize large stroke positioning with high accuracy, and the decoupling control strategy is adopted to reduce the accumulated coupling error. The analytical modeling is conducted to explore the step displacement of driving unit, and a prototype is fabricated to investigate the performance of the positioning stage. The experimental results show that the step displacements in X and Y axes are 11.3 mu m and 10.6 mu m, and the cross-coupling rates after decoupling compensation are 0.07% and 0.14%, respectively. The maximum output velocity and horizontal loading capacity is 1.54 mm/s and 1.2 N, respec-tively, and the resolution is tested as 20 nm.
查看更多>>摘要：The stability and stiffness analysis of tensegrities is significant for their applications in robotic areas. Generally, tensegrity structures' stiffness is divided into a non-negative definite material stiffness and an indefinite geometric stiffness. The stability of tensegrities is closely related to the geometric stiffness caused by the prestress of cables. However, the nodal geometric stiffness derived from nodal static equilibrium equations hides the root of instability for tensegrity structures. This article develops a new derivation of the total stiffness for a general tensegrity structure based on rigid bodies' static equilibrium equations. And then, it subdivides the geometric stiffness into a non-negative definite stiffness and an indefinite stiffness. The indefinite stiffness is purely rotational stiffness and the only root of instability for tensegrity structures, which has remarkable geometrical significance. By analyzing such indefinite stiffness, a set of sufficient and necessary conditions are derived to guarantee tensegrity structures' stability. Some numerical examples are presented to verify the effectiveness and versatility of the proposed approach.
查看更多>>摘要：The reconfiguration capability given by the use of kinematic redundancy can be an alternative for enlarging the useable workspace of parallel manipulators. However, the inverse kinematic model of a kinematically redundant parallel manipulator presents an infinite number of solutions requiring redundancy resolution strategies. These decision-maker strategies are responsible for keeping the manipulator away from singular configurations, which is considered a failure. However, singular regions might be affected by uncertainties. Therefore, every possible solution for the kinematic model presents a probability of failure according to the system's uncertainties. In this work, the probability of failure is assessed using the Monte Carlo Simulation and surrogate models. Reliable redundancy resolution strategies using these surrogate models are proposed and numerical results considering geometrical uncertainties demonstrate the proposal's applicability.
Yuan, HuiLi, YuanJiang, Jason ZhengAl Sakka, Monzer...
15页
查看更多>>摘要：Passive mechatronic vibration absorbers have demonstrated great performance potential in previous studies. For such devices, optimal design of the electrical circuits therein is critical but challenging since existing techniques have evident limitations: those investigating a few specific circuits leave huge possibilities unexplored; those optimising circuit impedances potentially lead to circuits which cannot be physically implemented. Another challenge lies in the need for considering device parasitic effects (e.g., transducer1 resistance) to guarantee the predicted performance accuracy-this can be extremely time-consuming, especially when exploring numerous design possibilities (e.g., circuits, transducers). To address these two challenges, this paper proposes a novel design methodology, which (1) allows the optimal and practically implementable circuit to be identified among all layouts with predefined complexity; (2) considers the device parasitic effects where necessary, to efficiently explore various possibilities. The validity of this methodology is demonstrated via an automotive suspension design case study, where the obtained significant performance improvement is successfully verified via experiments. This methodology is directly applicable to vibration suppression of other engineering structures and can also be adopted for other mechatronic absorber types.
查看更多>>摘要：This study aims to implement multi-objective optimization of a gear unit in order to minimize the power loss and the vibrational excitation generated by the meshing, via a multi-scale approach that extends from gear contact to the complete transmission. All these indicators are closely linked to the macro and micro-geometry definition of the gear pair. The optimization is carried out using a genetic algorithm, namely the Non-Dominated Sorting Genetic Algorithm II (NSGAII). The design variables chosen for the problem are the pressure angle and the helix angle, as macro-geometry characteristics of the gear, and/or the length and the amount of tooth profile modifications, as micro-geometry characteristics of the gear. Constraints are imposed in order to not exceed a maximum bending stress at the tooth root of the gear and to not fall below a minimum total contact ratio. From the results obtained, it is found that the multi-objective optimization with both micro and macro-geometry parameters simultaneously gives different results than those obtained with macro-geometry first and then micro-geometry parameters. In order to study the importance, or not, to take into account the complete gear unit, a comparison is made between the local power loss generated by gear tooth friction and the total power loss in the single stage gear unit in terms of design variables values.
查看更多>>摘要：Aiming at a 5-DOF hybrid optical mirror polishing robot, the explicit dynamic model considering the joint friction is established and the inertia coupling distribution is studied. Firstly, the kinematics of the manipulator is solved based on closed-loop vector method, and the dynamic model is established with Newton-Euler method based on the force analysis of manipulator components. Secondly, the kinematic parameters of the reference point of the moving platform are selected as the intermediate variables, and the explicit dynamic model of the parallel manipulator is obtained by parameters substitution considering the friction effects of spherical joints, universal joints and ball screws. Finally, on the basis of the dynamic model, the inertia coupling strength evaluation index for active branched-chains is proposed, and the distribution law of the coupling strength in a certain trajectory and workspace is studied. The results show that the inertia coupling strength indices between active branched-chains vary with the manipulator position and are symmetrically distributed in the workspace. This paper provides a theoretical basis for the joint controller design and structural parameter optimization of the polishing robot.
查看更多>>摘要：This paper proposes a new compliant mechanism for the stroke amplification of piezoelectric actuators. Compared with the existing ones, this compliant stroke amplification mechanism (CSAM) has several advantages including lightweight, less stress concentration, large motion range, as well as ease of manufacture in macro- and micro-scales, mainly due to the completely distributed compliance and largely reduced moving mass. Kinetostatic models of the CSAM, with consideration of the payloads applied on the output stage, are derived for quick and insightful determinate analysis, which enables optimization of the associated parameters to achieve different objectives. The results obtained from the kinetostatic models are in reasonable agreement with the FEA simulation results, with less than 3.8% difference when the input displacement is less than 10 mu m. An optimization method, based on the analytical models, is introduced and employed to increase the amplification ratio of the CSAM by up to 240%. The optimized CSAM is an excellent candidate for the stroke amplification of piezoelectric actuators, which is fabricated and experimentally tested. The optimization method is able to be extended to design other compliant mechanisms with optimized size, shape and topology configuration simultaneously.
NSTL
Elsevier