查看更多>>摘要：This paper investigates whether Lorentz geometry can be systematically implemented to study the geometric kinematics of persistent rigid motions in three-dimensional Minkowski space. The notion of persistence of a one-parameter rigid motion is identified by the property that the instantaneous twist of the motion has a constant pitch. The main difference between three-dimensional Euclidean and Minkowski spaces is that the pitch of twists will take three different values in Minkowski space depending on the causal character of the curve on which the motions are based. Furthermore, based on the fundamentals of screw theory, the paper establishes necessary and sufficient criteria for modeling the persistence of some significant frame motions, including Frenet-Serret, adapted frame, and Bishop motions. Then, the axode surfaces of these special motions and their geometric concepts are defined. Finally, for a thorough treatment of special frame motions in three-dimensional Minkowski space, this paper reveals some illustrative examples of persistent rigid motions and axode surfaces.
查看更多>>摘要：Amplitude modulation (AM) in planetary gears, arising from rotation of carrier, is a predominant phenomenon that yields unique yet complicated dynamic behavior. However, the effect of gravity of planetary gear components contributes additional frequency components in the modulation sidebands. In this paper, an extensive experimental investigation is performed to obtain the frequency components of the test rig having the configuration of a modern wind turbine gearbox. The experimental results present some new insight into the combined effect of AM and gravity. A dynamic model of a wind turbine gearbox (WTG) having a two-stage planetary gear set is developed to predict the dynamic response as observed in the experiment. The AM effect due to carrier rotation and the effect of gravity is implemented in the dynamic model. Frequency response and order analysis are carried out for the simulated and experimental signals. It is observed from the comparison of simulation and experimental results that the developed model is capable of correctly describing the dynamic characteristics of the WTG. These results help to understand the complex vibration response of multi-stage planetary gears in a WTG.
查看更多>>摘要：A spatial redundantly actuated parallel mechanism constrained by two point-contact higher ki-nematic pairs (HKPs) has been designed to evaluate food texture changes during the mastication process. To evaluate its elastodynamic performance, a model reduction algorithm that mainly incorporates the idea of the matrix structural analysis is employed. Two models are established by treating the end effector as completely and partially rigid, respectively, to explore how the HKPs influence its performance. In the first model, the overall stiffness and mass matrices contain deformation nodal coordinates, and the generalised coordinate vector in the second model is longer than that in the first model. The roles of HKPs, actuator and stiffness, and static condensation on the performance are thoroughly studied and compared. The results confirm that the mechanism has a high natural frequency and large stiffness. Increasing the diameter of the HKP-related links can effectively improve the performance. HKPs that bring constraints directly and then cause redundant actuations considerably improve the performance. Actuator stiffness is significantly important in determining the performance. The comparison between the reduced and full models shows that the former can enhance the computational efficiency, and the lower orders of the natural frequencies are accurate.
查看更多>>摘要：The dual motor powertrain is superior to the single motor powertrain in terms of economic performance for electric vehicles. To further improve the dynamic and economic performance of dual motor powertrain, a new Simpson planetary gearset based dual motor powertrain (SPGDMP) is proposed. The SPGDMP can realize six driving modes, including four single motor driving modes and two dual-motor driving modes. A simplified dynamic model which considers the gear meshing efficiency is built to implement the parameters design and formulate the energy management strategy (EMS). The genetic algorithm is used to optimize the parameters of SPGDMP to minimize the total power of the drive motor and meet the predetermined dynamic performance requirements at the same time. The EMS is formulated by minimizing the instantaneous consumed power of two motors. To demonstrate the performance of SPGDMP, the parallel axle based dual motor powertrain (PADMP) that meets the same dynamic performance requirement is used as the reference. The simulation results show that the proposed SPGDMP requires lower total power of driving motors to achieve the same dynamic performance and has much better economic performance.
查看更多>>摘要：This study proposes a novel mathematical framework for optimal synthesis of high-speed cam curves, comprising three key aspects: piecewise high-order interpolation (PHOI), pointwise scaling and piecewise modulation. In this framework, PHOI is responsible for constructing a smooth and faithful cam curve under multiorder motion constraints (including displacement, velocity, acceleration and jerk), and pointwise scaling and piecewise modulation are further introduced for optimal tuning of nodal and internodal motion parameters. Mathematically, the combination of PHOI, pointwise scaling and/or piecewise modulation will enable a full and direct control of local/global motion parameters for enhanced high-speed performance of the synthesized cam curve. Concerning the validation of this framework, three detailed numerical examples (curve reconstruction, kinematic and dynamic optimizations) are performed. The excellent interpolation accuracy of PHOI, improved motion continuity by pointwise scaling, lowered motion peaks by pointwise scaling and piecewise modulation, and reduced dynamic error of the optimized cam curve collectively demonstrate the effectiveness and versatility of the proposed framework in data-driven reconstruction and application-oriented optimization of high-speed precision cam profiles.
查看更多>>摘要：In this paper, the kinematics, dynamics, and load distribution algorithm of a 4-PPPS redundantly actuated parallel manipulator are investigated with the screw theory. For the forward kinematic analysis, we propose the major joint set, a minimum set for determining the kinematic and dynamic state of the mobile platform with six specially selected prismatic joints. The reciprocity of screws is applied for simplifying the derivation of the Jacobian matrix. The driving forces of the active joints are solved with the principle of virtual work for the non-redundant and the fully redundant actuation mode with the major joint set. For the fully redundant actuation mode, to avoid joint overload resulted from the conventional least-norm load distribution solution, to smooth the force transition, and to increase the positioning accuracy of the manipulator, a load distribution algorithm based on Lagrange optimization is proposed. These effects are achieved by means including reducing the deformations of the z-axis links and considering the sensitivity and elasticity of major joints. At last, the effectiveness of the modeling method and the proposed algorithm is verified with a case study.
查看更多>>摘要：The kinematics is developed and investigated deeply for the point-conjugate tooth surface couple. The formation principle of the conjugate tooth surface couple is studied by means of the kinematics, and the formation mechanism and law are revealed. The kinematic theory is established for the point-conjugate gear drive to measure its motion stability, in which the method to compute the angular acceleration of the driven gear is presented in detail. A novel kind of crossed-axis gearing that is convenient to be machined is proposed and named the mixed mismatched conical worm drive. The kinematic meshing quality is investigated for the worm drive by applying the established kinematic theory. The numerical results reflect that the transmission error of the worm drive is little and the adjacent error curves are intersectant. The angular acceleration of the worm gear is extremely small, and therefore the vibration and impact caused by the mismatch are weak for the worm drive. It is more reasonable that the curve of transmission error of the worm drive is a high-order polynomial curve since the angular acceleration is not constant.
查看更多>>摘要：The preloaded double-nut ball screw (DNBS) is widely used in precision transmission for its high load capacity and contact stiffness. However, few researches have been done on the influence of load distribution on the loading performance of a DNBS, and no solution has been found for the problem of non-loaded balls in the raceway. Therefore, we propose a static load distribution (SLD) model of a preloaded DNBS considering geometric errors, which takes into account the influence of non-loaded balls and the interaction between the elastic deformation of a screw/nut and the Hertz contact forces of screw-ball/nut-ball contact areas. This model is verified experimentally. The maximum deviation between the theoretical and experimental values is 6.21%. We numerically simulate the effects of geometric errors on the SLD and axial static contact stiffness (ASCS) of a preloaded DNBS. The SLD varies significantly with the geometric error, preload and external axial forces, and the critical external axial force on the preloaded DNBS increases with the preload and geometric error. For a preloaded DNBS with a given geometric error, the ASCS can be kept more stable by selecting the appropriate preload.
查看更多>>摘要：The modeling of beam mechanisms, especially non-uniform beams, becomes complicated due to the geometric nonlinearity that is proved to be significant with large deflection. A new method, called optimization algorithm-based approach (OABA), is proposed to predict the large deflection of uniform and non-uniform cantilever beams, in which an optimization algorithm is exploited to find the locus of the beam tip. The Euler-Bernoulli beam theory is employed here. With the derived locus of the beam tip, the deflection curve of the cantilever beam can be calculated. The optimization algorithm in this paper is embodied in a particle swarm optimization (PSO) algorithm. Experimental results show that the proposed method can precisely predict the deflection of the uniform and non-uniform cantilever beams. The maximum error is limited to 4.35% when the normalized maximum transverse deflection reaches 0.75. To demonstrate the effectiveness of this method in analyzing compliant mechanisms, we also exploited this method to predict the deformation of a compliant parallel-guiding mechanism.
da Silva, Mariana RodriguesMarques, Filipeda Silva, Miguel TavaresFlores, Paulo...
20页
查看更多>>摘要：The selection of the contact force model plays a crucial role in the modeling and analysis of dynamical systems. The seminal work by Hunt and Crossley, published in 1975, is one of the most prominent contact force models that finds application in different areas of science and engineering. The contact force approach proposed by Hunt and Crossley has motivated and inspired a large number of researchers that, eventually, led to the publication of numerous solutions to evaluate contact forces. This paper presents an extensive collection of contact force models available in the literature that have been developed on the basis of the Hunt and Crossley's cornerstone work. The behavior of each contact force model is assessed with a simple example of application and their performance is analyzed.
NSTL
Elsevier