查看更多>>摘要：Line gear (LG) is a recently proposed gear, which can realize transmissions between the parallel-axis, crossing-axis, and skewing-axis. To extend LG from basic research to practical application, efficient machining methods and measuring methods are necessary. In this paper, based on the LG meshing theory, driving contact curves and driven contact curves were solved. And the LG generated by the face-milling method was proposed, which was abbreviated as FMLG. The virtual simulations for machining the FMLGs were studied, and the models obtained by simulations were used for finite element analysis (FEA). From FEA results, the feasibilities of the design of contact curves and the models obtained by simulations were verified. Afterwards, three pairs of FMLGs were processed by using of special machine tool, and the measuring methods and accuracy evaluations of FMLGs were studied. Finally, performance experiments of FMLG boxes were carried out. From the measurement and experiment results, it can be concluded that the face-milling method is feasible for the rough machining of LG. Furthermore, the measuring method and accuracy evaluation are helpful for the subsequent optimization of processing parameters.
查看更多>>摘要：The centrifugal effect is one of the most common phenomena in rotor dynamic systems, while typically ignored in the mesh stiffness evaluation by many research papers. Focusing on the centrifugal force in high-speed working condition, this paper developed an analytical-FEM framework to integrate the centrifugal field into the mesh stiffness and nonlinear dynamics. The additional potential caused by centrifugal force is condensed in the mesh stiffness calculation. The gear torsional dynamic model is further extended to embody the internal dynamic effect in centrifugal field. Solutions of gear statics and dynamics are compared with existing models and experiments, and results demonstrate the reasonable accuracy of the present model.
查看更多>>摘要：The clutchless automated manual transmissions (CLAMTs) can make electric vehicles improve the dynamic and economy performance by fully playing the role of drive motor. As one of the most important component in the transmission system, synchronizer is used to ensure smooth shift. However, the inertial lock ring synchronizer (ILRS) that used commonly cannot give full paly to the dynamics characteristics of the electric drive system. To improve the shift quality of CLAMTs based on the unique needs of electric vehicles, the weaknesses at declining shifting impact of ILRS and harpoon-shift synchronizer which are typical representatives of existing synchronizers are explained, a novel synchronizer named elastic load friction ring synchronizer (ELFRS) is designed and the working principle at eliminating the shifting impact is analyzed. After establishing the transmission and actuator models, a control strategy matching the synchronizers based on Fuzzy-PID is proposed, which achieves the comfortable shift and dynamic shift control goals. The simulation results show that ELFRS reduces most of the shift shock compared to ILRS and harpoon-shift synchronizer. The research has practical application value to improve the performance of CLAMTs.
查看更多>>摘要：A dynamic model of light-weight spur gear transmission system (SGTS) considering the elasticity of shaft and gear body is established to study the influences of the elasticity of the gear body on the dynamic characteristics. The spur gear is simplified as elastic ring and support springs stemming from the elasticity of the gear web. The shaft and ring are modelled based on Timoshenko beam theory. The kinetic energy of the elastic shaft-ring gear rotor is obtained based on multibody dynamic theory. A time-varying meshing model is proposed considering the movements of the meshing points along the base circles of gears. The differential equations of the SGTS are formulated by differential quadrature finite element method (DQFEM). The present model is validated by compared to lumped-mass model (LMM) by setting the elasticity of the gear body to be infinitely small. The influences of the elasticity of the gear web are studied. The results show that the elasticity of the gear web can reduce the intensity of the vibration.
查看更多>>摘要：This article presents an adaptive feed-forward method to compensate for the dynamic friction in the machine tool systems so that the tracking errors of the machine axes can be reduced. To achieve this aim, a dynamic friction model is firstly established by constructing a continuous and differentiable two-segmented arc tangent curve to characterize the asymmetrical and nonlinear static friction phenomenon in relation to the positive and negative velocity ranges of the machine axes. Subsequently, a new feed-forward method is proposed to compensate for the friction by constructing an adaptive controller with three advantages, i.e. no need of velocity and acceleration measurement, large adaptive rate and high steady-state accuracy. During the model establishment, a discontinuous projection mapping in the learning process is constructed. Especially, the stability of the adaptive controller is strictly proved by theoretical derivation. Besides, a new two-step adaptive method is formulated to analytically calculate the unobservable parameter z. Finally, both simulations and experiments confirm that the proposed compensation method can reach to lower tracking errors, especially in the velocity reversal area, by comparing with the existing approaches.
查看更多>>摘要：In this paper, the concept of adaptive landing and aerial manipulation mechanism (ALAM) is proposed. The mechanism can be installed on a rotary-wing unmanned aerial vehicle (UAV), allowing the UAV to land on uneven terrain and perform aerial manipulation. Based on the Lie group, the design principles of the ALAM are proposed by combining the advantages of the generalized parallel mechanism. The design procedure of the mechanism is introduced. Then, the structure synthesis is performed for the ALAMs with 1 to 3 degrees of freedom (DOF) generalized moving platform. In order to evaluate the landing performance of the mechanism, two general indexes for evaluating landing adaptability and stability are established based on three typical structured terrains. Multi-objective parameter optimization of a 3T1R ALAM is carried out. Finally, a prototype is developed and validated for its workspace range and landing performance.
查看更多>>摘要：The replacement of spiral bevel gears represents a challenge when the design data is missing and only the physical gears are available. In this case, application of reverse engineering is required to determine the design data and machine-tool settings that would allow the default gears to be replaced and/or improved. This paper proposes a methodology of reverse engineering of spiral bevel gears reconstructed from point clouds. Point clouds of the gear tooth surfaces are obtained from non-contact metrology machines using a 3D laser scanner. Non-uniform rational B-splines surfaces are obtained to fit a set of predefined points of the point cloud. Once the reconstructed tooth surfaces are available, a bound-constrained optimization algorithm is used to derive the finishing machine-tool settings of the gears to produce the closer tooth surfaces to the reconstructed ones. The resulting reconstructed gear drive can be analyzed throughout tooth contact and finite element analyses to evaluate its mechanical performance and improve it if necessary. A numerical example, comprising a given design of a face-milled spiral bevel gear drive and the corresponding manufactured gears, shows the advantages and disadvantages of the proposed procedure to capture the designer's intent and analyze the existing gear drive.
查看更多>>摘要：A Ravigneaux planetary gear set (RPGS) system with an unloaded floating ring gear is studied in this paper. Aiming at investigating the three-dimensional vibration response of the long planet and the dynamic load on the floating ring gear, a flexible-rigid coupling dynamic (FRCD) model is proposed by coupling the condensed substructure of finite element (FE) flexible bodies with rigid dynamic model. Relative positions of different force elements are taken into consideration, as well as time-varying mesh stiffness and gear backlash. Based on this model, the effect of sun gear positions on the dynamic response of the long planet is performed and the mechanism for the vibration of the floating ring gear is revealed. The results show that the bearing force of the long planet varies nearly linearity with sun gear positions, and dynamic loads on the floating ring gear are induced by gear mesh excitations and carrier vibrations, while the former affects impact amplitudes and the latter influences impact frequencies. A further investigation is conducted on the effects of gear backlash and support stiffness, and it is indicated that increasing the support stiffness of the floating ring gear can reduce its dynamic load significantly.
查看更多>>摘要：The development of high-speed motors has stimulated the demand for high-speed reducers. Aiming at the lack of high-speed reducer and the NVH problem of high-speed gear transmission, an asymmetric loading multi-roller planetary traction drive (AL-MPTD) scheme is proposed to fill the gap of traction drive with large speed ratio, zero spin and self-adaptively loading. By comprehensively considering the effects of axis tilt, elastic deformation, rough surface contact and elastohydrodynamic lubrication (EHL), this paper establishes a more refined theoretical analysis model and provides the analysis method under the condition of the non-smooth surface and non-ideal contact. This paper also studies the transmission performance of AL-MPTD from the aspects of traction ability, transmission efficiency and so on. The results obtained by theoretical calculations show that AL-MPTD can be considered to achieve zero-spin transmission in the entire operation range. In addition, the loading mechanism achieves a good self-adaptively loading effect, effectively reducing the sliding of the AL-MPTD and improving its efficiency, with the peak of the global sliding coefficient being only 0.402% and the maximum transmission efficiency of 98.5%.
查看更多>>摘要：Planetary gearboxes (PGs) are prone to gear local faults, such as cracking, pitting, and spalling, because of their difficult working environment. These faults may lead to significant capital losses and catastrophic events. Numerous phenomenological modulation models of vibration signals of PGs have been proposed for diagnosis purposes. However, local fault diagnosis remains extremely challenging due to two aspects: (1) Most vibration modulation models cannot reflect the local fault-induced pulse modulation characteristic. (2) Studies on local fault characteristic frequencies (LFCFs) of gears lack a unified mechanism explanation. To solve these problems, an improved phenomenological vibration model of a gear pair with local fault is first proposed. This model can reflect the pulse modulation characteristic. Then, relative phases between multiple gear pairs in the PG are calculated based on a modified phase model. Based on these, phenomenological vibration models of PGs with/without local faults are established, spectral structures are derived using Fourier series analysis, and LFCFs are deduced for local fault diagnosis. Simulation and experimental studies demonstrate the effectiveness of the proposed models, which exhibit higher descriptive capability than traditional models.
NSTL
Elsevier