查看更多>>摘要：The present work is devoted to analyze the kinematics of twin lip vanes adopted in balanced vane pumps. The work provides the analytical description of the vane motion according to its geometrical parameters and the cam ring profile. Attention is given to the duality of the solution, an intrinsic property of twin lip vanes that may be considered as followers with two symmetrical half-circular tips. Based on the linkage kinematics, the analytical dissertation is further deepened to define the geometrical admissibility of the vane design and its mathematical domain. In order to evaluate the proposed approach, an extended parametric study is performed on the basis of the Buckingham theorem, detailing how the twin lip configuration affects the machine kinematics. Additional calculations are proposed to determine the vane design configurations that satisfy the fundamental law of cam design and to highlight how this requirement dramatically reduces the subset of available choices in presence of cam ring with a precompression profile. Finally, design guidelines are proposed in order to overcome these drawbacks and expand the admissibility domain.
查看更多>>摘要：Current research concerning passive locomotion ability primarily focuses on open-chain legged platforms to enhance energy efficiency and walking stability. However, closed-chain legged platform with single degree of freedom (DOF) mechanism has the advantages of rotational driving property, control simplicity and payload capability. To further reduce dependence on ground friction and improve walking efficiency, a closed-chain passive-locomotion legged platform (CPLP) is proposed. First, the leg mechanism is analysed based on kinematic analysis, and three different types of leg groups are proposed as mathematical examples, after which the dimensional parameters are optimized. Then, walking period, walking critical conditions on horizontal ground are analysed based on zero moment point (ZMP) principle to quantitatively analyze the optimal leg group layout. Moreover, the critical conditions of passive locomotion ability are analysed and then verified by dynamic simulations. Finally, a series of experiments are conducted to verify the performance of the CPLP. This study of passive locomotion ability contributes to a high-efficiency thrust-propelled method of closed-chain legged platform.
查看更多>>摘要：The large stroke is usually realized by lowering stiffness along the degrees of freedom, which usually leads to a decrease of stiffness along the degrees of constraint. A high stiffness ratio is crucial for reducing the deflections induced by disturbances such as eccentric force and the gravity of the load. Besides, the fatigue life of these mechanisms will be shortened due to the large stress caused by the large deflection. This paper proposed a new guiding mechanism using orthogonally oriented flexures to improve the stiffness along the degrees of constraint and reduce stress concentration. The energy method is utilized to obtain the kinetostatic model of the guiding mechanism by taking the nonlinear deflection into account, based on which the mechanism is optimized by simultaneously considering the topology and size. As compared to the performance of traditional design obtained through the same optimization objective and constraints, the optimal design effectively improves the stiffness along the degrees of constraint, whose accuracy is also validated by the finite element analysis results. Experimental results show that the proposed mechanism increases the stiffness ratio Kaz/Kx by 3.54 times compared to the traditional mechanism.
查看更多>>摘要：Comprehensive modification refers to a modification method that simultaneously performs lead crown modification and tooth profile modification, which is widely used in precision gear manufacturing. However, there are few time-varying meshing stiffness (TVMS) models of spur gears with comprehensive modification. Based on the actual manufacturing methods and slice theory, an improved analytical model (IAM) for calculating the TVMS considering the coupling modification is established. The model does not require to use the finite element method (FEM) to determine the correlation coefficients. The IAM is compared with the published models and verified by the FEM. The results show that the IAM has higher accuracy and efficiency in the calculation of lead crown modification, tooth profile modification and comprehensive modification. The gear bearing capacity of machining method 2 is better than that of method 1. It is useful to improve the calculation accuracy to choose the number of slices reasonably according to the modification amount.
查看更多>>摘要：The complex structures, small workspaces and complex control systems of traditional parallel mechanisms are the largest hurdles to using them as leg mechanisms in walking robots. This paper synthesizes a family of novel 3-degrees-of-freedom (DOF) parallel leg mechanisms (PLMs) that have the potential to avoid these drawbacks. The novel parallel leg mechanism consists of a 3-DOF drive system (DS) and a walking mechanism, which can be designed modularly. Using the motion characteristics of the 3-DOF drive system, a simplified method for constructing 3-DOF parallel leg mechanisms is presented. Then, satisfactory 2-DOF walking mechanisms are synthesized based on Lie group theory. A family of novel 3-DOF parallel leg mechanisms in which the workspace of the foot-endpoint is a three-dimensional volume is constructed using the 3-DOF drive systems and 2-DOF walking mechanisms. Finally, the performance of the novel parallel leg mechanism is analysed, revealing the potential merits of this novel parallel leg mechanism in walking robots.
查看更多>>摘要：In this paper a finite element (FE) model for the analysis of the contact stresses in flat belt transmissions was developed, with the intent of comparing the numerical with the theoretical results of the brush model and those of the classical Euler-Grashof (creep) model. The FE model consists of two pulleys and a belt composed of a thin layer of inextensible reinforcement fibers and a rubber matrix in contact with the pulley. The analysis is performed incrementally, under quasi-static conditions; as a consequence, any inertia effect is not accounted for. In the paper, the capabilities of the analyzed models are discussed. The brush model is generally better correlated with the FE results, both in terms of tangential stress along the winding arc and belt tension and it is capable of estimating the power losses due to friction with low computational and time effort. In addition, the effect of the belt thickness on the tangential stress at the entrance and the exit from the pulley, which are generally neglected by simplified model, are highlighted by the FE analysis.
NSTL
Elsevier