查看更多>>摘要：This paper introduces a design method to realize the transition of variable stiffness from discrete to continuous through contact interaction. Based on this, a Contact-Aided Leaf Hinge (CALH) with passive variable stiffness is proposed, which consists of a flexible segment and a rigid part. As the deformation increases, the flexible segment contacts with the rigid part continuously, resulting in the variation of bending stiffness. The configuration, modeling and deformation process are illustrated in detail. Several examples of conic contact regions are analyzed through the chained pseudo-rigid-body model (CPRBM) and finite element analysis (FEA). Besides, physical prototypes are manufactured and experimental tests are performed to verify the feasibility of the design. Finally, some applications, parasitic motion and coupling effects are discussed. By further designing the dimensions and contact surface, the CALH can satisfy various requirements.
查看更多>>摘要：During a multi-speed transmission development process, the final calibration of the gearshift controller parameters is usually performed on a physical test bench. Engineers typically treat the mapping from the controller parameters to the gearshift quality as a black-box, and use methods rooted in experimental design - a purely statistical approach - to infer the parameter combination that will maximize a chosen gearshift performance indicator. This approach unfortunately requires thousands of gearshift trials, ultimately discouraging the exploration of different control strategies. In this work, we calibrate the feedforward and feedback parameters of a gearshift controller using a model-based reinforcement learning algorithm adapted from pilco. Experimental results show that the method optimizes the controller parameters with few gearshift trials. This approach can accelerate the exploration of gearshift control strategies, which is especially important for the emerging technology of multi-speed transmissions for electric vehicles.
查看更多>>摘要：The aim of the article is to investigate the efficiency of the novel eccentric rolling transmission, which is a simplification of the cycloidal reducer, with parallel but not overlapping shaft axes. In this paper, a kinematic and load distribution analysis are presented with a view to determining the forces and rotational speeds necessary for efficiency calculation. The developed efficiency model involved power losses in rolling bearings, at meshing, as well as churning and windage power losses. For the verification, a transmission prototype with a 10:1 gear ratio and a dedicated test stand were designed and built. The results of the research showed that most substantial power losses occurred in the bearings and were several times greater than the losses associated with friction between the active surfaces of its main components. The transmission efficiency improved with increasing load and decreased with increasing rotational speed, reaching a maximum of 96% at nominal torque. The proposed model allows predicting the efficiency of the transmission at the stage of its design, which can further facilitate the optimization of the transmission parameters considering expected operational conditions.
查看更多>>摘要：This paper presents a class of single degree-of-freedom (DOF) grasping manipulators (GMs) with multi-finger design composed of multiple single-loop mechanisms. A method is proposed to type synthesize single-DOF single-loop mechanisms (SLMs) using the improved atlas method. The conventional atlas method produces redundant mechanisms when the diversity of mechanisms is considered; the proposed method addresses this problem. SLM is split into two sub-chains. Subchain 1 has only one revolute pair, and one kinematic pair of sub-chain 2 is one revolute pair. Using these two revolute pairs, the type synthesis of SLMs is transformed into the type synthesis of the residual kinematic pairs of sub-chain 2. First, the constraint space of sub-chain 1 is analyzed using screw theory, and the constraint space of sub-chain 2 is further determined and classified. Subsequently, according to the classification of constraints, SLMs are further synthesized using the improved atlas method. Finally, this paper introduces the connection methods for typical SLMs and describes the construction of single-DOF GMs with multi-finger design.
查看更多>>摘要：This study provided a design method to determine the basic data and tooth form parameters that includes geometric design, cutter head parameters and additional data of hypoid gear pair. The theoretical calculated model of contact stress for hypoid gear was established by pitch cone and surface durability method. The geometric parameters of hypoid gear and equivalently virtual cylindrical gears parameters were derived. A novel optimization method to prioritizes the cutter head mean radius then optimizes other design variables was proposed. An example shows that the impacts of other parameters were obvious on contact stress except to the number of blade groups, mean dedendum coefficient and tooth thickness factor. In addition, the contact stress reduced by 12.95% and the transmission efficiency only decreased by 0.47% after using optimization method.
查看更多>>摘要：In this work, the kinematics of a symmetrical hexapod parallel manipulator is investigated by means of Denavit-Hartenberg method and differential transformation method. When compared with a general Gough-Stewart platform, the limbs of the parallel manipulator are connected to the mobile and fixed platforms through offset hinges, rather than traditional spherical and universal hinges. Because the offset variable of the hinge axis are introduced by the offset hinge, the kinematics of the parallel manipulator studied becomes more complicated. The forward and inverse displacement analysis are approached by means of the Denavit-Hartenberg method. Then, the velocity and acceleration are analyzed using differential transformation method. The concise expression is obtained and can be easily translated into computer program. The derivation of acceleration analysis of the 6-RR-RP-RR parallel manipulator using the hybrid approach is novel in this research field. Finally, a numerical example is given and the numerical results are verified via co-simulation.
查看更多>>摘要：Terramechanics plays an important role in planetary exploration rovers. Conventional terramechanics models contain approximately eight parameters and several variables. The coupled equations are complex and computationally expensive. The wheel-terrain interaction data under various slip ratios are required to identify the parameters. However, there is no guarantee that the desired slip states will be achieved, when a rover is exploring. Moreover, high accurate measurement of the slip ratios is difficult. In this study, a novel model for calculating the maximum stresses of a wheel is proposed, which satisfies a modified Hooke's law. Two minimized models for estimating the interaction forces are then derived. The first minimal model contains four parameters and two variables, and the estimation errors are mostly within 10%. By simplifying further, a second minimalist model, containing two parameters and one variable is obtained. Finally, by introducing an additional parameter, which can be identified with the data obtained under different vertical loads, the proposed models extended to adapt to various loads. The results from single-wheel experiments demonstrate the high efficiency and accuracy of the proposed models.
查看更多>>摘要：As one of the main error sources, the geometric errors are compensated in this work for the accurate worm grinding of spur face gears. The previous methods of the geometric error compensation are usually applied to the machining with rotary cutters, of which the error of cutter rotation angle is not compensated since it does not affect the machining result. These methods are inappropriate to the worm grinding of face gears, because the worm is a non-rotary cutter and the machining result is sensitive to the error of cutter rotation angle. In this work, an innovative geometric error compensation method is proposed to the machining with non-rotary cutters based on two main points. First, the cutter rotation angle is considered to both the modeling and compensation of the geometric errors. Second, the instantaneous ideal contact point, which is calculated according to the generation process of the worm grinding of face gears, is chosen as the reference point to the compensation algorithm rather than the cutter tip point used in the previous method. The proposed method is validated by the example with both the theoretical calculation and practical machining.
查看更多>>摘要：In addition to radial force, deep groove ball bearings inevitably bear a certain degree of axial force and overturning torque under actual working conditions. Excessive axial force and overturning torque may make part of balls exceeding the rib of the raceway and accelerate the damage of the bearing. Therefore, a method for calculating the axial and overturning ultimate load-bearing capacities of deep groove ball bearings under combined loads and arbitrary rotation speed based on the quasi-static model is proposed. In the process of solving the quasi-static model, a Newton-Raphson method based on the analytical Jacobian matrix is adopted, which significantly reduces the difficulty of selecting the initial values, and the sensitivity of initial values is analyzed. Compared with the traditional method, the accuracy of the proposed calculation method of ultimate load-bearing capacities is verified. In addition, the effects of different factors such as radial force, bearing geometric parameters (radial clearance, raceway curvature, and rib height), and rotation speed on the ultimate load-bearing capacities are discussed. The results show that the radial force and bearing geometric parameters significantly change the ultimate load-bearing capacities. However, the effect of rotation speed is weak.
查看更多>>摘要：The design of a gear skiving cutter is particularly concerned with the interference problem between cutter flank and tooth gap. In this study, we propose an interference-based technique (IBT) to help with the cutter flank design by calculating the critical interference surface, which acts as the criterion surface for cutter flank interference check and provides the guidance to the design parameter determination for an interference-free cutter flank. By applying multiple radial infeed strategy, this study shows that the interference-check for cutter flank in skiving rough or semi pass is necessary even it can obtain interference-free in the finishing pass. Specifically, the interferences primarily occur at the recess flank of gear because of the decreasing local relief angle during a single-cut. The numerical results clearly reveal the interference moments that help provide a comprehensive understanding of the interactive between cutter and tooth gap. Because the zero-level of the critical interference surface equals to the cutting edge, this method can also be used for cutting-edge profile generation based on the given tooth gap. Case studies are presented for the clarification on interference condition, interference-free flank design process and cutting-edge profile design based on the non-standard tooth gap profile.
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Elsevier