查看更多>>摘要：The two-limb(1) parallel mechanisms (PMs) can have the advantages, in terms of avoidance of mechanical collision, simple architecture, rapid configuration transformation and large work -space volume. This paper consists of two major contents. The first aspect pertains to the design of a class of two-limb PMs with two translations and one rotation (2T1R), where a family of PMs featuring two translations actuated by sliding units are proposed, with decoupled position and orientation as well as symbolic forward position solution, without parasitic motions. The second aspect is to analyze the influence of the arrangement of limbs onto the kinematic, dynamic and stiffness performance of the PMs. Using the kinematic modeling method based on topological characteristics, the unified symbolic forward and inverse position solutions of the PMs are derived, together with the workspace, rotational capacity and singularity. Finally, a comparative study regarding the kinematics, dynamics and stiffness of the two PMs is carried out to find the optimal PM configuration. This paper presents a systematic analysis for the synthesis, optimal design and performance evaluation of two-limb parallel mechanisms.
查看更多>>摘要：Hybrid simulation is used to obtain the dynamic response of a system whose components consist of physical and numerical substructures. The coupling of these substructures is achieved by actuation systems, which are commanded in closed-loop control setting. To ensure high fidelity of such hybrid simulations, performing them in real-time is necessary. However, real-time hybrid simulation poses challenges since the inherent dynamics of the actuation system introduce time delays, thus modifying the dynamic response of the investigated system. Therefore, a tracking controller is required to adequately compensate for such time delays. In this study, a novel tracking controller is proposed for dynamics compensation in real-time hybrid simulations. It is based on adaptive model predictive control, a linear time-varying Kalman filter, and a real-time model identification algorithm. Within the latter, auto-regressive exogenous polynomial models are identified in real-time to estimate the changing plant dynamics. A parametric virtual case study, encompassing a virtual motorcycle, is used to validate the performance and robustness of the proposed controller. Results demonstrate the effectiveness of the proposed controller for real-time hybrid simulations.
查看更多>>摘要：Compared with active prostheses, passive compliant ankle prostheses offer the advantages of reduced energy consumption, a lighter weight, a simple structure, and lower costs. However, although various commercial products are available, these designs do not provide adequate degrees of freedom (DOFs) for movement. This paper presents a compliant passive ankle-foot prosthesis (CPAF) capable of 2-DOF rotation during locomotion. The CPAF uses a 2-DOF parallel mechanism to support the bodyweight and offer limited rotation during movement, and it incorporates a compliant component to facilitate and generate torque to conform to uneven terrains. The kinematics of the parallel mechanism, including the workspace and singularities, were investigated. Then, a prototype was developed, and the performance evaluations showed that sufficient torque could be generated with an appropriate range of motion for the ankle. Concequently, clinical validations were conducted: the dynamic analysis indicated that the CPAF provided good gait movement and generated sufficient ankle torque during level-ground walking, and the metabolic tests demonstrated that the configuration-4 of the compliant component could achieve the best efficiency during walking.
查看更多>>摘要：A method for topological modification of gear flanks in continuous generating grinding based on contact trace evaluated genetic algorithm (CTEGA) has been proposed to solve the problem of flank twist caused by lead modifications of gear flanks. Firstly, according to the theory of conjugate surface, a mathematical model calculating the generating surfaces of worm wheel as well as representing the wheel as two-parametric form spiral surface has been established. Secondly, by representing the radial, axial, and tangential feed of worm wheel in forms of polynomials of the axial feed of worm wheel, a mathematical model of generating gear grinding process has been established where the axis linkage relationship in CNC machine is intentionally changed for topological modification of target tooth surface. Finally, the validity of the proposed topological modification method was numerically demonstrated using a helical gear made by the CNC continuous generating grinding machine. The method proposed in this paper can realize the topological modification of gear flanks by only adjusting motions of numerically controlled axes in the grinding process without adopting a specific dressing of the grinding wheel.
查看更多>>摘要：This study aims to build a unified stiffness model of three 4-degree of freedom (DOF) overconstrained parallel manipulators (PMs), which comprise a novel PM with four constrained forces, a PM with four constrained torques, as well as a PM with two constrained forces and two constrained torques. First, with the geometrical conditions as a starting point, a research is discussed on the constrained wrenches and kinematics analysis of the three PMs. Second, oriented to different constrained wrench forms in the three over-constrained PMs, the wrenches directly causing deformations are determined based on the deformation and force decomposition method, and the correlations between the wrenches and their corresponding deformations are explored according to the material mechanics. Third, all of the above analysis, combined with the virtual work principle of deformed body and the static balance principle, a unified stiffness model which is suitable for the three 4-DOF over-constrained PM with various constrained wrench forms is established. Lastly, an integrated finite element (FE) simulation model of the three PMs is built to verify the correctness of the analytic stiffness model. This study proposes a general and straightforward approach to solve the stiffness problem of 4-DOF over-constrained PMs with various constrained wrench forms.
查看更多>>摘要：High-strength fiber ropes have a number of advantages over steel ropes, therefore they currently enjoy great research interest in conjunction with rope winches. However, what is lacking in the art are suitable drives, since concepts for steel ropes cannot be easily transferred to high-strength fiber ropes. A promising innovative principle is the belt wrap capstan, although adequate and validated models for predicting optimal rope force with the lowest possible belt force are still missing. This paper aspires to contribute towards closing this gap by presenting a validated model of a double layered belt wrap capstan First, a general law of friction is considered. Then, special focus is given to power law friction. This law of friction implies the zero force phenomenon which is also discussed.
查看更多>>摘要：Considering both spatial crack fault and complex foundation structure, the dynamic finite element model and multi-body dynamic model are established simultaneously to analyze the dynamic characteristics of gear-rotor systems. Firstly, the extended finite element method is used to simulate the three-dimensional crack propagation paths of spur gears under partial load. Then, based on the proposed three-dimensional loaded tooth contact analysis (3D-LTCA) method, the mesh stiffness of spur gears with the spatial crack and complex foundation is calculated and the results are verified by the finite element method. Finally, the dynamic finite element model and multi-body dynamic model of the gear-rotor system are established. The dynamic responses under different crack levels are analyzed. The advantages and disadvantages of these two dynamic models are evaluated. According to the above analysis, it is indicated that the 3D-LTCA can accurately consider the influence of complex foundation and spatial crack on mesh stiffness. The finite element model and multi-body dynamic model can effectively analyze the influence of crack fault and foundation structure on dynamic responses.
查看更多>>摘要：Since the twenty-first century, research on tensegrity structures has been extended from the field of architecture to robotics, considering their promising environmental adaptability and safe human-machine interactivity. Tensegrity robots usually utilize strut-cable coupled dynamics to achieve crawling or rolling movement. Whereas, when it comes to a simple structure, e.g., the Four-Prism Tensegrity Robot (FPTR), its rolling locomotion has been challenging to realize. Therefore, this paper presents a design method utilizing the structural deformation of the FPTR to achieve steerable rolling locomotion. To investigate the parameter-selection process and the possible deformation of the FPTR, kinematic, static, and dynamic models are built and relevant simulations are implemented. Then this paper proposes four basic rolling steps of the FPTR and one specific control pattern allowing for going straight and turning left/right. A robotic prototype is further developed to validate the reliability of the model and the feasibility of the FPTR's steerable rolling gait. It eventually proves that even the prismatic single-unit tensegrity robot is qualified to make use of its structural deformation to achieve controllable and steerable rolling locomotion.
Gomez-Jauregui, ValentinGutierrez-Garcia, AndresGonzalez-Redondo, Francisco A.Iglesias, Miguel...
14页
查看更多>>摘要：Leonardo Torres Quevedo worked intensively in analogue calculating machines during the last years of the 19th century. The algebraic calculators were calculating machines in which numbers are represented by quantities of a given physical magnitude(s). The physical result is a magnitude of a physical quantity whose measurement in the coherent unit is the result of the algebraic equation. This article shows the three-dimensional (3D) modelling, virtual reconstruction and simulation of the first mechanical calculating machine for solving second-degree equations with complex coefficients, to prove that the functionality was correct and the machine could be built. Sketches of said machine provide enough information on the shape and mechanisms of the machine. By means of the simulation, it has been possible to prove its operation and feasibility of construction so that it is possible to replicate it as a real physical model. The mechanical calculator for second-degree equations with complex coefficients constituted a major milestone in the technological development of the time and helped to originate and improve the design of other algebraic calculators like the machine for solving eighth-degree equations.
查看更多>>摘要：This paper takes the motion units of the series-parallel machine tool (SPMT) as the basic research objects. Combined with the meta-action theory, the FMA-MBS structure model is proposed to describe the spatial structure relationships and motion transfer relationships of SPMT. Based on the simplified model, the kinematics characteristics of the machine tool are gradually researched from four layers: joint layer, limb layer, subsystem layer, and the whole machine. According to the twist system of limbs and moving platform, the parallel motion system can be simplified into a virtual motion chain with specific constraints. Then, the kinematics model of SPMT is constructed in twist exponential form. By introducing two virtual degrees of freedom (DOFs), the unified expressions of active and passive joint errors are obtained. All motion systems error models are derived based on three basic error terms of the meta-action layer. Based on the error mapping relationships, the precision of the machine tool can be calculated and evaluated. In order to illustrate the applicability and effectiveness of the proposed method, a sample library of common SPMTs and a case study of a 5-axis series-parallel machining center are provided.
NSTL
Elsevier