查看更多>>摘要：A low computational cost and generalized ray-based interference-free workspace (IFW) analysis method for arbitrary types of CDPRs is proposed in this paper. This work extends the existing ray-based method (RBM) properties to solve the ray-based workspace under cable-cable and cable-obstacle interference-free conditions. The proposed method covers a broader range of obstacles defined by polynomial surfaces than existing methods. After determining the IFW, the ray-based workspace under different workspace conditions can be combined. Path planning can be performed similarly to the existing point-wise approach but with guaranteed connectivity inside the available workspace. Meanwhile, the proposed approach can simultaneously handle different CDPRs with translation and orientation.
查看更多>>摘要：The paper focuses on the stiffness analysis of multi-link serial planar manipulators, which may demonstrate nonlinear stiffness behavior under the compressive loading. Two important cases are considered, where the manipulator has either a straight or non-straight initial configuration. It was proved that in the first case the loading may cause the buckling if it exceeds some critical value, and the manipulator suddenly changes its straight shape and stiffness properties. For computing this critical force, a general eigenvalue-based technique was proposed that can be applied to any multi-link serial manipulator. For the second case dealing with non-straight initial configurations, a universal energy-based technique was applied that allowed to detect quasi buckling phenomenon when it is observed very fast but not instant change of the manipulator shape and its stiffness coefficient under the loading. These results are illustrated by numerous examples of non-linear stiffness behavior of three-and four-link manipulators that are subjected to compressive force.
查看更多>>摘要：The dynamic balancing of flexible mechanisms, that is, the reduction or elimination of shaking forces and shaking moments on the support structure, is considered. Two approaches are pursued: one uses similarity and the other modal balancing. A single rotating link can be balanced by a properly scaled countermass, for which balancing criteria are given. If all balancing conditions are satisfied, shaking force balance can even be achieved if geometric non-linearities are taken into account. This single link can be extended to a translator. Owing to the unscaled pitch of the translator and the asymmetric driving motor, no perfect shaking force balance is achieved, but the results can be considered satisfactory. Then, the dynamic balancing of a four-bar mechanism with a flexible coupler by means of modal balancing is shown. If the coupler is supported at the nodes of the first free vibration mode, this mode can be suppressed in the shaking force and shaking moment response. By supporting the coupler at four points with two whippletree mechanisms, the contribution of the first three symmetric vibration modes can be significantly reduced.
查看更多>>摘要：This paper introduces the design, analysis, and control of a novel 5 degrees of freedom (DOFs) redundantly actuated parallel mechanism with a large tilting capacity. Firstly, a novel parallel mechanism consisting of four prismatic-universal-spherical (PUS) peripheral limbs and one special central prismatic-prismatic-prismatic-universal (PPPU) limb (4PUS-PPPU) is proposed. Secondary, analytical solution for the inverse kinematics of the proposed 4PUS-PPPU parallel mechanism is solved, singularity reduction by using a redundantly actuated central limb is analyzed, the workspace is also analyzed to show the perfect tilting capability of the proposed mechanism. Thirdly, computed-torque synchronization control is constructed to obtain the desired torque for each actuator when tracking a given trajectory. Fourthly, the adaptive hybrid position/force control strategy which is suitable for the redundantly actuated parallel mechanism is proposed to effectively adjust the internal force of the mechanism. Finally, a physical prototype is fabricated, the titling capacity and the effectiveness of the adaptive hybrid position/force control strategy are verified, polishing machining is employed as an example to demonstrate the performance of the proposed 4PUS-PPPU parallel mechanism.
查看更多>>摘要：A systematical procedure of model order reduction for the thermo-mechanical coupling flexible multibody system (FMS) is proposed. The displacement and temperature field are discretized by unified element mesh based on the absolute nodal coordinate formulation (ANCF). Since the expression of the elastic forces is highly nonlinear and the tangential stiffness matrix of ANCF is time varying, the Taylor expansion is used to linearized the dynamic and heat transfer equations to obtain constant tangential stiffness matrix. The thermo-mechanical coupling system is divided into several substructures and the free-interface component mode synthesis method is used at the interface. The modal truncation for the dynamic and thermal coordinates are performed to reduce the system degrees of freedom (DOF). Therefore, the computational efficiency is greatly improved. The system thermo-mechanical equations are reunited and the solving scheme is given. Numerical results show that the proposed method can significantly improve the simulation effi-ciency without losing accuracy.
查看更多>>摘要：This work presents a three-dimensional, variable viscosity, thermo-hydrodynamic model of multi lobed journal bearings, capable to estimate the pressure and temperature distributions of the lubricant flowing between a rotating shaft and the partial arcs composing the multi-lobed bearing configuration, that must support the external applied load. The thermal model estimates the lubricant temperature increase and its effect on the pressure distribution, the bearing hydrodynamic forces and its equivalent stiffness and damping coefficients. Estimation of the temperature increase requires numerical solution of the energy equation, which depends on the assumed thermal boundary conditions. Consequently, the model must take into account the shaft and bush surfaces either isothermal or adiabatic. This work investigates the effect of such cases on the predictions of the pressure, temperature, locus, stiffness and damping coefficients on two and three lobed bearings. It shows that if both surfaces are isothermal, the lubricant temperature increase is smaller. If both surfaces are adiabatic, temperature increase is higher. The effect of lobe preload is also investigated, showing that the bearing coefficients increase with preload.
查看更多>>摘要：On-demand stiffening methods are receiving increasing attention from the soft robotics community, due to the need of both flexibility and stiffness in many applications. Among the various methods, jamming-based techniques became very popular thanks to features such as fast and reversible transition between flexible and rigid states and easy fabrication. However, an analytical model of these structure, taking into account the nonlinearities involved in the change in stiffness, is a challenging task. In this effort, we propose an analytical model for predicting the change in the bending stiffness of a multi-layer jamming structure. We then compare our model with finite elements simulations, showing a very good agreement. The proposed model captures the intrinsic mechanics of these systems and provides a powerful tool for properly design their response to meet the requirement needed for a specific application.
查看更多>>摘要：This paper presents a novel three-limb deployable mechanism (TLDM) using a set of metamorphic mechanism modules, which has potential applications in providing support to the large curved surface deployable membrane structures. The deployable mechanism consists of three modular limbs, and each limb is composed of two types of metamorphic mechanism modules; one is for supporting the curved-surface deployable membrane structure, the other that inspired by thick panel origami is used for the connection of basic supporting modules and curvature adjustment of membrane structure. Both the basic supporting module and connection module are metamorphic mechanisms with mobility bifurcation, which makes the TLDM transform from a compact folded configuration to the deployed configuration. The design parameters that enable the mechanism to have a large deploy/fold ratio and high curved-surface fitness are analyzed. A physical prototype is also fabricated to verify the feasibility of the proposed mechanism.
Zschippang, H. AndreasWeikert, SaschaWegener, Konrad
21页
查看更多>>摘要：Gear shaping is the most important process for manufacturing internal gears. Even if this method is also suitable for the production of spur gears, these can be produced more effectively using hobbing. Gear shaping is also interesting for manufacturing of face-gears. Since the shaper cutter is quite simple compared to a hob and the tool costs are therefore relatively low, this method is particularly suitable for small series production. This manuscript deals with the simulation of gear shaping of face-gears with the aim of determining suitable process parameters such as radial and rotary infeed and thus achieving a stable manufacturing process as fast as possible and with low reject rate. The cutting forces are determined on the basis of the theoretical uncut chip thickness, whereby the tool deflection can be calculated using these, provided that the stiffness of the tool, machine tool and component holder is known. In addition, the tool wear can be estimated using a suitable wear model. Experimentally determined cutting forces during the shaping of a face-gear are used to validate the simulation model.
查看更多>>摘要：Due to the structural complexity of planetary gearbox, it is difficult to extract the fault information in the vibration signal of planetary gearbox, which seriously affects the accuracy of fault diagnosis. Although the existing fault diagnosis methods, such as local characteristic-scale decomposition (LCD) and ensemble empirical mode decomposition (EEMD), are widely used in the field of fault diagnosis, they are difficult to decompose complex signals effectively. Therefore, a new signal processing method, called cyclic symplectic component decomposition (CSCD) based on the Toeplitz matrix and the cyclic matrix, is proposed in this paper. In CSCD, to obtain the closed-loop solutions, each row is the right cyclic shift of the previous row, so as to avoid information leakage. Meanwhile, the combination of sample covariance and symplectic geometry similarity transformation is constructed to further protect the status information and weaken the influence of noise. In addition, the reconstruction of the same mode is completed by using the extreme difference similarity (EDS), which can realize the adaptive decomposition of the signal. The research results of simulation signal and actual planetary gearbox fault signal show that the proposed CSCD method has superior decomposition performance.
NSTL
Elsevier