查看更多>>摘要：This paper provides an insight into the efficiency and accuracy of a multibody approach to model gear transmission error. The multibody model is based on an augmented Lagrangian contact formulation considering a surface-to-surface contact detection. The case of spur and helical gears transmitting power between parallel shafts is considered. The static transmission error is computed without any assumptions about the contact lines positions and orientations. Tooth and wheel body flexibility and tooth profile deviations are taken into account. The main objective of this study is to evaluate the efficiency and possibilities of the proposed methodology. To this end, the static transmission error is benchmarked against the results obtained from a classical approach which is based on the computation of the equation describing the static equilibrium of the gear pair for a set of successive positions of the driving wheel.
查看更多>>摘要：This paper proposes an approach to designing rigid origami flashers that can be deployed onto curved-surface configurations. The method of designing planar origami flashers that can be wrapped around regular polygonal central hubs is presented. Based on the principle of parallel projection, planar origami flashers are projected onto target spherical surfaces to obtain the vertices on the boundary creases between sections of adjacent origami flashers. The geometric relationships of thin-panel curved origami flashers are established in terms of foldability, and other vertices in each section are calculated using numerical methods. Flexible and elastic hinges modify the thin-panel curved origami flashers into thick-panel rigid flashers. The thick rigid panels maintain the shape of flashers, and the flexible creases treated using thicknessaccommodating methodologies are used to maintain the foldability of the thick panels. Additionally, we analysed the parameters that affect the accuracy of the surface fitting. The feasibility of the proposed approach is verified using numerical simulations and physical prototypes. The novel designing of deployable curved-surface rigid origami flashers facilitates their potential applicability in solid surface antennas, surface reflectors, and other space engineering applications.
查看更多>>摘要：A tape spring is a thin-walled open cylindrical structure with a natural transverse curvature. The localized folds in the tape spring serve as revolute joints, and the unfolded straight segments serve as links. If an external torque is imposed on a fold, it can slide along the tape spring. Inspired by this, two novel deployable closed-loop tape-spring manipulators with mobile drive components on the folds are proposed. The first one comprises a folded tape spring and two drive components in a V shape. The buckling stability space and the stiffness of the mechanism are investigated, and the boundary equations of the stability space are derived. The deviation angles of the orientation of the moving platform are analyzed. Besides, an improved W-shaped deployable manipulator comprising two V-shaped mechanisms is developed to solve the problem that is a small stochastic deviation angle of the attitude of the platform. The pure translational motion of the manipulator is produced through employing two master motors and one slave motor. Finally, two prototypes are manufactured and subjected to experiments to validate the presented design and analysis.
查看更多>>摘要：Nowadays, profile shift is one of the most powerful techniques to achieve high-performance spur gear transmission system. Although this technique has been widely used in industry, its influence on time-varying meshing stiffness (TVMS) and dynamic characteristics is still unclear. This paper presents a novel analytical model of TVMS for profile-shifted spur gears. The modification coefficient and transition curve revise the proposed model. Afterward, numerical simulations are carried out to analyze individual and compound shifts based on a six-degree of freedom gear model. For individual shifts, the positive shift can decrease the gear tooth's stiffness and TVMS so that it causes stronger vibrations in the gear system. On the contrary, the negative shift can improve the gear tooth's stiffness and TVMS, thereby mitigating the gear system's vibration. For compound shift, S0-gearing poses a slight impact on TVMS, but an unneglectable effect on dynamic characteristics. Besides, the S-gearing with the positive compound shift can decrease TVMS and increase vibration. In contrast, the S-gearing with the negative compound shift leads to TVMS rising and significantly reducing vibration. The insightful findings derived from the study can help engineers and manufacturers better understand the operation performance and dynamic features of profile-shifted spur gears.
查看更多>>摘要：This paper addresses the robust control problem of mechanical systems with hybrid dynamics in port-Hamiltonian form. It is assumed that only the position states are measurable, and time delay and saturation constraint affect the control signal. An extended state observer is designed after a coordinate transformation. The effect of the time delay in the control signal is neutralized by applying Pade approximant and augmenting the system states. An assistant system with faster convergence is developed to handle actuators saturation. Fractional-order sliding mode controller acts as a centralized controller and compensates for the undesired effects of unknown external disturbance and parameter uncertainties using the observer estimation results. Stability analysis shows that the closed-loop system states, such as the observer tracking error, and the position/velocity tracking errors, are finite-time stable. Simulation studies on a two ball-playing juggler robot with three degrees of freedom validate the theoretical results' effectiveness.
查看更多>>摘要：In this paper, based on LuGre friction model, a compensation method by combining of model reference adaptive control and periodic adaptive learning control (MRAC-PALC) is proposed to eliminate the adverse influence of nonlinear friction disturbance on tracking performance in permanent magnet synchronous motor (PMSM) servo systems under periodic task conditions. Specifically, the controller consists of a linear algorithm with PD, feedforward and velocity feedback components and a nonlinear friction compensator which is divided into two parts as follows: in the first time period, an MRAC algorithm is developed to ensure the boundedness of tracking errors; from the second time period, a PALC compensation algorithm, which learns from past information and updates the controller parameters in real time, is deployed to accurately capture the friction dynamics and guarantee the tracking performance. The stability of the proposed MRAC-PALC approach is guaranteed through Lyapunov stability theorem. Some comparative simulations and experiments are conducted to illustrate the superiority of the proposed MRAC-PALC strategy.
查看更多>>摘要：Grasping is a complex human activity performed with readiness through a complicated mechanical system as an end effector, i.e. the human hand. Here, we apply a direct transcription method of discrete mechanics and optimal control with constraints (DMOCC) to reproduce human-level grasping of an object with a three-dimensional model of the hand, actuated through joint control torques. The equations of motions describing the hand dynamics are derived from a discrete variational principle based on a discrete action functional, which gives the time integrator structure-preserving properties. The grasping action is achieved through a series of constraints, which generate a hybrid dynamical system with a given switching sequence and unknown switching times. To determine a favourable trajectory for grasping action, we solve an optimal control problem (OCP) with different physiological objectives subject to discrete Euler-Lagrange equations, boundary conditions and path constraints.
查看更多>>摘要：The paper tackles conceptual solutions and theoretical and experimental analysis methods to prototype a robotic system used in surgery. The system put forward consists of an actuation unit, a command and control unit, and a flexible unit. The flexible unit displays a complex structure consisting of rigid bodies (vertebrae) and deformable bodies (drive wires). The present research study was carried out during three stages: establishing the mathematical models according to the analysis of the flexible unit movement, the development of virtual prototyping of the flexible unit, and the experimental study of the developed prototype. The dynamic analysis of the flexible unit is based on the theory of multi-body systems; hence major challenge was to model the rigid-body and the deformable-body contact in reliance on the theory developed by Craig&Bampton. Nevertheless, the theoretical, virtual, and experimental results reported following our comparative analysis highly recommend the use of the prototype obtained in minimally invasive explorations.
查看更多>>摘要：This study aims at revealing the coupling vibration mechanism of RSDB system. First, a comprehensive coupling dynamic model of RSDB system including the shaft bending, shaft torsion, blade bending, and blade radial deformation is formulated based on continuum beam theory and Lagrange equation. The validity of the proposed dynamic model is verified through a comparison with FEM and experimental results. Second, the general coupling mechanism of RSDB system is theoretically interpreted based on the proposed analytical coupling vibration model, which indicates that the blade vibration and shaft vibration, especially the shaft torsion vibration and blade bending vibration, may affects each other significantly. At last, the steadystate coupling vibration responses and the effects of structure parameters on the coupling vibration of RSDB system are comparatively investigated through numerical investigations. The comparative results suggest that the blade setting angle, blade-blade coupling stiffness, and the disc location on shaft will greatly affect the coupling vibrations. It worth more attention that the general coupling vibration mechanism obtained by analytical analysis and the results obtained by numerical study can be cross-verified by each other.
查看更多>>摘要：Lower extremity exoskeletons are often used as walking assistance rehabilitation robots for paralyzed patients. However, due to the requirement of crutches or other devices to maintain balance, the under-actuated exoskeleton has limited applicability. This paper aims to design a novel mechanism for the self-balancing lower extremity exoskeleton, which structurally consistent with the human anatomy and fully actuated with 12 DOFs. In this study, based on the humancentered design principles, a bio-inspired exoskeleton mechanism synthesis methodology is presented. The novel serial-parallel hybrid mechanism is designed based on a 3-DOF RCM hip mechanism, 1-DOF parallelogram-linkage knee mechanism, and 2-DOF decoupled parallel ankle mechanism. To describe the forward and inverse kinematics of the mechanism, the closed-form solutions by the D-H method and geometric method are obtained, respectively. In addition, to analyze the exoskeleton workspace, the reachable workspace equations in the double foot support and single foot support phases are established. The numerical simulation and experimental results show the kinematics model validity and self-balancing walking ability, which illustrate the feasibility of the proposed exoskeleton mechanism.
NSTL
Elsevier