查看更多>>摘要：This paper presents a lightweight and low-inertia cable-driven upper-limb exoskeleton powerful enough to meet the requirements for activities of daily living. It presents the mechanical design, kinematic structure,the underlying actuation system, sensors, other electronic components as well as the controller of the exoskeleton. The extensive effect of friction on cable-driven designs, such as the one presented in this paper, requires proper mathematical modelling for controller design. Thus, we propose a current actuator model that describes the relationship between the motor current, velocity, and external load. The model relies on an underlying Stribeck+Coulomb friction representation and an additional parameter that modifies its Coulomb friction representation with an offset to represent adhesion between a cable and sheath. The model has been validated based on experimental data collected with the exoskeleton. The results show that the proposed model better captures the non-linear behaviour of the exoskeleton's actuation system, increasing overall descriptive performance by 15%. However, adding the adhesion offset to extend the relation of static friction, does not improve the model.
查看更多>>摘要：To improve robots’ mobility on flat ground and rough terrain, we designed and implemented a novel spherical robot with a combined rolling and leaping capability. The robot has two individually driven semi-spheres, which generate rolling and turning motions. The robot also has a five-bar linkage with a release/retract mechanism for leaping. The release/retract mechanism only uses one DOF to control and switch the mechanism in three different stages: retracting, maintaining, and releasing. In this paper, the dynamics of the robot in rolling and leaping are analyzed. The robot was empirically built, and its performance was experimentally evaluated. The results confirm that the robot can leap close to 25.4 cm diameter of the sphere, which, to the best of our knowledge, is the best among reported spherical robots. The robot can also leap while rolling over a 14 cm barrier, which is equal to 1.14 times the sphere's radius.
查看更多>>摘要：This paper proposes two optimized designs of an advanced compliant stroke amplification mechanism (CSAM) with completely distributed compliance. The optimization is performed by improving the dimensions of the CSAM based on linear analytical models. The optimized CSAMs possess approximately 5.6% and 7.8% larger displacement amplification ratios than the original one does. The optimization results are verified through finite element simulations, with less than a 2% difference being observed. To analyze the optimized CSAMs rapidly within relatively large motion ranges, nonlinear analytical models of the optimized CSAMs are also obtained, considering the parameters associated with manufacturing errors and external payloads. The concept of reliability is introduced, and the failure modes of the two optimized CSAMs are defined based on kinematics using the nonlinear analytical models. The sensitivity of the failure probability to manufacture errors at different positions is analyzed. The findings show that the failure probability of the CSAMs is more sensitive to parameters associated with the X-direction coordinates of the output stage and the top endpoint.
查看更多>>摘要：The truss deployable antenna mechanism based on tetrahedral unit belongs to spatial multi closed-loop coupled overconstrained mechanism, which has the advantages of high stiffness, strong expansibility and high folding rate. The mechanical and vibration characteristics of a tetrahedral deployable unit and its combined unit mechanism based on 3RR-3URU are studied. Firstly, the idea of equivalent stiffness is applied to the force analysis of the motion process of tetrahedral unit mechanism, and the relationship among motion, actuation stiffness and actuation force is revealed by using Lagrange method and displacement coordination relationship. Secondly, the vibration simulation analysis of the combined unit based on tetrahedral unit is carried out by using ADAMS vibration analysis module, the first 20 modes and natural frequencies are solved. In addition, the harmonic response is analyzed to obtain the sensitive frequency that the mechanism should avoid. Finally, the program modeling and detailed structure design of tetrahedral truss deployable antenna mechanism are investigated. Furthermore, experiments are carried out based on the developed combined unit prototype and one circle deployable mechanism prototype. The research results provide a reference for the structural optimization and engineering application of this kind of deployable antenna mechanism.
查看更多>>摘要：Increasing the working stroke of compliant mechanisms in a limited space has always been an important topic in mechanics. One effective method is to develop a more fundamental design model that considers the multi-physical coupling characteristics of compliant mechanisms and actuators. This paper presents a new method for the integrated design of compliant mechanisms and piezoelectric actuators, which incorporates the projective transformation-based moving morphable components method with the parametric level set method (PMMC-PLS), based on the use of explicit and implicit topology optimization methods to drive the layout evolution of the embedded actuator and host structure, respectively. The extended finite element method (XFEM) is adopted to accurately capture the boundary of the multi-component system, thereby increasing the accuracy of the structural response and sensitivity analysis. To circumvent defacto hinges and thin wall features, a global manufacturability constraint is proposed by applying the minimum length scale control to the host structure and a non-overlap constraint to embedded actuators. Moreover, the output stiffness is considered to enhance the mechanical performance of the mechanism. The effectiveness of the proposed method is verified considering numerical examples.
查看更多>>摘要：Current linkage-driven prosthetic hands still show limitations in aspects such as the thumb design and fingertip sensor. Moreover, linkage-driven prosthetic hands still lack quantitative precision grasp quality. In this study, we developed a novel thumb structure with coupled abduction–adduction and pronation–supination movement in the trapeziometacarpal joint. We also developed a fully integrated fingertip tactile sensor with all components embedded in the distal phalanx designed to facilitate in-hand precision manipulation. Furthermore, we devised a new metric to evaluate the precision grasp quality based on the force conditions during grasp. On the basis of this metric, we optimized the geometry parameters of the thumb and index finger using the Monte Carlo method. The results show that, compared with the anthropomorphic trajectory measured from a human index, the proposed method improves the grasping ability by more than 10%. Finally, we developed a prototype prosthetic hand based on the proposed design methods and demonstrated by experiment that it was able to perform human-like thumb opposition and to pass both precision and power grasp tests.
查看更多>>摘要：This paper proposes a new effective mesh stiffness calculation method for spur and helical gear pairs, which is explicitly formulated by an original FE-analytical slice model for tooth local contact deformation, efficient FE model for gear global deformation and mathematical programming approach for gear contact. The original FE-analytical slice model comprehensively integrates the advantages of FE method, Hertz contact theory and slice approach, which can address the displacement datum and elastic interaction of tooth slices effectively, so that tooth contact deformation is determined accurately. The geometry modeling of tooth slices is established and the pressure configuration in the contact region of each slice is prescribed by Hertz distribution. A specified FE programming is developed to derive the tooth contact flexibility matrix accurately. Thus, the mesh stiffness can be effectively calculated by using the proposed method with the FE-analytical slice model. The local contact deformation of gear tooth and mesh stiffness of gear pairs under ideal and error conditions are simulated. The accuracy and efficiency of the proposed method are validated against the ANSYS benchmark and common existing methods.
查看更多>>摘要：Given their advantages of large workspaces and high payload-to-weight ratios, cable-driven parallel mechanisms have great potential for use in on-site autonomous construction. This paper proposes a configuration containing two cable-suspended robots driven by eight cable pairs (four cable pairs each), which form parallelograms, to perform construction efficiently in terms of time and space. A core issue of this system is the collision problems that occur in dynamic construction processes. The use of the distance between two spatial line segments is proposed to calculate collision detection, and the wrench-feasible workspace is examined to analyze the collision-free buildable workplace. The operation mode of dual cable-suspended robots for construction is discussed herein. Further, the design variables of the dual cable-suspended robot are optimized using multi-objective particle swarm algorithm to ensure a sufficiently large collision-free buildable workspace with suitable scale and payload of the frame of the cable robots for construction.
查看更多>>摘要：The estimation of the losses due to friction of meshing tooth flanks is an important point in the design of gear drives. In addition to other design factors, the efficiency of a gear stage is an important criterion for selecting the type of gear and the number of gear stages in order to achieve a desired gear ratio. This manuscript deals with various approaches with which the friction losses that result from the meshing flanks of a face-gear stage can be estimated. In addition, the influence of the directions of sliding and rolling speed is investigated, which is particularly important for gear stages with axle offset, since the two velocities are not collinear. The calculation method is validated for low speeds by means of experiments on a transmission test bench.
查看更多>>摘要：In the traditional gear dynamic model, the mesh stiffness is obtained under static load. When the mesh stiffness changes greatly with the change of load, the traditional dynamic model is not accurate enough to analyze the gear system. Therefore, this paper proposes a new dynamic model with a more realistic dynamic mesh force based on gear compatibility conditions. The proposed dynamic mesh force model is applicable to the gear system with and without tooth modification and verified by the finite element method. Afterward, the paper compares the differences in the dynamic responses between the proposed model and the traditional model. The results indicate the dynamic responses of the proposed model are generally consistent with those of the traditional model for the standard involute gear system. For the lead crown gear system, compared with the proposed model, the traditional model will lose important nonlinear characteristics in the high-speed area. At most speeds, the amplitudes of vibration and dynamic mesh force of the proposed model are greater than that of the traditional model, especially in the bifurcation, quasi-periodic and chaotic regions.
NSTL
Elsevier