查看更多>>摘要：Foot and ankle deformity remains a common presenting complaint in orthopedic surgery. External fixator is a key medical device to assist gradual correction. Its configuration selection has a significant influence on correction results. Among two external fixators currently used in clinic, conventional Ilizarov external fixator (IEF) has high use difficulty and low accuracy, whereas the single configuration of later hexapod external fixator (HEF) leads to inadequate adaptation to diverse deformity types in foot and ankle. To solve the above problems, this paper presents a novel parallel distraction apparatus (PDA). First, corrective degree-of-freedom (c-DOF) is defined to determine expected posture transformation of external fixator required by corrective manipulation. By summarizing and classifying c-DOF, predominant foot and ankle deformities with fewer correction requirements are divided into six types. Subsequently, six lower-mobility parallel mechanisms are introduced as the configurations of external fixators via the c-DOF based configuration synthesis approach. After performing reconfigurable structural design, PDA can respectively form six types of parallel external fixators for six deformity types. Finally, clinical case simulations are provided to verify the application potential and advantages of PDA.
查看更多>>摘要：Compared with other gear transmissions travelling along meshing line, the motion of crown gear coupling is much more complex, which makes more difficult for its tooth surface wear simulation. To reduce the computational costs associated with the wear simulation of crown gear coupling with misalignment angle, a quick multi-step discretization and parallelization wear simulation model is proposed. The model combines the finite element method based on self-compiled high-precision finite element mesh, kinematic analysis and Archard's formula to predict the tooth surface wear. The characteristics of the relative sliding distance are also discussed, while the effects of the misalignment angle and load torque on the wear depth are investigated. The numerical results show that the maximum relative sliding distance increases with an increase in the misalignment angle, and the relative sliding distance between the teeth near the pure tilted area is larger than that near the pure pivoted area. In addition, when crown gear coupling is aligned, the tooth surface doesn't produce wear, while the tooth surface wear pattern is symmetrical about the middle of the tooth width.
查看更多>>摘要：This study proposes a dynamics model for hypoid gears, considering mesh stiffness that is dependent on dynamic mesh force. Owing to the fundamental role of mesh stiffness in gear dynamics, its proper and accurate description is critical in any modeling effort. Unlike many works in the literature, which adopted mesh stiffness arrived under quasi-static condition, this study establishes the interaction between mesh stiffness and dynamic response to allow the real time variation of mesh stiffness under dynamic condition. To overcome the unaffordable computational time involved in the determination of dynamic mesh stiffness, a parametric surface approach is employed. A set of parametric simulations is carried out to show evident impact of dynamic mesh stiffness on hypoid gear dynamic response, which is more significant when load becomes lower. The introduced model provides a physics based tool to quantify the interaction between mesh stiffness and dynamic mesh force, capable of capturing more complicated dynamic response of hyoid gear mesh.
查看更多>>摘要：The terrain adaptability and the walking speed are two key performances of legged robots. However, methods to optimize these performances are seldom developed, especially in real-time application. This paper proposes a novel gait planning method for six-legged robots to optimize both the terrain adaptability and the walking speed. First, a six-legged robot with parallel mechanisms and the typical tripod gait are introduced. Then, the optimization problem is addressed by minimizing the displacements of the active joints and solved by applying the pseudo-inverse. Further, the performance improvements are analyzed by comparing the optimized gait with the non-optimized gait. Finally, experiments are conducted on the prototype to validate the method. The results show that the maximum AoS (angle of the slope) and the maximum SHR (step to body height ratio) are improved by 48.8% and 96.0%, respectively. The maximum SLR (speed to body length ratio) is improved by 17.1%. More importantly, all essential calculations are fulfilled within 1ms, which proves the feasibility of the method in real-time control systems.
查看更多>>摘要：The paper presents a model of the positioning process of cuboidal objects on an oblique plane with barriers, caused by the interaction of inertia, gravity and contact forces. In this model, the contact area of the object base with the bearing planes is represented by evenly spaced discrete elements and the corners and edges of the object identify the contact with the positioning barriers. The object performs free spatial movement and may be in simultaneous contact with many bearing surfaces with different frictional properties. The static Bengisu-Akay friction model represents tangent contact forces, and the nonlinear Kelvin collision model describes normal forces. Due to high sliding velocities, the Stribeck's effect in the friction model does not have a significant impact on the course of the positioning process, hence it was assumed that the static and kinetic friction coefficients are equal to each other. Moreover, on the basis of the conducted analyses of the results of numerical and experimental tests, a geometrical configuration of the positioning barriers was proposed, allowing the object to be intercepted on an oblique plane and placed on the outfeed conveyor.
查看更多>>摘要：Despite the importance of grasp synthesis for autonomous robotic operations, its formulation for continuum robots (CRs) has yet to be investigated. This paper presents a grasp taxonomy and a synthesis approach for CRs. The proposed synthesis relies on an analytical model for grasping using CRs. The method is extended for the application of cooperative continuum robots (CCRs). To present a comprehensive formulation of the problem, both constant-curvature and Cosseratrod models are adopted in the proposed grasp synthesis. A set of grasp quality measures are formulated for this study, in which a new quantitative grasp quality measure is introduced to reflect the limited workspace of CRs. Finally, two experimental grasp quality measures are introduced (i.e., path-following error and grasp success rate) to compare and assess the grasps using statistical tests. The effectiveness of the proposed methodology is shown through extensive simulations and experiments using single-segment tendon-driven catheters.
查看更多>>摘要：In this study, a novel single-motor hybrid electric vehicle (HEV) equipped with a power-reflux coupling transmission system is proposed for improving the fuel economy of HEVs. The structural characteristics and operating principles of the proposed HEV were analyzed, and a detailed driveline dynamic model was established. Then, a rule-based energy management strategy regulated by the optimal comprehensive energy economy was adopted to divide its working mode regions. As a result, the engine starting process in vehicle motion may involve not only a driving mode switch but also a speed regulation mode conversion, resulting in noticeable jerks and an unpleasant driving sensation. To address this problem, this study presents a multilevel torque coordination method that synergizes the transient intervention of torques from two power sources and clutches and changes the transmission ratio. Compared with the simulation results of the dynamic performance of a vehicle under conventional control strategy, the results of the proposed control strategy demonstrate a better control effect, which can ensure the smoothness of power transmission during engine startup to effectively minimize the impact on the system and improve the ride comfort.
查看更多>>摘要：The functionality of a workspace is one of the most important considerations in planar parallel manipulators (PPMs) design. Dexterous workspace (DW) is the subset of the reachable workspace (RW) and it means that full rotational dexterity is preserved in every translational position in space. However, DW is impractical as PPMs cannot rotate a full 360 degrees because of interference. This paper proposes a workspace called prescribed flexible orientation workspace (PFOW) that characterizes the orientation capability of PPMs. To optimize and compare 3 degree-of-freedom (3-DOF) PPMs, a normalized and unified performance characteristic index is built based on indices including PFOW, condition number, velocity, payload, stiffness, and transmission indices which plays a guiding role in the optimization process. The best configuration is obtained through graphical performance comparison. In general, this work presents the analysis of rotational dexterity of PPMs and provides a guidance for optimization and selection.
查看更多>>摘要：This paper investigates the gearshift transient response and the shift control of a new spring-based synchronizer used in the automated manual transmission (AMT) for electric vehicles (EVs). The spring-based synchronizer uses torque spring to provide a torque to synchronize the speed difference between the target gear and the shaft, which reduces the wear caused by friction in traditional synchronizer, as well as decreases the engaging time and the vehicle jerk. The dynamics model of a two-speed AMT in EV equipped with the spring-based synchronizer is built in AMESim software, and the shift control model is established in MATLAB/Simulink environment. The simulation results of the dynamics model demonstrate that the spring-based synchronizer reduces the engaging time and the vehicle jerk compared to the traditional synchronizer. Furthermore, the influences of the motor inertia, speed difference, spring stiffness and shift force on the engaging time and vehicle jerk are quantitatively analyzed. Finally, several control strategies of shift force are proposed, including the single-closed loop PI position control, dual-closed loop PI control, and dual-closed loop fuzzy PI control, which further reduce the vehicle jerk.
查看更多>>摘要：Human-robot coexistence has become an important trend of the new generation of robots. Both rigid structures and soft structures have their own limitations in certain application scenarios. The tensegrity structure, which is widely used in the field of architecture and structural engineering, is a self-supporting and self-stressed spatial grid structure composed of discrete compression elements and continuous tension elements. This kind of structure combines the advantages of rigid structures and soft structures, and conforms to the natural evolutionary laws of creatures, providing helpful inspirations for the research of the new generation of robots. Tensegrity structures are being more and more widely used in robotics. The objective of this paper is to review the state-of-the-art of tensegrity structures-based robots and analyze the key techniques in aspects of design and fabrication, modeling and analysis, motion and controlling. Possible future applications of tensegrity robots are also prospected. Although there are still few actual applications in practice, tensegrity structures-based robots, as a unique rigid-flexible coupling structure, have great potentials in the future.
NSTL
Elsevier