查看更多>>摘要：Mobile robots are essential for inspection, surveillance, and disaster relief. The legged robot can adapt to challenging terrains such as stairs and debris. The hexapod robot has better stability, payload capability, and fault-tolerant ability than the biped and quadruped robot. This paper proposes a novel hexapod robot composed of two walking platforms and an actively actuated waist joint. The mechanical topology of the robot is determined by comprehensively considering the walking stability, energy consumption, and operating dexterity. The modular leg mechanism is selected by analyzing the reachable workspaces of three typical 2-DOF parallel leg mechanisms. Besides, the analytical method of calculating the reachable workspace of the robot body with shank-ground interferences is studied for the first time, which helps to enhance the efficiency of foothold selection. The feasibility of integrating the analytical workspace in obstacle-surmounting is verified by climbing a 45-degree staircase. Simulations including avoiding obstacles, spot turning, and climbing a staircase are carried out to verify the correctness of the theoretical analysis. A robot prototype is fabricated, and the field experiments corroborate the results of the computational simulations.
查看更多>>摘要：A multisymplectic Lie algebra variational integrator (MLAVI) for simulating the dynamics of a flexible multibody system is proposed. The flexible bodies are described by the geometrically exact beam elements established on the special Euclidean Lie group SE(3). A lemma is also provided to demonstrate that the used discrete compatibility equation can make temporal and spatial interpolation independent. Then, the reduced Lagrangian density on the Lie algebra is derived, and the discrete dynamics of motions are established by the discretization of the covariant variational principle. Furthermore, another novel closed-form equality relation lemma on the right tangent maps of the associated exponential map and Cayley map is originally proved, which greatly helps to simplify the Jacobi matrix of the proposed MLAVI in the Newton iteration process. The accuracy and efficiency of the proposed MLAVI are validated by six static and dynamic numerical examples. Numerical results show that the proposed MLAVI can preserve the system's symplectic structure, momentum, and energy for long-time simulation.
查看更多>>摘要：To overcome current challenges in variational mode decomposition (VMD) and its variants for the fault diagnosis of rotating machines, the decomposing characteristics of two sub-models buried in VMD are thoroughly explored to seek a novel way to realize effective and adaptive signal decomposition. A central frequency mode decomposition (CFMD) is proposed based on the investigation results of their decomposing characteristics. The CFMD consists of three parts. (1) A strategy for locating effective ICFs is constructed by using the first sub-model of the VMD, where a tendency discriminant function is designed to detect ICFs with good accuracy and efficiency. (2) Through the second sub-model of the VMD, a decomposing strategy induced by the located ICFs is presented to decouple the analysis signal directly, in which the optimizing procedure and incorporating balance parameter are unneeded. (3) A dichotomy strategy for updating the bandwidth parameter is built to rapidly identify possibly decomposed results of the analysis signal provided that the expected range of bandwidth parameter is input in advance. A numerical simulation and two experimental cases validate the effectiveness of the proposed CFMD method and its superiority over some advanced methods in the fault diagnosis of rotating machines.
查看更多>>摘要：The nonlinear characteristics of kinematic joints for the column-spindle system have a significant influence on machining accuracy. This paper proposes a comprehensive dynamic model of the column-spindle system considering the nonlinear characteristics of kinematic joints. First, the nonlinear restoring forces of kinematic joints are derived as the functions of the corresponding vibration displacements. The lumped mass method is applied to model the ball screw feed system with nine DOFs including the spindle head, and the spindle system is modeled applying finite element method. Then, the two developed models are coupled with each other through the contact forces and moments of spindle bearings to construct an integral dynamic model. Additionally, the proposed dynamic model is verified by static loading tests, modal hammering tests and vibration response experiments. Finally, the effects of the spindle bearing preload, the pre-deformation and number of effective loaded rollers in each row of raceways, and the installation parameters of ball screw feed system on dynamics are analyzed. The potential value of this research is to guide the optimization of column-spindle system at the design stage.
查看更多>>摘要：Taking-off and landing on unstructured terrain can effectively expand the application of aircrafts. The terrain-adaptive taking-off and landing technology is achieved through adaptive landing gear. The performance of the adaptive landing gear determines the safety performance of the aircraft during taking-off and landing. This paper proposes a comprehensive performance optimization method for four-leg landing gears based on the virtual equivalent parallel mechanism (VEPM). This method associates the motion variables of the parallel mechanism with the terrain data, and combines the original mechanism to form a VEPM. By analyzing the comprehensive performance of the equivalent parallel mechanism, the particle swarm algorithm is used to optimize the dimensions of the landing gear mechanism. The new optimization method can enhance the comprehensive performance of the landing gear mechanism, which contributes to the structural design and optimal control of the terrain-adaptive landing gear.
查看更多>>摘要：With the improvement of space-to-earth observation range and observation accuracy, the demand for large deployable antenna mechanism is becoming increasingly urgent. This paper proposes a new configuration that can realize two-dimensional planar deployment and designs a new large-scale two-dimensional deployable planar antenna mechanism. First, four folding schemes are proposed, and the folding scheme with the best comprehensive performance is determined through optimization. The antenna mechanism is designed in detail. The kinematic model of the basic configuration is established to analyze its kinematic characteristics. The antenna can be deployed smoothly by planning the deployment speed. The finite element model of the antenna is then established. The structural parameters of the antenna are optimized, the rigidity of each joint hinge is reasonably configured, and the comprehensive mechanical properties of the antenna are improved. Finally, the principle prototype of the two-dimensional deployable antenna is developed by 3D printing technology. The rationality and feasibility of the folding principle of the antenna are verified by experiments.
查看更多>>摘要：In order to enhance the adaptability of closed-chain multi-legged platform to uneven terrain, a reconfigurable passive locomotion closed-chain platform (RPCP) is proposed. On the basis of our previous research which focused on the locomotion on structured ground, we adopt reconfigurable design for trajectory flexibility. First, based on kinematics analysis, a reconfigurable design of the leg mechanism is proposed and adjustable trajectory parameters are analysed. Next, for the whole platform, reconfigurable assignments and strategies are analysed to satisfy different obstacle-surmounting requirements. Finally, a series of dynamic simulations and experiments are performed to testify the RPCP's walking performance and its passive obstacle-surmounting capability. It is shown that the RPCP can walk and accelerate on relatively slippery or soft ground, and can climb obstacles such as slopes and vertical walls by vector thrust. The research of RPCP provides a vector thrust-propelled method of reconfigurable closed-chain legged platform to improve the adaptability to terrain.
NSTL
Elsevier