查看更多>>摘要：The representation and isomorphism identification of kinematic chains (KCs) with multiple joints are crucial issues to be solved in mechanism research. In this paper, a modified graph-planar face graph (PF graph), is proposed. As a key concept, "face " has been put forward to represent the case that a single, specific relationship is incident with multiple incidents. Some other basic concepts relating to PF graph are also explained in detail. PF graph is used to represent KCs with multiple joints and it reflects the uniqueness of KCs and realizes the one-to-one correspondence between KCs and adjacency and incident matrices. It also establishes relationships with other methods for representing KCs and it is proved to be suitable for complex mechanical systems. Moreover, the sufficient and necessary condition of isomorphism are derived, and two properties of permutation similarity are analysed. Based on them, the modified eigenvalue eigenvector method and the maximum path method are proposed, and they are integrated to form a new algorithm. In addition, the reliability and efficiency of the algorithm are proved.
查看更多>>摘要：The performance measurements for the parallel manipulator can be divided into kinematic and dynamic indexes. The kinematic estimations have been well explored and contributed in the parallel structure selection, singularity avoidance and dimension synthesis. The dynamic performance assessments will also have significant contributions for parallel robots. In this research, the complete inverse dynamic model is formulated via the Lagrangian approach and verified by the simulation results. Two novel dynamic indices are proposed to explore the coupled inertia features among different kinematic limbs. The multiple dynamic indices are analyzed and compared on two translational parallel mechanisms with similar joint configurations. A feasible controller is provided to track the desired trajectory of the mobile platform.
查看更多>>摘要：This article introduces a new kinematic identification approach for serial robots using a motion capture system in the recurrence way. This method is based on the motion capture system as a measuring instrument, which can measure and identify the robot's movements in any feasible domain. Different from the traditional method of obtaining measurement information from the end effector of a robot, multiple markers pasted on a robot each joint are identified and tracked by a motion capture system to obtain the 3-D coordinates of markers of each joint in every frame when the robot is being moved continuously. After optimally fitting the rotation matrix and the translation vector of each joint according to the singular value decomposition, the joint axis vectors and DH parameters can be reconstructed in the recurrence way. Both simulation and experiment of a six revolute joint robot are conducted to verify the effectiveness and efficiency of the method. The identification results including 3 invariants are close to the accuracy of the laser tracker. Interestingly, the identified joint angle is in close proximity to that obtained by the control system of the calibration robot.
查看更多>>摘要：This paper proposes a robotic fish scale that serves as a cover driven by a muscle mechanism. A combinatory design method is put forward to design the underlying mechanism and the cover enclosing it for shape morphing. The muscle mechanism is bio-inspired to mimic the motion of the skin muscle. It is designed to consist of multi-loop linkages to serve as a driving skin muscle. The tracer points of the linkages are required to follow three different curves mimicking the shape morphing of a fish. The key design variables and constraints are defined to determine the degrees of freedom (DOFs) of the mechanism. To reduce the DOFs of the structure while possessing flexibility, two types of basic linkage units, 4-bar and 5-bar, are combined to design the final muscle mechanism that can be actuated by a single actuator. The cover is designed as passive morphing along the mechanism. The directions and placement of the scales are investigated for interference avoidance. At the end, the two designs are combined to realize a complete system with robotic scales and underlying muscle mechanism. Based on the proposed method, a prototype is built and tested to demonstrate the shape-changing capability of the proposed system through three different curved shapes.
查看更多>>摘要：Rod-driven Parallel Continuum Robots (PCR) are a class of continuum robots (CR) that possess the potential to combine advantages of parallel structure into CRs. However, rod-driven PCRs usually have a limited workspace due to the designed constraints, which restrict the exploitation of their potentials. This paper presents the design, statics modeling, and workspace analysis of a rod-driven PCR for extending its motion range. The proposed design has 5 degrees of freedom (DoFs) for manipulation by reasonably arranging constraints and kinematic pairs. We employ a known modeling method based on the Cosserat equations and a variant of the Levenberg-Marquardt method to solve the model, making the PCR with multi-intermediate constraints approach real-time applications. The design's feasibility is experimentally verified on a developed prototype. We then present a numerical procedure for analyzing partial workspace efficiently. Our results highlight the design's feature to enlarge workspace, of which a set of configurations can reach about 64% of the cube volume of max arm length, and an average of 4 s solving spatial paths, with max errors of 2.5% of max arm length.
查看更多>>摘要：Emerging applications of force-sensitive manipulation with the requirements on grasping safety and efficiency pose significant challenges on the design of compliant constant-force mechanisms with large operating ranges. In this paper, we propose a novel curved-beam based quasi-constant force mechanism fully compatible with the additive manufacturing technology, which is configurable with appropriate arc-elements to achieve quasi-constant force output with a large motion stroke. We develop an analytical model to describe the static deformation behavior of the proposed mechanism and analyze the performance sensitivity of its structural parameters, with which we also propose the optimization formulation and general guidelines for the design of curved-beam based compliant quasi-constant force mechanisms to meet force and displacement requirements. Finite element analysis and experiments are also conducted to comprehensively evaluate the proposed design, demonstrating significant performance improvement over existing results.
查看更多>>摘要：Industrial cranes transporting bulky loads are widely used in many engineering applications. However, heterogeneous loads give rise to eccentricity between the mass center and centroid of the load. Natural frequencies of the swing and twisting under eccentric-load mechanisms differ from those under uniform-load configurations. Therefore, load swing and twisting dynamic models that account for eccentricity are required to adequately understand and accurately control such cranes. Although significant work has been directed at the uniform-load dynamics of industrial cranes, little attention has been focused on the eccentric-load dynamics. This article presents a dynamic model of bridge cranes transporting heterogeneous loads. The frequency analyses of double-pendulum swing and twisting for eccentric loads is described. Additionally, a control method is designed using a simplified spherical pendulum with load-twisting dynamics and eccentric-load dynamics. Simulated and experimental results obtained from a small-scale bridge crane transporting a heterogeneous bar verify the utility of the analytical model and validate the effectiveness and robustness of the proposed control method.
查看更多>>摘要：We present two new arm exoskeletons based on a pantograph linkage. The exoskeletons can support a tool or load held in the hand of up to 9 kg. The pantograph linkage follows the geometry of a user's upper arm and forearm, and supports the held mass with any arm orientation. The downward force of the load weight is supported by a fulcrum near the user's shoulder and balanced by a countering downward force behind the user's back. We present a Passive exoskeleton, which uses a gas spring mechanism to supply the downward force, and an Active exoskeleton that uses a motor. We analyze the forces produced by the gas spring mechanism as its geometry is varied, and explore different possible arrangements of the gas spring mechanism or motor relative to the pantograph linkage. We derive the equations governing the pantograph linkage, and simulate the forces resulting from the two exoskeletons. We conduct measurements of the forces produced by each exoskeleton, and compare them with the simulated forces.
查看更多>>摘要：Accurate setting of the gear machining error to a certain expected value is a difficult task. A non ideal value may cause the system to not meet the complete similarity condition and reduce the prediction accuracy of the scale model (SM). In this study, the similarity relationship of a gear transmission system, considering the machining error, was derived using the equation analysis method. To address the problem of machining error distortion, a similarity ratio of the peak-to peak value of the vibration response, and two modification methods for SM prediction are proposed herein. In the first method, the load is modified, whereas in the second method, the similarity ratio is modified. A node finite-element model and transmission error experiment were used to verify the accuracy of the two methods. The results indicate that the prediction of the changing trend and amplitude of the vibration response was accurate. The modified load method should be used in the design stage for the working conditions, and the modified similarity ratio method should be used in the experimental data processing stage.
查看更多>>摘要：In this study, a dual-clutch transmission start control strategy based on pseudo-spectral optimization and data-driven control is proposed to respond to the time-varying start intentions, to reduce friction and jerk, and to improve the start quality. First, taking the jerk, start time, and friction work as the optimization indexes, the adaptive pseudo-spectral method is used to accurately determine the optimal clutch engagement target trajectory. Then, a real-time planning method for the target clutch engagement trajectory is proposed based on a dual deep gated recurrent unit network. Second, through partial least squares identification, a data-driven predictive control (DDPC) method based on the autoregressive with exogenous model is proposed. The model parameters are updated online by a multi-model filtering algorithm based on input and output data, allowing real-time adaptation to the system uncertainty and nonlinear characteristics. Simulations and experiments show that the proposed target clutch trajectory planning method can effectively respond to time-varying start intentions in real-time. In addition, the DDPC controller can adapt to the uncertainty and nonlinear characteristics of the system and, hence, improve the control accuracy.
NSTL
Elsevier