查看更多>>摘要：Single degree-of-freedom (DOF) planar linkage mechanism has been widely used in bio-inspired robots because of its simple control. However, designing a single DOF mechanism to meet the complex motion law of creatures is difficult, and the multiple variables of six- or eight-bar mechanism further increase the design difficulty. A design method of single DOF planar linkage bionic mechanism is proposed in this paper. Through the continuous constraints on the position of all reference points with constraint descent method, the requirements of the bionic mechanism in shape, motion trajectory, and posture are met. As for the mechanism by which reference point coordinates cannot be expressed as the analytical solution of the driving angle, a single DOF mechanism is equivalent to a double DOF mechanism containing additional optimization variables, which further improves the design efficiency. For example, the design process of six- and eight-bar bionic mechanisms is given, confirming the feasibility of the method. Then, the effects of the constraint conditions on the design process are analyzed in detail. This study provides a reference for the design of bio-inspired robots.
查看更多>>摘要：Parasitic force caused by joint misalignment is a common and challenging problem in the design and control of lower limb exoskeletons due to the complex human joint morphology. The force will generate high tangential force on the skin, which leads pain or at least discomfort for the wearer. This paper presents a model of the parasitic force in a lower limb exoskeleton, aiming to minimize this force with an adaptive trajectory controller (ATC). The controller uses parasitic force in the shank between the human and the exoskeleton as the control signal, and adjusts joint trajectories to minimize the parasitic force. In this paper, a lower limb exoskeleton with two-degrees of freedom (DOFs) in the knee joint is presented. Parasitic force relates to the joint misalignment is modeled and analyzed, upon which a trajectory controller is developed. Both simulations and experimental results are included, which showed that the proposed method was capable of effectively reducing the parasitic force in motion assistance.
查看更多>>摘要：Increasing the rotating speed of the axial piston pump is effective in improving the power-to-weight ratio. However, the cylinder block tilts severely at high speed, which causes significant leakage. In this paper, a dynamic model of the rotating assembly in a high-speed axial piston pump is established to investigate the tilt behavior of the cylinder block when fully considering the relevant factors within the whole rotating assembly, such as the tilt moments due to the inertia of piston-slipper assemblies and the periodic pressure in piston chambers, the elastic deformation of the shaft, and the nonlinear bearing characteristics of the oil film. Furthermore, the cylinder block tilt behavior is measured to validate the established dynamic model. The theoretical and experimental results show that the tilt angle of the cylinder block increases with the increasing rotating speed. And at high rotating speed, the cylinder block tilts much more severely under low outlet pressure. Finally, the bearing capacities of the oil film and the spline coupling are analyzed to find out the dominant factors affecting the tilt behavior of the cylinder block.
查看更多>>摘要：This paper proposes a new calibration method for a 5-DOF hybrid robot, concentrating particularly on addressing the contradiction between measurement efficiency and calibration accuracy and the real-time compensation with high precision. The approach involves two successive steps: (1) an error prediction model based on a back propagation neural network (BPNN) and the Denavit-Hartenberg (D-H) method is established by the strategy of pose error decomposition; (2) an embedded joint error compensator based on a BPNN is designed to achieve real-time compensation with high precision. Experimental verification shows that the maximum position/orientation errors can be reduced by 87.05%/85.62% over the entire workspace of the robot after calibration.
NSTL
Elsevier