Kinematics And Dynamics Of A Novel Bionic Wheelled-Legged-fused Mechanism

Mobile robots are being used widely in such diverse applications as reconnaissance operations, rescue operations, exploder removing, planetary explorations, mining, entertainment industries, sports competition etc., and play more and more important roles in military mission, safety guard, manufacturing, daily life of human beings and scientific research, and so on. Along with the environments becoming more and more complex, the locomotion ability must be improved so as to make mobile robots have the adaptability to maneuver on different types of terrains. As a result, tremendous hybrid locomotion systems have been presented in the past decades. Wheelled-legged hybrid locomotion mechanism inherits the merits of both legged mechanism and wheeled mechanism, and can move with excellent locomotive efficiency, while maintaining excellent locomotion performance. Consequently, more attention is focus on it, and large amounts of achievements with versatile structural forms have been come up with. However, there are still few structural hurdles in them, and need to be improved or overcomed, such as the switching system whose function is to alter the locomotion mode according to different terrains, the arrangement of the actuator which is usually mounted on every joint and drive it directly, the phenomena of redundant mechanism in special locomotion mode, and so on. All of these not only increase the difficulty in structural design, but also give rise to a higher possibility of making the dynamical performance of the hybrid locomotion mechanism worse. In this work, a novel bionic wheelled-Legged-fused mechanism is presented, which is distinctly different in structure and principle of realizing the locomotion modes, and eliminats or corrects the shortcomings in traditional hybrid locomotion mechanisms mentioned above. An in-depth study on this new mechanism is useful for the development of high performance locomotion mechanism.A series of researches are carried out on it as follows:The structural principle and the locomotion capabilities of the bionic wheelled-legged-fused mechanism are introduced. Also, its structural characteristics are summarized in accord with the shortcomings existing in the wheelled-legged hybrid locomotion mechanisms. The wheelled-Legged-fused mobile mechanism has an innovative structure and can execute legged-mode, wheelled-mode, and wheelled-legged mode according to the environment. Based on several conventional mechanisms with similar function to the new mechanism, the paper presents its forming principle, the structural characteristics and the principle of realizing the three locomotion modes, and summarizes them as a conclusion.The time-variable characteristics of the meshing force in the bionic joint transmission are studied, and the time-variable-meshing-stiffness coefficient curves are obtained. The bionic joint is the main component of the new mechanism not only in structure but in function. Affected by the structural features of the joint, the meshing force in the bionic joint transmission shows time-variable characteristics. Based on the essential principle of differential geometry, the characteristics of the working flanks of the involute ring tooth are analyzed. The variety between single-tooth-meshing-span and two-teeth-meshing-span alternatively in transmission is studied. The equations to solve the position of the inverse meshing point are deduced. And then, based on the Hertz elastic contact theory, the formula for the calculation of the meshing-stiffness is given and the time-variable-meshing-stiffness coefficient curves are drawn, which is essential in dynamics.The related kinematics analysis for the new mechanism is accomplished, and the forward kinematics and inverse kinematics equations are derived. In kinematics analysis, three key parameters and an important plane are defined. The three parameters, named azimuth angle, deflection angle and deflection axis, respectively, are used to describe the spatial orientation of the new mechanism, while the plane, called deflection plane, is used to analyze the instantaneous configuration of the mechanism at anytime of the whole process. Then, combining the sequential cosines transformation matrix with the Euler's theorem on rotation, the kinematics models are derived correspond to three types of locomotion modes.The dynamics model of the wheelled-legged-fused mechanism is set up using the Newton-Euler formulation. In this section, the interaction between ground and the wheel mounted on the output shaft of the new mechanism is analyzed firstly. Then, the expression for determined the meshing force vector and the arm of the meshing force vector is derived. After the inertia force and inertia moment of each component are calculated, the equilibrium equations for each body are written based on the Newton-Euler formulation. In order to meet the practical requirement, the transformation method of the actuating force from reference frame to gravity frame is presented in the last.The virtual prototype of the new mechanism is established, and the feasibility for the new mechanism to realize the design functions is examined and evaluated based on it. Also, the experimental results are employed to determine the reliability of the kinematics and dynamics models, by comparing them with the calculations of the models. In this process, the application of the virtual prototype in the wheel-leg-fused mechanism is introduced in details. A spline curve is used to define the contact force in establishing the virtual prototype, which is a key parameter in impact-function-based contact force calculations in ADAMS. In the experiments, emphasis is focus on the motion state of several important components, and load state of them is analyzed, especially, the contact forces from the gear pairs are measured. All of the experimental results demonstrate that the new mechanism can meet the design requirement and have the capability of executing the wheelled-mode, legged-mode and wheelled-legged mode. Results of the comparison drawn between the experimental results and the calculations of the kinematics and dynamics models validate the reliability of the models.A physical prototype of the new mechanism is established, and meanwhile, a quadruped vehicle based on it is assembled. Results from a preliminary kinematics test based on them verifies that the mechanism design meet its requirements for traversing with the wheelled-mode, legged-mode and wheelled-legged mode, and the vehicle can realize multi-locomotion-configurations, such as straight movement, side movement, turning in place, walking, and turning in small radius, and so on. which make the vehicle have a strong locomotion performance and a better adaptability on extreme environments.