Mechanism Analysis And Gait Research On The Quadruped Imitating A Horse

With good performance in capacity, mobility and versatility, quadruped robot can be applied in many fields. This dissertation studies the structure and gaits of quadruped robot imitating a horse, presents the timing sequence analysis models of common gaits as well as the transition model between symmetric gaits, builds up a mini-quadruped imitating a horse, and carries out a gait transition experiment. It also studies the passive bounding gait of the quadruped and the articulated leg with Poincarémap, and conducts a basic research on quadruped from walk to bounding.Firstly, a structural model of a quadruped robot is designed according to a horse, and then kinematic and dynamic analyses of the model are conducted. Thus the relationship between body and limbs as well as the system Lagrange equation is achieved. The structural variables are laid out according to walking simulation and energy consumption simulation during locomotion. A mini-quadruped robot is built up for the experiment.Secondly, on the basis of the timing sequence of quadruped's limbs movements, a timing sequence analysis model on common gaits in quadruped is presented with five variables. The timing sequence of common gaits in a stride cycle is achieved after being standardized, and then the gait transition analysis model is established. This dissertation proves that the gait transition between symmetrical gaits with the same duty factor or stride cycle can be completed in one stride cycle under a constant speed. The result of the experiment shows that the quadruped can perform the steady gait transition.Thirdly, the dynamic equations of the quadruped in the phases of bounding gait are derived with Lagrange method, and the transition equations between phases are presented according to the characteristic of bound gait. The Poincarémap of the quadruped bound gait is defined with reasonable dimensional reduction according to the characteristics of the periodic cycle. A fix point of Poincarémap is figured out with Newton-Raphson method. With the fixed point as initial condition, the dynamic equations are integrated numerically with Matlab, and the periodic motion curves are achieved. It is proved that quadruped robot can realize steady passive bound gait with a suitable initial condition. Fourthly, an articulated leg mechanism, consisting of links, a linear tension spring, which is used to isolate the ground impact on legged robot is presented. The equivalent stiffness of the leg mechanism is expressed in piecewise as a cubic stiffness and a linear stiffness through least-squares procedure. The mechanic model of buffering is built up, and it is calculated with numeric method. The result shows that when the leg mechanism connects to an optimal damping ratio in parallel, it can achieve a small buffer coefficient.Finally, in the same way, the periodic motion curves of the spring load inverted pendulum equivalent to the articulated leg are achieved. It is proved that the articulated leg can realize steady passive bound gait with a suitable initial condition.