Study On Walking Gait And CPG Control Of A Quadruped Robot

Walking robot is not only required to adapt to the known and structured environment, but also the unknown and unstructured environment. Since the legged robot is capable of navigating obstacles, sand land and rugged road, it possesses good environmental adaptability and could be applied to the tasks which are dangerous or couldn't be accomplished by human beings, such as engineering exploration and survey, anti-terrorism detection, military reconnaissance, etc. Quadruped robot possesses the preferred all-round performance in legged robot field for its better stability than biped, and the mechanism and control system is simpler than hexapod and octopod. The shortcoming of legged robot is the low velocity, whereas the wheeled robot possesses the complementary characteristics. Therefore, the purpose of this thesis is aimed at the study of a wheel-leg hybrid quadruped robot, which could combine the virtue of legged robot and wheel robot. On the basis of robot platform design, the thesis focuses on the correlative research of the stable gait and biological control.Based on thorough analysis, a wheel-leg hybrid crocodile-like quadruped robot is proposed. Each leg of the robot possesses three joints and one wheel on the toe, by which the robot could move ahead quickly and step over obstacles. There is also independent DSP controller node for each leg, which is responsible for sensor signal collection, state judgment and inner joints control. And moreover, the embedded master computer communicates with DSP nodes via CAN bus. So the robot is capable of rapid mobility as the wheeled robot and flexibility for stepping over the obstacles as the legged robot. Rolling ability, kinematics, working space and Center of Mass solve method is studied, which provides the basis for stability analysis and gait plan.Balanced gait study is important guide for robot stable walk. Taking stability margin as the criterion of the robot's stability, and quadrant boundary as the criterion of swing leg possibility for the robot in different initial posture, gait mathematical model is established, which is classified by duty facotr; and statically balanced gait parameters are proposed. All quadruped gaits are classified into 24 kinds by swing orders; three essential characteristic parameters are contrasted with all 24 kinds of gaits: working space demand, minimum stability margin and body adjustment harmony. According to the robot actual structure parameters, plane walking and turning gaits are simulated. Dynamic balanced gait is simulated based on ZMP (zero moment point) theory, which establishes the theoretical basis for multi-locomotion ways of robot.In order to enhance the ability of environmental adaptation, stair climbing gait study based on projection analysis method is proposed. Stairs climbing gaits of minimum working space demand, maximum stability margin, and the most harmony body adjustment are simulated, and furthermore to obtain the suitable gait parameters for all necessities. The lateral stair climbing gaits and parameters are studied, which provide the theoretical basis for robot locomotion in classical environment.Based on mutual inhibition neurons, the oscillating model is established, by which the CPG (Central Pattern Generator) control network of the quadruped robot is developed. The impact on the output by parameters of CPG model is analyzed by computer simulation, and the CPG control network parameters of the robot is set. The CPG control model of the robot's gait is constructed. Output threshold is adopted for different duty factor gait control, and the gait switching mode by CPG is described, then robot reflex mechanism is established based on the adaptive property of CPG network, which testifies the excellent environment adaptation ability of CPG gait control method.Finally, an experiment robot platform based on 3-hierachical control architecture is established. Plane walking of different duty factor, turning, stairs climbing and rolling ahead experiments confirmed the validity of the designing and theoretical analysis of the robot system.