The Study Of Omni-directional Static Walking And Stability Analysis Of A Quadruped Robot On A Slope

Legged robots possess flexible adaptability on various complex environments, also can walk and complete tasks such as transportation. Legged robots are widely used in areas such as disaster relief and engineering. Quadruped robot is the most practical kind of them, which has great carrying ability and static stability. The current research on static walking of quadruped robot on a slope can not meet the two important factors in the walking movement: first is to ensure rapid and continuous walking; second is to guarantee the stability.In this paper, the author analysis and compares various methods of walking pattern. To achieve rapid, continuous and stable omni-directional static walking on a slope, the theory of omni-directional static walking on the ground is taken as basis, and research on the stability analysis of waking movement on a slope is done. By analyzing the causes of the unstable problem, a solution has been proposed. Specific research works are as follows:(1) Study on the omni-directional static walking. Taking account of the complexity of the slope environment, first of all, the body posture has been selected, the coordinate system has been set, and the leg reachable region has been set. According to the offset of the center of gravity, the standard positions of foots have been set, and the positions of CFP have been calculated by the algorithm. Then the static gaits on a slope have been planed: selecting a gait based on the position of the turning center of rotation gait, deriving the positions of foot during the movement planning leg trajectories and so on. Finally the transitions between all the gaits have been implemented and the omni-directional static walking on a slope has been realized.(2) Stability analysis of the waking on a slope. The common method of stability analysis is Sm( Stability Margin), however the robot tumbles around the line connecting two support feet although the stability margin is greater than 0. This problem should not occur in practical applications of quadruped robot, which would greatly affect the stability and precision during the actual operation. After analyzing different stability criteria and the caution, Sne (Normalized Energy Stability Margin) has been selected. By analyzing the stability characteristic, the method has been proposed, that is: making sure that the rapid and continuous walking movement can be realized, then dynamic changing the height of the center of gravity during the preset range to enhance Sne. In order to improve the stability analysis of the walking on a slope, the method to combine the stability margin and Sm has been proposed, which not only can determine whether the quadruped robot is stable at split second but also can analyze the tumble trend during a period. The method is suitable for stability analysis of various gaits movement on a slope.(3)Simulation .In this paper, through simulation experiment, the validity of the planning of omni-directional static walking on a slope has been verified. The result of the experiment can be seen, that is: the stability margin is not less than 0 throughout the gait transition process and also meet the requirement of Sne, the fast, continuous and stable walking thus has been realized. Also, the proposed method to solve the tumbling problem during walking on a slope has been verified. The conclusion can be derived that the method by dynamic changing the height of center of gravity ensure the stability of omni-directional walking on a slope and the tumbling problem can be solved.