Optimal and stable gait planning of a quadruped robot for trotting over uneven terrains

To obtain satisfactory performance for legged robots, they should be able to move on natural environment stably. In this article, the path planning of a quadruped robot in the motion over uneven terrains will be investigated. One of major problems for traversing uneven terrains is the robot stability. Thus, a condition to guarantee the robot stability over such terrains will be proposed. This condition defines a point with zero moment in 3D space. This condition makes it possible to vary of the height of main body stably during trotting which is a main issue for traversing uneven terrains. Based on this condition, a linear ZMP equation will be defined so that the main body acceleration acts as control input and the ZMP acts as output. A linear quadratic regulator with stability constraint and fixed final states will be proposed to obtain the COG path which results in minimum acceleration. The tip of swing foot path planning will be fulfilled so that the generated path leads to avoid any collision with environment. Furthermore, the path of tip of swing legs is designed with minimum acceleration. The simulation results confirm the validity of proposed methods in terms of stability and the improvement of the consumption energy over uneven terrains.