Research On Structure Optimization And Control Of Quadruped Robot With Flexible Spine

With good environmental adaptability and flexibility, along with its wide use in military, industrial and life, quadruped robots has become a key issue in the field of robotics. On the basis of previous studies, this paper proposes design methods for quadruped robot with flexible spine, then builds its dynamics model, puts forward analysis method of stability, studies the structure parameter optimization and gait control, and analyses the effect of the spine rigidity, inertia and length on motion performance and stability.Cheetah is considered to be the fastest four-legged mammals. First, based on its configurations and mode of motion, we developed our HUST cheetah robot. Referring to the bone structure of cheetah, the basic configuration framework of robot is determined. And, basic design principles of HUST cheetah robot are proposed based on stress analysis of the cheetah during movement. Then, because of the synergy between animal joints, the correlations between joints of cheetah were analyzed to couple relevant joint by principal component analysis, which aims not only at optimizing the structure, but also decreasing the number of driven motors. On this basis, the overall design principle and scheme was put forward about the HUST cheetah robot.The dynamical model of HUST cheetah robot was established through reasonable hypothesis and simplification after observing the movement characteristics of cheetah bound gait. Dimensionless analysis is used in order to reduce the structural parameters variables of the model and to make it more general. Poincare mapping method were carried out to study passive dynamics of this model, and the solving method of fixed point was proposed using Newton-laffer method. The characteristics of passive movement under the model of fix point were analyzed and the determination method of the fixed point was proposed, which laid the theoretical basis for the structural parameters optimization and control research.Stability studies found that reasonable structure parameters is the key to the stability of the robot. In order to improve the movement performance and stability at the fixed point, the method of calculating the fixed point under the same energy system was put forward to analysis the influence of spinal length inertia and stiffness on fixed point under certain energy system. Leg and spinal stiffness is found to be the key factors influencing the stability of quadruped robot, which contributed to the optimization of motion performance and stiffness of the quadruped robot. Further analysis of the influence of the parameters of asymmetric spine on robot's movement performance and stability were carried out, which found that the reasonable reduce of the ratio of front body-mass to rear body-mass could optimize the movement performance of the fixed point under the premise of the guarantee of stability. Further through rigid spine model and flexible spine model contrast test, we verify the flexible spine can improve the movement performance of the quadruped robot.Based on conclusions of passive dynamics,robots could implement a stable periodic motion without using external drive in an ideal world of. However, because of friction, interference and other influence factors, it will be hard for robots to sustain stable movement. To achieve sustained and stable movement for HUST cheetah robot through passive movement, the passive dynamic hierarchical controller is constructed. In the upper controller, joint control method is proposed based on target state by use of passive dynamic. In the bottom controller, PD torque control is proposed based on the position and speed closed loop, and the effectiveness of the control algorithm is verified by simulation experiment. In addition, the common cheetah gait includes bound gait for high-speed movement and the tort gait for low movement. The control method of tort gait for HUST cheetah was introduced using spring inverted pendulum model (SLIP). Finally based on the platform of HUST cheetah robot, the of gait motion and theory was validated, which proves the quality of stable high speed movement of the HUST cheetah robot.