Reserch On High-speed Locomotion Control Strategy Of The Planar Spinal Quadruped Robot

More than 50% of the earth's land is rugged terrain.A quadruped robot can pass through terrain quickly with the best static stability and the lowest complexity.Therefore,transportation,reconnaissance and rescue in high-risk and unstructured environment is urgently demanded for high-speed and high flexibility legged robot.The legged robot has a typical transmission mechanism with high redundancy,multi branch chains and real-time dynamic topology transformation;and the extremely short ground contact time,great ground impact and strong nonlinear motion coupling in high-speed motion bring higher challenges to the dynamic locomotion.In contrast,cheetahs in nature have flexible spines,light bones,and slender and powerful limbs,which can accelerate to 120 kph in 5 seconds.It has become a consensus for researchers at home and abroad to design the body according to the structure of cheetah,introduce spinal link in sagittal plane and fully analyze the mechanism of high-speed running when studying the high-speed locomotion of quadruped robot.The research on the dynamic locomotion of the bionic quadruped robot has experienced a transition from low speed to high speed,rigid body to multi-segment body,simple spine control to spine-leg coordinated control.Spring Loaded Inverted Pendulum(SLIP)is widely used as the fundamental model in the medium to low speed dynamic control of the traditional rigid body legged robot.While the existing simplified SLIP model ignores the obvious characteristics of high-speed running such as leg swing angle and speed.The strong coupling reduces the motion stability.Under the requirements of large stride length and even making the hind foots surpass the front foots,the introduction of the spine aiming at high-speed movement not only disturbed the virtual-leg connecting the toe to the shoulder/hip joint in original rigid body,but also made the touch-down angle exceed the original friction cone.Using traditional simplified SLIP model would bring about motion failure such as toe slipping.This thesis focuses on the speed generation mechanism of high-speed motion,analyzes the restricting factors,and introduces spine to improve the limit of locomotion speed.Guided by the SLIP model and starting from the structural foundation of high-speed robot,a lightweight,high-efficiency and long-span parallel driving pantograph leg for high-speed motion was established and optimized,which improved the limit swing frequency.The steady state "Triangular Motion Model(TMM)" in the stance phase was constructed by including leg swing angle and horizontal velocity to estimate the leg stiffness more accurately and realized precise control of the stance time.To solve the coupling problem between horizontal velocity and vertical height in high-speed motion,an apex height feed forward controller(MFC)based on simplified SLIP model and relevant energy regulation method were proposed by embedding the leg length controller(LLC)into the stance phase model and the results illustrated the energy flow relationship around the energy ‘Balance Point'.To expand the step length furtherly,a dual-joint spine configuration and spine-driving model were established according to the bionics principle,and a spine-leg coordination control strategy based on SLIP Migration Model was proposed to solve the core contradiction between step length and friction angle constraint in high-speed running,achieving the unification of the SLIP model and an organic coordination of body movement from monopod to spine driven quadruped robot.The prototype of a hydraulic drive spinal quadruped robot and the experimental platform of two-dimensional orthogonal motion treadmill were built.The performance of the passive gait and the active torque method in high-speed motion were compared.The feasibility of the spine leg coordinated control strategy based on SLIP Migration Model was verified by using different proportions of spinal motion to step length.Meanwhile,the influence of step length proportion and spine movement on the overall motion performance of the robot was analyzed.This project has important theoretical and practical significance in exploring the high-speed running mechanism of quadruped robot,extending the SLIP model's application to the spinal quadruped robot and developing the spine-leg coordination control strategy.