Research On Characteristic Analysis And Motion Control Of Bionic Bird Neck Of Tensegrity

Tensegrity structure are composed of interconnected tensile elements and isolated compressive elements.In organisms,the structures of tensegrity is not only reflected in the cell level,but also in the musculoskeletal system,which is a complex network system composed of muscles,bones,nerves and soft tissues.At present,it is still hard to replicate accurately in robots.However,althoug h the musculoskeletal system is complex,it is well organized and can be controlled b y the neural system,enabling it to achieve flexible motor synergy at a very low energy cost.To make the most of an animal's physical structure,the nervous system needs to be flexible and complementary to adapt to the current environment and behavior.In contrast,the c urrent robot resistance to external shocks are relatively weak.For example,the head of a robot is mostly rigidly connected to the body,with relatively few degrees of freedom and insufficient degree of flexibility,which is not conducive to resisting ext ernal disturbance.Therefore,this paper proposes to build a lightweight,multi-degree-of-freedom flexible connector by using the tensegrity structure to imitate the bird neck structure.Based on the real bird neck structure,the skel etal structure of the imitation bird neck mechanism is established.The multi-stage structure adopts the same configuration to simplify structure design.The two adjacent stages are connected by flexible strings.In view of the bird neck structure proposed in this topic,a revised dynamic relaxation method for bionic bird neck form-finding is presented,and the balance condition is transformed from node-based force equilibrium to the force moment equilibrium of rigid sub-structure,so that fast form-finding for tensegrity bird neck with interconnected rigid bars can be performed.During the inverse solution calculation,the inverse kinematics is divided into two steps by decomposition to reduce the number of optimization variables.The first step is to define the connected lines of center points of all stages as "backbone curve".Spline curve is used to fit the "back bone curve" to optimize the optimal configuration of the structure.Meanwhile,a floating coordinate system is distributed uniformly on the curve to determine the node coordinates of the whole structures.In the second step,the inverse kinematics of unit structure is extended that internal force adjustment is integrated into inverse kinematics calculation process.Internal forces in all strings are optimized and are guaranteed to be greater than zero.Based on the theoretical analysis,workspace of unit structure thereof workspace of multilevel structure is also obtained.According to the structure design,virtual dynamic model of the bird neck mechanism is built.Throu gh simulation,the spatial location,trajectory tracking and terminal stability of the bird neck mechanism are verified.In this thesis underactuated method is also explored to realize the trajectory tracking and periodical rhythm control of underactuated system.