| Continuum robots are famous for their flexibility and dexterity.They have high technical advantages in narrow space exploration,medical surgery,dexterous operation,and man-machine integration.In order to reconcile the technical contradiction between load-bearing capacity,flexibility,and accuracy,continuum robots mainly develop towards rigid-flexible-soft coupling design.The super redundant degrees of freedom and multimaterial coupling characteristics of continuum robots further increase their theoretical modeling difficulty.This paper focuses on the rigid-flexible-soft coupling design and multibody deformation analysis for single/multi-backbone continuum robots.This paper proposes a pure cruciform as well as a bioinspired fishbone cruciform single-backbone continuum robot,and a multi-backbone continuum robot with variable diameter.And their constant curvature and variable curvature deformation models are constructed.The aim is to provide new configurations for the development of high-performance and highdexterity continuum robots,and to provide theoretical references for the shape analysis of rigid-flexible-soft coupling continuum robots.The main research content is as follows:New rigid-flexible-soft coupling configurations are proposed for single/multibackbone continuum robots,to compensate for the shortcomings of continuum robots in high-performance backbone structure and biomimetic flexibility design.In response to the shortcomings of large unloaded driving force,small ultimate curvature,and complex biomimetic backbone structure of single-backbone continuum robots,a new pure cruciform and a bioinspired fishbone cruciform single-backbone continuum robot are proposed based on a rigid-flexible-soft coupling design strategy.They have a simplified backbone structure,while they also can achieve increased stiffness in the load-bearing dimension and weakened resistance in the deformation dimension,as well as small driving force and large bending angle.A multi-backbone structure is a flexible upgrade to a singlebackbone structure.Further,focusing on the design challenges of biological flexibility and adaptability for continuum robots,a new configuration of multi-backbone continuum robot with variable diameter is proposed based on the rigid-flexible-soft coupling design strategy.This continuum robot can achieve stiffness performance regulation,workspace control,and motion resolution regulation from the perspective of structural scaling.Constant curvature shape models are constructed for the cruciform single-backbone continuum robots,in order to analyze their mapping relationship among the work space,shape space,and driving space.Based on the piecewise constant curvature modeling theory and geometric analysis method,the forward and inverse shape models are established for the pure cruciform and bioinspired fishbone cruciform continuum robots,and their workspaces are drawn.The advantages of the two cruciform single-backbone structures in improving the modeling efficiency and simplifying the shape model.The established single-backbone constant curvature model lays a foundation for the constant curvature shape modeling of the multi-backbone continuum robot.A variable curvature deformation model is constructed for the cruciform singlebackbone continuum robot,to accurately predict the deformation characteristics of the bioinspired fishbone cruciform single-backbone continuum robot under external force interference.Based on the Cosserat theory,the kinematics analysis and statics analysis of the bioinspired fishbone bending unit and the driving cable are carried out respectively.Then,the kinematics variables and the force/torque are correlated to construct the Cosserat rod and Cosserat string models as well as their coupling model by using constitutive equations.Further,the variable curvature deformation model of the cable-driven singlebackbone continuum robot are hierarchically established under different driving forces and loads.Meanwhile,the established variable curvature deformation model for the single backbone lays a foundation for the analysis of multi-backbone variable curvature deformation.A constant curvature shape model is constructed for the multi-backbone continuum robot with variable diameter to analyze the mapping relationship between its shape space and driving space.Compared with single-backbone continuum robots,multi-backbone structures have stronger coupling,making their deformation modeling more challenging.On the basis of the single-backbone piecewise constant curvature analysis method,a new method is proposed that using the equivalent discrete series parallel mechanisms and numerical iteration to solve the multi-backbone constant curvature shape model.The inverse kinematics of the equivalent discrete parallel mechanism and the forward kinematics of the equivalent discrete series mechanism are easy to solve,which can be used to solve the forward and inverse shape models as well as the variable workspace of the 9-degree of freedom multi-backbone continuum robot with variable diameter.A variable curvature deformation model is constructed for the multi-backbone continuum robot with variable diameter,to accurately predict the deformation of the multibackbone continuum robot with variable diameter under external load.Firstly,a statics model of the pneumatic artificial muscle is established based on the principles of energy balance and error minimization,and its stiffness matrix is established.Further,on the basis of the variable curvature shape modeling of the single-backbone,the statics model of the multi-section multi-backbone flexible joints is built hierarchically considering the coupling factors of internal and external forces.and its variable curvature deformation model under the action of different driving forces and external loads is derived.And its accurate variable curvature deformation model is derived under the action of different driving forces and external loads.Based on the above configuration schemes,constant curvature shape models and variable curvature deformation models,the prototypes of the pure cruciform and bioinspired fishbone cruciform single-backbone continuum robots as well as the multibackbone continuum robot with variable diameter are developed by comprehensively utilizing multi-material 3D printing technology,high-performance artificial muscles,and electromechanical integration technology.The combination of theory and experiment verifies the characteristics of small driving force and large bending angle of the cruciform single-backbone continuum robots,and proves the quantitative impact of the variable diameter function on the stiffness performance regulation and motion resolution regulation of the multi-backbone continuum robot.Meanwhile,the validity and accuracy of the established constant curvature shape models and variable curvature deformation models of the continuum robots are verified by comparing the theoretical and experimental results.The dexterous operation ability of the proposed continuum robots is demonstrated through operational demonstration experiments such as obstacle crossing,medical sample collection,and material handling. |
