Research On Spine-inspired Continuum Robot Design And Stiffness Characteristics

With the increasing aging of population,the imbalance of labor force brings new challenges to the robot industry.Inherent elastic structure allows continuum robots exhibit excellent dexterity and inherent flexibility,which makes it a rapidly expanding research field.Continuum robots are widely used when dexterity and flexibility are required,such as minimally invasive surgical robots,robots for detection and maintenance in confined spaces and dexterous hand,especially thumb design.However,insufficient stiffness limits the performance of continuum robots in these fields.How to improve the stiffness of continuum robots with dexterity and flexibility is the focus.To solve this problem,functional analysis and evaluation on related biological structures are given,based on which a continuum manipulator inspired from the vertebral column with acoelous centra is developed,and the essential relationship between structure and stiffness and dexterity is explored through stiffness model,dexterity analysis and comparative experiments.Main work is as follows:Biology has always been an important source of inspiration in the field of robotics.In order to solve the above problems,biological structures with dexterity,flexibility and stiffness are qualitatively analyzed and synthesized from the perspectives of structure,function and evolution.The results show that the notochord and the vertebral column with acoelous and amphicoelous centra are the compromise of dexterity,flexibility and stiffness,and the vertebral column with acoelous is a more effective biological structure to improve the stiffness.Inspired by the vertebral column with acoelous,a continuum manipulator is developed.And a notochord continuum robot and a basic continuum robot are constructed and developed as a comparison to explore how the vertebral column with acoelous centra improves the stiffness.The above three continuum robots are designed based on module method,which makes them share a set of drive system,and most parts can be interchanged and quickly connected,which is convenient for maintenance.Dexterity is the main advantage of continuum robots when comparing traditional joint robots and continuum robots.Therefore,the dexterity of continuum robots is studied quantitatively.In order to be consistent and fair in dexterity analysis,this paper describes the kinematics of robot from the view of analytical mechanics,and decomposes the kinematics of robot into mapping among task space,configuration space and driving space,based on which the constant curvature kinematics model and differential kinematics model of continuum robots are established.Then,a dexterity evaluation method is proposed from dimensions of position,speed and acceleration based on the mapping between configuration space and task space.Then,taking thumb design as the object,two continuum-style thumb configurations are given on the basis of holistic analysis of thumb movements,and the above evaluation method is applied to the dexterity evaluation of thumb design.The results show that the dexterity of continuum-style thumb is better than joint-style thumb under the same conditions.The feasibility and advantage of continuum robots in thumb design are verified.As both the notochord and the vertebral column with acoelous centra possess the characteristics of thin elastic rod,the stiffness model of thin elastic rod is studied.Firstly,according to the energy principle,the relationship between the deformation and strain energy of the elastomer in the direction of external force is established.On this basis,the stiffness models of thin elastic rod in different force directions under straight configuration and bending configuration are proposed,including axial stiffness,torsional stiffness and transverse stiffness under straight configuration,tangential stiffness,main normal stiffness and binormal stiffness under bending configuration.Finally,the stiffness model of thin elastic rod in arbitrary direction on the normal plane and in space under bending configuration is extended and compared,which provides guidance for the design and application of continuum robots.Furthermore,the mechanism of rigid-flexible segment to improve the stiffness of continuum robots is studied quantitatively.Due to the characteristics of the thin elastic rod of continuum robots,the elastic stability of the compressed bar under the following force exists under the tangential force.The problem is studied in this paper from the aspects of statics and dynamics,and the critical conditions are given to ensure the stability of continuum robots in application.Then,two experiments based on the shape recognition and the end trajectory are carried out to verify that the three continuum robots basically meet the assumption of constant curvature.Finally,the stiffness models of the above three continuum robots are proposed based on the stiffness model of the thin elastic rod,and the comparative experiments of stiffness is carried out,which verifies the stiffness model and the effectiveness of the rigid-flexible segment to improve the stiffness of continuum robots.