Study On The Design Method And Performance Analysis Of Large-deflection Variable Stiffness Compliant Joints

Coexisting-Cooperative-Cognitive Robots(Tri-Co Robots)can interact with the environment,humans and robot peers,which become the research focus of future robots.Since that they continually interact with humans,there is an urgent need to ensure the safety of human-machine collaboration.It is an effective solution to incorporate compliant elements,especially when the stiffness is changeable.Compliant mechanisms gain their mobility from the elastic deformation of flexible members.The design theory of compliant mechanisms can be combined with the design of robotic arms and compliant actuators.Compliant joints are the bases of compliant mechanisms,this research mainly focus on the design and analysis of large-deflection variable stiffness compliant joints,the design methods of large deflection and variable stiffness are proposed,some novel complaint joints are designed to satisfy the requirement of being used in Tri-Co Robots.The specific contents can be summarized as follows:(1)A design method of large-deflection compliant joints is proposed,two novel large-deflection lamina emergent joints are designed.In the design of lamina emergent joints,flexible segments are usually deployed between two rigid linkages,which limits the number and length of flexible segments,resulting in the limitation of the joints' deflection.Change the position of flexible segments,and combine more segments in series and/or parallel,two large-deflection lamina emergent joints are designed,named as Outside-Deployed Lamina Emergent Joint(OD-LEJ)and Inside-Deployed Lamina Emergent Joint(ID-LEJ).The appropriate spring systems are established,the equations needed to calculate the joints'equivalent stiffness are derived.Examples are proposed and analyzed through theoretical calculation and finite element analysis(FEA)to verify the joints'ability of large-deflection.They are also compared with Lamina Emergent Torsional(LET)joint.(2)The design method of variable stiffness lamina emergent joint is proposed.The joint's stiffness can be changed by changing flexible segments'effective length.Based on ID-LEJ,a variable stiffness ID-LEJ is proposed.The effective length of flexible segments can be changed by sliding the sliders along the flexible segments,resulting in the variation of stiffness.Since that the sliders can slide symmetrically as well as unsymmetrically,the joint is analyzed in two different situations.The appropriate spring systems are given,the equations needed to calculate the joints' equivalent stiffness are derived.An example is proposed and analyzed through FEA to verify the joint's characteristic of variable stiffness and the equations proposed.(3)A novel tubular shape variable stiffness compliant joint is proposed and analyzed which is suitable for being used in robot arms.In the joint,some segments are combined in series and form an S shape.Sliding the sliders along the flexible segments,the effective length is changed,resulting in the variation of the joint's stiffness.Because of the unique design of flexible segments,the joint's stiffness can be changed in a large range.Similarly,the appropriate spring systems are established,the equations are derived and verified.(4)The design methods proposed above mainly focus on flexible segments,while the cutouts of compliant joints can also be design to help to achieve the characteristics of variable stiffness.Take LET joint for example,the cutouts are designed to increase the tensile stiffness or compressive stiffness when the joint's deformation reaches a threshold.It is analyzed through FEA and experiment,and some prototypes are made to illustrate the design idea.(5)As for filleted leaf hinge,the cutouts are designed to function as supports and a variable stiffness filleted leaf hinge is proposed,which can achieve complex variable stiffness characteristics.The hinge is analyzed through both linear method and nonlinear method,the relationship between stiffness and dimensions of the hinge is deduced,and a simple synthesis process is proposed.An example is proposed and analyzed through linear method,nonlinear method,and FEA,which confirms the design and the equations proposed.In summary,this research proposes the design methods of large deflection and variable stiffness,some novel large-deflection variable stiffness compliant joints are designed,the equivalent models are established,the equations needed are derived,the joints'characteristics are analyzed,which provides new ideas for the design of compliant joints,and new methods for the analysis of compliant joints,has extensive theoretical and practical significance.