Numerical And Experimental Studies On Mechanical Behavior Of A Novel Flexible Inflatable Manipulation Arm

Inflatable membrane structure satisfies the principle of tensegrity,where the fabric skin is subjected to tension,while the inner pressurized air bears compression.Over the past few decades,owing to their unique mechanical properties,e.g.light weight,capable of being compressed into small packages,and low cost,the applications of inflatable structures are more and more popular.Inflatable structures have been widely used in many engineering applications such as buildings,boats,balloons,space antennas,and airship.Recently,the application of inflatable membrane structures has been extended to the area of robot manipulators and these flexible robot arms can overcome limitations of traditional ones because of their inherent features,e.g.light weight,low cost,and good crash safety.The current paper proposed a novel kind of inflatable manipulator which consists of inflatable tubes and inflatable joints with creases structure to allow flexible and large angle rotation.The geometric shape of inflatable joints proposed here looks like the bellows-type elbow of spacesuit.The current work carries out numerical and experimental studies to evaluate the mechanical performance of the inflated arm structure.Firstly,the design of this novel inflatable manipulator is proposed,including the overall conceptual design,detailed design and implementation method of the special inflatable joint with creases structure.The arrangement and working principle of the tendon driven system are also described.Secondly,the biaxial tensile and shear tests are carried out to evaluate the elastic constants of the PVC-coated fabric membranes of the inflatable arm.Different load ratios are applied to evaluate the material properties of fabrics under various stress states.Hence,the material parameters of the PVC membrane under biaxial tension and wrinkle conditions are calculated based on the assumption of orthogonality.Finite element models are developed by the software Abaqus to simulate the forming process of the joint with creases and study the mechanical behavior of inflated arm structure.Results show that the creases structure can effectively reduce the actuation moment of the joint and therefore the design goal is achieved.Thirdly,a prototype of the inflatable arm which has the same geometrical dimensions as the precious finite element model is designed and made to perform an experimental investigation on its mechnical performance.The accuracy of the numerical predictions is validated by the test data.Finally,based on the control volume method,the dynamic response of internal pressure of inflatable structure under transient load is simulated by using the airbag model of the software LS-DYNA.On the basis of the achievement of constant pressure simulation of ETFE cushion,the dynamic response of cushion internal pressure under external loads is simulated.Its results agree well with the experimental results,and therefore the feasibility of the simulation method of constant pressure is verified.According to the maximum stress process of the upper and lower membrane surface of the ETFE cushion,the design principle under wind pressure or wind suction condition is proposed respectively.And the dynamic internal pressure response of the inflatable manipulator under constant pressure condition is also simulated by this method.