| Variable stiffness materials such as shape memory polymers(SMPs),low melting point alloys(LMPAs)and magneto-rheological(MR)as well as electrorheological fluids(ER)have attracted extensive research interest in soft robotics.In this study,we developed a large range of variable stiffness elastomer based on liquid metal,which is composed of variable stiffness functional module and high phase change response flexible module(EGaln-PDMS).The variable stiffness functional module is mainly composed of functional liquid metal magnetorheological fluid encapsulated by silicone.The high phase change response flexible module(EGaIn-PDMS)is used to realize the high phase change response of the variable stiffness functional module by coupling the Ni-Cr heating module and the EGaln-PDMS flexible heat dissipation module.The test results show that the large range of flexible stiffness elastomers designed in this study can achieve up to 10 times of stiffness change,among which,in the magnetorheological interval,can achieve 4 times of continuous stiffness change,the corresponding time is only a few tens of milliseconds;In the phase transition interval,up to 10 times of stiffness change can be realized,and the response time can reach 37s.Finally,we designed a flexible pneumatic manipulator based on a large range of variable stiffness elastomers.The experimental results show that by adjusting the stiffness of the pneumatic flexible manipulator,its load capacity can be effectively increased.This paper makes a detailed study of the following four aspects:Firstly,the structure and process of a large range of variable stiffness elastomers in liquid metal are studied.A new process was developed to prepare functional liquid metal magnetorheological fluid(MRF)by successfully mixing micron Fe particles into the liquid metal Ga and encapsulating it in silicone.EGaln liquid metal was innovatively added to PDMS flexible material to prepare EGaIn-PDMS flexible heat dissipation module with high thermal conductivity.Furthermore,the Ni-Cr heating module was coupled with the EGaln-PDMS flexible cooling module to achieve a high phase change response of the variable stiffness functional module.Secondly,the rheological properties of a wide range of variable stiffness elastomers of liquid metal are investigated.The rheological principle is explained in detail.The effects of magnetic field strength and iron powder content on rheological properties of a wide range of liquid metal variable stiffness elastomers were studied.Experiments show that the stiffness of the elastomer can be effectively increased by about 4 times when the external magnetic field of 4000 GS is applied.At the same time,experimental studies have proved that the content of Fe particles in liquid metal magnetorheological fluid has a great influence on the rheological properties of its elastomer.At the same time,the particle diameter of Fe particle iron powder in liquid metal magnetorheological fluid also has certain influence on the rheological properties of elastomer.In short,the liquid metal variable stiffness elastomers exhibit excellent magnetorheological properties over a wide range.Thirdly,the phase change characteristics of a wide range of variable stiffness elastomers in liquid metal are studied.The stiffness test results show that up to 10 times of elastic stiffness can be achieved by changing the solid-liquid phase of the liquid metal in the variable stiffness module.Furthermore,the thermal response testing platform of the elastomer was constructed,and the phase change response time of the liquid metal variable stiffness elastomer in a large range was measured to be 37s,which fully demonstrated the excellent phase change characteristics of the liquid metal variable stiffness elastomer in a large range.Finally,the high thermal conductivity mechanism of EGaIn-PDMS composite was revealed by SEM and EDS imagesFinally,the application of liquid metal variable stiffness elastomer in flexible manipulator is studied.We applied a large range of liquid metal variable stiffness elastomer to the pneumatic flexible manipulator as the variable stiffness layer of the pneumatic flexible manipulator.The experimental results show that the load capacity of the pneumatic flexible manipulator can be effectively increased by adjusting the stiffness of the pneumatic flexible manipulator. |
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