Variable Stiffness Driving Method And Experimental Research Of Soft Finger Based On SMA

The performance of the robotic hand is an important indicator of the level of robot operation,which directly affects whether the robot can complete the specified task requirements,so the study of robotic hand is very important.Traditional robotic hand can efficiently implement single,repetitive grasping operations,but they are limited to work under the unstructured and workspace-constrained environments.And the soft hand can be used to grab the various shape and weight objects in the unstructured environment due to the high flexibility to change their shape properly.But the highly flexible soft hand is also faced with the problem of lack of the stiffness and grasping force.Therefore,the soft hand need to be driven easily and be able to control the stiffness.So,it is important to study the variable stiffness driving method of soft finger.In this paper,a novel variable soft finger was manufactured by 3D printing technology.The skeleton component of the soft finger contains shape memory alloy with variable stiffness.The variable stiffness of the soft finger was tested by experiments,and demonstrate that the variable stiffness driving method is effective.In order to analysis the soft finger grasping performance after its stiffness is changed,statics model of the soft finger was established based on the Cosserat elastic rod theory.This model can address the weight of the finger and the deformation caused by the action of the object,to solve the shortcomings of the constant curvature model,and has certain significance on the study of soft fingers.Through the equivalent analysis of the gravity of parts on the soft finger,it is necessary to consider the component weight of the soft fingers in some cases.In order to verify the accuracy of the model of finger,the bending deformation experiments were carried out,and the experimental results were in good agreement with the simulation.Finally,based on the finger static model,the reverse application of this method was put forward,and the grasping force of the finger was calculated by Matlab simulation for a given initial condition.Simulation and experimental results showed that this kind of soft finger after the stiffness increase,finger grasping force of the fingertip can increase by more than 40%,reflecting the meaning of variable stiffness of soft finger.In addition,the griping force of the fingertip is controlled by PID,and the controlling effect of different parameters were compared.The control effect can be achieved by adjusting the control parameters.In order to reflect the improvement of the grab force in the case of variable stiffness,a two-finger soft robotic hand was designed and the condition of the robot's stable grasping was analyzed,and the experiment intuitively showed the grasping effect of soft fingers with the increase of the stiffness.Finally,through a group of experiments confirmed that the grasping ability of the soft hand composed of this soft fingers can improve more than 40% with the increase of the stiffness,and can be used to guide the stiffness requirements of the soft finger,based on the actual grasping needs.