Research On Soft Under-actuated Hand Based On Fin-ray Structure

In recent years,robots has been widely used in the field of home service and industrial manufacturing.The mechanical hand,as the end-effector of a robot,are often designed for purpose according to the shape,size and hardness of the grasped object,which lacks flexibility.In order to make the ability of hand to grasp objects more universal,a new type of soft under-actuated hand is designed based on rigid under-actuated structure and soft fin-ray structure.The hand not only retains the advantages of large grasping force of under-actuated structure,but also absorbs the advantages of soft structure when it is easy to grasp small and smooth objects.The contents of this paper are as follows.Firstly,the overall structure of soft under-actuated hand is designed,which includes two parts: finger structure and palm structure.The finger structure consists of three knuckles.The first and second knuckles adopt under-actuated linkage mechanism to facilitate parallel movement and envelope grasping of objects,while the third knuckle uses soft fin-ray structure to facilitate soft pinching of objects with small sizes and enhance the stability of pinching process.The palm structure mainly includes a pair of four-bar linkages,which can realize different finger layouts.Four grasping gestures can be achieved with this design,to support various objects.Secondly,the mechanical analysis and simulation of the key mechanical structure and grasping modes are done to verify the feasibility of the design.In the enveloped grasping mode,the static and dynamic force analysis of the under-actuated linkage mechanism of finger are performed,and the relationship between the contact forces of three fingers and the moment on the driving linkage is obtained through the analysis.In the soft pinching mode,the static analysis of the fin-ray structure of finger and the parallel linkage mechanism is made.The mechanical model of the fin-ray structure and the relationship between the pinching force and the driving force of the motor when soft pinching are obtained.The simulation results of ANSYS and ADAMS are carried out respectively.In addition,the stability analysis and rigid-soft coupling simulation experiments of the whole hand are also done.Then,the motor control system based on force feedback is designed,which realizes the transformations between the robotic gestures and the different grasping forces.Before the hand grasps the object,various gestures and different grasping forces are preset;when the hand grasps the object,the grasping gesture and the grasping force are determined according to the force feedback,and the upper machine sends the corresponding instructions to the Arduino microcontroller to control the motion of motor and servo.Finally,according to the design of mechanical structure and the design of control system,a prototype platform is built,and the grasping test experiment and pinching contrast experiment are carried out on the prototype.The results of grasping test show that under-actuated soft hands can use four gestures to grasp daily objects with a length of less than 10 cm and a weight of less than 1.5 kg.By comparing the results of pinching experiments,it can be concluded that after introducing soft fin-ray structure,the new soft under-actuated hand has better pinching stability than the traditional under-actuated hand.There are still many shortcomings in the soft under-actuated hand based on finray structure.In the future,improvement will be continued from three aspects: structure,control and perception,and its methods of performance evaluation and analysis.The research and development of universal hand will become more systematic,efficient and practical.