Research On Mechanical System Design, Grasping Force Analysis And Experiment Of Under-actuated Multi-fingered Hands

With the improvement of living standards, people set higher requirements of their workingenvironment and comfort. Under that background, with study of agriculture robot warming，anumber of end-effectors, but most of them are not able to control grasping force accurately. Inthis dissertation，we designed a new end-effectors where embedded under-actuated mechanismand force measuring—under-actuated multi-fingered hands with force measuring. Staticanalysis，mechanical structure and stability analysis of under-actuated multi-fingered hands wasstudied. A prototype of the under-actuated robotic hand was built. Completing graspingexperiments were performed with force sensor and the accuracy of the grasping force analysiswas verified. Manipulator could realize to grasp the fragile of fruit-vegetable without anydamage. The main research contents and the results are as follows:By Solidworks software to model the under-actuated multi-fingered hand，finger，palm，driver system of the hand were analyzed and designed. Based on human graspexperience the preshaping mode was completed. At last，the geometric parameters ofthe under-actuated robotic hand was optimized.In this chapter mainly explains the precision pinching grasp mode and the envelopinggrasp mode to analyze grasping force. The method of forces moment equilibrium toanalyze the precision pinching grasp，describing the relation between the end phalanxand driving force；based on screw theory to state the enveloping grasp mode，detailedanalysis the relationship between grasping force and driving force. The use oftheoretical analysis, combined with prototypes of the under-actuated robotic handgiving the expression of the force.From five aspects in detail introduced grasping force situation: changed of object andphalanx contact position, force distribution between the phalanx，consider springinfluence，size dimension of phalanx and driving force. Finally, using Matlab softwareto simulate the contact trajectories and static equilibrium, if there had an intersection agrasp is stable can be achieved.Designed the test device to measure the grasping force and the driving force. First ofall，second phalanx, third phalanx of different finger grabbing posture and connectionplate were applying standard pressure on the strain gauge in the static calibrated； Secondly，based on calibration，experiments on grasping diameter of50-130mm ofpomegranates and stainless steel balls were finished and measured strain of thecorresponding phalanx and connection plate，and strain converted into information ofgripping force and driving force；Finally，acquisition and processing informationgrasping force which that under-actuated multi-fingered hand can be automatic detectthe contact between hand and object.