Research On Multi-fingered Robot Hand Based On The Flexible Pneumtatic Actuator FPA And Its Application In Fruit Picking

As executing manipulator for robot to interact with outside environment, themulti-fingered robot hands have been paid much attention. Earlier conventional mechanicalhand is of simple structure, fewer degrees of freedom DOFs, poor adaptability and othershortcomings, which restricts the development and application of robots.The work of picking fruit mainly depends on manpower. The picking work is a mosttime-consuming and laborious production process. In order to improve the efficiency ofpicking fruit the mechanization should be attached importance to. With farms population isobviously reduced and aging population has been gradually become a common trend in theworld, development of fruit picking robot is of enormous economic potential and broadmarket prospects. Found on the previous research, bending joint driven by flexible pneumaticactuator FPA is studied profoundly in this paper. The3-DOF finger based on FPA and themulti-fingered hand for fruit picking are proposed. The main research work in this paper is asfollows:(1) Bending joint driven by FPA directly is proposed. Based on statics and elasticity, thestatic model about angle and output force of the bending joint is obtained. According to thefirst law of thermodynamics, combined with the joint’s dynamic equation, the dynamic modelof the bending joint is established. Experiments are carried out to verify the static model. It isconcluded from theoretical and experimental results that the experimental curve matches withthe simulated curve. Experimental results show that the angle step response time of the joint isabout1s, and the force step response time of the joint is about0.5s. The accurate angle can begot based on PI feedback control and feed forward compensation.(2) Finger-tip grasping model based on3-DOF fingers is proposed. A3-DOF fingerbased on bending joint is design. Using D-H method, kinematics equation and Jacobin matrixof the finger are educed. The statics of the finger is analyzed, and then static model aboutfingertip force and the values of the pressured air in the three FPAs is built. Experiments arecarried out to verify the static model, and it is concluded from theoretical and experimentalresults that the experimental force value matches with the simulated force value basically. Stiffness model about the bending joint is established. Experiments of the stiffness about thebending joint are carried out, and the theoretical and experimental results show that theexperimental curve matches with the simulated curve. Stiffness about the fingertip is alsoanalyzed. This paper presents a new flexible fingertip grasping mode. In view of differenttype of disturbing forces, stability of the fingertip grasping is analyzed, and the fingertip graspbased on expert controller is proposed. Experiment was done to verify the control algorithm.(3) Envelop grasping model based on3-DOF fingers is proposed. Based on the principleof equalization, the interaction forces between the object and knuckle is optimized. The staticmodel about the values of the pressured air in FPAs and the positive pressure on knuckle orcorrelative friction force is built. The measure model about the positive pressure and itsposition, based on leverage principle depending on two touch-force sensors, is obtained.Using a series dual loops control method and the compensator about friction force, thepositive pressure can be controlled precisely. In order to filtrate the high-frequency noise, thefeedback signal of the pressured air in FPA is processed by differential analysis. Theexperimental results show that dynamic response time of the positive pressure is about1s andthe steady-state deviation is less than±0.5N.(4) The compressibility characteristic of cucumber and apple, the cutting characteristic ofcucumber peduncle and apple peduncle, the friction coefficient between cucumber coat andsilica gel, the friction coefficient between apple coat and silica gel have been testedrespectively.(5) Design objective, mechanical structure, sensor system and control system ofmulti-fingered robot hand for picking are illustrated in detail. The calibration multi-fingeredrobot hand and the practicable multi-fingered robot hand are proposed, which have differentprecision ratings. The calibration multi-fingered robot hand is equipped with joint anglesensors,5-component force/torque sensor, touch force sensors and proportional pressure valve,and the practicable multi-fingered robot hand is only equipped with proportional pressurevalve which can be used in loop control on the value of the pressured air in FPA. The holdingmodels of cucumber and apple are established with mechanical analysis method, therelationships between the pressure value of compressed air in the FPA and picking capacityare analyzed. A picking robot hand for cucumber is developed. The effect of cucumberpicking using this hand is well, and the success ratio of picking cucumber is90percent. Thesuccess ratio of cutting cucumber peduncle is100percent, and the time of picking a cucumberis about3s.A new type of multi-fingered robot hand for picking, which is directly driven by FPA developed by our research team, is proposed in this paper. This robot hand has characteristicsof simple structure, easy control, and easy miniaturization and so on. It has better passiveflexibility, and without lack of stiffness. It is suitable for application situation that requiresrelatively high flexibility and low response speed of the fingers, such asagricultural harvesting robot, finger rehabilitation robot and so on.