Research And Design Of The Key Technology Of The End-effector Of The Dragon Fruit Picking Robot

The dragon fruit is increasingly popular due to its high nutritional value.With the increasing production and shortage of manpower,there is an urgent need for machines to replace human intelligent harvesting technology and equipment.Therefore,based on the research foundation of our research group on dragon fruit,we have designed a dragon fruit picking end effector,expecting to achieve rapid picking based on the positioning of dragon fruit leaf edges,while achieving the goal of reducing the cut length to equivalent to manual cutting while ensuring picking quality.In this paper,Nanjing Lile Taiwan red heart dragon fruit was taken as the research object,and the end-effector of dragon fruit picking robot was designed.The following aspects were mainly studied.(1)Study on physical properties of dragon fruit.The basic parameters of dragon fruit were obtained through field investigation on the orchard base.The mechanical parameters of dragon fruit fruit are important parameters for the design of end-effector.This paper conducted compression characteristics,single knife shear characteristics,double knife shear characteristics,mechanical characteristics of scissors inserted into the mesophyll,mechanical characteristics of scissors cutting fleshy stems with mesophyll,and other tests on dragon fruit.It was found that when the loading speed was 5 mm/min,50 mm/min,The maximum compression force of dragon fruit shall not exceed 96.81N;The maximum force of single knife shearing force is about 201.5N,and the maximum force of double knife shearing force is about 91.2N when the cutting speed of dragon fruit with fleshy stems with mesophyll is 5mm/s,20mm/s,100mm/s,and 200mm/s respectively;The pushing force required for the scissors to insert into the mesophyll shall be at least 13.3N,and the shearing force required for the scissors to cut the fleshy stems with mesophyll shall be at least 97 N.(2)Design and simulation of the end-effector for picking pitaya fruit.Design two different types of dragon fruit picking end-effector based on the basic physical parameters of dragon fruit and the mechanical parameters of shearing dragon fruit.One type is a biting elliptical trajectory end-effector,which mainly cuts fruits growing on the front side.The length,width,and height of the end effector are determined to be 195 mm,140mm,and 157 mm,respectively;In order to reduce the cutting length of the blade edge,the running trajectory of the cutting mechanism is an elliptical trajectory resembling a dragon fruit shape.Based on its running trajectory,an elliptical graph is fitted,and the width range of the cutting blade edge is calculated to be 36.34～41.64 mm.Considering that the installation position of the pressure sensor has a certain impact on the blade edge shear length,an adjustable pressure sensor installation length device has been designed.Another type is a scissor type end-effector,which mainly cuts fruits growing on the side and determines the size of key components of the end-effector;In order to reduce the surface damage of the dragon fruit caused by the clamping mechanism,flexible materials are tested and pasted inside the clamping fingers.(3)The design of the control system of dragon fruit picking end actuator.The biting elliptical trajectory end effector uses STM32F103C8T6 microcontroller as the core system,including FSR resistive pressure film sensor,model 4V110-M5 solenoid valve,and TN20×20S Yadeke dual axis cylinder,etc;The scissor shear end effector uses STM32F4 microcontroller as the system,including DF9-40 flexible film pressure sensor,36GP-3650 DC reduction motor,and+6V servo motor;The software is programmed in C language.(4)Picking test.This paper use monte carlo method to analyze the six axis robotic arm S6H4D＿Plus and plan the spatial trajectory and construct a harvesting experimental platform in a laboratory environment;By conducting picking tests on the biting elliptical trajectory endeffector and the biting circular trajectory end-effector with a pressure range of 0.4～0.7 MPa,and comparing the results,it was found that the average length of the cutting blade edges of the biting elliptical trajectory end effector was 39.68 mm,36.69 mm,40.99 mm,42.55 mm,and the average length of the cutting blade edges of the biting circular trajectory end effector was 74.13 mm,70.34 mm,79.91 mm,and 82.40 mm,respectively,The length of the cutting blade edge of the interlocking elliptical trajectory end-effector has decreased by 46.47%,47.84%,48.70%,and48.36% compared to the interlocking circular trajectory end effector.The optimal harvesting result for both end effectors is 0.5MPa.At this time,the success rate of the biting elliptical trajectory end effector is 90%,the average picking time for a single fruit is 0.46 s,the average length of the cut leaf edge is 36.69 mm,and the average width of the cut leaf edge is 8.85 mm.In the field picking experiment of orchards,the optimal air pressure for picking pitaya was 0.5 MPa and 0.6 MPa,with a success rate of 85%,a single fruit picking time of 0.43 seconds,an average length of cut leaf edges of 39.8mm,and an average width of cut leaf edges of 9.6mm.By applying a speed of 100 r/min,130 r/min,and 160 r/min,to the reducer motor of the scissor shear endeffector,it can be found that the optimal motor speed is 130 r/min.At this time,the average picking time of a single fruit is 7.27 seconds,the average length of the shear leaf edge is 22.93 mm,and the success rate of picking is 87.50%,which verifies the rationality of the design.