Development Of Kiwifruit Picking End Actuator Based On Separation And Picking Of Fruit Stems

At present,the main harvesting method of kiwifruit is artificial harvesting,which requires a lot of manpower and material resources.There are problems of high labor intensity,timeconsuming and high cost.The traditional picking method of kiwifruit picking end effector is to hold the fruit to pull or rotate.This picking method has great damage to the fruit,and has the problems of high damage rate and low picking efficiency.Therefore,it is of great significance to study the end effector of kiwifruit stalk separation movement picking for promoting the development of mechanized and non-destructive kiwifruit picking industry.In this paper,a kind of kiwifruit harvesting end-effector based on stem separation movement was developed,taking the natural conditions of kiwifruit growing in the northern foot of Qinling Mountains in Shaanxi Province as the research object.The main contents of this paper are as follows:(1)Study on the Separation Movement of Kiwifruit Stem Picking Method.The results showed that the compressive strength of fruit length,big diameter and small diameter direction from big to small was small diameter > big diameter > length.When the loading force of fruit was greater than 15 N,the damage of fruit increased obviously.Therefore,the holding force of fruit should not be greater than 15 N.The damage rate of fruit had a linear relationship with the loading force of experiment.The experimental results showed that the damage threshold force of fruit was the damage threshold force.Provide the basis for the determination.The results showed that the holding force of 1.04 N was needed to keep the fruit from falling off.The force closure could be achieved by holding the pedicel with human fingers.A model of separating and moving picking of kiwifruit pedicels was established.The experiment of fruit stalk separation was carried out.Considering comprehensively,the method of separating fruit stalk from middle point was selected.The mean shear force and moving distance were 2.16 N and 36.45 mm respectively.(2)Mechanical structure design of picking end effector.According to the principle of fruit stalk separation movement picking,three kinds of picking schemes were put forward.Through the comparison of six indicators,the motor-driven fruit stalk separation scheme with two sides clamping was chosen as the final scheme.Firstly,the whole structure is designed;secondly,the fruit clamping mechanism and the fruit stalk separating mechanism are designed,and the three-dimensional model is built by SolidWorks software and the virtual prototype is assembled.Finally,the static simulation analysis of key parts is carried out based on ANSYS Workbench 18.1,and the rigid body dynamics analysis of the three-dimensional assembly is carried out by using DMU module in CATIA software.The results show that the mechanical structure design of the end effector satisfies the principle of fruit stalk separation and motion picking,without motion interference,and the layout of each mechanism is reasonable.(3)Design of control system for picking end effector.STC89C52 MCU is used as controller,and infrared switch sensor,Hall position sensor and thin film pressure sensor are used as sensing elements to detect fruit information.Based on terminal control principle,stepping motor I drives V-shaped gripping finger to grip fruit at 8 mm/s speed,pressure sensor I sets threshold force 2.08 N,and stepping motor II drives anthropomorphic gripping finger to 10 mm./ S holds the fruit stalk,and the pressure sensor II sets the threshold force of 2.16 N.The stepper motor III driving frame II advances at a speed of 12 mm/s,reaching the preset 45 mm position,and completes the fruit stalk separation movement picking.The data of sensor is collected by single chip computer,and the stepper motor is controlled orderly by controlling the pulse frequency,direction signal and pulse number of the stepper motor driver.(4)Picking end effector prototype and picking test.The mechanical part of the end effector was processed and assembled,and the mechanical part was integrated with the control system for comprehensive debugging.In the early stage,a simulated shelf of kiwifruit was set up in the school for harvesting experiments.A total of 10 kiwifruit were harvested.The success rate was 90%.The average harvesting time of single fruit was 15±0.7 s.In the later stage,the kiwifruit orchard was carried out at the Kiwifruit experimental station of Northwest Agricultural and Forestry University of Meixian,Shaanxi Province.Picking performance test,a total of 50 kiwifruit were picked,the success rate of peduncle separation movement was 86%,the average picking time of single fruit was 17±0.5 s.After 30 days of cold storage,46 undamaged fruits and 4 damaged fruits were detected.The damage rate was 8%,and the damage rate was low.