Development Of Multi-fruit Picking End-effector Of Kiwifruit Based On The Relative Movement Picking Pattern

The planting area of kiwifruit in China ranks the first in the world.In 2017,the planting area in Shaanxi Province(more than 1 million mu)and annual production(more than 1.3 million tons)ranked the first in China.However,the picking operation of kiwifruit in China mainly depends on the labors,which increases the labor costs and reduces international export competitiveness.The No.1 National Document vigorously advocated the development of agricultural robots.However,the picking efficiency is one of the most important factors that limit the practicality and commercialization of agricultural robots.The end-effector is the key actuator that determines the picking efficiency,and the fruit picking pattern determines the working efficiency of the end-effector.Therefore,researching new multi-fruit picking patterns and developing multi-fruit picking end-effector have important significance for promoting the industrialization of kiwifruit picking robot.This article focuses on the “Hayward” kiwifruit,which grows in cluster under the scaffolding mode at the Kiwifruit Experimental Station of Northwest A&F University,to develop the multi-fruit picking mode and multi-fruit picking end-effector.The main research content is as follows:(1)The relative movement multi-fruit picking pattern was studied.The cluster growth distribution and fruit stalk separation characteristics of kiwifruit will provide theoretical basis for studying the multi-fruit picking mode.In this paper,the height distribution characteristics of kiwifruit's pedicel in cluster were measured.Then put forward the relative movement multi-fruit picking pattren.The kiwifruit stalk separation test and kiwifruit spacial rotation separation test were performed to verify it's feasibility.The results showed that the average height of pedicel in cluster was 155.0cm,and the average height difference of kiwifruit clusters pedicle was 35.3mm,and the multi-fruits picking rate was 63.6%.The average rotation angle of the kiwifruit around its centroid was 35.78°.The average picking force of kiwifruit after refrigerating(4°C)for 32 days was 8.23 N.However,the average picking force of kiwifruit after refrigerating(4°C)for 1 day was 4.91 N.It can be seen that the absciss layer has brittleness and is easily broken by shear force,meanwhile,the absciss layer is easy to lose water,which will decrease it's brittleness and increase the picking force.(2)The multi-fruit picking model and the multi-fruit picking end-effector designing scheme were determined.This paper puting forward a kind of relative movement multi-fruit picking mode with combination of kiwifruit cluster distribution and absciss layer brittleness characteristics.Solve the formula to obtain the mathematical relationship between the length of the stalk,the length of the fruit,the rotation angle of the carpopodium,and the rotation angle of the fruit,and establish a multi-fruit picking model.Three kinds of design schemes were put forward,after comparing and analyzing the nine indicators,the third scheme(row-shaped fruits spacial rotation type)was determined as the optimal scheme.(3)The mechanical structure of the multi-fruit picking end-effector and the control system were designed.The multi-fruit picking end-effector was mainly composed of an inclined surface pushing plate mechanism,a swing cam mechanism,a fruit diversion and dropping device and a control system.Based on ANSYS Workbench 14.5,carried out static analysis of inclined surface plate and swing cam,carried out dynamic analysis of assembly.Used 3D printing technology to develop prototypes.In order to achieve non-destructive picking of kiwifruit,the control system used an STM32F103ZET6 processor with a frequency of 72 MHz for precise PWM control and integrated the FSR402 pressure sensor,Hall sensor,GP2A25 sensor and limit switch.(4)The picking verification test of multi-fruit picking end-effector was Studied.In order to verify the adaptability of multi-fruit picking end-effector.Firstly,carring out the test in the laboratory of agricultural machinery,where established the picking environment of the kiwifruit scaffolding,finding out the problem of falling fruit,and the device for fruit diversion and dropping was set.Then went to the Kiwifruit Experiment Station in Mei County for field picking test.A total of 98 kiwifruits were picked,and the success rate of multi-fruit picking was 90.8%,the success rate in the morning,noon and evening were 92.9%,84.3% and 95.8% respectively.Strong sunlight had effect on the sensors system.The single-fruit picking time is 2.49 s.The injury rate of the picking test at the Meixian Experimental Station was 12.36%,of which the shedding kiwifruit injury rate was 88.9%,and the sliding kiwifruit injury rate was 3.75%.It can be seen that the corrugated sliding tube can effectively reduce the damage rate.