Development Of Fruit-stalk Separation Kiwi Fruit Picking End-effector

China has the largest kiwifruit plantation in the world,and the large number of plantations is bound to put enormous pressure on the harvesting season.At present,kiwifruit harvesting is not fully mechanised and therefore still relies on manual harvesting,resulting in long working hours and high costs.With the advent of technology,mechanised harvesting is set to replace manual harvesting.The fruit picking end-effector is the direct part of the mechanised harvest that comes into contact with the fruit,so the simplicity and efficiency of its structure will directly determine the efficiency of the fruit picking.The differences in the structure of the fruit growth and the way it is picked will also lead to some specificity in the design of the fruit picking end-effector.The fragility of most picking objects and the variability of the surrounding environment make the design of the end-effector also demanding in terms of protecting the fruit and therefore the study of efficient kiwifruit picking end-effectors is of great practical importance.In this paper,the fruit of the "Hongyang" kiwifruit is used as the object of study.The research and development of the end-of-pick actuator was carried out as follows.(1)The physical size and mechanical characteristics of the kiwifruit were investigated.The coefficient of friction of the "Hongyang" kiwifruit on the porous rubber was studied and the minimum gripping force to keep the fruit from falling was determined to be 0.62 N.The results of the experiments on a universal testing machine showed that the size of the influence on the picking force was ranked as angle of inertia between the fruit inertia axis and the fruit stalk >diameter size > shear speed,so that the angle between the fruit inertia axis and the fruit stalk The picking force is fundamentally determined by the angle between the inertia axis and the stalk.Based on field research into the growth patterns and manual picking patterns of the "Hongyang" kiwifruit,a fruit picking model was established and the principle of kiwifruit picking was analysed to propose two imitation manual end-effectors.The single fruit picking end-effector realises the function of "gripping-change of picking angle-picking-unloading" and is fitted with multiple sensors to enhance the accuracy of fruit picking.The multi-fruit picking end-effector is simple to operate,picks rows of fruit and uses pure rubber in contact with the fruit,further reducing the damage rate of fruit picking.The efficiency of the different picking methods on fruit picking and the damage to the fruit is investigated.Both kiwifruit picking end-effector picking modes imitate the manual stalk separation method,reducing damage to the fruit tree and to the fruit during the post-picking accumulation process,and their picking principles are somewhat reasonable.(2)The single-fruit picking solution is based on the physical dimensions of the "Hongyang" kiwifruit itself,with a three-dimensional bionic finger arc of 100 mm radius and30° radius.The crank and rocker mechanism has a length of 35 mm and 100 mm respectively,and the frame and linkage lengths are 60 mm and 90 mm respectively,which means that there is no dead space in the mechanism and avoids forward and reverse rotation of the reduction stepper motor within a short period of time.Static simulation and overall kinematic simulation analysis of the key parts of the two picking end-effectors that are subject to large forces were carried out to verify the feasibility of their movements,and both end-effectors met the design requirements.(3)The end-effector control system structure was designed.Using the STM32F103ZET6 microcontroller as the controller,the single-fruit picking end-effector drive control system selects a 42 linear stepper motor,a 4234 type reduction stepper motor,a counter-infrared sensor,a NJK-5002 C type Hall sensor and a FSR402 long-tail resistive pressure sensor,while the multi-fruit picking scheme uses a 4234 type reduction stepper motor,a FSR resistive The multi-fruit picking solution uses a 4234 reducer stepper motor,FSR resistive pressure sensor and GP2A25 sensor as the main drive and control components to complete the picking action,and both solutions have built the hardware system and completed the software design.(4)Both end-effectors were tested on a three-degree-of-freedom screw test rig.The multi-fruit picking end-effector was mounted on a 6-DOF robot arm and a systematic picking test was carried out to verify the end-effector’s ability to pick kiwifruit and to test the damage rate of the final picked fruit.In the single fruit picking end-effector simulation,the kiwifruit fruit inertia axis was angled at 30°,60° and 90° to the fruit stem,resulting in picking success rates of 79.49%,82.05% and 74.36% respectively.On balance,the single-fruit picking end-effector is most efficient when the inertia axis is at an angle of 30° to the fruit stalk,so the actual picking should be controlled when the inertia axis is at an angle of 30° to the fruit stalk;in the multi-fruit picking end-effector simulation,the success rate of three-fruit picking was77.5%.In order to improve the picking efficiency,the final selection of the multi-fruit end-effector for the 6-DOF robotic arm-based picking system tests showed that the multi-fruit picking end-effector system picking tests had a 75% success rate for fruit picking;in terms of damage rate,the simulated picking tests showed a 19.4% damage rate for kiwifruit picked by the single-fruit picking end-effector;the multi-fruit picking end-effector picked The damage rate was 6.5% for kiwifruit picked by the multi-fruit end-effector and 6.7% for kiwifruit picked by the multi-fruit end-effector in the robotic system picking trial.In conclusion,the multi-fruit picking end-effector is more suitable for mechanised kiwifruit picking.