Development Of Pear Picking-Packing System Based On Machine Vision And Six-Axis Robotic Arm

In recent years,with the rapid development of pear planting industry in China,the annual yield of pears continued to rise,the types and number of pears that need post-harvest processing increased as well.In the face of such an enormous pear yield,it is particularly important to improve the speed and quality of pear post-harvest processing.Currently,the post-harvest pear processing technology has achieved great improvements.However,during the post-harvest processing of pears,the traditional manual picking is still used in the stage of pear picking-packing,especially in China.In order to alleviate this problem,this paper designed a pear picking-packing system that is used in the picking-packing stage of postharvesting processing.This system uses a vehicle-mounted robotic arm,and a robotic hand unit,with a camera and a ranging LIDAR,to automatically pick pears and put into the box during post-harvest processing.The main research contents of this thesis are as follows:(1)Overall scheme design of pear picking-packing system.Considering the operating environment of the pear post-harvest processing,the pear picking-packing system is required to having small size,simple operation and stable working performance.According to the mentioned requirements,the overall scheme of the device was designed.It includes robotic arm-hand device,machine vision device,walking device,control system.The pear pickingpacking system used a wheeled walking device and a six-axis mechanical arm.The movement and operation of this system could be controlled by a remote control handle.(2)Design and analysis of the key components of the pear picking-packing system.The Grignard lithium battery was selected to provide power for the pear picking-packing system,and the brushless hub motor was selected according to the required driving torque of the single wheel.In view of thin peel of pear fruit,the robotic hand unit selected the fin-rayshape flexible claw and designed the other parts of the hand.Finite element analysis was carried out on the frame,and equivalent stress cloud map and total displacement cloud map of the frame were obtained through the analysis.The results showed that the maximum stress value of the frame was 5.097 MPa,which was less than the 90 MPa the yield limit of 6063 aluminum alloy material,and total displacement value of the frame were within a reasonable range.Therefore,the strength and stiffness of the frame meet the requirements for use,and the design is reasonable.Raspberry Pi camera and Time of Flight(TOF)ranging LIDAR were chosen to implement the functions of identifying and locating pear and detecting whether the hand unit successfully picking up pear or not.(3)The design of the control system and prototype test.Firstly,the design goal of the control system of the pear picking-packing system was determined,the movement of the whole machine were determined to be through the remote control handle,and the control mode of robotic arm device was determined to be manual/automatic dual control mode.Then the hardware of the system-on-module and communication in the control system was designed and selected,and the software part of the control system was designed.Among them,NVIDIA’s Jetson Nano was selected to be run the control system,and Wi-Fi was selected as the communication.The prototype of the pear picking-packing system was tested.It was determined that the background of the conveyor belt matched with the equipment was black,the driving current of the manipulator unit was 1A,the forward speed of the equipment was0.6m/s,and the working efficiency was 4 pcs/min.(4)Robotic grasping experiment to verify if the pear picking-packing system can pick up pears nondestructively.The Korla pear was selected as the test pear fruit,and three repeated experiments were carried out.Three sets of data were collected for each experiment.The stress value of robotic hand during it grasping and the fracture stress of pear fruits were recorded in this experiment.And the damage situation of the test pears was visually observed after being placed for seven days.The results showed that the stress value of the hand during grasping was much smaller than the damage stress of Korla pears,and there was no obvious damage on the surface of Korla pears in the test seven days later.Therefore,it was concluded that the pear picking-packing system could realize the non-destructive grasping of pears.