| The end-effector is a key component in the actuation of apple picking robots.In order to achieve efficient apple picking,combined with the current situation of picking execution research at home and abroad,and taking red Fuji apples as the picking object,this paper designs a rotary screw type picking end-effector combining an air suction device and a three-finger manipulator.The end-effector design is based on the analysis of apple fruit growth,physical and mechanical characteristics,and the imitation of manual picking methods.CANopen-based end-effector drive module hardware and software;prototyping and setting up a simulated experimental scenario,and testing the end-effector performance in both simulated and field scenarios.The main research work is as follows:(1)The design requirements of the end-effector for apple picking were clarified.Based on the dwarf dense orchard scenario where the apple fruit is shaded by branches and the fruit grows in clusters,the picking requirements for separated fruit were proposed.Using instrumentation,the physical and mechanical properties of the apple fruit were measured and the results were as follows: the maximum diameter of the fruit was 117.3mm,the minimum diameter was 57.5mm and the average diameter was approximately 80.0mm,the maximum mass was 235.6g,the minimum mass was 141.1g and the average mass was approximately 185.1g.The threshold of the clamping force for breakage of the apple skin was 15.35 N,which provides a reference for the design of key component parameters for the end-effector.Comparing the advantages and disadvantages of the three manual picking methods,the end-effector picking method was determined to be a combination of rotary twisting force and horizontal force.(2)Developed an air-priming screwing type apple picking actuator.The end-effector design requirements were analysed and a screwing end-effector combining air suction and a three-finger manipulator was designed,with the end-effector workflow determined as "suction-clamping-screwing".The hydrostatic analysis of the force transmission process from the clamping servo to the finger and the calculation of the working loss of the screwing servo were carried out separately to determine the torque of the clamping servo as 4.5 N·m and the screwing servo as 2 N·m;the size of the fruit was analysed to determine the length of the manipulator finger as 120 mm and the opening and closing size as 30 mm to 120mm;the object of the vacuum suction cup was analysed and an organ type vacuum suction cup was selected,according to the load The diameter of the vacuum suction cup is calculated to be 15mm;with reference to the actual working conditions,a cylinder with a stroke of 150 mm and a bore of 20 mm is selected.(3)Design of a drive-controlled integrated picking end-effector control solution.In order to meet the end-effector control requirements,a distributed computing and I/O control structure and a CANopen-based communication structure are proposed.In order to realise the above control scheme,a CANopen based end-effector drive module is designed.The overall hardware structure of the drive module is built according to the actuating components on the end-effector,with the STM32F103 microprocessor as the core,including the power supply module,the servo signal processing module and the relay module.Based on the hardware structure,the main driver module control program was designed,defining and encapsulating the initialisation subroutine,the CANopen protocol stack subroutine,the relay control subroutine,the servo control subroutine and the gripping detection subroutine.A pressure feedback control program was designed for a smoother gripping process of the fruit.For uniformity of communication,the contents of the data packets for communication between the drive module and the servo and with the CANopen bus are defined.(4)Trial production of a prototype picking actuator and production test verification.The design was based on the above requirements,the prototype was prototyped and a simulated test rig was built in the laboratory.The end-effector vacuum suction cups were tested and optimised for an optimum suction time of 1s and an optimum suction distance of 1mm,and the average picking time of the end-effector was tested at 5.83 s.A pressure feedback test was conducted and the finger gripping force was measured to be no more than the threshold force to break the fruit.In field trials in orchards,the fruit picking success rate was tested at 85%.In order to analyse the factors affecting the picking success rate and to count the characteristics of the fruit picked successfully,it was concluded that the end-effector was more suitable for picking medium sized fruit between60 mm and 100 mm in diameter,with a success rate of 90%.The end-effector was tested with a success rate of 70% when picking fruit with branches in the way,no damage to branches at a 270°twist angle and zero fruit breakage after picking. |
