| Nowadays,plant factory has achieved the automatic environment control,intelligent network control,production process specification and so on,but there is less application in leafy vegetable production.And the tradition leafy harvest machine and system could not be used for lettuce in plant factory due to the disadvantages such as large and expensive.This project is based on the plant factory of Jiangsu University and treats lettuce as the research object,and mechanical properties of lettuce is tested.This project designs one kind of lettuce automated harvesting system which apply to the plant factory,this system contains the transport mechanism,the moving mechanism,the terminal actuators,and the control system.Then the system is debugged and makes the performance test validation.(1)Mechanical properties test of lettuceThe nutrient lettuce is used as the research object,the compression characteristics,and stem shear mechanical properties of lettuce is tested.The maximum static friction coefficient among silicone,rubber,PU polyurethane and lettuce’s leaf are tested separately.The result shows that the compression capacity of lettuce will be enhanced after the compression position is gradually moved up;the peak of shear force is negatively correlated with the velocity and angle;the effect of the diameter of lettuce on the peak of shear force is less obvious when the velocity is increased.The maximum static friction coefficient among silicone,rubber,PU polyurethane and lettuce’s leaf are 0.774,0.726 and 0.611 separately.Silicone is best suited for the protect material for lettuce harvest operations.(2)Design of the harvesting system actuator and control systemDesign and layout the automatic lettuce harvest system,carry out structural design and parameter calculation for the transport device,platen device,XYZ coordinate right angle movement mechanism and end actuators.Among them,design 2 different kinds of end actuators,one is double crank slider translation mechanism and another is gear meshing mechanism,designs the structural and determines work parameters of the two end actuators.At the same time,select PLC as the control scheme of the system and select the relevant hardware(sensors,PLCs and industrial touch screens)according to the requirements of harvesting operations.(3)Harvesting system performance testDisplacement accuracy,harvest performance and vibration are tested on the automatic lettuce harvest system separately.The result shows that harvest operation of system is reliable;there is no significant difference of the measured displacement amount of XYZ directions with the hole interval of 9 hole(3 × 3)cultivation plate and set point of Z direction.The significance is more obvious with the increase of harvest velocity that means the positioning accuracy is higher after the decrease of harvest velocity;the system meets the accuracy requirements of harvest operations.Carry out automatic harvesting performance test of the two different end actuators,the results show that the harvest success rate of gear meshing rotary end actuator is higher than double crank slider type end actuator under the same operating efficiency.The harvest success rates of gear meshing rotary end actuator are 94.4%、91.6%、83.3% when the harvest velocity are 15、20、30 pieces per hour,that means the harvest success rate decreases when the harvest velocity increases.Carry out vibration test of the system with gear meshing rotary end actuator,the results show that the vibration of system is significant when the harvest velocity increases to 30 Pieces per hour,the stability of system is decreased,leading to harvest success rate to 83.3%.The natural frequency of a certain order of gripper floor is similar with the excitation frequency of the system motor,resulting in the possibility of resonance of the holder floor.Then in practical work,to balance the harvest efficiency and harvest success rate,the harvest velocity should among 15 to 20 pieces per hour and less than 20 pieces per hour. |
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