| Tomato harvesting is time-consuming,labor-intensive and costly.The cost of artificial harvesting has become the main factor affecting tomato industrialization.At present,most domestic and foreign research and development of tomato harvesting manipulator harvesting object is tomato single fruit,single fruit harvesting efficiency relative to the string harvesting is low.The study of tomato fruit harvesting in clusters is of great significance in reducing costs,improving the quality and efficiency of harvesting.In this study,the design and experiment of tomato fruit string picking manipulator were carried out.The specific research contents are as follows:(1)The physical and mechanical properties of tomato fruit bundles were studied by Universal Ability Test-bed,and the mass distribution,stem diameter distribution and stem shear characteristics at different maturity were obtained.The results showed that the diameter of the stem of tomato approximated to the normal distribution law,and the proportion of the stem diameter was more than 95% in 4~8.4mm;the maximum mass of the tomato string sample was 0.91kg;the shear force needed for the tomato string with higher maturity and thicker stem diameter was larger.(2)According to the physical and mechanical characteristics of tomato,the end effector was designed.A parallel finger cylinder was used to clamp the stalk of tomato bunches;a DC motor was used to drive the circular saw blade to rotate at high speed through a steel flexible shaft,and a stepper motor was used to cut the stalk by moving the saw blade back and forth through a screw nut and a sleeve.The kinematics analysis of the picking action of the end-effector is carried out by ADAMS,and the results show that the designed end-effector meets the requirements of the picking summary.The strength of the joint parts of the end-effector is checked.According to the checking results,the clamp is optimized and improved by ANSYS,and the end-support is optimized based on lightweight.(3)According to the design results of the target load of 1kg and the end effector of the manipulator,a seven-degree-of-freedom picking manipulator is designed.Its mechanical structure includes two moving joints(horizontal moving joints and lifting joints)and five rotating joints(waist,upper arm,lower arm,wrist and end effector).SolidWorks is used to model the picking manipulator,and kinematics and dynamics of the picking manipulator are studied.The results show that the end-effector runs smoothly and the motor is selected correctly.Strength checking of the lifting joint and the upper arm joint of the picking manipulator is carried out.The results show that the equivalent stress and deformation can meet the design requirements;the overturning resistance of the whole machine of the manipulator is divided into two parts.The results show that in order to ensure the normal operation of the manipulator,it is necessary to install a steel plate larger than 9.81 kg on the base.(4)The control system of picking manipulator is designed,and the single joint control system based on STM32 microcontroller is made,and the software of lower and upper computer is compiled.The experimental platform for tomato string picking was established and theoretical error calculation was carried out.The results showed that the maximum error of the manipulator in X,Y and Z directions was 4.55 mm,3.30 mm and 5.76 mm,respectively.The no-load positioning accuracy test was carried out.The results showed that the maximum error of the manipulator in X,Y and Z directions was 3.7mm,0.994 mm and 8.48 mm,respectively.The repetitive positioning accuracy of the manipulator in X,Y and Z directions was(+2.85 mm,+3.05 mm,+4.85mm).The experiment of tomato fruit string picking with the designed manipulator showed that the average picking success rate was 61.4%. |
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