Research On The End-effector Of Citrus Harvesting Robot Based On Shearing Characteristics

Citrus is one of the large-scale cultivated agricultural products in Southwest China,Its harvesting is mainly based on artificial methods at present,It has the disadvantages of high labor intensity and high cost,citrus harvesting robots can effectively reduce the intensity of manual operations and reduce production costs,however,the end-effector is the important part of the harvesting robot,the rationality of the design about end-effector directly affects the damage rate and harvesting effect when picking of fruit.Therefore,it is of great significance to carry out research on the end-effector of citrus harvesting robots.This thesis relies on the key technology innovations of key industries in Chongqing,and uses the occluded end-effector developed by the research group in the early stage as the object.It analyzes,optimizes,and performs experimental research on the basis of the research of shear characteristics about pedicel.The main research content of the thesis includes:(1)The research of shearing characteristics of pedicel.A shear test bench was made by myself,The relationship between pedicel diameter,shearing method,cutting speed and peak shear resistance force and shear depth was studied,it was determined that the power of the shearing mechanism was aerodynamic,the single tool straight edge type was used,and the minimum shear depth was 5.34mm.Counting horizontal declination angle of pedicel,it was determined that actuator shear mechanism needs to achieve shear within the horizontal deviation angle of the pedicel from-30°?30°,analyzing the relationship between the angle and the shear resistance,it was determined that the peak shear resistance force that shearing mechanism has was 69.99N,(2)End-effector shear mechanism optimization.The shearing mechanism of the occlusal actuator was optimized through adding a rotation of the shearing mechanism around the fixed axis,expanding the occlusal angle to 180°,increasing the transmission angle,and optimizing the shear force.Analysizing the reset motion of end-effector,angular displacement of tool,angular velocity of tool and angular acceleration of tool,and the rationality of the design was verified by simulation analysis.The results showed that the maximum linear acceleration,linear speed,and total cutting time of the tool after optimization were:9 × 104 mm/s2,1260mm/s and 0.52s.(3)The design of end-effector clamping mechanism.Based on the analysis of the shear characteristics of the pedicel and the damage analysis of the fruit surface,the idea of using the clamping mechanism to fix the fruit during harvesting was proposed.According to the squeeze test data,fruit diameter and fruit shape the design parameters of the clamping mechanism are determined;According to the test obtained friction coefficient of 0.71 to determine the minimum clamping force is 0.19N and the ultimate extrusion force is 102.41N;The control loop was built based on the movement of the clamping mechanism during the reset and clamping process.The test results showed that the prototype of the developed clamping mechanism can achieve non-destructive gripping to fruit and the gripping effect very well.(4)The optimized occlusive end-effector was experimentally researched in a laboratory environment and natural environment.In the laboratory environment,the shear tests with different declination angle and different thicknesses of pedicel were performed.The results showed that the success rate of harvesting was 92%,which was 28%higher than that before optimization.In the natural environment,the comparison experiment about the three different working conditions including the horizontal attitude of the partial optimized end-effector,the 45° of the partial optimized end-effector,and the final optimization scheme is carried out.The results showed that the final harvesting success rate of the optimized was 85%.Compared with the partial optimized end-effector at horizontal attitude was improved by 55%,compared with the partial optimized end-effector at 45° was improved by 35%.This fully demonstrates the rationality and effectiveness of the optimization to the occluded end-effector in this thesis.