| Fruit and vegetable harvesting is seasonal and time-intensive,which requires a lot of labor,and the most time-consuming and energy-consuming link in agricultural production is fruit and vegetable harvesting.At the same time,based on the social and economic transformation and development of our country,the aging of agricultural employees is becoming more and more serious.Mechanization and automation of fruit and vegetable planting and harvesting is the only way for sustainable development of agriculture.The banana yield in China has been ranked the second in the world steadily.Based on its biological characteristics,bananas have row spacing of 3-3.5 m and plant height of 2.5-3.2m according to varieties.Banana harvesting is a typical work at high altitude,and the quality of fruit string is between 30 kg and 80 kg.The efficiency of manual harvesting is low and the harvesting workers are liable to be damaged.In accordance with the actual working conditions and tasks of banana harvesting robot,an intelligent banana harvesting robot arm with large vertical/horizontal travel and large load capacity is designed based on the principle of cylindrical coordinates.Mainly completed the following research:(1)According to the specific working environment of banana harvesting,an integrated design scheme of intelligent banana harvesting manipulator arm with large vertical/horizontal travel and large load capacity based on improved cylindrical coordinate principle is proposed.According to the planting environment and growth characteristics of banana,the vertical working height of intelligent banana harvesting manipulator arm is0.8-3.0 m and the horizontal arm is extended up to 2.1 m.An improved cylindrical coordinate principle design scheme is used for the overall design of the robot arm,and a bipolar telescopic rod with synchronous driving ability is used for lifting and harvesting in the vertical direction.Horizontal direction adopts the structure of " back arm/ forearm " with series structure to meet the application requirement of arm spread up to 2.1 m.The end of the arm is designed with an end actuator for banana "clamping-shearing" operation.Considering the overall stability of the robot caused by heavy load at the end of the robot arm(80 kg)and arm extension in horizontal direction,a horizontal balancing device symmetrical to the transverse "back arm/ forearm" structure and a 2DOF balancing cloud platform mechanism between the robot arm and the moving chassis are specially designed in this study.The center of gravity position of the transverse "back arm/ forearm" is adjusted by active drive.And the tilt angle adjustment of vertical bipolar telescopic rod can improve the anti-overturning performance of banana harvesting robot.According to the harvesting limit application condition(maximum load 80 kg,"mechanical arm/banana plant" maximum spacing 2 m,and maximum harvesting height 3 m),the change range of the whole gravity center of gravity of the mechanical arm during the process from the starting point to the end point of harvesting is calculated,and the anti-overturning performance of the robot is analyzed and verified by gravity method.At the same time,the static analysis of key parts of the mechanical arm is carried out.(2)Based on modified Denavit-Hartenberg method,the overall kinematic model of banana harvesting manipulator is established,and then the mapping relationship between the end actuator of banana harvesting manipulator and the joint space of the manipulator is established.The forward and reverse kinematic analysis of the manipulator is carried out,and the correctness and validity of the kinematic model is verified by MATLAB.On the basis of kinematics analysis,the reachable motion space at the end of the manipulator arm is obtained by using stochastic probability-Monte Carlo method,and the whole working space range of the manipulator arm is analyzed.For the dynamic problem of the mechanical arm,the multi-rigid body dynamic equation of the mechanical arm is established based on Lagrange method,and the relationship between motion and force of joints in each part of the mechanical arm is analyzed,which lays a foundation for subsequent forward/reverse dynamic analysis based on ADAMS.A differential method is used to solve the velocity Jacobi matrix.The result shows that there is no singular position of the arm and the relationship between the end motion speed and joint velocity.(3)Based on the kinematics and dynamics analysis of the manipulator arm,the overall trajectory planning of the "harvesting-transporting-storing" process of the manipulator arm is carried out according to the actual banana harvesting process.From the angle of smoothness of control of driving joint motion and stability under the condition of "arm extension/large load",a simplified mapping relationship and constraints for trajectory planning of end-effector of robot arm from three-dimensional space to two-dimensional space are established.The interpolation points on the trajectory curve in Descartes space are transformed into joint variables of each joint in joint space by analytic method,and then the end trajectory is planned by polynomial interpolation method in joint space,and the polynomial coefficients are obtained by constraint conditions of the joint.Using the MATLAB robot toolbox,the displacement,speed and acceleration curves of each joint driving space are obtained by cubic polynomial and quintic polynomial interpolation at the end of the arm respectively,and the three-dimensional trajectory of the harvesting operation in the overall working space of the arm is obtained.For the experimental analysis and verification,this paper uses ADAMS multi-body dynamics software to establish the simulation analysis model of the mechanical arm.The joint parts of the mechanical arm and the load parameters are the same as the real harvesting environment.The planned three-dimensional trajectory curve of the manipulator is guided to solve kinematics and dynamics,and the parameters of joint angle,speed,acceleration and driving torque of the manipulator under specific load conditions are obtained.In order to verify the banana harvesting robot overall motion scheme and joint drive performance parameters designed in this subject meet the specific banana harvesting needs and successfully complete the harvesting task. |
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