Control Method Of Dual Arm Picking Robot For Kiwifruit

China is one of the main producing countries of kiwifruit,but kiwifruit mainly depends on manual picking.The picking robots for Kiwi fruit can reduce labor costs and solve labor shortages by replacing hand picked kiwi fruit.The damage rate and efficiency of picking robot are important indexes to evaluate the performance of the robot.In order to reduce mechanical collision of kiwifruit by mechanical arm to kiwi fruit outside the target fruit,a method of sequential planning for continuous picking of kiwi fruit with multiple targets was proposed in this paper.In order to improve the efficiency of picking kiwi fruit,a dual-arm coordinated scheme of picking kiwi fruit was established.The main research content is as follows:（1）Dual-arm coordinated robot scheme for the picking of kiwifruit is determinedThrough investigating the agronomic and physical characteristics of kiwifruit and the identification and location methods of kiwifruit,the relevant parameters of agronomic and physical characteristics of kiwifruit were obtained,which prepared for the proposal of picking sequence scheme of kiwifruit.In order to solve the problem of low efficiency of single-arm for the picking of kiwi fruit,the overall scheme of multi-joint dual-arm coordination was proposed.The advantages and disadvantages of Cartesian single manipulator and multi-joint double manipulator were compared and analyzed,and the coordinated picking scheme of rhesus monkey multi-joint dual manipulator was determined.The forward and inverse kinematics equations of UR5 manipulator were solved to obtain theconditionofthesingularityofthemanipulator provided the theoretical basis for avoiding the singularity of the manipulator.Multi-articulated kiwifruit picking robot with dual-arms is mainly composed of machine vision system,two robotic arms,end-effectors,intermittent mobile platform and control system.It’s working principle is that the machine vision system is used to locate kiwi fruit through image processing for kiwi fruit under the camera coordinate system of the space coordinates(x_1,y₁ z₁).Through coordinate transformation,the three-dimensional coordinate of kiwi fruit can be obtained which based on the coordinate of mechanical arm base.The manipulator sends the end effectors to the bottom of the kiwifruit to break off the kiwifruit and complete the picking of the kiwifruit.（2）Study on sequential picking sequence method for the picking of multi-objective fruitsIn order to avoid mechanical damage to kiwi fruit other than the target fruit,the picking order of kiwi fruit needs to be determined.Firstly,The RGB image and depth image of the kiwifruit can be obtained by Kinect sensor.Then,the pixel coordinates of kiwifruit calyx centroid are identified by combining improved K-means++and Otus threshold segmentation.Finally,the three-dimensional coordinates of kiwifruit calyx centroid are obtained by matching the depth image of kiwifruit,and the multi-objective kiwifruit is obtained.The three-dimensional coordinates of the calyx centroid are transferred to the corresponding manipulator.The kiwifruits were picked in accordance with the established rules.Monte Carlo method was used to analyze the working space and the picking space of kiwifruit picked by dual-arm manipulators in coordination,and the recognition range of Kinect sensor was compared with that of the picking space of kiwifruit picked by dual-arm manipulators in coordination.The principle of determining picking order for the picking of kiwifruit is as follows,the average of the region identified camera can be divided into two areas,and the adjacent kiwi in each area are divided into different areas,sub area of the picking order picking down on the grounds.The principle of picking order of kiwifruit in sub-region is to calculate the center pointc_eim（7）x_eiy_ei（8）（7）e=1、2;i（28）1 n;k=1 m（8）of multi-objective kiwifruit in sub-region,and calculate the distance between calyx point and center pointc_eim（7）x_eiy_ei（8）（7）e=1、2;i（28）1 n;k=1 m（8）of Kiwifruit in sub-region in xoy plane.Kiwifruit is picked from far to the near.The Cartesian space linear programming method is selected for path planning of the end joint of the manipulator,which makes the end joint maintain a 90 degree vertical ground attitude during the picking process,and avoids the singularity of the manipulator.In addition,the avoidance of singular configuration is achieved in the process of continuous reaching multiple target points.Based on the Matlab/Simulink simulation platform,the proposed control method was verified with UR5 manipulator as the theoretical research tool.The results showed that the joint velocity of each joint did not change during the continuous picking of kiwi fruit,indicating that the singular configuration of the manipulator was avoided.End joint posture to keep vertical ground 90°,can meet the control of the manipulator end joint,verify the effectiveness of the algorithm.（3）Research on the control of dual-manipulator coordination picking.In view of the obstacle avoidance problem of the dual arm robot,the constraint method was put forward based on position layer and velocity layer.When the distance between the corresponding joints less than the threshold value,the movement speed of the manipulators in this direction was controled 0 for the obstacle avoidance,ensuring that the distance between the joints does not exceed the threshold value.To solve the path planning problem of the dual-arm manipulators,this paper uses parabolic fitting function to interpolate the position and attitude of the end joint to ensure the trajectory of the end joint of the linear spline smooth.To solve the problem of singularity of manipulator,the common inversion method and the damped minimum variance method were used to avoid the singularity,and the effect of the two methods was compared.The Matlab/Simulink module was used to verify the coordinated picking method of kiwifruit with double arms.The results show that the damped minimum variance method is more effective in avoiding singularity.The posture of the end joint of the manipulator is kept perpendicular to the ground at 90 degrees,the velocity of each joint does not change abruptly,and the singularity of the manipulator is avoided.The space trajectory of the end joint is linear motion without collision.（4）Dual-arm coordination picking test.The picking experiment platform of kiwi fruit with two mechanical arms was set up,and the position error test and the picking performance test of kiwi fruit with two mechanical arms were carried out.The position error test of the dual-arm kiwi fruit picking was designed to verify the stability of the kiwi fruit coordinating system.The experiment shows that the position error is controlled within 5mm,which verifies the stability of dual-arm manipulators coordination for kiwi fruit picking system.Dual arm picking kiwi fruit picking performance test results show that the average harvest time was 8.25 s.the success rate was 90%compared to the cartesian robot.The picking efficiency increased by29.3%.