Research On Motion Planning And Concrol Sysytem Of The Cucumber Picking Robot

Fruits and vegetables harvest belongs to labor-intensive task. Because of population aging and lack of agricultural labor resources, the ratio of harvest price of human labor in the whole production price reaches to 33~50%, which greatly recedes their market competition. Therefore, studying and developing intelligent picking robots can not only liberate labor, improve productivity, decrease production price and maintain fresh quality of fruits and vegetables, but also promote further study and application of related techniques, such as mechanics, robotics, image processing, intelligent control and sensor. So it has significant practical meaning and academic value to develop picking robots.On the comprehensive analysis of advantages and disadvantages of picking robots at home and abroad, taking the cucumber as research object, motion planning and control system of the cucumber picking robot are systematically studied based on techniques of robot mechanics, kinematic and dynamic analysis, trajectory planning and tracking, position error compensation and so on. Research contents and achievements are listed as follows:1. Aiming at characteristics of cucumber picking operation, an articulated picking manipulator with four degree-of-freedom is developed, and the designed manipulator possesses favorable property of simple and compact structure, light weight, low price, flexible and stable picking motion. In order to harvest all of the fruits and vegetables in the target space, the general structure optimization method of articulated manipulators is proposed, which is applied in random cube of the picking space. Then the manipulator is optimized by MATLAB optimization Toolbox according to the target picking space of the cucumber.2. Analysis and simulation on kinematics and dynamics of the designed manipulator are implemented. Forward kinematics is constructed based on the D-H method and the inverse kinematics is solved by analytical mehod; meanwhile, the simplified dynamics are constructed by utilizing Lagarange method. Finally, simulation experiments of kinematics, workspace, and dynamics are carried out, results verified the validity of the models and resonability of the structure parameters optimization method. 3. Algorithms of trajectory planning and tracking of the picking robot are studied. The trajectory planning algorithm based on combination of two cycloidal motions with grasping horizontally is proposed by comparing various planned algorithms and combined with the structure and picking operation characteristics of the cucumber picking robot. Moreover, in order to achieve precise tracking of the desired trajectory, a fast and non-singular terminal sliding mode controller is constructed, it can solve the problems of asymptotic convergence of the linear sliding mode controller, and the singularity and chattering of the conventional terminal sliding mode controller. Simulation experimental results show that the desired trajectory can be tracked precisely, and the postion tracking error can converge to equilibrium point in finite time, faster and high-precision tracking performance is obtained by using the presented algorithm.4. Position error compensation algorithms of the picking robot are studied. The direct error compensation method based on LMBP network and the preseting position offsets are proposed, which are used to compensate for position error caused by structure parameter deviation, the validity of the proposed algorithms has verified by simulation experiments.5. Control system of the cucumber picking robot is designed based on CAN bus communication. The distributed control mode of supervisory motion controller based on DSP+CAN bus+joint controllers based on DSP is presented. Hardware platform of control system is constructed; and programs for realizing the control system are designed by using modular principle, such as initiation, inverse kinematic computation, trajectory planning, the end effector control, CAN module, collection and control of the joint position and so on.6. The performance test experiments of the cucumber picking robot are carried out. Experimental results show that the robot system can run stably and reliably, the repetitious position precision is about 2.4mm; after compensation, the maximum position errors in x and y axis have expectively declined from 4.3mm to 3.5mm, 6.9mm to 3.7mm; and position errors in z axis are nearly no changing. The ratio success of the robot's picking is approximately 86%, and the average time consumed for picking a cucumber is about 18s.This thesis provides favorable base for further research on intelligence and practicality of picking robots, and in the future, optimization of the mechanic structure and control accuracy should be studied more deeply.