| Facility agriculture is a modern agricultural production mode for the high-efficient production of animals and plants to gain better agricultural products with less dependence on environment in certain extent. Thus, facility agriculture has become a crucial industry in many countries and regions. With the continuous development of the facilities for nursery factory, the automatic grafting machine, nursery box, automatic seeding machine and environment control system have been widely used. However the transportation of seedling plates in facilities are mainly based on manpower. Therefore, it is crucial for reducing labor and cost and improvement of productivity to achieve intelligent and automatic transport of seedling plates under the development trend of mechanical automation. More specifically, it is of practical significance to develop the seedling tray automatic handling machine to solve the movement problem of seedling tray in the factory. In this paper, a kind of mobile platform under seedling tray automatic move device was designed. The research contents are the following:(1) Determination of the mobile platform overall scheme of seedling tray automatic conveying device. The structure and implementation of mobile platform were determined by many factors such as the structure of seedling box and seedling disc, the seedling height, ground environment of the plant and handling structure. The mobile platform chassis wheel structure and the overall design scheme have been determined through analysis and comparison of mobile platform chassis wheel structure. The the turning radius of designed differential gear train type four wheel chassis is small and flexible, can better adapt to the factory handling operation. The driving mechanism is controlled by a brushless DC motor, which can simplify the mechanical structure and control algorithm. According to the actual working environment, the method of magnetic guidance control is adopted to carry out the path tracking.(2) Structural design and optimization on moving platform. In order to ensure the operational stability and reliability of the mobile platform. The supporting frame structure is designed according to the structure and size of the handling device, driving wheel driving mechanism, driven wheel mechanism, can satisfy the load 100 kg strength requirements, using software ProE to every part of the body structure of three-dimensional modeling design and complete the virtual assembly, no interference phenomenon, and using ANSYS Workbench software on the key parts of the bond and the transmission shaft of finite element analysis and verification, it was found that the deformation is smaller, meet the strength requirements.(3) Control system design on mobile platform of the seedling tray automatic conveying device. Using 51 single chip as a micro controller integrated with multi sensors to realize mobile platform cooperative control on path tracking, straight line, turn, stop, obstacle avoidance alarm, remote control and serial communication in stripe-guided approach. The control system consists of the STC89C52 RC microcontroller, the magnetic navigation sensor, landmark sensor, infrared obstacle avoidance sensor and other sensors. The main control board, motor drive, magnetic navigation, obstacle avoidance alarm, DC power supply and the infrared remote control module of hardware and software programming were designed to realize mobile platform cooperative control on path tracking, straight line, turn, stop, obstacle avoidance alarm, remote control and serial communication in stripe-guided approach.(4) Trial production and evaluation of a mobile platform. Through the measurement analysis to determine fitting relationships between speed and PWM duty ratio as well as Holzer speed feedback signal cycle for motor speed control. Through the test, the optimal installation distance of magnetic navigation sensor is 50 mm and the position deviation was determined by measuring position deviation. Obstacle avoidance sensor threshold was set to 80 cm and performance requirements was met through completing the whole assembly of mobile platform and testing the performance of each functional module. Through the no-load operation, it was found that the rationality of the mechanical structure design of the mobile platform and the accuracy of the control system are verified by repeated experiments. the results of carry test showed that the mobile platform can achieve steady speed operation and can better realize the path following a straight line and turning driving, the straight path position deviation was less than 40 mm, turning path position deviation was less than 70 mm. Moreover, the mobile platform can park smoothly and fast as well as accomplish timely obstacle avoidance alarm. Furthermore, the mobile platform can operate continuously for 2 hours to meet the design requirements. |
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