Optimization and experiment of the multifunctional operation platform of the stereo cultivation system for plant factory

Stereo cultivation is usually used in plant factories for seedling and cultivation. Transportation of cultivation bed is an important part of the stereo cultivation automation. At present, cultivation bed is mostly handled manually, which has problems such as high labor intensity and low level of automation. To solve this problem, a multifunctional operation platform, which had the functions of autonomous tracking, automatic positioning, and automatic conveying of cultivation bed, was developed in this paper. The multifunctional operation platform mainly consists of navigation system, positioning system, communication system, walking system, lifting system, automatic docking system, and automatic conveying system. The working principle and technical parameters of the multifunctional work platform were introduced. During operation, the cultivation bed was transported from nursery workshop to greenhouse by the multifunctional operation platform firstly. Then，the multifunctional operation platform reached the target stereo cultivation rack through the road reserved in greenhouse and lifted the cultivation bed to the target height. The automatic conveying mechanism started to push cultivation bed to stereo cultivation rack by automatic docking mechanism. The cultivation bed was transported to stereo cultivation rack when the proximity switch installed on stereo cultivation rack detected the cultivation bed. Finally, the multifunctional operation platform stopped working and go back to the charger area. When the crops were mature, the multifunctional operation platform would automatically transport the cultivation bed to the picking area, so as the logistics automation of the crop production process was realized by the multifunctional operation platform. To meet the requirements of multi-layer cultivation of stereo cultivation rack, the lifting mechanism was designed based on principle of virtual displacement according to the weight of the cultivation bed and the height of the stereo cultivation rack. Single hydraulic cylinder driving and two scissor lift mechanisms were chosen. The maximum driving force of the hydraulic cylinder was about 15 443.9 N through theoretical analysis. The length, stroke, outer diameter and inner diameter of the hydraulic cylinder were determined to 940, 360, 63, and 35 mm respectively. The automatic docking and automatic conveying mechanism of the cultivation bed were studied. The automatic docking was realized between the multifunctional operation platform and stereo cultivation rack by automatic docking mechanism, and two-way transportation of the cultivation bed was realized by automatic conveying mechanism. Thus, the automatic loading and unloading of the cultivation bed was realized. The positioning system based on the RFID (Radio Frequency Identification) sensor was determined. Walking system and the lifting mechanism of the working platform would stop working when the RFID sensor detected the electronic labels on the ground and stereo cultivation rack.STM32 was used as the main controller of the automatic control system. The software and hardware of the control system were designed. A human-machine interaction interface was designed based on the Android. It was to monitor the motion status and operating parameters of the multifunctional operation platform in real time. To evaluate the operation performance of the multifunctional operation platform, the experiments were conducted. The test indexes were the height range of the lifting mechanism, the front and rear positioning deviation, the height positioning deviation, and the success rate of the platform and the stereo cultivation frame docking. The experiment results show that the height range and effective lift height of the multifunctional mobile platform was 833-2 460 mm and 1 627 mm. The front and rear positioning deviation is less than 9 mm, average value was 4.5 mm. The height positioning deviation was less than 5 mm, average value was 3.7 mm. And the docking success rate was not less than 96%, which meet the requirements of the operation. This study provides a reference for further improving the automation level of stereo cultivation of plant factories.