针对果园单轨运输机在轨位置精准感知的应用需求,该文基于超高频射频识别技术(radio frequency identification, RFID)接收信号强度数据进行了运输机定位试验研究.该研究通过分析RFID通信特征,设计了RFID双天线双标签对照的运输机定位方法,构建了能量传输定位模型和路径损耗定位模型;通过阅读器单天线试验,得到当前 RFID 设备的安装参数,确定了阅读器天线与轨道标签之间的最优垂直距离为20 cm,双标签之间的最优水平在轨距离为45 cm;通过双天线试验及数据分析,得到适用于试验环境的最优定位模型系数.试验结果表明,该研究提出的定位模型能够有效降低噪声干扰,减少定位误差.RFID设备在最优定位参数条件下,使用路径损耗定位模型得到的最小定位误差均值为1.0070 cm.该研究验证了基于超高频RFID对果园单轨运输机定位的可行性,提升了运输机运行安全性和可靠性.%As the main transportation equipment in mountainous orchards, monorail conveyers have strong climbing capacity and high reliability. However, monorail conveyers in working status can be invisible frequently because of tree shades. It is impossible for operators to monitor a working monorail conveyer with a remote control in real time. Thus the monorail conveyer should have the capacity of arriving at the designated locations autonomously. The key technology is to locate the conveyer on the monorail accurately. In recent years, there has been growing attention on the technology of ultra high frequency RIFD (radio frequency identification) location, which is based on RSSI (received signal strength indicator) data. The ultra high frequency RIFD location has been applied in many fields including workshop inspection, warehouse management and staff supervision. However, these applications are carried out in indoor environment. There is little research on locating agricultural implements using ultra high frequency RIFD. Considering the application requirement of locating the conveyer on the monorail accurately, experiments of the monorail conveyer location awareness have been carried out in this paper, which is based on the RFID RSSI data. The RFID equipment used in this paper include an XC-RF807 UHF RFID reader with 2 separated unidirectional antennae and several XCTF-8405 anti-metal passive tags, which are provided by Invengo Technology Pte. Ltd, Shenzhen, China. The operating frequency of reader is 902-928 MHz and the transmitted power can be varied from 15 to 36 dbm. Firstly, RFID communicative features are analyzed. The approach of conveyer location is proposed by comparing the RSSI data between dual antennae and dual tags, which aims to reduce the noise interference in conveyer location. Then the energy transferring location model and path loss location model are formulated. Secondly, several experiments are carried out in the citrus orchard, which is located in the China Agriculture Research System, Guangzhou, China. The 2 significant setting parameters of RFID equipment, i.e. the optimal perpendicular distances between RFID antenna and the tag on the monorail, and the optimal horizontal distances between tags on the monorail, are obtained in the experiments of RFID single antenna. Parameters of the 2 location models are fitted to be applicable to experiment environment through the analysis of RSSI data, which can be obtained in the experiments of RFID dual antennae. Finally, the results of performance experiments on location models show that the approach of conveyer location, which is implemented by comparing the data of dual antennae and dual tags, can reduce the noise interference effectively. It can reduce the location error and improve the location system accuracy, but the interference cannot be eliminated completely. The experiment results also demonstrate that reducing the distance between dual tags on the monorail, which increases the density of deployed tags, is not a good way to improve the location system accuracy. The optimal horizontal distances between tags, and the optimal perpendicular distances between RFID antenna and the tag on the monorail are 45 and 20 cm, respectively, and the optimal coefficients in path loss location model are 63.19 and 2.988, respectively, which are applicable to the experiment environment. The varying lengths of conveyers should be considered when different types of conveyers are used. Under the optimal conditions, the minimal average location error is 1.077 4 cm by using the path loss location model, and the minimal location error is 0.017 0 cm by using the energy transferring location model. In order to further verify the effectiveness of the proposed approach, another experiment is carried out in Germplasm Resource Garden of Southern Subtropical Fruit Trees, Guangzhou, China. It shows the similar location results. The research in this paper verifies the feasibility of locating the conveyer on the monorail accurately by using ultra high frequency RIFD equipment. The proposed location approach can improve the safety and reliability of working monorail conveyers. It also can provide accurate data support for applications including multiple transportation tasks planning and scheduling.
展开▼
