Study On Indoor Mobile Robot Positioning Based On RFID

In the field of indoor storage,mobile robots can efficiently complete various tasks such as cargo sorting and transportation,and positioning technology is one of the most critical technologies for accomplishing these tasks.Many indoor positioning method have been proposed including infrared positioning,ultrasonic,RFID and so on.However,infrared can only be transmitted with line-of-sight and ultrasonic system is too expensive.UHF passive RFID has become a research hit in positioning field because that it's cheap,NLOS and it can recognize tags through tag id.In this paper,a new positioning method based on RFID phase,RSSI and mobile robot is proposed to solve indoor mobile robot positioning.Main research contents are listed as follows:A coarse positioning method based on RSSI information of the RFID system is proposed.The radiation model of the RFID system was analyzed and the effect of the angle on the RSSI was experimentally verified.Aiming at the fact that RSSI is susceptible to the antenna directivity,a RSSI positioning method based on the maximum RSSI value of the tag obtained by the rotating antenna is proposed.Experiments comparing and analyzing the original RSSI positioning method and RSSI positioning method by rotating antenna are conducted.The validity of the rotating antenna is proved,and the accuracy of positioning is simulated.The results show that the coarse positioning can achieve a positioning accuracy of 1m.A phase-distance model of RFID is proposed in which the phase is pre-processed to avoid Ambiguity.Combined with the parametric representation of robot poses in global coordinates,a new phase-pose positioning method is proposed.An optimizing method is used to identify unknown parameters in the new model and finally the position of the mobile robot in global coordinate is obtained.Combined with the coarse positioning method base on RSSI,the new positioning model can achieve good results.A tag selection strategy based on the GDOP minimization principle is studied.Firstly,it's proved that at least 3 tags are needed.Secondly,a simulation verifies that using 4 tags to position is the best considering both positioning accuracy and efficiency.When the robot can detect more than 4 tags,choose the 4 tags whose GDOP is the minimum.The experiment platform is based on Pioneer robot platform and Implij RDID system and a software is completed to control the robot and the reader as well as collecting data.The robot's linear positioning experiment and circular positioning experiment were completed.The average linear positioning error was no more than 10 cm and the average circular positioning error was no more than 30 cm.