Relative position measurement system for vehicles using diffuse light

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For the purpose of saving labor and improving safety in farm operations conducted with a pair of vehicles, automatic driving system of the following or preceding vehicle have been studied. These systems require real-time and precise measurement of the relative position of vehicles. The authors have proposed a relative position detection system using intensity modulated diffuse light from LEDs. In the first stage of this study, a range-finder was developed and tested, consisting of two stations which emit high-frequency modulated light at each other. The range between the stations is obtained from the phase difference between the two low-frequency beat signals generated in both stations. The results of this study may be summarized as follows :1. A relative position detection system using diffuse light was proposed for automatic driving of the following or preceding vehicle used for farm operations.2. A prototype range-finder was manufactured and tested to investigate the feasibility of the proposed system. It consisted of optical transmitters and receivers to transfer intensity modulated light to each other. Each transmitter had 25 high-speed infrared LEDs, and an avalanche photodiode module was used for each receiver.3. Performance tests of the range-finder were conducted under direct sunshine. The maximum and standard errors from the regression values were about 5 and 3 cm respectively in the range from 1 to 10 m.4. The tests results achieved the target accuracy of the development. However, the effects of temperature change, rain or fog were not considered and should be investigated in the next stage of the study.