Fumio Ohtomo

High-resolution rangefinder with a pulsed laser developed by an undersampling method

A high-resolution rangefinder equipped with a pulsed laser has been developed by introducing a high-resolution interpolation technique based on an undersampling method. Using this pulse method employed by the rangefinder, a new time-scale expansion has been realized that is similar to the heterodyne of the rangefinder that also employs the phase difference method. Therefore, high-resolution measurements are now possible. A bandpass-filtered temperature-compensated crystal oscillator signal with a reference frequency of 15 MHz is sampled at a timing determined by a received pulsed light with a repetition rate of 8.5 kHz. With this process, a time series of undersampled 2.5-kHz data are obtained as an intermediate step that can be further lowered to 85 Hz by final rearrangement of the undersampled data. With this technique, a reference frequency is transformed into a lower frequency. A distance is then calculated from the phase of this low frequency. The rangefinder developed shows good performances that include a range resolution of better than 1 mm, nonlinearity within ±1 mm, and a measurement range of up to 7000 m.