초록 ▼

An improved method and apparatus for precision ranging is described using a frequency-modulated signal source to stimulate creation of interference fringes at a rate proportional to absolute distance to a target. According to the invention, a low frequency modulating signal modulates a relatively hi

An improved method and apparatus for precision ranging is described using a frequency-modulated signal source to stimulate creation of interference fringes at a rate proportional to absolute distance to a target. According to the invention, a low frequency modulating signal modulates a relatively high frequency signal source having a predetermined long coherent length compared to the distance to be measured. The resulting frequency-modulated signal is transmitted to the target to generate a reflected version thereof. Because of the long coherent length of the signal source, the transmitted frequency-modulated signal maintains spatial coherence as it travels to and from the target. Moreover, the low frequency modulating signal stimulates production of 360°instantaneous phase differences between the transmitted and received frequency-modulated signals when these signals are superimposed. The number of these 360°phase differences per period of the modulating signal is proportional to a time-of-flight of the transmitted frequency-modulated signal to and from the target and thus absolute distance. In operation, the transmitted and received frequency-modulated signals are logically compared by a balanced demodulator to generate a beat frequency signal from which the number of 360°phase differences per period of the modulating signal is extracted. The beat frequency signal is then processed to determine the distance to the target. Preferably, a reference circuit is used to maintain the frequency stability of the signal source.

대표청구항 ▼

A precision optical ranging apparatus for measuring absolute distance to a target, comprising: means for generating a sinusoidally-varying modulating signal having a predetermined first frequency, the first frequency inversely proportional to a period; a signal source having a long coherent length c

A precision optical ranging apparatus for measuring absolute distance to a target, comprising: means for generating a sinusoidally-varying modulating signal having a predetermined first frequency, the first frequency inversely proportional to a period; a signal source having a long coherent length compared to the distance to be measured and having a predetermined second frequency substantially greater than the predetermined first frequency, the signal source having an input for receiving the modulating signal and in response thereto generating a frequency-modulated signal; means for converting the frequency-modulated signal into an optical waveform and for transmitting the frequency-modulated signal in its optical waveform to the target, the transmitted frequency-modulated signal maintaining spatial coherence as it travels to and from the target due to the long coherent length of the signal source; a receiver for receiving from the target a reflected version of the transmitted frequency-modulated signal in its optical waveform and in response thereto generating a received frequency-modulated signal; means for comparing the frequency-modulated signal and the received frequency-modulated signal to generate a beat frequency signal representing a number of 360°instantaneous phase differences between the frequency-modulated signal and the received frequency-modulated signal per period caused by the sinusoidally-varying modulating signal, wherein the beat frequency signal is proportional to the absolute distance to the target provided the absolute distance is smaller than the coherent length of the signal source; means for processing the beat frequency signal to determine the absolute distance to the target; a reference target; a reference transmitter located a predetermined distance from the reference target and connected to the signal source, the reference transmitter for transmitting the frequency-modulated signal in its optical waveform to the reference target; a reference receiver located a predetermined distance from the reference target for receiving from the reference target a reflected version of the transmitted frequency-modulated signal in its optical waveform and in response thereto generating a received reference frequency-modulated signal; means for comparing the reference frequency-modulated signal and the received reference frequency-modulated signal to generate a reference beat frequency signal representing a number of 360°instantaneous phase differences between the reference frequency-modulated signal and the received reference frequency-modulated signal per period caused by the modulating signal; and means for processing the reference beat frequency signal to maintain the frequency of the frequency-modulated signal output from the signal source within predetermined limits.