Patent ID: 9631921
Date: 2017-04-25
CPC Classifications: G01B,G01C,G01S

Claim:
1. A method for measuring a distance, the method comprising: providing a light source, an electronics circuit, an optical detector, and a retroreflector, wherein the light source produces a light beam, a portion of the light beam being reflected by the retroreflector as a second beam received by the optical detector; in a first instance: modulating the light beam at a first frequency; receiving the second beam by the optical detector to produce a first electrical signal having the first frequency and a first phase; measuring the first phase by the electronics circuit in response to the first electrical signal; modulating the light beam at a second frequency, the second frequency being different than the first frequency; receiving the second beam by the optical detector to produce a second electrical signal having the second frequency and a second phase; measuring the second phase by the electronics circuit in response to the second electrical signal; in a second instance occurring later than the first instance: moving the retroreflector while modulating the light beam continuously at the second frequency; receiving the light beam modulated continuously at the second frequency by the optical detector to produce a third electrical signal having the second frequency and a third phase; measuring the third phase by the electronics circuit in response to the third electrical signal; determining a first distance to the retroreflector based at least in part on a speed of light, the first frequency, the second frequency, the measured first phase, the measured second phase, and the measured third phase; and storing the first distance.