Patent Document ID: 5430537
Application ID: 08116371
Patent Flag: 1

Claim One:
1. A light beam encoder for measuring distance between a light beam source and a device along a linear path comprising: a reflector coupled to said device; a light beam source for amplitude modulating a light beam and directing said amplitude modulated light beam towards said reflector; a light beam detector for receiving said amplitude modulated light beam reflected by said reflector and for providing a high frequency phase shifted distance signal; a mixer for shifting the frequency of said high frequency phase shifted distance signal to a lower frequency and maintaining the phase of said high frequency phase shifted distance signal to provide a low frequency distance signal; a measurement circuit for measuring the time interval between successive transitions of said low frequency distance signal and a reference signal to provide a measurement signal; a processor, receiving said measurement signal for generating a distance output signal representing said distance between said light beam source and said device in response to said measurement signal with a resolution of approximately 1-10 microns; a reference oscillator providing a reference oscillator signal, wherein said light beam is amplitude modulated in accordance with said reference oscillator signal and wherein said reference signal is derived from said reference oscillator signal and has a phase substantially identical thereto; and a phase locked loop including a phase detector, a voltage controlled oscillator, and a second mixer coupled in a feedback relationship with said phase detector and said voltage controlled oscillator, said voltage controlled oscillator generating a local oscillator signal, wherein said second mixer receives said reference oscillator signal and said local oscillator signal to provide said reference signal.