Rf modulated optical beam distance measuring system and method

An optical distance measurement system comprising:

• means for producing a first light beam for transmission over a distance that is to be measured and including means for amplitude modulating the first light beam with a first radio frequency having a phase, relative to the phase of a reference frequency that is equal to said first radio frequency, that is dependent on distance;
• means for producing a second light beam that is not transmitted, and including means for amplitude modulating it with a second radio frequency functioning as a local signal source;
• an electro-optical detecting means for receiving said first and second light beams and functioning as a mixer to cause electro-optical heterodyning of said first and second radio frequencies modulated on the first and second light beams respectively, said electro-optical heterodyning producing a resultant difference radio frequency signal the phase of which is representative of the relative phase of said first modulated light beam;
• and
• phase measuring means responsive to said resultant difference radio frequency signal for producing an output signal representing distance.

An optical distance measurement system comprising:

• a radio frequency generator means for generating single and dual frequency modulation signals, the single and dual frequency modulation signals being electronically mixed, for developing first and second beat reference signals each defining a reference phase;
• a ranging laser having a return and driven by the dual frequency modulation signal;
• a local laser having an output and driven by the single frequency modulation signal;
• an electro-optical detecting means for electro-optically heterodyning said return of said ranging laser and said output of said local laser;
• optical means for directing the output of the local laser and the return from the ranging laser on the electro-optical detector means for developing a heterodyne signal representing fine distance measurement and a coarse signal representing relatively longer distance, the heterodyne and coarse signals each having a phase that varies with distance;
• and
• phase comparing means for comparing the phase of the heterodyne signal representing fine distance measurement and the coarse signal representing longer distance with the respective first and second beat reference signals, said phase comparing means having a first output of a precision distance measurement signal obtained by phase comparison of a relatively low frequency difference of the single frequency modulation on the local laser and one of the dual frequencies modulated on the ranging laser, and having a second output of a signal resolving distance ambiguities in such first mentioned phase comparison by phase comparison of the second beat reference signal and coarse signal.

A method of measuring distance by electro-optical light transmission and radio frequency modulation of light comprising:

• transmitting a first light beam over a distance that is to be measured and amplitude modulating the first light beam with a first radio wave frequency, the phase of such first radio frequency amplitude modulation at any given location on the beam being dependent on the transmission distance;
• producing a second light beam that is not transmitted over such distance, and amplitude modulating the second light beam with a second radio wave frequency functioning as a local signal source for heterodyning with the first radio wave frequency;
• electro-optically detecting and mixing said first and second light beams to cause electro-optical heterodyning of said first and second radio wave frequencies modulated on the first and second light beams respectively, said electro-optical heterodyning producing a resultant difference radio frequency signal representing the phase of said first radio wave frequency after transmission of the first light beam over such distance;
• and
• producing a distance measurement signal from said resultant difference radio frequency signal.

A method of optical distance measurement for machine tool, quality control and similar applications comprising:

• producing a first laser light beam for transmission over a distance that is to be measured and amplitude modulating the first light beam with a first radio frequency having a phase that is dependent on distance and is measured relative to the phase of a reference frequency that is equal to said first radio frequency;
• producing a second laser light beam that is not transmitted over such distance, and amplitude modulating it with a second radio frequency functioning as a local signal source for heterodyning with the first radio frequency;
• electro-optically detecting and mixing said first and second laser light beams to cause electro-optical heterodyning of said first and second radio frequencies modulated on the first and second laser light beams respectively, said electro-optical heterodyning producing a resultant difference radio frequency signal the phase of which, relative to the phase of a reference radio frequency equal to the said difference radio frequency signal, is representative of the change in phase of said first modulated light beam due to its transmission over the distance to be measured;
• and
• comparing the phase of said resultant difference radio frequency signal and the phase of said reference radio frequency to produce an output signal representing a measured distance.