Detecting the position of a surface by focus modulating the illuminating beam

Claim 2

An optical noncontacting surface sensor for measuring the distance between a reflecting test surface and a predetermined reference plane comprising (A) a source of radiant energy; (B) means for focusing at least a portion of the radiant energy on the reflecting surface; (C) means for modulating said focusing of said portion of radiant energy at a desired frequency along its optical path; (D) means for collecting radiant energy reflected from the test surface onto a single photodetector; and (E) means for monitoring the first harmonic of said collected radiant energy to obtain information with respect to the direction and amplitude of the distance between the test surface and the reference plane.

Claim 3

The apparatus of claim 1, in which the modulating means is a mirror which oscillates along the optical axis about the focus of the energy delivered to it.

Claim 4

The apparatus of claim 1, in which there are two means for modulating the focusing of each of two portions of said radiant energy at two different frequencies, and the foci of the two modulated beams are offset laterally from each other so that they fall at a distance apart on the test surface, and the monitoring means separates the two frequencies received in the single photodetector and delivers them to separate measuring devices, whereby the angle of inclination of the test surface to the reference plane can be determined.

Claim 5

The apparatus of claim 3, in which each of the modulating means are mirrors which oscillate at different frequency along the optical axis about the foci of the energies delivered to them.

Claim 6

The apparatus of claim 1, in which the energy source is a laser.

Claim 7

The apparatus of claim 1, in which the energy source is a gas laser which emits polarized light which is directed into a beam expander which expands the light into a collimated beam, the collimated beam passes into a first polarization beam splitter which delivers a portion of the light through a quarter-wave retardation plate into a first lens which focuses the now circularly polarized light onto an oscillating mirror which serves both to modulate the light along its optical axis at a desired frequency and to change the handedness of the light so that the polarization of the reflected light is rotated by a total of 90so that all of the light incident on the beam splitter is delivered, through a half-wave phase retardation plate, to a second polarization beam splitter which directs a portion of the light through a second lens onto a photodetector, and a portion of the light through a second quarter-wave phase retardation plate through a third lens onto the test surface, and the light reflected from the test surface onto the photodetector, so that substantially all of the light from the laser, minus accidental losses, is delivered to the photodetector.

Claim 8

The apparatus of claim 1, in which (A) said source of radiant energy is a beam of collimated light; (B) said means for focusing said portion of radiant energy on the test surface comprises a first and second beam splitter and a first lens; (C) said means for modulating the energy comprises a second lens which focuses a portion of the light from the first beam splitter onto a mirror which oscillates along the optical path of the light about the focal point of the energy delivered to it and reflects the light as a modulated beam back through the first beam splitter into the second beam splitter which delivers a portion of the now modulated light from the first beam splitter through the first lens onto the test surface, and delivers a portion of the light reflected from the test surface through (D) said means for collecting the reflected light which is a third lens which focuses the light onto the single photodetector.