Length measuring apparatus

Claim 2

A length measuring apparatus for measuring a dis­tance up to an object to be measured, comprising: first light source means for projecting a light beam having a first frequency onto the object to be measured; first phase detection means for detecting a phase of a light beam incident upon a predetermined position from said first light source means via the object to be measured; second light source means for projecting a light beam having a second frequency different from the first frequency onto the object to be measured; second phase detection means for detecting a phase of a light beam incident upon a predetermined position from said second light source means via the object to be measured; a distance up to the object to be measured being detected at least according to results of detection by said first phase detection means and second phase detection means; third light source means for projecting a light beam having a third frequency onto the object to be measured; and third phase detection means for detecting a phase of a light beam incident upon a predetermined position from said third light source means via the object to be measured, a relative amount of displacement of the object to be measured being detected according to a result of detection by said third phase detection means; the light beam whose phase is detected by said third phase detection means and the light beam whose phase is detected by said first phase detection means having an iden­tical optical path.

Claim 3

A length measuring apparatus according to Claim 1, wherein said first light source means and said third light source means are the same light source, and wherein said first phase detection means and third phase detection means are the same photodetector for detecting a light beam emitted from said same light source.

Claim 4

A length measuring apparatus according to Claim 2, wherein a result of detection by said same photodetector for detecting the light beam emitted from said same light source is used for detecting a relative distance up to the object to be measured by said first phase detection means, and is then used for detecting a relative displacement from said detected position of the object to be measured by said third phase detection means.

Claim 5

A length measuring apparatus according to Claim 2, wherein said first light source means and second light source means are the same light source, and wherein said ap­paratus further comprises means for changing a frequency of the light beam emitted from said same light source.

Claim 6

A length measuring apparatus according to Claim 4, wherein said frequency changing means performs frequency modulation so that the frequency of the light beam changes between said first frequency and said second frequency with a predetermined frequency.

Claim 7

A length measuring apparatus according to Claim 5, wherein said first phase detection means and second phase detection means include the same photodetector for detecting the light beam emitted from said same light source, phase change detection means for detecting a phase change in an output signal from said photodetector, and a lock-in amplifier for detecting a width of variations of an output signal from said phase change detection means, wherein a relative distance up to the object to be measured is detected by the width of variations of the signal detected by said lock-in amplifier.

Claim 8

A length measuring apparatus according to Claim 4, wherein said same light source is a semiconductor laser, and wherein said frequency changing means changes the frequency of the light beam at least to said said first frequency and said second frequency by changing an injection current for said semiconductor laser.

Claim 9

A length measuring apparatus according to Claim 6, wherein said frequency changing means changes the injection current for said semiconductor laser until said semiconduc­tor laser causes mode hop.

Claim 10

A length measuring apparatus according to Claim 4, further comprising fixing means for maintaining the frequency of the light beam emitted from said identical light source constant, and a switch for switching between said fixing means and frequency changing means.

Claim 11

A length measuring apparatus according to Claim 3, wherein at least one of said first light source means and second light source means further includes means for chang­ing the frequency of the emitted light beam.

Claim 12

A length measuring apparatus according to Claim 10, wherein said frequency changing means performs frequency modulation so that the frequency of the light beam changes between a fourth frequency and a fifth frequency different from said first and second frequencies with a predetermined frequency.

Claim 13

A length measuring apparatus according to Claim 11, further comprising fourth phase detection means for detect­ing a phase of the light beam subjected to frequency modula­tion by said frequency changing means, and wherein a rela­tive distance up to the object to be measured is detected at least by results of detection by said fourth phase detection means, said first phase detection means and said second phase detection means.

Claim 14

A length measuring apparatus according to Claim 11, wherein said frequency changing means further includes means for changing a gain of said frequency modulation.

Claim 15

A length measuring apparatus according to Claim 3, further comprising means for detecting a change in a wavelength of the light beam emitted from said second light source means, and means for controlling the wavelength of the light beam emitted from said second light source means according to a result of detection by said wavelength change detection means.

Claim 16

A length measuring apparatus according to Claim 1, further comprising fourth light source means for projecting a light beam having a fourth frequency onto the object to be measured, fourth phase detection means for detecting a phase of a light beam incident upon a fourth predetermined posi­tion from said fourth light source means via the object to be measured, fifth light source means for projecting a light beam having a fifth frequency different from the fourth frequency onto the object to be measured, and fifth phase detection means for detecting a phase of a light beam inci­dent upon a fifth predetermined position from said fifth light source means via the object to be measured, and wherein, after a relative distance up to the object to be measured has been detected with low accuracy according to results of detection by said first phase detection means and second phase detection means, the relative distance up to the object to be measured can be detected with high accuracy by results of detection by said fourth phase detection means and fifth phase detection means.

Claim 17

A length measuring apparatus according to Claim 15, wherein said first through fifth light source means are the same light source.

Claim 18

A length measuring apparatus for measuring a length by making a light beam passing an optical path for measure­ ment including an object to be measured and a light beam passing a reference optical path not including the object to be measured interfere with each other, said apparatus comprising: first light beam guiding means for guiding a light beam having a first frequency from a first light source and a light beam having a second frequency slightly different from said first frequency to said optical path for measure­ment and said reference optical path, respectively; second light beam guiding means for guiding a light beam having a third frequency different from said first frequency and a light beam having a fourth frequency slightly different from said third frequency to said optical path for measurement and said reference optical path; first photosensing means for sensing the light beams having said first and second frequencies guided by said first light beam guiding means and passing said respec­tive optical paths; second photosensing means for sensing the light beams having said third and fourth frequencies guided by said second light beam guiding means and passing said respective optical paths; first arithmetic means for calculating a relative amount of change of the object to be measured according to a phase difference obtained from at least one of outputs from said first and second photosensing means; and second arithmetic means for calculating an absolute position of the object to be measured according to respec­tive phase differences obtained from respective outputs from said first and second photosensing means; optical paths for measurement, along which the light beams having said first and third frequencies go toward the object to be measured, being identical.

Claim 19

A length measuring apparatus for measuring a length by making a light beam passing an optical path for measure­ ment including an object to be measured and a light beam passing a reference optical path not including the object to be measured interfere with each other, said apparatus comprising: first light beam guiding means for guiding a light beam having a first frequency from a first light source and a light beam having a second frequency slightly different from said first frequency to said optical path for measure­ment and said reference optical path, respectively; second light beam guiding means for guiding a light beam having a third frequency different from said first frequency and a light beam having a fourth frequency slightly different from said third frequency to said optical path for measurement and said reference optical path; first photosensing means for sensing the light beams having said first and second frequencies guided by said first light beam guiding means and passing said respec­tive optical paths; second photosensing means for sensing the light beams having said third and fourth frequencies guided by said second light beam guiding means and passing said respective optical paths; first arithmetic means for calculating a relative amount of change of the object to be measured according to a phase difference obtained from at least one of outputs from said first and second photosensing means; and second arithmetic means for calculating an absolute position of the object to be measured according to respec­tive phase differences obtained from respective outputs from said first and second photosensing means; optical paths for measurement, along which the light beams having said first and third frequencies go toward the object to be measured, being identical.

Claim 20

A length measuring apparatus for measuring a length by making a light beam passing an optical path for measure­ment at least including an object to be measured and light beams passing a reference optical path, serving as a stand­ard of length measurement, interfere with each other, said apparatus comprising: first arithmetic means for guiding a light beam having a single frequency to said optical path for measure­ment, and for calculating a relative amount of change of position of the object to be measured according to a light output when said light beam having the single frequency in­terferes with the light beam passing said reference optical path; and second arithmetic means for guiding light beams having a plurality of frequencies to said optical path for measurement and for calculating an absolute position of the object to be measured according to a light output when said light beams having the plurality of frequencies interfere with a plurality of light beams passing said reference opti­cal path, respectively; an optical path for measurement along which said light beam having the single frequency goes toward the ob­ject to be measured and an optical path for measurement anong which at least one of said light beams having the plurality of frequencies goes toward the object to be measured being identical.

Claim 21

A length measuring apparatus for measuring a length by making a light beam passing an optical path for measure­ment at least including an object to be measured and light beams passing a reference optical path, serving as a stand­ard of length measurement, interfere with each other, said apparatus comprising: first arithmetic means for guiding a light beam having a single frequency to said optical path for measure­ment, and for calculating a relative amount of change of position of the object to be measured according to a light output when said light beam having the single frequency in­terferes with the light beam passing said reference optical path; and second arithmetic means for guiding light beams having a plurality of frequencies to said optical path for measurement and for calculating an absolute position of the object to be measured according to a light output when said light beams having the plurality of frequencies interfere with a plurality of light beams passing said reference opti­cal path, respectively; an optical path for measurement along which said light beam having the single frequency goes toward the ob­ject to be measured and an optical path for measurement anong which at least one of said light beams having the plurality of frequencies goes toward the object to be measured being identical.

Claim 22

A length measuring apparatus for measuring a length by making a light beam passing an optical path for measure­ment at least including an object to be measured and light beams passing a reference optical path, serving as a stand­ard of length measurement, interfere with each other, said apparatus comprising: first arithmetic means for guiding a light beam having a single frequency to said optical path for measure­ment, and for calculating a relative amount of change of position of the object to be measured according to a light output when said light beam having the single frequency in­terferes with the light beam passing said reference optical path; and second arithmetic means for guiding light beams having a plurality of frequencies to said optical path for measurement and for calculating an absolute position of the object to be measured according to a light output when said light beams having the plurality of frequencies interfere with a plurality of light beams passing said reference opti­cal path, respectively.

Claim 23

A length measuring apparatus for measuring a length by making a light beam passing an optical path for measure­ment at least including an object to be measured and light beams passing a reference optical path, serving as a stand­ard of length measurement, interfere with each other, said apparatus comprising: first arithmetic means for guiding a light beam having a single frequency to said optical path for measure­ment, and for calculating a relative amount of change of position of the object to be measured according to a light output when said light beam having the single frequency in­terferes with the light beam passing said reference optical path; and second arithmetic means for guiding light beams having a plurality of frequencies to said optical path for measurement and for calculating an absolute position of the object to be measured according to a light output when said light beams having the plurality of frequencies interfere with a plurality of light beams passing said reference opti­cal path, respectively.