Optical instrument for measuring displacement

Claim 2

An optical instrument for measuring displacement characterised in that it comprises a movable diffraction grating (3) used as a scale, a light source (1), photodetectors (10, 11), and means (2, 4, 5, 6, 7) for making two light beams diffracted by said diffraction grating interfere with each other, in which displacement of said diffraction grating is detected, based on variations of interference signals, and wherein said light source is a multimode semiconductor laser device having a suitable coherency for making two necessary light beams with equal optical path lengths selectively interfere with each other.

Claim 3

An optical instrument for measuring displacement according to claim 1, wherein the difference between optical path lengths of said two beams, which are to be made interfere, is detected as variations in modulation of interference fringes.

Claim 4

An optical instrument for measuring displacement according to claim 1, wherein said optical path lengths are adjusted on the basis of said variations in modulation of interference fringes.

Claim 5

An optical instrument for measuring displacement according to claim 1, wherein variations of said difference between optical path lengths of said two beams, which is to be made to interfere, are detected by detecting said variations in modulation.

Claim 6

An optical instrument for measuring displacement according to claim 1, wherein each of said photodetectors comprises a polarizing beam splitter (28, 29) on which interference light of two beams is projected and which divides the incident light beam into two, one of which is a light beam proceeding along the first optical path which is the direction of the incident light beam and the other of which is a light beam, proceeding along the second optical path, a first photodiode (30, D3) which is mounted on said first optical path, a second photodiode (33, D4), which is mounted on said second optical path, said first and second photodiodes being connected in series, a reverse bias source connected to said first and second photodiodes, and an amplifier (AMP) whose input is connected with the connection point of said first and second photodiodes (D3, D4) each of said photodiodes being so constructed that when interference light enters said beam splitter, said amplifier outputs detection signals containing no D. C. component.

Claim 7

An optical instrument for measuring displacement, characterised in that it comprises a light source consisting of a multimode semiconductor laser device (44), a beam splitter (54) for dividing the beam emerging from said light source into two, a diffracting grating (41), on which these two split beams are projected, first reflectors (52, 53) which make two diffraction light beams of first order by the diffraction grating enter again said diffraction grating, said two diffracted light beams of first order diffracted again by said diffraction grating being made interfere with each other, a detector (45) which detects interference light, variations in position of said diffraction grating being detected by measuring interference intensity of said interference light by means of said detector.

Claim 8

An optical instrument for measuring displacement, characterised in that it comprises a light source consisting of a multimode semiconductor laser device (44), a beam splitter (54) for dividing the beam emerging from said light source into two, a diffracting grating (41), on which these two split beams are projected, first reflectors (52, 53) which make two diffraction light beams of first order by the diffraction grating enter again said diffraction grating, said two diffracted light beams of first order diffracted again by said diffraction grating being made interfere with each other, a detector (45) which detects interference light, variations in position of said diffraction grating being detected by measuring interference intensity of said interference light by means of said detector.

Claim 9

An optical instrument for measuring displacement according to claim 6, further comprising second reflectors (42, 43) on the same side as said beam splitter with respect to said diffraction grating.

Claim 10

An optical instrument for measuring displacement according to claim 6, wherein said diffraction grating is a volume type hologram, the direction of the grating vector of said hologram coinciding with the measurement direction.

Claim 11

An optical instrument for measuring displacement according to claim 6, wherein said first reflectors (52, 53) are located below said diffraction grating (41).

Claim 12

An optical instrument for measuring displacement according to claim 2, further comprising means for displaying said difference between optical path lengths of said two beams, which are to be made interfere, detected as variations in modulation of interference fringes.

Claim 13

An optical instrument for measuring displacement according to claim 2, further comprising means for examining variations in modulation whereby, when said difference between the optical path lengths of said two beams is greater than a predetermined value, said difference is displayed.

Claim 14

An optical instrument for measuring displacement according to claim 2, further comprising means for examining variations in modulation, and means for stopping the measurement in middle course, when said difference between the optical path lengths of said two beams is greater than a predetermined value.