FR2628198A1 - INTERFEROMETRIC LENGTH MEASURING DEVICE - Google Patents

Abstract

Interferometric length measuring device for medium and long lengths, characterized in that on the return path 14; 15 of the light beam reflected by the measuring reflector 7; 18 or reference 8, there is provided on the interference divider block 2, or in the immediate vicinity thereof, an interference with the corner piece or the prism providing the finite order spacings, at a corner angle .

Description

(i) FRENCH REPUBLIC Publication No. 2 628 198 (use only

  for NATIONAL INSTITUTE reproduction orders)

INDUSTRIAL PROPERTY

  D National registration number 89 01760 PARIS

(Int CI4: G 01 B 9/02.

@ A1 PATENT APPLICATION

  Filing date: February 10, 1989. (Applicant (s): Firm known as: VEB Carl Zeiss Jena,

Company under German law. - DD.

  Priority: DD, March 7, 1988, n WP G 01 B / 313 426 4.

  (inventor (s): Werner Krieg: Gerhard Bôhme; Ulrike

Hentschel; Johannes Môbius.

  ) Date of public availability of the

  application: BOPI "Patents" n 36 of September 8, 1989.

  References to other national documents appearing

rented: (rt Holder (s):

\ 7 Agent (s): Cabinet Madeuf.

  (i Interferometric length measuring device.

  @ Interferometric length measuring device for medium and long lengths, characterized in that on the return path 14; 15 of the light beam reflected by the measurement reflector 7: 18 or of reference 8, it is 14

  provided on or near the interference divider block 2, -

  immediate of it, interference with the corner piece \ '. Sr 1

  or the prism realizing the finite order spacings, under a -

corner angle.

  1M À I (O III <l..4 *; a, = 'MIIIr9ionvention 75732 PARIS CEDEX 15 Ilvnn + An.

  .....:,. 1 I'IMP.AIMFOIF NATIt) NAl P 2 ............, 7 rulP dolas Convention - 75732 PARIS CEDEX 15 The invention relates to an interferometric length measurement device for average lengths to be measured and important, device applicable for mounting in measuring machines and machine tools and for use in a manual or workbench device for laboratory use and during machine inspection. Known interferometric measuring devices for medium and long lengths include a laser light source, a beam splitter and reflectors, which must guarantee both the exact return of the rays and also the maintenance of the direction and of the .DTD: the flatness of the wave. We work with interferen-

  those of equal thickness and with infinitely large spacings. The disadvantage of these known devices according to DD-PS 156141, DD-PS 111993 and according to "Reports VDI 548", Edition VDI-DUsseldorf 1985, pages 24 and following, consists mainly in that a slight disturbance of the shape of the light beam wave due to inaccuracies or tarnishing of the optics

  may already lead to a flattening of the electrical signals

  receptor and may cause failure

early warning.

  Interferential length measurement technique known from "ABC of optics", Editions VEB Brockhaus, Leipzig 1961, page 532 and Raentsch "Optics in the technique of precision measurements", Editions Hanser, MUnich 1949, pages 260 to 267 and 285 to 289, uses interference of identical thickness, with

  visually appreciated final order spacings

  wheat. These are adjusted as necessary with adjustment tables or corners. The inclined position of the reflection surfaces on the entire area (length and width of the measurement area) is therefore modified accordingly. This technique is certainly usable visually, but is however not applicable to a

automatic length measurement.

  According to the document DD-PS 220698, a device is known for an interference measurement of small strokes and displacements, comprising a Koeter prism known for interference division hexahedron, which is composed of two prisms at right angles, glued by their face largest right angle city, these right angle side surfaces being partially reflective. The angle at 60 of these prisms is located between the hypotenuse surface and the smallest right angle face, the angle of 60 of one of the prisms arranged in the return measurement radius path deviating so that a desired band spacing appears. The order spacing is thus regulated by

  change of direction of a reflection face.

  Since, however, the surface intended to modify the direction of the ray is situated in the middle of the ray path, the inclined position of the path of the measuring ray thus produced causes an overlap of the beam of the measuring ray which is variable as a function of each position of the measurement reflector, which takes place at the point of obtaining the signal, therefore on the photoelectric receiver arrangement. For small displacements of the measuring reflector, i.e. for small ranges

  measurement, this has no appreciable effect. For travel

  medium and large cements of the measurement reflector, the variation in overlap would be so great that there could be no signal or measurement of

interferometric length.

  It is the object of the invention to eliminate the drawbacks of the state of the art and to create a high precision interferometric measuring device.

  likely to be manufactured for a limited cost. -

2628'198

  The invention aims to create a device for measuring interferometric length, construction

  simple, with no polarizing or spreading elements

  ment of finite order, high signal gain and suscepti-

  ble to be used for length and displacement measurement

medium and large cements.

  According to the invention, this problem is solved for an interferometric length measuring device for measuring medium and large lengths, with

  a laser light source, an inter-divider block

  ferences producing a ray path for measurement and reference, composed of several glued prisms, as well as with a measurement and reference reflector

  placed in the path of the measurement and reference radius

  and with photoelectric receivers, characterized in that,

  on the return path of the light beam

  neux reflected by the measuring or reference reflector

  rence, interference interference is provided on the interference divider, or in the immediate vicinity thereof

  with the corner piece or the prism realizing the spaces-

  finite order elements, at a corner angle.

  It is advantageous that the inter-dividing block

  ference, on the trajectory of the light beam emitted by the laser light source, presents two deflection prisms provided with Brewster angle, glued on the largest of their optically active surfaces, and two deflection prisms also glued on the largest of their optically active surfaces being provided on the return paths of the light beams reflected by the measurement reflector and by the reference reflector, one of the return prisms presenting on the path of the measurement or reference radius two angles of

  Brewster, between the larger and the other two surfa-

  these optically active, and the other of the return trajectory premiums having a Brewster angle between the largest surface and another optically active surface, and an angle deviating from the Brewster angle, between the most large surface and another optically active surface of this return prism, and in that the bonded surfaces are partially reflective. It is further advantageous that the interference dividing block is constructed from four identical deflection prisms having a Brewster angle, a thin glass corner with a corner angle being placed on one of the small optically active surfaces of the prism concerned, on the trajectory of

  return from the path of the measuring radius or in the path

  roof of return of the path of the reference radius.

  The interferometer block of the measuring device thus has an optical wedge in the return path of the path of the measurement ray or in a path of the path of the reference ray, in the immediate vicinity of the divider face of the block. This corner produces the virtual corner necessary for the formation of finite order spacing interferences, without influencing the geometry and quality.

  intrinsic to the measurement radius path by deviations

  disruptive. This device is thus well

  suitable for measuring in particular medium lengths

nes and important.

  The interfero-

  metric is furthermore of a construction which is not complicated, in particular as regards its optical structural elements. The small number of optically active faces reduces the deformation of the wave fronts of the beam of rays and is simultaneously the condition necessary for a gain and a quality of signal from the photoelectric receiver which are well reproducible. With identical paths in the glass, there is no

  reflection in the measuring device.

  Various other features of the invention

  moreover emerge from the detailed description which

follows.

  Embodiments of the object of the invention

  tion are shown, by way of non-limiting examples

tifs, to the accompanying drawings.

  Figure 1 is an interference divider block device with a Brewster angle and

  Figure 2 is an interfering block device.

  metric with a corner applied on it.

  The measurement device, shown in a highly simplified manner, comprises a laser light source 1, an interference divider block 2 producing a path of measurement and reference radius, consisting of four deflection prisms 3; 4; 5 and 6 glued together, as well as at least one measurement reflector 7 and a reference reflector 8 and at least one photoelectric receiver 9 and 10 placed in the path of measurement and reference radius. Receivers 9 and 10 are

  connected to an operating unit 11 intended for processing

signal.

  The interference dividing block 2 comprises in the path 12 of the coherent light beam emitted by the laser light source 1 of the return prisms 3 and 4 provided with Brewster angles a, which are glued on their common face 13 which happens to be the largest face

  optically active. The face 13 is partially reflected

  chissant. The two return prisms 5 and 6 glued on their face 16 being the largest active

  optically and partially reflective -

  transparent, are arranged in the return paths 14

  and 15 of the light beams reflected by the reflectors

  One of these two return prisms, the return prism 6, presents the Brewster angle each time between the most

  important 16 and the other two active optical faces-

  is lying. The other, the return prism 5 placed in the return path 14, has a Brewster angle e between the face 16 and one of its smaller optically active faces. The angle between face 16 and its other smaller optically active face deviates from the angle

  of Brewster 4 of the value of the corner angle ô.

  The interference divider block 2 can be produced by deviating in the manner shown, a small glass corner, with an optically active corner angle f, being applied. in the return path 14 of the measurement radius path, or in the return path 15 of the reference radius path, on one end of the smallest optically active surface of the

  reference prism concerned, for example prism 5.

  The corresponding corner angle I is also achievable by means of a small rotation, for example of the return prism 5, around an axis

  perpendicular to face 16 (not shown

  tee). In the device according to the invention, the wave fronts of the light beam in the path of the measurement or reference ray are rotated relative to each other by means of an optical wedge, and thickness interference appears identical with a finite order spacing, picked up in the measurement radius path by the photoelectric receiver 9 and reprocessed by the processing unit 11 to obtain the measurement value. So that, unlike what happens

  in the state of the art, the light beam

  nant is not assigned in the radius path of

  measures no significant transverse displacement, not allowed

  sible for large displacements, this optical corner is provided with the corner angle t in the return paths of the path of measurement and reference radius, at

  proximity of the face 16 dividing the radius.

  The photoelectric receiver 10 placed in the reference ray path can for example be used for redundant processing of the signals arriving here, offset by 180, to carry out the signaling of a fault or also for the measurement of brightness. The device shown in FIG. 2, with the

  light source 1 comprises an interface divider block

  rence 17 with a divider face 22, a measurement reflector 18 and a reference reflector 19. A prism 21 having a corner angle is disposed on the interference divider block 17, in the return path 20 of the reflected light beam by the measuring reflector

  18. In FIG. 2, the photoelectric receiver is designated by 9

  stick placed in the path of the measurement radius and producing the measurement signals. For this interference divider block 17, the light beams exit at an angle different from the Brewster angle, for example perpendicularly.

2628 1 98

Claims (3)

  1. Interference length measuring device   metric for medium and large lengths, with a laser light source, an interference divider block producing a ray path for measurement and reference and composed of several glued prisms, as well as with a measurement reflector and a reference reflector, placed in the path of the measurement and reference radius, and with photoelectric receivers, characterized in that on the return path (14; 15; 20) of the light beam reflected by the measurement reflector (7 ; 18) or of reference (8; 19), there is provided on the interference divider block (2; 17), or in the immediate vicinity thereof, interference   the corner piece or the prism (21) providing the spaces   finite order elements, at a corner angle.   2. Interference length measurement device   metric according to claim 1, characterized in that the interference dividing block (2), on the path (12) of the light beam emitted by the laser light source (1), has two deflection prisms (3; 4) provided with Brewster angle, glued on the largest of their optically active surfaces (13), and two deflection prisms (5; 6) also glued on the largest of their optically active surfaces (16) being provided on the trajectories return (14; 15) of the light beams   reflected by the measurement reflector and by the reflec-   one of the reference prisms (7; 8), one (6) of the return prisms (5; 6) having two angles on the path of the measurement or reference radius. Brewster has, between the largest and the other two optically active surfaces, and the other (5) return premiums (5; 6) of the return trajectory having a Brewster angle a between the largest surface (16) and another optically active surface, and an angle deviating from the Brewster angle ô, between the largest surface (16) and another optically active surface of this deflection prism, and in that the bonded surfaces are partially reflective.   3. Interference length measuring device   metric according to claim 1 and 2, characterized in that the interference dividing block (2) is constructed from four identical return prisms (3; 4; 5; 6) having a Brewster angle A, a thin corner glass wedge (21) being placed on one of the smallest optically active surfaces of the prism concerned (for example 5), on the return path (14) of the path of the measuring radius or in the path of   return (15) of the path of the reference radius. PL 1/1 Fig. 1 Fig. 2