DEVICE AND METHOD FOR MEASURING A SEMIFINISHED PRISM

Abstract

A method for measuring a semifinished prism in which a first test beam path is produced, by which a first test image is imaged to infinity, and in which the first test beam path is guided as an incident beam path onto a first non-polished surface of the prism. A beam path reflected from the first non-polished surface is captured by a telescope, wherein the first test image is imaged onto a detector in the telescope. The incident beam path forms an obtuse angle with the reflected beam path. A second test beam path reflected from a second surface of the prism is captured by a telescope, wherein a second test image, which is imaged to infinity by the second test beam path, is imaged onto a detector by the telescope. The angle between the first surface and the second surface is determined on the basis of the difference between an orientation of the first surface, derived from the first test image, and an orientation of the second surface, derived from the second test image. The invention also relates to an associated measuring device.

Claims

1. A method for measuring a semifinished prism, having the following steps: a. generating a first test beam path, with which a first test image is imaged at infinity; b. guiding the first test beam path as an incident beam path onto an unpolished first face of the prism; c. acquiring a beam path reflected by the unpolished first face with a telescope, the first test image being imaged in the telescope onto a detector, and the incident beam path making an obtuse angle with the reflected beam path; d. acquiring a second test beam path reflected by a second face of the prism with a telescope, a second test image, imaged at infinity with the second test beam path, being imaged by the telescope onto a detector; e. determining the angle between the first face and the second face with the aid of the difference of an orientation of the first face, derived from the first test image, and an orientation of the second face, derived from the second test image.

2. The method of claim 1, wherein the unpolished first face is in a finely ground state.

3. The method of claim 1, wherein the prism is rotated about an axis of rotation between the measurement of the first face and the measurement of the second face.

4. The method of claim 3, wherein more than two faces of the prism are measured without the prism being displaced relative to the axis of rotation.

5. The method of claim 1, wherein the central axis of the reflected first test beam path) is offset by a deviating element relative to the optical axis of the telescope.

6. The method of claim 5, wherein switching between a first measurement mode and a second measurement mode is carried out by arranging the deviating element in the first test beam path and removing the deviating element from the first test beam path.

7. The method of claim 1, wherein the first test beam path is generated by a collimator, and in that the prism is arranged between the collimator and the telescope.

8. The method of claim 1, wherein the test image acquired by the detector is represented together with a test image reproduction, the test image reproduction-pig) being arranged in a target position.

9. The method of claim 1, wherein the angle between the first face and the second face is compared with a target angle, and in that the first face and/or the second face is reprocessed if the deviation of the angle from the target angle is more than a predetermined threshold value.

10. A measuring device for measuring a semifinished prism, comprising a light source for generating a test beam path with which a test image is imaged at infinity, the test beam path being guided as an incident beam path onto a face of a prism, and having a telescope for acquiring the beam path reflected by the face of the prism, the telescope comprising a detector onto which the test image is imaged, and the incident beam path making an obtuse angle with the reflected beam path.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The invention will be described by way of example below with reference to the appended drawings with the aid of advantageous embodiments. In detail:

[0034] FIG. 1: shows a first embodiment of a measuring device according to the invention;

[0035] FIG. 2: shows a second embodiment of a measuring device according to the invention;

[0036] FIG. 3: shows a third embodiment of a measuring device according to the invention;

[0037] FIG. 4: shows a representation of a test image; and

[0038] FIG. 5: shows a possible image on the detector of a measuring device according to the invention.

DETAILED DESCRIPTION

[0039] In a measuring device in FIG. 1, a prism 14 is arranged on a turntable 15. The turntable 15 is mounted rotatably about an axis of rotation 16, which is indicated in FIG. 1 as a point of intersection of a vertical axis 17 with a horizontal axis 18. The turntable 15 is equipped with an angle measuring instrument (not represented) by which an angle of rotation about the axis of rotation 16 can be recorded precisely.

[0040] The prism 14 has a bottom face, with which it rests on the turntable, and three side faces 19, 20, 21, which are respectively intended to make a right angle with the bottom face. The edge arranged between a first face 19 and a second face 20 of the prism 14 coincides approximately with the axis of rotation 16 of the turntable 15.

[0041] The prism 14 is a semifinished prism, in which the side faces 19, 20, 21 are finely ground but not yet polished. The fine grinding is the last processing step before the polishing. The surfaces then have a roughness of between Rq=10 μm and Rq=0.2 μm in terms of mean roughness. With this roughness, visible light that impinges at a small angle of incidence is diffusely scattered while light impinging at a large angle of incidence generates a specular reflection.

[0042] The measuring device comprises a collimator 22 and a telescope 33. The collimator 22 has a light source 23, the light of which illuminates via a lens arrangement 24 the test image 27 in the focal plane of the objective 28. The test image 27 has according to FIG. 4 the shape of a crosshair 27.

[0043] The test image 27 is imaged at infinity by the objective 28. The beam path thereby collimated is guided as a first test beam path 29 onto the first face 19 of the prism. Since the first test beam path 29 makes a small angle of about 5° with the first face 19 of the prism, a specular reflection occurs so that the first test beam path 29, which before impinging on the first face 19 is referred to as an incident beam path 30, continues in a reflected beam path 31.

[0044] The reflected beam path 31 passes through the objective lens 32 of the telescope 33 and is focused in a plane 34. With a lens arrangement 35, the test image 27 is observed by eye or is imaged onto a detector 36 and represented on a display 37. The display 37 shows the actual position, acquired by the detector 36, of the test image 27 relative to a test image reproduction 38 in a target position. In the example according to FIG. 5, the actual position of the test image 27 is displaced to the right and downward relative to the target position. The orientation of the first face 19 may be deduced from the direction and the magnitude of the displacement.

[0045] After the measurement of the first face 19, the turntable 15 is rotated about the axis of rotation 16 until the collimated beam path emitted by the collimator 22 impinges as a second test beam path at the same angle of about 5° on the second face 20 of the prism 14. The orientation of the second face 20 may now be read with the aid of a second test image on the detector 37 in the same way.

[0046] With the aid of the position of the two test images on the detector 37 and while taking into account the angle through which the turntable 15 was rotated between the measurements of the first face 19 and the second face 20, the angle included between the first face 19 and the second face 20 may be determined.

[0047] The angle may be compared with a target angle. If the deviation between the actual value and the target angle is more than a predetermined threshold value, the first face 19 and/or the second face 20 may be processed again by fine grinding in order to correct the deviation. If the deviation is less than the predetermined threshold value, the finely ground faces 19, 20 may be polished in order to complete the semifinished prism 14.

[0048] In the embodiment according to FIG. 1, the optical axis 39 of the collimator 22 and the optical axis 40 of the telescope 33 are aligned with the axis of rotation 16 of the turntable 15. By rotation of the turntable 15, the test beam path 29 may be directed either onto the first face 19 or onto the second face 20, but not onto the third face 21. If a different angle of the prism 14 is intended to be measured, the prism 14 must be brought into a different position on the turntable 15.

[0049] FIG. 2 shows an embodiment in which the optical axis 39 of the collimator 22 and the optical axis 40 of the telescope 33 are displaced parallel relative to a straight line which extends through the axis of rotation 16 of the turntable 15. The prism 14 rests approximately centrally on the turntable 15, so that the prism 14 is intersected by the axis of rotation 16. The offset of the optical axes 39, 40 relative to the axis of rotation 16 is dimensioned so that all side faces 19, 20, 21 of the prism 14 can be measured without changing the position of the prism 14 on the turntable 15.

[0050] In the further embodiment according to FIG. 3, the telescope is part of an autocollimator 41. The autocollimator 41 comprises a light source 43, the light of which is guided by a beam splitter 44 in the direction of the objective 32 of the autocollimator 41. The light passes through an aperture 26, which represents a test image 27, arranged at the focal point of the objective 32. The light is shaped by the objective 32 into a collimated beam path in which the test image 27 is imaged at infinity.

[0051] If the light impinges as a test beam path on a reflective face which makes approximately a right angle with the optical axis of the autocollimator 41, the test beam path is reflected and passes back through the objective 32 into the autocollimator. The light is focused onto a detector 36, on which the position of the test image 27 may be seen. From the position of the test image 27 on the detector 36, it is possible to deduce whether the reflective face exactly makes a right angle with the optical axis of the autocollimator 41 or whether there is small deviation from this target value.

[0052] The measuring device comprises, arranged in front of the objective 32 of the autocollimator 41, an auxiliary prism 42 which in a first state is arranged in the beam path in front of the objective 32 of the autocollimator 41 and in a second state is removed from the beam path. The measuring device may, for example, comprise a swivel mechanism which makes it possible to change the auxiliary prism 42 between the two states.

[0053] When the auxiliary prism 42 is removed from the beam path, the measuring instrument may be used like a conventional goniometer. The test image 27 generated by the light source 43 impinges on a reflective face oriented perpendicularly to the optical axis 40 of the autocollimator 41, so that the test image 27 is reflected back into the autocollimator 41. In this way, it is possible to measure a prism whose surfaces are reflective (this is not represented).

[0054] When the auxiliary prism 42 is swiveled into the beam path, the beam path is offset parallel relative to the optical axis 40 of the autocollimator 41. The functionality then corresponds to the exemplary embodiment according to FIG. 2. The test image is generated by the collimator 22 and directed at a small angle onto an unpolished face 19 of the prism 14. The reflected test beam path 29 impinges on the auxiliary prism 42 and is guided through the objective 32 of the autocollimator 41.