GB2126715A

GB2126715A - A probe for the automatic checking of surfaces

Info

Publication number: GB2126715A
Application number: GB08321062A
Authority: GB
Inventors: Gerhard Benz; Eberhard Lohner; Gunter Schneider
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1982-09-04
Filing date: 1983-08-04
Publication date: 1984-03-28
Also published as: GB2126715B; DE3232904C2; CH660629A5; JPH0418602B2; GB8321062D0; DE3232904A1; JPS5965708A

Abstract

In a probe for the automatic checking of workpiece surfaces 12, particularly precision treated bores, laser light 21 is scanned linearly or in the form of areas over the surface 12 and the reflected light in the bright field and the dark field are measured separately. The reflected rays in the bright field are reflected to a single detector (23) through a central duct 14, through which the laser light 21 enters, and the scattered rays in the dark field are reflected through an array of light conductors 18 onto individual detector elements of an evaluating circuit. A mirror 20 directs the laser light and the scattered light to and from the workpiece surface. Either the mirror or the whole probe may be rotated to scan the surface. <IMAGE>

Description

SPECIFICATION A probe for the automatic checking of surfaces State of the art The invention originates from a probe according to the preamble to the main claim. With known devices and methods for the automatic surface checking of work pieces, particularly of precision treated work piece surfaces in bores, light conductor systems have been used by which the surface was illuminated and inspected through a fibreglass cable. In so doing, a bright field measurement resulted as a rule which had only a limited strength as evidence.

Furthermore, bevelled mirror arrangements have been known for introducing into a bore in which the surface to be checked is inspected by means of a camera with an annular photo diode arrangement.

Advantages of the invention As opposed to this, the probe in accordance with the invention comprising the characterising features of the main claim has the advantage that an arrangement has been provided for easily checking automatically without contact by which the smallest surface units can be checked separately. The illumination no longer takes place through a bunch of glass fibres but with a focused laser beam which has been focused to a diameter of about 0.1 mm on striking the surface to be checked. Due to the coherence and to the good local scattering achieved by the focusing, the reflected light is very strongly dispersed and deflected by a possible surface error with a large signal to noise ratio.On the other hand, the local scattering was worse by many orders of magnitude with known arrangements illuminating through a bundle of glass fibres since the flare angle of the illuminating beam was not determined by the light source aperture but by the refractive index of the core and of the sheath of the individual fibres. For that reason, flare angles of between 1 0O and 600 resulted.

Moreover, with the probe in accordance with the invention, it is possible in a very simple manner to carry out simultaneously a measurement in the bright field and in the dark field of the reflected light whereby the dark field measurement can be resolved if necessary in accordance with the angle of the reflected beam.

That means that not only is the intensity of the directly reflected light determinable at each point on the surface but that in addition the intensity and the direction of distribution of the laterally dispersed or bent light are detected.

Drawing Two embodiments of the invention are illustrated in the drawing and are explained in detail in the following description. Figure 1 shows a first embodiment with a central light conducting cable for the reflection of the central beam and Figure 2 shows a second embodiment of the invention comprising a widened central duct through which the reflected light of the bright field is reflected through air.

Description of the embodiments In Figure 1, a work piece is referenced 10 having a bore 11 the surface of which is referenced 1 2. At its end, the bore 11 extends conically at an angle .

A probe 13 is introduced into the bore 11 and serves for the automatic checking of the surface 12. The probe consists of a central tubular linear duct 14 within a tube 1 5 of metal or plastics material. A fibreglass ring 1 6, surrounded externally by an optically dead zone 1 7 consisting of a sheet metal or plastics tube, is arranged coaxially around the tube 1 5. Light conductors 1 8 in the form of fibreglass sectors are arranged around the tube 17. The entire arrangement is covered externally by a protective tube 1 9.

Furthermore, a deflecting mirror 20 is arranged within the protective tube 1 9 and which, together with the protective tube 1 9 or with the central laser beam 21, includes an angle p such that the laser beam 21 is deflected perpendicularly onto the surface 12 of the work piece 10. During the checking or measuring operation, the work piece 10 is rotated about the probe 1 3 during a simultaneous advance of the probe 1 3 so that scanning of the surface 1 2 over a spiral line takes place. However, it is also possible with a large or non-rotationally symmetrical work piece 10 to rotate the probe 13 instead or to arrange the deflecting mirror 20 rotatable within the probe 13.

Figure 1 b shows a section on the line b-b in Figure 1 a for the clarification of the arrangement at the inner end surface of the probe 13. Eight light conductors in the form of fibreglass sectors 1 8 are arranged within the protective tube 19, within those the tube 1 7 has an optically dead zone, within that a fibreglass ring 1 6 has a light conductor and within that the tube 1 5 the interior of which forms the duct 14.

The arrangement according to Figure 1 acts in such a manner that the laser beam 21 passes through the duct 14 in a straight line and leaves the deflecting mirror 20 deflected through 900 and perpendicular to the lower region of the surface 1 2 of the bore 11. According to the quality of the surface, the reflection and scattering of the laser beam 21 takes place at the surface 12 so that a portion of the beam, namely the bright field, is reflected substantially parallel to the incident laser beam 21. This light component is once again deflected at the deflection mirror 20 substantially parallel to the laser beam 21.The insignificant light deflected laterally through about 50 is detected by the fibreglass ring 1 6 and is conveyed to a measuring arrangement comprising light sensitive detector elements which are not shown in the drawing. A further portion of the incident laser light is scattered to a greater extent according to the surface quality of the surface 12 whereby surface damage such as scratches and grooves are made particularly noticeable by the scattering of the laser beam.

The return of this portion of the reflected light takes place, dependent on direction, through separate light conductors 1 8 in the form of fibreglass sectors which are associated with light sensitive detector elements outside the probe 13 which are once again not shown. For the clear separation of the bright field component or of the stronger laser light scattered in the dark field reflected respectively into the two angular regions of the light conducting cables 16 and 18, an optically dead zone 1 7 is introduced between them. Thus, for example, the light conductor arrangement 1 6 detects the angular region 40-- 50 and the light conductor arrangement 1 8 an angular region of 150--200 or more depending on the outer diameter of the probe 13.

The illumination of the surface to be checked takes place with a focused laser beam 21 which has a diameter of about 0.1 mm. In the centre of the probe 13, the laser beam passes in a straight line through the small tubular duct 14 which has an inner diameter of about 1 mm. After leaving the duct 14, the laser beam 21 strikes a deflecting mirror 20 the inclination k of which matches the inclination of the surface a of the bore 11. In so doing, the mirror inclination p amounts to 90a A= 2 The return of the reflected or scattered light takes place through light cables 1 6 and 18 wherein the end surfaces of the light conductor 18 are in the form of sectors arranged in a ring.Photo receivers which are not shown in the drawing are connected to the light cables 1 6 and 18 as evaluating circuits. The fibreglass ring 1 6 closely engaging the tube 1 5 serves for the detection of the light only slightly varied from the reflection direction. This component is inversely proportional to the roughness of the surface 12 to be checked. After an annular optically dead zone 17, arranged outside the fibreglass ring 16, there follows n-sectors with light conductors 1 8 which subdivide the outer light conductor ring into npartial regions. The component of the light which is scattered in the entire outer annular regions 18 is proportional to the surface roughness.The directional distribution of the scattered light depends on the surface curvature and in particular on the directional structure in preparing the surface to be tested.

The inner surface 12 of the bore 11 to be checked is scanned at points over circular or spiral tracks by, for example, introducing the probe 1 3 into the bore 11 and rotating the work piece 10 about the bore axis. Alternatively, the probe 1 3 or parts of the probe, particularly the deflecting mirror 20, can be rotated.

The following measurements permit a complete characterisation of the surface 1 2 to be checked: A first measurement serves for determining the ratio of the light intensity received in the fibreglass ring 1 6 to the primary illuminating intensity by the laser beam 21. The ratio performed by these two values shows dark locations on the surface 1 2 and enables residues on the surface, cavities, cracks and similar faults to be considered.

During a second measurement, the ratio is formed between the light intensity received inside the fibreglass ring 1 6 and that in the fibreglass sectors 1 8 whereby the integral value is formed by the measurements in the various light conductors 18. The light intensity ratios thus produced, provide information concerning the quality of polish and thus permits the recognition of lapping or honing errors, grooves, flaws, scratches and the like.

In a third measuring operation, the ratio is formed between the light intensities received in the respective individual glass fibre sectors 18.

This ratio provides information concerning the variations in the structural direction and thus shows lapping errors, scratches and the like.

The arrangement according to Figures 2a and 2b is basically of the same construction as the arrangement according to Figure 1 thus, like parts are provided with the same references as in Figure 1. The essential difference in the arrangement according to Figure 2 with respect to the previously described arrangement consists in the fact that the central tube 1 5 has a larger inner diameter of about 2 mm and that the central fibre glass ring 1 6 is omitted. In this embodiment, the return of the laser rays in the bright field scattered at the surface 1 2 takes place in air through the central duct 1 4 through which the laser beam 21 is transmitted to the surface.Also in the arrangement according to Figure 2, the central duct 1 4 terminates in a plane together with the end surfaces of the light conducting cable 18 surrounding it. A semi-transparent mirror 22 is arranged at the inlet of the probe 13 for separating the various rays and by means of which the reflected light rays are deflected onto a measuring device 23 for the bright field. In the probe according to Figure 2, the reflected light only slightly changed in the reflection direction and which is not returned through the light conductive fibres but through the enlarged tube 1 5 and is coupled to the photo receiver of the measuring device 23 by the semi-transparent mirror 22. This arrangement has the advantage that light, particularly that reflected directly by the work piece surface, is detected whereas with the arrangement according to Figure 1, only an outer ring of 4"--5 0 opening is detected from this reflection whereby dark field components are also registered therewith. Consequently, with the arrangement according to Figure 2, a clearer separation between bright and dark reflection is possible.

Claims

1. A probe for the automatic checking of surfaces, particularly of mechanicaily treated precision surfaces in bores, with laser light which is guided over a work piece surface linearly or in the form of areas, wherein the light reflected from the surface as a criterion for the surface characteristics appears on the one hand at at least one light sensitive detector element for determining the reflected component in the bright field and appears on the other hand at a plurality of light sensitive detector elements for determining the scattered component in the dark field, according to Patent (Patent Application P ) characterised by a central linear duct (14) for transmitting the approaching laser beam (21) and by a plurality of light conducting cables (18) which, whilst leaving an optically dead zone (17) free, are arranged about the central duct (14) for the return of the light in the dark field scattered at the surface (1 2) to be checked.

2. A probe according to claim 1, characterised in that, the central duct (14) is made tubular with a circular cross-section.

3. A probe according to claim 1 or 2, characterised in that, the central duct (14) terminates in a plane together with the end surfaces of the light conducting cables (16, 18) surrounding it.

4. A probe according to one of claims 1 to 3, characterised in that, in the region of the end surface, the light conducting cables (18) have a cross-section in the form of sectors of a circular disc with n sectors.

5. A probe according to one of claims 1 to 4, characterised in that, the light of the bright field or the light reflected through a narrow angular region of the bright field reflected by the surface (1 2) to be checked is reflected through a light conducting cable (16) which is arranged coaxially with respect to the central duct (14) for the light supply (21).

6. A probe according to claim 5, characterised in that, the inner diameter of the central duct (14) amounts to about 1 mm.

7. A probe according to one of claims 1 to 4, characterised in that, the light in the bright field reflected by the surface (12) to be checked is reflected through the same duct (14), is conveyed through the incident laser beam (21), wherein a semi-transparent mirror (22) is arranged in the path of the beam.

8. A probe according to claim 7, characterised in that, the portion of the incident laser beam (21) used for the surface illumination passes linearly through the semi-transparent mirror (22) and that the portion of the reflected light in the bright field used for measuring can be deflected onto a measuring device (23) by means of the semitransparent mirror (22).

9. A probe according to claim 7 or 8, characterised in that, the inner diameter of the central duct (14) amounts to about 2 mm.

10. A probe according to one of the preceding claims, characterised in that, the incident laser beam (21) and the light reflected by the work piece surface (12) is deflected by a deflecting mirror (20) substantially perpendicularly onto the work piece surface (12) or onto the end surface of the central duct (14) and the light cables (16, 18) surrounding it.

11. A probe according to claim 10, characterised in that, the adjustment angle (,3) of the deflecting mirror (20) can be varied in accordance with the surface (12) to be checked.

12. A probe according to claim 10 or 11, characterised in that, the deflecting mirror (20) is rotatable about the axis of the incident laser beam (21).

1 3. A probe according to one of the preceding claims, characterised in that, the central tubular duct (14), the light conducting cables (16, 18) surrounding it and the deflecting mirror (20) are arranged in a protective tube (19).

14. A probe for the automatic checking of surfaces, substantially as herein described with reference to Figure 1 or Figure 2 of the accompanying drawings.