WO2009040161A1

WO2009040161A1 - Probe and apparatus for optically testing measurement objects

Info

Publication number: WO2009040161A1
Application number: PCT/EP2008/059723
Authority: WO
Inventors: Tobias Gnausch; David Rychtarik
Original assignee: Robert Bosch Gmbh
Priority date: 2007-09-24
Filing date: 2008-07-24
Publication date: 2009-04-02
Also published as: DE102007045569A1

Abstract

Proposed is an optical probe (1) for optically testing measurement objects, which comprises: a positionally fixed probe portion (10) and a rotatable probe portion (20) which is mechanically and optically coupled to the former, wherein the rotatable probe portion (20) comprises at least one optical element (25) and a means (21) for interchanging the at least one optical element (25). Further described is an apparatus for the interferometric measurement of measurement objects, wherein in the apparatus an interferometer is connected to the optical probe (1).

Description

Probe and device for optical testing of test objects

State of the art

The invention relates to an optical probe for the optical testing of test objects according to the preamble of claim 1 and to an apparatus for the interferometric measurement of test objects with the probe.

It is e.g. in the industrial manufacturing of components known to visually inspect the components during or after their manufacturing process. The surfaces of the components are illuminated with an optical probe and a usable image of the surface is obtained. In this context, also referred to as an "optical scanning" and the probe is referred to as a "Tastarm".

In particular, optical probes have been used which have a

Subdivision into a fixed and a rotatable probe part. Such a device is described, for example, in DE 100 57 540 A1. According to the teaching in the specification, such an arrangement allows a relatively simple orientation for scanning the measurement object and a design of the probe part for a precise rotating scan. For example, a very narrow bore of an injection nozzle can be scanned from the inside by a rotating probe part. Advantageously, therefore, the measurement object itself does not need to be rotated. However, it is not intended to replace certain elements of the probe as needed. Consequently missing in the probe means that allow easy replacement of individual elements of the probe.

However, if several components are to be connected to e.g. Measuring different bore diameters, a testing of all components with a single, previously known probe is not possible because neither the focal length of the probe can be flexibly adjusted nor the relevant optical element can be easily replaced. The same problem arises when due to the shape of the measurement objects very many different exit angles of the probe are necessary.

The hitherto known optical probes with a rotatable probe part therefore have the disadvantage that in the case of components to be measured with different dimensions, replacement of the entire probe is necessary.

Advantages of the invention

The optical probe according to the invention or the device according to the invention with the probe has the advantage that a very flexible use of the probe is made possible. Advantageously, only a part or only certain parts of the probe needs to be replaced, namely only the optically relevant elements of the probe.

Consequently, there is no need to replace the entire probe with respect to the probe or the output of the probe with the distance changed or the viewing direction of the test surface to be measured.

Advantageous developments of the invention are specified in the subclaims and described in the description.

drawing Embodiments of the invention will be explained in more detail with reference to the drawings and the description below. Show it:

1 shows the basic mechanical structure of an embodiment of the probe according to the invention,

Figure 2 shows the basic optical structure of an embodiment of the probe according to the invention, and

FIGS. 3a to 3e each show an exchange unit for the probe according to the invention.

Description of the embodiments

A first embodiment of the probe according to the invention is using the

Figures 1 and 2 explained. For clarity, Fig. 1 shows the basic mechanical structure of the probe 1, while in Fig. 2, the basic optical structure of the same probe 1 is outlined.

The probe 1 has a fixed probe part 10 and a mechanically and optically coupled rotatable probe part 20. The two probe parts 10, 20 are mechanically coupled to each other via a bearing 14. Therefore, an air gap 9 with a thickness approximately equal to the diameter of the bearing balls is formed between the two probe parts 10, 20. Notwithstanding this embodiment of FIG. 1, the bearing 14 may be disposed at a different position of the probe 1. Also, the air gap 9 may be significantly smaller than the diameter of the bearing balls, in particular, there may be almost a physical contact between the two probe parts 10, 20. However, since there should still be enough space to adjust the optics in both probe parts 10, 20, the distance is typically a few 100 μm.

An input beam is introduced by means of an optical fiber 11 via an input 5 in the probe 1, wherein the input beam first in the fixed Probe part 10 is introduced. In this fixed probe part 10, the collimating optics 12 is arranged, which collimates the input beam. The thus collimated beam 13 is further supplied to the rotatable probe part 20. The rotatable probe part 20 is mounted so that it can rotate about a rotation axis 31.

At least one optical element 25 is provided in the rotatable probe part 20. The at least one optical element 25 may be a focusing lens 25a or a deflecting unit 25b. The focusing lens 25a is advantageously formed by a so-called GRIN lens, which is a short form of "Graduate

Index lens "," Graded Index lens "or" Gradient index lens. "In contrast to conventional lenses, the refractive index of a GRIN lens changes continuously and steplessly in the material of the lens, for example, a curved surface shape such as be dispensed with in the case of conventional lenses.

The beam deflection unit 25b is formed in FIG. 2 by a prism. However, the beam deflecting unit 25b can also be formed by a mirror as needed. The measuring beam focused by the focusing lens 25a is deflected by the beam deflecting unit 25b in a direction perpendicular to the rotation axis 31 and exits from an exit 30 of the probe 1. The focus 32 of the measuring beam strikes the surface of the measuring object in the ideal case.

According to the invention, the rotatable probe part 20 now comprises a means 21 for exchanging the at least one optical element 25. By this means

21, it is possible, if necessary, to replace the at least one optical element 25 in a simple and fast manner. Thus, the rotatable probe part 20 itself comprises two subunits: In addition to a first solid subunit, a second subunit of the rotatable probe part 20 - a so-called exchange unit 26 - is provided. The replacement unit 26 comprises at least the at least one optical element 25.

The means 21 for exchanging the at least one optical element 25 in this example is itself an element of the first, massive subunit. Deviating from this, however, the means 21 may be an element of the exchange unit 26 if necessary.

The following situations illustrate the advantages of the means 21: Typically, the probe 1 is fixed to a holder when a measurement object is to be measured. If, during use, an optical element 25 such as the focusing lens 25a or the deflection unit 25b is damaged, because e.g. the probe 1 collides unplanned with the measurement object or other objects and suffers a shock, the optical element 25 must be replaced. Previously, this meant replacing the entire probe 1, even though only one or a few elements were damaged. The probe 1 must then be removed from the holder and a new probe 1 to be reinstalled. In addition, the new probe 1 must be gauged, i. be reset to the target.

On the other hand, even with an undamaged optical element 25, there may be a need to replace the element 25, e.g. an optic with another property is required. Thus, a new focal length or another exit angle of the measuring beam from the output 30 of the probe 1 may be desired. In previously known probes 1, the entire probe 1 had to be replaced in such cases as well.

With the probe 1 according to the invention, it is now possible to replace only the optically relevant element 25, without at the same time having to remove the probe 1 from the holder and, later, to mount a new probe 1 again. The invention is based on the finding that even with probes 1 with different optics and optionally the mechanics, many of the remaining elements of the probe 1 have the same dimension and design. These did not really need to be replaced. Therefore, it is proposed to collect such elements in the fixed probe part 10.

Advantageously, the means 21 may be designed in the form of a closure. A closure offers the possibility of easy replacement by simply loosening and closing the closure. In the first embodiment according to Fig. 1, the means 21 is a bayonet 21a. The bayonet closure 21a ensures a constant contact force and prevents the replacement unit 26 from falling out. In addition, the bayonet lock 21a ensures a defined position of the exchange unit 26 in the vertical direction.

Now, further possible components of the replacement unit 26 will be explained. First, it is proposed to arrange the at least one optical element 25 in a tube 27. On the one hand, this tube 27 serves as a protective cover for the one or more optical elements 25. On the other hand, the tube 27 also serves to guide the optics and is important for determining the opto-mechanical axis of the optics. This tube 27 corresponds to the actual probe arm of the probe. 1

In order for the tube 27 to be precisely aligned with the solid subunit of the rotatable probe portion 20, the replacement unit 26 further includes an alignment pin 28. This alignment pin 28 encloses the tube 27 in plan view and fits snugly into a corresponding recess of the solid subunit. As a result, the angle of view of the focus 32 is defined very precisely.

Finally, a Führungsferrule 29 may be provided for guiding the tube 27 in the exchange unit 26. The tube 27 must be mounted in a very precise Führungsferrule 29 so that a change of the exchange unit 26 can always be made reproducible and there is no play between the tube 27 and the Führungsferrule 29. It is of fundamental importance in optical metrology that the individual elements of the probe 1 have no play. The position of the focus 32 must be reproducible to within a few micrometres. The Führungsferrule 29 may consist of either a ceramic, stainless steel or other material that allows a multiple change without wear and is made very precisely.

In a further, not shown in Fig. Embodiment of the probe 1, the means 21 is a screw cap. An exchange then takes place through simply unscrewing the replacement unit 26 and then screwing another replacement unit 26. All other features of the probe 1 are the same as described in the first embodiment.

The means 21 may in a further embodiment of the probe 1 by a

Raster closure be formed. In this case, the replacement unit 26 can be mounted by snapping into the solid subunit of the probe 1.

FIGS. 3 a to 3 e each show a replacement unit 26 for the inventive probe 1 described so far

Exchange unit 26 as needed a tube 27 with at least one optical element 25, a Führungsferrule 29 and an alignment pin 28 include. The 5 examples of the exchange units 26 in FIGS. 3a to 3e have different optics from each other. Comparing the first two exchange units 26 according to FIGS. 3a and 3b, it can be seen that the second

Exchange unit 26 according to FIG. 3b has a longer tube 27 than the first exchange unit 26 according to FIG. 3a. Thus, a longer feeler arm is achieved for e.g. Measurement of very deep holes.

The third exchange unit 26 according to FIG. 3c, on the other hand, has a focus 32, which is arranged further from the exit 30 of the probe 1. Finally, according to FIG.

4d, an exchange unit 26 is proposed which comprises a plurality of outlets 30.

The outputs 30 may have different exit angles.

Alternatively, the exchange unit 26, as in FIG. 3e, has only one exit 30, which provides a very specific exit angle.

Further embodiments for exchange units 26 will now be explained without a representation in Fig.: Different exchange units 26 may have tubes 27 of different thickness, the exchange units 26, however, each a Führungsferrule 29 with the same geometric

Dimensions include. The exchange units 26 thus differ only by thinner or thicker tubes 27 from each other. Finally, it is also possible that the replacement units 26 have different types of feeler arms. For example, a Fasertastarm be part of a replacement unit 26. In this case, the small hole 27 is often missing in the exchange unit 26. Thus, the probe arm is not formed by the tube 27 but by an optical fiber. Accordingly, the leadership leadership leads

29 of the exchange unit 26 not the tube 27, but the optical fiber. The optical fiber is partially disposed in the Führungsferrule 29, partially protruding from the Führungsferrule 29 out. Such replacement units 26 with a Fasertastarm are particularly suitable when the bore to be measured is very small. The Fasertastarm is also designed so that the measuring beam emerges perpendicular to the axis of rotation 31 of the probe 1.

Incidentally, the measurement beam reflected on the surface of the measurement object is picked up again by the probe 1. Typically, the reflected measuring beam now passes through the previous beam path in reverse

Direction, i. it is introduced again into the probe 1 at the exit 30 of the probe 1 and leaves the probe 1 at the input 5. The terms "input" and "output", as is familiar to a person skilled in the art, do not refer to the measuring beam reflected by the test object. The guided out again from the probe 1 measuring beam is then fed to a detection unit, at the one

Evaluation unit is connected. Thus, an analysis of the illuminated with the probe 1 measurement objects is possible.

Incidentally, all embodiments of the probe 1 described so far are suitable for being connected to a known interferometer.

Together they then form a device for the interferometric measurement of measurement objects. Ideally, the interferometer is connected to the probe 1 by means of the already mentioned optical fiber 11. The structure of a typical interferometer will not be further explained, since this has already been described in detail, for example, in the initially cited document DE 100 57 540 A1. It should only be emphasized that the interferometer can comprise an evaluation unit in addition to a detection unit. In summary, it is stated that an optical probe 1 has been described with a fixed probe part 10 and a rotatable probe part 20, in which a flexible replacement of at least one optical element 25 of the probe 1 is made possible. For this purpose, a means 21 for exchanging the at least one optical element 25 is provided in the rotatable probe part 20. Furthermore, a device has been proposed which comprises a per se known interferometer and the probe 1 described. Overall, this achieves a very versatile optical probe 1 which can be used with different measuring objects.

Claims

claims

Optical probe (1) for optically testing measuring objects, comprising a stationary probe part (10) and a mechanically and optically coupled rotatable probe part (20), the rotatable probe part (20) having at least one optical element (25), characterized in that the rotatable probe part (20) comprises means (21) for exchanging the at least one optical element (25).

2. Probe (1) according to claim 1, characterized in that the means (21) is designed in the form of a closure.

3. Probe (1) according to claim 1 or 2, characterized in that the means (21) is a bayonet closure (21a), a screw cap or a grid fastener.

4. Probe (1) according to one of claims 1 to 3, characterized in that the at least one optical element (25) is a focusing lens (25a) or a deflection unit (25b).

5. probe (1) according to one of claims 1 to 4, characterized in that the at least one optical element (25) is part of a replacement unit (26).

6. probe (1) according to one of claims 1 to 5, characterized in that the at least one optical element (25) in a tube (27) is arranged.

7. probe (1) according to claim 6, characterized in that the exchange unit (26) comprises an alignment pin (28) for precise alignment of the tube (27).

8. probe (1) according to one of claims 5 to 7, characterized in that the exchange unit (26) comprises a Führungsferrule (29) for guiding the tube (27).

9. probe (1) according to one of claims 5 to 8, characterized in that the exchange unit (26) has a plurality of outputs (30).

10. An apparatus for interferometric measurement of measurement objects, wherein a

Interferometer is connected to a probe (1) according to one of claims 1 to 9.