Title of Invention	DEVICE AND PROCESS FOR INSPECTING SURFACES IN THE INTERIOR OF HOLES
Abstract	The invention relates to a device and a method for inspecting the internal surfaces of holes, recesses or the like. Said device (1) comprises a light source (3) for producing a light beam (4), said light beam (4) being focusable by means of a projection lens (7) and the focused light beam being directed onto the surface (9). A sensor device (11) is provided for detecting the reflected light beam (10). The aim of the invention is to provide a device which allows as rapid and easy a measurement as possible and which can be easily miniaturized. For this purpose, the light source (3) allows for production of a multicolor light beam (4) that is focused onto a plurality of points that are at different distances from the projection lens (7) due to chromatic aberrations of the projection lens (7). The distance to the surface (9) can be determined from the spectrum of the detected light beam (10).

Title of Invention

DEVICE AND PROCESS FOR INSPECTING SURFACES IN THE INTERIOR OF HOLES

Abstract

The invention relates to a device and a method for inspecting the internal surfaces of holes, recesses or the like. Said device (1) comprises a light source (3) for producing a light beam (4), said light beam (4) being focusable by means of a projection lens (7) and the focused light beam being directed onto the surface (9). A sensor device (11) is provided for detecting the reflected light beam (10). The aim of the invention is to provide a device which allows as rapid and easy a measurement as possible and which can be easily miniaturized. For this purpose, the light source (3) allows for production of a multicolor light beam (4) that is focused onto a plurality of points that are at different distances from the projection lens (7) due to chromatic aberrations of the projection lens (7). The distance to the surface (9) can be determined from the spectrum of the detected light beam (10).

Full Text	DEVICE AND PROCESS FOR INSPECTING SURFACES IN THE INTERIOR OF HOLES The invention relates to a device for inspecting surfaces in the interior of holes, recesses, or the like, where the device comprises a light source for producing a light beam, where the light beam can be focused by imaging optics, where the focused light beam can be deflected onto the surface, and where a sensor device is provided for detecting the reflected light beam Surface inspections in the interior of holes, recesses, or the like, in particular of boreholes or small cracks with dimensions in the millimeter range, represent an important task in many fields of technology. Qualitatively high-value and close-tolerance bore holes are frequently needed when they are provided to receive movable parts such as pins, cylinders, or small pistons, eg in pressure valves Pressure valves are used in pneumatics but also in other fields such as in automobile technology for fuel injection. There in the meantime, test pins for electrical circuits with pneumatic cylinders with a diameter of 2 mm are finding application. These very small cylinders are necessary in order to keep up with electrical circuits which are constantly getting smaller. Close-tolerance bore holes are also required for shrink connections, where said bore holes cannot be allowed to be subject to damage due to burrs or bubbles Moreover, it can also be of importance in holes outside of the millimeter range to know the surface quality precisely Thus, for example, brake cylinders in a motor vehicle must have a particularly high-quality surface since small chips or burrs in the cylinders can lead to the destruction of the parts after even a short time For the inspection of surfaces, essentially two processes are used in practice at present. In one system a glass wedge forms optics with which nearly 360° of the surrounding surface can be imaged on a light wave guide bundle The light wave guide bundle frequently comprises several thousand individual fibers which together conduct an image to a camera By suitable image processing, structures on the surface can be recognized thereby Their actual size, in particular their three-dimensional extension, cannot be determined however. In another technology customary in practice a monochromatic light beam is deflected onto the surface to be examined, where this light beam is always kept focused on the surface. If the distance between the optics and the illuminated image point changes as a consequence of unevenness of the surface and thus the light beam is no longer focused, then an automatic focusing circuit adjusts the optics in such a manner that the light beam is once again focused on the surface. Via this correction of the optics the change in distance can be detected. In this way the surface can indeed be measured in three dimensions, but due to the necessary tracking of the focusing only relatively slow measurement speeds can be achieved An inspection in a running production process thus cannot be realized. The present invention is thus based on the objective of developing and extending a device of the type stated in the introduction in such a manner that, as far as possible, a rapid, simple, and reproducible inspection of surfaces in the interior of holes, recesses, or the like is possible with dimensioning up into the millimeter range and with the simplest construction. Furthermore, a corresponding process will be specified According to the invention the above objective is realized by the features of claim 1. According thereto, the device under discussion is developed in such a manner that a multicolor laght beam can be produced with the light source, said light beam, due to the chromatic aberration of the imaging optics, being focused onto several points at different distances from the imaging optics, and that from the spectrum of the detected light beam the distance to the surface can be determined. With regard to the process, the above objective is realized by the features of claim 17. According thereto, the process under discussion is characterized by the fact that with the light source a multicolor light beam is produced which, due to the chromatic aberration of the imaging optics, is focused onto several points at different distances from the imaging optics, and that from the spectrum of the detected light beam the distance to the surface can be determined. In the manner according to the invention it has first been recognized that the re-focusing of the optics can be omitted Turning away from the process known in practice, multicolor light is intentionally used and, arising thereby and frequently undesirable, the chromatic aberration associated with multicolor light is exploited in the optics. Due to the chromatic aberration, light beams of different wave lengths are focused onto different focal points. Depending on the degree of chromatic aberration, these focal points lie in a more or less widely extended area and at a greater or lesser distance from the imaging optics on the optical axis of the imaging optics Since those spectral fractions which are essentially focused on the illuminated point of the surface are reflected best by the irradiated surface, conclusions about the distance between the optics and the illuminated image point can be drawn according to the invention from a spectral analysis of the reflected light beam If an entire area on the surface is scanned by deflecting the focused light beam, then a profile concerning the condition of the surface can be developed in this manner The device according to the invention and the process according to the invention can be used in an advantageous manner anywhere that surfaces have to be measured in surroundings which are very restricted spatially. Thus, for example, bore holes, but also depressions, cracks, or other recesses, can be measured. According to the invention a multicolor light beam is produced for this purpose which is preferably conducted via one or more light wave guides to imaging optics. This is preferably white light since a particularly simple situation with regard to the evaluation of the spectral fractions results thereby. The imaging optics comprises in an advantageous manner a lens or a system of lenses With regard to a miniaturization which is as simple as possible and imaging optics which is as economical as possible, said imaging optics preferably comprises a GRIN (gradient index) lens GRIN lenses usually consist of cylindrical blocks which are provided by special production processes with a continuous radial change in the index of refraction. In so doing, the same effects are obtained on a light beam passing through the lens as with conventional lenses However, GRIN lenses can be miniaturized significantly further with lower production costs, which is of great advantage in particular in spatially restricted surroundings. In a particularly advantageous manner the GRIN lens can be assigned to a positioning device, a so-called spacer, with which the aberration of the lens can be adapted. With this, a lens of this type can be adapted particularly simply to changed system configurations. In measurement situations in which greater distances between the optics and the measured object must be overcome, the GRIN lens can be connected later to additional optics Here, for example, imaging optics known in the case of aspheric telescopes can be used In an advantageous manner, for example, a light wave guide can be coupled between the lenses of the telescope optics to deflect light into the beam path, whereby still greater coverage is possible With regard to a particularly simple deflectability of the focused light beam, a deflecting device could be provided which preferably is structured in such a manner that it can be moved In this connection, prisms, mirrors, or also plane-parallel plates are used. Advantageously the deflecting device is adapted to achieve reproducible measurement processes through electrical, piezoelectric, magnetic, or comparable positioning elements, which preferably are driven by an electronic circuit, e g. a microcontroller. By suitable control of the deflecting device the entire surface, or at least a part of the surface, in the interior of a hole, specifically the part to be inspected, can be illuminated and measured. In so doing, the light beam can be guided in a linear, circular, spiral, meandering, or any other suitable manner. With regard to a particularly simple and space-saving development of the device, the reflected light beam could take the same path as the light beam produced by the light source, only in the reverse direction. At a suitable point the reflected light beam could be separated by an optical separating filter and conducted to a sensor device The sensor device advantageously comprises an electronic component which is in the position to convert multicolor light, depending on the spectrum of the incident light beam, into suitable electrical signals. Preferably, a CCD chip or other photodetector arrays are used here The device according to the invention can be operated in a relatively simple manner as a multi-channel system, whereby several measurements can be carried out simultaneously In so doing, the light exiting from the imaging optics can be divided onto several measurement points and the respective reflections of the measurement points conducted via, preferably several, light wave guides In a particularly advantageous manner when so doing, the measurement points are disposed depending on the measurement situation Here a disposition in the form of a row and a circle would be conceivable With regard to a particularly versatile evaluation capability of the signals obtained by the sensor device, they could be conducted to an electronic device which, for example, comprises a digital computer in the form of a microcontroller or a digital signal processor. With this, signal processing can be carried out and the data obtained prepared in a suitable manner for later use, e.g a visualization. Perhaps evaluation of measurement results could also be done here and the surface classified according to certain criteria. There are various possibilities for developing and extending the teaching of the present invention in an advantageous manner. For this, reference is made, on the one hand, to the claims subordinate to claims 1 and 17 and, on the other hand, to the following explanation of preferred embodiment examples of the invention with the aid of the drawings In connection with the explanation of the preferred embodiment examples of the invention with the aid of the drawings, preferred developments and extensions of the teaching are also explained in general In the accompanying drawings. FIG 1 shows in a schematic view a conceptual layout of a device according to the invention, FIG. 2 shows m a schematic view the use of a GRIN lens in connection with a lens system, and FIG 3 shows in a schematic view a deflecting device with a plane-parallel plate FIG 1 shows in a schematic representation a conceptual layout of a device 1 according to the invention for inspecting the surface 9 in the interior of a hole 2 The device 1 comprises a light source 3 with the aid of which a multicolor light beam 4 can be produced This light beam 4 passes unaffected through an optical separating filter 5 and is coupled into a light wave guide 6 to deflect the light beam 4 The light beam 4 is focused, with a lens system 7 using its chromatic aberration, onto a series of focal points and is deflected with a deflecting part 8 onto the surface 9 of the hole 2 The lens system 7 and the deflecting part 8 are coordinated with one another in such a manner that at least one of the focal points lies on the surface 9. Under certain circumstances a corresponding adaptation device, not represented here, must be provided so that this requirement can be met. The optical system comprising the lens system 7 and deflecting part 8 is mounted in such a manner that it can turn and can be moved along the longitudinal axis of the hole 2 These movements are preferably carried out via an electrical positioning device not represented here so that the surface 9 of the hole 2 can be scanned as completely and reproducibly as possible. On the surface 9 the light beam is reflected and conducted via the deflecting wedge 8 and the lens system 7 to the light wave guide 6 The optical separating filter separates the light beam 4 produced by the light source 3 from the reflected light beam 10 which is conducted to the sensor device 11 This sensor device is coupled to evaluation electronics, also not represented, which calculates from the spectrum of the reflected light beam 10 the distance between the device 1 according to the invention and the surface 9 and makes the data available for a later evaluation and/or visualization In FIG. 2 the use of a GRIN lens 12 with conventional optics 13 is represented in a schematic view. In the drawing an approximately 1.0 pitch GRIN lens 12 is represented, that is, the lens is dimensioned in such a manner that an incident light beam describes a period of a sinusoidal oscillation in the interior of the GRIN lens 12. To adjust the chromatic aberration the GRIN lens 12 is connected at the front to a positioning device 14, a so-called spacer. The light beam exiting from the GRIN lens 12 is conducted by optics 13, which is preferably formed by 1-1 imaging optics with two aspheric lenses, such imaging optics being known in aspheric telescopes Between the two lenses 15 and 16 a light wave guide not represented here can be disposed to bridge still greater distances The light beam exiting from this optics is conducted to the surface 9, under certain circumstances with the use of a deflecting device 8. FIG. 3 shows a development of the deflecting device 8 by a plane-parallel plate 17. The incident light beam 4 is refracted at each of the two boundary surface 18 and 19, whereby a shifted, parallel light beam 20 results. The shift v follows from the thickness d of the plate 17, the angle £ between the incident light beam 4 and the perpendicular to the plate 17, and the index of refraction n. If the plane-parallel plate 17 is rotated about the axis 21, then the shifted, parallel light beam 20 describes a circular path on the surface to be examined If, in addition, the inclination of the plane-parallel plate 17 is varied, surfaces can be scanned in an annular pattern. Finally, let it be noted that the embodiment examples discussed above explain the claimed teaching but do not restrict it to the embodiment examples WE CLAIM : 1. Device for inspecting surfaces in the interior of holes, recesses, or the like, where the device (1) comprises a light source (3) for producing a light beam (4), where the light beam (4) can be focused by imaging optics (7), where the focused light beam can be deflected onto the surface (9), and where a sensor device (11) is provided to detect the light beam (10) reflected from the surface (9), characterized in that a multicolor light beam (4) is produced with the light source (3), said light beam, due to the chromatic aberration of the imaging optics (7), being focused onto several points at different distances from the imaging optics (7), that from the spectrum of the detected light beam (10) the distance to the surface can be determined, and that the imaging optics (7) comprises a GRIN (gradient index) lens (12). 2. Device as claimed in claim 1, wherein the multicolor light beam (4) produced by the light source (3) is a polychromatic light beam, preferably white light. 3. Device as claimed in claim 1 or 2, wherein the light beam (4) is conducted from the light source (3) by one or more light wave guides (6) to imaging optics (7). 4. Device as claimed in one of claims 1 to 3, wherein the imaging optics (7) comprises a lens or a system of lenses. 5. Device as claimed in claim 4, wherein the GRIN lens (12) can be adapted in its aberration by positioning device (14). 6. Device as claimed in claim 4 or 5, wherein the GRIN lens (12) is connected after additional optics (13) with the aid of which, in measurement, a greater distance between the GRIN lens (12) and the surface (9) to be measured can be achieved and/or a coupling of the light beams exiting from the GRIN lens (12) into a light wave guide is possible. 7. Device as claimed in one of claims1 to 6, wherein the focused light beam is deflected by a deflecting device (8) to a certain point on the surface (9). 8. Device as claimed in claim 7, wherein the deflecting device (8) is structured in such a manner that it can move. 9. Device as claimed in claim 7 or 8, wherein the deflecting device (8) can be moved by electrical, piezoelectric, magnetic, or comparable positioning devices. 10. Device as claimed in one of claims 7 to 9, wherein the deflecting device (8) comprises a prism, a plane-parallel plate, a mirror, or other devices affecting the direction of propagation of the light beams. 11. Device as claimed in one of claims 1 to 10, wherein the light beam (4) produced by light source (3) and the light beam (10) reflected from the surface (9) are separated by an optical separating filter (4) [sic]. 12. Device as claimed in one of claims 1 to 11, wherein the sensor device (11) comprises a photodetector array, preferably a linear array. 13. Device as claimed in one of claims 1 to 12, wherein the device is constructed as a multi-channel system, wherein several measurements can be carried out simultaneously. 14. Device as claimed in one of claims 1 to 13, wherein the light exiting from the imaging optics (7) can be divided onto several measurement points and the reflections of the measurement points can be conducted via several light wave guides (6) to the sensor device (11). 15. Device as claimed in one of claims 1 to 14, wherein the signals produced by the sensor device (11) are conducted to an electronic device, preferably to a digital computer in the form of a microcontroller or a digital signal processor for signal processing. 16. Process for inspecting surfaces in the interior of holes, recesses, or the like, preferably for operating a device as claimed in one of claims 1 to 15, wherein the device (1) comprises a light source (3) for producing a light beam (4), where the light beam (4) can be focused by imaging optics (7), where the focused light beam can be deflected onto the surface (9), and where a sensor device (11) is provided for detecting the reflected light beam (10), wherein a multicolor light beam (4) is produced with the light source (3), said light beam, due to the chromatic aberration of the imaging optics (7), being focused onto several points at different distances from the imaging optics, and that from the spectrum of the detected light beam (10) the distance to the surface can be determined. 17. Process as claimed in claim 16, wherein the light beam (4) is guided by deflecting device (8) in a linear, circular, spiral, meandering, or any other suitable manner over the surface (9) and thus the surface (9) is scanned ABSTRACT DEVICE AND PROCESS FOR INSPECTING SURFACES IN THE INTERIOR OF HOLES The invention relates to a device and a method for inspecting the internal surfaces of holes, recesses or the like. Said device (1) comprises a light source (3) for producing a light beam (4), said light beam (4) being focusable by means of a projection lens (7) and the focused light beam being directed onto the surface (9). A sensor device (11) is provided for detecting the reflected light beam (10). The aim of the invention is to provide a device which allows as rapid and easy a measurement as possible and which can be easily miniaturized. For this purpose, the light source (3) allows for production of a multicolor light beam (4) that is focused onto a plurality of points that are at different distances from the projection lens (7) due to chromatic aberrations of the projection lens (7). The distance to the surface (9) can be determined from the spectrum of the detected light beam (10).

Full Text

DEVICE AND PROCESS FOR INSPECTING
SURFACES IN THE INTERIOR OF HOLES
The invention relates to a device for inspecting surfaces
in the interior of holes, recesses, or the like, where the
device comprises a light source for producing a light beam,
where the light beam can be focused by imaging optics, where the
focused light beam can be deflected onto the surface, and where
a sensor device is provided for detecting the reflected light
beam
Surface inspections in the interior of holes, recesses, or
the like, in particular of boreholes or small cracks with
dimensions in the millimeter range, represent an important task
in many fields of technology. Qualitatively high-value and
close-tolerance bore holes are frequently needed when they are
provided to receive movable parts such as pins, cylinders, or
small pistons, eg in pressure valves Pressure valves are used
in pneumatics but also in other fields such as in automobile
technology for fuel injection. There in the meantime, test pins
for electrical circuits with pneumatic cylinders with a diameter
of 2 mm are finding application. These very small cylinders are
necessary in order to keep up with electrical circuits which are
constantly getting smaller. Close-tolerance bore holes are also
required for shrink connections, where said bore holes cannot be
allowed to be subject to damage due to burrs or bubbles
Moreover, it can also be of importance in holes outside of the
millimeter range to know the surface quality precisely Thus,
for example, brake cylinders in a motor vehicle must have a
particularly high-quality surface since small chips or burrs in
the cylinders can lead to the destruction of the parts after
even a short time

For the inspection of surfaces, essentially two processes
are used in practice at present. In one system a glass wedge
forms optics with which nearly 360° of the surrounding surface
can be imaged on a light wave guide bundle The light wave guide
bundle frequently comprises several thousand individual fibers
which together conduct an image to a camera By suitable image
processing, structures on the surface can be recognized thereby
Their actual size, in particular their three-dimensional
extension, cannot be determined however.
In another technology customary in practice a monochromatic
light beam is deflected onto the surface to be examined, where
this light beam is always kept focused on the surface. If the
distance between the optics and the illuminated image point
changes as a consequence of unevenness of the surface and thus
the light beam is no longer focused, then an automatic focusing
circuit adjusts the optics in such a manner that the light beam
is once again focused on the surface. Via this correction of the
optics the change in distance can be detected. In this way the
surface can indeed be measured in three dimensions, but due to
the necessary tracking of the focusing only relatively slow
measurement speeds can be achieved An inspection in a running
production process thus cannot be realized.
The present invention is thus based on the objective of
developing and extending a device of the type stated in the
introduction in such a manner that, as far as possible, a rapid,
simple, and reproducible inspection of surfaces in the interior
of holes, recesses, or the like is possible with dimensioning up
into the millimeter range and with the simplest construction.
Furthermore, a corresponding process will be specified
According to the invention the above objective is realized
by the features of claim 1. According thereto, the device under
discussion is developed in such a manner that a multicolor laght

beam can be produced with the light source, said light beam, due
to the chromatic aberration of the imaging optics, being focused
onto several points at different distances from the imaging
optics, and that from the spectrum of the detected light beam
the distance to the surface can be determined.
With regard to the process, the above objective is realized
by the features of claim 17. According thereto, the process
under discussion is characterized by the fact that with the
light source a multicolor light beam is produced which, due to
the chromatic aberration of the imaging optics, is focused onto
several points at different distances from the imaging optics,
and that from the spectrum of the detected light beam the
distance to the surface can be determined.
In the manner according to the invention it has first been
recognized that the re-focusing of the optics can be omitted
Turning away from the process known in practice, multicolor
light is intentionally used and, arising thereby and frequently
undesirable, the chromatic aberration associated with multicolor
light is exploited in the optics. Due to the chromatic
aberration, light beams of different wave lengths are focused
onto different focal points. Depending on the degree of
chromatic aberration, these focal points lie in a more or less
widely extended area and at a greater or lesser distance from
the imaging optics on the optical axis of the imaging optics
Since those spectral fractions which are essentially focused on
the illuminated point of the surface are reflected best by the
irradiated surface, conclusions about the distance between the
optics and the illuminated image point can be drawn according to
the invention from a spectral analysis of the reflected light
beam If an entire area on the surface is scanned by deflecting
the focused light beam, then a profile concerning the condition
of the surface can be developed in this manner

The device according to the invention and the process
according to the invention can be used in an advantageous manner
anywhere that surfaces have to be measured in surroundings which
are very restricted spatially. Thus, for example, bore holes,
but also depressions, cracks, or other recesses, can be
measured.
According to the invention a multicolor light beam is
produced for this purpose which is preferably conducted via one
or more light wave guides to imaging optics. This is preferably
white light since a particularly simple situation with regard to
the evaluation of the spectral fractions results thereby. The
imaging optics comprises in an advantageous manner a lens or a
system of lenses
With regard to a miniaturization which is as simple as
possible and imaging optics which is as economical as possible,
said imaging optics preferably comprises a GRIN (gradient index)
lens GRIN lenses usually consist of cylindrical blocks which
are provided by special production processes with a continuous
radial change in the index of refraction. In so doing, the same
effects are obtained on a light beam passing through the lens as
with conventional lenses However, GRIN lenses can be
miniaturized significantly further with lower production costs,
which is of great advantage in particular in spatially
restricted surroundings.
In a particularly advantageous manner the GRIN lens can be
assigned to a positioning device, a so-called spacer, with which
the aberration of the lens can be adapted. With this, a lens of
this type can be adapted particularly simply to changed system
configurations.
In measurement situations in which greater distances
between the optics and the measured object must be overcome, the
GRIN lens can be connected later to additional optics Here, for

example, imaging optics known in the case of aspheric telescopes
can be used In an advantageous manner, for example, a light
wave guide can be coupled between the lenses of the telescope
optics to deflect light into the beam path, whereby still
greater coverage is possible
With regard to a particularly simple deflectability of the
focused light beam, a deflecting device could be provided which
preferably is structured in such a manner that it can be moved
In this connection, prisms, mirrors, or also plane-parallel
plates are used. Advantageously the deflecting device is adapted
to achieve reproducible measurement processes through
electrical, piezoelectric, magnetic, or comparable positioning
elements, which preferably are driven by an electronic circuit,
e g. a microcontroller. By suitable control of the deflecting
device the entire surface, or at least a part of the surface, in
the interior of a hole, specifically the part to be inspected,
can be illuminated and measured. In so doing, the light beam can
be guided in a linear, circular, spiral, meandering, or any
other suitable manner.
With regard to a particularly simple and space-saving
development of the device, the reflected light beam could take
the same path as the light beam produced by the light source,
only in the reverse direction. At a suitable point the reflected
light beam could be separated by an optical separating filter
and conducted to a sensor device
The sensor device advantageously comprises an electronic
component which is in the position to convert multicolor light,
depending on the spectrum of the incident light beam, into
suitable electrical signals. Preferably, a CCD chip or other
photodetector arrays are used here
The device according to the invention can be operated in a
relatively simple manner as a multi-channel system, whereby

several measurements can be carried out simultaneously In so
doing, the light exiting from the imaging optics can be divided
onto several measurement points and the respective reflections
of the measurement points conducted via, preferably several,
light wave guides In a particularly advantageous manner when so
doing, the measurement points are disposed depending on the
measurement situation Here a disposition in the form of a row
and a circle would be conceivable
With regard to a particularly versatile evaluation
capability of the signals obtained by the sensor device, they
could be conducted to an electronic device which, for example,
comprises a digital computer in the form of a microcontroller or
a digital signal processor. With this, signal processing can be
carried out and the data obtained prepared in a suitable manner
for later use, e.g a visualization. Perhaps evaluation of
measurement results could also be done here and the surface
classified according to certain criteria.
There are various possibilities for developing and
extending the teaching of the present invention in an
advantageous manner. For this, reference is made, on the one
hand, to the claims subordinate to claims 1 and 17 and, on the
other hand, to the following explanation of preferred embodiment
examples of the invention with the aid of the drawings In
connection with the explanation of the preferred embodiment
examples of the invention with the aid of the drawings,
preferred developments and extensions of the teaching are also
explained in general In the accompanying drawings.
FIG 1 shows in a schematic view a conceptual layout of a
device according to the invention,
FIG. 2 shows m a schematic view the use of a GRIN lens in
connection with a lens system, and

FIG 3 shows in a schematic view a deflecting device with a
plane-parallel plate
FIG 1 shows in a schematic representation a conceptual
layout of a device 1 according to the invention for inspecting
the surface 9 in the interior of a hole 2 The device 1
comprises a light source 3 with the aid of which a multicolor
light beam 4 can be produced This light beam 4 passes
unaffected through an optical separating filter 5 and is coupled
into a light wave guide 6 to deflect the light beam 4 The light
beam 4 is focused, with a lens system 7 using its chromatic
aberration, onto a series of focal points and is deflected with
a deflecting part 8 onto the surface 9 of the hole 2 The lens
system 7 and the deflecting part 8 are coordinated with one
another in such a manner that at least one of the focal points
lies on the surface 9. Under certain circumstances a
corresponding adaptation device, not represented here, must be
provided so that this requirement can be met. The optical system
comprising the lens system 7 and deflecting part 8 is mounted in
such a manner that it can turn and can be moved along the
longitudinal axis of the hole 2 These movements are preferably
carried out via an electrical positioning device not represented
here so that the surface 9 of the hole 2 can be scanned as
completely and reproducibly as possible.
On the surface 9 the light beam is reflected and conducted
via the deflecting wedge 8 and the lens system 7 to the light
wave guide 6 The optical separating filter separates the light
beam 4 produced by the light source 3 from the reflected light
beam 10 which is conducted to the sensor device 11 This sensor
device is coupled to evaluation electronics, also not
represented, which calculates from the spectrum of the reflected
light beam 10 the distance between the device 1 according to the

invention and the surface 9 and makes the data available for a
later evaluation and/or visualization
In FIG. 2 the use of a GRIN lens 12 with conventional
optics 13 is represented in a schematic view. In the drawing an
approximately 1.0 pitch GRIN lens 12 is represented, that is,
the lens is dimensioned in such a manner that an incident light
beam describes a period of a sinusoidal oscillation in the
interior of the GRIN lens 12. To adjust the chromatic aberration
the GRIN lens 12 is connected at the front to a positioning
device 14, a so-called spacer.
The light beam exiting from the GRIN lens 12 is conducted
by optics 13, which is preferably formed by 1-1 imaging optics
with two aspheric lenses, such imaging optics being known in
aspheric telescopes Between the two lenses 15 and 16 a light
wave guide not represented here can be disposed to bridge still
greater distances The light beam exiting from this optics is
conducted to the surface 9, under certain circumstances with the
use of a deflecting device 8.
FIG. 3 shows a development of the deflecting device 8 by a
plane-parallel plate 17. The incident light beam 4 is refracted
at each of the two boundary surface 18 and 19, whereby a
shifted, parallel light beam 20 results. The shift v follows
from the thickness d of the plate 17, the angle £ between the
incident light beam 4 and the perpendicular to the plate 17, and
the index of refraction n. If the plane-parallel plate 17 is
rotated about the axis 21, then the shifted, parallel light beam
20 describes a circular path on the surface to be examined If,
in addition, the inclination of the plane-parallel plate 17 is
varied, surfaces can be scanned in an annular pattern.
Finally, let it be noted that the embodiment examples
discussed above explain the claimed teaching but do not restrict
it to the embodiment examples

WE CLAIM :
1. Device for inspecting surfaces in the interior of holes, recesses, or the like,
where the device (1) comprises a light source (3) for producing a light beam (4),
where the light beam (4) can be focused by imaging optics (7), where the
focused light beam can be deflected onto the surface (9), and where a sensor
device (11) is provided to detect the light beam (10) reflected from the surface
(9), characterized in that a multicolor light beam (4) is produced with the light
source (3), said light beam, due to the chromatic aberration of the imaging
optics (7), being focused onto several points at different distances from the
imaging optics (7), that from the spectrum of the detected light beam (10) the
distance to the surface can be determined, and that the imaging optics (7)
comprises a GRIN (gradient index) lens (12).
2. Device as claimed in claim 1, wherein the multicolor light beam (4) produced by
the light source (3) is a polychromatic light beam, preferably white light.
3. Device as claimed in claim 1 or 2, wherein the light beam (4) is conducted from
the light source (3) by one or more light wave guides (6) to imaging optics (7).
4. Device as claimed in one of claims 1 to 3, wherein the imaging optics (7)
comprises a lens or a system of lenses.
5. Device as claimed in claim 4, wherein the GRIN lens (12) can be adapted in its
aberration by positioning device (14).
6. Device as claimed in claim 4 or 5, wherein the GRIN lens (12) is connected
after additional optics (13) with the aid of which, in measurement, a greater
distance between the GRIN lens (12) and the surface (9) to be measured can

be achieved and/or a coupling of the light beams exiting from the GRIN lens
(12) into a light wave guide is possible.
7. Device as claimed in one of claims1 to 6, wherein the focused light beam is
deflected by a deflecting device (8) to a certain point on the surface (9).
8. Device as claimed in claim 7, wherein the deflecting device (8) is structured in
such a manner that it can move.
9. Device as claimed in claim 7 or 8, wherein the deflecting device (8) can be
moved by electrical, piezoelectric, magnetic, or comparable positioning devices.
10. Device as claimed in one of claims 7 to 9, wherein the deflecting device (8)
comprises a prism, a plane-parallel plate, a mirror, or other devices affecting
the direction of propagation of the light beams.
11. Device as claimed in one of claims 1 to 10, wherein the light beam (4)
produced by light source (3) and the light beam (10) reflected from the surface
(9) are separated by an optical separating filter (4) [sic].
12. Device as claimed in one of claims 1 to 11, wherein the sensor device (11)
comprises a photodetector array, preferably a linear array.
13. Device as claimed in one of claims 1 to 12, wherein the device is constructed
as a multi-channel system, wherein several measurements can be carried out
simultaneously.

14. Device as claimed in one of claims 1 to 13, wherein the light exiting from the
imaging optics (7) can be divided onto several measurement points and the
reflections of the measurement points can be conducted via several light wave
guides (6) to the sensor device (11).
15. Device as claimed in one of claims 1 to 14, wherein the signals produced by the
sensor device (11) are conducted to an electronic device, preferably to a digital
computer in the form of a microcontroller or a digital signal processor for signal
processing.
16. Process for inspecting surfaces in the interior of holes, recesses, or the like,
preferably for operating a device as claimed in one of claims 1 to 15, wherein
the device (1) comprises a light source (3) for producing a light beam (4), where
the light beam (4) can be focused by imaging optics (7), where the focused light
beam can be deflected onto the surface (9), and where a sensor device (11) is
provided for detecting the reflected light beam (10), wherein a multicolor light
beam (4) is produced with the light source (3), said light beam, due to the
chromatic aberration of the imaging optics (7), being focused onto several
points at different distances from the imaging optics, and that from the
spectrum of the detected light beam (10) the distance to the surface can be
determined.
17. Process as claimed in claim 16, wherein the light beam (4) is guided by
deflecting device (8) in a linear, circular, spiral, meandering, or any other
suitable manner over the surface (9) and thus the surface (9) is scanned

ABSTRACT

DEVICE AND PROCESS FOR INSPECTING SURFACES
IN THE INTERIOR OF HOLES
The invention relates to a device and a method for inspecting the internal surfaces
of holes, recesses or the like. Said device (1) comprises a light source (3) for
producing a light beam (4), said light beam (4) being focusable by means of a
projection lens (7) and the focused light beam being directed onto the surface (9).
A sensor device (11) is provided for detecting the reflected light beam (10). The
aim of the invention is to provide a device which allows as rapid and easy a
measurement as possible and which can be easily miniaturized. For this purpose,
the light source (3) allows for production of a multicolor light beam (4) that is
focused onto a plurality of points that are at different distances from the projection
lens (7) due to chromatic aberrations of the projection lens (7). The distance to the
surface (9) can be determined from the spectrum of the detected light beam (10).

DEVICE AND PROCESS FOR INSPECTING SURFACES IN THE INTERIOR OF HOLES

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