HK1105447B - Device and method for inspecting the internal surfaces of holes - Google Patents

Description

Device and method for detecting inner surface of hole

Technical Field

The invention relates to a device for detecting the inner surface of holes, recesses etc., wherein said device comprises a light source for generating a light beam which can be focused by means of an imaging lens, said focused light beam being foldable onto said surface, and wherein a sensing means is arranged for detecting the reflected light beam.

Background

In many technical fields, an important task is the inspection of the inside surfaces of holes, recesses, etc., in particular of drilled holes or micro-cracks of size in the micrometer range. When the bore is used to receive a movable component, such as a pin, a cylinder or a small piston as in a pressure valve, a high quality and high precision tolerance bore is often required. Pressure valves are used not only in pneumatic systems but also in other fields, such as automotive fuel injection technology. At the same time, test needles are being sought that employ circuits having pneumatic cylinders of 2 mm diameter. These very small cylinders are necessary to keep pace with the ever shrinking circuit designs. For shrink connections, high precision tolerance drilling is also required, wherein the drilling cannot be damaged by burrs or blistering. In addition, for holes of sizes exceeding a millimeter, it is also important to know their surface quality accurately. Thus, for example, brake cylinders in motor vehicles must have a surface of particularly high quality, since even small flaws or burrs in the cylinder can lead to component damage after a short time.

In order to detect a surface, there are two general methods actually used at present. In a system, a glass wedge-shaped lens is used to image an optical waveguide bundle with its near 360 ° peripheral surface. The optical waveguide bundle typically includes thousands of individual fibers that together transmit an image to a camera. By means of a suitable imaging process, the structures on the surface can be identified thereby. However, their actual size, and in particular their three-dimensional extension, cannot be determined.

In another conventional technique, a monochromatic light beam is reflected onto the surface to be inspected, wherein the beam is often kept focused on said surface. If the distance between the lens and the illuminated spot varies due to the surface irregularities so that the beam is no longer in focus, an auto-focusing system then aligns the lens in such a way that the beam is refocused on the surface. By such lens correction, a distance change can be detected. In this way, a true three-dimensional measurement of the surface is possible, but only slower measurement speeds are achievable due to the necessity of tracking the focus. Thus, the inspection in the continuous production process cannot be realized.

The object of the invention is therefore to develop and generalize a device of the type mentioned in the introduction in such a way that it can detect the inner surfaces of holes, recesses etc. in a fast, easy and reproducible manner and as small as possible in the millimeter range and with the simplest structure. In addition, a corresponding method is described.

Disclosure of Invention

According to the present invention, the above object is achieved by the first aspect of the present invention. According to a first aspect of the invention, the device is developed in such a way that a polychromatic light beam can be generated by a light source, which light beam is focused on a plurality of points at different distances from the imaging optics due to chromatic aberration of the imaging optics and the distance to the surface can be determined from the spectrum of the detected light beam.

With respect to the method, the above object is achieved by a second aspect of the present invention. According to a second aspect of the invention, the process is characterized in that a polychromatic light beam is generated with a light source, the light beam is focused on multiple points at different distances from the imaging optics due to chromatic aberration of the imaging optics and the distance to the surface can be determined from the spectrum of the detected light beam.

According to an embodiment of the invention, it should first be realized that the lens refocusing may be omitted. Beyond the methods known per se, polychromatic light is deliberately used and the chromatic aberration associated therewith, which is thus present and undesirable, is used in the lens. Due to said chromatic aberration, the light beams of different wavelengths are focused at different focal points. Depending on the degree of chromatic aberration, these focal points lie within a substantially widely spread area and at different distances from the imaging lens on the optical axis of the imaging lens. Since the number of these spectral portions focused substantially at the illuminated spot on the surface is preferably reflected by the illuminated surface, conclusions about the distance between the lens and the illuminated spot can be drawn from the spectral analysis of the reflected beam according to the invention. If the whole area on the surface is scanned by reflecting the focused beam, a cross-sectional view about the surface condition can be developed in this way.

The device according to the invention and the method according to the invention can be used in a preferred manner wherever the space around the surface that has to be measured is very limited. Thus, for example, not only the bore hole but also depressions, cracks or other recesses can be measured.

According to the invention, a polychromatic light beam is generated for this purpose, which is preferably transmitted to the imaging optics via one or more light guides. This is preferably white light, since this results in a particularly simple state for evaluating the spectral portion. The imaging optics advantageously comprise a mirror or a mirror system.

With regard to the simplest possible miniaturization and the most economical imaging lens, the lens preferably comprises a GRIN (gradient index) lens. GRIN lenses are typically composed of cylindrical components that are provided by a specialized manufacturing process with a continuous change in refractive index along the axial direction. In doing so, the same effect can be obtained with a beam of light that passes through the lens as with a conventional lens. However, GRIN lenses can be further significantly miniaturized at a low production cost, particularly advantageous for the limited surrounding space.

The GRIN lens can be mounted in a particularly advantageous manner in a positioning device, a so-called spacer, with which the chromatic aberration of the lens can be matched. By means of such a spacer, it is particularly simple to fit such a lens to the configuration of the changed system.

In the measuring state, in which a large distance between the lens and the object to be measured has to be overcome, the GRIN lens can then be connected with an additional lens. For example, an imaging lens in an aspherical telescope may be used. For example, an optical waveguide can be coupled in an advantageous manner between the imaging optics in the aspherical telescope to reflect light into the beam path, whereby a larger coverage is still possible.

For a particularly simple reflectivity of the focused light beam, a reflecting device can be provided, which is preferably constructed in a movable manner. In this regard, prisms, mirrors, or plane-parallel plates may be used. Advantageously, the reflection means are adapted to enable reproducible measuring methods by means of electrical, piezoelectric, magnetic or comparison positioning means, which are preferably driven by an electronic circuit, such as a microcontroller. By suitably controlling the reflecting means, it is possible to illuminate and measure the entire surface inside the hole, or at least a part of this surface, in particular the part to be detected. In doing so, the light beam may be directed in a straight line, a loop, a spiral, a curve, or any other suitable manner.

With a particularly simple and space-saving development of the device, it is possible for the reflected light beam to take the same path as the light beam generated by the light source only in the opposite direction. At a suitable point, the reflected beam may be separated and conducted to a sensor by an optical separation filter.

The sensor preferably comprises an electronic component capable of converting polychromatic light into an appropriate electrical signal according to the spectrum of the incident light beam. A CCD wafer or other photodetector array is preferred here.

According to the invention, the device can function in a simpler manner as a multi-channel system, whereby several measurements can be carried out simultaneously. In doing so, the light present from the imaging optics can be split into individual reflections at a plurality of measurement points and corresponding measurement points and preferably transmitted through a plurality of optical waveguides. In a particularly advantageous manner, when this is done, the measuring points are configured according to the measuring situation. The conceivable arrangements here are row and loop arrangements.

With regard to the particularly versatile evaluation capability of the signals obtained by the sensors, the signals can be transmitted to an electronic device, for example comprising a microcontroller-type digital computer or a digital signal processor. In order to allow signal processing, the data obtained is prepared in a suitable manner for subsequent use, for example a visualization. It is also possible here to evaluate the measurement results and to classify the surface according to certain criteria.

There are various possibilities for developing and extending the inventive concept in an advantageous manner. For this purpose, reference is made, on the one hand, to the appended claims and, on the other hand, to the following description of a preferred embodiment of the invention, taken in conjunction with the accompanying drawings. Preferred developments and extensions of the inventive concept are also generally described in connection with the description of preferred embodiments of the invention with reference to the drawings.

Drawings

FIG. 1 is a schematic diagram of a device according to the present invention;

FIG. 2 is a schematic diagram of a GRIN lens for use in a lens system; and

FIG. 3 is a schematic diagram of a refractive device having plane-parallel plates.

Detailed Description

Fig. 1 shows a schematic design configuration of a device 1 for detecting the inner side surface 9 of a hole 2 according to the present invention. The device 1 comprises a light source 3 by means of which a polychromatic light beam 4 can be generated. This light beam 4 passes unaffected through the optical separating filter 5 and is coupled into the optical waveguide 6 to reflect the light beam 4. The light beam 4 is focused by a system of lenses 7 with its chromatic aberrations onto a succession of focal points and reflected by a reflector 8 onto the surface 9 of the hole 2. The lens system 7 and the reflector 8 are mutually coordinated in such a way that at least one focal point falls on the surface 9. In some cases it is necessary to provide a corresponding mating device (not shown) so that this requirement can be met. The optical system comprising the lens system 7 and the reflector 8 is arranged in such a way as to be rotatable and movable along the longitudinal axis of the hole 2. These movements are preferably performed by an electrical positioning device (not shown) so that the surface 9 of the hole 2 can be scanned as completely and reproducibly as possible.

The light beam is reflected on the surface 9 and conducted to the optical waveguide 6 via the reflective wedge 8 and the mirror system 7. The optical separating filter separates the light beam 4 generated by the light source 3 from the reflected light beam 10 conducted to the sensor device 11. This sensor device is coupled to an evaluation electronics system (also not shown) which calculates the distance between the device 1 and the surface 9 according to the invention from the spectrum of the reflected light beam 10 and acquires data which can be used for subsequent evaluation and/or visualization.

In fig. 2, a GRIN lens and a general lens 13 are schematically shown. The figure shows a GRIN lens 12 at about 1.0 wavelength, i.e., the lens is sized in such a way that an incident beam travels along a sinusoidal vibration period in the inner side of the GRIN lens 12. To adjust for the chromatic aberration, the GRIN lens 12 is brought to a certain positioning device 14, referred to as a spacer, in front.

The light beam emitted from the GRIN lens 12 is guided by an optical device 13, and the optical device 13 is preferably formed by an optical device for 1: 1 imaging of two aspherical lenses, which is known in aspherical telescopes. An optical waveguide (not shown) may be disposed between the 2 lenses 15 and 16 to span a greater distance. The light beam emerging from this optics is conducted to said surface 9, in which case reflecting means 8 are used.

Fig. 3 shows a reflecting device 8 developed as a plane parallel plate 17. The incident light beam 4 is refracted at one of two boundary surfaces 18 and 19, respectively, whereby a deviated parallel light beam 20 is obtained. The deviation V depends on the thickness d of the plate 17, the angle between the incident light beam 4 and the perpendicular to the plate 17 and the refractive index n. If the plane parallel plate 17 is rotated along the axis 21, then the deviating parallel beam 20 follows a circular path on the surface to be inspected. Furthermore, if the oblique angle of the plane parallel plate 17 is changed, those surfaces can be scanned in a circular loop.

Finally, it should be noted that the above embodiments merely illustrate the claimed concept and are not limited to the described embodiments.

Claims (19)

1. A device for detecting the inner surface of a hole or recess, wherein said device (1) comprises a light source (3) generating a light beam (4), wherein the light beam (4) is focused by means of imaging optics (7), the light beam focused by means of the imaging optics (7) being reflected onto the surface (9) by using reflection means (8), and a sensor (11) is provided to detect the light beam (10) reflected from the surface (9), characterized in that a polychromatic light beam (4) is generated by the light source (3), the polychromatic light beam will be focused at a plurality of points at different distances from the imaging optics (7) due to chromatic aberrations of the imaging optics (7) and the distance to the surface is determined from the spectrum of the light beam (10) detected by the sensor (11), the imaging optics (7) comprise a gradient index optic (12).

2. A device according to claim 1, characterized in that the polychromatic light beam (4) generated by the light source (3) is a polychromatic light beam.

3. The device of claim 2, wherein the polychromatic light beam is white light.

4. The device according to claim 1 or 2, characterized in that the light beam (4) emitted from the light source (3) is conducted to imaging optics (7) by one or more optical waveguides (6).

5. The apparatus according to claim 1, wherein said gradient index lens (12) is fitted with a positioning device (14) for chromatic aberration.

6. The device according to claim 1 or 5, characterized in that the gradient index optics (12) are connected after the additional optics (13), by means of which, during the measurement, a greater distance is achieved between the gradient index optics (12) and the surface (9) to be measured and/or it is possible to couple the light beam emanating from the gradient index optics (12) into the optical waveguide.

7. The device according to one of claims 1, 2 and 5, characterized in that the light beam focused by the imaging optics (7) is reflected by the reflection means (8) to a point on the surface (9).

8. Device according to claim 7, characterized in that the reflecting means (8) are constructed in a mobile manner.

9. Device according to claim 7, characterized in that said reflecting means (8) are moved by electric, piezoelectric or magnetic positioning means.

10. A device according to claim 7, characterized in that said reflecting means (8) comprise a prism, a plane-parallel plate or a mirror.

11. The device according to one of claims 1, 2, 5, 8-10, characterized in that the light beam (4) generated by the light source (3) and the light beam (10) reflected from the surface (9) are separated by an optical separating filter (4).

12. The device according to one of claims 1, 2, 5, 8-10, wherein the sensor (11) comprises a photodetector array.

13. The apparatus of claim 12, wherein the photodetector array is a linear array.

14. Device according to one of claims 1, 2, 5, 8-10, characterized in that the device constitutes a multi-channel system, whereby several measurements are performed simultaneously.

15. Device according to one of claims 1, 2, 5, 8-10, characterized in that the light emitted from the imaging optics (7) is distributed over a plurality of measuring points and the reflections of those measuring points are conducted to the sensor (11) by means of a plurality of optical waveguides (6).

16. Device according to one of claims 1, 2, 5, 8-10, characterized in that the signal generated by the sensor (11) is conducted to an electronic device.

17. The apparatus of claim 16, wherein the electronic device is a microcontroller-type digital computer or a digital signal processor for processing signals.

18. Method of detecting the inner surface of a hole or recess for controlling a device according to one of claims 1 to 17, wherein the device (1) comprises a light source (3) for generating a light beam (4), wherein the light beam (4) is focused by imaging optics (7), the light beam focused by imaging optics (7) is reflected by reflecting means (8) onto the surface (9) and a sensor (11) is provided for detecting the reflected light beam (10), characterized in that a polychromatic light beam (4) is generated by the light source (3), which due to chromatic aberrations of the imaging optics (7) will be focused at a plurality of points at different distances from the imaging optics (7) and the distance from the surface is determined from the spectrum of the light beam (10) detected by the sensor (11), the imaging optics (7) comprise a gradient index optic (12).

19. The method according to claim 18, characterized in that the light beam (4) is directed onto the surface (9) by means of a reflecting device (8) in a linear, circular, spiral or meandering manner, thereby scanning the surface (9).