WO2008022850A1

WO2008022850A1 - Method and arrangement for the optical measurement of surface profiles of objects

Info

Publication number: WO2008022850A1
Application number: PCT/EP2007/057243
Authority: WO
Inventors: Lucius Remer; Volker Seyfried
Original assignee: Leica Microsystems Cms Gmbh
Priority date: 2006-08-25
Filing date: 2007-07-13
Publication date: 2008-02-28
Also published as: DE102006039803A1; EP2073751A1

Abstract

A method and an arrangement for the optical measurement of surface profiles of objects, particularly of teeth, rows of teeth, or tooth stumps, are characterized, with respect to achieving a high level of measurement accuracy with simple means, in that a structure is applied to the surface of the object (1), wherein the structure comprises individual measuring points distributed on the surface of the object (1), that the object (1) is illuminated by means of a light source (4) and that the detection light emitted from the applied structure is detected at various observation angles by means of a camera and the surface profile of the object (1) is calculated from the image data of the camera.

Description

Method and arrangement for optical measurement of the surface profile of objects

The invention relates to a method and an arrangement for the optical measurement of the surface profile of objects, in particular of teeth, rows of teeth or tooth stumps.

Methods and arrangements of the type in question are known for some time in different configurations and are used in particular to achieve a high accuracy of fit or marginal accuracy of dental crowns. Some of the known methods work according to the fringe projection method, wherein a fringe pattern or a grating structure is optically projected onto the surface of the three-dimensional object to be measured. From a direction of view tilted by a triangulation angle, the stripes appear bent by the topography, i. the height information is translated into the phase of the detected and deformed stripe pattern. By means of a static or dynamic algorithm of phase extraction known from interferometry, the phase map can first be determined, which is then converted into the topography by the so-called phase unwrapping. Under this condition, the pixel coordinates of a stripe image on a CCD camera chip can be converted into the corresponding object coordinates.

In the known methods, which operate according to the strip projection method, the fact that the tooth material is translucent has a disadvantageous effect. Due to the translucency, the striped pattern projected onto the surface of the tooth partially penetrates the tooth. In addition, the penetration depth may also depend on the surface condition of the tooth material. The penetration of the stripe pattern into the tooth interior falsifies the image of the surface structure of the tooth, which results in a significant deterioration of the measurement result. To circumvent this problem, it has been proposed to apply to the surface a layer of matting contrast powder or a layer of fluorescent liquid. Although these measures solve the problem that the projected fringe pattern partially penetrates into the tooth. However, the provision of an additional layer entails a drawback in that it is unavoidable that the layer has different thicknesses, even when the user has great skill. However, different layer thicknesses again lead to measurement inaccuracies during the subsequent projecting of the strip structure.

As an alternative to the fringe projection method, the use of confocal laser scanning microscopes for tooth surveying is known. The use of a confocal microscope, however, is not only extremely costly, but also has serious disadvantages in terms of the recording speed to be achieved and in terms of the complexity of the system.

The present invention is based on the object, a

Method and an arrangement for optical measurement of the surface profile of objects, in particular of teeth, rows of teeth or tooth stumps, in such a way and further develop that with simple means a high accuracy of measurement is achieved.

According to the invention the above object is achieved with regard to a method having the features of patent claim 1. Thereafter, the inventive method is characterized in that a structure is applied to the surface of the object, wherein the structure composed of individual, distributed on the surface of the object measuring points, that the object is illuminated by a light source and that emanating from the applied structure Detection light detected by a camera at different observation angles and from the camera image data, the surface profile of the object is calculated.

Furthermore, the above object with regard to an arrangement for optical measurement of the surface profile of objects by the Characteristics of claim 28 solved. Thereafter, the arrangement according to the invention is characterized by a device for applying a structure of individual, distributed on the surface of the object measuring points, a light source for illuminating the object, a camera for detecting the emanating from the applied structure detection light at different observation angles and an evaluation unit for calculation the surface profile of the object from the camera image data.

In accordance with the invention, it has been recognized that inaccuracies in measurement due to uneven layer thicknesses are unavoidable both in a matting layer for producing a substrate for a striped pattern to be projected, and in a fluorescent layer which completely covers the surface of the object to be measured. In a further inventive manner has then been recognized that for the 3D measurement of an object is not the surface of the object completely or at least partially covering layer is necessary, but rather that sufficient individual, the surface of the object representing markings. According to the invention, therefore, a structure is applied to the surface of the object, wherein the structure is composed of individual measuring points distributed on the surface of the object. In other words, by applying the structure, randomly distributed vertices are generated on the surface of the object. These interpolation points define measuring points in such a way that the light emanating from the structure when the object is illuminated is detected as detection light by means of a camera. Specifically, the detection light emanating from the applied structure is detected at different observation angles and the surface profile of the object is calculated from the camera image data.

The method and the arrangement according to the invention operate with high accuracy, since the surface of the object can be measured directly on the basis of the structure applied in physical form to the object.

Within the scope of an advantageous embodiment, the structure used is a dot structure which is produced by applying individual particles to the surface of the object. As a detection light that of the - A -

Structure reflected and / or scattered and / or polarized light can be detected. The applied particles virtually act as individual scattered light centers. In the case of the use of a luminescent structure, the fluorescence and / or phosphorescence light emanating from the structure as a result of the illumination is detected as detection light.

With regard to a problem-free distribution of the particles on the surface of the object, it is advisable to apply the particles as a solution. The particles are preferably dissolved in alcohol, since this evaporates rapidly after application. Alternatively, it is also possible to apply the particles as an emulsion or as a suspension.

A particularly pleasant application for a patient can be achieved in that the particles, for example, by a (mouth) rinse or as

Spray applied. It is also conceivable to apply the particles as

Tincture or by means of a film or a foil. Especially at the

Measurement of teeth, the particles are preferably by means of a

Chewing gums applied. In view of easy removability after completion of the measurement, the particles are advantageously applied in a washable, rinsable and / or peelable form.

With regard to the specific embodiment of the particles, it may be provided that they are nanoparticles whose size is less than or equal to 1 μm. Nanoparticles prove to be particularly advantageous insofar as their size is smaller than the optical resolution. The disadvantage, however, is that nanoparticles can penetrate cells and have a toxic effect. To avoid this problem, particles having a size in a range between 1 μm and preferably 200 μm are advantageously used. On the one hand, they are not toxic, on the other hand they provide more detection light than nanoparticles in view of their larger area, their diameter still being smaller than the optical resolution.

With regard to the specific nature of the particles can be provided that they are made of metal, which would result in a particularly good reflection of the illumination light from the particles. Alternatively, so-called "Beads" or with so-called "quantum dots" labeled particles are used. "Quantum dots" are nanoscopic structures made of semiconductor materials whose optical properties can be tailored by influencing their shape, their size or the number of their electrons.

With regard to a simple identification of the individual particles, it can be provided that multicolored particles are used.

As an alternative or in addition to particles which essentially reflect and / or scatter the illumination light, it is also possible to use active particles which emit detection light themselves as a result of irradiation. In particular, these may be fluorophore-labeled particles, fluorescent proteins, for example in the form of bacteria with GFP (Green Fluorescence Proteins) and / or autofluorescent particles, as described, for example, in US Pat. occur in food, act.

Within the scope of a particularly preferred embodiment, it is provided that the surface profile of the object is calculated using a triangulation method. It is advantageous if the camera comprises two spatially spaced-apart photosensitive sensors or detectors. Each particle on the surface of the object is placed on each of the two sensors, i. double, pictured. The distance between the two sensors can be used as base length in the calculations in the triangulation process. For example, CCD chips, EMCCDs, CMOS sensors, avalanche photodiodes (APDs), MEMS (Micro-Electro-Mechanical System) -based detectors and / or PSDs (Position Sensitive Devices) can be used as photosensitive sensors / detectors.

Instead of a camera with two separate photosensitive sensors and the use of a camera with only one sensor is possible. In this case, the detection light emanating from one point of the structure is imaged in equal parts on each half of the sensor.

Advantageously, a cross correlation between the two sensors of the camera or the two halves of the one sensor of the camera carried out. In this way, a clear identification of the imaged points on the sensors of the camera is possible. As an additional aid for unambiguous identification of the imaged points, an evaluation of the focus size of the pixels of the particles on the sensors proves to be advantageous. When using multicolored particles, moreover, the color information can be used to identify the particles.

Within the scope of a particularly preferred embodiment, a plurality of images of the object are recorded at respectively different detection angles, wherein the individual images are taken in quick succession, preferably at a video rate (for example 24 images per second). These measures allow a tracking or a

Tracking the individual points of the structure across the individual images, so that the different digital images can be correctly combined to form a three-dimensional image of the object.

In a further advantageous manner, the light source is operated pulsed for illuminating the object. This opens up the possibility of synchronizing image acquisition and detection, in which case the sensors of the camera can be operated with shuttem. In the case of the use of CCD chips as sensors, preferably, frame transfer CCDs are used.

In the event that a structure of fluorescent or phosphorescent particles is applied to the object to be measured, the luminescent light can be detected advantageously with two colors. By means of linear unmixing, an interference light suppression can be achieved in this way by separating detection light, which results from a possible autofluorescence of the object, from the actual fluorescent light of the particles.

With regard to a particularly efficient evaluation, it can be provided that an artificial blur is generated for the image recording. This blurring can be realized, for example, by imposing a vibration movement with a small amplitude on the sensors and / or an upstream imaging optics, which can be embodied, for example, as a microlens array. This approach will be particular then applied if it turns out that the images of the particles on the sensor are too small. Due to the oscillatory motion of the pixel increases and by gravity formation can be determined its exact position.

The surface structure of the object can also be determined by means of a holographic method. For this purpose, the illumination light is split by means of a beam splitter into a reference beam and into an object beam. Since the temporal and spatial stability of an interference pattern formed by the superposition of the wave fields is a decisive prerequisite for the creation of holograms, a spatial fixation of object and camera is advantageous. In that regard, this method is particularly suitable for measuring teeth outside the oral cavity.

In principle, it is possible to measure the surface profile of objects in any type of body cavity, for example in the ear. It is also conceivable to measure objects within the body using endoscopic methods. The illumination light can be fed in a conventional manner via optical fibers.

With regard to a particularly simple application of the structure to the object to be measured, the device can be designed for application as a spray nozzle. In a particularly advantageous manner, the spray nozzle is arranged on a probe, which is fed by the illumination light source.

A probe-like arrangement could be inserted into any kind of body cavity.

There are now various possibilities for designing and developing the teaching of the present invention in an advantageous manner. For this purpose, on the one hand to the independent claims 1 and 29 subordinate claims and on the other hand to refer to the following explanation of preferred embodiments of the invention with reference to the drawings. In conjunction with the explanation of the preferred embodiments of the invention with reference to the drawings, also generally preferred embodiments and developments of the teaching are explained. In the drawing show 1 is a schematic view of a first embodiment of an inventive arrangement with a camera with two photosensitive sensors,

2 is a schematic view of a second embodiment of an inventive arrangement with a camera with a single photosensitive sensor,

3 is a schematic view of an image taken with the sensor of FIG. 2 and FIG

4 shows a schematic view of a third exemplary embodiment of an arrangement according to the invention for carrying out a holographic method.

Fig. 1 shows - schematically - a first embodiment of an inventive arrangement for optical measurement of the surface profile of an object 1, wherein it is in the concrete to the measurement of a tooth 2. First, the tooth 2 has been prepared by applying a dot-shaped structure to the surface. The punctiform structure consists of individual particles 3, which adhere to the surface of the tooth 2. Against the background of the translucent

Tooth material form the particles 3 an optical contrast and act in the illumination of the tooth 2 by means of an illumination light source 4 as individual scattered light centers.

The light source 4 is preferably designed as a laser, as an LED or as a cold light source. Also, the light of a normal lamp or sunlight can be used to illuminate the object 1. Preferably, illumination in the visible wavelength range between 400 and 800 nm is used.

In the illustrated embodiment, the detection light reflected or scattered by the individual particles 3 first passes through a color filter 5 and is then imaged with lenses 6 on two executed as CCD chips 7 sensors 8 a camera, not shown. The lenses 6 and the CCDs 7 are matched to one another such that the resolution of the optics or of the CCDs 7 is sufficient for the detection of the individual particles 3. Specifically, the vote is chosen so that the detection light of each particle 3 meets a few pixels of a CCD 7.

After the image has been taken, the viewing angle is changed and the dot structure is recorded again. In other words, a video sequence is created by consecutively taking a plurality of images of the object 1 from different directions. In this way, hidden areas of the object 1 are also detected during an image acquisition from a certain observation angle. From the present images, the three-dimensional image of the tooth 2 to be measured is calculated by means of a triangulation method. For the calculations in the triangulation method, the distance of the two CCD chips 7 of the camera serves as a base length.

2 and 3 show a second embodiment of an inventive arrangement, wherein - in contrast to the arrangement of FIG. 1 - the detection light of the individual particles 3 is detected only with a CCD 7. The same reference numerals designate the same components as in FIG. 1.

As already explained in connection with FIG. 1, a plurality of exposures of the object 1 are taken from different positions, i. taken at different viewing angles. The recordings are preferably made at a video rate, i. for example, with 24 frames per second, recorded. Taking advantage of the overdetermination or redundancy of the system, the relative position of the camera can be determined either from the relative camera position or, similar to the GPS principle, directly from the 3-D position.

Position of the individual particles 3 are calculated.

In the described method, one obtains another

Information gain in that - as shown schematically in Fig. 2 - the focus size of the pixels of the individual particles 3 are evaluated on the CCD 7. The resulting from this evaluation Additional information can be used to uniquely identify the points in each shot.

Fig. 4 finally shows - also schematically - a third embodiment of an inventive arrangement, wherein the three-dimensional structure of the tooth 2 to be measured is determined there by means of a holographic method. In this case, the illumination light beam emitted by an illumination light source 4 designed as a laser 9 first passes through a lens 10 and is then split into two partial beams by means of a beam splitter 11. The one partial beam reference beam 12 is directed via a first deflecting mirror 13 directly onto a photosensitive sensor 8 of a camera. The second partial beam - object beam 14 - is directed via a second deflection mirror 15 to the object 1 to be measured and serves to illuminate the applied to the surface of the object 1 point-like structure.

As schematically indicated in FIG. 4, each particle 3 generates Fresnel zone plates on the sensor 8 designed as a CCD 7. Its phase is stored on the CCD 7 by superposition with the reference beam 12.

Finally, it should be noted that the embodiments discussed above are merely illustrative of the claimed teaching, but are not limited to the embodiments.

C o m p a n c e m e n t i o n s

1 object

2 tooth

3 particles

4 illumination light source

5 color filters

10 6 lens

7 CCD chip

8 photosensitive sensor

9 lasers

10 lens

15 11 beam splitters

12 reference beam

13 deflection mirror

14 object ray

15 deflection mirror

Claims

Patent claims

1. A method for optical measurement of the surface profile of objects, in particular of teeth, rows of teeth or tooth stumps, characterized in that a structure is applied to the surface of the object (1), wherein the structure of individual, on the surface of the object (1) composed of distributed measuring points that the object (1) is illuminated by a light source (4) and that detected by the applied structure detection light detected by a camera at different observation angles and from the camera image data, the surface profile of the object (1) is calculated.

2. The method according to claim 1, characterized in that a dot structure is used as the structure, which is produced by applying individual particles (3) on the surface of the object (1).

3. The method according to claim 1 or 2, characterized in that as detection light of the structure reflected and / or scattered and / or polarized light is detected.

4. The method according to any one of claims 1 to 3, characterized in that as a detection light due to the illumination of the structure outgoing fluorescent and / or phosphorescent light is detected.

5. The method according to any one of claims 2 to 4, characterized in that the particles (3) are applied as a solution, preferably in alcohol.

6. The method according to any one of claims 2 to 4, characterized in that the particles (3) are applied as an emulsion or as a suspension.

7. The method according to claim 5 or 6, characterized in that the particles (3) are applied by rinsing or as a spray.

8. The method according to any one of claims 2 to 4, characterized in that the particles (3) are applied as a tincture, by means of a film or a film or by means of a chewing gum.

9. The method according to any one of claims 2 to 8, characterized in that the particles (3) are applied in a washable, rinsable and / or peelable form.

10. The method according to any one of claims 2 to 9, characterized in that it is the particles (3) to nanoparticles having a size in the range less than 1 micron.

1 1. Method according to one of claims 2 to 9, characterized in that the particles (3) are particles with a

Size is in the range between a 1 micron and preferably 200 microns.

12. The method according to any one of claims 2 to 1 1, characterized in that the particles (3) are metal particles, beads and / or quantum dots.

13. The method according to any one of claims 2 to 12, characterized in that multicolor particles (3) are used.

14. The method according to any one of claims 2 to 13, characterized in that it is the particles (3) labeled with fluorophores particles, fluorescent proteins and / or autofluorescent particles.

15. Method according to claim 1, wherein the surface profile of the object is calculated using a triangulation method.

16. The method according to any one of claims 1 to 15, characterized in that a camera with at least two separate photosensitive sensors (8) is used as the camera.

17. The method according to claim 16, characterized in that for the triangulation method, the distance between the two sensors (8) is used as the base length.

18. The method according to any one of claims 1 to 15, wherein the camera comprises only one sensor (8), characterized in that the light emanating from a point of the structure detection light is imaged in equal parts on each half of the sensor (8).

19. The method according to any one of claims 1 to 18, characterized in that a cross-correlation between the two sensors (8) of the camera or between the two halves of a sensor (8) of the camera is performed.

20. The method according to any one of claims 16 to 19, characterized in that the focus size of the pixels on the sensors (8) is evaluated.

21. Method according to one of claims 1 to 20, characterized in that the individual images are recorded at temporally short intervals in succession, preferably at video rate.

22. The method according to any one of claims 1 to 21, characterized in that the light source (4) for the illumination of the object (1) is operated pulsed.

23. The method according to any one of claims 1 to 22, characterized in that the image acquisition and the detection are synchronized.

24. The method according to any one of claims 4 to 23, characterized in that the fluorescent light is detected with two colors.

25. The method according to any one of claims 1 to 24, characterized in that a Störlichtunterdrückung is performed by linear unmixing.

26. The method according to any one of claims 1 to 25, characterized in that when recording an artificial blur is generated and the centers of gravity of the pixels are calculated.

27. The method according to any one of claims 1 to 26, characterized in that the surface profile of the object (1) is determined using a holographic method.

28. The method according to any one of claims 1 to 27, characterized in that the objects (1) are measured in body cavities or endoscopically.

29. Arrangement for optical measurement of the surface profile of objects, in particular of teeth, rows of teeth or tooth stumps, characterized by a device for applying a structure of individual measuring points distributed on the surface of the object (1), a light source (4) for illuminating the object ( 1), a camera for detecting the detection light emanating from the applied structure at different observation angles, and an evaluation unit for calculating the surface profile of the object (1) from the camera image data.

30. An arrangement according to claim 29, characterized in that the means for applying the structure is designed as a spray nozzle.

31. Arrangement according to claim 30, characterized in that the spray nozzle is arranged on or in a body cavity inserted into a, from the light source (4) fed probe.

32. Arrangement according to one of claims 29 to 31, characterized in that the camera one or more CCD chips (7), EMCCDs, CMOS sensors, avalanche photodiodes (APDs), MEMS (Micro-Electro-Mechanical System) -based detectors and / or PSDs (Position Sensitive Devices).

33. Arrangement according to one of claims 29 to 32, characterized by a suitable optics for imaging the detection light on the camera.

34. Arrangement according to one of claims 29 to 33, characterized by a camera upstream microlens array.