WO1999039232A1

WO1999039232A1 - Device for optically scanning an object

Info

Publication number: WO1999039232A1
Application number: PCT/EP1998/007433
Authority: WO
Inventors: Hans-Günter Vosseler
Original assignee: Vosseler Zweite Patentverwertungsgesellschaft Mbh
Priority date: 1998-01-30
Filing date: 1998-11-19
Publication date: 1999-08-05
Also published as: DE19803679A1; DE19803679C2

Abstract

The invention relates to a device for optically scanning an object, preferably in the form of an endoscope, comprising an elongated housing (14), a plurality of light guides (40) which are arranged concentrically inside said housing (14) to form several light guide rings (42), an illumination device (36) which is allocated to the proximal end of the light guides, an objective device (42) which is allocated to the distal end of the light guides (40) and a detecting device (28) for optically detecting an object (12). The invention is characterised in that a selection device (50) which enables light to be radiated into specific light guides (40) is provided, and in that the detection device (28) is configured to detect the light which is reflected by the object (12). An evaluation unit (54) for determining three dimensional data relating to the object (12) based on the light which is detected can be connected.

Description

Device for optically scanning an object

The invention relates to a device for optically scanning an object with a plurality of light guides, which are arranged concentrically to form at least one light guide ring, and with an illumination device which is assigned to the proximal end of the light guide.

In the area of industrial production, the quality of the product and thus the quality check during production is becoming increasingly important. Securing, optimizing and documenting the quality of the products produced requires continuous and complete control of the manufacturing process. For this purpose, optical test methods are used, in which cameras control the manufacturing process, i.e. optically capture the products. With the help of image processing programs, the data of the captured products can be compared with stored reference data in order to identify deviations from the norm.

The disadvantage of these test methods is, in particular, that the calculated image data cannot provide information, for example, about the surface course of the detected product, since the measurements are carried out in two dimensions. This two-dimensional quality inspection therefore very often does not meet the required requirements, so that additional personnel are required to carry out visual inspections. The degree of automation and thus the cost structure deteriorate due to the necessary deployment of personnel. In addition, it is often necessary to check places on the products that are not readily accessible to personnel from outside. The use of mirrors, optical fiber-based endoscopes or similar optical instruments allows an indirect visual inspection of inaccessible places, but the optical quality of such a test object is limited, so that small damage, cracks etc. are not recognized. In particular, there is a lack of spatial information from the investigated bodies, as is the case with a direct visual inspection.

The object of the present invention is therefore to create a device which enables three-dimensional detection of objects or object spaces even at inaccessible locations.

This object is achieved in a device of the type mentioned in the introduction in that a selection device is provided which enables selective light irradiation into certain light guides and thus the projection of a pattern.

The object of the invention is completely achieved in this way.

The device according to the invention enables three-dimensional data of the object to be determined with the aid of certain known optical methods, for example the triangulation method or the phase shift method. To carry out these methods, the selection device can be used to project a selectable pattern, for example in the form of rings, lines or individual points, onto the object to be measured. The projected pattern can then preferably be optically recorded using a recording device and, for example, converted into three-dimensional data using an evaluation unit. 3

With the aid of the device according to the invention, a housing with a very small cross-sectional area can be realized, which also enables testing of difficult to access places, for example bores in housings. The three-dimensional detection of the surface of the object enables inspection with high quality. On the one hand, the surface of the object can be reproduced three-dimensionally in order to enable a visual assessment. In addition, distance measurements and dimension measurements can be carried out. Furthermore, the three-dimensional data can be compared with the reference data, so that a subjectively failed test by one person can be dispensed with.

In an advantageous development of the invention, the selection device comprises an optical diaphragm.

This mechanically working diaphragm allows selective irradiation of individual light guides with simple means. In connection with the present invention, an optical grating is also to be understood as an optical grating.

In an advantageous development of the invention, the lighting device comprises a multiplicity of power light-emitting diodes (LEDs) which can be selectively controlled by means of the selection device, one power LED being assigned to one or more light guides.

The use of power LEDs has the advantage that individual light guides can be irradiated according to the desired pattern by means of a simply constructed control electronics serving as a selection device, and the flexibility of the system is thus significantly increased.

In an advantageous development of the invention, the receiving device has a CCD sensor which is arranged at the distal end of the light guide. This has the advantage that a very small structural unit can be realized, which can be integrated into a housing, with the transmission distal resulting in low transmission losses.

According to a further embodiment of the invention, the receiving device comprises a CCD sensor at the proximal end of the light guide and at least one light channel, preferably comprising at least one light guide, which runs coaxially with the plurality of light guides.

This has the advantage that more space is available for installing the sensor, so that cheaper components can be used. In addition, the CCD sensor is housed in an area of the device that is very well protected from damage.

In an advantageous development of the invention, an objective device assigned to the distal end of the light guide and a housing which at least partially accommodates the light guides are preferably provided, the housing preferably being tubular and flexible, the light channel preferably comprising at least one light guide.

This has the advantage that due to the flexibility, i.e. Flexibility of the housing is also optically detectable in places that are very difficult to access.

In an advantageous development of the invention, the housing is tubular and rigid, a rod lens system preferably being arranged in the light channel.

This has the advantage that the housing is mechanically robust and can therefore also be used under difficult external conditions. By means of the 5

ordered rod lens system, the light reflected from the object can be transmitted to the CCD sensor with only slight losses.

In an advantageous development of the invention, the lighting device is arranged in such a way that irradiation of the light that is axially parallel with respect to the light guide is made possible.

This has the advantage that there is a lobe-shaped luminous flux distribution with the maximum in the axial direction on the output side of the respective light guide. This improves the detectability, in particular the delimitation to areas that are not irradiated, since clear light-dark contours arise.

In an advantageous further development of the invention, the objective device has an objective assigned to the plurality of light guides and an objective assigned to the receiving device.

This has the advantage that the imaging of the pattern to be projected onto the object on the one hand and the reflected pattern projected onto the CCD sensor on the other hand are improved.

In an advantageous development of the invention, the objective device has an objective assigned to a light guide.

Compared to the use of a lens for all light guides, the image quality of the pattern can be significantly increased again.

In an advantageous development, the device is designed as an endoscope. 6

This has the advantage that a very compact unit can be realized with which even hard-to-reach places can be easily reached.

Further advantages and refinements of the invention result from the description and the accompanying drawing.

It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the combination indicated in each case, but also in other combinations or on their own without departing from the scope of the present invention.

The invention is explained in more detail below on the basis of exemplary embodiments with reference to the drawing. Show:

FIG. 1 a shows a first exemplary embodiment of the invention in a schematic sectional illustration,

FIG. 1b shows a schematic sectional illustration of a second exemplary embodiment of the invention,

FIG. 1 c shows a schematic sectional illustration of a third exemplary embodiment of the invention,

2a shows a perspective view of an endoscope according to the invention with a flexible housing, the distal end not being shown, and

Figure 2b is a perspective view of an endoscope according to the invention with a rigid housing, the distal end is not shown. 7

An endoscope as a device according to the invention is explained below purely by way of example. Of course, the invention is not limited to such an endoscope, rather other configurations of the device according to the invention are also conceivable.

An endoscope 10 is shown in a schematic sectional illustration in FIG. The endoscope 10 is used for the optical three-dimensional detection of objects 12 or their surfaces.

The endoscope 10 comprises an elongated housing 14 which has a distal end 16 and a proximal end 18. The housing 14 is divided into three longitudinal sections, namely a receiving section 20a at the proximal end 18, an adjoining coupling section 20b and a transmission section 20c which ends at the distal end 16. The three longitudinal sections 20a, 20b and 20c are preferably detachably connected to one another, which is indicated schematically by means of lines 22a and 22b.

The housing 14 is tubular, with a preferably square or circular cross section. Depending on the design variant and field of application, the transmission section 20c is rigid or flexible, while the other two longitudinal sections 20a, 20b are rigid. All three longitudinal sections 20a to 20c of the housing 14 are preferably made of metal.

The transmission section 20c of the housing 14 - viewed in cross section - is divided into an inner circular receiving channel 24 and an annular projection channel 26 arranged coaxially to the receiving channel 24. While the projection channel 26 ends within the coupling section, the receiving channel 24 completely penetrates the coupling section 20b and ends in the Receiving section 20a. A receiving device 28 is optically coupled to the proximal end of the receiving channel 24, which includes in particular an optical system 30, for example in the form of a lens, and a CCD sensor 32. The CCD sensor 32 and the optics 30 are aligned with one another in such a way that the light reflected from the object 12 can be sharply imaged on the CCD sensor 32. Optics 30 are preferably arranged so as to be displaceable in the longitudinal direction for focusing.

The light rays reflected by the object 12 are transmitted from the distal end 16 of the housing 14 to the receiving device 28 by means of an ordered bundle of light guides which extend within the receiving channel 24 over its entire length. These light guides are indicated by means of lines 34 in FIG.

The pattern to be projected onto the object 12 is generated by a projection device 36 and is coupled into an ordered bundle of light guides, which are only indicated in FIG. 1 a and are identified by the reference number 40. The bundle 38 is separated into a ring and extends in the projection channel 26 to the distal end 16 of the housing 14. As can be clearly seen from the sectional view AA, the individual light guides 40 are arranged in a ring within the projection channel 26, so that a multiplicity of rings 42 train. A total of three rings 42 can be seen in the present exemplary embodiment, this being merely an example. Of course, the number of rings 42 can be significantly higher, with which the resolution can be increased. The radial distance between adjacent rings and / or adjacent light guides should preferably be selected so that the projection lines or projection points on the object can be distinguished from one another. 9

For the sake of clarity, the bundle running in the receiving channel 34 is not shown in the sectional illustration A-A. Rather, the CCD sensor 32 can be seen.

The projection device 36 can be designed as an external structural unit, the bundle 38 being led out of the housing 14, as shown in FIG. However, the projection device can also be integrated into the housing 14.

To improve the imaging quality, a lens device 42 is arranged at the distal end 16 of the housing 14. The lens device 42 comprises a lens 44 assigned to the light guides 40 and a lens 46 assigned to the light guides 34 of the receiving channel 24. The two lenses 44, 46 can be moved in the longitudinal direction for focusing. The entire lens device 42 is preferably displaceable in the longitudinal direction and can be removed if necessary, so that it can be easily replaced. A particularly good projection result can be achieved if each light guide 40 in the projection channel 26 is assigned its own objective, for example in the form of a lens. Of course, it is also conceivable to assign individual lenses to groups of light guides 40 of the bundle 38.

The projection device 36 comprises an illumination unit 48 and a selection device 50. The illumination device 48 has at least one lamp 52, which should be a large-area light source. In the present exemplary embodiment, the selection device 50 is designed as an optical diaphragm 52, which enables the light 52 to selectively irradiate individual light guides 40 of the bundle 38. Depending on the design of the diaphragm, certain patterns can be projected onto the object 12. If, for example, it is a ring diaphragm, individual rings 42 of the bundle 38 can be selected so that the projected pattern encircles one or more rings. 10

summarizes. The ring diaphragm can be set manually or automatically, for example.

The use of ring-shaped patterns is advantageous because of their symmetry. With certain surface courses to be recorded, however, better results can be achieved with other patterns, such as lines, etc.

To increase the flexibility of the endoscope, the aperture within the selection device 50 is held releasably, in such a way that it can be replaced at any time and in a simple manner by another aperture, for example a line aperture. In this context, of course, optical gratings are also to be understood as screens.

Such an optical grating is required, for example, to carry out the phase shift method, this grating being mounted so as to be displaceable transversely to the beam direction.

The pattern generated by the projection device 36 and reflected by the object 12 is detected by the CCD sensor 32 and transmitted as an electrical signal to an evaluation device 54. The evaluation device 54 evaluates the electrical signals on the basis of known optical measurement methods, for example the triangulation method or the phase shift method, and calculates distance values, for example.

To calibrate the projection device 36, the projection device 36 is brought into a defined distance from a known object onto which a known pattern is projected. The projection surface of the object has a large number of elevations, the dimensions of which are known. The data evaluated by the evaluation device 54 are then set in relation to the known dimension data of the projection surface, the result in the evaluation device 54 is stored. These values are then included in the calculation for subsequent measurements of other objects.

In the triangulation method, the distance of the surface area irradiated with a mark (for example a light point) to a reference plane is determined with the aid of certain angular functions. If this measurement is carried out for the entire surface of the object, with the distance between the endoscope and the object not changing during the measurement, a “distance value field” is created which then contains the information about the surface course of the object with respect to a reference plane.

In the phase shift method, several images of the object are taken, the optical grating being shifted by a small amount (depending on the grating constant). A distance value field can then be calculated from these various recordings with the aid of known algorithms.

The evaluation device 54 then creates a pseudo-three-dimensional image of the object 12 or the recorded object surface on the basis of the calculated distance value field, which is displayed on a screen 56.

Depending on the selected measurement method, the evaluation device 54 controls the projection device 36 in order to select the correspondingly necessary pattern in the selection device 50. In the case of the phase shift method, the evaluation device 54 ensures, for example, that the aperture 52 in the selection device 50 is shifted by a defined distance.

A precise description of the optical measurement method and the evaluation of the information recorded is contained in the patent application 197 42 264.0. The content of this earlier patent application, in particular 12

re the measurement and evaluation method described there is included as a disclosure content in the present description.

An increase in the flexibility of the system can be achieved with an illumination device 48 which comprises a multiplicity of power LEDs 56. The number of power LEDs preferably corresponds to the number of light guides 40 contained in bundle 38, in which case a power LED 56 is assigned to each light guide 40. The selection device 50 is then designed as an electronic control which controls the corresponding power LEDs 56 depending on the desired pattern. With the aid of this preferred embodiment, in addition to the ring-shaped patterns already mentioned, it is also possible, for example, to produce line-shaped patterns. The advantage of this variant is in particular that the pattern can be adapted to the surface of the object, which significantly improves the measurement quality.

FIG. 1b shows a second exemplary embodiment of an endoscope 10, parts which correspond to the first exemplary embodiment being identified by the same reference numerals. Therefore, they will not be described again.

The difference compared to the first exemplary embodiment lies in the design of the receiving channel 24. This contains no light guides for transmitting the reflected light. Instead, a rod lens unit 58 is preferably arranged in the receiving channel 24 in the region of the distal end of the housing 14. Dispensing with light guides, however, presupposes that the transmission section 20c is rigid and straight.

A further exemplary embodiment of an endoscope 10 "is shown in FIG. 1c. Here too, parts that correspond to the first exemplary embodiment are included 13

same reference numerals, so that their repeated description can be omitted.

In contrast to the first exemplary embodiment, the receiving device 28 ′ is not arranged in the area of the proximal end 18 but in the area of the distal end 16. It is therefore no longer necessary to guide the light reflected by the object 12 through the receiving channel 24. The result is an improvement in the recording quality, since transmission losses caused by reflection, for example, are avoided.

All three previously described exemplary embodiments can be operated using the same optical measurement methods.

In FIGS. 2a and 2b, two endoscopes 10, 10 'are again shown in perspective, the two endoscopes differing only in the design of the transmission section 20c. In FIG. 2a, the transmission section 20c is flexible in the form of a tube, while the transmission section 20c of the endoscope 10 'according to FIG. 2b is a rigid tube.

In both endoscopes 10, 10 ', the lens device 42 is omitted at the distal end 16, so that the ring-shaped optical waveguides 42 in the projection channel 26 and the receiving channel 24 can be seen.

The described endoscopes 10, 10 ', 10 "can be used in many technical fields, whereby they are primarily used to test surfaces that are difficult or impossible for the user to see. In particular, 10 cavities can be examined with the described endoscopes. 14

With the aid of the selection device 50, it is advantageously possible to generate optical patterns which are necessary for the optical measurement of the object 12 using known optical measurement methods.

With the help of the endoscope 10, distance measurements can be carried out, whereby the individual distance values can be calculated using the triangulation method. In addition, the phase shift method can also be used. Of course, other optical measuring methods can also be used. For example, it is conceivable to record the object from different positions by moving the endoscope and to calculate a three-dimensional image from these recordings.

Claims

claims

1. Device for optically scanning an object, with a plurality of light guides (40) which are arranged concentrically to form at least one light guide ring (42), and with an illumination device (36) which is assigned to the proximal end of the light guides (40) is characterized in that a selection device (50) is provided which enables selective light irradiation into certain light guides (40).

2. Device according to claim 1, characterized in that the selection device (50) comprises an optical diaphragm (52).

3. Apparatus according to claim 1, characterized in that the lighting device (36) comprises a plurality of selectively controllable via the selection device (50) power light-emitting diodes (56), one power light-emitting diode being assigned to one or more light guides (40) .

4. Device according to one of the preceding claims, characterized by a receiving device (28) for optically detecting the object (12), which is designed to receive the light reflected by the object (12), an evaluation unit (54) for determining three-dimensional data of the object (12) can be connected from the recorded light.

5. The device according to claim 4, characterized in that the receiving device (28) comprises a CCD sensor (32) which is arranged at the distal end (16) of the light guide (40). 16

6. The device according to claim 4, characterized in that the receiving device (28) comprises a CCD sensor (32) at the proximal end (18) of the light guide (40) and at least one light channel (24) which is coaxial with the plurality of light guides (40) runs.

7. The device according to claim 6, characterized in that the light channel (24) comprises at least one light guide (34).

8. Device according to one of the preceding claims, characterized by an elongated housing (14) at least partially accommodating the light guides (40) and a lens device (42) which is assigned to the distal end of the light guides (40).

9. The device according to claim 8, characterized in that the housing (14) is tubular and flexible in at least one longitudinal section (20c).

10. The device according to claim 8, characterized in that the housing is tubular and rigid.

11. The device according to claim 10 and 6 or 7, characterized in that the light channel (24) comprises a rod lens system (58).

12. Device according to one of the preceding claims, characterized in that the lighting device (36) comprises a lamp (52) which is arranged such that an axially parallel irradiation of the light is possible with respect to the light guide (40).

13. The apparatus according to claim 9, characterized in that the lens device (42) comprises one of the plurality of light guides (40) associated lens (44) and one of the recording device (28) associated lens (46).

14. The apparatus according to claim 13, characterized in that each light guide (40) is assigned a lens (44).

15. Device according to one of the preceding claims, characterized in that it is designed as an endoscope.