Abstract:
An endoscope measures the topography of a surface. The endoscope contains a projection unit and an imaging unit. The endoscope is characterized in that an objective unit is provided as a component both of the projection unit and the imaging unit. By the integration of the projection unit and the imaging unit, which both use a common objective unit, the structural volume required by both units is reduced resulting in a smaller endoscope.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to an endoscope for measuring the topography of a surface, and a method for measuring the topography of a surface. 
     Conventional and well-researched techniques for measuring three-dimensional geometries are often based on active triangulation. However, in confined environments, such as human auditory canals or in bore holes, it becomes ever more difficult to implement triangulation as such. Particularly in the field of measuring endoscopy, it is not easy to achieve the spatial arrangement of transmitting and receiving units or to position projection and imaging units at the appropriate angles. It is also not usually possible to record relatively longer or larger hollow chambers in one image. This means that it is necessary to measure spatially overlapping regions three-dimensionally chronologically one after another in order subsequently to combine said images into a 3D representation using data processing (3D data sticking). The larger the overlapping regions are, the more precisely the linking of individual recordings in 3D space can be achieved. This presupposes that the individual recordings themselves have as many measuring points as possible in fixed relationship to one another. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an endoscope for measuring surface topographies, which occupies less space in relation to the prior art and is able, for example when using active triangulation, to record relatively large measurement regions. 
     The endoscope according to the invention for measuring the topography of a surface has a projection unit and an imaging unit. The endoscope is characterized in that an objective unit is provided which is both a component of the projection unit and also of the imaging unit. 
     By means of an integrated configuration of the projection unit and the imaging unit, which both use a common objective unit, the structural volume required by both units, the imaging units and the imaging units with the projection unit can be significantly reduced, leading thereto that the endoscope can also be designed smaller. Furthermore, given a similar structural size for measuring the topography of the surface, larger measurement regions can be recorded. 
     In a further embodiment of the invention, the projection unit comprises a projection structure and the imaging unit comprises an imaging medium. The imaging medium and the projection structure are preferably disposed centrally to an optical axis. This measure also contributes to saving structural volume. 
     In a preferred embodiment of the invention, the projection structure is configured in the form of a transparency. The projection structure, or in the special form, the transparency, has, in an external region thereof, concentric colored rings. The concentric colored rings serve for color coding and result in different colored projection rays, the reflection pattern of which allows conclusions be drawn regarding the topography and character of the surface. 
     In a further embodiment of the invention, the projection structure has a central region which is covered relative to the optical axis by the imaging medium. Usually, in this central region of the projection structure, in particular of the transparency, no concentric colored rings are provided. This zone of the projection structure which is free from colored rings can be used to accommodate the imaging medium on the same optical axis in a space-saving manner. The imaging medium and the projection structure can essentially lie in one plane, but can also be displaced parallel to one another relative to the optical axis. 
     Furthermore, in another embodiment of the invention, the projection unit has, adjacent to the objective unit, an annular mirror lens which is rotationally symmetrical relative to the optical axis. Said annular mirror lens enables projection rays to be deflected differently than the imaging rays arriving through the objective unit. It is expedient in this case for projection rays to pass through the objective unit and be deflected by the annular mirror lens. By contrast, imaging rays reflected from the surface—i.e. reflected projection rays—and impinging upon the objective unit are not deflected by the annular mirror lens. The annular mirror lens therefore allows projection rays and imaging rays to be deflected into a different ray path. 
     Further advantageous embodiments of the invention are described below based on the following figures, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  shows a schematic representation of a projection unit and an imaging unit of an endoscope with a suitable ray path, 
         FIG. 2  shows a more detailed representation of the combined projection unit and imaging unit, and 
         FIG. 3  shows an arrangement of lenses, imaging medium and projection structure in the combined imaging unit-projection unit. 
     
    
    
     DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a schematic representation of an endoscope  2  (shown here without an endoscope external wall) having a projection unit  6  and an imaging unit  8 . Schematic ray paths of projection rays  26  and imaging rays  28  are also shown. The projection unit  6  and the imaging unit  8  are integrated in such a manner that both the projection unit and the imaging unit comprise an overall objective unit  10  (see  FIG. 2 ). Furthermore, the projection unit  6  has an annular mirror lens  24  which serves to deflect projection rays  26 . 
     In  FIG. 1 , projection rays  26  are shown with a dotted and dashed line, whilst imaging rays  28  are shown with a dashed line. The dashed lines  28  and the dotted and dashed lines  26  each show the outer limit of a projection region  32  or a field of view  30 . 
     In the representation in  FIG. 1 , the optical system used results in two projection regions  32  and a field of view  30 . In order to measure the topography of the surface  4 , which is also shown schematically here as a cylindrical channel, the triangulation method is used. For this purpose, the projection rays  26 , which possibly comprise different color spectra (see below), are emitted by the projection unit  6 . Said projection rays  26  impinge upon the surface  4  and are reflected therefrom. The reflected projection rays are designated imaging rays  28 . The imaging unit accepts and guides the imaging rays to an imaging medium which also serves for evaluating the imaging rays. 
     The region which is enclosed by both the projection rays  26  or the projection region  32  and by the field of view  30  is designated the measurement region  34 . The measurement region  34  is therefore the region in which the projection region  30  and the field of view  32  intersect. Measurement by the triangulation method can only be carried out in the region in which projection rays  26  and the field of view  30  intersect. The larger the measurement region  34  is configured, the larger is the region in which a measurement can be carried out. Particularly in confined hollow spaces, it is often difficult, using known methods, to configure the field of projected rays  26  (projection region  32 ) and the field of view  30  such that an adequately large measurement region  34  is formed. 
       FIG. 2  shows a detailed representation of the projection unit  6  and the imaging unit  8  with the common objective unit  10  thereof. The endoscope  2  has an optical axis  16  which extends through the center point of the endoscope  2 . In relation to  FIG. 2 , a viewing direction of the endoscope extends from left to right. A light source (not shown), which is preferably configured in the form of a light waveguide with a collimator optical system or a fiber optic bundle or a light source, for example an LED, emits light rays through a projection structure  12  which, in this case, is configured in the form of a transparency  18 . The transparency  18  is configured annular and has concentric color rings  20  in an external region. The transparency  18 , which in  FIG. 2  is shown as a line in relation to the ray path, is shown again for the sake of clarity, next to  FIG. 2  in a plan view. 
     The light rays which extend through the outer region of the transparency  18  and thus pass through the colored concentric rings are designated projection rays. The projection rays extend through the common objective unit  10 , are deflected therein and strike an annular mirror lens  24  arranged upstream of the objective unit  10  or the projection lens system  6 . The mirror lens  24  deflects the projection rays  26  laterally with rotation symmetry from one wall  38  of the endoscope  2 , after which said rays strike the surface  4  to be investigated. The projection rays  26  are reflected from the surface  4  and, from then on, are designated imaging rays  28 . The angle that the projection rays  26  and the imaging rays  28  enclose is designated the triangulation angle  36 . 
     The imaging rays  28  are reflected back and pass, shaded by the mirror lens  24  through the objective unit  10 , the objective unit  10  being configured such that non-deflected rays impinge close to the center in relation to the optical axis  16  upon an imaging medium  14  which here takes the form of a sensor chip  15  as used in digital cameras. According to the representation in  FIG. 2 , the sensor chip  15  and the transparency  18  lie on an optical axis and in one plane. This is a special case, as illustrated in  FIG. 3 , where the camera chip is arranged at a small distance in front of the transparency. The camera chip  15  is smaller than the transparency  18  and is positioned in a central region of the transparency  18  in relation to the optical axis  16 . The central region of the transparency  18  is not filled with colored rings  20  and does not need to be penetrated by the light rays. The arrangement of the sensor chip  15  therefore does not hinder the ray path of the projection rays  28 . 
     The method of triangulation using color coding will now be briefly described. The color structure projected onto an irregular topography of the surface  4  (not shown here) appears, at an observation angle (the triangulation angle) different from the projection angle, to be distorted. The distorted pattern detected by the imaging lens system (the objective unit  10 ) is imaged on the imaging medium  12 . What is produced here is therefore a planar image of the three-dimensional surface. 
     By means of a suitable evaluation method, the topography of the surface  4  can be calculated by a computer by evaluating the color transitions and the distortion of the color lines. The configuration of the transparency with colored concentric circles is merely one of the advantageous embodiments. This embodiment suggests itself particularly in the case of a light waveguide having a circular cross-section. Other encoding patterns, such as linear patterns, can essentially also be used. 
       FIG. 3  again shows a somewhat enlarged schematic representation which illustrates the combined projection unit  6  and imaging unit  8 . From left to right, firstly the transparency  18  is to be seen, which has, in an outer region, concentric colored rings  20 ; also shown is the central region  22  which is not provided with colored rings. Arranged in front of the transparency  18  is the sensor chip  15 . Arranged in front of the sensor chip is the objective unit  10 , in front of which is arranged the annular mirror lens  24 . The endoscope per se preferably consists of a transparent glass which is suitable for allowing the projection rays  26  to emerge at the endoscope wall  38 . A transparent plastics material can also serve as a suitable endoscope material. The endoscope usually has a diameter in the range of 3 mm to 5 mm. The combined imaging and projection unit  6 ,  8  usually has a length in the range of 8 mm to 12 mm. 
     Usually, the sensor chip is illuminated at a frequency of 10 Hz to detect the imaging rays  28 . The shutter opening time is approximately 10 ms. (The shutter opening time is the time during which imaging rays  28  impinging upon the sensor chip are measured.) This means that at an illumination frequency of 10 Hz, there is a pause of 90 ms between the shutter opening times and that, during this time, the sensor chip recordings are evaluated by calculation software. 
     The above described arrangement of the measuring endoscope  2  can be applied essentially for all measurements in confined hollow spaces. A particularly advantageous application of the endoscope  2  is in the form of an otoscope, which is introduced into an ear and is used to measure the auditory canal or the ear lobe. The above described “color-coded triangulation” has the advantage, in this regard, that the projection of an encoded color pattern, together with just one image recording of the receiving unit (imaging unit  8 ) is sufficient to calculate the 3D form of an object. This means that simple projection can be used similarly to transparency projection and that sequential projection of different projection structures is not necessary. This also has the advantage that almost wobble-free freehand scanning by a physician is possible. 
     Other applications of the endoscope  2  may be found in technical fields. If, for example, for quality-control purposes, bores or other hollow spaces need to be precisely measured, the use of a space-saving endoscope  2  of this type is suitable. For example, in the case of rivet bores which serve for riveting aircraft components, very high demands are placed on the topography of said bores. With an endoscope according to the invention, highly accurate topographical measurements can be made in very confined bores.