Patent Publication Number: US-2011050855-A1

Title: Optical measuring device with two camera units

Description:
RELATED ART 
     The present invention is based on an optical measuring device with an image acquisition unit, which includes at least two camera units assigned to each other on a holding structure, with spatial positioning and alignment. 
     An optical measuring device of this type may be used for various measurement tasks, e.g., for measuring the ground drive of motor vehicles, as described in DE 197 51 763 A1 and DE 197 57 760 A1, in conjunction with three-dimensional (3D) image measuring to technology. 
     3D image measuring technology typically uses image measuring units that include image acquisition units with two or more cameras. To perform a precise 3D measurement, it is necessary to ascertain how the cameras are positioned relative to each other by using a calibration procedure, and to provide this information to the measuring system with each measurement. In practical application, it is crucial to the accuracy of the 3D measurement that the position of the cameras relative to each other remain stable for the longest period of time possible, even when temperatures fluctuate and under mechanical loads. When designing image measuring units, it is entirely common to attach complete cameras to a supporting structure, e.g., a special support tube, using stable, play-free, detachable connections. Other design solutions are known (without mentioning publications as evidence), with which the main components of a camera are attached to the supporting structure without the housing that encloses the complete camera. For example, the camera chips, the electronics close to the sensor, and the associated camera lens are attached in a special mounting part. These mounting parts are then attached to the supporting structure, which is composed of several components. Structures of this type are complex in design, expensive, and not adequately stable over the long term, and they require recalibration in the field when used for a moderately long period of time. If a technical expert (e.g., customer service) is required to carry out the required calibration procedure, this often greatly reduces the acceptance of the 3D image measuring technology and results in additional operating costs. 
     The object of the present invention is to provide an optical measuring device of the type described initially that results in a robust design that is stable over the long term, that may be installed simply and precisely, and is cost-favorable. 
     DISCLOSURE OF THE INVENTION 
     Advantages of the Invention 
     This object is achieved via the features of Claim  1 . It is provided that the holding structure includes a one-piece supporting body with mounting structures molded thereon, in which the main components of a camera are accommodated. The main components of a camera—the camera chip, electronics close to the sensor, and optical attachment elements—are referred to below as the camera unit. 
     The one-piece supporting body with the mounting structures results in an unequivocal is assignment of the camera units to each other and a robust design with a high level of mechanical and thermal stability. 
     The installation and unequivocal assignment of the camera units to each other are simplified by the fact that the mounting structures all have the same design, to accommodate identical camera units. 
     In a design that is advantageous in terms of the configuration in a measuring device, the supporting body has a longitudinal profiled section that is composed of metal or plastic. 
     The design is stable due to the fact that the profiled section includes reinforcement ribs that extend longitudinally or transversely. 
     The design and installation are further simplified by the fact that a further end section is integrally formed on both sides of the longitudinal profiled section in which the mounting structure is formed. 
     Further advantageous measures, in particular for a stereo measurement, lie in the fact that the mounting structures are designed and oriented such that the optical axes of the at least two camera units accommodated therein extend toward each other in the space in front of the camera units, and they intersect at a point. 
     In a design that is advantageous in terms of manufacture and installation, the two end sections are bent inwardly toward each other relative to the straight, longitudinal profiled section, forming an obtuse angle. 
     Installation is simplified and the design is made robust by the fact that at least some of the mounting structures are designed as recesses in the supporting body, and a camera chip and optical attachment elements are placed in the particular recess. 
     The mode of operation of the measuring device with a precise design is enhanced by the fact that the mounting structures for the camera chips and the optical attachment elements are manufactured in a single machine set-up, thereby making it possible to attain a high level of precision. 
     The design is advantageous and compact also due to the fact that illumination units are also accommodated in the mounting structures, and sensor electronics are located on the supporting body on the back side of the mounting structures facing away from the camera units. 
     The particular advantages are realized, e.g., when the optical measuring device as recited in one of the preceding claims is used with a test station for performing optical measurements of the ground drives of motor vehicles. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The present invention is explained in greater detail below using exemplary embodiments, with reference to the drawings. 
         FIG. 1  is a schematic depiction of an image measuring unit of an optical measuring device, 
         FIG. 2  is a perspective view of a supporting body for camera units to be used in the image measuring unit, 
         FIG. 3  shows an end section of the supporting body in  FIG. 2  with elements of an image acquisition unit to be installed therein, in a perspective view, and 
         FIG. 4  is an enlarged, perspective view of an end section of the supporting body in  FIG. 2 . 
     
    
    
     EMBODIMENT OF THE INVENTION 
       FIG. 1  shows an image measuring unit  20 , with which two camera units  10  are located in a housing  21  in the region of optical housing openings  22 , which are accommodated on a supporting body  1  installed in the housing. An electrical circuit to module  9  for operating the two camera units  10 , and, possibly, an illumination device, e.g., with illumination units  6  as shown in  FIG. 3 , are also located in housing  21 . 
     As shown in  FIG. 2 , supporting body  1  is designed as a single piece, and is composed, in the center, of a longitudinally extending profiled section  1 . 1  that is reinforced with longitudinal ribs, and has, e.g., a U-shaped or double T-shaped cross is section. Profiled section  1 . 1 , which extends, e.g., in a straight line, includes fastening elements  14  in housing  21  or a similar supporting structure, e.g., through-holes or pegs or the like, and transitions at its ends and as a single piece into end regions that are bent inward at identical, obtuse angles, the end regions expanding to form end sections  1 . 2 . Mounting structures for the elements of camera units  10  and illumination units  6  and, possibly, further components are formed in expanded end sections  1 . 2 . The mounting structures may be located on both sides of expanded end section  1 . 2  and possibly in regions adjacent thereto, e.g., with the optical elements and their supporting elements installed on one side, and the electronic elements and their carrier installed on the other side. This results in a compact design of the components of particular camera unit  10  and its assigned electronic elements that interact in an optical, mechanical, and electronic manner that may be installed in a simple, defined manner, with exact positioning and orientation relative to each other. 
     With the exemplary embodiment shown in  FIG. 3  for the components of camera unit  10  and illumination unit  6  to be placed in expanded end section  1 . 2  of supporting body  1  on one side, and associated sensor electronics  3  on the other side, the following are placed at least partially in a recess in expanded end section  1 . 2 , in succession on a mounting surface  11  of the mounting structure: A camera chip  2  and a lens  5  to be placed in a lens holder  4  on a parallel mounting surface  11 . 1 , an illumination unit  6  with light-emitting diodes located in an annular pattern on a carrier around lens  5 , and protective glass  7 . Suitable holding elements and/or fastening elements, e.g., with fastening holes  17 , are used, if necessary. Sensor electronics  3 , which are covered with a cap  8 , are installed on the side of end section  1 . 2  facing away from camera unit  10 , opposite to camera chip  2 . As an alternative, camera chip  2  may be mounted, e.g., on a carrier of sensor electronics  3 , it may be fixed in position on the mounting structure on the same side as sensor electronics  3 , and it may be connected optically with the further elements of camera unit  10  on the opposite side through an opening. As also shown in  FIG. 4  in particular, receiving elements  12  and assembly elements  13  such as is mounting surfaces, holes, projections, and/or openings are also provided in the supporting structure. In the exemplary embodiment shown, camera chip  2  is contacted with sensor electronics  3  via openings, through which the connecting elements are guided. Further fastening elements  16  in the form of holes or pegs are also provided on expanded end section  1 . 2  for attaching cap  8 . Further fastening elements, e.g., a thread for accommodating a counter-thread, or recesses or projections for snapping counter-elements into place are provided on the circumferential edge of the recess of the supporting structure for attachment of protective glass  7  and/or any optical filters to be used. 
     Supporting body  1 , which is designed as a one-piece carrier, is composed of a profile that is torsionally stiff and rigid, that is dimensionally stable even under the influence of temperature, and that may be manufactured, advantageously, simply by shaping a crude part. Mounting surfaces  11  are provided in end sections  1 . 2  at a defined angle for camera chips  2  and lens holder  4 , which are processed mechanically in a single set-up. The positioning of camera units  10  relative to each other is therefore established mechanically, with their optical axes preferably pointing toward each other and intersecting at a point in the space in front of camera units  10  and/or measuring unit  20 . 
     In this manner, a stereo measuring bar is formed with supporting body  1  and camera units  10 . Positioning aids for ensuring that camera chips  2  are attached to supporting body  1  in a precise and simple manner, e.g., via bonding, are provided on mounting surface  11  for camera chip  2 . These positioning aids may be designed, e.g., as contact surfaces for camera chip  2 , or as positioning pins (e.g., as in the chip-manufacturing process). The holding structure with supporting body  1  is advantageously designed such that sensor electronics  3  with a small electronics printed circuit board are bonded to the back side of mounting surface  11  of camera chip  2  after installation on the particular mounting structure of end section  1 . 2 . This results in dust and moisture protection for camera chip  2  and lens  5  on the back side. After camera chip  2  and sensor electronics  3  are mounted on supporting body  1 , camera chip  2  is soldered together with sensor electronics  3 . 
     A further mounting surface  11 . 1  for lens holder  4  is provided in parallel with mounting surface  11  for camera chip  2 . The particular mounting surface and lens holder  4  include a circular collar for the simple yet precise orientation of lens  5  relative to the main point of camera chip  2 . This collar may extend around the entire circular circumference, or only along individual circular segments. Lens holder  4  is installed by screwing it onto the particular mounting surface, with the aforementioned collar ensuring that it is centered. The mounting surface may be designed as a three-point contact surface for lens holder  4  to simplify the fine-tuning of the installation. All of the processing steps that are relevant for the precise alignment of the two camera chips  2  and associated lens  5  are preferably carried out in a single set-up of supporting body  1  and/or stereo measuring bar. 
     In addition, mounting elements for illumination unit  6  with the annular LED illumination are provided in the mounting region of lens holder  4 . Illumination unit  6  is composed of several light-emitting diodes that are soldered to a printed circuit board, and it is designed such that the light-emitting diodes are located concentrically with lens  5 . An opening is provided in supporting body  1  and lens holder  4  for the installation of the connecting cable between illumination unit  6  and the printed circuit board of electrical circuit module  9 . As an alternative, fastening elements  17  for illumination units  6  may also be provided in lens holder  4 . 
     In addition, a fastening thread for an optical filter or a protective disk  7  for the simultaneous protection of lens  5  and illumination unit  6  is provided concentrically to lens holder  4 . This thread is designed such that common commercial protective glasses  7  or filters may be used for standard lenses. Dust and moisture protection for lens  5 , illumination unit  6 , and camera chip  2  is therefore provided in a simple manner. 
     Supporting body  1  includes, in its center region, a fixed bearing and a floating bearing, which are provided for installation in housing  21  of imaging measuring unit  20 . 
     Lens  5  is mounted in lens holder  4  via a centrally located thread. It is therefore provided that the lens may be adjusted in a finely-tuned manner relative to camera chip  2 , to ensure that a sharp image is obtained after lens holder  4  is installed. After the finely-tuned adjustment, lens  5  is bonded with lens holder  4 , or it is locked in position mechanically. 
     The design of housing  21  of image measuring unit  20  is kept very simple. It includes the is counter-pieces for the floating bearing and fixed bearing of supporting body  1 , a receptacle for the printed circuit board, and the plug connector of image measuring unit  20 , mountable housing parts for covering the front of image measuring unit  20 , and fastening elements for the complete image measuring unit  20 . 
     As an alternative to the basic design described above, with the direct attachment of camera chips  2  on supporting body  1  and/or stereo measuring bar, and the installation of lens  5  via lens holder  4 , it is also possible to provide a basic design that includes the direct attachment of lens  5  to the mounting structure of supporting body  1  and installation of camera chips  2  via a camera chip carrier, on which sensor electronics  3  are also mounted.