Abstract:
A stereoscopic camera for recording the surroundings is provided with a right and a left image sensor having one lens each to display the surroundings on the image sensors, with the image sensors and the lenses being held by a carrier side-by-side and at a distance in reference to each other. The stereoscopic camera is additionally provided with a circuit board arranged on the carrier and comprising at least the signal and the supply lines of both image sensors. The image sensors are each mounted on a carrier substrate, which similar to the lenses, are arranged on the carrier and are distanced in reference to the circuit board, and have a flexible electric connection to the circuit board.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of German application no. 10 2007 057 172.2 filed on Nov. 26, 2007, the entire disclosure of this application is hereby incorporated herein by reference. 
     BACKGROUND ART 
     The invention relates to a stereoscopic camera for recording the surroundings with a right and a left image sensor, with one lens each being allocated to display the surroundings on the image sensors, with the image sensors being held by a carrier side by side and at a distance in reference to each other, and with a circuit board arranged on said carrier and provided with at least the signal and the supply lines of both image sensors. 
     Such stereoscopic cameras are used for various applications, in order to control the movement of a mobile device based on the optic collection and processing of the three-dimensional surroundings. In order to realize the potential functions of the device, its positioning, and also to avoid collisions when in motion it is necessary to constantly detect objects of the surroundings and their distance from the device and to supply it for real-time processing. 
     It is known to spatially detect the surroundings based on synchronously taking images with two imaging devices that are at a lateral distance in reference to each other when facing the object so that two images of the respective objects of the surroundings from slightly deviating directions are constantly available for processing. These stereoscopic images are subjected to special image processing in order to constantly detect the surroundings in a three-dimensional fashion. 
     The design of such a stereoscopic camera regularly comprises two electronic image sensors, with a lens being allocated thereto adjusted to the respective application and also the sensor. One image sensor and one lens each form one of the above-described imaging units. The image sensors are mounted on a circuit board, on which signal lines, supply lines, and if applicable at least preliminary signal processing units are arranged. 
     The circuit board including the described accessories is mounted on a carrier. The lens is arranged above each image sensor at a distance necessary according to the optic system of the lens. It is mounted to the carrier and the circuit board such that the image sensor is entirely encased and light only impinges the image sensors via the lenses. If necessary, the lens has a separate housing therefor. 
     The carrier and also its connections to the circuit board and the lens or its housing must fulfill various mechanic, thermal, chemical, and electric requirements for the different applications, where here particularly the mechanic stability is to be ensured for the use in mobile devices. For this reason, the carriers are usually made from metal. 
     Furthermore, the thermal expansion behavior of the carrier and the circuit board mounted fixed on the carrier influences the images taken by the camera. The different expansion coefficients of the two materials connected to each other lead to a displacement of the image sensors in reference to their objects based on the heat created by the electronic components during operation. Therefore, a loss of image quality is detected, e.g., during extended operation of a stereoscopic camera. These interferences are caused, on the one hand, by a displacement of the optic axes of the two recording units in reference to each other due to the different expansion of the carrier and the circuit board. This way, the stereoscopic images no longer overlap each other entirely so that a spatial detection of the surroundings is possible to a limited extent only or not at all. On the other hand, the interferences are caused by diffused light, which impinges an image sensor through defective connections between the carrier and the lens. The connection between the carrier and the lens is usually adhesive connections, which can tear due to the thermal expansions of the carrier and the lens. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is therefore based on the object to provide a stereoscopic camera which ensures a temporarily stable optic of both imaging units per se and in reference to each other, even under thermal and mechanical stress. 
     The stereoscopic camera described in the following prevents any influence of the optic axes of the two imaging units by the circuit board or the connection of the circuit board to the carrier under mechanical or thermal stress. Both the lenses as well as the image sensors have a mechanical connection to the carrier only. 
     By uncoupling the lens from the circuit board, the position and the angle of the optic axis can be adjusted very stably in reference to each other. A drift of the optic axes of less than one pixel from the optic axis was determined, both under mechanic impact of up to the 150-fold gravitational acceleration as well as operating temperatures ranging from −20° C. to 70° C. These values could be achieved with a carrier having a lower material thickness than known carriers, so that particularly for high-valued materials cost savings could be achieved. 
     Furthermore, based on the arrangement of the image sensors on the carrier substrates and due to a flexible contacting between the circuit board and the carrier substrates the known electronic image sensors and lenses can be used. Thus, depending on the design of the lens, image sensors can be used with and without a housing, the image sensors in a housing making it possible to perform the assembly of the camera outside a clean room environment. 
     The higher mechanical and thermal resistance of the stereoscopic camera is also met when the lens is mounted on the carrier by the lens being arranged above the image sensor via a lens fastener and here creates an optically sealed hollow space around the image sensor, except for the optic path of the lens. This allows a mounting of the lens over a more extensive area, enabling the compensation of mechanical stress between the carrier and the lens fastener while maintaining a joint between the two components to be connected and using flexible joint material to create the connection. This way, any tearing of the connection can be avoided over a wide thermal and mechanical range of stress. 
     Furthermore, the production of a hollow space around the image sensor also allows the use of open parts, if the performance requirements for the image sensor demand such. Of course, inside the hollow space encased parts can be used just as well. 
     Further, it is possible by the arrangement of a hollow space around the image sensor and thus around the carrier substrate to protect the flexible electric connection between the image sensor and the circuits of the circuit boards from any damage by the flexible connection being arranged inside the hollow space. For this purpose, the lens fastener has a penetration with the conductor extending into the hollow space. In order to realize a comparable connection at this location, such a joint is also given between the lens fastener and the circuit board, as between the lens fastener and the carrier. This joint with the circuit board is closed in the same manner as the other one with the carrier. For example, silicon shows the necessary adhesive properties, as well as the required flexibility over a wide range of temperatures and the chemical resilience. 
     The use of the lens fastener also makes it possible to integrate elements in the lens holder, which allow an assembly of the lens, if applicable including an automated one, in the correct position and the correct distance from the image sensor and to permanently ensure said position. Such elements are spaces, for example, adjusting a defined distance between the lens fastener and the carrier, so that the optic system of the lens is precisely adjusted to the image sensor and with its distance being uniform over the entire sensor surface. Similarly, guidance elements are to be integrated as well, which may be provided with an equivalent in the carrier so that the lateral position of the lens in reference to the image sensor is defined. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       In the following, the invention is to be explained in greater detail using an exemplary embodiment. In the respective drawing 
         FIG. 1  shows the essential components of a stereoscopic camera in a cross section, and 
         FIG. 2  shows an imaging unit of a stereoscopic camera according to  FIG. 1  in an enlarged illustration. 
     
    
    
     DETAILED DESCRIPTION 
     The stereoscopic camera according to  FIG. 1  comprises a plate-shaped carrier  3  with a rectangular base, in the present exemplary embodiment made from stainless steel. In its longitudinal extension the carrier  3  has a pedestal  5  at the two ends located opposite each other, on which an electronic image sensor  1  is supported on a flat carrier substrate  8 , not shown in greater detail. Each pedestal  5  has a support area slightly larger than the carrier substrate  8 . 
     A lens  9  is arranged via an object fastener  11  above the image sensor  1  and at a distance therefrom. One image sensor  1  and one lens  9  each form a single imaging unit. An optic system shall be called lens  9 , comprising various optic elements, such as lenses or mirrors or the like and displaying an object on the image sensor  1 . The focus of the lens  9  can be adjusted in a fixed manner in various embodiments, known as a fix-focus system, or be adjustable in the installed condition, so that only after the installation of the lens  9  the focused display of objects of certain distances is adjusted based on the then existing distance between the lens  9  and the image sensor  1 . 
     A circuit board  13  is arranged on the carrier  3  between the two pedestals  5  and at a distance in reference thereto, provided with an electronic circuit (not shown in greater detail) with integrated circuits, active and passive switch elements, and the conductors necessary therefor as well as conductors (not shown in greater detail) for conducting signals to and from the image sensors  1  and for the power supply of the image sensors  1 . The electronic switch comprises, for example, a control of the two imaging units, among other things, to synchronously record the images, the power supply for the image sensors  1 , or a unit for a preliminary processing of the signals received by the image sensors  1 , in which the signals are processed for forwarding to a processing unit. For the signal transmission between these components of the circuit board  13  and the image sensors  1  and for the power supply of the image sensors  1  each carrier substrate  8  of an image sensor  1  is electrically connected to the circuit board  13  via flexible connectors  15 . For this application, suitable embodiments from semi-conductor technology are known for the flexible electric connections  15  of components, such as e.g., the connection via wire bridges. The image sensors  1  are in an electric contact by the carrier substrates  8  (not shown in greater detail). 
     The embodiment of an imaging unit is shown in detail in  FIG. 2 . The lens fastener  11  of the imaging unit holds, protects, and positions a lens  9 , i.e. an optic system to display the objects surrounding the mobile device, and has the shape of a cuboid. The optic system therefore comprises several different optic elements according to the requirements for the imaging; however, for better clarity here only one lens  10  is shown. Standard embodiments of lenses  9  can also be used for the stereoscopic camera described. 
     The lens fastener  11  has a recess  17  at its side facing the carrier  3 , with its base  18  being larger than the pedestal  5 , on which the image sensor  1  arranged on a carrier substrate  8  is supported. The lens fastener  11  is arranged on the carrier  3  such that the recess  17  arches over the pedestal  5  and the image sensor  1 , having a defined distance between the base  18  of the recess  17  and the image sensor  1 . The lens fastener  11  has rod-shaped support bearings  19  in the recess  17  and originating at its base  18 , serving as spacers and adjusting a distance between the lens  9  and the image sensor  1  and supporting the lens fastener  11  on the pedestal  5  next to the carrier substrate  8 . 
     According to the height of the support bearings  19  and the height of the pedestal  5 , the depth of the recess  17  is embodied such that the lens fastener  11  ends circumferential with a joint  21  above the carrier  3 , but not having any further direct mechanical contact thereto than the one via the support bearings  19 . The lens fastener  11  also has an equivalent joint  21  in reference to the circuit board  13 , extending through a flat penetration or opening  23  in the lens fastener  11  to the hollow space formed by a recess  17  around the pedestal  5 . The joint  21  of the lens fastener  11  with the carrier  3  as well as the circuit board  13  is closed circumferentially with a flexible joint material  25 , so that based on the optically dense materials of the lens fastener  11  and the joint material  25  the hollow space is embodied in an optically tight manner, with the only potential radiation entering via the lens  9  positioned above the image sensor  1 . The use of a flexible joint material  25  makes possible the compensation of thermally caused stress between the usually different materials of the carrier  3  and the lens fastener  11 . The optic density not only relates to visible light but can relate to all ranges of wavelengths that can be used for the detection of the surroundings in the respective application. 
     In the exemplary embodiment shown, the joint material  25  simultaneously fulfills the function of fastening the lens fastener  11  on the carrier  3  having adhesive properties. Alternatively particular fastening means may also be arranged at the lens fastener  11  and the carrier  3 . 
     The fixation of the precise lateral position of the lens fastener  11  in reference to the image sensor  1  and also its angular alignment is realized by providing fastening means  27  at the lens fastener  11 , each of which extend into a recess  29  in the carrier  3 . By the number, position, and design of the fastening means  27  and recesses  29  it is possible to define an unambiguous allocation of a certain lens fastener  11  in reference to an imaging unit of the stereoscopic chamber and to its exact position so that its assembly is also possible at least in a partially automated fashion. This way, fastening means  27  and recesses  29  of the right and the left imaging unit may be different. 
     One function of the fastening means  27  is the fixation of the lens fastener  11  in its position even under mechanical stress, because said position is not ensured by the adhesive connection in the above-described adhesion of lens fasteners  11  and carriers  3  by way of a flexible material. For this purpose, the height of the fastening means  27  and the depth of the recess  29  are selected of such a size that a distance remains between the two bases  31 ,  33  of the fastening means  27  and the recess  29  positioned opposite each other. Simultaneously, the cross sections of fastening means  27  and the recess  29  are of the same size everywhere, so that here too a clear space remains in reference to the lateral wall of the recess  29  circumferentially around the fastening means  27 . 
     The distance and intermediate clear space around the fastening means  27  is filled with a curable mass, which is set in the assembled state of the imaging unit shown. During the curing process, in which the fastening means  27  is enwrapped by the mass, this mass leads to tensile stress on the fastening means  27  in the recess  29  based on the shrinkage connecting with curing, due to the particular shape of the fastening means  27  described in the following and also due to the material present below the fastening means  27 . 
     In order to form an engagement area at the fastening means  27  for the forces acting during the shrinkage process and acting in the recess  29  the fastening means  27  is shaped such that its cross section, i.e. the virtual cross section positioned parallel in reference to the base  31  of the fastening means  27 , increases towards the base  31 . This shape of the fastening means  27  can be realized, e.g., by a regular conical design. However, other embodiments are also possible, e.g., an irregular or a one-sided cone as shown in  FIG. 1 , or a gradual increase based on a step, as long as the curable mass during the immersion of the fastening means  27  or during the subsequent filling of the clear space in the recess  29  entirely encloses the fastening means  27  with the mass and the tensile force on the fastening means  27  acting downward by the shrinkage of the mass has an engagement area. 
     The second of the two imaging units of the camera shown in  FIG. 1  is essentially identical as well, however shown mirror-inverted to the one shown in  FIG. 2 .