Patent Publication Number: US-2003234923-A1

Title: Scanner for optically detecting objects

Description:
[0001] The present invention relates to a scanner defined in the preamble of claim 1.  
       [0002] Scanners of this species are used in particular to measure distances and to detect objects within a monitoring range which for instance extends in front of vehicles.  
       [0003] Scanners of this species comprise a light emitter generating a pulsed, point-like transmitted beam which is rotationally deflected by a rotating light deviating element. Said scanners furthermore comprise a receiving unit which by means of the light deviating element looks in the direction of the transmitted beam and which, when the transmitted beam is incident on an object, will image the generated light spots on a light-sensitive receiving sensor.  
       [0004] Based on the particular angle of transmission and the pulse transit times between transmitter and receiver, the scanners of the above species allow ascertaining one or more distances to objects and the contours of these objects. This design requires a correspondingly programmed analyzer which may be fitted within the scanner or into a separate vehicle computer and may be connected to several vehicle scanners.  
       [0005] One drawback of the above described species&#39; design is that objects may be measured only in one plane.  
       [0006] Accordingly it is the objective of the present invention to create a scanner which is of minimal complexity relative to the state of the art and allows three-dimensional (3D) detection of its environment.  
       [0007] This objective is attained by a scanner exhibiting the features of claim 1.  
       [0008] In the present invention, an optical device is mounted in the path of the transmitted beam and converts the transmitted beam into a cross-sectionally stripe-shaped beam. In this simple manner, when the transmitted beam is oriented so its cross-sectional stripe shall be vertical for instance, objects may be scanned in 3D.  
       [0009] In this respect the present invention provides that the optical device, which illustratively may be a cylindrical lens, shall be coupled in rotationally synchronized manner with the light deviating element that deviates the transmitted beam. Such coupling between the light deviating element and the optical device illustratively may be rigid and assures that the transmitted beam shall preserve constant orientation (relative to the axis of rotation) at the various deviation angles. A transmitted beam of which the stripe-shaped cross-section for instance runs vertically shall retain this vertical orientation while the light deviating element is revolving, and as a result the transmitted beam always is able to sense a constant range of angular height at the different angles of transmission. It is understood with respect to the desired spatial object scanning that the optical device and the light deviating element must be mutually configured in such a way that the transmitted beam&#39;s stripe-shaped cross-section shall subtend an angle relative to the plane of pivoting and shall not run parallel to this plane.  
       [0010] Moreover the invention includes a receiving unit imaging the light stripes generated when the transmitted beam is incident on objects—or, as regards objects on which only segments of the transmitted beam are incident, the corresponding light-stripe segments—onto a planar receiving sensor. This receiving sensor comprises several, separately analyzed receiving zones which, for a given angular position of the light deviating element, are each associated with defined length segments of the transmitted beam&#39;s stripe-like cross-section.  
       [0011] In the above described design of the scanner of the present invention, the image of the light stripe on the receiving sensor rotates synchronously with the light deviating element.  
       [0012] Conceivably therefore the receiving sensor might be a row of diodes, where this row rotates synchronously with the light deviating element. However such a design is comparatively complex.  
       [0013] Accordingly, in a preferred embodiment of the invention, the receiving sensor shall be mounted irrotationally within the scanner.  
       [0014] In this respect a suitable receiving sensor might be a plurality of detecting diodes of which only a small percentage shall be loaded in the different angular positions of the light deviating element. While such a design solution is theoretically conceivable, it would on the other hand entail high construction costs.  
       [0015] Therefore, in a further preferred embodiment of the present invention, the irrotational receiving sensor comprises receiving zones each associated to a defined angular range of the light deviating element.  
       [0016] In an especially preferred embodiment of the present invention, a first, inner, circular receiving zone is enclosed by at least two external, partially circular receiving zones each subtending an angle of at most 180°. Using a receiving sensor commensurately divided into three receiving zones, the stripe-shaped transmitted beam may be resolved at all deviation angles into three longitudinal zones.  
       [0017] Obviously as well the “concentric ring” enclosing the central receiving zone may comprise more than two receiving zones, for instance comprising four smaller zones each subtending an angular range of 90°. The number of selected zones depends on optimization, namely whether the interference/noise effects that increase with zone size are admissible or whether they must be dealt with by reducing the zone sizes.  
       [0018] Again, the number of the surrounding concentric annular zones consisting of at least two partial zones may easily be increased. In this manner the transmitted beam may be resolved into commensurately more longitudinal segments.  
       [0019] Obviously the present invention is not restricted to flat receiving sensors in the form of concentric rings. Other shapes, for instance polygonal zones etc. also are conceivable.  
       [0020] The receiving system of the invention allows high resolution using a very minimal number of separate receiving zones. In the simplest case, the number of receiving zones corresponds precisely to the number of length segments that resolve the transmitted beam. The scanner of the present invention therefore allows 3D object sensing at a cost of only very minimal construction. 
     
    
    
     [0021] The present invention is elucidated below in relation to drawings.  
     [0022]FIG. 1 is a schematic elevation of the significant components of the scanner of the invention, and  
     [0023]FIG. 2 is a topview of an embodiment mode of a receiving sensor used in the scanner of the invention. 
    
    
     [0024]FIG. 1 shows a scanner  10  comprising a transmitter  11  which illustratively is a laser diode. The transmitter  11  generates a pulsed transmitted beam  12 . A cylindric lens  13  is configured in the path of the transmitted beam  12  and fans out said beam  12  into a transmitted beam  120  exhibiting a stripe-shaped cross-section. The fanned-out transmitted beam  120  is incident on a rotating mirror  14  which while revolving deflects the transmitted beam  120 . The rotating mirror  14  is driven in rotation by a drive  21  about an axis  15 , the particular angular positions of the rotating mirror  14  being detected by an angle encoder  16 .  
     [0025] The deflected and fanned-out transmitted beam  120  may fall on omitted objects, in which case a stripe-like light spot is generated that will be imaged by a receiver unit  19  looking in the direction of the transmitted beam through a convex lens  18  onto an irrotational, planar, receiving sensor  22 .  
     [0026] An essential feature of the shown design is that the cylindrical lens  13  is connected in rotationally synchronized manner by a bracing means  20  to the mirror  14 . In this manner the stripe shaped transmitted beam  120  shall retain its alignment during the rotation of the mirror  14 .  
     [0027] As already mentioned above, the receiving unit  19  generates as a rule a stripe-like image  17  on the receiving sensor  22 , the image  17  rotating jointly with the rotating mirror  14 . In order that this stripe-like image  17  may be analyzed in satisfactory manner easily implemented by hardware in all different angular positions of the mirror  14 , the invention provides that the receiving sensor  22  exhibit several receiving zones each associated to length segments  120   a,    120   b,    120   c  of said stripe-like cross-section of the transmitted beam  120  and to defined angular deviation zones.  
     [0028] In this respect the receiving sensor  22  of FIG. 2 comprises an inner, central, circular receiving zone  30 , further two partly annular receiving zones  31   a  and  31   b  each subtending an angle of 180° and both jointly enclosing, in the form of a concentric ring, the inner circular segment  30 . In the shown embodiment mode, the central, circular segment  30  is configured centrally in the receiving unit  19  and the enclosing ring constituted by the two receiving zones  31   a  and  31   b  exhibits a constant radius.  
     [0029] In the shown embodiment, the middle, central receiving zone is associated with the longitudinal range  120   b  of the transmitted beam  120  across the full deviation range (360°) of the transmitted beam  120 . The receiving zones  31   a,    31   b  each are associated alternatingly to the length segments  120   a  or  120   b,  a changeover taking place every 180° with respect to the deviation of the transmitted beam  120 .  
     [0030] The shown design of the invention is an especially simple assembly which allows resolving the transmitted beams  120  observed by the receiving unit  19  into three length segments at all deviation angles.  
     [0031] A spatial object contour can be generated from the angle encoder data when using the shown scanner of the invention.