Abstract:
An elongated bar shaped housing contains an optical sensing apparatus with at least one light source to create a sensing beam and a deflecting arrangement which moves the sensing beam back and forth between the longitudinal ends of the housing. One of the walls of the housing has an output window extending in the longitudinal direction of the housing for the sensing beam and an input window parallel to the output window for the sensing beam reflected from a workpiece or its support. In the housing behind the input window there is a strip shaped light receiving arrangement with a plurality of optical sensors, as well as an evaluation unit connected to the light receiving arrangement to which the output signals of the light receiving arrangement are sent.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Applicants hereby claim foreign priority benefits under 35 U.S.C. § 119 of German Patent Application No. 10 2006 012 941.5 filed Mar. 21, 2006 and German Patent Application (not yet known) filed Aug. 10, 2006, the disclosures of which are herein incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field 
         [0003]    The invention concerns an apparatus for optically determining the surface contour of flat workpieces in a wide belt abrading machine. 
         [0004]    2. Background Art 
         [0005]    A belt abrading machine is known, from DE 32 02 104 A1, which has a presser bar extending transversely to the advancement direction of a workpiece and having a number of presser shoes arranged next to one another for pressing the abrading belt onto the upper surface of the workpiece. In it the pressing force of each presser shoe is individually controllable in dependency on the contours of the workpieces on a transport belt running under the abrading belt. For this the workpieces are sensed by means of detectors, for example non-contactingly by laser light fences. The detectors are arranged next to one another transversely to the transport direction of the workpieces, with each presser shoe of the presser bar having several detectors arranged in a row with it. 
         [0006]    The optical detectors allow a better resolution than mechanical scanner elements, are however expensive in their multiplicity, and under the operating conditions of an abrading machine are capable of being disturbed by the yielded abrasion dust. 
       SUMMARY OF THE INVENTION 
       [0007]    The invention has as its basic object the provision of an apparatus of the previously mentioned kind whereby with higher spatial resolution less expense is necessary and the apparatus is less capable of being disturbed. 
         [0008]    This object is solved in accordance with the invention by an elongated bar shaped housing containing an optical sensing apparatus with at least one light source to create a sensing beam and a deflecting arrangement which moves the sensing beam back and forth between the longitudinal ends of the housing, and in that one of the walls of the housing has an output window extending in the longitudinal direction of the housing for the sensing beam and an input window parallel to the output window for the sensing beam reflected from a workpiece or its support, with there being in the housing behind the input window a strip shaped light receiving arrangement with a plurality of optical sensors, as well as an evaluation unit connected to the light receiving arrangement to which the output signals of the light receiving arrangement are sent. 
         [0009]    In the solution of the invention the sensitive optical elements are given protection in the housing and thereby are protected against the environmental influences inside the abrading machine, especially against the penetration and depositing of abrasion dust. Dust cannot stick as easily to the flat windows of the housing. Moreover it is easier to clean said windows. At the same time by means of the roaming sensing beam the entire working width of the abrading machine can be continuously sensed, so that a high spatial resolution is possible, which is essentially limited only by the arrangement of the optical sensors. 
         [0010]    In practice the precision of the sensing can be disturbed by the widening of the sensing beam on its way from the deflecting device to the workpiece, by the diffusion of the light of the sensing beam and by the light reflection. 
         [0011]    These problems in a first embodiment can be solved in that the deflecting device includes a position sensor whose output signal contains information for determining the deflection direction of the sensing beam. If the deflecting device is made for example with a rotatable mirror, this mirror or its drive can be coupled to an angular position detector. 
         [0012]    According to a second embodiment the sensing beam has associated with it a reference beam which reference beam inside of the housing is directed onto a second strip shaped light receiver arrangement with a plurality of optical sensors and along which second strip the reference beam is deflected in synchronism with the sensing beam, with the output signals of both light receiving arrangements being transmitted to a common evaluation unit. The evaluation now proceeds in such way that the signal of the first light receiving arrangement, which is hit by the sensing beam, is only evaluated in regard to its relation to whether a workpiece is present at all. The second light receiving arrangement, which is hit by the reference beam deflected in synchronism with the sensing beam delivers the location information, that is where the workpiece has been sensed on its support surface. Since the reference beam extends only inside of the bar shaped housing and preferable from the deflecting device is directed immediately onto the second light receiving arrangement, this reference beam is not influenced by diffusion and other disturbances, so that its striking spot on the second light receiving arrangement can be essentially more precisely localized than it may be the case with the sensing beam on the first light receiving arrangement. By combining the two signals in the common evaluation unit a precise localizing of a workpiece on the supporting surface can result without being influenced at all by external disturbances. 
         [0013]    The sensing beam and the reference beam can be derived from a common light source. It is however, simpler and more disturbance free to create each of the sensing beam and reference beam from its own light source. 
         [0014]    To deflect the sensing beam and reference beam in synchronism with one another it is advantageous if the sensing beam and reference beam are deflected by the same deflecting device, for example by a rotatable mirror associated with both beams. 
         [0015]    Preferably arranged between the rotatable mirror and the output window is at least one stationary mirror which is so positioned that the deflected sensing beam escapes from the output window of the housing at a pregiven angle. This way one obtains larger freedom for the arrangement of the light sources and the deflecting device inside of the housing. The stationary mirror or one of the stationary mirrors is preferably adjustable so as to be able to adjust the output direction of the sensing beam from the output window. 
         [0016]    The light receiving arrangements are advantageously each made from a row of photoelectric elements which makes possible a very high spatial resolution. 
         [0017]    The invention concerns further an abrading machine, especially a wide belt abrading machine, with a workpiece support surface on which flat workpieces are transported in a transport direction through the abrading machine, with a circulating abrading belt running parallel to the transport direction and with a presser bar extending across the width of the abrading belt and having a number of presser elements independently controllable from one another by a control unit. Such wide belt abrading machines are known as such and need not be described in more detail. In accordance with the invention the abrading machine includes a previously described apparatus for optically determining the surface contour of flat workpieces, with the bar shaped housing upstream of the abrading belt extending transversely to the transport direction across the workpiece support surface with the output window and the input window turned toward the workpiece support surface, and with the evaluation unit being connected to the control unit so that the determined surface contour can be used in control signals for controlling the presser elements of the presser bar. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The following description in combination with the accompanying figures explains the invention by way of exemplary embodiments. The figures are: 
           [0019]    FIG.  1 —is a schematic illustration of a wide belt abrading machine with an apparatus for optically determining the surface contour of flat workpieces, 
           [0020]    FIG.  2 —is a schematic cross-section through the determining apparatus according to a first embodiment of the invention, 
           [0021]    FIG.  3 —is a schematic cross-section through the determining apparatus according to a second embodiment of the invention, and 
           [0022]    FIG.  4 —is a cross-section through the determining apparatus, and corresponding to that of  FIG. 3 , according to a third embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    The wide belt abrading machine of  FIG. 1  includes a transport belt  10  forming the workpiece support surface on which a workpiece  12  can be transported in the direction of the arrow A. Above the transport belt  10  is arranged an abrading device  14  with an abrasive belt  16 , which belt is guided over a drive roll  18 , a turning roll  20  and a tensioning roll  21 , and which belt in the viewing direction of  FIG. 1  extends transversely over the width of the transport belt  10 . The abrading device  14  also includes a presser bar  22 , which in known way consists of a number of pressure elements or presser shoes which transversely of the transport direction A are arranged next to one another and by way of a control unit  24  are individually and independently of one another controllable to press the abrading belt  16  onto the surface of the workpiece  12  in accordance with its contour. 
         [0024]    To determine the contour of the workpiece and its position on the transport belt  10 , a scanner bar  26  is arranged upstream of the abrading device  14 , which scanner bar likewise extends transversely over the width of the transport belt  10 , and whose construction and function will now be explained in more detail by way of  FIG. 2 . 
         [0025]      FIG. 2  shows the scanner bar  26  in a section perpendicular to the transport belt  10  and parallel to the transport direction A. The scanner bar  26  has a nearly cuboidal housing  28  with a bottom plate  30  and a cover bonnet  32 . Near the top surface of the bonnet  32 , inside of the housing  28  and at its middle in the longitudinal direction, is the light source  34  formed by a laser. The light source  34  is associated with a rotatable mirror  36  driven by a drive  38 , so that the sensing beam  40  emitted from the light source  34 , at a frequency dependent on the number of facets of the rotatable mirror  36  and the rotational speed of the drive  38 , is deflected along the length of the housing  28 . Associated with the rotatable mirror  36  are two stationary mirrors  42  and  44  which are parallel to one another and which extend over the length of the housing  28 . The mirrors  42  and  44  are faced toward one another and have such a spacing from one another that the sensing beam  40  falling on the rotatable mirror  36  is reflected in several steps back and forth, as indicated in  FIG. 2  by the zigzag beam path. Near the bottom plate  30  is arranged an adjustable mirror  46  which likewise extends over the entire length of the housing  28  and can be inclined about an axis  48 . It deflects the sensing beam  40  through an output window  50  in the bottom plate  30 . The output window is formed by a slot  52  extending over the length of the bottom plate and covered by a transparent plate  54  screw fastened to the bottom plate. 
         [0026]    Near the other longitudinal edge of the bottom plate  30  is an input window  56  for the reflected sensing beam, which window  56  in the same way as the output window  50  is formed by an elongated slot  58  in the bottom plate covered by a transparent plate  60  fastened by screws to the bottom plate. Behind the input opening is a photodiode panel  62  forming the light receiving arrangement. 
         [0027]    The sensing beam  40 , with the help of the adjustable mirror  46 , is so deflected through the output window  50  that it upon striking a workpiece  12  moves through the input window  56  and hits the photodiodes  64  of the photodiode panel  62 , insofar as the thickness of the workpiece  12 , by a certain tolerance, is not above or below a pregiven value. If on the other hand the sensing beam strikes the transport belt  10 , that is the workpiece support surface, the beam reflected from it will not reach the slot  58  and therefore will also not reach the photodiode panel  62 , as is indicated by the broken lines. Therefore, the surface contour of the workpiece  12  and its position on the transport belt can be determined. The photodiode row  62  is connected through an evaluation circuit  66  with the control unit  24 , which then based on the signals delivered by the photodiode row  62  or the evaluation circuit  66  determines which segments of the presser bar  22  have to be controlled to press the abrasive belt in the desired way onto the upper surface of the workpiece  12 . For this the signals received by the control unit from the evaluation circuit  66  are amplified in the control unit in order to obtain the control signals for controlling the segments of the presser bar. 
         [0028]    A scanner bar  26  of the previously described type can also be arranged in the transport direction of the workpiece behind the abrading device  14 . Then the signals obtained from the evaluation circuit before their amplification can be evaluated as to their intensity. This provides information about the reflection properties of the workpiece top surface and allows, by comparison with reference values, statements to be made about the quality of the workpiece top surface or the wear of the abrading means. 
         [0029]      FIG. 3  shows a modified embodiment of the invention wherein parts corresponding to similar parts of the embodiment shown in  FIG. 2  have been given the same reference numbers. 
         [0030]    The sensing beam  40  experiences in its path from the rotatable mirror  36  and via the mirrors  42 ,  44  and  46  a certain widening. Further the light of the sensing beam at the workpiece is dispersed and by light reflection is “contaminated”. This results in the light spot, which the light reflected from the workpiece creates on the photodiode row  62 , being relatively wide, so that the location information is not so precise as it actually could be considering the construction of the photodiode row. This problem is solved by the embodiment according to  FIG. 3  in that the rotatable mirror  36  or its drive  38  is coupled to an angular position sensor  65  whose output signal is transmitted to the evaluation circuit  66  to deliver information as to the direction of the sensing beam  40 . 
         [0031]    In the modified embodiment according to  FIG. 4 , instead of the angular position sensor, in addition to the light source  34  which produces the sensing beam is a further light source  68  which produces a reference beam  70 , which in the illustrated embodiment is directed parallel to the sensing beam created by the light source  34  and which is deflected by the rotatable mirror  36  synchronously with the sensing beam  40 . The reference beam  70  falls directly onto a second light receiving arrangement, which likewise is formed by a photodiode panel  72 . Since the reference beam  70  is subject to no disturbing influences, and from the rotatable mirror  36  falls onto the photodiode panel  72  without detour, it is still sharply bundled so that its strike location on the photodiode panel  72  can be precisely determined. Since the reference beam  70  is deflected in synchronism with the sensing beam  40 , one from the reference beam can precisely determine the place where the sensing beam  40  would have to hit the photodiode panel  62  if it were in sharply bundled condition and without external disturbances to reach the photodiode panel  62 . In the evaluation circuit the signals of both photodiode rows  62  and  72  are evaluated. The signal of the photodiode panel  62  is evaluated only with regard to whether the sensing beam has struck a workpiece or not. The place where the workpiece has been struck by the sensing beam, that is where the workpiece is located on the transport belt  10 , on the other hand is determined from the signals from the photodiode row  72  which is hit by the reference beam  70 . Therefore, the contour and the position of the workpiece  12  on the transport belt  10  can be determined with high spatial resolution and exactness entirely uninfluenced by external disturbances. 
         [0032]    It is further to be added that in the embodiments according to  FIGS. 3 and 4  the bottom plate  30  with individual windows has been replaced by a transparent bottom plate  30 . Also, onto the underside of the scanner bar  26  is fastened by screws a ram protection plate  74 , which serves to protect the scanner bar from blows from workpieces running from the right in  FIG. 3  and which defines a limiting thickness of the workpiece. Further, this ram protector also serves to screen off reflections from the transport belt. 
         [0033]    While the present invention has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this invention may be made without departing from the spirit and scope of the present invention.