Abstract:
A scanning device for determining the shape of irregular substantially cylindrical objects. Lines of light are projected onto the surface of the object. The position of the images of the lines on the surface are measured at predetermined positions to obtain a three dimensional profile of the object. The device can be incorporated into a log cutting system and the position of the log can be adjusted based on the profile determination to obtain maximum yield from the log.

Description:
SUMMARY OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a scanning device for determining the shape of irregular cylindrical objects. More specifically, the invention relates to a laser scanning device which can determine the shape of a log in three dimensions to allow a log to be properly positioned during a sawing operation in order to maximize the yield from a log. 
     2. Description of the Related Art 
     It is well known to utilize a scanner to control the position of a log during a sawing operation. A conventional log scanning system is illustrated in FIG. 1. A row of photoemitters  2  is positioned above log L which is movably supported on a saw apparatus by headblocks  6 . A row of photoreceivers is disposed below log L in opposition to the row of photoemitters  2 . Each photoemitter is directed toward a corresponding photoreceiver. In this manner, the outline of front edge  7  of log L can be determined as log L is moved into the path of the light emitted by the photoreceivers while simultaneously monitoring the position of headblocks  6 . An outline of back edge  8  of log L can be obtained by the relative positions of each headblock  6  (see FIG.  2 ). Combining the two outlines (front edge and back edge) provides a horizontal longitudinal log profile which can be used to detect curvature of the log in the horizontal plane (see FIG.  2 ). Since this type of system does not measure curvature of log L in the vertical plane, the sawing pattern of log L must be determined on the assumption that there is not curvature in the vertical plane. This assumption is usually erroneous and thus causes error in determining optimum sawing patterns (see FIG.  3 ). 
     A primary function of a log scanner is to properly position the log with respect to a vertical sawblade so that slab can be removed on the first cut which enables the first board removed (on the second cut) to be of a minimum width and length after round edges thereof have been removed. Of course, the board must also be straight. If log position for this open face is determined by the conventional scanner discussed above, any curvature in the vertical plane will cause the resulting board to be curved. Such a board cannot be edged to the desired width unless a large amount of extra wood is removed from log L to compensate for the error. This is wasteful of time and natural resources 
     In addition, to the device disclosed above, it is well known to use a laser to scan a log in two dimensions as the log is moved through the path of the laser. Such a device is disclosed in U.S. Pat. No. 4,941,100 (issued Jul. 10, 1990) and is useful to allow control of a vertical edger which removes top and bottom portions of a log to allow a rectangular board to be cut. However, because such a device also determines contour in only two dimensions, it does not aid in determining the proper thickness of a slab in order to open the face of the log for optimum yield. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a log position control device which can accurately position the log for a sawing operation in order to maximize the yield of the log. 
     Another object of the invention is to position a log to allow a first cut of a saw operation to open a face of the log which is just high enough to allow the desired sized board to be cut during the second saw operation. 
     A still further object of the invention is to provide an apparatus which can easily determine the contour of a log in three dimensions. 
     These objects are achieved by directing beams from a series of line projecting lasers onto a log which is to be cut. A camera is positioned in opposition to the log to detect the position of the laser beam lines on the log. The position of the headblocks is also detected. A three dimensional contour of the log is determined by the position and straightness of the laser lines as a function of headblock position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a conventional log position scanning system; 
     FIG. 2 is top view of a portion of the device illustrated in FIG. 1; 
     FIG. 3 is a side view of a log having curvature in a vertical plane; 
     FIG. 4 is a top view of a log when it is placed in the preferred embodiment of the invention; 
     FIG. 5 is a side view of a log placed in the preferred embodiment of the invention; 
     FIG. 6 is a perspective view of the preferred embodiment of the invention; 
     FIG. 7 illustrates a modification of the preferred embodiment which utilizes a single laser; 
     FIG. 8 is a schematic illustration of the signal processing unit of the preferred embodiment; 
     FIG. 9 is a flowchart of the process for determining contour; and 
     FIG. 10 illustrates a cylindrical object in cross section. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 6 illustrates a preferred embodiment of the invention. Log L is movably supported in a headsaw system by headblocks  6  in a known manner. Head blocks  6  can be moved through known means such as cylinder piston arrangements, or the like. Further, position of head blocks  6  can be monitored in a known manner. At least one line projecting laser  10  is positioned above log L to project a line  12  onto a cutting area proximate sawblade  20 . The preferred embodiment uses four lasers  10  and thus four lines  12  are projected onto the log. Camera  14  is positioned to the cutting area in a field of view thereof. Camera  14  of the preferred embodiment is positioned in advance of the log and slightly above the log. However, the camera can be positioned in any appropriate position as long the cutting area is in its field of view. 
     Log L is moved forward (toward sawblade  20  along horizontal axis H) and eventually enters the cutting area. The position of headblocks  6  when light from one of lasers  6  first appears on a surface of log L indicates the outline of the front edge of the log and allows the horizonal profile of log L, in the horizontal axis H, to be calculated, in a manner similar to the conventional manner described above (see FIG.  4 ). However, the camera also detects the straightness of the laser lines reflected off of the surface of log L and thus the straightness of log L in the vertical axis V (see FIG.  5 ). Of course, the position of headblocks  6 , lasers  10  and camera  14  is known at all times. Accordingly, position adjustments can be made to headblocks  6  to position the log properly. 
     Particularly, because both the horizontal profile of the log and the vertical curvature of log L is known, the log can be positioned to allow sawblade  20  to remove a slab on the first cut so that a first board taken on the second cut will be of minimum width and length and straight after rounded edges are removed from the board. This allows the log to be cut efficiently. A sawing operation is accomplished by moving log L relative to sawblade  20  in a direction perpendicular to horizontal axis H. 
     The entire operation can be controlled by controller  100 . The camera can use known circuitry, such as a CCD device or the like, to detect the line images. Also, known processing circuitry, such as a microprocessor based device, can be used for controller  100 . 
     FIG. 8 illustrates the components which constitute a signal processing unit of the preferred embodiment. Camera  14  outputs a signal, such as a bit-mapped signal, to signal processor  101 . Signal processor  101  determines the position of a plurality of points on each of the projected lines. Signal processor  101  also receives a position signal from headblock position controller  102  and outputs a signal to headblock position controller  102  to properly position the log. Signal processor  101  and headblock position controller  102  can be part of controller  100 , e.g. a programmed subroutine, or they can be separate microprocessor based devices or the like. 
     FIG. 9 illustrates a flow chart of the logic programmed in signal processor  101 . Initially, the image signal, which represents the image of the lines on the log, is input, in a bit mapped form or the like, to signal processor  101  from camera  14  (step S 1 ). Then, signal processor  101  determines a present log position based on a signal from headblock position controller  102 . Next, the image signal is threshold processed to determine the x and y coordinates of a plurality of points on each projected line (step S 3 ). The relative z coordinate of each point can be determined by the distance between points on adjacent lines and the known camera geometry (step S 4 ). The coordinate data is then downloaded to controller  100  (step S 5 ). Controller  100  can position the log properly based on this coordinate data, size data of boards to be cut and known geometrical relationships. 
     A second preferred embodiment is illustrated in FIG.  7 . In this embodiment, a single line producing laser  10 ′ is moved across the log to produce a plurality of lines on log L. Specifically, mirror  30  pivots to reflect the line produced by laser  10 ′ to different positions on log L. These different positions are offset from one another in a direction which is perpendicular to the sawline. In this manner, a single line laser can be used to produce a plurality of lines. In the alternative, the single line laser can be directed toward the log and moved linearly in a direction perpendicular to the sawline in order to produce the plurality of lines on the log. Of course, laser  10 ′ and/or camera  14  can be modulated by controller  100 , in a known manner, in order to produce the proper lines on log L. For example, laser  10 ′ can be deenergized while mirror  30  is pivoted or while laser  10 ′ is moved or laser  10  can be color or brightness modulated. Alternatively, the signal from camera  14  can be processed to eliminate portions thereof which correspond to movement of laser  10 ′ or mirror  30 . Other portions of this embodiment are similar to the first embodiment described above and thus detailed description thereof has been omitted. 
     FIG. 10 illustrates a cross section of a scanned log. Data from one quadrant of the log, in this case quadrant IV, can be extrapolated to reconstruct the entire surface contour of the log. Further definition of the true shape of the log in three dimensions may be obtained by extending the described scanning to other quadrants of the log. This can be accomplished by adding cameras and extending the area covered by the projected lines. 
     Once the contour of the log has been determined, known geometrical relationships can be utilized to determine optimum log positioning and the headblocks can be positioned accordingly. 
     The preferred embodiments utilize line lasers. However any type device which can produce a line on the log can be used. For example, a raster scanning point laser or other light source can be used. The light can be visible or invisible as long as it can be detected by the camera. Also, any number of appropriate lines can be produced on the log. The primary aspect of the invention is that lines, which extend in a direction which is parallel to the sawline are produced on the log to allow the profile of the log to be determined in three dimensions. 
     The invention has been described through preferred embodiments. However, one skilled in the art will readily recognize that various modifications can be made without departing from the scope of the invention as defined by the appended claims. 
     The invention is applicable to determining the profile of any generally cylindrical object such as scanning the positioning logs in twin saws, quad saws, transverse saws, etc. . . The invention can also be used to scan cants or flitches in partially sawed logs before secondary processing to determine optimum positioning.