Abstract:
A lumber check grader-actuatable interface enables a check grader to interact with grade-quality measured boards of lumber conveyed along a flow path and passing in front of the check grader. The interface accurately and continuously tracks the location of each board in front of a check grader and tracks the location of the check grader&#39;s hands relative to the boards. Gestures can, therefore, be used for a selected board to perform additional actions, such as changing the grade or changing the trims. The interface enables a check grader to walk alongside and keep pace with a board of interest as it is transported and to provide feedback to the interface about a needed change for the board of interest. By knowing which board is of interest to a check grader, the interface can display additional information for only that board without overwhelming the check grader with non-stop information overload.

Description:
COPYRIGHT NOTICE 
       [0001]    © 2015 Lucidyne Technologies, Inc. A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. 37 CFR §1.71(d). 
       TECHNICAL FIELD 
       [0002]    This disclosure relates to grading board lumber quality and, in particular, to a lumber check grader-actuatable interface that enables a check grader to interact with grade-quality measured boards of lumber conveyed along a flow path and passing in front of the check grader. 
       BACKGROUND INFORMATION 
       [0003]    Lumber is graded by application of regional grading standards, for example, the American Lumber Standards, which are based on one or more of the structural integrity, shape, dimensions, and appearance of a board. These grades take into account the sizes and locations of defects, together with the slopes of grains, shape, and dimensions to predict one or more of the load-bearing capacities and acceptable appearance of the boards. (These attributes of the boards, together with grade and trim symbols, are hereafter referred to collectively as “board attribute information.”) For several decades, board lumber scanning systems have projected onto boards and displayed on monitors board attribute information solutions including board feature and quality information. With the advent of low-cost projectors, large format televisions, and augmented reality devices, however, the possibilities for what data can be presented to check graders have increased. There is still, however, a limit to the amount of board attribute information a check grader can absorb in the short amount of time available to check a board transported on a conveyor. 
         [0004]    It is not unusual for a check grader to roam several steps in either direction along a board conveyor to interact with a particular board of interest, but existing systems have no real time feedback capability indicating that the check grader is interacting with a specific board. Typically, the check grader can observe the solution computed by a board scanning system and then choose to override that solution by writing a mark on the board indicating that it is to be processed at a later time. The amount of board attribute information available to the check grader is, however, limited by time and space. 
         [0005]    Existing systems can visually project the solution onto the boards for the check grader to see and effect a grade/trim override if necessary. If, in these existing systems, the check grader changes the position of a board transported by a moving conveyor, the solution overlay is projected in the wrong location, i.e., to a place where the board was, not to the place where the board has been moved. 
       SUMMARY OF THE DISCLOSURE 
       [0006]    The disclosed check grader-actuatable interface overcomes the solution overlay displacement problem by accurately and continuously tracking the location of each board in front of a check grader and tracking the location of the check grader&#39;s hands relative to the boards. As such, gestures can be used for a selected board to perform additional actions, including but not limited to, changing the grade or changing the trims and to request additional board attribute information be projected onto the board, displayed on a nearby monitor, or rendered in an augmented reality device (such as Google Glass or Microsoft HoloLens) worn by the operator. 
         [0007]    The check grader-actuatable interface functions among a check grader, the board lumber the check grader is inspecting, and the automated board grading machine the check grader is supplementing. By measuring where the boards are located and the location of the check grader, the interface creates an association between them that allows the check grader to interact with the board and the solution in a way never before possible. 
         [0008]    For example, when the check grader touches a board of particular interest, more detailed information can be rendered (by one or more of a projector, television, augmented reality device) for the check grader to learn more about that particular board. With this additional information, the check grader can then make a more informed decision about whether to change one or both of the grade and trims. Although some existing systems use voice recognition to allow the check grader to change the grade/trim, the check grader is constrained to a specific location where boards are presented in a controlled manner, one at a time to the check grader. The disclosed interface enables the operator to walk alongside and keep pace with a board of interest as it is transported and to provide feedback to the interface about a needed change for the board of interest. By knowing which board is of interest to a check grader, the interface can display additional information for only that board without overwhelming the check grader with non-stop information overload. 
         [0009]    Additional aspects and advantages will be apparent from the following detailed description of preferred embodiments, which proceeds with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIGS. 1A and 1B  show from two different vantage points pictorial isometric views of a check grader-actuatable interface operating in a preferred embodiment in accordance with the present disclosure. 
           [0011]      FIGS. 2A and 2B  are diagrams showing in, respectively, the direction of a board flow path and the viewing direction of a check grader, the overlap of a field of view of an image projector and a field of view of a 3D depth camera shown in  FIGS. 1A and 1B . 
           [0012]      FIG. 3  is an enlarged fragmentary pictorial isometric view of enclosures for the image projector and 3D depth camera and of the field of view of the image projector shown in  FIG. 1A . 
           [0013]      FIG. 4  is a block diagram of major sources of data and a personal computer contained in the image projector enclosure of the check grader-actuatable interface of  FIGS. 1A and 1B . 
           [0014]      FIGS. 5-1, 5-2, 5-3, and 5-4  are images developed by sequential processing of a depth image signal output of the 3D depth camera shown in  FIGS. 1A and 1B . 
           [0015]      FIG. 6A  is a diagram showing a top plan view of a group of twelve grade-quality measured boards transported along a board flow path.  FIG. 6B  is an enlarged fragmentary pictorial isometric view of five boards enclosed by a circle A drawn on  FIG. 6A  to identify a region within the field of view of the image projector and proximal to a check grader workspace. 
           [0016]      FIGS. 7A and 7B  are reproductions of  FIGS. 6A and 6B , respectively, with exception that  FIGS. 7A and 7B  show one of the five boards displaced from its original spatial alignment relative to adjacent boards. 
           [0017]      FIGS. 8A, 8B, 8C, and 8D  are, respectively, top plan, side elevation, end (upstream-directed), and pictorial isometric views of an embodiment of the disclosed check grader-actuatable interface constructed with two check grader workspaces. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0018]      FIGS. 1A and 1B  show from two different vantage points a check grader-actuatable interface  10  operating in a preferred embodiment in accordance with the present disclosure. With reference to  FIGS. 1A and 1B , a check grader  12  inspects each one of eight grade-quality measured, generally parallel aligned boards  14   1 ,  14   2 ,  14   3 ,  14   4 ,  14   5 ,  14   6 ,  14   7 , and  14   8  (collectively, “boards  14 ”) transported along a board flow path  16  defined by a conveyor  18  formed of spaced-apart lug chains  20   1 ,  20   2 ,  20   3 ,  20   4 , and  20   5  (collectively, “lug chains  20 ”). Check grader  12  can be a human grader, quality control inspector, machine operator observing equipment operation, operation supervisor, or any other individual interested in system operation. Boards  14  are set in a generally perpendicular orientation relative to the lengths of lug chains  20  as they move boards  14  along board flow path  16 . There are no lane dividers separating, or upwardly projecting lugs maintaining a uniform parallel alignment of, adjacent boards  16  transported by conveyor  18 . 
         [0019]    An upright mounting member  30  supports at its top an L-shaped mounting arm  32  having a longer arm portion  34  extending along the lengths of lug chains  20  and a shorter arm portion  36  forming a right angle relative to arm portion  34  and extending in plane parallel relationship over boards  14  transported by conveyor  18 . The free end of shorter arm portion  36  terminates in a mounting plate  38 , to which is secured an enclosure  40  of an overhead image projector  42  ( FIG. 2A ). Enclosure  40  also houses a personal computer on which operate the image processing algorithms described below. An enclosure  44  of a three-dimensional depth camera (“3D depth camera”)  46  ( FIG. 2A ) providing a depth image signal output to a board location tracking module  48  ( FIG. 4 ) operating on the personal computer is affixed to enclosure  40  of image projector  42 . Image projector  42  has a field of view  50 , which, as shown in  FIGS. 1A and 1B , covers about 7 ft. (2.13 m) down the length of boards  14   2 ,  14   3 ,  14   4 ,  14   5 ,  14   6 , and  14   7  to project onto their surfaces images of one or more items of board attribute information, including grade symbols and trim symbols. The 3D depth camera  46  has a field of view  52 .  FIGS. 2A and 2B  are diagrams showing, respectively, in the direction of board flow path  16  and in the viewing direction of check grader  12 , the overlap of field of view  50  of image projector  42  and field of view  52  of 3D depth camera  46 . With reference to  FIGS. 2A and 2B , field of view  52  need not be the same size as that of field of view  50 , but for practical reasons it is advantageous to have field of view  52  overlap field of view  50  as much as possible.  FIG. 2A  shows that field of view  52  spans farther in the direction transverse to board flow path  16  than does field of view  50 .  FIG. 2B  shows that fields of view  50  and  52  span about the same distance in the direction of board flow path  16 .  FIG. 3  is an enlarged fragmentary view of enclosures  40  and  44  and field of view  50 . The portion of conveyor  18  within field of view  50  is called a grading table. 
         [0020]    Upright mounting member  30  supports along its length a mounting arm  60  from which suspends a board recognition system  62  positioned adjacent the upstream side of field of view  50 . A preferred board recognition system  62  is a True-Q® board tracking system manufactured by Lucidyne Technologies, Inc., which is the assignee of this patent application. The True-Q® system is disclosed in U.S. Pat. Nos. 7,426,422 and 7,200,458 and, as described below, implements a board recognition method that uses a previously acquired fiberprint of each board to confirm its identification upon reaching lug chains  20 . 
         [0021]    A closed loop air conditioner  64  mounted to upright mounting member  30  propels cold air flow at 4000-5000 BTU/hr through an insulated inlet duct  66  and an insulated outlet duct  68  connected to enclosure  40  to maintain an acceptable temperature environment for the electrical and electronic equipment operating inside of it. ( FIGS. 2A and 2B  show a version of air conditioner  64  that is mounted directly onto enclosure  40 , thereby eliminating the ductwork shown in  FIGS. 1A and 1B .) 
         [0022]    Check grader  12  stands in a check grader work space  72  to visually inspect boards  14  as they are transported downstream from board recognition system  62  and pass through field of view  50 . Check grader work space  72  is defined as an area located generally outside of field of view  50  and adjacent lug chain  20   1  of the grading table. Check grader  12  standing in work space  72  performs one or both of two tasks. The first task is reading the board attribute information or symbols projected onto boards  14  on the grading table, and the second task is reaching into field of view  50  and manipulating or marking boards  14  on the grading table.  FIGS. 1A and 1B  show boards  14   2 ,  14   3 ,  14   4 ,  14   5 ,  14   6 , and  14   7  lying on, board  14   8  positioned upstream of, and board  14   1  positioned downstream of, the grading table. 
         [0023]      FIG. 4  is a block diagram of the major sources of data and the information processing modules of check grader-actuatable interface  10 . With reference to  FIGS. 1A, 1B, and 4 , before reaching board recognition system  62 , boards  14  are scanned and assigned sequential board numbers that are used for all internal tracking and processing. A preferred board scanning system  80  ( FIG. 4 ) performing these operations is a GradeScan® automated lumber scanner, which is manufactured by Lucidyne Technologies, Inc. Board scanning system  80  uses sensor technologies to detect defects in and other attributes of boards  14 . Board scanning system  80  captures images on all four sides of each one of boards  14  and associates the four images of the board with its sequential board number. These image data, board attribute information including defect information, and the associated board number are stored in memory. The GradeScan® board scanning system  80  places no tracking symbols (e.g., ink, labels, and spray) on boards  14 . 
         [0024]    Boards  14  leaving board scanning system  80  are transported by an endless conveyor (not shown) to lug chains  20 . Boards  14  transported between board scanning system  80  and lug chains  20  might become out of sequential order, or one of boards  14  might break and fail to reach lug chains  20 . Board recognition system  62 , which is positioned upstream of field of view  50 , detects such re-ordering or absence of one of boards  14 . Board recognition system  62  has a photoeye and an area camera, the photoeye detecting each one of incoming boards  14  and providing a trigger signal to which the area camera responds by capturing a single image of each one of boards  14  as they reach lug chains  20 . Board recognition system  62  compares the single image with the images of the primary faces of the board captured by and stored in board scanning system  80  to confirm the identity of the board before it enters field of view  50 . If the single image does not match the expected board, board recognition system  62  looks upstream and downstream at images of several boards  14  previously measured by board scanning system  80  in an attempt to find a match. Board recognition system  62  more heavily favors the closest boards  14 . 
         [0025]    Boards  14  leaving board recognition system  62  are transported into field of view  52  of 3D depth camera  46 . A preferred three-dimensional depth camera is a Kinect2 sensor, manufactured by Microsoft® Corporation. The Kinect2 sensor is a physical device with depth sensing technology, a built-in color camera, an infrared (IR) emitter, and a microphone array, enabling it to sense the locations, movements, and voices of people. Board tracking module  48  acquires at 30 frames/sec the depth image signal output of 3D depth camera  46 . 
         [0026]      FIGS. 5-1, 5-2, 5-3, and 5-4  are images developed by sequential processing of a depth image signal output of 3D depth camera  46 . 
         [0027]      FIG. 5-1  shows a depth image acquired from 3D depth camera  46  by board location tracking module  48 . Image  82  represents 6 ft.-8 ft. (1.83 m-2.44 m) of the ends of boards  14  nearer to check grader workspace  72 . 
         [0028]      FIG. 5-2  shows a thresholded image  84  that is the result of application to image  82  of an image threshold algorithm masking all depth image information other than that of the top faces of boards  14 . The image threshold algorithm can be any one of many well-known image threshold algorithms implemented in open source library software. The white regions of thresholded image  84  are categorized into blobs by application of software available from the Open Source Computer Vision (OpenCV) library of real-time computer vision programming functions. The blobs are filtered by size and shape; and blobs that are too small, wide, oblong, or excessively rotated in the plane of the board-carrying surface of conveyor  18  are discarded. 
         [0029]      FIG. 5-3  shows an edge detected image  86  that is the result of vertical edge (both left and right) detection performed on the blobs. The vertical edges of each of the blobs are stored in a list of x, y coordinates. 
         [0030]      FIG. 5-4  shows a board blob location image  88  that is the result of applying to image  86  a random sample consensus (RANSAC) line-fitting algorithm or any one of many well-known line-fitting algorithms implemented in open source library software. A line fit is performed on the left and right edge points of each blob. The left and right lines fitted for each blob are compared for parallelism and separation distance to confirm that the blob has parallel left and right edges (as does a board) and that the edges are about the same width apart as that of boards  14 . The remaining left/right line pairs and associated blob bounds are assumed to be boards  14 . At this stage of image processing, the locations but not the identities of boards  14  are known. 
         [0031]    With reference to  FIG. 4 , a system modeling module  90  receives from board recognition system  62  board identity information for each one of boards  14  and from board scanning system  80  the defect information or “solution” associated with each one of boards  14 . The solution includes a set of board attribute information, such as lumber grade, species of lumber, moisture content, grading solution, trimming solution, strength, shape, thickness, width, and identification number. The location, identity, and solution set of each of boards  14  are grouped together in a list of virtual boards formed in system modeling module  90 . 
         [0032]    A programmable logic controller (“PLC”)  92  controls the movement of lug chains  20  and includes an encoder  94  ( FIG. 2B ) that produces a board conveyor movement signal indicating the speed of lug chains  20 . 
         [0033]    The speed of lug chains  20  is read periodically (e.g., 4 times/sec) from PLC  92  by system modeling module  90 . The location of lug chains  20  is derived by interpolation from the speed values read between 0.25 second intervals. This approach to measuring expected speed and location is called the chain movement model. System modeling module  90  uses the periodic readings of the location of lug chains  20  to periodically “move” forward in space the virtual boards represented in  FIG. 5-4 . System modeling module  90  uses the well-known Kalman filter algorithm to create a balance between measured speed of lug chains  20  transporting boards  14  and the measured locations of boards  14  by board location tracking module  48  so as to minimize lag and jitter. If 3D depth camera  46  detects no hand gestures of check grader  12  on the board, the Kalman filter weights favor the chain movement model to compute the location of the board. If 3D depth camera  46  detects a hand of check grader  12  on the board, system modeling module  90  is programmed to expect that check grader  12  is going to physically move the board in an unpredictable fashion. In this case, board location tracking module  48  is favored over the chain movement model to measure the location of the board. The detection of hand gestures is described in detail below. System modeling module  90  periodically, i.e., 30 times/sec, receives board blob locations from board location tracking module  48 . System modeling module  90  compares the virtual boards in the list to the blob locations and pairs the virtual boards with the blob locations based on how close they are. System modeling module  90  then micro-adjusts the board locations and orientations to match what board location tracking module  48  is detecting. This operation of system modeling module  90  allows check grader  12  to displace boards  14  and thereby change their locations and angles, and the virtual board locations remain properly tracked with the actual boards  14 . 
         [0034]    As described above, each one of boards  14  enters the grading table, and board location tracking module  48  reads the location of that board. As the board moves down the grading table, board location tracking module  48  continuously tracks the location of that board (and all other previous boards  14 ). If check grader  12  reaches out and touches a specific one of boards  14 , 3D depth camera  46  detects that interaction. (Check grader  12  touching a board essentially always displaces the board from its original orientation on lug chains  20 .) Any inputs to interface  10  from the check grader  12  can now be associated with that board. These inputs could be, but are not limited to, additional hand gestures, to which 3D depth camera  46  is responsive; oral statements via microphone; or pressing of buttons on an input device. 
         [0035]    With respect to detection of hand gestures of check grader  12 , system modeling module  90  computes a high/low gesture zone and a left/right gesture zone. High/low gesture zone extends a fixed first distance, e.g., 2 ft. (0.61 m), along the length of a board from its end nearer to check grader workspace  72 , and left/right gesture zone extends a fixed second distance, e.g., 6 in. (15.24 cm), along the width of the board in the direction of board flow path  16 . System modeling module  90  establishes a reference depth by computing an average depth of the top surface of the board and average depths at the left- and right-hand sides of the board. This computation can be performed with use of any one of well-known algorithms. 
         [0036]    Whenever 3D depth camera  46  detects a depth of the high/low gesture zone that differs from the reference depth, this condition indicates that a hand of check grader  12  has reached into that gesture zone. Since the depth of the gesture zone is known, system modeling module  90  can detect whether the hand of check grader  12  is in contact with or above the surface of the board. 
         [0037]    Whenever 3D depth camera  46  detects a depth of the left/right gesture zone that differs from the average depths, this condition indicates that a hand of check grader  12  has been placed at the left-hand side of the board, if the depth of the left gesture zone has changed, or at the right-hand side of the board, if the depth of the right gesture zone has changed. 
         [0038]    Establishing left/right and high/low gesture zones provides eight unique combinations of detectable gestures. These gestures made by check grader  12  include placing the left hand above or on the board surface, right hand above or on the board surface, left hand on the left-hand side of the board, right hand on the right-hand side of the board, left hand above the board surface and the right hand on the right-hand side of the board, and right hand above the board surface and the left hand on the left-hand side of the board. 
         [0039]    System modeling module  90  is programmable to deliver to a solution rendering module  96  a complete set or a subset of the set of board attribute information in response to a specific gesture made by check grader  12 . Board tracking module  48 , system modeling module  90 , and solution rendering module  96  operate on processor circuitry of the personal computer contained in enclosure  40 . A rectangular block  98  containing modules  48 ,  90 , and  96  in  FIG. 4  represents the personal computer. 
         [0040]    For example, under nominal operating conditions, check grader  12  does not touch a board that check grader  12  concludes has the proper lumber grade projected onto the board surface. This nominal operating condition is illustrated in  FIGS. 6A and 6B .  FIG. 6A  is a diagram showing a top plan view of a group of twelve grade-quality measured, generally parallel aligned boards  14  transported along board flow path  16 . The three left-most and the one right-most boards  14  are outside of field of view  50  and, therefore, have no grade mark symbols or other board attribute information projected onto their top surfaces.  FIG. 6B  is an enlarged fragmentary view of boards  14   a ,  14   b ,  14   c ,  14   d , and  14   e  enclosed by circle A drawn on  FIG. 6A  to identify a region within field of view  50  of image projector  42  and proximal to check grader workspace  72 . Boards  14   a ,  14   b ,  14   d , and  14   e  show projected on their top surfaces board length symbols  110 , grade mark symbols  112 , trim symbols  114 , and board identification numbers  116 . Board  14   b  shows two board length symbols  110  and two grade mark symbols  112  because board  14   b  is to be cut into two-8 ft lengths as indicated. Board  14   d  has a knot defect  118 , and any board attribute information projected onto board  14   c  is obscured in  FIGS. 6A and 6B  by enclosure  40  and air conditioner  64 . 
         [0041]    If upon inspection check grader  12  concludes that a board has projected on its surface board attribute information that was erroneously computed by board scanning system  80 , check grader  12  touches the surface of the board. The operating condition resulting from the touching of a board by check grader  12  is illustrated in  FIGS. 7A and 7B .  FIG. 7A  differs from  FIG. 6A  in that a circle B replaces circle A of  FIG. 6A  to show check grader  12  moving board  14   d  and a consequent projection of additional board attribute information  120  onto the top surface of board  14   d .  FIGS. 7A and 6A  are otherwise the same.  FIG. 7B  is an enlarged fragmentary view of boards  14   a ,  14   b ,  14   c ,  14   d , and  14   e  and of check grader  12  enclosed by circle B. 
         [0042]    The detection by board location tracking module  48  and system modeling module  90  of the hand of check grader  12  touching board  14   d  causes delivery to solution rendering module  94  board attribute information  120  that would be useful for check grader  12  to know.  FIGS. 7A and 7B  illustrate board attribute information  120  as an image of a rectangle representing a small scale rendering of board  14   d , in which rectangle a smaller shaded area marked with “K” indicates a portion of board  14   d  spoiled by knot  118 . Board  14   d  is shown displaced from its original generally parallel spatial alignment with adjacent boards  14   e  and  14   c  shown in  FIGS. 6A and 6B . Board attribute  120  is a member of a subset of board attribute information that is different from the subset of board attribute information shown in  FIGS. 6A and 6B  before the displacement of board  14   d . The output of solution rendering module  96  is a 30 frames/sec stream of video, which is delivered to image projector  42 . System modeling module  90  provides the different subset of solution information for projection onto the surface of the board. Board location tracking module  48  continuously monitors the location and orientation of each board; therefore, check grader  12  displacing board  14   d  to inspect it sees the projected information  110 ,  112 ,  114 ,  116 , and  120  remain spatially aligned on the top surface of displaced board  14   d  as a consequence of the above-described adjustments made by system modeling module  90 . This continuous monitoring enables check grader  12  to walk at a pace that permits observation of the projected information as lug chains  20  transport board  14   d.    
         [0043]    In the preferred embodiment described above, image projector  42  is the image display device that receives the set or subset of board attribute information from solution rendering module  96 . First and second alternative image display devices include, respectively, a large format display screen and an augmented reality device. Each of the first and second alternative image display devices displays to an observer a rendering of a subset of the set of board attribute information in spatial alignment with renderings of images of virtual boards produced in accordance with the operation of board location tracking module  48  or captured by the color camera of 3D depth camera  46 . The above-described operation of system modeling module  90  maintains spatial alignment between the rendering of board attribute information and renderings of images of a displaced selected grade-quality measured board transported on lug chains  20 . 
         [0044]      FIGS. 8A, 8B, and 8C  are diagrams and  FIG. 8D  is a pictorial view of an embodiment of the disclosed check grader-actuatable interface  10 ′ constructed for simultaneous use by two check graders  12  and  12 ′ standing at respective check grader workspaces  72  and  72 ′. With reference to  FIGS. 8A, 8B, 8C, and 8D , check grader-actuatable interface  10 ′ constitutes an expanded version of check grader-actuatable interface  10 , by addition of a second enclosure  40 ′ of a second overhead image projector  42 ′ and a second enclosure  44 ′ of a second 3D depth camera  46 ′. Enclosure  40 ′ contains a personal computer having processor circuitry on which board tracking, system modeling, and solution rendering modules operate as described above for check grader-actuatable interface  10 . 
         [0045]    Upright mounting member  30  and an upright mounting member  30 ′ support at their top ends a beam  34 ′ to form an inverted U-shaped structure. Arm portion  36  terminating in mounting plate  38  and an arm portion  36 ′ terminating in a mounting plate  38 ′ extend from beam  34 ′ and support enclosures  44  and  44 ′, respectively.  FIG. 8D  shows field of view  50  of image projector  42  covering four boards  14  in front of check grader  12  and a field of view  50 ′ of image projector  42 ′ covering five boards  14  in front of check grader  12 ′. Check graders  12  and  12 ′ may coordinate their inspection activities in any number of ways such as, for example, check graders  12  and  12 ′ alternating inspections of boards  14  as they are transported by conveyor  18  along board flow path  16  through check grader-actuatable interface  10 ′. 
         [0046]    It will be obvious to those having skill in the art that many changes may be made to the details of the above-described embodiments without departing from the underlying principles of the invention. The scope of the present invention should, therefore, be determined only by the following claims.