Method and apparatus for improved inspection and classification of attributes of a workpiece6901352Abstract A generic, scalable consumer subsystem/producer subsystem interface controller for exchanging data between at least one producer subsystem configured to produce a set of services characterized in a producer generated data set, and at least on consumer subsystem configured to consume the set of services, including an object-oriented producer application program interface configured for use on a multi-threaded, client-server operating system, wherein producer routines are configured to: initialize producer server objects maid producer client objects; receive requests for data from a consumer subsystem via the producer client objects; send acknowledgments to a consumer subsystem in response to requests from the consumer subsystem via the producer server objects; send data to a consumer subsystem in response to requests from the consumer subsystem via the producer server objects; and wherein consumer routines are configured to: initialize consumer server objects and consumer client objects; send requests for data to a producer subsystem via the consumer server objects; receive acknowledgments from a producer subsystem in response to requests from the producer subsystem via the consumer client objects; and, receive data from a producer subsystem in response to requests from the producer subsystem via the consumer client objects. Claims 1. A generic, scalable consumer subsystem/producer subsystem interface controller for exchanging data between at least one producer subsystem configured to produce a set of services characterized in a producer generated data set, and at least one consumer subsystem configured to consume the set of services, comprising: Description FIELD OF THE INVENTION
The invention further includes a computer readable medium having computer executable instructions for performing the steps of the above-described method. The invention further includes a workpiece characterization system including at least one producer subsystem configured to produce a set of services relating to physical characteristics of a workpiece, at least one consumer subsystem configured to consume the set of services, and an interface controller for exchanging data between the subsystems in a generic, scalable manner. The interface controller includes an object-oriented producer application program interface (API) and an object-oriented consumer API. The APIs are configured for use on a multi-threaded, client-server operating system. The producer API is configured to initialize producer server objects and producer client objects, to receive requests for data from a consumer subsystem via the producer client objects, to send acknowledgments to a consumer subsystem in response to requests from the consumer subsystem via the producer server objects, and to send data to a consumer subsystem in response to requests from the consumer subsystem via the producer server objects. The consumer API is configured to initialize the consumer server objects and consumer client objects, to send requests for data to a producer subsystem via the consumer server objects, to receive acknowledgments from a producer subsystem in response to requests from the producer subsystem via the consumer client objects, and to receive data from a producer subsystem in response to requests from the producer subsystem via the consumer client objects. The invention further includes an apparatus for tracking select kinematics of a workpiece moving at a linear velocity. The tracking apparatus includes an encoder wheel, a drive mechanism, and a signal generator. The encoder wheel is configured to tangentially contact a workpiece and rotate at an angular velocity coincident with the linear velocity of the workpiece in response to contact between the encoder wheel and the workpiece. The drive mechanism is configured to drive the encoder wheel at a first angular velocity approaching an angular velocity of the encoder wheel coincident with the linear velocity of the workpiece. The signal generator is configured to interact with the encoder wheel and generate a signal in response to the angular velocity of the encoder wheel. The invention further includes an apparatus for detecting the probable existence, location, and type of defects in a workpiece. The apparatus includes a sensor subsystem, a defect assembler, an optimizer, a computer controllable workpiece segmenter, a control subsystem, a computer system, and a tracking device. The sensor subsystem is configured to sense a first section of a workpiece and produce signals corresponding to at least one physical characteristic of the section of the workpiece. The defect assembler is configured to generate defect assembler data subscription requests, to receive the signals, and to generate a workpiece data model based on the signals. The optimizer is configured to generate workpiece segmentation recommendations based on the workpiece data model and generate optimizer data subscription requests. The computer controllable workpiece segmenter is configured to segment a workpiece according to the segmentation recommendations. The control subsystem is configured to control the workpiece segmenter in response to the location of a workpiece within the apparatus and in response to the workpiece data model and the segmentation recommendations. The computer system includes a processor and computer readable memory. The computer system is configured to receive signals from the sensor subsystem and store them in the computer readable memory. The processor is configured with a first producer thread program which, in response to the receipt of a first set of signals by the computer system, receives one of the data subscription requests and transmits the first set of signals from the computer readable memory to the generator of the data subscription request. The processor is further configured to generate a second producer thread in response to storage of a second set of signals in the computer readable memory, the second producer thread being configured to receive one of the data subscription requests and selectively send the second set of signals to the generator of the data subscription request. The tracking device is configured to track selected kinematics of a workpiece moving in a linear velocity within the apparatus. The tracking device includes an encoder wheel, a drive mechanism, and a signal generator. The encoder wheel is configured to tangentially contact a workpiece and rotate at an angular velocity coincident with the linear velocity of the workpiece in response to contact between the encoder wheel and the workpiece. The drive mechanism is configured to drive the encoder wheel at a first angular velocity approaching an angular velocity of the encoder wheel coincident with the linear velocity of the workpiece. The signal generator is configured to interact with the encoder wheel and generate a signal in response to the angular velocity of the encoder wheel and provide the signal to the control subsystem. The invention provides other advantages which will be made clear in the description of the preferred embodiments. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood by reference to drawings, wherein: FIG. 1 is an isometric schematic diagram showing a modern lumber mill and the system for determining the presence of defects in a board and making optimization decisions based thereon. FIG. 2 is a schematic diagram showing the interrelation between the various components of the system in a block diagram format. FIG. 3 is table showing the different attributes of a workpiece such as a board which can be sensed by various sensing or measuring subsystems. FIG. 4 is an end view of a workpiece such as a board showing the 9 segments that the board may be divided into for purposes of producing a board model. FIG. 5 is an isometric diagram of a visual representation of a board model or "virtual board". FIG. 6 is an end view diagram of the board model of FIG. 5 wherein the corner vertices collapse for a rectangular board. FIG. 7 is an end view diagram of the board model of FIG. 5 wherein the corner vertices and the top vertices collapse for a board exhibiting severe wane. FIG. 8 is an end elevation view of a section of a board having a knot passing therethrough. FIG. 9 is a plan view of a defect map showing a defect sensed by two different sensing subsystems, and how the defects might be merged into a single defect. FIG. 10 is a side elevation view of a board tracking device. FIG. 11 is a plan view of the board tracking device of FIG. 10. FIG. 12 is an end view of the board tracking device of FIG. 10. FIG. 13 is a schematic diagram of a model of the type of message used in the interface control subsystem. FIG. 14 is a diagram of a four-point defect bounding box for external bounding and secondary internal feature bounding. FIG. 15 is another diagram of a four-point defect bounding box for external bounding and secondary internal feature bounding. FIG. 16 is a schematic diagram of the defect assembler architecture. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION Referring to FIG. 1, the system 10 is made up of a number of modules or subsystems which beneficially work together to scan each board and produce an optimized decision. These subsystems detect board features and defects, optimize the board, and preferably pass the optimized decision for each board to the appropriate saw. The sensing subsystem 100 can include x-ray 110, profile 120, laser profile (not shown), color vision 130, fluorescent mark reader (not shown), moisture (not shown), and inspection and sensing systems (not shown). The optimizing subsystems include the defect assembler 36, scheduler (not shown), and the optimizer and control subsystems 38, 42 and 138 of FIG. 2. These subsystems get their operational instructions such as product definitions, prices, etc., from a database maintained by the host subsystem 46 and accessed by the graphical user interfaces 44 and 45. When a board enters the system 10 it is detected by a barrier photoeye 34 and can be tracked using an electronic encoder 136. Images of the board are collected from the various sensors 110, 120 and 130 one "slice" (data slice) at a time as the board travels through the scanner 100. When a number of "slices" have been acquired this is termed a "frame" of data. Frames can then be evaluated for the features and defects that the sensors identify as likely to exist in the board. As each frame is evaluated the features and defects are passed from the sensing subsystems 100 to the defect assembler 36. The defect assembler 36 adds all of the defect and feature information together from the various sensing subsystems and passes the board model on to the optimizer 38. The optimizer 38 evaluates the board for the products defined in the current cut order and generates an optimum decision. This decision may include fixed length products, finger joint (variable length) products, and re-rip products. It can place the products towards the leading end of the board, the trailing end of the board, or centered in the board between defects. The decision will be based on either recovery optimization (get the most wood possible out of the board) or on value (get the most money possible out of the board). Each product can be defined to allow or not allow certain defects in certain parts of the product cross section. This means that products that will be machined further can allow defects in the product where the defect will be removed at a later step in the process. This decision is preferable complete by the time that the board exits the scanner 100 and is in turn displayed on the graphical user interface 44 or 45 (real-time display) and is passed on to the control subsystem 138 of FIG. 2. The control subsystem 138 tracks the board through the system by assigning it an identification number which all of the other subsystems use to make sure that they are referencing the same board. Once a board decision has been made the control subsystem communicates with a material handling process controller (not shown and not part of the system) to determine which saw the cut decision is to be sent to. At the appropriate time, the cut decision (including positions along the board at which to cut, and which storage bin the resulting block of wood is to be sent to) is then transmitted directly to the computer controlled saw 50. A plurality of saws can be fed simultaneously by one system. As each board passes through the system 10 and a decision is made, the board data and decision are stored in a database in computer 46. Production summary reports can be generated from this data providing users with a clear picture of what product volumes were produced. Each board's information may also be saved in a manner that allows it to be re-optimized later during a "what-if" system tuning exercise. This is an effective way to tune the system without the time and cost of processing real wood. In addition to using the board model generated by the system for purposes of optimizing board segmentation and for controlling the execution of board segmentation by saws and the like, the board model can be saved on a computer readable medium for future use. For example, rather than segmenting the boards associated with a saved board model, the physical boards might be sold to a customer for further processing along with an accompanying copy of the board model on computer readable medium. This will allow the buyer to make local decisions regarding segmenting the boards, and can also allow the buyer to perform such segmentation of the board with machines capable of using the board model for machine positional control. Likewise, a potential buyer of boards can preview the boards by viewing the board model to determine whether the boards meet the buyers needs. Overview of the System FIG. 1 shows an overview of the system 10 for grading and handling graded lumber, including the cutting of boards, which is generally found in a sawmill. Lumber or a workpiece 1 generally advances into the plant from a planer 12 on a feed belt 14 adjacent a fence 16. The system 10 is preferably provided with sensors to allow the tracking a detection of workpieces as they move through the system. Workpieces may be marked with bar code by bar coder 52, allowing the board to be tracked as it moves through the plant or identified in a package of boards for later distribution or use. For workpieces such as lumber where it can be undesirable to visibly mark boards, bar coding may be accomplished by using ink which can only be read by non-visible light frequencies (such as ultraviolet). It is also desirable to know, at various points in the system, the precise location of a board. Such is particularly useful after a board has been optimized to identify defects and then presented to a saw for the cutting. Without precise location identification of the board, defects may be left in the board, or alternately, good wood cut out of the board. Preferred apparatus for such tracking of boards in a computerized optimization sawmill are described herein. Turning to FIG. 2, a hierarchal block diagram is provided showing the relationship between the subsystem components. The system 10 includes sensing or inspection subsystem shown as x-ray 110, profile 120, and visual 130. The x-ray inspection subsystem can determine density defects and shuttle profile of the workpiece. The profile sensing subsystem can determine a geometric 3-dimensional profile of the board or workpiece, as well as the existence of surface defects. The visual inspection subsystem can determine visual surface defects. As described above, other sensing and inspection subsystems can be added to the system. The particular system provided makes it easy to add additional inspection subsystems as will be described further below. The system 10 further comprises a board tracking subsystem 138 which, in addition to tracking the position of the board within the plant as well as the position of the board within subsystems such as the sensing subsystems, can determine the length of the board. The control subsystem 138 further communicates with a computer controlled saw 50 of FIG. 1 as well as the programmable logic controller or PLC 42 of FIG. 1. The sensing subsystems as well as the control subsystem communicate directly with the defect assembler 36. As described above, the defect assembler generates a board model or a "virtual board." The defect assembler is in communication with the optimizer 38. The optimizer 38 is in communication with the controller 138 such that the optimized decisions made by the optimizer 38 can be communicated to the controller 138 allowing the controller to execute the decisions. The optimizer 38 is in further communication with the host 46 allowing the optimizer 38 to access and store data, including computer programs, on the computer readable medium of the host. In traditional network architecture, the host supports user interfaces such as terminals 44 and 45. The host may be in further communication with a main bus line to 40 which can support additional user interfaces such as operator console 54 of FIG. 1 or user interface 213 of FIG. 2, as well as communicate with the existing mill networks by node 360. Connecting all of the subsystems is the interface controller (IFC) 200 of FIG. 2. The interface controller 200 consists of communication links 201, 202, 204 through 212, inclusive, and 214. The interface controller 200 is further configured such that future subsystems 220 can be added and accommodated through communication channel 221. Likewise, components such as user interface 213 may be removed and communication channel 212 removed without difficulty, due to the structure of the interface controller as will be further described below. The system 200 can further beneficially include a communication link 214 between the defect assembler and the host allowing the defect assembler to store the board model on the computer readable medium of the host 46. It is understood that, while the system of the present invention is primarily described as having a plurality of sensor subsystems, the system can comprise only a single sensor subsystem. An example of single sensor subsystem use is in a primary breakdown operation wherein large pieces of wood (as for example, logs) are cut into primary bulk pieces for latter processing into smaller, commercial sized pieces. A primary breakdown operation can be performed using only a profile sensor to determine wane or a "no-board" condition. The resulting information can then be provided to the optimizer and the controller for cutting of the log into primary components. In such case the interface controller cans still be used to integrate the optimizer and the optimizer. Turning to FIG. 3 a block diagram table is provided showing a variety of sensing subsystems and the types of data that they produce. Board data may be generally separated into three different categories. The first category is a profile data set which provides information about the physical dimensions of the board in 1, 2, or 3 dimensions (represented by Cartesian coordinates x, y and z). The next category is defect information which may either be 2-dimensional or 3-dimensional. For example, a single source x-ray system can provide 2-dimensional defect information, particularly relating to density variations in the work piece. A profile subsystem can provide defect information in 3-dimensions, but is limited to detecting such defects as gouges, holes, and other defects which affect the profile of the board itself. A third category is a dimensional category. Again, different subsystems can provide different dimensional information. For example, the x-ray subsystem can provide dimensional information relating to the width and length (x and y) of the board while the control system can only provide information relating to the length of the board. In FIG. 3, each of the three categories are shown with respect to four sensing subsystems 110, 120, 130 and 238, and each category is further defined with respect to the number of dimensions (referenced by coordinates x, y and z) in which the category can be measured for each of the shown subsystems. The information collected from the subsystem shown in FIG. 3 is used to build a board model. Turning to FIG. 4, an end view of a workpiece or board is shown. For modeling purposes, it is convenient to segment the board into eight segments. Assuming that FIG. 4 shows the end of a board which leads travel through the system, segments 1, 2 and 3 border the top of the board, while segments 5, 6 and 7 border the bottom of the board. Likewise, segments 1, 8 and 7 border the port side of the board (referenced by looking at the top facing towards the leading edge), while segments 3, 4 and 5 border the starboard side of the board. It is convenient to segment the board into eight of segments since such segmentation conveys the Wandefelt information relevant to board characterization. Turning to FIG. 5, an isometric visual diagram of a board model or "virtual board" is shown. The board model is preferably constructed using 8 vertices 301 through 308. Eight vertices are selected since most physical board shapes may be accommodated with an 8-point model. Briefly referring to FIG. 6, it is seen that when a perfectly rectangular board is encountered that the corner vertices will collapse, as exemplified by vertices 301 and 308. Briefly turning to FIG. 7, it is further seen that for a board such as a piece of wood cut near the edge of a tree exhibiting significant roundness on one side, the vertices will collapse even further as shown by vertices group 302, 303, 304 and 305. Returning now to FIG. 5, a Cartesian coordinate system having coordinates of x, y and z corresponding respectively to the length, width, and height of the virtual board is shown. Such a reference system is useful for generating, storing, and manipulating a computer model such as the virtual board described herein. The virtual board of FIG. 5 is further shown with defects 310 on the top side, 320 on the bottom side, 330 on the port side, and 340 on the starboard side. It is the job of the defect assembler to take this information and assemble it into a board model to generate a model which is representative of the physical board. For example, a visual scanner may determine only that defect 310 and defect 320 exist on the top and bottom respectively of the actual board. However, there is no data which connects these two together so it is impossible for a visual scanning subsystem to determine whether there is any relationship between the two defects. If the defect is a knot which passes through the board at an angle, as shown in FIG. 8 showing knot 350 having top 310 and bottom 320, an x-ray scanner will only determine that a defect of width x exists in the board, since it will not have any information regarding the location of the defect with respect to the depth of the board. The defect assembler can take both the visual information showing defects 310 and 320, as well as the x-ray information showing a block defect 360, and combine them together to determine that in fact the defect is a knot which passes through the board. This type of data combining is shown graphically in FIG. 9 wherein an x-ray defect 371 is combined with a visual defect 372 producing an overlapping defect zone 373. It is the function of the defect assembler to compare this information against other acquired information and determine the probable existence, type, and location of a real defect within the board and generate an appropriate board model in response thereto. The defect assembler as well as the other components and subsystems of the system, will be described more fully below. Subsystems Inspection and Sensing Subsystems X-Ray The x-ray subsystem 110 of FIG. 1 transmits x-rays through lumber as it travels lengthwise through the scanner 100. The x-rays are blocked according to the density of the wood at given locations which results in greater attenuation of x-rays at the detectors when there is high density wood present such as knots, and less attenuation of x-rays when there is lower density such as clear wood, and even less attenuation when there is extremely low density in the cases of rot. By evaluating the x-rays that are received, the system can locate knots, rot, and clear wood. This information is summarized by the system and preferably passed on to the defect assembler 36. Vision The vision subsystem 130 illuminates a board with white light which is reflected into a color linescan camera. The amount and color of the reflected light varies according to the type of wood traveling through the scanner and the features or defects at a particular location on the board. Using this color visual information the system can locate the surface locations of knots, cracks, holes, stains, insect damage, etc. A number of techniques are used in evaluating the image to locate these features which are then summarized and preferably passed on to the defect assembler 36. Profile The profile subsystem 120 illuminates the sides of a board with white light which is then reflected to cameras above and below the board faces. The amount of light reflected from the edge depends on the slope of the board edge. In this way, the system determines the presence and width of wane along the board edges. This information is summarized and preferably passed on to the defect assembler 36. Laser Profile A laser profile subsystem (not shown) projects lines of laser light onto a board at an angle. The light is reflected to a camera looking at the board from a different angle. The difference in projection and viewing angles of the light and the camera are used to determine the location of the board surface by a method such as triangulation. The resulting image represents the range to the board surface and the conveyor. The range image is evaluated using a number of techniques to locate geometric defects such as wane, holes, cracks, skip, scant, bow, etc., which are summarized and preferably passed on to the defect assembler 36. Moisture A moisture subsystem (not shown) transmits radio waves through the board. The radio waves are blocked by the water in the wood. The more water there is in the board the more the radio waves are attenuated at the receiver. In this way the moisture profile along the length of the board is determined. Acceptable moisture levels are used to determine what part of the board is likely to be wet, and is to be cut out and/or sorted for further drying or some other type of processing. Fluorescent Mark A fluorescent marks reader subsystem (not shown) detects crayon marks placed on the wood surface. These marks can be used to indicate special grade zones to the optimizer 38. As the board passes through the scanner 100 this system detects the crayon mark locations along the length of the board, and summarizes and passes this information to the defect assembler. Other Sensor Sub-Systems Other sensor subsystems, both existing and prospective, can be used in the system 10 of the present invention. For example, the three dimensional color imaging system disclosed in U.S. Pat. No. 5,708,498 to Rioux et al can be employed to essentially replace the two separate Profile and Vision sensor subsystems. Defect Assembler The defect assembler 36 collects all of the board feature and defect information from the sensing subsystems 100 and adds them together into a single board model for the optimizer to evaluate. More than one sensing subsystem can detect the same defect type and it is the defect assembler 36 that referee's and decides how to summarize the information in the most meaningful manner. Scheduler The scheduler (not shown) controls the production and inventory levels by monitoring the production of each product. The current production levels are compared with the order size to be filled and the current recovery of the product for the raw material being processed. This comparison is used to adjust the product weighting so that the order is filled without overproducing the product. This affects the product values used by the optimizer. The scheduler can be incorporated into the host 46. Optimizer The optimizer 38 uses a model of each board prepared by the defect assembler and a set of product definitions and cut order to determine the best way to cut the board into product components. The optimizer can be configured for each defect type and size category to expand the defect bounds to ensure that the defect fringes are not included in "good wood." Once these "back offs" have been applied to the defect, the optimizer starts fitting the longest and highest valued products that it can into the board based on the board size, wane profile, and defect locations. This process continues until the defined products have been considered and then the combination that results in the highest volume or value is determined. The decision is then passed to the host 46, graphical user interface 44 or 45, and control subsystems 138. Alternately, a report may be produced which can accompany the boards if sold or sent to another location for processing. Additionally, the resulting decisions from the optimizer can be saved on a computer readable medium and sold with the boards in order to enable the buyer to optimize yield or value from the purchased boards, or to enable a potential buyer to determine the value of the boards. The optimizer results, if stored on a computer readable medium, can also be modified according to factors not within the scope of the optimizer's optimization program. All of the optimizer functions can be accomplished by a computer program or programs. Such optimizers and optimizer programs are known in the art and will not be described further herein. Control The control subsystem 138 of FIG. 2 tracks each board as it passes through the system, conveys the board decisions to the appropriate saws, and interfaces with the material handling process control system. Data processing elements of the control subsystem can be incorporated into the host 46. Programmable Logic Controller (PLC) Once the optimizer has made a decision regarding a particular workpiece, the decision is preferably communicated to the programmable logic controller (PLC) 42 for execution. The PLC 42 preferably includes computer readable medium for storing computer programs. Examples of computer readable medium include, without limitation, ROM, RAM, a hard drive, a diskette and diskette drive, a CD ROM and CD drive, a tape and tape drive, and an EPROM. The logic controller 42 can decide whether the board is to be cut or not, and if so, by which saw. Typically a plant for processing boards has a plurality of computer controllable saws. Such ensures that the sawing of the boards do not become a bottleneck for throughput through the plant. Further, depending on the type of cut to be made (for example, rip or cross-cut), one saw may be preferably configured over the other. Boards can be routed to a selected saw via a conveyor interchange (not shown) which can be for example a pneumatically actuated conveyor interchange system actuated by the PLC 42. The conveyor interchanger can move a workpiece from a first conveyor to a second conveyor. Host The host subsystem 46 comprises a computer-readable medium such as a hard drive, and acts as an "information warehouse" to store the product definitions and save the board production statistics. The host subsystem controls the other subsystems and monitors their status. An uninterruptible power supply preferably communicates with the host, informing of a pending loss of power with enough time to save working data and shut down the system securely. A service modem access can be connected to the host permitting remote diagnostic and troubleshooting, and allowing software upgrades to be transferred to the system from remote locations. The host or network server 46 can also perform other known functions such as communication with remote devices through modem 48, and interfacing with other computer systems in the sawmill or other facilities through line 360. For example, the network server 46 can provide production information to an accounting or shipping office. It should be appreciated that the control system, including the DFA 36, the PLC 42, the control module 38, and the host 46 can be considered as a "computer." Alternately, each of the components such as the DFA 36, the PLC 42, the control subsystem 38 module and the network server 46 can also properly be considered separately as computers. While the control scheme is describe herein in a particular configuration, it should be appreciated by one skilled in the art that the necessary functions of the invention, as described fuller herein below, can be accomplished with any one of a variety of control system configurations. Graphical User Interface (GUI) The graphical user interface 44 and 45 allows a human/machine interface with the system. Each board decision can be displayed on the GUI as it is processed, with the capability of displaying prior board decisions. The GUI can also display boards with their solutions based on where they are in the material handling system at any given moment. Production reporting, diagnostics, setup, and alarm monitoring can all be handled through the GUI. The system preferably supports multiple GUI's simultaneously, permitting the machine operator to view real-time decisions at the machine while a supervisor can define products from an office off the shop floor. Board Tracking Apparatus Since inspection of the board by the system results in a board model having spatial reference to locations on the board, it is important to have a reference point on the board when scanning the board such that the physical measurements accurately represent the board in the board model. Further, when the board is provided to alternate systems, as for example a computer controlled saw, it is important that the board be capable of being aligned such that a board defect in the physical board which is represented in the board model is accurately located with respect to the saw such that optimization decision are effectively carried out by the saw. Data from the tracking system is provided to the control system 38 of FIG. 2. Preferably, the system 10 is provided with a plurality of tracking devices such that the location of a workpiece within the system can generally be known at any time, as well as specifically known within a subsystem itself, as for example within the sensor subsystems 100 or the saw 50. One method of tracking the board is with a laser dopler velocimeter 136 of FIG. 1. Such are available for example from Canon as model LV-20Z. The laser dopler velocimeter permits contact-free measuring of the velocity of the board within the system, movement distances of the board, speed irregularities, and rotation irregularities. Contact-free measurement of the parameters outlined is desirable since contact tracking devices can be prone to slippage or other mechanical problems. An alternate workpiece tracking apparatus is shown in FIGS. 10 through 12. FIG. 10 shows a side elevation view of the apparatus which comprises a plurality of encoder wheels 20. Encoder wheels are configured such that a rotation of the wheel produces a signal, preferably a digital signal, which can be provided to the control subsystem 38 of FIG. 2. In operation, a encoder wheel is in contact with a workpiece and the workpiece is moved past the encoder wheel. The friction of the workpiece on the encoder wheel causes the encoder wheel to rotate. Since the outside diameter of the encoder wheel 20 is known, travel of the encoder wheel over a workpiece can be measured by the number of rotations or partial rotations of the encode wheel, and converted into a lineal distance. In order to reduce the potential slippage between the encoder wheels 20 and the workpiece, the apparatus 250 is preferably provided with a mechanism for driving the encoder wheels at speed approximating, but slightly less than, that at which the workpiece is expected to move across the encoder wheels. In this manner the encoder wheels have only a slight differential driving force applied to them by the workpiece, reducing wear on the encoder wheels and slippage which can contribute to error. Preferably, the encoder wheels 20 are provided with a unidirectional clutch (not shown) allowing the encoder wheels to be driven at a predetermined minimum percentage of the corresponding speed of the belt 16, but not less than this speed. Thus, if there is slippage of the board relative to the belt 16, the encoder wheels will still rotate at the predetermined percentage. If the board is moving faster than the predetermined minimum percentage of the corresponding speed, the encoder wheels will track the faster velocity. The mechanism for driving the plurality of encoder wheels is shown in FIG. 11. An electric motor 22 drives a series of belts 138. The belts are attached to pulley assemblies 150. The pulley assemblies are driven by the belt 138 at a first end and have the encoder wheel 20 at a second end. Turning to FIG. 10, the belt and pulley assembly 150 is shown in side view. Preferably, the first pulley 142 drives the encoder wheel 20 by a secondary belt 146. The pulley assembly 150 comprising pulley 142, encoder wheel 20, and secondary belt 146 is configured to pivot about pivot point 152. In this manner, the encoder wheel 20 can move through an arch to effectively raise and lower the encoder wheel, allowing the encoder wheel to encounter workpieces of varying thicknesses and to maintain contact with the board notwithstanding height irregularities in the board surface. Belts 138 are preferably provided with tensioners 166 as shown in FIG. 10. Since rotation of the encoder assembly 150 about pivot point 152 can alter the geometry of the belt 138 and produce slack in the belt, tensioners 166 are provided to ensure that the drive belts maintain the proper tension against the pulleys 142 during such rotation. In order to accommodate various heights of boards which can be encountered by the tracking mechanism, the tracking mechanism 250 can be provided with a manual board height adjustment mechanism comprising linkage 19 which, when moved to the left as shown in FIG. 10, causes the encoder wheel 20 to pivot about the pivot point 152, thereby raising the encoder wheel relative to a workpiece on conveyor 14. In one embodiment the linkage 19 is manually adjusted to accommodate a know height of boards to be encountered by the tracking apparatus 250. In a preferred embodiment, the tracking apparatus 250 is provided with an automatic actuating mechanism to automatically raise the encoder wheels 20 to a height approximating that of the workpiece as the workpiece approaches the apparatus 250. The automated actuating mechanism can comprise a photoeye 21 which is attached to a cylinder 156 having a piston 154. Attached at a second end of the piston 154 is a linkage 19 which is attached to the encoder wheel assembly 150 in a manner such that as the piston 154 is retracted into the cylinder 156, the linkage 19 moves to the left as shown in FIG. 10, causing the encoder wheel 20 to pivot about the pivot point 152, thereby raising the encoder wheel relative to a workpiece on conveyor 14. The amount of retraction of piston 154 into cylinder 156 is governed by the photoeye 21 which determines the height of the workpiece. Turning to FIG. 12, the tracking apparatus 250 is preferably mounted at an angle with respect to the grade 2 such that a workpiece supported on conveyor 14 is urged by gravity towards fence 16 against which the workpiece can rest. This assures that he workpiece will be oriented to a fixed plane, being the fence 16, as it passes through the sensor system. Such essentially establishes a "y=0" reference point for the (x, y) Cartesian coordinate system used to generate the board model. Returning to FIG. 10, in the preferred embodiment the tracking apparatus 250 comprises a feed conveyor 158 which urges a workpiece toward the sensor system 30, an intermediate conveyor 162, and a discharge conveyor 164. This allows the first conveyor 158 to be separated from the intermediate conveyor 162. Separation of the conveyors can be useful in providing a separation between workpieces to allow a photoeye or other detection system to determine the leading edge of the workpiece. In an alternate embodiment, a laser dopier tracking device and the tracking apparatus 250 may be used together to confirm each other. Defect Assembler (DFA) The defect assembler (DFA) 36 of FIG. 1 is driven by a computer program which is configured to perform the necessary functions of the board model assembler. The purpose of the DFA subsystem is to build a board model using information (for example, the defect and profile list) from any number and combination of sensor subsystems, including a single sensor subsystem. When a single sensor subsystem is employed, it is more appropriate to refer to the defect assembler subsystem as a "data modeler", since it uses data (albeit from a single sensor subsystem) to model a board. In the following discussion, the expression "defect assembler" or "DFA" may be used to refer to the program which drives the defect assembler subsystem. "DFA" or "defect assembler" will also be understood to include a data modeler in a single-sensor or no-sensor configuration. The defect assembler program is constructed in a classical "producer-consumer" architecture, wherein certain subsystems are producers of information and other subsystems are consumers of information. For example, sensor subsystems 110, 120 and 130 are considered producer subsystem since they produce information relating to the physical attributes of the board, while the saw is a consumer of information since it uses or consumes the board model to cut the board into finished product. Some components, such as the defect assembler, are both producer and consumer. That is, with respect to the defect assembler, it consumes the information produced by the sensing systems and produces a board model which is used by other subsystems. The defect assembler (DFA) functions primarily as a consumer of incoming data from scanning subsystems and as a producer of board model data to subscribers, including the optimizer subsystem (OPT). As boards travel through a scanner, each scanning subsystem generates a list of defects and other attributes to describe the board. These lists are sent to DFA 36 where they are combined into a single board model. The board model is then passed from DFA to OPT 38 where the "best cut" solution is determined. The DFA 36 is configured to generate board models from any combination of scanning subsystem data produced in the system. In some cases, more than one scanning subsystem will report the same defect. It is the responsibility of DFA to rationalize these instances into the single board model according to a set of arbitration rules. The DFA's hardware consists of a processor, preferably one having multiple network connections to other subsystems. An exemplary operating system is Windows NT available from Microsoft Corporation. Board Model Framework The foundation of the defect assembler subsystem's operation lies in a board model framework that is common to the defect assembler subsystem and the various scanning subsystems. The board model geometry is a combination of three-dimensional (x, y, z) Cartesian coordinates and two-dimensional (x, y) and (x, z) coordinates with reference to the board face as shown in FIG. 5. The principle of datum referencing is used to relate geometrical features to the reference surface of the ideal board model, and maintain functional similarity of the scanning subsystems to the saw. A datum indicates the origin of a dimensional relationship between a tolerance feature and a reference surface of the wood, i.e., bottom, port, and lead side. The reference surface serves as a datum feature, whereas its true geometric counterpoint establishes the datum. FIG. 5 illustrates the construction of reference surfaces defined by the scanning system datum. The continuous belt conveyor 14 of FIG. 1 is a datum plane establishing the bottom surface, the fixed fence 18 of FIG. 1 is a datum plane establishing the port surface, and the photoeye 34 is a datum line establishing the lead surface of the board model. The photoeye datum line also establishes the trail surface of the board model, as further described below. The true geometry of the board referenced from the three datums defines the board model as follows: Three-dimensional Cartesian (x, y, z) coordinate system referenced to lead surface, bottom surface and port surface whereby the origin is the hypothetical intersection of the these three surfaces. Visually, the coordinate system is determined by looking into the scanner from the outfeed, assuming that the board contacts the belt and fence at this point, and applying the "right hand rule" for x, y and z coordinates along the line where the fence and conveyor meet, as indicated by the axes in FIG. 5. At least six two-dimensional faces (top, bottom, port, starboard, lead, trail) comprise a volume describing length, width, and thickness of the board model in x, y, and z Cartesian space, respectively. Leading and trailing faces of the board are defined here for future use. An ambiguous volume within the board (internal) where only two Cartesian coordinates are known (usually x, y) and thickness is defined externally as nominal. Base line dimensioning is used for all coordinates with respect to the datum origin. The photoeye datum line is preferably used to establish both the lead and trail surfaces of the board model. Each subsystem can receive the photoeye hi/lo signal and the encoder pulses from the conveyor. The photoeye 34 will transition from lo/hi to hi/lo (or visa versa) when a moving board breaks the photoeye beam. Each subsystem will define the lead surface and coordinate origin from this mark. Encoder pulses are recorded and used to measure the distance the conveyor moves the board for a given constant conveyor speed. The photoeye will transition from hi/lo to lo/hi (or visa versa) when the board passes the photoeye and the beam is restored. Each subsystem will define the trail surface and total length from this mark. Because each subsystem preferably measures board length the same, i.e., according to the precision of the encoder pulse train, each subsystem passes a standardized total board length to the defect assembler subsystem. The photoeye (34 of FIG. 1) is preferably upstream of the sensor subsystems 110, 120 and 130, and each subsystem preferably uses encoder pulses to determine the board lead surface with respect to the constant conveyor speed. That is, as the board moves along the conveyor, each subsystem can determine when the board lead surface passes through the scanning apparatus and when to begin recording data by offsetting the virtual lead surface a pre-defined number of encoder pulses. If a subsystem determines that a board's lead surface has slipped ahead or behind the expected or virtual lead surface, the subsystem preferably does not re-position the board's lead surface or origin to the determined mark. Preferably, the subsystem will begin sending board data at the determined mark with coordinates referenced to the expected or virtual origin. That is, board data may have negative x-axis coordinates. In addition, the subsystem will preferably record the difference between the mark and the expected lead surface as pre-slippage. If a subsystem determines that a board's trail surface has slipped ahead or behind the expected or virtual trail surface, the subsystem will preferably not re-position the board's trail surface to the determined mark, but will instead continue sending board data after the expected or virtual trail surface, and will also record the difference between the mark and the expected trail surface as post-slippage. The total board length as determined by counting encoder pulses preferably will not change; total length is a data parity check for out-of-sequence defect recognition. Preferably, each subsystem records the maximum amount of data obtainable for each board. The defect assembler subsystem arbitrates differences in measurements when building the board model from each subsystem's data. The defect assembler subsystem uses pre- and post-slippage information when combining defects from different subsystems and when adding buffer zones around defect features. Each subsystem preferably sends the defect assembler subsystem exact measured coordinates with respect to the coordinate system described above. Other than mechanical board handling, which is assumed to be similar to the saw, a subsystem preferably does not remove board warp, bow, twist, or cup geometry to produce similitude with nominal board dimensions, nor does a subsystem add buffer material to defect features. Each subsystem preferably measures and bounds features as closely as possible, within the constraints of the subsystem. Note that each subsystem preferably removes measurement distortion effects, for example, x-ray point-source triangulation through the board center and lens barrel correction on the board surface. Depending on the sensing method at each scanner and what is necessary for optimization, feature coordinate locations may be described in any of the following ways: (1) three-dimensional coordinates in (x, y ,z) format; (2) face and two-dimensional coordinates in (port, x, z), (top, x, y), (starboard, x, z), (bottom, x, y), (lead, y, z), or (trail, y, z) format; or (3) unknown volume and two-dimensional coordinates in (internal, x, y) format. This last model facilitates the combination of two-dimensional data from subsystems including the vision subsystem, the x-ray subsystem, and the moisture subsystem, with three-dimensional data from the profile subsystem. Because the coordinates available from a given scanning subsystem are typically fixed, some of this information is not required in data lists sent to the defect assembler subsystem. For example, all defects bounded by the x-ray subsystem are described in the board model as (internal, min. x1, min. y1, max. x1, max. y1, min. x2, min. y2, max. x2, max. y2) where the z value (internal) remains constant. Therefore, the z value is implied and not sent from the x-ray subsystem for each defect element, but is assumed to be nominal thickness at the defect assembler subsystem when constructing the board model without z data from other scanning subsystems. Defect coordinate information from each subsystem is defined in FIGS. 3, 5, and 14 and as follows:
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