Abstract:
There is provided an improved panel tester and grader which is used for determining the strength and stiffness values for individually tested panels. In one aspect of the present invention, an improvement resides in providing an apparatus and method which more accurately determines when a panel is properly located within a test load zone such that certain measurements regarding the panels characteristics may be properly measured. These variables ultimately contribute to the calculated overall strength and stiffness values. Pairs of opposing rolls are provided to process the panels therebetween along a processing line. The opposing rolls each include a groove extending completely around their outer surfaces. The grooves of the opposing rolls are aligned so as to define respective channels extending between the pairs of opposing rolls. Individual location sensors are positioned relative to the channels to determine where the panels are located along the processing line at any given moment. In another aspect of the present invention, an improvement resides in providing a thickness measuring device coupled to the framework to more accurately determine the thickness of each panel travelling through the machine thereby improving the accuracy of the calculated strength and stiffness value of each panel. The opposing rolls are supported by at least two frames wherein at least one frame is movable with respect to the other. As the panels travel between the rolls, the varying thicknesses of the panels will cause the movable frame to move up or down. The thickness measuring device measures this movement which corresponds to the thickness of each panel.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to nondestructive testing of composite materials or panels, particularly wood based materials, such as plywood, oriented strand board, wafer board, particle board, and the like, to determine the strength and stiffness of such panels. 
     BACKGROUND OF THE INVENTION 
     The use and acceptance of composite materials and panels for various applications, such as, building constructions, continues to increase in the market place. As a result, it is becoming increasingly desirable to monitor the strength and stiffness of the panels being produced. This is so because the strength and stiffness of composite materials varies greatly due to the composite nature of the products and the difficulty in achieving uniform strength in the bonding materials used to join the composites together. Moreover, variations in feedstocks and other factors make manufacture of uniformly strong and elastic structures from composite elements difficult and costly. 
     Nondestructive inspection and testing of materials of all sorts is known. Many of the known methods for performing certain standards tests are manual or static methods. For example, to conduct a concentrated load test, it is known to build a frame with beams simulating joists in a building construction. The beams are spaced apart depending upon the end use and span rating of the panel to be tested. A hydraulically-actuated load is applied to the stationary panel at a specified distance from a non-secured edge and the deflection of the panel is measured by placing a dial-micrometer under the panel at a position opposite the load and reading the deflection on the micrometer scale. 
     U.S. Pat. No. 4,708,020 to Lau et al., which is incorporated herein by reference, relates to another form of nondestructive inspection and testing of composite panels to determine the strength and stiffness of the panels. More particularly, Lau et al. provide an apparatus and process for correlating end-use strength and stiffness values when the testing is carried out on hot panels. The panels may be tested at one temperature, approaching the press temperature, and the strength and stiffness determined for the end products at another temperature, generally ambient or end-use temperature. Lau et al. also provide a testing machine suitable for in-line testing for determining the strength and stiffness of panel products having different thicknesses. The testing machine of Lau et al. also enables panels to be graded so that rejects can be identified and panels can be separated into grade groups representing different strength and stiffness ranges. 
     The continuous panel tester of Lau et al. imposes a double reverse bend or “S” shaped configuration on the panels as they pass through the conveyor at line speed. The device of Lau et al. is configured and operated such that either the deflection of each panel may be measured for a specific load, or the load is measured for a particular deflection of each panel. 
     As set forth in Lau et al., there is provided a first in-feed roll and a last out-feed roll to direct each panel to be tested into and out of the overall continuous panel tester and grader. As also described in Lau et al., a plurality of photo switches along the conveyor line have the function of informing the microprocessor when a panel is in the tester. The photo switches of Lau et al. determine when one panel ends and a second panel commences to pass through the tester so as to ensure that readings from the load cells and temperature sensor represent strength and stiffness figures for one panel. Another feature of Lau et al. is the ability of the panel grader to test panels having different thicknesses by merely selecting the required nominal panel thickness. The microprocessor is programmed to control the necessary equipment to position the rolls of the apparatus to process the panels of the selected nominal thickness. Based on the selected nominal thickness which is inputted to the microprocessor, the microprocessor utilizes information received from the load cells and temperature sensor to calculate the hot strength and stiffness values for each panel and then the microprocessor uses a preprogrammed algorithm to determine the ambient or cold end-use strength and stiffness value for each of the tested panels. Lau et al. do provide that it may be desirable to use a thickness measuring sensor such as a laser sensor or an ultrasonic sensor, which is placed near the in-feed rolls of the panel tester, to obtain a more actual thickness measurement of each panel, as compared to using the selected nominal thickness for each panel, thereby providing for a more accurate calculation of the strength and stiffness properties for each panel. 
     Despite the increased use of composite materials for all sorts of building constructions and other uses, and the general desire to test the composite materials for strength and stiffness, a need still exists for an improved panel tester and grader which is efficient and economical in its manufacture and use and which also provides improved accuracy in terms of measuring and grading panel like products according to desired strength and stiffness values. 
     As can be appreciated by those skilled in the art, the many known manual methods for performing certain standards tests for panels or the like are generally labor intensive, slow processing, somewhat costly procedures that can readily lead to error or operator mistakes when trying to determine the strength and stiffness values for panels. Moreover, the known static testing machines do not allow a panel to continually move along the production line during testing, thereby limiting the usefulness of such testing equipment. 
     Although Lau et al. describe an automatic, continuous panel tester and grader which is in many aspects an improvement over the known manual or static methods, the device of Lau et al. also exhibits several problems. One problem with Lau et al. concerns the bending forces that are applied to the panels as they are fed to and passed out of the panel tester. Although Lau et al. recognize that no significant forces should be applied to the panels that would distort the loading forces of the panels in the “S” shaped path, it has actually been determined according to the present invention that the first in-feed roller ( 40 ) and the last out-feed roller ( 70 ) of Lau et al. (see FIG. 2 thereof) do in fact apply undesirable bending forces or moments to the panels as they travel thereover, thereby resulting in significantly less than accurate strength and stiffness values for the tested panels. It has been determined according to the present invention that if the panels are subjected to a bending force outside the critical load zone or path, the deflection for a specific load or the load applied for a particular deflection may be greater than or less than what the actual deflection or load would be absent the undesirable bending force, depending on the direction the panels are caused to bend outside the load zone. 
     Another problem with Lau et al. concerns the location of the photo switches ( 1 )-( 4 ) (see FIG. 1 thereof) which communicate with the microprocessor ( 22 ) so that the microprocessor knows when to begin and when to end taking and recording loading and temperature readings for a specific panel traveling through the panel tester. Lau et al. disclose that a composite panel ( 10 ) moves in an “S” shaped path through the tester. The first deflector roll ( 14 ) is positioned midway between a first pair of spaced positioning rolls ( 13 ) each of which cooperates with its respective reaction roll ( 50 ) to clamp the panel ( 10 ) therebetween, all of which function to bend the panel in a first direction in the first curved portion of the “S” shaped path. The second deflection roll ( 16 ) is positioned substantially midway between a second pair of positioning rolls ( 13 ) each of which cooperates with its respective reaction roll ( 60 ) to clamp the panel ( 10 ) therebetween, all of which function to bend the panel in a second direction opposite to the first direction in the second curved portion of the “S” shaped path, i.e., in a reverse curvature to that forced by the first deflection roll ( 14 ). According to Lau et al., when the photo switches indicate that a panel is in the tester, readings from the load cells ( 18 ) and temperature sensor ( 24 ) are taken at predetermined intervals and the microprocessor uses these readings to calculate a strength and stiffness value for each panel tested. As shown and described in Lau et al., the photo switches are placed along the processing line with no particular regard as to how their placement may affect the calculated strength and stiffness values. In other words, what Lau et al. fail to recognize, and what has been determined according to the present invention, is that the location of the photo switches or sensors relative to the load zone of the “S” shaped path is important in terms of the overall calculated strength and stiffness value for each panel tested. 
     According to the present invention, it has been determined that in order to compute more accurate strength and stiffness values for the panels, each panel should be subjected to bending forces in the first and second curved portions of the “S” shaped path or load zone between the pairs of opposed positioning and reaction rolls adjacent to the respective deflector rolls. Any forces or adverse bending moments applied to the panels outside the load zone which causes the panels to bend in an undesirable manner, will result in less than accurate strength and stiffness values. Accordingly, since the panels should only be subjected to the appropriate bending forces within the load zone, and since the microprocessor calculates a strength and stiffness value for each panel traveling through the panel tester, it is desirable for the microprocessor to take and record the desired measurement readings only when each panel is in or substantially in the load zone of the “S” shaped path as defined between the pairs of opposed positioning and reaction rolls. Locating the photo switches as illustrated in Lau et al. results in the microprocessor taking and recording the load and temperature readings for the panels when the panels are not properly in the defined load zone of the “S” shaped path, thereby undesirably skewing the calculated strength and stiffness values for the panels. 
     Yet another problem with Lau et al. is that the panel tester and grader does not provide a mechanism to measure the thickness of each panel tested with a high degree of accuracy. As explained in Lau et al., a thickness value for the panels is needed in order to calculate the strength and stiffness values for the panels. In the preferred embodiment of Lau et al., a nominal thickness value for a set of panels (see, e.g., TABLES I and II therein and the description thereof) is simply inputted into the microprocessor, so that the appropriate calculations can be made. As noted, Lau et al. do teach that if a more accurate calculation of strength and stiffness is desired, a thickness sensor such as a laser sensor or an ultrasonic sensor may be used to measure the actual thickness instead of using the nominal thickness of each panel. Even so, what Lau et al. fail to recognize, and what has been determined according to the present invention, is that the thickness of each panel is a very significant parameter in determining the most precise measure of the strength and stiffness value for each tested panel. For example, a laser sensor will only measure the thickness of a panel at the specific location where the laser contacts the panel. As can be appreciated by those skilled in the art, panels of the type described herein can have varying thicknesses over the length and width of each panel. A single laser sensor cannot take into account the varying thicknesses throughout the panels. As a result, the averaged thickness measurement obtained by a laser sensor may not be a true representative measurement of the overall thickness of the particular panel. It is possible that multiple laser sensors could be used to improve the accuracy of the averaged thickness measurement for each panel, but multiple sensors would add undesirable cost and complexity to the overall panel tester, thereby resulting in a less than optimum machine. Likewise, an ultrasonic sensor will simply not provide accurate thickness measurements. As can be appreciated by those skilled in the art, panels of the type described herein have a tendency to vibrate as they are processed along the continuously operating panel tester and grader. Such vibrations in the panels will undoubtedly adversely affect the readings taken by an ultrasonic thickness tester. Thus, according to the present invention, it has been determined that in order to obtain a more accurate calculated strength and stiffness value for each panel, a new and improved thickness measuring device is required. 
     In sum, what is needed is a panel tester and grader that improves on the apparatus and method described in Lau et al., thereby providing a more accurate account of the strength and stiffness properties of each panel tested. 
     SUMMARY OF THE INVENTION 
     The present invention provides a panel tester and grader that accomplishes the features described herein as well as other features while at the same time alleviating the noted problems and other problems of the prior art. In one aspect, the present invention is an improvement over the apparatus and method of Lau et al. The noted advantages and other advantages of the present invention are realized in one aspect thereof in a panel tester and grader which provides a fully automatic structural-use panel performance test and grade system, and which also provides timely and tamper-free quality control testing. As such, the panel tester and grader system hereof provides reliable strength and stiffness testing and grading of product quality, heretofore unheralded in the prior art. The system in accordance with the present invention is particularly suited for continuous non-destructive in-line testing of wood panels. The system automatically applies a load to panels to be tested, preferably to deflect each panel a predetermined amount, reads and records the load required to deflect each panel, measures the thickness and temperature of each panel, all without operator involvement, and provides a printout test report which includes a strength and stiffness value for each tested panel. The system is extremely cost effective to the manufacturer as well as the ultimate user. Savings are realized, for example, in the ability to correct quality performance problems directly after they arise, thereby getting the most value as well as quality out of the processed panels. If the panel tester and grader of the present invention identifies poor quality panels, adjustments can be made to the upstream panel processing equipment so as to improve the quality of the finished panel products, thereby enabling the overall panel making process to operate in an efficient and economical manner which ultimately contributes to the overall realized profits. 
     In one aspect, the present invention prevents or substantially minimizes unwanted bending forces from being applied to the panels as the panels travel through the panel tester and grader. Like Lau et al., the present invention imposes a double reverse bend or “S” shaped configuration on the panels as they pass through the conveyor at line speed, and the loads and the amount of deflection required to form this “S” shaped configuration are used to determine the strength and stiffness values of the panels. Like Lau et al., the panel tester and grader according to the present invention allows panels to be graded so rejects can be identified and panels can be separated into grade groups representing different strength and stiffness ranges. Like Lau et al., the panels may be tested at one temperature, approaching the press temperature, and the stiffness and strength values are determined for the end products at another temperature. There are other similarities between the present invention and Lau et al. which can be observed from a comparison of one to the other. However, as will be further explained below, there are many differences between the present invention and Lau et al. such as, for example, the manner in which the positioning and reaction rolls are located in a predetermined position prior to sending the panels therebetween. One particular difference between the present invention and Lau et al. resides in the elimination of the first in-feed roll and the last out-feed roll and the problems attributable thereto, so as to provide more accurate strength and stiffness values for the tested panels. As a result, according to one embodiment of the present invention, panels are fed to a pair of opposed positioning and reaction rolls which represent the beginning of the first curve of the “S” shaped path or the beginning of the load zone without substantially subjecting the panels to a premature bending force which, if present, could undesirably affect the overall strength and stiffness value for each panel. Additionally, the present invention allows the panels to exit out of the panel tester and grader from between a pair of opposed positioning and reaction rolls which represent the end of the second curve of the “S” shaped path or the end of the load zone without substantially subjecting the panels to an extra, unnecessary bending force which, if present, could also undesirably affect the strength and stiffness value for each panel. 
     In another aspect of the present invention, sensors are strategically positioned along the processing line to prevent or to substantially minimize the taking and recording of unwanted load and temperature readings by the microprocessor. As noted, panels move in an “S” shaped path through the panel tester and grader. A first load roll is positioned generally midway between a first pair of spaced positioning rolls each of which cooperates with a respective reaction roll to clamp each panel therebetween, all of which function to bend each panel in a first direction in a first curved portion of the “S” shaped path or load zone. A second load roll is positioned generally midway between a second pair of spaced positioning rolls each of which cooperates with a respective reaction roll to clamp each panel therebetween, all of which function to bend each panel in a second direction opposite the first direction in a second curved portion of the “S” shaped path or load zone. The positioning and reaction rolls are advantageously located one above the other such that a vertical or substantially vertical plane extends through the centers of the respective opposing rolls. The planes extending through the centers of the rolls define nip areas between the opposing rolls and further define the beginning and ending boundaries of the curved portions of the “S” shaped path or load zone. A feature of the present invention involves the taking and recording of the load and temperature measurements of each panel when the panels are traveling within or substantially within the load zone. Thus, according to the present invention, it is desirable to properly position the necessary sensors as close as is practically possible to the planes extending through the opposed positioning and reaction rolls, thereby, in effect, being as close as possible to the boundaries of the curved portions. 
     In one embodiment, the positioning and reaction rolls are mounted for rotation about respective shafts. Each roll contains a circular groove which is preferably located midway between the ends of the roll, and which preferably has a depth which extends through the outer surface of the roll to the outer surface of the shaft. The positioning rolls are located relative to its opposing reaction roll such that the grooves of the positioning rolls align with the grooves of the respective reaction rolls, thereby providing a channel extending between the outermost vertical peripheries for each set of opposed rolls. A plurality of sensors, one for each channel, are positioned along the processing path traveled by the panels such that each sensor emits a signal which travels through its complementary channel. In this way, as a panel traveling through the processing line breaks the plane of the signal of any particular sensor, that sensor sends a signal to the microprocessor indicating that the sensor plane has been broken, whereby the microprocessor knows whether or not a panel is properly within or substantially properly within the load zone of the “S” shaped path. The sensors and microprocessor are programmed to cooperate together such that the microprocessor begins taking and recording load and temperature readings when certain sensor planes are broken thereby indicating that a panel is properly within the load zone, and stops taking and recording load and temperature readings when the other sensor planes are broken thereby indicating that a panel is not properly within the load zone. Since the planes extending through the opposing positioning and reaction rolls represent the beginning and ending points of the curved portions of the “S” shaped path or load zone, and since the sensors pass sensing signals or mediums through the grooves or channels extending between the respective opposing rolls near the outer diameter of the shafts of the rolls, the load and temperature readings are only taken and recorded while the panels are substantially within the load zone. This is an improvement over the Lau et al. reference because, unlike Lau et al., the panel tester and grader according to the present invention includes sensors which are strategically placed along the panel processing line with respect to the load zone so as to communicate with a microprocessor in such a manner that prevents or substantially minimizes the taking of undesirable load and temperature readings. Contrary to the present invention, the photo switches of Lau et al. are located in areas far removed from the intended load zone of the “S” shaped path. 
     In a further aspect of the present invention, a panel thickness measuring device is positioned relative to the framework of the panel tester and grader in order to provide a more accurate measurement of the thickness of each panel as the panels are fed through the machine. As mentioned, the thickness of each panel contributes to the final calculated strength and stiffness value for each panel. Thus, the more accurate the thickness measurement is for each panel, the more accurate the strength and stiffness values will be for each panel. The positioning and reaction rolls are supported by suitable framework which may be moved in a vertical direction through connection with electro-mechanical actuators. The electro-mechanical actuators move the appropriate portions of the framework, thereby moving the rolls, into a preset position depending on the general thickness of the panels to be tested. Preferably, the gap between each pair of cooperating rolls will be slightly smaller than the thickness of the panels to be tested. The electro-mechanical actuators are preferably provided with spring mounts so that when a panel passes between the cooperating rolls, the actuators can absorb the difference in the thickness of each panel while maintaining the rolls in contact with the adjacent face of the panel being tested. Thus, at least portions of the framework has, in effect, a limited range of motion during operation which enables panels having varying thicknesses to pass through the machine so that the panels are not damaged when passing between the opposed sets of rolls. According to the present invention, a thickness measuring device such as a LVDT is coupled to the framework so as to be able to measure the distance between the cooperating sections of the framework as this distance varies, according to the thickness of each panel traveling through the machine. A thickness measuring device according to the prevent invention will pick up most, if not all, of the variations or aberrations of thickness in each panel to be tested. In this way, the microprocessor is able to calculate a more accurate averaged thickness measurement for each panel which will result in a more accurate overall strength and stiffness value. 
     In yet another aspect, the present invention provides a method of testing the strength and stiffness characteristics of panel-like materials comprising the steps of feeding each panel in an “S” shaped load zone between a plurality of pairs of rolls, deflecting each panel from both sides and measuring the deflection load for a deflection amount when the panel is substantially within the load zone, measuring the temperature of the panel being tested when each panel is substantially within the load zone, measuring the actual thickness of each panel when each panel is substantially within the load zone, providing a plurality of sensors which are strategically placed along the processing line which determine when each panel is substantially within the load zone and, preferably, calculating an end-use strength and stiffness value for each panel tested based on the load, deflection, temperature and thickness readings for each panel. 
     Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings in which like numerals are used to designate like features. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a side elevational view of certain components of a continuous panel tester and grader embodying the features of the present invention. 
     FIG. 2 is a view taken along line II—II of FIG. 1 illustrating one aspect of the present invention. 
     FIG. 3 is a view taken along line III—III of FIG. 1 illustrating another aspect of the present invention. 
    
    
     Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates an in-line panel tester and grader  10  wherein a composite panel  12  moves in an “S” shaped path. Since the present invention is intended to provide certain improvements over the apparatus and method described in Lau et al., a complete description regarding many of the details of the apparatus  10  is not needed. Reference can be made to Lau et al. for a more complete description of the nonessential components of the apparatus and method according to the present invention. However, it should be noted that, like Lau et al., it is envisioned that the present invention may mark the end-use stiffness and strength figures on each panel and the present invention may also grade panels identifying rejects which can be discarded. In addition, it is envisioned that the panels may be sorted out into different grade bins thereby identifying premium quality panels and lesser quality panels. Lau et al. describes one method of calculating an end-use strength and stiffness value for each tested panel which the present invention can employ. Moreover, as will be evident below, the present invention is also capable of use in other panel testing and grading systems wherein the end-use strength and stiffness value is based at least in part on the thickness of each panel and/or on the deflection for a specific load or the load for a particular deflection. As such, even though the present invention is described as having many improvements over Lau et al., it should be appreciated that the apparatus and method described herein is capable of use in other panel testers and graders according to the principles of the present invention. The present invention is directed toward improving the accuracy and reliability of data used to determine the end-use strength and stiffness value for each tested panel, such as, for example, the applied load for a particular deflection and the actual thickness for each panel. Thus, the present invention can be used in other situations where similar improvements are desired. 
     With reference to FIG. 1, a pair of cooperating in-feed guide rolls  14  and  18  guide the panel  12  past a first pair of spaced apart positioning rolls  22  each of which cooperate with a respective spaced apart reaction roll  26  to clamp the panel  12  therebetween and position the panel  12  against the reaction rolls  26 . A first deflector roll  30  is positioned generally midway between the rolls  22  and functions to bend the panel  12  in a first direction into a first curved portion  34  of the “S” shaped path. 
     The panel  12  then passes and is guided by a second pair of spaced apart positioning rolls  38  each of which cooperates with a respective spaced apart reaction roll  42  to clamp the panel  12  therebetween. A second deflector roll  46  is positioned generally midway between the second pair of positioning rolls  38  and bends the panel  12  in a second direction opposite to the first direction in which the panel  12  is bent by deflector roll  30  and into the second curved portion  50  of the “S” shaped path, i.e., in a reverse curvature to that formed by the first deflector roll  30 . The panel  12  then exits through a pair of cooperating out-feed guide rolls  54  and  58 . The deflector rolls  30  and  46  each have a pair of load cells (not shown), one on each end, which sends a signal to further processing equipment corresponding to the amount of load being applied to the panel  12 . The load cells may be any type of load cell commonly known to those skilled in the art which functions according to the principles of the present invention. A temperature sensor  60 , which may be any suitable sensor known to those skilled in the art, senses the temperature of the panel  12  being tested and sends a signal to the further processing equipment which corresponds to the temperature of the panel  12  being tested. 
     The positioning of the guide rolls  14 ,  18 ,  54  and  58 , positioning rolls  22  and  38 , reaction rolls  26  and  42 , and deflector rolls  30  and  46  are all suitably controlled by a computer or microprocessor (not shown) operatively connected thereto. The microprocessor suitably utilizes the information from the load cells, the temperature sensor, and the data concerning the make-up and size of each panel to calculate the end-use strength and stiffness properties for each panel as such is described, for example, in Lau et al. Such information may naturally be shown on a computer screen or printed by a printer (not shown). In any event, the microprocessor is of a suitable type which is capable of receiving, interpreting and analyzing the necessary information to output the desired results. 
     The panel tester and grader  10  includes a main frame  62  which has three subframes therein. A first loading frame  66  supports the first deflector roll  30  and the two lower positioning rolls  22 . A second loading frame  70  supports the second deflector roll  46  and the two upper positioning rolls  38 . A third subframe  74  supports the lower reaction rolls  42 . The upper reaction rolls  26  are supported directly by the main frame  62 . 
     The in-feed guide rolls  14  and  18  are supported by an “L” shaped arm  78  which is pivotally mounted on the axis of rotation  80  of the adjacent reaction roll  26 . A second “L” shaped arm (not shown) is positioned at the other ends of the rolls  14  and  18 , such that reference to one can be viewed as reference to the other. The angular position of the arm  78  is adjusted by an electro-mechanical actuator  82  which pivots the arm  78  about the axis  80  of roll  26 . The position of arm  78  is preferably predetermined based on the intended travel path for the panel  12  through the machine  10 . The microprocessor is operatively coupled to the actuator  82  for controlling the location of the arm  78 . Although the actuator  82  may be one of many different types of actuators capable of performing the desired functions, a linear actuator sold under the name of Warner Electrak 100, by Warner Electric of South Beloit, Ill., is particularly well suited for use according to the principles of the present invention. 
     The bottom in-feed guide roll  18  is connected to an electro-mechanical actuator  86  having a spring mount. The spacing between the top in-feed guide roll  14  and its cooperating nip forming bottom in-feed roll  18  is adjusted by the electro-mechanical actuator  86  which moves roll  18  the required amount depending on the general thickness of the panel to be tested. The microprocessor is operatively coupled to the actuator  86  for controlling the location of the roll  18  relative to roll  14 . As will be further explained below, the spring mount of the actuator  86  allows the cooperating rolls  14  and  18  to accommodate panels passing therebetween which are of varying thicknesses so as not to damage the panels. Although the actuator  86  may be one of many different types of actuators capable of performing the desired functions, a linear actuator like actuator  82 , would work according to the present invention. 
     The position of arm  78  is determined in one aspect on the position of the first deflector roll  30  which determines the degree of bending of the panel  12  in the first curved position  34  of the “S” shaped path. The panel  12  passes over the pair of rolls  22  and is deformed by the roll  30  which causes the panel  12  to be pressed against the reaction rolls  26  thereby causing the panel  12  to bend. When the lead end of the panel  12  passes over roll  30 , its direction of travel will not intersect with the nip formed between the next pair of cooperating rolls  22  and  26 , thus a deflector  90  is provided to deflect the leading end of the panel  12  into the predetermined nip formed between the next pair of opposite rolls  22  and  26 . 
     The first deflector roll  30  is mounted on the first loading frame  66  with an arm  94  which is pivotally mounted on the frame  66 . The position of the roll  30  relative to the frame  66  in the vertical direction can be determined in any number of different ways, one such way being described, for example, in Lau et al. The roll  30  is generally positioned at a selected distance above the horizontal plane defined by the upper portions of the outer peripheries of the two spaced-apart rolls  22  so as to impose the desired degree of bending to the panel  12  being tested. 
     Electro-mechanical actuators  98  are supported by the main frame  62  and connected to the first loading frame  66 . There are a total of four actuators  98 , one for each corner of frame  66 . The actuators  98  control the vertical movement of the frame  66  and are set depending on the general thickness of the panels to be tested to provide the desired gap between the rolls  22  and  26 . The gap between each pair of cooperating rolls  22  and  26  should be slightly smaller than the thickness of the panel to be tested. The actuators  98  include spring mounts so that when a panel having varying thickness passes between the positioning rolls  22  and reaction rolls  26 , the actuators  98  absorb the difference in the thickness of the panel while maintaining the rolls  22  and  26  in contact with the adjacent faces of the panel  12  being tested. It should be noted that when the general panel thickness for the panels to be tested is changed (e.g., from ½-inch panels to ⅞-inch panels), the position of the roll  30  (as well as roll  46 ) is changed so that the degree of deformation of the panel changes and the “S” shaped path is thus varied. Although the actuators  98  may be one of many different types of actuators capable of performing the desired functions, a stepper motor actuator sold under the part number EC2S32T-5004A-50-MSZ-MT1E, by Industrial Device Corporation of Novato, Calif., is particularly well suited for use according to the principles of the present invention. 
     The subframe  74  is moved up or down depending upon the required “S” shaped configuration by electro-mechanical actuators  102 , although other suitable positioning devices may be employed. Actuators  102  are supported by the main frame  62  and connected to the subframe  74 . There are a total of four actuators  102 , one for each corner of the subframe  74 . Actuators  102  are preferably of the same type as actuators  98  including the same type of spring mount system. 
     The second loading frame  70  is substantially the same as the first loading frame  66 , but is inverted with the second deflector roll  46  pushing down on the panel between the two positioning rolls  38  which cooperate with reaction rolls  42 . The second deflector roll  46  is mounted on frame  70  in much the same fashion as deflector roll  30  is mounted on frame  66 . As shown, an electro-mechanical actuator  106  may be used independently or in connection with a step cam (not shown) to vertically maneuver the roll  46  with respect to frame  70 , although the roll  46  may be positioned relative to the frame  70  in any number of different ways suitable for use with the present invention. Electro-mechanical actuators  110  are placed in each corner of frame  70  in order to move the frame  70  in a vertical direction. Such actuators  110  are like actuators  98  and  102 . It will be apparent that because the roll  46  is beneath the frame  70 , it will be mounted in a suitable manner to prevent it from falling out of position. 
     A deflector shoe  114 , substantially equivalent to deflector  90 , is provided to guide the panel  12  to the last positioning roll  38  in the second curved portion  50  in much the same way deflector  90  guides panel  12  to the last positioning roll  22  in the first curved portion  34 . 
     The panel  12  passes from between the last positioning roll  38  and last reaction roll  42  and then from between the out-feed guide rolls  54  and  58 . Guide rolls  54  and  58  are mounted on a pair of “L” shaped arms  118  (only one shown) in much the same way as in-feed guide rolls  14  and  18  are mounted on arms  78 . Arm  118  is pivotally mounted on the axis of rotation  122  of the adjacent reaction roll  42 . The angular position of the arm  118  is adjusted by an electro-mechanical actuator  126  which pivots the arm  118  around the axis  122  of roll  42 . The position of arm  118  is preferably predetermined based on the intended travel path for the panel  12  through the machine  10 . The microprocessor is operatively coupled to the actuator  126  for controlling the location of the arm  118 . Actuator  126  is preferably of the same type as actuator  82 . The top out-feed guide roll  54  is connected to an actuator  119 , which is like actuator  86 , and is operable much like the bottom in-feed guide roll  18  is operable. 
     As in Lau et al., during movement through the “S” shaped path, forces are applied to each panel by the deflector rolls  30  and  46  and their respective reaction rolls  26  and  42  against which the panel is positioned by the positioning rolls  22  and  38 . The in-feed guide rolls  14  and  18  and the out-feed guide rolls  54  and  58  ensure that the panel  12  stays in its normal path or trajectory and does not exert any significant forces on the panel as this would distort the loading. Unlike Lau et al., the present invention eliminates the first in-feed roll ( 40 ) and last out-feed roll ( 70 ) to substantially ensure that there are no bending forces applied to the panel  12  outside of the “S” shaped load zone. 
     The actuators, in conjunction with the microprocessor, move the appropriate framework to position all of the rolls in a preset position based on the general size of the panels to be tested. Once the rolls are properly positioned, a panel is passed through the testing machine which will appropriately activate the load cells to measure the applied load for the particular deflection of the panel and the temperature sensor to sense the temperature. A thickness measuring device described below measures the thickness of each panel. The load, temperature and thickness values, among other things, are utilized by the microprocessor to determine the strength and stiffness value for each panel at ambient or end-use temperature. Lau et al. describes one algorithm which may be used to calculate such a value. Moreover, other algorithms may be used in accordance with the present invention. 
     FIG. 2 illustrates one aspect of the present invention in more detail. As previously explained, the location of the photo switches or sensors  130 ,  134 ,  138  and  142  (FIG. 1) is important in terms of determining when a panel is in the “S” shaped load zone so that a more accurate strength and stiffness value can be calculated. Although many different types of sensors may be employed, such as reflector-type sensors, typical pass through optical sensors are particularly suited for use according to the principles of the present invention. 
     As shown in FIG. 1, the positioning rolls  22  and  38  are located opposite their respective reaction rolls  26  and  42 . In this manner, vertical or substantially vertical planes  146  (see FIG. 2) extend through the axis of rotation of each of the respective opposing rolls. The first curved portion  34  of the load zone of the “S” shaped path is defined by the vertical planes  146  extending through the positioning rolls  22  and their respective reaction rolls  26 . The second curved portion  50  of the load zone of the “S” shaped path is defined by the vertical planes  146  extending through the positioning rolls  38  and their respective reaction rolls  42 . As noted, a feature of the present invention involves the taking and recording of the load and temperature measurements of each panel when the panels are traveling within or substantially within the “S” shaped load zone. 
     As illustrated in FIG. 2, each positioning and reaction roll is mounted about a shaft  150  for rotation therewith. Each positioning and reaction roll includes a circular groove  154  which is preferably located midway between the ends of each roll and which preferably has a depth which extends through the outer surface  158  of each roll to the outer surface  160  of each shaft  150 . The positioning rolls, such as positioning roll  22 , are each located relative to its opposing reaction roll, such as reaction roll  26 , such that the grooves  154  of the positioning rolls align with the grooves of the respective reaction rolls. Thus, as can be observed, a channel  162  extends between the outermost vertical peripheries for each set of opposed rolls. One of the sensors or emitters  130 ,  134 ,  138  and  142  and its respective reflector or receiver  166  is positioned in each channel  162  defined by the opposing rolls. Preferably, for reasons more fully explained below, the light-emitting source or sensing medium of each sensor is located ½ inch away from the outer surface  160  of the shaft  150 . 
     The sensors communicate with the microprocessor as follows. When the front edge of the leading end of the panel  12  breaks the sensing beam or plane of the sensor  134 , a signal is sent to the microprocessor indicating that the panel  12  is properly located in the first curved portion  34  of the load zone. Once the computer knows the panel is in the first portion of the load zone, it starts receiving and recording signals transmitted from the load cell of the deflector roll  30  corresponding to the load being applied to obtain a particular deflection, as well as signals from the temperature sensor  60 . When the front edge of the leading end of the panel  12  breaks the sensing beam or plane of the sensor  142 , a signal is sent to the microprocessor indicating that the panel  12  is located in the second curved position  50  of the load zone. Once the computer knows the panel is in the second portion of the load zone, it starts receiving and recording signals transmitted from the load cell of the deflector roll  46  corresponding to the load being applied to obtain a particular deflection, as well as signals from the temperature sensor  60 . When the trailing edge of the back end of the panel  12  breaks the sensing beam or plane of the sensor  130 , a signal is sent to the microprocessor indicating that the panel  12  is no longer properly in the first curved portion  34  of the load zone. Once the computer knows the panel  12  is not properly located in the first curved portion  34  of the load zone, it stops receiving and recording information concerning the load and temperature readings. When the trailing edge of the back end of the panel breaks the sensing beam or plane of the sensor  138 , a signal is sent to the microprocessor indicating that the panel  12  is no longer properly in the second curved portion  50  of the load zone. Once the computer knows the panel  12  is not properly located in the second curved portion  50  of the load zone, it stops receiving and recording information concerning the load and temperature readings. 
     Various features of the invention are explained below by way of reference to the following exemplary example. 
     A tester and grader according to the present invention is configured to handle 4×8 feet panel sheets. The first and second curved portions have a dimension of thirty inches and the deflector rolls  30  and  46  would be located midway between the respective curved portions. The positioning rolls and reaction rolls each have a 4-inch diameter with 2-inch diameter shafts. The microprocessor does not begin receiving and recording load or temperature values for each panel until the sensing plane of the sensor  134  is broken. In this arrangement, load and temperature data would not be taken for the first 16.5-inches of the 96-inch panel sheet (i.e., the distance between the center of the deflector roll  30  and the appropriate vertical plane  146 , plus ½ inch which is the preferred location of the sensing beam or plane from the outer surface of the shaft  150 ). Likewise, the microprocessor would stop receiving and recording load or temperature values for each panel when the sensing beam or plane of the sensor  138  is broken, thereby resulting in no load or temperature data for the last 16.5-inches of the 96-inch panel. Although the end-use strength and stiffness value of the panels is based only on data received for 62 out of the 96-inches of the panel, this is a tremendous improvement over what is shown in Lau et al. due to the location of the photo sensors therein. 
     Accordingly, locating the sensors as described herein greatly improves upon the overall strength and stiffness value for each tested panel because the microprocessor only takes and records data when the panels are properly located in the panel tester and grader. 
     FIG. 3 illustrates another aspect of the present invention in greater detail. As previously noted, a panel thickness measuring device  170  is positioned relative to the framework  70  and  74  in order to provide a more accurate measurement of the thickness of each panel as the panels are fed through the machine. Although the device  170  is shown in the second curved portion  50  (FIG.  1 ), it should be understood that the device  170  or a second device in addition to device  170  could be placed in the first curved portion  34 . 
     The thickness measuring device comprises an LVDT  182  having a probe  186  and a cable  190 , an “L” shaped plate  174  and a plate  178 . LVDT&#39;s are commonly known and available from numerous commercial suppliers. Plates  174  and  178  may be a suitable material, but ¼-inch thick appropriately dimensioned aluminum plates would work well according to the principles of the subject invention. 
     Plate  174  is appropriately fastened to frame  70 . Plate  178  is properly secured to frame  74 . In addition, LVDT  182  is firmly attached to plate  178 . The probe  186  is moved in and out of the cylindrical body of the LVDT due to its abutment against plate  174 , as will be further explained below. Cable  190  provides the conduit for the signals being sent back and forth between the LVDT and the microprocessor for reasons which will be apparent below. 
     As explained, panel  12  travels between the positioning rolls and reaction rolls during the bending and loading process of the panel tester. When the panel  12  is located between the respective rolls, the gap between the opposing rolls is substantially equal to the thickness of the panels. This gap varies for each panel as the thickness of each panel varies. The spring-mounted actuators attached to the respective frames allow the gap to vary so the panels are not damaged as they pass between the opposing rolls. As the framework  70  moves up and down relative to the framework  74 , the plate  174  will cause the probe  186  to move inward or allow it to move outward with respect to the body of the LVDT based on the thickness of the panel. The LVDT  182  sends a signal to the microprocessor corresponding to the thickness values of each panel. Preferably, there is an LVDT  182  on each side of the machine  10  to provide a better account for the panel thickness. The LVDT  182  takes two thickness readings at any given instant in time which the computer then averages for a single value. The LVDT  182  continuously measure the thickness of each panel so long as the panel is within one or both curved portions of the load zone as determined by the sensors  130 ,  134 ,  138  and  142 . The microprocessor will record all of the thickness measurements and then average the measurements to obtain a single thickness value which is used by the microprocessor in computing the actual end-use strength and stiffness value. 
     The device  170  provides a more accurate measure of the thickness of each panel  12 , thereby providing a more accurate strength and stiffness value as compared to prior devices. The device  170  is capable of picking up most, if not all, of the variations or aberrations in a panel which could affect the average thickness value for each panel. 
     The foregoing description of the present invention has been presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention in the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings in skill or knowledge of the relevant art, are within the scope of the present invention. The embodiments described herein are further intended to explain the best modes known for practicing the invention and to enable others skilled in the art to utilize the invention as such, or other embodiments and with various modifications required by the particular applications or uses of the present invention. It is intended that the appended claims are to be construed to include alternative embodiments to the extent permitted by the prior art. 
     Various features of the invention are set forth in the following claims.