Apparatus and method for testing stiffness of articles

An apparatus for testing stiffness characteristics such as modulus of elasticity E of an article such as a piece of lumber moving in a conveying direction transverse to the testing axis, comprises a bearing unit capable of contacting the piece of lumber at two spaced apart portions thereof. There is provided a first deflecting unit including a first working element being normally disposed in a first static position relative to the conveying path for applying a first thrust against a loaded area on the article at an intermediary portion thereof located between the spaced apart portions, to produce an article deflection of a first magnitude. Each working element defines a loading surface extending substantially parallel to the article-conveying path. There is further provided a second deflecting unit including a second working element being normally disposed in a second static position relative to the conveying path for applying a second thrust against a loaded area of the article intermediary portion, to produce an article deflection of a second magnitude, wherein the second position differs from the first position relative to the conveying path by a differential value. The apparatus further comprises load cells coupled to the bearing unit for generating signals indicative of respective magnitudes the first and second thrusts as applied by first and second deflecting units, and a computer for deriving from such signals and differential value an indication of the stiffness of the article, such as modulus of elasticity E.

FIELD OF THE INVENTION

The present invention relates generally to the field of structural products testing, and more particularly to apparatus and methods for the testing of stiffness of such products, and is particularly useful for carrying out Machine Stress Rating (MSR) tests for the purpose of grading lumber according to stiffness characteristics.

BRIEF DESCRIPTION OF THE BACKGROUND ART

Over the past years, stiffness testing of structural products has been widely used in manufacturing and building industries as an important quality concern warranting security of use of these products in the field. Stiffness characteristics of structural products are usually tested through the measurement of a parameter known as modulus of elasticity (E) also known as Young modulus, which is essentially defined as the ratio of the magnitude of a load applied to the article over the magnitude of the corresponding deformation induced to the same article as a result of the applied load. In the lumber processing industry, stiffness measurement is usually performed as part of a standard quality testing procedure known as Machine Stress Rating (MSR) in addition to the assessment of other lumber characteristics such as geometric and surface features, to comply with the requirements of specific applications such as I-beams for flooring and roof truss structures. Typically, the measured modulus of elasticity value for each piece of lumber is compared to reference threshold of increasing values associated with increasing quality of lumber, so as to assign a corresponding grade to each piece of lumber tested.

A first approach to measure the stiffness of lumber consists of using a static testing bench wherein the piece of lumber is disposed on two spaced apart support elements while a load of a predetermined magnitude is applied onto an area of the piece of lumber located between the two support elements, for measuring the corresponding deflection induced. Such basic approach is employed by the apparatus disclosed in U.S. Pat. No. 4,589,288 issued to Porter et al on May 20, 1986 which makes use of two series of parallel rolls for laterally supporting a wood panel to be tested and a loading bar capable of applying a linear load at a center area of the panel and transversally thereto, by means of a two-way cylinder for sequentially applying a first load magnitude followed by a second load of an incremented magnitude, which load magnitudes are chosen so as to involve a substantially linear portion of the deflection curve characterizing the tested panel. The applied load magnitudes are measured with a load cell and the extension or distance moved by the cylinder in applying the incremental load is either predetermined or measured in real-time. A similar testing approach is also used by the system disclosed in U.S. Pat. No. 6,053,052 issued to Starostovic on Apr. 25, 2000. Although such static approach has become considered in the wood processing industry as a standard procedure whose results are widely employed as reference values according to which MSR grades are established, in the context of on-line quality procedures, its use is limited to the testing of sampled pieces coming from the production line, and cannot be implemented as a real-time, dynamic testing procedure for all pieces being processed while they are conveyed through the production line.

A second, dynamic approach for carrying out stiffness testing consists of measuring the modulus of elasticity E of a piece of lumber while it is conveyed lengthwise, typically downstream from a lumber planer. Such dynamic stiffness testing approach is used by the apparatus disclosed in U.S. Pat. No. 3,196,672 issued to Keller on Jul. 27, 1965, which apparatus includes first and second series of rolls between which is disposed a load-measuring roll in such a manner to impart a predetermined deflection to the piece of lumber passing thereon. A third series of rolls at a location downstream from the first load-measuring roll, and a second load-measuring roll disposed between the second and third series of rolls are used to impart a second predetermined deflection onto an opposed face of the piece of lumber as compared to the face onto which the first deflection is imparted. The opposed deflection removes the effect of bow and warp naturally present in the piece of lumber. Load measurement signals are then integrated as the piece of lumber is passing through the apparatus, and a main value as an estimation of the modulus of elasticity E of the entire piece of lumber is obtained.

A similar dynamic stiffness measurement approach involving longitudinal piece conveying is also employed by the apparatus disclosed in U.S. Pat. No. 5,503,024 issued to Bechtel et al on Apr. 2, 1996, and in U.S. Pat. No. 5,564,573 issued to Palm et al on Oct. 15, 1996. While representing an improvement over the static testing approach as to the capability of these prior dynamic testing apparatus to systematically test all pieces of lumber as they are processed in the production line, the use of such apparatus is limited to industrial installations where there is sufficient available space within the production line to receive these prior art apparatus whose dimensions generally exceed the length of the longer piece of lumber to be processed.

A variant of above-mentioned dynamic stiffness testing approach is disclosed is U.S. Pat. No. 4,289,037 issued to Vinopal on Sep. 15, 1981 which describes a system making use of a conveyer for transporting wood pieces lengthwise through a first roll-based load applying device used to apply a transversal load on a central area of the wood piece located between two supporting rolls to induce a corresponding longitudinal deflection of the wood piece, means for measuring respective magnitudes of the applied load and the induced deflection, a second roll-based device for applying a load of a second magnitude on the same area of the wood piece, means for measuring respective magnitude of the second load and second corresponding deflection induced on the wood piece, and a computer for classifying the tested wood piece according to load and deflection magnitudes and to assign a grade accordingly. A similar approach for on-line stiffness testing of wood panels is disclosed in U.S. Pat. No. 5,804,738 (CA 2,220,789) issued to Bach et al on Sep. 8, 1998. The use of roll-based load applying device as taught by the above-mentioned prior patents is associated with problems related to load measurement signals stability which adversely affects consistency and reliability of stiffness estimation. The fact that a load applying roll is characterized by a loading surface that is limited to a peripheral portion of its circumference adjacent the loaded surface of the article in the conveying direction yields to such load measurement signal stability problems, especially in cases where significant vibration occurs when the article is transported on the conveyer. The ultimate effect of this limitation is to yield inconsistent stiffness estimation that may result to classification errors such as under-grading or over-grading of pieces of lumber.

An alternative approach that has been developed to comply with minimum space requirement consists of measuring stiffness characteristics while each piece of lumber is conveyed along a path in a direction parallel to the transverse dimension of the piece of lumber. Such approach is employed by the apparatus disclosed in U.S. Pat. No. 3,158,021 issued to Walters et al on Nov. 24, 1964, according to which limit bending stress of wood pieces are measured using a transverse conveyer provided on a loading station making use of two parallel lever-mounted weights disposed over the transverse conveyer so as to distribute a corresponding load onto a central area of each wood piece transversally conveyed. Such prior art apparatus carrying out a single load measurement corresponding to a single deflection measurement to obtain the desired bending stress limit measurement, the significant influence of bow and warp that are naturally present on most pieces of lumber cannot be adequately compensated according to the proposed technique.

There is still a need for testing stiffness apparatus and methods which advantageously comply with minimum space requirements imposed by industrial users of stiffness testing system, while ensuring enhanced load measurement signals stability to provide reliable and consistent stiffness estimation.

BRIEF SUMMARY OF THE INVENTION

It is therefore a main object of the present invention to provide apparatus and method for testing stiffness of an article that allow compact implementation while providing reliable stiffness estimation.

According to the above-mentioned object, from a broad aspect, there is provided an apparatus for testing stiffness of an elongate article such as a piece of lumber along a predetermined testing axis associated therewith, the article having first and second opposed surfaces aligned with the conveying path in a predetermined conveying position. The apparatus comprises transport means for moving the article along a predetermined path through the apparatus in a conveying direction substantially transverse to said testing axis. The apparatus further comprises at least one article bearing unit capable of contacting at least the first article surface at two spaced apart portions of the article, and a first deflecting unit including a first working element capable of being disposed in a first, substantially static position relative to the article conveying path and cooperating with the article bearing unit for applying a first thrust against a loaded area of the second article surface at an intermediary portion located between the spaced apart portions of the article as it moves transversely through the apparatus, to produce an article deflection of a first magnitude extending along a first deflection axis perpendicular to the conveying direction and the testing axis. The apparatus further comprises a second deflecting unit including a second working element capable of being disposed in a second, substantially static position relative to the article conveying path and cooperating with the article bearing unit for applying a second thrust against a loaded area of the first article surface at the intermediary portion of the article as it further moves transversely through the apparatus, to produce an article deflection of a second magnitude opposite to the first deflection magnitude and extending along a second deflection axis substantially parallel to the first deflection axis. The apparatus further comprises at least one load measuring unit capable of generating signals indicative of respective magnitudes of the first and second thrusts, and a data processing device for deriving an indication of the stiffness of the article from the opposed deflection magnitudes and thrust indicative signals. Furthermore, each working element defines a loading surface extending substantially parallel to the article conveying path when disposed in its respective substantially static position, thereby maximizing transverse load distribution over the loaded area, for enhanced load measurement signals stability and more reliable and consistent stiffness estimation.

According to the above-mentioned object, from a further broad aspect of the invention, there is provided a method for testing stiffness of an article along a predetermined testing axis while the article moves along a predetermined path in a conveying direction substantially transverse to the testing axis, the article having first and second opposed surfaces aligned with the conveying path in a predetermined conveying position. The method comprises the steps of: i) contacting the first article surface at two spaced apart portions of the article while applying a first thrust against a loaded area of the second article surface at an intermediary portion located between the spaced apart portions of the article as it moves along the conveying path, to produce an article deflection of a first magnitude extending along a first deflection axis perpendicular to the conveying direction and the testing axis; ii) contacting the first article surface at two spaced apart portions of the article while applying a second thrust against a loaded area of the second article surface at the intermediary portion of the article as it further moves along the conveying path, to produce an article deflection of a second magnitude extending along a second deflection axis substantially parallel to the first deflection axis, the second position differing from the first position relative to the conveying path by a predetermined differential value; iii) measuring respective magnitudes of the first and second thrusts; and iv) deriving an indication of the stiffness of the article from the differential value and the thrust magnitudes; wherein each loaded area substantially extends over the whole transverse dimension of the article while the thrust magnitudes are measured.

According to the above-mentioned object, from another broad aspect of the invention, there is provided a method for testing stiffness of an elongate article along a predetermined testing axis, the article having first and second opposed surfaces aligned with the conveying path in a predetermined conveying position. The method comprises the steps of: i) moving the article along a predetermined path in a conveying direction substantially transverse to said testing axis; ii) contacting the first article surface at two spaced apart portions of the article while applying a first thrust against a loaded area of the second article surface at an intermediary portion located between the spaced apart portions of the article as it moves transversely along the conveying path, to produce an article deflection of a first magnitude extending along a first deflection axis perpendicular to the conveying direction and the testing axis; iii) measuring the magnitude of said first thrust; iv) contacting the second article surface at two spaced apart portions of the article while applying a second thrust against a loaded area of the first article surface at the intermediary portion of the article as it further moves transversely along the conveying path, to produce an article deflection of a second magnitude opposite to said first deflection magnitude and extending along a second deflection axis substantially parallel to the first deflection axis; v) measuring the magnitude of the second thrust; and vi) deriving an indication of the stiffness of the article from the opposed deflection magnitudes and the thrust magnitudes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, preferred embodiments of apparatus and method for testing stiffness of article according to the invention will now be described in detail in the context of a MSR lumber grading application wherein structural pieces of lumber such as studs (2×3, 2×4, etc.) are transversally conveyed through the apparatus of the invention to be assigned a specific MSR grade. However, it is to be understood that the present invention can also be used for testing stiffness of other types of articles such as wood panels or any other kind of boards produced in the lumber processing industry, as well as articles made of other materials that may require stiffness measurement in the context of other industrial fields such as in plastic and metal product manufacturing industries.

Referring now toFIG. 1, the article testing apparatus according to the first preferred embodiment of the invention and as generally designated at20is adapted for use with a conventional transverse conveying system generally designated at22for transporting a plurality of articles such as pieces of lumber24each having opposed main bottom and top surfaces26,26′, which pieces of lumber24move along a predetermined path through apparatus20in a conveying direction indicated by arrow28substantially transverse to a testing axis30associated with each piece of lumber24along which stiffness will be estimated as described below. Conveniently, the transverse conveyer system22that is used in combination with the stiffness testing apparatus20of the invention is an existing conveyer system already present in the processing line, such as used at a transfer station between the output of a planer and downstream a manual grading station. Typically, such transverse conveyer system22includes two or more longitudinally extending frame beams32,32′,32″ onto each of which is mounted a guide rail34defining a channel through which a driving chain36extends as better shown inFIG. 4. Secured to each chain36in a predetermined spaced relationship are a series of transverse catch blocks38for driving forward each piece of lumber24along the conveying path in direction28while maintaining the pieces24in a parallel spaced relationship. The conveyor system22is also provided with a known driving device (not shown) adjusted to impart movement to the pieces of lumber24in a predetermined conveying speed which is typically of about 1 m/s and is also provided with a displacement sensor such as rotary encoder40as shown inFIG. 2for generating a signal indicating article displacement along the conveying direction as will be explained later in more detail. As shown inFIG. 1, the apparatus includes a main frame42formed by two pairs of lateral upright columns44,44′ which are secured one to each other at upper portion thereof with a pair of overhead horizontal beams48. Overhead horizontal beams48are connected to one another using a plurality of link members51. Each column44is secured to a left-side conveyer frame beam32using a pair of lateral beams46linked by a transverse member47. In a similar way, while being not illustrated inFIG. 1, each upright columns44′ is secured to the base frame portion49of the conveyer system22as shown inFIG. 3A, using a pair of right-side lateral beams50.

Turning back toFIG. 1, the apparatus20further includes first and second deflecting units generally designated at52,54as better shown inFIG. 2, which are adjustably secured to the frame overhead beams48using an overhead mounting unit having top mounting plates56being maintained in a suspended position using a pair of displaceable attachments58, with a pair of parallel vertical walls60,60′. Secured to top mounting plate56are first and second bottom mounting plates62,62′ to which are in turn respectively secured the first and second deflecting units52,54, using a plurality of pivot members pairs64,65,66and67,68,69attached to bottom mounting plates62and62′, respectively. The first deflecting unit52includes a first working element72capable of being disposed in a first, substantially static position as indicated by axis74inFIG. 2relative to an article conveying path represented by axis76and as also presented inFIG. 3Bby an axis74′ which is coplanar with axis74shown inFIG. 2. The apparatus20further includes an article bearing unit including first and second pairs of rails78,78′ and80,80′ for contacting the bottom surface26of each piece of lumber24under test at two spaced apart portions thereof, as better shown inFIG. 1. The rails78,78′ and80,80′ define load bearing surfaces extending substantially parallel to the conveying direction indicated by arrow28, for contacting the bottom surface26at spaced apart portions77,77′ thereof. First and second pairs of rails78,78′ and80,80′ are also disposed in a spaced relationship in the same conveying direction28, whereby their respective load bearing surfaces82sequentially receive the bottom surface26of each piece of lumber24when the latter moves past first and second locations along the conveying path76as shown inFIG. 2, at which first and second locations the first and second deflecting units52,54are disposed to face the top surface26′ of each piece of lumber24under test.

Referring toFIG. 2in view ofFIG. 1, the first working element72when being disposed in the first static position indicated by axis74relative to the article conveying path76and cooperating with rails78,78′ of the article bearing unit, is used to apply a first thrust against a loaded area84of the top surface26′ of piece of lumber24at an intermediary portion located between spaced apart portions77,77′ as piece of lumber24is moving through the apparatus20, as better shown inFIG. 3A. The thrust applied against loaded area84produces a deflection dsof the piece of lumber24of a first magnitude extending along a first deflection axis86perpendicular to conveying direction28and testing axis30as shown inFIG. 1. Turning back toFIG. 2, secured to the bottom mounting plate62′, the second deflecting unit54is disposed laterally and adjacent first deflecting unit52in a location downstream from the corresponding location of first deflecting unit52, to receive a piece of lumber24leaving the thrust applying area defined by the first working element72provided on first deflecting unit52. The second deflecting unit54includes a second working element90capable of being disposed in a second, substantially static position indicated by axis92inFIG. 2relative to conveying path76and cooperating with rails80,80′ of the article bearing unit for applying a second thrust against a loaded area94of top surface26′ of piece of lumber24at intermediary portion thereof between spaced apart portions77,77′ as the piece of lumber24further moves through the apparatus20, as also represented inFIG. 3Bby an axis92′ which is coplanar with axis92shown inFIG. 2. The second thrust applied against loaded area94produces a deflection dlof piece of lumber24of a second magnitude extending along a second deflection axis96substantially parallel to first deflection axis86. It is pointed out that the schematic deflection representation shown inFIG. 3Bemploys a scale that has been intentionally amplified as compared with actual deflection imparted to a tested piece of lumber for the purpose of illustration. It can be seen fromFIG. 3Bthat the second position as indicated by axis74′ in which the first working element72is disposed differs from the first position of second working element90by a differential value Ad associated with a nominal predetermined value Δdnas will be later explained in detail, so that second deflection magnitude dldiffers from first deflection magnitude dsby this differential value Δd so that:
dl=ds+Δd(1)
It is to be understood that according to the first preferred embodiment of the invention, the deflecting unit52has been chosen to receive the piece of lumber24first so as to produce a deflection of a first magnitude dswhich is smaller than the second larger magnitude dlobtained when the piece of lumber24passes under the second deflecting unit54as located downstream from first deflecting unit52. However, the respective position of first and second working elements72,90may be alternatively set so that the deflection of larger magnitude dlcould be measured first, followed by the measurement of the deflection of smaller magnitude ds. Moreover, while first and second deflecting units52,54are preferably disposed in laterally adjacent locations one to each other so that distinct respective loaded areas84,94are subjected to thrust applied by first and second deflecting units52,54, the latter units may alternatively be disposed in alignment one to each other in a spaced apart relationship along the conveying direction so to apply the respective thrust on a same loaded area.

Turning now toFIG. 5, the first deflecting unit52further includes a first displaceable mechanism98for holding the first working element72, which mechanism98s selectively controllable to move the working element72between the first substantially static position indicated by axis74,74′ inFIGS. 2 and 3Brespectively, relative to the conveying path indicated by axis76onFIG. 2, and a retracted position as shown inFIG. 6wherein the first working element72is away from the article conveying path to prevent obstruction thereof. The latter function is especially useful for preventing apparatus blockage due to abnormal article position feeding condition such as edge-standing or additional piece of lumber driven by a same catch block, or for performing maintenance tasks. Turning back toFIG. 5in view ofFIG. 2, the first displaceable mechanism98includes a lever unit provided with a first double- member100having a bearing end102pivotally secured to the apparatus frame through pivot member pair65, first bottom mounting plate62, top mounting plate56, wall60and displaceable attachments58. The first double-member100further has a working end104pivotally connected to the first working element72through a further pivot member pair106. The displaceable mechanism98is further provided with an actuator108which a preferably a pneumatic linear actuator readily available in the marketplace such as supplied by Gilbert-Tech (Roberval, Quebec, Canada), which actuator108is mounted to the apparatus frame through pivot member pair66secured to first bottom mounting plate62in a same way as pivot member pair65. The pneumatic actuator108is provided with a conventional mechanism123for adjusting the limit stroke of piston110using a rotary handle125provided thereon, allowing accurate adjustment of the first static position, indicated by axis74,74′ inFIGS. 2 and 3Brespectively, of the first working element72relative to the conveying path indicated by axis76onFIG. 2, in a direction perpendicular to the associated conveying direction28and testing axis30as shown inFIG. 1. At the end of a linearly displaceable piston110provided on actuator108is an end coupling element112that is pivotally secured to a central portion of first double-member100to selectively exert thereon a compression force maintaining the first working element72in the first static position as indicated by axis74shown inFIGS. 2 and 3B, and to provide the movement of first working element72between the position shown inFIGS. 2 and 5and the retracted position as shown inFIG. 6. The first actuator108is capable of exerting the compression force within a compliance range whenever the counteracting force exerted by loaded area84onto first working element72in reaction of the applied thrust exceeds the rated pressure developed by the pneumatic actuator108, the value of which being maintained at a preset value as will be later explained in more detail.

Turning again toFIG. 5, the first double-member100is pivotally connected to a rear portion114of first working element72, while a second double-member116provided on displaceable mechanism98has a working end118pivotally connected to a front portion120of first working element72, and a bearing end122pivotally secured to the apparatus frame through pivot member pair64secured to second bottom mounting plate62in a same way as pivot member pairs65and66. The first working element72defines a loading surface124extending substantially parallel to the conveying path as indicated by axis76inFIG. 2when disposed in the first static position as indicated by axis74,74′ inFIGS. 2 and 3B, respectively. It can be seen fromFIG. 5in view ofFIGS. 3A and 3Bthat the loading surface124provided on first working element72preferably has first and second symmetrical portions126,128with respect to a transverse plane defined by truncated lines132,133and134inFIG. 5and passing through first deflection axis86shown inFIG. 3A. It can be appreciated fromFIG. 5in view ofFIGS. 3A and 3Bthat first and second loading surface portions126,128further extend toward respective spaced apart portions77,77′ of piece of lumber24transversely to the conveying direction according to a symmetrical angle αsdefined by axis136onFIG. 5which extends from surface loading portion128and with respect to an axis30′ parallel to testing axis30shown inFIG. 3B, which symmetrical angle as being substantially proportional to the first deflection magnitude dsalong axis86ofFIGS. 3A and 3B, which is parallel to axis132,134shown inFIG. 5. For a given transverse span between rails78,78′ as shown inFIG. 1, which is typically of about 6 feet for a 10-feet piece of lumber, symmetrical angle αswill have a value of about 1°. As shown inFIG. 5, such angular requirement in respect of first and second symmetrical portions126,128of loading surface124defined by the first working element72allows the entire loading surface124to follow the shape of the loaded area84of the piece of lumber surface when the latter moves past the location of the deflecting unit52. It can be seen fromFIG. 5that the central transverse portion of surface124defined between symmetrical portions126,128extends in parallel relationship with axis30′ to prevent any significant deformation of the piece of lumber24at loaded area84thereof. The first displacement mechanism98is further provided with a first position sensor including a first limit switch138as part of a switch block140fit into first bottom mounting plate62, which limit switch138has a protruding contact-activating element secured to a first front mounting flange142which is in turn secured to the bearing end102of first double member100, in such a manner that the first limit switch138is capable of generating a first control signal whenever the first working element72departs from the first static position as shown inFIG. 5by a first predetermined overload threshold as a result of significant departure of the piece of lumber24from the conveying position on rails78,78′ shown inFIG. 2as will be later explained in more detail. It can be seen fromFIG. 5that the first working element90defines a loading surface124extending substantially parallel to the conveying path as indicated by axis76inFIG. 2when disposed in the second static position as indicated by axis92,92′ inFIGS. 2 and 3B, respectively. It can be also appreciated fromFIG. 5in view ofFIGS. 3A and 3Bthat first and second surface loading portions126′,128′ defined by the second working element90also extend toward respective spaced apart portions77,77′ of piece of lumber24transversely to the conveying direction according to a symmetrical angle αldefined by axis136′ onFIG. 5which extends from surface loading portion128′ and with respect to an axis30″ parallel to testing axis30shown inFIG. 3B, which symmetrical angle a, being substantially proportional to the second deflection magnitude dlalong axis86ofFIGS. 3A and 3B. For a given transverse span between rails80,80′ as shown inFIG. 1, which is typically of about 6 feet for a 10-feet piece of lumber, symmetrical angle αlwill have a value of about 2°, to allow the entire loading surface124defined by second working element90to follow the shape of the loaded area94of the piece of lumber surface when the latter moves past the location of second deflecting unit54. It can be seen fromFIG. 5that the central transverse portion defined between symmetrical portions126′,128′ is shaped in parallel relationship with axis30″ to prevent any significant deformation of the piece of lumber24at loaded area94thereof.

Turning back toFIG. 5, the second deflecting unit54further includes a second displaceable mechanism98′ for holding the second working element90, which displaceable mechanism95′ is preferably identical to the first double displaceable mechanism98as described above, and therefore similarly includes pivot member pairs67,68,69and third double-member100′ having bearing end102′ and working end104′ secured to a further pivot member pair106′ as better shown inFIG. 2, a second actuator108′ having a linearly displaceable piston110′ at the end of which is attached a second end coupling element112′ as better shown inFIG. 5, a fourth double member116′ having bearing and working ends122′ and128′. Similarly, the second working element90has its rear portion115pivotally secured to the pivot member pair106′ through pivot member pair106′ and has a front portion121pivotally secured to working end118′ as part of the forth double member116′. In a same way, the second displaceable mechanism98′ is selectively controllable to move the second working element90between the second static position indicated by axis92inFIG. 2and a retracted position as shown inFIG. 6wherein the second working90is brought away from the conveying path to prevent obstruction thereof. The second displaceable mechanism98′ is provided with a second position sensor in the form of a second limit switch144as part of a switch block146fitted into second bottom mounting plate62′, which limit switch144has a contact-activating element secured to a second mounting flange142′ which is in turn secured to bearing end102′ of the third double member100′ provided on second displaceable mechanism98′. As will be later explained in more detail, the second limit switch144generates a second control signal whenever the second working element90departs from the second static position as indicated by axis92and92′ inFIGS. 2 and 3Brespectively, by a second predetermined overload threshold as a result of the departure of piece of lumber24from its normal conveying position onto the rails80,80′ as shown inFIGS. 1 and 2.

Turning again toFIG. 5, the first displaceable mechanism98is provided with a third position sensor in the form of a third limit switch148which cooperates with double-switch block140to generate a third control signal whenever the first working element72substantially departs from the first static position indicated by axis74,74′ inFIGS. 2 and 3Brespectively, by a third predetermined overload threshold greater than the above-mentioned first overload threshold as a result of the departure of the piece of lumber24from its normal conveying position on rails78,78′ as will be later explained in more detail. Also secured to front mounting flange142is a stopper139adjusted to prevent any damage that could be made to either switch138or148in case where the first displaceable mechanism98is over-extended when reaching the limit stroke of piston110. A further stopper (not shown) is mounted on the flange142′ to prevent any damage that could be made to switch144. Each working element72,90preferably defines an article feed guiding surface150generally extending toward the loading surface124according to an appropriated acute angle β1, β2with respect to the conveying path represented by axis76′,76″ inFIG. 5which angles β1, β2have typical values of about 15° and 7°, respectively. It can also be seen fromFIG. 5that the second working member90is provided with a symmetrical article output guiding surface152presenting an angle θ with respect to conveying path represented by axis76″ the value of which angle θ being typically set to about 15°. It can be appreciated fromFIG. 5that no such output guiding portion is provided on the first working element in the example shown since first and deflecting units52,54are located so as to provide and uninterrupted testing sequence to obtain first and second deflection magnitudes dsand dlas will be later explained in more detail.

Turning back toFIG. 2, the apparatus20further includes a load measuring unit formed by right and left side subunits generally designated at154,154′ inFIG. 1. Load measuring subunits154,154′ are capable of generating signals indicative of respective magnitudes of first and second thrusts as applied by first and second deflecting units52,54as will be later explained in more detail. Since subunits154,154′ conveniently include the same components in symmetrical configurations, the description below will be limited to the right side subunit154, which description can be also applicable to subunit154′ using corresponding reference numerals as shown inFIG. 7. It can be further seen fromFIG. 5in view ofFIG. 2that the dimension of loading surface124parallel to the conveying direction along the conveying path indicated at76in FIG.2and76′,76″ inFIG. 5, is larger than the transverse dimension of the piece of lumber24under test at the intermediary portion thereof wherein loaded areas84and94are located as shown inFIG. 3A, so that each loaded area84,94substantially extends over the whole transverse dimension of the piece of lumber24while the thrust magnitude indicated signals are generated by the load measuring unit.

Turning toFIG. 7in view ofFIG. 2, the load measuring subunit154preferably makes use of two load sensors using load cells156,158, such as 250 kg rated load cells model no.125-250KG-I5-IP65 from Tedea-Huntleigh Inc. (Canoga Park, Calif., U.S.A.) used in combination with conditioning amplifying filter unit model no. 460-115 from the same supplier, having load coupling members160,162receiving corresponding rails78,80in rigid connection thereto. The load subunit154further includes an elongate guide member164to which is attached a load cell supporting plate166using flanged plate168, which guide member164is in turn rigidly secured to conveyor frame beam32″ shown inFIG. 1, in a same way as guide member164′ is secured to frame beam32using back wall170′ as shown inFIG. 4. Turning back toFIG. 7in view ofFIG. 1, it can be seen that each elongate guide member164,164′ is disposed relative to the article conveying path represented by axis76′,76″ inFIG. 5in the conveying direction indicated at28inFIG. 1, to set the piece of lumber24on the load bearing surface82of rails78,78′ and80and80′ as the piece of lumber24moves through the apparatus20. The elongate guide members164,164′ are disposed in a parallel spaced relationship and longitudinally extend in the conveying direction28as shown inFIG. 1. As better shown inFIG. 4, each load bearing surface82defined by first and second pairs of rails78,78′ and80,80′ disposed at first and second spaced apart location along the conveying path in conveying direction28, further extends toward the intermediary portion of the piece of lumber24transversely to the conveying direction according to angles γs, γlwith respect to the testing axis30which are respectively proportional to the first deflection magnitude dsfor rails78,78′ and to the second deflection magnitude dlfor rails80,80′. Such angular configuration allows each load bearing surface82to best follow the shape of loaded areas84,94as shown inFIG. 3Awhen the piece of lumber24moves past the location of first and second deflecting units52,54along the conveying path. The guide member164has first and second transfer sections172,174disposed in a spaced relationship in the conveying direction indicated by arrow28to sequentially set a piece of lumber24on respective load bearing surfaces82of first and second rails78,80when the piece of lumber respectively moves past the locations of first and second deflecting units52and54shown inFIG. 1. As shown inFIG. 7, the first transfer section172has a receiving portion176disposed upstream article setting portions180. The setting portion180of first transfer section172extends toward the intermediary portion of piece of lumber24transversely to the conveying direction28according to angle γswith respect to axis30′ parallel to testing axis30ofFIG. 3B, which angle γsis substantially proportional to first deflection magnitude ds, corresponding typically to an angular value of about 1°. In a similar way, the setting portion182of second transfer section174adjacent to transition178, extends toward the intermediary portion of the piece of lumber transversely to conveying direction28according to the same angle γsvalue, to provide stability to the piece of lumber while it leaves the support surface82of first rail78. The same article setting portion182of second transfer section174further extends toward intermediary portion of the piece of lumber transversely to conveying direction28according to an angle γlwith respect to axis30″ parallel to testing axis30ofFIG. 3B, which angle γlprogressively reach a value substantially proportional to second deflection magnitude dl, corresponding typically to an angular value of about 2°, to provide a progressive, smooth transfer of the tested piece of lumber between respective surfaces82of first and second rails78,80. It can be seen fromFIG. 7that intermediary portions184,186of guide member164which are transversely aligned with the support surfaces82of rails78,80respectively, each extends at a lower level with respect to support surfaces82to prevent any mechanical interference with the piece of lumber moving past rails78,80. It can also be seen that the load measuring units154,154′ are provided with two sets of stop elements188,188′ associated with each rail78,80, as well as with a further central stopper189aligned with the loading axis of each load cell as shown inFIG. 4, to prevent damage of load cells156,158whenever overload is applied thereto.

Turning back toFIG. 2, the apparatus further includes a data processing device in the form of a computer190receiving through lines192,192′ and194,194′ the applied thrust magnitude indicative signals generated by pairs of load cells156and158as described before. The computer190is provided with suitable logic and analog input signals conditioning circuitry (not shown) such as a low-frequency filter, as well known in the art. Connected to computer190are a terminal display196and a data entry device such as keyboard198as part of a control panel for use by an operator. The computer190may be any suitable industrial microcomputer such as supplied by Advantech Inc. (Cincinnati, Ohio, U.S.A.) making use of Pentium III—800 MHz CPU provided with a suitable digital conversion board such as model No. 3107 from Keithley Instruments Inc. (Cleveland, Ohio, U.S.A.) having 16-bits resolution in analog mode with 16 analog input ports with four groups of 8 digital input/output ports. In the preferred implementation, 4 analog inputs ports in differential mode with two groups of 8 digital inputs with a single group of 8 digital outputs are used. Also operatively connected to the computer190is a controller such as programmable logic controller (PLC)200connected through analog control lines202,204to a pair of pneumatic servo regulators210,212, such as model number ITV3050-31N1L4 from SMC Corp. (Indianapolis, Ind.), which regulators210,212have respective output pneumatic lines203,205operatively connected to a pair of reversing valves207,209whose output are connected to respective air inputs of first and second pneumatic actuator108,108′ using air lines (not shown). The servo regulators210,212are fed with pressurized air source (not shown) in a known manner, to set air pressure delivered by valves207,209at appropriate levels according to the analog signals received from PLC200, as will be later explained in more detail. The PLC200is connected to reversing valves207,209via further control lines202′,204′ to command either lifting or extension of deflecting units52,54. The controller200has a further control line214connected to a marker or printing device211that is used for applying a mark onto a tested piece of lumber as will be explained later in more detail. The apparatus20further includes a first presence sensor associated with the first deflecting unit52, which device is preferably formed of three photo-sensitive cells (PSC),216,217,218such as Allen Bradley model No. 42GRU-9200-QD1 from Rockwell Automation (Milwaukee, Wis.) respectively aligned with light-reflective elements220,221,222such as Allen Bradley model No. 92-39 form the same supplier. In a well known manner, adjustably secured to a holding track219fixed to the conveyer frame central beam32′ as shown inFIG. 1, PSCs216,217,218are disposed at the first deflecting unit location along article conveying path76so as to be capable of generating control signals fed to the computer190through control lines223,224,225whenever the piece of lumber24under test moves past the location of the first deflecting unit52. Similarly, a second presence sensor associated with a second deflecting unit54in the form of three further PCS's226,227,228respectively aligned with light-reflective elements235,237,239adjustably secured to holding track219, is disposed at the location of the second deflecting unit54along article conveying path76for generating control signals fed to computer190via control lines229,230,231, whenever the piece of lumber24moves past the second location. It can be seen fromFIG. 2that the first limit switch138uses a corresponding control line232to send a first overload position indicating signal to the computer190. Similarly, the second limit switch144uses a corresponding control line233to send a second overload position indicative control signal to computer190. In a similar manner, the third limit switch148as shown inFIG. 5uses a further control line234to send a corresponding third overload position indicative signal to the PLC200, as will be explained later in more detail. The stiffness apparatus20preferably includes an obstacle presence sensor236provided with a contact-activation rod238disposed upstream from the location of the first deflecting unit52to be capable of detecting any coming article to be tested that significantly departs from the normal, predetermined position relative to catch blocks38used by the conveyer system22while moving in a conveying direction along conveying path76. The extremity of rod38is positioned in such a manner than any misplaced article such as edge-standing or additional piece of lumber driven by a same catch block will deviate the contact activation rod to cause a fourth control signal to be fed to the PLC200through line240. The rotary encoder40uses a corresponding line242fed to the PLC200with a displacement indicative signal as will be later explained in more detail. Conveniently, the computer190may be linked to production control equipment provided in the processing line such as master PLC244, sending pacer and running conveyer signal through lines245,250in a known manner. A main task of the computer190is to generate an estimation of the stiffness of the article tested, which estimation is preferably expressed at the modulus of elasticity E of the article, derived from applied thrust magnitudes as measured by the load cells of the load measuring unit and from the differential deflection value which is mainly dependant from the initial, static relative positions of first and second working elements72,90, but also to a significant extent to the structural deformation occurring when thrusts are applied by deflecting units52and54as will be later explained in more detail. The program stored in the computer190makes a calculation of the modulus of elasticity E of each tested piece, considering its specific dimensions, applied load measurement values and corresponding deflection values, according to an approach which is insensitive to the natural curvature exhibited by each piece tested. According to the present example, the software has been programmed using Labview™ (version 6) graphic programming tool available from National Instruments Corp. (Austin, Tex.) which runs within Microsoft Windows™ NT4 environment. Conveniently, an executable version off the program is loaded in the computer, along with a parameter setup file that contains all program initialization parameter values that can edited at will by the operator. The raw Young modulus values so obtained are preferably corrected using predetermined dynamic and static correction factors, to convert the raw data into usable data that can be compared to standard modulus of elasticity data obtained with a reference static testing bench. The corrected resulting values are then compared to a table of predetermined reference values defining ranges corresponding to a number of MSR grades or classes to assign a specific one of these classes to each tested piece of lumber. Preferably, the resulting classification information is communicated through one of output lines246,247,248associated with three different color codes corresponding to pre-selected MSR classes, causing PLC200to control the printing device211accordingly, the latter being provided with three corresponding printing nozzles in a fluid communication with tanks containing inks of different colors. The computer program is also adapted to monitor the various functions of the apparatus20through the various sensors, to communicate via computer display92function monitoring data to an operator, or to a master PLC244as part of the production line. The main programs stored in computer190provides a plurality of screens and sub-screen which allow an operator to assign desired values for the operating parameters, to have access to values indicators giving in real-time the classification results in term of assigned MSR grade for each tested piece, to receive apparatus functions status information along with alarm messages for directing the operator's attention to specific anomalies that may occur when the apparatus is working.

Prior to the operation of the apparatus20, first and second static positions of first and second working elements72and90are set using the adjustment mechanism123provided on each actuator108,108′ as described before with reference toFIG. 5, so as to obtain a resulting differential deflection value Δd preferably involving a substantially linear portion of the curve representing bending stress behavior of the article under test. Typically, on the basis of equation (1) described before, the first working element72is positioned so as to have ds=0.65 cm and to have dl=1.3 cm to obtain a resulting value for Δd close to a nominal value Δdn=0.65 cm, after applying correction factors as will be described later in detail.

In operation, a first incoming piece of lumber24adequately positioned against an adjacent transverse series of catch blocks38as driven by chain36of conveyor system32passes under obstacle presence sensor236which is not activated since the piece of lumber24is in a proper conveying position as shownFIG. 2. Then, the incoming piece of lumber24reaches the guiding surface150provided on the first working element72while contacting the article receiving portion176of each guide member164as shown inFIG. 7, intersecting the detecting beam of the first photo-sensitive cell216which is caused to generate a “on” signal transmitted to the computer190, indicating that a piece of lumber24will shortly enter the thrust applying zone defined by the first working element72. Then the leading side edge of the lumber piece24reaches the article setting portion180of first working element72to guide and progressively set the piece of lumber24under test onto the load bearing surface82of first pair of rails78,78′ in sliding movement relative thereto. Then, the piece of lumber24intersects the detecting beam of the second photo-sensitive cell217causing the generation of a control signal sent to the computer190through line224for triggering data acquisition of load measurement signals from the first pair of load cells156transmitted to the computer190through lines192,192′. It can be seen fromFIG. 2that the second photo-sensitive cell217and its associated reflective device221are aligned in a position relative to the first pair of rails78,78′ in the direction of the conveying path76so as to ensure that the tested piece of lumber24is completely in contact with the load bearing surface82and the loading surface124of the first working element72, in such a manner that the load cells156generates substantially stable signals. While the computer190performs load measurement data acquisition at a predetermined sampling frequency, it also reads the status of binary signals coming from PSCs216,217,218as well as from limit switches138,138′ and144for storing in computer memory. The computer continues to read and store analog and binary signals until the piece of lumber24intersects the detecting beam of the third photo-sensitive cell218or after a preset duration stored in the computer which is determined according to a maximum duration required for data acquisition. It is pointed out that the effective load measuring zone defined by the positions of second and third photo-sensitive cells217,218must extend over a sufficient length to allow reliable data acquisition, considering the acquisition sampling rate, transverse dimension of piece of lumber24as well as conveying speed of the conveyor system32. Furthermore, the load-measuring zone preferably extends over a distance corresponding to two conveyor chain links in such a manner to substantially cancel load measurement fluctuation due to the use of a chain to drive the catch blocks38. Then, while leaving the load bearing surface82of first pair of rails78,78′ the piece of lumber24reaches the article receiving portion178of the second transfer section174as part of guide member164so as to progressively enter within the thrust applying and load measuring zone defined by the second working element90and corresponding pair or rails80,80′. Then, the piece of lumber24intersects the detecting beam of photo-sensitive cell226as part of the second presence sensor, causing the generation of a control signal sent to the computer190through line229for triggering data acquisition of load measurement signals from the second pair of load cells158transmitted to the computer190through lines194,194′. It can be seen fromFIG. 2that the photo-sensitive cell226and its associated reflective device235are aligned in a position relative to the second pair of rails80,80′ in the direction of the conveying path76so as to ensure that the tested piece of lumber24is completely in contact with the load bearing surface82and the loading surface124of the second working element72, in such a manner that the load cells158generates substantially stable signals. While the computer performs load measurement data acquisition at a predetermined sampling frequency, it also reads the status of binary signals coming from PSCs226,227,228as well as from displacement encoder40, limit switches138,148and144for storing in computer memory. The computer continues to read and store analog and binary signals until the piece of lumber24intersects the detecting beam of the photo-sensitive cell227or after a preset period of time stored in the computer which is determined according to a normal period of time required for data acquisition. Here again, the effective load measuring zone defined by the positions of photo-sensitive cells226,227must extend over a sufficient length to allow reliable data acquisition. The data acquisition being completed, the computer program automatically starts calculation of the modulus of elasticity value associated with each tested piece of lumber24according to a process that will be now described below. First, a mean load measurement value is calculated for each load cell as follows:

i is a cell identification indicia, with i=1,2 indicating the load cells156coupled to the first pair of rails78,78′ and associated with the first deflecting unit52, while i=3,4 indicating the load cells158coupled to the second pair of rails80,80′ and associated with the second deflecting unit54;

n is the number of load measurement data samples read;

Kkgis a predetermined factor (kg/Δvolt) for converting the measurement in kg unit;

Load is a corrected load measurement voltage generated by each load cell156as corrected by a predetermined offset value characterizing the load cell when unloaded.

Then, the obtained value for RawLoad[i] is preferably corrected using a predetermined tare correction value to compensate for the output level drift to which each load cell is subjected with time, the value of which can be measured when no load is applied to the load cell. The offset value can be established through an initial or periodic manual calibration procedure. The computer calculates a corrected or net load measurement value from the estimated tare value for each load cell of indicia i as follows:
NetLoad[i]=RawLoad[i]+Tare[i]  (3)

Then, the computer program calculates the load applied by each deflecting unit52,54as well as a total applied load value as follows:
NetLoadDs=NetLoad1+NetLoad2(4)
NetLoadDl=NetLoad3+NetLoad4(5)
LoadT=NetLoadDs+NetLoadDl(6)
wherein:

NetLoadDsis the net load value applied by the first deflecting unit52imparting the smaller deflection magnitude ds; and

NetLoadDlis the net load value applied by the second deflecting unit54imparting the larger deflection magnitude dl; and

LoadTis the total applied load value.

On the basis of the above calculations, the computer preferably applies a correction to the nominal deflection values as set prior to the operation of the apparatus, to compensate the inherent deformation to which the whole structural components of the apparatus are subjected, such as load cells flexion, flexion of overhead beams48, twist induced by the second deflecting unit54imparting the larger deflection dl, and friction with the load bearing surfaces82of each rail78,78′,80,80′ while the tested articles are sliding thereon. It is pointed out that some marginal factors such as twist induced by the second deflecting unit54imparting the smaller deflection dsmay be ignored as having non-significant effect on the result. The correction is made on the basis of estimated deflection error values associated with the smaller and larger deflection values ds, dlas calculated as follows:

KCellis a predetermined constant factor (N*m) representing stiffness characterizing the load cells and corresponding load measuring subunits;

KS is a predetermined constant factor (N*m) representing stiffness characterizing the structural components of the frame including overhead beams48and conveyer frame beams32,32″;

KTwistlsis a predetermined constant factor (N*m) representing cross-twist induced by the thrust applied by the second deflecting unit54to the first working element72;

KTwistllis a predetermined constant factor (N*m) representing twist induced by the thrust applied by the second deflecting unit54to the second working element90;

KFricsis a predetermined constant factor (N*m) representing twist induced by the friction between the loaded surface of the tested article and the loading surfaces of first and second working elements72,90, having a corresponding influence to the smaller deflection value;

KFriclis a predetermined constant factor representing twist induced the friction between the loaded surface of the tested article and the loading surfaces of first and second working elements72,90having a corresponding influence to the larger deflection value;

Then, on the basis of the above error estimates, a corrected differential value is derived from the nominal deflection Δdnvalue as follows:
Δd=Δdn−ErDl+ErDs(9)

Then, the computer proceeds with calculation of a raw modulus of elasticity for the tested article according to the following relations:

S is the span (in cm) extending between the load bearing surfaces82of each pair of rails78,78′ and80,80′;

I is the inertia modulus value for a tested piece having rectangular section;

W is the transverse width dimension (in cm) of the tested piece; and

T is the thickness dimension (in cm) of the tested piece.

From the raw modulus of elasticity obtained, the computer program then applies dynamic and static edge corrections based on the relation existing between dynamic and static edge bench testing results, characterizing the mechanical stress behavior of the specific type of article being tested (i.e. 2×3, 2×4 pieces of lumber), for obtaining an modulus of elasticity estimation that could be compared to reference data obtained from standard static bench testing. Such relation may be expressed as follows:
E=KStat×KDyn×RawE
wherein

KDynis a factor characterizing the relation between dynamic and main surface-based static testing results;

KStatis a factor characterizing the relation between main surface-based and edge-based static testing results.

Such relation may be experimentally established by testing first a batch of pieces using a standard edge testing static bench, on the basis of a known Standard such as NLGA SPS-2, SPS-3 as well known in the art, which pieces are classified by comparing the standard edge-based modulus of elasticity values obtained with predetermined ranges defining a group of selected standard MSR classes, for example a group of three selected MSR classes. The same batch of pieces is also tested using a standard bench capable of applying load onto the main surfaces of the lumber pieces, to obtain surface-based modulus of elasticity values that can be associated with the standard edge-based modulus of elasticity values. The same batch of pieces is further tested according to the procedure described above to obtain raw modulus of elasticity RawE values that can be associated with the standard edge-based and main surface-based modulus of elasticity values. Average values associated with each MSR class considered are then computed for the raw modulus of elasticity as well as for associated main surface-based and edge-based modulus of elasticity values. From the resulting average values, the dynamic correction factors as well as static correction factors for each type of article involved (i.e. 2×3, 2×4 pieces) are calculated. The above procedure may be repeated with additional groups of selected MSR classes so as to establish the correction factors for a complete set of MSR classes, as given in the exemplary table shown in the displayed screen ofFIG. 12. To perform calculation of the resulting net modulus of elasticity value E for a given raw modulus of elasticity RawE value, the computer relies on such table to select the more appropriate values of dynamic and static correction factors, which can be conveniently factor values associated with the closest AverageE value given in the table. The computer program then compares the modulus of elasticity E value as estimated for each tested article with predetermined reference ranges data defining the set of standard MSR classes, for assigning classification data to the tested article accordingly. Such reference ranges data are given in the exemplary table shown in the displayed screen ofFIG. 11, wherein the minimum threshold value associated with each MSR class listed has been given the average value as established by the MSR Standard for each MSR class, to ensure that no more than 5% of the classified pieces are over-graded.

Finally, the tested piece of lumber24is further advanced through the action the catch blocks38past the output guiding surface152of second working element90while intersecting the detecting beam of the photo-sensitive cell228causing the latter to transmit through line231a control signal to the PLC200indicating that the controller200can be set to activate a selected ink nozzle provided on the printing device210when the tested piece of lumber24passes thereunder. To perform classification, the computer program compares the resulting net E with the threshold value given in the table as displayed on the screen ofFIG. 11which is associated with the MSR class representing the highest quality amongst selected MSR classes. If the current tested piece does not comply with the requirement of such highest quality MSR class, i.e. the resulting E has a lower value compared to the threshold value established for such higher rank class, the computer program makes a further comparison with the threshold value associated with a following MSR class of a lower quality, and the process is continued until the threshold value for the tested piece is found greater than the threshold value of such following MSR class. In cases where the E value for a particular piece is found to be lower than any of threshold values associated with the selected MSR classes, such piece is considered as unclassified and rejected accordingly. After a tested piece has been assigned classification data, the computer software generates a control signal for the PLC200via a selected one of lines246,247,248corresponding to the classification data assigned to the tested piece, which PLC200stores such control signal for activating a corresponding valve provided on the printing device210which is in fluid communication with a corresponding tank filled with ink of a specific color, following an indication from the computer190that a presence detecting signal has been received from PSC228. It is pointed out that the position of PCS228along conveying path76as well as the position of the nozzles provided on the printing device210are chosen in such a manner that the computer software is capable of completing E calculation before the tested piece reaches the printing device210, provided the distance between PCS226and printing device210is within the spacing between two successive transverse series of catch blocks38as shown inFIG. 2.

Regarding the tare monitoring function performed by the computer program, the control signal generated by conveyor displacement encoder40and first PSC216are used by the computer190to verify if the apparatus is running while a next piece to be tested is not present in conveying position against a following series of transverse catch blocks38. If the apparatus is free-running during a period of time exceeding a predetermined duration, the computer software starts a tare estimation subroutine by performing data acquisition of a predetermined number of measurement samples, converts the mean load measurement values in pound unit, and then makes a verification of the tare value for each load cell78,78′,80,80′ by comparing the measured value with a predetermined reference value. If the calculated deviation is higher than a predetermined maximal tare error value, the computer program increments a tare error counter, a corresponding tare error signal is sent to the master PLC244of the plant, and the classification process may be interrupted depending upon a maximum error as set by the operator is reached. Whenever PSC216detects that a next piece is incoming while the tare verification process is in progress, the subroutine is interrupted to return to the normal load measurement mode. The accumulated number of tare errors detected is preferably displayed on the computer screen as shown inFIG. 8.

The computer is also preferably programmed to continuously monitor the status of each of PSCs216,217,218and226,227,228used as first and second presence sensors. The program cumulates the number of signal raising fronts generated by each PSC and stores such number in a FIFO dedicated to each PSC. The program calculates the deviation between maximum and minimum numbers of signal transition observed for all PSCs and compares such deviation value with a predetermined maximum deviation threshold to generate an error indicative signal sent to master PLC244, and the classification process may be interrupted according to criteria set by the operator. The error signal is also used by the computer190to display a piece of lumber detection error as shown in the computer screen illustrated inFIG. 8.

The computer190is further programmed to perform monitoring of overload detecting limit switch138,138′ and144provided on the apparatus20. The limit switches138,144are normally in a “on” status indicating that the corresponding working elements72,90are adequately maintained in their respective substantially static positions when the pieces of lumber24are traveling through the apparatus. Whenever one of working element72or90departs from its corresponding static position by a first or second predetermined overload threshold as a result of significant departure of the article from the normal conveying position against catch blocks38, a corresponding control signal is generated by a corresponding one of limit switches138,144through either lines232or233depending on which working element has been displaced, causing the computer190to cancel the derivation of the modulus of elasticity E for any piece of lumber24located within the measuring zone defined by working elements72and90. Conveniently, the first and second threshold may be preset to a same threshold value as desired. The computer program cumulates the number of working element displacements that have occurred when a predetermined number of last tested pieces, ex. 50 pieces, have sequentially passed through the apparatus, by incrementing a counter and storing the event in a FIFO, the FIFO being decremented whenever data is read out from the FIFO. Whenever the displacement rate exceeds a predetermined maximum overload value, such information is displayed in the computer screen illustrated inFIG. 8. When an overload detection error is observed, a control signal is sent to the master PLC,244, and the classification process may be interrupted depending upon the criteria set by the operator. More specifically, the additional limit switch148associated with the first working element72generates a control signal transmitted through line234that is received by the PLC200, whenever the working element72substantially departs its static position by a predetermined overload threshold greater than the first overload threshold, causing the PLC200to generate a control signal addressed to computer190through line143, which PLC200in turn commands the first and second displacement mechanism98,98′ provided on first and second deflecting units52,54to move respective first and second working elements72,90from respective first and second static position shown inFIG. 2to respective retracted positions as shown inFIG. 6. Furthermore, the computer190interrupts the classification process while a corresponding interrupted operation indicative signal is sent to master PLC244through line241. In a similar way, the PLC200lifts deflecting units52,54to their respective retracted positions shown inFIG. 6whenever the PLC200receives from upstream presence detector236through line240a signal indicating that an incoming piece of lumber24is not in proper conveying position against adjacent catch blocks38. While deflecting units52,54may be manually returned to their respective first and second static positions shown inFIG. 2using a manual selector (not shown) provided on the apparatus, the apparatus preferably uses the displacement indicating signal generated by the encoder40and continuously sent to the PLC200through line242, to verify that the transverse series of catch blocks38associated with the improperly positioned piece at the origin of the actual or expected overload error condition has been displaced beyond the load applying zone of the second deflecting unit54, and to command PLC200to move back first and second displaceable mechanisms98,98′ so as to move first and second working elements72,90from their respective retracted positions to respective first and second static positions shown inFIG. 2. The computer190also generates a heartbeat binary signal toward the master PLC244through line243. The value of such control binary signal periodically changes every few seconds so that when the master PLC244does not detect a signal transition after a predetermined duration, the apparatus20is considered as being in an “not ready” mode. Furthermore, the computer190may transmit error indicative signals to the master PLC244through a further line249whenever a problem requiring operator intervention is observed. The computer is also programmed to store in computer memory measurement historical data for a predetermined number of last tested pieces. Typically, for each tested piece, the stored data includes testing date and hour, net load NetLoad[E] value for each load cell, differential load ΔLoad value, resulting modulus of elasticity E and the MSR class assigned to the tested piece. Furthermore, for a given batch of tested pieces, the program stores the current number of pieces for which data has been stored and distribution percentage associated with each MSR class. The load applying force delivered by each pneumatic actuator108,108′ can be adjusted through corresponding settings made at PLC200as commanded by computer190through control signals transmitted via line143, which indicate in the present example whether 2×3 or 2×4 pieces of lumber are being tested. PLC200sends a corresponding pressure level indicative signal to pneumatic servo regulators210,212through control lines202,204. Typically, the pressure level applied to the first actuator108may vary from about 24600 kg/m2for a 2×3 piece of lumber, to about 35150 kg/m2for a 2×4 piece of lumber, while the pressure level applied to second actuator108′ may vary from 31600 kg/m2for a 2×3 piece of lumber to about 42200 kg/m2for a 2×4 piece of lumber. A predetermined pressure level is further stored in PLC200to send corresponding pressure level control signals whenever valves207,209are activated to cause first and second actuators108,108′ to lift first and second deflecting units52,54in the respective retracted position. The computer190receives from PLC200through line145a further signal whenever the PLC200is manually operated to lift deflecting units52,54, as well as an echo running conveyer signal through line149. A preset pressure level applied to actuators108,108′ to lift both deflecting units52,54is typically of about 63300 kg/m2. It is pointed out that for security purposes, the computer is also programmed to ensure that deflecting units52,54are never automatically raised in their respective retracted position when the displacement encoder40indicates that the conveyor system is not running.

Referring now toFIG. 8, a computer screen corresponding to a normal mode of operation of the stiffness testing apparatus according to the invention is illustrated, wherein a “On /Off” button101can be activated by the operator through the keyboard198provided with computer190so as to selectively switch the apparatus between running mode according to which testing are performed on pieces of lumber as conveyed through the apparatus, and a stop mode enabling the operator to set classification parameters, start a tare calibration procedure, or obtain perform dynamic analysis as later explained in detail. As shown inFIG. 8, the window103disposed under heading “Sizes” provides an indication of the type of pieces currently being processed. Typically, four types of piece of lumber can be handled, namely 2×3 regular, 2×3 oversized, 2×4 regular and 2×4 oversized. Three light pilots251are preferably displayed to indicate that logic input reading, piece classification and logic output management as background running tasks are being performed normally. The “status” window105is used to indicate whether the apparatus works normally or to indicate one or more abnormal detected conditions such as lifted deflecting units, tare error, piece of lumber detection error, overload detection error or stop status. To the right of the “status” window105, a “Work in Process” window107displays classification results according to selected MSR classes, wherein quantity of pieces of lumber classified according to each selected MSR class is indicated along with corresponding percentage distribution. A further window109displays the testing result obtained for the “last piece” classified, namely differential load measured, the net modulus of elasticity E and the specific MSR class that has been assigned to this last piece. A last window appearing at the bottom of the screen shown inFIG. 8gives errors status and current counts for tare, piece of lumber detection and overload detection functions as explained before. Whenever the number of abnormal events related to one of these error categories exceeds a corresponding preset threshold, the status indicator switches from “OK” to “alarm” for a preset duration as set by the operator. Furthermore, for some temporary detected events such as limit switch activations that do not justify processing interruption, a corresponding massage can be temporarily displayed as such condition exists.

Turning now toFIG. 9, a parameter setting screen as generated by the computer program is illustrated, enabling the operator to assign desired values for a number of parameter categories that can be accessed through corresponding number of sub-screens as illustrated inFIGS. 9 to 12. InFIG. 9, MSR classes or grades under processing can be selected by the operator through window111on the basis of the set of MSR classes or grades that has been previously defined such as listed inFIG. 11. In the example shown, up to three selected MSR classes in process can be entered by the operator, each of which being associated with an ink tank that can be selected through window113whenever printing is required for these specified MSR classes. At the bottom window117of the screen shown inFIG. 9, the specific size for pieces of lumber under processing can be selected by the operator amongst the types listed inFIG. 11.

Turning now toFIG. 10, a further sub-screen allows the operator to reset the various counters as well as modify some operating conditions according to which classification is performed, and to set a desired action to be performed by the computer190whenever a particular alarm is activated. A button “Piece Count” at252allows the operator to reset to zero the total number of classified pieces as well as corresponding distribution percentage values associated with the specific MSR class displayed on the normal mode screen as shown inFIG. 8. A button “Tare errors” at253allows the operator to set the tare error counter to zero. A button “Error Lbr Det.” at254allows the operator to reset the piece detection error counter to zero. A button “Overloads” at255allows the operator to reset the overload error counter to zero. Associated with buttons253,254and255are a set of windows256,257and258which allow the operator to select an specific action to be taken by the computer program when an alarm is activated, namely: displaying an error message and/or switch to an “off” classification status.

Turning now toFIG. 11, the sub-screen shown allows the operator to modify parameters associated with MSR grades and lumber Sizes to be processed, provided the apparatus is set to “off” mode of operation, and an appropriate password is entered via input window259, to ensure that such basic parameters are set by an authorized person. As explained before, at the left portion of the screen, the definition of pre-established MSR grades with associated minimum threshold values are displayed. At the right portion of the same sub-screen, the various sizes of the predetermined types of pieces are displayed, which sizes are considered in the calculation of the modulus of elasticity E or each piece of lumber as explained before.

Turning now toFIG. 12, a last sub-screen under the heading “Parameters” is shown, which can be used by the operator upon entry of an appropriate password through window119to modify correction factors employed by the computer program to calculate the net modulus of elasticity E for each piece, provided the apparatus is set to “off” mode and that an appropriated password is entered. As explained before, a list of predetermined averageE values is used by the computer to determine which ones amongst static correction edge factor KStatvalues and dynamic direction factor KDynwould be the best pair of factor values to use according to the raw modulus of elasticity RawE value obtained for a given piece tested, in a calculation of a net modulus of elasticity E value which can be compared to standard reference classification data.

Referring now toFIG. 13, a further screen associated with heading “System Check-up” allows the operator to visualize the operating status of the main components of the apparatus. At the left of the screen, a window260provides an indication of tare level fluctuations that usually occur as the apparatus is running. Through window260, the operator is allowed to update current tare values set in the apparatus provided the latter is set to “off” mode. To the left of window260, a first column at125gives values of gross tare deviation from zero as measured for each load cell (in pound). A next column127gives tare correction values as applied by the computer program to the gross load cell deviation to obtain net values as indicated in a third column129of window260. A new, updated correction value for a specific load cell can be set and stored in the computer memory by activating a corresponding on of buttons “Tare” as shown to the right of window260. A first column131displayed in a second window261allows the operator to visualize the current logic “On/Off” status of the various logic inputs received by the computer190, namely, from PSCs216,217,218,226,227,228(1–6), limit switches138,144,148(1–3), PLC line145indicating manual lifting, and conveyer signal from PLC200. A second column135displayed in window261gives the current cumulative values generated by the input counters associated with each PCS, as well as first and second limit switches138,144. Normally, the reading of input counters associated to the PSCs should be at a maximum value if all transverse series of catch blocks are loaded with pieces of lumber, while the input counters associated with first and second limit switches shall be near zero. A third window262allows the operator to visualize the current status of the various logic outputs of computer190as transmitted to the master PLC244and local PLC200, as explained before. Associated with the logic output displayed a series of “On/Off” buttons137that can be selectively activated provided the apparatus is set to “Off” mode, for checking if the selected logic output functions normally. Optionally, the computer program may display a chart (not shown) representing curves of load measurement signal values as a function of time over a predetermined duration corresponding to a complete testing cycle for a given piece of lumber processed, with curves of current logic states of the PLCs and limit switches, to verify synchronicity between load measurement signals and control signals. Such optional function may be useful to adjust the positions of the PSCs and limit switches on first and second deflecting units.

Referring now toFIG. 14, the article testing apparatus according to the second preferred embodiment of the invention and as generally designated at20′ is especially designed to provide reliable stiffness measurement on elongated articles such as pieces of lumber exhibiting different mechanical behavior depending on the feeding orientation through the testing apparatus, mainly due to internal, non-isotropic structure of most wooden materials forming pieces of lumber. In accordance with the second embodiment, there are provided first and second article bearing units capable of contacting first and second article surfaces respectively, the first deflecting unit cooperating with the first article bearing unit for applying the first thrust against the loaded area of the second article surface, while the second deflecting unit cooperates with the second bearing unit for applying the second thrust against the loaded area of the first article surface. The load measuring unit is capable of generating signals indicative of respective magnitudes of the first and second thrusts, from which signals the data processing device is responsive to derive an indication of the stiffness of the article, considering also the first and second deflection magnitudes, as will be explained later in more detail. Since the second embodiment that will now be described makes use of numerous same components as compared to the first embodiment described above with respect toFIGS. 1 to 13, such same components will be designated using same corresponding reference numbers in the following description, and it can be appreciated that the detailed structure and operation of such common components are not needed to be repeated so as to enable a person skilled in the art to reduce the second embodiment to practice in view of the present specification as a whole. The apparatus20′ is adapted for use with the conventional transverse conveying system22for transporting a plurality of articles such as pieces of lumber24each having opposed main bottom and top surfaces26,26′, which pieces of lumber24move along a predetermined path through apparatus20′ in a conveying direction indicated by arrow28substantially transverse to testing axis30associated with each piece of lumber24along which stiffness will be estimated as described below. The apparatus20′ further includes first and second deflecting units generally designated at52,54′ as better shown inFIG. 15, in view ofFIGS. 17 and 18. The first deflecting unit52is adjustably secured to the frame overhead beams48using an overhead mounting unit having top mounting plate56′ being maintained in a suspended position using a pair of displaceable attachments58, with a pair of parallel vertical walls60,60′. As shown inFIG. 15, secured to top mounting plate56′ is a bottom mounting plate62to which is in turn secured the first deflecting unit52using a plurality of pivot members pairs64,65,66attached to bottom mounting plates62. The first deflecting unit52includes a first working element72capable of being disposed in a first, substantially static position shown inFIG. 15relative to an article conveying path represented by axis76and as also presented inFIG. 16Bby an axis73which is coplanar with axis76shown inFIG. 15. It can be seen fromFIG. 15that the first position has been conveniently chosen to be in substantial alignment with the conveying path76so as to provide a first deflection value d1as shown inFIG. 16Band as will be explained later in more detail. The apparatus20′ further includes a first article bearing unit including first and second pairs of rails78,78′ as shown inFIGS. 15 and 16Afor contacting the bottom surface26of each piece of lumber24under test at two spaced apart portions thereof, as better shown inFIG. 16A. The rails78,78′ define load bearing surfaces extending substantially parallel to the conveying direction indicated by arrow28, for contacting the bottom surface26at spaced apart portions77,77′ thereof. The rails78,78′ are provided with load bearing surfaces82for receiving the bottom surface26of each piece of lumber24when the latter moves past a first location along the conveying path76as shown inFIG. 15, at which first location the first deflecting unit52is disposed to face the top surface26′ of each piece of lumber24under test.

Referring again toFIG. 15in view ofFIG. 14, the first working element72, when being disposed in the first static position relative to the article conveying path76and cooperating with rails78,78′ of the article bearing unit, is used to apply a first thrust against a loaded area84of the top surface26′ of piece of lumber24at an intermediary portion located between spaced apart portions77,77′ as piece of lumber24is moving through the apparatus20′, as better shown inFIG. 16A. The thrust applied against loaded area84produces a deflection d1of the piece of lumber24of a first magnitude extending along a first deflection axis86perpendicular to conveying direction28and testing axis30as shown inFIG. 16Ain view ofFIG. 16B. Turning back toFIG. 14, secured to the conveyer frame beam32′ through mounting plate33, the second deflecting unit54′ is disposed at a location downstream from the corresponding location of first deflecting unit52, to receive a piece of lumber24leaving the thrust applying area defined by the first working element72provided on first deflecting unit52. The second deflecting unit54′ includes a second working element90′ capable of being disposed in a second, substantially static position shown inFIG. 15relative to conveying path76′ and cooperating with a second pair of spaced apart rails80,80′ provided on a pair of corresponding spaced apart pushing devices264,264′ as part of a second article bearing unit and as better shown inFIG. 16A, which devices264,264′ are disposed to respectively face the top surface26′ of the article at spaced apart portions77,77′ thereof as also shown inFIG. 16A. The second working element90′ is used to apply a second thrust against a loaded area94′ of bottom surface26of piece of lumber24at intermediary portion thereof between spaced apart portions77,77′ as the piece of lumber24further moves through the apparatus20′, and as also presented inFIG. 16Bby an axis73′ which is coplanar with axis76′ shown inFIG. 15. The second thrust applied against loaded area94′ produces a deflection d2of piece of lumber24of a second magnitude extending along a deflection axis substantially parallel to first deflection axis86represented inFIG. 16A. Deflection values d1and d2, which are of opposite signs as shown by lengthwise profiles of piece of lumber24as represented by dotted lines75,75′ respectively, are preferably set to a same predetermined magnitude, since bow and warp generally do not exhibit predominant orientation amongst pieces of lumber as they are fed to the testing apparatus. It is pointed out that the schematic deflection representation shown inFIG. 16Bemploys a scale that has been intentionally amplified as compared with actual deflection imparted to a tested piece of lumber for the purpose of illustration. As will be explained later in more detail, absolute values of deflection d1and d2are used to derive a resulting deflection parameter D expressed as follows:
DT=|d1|+|d2|  (14)
It is to be understood that according to the second preferred embodiment of the invention, the deflecting unit52has been chosen to receive the piece of lumber24first so as to produce a deflection of a first, negative magnitude as opposed to positive magnitude d2obtained when the piece of lumber24passes over the second deflecting unit54′ as located downstream from first deflecting unit52. For so doing, first and second pairs of rails78,78′ and80,80′ are disposed in a spaced relationship in the conveying direction so their respective load bearing surfaces82sequentially receives corresponding first (bottom) and second (top) contacted surfaces26,26′ of article24when it moves past first and second locations along the article conveying path. However, the respective position of first and second working elements72,90′, and associated bearing units may be alternatively set so that the deflection of positive magnitude d2be measured first, followed by the measurement of the deflection of negative magnitude d1. Moreover, while first and second deflecting units52,54′ are preferably aligned in a spaced apart relationship along the conveying direction so to apply their respective thrust on a same loaded area, other configurations may involve distinct loaded areas, insofar reliable measurements are obtained.

Turning now toFIG. 17in view ofFIG. 5, it can be seen that the first deflecting unit52provided on the second embodiment includes a displaceable mechanism98essentially identical to the one included in the first deflecting unit provided on the first embodiment that has been described in detail above, and is adapted to perform the same function of holding the first working element72, and more particularly of providing selective controlled movement of the working element72between the first substantially static position as described above with respect toFIGS. 15 and 16Brelative to the conveying path indicated by axis76,76′ onFIG. 15, and a retracted position wherein the first working element72is away from the article conveying path to prevent obstruction thereof. The displaceable mechanism98may be provided with a pair of tension springs71extending between a member79secured to the bottom mounting plate62, and the first working element72, for ensuring that the latter maintain its working position during operation. It can be appreciated that similar springs may be advantageously installed on the deflecting unit52provided on the first embodiment as described above in view ofFIG. 5. Turning again toFIG. 17, the first working element72defines a loading surface124extending substantially parallel to the conveying path when disposed in the first static position. Preferably, the dimension of the loading surface124parallel to the conveying direction is larger than the transverse dimension of the piece of lumber24at the intermediary portion thereof extending between end portions77,77′ shown inFIG. 16A, so that the loaded area84substantially extends over the whole transverse dimension while the thrust magnitude indicating signals are generated, in a same manner as explained before in respect of the first embodiment. It can be seen fromFIG. 17that the working element72preferably defines an article feed guiding surface150generally extending toward the loading surface124according to an appropriated acute angle β1with respect to the conveying path at76, according to a similar design as applied to the first working element of the first embodiment shown inFIG. 5. However, the first working element52according to the second embodiment is further provided with a symmetrical article output guiding surface152′ presenting an angle θ1with respect to conveying path at76the value of which angle θ1being typically set to about 15° according to a similar design as applied to the second working element90provided on the first embodiment shown inFIG. 5. Such output guiding portion is provided since first and second deflecting units52,54′ are not located in adjacent relationship according to the second embodiment. The loading surface124provided on first working element72preferably has first and second symmetrical portions126,128also extending toward respective spaced apart portions77,77′ of piece of lumber24transversely to the conveying direction according to a symmetrical angle α1defined by axis136onFIG. 17which extends from surface loading portion128and with respect to an axis30′ parallel to testing axis30shown inFIG. 16A, which symmetrical angle α1being substantially proportional to the first deflection magnitude d1along axis86ofFIGS. 16A and 16B, which is parallel to axis132,134shown inFIG. 17. Similarly to the first embodiment, the first displaceable mechanism98is provided with a third position sensor in the form of a third limit switch148for generating a third control signal whenever the first working element72substantially departs from the first static position by a third predetermined overload threshold greater than the above-mentioned first overload threshold as a result of the departure of the piece of lumber24from its normal conveying position on rails78,78′.

Turning now toFIG. 18, the second deflecting unit54′ provided on the second embodiment includes a further displaceable mechanism99for holding the second working element90′. The mechanism99is preferably of a two-position latch type that is selectively controllable to move the second working element90′ between the second, substantially static, locking position relative to conveying path76′ as shown inFIG. 15and a retracted, release position (not shown) wherein the second working element90′ is away from the article conveying path to prevent obstruction thereof, in case of abnormal feeding position of article or for maintenance purpose as will be explained later in more detail. The displaceable mechanism99preferably comprises a pair of latch assemblies151secured to the mounting plate33as also shown inFIG. 14, each assembly151comprising a lifting platform153secured to a first pivoting element155that is in turn coupled to a linking element157having an ear159pivotally attached to the piston161of a hydraulic actuator163secured to the body of the corresponding latch assembly151. Each hydraulic actuator is fed by fluid pressure through hydraulic lines (not shown) connected to the output of a reversing valve266shown inFIG. 15that is controlled by PLC200through control line265. The PLC200is also used to send through line269an enabling signal to the computer190whenever the second working element90′ in its working position. The linking element157provided on each latch assembly151is also coupled to a second pivoting element165also secured to the body of the corresponding assembly151. Mounted on the lifting platform153is the second working element90′ in the form a multi-level rail defining a receiving portion167, a setting portion169and a loading surface171extending substantially parallel to the article conveying path when disposed in the second substantially static position. Preferably, the dimension of the loading surface124parallel to the conveying direction is larger than the transverse dimension of the piece of lumber24at the intermediary portion thereof extending between end portions77,77′ shown inFIG. 16A, so that the loaded area84substantially extends over the whole transverse dimension while the thrust magnitude indicating signals are generated, in a same manner as explained before in respect of the first embodiment. Turning back toFIG. 18, the second working element90′ further defines an output portion173in the form of a declining ramp, causing release of the second thrust applied against the loaded area84shown inFIG. 16A, as the piece of lumber24further moves through the apparatus, toward the second deflecting unit that will be described later. The second working element90′ is preferably mounted onto the lifting platforms153using a pair of tilting devices175,175′ allowing position adjustment of the loading surface171with respect to the conveying path in direction28. Tilting devices175,175′ include conventional rotary-to-linear actuators177,177′ coupled to linear tooth racks (not shown) secured to corresponding platforms153, and a pair of displaceable members (not shown) to which front and rear portions of the working element90′ are respectively attached. The selective operation of tilting devices175,175′ by the operator provides the desired position adjustment.

Turning back toFIG. 15, the apparatus20′ according to the second embodiment further includes first and second load measuring units generally designated at179,181and respectively associated with first and second deflecting units52,54′. The first load measuring unit179is formed by a pair of right and left sides subunits183,183′ mechanically coupled to first and second rails78,78′ of the first bearing unit as shown inFIG. 14, and the second measuring unit181is formed by a similar pair of right and left sides subunits185,185′ mechanically coupled to the pushing devices264,264′ provided on the second bearing unit as will be described later in more detail. Load measuring units179,181are capable of generating signals indicative of respective magnitudes of first and second thrusts as applied by first and second deflecting units52,54′ as will be later explained in more detail.

Turning now toFIG. 19, first (right) rail78as part of the first article bearing unit is shown with a corresponding load measuring subunit183according to the second embodiment. Since subunits183,163′ are identical, the description below will be limited to the right side subunit183, which preferably makes use of a single load sensor using load cell156having load coupling members160receiving rail78in rigid connection thereto. It can be seen that the load measuring subunit183does not necessarily require that the guiding means be adjacently disposed with respect to rail78in an offset, parallel configuration provided on the first embodiment and depicted inFIG. 7. As shown inFIG. 19, a linear configuration may be employed wherein rail78is aligned with the guide member164, using a load cell supporting plate166of an appropriate design. The guide member164is rigidly secured to conveyor frame beam32″ in a same manner as described before in respect of the first embodiment in view ofFIGS. 4 and 7. However, it can be seen fromFIG. 14that the linear configuration allows to use a same design for load measuring subunits183,183′ and guide members164,164′, provided specific transverse angular profile is adapted. It can be seen fromFIG. 19in view ofFIG. 14that each guide member164,164′ is disposed relative to the article conveying path represented by axis76inFIG. 17in the conveying direction at28to set the piece of lumber24on the load bearing surface82of rails78,78′ as the piece of lumber24moves through the apparatus20′. The elongate guide members164,164′ are disposed in a parallel spaced relationship and longitudinally extend in the conveying direction28as shown inFIG. 14. As explained before in respect of the first embodiment in view ofFIGS. 4 and 7, each load bearing surface82defined by rails78,78′ longitudinally extends along the conveying path in conveying direction28, while extending toward the intermediary portion of the piece of lumber24transversely to the conveying direction according to a angle γ1with respect to the testing axis30′ which is parallel to testing axis30ofFIG. 16A, which angle γ1is substantially proportional to the first deflection magnitude d1for rails78,78, corresponding typically to an angular value of about 1°. Such angular feature allows each load bearing surface82to follow the shape of corresponding contacted article surface when the article moves past the first thrust applying location along the article conveying path. Each guide member164,184′ has a guide element172′ defining an article setting portion180disposed upstream corresponding rails78,78′ in an adjacent relationship therewith to set a piece of lumber onto load bearing surface82when the piece of lumber moves past the location of first deflecting unit52shown inFIG. 14. As shown inFIG. 19, the guide element172′ has a receiving portion176disposed upstream article setting portions180. The setting portion180of guide element172′ extends toward the intermediary portion of piece of lumber24transversely to the conveying direction28according to angle γ1with respect to axis30′. Each guide member164,164′ includes a further section187having a declining ramp portion191disposed to receive each article leaving the load bearing surface82, followed by a lower level portion193providing sufficient clearance to the article end portions as the article reaches the second location along the conveying path where it is subjected to the second thrust applied by the second deflecting unit54′ cooperating with the pushing devices264,264′ provided on the second bearing unit. As also shown inFIGS. 15 and 19, the testing apparatus20is preferably provided with a profile sensing device conveniently formed by a pair of presence sensors195,195′ disposed within the article conveying path for providing a signal indicative of the twist characterizing the article, whose level may have an effect on the stiffness measurement derived by the data processing device as will be explained later in more detail. Each presence sensor195,195′ is disposed at the further section187of a corresponding one of guide member164,164′ and includes a body197secured to the guide member, a pneumatic cylinder199provided with a piston201connected to a movable platform213defining a contacting member215. Each cylinder199is fed by fluid pressure through pneumatic lines (not shown) connected to the output of a reversing valve267shown inFIG. 15that is controlled by PCL200through control line268, allowing the contacting member215to be moved between an upper, presence detecting position and a lower, disable position. A guide rod cooperating with a corresponding bore extending through the body197allow a vertical displacement of the platform with respect to the body197, while maintaining alignment of the platform with respect to the guide member section187in the conveying direction. Disposed adjacent the piston to sense the stroke thereof is a displacement sensor250such as ultrasonic probe model no. M18C2 from Banner Engineering carp. (Minneapolis, Minn, U.S.A.) for generating a twist indicating signal toward the computer through line263′, as also shown inFIG. 15on which are illustrated a further line263coming from presence sensor195associated with guide member164, along with lines192,192′ and194,194′ sending to computer190the applied thrust magnitude indicative signals generated by pairs of load cells156as described before, as well as by pair of load cells158′ as part of the second article bearing unit that will be now described in more detail.

Referring now toFIG. 20, the pushing device264is shown, which is identical to the pushing device264′ completing the second article bearing unit. The pushing device264includes second displaceable mechanisms98′,98″ of a similar design as compared with the displaceable mechanism98provided on the deflecting unit52described hereinabove in view ofFIG. 17, wherein the actuator108′ is preferably mounted under the bottom plate56′ secured to top mounting plate56″,62′ through a cut provided thereon as better shown inFIG. 14, to present a higher rake within the vertical plane, thereby increasing the effective thrust applying capacity of the pushing device264. The pneumatic actuator108′ is also provided with a mechanism123′ for adjusting the limit stroke of piston110′ using rotary handle125′ provided thereon, allowing accurate adjustment of the thrust applying position of the pushing device264. It can be seen fromFIG. 20in view ofFIG. 17that the double member100′ has been strengthened accordingly as compared with the double member actuator100′ provided on the mechanism shown inFIG. 17. As part of the second article bearing unit, the displaceable mechanisms98′,98″ are used to hold a second pair of spaced apart rails80,80′ as load bearing elements defining load bearing surfaces82extending substantially parallel to the conveying direction for contacting the second, top article surface at spaced apart portions77,77′ thereof, as explained above with reference toFIG. 16A. As mentioned before with respect toFIG. 15, the second measuring unit181is formed by a pair of right and left sides subunits185,185′ mechanically coupled to the pushing devices264,264′, and includes a pair of load sensors158operatively coupled to the pushing devices by incorporating them within a compartment defined in a end support member93pivotally connected to the double members100′,116′ provided on each mechanism98′,98″. Each subunits185,185′ includes a load coupling members162′ for holding rail80in rigid connection thereto. Also as part of the load measuring are guide means in the form of input and output guide members87,87′ provided on each subunits185,185′ and respectively disposed upstream and downstream corresponding rails80,80′ in an adjacent relationship therewith along the article conveying path to set the article on the load bearing surfaces82, and to guide the article out of the testing area as the article moves forward. The input guide member87preferably defines an article feed guiding surface150′ generally extending toward the load bearing surface82according to an appropriated acute angle β2with respect to the conveying path at76′, while the output guide member88symmetrically defines an article output guiding surface152′ presenting an angle θ with respect to conveying path at76′ the value of which angle θ being typically set to about 15°. Each load bearing surface82defined by rails80,80′ longitudinally extends along the conveying path indicated by axis76′, while extending toward the intermediary portion of the piece of lumber24transversely to the conveying direction according to a angle γ2with respect to the testing axis30″ which is parallel to testing axis30ofFIG. 16A, which angle γ2is substantially proportional to the second deflection magnitude d2for rails80,80′, corresponding typically to an angular value of about 1°. As explained before, such angular feature allows each load bearing surface82to follow the shape of corresponding contacted article surface when the article moves past the second thrust applying location along the article conveying path. It can be appreciated fromFIGS. 19 and 20in view ofFIG. 14that first and second pairs of spaced apart guide elements180and87are disposed to sequentially set the article on corresponding load bearing surfaces82when the article moves past the first and second thrust applying locations along the article conveying path. Similarly to the displaceable mechanisms98′ described above in view ofFIG. 5, the displaceable mechanisms98′,98″ shown inFIGS. 15 and 20are selectively controllable to move the support member93and rails80,80′ between a thrust applying position adjacent article conveying path indicated by axis76inFIG. 20and a retracted position similar to the position shown inFIG. 6with respect to the first embodiment, wherein sets of guide members87,88and each associated rail80,80′ are brought away from the conveying path to prevent obstruction thereof. As explained before with respect to the first embodiment, the second limit switch144generates a second control signal whenever the associated rail80,80′ departs from the thrust applying position by a second predetermined overload threshold as a result of the departure of piece of lumber24from its normal conveying position onto the rails80,80′ as shown inFIG. 15, the computer190being responsive to that second control signal to cancel the derivation of article stiffness indication in a same manner as explained before with respect to the first preferred embodiment. Moreover, the controller provided in the apparatus is responsive to the third control signal generated by the third limit switch148provided on the first mechanism described before in view ofFIG. 17, to cause the first displaceable mechanism98to move the first working element72from the first static position to its retracted position, and to cause each second displaceable mechanism98′,98″ to move each load bearing rail80,80′ from its working position to its retracted position. Preferably, second displaceable mechanism98′,98″ are respectively provided third and fourth position sensor in the form of further limit switches148′ as shown inFIG. 20, which cooperate with double-switch block140to generate fourth and fifth control signal whenever any of rails80,80′ substantially departs from their respective thrust applying positions by a further predetermined overload threshold greater than the above-mentioned second overload threshold as a result of the departure of the piece of lumber24from its normal conveying position in contact with rails80,80′. Furthermore, as described before with respect of the first embodiment in view ofFIG. 2, a presence sensor236disposed upstream from the first thrust applying location may be also used to detect any article significantly departing from the predetermined conveying position while moving in the conveying direction, to generate a further control signal directed to the controller, the latter being further responsive to that control signal to cause the first displaceable mechanism98shown inFIG. 17to move the first working element72from the first static position to its retracted position, to cause each second displaceable mechanism98′,98″ to move each corresponding load bearing rail80,80′ from its working position to its retracted position, and to cause the displaceable mechanism99shown inFIG. 18to move the second working element90′ from the second static position to its retracted position. Moreover, while deflecting units52,54′ may be manually returned to their respective first and second static positions shown inFIG. 15using a manual selector (not shown) provided on the apparatus, it preferably uses the displacement indicating signal generated by the encoder40and continuously sent to the PLC200, to verify that the transverse series of catch blocks38associated with an improperly positioned piece at the origin of the actual or expected overload error condition has been displaced beyond the load applying zone of the second deflecting unit54′, and to command PLC200to move back displaceable mechanisms98,98′ and99so as to move first and second working elements72,90from their respective retracted positions to respective first and second static positions and to move each load bearing rail80,80′ from its retracted position to its working position as shown inFIG. 15.

Prior to the operation of the apparatus20′, first and second static positions of first and second working elements72and90′ are respectively set using adjustment mechanism123provided on actuator108as shown inFIG. 17, and tilting devices175,175′ a shown inFIG. 18. An appropriate adjustment of the thrust applying position of the pushing device264is also made using mechanism123′ shown inFIG. 20. Typically, on the basis of equation (14) above, the working elements72,90′ are positioned so as to have a first deflection nominal value dn1=−1,9 cm and to have a second deflection nominal value dn2=1,9 cm to obtain a resulting value for DTclose to a nominal value Dn=3,8 cm, after applying correction factors as will be described later in detail.

The mode of operation of the second embodiment of the present invention is in most part identical to the operation mode explained before with respect to the first embodiment, with some variations due to the additional components provided at the second testing location, and due to the use of the profile sensing device. Referring toFIG. 19, after leaving the load bearing surface82of first pair of rails78,78′, the piece of lumber24reaches the declining ramp portion191to progressively enter within the thrust applying and load measuring zone defined by the second working element90′ of the second deflecting unit54′ and corresponding pair or rails80,80′ mounted on the pushing devices264,264′. Then, the piece of lumber24intersects the detecting beam of photo-sensitive cell226as part of the second presence sensor as explained before in view ofFIG. 2, causing the generation of a control signal sent to the computer190for triggering data acquisition of load measurement signals from the second pair of load cells158,158′ transmitted to the computer190through lines194,194′ as shown inFIG. 15. Simultaneously, the leading end of tested piece24reaches the front end of contacting member215provided on each presence sensor195,195′ as part of he profile sensing device and as shown inFIG. 19, which sensors195,195′ have been previously set by PLC200through line268to their presence detecting position as better shown inFIGS. 21A and 21B. It can be seen that the uppermost limit position of each contacting member215is initially set to ensure that every piece24makes contact with it, no matter its specific profile. In the example shown inFIG. 21B, it can be seen that the displacement induced by the article24to the contacting member215with respect to its reference initial level indicated in dotted lines, which displacement is associated with an extra thickness value corresponding to a low twist level, is not greater that threshold t under which the torsion level is not considered as significant, as will be explained later in more detail with reference to equations (26) and (27). Referring toFIG. 21B, it can be seen that the displacement or extra thickness t′ has a magnitude greater than threshold t, so that the resulting twist indication signal generated by the ultrasonic probe integrated in the profile sensor through lines263,263′ shown inFIG. 15, will be preferably used by the computer190to derive article stiffness indication, as will be now explained in detail. When data acquisition is completed, the computer program automatically starts calculation of the modulus of elasticity value associated with each tested piece of lumber24according to a process that will be now described below.

First, a mean load measurement value is calculated for each load cell as follows:

n is the number of load measurement data samples read;

Kkgis a predetermined factor (kg/Δvolt) for converting the measurement in kg unit;

Load is a corrected load measurement voltage generated by each load cell156as corrected by a predetermined offset value characterizing the load cell when unloaded.

Then, the obtained value for RawLoad[i] is preferably corrected using a predetermined tare correction value to compensate for the output level drift to which each load cell is subjected with time, the value of which can be measured when no load is applied to the load cell. The offset value can be established through an initial or periodic manual calibration procedure. The computer calculates a corrected or net load measurement value from the estimated tare value for each load cell of indicia i as follows:
NetLoad[i]=RawLoad[i]+Tare[i]  (16)

Then, the computer program calculates the load applied by each deflecting unit52,54′ as well as a total applied load value as follows:
NetLoadD1=NetLoad1+NetLoad2(17)
NetLoadD2=NetLoad3+NetLoad4−2*ThrustP(18)
LoadT=NetLoadD1+NetLoadD2(19)
wherein:

NetLoadD1is the net load value applied by the first deflecting unit52imparting the first, negative sign deflection magnitude d1; and

NetLoadD2is the net load value applied by the second deflecting unit54′ imparting the second, positive sign deflection magnitude d2;

ThrustP is the thrust value applied by each presence sensor195,195′; and

LoadTis the total applied load value.

On the basis of the above calculations, according to a similar approach used for the first embodiment, the computer preferably applies a correction to the nominal deflection values as set prior to the operation of the apparatus, to compensate the inherent deformation to which the whole structural components of the apparatus are subjected, such as flexion of load cells156,158, overhead beams48, first deflecting unit52and pushing devices264,264′ associated with second deflecting unit54′.

The correction is made on the basis of estimated deflection error values associated with first and second deflection values d1, d2as calculated as follows:

Kcell1is a predetermined constant factor (N*m) representing stiffness characterizing load cell156coupled to rail78and corresponding load measuring subunit183;

Kcell2is a predetermined constant factor (N*m) representing stiffness characterizing load cell156coupled to rail78′ and corresponding load measuring subunit183′;

InD1represents intrinsic deflection induced to first deflecting unit52when a piece is passing through the first testing location;

InD2LeftPushrepresents intrinsic deflection induced to left pushing device264when a piece is passing through the second testing location;

InD2Rightpushrepresents intrinsic deflection induced to right pushing device264′ when a piece is passing through the second testing location;

TwistD1represents deflection of the piece induced by its inherent twist when the piece is passing under thrust through the first testing location;

TwistD2represents deflection of the piece induced by its inherent twist when the piece is passing under thrust through the first testing location as estimated from thickness measurements provided by presence sensors195,195′;

KS1,1is a predetermined constant factor (N*m) representing stiffness characterizing the structural components of the frame including beams48just above the first deflecting unit52, when the latter is applying a thrust against a piece at the first testing location;

KS2Left,1is a predetermined constant factor (N*m) representing stiffness characterizing the structural components of the frame including beams48just above the first deflecting unit52, when the left pushing device264is applying a thrust against a piece at the second testing location;

KS2Right,1is a predetermined constant factor (N*m) representing stiffness characterizing the structural components of the frame including beams48just above the first deflecting unit52, when the right pushing device264′ is applying a thrust against a piece at the second testing location;

K1,1is a predetermined constant factor (N*m) representing stiffness characterizing the first deflecting unit52, when the latter is applying a thrust against a piece at the first testing location;

KS1,2Leftis a predetermined constant factor (N*m) representing stiffness characterizing the structural components of the frame including beams48just above the left pushing device264, when the first defecting unit52is applying a thrust against a piece at the first testing location;

KS2Left,2Leftis a predetermined constant factor (N*m) representing stiffness characterizing the structural components of the frame including beams48just above the left pushing device264, when the latter is applying a thrust against a piece at the second testing location;

KS2Right,2Leftis a predetermined constant factor (N*m) representing stiffness characterizing the structural components of the frame including beams48just above the left pushing device264, when the right pushing device264′ is applying a thrust against a piece at the second testing location;

K2,2is a predetermined constant factor (N*m) representing stiffness characterizing the first deflecting unit52, when the latter is applying a thrust against a piece at the first testing location, which factor includes stiffness characterizing load cells156coupled to rails80,80′ and corresponding load measuring subunits185,185′.

KS1,2Rightis a predetermined constant factor (N*m) representing stiffness characterizing the structural components of the frame including beams48just above the right pushing device264′, when the first defecting unit52is applying a thrust against a piece at the first testing location;

KS2Left,2Rightis a predetermined constant factor (N*m) representing stiffness characterizing the structural components of the frame including beams48just above the right pushing device264′, when the left pushing device264is applying a thrust against a piece at the second testing location;

KS2Right,2Rightis a predetermined constant factor (N*m) representing stiffness characterizing the structural components of the frame including beams48just above the right pushing device264, when the latter is applying a thrust against a piece at the second testing location;

EfThickLeftrepresents the effective thickness as measured by left presence sensor195as part of the profile sensing device;

RawThickLeftrepresents the raw thickness as measured by left presence sensor195as part of the profile sensing device;

NomThick represents a predetermined nominal value for the thickness of pieces under test;

NomWidth represents a predetermined nominal value for the width of pieces under test;

ExThickRightrepresents the extra thickness as measured by right presence sensor195′ as part of the profile sensing device;

RawThickRightrepresents the raw thickness as measured by right presence sensor195′ as part of the profile sensing device;

t is the predetermined threshold value under which twist is considered as non-significant;

TwistD2′ represents deflection of the piece induced by its inherent twist when the piece is passing without trust through the first testing location as estimated from twist module KTand related inertia module IT;

Δτ represents twist angle variation under thrust applied at the second testing location;

S is the span extending between the load bearing surfaces82of each pair of rails78,78′ and80,80′;

Then, on the basis of the above error estimates, a total net deflection value considering first and second deflections induced with applied corrections is derived as follows:
DT=dn1−ErD1+dn2−ErD2(32)
wherein:

dn1represents a predetermined nominal value (ex. 0.75 in) for the deflection induced by the first deflection unit52;

dn2represents a predetermined nominal value (ex. 0.75 in) for the deflection induced by the second deflection unit54′.

Then, the computer proceed with calculation of a raw modulus of elasticity for the tested piece according to the following relations:

I is the inertia modulus value for a tested piece having rectangular section;

W is the transverse width dimension (in cm) of the tested piece; and

T is the thickness dimension (in cm) of the tested piece.

From the raw modulus of elasticity obtained, the computer program then applies dynamic and static edge corrections, in a same manner as explained before in view of equation (13). Finally, the tested piece of lumber24is further advanced through the action the catch blocks38past the rail output portion173provided on the second working element90′ as better shown inFIG. 18, toward the apparatus output, while the computer performs the classification of the tested piece according to the associated resulting net E through a comparison with a predetermined threshold value, in a same way as explained before regarding the first preferred embodiment. The computer also performs the various functions explained above, including tare monitoring function, PSCs status monitoring function and overload detection monitoring function involving extra limit switches148′, in essentially the same way as explained before regarding the first embodiment. As to the computer display interface provided for the operator, similar display screens such as those illustrated inFIGS. 8 to 12can be implemented by the computer software with some extra fields in the “System Check-up” screen shown inFIG. 22, wherein further indicators are included within first column131of second window261allowing the operator to visualize the current logic “On/Off” status of the logic inputs received by the computer190from limit switches144(LS2a, LS2b) provided on both pushing devices264,264′ with corresponding counters in second column135. A further column including status indicators270for extra limit switches148′ is also provided, also including an indicator271specifying whether the second deflecting unit is its working position or not.

It is to be understood that the stiffness testing apparatus and method according to invention is not limited to the specific embodiments described above, and that obvious variants may be implemented without departing from the scope of the invention. For example, as to the first embodiment, the support unit may be formed by a single pair of spaced apart rails rather than two pairs of rails as described before, so as to use a single corresponding pair of load cells to generate load measurement signals as the piece under test successively passes through first and second testing zones under first and second deflecting units. Moreover, to test longer workpieces (12–16 feet lumber) with more accuracy, a plurality of workpiece bearing units capable of contacting the workpiece at more than two spaced apart portions along the workpiece to define complementary transverse spans may be provided, using corresponding additional deflecting units and load measuring units. Furthermore, the apparatus may be readily modified so as to convey the piece of lumber in a direction parallel to its edge surfaces so as to apply the load to an edge rather than to a main surface of the piece of lumber, in which case the static correction factor KStatreferred to above would be no longer necessary. Moreover, it is to be understood that depending upon material characteristics and dimensions of the specific product to be tested, other conveying and load applying approaches may be used, which may involve mechanical devices disposed in different positions with respect to horizontal or vertical plane, provided the relative position between load measuring and load applying devices allows reliable stiffness testing.