Abstract:
The present invention is a wood grading apparatus including a robust “push” solenoid as a hammer means for impacting a lumber specimen under test. A conventional solenoid coil with stationary magnetic iron pole pieces is combined with a bimetallic armature including a magnetic portion and a non-magnetic portion; said armature is of uniform cross section through the solenoid coil. A magnetic steel portion of said armature is fastened to a nonmagnetic steel portion thereof, whereby the magnetic field may act upon the magnetic portion of said armature and drive said nonmagnetic portion in an outward direction whereby impact or striking action is achieved. The present invention includes said solenoid in a wood grading apparatus whereby physical properties of wood are measured in a conveyor line setting and wood grading is affected by combining sonic velocity and density measurements to determine the modulus of elasticity of the wood object. Sonic velocity in the wood specimen is determined either by reverberation frequency or by rolling transducers that detect the leading edge of a stress wave initiated by said hammer means. A weight measurement means including a horizontal-axis roller lug conveyor chain and a leaf-spring suspension with a load cell means provides for improved accuracy in weight measurement for wood density calculation.

Description:
REFERENCES 
       [0000]    
       
         U.S. Pat. No. 3,196,672 July 1965 Keller 
         Logan, James D., and Paul S. Kreager (1975) Using a Microprocessor, A Real-Life Application, COMPUTER DESIGN, September 1975 
         U.S. Pat. No. 4,201,093, Jul. 20, 1978, Logan 
         U.S. Pat. No. 4,926,350, May 15, 1990 Bechtel et al. 
         U.S. Pat. No. 5,237,870, Aug. 24, 1993 Fry et al. 
         U.S. Pat. No. 5,503,024 Apr. 2, 1996 Bechtel et al. 
         U.S. Pat. No. 7,066,007, Jun. 27, 2006 Ziegler, et al. 
         U.S. Pat. No. 7,194,916, Mar. 27, 2007, Ouellet, et al. 
         U.S. Pat. No. 7,340,958, Mar. 11, 2008 Huang, et al. 
         U.S. Pat. No. 7,603,904, Oct. 20, 2009 Harris, et al. 
         U.S. Pat. No. 7,974,803, Jul. 5, 2011 Logan, et al. 
       
     
       TECHNICAL FIELD 
       [0012]    This invention relates to the field of electromechanical devices, more specifically the field of electromagnetic solenoid striking means whereby a mechanical action is effected as a result of causing an electric current to flow in a coil of conducting wire. For purposes of the present invention, the mechanical action is an impact. A further technical field is that of grading wood pieces for use in construction whereby physical properties are measured and/or predicted whereby efficient sorting of a variable wood resource provides groupings of material with more tightly controlled physical characteristics. 
       BACKGROUND OF THE INVENTION 
       [0013]    In a lumber grading process one method of determining the modulus of elasticity E, (Young&#39;s modulus) of a lumber specimen is to strike a starting end of said lumber specimen to produce a compressive stress wave in the lumber specimen which travels to the opposite end thereof and reflects from the opposite end as a tensile wave. The tensile wave travels back to the starting end, where it reflects as a compression wave, thus producing an echo reverberation. A measurement of the frequency of reverberations provides a measurement of sonic velocity. Alternative detection means can be used to detect the progress of the original compression wave whereby sonic velocity is determined, so time domain measurement of the first compression wave is interchangeable with measurement of reverberation frequency. The sonic velocity value is then combined with measured lumber specimen density. The result is a measured E value that can be used in a sorting process to grade structural lumber for characteristics that are important in the design and serviceability of a wood structure. Making the sonic velocity measurement requires a means for producing a compression/tension sonic wave in the lumber specimen under test. Such means have included pneumatic cylinders, pendulum devices, manually operated hammers and electric solenoid actuated hammers. One solenoid actuated hammer device utilized a commercial solenoid attached to a sliding shaft means the hardened end of which impinged upon a steel clamping means which in turn was attached to the lumber specimen whereby the sonic energy from the impact of the sliding shaft means was transferred to the lumber specimen. This arrangement was suitable for stop-and-go laboratory conditions but did not lend itself to a production line situation in which the sonic energy must be transferred into a continuously moving specimen. 
         [0014]    The present invention provides a simple robust means for impacting the end of a moving lumber specimen, such as a lumber specimen riding on a conveyor chain, for the purpose of sonic lumber grading. 
       DEFINITIONS 
       [0015]    E—Young&#39;s modulus, or modulus of elasticity, typically expressed in units of pounds per square inch or Pascals (Newton/square meter). One pound per square inch equals 6894.76 Pascals This material property expresses the value of “stiffness” that is independent of shape. 
         [0016]    I—Moment of inertia, typically expressed in units of (inches) 4 , i.e., inches to the fourth power. For a rectangular cross section this is equal to (width times depth-cubed) all divided by 12. The depth dimension is the direction of applied bending load. Note that depth can be thickness or width of a lumber specimen depending upon the direction of applied load. 
         [0017]    Dimension lumber—structural wood lumber shapes typically with a rectangular cross section and often 1½ inch thick and 2½ inch to 11¼ inches wide in North America, also referred to as “timbers” in other countries with similar sizes expressed in metric units i.e., 35 mm to 45 mm thick by 70 to 300 mm wide. Metric sizes are typically actual cross section sizes whereas sizes in English units are smaller than the called-out sizes, thus leading to confusion until one gets the hang of it. This is a hold-over from history when lumber sizes were called out as the rough green size, and were smaller after drying shrinkage and surfacing. Now this is no longer true because the actual rough green sizes have been reduced by better understanding of drying shrinkage, improved precision in cutting and reduction of clean-up in the surfacing operation. What we know as a “two-by-four” is actually 1½ by 3½ inches in cross section. 
         [0018]    Boards—wood used for general applications typically with a rectangular cross section and thicknesses reckoned in quarters of an inch and widths ranging from 2½ inch to 11¼ inch. Again, actual sizes are smaller than the call-out size, so a “one-by-four” is ¾ inch by 3½ inches. 
         [0019]    Timber—In the US and Canada this term typically refers to wood in rectangular cross sections larger than 1½″ thick, but in other countries this term can refer to dimension lumber cross sections as well. 
         [0020]    Lumber specimen—for purposes of this invention, this term includes dimension lumber, boards and timbers. Lengths may range from less than 6 feet to more than 20 feet. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a side elevation view of the electric hammer portion of the present invention showing cut-away sections exposing an armature, a first bearing, a bearing mount, a coil and a first and a second pole pieces of a magnetic circuit, a second bearing, a spring and a bumper. 
           [0022]      FIG. 2  is a side view of the armature with spring retainer and a bolt. 
           [0023]      FIG. 3  is an end view of the armature. 
           [0024]      FIG. 4  is a schematic wiring diagram of a solenoid driver circuit. 
           [0025]      FIG. 5  is an isometric view of an alternative bearing part with acoustic sensor means included. 
           [0026]      FIG. 6  is an end view of an electric hammer assembly pivotably mounted on a fixed base plate. 
           [0027]      FIG. 7  is an elevation view showing a section of a chain conveyor means with a weight measurement means, an electric hammer assembly and acoustic sensor means operatively arranged for sonic grading of dimension lumber. 
           [0028]      FIG. 8  is a plan view of a chain conveyor means with a multiplicity of weight measurement means, electric hammer assembly, photo sensor means, shaft encoder means and acoustic sensor means operatively arranged for sonic grading of lumber specimens. 
           [0029]      FIG. 9  is an elevation view showing a section of chain conveyor means with weight measurement means, photo sensor means, shaft encoder means, electric hammer assembly and rolling transducer means. 
           [0030]      FIG. 10  is a plan view of a chain conveyor means with a multiplicity of weight measurement means, photo sensor means, and electric hammer assembly and a multiplicity of rolling transducer means operatively arranged for sonic grading of lumber specimens. 
           [0031]      FIG. 11  is a cut-away view of rolling transducer means. 
           [0032]      FIG. 12  is a schematic elevation view of electric hammer assembly arranged with a lumber specimen under test and in contact with a multiplicity of rolling transducer means. 
           [0033]      FIG. 13  is a vertical cross section of a weight measurement assembly. 
           [0034]      FIG. 14  is a block diagram illustrating information flow in an electronic means for a grading apparatus of the present invention. 
           [0035]      FIG. 15  is a vertical cross section of a chain conveyor with a horizontal axis roller lug carrying a lumber specimen under test over a weight measurement means with cut-away showing spring mounting means to reconcile vertical forces to a load cell. 
           [0036]      FIG. 16  is a plan view of a chain conveyor means with horizontal axis roller lug pushing a lumber specimen under test over a weight measurement assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0037]    One object of the present invention is to provide a hammer means with robust construction to impinge upon the ends of a lumber specimen whereby impulsive sound waves are caused to travel through the length of said lumber specimen and measurements of physical properties may be derived from sound velocity and/or reverberation frequency. 
         [0038]    Another object of the present invention is to provide a hammer means with a low wear rate whereby many millions of impacts may be applied with minimal service requirements. 
         [0039]    Another object of the present invention is to provide a hammer means that will avoid the problems of dirt, moisture and variable air pressure found in pneumatically operated hammer means. 
         [0040]    Another object of the present invention is to minimize the number of and fragile nature of moving parts typically found in pneumatically driven hammer means. 
         [0041]    Another object of the present invention is to provide for lumber grading in material with sufficient detail within each lumber specimen that trim decisions may be based on wood properties within potential trim segments of each lumber specimen rather than based only on average properties. 
         [0042]    Another object of the present invention is to include improved hammer means in a wood grading system that measures average wood properties by determining sonic reverberation frequency. 
       FEATURES AND ADVANTAGES OF THE PRESENT INVENTION WITH COMPARISON TO THE PRIOR ART 
       [0043]    Prior art pneumatic hammer devices contain many moving parts all subject to failure, and subject to damage from contamination in the air supply which is always a problem in the production line setting. When a pneumatic cylinder is used in an application requiring rapid cycling over a long period of time, problems arise with both internal and external seals which have a limited lifetime. When such a device is used in an impacting or hammer application, additional problems arise from shock loading of the internal components. 
         [0044]    Arrangements of equipment utilizing reverberation frequency as an indicator of sonic velocity do not provide detail that would be more useful in making structural assessments of a lumber specimen, whereas the rolling transducer features of this invention can provide that detail. In a preferred alternative embodiment of the present invention, sonic velocity is measured over incremental distances along the lumber specimen whereby portions of the specimen with low strength and stiffness properties may be identified and eliminated by trimming. 
       THE PRESENT INVENTION 
       [0045]    The present invention includes a robust hammer with essentially one moving part plus one spring and including a rotational break-away feature whereby damage to the hammer assembly is avoided in the event of a spring failure or entanglement with lumber specimens in the production line. There are no internal or external seals to wear out. The present invention can be arranged to use sonic reverberation frequency as an indicator of average wood properties in a specimen or by use of rolling transducers, internal detail may be measured to better make grade and trim decisions for each lumber specimen. The present invention electric hammer is capable of many millions of hammer blows between maintenance events and is capable of high speed operation up to and exceeding 250 strikes per minute. 
         [0046]    One preferred embodiment of the present invention is a push-type electrical solenoid assembly  2  shown in  FIG. 1  having an armature  1  slidably supported by a first bearing  4  in a bearing mount  6 , a first pole piece  10 , side pole pieces  15 , a second pole piece  18 , a second bearing  19 , a return spring  20 , a spring retainer  24 , a bumper  26 , a bumper mounting means  28 , bolt means  30  for connecting bumper  26  with bumper mount means  28 , a bobbin means consisting of coil bobbin end means  12  and coil bobbin core means  38 , coil  14  of insulated conducting wire wound on bobbin means and assembled using bolt means  8 , and mounted to a base plate  32  by fastening means  36 . Said bumper  26  is preferably made of an energy absorbent rubber such as polyurethane. Said bumper mounting means  28  fastened to base plate means  32  by fastening means  34  and tapped retainer means  35 . Pole pieces  10 ,  15 , and  18  constructed of magnetic iron the ferromagnetic properties of which provide for concentration of magnetic field inside coil bobbin means  38 . Electrical solenoid assembly coil  14  is connected to solenoid drive circuit shown in  FIG. 4  through electrical cable  118 . Said assembly  2  forming an electric hammer for the present invention. 
         [0047]    Armature means  1  shown in  FIG. 2  includes a first portion  42  composed of a magnetic material such as 1018 grade steel, and a second portion  40  composed of a nonmagnetic material such as grade 304 stainless steel, the two portions  40  and  42  fastened together by welding means  16 . Said magnetic portion  42  drilled and tapped  22  to receive a bolt means  44 , whereby spring retainer  24  is held in place. Spring retainer means  24  is preferably contoured whereby spring means  20  is maintained concentric with armature  1 . 
         [0048]      FIG. 3  shows an end view of armature means  1  with spring retainer  24  and showing the location of drilled and tapped hole  22 . 
         [0049]    In operation, upon energizing coil  14  a magnetic field is produced that pulls the ferromagnetic portion  42  of armature  1  into the magnetic field flux thereby moving the nonmagnetic portion of the armature in an outwardly directed motion through bearing  4 , and compressing return spring  20 . Said outwardly directed motion is sustained until armature  1  encounters a target material or the magnetic forces and inertial effects are balanced by the force exerted by return spring  20 , and until coil  14  is de-energized. Upon de-energizing coil  14 , armature  1  is accelerated in the inward direction by spring  20  until bolt means  44  encounters bumper means  26 , at which time armature  1  comes to a stop. 
         [0050]    For maximum impact force coil  14  continues to be energized while armature  1  is moving toward an impact target, and then de-energized at the instant of impact, allowing rebound and spring forces to return armature  1  to its starting position. If impact energy is desired to be reduced, a shorter energized time is selected. The impact target in the case of a lumber testing application is an end of a lumber specimen  103  such as shown in  FIG. 8 . 
         [0051]    Maximum impact velocity is achieved when the starting position of armature  1  is adjusted so impact occurs before return spring  20  begins to slow the outward progress of armature  1 . 
         [0052]    Electrical drive to coil  14  is provided in a preferred embodiment by means of the circuit shown in  FIG. 4 . A source of electrical power  60  is connected through appropriate switch gear (not shown) to the primary winding of transformer  62  and dc power supply  82 . The secondary winding of transformer  62  is connected to a full-wave bridge rectifier means  64 . The positive side of rectifier bridge  64  is connected through a resistor  66  and intermittently through charge control switch means  67  to a first side of an energy storage capacitor  68 , the negative side of rectifier bridge  64  is connected to a second terminal of energy storage capacitor  68  and grounding connection  84 . Said energy storage capacitor  68  is connected through cable  118  to a first winding connection of solenoid coil  14 . A second winding connection of solenoid coil  14  is connected through cable  118  to the collector of an Insulated Gate Bipolar Transistor (IGBT)  78 , and to an energy dissipating resistor  76 . 
         [0053]    A high-speed, high current Schottky diode  72  directs coil fly-back energy to the first winding connection of solenoid coil  14 . Resistor  76  and diode  72  suppress high voltages that occur when current in an inductor such as solenoid coil  14  is interrupted. In one preferred embodiment, the first winding connection of solenoid coil  14  is also supplied current from a dc power supply  82  through diode  70  while IGBT  78  is in the “ON” state and after the voltage across energy storage capacitor  68  is decreased to a value slightly below the output voltage of power supply  82 . The combination of high and low voltage power supplies and switching network of  FIG. 4  provide for rapid increase of current in solenoid coil  14  from the instant IGBT  78  is turned “ON”, which current is sustained until IGBT  78  is turned “OFF”. A logical input control signal  86  on input connection  88  is fed to integrated gate driver circuit  80  to provide appropriate control to the gate of IGBT  78  for rapid switching. The combination of voltage and current supplied to solenoid coil  14  greatly reduces the response time of the solenoid while limiting peak current to a workable level whereby quick response from the electric hammer is achieved. In a second preferred embodiment power supply  82  is not used, and the electrical energy is supplied by capacitor  68 . 
         [0054]    Referring to  FIG. 5 , for sonic lumber grading, impact energy imparted to the end of a lumber specimen induces a reverberating sound wave the fundamental frequency of which is detected by means of acoustic sensor  92  mounted in sound dampening means  90  and enclosed in alternative solenoid front bearing mount  7  and connected through shielded cable means  94  to electronic means further described in  FIG. 14 . Alternatively a sonic detection means such as a microphone or array of acoustic sensors may be mounted external to electrical solenoid assembly  2  whereby reverberation energy from the end of the lumber specimens is detected and the frequency thereof measured. 
         [0055]    An electric hammer assembly  126  is shown in  FIG. 6 . The end view of electrical solenoid assembly  2  is shown in  FIG. 6  pivotably mounted on base plate  49  with bolt  41 , lock nut  37  spring  39  washer  43  and jam nuts  45 . A slide-bearing plate  47  preferably made of UHMW polyethylene or other suitable material rotates against lower mounting plate  49  for rotational movement about a vertical axis at the center of bolt  41 . The upper end of bolt  41  is threaded into the upper mounting plate  32  of electrical solenoid assembly  2  and locked in place by means of lock nut  37 . It is recognized that spring  39  may take the form of an alternative wave washer or stacked lock washers if it is desirable to reduce the vertical length of the assembly. Rotational stop  48  and spring  57  allow freedom of rotational motion about bolt  41  in case of a fault in electrical solenoid assembly  2  that leaves it exposed to interference with lumber on lug chain conveyor described elsewhere, and provides for return to a normal operating position after such encounter. 
         [0056]      FIG. 7  shows an elevation view of a section of chain conveyor means with sequence of lugs  104  transporting lumber specimens  100 ,  102  and  103  over weight measurement means  124  and adjacent electric hammer assembly  126 . Each weight measurement assembly  124  is connected to weight input of  FIG. 14  by cable  112 . An alternative mounting of acoustic sensor means  114  is shown adjacent electric hammer assembly  126  with acoustic sensor means  114  in juxtaposition with the end of lumber specimen  103  (hidden) whereby sonic reverberation energy is detected from lumber specimen  103  after impact by electrical solenoid assembly  2 . Acoustic sensor means  114  is connected to sonic input of electronic means of  FIG. 14  by cable  94 . Conveyor chain  105  is driven by a sprocket shown schematically as  190 . A rotary shaft encoder  187  connects to conveyor motion input of electronic means of  FIG. 14  by cable  200  whereby position information is provided to electronic means for timing purposes. A photo sensor  188  connects through a cable  202  to electronic means of  FIG. 14  whereby the presence or absence of a lumber specimen on the conveyor chain and position information is available through shaft encoder  187  so the weight measurement process start and stop is affected and so electrical solenoid assembly  2  may be fired to hit the approximate horizontal center of an end of lumber specimen  103 . 
         [0057]    multiplicity of weight measurement assembly  124  can be supported from the conveyor flight structure by mounting means  106  composed of C-channel in the preferred embodiment shown in  FIG. 13 . 
         [0058]    A weight measurement assembly  124  is shown in vertical cross section in  FIG. 13 . Linkages  120  and  122  are composed of spring steel pieces clamped by bolts to frame member means  123 . Scale platform means  121  is suspended by linkages  120  and  122  in an arrangement that isolates load cell  110  from off-axis loads and makes weight determination independent of the horizontal placement of lumber specimen on scale platform means  121 . Load cell  110  is connected to operative electronics means shown in  FIG. 14  through cable  112 . Means are provided (not shown) for vertical adjustment of weight measurement assembly  124  with respect to mounting means  106  at a preferred elevation with respect to conveyor chains. The weight measurement assembly may be supported either directly from conveyor chain support structure or from building components. 
         [0059]    As shown in  FIG. 8 , a multiplicity of conveyor chains  105  may be fitted with weight measurement means  124 . Shear plate means  128  is used to position lumber specimen  103  at a preferred distance from electrical solenoid assembly  2  whereby electrical solenoid assembly  2  may deliver a single impact smartly to the end of lumber specimen  103  and thereby produce a useful reverberation of sonic energy within the lumber specimen, which reverberation produces sonic emanations from the end of lumber specimen  103  as a sound wave, which in turn is converted by acoustic sensor  114  into an electrical signal and operatively connected to sonic input of electronic means of  FIG. 14  through cable  94 . 
         [0060]    An alternative preferred embodiment of the present invention is shown in  FIG. 9  and  FIG. 10 . In this alternative preferred embodiment, sonic energy is detected by a multiplicity of rolling transducer assemblies  140  arranged to contact lumber specimen  103  at preferred distances along the length of lumber specimen  103 . With this alternative preferred embodiment the sonic wave leading edge is detected during the first transit of compressive wave energy emanating from a hammer impact produced by electrical solenoid assembly  2  on an end of said lumber specimen. This provides an advantage of obtaining localized sonic velocity and thus localized property information along the length of the lumber specimen, and the capability of measuring lumber specimens in which sonic wave attenuation prohibits measurement of reverberation frequency. 
         [0061]    A location photo sensor  188  with signal cable  202  and shaft encoder  187  with signal cable  200  as described above are used in the alternative preferred embodiment shown in  FIG. 9  and  FIG. 10  whereby each lumber specimen may be tracked as to its location as it proceeds along the conveyor. As shown in  FIG. 9 , a typical rolling transducer assembly  140  is suspended above the chain conveyor by a bridge means  176  to which is fastened a transducer mounting means including an air spring  186 , a first pivot bearing  178  whereby the wheel assembly may move in a vertical direction, a second bearing means  180  whereby the rolling transducer assembly  140  may swing through a limited angle about a vertical axis and automatically track the moving specimen  103  without skidding thereupon. The air spring  186  provides for an adjustable contact force between rolling transducer assembly  140  and lumber specimen  103 . A stop bolt and lock nut  182  provide for parking the rolling transducer assembly  140  at a preferred distance above the conveyor chain  105  to affect suitable contact force for detection of stress waves in the lumber specimen and reducing bouncing and vertical motion to a manageable value. Bridge means  176  may be a round steel tube as shown or it may another cross section shape such as a square or rectangular tube or truss capable of spanning the required distance while minimizing deflection from varying loads and providing convenient fastening of transducer mounting means. Conveyor chain  105  with lugs  104  carries lumber specimens shown as  100 ,  102  and  103  in sequence first under photo sensor means  188 , over weight measurement assemblies  124 , and into the sonic velocity measurement position where lumber specimen  103  is impacted by electrical solenoid assembly  2  while in contact with rolling transducer assemblies  140 . Movement of conveyor chain  105  is detected by shaft encoder  187  shown in  FIG. 9  which is connected to conveyor motion input shown in  FIG. 14  by cable  200 . By these features, the start and stop times of weight measurement for lumber specimen  102  is determined, signals from weight measurement assemblies  124  on cables  112  are properly processed by electronic means and the hammer firing time for hammer assembly  126  is known so that lumber specimen  103  is in proper position for measurement of sonic velocity along the segments described by rolling transducer assemblies  140 . 
         [0062]      FIG. 10  shows the relative locations of lumber specimens  100 ,  102  and  103  as they move in sequence past photo sensor  188 , weight measurement assembly  124  and hammer assembly  126 . 
         [0063]    Rolling transducer assembly  140  shown in  FIG. 11  includes a piezoelectric detection means  156  attached to a mounting means  160 . Shaft  148  includes a longitudinal passage for electrical connection  142  leading to external cable  154  through a suitable connector. A grounding wire  144  provides zero potential reference for piezoelectric detection means  156  by connecting through mounting means  160  to non-rotating shaft  148 . Bearings  146  and seals  162  allow for rotation of outer shell  158  about shaft  148 . A coupling fluid such as oil fills the internal space  164  and couples sonic energy entering shell  158  to piezoelectric detection means  156  through running gap  166  between shell  158  and piezoelectric detection means  156 . A grounding ring  152  provides for static electricity discharge through a carbon fiber brush not shown. 
         [0064]      FIG. 12  shows an arrangement of electric hammer assembly  126  arranged to strike the end of lumber specimen  103  which is in contact with rolling transducer assemblies  140  spaced apart by a preferred distance  172 . Said preferred distance  172  may be chosen to coincide with typical lumber trim cutting distances so that trim decisions may be made based on the wood properties within a preferred trim increment. 
         [0065]    In operation the weight of a lumber specimen under test is determined by the weight measurement means. A stress wave is initiated by electric hammer assembly  126 . The stress wave moves along the lumber specimen at a sonic velocity and is detected as it proceeds along the lumber specimen by rolling transducer assemblies  140 . The velocity is measured and the E is calculated for each increment of lumber between preferred distances  172 . Although the figures and descriptions indicated that weight is first determined then sonic velocity is determined, these steps may be carried out in opposite order. 
         [0066]      FIG. 14  shows a block diagram including the elements of the data processing system, whereby signals conducted by cables  112  from the weight measurement means, signal on cable  94  from the acoustic sensor or alternatively signals conducted by cables  154  from the rolling transducer means, signals conducted by cable  200  from the shaft encoder  187 , and a signal from photo sensor  188  for position input conducted by cable  202  are combined and processed. A hammer drive trigger signal  88  is derived from the conveyor motion input and the position input and a hammer drive impulse is conducted by cable  118  to coil  14 . Data from computations carried out in computer software may be supplied in the form of a grade spray control output or digital data output to network connections for use in downstream equipment. 
         [0067]      FIG. 15  illustrates a conveyor chain  105  with horizontal axis roller lug  104  pushing a lumber specimen  102  over a weight measurement assembly  124  which is supported by mounting means  106 . Mounting means  106  may be supported by chain conveyor flight not shown or from other support structures to avoid vibration motion being conducted to the load cell  110 . The lumber specimen under test  102  rests on a slide arrangement, the vertical force therefrom is directed to a load cell  110 . Springs  120  and  122  support horizontal forces only, so all the weight force is directed to the load cell  110  while lumber specimen  102  is in contact with slide arrangement  121 . As lumber specimen under test  102  moves across weight measurement assembly  124  moment forces are resolved into tensile and compression forces in springs  120  and  122  whereby the force applied to load cell  110  does not change as a function of position along the top of weight measurement assembly  124 . 
         [0068]      FIG. 16  is a plan view showing conveyor chain  105  with horizontal axis roller lug  104  pushing lumber specimen  102  across weight measurement assembly  124 . For clarity the support conveyor flight for chain  105  has been removed. Horizontal axis roller lug  104  provides motive force to convey lumber specimen  102  across weight measurement assembly  124  whereby vertical force arising from friction of contact between the roller lug  104  and lumber specimen  102  is reduce to a minimum value. By using this method of conveyance the accuracy of weight measurement is improved. 
         [0069]    In compliance with the statute, the invention has been described in language more or less specific as to structural features. It is to be understood, however, that the invention is not limited to the specified features shown, because the means and construction herein disclosed comprise a preferred form of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.