Abstract:
A load sensing pin disposed to receive a load applied in a direction substantially transverse to a longitudinal axis of the pin. A load sensor is substantially fixedly oriented with respect to the applied load or alternatively with respect to the pin which is rotationally restrained with respect to a support structure. The load sensor is disposed to generate a load signal corresponding to strain of the pin resulting from the applied load.

Description:
BACKGROUND 
       [0001]    When planting with a conventional row-crop planter such as a John Deere MaxEmerge® or MaxEmerge® Plus planter, it is recognized that sufficient down force must be exerted on the row unit to ensure full penetration of the furrow opening disk blades into the soil to the pre-selected furrow depth and also to provide some degree of soil compaction by the gauge wheels to ensure proper furrow formation. It is also recognized, however, that excessive down force will cause over compaction of the soil which may, in turn, result in improper root growth and/or poor germination due to re-opening of the furrow. 
         [0002]      FIGS. 1, 4 and 7  are intended to represent soil profiles under the furrow opening assembly  34  of a conventional planter that is subject to differing amounts of down force. Specifically,  FIG. 1  illustrates a soil profile with an ideal amount of down force being exerted so as to achieve full penetration to the preset depth of the disk blades  44 ,  46  and with just enough compaction exerted on the surrounding soil by the gauge wheels  48 ,  50  to ensure proper furrow formation but without excess soil compaction of the surrounding soil.  FIG. 2  represents the same soil profile after the seed  42  is deposited but prior to being covered with soil by the furrow closing assembly  36 .  FIG. 3  is intended to represent that same soil profile after being covered with soil by the furrow closing assembly  36 . 
         [0003]    FIGS. 4- 6  are similar to  FIGS. 1-3  but are intended to represent the effects of too little down force being exerted by the gauge wheels  48 ,  50 . In such a situation, the disk blades  44 ,  46  may not penetrate into the soil to the full desired depth and/or the soil may collapse into the furrow  38  as the seeds  42  are being deposited resulting in irregular seed depth. 
         [0004]      FIGS. 7-9  are also similar to  FIGS. 1-3  but represent the effects of excessive down force being applied. The soil is being compacted excessively adjacent to the seed furrow  38  resulting in substantial differences in soil density between the furrow walls when compared to the soil density on either side of the furrow. Under such extreme conditions, the compaction of the furrow walls and the soil below the furrow  38  prevents the roots from easily penetrating the adjacent soil, which may result in the roots being prevented from growing conically downward perpendicular to the direction of the furrow. Poor root penetration may result in weak stands and may place the crops under unnecessary stress during drier conditions. In addition to inadequate root penetration, as illustrated in  FIG. 9 , when the soil is overly compacted by the gauge wheels, the furrow may re-open along the centerline of the furrow due to the differing soil densities as the soil dries out, resulting in poor seed-to-soil contact and/or drying out of the seed causing poor germination and seedling death. 
         [0005]    Heretofore, growers could only speculate as to whether the amount of downforce set for the planter was appropriate by observing the soil profile after planting a stretch of soil to determine the looseness or compactness of the soil around the seed furrow. Simply visually inspecting the soil is imprecise and it is difficult for most growers to accurately judge whether or not they are planting with too little or too great of downforce. Furthermore, the appropriate amount of downforce to be applied may be different across the field due to varying soil conditions. 
         [0006]    U.S. Pat. No. 6,389,999 to Duello (hereinafter “Duello &#39;999) describes a system for dynamically controlling excess downforce during planting operations by employing a pressure sensor, such as a strain gauge or other pressure transducer, placed on or incorporated into the gauge wheel mounting structure to detect the compressive forces being exerted upon the gauge wheel mounting structure. Duello &#39; 999  further describes the use of a microprocessor, or the like, adapted to receive the signals from the pressure sensor and to actuate the planter&#39;s hydraulic system or a supplemental down-pressure system to regulate the amount of down force exerted on the planter row units in relation to a value previously selected by the grower. Duello &#39;999 further discloses that the pre-selected down force value may be variable based on pre-selected values entered into field mapping system utilizing global positioning. 
         [0007]    U.S. Pat. No. 6,701,857 to Jensen et al. (hereinafter “Jensen &#39;857”) also discloses a system for automatically adjusting the downforce during planting operations. Specifically, Jensen &#39;857 discloses the use of a Wheatstone bridge strain gage circuit applied to the gauge wheel arms to detect the amount of strain due to bending stresses exerted on the arms. The strain exerted on the gauge wheel arms corresponds to the change in resistance or output voltage of the Wheatstone bridge circuit. The output voltage is transmitted to a closed loop electronic control unit connected to the electrical and hydraulic or pneumatic system of the tractor used for regulating the downforce applied by the planter. A micro-processor functions to compare the detected downforce to a downforce value pre-selected by the grower and to automatically actuate the planter&#39;s hydraulic or pneumatic system accordingly to increase or decrease the downforce as required to maintain the detected downforce at or near the pre-selected downforce value. Jensen also proposes the concept of measuring a shear load at a pin in the depth control mechanism but fails to provide any discussion or drawing figures on how to do so. 
         [0008]    While the foregoing patents describe the benefit of being able to monitor and control downforce during planting operations and the general theory of utilizing a pressure sensor in the “gauge wheel mounting structure” (Duello &#39;999) or on the “gauge wheel arms” (Jensen &#39;857) neither patent describes in sufficient detail a practical working embodiment that can accurately and consistently determine and monitor down force during planting operations. For example, changes in the depth setting of the planter unit can result in a different loading conditions on the gauge wheel arms and gauge wheel mounting structure which can vary the output signal of the pressure sensor. Additionally, due to the location, the sensitive gauges and wires used for monitoring the downforce must be shielded or protected to avoid damage from debris during planting operations. 
         [0009]    Accordingly, there remains a need for a system for monitoring downforce on a planter row unit that is robust yet economical to produce and that provides accurate measurements (preferably without calibration) regardless of the position of the depth regulation member. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  represents a soil profile under a furrow opening assembly of a conventional row crop planter in which ideal down force is being applied. 
           [0011]      FIG. 2  illustrates the soil profile of  FIG. 1  after the seed is deposited and prior to the furrow being covered with soil by the furrow closing assembly. 
           [0012]      FIG. 3  illustrates the soil profile of  FIG. 2  after the furrow is covered with soil by the furrow closing assembly. 
           [0013]      FIG. 4  represents a soil profile under a furrow opening assembly of a conventional row crop planter in which too little down force is being applied. 
           [0014]      FIG. 5  illustrates the soil profile of  FIG. 4  after the seed is deposited and prior to the furrow being covered with soil by the furrow closing assembly. 
           [0015]      FIG. 6  illustrates the soil profile of  FIG. 5  after the furrow is covered with soil by the furrow closing assembly. 
           [0016]      FIG. 7  represents a soil profile under a furrow opening assembly of a conventional row crop planter in which excess down force is being applied. 
           [0017]      FIG. 8  illustrates the soil profile of  FIG. 7  after the seed is deposited and prior to the furrow being covered with soil by the furrow closing assembly. 
           [0018]      FIG. 9  illustrates the soil profile of  FIG. 8  after the furrow is covered with soil by the furrow closing assembly. 
           [0019]      FIG. 10  is a perspective view of conventional row crop planter. 
           [0020]      FIG. 11  is a side elevation view of a row unit of the conventional row crop planter of  FIG. 10 . 
           [0021]      FIG. 12  is a partial perspective view of the gauge wheel height adjustment mechanism of the row unit of  FIG. 11  and showing one embodiment of the system of the present invention installed on the row unit. 
           [0022]      FIG. 13  is a partial cross-sectional view of the embodiment of  FIG. 12  as viewed along lines  13 - 13  of  FIG. 12 . 
           [0023]      FIG. 14  is a perspective view of the embodiment of the system of the present invention illustrated in  FIGS. 12 and 13  showing one embodiment of a 4-point load sensing pin and a rotational restraint arm. 
           [0024]      FIG. 15  is a shear and bending moment diagram of the load sensing pin of  FIG. 14  under a balanced load. 
           [0025]      FIG. 16  is a shear and bending moment diagram of the load sensing pin of  FIG. 14  under an offset load. 
           [0026]      FIG. 17  illustrates a cross-sectional view of another embodiment of the system of the present invention showing an alternative embodiment of a 3-point load sensing pin and a rotational restraint arm. 
           [0027]      FIG. 18  is a side elevation drawing of another type of conventional depth adjustment mechanism for a row unit of a conventional row crop planter. 
           [0028]      FIG. 19  is a partial front perspective view of the depth adjustment mechanism of the row unit of  FIG. 18  showing another embodiment of the system of the present invention using another embodiment of a load sensing pin and rotational restraint arm installed on the row unit. 
           [0029]      FIG. 20  is a perspective view of the embodiment of the system of the present invention illustrated in  FIG. 19  showing another embodiment of a 4-point load sensing pin and a rotational restraint arm. 
           [0030]      FIG. 21  is a partial cross section view of the embodiment of  FIGS. 19 and 20  as viewed along lines  21 - 21  of  FIG. 19 . 
           [0031]      FIG. 22  is a schematic of one embodiment of a preferred strain gauge transducer used in connection with the load sensing pin system of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views,  FIG. 10  illustrates a conventional row-crop planter  10 , such as the type disclosed in U.S. Pat. No. 4,009,668, incorporated herein in its entirety by reference, and/or as embodied in commercially available planters such as the John Deere MaxEmerge or MaxEmerge Plus planters.  FIG. 18  illustrates yet another conventional commercially available row-crop planter such as the Kinze Evolution series planter. It should be appreciated that although reference is made throughout this specification to particular makes and models of planters, such references are examples only, made to provide context and a frame of reference for the subject matter discussed. As such, the present invention should not be construed as being limited to any particular make(s) or model(s) of planter. 
         [0033]    The planter  10  includes a plurality of spaced row-units  12  supported along a transversely disposed toolbar  14  comprising a part of the planter main frame  13 . The planter main frame  13  attaches to a tractor  15  in a conventional manner, such as by a drawbar  17  or three-point hitch arrangement as is well known in the art. Ground wheel assemblies (not shown) support the main frame  13  above the ground surface and are moveable relative to the main frame  13  through actuation of the planter&#39;s hydraulic system (not shown) coupled to the tractor&#39;s hydraulics to raise and lower the planter main frame  13  between a transport position and a planting position, respectively. 
         [0034]    As best illustrated in  FIG. 11 , each row unit  12  is supported from the toolbar by a parallel linkage  16  which permits each row unit  12  to move vertically independently of the toolbar  14  and the other spaced row units in order to accommodate changes in terrain or upon the row unit encountering a rock or other obstruction as the planter is drawn through the field. Biasing means  18 , such as springs, air-bags, etc., extend between the parallel linkage  16  to provide supplemental or additional downforce on the row unit. Each row unit  12  includes a front mounting bracket  20  to which is mounted a hopper support beam  22  and a subframe  24 . The hopper support beam  22  supports a seed hopper  26  and a fertilizer hopper  28  as well as operably supporting the seed meter  30  and seed tube  32 . The subframe  24  supports a furrow opening assembly  34  and a furrow closing assembly  36 . 
         [0035]    In operation, the furrow opening assembly cuts a V-shaped furrow  38  ( FIGS. 1 and 11 ) into the soil surface  40  as the planter is drawn through the field. The seed hopper  26 , which holds the seeds to be planted, communicates a constant supply of seeds  42  to the seed meter  30 . The seed meter  30  of each row unit  12  is typically coupled to the ground wheels through use of shafts, chains, sprockets, transfer cases, etc., as is well known in the art, such that individual seeds  42  are metered and discharged into the seed tube  32  are regularly spaced intervals based on the seed population desired and the speed at which the planter is drawn through the field. The seed  42  drops from the end of the seed tube  32  into the V-shaped furrow  38  and the seeds  42  are covered with soil by the closing wheel assembly  36 . 
         [0036]    Referring to  FIGS. 1 and 11 , the furrow opening assembly  34  typically includes a pair of flat furrow opening disk blades  44 ,  46  and a pair of gauge wheels  48 ,  50 . The disk blades  44 ,  46  are rotatably supported on shafts  52  mounted to a shank  54  depending from the subframe  24 . The disk blades  44 ,  46  are canted such that the outer peripheries of the disks come in close contact at the point of entry  56  into the soil and diverge outwardly and upwardly away from the direction of travel of the planter as indicated by the arrow  58 . Thus, as the planter  10  is drawn through the field, the furrow opening disks  44 ,  46  cut the V-shaped furrow  38  through the soil surface  40  as previously described. 
         [0037]    As best illustrated in  FIGS. 11 and 12 , gauge wheel arms  60 ,  62  pivotally support the gauge wheels  48 ,  50  from the subframe  24  about a first axis  61 . The gauge wheels  48 ,  50  are rotatably mounted to the forwardly extending gauge wheel arms  60 ,  62  at a second axis  63 . The gauge wheels  48 ,  50  are slightly larger in diameter than the disk blades  44 ,  46  such that the outer peripheries of the disk blades rotate at a slightly greater velocity than the gauge wheel peripheries. Each of the gauge wheels  48 ,  50  includes a flexible lip  64  ( FIG. 1 ) at its interior face which contacts the outer face of the respective disk blade  44 ,  46  at the area  66  ( FIG. 11 ) where the disk blades exit the soil. It should be appreciated that as the opening disks  44 ,  46  exit the soil after slicing the V-shaped furrow  38 , the soil will tend to adhere to the disk, which, if not prevented, would cause the furrow walls to be torn away as the disk rotates out of the soil causing poor furrow formation and/or collapse of the furrow walls, resulting in irregular seed planting depth. Thus, as best illustrated in  FIGS. 1 and 11 , to prevent the furrow walls from being torn away by the disks exiting the soil, the gauge wheels  48 ,  50  are positioned to compact the strip of soil adjacent to the furrow while at the same time serving to scrape against the outer face of the disks  44 ,  46  to shear off any soil buildup as the disks exit the soil. Accordingly, the opening disks  44 ,  46  and the gauge wheels  48 ,  50  cooperate to firm and form uniform furrow walls at the desired depth. 
         [0038]    As is well understood by those of ordinary skill in the art, the depth adjustment mechanism  47 , is used to set the relative distance between the bottom of the opening disks  44 ,  46  and the bottom surface of the gauge wheels  48 ,  50 , thereby establishing the depth of penetration of the opener disks  44 ,  46  into the soil surface. The term “gauge wheels” may be used interchangeably throughout this specification with “depth regulation member.” Thus any recitation in this specification of such terms are to be understood as including any type of depth regulating member, whether gauge wheels, skis, skids, runners, etc. 
         [0039]    Accordingly, in the conventional John Deere MaxEmerge planters, for example, to vary the depth of the seed furrow  38 , the gauge wheels  48 ,  50  are vertically adjustable relative to the furrow opening disk blades  44 ,  46  by a height adjusting arm  68  pivotally supported from the subframe  24  by a pin  70  ( FIG. 11 ). An upper end  72  of the height adjusting arm  68  is selectively positionable along the subframe  24 . As best illustrated in  FIG. 12 , a rocker  76  is loosely pinned to the lower end  74  of the height adjusting arm  68  by a pin or bolt  78 . As best illustrated in  FIGS. 12 , the rocker  76  bears against the upper surfaces of the pivotable gauge wheel arms  60 ,  62 , thereby serving as a stop to prevent the gauge wheel arms  60 ,  62  from pivoting counterclockwise about the first pivot axis  61  as indicated by arrow  82 . Thus, it should be appreciated that as the upper end  72  of the height adjusting arm  68  is selectively positioned, the position of the rocker/stop  76  will move accordingly relative to the gauge wheel arms  60 ,  62 . For example, referring to  FIG. 12 , as the upper end  72  of the height adjusting arm  68  is moved in the direction indicated by arrow  84 , the position of the rocker/stop  76  will move upwardly away from the gauge wheel arms  60 ,  62 , allowing the gauge wheels  48 ,  50  to move vertically upwardly relative to the furrow opening disk blades  44 ,  46  such that more of the disk blade will extend below the bottom of the gauge wheels  48 ,  50 , thereby permitting the furrow opening disk blades  44 ,  46  to penetrate further into the soil. Likewise, if the upper end  72  of the height adjusting arm  68  is moved in the direction indicated by arrow  86 , the rocker/stop  76  will move downwardly toward the gauge wheel arms  60 ,  62 , causing the gauge wheels  48 ,  50  to move vertically downwardly relative to the furrow opening disk blades  44 ,  46 , thereby shortening the penetration depth of the disk blades into the soil. When planting row crops such as corn and soybeans, the position of the rocker/stop  76  is usually set such that the furrow opening disk blades  44 ,  46  extend below the bottom of the gauge wheels  48 ,  50  to create a furrow depth between one to three inches. 
         [0040]    In addition to serving as a stop as previously described, the loosely pinned rocker  76  serves the dual function of “equalizing” or distributing the load carried by the two gauge wheels  48 ,  50 , thereby resulting in more uniform furrow depth. It should be appreciated that during planting operations, substantially the entire live and dead load of the row unit  12  along with the additional down-force exerted by the down-pressure springs  18  will be carried by the gauge wheels  48 ,  50  after the opening disks  44 ,  46  penetrate the soil to the depth where the gauge wheel arms  60 ,  62  encounter the preselected stop position of the rocker  76 . This load, represented by arrow L 1  ( FIG. 12 ), is transferred by the bolt  78  through the rocker  76  to the gauge wheel arms  60 ,  62 . This entire load is carried as well by the pin  70  which supports the depth adjustment link  68  relative to the row unit shank  54 . 
         [0041]    Referring to  FIG. 11 , the vertical loads carried by the gauge wheels  48 ,  50  include, including the dead load of the opener disk assembly  34  (including opener discs  44 ,  46  and gauge wheels  48 ,  50 ), the front mounting bracket  20 , the hopper support beam  22 , seed hopper  26 , insecticide hopper  28 , seed meter  30 , seed tube  32 , and the mass of any other attachments or devices supported on the row unit  12 . In addition, the gauge wheels  48 ,  50  carry all the live loads corresponding to the mass of the seed and insecticide stored within the hoppers  26 ,  28  and the supplemental downforce applied by the biasing means  18 . To achieve a static load balance all of the dead loads and live loads are resisted primarily by the reactionary force exerted by the soil against the opener disks  44 ,  46 , the gauge wheels  48 ,  50 . 
         [0042]    Referring to  FIGS. 12 and 13 , the load L 2  carried by the pin  70  is proportional to the load L 1  ( FIG. 12 ) as determined by the geometry of the depth adjustment mechanism. Likewise the load L 1  is proportional to the reactionary force exerted by the soil on the gauge wheels  48 ,  50 . The pin  70  is loaded in shear between the left side panel  90  and right side panel  92  of the row unit shank  54 . While this provides a distinct location to reliably measure the down force, there are three distinct challenges in measuring this load. First, the pin  70  is free to rotate during operation, which makes the routing of wires from a sensor disposed on the pin to remote processing circuitry difficult. Second, the pin  70  is loaded in pure shear at either end of the pin  70 . Shear loads are difficult to measure. Third, the area surrounding the pin  70  is subject to large amounts of debris and trash during planting operations and to the relative motion of the surrounding gauge wheel arms and gauge wheels. 
         [0043]    The system  100  of the present invention overcomes the foregoing challenges and provides the ability to accurately determine and monitor the downforce during planting operations by ensuring that the load being sensed acts at substantially the same known and consistent location no matter what the position of the depth adjustment mechanism and/or the depth regulating member. 
         [0044]    To the accomplishment of the foregoing, in the preferred embodiment of the system  100 , the pin  70  is replaced with a load sensing pin  101 . Different embodiments of the load sensing pin  101  are illustrated in  FIGS. 13, 17 and 20 . In the embodiment of  FIG. 13 , the load sensing pin  101  provides four bearing points (discussed below), and is hereinafter referred to as a “4-point pin”  200 . In the embodiment of  FIG. 17 , the load sensing pin  101  provides three bearing points (discussed later), and is hereinafter referred to as a “3-point pin”  300 . Naturally, other load sensing pin embodiments may be equally suitable. Accordingly, the system  100  of the present invention should not be construed as being limited to any particular load sensing pin embodiment, it being desirable, however, that the design of the load sensing pin  101  is one that can be accurately and relatively easily machined in high production, such as on a CNC machine, so as to minimize manufacturing costs. 
         [0045]    Referring to  FIG. 13  and  FIG. 14 , the 4-point pin  200  is provided with right and left shoulders  202 ,  204  for support from the right and left side panels  90 ,  92  of the row unit shank  54 . Two intermediate lobes  206 ,  208  are separated by a distance X in the center of the pin  200  and spaced symmetrically from the shoulders  202 ,  204  by a distance Y. The load L 2  is transferred from the height adjusting arm  68  bearing against these two lobes  206 ,  208 . The load L 2  is subsequently transferred from the 4-point pin  200  to each of the shoulders  202 ,  204  such that the load at the bearing points on the left and ride side panels  90 ,  92  is approximately half of the load L 2 . By the nature of the design of the row unit, any appreciable load L 2  will always act in the direction shown in  FIG. 13 . The shear/bending moment diagram for 4-point pin  200  can easily be calculated and is shown in  FIG. 15 . Thus, the advantage of the pin  200  is that regardless of where a given load L 2  is applied to height adjusting arm  68 , the resultant bending stress Fb at the center of the pin  200  is equivalent. 
         [0046]    For example,  FIG. 15  illustrates the 4-point pin  200  with a total balanced load L 2 , acting equally as L 2 / 2  on each lobe  206 , 208 . This balanced load results in equal and opposite reactionary forces S 1 , S 2  acting on shoulders  202 ,  204 . In the preferred embodiment of the 4-point pin, the distance X is approximately ⅞ inch and the distance Y is approximately 13/16 inch. Thus, assuming that load L 2  equals 1000 pounds, the reactionary forces S 1 , S 2  will equal 500 pounds each. The shear and bending moment diagrams are illustrated in  FIG. 15  for this loading condition. The peak bending moment (Mb) acting at the lobes  206 ,  208  can thus be calculated by determining the area under the shear diagram (i.e., Mb=500× 13/16=406 in-lbs), which remains uniform between the two lobes  206 ,  208 . Once the bending moment Mb has been determined at the desired point on the 4-point pin  200 , the bending stress Fb can be easily calculated from the formula Fb=Mb/S, where S is the section modulus of the 4-point pin  200  at that desired point. 
         [0047]    In another example as illustrated in  FIG. 16 , the same 4-point pin  200  is shown but in this example the 1000 pound load L 2  is offset from the center line of the 4-point pin  200  and is instead applied in line with lobe  208 . The corresponding shape of the shear and bending moment diagrams are illustrated. It should be understood that these graphs are not to scale but the calculations are well understood by those skilled in the art. As such, in this example, the reaction force R 1  acting at left shoulder  204  equals 325 lbs and the reaction force R 2  acting at the right shoulder  202  equals 675 lbs. Continuing to refer to  FIG. 16 , it should be appreciated that the peak bending moment (Mb) in this example does not occur at the center of the 4-point pin  200  as in the previous example, but instead occurs at the lobe  208 . However, as long as the load sensor is placed at the center of the 4-point pin  200 , the bending moment (Mb) at that point is the only moment of interest. In this example, calculating the bending moment (Mb) at the center of the 4-point pin  200  yields a bending moment of 406 in-lbs (i.e., 325×( 13/16+(⅞÷2))=406), which is identical to the bending moment of the balanced load of the previous example illustrated in  FIG. 15 . As such, the system  100  of the present invention is capable of accurately measuring a load regardless of the location the load is acting along the length of the pin  200 . This feature is advantageous in that some planters are not equipped with a rocker or equalizer  76  as shown in  FIG. 12  but rather have a depth adjustment mechanism which utilizes a single casting with two fixed lobes (not shown) to support left and right gauge wheel arms  60 ,  62  independently. In this situation the load on right and left sides are rarely equal and the resultant load L 2  will not act at the center of the load sensing pin  101 . Thus, in accordance with the present invention the shear load is simply resolved to a bending stress Fb at the center of a load sensing pin  101 . 
         [0048]    It is known that strain gauges can be used to determine the strain in an object subjected to bending stresses by measuring the changes in resistance of the strain gauge (discussed later). Thus, in the preferred embodiment of the system  100 , a strain gauge transducer  114  is provided along with appropriate circuitry, including processors and signal conditioners, etc., as recognized by those of skill in the art, to determine the strain resulting from the load L 2  and thus the corresponding downforce being exerted on ground surface by the gauge wheels. 
         [0049]    Heretofore the discussion of the design of the load sensing pin  101  and bending stress calculations have been in terms of the longitudinal axis of the load sensing pin  101 . However, it should be appreciated the location of the strain gage  114  in terms of its distance from the neutral axis of the pin relative to the load L 2  is also important. For example, when a beam is subjected to bending, the strain at the surface of the beam is a function of the distance from the neutral axis of the beam. Additionally, the stain will vary depending on the direction and location of the load with respect to that surface. For the preferred load sensing pin  101 , the “beam” is generally circular in cross section. Thus, if a strain gauge was applied to the curved outer surface of the load sensing pin  101 , then variation in the radial location of the strain gauge would contribute to inaccuracy of the measured strain and thus the load acting on the load sensing pin  101 . For example, if the load sensing pin  101  were allowed to rotate freely about its longitudinal axis  120  and the strain gauge  114  was at the front or rear of the pin (along the neutral axis relative to load L 2 ), then the measured strain (and correspondingly the stress) would be near zero. 
         [0050]    Accordingly, in the preferred embodiment, the system comprises a 4-point pin assembly  220  comprising the 4-point pin  200  and a restraint  230 . In the preferred embodiment, a flat surface  112  is provided on the 4-point pin  200  directly opposite the application of the load L 2  and this orientation is preferably maintained by the restraint  230  which restricts the ability of the 4-point pin  200  to rotate about its longitudinal axis  120 . As a result, the bending stress (Fb) will be substantially constant across the surface and accurate measurements are therefore not as dependent upon highly accurate placement of the strain gage  114 . 
         [0051]    Referring again to  FIGS. 12, 13 and 14 , the restraint  230  is preferably a rigid member fixedly secured to the 4-point pin  200 , such as by welding, threaded connection, snap rings, or other suitable means recognized by those skilled in the art, and is preferably configured to easily mount to the shank  54  with little or no modification to the shank  54 . Thus, in the preferred 4-point pin assembly  220 , the restraint  230  is fixedly secured at one end to the 4-point pin  200  by a screw  240  and washer  242  threaded into a tapped hole  244  in the end of the pin  200 . The top end  232  of the restraint  230  is preferably restrained relative to the shank  54  by a bolt or screw  248  threadably received into a weld-nut  146  and which extends into one of the plurality of slots  25  in the shank  54  into which the height adjustment arm  68  is selectively movable to permit adjustment of the furrow depth. In the preferred embodiment the screw  248  preferably extends into the forward most slot  25  such that depth adjustment will generally not be compromised. 
         [0052]      FIG. 14  best illustrates the preferred system by which the load sensor  114  is connected to the processing circuitry previously referenced. In the preferred embodiment, the strain gage  114  is preferably connected to a flexible tape  116  which is in turn connected to wires  118 . The wires  118  are preferably routed through a longitudinal bore  224  in the pin  200  and then upwards along the inner surface  234  of the restraint  230  through a conduit or sheath  219  preferably fastened to the restraint  230 , such as by a P-clip  236  or other suitable connection. The wire  118  is then preferably routed along the outside of the shank  54  until it reaches a convenient point to enter the interior of the shank  54 , such that it is protected from debris. 
         [0053]    The preferred strain gage transducer is illustrated in  FIG. 22  and preferably comprises four strain gage elements R 1 , R 2 , R 3 , R 4  electrically connected to form a balanced Wheatstone bridge circuit  142  such that in an unloaded condition (i.e., the gauge wheel arms  60 ,  62  are not in contact with the height adjustment arm  68 ) when a voltage (Vin) is applied between points A and C, the output voltage between points B and D will show no potential difference. Thus, R 1 /R 2 =R 4 /R 3 , and, therefore Vout equals zero. With a balanced bridge circuit  142 , any small change in the resistance of the sensing grid caused by the change in strain will throw the bridge circuit  142  out of balance producing an output voltage (Vout). The output voltage (Vout) is expressed in millivolts output per volt input (Vin). 
         [0054]    Thus, in use, the bridge circuit  142  will measure the minute changes in resistance corresponding to the strain experienced by the load sensing pin  101  as previously described resulting from the bending stress Fb exerted by the bending moment Mb. In the preferred four-element Wheatstone bridge, two strain gages are wired in compression and two in tension. In  FIGS. 22 , R 1  and R 3  are in tension (positive) and R 2  and R 4  are in compression (negative). The total strain, or output voltage of the circuit (Vout) is equivalent to the difference between the voltage drop across R 1  and R 4 . This expression is written as: 
         [0000]      Vout=Vin 
         [0055]    The load sensing pin  101  preferable provides sufficient accuracy without factory or field calibration. The tolerances of machining for this pin are generally sufficient enough that the strain gage will be accurate enough for this application without calibration. If for some reason an extremely accurate load measuring capability was desired, the capability to calibrate the measurement system could be readily provided. This linear correlation of the output voltage to known loads could be programmed into a microcontroller of the processing circuitry for monitoring and/or displaying the loads to the grower in the cab of the tractor and/or to automatically regulate the down force during planting operations. 
         [0056]    Preferably, as is well known in the art, such processing circuitry is coupled to the planter&#39;s hydraulic or pneumatic system to automatically regulate the downforce applied to the row units based on any one or more of the foregoing data values in which the detected down force is deemed too low or too high thereby automatically maintaining the appropriate amount of downforce on the row unit as the planter traverses the field. 
         [0057]    As previously identified,  FIG. 17  illustrates a partial cross section view of an alternative embodiment of the load sensing pin  101  providing three bearing surfaces (i.e. a 3-point pin  300 ) comprising a center lobe  302  and left and right shoulders  304 ,  306 . In this embodiment the load L 2  from the height adjustment arm  68  bears against the center lobe  302 . The strain gage  114  in this embodiment is applied at a location on one side of the center lobe. It should be appreciated that this 3-point pin  300  will function in substantially the same manner as the 4-point pin  200  except that the height adjustment arm  68  is not as well supported without a rocker/equalizer  76  so minor load measurement inaccuracies may result. 
         [0058]    To this point all discussion of the application of the present invention has been applied to John Deere row units  10 . Other row units  400  are commonplace such as those shown in  FIG. 18  as manufactured by Kinze. In many regards the operation of these row units  400  is similar to that of the Deere row units  10  except for the means of adjusting the planting depth. In the Kinze row units  400 , opening disks  444 ,  446  are supported from the row unit shank  402  and gage wheels  448 ,  450  are supported by gage wheel arms  404 , 406 . In order to regulate planting depth, the rotation of the arms  404 ,  406  about their mounting axis  408  is restrained. The arms  404 ,  406  are typically a casting provided with an opposing end  410 ,  412  containing sockets  414 ,  416 . The sockets  414 ,  416  receive a toggle link  418  containing a left end  420  and a right end  422 . The end  422  is received by the socket  414  of the right arm  404 . The toggle link  418  is constrained through a linkage comprising a loop  430 , a pin  432 , and an arm  434 . The arm  434  is secured at its bottom end  436  through a spacer  438  which is bolted into the shank  402 . The top end  446  of the arm  434  can be selectively positioned within slots  442  of the shank cover  444  as a means of regulating the planting depth. During planting operation, the toggle link  418  will experience loads L 4 , L 5  from the arms  404 , 406 . 
         [0059]      FIG. 21  shows the preferred embodiment of the present invention as adapted for use within the row unit  400 . The spacer  438  is still utilized but instead of being bolted into the row unit shank  402 , the bolt has been replaced by the load sensing pin  101  of the present invention. In order to accurately measure the load, the pin  101  must not place an axial load upon the shank panels  440 ,  442  and the spacer  438  must be allowed relative freedom of movement such that all loads are transferred to the load sensing pin  101 . In this embodiment, the load sensing pin  500  is again preferably provided with two lobes  502 ,  504  upon which the loads from the depth adjustment linkage are born. The pin  500  is supported at two shoulders  506 ,  508  at either end of the pin  500 . A strain gage is located at the center of the pin  510  at a location to maximize its distance from the neutral axis relative to the applied loads L 6 . The loads L 6  will be equal to (L 4 +L 5 )/2 as the geometry of this depth adjustment mechanism ensures the loads L 6  are equal on each lobe  502 ,  504 . 
         [0060]      FIGS. 20 and 21  show a preferred embodiment of the pin assembly  520  which preferably comprises the load sensing pin  500  and a restraint  530  secured thereto by a washer  532  and a screw  534  inserted into a threaded hole  536  in the pin  500 . The opposite end of the pin  500  is preferably constrained within the row unit shank  402  by means of a shim  538 , washer  540 , and screw  542 . The thickness of the shim  538  is selectable depending upon the tolerances in the width of the shank  402  in order to ensure that no axial load is placed upon the pin  500  when the screw  542  is fastened into the hole  544 . The restraint  530  is preferably provided with edges  550  that locate adjacent to the lower edge  552  of the row unit shank  402  as best seen in  FIG. 19 .  FIG. 19  illustrates a partial view of the row unit assembly  400  wherein the front portion and a portion of the side of the shank have been cut away to allow viewing the internal components of the depth adjustment mechanism. It should be appreciated that rotation of the restraint  530  and thus the pin  500  is prevented by nature of the close proximity of edges  550 ,  552 . The preferred location of the strain gage  560  is shown in  FIG. 20  along with wires  562  and sheathed wires  564 . The sheathed wires  564  are well protected by being installed adjacent the inner surface  566  of the restraint  530  and fastened securely by a clip  568  which is bolted through the hole  570  in the arm  530 . 
         [0061]    While all of the above descriptions have been made in the context of a planter row unit, it will be readily realized that the teachings contained herein are applicable to any pin subjected to shear from a load in a single and consistent direction. The methods of restraining rotation, converting shear to bending stress, and routing the wiring will see uses in many applications outside the field of agricultural planting. 
         [0062]    The foregoing description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodiment of the apparatus, and the general principles and features of the system and methods described herein will be readily apparent to those of skill in the art. Thus, the present invention is not to be limited to the embodiments of the apparatus, system and methods described above and illustrated in the drawing figures, but is to be accorded the widest scope consistent with the spirit and scope of the appended claims.