Abstract:
The knife head mounts to the sickle to hold a plurality of knife sections thereon while allowing removal of the knife sections individually without major disassembly for ease of in field repair and replacement. A knife pin of the knife head connects to a knife arm driven by the sickle drive mechanism and is removable from above also without major disassembly. The knife pin connection provides a vertical self adjustment capability to accommodate sickle wear and vertical misalignment between the sickle and drive. And the knife arm is streamlined for cut plant material flow thereabout and is also adapted for ease of removal and field repair.

Description:
[0001]    This application is the US National Stage for International Application No. PCT/US12/39869, filed on May 29, 2012, which itself is related to and claims the benefit of U.S. Provisional Application No. 61/491,060, filed May 27, 2011. 
     
    
     TECHNICAL FIELD 
       [0002]    This invention relates generally to a knife arm and head assembly for the sickle of a header of an agricultural cutting machine, such as a combine, windrower or other crop harvesting machine, or a mower, and more particularly, to a knife arm and head assembly that is easily serviceable, removable and replaceable, to reduce complexity and downtime for repair and replacement of components, particularly, the knife and knife sections of the sickle that are expected to wear and break from time to time, and which assembly is vertically self adjusting to compensate for wear and vertical misalignment of the sickle and sickle drive. 
       BACKGROUND ART 
       [0003]    The disclosure of U.S. Provisional Application No. 61/491,060, filed May 27, 2011, is hereby incorporated herein in its entirety by reference. 
         [0004]    Sickles typically including cutter bars supporting a row of knives, have been used to cut plants, including, but not limited to, hay, grasses, small grains and the like, for many years. The knives are composed of a plurality of knife or sickle sections which are mounted in side by side relation forming an elongate metal knife assembly. The elongate knife assembly is normally supported so as to slide longitudinally along an elongate stationary bar that has forwardly projecting, spaced apart guards bolted to a structural beam. The knife assembly moves back and forth in a reciprocating movement to move the knives relative to the guards so that the leading knife edges of the knives cross over the guards or through slots in the guards. This produces a shearing or cutting action which severs plant stems and stalks or other material captured between the knives and the guards. 
         [0005]    In a harvesting machine, such as a combine or windrower, the knife assembly and stationary bar are typically supported in connection with a cutting head or header, and are oriented so as to extend sidewardly along a forward edge portion of structure such as a floor or pan of the header, hereinafter sometimes referred to generally as the floor. The floor or pan defines the lower periphery of a cut crop or plant flow area, which can include conveying apparatus, such as one or more augers or belts, operable in cooperation with a reel in machines so equipped, for conveying the cut plant material and crops, for instance, to a feeder inlet of a combine or windrow forming apparatus of a windrower. 
         [0006]    A knife assembly, which will weigh from 35 to 38 pounds for a typical 20 foot wide header, typically must accelerate and decelerate two times per cycle as a result of the reciprocating movement. A typical speed for the knife assembly is up to about 16 hertz or cycles per second. Thus, it can be seen, the reciprocating motion at a high cycle per second generates high acceleration values and high deceleration values that in turn generate high forces on the structural components. Other damage that can occur includes dulled, chipped, and broken knife sections, that will result in unsatisfactory plant cutting, necessitating replacement of the damaged sections. 
         [0007]    The knife sections and supporting structure are also subject to general wear, e.g., from friction, which can be accelerated by use in abrasive environments such as dusty areas and some plant varieties. As a result, the vertical height or position of the knife assembly can gradually lower relative to the drive mechanism which reciprocatingly propels it sidewardly. And, when changing worn components such as knife sections, the new knife sections may be thicker, which can change the vertical relationship between the top of the knife assembly and the drive mechanism. Also, some stationary bars may have some vertical flexibility, which can result in variances between the heights of the knife assembly and drive during operation, for instance, resulting from passage of the sickle over uneven terrain. 
         [0008]    Known reciprocating sickle drives include, but are not limited to, an eccentric shaft on a rotating hub, a wobble drive, or a similar well known commercially available device. Such drives are typically located at the sides of the header, so as to drive the knife assembly from the end. Reference in this regard, the modern side located epicyclical sickle drive of Regier et al., U.S. Pat. No. 7,121,074 B1 issued Oct. 17, 2006, which illustrates a representative simple end connection to a sickle. An end connection is advantageous as it allows easy and quick disconnection of the drive from the knife assembly and removal and replacement thereof, it does not interfere with access to individual knife sections for removal and replacement, and it allows substantial flexibility and variance between the relative locations of the drive mechanism and the sickle. 
         [0009]    Disadvantages of the side drive location include that the header must include significant frame structure for supporting the drive and to withstand forces and vibrations generated thereby. The end structure or crop divider at the end of the header must also be relatively wide, to accommodate the drive and to direct adjacent standing crops therepast, and increasing the possibility of accidentally pushing down adjacent standing crops. Additionally, for headers utilizing two drives located on opposite sides of the header, it is usually desired to time the operation of the drives such that the forces and vibrations generated by the respective drives cancel one another. This typically involves relatively long mechanical drive lines connecting the two drives together, which is disadvantageous as it adds weight, cost and complexity. 
         [0010]    Driving a knife assembly or assemblies of a header from a more central location, such as the center of the header, is desirable as it provides several advantages compared to a side location. As a result, center drive mechanisms have been developed. Reference in this regard, Priepke U.S. Pat. Nos. 7,810,304; 7,805,919; 7,730,709; 7,520,118; and 7,401,458, and Bich U.S. Pat. No. 8,011,272 which disclose a family of vertically compact sickle drive or drives incorporated in or below a header floor, which overcome many of the disadvantages and shortcomings discussed above in regard to side drives. However, locating the sickle drive mechanism in or below the header floor can still result in the apparatus connecting the drive or drives with the knife assembly or assemblies being in the path of the cut plant material moving rearwardly past the sickle, so as to interfere with and/or split the material flow and even cause some plowing and accumulation of the cut plant material in front of the connecting apparatus. Therefore, it would be desirable to minimize such interference and splitting of the material flow. 
         [0011]    Reference also Bich et al. U.S. Pat. No. 8,151,547 which discloses a knife arm assembly, configured for attachment to a center drive, which has the shortcomings of a knife head requiring an intermediary member for attachment to the knife, and removal and replacement of the knife pin of which connecting the knife head to the knife arm requires removal of the entire knife head from the sickle knife. 
         [0012]    It would also be desirable to have a manner of adjusting or compensating for any differences or variances between the height of the drive mechanism or mechanisms and the knife assembly or assemblies, for accommodating manufacturing and assembly variations, tolerances, and wear, and to avoid increased friction and binding that can increase wear on both the sickle and drive and increase power consumption. 
         [0013]    As another consideration, when individual or groups of knife sections are worn beyond their useful life, or are broken or damaged, so as to require removal and replacement, it would be desirable to have a manner of replacing them quickly and easily, particularly in the field during plant cutting operations, to minimize downtime and effects on production. 
         [0014]    Still further, it would be desirable to have the ability to remove and replace the knife pin of a knife head, without having to remove the entire knife head from the sickle knife for service. 
         [0015]    Therefore, what is sought is apparatus for connection of a sickle drive to the knife of a sickle, adapted for use along the length of a sickle, e.g., at a more central location on a header, which provides ease of removal, service and replacement, minimizes interruption and splitting of plant material flow, is vertically self-adjusting, and provides one or more of the other features, while overcoming one or more of the shortcomings and limitations, set forth above. 
       SUMMARY OF THE INVENTION 
       [0016]    What is disclosed is a knife head and arm assembly for connecting a sickle drive to the knife of a sickle, adapted for use anywhere along the length of a sickle, which provides ease of removal, service and replacement, minimizes interruption and splitting of plant material flow, provides a vertical self-adjusting capability, and which overcomes one or more of the shortcomings and limitations set forth above. 
         [0017]    According to a preferred aspect of the invention, the knife head is an elongate, low profile member attached by an array of fasteners to an elongate structural beam of the sickle cutter. A longitudinally extending, side by side array of sickle knife sections are disposed between the knife head and the beam, and are securely clamped or captured by the attachment of the knife head. Attachment in this manner allows locating the knife head at any desired position along the knife assembly. 
         [0018]    As another preferred aspect of the invention, the knife head includes at least one longitudinally extending portion having increased vertical flexibility. This can be incorporated into the knife head as a stepped or tapered shape and additionally provides a low profile. The increased flexibility is advantageous as it allows the knife head and underlying portion of the sickle knife to flex if required, for instance, if bent, or if the sickle is of the flexible variety. 
         [0019]    As another preferred aspect of the invention, the knife head includes an upstanding knife pin. A single fastener, removable solely from above the knife head, secures the knife pin. This facilitates removal and replacement of the knife pin from above, without having to access the underside of the knife head, or removing it from the sickle. The knife pin is configured to be cooperatively received in a downwardly open receptacle of a knife arm of the invention which attaches to and will be supported by the sickle drive mechanism in cantilever relation above the knife head. 
         [0020]    The knife pin has an outer bearing surface therearound, preferably of a cylindrical or other suitable shape to facilitate limited relative vertical movements of the knife head and knife arm. As a result, this feature can provide an amount of self-adjustability in the relative positions of the knife arm and knife head, to reduce possible occurrence of binding, accelerated wear, power consumption, and other undesirable conditions. As the knife assembly and supporting structure wear, this will also allow the knife head to gradually lower relative to the knife arm, without affecting the ability of the assembly to reciprocatingly drive the sickle. If used with a flexible sickle, the capability of the knife head to move vertically relative to the knife arm can facilitate flexing of the sickle in the immediate vicinity of the knife head, which can reduce binding, wear and power consumption. 
         [0021]    According to another aspect of the invention, the knife arm has a mounting end configured for attachment to the drive mechanism for reciprocating sideward movement therewith, but which allows quick and easy removal of the knife head. The knife arm includes a distal end opposite the mounting end disposed to be supported in cantilever relation to the drive mechanism. The distal end includes an inner bearing surface bounding and defining the downwardly open receptacle configured for cooperatively receiving the knife pin with the inner bearing surface intimately contacting the outer bearing surface therearound for holding the pin in the receptacle sufficiently to allow the knife arm and attached knife assembly to follow their intended sideward reciprocating path, while optionally allowing a limited amount of upward and downward movement relative to the knife arm and thus the drive mechanism during the movement. The bearing surfaces are preferably relatively large, so as to be robust and to distribute loads and wear. 
         [0022]    According to another preferred aspect of the invention, the distal end of the knife arm has opposite sides that taper divergingly in the rearward direction from the distal end about the receptacle to the mounting end, to provide a streamlined shape for facilitating flow of plant material therepast and to reduce plowing and other undesirable effects. This is preferably embodied in the knife arm having a V- or U-shape about the receptacle that tapers sidewardly outwardly to about the width of the element of the driving mechanism to which the knife arm is attached. As another preferred aspect, the upper end of the receptacle is enclosed or covered. This contributes to the streamlined effect, and reduces possibility of entry of contaminants into the receptacle. This also covers and protects the fastener attaching the knife pin to the knife head. 
         [0023]    As another advantage of the present invention, the manner of attachment of the knife head to the sickle structure distributes the loads generated during the plant cutting operation over the several fasteners, e.g., preferably eight or more, as opposed to just one or two fasteners at the end of the sickle knife, while still enabling relatively smooth plant material flow thereover and desired flexure. This manner of attachment also enables selected ones of the fasteners to be removed while the knife head remains attached to the sickle, as necessary for removing and replacing selected ones of the sickle knife sections. This is advantageous for field service, as the knife sections can be removed and replaced with minimal disassembly, reassembly, and downtime. 
         [0024]    As another alternative according to the invention, the in place of a bearing element that provides substantially free relative pivotal movement between the knife head and knife arm, a torsion element can be used that connects the knife head and knife arm, comprising a rubber or rubbery material that is loaded in torsion when the knife head and knife arm are relatively pivoted or rotated. This element can be connected in the manner of a pillow block or clamp to the knife arm and with a simple threaded bolt or screw to the knife head, for easy and quick removal and replacement. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  is a fragmentary side view of a harvester including a header having sickle knife head and arm assemblies according to the invention; 
           [0026]      FIG. 2  is an enlarged fragmentary side view of the header and sickle knife head and arm assemblies of the invention; 
           [0027]      FIG. 3  is a front view of the harvester and header, showing the location of the sickle knife head and arm assemblies; 
           [0028]      FIG. 3A  is another front view of the harvester and header, with a sickle of the header flexed; 
           [0029]      FIG. 4  is a fragmentary perspective view of the header, showing aspects of the sickle knife head and arm assemblies; 
           [0030]      FIG. 5  is an enlarged side view showing aspects of the header, sickle drives, and the sickle knife head and arm assemblies; 
           [0031]      FIG. 6  is a fragmentary perspective view of the sickle, showing one of the knife head and arm assemblies; 
           [0032]      FIG. 7  is another fragmentary perspective view of the sickle, showing one of the knife head and arm assemblies; 
           [0033]      FIG. 8  is a fragmentary perspective exploded view of the sickle, showing aspects of one of the knife head and arm assemblies; 
           [0034]      FIG. 9  is a fragmentary perspective view of the sickle and one of the knife heads; 
           [0035]      FIG. 10  is a fragmentary sectional view of the sickle, showing one of the knife head and arm assemblies; 
           [0036]      FIG. 11  is another fragmentary sectional view of the sickle, showing one of the knife head and arm assemblies, with vertical separation between the knife head and knife arm; 
           [0037]      FIG. 12  is a fragmentary sectional view of the sickle, showing one of the knife heads; 
           [0038]      FIG. 13  is another fragmentary sectional view of one of the knife arms, showing removal of a bushing thereof; 
           [0039]      FIG. 14  is a fragmentary sectional view of an alternative knife head having a stepped surface for attachment of knife sections of the sickle; and 
           [0040]      FIG. 15  is a fragmentary perspective view of an alternative knife arm and head assembly connected together with a torsion element according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0041]    Turning now to the drawings wherein a preferred embodiment of the invention is shown, in  FIGS. 1 through 5 , a conventional, well known agricultural cutting machine, which is a combine  20 , is shown including a header  22 . Header  22  is shown supported in the conventional, well-known manner on a forward end  24  of combine  20 , and is operable for cutting or severing crops such as, but not limited to, small grains such as wheat and soybeans, and inducting the severed crops into a feeder  26  for conveyance into combine  20  for threshing and cleaning, in the well known manner, as combine  20  moves forwardly over a field. 
         [0042]    Header  22  includes a pan or floor  28  which is supported in desired proximity to the surface of the field during the harvesting operation, and an elongate, sidewardly extending sickle  30  along a forward edge portion  32  of floor  28 , sickle  30  being operable for severing the plants or crop for induction into header  22 , as will be explained. Header  22  additionally includes an elongate, sidewardly extending reel  34  disposed above sickle  30  and rotatable in a direction for facilitating induction of the severed plant material or crops into header  22 . Here, header  22  is configured as a draper type, having a system of elongate, flat, sidewardly moving draper belts  36  and  38  having upwardly facing surfaces disposed just rearwardly of forward edge portion  32 , operable in cooperation with reel  34  for conveying the severed plant material or crops toward an inlet opening of feeder  26  for induction into combine  20 , in the well-known manner. 
         [0043]    Referring more particularly to  FIG. 3 , sickle  30  extends in a sideward direction along the width of floor  28 , between a first side edge portion  40  of the floor, and an opposite second side edge portion  42 . Sickle  30  includes an elongate, sidewardly extending first cutter bar assembly  44 , and an elongate, sidewardly extending second cutter bar assembly  46  extending in end to end relation to cutter bar assembly  44 , cutter bar assemblies  44  and  46  being supported in substantially longitudinally aligned relation adjacent to forward edge portion  32  of floor  28 . 
         [0044]    Referring more particularly to  FIGS. 4 and 5 , cutter bar assemblies  44  and  46  each include a plurality of sidewardly facing aligned slots  48  through a sidewardly extending array of guards  50  which project forwardly from a stationary bar  52  at sidewardly spaced intervals therealong. Stationary bar  52  extends the length of sickle  30  just forwardly of forward edge portion  32  of floor  28 , and guards  50  are mounted to bar  52  with fasteners  54 . Bar  52 , in turn, is mounted to a frame  56  of header  22  adjacent to forward edge portion  32  by fasteners  54 , as best illustrated in  FIG. 5 . Each of cutter bar assemblies  44  and  46  supports an elongate knife assembly  58  for reciprocating longitudinal movement within slots  48 , each knife assembly  58  having a row of knife sections  60  including oppositely facing, angularly related knife edges which, in conjunction with adjacent guards  50 , effects a shearing or cutting action which severs plant stems and stalks or other material captured between the knives and the guards as the knife sections are reciprocatingly moved sidewardly, as denoted by arrow A in  FIG. 4 . 
         [0045]    Knife assemblies  58  are reciprocatingly driven utilizing first and second sickle drives  62 A and  62 B. First and second sickle drives  62 A and  62 B are illustrated in  FIGS. 3 and 4  at a center location on header  22  between side edge portions  40  and  42  at the opposite ends of the header, although it should be noted that it is contemplated that sickle drives  62 A and  62 B could alternatively be utilized at other locations on a header, and that multiple sickle drives  62  could be used at multiple locations on a header. Sickle drives  62 A and  62 B are preferably located completely within or beneath floor  28  as best shown in  FIG. 5 , to reduce interruption of flow of cut plant material thereover and thereabout. Drives  62 A and  62 B can comprise a variety of mechanisms, such as, but not limited to, epicyclical drives that impart purely linear sideward motion, or pivoting sideward motion, to the knife head assemblies, as desired or required for a particular application. The disclosures and teachings of Priepke U.S. Pat. Nos. 7,810,304; 7,805,919; 7,730,709; 7,520,118; and 7,401,458, and Bich U.S. Pat. No. 8,011,272 are hereby incorporated by reference herein in their entireties, as representative non-limiting examples of drives that can be utilized with the present invention. 
         [0046]    Sickle drives  62 A and  62 B include drive elements  102  that project forwardly through slots  104  or other openings in or in the vicinity of forward edge portion  32  of floor  28 , for connection to the respective knife assemblies  58 , and which are moved in a side to side reciprocating motion by the respective drive, for effecting the cutting action. Header  22  includes knife heads  64  and knife arms  66  cooperatively arranged in knife head and arm assemblies  68  constructed and operable according to the present invention, connecting drives  62 A and  62 B in driving relation with respective knife assemblies  58 . As is evident from the location of knife head and arm assemblies  68 , they will be located directly in the path of the rearward flow of cut plant material over forward edge  32  and onto the upper surface of floor  28  during plant cutting operations. As a result, if assemblies  68  are large and/or obtrusive, they can have a plowing effect, causing the plant material to build up forwardly thereof, and/or be split or interrupted, so as to not flow smoothly onto the floor. It is therefore desired to minimize such flow disruptions. 
         [0047]    Additionally, as noted above under the Background Art heading, from time to time, the knife sections  60  will be damaged, e.g., broken, chipped, become worn, or for other reasons require removal and replacement. Sometimes, this will be during plant cutting or harvesting, and thus in the field, and it will be desired to accomplish the removal and replacement as quickly as possible, with minimal removal/disassembly of components. It has also been found that a limited amount of relative vertical movement between the drive  62 A or  62 B and the knife assemblies  58  is desirable to facilitate free reciprocating movement of the knife assemblies, both to accommodate knife wear and flexing if so configured, as illustrated by the flexed cutter bar assemblies  46  and  48 , in  FIG. 3A . 
         [0048]    Referring also to  FIGS. 6 through 15 , knife head and arm assemblies  68  each comprise an elongate member  70  attached by an array of threaded fasteners  72  to an elongate structural beam  74  ( FIGS. 5 ,  10 ,  11 ,  12 , and  14 ) underlying the respective knife head assembly  58  of the sickle cutter (beam  74  omitted from knife assembly  58  of cutter bar assembly  44  in  FIG. 14  as will be discussed). Several of knife sections  60  of the respective knife assembly  58  are disposed between beam  74  and member  70 , so as to be clamped or captured by this attachment, while the other knife sections  60  of the knife assembly are mounted in the well known manner using additional fasteners  72  for direct attachment to beam  74 . Features of knife head  64  include controlled or limited vertical flexibility, which provides an ability to bend or flex to a limited extent with portions of a sickle attached thereto. This capability is preferably achieved by reducing the vertical height or extent of at least one longitudinal end  76  of member  70  relative to a middle or opposite end, as denoted by heights H1 and H2 in  FIG. 12 , resulting in a stepped shape, although it should be recognized that a tapered or other shape that imparts desired flexibility can alternatively be used. Fasteners  72  here comprise bolts which are inserted from below and extend upwardly through mating holes in beam  74 , knife sections  60  and knife head  64 , at the top of which they threadedly engage nuts  78 . On end  76 , nuts  78  are located on top of member  70 . On the thicker region, nuts  78  are located in upwardly facing sockets  80  recessed into the top surface of member  70 , such that the same length fasteners  72  can be used at both locations if desired. Fasteners  72  are arranged in a spaced apart longitudinally extending array, and are provided in sufficient number, e.g., eight or more, to provide secure attachment to beam  74  for clamping or capturing knife sections  60 , and for withstanding shear loads generated by the side to side cutting motion and reciprocating action, which will be longitudinal with respect to member  70 . 
         [0049]    To provide added shear strength and a means to better align the holes of knife head  64 , knife sections  60  and beam  74 , knife head  64  preferably carries at least one and preferably two downwardly extending pins  82  positioned to be received in aligned holes in one or more of the knife sections and the beam, as shown in  FIG. 12 . Pins  82  are preferably disposed at a predetermined location corresponding or in close proximity to a knife pin  84  which is positioned for connection to knife arm  66 . Knife pin  84  is preferably mounted on the top surface of knife head  64 , by a threaded fastener  86  threadedly received in a threaded hole  88  in the upper surface of knife head  64 . When fastener  86  is tightened, its head is brought to bear against a shoulder  90  extending about the upper end of a hole  92  through the pin which receives fastener  86 . This arrangement allows removal of knife pin  84  from knife head  64  merely by removing fastener  86 , without accessing the underside of the knife head or removing it from the sickle. 
         [0050]    Knife pin  84  is configured to be cooperatively received in a downwardly open receptacle  94  in a distal end  96  of knife arm  66  for connection to the respective drive  62 A or  62 B. Here, knife pin  84  has a smooth straight outer surface  98  therearound which is preferably cylindrical shaped and sized to be matingly received in receptacle  94 , optionally for up and down movement therein to facilitate relative up and down movement of knife head  64  and knife arm  66 , as denoted by arrows VM in  FIG. 11 . 
         [0051]    Knife arm  66  has a mounting end  100  opposite distal end  96 , configured for attachment to a drive element  102  of drive  62 A or  62 B for reciprocating sideward movement therewith, as denoted by arrow A in  FIG. 7  (and  FIG. 4 ). Recall here that the movement can be straight side to side or sideward pivoting movement, which will be a function of the type of drive used. Here also, it can be observed that the connection with drive element  102  includes a vertical key  106  which is cooperatively received in vertical keyway  108  in the drive element  102  to provide ease of alignment and strength under side to side shear loading conditions generated by the plant cutting action. Knife arm  66  is held in position on the end of element  102  by threaded fasteners  110  received in holes  112  in arm  66  and threadedly engaged with threaded holes  114  in drive element  102 , as illustrated in  FIG. 8 . 
         [0052]    Addressing receptacle  94  of knife arm  66 , it is preferably bounded and defined by an inner bearing surface  116  which bounds and defines receptacle  94 , and which here is also cylindrical shaped, and sized for receiving knife pin  84 . The fit between inner surface  116  and outer surface  98  of the knife pin can be tight, or can allow relatively free vertical movement between knife arm  66  and knife pin  84  if that is desired, but virtually no lateral play, which optional vertical movement will be limited to a maximum distance VM ( FIG. 11 ) by the fixed vertical location of knife arm  66  by virtue of its attachment to element  102  of drive  62 A or  62 B, and the retention of knife head  64 , by virtue of attachment to knife assembly  58  and its containment in slot  48  of cutter bar  44  or  46 . Both the knife pin and receptacle should be sufficiently robust to handle the repetitive lateral forces that will be generated by prolonged cutting operation of the sickle. It should be noted however, that alternative shapes for outer surface  98  and bearing surface  116  can be used, such as but not limited to, rectangular, square, hexagonal, octagonal, and other polygons. An advantage of the cylindrical shape is that it also allows rotation of the knife head and knife assembly relative to the knife arm about a vertical axis through the knife pin, without tilting of the knife head and knife arm one relative to another. 
         [0053]    Thus, for example, if a flexible sickle is employed, if the interface between surfaces  98  and  116  allows relative vertical movement, this movement will allow the flexible sickle to smoothly flex up and down by virtue of freedom of knife pin  84  to move upwardly and downwardly within receptacle  94 , but the knife pin will be restrained against tilting or rocking movements, so as to reduce possible occurrences of binding and resultant increase in power consumption and wear. 
         [0054]    To facilitate the ability of knife pin  84  and receptacle  94  to move freely upwardly and downwardly one relative to the other, and also rotate one relative to the other, knife arm  66  optionally includes an internal grease reservoir  118  configured for holding a quantity of grease for distribution within receptacle  94 , and a connecting grease fitting  120  usable for resupplying the grease as required. Alternatively, a grease or lubricant impregnated bushing or the like can be used in receptacle  94  for reducing friction at the interface between the knife pin and knife arm. The lower end and upper end of receptacle  94  is preferably enclosed to prevent entry of contaminants such as dust, dirt and the like into the interface between bearing surface  116  and outer surface  98 , a lower opening  140  being sealed with a conventional annular or ring seal  142 , and the upper end in a manner discussed below. 
         [0055]    It is anticipated that with use, bearing surface  116  of a bearing that includes this surface, and/or the bearing itself, and/or the knife pin, will wear to such an extent as to require replacement. To facilitate replacement, bearing surface  116  of receptacle  94  comprises an inner peripheral surface of a removable bearing element  122 , which can comprise for instance a solid or impregnated sleeve or bushing, or a ball, needle, or spherical type bearing, press fit into a cavity  124  through lower opening  140 , and the upper end of receptacle  94  is shown enclosed by a removable plug  126  which is also usable for removing the bearing element  122 . The ability easily and quickly remove and replace bearing element  122  with tools available in the field is highly desired when harvesting and time is of the essence. In one preferred configuration, plug  126  is located in sealed abutment with a lower surface of a shoulder  128  extending at least partially about and defining an upper opening  130  ( FIG. 13 ) of cavity  124 , above bearing element  122  and forming the desired sealed condition against entry of contaminants and moisture. When removal and replacement of element  122  is required, plug  126  can be pressed downwardly, using a press, or, if one is unavailable, e.g., service occurs in the field, suitable tools such as a hammer and a socket  132  or other suitable item of similar diameter to the bearing element, can be used to push or tap the plug downwardly through cavity  124 , and will also remove the ring seal  142  if used. In both instances, the downward movement of plug  126  will push bearing element  122  downwardly from cavity  124  through lower opening  140 . Replacement then entails simply replacing plug  126  in cavity  124  against shoulder  128 , and pressing or tapping the bearing element or a new one into position. 
         [0056]    Here, it can be observed that cavity  124  and lower opening  140  have a first transverse extent or diameter, that is larger than that of upper opening  130 , and that plug  126  has a transverse extent or diameter that is marginally smaller than that of the cavity  124  and lower opening, to facilitate passage of the plug therethrough, but which prevents passage through upper opening  130 . Plug  126  can include a protuberance  132  extending upwardly therefrom and configured to sealably mate with and engage shoulder  128  to form the upper sealed condition. The protuberance  132  also strengthens plug  126 . 
         [0057]    Thus, with the knife head and arm assembly of the invention, most of the knife sections  60  clamped to the sickle by knife head  64  can be removed and replaced by removal of just two fasteners  78  and nuts  80 , and knife pin  84  can be removed and replaced by removing knife arm  66  (requiring removing just two fasteners  110 ) and one fastener  86 . 
         [0058]    In another preferred configuration, as shown in various of the Figures, distal end  96  of knife arm  66  has opposite sides  136  and  138  that taper divergingly toward mounting end  100 . This imparts a streamlined shape to each of the knife arms for facilitating flow of plant material thereabout. This taper is preferably embodied in a V-shape or U-shape when viewed from above, extending about distal end  96 , and additionally serves to deflect the cut plant material to some extent away from the slots in forward end  32  of floor  28  of the header through which the driven elements of drives  62 A and  62 B extend. 
         [0059]    Optional features of knife head  64  include controlled or limited vertical flexibility, which provides an ability to bend or flex to a limited extent with portions of a sickle attached thereto. This capability is preferably achieved by reducing the vertical height or extent of at least one longitudinal end  76  of member  70  relative to a middle or opposite end, as denoted by heights H1 and H2 in  FIG. 12 , resulting in a stepped shape, although it should be recognized that a tapered or other shape that imparts desired flexibility can alternatively be used. 
         [0060]    As another optional variant of the invention, referring more particularly to  FIG. 14 , it is desired for knife assemblies  58  of respective cutter bar assemblies  44  and  46  to overlap in the vicinity of drives  62 A and  62 B, so that there is not a gap in the cutting action of the sickle. One option to avoid undesired flexing and wear of one or both of the cutter bars, one of the knife assemblies can be shimmed up or down so that neither need be flexed to travel above or below the other when reciprocatingly moved. As another option according to the invention, one of the elongate members  70  of one of the knife heads  64  has a further stepped portion  144  on its underside within the overlapping region, which here is member  70  of assembly  44 . Stepped portion  144  is raised an amount H3 above the lower surface of the rest of that member  70 , which amount is equal to the thickness of a knife section  60 . Additionally, the knife sections  60  are attached to stepped portion  144  of member  70  directly by fasteners  72  upwardly from the underside, so that the fasteners are flush with or recessed in the underside of those knife sections and thus can overlap and be capable of relative movement over knife sections  60  of knife assembly  58  of cutter bar assembly  46 , so as to eliminate this area as a source of additional wear due to bending, and any need for shimming for that purpose. To accommodate this, the knife sections  60  of cutter bar assembly  46  will be attached to beam  74  of that assembly with fasteners  72  that will be flush with or recessed in the upper surfaces of the knife sections. Here, it can be observed that stepped portion  144 , because of its reduced section can be configured to provide some desired flexibility for use with a flexible cutter bar assembly, if desired. 
         [0061]    Referring more particularly to  FIG. 15 , knife head and arm assembly  68  is shown including alternative knife pin structure for attaching knife head  64  to knife arm  66 , which comprises a torsion element  146  as the knife pin to allow some limited and controlled relative pivoting action therebetween. Torsion element  146  includes an annular bushing or block of a rubber or rubbery material having resilient elastic properties and a passage therethrough that receives or carries a threaded fastener  148  which is threadedly received in a threaded hole in elongate member  70  of knife head  64  in the same manner as described above for attachment of the knife pin  84 . An outer periphery of torsion element  146  is preferably received in a receptacle  150  here comprising concavities in the end of knife arm  66 , and in a companion strap  152 , strap being tightenable about element  146  and secured by fasteners  154 . As a result, the outer periphery of torsion element  146  is at least largely prevented from rotational movement relative to knife arm  66 , and the inner periphery of the element  146  is at least largely prevented from relative pivotal movement relative to knife head  64 , such that relative pivotal movement of knife head  64  and knife arm  66  is effected only by internal elastic torsional deformation of element  146 . Elasticity of torsion element  146  can be advantageously configured if desired so as to allow some very limited relative vertical movement and/or twisting between the knife head and knife arm to accommodate some flexure of the cutter bar. Torsion element can also advantageously be capable of absorbing and limiting transmission of some shock loads generated by the operation of the sickle to the drive  62 A or  62 B connected thereto. Like the above described construction involving knife pin  84 , use of torsion element  146  is also advantageous as it and fastener  148  can be removed and replaced solely from above quickly. 
         [0062]    In light of all the foregoing, it should thus be apparent to those skilled in the art that there has been shown and described a novel knife head and arm assembly. However, it should also be apparent that, within the principles and scope of the invention, many changes are possible and contemplated, including in the details, materials, and arrangements of parts which have been described and illustrated to explain the nature of the invention. Thus, while the foregoing description and discussion addresses certain preferred embodiments or elements of the invention, it should further be understood that concepts of the invention, as based upon the foregoing description and discussion, may be readily incorporated into or employed in other embodiments and constructions without departing from the scope of the invention. Accordingly, the following claims are intended to protect the invention broadly as well as in the specific form shown, and all changes, modifications, variations, and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention, which is limited only by the claims which follows.