Abstract:
When connecting two elements that are moveable with respect to one another, some amount of clearance, i.e., spacing between the elements, is included to minimize friction between the elements. The present invention is directed to setting the clearance within a desired range, regardless of manufacturing tolerances of the two elements. In particular, the present invention is directed to power cutting tools wherein it is necessary to set the clearance between one or more reciprocating blades and a blade support member.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention is generally directed to setting the spacing between two elements that are moveable with respect to one another. This spacing is commonly referred to as the “clearance” between the elements. Some amount of clearance, i.e., within a desired range, is included to minimize friction between the elements. However, manufacturing tolerances and conventional assembly techniques can result in deviations outside the desired range of clearance.  
           [0003]    In particular, the present invention is directed to power cutting tools wherein it is necessary to set the clearance between one or more moving, e.g., reciprocating, blades and a blade support member. The term “power cutting tool” includes hand-held power tools such as a hedge trimmers, as well as mechanisms which are not hand-held but whose operation is controlled by the hands of a user, e.g., a lawn mower.  
           [0004]    2. Description of the Related Art  
           [0005]    In order to perform a desired task using a cutting tool, it is important that the relatively moving blade or blades be separated from each other or from a relatively stationary blade by an optimum clearance for accomplishing the task efficiently.  
           [0006]    Conventionally, blade clearance for cutting tools is preset by the manufacturer. Alternatively, it is known to use a spring mechanism to force relative contact between the blades. It is also known to use jam nuts to periodically adjust the clearance. However, many non-professional users do not know how or take the time to make the necessary adjustments.  
           [0007]    Examples of known cutting devices associated with reciprocating blades include U.S. Pat. Nos. 5,771,583 to Kremsler et al., 5,689,887 to Heywood et al., 5,075,972 to Huang, 4,879,303 and 4,868,988 to Han, 4,075,760 to Germain, 3,579,827 to Grahn, 3,200,493 to Dodegge, and 2,275,180 to Holsclaw.  
         SUMMARY OF THE INVENTION  
         [0008]    An object of the present invention is to set, within a desired range, the clearance between first and second elements that are constrained to a prescribed relative motion. Thus, it is a further object of the present invention to constrain the first and second elements to the prescribed relative motion while maintaining friction in a desired range. It is yet a further object of the present invention to set an optimal range for the clearance between the first and second elements.  
           [0009]    An advantage of the present invention is that the need for grinding blades to give tighter control of their thickness is eliminated.  
           [0010]    The above objects and advantages, as well as other objects and advantages that will become clear from the following description of the present invention, are realized by a system for setting a clearance between relatively movable elements. The system comprises a first element; a second element relatively movable with respect to the first element; and a third element penetrating the second element along an axis, the third element being fixed against axial displacement with respect to the first element. The third element having a first axial portion extending a first dimension along the axis between first and second axial ends, the first dimension exceeding a thickness of the second element along the axis, and a second axial portion being connected to the first axial portion at the second axial end and having an enlarged radial dimension relative to the first portion, the second element being interposed between the first element and the second portion. Whereby the first axial end extends into a depression in the first element a second dimension that is less than the difference between the first dimension and the thickness.  
           [0011]    The above objects and advantages, as well as other objects and advantages that will become clear from the following description of the present invention, are also realized by a system for setting blade clearance in a power cutting tool. The system comprises a blade support member; a first cutting blade relatively movable with respect to the blade support member; a second cutting blade relatively moveable with respect to the blade support member and with respect to the first cutting blade; and a spacer penetrating the first and second cutting blades along an axis, the spacer being fixed against axial displacement with respect to the blade support member. The spacer having a first axial portion extending a first dimension along the axis between first and second axial ends, the first dimension exceeding a combined thickness of the first and second cutting blades along the axis, and a second axial portion being connected to the first axial portion at the second axial end and having an enlarged radial dimension relative to the first portion, the first and second cutting blades being interposed between the blade support member and the second portion. Whereby the first axial end extends into a depression in the blade support member a second dimension that is less than the difference between the first dimension and the combined thickness.  
           [0012]    The above objects and advantages, as well as other objects and advantages that will become clear from the following description of the present invention, are also realized by an apparatus for setting a clearance between relatively movable elements connected by a spacer having a flange. The apparatus comprises a first jaw adapted for engaging a first one of the relatively movable elements; a second jaw including a surface adapted for engaging a second one of the relatively movable elements, the surface having a recess adapted for engaging the flange; and a press moving the first and second jaws toward one another. Wherein the second jaw is adapted for displacing the spacer to deform the first one of the relatively moveable elements, and the surface is adapted for stopping spacer displacement by engaging the second one of the relatively movable elements.  
           [0013]    The above objects and advantages, as well as other objects and advantages that will become clear from the following description of the present invention, are also realized by a method of setting a clearance between relatively movable elements. The method comprises orienting adjacent first and second relatively movable elements against a first press jaw; inserting a third element along an axis extending through an aperture in the second element, the third element including a first axial portion extending a first dimension along the axis between first and second axial ends, the first dimension exceeding a thickness of the second element along the axis, and a second axial portion being connected to the first axial portion at the second axial end and having an enlarged radial dimension relative to the first portion, the second element being interposed between the first element and the second portion; aligning a second press jaw against the third element and in opposition to the first press jaw; pressing the third element along the axis against the first element; deforming the first element with the first axial end so as to create a depression extending into the first element a second dimension; whereby axial clearance between the first element, the second element, and the second portion is equal to the first dimension less a combined total of the thickness and the second dimension.  
           [0014]    These and other objects and advantages of the present invention are set forth in the description that follows, and in part will be readily apparent to those skilled in the art from the description and drawings, or can be learned by practice of the invention. These objects and advantages of the invention can be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    The following detailed description of preferred embodiments according to the present invention refer to the accompanying drawings, wherein identical numerals indicate like parts.  
         [0016]    [0016]FIG. 1 schematically illustrates a first preferred embodiment of the present invention.  
         [0017]    [0017]FIG. 2 is a cross-section view taken along line II-II on FIG. 1.  
         [0018]    [0018]FIG. 3 schematically illustrates a second preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]    Referring initially to FIGS. 1 and 2, a blade  10  is relatively movable with respect to a blade support member  20  supporting the blade  10 . A spacer  30  constrains the relative movement of the blade  10  with respect to the blade support member  20  to a prescribed path. A fastener  40  can secure the spacer  30  to the blade support member  20 .  
         [0020]    According to a preferred embodiment of the present invention, the blade  10  includes an aperture  12  that extends through the blade  10  from a first surface  10 A to a second surface  10 B. The shape of the aperture  12  at its intersection with the surfaces  10 A or  10 B can be a circle, a polygon, or any other shape. According to a most preferred embodiment, the aperture  12  includes an elongated slot having a pair of substantially parallel major sides  12 A and  12 B. The locus of midpoints between the sides  12 A, 12 B define a path  14  that can be linear, curvilinear, or a combination of linear and curvilinear segments.  
         [0021]    According to a preferred embodiment of the present invention, the blade  10  is supported for reciprocal movement with respect to the blade support member  20 . The blade support member  20  includes a face  22  generally confronting the surface  10 A. In the present disclosure, the expression “support member” refers to any three dimensional element including, but not limited to a sheet of material having a generally planar, convex, or concave topography, a partial or complete enclosure, or a solid body.  
         [0022]    According to a preferred embodiment of the present invention, the spacer  30  penetrates the blade  10  by extending through the aperture  12 . According to a most preferred embodiment, the spacer  30  includes a first portion  32  and a second portion  34 . The first portion  32  has a first end  32 A contiguously contacting the face  22  and a second end  32 B connected to the second portion  34 . A cross-sectional dimension of the first portion  32 , e.g., the diameter of a circle, generally corresponds to the distance between the sides  12 A,  12 B. Thus, relative movement of the blade  10  with respect to the blade support member  20  is constrained to movement along the path  14  without significant lateral deviation toward either of the sides  12 A,  12 B. The second portion  34  has a larger cross-sectional dimension than that of the first portion  32 . Thus, the blade  10  is sandwiched between the second portion  34  and the blade support member  20 . According to a most preferred embodiment of the present invention, the first and second portions  32 , 34  are configured as coaxial right circular cylinders, with the second portion  34  having a larger diameter than the first portion  32 .  
         [0023]    According to a preferred embodiment of the present invention, the length of the first portion  32 , i.e., from the first end  32  A to the second end  32 B, is greater than the thickness of the blade  10 , i.e., from the first surface  10 A to the second surface  10 B. According to a most preferred embodiment of the present invention, the first end  32 A is received in a depression  22 A in the face  22 . Referring to FIG. 1, the length of the first portion  32  is L 1 , the depth of the depression  22 A is D, the thickness of the blade  10  is T, the clearance between the surface  10 A and the face  22  is C 1 , and the clearance between the surface  10 B and the second portion  34  is C 2 . Thus, the sum of the clearances between the blade  10 , the face  22 , and the second portion  34  is set to be the difference between the thickness of the blade  10  and the length of the first portion  32  less the depth of the depression  22 A relative to the face  22 . This relationship is expressed in Equation (1).  
         ( C 1 +C 2)=( L 1 −D )− T   (1)  
         [0024]    Thus, according to the present invention, the sum of the clearances (C 1 +C 2 ) is not affected by deviations in the blade thickness T or the first portion length L 1  inasmuch as the depression depth D is adjusted to account for these deviations.  
         [0025]    The sum of the clearances (C 1 +C 2 ) is set by a preferred apparatus  50  according to the present invention. The apparatus  50  includes a first jaw  52  and a second jaw  54  that are driven toward one another in a pressing operation. The first jaw  52  engages the blade support member  20  and provides a reaction force against the force used to form the depression  22 A. The first jaw  52  can include a recess  52 A for defining the boundary of the depression  22 A or for freely accommodating a first terminus  40 A of the fastener  40 . The second jaw  54  includes a face  56  having a recess  56 A that engages a pressing end  34 A of the second portion  34  for pressing the spacer  30  against the face  22  in order to form the depression  22 A. The recess  56 A can also freely accommodate a second terminus  40 B of the fastener  40 . The first terminus can include threads which threadably engage a nut.  
         [0026]    According to a preferred embodiment of the present invention, the depth of the recess  56 A relative to the face  56  is greater than the length of the second portion  34 , i.e., from the pressing end  34 A to a shoulder end  34 B at the connection to the second end  32 B of the first portion  32 . Referring to FIG. 1, the depth of the recess  56 A is R, and the length of the second portion  34  is L 2 . Thus, the sum of the clearances between the blade  10 , the face  22 , and the second portion  34  is set to be the difference between the length of the second portion  34  and the depth of the recess  56 A. This relationship is expressed in Equation (2).  
         ( C 1 +C 2)= R−L 2  (2)  
         [0027]    Thus, variations within the desired range for the sum of the clearances (C 1 +C 2 ) depend solely on the manufacturing tolerances of the recess depth R and the second portion length L 2 , which are more easily controlled than the manufacturing tolerance of the blade thickness T.  
         [0028]    The desired range of values for the sum of the clearances (C 1 +C 2 ) can be more precisely controlled according to a preferred method of the present invention. Initially, the spacer  30  is extended through the aperture  12  and the blade  10  is arranged adjacent to the blade support member  20 . Thus, the first end  32 A of the spacer  30  confronts the undeformed face  22  of the blade support member  20 . The first jaw  52  is brought into engagement with the blade support member  20  to provide a reaction force opposing the force forming the depression  22 A, which is applied by the second jaw  56  against the pressing end  34 A of the spacer  30 . The first and second jaws  52 , 54  are pressed toward one another such that the spacer  30  deforms the blade support member  20 , i.e., forms the depression  22 A. The depression  22 A is completely formed when the face  56  of the jaw  54  engages the surface  10 B of the blade  10 . Finally, the first and second jaws  52 , 54  are withdrawn from one another. The sum the clearances (C 1 +C 2 ) is established within a desired range that is independent of variations in blade thickness T or first portion length L 1 .  
         [0029]    Of course, numerous variations can be practiced within the scope of the present invention. Rather than facilitating a relative reciprocating motion between the blade  10  and the blade support member  20 , the present invention can facilitate relative rotating or pivoting motion between the blade  10  and the blade support member  20 . The spacer  30  can be fixed to the blade  10  and pass through an aperture in the blade support member  20 . The first portion  32  or the second portion  34  of the spacer  30  can have any cross-sectional shape, i.e., they need not be circular. The depression  22 A can be formed by a hot pressing operation, e.g., heating the spacer  30  so as to melt and/or soften a portion of the blade support member  20 . Such a hot pressing operation can be performed in place of or in addition to the cold pressing operation described above. Rather than having the aperture  12  penetrating an interior portion of the blade  10 , the spacer  30  can cooperatively engage an edge of the blade  10 .  
         [0030]    Additional blades can be supported by a single spacer  30  for relative motion with respect to the blade  10  and to the blade support member  20 . Because the amount of blade clearance according to the present invention is not affected by variations in blade thickness, a common spacer  30  can connect any number of relatively moving blades and a blade support member.  
         [0031]    Specifically, FIG. 3 illustrates a first blade  10  and a second blade II that are each relatively translatable with respect to the blade support member  20 . The second blade  11  is sandwiched between first blade  10  and the blade support member  20  such that a first surface  11 A of the second blade  11  generally confronts the face  22  of the blade support member  20 , and a second surface  11 B of the second blade  11  generally confronts the first surface  10 A of the first blade  10 .  
         [0032]    The spacer  30  penetrates the second blade  11  in substantially the same manner as the first blade  10 . The length L 1  of the first portion  32  of the spacer  30  is greater than the combined thicknesses of the first and second blades  10 , 11 , i.e., the sum of the distances from the surface  10 A to surface  10 B and from the surface  11 A to the surface  11 B. Referring to FIG. 3, the length of the first portion  32  is L 1 , the depth of the depression  22 A is D, the thickness of the first blade  10  is T 1 , the thickness of the second blade  11  is T 2 , the clearance between the face  22  and the surface  11 A is C 1 , the clearance between the second portion  34  of the spacer  30  and surface  10 B is C 2 , and the clearance between the surfaces  10 A and  11 B is C 3 . Thus, the sum of the clearances between the face  22 , the second blade  10 , the first blade  11 , and the second portion is set to be the difference between the combined thicknesses of the first and second blades  10 , 11  and the length of the of the first portion  32  less the depth of depression  22 A. This relationship is expressed in Equation (3).  
         ( C 1 +C 2 +C 3)=( L 1 −D )−( T 1 +T 2)   (3)  
         [0033]    Thus, according to the present invention, the sum of the clearances (C 1  +C 2  +C 3 ) is not affected by deviations in the blade thickness (T 1  +T 2 ) or the first portion length L 1  inasmuch as the depression depth D is adjusted to account for these deviations.  
         [0034]    The identical reference numbers are used to indicate features in FIG. 3 that are the same as in FIG. 1. A duplicate description of these features is omitted with regard to this second embodiment. Moreover, the embodiment shown in FIG. 3 can be practiced in accordance with the same apparatus  50  and the same method of fabrication described with reference to FIG. 1.  
         [0035]    According to the preferred embodiments, apparatuses, and methods of the present invention, it is possible to provide a more precisely controlled amount of blade clearance. For example, the manufacturing tolerance for a blade is approximately ±0.0025 inches and the manufacturing tolerance for a spacer is approximately ±0.004 inches. Thus, for a conventional two-blade cutting tool, the variation of the clearance is ±0.009 inches. In contrast, the manufacturing tolerance for the recess  56 A according to the present invention is approximately ±0.001 inches; however, the effect of the manufacturing tolerance for the blades is eliminated. Thus, for the two-blade cutting tool shown in FIG. 3, the variation of the clearance is ±0.005 inches. This reduction in the variation of the clearance greatly improves cut quality.  
         [0036]    Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative devices, shown and described herein. Accordingly, various modifications can be made without departing from the spirit and scope of the general inventive concept as defined by the appended claims and their equivalents.