Abstract:
An anti-backlash gear system including a splined shaft and a gear is disclosed. The splined shaft has at least one spline. The gear has a splined bore having at least one spline, through which the splined shaft passes. The gear and the shaft have a clearance therebetween. The splined bore and the splined shaft are engaged in a driving direction, and the splined bore and the splined shaft are disengaged, thereby producing a backlash motion, in a direction opposite the driving direction.

Description:
TECHNICAL FIELD  
         [0001]    This invention is of the form of a system to drive a gear, and, more particularly, to such a system providing an anti-backlash feature.  
         BACKGROUND  
         [0002]    Many different machines include a shaft, or hub, turning in a driving direction. The shaft takes power from a source and transmits it to a driving gear, which then transmits the motion on to a driven gear. The shaft often includes splines which interact with splines on an inner bore of the driving gear to turn the driving gear in the driving direction. As the shaft turns in the driving direction, irregularities or periodic catches in the source can cause the shaft to momentarily slow, stop, or even turn in a direction opposite the driving direction. All of these unwanted motions are termed “backlash” and can cause damage to the components of the machine, as well as accelerating wear and decreasing power transmission in the machine.  
           [0003]    U.S. Pat. No. 6,098,726, issued Aug. 8, 2000 to Taylor et al. (hereafter referenced as &#39;726) discloses a torque transmitting device including a coupling which permits limited relative rotation between two members about a common central axis, but provides a resistance to rotation of the first member relative to the second member in a forward drilling direction which is greater than its resistance to relative rotation in the reverse direction.  
           [0004]    Accordingly, the art has sought a method and apparatus of an anti-backlash gear system which: prevents damage from backlash; contains a limited number of individual parts; absorbs backlash motion without permitting the motion to be transmitted; may be used in a timely and efficient manner; and is more economical to manufacture and use.  
           [0005]    The present invention is directed to overcoming one or more of the problems as set forth above.  
         SUMMARY OF THE INVENTION  
         [0006]    In an embodiment of the present invention, an anti-backlash gear system including a splined shaft and a gear is disclosed. The splined shaft has at least one spline. The gear has a splined bore having at least one spline, through which the splined shaft passes. The gear and the shaft have a clearance therebetween. The splined bore and the splined shaft are engaged in a driving direction, and the splined bore and the splined shaft are disengaged, thereby producing a backlash motion, in a direction opposite the driving direction.  
           [0007]    In an embodiment of the present invention, a torsionally elastic coupling having a driving shaft, a driven ring, and a radial member is disclosed. The driving shaft has at least one shaft backlash relief pocket. The driven ring surrounds the driving shaft and has at least one ring backlash relief pocket. The radial member is attached to the driving shaft along a longitudinal direction adjacent to the shaft backlash relief pocket and contacts the driven ring adjacent the ring backlash relief pocket. The radial member is engageable to transmit a driving force from the driving shaft to the driven ring in a driven direction and disengageable to cushion a backlash force between the driving shaft and the driven ring in a direction opposite the driving direction.  
           [0008]    In an embodiment of the present invention, a method of cushioning a backlash force from a driven ring to a driving shaft is disclosed. The driving shaft has at least one shaft backlash pocket and is surrounded by the driven ring, which has at least one ring backlash pocket. The method includes the steps of moving the driving shaft in a driving direction to produce a driving force, and transmitting the driving force to the driven ring via a radial member contacting both the shaft backlash pocket and the ring backlash pocket in an initial position. The method also includes the steps of providing a backlash force in a direction opposite the driving direction, and responsively allowing the radial member to move from the initial position within at least one of the shaft backlash pocket and the ring backlash pocket. The method additionally includes the steps of removing the backlash force, providing the driving force, and responsively allowing the radial member to return to the initial position. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a cutaway drawing of an anti-backlash gear system of a preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0010]    A preferred embodiment of the present invention provides an apparatus and method of an anti-backlash gear system.  
         [0011]    [0011]FIG. 1 depicts an anti-backlash gear system  100  according to the present invention. A splined shaft  102  has at least one spline  104  thereon. By “spline”, what is meant is a substantially radially oriented protrusion or plane, such as a shouder, vane, leaf spring, rib, tooth, or the like. The anti-backlash gear system  100  will be described herein as having one spline  104  and associated elements for the sake of simplicity, but any number of splines  104  could be present without departing from the spirit and scope of the present invention.  
         [0012]    As shown in FIG. 1, the spline  104  of the present invention is anchored to the splined shaft  102  by a first end  106 . The spline  104  need only be contacting the splined shaft  102  or any other element, not be attached thereto, but will be referred to as such for ease of reference in the below description.  
         [0013]    A gear  108  has a splined bore  110  therein, having at least one spline  104 , shown in FIG. 1 as a shoulder. The splined shaft  102  passes through the splined bore  110 , leaving a clearance  112  therebetween.  
         [0014]    At least one of the splined shaft  102  and the splined bore  110  has a spline pocket  116  adjacent to the spline  104 . Preferably, the spline pocket  116  has a viscoelastic material therein. Optionally, the spline pocket  116  may have a shaped profile (not shown) to help control the motion of the spline  104  in the spline pocket  116 . Also, the spline  104  may be flexible such that a second end  118  can be moved while the first end  106  remains anchored or vice versa.  
         [0015]    While aspects of the present invention have been particularly shown and described with reference to the preferred embodiment above, it will be understood by those skilled in the art that various additional embodiments may be contemplated without departing from the spirit and scope of the present invention. For example, the viscoelastic material could be a foam or fluid, the spline could be anchored to the gear  108 , or the spline pocket  116  could be of any suitable configuration. However, a device or method incorporating such an embodiment should be understood to fall within the scope of the present invention as determined based upon the claims below and any equivalents thereof.  
         [0016]    Industrial Applicability  
         [0017]    As the splined shaft  102  rotates in the driving direction  114 , the spline  104  of the splined shaft  102  transmits motion from the splined shaft  102  through contact with the spline  104  of the splined bore  110 , thus driving the gear  108  in the driving direction. When a backlash situation occurs—that is, when either the splined shaft  102  or the gear  108  momentarily ceases to rotate in the driving direction  114 , the spline  104  of the splined shaft  102  loses contact with the spline  104  of the splined bore  110 . The spline  104  of the splined shaft  102  then moves into at least a portion of the spline pocket  116  of the splined bore  110  until the backlash motion is removed, at which time the spline  104  of the splined shaft  102  reengages the spline  104  of the splined bore  110  to continue operating normally.  
         [0018]    In a backlash situation, should the spline  104  of the splined shaft  102  completely traverse the spline pocket  116  of the splined bore  110 , an outboard end  120  of the spline pocket  116  will contact the spline  104  of the splined shaft  102  and bend the second end  118  with respect to the first end  106 , forcing the spline  104  of the splined shaft  102  to travel into the spline pocket  116  of the splined shaft  102 . If the backlash force is significant enough to force the spline  104  of the splined shaft  102  to contact the outboard end  120  of the spline pocket  116  of the splined shaft  102 , the motion of the splined shaft  102  and gear  108  may hesitate or “catch”, but it is anticipated that any momentary backlash motion will cease before such a hesitation occurs.  
         [0019]    Should the backlash be great enough to cause the spline  104  of the splined shaft  102  to flex and travel into the spline pocket  116  of the splined shaft  102 , the spline pocket  116  of the splined shaft  102  may be contoured or shaped to allow for a smooth or controlled return of the spline  104  of the splined shaft  102  to its normal driving position.  
         [0020]    The spline  104  could be attached to either the splined shaft  102  or the splined bore  110 , or could be free-floating. It should be obvious to one skilled in the art that operation of the present invention will not be materially affected by the attachment condition of the spline  104 .  
         [0021]    Preferably, the spline pockets  116  contain therein a viscoelastic material which acts to absorb and dissipate some of the backlash force. The amount and type of such material can be adjusted to “tune” the anti-backlash gear system  100  for a desired result.  
         [0022]    The apparatus and method of certain embodiments of the present invention, when compared with other methods and apparatus, may have the advantages of: preventing damage from backlash; containing a limited number of individual parts; absorbing backlash motion without permitting the motion to be transmitted; may be used in a timely and efficient manner; and being more economical to manufacture and use. Such advantages are particularly worthy of incorporating into the design, manufacture, and operation of gears. In addition, the present invention may provide other advantages that have not yet been discovered.  
         [0023]    Other aspects, objects, and advantages of the present invention can be obtained from a study of the drawings, the disclosure, and the appended claims.