Abstract:
A zero backlash mechanism for a worm, spur or helical gears, using a spring loaded mechanism that tightens the meshing gear surfaces, thus eliminating the backlash between them.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    This patent application claims priority from and is related to U.S. Provisional Patent Application Ser. No. 61/129,311, filed 18 Jun. 2008, this U.S. Provisional Patent Application incorporated by reference in its entirety herein. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates generally to spur, helical or worm gearboxes, and more particularly, to such gearboxes in which the backlash between the gears is eliminated by spring force. 
       BACKGROUND OF INVENTION 
       [0003]    In the field of drive systems, there exist many types of gear arrangements: helical, spur, bevel, worm and other types. 
         [0004]    The driving and driven shafts vary from parallel to vertical arrangements. 
         [0005]    Properly functioning mechanical systems need to have a certain clearance/backlash (gap, play) between the components transmitting motion under load. 
         [0006]    Clearance is necessary to avoid interference, wear and excessive heat generation, insure proper lubrication, compensate for manufacturing tolerances etc. Clearance in the gear mesh means that the gap between the teeth of one gear is by a small amount larger than the tooth width of the mating gear. 
         [0007]    In some applications, especially at low speeds, where high accuracy is needed, for example, in closed loop tracking applications, zero or minimal backlash will enable better functioning of the system. There are many patents for mechanism that reduces or eliminates backlash in various types of gears. 
       SUMMARY OF INVENTION 
       [0008]    The primary object of the present invention is to overcome the drawbacks caused with other “rigid” or non-flexible solutions of backlash elimination between spur, helical, worm types of gear, especially for low speed, tracking or positioning applications. 
         [0009]    This object is achieved by using a spring loaded mechanism that tightens the meshing gear surfaces, thus eliminating the backlash between them. Another object of this invention is to create a repeatable, rotational positioning stage, with virtually zero backlash. 
         [0010]    The present invention relates to a backlash eliminating mechanism, comprising a housing with a base portion that acts as a support structure. The present invention is a simple, reliable and low-cost solution, applicable especially for low-speed systems. 
         [0011]    At the same time, the system has automatic compensation for wear of materials, hence re-adjustment is automatically achieved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings. 
           [0013]    With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. In the accompanying drawings: 
           [0014]      FIGS. 1A and 1B  show a schematic construction of the worm gearbox internal parts of the invention, illustrating the backlash elimination mechanism applied to the driving element; and 
           [0015]      FIGS. 2A and 2B  show a schematic construction of the spur (or helical) gearbox internal parts of the invention, illustrating the backlash elimination mechanism applied to the driving element. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0016]    The present invention provides a drive system used particularly (but not only) in low-speed tracking or positioning systems or applications. 
         [0017]    For Worm Sear Systems: 
         [0018]      FIGS. 1A and 1B  depict a first embodiment of the present system for backlash elimination. 
         [0019]    The system includes a driving (input) element ( 100 ) that is a worm pinion assembled on a shaft ( 105 ), or a combined wormshaft ( 100 + 105 ). 
         [0020]    A driven element ( 110 ), a worm gear, rotates inside housing ( 115 ), around shaft ( 120 ), fixed in the housing by bearings ( 125 ). 
         [0021]    The pinion ( 100 ) is usually a low speed element, a motor or a gear motor, or any other rotating element. 
         [0022]    A compression spring ( 125   a ) or an extension spring ( 125   b ) (or other types of springs that cause similar effect) is fixed to the housing ( 115 ) on one end and connected to the shaft ( 105 ) through sliding (or other type) of bearing ( 145 ), or even directly wrapped around the shaft ( 105 ) with the ability to slide on it, tightening the pinion ( 100 ) and gear flanks ( 130 ) towards each other, thus eliminating the natural backlash of a normal worm gear set. The springs can be fixed or adjustable. 
         [0023]    The shaft ( 105 ) is fixed to the internal part of a spherical (or other type) bearing ( 135 ), and is rotatable around its axis, but at the same time can have a small degree of freedom around the bearing center ( 140 ), to allow the backlash closing effect. 
         [0024]    As a result, the backlash between driving element ( 100 ) and driven element ( 110 ) is eliminated ( FIG. 1B ). 
         [0025]    The motor or gear motor that rotates shaft ( 105 ) must be rigidly mounted on shaft ( 105 ), or otherwise connected through a flexible element to shaft ( 105 ). 
         [0026]    For Spur or Helical Gear System: 
         [0027]      FIGS. 2A and 2B  depict a second embodiment of the present system for backlash elimination. 
         [0028]    The system includes a driving (input) element ( 200 ) that is a spur or helical gear (pinion) assembled on a shaft ( 205 ), or a combined gear+shaft ( 200 + 205 ). The driving element ( 200 ) rotates around shaft ( 205 ) by sliding or any type of bearings ( 245 ). 
         [0029]    A driven element ( 210 ), a spur or helical gear, rotates inside a housing ( 215 ), around shaft ( 220 ) that is held by bearings ( 250 ). 
         [0030]    The pinion ( 200 ) is usually a low speed element driven by a low speed motor or gearmotor, or any other rotating element. 
         [0031]    A lever ( 225 ) carries the shaft ( 205 ) and is rotatable around the axis of shaft ( 230 ) through sliding (or other) bearing ( 255 ), enabling the lever ( 225 ) a small rotation angle around the axis of shaft ( 230 ). 
         [0032]    A compression spring ( 235   a ) or an extension spring ( 235   b ) (or a torsion spring connected to shaft ( 230 ), that causes a similar effect) tightens the gears towards each other, thus eliminating the natural backlash of a regular spur or helical gear set. The springs can be fixed or adjustable. 
         [0033]    The spring ( 235   a  or  235   b ), extension or compression of any other type, is connected at one end to the housing ( 215 ) and on the other side to the lever ( 225 ). 
         [0034]    In an alternative embodiment, shaft ( 230 ) may be rigidly connected to the lever ( 225 ), in which case the lever ( 225 ) acts as a tension spring and the spring ( 235   a  or  235   b ) are not needed. 
         [0035]    As a result, the backlash between driving element ( 200 ) and driven element ( 210 ) is eliminated ( FIG. 2B ). 
         [0036]    The motor or gearmotor that rotates pinion ( 200 ) must be rigidly mounted on shaft ( 205 ), or otherwise connected through a flexible element to shaft ( 205 ). 
         [0037]    The springs, in all the embodiments described above, may be at fixed preloaded, push or pull type, but also with an option of adjusting the push or pull force by changing the preloads, (for example, changeable tensioning or compressing the springs). 
         [0038]    The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not as restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. 
         [0039]    The system according to the present invention has the additional advantage of automatically compensating for wear of materials, which has the effect of increasing the backlash effect in standard systems.