Patent Publication Number: US-6220920-B1

Title: Yo-yo with adjustable slot width

Description:
FIELD OF THE INVENTION 
     This invention relates to yo-yos. 
     BACKGROUND OF THE INVENTION 
     The typical construction of a tethered aerial top, commonly referred to as a yo-yo, includes an axle that joins a pair of spaced yo-yo halves and a string that is attached to the axle and can extend radially outwardly through the gap between the spaced yo-yo halves. The other free end of the string is controlled and manipulated by the user to perform various maneuvers and tricks. Many of such maneuvers rely on the ability of the yo-yo to “sleep”, that is, to spin while attached to the end of the string without winding the string about the axle and returning to the user. Toward the conclusion of the maneuver, when it is usually desired to cause the yo-yo to return to the user by winding the string about the axle, the user may jiggle the string in a manner that briefly releases the tension on the string. During the brief period that the string may be tension-free and is relatively loose within the gap between the yo-yo halves, the loose string can become frictionally caught between the inwardly facing surfaces of the yo-yo halves. The rotational inertia of the yo-yo halves then causes the yo-yo to climb along the string toward the user, winding the string about the axle as the yo-yo returns to the user. The physics and function of the yo-yo is described in a publication, “The Yo-Yo: A Toy Flywheel” by Wolfgang Büzger,  American Scientist , Vol. 72, Par.-Apr. 1984, pp. 137-142. 
     The width of the gap between the yo-yo halves is critical to proper control of the yo-yo. If the gap is too small, the yo-yo may not sleep, tending, instead, to frictionally grip the string notwithstanding the presence of tension in the string. If the gap is too wide, the inwardly facing surfaces of the yo-yo halves may not be able to engage the string with sufficient friction. Additionally, the width of the gap between the yo-yo halves also affects the precision with which the yo-yo will tend to rotate in a plane. If the gap is too wide, the yo-yo may precess out of a desired plane, resulting in undesirable interference between one of the yo-yo halves and the string, often near the periphery of the yo-yo halves. 
     Even if the yo-yo gap is set to what might ordinarily be considered a proper gap, with all other components properly balanced and aligned, changing atmospheric conditions can affect the performance of the yo-yo. Most yo-yo strings are formed from cotton that tends to absorb moisture from the air. Consequently, the string may tend to swell in the presence of higher humidity and may tend to shrink in the presence of lower humidity. The humidity also may affect the surface characteristics of the string fibers that, in turn, may affect the frictional interaction between the string and the inner surfaces of the yo-yo halves. 
     It would be desirable, therefore, to provide a yo-yo in which the gap between the inwardly facing surfaces of the yo-yo could be adjusted in order to maximize the ability of the yo-yo to perform as desired in a particular environment. Adjustment of the gap may, in many cases, compensate for differences in frictional characteristics between the yo-yo string and the inwardly facing, string-engaging surfaces of the yo-yo, whether those characteristics are affected by the composition of the string, the inwardly facing surfaces, atmospheric conditions or any other influence that may affect yo-yo performance. The desirability of providing a yo-yo that is adjustable to compensate for such variations in conditions of use has been recognized and is described in U.S. Pat. No. 5,100,361 (Kuhn). The Kuhn patent describes an arrangement in which the gap between the string-engaging surfaces of the yo-yo can be adjusted. The mechanism described in the Kuhn &#39;361 patent requires that the yo-yo be disassembled in order to provide access to internally adjustable members, that are adjusted by the use of a tool, such as a screw driver. Disassembly to expose an internal, tool-adjustable mechanism presents considerable inconvenience to the user in that play must be interrupted for a considerable period of time. Moreover, even if an adjustment is made, it often may be desirable or necessary to make further fine adjustments to obtain optimum performance. Each such fine adjustment necessarily would require one or more subsequent disassemblies, readjustments and reassemblies of the yo-yo. It would be desirable, therefore, to provide an adjustable-gap yo-yo in which the gap can be adjusted immediately, without requiring disassembly, internal adjustment and reassembly of the yo-yo. It is among the general objects of the invention to provide such a device. 
     SUMMARY OF THE INVENTION 
     The invention is incorporated in a yo-yo having an axle with ends that are rotatably attached to the yo-yo halves. The location and spacing of the yo-yo halves is adjustable simply by rotating the yo-yo halves relative to each other. A mechanism is provided to maintain the angular position of the yo-yo halves while the yo-yo is in use but also allows the angular orientation to be adjusted. The mechanism causes the gap between the yo-yo halves to vary as a function of the relative angular position of the halves. In the illustrative embodiment, the connection is threaded. The threaded connection between the yo-yo halves and the axle causes the gap to widen or become narrower, accordingly. The relative angular orientation of the yo-yo halves on the axle and with respect to each other is maintained by an arrangement that applies a firm outward bias in an axial direction to the yo-yo halves, by which the yo-yo halves are urged continually outwardly along the axle. The engaged surfaces of the threads of the axle and the yo-yo half thus are continually pressed axially and firmly against each other. That pressure is applied in sufficient magnitude to develop sufficient friction so that the yo-yo halves will maintain their relative angular position on the axle as the yo-yo spins. The frictional force resulting from the outward bias can be overcome manually and easily simply by manually rotating the yo-yo halves with respect to each other. That enables coarse as well as very fine adjustments in the gap to be made, depending on the extent to which the halves are rotated. The adjustment can be made immediately and accurately with no significant interruption of play. There is no need to disassemble the yo-yo, or to expose its inner components. There is no need for tools. 
     In another aspect of the invention, the inner faces of the yo-yo halves are contoured so that the more radially inward portion of the gap will be more narrow than the radially outward portion. That enhances the ability of the string to be frictionally engaged when the tension on the string is released momentarily in order to cause the yo-yo to return. The outer region of the inner face is provided with a wider angle that facilitates performance of a certain class of tricks, commonly referred to as “string tricks”. 
     It is among the general objects of the invention to provide an improved yo-yo in which the gap between the yo-yo halves can be easily adjusted. 
     Another object of the invention is to provide a yo-yo having an adjustable gap that does not require the use of tools or disassembly of the yo-yo. 
     A further object of the invention is to provide a yo-yo having an adjustable gap in which the adjustment can be made immediately and in precisely controllable increments. 
     Another object of the invention is to provide a yo-yo that exhibits greater sensitivity to control for returning it from a sleeping condition yet which also enables string tricks to be performed. 
     An additional object of the invention is to provide a yo-yo in which the inwardly facing surfaces of the yo-yo halves define an inner annular band and an outer annular band wherein the angle defined by the facing inner annular bands is less than the angle defined between the radially outer annular bands. 
     Still another object of the invention is to provide a yo-yo wherein the yo-yo halves are rotatably threaded and restrained in a selected angular position on the axle by biasing the yo-yo halves outwardly into firm frictional engagement with the yo-yo axle. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects and advantages of the invention will be appreciated more fully from the following further description thereof, with reference to the accompanying drawings wherein: 
     FIG. 1 is an exploded view of the components of a yo-yo incorporating an embodiment of the invention; 
     FIG. 2 is a fragmented, sectional illustration of the internal components of the yo-yo as shown in FIG. 1; 
     FIG. 3 is a fragmented, sectional illustration of a portion of a yo-yo embodying a modified form of the embodiment of the invention shown in FIGS. 1 and 2; 
     FIG. 4 is a greatly enlarged sectional illustration of the Bellville washers, a portion of the axle and the bearing; and 
     FIG. 5 is an enlarged illustration of the angular configuration of the inwardly facing surfaces of the yo-yo halves. 
    
    
     DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT 
     The yo-yo includes a pair of yo-yo halves  10 ,  12  that are threaded onto the threaded ends  14 ,  16  of an axle  18 . The axle  18  preferably is formed from a suitable metal, such as stainless steel and may include a central segment  20  that is unthreaded. The yo-yo also may include a bearing  22  mounted on the central segment  20  to the axle  18  to reduce rotational friction as the yo-yo spins at the end of the string (not shown). The bearing  22  may comprise a roller bearing having an inner race  24  and an outer race  26 . The yo-yo string (not shown) is looped about the outer surface  27  of the outer race  26 . 
     Each of the yo-yo halves  10 ,  12  may be considered as having an inwardly facing surface, indicated generally at  28 . A centrally located socket  30  may be formed in each of the yo-yo halves  10 ,  12 , each socket  30  being open inwardly and receptive to a threaded insert  32  having internal threads  34 . The insert  32  preferably is secured in the socket  30  by an interference fit and may be generally circular, hexagonal or other cross-section, with the hexagonal shape preferred. The configuration of the socket  30  and insert  32  should be such as to assure a secure attachment between the socket  30  and its associated yo-yo half  10 ,  12 . It should be understood that the principles of the invention may be incorporated in a yo-yo in which the ends of the axle are threadably connected to the yo-yo halves  10 ,  12 , either directly or by other suitable means. The connection between the end of the axle and the yo-yo halves should be such as to enable the gap G between the yo-yo halves to be varied by relative rotation of the yo-yo halves with respect to each other. In the illustrative embodiment, it will be appreciated that the gap G will vary depending on the extent to which the threaded ends  14 ,  16  of the axle  18  are threaded into the threaded inserts  32 . 
     In accordance with the principles of the invention, the relative position of the yo-yo halves  10 ,  12  with respect to the axle  18  and each other is maintained by frictional forces that, while sufficient to maintain a fixed relative angular position between the yo-yo halves  10 ,  12  when the device is in use, nevertheless may be easily manually overcome simply by rotating the yo-yo halves  10 ,  12  relative to each other. Thereafter, the adjusted orientation is maintained during use by the applied frictional forces. The periphery of each of the yo-yo halves may be provided with a rubber ring  11  received in a peripheral groove  13  of the yo-yo half. The rubber facilitates the frictional grip that the user may apply to the yo-yo halves when adjusting their relative angular position. It also protects the periphery of the yo-yo from damage, as when performing certain tricks in which the periphery is expected to contact other surfaces, such as in “walking the dog”. 
     In the illustrated embodiment of the invention, the frictional force for maintaining the angular orientation of the yo-yo halves with respect to themselves and the axle  18  may be effected by a series of Bellville washers indicated collectively at  36 . The Bellville washers  36  are dished and may be considered as having a concave side  38  and a convex side  40 . The dished configuration of the Bellville washers enables them to function as a compression spring, that is, when compressed from its normally dished shape toward a flattened shape, the washer will return to its dished shape when the compression force is removed. The arrangement of Bellville washers is selected, in the illustrative embodiment, to cooperate with the bearing  22  to permit free rotation of the outer race  26  with respect to the inner race  24  of the bearing  22 . To that end, the illustrative embodiment includes an arrangement, on each side of the bearing  22 , of an inner Bellville washer  36   a , an intermediate Bellville washer  36   b  and an outer Bellville washer  36   c . An O-ring  42  may be provided on each end of the axle to retain the Bellville washers  36  on the axle  18  in the event that the yo-yo is disassembled for example, to undo an inadvertently knotted string or for any other reason. It should be understood, however, that the present invention does not require or contemplate disassembly of the yo-yo in order to adjust the width of the gap. 
     The Bellville washers  36  are arranged so that the convex side  40  of the innermost of the Bellville washers  36   a  will face inwardly toward the bearing  22 . So positioned, only the radially inwardly disposed region  44  of the Bellville washer  36   a  will bear against the lateral surface  46  of the inner race  24 . The more radially outward regions  48  of the Bellville washer  36   a  will be dished outwardly and away from the outer race  26  so as not to interfere with rotation of the outer race  26  about the inner race  24 . The Bellville washers should be arranged sequentially and in opposition to each other, that is, with like concave or convex sides of adjacent washers facing each other. Thus, as shown in the drawings, the concave side  38  of the inner most Bellville washer  36   a  faces the concave side of the intermediate Bellville washer  36   b  and the convex side of the intermediate Bellville washer  36   b  faces the concave side of the outer washer  36   c . Thus, each pair of adjacent washers  36  will bear against each other either at their outer or inner peripheries  50 ,  52 , respectively. By orienting the adjacent washers in opposition to each other, the arrangement provides adequate range of axial motion of the yo-yo halves  10 ,  12  toward and away from each other, while maintaining sufficient outward bias on the yo-yo half to develop the necessary friction between the surfaces of the threads of the axle  18  and the internal threads  34  of the insert  32 . The outermost washer  36   c  preferably is oriented with its concave side  38  facing outwardly. Thus, the outer periphery  50  of the outer Bellville washer  36   c  engages an inwardly facing surface of the yo-yo half assembly, such as the surface  54  of the threaded insert. By way of example, a suitable Bellville washer for use in the invention may be formed from heat treated spring steel having a Rockwell hardness in the range of 44 to 48. The washer may have an outer diameter of 0.315 inch, an inner diameter of 0.165 inch. The spring steel from which it is formed preferably has a thickness of about 0.016 inch. The dished washer preferably has a height of the order of 0.028 inch. Such washers are commercially available from the Willie Washer Mfg. Co. in Elk Grove, Ill. 
     In the illustrative embodiment shown in FIG. 2, the O-rings are compressed between the outermost washers  36   c  and the inwardly facing surfaces  54  of the threaded insert  32 . In this configuration, the O-ring should be sufficiently soft and resilient as to permit such compression, preferably so that the outer periphery  50  of the outer Bellville washer  36   c  can firmly bear against the inwardly facing surface  54  of the threaded insert  32 . In this embodiment O-ring  42  should be sufficiently resilient as to maintain its washer-retaining function, described above, even after it has been firmly compressed for an extended period of time. 
     In a modified embodiment, as shown in FIG. 3, the inwardly facing  54  surface of the threaded insert  32  may be provided with a recessed annular shoulder  56  adapted to receive at least part of the O-ring  42  so that high compression and possible permanent distortion or rupture of the O-ring may be avoided. 
     In another aspect of the invention, the inwardly facing surfaces  28  of the yo-yo halves are arranged to facilitate frictional engagement of the yo-yo string with those surfaces while maintaining the ability of the yo-yo to be used to perform string tricks such as, for example, “brain twister”. Generally, string tricks are facilitated by having a relatively wider gap G by which the gap can be dynamically aligned with an intermediate portion of the yo-yo string to support the yo-yo on that intermediate portion while still spinning. In this aspect of the invention both objectives can be achieved by forming the inner surfaces of the yo-yo halves to define a progressively increasing gap width in a radially outward direction. Thus, each of the yo-yo halves  10 ,  12  may be considered with its inwardly facing surface  28  as having regions of an inner annular face  28   a  and outer annular face  28   b . The outer periphery of the outer annular face  28   b  should be considered as terminating at the region where the inner face makes a transition to the outer peripheral contour of the yo-yo half. Such region is indicated approximately at  60  in FIGS. 1 and 5. The transition between the inner annular face  28   a  and outer annular face  28   b  is represented approximately in phantom at  31  in FIG.  1 . The transition region  31  may be considered as being defined by a radius that extends from about the axis of the yo-yo half to a region that is about half the radius of the inner face  28 . Thus, as illustrated in FIG. 1, the radial segments  28   a  and  28   b  may be approximately equal in radial extent. As shown in further diagrammatic detail in FIG. 5, the inner annular faces  28   a  of the yo-yo halves  10 ,  12  are configured to define a first narrower angle A, and consequently smaller gap G, than the outer annular surfaces  28   b . The inner and outer annular surfaces  28   a ,  28   b  may be relatively flat or somewhat curved. In either case, the inner annular surfaces  28   a  preferably may define a gap G having an angle of about 3½° with the outer annular surfaces  28   b  defining a second, slightly greater gap angle B, of the order of about 4½°. Thus, the gap G is narrower in its more radially inward regions than in its more radially outward regions. The narrowed inner region facilitates frictional engagement with the string while the somewhat widened gap at the radially outer regions facilitates the performance of string tricks. 
     From the foregoing it will be appreciated that the invention provides an adjustable gap yo-yo in which the gap between the yo-yo halves can be quickly, easily and precisely adjusted without significant interruption in play. The yo-yo does not have to be disassembled. No tools are required in order to effect the adjustment. 
     It should be understood that the foregoing description of the invention is intended merely to be illustrative thereof and other embodiments, modifications and equivalents may be apparent to those skilled in the art without departing from its spirit.