Abstract:
Magnetic locker darts with a grip region of length equal to the width of a human thumb provide throwing accuracy while minimizing contact with other locker contents. The target is a decal that can be attached to the inside of a metal locker door or other metal appliance.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to locker accessories. More particularly, it relates to a dart game including darts designed for use with a metal locker and a target decal that can be attached to a locker door.  
       BACKGROUND OF THE INVENTION  
       [0002]     A dart game system consists of darts and a target. The target is partitioned into regions and is marked with symbols, allowing users to play various games involving throwing the darts at the target. The regions of the target have meaning of significance within those games adapted to a particular target layout. A player attempts to excel by throwing her darts so that they stick to regions of the target associated with high scores within the context of the game at hand.  
         [0003]     A variety of different target layouts and games have been created. All the games emphasize accuracy in throwing the darts at specific regions of the target. The target is typically mounted or printed on the surface of a dart board. Classical dart boards used in taverns are made of cork, straw, or paper.  
         [0004]     According to the official rules of the World Darts Federation, “darts . . . shall not exceed an overall length of 30.5 cm, nor weigh more than 50 grams. Each dart shall consist of a needle shaped point which shall be fixed to a barrel. At the rear of the barrel there shall be attached a flighted stem, which may consist of separate parts.” (WDF Playing and Tournament Rules, 6th Rev. Ed., Dec. 1, 2003) Historically, the flighted stem contained feathers, which have been replaced in many modern darts with fins. Each fin or feather is approximately planar, with the plane of each fin including the common centerline of the barrel and the point. The metal point at the tip of the dart sticks to the target by penetrating through the surface into the fabric of the underlying board.  
         [0005]     Needle-nose darts can cause injuries to the players, bystanders, the wall on which the board is mounted, or other nearby objects. This safety consideration has led recently to a variety of new materials and designs for dart/target combinations in which the sharp points are replaced by flat surfaces. Many of the new game systems use darts with tips that consist wholly or partially of magnets. The magnet tips cause the darts to stick to surfaces that contain ferromagnetic material. According to the American Heritage Dictionary, “ferromagnetic” is defined as: “Of or characteristic of substances such as iron, nickel, or cobalt and various alloys that exhibit extremely high magnetic permeability, a characteristic saturation point, and magnetic hysteresis.” Ferromagnetic material has the capability of being turned into a magnet, but which might not itself be magnetic. Magnetic darts sometimes employ dart tips that are rare-earth magnets, which are significantly stronger than more common iron magnets (e.g., Jonsson, U.S. Pat. No. 5,775,694; Gittens, U.S. Pat. No. 5,613,694).  
         [0006]     Some magnetic darts, such as those described by Kettlestrings (U.S. Pat. No. 4,119,316) and Seymour (U.S. Pat. No. 6,062,997), differ significantly in both shape and structure from traditional needle-nose darts, because they are designed for use primarily by children. But many magnetic darts retain the traditional elongated barrel and flighted stem design (e.g., Jonsson, U.S. Pat. No. 5,775,694).  
         [0007]     Prior art magnetic dart game systems contain a target board including either a rigid layer of magnetic material or a relatively rigid rubber layer impregnated with magnetic material. Jonsson (U.S. Pat. No. 5,775,694) suggests covering a board that includes magnetic material with a printed plastic decal target, attached to the board with an adhesive, which is easy to remove from the board  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention dart game consists of magnetic darts and a matching target designed for use in a metal locker, such as those commonly found in a school or an athletic facility. A locker has very limited space for the occupant to store possessions. A prior art magnetic dart has a barrel of length approximately equal to that of typical traditional pointed darts. Such a long dart, sticking to a target mounted on the inside of a locker door, will protrude unnecessarily far into the interior volume of the locker when the door is shut. As the locker door is being closed or opened, the dart can come into contact with other locker contents—coats and other clothing, books, athletic gear, footwear, and shelves. In consequence, the dart may become dislodged and fall, or might even disturb other items stored in the locker. From this standpoint, darts smaller than those of the prior art are generally preferable as locker darts.  
         [0009]     On the other hand, the skill in every dart game consists of accurately targeting the darts, so a dart should have a barrel length large enough to fit conveniently within a human hand. These two opposing length scale considerations suggested to the inventors the ideal size of the magnetic locker darts described herein, having a central barrel portion (i.e., between the retainer enclosing the magnetic tip and the fins) that just comfortably fits between an adult&#39;s thumb (having a width of approximately 24 mm) and forefinger. The dart of the preferred embodiment of the present invention has a length of about 50 to 70 mm.  
         [0010]     Because of its short length and strong magnetic tip, a locker dart can be helpful for purposes other than dart games. In a manner analogous to tacks on a message board, a dart can be used to post a sheet of paper, fabric, or other thin material on the inside of the locker door or elsewhere within the locker. The posted material is held between the magnet tip of the dart and the metal surface of the locker. Alternately, a lightweight article, such as a pair of swim goggles, can be hung from a dart, where the dart so employed serves as a peg.  
         [0011]     One aspect in which the locker darts game system of the present invention differs from the prior art is that it includes a target but no board. Its target contains essentially no metal or metal-impregnated surfaces or layers. Instead, the system takes advantage of the magnetic material present in a locker door, external to the product itself, to attract the magnetic dart tips. The target is printed on a thin sheet of plastic material. Once a backing is peeled off, the plastic sheet will adhere to a locker surface, by static electricity in the preferred embodiment. Of course, the target will also stick to various other objects having relatively smooth metal surfaces, such as some refrigerator doors and clothes washers, providing alternative environments where the darts game can be played. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is an isometric drawing of several lockers, one of which contains the present invention.  
         [0013]      FIG. 2  is an isometric drawing of a prior art magnetic dart.  
         [0014]      FIG. 3  is an isometric drawing of the magnetic dart of the present invention.  
         [0015]      FIG. 4  is a longitudinal view of a dart of the present invention showing details of the nose section and the tail section.  
         [0016]      FIG. 5  is a longitudinal view of the dart of the present invention illustrating various dimensions.  
         [0017]      FIG. 6  is a longitudinal view showing how the geometry of a dart of the present invention relates to gripping the dart with a human hand. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     The locker dart game of the present invention is used within a locker  100  made of ferromagnetic material such as steel or iron.  FIG. 1  shows a row of such metal lockers  100 , one with an open door  110 . Attached to the door  110  is a target  700  decal. A locker dart  300  is stuck to the target  700  (or more precisely to the door  110  behind the target  700 ). Two other locker darts  300  are being used to post a slip of paper  120  to the inside of the locker door  110 . The locker door  110  is typically steel, a ferromagnetic material.  
         [0019]      FIG. 2  illustrates a typical prior art magnetic dart  200 . It preserves much of the look and feel of a competition needle-nose dart, including a tip  210  and an elongated barrel  220  that terminates in a flighted stem  230 . The length of the prior art dart  200  shown is 100 mm (3.9 inches). The magnet tip  210  is a rare-earth magnet. Rare earth magnets have significantly stronger magnetic properties, and retain their magnetic properties better after repeated collision impacts, than ferrite magnets, which are more conventional. The feathers  240  of the flighted stem  230  are plastic fins  240 .  
         [0020]      FIG. 3  shows the locker dart  300  of the present invention. Like the prior art magnetic dart  200 , it has a rare-earth magnet tip  310 , a barrel  320  ending in a flighted stem  330 , and fins  340 . The most significant difference in the locker dart  300  of the present invention from the prior art magnetic dart  200  is its substantially shortened barrel  320 .  
         [0021]      FIG. 4  is an longitudinal view of the locker dart  300  in the preferred embodiment of the present invention. The dart is fabricated from three components: the magnet tip  310 , a metal nose section  400 , and a plastic tail section  410 . The nose section  400  is divided longitudinally into three axially symmetrical segments: a hollow tip retainer  420 , a nose taper  430 , and a hollow nose barrel  440 . The magnet tip  310  is bonded by adhesive within the tip retainer  420  (as shown with dashed lines in the figure), with a thin portion protruding at the tip whereby the dart can stick magnetically to ferromagnetic material. The tail section  410  consists of a stem  330  and four attached fins  340 . The stem  330  is divided into a tail barrel  450 , the tip-ward portion of which is bonded with adhesive to the inside of the nose barrel  440  (as shown with dashed lines in the figure); and a tail barrel taper  460 . Each fin  340  is divided longitudinally into a fin expansion segment  470 , a fin mid-segment  480 , and a fin contraction segment  490 . The barrel  320  consists of the nose barrel  440 , the exposed part of the tail barrel  450 , and the tail barrel taper  460 .  
         [0022]      FIG. 5  shows the important dimensions of the preferred embodiment. These are the diameter (9 mm)  655  of the magnet tip  310 ; the diameter (11 mm)  660  of the tip retainer  420 ; the diameter (7 mm)  665  of the nose barrel  440 ; the diameter (4 mm)  670  of the tail barrel  450 ; the width (13 mm)  680  of a fin  340 ; the radial dimension (26 mm)  675  of the tail section  410 ; the overall length (59 mm)  600  of the locker dart  300 ; the protrusion (1 mm)  620  of the magnet tip  310 ; the length (18 mm)  610  of the nose section  400 ; the length (39 mm)  605  of the (exposed) tail section  410 ; the length (4 mm)  640  of the tip retainer  420 ; the length (11 mm)  625  of the nose barrel  440 ; the length (7 mm)  650  of the cylindrical (exposed) portion of the tail barrel  450 ; the length (4 mm)  630  from the tail end of the nose section  400  to the start of the fins  340 ; the length (15 mm)  615  of the (exposed) stem  330 ; and the length (8 mm)  635  of the fin contraction segment  490 . Variations of up to ±20% for those dimensions greater than 5 mm, and up to ±50% otherwise, are considered approximately the same as these measurements as that term is considered relative to this invention.  
         [0023]     As illustrated by  FIG. 6 , the locations of the nose taper  430  and the fin expansion segment  470  have been separated just enough for a person to comfortably hold the dart  300  in that region, which constitutes the grip  500  of the dart  300 . An adult thumb  510  has a width of about 20 to 25 mm, with a curved “pad” that matches the approximately curved surface provided by the combination of the nose taper  430 , the nose barrel  440 , the tail barrel  450 , and the fin expansion segment  470 . The 23 mm length  645  of this grip  500  is chosen to balance the need for a small dart  300  in the locker  100  environment with the need to be able to comfortably hold and accurately throw the dart  300 . The overall length (59 mm) of the locker dart  300  (shown as length  600  in  FIG. 6 ) is scaled to be equal to the length (23 mm)  645  of the grip  500  multiplied by approximately 2.5.  
         [0024]     The shorter length of the locker dart  300  compared to the typical prior art dart  200  minimizes interference between the dart  300  and the contents of the locker  100  when the locker door  110  is being opened or closed. The rare-earth magnet tip  310  makes a single locker dart  300  sufficiently strong that it can be used to “tack” a sheet of paper  120  to an inside wall of the locker as illustrated by  FIG. 1 . The shorter length of the locker dart  300  also reduces the probability that the locker dart  300  will be accidentally dislodged.  FIG. 1  also shows two locker darts  300  tacking slips of paper  120  to the inside of the door  110 .  
         [0025]     The shorter length (59 mm)  600  also improves the usefulness of a locker dart  300  compared to the prior art as a peg from which to hang things within the locker  100 . Torque is the product of moment arm length (distance from a pivot axis) and force. An object of a given weight will apply more torque to a longer peg (i.e., dart) when suspended from its tail end than will the same object suspended near the tail of a shorter peg. Thus, a longer prior art magnetic dart  200  will only support a lighter suspended load, not to mention its increased likelihood of being dislodged by contact with other locker  100  contents. A locker dart  300  of the present invention can usefully suspend a lightweight object such as a pair of swim goggles.  
         [0026]     These benefits are obtained by the present invention locker dart  300  having a grip portion of approximately 23 mm and a length of approximately 59 mm. With the term approximately being defined as ±20% for these dimensions, the grip can range from 18 mm to 28 mm, and the overall length can range from 47 mm to 71 mm. These extremes are optimally restricted so that the ratio of overall length to grip length remains between 2:1 and 3:1.  
         [0027]     These length measurements are clearly dependent upon the definition of the “grip” for the locker dart  300 . The above description defines the grip  500  as the area running from the nose taper  430  to the fin expansion segment  470  where a person naturally grips the locker dart  300 . In  FIG. 5 , the length  645  of the grip  500  is shown from the beginning of the nose taper  430  to the end of the fin expansion portion  470 . However, one can easily imagine a fin  340  design without a separation between the fin expansion segment  470  and the fin mid segment  480 . In some circumstances, such as where there is no such separation, or where the separation between the fin expansion  470  and the find mid segment  480  occurs more than half-way through the length of fin  340 , a different definition can be used to define the grip  500 . In these circumstances, the grip  500  is still defined on one side by the nose taper  430  and the other side by the beginning of the fin  340  extending away from the tail barrel  450 . More specifically, the length of grip  500  can be defined by the beginning of the nose taper  430  to that portion of the fin  340  that first extends away from the nose tail barrel  450  to the same radial distance as the tip retainer  420 . In  FIG. 5 , this distance is 21 mm. Consequently, by subtracting a single millimeter from this dimension and adding a single millimeter to the previously determined grip length, it is clear that the present invention can be defined as a locker dart  300  having a grip portion between 20 to 24 mm, ±20%.  
         [0028]     The target  700  of the present invention is divided into regions having meaning within the context of a dart game. The target  700  can be made of a sheet of thin plastic material, as in the current invention, or any other essentially non-magnetic thin material, such as paper or fabric. In the preferred embodiment, the target  700  is a plastic that adheres to the locker  100  surface by static electricity. It is also within scope of the invention for the rear side of target  700  to be coated with non-permanent, removable adhesive. The target is packaged with a removable and disposable backing layer, which when removed allows the target  700  to be applied like a decal to a surface of a metal locker  100 . The present invention includes the target  700  in a package with the darts  300 , but does not include any surface on which the target  700  can be placed. Functionality of the target  700  of the present invention requires a ferromagnetic metal surface external to the product, such as the inside of a locker door or, for example, the side of a refrigerator, washing machine, or filing cabinet to which the decal can be affixed.  
         [0029]     The present invention is not to be limited to all of the above details, as modifications and variations may be made without departing from the intent or scope of the invention. Consequently, the invention should not be limited by the specifics of the above description, but rather be limited only by the following claims and equivalent constructions.