Abstract:
A toy top system that uses uniquely configured tops. The system contains a plurality of toy tops that can be stacked on top of one another while spinning. Each of the tops has a value for rotational inertia associated with it. At least some of the tops are configured to have a value for rotational inertia that varies as a function of the rotational speed of the top. The tops with a variable rotational inertia are capable of storing and providing rotational energy while maintaining a near constant rate of rotation.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     In general, the present invention relates to the structure of toy tops and the manufacturing techniques used to manufacture toy tops. More particularly, the present invention relates to toys tops and similar rotating toys that having a rotational inertia that varies as a function of rotational speed. 
     2. Description of the Prior Art 
     Toy tops have been in existence for thousands of years. In the many years that tops have been in existence, they have been built in a countless number of styles, shapes and sizes. Regardless of the form of a top, all tops share certain common functional features. Tops have a central axis around which they spin. The center of gravity associated with the top passes through the central axis and the mass of the top is evenly distributed around the central axis. As the top is put into motion, the top spins about its central axis. Since the mass of the top is evenly distributed around the central axis, the top spins in a uniform manner, thereby enabling the top to be balanced at a point in line with the central axis. The top will spin in a stable manner until the rotational speed of the top falls below a certain threshold level. As the speed of the top decreases, its angular momentum decreases. Eventually, the presence of angular momentum is insufficient to overcome the forces of gravity and the top tips over. 
     All tops have a rotational inertia. Rotational inertia is a function of the mass of the top and the square of the distance of that mass from the central axis of rotation. As such, if two tops of the same mass are provided and one top is wider than the other, the wider top will have a larger rotational inertia than the narrower top. As rotational energy is applied to a top, the speed at which the top spins is a function of its rotational inertia. Wide tops will spin slower than narrow tops if the tops have the same mass and are spun with the same degree or rotational energy. This same principle explains why ice skaters spin faster when they draw their arms closer to their bodies. As a skater brings their arms closed to their body, their rotational inertia decreases and the speed of their rotation increases. 
     In recent years, top systems have been manufactured that include a series of graduated tops that can be stacked on top of one another when spinning. An early example of such a system is shown in U.S. Pat. No. 3,906,660 to Voth, entitled, Toy Top. Today, such systems typically include at least three different tops of different sizes and a spring activated launcher for spinning the tops. In such systems, each of the tops embodies a different rotational inertia since each of the tops is a different size. Furthermore, all of the tops in such systems are launched by the same spring mechanism. Accordingly, each of the tops is launched with the same initial rotational energy. However, since each of the tops has a different rotational inertia, each of the tops spins at a different speed. 
     When stacking spinning tops, the tops do not become stable until two contacting tops are spinning at the same rate of rotation. If two contacting tops are spinning at different rates of rotation, then the tops are rotating relative one another. This tends to make the tops wander in position and separate from one another. In prior art top systems that use multiple stacked tops, it is difficult to have all the tops spin at the same rate of rotation since each top is initially launched at a different rate of rotation. Consequently, it is difficult to stack the spinning tops in a stable configuration and have the tops remain stable for any significant amount of time. Furthermore, no top can be added to the stack that is not spinning or is spinning slowly because the non-spinning top would immediately destabilize the faster spinning tops and cause the stacked structure to fall. 
     A need therefore exists for an improved top structure that would enable the top to change its rotational inertia as a function of speed. Such an improved top structure would enable tops spinning at different speeds to quickly synchronize when stacked. Furthermore, stored angular momentum can be readily transferred to stationary tops or to slow moving tops when such tops are stacked on rotating tops. As such, a stationary top can be stacked upon moving tops without destabilizing the spinning structure. Such an improved top structure is provided below as defined by the following specification and claims. 
     SUMMARY OF THE INVENTION 
     The present invention is a toy top system that uses uniquely configured tops. The system contains a plurality of toy tops that can be stacked on top of one another while spinning. Each of the tops has a value of rotational inertia associated with it. At least some of the tops are configured to have a value for rotational inertia that varies as a function of the rotational speed of the top. The tops with a variable rotational inertia are capable of storing and releasing rotational energy while maintaining a near constant rate of rotation. 
     The tops with variable rotational inertias each contain free weights that are symmetrically disposed around its axis of rotation. The weights are biased toward the axis of rotation by a spring or by gravity. As the top spins, the weights move away from the axis of rotation against the counteracting bias. Since the mass of the weights moves away from the axis of rotation, the rotational inertia of the top changes and rotational energy is stored without altering the rate of rotation. The stored rotational energy is used to prolong the spinning time of the top and help different tops synchronize in speed when stacked. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention, reference is made to the following description of an exemplary embodiment thereof, considered in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a perspective view of an exemplary embodiment of a system of toy tops in accordance with the present invention; 
     FIG. 2 is a top view of one top from the system of tops shown in FIG. 1, the top is shown in a stationary condition; 
     FIG. 3 is the same view as FIG. 2 with the top shown in a spinning condition. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Although the present invention top can be configured in many shapes and styles, the present invention toy top is particularly well suited for use in systems of graduated tops, where the tops are designed to be stacked when spinning. Accordingly, the illustrated example of the present invention toy top will show a top system containing five graduated tops in order to set forth the best mode contemplated for the invention. 
     Referring to FIG. 1, a toy top system  10  is shown. The toy top system  10  is comprised of five tops  20 ,  21 ,  22 ,  23 ,  24  that are graduated in size. The toy top system  10  also includes a spring powered launcher  12  that is used to spin the tops. The use of five tops is merely exemplary, and it should be understood that any plurality of tops can be contained within the system. 
     Each of the five shown tops  20 ,  21 ,  22 ,  23 ,  24  contains a central hub  14 . The hub  14  of each of the tops is identical and is sized to engage the spring powered launcher  12 . Accordingly, a single spring powered launcher  12  is capable of independently engaging and spinning each of the different tops  20 ,  21 ,  22 ,  23 ,  24  in the system  10 , regardless of the size of the top. The central hub  14  of each top also includes a central cylindrical projection  16 . When the various tops are stacked, a top rests within the central cylindrical projection  16  of the below lying top. The cylindrical projection  16  therefore limits the movement of each of the tops when the tops are stacked. This enables all five tops  20 ,  21 ,  22 ,  23 ,  24  to be stacked on top of one another. 
     Each of the tops  20 ,  21 ,  22 ,  23 ,  24  has a sloped base  18 . The sloped base  18  of each of the tops is identical in structure and size. At the apex of the sloped base  18  is a metal head  19 . The tops rotate on their metal heads  19  when spinning on a flat surface. Although the use of a metal head  19  is optional, it is preferred because is provides a strong spinning point for the tops having a low coefficient of friction. 
     The largest of the tops  20  has a first diameter D 1 . The diameter of each of the remaining tops becomes progressively smaller. Each top spins around its central axis. The central axis of each top passes through the center of the sloped base  18  on the bottom surface of the top and the central hub  14  on the top surface of the top. Since the large tops have a mass that is distributed farther from the central axis than the smaller tops, the larger tops have greater rotational inertia than do the smaller tops. 
     Referring to FIG. 2, a top view of the largest top  20  is shown. The structure of the largest top  20  is identical to the structure of the three largest tops  20 ,  21 ,  22  shown in FIG.  1 . From FIG. 2, it can be seen that the larger tops each contain weight chambers  30  symmetrically disposed around the central hub  14  of the top. In each weight chamber  30  is a weight  32 . Each weight  32  has the same mass. Accordingly, the existence of the weight chambers  30  and the weights  32  do not disrupt the balance of the top. Within each weight chamber  30 , the weights  32  are biased toward the inner end of the weight chamber  30  that is nearest the central hub  14 . In the larger tops, the bias to the weights can be provided by a spring  34  in the weight chamber  30 . In the smaller tops, if there is no room for a spring, the bias to the weights can be provided by a sloped floor within the weight chamber, wherein gravity would bias the weight toward the inner end. A sloped weight chamber is shown as part of the fourth top  23  in FIG.  1 . 
     In the shown embodiment of FIG. 2, a spring  34  is provided in each weight chamber  30  that biases each weight  32  toward the inner end of the weight chamber  30 . When the top is at rest, the each weight  32  in each weight chamber  30  is biased against the inner end of the weight chamber  30  by the spring  34 . This condition is shown in FIG.  2 . However, as the top begins to spin, centripetal forces act upon the weights  32  in the weight chambers  30 . The centripetal forces act to drive each weight  32  away from the inner end of the weight chamber  30  toward the outer end of the weight chamber  30 . 
     Referring to FIG. 3, it can be seen that as the top spins, the centripetal forces pull the weights  32  against the bias of the springs  34 . As a result, the weights  32  compress the springs  34  and move a distance D 2  from the inner end of the weight chamber  30 . The distance D 2  that the weights  32  move away from the inner end of the weight chamber  30  is dependent upon the mass of the weights  32 , the bias force of the springs  34  and the rotational speed of the top. The faster the top spins, the greater the centripetal forces are and the farther the weights  32  will compress the springs  34 . 
     The top is spun by the spring loaded launcher  12  (FIG.  1 ). Accordingly, the initial rotational energy used to spin the top is a known value. The mass of the weights  32  and the bias of the springs  34  are calibrated so that the springs  34  are compressed when the top is first spun by the spring loaded launcher. As the top spins, it loses energy and slows down. As the top slows down, the centripetal forces decrease and the weights  32  slowly fall back toward the inner end of the weight chambers  30 . When the top falls below a certain threshold rate of spin, the bias of the springs  34  surpasses the centripetal forces and the weights  32  are again biased against the inner end of the weight chambers  30 . 
     Since the positions of the weights  32  in the weight chambers  30  change as the top spins at different speeds, the distance of the weights  32  from the top&#39;s central axis also changes. Consequently, the rotational inertia of the top varies as a function of rotational speed. Rotational inertia is expressed by the following formula: 
     
       
         I=Σmr 2   
       
     
     Where I is rotational inertia, m is the mass of the spinning object and r is the distance of the mass from the axis of rotation. When the top is spinning rapidly, the weights  32  will be far from the axis of rotation and the rotational inertia will be great. When the top is spinning slowly, the weights  32  move toward the axis of rotation and the rotational inertia decreases. 
     The ability of the tops in the present invention system to change their rotational inertia has certain practical benefits. In an ordinary top, the rate of rotation of the top steadily decreases as the top loses energy. As such, prior art tops do not remain at one rotational rate for very long. However, with the present invention top, the rotational inertia of the top deceases as the top loses energy. As a spinning body decreases its rotational inertia, it tends to spin faster. This is evidenced by an ice skater spinning faster when the skater pulls his/her arms closer to their body. Consequently, when the present invention top is spun and energy is lost, the losses in rotational speed are balanced by the decrease in rotational inertia. As a result, the top stays at an equilibrium near a constant rate of rotation for a majority of the time in which the top spins. 
     The moving weights  32  in the top also act to store rotational momentum. When one top is spun, the weights  32  may be biased away from the inner end of the weight chambers  30 . If a another top is placed upon the first top and the upper top is spinning slower than the lower top or is not spinning at all, the lower top transfers rotational energy to the upper top. As rotational energy is transferred from the lower top to the upper top, the upper top begins to spin. The lower top, however, loses energy. As the lower top loses energy, the weights  32  in the lower top move closer to the center of the top and the rotational speed of the lower top remains the same. It is therefore possible to make the upper top spin at the same speed as the lower top without the lower top ever slowing down. 
     The ability to store and transfer rotational energy makes the task of stacking tops much easier. If a first top is placed on a second top and the two tops have different rates of rotation, each top will either store or release rotational energy until the tops spin at the same rate. Consequently, by using tops that store and release rotational energy in moving weights, the ability to stack multiple tops, such as those shown in FIG. 1, becomes simpler. 
     It will be understood that the embodiment of the present invention system of tops that is described and illustrated herein is merely exemplary and a person skilled in the art can make many variations to the embodiment shown without departing from the scope of the present invention. All such variations, modifications and alternate embodiments are intended to be included within the scope of the present invention as defined by the appended claims.