US Patent No. 5,863,235 -- Spinning/rolling disc

 

This invention is a disk which is optimized to spin/roll on a concave base surface for an extended period of time.  The product is sold under the trademark "Euler's Disk," since the Swiss mathematician Leonhard Euler developed the equations relating a rotating reference system to a stationary one which are used to solve for the relationship between the angle of orientation of the disk and its angular velocity.  An interesting aspect of the spinning/rolling motion is that the velocity at the point of contact of the disk with the base surface approaches infinity as the disk becomes more and more horizontal.  (Yes, that velocity can approach infinity since the point of contact is not actually a physical element.)  Because of that relationship and the acoustic characteristics of the base surface, the system emits a tone that rises in pitch as the disc loses energy and becomes more and more horizontal. 

 

Simple systems are often the most difficult to patent because there is a generally a great deal of close prior art.   In this case, the claims cover a disc with a top surface which is tessalated with reflective regions having effectively random optical angles of orientation.
 

Full patent

ABSTRACT
 

A cylindrical metal disc is optimized to spin/roll on a base for an extended length of time, and as the angle of inclination of the disc decreases to zero, a tone emitted by the spinning/rolling of the disc rises in pitch towards infinity. To optimize the spinning/rolling time, the radius-to-height aspect ratio of the disc is approximately three, the upper surface of the base and the lower edge of the disc are smooth and hard to enable the disc to spin/roll for an extended length of time, and the base has three legs and is solidly constructed to minimize energy losses due to vibration. The upper surface of the base is concave to prevent the disc from wandering as it spins/rolls. The top of the disc is tessellated with tiles having effectively random optic orientations to produce the appearance of a cloud of sparkling lights in the vicinity of the top surface of the disc as it spins/rolls.