Magnetic Positioning Mechanism for Fluid-Supported Self-Rotating Displays

Abstract

A self-rotating display device (1) includes and outer light transmissive container (2) containing a light transmissive fluid (6) and a body (4) containing an electric motor (14) for rotating the body with respect to the outer container. The body also carries a compass magnet (18) as a source of counter-torque for the motor to operate against. A magnetic positioning structure (20) made of ferromagnetic material secured to the container interacts with the magnetic field of the compass magnet to cause the body to migrate toward a location minimizing the distance between the magnetic positioning structure and compass magnet, so that the body can remain centered within the display while rotating.

What is claimed is: 
     
         1 . A self-rotating device comprises:
 a container carrying a fluid;   a self-powered hollow rotating body buoyantly supported by said fluid;   wherein said body comprises:
 an axis of rotation; 
 an electric motor comprising:
 a counter-torque element rotationally responsive to an ambient magnetic field; and, 
 
   wherein said device further comprises:
 a magnetic positioning structure fixed with respect to said container, 
 a local magnetic field generated by at least one of said magnetic positioning structure and said counter-torque element; 
 wherein said magnetic positioning structure is located an effective distance from said counter-torque element so as to interact with said local magnetic field to bias said body toward a position of magnetic equilibrium between said magnetic positioning structure and said counter-torque element. 
   
     
     
         2 . The device of  claim 1 , wherein said counter-torque element is a compass magnet aligned to said ambient magnetic field. 
     
     
         3 . The device of  claim 2 , wherein said ambient magnetic field is the earth's magnetic field. 
     
     
         4 . The device of  claim 1 , wherein said magnetic positioning structure comprises a positioning magnet generating a multipurpose magnetic field providing both said ambient magnetic field and said local magnetic field. 
     
     
         5 . The device of  claim 4 , wherein said positioning magnet is a permanent magnet. 
     
     
         6 . The device of  claim 1 , wherein said container comprises a light transmissive outer wall; and
 wherein said fluid comprises a light transmissive liquid.   
     
     
         7 . The device of  claim 1 , wherein said position of magnetic equilibrium minimizes a distance between said counter-torque element and magnetic positioning structure. 
     
     
         8 . The device of  claim 1 , wherein said position of magnetic equilibrium is located so that said axis of rotation intersects a region occupied by said magnetic positioning structure. 
     
     
         9 . The device of  claim 8 , wherein said axis passes through a void bounded by said magnetic positioning structure. 
     
     
         10 . The device of  claim 1 , wherein said effective distance is less than about 5 centimeters. 
     
     
         11 . The device of  claim 1 , wherein said local magnetic field generates a biasing force which is insufficient to overcome a buoyancy force buoyantly supporting said body against gravity. 
     
     
         12 . The device of  claim 1 , wherein said local magnetic field generates a biasing force which is insufficient to overcome a force of gravity acting on said body. 
     
     
         13 . The device of  claim 1 , wherein said magnetic positioning structure comprises an amount of ferromagnetic paint coating a portion of said container. 
     
     
         14 . The device of  claim 1 , wherein said fluid comprises two different density liquids, wherein said liquids are selected to buoyantly support said body within said container. 
     
     
         15 . The device of  claim 1 , wherein said device further comprises a light transmissive outer enclosure forming said container, wherein said enclosure is shaped and dimensioned to have an internal cavity containing an amount of a light transmissive liquid forming said fluid and said self-powered hollow rotating body being immersed in said liquid. 
     
     
         16 . The device of  claim 1 , wherein said local magnetic field has a strength which cannot overcome the weight of said body.