Magnetic positioning mechanism for fluid-supported self-rotating displays
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.
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 contained inside said body, said electric motor comprising:
a counter-torque element rotationally responsive to an ambient magnetic field; and,
wherein said device further comprises:
a magnetic lateral positioning structure apart from said body and apart from said electric motor, wherein said magnetic lateral positioning structure is fixed and adhered to a bottom part of said container in a non-rotating manner to said container, and wherein said magnetic lateral positioning structure has an aggregate center of mass located along said axis of rotation,
a local attractive magnetic force between said magnetic lateral positioning structure and said counter-torque element;
wherein said local attractive magnetic force has a strength which is insufficient to overcome a buoyancy of said body;
wherein said magnetic lateral positioning structure is located an effective distance from said counter-torque element so as to laterally bias said body toward a position of magnetic equilibrium between said magnetic lateral 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 lateral positioning structure is a permanent magnet.
5. The device of claim 1 , wherein said container comprises a light transmissive outer wall; and wherein said fluid comprises a light transmissive liquid.
6. The device of claim 1 , wherein said counter-torque element and magnetic lateral positioning structure are vertically aligned.
7. 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 lateral positioning structure.
8. The device of claim 7 , wherein said axis passes through a void bounded by said magnetic lateral positioning structure.
9. The device of claim 1 , wherein said effective distance is less than about 5 centimeters.
10. The device of claim 1 , wherein said magnetic lateral positioning structure comprises an amount of ferromagnetic paint coating a portion of said container.
11. 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.
12. 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.