Magnetic Levitation

Visual Levitation Patents

You can learn a great deal about a product's design from its patents. Here are some for, or related to, the Visual Levitation device. Better yet, you can follow the links to related patents to get even more design ideas.

To search, try these USPTO home pages for applied patents, and for approved patents. Also try searching which offers free PDF downloading and European patent data.

Magnetic Suspension System

Title Magnetic Suspension System
Patent No. US Patent 6,154,353
International PCT/GB96/02150, filed Sep. 2nd 1996
Filed Febrary 23, 1998
Approved November 28, 2000
Inventors Ed Bowers; Ron Jones, Nabeel Shirazee
Assignee Magnetic Patent Holdings Limited (Ramsey, GB)

A major part of this invention is to drive the coil from an H-bridge, reversing the field and providing both attraction and repulsion. This overcomes the attractive force between the two permanent magnets, in case they move too close together. As a result, it saves wasted current because the object can be parked exactly at the neutral point.

However, they acknowlege the object should be parked just above the neutral point, in case of power failure.

Dr. Shirazee has put a great deal of attention to the magnetic flux path.

  • A "flux concentrator" a the top of the lifting coil helps direct the flux downward. It mentions mu-metal, for its extremely high permeability to conduct magnetism out and downward from above.
  • The Hall effect sensor should be shielded from the upper magnet and coil using a non-magnetic material (aluminum) for AC effects
  • The Hall effect sensor should also be shielded using a Mu-metal from DC effects of magnetism

They mention the need for a very sensitive Hall effect sensor. To improve sensitivity they suggest using two sensors and summing the signals.

It also mentions a method of rotating the object, obscurely written in the most vague generalities. In theory, the idea is to distort the suspended object's field, so it is not rotationally symmetric. And also provide something on the support structure to interact with the distorted field. When done properly, it fools the sensor into increasing the attractive force while it rotates.

In practice, the field distortion is done by attaching two small magnets on opposite sides of the object. The structure receives two iron bars of about one inch in length, taped onto opposite sides of the lifting coil. This provides an effect similar to a shaded pole motor, and is sufficient to gently spin the object. However, this is very low torque -- the turning effect can be easily overcome by ambient air currents.

The patent suggests using multiple strands of small diameter wire as opposed to one larger strand. The stated goal is to reduce resistance while retaining a large number of turns. But unless you're trying to reduce the skin effect at higher frequencies, you might as well design the coil with the correct wire size to begin with.

Reading about the coil, the core is suggested to be mild steel, silicon iron (SiFe), ferro cobolt (FeCo), permendur, or a composition of nickel iron. I presume this is simply for high permeability and low hysterisis. There is no mention of reducing core eddy currents.

The patent also discusses typical current requirements. (This patent should win awards for clarity; it is quite a nice little research paper.) With proper adjustment, the holding current is around 10 mA. When the object moves from the balance point, the current increases exponentially (not linearly!) with distance. The maximum coil current could be as high as 700 mA.

Magnetic Floatation Control System

Title Magnetic Floatation Control System
Patent No. US Patent 6,373,676
Filed October 1, 1999
Approved April 16, 2002
Inventors William Baker, John Robinson, Andrew Artimovich
Assignee Span Inc. (Indianapolis, IN)

This patent is similar to Dr. Shirazee's but is microprocessor controlled. Some of the advantages include:

  • reduce parts by using a single Hall effect sensor, and digitally subtract the coil current from sensor readings (of course you must add a current sensor to do this)
  • reduce heat generation by shutting off coil current when the object is out of range
  • detecting over-current situation and shut off coil current
  • automatically adjust position according to weight (no manual adjustments needed)
  • self-calibrated to keep operating current below 90 mA, which can enable battery operation
  • they claim an object weight of one to six pounds

These features could be accomplished with analog electronics, but the circuit complexity quickly becomes prohibitive.

Identified Flying Object

Title Magnetic Suspension System
Application No. 20040052029
Filed June 18, 2003
Approved pending
Inventors Gabriel Joachim (Kowloon Bay, HK)
Assignee Identified Flying Objects, Limited

Here is a bonus, it is still in the application phase, but it is supposed to be an improvement to Dr. Shirazee's patent.

This patent is even more difficult to read than most. He describes positions of dynamic stability, I presume for the purpose of highlighting most levitators use a balance point just above the neutral spot. This allows most levitators to inherently snap the object upward when power fails. Then he goes on to describe a design for detecting power failures and using it to increase upward pull to rescue the object.

The main goal seems to be increasing the flying gap by using a balance point below the neutral spot.

One interesting thing is the "ring magnet" suspension. This seems counter to what I figured out. I still believe a good levitator needs a point source lifting from above, such as from a tapered iron core. This provides the lateral pull to return the object back to the middle of the lifting axis.

Another interesting point is that his main objective is to increase the air gap, so he wants to achieve a stable point below the magnetic neutral point. So he invented a power-fail detector, and big filter capacitors to suddenly yank the object upward for emergency parking. The circuit itself isn't new, so I guess he's claiming a novel application. Okay, not a bad thought. However it does increase the circuit complexity, so if a designer is willing to put up with the extra components, then he might gain another millimeter or two.

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