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Magnetic field permeable barrier for magnetic position measurement system
| Details |
Inventors: Ashe, Westley S.;
Assignee: Ascension Technology Corporation (Burlington, VT)
Primary Examiner: Snow; Walter E.
Assistant Examiner:
Attorney, Agent or Firm: Spiegel; H. Jay
A magnetic field position and orientation measurement system contains, confines and re-directs the magnetic field from one or more transmitters such that the fields are attenuated in areas outside of the operating volume in areas where metallic objects are commonly found. A thin barrier made of a highly permeable material such as ferrite or mumetal is placed on top of a conductive plate. The thickness of the permeable layer is from 0.01 inches to 0.25 inches while the conductive plate, preferably made of an aluminum alloy, may preferably be from 3/16 of an inch to 1/4 inch in thickness. On top of the permeable barrier, a rhombic three axis transmitter is placed. In the preferred embodiment, the transmitter consists of a PC board carrying the transmitter. PC boards having thicknesses varying from 0.03125-0.125 inches may be employed. Thus, the entire "stack" including the transmitter, the permeable barrier and the conductive plate may only be from 1/2 inch to 5/8 of an inch in thickness. The permeable barrier may have a flat, planar configuration. Alternatively, it may be made to resemble, in cross-section, a cake pan having a flat central region with uplifted peripheral edges. Alternatively, the permeable barrier may have a generally flat configuration with peripheral edges that taper outwardly from the top surface thereof to the bottom surface thereof with the taper making an angle with the bottom surface in the range of, preferably, 30.degree. to 85.degree.. |
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DETAILED DESCRIPTION The present invention relates to embodiments of a magnetic field position and orientation measurement system with means for substantially containing, confining and re-directing the magnetic field from one or more transmit elements such that the fields are attenuated in areas outside of the operating volume in areas where metallic objects are commonly found.
The present invention relates to devices for measuring the position of receiving antennae relative to transmitting antennae using magnetic fields.
Particularly, although not exclusively, such devices are for measuring that position in six degrees of freedom, namely, motion or translation in three coordinate directions (location) and rotational motion above three coordinate axes (orientation), location being commonly defined by X, Y, and Z linear coordinates referring to three mutually perpendicular directions and orientation being commonly described by pitch, roll and azimuth angular coordinates above three mutually perpendicular axes usually coincident with the three mutually perpendicular directions.
The present invention includes the following interrelated objects, aspects and features: (1) In the preferred embodiment, a flux containment means is used to re-direct the flux vectors such that they are enhanced inside of the sensor operating volume and decreased under and adjacent to the transmitter plane, which reduces the sensitivity of the system to metals under and near the transmitter.
The flux vectors from the transmitters are distorted by the flux containment means in a stable and repeatable manner, thus it is possible to precisely and repeatably characterize the distorted field.
Once the precise vector distribution from the transmitter assembly is known, solution of position and orientation from a receiving means is a straightforward task to those familiar with the magnetic position tracking art.
One reliable method for accomplishing this vector characterization is to utilize finite element analysis to compute the magnetic field vectors from the transmitter
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Communications 
