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Superconducting Tooth Structures for Electromagnetic Devices

IP.com Disclosure Number: IPCOM000034393D
Original Publication Date: 1989-Feb-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 3 page(s) / 41K

Publishing Venue

IBM

Related People

Karidis, JP: AUTHOR [+2]

Abstract

A technique is described whereby superconducting material is used within toothed electromagnetic structures of devices, such as stepper motors and magnetic encoders, to improve operational performance. The concept describes the use of superconducting material in the 'tooth spaces' of a variety of toothed electromagnetic structures to effectively confine the magnetic flux to the desired tooth regions. This is done by positively excluding the flux from the space regions. Typically, electromagnetic devices rely on the aligning force produced when magnetic flux passes between two opposing sets of ferromagnetic teeth.

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Superconducting Tooth Structures for Electromagnetic Devices

A technique is described whereby superconducting material is used within toothed electromagnetic structures of devices, such as stepper motors and magnetic encoders, to improve operational performance. The concept describes the use of superconducting material in the 'tooth spaces' of a variety of toothed electromagnetic structures to effectively confine the magnetic flux to the desired tooth regions. This is done by positively excluding the flux from the space regions. Typically, electromagnetic devices rely on the aligning force produced when magnetic flux passes between two opposing sets of ferromagnetic teeth. One example is the variable-reluctance stepper motor, where the functional operation strongly relies on the amount of magnetic energy stored in the air gap between the toothed structures of the motor and its variation as a function of relative tooth alignment. Similar tooth structures are widely used as sensors to transform a physical displacement into a change in magnetic flux. Sensing is then performed by various means, such as Hall-effect, magneto-restrictive, or search-coil techniques. The common feature of all of these electromagnetic devices is the use of toothed structures. The toothed structures attempt to constrain the magnetic flux passing between the opposing structures to the ferromagnetic teeth region and to minimize the amount of flux passing through the 'tooth space'. This creates a favorable flux path across a small 'air gap', whose reluctance varies as a function of tooth alignment. The term 'tooth space' refers to the region between adjacent ferromagnetic teeth on each half of the structure, while the term 'air gap' refers to the relatively small separation between the two opposing sets of teeth in their aligned, or partially aligned configuration. In the operation of a typical stepping motor, the torque will vary roughly sinusoidally as a function of the tooth alignment and will increase monotonically as a function of coil current. However, as the coil current increases, the ferromagnetic material in the teeth begins to saturate, thus decreasing the permeability of the tooth material. This permeability decrease causes proportionately more current to be required to achieve a given increase in flux density. This also causes the flux fringing and leakage in the tooth spaces to increase, since the permeability of the tooth material slowly approaches the permeability of the air space. The magnetic flux which is not passing through the tips of the teeth is generally undesirable. This is because it tends to saturate the ferromagnetic structure and degrade the torque output of the motor by decreasing the variation in stored magnetic energy as a function of tooth alignment. The concept described herein utilizes superconducting material to fill the...