US 3740683 A
A magnetic circuit made of a permanent magnet of high coercivity material, for example, barium ferrite ceramic material having a coercive force sufficiently high that the domains of the permanent magnet will not be reversed, and an electrical coil wound closely around the permanent magnet over its entire length. The electrical coil may be excited by a direct current of value and direction such that the magnetic field from the permanent magnet will be partially or completely neutralized, however, the domains of the permanent magnet will not be reversed and when the current in the coil is reversed from the first condition, the strength of the magnet becomes equal to the combined magnetic field from the permanent magnet and the magnetic field from the coil. This magnetic circuit is particularly useful for use in lifting magnets, although it is also applicable to magnets used for separating, holding, or otherwise exerting an external magnetic influence.
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Description (OCR text may contain errors)
Benson June 19,- 1973 ELECTROMAGNETIC TURNOFF SYSTEM FOR PERMANENT MAGNETS [75 I Inventor: William H. Benson, Erie. Pa.
 Assignee: Eriez Manufacturing Company,
 Filed: Apr. 7, 1972  .Appl. No.: 241,974
Related US. Application Data  Continuation-impart of Ser. No. 64,685, Aug. 18,
 US. Cl.... 335/284, 335/289 ] Int. Cl. ..H01f 13/00  Field of Search 335/284, 289, 290,
[56'] References Cited UNITED STATES PATENTS 3,089,064 5/1963 De Bennetot.....' 335/289 UX 3,146,381 8/I964 Moreau 335/289 UX 3,316,514 4/1967 Radus et al. 335/291 3,428,867 2/1969 Becker 335/284 X Primary Examiner-George Harris Att0rneyCharles L. Lovercheck  ABSTRACT A magnetic circuit made of a permanent magnet of high coercivity material, for example, barium ferrite ceramic material having a coercive force sufficiently high that the domains of the permanent magnet will not be reversed, and an electrical coil wound closely around the permanent magnet over its entire length. The electrical coil may be excited by a direct current of value and direction such that the magnetic field from the permanent magnet will be partially or completely neutralized, however, the domains of the permanent magnet will not be reversed and when the current in the coil is reversed from the first condition, the strength'of the magnet becomes equal to the combined'magnetic field from the permanent magnet and the magnetic field from the coil. This magnetic circuit is particularly useful for use in lifting magnets, although it is also applicable to magnets used for separating, holding, or otherwise exerting an external magnetic influence.
4 Claims, 4 Drawing Figures ELECTROMAGNETIC TURNOFF SYSTEM FOR PERMANENT MAGNETS CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of application, Ser. No. 64,685, filed Aug. 18, 1970 now abandoned.
I STATEMENT OF PRIOR ART Lifting or hoisting apparatus utilizing electromagnets have been in operation for many years. The electromagnet type of lifting apparatus has at least two serious disadvantages:
. 1. It is required that a large amount of electrical energy be supplied to the electromagnet in order to provide the lifting force and this is expensive; furthermore, most of this energy must come out as heat, which impairs the efficiency of the magnet, shortens its life, and is diff cult to dispose of.
2. If the magnet is inadvertently de-energized, the load will fall, unless an expensive power back-up system is used.
Various prior lifting magnets have been proposed; for
example 'U.S. Pat. No. 3,316,514, 3,389,357; 3,089,064, 3,389,358, and 3,441,807.
REFERENCE TO PRIOR ART US. Pat. No. 3,428,867 shows a magnetic circuit physically similar to applicants circuit but it discloses a magnetic material which is of insufficient coercive force to retain the magnetic domains in their original position when a current in the coil is reversed. The said patent suggests that material usedshould have a coercive force of 900 ampere turns per inch (450 oersteds), whereas in my invention, the permanent magnet material must have a coercive force of at least 4,400 ampere turns per inch (2,200 oersteds) to prevent de-magnetization.
OBJECTS OF THE INVENTION It is an object of the invention to provide an improved magnetic circuit.
Another object of the invention is to provide an improved magnetic lifting device or other magnetic device for exerting an external magnetic influence.
A further object of the invention is to provide a magnetic circuit that is simple in construction, economical to manufacture, and simple and efficient to operate.
GENERAL DESCRIPTION OF THE DRAWINGS DETAILED DESCRIPTION OF THE DRAWINGS Now with more particular reference to the drawings, in FIG. 1 the permanent magnet is shown supported by the pole pieces 12 and 13. These pole pieces may be of soft iron or steel. The permanent magnet 10 is made of high coercivity material, such as barium ferrite, which is made up of wafers stacked one on the other. A specific example of suitable magnetic material is Indox V having a coercive force of 4,400 ampere turns per inch (2,200 oersteds). Indox V is a registered trademark owned by the Indiana General Company. A coercive force in this range will prevent the magnetic domain of the permanent magnet from reversing and demagnetizing the magnet so that when the current in the coil is such as to produce a reverse magnetomotive force to that of the permanent magnet, the permanent magnet will retain its original magnetic condition. A coil 16 is disposed around the magnet as shown. The coil has terminals 17 and 18 to which a D.C. voltage may be connected. A suitable hoist can be connected to lifting eyes 40. A load 20 may be lifted by the permanent magnet field alone or by the combined permanent magnet and coil fields when coil current flows in a direction such as to aid the field of permanent magnet 10 indicated by arrows 30. When the current is in a direction to aid the permanent magnetic field, a magnetic field due to the current flow will be induced in the stack of permanent magnets 10 by the coil in the direction indicated by arrows 31. The resultant field is greater than the field produced by the permanent magnet alone indicated by arrows 30 when the current is turned off; stated another way, when the field induced by the coil is in thesame direction asthe magnetic field of the per manent magnet, the sum of fields 30 and 31 will be stronger than that of the permanent magnet alone.
When the D. C. voltage on terminals 17 and 18 is reversed, as indicated in FIG. 2, the permanent magnet field of magnet 10 will be partially or completely cancelled or neutralized by an opposite field 31 due to the coil and the load 20 will drop, provided the net field has been sufficiently weakened to allow this.
In the embodiment of the invention shown in FIG. 3, a permanent magnet made of a high coercivity material such as barium ferrite is shown supported on the back plate Ill-with the polepieces 112 and 113, supported on the back plate to provide ends 114 and 115 to which a load may be attracted between these pole pieces and magnet pole piece 121. The coil 116 is wrapped closely around the magnet and extends entirely from one end thereof to the other as does the coil 16 in the embodiment shown in'FlG. 1. Terminals 117 and 118 may have a source of electrical D.C. energy connected thereto whereby in one direction, the field 130 from permanent magnet 110 is aided by the electromagnetic field 131 from the coil 116 to make a stronger combined magnet. In the other direction (FIG. 4), the magnetic field 130 from the permanent magnet field may be completely or partially cancelled out by field 131 from the coil, so that little or no force will be applied to the load and, therefore, the load 120 will not be supported. A suitable hoist can be connected to the lifting eyes 140.
The foregoing specification sets forth the invention in its preferred practical forms but the structure shown is capable of modification within a range of equivalents without departing from the invention which is to be understood is broadly novel as is commensurate with the appended claims.
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. A magnetic circuit comprising a permanent magnet,
said coil being adapted to have a direct current pass therethrough and to produce a magnetic field through said permanent magnet,
said permanent magnet being made of a magnetic material having a sufficiently high coercive force that the magnetic domains of said material will not change substantially when said current from said coil is passed therethrough in a direction to produce a field of a direction opposing said permanent magnet field,
said coil being adapted to have the said current therethrough reversed whereby its magnetic field aids the field of said permanent magnet and therefore produces a stronger magnet.
2. The magnetic circuit recited in claim 1 wherein said permanent magnetic material is a material having a coercive force equal to or greater than 4,400 ampere turns per inch.
3. The magnetic circuit recited in claim 1 wherein said coil covers the outside surface of said permanent magnet to the extreme ends of said magnet.
4. The magnetic circuit recited in claim 3 wherein said ends of said magnet are adapted to attract a magnetic material thereto whereby said magnet may be used as a lifting magnet and means on said magnet for attaching it to a lifting member.