Magnetic field producing apparatus
United States Patent [1 1 Ballinger MAGNETIC FIELD PRODUCING APPARATUS [75] inventor: Dale 0. Ballinger, Denver. C010. [73] Assignee: Honeywell, Inc.. Minneapolis. Minn. [22] Filed: Nov. 29. 1973 [21] Appl. No.: 420,284  
 [52] US. Cl. 360/56; 360/66; 360/123; 360/1 18 [51] Int. Cl....G1lb 5/02; G1 1b 5/112; HOlf 13/00 [58] Field of Search 360/66. 118. 123. 56. 115;  
 [ 56] References Cited UN1TED STATES PATENTS 2.498.423 2/1950 Howell 360/118 2.550.753 5/1951 Andrews. 2.604.550 7/1952 Begun 2,908.768 10/1959 Steinegger 2.928.078 3/1960 Hagopian 3.449.529 6/1969 Camras 360/66 1 1 Apr. 22, 1975 Primary Examiner-Bernard Konick Assistant Examiner-Alan Faber Attorney. Agent. or Firm-Arthur H. Swanson; Lockwood D. Burton; Mitchell J. Halista ABSTRACT A magnetic field producing structure has a pair of U- shaped elongated core members with the end faces of the legs of one of the core members arranged in a confronting relationship across a predetermined gap with the end faces of the legs of the other one of the core members. A first winding on each of the core members is wrapped around the trough of each of the core v members. A source of alternating current is arranged to serially energize the first windings on both of the core members. A second winding is located on each of the core members and is wrapped around the corresponding core member at right angles to the first winding. A direct current source is arranged to serially energize the second windings on the core members.  
 4 Claims. 3 Drawing Figures MAGNETIC FIELD PRODUCING APPARATUS BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to magnetic field producing apparatus. More specifically, the present invention is directed to a magnetic field producing apparatus for producing a rotating magnetic field vector having an orientation in a predetermined plane.  
 SUMMARY OF THE INVENTION An object of the present invention is to provide an improved magnetic field producing means for producing a rotating magnetic vector parallel to a predetermined plane.  
  In accomplishing this and other objects, there has been provided, in accordance with the present invention, a magnetic field producing means including a first magnetic field core member having a generally U- shaped cross-section, a first winding wrapped on the member encompassing the trough of the U-shaped cross-section. A second winding is wrapped around the outside of the core member to produce a magnetic field emanating from the U-shaped cross-section ends of the core member. A second U-shaped core member having a pair of coils mounted thereon in a similar arrangement to the first core member is positioned on the other side of a recording medium with the ends of the legs of the second core member being aligned with the ends of the legs of the first core member. An alternating current source is arranged to energize the first coil on each of the core members in a series circuit interconnection. The second coil on each of the core members is connected in a series circuit across a direct current source.  
 BRIEF DESCRIPTION OF THE DRAWINGS A better understanding of the present invention may be had when the following detailed description is read in connection with the accompanying drawings, in which;  
 FIG. 1 is a pictorial illustration of a magnetic field producing structure embodying the present invention,  
  FIG. 2 is a cross-sectional illustration of the structure shown in FIG. 1 taken across the U-shaped crosssection of the core members used in the magnetic field producing structure, and  
  FIG. 3 is a cross-sectional illustration of the structure shown in FIG. 1 taken along the length of the core members of the magnetic field producing structure.  
 DESCRIPTION OF THE PREFERRED EMBODIMENT DETAILED DESCRIPTION cording medium with each capsule containing a suspension of a plurality of magnetically responsive, flakelike particles. The recording medium may be prepared for recording thereon by erasing any prior recordings thereon, i.e., pre-aligning all of the flake-like particles in an orientation having a major surface of each of the flake-like particles parallel to the plane of the recording medium, i.e., parallel to the recording surface of the recording medium. In this position of the encapsulated particles, the recording medium presents a uniform appearance at its recording surface.  
  A recording may be subsequently made upon the recording medium by reorienting the flake-like particles in a limited area encompassing a recording element, i.e., the particles are reoriented into a position perpendicular to the recording surface of the recording medium. Following such a recording operation, the recording medium may be again erased and the recording medium returned to its original state by reorienting the particles back into their original state, i.e., parallel to the recording surface of the recording medium. Thus, the same magnetic field is used to prepare the recording medium from an original state having nonoriented particles and to erase a recording on a recording medium previously placed into a recorded state. In either case, the net result is to align the encapsulated particles into astate wherein the major face of each of the flakelike particles (the major face of a particle is defined as a surface having a dimension several times greater than any dimension defining the thickness of each particle) is aligned parallel to the recording surface of the recording medium to present a uniform appearance thereon. In order to produce such a particle aligning operation, it is necessary to generate a magnetic field vector within the plane of the recording medium and within the encapsulated particles while continuously rotating the magnetic field vector within the plane of the magnetic particle to uniformly align the major faces of the particles parallel with the recording surface of the recording medium. Such a uniform alignment operation is effective to produce a uniform surface appearance on the recording medium since the major faces of the particles are arranged to reflect incident radiation from the recording medium. The result of a particle alignment wherein only one axis of the particles were aligned parallel with the recording surface of the recording medium would not assure the attainment of the uniformly reflective recording surface.  
  The core structure of the present invention is directed to a magnetic field generating structure for producing such a rotating magnetic field vector within a predetermined plane, i.e., the plane of the particles within the recording medium. The core structure includes a pair of generally U-shaped elongated core elements 4 and 6. The core elements 4 and 6 are arranged with the end faces of the legs of one of the U-shaped core elements in a confronting relationship with the respective end faces of the legs of the other one of the core elements. The end faces of the legs of the core element 4 are spaced from the end faces of the legs of the core element 6 by a distance sufficient to allow the recording medium 2 to pass therebetween.  
  The following discussion is directed to a description of the structure of the energizing winding wound around one of the core members 4 and 6, i.e., a first core member 4, inasmuch as the arrangement of the windings on the second core member 6 is substantially identical. A first energizing winding 8 is arranged on the first core member 4 to lengthwise encircle the core member 4 in the trough of the U-shaped core member. A first end of the first winding 8 is connected to one side of a source of an alternating current source 12 while the other end of the winding 8 is arranged to be connected to one end of a similar second winding 9 on the second core member 6. The other end of the second winding 9 on the second core member 6 is connected to the other side of the alternating current source 12.  
  A third energizing winding 16 is wound around the first core member 4 at right angles to the first winding 8 and encompassing the U-shaped cross-section of the first core member 4. A first end of the second winding 16 is arranged to be connected to one side of a direct current source 18. The other end of the third winding 16 is arranged to be connected to one end of a similar fourth winding on the second core member 6. The other end of the fourth winding 20 on the second core member 6 is connected to the other side of the direct current source 18. Accordingly, the alternating current source 12 is arranged to serially energize the similar windings 8 and 9 on the first and second core members 4 and 6 while the direct current source 18 is arranged to serially energize the similar windings l6 and 20 on the first and second core members 4 and 6.  
  The energization of the third and fourth windings l6 and 20 by the direct current source 18 is effective to produce corresponding constant magnetic fields in the respective core members 4 and 6. The magnetic fields produced by the energization of the windings l6 and 20 by the direct current source 18 is shown in FIG. 3. As shown in this figure, the constant magnetic fields from the opposing core members emanate from the U- shaped cross-sectional ends of the core members 4 and 6. By a selection of either current flow or winding direction, these constant magnetic fields are arranged in field opposing relationship within the record medium accepting space between the confronting leg end faces of the core members 4 and 6. Further, the constant magnetic field in this space between the core members 4 and 6 is in a direction parallel to a plane in which a recording medium 2 is placed between the core members 4 and 6. The recording medium 2 is shown in FIG. 3 as being positioned in this plane by any suitable means (not shown) to allow the magnetic field to pass through the recording member 2 parallel to the recording surface and through the encapsulated magnetic particles of the recording member 2.  
  Concurrently, the energization of the first and second windings 8 and 9 by the alternating current source 12, is effective to produce a magnetic field emanating from the ends of the legs of the core members 4 and 6. The energization of the first and second windings 8 and 9 is arranged to produce opposing magnetic fields at the confronting leg end faces of the core members 4 and 6. in FIG. 2, there is shown a representation of a magnetic field occurring during one half-cycle of the energization current from the alternating current source 12. During the other half-cycle of the energizing alternating current, the north and south poles occurring at the ends of the legs of the core members 4 and 6 would, of course, be interchanged. As may be seen from FIG. 2, the opposing relationship of the magnetic poles found at the confronting end faces of the legs of the core members 4 and 6 produces a second magnetic field in the plane of the recording medium 2 located between the ends of the legs of the core members 4 and 6. While this second magnetic field is also parallel to the plane of the recording medium 2 and in the magnetic particles contained therein, the magnetic field from the second magnetic field is reoriented as a result of the interchange of the poles of the magnetic field on alternate cycles of the alternating current energizing signal. The two magnetic fields, i.e., the direct current field and the alternating current field, accordingly, combine in the plane of the recording medium to produce a net magnetic field. vector which rotates in the plane of .the recording medium 2 and in the magnetic particles to orient the major surfaces of the flake-like particles parallel to the plane of the recording medium. This orientation of the flake-like particles with the surface of the recording medium 2 is effective to erase any prior recording from the recording medium 2 to prepare it for further recording. One example of a magnetic field producing structure constructed in accordance with the present invention and suitable for erasing the aforesaid magnetic flake recording medium had 230 turns of No. 28 wire in each of the first and second windings 8 and 9 while the third and fourth windings each had 1,220 turns of No. 28 wire. The first and second windings 8 and 9 were energized by an alternating current of 0.7 amperes while the third and fourth windings may be energized with a direct current of 0.5 amperes. The core members 4 and 6 were each made of soft iron arranged as a U-shaped channel having a total length of 6 inches and a leg height of 1 inch. The confronting end faces of the core legs may be spaced apart a distance of 15 thousands of an inch to accommodate the recording medium 2. Such a magnetic field producing structure produced a magnetic field within the recording medium 2 of approximately 200 Gauss.  
  Accordingly, it may be seen that there has been provided, in accordance with the present invention, a magnetic field producing structure for producing a rotating magnetic field vector within a predetermined plane.  
  The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:  
  l. A magnetic field producing apparatus comprisin a first U-shaped core member;  
 a second U-shaped core member, said first core member having leg end faces spaced a predetermined distance from confronting leg end faces of said second core member;  
 a first winding wound on the trough of said first core member;  
 a second winding wound on the trough of said second core member;  
 a first energizing means arranged to serially energize said first and second windings;  
 a third winding wound around said first core member at right angles to said first winding;  
 a fourth winding wound around said second core member at right angles to said second winding, and  
 a second energizing means arranged to serially energize said third and fourth windings.  
  2. A magnetic field producing apparatus as set forth in claim 1 wherein said first energizing means is a source of alternating current. i  
  3. A magnetic field producing apparatus as set forth in claim 2 wherein said second energizing means is a source of direct current.  
 windings are energized by said first energizing means to produce mutually opposing and variable amplitude magnetic fields across said predetermined distance.