US3047777A - High-performance electromagnetic transducer - Google Patents

Description

July 31, 1962 o. N. BECKER 3, 4

HIGH-PERFORMANCE ELECTROMAGNETIC TRANSDUCER Filed Dec. 24, 1958 2 SheetsSheet l FORCE INVENTOR. ADJUSTABLE CURRENT 5 ORLIEN N. BECKER SOURCE 1?. BY

ATTORNEY July 31, 1962 o. N. BECKER 3,047,777

' HIGH-PERFORMANCE ELECTROMAGNETIC TRANSDUCER Filed Dec. 24, 1958 2 Sheets-Sheet 2 INVENTOR.

ORLIEN N. BECKER ATTOR E) United States Patent 3,047,777 HIGH-PERFORMANCE ELECTROMAGNETIC TRANSDUCER Orlien N. Becker, Alderwood Manor, Wash, assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Filed Dec. 24, 1958, Ser. No. 782,781 8 Claims. (Cl. 317-123) The present invention is directed to a high-performance type electromagnetic transducer and more particularly to an improved linear moving iron armature type actuator. Devices of this type are generally old and the particular features of the present invention are directed to a double solenoid type actuator having an improved shape and arrangement of parts which provide a moving element having a minimum of inertia for accurate high-speed actuation. The particular servo or transducer of the double solenoid type provides a high performance linear output. These objects and others will become a part of the reading of the attached description together with a drawing wherein: FIGURE 1 is :a schematic view of a moving iron segment in an air gap provided between a pair of poles shown for explanation purposes, FIGURE 2 is a similar schematic of a moving iron segment between two sets of poles, with a magnetic structure, also shown for explanation purposes, FIGURE 3 is a sectional View of the actuator disclosing the arrangement, shape of parts and FIG- URE 4 is a top view or the actuator, and FIGURE 5 is a schematic wiring diagram for the actuator.

Referring to FIGURES 1 and 2, are included herein tor explanation purposes for the operation and theory of the transducer it will be seen that represents a segment or movable element of thin magnetic or iron material suspended in an (air gap 11 defined Ibetween poles 1'2 and 13. The segment presents a very short path length to the magnetic flux combined with a large cross sectional area. As will he later seen, this basically be the relationship to parts here in my improved device. In analyzing this arrangement of parts, a set of physical units, in particular a rationalized M.K.-S. system, in which all electrical units are practical and which incorporates the factor 41r into the permeability of free space, are assumed. In FIGURE 1, the force F on the iron segment may be given by:

ang;

wherein as indicated on the sketch w is the width of the iron segment and the width of the pole, x is the length of the segment positioned in the gap, d is the total depth length and t is the thickness of the iron segment. The permeance for the other part of the gap which does not include the segment will be expressed as:

ews -x Pb- 3) wherein Z is the length of the pole faceand l-x is the portion of the gap in which this segment is not positioned. The total gap permeance is the sum oi. 1? and P or If the magnetomotive force 1 is produced by an energizing winding, then IL wt 2 F- )nt (7) wherein n is the number of turns in the winding and 1' is the excitation current. It will be apparent that this configuration is non-linear, since the output force varies as i In FIGURE 2, the moving iron segment or the actuator is shown as moving between two sets of poles similar to the arrangement in FIGURE 1 to provide an output torce proportional to driving current, thus in FIGURE 2, the numerals 12 and 13 represent one set of poles and the numerals 22 and 23 represent the second set of poles between each of which is defined an air gap in which is positioned a portion of the iron segment indicated generally at 25. Although not shown, it will be assumed that for purposes here that the iron segment 25 has the same dimension along the width of the poles and perpendicular to the plane of the paper :as does the pole width and that the segment number 25 is positioned and movable in the gap between the poles and toward and away iirom respective sets of poles 12 and 13 and 2 2, 23- maintaining the same central locationship therein. Thus as in FIG- URE 2, if a differential magnetornotive force f is superimposed on a reference magnetomotive torce F in such a way as to add to the reference magnetornotive iforce across one gap and subtract across the other gap, a net force is produced which tends to pull the segment into the stronger gap. The force tending to pull toward the gap indicated by 3.0 in FIGURE 2 is +f1) Q52 T (a and the force tending to pull the segment toward the gap indicated at 31 in FIGURE 1 is 1 2 on 1 2 dx The net force toward gap 30 is This is true since the segment moves out of the gap 31 at the same rate at which it enters the gap 30. Thus Thus-if F is maintained constant, the net force exerted on 3 the segment is proportional to the differential magnetomotive force f and hence to the current i in a differential winding or windings energizing the same.

Referring now to FIGURES 3 and 4, the improved electromagnetic transducer or moving iron type actuator Otf a subject invention is shown in FIGURE 3, in section, as including an annular magnetic outer shell or magnetic yoke indicated at 40 to which is attached an end plate or closure member 41 having a centrally located pole member 42 integral therewith and extending toward the open extremity of the magnetic yoke. Although these parts may be integral, they are shown here as separate and held together by suitable means such as scr'ews indicated at 43. Positioned near the open extremity in the yoke is a first pole projection or annularly raised rim 45 which extends inwardly toward said pole member and forms therewith an air gap. A second pole member indicated at 46 is also positioned near the open extremity of the magnetic yoke 40 and is spaced from the first polar projection or pole ring defining a second annular pole. While this pole ring may be integral with the magnetic yoke, it is shown herein as a separate part secured thereto through screw means such as is indicated in 44. Positioned within the yoke is a first winding 50 which is the main biasing or reference winding supplying the magnetomotive force or flux to both of the poles :for purposes as will be later noted. Positioned adjacent thereto and within the confines of the yoke encircling the pole member 42 is a second coil 53 which as will be later noted supplies a magnetomotive force encircling both poles through a flux path which extends from the pole member 42 through the poles 45, 46 the main body of the yoke 40 and back through the end plate 41 to the pole member 42. A third winding indicated at 55 is positioned between the polar projections 45, 46 and as will be later noted supplies the magnetornotive force or flux which links only the pole member or polar projection 46 through a path including the annular shell or yoke 40, the end plate 41 and the pole member 42 and across the air gap to the polar projection 46. In the wiring diagram of FIGURE 5, the main winding is shown as connected to and energized from a continuous source of power which will provide a magnetomotive force or flux through the core structure linking both poles. FIG- URE also shows the 53 and 55 serially connected and to an adjustable source or signal source which is variable. The flux from the winding 53 links both of the pole members while the flux from the coil 55 links only the polar projection or pole 46 to provide the energization, coaction and operation outlined below.

Positioned in the air gaps between the polar members or projections 45, 46 and the central pole member 42 is an annular segment of iron or magnetic material indicated at 56 which is mounted on a supporting cup-shaped nonmagnetic member 51 to which an actuating shaifit 5'2 is adapted'to be connected. lSegment 56 is split as at 58 so that it will act as a segment and not a shorted turn in the magnetic fields. The shaft and the supporting structure are adapted to be connected to the device to be operated and the shaft will be lightly journalled and positioned so that it will maintain the position of the annular segment 56 in the air gap concentricwith thepole member 42. Thus, as in FIGURE 2, the segment is suspended between a pair of poles and has an effective length sub stantially equal to the distance between the center lines of the two polar projections 45 and 46 and is movable relative to the polar projections concentric with the pole member 42. This high speed cylindrical solenoid type actuator, for purposes of explanation, has the following turned ratio relationship between windings: winding 50 has N turns, winding 53 has 11 turns and winding 55 has 2n turns. This cylindrical magnetic yoke arrangement is somewhat similar to a dynamic loudspeaker with the exception that a pair of poles are included therein. The winding 50 provides the reference magnetomotive force F which appears between the central pole member and both poles 45, 46. The winding 53 provides a magnetomotive force or which as previously indicated also links both pole members 45, 46 and is connected in series for energization purpose with the coil 53 which links only the pole 46. When all of the windings are energized, the magnetomotive torce developed between the pole 45 and the central core member 42 is F-ni (where i is the current in windings 53, and the magnetomotiye torce developed between the pole 46 and the central core member 42 can be expressed as Fni+2ni which resolves or equals F+ni. This system is therefore linear, and since the width of the segment in the gap, and the width oi the poles may be expressed as W=1rr, wherein r is the radius of the air gap, the force output according to Equation 14 may be given as It should be noted that operation is linear with the assumptions previously mentioned over the range where ni is smaller than F, since the force on the iron segment depends only upon the magnitude of the gap M.M.Fs. In this device, however, a further limitation must be imposed since the flux density produced by the coil 50 or F and ni acting together must not be sufficient to saturate the magnetic yoke. Maximum flux density in the device will occur in a pole when the reference magnetomotive force F plus the differential magnetomotive force ni appears across the air gap with the segment present. If the maximum flux density is the maximum allowable flux density in the iron, is maximum flux in a pole and may be given by the following formula:

max) #0 IBEX d t or rting/ '0 IBEX d t Thus, for any given set of gap dimensions,

F+nim,= =K, (18) and correspondingly,

. 47l'7[.LgtF/Li nx 'max 2 'msx Thus 1" max and g F max= 2( 1 max max v In order to maximize the factor Fi dFi dmimax) K, (K 1 2m 0 (21) max= l= msx max Using the Equation 23 as a basis for an optimum design,

Thus with the maximum flux density prescribed, optimum output is obtained from the solenoid when the moving segment occupies one-halfof the air gap length, and the signal and the reference M.M.F.s are equal, that is ni=F. Applying these relationships,

The maximum acceleration or ratio of force to mass for the device is another important design consideration which can be expressed assuming that p of density of the iron, in M.K.S. units and the mass is max inal arrmdp then the acceleration is the ratio of, or equal to B force 4mm mass The flux linking the winding 53 is the sum of the fluxes in the two poles or wherein is the flux to across the gap to pole 45 as (P is the flux across the gap to pole 46.

Thus it is apparent that the total flux linking the coil 53 depends: on two variables that is the current and x the length of the gap in which the segment is present, then and correspondingly, the induced in the winding 55, is

The across the windings 53, 55 inseries is This corresponds to a winding inductance of The induced in winding 50 or the reference winding is equal to that of winding 53, since both are linked by the same flux, and its inductance is given as and is dependent upon segment position.

Strong lateral forces may be exerted on the cylindrical segment when the transducer is energized due to irregularities in the magnetic circuit. For this reason the segment should be carefully aligned and mounted with considerable lateral rigidity to prevent misalignment and rubbing on the pole surfaces. Thus the segment 56 may be connected through the shaft 52 to an integral part of the device of which it is to operate or may be mounted to lead springs (not shown) which permit axial but not lateral motion. In operation the single windings 53 and 55 and the reference winding 50 should be operated or energized from current sources. This is particularly true on the reference winding since a constant magnetomotive force or F is desired in the presence of a varying induced E.M.F. The differential windings may be operated from or controlled from vacuum tubes, transistors or magnetic amplifiers for continuous control or from relays, depending upon the desired rate of response. It will be recognized that the device is a high performance electromag netic transducer, in which a force output therefrom is extremely high with relatively little inertia, and in which the output force is directly proportional to the driving current, thus differing from the conventional solenoid type apparatus. Finally the signal windings, S3, 55 of the linear solenoid actuator have an inductance which is dependent of the position of the movable segment 56. This moving iron linear actuating device provides a relatively simple design which is economical to manufacture and is simple to maintain and provides high performance output.

I claim:

1. In an electromagnetic transducer, a cylindrical magnetic yoke having an open and a closed extremity with a centrally located center pole member extending from said closed extremity of said yoke to said open extremity thereof, first and second pole projections integral with said yoke near said open extremity thereof and concentric with said center pole member being spaced apart to define with said pole member an annular air gap, a first and second winding positioned in said yoke concentric with said pole member, a third winding positioned between said first and second pole projections, and a cylindrical armature member positioned in said air gap and adapted to move axially relative to said poles.

2. In an electromagnetic transducer, a cylindrical magnetic yoke having an open and a closed extremity with a centrally located center pole member extending from said closed extremity of said yoke to said open extremity thereof, vfirst and second pole projections integral with said yoke near said open extremity thereof and concentric with said center pole member being spaced apart to define with said pole member an annular air gap, a first and second winding positioned in said yoke concentric with said pole member, a third winding positioned between said first and second pole projections, and a cylindrical armature member having a length equal to the distance between the center lines of said pole projections being positioned in said air gap and adjacent to said pole projections and adapted to move axially relative thereto.

3. In an electromagnetic transducer, a cylindrical magnetic yoke having an open and a closed extremity with a centrally located center pole member extending from said closed extremity of said yoke to said open extremity thereof, first and second pole projections integral with said yoke near said open extremity thereof and concentric with said center pole member being spaced apart to define with said pole member an annular air gap, a first and second winding positioned in said yoke concentric with said pole member, a third winding positioned between said first and second pole projections, and an annular shaped member positioned in said air gap and adjacent to said pole projections and adapted to move axially relative thereto.

4. In an electromagnetic transducer, a cylindrical magnetic yoke having an open and a closed extremity with a centrally located center pole member extending from said closed extremity of said yoke to said open extremity thereof, first and second pole projections integral with said yoke near said open extremity thereof and concentric with said center pole member being spaced apart to de fine with said pole member an annular air gap, a first and second winding positioned in said yoke concentric with said pole member, a third winding positioned between said first and second pole projections, said first winding adapted to be energized from a constant current source and said second and third windings adapted to be simultaneously energized from a variable source, and armature means positioned in said air gap and adapted to move axially relative to said pole members.

5. In an electromagnetic transducer, a cylindrical magnetic yoke having an open and a closed extremity with a centrally located center pole member extending from said closed extremity of said yoke to said open extremity thereof, first and second pole projections integral with said yoke near said open extremity thereof and concentric with said center pole member being spaced apart to define with said pole member :an annular air gap, a first and second winding positioned in said yoke concentric with said pole member, a third winding positioned between said first and second pole projections, means adapted to connect said first winding to an energizing source, further circuit means connecting said second and third windings in a serial relation and to a variable source, and a cylindrical armature member positioned in said gap and adapted to move axially relative to said pole member and said projection.

6. In an electromagnetic transducer, a cylindrical mag netic yoke closed at one extremity and having a centrally located magnetic pole member extending from the closed extremity toward the opposite extremity, a pair or magnetic poles integral with said yoke and positioned near said opposite extremity being spaced at different distances from said closed extremity, first and second winding means electromagnetioally linking both of said spaced poles through said centrally located pole member, a third winding means eleotromagnetically linking only one of said spaced poles on said yoke located the furthest distance from said closed extremity, means energizing said first winding means to provide a reference magnetomotive force between said poles and said centrally located pole member, means energizing said second and third winding means simultaneously and variably, and a segment of magnetic material positioned between said poles and said centrally located pole member and adapted to be motivated by said magnetomotive force supplied by all of said winding means.

7. In an electromagnetic transducer, acylindrical magnetic yoke closed at one extremity and having a centrally located magnetic pole member extending from the closed extremity toward the opposite extremity, a pair of magnetic poles integral with said yoke and positioned near said opposite extremity being spaced at different distances from said closed extremity, first and second Winding means electromagnetically linking both of said spaced poles through said centrally located pole member, a third winding means electromagnetically linking only one of said spaced poles on said yoke located the furthest distance from said closed extremity, means energizing said first winding means to provide a reference magnetomotive force between said poles and said centrally located pole member, means energizing said second and third winding means simultaneously and variably, and an annular shaped magnetic member positioned between said poles and said centrally located pole member and adapted to move relative thereto in response to the energization of all of said winding means.

8. In an electromagnetic transducer, a cylindrical magnetic yoke closed at one extremity and having a centrally located magnetic pole member extending firom the closed extremity toward the opposite extremity, a pair of magnetic poles integral with said yoke and positioned near said opposite extremity being spaced at diflerent distances from said closed extremity, first and second means electromagneti-cally linking both of said spaced poles through said centrally located pole member, a third winding means electromagnetically linking only one of said spaced poles on said yoke located the furthest distance from said closed extremity, means energizing said first winding means to provide a reference magnetomotive' force between said poles and said centrally located pole member, means energizing said second and third winding means simultaneously and variably, and an annular shaped magnetic member positioned between said poles and said centrally located pole member and adapted to move relative thereto in response to the energization of all of said' winding means, said annular shaped member having a length equal to the distance between centers of said pair of spaced magnetic poles.

References Cited in the file of this patent UNITED STATES PATENTS 1,931,701 Pvasooe Oct. 24, 1933

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