US2835832A - Vibration generating apparatus - Google Patents

Description

May 20, 1958 P. c. EFROMSON 2,835,832

7 VIBRATION GENERATING APPARATUS Filed May 3, 1954 2 Sheets-Sheet 1 IN V EN TOR. PH/L/P C. [FRO 1150A! HTTOR/VE Y5 y 1958 P. c. EFROMSON 2,835,832

VIBRATION GENERATING APPARATUS Filed May 3, 1954 2 Sheets-Sheet 2 IN V EN TOR PH/L/P 61 FF/P0446 014/ mmviaw United States Patent ()fiice VIBRATION GENERATING APPARATUS Philip C. Efrornson, Winchester, Mass., assignor, by inesne assignments, to The Calidyne Company, Ina, a corporation of Massachusetts Application May 3, 1954, Serial No. 427,131

13 Claims. (Cl. Mil-27) This invention relates to electromagnetic vibration generators such as are used in the vibration testing of mechanical and electrical devices and structures.

As manufactured, heretofore, such generators have comprised a core structure which is magnetized by means of a direct current winding so that a high flux concen- L.

tration exists across an air gap in the structure. An armature coil is located within the air gap and energized from an alternating power supply so that a reciprocating movement is imparted to the coil and attached armature assembly. suppored by elastic members or ilexures generally in the form of cantilever leaf springs which limit the axial movement of the armature assembly and maintain the armature coil centrally within the air gap. These supporting fiexures have their own natural periods and modes of vibration which cause unwanted movements in the armature assembly and increase materially the possibility of flexure breakage due to fatigue. While it is possible by proper design and operation of the generator to minimize the troubles caused by such inherent factors, the leaf fiexures also preclude the possibility of obtaining a true linear motion of the armature assembly and limit the allowable armature assembly axial motion to relatively short distances.

It is accordingly the principal objects of the present invention to provide vibration producing apparatus wherein the armature assembly is not restrained in an axial direction, in which the axial travel of the armature assembly is a substantially true linear movement, in which the supports for the armature assembly do not depend upon their elastic or resilient properties and are not subjected to fatigue failures, in which the armature assembly supports do not have troublesome periods and modes of vibration, and which advances the art generaily.

According to the present invention, apparatus for producing a reciprocating movement of relatively great amplitude comprises a core structure which is provided with a direct current winding for producing a unidirectional flux across an air gap in the structure. air gap is an alternating current coil carried by an armature to which a reciprocating movement is imparted. The armature is carried by rotatable supporting means such as rollers which constrain radial movement of the armature while permitting t'ree reciprocal movement in an axail direction. In one aspect the armature comprises a. central rod which extends through an aperture in the core structure and several equally spaced webs which extend radially between the rod and the armature coil. An attics. ated linkage is interposed between the armature and the core structure so that the armature cannot rotate to bring the webs into contact with the adjacent core structure. In another aspect the webs supporting the armature cell are located outside of the core structure so that the armature can be rotated with respect to the core.

ln such generators the armature assembly is Disposed in the Cir These and other objects and aspects will be apparent from the following description of several embodiments of the invention which refers to drawings wherein:

Fig. 1 is a sectional view of one embodiment of the invention;

Fig. 2 is a sectional view on lines 2-2 of Fig. 1;

Fig. 3 is a sectional view of a second embodiment of the invention; and

Fig. 4 is an enlarged fragmentary view of one of the electrical connections.

The vibration generating apparatus shown in Fig. 1 comprises a generally cylindrical core structure 10, one end of which is removable as a cover 12 to permit a direct current magnetizing winding 14 to be inserted in the cylindrical recess about the central pole piece 16. The cover 12 has a central aperture which is sufficiently greater in diameter than the pole piece 16 so that a cylindrical air gap is formed between the wall of the cove aperture and the periphery of the pole piece.

The 'moving armature comprises an alternating current coil 18 carried by three equally spaced webs 20 which extend radially outward from a rod 22, the webs being secured to the rod by bolts 24. The central portion. of each web is cut away to decrease the mass and inertia of the armature. The rod 22 passes through a central aperture in the core structure 10, and the pole piece 16 is provided with three radial slots, as is best shown, in Fig. 2, so that the armature is free to move in an axial direction without interfering with the core structure. The direct current winding 14 has a great enough internal diameter and is secured in the annular recess in the core structure 16 by spacers 26 so that the end of the armature coil 18, which extends inwardly through the air gap in the annular recess, passes inside of the coil.

To reduce the mass and inertia of the rod 22 to a minimum it is preferably made of a relatively light weight material such as aluminum or a suitable plastic. As such materials are relatively soft, two sleeves 28 and 30 of a hardened material such as steel, are pressed over the ends of the rod 22 to act as bearing surfaces for two sets of rollers 32 which maintain the rod and armature in a central position in the core structure. Each set consists of three rollers 32 equally spaced about the rod 22 intermediate the webs 20 of the armature. Each of the rollers 32 is journalled upon one end of a bell crank lever .34 which is pivotally mounted upon a strap 36 secured to the end of the core structure 10. The radial position of each roller is adjusted by means of a respective screw 38 which projects through the opposite end of the bell crank 34 to engage a threaded aperture in the strap 36. It will be apparent that with the armature supported by means of rollers 32 the length of the stroke which can be imparted to a table (not shown) or a structure under test secured directly to the threaded stud 40 in the end of the rod 22 is limited not by the deflection of the supporting means but by the length of the coil 18. Furthermore, as the support for the armature does not depend upon the elastic properties of the rollers 32 or their supporting bell cranks 34, the eilect of their periods of natural vibration upon the axial movement of the armature is minimized. A linkage 42 is provided to prevent the rotation of the armature about the axis of the rod 22 which would tend to bring the webs 20 into contact with the walls of the radial slots in the central pole piece 16 of the core structure 10. The linkage 42, which extends between the end of the armature rod 22 and the cover 12 of the core structure 10 in a plane passing through the axis of the rod 22, comprises a clevis member 44 that is attached to a boss on the cover 12 by means of a cap screw 46. The bi- Patented May 20, 1958.

assasaa furcatecl end of the clevis member 44 is pivotally connected to one end of a link 48 by a transverse pin 50. A similar pin 52 pivotally connects the other end of the link 48 in a clevis 54 at the lower end of a second link 56 whose upper end also carries a clevis 58 which pivotally connects to an extension member 60 bolted on the end of the rod.

Alternating electrical power is brought to the armature coil 18 by means of electrical brushes 62 and 64 which slidingly engage the hardened sleeves 28 and 30. The brushes 62 and 64 are connected to an external alter-nating power supply (not shown) by the conductors 66 and 68 and the sleeves 28 and 30 are linked with the ends of the armature coil 18 by conductors (not shown) carried along the rod 22. Alternatively, two electrical conductors can be secured.- to the various links of the above described linkage 42 with a bight at each of the pivotal connections so that the brushes are eliminated.

A second embodiment of the invention in which the armature is free to rotate is shown in Fig. 3. In the second embodiment the core structure 80, cover plate 82 and direct'current magnetizing winding 84 are generally similar to those described above with respect to the first embodiment. The armature rod 86, which in the second embodiment is hollow to reduce its weight, likewise extends through an axial aperture in the central pole piece 38 of the core structure 80. The opposite faces of the core structure are counterbored adjacent the axial aperture to receive the blocks to which the two sets of armature rod supporting rollers 92 are rotatably secured. Although only one roller 92 of each set is shown in Fig. 3, it is to be understood that each set includes those rollers which are equally spaced about the rod 86 so that the rod is restrained radially.

At one end or" the rod 86 is carried a coupling 94 with a threaded portion 96 to which a test table (not shown) or the structure to be tested are connected. The other end of the rod 86 has a bushing 98 pressed thereupon from which project four equally spaced webs 100 to form a spider. Upon the outer ends of the webs 100 is carried a metal ring 102 which is stepped so that an insulating ring 104 of a suitable plastic can be pressed thereupon. The insulating ring 104 is the end ring of the armature coil 106 which is wound of a square conductor of sufiicient thickness and stiffness so that the turns are selfsupporting when suitably bonded with a conventional cement or varnish. The armature coil 106 is completed by a second insulating ring 108 at its opposite end. The

inner diameter of the armature turns is great enough so .1:

that the coil 106 passes over the central pole piece 88 and lies in the cylindrical air gap between the pole piece and the cover plate 82. As the webs 100 of the coil supporting spider are located without the core structure 80 and the cover plate 82, these do not interfere therewith and the armature assembly is free to rotate.

Although it is possible to bring the electrical connections for the armature coil 106 through brushes which engage sleeves upon the rod 86 as was shown in Fig. 1, the second embodiment employs an alternate construction. As is shown in Figs. 3 and 4, an insulating bushing 110 is pressed. into the end of the rod 86. Diametrically attached to the inner surface of the bushing 110 are the respective ends of two flexible strips of a resilient electrically conducting strip 112 of a material such as Phosphor bronze. Each of the strips 112 is bent inwardly back upon itself 180 degrees on a relatively large radius so that its ends are in parallel relationship. The innermost ends vare secured to a spacing member such as the insulating rod 114 which is axially disposed with respect to the hollow armature rod 86. The insulating rod 114 is jou-rnalled in an aperture in an insulated insert 116 which is centrallylocated man end bell 118 bolted to the cover plate 32. Carried upon the insulating rod 114 so as to rotate conjointly therewith are two disks 129 which are I located upon either side of the end bell insert 116. Each of the disks 120 carries a slip ring 122 which engages a corresponding slip ring 124.11POD the adjacent end face of the insert 116. One of the disks 120 is fixed with respect to the insulating rod 114 and the other is free to more axially along the rod (although rotating conjointly therewith) so that a spring 126 interposed between the outermost disk and a nut 128 on the end of the rod causes the rotating slip rings 122 forcibly to contact the stationary slip rings 124.

The rotating slip rings 122 are connected respectively by conductors 130 with the ends of the flexible strips 112 attached to the insulating rod 114. The ends of the flexible strips 112 attached to the bushing are connected with the ends of the armature coil 106 by leads (not shown). The stationary slip rings 124 are connected with an external alternating power supply (not shown) by conductors 132 so that a circuit to the armature coil .106.

is completed which includes the conductors 132, the stationary slip rings 124, the rotatable slip rings 122, the conductors 130, the flexible strips 112 and leads (not shown) to the ends of the coil 106.

The insulating rod 114 is held in an axial direction by the end bell 118, and the axial movement of the armature relative thereto is pemitted by the bending of the flexible strips 112, the particular portion in which the Light is formed varying as the armature moves. Rotation of the armature is also permitted as the flexible strips 117,, the insulating rod 114, the disks 120 and slip rings 1 2 rotate conjointly therewith.

it should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

I claim:

1. In apparatus of the type wherein a reciprocating axial motion is imparted to an armature assembly carrying an electrical coil, conducting means for connecting the coil with an alternating current power supply, said means including two spaced flexible ribbons of a resilient electrically conducting material, each ribbon being bent back upon itself at a position intermediate its ends so that the ends thereof lie in spaced parallel relationship, one end of each ribbon being attached to the armature assembly and electrically connected with the coil, the other end of each ribbon having means for electrically connecting the ribbon with the power supply, and a spacing member having planar portions for engaging the other ends of the ribbons to act as a support therefor which member is relatively stationary with respect to axial movements of the armature assembly so that, as the assembly is moved axially, the bend in the ribbon progressively takes place at successive intermediate positions of the ribbon.

2. Connecting means according to claim l wherein the spacing member is rotatable about the axis of the armature assembly so that the armature assembly, flexible ribbons and the spacing member can turn as a unit about the axis of the armature.

3. Connecting means according to claim 2 wherein the spacing member is provided with two slip rings which cooperate with stationary slip rings to complete the connection of the coil to the power supply.

4. Apparatus for producing a reciprocating movement of relatively great amplitude comprising a hollow cylindrical core structure having a central pole piece one end of which is separated from the remainder of the core structure by an air gap, the pole piece having an axially disposed aperture therethrough and a plurality of radial slots extending between the air gap and the aperture; a direct current winding for magnetizing the core structure to produce a unidirectional magnetic flux across the air gap; an armature having a central rod extending through the aperture in the core piece, an alternating current coil positioned in the air gap and a plurality of webs located respectively in the slots in the core piece and interconnecting the rod and the alternating current coil; and rotatable supporting means for constraining radial move ment of the armature while permitting free reciprocal movement in an axial direction.

5. Apparatus according to claim 4 wherein the air gap is defined by the wall of one end or the core piece and the contiguous wall of the portion of the core structure which forms one of the ends of the structure, the inner diameter of the armature coil being greater than the diameter of the core piece so that the coil passes over the end of the core piece into the cavity within the core structure during the axial movement of the armature.

6. Apparatus according to claim 5 wherein the axial length of the armature coil is several times that of the air gap.

7. Apparatus according to claim 4 wherein a linkage is interposed between the armature and the core structure to prevent rotation of the armature while permitting free reciprocal movement in an axial direction.

8. Apparatus according to claim 7 wherein the linkage comprises two links lying in a plane passing through the axis of the rod, one end of one of the links being pivotally connected to the rod, one end of the other link being pivotally connected to the core structure, the other ends of the links being pivotally interconnected, and the axes of rotation of the pivots being disposed normally to said plane.

9. In apparatus of the type wherein an armature assembly carrying an electrical coil axially moves with respect to a relatively stationary core structure, conducting means for supplying electrical energy to the coil, said means including one or more flexible ribbons of a resilient electrically conducting material, each ribbon being bent back upon itself in a single 180 degree bight intermediate its ends, the ribbon ends being disposed in spaced relationship parallel to the axis along which the armature assembly moves, one end of the ribbon being attached to the armature assembly and electrically connected with one end of the coil, the other end of the ribbon having means for connecting the ribbon with an external power supply to impress an energizing potential upon the coil, said other end being attached to the core structure so that as the armature assembly is moved axially, the bight in the ribbon progressively takes place at successive locations along the ribbon intermediate the ends thereof.

10. In apparatus of the type wherein an armature assembly carrying an electrical coil has a substantially translational movement with respect to a relatively stationary structure, conducting means for interconnecting the terminal ends of the coil with an external power supply, said means including two flexible ribbons of a resilient electrically conducting material, each ribbon being bent back upon itself in a single degree bi-ght intermediate its ends, the ends being disposed in spaced planes parallel to the axis along which the armature assembly moves, one end of each of the ribbons being attached to the armature assembly and the other ends thereof being secured to the stationary structure so that during movement of the armature assembly, the bights in the respective ribbons progressively take place at successive locations along the ribbons intermediate the ends thereof.

ll. in apparatus according to claim 10 wherein the corresponding ends of the ribbons are parallel to and equally spaced from the axis along which the armature assembly moves.

12. In apparatus according to claim 10 wherein insulating members are interposed between the ends of the ribbons and the armature assembly and stationary structure respectively, electrically to isolate the ribbons therefrom.

13. Apparatus for producing a reciprocating movement of relatively great amplitude comprising a core structure including a pole piece Whose periphery forms one face of a cylindrical air gap, a. field winding encircling the pole piece for establishing a unidirectional magnetic llux across the air gap, said pole piece having a central aperture extending therethrough and a plurality of equally spaced slotted recesses in one end thereof which project radially outwardly from the central aperture, an armature assembly including an axially disposed rod which passes through the aperture in the pole piece, a plurality of webs extending radially outwardly from the rod so as to be located in said slotted recesses and an alternating current coil positioned in the air gap by the webs, supporting means for the armature assembly including two sets of rotatable members located respectively at the opposite ends of the core structure, each set including at least three rotatable members equally spaced circumferentially to engage the rod, and a mechanical linkage extending between the core structure and one end of the rod to restrain the armature assembly from rotating relatively to the core structure, said linkage having at least one pivotal joint whose axis is normal to the axis of the armature rod so that the linkage does not interfere With the reciprocating movement of the armature assembly.

References Cited in the file of this patent UNITED STATES PATENTS 839,713 Bijur Dec. 25, 1906 1,333,298 Evershed Mar. 9, 1920 1,808,149 Smith June 2, 1931 1,925,659 Giles Sept. 5, 1933 2,118,862 Rayrnent May 31, 1938 2,286,897 Costa June 16, 1942 FOREIGN PATENTS 903,046 France Jan. 5, 1945

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