US2838698A

US2838698A - Tuning fork assembly

Info

Publication number: US2838698A
Application number: US526894A
Authority: US
Inventors: Jr William J Holt
Original assignee: VARO Manufacturing CO Inc
Current assignee: VARO Manufacturing Co Inc
Priority date: 1955-08-08
Filing date: 1955-08-08
Publication date: 1958-06-10
Anticipated expiration: 1975-06-10

Description

June 10, 1958 w. J. HOL-r, JR

TUNING FORK ASSEMBLY Filed Aug. 8, 1955 INVENTOR William J. Holi, Jr.

United States Patent() TUNING FORK ASSEMBLY William J. Holt, Jr., Garland, Tex., assignor to Varo Mfg. Co., Inc.

Application August 8, 1955, Serial No. 526,894

Claims. (Cl. 310--25) My invention relates to the construction and arrangement of tuning fork assemblies, and more particularly to tuning fork assemblies of the type designed to function as elements of constant frequency electronic oscillators.

An important problem in the construction of tuning fork assemblies has always been that of dealing with the adverse eiects of external vibrations. In many instances in the prior art of which l am aware, substantial sacrilices have been made in the Q of tuning fork assemblies in order to circumvent theV problems of external vibrations. It has been known that solid base type forks have a high Q, if they are dynamically balanced. However the dynamic balancing has in itself presented serious problems. In addition to the problems above-mentioned, there have been increasing demands for tuning fork assemblies that are more rugged, more dependable, smaller in size, and susceptible to more economical manufacture.

It is accordingly an object of my invention to provide an improved tuning fork assembly which shall obviate the above-mentioned problems.

It is another object of my invention to provide a tuning fork assembly having high Q, and which is insensitive to effects of external vibrations.

It is another object of my invention to provide a tuning fork assembly utilizing a solid base type fork in an arrangement which allows convenient dynamic balancing of the fork.

' It is another lobject of my invention to provide a tuning fork assembly which is smaller in size and more economical to manufacture than those heretofore available.

yThese and other objects are effected by my invention, as will be apparent from the following description, taken in accordance with the accompanying drawings, in which:

Figure l is an elevational view of a completed tuning fork assembly;

Figure 2 is a center longitudinal section View of the tuning fork assembly; and

Figure 3 is an exploded view showing all of the parts of a complete tuning fork assembly.

Referring now to the drawings and particularly to Figure 3, it will be seen that the tuning fork assembly comprises a base plug 11, a resilient ring 13, a fork 15, a driving coil 17 and a pick-up coil 19, a two-piece fork and coil housing including identical matching left hand and

right hand parts

21, 23, housing bolts 25 and nuts 27, a three-piece assembly envelope including a cap 29, and identical matching left hand and right hand skirts 31, 33.

The fork is of the solid base type made from a metal bar of rectangular cross-section. A deep U-shaped slot is formed in the bar so that the metal remaining at the slot sides constitutes the

fork tines

35, 37. The fork 15, has a pair of longitudinally aligned mounting holes 39, in its base portion.

The matching fork and

coil housing pieces

21, 23, are made of molded non-conducting material. The lower outside surface 41 of each housing piece is cylindrical. The inner faces of the housing pieces are complementary, with the upper face portion in each case presenting a plane surface 43 and the lower portion having a projection 45 at one side comprising a rst plane surface sloping having a single winding thereon.

ICS

downwardly and outwardly from the upper portion and a second plane surface extending downwardly and parallel to the upper portion. The other side of the lower portion of the housing inner face has a rst plane surface extending downwardly and inwardly from the upper portion, and a second plane surface extending downwardly from the rst and parallel to the upper portion. A deep U-shaped groove 47 is formed in the lower inside'surface of each housing piece. Thisgroove is centered on the longitudinal axis of the respective housing piece and extends to approximately the middle of the housing length. The depth of the groove on the projection side is substantially equal to the width of the fork base, while the width of the groove is substantially equal to the fork width. Each housing piece projection 45 carries a pair of `transversely extending longitudinal bolt holes 49 which are located to register with the bolt holes 39 in the fork base when assembled. The projection on each housing piece has a recessed portion 51 on its outer surface for receiving the bolt heads and nuts. The upper portion of each housing piece has a plane outer face 53 parallel to the inner face. Each housing piece has an additional surface 55 sloping downwardly and outwardly from the lower portion of the outer plane face 53. The last mentioned surface 55 intersects the upper portion of the housing piece groove 47 so as to provide a passage for the respective fork tine from the groove to the housing outside upon assembly. The outer surface 57 of the upper portion of each housing piece between the upper inner and

outer faces

43, 53 has an inverted U-shaped contour. The thickness of the housing upper portion between the inner and outer upper faces is slightly less than one half the distance between the fork tines for a reason to be hereinafter explained. The upper portion of the inner face of each housing piece has a pair of

cylindrical wells

59, 61 formed therein. The wells are centered on the housing piece longitudinal axis, and have a diameter substantially equal to the coil diameter and a depth substantially equal to one half the coil width.

There is a transversely extending hole 63 through the housing piece at the center of each well having a diameter substantially equal to the coil core diameter. Each

housing piece

21, 23 has a pair of small holes 65 communicating between the inner and outer upper faces of the piece for a purpose to be hereinafter explained. Each housing piece has a pair of oppositely disposed inwardly extending dimples 67-69 at the marginal edges of their outer surfaces. These dimples are located longitudinally of the housings at a point corresponding to the center of gravity of the fork, housing, and coil assembly for a purpose to be hereinafter explained. Each

housing piece

21, 23 has a small groove 71 in its inner face which communicates with both coil wells and provides a channel for the coil leads 73 from the coils out through the bottom of the housing pieces, and also a passage for filler material.v

The drive coil 17 and pick-up coil 19, which are identical, are in the form of short cylindrical bobbins, each The

coil cores

75, 77 are cylindrical pins of magnetic material which extend through registering holes 63 in the housing wells, 59, 61.

The envelope skirts 31, 33 are identical halves of a thin metal cylinder each having an inwardly extending dimple '7 9 in its upper portion.

The resilient ring 13 is simply a heavy rubber band designed to t closely over the cylindrical end of the coil and fork housing upon assembly. The base plug 11 is a metal ring 81 having a disc 83 of non-conducting ,marte-V rial fixed to its inner periphery with plug pins S5 xed to the disc. The base plug outer diameter is such that the plug will t snugly inside the lower end portion of the envelope skirts upon assembly. The cap 29 isV a es hollow thin metal cylinder with one end rounded and closed.

To assemble the device, the pick-up coil 19 is placed in the upper well 59 of one housing piece 23, while the drive coil'l is placed in the lower well 6l of the other housing piece 2l and the coil leads 73 are laid in their respective housing channels 7l to extend from the bottom thereof. The

housing pieces

21, 23 are then tted together and the

coil core pins

75, 77 inserted. Next, the fork is inserted so that its

tines

35, 37 extend up through the appropriate housing openings with the inner faces of the tines closely adjacent the respectiveouter plane faces 53 of the housing pieces. The bolts Z5 are then passed through the registered holes 49 in the housing piece projections 45 and the fork base and secured by the nuts 27.

Next, impregnating material is injected through the small holes 65 in the housing piece upper portions until the coil' and fork housing is completely filled. The impregnating material hardens so that the coils, their cores, the fork base andthe bolts and nuts arc all held rigid, and the entire assembly is completely sealed. Next, the resilient ring 13 is slipped on the cylindrical portion of the housing and centered onV the housing dimples 67, 69. Next, the envelope skirts 3l, 33 are assembled on the housing with their inwardly extending dimples 79 centered on the resilient ring 13 and registered with corresponding dimples 67, 69 on the housing. Then the cap 29 is placed over the upper end of the housing andV down over the skirts 31, 33, making a tight friction t over the skirtsV and clamping them together in matched relation. Then the coil leads 73 are connected to appropriateV base plug pins S5, and the base plug 11 is inserte inside the bottom portion of the skirts 3l, 33, making a snug t therewith. The assembly is completed by solderingthe base plug ring 8l to the envelope skirts.

It is evident that the arrangement and construction of the tuning fork assembly of my invention provides a large measure of compactness and ruggedness. In addition, the' coilV and fork housing assembly is shockmounted at' its center of gravity by means of the dimples on the housing Vand the envelope skirts, in co-operation with the resilient ring. This means that external vibrations have minimum effect on the fork. Furthermore, the rco-axial construction of the device with the coils between the fork tines not only lends itself to small size and compactness, but also balances out the effects of external vibrations. Thus, if one fork tine is caused by an external shock to vibrate further away from one side of the coils than normal, the other fork tine will at the same time vibrate closer to the other side of the coils than normal by a like amount, thereby balancing out the adverse eect. Another important attribute of the arrangement and construction of my invention is that it permits precise and convenient dynamic balancing of the fork under actual operating conditions with the fork and coils and their housing completely assembled and sealed in final form. This is true because the fork tines are exposed in the final assembly so that test equipment can be readily applied and the metal necessary for precise dynamic balance can be readily removed from the fork tines. A further advantage of my construction and arrangement is that it lends itself to more economical manufacture. it has been found in actual practice that assemblies embodying my invention can be manufactured forjas Ylittle as one half the cost per unit of assemblies heretofore manufactured. A

While I have shown my invention in only one form, it will be apparent to those skilled in the art that it is not soY limited, but is susceptible of vario1 s changes and modifications without departing from the spirit thereof.

I claim:V

l. A tuning fork assembly comprising, a soiid base type'tuning fork having tines, a drive coil, a pick-up coil,'a housing presenting a cylindrical outer surface at ,4 itslower portion tapering rto spaced parallel plane outer surfaces at its upper portion, a cavity in the lower inside portion of said housing for receiving the base of said fork with the fork tines extending exteriorly of the housing with their inner faces parallel to and closely adjacent said spaced parallel housing outer surfaces, cavities in the upper portion of said housing centered on the housing longitudinal axis for receiving said coils, means for rigidly securing the base of said fork and said coils within said housing, and means for sealing the assembly.

2. A tuning fork assembly comprising, a solid base type tuning fork having tines, a drive coil, la pick-up coil, a housing presenting a cylindrical outer surface at its lower portion tapering to spaced parallel plane outer surfaces at its upper portion, a cavity in the lower inside portion of said housing for receiving the base ot' said fork with the fork tines extending exteriorly of the housing with their inner faces parallel to and closely adjacent said spaced parallel housing outer surfaces, cavities in the upper portion of said housing and centered on the housing longitudinal axis for receiving said coils, means for rigidly securing the base of said fork and said coils within said housing, and means for shock mounting the assembly at its center of gravity. Y

3. A tuning fork assembly comprising a solid base type tuning fork having tines, a drive coil, a pick-up coil, a housing presenting a cylindrical outer surface at its'lower portion tapering to spaced parallel plane outer surfaces at its upper portion, a cavity in the lower inside portion of said housing for receiving the base of said fork with the fork tines extending exteriorly of the housing with their inner faces parallel to and closely adjacent said spaced parallel housing outer surfacesLcavities in the upper portion of said housing and centered on the housing longitudinalV axis for receiving said coils, means for rigidly securing the base of said fork and said coils within said housing, inwardly extending dimples disposed on opposite sides of said housing outer surface at the assembly center of gravity, a resilient ring girding said housing and centered over the housing dimples, a three piece envelope comprising a pair of identical semi-cylindrical metal skirts each having all inwardly extending dimple centered at its upper portion, a cylindrical cap closed at one end, said skirts being assembled on said i housing cylindrical portion and extending downwardly therefrom with the dimples registered over respective housing dimples, the cap covering the upper portion of saidhousing and making a friction tit over the upper portions of said skirts, a base plug making a frictioniit inside the lower portions of said skirts andhaving plug piece, and electrical connection between said coils and said pins.

4. A housing for a tuning fork assembly, said housing comprising a pair of substantially identical matching pieces, each piece having a cylindrical outer surface at its lower portion tapering to a plane surface atits upper portion,1a plane surface at the piece inner face with an outwardly extending projection a-t one side of the lower portion and an inwardly extending recess at the other side, a deep U-shapedV groove centered on the inner face and extending upwardly between said projection and recess to intersect the tapered portion of ythe housing piece outer surface forming an opening through the housing, a cavity inV said lower portion of said housing piece inner face and centered' on its longitudinal axis for receiving tuning fork base, a pair of transversely extending cylindrical openings being ywe'lls'in said housing piece for receiving coil cores, a groove in said housing piece inner face communicating between said wells and the lower end of said 'housing piece, and means forV holding said housing pieces in matched rigid relation. Y

5. A tuning fork assembly comprising a tuning fork having a base and tines, a drivecoil, 'a pickup coil and a housing, said housing havingV upper and lower portions, said upper' portion adapted'to hold' said coils firmly between said tuning fork tines so that the said tines extend exteriorly of said upper portion of said housing and said lower portion adapted to hold the said tuning fork base tirmly in said lower portion of the housing.

6. A tuning fork assembly comprising a tuning fork having a base and tines, a drive coil, a pick up coil and a housing, said housing having upper and lower portions, said upper portion adapted to hold said coils firmly between said tuning forli ltines so that the said tines extend exteriorly of said upper portion of said housing and said lower portion adapted to hold the said tuning fori; base rmly in said lower portion of the housing, said housing being comprised of a pair of matched housing pieces which join together to make a unitary housing.

7. A tuning fork assembly comprising a tuning fork having a base and tines, a drive coil, a pick up coil and a housing, said housing having upper and lower portions, said upper portion adapted to hold said coils tirmly oetween said tuning fork tines so that the said tines extend exteriorly of said upper portion of said housing and said lower portion adapted to hold the said tuning fork base rmly in said lower portion of the housing, said houdq ing being comprised of a pair of matched housing pieces which join together to make a unitary housing and means for shock mounting the assembly to minimize external shock vibrations.

8. A tuning fork assembly comprising a tuning fori; having a base and tines, a drive coil, a pick up coil and a housing, said housing having upper and lower portions, said upper portion adapted to hold said coils firmly between said tuning fork tines so that the said tines extend exteriorly of said upper portion of said housing and said lower portion adapted to hold the said tuning fork base tirrnly in said lower portion of the housing and means for shock mounting the assembly to minimize external shock vibrations.

9. A tuning fork assembly comprising a tuning fori; having a base and tines, a drive coil, a pick up coil and a housing, said housing having upper and lower portions, said upper portion adapted to hold said coils iirrnly between said tuning fork tines so that the said tines extend exteriorly of said upper portion of said housing and said lower portion adapted to hold the said tuning fork base lirmly in said lower portion of the housing, an enclosure for said tuning fork assembly and means to shock mount said tuning fork assembly in said enclosure.

10. A tuning forli assembly comprising, a tuning fork having a base and tines, a drive coil, a pick up coil, a housing presenting a cylindrical outer surface at its lower portion tapering to spaced parallel plane outer surfaces at its upper portion, a cavity in the lower inside portion of said housing for receiving the base of said fork with the fork tines extending exteriorly of the housing with their inner faces parallel to and closely adjacent said spaced parallel housing outer surfaces, said upper portion having a cavity for receiving said coils, means for rigidly securing the base of said fork and said coils within said housing, and means for sealing the assembly.

11. A tuning fork assembly comprising, a tuning forli having a base and tines, a drive coil, a pick up coil, a housing presenting a cylindrical outer surface at its lower portion tapering to spaced parallel plane outer surfaces at its upper portion, a cavity in the lower inside portion of said housing for receiving the base of said fork with the fork tines extending exteriorly of the housing with their inner faces parallel to and closely adjacent said spaced parallel housing outer surfaces, the upper portion 0f said housing having a cavity for receiving said coils, means for rigidly securing the base `of said fork and said coils within said housing, and means for shock mounting the assembly.

12. A tuning for assembly comprising tuning fork having a base and tines, a drive coil, a pick up coil, a housing presenting a cylindrical outer surface at its lower portion tapering to spaced parallel plane outer surfaces at its upper portion, a cavity in the lower inside portion of said housing for receiving the base of said fork with tl e fork tines extending exteriorly of the housi' wit` their inne* races pt allel to and closely adjacent sp ed parallel housing outer surfaces, said upper portion of said housing having a cavity for receiving said coils, means for rigidly securing the base of said fori; and said coils within said housing, inwardly extending dimpies disposed on opposite sides of said housii 'f o ico at substantially the assembly center of g avity, a resilient ring girding said housing and centered over the housing dimples, a three piece envelope comprising a pair of identical semi-cylindrical metal skirts each having ail inwardly extending dimple centered at a cylindrical cap closed at one end, ts being assembled on said housing cylindrical portion and extending downwardly therefrom with the dimples reg, ered over 'respective housing dimples, the cap covering the upper portion of said housing and maliing a friction tit over the upper portions of said skirts, a base plug making a friction tit inside the lower portions of said skirts and having ping piece, and electrical connection between said coils and said pins.

13. A housing for a tuning assembly, said housin' compi ,ing a pair ot suo l ;ntiaily identical matching pieces, caca piece having a cylindricai outer surface at its tower portion tap ng to a plane surface at its upper portion, a pla surfae tl iecc inner tace with outwardiy extendin one side of the lower portion i ing recess at the other side, a deep U-so ntered on the inner face and extending u ,v between said projection and recess to intersect the tapered portion of the housing piece outer surface forming an opening through the housing, a cavity in said -wer 'ortion of said housing piece inner and centered on its longitudinal axis for recei g tuning fork base, a cavity in said upper portion cf housing piece for receiving coil cores, a groove in said housing piece inner face communicating between said upper portion cavity and the iower end cf said housing piece, and means for holding said housing pieces in matched rigid relation.

14. A tuning fori: assembly comprising a tuning fori housing, a tuning fork having a base and spaced legs extending therefrom, a pick up coil, a driving coil, said he* ing having an upper portion adapted to hold said coils between the legs of the tuning fork and a lower portion to hold the tuning fork base, a shock absorbing means positioned about said tuning fork housing and enclosure adapted to enclose said tuning forli housing and said shock absorbing means whereby the tuning forli housing and tuning fork are effectively protected from external shock vibrations to the enclosure.

l5. A tuning fork assembly comprising a tuning fork housing, a tuning fork having a base and extending tines, a pick up coil, a driving coil, said housing having an upper portion adapted to hold said coils between the tines of the tuning fork, a lower portion to hold the tuning forli hase and a plurality of indentations on the outer periphery of said housing, a shock absorbing means positioned about said tuning forli housing, a, plurality of A icing plates having protuberances adapted to provide a xed relationship of the said plates and fork housing by virtue of the said indentations and an en closure adapted to enclose said spacing plates and said tuning fori: housing whereby external shock vibrations to the enclosure are minimized in the tuning fork.

References tCited in the tile of this patent UNlTED STATES PATENTS