US1792497A

US1792497A - Vibration-damping device

Info

Publication number: US1792497A
Application number: US191527A
Authority: US
Inventors: Arthur C Keller; Edward L Norton
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1927-05-14
Filing date: 1927-05-14
Publication date: 1931-02-17
Anticipated expiration: 1948-02-17
Also published as: NL30962C; FR651221A; DE559010C; GB290558A

Description

Feb. 17, 1931. A. c. KELLER ET AL VIBRATION DAMPING DEVICE Filed May 14, 1927 WW ATTORNEY mat-En; STATES a modified unit of this invention. y 1 Referring particularly to Figs. 1 t o 4; there isshown an electromagnetic phonograph" recorder or reproducer having an electromag-Q Patented Feb. 17, 1931 menu 'c'. KELLERAim EDWARD. 1;. woman; or Yo'xm, N." in, nssreivons 'ro narrow or may; rom:

vrsmmonnmrme ap licat on Med May 14.,

-"'This.invention relates to--.damping devices and more particularly to-a device for damping mechanical vibrations, such for example as occur in electro-mechanical translating devices adapted to respond toall frequencies within theaudible range. v e

The object of. the invention is to provide a unitary damping means having a substantially straight line-response characteristic over a wide band of frequencies regardless of normal temperature changes.

invention, there is provided a structure comprising two relatively movable flat parallel surfaces-located in a chamber, filled or'substantially filled with a viscous material which is displaced laterallyofi the flat surfaces in response to reciprocal movement between them.

The viscous material is one which iscomchanges and the other materials o fthe .unit

broken away ofan electromagnet system with the device of this invention applied thereto;

Fig. 2 is a viewin front elevation. of, the parts shown in Fig. ,1;- l Fig. 3. is sectionalview of the parts'illustrated.in*Fig..2;

with the-various elements shown in perspectivegand Fig.5 1s a detailed cross-sectional view of net 10 energized by a winding 11. Secured to thev magnet are pole pieces .12 between which'is mounted an armature 13. The armature is provided with a notch and is pivoted on a lmife edge '1 being-held in place by a. spring 15. 1 Attached tothe armature is a" stylus holder A; pair of windings 17ers] 1927. Serial No. 191,517..

( BELT; TELEPHONE mom'romns, 'IN'COBBORAIEEWF-NEW Yemen. 1;, A sonromounted coaxially'with the armature and arranged to be connected to a suitable electrical ,circuitby means of the leads 18. The downward 'prdj'eetin 'endof the St 1115 holder '16 isprovidedwit a socket in'w 'chf'ismouhtthis'i'n-Yentio'n y means f the shortmet'allie flr'Ql;

; [The damping device comprises a cylindrt In accordance with the features ofthis v I to 'the magnet 10'. In the center of the chaincal chambe'r 22 rig'idly mounted with respect her there is mounted'a"post"member 23,"the face of which is in-close space relation to the flexible metallic", diaphragm 24. This diaphragm closes the opening of the chamber and is -rigid'ly" attached to the =bar=2lv so that itismoved by vi'brations of the armature l3 and {stylus bar 16." 'A's shown in-Fig. 4, washparatively insensitive te normal temperature ed aphonograiph'styliis 19 which engages the record 20. The o'ppositeiend ofthe' stylus {bar isconnected jtothdamping device of

ers

25', 26 and 27 anda clamping'r1ng28 are "provided so thatthe' diaphragm 24 maybe mounted in the chamber opening in suchla way as to :com letely seal the chamber; Before the chain er isclosed it is filled with a viscous liquid 29, preferably a mixture of about 75% polymerized castor-oil and 25% nitro-benzol, which has a viscosity of the order of 2 vdyne-seconds per square centimeter.

The vibrationlof the diaphragm displaces the oil from betweenit and the postmember'23.

The result is that the diaphragm has a mechanical impedance .to'motion which is substantially constantf and a substantially pure H resistance over a'wide range of frequencies. Fig. 4 is an exploded view of -the device ,In order 'to'icom ensate for changes in the viscosity o'fthe oil produced by changes in 22 is. constructed'of, a material with a 'comparati vely ow "linear expansion coefiicient and therlength of 'the'post' is made such that the cha ngesin thelength of the gap with tem peratjure. will be such as to compensate with the1correspondingfchanges in the viscosity Yoffloil, j e

F'gfashows a modification of the damping unitinfwhiclra metallic plate 30 is mountedon the i'n'ne'rf surface of the diaphragm so,

that the surfaces formin the gap will always be in substantial paralle relation. For most purposes the arrangement shown in the other gures is satisfactory as the variation from a parallel relation will not be sufiicient to materially affect the mechanical impedance characteristic.

In many systems the values of the mass and stiffness are known and from the required degree of dam ing the value of resistance reu1red can be etermined. It has been found t at the mechanical resistance which will be added by the use of the unit of this invention is given by the expression:

Ba A R 2d E being the bulk modulus of the viscous material and {)being the frequency which in the case of a and of frequencies is the upper limitin frequency. For values of d be ow this va ue a stifiness reaction will be introduced. 7

Also if the length of the gap is greater than that given by the expression I m I d f!- p being the density of the viscosity material the mass reactance is at the resistance.

What is claimed is: 1. In an electro-mechanical translating device responsive to all. frequencies within the audible range, a vibration damping means comprising a container, viscous matter in said container, and a vpair of spaced relatively movable members in said container adapted in their movement to move the viscous matter laterally between their faces, the container and one of the members being made of materials having such different jcoeilicients of expansion as to compensate for changes in viscosity of the matter in the container.

- 2. In an electro-mechanical translating device responsive to all frequencies within the audible range, a vibration damping means comprising a container for viscous matter viscous matter in the container, and a pair of relatively movable flat-faced members of least comparable to approximately equal areas mounted in spaced relation in said container, the viscous matter filling the chamber to an extent to cover the opposed faces but with sufficient clearance to provide free lateral movement of the viscous matter between the opposing faces.

3. In an electro-mechanical translating device responsive to all frequencies within the audible range, a vibration damping means comprisin a container, a vibrating diaphragm orming a closure for said container, a fiat-faced member carried by the diaphragm, a stationary member in said container having a flat face comparable in area to the area of the first mentioned flat-faced member and located in opposed spaced relation thereto, and viscous matter in the casing adapted for free lateral movement across the adjacent fiat faces in response to movement of the vibrating member to control the character of the vibrating movement.

4:. In an electro-mechanical translating device responsive to all frequencies within the audible range, a vibration dampin means comprising a container, a flat-faced vibrating member in one end of the container, a stationary member in the container having a flat face comparable in area to the area of the vibrating member and located in opposed spaced relation to the vibrating member, and viscous matter in the container filling said container to an extent to cover the opposed faces but with sufiicient clearance to permit free lateral movement of the viscous matter between said faces,

vice responsive to all freqeuncies within the audible ran e, a vibration damping means having a su stantially constant mechanical impedance and a pure resistance over a wide range of frequencies and comprising a container opposing relatively reciprocal fiatfaced members in thecontainer, and viscous matter in the container moved laterally of the flat-faced members in their relative movement to produce the desired impedance and resistance in the movable parts.

6. In an electro-mechan1cal translating device responsive to all frequencies within the audible range, a vibration damping means comprising a container, a pair of opposing relative movable flat-faced members in the container, and viscous matter in the container moved laterally between the flat-faced members in their relative movement, the area and separation of the flat-faced members being predetermined and so related to a chosen viscosity of the matter that the movable part has a substantially pure resistance over a range corresponding to useful sound vibrations.

7 In an electro-mechanical translating device responsive to all frequencies within the audible range, a vibration damping means comprising a container, a pair of opposing 5. In an electro-mechanical translating demembers by the reciprocation of one member to produce a resistance equal to Where a is the radius and A the area of the fiat-faced members, (1 the separation of the surfaces and the viscosity of the viscous matter.

9. In an electro-mechanical translating device responsive to all frequencies Within the audible range, a vibrational damping means comprisin a container of material having a relatively low linear expansion coefiicient, a flexible diaphragm closing one end of the container, a post in the container having one end in close spaced relation to the diaphragm and having a relatively high linear expansion coefficient, and viscous material in said con-- tainer moved laterally between the adjacent faces of the diaphragm and post in the move ment of the diaphragm.

In witness whereof, we hereunto subscribe our names this 12th day of May, A. D., 1927.

ARTHUR G. KELLER. EDWARD L. NORTON.