US2476684A - Phonographic transducer - Google Patents

Description

July 19, 1949. w. K. RIE BER PHONOGRAPHIC TRANSDUCER Filed Oct. 12, 1945 INVENTOR. KM

Patented July 19, 1949 UNITED I STATES PATENT OFFICE PHONOGRAFHIC TRANSDUCER William K. Richer, Los, Angeles, Calif. Application October 12, 1945, Serial No. 622,061 13 Claims. (01479-10031) My invention relates generally to the translating means for converting mechanical vibration into pulsating or alternating electric current or the reverse of this, converting pulsating or alternating current into mechanical vibration.

My invention relates more particularly to such translating devices used in phonographic recording and transcribing equipment of the engraving, or embossing class wherein an undulating groove is embossed or engraved in a moving record medium. I

Several such translating means, which are reversible, are known in the art. Among such reversible means are the variable reluctance magitietic system and the piezo-electric crystal sys- In the present embodiment, my invention is shown employed in an electro-magnetic phonographic tone head which is adapted for use either asa sound recording head or a sound pick-up head.

For an understanding of my invention, it is well to consider now the factors and characteristics which should be variable in such a device in order to adapt it for either of the two above mentioned purposes. In this discussion, the following terms will hereafter be used to define the tone head and its functions: When used as a transducer for translating mechanical motion into electrical energy, the device will be called a pick-up, and when used for the reverse'purpose it will be called a recording head two functions will be described as playing bac and recording" respectively and the apparatus employing the device will be referred to as a transcriber and recorder respectively.

Tone heads have been designed which are adaptable for use, both as pick-ups and recording heads, but in all such devices used'previously the value of variable factors therein represent compromises between the best value for recording and the best value for playing back. However, to secure optimum efliciency, it is desirable to change the value of at least some of such variable factors when changing the function of the device from that of recording to that of playing back. Among such variable factors in a tone The 2 1 4 the ability of the entire structure to ride the groove or tracki It is desirable that all, or at least several of the factors listed aboveybe automatically and simultaneouslychanged byv one simple adjust-v ment which thus converts the'device from the function of recording to the function of playing back or vice-versa.

- .I have found by experiment that the factors, which it. is most desired to change between functions are those of stylus pressure and stiffness and;

my invention deals therefore with-these two var-- iable factors. a

- It is one object of myinvention to provide a sound translating head which is adaptable for use as a transducer, either toconvert electrical pulsations into mechanicalyibrations, when used in a recorder, or to perform the reverse of this function when used in a transcriber, Y

It is another object of my invention to provide a sound head of the class describedin which the mechanical stiffness is dependent on the pressure which is applied to engage an engraving or embossing stylus with a record medium. These and other objects of my invention will appear in 80 rying armature moves in a magnetic field. Such motion of the armature results in electric cur rent flow in a pick-up coil or, conversely, current in the coil produces motion of the armature. In the illustrated embodiment, I prefer to use 85 a stretched ligament as a spring for constraining the motion of the armature. In order to change the mechanical stiffness of the system;

therefore, it is only necessary to increase the tension in the ligament. I provide a lever for this 40 purpose which is so mounted .in the tone head that when weight is added for the purpose of increasing stylus pressure such added Weight also results in increasing the ligament tension.

For a more detailed description of the tone head embodying my invention, reference should now be had to the attached drawings wherein:

Fig. 1 is an elevational sectional view taken on a vertical plane passed longitudinally through the center, of the tone head, with the parts in head of the variable reluctance magnetic type are playback position,

the following: (1) the strength of the permanent magnetic field, (2) the mechanical stiffness or spring factor of the moving armature, (3) the mechanical damping, (4) the pressure of the re- Fig. 2 is a partially sectioned the device shown in Fig. 1,

Fig. 3 is an elevational, partially sectioned view taken on the line 3-3 in Fig. 1 but with the parts cording stylus against the recording medium, (5) in recording position, and

plan view of 5 aeiaesi Fig. 4 is an isometric view of the armature portion of the device.

Referring now to the above drawings, a casting forms the frame 6 which supports the various members of an electromagnetic transducer. A stylus-carrying armature 1 constructed of ferromagnetic material is pivotally supported by the frame 6 in two jewel bearings 8 and 9, one of which 8 is held in an adjustment screw 10. A supportingpivot H is pressed into the annature which is thereby adapted for transverse swingin motion.

A jewel pointed embossing or engraving stylus I2 is supported in the lower end of therarmature and secured therein by a set screw 13. Projecting upwardly from the armature at pivot PI is a blade portion [4 of the armature whichiis substantially centrally located in a gap [5 between the upper arms of two U-shaped magnetic pole pieces I6 and I1, asibest seen in Fig. 3. The two lower :arm'sof "the magnetic polej-p'ieces HE and I! are brought into a pointadiacent'to fthe armature and near its1piVht H y Magnetic flux :is produced in ime system by means of a permanent magnet l8 mounted to the back of the frame .6, flux being carried :forward and into the pole pieces l5 :and flbyitwo flux conducting members l9 and 20. Themagnetization of the permanent magnetic is such was to produce a south pole-in the left hand 130 piece :and a north pole in the right h'and pole piece as best seen in Fig. 3 and indicated by the letters N and S.

It will now be seen that as long as the armature l, and hence the blade portion thereof, remains in a substantially vertical position, as shown in Fig. 3, the magneto-motive forces thereon are balanced and no flux ilows downwardly or upwardly "through the blade portion. However, when the stylus is engaged with a moving sound record-andcaused to vibrate laterally thereby, the blade portion 14 of the-armature-will ture blade 14 and hence an alternating passes therethrough. This -'alternating magnetic flux is converted into alternating electric cur rent by means of apick-up coil 2| mounted in the frame and between the arms of the U-shaped pole pieces and '50 positioned that the bladeportion 14 of the armature passes therethroug-h.

Electric leads 38 are broughtout from the coil 2i and may be connected to'the input of am amplifier for the function of playing back, or the output of an amp'lifierforthe function of recording. The method of making such connections is well known in the art and {need not be shown here.

The process of mechanical, electrical trans: duction performed in this manner is reversible since alternating current flowing in the coil 2| will produce alternating magnetic flux 'in the blade portion 14 of the armature, thus causing it to vibrate in the gap 15 and thereby producing lateral vlbrationof the stylus point [2.

in order to maintain the armature 1 .in a sub-,

stantially vertical position, a stretched ligament 22 is provided which serves as a centeringspring.

stretched rearwardly, passing through .a lon-- gitudinal hole 25 in thearmature "1, and also through a hole 26 in a downwardly projecting portion of the frame. The ligament 22 is secured at its rearward end by passing through two holes in the lower end of an L-shaped lever member 21 and being clamped thereto by a screw 28. The lower end of the lever 21 is bent into a U shape and a screw 29 is provided for closing this U, thereby to adjust the initial tension of the ligament 22.

The L-shaped lever 21 is fulcrumedon a blade 30 which in turn is secured to the main frame 6. The top arm of the lever 21 extends forwardly above the main frame and in adjustment screw 3! is provided in the main frame which projects upwardly through a hole in the forward end of the upper 'lever arm, as indicated in Fig. 1. Two

nuts .62 ant-1 :33 zare i=provided on this screw, one

32 below and one 33 above the lever arm 21. The

'nuts "32 and 33 form upper and lower stops, thus the ho'le'25 in-the main frame 6.

Two lateral downwardly projecting arms 35 and'36 are provided on threarward end of the main frame 6, and have journal bearings in the lower ends thereof, thereby to mount the'entire structure for vertical swinging motion above a moving record medium.

The device described is adapted for the dual purpose of recording and playing back and 0perates as follows: In the condition shown in Fig. 1; the tone head is adapted to function *as "a pickup, that is, =when=the -stylus l 2 *is engagedwith an undulatinggroove in a moving 'recordfthe lateral vibration of the stylus and hence the armature 1 produces "correspondingly plusating electric current in thecoil 2'! Now toconvert the tone liead-for' th'e function of recording, pressure is applied at a point indicated 'by the numeral 31 in Fig. 1, as for example by-th'e addition of a weight 3l thereat as shown in Fig.3 or by a downwardly thrusting spring.

The added down-ward pressure first moves the upper arm of the-lever Z'l dowri-wi'rrdlyagain-st the lower adjustingnut 32 thus *rotating the lever counterclockwise-about the "fulcrum 30 and mcreasing the-tension-in=the 1igame1'it 22. The in- 1 recordmediumv for the ipui pose 0f embossing or engravingn groove therein. JDuringthe recording function, relatively vgreater magnetic flux strength must be aprcducedlin the ibladenportion IA of the warmature ..than .during the play-back funct on, :since during IECDId-ing, :it is necessary to deform the record medium. Greater magnetic flux strength in the armature .tends to, produce greater lateral excursions thereof :during which the armature bladel'd would tend to strike the pole pieces 15 and III. This atendencyais .overcome in thepresent pmbodiment by the aforementioned increased :stifiness .during the recording function.

The armature .I and stretched ligament 22 if undamped would form an oscillating system in which sustained vibration would be possible and which would be alinear in its response to varying frequencies of alternating current in the coil 2|. In order to preventsuch :resonancein the. armature system, the .damping sleeve 34 is provided which is so proportioned andof energy absorbing material such as to critically damp the armature motion. U i i a It will be seen by those skilled in the art that it is the essence of my invention to provide in a phonographic transducer, a mechanical oscillator,..the compliance factor of which is varied between the functions of recording and playing back and to so construct the transducer that. the stiffness of the variable compliance is increased automatically when additional stylus pressureis produced..., Various alternate methods.- of embodying my invention will be apparent and I do not mean to be limited to the embodiment disclosed herein but rather to the scope of the appended claims.

I claim:

1. In a dual purpose phonographic transducer: a supporting frame; a stylus carrying ferro-magnetic armature, pivotally mounted in said frame for laterally swinging motion therein; a stretched ligament connecting said armature to said frame and constraining said swinging motion; a damping sleeve of energy absorbing material surrounding said stretched ligament; a lever fulcrumed in said frame and moving in response to record engaging pressure of a stylus carried by said armature, one end of said lever being connected to said ligament whereby said stylus pressure responsive motion results in corresponding variation in said ligament tension; means for producing a permanent magnetic field surrounding said armature such that laterally swinging motion is accompanied by alternating magnetic flux flow in a portion of said armature; a coil surrounding said alternating magnetic flux-carrying armature portion, said coil so connected that current flow therein is accompanied by corresponding magnetic flux flow in said armature portion; and means for selectively connecting said coil to a source of alternating electric current or to a means for detecting such current.

2. In a dual purpose transducer: a supporting frame; an armature movably mounted in said frame; a spring connecting said armature and frame and under initial tension to constrain said armature movement; a movable member in said frame connected to said spring; means to selectively detect or produce mechanical vibration in said armature; an element in said armature adapted to selectively produce a sound record in a moving sound recording medium engaged therewith or to vibrate said armature in response to a moving sound record engaged thereto; and means to selectively apply pressure to said movable memher to move the same whereby to increase the tension in said spring and simultaneously increase pressure of engagement of said element.

3. In a dual purpose transducer: a supporting frame; an armature movably mounted in said frame; a spring constraining motion of said armature; stylus means to selectively engage said armature with a source of mechanical vibrations or with a medium for recording such vibrations; a movable member in said frame connected to said spring; and means to selectively apply pressure to said member whereby to simultaneously increase tension in said spring and apply medium engaging pressure to said armature.

4. In a dual purpose transducer: a supporting frame; an armature movably mounted in said frame; stylus means to selectively engage said armaturewith a sourceof. mechanical vibrations or with a medium for recording such vibrations; movable means insaid frame resiliently connected to said armature; and means to-selectively apply pressure to said movable means whereby to simultaneously decrease the mechanical compliance of said armature and apply medium engaging pressure to said stylus means. I

5. In a dual purpose transducer: a supporting frame; an armature movably'mounted in said frame; a spring connecting'said armature and frame and under initial tension to constrain said armature movement; a movable member in said frame connected to said spring; means to selectively detect or produce mechanical vibration in said armature; an element in said armature adapted to selectively produce a sound record in a moving sound recording medium engaged therewith or to vibrate said armature in response to a moving sound record engaged thereto; means to selectively apply pressure to said movable member to move the same whereby to increase the tension in said spring and simultaneously increase pressure of engagement of said element; and adjustable means for limitin the motion of said movable means whereby to adjust the amount by which said spring tension is increased by said movable means.

6. In a dual purpose transducer: a supporting frame; an armature movably mounted in said frame; a spring constraining motion of said armature; stylus means to selectively engage said armature with a source of mechanical Vibrations or with a medium for recording such vibrations; a movable member in said frame connected to said spring; means to selectively apply pressure to said member whereby to simultaneously increase tension in said spring and apply medium engaging pressure to said armature; and adjustable means for limiting the motion of said movable means whereby to adjust the amount by which said spring tension is increased by said movable means.

7. In a dual purpose transducer: a supporting frame; an armature movably mounted in said frame; stylus means to selectively engage said armature with a source of mechanical vibrations or with a medium for recording such vibrations; movable means in said frame resiliently connected to said armature; means to selectively apply pressure to said movable means whereby to simultaneously decrease the mechanical compliance of said armature and apply medium engaging pressure to said armature; and adjustable means for limiting the motion of said movable means whereby to adjust the amount by which said compliance is changed.

8. In a dual purpose transducer: a supporting frame having aligned bearings therein; a vibratory member pivctally mounted in said bearings; means in said frame to selectively vibrate or detect vibration in said vibratory member; stylus means fixed to said vibratory member and adapted to engage the same selectively with an external source of mechanical vibration or with a medium for recording such vibration; a compliance control member movably mounted in said frame; a pre-stressed spring connected between said control member and vibratory member and adapted to resist movement of said vibratory member; and means positioned and adapted to apply pressure to said compliance control member and frame whereby to increase the medium-engaging pressure of said stylus means and simultaneously to increase the resistance of ,Said spring.

57$ 1 a 9 The construction oi claim. 8 WM mztlmt: me tenized that'sai'd-i l'szst named meansincludes a, aleven fulcmmedz'imsaid weight afiapteef tureshon ccmfirol' memirem 11 159*. Thecans-tructlon of alarm & fm'fiher char-- 7 (ms acfierized? byhaving adfiustabl'e abutment? mm 61 bers in said frame; positioned and adaptedto li'n'r- The following refmtenlces are of record in the it the movement ofsai'cf control member; We of this patfemir 11. The construction ofclaim gmrther characmm ST terizedj'inthat said sprihgis afiensioned ligament w V 1'2. The construction efclaimii further chamzm- Name W terizerL by having a. body ofenergy-ahsorb'ing mai f; terial engaged withsaidvibratuxymemben wher;& 3 f; 15 i 'm 1932; by damp thesame" 211mm EeMacIaiIer- Sepia-1 231939 Theconstmctim (if hereha ab x 2,318,398 1 1

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