US2092884A - Signal translating apparatus - Google Patents

Description

Patented Sept. 14, '.1937

UNITED STATES PATENT rol-FICE y 2,092,884 SIGNAL TRANSLATING APPARATUSl James M. Kendall, Woodbury Heights, N. J., as-

slgnor to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application November 1, 19.32, Serial No. 640,591 l The present invention relates to signal translating apparatus of the type employed in electrical phonograph sound recording and reproducing systems, wherein the sound record is provided in a mechanical groove or other sound.

character above referred to, a vibratory system isY provided, comprising, in one Well known type, an amature adapted to carry a stylus for engagement with a record groove and pivotally mounted to vibrate at one end between magnetic pole pieces in association with an electrical winding or pickup coil.

The vibratory mechanism or system, of which g5 the armature `is a part, may have one 'or more natural periods of vibration within the audible range at which the amplitude of vibration may be over-'emphasized or under-emphasized, resulting in distortion of signals being translated by the device. Obviously this is undesirable. As indicated, 'for example, by the construction shown in the patents above referred to, various means have been provided in the past for correcting for such conditions of operation such as damping the armature action to effectively smooth the operating characteristic as represented by the usual frequency-voltage response curve to remove the undesired peaks or resulting dips therein caused by resonance. In general, the prior art devices employ damping and centering means comprising blocks of resilient material engaging the amature on opposite sides and are characterized by the fact that the damping means (1) Is interposed between and connects the armature and a fixed supporting means,

' (2) Is both the-damping and the centering or restoring means,

- (3) Has a limited damping'action, because of rigidtyand (4) Unduly loads the armature,l`

whereby the latter is less flexibly mounted and is less responsive in the translating action because of the connection with the nxed supporting means.

05 The damping action is limited because of the material employed, usually soft rubber, and because the damping means is so mounted that it attenuates desired vibrations because of its rigidity. Furthermore, vthe rubber ages and must be replaced occasionally for best results in opera- 5. tion,'and while providing damping to a certain extent, does not provide enough entirely to eliminate certain peaks in the audio frequency response characteristic of electric pickup devices for high frequency electric signal translation. 10 .It is, therefore, a primary object of the present invention to provide an improved signal translating device for electric phonograph sound recording andreproducing systems, that shall have an improved frequency response character- 15 -istic and that shall obviate the above mentioned and vcertain other disadvantages of known devices.

It is a further object of the present invention to provide an improved mounting, centering and damping system for the vibratory element of a device of the above character that shall eectively attenuate undesired resonant peaks inthe operating characteristic thereof, without loading the armature orvibratory system appreciably outside the frequency range of such peaks, whereby' the frequency response characteristic may be improved. l

In accordance with the invention, in a preferred embodiment thereof, a vibratory member 30 or armature is separately mounted in fixed pivot bearings with a torsional restoring or centering spring extending therefrom along the pivot axis, separately connected to a xed, spaced supporting frame. The armature member is provided 35 `with a body of dampingmaterial directly se-,

cured or connected thereto. The damping' body is free to vibrate and to move with the armature since it has no other support, and at least one of'` its largest dimensions is parallel to the plane of 40 vibration of the armature member, the plane of vibration being at a right angle to the pivot axis of the armature..A l l The-shaft bearings have the separate function 1 of providing, with the pivot shaft, a fixed, inde- 45 pendent, pivot axis for the armature-member. l' The fixed torsional spring, which may have a low l hysteresis effect as hereinafter discussed, provides a restoring and centering force without appreciably affecting the moment of inertia of the 50. vibratory system, since it lies in the axis of vibration. The damping means has the separate functionof damping the armature, and, being free to move with the amature, .may be shaped to selectively remove undesired higher frequency ,55

peaks in the operating characteristic of the device without having Vany appreciable damping effect at other and lower frequency ranges. By this construction, furthermore, the use of resilient 5 material of a non-permanent nature, such as rubber, is substantially eliminated and is employed only as a friction reducing means as a part of the shaft bearing for the armature.

It is a still further object of the present invention to provide an improved electromagnetic pickup device ofthe type adapted to be provided with a stylus, wherein the vibratory element or armature is more flexibly mounted, thereby to reduce record wear and to improve the frequency response characteristic.

Contrastedwith the selective frequency responsive damping means above mentioned, the torsional centering spring arrangement provides for restoring the vibratory element to a centralncrmal position with a stiffness that is constant within the audio frequency band. No resonance and a very low moment of inertia are the characteristic of a restoring means of this character, and by properly choosing the material, very low mechanical hysteresis is obtained.

Hysteresis in vibratory systems is the equivalent of friction, so that when the vibratory element or armature is deflected from its normal position, it does not return exactly thereto, but only to apoint where the centering force is balanced to a force that is necessary to overcome the friction. The greater the hysteresis the more oif center will the armature be after it is deflected. In electric signal translating devices of the .present electric pickup type,v the amature, ,in its unexcited condition, stands normally in a central position with one end midway between the two pole pieces. this character, in operation, the armature is deflected from the central position either by mechanical forces or by forces derived from electric currents owing in the coil.

- If rubber damping blocks are employed' in connection with the armature element for restoring the armature to and for normally maintaining it in a centered position, it has been found that the hysteresis effect above mentioned is relatively high. Accordingly, to overcome the effects of hysteresis in such a case, it has heretofore been necessary to provide a restoring force in the form of a spring in certain cases, or to rely on the rubber only, the spring being thereby stiffened to overcome the hysteresis effects.

In a translating device embodying the present invention, the damping means is carried entirely by the moving or vibratory armature whereby it imparts no fixed rigidity thereto and, accordingly, lthe restoring force or spring may be reduced to a point which makes -it possible to provide a 00 flexible armature element or stylus carrying member and thereby appreciably to reduce record wear. In this position, the response characteristic of the device is improved because of the flexibility of themoving parts. l 6 The invention will, however, be better understood from the following description when taken in connection with the accompanying drawing, and itsscope will be pointed out in the appended 75 Fig-2 is a cross sectional view taken on line As is well known with devices of is a front view. on a' y is rigid against 2-2 of the device shown in Figafl, on Ithe sameV .scale and with a cover plate in place;

of the devices of Figs. 1, 2, and 3, showing modi` fications; and

Fig. 6 is acurve diagram illustrating an operating characteristic of the device shown in Figs. l, 2, and 3.

Referring to Figs. 6 is the molded insulation base of an electromagnetic pickup-device on which is mounted a metallic frame 'l providing magnetic pole pieces 8 to which is connected a permanent magnet 9 f or supplying flux thereto. An armature or vibratory member i0 provided with an integral pivot shaft ii is journalled in the frame i in suitable spaced bearings provided by rubber sleeves i'Z-IZ mounted on the shaft and clamped with it between two frame members i3.

In the present example, the armature is hollow at one end and may be provided with a suitable stylus i4, which is clamped within the hollow end of the armature by a clamping screw or' thumb screw I5, threaded axially into the shaft I i. The opposite end I6 of t'ner armature is'ada'pted to lie between the pole pieces 8 and is surrounded by a suitable electric pickup winding or coil I'I provided with terminal leads I8 which, in turn, are connected to output terminal members i9 embedded in the body 6 of the pickup device for external connection with an electrical circuit (not shown).

The permanent magnet 9 is held in place on the frame 1 by a. spring retaining member 20 connected with the body 6 in a position to engage the top of the magnet. -The pickup device is `also provided 4with an external main cover 2i, all as shown more clearly in Fig. 2.

It will be noted that the vibratory member or armature is pivotally mounted in the .bearing sleeves |2-I2 which, as hereinbefore stated, are preferably of rubber, whereby friction is avoided or reduced to a The bearings are y spaced, and it will be noted that the armature member is thereby prevented from `movement in the radial directions.v This arrangement prevents the weight of the device on the stylus from displacing the armature member. In other words, vthe armature member is Ijournalled in means which function exclusively as pivot bearings, to constrain the armature to rotary motion without radial movement. y

The armature member is retained in a central or normal position with respect Vto the pole pieces 8, by an elongated spring' member or torsional restoring and centering spring 22 which lies in axial extension of the pivot shaft Il at one end thereof and which is connected with said end and with a spaced bracketI member 2E forming part of the frame 1. The spring may be either round or rectangular in cross section. In the present example, the spring is substantiallyrectangular in cross section and' is dat at its ends whereby it may be secured in holes or slots i'n the shaft end'and in the frame extension' or bracket'member 23.

The bracket member 23 and the spring are preferably united permanently by suitable means auch as by soldering (not shown), whereby the spring is rigidly connected with the frame and movement in{any direction ex-.v

'cept torsionally, that is, about its own 'sais 1, 2, and 3 of the drawing,`

and that of the shaft Il. The spring is secured to the armature by any suitable means, such as by slot 24, in one end of the shaft I I, over. which is forced a sleeve 25.

By this arrangement, it will be seen that the vibratory member or armature is not only rigid-v ly constrained to rotary motion by spaced bearing means provided in a rigid frame, but it is also connected with said frame by further means comprising a torsional spring which serves to prevent longitudinal movement of the shaft and armature within the bearings should there be any tendency for such movement, and which also holds the armature resiliently centered between the pole pieces; The torsional spring connection between the armature and the frame is of such cross section, although relatively small since it is preferably of steel, that it may impart sufiicient centering action to properly return the armature to and normally hold it in the centered position. Y

It will also be noted that the frame and the adjacent shaft end are relatively widely spaced, whereby the torsional spring may be relatively long, thereby reducing the stresses in the spring material. The stiffness of the spring is substantially constant and it is non-aging as com` 'pared with rubber as a restoring means for the armature. Being of steel and of xed dimensions it may be made very uniform in quantity production. Furthermore, it is rigid in all directions, except torsionally, and has no resonance in itself. Because it liesin the axis ofthe armature pivot shaft, it has substantially no appreciable inertia or -resonance in itself and has no appreciablemechanical hysteresis.

The sleeve 25 is arranged to exten'd'in the direction of the spring 22 into the space Abetween the frame member 23 and the main portion of the frame, and is there enlarged to form the cylinder 26 on which is mounted a block -of damping material 21. `In the present example,

the block of damping material is rectangular in shape and is relatively thin, having at least one of its largest dimensions in a plane parallel to that of vibrational movement of the armature, that is, at a right angle to the shaft axis. The exact dimensions of the block 21 are not critical. It is desirable, however, that the moment of inertia thereof, about the axis of vibration of the armature member, shall be greater than the moment of inertia of the armature member. about the same axis. l The function of the sleeve or cylinder jis to providea rigid connection between theVl` block of damping material 21 and the armature, thereby to impart to the mass of damping material,

through the cylinder, and in the plane of one of its larger dimensions, a predetermined vibratory force corresponding to that to which the amature member is subjected at its resonance peaks. The damping block is subjected to rotational and torsional movement in the example shown, but it may be attached to the armature by other means, as indicated in Fig. 4 for example, to which attention is now directed.

In Fig. 4, the armature member I0 is provided e with a cylindrical extension piece Illaon which is mounted a relatively large block of damping material 21a. The damping action is similar to that provided by the block 21 in Fig. v3 and the material and the damping action per se will be further considered hereinafter, Fig. 4 being illustrative, along with the precedingfivgures, of an arrangement of the damping means in connecor the cylinder 26 of Figs. 2 and 3. In general,

friction may be depended upon .for this connection, `or in the caseof a fusible material, friction, supplemented by fusion', yproduced by suitably heating the cylinder 26, for example by a soldering iron or the like, until the material of the block fuses and thereby more rmly adheres to the cylinder 26. In the case of non-fusing materials, these parts may be cemented together to supplement the frictional connection.

In certain cases, however, it will be desirable to provide additional means, as shown in Fig. 5, for example, for insuring that the block does not slip or twist `on its supporting mediumand to this end a cylinder 29, corresponding to cylinder 26 of Fig. 3, may be provided with radially extending fins 30, which will cut into and, therefore, grip the damping material when the damping block is pressed onto the cylinder. l

'I'he damping material found most suitablefor the use shown, is a soft, pliable and solid substance, such as that known vcommercially as Glyptal, or another commercial product known as Du Pont Viscoloid, X'17'15-3.

'Ihe material should preferably have all the properties of a solid, but should be inert and almost fluid, while being self supporting or adapted to hold a permanent shape.

Specifically, the damping material preferably has the following properties and characteristics:

Masa-The important thing about mass is that it has inertia,'or resistanceto change of velocity. The materials at present found most'satisfactory j vhave a density of about 1, but this value does not appear to be critical.

Rz'gz'dity. -One of the differences between ya solid anda liquid. The material should have sufficient rigidity and mechanical strength to make it self supporting. Too much rigidity adversely affects the performance in a translating device.

Damping.-Ordinarily, most easily thought of.

as a property ofheavy oil. 'I'he resisting force is proportional to the velocity. (In a mechanical system it is similar in its effect to resistance in an electric circuit). .In regard to solids, it is often confused with hysteresis, but it relates to hysteresis as eddy currents do to magnetic hys- The operation of the vibratory system em? bodying the invention is as follows: y

'I'he damping mass orblock is free to rotate With the armature when the armature is slowly deflected in a normal manner. If, however, the armature `is suddenly deflected, or shock excited, as in normal operation, the outer edge portions of the mass or block will tend to 'I'he present preuse in a systemv stand still at first.

have rotated through an angle corresponding to the angle through which the armature was suddenly deflected. The inner portion of the mass or block adjacent to the cylinder obviously must rotate with the armature since it is directly connected thereto, The motion of the outer edge lags behind the motion of the inner or center portion under these conditions, and thus the material is worked or deformed, when the deflection is l required to oscillate the damping block di' mass.

The damping and rigidity of the vmaterial are sumcient to transmit this force from the cylinder t the outsideedge of the block or mass without deforming the material. Hence, the entire block or mass oscillates in phase with the armature in a low frequency range.

At a, higher frequency range, the damping and rigidity of the material are not sufficient to transmit to the edge of the block the increased force necessary to overcome the increased mass reactance at the higher frequency and when the material is deformed, the portion near the cylinder or sleeve vibrates therewith, while the edge portions tend to stand still, thereby causing the damping and rigidity of the material to become effective and to control resonance effects in the higher frequency range.

reproduction, and should be eliminated if possible. By making the damping and rigidity of the damping means effective at a somewhat lower frequency, this resonance may be largely suppressed, thus improving the quality of reproduction.

The advantages inherent in the free selective damping system thus provided may further be seen after a brief consideration of a ,system wherein the damping material is bound or rigidly held, as in certain prior art devices. If, in accordance with such systems, the damping block were held by its outer edges, while the cylinder oscillates, thev clamping material is worked at all frequencies.V 'I'his has the objection of introducing the damping and rigidity at frequency ranges wherein it is not required, thereby putting an unnecessary load on the needle point, with a consequent increase in record and needle wear. This is especially true since the major portions of recorded sounds appear in a lower rather than a higher frequency range. If the load on the Vneedle is light, or in other words, if the mechanical impedance is low, in this lower range, as is the case with a construction like that of the present embodiment of the invention, a major portion of what is usually considered normal record wear is avoided. 'I'he preferred arrangement is, therefore; to have the outer peripheral portion or edges 2,092,584. and then begin to rotate rather slowly until they of the damping block or mass free and the shape and mass so adjusted as to make the damping effective at a frequency somewhat below the usual resonance.

The preferred embodiment, therefore, includes a torsional type damper which replaces the customary damping blocks on the tall of the armature. l'

If loading of the armature is unobjectionable, in certain cases it may be desirable to increase the moment of inertia of the damping block as by adding to the mass at the edges by the same or heavier material, or by other suitable meansV such as clamping the edge of the block by a screw 35. for example.

The effect of the damping introduced is to control the armature resonance. The effect of the rigidity inherent in the damping material von the operation is to extend the frequency range. The upper limit of this range depends primarily on the moment of inertia of the armature and the stiffness of the stylus or needle. In general, the greater the stylus stiffness and the smaller the moment of inertia of the armature, the greater the range. To a lesser degree, it is also true that the greater the centering stiffness, the greater the range. The rigidity inherent in the damping material at high frequencies is added to the centering stiffness, thereby increasing the range. Furthermore, in designing the pickup, the diameter of the cylinder and the thickness of thedamper'block are.

adjusted to give the best frequency response. In I adding the least mass to the armature, because the cylinder is located coaxially with center of oscillation of the armature. This makes its moment of inertia minimum and makes possible a design with better performance.

It has been found that the construction in aocordance with the present invention, as shown and described, has an improved range of operation extending effectively to 4500 cycles as compared with previous performance of known devices of 3500 cycles.

From the foregoing description, it will be seen that a signal translating device in accordance with the invention comprises a vibratory element through the movement of which the translating action is effected and on which is mounted, or with which is rigidly connected, a block of material especially chosenI for damping characteristics, the shape of which and the mounting means for which is determined by the frequency range 4'within which damping is desired.

It will also be seen that, in response to low frequency vibrations, the damping block vibrates cient inertia to hold them substantially stationary, while the inner portion adjacent to the hub or cylinder vibrates relatively thereto permitting the absorption of the excess energy in the frequency range to which the-vibratory system is responsive.

Thus, it will be seen that the damping means,

instead of acting throughout the full audio frequency range, is selectively responsive and may K properly be termed a 4selective damping means.

Referring now to Fig. 6, the electrical voltageoutput frequency characteristic of the pickup device shown in Figs. 1, 2 and 3 is plotted in two curves 3| and 32. These curves are not plotted throughout the lower frequency range, but only for the higher frequency range in which correction for distortion is desired in the particular type of translating-device referred to.

'I'he curve 3l indicates the operating characteristic without employing the damping block 21, Aand it will be noted that this characteristic indicates distortion in the region of 3500 cycles, while curve 3 2, showing the operation when provided with the damping block 21, is free from any appreciable -peaks of that character. This in. dicates an improved or extended higher frequency range, or an improved performance, and shows that the resonance characteristic of the vibratory system is compensated for. By varying the size and the shape of the block, the damping characteristic may, of course, be varied and may be caused to provide any degree of correction between the curves indicated fory the particular example herein given. For example, if the armature is loaded, as by increasing the inertia of the edges ofthe damping block by meanssuch as that hereinbefore mentioned, while the mechanical impedance is increased, the frequency characteristic is not' appreciably aii'ected, as indicated by the curve 33 taken with the armature so loaded.

It should be understood, however, that the invention is not limited to electromagnetic pickup 30 devices, although the vibratory system of the present example represents the present pre-- connected with said armature shaft, and having 4;, its major portion to one side of the axis of vibration of said shaft to provide a center of mass eccentric with respect to said axis and a higher moment of inertia than the armature member about the axis of vibration of said shaft.

2. In an electric signal translating device, the combination with a vibratory armature member of a frequency responsive selective damping means therefor including a free mass of damping material rigidly connected with said arma- 55 ture member, and having its maior portion to one side of the axis of vibration 4of said member to provide a Icenter of mass eccentric with respect to said axis and a higher moment of inertia than the armature member about the axis of vibration i 60 of said member, a supporting frame, a torsionally iiexible spring bar extending axially of and from the armature to the frame and providing therewith a rigid connection for the armature.

3, In an electric translating device, the combi- 65 nation with a vibratory armature member of a frequency responsive selective damping means therefor including a normally free mass of damping material rigidly connected with said armature member and having its major portion 70 extending to one side of the axis of vibration there-of, and means associated with said major portion for variably applying a load to said mass of damping material at will.

4. In an electric signal translating device, the

75 combination with a vibratory armature member,

of a block of damping material having a direct connection only with and surrounding an extension of the armature member to move there- -with as a unit in response to vibrations within a predetermined frequency range, said damping.

material having the characteristic of offering to an' external force tending to distort it a resisting force which is proportional to the velocity of distortion whereby it moves only in part adjacent to .and Vin a region surrounding said extension of the armature member freely in response to vibrations within a second frequencyrange. n

v5. In an electric pickup device, the combination of a supporting frame, an armature membe'r journalled in said frame to vibrate about a i-lxed pivot axis, an elongated torsional spring member having substantially no moment of vinertia about said axisconneoted with the shaft and extending axially therefrom into rigid connection with a portion ofthe frame, and a block of vibration damping material rigidly connected with the armature member to vibrate therewith about said pivot axis.

6. In an electric pickup device, 'the combina# tion of a supporting frame, an armature member journalled in `said frame to vibrate about a fixed pivot axis, an elongated torsional spring member connected Withthe shaft and extending axially therefrom into rigid connection with a portion of the frame, a block of vibration damping' material rigidly connected with the armature member to vibrate therewith about said pivot axis, and a cylinder surrounding said torsional spring member and providing said connection between the armature and the block of damping material.

7. In an electric pickup device, the combination of a supporting frame, an armature member journalled in said frame to vibrate about a fixed I pivot axis, an elongated torsional springA member having substantially .no moment of inertia about said axis connected with the shaft and extending axially therefrom into rigidv connection with a portion of the frame, and a block of vibration damping material rigidly connected with the armature member to vibrate therewith about said pivot axis, the block of damping material having at least one of its greater dimensions in the plane of vibration in which lit moves, and having a mass such that it has a higher moment of inertia about said pivot axis than the armature member.

8. In an electric pickup device, the combination of a supporting frame, an armature member journalled in said frame to vibrate about a fixed pivot axis, an elongated torsional spring member having substantially no moment of inertia about said axis connected with theshaft and extending axially therefrom into rigid connection with a portion of the frame, and a block of vibration damping material rigidly connected with the armature member to vibrate therewith about said pivot axis, the block of damping material having at least one of its greater dimensions in the plane of vibration in which it moves, and said block being freely movable as a unit with the armature member within a predetermined low frequency range and having a mass such that it has a higher moment of inertia about said pivot axis than said armature member.

9. In an electric signal translating device, the combination with a vibratory armature member, of means providing a fixed pivot axis for the armature member, a torsional spring member connected at one end with said armature member and extending therefrom along said pivot axis, a

xed supporting means for the armature member rigidly connected with the opposite end of said spring member, said spring member having a lower moment of inertia than the armature niember about said pivot axis, and a block of damping material connected with the armature to move axis, and damping means for said amature member having a common axis of rotation there- With, said damping means including a body of damping material connected with said. amnature and having its major portion extending to one side of said aids whereby said damping means has a moment -of inertia about said axis greater than that of the armature.

11. An electric pickup device including in 'combination, a pivotally mounted armature member, torsional damping means for the armature and centering means for the armature member, said vcentering means extending axially along the pivot axis of the armature and having substantially no moment of inertia with respect thereto andsaid damping means surrounding said axis and comprising a block of damping material having a major dimension extending at a right angle to the said axis of rotation.

12. In an electric signal translating device, the combination of an armature member having a pivot shaft, a frame in which said pivot shaft is journalled, a cylindrical extension piece for the armature member` a block of damping material mounted on and surrounding said extension piece, said block of damping material having dlmensions and shape such that its outer edges are relatively widely spaced from said cylindrical extension piece, an elongated torsional spring member connected with the shaft and extending axially therefrom into rigid connection with a portion of said frame. Y

- JAMES M. KENDALL.

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