US2300778A - Sound reproducer drive - Google Patents

Description

NOV- 3, 1942- L.. B. coRNwx-:LL 2,300,778

SOUND REPRODUCER DRIVE Filed Nov. 22, 193s 2 sheets-sheet 1 Was' A M lNvENToR S; 6. M j BY am, wfw

NGV. 3, 1942. L E, CQRNWELL 2,300,778

` SOUND REPRODUGER DRIVE Filed Nov. 22. 193s 2 sheets-sheet 2 italy-L 5v N S/' 3 Y 1 l[/5 IML 1 s linx. [vll-1 1 54705 (4m 74Ij 4% INVENTOR ATToRNEYs Patented Nov. 3,1942 l UNITED STATES PATENT OFFICE Cinamlagra ph Corporation, Stamford, Conn., a

corporation of Delaware Application November 22, 1939, Serial No. 805,590

ZCIaims.

` This invention relates to apparatus for driving a rotating element and maintaining its speed closely constant.

'I'he principal feature of the invention is the provision of such an apparatus which is simple and inexpensive in construction and effective in operation.

The invention is shown and described as applied to a turntable of a phonograph or other shaft 20 and engages the walls of slots 25 in hub Il for preventing relative rotation between the shaft 20 and the turntable Member 22 is formed with a sleeve 26 which extends downwardlly through the aperture ln plate |=6 and serves to guide the shaft 20 which is positioned within it.

iThe motor I2, gearing 'Il and friction clutch I4 are positioned below plate I6 and are supported upon a chassis 30. This chassis is susdevice 4for rotating a record in the recording or vlil pended from plate I3 by the rods 3|, the lower reproduction of sound. In such devices, particularly for those used where high :fidelity sound recording and reproduction are required, as in radio broadcast and motion picture work, it is essential that there be no variation in the speed of the turntable.

Other features of the invention.and'its advantages, will become apparent from the following description taken in connection with theaccompanying drawings in which:

Fig. 1 is a vertical section through the center of the apparatus;

2 is a horizontal section of a portion of the apparatus shown in Fig. 1, the section being taken along the line 2-2 thereof; i

Fig. 3 is a diagrammatic view of the portion of the apparatus shown in Fig. l, the view being a development of a vertical elevatiomabou-t the portion of the periphery indicated by the line I-I of F18. 2:

Figs. 4 and 5 are diagrammatic views similar to Fig. 3 showing 'other relative positions of the parts; and

6 is a vertical section through the center of an alternate construction.l

Referring to Fig. 1, the disc or turntable is mounted to rotate about a vertical axis and is driven by the motor |-2 through the reduction gearing il, friction clutch I4 and coupling device Il.

The turntable is positioned above the plate il, the plate .being suitably supported around its edge by the cabinet Il which houses the apparatus, and the turntable being rotatably supported upon the plate "l0, -In the construction shown, the hub |l of turntable rests upon the top of enlarged head I! of the vertical shaft 20, the under side of head i! resting upon the supporting bearing 2|, the bearing 2| resting in a recess in the head of a member 22, and the latter being in engagement with and supported by the plate il. The shaft 20 extends upwardly into the hub I l and has a portion 23 projecting above the top of the turntable for centering the record thereon. A pin 24 extends radially from 65 end of each such rod being secured to the center of a sponge rubber cushion I2, with the cushion secured to the chassis by the mounting ring 3l which engages a peripheral shoulder on the cushion 22. The motor, gearing and friction clutch are thus mounted upon the cabinet in such a manner that the mechanical vibrations developed therein are not transmitted by the supports therefor to the turntable I.

'Ihe gearing 'I3 consists of a worm 38 and worm wheel 3l, the former being secured to the shaft of the motor l2 and the latter being rotatably mounted upon a vertical shaft which is coaxial with shaft 20. The shaft 3l is rotatably 5 mounted in a sleeve 29 which is suitably secured to the chassis I0.

The friction clutch I4 consists of the top surface of worm wheel 31, the bottom surface of a disc 4| which is secured to the shaft 38 by the 30 pin 42, a friction ring 4I positioned between and in engagement with these two surfaces, and the helical compression spring 44. The helical compression spring 44 is positioned about shaft '20 and urges the worm wheel 2l upward toward the disc 4| and thus furnishes the friction-creating pressure for the clutch. The lower end of the spring presses against a bearing 45 which rests upon a radial shoulder`formed on sleeve 39.

The coupling device I5, coupling shaft 38 with 40 shaft 20, consists (referring also to Fig. 2), of

the disc 4| secured to shaft 3-0, a disc 40 secured to the shaft 20, a number of permanent magnets 41a, 41h, 41c` and 41d secured around the periphery of disc 4|, a corresponding number of similar 45 permanent magnets 48a, 48h, 48e and 48d secured around the periphery of disc 48, and one or more pins 49 each having one end thereof mounted in the disc 4| and having the other end thereof positioned in an arcuate slot 50 in disc 46.

50 Each ofthe pennanent magnets 41 and 48 is formed with two oppositely magnetized poles N and S joined by a yoke, with magnets 4l on the lower disc 4I mounted so that the poles thereof extend upwardly, with magnets 48 on the upper disc 46 mounted so that the poles thereof vextend downwardly, and with substantial clearance between the ends of the upper and lower sets of poles. To maintain this clearance the shaft 3i is provided with thrust bearing l positioned between the lower surface of sleeve 39 and a washer Il, the latter being suitably secured to shaft l as by lock nuts BI. Magnets 41 and I8 are correspondingly spaced on their respective discs ll and with alternate poles on each disc havinl the same polarity and with corresponding lupper and lower poles having opposite polarity.

Thus. when the discs 4i and 48 are positioned relative to each other so that the corresponding magnets l1 and ll are opposite each other, as shown in Fig. 3, the magnetic force between the several poles tend to keep the discs in this relative position. For convenience this relative position is referred to as the static" position of the coupling device il. r

In considering the operation of the apparatus, assume initially that all the parts are stationary and that the coupling device i5 is in the static position (i. e. the position shown in Fig. 3) and that motor i2, when in operation, rotates worm Il clockwise, as viewed in Fig. l. Thus, upon the starting of motor i2, worm wheel 31 is rotated clockwise, as viewed from above, or forward as this direction of rotation is for convenience hereinafter termed. Likewise, disc Il rotates for- Ward lince at llrst there is no slipping of the friction clutch' Il.

As soon as lower disc Il rotates forward relative to upper disc IB, as shown in Fig. 4, the magnetic forces between magnets I1 and 48 tend to rotate upper disc forward (see Fig. 4) However,-opposlng this starting movement of upper disc Il is its inertia and the inertia of the turntable li, the inertia of the latter having been made large by constructing the turntable of heavy material and with an oversize flange 5i at its perimeter to obtain a fly-wheel action. As a consequence the magnetic forces of coupling device Il are insufficient to overcome all this inertia so that the lower disc Il advances relative to the upper disc Il until pins I9 on the lower disc engage the forward ends of slots 50 in the upper disc Il. The lower disc 4I is then unable to advance any further relative to the upper disc 46 and for the time being the two discs are mechanically coupled for joint forward motion. The politigns oi' the magnets at this time are shown in Pig. 5, the positions of the pins I9 being indicated by the dotted outlines I9" in Fig, 2.

Thereupon the inertia of the turntable Ii and dise Il is mechanically applied to the lower disc 4|, and as the friction clutch il is unable to transmit, without slipping, sufllcient force to overcome this inertia, the friction clutch I4 commences to slip.

However, the force that is transmitted by the friction clutch I4 gradiially overcomes the inertia of the turntable ii and disc I8 and eventually brings the speed of the turntable il substantially up to that of lower disc 4i Thereupon the magnetic forces between the magnets l1 and I8 bring -the upper set oi' magnets into substantial alignment with the lower set of magnets and thereby substantially eliminate the advance of the lower disc Il with respect to the upper disc I6. During further operation the coupling between the discs is solely by means of the magnetic forces, so the drive thereupon becomes exclusively magnetic. To overcome the friction and other losses attendant upon the rotation of turntable il, a small rotative force must be applied to the upper 15 aecomo disc ll. This is supplied by the slight advance of the lower disc 4I with respect to the upper disc I6. as shown in Fig. 4. Fig. 4 thus illustrates the positions of the parts under normal full speed running conditions, while Fig. 5 represents the positions of the parts during their acceleration up to normal full speed running condition. The position of the pins Il under the conditions illustrated in Fig. 4 is shown by the dotted pin outlines 4l' in Fig. 2; similarly, the position of pins 40 under the conditions illustrated in Fig. 5 is shown by the dotted pin outlines Il" in Fig. 5.

After the turntable has been brought up to full speed, none of the vibrations of the motor il or of the gearing Il is transmitted to the turntable. Also, momentary variations in tbe speed of disc Il due to any cause, (such as to a change in the line voltage of the motor, or to irregularities in gear teeth or to back lash in the gearing), are not transmitted to the turntable as these momentary speed variations are absorbed by momentary movements of the lower disc Il Vrelative to the upper'disc Lf-the speed variation and lthus the relative displacement of the discs, becomes more than momentary, the magnetic forces between the magnets 41 and 4I gradually change the speed of the turntable, against the inertia of the turntable, until the parte are restored to their normal positions. In other words, momentary speed variations of the motor and gearing are not transmitted to the turntable, but any permanent change in speed of the motor and gearing results in a very gradual change in speed of the turntable.

To insure that under normally full speed running conditions under very light driven loads the lower disc Il is slightly in advance of the upper disc 46, a small frictional load, preferably adjustable, may be applied either to the upper disc Il or to the turntable Ii. Such a load may be applied by a leaf spring 00 secured at one end to plate iB and having its other end engaging an annular surface 6I on the top of disc I8. Alternately, such a load may be applied by a leaf spring 62 secured at one end to plate II and having its other end engaging an annular surface 6I on the underside of turntable ii, preferably near the rim. In either case the leaf spring is preferably provided with some means, such as screw 8l, to regulate the engaging pressure of the spring and thus the friction which is thereby created. While the amount of friction'created is small, it sh'ould be substantially larger than the torque otherwise required to drive the turntable so that any incidental variations in such torque are relatively insignificant in comparison to the total torque required to' drive the turntable. Thus the drag of the turntable upon the coupling device IB is substantially constant and of sufficient quantity to insure that the upper disc I6 lags enough behind the lower disc Il to avoid hunting Fig. B shows an alternate construction. yThe turntable 10 is mounted on the upper end of a vertical shaft 1|, th'e lower end of which is supported, through the bearing 12, upon the frame 13, the latter being secured to and positioned below plate 1I. Surrounding shaft 1I isla sleeve 15, the upper end of which is formed with a collar 18 engaging the. upper surface of plate 14. This sleeve is preferably Vstationary. Rotatably mounted upon sleeve 15 is a pulley 11 and a disc 1B, pulley 11 being positioned above/disc 1l. The motor l0 for driving the turntable is at one side of the apparatus and is supported from plate 1l through cushions such as 32, 33 of Fig. 1. or by any other suitable means,.which does not transmit the motor vibrations to the plate 1l. A pulley 8l is secured to the shaft of motor 88, and pulleys 8l and 11 are connected by a belt 82. In the construction illustratedeach pulley 8| and 11 has two surfaces of l.different diameter so that by shifting belt 82 from one surface to the other the pulley may be driven at either of two different speeds without changing the motor speed.

Between pulley 11 and disc 18, and engaging the lower and upper surfaces thereof respectively, is the annular friction disc 83. This, in conjunction with the surfaces which it engages and in conjunction with the helical spring 84, serves as a friction clutch 85 between pulley 11 and disc 18. Helical compression spring 8l surrounds sleeve 15, has its lower end engaging pulley 11 and has its upper end engaging a bearing 88 which abuts against the plate 18.

Disc 18 is coupled to shaft 1I `by the coupling device 81 positioned below the pulley 11 and friction clutch 85. This coupling device 81 is similar to the coupling device I5 of Fig. 1, and consists of the disc 18 driven by pulley 11 through the friction clutch 88, of the disc 88 positioned below disc 18 and secured to shaft 1I (as by the pin 84), of the permanent magnets 88 and 80 secured along the perimeters'of discs 18 and 88 respectively, and of pins 8| secured to disc 18 and extending into slots 8l in disc 88. To maintain the separation between. magnets 88 and 98, and to support disc 18 and pulley 11 upon sleeve 15, a thrust bearing 82 is provided at the lower end of sleeve 15. the lower surface of this bearing engaging a collar 83 removably secured to sleeve 15, and the upper surface of this bearing engaging disc 18.

The turntable 18 has substantial inertia, as with the turntable Il of Fig. 1 and, as in Fig. 1, a small frictional load is applied to the turntable.

The detailed description of theA operationv of the apparatus of Fig. 1 also is applicable to-the operation of the alternate construction shown' in Fig. 6. It is believed sufficient to note further that pulley 11, friction clutch 85 and coupling device 81 of Fig. 6 correspond respectively to worm wheel 31, friction clutch il and coupling device i5 of Fig. 1. An advantage of the construction of Fig. 6 is that vibrations and speed variations due to imperfect gears are avoided by dispensing with their cause-the gearing. Another advantage is that with the same apparatus the turntable may be driven at either of two speeds, such as at 33.3 or '18 revolutions per minute.

In thesystem of this invention the turntable Il, 10 with its magnet is rotatable around a vertical axis independently of the cooperating drive magnet and its motor or. belt. In normal operation only the attraction'and repulsion between the magnets deliver the driving torque for the turntable. structurally the parts are separate so that any vibrations of the driving motor, belts or gearing will not be mechanically transmitted to the turntable. The magnetic coupling effectively smooths out all irregularities in the drive and'maintains an even torque on the turntable and completely protects it from mechanical shocks or vibrations originating in the driving mechanism.

Although the invention has been shown and described as applied to a turntable for a phonograph or other device, the invention is applicable to other rotating elements which are to be driven and maintained at a uniform speed, for example, the sprocket controlling the passage of sound illmpast the light beam of a sound recording or reproducing apparatus.

I claim:

1. A magnetic coupling comprising a rotatable driving rotor, a series of separate closely spaced U-shaped magnets carried by said rotor, each magnet having axially directed north and south poles with a connecting yoke, a driven rotor coaxial with said driving rotor, a series of separate spaced U-shaped magnets each having anaxially directed north and south pole with a connecting yoke carried by said driven rotor, the south poles of the driving magnets facing the north poles of the driven magnets and vice versa and said poles being so closely spaced around the peripheries of the rotors that relative rotary motion between said rotors develops substantial repulsion between like `poles of all the magnets while attraction between opposite poles of all the magnets is still maintained, and means rotatably supporting said rotors to drive the driven rotor from the driving rotor through the combined attraction and repulsion of the poles of said magnets.

2. A coupling as set forth in claim 1 in which the distance between successive magnets is less than the length of each magnet measured peripherally around the rotor.

LIONEL B. CORNWE'LL.

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