US2603977A - Turntable speed compensator - Google Patents

Description

July 22, 1952 R. M. CAIN 2,603,977

TURNTABLE SPEED COMPENSATOR Filed Feb. 27. 1947 3 Sheets-Sheet 1 I I1 1 I INVENTOR. H v ROBERT-M. CA/N ATTOPNE V y 22, 1952 R. M. CAIN. 2,603,977

TURNTABLE SPEED COMPENSATOR Filed Feb. 27. 1947 3 Sheets-Sheet 2 4a 4 5 INVENTOR. H ROBERT M. CA/N A T TORNE VS July 22, 1952 R. M. CAIN 2,603,977

TURNTABLE SPEED COMPENSATOR Filed Feb. 27. 1947 3 Sheets-Sheet 3 INVEN TOR. ROBERT M CAIN 1 4 q [mi/ m ATTORNEYS Patented July 22, 1952 TURNTABLE SPEED COMPENSATOR 7 Robert M. Cain, Charlotte, Micht, assignor to Wilcox-Gay Corporation, Charlotte, Mich; a

corporation of Michigan Application February 27, 1947, Serial 731,319

3 Claims. (Cl. 74'-190.5)

My present invention relates to sound record ing' and play-back devices, and moreparticularly to speed compensating means specificallyv to adapted to sounderecording and playeback devices and utilized v .intconnection therewith to,

maintain theturntablefspeed at a constant rate irrespectiveof variations inload. r t

My invention-as primarily an improvement over the device set forth in Patent No. 2,351,948 in which a single unitary, substantially inexpensive unit is described which can be used by the unskilled home user bothwto make records and to play them back I I h In the said Patent. No; 2,351,948 many compensatin elements are described. fortthe purposes of making-itpossible to use light-weight and inexpensive par ts thus bringing the device within the reach or the home user.- Such com-.- pensating devices which include the resilient mounting of the motorand the resilient mount.

ing of the cuttingandthe pick-up elements as well as other compensating means therein described, made it possible 'to 'make a home record with a very light turntable and'even with records which are not truly flat. However,'wherelightweight parts are used so that no-substanti'al flywheel effect occurs, theredoes result a slight speed variation'l'in the operation of the turntable'for play-backand recording.

In a combined record makin and play-back unit, more power -is required during the cutting operation than during the play-back operation because during cuttingsome of the material of the record is f bei'ngremoved. This results in more work being doneaduring cutting than during play-back in which; latter case, the needle need merely follow the groove.

With the commercial device made: in accordance with Patent No. 2,351,948, it was found that the braking loadduringjcutting of a record was of the order'oi '14 inch ouncesadjacentthe periphery of a 10 inch record; decreasingto about 3 /2 inch ounces at the innerportion of the record;

The play-back'loadas' above pointed out; however, was measured in fractions of an inch 'ounce. The speed variation is of a two-fold nature. It is'primarily a slippagefactor and to: a lesser extent-a'variation in motor speed; In the drive from the motor shaft to the turntable flange, there exists a changing phenomenon of-transmission efliciency which is a function of the load on the turntable. As the load on the turntable increases, theefiiciency of the drive; drops; this is termeds1ippage.--. 1

If the slippage were to remainconstant; then allowance would be made-in pulley sizes and other permanent adjustments. :Butthe slippage is greater with a heavy load; as in-cuttingthe outside diameter of arecord, than it is during.

play-back. l I

The use of mynovel compensator, in addition to compensating for slippage,-can and does com pensate for variationinmotor speed. It thus becomes possible'to us va :motor about one-fourth.

the size and weightjofthermotorpreviously used without the compensator at a saving of half the costof the motor, thus more-than payingv forthe addition of the compensator. I I s r It was found thatthe difference in speed .between record cutting and play-back was such that the playback.operation. occurred-,at a sufficiently higher speed to create anoticeable-change in pitch, This was particularly so at the periphary of a record where the cutting load was greatest. The only method-previously available was to apply a synthetic load during play-back in an attempt to make up for theload difference :between cutting and play-back. Of course; by making the parts-extremely heavy with relation to the load, the variations in'the load might be reduced, but the recorder would no-longer be a simple home unit. t I Applying an additional load during play-back simply amounted to decreasing the efficiency of operation; and also arranging speedshift mechanism to change'from ;one fixed gear ratio to another fixed gear ratio when shifting fromcutting to playback would tend to add'unnec essary complexity, increase the expenseof the device.

Neitherflthe additional synthetic load'nor. the change-over between two gear. ratios would com pensjate for; the varying load during cutting; but would compensate only forjan average cutting load. a. V M 4. I My invention is directed toward the incorporation in the drivezbetwe'en th motorv'and the turntable of an automatic speed compensator responv sive to the torque on the-turntable automatically to controlthe final speedof the-turntable A Essentially .my speed; compensator; 1 so arries another idler keyed thereto.

ranged that on an increase in torque demand tending to slow down the turntable, the driving ratio between the motor and the turntable is changed in accordance with the torque to increase the relative speed of the turntable with respect to the motor and thus compensate for the tendency to go at a slower speed owing to increased torque demand.

Similarly, my device is so arranged that when there is a decrease in torque on the turntable tending to permit the motor to drive the turntable more rapidly, the ratio of the drive from the motor to the turntable is automatically changed to a degree exactly corresponding to the decrease in torque so that the speed of the turntable relative to the motor is decreased. Thus changes in slippage as above defined and changes in motor speed are automatically compensated to produce a constant speed.

Essentially the motor armature carries a conical shaft which drives an idler wheel, which in turn is vertically slidable on a shaft which car- The conical shaft drives the first idler and the first idler drives the shaft of the second idler which in turn drives the turntable. The first idler is supported on the shaft of the second idler by a compression spring at a positionwhere it registers with the smallest diameter of the cone and thus where the driving ratio is such as to produce the basic no-load turntable speed. or the exact speed required for both cutting and play-back.

As the torque'on the turntable increases, the first idler is'correspondingly driven down against the compression of the spring to a point where the increased compression-of the spring counterbalances the increased torque. The sprin .is selected so that, for the height of the conical drive shaft, the driving ratio between the motor shaft and the turntable when the idler is in equilibrium produces a constant turntable speed, compensating for the drive slippage-and slowing of the motor under the load.

Thus, as the torque varies, the first idler shifts up and down always reaching a point of equilibrium between torque and spring at a point where its contact with the cone changes the gear ratio to maintain the constant basic speed.

The variations which must be compensated for are relatively small. Thus, where the turntable is designed" to rotate at '78 R. P. M. a variation plus or minus 1 or 2 R. P. M. will produce a noticeable change in pitch. It has been found that without any compensator, the variation in load between the extreme 14 inch ounce load at the outer periphery of a record being cut and no load at all did not produce a difference of much more than 2 to 4 R. in a turntable a turntable in a recording device so that the turntable will rotate ,at the same speed whena record is being cut as when the record is beingpl'ayed back. j

Another object of my invention is a provision of novel speed compensating means for the turntable of asound recording device wherein the torque on the turntable automatically varies the driving ratios between the motor and the turntable in accordance with the load on the turn table in order to maintain constant speed.

The foregoing andmany other objects of my invention will become apparent in the following description and drawings in which Figure 1 is a top view, partially broken away,

showing my recorder and its compensating deshowing a detail of the device.

Referring now to Figures 1, 2 and 3, my novel home recording device and compensator comprises a base plate l0, to theunderside of'which is secured the motor H by means of the bracket l2 on plate |2a. Plate |2a is secured by bolts I21) and grommets |2c to base plate Ill. The grommetmount for the motor, permits the motor itself to yield as ,a wh'olej in'the' event'of any power surge and thereby avoid a f" wow;" this" mounting follows the principles ofPatent No. 2,351,948.: Motor sharp e is" provided with a conical pulley l 4. I Pulleylli drives'the first idler I5. Idler I5 is 'slidable on shaft 16 and is rotatably mounted with respect thereto; but idler |5 drivesrthe shaft lfi by the cam surfaces l8 thereof which engage the pin I!) which extends throughthe sh'aft|6. I I 2 Shaft I6 carries the "id1er"20 keyed thereto. Idler 20 is in engagement with and drives the flange 2| of turntable '22.. Turntable 22 is rotatably mounted on'the spindle 23 which is carried by the base plate l0, saidturntable 22 and spindle 23 being preferably recessed in a well 25 formed in the mounting plate. 10. i

The pick-up arm126 ispivotally mounted at 21 on base plate H] and carries astylus at the-end 28 which may engage a record 30 mounted on the turntable 22. Cutting arm 3| is pivotally mounted at the end 32 and isprovided with a stylus at the end 33 which'may also engage the record 30.

As shown in Patent No. 2,351,948, the cutting arm 3| is driven from the spindle 23 in accordance with the rotation of the turntable 22. The specific operation of the cutting arm 3| need not be described here since it isthe same asthat shown in the said Patent .No., 2,'351,948. The shaft ts is rotatably supported in bearings 4|, 42 in the U-shaped bracket 40. Bracket is in turn pivotally mounted on thepost 43 which passes through appropriate openings in the top and bottom of, the bracket 40, said post being carried by the arm 44 which in turn is carried by bolt- 45 secured to theunderside of the base plate'lfL f. 1

Thebrack'et 40 is pivotal on the post 43. Arm 44 is pivotally mounted on bolt 45 to permit the tension spring hereinafter described to move the idlers into engagement with the cone l4 and turntable flange 2|. 1

The bracket 40 and the idlers .20 and I operate in the keyhole slot 41 in'the base plate.

Tension spring 50 is secured to the vertical portion 5I of the bracket 40 and biases the bracket 40 and hence the idlers I5 andZIl into engagement respectively with the cone I 4 and .theturntable flange 2|. I

As will be seen, especially from Figures 2 and. 4, in order to maintain the idler shaft IB vertically, the cone I4 must be tipped so that-the side thereof facing the idler may be vertical; In order to obtain this result the entire motor mounting bracket I2 is so arranged that the whole'motor II, together-with the cone I4, is mounted at an angle to the vertical so that the "side of the cone adjacent the idler I5 may always be vertical. 1

Thus idler I5 may move up anddown on the vertical shaft I6 and still remain in contact with the cone I4 at every position of idler I5. vertical position of idler I5 with respect to the cone I4 will of course, determine the ratio between cone I4 and idler I5.

When now the phonograph is operated, motor II drives the cone I4 which" drives idler I5. Idler I5 which is freely rotatable and slidable on shaft I6 drives the pin'I9 through cammed surfaces I8 on collar 68 of idler I5. Pin I9 thus turns the shaft I6 which carries the idler 20 in engagement with the turntable flanges M and drives the turntable 22. The pin I9 as shown in Figure 5 passes through a hole 64 in the shaft I6, the hole 64 being sufficiently large to permit pin I9 to wobble a bit without binding. Pin I9 is also prevented from slipping out of the hole 64 by the bushings 66 mounted on either side thereof. f

The cammed surface I8 on'each side of idler I5 is provided in the collar .68 of idler I5 and the driving direction is indicated by the arrow III of Figure 2. It will thus be seen -that as the the decreased slippageiand the entire system; in-

cluding the motor,-wi1l tend to rotatemore rapidly due to the decreased torque on the motor, both of these elements tending to cause increased speed of the turntable and of the entire system are immediately compensated for by the shifting of idler I5 to a point where the changed torque is again counterbalanced by the spring 60 to maintain the constant speed. Lock nut I52 (Figures 5 and 6) holds the spring60 at-the proper adjustment. After the machine isbuilt, by the use of a stroboscopic disc, the free speed can be set at the precise level by turning-thenut up or down on the shaft.

Thus my novel device operates as a speed compensator rather than aspeed governor, being immediately responsive to variations in torque to adjust the relative speed'of the turntable and motor so as to maintain the turntable speed constant even though the motor speed varies.

I have tested my novel device withfa stroboscopic disc in order to determine that the turn- Y table speed is maintained constant even though the load may vary and have actually found that this is so. Thus, in one experiment I placed a 10 inch record disc on the .turntable and placed a 6 inch stroboscopic disc over the record disc. All of the elements were adjusted so that with no :load on the turntable other than the record disc and thestroboscopic disc above it, the stroboscopic disc was apparently stationary at the 78.26 R. P. M. ring. I then placed the cutting arm at the outer periphery'of the 10 inch'record disc.

cone I4 drives idler I5, there is a tendency for i the cammed surfaces I8 to slip down under the pin I9, moving idler I5 down., This. is'resisted by the compression spring 60.

As the torque increases, however, the spring 60- permits the cammed surfaces I8 to slip down somewhat under the pin I 9 to the position shown in Figure 2. This has caused idler I5 to be pushed down and this downward force is counterbalanced by the compression of the spring 60.

As the load increasesresulting in added torque,

the increased slippage in the driving, elements turntable, thus tending to cause the turntable to rotate at the speed whichis less than the required constant speed. This too is compensated'for by the changed position of idler I5 with respectto cone I4 to produce a greater relative speed between idler I5 and cone I4 for-the sole purpose ofmaintainirlg the constant: speed of the turntable. Likewise, when the load decreases reducing the torque and hence reducing the degree to which the motor is slowed down. the turntable first would tend to rotate relatively more rapidly For from one to two seconds after the cutting arm was placed on the outer edge of the 10 inch disc, there was slight movement of the 78.26 RJP. M. ring, but thisymovement'halted within two sec onds. Withthe turntable rotating'and a record being'cut, the 78.26 R. P. M. ringof thestroboscopic disc remained stationary. Then atthe end of slightly more than one minute with approximately one inch of the record having been cut,

the cutting arm was lifted. Again there was a slight'movement of the 78.26 R. P. M. ring on the disc and this ring again became apparently stationary within two seconds. I I then placed. the

play-back arm on the cut groove. This resulted in no perceptible movement of the 78.26 R. P. M. ring; nor did the removal of the play-back arm.

This contrasts with prior experiments where no speed compensator was used wherein the placement of the cutting arm on the outer periphery of the record'disc caused the. originally apparently stationary ring of the stroboscopic disc tobegin to move-in a vregular unchanging manner until the cutting arm was removed.

The one or two seconds required for the turntable to adjust itself during this experiment was due to the fact that the. load was shifted from zero load to 14 ounce drag without any intermediate shifting. Accordingly it was necessary for the idler I5 to movefrom the top of cone I.4.all the way down to the bottom of the cone I4 and this required a second or twoa 1 The principalpoint is that during the recording itself, the speed remained constant and did not vary from the-no loadspeed or from the speed ofplaybacle Actually during a; home recording operation, the outtingarm-is placedon the record disc and the record disc is rotated for from one to three revolutions before actual voice recording begins. Similarly at the end of the record when the cutting arm. is lifted, the pla y-back arm is. cusafterwards since it 'is necessary for the cutting arm to be removed and a switch to be operated to de-energiz'e the cutting arm and energize 'the pick-up. Consequently the'few seconds required for automatic adjustment from no load to full load and back again does not at all interfere with operation. 1

In actual operation the grommeted mounting of the motor as described in Patent No; 2,351,948 will take care of instantaneous loads which would otherwise result wows." The resilient mounting of the cutting stylus and the playback stylus will permit momentary irregularities in the record to be compensated for.

My novel device compensates primarily for the continuous difference in load between cutting and play back and also compensates for the steadily changing difierence in load between cutting 'at the outer periphery of the record and cutting at the inner portion of the record. c

Accordingly my novel compensator maintains predetermined correct speed of the turntable, and

the record cut on a home recorder embodying my novel device can be played back thereon at the same speed without an intervention by the operator and without any intervention by the operator and without any adjustment'of any elements by him. i g

Accordingly the naturalness and clarity of the recording is preserved and the entire recording operation is balanced and-effective so that the same result'may be achieved with the simple in"- expensive home recording device as has heretofore been possible only on heavy and expensive commercial record makingoutfits. l

In'the foregoing I have described my invention solely in connection with a preferred-illustrative embodiment thereof. Since many variations and modifications of my invention should nowbe obvious to those skilled in the art, 'I prefer to be bound not by the specific disclosures herein but by the appended claims;

I claim: I a H '1. In a sound recording unit arranged to cut and play back records; a motor; a turntablea positive driving connection between said motor and turntable; speed compensating means in said positive driving connection responsive to vari-- ations in torque for maintaining the turntable at constant speed when id1ing,'when subject to'the play-back load and when subject to the cutting load; said speed compensating means comprising a conical driving memberya driven member en=- gaging the surface of said conical driving member; means biasing said driven member to a'posif tion where it engages a smaller diameter of the conical driving member and means responsive to increase in torque for moving said driven member to engage a larger diameter of the cone; said driven member being moved bysaid last mentioned means against said biasing means to a point of equilibrium'betw'een the torque and the biasing means; said biasing means being en abled on decrease of torque to move said driven member to engage a smaller diameter ofsaid conical driving means at another point of equilibriumbetween the torqueand; said f biasing means; said driven member being freely mounted on a shaft in driving relation with said turntable; saidbefore mentioned means responsive to increase in'torque comprising a cam connection betweensaidshaft and said driven member; said biasing means maintaining said driven member'in engagement with said cam connection; said cam 8 connection moving said driven member against the force of said'biasing -means on" increase in torque. W

2. In a sound'recording unit arrang'd'to cut and play back records; a motor; a turntable; a positive driving connection between said motor and turntable; speed compensating meansin said positive driving connection responsivieifto variations in torque for maintaining the "turntable at constant speed when (idling, when 'subject tol the play-back load 'and'whensubiect to the cutting load; said speed compensating-means comprising a conical driving member a-driven membei en gaging the surfacei'of said conical driving member; meansibiasing said= driven member to a position where it engages a smaller diametercf the conical driving member and meansresponsive to increaseinstorque for, moving said'driven member to engage a larger diameterof the cone, said driven member being moved bysa'id last mentioned meansagainst said biasingmean's to a point of equilibrium between the torque and the biasing means; said biasing means being enabled on decrease-of torqueto move said-,d-riVen memiher to engageaismaller diameter; ofsaid conical driving means at another 'point of equilibrium between the torque and said biasing means; said driven member being freelymounted on a shaft in driving 'relation-ywith said turntable; said before mentioned. means responsive to increase in torque comprisinga cam connection between-said shaft and said driven member; "said bias means maintaining said driven-memberinsengagement with said camconnection; -s'aid cam-connection moving said drivenmember againstthe force of said biasing means on increase in torqueysaid biasing means moving said driven memberto change its position omits shaft and with respect to its cam connection on decrease i i-torque, the axis of said conical driving-means 'beinginclined ctdthatcof the shaft at an angleeq ual to half the apical angle of the cone; :the sidev of said cone .in engagement with the driven member being parallel to the axis of the shaft.

3. In a sound recording unit arranged to cut and-play back records; a'motor, a-turntable,--a driving "connection between [said motor turntable; speed compensatingmeans in said driving connection responsive lto riations intorque-for maintaining the turntabl tv'constant speed when idling, when subjefitto the play -backiload and when subjectto the cutting load; said. speed compensating means comprisinga conical driving memberflrigidly 'connectedto said, motor; a driven memberengaging the surface of saidconical driving member; means biasing said driven member to a position where it engages a smaller diameter of the.v conical driving member and meansrespons'ive to increase in torque for moving said driven member'to engageia larger diameter of the cone, c saild driven member being moved by said last mentioned means ,against .said biasing means to al oint of equilibrium between the torque.an d thelbiasing means; said biasing means being enabled ondecrease of torque to move said driven member to engage a smaller diameter of said conical driving means at anotherpoint of equilibrium between the torque and said biasing means;-said.drivenmemberibeing-freelyimounted on g shaft in positive driving-relation with said turntable said- ;before mentioned 9 "means *r'e' sponsive to increas'e in 'torquepomprising a 'cani connection between: said shaft and said driven member; said biasing means amiss-sai driven member 'ineng-agement with said cai'n connection; said cam connection moving said driven member against the force of said biasing means on increase in torque; said biasing means moving said driven member to change its position on its shaft and with respect to its cam connec- 5 tion on decrease in torque, said cam connection Number comprising a collar carried by said driven member 942,910 surrounding said shaft; a cam surface on said 1,391,707 collar extending at an acute angle to the axis of 2,244,120

said shaft; a transverse pin on said shaft en- 10 2,312,793 gaging said cam surface.

ROBERT M. CAIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Keller Dec. 14, 1909 Viviand Sept. 27, 1921 Schneider June 3, 1941 Carrington Mar. 2, 1943

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