US2664293A - Drive construction for phonographs or the like - Google Patents

Description

Dec. 29, 1953 's. YERKOVICH DRIVE CONSTRUCTION FOR PHONOGliAPHS OR THE LIKE Filed Aug. 30, 1949 4 Sheets-Sheet 1 INVENTOR Smou Yeax vmu I ATTo N S Dec. 29, 1953 YERKOVICH 2,664,293

DRIVE CONSTRUCTION FOR PHONOGRAPHS .OR THE LIKE Filed Aug. 30, 1949 I 4 Sheets-Sheet 2 INVENTOR sl YERKOVICH M.Wi Jafhd ATTO NEYS Dec.

Filed s. YERKOVICH 2,664,293

DRIVE CONSTRUCTION FOR PHONOGRAPHS OR THE LIKE Aug. 50, 1949 4 Sheets-Sheet .5

'04 -i00 W//////////////I Dec. 29, 1953 s. YERKOVICH DRIVE CONSTRUCTION FOR PHONOGRAPHS OR THE LIKE 4 Sheets-Sheet 4 Filed Aug. 30, 1949 u|,l|l|IlllllllllllllIlllllllllllllllllllll! HHF I I I IHU S. U NW m 5 0 V m. 7 WYWM W m 5 surface of the recording belt. [in the recording head is enabled to impress a Patented Dec. 29, 1953 ersNr OFFICE DRIVE CONSTRUCTION FOR PHONO- GRAPHS OR THE LIKE Simon Yerkovich, Los Angeles, Calif., assignor to Dictaphone Corporation, Bridgeport, Conn., a

corporation of New York Application August 30, 1948, Serial No. 46,747

1 Claim.

This invention is described in relation to variable speed sound reproducing equipment and in such equipment more particularly to a commercially practicable backspacing construction by which the sound reproducing element may quickly and automatically be caused to assume a position from which to'repeat a predetermined amount of the recording being reproduced. Recording and reproducing equipment generally is well known and has commonly been used by typists and the like while making Written transcriptions of recorded material. Sometimes while making such transcriptions it becomes necessary to have repeated a brief portion of the recording. I am aware that various backspacing mechanisms for accomplishing such repetitions have heretofore been offered. I have devised a novel power transmitting construction which is ideallysuited to rapid performance of intermittently desired backspacing operations I and which is readily adaptable to other applications which Will suggest themselves to those skilled in the art of mechanical power supply and transfer.

In United States Patent No. 2,318,828 to Yerkbvioh and No. 2,371,116 to Yerkovioh et a1. there described certain generally similar machines capable of recording on an endless belt of paper thin pliable plastic material and of reproducing the recordings made on such belts. During recording, one of these belts is stretched between a pair of: pulleys, or mandrels, each of a diameter of about 2 in. in the illustrative embodiments, mounted for rotation about substantially parallel, horizontally disposed axes spaced about 2% in. apart. known as a drive mandrel; the other is free to rotate about its axis and is known as an idler mandrel. lThe idler mandrel is yieldably mounted so as to hold the recording belt under a small amount of tension against thesurface of the drive mandrel.

In the above-mentioned Yerkovich et a1. patent the mandrel axesof rotation are disposed in substantially the same horizontal plane. A sound recording head and a sound reproducing head are independently associated with the mandrels formovement through independent paths, parallel to the axes of the mandrels and transversely with respect to the path followed by the Thus a stylus held sound groove ontothe moving belt. And as the belt moves, the recording head is moved transve'rsely at a low constant speed across the surnew: the 'beltso that the groove begins .at one One of the two mandrels is driven and is side edge of the belt and proceeds around and around the belt and finally ends at the other side edge of the belt. The speed ratios, between linear velocity of a point on the surface of the belt and linear velocity of the recording head as it travels transversely with respect to the movement of the belt, are such that the belt makes 20o complete revolutions while the stylus moves transversely a distance of one inch. Thus the sur face of the recording belt, after a sound groove has been impressed upon it, bears a succession of closely spaced loops the distance from the. bottom of one groove trough to the bottom of the next adjacent groove trough being approximately .005 in. It is apparent, of course, that the closer the spacing of the loops of the sound groove the greater the number of loops that may be contained on a belt of a given size and accordingly the greater the amount of recorded material that may be impressed upon that belt. Mechanical complications and the finite width of the sound groove per se set a practical limit upon the closeness of adjacent loops.

In the embodiment disclosed in the Yerkovich patent the linear velocity of apo nt on the recording belt during normal reproducing is disclosed as being on the order of '20 feet per minute. Thus, in ordinary usage. when the auditor who is listening to the recording misses a word or a phrase, she probably will not want a greater amount repeated than is contained in a single s und groove loop on the recordin belt. And if the auditor ba kspaces the reproducing head with respect to the surface of the recording belt a distance, for example, of as much as of an inch it results that she has backspaced a matter of ten sound groove loops, which is surely verv much more than she wants repeated. An error in backspacing movement of as much as A in. will result in a repetition of twice as much as the auditor intends.

Another complication is introduced by the fact that these machines are commonly used to record a message at a point of origin, to relay the message over a communication channel to a point of destination and there to rerecord the message and repeat it to a transcriber or auditor. For coding purposes, and to make the most efiicient use of the communication channel, it is the regular practice to transmit the recorded material over the channel at a rate several times greater than that at which the recording was made. In order to accomplish such transmission the machines are equipped with variable speed motors having a range on the order of 10:1. Thus, a

conversation or message recorded at a rate of 150 words per minute might be transmitted at a rate of 1000 words per minute. And the machine at the point of destination must be capable of rerecording at such higher rate and reproducing for transcribing purposes at a rate even below that of the original.

It is obvious that where backspacing accuracy must be in terms of a few thousandths of an inch, the speeds of movement of the parts must be below certain limits or their inertia will introduce such variancies as to render the mechanism undependable. And if the structure is designed for efiicient operation at the higher motor speeds, a disproportionate period of time will be consumed by each operation when the motor is running at lower speeds. Thus, whereas a backspacing operation completed in one half a second might be wholly satisfactory to a typist,

a delay of even two seconds-only a 4:1 reduction in motor speed-might after a period of transcribing become an excessive annoyance. A reduction on the order of 4:1 for transcribing would not be unusual in the routine conduct of business quite apart from the channel transmission capabilities of the equipment.

Accordingly it will be understood that a satisfactory backspacing mechanism for a modern machine such as referred to not only must accurately backspace within a few thousandths of an inch but it must perform its function without appreciable passage of time regardless of the speed setting of the main motor or drive mandrel.

Various mechanisms have been suggested and tried in the past for effecting automatic backspacing under such circumstances. I have devised a slippable coupling construction which will cooperate with related assemblies to move the reproducing head backwardly with respect i to the recording belt a distance of .005 in., or whatever distance may be required for a given machine, and which facilitates completing each operation in a negligible time regardless of the number of revolutions per minute being turned by the variable speed drive motor.

I shall describe my invention as it may be applied to a reproducing machine of the general type disclosed in the Yerkovich et al. patent. Accordingly, in my illustrative embodiment, backspacing of one sound groove will require a transverse movement of the reproducing head equal to the spacing between adjacent sound groove loops where there are two hundred loops to the inch. It is to be noted that the illustra tive embodiment of the Yerkovich et al. patent is a recorder-reproducer; for simplicity and to avoid repetition the machine which I have selected to exemplify my invention is a reproducer only. Machines which will be used only for reproducing omit those parts which are required only for recording.

It is an object of my invention to provide a device of the character described having to a notable extent the characteristics and capabilities set forth. Another object is to produce a commercially practicable component useful in a backspacing mechanism which facilitates backspacing upon demand independently of the condition of the main motor drive. A further objective is the provision of a backspacing structure which is both feasible in manufacture and foolproof in operation and which will consistently give the desired extent of backspacing. A further object is to provide a novel sort of gear train mechanism which is useful in turning a shaft through a given angle upon demand. Other objectives will be in part pointed out as the description proceeds and will in part become apparent therefrom.

The invention accordingly consists in the features of construction, combinations of elements, methods of operation, and arrangements of parts as will be exemplified in the structure and sequences and groups of related steps to be hereinafter described and the scope of the application of which will be set forth in the accompanying claims.

In this specification and the accompanying drawings I have shown and described a preferred embodiment of my invention and suggested various modifications thereof; but it is to be understood that these are not intended to be exhaustive nor limiting of the invention but, on the contrary, are given for purposes of illustration in order that others skilled in the art may fully understand the invention and the principles thereof and the manner of applying it in various forms, each as may be best suited to the conditions of a particular use.

In the drawings: Figure 1 is a rear elevation (taken along the line l-l of Figure 2) of a sound reproducing machine of the type disclosed in the Yerkovich et al. patent and in which my invention has been incorporated;

Figure 2 is a plan view (taken along the line 22 of Figure 1) of the machine;

Figure 3 is a sectional end view taken along the line 33 of Figure 1;

Figure 4 is a fragmentary view on an enlarged scale of a friction clutch assembly illustrating one form of the invention employed in the machine;

Figure 5 is a fragmentary view on an enlarged. scale of a mutilated gear assembly used in the illustrative form;

Figure 6 is a sectional view taken along the line 66 of Figure 5;

Figure '7 is a fragmentary view taken along the line 1'I of Figure 1 showing a part of the backspacing gearing and related mechanisms:

Figure 8 is a sectional view taken along the line 88 of Figure '7;

Figure 9 is a fragmentary sectional view taken on an enlarged scale along the line 9-9 of Figure 1; and

Figure 10 is a diagrammatic representation of certain of the electrical circuits and some of the parts related thereto.

The machine shown in Figure 1 includes a machine frame 20, which may take the form of a metal casting, and which includes a supporting plate 22 rising from its right-hand end (see Figure 1) and a supporting plate 24 rising from its left-hand end. A relatively heavy fly wheel 26 is disposed in a substantially vertical-plane at one end of the machine for rotation about a horizontal axis. Fly wheel 26 is driven by a pair of belts 28 from a variable speed motor. For a more complete disclosure of the motor arrangement and of other conventional aspects of the present embodiment not otherwise detailed herein reference should be made to the disclosure of Yerkovich et al., Patent No. 2,371,116

The fly wheel is mounted upon a fly wheel shaft 30 (see Figure 1) journaled in supporting plate 22 and carried by the machine frame. Drive mandrel 32 is turned by means of fly wheel shaft 30; since the motor which drives the fly wheel is of the variable speed type the rate at which the drive mandrel is turned is variable in accordance with the motor speed. Ordinarily a constant speed is used throughout any one recording, variations in .speed being employed for transcribing purposes to pace the rate of reproduction to the optimum capacity of the typisft .or auditors idler mandrel 34 .(see also Figure 2) is disposed 'for free rotation about an axis parallel to the axis ofrotation of drive mandrel '32. A recording belt 36 is placed around and stretched by .the mandrels and as drive mandrel '32 is rotated, thebelt, which is held against the drive mandrel by the yieldable mounting of the idler mandrel, is driven and transfers rotation from the drive mandrel to the idler mandrel while it .is .held smoothly taut.

A reproducing carriage 3.8 is disposed above the drive mandrel for transverse movement with respect to the path through which the belt moves. The reproducing carriage is slidable upon ,a horizontally disposed carriage guide rod 48 (see Figures '.1 and 23 held between supporting plates 22 and 24. The carriage is caused to slide along the carriage guide rod by a feed screw 132 (see Fi ure 1) positioned in conventional manner within the uide rod. The axis of the feed screw is substantially coextensive with the axis of the carriage guide rod, A feed nut, not shown but held within the carriage, meshes constantly with the feed Iscrew so that rotation of the screw advances or backspaces the carriage with respect to the recording belt depending upon the direction of rotation of the reed screw,

In normal transcribing the feed screw is driven from the fly wheel shaft by a gear train mechanism, to be described. Feed screw 42 is identical to the feed screw used with therecording carriage. Hence the reproducing carriage is advanced across the moving belt ata rate which makes it possible for the reproducing stylus to follow exactly the soundgroove which was embossed in the belt by the recording stylus. In the described embodiment the feed screw is rotated through 120 degrees while the recording belt is making one revolution. Accordingly, in order to backspace one sound groove, the feed screw will have to be reversed through an angle of 120 degrees.

As shown in Figure 3, fly wheel shaft 30 drives a fly wheel gear it held in mesh with an intermediate gear lfi on an intermediate shaft 48. Gear dB is maintained in meshing relationship with a second intermediate gear til which turns a pinion 52 constantly meshed with a feed screw gear 54. The effect of this gear train is to reduce the number of revolutions made by the feed screw gear as compared to the number of revolutions made by the fly wheel shaft.

In accordance with my invention the drive relationship between feed screw gear 54 and feed screw 42 is not positive. As shown in Figure 4, feed screw gear 54 has secured to its inner face an annular rim 56. This rim may be removed, if need be, by unscrewing machine screws 58. A drive fiangedu is keyed in driving relationship to feed screw 42; feed screw gear 54 is freely rotatable upon a hub 62 of drive flange 6%). Feed screw gear 5:; is held in position upon hub 62 by rim dfirwhioh overlaps peripheral portions d-i' of flange 66. Feed screw gear so may be removed by removing machine-screws 58 so that the'gear can be separated from annular rim iii. A spider spring til (see also Figure 3) is also 'rotatably positioned on hub 62 and is normally compressed between the opposing faces of the inside ol'gear L54 andthe ouslde of flange Bil. Thus the spider spring tends to push gear 54 axially ofi of hub 52 but rim "56 prevents any separation more than that shown in Figure 4. Accordingly, feed screw gear Ed is held relatively firmly with respect to fiange BB and ordinarily the driving force impartedto feed screw gear 54 by pinion 52 is transterred through flange Bil to the feed screw to cause operative rotation thereof. The feed screw is mounted .for .ro'tation'in a feed screw bearing .63 supported within .a bearing bushing l0 conventionally held within carriage guide rod Aid. The carriageguide rod, as pointed'out previously, is nomtotatably fixed between supporting plates 22 and 24- In the present embodiment there is provided, as disclosed in Figure 3, a small self-starting motor '52 (see also Figures 1 and 8); this motor I use, as will'be described, to effect reverse rotation of the feed screw. The motor (see Figure '2) drives a spur gear l4 mounted upon a motor countershait l6 which drives a bevel gear is held in meshing relationship with a bevel gear $3 which gear in turn'is locked to and drives a shaft 82 (see also Figure 3). A gear 84 driven by shaft 82 is in mesh with and drives an intermediate gear 8&3 which in turn meshes with and drives a spur gear 33 (see Figure 6). A mutilated gear a part of which is broken away in Figure 3 to showgear B8 juxtaposed therebehind) is disposed coaxially with respect to gear '88 and is rotated thereby.

Mutilated gear 911 is arranged to mesh with an intermediate gear 92 which gear is in mesh with a backspacing gear 94 solidly secured to flange 69 (see also Figure 4). During ordinary operation of the transcribing equipment a mutilated portion of gear 96, .as will be described, faces gear 92 so that there is no driving relationship therebetween and accordingly feed screw 42 is driven through the friction clutch between gear 54 and flange 60.. However, when it is sought to effect a backspacing operation, the small electric motor 12 is energized, as Will be described, and the train of gears including members i l, 18, 80, 84, 85 and 88 comes into operation to move mutilated gear 99 into meshing relationship with gear 92 to cause reverse rotation of backspacing gear 94. During thereverse movement of gear 54 the main machine motor continues to drive the iiy wheel and accordingly a slipping occurs betweenfiange 60 (nowmoved by gear 94) and gear 54 (driven from the fly wheel). The energizationof motor 12 is of limited and predetermined duration, as will be developed hereinafter, so that the reverse movement of backspace gear 94 extends through degrees. As will be described, gear 92 is then again unmeshed from mutilated gear 90.

It is to be observed that the fly wheel turns at its ordinary speed whether a backspacing operation is occurring or not and accordingly the train of gears which ordinarily drives the feed screw continues to operate at itsnormal rate of speed. When a backspacing operation is called for, how ever, the drive is broken at the frictional coupling and the backspacing mechanism takes precedence as it meshes with moving gear 92 to effect the intended backspacing operation.

Because normal fly wheel operation is uninterrupted some provision must be made for enabling the backspacing mechanism to be meshed into the drive to the feed screw. Since there is no interruption of the main motor, it is obvious that "ordinary gearing, Geneva mechanisms, and

the like would jam unless the engaging. parts happened by chance to fall into mesh. It is equally evident that the backspacing movement must be of a measured amount which can invariably be imposed at will upon the normal drive and which will be independent of the speed adjustment at which the normal drive is running. As disclosed and claimed in the application of Charles L. Bossmeyer, Serial No. 773,823, filed September 13, 1947, the mutilated gear may be made to mesh properly with gear 92 each time power is supplied to the backspacer motor by providing the mutilated gear with a flexible feeler 95 which is clamped in place by a clamp screw 98 on the peripheral portions of gear 9%. The feeler is formed in the present embodiment from stiff wire similar to piano wire and has a cross sectional diameter which is approximately equal to the chordal thickness of one of the teeth of the mutilated gear. The feeler is provided at its outer end portion with a detent I38 (see Figure 6) formed by a right angle bend in the wire. The axis of this detent is substantially parallel to the axis of rotation of the gear. The feeler is so adjusted and held in place by clamp screw 98 that detent Iilii occupies approximately the region in space that would be occupied by the working part of a tooth of gear 98 if there were another tooth beyond tooth I02. Actually, the detent is adjusted so as to extend slightly beyond the outside diameter of the toothed portion of the mutilated gear. In addition, the detent is spaced from tooth I82 slightly more than the normal spacing between two adjacent gear teeth. The location shown of clamp screw 98 with respect to tooth I02 and the configuration of feeler 96 are such that as the mutilated gear rotates toward meshing relationship with gear 82, the first contact made is between detent I06 and some tooth portion of gear 82. With the arrangement shown, the inherent flexibility of feeler 96 is such that even if the detent should in the first instance be squarely abutted against an outer end of a tooth, the detent will yield inwardly toward the center of the mutilated gear and, as the approaching gears tend to move at different peripheral rates, will find its way into the solid line position illustrated in Figure 6 between two of the teeth of gear 92. When the detent assumes the location illustrated, gears 93 and 92 are oriented so that the rigid teeth will mesh perfectly. Thus, no matter what the angular relationships between and peripheral speeds of the unmeshed gears may be, when a driving force of rotation is applied to the mutilated gear; ieeler 38 and detent I automatically align the teeth of gears 90 and 82 so that they are brought into proper mesh. Gear 90 is relieved by a clearance groove I04 across its edge into which the detent may upon occasion enter.

When a backspacing operation is called for, the feed screw must be turned backwardly rapidly through 120 degrees. Hence, gear $2 must be rotated through a finite number of degrees and to do this there must be a certain number of teeth in the toothed portion of. the mutilated gear in order that gear 92 shall be turned through the correct angle. In the embodiment here described (see Figure 3) the mutilated gear is pro: vided with two toothed portions, each' portion having ten teeth, and each portion is provided with an advance feeler 96 carrying a detent Iilii. The detent serves as an additional tooth, making eleven operative teeth on each side of the gear. And the mutilated gear must be turned through degrees.

180 degrees to bring the eleven effective teeth of one of its toothed portions into and out of mesh with the opposing teeth of gear 92 so as to turn the feed screw backwardly through 120 Thus with a single backspacing operation, eleven teeth of gear 92 are caused to reverse the direction of normally ineffective backspacing gear 94 (see also Figure 4) The friction clutch between feed screw gear 56 and backspacing gear 95 has a damping effect on any overrunning which might otherwise occur from the inertia of the parts so that when the eleven teeth of gear 92 have done their work there is a clean break from the backspacing movement and gear 94 now finds itself displaced backwardly through the friction clutch an accurately measured, predetermined amount. The feed screw also, of course, has been turned back, through the same measured amount. The over-all time cycle required for a complete operation and the amount of feed screw reverse displacement remain constant under all conditions and are accomplished independently of the speed at which the variable speed motor is turning.

The backspacing gear train is such that for one half a revolution of countershaft H5 there follows a one-half revolution by the mutilated gear. One end of countershaft It carries a timing cam Hit (see Figure 8). Cam IE6 is provided with a pair of diametrically spaced dwells I08. During ordinary transcribing operation, a foot IIU. of a normally open short travel limit switch I I2 occupies the space within one of the cam dwells Hi8. When the backspacer motor circuit is closed, however, and countershaft I6 is caused to rotate, therise on cam I06 comes into engagement with foot Ill! and switch I I2 closes a holding circuit which, once closed, remains closed until motor 12 has turned countershaft i6 through 180 degrees again to present a dwell I03 to foot III] so as to enable holding switch II2 to open and die-energize the backspacer motor circuit. Thus, a momentary closing of the backspacer motor circuit suifices to initiate movement of countershaft I6 and thereafter, through the action of holding switch IIZ, the backspacer motor continues automatically to operate the exact length of time required not only to turn countershaft I6 through 180 degrees but also to turn mutilated gear 90 through 180 degrees and accordingly to turn feed screw 42 backwardly through degrees. During such operation of the backspacer motor and by virtue of my frictional coupling the variable speed motor continues to operate in its normal direction. The backspacer motor need not be powerful for it has to overcome only the inertia of a small part of the record drive plus the force required to make the coupling slip. This force can, of course, be kept small; it is substantially less than the inertia force of the remaining parts of the record drive against which the coupling insulates the backspacer motor. As soon as the backspacer motor has caused the feed screw to reverse through 120 degrees ordinary transcribing motion is restored to the feed screw automatically and without pause.

When feed screw 42 is reversed, reproducing carriage 38 is caused to move to the left, as shown in Figure 2, by one sound groove loop. It is desirable that the reproducing stylus which ordinarily'rides in the sound groove be lifted from the surface of the recording medium while the reproducing carriage is being backspaced. The application of Arthur W. Skoog, Serial No. 46,752,

filed August 30, 1948, discloses and claims mechanism which automatically synchronizes with a backspacing operation to lift the stylus of the reproducing carriage off of the surface of the recording medium at the beginning of a backspacing operation and to set it down gently at the end of a backspacing operation.

Gears 88 and 90 are located upon a shaft II 3 (see Figures 2 and 3). This shaft includes an extended portion I It which reaches behind reproducing carriage 38 even when this carriage is in its extreme right-hand position. Portion III; throughout its length behind the path of travel of the reproducer carriage has a non-circular cam-like cross section (see also Figure 9). The reproducer carriage is provided with a bracket H8 (see Figure 9) which includes an opening I20 through which cam-like portion II6 extends. Bracket H8 serves as a pivot support for a bell crank lever I22 (see Figure 9) normally urged by gravity in a counterclockwise direction so that its upper arm I24 bears slidably upon the flat vertical face of portion H6 as the reproducing carriage is moved by the feed screw during normal operation. However, when a backspacing operation is instituted and shaft I I I and its cam-like portion H6 are caused to turn, bell crank lever I22 is caused to rotate through a small angle in a clockwise direction and is there held until portion H6 is turned through 180 degrees. While the bell crank lever is held against gravity in its clockwise position, its other arm I26 is raised somewhat from the position illustrated in Figure 9 and in its raised position it is in lifting contact with the underside of the bottom edge of the transducing cartridge I28 of the reproducing carriage. The stylus is conventionally mounted in this cartridge and is held elevated slightly off the recording medium during the period while bell crank lever I22 occupies its clockwise position. It is during this period that the feed screw is rotated backwardly. This construction obviously raises and lowers the stylus with a smooth, gentle motion which cannot damage the delicate point.

As shown in Figure as, a normally-closed travel limit switch I30 is fixed in position near switch Hz with its switch-throwing button I32 so disposed as to be engaged and actuated by the head of a screw I34 (see Figure 2) mounted in the lefthand race OI the reproducing carriage. 'lhe position of screw I64 with respect to the reproducing carriage may be ad usted and locked by an adjustment nut I30. Thus, when carriage 3u is moved to its most left-hand position at the beginnihg of a reproducing operation, screw I is brought into contact with button I52 so as to open switch I30. With switch I30 open the circuit oi the backspacing motor is open so that a backspacing operation cannot be instituted; switch [so will not close until the re roducing carriage is moved Irom its most left-hand position. in this manner it is made impossible ior the backspacing motor to be energized unless the reproducing carriage is in a position Irom which it may be backspaced without Jamming.

Figure indicates diagrammatically the electrical circuit of the backspacing motor. As here shown, a backspacing operation instituted by momentarily closing a normally open sw tch I36. Ordinarily this switch is arranged I01 loot operation. When switch I38 is closed current flows from a supply line I40 through a branch line I42, switch I38, normally closed safety switch I30, and branch lines I I4 and I46 into motor '52, thence to a branch line I43 and back to main line I50. When switch I 38 is closed motor 12 starts and cam I09 immediately operates to close holding switch II2. Power is then available through branch line I 54 to branch line I46 and thence through the motor and line I 48 to line I50. Thus, when the starting switch is closed, holding switch II2 assures that a complete backspacing operation is accomplished. When the reproducing carriage is moved to its most left-hand position, however, screw I34 comes into contact with button I32 and opens switch I30. As long as switch I30 is open nothing is accomplished by closing switch I38 and so backspacing is prevented until such time as the reproducing carriage is moved to a position from which it may be backspaced without jamming.

From the foregoing it will be seen that a backspacing structure made in accordance with the present invention is well adapted to attain the ends and objects hereinbefore set forth and to be economically manufactured since the several parts and assemblies are suited to common production methods and are susceptible to a wide latitude of variations as may be desirable in adapting the invention to different applications.

As various embodiments may be made of the above invention and as changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

I claim:

In a phonograph transmission system, a rotatably mounted feed screw, a first gear-like unit keyed to said feed screw and having an annular surface, a second gear-like unit freely rotatable upon and axially slidable along said feed screw and having an annular surface opposing said first-mentioned annular surrace, and a spider spring compressed between said units and Irictionaliy engaging said annular surfaces; one of said units including portions interengaging portions of the other unit and holding said units against axial separation by said spring.

SIMON YERKOVICH.

References Cited in the file of this patent UNITED STATES PATENTS

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