US2420671A - Magnetic recorder - Google Patents

Description

MAGNETIC RECORDER Fil ed Oct. 27; 1944 v 2 Sheets-Sheet 1 FIG] - ATTORNEY y 20, '1 9 J. B. LITTLE MAGNETIC RECORDER Filed Oct. 27, 1944 2' Sheets-Sheet 2 FIG. 3

FIG. 4

INVENTOR By J.B.L/TTLE umfi HHIlllllllllllllllllll ATTORNEY Patented May 20, 1947 ll/IAGNETIC RECORDER John B. Little, Summit, N. J'., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application October 27, 1944, Serial No. 560,699

Claims.

This invention relates to magnetic recording and the object of the invention is a very compact recorder of this type which is capable of giving both long playing time and high quality of reproduction.

As is well known, both the playing time and the quality of reproduction obtained with a magnetic recorder are dependent.on the speed .of the wire or tape used as the record member and, other conditions being equal, the normal playing time can be increased only by accepting a corresponding reduction in quality and vice versa. It is also generally recognized that wire must be operated at several times the speed necessary with tape in order to give the same quality of reproduction.

On the other hand, wire may be readily spooled thereby permitting it to be stored in a very compact manner whereas the tapes commonly used heretofore have been reeledin flat coils which are necessarily of large diameter in the case of long play machines. Many attempts have been made to spool these tapes in order to avoid the necessity of using large reels but, insofar as applicant is aware, none of these eiforts has been commercially successful since such tapes always .buckled or warped and could not be spooled so as to lie in smooth regular layers.

According to this invention spooling of tape is effected satisfactorily by using a tape which is much narrower and hence exhibits less tendency to buckle than those commonly used heretofore and spooling this tape by means of a pivoted oscillating tape distributing mechanism'in which the tape is free to twist or deflect in a torsional sense thereby relieving the edgewise stresses which oscillation where it is in offset relation to the reels. The section of tape extending from one spool to the other is pulled through between the. spools to form an offset loop extending around the distributing mechanism between guides which have a substantially right-angle bend adjacent each spool. As the tape is transferred from one spool to the other .by the oscillating action of the distributing mechanism it always approaches the take-up spool at the proper angle to lie in a fiat spiral due to its freedom to twist in the guides on the other side of the bend.

These and other important features are exp'eined in more detail in connection with the drawing in which:

Figs. 1, 2 and 3 are plan, side and end views respectively of a recorder according to the invention; and

Figs. 4 to 6 are detail views of the time spooling mechanism. I

In the'drawing the upper and lower mounting plates l and 2 are secured to a frame 3v carrying a centrally disposed driving motor 4. The tape reels or spools5 and 6 are mounted on shafts 1 and 8 which are connected through suitable speed reduction mechanisms 9, 9 to drive shafts Ill and il. In the structure shown these latter shafts are equidistant from the shaft l2 of the motor so that the drive pulley l3 may be readily placed on either of the shafts H1 or I I and the motor reversed as required to drive the tape in opposite directions for recording and rewinding, respectively.- It will be understood, of course, that this particular form of reversing drive is merely illustrative and may be replaced by any other known mechanism suitable for the purpose.

The record member M is preferably a tape about .020 inch wide and .002 inch thick which is somewhat less than half as wide as the tapes commonly used heretofore.

The tape spooling mechanism comprises essentially a rigid distributor plate [5 mounted on the plate I by means of the shafts l6, l6 and a reversing screw l1 against the upper end of which theplate i5 is held by stifi springs l8, it so that driving contact is maintained with the machine in any position. The tape extends from the spool 5 between the guides 59 and 2!], the polepieces of the talking head magnets 2|, 22,23 and the guides 2t! and 25 to the spool 6. The guides are mounted on a plate member 26 of a thickness only slightly in excess of the tape width and the lower guides 28 and 25 preferably extend beyond the upper guides as shown to facilitate threading of the tape between them. The plate member 26 is secured to the plate l5 with the edge 21 (Fig. 1) extending along the pivot axis defined by the shafts Iii, it so that the portion of the tape passing through the talking head is always on the axis of the distributor plate. The width of the member 26 is somewhat greater than the spacing of the spool shafts l and 8 and the tape is fed axial motion to the screw and when at either end of the screw travel the pawl strikes the reverse pitch portion of the thread it -is thereby rotated in its housing into the proper position for producing the return movement. By proper choice of, the driving gear ratio and the length and pitch of the screw threads the distributor plate I is oscillated about the axis l6, l6 at the proper rate and amplitude to lay the tape evenly on the take-up spool. Some adjustment of the throw of the plate to adapt the machine to the use of spools of different lengths is provided by mounting the screw I! so thatvits distance from the axis of the distributor plate may be varied as required. For this purpose the bearings 36 and 40 are mounted in the arms 4| and 42 which are secured together by the strap 43 extending through slots 44 and 45 in the upper and lower mounting plates I and 2 as shown in Figs. 4and 5. Similar arcuate slots 46 and 41 are provided for the bearings 36 and 40 so that the arms M and 42 may be rotated about the outer surfaces of the bearings 48 and 49 of the pinion 33 and fixed in any desired position in their travel by the set screw 50. In Fig. 4 the screw is shown in its extreme backward position or furthest from the axis l6, Hi to give minimum throw of the plate IE but as the screw supporting structure is rotated in a clockwise sense the screw moves toward the axis to increase'the throw. The contact plate 29 is of sufficient diameter to engage the rounded portion 28 of the screw inany position throughout its range of adjustment and when the throw is correct for the length of the spools used, the upper and lower limits of motion may be adjusted with respect to the ends of the spools by means of the set screw 30.

As already pointed out the tape used with this machine is relatively narrow and this in itself is a large contributing factor in the successful spooling of the tape in regular even layers without buckling or forming deep crevices as in prior machines. It is also found however that by mounting the spools close together and passing the tape from one spool to the other around the distributor plate in an offset loop in the manner shown it is possible to obtain smooth spooling with a very compact structure. With this construction, the edgewise bending stresses in the tape produced by laying the tape on the spools in spiral form are relieved as the tape passes around the 90-degree bend to the straight portion of the guides since any such stresses in the portion of the tape being spooled merely causes the tape to twist slightly in the guides instead of buckling on the spool.

The location of the magnets 2| to 23 on the distributor plate in the line of the pivot axis where they are remote from the spools has several advantages. Since both the magnets and the section of tape involved in the recording and reproducing operations are on the pivot axis their displacement during the spooling operation is very small. For the limited rotary motion which does occur, the tape and magnets move as a unit and such motion does not adversely affect the quality of reproduction. The fact that the magnets remain practically stationary also has the further advantage that the leads to the magnets are not subjected to excessive bending stresses. Due to the fact that a long curved tape guide is interposed between the magnets and each spool, tape vibration at the translating point is substantially eliminated and any longitudinal flutter in the tape tends to vibrate the distributor mechanism, including the magnets, as a unit and hence does not introduce appreciable distortion.

While no amplifier apparatus or circuits have been shown, since they form no part of this invention, it will be understood that in a commercial machine of the type contemplated such apparatus of any suitable known type would be mounted on the underside of the plate I and enclosed with the mechanical structure as a compact unit in a suitable casing.

In one machine according to this invention it was found that 3,000 feet of tape could be stored Y on spools only 2 inches in diameter and 1 inch long. Operating at only 5 feet per second this machine was capable of recording and reproducing over a frequency range up to 30,000 cycles per second for a playing time of 10 minutes. For good quality voice reproduction up to about 5,000 cycles the tape speed may be correspondingly reduced to give a playing time of half an hour.

What is claimed is:

1. In a magnetic recorder, the combination with two reels, a record member on the reels and driving means therefor, a guiding distributor, a sound head mounted thereon, means for conducting the member from one reel to the other through said sound head, said distributor including loop-forming means, a pivot axis for the distributor extending through the sound head and means for oscillating the distributor about the axis to spool the member from one reel to the other. i

2. A recorder, according to claim 1, in which the distributor is oscillated by a reversing screw rotated by the driving means and in which the screw is adjustably mounted with respect to the pivot axis of the distributor to control the amplitude of the distributor oscillations.

3. In a magnetic recorder, two reels mounted in closely spaced relation, a narrow magnetic tape wound on the reels, a tape distributor pivotally mounted for oscillation about an axis in offset relation to the reels, a source of power for rotating the reels and oscillating the distributor to spool the tape from one reel to the other, guides for conducting the portion of the tape between the reels around the distributor and bends in the guides adjacent the spools for relieving stresses produced in the tape by the spooling operation.

4. In 'a recorder, the combination with two reels mounted in closely spaced relation, pivotally mounted distributor mechanism for spooling a-record member from one reel to the other and driving means for the reels, of an oscillating member driven by one of the reels for operating the distributor mechanism and means for adjusting the oscillating member with respect to the pivot mounting to vary the throw of the distributor mechanism.

5. In a magnetic recorder, two reels mounted in closely spaced relation, 2. narrow tape onthe reels, a distributor plate having peripheral guides conducting the tape around a loop offset with respect to the reels, a pivot axis for the plate remote from the reels, magnets mounted on the plate and cooperating with the tape along the pivot axis, driving means for the reels, a pinion driven by one of the reels, a reversing screw driven by the pinion for oscillating the plate and a support for the screw rotatably adjustable with respect to the pinion for varying the amplitude of the plate oscillations. r

6. In a magnetic recorder, two reels in closely spaced relation, a tape on the reels, driving means therefor, an oscillating distributor for spooling the tape from one reel to the other, guides on the distributor for conducting the tape between the reels around an ofisetloop and bends in the guides adjacent the reels for permitting the tape to twist in the guides to relieve the edgewise bending stresses produced in the tape in the spooling operation.

*7. In a magnetic recorder, the combination with two reels, a record member on the reels and driving means therefor, a guiding distributor for feeding said member to and from said reels, said distributor including loop-forming means, a sound head in operative relation to said member at a point in said loop, means for oscillating the distributor to spool the member from one reel to the other.

8. In a magnetic recorder, the combination with two reels, a record member on the reels and driving means therefor, a guiding distributor for feeding'said member to and trom said reels, said distributor including loop-formingmeans, a sound head in operative relation to said member at a point in said loop, means 1 6 4 for ,oscillating the distributor about an axis in spool the member from one reel to the other.

9. A recorder, according to claim 8, in which the distributor is oscillated by a reversing screw rotated by the driving means and in which the screw is adjustably mounted with respect to the pivot axis of the distributor to control the amplitude of the distributor oscillations.

10. In a magnetic recorder, the combination with two reels, a record member on the reels and driving means therefor, a guiding distributor for feeding said member to and from said reels, said distributor including loop-forming means, a sound head in operative relation to said member at a point in said loop and mounted on and movable with the distributor, means for oscillating the distributor to spool the member from one reel to another.

J OHN B. LITTLE.

nnr'nnnnens crrnn The following references are of record in the file of this patent:

Number Name Date 2,078,357 Woodmansee Apr. 27, 1937 FOREIGN PATENTS Number Country Date 4933(26) Australia Aug. 2, 1927 61,052 Sweden Mar. 29, 1922

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