US2954939A - Control of tension on tape in tape recorders - Google Patents

Description

Oct. 4, 1960 A. L. HERRMANN 2,954,939

CONTROL OF TENSION ON TAPE IN TAPE RECORDERS Filed June 23, 1955 .III I: 16 Jl lllllllll? IIIIIIIIIIIIIIIIIIIIII!Illlllllllll Willi INVENTOR.

Adolf L.Herrmann ATTORNEYS United States Patent 2,954,939 CONTROL OF TENSION ON TAPE IN TAPE RECORDERS Adolf. L. Herrmann, Huntsville, Ala., assignor to the United States of America as represented by the Secretary'of the Army Filed June 23, 1955, Ser. No. 517,671 '4 Claims. (Cl. 242-5512) (Granted under Title 35, US. Code (1952), see. 266) This invention may be manufactured and used by or for the U.S. Government without the payment to me of any royalties thereon.

This invention relates to a novel arrangement for maintaining. substantially constant tension in a web or filament during winding and uwindi-ng thereof and for maintaining such tension on the web or filament after stopping, and more particularly to a system. particularly adapted for use in tape recorders.

It is very important that thetension in the tape of tape recorders be of the proper value. If the tension is too high, the tape is apt to tear or slip on the driving sprocket; If there are teeth on. the driving sprocket, they are apt'to tear through the perforations. On the other hand-if the tension is not high enough, the tape will tend to. slip on the driving sprocket. Also, if tension is too low, the tape will wind itself loosely on the reels, which willlnot be filled to capacity. In an extreme case, it is possible that. the tape leave its normal path altogether.

In the past, one of the most common ways of correcting'this trouble was to have another motor besides the synchronous motor that drives the tape sprocket. This second motor was connected through friction devices to the two reels and in this manner tried to keep the tension as the proper value. In this way, it was necessary that.the torque in. the friction devices be high enough when the reels were full and that the speed of the motor be high enough when the reels were empty.

This meant that the motor and friction devices had' to. be. designed with respect to the torque. of the full reel an'd'the speed of the empty reel. In order that the tape be under tension it. is necessary that the torque motor run in only one direction. But, since the tape must also be rewound, wefind that the friction devices mustnot only account for the change in speed when the reels are rotating in the same direction, but must also dissipate the energy brought about when the direction of'.

the reels. is opposite that of the motor. This. always occurs when the reels run from full to empty. Because. of thegreat. losses of power it is necessary that we use alarge motor and of course, the larger the motor, the larger the losses in the motor itself.

Besides this, here is continuous trouble with the, friction device because the friction is always subject to be changed. Therefore, constant checking and adjusting is.

necessary.

To eliminate friction devices, with their troubles, separate tensioning motors may be used for each reel. But this solution is farfrom being satisfactory, because each motor needs to be designed for the speed of the empty reeland the torque of the full reel.

. It is therefore an object of my invention to provide a.'novel. tensioncontrol system which will eliminatethe necessity for friction type drives and which will maintain substantially constant tension during winding and unwinding and while the motor is stopped.

further object is to provide a tension control system which incorporates. means for differentially driving the take-up and supply reels and also has a pretensioning- 2,954,939 7 Patented Oct. 4, 1960 arrangement and a stop arrangement for pretensioning and. maintaining the tension in the material in stopped position as well as while running.

Still other objects and many attendant advantages of. my inventionwill become apparent to one skilled in the art from a reading of the following detailed descrip tion of an illustrative embodiment thereof, taken in conjunction with the accompanying drawing, wherein Figure 1 is a plan view taken along line 1-1 of Fig. 2 and looking in the direction of the arrows, of a device incorporating my invention- Figure 2 is a view partially in section taken along line 2--2, of Fig. 1 and looking in the direction of the arrows, embodiment of Figure 1, showing in detail the tape-tensioning mechanism.

This invention eliminates the need of friction devices, and requires only one tensioning electromotive (combined motor. and generator) unit of small power.

In the preferred embodiment of my invention the tape and. reels are driven by a reversible motor and sprocket unit; and on the two reel axles there are fixed gears that are interconnected through a differential gearing, the axle of which gearing is rotated by any difference in the speeds of the reels. To this differential gear axle there is drivingly connected an electromotive device that acts as a tensioning motor when one of the reels is turning faster than a second reel and as a tensioning generator or braking means when the rotation of the reels is reversed and said second reel is turning faster than the above-mentioned first reel. My optional addition of a light spring motor to this assembly makes it possible to retain the desired tension of the tape for a brief time. when the electromotive unit is disconnected from its source of electric power, as in a temporary loss of such power.

In Figure l, the tape 3 is equally rolled on reels 1 and 2. The ends of the tape are fastened to pins 4 and 5.

The tape is reversibly driven by the unit 6, of known type, which comprises a reversible, synchronous electric motor and a sprocket that is driven by the motor. In the embodiment illustrated, the tape is shown as being driven, by motor-sprocket unit 6-, from reel 1 in the direction of the arrow, over idler reels 7 and past the recording head 8, to reel 2. When driven in this direction the tape. will rotate reel 1 but will not rotate reel 2 unless there is gearing between 1 and 2. Such gearing: is shownin Figure 2 as located on the opposite side of support. 9' from the reels and tape that are shown in. Figure 1.

Spur gears 10 and 11, which are rigid with' reels 1 and. 2, respectively, are journaled relative to supporting plate 9, and are connected by spur and differential gears 12,.

13 and 14. Element 12 is a combined spur and bevel gear, the bevel-gear part 12A of which engages bevel gear. 13 of the differential gearing. The axle 13A- of bevel gear 13 is welded or otherwise fixed to shaft 15, so that in-ditferential movement gear 13 can revolve around the axis of shaft 15, as well as rotate on its axle. Shaft 15* is also fixed to spur gear 16, which is in engage ment-withgear. 1-7. The latter gear is drivingly connected to electromotive device 18, which functions as a tensiorv ingsmeansfor'the tape and serves part'of the time as'a motor and part. of the time as a generator.

Electromotive deVice-ll-S-is connected to a power "source through variable. resistor 19. With this resistor," itis possible to -change the: tapeetensioning' torque of said eleetromotive device.

When the motor is'switchedon, torque-is applied through gears-1.7, 16 and shaft 15, which transmits torque on. the axle 13Aofgear 13. Gear 1-3, which is journaled" on said axle, works on the same principle as a scale bal ance andrtransmits half of the torque to gear IZAand half. of the. torque. to gear '14.

Gear 13 will revolve around the axis of shaft and drive gears 12A and 14 until all slack is taken up in the tape and the motor stops turning, thereafter holding the tape taut due to its torque.

By changing resistance in the resistor 19 the torque on the motor 18 will change, and the tension on the tape can be adjusted. I

When reels '1 and 2 are half filled, that is, when they have the same number of turns on each reel, and sprocketand-motor unit 6 is energized, gears 12 and 14 are turned in opposite directions and at the same speed, thereby turning gear 13; but the axle of gear 13 for the moment does not revolve around the axis of shaft 15.

Thus, for the moment, the electromotive device 18 supplies only torque, without need of its turning, While holding the tape in tensioned position. In this case, the speed of the reels may be as high as possible, without power from the motor 18.

With the tape moving from left to right, in the direction of the arrows of Figure 1, reel 2 will fill and reel 1 will empty, thereby increasing the speed of reel 1, and decreasing the speed of reel 2, making gear lil rotate faster than gear 11, and gear 12 rotate faster than gear 14. The difference between the two speeds will be taken through the axle of gear 13, transmitted to shaft 15 and motor 1%, whose torque remains constant. The motor then will turn gear 17 in the direction indicated by the arrow near this gear in Figure 2, thus compensating for the diiference in reel speeds. In this case the motor thus operates in effect as a driving means, while its torque still holds the tape tensioned. When the tape is moving from right to left, opposite to the direction of the arrows in Figure 1, reel l'wili fill and reel 2 will empty, thereby decreasing the speed of reel 1, and increasing the speed of reel 2, making gear 11 rotate faster than gear 1th. The difference between the two speeds will be taken through gear 13, transmitted to shaft 15 and gears 16 and 17 and then to device 18. Device 18 then will be forced to turn counterclockwise to compensate for the difierence between the reel speeds, so that in this case it functions as a generator. Its functioning thus is like the loading and unloading of a coil spring, because at one time the device is taking on power and another time it is giving off power.

The system just described works only as long as the motor is connected to the power source, but when the motor 18 is switched off, as by a power failure, tension is immediately lost in the recording tape. To provide a means to eliminate this problem, there is provided a spring in the mechanism between the motor and the reels. This spring may be incorporated into the design between gear 11 and reel 2. It is also possible to apply this spring between gear 10 and reel 1, or between the motor and shaft 15. In all cases the effect will be the same; therefore two or three springs could be used, if necessary, for greater capacity. In the mechanism shown (Figure 2) the spring 20 is applied between gear 11 and reel 2. This spring initially will absorb the energy of several revolutions of the motor 18 and store this energy until the torque in it is equal to that developed by the motor; The spring 20 thus is able to act as an elastic coupling between gear 11 and reel 2 and will turn clockwise or counterclockwise with reel 2.

' When the motor 18 is turned on, spring 20 immediately will load until the torque on thespring is equal to the torque being applied by the motor. Therefore, the tape immediately will acquire the necessary tension. Thereafter, the system works as described in previous paragraphs. I p

If after recording, or accidentally during operation of the tape, supply of current to the motor ceases, the spring immediately tries to unload its tension; this is prevented on one side by the tape being connected to the two reels. The tendency of the spring to unload on the other side, through the motor, is preventedby a spring-and-solenoid brake 2:1, 22 which is applied to gear 16 and is in the same circuit with the motor. The brake is held against the gear by the spring 22 until the motor is again turned. V on, and current energizes the solenoid compressingspring 22 against spring seat 23, thus withdrawing the brake. The brake can be applied as shown, or it can be applied on the motor shaft, or the brake and the motor can be combined into one unit.

It will be readily apparent that many modifications may be made without departing from the scope of the invention. Therefore it is to be understood that the scope of the invention is restricted only as described in the appended claims. I

I claim I 1. A reeling mechanism, for winding and unwinding a I flexible element comprisingzan elongated support; a pair of laterally spaced bearings onsaid support; a third bear ing on'said support betweensaidpair of bearings; a pair of shafts journalled in'said pair of bearings, each of said shafts extending a substantial distance oneach side of said support; a pair of reels fixedto said shafts on one side of said support; means for attaching the ends of said flexible element to said reels; means connected to said flexible "element for driving said element; a first reel-coaxial gear, parallel with and adjacent said support,

' fixed to one of said shafts on the side of. said support op-.,

posite from said reels; a second reel-coaxial gear, parallel with said support, and spaced from the support farther than saidfirst reelcoaxial gear; means operatively connecting said second reel-coaxial gear to the other one of said pair of shafts; a third shaft, journalled at one of its ends in said third bearing, extending a substantial distance from-the side of said support that is opposite from said reels; a first differential gear, journalled on said third shaft, adjacent said support, and in meshwith said first reel-coaxial gear; a second differential gear, fixed to said third shaft and in mesh with said second reelcoaxial gear; an axle fixed to and normal to said third shaft; a third differential gear journalled on said axle and in mesh with said first and second differential gears; an electromotive torque-supplying device; means for supplying electric current to saidelectromotive device; and reduction gearing for transmitting torque between said electromotive device and an end of said third shaft.

2. A device as set forth in claim 1, in which said reduction gearing is drivingly connected to the end of said third shaft that is farthest from said third bearing.

3. A device as set forth in claim 1, in which said means operatively connecting said second reel-coaxial gear to said other one ofsaid pair of shafts comprises a spring motor that stores energy whencurrent is being supplied 9 to said electromotive device, and that rotates said reels References Cited in the file of this patent UNITED STATES PATENTS 1,996,815 Kimpton et are; Apr. 9, 1935 2,034,543 'Iwiss et al. Mar. 17, 1936 2,389,047 Heinz -1 Nov. 13, 1945 2,517,055 Thompson Aug. 1, 1950 2,626,760 Chick 'Jan. 27, 1953 2,632,060 Foote et a1 Mar. 17, 1953 FOREIGN PATENTS 1,067,954 France Feb. 3, 1954 Warn

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