US3317157A

US3317157A - Tension maintaining device

Info

Publication number: US3317157A
Application number: US455157A
Authority: US
Inventors: Leiber Heinz
Original assignee: Teldix Luftfahart Ausrustungs GmbH
Current assignee: Rockwell Collins Deutschland GmbH
Priority date: 1964-05-13
Filing date: 1965-05-12
Publication date: 1967-05-02
Anticipated expiration: 1984-05-02
Also published as: GB1058897A

Description

y 2, 1967 H. LEIBER TENSION MAINTAINING DEVICE 5 Sheets-Sheet 1 Filed May 12, 1965 INVENTOR Heinz Leiber BY M e 7% ATTORNEYS May 2, 1967 I H. LEIBER 3,317,157

TENSION MAINTAINING DEVICE Filed May 12, 1965 3 Sheets-Sheet I5 INVENTOR Heinz Lei ber BY Qgmaw W ATTORNEYS United States Patent Claims The present invention relates generally to a device for maintaining the tensile stress of a material which is wound on two drums and, more particularly, to a device for maintaining the tensile stress of a material stretched between two drums when winding in the form of an Archimedean spiral, for example, which may automatically result when winding strips and foils on cylindrical drums.

It is already known to stress strips which are Wound on drums by producing opposite moments on the drums by means of two separate elements which are mainly electrical torque producing elements, but which require a continuous power supply. In order to move the strip in its stressed condition, driving and braking moments of different magnitudes are needed. Also, in this arrangement, the power supply is higher than is actually needed for acceleration of the masses involved and to overcome friction. In order to adjust the driving and braking moments with respect to each other, voluminous control devices are necessary. A further disadvantage of the electrical tensioning system is that upon failure of the power supply or interruption of the line, the tensile stress of the strip is not assured and in such an event, the drums can move accidentally.

With this in mind, it is a main object of the present invention to provide a device for maintaining the tensile stress of a strip which is wound on drums without the need for a continuous supply of energy.

Another object of the invention is to provide a device of the character described wherein the tensile stress of the strip wound on drums can be maintained while the arrangement is at a standstill as well as during rewinding at any speed.

A further object of the invention is to provide such an arrangement which does not exert any power exteriorly of the system and for which only a small driving motor need be provided for overcoming the moments of acceleration and friction which occur.

These objects and others ancillary thereto are accomplished in accordance with preferred embodiments of the invention wherein two conical rope pulleys are provided for the positioning of a rope or tape. These pulleys have a spiral or threaded groove in their conical surfaces. The

rope or tape has its ends fixed to the conical pulleys and is partly wound around the rope pulleys and disposed in the grooves. By this means, the torsional force of the grooves and the arrangement of the rope pulleys is such such that with both pulleys rotating in the same direction, the tendency of variation of the effective levers constituted by the conical rope pulleys, are opposite to each other. Also, the drum on which the strip is wound is connected by gearing with the rope pulley from which the rope is unwound. Furthermore, the drum from which the strip is unwound is connected by gearing with the rope pulley onto which the rope is wound, and at least one torsion spring element is connected into the operative connection which is thereby formed.

As the rope falls into the grooves obliquely and can, under certain circumstances, wear out, a further feature of the invention porvides an increase in the reliability of operation. This is performed by having one pulley so arranged that it can be displaced axially. A linearly movable guide member is provided which is threadedly connected with the rope pulleys. By this means, the rope pulleys are axially displaced relative to each other in such manner that the rope does not rub on the edges of the grooves.

Additional objects and advantages of the present invention will become apparent upon consideration of the following description when taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a diagrammatic perspective view of the present invention.

FIGURE 2 is a diagrammatic partial sectional view illustrating a simple device to provide for axial movement of one of the two rope pulleys.

FIGURE 3 is a diagrammatic perspective view of the cam of a further embodiment of the invention.

FIGURE 4 is a diagrammatic side elevational view of the cam together with the rope pulleys.

FIGURE 5 is a diagrammatic plan view of the cam together with the rope pulleys.

Wit-h more particular reference to the drawings, FIG- URE 1 illustrates an embodiment of the invention wherein a film strip 1 is wound on and disposed between two cylindrical drums 2 and 3. The film strip 1 is stretched between the drums which are mounted on two rotatable shafts 4 and 5. The strip 1 is a transparent film which has a map imprint thereon, although the details of the indicia of the map are not shown. A bug or other type of marking device can be moved in the direction of the double arrow 6 to indicate the position of a vehicle or the like on the map. The bug is not shown. If the vehicle moves on the map at a right angle to the direction of arrow 6, the two drums are rotated accordingly so that the correct portion of the map is placed under the bug. For an exact indication, it is necessary that the film with the map thereon does not flutter, even though the entire apparatus may vibrate. The tensile must not fall below a predetermined minimum value at any time.

Two identical gearing arrangements 7 and 8 are connected with shafts 4 and 5, respectively. The driving shafts 9 and 10 of these gears reduce the rotations of these shafts 4 and 5. The direction of rotation of the drive and driven shaft is the same. A conical pulley 11 is mounted on shaft 9 and an identical pulley 12 is loosely mounted on shaft 10. Pulley 12 can thus rotate about the shaft 10. A disc 13 is fixed to the shaft 10 and has an eccentric pin 14 mounted thereon. A torsion spring 16 is connected between this pin 14 and a corresponding eccentric pin 15 mounted on the smaller end of rope pulley 12.

A groove 17 is provided in each of the rope pulleys and this groove extends from one end to the other and has a clockwise spiral or right-hand thread. These grooves serve for guiding the rope 18 which is connected to the end of the grooves. The rope is connected to the larger diameter ends of the cones. Those grooves which are filled with rOpe are indicated 19. The rope is fastened to the rope pulley 11 at point 20. The gearing ratio of the gears 7 and 8 and the pitch of the grooves are adjusted in such manner that the radii 21 and 22 of the drums 2 and 3, respectively, and the radii of the grooves of the rope pulleys 11 and 12 from which and into which the rope is wound, are always proportional.

The torsional force of the grooves and the arrangement of the rope pulleys is such that with both pulleys rotating in the same direction, the tendency of variation of the effective levers constituted by the conical rope pulleys, are opposite to each other.

Torsion spring 16 is under an initial stress and always applies moments of rotation of equal magnitude on the rope pulley 12 and the disc 13. Thus, the pulley has the tendency to wind on more rope while the drum 3 has a 3 tendency to Wind on more film. Since the drum 2 and the rope pulley 11 are connected to each other by the gearing '7, these tendencies can not cause rotary movements but only a tensioning of the map strip 1 and the rope 18.

Movement of the rope pulleys and thus movement of the strip can only be caused by an outside moment of rotation. For this purpose, a DC. motor 23 is provided which, via a gear 24, drives a gear 25 fixed to shaft 9. This motor is fed by two voltages V and V which are in series. The voltage V corresponds to the position coordinate in the direction of movement of the map and is supplied by a navigation calculator. The voltage V is a voltage provided from a potentiometer and which is tapped off between the center tap and the wiper arm 26 of a potentiometer 27. A voltage source 28 feeds the potentiometer while the wiper arm 26 is operated by a toothed roller 29 which is in engagement with the edge perforations 30 of the map strip 1. The dashed line 31 indicates a mechanical connection between the toothed roller 29 and the wiper arm 26. The motor 23 is arranged to rotate in a direction so that it decreases its supply voltage continuously by means of the potentiometer 27. When voltages V and V have the same value, the motor stops. In this manner, the coordinate voltage V controls the position of the map strip 1.

The sensitive driving system provides that the present invention does not have any residual moment. Starting from the stopped position of the motor at which V =V it is assumed that the vehicle or airplane whose position is to be indicated moves in the direction of the map strip 1. The navigation calculator, as a result, increases its output voltage V Thus, a voltage difference is provided at the motor 23 and this causes the motor to rotate shaft 9 in a direction which increases voltage V The rope pulley 11 and the drum 2 may thereby rotate in counter-clockwise direction with the corresponding gear transmission ratio. This causes the angular radius 21 to increase. On the other side, the angular radius 22 decreases and to the same extent the effective lever on the rope pulley 12 decreases because the rope is wound on downwardly and the radius on which the rope is wound on pulley 12 decreases. The torsion spring 16 also rotates. However, this occurs without the ends thereof turning with respect to each other. The two opposite tensioning moments mentioned above and produced by this spring always remain equal independently of the change of the angular radii.

FIGURE 2 illustrates a schematic view of two rope pulleys 40 and 41 in the form of truncated cones. In use, they correspond exactly to the rope pulleys shown in FIGURE 1 although the details of the drive are not shown in FIGURE 2. The two rope pulleys 40 and 71 are fixedly connected with coaxially extending threaded

lugs

42 and 43, respectively. The threads of these lugs are shown as simple lines.

Points

44 and 45 are shown in this figure to indicate that the rope pulley 40 can not move in axial direction. However, the rope pulley 41 is arranged on a shaft 46 which can be displaced in its

bearings

47 and 48. A connecting member 49 is provided which has two threaded openings into which the threaded lugs 42 and 43 are disposed.

The pitch of the thread on the

lugs

42 and 43 and the pitch of the rope grooves 50 are the same. Therefore, the angle at which is formed between the rope segment 51 and a line projected at right angles to the axes of

lugs

42 and 43 at the point where the rope intersects with the axis of lug 42, remains constant independently of the position of the rope. It is therefore possible to adjust the angle a in such manner by adjusting the rope pulleys suitably before the rope is placed onto and fixed in the pulleys, that the rope will not rub on the edges of the grooves, since these edges might be sharp and in any event wearing would occur.

Assuming that the device is positioned as shown in FIGURE 2, the rope is mostly wound on the pulley 41 While the pulley 40 is nearly empty of rope. Assuming, now that the pulley 40 rotates twice in a direction to wind rope onto this pulley, this then corresponds to one rotation of pulley 41 in its unwinding direction since in the positions illustrated, the effective diameter of pulley 41 is twice that of pulley 40. The connection member 49 thus moves by two pitches (2/1) to the position indicated in dashed lines. At the same time, the pulley 41 threads itself by a movement equal to one pitch, out of the con= nection member and attains the position indicated by dashed lines 52. However, during this time, the rope has moved on the pulleys in the direction of arrow 53 and the movement has been an amount equal to two pitches on the pulley 40 and one pitch on pulley 41. This difierence in axial travel is compensated for by the opposite axial movement of pulley 41 so that the rope angle on is also maintained in the new position 52 of the pulley 41.

The rope angle a is thus maintained during the entire winding and unwinding process, even though the ratio resulting from the rotary speeds of the two rope pulleys changes constantly. In the two end positions in which the entire length of rope is wound on one of the two pulleys, the displaceable pulley 41 is in the position 52a shown in dashed lines. Starting from this position, it moves into the position 52b shown in dashed lines and then back to position 52a without changing the direction of winding. Position 52b corresponds to the middle position of the rope, that is, when the rope has an equal length wound on each pulley.

Since the pitch angle of the rope grooves is different at each point, contrary to what occurs in a cylindrical thread, the rope angle on will preferably be adjusted to a medium value between the largest and the smallest pitch angle and this compromise of pitch angle can be seen from the example shown in FIGURE 2 The embodiment shown in FIGURES 3 through 5 above all provides a considerable saving in space. In this embodiment, the thread lugs are eliminated and a threaded type of connection is provided by means of a double cam which directly engages the rope grooves. This cam is shown in FIGURE 3 and includes two halves which are pivotally connected by a shaft 60. One half of this cam can be displaced along two

guide bars

61 and 62 and includes two

longitudinal girders

63 and 64 connected to each other by a bridge, the end 65 of which can be seen. The two guide bars pass through the lon gitudinal girders.

A lever 66 is mounted on the shaft 60 and a tension spring 67 is connected to the other end of lever 66. Therefore, the cam half 68 has a tendency to tilt upwardly toward the right as viewed in FIGURE 3 since this cam part is fixed to shaft 60 which is mounted for rotational movement in

girders

63 and 64. Cam portion 68 is provided with two ridges 69 which are elongated and have rounded upper ends and are designed to engage in the empty grooves of the rope pulley 70. Corresponding ridges are provided on the bridge 65 although they are not visible in FIGURE 3. They are, however, indicated at 71 in FIGURES 4 and 5.

FIGURES 4 and 5 illustrate the double cam in a simplified manner and also illustrate the rope pulleys 70 and 72 as well as the rope 73 which is disposed about the pulleys. Pulley 72 can not be moved in axial direction whereas the pulley 70 can be displaced on its shaft (not shown) in the direction of double arrow 70'. The guide bars 61 and 62 are fixedly mounted to be parallel to the opposing surfaces of the two cones. By having the ridges 71 displaced relative to the ridges 69 in the direction of the guide bars, these ridges can then engage into grooves of the two rope pulleys which are free of the rope, even though the rope runs over the double cam.

The functioning corresponds to the embodiment of FIGURE 2. If the pulley 70 moves axially, then the distance between the surface lines of the cones changes. However, this is compensated for because the ridges 69 are always spring-pressed into the grooves because of the spring 67 and thereby follow the movement of pulley 70.

It will be understood that the above description of the present invention is susceptible to various modifications, changes, and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

What is claimed is:

1. A device for maintaining the tensile stress of a strip stretched between two drums, comprising, in combination:

two conical pulleys for positioning a rope and having spiral grooves in their conical surfaces; a rope having its ends fixed to the conical pulleys and partly wound about the rope pulleys in the grooves;

two drums having a strip stretched between them and Wound on the drums; and

gearing means for connecting the drum on which the strip is wound with the rope pulley from which the rope is unwound, and the drum from which the strip is unwound with the rope pulley on which the rope is wound, and including means lfOI providing torsional biassing interposed between one of the drums and the pulley to which it is connected.

2. A device as defined in claim 1 wherein said pulleys are arranged with the smaller end of one opposite the larger end of the other.

3. A device as defined in claim 2 wherein said rope is wound on the pulleys so that they rotate in the same direction.

4. A device as defined in claim 1 wherein said rope and pulleys are arranged so that both pulleys rotate in the same direction and the tendency of the effective levers of the rope pulleys are opposite to each other.

5. A device as defined in claim 1 wherein one of said pulleys is mounted for axial displacement.

6. A device as defined in claim 5 wherein said pulleys have threaded lugs projecting therefrom, and a connected member disposed between the lugs and into which the lugs are threaded.

7. A device as defined in claim 5 comprising a cam having a first portion engaging the .grooves of one pulley and a second portion engaging the grooves of the other pulley.

8. A device for maintaining the tensile stress of a strip stretched between two drums, comprising, in combina- .tion:

two conical pulleys for positioning a rope and having similar spiral grooves in their conical surfaces with the large end of one pulley opposite the small end of the other pulley;

a rope having its end fixed to the conical pulleys and partly wound about each of the rope pulleys in the grooves thereof;

two drums having a strip stretched between them and wound on the drum;

means for maintaining a similar tangle of approach between the rope and those grooves which the rope is entering regardless of where on the pulley such grooves are disposed; and

gearing means for connecting the drum on which the strip is wound with the rope pulley from which the rope is unwound, and the drum from which the strip is unwound with the rope pulley on which the rope is wound, and including means for providing torsional biassing interposed between one of the drums and the pulley to which it is connected.

9. A device as defined in claim 8 wherein said means includes means for mounting one of said pulleys for axial movement, and means connected between said pulleys for causing said one pulley to move axially with respect to the other upon rotation of said pulleys.

References Cited by the Examiner UNITED STATES PATENTS 2,376,777 1/1945 Hornbostel 242- .5 3,233,843 2/ 1966 Dockstader 242-755 FOREIGN PATENTS 708,792 5/ 1931 France.

FRANK J. COHEN, Primary Examiner. N. L. MINTZ, Assistant Examiner.

Claims

1. A DEVICE FOR MAINTAINING THE TENSILE STRESS OF A STRIP STRETCHED BETWEEN TWO DRUMS, COMPRISING, IN COMBINATION: TWO CONICAL PULLEYS FOR POSITIONING A ROPE AND HAVING SPIRAL GROOVES IN THEIR CONICAL SURFACES; A ROPE HAVING ITS ENDS FIXED TO THE CONICAL PULLEYS AND PARTLY WOUND ABOUT THE ROPE PULLEYS IN THE GROOVES; TWO DRUMS HAVING A STRIP STRETCHED BETWEEN THEM AND WOUND ON THE DRUMS; AND GEARING MEANS FOR CONNECTING THE DRUM ON WHICH THE STRIP IS WOUND WITH THE ROPE PULLEY FROM WHICH THE