Motion-transmitting Arrangement

Abstract

A drafting head of a drafting apparatus is mounted for to-and-fro movement in a predetermined direction. A flexible elongated rope is connected to the drafting head for exerting pull thereon to thereby move it in this predetermined direction. A rotatable drum is mounted for rotation about its axis and has the rope convoluted about its circumference. The drum includes a radially expansible annular member and end disks cooperating therewith for expanding and contracting it so as to vary the diameter of the drum; a drive serves to rotate the drum about its axis.

Description

BACKGROUND OF THE INVENTION

The present invention relates generally to a motion-transmitting arrangement, and more particularly to an arrangement for driving a flexible element to thereby transmit motion to an element connected with a flexible element.

The present invention will be described hereafter with respect to a drafting apparatus. However, we wish it to be understood that this is merely an exemplary description for purposes of better understanding, and is not to be considered a limitation of the invention to this particular type of arrangement.

A drafting apparatus is known wherein a so-called bridge member is movable in a first direction and carries a drafting head, provided with drafting pens which engage paper located below the drafting head, which drafting head is movable along the bridge member is a second direction normal to the first direction. Movement of the bridge member and the drafting head is accomplished by providing two drums about which two ropes or lines or similar elongated flexible elements are convoluted which are suitably secured with the bridge member and the drafting head, respectively. Each of the drums is driven in rotation by its associated motor.

Each rotation of one of the drums responds to a shifting of the associated member, that is either the bridge member or the drafting head. Accordingly, because the drafting head is carried by and on the bridge member, the rotation of either one of the drums results in shifting of the drafting pen or pens carried by the drafting head and in making of a line on the drafting paper located below the bridge member and the drafting head. For this reason, and in order to assure the desired accuracy in the drafting which is made by means of such an apparatus, the drums for the elongated flexible elements must be precisely machined. This, however, makes these relatively expensive and, as has been established, the drafting accuracy which can be obtained is particularly good even then.

A further prior art construction of a drafting apparatus again utilizes the principle of effecting shifting of the drafting pen by means of elongated flexible elements. In addition, however, there is a constant automatic correction of the shifting of the drafting pen in dependence upon the angular position of the drums associated with the elongated flexible elements. In this construction, the elongated flexible elements are convoluted about the roller mounted on a level, with deflection of the pivotable level being and providing the desired correction. However, this requires a relatively great technological expenditure if the requisite accuracy of corrections is to be obtained. Aside from this, the construction in question necessitates the use of spring members which may result in vibrations intermediate the drum and the drafting pen which in turn may lead to increased difficulties in maintaining the desired drafting accuracy.

SUMMARY OF THE INVENTION

It is a general object of the present invention to overcome the aforementioned disadvantages.

A more particular object of the present invention is to provide a motion-transmitting arrangement which, employed in apparatus of the type in question or in apparatus analogous to it, avoids the disadvantages described with respect to the prior art.

A further object of the present invention is to provide an arrangement of the type in question which avoids the aforementioned disadvantages while requiring only small technological expenditures.

An additional object of the invention is to provide such an arrangement which requires no components which could produce or aid to the production of vibrations.

In pursuance of the above objects, and others which will become apparent thereafter, one feature of my invention resides, briefly stated, in an arrangement of the type in question which comprises a first element mounted for to-and-fro movement in a predetermined direction, and a flexible elongated second element which is connected to the first element for exerting pull thereon and for moving the first element in the aforementioned predetermined direction. Rotatable drum means is mounted for rotation about its axis, and the second element is convoluted about the drum means. Varying means is provided on the drum means for varying the diameter of the same, and drive means is operative for rotating the drum means about its axis.

Thus, according to the invention, a variation in the diameter of the drum provides in simple manner for shifting of the first element-- which may be the bridge element and/or the drafting head of the drafting apparatus--in dependence upon the angular position of the drum. A variation in the diameter of the drum can be effected in simple manner with great accuracy.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagrammatic plan view of a drafting apparatus embodying the present invention;

FIG. 2 is a diagrammatic longitudinal section through a drum according to the present invention;

FIG. 3 is a fragmentary end elevational view of a drum constructed in accordance with FIG. 2;

FIG. 3a is an axially section through FIG. 3;

FIG. 4 is a view analogous to FIG. 3 but having a complete end-elevational view of the drum;

FIG. 5 is a fragmentary developed view of a portion of the circumference of the drum shown in FIGS. 3-4; and

FIGS 6-8 are somewhat diagrammatic cross-sectional views illustrating further embodiments of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Discussing firstly FIG. 1, it will be seen that for purposes of explanation we have shown an invention embodied in a drafting apparatus which is generally identified with reference numeral 1. Drafting paper, on which a drawing is to be made, is identified with reference numeral 2 and the apparatus comprises a bridge member of first element 3 which is movable in the direction identified with the arrow x. The bridge member 3 carries a drafting head 4 which is movable on and with reference to the bridge member 3 in the direction identified with arrow y. Holding means 5 is provided on the drafting head 4 and holds one or more drafting pens which are well known to those skilled in the art and are not illustrated in detail because they do not form a part of the present invention.

Reference numerals 6x and 6y identifies two motors, such as electromotors, reference numerals 7x and 7y two drums each of which is to be driven by one of the motors 6x and 6y, and reference numerals 8x and 8y identify two lines or ropes each of which is convoluted about one of the lines or ropes each of which is convoluted about one of the drums 7x and 7y. There are also provided a plurality of reversing rollers which are illustrated but not designated with reference numerals. How the motors can be reversed in their operation, so that the bridge member 3 and the drafting head 4 may move to-and-fro, is well known to those skilled in the art and therefore not illustrated, particularly because it does not constitute a part of the present invention.

It is, however, pointed out that the rope 8x is connected with the bridge member 3 at the locations 9 and 10. It is also convoluted about the drums 7x which is driven by means of the motor 6x. Rotation of the drums 7x therefore causes movement of the bridge member 3 in the direction of the arrow x. Rope member 8y is connected with the base of the apparatus 1 at the locations 11 and 12 and is convoluted about the drum 7y which is driven in rotation by the motor 6y. Thus, the drawing head 4 is shiftable with respect to the bridge member 3 in the direction of the arrow y. Evidently, reversing rollers are associated with the ropes 8x and 8y, as mentioned before.

Thus, rotation of the drums 7x and 7y causes movement of both the drafting head 4 and the bridge member 3 in the direction of their respectively associated arrows so that a drafting pen carried by the holder member 5 which is provided on the drafting head 4, performs a movement which is provided on the drafting head 4, performs a movement which is dictated by the components of movement of the members 3 and 4, and draws a corresponding line on the drafting paper 2. With a given change in the angle of rotation of the axis of the motors 6x and 6y, shifting of the drafting head 4 is dependent upon the diameter of the drums 7x and 7y. If a drafting accuracy of 0.2 millimeter or less is required, and if a given area limit on the drafting paper 2 must not be exceeded, then it is advantageous to employ the present invention which makes it possible to adjust the diameter of the drums 7x and 7y.

How this can be accomplished is diagrammatically illustrated in FIG. 2. The drum shown there is composed of two ends discs 14 and 15 and an annular member 17 located between the end discs 14 and 15. The end y14 and 15 are provided with edge faces which are constructed as surfaces of rotation and which taper concentrically towards the axis 16 of the drum in inward direction. The open ends of the annular member 17 are so dimensioned that the end discs 14 and 15 can enter only partly into the open ends. A suitable device, to be described later in more detail, serves to press the end discs 14 and 15 inwardly towards one another in direction of the arrows F1 and F2, respectively. The thus-exerted forces, in conjunction with the conical configuration of the dam faces or surfaces of rotation provided on the end disc 14 and 15, tend to radially extend expand to annular member 17 and to increase the diameter thereof within the elastic limits. Evidently, movement of the end discs 14 and 15 in the direction opposite the arrows F1 and F2, respectively, results in a decrease in the diameter of the annular member 17.

FIGS. 3, 3a and 4 illustrate in detail a drum constructed in accordance with the principle of FIG. 2 and suitable for use as one of the drums 7x, 7y of the apparatus shown in FIG. 1. A shaft, on which the drum is mounted for rotation, is identified with reference numeral 20. Mounted on this shaft are two conically configurated members 21 and 22 which taper inwardly in direction towards one another. An annular member 23 surrounds the members 21 and 22. Bushings 24 and 25 are provided, screws 26 and 27 serve to secure the ends of the rope 32 in the manner still to be described, a nut 30 is threaded onto an externally threaded portion of a hub constituting a part of the member 21 with a washer 29 interposed between the hub and nut 30, and an expansion spring 28 urges the members 21 and 22 axially apart.

It will be appreciated that the member 22 is shifted in direction of the arrow F2 towards the member 21 if the nut 30 is turned in a sense threading it deeper onto the hub portion of the member 21. Because of the conically configurated cam faces of the members 21 and 22, such shifting in the direction of the arrow F2 results in radial expansion of the annular member 23 within the elastic limits of the same. In the illustrated embodiment, the diameter of the annular member 23 is approximately 50 millimeters and the diameter may be varied within a range of between zero and substantially 1 millimeter because it is essential that the diameter increase be capable of being reversed in simple and ready manner, the expansion spring 28 is provided which, when the nut 30 is again loosened, moves the members 21 and 22 axially apart, thereby permitting the diameter of the annular member 23 to decrease. If the annular member 23 is of a material whose inherent elasticity is relatively high, and if certain structural requirements obtain with respect to the frictional contact between the members 21 and 22 on the one hand, and the annular member 23 on the other hand, it is possible to eliminate the expansion spring 28. In this context it is pointed out that it is not only the contact surfaces on the members 21 and 22 which taper conically, but that the corresponding surfaces on the inside of the annular member 23 are complementarily configurated, as is clearly evident both from FIG. 3a and the diagrammatic illustration in FIG. 2. However, this is not absolutely necessary and the diameter variation can also be obtained if there are tapering contact surfaces only on the members 21, 22 or on the member 23.

As shown in FIG. 3a, the rope or line 32 is convoluted about the circumference of the annular member 23 and has one of its ends secured in the bushing 24 via the screw 26, whereas its other end is secured in the bushing 25 via the screw 27. This manner of securing the rope 32 is not absolutely necessary, and it will be possible simply to convolute it about the circumference of the annular members 23 so that the rope 32 is frictionally entrained. However, the solution shown in FIG. 3a has the advantage that there is no slippage between the rope 32 and the annular member 23. It is evident, of course, that intermediate its two connected ends the rope 32 is trained about the various reversing rollers mentioned with respect to FIG. 1 and connected with the base of the apparatus 1 or the bridge member 3, depending upon whether the rope 32 corresponds to the rope 8y or 8x in FIG. 1.

The axis 20 is driven in rotation in suitable manner, for instance by a motor which is not shown in FIGS. 3-4 but which may correspond to one of the motors 6x or 6y of FIG. 1. The friction between the contact surfaces of the members 21 and 22 on the one hand and those of the annular member 23 on the other hand is so large that the annular member 23 will be turned in rotation when the shaft 20 turns, without undergoing any slippage. As FIG. 3, the hub 21b is a separate element from the member 21, but the latter is a pushed onto one end of the hub 21b, as shown. The hub 21b, on the other hand, is pressed-fitted on the shaft 20, although evidently it would also be possible to key it to be the shaft 20. The screw threads provided on the hub 21b and with which the nut 30 meshes, are of very low pitch in order not only to provide for self-locking of the nut 30, but also to assure that relatively large turning movements of the nut 30 permit relatively small diameter variations of the annular members 23. An extension of the hub 21b is provided with surfaces 21c which serve to retain the hub 21b and thereby the shaft 20 against rotation when the nut 30 is tightened or loosened. Bores or analogous recesses 33 provided in the member 22 (compare FIGS. 3 and 3a) afford access to the screws 26,27.

FIG. 5, finally, shows a further embodiment of the invention, and in fact a preferred embodiment of the configuration of the annular member 23. It this embodiment the annular member 23 is provided with slots or cutouts 34 extending inwardly from opposite axial sides in parallelism with the generatrices 34 but being so offset relative to one another in circumferential direction that each slot at one axial side is located intermediate to adjacent slots at the other axial side. While the annular member 23 may be made of different materials, including synthetic plastic material, the one illustrated in FIG. 5 advantageously consists of steel and has been found to, one the one hand, have considerable elasticity, but on the other hand, to be capable of being manufactured economically but with considerable accuracy. It is particularly well-suited for use in a drum which is to be used in a drafting table of the type shown in FIG. 1.

It is also possible to construct the annular member 23 of several sections, for instance of a plurality of rods or, as shown in FIG. 8, of shell-shaped members 23b, 23bb extending in parallelism with the axis 20 and together constituting a member corresponding to the annular member 23. They would, of course, have to be connected in suitable manner as shown at 23b' but this is a simple matter for those skilled in the art.

Under certain circumstances, particularly if the annular member 23a should be made of elastically deformable synthetic plastic material as for instance in FIG. 6, it might be advisable to surround it with a cylindrical protective sleeve which would be intended to counteract possible deformation of the annular member by the rope 32. Such a sleeve again could consist of a single section 70 as shown in FIG. 7, or of a plurality of sections 60a, 60b which are connected at 60c as in FIG. 6. It would, of course, have to be able to undergo diameter variations in the same manner as the annular member 23.

A further possibility would be to construct the annular member 23 as a circumferentially incomplete member 23a as shown in both FIGS. 6 and 7, that is to provide it with an axially extending slot 23a'.

We wish to reiterate that the present invention is by no means limited to use in conjunction with a drafting apparatus of the type shown in FIG. 1, or even to an arrangement wherein motion is transmitted in the same manner as in FIG. 1. However, where the arrangement requires motion transmission in the same manner as in FIG. 1, it is also evident that motion may be transmitted not only for moving a drafting pen, but also for moving an engraving stylus, a tool carrier or in fact any other member which must be moved with precision.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in a motion-transmitting arrangement, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention .

Claims

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. An arrangement of the character described, comprising a first element mounted for to-and-fro movement in a predetermined direction; a flexible elongated second element connected to said first element for exerting pull thereon and moving said first element in said predetermined direction; rotatable drum means mounted for rotation about its axis, said second element being convoluted about said drum means and the latter comprising a radially expansible annular first member having opposite ends, a pair of axially spaced second members just receivable in the respective open ends, and axially inwardly converging cam faces on at least one of said first and second members; varying means on said drum means for effecting relative axial movement of said second members and for thereby varying the diameter of said drum means; and drive means operative for rotating said drum means about said axis thereof.

2. An arrangement as defined in claim 1, wherein said second members are parallel disc members coaxial with said axis and spaced from one another in direction thereof, said cam faces being bevelled edge faces provided on the respective disc members and each conically diverging in direction away from the respective other disc member; said opposite open axial end of said radially expansible annular first member being dimensioned so as to just accommodate the smallest diameter of the respective disc members.

3. An arrangement as defined in claim 1, said varying means comprising a coaxial rod fast with one of said second members and having an end portion extending through a coaxial aperture in the other of said second members; and abutment means on said end portion at the outer axial side of said other second member and shiftable axially thereon so as to displace said other second member towards said one second member in response to shifting of said abutment means towards said one second member.

4. An arrangement as defined in claim 1, wherein said annular first member is of one piece.

5. An arrangement as defined in claim 1, wherein said annular first member is of one piece and circumferentially incomplete.

6. An arrangement as defined in claim 4, wherein said annular first member consists at least in part of synthetic plastic material.

7. An arrangement as defined in claim 1, wherein said annular first member is composed of a plurality of discrete sections connected to one another.

8. An arrangement as defined in claim 1; and further comprising biasing means permanently urging said second members axially away from one another.

9. An arrangement as defined in claim 8, said biasing means being a pressure spring arranged within the confines of said annular member and bearing against said second members concentrically therewith.

10. An arrangement as defined in claim 1, wherein said annular member consists of synthetic plastic material.

11. An arrangement as defined in claim 1, wherein said first and second members are both provided with cooperating ones of said cam faces.

12. An arrangement as defined in claim 11, wherein said cam faces are annular faces surrounding said axis of said drum means and constituting surfaces of rotation.

13. An arrangement as defined in claim 1; and further comprising a radially expansible cylindrical sleeve surrounding said annular member so as to vary in diameter in response to variations in the diameter of said annular member.

14. An arrangement as defined in claim 13, wherein said sleeve is of one piece.

15. An arrangement as defined in claim 13, wherein said sleeve is composed of a plurality of discrete connected sleeve sections.

16. An arrangement as defined in claim 1, said annular member having a cylindrical circumferential surface and being provided with a plurality of axial slots extending in parallelism with the generatrices.

17. An arrangement as defined in claim 16, wherein said slots extend axially inwardly from the opposite ends of said axial member, the slots at one of said opposite ends being circumferentially offset with respect to the slots at the other of said axial ends.

18. An arrangement as defined in claim 3, said abutment means comprising nut means; and said nut means and said end portion of said rod being provided with cooperating screw threads.

19. An arrangement as defined in claim 1, and further comprising securing means securing said flexible member to said drum means against slippage relative thereto.