NZ209806A - Winch;friction of rotatable cable bearing surface varies along rotational axis - Google Patents

Description

Mwxsaqiii^ No.: Date: 2.0 9 8 Priority Date(s): Complete Specification Filed; V?."/*?'. Class: .,.-............. '2 0 FEB 1987 Publication Date: ........Ft.

I P.O. Journal, No: ..... /. .

NEW ZEALAND PATENTS ACT, 1953 COMPLETE SPECIFICATION "Improvements in or relating to Winches" IfW-"- JOHN THOMAS HIRD WEBB, A BRITISH SUBJECT.OF INYANGA, FIREBALL HILL, SUNNINGDALE, BERKSHIRE, UNITED KINGDOM. hereby declare the invention for which I / pray that a patent may be granted to me/«M>> and the method by which it is to be performed, to be particularly described in and by the following statement: - - 1 ^ss>«tstfit : ; -la- 2 098 0 6 THIS INVENTION relates to improvements in or relating to winches.

Winches have been proposed, and are described and illustrated in U.S. Patent Specification Nos. 4,274,606 and 4,230,306, in which a tailing means is provided at the tail end of a rotatable drum. The tailing means is intended to receive only a single turn of rope or cable and comprises a circumferential groove and/or a high friction material. An increase in tension in the turn of rope received by the tailing means has the effect of increasing the force with which the same is gripped by the tailing means. The tailing means holds the tail end of rope in position so that, on the one hand, an increase in the tension applied to the load end of the rope will not cause the turns of rope to slip around the drum and, on the other hand, the tail end of the rope will not become slack and, possibly, foul the line. U.S. Patent Specification No. 4,272,606 stresses that the area of increased friction must only be provided at the tail end of the drum, because a number of turns of rope adjacent the tail end might otherwise become slack. Thus, in these previously proposed winches, the rope or cable and the cable bearing surface are subjected to uneven frictional wear.

U.K. Patent Specification No. 1,599,521 describes a dual axis quadruple capstan winch in which cable tension is overcome by providing a large number of grooves so that a large number of turns of cable are borne by the winch. However, because the driving capstans of the winch are disposed on more than one axis, it is difficult correctly to balance the torque applied by the load about the two axes.

. \ It is an object of the present invention to enable the provision of a winch whereby the above disadvantages may be overcome or at least mitigoted. ; ciJhttB ^if « & ^ J o This invention provides a winch comprising a rotatable bearing surface for a cable, wherein the friction between the surface and a given cable material at a given cable tension varies continuously, or stepwise in a plurality of steps, along a rotational axis. n Advantageously, the winch includes a capstan having a surface the coefficient of friction of which increases along the rotation axis of the capstan. Additionally, or alternatively, the winch comprises a capstan provided with a plurality of circumferential grooves, the cable bearing surface area of each groove being different.

Thus, as the tension in the cable decreases, the friction acting between the cable and the capstan can be kept at substantially the same level by increasing the coefficient of friction and/or by decreasing the effective contact 15 area (and thus increasing the pressure) between the cable and the capstan. As a result, the circumferential grooves are worn at substantially the same rate, facilitating maintenance. Also, whilst in the absence of the features of the present invention the cable tension would decrease very gradually as the number of turns of cable increases, the present invention enables the provision 20 of a winch in which cable tension is overcome in relatively few turns of cable, so that a single axis twin capstan winch, which has not been previously proposed, becomes feasible.

Accordingly, the present invention also provides a capstan winch in 25 which the driving capstans of the winch are disposed on a single axis and comprise first and second capstans. Preferably, the first and second capstans are drivable in contrarotation, for example by means of an epicyclic gear train, and a brake is provided for securing the first and second capstans against rotation with respect to each other, so that they act as a single fixed capstan. 30 When fixed in this way the first and second capstans can continue to support a load even whilst parts of the driving mechanism are removed for inspection or repair.

For a better understanding of the present invention, and to show how the 35 same may be put into effect, reference will now be made, by way of example, to the accompanying drawings, in which: y a -n Figure 1 is a schematic side elevational view of a single-axis twin capstan winch in accordance with the invention, Figure 2 illustrates the path followed by a cable guided by the twin capstan winch of Figure I, and Figure 3 is a cross-sectional view taken along the line Ill-Ill of Figure I.

Referring now to the drawings, Figure I shows a twin capstan winch comprising a first, single groove, capstan I and a second capstan 2, sharing a common rotation axis, and a plurality of sheaves or grooved pulleys 3. As can be seen in Figure 3, three sheaves 3 are rotatably mounted on a shaft h which is parallel to the common rotation axis of the first and second capstans I, 2. Also, a fourth sheave 3 is rotatably mounted on a shaft 5 which is slightly offset from that axis to facilitate passing cable over the fourth sheave 3 and the single groove capstan 1. The capstans I, 2 are adapted to be driven in rotation by means of a motor 6, a sun gear 7 fixed to a drive shaft of the motor 6, a planet gear 8 rotatably mounted on an integral shaft 9 of the second capstan 2 and an internal gear 10 of the first capstan I. A brake (not shown) is also provided for preventing relative rotation of the capstans I, 2 if desired.

The second capstan 2 is provided with three circumferential grooves I I which are offset along the capstan rotation axis relative to the grooves of the three sheaves 3 on the parallel shaft 4 by half a groove's width. The circumferential grooves II comprise a high friction material and the coefficient of friction increases from the high tension (load) end to the low tension (tail) end of the second capstan 2.

Preferred high friction materials include Silumin, which is a high silicon content aluminium such as AL20 with more than 12% silicon content, and, for use in potentially corrosive environments, high friction polymers such as polyurethanes, polypropylenes and Kautex, which is a polyvinylchloride based material. "Silumin" and "Kautex" are Trade Names. In a preferred arrangement, each groove comprises alternating areas of Kautex and Silumin, the former providing the high friction component and the latter serving to support the cable. The coefficient of friction of at least some of the surface of the second capstan 2 for a steel cable should preferably be significantly greater than that of steel on steel. It has been found that, for some materials at least, such as polyurethane, a relationship exists between the density of the material and its coefficient of friction for a given cable material. Accordingly, in one arrangement the density decreases exponentially from the high tension (load) end to the low tension (tail) end of the second capstan 2. The widths of the grooves may also be varied (not shown) so as to vary the pressure between the cable and the surface of each groove at a given cable tension.

During use, tension in the cable guided by the winch is overcome by friction between the cable and the capstans, so that the cable at the tail end of the winch is almost completely slack. At least 40%, and as much as 50%, of the cable tension is taken up by the first capstan I, about which the degree of wrap is between 250° and 280°, usually about 270°. The friction would normally decrease gradually from the load end to the tail end of the second capstan 2. However, because the coefficient of friction between the grooves 11 and the cable increases from the load end to the tail end of the second capstan 2, the frictional force is spread evenly over the second capstan 2, as a result of which the cable, and the grooves 11, are not subjected to unduly high frictional forces in any one place. At the same time, sufficient tension is maintained in the last few turns of cable adjacent the tail end to prevent the same from becoming slack.

Claims (12)

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1. A winch comprising a rotatable bearing surface for a cable, wherein the 5 friction between the surface and a given cable material at a given cable tension varies continuously, or stepwise in a plurality of steps, along a rotational axis.

2. A winch according to Claim I, wherein the coefficient of friction of the surface for a given cable material increases gradually, or stepwise in a plurality 10 of steps, along the rotational axis.

3. A winch according to Claim 2, wherein the surface comprises a high friction material. 15

4. A winch according to Claim 3, wherein the coefficient of friction of the high friction material on steel is substantially greater than the coefficient of friction of steel on steel.

5. A winch according to Claim 3, wherein the high friction material 20 comprises a high friction polymer.

6. A winch according to Claim 5, wherein the high friction polymer is a polyurethane, a polypropylene or a polyvinylchloride. 25

7. A winch according to Claim 3, wherein the high friction material comprises silicon enriched aluminium.

8. A winch according to Claim 2, which comprises a capstan provided with a plurality of circumferential grooves, the coefficient of friction of the surface 30 of each groove being different.

9. A winch according to Claim 2, wherein the surface comprises material the density of which decreases exponentially along the rotational axis. 35

10. A winch according to Claim I, which comprises a capstan provided with a plurality of circumferential grooves, the cable bearing surface area of each groove being different. -6- 209806 %

11. A winch according to any one of the preceding claims, which is a single axis twin capstan winch.

12. A single axis twin capstan winch, substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings. DAT£-0 TH(S 5!nol I3AY OF OscGrrke.s' A. J. PARK & SON AGENTS FOR THE XPWJCAN7 ■>