GB1574238A

GB1574238A - Clamping jaws

Info

Publication number: GB1574238A
Application number: GB14744/77A
Authority: GB
Original assignee: Tractel SAS
Current assignee: Tractel SAS
Priority date: 1976-04-13
Filing date: 1977-04-07
Publication date: 1980-09-03
Also published as: FR2348405B1; JPS52124658A; FR2348405A1; DE2715564A1

Description

(54) IMPROVEMENTS IN OR RELATING TO CLAMPING JAWS (71) We, TRACTEL S.A. a French body corporate, of 85-87 Avenue Jean Lolive 93170 Bagnolet, France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to self-clamping of jawblock systems, of the type adapted to grip a rope or cable by means of a pair ofjaws.

In certain known versions of such driving systems, as illustrated diagrammatically in Figures 1 and 2 of the attached drawings, a pair of cams 2,3 disposed symmetrically in relation to the axis of rope 1 are pivotally mounted on fixed pivot pins 4,5 carried by a suitable frame structure for engagement either directly with the rope 1 (Figure 1) or with each jaw of the pair of jaws 6,7 (Figure 2) adapted to clamp the rope 1, respectively. These jaws 6, 7 are advantageous in that they comprise a rectilinear groove affording a better gripping or clamping action than the curved groove of the cams. The arrows added to the various Figures of the attached drawings designate the direction of the movements corresponding to a selfclamping action of the device.

These self-clamping or jaws-block systems may be utilized for connecting a load to a rope, cable, rod or the like, or incorporated in safety devices or apparatus for the purpose of sustaining, holding or recovering a load on a rope or rod in case of failure of the hoisting apparatus or alternatively disposed to constitute two blocks in a mechanical, hydraulic or other linkage or connecting-rod system imparting simultaneously to these two blocks a reciprocating motion permitting the hauling in or out of a rope or rod.

In the simplest embodiment of the abovedefined structure, as illustrated in Figure 2, these devices are objectionable in that they do not provide a positive drive for each jaw through the associated cam member. According to another version illustrated in perspective view in Figure 3, the positive drive is provided by a gear coupling between each jaw and the associated cam member. In this Figure 3, the rope is again designated by the reference numeral 1, the toothed cams being shown at 8,9 and the clamping jaws 10,11 carry teeth 12 meshing with the teeth 13 of the associated cam members members. A chief inconvenience of these gear system is that considerable pressures are exerted on the meshing teeth by the loads through the jaws. Beyond certain limits, these pressures are likely to break the meshing teeth.

It is a prime object of the present invention to provide novel improvements in a known device operating with a positive and controlled drive permitting the transmission of pressures between cam members and jaws under considerably improved conditions while using relatively simple, easily manufactured or machined parts.

According to the present invention there is provided a clamping mechanism for clamping a rope or rigid rod comprising a pair of jaws which are arranged to tightly engage the rope or rigid rod under the action of cams, at least one cam acting on each jaw, one of the interengaging surfaces of each cam and jaw pair having a series of cavities therein and the other having a series of studs thereon arranged to engage in said cavities to prevent relative slip between the interengaging surfaces, the studs and cavities disposed in a zig-zag fashion.

The invention is further described, by way of example, with reference to the accompanying drawings, in which: Figures 1 to 3 already mentioned hereinabove in connection with the description of the prior art illustrate diagrammatically known devices pertaining to the art of the present invention Figure 4 is a first embodiment of a device according to the present invention, shown diagrammatically in side elevational view with parts broken away; Figure 5 is a side elevational view showing a modified embodiment of the device according to this invention; Figure 6 is a plan view from above showing a jaw provided with zig-zag arranged studs as in the device of Figure 5; and Figure 7 is a view similar to Figure 5 showing on a smaller scale a device comprising two pairs of cams engaging a single pair of jaws.

Referring now to the embodiment illustrated in Figure 4, the rope or cable is disposed between a pair of antagonistic jaws 6,7 responsive to the pressure of cams 2,3 as in the case of Figure 2, the device further comprising a pair of contact springs 14,15 adapted to urge the cams and jaws of the device for mutual engagement. A pre-clamping member illustrated in this example is hydraulic cylinder 16 operating in a direction parallel to the rope axis so that the longitudinal movement of the jaws is attended by a movement thereof towards the rope and the clamping of the rope by said jaws due to the driving contact thus produced between the jaws and the cams by studs and cavities later described by reference to Figure 5 but not shown in the schematic illustration of Figure 4.

The preclamping member may also consist of a spring or any other device capable of exerting on the jaws an action involving a movement of the cams in the clamping direction.

The driving contact between the jaws and the cams is enhanced through the action of said contact springs 14,15 incorporated in the device of the present invention.

In order to impart a positive character to the driving action exerted on each jaw by each cam and prevent a relative sliding movement between their respective rolling surfaces, the rolling surface of each jaw has two alternate or zig-zag arranged rows of cavities formed therein and each cavity has force-fitted therein a stud 1 7 having a hemispherical head adapted to engage corresponding recesses 22 formed in the registering rolling surface of the cam, as illustrated diagrammatically in Figure 5 showing two cams 18,19 engaging relevant jaws 20,21 respectively, Figure 6 showing in plan view one of the jaws disposed on the rope Without the corresponding cam.

The hemisperical heads of studs 17 are thus caused to mesh with said cavities 22 formed in the rolling surfaces of cams 18 and 19, as shown in Figure 5.

The zig-zag or alternate arrangement of the studs 17 and relevant cavities 22 constitute a specific feature characterizing this invention in that it avoids a continuous weak area in the parts concerned.

Due to the considerable pressure exerted on the contact generatrix line of the cam, an elastic distortion is produced in the cam and this distortion can be calculated in as much as it is a hertzian distortion generating a contact surface more propitious to the application of pressure than gear teeth. In this case, the studs 17 are not strained as a consequence of the clamping pressure and can therefore operate like positive drive members without any risk of failure.

In the above description only one cam per jaw is mentioned, which corresponds to one pair of cams for one pair of jaws. Of course, it would not constitute a departure from the scope of the present invention to provide a modified embodiment shown diagrammatically in Figure 7 wherein a plurality of cams are disposed coaxially, or sequentially along the rope, in order to ensure a better distribution of the stresses involved. In Figure 7, the same reference numerals as in Figure 5 are used, the tandem-arranged cams being designated by the same reference numerals 18 and 19 although they co-act with a same and common pair of jaws.

Although specific forms of embodiment of this invention have been described hereinabove and illustrated in the attached drawing, it will readily occur to those skilled in the art that various modifications and changes may be brought thereto without departing from the scope of the invention as set forth in the ap

Claims

pended claims. The mechanism illustrated in Figures 4 to 7 may be used in combination with a mechanism capable of detecting a load rupture in or the linear velocity of the rope and a parachute system capable of supporting the load in case of failure of or excessive velocity of the hoisting equipment. Alternatively the mechanism illustrated in Figures 4 to 7 can be operatively connected to another similar device through suitable linkage means in order to constitute hauling in and hauling-out system for a rope or a rigid rod. WHAT WE CLAIM IS:

1. A clamping mechanism for clamping a rope or rigid rod comprising a pair of jaws which are arranged to tightly engage the rope or rigid rod under the action of cams, at least one cam acting on each jaw, one of the interengaging surfaces of each cam and jaw pair having a series of cavities therein and the other having a series of studs thereon arranged to engage in said cavities to prevent relative slip between the interengaging surfaces, the studs and cavities being disposed in a zig-zag fashion.

2. A mechanism as claimed in claim 1, in which spring means are enclosed in blind holes formed at each end of the jaw and have their axes disposed at right angles to the rolling surface of said jaw to urge said jaw towards said cam.

3. A mechanism as claimed in claim 1 or 2.

further comprising a pre-clamping device for urging said jaw in a direction in which the cam co-acts with the jaw to urge the latter into engagement with the rope or rod and thus provide a self-clamping arrangement particularly efficient for handling relatively heavy loads.

4. A mechanism as claimed in claim 3, in which said pre-clamping device comprises a hydraulic jack operating in a direction parallel to the rope or rod axis and connected to said jaw.

5. A mechanism as claimed in any preceding claim in which said studs have hemispherical heads and said cavities are hemispherical.

6. A mechanism as claimed in any preceding claim in which said studs are force-fitted in holes in the jaw or the cam, as the case may be.

7. A mechanism as claimed in any preceding claim in which the studs are on the jaw and the cavities are in the cam.

8. A mechanism as claimed in any preceding claim in which a second cam also co-operates with each jaw and the mutually engaging rolling surfaces of said second cams and the respective jaws have interengaging studs and cavities.

9. A clamping mechanism constructed substantially as herein described with reference to and as illustrated in Figures 4 to 7 of the accompanying drawings.

10. A mechanism as claimed in any of claims 1 to 9 in combination with a mechanism capable of detecting a load rupture in or the linear velocity of the rope and a parachute system capable of supporting the load in case of failure of or excessive velocity of the hoisting equipment.

11. A mechanism as claimed in any of claims 1 to 9 which is operatively connected to another similar device through suitable linkage means in order to constitute a hauling-in and hauling-out system for a rope or a rigid rod.