Patent GB-1250897-A (GB)
IPC: E02D13/10
Filed: 1968-05-22
Abstract: 1,250,897. Clamps. H. O. R. DEW. 25 Feb., 1969 [22 May, 1968], No. 24293/68. Heading E2B.  A gripping means comprises a pair of gripping jaws 7, 8 mounted in a recess 2 in support means 1 said recess having an open end into which an object 17 to be gripped can be entered for engagement by the gripping jaw, walls 3, 4 of the recess which are engaged by the gripping jaws converging towards said open end, and each gripping jaw has an inwardly-facing surface comprising inner and outer portions inclined to one another at an obtuse angle and an outwardly-facing surface comprising inner and outer portions also inclined to one another at an obtuse angle such that the gripping jaw has the inner portion 12 of the inwardly facing surface inclined to the outer portion 9 of the outwardly facing surface at an angle which is smaller than the angle between the outer portion 11 of its inwardly facing surface and the inner portion 10 of its outwardly facing surface and in that spring means 13 is provided normally urging the outer portion of the inwardly facing surface of each gripping jaw in a direction towards the article to be gripped. In the construction shown, the spring means is aN single leaf spring 13 bent into substantially U shape and the jaws do not engage the walls 3, 4 directly but instead engage them via the spring, each outwardly facing jaw surface being the base of a recess in the jaw. The arrangement of the various surfaces is such that in the gripping positions the inner portions of the inwardly facing surfaces of the jaws grip the object while the outer portions of the outwardly facing surfaces engage the walls through the springs, in these positions of the jaws the spring being unstressed. When however force between the support means 1 and the object 17 is removed, the jaws are pivoted by the spring so that the outer portions of the inwardly facing surfaces of the jaws engage the object and the inner portions of the outwardly facing surfaces engage the walls via the spring. In a modification, the leaf spring is replaced by a pair of springs made from rod of circular cross section; these are located in recesses in the jaws. The support means can form part of a quick release shackle and in this case the jaws are moved into engagement with the object by a member above the jaws which is itself moved by a hand wheel via a threaded rod; the threaded rod is engaged in a threaded bore in a block slidably mounted in the support means and held in position by a spring loaded detent which can be manually released to enable the block to slide to release the jaws. The gripping means can also form part of a tensioning device, in this case the support means is mounted in a casing and have a screw threaded rod (41, Fig. 6, not shown) which passes through a boss in the casing to be engaged by a nut externally of the casing; the spring can be connected to an indicating device for indicating the separation of the ends of the spring limbs and hence the force being exerted upon the object by the tensioning device. The gripping device can also form part of an overload warning indicator and in this construction the support means has a cross sectional shape which is a segment of a circle and which is received in a support housing which forms part of a structure of a hoisting device such as a crane. Adjacent the ends of the leaf spring, electric switches are carried by the support means and when the force exerted on the object 17 which is for example a hoisting member of the crane exceeds a safe value the free end portions of the spring limbs are forced outwardly into engagement with the movable contacts of the switches to close the switches which can be used to initiate an alarm or reduce the force. In this construction the outwardly facing surfaces of the jaws are provided with rollers to reduce the friction between the jaws and the limbs of the spring. It is stated that where the object to be gripped is fragile the inwardly facing surface of the jaws can be lined with soft material, for example rubber.