Patent GB-606503-A (GB)
Title: Improvements in and relating to lifting apparatus or jacks
IPC: B66F1/02
Filed: 1945-04-06
Abstract: 606,503. Load-handling apparatus; lifting jacks. BRADBURY & SONS, Ltd., J., POWELL, A. D., and POWELL, V. April 6, 1945, No. 8607. [Class 78 (iii)] [Also in Group X] Relates to working platforms for scaffolding, and is a development of the invention of Specification 591,596, [Group X], which provides means for stepwise elevation of a platform by the alternate operation of upper and lower gripping plates on a scaffolding standard. According to the invention the gripping plates are actuated for stepwise lowering by the trip bar 16, Fig. 2. Projections 19, 19a actuate the upper gripping plate 5 and projections 20, 20a actuate the lower gripping plate 9. In Fig. 2, the upper gripping plate 5 is in gripping relation with the standard, i.e. tilted, in which position it is resiliently held by the pressure on its wedgeshaped end 32 of the ramp 36 in the block 33 attached to the blade spring 34. The plate is resiliently held in its free, i.e. horizontal position by engagement of the wedge 32 in the notch 35 in the block 33. A pair of blade springs 22 provides a means, whereby the plate may be biassed towards its free position without actually moving thereto until the load is removed from it. The bias is impressed by the downward movement of the trip bar, which causes the projections 19 to flex the blade springs 22 downwards. A pair of blade springs 23 provides a similar biassing means for the lower gripping plate, which is also held resiliently in either position in the same manner as the upper gripping plate, similar parts being indicated by the same numerals (32, 33, 34, 35, 36). In Fig. 2 the trip bar 16 is shown in its disengaged position, being held there by a pin 24 which fits into a hole in one of the brackets 18 by which the 'trip bar is guided. The apparatus then operates as described in Specification 591,596. To bring the trip bar into operation, the pin 24 is removed from the bracket and passed through the holes 28 in the forked end of the operating lever 4 and a slot 29 formed between two lugs on the trip bar. The sequence of operations for stepwise lowering is then as follows : (1) The operating lever is depressed, pivoting on the pin 8. This causes the guide 1 (to which the platform is attached as in Specification 591,596) to rise initially and causes the trip bar 16 to rise so that the projections 20a strike the blade springs 23 and tip the plate 9 to its neutral position. The load is now suspended from the upper gripping plate 5, through the operating lever. (2) The operating lever is raised, pivoting on the pin 8, and the guide is therefore lowered. The trip bar 16 is also lowered, so that the projections 19 stress the blade springs 22 in the direction tending to force the plate 5 to the free position and the projections 20, by engagement with the blade springs 23, trip the plate 9 to the gripping position. Immediately the plate 9 grips, it takes the load, with the result that the stressed blade springs 22 snap the plate 5 to the free position. (3) The operating lever is depressed, pivoting on the pin 3, and the plate 5 is lowered and the trip bar 16 raised. The projections 20a strike the blade springs 23 and bias the plate 9 towards its free position. The projections 19a then strike the blade springs 22 and trip the plate 5 to its gripping position, and the plate 9 snaps over to its free position. Operations (2) and (3) are then repeated alternately and the apparatus thus lowered down the standard in steps. In a modification, the biassing of the gripping plates is effected by spring toggles, extensions from which enter the spaces between the projections on the trip bar, and which apply pressure to the gripping plates on one side or other of the pivots thereof, so holding them in position. The trip bar may be in two parts hinged together, the upper part being swung into and out of engagement with the operating lever. Fig. 5 shows another means of biassing the gripping plate, according to the degree of flexure of a blade spring 56. As shown in full line, the plate is biassed to its gripping position. When the trigger 59 is raised by the projection 20a the cross-pin 58 sits in the kink 61 of the spring and causes it to bias the plate towards its free position as shown in dotted line.