Patent GB-641752-A (GB)
Title: Improvements in lifting devices
IPC: B66F5/02
Filed: 1948-02-26
Abstract: 641,752. Lifting-jacks. AERONAUTICAL MACHINERY CORPORATION. Feb. 26, 1948, No. 5876. Convention date, Oct. 20, 1942. [Class 78 (iii)] A lifting jack lifts a load with two separate movements which comprise first lifting the load to an intermediate level on the free end of a pivoted lever arm and secondly lifting the load from said arms by a linearly extending jack which raises the load to a higher level. The embodiment disclosed comprises a pair of such jack elements mounted on a wheeled chassis and coupled so that they work synchronously. Each head 14 or 15 is lifted by means of a parallelogram linkage comprised of links 16, 17, 18 and 19, Figs. 4 and 5, the lower ends of which are formed as bell-cranks and are connected to members 26 which, when reciprocated, cause the arms to pivot. The reciprocation of this member is effected by a nut 30 secured thereto and a screw 32 which is rotated through ratchet gearing 48 by a hand lever 47, bevel gears 40, 42 being provided to transmit movement of this handle to the other handle (not shown) so ensuring even lifting of the heads. To allow for the horizontal movement of the heads during their arcuate movement in lifting the load, the load-engaging crutches 53 are mounted on wheels 54, see also Fig. 8, which normally engage rails 51, the crutches being prevented from moving in any direction other than longitudinally of the jack chassis by guide plates 60 integral with members 59 which normally seat loosely on the heads. The second lift is effected by screw jacks 55, 57, each carrying a head 69 which, when lifted engage sockets in the members 59 and lift them, together with the crutches 53, off the heads. During the second lift the crutches may remain out of alignment with the axes of the jacks and remain supported thereby through the guide plate 60. The jacks 55, 57 are of similar construction and the former comprises a non-rotatable sleeve 62 constituting the nut and a non-axially movable screw 64 which is rotatable through ratchet gearing 76 by an operating handle 11, Fig. 4, synchronous movement of the two screws being effected by bevel gearing (not shown) and a coupling shaft 79. The upper end of each of these jacks is pivoted to its associated head by trunnions 56, 58 which allow the jacks to lie horizontally when the arms are lowered, and to guide the jacks during their movement to and from a vertical position slotted guide plates 80<1>, pivoted on the chassis are provided to engage their lower ends. In a modification, Fig. 10, one crutch 53 is carried by both heads on a plate 83 which is mounted for movement longitudinally of the chassis by means of wheels 54 and rails 51, and in addition the crutch has a wheel and rail mounting on the plate 83 so allowing the crutch to slide across the chassis also. The height of the crutch is lowered by bending the plate 83 as shown, and in a further modification, Fig. 13, this is effected by constructing the middle portion of a load-engaging plate 85 in a Z formation. To take the weight of the load off the jack wheels a simple screw jack 12 is provided to lift the wheels 7 off the ground prior to raising the load.