Patent GB-606507-A (GB)
Title: Improvements in and relating to lifting apparatus or jacks
IPC: B66F1/02
Filed: 1945-05-28
Abstract: 606,507. Load-handling apparatus; lifting jacks. BRADBURY & SONS, Ltd., J., POWELL, A. D., and POWELL, V. May 28, 1945, No. 13344. [Class 78 (iii)] [Also in Group X] Relates to working platforms for scaffolding, and is a development of the invention of Specification 606,503, which provides means for stepwise raising and lowering of a platform by the alternate engagement of upper and lower gripping plates with a scaffolding standard, the gripping plates being suitably actuated in the case of lowering by the reciprocation of a trip bar, the change from lifting to lowering and vice-versa being effected by moving the trip bar into and out of engagement. According to the invention the trip bar cannot be moved from either position unless the parts of the apparatus are suitably disposed for the next operation, either of lowering or lifting. At the commencement of a lowering operation the lower gripping plate must be in gripping relation to the standard and the upper gripping plate must be in its free or non-gripping position, and the upper gripping plate must also be at the top of its stroke, i.e. it must have full scope to slip down the standard, for its full distance, corresponding to a full stroke of the handle. At the commencement of a lifting operation the lower gripping plate must be in gripping relation to the standard and the upper gripping plate must be in its free or non- gripping position, as for lowering, but the upper gripping plate must be at the bottom of its stroke, i.e. able to slip up the standard for its full distance. The mechanism is enclosed in a box-like casing which has top and bottom bearings which enable it to slide up and down the standard. The trip gear, Fig. 3, comprises a rod 30 slidable in guides 31 fixed to one side of the casing, a gate bar 32 pivoted to the rod 30, and a trip-bar 33. The change-over means comprises a plate 40 hinged at 41 to a side of the casing and connected to the trip bar 33 by a pin 42 which also passes into a guide slot 43 in the gate bar 32. A spring bolt 44 at the end of the plate 40 engages either of two recesses in the side of the casing, and locks the plate in the lowering or raising position. In Fig. 3 the plate 40 is shown in its top position, with the trip gear held back out of engagement through the pin 42 thrusting back the gate bar 32. Alternate depression and raising of the handle 22 then raises the apparatus, in the manner explained in Specification 591,596, [Group X]. To engage the trip gear, and so to change from step-by-step lifting to step-by-step lowering, the plate 40 is swung down to the position shown in Fig. 4. When the plate 40 is so moved the slot 36a in the gate bar 32 receives the projection 38 on the extension 39 of the handle and the slot 35a in the gate bar is removed from the projection 37 on the casing 1. In addition, the top of the slot 53 in the trip bar engages the laterally turned end of the cranked end 51 of the upper element of the spring toggle 20 and trips the toggle 20 to the position in which a shoulder 20b on its upper element, (Fig. 5A) presses the -plate 13 to its free position. The plate 13 is now at the top of its stroke and the plate 7 is in its gripping position. If the plate 13 had not been at the top of its stroke the extension 39 of the handle would have been raised and the projection 38 would not have entered the slot 36a. If the plate 7 had not been in its gripping position the rod 30 would have been holding up the gate bar 32 and the slot 36a would again not have engaged with the projection 38. Depression of the handle now causes it to turn on the trunnions 19, fixed to the casing, and thus to pull the plate 13 down the standard and to raise the trip gear. Near the end of the down stroke of the handle the lower projection 52 on the rod 30 strikes the cranked end 50 of the upper element of the spring toggle 11 and reverses the toggle, and the lower step 54 of an elbow 55 rigid with the gate bar 32 reverses the toggle 20. The shoulder 11b of the upper element of the toggle 11 tends to thrust the plate 7 into its free position, Fig. 5B, and does so immediately the plate 13 grips the standard and takes the load, the load being removed from the plate 7 by the remaining downward movement of the handle. The handle is now raised and turns on the pivots 17 at the end of the links 14 suspended from the plate 13. The trunnions 19, and therefore the casing 1 with the platform attached to it, are thus lowered, together with the trip gear. Shortly before the end of the stroke the upper projections 52 and the top of the slot 53 restore the respective toggles to the condition shown in Fig. 4. The lower plate 7 takes the load and the upper plate 13, being relieved of the load by the remaining upward movement of the handle, is thrust into its free position. The cycle is then repeated and the guide lowered in steps down the standard. To change back from lowering to lifting the plate 7 must be gripping, and the plate 13 must be free and at the bottom of its stroke. This is the condition shown in Fig. 4. In this position the slot 35a is opposite the projection 37 and the trip gear can be disengaged by raising the plate 40. For lifting, the plate 13 must be in gripping relation to the standard as well as the plate 7. The disengagement of the trip gear is therefore made to cause an upper step 58 on the elbow 55 to move into the path of the cranked extension 51, so that the plate 13 is tipped to its gripping position as soon as the handle is lowered initially. The apparatus will then operate to effect stepwise raising as already referred to. It may either be arranged to move the plate 40 by the insertion of a suitable tool into the casing, or to provide it with a handle or knob which is permanently accessible from outside the casing and can be locked in either extreme position.