Patent GB-1524026-A (GB)
Title: Structures which deform substantially with a controlled negative spring rate
IPC: B21C35/04
Filed: 1975-08-12
Abstract: 1524026 Counterbalancing apparatus J H ELLINGER 12 Aug 1975 [9 Aug 1974] 35377/74 Heading B8B An apparatus securable to a bath for counterbalancing an invalid carrying platform vertically movable into and out of the bath water, comprises a pair of inclined struts 41, 42 pivotally connected at their lower ends 43, 44 to a frame 10 for rotation about horizontal axes, the top ends of the struts slidably supporting the platform therebetween, and constant on negative rate springs 58 adjustably connected between the frame and the struts through flexible ties 59 to operate in a sense to rotate the struts to raise the platform. With negative rate springs, the lifting counterbalancing force for the platform is reduced as it lowers and moves into the bathwater where buoyancy assists the springs. When constant rate springs are used, the points of connection between the ties 59 and struts 41, 42 are slidable under cam control, towards the strut pivots 43, 44 as the struts pivot downwardly to reduce the spring force applied. The two struts 41, 42 are slidingly pivoted at 53 to a crosshead 39 vertically movable along a guide rail 38 forming part of the frame 10. The latter further comprises parallel front and rear oval section rails 30, 31 at each side thereof, the invalid carrying platform running up and down the front rails 30 through vertically spaced pulley bogies on the platform engaging each rail 30. The upper pulley bogey at each side of the platform engages the rear face of the associated rail 30 whilst the lower bogey engages the front face, a spring loaded plastics slide block being mounted on the platform to react with the rail 30 on the opposite side to each pulley bogey. The platform is vertically movable by rollers 60 at the free ends of the struts 41, 42 slidingly engaging respective forwardly and backwardly facing channels extending across the platform which has a seat portion pivotal into a vertical storage position. The springs 58, which are mounted in back-to-back pairs at each side of the frame 10, are housed in selfaligning casings secured to the outside of the frame intermediate its height, the casings each being associated with structure supporting a horizontal telescopic member 100, 101 pivotally adjustable in a horizontal plane to engage the associated bath rim to support the frame thereon. In another embodiment of Fig. 16 (not shown) the strut rollers engage slots in the sides of the platform and the tie elements pass in frictional engagement around opposite ends of a rotatable tube at the top of the frame, to balance out uneven tensions in the ties.  In a further embodiment of Fig. 17 (not shown) the platform is controlled by pairs of rollers on a parallelogram linkage at each side of the platform engaging side slots therein, a tie extending from each roller pivot, over a pulley on a load balancing tube end on to a spring. In the embodiment of Fig. 18 (not shown) the platform is controlled by pairs of parallel links interconnected and pivotally connected to each side of the platform, the links at each side being associated with a tie and spring arrangement. In a final embodiment of Fig. 19 (not shown) the arrangement is similar to that in Fig. 5 except that the struts are held in equal operation by chain and sprocket interconnection between pulleys over which the ties pass with frictional grip.