Control system for multi-stage lift

Claim 2

A compressible fluid-operated multi-stage telescopic hoist for operating up to a given load limit comprising, an extendable and retractable hoist assembly having a plurality of intermediate stages progressing telescopically from a base stage of largest cross section to a top stage of smallest cross section, said base stage together with a bottom group of said intermediate stages comprising a bottom set of stages and the remainder of said intermediate stages together with said top stage comprising a top set of stages, controlled supply means for selectively supplying a compressible fluid to said bottom set via the base stage at a predetermined pressure above the minimum pressure level sufficient for the top stage to meet the given load limit and for selectively supplying a compressible fluid to said top set via the top stage at a pressure at least as high as said minimum level, whereby the column composed of said bottom set is always stiffer than the telescopically superposed column composed of said top set whenever the hoist assembly is extended beyond said bottom set, and vent means for selectively venting said sets such that the pressure in the bottom set is maintained at least as high as the pressure in the top set while the hoist assembly is being retracted.

Claim 3

A hoist according to claim 1 in which said top set is always internally separated from communication with said bottom set by divider means, and in which said vent means is arranged to vent said top set via said top stage and to vent said bottom set via said bottom stage.

Claim 4

A hoist according to claim 2 in which said vent means is arranged to vent said top and bottom sets simultaneously.

Claim 5

A hoist according to claim 1 in which said controlled supply means includes normally closed valve means controlling the supply of fluid to said top set, said valve means being adapted to open responsive to full extension of said bottom set at said predetermined pressure.

Claim 6

A hoist according to claim 4 in which said vent means includes a check valve bypassing said valve means in a flow direction opposite that through the valve means.

Claim 7

A hoist according to claim 1 in which said vent means is arranged and adapted to vent said top set via said top stage and to vent said bottom set via the top set after the top set is substantially retracted.

Claim 8

A hoist according to claim 6 in which said sets are internally separated by a divider means and said vent means includes a normally closed valve in said divider means and means in said top set for opening said valve responsive to a substantial retraction of said top set whereby said bottom set can then vent through said top set.

Claim 9

A compressible fluid-operated multi-stage telescopic hoist for operating up to a given load limit comprising, an extendable and retractable hoist assembly having a plurality of intermediate stages progressing telescopically from a base stage of largest cross section to a top stage of smallest cross section, said base stage together with a bottom group of said intermediate stages comprising a bottom set of stages and the remainder of said intermediate stages together with said top stage comprising a top set of stages, controlled supply means for selectively supplying a compressible fluid to said bottom set via the base stage at a supply pressure well above the minimum pressure level sufficient for the top stage to meet the given load limit and for selectively supplying a compressible fluid to said top set via the top stage at a pressure at least as high as said minimum level and only when said bottom set is in a fully extended condition, and vent means for selectively venting said sets such that the pressure in the bottom set is maintained at said supply pressure while the top set is being retracted, whereby the column composed of said bottom set is always stiffer than the telescopically superposed column composed of said top set whenever the hoist assembly is extended to a height greater than the fully extended height of said bottom set.

Claim 10

A compressible fluid-operated multi-stage telescopic hoist for operating up to a given load limit comprising, an extendable and retractable hoist assembly having a plurality of intermediate stages progressing telescopically from a base stage of largest cross section to a top stage of smallest cross section, said base stage together with a bottom group of said intermediate stages comprising a bottom set of stages and the remainder of said intermediate stages together with said top stage comprising a top set of stages, controlled supply means for selectively supplying a compressible fluid to said bottom set via the base stage at a supply pressure well above the minimum pressure level sufficient for the top stage to meet the given load limit and for selectively supplying a compressible fluid to said top set via the top stage at a pressure at least as high as said minimum level and only when said bottom set is in a fully extended condition, and vent means for selectively venting said sets such that the pressure in the bottom set is maintained at said supply pressure while the top set is being retracted, whereby the column composed of said bottom set is always stiffer than the telescopically superposed column composed of said top set whenever the hoist assembly is extended to a height greater than the fully extended height of said bottom set.

Claim 11

A compressible fluid-operated multi-stage telescopic hoist for operating up to a given load limit comprising, an extendable and retractable hoist assembly having a plurality of intermediate staGes progressing telescopically from a base stage of largest cross section to a top stage of smallest cross section, said base stage together with a bottom group of said intermediate stages comprising a bottom set of stages and the remainder of said intermediate stages together with said top stage comprising a top set of stages, supply means for supplying a compressible fluid to said hoist assembly at a supply pressure well above the minimum level sufficient for the top stage to meet the given load limit, first supply control means for selectively conducting the supplied fluid to said bottom set via the base stage, second supply control means operating responsive to a fully extended condition of said first set at said supply pressure for conducting the supplied fluid to said top set via the top stage, and vent means for selectively venting said sets through said top stage such that the top set is substantially fully retracted before venting of the bottom set is commenced, whereby the column composed of said bottom set is always stiffer than the telescopically superposed column composed of said top set whenever the hoist assembly is extended beyond said bottom set.

Claim 12

A compressible fluid-operated multi-stage telescopic hoist for operating up to a given load limit comprising, an extendable and retractable hoist assembly having a plurality of intermediate staGes progressing telescopically from a base stage of largest cross section to a top stage of smallest cross section, said base stage together with a bottom group of said intermediate stages comprising a bottom set of stages and the remainder of said intermediate stages together with said top stage comprising a top set of stages, supply means for supplying a compressible fluid to said hoist assembly at a supply pressure well above the minimum level sufficient for the top stage to meet the given load limit, first supply control means for selectively conducting the supplied fluid to said bottom set via the base stage, second supply control means operating responsive to a fully extended condition of said first set at said supply pressure for conducting the supplied fluid to said top set via the top stage, and vent means for selectively venting said sets through said top stage such that the top set is substantially fully retracted before venting of the bottom set is commenced, whereby the column composed of said bottom set is always stiffer than the telescopically superposed column composed of said top set whenever the hoist assembly is extended beyond said bottom set.

Claim 13

A compressible fluid-operated multi-stage telescopic hoist for operating up to a given load limit comprising; an extendible and retractable hoist assembly having a plurality of intermediate stages progressing telescopically from a base stage of largest cross section to a top stage of smallest cross section, said base stage together with a bottom group of said intermediate stages comprising a bottom set of stages and the remainder of said intermediate stages together with said top stage comprising a top set of stages, controlled supply means for simultaneously supplying a compressible fluid to said bottom set and to said top set via both the base stage and the top stage whereby the pressure in the bottom set is increased above the pressure level sufficient for the uppermost stage to meet the upper limit, whereby the column composed of said bottom set is always stiffer than the telescopically superposed column composed of said top set whenever the hoist assembly is extended beyond said bottom set.

Claim 14

A compressible fluid-operated multi-stage telescopic hoist for operating up to a given load limit comprising; an extendible and retractable hoist assembly having a plurality of intermediate stages progressing telescopically from a base stage of largest cross section to a top stage of smallest cross section, said base stage together with a bottom group of said intermediate stages comprising a bottom set of stages and the remainder of said intermediate stages together with said top stage comprising a top set of stages, controlled supply means for simultaneously supplying a compressible fluid to said bottom set and to said top set via both the base stage and the top stage whereby the pressure in the bottom set is increased above the pressure level sufficient for the uppermost stage to meet the upper limit, whereby the column composed of said bottom set is always stiffer than the telescopically superposed column composed of said top set whenever the hoist assembly is extended beyond said bottom set.