Multi-stage extendible and contractible shaft with shock absorption

Claim 1

In an extendible and contractible shaft having a plurality of shaft members having a common longitudinal axis, each shaft member having a head at an end thereof, and each, except the outermost shaft member, being telescoped within the one next adjacent, the head of each telescoped shaft member comprising a piston slidably seated to the inner wall of the next adjacent outer shaft member to form a series of tandem arranged sealed pistons having respective cross-section areas which progessively increase from the innermost piston sealed to the outermost shaft member, each of said piston having a first side and a second side, a first fluid pressure surface defined on said first side of each pistons, a second fluid pressure surface defined on said second side of each of said pistons, said second fluid pressure surface extending circumferentially outwardly from each of said shaft members towards the next adjacent shaft member, a third fluid pressure surface defined on said second side of each of said pistons except the innermost piston, said third fluid pressure surface extending circumferentially inwardly from each of said shaft members except the innermost towards the longitudinal axis. a fluid passageway through each piston, except the innermost piston in the tandem of said pistons so that said first fluid pressure surfaces of said first sides of all the pistons are in fluid communication with each other, fluid passageways between adjacent shaft members, first fluid communication means providing fluid communication between adjacent fluid passageways at positions at the second sides of the respective pistons, so that said second fluid pressure surfaces of all the pistons are in fluid communication with each other, second fluid communication means providing fluid communication between said first fluid pressure surfaces and said third fluid pressure surfaces of each of said pistons except the innermost and a first inlet port means communicating with said first fluid pressure surface of one of said pistons and a second inlet port means communicating with said second fluid pressure surface said one of said pistons, whereby application of fluid pressure at said first inlet port means introduces pressurized fluid to said first sides of the pistons, which extends the length of said shaft, and application of fluid pressure at said second inlet port means introduces pressurized fluid to said second sides of said pistons, which contracts the length of said shaft, the improvement comprising: means providing a metering channel in the path of fluid flow between the first side of said one of said pistons and said first inlet port means, thereby permitting metered release of fluid toward said first inlet port means near the end period of the contraction movement of said one piston, and causing blockage of fluid flow at the metering means at the end of said period, and means comprising a channel through said one piston providing fluid communication between the second fluid communication means and the first inlet port means thereby by-passing said blockage. whereby the contraction movement of said one piston is slowed, thereby alleviating shock, and then stopped, whereupon fluid continues to be released to said first inlet port means, so that said period of slowing is accomplished without affecting the rate of movementof another piston during said perid.