Elevatable scaffold

Claim 2

An elevatable scaffold including a base and a platform connected therebetween by a lift assembly movable between a collapsed position and extended positions for elevating said platform above said base, said lift assembly comprising: a series of elongated structural assemblies each pivoted at one end and the middle thereof to some other structural assembly in said series; a cable passing substantially parallel with some of said structural assemblies and between the ends of mutually pivoted structural assemblies, one end of said cable being secured near the end of one of said structural assemblies; winch means mounted on said base and the other end of said cable wound thereon so that operation of said winch means may effect said elevating of said platform by further winding of said cable thereon; and means engageable by said cable when said lift assembly is in said collapsed position for providing a mechanical advantage in initiating the movement of said lift assembly toward said extended positions, comprising a sheave assembly mounted near the midpoint of one of the lowermost of said elongated structural assemblies and including at least first and second sheave members engageable by said cable between said winch means and one end of said one of the lowermost of said elongated structural assemblies, forcing a portion of said cable to assume an inclined path from said first sheave member toward said one end of said one of the lowermost of said elongated structural assemblies for creating a vertical force, upon operation of said winch means, to initiate movement of said lift structure from said collapsed position toward said extended positions.

Claim 3

An elevatable scaffold as set forth in claim 1 in which said sheave assembly is mounted for rotation about an axis allowing said cable to assume a straight line disposition upon movement of said lift structure to a predetermined extended position.

Claim 4

An elevatable scaffold as set forth in claim 1 in which said sheave assembly and said base are provided with cooperative cam and cam follower means mutually engageable upon operation of said winch means for effecting movement of said lift structure from said collapsed position to said predetermined extended position.

Claim 5

An elevatable scaffold as set forth in claim 3 in which said sheave assembly is attached to said one of the lowermost of said elongated structural assemblies near the midpoint thereof for rotation about said axis.

Claim 6

An elevatable scaffold as set forth in claim 4 in which said sheave assembly, upon movement of said lift structure to a more extended position than said predetermined extended position, is liftable above said base becoming inactive in providing said mechanical advantage.

Claim 7

An elevatable scaffold as set forth in claim 4 in which said sheave assembly comprises a pair of parallel plate members between which said first and second sheave members are mounted.

Claim 8

An elevatable scaffold as set forth in claim 1 in which each of said elongated structural assemblies comprises a pair of parallel elongated tong members, the ends of which are connected by header members, other sheave assemblies being attached to at least some of said header members for engagement by said cable between said winch means and the secured end of said cable.

Claim 9

An elevatable scaffold including a base and a platform connected therebetween by a lift assembly movable between a collapsed position and extended positions for elevating said platform above said base, said lift assembly comprising: a series of elongated structural assemblies, each pivoted at one end and the middle thereof to some other structural assembly in said series; a cable passing substantially parallel with some of said structural assemblies and between the ends of mutually pivoted structural assemblies, one end of said cable being secured near the end of one of said structural assemblies; winch means mounted on said base and the other end of said cable wound thereon so that operation of said winch means may effect said elevating of said platform by pulling the ends of said mutually pivoted structural assemblies together upon further winding of said cable thereon; and a sheave assembly mounted near the midpoint of the lowermost of said mutually pivoted structural assemblies and including at least one sheave member disposed above said base and engageable by said cable forcing a portion of said cable to assume an inclined path from said sheave member toward one end of one of said mutually pivoted lowermost structural assemblies creating a vertical force, upon operation of said winch means, to initiate movement of said lift structure from said collapsed position toward said extended positions, said sheave assembly also including a pair of plate members between which said sheave member is mounted, said plate members having arcuate cam surfaces thereon engageable with a cam follower mounted on said base and by which said vertical force to initiate movement of said lift structure is effected.

Claim 10

An elevatable scaffold including a base and a platform connected therebetween by a lift assembly movable between a collapsed position and extended positions for elevating said platform above said base, said lift assembly comprising: a series of elongated structural assemblies, each pivoted at one end and the middle thereof to some other structural assembly in said series; a cable passing substantially parallel with some of said structural assemblies and between the ends of mutually pivoted structural assemblies, one end of said cable being secured near the end of one of said structural assemblies; winch means mounted on said base and the other end of said cable wound thereon so that operation of said winch means may effect said elevating of said platform by pulling the ends of said mutually pivoted structural assemblies together upon further winding of said cable thereon; and a sheave assembly mounted near the midpoint of the lowermost of said mutually pivoted structural assemblies and including at least one sheave member disposed above said base and engageable by said cable forcing a portion of said cable to assume an inclined path from said sheave member toward one end of one of said mutually pivoted lowermost structural assemblies creating a vertical force, upon operation of said winch means, to initiate movement of said lift structure from said collapsed position toward said extended positions, said sheave assembly also including a pair of plate members between which said sheave member is mounted, said plate members having arcuate cam surfaces thereon engageable with a cam follower mounted on said base and by which said vertical force to initiate movement of said lift structure is effected.

Claim 11

An elevatable scaffold as set forth in claim 8 in which said plate members are rotatable about an axis parallel to the axis of said sheave member.

Claim 12

An elevatable scaffold as set forth in claim 9 in which said sheave assembly includes at least one other sheave member mounted between said plate members and below said first mentioned sheave member, when said lift structure is in said collapsed position, said cable engaging said other sheave member between said winch means and said first mentioned sheave member when said lift structure is in said collapsed position.

Claim 13

An elevatable scaffold as set forth in claim 9 in which said sheave assembly includes second, third and fourth sheave members engageable by said cable when said lift structure is in said collapsed position and effective upon said operation of said winch means for rotating and lifting the axis of said plate members while initiating said movement of said lift structure from said collapsed position toward said extended positions.

Claim 14

An elevatable scaffold as set forth in claim 11 in which said cable assumes a straight line position, between said winch means and said one end of said one of said mutually pivoted structural assemblies, upon movement of said lift structure to a predetermined extended position, relegating said sheave assembly to a passive role in further movement of said lift structure toward more extended positions.

Claim 15

An elevatable scaffold as set forth in claim 10 in which said cable assumes a straight line position, between said winch means and said one end of said one of said mutually pivoted structural assemblies, upon movement of said lift structure to a predetermined extended position, relegating said sheave assembly to a passive role in further movement of said lift structure toward more extended positions,

Claim 16

An elevatable scaffold as set forth in claim 13 in which said arcuate cam surfaces of said plate members are disengageable from said cam follower upon movement of said lift structure to said more extended positions.

Claim 17

An elevatable scaffold as set forth in claim 14 in which said arcuate cam surfaces of said plate members are reengageable with said cam follower upon unwinding of said winch means and consequent lowering of said lift structure below said predetermined extended position.

Claim 18

An elevatable scaffold as set forth in claim 15 in which said sheave assembly is rotatable about said axis of said plate members upon further lowering of said lift structure to said collapsed position until said cable assumes the same inclined path assumed prior to said movement of said lift structure from said collapsed position toward said extended positions.