Elevatable scaffold

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.