Platform elevating apparatus

Claim 1

An elevating device for a workman's platform having a base and a platform vertically movable between a fully retracted position and a raised position, comprising: (a) a plurality of interconnected lift arms having central and end pivotal interconnecting points, certain lower of said lift arms being adapted for pivotal connection to the base and certain upper of said lift arms being adapted for pivotal connection to the platform; (b) a power lift cylinder mounted entirely below said lift arms when said arms are fully retracted, said cylinder having an extendible piston pivotally connected at one end to one of said lower lift arms; (c) a cam plate connected to said one lower lift arm at a point on the opposite side of said central interconnection point of said one lower lift arm, said cam plate having a cam surface, (d) pivot arm means mounted for rotation about a horizontal fixed axis, one end of said pivot arm means being operatively connected to the end of said lift cylinder opposite said piston, and the other end of said pivot arm means having mounted thereon a cam roller for engaging said cam surface when said lift arms are retracted and during initial lifting movement of said arms from such retracted position, said cam roller and cam surface being so oriented as to provide a vertical lifting force on said one lower lift arm when said power lift cylinder is actuated, whereby actuation of said lift cylinder to raise said arms and platform results in rotation of said pivot arm means and lifting of said cam roller whereby said one lower lift arm is raised both at its connection to the cylinder piston and at the point of engagement between said cam surface and said cam roller.