Safety device for mobile work platform lift

Claim 1

In a mobile work platform lift assembly wherein a wheeled vehicle carries a pivoted tower movable from a substantially lowered position to an upright substantially vertical position for carrying a work platform and having a platform carriage movable responsive to a supporting cable on parallel rails longitudinally mounted on said tower, the improvement including: A. means mounting the horizontal work platform on said platform carriage extending outwardly in cantilevered relation on said platform carriage; B. a first pair of transversely spaced wheels carried on an upper portion of said platform carriage engageable with the rails on a side thereof remote from the work platform; C. a second pair of transversely spaced wheels carried on a lower portion of said platform carriage engageable with the rails on the other side of the rails; D. a stop member opposite said first pair of wheels on said other side of the rails in spaced relation thereto; E. wedging means carried by said carriage opposite said stop member held out of engagement by said supporting cable when said platform carriage is supported thereby; F. an oscillatable shaft carried transversely of said platform carriage in horizontal alignment with a respective rail; G. linkage means normally held by cable tension so as to maintain said wedging means in deactivated position; H. resilient means normally urging said linkage means to move said wedging means into wedging engagement with said rail; I. an outwardly extending crank arm fixed adjacent one end to said shaft; J. a pair of arms extending across said platform carriage; K. means pivotally supporting each of said arms with respect to said platform carriage in an intermediate portion thereof; L. means connecting an adjacent end of each of said arms to a respective crank arm; M. means connecting the other end of each arm to an adjacent cable; O. a compression spring bearing against each arm intermediate said means pivotally supporting each of said arms and said means connecting the other end of each arm to an adjacent cable; and P. means limiting upper movement of said arms as a result of force exerted thereon by said cable; whereby when said cable is no longer supporting said platform carriage said wedging means engages said rails engaging said stop member.