Vertical retractable rail clamp

A rail clamp comprising:

• a carriage having a lower end and an opposite upper end, wherein said carriage has a rigid base mounted at said lower end and an actuator frame mounted to said base so as to extend upwardly from said base to said upper end,
• at least one spring mounted in said actuator frame at said upper end of said carriage,
• a selectively actuable actuator mounted between said base and said at least one spring, and actuable between a retracted position, a first extended position, and a fully extended position,
• at least one guide wheel mounted on a wheel support so as to depend therefrom for rolling engagement along a rail,
• at least one suspension frame pivotally mounted at a first end thereof to said carriage and pivotally mounted at an opposite second end thereof to said wheel support, said actuator operating on said first end of said suspension frame so as to elevate said carriage to a fully elevated position on said suspension frame as said actuator extends from said first extended position to said fully extended position,
• a substantially vertically aligned, opposed facing pair of clamping levers pivotally mounted to said base of said carriage, wherein lower-most ends of said pair of clamping levers are adapted for mounting a corresponding opposed facing pair of brake shoes thereon, and said pair of clamping levers are pivotable relative to said base so as to clamp said lower-most ends together when opposite upper ends of said pair of clamping levers are moved apart,
• a clamping lever retractor acting on said pair of clamping levers to move said lowermost ends of said pair of clamping levers apart to unclamp the rail when said actuator extends from said retracted position to said first extended position,
• wherein said actuator when extending from said first extended position to said fully extended position so as to position said carriage in said fully elevated position, simultaneously elevates said lower-most ends of said pair of clamping levers above a substantially horizontal plane containing a lower-most surface of said at least one guide wheel so that brake shoes mounted on said lower-most ends of said pair of clamping levers are elevated above the rail when said at least on guide wheel is on the rail,
• and wherein said actuator when retracting from said fully extended position to said first extended position, so as to position said carriage in a fully lowered position, simultaneously lowers said lower-most ends of said pair of clamping levers to bracket opposite sides of the rail when said at least on guide wheel is on the rail,
• and wherein said actuator when retracting from said first extended position to said retracted position operates on said upper ends of said pair of clamping levers to move said upper ends of said pair of clamping levers apart thereby clamping said lower most ends together onto the opposite sides of the rail.