Patent ID: 7712389

Claim:
A lifting device having parallel double screw rods, the lifting device connected respectively to a first, a second and a third sliding units interconnecting with each other so as to control the relative sliding movement among each sliding unit, comprising: a driving means fixedly connected to one end of the first sliding unit; a first transmission means comprising a first screw rod fixed to one end of the first sliding unit and a first telescopic tube assembly threadedly connected to the first screw rod and linearly movable relative to the first screw rod, the first screw rod driven by the driving means, a distal end of the first telescopic tube assembly fixedly connected on a connecting piece, the connecting piece further connected to a distal end of the second sliding unit; and a second transmission means provided at one side of the first transmission means and parallel thereto, the second transmission means comprising a sleeve driven by the driving means to rotate, a second telescopic tube assembly accommodated within the sleeve and axially movable relative to the sleeve, and a second screw rod threadedly connected to the second telescopic tube assembly and linearly movable relative to the second telescopic tube assembly, an inner wall of the sleeve provided with a plurality of guiding grooves parallel to an axial direction of the sleeve, the second telescopic tube assembly provided with a positioning plug, a plurality of guiding rails protruded from an outer periphery of the positioning plug for slidably mating with each guiding groove, the guiding rails being non-rotatable relative to the guiding grooves, so as to make the second telescopic tube assembly be rotatable with the sleeve, a distal end of the second telescopic tube assembly connected on the connecting piece of the first transmission means, a distal end of the second screw rod fixedly connected on the third sliding unit, wherein the driving means simultaneously drives the second and third sliding units to protrude or retract relative to the first sliding unit.