Ball screw with support devices

A ball screw with support devices, comprising:

• a screw;
• a nut, fixed to a nut base and mounted around the screw;
• two support units, each including two said support devices, the support device having a bush that is fixed to a bush seat and is slidably mounted around the screw, wherein the two support devices of each of the support units are symmetrically arranged at two sides of the nut base;
• and
• a speed-controlling unit, including two runner structures, an active connecting element and a plurality of passive connecting elements, wherein each said runner structure has a foundation on which a driving wheel and two driven wheels are installed concentrically and rotatably, and diameter ratios between the driving wheel and the two driven wheels decrease progressively so that a diameter ratio among the driving wheel and the two driven wheels is 3:2:1, the runner structures being deposited near two ends of the screw, the active connecting element being wound around the driving wheels of the two runner structures and having two ends thereof fixed to the nut base, and the passive connecting element having one end wound around the two driven wheels and an opposite end connected to the bush seat.