Linear actuator and safety mechanism for the same

A linear actuator comprising:

• a driving mechanism having a base and a motor mounted on the base;
• a guide screw driven by the motor;
• an outer tube put around the guide screw and fixed on one side of the base;
• a telescopic tube slidably penetrating the outer tube;
• and
• a safety mechanism comprising:
• a nut with a hollow portion adapted for the guide screw passing through, a first inner thread being formed on the hollow portion to engage with an outer thread of the guide screw, the nut having a larger diameter cylinder and a smaller diameter cylinder extending from one end of the larger diameter cylinder;
• a nut sheath fixed on the smaller diameter cylinder of the nut to form an integer, wherein an outside of the nut sheath is provided with a plurality of bumps;
• a sleeve having one end formed with a plurality of rabbets corresponding to the bumps to sleeve on the outside of the nut sheath, and the other end adapted to be connected with the telescopic tube;
• and
• a torsion spring disposed around the bumps and the rabbets;
• wherein when the guide screw is rotated, the nut sheath is engaged with the sleeve by embedding the bumps into the rabbets to form a tough joint by circular shrinking of the torsion spring;
• when the sleeve stops, the bumps and the rabbets leveled at each other by a pretorsion effect of the torsion spring depart from engagement to make the nut sheath and the nut freely rotate against the sleeve.