1. Field of the Invention
The present invention relates to an actuator for lifting device and more particularly, to such an actuator, which comprises a linking rod assembly for moving a lifting device, and a transmission gear set and a brake module arranged at one side of the linking rod assembly and rotatable by a motor to move the linking rod assembly in extending out or retracting an extension tube.
2. Description of the Related Art
A lifting device is a mechanism for changing the elevation of an object. Different lifting devices differently configured to fit different application requirements.
FIG. 11 illustrates an actuator A for use in a lifting device. As illustrated, the actuator A comprises an electric motor A1 having a worm A11 fixedly connected to the output shaft thereof, a worm gear A2 meshed with the worm All, a spiral spring A3 sleeved onto the gear shaft of the worm gear A2, and a retractable rod A4 coupled to the worm gear A2. According to this design, the retractable rod A4 and the worm gear A2 are on the same axis. When starting the electric motor A1, the worm A11 is driven to rotate the worm gear A2, the retractable rod A4 is moved axially subject to rotation of the worm gear A2, and the spiral spring A3 is wound tightly on the periphery of the gear shaft of the worm gear A2.
The aforesaid prior art actuator provides a braking effect to prevent an accident, however it still has drawbacks as follows:
1. Because the retractable rod A4, the spiral spring A3 and the worm gear A2 are arranged on one same path, the worm bear A2 occupies a part of the reciprocating path of the retractable rod A4. Thus, the length of the retractable rod A4 is limited, lowering the performance of the actuator.
2. The worm gear A2 is directly connected in series to one end of the retractable rod A4. When the retractable rod A4 receives an external pressure, the pressure will be directly transferred by the retractable rod A4 to the worm gear A2. If the worm gear A2 is held down by the spiral spring A3 at this time, direct transfer of the external pressure by the retractable rod A4 to the worm gear A2 may damage the worm gear A2 and the spiral spring A3.