An actuator for converting a rotating motion into a linear reciprocating motion, comprising: a motor having a front end and an output worm shaft extending from the front end; a transmission mechanism comprising: a bracket mounted onto the front end of the motor, having a base; and a fixing pin extending from the base along a direction perpendicularly to the worm shaft of the motor; a worm wheel having a first side (1231; 1231'), an opposite, second side, and a recess defined in the second side, the worm wheel being connected onto the base through the fixing pin on the first side, and meshing with the worm shaft of the motor; and a connector having a first end portion and a second end portion extending oppositely from the first end portion; and an adjustable member operatively connected to the second end portion of the connector of the transmission mechanism, such that when the motor rotates in one direction, the adjustable member is in an extending movement, and when the motor rotates in the other direction, the adjustable member is in a retracting movement; characterized in that the said recess of the worm wheel is polygon-shaped, the connector further comprises the first end portion formed in a polygon shape substantially complemental to that of the polygon-shaped recess such that the first end portion is tightly received in the polygon-shaped recess. a motor having a front end and an output worm shaft extending from the front end; a transmission mechanism comprising: a bracket mounted onto the front end of the motor, having a base; and a fixing pin extending from the base along a direction perpendicularly to the worm shaft of the motor; a worm wheel having a first side (1231; 1231'), an opposite, second side, and a recess defined in the second side, the worm wheel being connected onto the base through the fixing pin on the first side, and meshing with the worm shaft of the motor; and a connector having a first end portion and a second end portion extending oppositely from the first end portion; and an adjustable member operatively connected to the second end portion of the connector of the transmission mechanism, such that when the motor rotates in one direction, the adjustable member is in an extending movement, and when the motor rotates in the other direction, the adjustable member is in a retracting movement; a bracket mounted onto the front end of the motor, having a base; and a fixing pin extending from the base along a direction perpendicularly to the worm shaft of the motor; a worm wheel having a first side (1231; 1231'), an opposite, second side, and a recess defined in the second side, the worm wheel being connected onto the base through the fixing pin on the first side, and meshing with the worm shaft of the motor; and a connector having a first end portion and a second end portion extending oppositely from the first end portion; and an adjustable member operatively connected to the second end portion of the connector of the transmission mechanism, such that when the motor rotates in one direction, the adjustable member is in an extending movement, and when the motor rotates in the other direction, the adjustable member is in a retracting movement; characterized in that the said recess of the worm wheel is polygon-shaped, the connector further comprises the first end portion formed in a polygon shape substantially complemental to that of the polygon-shaped recess such that the first end portion is tightly received in the polygon-shaped recess.