Transmission mechanism having hourglass enveloping worm and helical gear

A transmission mechanism having an hourglass enveloping worm and a helical gear, comprising:

• a shell;
• a helical gear;
• a protective column;
• and
• an hourglass enveloping worm,
• wherein the shell comprises a first cavity and a second cavity inside, the first cavity is communicated with the second cavity;
• the helical gear is rotatably provided in the first cavity;
• the protective column is rotatably provided in the second cavity, the protective column comprises a placement cavity and a clearance opening communicating the first cavity and the second cavity;
• an axis of the protective column is parallel to an axis of the placement cavity, the protective column is provided with a limiting mechanism, the limiting mechanism is connected to the protective column and the shell to restrict a lateral movement of the protective column;
• and
• the hourglass enveloping worm is rotatably provided in the placement cavity, an axis of the hourglass enveloping worm and the axis of the placement cavity are collinear;
• the hourglass enveloping worm is at least partially exposed in the clearance opening to mesh with the helical gear;
• and a rotation of the protective column causes the hourglass enveloping worm to move toward or away from the helical gear along a circumferential direction of the protective column.