by the linear actuator 12, the linear movement of the drive shaft 11 may be converted into the rotational movement of the drive casing 13 by the conversion mechanism 15.

When the drive shaft 11 moves upwardly by the linear actuator 12 (see direction L1 in FIG. 4), the plurality of balls 15c may transmit the axial force of the drive shaft 11 from the first spiral grooves 15a to the second spiral grooves 15b. The lifting of the drive casing 13 may be suppressed by the weight of the swing door 3 and an elastic force of the spring 19, and the plurality of balls 15c in the first spiral grooves 15a and the second spiral grooves 15b may transmit the axial force of the drive shaft 11 in the upward spiral direction so that the drive casing 13 may rotate in a first rotation direction (see direction S1 in FIG. 4). As the drive casing 13 rotates in the first rotation direction S1, the swing door 3 may move to the closed position (see a dotted line in FIG. 2). As the swing door 3 moves to the closed position, and the swing door 3 contacts the edges of the door aperture 2, the rotation of the drive casing 13 may be restricted, and a lift force of the drive casing 13 may overcome the weight of the swing door 3 and the elastic force of the spring 19. Accordingly, as the drive casing 13 moves upwardly, the sleeve 16 and the swing door 3 connected to the drive casing 13 may be lifted together, and thus the swing door 3 may fully cover the door aperture 2.

When the drive shaft 11 moves downwardly by the linear actuator 12 (see direction L2 in FIG. 4), the plurality of balls 15c may transmit the axial force of the drive shaft 11 from the first spiral grooves 15a to the second spiral grooves 15b. The drive casing 13 may move downwardly due to the addition of the weight of the swing door 3 and the elastic force of the spring 19. After the drive casing 13 moves downwardly, the plurality of balls 15c in the first spiral grooves 15a and the second spiral grooves 15b may transmit the axial force of the drive shaft 11 in the downward spiral direction so that the drive casing 13 may rotate in a second rotation direction (see direction S2 in FIG. 4). As the drive casing 13 rotates in the second rotation direction S2, the swing door 3 may move to the open position (see a solid line in FIG. 2). Thus, the swing door 3 may fully uncover the door aperture 2.

According to an exemplary embodiment, the linear actuator 12 may be a fluid cylinder such as a pneumatic cylinder. As a fluid such as compressed air is supplied to or recovered from the linear actuator 12, the linear actuator 12 may cause the drive shaft 11 to move along the axis X of the driving apparatus 10.

Referring to FIG. 7, the linear actuator 12 may include a cylinder tube 21 having a first open end and a second open end opposing each other, a piston 22 movable in the cylinder tube 21, a first end cover 23 mounted in the first open end of the cylinder tube 21, and a second end cover 24 mounted in the second open end of the cylinder tube 21.

The cylinder tube 21 may have a chamber 21a defined therein. The first open end of the cylinder tube 21 may be sealed by the first end cover 23, and the second open end of the cylinder tube 21 may be sealed by the second end cover 24.

An internal rod 25 may be mounted at the center of the piston 22, and the internal rod 25 may include a first extension portion 25a extending from the piston 22 toward the first end cover 23 and a second extension portion 25b extending from the piston 22 toward the second end cover 24.

A bottom end of the drive shaft 11 may be connected to the first extension portion 25a, and the drive shaft 11 may move together with the piston 22 and the internal rod 25 along the axis X of the driving apparatus 10.

The first end cover 23 may have a first rod seat 26 extending toward the internal rod 25. A first port fitting 23a may be mounted on the first end cover 23, and a fluid hose may be connected to the first port fitting 23a. The first rod seat 26 may have a first cavity 26a defined therein, and the chamber 21a of the cylinder tube 21 and the first port fitting 23a may fluidly communicate with the first cavity 26a of the first rod seat 26. When the piston 22 moves upwardly, the first extension portion 25a of the internal rod 25 may be received in the first cavity 26a of the first rod seat 26. When the piston 22 moves downwardly, the first extension portion 25a of the internal rod 25 may be out of the first cavity 26a of the first rod seat 26. A first sealing member 26b may be mounted in a bottom opening of the first rod seat 26, and the first sealing member 26b may provide sealing between the first extension portion 25a of the internal rod 25 and the first rod seat 26. As the fluid (the compressed air) is supplied to the first cavity 26a of the first rod seat 26 and the chamber 21a of the cylinder tube 21 through the first port fitting 23a, the piston 22 may move downwardly, and accordingly the drive shaft 11 may move downwardly.

The second end cover 24 may have a second rod seat 27 extending toward the internal rod 25. A second port fitting 24a may be mounted on the second end cover 24, and the fluid hose may be connected to the second port fitting 24a. The second rod seat 27 may have a second cavity 27a defined therein, and the chamber 21a of the cylinder tube 21 and the second port fitting 24a may fluidly communicate with the second cavity 27a of the second rod seat 27. When the piston 22 moves upwardly, the second extension portion 25b of the internal rod 25 may be out of the second cavity 27a of the second rod seat 27. When the piston 22 moves downwardly, the second extension portion 25b of the internal rod 25 may be received in the second cavity 27a of the second rod seat 27. A second sealing member 27b may be mounted in a top opening of the second rod seat 27, and the second sealing member 27b may provide sealing between the second extension portion 25b of the internal rod 25 and the second rod seat 27. As the fluid (the compressed air) is supplied to the second cavity 27a of the second rod seat 27 and the chamber 21a of the cylinder tube 21 through the second port fitting