Method for transporting wafers

1. A method comprising:

moving a wafer transport device to a position above a load port;

lowering a hoist unit of the wafer transport device above the load port, wherein the wafer transport device has a plurality of belts, each of the belts is connected to the hoist unit and wound around a respective belt winding drum;

detecting sound waves from the belts by using acoustic sensors to measure tensions of the belts; and

comparing the tensions of the belts to determine an inclination of the hoist unit.

2. The method according to claim 1 , further comprising:

gripping a wafer container unit prior to lowering the hoist unit; and

after determining the inclination of the hoist unit, if a top surface of the hoist unit is substantially parallel to a top surface of the load port, releasing the wafer container unit onto the top surface of the load port.

3. The method according to claim 1 , further comprising:

after determining the inclination of the hoist unit, if a top surface of the hoist unit is substantially parallel to a top surface of the load port, gripping a wafer container unit placed on the top surface of the load port.

4. The method according to claim 1 , further comprising:

after determining the inclination of the hoist unit, if a top surface of the hoist unit is not parallel to a top surface of the load port, raising the hoist unit; and

sending the wafer transport device to a maintenance area.

5. The method according to claim 4 , further comprising:

calibrating the inclination of the hoist unit after sending the wafer transport device to the maintenance area.

6. The method according to claim 1 , further comprising:

raising the hoist unit after determining the inclination of the hoist unit;

determining a degree of winding of each of the belts around the corresponding belt winding drum; and

providing a response, by a controller, according to the determined degree of winding.

7. A method comprising:

moving a wafer transport device on a transport rail, wherein the wafer transport device comprises a main body, a plurality of belt winding drums disposed on the main body, a hoist unit configured to grip a wafer container unit, and a plurality of belts connected between the belt winding drums and the hoist unit;

stopping the wafer transport device above a load port;

after stopping the wafer transport device, lowering the hoist unit through the belts;

measuring a tension status of each of the belts during lowering the hoist unit;

comparing the tension statuses of the belts; and

in response to a comparison result of the tension statuses, determining whether the hoist unit is inclined.

8. The method according to claim 7 , wherein measuring the tension status is performing with using a tension sensor disposed on the main body of the wafer transport device and in a position vertically between the belt winding drums and the hoist unit.

9. The method according to claim 8 , wherein the tension sensor is an acoustic sensor.

10. The method according to claim 7 , wherein measuring the tension status is performed by detecting frequencies of vibrations on the belts.

11. The method according to claim 10 , further comprising:

performing a machine learning on the frequencies of the vibrations on the belts to determine the tension statuses of the belts by a machine learning system.

12. The method according to claim 7 , measuring the tension status is performed by inspecting windings of the belts around the belt winding drums.

13. The method according to claim 7 , further comprising:

measuring frequencies of vibrations of the belts during lowering the hoist unit.

14. The method according to claim 13 , further comprising:

analyzing a plurality of data pairs of the vibration frequencies and the tension statuses to receive a vibration frequency and tension relationship by a machine learning system.

15. A method comprising:

transferring a wafer container unit by using a wafer transport device, wherein the wafer transport device comprises:

a main body;

a plurality of belt winding drums disposed on the main body;

a hoist unit; and

a plurality of belts connecting the belt winding drums to the hoist unit;

stopping the wafer transport device with the wafer container unit above a load port;

lowering the hoist unit of the wafer transport device above the load port;

measuring vibration frequencies of the belts;

in response to the vibration frequencies of the belts, determining lengths of the belts extending between the belt winding drums and the hoist unit; and

in response to the determination determines that an attitude of the hoist unit is acceptable, actuating a movement of a wafer container relative to the load port through the hoist unit.

16. The method according to claim 15 , wherein measuring the vibration frequencies is performed by receiving sound waves generated from the belts during lowering the hoist unit.

17. The method according to claim 15 , wherein the step of actuating the movement of the wafer container relative to the load port through the hoist unit is to release the wafer container unit form the hoist unit to the load port.

18. The method according to claim 15 , wherein the step of actuating the movement of the wafer container relative to the load port through the hoist unit is to grip the wafer container unit placed on the load port.

19. The method according to claim 15 , further comprising:

in response to the determination determines that the attitude of the hoist unit is not acceptable, calibrating the attitude of the hoist unit.

20. The method according to claim 15 , further comprising:

raising the hoist unit after determining the attitude of the hoist unit;

determining a degree of winding of each of the belts around the belt winding drums; and

providing a response, by a controller, according to the determined degrees of windings.