In some embodiments of the present disclosure, as shown in FIG. 3, the attitude of the hoist unit 120 is determined by measuring a first distance between a first position P1 of a top surface 121 of the hoist unit 120 and a bottom surface 111 of the wafer transport device 100, measuring a second distance between a second position P2 of the top surface 121 of the hoist unit 120 and the bottom surface 111 of the wafer transport device 100, and comparing the first distance and the second distance. In some embodiments, the hoist unit 120 and a predetermined surface have substantially the same attitude when the first distance and the second distance are substantially the same. The predetermined surface can be the ground, or the top surface 301 of the load port 300, or both. As shown in FIG. 3, the wafer transport device 100 further includes two distance sensors 170 arranged on the bottom surface 111 of the wafer transport device 100. The distance sensors 170 are directed toward the first position P1 and the second position P2 of the top surface 121 of the hoist unit 120. In some embodiments, the distance sensors 170 are laser distance sensors or other suitable sensors.

FIGS. 5A and 5B show top views of the top surface 121 of the hoist unit 120 of FIG. 1 according to some embodiments of the present disclosure. In some embodiments of the present disclosure, the hoist ends 132 of the belts 130 are connected to the hoist unit 120 near four corners of the top surface 121 of the hoist unit 120. Line L1 passes through the center C of the top surface 121 of the hoist unit 120, and is parallel to two edges of the top surface 121 of the hoist unit 120. Line L2 passes through the center C of the top surface 121 of the hoist unit 120, and is parallel to the other two edges of the top surface 121 of the hoist unit 120. Line L3 passes through the center C and the corners C1, C3 opposite each other. Line L4 passes through the center C and the corners C2, C4 opposite each other. The winding drum 140 connected to one of the belts 130 and the hoist end 132 of said belt 130 has a distance therebetween. When said belt 130 is connected to the top surface 121 of the hoist unit 120 at the corner C1, and said distance between the winding drum 140 and the hoist end 132 corresponding to said belt 130 is shorter or longer than distances between the winding drums 140 and the hoist ends 132 corresponding to the other belts 130 connected at the corners C1, C2, and C4, the corner C1 is respectively titled upward or downward with respect to the rest of the top surface 121 of the hoist unit 120. Similarly, when one of the belts 130 is connected to the top surface 121 of the hoist unit 120 at the corner C2, C3, or C4, and the distance between the winding drum 140 and the hoist end 132 corresponding to said belt 130 is shorter or longer than distances between the winding drums 140 and the hoist ends 132 corresponding to the other belts 130 connected at the other corners, the corner C2, C3, or C4 is respectively titled upward or downward with respect to the rest of the top surface 121 of the hoist unit 120. Referring to FIG. 5A, when the corner C1 is tilted upward or downward, the first distance and the second distance are different if the first position and the second position of the top surface of the hoist unit are on different sides of the line L4. Similarly, when the corner C3 is tilted upward or downward, the first distance and the second distance are different if the first position and the second position on the top surface of the hoist unit are on different sides of the line L4. Similarly, when the corner C2 or the corner C4 is tilted upward or downward, the first distance and the second distance are different if the first position and the second position on the top surface of the hoist unit are on different sides of the line L3.

When the adjacent corners C1 and C4 are both tilted upward or both tilted downward with respect to the other two corners C2 and C3, then the first distance and the second distance are different if the first position and the second position on the top surface of the hoist unit are on different sides of the line L2. Similarly, when the adjacent corners C1 and C2 are both tilted upward or both tilted downward with respect to the other two corners C3 and C4, then the first distance and the second distance are different if the first position and the second position on the top surface of the hoist unit are on different sides of the line L1.

Therefore, if the first position and the second position are on different sides of the four lines L1, L2, L3, and L4, then the first distance and the second distance are different when the top surface of the hoist unit tilts toward any one or any two adjacent of the corners C1, C2, C3, C4. In some embodiments of the present disclosure, the first position and the second position are on different sides of each of the four lines L1, L2, L3, and L4. In other words, the four lines L1, L2, L3, L4 partition the top surface 121 of the hoist unit 120 into eight sections S1-S8, and the first position P1 and the second position P2 are on opposite sections, such as sections S1 and S5 as shown in FIG. 5A, or sections S3 and S7 as shown in FIG. 5B.

In some embodiments of the present disclosure, the attitude of the hoist unit 120 is determined by measuring a tension of each of the belts 130. Referring to FIG. 2, the wafer transport device 100 further includes a tension sensor 160, and the tension of each of the belts 130 can be measured by using the tension sensor 160. In some embodiments, the tension sensor 160 may be an acoustic sensor configured to detect and analyze sound waves from the belt 130. Specifically, when the hoist unit 120 is lowered, the belts 130 will vibrate. The frequency of the vibration of the belt 130 depends on the length thereof. As such, the tension sensor 160 may sense the sound waves of the corresponding belt 130, and the vibration frequency may be analyzed, e.g., via machine learning, to determine the tension of the belt 130. The tension sensor 160 may be arranged proximal to a portion of the belt 130 under stress, namely the portion of the belt 130 extending between the belt winding drum 140 and the hoist unit 120. The tensions may be uneven when the hoist unit 120 is tilted toward one side or one corner. It is noted that the acoustic sensor mentioned above is an example, and should not limit the scope of the present disclosure. Other suitable sensors may be applied to this operation as long as the length of the belt 130 can be detected.

In some embodiments of the present disclosure, data are fed to a machine learning system to analyze relationship between vibration frequencies of the belts 130 and the tensions of the belts 130. Specifically, the vibration frequency of the belt 130 is measured by the acoustic tension sensor 160, and the tension of the belt 130 is determined by another sensor (e.g. a tension meter) or by inspecting the winding of the belt 130 around the corresponding winding drum 140, and the vibration frequency and the tension of the belt 130 are fed as a related data pair to the machine learning system. The machine learning system analyzes a plurality of data pairs of related vibration frequencies and tensions, and derives a rule for associating specific vibration frequencies of the belt 130 to specific tensions of the belts 130, respectively. In operation S18, S20, and S22 of the method M10, a response is provided according to the determined attitude. In some embodiments of the present disclosure, when the determined attitude of the hoist unit is not the same as the attitude of a predetermined surface (e.g. the top surface of the load port, and/or the ground), the response includes raising the hoist unit (operation S18) and sending the wafer transport device to a maintenance area (operation S20). Specifically, the hoist unit 120 of the wafer transport device 100 may be inclined if the determined attitude is not the same as the attitude of the predetermined surface. This inclined hoist unit 120 is sent to the maintenance area, and an attitude calibration is performed on the inclined hoist unit 120.

When the determined attitude of the hoist unit is the same as the attitude of the predetermined surface, the response includes operating the gripper 122 of the hoist unit to grip or release the wafer container unit (operation 22). In some embodiments, the wafer container unit 400 is initially disposed on the load port 300, and the hoist unit 120 may grip the wafer container unit 400 after the attitude is determined to be the same as the attitude of the predetermined surface. In some other embodiments, the wafer container unit 400 is initially gripped by the hoist unit 120 and is transported using the wafer transport device 100. The hoist unit 120 may release the wafer container unit 400 on the load port 300 after the attitude is determined to be the same as the attitude of the predetermined surface.

FIG. 4B shows a flowchart of a method M10′ according to some embodiments of the present disclosure. The method M10′ is merely an example, and is not intended to limit the present disclosure beyond what is explicitly recited in the claims. Additional operations can be provided before, during, and after the method M10, and some operations described can be replaced, eliminated, or moved around for additional embodiments of the process. The operations S12, S14, S16, S18, S20, and S22 of method M10′ are the same as the operations S12, S14, S16, S18, S20, and S22 of method M10, and the detailed description is omitted herein.

In operation S26 of method M10′, the hoist unit is raised. Referring to FIGS. 1 and 2, after the hoist unit 120 grips or releases the wafer container unit 400, the hoist unit 120 is raised by the controller 180 for the next transporting mission. In some embodiments, the belt winding drums 140 rotate, such that the belts 130 respectively wind the belt winding drums 140 again, and the hoist unit 120 is raised to a predetermined level.

In operation S28 of method M10′, a degree of winding of at least one belt around the belt winding drum is determined. FIGS. 6A and 6B show schematic diagrams of a belt 130 wound around a belt winding drum 140 according to some embodiments of the present disclosure. In some embodiments of the present disclosure, at least one of the belts 130 has a plurality of belt markings 133 on a side thereof. After the hoist unit 120 is raised, an image of the belt markings 133 of the belt 130 is captured by the winding camera 150 positioned proximal to a portion of the belt 130 wound around the respective belt winding drum 140 as shown in FIG. 2. In some embodiments, the winding camera 150 is positioned to directly face the side of the belt 130 formed with the belt markings 133 as shown in FIGS. 6A and 6B. The positions of the belt markings 133 in the captured image are compared to predetermined positions of the belt markings 133, so as to determine the degree of winding of the belt 130. In some embodiments, the predetermined positions of the belt markings 133 may be determined by capturing an image of the belt markings 133 when the corresponding wafer transport device 100 is new. Alternatively, the predetermined positions of the belt markings 133 may be determined by capturing an image of the belt markings 133 after the attitude of the hoist unit 120 is properly calibrated.

In operation S30 of method M10′, the wafer transport device is moved to another load port when the positions of the belt markings in the image are consistent with the predetermined positions of the belt markings. That is, the wafer transport device 100 is in a good condition to transport wafer container units. In operation S32 of method M10′, the wafer transport device is sent to a maintenance area when the positions of the belt markings in the image are inconsistent with the predetermined positions of the belt markings. When the positions of the belt markings 133 as shown in FIG. 6B are not the same as the predetermined positions of the belt markings 133 as shown in FIG. 6A, the wafer transport device 100 is sent to the maintenance area to recalibrate the attitude of the hoist unit 120.

In some embodiments of the present disclosure, the belt markings 133 on the side of the belt 130 form a line pattern when they are at their respective predetermined positions, as shown in FIG. 6A. The belt markings 133 align at every 180 degrees of the belt wrapped around the belt winding drum 140. The belt distance between consecutive belt markings on the belt increases from the drum end 131 of the belt 130 to the hoist end 132 of the belt 130. FIG. 7 shows a schematic diagram of a belt having belt markings 1331, 1332, and 1333 wound around a belt winding drum 140 according to some embodiments of the present disclosure. Specifically, a diameter D1 is a straight distance between the first belt marking 1331 and the second belt marking 1332, and diameter D2 is a straight distance between the second belt marking 1332 and the third belt marking 1333. The belt distance BD1 between a first belt marking 1331 and a second belt marking 1332 lies substantially along a circular path, so is substantially equal to diameter D1 times π divided by 2. Similarly, the belt distance BD2 between the second belt marking 1332 and a third belt marking 1333 is substantially along a circular path, so is substantially equal to diameter D2 times π divided by 2. The difference between diameter D1 and diameter D2 is about a thickness T of the belt. Therefore, the difference between the belt distance between the first and second belt markings 1331, 1332, and the belt distance between the second and third belt markings 1332, 1333 is about the thickness T times π divided by 2. Similarly, the belt distance for each successive belt marking toward the hoist end increases by about the thickness T times π divided by 2.

Note that the proportions of the belts shown in FIGS. 6A, 6B, and FIG. 7 are not necessarily precise, and may be exaggerated for purpose of illustration. Specifically, the thickness of the belts is exaggerated for ease of description.

When loading or unloading the wafer container unit 400 on the load port 300, the horizontal position and orientation of the hoist unit 120 may be aligned to the horizontal position of the load port 300 so as to allow the wafer container unit 400 to successfully engage or disengage the load port 300 in a smooth manner.

In some other embodiments, the method M10 (or M10′) further includes collecting an operating pulse of a motor of the wafer transport device. For example, the controller 180 may collect the operating pulse of the motor when the wafer transport device 100 moves on the transport rails 200. The controller 180 may auto-learn the proper pulse range of the motor by using the collected operating pulses as a database. The controller 180 may determine if the motor is abnormal (e.g., the transport speed is too slow or too fast) by comparing the collected operating pulse to the proper pulse range. If the collected operating pulse is out of the proper pulse range, the controller 180 will transport the corresponding wafer transport device to the maintenance area for maintenance.

In some other embodiments, the method M10 (or M10′) further includes collecting an operating temperature of the motor of the wafer transport device. For example, the controller 180 may collect the operating temperature of the motor when the wafer transport device 100 moves on the transport rails 200. The controller 180 may auto-learn the proper temperature range of the motor by using the collected operating temperatures as a database. The controller 180 may determine if the motor is abnormal (e.g., the temperature of the moter is too high) by comparing the collected operating temperature to the proper temperature range. If the collected operating temperature is out of the proper temperature range, the controller 180 will transport the corresponding wafer transport device to the maintenance area for maintenance.

FIG. 8A shows a flowchart of a method M20 according to some embodiments of the present disclosure. The method M20 is merely an example, and is not intended to limit the present disclosure beyond what is explicitly recited in the claims. Additional operations can be provided before, during, and after the method M20, and some operations described can be replaced, eliminated, or moved around for additional embodiments of the process. In some embodiments, the method M20 may be applied in a FAB. Specifically, the method M20 may be applied to, but should not be limited to, the wafer transport device 100 of FIG. 1. For clarity and ease of explanation, some elements of the figures have been simplified.

In operation S52 of the method M20, a wafer transport device 100 is moved on a transport rail 200. Referring to FIGS. 1 and 8A, the wafer transport device 100 is suspended from the transport rail 200. The controller 180 of the wafer transport system controls the movement of the wafer transport device 100, such that the wafer transport device 100 is moved on the transport rail 200.

In operation S54 of the method M20, the wafer transport device 100 is stopped above the load port 300 having the top surface 301. In some embodiments, there are many rail marks 210 on the bottom surface of the transport rail 200. The marking scanner of the wafer transport device 100 senses the bottom surface of the transport rail 200 when the wafer transport device 100 is moving on the transport rail 200. When the marking sensor senses a predetermined rail mark 210, the wafer transport device 100 receives a stop demand from the wafer transport system. Hence, the wafer transport device 100 is stopped over the predetermined load port 300. On the other hand, when the marking sensor senses another rail mark, the wafer transport system does not send a stop demand to the wafer transport device 100. In this case, the wafer transport device 100 is still moving on the transport rail 200.

In some embodiments, the wafer transport device 100 may be stopped at the wrong position because of inertia. For example, the wafer transport device 100 may be stopped past the predetermined position if the wafer transport device 100 was moving at a high speed. In this case, the wafer transport device 100 and the corresponding load port 300 are not aligned vertically. In some other embodiments, the orientation of the wafer transport device 100 is not aligned with the orientation of the corresponding load port 300 when the wafer transport device 100 is stopped over the corresponding load port 300. The controller 180 may thus send a rotation demand to the wafer transport device 100 (according to the data stored in the rail mark 210) to rotate the wafer transport device 100 (as described in operation S58 in FIG. 8B). As such, the orientations of the wafer transport device 100 and the load port 300 may be aligned. However, due to the law of inertia, the wafer transport device 100 may be over-rotated, and the orientations of the wafer transport device 100 and the load port 300 are misaligned again.

Due to the misalignment problems mentioned above, an alignment process may be performed after the wafer transport device 100 is stopped. In operation S56 of the method M20, a light beam is projected onto the top surface of the load port. FIG. 9 shows a bottom view of the wafer transport device 100 and the wafer container unit 400 in FIG. 1 according to some embodiments of the present disclosure. In some embodiments of the present disclosure, at least one light beam projector 190 is arranged on the main body 110 of the wafer transport device 100. The light beam projector 190 is configured to project a light beam onto the top surface 301 of the load port 300. The light beam projected onto the top surface 301 of the load port 300 can include a laser dot 910 as shown in FIG. 10A, a laser line 920 as shown in FIGS. 10B and 10D, or two laser lines 920, 930 as shown in FIG. 10C. In some embodiments, the laser lines 920 and 930 are not parallel. In some embodiments, the laser lines 920 and 930 are substantially perpendicular.