Patent Publication Number: US-2023159306-A1

Title: Oht vehicle and method of controlling operation of same

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Korean Patent Application No. 10-2021-0163665, filed Nov. 24, 20121, the entire contents of which is incorporated by reference herein for all purposes. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present disclosure relates generally to an OHT vehicle and a method of controlling the operation of the same. More particularly, the present disclosure relates to a technology in which when a hand unit of an OHT vehicle loads a transfer container and unloads the same to a destination load port, an error between a recess of the transfer container and a positioning pin of the load port caused by the tilt of the transfer container is resolved through position correction of the hand unit, thereby enabling the transfer container to be accurately placed on the load port. 
     Description of the Related Art 
     In semiconductor manufacturing, a variety of numerous processes are performed to yield the final product, and hundreds of thousands of cargo transfers occur in the process of performing the semiconductor manufacturing process. To prevent contamination and damage to semiconductor materials and delivery accidents during the cargo transfer process, an overhead hoist transfer (OHT) is utilized as an automated transfer system on the semiconductor manufacturing line. 
     An OHT vehicle holds and loads a transfer container, such as a front opening unified pod (FOUP) or front opening shipping box (FOSB), from an arbitrarily port and moves along a rail installed on the ceiling to unload the transfer container to a destination port. 
     The destination port may be provided with a load port on which the transfer container transferred by the OHT vehicle is placed. For example, a load port for supporting a general wafer cassette, a load port for supporting a FOUP, a load port for supporting a FOSB, a load port for supporting a magazine, a load port for supporting trays for storing semiconductor packages, etc. may be provided on the shelf of a side buffer device or an under buffer device. 
     The load port may be provided with a loading table on which the transferred transfer container is placed, and a positioning pin for determining a placement position of the transfer container may be provided on the loading table. In addition, a recess corresponding to the positioning pin provided on the loading table may be provided in a lower surface of the transfer container such as a FOUP, FOSB, etc. 
     In a case where the OHT vehicle unloads the transfer container on the loading table of the load port while the transfer container held by the OHT vehicle is tilted due to various factors, there is a problem in that the positioning pin of the loading table and the recess formed in the lower surface of the transfer container are misaligned, so that the transfer container cannot be placed in an appropriate position. 
     When the transfer container is placed in a misaligned position on the loading table, an error occurs in opening a door of the transfer container to unload wafers from the transfer container, causing a problem in the operation of the overall process. 
     Therefore, there is a need to unload the transfer container transferred by the OHT vehicle to a correct position on the loading table of the load port. 
     The foregoing is intended merely to aid in the understanding of the background of the present disclosure, and is not intended to mean that the present disclosure falls within the purview of the related art that is already known to those skilled in the art. 
     SUMMARY OF THE INVENTION 
     The present disclosure has been made keeping in mind the above problems occurring in the related art, and an objective of the present disclosure is to provide a method of accurately placing a transfer container on a loading table of a load port by determining the degree of tilt of the transfer container transferred by an OHT vehicle and correcting an unloading position of the transfer container. 
     An objective of the present disclosure is to solve the problem in which when a transfer container held by an OHT vehicle is unloaded in a tilted state, the transfer container cannot be placed in an appropriate position because a positioning pin of a loading table and a recess formed in a lower surface of the transfer container are misaligned. 
     Furthermore, an objective of the present disclosure is to solve the problem in which the position of a lower surface of a transfer container placed on a loading table of a load port cannot be determined because the degree of tilt of the transfer container is variously changed depending on situations. 
     The objectives of the present disclosure are not limited to the objectives mentioned above, and other objectives and advantages of the present disclosure which are not mentioned may be understood by the following description. 
     In order to accomplish the above objectives, according to an aspect of the present disclosure, there is provided a method of controlling operation of an OHT vehicle, the method including: a transferring step of loading a transfer container and moving the transfer container to a destination port; an error determining step of measuring a distance between a hand unit and the transfer container and determining a degree of tilt of the transfer container on the basis of the distance value; a position correcting step of adjusting a position of the hand unit by moving the transfer container to a load port of the destination port where the transfer container is to be unloaded on the basis of the degree of tilt of the transfer container; and an unloading step of unloading the transfer container to the load port of the destination port. 
     As an example, the error determining step may include: a distance measuring step of measuring a front end distance between a front end of the hand unit and a front end of the transfer container; and a tilt determining step of determining the degree of tilt by comparing the front end distance value with a reference value. 
     Here, the tilt determining step may be performed by calculating a tilt angle according to a ratio between the front end distance value and the reference value. 
     As an example, the error determining step may include: a distance measuring step of measuring a rear end distance value between a rear end of the hand unit and a rear end of the transfer container; and a tilt determining step of determining the degree of tilt by comparing the rear end distance value with a reference value. 
     Here, the tilt determining step may be performed by calculating a tilt angle according to a ratio between the rear end distance value and the reference value. 
     As an example, the error determining step may include: a distance measuring step of measuring a front end distance value between a front end of the hand unit and a front end of the transfer container and a rear end distance value between a rear end of the hand unit and a rear end of the transfer container; and a tilt determining step of determining the degree of tilt by comparing the front end distance value with the rear end distance value. 
     Here, the tilt determining step may be performed by calculating a tilt angle according to a ratio between the front end distance value and the rear end distance value. 
     As an example, the error determining step may include: a recess position determining step of determining a position of a recess of the transfer container on the basis of the degree of tilt of the transfer container; and an error distance calculating step of calculating an error distance between the calculated position of the recess and a normal position. 
     As an example, the error distance calculating step may be performed by calculating an error distance between a downward vertical extension line for the determined position of the recess and a positioning pin provided on the load port of the destination port as a correction distance. 
     Furthermore, the position correcting step may be performed by moving the transfer container to the load port of the destination port where the transfer container is to be unloaded on the basis of the degree of tilt of the transfer container and moving the hand unit through a slide unit. 
     As an example, the position correcting step may be performed by horizontally moving the hand unit by the correction distance through a slide unit. 
     According to an aspect of the present disclosure, there is provided an OHT vehicle including: a transfer module configured to be movable along a rail; a hoist module including a hand unit configured to hold a transfer container, a hoist unit configured to move the hand unit in a vertical direction, and a slide unit configured to move the hand unit in a horizontal direction; a displacement measuring means mounted on the hand unit and configured to measure a distance between the hand unit and the transfer container held by the hand unit; and a controller configured to adjust a position of the hand unit by determining a degree of tilt of the held transfer container on the basis of the distance value between the hand unit and the transfer container. 
     As an example, the displacement measuring means may include a distance measuring sensor disposed at one of a front end of the hand unit and a rear end of the hand unit and configured to measure a distance between one of the front end of the hand unit and the rear end of the hand unit and a corresponding one of a front end of the transfer container and a rear end of the transfer container. 
     As an example, the displacement measuring means may include: a front end distance measuring sensor disposed at a front end of the hand unit and configured to measure a distance between the front end of the hand unit and a front end of the transfer container; and a rear end distance measuring sensor disposed at a rear end of the hand unit and configured to measure a distance between the rear end of the hand unit and a rear end of the transfer container. 
     As an example, the controller may include: an error determining part configured to calculate an error distance according to a recess position by determining the degree of tilt of the held transfer container on the basis of the distance value between the hand unit and the transfer container and by determining a position of a recess of the transfer container on the basis of the degree of tilt of the transfer container; and a position correcting part configured to adjust the position of the hand unit on the basis of the error distance. 
     As an example, the error determining part may calculate a tilt angle by comparing a front end distance value between a front end of the hand unit and a front end of the transfer container or a rear end distance value between a rear end of the hand unit and a rear end of the conveying container with a reference value, and determine the position of the recess of the transfer container on the basis of the tilt angle. 
     As an example, the error determining part may calculate an error distance between a downward vertical extension line for the determined position of the recess and a positioning pin provided on a load port of a destination port as a correction distance. 
     As an example, the position correcting part may control the slide unit to horizontally move the hand unit by the correction distance. 
     As an example, the controller may correct the position of the hand unit through the position correcting part and then controls the hoist unit to lower the hand unit and unload the transfer container so that the recess of the transfer container corresponds to a positioning pin provided on a load port of a destination port. 
     According to an aspect of the present disclosure, there is provided a method of controlling operation of an OHT vehicle, the method including: a transferring step of loading a transfer container and moving the transfer container to a destination port; a distance measuring step of measuring a distance between at least one of a front end and a rear end of a hand unit and at least one of a front end and a rear end of the transfer container; a tilt determining step of calculating a tilt angle according to a degree of tilt of the transfer container by comparing a front end distance value or a rear end distance value with a reference value or by comparing the front end distance value with the rear end distance value; a recess position determining step of determining a position of a recess of the transfer container on the basis of the degree of tilt; and an error distance calculating step of calculating an error distance between a downward vertical extension line for the determined position of the recess and a positioning pin provided on a load port of the destination port as a correction distance; a position correcting step of horizontally moving the hand unit by the correction distance through a slide unit; and an unloading step of lowering the hand unit through a hoist unit and unloading the transfer container to the load port of the destination port. 
     According to the present disclosure as described above, it is possible to accurately place the transfer container on the loading table of the load port by determining the degree of tilt of the transfer container transferred by the OHT vehicle and correcting the unloading position of the transfer container. 
     In particular, it is possible to solve the problem in which when the transfer container held by the OHT vehicle is unloaded in a tilted state, the transfer container cannot be placed in an appropriate position because the positioning pin of the loading table and the recess formed in the lower surface of the transfer container are misaligned. 
     Furthermore, it is possible to solve the problem in which when the OHT vehicle unloads the transfer container in a tilted state to the loading table of the load port connected to substrate processing equipment, etc., a sealed state of an inner space of the substrate processing equipment is released because a container door and a port door cannot make close contact with each other, so that the overall semiconductor process cannot be performed properly. 
     The effects of the present disclosure are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objectives, features, and other advantages of the present disclosure will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: 
         FIG.  1    illustrates an embodiment of an OHT vehicle  100  according to the present disclosure. 
         FIGS.  2 A and  2 B  are views illustrating an embodiment of a transfer container transferred by the OHT vehicle according to the present disclosure; 
         FIG.  3    is a view illustrating an example of transferring and unloading the transfer container to a destination port through the OHT vehicle; 
         FIGS.  4 A and  4 B  are block diagrams illustrating an embodiment of a hoist module and an embodiment of a controller of the OHT vehicle according to the present disclosure; 
         FIG.  5    is a side view illustrating an embodiment of an OHT vehicle according to the present disclosure; 
         FIGS.  6 A and  6 B  are front views illustrating the embodiment of the OHT vehicle according to the present disclosure in a state where a vehicle body is removed; 
         FIG.  7    is a flowchart illustrating an embodiment of a method of controlling the operation of an OHT vehicle according to the present disclosure; 
         FIG.  8    is a flowchart illustrating a first embodiment of a process of position correction by determining the tilt of a transfer container in the method of controlling the operation of the OHT vehicle according to the present disclosure; 
         FIGS.  9  to  11    are views illustrating an example of unloading the transfer container through position correction according to the first embodiment of the method of controlling the operation of the OHT vehicle according to the present disclosure; 
         FIG.  12    is a flowchart illustrating a second embodiment of a process of position correction by determining the tilt of a transfer container in the method of controlling the operation of the OHT vehicle according to the present disclosure; and 
         FIGS.  13  to  16    are views illustrating an example of unloading the transfer container through position correction according to the second embodiment of the method of controlling the operation of the OHT vehicle according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings, but the present disclosure is not limited or restricted by the described embodiments. 
     For a better understanding of the disclosure, its operating advantages and the specific objectives attained by its uses, reference is made to the descriptive matter in which the exemplary embodiments of the disclosure are illustrated. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprise”, “include”, “have”, etc. when used in this specification, specify the presence of stated features, integers, steps, operations, elements, components, and/or combinations of them but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or combinations thereof. 
     In the following description, detailed descriptions of known functions and components incorporated herein will be omitted when it may make the subject matter of the present disclosure unclear. 
     The present disclosure proposes a method in which when a hand unit of an OHT vehicle loads a transfer container and unloads the same to a destination load port, an error between a recess of the transfer container and a positioning pin of the load port caused by the tilt of the transfer container is resolved through position correction of the hand unit, thereby enabling the transfer container to be accurately placed on the load port. 
       FIG.  1    illustrates an embodiment of an OHT vehicle  100  according to the present disclosure. 
     The OHT vehicle  100  may include a traveling module  110 , a steering module  150 , a hoist module  200 , and a controller (not illustrated). 
     The OHT vehicle  100  may be traveled on a rail through the traveling module  110 , and the traveling direction thereof may be changed through the steering module  150 . 
     As an example, the OHT vehicle  100  may include a front end traveling unit  110   a  and a rear end traveling unit  110   b , and a front end steering unit  150   a  and a rear end steering unit  150   b  may be disposed to correspond to the front end traveling unit  110   a  and the rear end traveling unit  110   b , respectively. 
     The traveling module  110  and the steering module  150  may be variously modified, and various known technologies may be appropriately applied to the configuration and operation relationship of the traveling module  110  and the steering module  150 . 
     The hoist module  200  may load and hold a transfer container  10  from a specific port, and unload the transfer container  10  upon reaching a destination port. 
     The controller (not illustrated) may control the operation of each configuration of the OHT vehicle  100 . In particular, the controller may control the operation of the hoist module  200  to accurately unload the transfer container  10  to a corresponding position on a load port of the destination port through position correction. This technical feature of the present disclosure will be described later in detail with reference to an embodiment. 
     In regard to the transfer container  10  transferred by the OHT vehicle  100 ,  FIGS.  2 A and  2 B  illustrate an embodiment of a transfer container  10  transferred by the OHT vehicle  100  according to the present disclosure. 
     Although a front opening unified pod (FOUP) is described as an example as the transfer container  10 , the present disclosure is not limited thereto and can be applied to transfer various transfer containers. 
     The size of wafers used in a semiconductor manufacturing process is standardized according to the Semiconductor Equipment and Materials International (SEMI) standard, and accordingly, the size of the transfer container  10  such as a front opening unified pod (FOUP) and front opening shipping box (FOSB) may also be standardized to correspond to the size of wafers to be transferred. Of course, the present disclosure can also be applied to a case of transferring a non-standardized transfer container. 
     The transfer container  10  includes a container body  12  and a container door  13 . An inner space  17  is provided in the container body  12  to store objects such as wafers. As an example, a plurality of ribs  19  between which a plurality of wafers are sequentially inserted and stacked may be provided on a sidewall of the inner space  17  of the transfer container  10 . The container body  12  may have a front side opened and closed by the container door  13 . 
     A plurality of recesses  30   a ,  30   b , and  30   c  may be provided in a lower surface of the container body  12 . The plurality of recesses  30   a ,  30   b , and  30   c  provided in the transfer container  10  may be formed to correspond to positioning pins provided on a loading table of the load port of the destination port. In other words, the recesses  30   a ,  30   b , and  30   c  may be formed in the lower surface of the container body  12  to correspond to the arrangement position, number, size, etc. of the positioning pins provided on the loading table of the load port. 
     When the hoist module  200  of the OHT vehicle  100  unloads the transfer container  10  to the loading table of the load port of the destination port, the recesses  30   a ,  30   b , and  30   c  formed in the lower surface of the container body  12  are engaged with the positioning pins on the loading table so as to allow the transfer container  10  to be placed on the loading table. 
     A flange  15  may be provided on an upper surface of the container body  12 . The OHT vehicle  100  may transfer the transfer container  10  by holding the flange  15  of the transfer container  10  through the hoist module  200  of the OHT vehicle  100 . 
     When the OHT vehicle  100  holds and transfers the transfer container  10 , the transfer container  10  may be tilted due to various factors. For example, the container body  12  and the flange  15  of the transfer container  10  may be separately produced and assembled in such a manner that the flange  15  is coupled onto the container body  12 . 
     Due to the assembly structure of the container body  12  and the flange  15 , the container body  12  and the flange  15  may be disengaged from each other, resulting in tilt of the transfer container  10 . In addition, the center of gravity of the container body  12  does not correspond to the center of gravity of the flange  15 , so that the transfer container  10  may be tilted when the hoist module  200  of the OHT vehicle  100  holds the transfer container  10 . In addition, the position of the center of gravity of the transfer container  10  is changed depending on the weight and quantity of the objects loaded in the transfer container  10 , so that when the hoist module  200  of the OHT vehicle  100  holds the transfer container  10 , the transfer container  10  may be tilted. 
     Due to such various factors, the transfer container  10  held and transferred by the OHT vehicle  100  may become a tilted state. 
     In a tilted state of the transfer container  10 , the OHT vehicle  100  cannot accurately unload the transfer container  10  to the loading table of the load port of the destination port. 
     In this regard,  FIG.  3    illustrates an example of transferring and unloading the transfer container  10  to a destination port through OHT vehicle. 
     As an example, a load port  50  connected to substrate processing equipment, etc. may constitute a part of an equipment front end module (EFEM). The load port  50  is provided with a loading table  70  on which the transfer container  10  is placed. Positioning pins  70   a ,  70   b , and  70   c  may be provided on the loading table  70  so as to determine an accurate position of the transfer container  10  unloaded by the OHT vehicle  100 . As the positioning pins  70   a ,  70   b , and  70   c  on the loading table  70 , kinematic pins may be used. 
     When unloading the transfer container  10  on the loading table  70 , the OHT vehicle  100  places the transfer container  10  so that the recesses  30   a ,  30   b , and  30   c  formed in the lower surface of the transfer container  10  are correspondingly engaged with the positioning pins  70   a ,  70   b , and  70   c  of the loading table  70 . 
     As described above, the transfer container  10  has to be placed on the loading table  70  so that the recesses  30   a ,  30   b , and  30   c  of the transfer container  10  correspond to the positioning pins  70   a ,  70   b , and  70   c  of the loading table  70 . This ensures that when the container door  13  of the transfer container  10  corresponds to a port door  51  of the load port  50  and the container door  13  and the port door  51  are opened, the inner space  17  of the transfer container  10  and the inner space of the substrate processing equipment connected to the load port  50  are connected to each other to maintain a sealed state from the outside. 
     However, as described above, the transfer container  10  held by the hoist module  200  of the OHT vehicle  100  may become a tilted state due to various factors. When the transfer container  10  is placed on the loading table  70  of the load port  50  in a state where the transfer container  10  is tilted, the recesses  30   a ,  30   b , and  30   c  of the transfer container  10  cannot be properly engaged with the corresponding positioning pins  70   a ,  70   b , and  70   c  of the loading table  70 . In particular, when the container door  13  and the port door  51  are opened in a state where the transfer container  10  is not placed in a correct position on the loading table  70 , the sealed state of the inner space of the substrate processing equipment is released, causing a problem that the overall semiconductor process cannot be performed properly. 
     In order to solve such a problem, the OHT vehicle  100  according to the present disclosure detects the degree of tilt of the transfer container  10  through a displacement measuring means  260  provided in the hand unit  250  and corrects the position of the transfer container  10 , thereby enabling the transfer container  10  to be unloaded to the correct position on the loading table  70  of the load port  50 . 
     As a more specific embodiment along with the embodiment of  FIG.  1    with respect to the OHT vehicle  100  according to the present disclosure, the configuration of the hoist module  200  and the controller of the OHT vehicle  100  will be described with reference to  FIGS.  4  to  6   . 
       FIGS.  4 A and  4 B  illustrate block diagrams of an embodiment of a hoist module  200  and an embodiment of a controller  300  of the OHT vehicle  100  according to the present disclosure.  FIG.  5    illustrates a side view of an embodiment of an OHT vehicle  100  according to the present disclosure.  FIGS.  6 A and  6 B   6  illustrate front views of the embodiment of the OHT vehicle  100  according to the present disclosure in a state where a vehicle body  210  is removed. 
     In the present embodiment, the controller  300  is illustrated and described as controlling only the hoist module  200 , but this is for convenience of description of the present disclosure. The controller  300  may control various configurations included in the OHT vehicle  100  as well as the hoist module  200 , and for this purpose may include additional control means for controlling each configuration. 
     The hoist module  200  may include the vehicle body  210 , a slide unit  230 , a hoist unit  240 , a hand unit  250 , and a displacement measuring means  260 . 
     The vehicle body  210  may be positioned under a traveling module  110  and may be provided with an inner space in which a transfer container  10  is inserted and stored. The hoist unit  240  may be disposed at the top of the inner space of the vehicle body  210 . 
     The hand unit  250  may hold and support the transfer container  10 . For this purpose, the hand unit  250  may include a gripper  255  for holding a flange  15  of the transfer container  10  and a gripper driving means (not illustrated) for driving the gripper  255 . 
     The hoist unit  240  may lift the hand unit  250 . When loading the transfer container  10 , the hoist unit  240  may lower the hand unit  250  to allow the hand unit  250  to hold the transfer container  10  and then may lift the hand unit  250 . When unloading the transfer container  10 , the hoist unit  240  may lower the hand unit  250  to allow the hand unit  250  to release and unload the transfer container  10  to a destination port. 
     For this purpose, the hoist unit  240  may include a lifting belt  245  and a belt driving means (not illustrated) for lifting and lowering the lifting belt  245 . The number and arrangement position of the lifting belt  245  may be appropriately changed as needed. 
     The slide unit  230  may move the hoist unit  240  in a horizontal direction. As an example, the slide unit  230  may include a slide rail (not illustrated) for supportably moving the hoist unit  240  in the horizontal direction and a slide driving means (not illustrated). 
     The displacement measuring means  260  may measure a distance between the hand unit  250  and the transfer container  10  held by the hand unit  250 . For this purpose, the displacement measuring means  260  may include a distance measuring sensor. As the distance measuring sensor, various sensors capable of measuring a distance, such as an optical sensor, a sound wave sensor, etc. may be used. 
     The sensor of the displacement measuring means  260  may be disposed on the hand unit  250 , and may be disposed on an outer peripheral portion of a lower surface of the hand unit  250 . 
     As an example, as illustrated in  FIG.  6 A , the displacement measuring means may include a front end distance measuring sensor  260  disposed at a front end of the hand unit  250 , and may measure a distance DF between the front end of the hand unit  250  and a front end of the transfer container  10 . Alternatively, the displacement measuring means may include a rear end distance measuring sensor disposed at a rear end of the hand unit  250 , and may measure a distance DR between the rear end of the hand unit  250  and a rear end of the transfer container  10 . 
     As an example, as illustrated in  FIG.  6 B , the displacement measuring means may include a front end distance measuring sensor  260   a  disposed at the front end of the hand unit  250  and a rear end distance measuring sensor  260   a  disposed at the rear end of the hand unit  250 , and may measure both the distance DF between the front end of the hand unit  250  and the front end of the transfer container  10  and the distance DR between the rear end of the hand unit  250  and the rear end of the transfer container  10 . 
     The controller  300  may control each configuration of the hoist module  200 . In particular, the controller  300  may include an error determining part  310  and a position correcting part  330  and may adjust the position of the hand unit  250  by determining the degree of tilt of the gripped transfer container  10  on the basis of a distance value between the hand unit  250  and the transfer container  10  measured through the displacement measuring means  260 . 
     For this purpose, the controller  300  may include the error determining part  310  and the position correcting part  330 . 
     The error determining part  310  may calculate an error distance according to a recess position by determining the degree of tilt of the held transfer container  10  on the basis of the distance value between the hand unit  250  and the transfer container  10  and by determining the positions of recesses  30   a ,  30   b , and  30   c  of the transfer container  10  on the basis of the degree of tilt of the transfer container  10 . 
     In other words, in a case where the transfer container  10  is unloaded on a loading table of a load port in a tilted state, the error determining part  310  may calculate an error distance according to the degree of misalignment between positioning pins arranged on the loading table and the recesses  30   a ,  30   b , and  30   c  of the transfer container  10 . 
     As an example, in a case where the displacement measuring means  260  measures the distance between the front end of the hand unit  250  and the front end of the transfer container  10  to obtain a front end distance value or measures the distance between the rear end of the hand unit  250  and the rear end of the transfer container  10  to obtain a rear end distance value, the error determining part  310  may compare the front end distance value or the rear end distance value with a reference value to calculate a tilt angle, and may determine the positions of the recesses  30   a ,  30   b , and  30   c  of the transfer container  10  on the basis of the tilt angle. 
     Here, the reference value may be set to be a distance between the hand unit  250  and the transfer container  10  in a normal state where the transfer container  10  is not tilted. 
     Furthermore, the error determining part  310  may calculate an error distance between a downward vertical extension line for the determined positions of the recesses  30   a ,  30   b , and  30   c  and the positioning pins provided on the load port of the destination port and may calculate a correction distance on the basis of the error distance. 
     The position correcting part  330  may adjust the position of the hand unit  250  on the basis of the error distance calculated by the error determining part  310 . As an example, the position correcting part  330  may control the slide unit  230  to horizontally move the position of the hand unit  250  by a distance corresponding to the correction distance calculated by the error determining part  310 . 
     In addition, the controller  300  may correct the position of the hand unit  250  through the position correcting part  330  and then control the hoist unit  240  to lower the hand unit  250  and unload the transfer container  10  to the loading table of the load port so that the recesses  30   a ,  30   b , and  30   c  of the transfer container  10  correspond to the positioning pins provided on the load port of the destination port. 
     The present disclosure also proposes a method of controlling the operation of an OHT vehicle according to the present disclosure, in which an error between a recess of a transfer container and a positioning pin of a load port caused by the tilt of the transfer container is resolved through position correction of a hand unit, thereby enabling the transfer container to be accurately placed on the load port. Hereinafter, the method of controlling the operation of the OHT vehicle according to the present disclosure will be described with reference to an embodiment. The method of controlling the operation of the OHT vehicle according to the present disclosure implemented in the above-described OHT vehicle according to the present disclosure, so the embodiment of the OHT vehicle according to the present disclosure will also be referred to hereinafter. 
       FIG.  7    illustrates a flowchart of an embodiment of a method of controlling the operation of an OHT vehicle  100  according to the present disclosure. 
     The OHT vehicle  100  may load a transfer container  10  from a specific port and move the transfer container  10  to a destination port (S 110 ). 
     In a case where the transfer container  10  is loaded from the specific port, or is being moved the destination port, or is arrived at the destination port, a distance between a hand unit  250  and the transfer container  10  may be measured S 130  through displacement measuring means  260 ,  260   a , and  260   b  (S 130 ). 
     A controller  300  may determine the degree of tilt of the transfer container  10  held by the hand unit  250  on the basis of the distance value measured by the displacement measuring means  260 ,  260   a , and  260   b  and my calculate an error distance of how far the recesses  30   a ,  30   b , and  30   c  of the transfer container  10  are misaligned from normal positions thereof on the basis of the degree of tilt of the transfer container  10  (S 150 ). 
     Then, the controller  300  may adjust and correct the position of the hand unit  250  by corresponding (i.e., moving) the transfer container  10  to a load port of the destination port where the transfer container  10  is to be unloaded on the basis of the degree of tilt of the transfer container  10  (S 170 ). For example, the controller  300  may control a slide unit  230  on the basis of the calculated error distance to horizontally move the hand unit  250  to thereby adjust an unloading position of the transfer container  10 . 
     When the unloading position of the transfer container  10  is adjusted through the position correction of the hand unit  250 , the controller  300  may control a hoist unit  240  to lower the hand unit  250  and release a held state of the hand unit  250  to unload the transfer container  10  to the load port of the destination port (S 190 ). 
     A more specific process for the method of controlling the operation of the OHT vehicle according to the present disclosure will be described with reference to an embodiment. 
       FIG.  8    illustrates a flowchart of a first embodiment of a process of position correction by determining the tilt of a transfer container  10  in the method of controlling the operation of the OHT vehicle  100  according to the present disclosure.  FIGS.  9  to  11    illustrate an example of unloading the transfer container  10  through position correction according to the first embodiment of the method of controlling the operation of the OHT vehicle  100  according to the present disclosure. 
     The present embodiment illustrates a process of position correction by determining the tilt of the transfer container  10  in a case where a distance measuring sensor  260  of a displacement measuring means is disposed at a front end of a hand unit  250 . 
     A distance DF1 between the front end of the hand unit  250  and a front end of the transfer container  10  may be measured through a front end distance measuring sensor  260  disposed at the front end of the hand unit  250  (S 230 ). 
     In a case where the transfer container  10  held by the hand unit  250  is tilted, a difference occurs between a front end distance value DF1 measured through the front end distance measuring sensor  260  and a distance DF between the front end of the hand unit  250  and the front end of the transfer container  10 , the distance DF being measured in a normal state of the transfer container  10 . 
     The controller  300  may compare the front end distance value DF1 with a reference value (S 251 ) to determine the degree of tilt of the transfer container  10  held by the hand unit  250 . Here, the reference value may be set to be the normal state distance DF. 
     The controller  300  may calculate a tilt angle AF1, i.e., the degree of tilt of the transfer container  10 , according to the ratio between the front end distance value DF1 and the reference value DF (S 253 ), and may determine the positions of recesses  30   a  and  30   b  of the transfer container  10  on the basis of the tilt angle AF1 (S 255 ). Then, the controller  300  may calculate an error distance S1 between the positions of the recesses  30   a  and  30   b  of the transfer container  10  and normal positions thereof on the basis of the tilt angle AF1 (S 257 ). 
     Referring to a conceptual diagram illustrated in  FIG.  10   , the transfer container  10  may obtain information about a width length UL and a height SL of the transfer container  10  in advance according to the SEMI standard or according to the size setting during the manufacture of the transfer container  10 . 
     A vertical distance error D1 corresponding to the degree of tilt of a transfer container  10   b  in a tilted state with respect to a transfer container  10   a  in a normal state may be calculated by comparing the front end distance value DF1 and the normal state distance DF. For example, the vertical distance error D1 may be calculated by subtracting the normal state distance DF from the front end distance value DF1. 
     A horizontal tilt angle A1 may be calculated on the basis of the width length UL and the vertical distance error D1. For example, the tilt angle A1 may be calculated through the following [Equation 1] below. 
     
       
         
           
             
               
                 
                   
                     Sin 
                     ⁢ 
                         
                     A 
                     ⁢ 
                     1 
                   
                   = 
                   
                     
                       D 
                       ⁢ 
                       1 
                     
                     
                       ( 
                       
                         UL 
                         2 
                       
                       ) 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     The tilt angle in the vertical direction corresponds to the tilt angle in the horizontal direction, so a vertical tilt angle A1 may be determined. 
     By determining the vertical tilt angle A1, the recesses  30   a  and  30   b  of the transfer container  10  may be determined to be located in a position that is misaligned by the vertical tilt angle A1. 
     In addition, the error distance S1 between the positions of the recesses  30   a  and  30   b  of the transfer container  10  and the normal positions thereof may be calculated through the following [Equation 2] below. 
         S 1= SL ×arctan  A 1  [Equation 2]
 
     Here, as illustrated in  FIG.  9   , the calculated error distance S1 may be an error distance S1 between a vertical downward extension line for the positions of the recesses  30   a  and  30   b  and positioning pins  70   a  and  70   b  provided on a loading table  70  of a load port of a destination port. 
     Through such a process, the error distance S1 between the recesses  30   a  and  30   b  of the transfer container  10  and the positioning pins  70   a  and  70   b  of the loading table  70  may be determined. 
     In addition, to resolve the error between the recesses  30   a  and  30   b  of the transfer container  10  and the positioning pins  70   a  and  70   b  provided on the loading table  70  of the load port, a correction distance for moving the hand unit  250  may be calculated. 
     In the present embodiment, the correction distance for moving the hand unit  250  may correspond to the calculated error distance S1. 
     Then, as illustrated in  FIG.  11   , the controller  300  may control the operation of a slide unit  230  (S271) to move the hand unit  250  in the horizontal direction by the correction distance S1 to thereby correct the position of the transfer container  10  (S273). 
     As a result of correcting the position of the hand unit  250 , the recesses  30   a  and  30   b  of the transfer container  10  may be positioned on a vertical line to be accurately aligned with the positioning pins  70   a  and  70   b  provided on the loading table  70  of the load port. 
     The controller  300  may lower the hand unit  250  through the hoist unit  240  in a state where the position of the transfer container  10  is corrected and unload the transfer container  10  so that the recesses  30   a  and  30   b  of the transfer container  10  are accurately engaged with the corresponding positioning pin  70   a  and  70   b  provided on the loading table  70  of the load port. 
     In the previous embodiment, position correction was performed by determining the degree of tilt on the basis of the distance between the front end of the hand unit  250  and the front end of the transfer container  10  through the distance measuring sensor  260  disposed at the front end of the hand unit  250 . However, the present embodiment may be applied even to a case where a distance measuring sensor is disposed at a rear end of the hand unit  250 , and position correction is performed by determining the degree of tilt on the basis of the distance between the rear end of the hand unit  250  and a rear end of the transfer container  10 . 
       FIG.  12    illustrates a flowchart of a second embodiment of a process of position correction by determining the tilt of a transfer container  10  in the method of controlling the operation of the OHT vehicle  100  according to the present disclosure.  FIGS.  13  to  16    illustrate an example of unloading the transfer container  10  through position correction according to the second embodiment of the method of controlling the operation of the OHT vehicle  100  according to the present disclosure. 
     The present embodiment illustrates a process of position correction by determining the degree of tilt of the transfer container  10  on the basis of a front end distance and a rear end distance measured through a front end distance measuring sensor  260   a  disposed at a front end of a hand unit  250  and a rear end distance measuring sensor  260   b  disposed at a rear end of the hand unit  250 . 
     A distance DF21 between the front end of the hand unit  250  and a front end of the transfer container  10  may be measured through the front end distance measuring sensor  260   a  disposed at the front end of the hand unit  250  (S 330 ). A distance DF22 between the rear end of the hand unit  250  and a rear end of the transfer container  10  may be measured through the rear end distance measuring sensor  260   b  disposed at the rear end of the hand unit  250  (S 330 ). 
     Referring to  FIG.  14   , which is an enlarged view of the sections X and Y illustrated in  FIG.  13   , in a case where the transfer container  10  held by the hand unit  250  is tilted, a difference occurs between a front end distance value DF21 measured through the front end distance measuring sensor  260   a  and a rear end distance value DF22 measured through the rear end distance measuring sensor  260   b.    
     A controller  300  may compare the front end distance value DF21 with the rear end distance value DF22 (S 351 ) to determine the degree of tilt of the transfer container  10  held by the hand unit  250 . 
     The controller  300  may calculate a tilt angle AF2, i.e., the degree of tilt of the transfer container  10 , according to the ratio between the front end distance value DF21 and the rear end distance value DF22 (S 353 ), and may determine the positions of recesses  30   a  and  30   b  of the transfer container  10  on the basis of the tilt angle AF2 (S 355 ). Then, the controller  300  may calculate an error distance S2 between the positions of the recesses  30   a  and  30   b  of the transfer container  10  and normal positions thereof on the basis of the tilt angle AF2 (S 357 ). 
     Referring to a conceptual diagram illustrated in  FIG.  15   , the transfer container  10  may obtain information about a width length UL and a height SL of the transfer container  10  in advance according to the SEMI standard or according to the size setting during the manufacture of the transfer container  10 . 
     A vertical distance error D2 corresponding to the degree of tilt of a transfer container  10   b  in a tilted state with respect to a transfer container  10   a  in a normal state may be calculated by comparing the front end distance value DF21 and the rear end distance value DF22. For example, the vertical distance error D2 may be calculated by subtracting the rear end distance value DF22 from the front end distance value DF21. 
     A horizontal tilt angle A2 may be calculated on the basis of the width length UL and the vertical distance error D2. For example, the tilt angle A2 may be calculated through the following [Equation 3] below. 
     
       
         
           
             
               
                 
                   
                     Sin 
                     ⁢ 
                         
                     A 
                     ⁢ 
                     2 
                   
                   = 
                   
                     
                       D 
                       ⁢ 
                       2 
                     
                     UL 
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     3 
                   
                   ] 
                 
               
             
           
         
       
     
     The tilt angle in the vertical direction corresponds to the tilt angle in the horizontal direction, so a vertical tilt angle A2 may be determined. 
     By determining the vertical tilt angle A2, the recesses  30   a  and  30   b  of the transfer container  10  may be determined to be located in a position that is misaligned by the vertical tilt angle A2. 
     In addition, the error distance S2 between the positions of the recesses  30   a  and  30   b  of the transfer container  10  and the normal positions thereof may be calculated through the following [Equation 4] below. 
         S 2= SL ×arctan  A 2  [Equation 4]
 
     Here, as illustrated in  FIG.  13   , the calculated error distance S2 may be an error distance S2 between a vertical downward extension line for the positions of the recesses  30   a  and  30   b  and positioning pins  70   a  and  70   b  provided on a loading table  70  of a load port of a destination port. 
     Through such a process, the error distance S2 between the recesses  30   a  and  30   b  of the transfer container  10  and the positioning pins  70   a  and  70   b  of the loading table  70  may be determined. 
     In addition, to resolve the error between the recesses  30   a  and  30   b  of the transfer container  10  and the positioning pins  70   a  and  70   b  provided on the loading table  70  of the load port, a correction distance for moving the hand unit  250  may be calculated. 
     In the present embodiment, the correction distance for moving the hand unit  250  may correspond to the calculated error distance S2. In an embodiment, the error distance S2 between the positions of the recesses  30   a  and  30   b  of the transfer container  10  and the normal positions thereof may be calculated through the [Equation 4] as the correction distance. 
     Then, as illustrated in  FIG.  16   , the controller  300  may control the operation of a slide unit  230  (S 371 ) to move the hand unit  250  in the horizontal direction by the correction distance S2 to thereby correct the position of the transfer container  10  (S 373 ). 
     As a result of correcting the position of the hand unit  250 , the recesses  30   a  and  30   b  of the transfer container  10  may be positioned on a vertical line to be accurately aligned with the positioning pins  70   a  and  70   b  provided on the loading table  70  of the load port. 
     The controller  300  may lower the hand unit  250  through the hoist unit  240  in a state where the position of the transfer container  10  is corrected and unload the transfer container  10  so that the recesses  30   a  and  30   b  of the transfer container  10  are accurately engaged with the corresponding positioning pin  70   a  and  70   b  provided on the loading table  70  of the load port. 
     According to the present disclosure as described above, it is possible to accurately place the transfer container on the loading table of the load port by determining the degree of tilt of the transfer container transferred by the OHT vehicle and correcting the unloading position of the transfer container. 
     In particular, it is possible to solve various problems that occur when the transfer container cannot be unloaded to an accurate position on the loading table of the load port. 
     While the exemplary embodiments of the disclosure have been described above, those skilled in the art will appreciate that various modifications, additions, and substitutions are possible, without departing from the scope and spirit of the disclosure. Therefore, the embodiments disclosed in this specification are only for illustrative purposes rather than limiting the technical spirit of the present disclosure. The scope of the present disclosure should be defined only by the accompanying claims and equivalents thereof.