Patent Publication Number: US-2022227578-A1

Title: Stacker Crane Control System

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2021-007749 filed Jan. 21, 2021, the disclosure of which is hereby incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a stacker crane control system for controlling a stacker crane. 
     2. Description of the Related Art 
     An example of such a stacker crane control system is disclosed in Japanese Examined Patent Publication H04-22801 (Patent Document 1). Hereinafter, in “Description of the Related Art”, the reference numerals and names in Patent Document 1 are cited in parentheses. 
     The stacker crane control system of Patent Document 1 detects parameters that affect swaying of a stacker crane ( 1 ) before the stacker crane ( 1 ) stops, and estimates, based on the detected parameters, a swaying state that the stacker crane ( 1 ) will enter after it is stopped. Then, the stacker crane control system determines the waiting time until the estimated swaying state has an allowable swaying amount or less, and controls a transfer apparatus (fork apparatus ( 8 )) to operate immediately once the waiting time has elapsed. Here, the weight of a lift ( 7 ) that includes an article (package ( 13 )), and the lifting height of the lift ( 7 ) are used as the parameters that affect swaying of the stacker crane ( 1 ). 
     SUMMARY OF THE INVENTION 
     However, in the technique disclosed in Patent Document 1, the swaying state of the stacker crane that is used to determine the waiting time is merely theoretically estimated based on parameters such as the weight or the lifting height of the lift, and may be different from the actual swaying state. Also, if the actual swaying amount is greater than the estimated swaying amount, there may be cases where an article cannot be appropriately transferred. On the other hand, if a longer waiting time is set in order to avoid such a situation, the start of the article transfer operation will be delayed, and the operation efficiency of the stacker crane will be reduced. 
     Also, even if the actual swaying amount of the stacker crane is detected in order to avoid such situations, the swaying amount of the transfer apparatus varies according to the lifting height of the lift that varies with time, and thus a large number of sensors are required to detect the actual swaying amount along the entire height of the lift. In this case, an increase in the installation cost of the stacker crane is unavoidable. 
     Thus, there is a demand for realizing a technique that avoids an increase in the installation cost of a stacker crane, and can start a transfer operation at an appropriate time based on an actual swaying amount of the stacker crane. 
     According to the present disclosure, a stacker crane control system for controlling a stacker crane including: a travel carriage that travels along a travel route; a mast supported on the travel carriage in an orientation along a vertical direction; a lift that moves up and down within a predetermined lifting range along the mast; a lifting apparatus that raises and lowers the lift; and a transfer apparatus supported by the lift and including a holding unit for holding an article, the stacker crane being configured to perform a transfer operation of transferring the article between the holding unit and a transfer destination, the stacker crane control system including: a sway detection unit configured to detect a reference swaying amount that is a swaying amount of the mast at a detection height, the detection height being set greater than or equal to the height of a lowermost part of the transfer apparatus when the lift is located at an upper limit of the lifting range; a lifting height acquiring unit configured to acquire lifting height information that indicates a lifting height, which is the height of the lift, at a plurality of points in time; and a transfer control unit configured to control the transfer apparatus, wherein the transfer control unit converts the reference swaying amount detected by the sway detection unit into a lifting height swaying amount that is a swaying amount of the mast at the lifting height indicated by the lifting height information, and starts the transfer operation of the transfer apparatus if the lifting height swaying amount is stably smaller than or equal to a predetermined determination threshold. 
     According to the present configuration, it is possible to obtain a lifting height swaying amount that is a swaying amount of the mast at the actual lifting height, based on an actual swaying amount of the mast that is detected by the sway detection unit, and an actual lifting height of the lift at each point in time that is acquired by the lifting height acquiring unit. Then, if the lifting height swaying amount is stably smaller than or equal to a predetermined determination threshold, the transfer operation of the transfer apparatus is started. Since the transfer operation is started in this way based on a detection result of the actual swaying amount of the mast, the transfer operation of the transfer apparatus can be started at an appropriate time according to the actual swaying amount of the mast that varies depending on various operation conditions. 
     Further features and advantages of the stacker crane control system will become apparent from the following description of embodiments given with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating part of an article transport facility. 
         FIG. 2  is a control block diagram. 
         FIG. 3  is a schematic side view illustrating a stacker crane. 
         FIG. 4  is a diagram schematically illustrating swaying of masts after a travel carriage is stopped. 
         FIG. 5  is a diagram schematically illustrating temporal changes in a reference swaying amount and a lifting height swaying amount. 
         FIG. 6  illustrates a mast reference position. 
         FIG. 7  illustrates a corrected mast reference position. 
         FIG. 8  is a flowchart illustrating processing for determining the start of a transfer operation according to a first embodiment. 
         FIG. 9  is a flowchart illustrating processing for determining the start of a transfer operation according to a second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     First Embodiment 
     The following will describe a first embodiment of a stacker crane control system with reference to the drawings ( FIGS. 1 to 8 ). The description is given taking an example where the stacker crane control system according to the present disclosure is applied to an article transport facility as exemplified in  FIG. 1 . Note that, in the present embodiment, a control system  1  corresponds to the “stacker crane control system”. 
     As shown in  FIG. 1 , a stacker crane  20  that is controlled by the control system  1  (see  FIG. 2 ) includes a travel carriage  21 , masts  22 , a lift  24 , a lifting apparatus  25 , and a transfer apparatus  26 . The travel carriage  21  travels along a travel route  4 . The travel operation of the travel carriage  21  is controlled by a later-described travel control unit  16  (see  FIG. 2 ). The travel control unit  16  controls driving of a travel drive unit (for example, an electric motor such as a servomotor) included in the travel carriage  21  so as to control the travel operation of the travel carriage  21 . Here, the longitudinal direction of the travel route  4  (direction in which the travel route  4  extends) is defined as the “route longitudinal direction L”, and the width direction of the travel route  4  is defined as the “route width direction W”. The route width direction W refers to a direction that is orthogonal to both the route longitudinal direction L and a vertical direction V. In the present embodiment, the route longitudinal direction L corresponds to a “direction along the travel route”. 
     As shown in  FIG. 1 , the travel route  4  is formed of a travel rail  7 . The travel rail  7  is provided on a floor part  5  (see  FIG. 3 ). The travel carriage  21  includes travel wheels that roll on a travel surface of the travel rail  7 , and as a result of the travel wheels being driven to rotate by the travel drive unit, the travel carriage  21  travels along the travel rail  7 . Note that, in  FIG. 3 , the stacker crane  20  is shown in a simplified manner, and the travel rail  7  provided on the floor part  5  and a later-described guide rail  8  provided on a ceiling part  6  are omitted. 
     As shown in  FIGS. 1 and 3 , the masts  22  are supported on the travel carriage  21  in an orientation along the vertical direction V. The masts  22  stand upright from the travel carriage  21  so as to extend upward from the travel carriage  21 . In the present embodiment, two masts  22  are supported on the travel carriage  21  while being lined up in the route longitudinal direction L. Upper end portions of the two masts  22  are coupled to each other by a connection part  23  such as an upper frame. The connection part  23  includes guide wheels that are guided by the guide rail  8  provided on the ceiling side such as the ceiling part  6 , and the connection part  23  moves in the route longitudinal direction L while being guided by the guide rail  8 . 
     The lifting apparatus  25  raises and lowers the lift  24 . The operation performed by the lifting apparatus  25  to raise and lower the lift  24  is controlled by a later-described lifting control unit  17  (see  FIG. 2 ). The lifting control unit  17  controls driving of a lifting drive unit (for example, an electric motor such as a servomotor) included in the lifting apparatus  25  so as to control the operation performed by the lifting apparatus  25  to raise and lower the lift  24 . The lifting apparatus  25  raises or lowers the lift  24  by, for example, using driving by the lifting drive unit to rotate a wind-up drum on which a wire connected to the lift  24  is wound, so that the wire is wound up or unwound. 
     The lift  24  moves up and down in a predetermined lifting range E (see  FIG. 3 ) that extends along the masts  22 . The lift  24  moves up and down between an upper limit E 1  and a lower limit E 2  of the lifting range E. The lift  24  includes guide wheels that are guided by the masts  22 , and moves up and down along the masts  22  while being guided by the masts  22 . In the present embodiment, the lift  24  moves up and down in a state of being arranged between the two masts  22  lined up in the route longitudinal direction L. The lift  24  is suspended by a wire and moves up and down along the masts  22 . 
     The transfer apparatus  26  is supported by the lift  24 . As shown in  FIGS. 1 and 3 , the transfer apparatus  26  includes a holding unit  27  for holding an article  2 , and performs a transfer operation of transferring the article  2  between the holding unit  27  and a transfer destination  3 . When the transfer apparatus  26  is located at a position that corresponds to a transfer destination  3  (specifically, a position at which the transfer apparatus  26  faces the transfer destination  3  in the route width direction W) according to the travel operation of the travel carriage  21  and the operation of raising and lowering the lift  24 , the transfer apparatus  26  performs the transfer operation. In the present embodiment, the holding unit  27  supports the article  2  (specifically, a central portion of the article  2  in the route longitudinal direction L) from below to hold the article  2 . In other words, the article  2  is placed on and supported by the holding unit  27 . The operation performed by the transfer apparatus  26  to transfer the article  2  is controlled by a later-described transfer control unit  18  (see  FIG. 2 ). The transfer control unit  18  controls driving of a transfer drive unit (for example, an electric motor such as a servomotor) included in the transfer apparatus  26  so as to control the transfer operation of the transfer apparatus  26 . 
     In the present embodiment, the transfer apparatus  26  is configured to advance and retract the holding unit  27  in the route width direction W (advancing movement away from the lift  24 , and retracting movement toward the lift  24 ). As a result of the operation performed by the transfer apparatus  26  to advance and retract the holding unit  27 , and the operation performed by the lifting apparatus  25  to raise and lower the lift  24 , the article  2  is transferred between the holding unit  27  and the transfer destination  3 . That is to say, in the present embodiment, the transfer operation of the transfer apparatus  26  is the operation of advancing and retracting the holding unit  27 , and through cooperation between the transfer apparatus  26  and the lifting apparatus  25  (specifically, by performing the operation of raising and lowering the lift  24  in accordance with the transfer operation of the transfer apparatus  26 ), the article  2  is transferred between the holding unit  27  and the transfer destination  3 . 
     Specifically, when transferring the article  2  from the holding unit  27  to the transfer destination  3 , the transfer apparatus  26  performs the transfer operation and the lifting apparatus  25  performs the operation of raising and lowering the lift  24 , such that the holding unit  27  that holds the article  2  is advanced from a retracted position (position at which the holding unit  27  is retracted to the lift  24 ) to an advanced position (position at which the holding unit  27  is advanced to the transfer destination  3 ), then the lift  24  is lowered, and then the holding unit  27  is retracted from the advanced position to the retracted position. With this, the article  2  is unloaded from the holding unit  27  to the transfer destination  3 , and thus the article  2  is transferred from the holding unit  27  to the transfer destination  3 . Also, when transferring the article  2  from the transfer destination  3  to the holding unit  27 , the transfer apparatus  26  performs the transfer operation and the lifting apparatus  25  performs the operation of raising and lowering the lift  24  such that the holding unit  27  not holding any article  2  is advanced from the retracted position to the advanced position, then the lift  24  is raised, and then the holding unit  27  is retracted from the advanced position to the retracted position. With this, the article  2  is scooped by the holding unit  27 , and thus the article  2  is transferred from the transfer destination  3  to the holding unit  27 . 
     As shown in  FIG. 1 , an article transport facility  100  includes at least one storage rack  30 . The storage rack  30  is arranged in an orientation such that its rack width direction matches the route longitudinal direction L and its rack depth direction matches the route width direction W. The travel route  4  is provided on the front side of the storage rack  30  (on the side on which the article  2  is loaded to and unloaded from the storage rack  30 ). The storage rack  30  includes a plurality of storage spaces  31  for storing articles  2 . The plurality of storage spaces  31  are arranged in multiple rows in the vertical direction V and multiple columns in the route longitudinal direction L. In the example shown in  FIG. 1 , each article  2  is stored in a storage space  31  with its side portions in the route longitudinal direction L supported from below. In the example shown in  FIG. 1 , the storage racks  30  are provided on both sides of the travel route  4  in the route width direction W. In the present embodiment, the storage spaces  31  are included in the transfer destination  3 . The storage spaces  31  serve as transfer destinations  3  set at a plurality of positions determined in the route longitudinal direction L and the vertical direction V. 
     The article transport facility  100  includes a support unit  40  for supporting an article  2  (in the example shown in  FIG. 1 , a pair of support units  40  that face each other in the route width direction W with the travel route  4  interposed therebetween). The support unit  40  is used as a loading unit that supports an article  2  to be loaded to the storage rack  30 . Also, the support unit  40  is used as an unloading unit that supports an article  2  unloaded from the storage rack  30 . In the present embodiment, the support units  40  are included in the transfer destination  3 . 
     As shown in  FIG. 2 , the control system  1  includes an operation control unit  15  for controlling the operation of the stacker crane  20 . The control system  1  includes, in addition to the operation control unit  15 , a sway detection unit  10 , a lifting height acquiring unit  14 , and a storage unit  19 , which will be described in detail later. The functions of the control system  1  (specifically, the functions of the sway detection unit  10 , the lifting height acquiring unit  14 , and the operation control unit  15 ) are realized by cooperation between hardware such as an arithmetic processing unit, and a program executed on the hardware. The storage unit  19  includes, for example, a storage medium such as a flash memory or a hard disk. 
     The plurality of constituent components of the control system  1  are configured to be able to exchange information with each other. Note that the constituent components of the control system  1  shown in  FIG. 2  are distinguished from each other at least logically, but do not need to be physically distinguished from each other. Also, the constituent components of the control system  1  may be provided on the stacker crane  20  (for example, on a device controller included in the stacker crane  20 ) or may be provided independently from the stacker crane  20 . Some of the constituent components of the control system  1  may be provided on the stacker crane  20 , and the remaining constituent components of the control system  1  may be provided independently from the stacker crane  20 . 
     The operation control unit  15  includes the travel control unit  16 , the lifting control unit  17 , and the transfer control unit  18 . The travel control unit  16  controls the travel operation of the travel carriage  21 , the lifting control unit  17  controls the operation performed by the lifting apparatus  25  to raise and lower the lift  24 , and the transfer control unit  18  controls the transfer operation of the transfer apparatus  26 . In the present embodiment, as a result of the transfer control unit  18  controlling the transfer operation of the transfer apparatus  26  and the lifting control unit  17  controlling the operation performed by the lifting apparatus  25  to raise and lower the lift  24 , the article  2  is transferred between the holding unit  27  and the transfer destination  3 . 
     In response to an instruction from a superordinate control unit or the like, the operation control unit  15  controls the stacker crane  20  to perform a loading operation of loading an article  2  into a storage space  31 , or an unloading operation for unloading an article  2  from a storage space  31 . 
     When the operation control unit  15  controls the stacker crane  20  to load the article  2 , the travel control unit  16  controls the travel operation of the travel carriage  21  such that the transfer apparatus  26  is located at a position that corresponds to the support unit  40  (specifically, a position at which the transfer apparatus  26  faces the support unit  40  in the route width direction W), and the lifting control unit  17  controls the lifting apparatus  25  to raise and lower the lift  24 . Then, the transfer control unit  18  controls the transfer operation of the transfer apparatus  26  such that the article  2  is transferred from the support unit  40  to the holding unit  27 . Then, the travel control unit  16  controls the travel operation of the travel carriage  21  such that the transfer apparatus  26  is located at a position that corresponds to the storage space  31  serving as the loading destination for the article  2  (specifically, a position at which the transfer apparatus  26  faces the storage space  31  in the route width direction W), and the lifting control unit  17  controls the lifting apparatus  25  to raise and lower the lift  24 . Then, the transfer control unit  18  controls the transfer operation of the transfer apparatus  26  such that the article  2  is transferred from the holding unit  27  to the storage space  31 . 
     Also, when the operation control unit  15  controls the stacker crane  20  to unload the article  2 , the travel control unit  16  controls the travel operation of the travel carriage  21  such that the transfer apparatus  26  is located at a position that corresponds to the storage space  31  in which the article  2  is stored, and the lifting control unit  17  controls the lifting apparatus  25  to raise and lower the lift  24 . Then, the transfer control unit  18  controls the transfer operation of the transfer apparatus  26  such that the article  2  is transferred from the storage space  31  to the holding unit  27 . Then, the travel control unit  16  controls the travel operation of the travel carriage  21  such that the transfer apparatus  26  is located at a position that corresponds to the support unit  40 , and the lifting control unit  17  controls the lifting apparatus  25  to raise and lower the lift  24 . Then, the transfer control unit  18  controls the transfer operation of the transfer apparatus  26  such that the article  2  is transferred from the holding unit  27  to the support unit  40 . 
     In the present embodiment, the travel carriage  21  is controlled so as to be stopped at reference stop positions S (see  FIG. 6 ) that are preset at a plurality of locations in the route longitudinal direction L. A reference stop position S is set for each transfer destination  3 . Each reference stop position S is set such that, when the travel carriage  21  is stopped at the reference stop position S, the lift  24  can be located at a position that corresponds to a transfer destination  3  (the transfer destination  3  set for the reference stop position  5 ). A common reference stop position S may be set at a plurality of transfer destinations  3  located at the same level in the route longitudinal direction L. For example, also when there is a small position shift in the route longitudinal direction L between a plurality of storage spaces  31  that belong to the same column, a common reference stop position S may be set for the plurality of storage spaces  31  that belong to the same column. 
     Meanwhile, as schematically shown in  FIG. 4 , the masts  22  sway with their portions connected to the travel carriage  21  (i.e., lower ends of the masts  22 ) serving as fulcrums for a while after the travel carriage  21  is stopped, due to inertia that occurs when the travel carriage  21  decelerates. In response to the swaying of the masts  22 , the lift  24  and the transfer apparatus  26  supported by the lift  24  sway in the route longitudinal direction L. Note that, in  FIG. 4 , the stacker crane  20  in a static state in which the swaying of the masts  22  is stopped and the masts  22  are standing still is indicated by solid lines, and the masts  22  in a state in which the masts  22  are bent to one side (to the right in the drawing) in the route longitudinal direction L with respect to the static state are indicated by dotted lines. The masts  22  change to the static state while bending to both sides in the route longitudinal direction L with respect to the static state. 
     In order to prevent a decrease in the operation efficiency of the stacker crane  20 , it is desirable that, for example, the transfer operation can be started as soon as possible when the swaying amount is in a range in which no failure will occur in the transfer operation of the transfer apparatus  26 . In the present embodiment, by configuring the control system  1  in the following manner, it is possible to start the transfer operation at an appropriate time based on the actual swaying amount of the stacker crane  20  (it is possible to start the transfer operation as soon as possible when the swaying amount is in a range in which no failure will occur in the transfer operation of the transfer apparatus  26 ), while suppressing an increase in the installation cost of the stacker crane  20 . 
     As shown in  FIG. 2 , the control system  1  includes the sway detection unit  10 , the lifting height acquiring unit  14 , and the above-described transfer control unit  18  for controlling the transfer apparatus  26 . In the present embodiment, the control system  1  further includes the storage unit  19 . In the present embodiment, the sway detection unit  10  includes a position detection sensor  11  and a stop position acquiring unit  12 . In the present embodiment, the stop position acquiring unit  12  includes a stop-position detection sensor  13 . 
     The sway detection unit  10  detects a reference swaying amount X 1  (see  FIGS. 4 and 5 ), which is a swaying amount X of the masts  22  at a detection height H 1 . Here, as shown in  FIG. 3 , the detection height H 1  is set to at least the height of a lowermost part  26   a  of the transfer apparatus  26  when the lift  24  is located at the upper limit E 1  of the lifting range E. In the example shown in  FIG. 4 , the detection height H 1  is set to the height of the upper ends (uppermost parts) of the masts  22 . In the present embodiment, the swaying amount X is the amount of swaying in the route longitudinal direction L, although the swaying amount X may include, in addition to the swaying amount in the route longitudinal direction L, the swaying amount in the vertical direction V. 
     As shown in  FIGS. 2 and 3 , in the present embodiment, the sway detection unit  10  includes the position detection sensor  11  that dynamically detects the positions of the masts  22  at the detection height H 1  in the route longitudinal direction L. As shown in  FIG. 3 , in the present embodiment, the position detection sensor  11  is an optical distance detection sensor. The position detection sensor  11  projects detection light D toward a first reflective plate  51 , and receives light reflected from the first reflective plate  51 , thereby detecting the distance between the position detection sensor  11  and the first reflective plate  51 . Based on the distance between the position detection sensor  11  and the first reflective plate  51 , the positions of the masts  22  at the detection height H 1  in the route longitudinal direction L are derived. 
     Either the position detection sensor  11  or the first reflective plate  51  (in the example shown in  FIG. 3 , the first reflective plate  51 ) is fixed to a portion whose position in the route longitudinal direction L does not change, such as the ceiling part  6 . The remaining one of the position detection sensor  11  and the first reflective plate  51  (in the example shown in  FIG. 3 , the position detection sensor  11 ) is fixed to a fixation target portion of the stacker crane  20 . The fixation target portion is a portion that sways with the same swaying amount as the swaying amount X of the portion of the mast  22  (in the example of  FIG. 4 , the upper end of the mast  22 ) that is located at the detection height H 1 . In the example shown in  FIG. 3 , the position detection sensor  11  is fixed to the connection part  23  serving as the fixation target portion. Note that the position detection sensor  11  may be a sensor (e.g., a rotary encoder) other than an optical distance detection sensor. 
     As shown in  FIG. 5  that shows changes in the swaying amounts X of the masts  22  relative to time T, after the travel carriage  21  is stopped, the masts  22  vibrates around a reference position A, which is a position in the static state, and the vibration attenuates. In the present embodiment, the sway detection unit  10  detects a difference between the reference position A and a detection result of the position detection sensor  11 , as the reference swaying amount X 1 . The method for deriving the reference position A will be described later. 
     The lifting height acquiring unit  14  acquires lifting height information that indicates a lifting height  112 . Here, the lifting height H 2  is a height (position in the vertical direction V) of the lift  24  at each point in time, as shown in  FIGS. 3 and 4 . The lifting height H 2  varies between the upper limit E 1  and the lower limit E 2  of the lifting range E of the lift  24 . The lifting height acquiring unit  14  includes a height detection sensor  28  that detects the height of the lift  24 , and acquires a detection result of the height detection sensor  28  as lifting height information. A sensor that is used when the lifting control unit  17  controls the operation of raising and lowering the lift  24  may also be used as the height detection sensor  28 , or another sensor may be used as the height detection sensor  28 . 
     As shown in  FIG. 3 , in the present embodiment, the height detection sensor  28  is an optical distance detection sensor. In the example shown in  FIG. 3 , the height detection sensor  28  is fixed to a part of the stacker crane  20  whose position in the vertical direction V does not change. Then, the height detection sensor  28  projects detection light D toward the lift  24  (specifically, a reflective plate provided on the lift  24 ), and receives light reflected from the lift  24 , thereby detecting the distance between the height detection sensor  28  and the lift  24 . Based on the distance between the height detection sensor  28  and the lift  24 , the height of the lift  24  is derived. In contrast to this configuration, a configuration is also possible in which the height detection sensor  28  is provided on the lift  24 . Also, the height detection sensor  28  may be a sensor (e.g., a rotary encoder) other than an optical distance detection sensor. 
     The transfer control unit  18  converts the reference swaying amount X 1  detected by the sway detection unit  10  into a lifting height swaying amount X 2  (see  FIGS. 4 and 5 ), which is a swaying amount X of the masts  22  at the lifting height H 2  that is indicated by the lifting height information. The lifting height swaying amount X 2  corresponds to the swaying amount of the lift  24 . That is to say, the transfer control unit  18  converts the swaying amount X of the masts  22  at the detection height H 1  into the swaying amount of the lift  24 . The conversion from the reference swaying amount X 1  into the lifting height swaying amount X 2  can be made based on, for example, a vibration model that approximates the displacement using a cubic function. In this case, the transfer control unit  18  can obtain the lifting height swaying amount X 2  from the reference swaying amount X 1  based on the following expression (1). 
         X 2= X 1( H 2/ H 1) 3  . . .   (1)
 
     The conversion from the reference swaying amount X 1  into the lifting height swaying amount X 2  can also be made based on, for example, a vibration model that approximates the displacement using a linear function. In this case, the transfer control unit  18  can obtain the lifting height swaying amount X 2  from the reference swaying amount X 1  based on the following expression (2). 
         X 2= X 1( H 2/ H 1) . . .   (2)
 
     Note that the detection height H 1  and the lifting height H 2  (height of the lift  24 ) in these expressions refer to heights from a common reference height, which can be the height of the connection part that connects the masts  22  and the travel carriage  21  (i.e., lower ends of the masts  22 ). 
     The transfer control unit  18  performs the above-described conversion using an amplitude of swaying of the masts  22  at the detection height H 1  (amplitude with the reference position A used as a reference) as the reference swaying amount X 1 . Therefore, the lifting height swaying amount X 2  derived by the transfer control unit  18  indicates the amplitude (crest value) of swaying of the masts  22  at the lifting height  112 . Accordingly, in the expressions (1) and (2), the reference swaying amount X 1  is an amplitude of swaying of the masts  22  at the detection height H 1 , and the lifting height swaying amount X 2  is an amplitude of swaying of the masts  22  at the lifting height  112 . 
     The sway detection unit  10  acquires the reference swaying amount X 1  repeatedly, and detects an amplitude of the swaying of the masts  22  at the detection height H 1  based on time-series data of the reference swaying amount X 1 . The sway detection unit  10  subjects the time-series data of the reference swaying amount X 1  to differential processing or the like to detect a peak of the swaying of the masts  22  (peak in vibration waveform), and detects the (absolute) value of the reference swaying amount X 1  at the peak as the amplitude of the swaying of the masts  22  at the detection height H 1 . A peak of swaying of the masts  22  appears at a period of half of the natural period of the swaying of the masts  22 , and in the example shown in  FIG. 5 , peaks of the swaying of the masts  22  appear at time T 1 , time T 2 , time T 3 , time T 4 , and time T 5 . The transfer control unit  18  converts the amplitude of the swaying of the masts  22  at the detection height H 1  that was detected by the sway detection unit  10  in this way into the amplitude of the swaying of the masts  22  at the lifting height  112 . 
     As described above, the transfer control unit  18  derives the lifting height swaying amount X 2  by converting the reference swaying amount X 1  into the lifting height swaying amount X 2 . Then, the transfer control unit  18  starts the transfer operation of the transfer apparatus  26  if the lifting height swaying amount X 2  is stably smaller than or equal to a predetermined determination threshold ΔX. In this context, “stably” means a period of predetermined determination time or longer. As described above, in the present embodiment, by performing the above-described conversion, the transfer control unit  18  derives the amplitude of swaying of the masts  22  at the lifting height  112  as the lifting height swaying amount X 2 . Then, if the derived lifting height swaying amount X 2  is smaller than or equal to the predetermined determination threshold ΔX, the transfer control unit  18  determines that the lifting height swaying amount X 2  is stably smaller than or equal to the predetermined determination threshold ΔX, and starts the transfer operation of the transfer apparatus  26 . In this case, if the lifting height swaying amount X 2  is smaller than or equal to the predetermined determination threshold ΔX for at least a quarter of the above-described natural period, it is determined that the lifting height swaying amount X 2  is stably smaller than or equal to the predetermined determination threshold ΔX. In the example shown in  FIG. 5 , at the time T 2 , the lifting height swaying amount X 2  is determined as being stably smaller than or equal to the predetermined determination threshold ΔX. 
     In this way, the transfer control unit  18  regards the lifting height swaying amount X 2  as the swaying amount of the transfer apparatus  26  supported by the lift  24 , and determines whether or not to start the transfer operation of the transfer apparatus  26 . The above-described determination threshold ΔX is preferably set to a value as large as possible within a range in which no failure will occur in the transfer operation of the transfer apparatus  26 . Also, the determination threshold ΔX is preferably set taking into consideration the connection relationship or positional relationship between the lift  24  and the transfer apparatus  26  (taking into consideration that, for example, sway may be amplified at the connection part that connects the lift  24  and the transfer apparatus  26 ). 
     As described above, in the present embodiment, the sway detection unit  10  detects a difference between the reference position A and a detection result of the position detection sensor  11 , as the reference swaying amount X 1 . The following will describe the method for deriving the reference position A that is performed in the control system  1  of the present embodiment. 
     As described above, in the present embodiment, the travel carriage  21  is controlled so as to be stopped at the reference stop positions S (see  FIG. 6 ) that are preset at a plurality of locations in the route longitudinal direction L. In the present embodiment, the control system  1  includes the storage unit  19  (see  FIG. 2 ) in which information regarding a mast reference position A 0  measured when the travel carriage  21  is stopped at each of a plurality of reference stop positions S is stored, the mast reference position A 0  being a position of the masts  22  at the detection height H 1  in a state in which the travel carriage  21  is stopped at the reference stop position S, and the masts  22  are standing still (are in the static state). Each piece of information regarding the mast reference position A 0  is stored in the storage unit  19  in association with a reference stop position S (specifically, the reference stop position S at which the mast reference position A 0  was measured).  FIG. 6  shows the masts  22  and the mast reference position A 0  in the static state at three reference stop positions S, namely, a first stop position S 1 , a second stop position S 2 , and a third stop position S 3 . 
     As shown in  FIG. 6 , the positional relationship between the reference stop position S and the mast reference position A 0  in the route longitudinal direction L is common between a plurality of reference stop positions S, in terms of design. However, actually, the positional relationship may vary between the reference stop positions S due to a level difference (difference in height) of the travel rail  7 , or the like. In this regard, in the present embodiment, since the travel carriage  21  is stopped at each of the plurality of reference stop positions S and the mast reference position A 0  is measured as described above, the mast reference position A 0  can be appropriately set for each of the plurality of reference stop positions S even if the above-described positional relationship varies between the reference stop positions S. 
     As shown in  FIG. 2 , the sway detection unit  10  includes the stop position acquiring unit  12  that acquires stop position information that indicates at which of the plurality of reference stop positions S the travel carriage  21  is stopped. The stop position acquiring unit  12  acquires the stop position information, for example, from the operation control unit  15  (specifically, the travel control unit  16 ). If the reference stop position S is set at a position common between a plurality of storage spaces  31  belonging to the same column, the stop position information is information that indicates, for example, at which column of the storage rack  30  the travel carriage  21  is stopped. The sway detection unit  10  acquires, from the storage unit  19 , the mast reference position A 0  associated with the reference stop position S indicated by the stop position information, and detects a difference between the mast reference position A 0  and a detection result of the position detection sensor  11 , as a reference swaying amount X 1 . That is to say, in this case, the mast reference position A 0  serves as the above-described reference stop position A (see  FIGS. 4 and 5 ). 
     Meanwhile, if the travel carriage  21  is controlled to stop at the reference stop position S, an actual stop position R, which is a stop position at which the travel carriage  21  is actually stopped, may be shifted from the reference stop position S.  FIG. 7  shows a situation in which the travel carriage  21  controlled so as to stop at the second stop position S 2  is stopped at a position shifted from the second stop position S 2  by a stop position error ΔL. Note that, in  FIG. 7 , the stop position error ΔL is exaggerated for ease of understanding. It is also possible to take into consideration this stop position error ΔL to correct the reference stop position S, which serves as a reference for use in detecting the reference swaying amount X 1 , as will be described below. 
     In the case where the reference stop position S is to be corrected, the stop position acquiring unit  12  includes the stop-position detection sensor  13  that detects the actual stop position R, as shown in  FIG. 2 . A sensor that is used when the travel control unit  16  controls the travel operation of the travel carriage  21  may also be used as the stop-position detection sensor  13 , or another sensor may be used as the stop-position detection sensor  13 . 
     As shown in  FIG. 3 , in the present embodiment, the stop-position detection sensor  13  is an optical distance detection sensor. The stop-position detection sensor  13  projects detection light D toward a second reflective plate  52 , and receives light reflected from the second reflective plate  52 , thereby detecting the distance between the stop-position detection sensor  13  and the second reflective plate  52 . Based on the distance between the stop-position detection sensor  13  and the second reflective plate  52  in a state in which the travel carriage  21  is stopped, the actual stop position R is derived. 
     Either the stop-position detection sensor  13  or the second reflective plate  52  (in the example shown in  FIG. 3 , the second reflective plate  52 ) is fixed to a portion whose position in the route longitudinal direction L does not change, such as the floor part  5 . The remaining one of the stop-position detection sensor  13  and the second reflective plate  52  (in the example shown in  FIG. 3 , the stop-position detection sensor  13 ) is fixed to the travel carriage  21 . Note that the stop-position detection sensor  13  may be a sensor (e.g., a rotary encoder) other than an optical distance detection sensor. 
     The sway detection unit  10  obtains a corrected mast reference position A 1  based on a detection result of the actual stop position R obtained by the stop-position detection sensor  13 . Specifically, by correcting the mast reference position A 0  based on a difference between the actual stop position R and the reference stop position S that corresponds to the actual stop position R, the sway detection unit  10  obtains the corrected mast reference position A 1 . In the example shown in  FIG. 7 , the difference between the actual stop position R and the reference stop position S (here, the second stop position S 2 ) that corresponds to the actual stop position R is the stop position error ΔL, and the corrected mast reference position A 1  is the position obtained by shifting the mast reference position A 0  by the stop position error ΔL in the same direction as the direction of the shift of the actual stop position R from the reference stop position S. Also, the sway detection unit  10  detects a difference between the corrected mast reference position A 1  and a detection result of the position detection sensor  11 , as the reference swaying amount X 1 . That is to say, in this case, the corrected mast reference position A 1  serves as the above-described reference stop position A (see  FIGS. 4 and 5 ). 
     The following will describe a procedure of processing for determining the start of the transfer operation of the transfer apparatus  26  that is executed in the control system  1  according to the present embodiment, with reference to  FIG. 8 . The technical features of the control system  1  disclosed in the present specification are applicable to the method for controlling the stacker crane  20 , and the method for controlling the stacker crane  20  is also disclosed in the present specification. The control method includes processing (steps) shown in  FIGS. 8 and 9 . 
     As shown in  FIG. 8 , when, for positioning the transfer apparatus  26  at a position that corresponds to the transfer destination  3 , the travel operation of the travel carriage  21  and the operation performed by the lifting apparatus  25  to raise and lower the lift  24  are complete, and these operations are stopped (Yes in step # 01 ), the sway detection unit  10  (specifically, the position detection sensor  11 ) detects the positions of the masts  22  at the detection height H 1  in the route longitudinal direction L (step # 02 ). The detection of the positions of the masts  22  in step # 02  is repeated until a peak of swaying of the masts  22  is detected (No in step # 03 ). When a peak of the swaying of the masts  22  is detected (Yes in step # 03 ), the sway detection unit  10  calculates the reference swaying amount X 1  (specifically, the amplitude of the swaying of the masts  22  at the detection height H 1 ) (step # 04 ). In the present embodiment, the sway detection unit  10  derives a difference between the reference position A (mast reference position A 0  or corrected mast reference position A 1 ) and a detection result of the position detection sensor  11 , as the reference swaying amount X 1 . 
     Then, the transfer control unit  18  calculates the lifting height swaying amount X 2  (the amplitude of swaying of the masts  22  at the lifting height H 2 ) (step # 05 ). The transfer control unit  18  converts the reference swaying amount X 1  calculated in step # 04  into the lifting height swaying amount X 2 , thereby deriving the lifting height swaying amount X 2 . The processing from steps # 02  to # 05  is repeatedly executed until the lifting height swaying amount X 2  calculated in step # 05  is smaller than or equal to the determination threshold ΔX (No in step # 06 ). When the lifting height swaying amount X 2  calculated in step # 05  is smaller than or equal to the determination threshold ΔX (Yes in step # 06 ), the transfer control unit  18  starts the transfer operation of the transfer apparatus  26  (step # 07 ). 
     Second Embodiment 
     The following will describe a second embodiment of the stacker crane control system with reference to a drawing ( FIG. 9 ). The present embodiment differs from the first embodiment in the method for detecting the reference swaying amount X 1  that is executed by the sway detection unit  10 . The following description is given focusing on the difference from the first embodiment. Features that are not stated clearly are the same as those of the first embodiment, and the same reference numerals are given thereto and detailed descriptions thereof are omitted. 
     In the first embodiment, the sway detection unit  10  detects a difference between the reference position A and a detection result of the position detection sensor  11 , as the reference swaying amount X 1 . In contrast, in the present embodiment, the sway detection unit  10  detects a detection result of the position detection sensor  11  as a reference swaying amount X 1 , and detects the amplitude of swaying of the masts  22  at the detection height H 1  without using the reference position A. Therefore, in the present embodiment, there is no need for the sway detection unit  10  to include the stop position acquiring unit  12  nor store information regarding the mast reference position A 0  in the storage unit  19 . 
     In the present embodiment, the sway detection unit  10  acquires the amplitude of a dynamic change in the positions of the masts  22  (i.e., the amplitude of swaying of the masts  22 ) at the detection height H 1  indicated by the detection result of the position detection sensor  11 , and detects the amplitude as the reference swaying amount X 1 . Specifically, the sway detection unit  10  repeatedly acquires a detection result of the position detection sensor  11 . The sway detection unit  10  subjects time-series data of the detection results of the position detection sensor  11  to differential processing or the like to detect a peak of the swaying of the masts  22 , and acquires the detection result of the position detection sensor  11  at this peak, as a crest value. Also, after having detected the peak of the swaying of the masts  22 , the sway detection unit  10  detects the value of half of a difference (i.e., peak-to-peak value) between the currently acquired crest value and the previously acquired crest value, as the amplitude of the dynamic change in the positions of the masts  22  at the detection height H 1  (i.e., as the reference swaying amount X 1 ). In the example shown in  FIG. 5 , at the time T 2  for example, the value of half of a difference between the detection result of the position detection sensor  11  at the time T 2  and the detection result of the position detection sensor  11  at the time T 1  is detected as the reference swaying amount X 1 . 
     The following will describe a procedure of processing for determining the start of the transfer operation of the transfer apparatus  26  that is executed in the control system  1  according to the present embodiment, with reference to  FIG. 9 . 
     As shown in  FIG. 9 , when, for positioning the transfer apparatus  26  at a position that corresponds to the transfer destination  3 , the travel operation of the travel carriage  21  and the operation performed by the lifting apparatus  25  to raise and lower the lift  24  are complete, and these operations are stopped (Yes in step # 10 ), the sway detection unit  10  (specifically, the position detection sensor  11 ) detects the positions of the masts  22  at the detection height H 1  in the route longitudinal direction L (step # 11 ). The detection of the positions of the masts  22  in step # 11  is repeated until a peak of swaying of the masts  22  is detected (No in step # 12 ). When a peak of the swaying of the masts  22  is detected (Yes in step # 12 ), the sway detection unit  10  acquires the detection result of the position detection sensor  11  at this peak as a crest value, and stores this crest value as the previous value (step # 13 ). 
     Then, the sway detection unit  10  (specifically, the position detection sensor  11 ) detects the positions of the masts  22  at the detection height H 1  in the route longitudinal direction L (step # 14 ). The detection of the positions of the masts  22  in step # 14  is repeated until a peak of the swaying of the masts  22  is detected (No in step # 15 ). When a peak of the swaying of the masts  22  is detected (Yes in step # 15 ), the sway detection unit  10  calculates the reference swaying amount X 1  (specifically, the amplitude of the dynamic change in the positions of the masts  22  at the detection height H 1 ) (step # 16 ). In the present embodiment, the sway detection unit  10  acquires a detection result of the position detection sensor  11  at the currently detected peak as a crest value, and derives the value of half of a difference between the currently acquired crest value and the previously acquired crest value (crest value stored as the previous value), as the reference swaying amount X 1 . 
     Then, the transfer control unit  18  calculates the lifting height swaying amount X 2  (the amplitude of swaying of the masts  22  at the lifting height H 2 ) (step # 17 ). The transfer control unit  18  converts the reference swaying amount X 1  calculated in step # 16  into the lifting height swaying amount X 2 , thereby deriving the lifting height swaying amount X 2 . If the lifting height swaying amount X 2  calculated in step # 17  is not smaller than or equal to the determination threshold ΔX (No in step # 18 ), the previous value is updated to the crest value currently acquired by the sway detection unit  10  (step # 19 ), and the procedure returns to step # 14 . The processing from steps # 14  to # 17 , and # 19  is repeatedly executed until the lifting height swaying amount X 2  calculated in step # 17  is smaller than or equal to the determination threshold ΔX (No in step # 18 ). When the lifting height swaying amount X 2  calculated in step # 17  is smaller than or equal to the determination threshold ΔX (Yes in step # 18 ), the transfer control unit  18  starts the transfer operation of the transfer apparatus  26  (step # 20 ). 
     Other Embodiments 
     The following will describe other embodiments of the stacker crane control system. 
     (1) The first embodiment has described a configuration in which information regarding the mast reference position A 0  measured when the travel carriage  21  is stopped at each of the plurality of reference stop positions S is stored in the storage unit  19 , as an example. However, the present disclosure is not limited to such a configuration. Based on the information regarding the mast reference position A 0  measured when the travel carriage  21  is stopped at one reference stop position S, the mast reference position A 0  may be set for a plurality of reference stop positions S, as long as no failure will occur in the transfer operation of the transfer apparatus  26  even if the positional relationship between the reference stop position S and the mast reference position A 0  in the route longitudinal direction L is regarded as constant. 
     (2) The first embodiment has described a configuration in which, assuming that the mast reference position A 0  or the corrected mast reference position Al is the reference position A (position of the mast  22  in the static state), the sway detection unit  10  detects a difference between the reference position A and a detection result of the position detection sensor  11 , as the reference swaying amount X 1 , as an example. However, the present disclosure is not limited to such a configuration. A configuration is also possible in which the sway detection unit  10  detects a difference between the reference position A set according to the actual stop position R and a detection result of the position detection sensor  11 , as the reference swaying amount X 1 , as long as no failure will occur in the transfer operation of the transfer apparatus  26  even if the positional relationship between the actual stop position R and the reference position A is regarded as constant. 
     (3) The above-described embodiments have described a configuration in which the transfer apparatus  26  is configured to advance and retract the holding unit  27  in the route width direction W, and as a result of the advancement and retraction of the holding unit  27  (specifically, as well as raising and lowering of the lift  24 ), the article  2  is transferred between the holding unit  27  and the transfer destination  3 , as an example. However, the present disclosure is not limited to such a configuration. A configuration is also possible in which, for example, the transfer apparatus  26  advances and retracts a pair of forward/rearward moving members (for example, a pair of clamp units, or a pair of arms equipped with a hook) in the route width direction W, the pairs of forward/rearward moving members being arranged on both sides of the article  2  in the route longitudinal direction L, and as a result of the transfer operation of the transfer apparatus  26  (specifically, operation of advancing and retracting the pair of forward/rearward moving members), the article  2  is transferred between the holding unit  27  and the transfer destination  3 . In this case, a configuration is also possible in which a conveyor (such as a belt conveyor) for conveying the article  2  in the route width direction W is provided on the holding unit  27  or the above-described forward/rearward moving members, and as a result of the conveying operation of the conveyor as well as the operation of advancing and retracting the pair of forward/rearward moving members, the article  2  is transferred between the holding unit  27  and the transfer destination  3 . 
     (4) The above-described embodiments have described a configuration in which two masts  22  are supported on the travel carriage  21  while being lined up in the route longitudinal direction L, as an example. However, the present disclosure is not limited to such a configuration. A configuration is also possible in which, for example, only one mast  22  is supported on the travel carriage  21 , and the lift  24  and the one mast  22  are lined up in the route longitudinal direction L. 
     (5) Note that the configurations disclosed in the above-described embodiments may be applied while being combined with configurations disclosed in other embodiments (including a combination of embodiments described as other embodiments), provided there is no inconsistency. With respect to other configurations, the embodiments disclosed in this specification are merely examples in all aspects. Accordingly, those skilled in the art may make various changes as appropriate, without departing from the spirit of this disclosure. 
     Overview of The Embodiments 
     The following will describe an overview of the stacker crane control system explained above. 
     A stacker crane control system for controlling a stacker crane including: a travel carriage that travels along a travel route; a mast supported on the travel carriage in an orientation along a vertical direction; a lift that moves up and down within a predetermined lifting range along the mast; a lifting apparatus that raises and lowers the lift; and a transfer apparatus supported by the lift and including a holding unit for holding an article, the stacker crane being configured to perform a transfer operation of transferring the article between the holding unit and a transfer destination, the stacker crane control system including: a sway detection unit configured to detect a reference swaying amount that is a swaying amount of the mast at a detection height, the detection height being set greater than or equal to the height of a lowermost part of the transfer apparatus when the lift is located at an upper limit of the lifting range; a lifting height acquiring unit configured to acquire lifting height information that indicates a lifting height, which is the height of the lift, at a plurality of points in time; and a transfer control unit configured to control the transfer apparatus, wherein the transfer control unit converts the reference swaying amount detected by the sway detection unit into a lifting height swaying amount that is a swaying amount of the mast at the lifting height indicated by the lifting height information, and starts the transfer operation of the transfer apparatus if the lifting height swaying amount is stably smaller than or equal to a predetermined determination threshold. 
     According to the present configuration, it is possible to obtain a lifting height swaying amount that is a swaying amount of the mast at the actual lifting height, based on an actual swaying amount of the mast that is detected by the sway detection unit, and an actual lifting height of the lift at each point in time that is acquired by the lifting height acquiring unit. Then, if the lifting height swaying amount is stably smaller than or equal to a predetermined determination threshold, the transfer operation of the transfer apparatus is started. Since the transfer operation is started in this way based on a detection result of the actual swaying amount of the mast, the transfer operation of the transfer apparatus can be started at an appropriate time according to the actual swaying amount of the mast that varies depending on various operation conditions. 
     Here, preferably, the reference swaying amount is an amplitude of swaying of the mast at the detection height, and the lifting height swaying amount is an amplitude of swaying of the mast at the lifting height, and the transfer control unit caluculates, as the lifting height swaying amount, X 2  defined by the following expression (1) 
         X 2 = X 1( H 2/ H 1) 3  . . .   (1)
 
     where H 1  is the detection height, H 2  is the height of the lift, and X 1  is the reference swaying amount. 
     According to the present configuration, taking into consideration actual deformation due to swaying of the mast supported on the travel carriage, it is possible to convert an actual swaying amount of the mast detected by the sway detection unit into the actual lifting height swaying amount, which is a swaying amount of the mast at a lifting height. Therefore, it is possible to accurately obtain the lifting height swaying amount. 
     Also, preferably, the travel carriage is controlled so as to be stopped at reference stop positions that are preset at a plurality of locations along the travel route, the stacker crane control system further includes a storage unit in which information regarding a mast reference position measured when the travel carriage is stopped at each of the plurality of reference stop positions is stored, the mast reference position being a position of the mast at the detection height when the travel carriage is stopped at the reference stop position and the mast is standing still, and the sway detection unit includes a position detection sensor configured to dynamically detect the position of the mast at the detection height in a direction along the travel route, and a stop position acquiring unit configured to acquire stop position information that indicates at which of the plurality of reference stop positions the travel carriage is stopped, and the sway detection unit acquires from the storage unit the mast reference position associated with the reference stop position indicated by the stop position information, and detects, as the reference swaying amount, a difference between the mast reference position and a result of the detection by the position detection sensor, as the reference swaying amount. 
     According to the present configuration, since the travel carriage is controlled so as to stop at reference stop positions preset at a plurality of locations in a direction along the travel route, it is possible to appropriately detect the reference swaying amount, which is an actual swaying amount of the mast at the detection height, based on the mast reference position information measured in advance and stored in the storage unit, and a detection result of the position detection sensor. 
     In the above-described configuration in which the sway detection unit detects a difference between the mast reference position and a detection result of the position detection sensor, as the reference swaying amount, preferably, the stop position acquiring unit includes a stop-position detection sensor configured to detect an actual stop position, which is a position at which the travel carriage is actually stopped, and the sway detection unit determines a corrected mast reference position by correcting the mast reference position based on a difference between the actual stop position and the reference stop position that corresponds to the actual stop position, and detects, as the reference swaying amount, a difference between the corrected mast reference position and the detection result of the detection by the position detection sensor. 
     According to the present configuration, taking into consideration an error between the actual stop position, which is a position at which the travel carriage is actually stopped, and the reference stop position, it is possible to correct the reference stop position, which serves as a reference for use in detecting the reference swaying amount. Therefore, according to the present configuration, it is possible to improve the accuracy in detecting the reference swaying amount. 
     In the stacker crane control system according to the above-described configurations, preferably, the sway detection unit includes a position detection sensor configured to dynamically detect the position of the mast at the detection height in a direction along the travel route, and the sway detection unit detects, as the reference swaying amount an amplitude of a dynamic change in the position of the mast at the detection height which dynamic change is indicated by a result of the detection by the position detection sensor. 
     According to the present configuration, it is possible to appropriately detect the reference swaying amount, which is an actual swaying amount of the mast at the detection height, based on an amplitude of a dynamic change in the position of the mast at the detection height indicated by the detection result of the position detection sensor. Therefore, according to the present configuration, there is no need to store information regarding the mast reference position in the storage unit, for example, and it is possible to appropriately detect the reference swaying amount with a relatively simple configuration. Also, according to the present configuration, even if the stop position of the travel carriage is not limited to a preset position, it is possible to appropriately detect the reference swaying amount. 
     It is sufficient for the stacker crane control system according to the present disclosure to be able to realize at least one of the above-described effects.