Patent Publication Number: US-2023136488-A1

Title: Transfer apparatus, control device, transfer method, and storage medium

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-179610, filed on Nov. 2, 2021; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described below relate to a transfer apparatus, a control device, a transfer method, program, and a storage medium. 
     BACKGROUND 
     There is a transfer apparatus for transferring articles. Improvements in work efficiency are required for the transfer apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view schematically showing a transfer apparatus according to an embodiment; 
         FIG.  2    is a perspective view showing a suction hand according to the embodiment; 
         FIG.  3    is a cross-sectional view showing a part of the suction hand according to the embodiment; 
         FIG.  4    is a side view schematically showing the suction hand according to the embodiment; 
         FIGS.  5 A and  5 B  are side views schematically showing an operation of the suction hand according to the embodiment; 
         FIG.  6    is a perspective view showing the hand according to the embodiment; 
         FIG.  7 A  is a front view schematically showing the holding method in the first operation, and  FIG.  7 B  is a side view schematically showing the holding method in the first operation; 
         FIGS.  8 A to  8 C  are side views schematically showing states when the article is held in the first operation; 
         FIG.  9 A  is a front view schematically showing the holding method in the second operation, and  FIG.  9 B  is a side view schematically showing the holding method in the second operation; 
         FIG.  10    is a flowchart showing an outline of a transfer method by the transfer apparatus according to the embodiment; 
         FIG.  11    is a flowchart showing processing in the first determination; 
         FIG.  12    is a schematic view for explaining the processing in the first determination; 
         FIG.  13    is a flowchart showing a part of the first operation; 
         FIG.  14    is a flowchart showing another part of the first operation; 
         FIGS.  15 A to  15 C  are schematic views showing the first operation; 
         FIGS.  16 A to  16 C  are schematic views showing the first operation; 
         FIGS.  17 A to  17 C  are schematic views showing the first operation; 
         FIG.  18    is a flowchart showing the processing in the second determination; 
         FIG.  19    is a schematic view for explaining the processing in the second determination; 
         FIG.  20    is a flowchart showing a part of the second operation; 
         FIG.  21    is a flowchart showing another part of the second operation; 
         FIGS.  22 A and  22 B  are schematic views showing the second operation; 
         FIGS.  23 A to  23 C  are schematic views showing the second operation; 
         FIGS.  24 A to  24 C  are schematic views showing the second operation; 
         FIG.  25    is a front view schematically showing another suction hand according to the embodiment; 
         FIG.  26 A  is a front view schematically showing the holding method in the third operation, and  FIG.  26 B  is a side view schematically showing the holding method in the third operation; 
         FIG.  27    is a flow chart showing the outline of the transfer method by the transfer apparatus according to the variation of the embodiment; 
         FIG.  28    is a flowchart showing the processing in the third determination; 
         FIG.  29    is a schematic view for explaining the processing in the third determination; and 
         FIG.  30    is a schematic view showing a hardware configuration. 
     
    
    
     DETAILED DESCRIPTION 
     According to one embodiment, a transfer apparatus includes a suction hand, a moving device, a first detector, and a controller. The suction hand includes a first suction unit and a second suction unit. The first suction unit includes a plurality of first suction portions and is configured to contact with an article in a first direction. The second suction unit includes a plurality of second suction portions and is configured to contact with the article in a second direction crossing the first direction. the first suction unit and the second suction unit each are provided multiply in a third direction crossing a first plane parallel to the first direction and the second direction. The moving device moves the suction hand. The first detector detects a first surface and a second surface of the article. The first surface crosses the first direction. The second surface crosses the second direction. The controller controls the suction hand and the moving device based on a first detection result from the first detector. The controller performs at least a first operation and a second operation. The first operation causes a plurality of the first suction units to respectively suction a plurality of the first surfaces of a plurality of the articles. The first operation further causes a plurality of the second suction units to respectively suction a plurality of the second surfaces of the articles. The first operation moves the articles. The first operation is performed in a case where a placement state of the articles calculated using the first detection result satisfies a first condition. The second operation causes one of the first suction units to suction the first surface of one of the articles. The second operation does not cause the second suction units to suction the articles. The second operation moves the one of the articles. The second operation is performed in a case where the placement state satisfies a second condition. 
       FIG.  1    is a perspective view schematically showing a transfer apparatus according to an embodiment. 
     The transfer apparatus  100  according to the embodiment is installed at a site where an article transfer operation is performed, such as a warehouse. In the transfer operation, the loaded articles are sequentially moved to a carrier device or another position. As shown in  FIG.  1   , the transfer apparatus  100  includes a suction hand  1 , a controller  25 , a support frame  110 , a first detector  121 , a second detector  122 , a third detector  123 , a moving device  130 , and a negative pressure generator  140 . 
     The suction hand  1  can suction an upper surface (first surface) and a side surface (second surface) of an article by vacuum. The suction hand  1  can hold (stably grip) the article by suctioning at least one of the upper surface and the side surface of the article. 
     Specifically, the suction hand  1  includes an upper surface suction unit  16  and a side surface suction unit  22 . Here, a direction of which the upper surface suction unit  16  is in contact with the article A is taken as Z-direction (up-down direction or a first direction). A direction of which the side surface suction unit  22  is in contact with the article A is taken as X-direction (front-rear direction or second direction). A direction crossing X-Z surface is taken as Y-direction (left-right direction or third direction). For example, the X-direction and the Y-direction are parallel to the horizontal plane and the Z-direction is parallel to the vertical direction. The X-direction, the Y-direction, and the Z-direction may be orthogonal to each other. 
     The support frame  110  supports each component of transfer apparatus  100 . The first detector  121  detects the upper surface and the side surface of the article A. The second detector  122  detects the height of the article A and the like. The side surface specifically refers to a surface that crosses the X-direction and faces the conveyor  150  among the multiple surfaces of the article A. The third detector  123  detects the position of the bottom surface of the article A held by the suction hand  1 . The moving device  130  moves the suction hand  1 . The negative pressure generator  140  generates negative pressure in the suction hand  1  for suction. 
     The transfer apparatus  100  may further include a conveyor  150  and a lifting-and-lowering device  160  for cargo-handling operations. In other words, the transfer apparatus  100  may be used as a cargo-handling apparatus. For example, the cargo-handling operation includes unloading and loading. As an example, the pallet P on which the article A is loaded is placed adjacent to the transfer apparatus  100 . The transfer apparatus  100  is located between the conveyor C and the pallet P. The transfer apparatus  100  holds the article A loaded on the pallet P, and transfers to the conveyor  150  in the support frame  110 . The conveyor  150  further conveys the transferred article A toward the conveyor C. The lifting-and-lowering device  160  lifts or lowers the conveyor  150 . 
     A specific example of each component will be described in detail below. 
     The support frame  110  constitutes the outline of the transfer apparatus  100  and is fixed to the floor surface. The support frame  110  includes a main body  111  and a protruding portion  112 . The shape of the main body  111  is a rectangular parallelepiped. The conveyor  150  is provided inside the main body  111 . The main body  111  has an opening  113  facing the pallet P side and an opening  114  facing the conveyor C side. The article A is transferred from pallet P to conveyor  150  through opening  113 . Also, the article A is transferred from the conveyor  150  to the conveyor C through the opening  114 . 
     The main body  111  is composed of, for example, four vertical frames  111   a  and multiple horizontal frames  111   b  connecting the upper ends and the lower ends of the four vertical frames  111   a.  The protruding portion  112  is attached to the front of the upper portion of the main body  111  and protrudes forward. The protruding portion  112  is positioned above the pallet P. 
     The first detector  121  detects the upper surface and the side surface of the article from the Z-direction. The first detector  121  includes an imager  121   a.  The imager  121   a  is fixed to a support portion  112   a  provided on the protruding portion  112 . The imager  121   a  includes one or two selected from an image sensor and a distance measuring sensor. The imager  121   a  images the article A placed on the pallet P from above. The imager  121   a  transmits the acquired image (still image) to the controller  25 . The imager  121   a  may acquire a moving image. In this case, a still image is cut out from the moving image. 
     The controller  25  calculates data related to the article from the image acquired by the imager  121   a.  The calculated data includes the recognition result of the upper surface of the article A in the image, the position of the upper surface in each of the X-direction, the Y-direction, and the Z-direction, the length of the upper surface in the X-direction, the length of the upper surface in the Y-direction, the area of the upper surface, etc. In the transfer apparatus  100 , the imager  121   a  and the controller  25  function as the first detector  121  for detecting the upper surface of the article A. An image recognition system other than the controller  25  may be incorporated into the imager  121   a  and it may be used as the first detector  121 . 
     The second detector  122  detects the side surface of the article in a direction crossing the Z-direction. The second detector  122  includes a distance measuring sensor  122   a.  The distance measuring sensor  122   a  measures the distance to the article in a direction crossing the Z-direction. In the illustrated example, the distance measuring sensor  122   a  is provided on one of the multiple vertical frames  111   a,  and measures the distance to the article from a direction perpendicular to the Z-direction and inclined from the X-direction and the Y-direction. The distance measuring sensor  122   a  emits infrared rays, laser beams, or ultrasonic waves toward the article. From the viewpoint of distance measurement accuracy, the distance measuring sensor  122   a  is preferably a laser range finder (LRF) using a laser beam. 
     The controller  25  recognizes the side surface of the article A and calculates the position of the side surface of the article A in the X-Y plane based on the measurement result of the distance measuring sensor  122   a.  The distance measuring sensor  122   a  and the controller  25  function as the second detector  122 . 
     For example, the second detector  122  is attached to the lifting-and-lowering device  122   b.  The lifting-and-lowering device  122   b  lifts or lowers the second detector  122  along the Z-direction. In this case, the controller  25  can calculate the position of the bottom surface of the article A in the Z-direction, the position of the upper surface of the article A in the Z-direction, and the height (length in the Z-direction) of the article A from the measurement result by the distance measuring sensor  122   a  and the movement amount of the lifting-and-lowering device  122   b.    
     Similarly to the first detector  121 , the second detector  122  may include an imager. The imager images the article A placed on the pallet P from the side. The imager transmits the acquired image to the controller  25 . The controller  25  calculates a recognition result of the side surface of the article A, the position of the side surface of the article A in the X-Y plane, the position of the bottom surface of the article A in the Z-direction, the position of the upper surface of the article A in the Z-direction, the height of the article A, etc., from the image. That is, the imager and the controller  25  function as the second detector  122 . 
     The third detector  123  may include a distance measuring sensor  123   a  installed between the main body  111  and the pallet P. The distance measuring sensor  123   a  detects the position in the Z-direction of the bottom surface of the article A passing above. The distance measuring sensor  123   a  transmits the measurement result to the controller  25 . The controller  25  calculates the position of the bottom surface of the article A in the Z-direction from the measurement result of the distance measuring sensor  123   a.  The distance measuring sensor  123   a  and the controller  25  function as the third detector  123 . The distance measuring sensor  123   a  is preferably a LRF using laser light. 
     Similarly to the first detector  121 , the third detector  123  may include an imager. The imager is installed between the main body  111  and the pallet P, and images the article A passing above from below. The imager transmits the acquired image to the controller  25 . The controller  25  calculates the position of the bottom surface of the article A in the Z-direction from the image. That is, the imager and the controller  25  function as the third detector  123 . 
     The moving device  130  includes a horizontal moving device  131  and a lifting-and-lowering device  132 . The horizontal moving device  131  moves the suction hand  1  along the X-Y plane. The lifting-and-lowering device  132  lifts or lowers the horizontal moving device  131 . Thus, the suction hand  1  connected to the horizontal moving device  131  moves along the Z-direction. 
     The horizontal moving device  131  includes an arm  131   a  and a support portion  131   b.  The arm  131   a  is connected to the arm  10  of the suction hand  1  and can extend and contract in the X-direction. By the operation of the arm  131   a,  the suction hand  1  can be moved along the X-direction. The support portion  131   b  extends in the Y-direction and supports the arm  131   a  from below so that it enables to move. The support portion  131   b  moves the arm  131   a  along the Y-direction. The suction hand  1  can be moved along the Y-direction by the operation of the support portion  131   b . The arm  131   a  and the support portion  131   b  are respectively operated by an actuator such as a motor or an air cylinder. 
     The lifting-and-lowering device  132  includes a drive unit  132   a,  a shaft  132   b,  and a wire  132   c.  The drive unit  132   a  is attached to the upper end of the main body  111 . The shaft  132   b  extends along the Y-direction and is connected to the drive unit  132   a.  The wire  132   c  is wound around shaft  132   b.  One end of the wire  132   c  is connected to the horizontal moving device  131 . The drive unit  132   a  rotates the shaft  132   b.  The wire  132   c  is wound or unwound according to the rotation of the shaft  132   b , thereby the horizontal moving device  131  moves along the Z-direction. 
     The negative pressure generator  140  can individually adjust the pressure of each upper surface suction unit  16  and the pressure of each side surface suction unit  22 . The negative pressure generator  140  includes multiple pipes  141  respectively connected with the multiple upper surface suction units  16  and the multiple side surface suction units  22 . In addition, the negative pressure generator  140  includes a vacuum pump, an ejector, a valve, etc. (not shown). 
     The conveyor  150  includes a belt  151 , a pulley  152 , and a motor  153 . The belt  151  is an endless belt hung on a pair of pulleys  152  separated from each other in the X-direction. One end of the belt  151  is adjacent to the conveyor C. The rotation axis of the pulley  152  is parallel to the Y-direction. The motor  153  drives the belt  151  by rotating one of the pair of pulleys  152 . The article A placed on the conveyor  150  is conveyed toward the conveyor C by driving the belt  151 . 
     The lifting-and-lowering device  160  includes a drive unit  161 , a shaft  162 , and a wire  163 . The drive unit  161  is attached to the upper end of the main body  111 . The shaft  162  extends in the Y-direction and is connected to the drive unit  161 . The wire  163  is wound around the shaft  162 . One end of the wire  163  is connected to the conveyor  150 . The drive unit  161  rotates the shaft  162 . The wire  163  is wound or unwound according to the rotation of the shaft  162 , thereby the conveyor  150  moves along the Z-direction. 
     The controller  25  controls the operation of the above-described components. For example, the controller  25  is electrically connected to the suction hand  1 , the imager  121   a,  the distance measuring sensor  122   a,  the distance measuring sensor  123   a,  the moving device  130 , the negative pressure generator  140 , the conveyor  150 , and the lifting-and-lowering device  160 . The controller  25  controls the suction hand  1 , the moving device  130 , the negative pressure generator  140 , the conveyor  150 , the lifting-and-lowering device  160 , etc., based on the detection result (first detection result) by the first detector  121 , the detection result (second detection result) by the second detector  122 , and the detection result by the third detector  123 . 
       FIG.  2    is a perspective view showing the suction hand according to the embodiment.  FIG.  3    is a cross-sectional view showing a part of the suction hand according to the embodiment.  FIG.  4    is a side view schematically showing the suction hand according to the embodiment. 
     A specific example of the suction hand  1  according to the embodiment will be described with reference to  FIGS.  2  to  4   . As shown in  FIGS.  2  to  4   , the suction hand  1  includes an arm  10 , a base  11 , an inclination mechanism  12 , a linear guide  13 , a connection frame  14 , a fixing mechanism  15 , an upper surface suction unit  16  (a first suction unit), a linear guide  17 , a connection plate  18 , a cylinder  19 , a link mechanism  20 , a drive mechanism  21 , a side surface suction unit  22  (a second suction unit), and a detector  23 . 
     As shown in  FIG.  2   , the arm  10  extends along the X-direction and supports each constituent element of the suction hand  1 . The arm  10  is connected to an external device such as an X-Y orthogonal robot. The arm  10  may also be a part of the external device. 
     The base  11  is a plate-shaped member extending along an X-Z plane. A rear end of a lower portion of the base  11  is connected to a tip end  10   a  of the arm  10  via a rotation shaft  10   b , and is rotatable with respect to the tip end  10   a.    
     The inclination mechanism  12  is provided between the arm  10  and the base  11 . Specifically, the inclination mechanism  12  includes a cylinder  12   a,  a rotation shaft  12   b,  and a rotation shaft  12   c.  The arm  10  includes a bent portion  10   c  that is bent downward. One end of the cylinder  12   a  is connected to the bent portion  10   c  via the rotation shaft  12   b,  and is rotatable with respect to the bent portion  10   c.  The other end of the cylinder  12   a  is connected to a rear end of an upper portion of the base  11  via the rotation shaft  12   c,  and is rotatable with respect to the rear end. Rotation centers of the rotation shafts  10   b,    12   b,  and  12   c  are parallel to the Y-direction. 
     The cylinder  12   a  can extend and contract along the X-direction. A positions in the Z-direction of the cylinder  12   a,  the rotation shaft  12   b,  and the rotation shaft  12   c  are different from a position in the Z-direction of the rotation shaft  10   b.  Accordingly, when a length of the cylinder  12   a  changes, an angle of the base  11  around the Y-direction changes. In the suction hand  1 , the cylinder  12   a,  the rotation shaft  12   b,  and the rotation shaft  12   c  are located above the rotation shaft  10   b.  For example, as the cylinder  12   a  extends, a front end of the base  11  is inclined downward. 
     The linear guide  13  is provided on a side surface of the base  11 . In the suction hand  1 , two linear guides  13  are provided on one side surface of the base  11 . The linear guide  13  includes a rail and a block. The rail is fixed to the base  11  and is provided along the Z-direction. The block is movable in the Z-direction along the rail. 
     The connection frame  14  includes a vertical frame portion  14   a  extending along the X-Z plane and a horizontal frame portion  14   b  extending along the X-Y plane. One end of the horizontal frame portion  14   b  in the Y-direction is connected to a lower end of the vertical frame portion  14   a.  The vertical frame portion  14   a  is fixed to the block of the linear guide  13 . Accordingly, the connection frame  14  is movable in the Z-direction with respect to the base  11 . 
     The fixing mechanism  15  is provided on the side surface of the base  11  so as to be close to the vertical frame portion  14   a . The fixing mechanism  15  can switch between a locked state in which the connection frame  14  is fixed and an unlocked state in which the connection frame  14  is movable.  FIG.  3    shows an X-Z cross section passing through the fixing mechanism  15 . As shown in  FIG.  3   , the fixing mechanism  15  includes a rod  15   a,  a fixed plate  15   b,  a movable plate  15   c,  a clamper  15   d,  and a cylinder  15   e.    
     The rod  15   a  is fixed to the base  11  and extends along the Z-direction. The fixed plate  15   b  is a plate-shaped member extending along the X-Y plane, and is fixed to the connection frame  14 . The movable plate  15   c  is a plate-shaped member extending along the X-Y plane, and is attached to the fixed plate  15   b  via the clamper  15   d  and the cylinder  15   e.  In the unlocked state, the fixed plate  15   b,  the movable plate  15   c,  the clamper  15   d,  and the cylinder  15   e  are slidable with respect to the rod  15   a.  When the connection frame  14  moves along the Z-direction, the fixed plate  15   b,  the movable plate  15   c,  the clamper  15   d,  and the cylinder  15   e  also move along the Z-direction. 
     The cylinder  15   e  can extend and contract along the Z-direction. When the cylinder  15   e  extends or contracts, the movable plate  15   c  moves in the Z-direction with respect to the fixed plate  15   b.  When a distance between the fixed plate  15   b  and the movable plate  15   c  is increased by the operation of the cylinder  15   e,  a component of the clamper  15   d  is pressed toward the rod  15   a.  Accordingly, positions of the fixed plate  15   b,  the movable plate  15   c,  the clamper  15   d,  and the cylinder  15   e  in the Z-direction are fixed. As a result, a position of the connection frame  14  in the Z-direction is fixed. When the distance between the fixed plate  15   b  and the movable plate  15   c  is decreased, the pressing of the component of the clamper  15   d  toward the rod  15   a  is released. Accordingly, the fixed plate  15   b,  the movable plate  15   c,  the clamper  15   d,  and the cylinder  15   e  are movable. As a result, the connection frame  14  is movable in the Z-direction. 
     As shown in  FIG.  2   , the upper surface suction unit  16  is fixed to the horizontal frame portion  14   b  of the connection frame  14 . The upper surface suction unit  16  includes a housing  16   a  and multiple suction portions  16   b  (first suction portions). Each suction portion  16   b  includes a rod  16   c  (first rod) and a suction pad  16   d  (first suction pad). The rod  16   c  extends along the Z-direction. For example, the rod  16   c  is fixed to the housing  16   a.  The rod  16   c  may also be slidable in the Z-direction with respect to the housing  16   a.  In this case, the upper surface suction unit  16  is further provided with a clamper configured to fix the rod  16   c.  The suction pad  16   d  has flexibility and is provided at a tip end of the rod  16   c . Spaces are provided inside the rod  16   c  and inside the suction pad  16   d,  and these spaces communicate with each other. 
     The multiple suction portions  16   b  are arranged along two directions crossing each other. A suction face of the suction pad  16   d  is parallel to a direction in which the multiple suction portions  16   b  are arranged. In the suction hand  1 , the multiple suction portions  16   b  are arranged along the X-direction and the Y-direction. The number of the suction portions  16   b,  a size of each suction portion  16   b,  an interval between the suction portions  16   b,  and the like are appropriately designed according to an article to be held. 
     A pipe or the like configured to connect an exhaust system (not shown) and the multiple suction portions  16   b  is provided inside the housing  16   a.  By an operation of the exhaust system, the inside of each suction pad  16   d  is collectively depressurized for one upper surface suction unit  16 . 
     The linear guide  17  is provided along an upper surface of the housing  16   a.  In the suction hand  1 , one linear guide  17  is provided on the upper surface of the housing  16   a,  and another linear guide  17  is provided on an upper surface of the horizontal frame portion  14   b.  Each linear guide  17  includes a rail and a block. The rail is fixed to the horizontal frame portion  14   b  and the housing  16   a,  and extends along the X-direction. The block is movable in the X-direction along the rail. 
     The connection plate  18  is a plate-shaped member extending along the X-direction. A front portion of the connection plate  18  is parallel to the X-Y plane and is fixed to the block of each linear guide  17 . Accordingly, the connection plate  18  is movable in the X-direction with respect to the upper surface suction unit  16 . A rear portion of the connection plate  18  is slightly inclined downward. 
     The cylinder  19  moves the side surface suction unit  22  in the X-direction with respect to the upper surface suction unit  16 . Specifically, as shown in  FIG.  2    and  FIG.  4   , a tube body of the cylinder  19  is fixed to the housing  16   a.  A piston of the cylinder  19  is fixed to the connection plate  18 . The cylinder  19  can extend and contract along the X-direction. When the cylinder  19  extends or contracts, the connection plate  18  moves in the X-direction with respect to the upper surface suction unit  16 . Accordingly, the side surface suction unit  22  connected to the connection plate  18  moves along the X-direction. 
     The link mechanism  20  is connected between the connection plate  18  and the side surface suction unit  22 . As shown in  FIG.  4   , the link mechanism  20  includes a pair of links  20   a  and  20   b.  The links  20   a  and  20   b  extend parallel to each other and are rotatable in synchronization with each other. One end of the link  20   a  and one end of the link  20   b  are connected to a rear end of the connection plate  18  via rotation shafts  20   c  and  20   d , respectively. The rotation shafts  20   c  and  20   d  are rotatable with respect to the connection plate  18 . Meanwhile, the links  20   a  and  20   b  are fixed to the rotation shafts  20   c  and  20   d,  respectively. Therefore, when the rotation shafts  20   c  and  20   d  rotate with respect to the connection plate  18 , the links  20   a  and  20   b  also rotate. 
     The drive mechanism  21  is connected to the connection plate  18  and the link mechanism  20 , and changes a position of the side surface suction unit  22  in the Z-direction. Specifically, the drive mechanism  21  includes a cylinder  21   a,  a rotation shaft  21   b,  a rotation shaft  21   c,  and a bar  21   d.  The cylinder  21   a  is provided along the rear portion of the connection plate  18 . A tube body of the cylinder  21   a  is connected to the connection plate  18  via the rotation shaft  21   b,  and is rotatable with respect to the connection plate  18 . A piston of the cylinder  21   a  is connected to one end of the bar  21   d  via the rotation shaft  21   c,  and is rotatable with respect to the bar  21   d.  The other end of the bar  21   d  is fixed to one of the rotation shafts  20   c  and  20   d.  In the suction hand  1 , the bar  21   d  is fixed to the rotation shaft  20   c.  The side surface suction unit  22  is connected to the other end of the link  20   a  and the other end of the link  20   b  via rotation shafts  20   e  and  20   f,  respectively, and is rotatable with respect to the links  20   a  and  20   b.    
       FIGS.  5 A and  5 B  are side views schematically showing an operation of the suction hand according to the embodiment. In  FIG.  5 A , the cylinder  21   a,  the rotation shaft  21   b,  and the rotation shaft  21   c  are shown by broken lines. In  FIG.  5 B , the cylinder  21   a  and the rotation shaft  21   b  are omitted, and the rotation shaft  21   c  is shown by a broken line. 
     The rotation shafts  20   c  to  20   f,    21   b,  and  21   c  are parallel to the Y-direction. As shown in  FIGS.  5 A and  5 B , when the cylinder  21   a  extends or contracts, the bar  21   d  rotates around the Y-direction about the rotation shaft  20   c.  Since the bar  21   d  is fixed to the rotation shaft  20   c,  the rotation shaft  20   c  rotates in accordance with the rotation of the bar  21   d.  The link  20   a  fixed to the rotation shaft  20   c  rotates around the Y-direction about the rotation shaft  20   c.  The link  20   b  also rotates around the Y-direction in synchronization with the link  20   a.  Accordingly, the side surface suction unit  22  rotates around the Y-direction about the rotation shaft  20   c.  The position of the side surface suction unit  22  in the X-Z plane can be changed by an operation of the drive mechanism  21 . For example, the position of the side surface suction unit  22  is switched according to an arrangement of the article to be held by the suction hand  1 . 
     The side surface suction unit  22  includes a housing  22   a  and multiple suction portions  22   b  (second suction portions). Each suction portion  22   b  includes a rod  22   c  (second rod) and a suction pad  22   d  (second suction pad). The rod  22   c  extends along the X-direction. For example, the rod  22   c  is fixed to the housing  22   a . The rod  22   c  may also be slidable in the X-direction with respect to the housing  22   a.  In this case, the side surface suction unit  22  is further provided with a clamper configured to fix the rod  22   c.  The suction pad  22   d  has flexibility and is provided at a tip end of the rod  22   c.  Spaces are provided inside the rod  22   c  and inside the suction pad  22   d,  and these spaces communicate with each other. 
     The multiple suction portions  22   b  are arranged along two directions crossing each other. A suction face of the suction pad  22   d  is parallel to a direction in which the multiple suction portions  22   b  are arranged. In the suction hand  1 , the multiple suction portions  22   b  are arranged along the Y-direction and the Z-direction. The number of the suction portions  22   b,  a size of each suction portion  22   b,  an interval between the suction portions  22   b,  and the like are appropriately designed according to the article to be held. 
     A pipe or the like configured to connect the exhaust system (not shown) and the multiple suction portions  22   b  is provided inside the housing  22   a.  By the operation of the exhaust system, the inside of each suction pad  22   d  is collectively depressurized for one side surface suction unit  22 . Pressure control on the side surface suction unit  22  is executed independently of pressure control on the upper surface suction unit  16 . 
     The detector  23  is fixed to the base  11 . The detector  23  detects lifting of the connection frame  14  with respect to the base  11 . Based on a detection signal from the detector  23 , it can be determined whether the upper surface suction unit  16  is in contact with the article. For example, the detector  23  includes one or more sensors selected from an optical sensor, a proximity sensor, a distance measuring sensor, and a transmissive sensor. The detector  23  may also be provided at a place other than the shown place. For example, the detector  23  may be provided in the upper surface suction unit  16 , and may more directly detect approaching of the article with respect to the upper surface suction unit  16 . 
     The controller  25  controls each component of the suction hand  1 . For example, the controller  25  operates the cylinders  12   a,    15   e,    19 , and  21   a.  The controller  25  also the control exhaust systems for exhausting the upper surface suction unit  16  and the side surface suction unit  22 , respectively. 
     The cylinders  12   a,    15   e,    19 , and  21   a  are air cylinders (an example of actuators). Other actuators may be provided instead of the cylinders  12   a,    15   e,    19  and  21   a.  For example, a motor and a mechanical element that converts the rotational motion of the motor into linear motion may be provided. 
     In addition, the controller  25  switches between a first state in which the side surface suction unit  22  is at a first position and a second state in which the side surface suction unit  22  is at a second position.  FIG.  5 A  shows the state when the side surface suction unit  22  is at the first position. The side surface suction unit  22  can hold the side surface of the article at the first position. When the side surface suction unit  22  is at the first position, the side surface suction unit  22  is positioned below at least a portion of the upper surface suction unit  16 . For example, the suction portion  22   b  is located below the upper ends of the housing  16   a  and the rod  16   c  of the upper surface suction unit  16 .  FIG.  5 B  shows the state when the side surface suction unit  22  is at the second position. The second position is above the first position. When the side surface suction unit  22  is at the second position, the side surface suction unit  22  is positioned above at least a portion of the upper surface suction unit  16 . For example, the suction portion  22   b  is located above the suction portion  16   b  of the upper surface suction unit  16 . 
       FIG.  6    is a perspective view showing the hand according to the embodiment. 
       FIG.  6    shows a state when the suction hand  1  is viewed from a direction different from that of  FIG.  2   . The direction in which the suction hand  1  is viewed in  FIG.  6    is substantially symmetrical to the direction in which the suction hand  1  is viewed in  FIG.  2    with respect to the X-Z plane passing through a center of the suction hand  1  in the Y-direction. As shown in  FIG.  2    and  FIG.  6   , suction mechanisms  5  each including the linear guide  13 , the connection frame  14 , the fixing mechanism  15 , the upper surface suction unit  16 , the linear guide  17 , the connection plate  18 , the cylinder  19 , the link mechanism  20 , the drive mechanism  21 , and the side surface suction unit  22  are provided on two side surfaces of the base  11 . Therefore, for example, multiple upper surface suction units  16  and multiple side surface suction units  22  are provided in the Y-direction. 
     The suction mechanisms  5  are movable independently of each other. Further, the cylinders  19  and  21   a  shown in  FIGS.  4  and  5    are provided for each suction mechanism  5 . The cylinders  19  and  21   a  can operate independently for each suction mechanism  5 . Therefore, the positions of the respective upper surface suction units  16  in the Z direction may be different from each other. The positions of the respective side surface suction units  22  in the X-Z plane may be different from each other. 
     The transfer apparatus  100  can perform a first operation and a second operation. The first operation and the second operation differ from each other in the number of articles to be held, the holding method, and the transfer method. 
       FIG.  7 A  is a front view schematically showing the holding method in the first operation.  FIG.  7 B  is a side view schematically showing the holding method in the first operation. 
     As shown in  FIGS.  7 A and  7 B , the suction hand  1  holds the multiple articles A in the first operation. The multiple articles A are suctioned by multiple suction mechanisms  5 , respectively. Specifically, the upper and side surfaces of one article A are respectively suctioned by the upper surface suction unit  16  and the side surface suction unit  22  of one suction mechanism  5 . The upper and side surfaces of another article A are respectively suctioned by the upper surface suction unit  16  and the side surface suction unit  22  of the other suction mechanism  5 . The transfer apparatus  100  slide multiple held articles A on the upper surface of another article A or the upper surface of the pallet P to move the multiple articles A. Alternatively, the transfer apparatus  100  may lift the article A while suctioning the upper and side surfaces of the article A. 
       FIGS.  8 A to  8 C  are side views schematically showing states when the article is held in the first operation. 
     When the article is suctioned, as shown in  FIG.  8 A , the upper surface suction unit  16  comes into contact with the upper surface of the article A and suctions the upper surface. Next, as shown in  FIG.  8 B , the side surface suction unit  22  is brought into contact with a side surface of the article A by an operation of the cylinder  19 . The side surface suction unit  22  suctions the side surface. The suction hand  1  holds the article A by the suction of the upper surface and the side surface of the article A. 
     Subsequently, the suction hand  1  is lifted. At this time, when the cylinder  12   a  is opened or thrust of the cylinder  12   a  is weak, the cylinder  12   a  extends due to weight of the suction mechanism  5  and the article A. Accordingly, as shown in  FIG.  8 C , the upper surface suction unit  16  and the side surface suction unit  22  are inclined with respect to the X-Y plane in a state where the article A is held. If the inclination is too large, contents of the article A may collapse. Therefore, an inclination angle with respect to the X-Y plane is preferably larger than 0° and less than 15°. 
     For example, an adhesive for attaching a label, an adhesive of a packing tape, or the like may be adhered to the upper surface of the article A. There may be a case where the upper surface of another article A is stuck to a bottom surface of the held article A by the adhesive. By being inclined, the held article A can be easily peeled off from the other article A. Accordingly, when the article A is conveyed, friction between the conveyed article A and the other article A can be reduced. 
       FIG.  9 A  is a front view schematically showing the holding method in the second operation.  FIG.  9 B  is a side view schematically showing the holding method in the second operation. 
     As shown in  FIGS.  9 A and  9 B , in the second operation, one article A is held by the suction hand  1 . The upper surface of the one article A is suctioned by the upper surface suction unit  16 . The side surface suction unit  22  is located at the second position, and the side surface of the article A is not suctioned. The transfer apparatus  100  lifts the one held article A and then moves it along the X-Y plane. 
     According to the first operation, since multiple articles A can be moved, work efficiency can be improved. Further, according to the first operation, the upper surface and side surfaces of the article A can be suctioned. Thus, the article A can be moved more stably. Furthermore, when the article A is slid in the first operation, it is not necessary to lift the article A greatly, so the movement time of the article can be shortened. According to the second operation, since the article A is lifted, the article A can be moved regardless of the state between the held article A and the conveyor  150 . 
       FIG.  10    is a flowchart showing an outline of a transfer method by the transfer apparatus according to the embodiment. 
     In the transfer method M 1 , first, the first detector  121  detects the upper surface of the article A placed on the pallet P (step S 0 ). The controller  25  determines whether the placement state calculated based on the detection result of the first detector  121  satisfies the first condition (step S 1 : first determination). The placement state indicates the state of multiple articles placed on the pallet P, and includes data such as the recognition result of the upper surface of each article, the position of each upper surface, and the size of each upper surface. To obtain a more accurate placement state, the placement state may be calculated based on both detection results of the first detector  121  and the second detector  122 . In this case, the placement state further includes data such as the recognition result of the side surface of each article, the position of each side surface, and the height of each article. 
     In the case where the first condition is satisfied, the controller  25  performs the first operation (step S 1   a ). In the case where the first condition is not satisfied, the controller  25  determines whether the placement state satisfies the second condition (step S 2 : second determination). In the case where the second condition is satisfied, the controller  25  performs the second operation (step S 2   a ). In the case where the second condition is not satisfied, the transfer apparatus  100  determines that there is no article A to be transferred. The transfer apparatus  100  ends the transfer operation. 
     After the first operation or the second operation, the controller  25  determines whether or not another article A remains on the pallet P (step S 5 ). If there is any article A remaining, step S 0  is executed again. When there is no remaining article A, the transfer apparatus  100  ends the transfer operation. 
     Details of the first determination, the first operation, the second determination, and the second operation in the transfer method M 1  will be described below. 
     (First Determination) 
       FIG.  11    is a flowchart showing processing in the first determination. 
     First, the controller  25  determines whether data on the upper and side surfaces of multiple articles has been acquired (step  100 ). Specifically, the controller  25  determines whether or not the positions of the upper surfaces of the multiple articles and the positions of the side surfaces of the multiple articles has been detected by the first detector  121 . This determination may be performed based on the detection result by the second detector  122  in addition to the detection result by the first detector  121 . 
     In the case where data on the upper and side surfaces of multiple articles has been acquired, the controller  25  determines whether there is a set of articles in which the arrangement direction of two or more articles is the same as the arrangement direction of the suction unit (step  101 ). In the transfer apparatus  100 , the multiple upper surface suction units  16  and the multiple side surface suction units  22  are arranged in the Y-direction. Therefore, the controller  25  determines whether there is a set of articles arranged in the Y-direction. 
     In the case where there is a set of articles arranged in the Y-direction, the controller  25  determines whether there is a set of articles whose upper surface size difference is less than the first threshold (step S 102 ). For example, the controller  25  compares the length difference in the X-direction between the articles with the first threshold. The controller  25  may compare the length difference in the Y-direction between the articles with the first threshold. The controller  25  may compare the difference in the area of the upper surfaces of the articles with the first threshold. The controller  25  may compare two or more selected from the length in the X-direction, the length in the Y-direction, and the area between the articles. In this case, different first thresholds may be respectively set for the length in the X-direction, the length in the Y-direction, and the area. A value that allows the multiple articles to be stably slid in the first operation is set as the first threshold. 
     In the case where there is a set of articles whose upper surface size difference is less than the first threshold, the controller  25  calculates the distance between the position of the upper surface of one article in the Z-direction and the position of the upper surface of the other article in the Z-direction. The controller  25  determines whether the distance is less than the second threshold (step S 103 ). The second threshold is set based on the movable range of the suction mechanism  5  in the Z-direction, the variable amount of the suction pad  16   d  in the Z-direction, and the like. In the step S 103 , it is determined whether the difference in the positions of the upper surfaces of the multiple articles is small enough to hold the articles at the same time. 
     In the case where the distance between the upper surfaces is less than the second threshold, the controller  25  determines whether the height difference between the articles is less than the third threshold (step  104 ). A value that allows the multiple articles to be stably slid in the first operation is set as the third threshold. 
     In the case where the height difference is less than the third threshold, the controller  25  determines whether the distance between the side surfaces of the articles in the X-direction is less than the fourth threshold (step  105 ). The fourth threshold is set based on a movable range in the X-direction of the side surface suction unit  22  with respect to the upper surface suction unit  16 , a variable amount in the X-direction of the suction pad  22   c,  and the like. That is, in the step  105 , it is determined whether the difference in the positions of the side surfaces (front surfaces) of the multiple articles is small enough to simultaneously hold the articles. 
     In the case where the distance between the side surfaces is less than the fourth threshold, the controller  25  determines whether the level differences in the movement paths of the multiple articles are less than the fifth threshold (step S 106 ). For example, in the first operation, the held article slides over the upper surface of another article between the held article and conveyor  150 . That is, the moving path is the upper surface of the other article. The level difference is, in other words, the distance in the Z-direction between the upper surfaces of the other article. If the level difference is large, when the article is slid, the held article is caught and the sliding is disturbed. A value that allows the multiple articles to be stably slid is set as the fifth threshold. Alternatively, the movement path may be the upper surface of the pallet P. Since the upper surface of the pallet P is substantially flat, it is determined that the level difference is less than the fifth threshold. 
     In the case where it is determined that the condition is not satisfied in any one of the steps S 100  to S 106 , the controller  25  determines that the placement state of the article does not satisfy the first condition. The first determination ends. 
     In the case where the level difference is less than the fifth threshold, the controller  25  determines whether multiple sets of articles satisfying the conditions of steps S 100  to S 106  exist (step S 107 ). In the case where there are multiple sets, the controller  25  selects one set including an article whose upper surface is at the highest position from the multiple sets (step  108 ). The controller  25  determines whether multiple sets selected in the step S 108  exist (step S 109 ). In the case where there are multiple sets, the controller  25  selects one set including an article whose side surface is nearest from the multiple sets (step S 110 ). “Nearest” means that the distance in the X-Z plane between the article and the distance measuring sensor  122   a  is the shortest. In the step S 107  or S 109 , if multiple sets do not exist, one set is selected as the object to be held simultaneously. In the case where there are multiple sets selected in the step S 110 , an arbitrary set is selected from the multiple selected sets. For example, the set including an article closest to the distance measuring sensor  122   a  is selected from the multiple sets. The transfer apparatus  100  simultaneously moves multiple articles included in the selected set by the first operation. 
     As described above, the first condition for the first operation includes that the upper and side surface of each of the multiple articles A can be detected, that the multiple articles A are arranged in the Y-direction, that the upper surfaces of the multiple articles A can be simultaneously suctioned by the multiple upper surface suction units  16 , that the side surfaces of the multiple articles A can be simultaneously suctioned by the multiple side surface suction units  22 , and that the multiple articles A can be simultaneously slid along the X-direction. Multiple articles which can be stably moved are selected by first determination using the first condition. 
     Only part of the conditions described above may be used in the first determination. Relaxing the conditions may reduce the stability of holding or transferring, but may increase the number of cases where multiple articles can be held at the same time. It improves the efficiency of transferring. 
     The conditions used in the first determination may include another condition in addition to the conditions described above. For example, the detection result by the first detector  121  includes the centroid of the article in the X-Y plane. The first condition includes that the centroid of the article is positioned within a preset first range when the article is held. The first range is set based on the position of the upper surface suction unit  16  when holding the article. As an example, the outer edge in the X-Y plane of the upper surface suction unit  16  when holding the article is set as the outer edge of the first range. When the upper surface suction unit  16  contacts the article, it is determined whether the centroid is located inside the outer edge of the upper surface suction unit  16  in the X-Y plane. In order to improve holding stability, the outer edge of the first range may be set smaller than the outer edge of the upper surface suction unit  16 . 
       FIG.  12    is a schematic view for explaining the processing in the first determination. 
     As an example, multiple articles A are loaded as shown in  FIG.  12   . The imager  121   a  images the articles A from above. The second detector  122  detects the positions of the side surfaces of the articles A. Of the multiple articles A, articles A 1  to A 4  are not loaded with other articles. At the height (position in the Z-direction) where the articles A 1  and A 2  are arranged, no other article is placed in front of the articles A 1  and A 2 . At the height where the articles A 3  and A 4  are arranged, no other article is placed in front of the articles A 3  and A 4 . Therefore, in the step S 100 , the articles A 1  to A 4  are extracted as articles for which data on both the upper surface and the side surface can be obtained. 
     In the step S 101 , it is determined whether a set of articles arranged in the Y-direction exists for the extracted articles A 1  to A 4 . As a result, it is determined that there is a set Se 1  consisting of the articles A 1  and A 2  and a set Se 2  consisting of the articles A 3  and A 4 . 
     In the step S 102 , it is determined whether the difference between the size of the upper surface of the article A 1  and the size of the upper surface of the article A 2  is less than the first threshold. It is also determined whether the difference between the size of the upper surface of the article A 3  and the size of the upper surface of the article A 4  is less than the first threshold. In the example shown in  FIG.  12   , multiple articles of substantially the same size are stacked. Therefore, in the step S 102 , it is determined that any difference is less than the first threshold. 
     Similarly, in the step S 103 , it is determined that the distance in the Z-direction between the upper surface of the article A 1  and the upper surface of the article A 2  is less than the second threshold, and determined that the distance in the Z-direction between the upper surface of the article A 3  and the upper surface of the article A 4  is less than the second threshold. In the step S 104 , it is determined that the difference between the heights of the articles A 1  and A 2  is less than the third threshold, and determined that the difference between the heights of the articles A 3  and A 4  is less than the third threshold. In the step S 105 , it is determined that the distance in the X-direction between the front surface of the article A 1  and the front surface of the article A 2  is less than the fourth threshold, and determined that the distance in the X-direction between the front surface of the article A 3  and the front surface of the article A 4  is less than the fourth threshold. 
     In the step S 106 , the upper surfaces of the articles A 3  to A 6  are determined to be the movement path of the set Se 1 . For example, it is determined that the level difference in the movement path of the set Se 1  is less than the fifth threshold. That is, it is determined that the distance in the Z-direction between the upper surface of the article A 3  and the upper surface of the article A 5  is less than the fifth threshold, and determined that the distance in the Z-direction between the upper surface of the article A 4  and the upper surface of the article A 6  is less than the fifth threshold. There are no other articles between the set Se 2  and the conveyor  150 . Therefore, it is determined that the level difference in the movement path of the set Se 2  is less than the fifth threshold. 
     In the step S 107 , it is determined that multiple sets satisfying the conditions of steps S 100  to S 106  exist. In the step S 108 , the positions of the respective upper surfaces of the articles A 1  to A 4  are compared. As a result, the set Se 1  including the articles A 1  and A 2  with the upper surface at the highest position is selected. In the step S 109 , a number of the set selected in the step S 108  is one. Therefore, the set Se 1  is selected as the object to be held by the first operation. After the set Se 1  is moved by the first operation, the set Se 2  is selected as the object to be held by the first operation in the next first determination. 
     (First Operation) 
       FIG.  13    is a flowchart showing a part of the first operation.  FIG.  14    is a flowchart showing another part of the first operation.  FIGS.  15 A to  15 C ,  FIGS.  16 A to  16 C , and  FIGS.  17 A to  17 C  are schematic views showing the first operation. 
     The horizontal moving device  131  moves the suction hand  1  along the X-Y plane (step S 120  in  FIG.  13   ). As shown in  FIGS.  15 A and  15 B , the suction hand  1  is located above the article A selected in the first determination. Also, the position of the conveyor  150  in the Z-direction is set to the same position as the bottom surface of the article A to be held. Since  FIGS.  15 A to  17 C  are side views, only one upper surface suction unit  16  and one side surface suction unit  22  are shown. In the depth direction, there are another upper surface suction unit  16 , another side surface suction unit  22 , and another article A (not shown). 
     The cylinder  21   a  of the drive mechanism  21  is opened (step S 121 ). That is, no force is applied from the cylinder  21   a  to the link mechanism  20 , and the side surface suction unit  22  is in the movable state. The fixing mechanism  15  is set to the unlocked state (step S 122 ), and the connection frame  14  is in the movable state. As shown in  FIG.  15 C , the lifting-and-lowering device  132  lowers the suction hand  1  toward the article A (step S 123 ). The suction hand  1  is lowered to the position of the upper surface of the selected article A. 
     The upper surface suction unit  16  starts suction of the upper surface of the article A (step S 124 ). Specifically, the controller  25  operates the negative pressure generator  140  to exhaust the inside of the suction portion  16   b.  The controller  25  determines whether the upper surface suction unit  16  is in contact with the article A (step S 125 ). The contact is determined based on the detection signal of the detector  23 . When it is determined that the upper surface suction unit  16  is not in contact with the article A, the lifting-and-lowering device  132  lowers the suction hand  1  again (step S 126 ). After the execution of step S 126 , the step S 125  is executed again. 
     When it is determined that the upper surface suction unit  16  is in contact with the article A, the controller  25  determines whether the suction of the article A by the upper surface suction unit  16  is completed (step S 127 ). Whether the suction is completed is determined based on the pressure in the upper surface suction unit  16 . When it is determined that the suction is not completed, the suction by the upper surface suction unit  16  is continued. The controller  25  determines whether a preset time has elapsed from the start of the suction (step S 128 ). When the suction is not completed even after the set time has elapsed, the controller  25  ends the first operation. 
     When the suction is completed, the fixing mechanism  15  is set to the locked state (step S 129 ), and the position of the upper surface suction unit  16  in the suction hand  1  is fixed. The cylinder  12   a  of the inclination mechanism  12  is opened (step S 130 ). Accordingly, the upper surface suction unit  16  and the side surface suction unit  22  are in a state of being inclinable with respect to the X-Y plane. The drive mechanism  21  lowers the side surface suction unit  22  by an operation of the cylinder  21   a  (step S 131 ). Fluid is injected into the cylinder  21   a,  and the position of the side surface suction unit  22  is fixed with respect to the upper surface suction unit  16 . The side surface suction unit  22  starts suction (step S 132 ). Specifically, the controller  25  operates the negative pressure generator  140  to exhaust the inside of the suction portion  22   b.    
     The cylinder  19  moves the side surface suction unit  22  forward (step S 133 ). The side surface suction unit  22  comes into contact with the side surface of the article A as shown in  FIG.  16 A . The controller  25  determines whether the suction of the article A by the side surface suction unit  22  is completed (step S 134 ). Whether the suction is completed is determined based on the pressure in the side surface suction unit  22 . When it is determined that the suction is not completed, the suction by the side surface suction unit  22  is continued. The controller  25  determines whether a preset time has elapsed from the start of the suction (step S 135 ). When the suction is not completed even after the set time has elapsed, the controller  25  ends the first operation. 
     When the suction is completed, the lifting-and-lowering device  132  slightly lifts the suction hand  1  (step S 136 ). At this time, since the cylinder  12   a  of the inclination mechanism  12  is opened, the cylinder  12   a  extends due to the weight of the suction mechanism  5  and the article A. As shown in  FIG.  16 B , the upper surface suction unit  16  and the side surface suction unit  22  are inclined with respect to the X-Y plane. After the step S 136 , the horizontal moving device  131  moves the suction hand  1  toward the conveyor  150  along the X-Y plane (step S 140  in  FIG.  14   ). Accordingly, as shown in  FIG.  16 C , the held article A is conveyed onto the conveyor  150 . The side surface suction unit  22  ends the suction to the side surface of the article A (step S 141 ). Specifically, the controller  25  increases the pressure of the side surface suction unit  22 . For example, the controller  25  opens the inner space of the side surface suction unit  22  to the atmosphere. 
     The cylinder  19  moves the side surface suction unit  22  rearward (step S 142 ). Accordingly, the side surface suction unit  22  is separated from the article A. The controller  25  determines whether the side surface of the article A suctioned by the side surface suction unit  22  is released (step S 143 ). Whether the side surface is released is determined based on the pressure in the suction portion  22   b.  When it is determined that the suctioned side surface is not released, the controller  25  stands by. When the pressure of each of the suction portions  22   b  increases during the standby, the side surface is released. In addition, during the standby, the controller  25  determines whether a preset time has elapsed from the end of the suction to the side surface (step S 141 ). When the side surface is not released even after the set time has elapsed, the controller  25  ends the first operation. 
     When the suctioned side surface is released, the upper surface suction unit  16  ends the suction to the upper surface of the article A (step S 145 ). Specifically, the controller  25  increases the pressure of the suction portion  16   b.  For example, the controller  25  opens the inside of the suction portion  16   b  to the atmosphere. The cylinder  21   a  of the drive mechanism  21  is opened (step S 146 ). The controller  25  determines whether the upper surface of the article A suctioned by the upper surface suction unit  16  is released (step S 147 ). Whether the upper surface is released is determined based on the pressure in the suction portion  16   b.  When the pressure of each of the suction portions  16   b  exceeds a preset threshold, it is determined that the upper surface is released. 
     When it is determined that the suctioned upper surface is not released, the controller  25  stands by. When the pressure of each of the suction portions  16   b  increases during the standby, the upper surface is released. In addition, during the standby, the controller  25  determines whether a preset time has elapsed from the end of the suction to the upper surface (step S 148 ). When the upper surface is not released even after the set time has elapsed, the controller  25  ends the first operation. When the upper surface is released, the transferred article A is placed on the conveyor  150  as shown in  FIG.  17 A . The inclination mechanism  12  operates the cylinder  12   a  so that the suction plane of the upper surface suction unit  16  is horizontal (parallel to the X-Y plane) (step S 149 ). As shown in  FIG.  17 B , the lifting-and-lowering device  132  lifts the suction hand  1  (step S 150 ). As shown in FIG.  17 C, the conveyor  150  conveys the placed article A to the conveyor C (step S 151 ). The conveyor C conveys the article A to another location. According to the above steps, the first operation is finished. 
     (Second Determination) 
       FIG.  18    is a flowchart showing the processing in the second determination. 
     First, the controller  25  determines whether there is an article for which data on the upper surface has been acquired (step S 200 ). Next, it is determined whether or not there are multiple articles for which data has been acquired (step S 201 ). In the case where the data on multiple articles have been acquired, the article with the highest upper surface is selected (step S 202 ). It is determined whether a number of the selected articles is two or more (step S 203 ). In the case where multiple articles are selected, the article whose side surface is positioned nearest is selected (step S 204 ). 
     In the case where it is determined in the step S 200  that there is no article for which data has been acquired, the second determination ends without selecting the article to be held. In the case where it is determined in the step S 201  that there is only one article for which data has been acquired, the one article is selected as the object to be held. In the step S 203 , in the case where it is determined that only one article has been selected in the step S 202 , the one article is finally selected as the object to be held. In the case where there are multiple articles selected in the step S 204 , an arbitrary one is selected from the selected articles. For example, an article closest to the distance measuring sensor  122   a  is selected from multiple articles. The transfer apparatus  100  moves the selected article by the second operation. 
       FIG.  19    is a schematic view for explaining the processing in the second determination. 
     As an example, multiple articles A are loaded as shown in  FIG.  19   . First, similarly to the example shown in  FIG.  12   , the articles A 1  to A 4  are extracted as articles for which data on both the upper surface and the side surface have been obtained based on the detection results of the first detector  121 , in the first determination. The detection result by the second detector  122  may be further used. For the set of articles A 1  and A 2 , there is a level difference between the upper surface of article A 1  and the upper surface of article A 2 . For the set of articles A 3  and A 4 , there is a level difference between the upper surface of article A 3  and the upper surface of article A 4 . Therefore, in the step S 106  in the first determination, it is determined that there is no set of articles that satisfies the condition. 
     In the step S 200  in the second determination, multiple articles A 1  to A 8  are extracted as articles for which data on the upper surface has been acquired. In the step S 202 , the articles A 1  and A 8  with the highest upper surfaces are selected. Since multiple articles are selected, in step S 204 , the article A 1  whose side surface is nearest is selected as the object to be held by the second operation. After the article A 1  is moved by the second operation, the article A 8  is selected as the object to be held by the second operation in the following second determination. 
     As described above, the second condition includes that the upper surface of any article can be detected. The second condition is easier than the first condition. Therefore, even if the first condition is not satisfied, the second condition may be satisfied. Any article that can hold the upper surface is selected by the second determination using the second condition. 
     (Second Operation) 
       FIG.  20    is a flowchart showing a part of the second operation.  FIG.  21    is a flowchart showing another part of the second operation.  FIGS.  22 A and  22 B ,  FIGS.  23 A to  23 C , and  FIGS.  24 A to  24 C  are schematic views showing the second operation. 
     The horizontal moving device  131  moves the suction hand  1  along the X-Y plane (step S 220 ), and positions the suction hand  1  above the article A selected in the second determination, as shown in  FIGS.  22 A and  22 B . The controller  25  checks whether the side surface suction unit  22  is located at the second position (step S 221 ). When the side surface suction unit  22  is not located at the second position, the controller  25  operates the drive mechanism  21  to move the side surface suction unit  22  to the second position. 
     The fixing mechanism  15  is set to the unlocked state (step S 222 ), and the connection frame  14  is in the movable state. As shown in  FIG.  23 A , the lifting-and-lowering device  132  lowers the suction hand  1  toward the article A (step S 223 ). The suction hand  1  is lowered to the position of the upper surface of the selected article A. The upper surface suction unit  16  starts suction of the upper surface of the article A (step S 224 ). Specifically, the controller  25  operates the negative pressure generator  140  to exhaust the inside of the suction portion  16   b.  The controller  25  determines whether the upper surface suction unit  16  is in contact with the article A (step S 225 ). The contact is determined based on the detector  23 . When it is determined that the upper surface suction unit  16  is not in contact with the article A, the lifting-and-lowering device  132  lowers the suction hand  1  again (step S 226 ). 
     When it is determined that the upper surface suction unit  16  is in contact with the article A, the controller  25  determines whether the suction of the article A by the upper surface suction unit  16  is completed (step S 227 ). Similarly to the first operation, whether the suction is completed is determined based on the pressure in the upper surface suction unit  16 . When it is determined that the suction is not completed, the suction by the upper surface suction unit  16  is continued. The controller  25  determines whether a preset time has elapsed from the start of the suction (step S 228 ). When the suction is not completed even after the set time has elapsed, the controller  25  ends the second operation. 
     When the suction is completed, the fixing mechanism  15  is set to the locked state (step S 229 ), and the position of the upper surface suction unit  16  in the suction hand  1  is fixed. As shown in  FIG.  23 B , the lifting-and-lowering device  132  lifts the suction hand  1  (step S 230 ). After the step S 230 , the horizontal moving device  131  moves the suction hand  1  along the X-Y plane (step S 240  in  FIG.  21   ). As shown in  FIG.  23 C , the held article A is conveyed above the conveyor  150 . The controller  25  checks whether the side surface suction unit  22  is located at the second position (step S 241 ). When the side surface suction unit  22  is not located at the second position, the controller  25  operates the drive mechanism  21  to move the side surface suction unit  22  to the second position. 
     The lifting-and-lowering device  132  starts to lower the suction hand  1  (step S 223 ). As shown in  FIG.  24 A , when the position of the bottom surface of the held article A is lowered to a position of an upper surface of the conveyor  150 , the lifting-and-lowering device  132  ends the lowering of the suction hand  1  (step S 243 ). The position of the bottom surface of the article A is calculated by the controller  25  based on the detection result of the third detector  123 . The upper surface suction unit  16  ends the suction to the upper surface of the article A (step S 244 ). Specifically, the controller  25  increases the pressure of the upper surface suction unit  16 . For example, the controller  25  opens the inside of the upper surface suction unit  16  to the atmosphere. The controller  25  determines whether the upper surface of the article A suctioned by the upper surface suction unit  16  is released (step S 245 ). Similarly to the first operation, whether the upper surface is released is determined based on the pressure in the inner space of the upper surface suction unit  16 . 
     When it is determined that the suctioned upper surface is not released, the controller  25  stands by. When the pressure of each of the suction portions  16   b  increases during the standby, the upper surface is released. In addition, during the standby, the controller  25  determines whether a preset time has elapsed from the end of the suction to the upper surface (step S 246 ). When the upper surface is not released even after the set time has elapsed, the controller  25  ends the second operation. When the upper surface is released, the lifting-and lowering device  132  lifts the suction hand  1  as shown in  FIG.  24 B  (step S 247 ). As shown in  FIG.  24 C , the conveyor  150  conveys the placed article A to the conveyor C (step S 248 ). The conveyor C conveys article A to another location. According to the above steps, the second operation is finished. 
     In the above example, the multiple articles are slid in the first operation. The embodiment is not limited to this example. In the first operation, the transfer apparatus  100  may lift the multiple articles after holding similarly to the second operation. Even in this case, both the upper surface and the side surface of the article are held. Thereby, it can prevent large local forces from being applied to the article. For example, the possibility of an article being damaged can be reduced. In the case where multiple articles are lifted in the first operation, the determination in the step S 106  may be omitted. The transfer apparatus  100  may switch between sliding and lifting the multiple articles depending on whether the condition is satisfied in the determination of the step S 106 . 
     Advantages of the embodiment will be described. 
     There are various requirements for transfer apparatus for articles. For example, there is a need to improve work efficiency for transfer apparatus. In other words, it is required to be able to transfer more articles in a shorter time. Conventionally, there is an apparatus that suctions the upper surface of one article and transfers the article. Since the transfer apparatus can only transfer articles one by one, the work efficiency is not good. With respect to this problem, there is another apparatus that suctions upper surfaces of multiple articles and transfers them. On the other hand, in transfer of multiple articles by suctioning upper surfaces, the transfer may be unstable, especially when each article is heavy. For example, the suction may be released during transfer and the article may drop. Or, too much load may be applied to the suction hand and the suction hand may be damaged. 
     To improve transfer stability, there is a transfer apparatus that suctions not only the upper surface but also the side surface. The transfer apparatus suctions the upper and side surfaces of each of the articles and then moves the articles. This prevents the dropping of articles and reduces the load on the suction hand. On the other hand, such transfer apparatus is mainly used when articles of the same size are regularly loaded. Irregularly sized articles make it difficult to hold multiple articles at the same time because the upper surfaces of adjacent articles are in different positions. Or, the path between the transferred article and the transfer destination is not flat, and the article cannot be slid. In this regard, it is conceivable to use different transfer apparatus in different situations, such as when articles of the same size are loaded and when articles of different sizes are loaded. However, according to this method, pallets must be allocated appropriately for each transfer apparatus according to the type of transfer apparatus and the articles to be transferred. This makes management cumbersome. In addition, the operating rate of the transfer apparatus may also decrease. 
     With respect to these problems, the transfer apparatus  100  according to the embodiment can switch between the first and second operations for transfer. Specifically, when the placement state satisfies the first condition, the upper surfaces of the multiple articles are respectively suctioned by the multiple upper surface suction units  16 , and the side surfaces of the multiple articles are respectively suctioned by the multiple side surface suction units  22 . Then, the articles are moved in the state where the upper surfaces and side surfaces of the articles are suctioned. When the placement state satisfies the second condition, the upper surface of one article is suctioned by one of the multiple upper surface suction units  16 , and the one article is moved. At this time, the side surface suction unit  22  does not suction the article. 
     According to the first operation, the multiple articles can be moved stably by suctioning both the upper surfaces and the side surfaces of the multiple articles. On the other hand, according to the second operation, even if the movement of multiple articles by the first operation is not feasible, the articles can be moved one by one stably. In addition, by switching the first and second operations depending on the placement state, the articles can be efficiently and stably moved regardless of the size of the articles or how the articles are loaded. 
     The switching of the first and second operations by the transfer apparatus  100  is based on the placement state of the articles calculated from the detection result by the first detector  121 . Thus, for example, it is not necessary to input prior information to switch the first and second operations. Even if a regular arrangement of same-sized articles is unintentionally disrupted, the operation can be switched appropriately. Therefore, transfer can be continued stably and the reliability of the transfer apparatus  100  can be improved. 
     The placement state is preferably calculated based on the detection result by the second detector  122  in addition to the detection result by the first detector  121 . Further use of the detection result by the second detector  122  provides more information than using only the detection result by the first detector  121 . Thus, the placement state can be calculated in more detail. As a result, the difference between the placement of the article indicated by the placement state and the actual placement of the article can be reduced. 
     Preferably, the transfer apparatus  100  can switch between the first state where the side surface suction unit  22  is in the first position and the second state where the side surface suction unit  22  is in the second position. In the first operation, the side surface suction unit  22  is located in the first position where the side surface of the article can be suctioned. In the second operation, the side surface suction unit  22  is located in the second position above the first position. Thus, when the suction hand  1  holds the article A in the second operation, the possibility of the side surface suction unit  22  interfering with the article A which is different from the object to be held can be reduced. 
       FIG.  25    is a front view schematically showing another suction hand according to the embodiment. 
     In the examples shown in  FIGS.  2  and  4   , the multiple upper surface suction units  16  are movable independently of each other, and the multiple side surface suction units  22  are movable independently of each other in the suction hand  1 . The suction hand according to the embodiment is not limited to this example. For example, in the suction hand la shown in  FIG.  25   , the multiple upper surface suction units  16  are fixed to each other. The multiple side surface suction units  22  are fixed to each other. 
     Even when the suction hand la is used, the multiple upper surface suction units  16  can respectively suction the upper surfaces of the multiple articles. The multiple side surface suction units  22  can respectively suction the side surfaces of the multiple articles. 
     More preferably, the transfer apparatus  100  includes the suction hand  1  shown in  FIGS.  2  to  6   . When the multiple upper surface suction units  16  are movable independently of each other in the Z-direction, the upper surfaces of the multiple articles can be simultaneously suctioned by the multiple upper surface suction units  16  even if the positions of the upper surfaces of the multiple articles are different from each other. The second threshold in the flowchart shown in  FIG.  11    can be larger. The number of cases in which multiple articles can be held at the same time increases, and it improves the efficiency of transfer. 
     Similarly, when the multiple side surface suction units  22  are movable independently of each other in the X-direction, the side surfaces of the multiple articles can be simultaneously suctioned by the multiple side surface suction units  22  even when the positions of the side surfaces of the multiple articles are different from each other. The fourth threshold in the flowchart shown in  FIG.  11    can be larger. The number of cases in which multiple articles can be held at the same time increases, and it improves the efficiency of transfer. 
     (Variation) 
     The transfer apparatus  100  may be capable of performing a third operation in addition to the first and second operations. The third operation differs from the first and second operations in terms of the number of articles to be held, the method of holding, or the method of transfer. 
       FIG.  26 A  is a front view schematically showing the holding method in the third operation.  FIG.  26 B  is a side view schematically showing the holding method in the third operation. 
     As shown in  FIG.  26 A  and  FIG.  26 B , in the third operation, one article A is held by the suction hand  1 . In the example of  FIG.  26 A , the upper surface and the side surface of one article A are respectively suctioned by the upper surface suction unit  16  and the side surface suction unit  22  of one suction mechanism  5 . Depending on the size of the article, the upper surface and the side surface of one article A may be suctioned by the multiple upper surface suction units  16  and the multiple side surface suction units  22 . The transfer apparatus  100  moves the one held article A by sliding on the upper surface of the pallet P or the upper surface of the other article A. According to the third operation, since the upper surface and the side surface of the article A can be suctioned, the article A can be moved more stably than in the second operation. In addition, by sliding the article A in the third operation, it is not necessary to lift the article A significantly. The transfer time can be shortened compared with the second operation. 
       FIG.  27    is a flow chart showing the outline of the transfer method by the transfer apparatus according to the variation of the embodiment. 
     A transfer method M 2  shown in  FIG.  27    further includes steps S 3  and S 3   a  compared to the transfer method M 1  shown in  FIG.  10   . The controller  25  executes the step S 1  in the same manner as the transfer method M 1 . In the case where the first condition is not satisfied, the controller  25  determines whether the placement state satisfies the third condition (step S 3 : third determination). In the case where the third condition is satisfied, the controller  25  performs the third operation (step S 3   a ). In the case where the third condition is not satisfied, the controller  25  determines whether the placement state satisfies the second condition (step S 2 ). Thereafter, the same steps as the transfer method M 1  are executed. 
     (Third Determination) 
       FIG.  28    is a flowchart showing the processing in the third determination. 
     First, the controller  25  determines whether there is an article for which data on the upper surface and side surface have been acquired (step S 300 ). In the case where there is an article for which data have been acquired, the controller  25  determines whether the level difference in the movement path of the article is less than the fifth threshold (step S 301 ). The movement path is the upper surface of the other article or the upper surface of the pallet P, as in the first operation. In the case where the level difference is less than the fifth threshold, the controller  25  determines whether there is more than one article satisfying the condition of step S 301  (step S 302 ). In the case where multiple articles satisfy the condition of step S 301 , the controller  25  selects the article whose upper surface is in the highest position (step S 303 ). The controller  25  determines whether there are multiple selected articles (step S 304 ). In the case where multiple articles are selected, the controller  25  selects the article whose side is nearest to the front (step S 305 ). If there are multiple articles selected in the step S 305 , any one of the selected articles is selected. For example, the article closest to the distance measuring sensor  122   a  is selected from the multiple articles. The transfer apparatus  100  moves the selected article by the third operation. 
       FIG.  29    is a schematic view for explaining the processing in the third determination. 
     As an example, multiple articles A are loaded as shown in  FIG.  29   . In the first determination, it is determined that there is no set of articles satisfying the conditions, similarly to the example shown in  FIG.  19   . In the third determination, articles A 1  to A 4  are extracted as the articles from which data on the upper surface and the side surface have been acquired. 
     In the step S 301 , the upper surface of the article A 3  and the upper surface of the article A 5  are determined as the movement path of the article A 1 . The upper surface of the article A 4  and the upper surface of the article A 6  are determined to be the movement path of the article A 2 . A level difference exists between the upper surface of the article A 3  and the upper surface of the article A 5 . For example, the level difference in the movement path is determined to be not less than the fifth threshold. On the other hand, there is no level difference between the upper surface of the article A 4  and the upper surface of the article A 6 . The level difference in the movement path is determined to be less than the fifth threshold. There is also no article between the article A 3  and the conveyor  150  or between the article A 4  and the conveyor  150 . Therefore, the level difference in the respective movement paths of the articles A 3  and A 4  is determined to be less than the fifth threshold. As a result, it is determined that the multiple articles A 2  to A 4  satisfy the condition of the step S 301 . 
     In the step S 303 , the article A 2  with the upper surface at the highest position is selected from the multiple articles A 2  to A 4 . Thus, the article A 2  is selected as the object to be held by the third operation. After the article A 2  is transferred by the third operation, the article A 4  is selected as the object to be held by the third operation in the next third determination. 
     As described above, the third condition for the third operation includes being able to acquire data on upper and side surfaces and being able to slide the article A along the X-direction. The third determination using the third condition selects one article that can be moved stably. 
     Only a part of the conditions described above may be used in the third determination. Relaxing the conditions increases the number of cases in which the upper and side surfaces of the article can be simultaneously held, although the stability of holding or transfer can be reduced. The transfer stability may be improved compared to when the second operation is performed. 
     The third operation is substantially the same as the first operation except that the number of articles held is different. In the third operation, the same operation as in  FIGS.  13  to  17    is performed for one article. 
     Not limited to the example described above, the transfer apparatus  100  may lift the article after holding it in the third operation, similarly to the second operation. Even in this case, both the upper surface and the side surface of the article are held, and it prevents large local forces from being applied to the article. For example, the possibility of the article being damaged can be reduced. In the case where the article is lifted in the third operation, the determination in step S 301  may be omitted. The transfer apparatus  100  may switch between sliding and lifting the article depending on whether the condition is satisfied in the determination of the step S 301 . 
     According to the variation, a third operation can be performed even if the first operation is not feasible. By performing the third operation, the stability of the movement of the article can be improved. 
       FIG.  30    is a schematic view showing a hardware configuration. 
     The controller  25  includes, for example, the hardware configuration shown in  FIG.  30   . A processing device  90  shown in  FIG.  30    includes a CPU  91 , a ROM  92 , a RAM  93 , a memory device  94 , an input interface  95 , an output interface  96 , and a communication interface  97 . 
     The ROM  92  stores a program configured to control an operation of a computer. The ROM  92  stores a program necessary for the computer to implement the above-described processes. The RAM  93  functions as a memory area onto which the program stored in the ROM  92  is loaded. 
     The CPU  91  includes a processing circuit. The CPU  91  executes a program stored in at least one of the ROM  92  and the memory device  94  using the RAM  93  as a work memory. During the execution of the program, the CPU  91  controls each configuration via a system bus  98  to execute various processes. 
     The memory device  94  stores data necessary for the execution of the program and data obtained by the execution of the program. 
     The input interface (I/F)  95  connects the processing device  90  and an input device  95   a.  The input I/F  95  is, for example, a serial bus interface such as a USB. The CPU  91  can read various types of data from the input device  95   a  via the input I/F  95 . 
     The output interface (I/F)  96  connects the processing device  90  and an output device  96   a.  The output I/F  96  is, for example, a video output interface such as a digital visual interface (DVI) or a high-definition multimedia interface (HDMI (registered trademark)). The CPU  91  can transmit data to the output device  96   a  via the output I/F  96  and cause the output device  96   a  to display an image. 
     The communication interface (I/F)  97  connects a server  97   a  outside the processing device  90  to the processing device  90 . The communication I/F  97  is, for example, a network card such as a LAN card. The CPU  91  can read various types of data from the server  97   a  via the communication I/F  97 . A camera  99   a  captures an image of the article and stores the image in the server  97   a . The camera  99   a  functions as the imager  121   a.  LRFs  99   b  and  99   c  measure the distance and store the measurement results in the server  97   a.  LRFs  99   b  and  99   c  function as distance measuring sensors  122   a  and  123   a,  respectively. 
     The memory device  94  includes one or more selected from a hard disk drive (HDD) and a solid state drive (SSD). The input device  95   a  includes one or more selected from a mouse, a keyboard, a microphone (voice input), and a touch pad. The output device  96   a  includes one or more selected from a monitor and a projector. A device having functions of both the input device  95   a  and the output device  96   a,  such as a touch panel, may be used. 
     Processes of the various types of data described above may be recorded on a magnetic disk (a flexible disk, a hard disk, or the like), an optical disk (CD-ROM, CD-R, CD-RW, DVD-ROM, DVD±R, DVD±RW, or the like), a semiconductor memory, or another non-transitory computer-readable recording medium as the program that can be executed by the computer. 
     For example, information recorded in the recording medium can be read by the computer (or an embedded system). In the recording medium, a recording format (storage format) is set as desired. For example, the computer reads the program from the recording medium and causes the CPU to execute instructions described in the program based on the program. In the computer, acquisition (or reading) of the program may be performed through a network. 
     According to the embodiment described above, the transfer apparatus, the controller (control device), the transfer method, the program, and the storage medium capable of efficiently and stably moving articles are provided. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention. The above embodiments can be practiced in combination with each other.