Patent Publication Number: US-2022219337-A1

Title: Holding device, cargo handling apparatus, and holding method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-004521, filed on Jan. 14, 2021; and Japanese Patent Application No. 2021-145766, filed on Sep. 7, 2021; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a holding device, a cargo handling apparatus, and a holding method. 
     BACKGROUND 
     There is an apparatus that holds an article. It is desirable to improve the convenience of such an apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating a holding device according to a first embodiment; 
         FIG. 2  is a side view illustrating a portion of the holding device according to the first embodiment; 
         FIG. 3  is a perspective view illustrating a portion of the holding device according to the embodiment; 
         FIG. 4  is a perspective view illustrating a portion of the holding device according to the embodiment; 
         FIGS. 5A and 5B  are side views illustrating a portion of the holding device according to the first embodiment; 
         FIGS. 6A to 6C  are schematic views illustrating the first operation of the holding device according to the first embodiment; 
         FIGS. 7A to 7C  are schematic views illustrating the first operation of the holding device according to the first embodiment; 
         FIGS. 8A and 8B  are schematic views illustrating the first operation of the holding device according to the first embodiment; 
         FIGS. 9A and 9B  are schematic views illustrating the second operation of the holding device according to the first embodiment; 
         FIGS. 10A and 10B  are schematic views illustrating the second operation of the holding device according to the first embodiment; 
         FIGS. 11A and 11B  are schematic views illustrating the second operation of the holding device according to the first embodiment; 
         FIGS. 12A and 12B  are schematic views illustrating the second operation of the holding device according to the first embodiment; 
         FIG. 13  is a perspective view illustrating a portion of a holding device according to a first modification of the first embodiment; 
         FIGS. 14A and 14B  are perspective views illustrating the first and second holders of a holding device according to a second modification of the first embodiment; 
         FIG. 15  is a perspective view illustrating a portion of a holding device according to a second modification of the first embodiment; 
         FIGS. 16A to 16C  are side views schematically illustrating a first holder and a second holder of a holding device according to a third modification of the embodiment; 
         FIGS. 17A to 17C  are side views schematically illustrating a first holder and a second holder of a holding device according to a fourth modification of the embodiment; 
         FIG. 18  is a side view schematically illustrating a first holder and a second holder of a holding device according to a fifth modification of the embodiment; 
         FIGS. 19A to 19C  are side views schematically illustrating an operation of the holding device according to the fifth modification of the embodiment; 
         FIGS. 20A to 20C  are side views schematically illustrating a first holder and a second holder of a holding device according to a sixth modification of the embodiment; 
         FIG. 21  is a side view schematically illustrating a portion of a holding device according to a seventh modification of the embodiment; 
         FIGS. 22A and 22B  are side views schematically showing operations of the holding device according to the seventh modification of the embodiment; 
         FIGS. 23A to 23D  are side views schematically showing states when the suction hand according to the embodiment holds the article; 
         FIG. 24  is a front view schematically illustrating a portion of a holding device according to an eighth modification of the embodiment; 
         FIG. 25  is a front view schematically showing a state when the holding device according to the eighth modification of the embodiment holds articles; 
         FIG. 26  is a front view schematically showing a state when the holding device according to the eighth modification of the embodiment holds articles; and 
         FIG. 27  is a schematic view illustrating a hardware configuration. 
     
    
    
     DETAILED DESCRIPTION 
     According to one embodiment, a holding device includes a first holder configured to hold an upper surface of an article, and a second holder configured to hold a side surface of the article. The holding device performs at least a first operation of the first and second holders holding the article, and a second operation of only the first holder holding the article. 
     Various embodiments are described below with reference to the accompanying drawings. 
     The drawings are schematic and conceptual; and the relationships between the thickness and width of portions, the proportions of sizes among portions, etc., are not necessarily the same as the actual values. The dimensions and proportions may be illustrated differently among drawings, even for identical portions. 
     In the specification and drawings, components similar to those described previously or illustrated in an antecedent drawing are marked with like reference numerals, and a detailed description is omitted as appropriate. 
     First Embodiment 
       FIG. 1  is a perspective view illustrating a holding device according to a first embodiment. 
     As illustrated in  FIG. 1 , the holding device  100  according to the first embodiment includes a first holder  1 , a second holder  2 , drivers  11   x ,  11   y ,  12   x ,  12   y , and  13   z , base plates  20   a  and  20   b , a frame  21 , a lift  30 , and a controller  50 . 
     The first holder  1  is configured to hold an upper surface of an article. The second holder  2  is configured to hold a side surface of the article. The article can be more stably held by both the first holder  1  and the second holder  2  holding the article. Or, even when another article is frontward of the article, only the article can be selectively held by only the first holder  1  holding the upper surface of the article. 
     Here, an X-direction (a longitudinal direction), a Y-direction (a lateral direction), and a Z-direction (a vertical direction) are used in the description. The Z-direction is parallel to a direction connecting the first holder  1  and the article when the first holder  1  holds the article. The X-direction is parallel to a direction connecting the second holder  2  and the article when the second holder  2  holds the article. The Z-direction crosses the X-direction. The Y-direction crosses a plane parallel to the X-direction and the Z-direction. For example, the X-direction and the Y-direction are parallel to a horizontal plane. The Z-direction is parallel to the vertical direction. The X-direction, the Y-direction, and the Z-direction are orthogonal to each other. 
       FIG. 2  is a side view illustrating a portion of the holding device according to the first embodiment. 
     In the example of  FIGS. 1 and 2 , the first holder  1  and the second holder  2  hold (stably grip) an article by vacuum-gripping. 
     As illustrated in  FIG. 2 , the first holder  1  includes a housing  1   a , and a gripping unit  1   b  that is mounted to the housing  1   a . The housing  1   a  includes piping, valves, etc., necessary for vacuum-gripping. The gripping unit  1   b  includes a rod  1   c  and a suction pad  1   d . The rod  1   c  extends in the Z-direction. The suction pad  1   d  is located at the tip of the rod  1   c . The gripping surface of the tip of the suction pad  1   d  faces downward. 
     Similarly to the first holder  1 , the second holder  2  includes a housing  2   a , and a gripping unit  2   b  that is mounted to the housing  2   a . The housing  2   a  includes piping, valves, etc., necessary for vacuum-gripping. The gripping unit  2   b  includes a rod  2   c  and a suction pad  2   d . The rod  2   c  extends in the X-direction when the second holder  2  holds the article. The suction pad  2   d  is located at the tip of the rod  2   c . The gripping surface of the tip of the suction pad  2   d  faces frontward when the second holder  2  holds the article. 
     The internal spaces of the gripping units  1   b  and  2   b  are connected to piping and valves located inside the housings  1   a  and  2   a  and to a not-illustrated exhaust system such as an exhaust device located outside the first holder  1  and the second holder  2 , etc. The internal space of the gripping unit  1   b  can be exhausted independently of the internal space of the gripping unit  2   b . Pluralities of the gripping units  1   b  and  2   b  may be included. 
     In the example of  FIGS. 1 and 2 , the first holder  1  includes multiple gripping units  1   b  arranged in two mutually-orthogonal directions. The second holder  2  includes multiple gripping units  2   b  arranged in one direction. 
       FIG. 3  is a perspective view illustrating a portion of the holding device according to the embodiment. 
     A driver  11   x  (an example of a first driver) moves the first holder  1  in the X-direction. A driver  11   y  moves the first holder  1  in the Y-direction. 
     For example, as illustrated in  FIG. 3 , the driver  11   x  includes an actuator  11   a , a pulley  11   b , a belt  11   c , a bar  11   d , and a guide  11   e . In the example, the actuator  11   a  is a motor. The rotary shaft of the actuator  11   a  is parallel to the Y-direction. The rotary shaft of the actuator  11   a  is coupled to the pulley  11   b . Another pulley  11   b  is positioned distant to the pulley  11   b  in the X-direction. The belt  11   c  is threaded over the pair of pulleys  11   b . The bar  11   d  is fixed with respect to the belt  11   c . The bar  11   d  engages the guide  11   e  that extends along the X-direction. The belt  11   c  is moved along the X-direction between the pair of pulleys  11   b  when the actuator  11   a  rotates the pulley  11   b  around the Y-direction. The bar  11   d  that is fixed with respect to the belt  11   c  moves in the X-direction along the guide  11   e.    
     A rod  11   f  extends along the Y-direction and is fixed with respect to the bar  11   d . In the example, a pair of rods  11   f  is separated from each other in the X-direction. The first holder  1  is coupled to each of the rods  11   f . The rods  11   f  and the first holder  1  move in the X-direction according to the movement of the bar  11   d.    
     The driver  11   y  moves in the X-direction together with the bar  11   d . The driver  11   y  includes an actuator  11   h , a pulley  11   i , and a belt  11   j . The actuator  11   h  is a motor. The rotary shaft of the actuator  11   h  is coupled to the pulley  11   i . Another pulley  11   i  is positioned distant to the pulley  11   i  in the Y-direction. The belt  11   j  is threaded over the pair of pulleys  11   i.    
     The first holder  1  is slidably coupled to the rod  11   f  in the Y-direction. The first holder  1  is fixed with respect to the belt  11   j . The belt  11   j  is moved along the Y-direction between the pair of pulleys  11   i  when the actuator  11   h  rotates the pulley  11   i . The first holder  1  that is fixed with respect to the belt  11   j  moves in the Y-direction. 
     A driver  12   x  (an example of a second driver) moves the second holder  2  in the X-direction. A driver  12   y  moves the second holder  2  in the Y-direction. 
       FIG. 4  is a perspective view illustrating a portion of the holding device according to the embodiment. 
     For example, as illustrated in  FIGS. 3 and 4 , the driver  12   x  is located higher than the driver  11   x , and includes an actuator  12   a , a pulley  12   b , a belt  12   c , a bar  12   d , and a guide  12   e . In the example, the actuator  12   a  is a motor. The rotary shaft of the actuator  12   a  is parallel to the Y-direction. The rotary shaft of the actuator  12   a  is coupled to the pulley  12   b . Another pulley  12   b  is positioned distant to the pulley  12   b  in the X-direction. The belt  12   c  is threaded over the pair of pulleys  12   b . The bar  12   d  is fixed with respect to the belt  12   c . The bar  12   d  engages the guide  12   e  that extends along the X-direction. The belt  12   c  is moved along the X-direction between the pair of pulleys  12   b  when the actuator  12   a  rotates the pulley  12   b  around the Y-direction. The bar  12   d  that is fixed with respect to the belt  12   c  moves in the X-direction along the guide  12   e.    
     One end of a link  12   k  is rotatably coupled to the bar  12   d . A bar  12   m  is rotatably coupled to the other end of the link  12   k . A rod  12   f  extends along the Y-direction and is fixed with respect to the bar  12   m . In the example, a pair of rods  12   f  that is separated from each other in the X-direction is fixed with respect to the bar  12   m . Each of the pair of links  12   k  that is separated from each other in the X-direction is rotatably coupled to the bar  12   m . The link  12   k , the bar  12   m , the rod  12   f , and the second holder  2  move in the X-direction according to the movement of the bar  11   d.    
     The driver  12   y  moves in the X-direction together with the bar  12   d . The driver  12   y  includes an actuator  12   h  (an example of a fourth driver), a pulley  12   i , and a belt  12   j . The actuator  12   h  is a motor. The rotary shaft of the actuator  12   h  is coupled to the pulley  12   i . Another pulley  12   i  is positioned distant to the pulley  12   i  in the Y-direction. The belt  12   j  is threaded over the pair of pulleys  12   i . The rotary shaft of the actuator  12   h  is parallel to the X-direction and is coupled to one of the pulleys  12   i.    
     The second holder  2  is movably coupled to the rod  12   f  in the Y-direction. The second holder  2  is fixed with respect to the belt  12   j . The belt  12   j  is moved along the Y-direction between the pair of pulleys  12   i  when the actuator  12   h  rotates the pulley  12   i . The second holder  2  that is fixed with respect to the belt  12   j  moves in the Y-direction. 
     An actuator  12   n  is fixed with respect to one of the bars  12   m . For example, the actuator  12   n  is a motor. The rotary shaft of the actuator  12   n  is parallel to the Y-direction and coupled to the other end of one of the links  12   k . The link  12   k  is rotated with respect to the bar  12   m  by the driving of the actuator  12   n . Thereby, the second holder  2  is rotated around the one end of the link  12   k . The X-direction position and the Z-direction position of the second holder  2  are changed by the rotation of the second holder  2 . For example, the second holder  2  rotates while maintaining the orientations of the suction pad  2   d  and the rod  2   c.    
     The one end of the link  12   k  is positioned higher than the first holder  1 . In other words, the rotation center of the second holder  2  is positioned higher than the first holder  1 . The second holder  2  is switched between a state in which the second holder  2  is higher than the first holder  1  and a state in which the second holder  2  is lower than the first holder  1  by rotating the second holder  2  around its rotation center. 
     The base plates  20   a  and  20   b  are supporters for supporting the first holder  1  and the second holder  2 . The base plate  20   a  (a first supporter) and the base plate  20   b  (a second supporter) are plate members that spread along the X-Z plane and are separated from each other in the Y-direction. The pulleys  11   b  and  12   b  are mounted to the base plate  20   a . The base plates  20   a  and  20   b  support the first holder  1  via the pulley  11   b , the belt  11   c , the bar  11   d , and the rod  11   f . Also, the base plates  20   a  and  20   b  support the second holder  2  via the pulley  12   b , the belt  12   c , the bar  12   d , the link  12   k , the bar  12   m , and the rod  12   f.    
     The pulley  11   b , the belt  11   c , the bar  11   d , the guide  11   e , the pulley  12   b , the belt  12   c , the bar  12   d , the guide  12   e , the link  12   k , and the bar  12   m  are mounted to each of the base plates  20   a  and  20   b  and are positioned between the base plates  20   a  and  20   b  when viewed along the Z-direction. The rod  11   f  is fixed to the bars  11   d  that face each other in the Y-direction. The rod  12   f  is fixed to the bars  12   d  that face each other in the Y-direction. The actuators  11   a  and  12   a  are mounted to the base plate  20   a . The actuators  11   a  and  12   a  may be mounted to the base plate  20   b  or to both the base plates  20   a  and  20   b.    
     The pulley  11   b  that is at the front of the base plate  20   a  and the pulley  11   b  that is at the front of the base plate  20   b  are coupled to each other by a rod  20   c  that extends in the Y-direction. The drive force of the actuator  11   a  mounted to the base plate  20   a  is transferred to the pulley  11   b  of the base plate  20   b  by the rod  20   c . The pair of pulleys  11   b  of the base plate  20   b  rotate synchronously with the pair of pulleys  11   b  of the base plate  20   a . Thereby, the bar  11   d  of the base plate  20   b  is moved in the X-direction synchronously with the bar  11   d  of the base plate  20   a.    
     The pulley  12   b  that is at the front of the base plate  20   a  and the pulley  12   b  that is at the front of the base plate  20   b  are coupled to each other by a rod  20   d  that extends in the Y-direction. The drive force of the actuator  12   a  mounted to the base plate  20   a  is transferred to the pulley  12   b  of the base plate  20   b  by the rod  20   d . The pair of pulleys  12   b  of the base plate  20   b  rotates synchronously with the pair of pulleys  12   b  of the base plate  20   a . Thereby, the bar  12   m  of the base plate  20   b  is moved in the X-direction synchronously with the bar  12   m  of the base plate  20   a.    
     The first holder  1  and the second holder  2  can be more stably supported by the rods  11   f  and  12   f  and the rods  20   c  and  20   d  bridging between the base plates  20   a  and  20   b . For example, the positions in the Z-direction of the first and second holders  1  and  2  can be more stable. 
     As illustrated in  FIG. 1 , multiple drivers  13   z  (examples of the third driver) are arranged in the Y-direction. A pair of drivers  13   z  moves the base plates  20   a  and  20   b  in the Z-direction. The first holder  1  and the second holder  2  are moved in the Z-direction by the operation of the drivers  13   z.    
     For example, each of the drivers  13   z  includes an actuator  13   a , a pair of pulleys  13   b , a belt  13   c , a block  13   d , and a guide  13   e . The actuator  13   a  is a motor. The rotary shaft of the actuator  13   a  is parallel to the Y-direction. The rotary shaft of the actuator  13   a  is coupled to one of the pulleys  13   b . The pair of pulleys  13   b  is separated from each other in the Z-direction. The belt  13   c  is threaded over the pair of pulleys  13   b.    
     The blocks  13   d  are fixed respectively to the side surface of the base plate  20   a  and the side surface of the base plate  20   b . The block  13   d  is fixed to the belt  13   c . The base plates  20   a  and  20   b  respectively engage the guides  13   e . By the rotation of the actuator  13   a , the pulley  13   b  is rotated around the Y-direction, and the belt  13   c  is moved along the Z-direction between the pair of pulleys  13   b . Thereby, the base plates  20   a  and  20   b  that are fixed with respect to the belts  13   c  are moved in the Z-direction. 
     The drivers  13   z  are mounted to the frame  21 . The first holder  1  and the second holder  2  are movable in the X-direction, the Y-direction, and the Z-direction with respect to the frame  21  by the drivers  11   x ,  11   y ,  12   x ,  12   y , and  13   z.    
     For example, the frame  21  includes vertical frames  21   a  to  21   d  and horizontal frames  21   e  to  21   k . The vertical frames  21   a  and  21   b  are separated from each other in the X-direction. The vertical frames  21   c  and  21   d  are separated from each other in the X-direction. The vertical frames  21   a  and  21   b  face the vertical frames  21   c  and  21   d  in the Y-direction. The horizontal frames  21   e  and  21   f  couple the lower ends of the vertical frames  21   a  and  21   b  to each other and couple the upper ends of the vertical frames  21   a  and  21   b  to each other. The horizontal frames  21   g  and  21   h  couple the lower ends of the vertical frames  21   c  and  21   d  to each other and couple the upper ends of the vertical frames  21   c  and  21   d  to each other. The horizontal frames  21   i  and  21   j  couple the lower ends of the vertical frames  21   b  and  21   d  to each other and couple the upper ends of the vertical frames  21   b  and  21   d  to each other. The horizontal frame  21   k  couples the upper ends of the vertical frames  21   a  and  21   c  to each other. The guides  13   e  are mounted respectively to the vertical frames  21   a  and  21   c.    
     The lift  30  is located inside the frame  21 . In other words, the lift  30  is the positioned inside a rectangular region surrounded with the vertical frames  21   a  to  21   d  when viewed along the Z-direction. The upper surface of the lift  30  is parallel to the X-direction and the Y-direction. The lift  30  is moved in the Z-direction by a not-illustrated driver. 
     As shown in  FIG. 1 , the lift  30  includes a pair of rollers  30   a  and a belt  30   b . The pair of rollers  30   a  are separated from each other in the X-direction. The belt  30   b  is threaded over the pair of rollers  30   a . The rotary shafts of the rollers  30   a  are parallel to the Y-direction. The belt  30   b  is moved along the X-direction between the pair of rollers  30   a  when a not-illustrated motor rotates the rollers  30   a.    
     A conveyor C is located outside the frame  21 . A driver of the lift  30  sets the lift  30  to a state in which the lift  30  is at the same level as the conveyor C, a state in which the lift  30  is at a lower position than the conveyor C, or a state in which the lift  30  is at a higher position than the conveyor C. 
     When a pallet P on which articles are loaded is placed in front of the holding device  100 , the holding device  100  sequentially transfers the articles to the lift  30 . The lift  30  is set to the same level as the conveyor C. Subsequently, the articles that are placed on the lift  30  are transferred onto the conveyor C. In other words, the holding device  100  functions as a cargo handling apparatus  100   a  that uses the first holder  1 , the second holder  2 , the lift  30 , etc., to unload, onto the conveyor C, the articles loaded on the pallet P. 
     The holding device  100  may include a detector  35 . The detector  35  detects the articles that are loaded on the pallet P. For example, the detector  35  detects the position of an article A. The detector  35  includes at least one selected from the group consisting of an image sensor, a through-beam sensor, a laser sensor, and an infrared sensor. Favorably, the detector  35  is a camera that includes an image sensor. 
     The controller  50  is connected with and controls the drivers, the exhaust device, and the detector  35  of the holding device  100 . The controller  50  processes data necessary for holding and transferring the articles A. The controller  50  includes a processing circuit that includes a central processing unit, memory in which programs are stored, etc. The controller  50  may calculate the positions of the articles based on an image acquired by the detector  35 . 
       FIGS. 5A and 5B  are side views illustrating a portion of the holding device according to the first embodiment. 
     The controller  50  switches between a first state in which the second holder  2  is at a first position and a second state in which the second holder  2  is at a second position. 
     The second holder  2  can hold the side surface of the article at the first position. The second holder  2  is positioned lower than at least a portion of the first holder  1  when the second holder  2  is at the first position. For example, the gripping unit  2   b  is positioned lower than the housing  1   a  and the upper end of the rod  1   c  of the first holder  1 . 
     The second position is separated from the first position. For example, the second position is higher than the first position. The second holder  2  is positioned higher than at least a portion of the first holder  1  when the second holder  2  is at the second position. For example, the gripping unit  2   b  is positioned higher than the housing  1   a  and the gripping unit  1   b  of the first holder  1 . When the actuator  12   n  operates, the link  12   k  is rotated, and the position of the second holder  2  is changed. The second holder  2  is movable between the first position and the second position by the actuator  12   n.    
       FIG. 5A  illustrates the state when the second holder  2  is at the first position.  FIG. 5B  illustrates the state when the second holder  2  is at the second position. As illustrated in  FIG. 5A , at least a portion of the second holder  2  is at the same level as the first holder  1  when the second holder  2  is at the first position. As illustrated in  FIG. 5B , the second holder  2  is positioned higher than the first holder  1  when the second holder  2  is at the second position. In the example, at least a portion of the second holder  2  is positioned directly above the first holder  1 . 
     The holding device  100  performs the first operation when transferring articles of a first arrangement. The position of the second holder  2  is set to the first position in the first operation. The holding device  100  performs the second operation when transferring articles of a second arrangement. The position of the second holder  2  is set to the second position in the second operation. In the first arrangement, articles of substantially the same size are arranged in the X-direction and the Y-direction and loaded in the Z-direction. In the second arrangement, articles of different sizes are irregularly loaded. 
       FIGS. 6A to 6C ,  FIGS. 7A to 7C ,  FIG. 8A , and  FIG. 8B  are schematic views illustrating the first operation of the holding device according to the first embodiment. 
       FIG. 9A ,  FIG. 9B ,  FIG. 10A ,  FIG. 10B ,  FIG. 11A ,  FIG. 11B ,  FIG. 12A , and  FIG. 12B  are schematic views illustrating the second operation of the holding device according to the first embodiment. 
     When transferring articles of the first arrangement, the holding device  100  sequentially transfers from the article positioned at the front. The controller  50  drives the actuator  12   n  to position the second holder  2  at the first position as illustrated in  FIG. 6A . The controller  50  positions the upper surface of the lift  30  at the same level as the bottom surface of the article A to be transferred. 
     The controller  50  drives the drivers  11   x  and  11   y  to move the first holder  1  directly above the article A as illustrated in  FIG. 6B . The controller  50  drives the driver  13   z  to press the first holder  1  onto the upper surface of the article A as illustrated in  FIG. 6C . Each rod  1   c  is displaced, and the suction pad  1   d  deforms according to the shape of the upper surface. The controller  50  operates the exhaust system to set the internal pressure of the gripping unit  1   b  to be less than atmospheric pressure. Thereby, the first holder  1  holds the upper surface of the article A. 
     The controller  50  drives the drivers  12   x  and  12   y  to press the second holder  2  onto the side surface of the article A as illustrated in  FIG. 7A . Each rod  2   c  is displaced, and the suction pad  2   d  deforms according to the shape of the side surface. The controller  50  operates the exhaust system to set the internal pressure of the gripping unit  2   b  to be less than atmospheric pressure. Thereby, the second holder  2  holds the side surface of the article A. 
     As illustrated in  FIG. 7B , the controller  50  operates the drivers  11   x  and  12   x  to transfer the article A from the pallet P onto the lift  30 . At this time, the controller  50  may operate the driver  13   z  to lift the article A. When the article A is transferred onto the lift  30 , the controller  50  releases the holding by the first and second holders  1  and  2 . Namely, the controller  50  increases the pressure of the internal space of the gripping unit  1   b  and the pressure of the internal space of the gripping unit  2   b  and weakens the gripping force of the first and second holders  1  and  2 . The controller  50  operates the drivers  12   x  and  13   z  to separate the first and second holders  1  and  2  from the article A as illustrated in  FIG. 7C . 
     As illustrated in  FIG. 8A , the controller  50  positions the upper surface of the lift  30  at the same level as the upper surface of the conveyor C. As illustrated in  FIG. 8B , the lift  30  is operated to transfer the article A onto the conveyor C. The conveyor C transfers the article A to another location. The holding device  100  repeats the first operation illustrated in  FIGS. 6A to 8B  until all of the articles A placed on the pallet P are transferred onto the conveyor C. 
     When transferring articles of the second arrangement, the holding device  100  sequentially transfers from an article that is at a high position. As illustrated in  FIG. 9A , the controller  50  drives the actuator  12   n  to position the second holder  2  at the second position. At this time, the controller  50  may position the upper surface of the lift  30  at the same level as the bottom surface of the article A to be transferred. The controller  50  drives the drivers  11   x  and  11   y  to move the first holder  1  directly above the article A that is the transfer object as illustrated in  FIG. 9B . 
     The transfer object is, for example, the article A of which the upper surface is at the highest position. When the first holder  1  approaches an article A of which the upper surface is at a low position, a portion of the holding device  100  interferes with the articles A of which the upper surfaces are at higher positions, and there is a possibility that the article A cannot be transferred. The transfer object may be determined by a user of the holding device  100 . The positions of the upper surfaces of the articles A may be calculated based on the detection result of the detector  35 . The controller  50  determines the article A to be transferred based on the calculated positions of the upper surfaces. 
     The controller  50  drives the driver  13   z  to press the first holder  1  onto the upper surface of the article A as illustrated in  FIG. 10A . The controller  50  operates the exhaust system to set the internal pressure of the gripping unit  1   b  to be less than atmospheric pressure. Thereby, the first holder  1  holds the upper surface of the article A. The controller  50  operates the driver  13   z  to lift the article A as illustrated in  FIG. 10B . At this time, the second holder  2  is still at the second position. The second holder  2  does not hold the article A. 
     The controller  50  operates the drivers  11   x  and  12   x  to transfer the article A from the pallet P onto the lift  30 . The controller  50  operates the driver  13   z  to place the article A onto the lift  30  as illustrated in  FIG. 11A . The controller  50  releases the holding by the first holder  1 . The controller  50  operates the driver  13   z  to separate the first and second holders  1  and  2  from the article A as illustrated in  FIG. 11B . 
     As illustrated in  FIG. 12A , the controller  50  positions the upper surface of the lift  30  at the same level as the upper surface of the conveyor C. As illustrated in  FIG. 12B , the lift  30  is operated to transfer the article A onto the conveyor C. The conveyor C transfers the article A to another location. The holding device  100  repeats the second operation illustrated in  FIGS. 9A to 12B  until all of the articles A placed on the pallet P are transferred onto the conveyor C. 
     Data of the arrangement of the articles A on the pallet P may be input by the user or may be transmitted to the controller  50  by a communicator. For example, the controller  50  receives the data of the arrangement. The controller  50  switches the position of the second holder  2  based on the received data. 
     Advantages of the first embodiment will now be described. 
     When the multiple articles A are loaded in the regular first arrangement, the heights of the articles A are the same as those illustrated in  FIG. 6A . For example, products of the same product type are packaged in each article A. In such a case, the article A can be more stably held by both the first holder  1  and the second holder  2  by transferring the article A at the front first. Compared to when the article A is held by only one of the first holder  1  or the second holder  2 , the application of a locally-large force to the article A can be suppressed. The likelihood of damaging the article A can be reduced thereby. Both the first holder  1  and the second holder  2  are used for the articles A of the first arrangement. 
     When the multiple articles A are loaded at the irregular second arrangement, the sizes of the articles A are different from each other as illustrated in  FIG. 9A . For example, the articles A are courier parcels. In such a case, when the first holder  1  approaches an article A of which the upper surface is at a low position, a portion of the holding device  100  interferes with other articles A of which the upper surfaces are at higher positions, and there is a possibility that the other articles A may be damaged. Therefore, the holding device  100  holds the article A of which the upper surface is at the highest position when transferring. For the articles A of the second arrangement, only the first holder  1  is used, and the second holder  2  is not used. 
     Conventionally, different holding devices are used between when transferring the articles A of the first arrangement illustrated in  FIG. 6A  and when transferring the articles A of the second arrangement illustrated in  FIG. 9A . In other words, a holding device that includes the first and second holders  1  and  2  is used for the articles A of the first arrangement. A holding device that includes only the first holder  1  is used for the articles A of the second arrangement. However, in a conventional method, it is necessary to assign the pallets to the holding devices according to the type of the holding device and the arrangement of the articles. Therefore, management is complex. Also, the operation rate of the holding device may decrease. 
     For this problem, the holding device  100  according to the first embodiment performs the first operation of holding the article A with both the first holder  1  and the second holder  2 , and the second operation of holding the article A with only the first holder  1 . By selectively performing one of the first operation or the second operation, the article A can be held regardless of the arrangement. According to the first embodiment, the convenience of the holding device  100  can be improved. For example, the operation rate of the holding device  100  can be improved thereby. 
     Favorably, the holding device  100  switches between the first state in which the second holder  2  is at the first position and the second state in which the second holder  2  is at the second position. When holding the articles A of the second arrangement, there is a possibility that the second holder  2  may interfere with an article A other than the holding object. When the second holder  2  is at the second position in the second operation, the likelihood of the second holder  2  interfering with the other article A can be reduced. 
     More favorably, the second position is higher than the first holder  1 . The likelihood of the second holder  2  interfering with the other article A in the second operation can be further reduced thereby. 
     More favorably, at least a portion of the second holder  2  is positioned directly above the first holder  1  when the second holder  2  is at the second position. The likelihood of the second holder  2  interfering with the other article A in the second operation can be further reduced thereby. 
     Favorably, the distance in the Y-direction between the base plate  20   a  and the base plate  20   b  is greater than the length in the Y-direction of the lift  30 . The lift  30  is positioned between the base plate  20   a  and the base plate  20   b  when viewed along the Z-direction. Therefore, the interference of the lift  30  with the base plates  20   a  and  20   b  when the base plates  20   a  and  20   b  are moved in the Z-direction or when the lift  30  is moved in the Z-direction can be suppressed. 
     The first holder  1  and the second holder  2  are movable to a position that does not interfere with the lift  30  when the lift  30  moves to be higher than the first holder  1 . The interference of the lift  30  with the first holder  1 , the second holder  2 , the base plate  20   a , and the base plate  20   b  can be suppressed thereby, and the operation rate of the holding device  100  can be improved. 
     Specifically, in the holding device  100 , the first holder  1  and the second holder  2  are movable further frontward than the lift  30 . The first holder  1  and the second holder  2  do not overlap the lift  30  when viewed along the Z-direction. For example, when only the first holder  1  holds the article A as illustrated in  FIGS. 9B to 10B , the first holder  1  and the second holder  2  can be moved in the Z-direction regardless of the Z-direction position of the lift  30 . 
     First Modification 
     In the holding device according to the first embodiment, the second holder  2  may be fixed with respect to the bar  12   d . For example, the two ends of the link  12   k  are fixed respectively to the bars  12   d  and  12   m . The actuator  12   n  is not included. 
       FIG. 13  is a perspective view illustrating a portion of a holding device according to a first modification of the first embodiment. 
     Parts of the holding device  110  such as the bar  12   d , the guide  12   e , the pulley  12   i , the link  12   k , etc., are not illustrated in  FIG. 13 . In the holding device  100 , the second holder  2  is movable by the actuator  12   n  in the Z-direction with respect to the first holder  1 . Conversely, in the holding device  110  according to the first modification, the second holder  2  is movable only in the X-direction or the Y-direction with respect to the first holder  1 . 
     The controller  50  switches between the first state in which the second holder  2  is at the first position and the second state in which the second holder  2  is at the second position. The second holder  2  can hold the side surface of the article at the first position. The second position is further backward of the first position and is at the same level as the first position. For example, the second position is directly above the lift  30 . 
     When the first operation is performed, the first holder  1  moves to the first position at the front. When the second operation is performed, the second holder  2  withdraws to the second position at the back as illustrated in  FIG. 13 . According to the first modification, similarly to the holding device  100 , the article A can be held regardless of the arrangement. Therefore, the convenience of the holding device  110  can be improved. 
     Second Modification 
       FIGS. 14A and 14B  are perspective views illustrating the first and second holders of a holding device according to a second modification of the first embodiment. 
     In the holding device according to the first embodiment, the second holder  2  may be coupled to the first holder  1 . In the holding device  120  according to the second modification, the second holder  2  is detachably coupled to the first holder  1 .  FIG. 14A  illustrates a state when the second holder  2  is coupled to the first holder  1 .  FIG. 14B  illustrates a state when the second holder  2  is separated from the first holder  1 . 
     A coupler  15  is included in the first and second holders  1  and  2 . The coupler  15  couples the first holder  1  and the second holder  2 . The coupler  15  includes a first coupling part  15   a  and a second coupling part  15   b . The first coupling part  15   a  and the second coupling part  15   b  are mounted respectively to the first and second holders  1  and  2 . In the example, the first coupling part  15   a  and the second coupling part  15   b  are coupled by a magnetic force. The first coupling part  15   a  and the second coupling part  15   b  may be mechanically coupled. 
     The first coupling part  15   a  includes an electromagnet. A current is supplied to the first coupling part  15   a  via the first holder  1 . A magnetic field is generated at the periphery of the first coupling part  15   a  when electrical power is supplied to the first coupling part  15   a . Thereby, as illustrated in  FIG. 14A , the first coupling part  15   a  and the second coupling part  15   b  are coupled by a gripping force. 
     The second coupling part  15   b  is mounted to the second holder  2  via an actuator  15   c  (an example of a second driver). In the example, the actuator  15   c  is a power cylinder. The actuator  15   c  extends and retracts along the X-direction. The actuator  15   c  functions as a driver that moves the second holder  2  in the X-direction with respect to the first holder  1 . 
     The first coupling part  15   a  and the second coupling part  15   b  are separable when the supply of the current to the first coupling part  15   a  is stopped. The second holder  2  is separated from the first holder  1  by moving the first holder  1  in the state in which the coupling is released. 
       FIG. 15  is a perspective view illustrating a portion of a holding device according to a second modification of the first embodiment. 
     For example, the holding device  120  according to the second modification includes a placement platform  40 . The placement platform  40  is located at a position that does not interfere with the first and second holders  1  and  2  when the holding device  120  transfers the article. The placement platform  40  is located at a position that does not interfere with the lift  30  when the lift  30  moves in the Z-direction. For example, the placement platform  40  is located higher than the range of movement of the lift  30  in the Z-direction. 
     When performing the first operation, the second holder  2  is coupled to the first holder  1 . When performing the second operation, the second holder  2  is placed on the placement platform  40 . In other words, the state in which the second holder  2  is coupled to the first holder  1  corresponds to the first state. The state in which the second holder  2  is placed on the placement platform  40  corresponds to the second state. The second position is on the placement platform  40 . The first holder  1  holds the article at a lower position than the second position. 
     When the second operation is performed after performing the first operation, the drivers  11   x  and  11   y  move the first holder  1  and the second holder  2  so that the second holder  2  is positioned on the placement platform  40 . The second holder  2  is placed on the placement platform  40  by releasing the coupling of the coupler  15 . Subsequently, the second operation is performed using the first holder  1 . 
     According to the second modification, similarly to the holding device  100 , the convenience of the holding device  120  can be improved. Furthermore, the interference of the second holder  2  with the article can be avoided by placing the second holder  2  on the placement platform  40  in the second operation. The operation rate of the holding device  120  can be improved by providing the placement platform  40  at a position that does not interfere with the other components (e.g., the lift  30 ). 
     Third Modification 
       FIGS. 16A to 16C  are side views schematically illustrating a first holder and a second holder of a holding device according to a third modification of the embodiment. 
     In the holding device  130  according to the third modification, the second holder  2  is coupled to the first holder  1 . The driver  12   x  moves the second holder  2  in the X-direction with respect to the first holder  1 . A driver  12   z  moves the second holder  2  in the Z-direction with respect to the first holder  1 . 
     For example, the second holder  2  is coupled to a coupling part  16   a  via the driver  12   x . The coupling part  16   a  is coupled to a support frame  16   b  via the driver  12   z . The first holder  1  is fixed with respect to the support frame  16   b . The support frame  16   b  is fixed with respect to an arm  16   c . For example, the arm  16   c  is movable in the X-direction and the Y-direction by the drivers  11   x  and  11   y . Or, the arm  16   c  may be a portion of an X-Y orthogonal robot. The arm  16   c  may be a portion of an arm of a vertical articulated robot or a horizontal articulated robot. 
       FIG. 16A  illustrates the first state in which the second holder  2  is at the first position. When the second holder  2  moves from the first position to the second position, the driver  12   x  moves the second holder  2  backward as illustrated in  FIG. 16B . Then, as illustrated in  FIG. 16C , the driver  12   z  moves the second holder  2  upward. Thereby, the second holder  2  is positioned higher than at least a portion of the first holder  1  (the suction pad  1   d ).  FIG. 16C  illustrates the second state in which the second holder  2  is at the second position. The holding device  130  performs the first operation of transferring the articles of the first arrangement in the first state illustrated in  FIG. 16A . The holding device  130  performs the second operation of transferring the articles of the second arrangement in the second state illustrated in  FIG. 16C . 
     When the second holder  2  is at the first position, the gripping unit  2   b  is positioned lower than the housing  1   a  and the upper end of the rod  1   c  of the first holder  1 . When the second holder  2  is at the second position, the gripping unit  2   b  is positioned higher than the lower end of the rod  1   c  and the suction pad  1   d  of the first holder  1 . 
     According to the third modification, similarly to the holding device  100 , the convenience of the holding device  130  can be improved. By positioning the second holder  2  higher than at least a portion of the first holder  1  in the second operation, the interference of the second holder  2  with the article can be suppressed. The operation rate of the holding device  130  can be improved thereby. 
     Fourth Modification 
       FIGS. 17A to 17C  are side views schematically illustrating a first holder and a second holder of a holding device according to a fourth modification of the embodiment. 
     In the holding device  140  according to the fourth modification, the driver  12   x  moves the second holder  2  in the X-direction with respect to the first holder  1 . A driver  11   z  moves the first holder  1  in the Z-direction with respect to the second holder  2 . 
     For example, the second holder  2  is coupled to the support frame  16   b  via the driver  12   x  and the coupling part  16   a . The first holder  1  is coupled to the support frame  16   b  via the driver  11   z . The support frame  16   b  is fixed with respect to the arm  16   c.    
       FIG. 17A  illustrates the first state in which the second holder  2  is at the first position. When the holding device  140  transitions from the first state to the second state, the driver  12   x  moves the second holder  2  backward as illustrated in  FIG. 17B . The driver  11   z  moves the first holder  1  downward with respect to the second holder  2 . Thereby, as illustrated in  FIG. 17C , the second holder  2  is positioned higher than at least a portion of the first holder  1 .  FIG. 17C  illustrates the second state in which the second holder  2  is at the second position. The holding device  140  performs the first operation in the first state illustrated in  FIG. 17A . The holding device  140  performs the second operation in the second state illustrated in  FIG. 17C . 
     When the second holder  2  is at the first position, the gripping unit  2   b  is positioned lower than the housing  1   a  and the upper end of the rod  1   c  of the first holder  1 . When the second holder  2  is at the second position, the gripping unit  2   b  is positioned higher than the lower end of the rod  1   c  and the suction pad  1   d  of the first holder  1 . 
     According to the fourth modification, similarly to the holding device  100 , the convenience of the holding device  140  can be improved. The interference of the second holder  2  with the article can be suppressed by positioning the second holder  2  higher than at least a portion of the first holder  1  in the second operation. The operation rate of the holding device  140  can be improved thereby. 
     Fifth Modification 
       FIG. 18  is a side view schematically illustrating a first holder and a second holder of a holding device according to a fifth modification of the embodiment. 
     The tilts of the first and second holders  1  and  2  with respect to the X-Y plane may be changeable. For example, compared to the holding device  130 , the holding device  150  according to the fifth modification further includes a rod  16   d , a coupling part  16   e , and a driver  16   z  as illustrated in  FIG. 18 . 
     The driver  16   z  is mounted to the support frame  16   b . One end of the rod  16   d  is coupled to the driver  16   z . The driver  16   z  slides the rod  16   d  in the Z-direction. The other end of the rod  16   d  is coupled to the first holder  1  via the coupling part  16   e . The second holder  2  and the rod  16   d  are rotatably coupled to the coupling part  16   e  around the Y-direction. 
     The first holder  1  is rotatable around the Y-direction with respect to the support frame  16   b  around a rotary shaft  16   f . The Z-direction position of the front portion of the first holder  1  changes according to the operation of the driver  16   z . The Z-direction position of the front portion of the first holder  1  is fixed. Therefore, the tilt of the first holder  1  with respect to the X-Y plane changes when the driver  16   z  moves the rod  16   d  in the Z-direction. Simultaneously, the tilt of the second holder  2  with respect to the X-Y plane also changes. The tilts of the first and second holders  1  and  2  with respect to the support frame  16   b  and the arm  16   c  are changed by the operation of the driver  16   z.    
       FIGS. 19A to 19C  are side views schematically illustrating an operation of the holding device according to the fifth modification of the embodiment. 
       FIG. 19A  illustrates a state when the holding device  150  is in the first state.  FIG. 19B  illustrates a state when the holding device  150  is in the second state.  FIG. 19C  illustrates the state when the holding device  150  is in the first state and the first holder  1  and the second holder  2  are tilted. 
     The holding device  150  tilts the first holder  1  and the second holder  2  when holding the article or when placing the article. For example, the holding device  150  tilts the first holder  1  and the second holder  2  after placing the article and releasing the gripping of the article. Thereby, the contact area between the first holder  1  and the article and the contact area between the second holder  2  and the article can be reduced even when there is no space to move the second holder  2  backward. The friction between the second holder  2  and the article when raising the first holder  1  and the second holder  2  can be reduced. As a result, damage of the article can be suppressed, the load of the drivers raising the first holder  1  and the second holder  2  can be reduced, etc. 
     Sixth Modification 
       FIGS. 20A to 20C  are side views schematically illustrating a first holder and a second holder of a holding device according to a sixth modification of the embodiment. 
     The second holder  2  may rotate to change the orientation of the gripping surface of the suction pad  2   d . As illustrated in  FIG. 20A , the second holder  2  is coupled to the link  12   k . One end of the link  12   k  is coupled to the actuator  12   n . The link  12   k  and the second holder  2  are rotated by the actuator  12   n . The rotation center of the second holder  2  is positioned higher than the gripping surface of the suction pad  1   d  and is parallel to the Y-direction. The level of the suction pad  2   d  is changed by the rotation of the second holder  2 . 
       FIG. 20A  illustrates the first state in which the second holder  2  is at the first position. When the second holder  2  is at the first position, the gripping unit  2   b  is positioned lower than the upper end of the rod  1   c . When the second holder  2  moves from the first position to the second position, the second holder  2  is rotated by the actuator  12   n  as illustrated in  FIG. 20B . The second holder  2  reaches the same level as the first holder  1 . In other words, the gripping surface of the suction pad  2   d  reaches the same level as the gripping surface of the suction pad  1   d . The second holder  2  can hold the upper surface of the article when the first holder  1  holds the upper surface of the article. 
     The second holder  2  may be slidable along the link  12   k . For example, a driver  12   s  is coupled to the second holder  2  and the link  12   k . The driver  12   s  causes the second holder  2  to slide along the link  12   k . As illustrated in  FIG. 20C , the distance between the first holder  1  and the second holder  2  is reduced by the operation of the driver  12   s . In other words, the distance between the second holder  2  and the article is reduced when the first holder  1  holds the article. Thereby, the second holder  2  can easily contact the upper surface of the article. 
       FIG. 20B  or  FIG. 20C  illustrate the second state in which the second holder  2  is at the second position. For example, the holding device  160  performs the first operation of transferring the articles of the first arrangement in the first state illustrated in  FIG. 20A . The holding device  160  performs the second operation of transferring the articles of the second arrangement in the second state illustrated in  FIG. 20C . 
     According to the sixth modification, similarly to the holding device  100 , the convenience of the holding device  160  can be improved. Furthermore, the interference of the second holder  2  with the article can be suppressed by the second holder  2  approaching the first holder  1  in the second operation. For example, the interference between the second holder  2  and the lift  30  can be suppressed, and the operation rate of the holding device  160  can be improved. 
     Seventh Modification 
       FIG. 21  is a side view schematically illustrating a portion of a holding device according to a seventh modification of the embodiment. 
     As shown in  FIG. 21 , the holding device  170  according to the seventh modification includes an arm  17   a , a base  17   b , a tilt mechanism  17   c , a linear guide  17   d , a coupling frame  17   e , a fixing mechanism  17   f , a linear guide  17   g , a coupling plate  17   h , a cylinder  17   i , a linkage  17   k , and a drive mechanism  17   m  (an example of a fourth driver). 
     The arm  17   a  is connected with an X-Y orthogonal robot (an example of the first driver) that is included as the drivers  11   x  and  11   y . The arm  17   a  may be a portion of an X-Y orthogonal robot. The base  17   b  is a plate member that spreads along the X-Z plane. The back end of the lower portion of the base  17   b  is coupled with a tip  17   a   1  of the arm  17   a  via a rotary shaft  17   a   2 , and is rotatable with respect to the tip  17   a   1 . 
     The tilt mechanism  17   c  is located between the arm  17   a  and the base  17   b . Specifically, the tilt mechanism  17   c  includes a cylinder  17   c   1 , a rotary shaft  17   c   2 , and a rotary shaft  17   c   3 . The arm  17   a  includes a bent portion  17   a   3  that is bent downward. One end of the cylinder  17   c   1  is coupled to the bent portion  17   a   3  via the rotary shaft  17   c   2  and is rotatable with respect to the bent portion  17   a   3 . The other end of the cylinder  17   c   1  is coupled to the back end of the upper portion of the base  17   b  via the rotary shaft  17   c   3  and is rotatable with respect to the back end. The rotation centers of the rotary shafts  17   a   2 ,  17   c   2 , and  17   c   3  are parallel to the Y-direction. 
     The cylinder  17   c   1  is extendable and retractable along the X-direction. The levels at which the cylinder  17   c   1 , the rotary shaft  17   c   2 , and the rotary shaft  17   c   3  are located are different from the level at which the rotary shaft  17   a   2  is located. Thereby, the angle of the base  17   b  around the Y-direction is changed when the length of the cylinder  17   c   1  is changed. The cylinder  17   c   1 , the rotary shaft  17   c   2 , and the rotary shaft  17   c   3  are positioned above the rotary shaft  17   a   2  in the holding device  170 . For example, the front end of the base  17   b  is tilted downward by the extension of the cylinder  17   c   1 . 
     The linear guide  17   d  is located at the side surface of the base  17   b . In the holding device  170 , two linear guides  17   d  are located at one side surface of the base  17   b . The linear guide  17   d  includes a rail and a block. The rail is fixed with respect to the base  17   b  and is located along the Z-direction. The block is movable in the Z-direction along the rail. The coupling frame  17   e  is fixed with respect to the block of the linear guide  17   d . Thereby, the coupling frame  17   e  is movable in the Z-direction with respect to the base  17   b.    
     The fixing mechanism  17   f  is located at the side surface of the base  17   b  proximate to the coupling frame  17   e . The fixing mechanism  17   f  is switchable between a locked state in which the coupling frame  17   e  is fixed and an unlocked state in which the coupling frame  17   e  is movable. Specifically, the fixing mechanism  17   f  includes a rod  17   f   1  and a clamper  17   f   2 . The rod  17   f   1  is fixed with respect to the base  17   b  and extends along the Z-direction. The clamper  17   f   2  is coupled to the coupling frame  17   e  and is slidable in the Z-direction along the rod  17   f   1 . In the locked state, the clamper  17   f   2  is fixed with respect to the rod  17   f   1 , and the coupling frame  17   e  also is fixed thereby. 
     The first holder  1  is fixed with respect to the coupling frame  17   e . The linear guide  17   g  is located along the upper surface of the housing  1   a . The linear guide  17   g  includes a rail and a block. The rail is fixed with respect to the housing  1   a  and extends along the X-direction. The block is movable in the X-direction along the rail. 
     The coupling plate  17   h  is a plate member that extends along the X-direction. The front portion of the coupling plate  17   h  is parallel to the X-Y plane and is fixed with respect to the blocks of the linear guides  17   g . Thereby, the coupling plate  17   h  is movable in the X-direction with respect to the first holder  1 . The back portion of the coupling plate  17   h  is slightly tilted downward. 
     The cylinder  17   i  (an example of the second driver) is coupled to the coupling plate  17   h  and the housing  1   a  of the first holder  1 . The cylinder  17   i  is extendable and retractable along the X-direction. The coupling plate  17   h  moves in the X-direction with respect to the first holder  1  when the cylinder  17   i  extends or contracts. Thereby, the second holder  2  that is coupled to the coupling plate  17   h  is moved along the X-direction. 
     The linkage  17   k  is coupled between the coupling plate  17   h  and the second holder  2 . The linkage  17   k  includes a pair of links  17   k   1  and  17   k   2 . The links  17   k   1  and  17   k   2  extend parallel to each other and are synchronously rotatable. One end of the link  17   k   1  and one end of the link  17   k   2  are coupled respectively via rotary shafts  17   k   3  and  17   k   4  with the back end of the coupling plate  17   h . The rotary shafts  17   k   3  and  17   k   4  are rotatable with respect to the coupling plate  17   h . On the other hand, the links  17   k   1  and  17   k   2  are respectively fixed with respect to the rotary shafts  17   k   3  and  17   k   4 . Therefore, the links  17   k   1  and  17   k   2  also rotate when the rotary shafts  17   k   3  and  17   k   4  rotate with respect to the coupling plate  17   h.    
     The drive mechanism  17   m  is coupled to the coupling plate  17   h  and the linkage  17   k  and changes the Z-direction position of the second holder  2 . Specifically, the drive mechanism  17   m  includes a cylinder  17   m   1 , a rotary shaft  17   m   2 , a rotary shaft  17   m   3 , and a bar  17   m   4 . The cylinder  17   m   1  is located along the back portion of the coupling plate  17   h . The tube main body of the cylinder  17   m   1  is coupled with the coupling plate  17   h  via the rotary shaft  17   m   2  and is rotatable with respect to the coupling plate  17   h . The piston of the cylinder  17   m   1  is coupled to one end of the bar  17   m   4  via the rotary shaft  17   m   3  and is rotatable with respect to the bar  17   m   4 . The other end of the bar  17   m   4  is fixed with respect to one of a rotary shaft  17   k   3  or  17   k   4 . In the holding device  170 , the bar  17   m   4  is fixed with respect to the rotary shaft  17   k   3 . The second holder  2  is coupled with the other end of the link  17   k   1  and the other end of the link  17   k   2  respectively via rotary shafts  17   k   5  and  17   k   6  and is rotatable with respect to the links  17   k   1  and  17   k   2 . 
       FIGS. 22A and 22B  are side views schematically showing operations of the holding device according to the seventh modification of the embodiment. The cylinder  17   m   1 , the rotary shaft  17   m   2 , and the rotary shaft  17   m   3  are illustrated by double dot-dash lines in  FIG. 22A . In  FIG. 22B , the cylinder  17   m   1  and the rotary shaft  17   m   2  are not illustrated, and the rotary shaft  17   m   3  is illustrated by a dashed line.  FIG. 22A  illustrates a state in which the second holder  2  is at the first position; and  FIG. 22B  illustrates a state in which the second holder  2  is at the second position. 
     The rotary shafts  17   k   3  to  17   k   6 ,  17   m   2 , and  17   m   3  are parallel to the Y-direction. As illustrated in  FIGS. 22A and 22B , the bar  17   m   4  rotates around the Y-direction with the rotary shaft  17   k   3  as a center when the cylinder  17   m   1  extends or contracts. Because the bar  17   m   4  is fixed with respect to the rotary shaft  17   k   3 , the rotary shaft  17   k   3  rotates according to the rotation of the bar  17   m   4 . The link  17   k   1  that is fixed to the rotary shaft  17   k   3  rotates around the Y-direction with the rotary shaft  17   k   3  as a center. The link  17   k   2  also rotates around the Y-direction synchronously with the link  17   k   1 . Thereby, the second holder  2  rotates around the Y-direction with the rotary shaft  17   k   3  as a center. The position in the X-Z plane of the second holder  2  can be changed by the operation of the drive mechanism  17   m . In the second state illustrated in  FIG. 22B , the gripping unit  2   b  is positioned higher than the housing  1   a  and the gripping unit  1   b  of the first holder  1 . 
       FIGS. 23A to 23D  are side views schematically showing states when the suction hand according to the embodiment holds the article. 
       FIGS. 23A to 23C  illustrate the first operation.  FIG. 23D  illustrates the second operation. When the article is gripped, the first holder  1  contacts the upper surface of the article A and grips the upper surface as shown in  FIG. 23A . Then, as shown in  FIG. 23B , the second holder  2  is caused to contact the side surface of the article A by the operation of the cylinder  17   i . The second holder  2  grips the side surface. The holding device  170  holds the article A by the gripping of the upper surface and the side surface of the article A. 
     Continuing, the holding device  170  is raised. At this time, the cylinder  17   c   1  is extended by the weight of the first holder  1 , the second holder  2 , the article A, etc., when the cylinder  17   c   1  is released or the thrust due to the cylinder  17   c   1  is weak. Thereby, as shown in  FIG. 23C , the first holder  1  and the second holder  2  are tilted with respect to the X-Y plane in the state in which the article A is held. There is a possibility that the contents of the article A may be broken if the tilt is too large. Therefore, it is favorable for the tilt angle with respect to the X-Y plane to be greater than 0 degrees and less than 15 degrees. 
     For example, an adhesive for adhering a label, an adhesive of tape for packaging, etc., can be adhered to the upper surface of the article A. There are cases where the upper surface of another article A is stuck by the adhesive to the bottom surface of the article A that is held. By tilting, the article A that is held can be easily peeled from the other article A. Thereby, the friction between the other article A and the article A that is transferred can be reduced when transferring the article A. 
     As shown in  FIG. 23D , in the second operation, the holding device  170  also can grip the article A by attaching only the first holder  1  to the upper surface of the article A. At this time, the second holder  2  is positioned at the same level as the first holder or higher than at least a portion of the first holder  1 . Subsequently, similarly to  FIG. 23C , the first holder  1  may be tilted with respect to the X-Y plane in the state in which the article A is gripped. 
     According to the seventh modification, similarly to the holding device  100 , the first state in which the second holder  2  is at the first position and the second state in which the second holder  2  is at the second position can be switched. Therefore, the convenience of the holding device  170  can be improved. In the second state, similarly to the holding device  100 , the second holder  2  can be positioned higher than the first holder  1 . Thereby, the likelihood of interference with the other article A of the article A held by the second holder  2  can be further reduced. 
     Eighth Modification 
       FIG. 24  is a front view schematically illustrating a portion of a holding device according to an eighth modification of the embodiment. 
     The holding device  180  according to the eighth modification differs from the holding device  170  in that multiple first holders  1  and multiple second holders  2  are included as shown in  FIG. 24 . 
     Suction mechanisms  17   z  that each include the first holder  1 , the second holder  2 , the linear guide  17   d , the coupling frame  17   e , the fixing mechanism  17   f , the linear guide  17   g , the coupling plate  17   h , the cylinder  17   i , the linkage  17   k , and the drive mechanism  17   m  are located respectively at two side surfaces of the base  17   b . Thereby, the multiple first holders  1  and the multiple second holders  2  are arranged in the Y-direction. 
       FIGS. 25 and 26  are front views schematically showing states when the holding device according to the eighth modification of the embodiment holds articles. 
     The suction mechanisms  17   z  are mutually-independently movable. The cylinders  17   i  and  17   m   1  are independently operable for each suction mechanism  17   z . Therefore, as shown in  FIGS. 25 and 26 , the positions in the Z-direction of the first holders  1  may be different from each other. The positions in the X-Z plane of the second holders  2  may be different from each other. 
     As shown in  FIG. 25 , multiple suction mechanisms  17   z  may hold multiple articles A. As shown in  FIG. 26 , the multiple suction mechanisms  17   z  may grip one article A. As an example, the shapes of the gripped articles A are rectangular parallelepipeds as shown in  FIGS. 25 and 26 . The upper surface of the article A may be tilted with respect to the X-Y plane. As shown in  FIG. 26 , the article of which the upper surface is tilted can be stably gripped by the positions in the Z-direction of the suction mechanisms  17   z  changing according to the upper surface and by the suction pads  2   d  deforming according to the position of the upper surface. 
     According to the eighth modification, compared to the holding device  170 , diverse articles can be more stably held. The convenience of the holding device  180  can be further improved thereby. 
     The forms described above can be combined as appropriate as long as the first state and the second state can be switched. For example, the fourth modification may be combined with the third modification. For example, both the first holder  1  and the second holder  2  may be movable in the vertical direction. The coupler  15  may be included in the holding devices  100 ,  110 ,  130 ,  140 ,  150 ,  160 ,  170 , and  180  as in the holding device  120 . In the holding devices  100  to  140  and  160 , the tilts of the first and second holders  1  and  2  with respect to the X-direction may be changeable. 
     An example is described above in which the first holder  1  and the second holder  2  hold the article by suction. The first holder  1  and the second holder  2  may hold the article by clamping. For example, the first holder  1  clamps two ends of the upper surface of the article. The second holder  2  clamps two ends of the side surface of the article. In such a case as well, the convenience of the holding device can be improved by the structures of the first and second holders  1  and  2  described above. 
       FIG. 27  is a schematic view illustrating a hardware configuration. 
     For example, the controller  50  has the hardware configuration illustrated in  FIG. 27 . A processing device  90  illustrated in  FIG. 27  includes a CPU  91 , ROM  92 , RAM  93 , a memory device  94 , an input interface  95 , an output interface  96 , and a communication interface  97 . 
     The ROM  92  stores programs that control the operations of a computer. Programs that are necessary for causing the computer to realize the processing described above are stored in the ROM  92 . The RAM  93  functions as a memory region into which the programs stored in the ROM  92  are loaded. 
     The CPU  91  includes a processing circuit. The CPU  91  uses the RAM  93  as work memory to execute the programs stored in at least one of the ROM  92  or the memory device  94 . When executing the programs, the CPU  91  executes various processing by controlling configurations via a system bus  98 . 
     The memory device  94  stores data necessary for executing the programs and/or data obtained by executing the programs. 
     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 USB, etc. The CPU  91  can read various 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, an image output interface such as Digital Visual Interface (DVI), High-Definition Multimedia Interface (HDMI (registered trademark)), etc. The CPU  91  can transmit the 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 the processing device  90  and a server  97   a  that is outside the processing device  90 . The communication I/F  97  is, for example, a network card such as a LAN card, etc. The CPU  91  can read various data from the server  97   a  via the communication I/F  97 . A camera  99  images articles and stores the images in the server  97   a . The camera  99  functions as the detector  35 . 
     The memory device  94  includes not less than one selected from a hard disk drive (HDD) and a solid state drive (SSD). The input device  95   a  includes not less than one selected from a mouse, a keyboard, a microphone (audio input), and a touchpad. The output device  96   a  includes not less than one selected from a monitor and a projector. A device such as a touch panel that functions as both the input device  95   a  and the output device  96   a  may be used. 
     According to embodiments described above, a convenient holding device, cargo handling apparatus, or holding method can be 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.