Patent Publication Number: US-2023140538-A1

Title: Article gripping system

Description:
TECHNICAL FIELD 
     The present invention relates to an article gripping system. 
     BACKGROUND ART 
     As a weighing and distributing apparatus, for example, patent document 1 (JP-A No. H6-3182) discloses an apparatus having plural picking units each provided with a gripping means that grips and removes a portion of a product and a weighing means that records the weight of the portion of the product. 
     The apparatus further comprises a distribution means and a computer preprogrammed for a predetermined total weight, wherein the weighing means measures the weight of the product gripped by the gripping means and feeds it to a predetermined place. 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in the above apparatus, a region for gripping the product and a region for feeding the product are separately necessary, and the installation area of the apparatus becomes large and the amount of time from when it grips to when it feeds the product becomes long. 
     It is a problem of the present invention to provide an article gripping system that reduces the installation area of the apparatus and further shortens the amount of time from when it grips to when it feeds articles. 
     Solution to Problem 
     An article gripping system of a first aspect is an article gripping system that grips and discharges articles from an article group stored in a container, the article gripping system including plural gripping units, a drive unit, and a control unit. The gripping units grip the articles. The drive unit moves at least one of the container and the gripping units relative to the other. The control unit controls the drive unit to move at least one of the container and the gripping units. Moreover, the control unit switches the positional relationship between the container and a specific gripping unit between a first positional relationship and a second positional relationship. The first positional relationship is a positional relationship in which the container obstructs discharge of the articles gripped by the specific gripping unit. The second positional relationship is a positional relationship in which the container does not obstruct discharge of the articles gripped by the specific gripping unit. 
     In this article gripping system, for example, the container can also be moved to gripping positions of the gripping units, and in this case, the gripping units do not move while they are holding the articles, and the articles can be prevented from falling out of the gripping units. 
     An article gripping system of a second aspect is the article gripping system of the first aspect, wherein the drive unit includes a first horizontal moving mechanism. The first horizontal moving mechanism moves at least one of the container and the gripping units relative to the other in a first horizontal direction. 
     In this article gripping system, in a case where the plural gripping units are disposed in the horizontal direction, the position of the article group in the container and article gripping positions set for each of the gripping units can be aligned by the first horizontal moving mechanism. 
     An article gripping system of a third aspect is the article gripping system of the second aspect, wherein the drive unit further includes a second horizontal moving mechanism. The second horizontal moving mechanism moves at least one of the container and the gripping units relative to the other in a second horizontal direction different from the first horizontal direction. 
     In this article gripping system, in a case where the plural gripping units are disposed in the horizontal direction, the position of the article group in the container and article gripping positions set for each of the gripping units can be aligned by the second horizontal moving mechanism. 
     An article gripping system of a fourth aspect is the article gripping system of any one of the first aspect to the third aspect, wherein the drive unit further includes a vertical moving mechanism. The vertical moving mechanism moves at least one of the container and the gripping units relative to the other in a vertical direction. 
     In this article gripping system, in a case where the container is disposed away from the gripping units in the vertical direction, the position of the article group in the container and article gripping positions set for each of the gripping units can be aligned by the vertical moving mechanism. 
     An article gripping system of a fifth aspect is the article gripping system of the fourth aspect, wherein the control unit raises or lowers the container via the vertical moving mechanism. Moreover, when raising the container, the control unit finishes operating the first horizontal moving mechanism and the second horizontal moving mechanism before the container finishes rising. 
     In this article gripping system, when raising the container, the control unit finishes operating the first horizontal moving mechanism and the second horizontal moving mechanism before the container finishes rising, so the article group in the container is kept from ending up being shifted in either forward and backward or leftward and rightward directions. 
     An article gripping system of a sixth aspect is the article gripping system of any one of the first aspect to the fifth aspect, wherein the gripping units include plural claws. The plural claws are switched to at least either of a first state and a second state. The first state is a state in which the relative distance between the claws is decreased to a first distance so that the claws grip the articles. The second state is a state in which the relative distance between the claws is increased to a second distance greater than the first distance so that the claws release the articles. 
     An article gripping system of a seventh aspect is the article gripping system of the sixth aspect, wherein the control unit raises or lowers the container via the vertical moving mechanism. Moreover, when raising the container the control unit switches the plural claws to the second state before the container finishes rising. 
     In this article gripping system, when raising the container the control unit switches the claws to the second state (a state in which the claws are open) before the container finishes rising, so the articles in the container are kept from ending up being shifted in either forward and backward or leftward and rightward directions. 
     An article gripping system of an eighth aspect is the article gripping system of the seventh aspect, wherein the control unit switches the plural claws to the first state after it has raised the container. 
     In this article gripping system, the claws are switched to the first state (a state in which the claws are closed) in a state in which they are in the middle of the article group in the container, so the articles can be reliably held. 
     An article gripping system of a ninth aspect is the article gripping system of any one of the third aspect to the eighth aspect, wherein the second horizontal moving mechanism moves the gripping units in a second horizontal direction different from the first horizontal direction. 
     In this article gripping system, in the case of a type that moves the gripping units up and down, the gripping units need to weigh the articles after they grip hold of them and finish rising. In contrast, in the case of a type where the container moves upward, downward, leftward, and rightward and the gripping units move forward and backward, the gripping units can move in advance in forward and backward directions before gripping the articles and weigh the articles right after gripping hold of them. 
     An article gripping system of a tenth aspect is the article gripping system of any one of the fourth aspect to the ninth aspect, wherein the first horizontal moving mechanism moves the container and the vertical moving mechanism in the first horizontal direction. 
     In this article gripping system, the vertical moving mechanism does not need to raise and lower the first horizontal moving mechanism and need only raise and lower just the container, so the load when raising and lowering the container is mitigated. 
     An article gripping system of an eleventh aspect is the article gripping system of the tenth aspect, further including a discharge chute. The discharge chute has an inlet positioned lower than the container, receives, in the inlet, the articles released and dropped by the gripping units, and discharges them to a predetermined place. The first horizontal moving mechanism operates below the inlet of the discharge chute. 
     In this article gripping system, by avoiding disposing a sliding object (the first horizontal moving mechanism) in the space above the inlet of the discharge chute, contamination of the discharge chute is prevented. 
     An article gripping system of a twelfth aspect is the article gripping system of the eleventh aspect, wherein the vertical moving mechanism completely finishes moving the container in the vertical direction below the inlet of the discharge chute. 
     In this article gripping system, by avoiding disposing a sliding object (e.g., the vertical moving mechanism) in the space above the inlet of the discharge chute, contamination of the discharge chute is prevented. 
     An article gripping system of a thirteenth aspect is the article gripping system of any one of the first aspect to the twelfth aspect, wherein the plural gripping units include at least a first gripping unit and a second gripping unit. The control unit moves the article group in the container to a first gripping position where the first gripping unit grips the articles. Moreover, the control unit causes the first gripping unit to grip the articles and thereafter moves the article group in the container to a second gripping position where the second gripping unit grips the articles. 
     An article gripping system of a fourteenth aspect is the article gripping system of the thirteenth aspect, wherein the control unit moves the article group in the container to the second gripping position and thereafter causes the first gripping unit to release the articles and causes the second gripping unit to grip the articles from the article group in the container. 
     An article gripping system of a fifteenth aspect is the article gripping system of the fourteenth aspect, wherein the control unit interlinks the operation of causing the first gripping unit to release the articles and the operation of causing the second gripping unit to grip the articles. 
     Advantageous Effects of Invention 
     In this article gripping system, for example, the container can also be moved to the gripping positions of the gripping units, and in this case, the gripping units do not move while they are holding the articles, and the articles can be prevented from falling out of the gripping units. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1 A  is a front view of an article gripping system pertaining to an embodiment of the present invention. 
         FIG.  1 B  is a side view, when viewed from the right side, of the article gripping system of  FIG.  1 A . 
         FIG.  1 C  is a plan view, when viewed from directly above, of the article gripping system of  FIG.  1 A . 
         FIG.  1 D  is a bottom view, when viewed from directly below, of the article gripping system of  FIG.  1 A . 
         FIG.  2    is a block diagram of the article gripping system. 
         FIG.  3    is a schematic perspective view of a gripping unit. 
         FIG.  4 A  is a bottom view, as viewed from below, of gripping members of a gripper. 
         FIG.  4 B  is a bottom view, as viewed from below, of the gripping members of the gripper. 
         FIG.  4 C  is a bottom view, as viewed from below, of the gripping members of the gripper. 
         FIG.  5 A  is a front view of the article gripping system of  FIG.  1 A  when a container of the article gripping system has moved horizontally rightward. 
         FIG.  5 B  is a bottom view, when viewed from directly below, of the article gripping system of  FIG.  5 A . 
         FIG.  6    is a side view, when viewed from the right side, of the article gripping system of  FIG.  5 A  when the container of the article gripping system has moved vertically upward. 
         FIG.  7    is a timing diagram of operations of the article gripping system. 
         FIG.  8 A  is a flowchart of operations of the article gripping system. 
         FIG.  8 B  is a flowchart of operations of the article gripping system. 
         FIG.  8 C  is a flowchart of operations of the article gripping system. 
         FIG.  8 D  is a flowchart of operations of the article gripping system. 
         FIG.  8 E  is a flowchart of operations of the article gripping system. 
         FIG.  9    is a plan view showing an example of a forward and backward moving mechanism. 
         FIG.  10 A  is a front view showing an example of a container drive unit that houses a leftward and rightward moving mechanism. 
         FIG.  10 B  is a front view showing an example of the container drive unit that houses a vertical moving mechanism. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     An embodiment of the present invention will be described with reference to the drawings. The embodiment described below is a specific example of the present invention and is not intended to limit the technical scope of the present invention. 
     (1) Configuration of Article Gripping System  110   
       FIG.  1 A  is a front view of an article gripping system  110  pertaining to an embodiment of the present invention, and  FIG.  1 B  is a side view, when viewed from the right side, of the article gripping system  110  of  FIG.  1 A . Furthermore,  FIG.  1 C  is a plan view, when viewed from directly above, of the article gripping system  110  of  FIG.  1 A , and  FIG.  1 D  is a bottom view, when viewed from directly below, of the article gripping system  110  of  FIG.  1 A . 
     In  FIG.  1 A ,  FIG.  1 B , and  FIG.  2   , the article gripping system  110  is an apparatus that removes and discharges a portion of articles A from an article group A 1  that is a collection of the articles A. 
     Specifically, the article gripping system  110  removes from the article group A 1  and discharges a portion of the articles A so that their weight falls within a target weight range. The articles A discharged by the article gripping system  110  become packaged in bags or put into containers in a process after the article gripping system  110  and shipped as products. 
     The article gripping system  110  is provided with unit drive units  10 , gripping units  15 , a container  50 , a container drive unit  54 , discharge chutes  60 , and a control unit  70 . 
     The unit drive units  10  have the gripping units  15  attached to them. The gripping units  15  each have one or more gripping modules  20 . In each gripping module  20 , a gripper  30  that grips the articles A and a weigher  40  that measures the weight value of the articles A are integrally assembled. Each gripper  30  has gripping claws  30   a  serving as gripping members that grip the articles A. Furthermore, incorporated into each gripper  30  is a gripping member drive mechanism  30   b  that drives the gripping claws  30   a . The weigher  40  measures the weight value of the articles A gripped by the gripper  30 . 
     The container  50  contains the article group A 1 . The articles A are, for example, a sticky food, such as spaghetti or other noodles or foods containing a lot of sugar. 
     The container  50  is moved by the container drive unit  54  between a first position where the grippers  30  grip the articles A in the article group A 1  placed in the container  50  and a second position where the grippers  30  do not grip the articles A from the article group A 1  placed in the container  50 . The discharge chutes  60  receive and discharge the articles A released by the grippers  30 . 
       FIG.  2    is a block diagram of the article gripping system  110 . In  FIG.  2   , the control unit  70  performs control of the operations of various configurations of the article gripping system  110 , including the container drive unit  54  and the gripping member drive mechanisms  30   b , and combination calculations utilizing the weight values of the articles A weighed by the weighers  40 . 
     The control unit  70  moves the unit drive units  10  and the container  50  to move the grippers  30  and the container  50  having the article group A 1  placed therein closer to each other. The control unit  70  controls the gripping member drive mechanisms  30   b  of the grippers  30  to cause the gripping claws  30   a  of the grippers  30  to grip a portion of the articles A in the article group A 1  placed in the container  50 . 
     The weighers  40  measure the weight values of the articles A gripped by the grippers  30  corresponding to those weighers  40 . The control unit  70  performs a combination calculation based on the weight values of the articles A gripped by the grippers  30  and weighed by the weighers  40 . 
     The combination calculation is a process for finding a combination of weight values whose total value falls within a target weight range as a result of adding together the weight values of the articles A gripped by the grippers  30 . The control unit  70 , based on the result of the combination calculation, causes the gripping claws  30   a  of the grippers  30  corresponding to the combination of the weight values falling within the target weight range to release the articles A over the discharge chutes  60  and discharges from the discharge chutes  60  the articles A in the target weight range. 
     (2) Detailed Configurations 
       FIG.  3    is a schematic perspective view of a gripping unit  15 .  FIG.  4 A  and  FIG.  4 B  are bottom views, as viewed from below, of the gripping claws  30   a  of a gripper  30 . The unit drive units  10  and the gripping units  15  will be described below using  FIG.  1 A ,  FIG.  1 B ,  FIG.  3   ,  FIG.  4 A , and  FIG.  4 B . 
     (2-1) Unit Drive Units  10   
     As shown in  FIG.  1 A , the article gripping system  110  includes two unit drive units  10 . The unit drive unit  10  on the left side as viewed head-on in  FIG.  1 A  will be called a first unit drive unit  10 A, and the unit drive unit  10  on the right side as viewed head-on in  FIG.  1 A  will be called a second unit drive unit  10 B. However, when describing shared configurations and functions, they will simply be called the unit drive units  10 . 
     The unit drive units  10  each have two frames  12  that extend parallel to each other and a forward and backward moving mechanism  11  that horizontally moves the gripping unit  15  along the frames  12 . As shown in  FIG.  1 B , the unit drive units  10  can, using the forward and backward moving mechanisms  11 , cause blocks  111  that hold the gripping units  15  to move in the direction of arrow D 1  (forward) or arrow D 2  (backward). The unit drive units  10  each have a servo motor  113  (see  FIG.  9   ) that moves the block  111 . 
     In this way, in the article gripping system  110 , the first gripping unit  15 A and the second gripping unit  15 B are disposed in the horizontal direction, the first gripping unit  15 A can be horizontally moved in forward and backward directions by the first unit drive unit  10 A, and the second gripping unit  15 B can be horizontally moved in forward and backward directions by the second unit drive unit  10 B, so that the position of the article group in the container  50  and article gripping positions set for each of the gripping units  15  can be aligned. 
     Furthermore, instead of a servo motor, the unit drive units  10  may also each have an air cylinder capable of moving the block  111  in the direction of arrow D 1  or arrow D 2 . 
     (2-2) Gripping Units  15   
     As shown in  FIG.  1 A , the article gripping system  110  includes two gripping units  15 . The gripping unit  15  on the left side as viewed head-on in  FIG.  1 A  will be called a first gripping unit  15 A, and the gripping unit  15  on the right side as viewed head-on in  FIG.  1 A  will be called a second gripping unit  15 B. However, when describing shared configurations and functions, they will simply be called the gripping units  15 . 
     The gripping units  15  each include a tabular coupling member  16  coupled to the block  111  of the unit drive unit  10  and one or more gripping modules  20 . 
     (2-2-1) Coupling Member  16   
     The coupling member  16  is coupled to the block  111  of the unit drive unit  10  by screws, for example. 
     (2-2-2) Gripping Module  20   
     As shown in  FIG.  3   , the gripping module  20  is a device in which the gripper  30  and the weigher  40  are integrally assembled. The top surface of the weigher  40  is secured to the coupling member  16  via a mounting bracket  400 , and the bottom surface of the weigher  40  has the gripper  30  secured to it. 
     (2-2-2-1) Gripper  30   
     The gripper  30  is a device that grips the articles A. Each gripper  30  has the gripping claws  30   a  and the gripping member drive mechanism  30   b  serving as a drive mechanism that drives the gripping claws  30   a . The gripping member drive mechanism  30   b  drives the gripping claws  30   a  using, for example, a motor or fluid pressure as a drive source. 
     In the present embodiment, as shown in  FIG.  3   , the gripping claws  30   a  are each formed by bending the distal end of a rod-like or finger-like member inward so that it can catch onto the articles A. Each gripper  30  has a plurality (e.g., three) of the gripping claws  30   a . It will be noted that the number and shape of the gripping claws  30   a  shown in  FIG.  3   , etc., are merely illustrative and can be appropriately changed. 
     As shown in  FIG.  4 A  and  FIG.  4 B , when each gripper  30  is viewed from the gripping claw  30 A side, the plural gripping claws  30   a  are arranged along a circumferential direction. Furthermore, when each gripper  30  is viewed from the gripping claw  30   a  side, the plural gripping claws  30   a  are arranged at generally regular intervals in the circumferential direction. Moreover, when each gripper  30  is viewed from the gripping claw  30   a  side, the gripping claws  30   a  are movable in a radial direction. 
     Furthermore, each gripper  30  holds and grips the articles A between the plural gripping claws  30 A by using the gripping member drive mechanism  30   b  to move the gripping claws  30 A that are away from each other inward in the radial direction so that they are close to each other. 
     Moreover, each gripper  30  releases the articles A by using the gripping member drive mechanism  30   b  to move the gripping claws  30   a  that are close to each other outward in the radial direction so that they are away from each other. 
     In other words, the plural gripping claws  30   a  of the gripping units  15  are switched to at least either of a first state and a second state. The first state is a state in which the relative distance between the gripping claws  30   a  is decreased to a first distance so that the gripping claws  30   a  grip the articles. The second state is a state in which the relative distance between the gripping claws  30   a  is increased to a second distance greater than the first distance so that the gripping claws  30   a  release the articles. 
     However, in a case where a gripping force limiting function is provided so that the articles A are not crushed by the gripping claws  30   a  or for the purpose of overload protection, the gripping claws  30   a  stop due to external force from the articles A before the relative distance between the gripping claws  30   a  is decreased to the first distance. Therefore, the first state does not invariably need to be a “state in which the relative distance between the gripping claws  30   a  is decreased to a first distance, and the first state may also be a state in which the relative distance between the gripping claws  30   a  is decreased to a distance at which the gripping claws  30   a  are able to grip the articles A. 
     (2-2-2-2) Weigher  40   
     Each gripping module  20  is provided with one weigher  40  for each gripper  30 . The weigher  40  measures the weight value of the articles A being gripped by the gripping claws  30   a  of the corresponding gripper  30 . 
     Each weigher  40  includes a sensor unit  40   a  (see  FIG.  3   ) and an internal control unit not shown in the drawings. The sensor unit  40   a  includes a force sensor and an acceleration sensor. As the force sensor, for example, a strain gauge load cell is employed. As the acceleration sensor, for example, a strain gauge load cell or a MEMS small acceleration sensor is used. 
     The internal control unit of the weigher  40  measures the mass of the articles A being gripped by the gripper  30  based on force and acceleration measured by the sensor unit  40   a  when the gripper  30  gripping the articles A is moved in accompaniment with the movement of the unit drive unit  10 . Specifically, the internal control unit of the weigher  40  measures the mass of the articles A being gripped by the gripper  30  by dividing the force measured by the force sensor by the acceleration measured by the acceleration sensor. 
     However, the weigher  40  is not limited to a method that weighs the mass of the articles A based on force and acceleration measured when the gripper  30  is moved. The weigher  40  may also be one that uses a load cell or the like to measure the weight of the articles A being gripped by the gripper  30  in a stationary state. 
     (2-3) Container  50   
     The container  50  contains the article group A 1 . As for the container  50 , the container  50  is placed on a placement surface  52  that moves horizontally and moves vertically. 
     The grippers  30  grip a portion of the articles A from the article group A 1  contained in the container  50 . In the present embodiment, the container  50  is a cuboidal container whose top is open. The container  50  is configured in such a way that when the quantity of the articles A contained inside decreases, a human or a machine can replace the container  50  in which the quantity of the articles A inside has decreased with a container  50  that is new (that contains many articles A). 
     It will be noted that instead of configuring the container to be replaceable, the container  50  may also have an article supply mechanism for supplying the articles A to the container  50 . 
     The container  50  is moved by the container drive unit  54  between a first position and a second position. 
     The first position is a position directly below the grippers  30  of the first gripping unit  15 A and is a position where the grippers  30  of the first gripping unit  15 A can grip the articles A in the container  50 . When the container  50  is in the first position, the grippers  30  of the second gripping unit  15 B cannot grip the articles A in the container  50 . 
     The second position of the container  50  is a position directly below the grippers  30  of the second gripping unit  15 B and is a position where the grippers  30  of the second gripping unit  15 B can grip the articles A in the container  50 . When the container  50  is in the second position, the grippers  30  of the first gripping unit  15 A cannot grip the articles A in the container  50 . 
     (2-4) Container Drive Unit  54   
       FIG.  5 A  is a front view of the article gripping system  110  of  FIG.  1 A  when the container  50  of the article gripping system  110  has moved horizontally rightward.  FIG.  5 B  is a bottom view, when viewed from directly below, of the article gripping system  110  of  FIG.  5 A . 
     In  FIG.  5 A  and  FIG.  5 B , the container drive unit  54  can horizontally move the container  50  using a motor or fluid pressure as a drive source. 
     As shown in  FIG.  1 A ,  FIG.  1 B ,  FIG.  5 A , and  FIG.  5 B , the container drive unit  54  has two cuboidal drivers  540 . When the near side as viewed head-on in  FIG.  1 A  is taken as the front, the driver located in front of the two discharge chutes  60  is a first driver  541  and the driver located in back of the two discharge chutes  60  is a second driver  542 . 
     Furthermore, as shown in  FIG.  1 A  and  FIG.  1 B , two horizontal supports are provided one above the other and parallel to each other in front of the two discharge chutes  60 , and two horizontal supports are also provided one above the other and parallel to each other in back. As viewed head-on in  FIG.  1 B , the support on the lower left side is a first horizontal support  551 , followed clockwise by a second horizontal support  552 , a third horizontal support  553 , and a fourth horizontal support  554 . Consequently, the horizontal support on the lower side as viewed head-on in  FIG.  1 A  is the first horizontal support  551  and the horizontal support on the upper side is the second horizontal support  552 . 
     The first driver  541  of the container drive unit  54  has a leftward and rightward moving mechanism  56  (see  FIG.  10 A  and  FIG.  10 B ) and can horizontally move along the first horizontal support  551  and the second horizontal support  552 . Furthermore, the second driver  542  of the container drive unit  54  also has a leftward and rightward moving mechanism  56  and can horizontally move along the third horizontal support  553  and the fourth horizontal support  554 . The first driver  541  and the second driver  542  move in synchronization with each other. 
     In this way, in the article gripping system  110 , the first gripping unit  15 A and the second gripping unit  15 B are disposed in the horizontal direction, the container  50  can be horizontally moved in leftward and rightward directions by the leftward and rightward moving mechanisms  56 , so the position of the article group A 1  in the container  50  and the article gripping positions set for each of the gripping units  15  can be aligned. 
       FIG.  6    is a side view of the article gripping system  110  of  FIG.  5 A  when the container  50  of the article gripping system  110  has moved vertically upward. In  FIG.  6   , the container drive unit  54  can vertically move the container  50  using a motor or fluid pressure as a drive source. 
     As shown in  FIG.  1 A ,  FIG.  1 B , and  FIG.  1 D , the placement surface  52  has four vertical supports that extend vertically downward from the four corners of its undersurface. As viewed head-on in  FIG.  1 D , the support on the upper left side is a first vertical support  521 , followed clockwise by a second vertical support  522 , a third vertical support  523 , and a fourth vertical support  524 . Consequently, the support on the left side as viewed head-on in  FIG.  1 A  is the first vertical support  521  and the support on the right side is the second vertical support  522 . Furthermore, the support on the right side as viewed head-on in  FIG.  1 B  is the third vertical support  523 . 
     The first driver  541  has a vertical moving mechanism  57  ( FIG.  10 A  and  FIG.  10 B ), and the first vertical support  521  and the second vertical support  522  can be moved in the vertical direction. Furthermore, the second driver  542  also has a vertical moving mechanism  57 , and the third vertical support  523  and the fourth vertical support  524  can be moved in the vertical direction. The first driver  541  and the second driver  542  can cause the first vertical support  521  and second vertical support  522  and the third vertical support  523  and fourth vertical support  524  to move in synchronization with each other in the vertical direction. 
     In this way, in the article gripping system  110 , the container  50  can be moved in upward and downward directions by the vertical moving mechanisms  57 , so even in a case where the container  50  is disposed away from the gripping units  15  in the vertical direction, the position of the article group A 1  in the container  50  and the article gripping positions set for each of the gripping units  15  can be aligned. 
     Furthermore, in the article gripping system  110 , the vertical moving mechanisms  57  do not need to raise and lower the leftward and rightward moving mechanisms  56  and need only raise and lower just the container  50 , so the load when raising and lowering the container  50  is mitigated. 
     Moreover, in the article holding system  110 , the leftward and rightward moving mechanisms  56  are not disposed in the space above the inlets of the discharge chutes  60 , so contamination of the discharge chutes  60  is avoided. Likewise, the vertical moving mechanisms  57  are not disposed in the space above the inlets of the discharge chutes  60 , so contamination of the discharge chutes  60  is avoided. 
     It will be noted that, as a contamination prevention measure, it is also possible to provide a cover for countering contamination and dispose it above the discharge chutes  60 , in addition to the configuration described above where the leftward and rightward moving mechanisms  56  and the vertical moving mechanisms  57  are not disposed in the space above the inlets of the discharge chutes  60 . 
     (2-5) Discharge Chutes  60   
     As shown in  FIG.  1 A , the article gripping system  110  includes two discharge chutes  60 . The discharge chute  60  on the left side as viewed head-on in  FIG.  1 A  will be called a first discharge chute  60 A, and the discharge chute  60  on the right side as viewed head-on in  FIG.  1 A  will be called a second discharge chute  60 B. However, when describing shared configurations and functions, they will simply be called the discharge chutes  60 . 
     The discharge chutes  60  are funnel-shaped members. The discharge chutes  60  are disposed directly below the gripping units  15 . Specifically, the first discharge chute  60 A is disposed directly below the first gripping unit  15 A, and the second discharge chute  60 B is disposed directly below the second gripping unit  15 B. 
     The container  50  is disposed between the first gripping unit  15 A and the first discharge chute  60 A or between the second gripping unit  15 B and the second discharge chute  60 B. 
     When the container  50  is positioned between the second gripping unit  15 B and the second discharge chute  60 B, the first discharge chute  60 A receives, and discharges outside the article gripping system  110 , the articles A released and dropped by the grippers  30  of the first gripping unit  15 A. 
     Likewise, when the container  50  is positioned between the first gripping unit  15 A and the first discharge chute  60 A, the second discharge chute  60 B receives, and discharges outside the article gripping system  110 , the articles A released and dropped by the grippers  30  of the second gripping unit  15 B. 
     Although in the present embodiment the article gripping system  110  uses two discharge chutes, it is not limited to this, and the first gripping unit  15 A and the second discharge unit  15 B sometimes also share one discharge chute. Furthermore, it is also possible to discharge the articles A directly to the outside without using discharge chutes. 
     (2-6) Control Unit  70   
     The control unit  70  has a CPU and memories such as a ROM and a RAM that are not shown in the drawings. As shown in  FIG.  2   , the control unit  70  is electrically connected to the unit drive units  10 , the gripping member drive mechanisms  30   b , the weighers  40 , and the container drive unit  54 . 
     The control unit  70 , as a result of the CPU executing programs stored in the memories, performs control of the operations of various configurations of the article holding system  110 , such as the unit drive units  10 , the gripping member drive mechanisms  30   b , and the container drive unit  54 , and combination calculations utilizing the weight values of the articles A weighed by the weighers  40 . 
     It will be noted that the various functions of the control unit  70  do not need to be realized by software and, even when they are realized by hardware, may also be realized by the cooperation of hardware and software. 
     The control unit  70  drives the gripping claws  30   a  via the gripping member drive mechanisms  30   b , causes the gripping claws  30   a  to grip the articles A, and thereafter causes the gripping claws  30   a  to release the articles A. Here, “to grip” means that the plural gripping claws  30   a  that are in positions away from each other such as shown in  FIG.  4 A  move inward in the radial direction to positions close to each other such as shown in  FIG.  4 B , and “to release” means that after gripping the articles A the gripping claws  30   a  return again to positions away from each other such as shown in  FIG.  4 A . 
     (3) Operation of Article Gripping System 
     The operation of the article gripping system  110  controlled by the control unit  70  will be described with reference to the drawings. It will be noted that although here gripping units  15  each having a plurality of gripping modules  20  are described as an example, the description can also be applied to gripping units  15  each including a single gripping module  20 . 
       FIG.  7    is a timing diagram of operations of the article gripping system  110 . Furthermore,  FIG.  8 A  to  FIG.  8 E  are flowcharts of operations of the article gripping system  110 . 
     In  FIG.  7   , the uppermost timing diagram shows the position, in the up and down direction, of the container  50 . The timing diagram that is second from the top shows the position, in the left and right direction, of the container  50  as viewed head-on in  FIG.  5 A . 
     The timing diagram that is third from the top shows the position, in the front and rear direction, of the first gripping unit  15 A, with the near side as viewed head-on in  FIG.  5 A  being taken as the front. The timing diagram that is fourth from the top shows the open and closed states of the first gripping unit  15 A. The timing diagram that is fifth from the top shows the position, in the front and rear direction, of the second gripping unit  15 B. The timing diagram that is sixth from the top shows the open and closed states of the second gripping unit  15 B. 
     In  FIG.  7   , the left side of time t 0  is a state in which operation is stopped, and is the state shown in  FIG.  5 A . Time t 0  is the point in time when the first gripping unit  15 A starts moving forward and the container  50  starts moving leftward. 
     (Step S 1 ) 
     First, the control unit  70  judges whether or not there is a command to start operating, and proceeds to step S 2  when there is a command to start operating. 
     (Step S 2 ) 
     Next, the control unit  70  performs an initial operation. Because of the initial operation, the first gripping unit  15 A and the second gripping unit  15 B are moved to unit initial positions shown in  FIG.  1 B . Furthermore, because of the initial operation, the gripping claws  30   a  of the grippers  30  switch to an initial state in which they close as far as the position of a virtual circle C 1  shown in  FIG.  4 C . Moreover, because of the initial operation, the container  50  moves to a container initial position shown in  FIG.  5 A . 
     The control unit  70  performs the initial operation for a fixed amount of time even if the first gripping unit  15 A and the second gripping unit  15 B are right from the start in the unit initial positions and even if the gripping claws  30   a  are right from the start in the initial state and even if the container  50  is right from the start in the container initial position. When the initial operation is completed, the control unit  70  proceeds to step S 3 . 
     (Step S 3 ) 
     Next, the control unit  70  starts counting time with a timer and at the same time moves the first gripping unit  15 A forward, switches the gripping claws  30   a  of the grippers  30  from the initial state to a second state (an open state), and moves the container  50  leftward. The control unit  70  marks this point in time as t 0 . 
     (Step S 4 ) 
     Next, when t 1  seconds elapse since t 0 , the control unit  70  stops moving the first gripping unit  15 A forward and stops moving the container  50  leftward. 
     At this time, the container  50  is positioned below the first gripping unit  15 A. Furthermore, as viewed from the container  50 , the first gripping unit  15 A is entirely positioned above a region offset toward the front side of the inside of the container  50 . 
     (Step S 5 ) 
     Next, the control unit  70  raises the container  50 . At this time, the control unit  70  causes the second gripping unit  15 B to perform a discharge operation, but the first time is an empty discharge. In the timing diagram of  FIG.  7   , the container  50  moves upward at the same time as time t 1  when it stops moving leftward. However, the control unit  70  may also start moving the container  50  upward between time t 0  and time t 1 . 
     At this time, the control unit  70  performs an operation to switch the state of the gripping claws  30   a  of the second gripping unit  15 B to the second state (an open state) and release the articles A. This is because it is necessary to discharge here the articles A that were finally gripped by the second gripping unit  15 B, because the flow of this operation cycles from step S 3  to step S 49  as one cycle. 
     (Step S 6 ) 
     Next, when t 2  seconds elapse since t 0 , the control unit  70  stops raising the container  50 . At this time, the container  50  reaches a position directly below the first gripping unit  15 A where the gripping claws  30   a  of the grippers  30  can grip the articles A in the container  50 . In this position, the gripping claws  30   a  are in the article group A 1  in the container  50 , and at the same time the gripping claws  30   a  return to the initial state. 
     Here, in the article gripping system  110 , the control unit  70  finishes moving the container  50  leftward or rightward and moving the unit drive units  10  forward or backward before the container  50  finishes rising, so the article group A 1  in the container  50  is kept from ending up being shifted in either forward and backward or leftward and rightward directions. 
     Furthermore, in the article gripping system  110 , the control unit  70  switches the gripping claws  30   a  to the second state (an open state in which the gripping claws  30   a  are open) before the container  50  finishes rising, so the articles A in the container  50  are kept from ending up being shifted to the outer sides of the gripping claws  30   a.    
     (Step S 7 ) 
     Next, when t 3  seconds elapse since t 0 , the control unit  70  switches the gripping claws  30   a  from the initial state to the first state (a closed state) to cause the gripping claws  30   a  to grip the articles A. 
     In this way, in the article gripping system  110 , the gripping claws  30   a  are switched to the first state (a closed state in which the gripping claws  30   a  are closed) in a state in which the gripping claws  30   a  are in the middle of the article group A 1  in the container  50 , so the articles A can be reliably held. 
     Preferably, the control unit  70  causes the plural grippers  30  to grip the articles A at the same time. However, the control unit  70  is not limited to this and may also cause the plural grippers  30  to grip the articles A at different timings. 
     (Step S 8 ) 
     Next, when t 4  seconds elapse since t 0 , the control unit  70  lowers the container  50  while maintaining the state in which the plural grippers  30  are gripping the articles A. 
     (Step S 9 ) 
     Next, when t 5  seconds elapse since t 0 , the control unit  70  moves the first gripping unit  15 A backward. The gripping claws  30   a  and the article group A 1  in the container  50  are away from each other as a result of the container  50  moving downward a predetermined distance between time t 4  and time t 5 , so even when the first gripping unit  15 A moves backward, the articles A gripped by the gripping claws  30   a  and the article group A 1  in the container  50  do not interfere with each other. 
     (Step S 10 ) 
     Next, the control unit  70  measures the weights of the articles A gripped by the grippers  30  corresponding to the weighers  40  of the first gripping unit  15 A. 
     In this way, because the article gripping system  110  is a type where the container  50  moves upward, downward, leftward, and rightward and the gripping units  15  move forward and backward, the gripping units  15  can move in advance in forward and backward directions before gripping the articles A and weigh the articles A right after gripping hold of them. 
     (Step S 11 ) 
     Next, the control unit  70  determines whether or not at least one of the weighing results of the weighers  40  meets a predetermined condition for returning the articles A gripped by the grippers  30  to the container  50  without discharging them to the discharge chute  60 . 
     Here, the predetermined condition specifically is a condition where the weight values of the articles A weighed by the weighers  40  are not a preset target weight value. In the case of combination weighing utilizing the weight values of the articles A weighed by the weighers  40 , as a result of the combination calculation the weight values of the articles A gripped by the grippers  30  that will not participate in discharge are also not the target weight value and meet the predetermined condition. 
     The control unit  70  moves to step S 17  when it determines that none of the weighing results of the weighers  40  meet the predetermined condition. 
     (Step S 12 ) 
     Next, the control unit  70  controls the gripping member drive mechanisms  30   b  of the grippers  30  meeting the predetermined condition to cause those grippers  30  to release the articles A. 
     In other words, if there are grippers  30  gripping articles A whose weight values are not the target weight value, the control unit  70  causes those grippers  30  to release the articles A and drop the articles A into the container  50 . The articles A that have dropped into the container  50  are reutilized as the articles A in the article group A 1 . 
     Meanwhile, the control unit  70  causes the grippers  30  gripping the articles A whose weight values are the target weight value to maintain their grip. 
     (Step S 13 ) 
     Next, when t 6  seconds elapse since t 0 , the control unit  70  stops lowering the container  50  and at the same time moves the container  50  rightward. 
     (Step S 14 ) 
     Next, when t 7  seconds elapse since t 0 , the control unit  70  moves the second gripping unit  15 B forward and switches the gripping claws  30   a  of the grippers  30  from the initial state to the second state (an open state). The control unit  70  continues to move the container  50  rightward. 
     (Step S 15 ) 
     Next, when t 8  seconds elapse since t 0 , the control unit  70  stops moving the second gripping unit  15 B forward and stops moving the container  50  rightward. 
     At this time, the container  50  is positioned below the second gripping unit  15 B. Furthermore, as viewed from the container  50 , the second gripping unit  15 B is entirely positioned above a region offset toward the front side of the inside of the container  50 . 
     (Step S 16 ) 
     Next, the control unit  70  raises the container  50 . In the timing diagram of  FIG.  7   , the container  50  moves upward at the same time as time t 8  when it stops moving rightward. However, the control unit  70  may also start moving the container  50  upward between time t 7  and time t 8 . 
     (Step S 17 ) 
     Next, when t 9  seconds elapse since t 0 , the control unit  70  switches the gripping claws  30   a  of the first gripping unit  15 A that are gripping the articles A whose weight values were the target weight value in prior step S 12  from the first state (a closed state) to the second state (an open state) to cause the gripping claws  30   a  of the first gripping unit  15 A to release the articles A and discharge the articles A to the first discharge chute  60 A below. 
     In this way, the positional relationship between the gripping units  15  and the container  50  is a second positional relationship in which the container  50  obstructs discharge of the articles gripped by the second gripping unit  15 B but does not obstruct discharge of the articles gripped by the first gripping unit  15 A. 
     (Step S 18 ) 
     Next, when t 10  seconds elapse since t 0 , the control unit  70  stops raising the container  50 . At this time, the container  50  reaches a position directly below the second gripping unit  15 B where the gripping claws  30   a  of the grippers  30  can grip the articles A in the container  50 . In this position, the gripping claws  30   a  are in the article group A 1  in the container  50 , and at the same time the gripping claws  30   a  return to the initial state. 
     Here also, the control unit  70  finishes moving the container  50  leftward or rightward and moving the unit drive units  10  forward or backward before the container  50  finishes rising, so the article group A 1  in the container  50  is kept from ending up being shifted in either forward and backward or leftward and rightward directions. 
     Furthermore, the control unit  70  switches the gripping claws  30   a  to the second state (an open state in which the gripping claws  30   a  are open) before the container  50  finishes rising, so the articles A in the container  50  can be kept from ending up being shifted to the outer sides of the gripping claws  30   a.    
     (Step S 19 ) 
     Next, when t 11  seconds elapse since t 0 , the control unit  70  switches the gripping claws  30   a  of the second gripping unit  15 B from the initial state to the first state (a closed state) to cause the gripping claws  30   a  to grip the articles A. 
     In this way, in the article gripping system  110 , the gripping claws  30   a  are switched to the first state (a closed state in which the gripping claws  30   a  are closed) in a state in which the gripping claws  30   a  are in the middle of the article group A 1  in the container  50 , so the articles A can be reliably held. 
     (Step S 20 ) 
     Next, when t 12  seconds elapse since t 0 , the control unit  70  lowers the container  50  while maintaining the state in which the plural grippers  30  of the second gripping unit  15 B are gripping the articles A. 
     (Step S 21 ) 
     Next, when t 13  seconds elapse since to, the control unit  70  moves the second gripping unit  15 B backward. The gripping claws  30   a  and the article group A 1  in the container  50  are away from each other as a result of the container  50  moving downward a predetermined distance between time t 12  and time t 13 , so even when the second gripping unit  15 B moves backward, the articles A gripped by the gripping claws  30   a  and the article group A 1  in the container  50  do not interfere with each other. 
     (Step S 22 ) 
     Next, the control unit  70  measures the weights of the articles A gripped by the grippers  30  corresponding to the weighers  40  of the second gripping unit  15 B. In this way, because the article gripping system  110  is a type where the container  50  moves upward, downward, leftward, and rightward and the gripping units  15  move forward and backward, the gripping units  15  can move in advance in forward and backward directions before gripping the articles A and weigh the articles A right after gripping hold of them. 
     (Step S 23 ) 
     Next, the control unit  70  determines whether or not at least one of the weighing results of the weighers  40  meets a predetermined condition for returning the articles A gripped by the grippers  30  to the container  50  without discharging them to the discharge chute  60 . 
     The predetermined condition specifically is a condition where the weight values of the articles A weighed by the weighers  40  are not a preset target weight value. 
     The control unit  70  moves to step S 29  when it determines that none of the weighing results of the weighers  40  meet the predetermined condition. 
     (Step S 24 ) 
     Next, the control unit  70  controls the gripping member drive mechanisms  30   b  of the grippers  30  meeting the predetermined condition to cause those grippers  30  to release the articles A. 
     In other words, if there are grippers  30  gripping articles A whose weight values are not the target weight value, the control unit  70  causes those grippers  30  to release the articles A and drop the articles A into the container  50 . The articles A that have dropped into the container  50  are reutilized as the articles A in the article group A 1 . 
     Meanwhile, the control unit  70  causes the grippers  30  gripping the articles A whose weight values are the target weight value to maintain their grip. 
     (Step S 25 ) 
     Next, when t 14  seconds elapse since t 0 , the control unit  70  stops lowering the container  50  and at the same time moves the container  50  leftward. 
     (Step S 26 ) 
     Next, when t 15  seconds elapse since t 0 , the control unit  70  moves the first gripping unit  15 A backward. The control unit  70  continues to move the container  50  leftward. 
     (Step S 27 ) 
     Next, when t 16  seconds elapse since t 0 , the control unit  70  stops moving the first gripping unit  15 A backward and stops moving the container  50  leftward. 
     At this time, the container  50  is positioned below the first gripping unit  15 A. Furthermore, as viewed from the container  50 , the first gripping unit  15 A is entirely positioned above a region offset toward the rear side of the inside of the container  50 . 
     (Step S 28 ) 
     Next, the control unit  70  raises the container  50 . In the timing diagram of  FIG.  7   , the container  50  moves upward at the same time as time t 16  when it stops moving rightward. However, the control unit  70  may also start moving the container  50  upward between time t 15  and time t 16 . 
     (Step S 29 ) 
     Next, when t 17  seconds elapse since t 0 , the control unit  70  switches the state of the gripping claws  30   a  of the second gripping unit  15 B that are gripping the articles A whose weight values were the target weight value in prior step S 24  from the first state (a closed state) to the second state (an open state) to cause the gripping claws  30   a  of the second gripping unit  15 B to release the articles A and discharge the articles A to the second discharge chute  60 B below. 
     In this way, the positional relationship between the gripping units  15  and the container  50  is a first positional relationship in which the container  50  obstructs discharge of the articles gripped by the first gripping unit  15 A but does not obstruct discharge of the articles gripped by the second gripping unit  15 B. 
     (Step S 30 ) 
     Next, when t 18  seconds elapse since t 0 , the control unit  70  stops raising the container  50 . At this time, the container  50  reaches a position directly below the first gripping unit  15 A where the gripping claws  30   a  of the grippers  30  can grip the articles A in the container  50 . In this position, the gripping claws  30   a  are in the article group A 1  in the container  50 , and at the same time the gripping claws  30   a  return to the initial state. 
     Here also, the control unit  70  finishes moving the container  50  leftward or rightward and moving the unit drive units  10  forward or backward before the container  50  finishes rising, so the article group A 1  in the container  50  is kept from ending up being shifted in either forward and backward or leftward and rightward directions. 
     Furthermore, the control unit  70  switches the gripping claws  30   a  to the second state (an open state in which the gripping claws  30   a  are open) before the container  50  finishes rising, so the articles A in the container  50  are kept from ending up being shifted to the outer sides of the gripping claws  30   a.    
     (Step S 31 ) 
     Next, when t 19  seconds elapse since t 0 , the control unit  70  switches the gripping claws  30   a  of the first gripping unit  15 A from the initial state to the first state (a closed state) to cause the gripping claws  30   a  to grip the articles A. 
     In this way, in the article gripping system  110 , the gripping claws  30   a  are switched to the first state (a closed state in which the gripping claws  30   a  are closed) in a state in which the gripping claws  30   a  are in the middle of the article group A 1  in the container  50 , so the articles A can be reliably held. 
     (Step S 32 ) 
     Next, when t 20  seconds elapse since t 0 , the control unit  70  lowers the container  50  while maintaining the state in which the plural grippers  30  are gripping the articles A. 
     (Step S 33 ) 
     Next, when t 21  seconds elapse since t 0 , the control unit  70  moves the first gripping unit  15 A forward. The gripping claws  30   a  and the article group A 1  in the container  50  are away from each other as a result of the container  50  moving downward a predetermined distance between time t 20  and time t 21 , so even when the first gripping unit  15 A moves forward, the articles A gripped by the gripping claws  30   a  and the article group A 1  in the container  50  do not interfere with each other. 
     (Step S 34 ) 
     Next, the control unit  70  measures the weights of the articles gripped by the grippers  30  corresponding to the weighers  40  of the first gripping unit  15 A. In this way, because the article gripping system  110  is a type where the container  50  moves upward, downward, leftward, and rightward and the gripping units  15  move forward and backward, the gripping units  15  can move in advance in forward and backward directions before gripping the articles A and weigh the articles A right after gripping hold of them. 
     (Step S 35 ) 
     Next, the control unit  70  determines whether or not at least one of the weighing results of the weighers  40  meets a predetermined condition for returning the articles A gripped by the grippers  30  to the container  50  without discharging them to the discharge chute  60 . 
     Here, the predetermined condition specifically is a condition where the weight values of the articles A weighed by the weighers  40  are not a preset target weight value. 
     The control unit  70  proceeds to step S 41  when it determines that none of the weighing results of the weighers  40  meet the predetermined condition. 
     (Step S 36 ) 
     Next, the control unit  70  controls the gripping member drive mechanisms  30   b  of the grippers  30  meeting the predetermined condition to cause those grippers  30  to release the articles A. 
     In other words, if there are grippers  30  gripping articles A whose weight values are not the target weight value, the control unit  70  causes those grippers  30  to release the articles A and drop the articles A into the container  50 . The articles A that have dropped into the container  50  are reutilized as the articles A in the article group A 1 . 
     Meanwhile, the control unit  70  causes the grippers  30  gripping the articles A whose weight values are the target weight value to maintain their grip. 
     (Step S 37 ) 
     Next, when t 22  seconds elapse since t 0 , the control unit  70  stops lowering the container  50  and at the same time moves the container  50  rightward. 
     (Step S 38 ) 
     Next, when t 23  seconds elapse since t 0 , the control unit  70  moves the second gripping unit  15 B backward. The control unit  70  continues to move the container  50  rightward. 
     (Step S 39 ) 
     Next, when t 24  seconds elapse since t 0 , the control unit  70  stops moving the second gripping unit  15 B backward and stops moving the container  50  rightward. 
     At this time, the container  50  is positioned below the second gripping unit  15 B. Furthermore, as viewed from the container  50 , the second gripping unit  15 B is entirely positioned above a region offset toward the rear side of the inside of the container  50 . 
     (Step S 40 ) 
     Next, the control unit  70  raises the container  50 . In the timing diagram of  FIG.  7   , the container  50  moves upward at the same time as time t 24  when it stops moving rightward. However, the control unit  70  may also start moving the container  50  upward between time t 23  and time t 24 . 
     (Step S 41 ) 
     Next, when t 25  seconds elapse since t 0 , the control unit  70  switches the state of the gripping claws  30   a  of the first gripping unit  15 A that are gripping the articles A whose weight values were the target weight value in prior step S 36  from the first state (a closed state) to the second state (an open state) to cause the gripping claws  30   a  of the first gripping unit  15 A to release the articles A and discharge the articles A to the first discharge chute  60 A below. 
     In this way, the positional relationship between the gripping units  15  and the container  50  is switched to the second positional relationship in which the container  50  obstructs discharge of the articles gripped by the second gripping unit  15 B but does not obstruct discharge of the articles gripped by the first gripping unit  15 A. 
     (Step S 42 ) 
     Next, when t 26  seconds elapse since t 0 , the control unit  70  stops raising the container  50 . At this time, the container  50  reaches a position directly below the second gripping unit  15 B where the gripping claws  30   a  of the grippers  30  can grip the articles A in the container  50 . In this position, the gripping claws  30   a  are in the article group A 1  in the container  50 , and at the same time the gripping claws  30   a  return to the initial state. 
     Here also, the control unit  70  finishes moving the container  50  leftward or rightward and moving the unit drive units  10  forward or backward before the container  50  finishes rising, so the article group A 1  in the container  50  is kept from ending up being shifted in either forward and backward or leftward and rightward directions. 
     Furthermore, the control unit  70  switches the gripping claws  30   a  to the second state (an open state in which the gripping claws  30   a  are open) before the container  50  finishes rising, so the articles A in the container  50  are kept from ending up being shifted to the outer sides of the gripping claws  30   a.    
     (Step S 43 ) 
     Next, when t 27  seconds elapse since t 0 , the control unit  70  switches the gripping claws  30   a  of the second gripping unit  15 B from the initial state to the first state (a closed state) to cause the gripping claws  30   a  to grip the articles A. 
     In this way, in the article gripping system  110 , the gripping claws  30   a  are switched to the first state (a closed state in which the gripping claws  30   a  are closed) in a state in which they are in the middle of the article group A 1  in the container  50 , so the articles A can be reliably held. 
     (Step S 44 ) 
     Next, when t 28  seconds elapse since t 0 , the control unit  70  lowers the container  50  while maintaining the state in which the plural grippers  30  are gripping the articles A. 
     (Step S 45 ) 
     Next, when t 29  seconds elapse since t 0 , the control unit  70  moves the second gripping unit  15 B forward. The gripping claws  30   a  and the article group A 1  in the container  50  are away from each other as a result of the container  50  moving downward a predetermined distance between time t 28  and time t 29 , so even when the second gripping unit  15 B moves forward, the articles A gripped by the gripping claws  30   a  and the article group A 1  in the container  50  do not interfere with each other. 
     (Step S 46 ) 
     Next, the control unit  70  measures the weights of the articles A gripped by the grippers  30  corresponding to the weighers  40  of the second gripping unit  15 B. In this way, because the article gripping system  110  is a type where the container  50  moves upward, downward, leftward, and rightward and the gripping units  15  move forward and backward, the gripping units  15  can move in advance in forward and backward directions before gripping the articles A and weigh the articles A right after gripping hold of them. 
     (Step S 47 ) 
     Next, the control unit  70  determines whether or not at least one of the weighing results of the weighers  40  meets a predetermined condition for returning the articles A gripped by the grippers  30  to the container  50  without discharging them to the discharge chute  60 . 
     The predetermined condition specifically is a condition where the weight values of the articles A weighed by the weighers  40  are not a preset target weight value. 
     The control unit  70  proceeds to step S 3  when it determines that none of the weighing results of the weighers  40  meet the predetermined condition. 
     (Step S 48 ) 
     Next, the control unit  70  controls the gripping member drive mechanisms  30   b  of the grippers  30  meeting the predetermined condition to cause those grippers  30  to release the articles A. 
     In other words, if there are grippers  30  gripping articles A whose weight values are not the target weight value, the control unit  70  causes those grippers  30  to release the articles A and drop the articles A into the container  50 . The articles A that have dropped into the container  50  are reutilized as the articles A in the article group A 1 . 
     Meanwhile, the control unit  70  causes the grippers  30  gripping the articles A whose weight values are the target weight value to maintain their grip. 
     (Step S 49 ) 
     Next, when t 30  seconds elapse since t 0 , the control unit  70  stops lowering the container  50  and thereafter repeats the operations from step S 3  on. 
     The operations from step S 1  to step S 49  are an example, and the order of the operations of the steps may also be interchanged. 
     (4) Characteristics 
     (4-1) 
     The article gripping system  110  switches between the first positional relationship in which the container  50  obstructs discharge of the articles gripped by the first gripping unit  15 A but does not obstruct discharge of the articles gripped by the second gripping unit  15 B and the second positional relationship in which the container  50  obstructs discharge of the articles gripped by the second gripping unit  15 B but does not obstruct discharge of the articles by the first gripping unit  15 A, so the gripping units do not move while they are holding the articles A, and the articles can be prevented from falling out of the gripping units  15 . 
     (4-2) 
     In the article gripping system  110 , the first gripping unit  15 A and the second gripping unit  15 B are disposed in the horizontal direction, the container  50  can be horizontally moved in leftward and rightward directions by the leftward and rightward moving mechanisms, and the position of the article group A 1  in the container  50  and the article gripping positions set for each of the gripping units  15  can be aligned. 
     (4-3) 
     In the article gripping system  110 , the first gripping unit  15 A and the second gripping unit  15 B are disposed in the horizontal direction, the first gripping unit  15 A can be horizontally moved in forward and backward directions by the first unit drive unit  10 A, the second gripping unit  15 B can be horizontally moved in forward and backward directions by the second unit drive unit  10 B, and the position of the article group in the container  50  and the article gripping positions set for each of the gripping units  15  can be aligned. 
     (4-4) 
     In the article gripping system  110 , the container  50  can be moved in upward and downward directions by the vertical moving mechanisms, so that even in a case where the container  50  is disposed away from the gripping units  15  in the vertical direction, the position of the article group A 1  in the container  50  and the article gripping positions set for each of the gripping units  15  can be aligned. 
     (4-5) 
     In the article gripping system  110 , when raising the container  50 , the control unit  70  finishes moving the container  50  leftward or rightward and moving the unit drive units  10  forward or backward before the container  50  finishes rising, so the article group A 1  in the container  50  is kept from ending up being shifted in either forward and backward or leftward and rightward directions. 
     (4-6) 
     The plural gripping claws  30   a  of the gripping units  15  are switched to at least either of the first state and the second state. The first state is a state in which the relative distance between the gripping claws  30   a  is decreased to the first distance so that the gripping claws  30   a  grip the articles. The second state is a state in which the relative distance between the gripping claws  30   a  is increased to the second distance greater than the first distance so that the gripping claws  30   a  release the articles. 
     (4-7) 
     In the article gripping system  110 , when raising the container  50 , the control unit  70  switches the gripping claws  30   a  to the second state (an open state in which the gripping claws  30   a  are open) before the container  50  finishes rising, so the articles A in the container  50  are kept from ending up being shifted to the outer sides of the gripping claws  30   a.    
     (4-8) 
     In the article gripping system  110 , the gripping claws  30   a  are switched to the first state (a closed state in which the gripping claws  30   a  are closed) in a state in which they are in the middle of the article group A 1  in the container  50 , so the articles A can be reliably held. 
     (4-9) 
     The article gripping system  110  is a type where the container  50  moves upward, downward, leftward, and rightward and the gripping units  15  move forward and backward, so the gripping units  15  can move in advance in forward and backward directions before gripping the articles and weigh the articles right after gripping hold of them. 
     (4-10) 
     In the article gripping system  110 , the vertical moving mechanisms  57  do not need to raise and lower the leftward and rightward moving mechanisms  56  and need only raise and lower just the container  50 , so the load when raising and lowering the container  50  is mitigated. 
     (4-11) 
     In the article gripping system  110 , by avoiding disposing the leftward and rightward moving mechanisms  56  in the space above the inlets of the discharge chutes  60 , contamination of the discharge chutes  60  is prevented. 
     (4-12) 
     In the article gripping system  110 , by avoiding disposing the vertical moving mechanisms  57  in the space above the inlets of the discharge chutes  60 , contamination of the discharge chutes  60  is prevented. 
     (4-13) 
     In the article gripping system  110 , the control unit  70  moves the article group A 1  in the container  50  to a first gripping position where the first gripping unit  15 A grips the articles A. Moreover, the control unit  70  causes the first gripping unit  15 A to grip the articles A and thereafter moves the article group A 1  in the container  50  to a second gripping position where the second gripping unit  15 B grips the articles. 
     (4-14) 
     In the article gripping system  110 , the control unit  70  moves the article group A 1  in the container  50  to the second gripping position and thereafter causes the first gripping unit  15 A to release the articles A and causes the second gripping unit  15 B to grip the articles A from the article group A 1  in the container  50 . 
     (4-15) 
     The article gripping system  110  interlinks the operation where the control unit  70  causes the first gripping unit  15 A to release the articles A and the operation where the control unit  70  causes the second gripping unit  15 B to grip the articles A. 
     (5) Other 
     Here, exemplary description will be given in regard to the configurations of the forward and backward moving mechanisms  11  of the unit drive units  10  and the leftward and rightward moving mechanisms  56  and the vertical moving mechanisms  57  of the container drive unit  54 . 
     (5-1) Forward and Backward Moving Mechanism  11   
       FIG.  9    is a plan view showing an example of the forward and backward moving mechanism  11 . In  FIG.  9   , the forward and backward moving mechanism  11  includes a block  111 , a ball screw  112 , a servo motor  113 , two linear guides  114 , and two guide blocks  115 . 
     The coupling member  16  of the gripping unit  15  is secured to the block  111 . The guide blocks  115  are secured to the left and right end portions of the block  111 . One guide block  115  is slidably fitted together with one linear guide  114 . The linear guides  114  are supported by the frames  12  of the unit drive unit  10 . When the block  111  moves, the guide blocks  115  move along the linear guides  114 . 
     A screw hole into which the ball screw  112  screws is formed through the center of the block  111 . The ball screw  112  is rotated by the servo motor  113 . 
     When the servo motor  113  rotates the ball screw  112  in one direction, the block  111  moves forward, and when the servo motor  113  rotates the ball screw  112  in the other direction, the block  111  moves backward. 
     As a result, the gripping unit  15  coupled via the coupling member  16  to the block  111  can horizontally move forward and backward. 
     ( 5 - 2 ) Leftward and Rightward Moving Mechanism  56   
       FIG.  10 A  is a front view showing an example of the container drive unit  54  that houses the leftward and rightward moving mechanism  56 . In  FIG.  10 A , the leftward and rightward moving mechanism  56  is provided in each of the first driver  541  and the second driver  542 . Below, the first driver  541  will be taken as an example and described. 
     The leftward and rightward moving mechanism  56  includes a servo motor  561 , two linear guides  562 , two guide blocks  563 , and a ball screw  564 . The guide blocks  563  are secured to the upper and lower end portions of the first driver  541 . One guide block  563  is slidably fitted together with one linear guide  562 . 
     In the case of the first driver  541 , the linear guides  562  are supported by the first horizontal support  551  and the second horizontal support  552 . In the case of the second driver  542 , the linear guides  562  are supported by the third horizontal support  553  and the fourth horizontal support  554 . 
     When the first driver  541  moves, the guide blocks  563  move along the linear guides  562 . A screw hole into which the ball screw  564  screws is formed horizontally through the center of the first driver  541 . The ball screw  564  is rotated by the servo motor  561 . 
     When the servo motor  561  rotates the ball screw  564  in one direction, the first driver  541  moves leftward, and when the servo motor  561  rotates the ball screw  564  in the other direction, the first driver  541  moves rightward. 
     (5-3) Vertical Moving Mechanism  57   
       FIG.  10 B  is a front view showing an example of the container drive unit  54  that houses the vertical moving mechanism  57 . In  FIG.  10 B , the vertical moving mechanism  57  is provided in each of the first driver  541  and the second driver  542 . Below, the second driver  542  will be taken as an example and described. 
     The vertical moving mechanism  57  includes a servo motor  571 , two linear guides  572 , two guide blocks  573 , and a ball screw  574 . The guide blocks  573  are secured to the left and right end portions of the second driver  542 . One guide block  573  is slidably fitted together with one linear guide  572 . 
     In the case of the second driver  542 , the linear guides  572  are supported by the third vertical support  523  and the fourth vertical support  524 . In the case of the first driver  541 , the linear guides  572  are supported by the first vertical support  521  and the second vertical support  522 . 
     When the second driver  542  moves, the guide blocks  573  move along the linear guides  572 . A screw hole into which the ball screw  574  screws is formed vertically through the second driver  542 . The ball screw  574  is rotated by the servo motor  571 . 
     When the servo motor  571  rotates the ball screw  574  in one direction, the second driver  542  moves upward, and when the servo motor  571  rotates the ball screw  574  in the other direction, the second driver  542  moves downward. 
     REFERENCE SIGNS LIST 
       10  Unit Drive Units (Drive Unit) 
       10 A First Unit Drive Unit (Drive Unit) 
       10 B Second Unit Drive Unit (Drive Unit) 
       11  Forward and Backward Moving Mechanisms (Second Horizontal Moving Mechanism) 
       15  Gripping Units 
       15 A First Gripping Unit (Gripping Unit) 
       15 B Second Gripping Unit (Gripping Unit) 
       56  Leftward and Rightward Moving Mechanisms (First Horizontal Moving Mechanism) 
       57  Vertical Moving Mechanisms 
       30   a  Gripping Claws (Claws) 
       60  Discharge Chutes 
       60 A First Discharge Chute 
       60 B Second Discharge Chute 
       70  Control Unit 
       110  Article Gripping System 
     CITATION LIST 
     Patent Literature 
     Patent Document 1: JP-A No. H6-3182