Patent Publication Number: US-2020282565-A1

Title: Transport device, transport method, and transport program

Description:
TECHNICAL FIELD 
     An embodiment of the invention relates to a transport device, a transport method, and a transport program. 
     BACKGROUND ART 
     In recent years, transport devices that automatically take out cargo from a palette in which a large number of pieces of cargo are loaded and transport the taken-out cargo have become known. The transport devices detect the position and posture of cargo from an image captured by an imaging device, and hold and transport the cargo using a robot arm or the like. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1 
     
         
         Japanese Unexamined Patent Application, First Publication No. 2007-130711 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in the devices of the related art, cargo may be transported in an unstable cargo holding state. 
     A problem to be solved by the invention is to provide a transport device capable of transporting cargo in a stable holding state, a transport method, and a transport program. 
     Solution to Problem 
     A transport device according to an embodiment includes a holder, a driver, a force sensor, a first acquirer, and a controller. The holder holds a piece of cargo. The driver, which is a driver connected to the holder, moves the holder. The force sensor, provided in the vicinity of a connection location where the holder and the driver are connected to each other, detects a force applied to the vicinity of the connection location. The first acquirer acquires holding information indicating a holding state of the holder holding the cargo. The controller causes the driver to transport the cargo in a case where it is determined that the driver is caused to transport the cargo, on the basis of holding information indicating a holding state of the holder which is acquired by the first acquirer and detection results of the force sensor. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a configuration diagram of a transport device  1 . 
         FIG. 2  is a diagram illustrating examples of an arm  12  and a holder  13  according to an embodiment. 
         FIG. 3  is a functional configuration diagram focusing on a control device  40 . 
         FIG. 4  is a flowchart illustrating a flow of processing executed by the control device  40 . 
         FIG. 5  is a diagram illustrating an example of a determination map  92 . 
         FIG. 6  is a diagram illustrating a position based on the center of gravity. 
         FIG. 7  is a diagram illustrating a holding state determination process (processes of step S 104  to step S 110 ). 
         FIG. 8  is a diagram illustrating a holding state determination process (processes of step S 112  to step S 118 ). 
         FIG. 9  is a flowchart illustrating a flow of a transport process. 
         FIG. 10  is a diagram illustrating a state where a piece of cargo M is transported along a track for avoiding contact with an object. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a transport device, a transport method, and a transport program according to an embodiment will be described with reference to the accompanying drawings. Illustration and description will be performed using an XYZ coordinate system as necessary. 
       FIG. 1  is a configuration diagram of a transport device  1 .  FIG. 1(A)  is a plan view of the transport device  1 .  FIG. 1(B)  is a side view of the transport device  1 . The transport device  1  illustrated in  FIG. 1  may be, for example, automatic unloading device. For example, the transport device  1  automatically takes out a piece of cargo M disposed on a box palette  3  and transports the taken-out cargo M to a predetermined position such as on a belt conveyor  4 . The transport device  1  and the belt conveyor  4  are fixed to, for example, a floor. In addition, the transport device  1  and the belt conveyor  4  may be movable using wheels, a rail, or the like. 
     Here, for convenience of description, a +X-direction, a −X-direction, a Y-direction, and a Z-direction will be defined. For example, the +X-direction, the −X-direction, and the Y-direction are directions along a substantially horizontal plane. The +X-direction is a direction from the transport device  1  to the box palette  3 . The −X-direction is a direction opposite to the +X-direction. The Y-direction is a direction intersecting the +X-direction (for example, a substantially orthogonal direction). The Z-direction is a direction intersecting the X-direction and the Y-direction (for example, a substantially orthogonal direction) and is, for example, a direction substantially vertically downward. The terms “upstream” and “downstream” in the following description mean “upstream” and “downstream” in a transport direction of the piece of cargo M. 
     As illustrated in  FIG. 1 , the transport device  1  includes a base  11 , an arm  12  (driver), a holder  13 , a first conveyor  16 , a second conveyor  17 , a cargo detector  18 , and a control device  40 . 
     The base (main body frame)  11  is installed on a floor. The base  11  includes a plurality of supports  21  extending in the Z-direction. For example, the support  21  may be formed in the form of a frame. The plurality of supports  21  include a pair of first supports  21   a  and a pair of second supports  21   b . The pair of first supports  21   a  are disposed separately on both sides of the first conveyor  16  in the Y-direction. The pair of second supports  21   b  are disposed separately on both sides of the second conveyor  17  in the Y-direction. 
     The arm  12  is, for example, an orthogonal robot arm and is an example of a multi-joint arm. A multi-joint arm is an arm in which a plurality of arms are connected to each other, a plurality of connected portions (joints) are provided, and each of the joints can be driven. The arm  12  is connected to the base  11 . For example, the arm  12  includes a first member  12   a , a second member  12   b , and a third member  12   c . The first member  12   a  is guided to a guide provided in the base  11  so as to be movable (liftable) in the Z-direction. The second member  12   b  is supported and guided by the first member  12   a  so as to be movable in the Y-direction. The third member  12   c  is supported and guided by the second member  12   b  so as to be movable in the +X-direction and the −X-direction. The holder  13  to be described later is attached to a tip portion of the arm  12 . The arm  12  moves the holder  13  to desired positions in the +X-direction (−X-direction), the Y-direction, and the Z-direction. 
       FIG. 2  is a diagram illustrating examples of the arm  12  and the holder  13  according to the embodiment. The holder  13  is an end effector capable of holding the piece of cargo M. The holder  13  includes, for example, a plurality of adhesive discs  13   a  and an electromagnetic valve. The plurality of adhesive discs  13   a  are connected to a vacuum pump. The electromagnetic valve controls an adsorption operation of the adhesive discs  13   a . The holder  13  holds (grips) the piece of cargo M by vacuum adsorption of the adhesive discs  13   a  in contact with the piece of cargo M. In the example illustrated in the drawing, the number of adhesive discs  13   a  is nine (three adhesive discs in the X-direction by three adhesive discs in the Y-direction). 
     In addition, each of the plurality of adhesive discs  13   a  is provided with a pressure sensor  14 . The pressure sensor  14  detects a pressure (the degree of vacuum) in the adhesive discs  13   a  and outputs a detection result to the control device  40 . 
     In addition, a force sensor  15  is provided in the vicinity of a connection location between the arm  12  and the holder  13 . The force sensor  15  detects a force applied to the holder  13  and the arm  12  (a force applied to the vicinity of a connection location) using a strain gauge system, a capacitance system, or the like. The force sensor  15  detects, for example, translational force components in three axial directions (X, Y, and Z-directions) and moment components around the translational force components and outputs detection results to the control device  40 . 
     The holder  13  is moved toward the box palette  3  by the movement of the arm  12  and holds the piece of cargo M disposed on the box palette  3 . In addition, the holder  13  is moved by the movement of the arm  12  to transport the held piece of cargo M to the first conveyor  16 . The holder  13  moves the piece of cargo M to the first conveyor  16  and then terminates the holding of the piece of cargo M. Thereby, the transport device  1  moves the piece of cargo M disposed on the box palette  3  to the first conveyor  16 . 
     Description will return to  FIG. 1 . The cargo detector  18  is, for example, a camera that captures an image. The cargo detector  18  is provided on the surface of the arm  12  (second member  12   b ) on the Z-direction side. In addition, the cargo detector  18  is installed such that a range in the Z-direction from the holder  13 , which is also in a range in the +X-direction from the holder  13 , is set to be an imaging range. Thereby, the cargo detector  18  captures an image of the piece of cargo M loaded on the box palette  3 . 
     The first conveyor  16  is positioned between the box palette  3  and the belt conveyor  4  in the −X-direction. The first conveyor  16  is provided in the base  11  and positioned below at least a portion of the arm  12 . The first conveyor  16  is connected to the base  11  and supported by the base  11 . 
     The first conveyor  16  is, for example, a belt conveyor which is positioned in a direction vertically downward from the arm  12 . The first conveyor  16  includes a transport surface (top face)  16   a  moving toward the belt conveyor  4 . 
     The first conveyor  16  is a lift conveyor which is movable in the Z-direction. For example, the first conveyor  16  is guided to a guide provided in the first support  21   a  of the base  11  so as to be movable (liftable) in the Z-direction. 
     The second conveyor  17  is positioned between the first conveyor  16  and the belt conveyor  4  in the −X-direction. The second conveyor  17  is provided in the base  11  and positioned below at least a portion of the arm  12 . The second conveyor  17  is connected to the base  11  and supported by the base  11 . 
     The second conveyor  17  is, for example, a belt conveyor positioned in a direction vertically downward from the arm  12 . The second conveyor  17  includes a transport surface (top face)  17   a  moving toward the belt conveyor  4 . The second conveyor  17  is positioned on a downstream side of the first conveyor  16 . In addition, the belt conveyor  4  is positioned on a downstream side of the second conveyor  17 . 
     The second conveyor  17  is a lift conveyor which is movable in the Z-direction, independently of the first conveyor  16 . For example, the second conveyor  17  is guided to a guide provided in the second support  21   b  of the base  11  so as to be movable (liftable) in the Z-direction. 
     Operations of the first conveyor  16  and the second conveyor  17  will be described. (1) The first conveyor  16  is moved to a desired position in the Z-direction in accordance with the height of the pieces of cargo M loaded into the box palette  3  (the height of the pieces of cargo M transported by arm  12 ) and receives the pieces of cargo M transported by arm  12 . (2) The second conveyor  17  is controlled so that the height of the second conveyor  17  is aligned with the height of the first conveyor  16 . (3) The first conveyor  16  transports the pieces of cargo received from the arm  12  in the −X-direction. (4) The second conveyor  17  receives the pieces of cargo M transported by the first conveyor  16 . (5) The second conveyor  17  is controlled so that the height of the second conveyor  17  is matched to the height of the belt conveyor  4 . (6) The second conveyor  17  transports the pieces of cargo M received from the first conveyor  16  to the belt conveyor  4 . In this manner, the pieces of cargo M in the box palette  3  are transported to the belt conveyor  4 . 
     In addition, each of the first conveyor  16  and the second conveyor  17  is not limited to a belt conveyor. Each of the first conveyor  16  and the second conveyor  17  may be a roller conveyor constituted by a plurality of rollers which are actively rotated. 
     The transport device  1  according to the embodiment includes two conveyers including the first conveyor  16  and the second conveyor  17 , but is not limited thereto. The transport device may include one conveyor. In this case, the transport device  1  disposes the piece of cargo M transported by the holder  13  in one conveyor and discharges the piece of cargo M to the belt conveyor  4  using one conveyor. 
       FIG. 3  is a functional configuration diagram focusing on the control device  40 . The control device  40  includes, for example, a recognizer  42 , an adsorption force detector  50 , an adsorption position detector  52 , a weight detector  60 , a coordinates detector  62 , a contact detector  64 , a controller  70 , and a storage  90 . The adsorption force detector  50  and the adsorption position detector  52  are examples of “a first acquirer”, the weight detector  60  is an example of “a second acquirer”, and the coordinates detector  62  is an example of “a third acquirer”. The contact detector  64  is an example of “a detector”. 
     Some or all of the recognizer  42 , the adsorption force detector  50 , the adsorption position detector  52 , the weight detector  60 , the coordinates detector  62 , the contact detector  64 , and the controller  70  may be implemented by a processor such as a central processing unit (CPU) executing a program. In addition, some or all of these functional units may be implemented by hardware such as a large scale integration (LSI), an application specific integrated circuit (ASIC), or a field-programmable gate array (FPGA). For example, the storage  90  is realized by a non-volatile storage medium such as a read only memory (ROM), a flash memory, a hard disk drive (HDD), or an SD card and a volatile storage medium such as a random access memory (RAM) or a register. The storage  90  stores a program executed by a processor, a determination map  92  to be described later, and the like. 
     The recognizer  42  performs a recognition process on an image captured by the cargo detector  18  to identify the position of the piece of cargo M in the image. In addition, the recognizer  42  converts the position of the piece of cargo M in the image into a position in a real space and outputs information of the converted position to the controller  70 . 
     The adsorption force detector  50  detects a holding force of the holder  13 . The holding force of the holder  13  is, for example, a vacuum adsorption force (adsorption force) of the adhesive discs  13   a  in contact with the piece of cargo M. The adsorption position detector  52  detects an adsorption center position where the holder  13  holds the piece of cargo M. The adsorption center position is a center position in a target region when a region including the adhesive discs  13   a  adsorbing the piece of cargo M is set to be the target region. The adsorption position detector  52  determines that an adhesive disc  13   a  having a pressure lower (a degree of vacuum higher) than a reference value by a predetermined level or more is an adhesive disc  13   a  adsorbing the piece of cargo M on the basis of, for example, detection results of the pressure sensor  14  to identify an adsorption center position of the target region including the adhesive discs  13   a . In addition, the same function as that of the adsorption force detector  50  or the adsorption position detector  52  may be included in the pressure sensor  14 . 
     The weight detector  60  acquires the weight of the piece of cargo M on the basis of detection results of the force sensor  15 . The coordinates detector  62  detects two-dimensional coordinates of the center of gravity of the piece of cargo M in the upper surface on the basis of detection results of the force sensor  15 . The two-dimensional coordinates indicate a position where the center of gravity of the piece of cargo M is approximately projected onto the top surface of the piece of cargo M. The coordinates detector  62  detects two-dimensional coordinates on the basis of, for example, the translational force components and the moment components which are acquired from the force sensor  15 . The two-dimensional coordinates are an example of “a position based on the center of gravity”. The contact detector  64  detects a force applied to the holder  13  from the outside on the basis of detection results of the force sensor  15  and estimates (acquires) the position on an object to which the detected force is applied. In addition, the same function as that of the weight detector  60 , the coordinates detector  62 , or the contact detector  64  may be included in the force sensor  15 . 
     The controller  70  includes, for example, a holding state determiner  72 , an operation track controller  74 , an operation speed controller  76 , a driving controller  78 , a conveyor controller  80 , a cargo regripping controller  82 , and a pump controller  84 . 
     The holding state determiner  72  determines whether or not the arm  12  is caused to transport the piece of cargo M, on the basis of a holding state where the holder  13  is holding the piece of cargo M and detection results of the force sensor  15 . The holding information indicating a holding state is information of a holding force when the holder  13  is holding the piece of cargo M or (either or both of) information of a range over which the holder  13  and the piece of cargo M are in contact with each other. The range over which the holder  13  and the piece of cargo M are in contact with each other is, for example, a range of the adhesive discs  13   a  adsorbing the piece of cargo M (a range over which the plurality of adhesive discs  13   a  are adsorbing the piece of cargo M in a case where the piece of cargo M is adsorbed by the plurality of adhesive discs  13   a ). In addition, a range over which the holder  13  and the piece of cargo M are in contact with each other may be the range of the piece of cargo M which is adsorbed by the adhesive discs  13   a  in the piece of cargo M recognized by an image. 
     Specifically, the holding state determiner  72  compares the weight of the piece of cargo M and a holding force of the holder  13  with each other to determine whether or not the arm  12  is caused to transport the piece of cargo M using the holding force of the holder  13 . In addition, the holding state determiner  72  compares a position based on the center of gravity of the piece of cargo M and a range over which the holder  13  and the piece of cargo M are in contact with each other (or an adsorption center position) to determine whether or not the piece of cargo M is transported in a state where the range over which the holder  13  and the piece of cargo M are in contact with each other is maintained. 
     The operation track controller  74  generates a track for the holder  13  to transport the piece of cargo M to the first conveyor  16 . The operation speed controller  76  determines a speed at which the holder  13  is to be transported. The operation speed controller  76  determines a speed at which the arm  12  transports the piece of cargo M on the basis of, for example, the weight of the piece of cargo M, holding information indicating a holding state where the holder  13  is holding the piece of cargo M, and the like. For example, in a case where the weight of the piece of cargo M is large, the operation speed controller  76  determines a speed to be lower than in a case where the weight of the piece of cargo M is small. Further, for example, the operation speed controller  76  may determine a speed to be higher in a case where the holding force of the holder  13  is large than in a case where the holding force is small. In addition, the operation speed controller  76  may determine a speed to be lower in a case where the holding force of the holder  13  is small than in a case where the holding force is large. For example, in a case where the position based on the center of gravity of the piece of cargo M and the adsorption center position are far from each other, the operation speed controller  76  may determine a speed to be lower than in a case where the position based on the center of gravity of the piece of cargo M and the adsorption center position are close to each other. 
     In a case where it is determined that the piece of cargo M is transported by the holding state determiner  72 , the driving controller  78  controls an arm driver  12   d  connected to the arm  12  and driving the arm  12  such that the arm  12  is driven on the basis of the track determined by the operation track controller  74  and the speed determined by the operation speed controller  76 . In addition, the driving controller  78  controls the arm driver  12   d  so as to drive the arm  12  on the basis of the track generated by the cargo regripping controller  82  to be described later. The conveyor controller  80  controls a first conveyor driving mechanism (not shown) such that the first conveyor  16  is moved in a predetermined direction. The conveyor controller  80  controls a second conveyor driving mechanism (not shown) so as to move the second conveyor  17  in a predetermined direction. 
     In a case where it is determined that the piece of cargo M is not transported by the holding state determiner  72 , the cargo regripping controller  82  generates a track for terminating the holding of the piece of cargo M and then holding the piece of cargo M again. Specifically, the cargo regripping controller  82  brings a reference position (for example, an adsorption center position) in a range over which the holder  13  and the piece of cargo M are in contact with each other after the holding of the cargo is terminated closer to a position based on the center of gravity of the piece of cargo M in a horizontal direction than to a reference position in a range over which the holder  13  and the piece of cargo M are in contact with each other before the holding of the cargo is terminated, and then holds the piece of cargo M again. In addition, the cargo regripping controller  82  outputs the generated track to the driving controller  78 . 
     The pump controller  84  controls the vacuum pump  19  sucking in air in the vicinity of the adhesive discs  13   a  to adjust a pressure in the adhesive discs  13   a . The pump controller  84  controls the output of the vacuum pump  19  on the basis of, for example, the weight of the piece of cargo M and holding information indicating a holding state where the holder  13  is holding the piece of cargo M. For example, the pump controller  84  may determine the output of the vacuum pump  19  to be larger in a case where the weight of the piece of cargo M is large than in a case where the weight of the piece of cargo M is small, and may determine the output of the vacuum pump  19  to be smaller in a case where the weight of the piece of cargo M is small than in a case where the weight of the piece of cargo M is large. 
       FIG. 4  is a flowchart illustrating a flow of processing (holding state determination process) executed by the control device  40 . First, the recognizer  42  recognizes the position of the piece of cargo M to be transported, on the basis of an image captured by the cargo detector  18  (step S 100 ). Next, the controller  70  holds the piece of cargo M to be transported, on the basis of a recognition result of the recognizer  42  (step S 102 ). For example, the driving controller  78  controls the arm driver  12   d  so as to bring the adhesive discs  13   a  close to the piece of cargo M from the upper surface of the piece of cargo M and bring the upper surface of the piece of cargo M and the adhesive discs  13   a  into contact with each other. Next, the pump controller  84  controls the vacuum pump  19  so as to generate an adsorption force in the adhesive discs  13   a  and hold the piece of cargo M. In addition, the driving controller  78  controls the arm driver  12   d  so as to lift up the piece of cargo M to a predetermined height (approximately several centimeters in a direction vertically upward) while holding the piece of cargo M. 
     Next, the adsorption force detector  50  acquires an adsorption force which is a force for adsorbing the piece of cargo M generated in the adhesive discs  13   a  from the pressure sensor  14  (step S 104 ). Next, the weight detector  60  acquires the weight of the piece of cargo M from the force sensor  15  (step S 106 ). Next, the holding state determiner  72  compares the adsorption force acquired in step S 104  and the weight acquired in step S 106  to determine whether or not the adsorption force is sufficiently large (step S 108 ). 
     For example, the holding state determiner  72  determines whether or not the adsorption force is sufficiently large, using the determination map  92  stored in the storage  90 .  FIG. 5  is a diagram illustrating an example of the determination map  92 . In the drawing, the vertical axis represents an adsorption force P [N] and the horizontal axis represents the weight W [kg] of cargo. The adsorption force P is calculated by the following Expression (1). “DT” is a pressure (the degree of vacuum) [Pa] detected by a pressure sensor, and “S” is a cross-sectional area [m 2 ] of the adhesive disc  13   a . “N” is the number of adhesive discs  13   a  which are in contact with the piece of cargo M. 
         P=DT×S× 0.1× N   (1)
 
     In addition, the above-described Expression (1) may be changed as shown in Expression (1-1). “1/n” is a safety rate which is set in advance. 
         P=DT×S× 0.1×(1/ n )× N   (1-1)
 
     As illustrated in the drawing, in a case where the adsorption force P is equal to or greater than a threshold value Th, it is determined that the adsorption force P is sufficiently large. That is, it is determined that a holding state is stable. The threshold value Th is, for example, a value obtained by adding a surplus adsorption force (a surplus adsorption force a) to a force (“F”) required to transport the piece of cargo M having a weight W at a set speed. The threshold value Th is expressed by, for example, the following Expression (2). 
         Th=F+α   (2)
 
     The threshold value Th is set in response to the weight of the piece of cargo MW. The threshold value Th is set to be larger when the weight W of the cargo increases. For example, when the weight W of the cargo increases, the surplus adsorption force a is set to be larger. Since the surplus adsorption force a is set in this manner, transport in an unstable holding state with respect to a piece of heavy cargo M and dropping of a piece of heavy cargo M are inhibited. This is because it is necessary to further reduce a risk of dropping due to a possibility that the heavy cargo M and cargo M located at a dropping position, and the like may be damaged when the heavy cargo M drops. 
     The processing proceeds to the process of step S 112  when the adsorption force is sufficiently large, and the controller  70  returns the piece of cargo M to a position where the piece of cargo M is disposed in order to hold the piece of cargo M again when the adsorption force is not sufficiently large (step S 110 ). In addition, the processing may proceed to the process of step S 102  after the process of step S 110 . 
     In addition, a position where the piece of cargo M is held by the holder  13  after the process of step S 110  (for example, in step S 102  after step S 110 ) and a position where the piece of cargo M was held by the holder  13  last time may be different positions. For example, the controller  70  may cause the holder  13  to hold the piece of cargo M by shifting a position where the holder  13  holds the piece of cargo M each time by a predetermined distance (for example, several centimeters) in the horizontal direction with respect to the position where the piece of cargo M was held last time. For example, an adsorption force may be reduced due to irregularities in the top face of the piece of cargo M and a gap generated between the adhesive discs  13   a  and the piece of cargo M, but the gap is reduced due to the shifted holding position and the adsorption force is increased. 
     When the adsorption force is sufficiently large, the adsorption position detector  52  acquires an adsorption center position (step S 112 ). Next, the coordinates detector  62  acquires a position based on the center of gravity of the piece of cargo M (step S 114 ). 
     Next, the holding state determiner  72  compares the adsorption center position acquired in step S 112  and the position based on the center of gravity acquired in step S 114  with each other to determine whether or not a deviation in these positions in the horizontal direction is within a predetermined distance (step S 116 ).  FIG. 6  is a diagram illustrating a position based on the center of gravity. The coordinates detector  62  acquires the position of the center of gravity of the piece of cargo M from the force sensor and detects the position of two-dimensional coordinates corresponding to the acquired center of gravity of the piece of cargo M as a position CG. In addition, the holding state determiner  72  determines whether or not a deviation in the horizontal direction of the position CG and an adsorption center position C in a target region AR including the adhesive discs  13   a  in contact with the piece of cargo M which is acquired from the adsorption position detector  52  is within a predetermined distance. The positional deviation within the predetermined distance refers to an upper limit value of a deviation allowable when transporting the piece of cargo M and means that, for example, the adsorption center position C and the position CG is within the predetermined distance.  FIG. 6(A)  illustrates a state where a deviation in the adsorption center position C and the position CG is not within a predetermined distance.  FIG. 6(B)  illustrates a state where a deviation in the adsorption center position C and the position CG is within a predetermined distance. 
     The above-described predetermined distance may be changed in accordance with one or more elements among the weight of the piece of cargo M, an adsorption force, the area of the piece of cargo M on the top face (an XY plane). For example, in a case where the weight of the cargo is large, the predetermined distance is set to be shorter than in a case where the weight of the cargo is small. In addition, for example, in a case where the adsorption force is small, the predetermined distance is set to be shorter than in a case where the adsorption force is large. In addition, for example, in a case where the above-described area is large, the predetermined distance is set to be shorter than in a case where the area is small. This is because there is a strong possibility that the center of gravity may be shifted during the transport of the piece of cargo M in this case. 
     In a case where the positional deviation is within a predetermined distance, the holding state determiner  72  determines that a holding state is stable and proceeds to the process of step S 120  to be described later. In a case where the positional deviation is not within the predetermined distance, the cargo regripping controller  82  returns the piece of cargo M to the original position where the piece of cargo M was disposed to generate a track for holding the piece of cargo M again so that the adsorption center position and the position based on the center of gravity of the piece of cargo M acquired from the holding state determiner  72  become closer to each other (step S 118 ). In addition, the driving controller  78  holds the piece of cargo M again on the basis of the track generated by the cargo regripping controller  82 . In addition, the processing may proceed to the process of step S 100  or step S 104  after the process of step S 118 . Thereby, the processing of one routine of this flowchart is terminated. 
     In addition, in the above-described flowchart, the control device  40  determines whether or not the piece of cargo M can be transported, on the basis of both a weight and a center of gravity, but the invention is not limited thereto. The transport device  40  may determine whether or not the piece of cargo M can be transported, on the basis of a weight or a center of gravity. For example, the processes of steps S 104  to step S 110  or the processes of steps S 112  to S 118  in the flowchart of  FIG. 4  may be omitted. 
     In addition, the order of the processes in the flowchart of  FIG. 4  may be changed. For example, in a case where the processes of steps S 112  to S 118  are performed after the process of step S 102  and a determination result in the process of step S 116  is affirmative, the processes of steps S 104  to S 110  may be performed. 
     In addition, the processes of gripping the cargo again in steps S 110  and S 118  may be integrated into one process and may be performed after the determination in steps S 108  and S 116 . For example, in a case where the holding state determiner  72  compares the adsorption force acquired in step S 104  and the weight acquired in step S 106  with each other to determine in step S 108  whether or not the adsorption force is sufficiently large, this determination result is stored in the storage  90 . Further, in step S 116 , the holding state determiner  72  compares the adsorption center position acquired in step S 112  and the position based on the center of gravity acquired in step S 114  with each other. In a case where the holding state determiner determines in step S 116  whether or not a positional deviation in these positions in the horizontal direction is within a predetermined distance, the determination result is stored in the storage  90 . 
     The controller  70  performs processes (A) to (D) on the basis of, for example, the above-described determination result stored in the storage  90 . (A) In a case where the determination results in steps S 108  and S 116  are affirmative, the processing proceeds to the process of step S 120 . (B) In a case where determination result in the step S 108  is affirmative and the determination result in step S 116  is negative, the controller  70  executes a process of gripping the piece of cargo M again so that the adsorption center position and the position based on the center of gravity of the piece of cargo M become closer to each other. 
     (C) In a case where the determination result in step S 108  is negative and the determination result in step S 116  is affirmative, the controller  70  executes a process of gripping the piece of cargo M again so that the adsorption center position and the position based on the center of gravity of the piece of cargo M become closer to each other or so that a state where a deviation in the horizontal direction of the adsorption center position acquired in step S 112  and the position based on the center of gravity acquired in step S 114  is within a predetermined distance is maintained. (D) In a case where the determination result in step S 108  is negative and the determination result in step S 116  is negative, the controller  70  executes a process of gripping the piece of cargo M again so that the adsorption center position and the position based on the center of gravity of the piece of cargo M become closer to each other. 
       FIG. 7  is a diagram illustrating a portion of the holding state determination process (the processes of steps S 104  to S 110 ). In the example illustrated in the drawing, it is assumed that the piece of cargo M is disposed on the upper surface of cargo Mx different from an object to be transported. The control device  40  acquires an adsorption force for adsorbing the piece of cargo M and the weight of the piece of cargo M in a state where the piece of cargo M is lifted up to a predetermined height from the piece of cargo Mx (step S 102 , an upper portion of  FIG. 7 ) (step S 104 ,  106 ). In a case where the adsorption force is sufficiently large with respect to the weight of the piece of cargo M and other conditions (step S 116 ) to be described later are satisfied, the control device  40  starts an operation of transporting the piece of cargo M in a direction vertically upward (step S 120 , a middle portion of  FIG. 7 ). Thereafter, the control device  40  lifts up the piece of cargo M by a predetermined height and then transports the piece of cargo M toward the first conveyor  16  (step S 120 , a lower left portion of  FIG. 7 ). On the other hand, in a case where the adsorption force is not sufficiently large with respect to the weight of the piece of cargo M, the control device  40  returns the piece of cargo M to the original position (step S 110 , a lower right portion of  FIG. 7 ). 
       FIG. 8  is a diagram illustrating a portion (the processes of steps S 112  to S 118 ) of the holding state determination process. In the example of  FIG. 8 , it is assumed that the piece of cargo M to be transported is lifted up in a state where a portion of the upper surface of the piece of cargo M and a predetermined adhesive disc  13   a  among the plurality of adhesive discs  13   a  are in contact with each other and the determination result in step S 108  is affirmative (step S 108 , an upper portion of  FIG. 8 ). In this case, the control device  40  acquires an adsorption center position C and a position CG based on the center of gravity of the piece of cargo M, and determines whether or not a positional deviation in these positions is within a predetermined distance. In a case where it is determined that the positional deviation is within the predetermined distance (“YES” in step S 116 ,  FIG. 8 (A 1 )), the control device  40  lifts up the piece of cargo M by a predetermined height and then transports the piece of cargo M toward the first conveyor  16  (step S 120 ,  FIG. 8 (A 2 )). On the other hand, in a case where it is determined that the positional deviation is not within the predetermined distance (“NO” in step S 116 ,  FIG. 8 (B 1 )), the control device  40  brings the adsorption center position C and the position CG based on the center of gravity of the piece of cargo M close to each other to correct the position of the holder  13  (step S 118 ,  FIG. 8 (B 2 )) and then transports the piece of cargo M toward the first conveyor  16  (step S 120 ,  FIG. 8 (B 3 )). 
     Here, in a case where a general transport device adsorbs and transports the piece of cargo M, it is not possible to confirm whether the holder  13  is holding the cargo in a stable state or the holder  13  is holding the cargo in an unstable state. On the other hand, the transport device  1  according to this embodiment compares an adsorption force of the holder  13  and the weight of the piece of cargo M with each other and further compares an adsorption center position and a position based on the center of gravity of the piece of cargo M with each other to determine whether or not the holder  13  is holding the piece of cargo M in a stable state. In this manner, the transport device  1  according to this embodiment can perform determination from the viewpoint of a weight and a position to determine whether or not a holding state of the piece of cargo M is stable with a higher level of accuracy and transports the piece of cargo M in a case where the holding state is stable. As a result, the transport device  1  can transport the piece of cargo M in a stable holding state. 
       FIG. 9  is a flowchart illustrating a flow of a transport process (step S 120  in  FIG. 4 ). First, the driving controller  78  controls the arm driver  12   d  to control the arm  12  so as to transport the piece of cargo M to the first conveyor  16  (step S 200 ). Next, the contact detector  64  determines whether or not the piece of cargo M being transported, the holder  13 , or the arm  12  and any one object are in contact with each other on the basis of a detection result of the force sensor  15  (step S 202 ). The object is an object which serves as an obstacle when the piece of cargo M is transported. The object is, for example, the box palette  3  or the piece of cargo M different from an object to be transported. For example, in a case where a detected value detected by the force sensor  15  changes largely (or changes by a predetermined value or more), as compared with a previous detected value, the contact detector  64  determines that contact with the object has been made. In a case where it is not detected that contact with the object has been made, the processing proceeds to the process of step S 210 . 
     In a case where it is detected that contact with the object has been made, the control device  40  executes a portion of the holding state determination process (for example, the processes of steps S 104  to S 110  and/or the processes of steps S 112  to S 118 ). Thereby, even when a state where the holder  13  is holding the piece of cargo M becomes unstable in a case where contact with the object is made, it is possible to hold the piece of cargo M again, and thus the object M is held in a stable state. In addition, the process of step S 204  (holding state determination process) may be omitted. 
     Next, the cargo regripping controller  82  generates a track for avoiding contact with an object (step S 206 ), and the driving controller  78  transports the piece of cargo M along the generated track (step S 208 ).  FIG. 10  is a diagram illustrating a state where the piece of cargo M is transported along a track for avoiding contact with an object. For example, in step S 200 , it is assumed that control is performed so that the holder  13  performs transport along tracks R 1  and R 2  generated by the controller  70 . In this case, it is assumed that there is an object OB and the holder  13  and the object OB come into contact with each other when the holder  13  transports the piece of cargo M along the track R 1 . In this case, the force sensor  15  detects that a force f has been applied from a direction of the top face of the holder  13 . Further, in step S 202 , the contact detector  64  detects contact between the holder  13  and the object OB using information of the force f acquired from the force sensor  15 . In addition, the operation track controller  74  acquires a position where the object OB is estimated to be present from the contact detector  64  to generate tracks R 3  and R 4  for avoiding the object OB and transporting the piece of cargo M to a predetermined position. In addition, the driving controller  78  performs control such that the holder  13  transports the piece of cargo M along the generated tracks R 3  and R 4 . Thereby, the piece of cargo M is transported to the first conveyor  16  while avoiding the object OB. 
     Next, the controller  70  determines whether or not the piece of cargo M has been transported to the first conveyor  16  (step S 210 ). The processing returns to the process of step S 200  in a case where the piece of cargo M has not been transported to the first conveyor  16 , and the processing of this flowchart is terminated in a case where the piece of cargo M has been transported to the first conveyor  16 . 
     Through the above-described process, the transport device  1  can transport the piece of cargo M to the first conveyor  16  while avoiding an object serving as an obstacle when the piece of cargo M is transported. 
     According to at least one embodiment described above, it is possible to transport cargo M in a stable holding state by including the holder  13  holding the piece of cargo M, the arm  12  connected to the holder  13  and moving the holder  13 , the force sensor  15 , provided in the vicinity of a connection location where the holder  13  and the arm  12  are connected to each other, which detects a force applied to the vicinity of the connection location, a first acquirer (the adsorption force detector  50 , the adsorption position detector  52 ) acquiring holding information indicating a holding state of the holder  13  holding the piece of cargo M, and the controller  70  causing the arm  12  to transport the piece of cargo M in a case where it is determined that the arm  12  is caused to transport the piece of cargo M, on the basis of holding information indicating a holding state of the holder  13  which is acquired by the first acquirer and detection results of the force sensor  15 . 
     Although some embodiments of the invention have been described above, those embodiments are described as examples, and do not intend to limit the scope of the invention. Those embodiments may be embodied in other various modes, and may be variously omitted, substituted, and modified without departing from the scope of the invention. Those embodiments and modification thereof are within the scope and the gist of the invention, and are within the scope of the invention described in the scope of claims and the equivalent thereof.