Patent Publication Number: US-2022219915-A1

Title: Holding device, transporting device, and method for controlling holding device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-004554, filed Jan. 14, 2021; the entire contents of (all of) which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a holding device, a transporting device, and a method for controlling a holding device. 
     BACKGROUND 
     A picking robot equipped with a robot hand having a holding unit has been conventionally known. This type of holding unit holds an object by a plurality of holding claws. The holding unit includes a sensor that detects that the holding claw has come into contact with the object, and controls the operation of the robot hand based on the detection value of the sensor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a picking robot according to an embodiment. 
         FIG. 2  is a side view of a robot hand of the embodiment. 
         FIG. 3  is a front view of the robot hand of the embodiment. 
         FIG. 4  is a perspective view of a main part of a holding unit. 
         FIG. 5  is a front view of a holding claw. 
         FIG. 6  is a perspective view showing an internal configuration of the holding claw. 
         FIG. 7  is a diagram showing a relationship between a displacement amount of a claw member and a reaction force. 
     
    
    
     DETAILED DESCRIPTION 
     According to one embodiment, a holding device includes: a plurality of holding parts configured to hold an object to be held; a holding part opening/closing part configured to open and close the plurality of holding parts; a first sensor configured to detect a load received by the holding part; and a controller configured to control an operation of the holding part. At least one of the plurality of holding parts includes a claw member configured to be displaceable along a length direction of the holding part, a second sensor configured to detect a displacement amount of the claw member, and a reaction force applying part configured to apply a reaction force corresponding to the displacement amount of the claw member to the claw member. The controller controls the operation of the holding part, based on a detection value of the second sensor when the displacement amount is equal to or less than a threshold value, and based on a detection value of the first sensor when the displacement amount exceeds the threshold value. 
     Hereinafter, the method for controlling the holding device, the transporting device, and the holding device of the embodiment will be described with reference to the drawings. 
     The XYZ Cartesian coordinate system is used for the description of the holding device and the transporting device of the embodiment. The Z-axis direction corresponds to the vertical direction, the +Z direction is defined as upward, and the −Z direction is defined as downward. The X-axis direction and the Y-axis direction are orthogonal to each other in the horizontal plane. The direction in which a holding claw  29  (holding part) of a holding unit  21 , which will be described later, opens and closes in the horizontal plane is defined as the X-axis direction. In the horizontal plane, the direction orthogonal to the opening/closing direction of the holding claw  29  is defined as the Y-axis direction. 
       FIG. 1  is a schematic diagram showing a schematic configuration of a picking robot  10  of the present embodiment. 
     As shown in  FIG. 1 , the picking robot  10  includes a robot hand  11 , an arm  12 , and a controller  13 . The robot hand  11  holds the holding object P that is a transporting target. The arm  12  moves the robot hand  11  to a predetermined place. The controller  13  controls each part of the robot hand  11  and the arm  12 . The configuration of the robot hand  11  will be described in detail later. 
     The picking robot  10  of the present embodiment corresponds to a transporting device within the scope of claims. The robot hand  11  of the present embodiment corresponds to a holding device within the scope of claims. 
     The outline of the configuration and operation of the picking robot  10  will be described below. 
     The picking robot  10  is used, for example, as a picking robot for physical distribution. The picking robot  10  holds various holding objects P placed in various situations in the transport source S 1  and moves them to the transport destination S 2 . The use of the picking robot  10  is not limited to logistics, but can be widely applied to industrial use, other uses, and the like. The picking robot  10  of the present embodiment is not limited to a device whose main purpose is to transport the holding object P, but also includes a device that transports or moves an object as a part of other purposes such as assembling a product. 
     The transport source S 1  is, for example, various conveyors, pallets, containers, or the like, but is not limited thereto. A plurality of types of holding objects P having different dimensions and weights are placed at random positions in an arbitrary orientation on the transport source S 1 . In the present embodiment, the dimensions of the holding object P to be transported vary from, for example, about several cm square to about several tens of cm square. The weight of the holding object P varies from, for example, about several tens of g to about several kg. The dimensions and weight of the holding object P are not limited to the above example. 
     The transport destination S 2  is, for example, various conveyors, pallets, containers, or the like, as in the transport source S 1 , but is not limited thereto. The container of the transport source S 1  and the transport destination S 2  broadly means a member capable of accommodating the holding object P, for example, a box-shaped member. 
     The arm  12  is composed of, for example, 6-axis vertical articulated arm. The arm  12  includes a plurality of arm members  15  and a plurality of joint portions  16 . The joint portion  16  rotatably connects the arm members  15  connected to the joint portion  16 . The arm  12  may be composed of, for example, 4-axis vertical articulated arm or 3-axis orthogonal arm. The arm  12  may be a mechanism for moving the robot hand  11  to a desired position by a configuration other than the vertical articulated arm and the orthogonal arm. Although not shown, the arm  12  includes a sensor or the like for detecting the angle formed by the arm member  15  in each joint portion  16 . 
     Although not shown, the picking robot  10  further includes sensors installed in the vicinity of the transport source S 1  and the transport destination S 2 . The sensor is composed of, for example, an RGB-D sensor, a camera, a contact sensor, a distance sensor and the like. The sensor acquires, for example, information about the holding object P placed in the transport source S 1 , information about the status of the transport source S 1  or the transport destination S 2 , and the like. 
     The controller  13  manages and controls each part of the picking robot  10 . The controller  13  acquires various information detected by the sensor, and controls the position and operation of the robot hand  11  based on the acquired information. The controller  13  is composed of a microcomputer including a processor such as a CPU (Central Processing Unit). The controller  13  is realized by a processor such as a CPU executing a program stored in a memory or an auxiliary storage device. At least a part of the controller  13  may be realized by hardware such as LSI (Large Scale Integration), ASIC (Application Specific Integrated Circuit), FPGA (Field-Programmable Gate Array), or may be realized by cooperation between software and hardware. 
     Hereinafter, the robot hand  11  will be described. 
       FIG. 2  is a side view of the robot hand  11  as seen from the +X direction.  FIG. 3  is a front view of the robot hand  11  as seen from the −Y direction. In the present specification, a view of each device viewed from the +X direction is referred to as a side view, and a view of each device viewed from the −Y direction is referred to as a front view. 
     As shown in  FIG. 2 , the robot hand  11  includes a base plate  20 , a holding unit  21 , a suction unit  22 , and a force sensor  23 . 
     The base plate  20  is a plate-shaped member and has a first surface  20   a  and a second surface  20   b  facing each other. The base plate  20  supports the holding unit  21  and the suction unit  22 . The holding unit  21  and the suction unit  22  face the first surface  20   a  of the base plate  20  and are arranged side by side in the Y-axis direction. The base plate  20  is arranged only on one side of the holding unit  21  and the suction unit  22 , and is not arranged on the other side. That is, the holding unit  21  and the suction unit  22  are not sandwiched from both sides by the base plate  20 , but are supported by the cantilever structure with respect to the base plate  20 . 
     The suction unit  22  is arranged so as to face the first surface  20   a  of the base plate  20 . The holding unit  21  is arranged on the side opposite to the side where the base plate  20  is located with respect to the suction unit  22 . That is, these two units  21  and  22  are arranged in the order of the suction unit  22  and the holding unit  21  from the first surface  20   a  side of the base plate  20 . A part of the base plate  20 , a part of the suction unit  22 , and a part of the holding unit  21  are arranged at positions where they overlap each other when viewed from the normal direction (Y-axis direction) of the first surface  20   a.    
     The suction unit  22  has a plurality of suction pads  32 . The suction unit  22  uses a plurality of suction pads  32  to hold the holding object Pin a form of negative pressure suction. The suction unit  22  is rotatably supported in a plane parallel to the first plane  20   a  (in the XZ plane) with respect to the base plate  20 . 
     The holding unit  21  has a plurality of holding claws  29  (holding parts). The holding unit  21  holds the holding object P from the side by using a plurality of holding claws  29 . The holding unit  21  is rotatably supported in a plane parallel to the first plane  20   a  (in the XZ plane) with respect to the base plate  20 . 
     The force sensor  23  is arranged on the upper part of the base plate  20 . The force sensor  23  detects the load received by the holding claw  29  when the holding claw  29  comes into contact with an arbitrary object such as a floor surface, a wall surface, another obstacle, or a holding object P. The detected value of the force sensor  23  is output to the controller  13  and used for controlling various operations of the holding unit  21 . 
     The force sensor  23  of the present embodiment corresponds to the first sensor in the claims. 
     The robot hand  11  has a function of switching which of the holding unit  21  and the suction unit  22  to be used for holding the holding object P according to the holding object P, a function of changing the orientation of the holding unit  21 , a function of changing the orientation of the suction unit  31  including a plurality of suction pads  32 , and a function of opening and closing the holding claw  29 . In order to realize these functions, the robot hand  11  includes a first motor  35 , a second motor  36 , a third motor  37 , and a fourth motor  38 . 
     The rotation of the first motor  35  is transmitted to the holding unit  21  via a rotation transmission mechanism (not shown). The holding unit  21  is rotated by the first motor  35 . As shown in  FIG. 3 , the holding unit  21  can change its orientation so that the holding center line H 1  faces, for example, in a counterclockwise direction at an angle −θ when the orientation in which the holding center line H 1  faces downward in the vertical direction is set to 0°. Contrary to  FIG. 3 , the holding unit  21  can change its orientation so that the holding center line H 1  faces the direction in which the angle+θ is formed clockwise. In this way, the orientations of the plurality of holding claws  29  can be changed. The holding center line H 1  is defined as a straight line parallel to the Z axis at the initial position (position before the orientation change) of the holding unit  21 , and a straight line passing through the center of the two holding claws  29  in the opening/closing direction (X-axis direction) and the center of one holding claw  29  in the width direction (Y-axis direction). 
     When switching the units  21  and  22 , the holding unit  21  and the suction unit  22  are integrally rotated by the first motor  35 . On the other hand, when changing the orientation of the holding unit  21 , due to the rotation of the second motor  36  together with the rotation of the first motor  35 , the suction unit  22  rotates in a direction that cancels the change in the orientation of the suction unit  22  due to the change in the orientation of the holding unit  21 . As a result, as shown in  FIG. 3 , even if the orientation of the holding unit  21  changes, the orientation of the suction unit  22  does not change while facing upward in the vertical direction. 
     The rotation of the third motor  37  is transmitted to the suction unit  31  including the plurality of suction pads  32  via the rotation transmission mechanism (not shown). As a result, the suction unit  31  rotates with the rotation of the third motor  37 , and the orientation is changed. 
     As shown in  FIG. 3 , the holding unit  21  includes a plurality of holding claws  29  and a holding claw opening/closing part  26  (holding part opening/closing part). The holding claw opening/closing part  26  includes a link portion  51 , a first gear  61 , a second gear  62 , and a third gear  63 . 
     The holding unit  21  of the present embodiment includes two holding claws  29  connected to the link portion  51 . The number of the holding claws  29  may be 3 or more, and is not particularly limited. 
     The link portion  51  is composed of two parallel links  52 . Each of the two holding claws  29  is connected to each of the two parallel links  52 . The two holding claws  29  move in a direction in which the two holding claws  29  are spaced apart from each other while rising in the height direction of the holding unit  21  due to the movement of the link portion  51 , and open and close by moving in a direction in which the distance between the two holding claws  29  is narrowed while descending in the height direction of the holding unit  21 . 
     The first gear  61  is connected to the fourth motor  38 . The second gear  62  meshes with the first gear  61 . The third gear  63  meshes with the second gear  62 . When the first gear  61  is rotated by the drive of the fourth motor  38 , the second gear  62  and the third gear  63  rotate in opposite directions in the XZ plane, and the two parallel links  52  move. The two holding claws  29  perform either an open operation or a closed operation depending on which direction the second gear  62  and the third gear  63  rotate. Hereinafter, the configuration of the holding claw  29  will be described. 
       FIG. 4  is a perspective view showing a main part of the holding unit  21 .  FIG. 5  is a front view of the holding claw  29 .  FIG. 6  is a perspective view showing the internal configuration of the holding claw  29 . In  FIG. 6 , in order to make it easier to see the internal configuration of the holding claw  29 , the illustration of the member surrounding the outside is omitted as appropriate. 
     As shown in  FIG. 4 , the two holding claws  29  have the same configuration as each other. The two holding claws  29  are arranged so that the first surfaces  79   a  of the inner claws  79 , which will be described later, face each other. 
     As shown in  FIGS. 4, 5 and 6 , the holding claw  29  includes a base member  71 , a linear guide  72 , a claw member  73 , a reaction force applying part  74 , a displacement sensor  75 , and a transmission sensor  76 . 
     The displacement sensor  75  of this embodiment corresponds to the second sensor in the claims. 
     As shown in  FIG. 5 , the base member  71  is composed of a plate-shaped member. The base member  71  has a first surface  71   a  and a second surface  71   b  opposite to the first surface  71   a . The upper end of the base member  71  is connected to the parallel link  52 . The first surface  71   a  of the base member  71  is provided with a linear guide  72  extending along the length direction (Z-axis direction) of the base member  71 . 
     The claw member  73  includes a slide base  78 , an inner claw  79 , and an outer claw  80 . The claw member  73  is arranged so as to face the first surface  71   a  of the base member  71 . The claw member  73  is connected to the base member  71  via a linear guide  72 . The claw member  73  can be displaced in the length direction (Z-axis direction) of the holding claw  29  by moving in parallel along the linear guide  72 . In other words, the holding claw  29  can be expanded and contracted by the claw member  73  moving in parallel along the linear guide  72 . 
     The slide base  78  is composed of a plate-shaped member. The slide base  78  has a first surface  78   a  and a second surface  78   b  opposite to the first surface  78   a . An inner claw  79  is connected to the upper portion of the first surface  78   a  of the slide base  78 . An outer claw  80  is connected to the lower portion of the second surface  78   b  of the slide base  78 . The slide base  78  is connected to the base member  71  via a linear guide  72 . 
     The inner claw  79  is arranged inside the holding claw  29  in the opening/closing direction (X-axis direction) (the side on which the holding object P is located) in the claw member. The inner claw  79  has a first surface  79   a  and a second surface  79   b  opposite to the first surface  79   a . The inner claw  79  holds the holding object P in a state where the first surface  79   a  is in contact with the holding object P. The inner claw  79  is composed of a leaf spring. The leaf spring is elastically deformable in the opening/closing direction (X-axis direction) of the holding claw  29 . The lower end of the inner claw  79  is located below the lower end of the slide base  78 . 
     As shown by the two-dot chain line in  FIG. 5 , in the initial state, the inner claw  79  is warped in the direction in which the tip of the inner claw  79  faces inward in the opening/closing direction. Therefore, in the initial state, the lower portion of the second surface  79   b  of the inner claw  79  is located at a position away from the first surface  78   a  of the slide base  78 . The initial state referred to here means a state in which the holding claw  29  does not hold the holding object P. As shown by the solid line in  FIG. 5 , in the state where the holding claw  29  holds the holding object P, the inner claw  79  is elastically deformed in a direction in which the tip opens outward in the opening/closing direction, and the second surface  79   b  comes into contact with the first surface  78   a  of the slide base  78 . 
     A stopper  82  is provided on the second surface  79   b  of the inner claw  79 . The stopper  82  has a pin-like shape. The stopper  82  penetrates the hole provided in the slide base  78 , and its head faces the second surface  78   b  of the slide base  78 . In  FIG. 5 , which shows a state in which the holding object P is held, there is a gap between the head of the stopper  82  and the slide base  78 . On the other hand, in the initial state in which the holding object P is not held, the head of the stopper  82  comes into contact with the slide base  78 . The inner claw  79  is prevented from warping more than necessary toward the inside in the opening/closing direction by the stopper  82  coming into contact with the slide base  78  in the initial state. 
     The outer claw  80  is arranged on the outside of the holding claw  29  in the opening/closing direction (X-axis direction) (the side opposite to the side on which the holding object P is located) in the claw member  73 . The outer claw  80  has a first surface  80   a  and a second surface  80   b  opposite to the first surface  80   a . The outer claw  80  includes a support plate  83  and two rollers  84 . The lower end of the outer claw  80  is located below the lower end of the slide base  78 . 
     The roller  84  of the present embodiment corresponds to the friction reducing member in the claims. 
     As shown in  FIG. 4 , an elongated hole  83   h  extending in the length direction (Z-axis direction) of the holding claw  29  is provided on the upper portion of the support plate  83 . The support plate  83  is supported by the slide base  78  via a screw  85  inserted through the elongated hole  83   h . With this configuration, the outer claw  80  is displaceably connected to the inner claw  79  in the length direction of the holding claw  29 . As shown in  FIG. 5 , the position where the position of the lower end of the outer claw  80  (the outer peripheral surface of the roller  84 ) coincides with the position of the lower end of the inner claw  79  in the length direction of the holding claw  29  is the reference position R 0  of the outer claw  80 . The lower end of the outer claw  80  can be displaced to the upper position R 1  and also to the lower position R 2  with respect to the reference position R 0 . The amount of upward displacement and the amount of downward displacement of the outer claw  80  with respect to the reference position R 0  can be appropriately adjusted. 
     The roller  84  is provided at the lower end of the support plate  83 . The roller  84  is rotatable about a rotation axis along the Y-axis direction. The roller  84  reduces the friction between the holding claw  29  and the object when the holding claw  29  comes into contact with an arbitrary object such as a floor surface. In the present embodiment, two rollers  84  are provided at intervals in the width direction (Y-axis direction) of the support plate  83 . Instead of this configuration, one roller having a wide width in the Y-axis direction may be provided, and the number of rollers is not particularly limited. Further, instead of the configuration in which the roller  84  is provided at the lower end of the support plate  83 , for example, another member that has been subjected to friction reduction processing may be provided. 
     As shown in  FIG. 4 , the transmission sensor  76  is provided on the first surface  78   a  of the slide base  78 . The transmission sensor  76  installed on one holding claw  29  faces the transmission sensor  76  provided on the other holding claw  29  via the opening  79   h  provided on the inner claw  79 . The transmission sensor  76  detects the presence or absence of an object located between the two holding claws  29  by detecting the transmission or blocking of light such as visible light and infrared light. 
     As shown in  FIG. 6 , the reaction force applying part  74  includes a tension spring  87  and a compression spring  88 . The reaction force applying part  74  applies a reaction force to the claw member  73  to return the claw member  73  to the initial position when the claw member  73  is displaced from the initial position. That is, the reaction force applying part  74  applies a reaction force to the claw member  73  according to the amount of displacement of the claw member  73 . 
     The tension spring  87  of the present embodiment corresponds to the first reaction force applying member within the scope of claims. The compression spring  88  of the present embodiment corresponds to the second reaction force applying member within the scope of claims. 
     As shown in  FIGS. 5 and 6 , a first spring fixing portion  89  is provided on the upper portion of the slide base  78 . A second spring fixing portion  90  is provided at the lower portion of the base member  71 . The tension spring  87  is arranged between the first spring fixing portion  89  and the second spring fixing portion  90 . The upper end of the tension spring  87  is connected to the first spring fixing portion  89 . The lower end of the tension spring  87  is connected to the second spring fixing portion  90 . The tension springs  87  are provided on both sides of the base member  71  in the Y-axis direction. 
     According to this configuration, when the claw member  73  comes into contact with, for example, the floor surface and is displaced upward from the initial position, the tension spring  87  is extended. At this time, a reaction force in the direction in which the tension spring  87  contracts is generated, and the tension spring  87  applies a reaction force to the claw member  73  to move the claw member  73  downward and return it to the initial position. 
     As shown in  FIG. 6 , the compression spring  88  is arranged between the base member  71  and the claw member  73 . The lower end of the compression spring  88  is supported by the slide base  78  of the claw member  73 . The upper end of the compression spring  88  is not in contact with the base member  71  in the initial state, and a gap C is provided between the compression spring  88  and the top plate portion  71 A of the base member  71 . The gap C is 5 mm as an example, but is not particularly limited and can be appropriately adjusted. 
     The gap C of the present embodiment corresponds to the threshold value of the displacement amount of the claw member in the claims. 
     According to this configuration, when the claw member  73  comes into contact with the floor surface and is displaced upward from the initial position, for example, the tension spring  87  acts until the displacement amount of the claw member  73  reaches 5 mm, while the tension spring  87  acts. Since the compression spring  88  does not come into contact with the base member  71 , no action is generated. Next, when the displacement amount of the claw member  73  reaches 5 mm, the compression spring  88  comes into contact with the base member  71  and the compression spring  88  starts to act. When the displacement amount of the claw member  73  exceeds 5 mm, a reaction force in the direction in which the compression spring  88  extends from the contracted state acts. In this way, the compression spring  88  applies a reaction force to the claw member  73  to move the claw member  73  downward and return it to the initial position. 
     The spring constant of the compression spring  88  is larger than the spring constant of the tension spring  87 . Specifically, for example, the wire rod constituting the compression spring  88  is thicker than the wire rod constituting the tension spring  87 . Therefore, the reaction force applied to the claw member  73  by the compression spring  88  is larger than the reaction force applied to the claw member  73  by the tension spring  87 . As described above, in the reaction force applying part  74 , the tension spring  87  that applies the first reaction force to the claw member  73  when the displacement amount of the claw member  73  is 5 mm or less, and the displacement amount of the claw member  73  exceeds 5 mm. In some cases, the claw member  73  is provided with the compression spring  88  that applies a second reaction force larger than the first reaction force. 
       FIG. 7  is a diagram showing an example of the relationship between the displacement amount of the claw member  73  and the reaction force. In  FIG. 7 , the horizontal axis is the displacement amount (mm), and the vertical axis is the reaction force (N). 
     As described above, when the displacement amount of the claw member  73  is 5 mm or less, the tension spring  87  generates a reaction force, and when the displacement amount of the claw member  73  exceeds 5 mm, the compression spring  88  generates a reaction force. Further, the reaction force due to the compression spring  88  is larger than the reaction force due to the tension spring  87 . 
     Therefore, as shown in  FIG. 7 , in the range of the displacement amount of 0 to 5 mm, the reaction force linearly increases as the displacement amount increases. When the displacement amount is 5 mm, the reaction force is, for example, 2N. Further, even when the displacement amount is in the range of 5 to 20 mm, the reaction force linearly increases as the displacement amount increases. However, the slope of the straight line in the range of the displacement amount of 5 to 20 mm is larger than the slope of the straight line in the range of the displacement amount of 0 to 5 mm. When the displacement amount is 20 mm, the reaction force is, for example, 40 N. It should be noted that these numerical values are examples and are not particularly limited. The numerical value of the reaction force corresponding to the displacement amount in  FIG. 7  is determined according to the thickness of the spring (spring constant). Therefore, the threshold value of the displacement amount can be appropriately changed by changing the combination of the thickness (spring constant) of the spring. 
     As shown in  FIG. 6 , the displacement sensor  75  is arranged above the base member  71 . The displacement sensor  75  detects the amount of displacement of the claw member  73  when the holding claw  29  comes into contact with an arbitrary object and the claw member  73  is displaced. As a mechanism for the displacement sensor  75  to detect the amount of displacement of the claw member  73 , the claw member  73  contacts on an object and escapes (displaces), so that the distance between the claw member  73  and the displacement sensor  75  changes. The sensor  75  detects the displacement amount of the claw member  73  by the change amount of this distance. The detected value of the displacement sensor  75  is output to the controller  13  and used to control the operation of the holding claw  29 . As the displacement sensor  75 , various displacement sensors such as a laser displacement sensor, a magnetic displacement sensor, and a capacitance type displacement sensor are used. 
     The controller  13  receives the detection signal from the displacement sensor  75  and determines which of the detection values of the displacement sensor  75  and the force sensor  23  is used to control the operation of the holding claw  29 . When the displacement amount of the claw member  73  is 5 mm or less, which is the threshold value, the controller  13  controls the operation of the holding claw  29  based on the detection value of the displacement sensor  75 . When the displacement amount of the claw member  73  exceeds the threshold value of 5 mm, the controller  13  controls the operation of the holding claw  29  based on the detection value of the force sensor  23 . 
     That is, the method for controlling the robot hand  11  of the present embodiment controls the operation of the holding claw  29  based on the detection value of the displacement sensor  75  when the displacement amount of the tip of the holding claw  29  is equal to or less than the threshold value, and the holding claw  29  is controlled. When the displacement amount of the tip of the tip exceeds the threshold value, the operation of the holding claw  29  is controlled based on the detected value of the force sensor  23 . 
     Hereinafter, the effects of the robot hand  11  and the picking robot  10  of the present embodiment will be described. 
     In this type of robot hand, a force sensor is widely used for the purpose of detecting the contact state of the holding claw with an object or an obstacle. A general force sensor detects the strain generated in the structure provided in the sensor when a load is applied by various methods. On the other hand, there is a demand for precisely detecting the contact state of the holding claw in order to precisely operate the holding claw. In this case, it is conceivable to use a force sensor having a low frequency detection range for the purpose of performing precisely contact detection. However, in this case, when the holding claw strongly collides with the floor surface due to, for example, a malfunction, an excessive load is applied to the structure in the force sensor, and the force sensor may be damaged. 
     In response to this problem, in the robot hand  11  of the present embodiment, the claw member  73  constituting the tip of the holding claw  29  can be displaced in the length direction of the holding claw  29 , and the controller  13  is the claw member  73 . When the displacement amount is equal to or less than the threshold value, the controller  13  controls the operation of the holding claw  29  based on the detection value of the displacement sensor  75 , and when the displacement amount of the claw member  73  exceeds the threshold value, the controller  13  controls the operation of the holding claw  29  based on the detection value of the force sensor  23 . 
     In this way, when detecting the contact state of the holding claw  29 , the displacement sensor  75  is in charge of the region where the load received by the claw member  73  is small and the displacement amount of the claw member  73  is small, and the force sensor  23  is in charge of the region where the load received by the claw member  73  is large and the displacement amount of the claw member  73  is large. Therefore, by using the displacement sensor  75  having a low detection range and the force sensor  23  having a high detection range in combination, precisely contact detection of the holding claw  29  can be performed without causing damage to the sensor. As a result, the precise movement of the holding claw  29  can be controlled with high accuracy. Further, the impact when the claw member  73  comes into contact with the object is alleviated by the displacement of the claw member  73 . As a result, damage to the holding object P or the holding claw  29  can be suppressed. Further, by switching from the displacement sensor  75  to the force sensor  23  based on the displacement amount of the claw member  73 , it is possible to obtain the effect of preventing the claw member  73  from interfering (contacting or colliding) with the holding object or a surrounding object. 
     In the robot hand  11  of the present embodiment, the reaction force applying part  74  includes the tension spring  87  that applies a first reaction force to the claw member  73  when the displacement amount of the claw member  73  is equal to or less than a threshold value, and the compression spring  88  that applies a second reaction force larger than the first reaction force to the claw member  73  when the displacement amount of the claw member  73  exceeds the threshold value. 
     According to this configuration, the reaction force applying part  74  applies a relatively small reaction force to the claw member  73  when the displacement amount of the claw member  73  is relatively small, and applies a relatively large reaction force to the claw member  73  when the displacement amount of the claw member  73  is relatively large. In this way, since the two types of springs are used properly in the reaction force applying part  74 , an appropriate reaction force is applied according to the displacement amount of the claw member  73 , and the precisely operation of the holding claw  29  can be enabled. In other words, the displacement of the smaller and thinner (smaller spring constant) tension spring  87  is measured by the displacement sensor  75 , and when the displacement exceeds the threshold, the tension spring  87  is switched to the larger and thicker compression spring  88  (which has a larger spring constant), so as to switch to the measurement of the force sensor  23 . The role of the compression spring  88  is to transmit a larger (exceeding the threshold value) force (load) caused by the displacement of the claw member  73  to the force sensor  23 . Therefore, by providing a larger and thicker compression spring  88 , the force (load) can be transmitted to the force sensor  23 . In the robot hand  11  of the present embodiment, the orientations of the plurality of holding claws  29  can be changed. 
     For example, as shown in  FIG. 1 , it is assumed that the holding object P 1  of the transport source S 1  has a flat plate portion, and the flat plate portion is placed in an orientation facing the horizontal direction. In this case, it is difficult for the holding claw  29  to hold the holding object P only by moving the holding claw  29  up and down while keeping the orientation facing the vertical direction. In that case, in the present embodiment, the orientation of the holding claw  29  can be changed. Therefore, if the flat plate portion is scooped up in an orientation in which the holding claw  29  is tilted from the vertical direction, the holding claw  29  can hold the holding object P 1 . As described above, the robot hand  11  of the present embodiment can correspond to the holding object P randomly placed in various orientations. 
     In the robot hand  11  of the present embodiment, the claw member  73  includes an inner claw  79  arranged inside the holding claw  29  in the opening/closing direction and holding the holding object P, and an outer claw  80  arranged outside the opening/closing direction with respect to the inner claw  79 . 
     According to this configuration, when the holding claw  29  is tilted from the vertical direction, the functions can be shared between the inner claw  79  that holds the holding object P and the outer claw  80  that is likely to come into contact with the floor surface before the inner claw  79 . Thereby, the holding performance of the holding claw  29  can be improved. 
     Specifically, in the case of the present embodiment, the inner claw  79  is composed of a leaf spring that can be elastically deformed in the opening/closing direction of the holding claw  29 . 
     According to this configuration, when the inner claw  79  holds the holding object P, the inner claw  79  elastically deforms in the direction of opening outward in the opening/closing direction. At this time, the inner claw  79  can stably hold the holding object P by the reaction force that tries to elastically return to the initial state. 
     Further, in the case of the present embodiment, the leaf spring constituting the inner claw  79  is warped in the direction in which the tip thereof faces inward in the opening/closing direction in the initial state. 
     According to this configuration, since the tip of the inner claw  79  is easily caught on the surface of the holding object P, the holding object P can be reliably held. In this case, since the inner claw  79  can precisely hold the holding object P like tweezers, it is suitable for holding a small and lightweight holding object P placed on the floor surface. 
     Further, as another method for precisely holding the holding object P, it is conceivable to attach an elastic body such as a rubber sheet to the inner surface of the holding claw. However, in that case, since the surface of the rubber sheet is sticky, when holding a holding object whose surface is made of vinyl, a small-sized holding object, or the like, a phenomenon may occur in which the holding object adheres to the surface of the rubber sheet and does not come off. On the other hand, in the present embodiment, the above phenomenon can be suppressed by using a leaf spring for the inner claw  79 . 
     Further, in the case of the present embodiment, the inner claw  79  has a stopper  82 , and the inner claw  79  is prevented from warping inward more than necessary in the initial state. 
     According to this configuration, the distance between the inner claw  79  and the outer claw  80  does not open more than necessary, and it is possible to prevent an object such as the holding object P from being caught in the gap between the inner claw  79  and the outer claw  80 . 
     In the robot hand  11  of the present embodiment, the outer claw  80  includes a roller  84  that reduces friction with an object such as a floor surface or the holding object. 
     According to this configuration, the holding claw  29  is tilted from the vertical direction, and when the outer claw  80  comes into contact with an object such as the floor surface before the inner claw  79 , the friction between the outer claw  80  and the object is reduced by the roller  84 . As a result, the claw member  73  can be smoothly displaced with respect to the base member  71 . Further, for example, when the friction between the outer claw  80  and the floor surface is large and the outer claw  80  is caught on the floor surface, there is a possibility that the holding claw  29  may malfunction due to erroneous detection of the contact state. On the other hand, according to the above configuration, the roller  84  reduces the friction between the outer claw  80  and the floor surface, and the outer claw  80  slides on the floor surface. As a result, there is little possibility that the holding claw  29  will malfunction, and the holding claw  29  can smoothly hold the holding object P. 
     Further, in the case of the present embodiment, the outer claw  80  is connected to the inner claw  79  so as to be displaceable in the length direction of the holding claw  29 . 
     According to this configuration, the position of the tip of the outer claw  80  with respect to the tip of the inner claw  79  can be adjusted. Thereby, the friction reducing effect of the roller  84  can be appropriately adjusted. 
     The picking robot  10  of the present embodiment includes a robot hand  11  that exhibits the above effects. 
     According to this configuration, the picking robot  10  can hold various holding objects P placed in various orientations and situations in the box of the transport source S 1  and efficiently transport them to the transport destination S 2 , for example. 
     The robot hand  11  of the above embodiment has a claw member  73  in which both of the two holding claws  29  are displaceable with respect to the base member  71 . Instead of this configuration, of the two holding claws, only one holding claw may have a claw member displaceable with respect to the base member. For example, in the case of a robot hand used for an application in which the direction in which the holding claws are always tilted from the vertical direction is always determined, a plurality of holding claws may be arranged on the lower side when tilted from the vertical direction and only the holding claws in contact with the floor surface may be configured as described above. That is, the robot hand of the embodiment may have a claw member in which at least one of the plurality of holding claws is displaceable with respect to the base member. 
     The claw member may have a tapered structure that tapers toward the tip. According to this structure, when there are, for example, a plurality of cylindrical objects as the objects to be held, the claw member easily enters the gap between the adjacent cylindrical objects. More specifically, in the case of the claw member  73  of the above embodiment, the claw member  73  may have a tapered structure at least in one of the thickness direction (X-axis direction in the drawing) and the width direction (Y-axis direction in the drawing). In this case, this kind of tapered structure may be formed with respect to the inner claw  79 , and it is desirable that the width of the outer claw  80  is narrowed so as not to exceed the width of the entire claw member  73  and the tip of the inner claw  79  in the Y direction, and it is not necessary to form a taper in particular. 
     Further, in the above embodiment, an example of a robot hand  11  that combines two holding functions of holding and suction, a so-called hybrid hand type robot hand, is given. Instead of this configuration, the present invention may be applied to, for example, a robot hand provided with only a holding unit. 
     According to at least one embodiment described above, the plurality of holding claws  29  that hold the holding object P, the holding claw opening/closing part  26  that opens and closes the plurality of holding claws  29 , the force sensor  23  that detects the load received by the holding claw  29  when the holding claw  29  comes into contact with an object, and the controller  13  that controls the operation of the holding claw  29  are provided. At least one of the plurality of holding claws  29  includes the base member  71 , the claw member  73  displaceably connected to the base member  71  in the length direction of the holding claw  29 , the displacement sensor  75  that detects the amount of displacement of the claw member  73 , and the reaction force applying part  74  that applies a reaction force to the claw member  73  to return the claw member  73  to the initial position when the claw member  73  is displaced from the initial position. The controller  13  performs control based on the detection value of the displacement sensor  75  when the displacement amount is equal to or less than the threshold value, and controls based on the detection value of the force sensor  23  when the displacement amount exceeds the threshold value. As a result, the risk of damage to the sensor can be reduced, and the robot hand  11  that enables the precisely operation of the holding claw  29  can be realized. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover the forms and modifications that fall within the scope and spirit of the inventions.