Patent Publication Number: US-2019184578-A1

Title: Grasping Hand And Robot

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to a grasping hand and a robot. 
     2. Related Art 
     A robot such as a vertical articulated robot or a horizontal articulated robot includes a robot arm. In general, an end effector such as a hand is mounted on the distal end of the robot arm. As a type of such an end effector, a grasping hand capable of grasping an object is known. 
     For example, an electric hand described in JP-A-2014-24134 (Patent Literature 1) includes an electric motor, a rotational-linear motion converting mechanism configured to convert a rotational motion of the electric motor into a linear motion, a pair of finger bases configured to linearly move via the rotational-linear motion converting mechanism, a pair of fingers fixed to the pair of finger bases, and a force sensor configured to detect a force (a grasping force) in an opening and closing direction of the fingers. The force sensor includes a pair of electrodes having a gap that changes according to an external force applied to the finger bases. The force sensor detects capacitance between the pair of electrodes to detect a grasping force. 
     However, in the electric hand described in Patent Literature 1, the gap between the pair of electrodes has to be changed according to the external force applied to the finger bases. Therefore, the influence of a moment depending on a grasping position of the finger bases is large. The grasping force cannot be directly detected. 
     SUMMARY 
     An advantage of some aspects of the invention is to provide a grasping hand that can highly accurately detect a force applied to a grasping section and provide a robot including the grasping hand. 
     The invention can be implemented as the following application examples or forms. 
     A grasping hand according to an application example of the invention includes: a grasping section; a motor configured to generate a driving force for moving the grasping section; and a transmitting mechanism including a first member and a second member configured to transmit the driving force to the grasping section. The first member is supported by a shaft member and moves along the shaft member to move the second member. The second member moves in a direction parallel to the shaft member to move the grasping section. A pressure sensor is provided between the first member and the second member. 
     With such a grasping hand, since the pressure sensor is provided between the first member and the second member of the transmitting mechanism configured to transmit the driving force generated by the motor to the grasping section, a force (a grasping force, a pressing force, etc.) applied to the grasping section can be directly detected by the pressure sensor. The force applied to the grasping section can be highly accurately detected by the pressure sensor because the rigidity of the pressure sensor is high. A reduction in the size and a reduction in the weight of the transmitting mechanism and a reduction in the size and a reduction in the weight of the grasping hand can be achieved because the pressure sensor is thin. 
     In the grasping hand according to the application example, it is preferable that the transmitting mechanism converts rotation of the motor into an opening and closing motion of a pair of the grasping sections. 
     With this configuration, the pair of grasping sections can be opened and closed by a relatively simple and inexpensive configuration. The mechanism that performs such conversion less easily transmits the force applied to the grasping section to the motor. Therefore, the grasping section can be prevented from being displaced by the force. 
     In the grasping hand according to the application example, it is preferable that the grasping hand includes: a case; and a guide member supported by the case and configured to guide the second member. 
     With this configuration, the second member can be stably moved in a desired direction. 
     In the grasping hand according to the application example, it is preferable that the first member and the second member are coupled by a screw. 
     With this configuration, it is possible to change an output of the pressure sensor according to the force applied to the grasping section while coupling the first member and the second member with relatively high rigidity. 
     In the grasping hand according to the application example, it is preferable that the pressure sensor includes: a first pressure sensor disposed on the grasping section side with respect to the screw; and a second pressure sensor disposed on an opposite side of the grasping section with respect to the screw. 
     With this configuration, a force applied to the grasping section when the pair of grasping sections approaches each other can be detected by one sensor of the first pressure sensor and the second pressure sensor. A force applied to the grasping section when the pair of grasping sections separates from each other can be detected by the other sensor. 
     In the grasping hand according to the application example, it is preferable that the first pressure sensor and the second pressure sensor are disposed on a same board. 
     With this configuration, wire laying of the pressure sensor can be simplified. Alignment of the first pressure sensor and the second pressure sensor can also be simplified. 
     In the grasping hand according to the application example, it is preferable that the pressure sensor is a pressure sensor of a resistance type including resin and a conductive material. 
     With this configuration, a reduction in the thickness and an increase in the rigidity of the pressure sensor can be achieved. 
     In the grasping hand according to the application example, it is preferable that the conductive material is a carbon nanotube. 
     With this configuration, the durability, the load resistance, and the rigidity of the pressure sensor can be improved. 
     A robot according to an application example of the invention includes the grasping hand according to the application example explained above. 
     With such a robot, characteristics of the robot can be improved using the effects of the grasping hand. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a sectional view of a grasping hand according to a first embodiment of the invention. 
         FIG. 2  is an enlarged sectional view showing a first member, a second member, and a pressure sensor included in the grasping hand shown in  FIG. 1 . 
         FIG. 3  is a plan view of the first member and the second member shown in  FIG. 2  viewed from an overlapping direction of the first member and the second member. 
         FIG. 4  is a plan view of the pressure sensor shown in  FIG. 2 . 
         FIG. 5  is an enlarged sectional view of a pressure sensitive section of the pressure sensor shown in  FIG. 2 . 
         FIG. 6  is a plan view showing a modification of the pressure sensor. 
         FIG. 7  is an enlarged sectional view showing a first member, a second member, and a pressure sensor included in a grasping hand according to a second embodiment of the invention. 
         FIG. 8  is a plan view of the first member and the second member shown in  FIG. 7  viewed from an overlapping direction of the first member and the second member. 
         FIG. 9  is a perspective view showing a robot according to an embodiment of the invention. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Preferred embodiments of the invention are explained in detail below with reference to the drawings. 
     1. Grasping Hand 
     First Embodiment 
       FIG. 1  is a sectional view of a grasping hand according to a first embodiment of the invention. In the following explanation, for convenience of explanation, the upper side in  FIG. 1  is referred to as “upper” and the lower side in  FIG. 1  is referred to as “lower”. 
     A grasping hand  1  shown in  FIG. 1  is attached to, for example, an arm distal end portion of an industrial robot and used to grasp an object. The grasping hand  1  includes a case  2 , a transmitting mechanism  3  and a motor  4  set in the case  2 , and a pair of grasping sections  5  attached to the transmitting mechanism  3 . 
     The transmitting mechanism  3  opens and closes the pair of grasping sections  5  with a driving force generated by the motor  4 . Pressure sensors  37  configured to detect a force applied to the grasping sections  5  are provided in the transmitting mechanism  3 . Consequently, it is possible to grasp the object with an appropriate grasping force with the pair of grasping sections  5  by performing driving control of the motor  4  on the basis of a result of the detection of the pressure sensors  37 . In particular, the force applied to the grasping sections  5  can be highly accurately detected by the pressure sensors  37 . Since the pressure sensors  37  are small and thin, a reduction in the size and a reduction in the weight of the transmitting mechanism  3  and a reduction in the size and a reduction in the weight of the grasping hand  1  can be achieved. First, the sections of the grasping hand  1  are briefly explained below. 
     The case  2  has a box shape opened upward. The case  2  has a function of supporting the transmitting mechanism  3  and the motor  4  and protecting the transmitting mechanism  3  and the motor  4  from the outside. A constituent material of the case  2  is not particularly limited. Examples of the constituent material include metal materials such as aluminum, stainless steel, and iron. In such a case  2 , the transmitting mechanism  3  and the motor  4  are set. A part of the transmitting mechanism  3  is exposed from the opening of the case  2 . The grasping sections  5  are attached to the part. The shape of the case  2  is not limited to the shape shown in  FIG. 1  as long as the case  2  can exert the function explained above. 
     Although not shown in detail, the motor  4  is a rotary motor capable of normally and reversely rotating. The motor  4  is not particularly limited. For example, a DC motor, an AC motor, a stepping motor, a reluctance motor, an ultrasonic motor (a piezoelectric motor), and the like can be used. The motor  4  is electrically connected to a not-shown motor driver and driven by a driving current received from the motor driver. Although not shown in  FIG. 1 , the grasping hand  1  includes an encoder configured to detect a rotation angle of the motor  4  or a feed screw  31  explained below. An output signal of the encoder is input to the motor driver and used for driving control of the motor  4 . A setting position of the motor  4  may be any position as long as the motor  4  can input the driving force to the transmitting mechanism  3 . The setting position of the motor  4  is not limited to the position shown in  FIG. 1  and may be, for example, the outside of the case  2 . 
     The transmitting mechanism  3  has a function of transmitting the driving force of the motor  4  to the pair of grasping sections  5 . In this embodiment, the transmitting mechanism  3  has a function of converting a rotational motion of the motor  4  into a linear motion. Consequently, the pair of grasping sections  5  can be opened and closed by the driving force of the rotary motor  4 . 
     Specifically, the transmitting mechanism  3  includes a feed screw  31 , a pair of bearings  32  configured to rotatably support the feed screw  31  with respect to the case  2 , a pair of first members  33  having portions that mesh with the feed screw  31 , a pair of second members  34  coupled to the pair of first members  33  using screws  35  and washers  36 , and a guide  39  configured to movably support the pair of second members  34 . Constituent materials of these sections are not particularly limited. Examples of the constituent materials include metal materials such as aluminum, stainless steel, and iron. 
     The feed screw  31  is disposed to extend in the left-right direction in  FIG. 1 . The feed screw  31  includes a pair of screw sections  311  provided on the left and the right. One of the pair of screw sections  311  is a forward screw (a right screw) and the other is a backward screw (a left screw). Both end portions of such a feed screw  31  are rotatably supported by the case  2  via the pair of bearings  32 . The bearings  32  are, for example, ball bearings. 
     Such a feed screw  31  rotates with the driving force of the motor  4 . Although not shown in  FIG. 1 , a gear is provided in the feed screw  31 . A gear provided in a rotating shaft of the motor  4  meshes with this gear. Consequently, the feed screw  31  can be normally or reversely rotated by the motor  4 . A configuration for transmitting the driving force from the motor  4  to the feed screw  31  is not limited to a configuration in which the gear is used. The configuration may be, for example, a configuration in which a belt and a pulley are used or may be a configuration in which the rotating shaft of the motor  4  is directly connected to the feed screw  31 . When the motor  4  is a piezoelectric motor, the feed screw  31  may be configured integrally with a rotating shaft of the piezoelectric motor. 
     The pair of first members  33  is respectively disposed to extend from the feed screw  31  side to the opening side of the case  2 . A lower part of one first member  33  is screwed with one screw section  311  (on the left side in  FIG. 1 ) of the feed screw  31 . A lower part of the other first member  33  is screwed with the other screw section  311  (on the right side in  FIG. 1 ) of the feed screw  31 . Therefore, by rotating the feed screw  31 , the pair of first members  33  moves (linearly moves) to approach or separate. The first members  33  are not limited to a configuration in which the first members  33  are directly screwed with the feed screw  31 . For example, the first members  33  may be attached to another member screwed with the feed screw  31 . 
     The pair of second members  34  is respectively disposed to extend from the feed screw  31  side to the opening side of the case  2  such that parts of the pair of second members  34  project to the outside from the opening formed in the upper part of the case  2 . One second member  34  (on the left side in  FIG. 1 ) is coupled to the one first member  33  using the screw  35  and the washer  36 . The other second member  34  (on the right side in  FIG. 1 ) is coupled to the other first member  33  using the screw  35  and the washer  36 . 
     The pair of second members  34  is respectively movably supported by the guide  39  to approach or separate from each other in the left-right direction in  FIG. 1  along the guide  39 . The guide  39  is configured by a bar-like member. The guide  39  is disposed to extend in the left-right direction in  FIG. 1  and supported by the case  2 . The configuration of the guide  39  is not limited to the configuration shown in  FIG. 1  as long as the guide  39  is capable of moving the pair of second members  34  to approach or separate from each other. For example, the guide  39  may be configured by a plurality of bar-like members disposed in parallel to one another. In this case, the guide  39  that supports one second member  34  and the guide  39  that supports the other second member  34  may be configured by separate members. 
     The pressure sensors  37  are disposed between the first members  33  and the second members  34  of the transmitting mechanism  3  configured as explained above. The pressure sensors  37  detect a force applied to the grasping sections  5 . Pressure sensors  38  are disposed between the second members  34  and the washers  36 . The pressure sensors  38  also detect the force applied to the grasping sections  5 . The pressure sensors  37  and  38  and configurations concerning the pressure sensors  37  and  38  are explained in detail below. 
     The grasping sections  5  are attached to the second members  34  of the transmitting mechanism  3  by a fixing method such as screwing. The pair of grasping sections  5  is portions that grasp an object. A constituent material of the grasping sections  5  is not particularly limited. Examples of the constituent material include metal materials such as aluminum, stainless steel, and iron and ceramic materials. The shape of the grasping sections  5  is determined according to, for example, a type of an object and is not limited to the shape shown in  FIG. 1 . 
     The sections of the grasping hand  1  are briefly explained above. In the grasping hand  1 , the driving force generated by the motor  4  is transmitted to the pair of grasping sections  5  by the transmitting mechanism  3 . The pair of grasping sections  5  moves in the lateral direction in  FIG. 1  and opposite directions according to a rotating direction of the motor  4  and approaches or separates from each other. When a force is applied to the grasping sections  5 , pressure applied to the pressure sensors  37  disposed between the first members  33  and the second members  34  of the transmitting mechanism  3  and pressure applied to the pressure sensors  38  disposed between the second members  34  and the washers  36  of the transmitting mechanism  3  change. Therefore, the force applied to the grasping sections  5  can be detected by the pressure sensors  37  and  38 . The pressure sensors  37  and  38  and matters related to the pressure sensors  37  and  38  are explained in detail below. 
       FIG. 2  is an enlarged sectional view of the first member, the second member, and the pressure sensor included in the grasping hand shown in  FIG. 1 .  FIG. 3  is a plan view of the first member and the second member shown in  FIG. 2  viewed from an overlapping direction of the first member and the second member.  FIG. 4  is a plan view of the pressure sensor shown in  FIG. 2 .  FIG. 5  is an enlarged sectional view of a pressure sensitive section of the pressure sensor shown in  FIG. 2 . 
     As shown in  FIGS. 2 and 3 , the first member  33  and the second member  34  are respectively formed in a substantially tabular shape. The first member  33  and the second member  34  are superimposed and disposed to face plate surfaces thereof to each other. The first member  33  includes a screw hole  331  in which the screw section  311  of the feed screw  31  is screwed and a screw hole  332  in which a screw section  351  of the screw  35  is screwed. The screw holes  331  and  332  respectively pierce through the first member  33  in the thickness direction of the first member  33 . The second member  34  includes a through-hole  341  through which the screw section  351  (a shaft section) of the screw  35  is inserted and a through-hole  342  configuring a guide surface through which the guide  39  is inserted. The shapes of the first member  33  and the second member  34  are not limited to the shapes shown in  FIGS. 2 and 3  as long as the pressure sensor  37  can be clamped between the first member  33  and the second member  34 . However, contact surfaces with the pressure sensor  37  are desirably planes. The screw hole  331  may be a through-hole through which the screw section  311  of the feed screw  31  is inserted. In this case, the screw section  311  only has to be fastened to another member such as a nut on the opposite side of the second member  34  with respect to the first member  33 . 
     The washer  36  including a through-hole  361  through which the screw section  351  of the screw  35  is inserted is disposed on the opposite side of the first member  33  with respect to the second member  34 . The screw  35  is fastened to the first member  33  from the second member  34  side via the washer  36  such that a head  352  of the screw  35  is present on the second member  34  side. Consequently, the first member  33  and the second member  34  are coupled using the screw  35  and the washer  36 . The shape of the washer  36  is not limited to the shape shown in  FIGS. 2 and 3  as long as the pressure sensor  38  can be clamped between the second member  34  and the washer  36 . However, a contact surface with the pressure sensor  37  is desirably a plane. 
     The pressure sensor  37  is disposed between the first member  33  and the second member  34 . The pressure sensor  37  includes, as shown in  FIG. 3 , a pressure sensor  37   a  located on the through-hole  342  side (i.e., the grasping section  5  side) via the screw  35  when viewed from a direction in which the first member  33  and the second member  34  overlap and a pressure sensor  37   b  located on the screw hole  331  side (i.e., the motor  4  side) via the screw  35  when viewed from the direction. In this embodiment, as shown in  FIG. 4 , the pressure sensors  37   a  and  37   b  are configured as separate bodies. In the pressure sensors  37   a  and  37   b  disposed in this way, for example, a force F in a direction shown in  FIG. 2  is applied to the grasping section  5 , a compressing force (a load) is applied to the pressure sensor  37   a . A resistance value of the pressure sensor  37   a  decreases to be smaller than the resistance value of the pressure sensor  37   b . On the other hand, when a force in the opposite direction of the force F in the direction shown in  FIG. 2  is applied to the grasping section  5 , a compression force (a load) is applied to the pressure sensor  37   b . The resistance value of the pressure sensor  37   b  decreases to be smaller than the resistance value of the pressure sensor  37   a.    
     Similarly, the pressure sensor  38  is disposed between the second member  34  and the washer  36 . The pressure sensor  38  includes pressure sensors  38   a  and  38   b . However, in the pressure sensors  38   a  and  38   b , when a force is applied to the grasping section  5 , the resistance value of the pressure sensor  38   b  decreases when the resistance value of the pressure sensor  37   a  decreases and, on the other hand, the resistance value of the pressure sensor  38   a  decreases when the resistance value of the pressure sensor  37   b  decreases. 
     The pressure sensors  37  and  38  are respectively sensors that output signals corresponding to pressures applied to the pressure sensors  37  and  38 . The pressure sensors  37  and  38  are respectively pressure sensors of a resistance type. The pressure sensor  37  is more specifically explained below with reference to  FIG. 5 . The pressure sensor  38  can be configured the same as the pressure sensor  37 . 
     The pressure sensor  37  includes, as shown in  FIG. 5 , a sheet-like pressure sensitive member  371 , a pair of electrodes  372  and  373  disposed on both surfaces of the pressure sensitive member  371 , a supporting board  374  supporting the electrode  372 , and a supporting board  375  supporting the electrode  373 . In the pressure sensor  37 , when a pressing force (a contact force) in the thickness direction of the pressure sensor  37  is applied to the pressure sensor  37  by contact with an object around the pressure sensor  37 , a resistance value of the pressure sensitive member  371  between the electrodes  372  and  373  changes according to the pressing force. Therefore, the pressing force applied to the pressure sensor  37  can be detected on the basis of the resistance value change. 
     The pressure sensitive member  371  is formed of a material (pressure sensitive conductive resin) including resin  371   a  and a conductive material  371   b . The resin  371   a  and the conductive material  371   b  are desirably mixed. Consequently, the pressure sensitive member  371  can be easily molded in a sheet shape as shown in  FIG. 5  (in other words, even if the pressure sensitive member  371  is molded in the sheet shape, the function of the pressure sensor  37  can be exerted). A reduction in the thickness and a reduction in the weight of the pressure sensor  37  can be achieved. Such a pressure sensitive member  371  can be manufactured by, for example, injection molding or roll forming. The thickness of the pressure sensor  37  is not particularly limited. However, for example, the thickness of the pressure sensor  37  is desirably 0.1 mm or more and 1 mm or less and more desirably 0.1 mm or more and 0.5 mm or less. Consequently, it is possible to realize the pressure sensor  37  having sufficiently small thickness while having sufficient mechanical strength. 
     The resin  371   a  included in the pressure sensitive member  371  is not particularly limited as long as a necessary function of the pressure sensitive member  371  can be exerted. However, the resin  371   a  is desirably thermoplastic resin. Consequently, the resin  371   a  and the conductive material  371   b  are easily kneaded and have high dispersibility. It is easy to manufacture the pressure sensitive member  371 . The thermoplastic resin is not particularly limited. Examples of the thermoplastic resin include polyethylene, polypropylene, polyolefin such as an ethylene-vinyl acetate copolymer, modified polyolefin, polyester (PET, PBT, etc.), polyamide, thermoplastic polyimide, liquid crystal polymer such as aromatic polyester, polyphenylene oxide, polyphenylene sulfide, polycarbonate (PC), polyester carbonate (PPC), polymethyl methacrylate, polyether, polyether ether ketone (PEEK), polyether imide, polyacetal, polyvinyl chloride, and copolymers, blends, polymer alloys, and the like mainly containing these resins. One kind of these resins can be used or one or two kinds of these resins can be mixed and used. 
     Among these resins, the resin  371   a  desirably includes at least one resin of polycarbonate (PC) and polyester carbonate (PPC), more desirably includes the resin by 50 weight % or more of the entire resin  371   a , and still more desirably includes the resin by 75% or more. Consequently, the effect explained above (kneading easiness) becomes more conspicuous. Since a relatively hard pressure sensitive member  371  is obtained, an allowable load per unit area increases. The mechanical strength of the pressure sensor  37  can be increased. Aged deformation and setting of the pressure sensitive member  371  are prevented. A decrease (fluctuation) in a detection characteristic over time can also be prevented. 
     A Young&#39;s modulus of the resin  371   a  is desirably GPa or more. Consequently, since a relatively hard pressure sensitive member  371  is obtained, the mechanical strength of the pressure sensor  37  can be increased. Aged deformation and setting of the pressure sensitive member  371  are prevented. A decrease (fluctuation) in a detection characteristic over time can also be prevented. 
     A load deflecting temperature of the resin  371   a  is desirably 100° C. or more. Consequently, a decrease in the elasticity of the pressure sensitive member  371  under a high-temperature environment can be prevented. Even under a high-temperature environment, the pressure sensor  37  can exert the same detection accuracy as detection accuracy under a normal temperature environment or a low-temperature environment. That is, the pressure sensitive member  371  is less easily affected by temperature. Fluctuation (drift) of a detection signal due to a temperature change can be reduced. The load deflecting temperature refers to temperature at which the magnitude of deflection reaches a fixed value when the temperature of a sample is raised in a state in which a predetermined load is applied. This means that, as the temperature is higher, heat resistance is higher. The load deflecting temperature can be measured by a test method conforming to JIS 7191. 
     The conductive material  371   b  included in the pressure sensitive member  371  is not particularly limited as long as a necessary function of the pressure sensitive member  371  can be exerted. However, a carbon nanotude (CNT) is desirably used. Consequently, the pressure sensitive member  371  is less easily affected by temperature. Fluctuation (drift) of a detection signal due to a temperature change can be reduced. Therefore, for example, excessive temperature correction is unnecessary. A grasping force can be accurately detected. By using the carbon nanotube as the conductive material  371   b , a resistance value between the electrodes  372  and  373  smoothly changes with respect to a change in a force (a load) applied to the pressure sensor  37 . Further, a resistance value change amount between the electrodes  372  and  373  with respect to the force (the load) applied to the pressure sensor  37  increases. Therefore, a pressing force applied to the pressure sensor  37  can be more accurately detected. As the conductive material  371   b , other carbon materials such as carbon black, metal materials, and the like may be used. 
     A form of the conductive material  371   b  is not particularly limited. Examples of the form of the conductive material  371   b  include a particle form and a fiber form. However, the form of the conductive material  371   b  is desirably the particle form. Consequently, the effect of kneading easiness explained above can be obtained. When the conductive material  371   b  is the carbon nanotube, for example, the diameter of the carbon nanotube can be set to 100 nm or more and 200 nm or less and the length of the carbon nanotube can be set to 1 μm or more and 5 μm or less. Consequently, the effect can be more effectively exerted. 
     The content of the conductive material  371   b  in the pressure sensitive member  371  is not particularly limited. However, for example, the content of the conductive material  371   b  is desirably 5 wt % or more and 30 wt % or less, more desirably 10 wt % or more and 30 wt % or less, and still more desirably 20 wt % or more and 25 wt % or less. Consequently, reasonable conductivity can be imparted to the pressure sensitive member  371 . A decrease in the mechanical strength of the pressure sensitive member  371  due to excessive mixing of the conductive material  371   b  can be prevented. 
     The thickness of the pressure sensitive member  371  is not particularly limited. However, for example, the thickness of the pressure sensitive member  371  is desirably 0.01 mm or more and 1 mm or less and more desirably 0.05 mm or more and 0.2 mm or less. Consequently, the pressure sensitive member  371  can sufficiently exert the function of the pressure sensitive member  371 . The pressure sensitive member  371  having sufficiently small thickness is obtained. Therefore, it is possible to achieve a reduction in the size of the pressure sensor  37  while maintaining a detection characteristic of the pressure sensor  37 . 
     The pair of electrodes  372  and  373  disposed on both the surfaces of the pressure sensitive member  371  explained above is respectively uniformly disposed over substantially the entire region in the surface direction of the pressure sensitive member  371 . A formation range, the shape, and the like of the electrodes  372  and  373  are not particularly limited. The electrodes  372  and  373  may be patterned in, for example, a comb teeth shape. Both of the electrodes  372  and  373  may be disposed on one surface of the pressure sensitive member  371 . In this case, for example, the electrodes  372  and  373  only have to be formed in a comb teeth shape to mesh with each other while separating from each other. The electrodes  372  and  373  may be configured such that an intensity distribution in the surface direction of a pressing force in the pressure sensor  37   a  or the pressure sensor  37   b  can be detected. 
     A constituent material of the electrodes  372  and  373  is not particularly limited. Examples of the constituent material include various kinds of metal such as nickel, cobalt, gold, platinum, silver, copper, manganese, aluminum, magnesium, titanium, and tungsten and alloys containing at least one kind of metal among these kinds of metals. One kind of these kinds of metal can be used or two or more kinds of these kinds of metal can be used in combination (e.g., as a stacked structure). 
     The pair of supporting boards  374  and  375  that supports the pair of electrodes  372  and  373  explained above is not respectively particularly limited. For example, various printed boards such as a flexible board and a rigid board can be used. By using the printed board as the supporting boards  374  and  375  in this way, formation of the electrodes  372  and  373  on the supporting boards  374  and  375  is facilitated. By using the flexible board as at least one of the supporting boards  374  and  375 , a reduction in the thickness of the pressure sensor  37  can be easily achieved. On the other hand, by using the rigid board as at least one of the supporting boards  374  and  375 , a pressing force is easily applied to the pressure sensitive member  371 . The pressing force can be more accurately detected. 
     As shown in  FIG. 4 , at least one of the supporting boards  374  and  375  (in  FIG. 4 , the supporting board  374 ) includes a portion that supports wires  376  drawn out from the electrodes  372  and  373 . In this embodiment, the supporting boards  374  and  375  of the pressure sensor  37   a  and the supporting boards  374  and  375  of the pressure sensor  37   b  are configured as separate bodies. 
     As explained above, the grasping hand  1  includes the grasping section  5 , the motor  4  configured to generate a driving force for moving the grasping section  5 , and the transmitting mechanism  3  including the first member  33  and the second member  34  configured to transmit the driving force generated by the motor  4  to the grasping section  5 . The pressure sensor  37  is provided between the first member and the second member  34 . The first member  33  is supported by the feed screw  31  (a shaft member). The first member  33  moves along the feed screw  31  to move the second member  34 . The second member  34  moves in a direction parallel to the feed screw  31  to move the grasping section  5 . 
     With such a grasping hand  1 , the pressure sensor  37  is provided between the first member  33  and the second member  34  that transmit the driving force generated by the motor  4  to the grasping section  5 . Therefore, a force (a grasping force, a pressing force, etc.) applied to the grasping section  5  can be directly detected by the pressure sensor  37 . Since the rigidity of the pressure sensor  37  is high, the force applied to the grasping section  5  can be highly accurately detected by the pressure sensor  37 . Since the pressure sensor  37  is thin, a reduction in the size and a reduction in the weight of the transmitting mechanism  3  and a reduction in the size and a reduction in the weight of the grasping hand  1  can be achieved. 
     In this embodiment, the transmitting mechanism  3  includes the washer  36  configured to transmit the driving force generated by the motor  4  to the pair of grasping sections  5 . The pressure sensor  38  is disposed between the second member  34  and the washer  36 . One of the second member  34  and the washer  36  only has to be grasped as the “first member” according to the invention. The other only has to be grasped as the “second member” according to the invention. The pressure sensor  38  can achieve the same effect as the effect by the pressure sensor  37 . By providing both of the pressure sensors  37  and  38 , improvement of detection accuracy or detection sensitivity can also be achieved. One of the pressure sensors  37  and  38  may be omitted. In this case, the washer  36  may be omitted. 
     The transmitting mechanism  3  converts rotation of the motor  4  into an opening and closing motion of the pair of grasping sections  5 . Consequently, the pair of grasping sections  5  can be opened and closed by a relatively simple and inexpensive configuration. The mechanism that performs such conversion less easily transmits a force applied to the grasping section  5  to the motor  4 . Therefore, displacement of the grasping section  5  by the force can be reduced. The transmitting mechanism  3  only has to be capable of transmitting the driving force generated by the motor  4  to the first member  33  and the second member  34  and opening and closing the pair of grasping sections  5 . The transmitting mechanism  3  is not limited to the configuration for performing the conversion explained above. For example, a linear motor may be used as the motor  4 . The transmitting mechanism  3  may transmit the driving force generated by the motor  4  to the first member  33  and the second member  34  and open and close the pair of grasping sections  5 . 
     The grasping hand  1  includes the case  2  and the guide  39 , which is a guide member supported by the case  2  and configured to guide the second member  34 . Consequently, the second member  34  can be stably moved in a desired direction. 
     The first member  33  and the second member  34  are coupled by the screw  35 . Consequently, it is possible to change an output of the pressure sensor  37  according to a force applied to the grasping section  5  while coupling the first member  33  and the second member  34  with relatively high rigidity. The screw  35  couples not only the first member  33  and the second member  34  but also the washer  36 . Consequently, it is possible to change an output of the pressure sensor  38  according to the force applied to the grasping section  5  while coupling the second member  34  and the washer  36  with relatively high rigidity. 
     The pressure sensor  37  includes the pressure sensor  37   a , which is a first pressure sensor, disposed on the grasping section  5  side with respect to the screw  35  and the pressure sensor  37   b , which is a second pressure sensor, disposed on the opposite side of the grasping section  5  with respect to the screw  35 . Consequently, a force applied to the grasping section  5  when the pair of grasping sections  5  approaches can be detected by one sensor out of the pressure sensor  37   a  and the pressure sensor  37   b . A force applied to the grasping section when the pair of grasping sections  5  separates can be detected by the other sensor. The same applies to the pressure sensor  38 . The number of pressure sensors included in the pressure sensor  37  or the pressure sensor  38  is not limited to two and may be one or may be three or more. 
     The pressure sensor  37  is desirably a pressure sensor of the resistance type including the resin  371   a  and the conductive material  371   b . Consequently, a reduction in the thickness and an increase in the rigidity of the pressure sensor  37  can be achieved. 
     When the pressure sensor  37  is the pressure sensor of the resistance type including the resin  371   a  and the conductive material  371   b  in this way, the conductive material  371   b  is desirably a carbon nanotube. Consequently, the durability, the load resistance, and the rigidity of the pressure sensor  37  can be improved. The same applies to the pressure sensor  38 . The pressure sensors  37  and  38  are respectively not limited to the configuration shown in  FIG. 5  and may have, for example, a configuration in which pressure sensitive conductive rubber or a piezoresistive element is used. 
     Modification 
       FIG. 6  is a plan view showing a modification of the pressure sensor. 
     In the embodiment explained above, the example is explained in which the supporting boards  374  and  375  of the pressure sensor  37   a  and the supporting boards  374  and  375  of the pressure sensor  37   b  are configured as the separate bodies. However, the supporting boards  374  and  375  may be used in common in the pressure sensors  37   a  and  37   b  as shown in  FIG. 6 . In  FIG. 6 , at least one of the supporting boards  374  and  375  (in  FIG. 6 , the supporting board  374 ) is used in common in the pressure sensors  37   a  and  37   b  and includes a portion that supports the wires  376  of the sensors. 
     In this way, the pressure sensor  37   a  (the first pressure sensor) and the pressure sensor  37   b  (the second pressure sensor) are disposed on the supporting board  374 , which is the same board. Consequently, laying of the wire  376  of the pressure sensor  37  can be simplified. Alignment of the pressure sensors  37   a  and  37   b  can also be simplified. 
     Second Embodiment 
       FIG. 7  is an enlarged sectional view showing a first member, a second member, and a pressure sensor included in a grasping hand according to a second embodiment of the invention.  FIG. 8  is a plan view of the first member and the second member shown in  FIG. 7  viewed from an overlapping direction of the first member and the second member. 
     In the following explanation, the second embodiment is explained centering on differences from the first embodiment. Explanation of similarities to the first embodiment is omitted. In  FIGS. 7 and 8 , the same components as the components in the first embodiment are denoted by the same reference numerals and signs. 
     A transmitting mechanism  3 A included in a grasping hand  1 A in this embodiment includes a first member  33 A and a washer  36 A as shown in  FIGS. 7 and 8  instead of the first member  33  and the washer  36  of the transmitting mechanism  3  in the first embodiment explained above. 
     The first member  33 A includes a pair of screw holes  333   a  and  333   b  in which a screw  6  is screwed. The screw holes  333   a  and  333   b  are disposed in positions overlapping the pressure sensors  37   a  and  37   b . The screw  6  screwed in the screw holes  333   a  and  333   b  is tightened to the pressure sensors  37   a  and  37   b  side to be capable of applying a preload to the pressure sensors  37   a  and  37   b . Consequently, outputs of the pressure sensors  37   a  and  37   b  can be adjusted. 
     Similarly, the washer  36  includes a pair of screw holes  362   a  and  362   b  in which the screw  6  is screwed. The screw holes  362   a  and  362   b  are disposed in positions overlapping the pressure sensors  38   a  and  38   b . The screw  6  screwed in the screw holes  362   a  and  362   b  is tightened to the pressure sensors  38   a  and  38   b  side to be capable of applying a preload to the pressure sensors  38   a  and  38   b . Consequently, outputs of the pressure sensors  38   a  and  38   b  can be adjusted. 
     The screw  6  is a hexagonal socket head locking screw (slotted set screw). The screw  6  is not limited to the hexagonal socket head locking screw. Various screws such as a slotted head set screw and a cross (plus) recessed slotted set screw can be used. In  FIGS. 7 and 8 , the number of screws  6  corresponding to each of the pressure sensors  37   a ,  37   b ,  38   a , and  38   b  is one. However, the number of screws  6  is not limited to this. Depending on the size and the like of the sensors, a plurality of screws may be used for one sensor. 
     According to the second embodiment explained above, the same effects as the effects in the first embodiment can be exerted. 
     2. Robot 
       FIG. 9  is a perspective view showing a robot according to an embodiment of the invention. In the following explanation, a base  110  side of a robot  100  is referred to as “proximal end side” and the opposite side of the base  110  side (a grasping hand  1  side) is referred to as “distal end side”. 
     The robot  100  shown in  FIG. 9  is a so-called six-axis vertical articulated robot. The robot  100  can perform work such as supply, removal, conveyance, and assembly of a precision instrument and components configuring the precision instrument (objects). As shown in  FIG. 9 , the robot  100  includes a base  110 , a robot arm  10  turnably coupled to the base  110 , a force detecting device  17  attached to the distal end portion of the robot arm  10 , the grasping hand  1  mounted on the force detecting device  17 , and a control device  50  configured to control driving of the robot arm  10 . 
     The base  110  is fixed on, for example, a floor, a wall, a ceiling, or a movable truck. The robot arm  10  includes an arm  11  (a first arm) turnably coupled to the base  110 , an arm  12  (a second arm) turnably coupled to the arm  11 , an arm  13  (a third arm) turnably coupled to the arm  12 , an arm  14  (a fourth arm) turnably coupled to the arm  13 , an arm  15  (a fifth arm) turnably coupled to the arm  14 , and an arm  16  (a sixth arm) turnably coupled to the arm  15 . The grasping hand  1  (or  1 A) is mounted on the distal end face of the arm  16  via the force detecting device  17 . 
     Although not shown in  FIG. 9 , in joint sections of the robot arm  10 , driving sections including motors and speed reducers and angle sensors configured to detect driving states (e.g., rotation angles) of the joint sections are set. 
     Although not shown in  FIG. 9 , the control device  50  includes a processor such as a CPU (Central Processing Unit), a memory such as a ROM (Read Only Memory) or a RAM (Random Access Memory), and an I/F (an interface circuit). The processor reads and executes, as appropriate, computer programs stored in the memory, whereby the control device  50  realizes processing such as control of the operation of the robot  100 , various arithmetic operations, and determination. The I/F is configured to be communicable with the driving sections, the angle sensors, and the grasping hand  1 . 
     In  FIG. 9 , the control device  50  is disposed inside the base  110  of the robot  100 . However, the control device  50  is not limited to this and may be disposed, for example, on the outside of the base  110 . A display device including a monitor such as a display, an input device including, for example, a mouse and a keyboard, and the like may be connected to the control device  50 . 
     As explained above, the robot  100  includes the grasping hand  1  (or  1 A). With such a robot  100 , characteristics of the robot  100  can be improved using the effects of the grasping hand  1 . For example, by achieving a reduction in the size and a reduction in the weight of the grasping hand  1  (or LA), the operation of the robot  100  can be smoothly and highly accurately performed. 
     The embodiments of the invention are explained above with reference to the drawings. However, the invention is not limited to the embodiments. The components of the sections can be replaced with any components having the same functions. Any other components may be added to the invention. 
     The invention may be a combination of any two or more configurations (features) in the embodiments explained above. 
     The robot according to the embodiments is not limited to a single arm robot if the robot includes a robot arm and may be other robots such as a double arm robot and a SCARA robot. The number of arms (the number of joints) included in the robot arm is not limited to the number (six) in the embodiments and may be one or more and five or less or seven or more. 
     In the embodiments explained above, the example is explained in which the number of grasping sections included in the grasping hand is two (a pair). However, the number of grasping sections is not limited to this and may be three or more or two pairs or more. 
     The entire disclosure of Japanese Patent Application No. 2017-241646, filed Dec. 18, 2017 is expressly incorporated by reference herein.