Patent Publication Number: US-2022227006-A1

Title: Tactile Sensor, Robot Hand, and Robot

Description:
TECHNICAL FIELD 
     The present disclosure relates to a tactile sensor, a robot hand, and a robot. 
     BACKGROUND ART 
     In Japanese Patent Application Laid-open No. 2016-205942 (patent document 1), for example, a multiaxial force sensor attached to the fingertip of a robot hand is described. 
     The multiaxial force sensor includes a sensor unit that has plural pressure sensors and a cover that covers the sensor unit. External forces input to the cover are transmitted to the pressure sensors of the sensor unit. 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in the conventional multiaxial force sensor, when an external force is input to, for example, an edge portion of the cover, the cover inclines. 
     Additionally, when the external force that is input increases, the inclination of the cover also increases. At this time, the cover becomes largely displaced, at the position to which the external force is input, in a direction toward a base portion. Meanwhile, the part of the cover away from the position where the external force is input becomes largely displaced in a direction away from the base portion. 
     Here, when a pressure sensor is disposed in the position where the cover is largely displaced in the direction toward the base portion, an unexpected overload is applied to the pressure sensor. Furthermore, when a pressure sensor is disposed in the position where the cover is largely displaced in the direction away from the base and a contact of the pressure sensor is adhered to the cover, the cover and the contact separate from each other. Because of these issues, there are concerns about the durability of the multiaxial force sensor being reduced. 
     It is an object of the present disclosure to provide a tactile sensor, a robot hand, and a robot that can inhibit failures regardless of the position where force is applied to a cover. 
     Solution to Problem 
     A tactile sensor of the present disclosure includes a cover that is provided so as to cover at least part of a base portion, a detection unit that is disposed between the cover and the base portion and detects force applied to the cover, and a limiting structure that limits inclination of the cover with respect to the base portion. 
     Advantageous Effects of Invention 
     According to the present disclosure, failures can be inhibited regardless of the position where force is applied to a cover. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram showing a robot equipped with a robot hand pertaining to a first embodiment. 
         FIG. 2  is a sectional view showing main parts of the robot hand having a tactile sensor pertaining to the first embodiment. 
         FIG. 3  is a partially transparent view showing main parts of the robot hand viewed from the direction of the arrow A in  FIG. 2 . 
         FIG. 4  is a sectional view showing main parts of the robot hand having a tactile sensor pertaining to a second embodiment. 
         FIG. 5  is a partially transparent view showing main parts of the robot hand viewed from the direction of arrow B in  FIG. 4 . 
         FIG. 6  is a sectional view showing main parts of the robot hand having a tactile sensor pertaining to a third embodiment. 
         FIG. 7  is a partially transparent view showing main parts of the robot hand viewed from the direction of arrow C in  FIG. 6 . 
         FIG. 8  is a sectional view showing main parts of the robot hand having a tactile sensor pertaining to a fourth embodiment. 
         FIG. 9  is a partially transparent view showing main parts of the robot hand viewed from the direction of arrow D in  FIG. 8 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     A first embodiment will be described below with reference to  FIG. 1  to  FIG. 3 . 
       FIG. 1  is a diagram showing a robot  10  pertaining to this embodiment. The robot  10  includes a robot body  12 , a robot arm  14  that extends from the robot body  12 , and a robot hand  16  that is provided on a distal end of the robot arm  14 . 
     The robot arm  14  is supported by the robot body  12  via a first joint  14 A, and the robot arm  14  can rotate and bend with respect to the robot body  12 . Furthermore, the robot arm  14  includes a second joint  14 B and a third joint  14 C and can bend in arbitrary directions at each of the joints  14 B,  14 C. The robot hand  16  is supported by the robot arm  14  via a fourth joint  14 D, and the robot hand  16  can rotate and bend with respect to the robot arm  14 . 
     The robot hand  16  includes a first finger  20  and a second finger  22 , which are disposed opposing each other, and can hold an object  24  between the two fingers  20 ,  22 . The first finger  20  is equipped with a tactile sensor  26 , and the second finger  22  configures an opposing member that opposes the first finger  20  equipped with the tactile sensor  26 . 
     A controller  28  is connected to the robot body  12 . The robot body  12  outputs drive signals to actuators of the robot arm  14  and the robot hand  16  based on control signals from the controller  28  to drive the robot arm  14  and the robot hand  16 . 
       FIG. 2  is a sectional view of main parts showing the first finger  20 , and a base portion  30  configuring the first finger  20  applies gripping force according to relative displacement of the two fingers  20 ,  22  to the object  24  when it grips the object  24  together with the second finger  22  (see  FIG. 1 ). The base portion  30  is equipped with the tactile sensor  26 . 
     [Tactile Sensor] 
     The tactile sensor  26  includes a cover  32 , which is provided so as to cover at least part of the base portion  30 , and a detection unit (detailed below), which is disposed between the cover  32  and the base portion  30  and detects force F 1  applied to the cover  32 . Furthermore, the tactile sensor  26  includes a limiting structure  34  that limits inclination of the cover  32  with respect to the base portion  30 . Additionally, a contact portion  36  that contacts a target place of the object  24  is replaceably attached to the cover  32 . 
     [Cover] 
     The cover  32  has a side face covering portion  40  that is disposed along a base portion side face  38 , which is a face of the base portion  30  positioned on the second finger  22  side, and an end face covering portion  44  that extends from the distal end of the side face covering portion  40  and is disposed along a base portion end face  42  on the distal end side of the base portion  30 . The cover  32  is configured by a stainless steel plate as an example. The cover  32  may also be configured by, for example, an acrylic plate. 
     The side face covering portion  40  and the end face covering portion  44  are formed as rectangular plates, which is an arbitrary shape, and the cover  32  is L-shaped in cross section. The shape of the side face covering portion  40  and the end face covering portion  44  is not limited to a rectangular shape and may also be another shape. 
     (Detection Unit) 
     As shown in  FIG. 2  and  FIG. 3 , the detection unit includes a side face detection unit  50  provided between the base portion side face  38  and the side face covering portion  40  and an end face detection unit  52  provided between the base portion end face  42  and the end face covering portion  44 . The side face detection unit  50  is disposed in a place corresponding to the central portion of the side face covering portion  40  when viewed from the second finger  22  side, and the end face detection unit  52  is disposed in a place corresponding to the width direction central portion of the end face covering portion  44 . 
     It will be noted that a plurality of the side face detection units  50  may be provided between the base portion side face  38  and the side face covering portion  40  and that a plurality of the end face detection units  52  may be provided between the base portion end face  42  and the end face covering portion  44 . 
     The side face detection unit  50  and the end face detection unit  52  detect applied forces F 1 , F 2  as electrical changes and transmit the detected electrical changes to the controller  28  via a harness not shown in the drawings. Examples of electrical changes include a change in capacitance, a change in resistance value, a change in current, a change in inductance, a charge transfer, and a change in resonance frequency. 
     The two detection units  50 ,  52  are configured by sensors, and the sensors can be called load sensors or force sensors. 
     The two detection units  50 ,  52  have identical configurations, and include rectangular sensor bodies  50 A,  52 A and cylindrical contacts  50 B,  52 B that project from the sensor bodies  50 A,  52 A. It will be noted that the two detection units  50 ,  52  may be different types of detection units and may be detection units with different measurement ranges. 
     The sensor body  50 A of the side face detection unit  50  is fixed to the base portion side face  38 , and the distal end of the contact  50 B of the side face detection unit  50  is adhered to the side face covering portion  40  of the cover  32 . The sensor body  52 A of the end face detection unit  52  is fixed to the base portion end face  42 , and the distal end of the contact  52 B of the end face detection unit  52  is adhered to the end face covering portion  44  of the cover  32 . Because of this, the cover  32  is supported by the base portion  30  via the detection units  50 ,  52 , and the side face covering portion  40  and the end face covering portion  44  can be integrally displaced with respect to the base portion  30 . 
     The contacts  50 B,  52 B of the detection units  50 ,  52  are configured to retract toward the sensor bodies  50 A,  52 A in accordance with the applied forces F 1 , F 2  as an example, and the forces F 1 , F 2  applied to the contacts  50 B,  52 B are measured from the amount of retraction of the contacts  50 B,  52 B. Because of this, the detection units  50 ,  52  detect the forces F 1 , F 2  applied to the cover  32  from the relative displacement of the cover  32  with respect to the base portion  30 . 
     (Limiting Structure) 
     The limiting structure  34  is configured by stoppers that limit movement of the cover  32  in a direction toward the base portion  30 . The stoppers are disposed so as to surround the side face detection unit  50  and are disposed in the four corners of the side face covering portion  40 . Because of this, the stoppers limit movement of the peripheral edge portion of the cover  32 , and the stoppers share and receive, with the side face detection unit  50 , the forces F 1 , F 2  before an overload is applied to the tactile sensor  26 . 
     The stoppers include side face stoppers  54  provided on the base portion side face  38  and end face stoppers  56  provided on the base portion end face  42 . The side face stoppers  54  are fixed to the base portion  30 , but they may also be fixed to the cover  32 . 
     A distance dimension R 1  from end faces  54 A of the side face stoppers  54  to the side face covering portion  40  is smaller than a projection dimension T 1  by which the contact  50 B projects from the sensor body  50 A when a rated load is applied to the side face detection unit  50 . A distance dimension R 2  from side faces  56 A of the end face stoppers  56  to an end face  44 B of the end face covering portion  44  is smaller than the projection dimension T 1  by which the contact  50 B projects from the sensor body  50 A when the rated load is applied to the side face detection unit  50 . 
     When the force F 1  is applied to the cover  32  and the contact  50 B of the side face detection unit  50  largely retracts, the cover  32  hits the stoppers  54 ,  56 . When this happens, the stoppers  54 ,  56  share and receive, with the side face detection unit  50 , the applied force F 1 . This regulates movement of the side face covering portion  40  toward the base portion side face  38  and thus limits retraction exceeding the allowable amount of the contact  50 B of the side face detection unit  50  and inhibits input of an overload to the side face detection unit  50 . 
     As shown in  FIG. 3 , the side face stoppers  54  are disposed in places opposing the two corner portions of the side face covering portion  40  on the robot arm  14  side, and the rectangular side face covering portion  40  can hit the side face stoppers  54  at two places on the base end side of the base portion  30 . Furthermore, as shown in  FIG. 2 , the end face stoppers  56  are disposed in places opposing both length direction end portions of the end face  44 B of the end face covering portion  44 , and the rectangular side face covering portion  40  can hit the end face stoppers  56  via the end face covering portion  44  at two places on the distal end side of the base portion  30 . 
     Because of this, movement of the rectangular side face covering portion  40  toward the base portion side face  38  is regulated by the stoppers  54 ,  56  at the four corners which are the peripheral edge portion, and inclination of the rectangular side face covering portion  40  exceeding the allowable amount with respect to the base portion  30  is limited. 
     (Contact Portion) 
     The contact portion  36  is configured by a rubber material formed in a tabular shape, and the contact portion  36  mitigates impact and shock between the first finger  20  and the object  24  when the first finger  20  and the second finger  22  grip the object  24 . 
     Recessed portions  58  are formed in the four corners of the contact portion  36 , and through holes  60  that penetrate to the reverse face are formed in bottom surfaces of the recessed portions  58 . Screw holes  62  are formed in places in the side face covering portion  40  corresponding to the through holes  60 , and screws  64  inserted into the through holes  60  in the contact portion  36  are screwed into the screw holes  62 , whereby the contact portion  36  can be replaceably attached to the cover  32 . 
     (Action and Effects) 
     Next, the action and effects of this embodiment will be described. 
     In the robot  10  of this embodiment, the first finger  20  of the robot hand  16  is provided with the tactile sensor  26 . The tactile sensor  26  includes the cover  32  that covers part of the base portion  30  configuring the first finger  20 , the detection units  50 ,  52  that are disposed between the cover  32  and the base portion  30  and detect the force F 1  applied to the cover  32 , and the limiting structure  34  that limits inclination of the cover  32  with respect to the base portion  30 . 
     Because of this, even when the large force F 1  (gripping force) is applied to part of the cover  32  when the first finger  20  and the second finger  22  grip the object  24 , inclination of the cover  32  with respect to the base portion  30  is limited by the limiting structure  34 . 
     For this reason, even when either of the detection units  50 ,  52  is disposed in the place where the cover becomes displaced in the direction closest to the base portion  30  when the cover inclines, application of an unexpected overload to that detection unit  50 ,  52  can be inhibited. Because of this, a failure of that detection unit  50 ,  52  can be inhibited. 
     Meanwhile, even when either of the detection units  50 ,  52  is disposed in the place where the cover becomes displaced in the direction farthest away from the base portion  30  when the cover inclines, separation of the contact  50 B,  52 B of that detection unit  50 ,  52  from the cover  32  can be inhibited. 
     Because of this, a reduction in the durability of the tactile sensor  26  can be inhibited and thus reduce the rate of occurrence of failures. Consequently, loss caused by a failure can be inhibited regardless of the positions where the forces F 1 , F 2  are applied to the cover  32 . 
     Furthermore, the detection units  50 ,  52  detect the forces F 1 , F 2  applied to the cover  32  from the relative displacement of the cover  32  with respect to the base portion  30 . For this reason, a reduction in detection accuracy caused by a failure of the detection units  50 ,  52  can be inhibited. 
     Additionally, the cover  32  has the side face covering portion  40  that is disposed along the base portion side face  38  of the base portion  30  and the end face covering portion  44  that extends from the distal end portion of the side face covering portion  40  and is disposed along the base portion end face  42  of the base portion  30 . Furthermore, the detection units  50 ,  52  are disposed between the base portion side face  38  and the side face covering portion  40  and between the base portion end face  42  and the end face covering portion  44 . 
     Because of this, in addition to the force F 1  (gripping force) applied from the side face of the base portion  30 , the force F 2  (pressing force) from the distal end side of the base portion  30  can also be detected. 
     Furthermore, the limiting structure  34  is configured by the stoppers  54 ,  56  that limit movement of the cover  32  in a direction toward the base portion  30 . For this reason, it becomes possible to adjust the arrangement of the stoppers  54 ,  56  in accordance with the inclination allowed of the cover  32 . 
     Moreover, the stoppers  54 ,  56  limit movement of the peripheral edge portion of the cover  32  formed in an arbitrary shape. For this reason, the stoppers  54 ,  56  can stably inhibit inclination of the cover  32  compared to a case where they limit movement of the central portion of the cover  32  formed in an arbitrary shape. 
     Additionally, the contact portion  36  that contacts the target place is replaceably attached to the cover  32 . For this reason, contact portions  36  suited to objects  24  to be gripped and the work to be performed by the robot hand  16  can be selected and attached. 
     Specifically, when gripping a slippery object  24 , for example, a contact portion  36  having a high coefficient of friction can be attached, so that workability resulting from the robot  10  can be improved. 
     Furthermore, when the contact portion  36  deteriorates, just the contact portion  36  can be replaced. Because of this, the maintainability of the robot hand  16  is improved. 
     Second Embodiment 
       FIG. 4  and  FIG. 5  are drawings showing a second embodiment; parts identical or similar to those of the first embodiment are denoted by the same reference signs and description thereof is omitted, and only parts that are different will be described. 
     The tactile sensor  26  provided on the first finger  20  of the robot pertaining to this embodiment differs from that of the first embodiment in that it has a different limiting structure  34  for limiting inclination of the cover  32  with respect to the base portion  30 . Specifically, the shape of the stoppers configuring the limiting structure  34  and the shape of the contact portion  36  are different compared to those of the first embodiment. 
     (Limiting Structure) 
     That is, the limiting structure  34  is configured by side face stoppers  54  and end face stoppers  56  that limit movement of the cover  32  in a direction toward the base portion  30 . 
     (Side Face Stoppers) 
     The side face stoppers  54  have sideward face contacting portions  70  that contact a reverse face  40 A of the side face covering portion  40  and limit movement of the side face covering portion  40  in a direction toward the base portion side face  38 . Furthermore, the side face stoppers  54  have sideward end contacting portions  72  that contact an end face  40 B of the side face covering portion  40  and limit movement of the end face covering portion  44  in a direction toward the base portion end face  42 . 
     The side face stoppers  54  are formed so as to be L-shaped in cross section, and the sideward face contacting portions  70  are configured by flat surfaces that oppose the reverse face  40 A of the side face covering portion  40 . Furthermore, the sideward end contacting portions  72  are configured by flat surfaces that oppose the end face  40 B of the side face covering portion  40 . 
     (End Face Stoppers) 
     The end face stoppers  56  have endwardface contacting portions  74  that contact a reverse face  44 A of the end face covering portion  44  and limit movement of the end face covering portion  44  in a direction toward the base portion end face  42 . Furthermore, the end face stoppers  56  have endward end contacting portions  76  that contact an end face  44 B of the end face covering portion  44  and limit movement of the side face covering portion  40  in a direction toward the base portion side face  38 . 
     The end face stoppers  56  are formed so as to be L-shaped in cross section, and the endward face contacting portions  74  are configured by flat surfaces that oppose the reverse face  44 A of the end face covering portion  44 . Furthermore, the endward end contacting portions  76  are configured by flat surfaces that oppose the end face  44 B of the end face covering portion  40 . 
     A distance dimension R 3  from the sideward face contacting portions  70  of the side face stoppers  54  to the side face covering portion  40  is smaller than the projection dimension T 1  by which the contact  50 B projects from the sensor body  50 A when the rated load is applied to the side face detection unit  50 . A distance dimension R 4  from the endward end contacting portions  76  of the end face stoppers  56  to the end face  44 B of the end face covering portion  44  is smaller than the projection dimension T 1  by which the contact  50 B projects from the sensor body  50 A when the rated load is applied to the side face detection unit  50 . 
     A distance dimension R 5  from the endward face contacting portions  74  of the end face stoppers  56  to the end face covering portion  44  is smaller than a projection dimension T 2  by which the contact  52 B projects from the sensor body  52 A when the rated load is applied to the end face detection unit  52 . A distance dimension R 6  from the sideward end contacting portions  72  of the side face stoppers  54  to the end face  40 B of the side face covering portion  40  is smaller than the projection dimension T 2  by which the contact  52 B projects from the sensor body  52 A when the rated load is applied to the end face detection unit  52 . 
     When the force F 1  is applied from the side face side of the cover  32  and the contact  50 B of the side face detection unit  50  largely retracts, the cover  32  hits the sideward face contacting portions  70  of the side face stoppers  54  and the endward end contacting portions  76  of the end face stoppers  56 . When this happens, the stoppers  54 ,  56  receive the applied force F 1 . This regulates movement of the side face covering portion  40  toward the base portion side face  38  and thus limits retraction exceeding the allowable amount of the contact  50 B of the side face detection unit  50  and inhibits input of an overload to the side face detection unit  50 . 
     Furthermore, when the force F 2  is applied from the distal end side of the cover  32  and the contact  52 B of the end face detection unit  52  largely retracts, the cover  32  hits the sideward end contacting portions  72  of the side face stoppers  54  and the endward face contacting portions  74  of the end face stoppers  56 . When this happens, the stoppers  54 ,  56  receive the applied force F 2 . This regulates movement of the end face covering portion  44  toward the base portion end face  42  and thus limits retraction exceeding the allowable amount of the contact  52 B of the end face detection unit  52  and inhibits input of an overload to the end face detection unit  52 . 
     Additionally, movement of the rectangular side face covering portion  40  toward the base portion side face  38  is regulated by the stoppers  54 ,  56  at the four corners, and inclination of the rectangular side face covering portion  40  exceeding the allowable amount with respect to the base portion side face  38  is limited. Furthermore, movement of the rectangular end face covering portion  44  toward the base portion end face  42  is regulated by the stoppers  54 ,  56  at the four corners, and inclination of the rectangular end face covering portion  44  exceeding the allowable amount with respect to the base portion end face  42  is limited. 
     (Contact Portion) 
     The contact portion  36  has a side face portion  36 A disposed along the side face covering portion  40  of the cover  32  and an end face portion  36 B disposed along the end face covering portion  44 , and the contact portion  36  is formed so as to be L-shaped in cross section. 
     Recessed portions  58  are formed in the four corners of the side face portion  34 A and the end face portion  36 B of the contact portion  36 , and screws  64  inserted into through holes  60  in the bottom surfaces of the recessed portions  58  are screwed into screw holes  62  in the cover  32 , whereby the contact portion  36  can be replaceably attached to the cover  32 . 
     (Action and Effects) 
     In this embodiment also, the same action and effects can be obtained in regard to parts identical or similar to those of the first embodiment. 
     Furthermore, in this embodiment, the force F 2  applied to the cover  32  from the distal end side of the base portion  30  can be received at the four corners of the end face covering portion  44  by the stoppers  54 ,  56 . Because of this, inclination of the end face covering portion  44  of the cover  32  with respect to the base portion end face  42  can be limited. 
     For this reason, application of an unexpected overload to the end face detection unit  52  can be inhibited, and a failure of the end face detection unit  52  can be inhibited. Furthermore, separation of the contact  52 B of the end face detection unit  52  from the cover  32  can be inhibited. 
     Because of this, a reduction in the durability of the tactile sensor  26  can be inhibited and thus reduce the rate of occurrence of failures, and loss caused by a failure can be inhibited regardless of the positions where the forces F 1 , F 2  are applied to the cover  32 . 
     Moreover, in this embodiment, the end face stoppers  56  having the endward face contacting portions  74  and the endward end contacting portions  76  and the side face stoppers  54  having the sideward end contacting portions  72  and the sideward face contacting portions  70  are used. Because of this, inclination of the end face covering portion  44  of the cover  32  with respect to the base portion end face  42  and inclination of the side face covering portion  40  of the cover  32  with respect to the base portion side face  38  can be limited. 
     Third Embodiment 
       FIG. 6  and  FIG. 7  are drawings showing a third embodiment; parts identical or similar to those of the first embodiment and the second embodiment are denoted by the same reference signs and description thereof is omitted, and only parts that are different will be described. 
     The tactile sensor  26  provided on the first finger  20  of the robot  10  pertaining to this embodiment differs from those of the first embodiment and the second embodiment in that it has a different limiting structure  34  for limiting inclination of the cover  32  with respect to the base portion  30 . Specifically, the stoppers configuring the limiting structure  34  are different compared to those of the first embodiment and the second embodiment. 
     (Limiting Structure) 
     That is, the stoppers configuring the limiting structure  34  include first side face stoppers  80  provided on the base portion side face  38  and second side face stoppers  82  provided on the side face covering portion  40 . Furthermore, the stoppers configuring the limiting structure  34  include first end face stoppers  84  provided on the base portion end face  42  and second end face stoppers  86  provided on the end face covering portion  44 . 
     The second side face stoppers  82  and the first end face stoppers  84  limit movement of the side face covering portion  40  in a direction toward the base portion side face  38 . The first side face stoppers  80  and the second end face stoppers  86  limit movement of the end face covering portion  44  in a direction toward the base portion end face  42 . 
     A distance dimension R 7  from the second side face stoppers  82  to the base portion side face  38  and a distance dimension R 8  from side faces  84 A of the first end face stoppers  84  to the end face  44 B of the end face covering portion  44  are smaller than the projection dimension T 1  by which the contact  50 B projects when the rated load is applied to the side face detection unit  50 . A distance dimension R 9  from side faces  80 A of the first side face stoppers  80  to the end face  40 B of the side face covering portion  40  and a distance dimension R 10  from the second end face stoppers  86  to the base portion end face  42  are smaller than the projection dimension T 2  by which the contact  52 B projects when the rated load is applied to the end face detection unit  52 . 
     When the force F 1  is applied from the side face side of the cover  32  and the contact  50 B of the side face detection unit  50  largely retracts, the second side face stoppers  82  hit the base portion side face  38 . Furthermore, the end face  44 B of the end face covering portion  44  hits the side faces  84 A of the first end face stoppers  84 . When this happens, the stoppers  82 ,  84  receive the applied force F 1 . This regulates movement of the side face covering portion  40  toward the base portion side face  38  and thus limits retraction exceeding the allowable amount of the contact  50 B of the side face detection unit  50  and inhibits input of an overload to the side face detection unit  50 . 
     Furthermore, when the force F 2  is applied from the distal end side of the cover  32  and the contact  52 B of the end face detection unit  52  largely retracts, the end face  40 B of the side face covering portion  40  hits the side faces  80 A of the first side face stoppers  80 . Furthermore, the second end face stoppers  86  hit the base portion end face  42 . When this happens, the stoppers  80 ,  86  receive the applied force F 2 . This regulates movement of the end face covering portion  44  toward the base portion end face  42  and thus limits retraction exceeding the allowable amount of the contact  52 B of the end face detection unit  52  and inhibits input of an overload to the end face detection unit  52 . 
     Additionally, movement of the rectangular side face covering portion  40  toward the base portion side face  38  is regulated at the four corners by the stoppers  82 ,  84 , and inclination of the rectangular side face covering portion  40  exceeding the allowable amount with respect to the base portion side face  38  is limited. Furthermore, movement of the rectangular end face covering portion  44  toward the base portion end face  42  is regulated at the four corners by the stoppers  80 ,  86 , and inclination of the rectangular end face covering portion  44  exceeding the allowable amount with respect to the base portion end face  42  is limited. 
     (Action and Effects) 
     In this embodiment also, the same action and effects can be obtained in regard to parts identical or similar to those of the first embodiment and the second embodiment. 
     Fourth Embodiment 
       FIG. 8  and  FIG. 9  are drawings showing a fourth embodiment; parts identical or similar to those of the first embodiment to the third embodiment are denoted by the same reference signs and description thereof is omitted, and only parts that are different will be described. 
     The tactile sensor  26  provided on the first finger  20  of the robot  10  pertaining to this embodiment differs from those of the first embodiment to the third embodiment in that it has a different limiting structure  34  for limiting inclination of the cover  32  with respect to the base portion  30 . 
     (Base Portion) 
     In the base portion  30  configuring the first finger  20  of the robot hand  16 , a cover housing portion  90  that is inwardly set back is formed in the distal end portion of the base portion side face  38  on the second finger  22  side and in the base portion end face  42  on the second finger  22  side. The cover  32  is disposed in the cover housing portion  90 , and part of the base portion  30  is covered by the cover  32 . 
     The contact portion  36  is attached to the cover  32 . An obverse face  36 C of a side face portion  36 A of the contact portion  36  and the base portion side face  38  are configured to be positioned in the same plane. An obverse face  36 D of an end face portion  36 B of the contact portion  36  and the base portion end face  42  are configured to be positioned in the same plane. 
     A side face mounting hole  94  is formed in the central portion of a side portion bottom surface  92  of the cover housing portion  90  that is set back from the base portion side face  38 , and the side face detection unit  50  is disposed in the side face mounting hole  94 . The side face mounting hole  94  is set to a depth where the contact  50 B of the side face detection unit  50  disposed therein projects from the side portion bottom surface  92 , and the contact  50 B of the side face detection unit  50  is adhered to the side face covering portion  40  of the cover  32 . 
     An end face mounting hole  98  is formed in the central portion of an end portion bottom surface  96  of the cover housing portion  90  that is set back from the base portion end face  42 , and the end face detection unit  52  is disposed in the end face mounting hole  98 . The end face mounting hole  98  is set to a depth where the contact  52 B of the end face detection unit  52  disposed therein projects from the end portion bottom surface  96 , and the contact  52 B of the end face detection unit  52  is adhered to the end face covering portion  44  of the cover  32 . 
     (Limiting Structure) 
     When the force F 1  is applied from the side face side of the cover  32  and the contact  50 B of the side face detection unit  50  largely retracts, the reverse face  40 A of the side face covering portion  40  hits the side portion bottom surface  92 . When this happens, the side portion bottom surface  92  receives the applied force F 1 . This regulates movement of the side face covering portion  40  and thus limits retraction exceeding the allowable amount of the contact  50 B of the side face detection unit  50  and inhibits input of an overload to the side face detection unit  50 . 
     Furthermore, when the force F 2  is applied from the distal end side of the cover  32  and the contact  52 B of the end face detection unit  52  largely retracts, the reverse face  44 A of the end face covering portion  44  hits the end portion bottom surface  96 . When this happens, the end portion bottom surface  96  receives the applied force F 2 . This regulates movement of the end face covering portion  44  and thus limits retraction exceeding the allowable amount of the contact  52 B of the end face detection unit  52  and inhibits input of an overload to the end face detection unit  52 . 
     Additionally, movement of the side face covering portion  40  toward the base portion  30  is regulated by the side portion bottom surface  92  on the outer peripheral portion of the side face mounting hole  94 , so inclination of the side face covering portion  40  exceeding the allowable amount with respect to the side portion bottom surface  92  is limited. Furthermore, movement of the end face covering portion  44  toward the base portion  30  is regulated by the end portion bottom surface  96  on the outer peripheral portion of the end face mounting hole  98 , so inclination of the end face covering portion  44  exceeding the allowable amount with respect to the end portion bottom surface  96  is limited. 
     The limiting structure  34  is configured in the tactile sensor  26  by the side portion bottom surface  92 , the end portion bottom surface  96 , the depth of the side face mounting hole  94 , and the depth of the end face mounting hole  98 . 
     (Action and Effects) 
     In this embodiment also, the same action and effects can be obtained in regard to parts identical or similar to those of the first embodiment to the third embodiment. 
     Furthermore, the configuration of the limiting structure  34  can be simplified compared to a case where the limiting structure  34  is configured by providing stoppers on the base portion  30  or the cover  32 . 
     It will be noted that although in the embodiments a case was described where the tactile sensor  26  is provided on the first finger  20  of the robot hand  16 , the tactile sensor  26  is not limited to this. For example, the tactile sensor  26  may also be provided on a wrist portion of the robot  10 . Furthermore, the tactile sensor  26  may also be provided on both the first finger  20  and the second finger  22 . Moreover, the end face detection unit  52  may also be omitted. Furthermore, the detection units  50 ,  52  may also be provided on the cover  32 . 
     Below is a description of the reference signs.
       10  Robot     12  Robot Body     16  Robot Hand     20  First Finger     22  Second Finger     24  Object     26  Tactile Sensor     30  Base Portion     32  Cover     34  Limiting Structure     36  Contact Portion     38  Base Portion Side Face     40  Side Face Covering Portion     42  Base Portion End Face     44  End Face Covering Portion     50  Side Face Detection Unit     52  End Face Detection Unit     54  Side Face Stopper     56  End Face Stopper     70  Sideward Face Contacting Portion     72  Sideward End Contacting Portion     74  Endward Face Contacting Portion     76  Endward End Contacting Portion     80  First Side Face Stopper     82  Second Side Face Stopper     84  First End Face Stopper     86  Second End Face Stopper   

     &lt;&lt;Additional Remarks&gt;&gt; 
     From this specification the following aspects are conceptualized. 
     Aspect 1 is a tactile sensor including: 
     a cover that is provided so as to cover at least part of a base portion; 
     a detection unit that is disposed between the cover and the base portion and detects force applied to the cover; and a limiting structure that limits inclination of the cover with respect to the base portion. 
     Aspect 2 is the tactile sensor of aspect 1, wherein the detection unit detects force applied to the cover from relative displacement of the cover with respect to the base portion. 
     Aspect 3 is the tactile sensor of aspect 1 or aspect 2, wherein; 
     the cover has a side face covering portion that is disposed along a base portion side face of the base portion and an end face covering portion that extends from the side face covering portion and is disposed along a base portion end face of the base portion, and 
     the detection unit is disposed between the base portion side face and the side face covering portion and between the base portion end face and the end face covering portion. 
     Aspect 4 is the tactile sensor of aspect 3, wherein the limiting structure comprises a stopper that limits movement of the cover in a direction toward the base portion. 
     Aspect 5 is the tactile sensor of aspect 4, wherein the stopper limits movement of a peripheral edge portion of the cover formed in an arbitrary shape. 
     Aspect 6 is the tactile sensor of aspect 4 or aspect 5, wherein 
     the stopper includes a side face stopper provided at the base portion side face and an end face stopper provided at the base portion end face, 
     the side face stopper has a sideward face contacting portion that contacts the side face covering portion and limits movement of the side face covering portion in a direction toward the base portion side face and a sideward end contacting portion that contacts an end face of the side face covering portion and limits movement of the end face covering portion in a direction toward the base portion end face, and 
     the end face stopper has an endward face contacting portion that contacts the end face covering portion and limits movement of the end face covering portion in a direction toward the base portion end face and an endward end contacting portion that contacts an end face of the end face covering portion and limits movement of the side face covering portion in a direction toward the base portion side face. 
     Aspect 7 is the tactile sensor of aspect 4 or aspect 5, wherein 
     the stopper includes a first side face stopper provided at the base portion side face, a second side face stopper provided at the side face covering portion, a first end face stopper provided at the base portion end face, and a second end face stopper provided at the end face covering portion, and 
     the second side face stopper and the first end face stopper limit movement of the side face covering portion in a direction toward the base portion side face, and the first side face stopper and the second end face stopper limit movement of the end face covering portion in a direction toward the base portion end face. 
     Aspect 8 is the tactile sensor of any of aspect 1 to aspect 7, wherein a contact portion that contacts a target place is replaceably attached to the cover. 
     Aspect 9 is a robot hand including: 
     the tactile sensor of any of aspect 1 to aspect 8; and an opposing member that is disposed opposing the tactile sensor and grips an object between itself and the tactile sensor. 
     Aspect 10 is a robot including: 
     the robot hand of aspect 9; and 
     a robot body that drives the robot hand. 
     All publications, patent applications, and technical standards mentioned in this specification are incorporated by reference herein to the same extent as if each individual publication, patent application, or technical standard were specifically and individually indicated to be incorporated by reference.