Patent Publication Number: US-2023133561-A1

Title: Gripper

Description:
The present invention relates to the handling field and more particularly the gripping field. 
     BACKGROUND OF THE INVENTION 
     Conventionally, a gripper comprises a clamp including a frame on which a proximal end of an actuated finger is articulated. The distal end of the finger comprises a jaw generally provided with an anti-slip surface. In general, the finger is rectilinear or curved. Such a clamp is particularly suitable for grasping objects with a similar and ideally predefined geometry. Such a clamp lacks versatility, particularly for grasping special objects such as objects that are large-sized, planar, or having a cylindrical or conical portion. It is then necessary to replace the clamp with a tool that is suitable for such special objects. 
     In order to improve the versatility of a gripper, it has been considered to make a clamp comprising two articulated phalanxes. In general, such a gripper comprises a finger composed by a distal first phalanx and a proximal second phalanx articulated on a frame and articulated together so as to enable a rotation of the first phalanx relative to the second phalanx so that the finger could switch from an opening configuration into a clamping configuration. A first actuator controls the movement of the first phalanx and a second actuator controls the movement of the second phalanx. In general, the motors and the reducers associated with the actuators are attached on the frame and the transmission is carried by the phalanxes. Control of the clamping force applied by such a finger requires equipping all of the actuators and the articulations with instrumentation. Such instrumentation is heavy, costly and the cumulated drift of all of the measuring instruments added to the frictions of the transmission does not allow for an accurate control of clamping of the gripper suited to handling of delicate objects. Finally, the inertia of such a gripper is also detrimental to the accuracy of the control of the clamping force. 
     OBJECT OF THE INVENTION 
     In particular, the invention aims to improve the accuracy of control of a clamping force of a gripper with fingers. 
     SUMMARY OF THE INVENTION 
     To this end, a gripper is provided including a frame and an actuated finger, the finger comprising a first distal phalanx and a second proximal phalanx which is articulated on the frame about a first axis, the first phalanx and the second phalanx being mechanically linked so as to enable a rotation of the first phalanx about a second axis substantially parallel to the first axis so that the finger could switch from an opening configuration into a clamping configuration when the first phalanx and/or the second phalanx performs a rotation in a first way relative to the frame. According to the invention, the second phalanx comprises a first bar comprising a first end linked to the first phalanx and a second end pivotally mounted on the frame about the first axis. The second phalanx also comprises a linear actuator comprising a third end linked to the first phalanx and a fourth end pivotally mounted on the frame, the first bar and the linear actuator being arranged so as to form a first four-bar linkage wherein a distance separating the third end from the fourth end can be modified. 
     This difference from four-bar linkages known in such applications wherein the distance that separates the articulation points of the bars is fixed contributes to the obtainment of a gripper that is lighter and in which the transmission of movement to the first phalanx has a reduced inertia of the gripper. The gripper of the invention is more transparent and has an improved reversibility of the actuation which allows for an accurate return and a control of the force by direct measurement of the motor current. 
     The presence of a force sensor at the actuator becomes useless. 
     The versatility of the gripper is improved when the finger comprises a third phalanx linking the first phalanx and the second phalanx. 
     The compactness of the gripper is improved when the third phalanx comprises a second bar comprising a fifth end articulated on the first phalanx and a six end articulated on a first connecting rod, the third phalanx also comprising a third bar comprising a seventh end articulated on the first phalanx and an eighth end articulated on the first connecting rod, the first end and the third end being articulated with the first connecting rod. 
     The compactness of the gripper is improved even further when an orthogonal projection of the third end on a line connecting the first end and the eighth end belongs to a section connecting the first end and the eighth end. 
     The compactness of the gripper is improved even further when the first end is articulated on the sixth end. 
     Advantageously, the second phalanx comprises a first member for biasing the finger towards the opening configuration and/or the third phalanx comprises a second member for biasing the finger towards the opening configuration. An economic embodiment is obtained when the biasing member comprises an elastic element. 
     The mass of the gripper and its inertia are improved when the linear actuator comprises a screw jack cylinder, preferably a cylinder comprising a ball screw. 
     The hyperstaticity of the mechanism is reduced when the linear actuator is linked to the finger and/or to the chassis by a sliding pivot type connection with a limited sliding with a third axis substantially parallel to the first axis. 
     The accuracy of the gripper is improved when the gripper comprises at least one rotary encoder. 
     The versatility of the gripper is improved when the finger comprises a controllable adhesive element. 
     A sensitive improvement of the versatility of the gripper is obtained when the adhesive element is arranged so as to exert a holding force according to a direction substantially orthogonal to the first axis. 
     Advantageously, the adhesive element is secured to the first phalanx. 
     The gripper enables handling of objects that cannot be gripped—such as planar objects—when the gripper comprises a first stop to limit a first angular stroke of a first rotation of the first phalanx about the second axis in a second way opposite to the first way. Optionally, the first angular stroke comprises a first angular sector strictly positive according to the second way and measured starting from a first plane comprising the first axis and the second axis. 
     Advantageously, the angular sector is comprised between ten and ninety degrees, preferably comprised between twenty and sixty degrees. 
     Still advantageously, the gripper comprises a third biasing member of the first phalanx for exerting a third biasing force which brings the first phalanx from a position located in the first angular sector towards a position leading to the opening configuration of the finger. 
     The gripper can be easily adapted when the third biasing member comprises means for setting an over-opening position of the first phalanx starting from which the third biasing force is exerted. 
     A simple design is obtained when the third biasing member comprises a spring and the means for adjusting the over-opening position comprise a cable with an adjustable length linked to one end of the spring. 
     The invention also relates to a gripping device which comprises a plurality of grippers of the above-described type or of an already known type. 
     According to other non-exclusive and optional particular embodiments of the invention:
         the plurality of grippers comprises a first gripper, a second gripper and a third gripper;   the first gripper and the second gripper are respectively carried by a first plate and a second plate slidably mounted relative to the chassis according to two opposite ways of a first direction;   the sliding movements of the first plate and of the second plate are actuated using a first actuation device provided with a unique second actuator.   the second actuator is a rotary actuator and/or the first plate comprises a second screw/nut set and/or the second plate comprises a third screw/nut set.   the first actuation device comprises a first pinion for driving a first transmission member with a drive force;   the first gripper comprising a first actuated finger, the second gripper comprising a second actuated finger, the first actuated finger is articulated relative to the first plate about a fifth axis and the second actuated finger is articulated relative to the second plate about a sixth axis, the fifth axis and the sixth axis being substantially orthogonal to the first axis;   a rotation of the first finger relative to the first plate about the fifth axis (O 5 ) and a rotation of the second finger ( 123 ) about the sixth axis (O 6 ) are actuated using a second actuation device.   the second actuation device is provided with a unique third actuator;   the second actuation device is arranged so that a sliding movement of the first plate and/or of the second plate is decoupled from a rotational movement of the first actuated finger and of the second actuated finger and vice versa;   the second actuation device is arranged so that the rotational movements of the first finger and of the second finger are performed in opposite rotational ways;   the third actuator is a rotary actuator secured to the first plate;   the second actuation device comprises a second pinion for driving a second transmission member with a drive force;   the second transmission member forming a closed loop, the second actuation device comprises a first idler of second transmission member and a second idler member of a second transmission member, the first idler and the second idler being secured to the chassis;   the second transmission member is a belt that is toothed over both faces thereof;   the plurality of grippers comprises a fourth gripper;   the third gripper and the fourth gripper are respectively carried by a third plate and a fourth plate slidably mounted relative to the chassis according to two opposite ways of a second direction;   the sliding movements of the third plate and of the fourth plate are actuated using a third actuation device provided with a unique fourth actuator;   the fourth actuator is a rotary actuator and/or the third plate comprises a fourth screw/nut set and/or the fourth plate comprises a fifth screw/nut set and/or the third actuation device comprises a third pinion for driving a third transmission member with a drive force;   the third gripper comprising a third actuated finger and the fourth gripper comprising a fourth actuated finger, the third actuated finger is articulated relative to the third plate about a seventh axis and the fourth actuated finger is articulated relative to the fourth plate about an eighth axis, the seventh axis and the eighth axis being substantially orthogonal to the first axis;   a rotation of the third finger relative to the frame about the seventh axis and a rotation of the fourth finger about the eighth axis are actuated using a fourth actuation device arranged so that the rotational movements of the third finger and of the fourth finger being performed in opposite rotational ways;   the fourth actuation device is arranged so that a sliding movement of the third plate and/or the fourth plate is decoupled from a rotational movement of the third actuated finger and of the fourth actuated finger and vice versa;   a device for coupling the fourth actuation device with the second actuation device arranged so that the third actuation device is driven by the third actuator;   the coupling device comprises a first roller rotatably mounted on the first plate or the second plate about a ninth axis and which is driven by the second actuation device, a second roller rotatably mounted on the third plate or the fourth plate about a tenth axis and which drives the third actuation device, a movement transmission device transmitting a rotation from the first roller to the second roller;   the coupling device comprises an articulated arm comprising a first arm section and a second arm section articulated together about an eleventh axis, the first arm section being articulated about the ninth axis and the second arm section being articulated about the tenth axis, the articulated arm comprising a third idler roller of a transmission element of the transmission device.       

     Other features and advantages of the invention will appear upon reading the following description of a particular and non-limiting embodiment/implementation of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference will be made to the appended drawings, among which: 
         FIG.  1    is a planar schematic representation of a gripper according to a first embodiment of the invention; 
         FIG.  2    is a schematic representation of the gripper of  FIG.  1    in a first clamping phase; 
         FIG.  3    is a schematic representation of the gripper of  FIG.  1    in a second clamping phase; 
         FIG.  4    is a schematic representation of the gripper of  FIG.  1    in a third clamping phase; 
         FIG.  5    is a planar schematic representation of a gripper according to a second embodiment of the invention in a clamping configuration; 
         FIG.  6    is a schematic representation of the gripper of  FIG.  5    in a first planar gripping phase; 
         FIG.  7    is a schematic representation of the gripper of  FIG.  5    in a second planar gripping phase; 
         FIG.  8    is a schematic representation of the gripper of  FIG.  5    in a third planar gripping phase; 
         FIG.  9    is a schematic representation of the gripper of  FIG.  5    in a fourth planar gripping phase; 
         FIG.  10    is a perspective schematic representation of a gripping device according to a third embodiment of the invention; 
         FIG.  11    is a partial perspective schematic representation of the embodiment of  FIG.  10    according to a first view angle; 
         FIG.  12    is a partial perspective schematic representation of the embodiment of  FIG.  10    according to a second view angle; 
         FIG.  13    is a partial schematic representation in bottom view of the embodiment of  FIG.  10    in a retracted state; 
         FIG.  14    is a partial schematic representation in bottom view of the embodiment of  FIG.  10    in a deployed state; 
         FIG.  15    is a partial schematic representation of a gripping device according to a fourth embodiment of the invention; 
         FIG.  16    is a partial schematic representation of a gripping device according to a fifth embodiment of the invention; 
         FIG.  17    is a schematic representation of a gripping device according to a sixth embodiment of the invention; 
         FIG.  18    is a partial perspective schematic representation of the embodiment of  FIG.  17    according to a first view angle; 
         FIG.  19    is a partial schematic representation in bottom view of the embodiment of  FIG.  17   ; 
         FIG.  20    is a partial perspective schematic representation of the embodiment of  FIG.  17   ; 
         FIG.  21    is a refined partial schematic representation of  FIG.  20   ; 
         FIG.  22    is a partial perspective schematic representation of different configurations of the gripper according to the embodiment of  FIG.  17   ; 
         FIG.  23    is a partial perspective schematic representation of the different configurations of  FIG.  22   , the flanges having been represented; 
         FIG.  24    is a partial perspective schematic representation of the different configurations of the gripping device of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS.  1  to  4   , and according to a first embodiment, the gripper according to the invention, and generally designated  1 , includes a frame  2  and an actuated finger  3 . The finger  3  comprises a distal first phalanx  10  and proximal second phalanx  20  articulated on the frame  2  about a first axis O 1 . The phalanx  10  and the phalanx  20  are herein mechanically linked by a third phalanx  30  so as to enable a rotation of the phalanx  10  about a second axis O 2  substantially parallel to the first axis O 1 . 
     The phalanx  20  comprises a first bar  21  including a first end  22  pivotally mounted at a first pivot point  22 . 1  to the phalanx  10  through a connecting rod  31  of the phalanx  30 . The bar  21  also comprises a second end  23  articulated on the frame  2  about the axis O 1  at a second pivot point  23 . 1 . The phalanx  20  also comprises a first linear actuator—herein a cylinder  40  comprising a first nut/ball screw set  41 —comprising a third end  42  pivotally linked at a third pivot point  42 . 1  to the connecting rod  31  and a fourth end  43  pivotally mounted on the frame  2  at a fourth pivot point  43 . 1 . The cylinder  40  comprises a first gear-motor  44  provided with a first rotary encoder  45  and with a current sensor  46 . The gear-motor  44 , the encoder  45  and the sensor  46  are connected to a command and control unit  50 . 
     As it appears in  FIG.  1   , the bar  21  and the cylinder  40  are arranged so as to form a first four-bar linkage  24  wherein a distance d 42 - 43  separating the end  42  from the end  43  can be modified. 
     Thus, the first four-bar linkage  24  comprises the frame  2 , the connecting rod  31 , the bar  21  and the actuator  40  which acts as a last bar with a modifiable length of the four-bar linkage  24 . 
     Each of the pivot points  42 . 1  and  43 . 1  herein linking the cylinder  40  respectively to the finger  3  and to the frame  2  achieve a sliding pivot type connection with a limited sliding respectively according to a third axis O 3  and a fourth axis O 4  substantially parallel to the first axis O 1 . Sliding according to the third axis O 3  and the fourth axis O 4  is said limited as the amplitude of sliding is limited by stops (not represented). 
     The phalanx  30  comprises a second bar  32  comprising a fifth end  33  articulated on the phalanx  10  at a fifth pivot point  33 . 1  and a sixth end  34  articulated on the connecting rod  31  at a sixth pivot point  34 . 1  coincident with the point  22 . 1 . The phalanx  30  also comprises a third bar  35  comprising a seventh end  36  articulated at a seventh pivot point  36 . 1  on the phalanx  10  and an eighth end  37  articulated at an eighth pivot point  37 . 1  on the connecting rod  31 . The connecting rod  31 , the phalanx  10 , the second bar  32  and the third bar  35  form a second four-bar linkage  38 . 
     As shown in  FIG.  1   , an orthogonal projection of the third end  42  on a first line D 1  connecting the first end  22  and the eighth end  37  belongs to a section Seg 1  connecting the first end  22  and the eighth end  37 . 
     The second phalanx  20  comprises a first tension spring  25  which extends between the point  23 . 1  and the point  42 . 1  so as to reduce the length of one of the diagonals of the four-bar linkage  24 , namely the distance separating the point  23 . 1  from the point  42 . 1  towards the opening configuration. 
     The frame  2  comprises a stop  4  against which the bar  21  bears by the effect of the cylinder  40  when the latter commands an opening movement of the finger  3 . 
     Thus, the stop  4  limits the amplitude of the rotation of the bar  21  about the axis O 1  in a second way S 2  opposite to the first way S 1 . 
     The third phalanx  30  comprises a second tension spring  39  which extends between the point  22 . 1  and the point  36 . 1  so as to reduce the length of one of the diagonals of the four-bar linkage  38 , namely the distance separating the point  22 . 1  from the point  36 . 1 . 
     The bar  32  comprises a stop  5  which projects from the end  34 . The stop  5  bears against the bar  21  by the effect of the spring  25 . Thus, the stop  5  limits the amplitude of the rotation of the bar  32  about the point  34 . 1  in the second way S 2  towards the opening configuration. 
     The phalanx  10  comprises a stop  6  which bears against the bar  32  by the effect of the spring  39 . Thus, the stop  6  limits the amplitude of the rotation of the phalanx  10  about the axis O 2  in the second way S 2 . 
     The stop  6  herein blocks the rotation of the phalanx  10  about the axis O 2  when the phalanx  10  is positioned so that an angle α 1  measured between a first plane P 1  comprising the axis O 1  and the axis O 2  and a second line D 2  orthogonal to the axis O 2  and which passes through a contact point Pc of the phalanx  10 —in the case of a phalanx  10  having a planar contact surface S, the contact point is any point of the planar surface S—is equal to ten degrees. 
     Finally, the pivot points  22 . 1 ,  23 . 1 ,  33 . 1  respectively comprise a second rotary encoder  51 , a third rotary encoder  52  and a fourth rotary encoder  53  connected to the unit  50 . 
     The operation of the gripper  1  will be described when applied to clamping of an object  60  (herein cylindrical shaped) and with reference to  FIGS.  1  to  4   . 
     According to a first step, the unit  50  commands the cylinder  40  so as to make the finger  3  switch into an opening configuration represented in  FIG.  1   . For this purpose, depending on the pitch of the screw  41 , the unit  50  can command a retraction of the screw  41 . The finger  3  then adopts its opening configuration by the effect of the actuator  40  and of the springs  25  and  39  which respectively bring the bar  21 , the bar  32  and the phalanx  10  in contact with the stops  4 ,  5  and  6 . Once an object  60  is presented to the gripper  1 , and according to a second step, the unit  50  commands the cylinder  40  so as to deploy the screw  41 —i.e. so as to increase the distance separating the points  23 . 1  and  42 . 1 . The finger  3  then performs a rotation about the first axis O 1  in a first way S 1 . Under the action of the springs  25  and  39  which keep the bar  32  and the phalanx  10  respectively in contact with the stops  5  and  6 , the rotation of the finger  3  consists of a rotation of the bar  21  about the axis O 1 , the other elements of the finger  3  remaining stationary relative to the bar  21 . In particular, the phalanxes  10  and  30  are stationary relative to each other as well as relative to the bar  21 . Once the bar  21  of the phalanx  20  comes into contact with the object  60 , the deployment of the screw  41  causes a rotation of the phalanx  30  relative to the phalanx  20  about the point  22 . 1  ( FIG.  2   ) in the way S 1 . Subjected to the action of the spring  39 , the phalanx  10  is held against the stop  6  and remains stationary relative to the phalanx  30 . 
     Carrying on the deployment of the screw  41  causes bringing the bar  32  of the phalanx  30  in contact with the object  60  ( FIG.  3   ). According to a third step, the rotation of the phalanx  30  being blocked, the phalanx  10  starts a rotation in the way S 1  about the axis O 2  until coming into contact with the object  60  ( FIG.  4   ). 
     On the basis of the information originating from the encoders  45 ,  51 ,  52  and  53  as well as from the current sensor  46 , the control unit  50  determines the positions of the phalanxes  10 ,  20  and  30 , the force applied at the end of the screw  41  and computes a clamping force applied by each of the phalanxes  10 ,  20 ,  30  of the finger  3  on the object  60 . Thus, it is possible to define and control a maximum clamping force to be applied on the object  60 . 
     Opening of the gripper  1  is done by commanding a retraction of the screw  41 . Opening of the gripper  1  follows the reverse order of the clamping steps. 
     Elements that are identical or similar to those described before will bear a reference numeral identical thereto in the following description of two other embodiments of the invention. 
     According to a second embodiment represented in  FIGS.  5  to  7   , the phalanx  10  comprises a pneumatic suction cup  70  arranged so as to exert a holding force Fp according to a direction substantially orthogonal to the first axis. The suction cup  70  is connected to a vacuum pump (not represented) connected to the unit  50 . 
     The phalanx  10  herein comprises a stop  11  which cooperates with a surface  26  of the bar  32  to limit a first angular stroke C 1  of a first rotation of the phalanx  10  about the axis O 2  in the second way S 2 . The angular stroke C 1  herein comprises a first angular sector Sa 1  strictly positive according to the second way and measured starting from the plane P 1 . The angular sector Sa 1  herein measures sixty degrees. 
     The finger  3  also comprises a third torsion spring  12  which extends around a shaft  13  for rotatably linking the phalanx  10  to the phalanx  30 . The spring  12  comprises a wire  14  one end  14 . 1  of which is linked to the first end  15 . 1  of a cable  15 . The second end  15 . 2  of the cable  15  is linked to the phalanx  20 . 
     The length of the cable  15  is adjustable using a cable-clamp  16 . The wire  14  bears against a surface  17  of the phalanx  10  so as to exert a third biasing force which brings the phalanx  10  from a position located in the first angular sector Sa 1  into a position leading to the opening configuration of the finger  3  represented in  FIG.  1   . The length of the cable  15  allows adjusting the over-opening position of the phalanx  10  from which the third biasing force is exerted. In other words, the rigid stop  6  of the first embodiment is replaced by an elastic stop formed by the wire  14 . The stop  11  is herein a first stop. 
       FIG.  5    illustrates a use of the gripper  1  according to the second embodiment for gripping a cylindrical object  71  a half-circumference of which is larger than a length of the finger  3 . 
     A particular use of the gripper  1  according to the second embodiment is described in connection with gripping of a second planar object  80  that rests on a support  81  and with reference to  FIGS.  6  to  9   . 
     According to a first step, the finger  3  is placed in the opening configuration and the phalanx  10  is brought close to the object  80 . One end of the phalanx  10  comes into contact with the object  80 . According to a second step represented in  FIG.  7   , an approach of the gripper  1  to the object  80  is commanded which causes a rotation of the phalanx  10  about the point  33 . 1  according to the way S 2 . The surface  17  of the phalanx  10  then bears on the wire  14  and compresses the spring  12 . According to a third step represented in  FIG.  8   , the approach movement of the gripper  1  is carried on until the phalanx  10  adopts a position in which the suction cup  70  is applied on the object  80 . According to a third step, the unit  50  commands the suction cup  70  so that it exerts a holding force on the object  80 . According to a fourth step represented in  FIG.  9   , a separation of the gripper  1  off the support  81  is commanded. The object  80  is kept secured to the phalanx  10  by the suction cup  70 . As the gripper  1  is brought away from the support  81 , the phalanx  10  performs a rotation about the axis O 2  in the way S 1  by the effect of the spring  12 . 
     Such a gripper  1  allows grasping large-sized planar objects and objects with a smaller size by clamping. 
     According to a third embodiment represented in  FIGS.  10  to  14   , a gripping device  100  comprises a first gripper  110 , a second gripper  120  and a third gripper  130  whose respective fingers  113 ,  123  and  133  are linked to the same chassis  101 . The first frame  112  of the gripper  110  and the second frame  122  of the gripper  120  are respectively carried by a first plate  111  and a second plate  121  slidably mounted according to a first direction D 3  relative to the chassis  101 . In turn, the third frame  131  of the third gripper  130  is fixedly mounted on the chassis  101 . 
     The first plate  111  comprises a first platform  114  from which projects a first foot  115  provided with a first bracket  116  equipped with a non-represented journal which rotatably receives the frame  112  about a fifth axis O 5 , herein substantially vertical according to the representations of  FIGS.  10  and  11   . The first plate  111  also comprises, in a manner known per se, two first shafts  117 . 1  for guiding the translation of the plate  111  relative to the chassis  101 . The plate  111  also comprises a second nut  118 . 1  of a second screw/nut set  118  whose second screw  118 . 2  is rotatably mounted relative to the chassis  101  and blocked in translation relative to the chassis  101 . One end  118 . 20  of the screw  118 . 2  comprises a first gear wheel  118 . 21  for driving the screw  118 . 2 . 
     Similarly, the second plate  121  comprises a second platform  124  from which projects a second foot  125  provided with a second bracket  126  equipped with a non-represented journal which rotatably receives the frame  122  about a sixth axis O 6 , herein substantially vertical according to the representations of  FIGS.  10  and  11   . The second plate  121  also comprises, in a manner known per se, two second shafts  127 . 1  and an aperture  127 . 2  for guiding the translation of the plate  121  relative to the chassis  101 . The plate  121  also comprises a third nut  128 . 1  of a third screw/nut set  128  whose third screw  128 . 2  is rotatably mounted relative to the chassis  101  and blocked in translation relative to the chassis  101 . One end  128 . 20  of the screw  128 . 2  comprises a first gear wheel  128 . 21  for driving the screw  128 . 2  as well as a second gear wheel  128 . 22  rotatably secured to the screw  128 . 2  and which meshes with the first gear wheel  118 . 21 . 
     The chassis  101  also comprises a second electric gear-motor  102  whose output shaft  103  is provided with a first pinion  104  which collaborates with a first toothed belt  105 . The toothed belt  105  rotatably links the first pinion  104  and the toothed wheel  128 . 21 . Thus, a rotation of the pinion  104  in a first rotational way causes the rotation of the gear wheel  128 . 21 —and therefore a rotation of the screw  128 . 2 —in the same first rotational way. The gear train composed by the gear wheels  128 . 22  and  118 . 21  transmits the rotation of the screw  128 . 2  to the screw  118 . 2  in a second rotational way opposite to the first rotational way of the second screw  118 . 2 . Preferably, the gear wheels  128 . 22  and  118 . 21  have an identical number of teeth. 
     Thus, the sliding movements of the first plate  111  and of the second plate  121  are actuated using a unique gear-motor  102  so that the first plate slides in a first way S 1  of the direction D 3  which is opposite to the second way S 2  of sliding of the second plate  121 . 
     The screw/nut sets  118  and  128 , the gear wheel  118 . 21  and  128 . 22 , the gear-motor  102 , the pinion  104 , the toothed wheel  128 . 21  and the belt  105  form a first actuation device  106 . 
     As shown in  FIGS.  13  and  14   , the rotation of the first finger  113  relative to the chassis  101  about the axis O 5  and the rotation of the second finger  123  about the axis O 6  are actuated using a unique third gear-motor  150  whose output  151  comprises a second toothed pinion  152  which drives a second toothed belt  153  which forms a closed loop. The gear-motor  150  is secured to the plate  111 . 
     As shown in  FIG.  14   , the second toothed belt  153  cooperates with a second toothed wheel  154  rotatably secured to the frame  112  of the first gripper  110 . The toothed wheel  154  also cooperates with a third toothed belt  155  over its external face  155 . 1  and over its internal face  155 . 2 . The belt  155  also cooperates with a third toothed wheel  156  rotatably secured to the frame  122  of the second gripper  120 . 
     The chassis  101  comprises a first idler  160  and a second idler  161  of the belt  155 . The first idler  160  is herein a toothed idler rotatably mounted relative to the chassis  101  and which cooperates with the external face  155 . 1  of the belt  155 . The second idler  161  is herein a toothed idler rotatably mounted relative to the chassis  101  and which cooperates with an internal face  155 . 2  of the belt  155 . 
     Auxiliary idlers  162  and  163  linked to the first plate  111  press the external face  155 . 1  of the belt  155  on the toothed wheel  154  while collaborating respectively with the internal face  155 . 2  of the belt  155  and the external face  155 . 1  of the belt  155 . 
     Additional auxiliary idlers  164  and  165  linked to the plate  121  press the internal face  155 . 2  of the belt  155  on the toothed wheel  156  while collaborating respectively with the external face  155 . 1  of the belt  155  and the internal face  155 . 2  of the belt  155 . Finally, auxiliary idlers  166  and  167  also linked to the plate  121  press the belt on the idlers  160  and  161  while collaborating respectively with the external face  155 . 1  of the belt  155  and the internal face  155 . 2  of the belt  155 . In particular, the idlers  162  to  167  contribute to a better compactness of the gripping device  100  and to an alignment of the grippers  110  and  120  on a line substantially parallel to the direction D 1 . 
     The gear-motor  150 , the belt  155 , the toothed wheels  154  and  156  as well as the idlers  160  to  167  form a second actuation device  170  arranged so that a sliding movement of the plate  111  and/or of the plate  121  is decoupled from a rotational movement of the first finger  113  and of the second finger  123  caused by activation of the gear-motor  150 . 
     Conversely, a rotational movement of the first finger  113  and of the second finger  123  caused by activation of the gear-motor  150  is decoupled from a sliding movement of the plate  111  and/or of the plate  121 . Indeed, the second actuation device  170  keeps a constant belt length  155  between the wheels  154  and  156 . This arises in particular from the examination of  FIGS.  14  and  15   . 
       FIGS.  15  and  16    illustrate other configurations of the second actuation device  170  allowing obtaining the same effects of decoupling the rotational movements of the fingers  113  and  123  with the translational movements of the plates  111  and  121 . 
     According to a fourth embodiment represented in  FIG.  15   , the actuation device  170  has no auxiliary idlers  162  and  163  and the toothed belt  155  is an internally-toothed belt. A non-represented known device for reversing the rotational way (for example a gear train) is interposed between the wheel  156  and the finger  123 . 
     According to a fifth embodiment represented in  FIG.  16   , the actuation device  170  has no auxiliary idlers  162  to  167  and the toothed belt  155  is an internally-toothed belt. The reversal of the rotational way of the toothed wheel  156  with respect to the wheel  154  is carried out by crossing of the strands of an internally-toothed additional transmission belt  157 . 
     Elements that are identical or similar to those described before for the fourth and fifth embodiments will bear a reference numeral identical thereto incremented by one hundred in the following description of a sixth embodiment of the invention. 
     Referring to  FIGS.  17  to  23   , and according to the sixth embodiment, the gripping device  100  comprises a fourth gripper  140  provided with a fourth finger  143 . The gripper  130  and the gripper  140  are respectively carried by a third plate  211  and a fourth plate  221  slidably mounted relative to the chassis  101  according to a second direction D 4  substantially parallel to the direction D 3 . The frame  132  of the gripper  130  is rotatably received according to a vertical seventh axis O 7  in a third bracket  216  of the third foot  215  of the plate  211 . The frame  142  of the gripper  140  is rotatably received according to a vertical eighth axis O 8  in a fourth bracket  226  of the fourth foot  225  of the plate  221 . 
     The sliding movements of the plate  211  and of the plate  221  are actuated using a third actuation device  206  similar to the first actuation device  106  and which is provided with a unique fourth electric gear-motor  202 . The output shaft  203  of the gear-motor  202  is provided with a third pinion  204  which collaborates with a fourth toothed belt  205 . The toothed belt  205  drives a fourth screw  218 . 2  of a fourth screw/nut set  218  in rotation. The fourth screw  218 . 2  is linked to the chassis  101  and the fourth nut of the fourth screw/nut set  218  is secured to the plate  211 . The rotation of the screw  218 . 2  is transmitted to a fifth screw  228 . 2  of a fifth screw/nut set  228 . The screw  228 . 2  is linked to the chassis  101  and the fifth nut  228 . 1  of the screw/nut set  228  is secured to the plate  221 . The transmission of the rotation of the fourth screw  218 . 2  to the fifth screw  228 . 2  is achieved using a gear comprising a third gear wheel  228 . 22  and a fourth gear wheel  228 . 21 . 
     Thus, a rotation of the pinion  204  in a first rotational way causes a translation of the plate  211  in one way S 3  of the direction D 3  and a translation of the plate  221  in a way S 4  opposite to the way S 3 . 
     Referring to  FIG.  20   , the rotation of the third finger  133  relative to the chassis  101  about the axis O 7  and the rotation of the fourth finger  143  about the axis O 8  are actuated using a fourth actuation device  270  identical to the actuation device  170  with the major exception that it has no gear-motor. Thus, the actuation device  270  comprises a fifth toothed belt  255  which forms a closed loop and which cooperates with a fourth toothed wheel  254  rotatably secured to the frame  132  of the third gripper  130 . The belt  255  is toothed over its external face  255 . 1  and over its internal face  255 . 2 . The belt  255  also cooperates with a fifth toothed wheel  256  rotatably secured to the frame  142  of the fourth gripper  140 . 
     The chassis  101  also comprises a third idler  260  and a fourth idler  261  of the belt  255 . The third idler  260  is herein a toothed idler rotatably mounted relative to the chassis  101  and which cooperates with the external face  255 . 1  of the belt  255 . The fourth idler  261  is herein a toothed idler rotatably mounted relative to the chassis  101  and which cooperates with an internal face  255 . 2  of the belt  255 . 
     Auxiliary idlers  264  and  265  linked to the third plate  211  press the internal face  255 . 2  of the belt  255  on the toothed wheel  254  while collaborating respectively with the external face  255 . 1  of the belt  255  and the internal face  255 . 2  of the belt  255 . 
     Additional auxiliary idlers  262  and  263  linked to the plate  221  press the external face  255 . 1  of the belt  255  on the toothed wheel  256  while collaborating respectively with the internal face  255 . 2  of the belt  255  and the external face  255 . 1  of the belt  255 . Finally, auxiliary idlers  266  and  267  also linked to the plate  211  press the belt on the idlers  260  and  261  while collaborating respectively with the internal face  255 . 2  of the belt  255  and the external face  255 . 1  of the belt  255 . In particular, the idlers  262  to  267  contribute to a better compactness of the gripping device  100  and to an alignment of the grippers  130  and  140  on a line substantially parallel to the direction D 4 . Thus, the actuation device  270  is arranged so that a sliding movement of the third plate  211  and/or the fourth plate  221  is decoupled from a rotational movement of the third actuated finger  133  and of the fourth actuated finger  143 . Conversely, a rotational movement of the third actuated finger  133  and of the fourth actuated finger  143  is decoupled from a sliding movement of the third plate  211  and/or of the fourth plate  221 . 
     As shown in  FIGS.  21  and  22   , a coupling device  290  links the second actuation device  170  with the fourth actuation device  270  so that the fourth actuation device  270  is driven by the gear-motor  150 . 
     To this end, the coupling device  290  comprises a first toothed roller  291  rotatably mounted on the second plate  121  about a substantially vertical ninth axis O 9  and which collaborates with the external face  155 . 1  of the belt  155  so as to be driven by the latter. 
     More specifically, the first toothed roller  291  is rotatably secured to the idler  167  which, in turn, is driven in rotation by the belt  155  external face  155 . 1 . The coupling device  290  also comprises a second toothed roller  292  rotatably mounted on the third plate  211  about a vertical tenth axis O 10  and which collaborates with the external face  255 . 1  of the belt  255  so as to drive the latter. More specifically, the second toothed roller  292  is rotatably secured to the idler  267  which collaborates with the external face  255 . 1  of the belt  255 . 
     The coupling device  290  also comprises an articulated arm  293  comprising a first arm section  294  and a second arm section  295  articulated together about an eleventh axis O 11 . A third toothed roller  296  is rotatably mounted about the axis O 11 . The first section  294  comprises two flanges  294 . 1  and  294 . 2  which extend parallel to each other so as to connect the axis O 11  and the axis O 9  about which they are articulated. The second section  295  comprises two flanges  295 . 1  and  295 . 2  which extend parallel to each other so as to connect the axis O 11  and the axis O 10  about which they are articulated. A sixth toothed belt  297  extends between the roller  291  and the roller  296 . A seventh toothed belt  298  extends between the roller  296  and the roller  292 . The roller  296 , the belts  297  and  298  as well as the flanges  295 . 1  and  295 . 2  form a movement transmission device  299  transmitting a rotation of the first roller  291  to the second roller  292 . 
     Thus, the coupling device  290  transmits a rotation of the first roller  291  caused by the gear-motor  150  to the second roller  292  which thus actuates the rotation of the wheels  254  and  256 , causing a rotation of the fingers  133  and  143  in opposite ways. The three articulation points of the arm  293  as well as the roller  296  allow keeping coupling of the two actuation devices  170  and  270  irrespective of the relative positions thereof, while keeping a decoupling between the translational and rotational movements of the fingers  113 ,  123 ,  133  and  143 . 
     The relative arrangement of the fingers  113 ,  123 ,  133  and  143  relative to the frame can then adopt a plurality of configurations represented in  FIG.  24    which confers a great versatility on the device  100 . 
     Of course, the invention is not limited to the described embodiment but encompasses any variant falling within the scope of the invention as defined by the claims. 
     In particular,
         although herein the gripper comprises a unique finger, the invention also applies to a gripper comprising one finger and one fixed obstacle;   although herein the gripping device comprises four grippers, the invention also applies to a gripping device comprising a different number of grippers such as two grippers, three grippers or more than four;   although herein the gripping device comprises four grippers whose fingers are linked to the same frame, the invention also applies to a gripping device wherein the frames of the different grippers are rigidly linked or articulated together;   although herein the first and second phalanxes are linked by a third phalanx, the invention also applies to a finger comprising a different number of phalanxes such as one finger comprising a first phalanx mechanically linked directly to a second phalanx, or a first phalanx linked to the second phalanx through more than one phalanx, such as two or three additional phalanxes;   although herein the second phalanx comprises a first spring, the invention also applies to other types of first member for biasing the finger towards the opening configuration such as a magnet, a counterweight or an elastic element other than a spring such as a stack of Belleville-type elastic washers, an elastomeric block and possibly a gas spring;   although herein the third phalanx comprises a second spring, the invention also applies to other types of second member for biasing the finger towards the opening configuration such as a magnet, a counterweight or an elastic element other than a spring such as a stack of Belleville-type elastic washers, an elastomeric block and possibly a gas spring;   although herein the first phalanx comprises a third spring, the invention also applies to other types of third member for biasing the phalanx towards the opening configuration such as a magnet, a counterweight or an elastic element other than a spring such as a stack of Belleville-type elastic washers, an elastomeric block and possibly a gas spring;   although herein the springs used in the second and third phalanxes are tension springs installed along the diagonal of the four-bar linkage which is stretched during the movement of the finger in the first closure way, the invention applies if the springs were compression springs installed along a second diagonal of the four-bar linkage which is compressed during the movement of the finger in a first closure way, or if the springs are torsion springs mounted between two adjacent sides of a four-bar linkage so as to store elastic energy during the movement of the finger in a first closure way;   although herein the biasing members in the second and third phalanxes are tension springs and the opening configuration of the gripper is defined by the mechanical balance respectively of the bar  21 , the bar  32  and the phalanx  10  in contact with the stops  4 ,  5  and  6  by the action of said biasing members and of the actuator  40 , the invention also applies to a gripper comprising double-acting biasing members—tension and compression around a zero-action central position—in the second and third phalanxes, comprising no stops  4 ,  5 ,  6 , and where the opening configuration is defined by a controlled extension length of the actuator and the central positions of the double-acting biasing members   although herein the finger comprises three rotary encoders for measuring the rotations of the phalanxes, the invention also applies to a gripper comprising a different number of rotary encoders such as two encoders for three articulations—and more generally one encoder lesser than the number of phalanxes, the angular position of the last articulation may be deduced from the data of the other encoders and from the measurement of the angular position of the motor which allows computing the extension of the ball screw;   although herein the suction cup is positioned on the first phalanx, the invention also applies to other setups of the suction cup on the finger, such as a suction cup secured to the second or third phalanx;   although herein the gripper comprises a pneumatic suction cup, the invention also applies to other types of controllable adhesive elements such as a mechanical, magnetic suction cup, an adhesive member by electrostatic effect, by Van der Walls type dry adhesion, or a pressure-sensitive adhesive similar to those of sticky notes;   although herein the angular sector measures sixty degrees, the invention also applies to other values of the angular sector such as an angular sector comprised between ten and ninety degrees, preferably comprised between twenty and sixty degrees;   although herein the fingers are rotatably mounted about a vertical axis, the invention also applies to other orientations of the axis of rotation of the finger relative to the frame, such as a random orientation and preferably orthogonal and/or secant to the first axis;   although herein the fingers are fitted with a rotational movement and with a translational movement relative to the frame, the invention also applies if the connection comprised two axes of rotation enabling a rotation perpendicular to the palm and adduction/abduction movements of the fingers, or any other architecture for moving the fingers relative to the palm   although herein the third phalanx has a four-bar linkage type structure, the invention also applies to other types of movement transmission structures such as a gear train or a pulleys/belts set;   although herein the grippers have been represented mounted on the chassis according to vertical axes, the invention also applies to other orientations of the axes of rotation of the grippers, preferably and in particular axes substantially orthogonal to the first axis O 1 ;   although herein, the gripping device comprises a first screw/nut set and a second screw/nut set, the invention also applies to other types of first actuation device such as a device comprising two distinct actuators for each plate, hydraulic or electric cylinders, a unique cylinder and a cable-and-pulley transmission;   although herein the first pinion cooperates with a toothed belt, the invention also applies to other types of first member for transmitting a drive force such as a smooth belt, whether flat or not, a chain or a gear train. This is also valid for all toothed belts of the invention that can advantageously be replaced by cables, chains, smooth belts or a gear train;   although herein the actuation devices comprise an electric gear-motor, the invention also applies to other actuator types such as an electric or hydraulic cylinder, a stepper motor;   although herein the first gear-motor is secured to the first plate, the invention also applies to a gear-motor secured to the second plate;   although herein the rollers are toothed so as to convey a toothed belt, the invention also applies to other types of idler rollers such as gear wheels in the case of a transmission element that would be a chain;   although herein, each plate comprises a screw/nut set, the invention also applies to other actuator types, including a transmission between the plates that would comprise a cable and an idler pulley;   although herein the gripping device has been described in connection with grippers provided with under-actuated fingers according to the invention, the invention also applies to a gripping device implementing other known types of grippers provided with fingers such as a gripper provided with fingers all phalanxes of which are actuated.