Abstract:
Provided is a robot hand that is capable of gripping an object and manipulating the gripped object in a manner similar to that of a human hand, and that makes it possible to reduce the number of actuators. This robot hand is provided with: a first actuator ( 31 ) that imparts driving force to a first finger link ( 11 ) so that the first finger link ( 11 ) pivots relative to a base section ( 1 ); and a second actuator ( 32 ) that imparts driving force to at least one of a second finger link ( 12 ) and a third finger link ( 13 ) so that the second finger link ( 12 ) pivots relative to the first finger link ( 11 ) and the third finger link ( 13 ) pivots relative to the second finger link ( 12 ).

Description:
TECHNICAL FIELD 
     The present invention relates to a robot hand having multiple joints, and being capable of gripping an object and manipulating the gripped object like a human finger. 
     BACKGROUND ART 
     As a robot hand having multiple joints like a human finger, there is known a robot hand that includes a base section corresponding to the back of a human hand, a first finger link corresponding to a proximal phalange of a finger, a second finger link corresponding to an intermediate phalange of a finger, and a third finger link corresponding to a distal phalange of a finger. The first finger link is pivotably connected to the base section. The second finger link is pivotably connected to the first finger link. The third finger link is pivotably connected to the second finger link. 
     When a robot hand grips an object, the object is wound by the finger. To wind the object with a finger, the first finger link, the second finger link and the third finger link are configured to be sequentially bent. As a typical robot hand, there is known a robot hand which is configured such that a second finger link is bent interlocking with a first finger link when the first finger link is bent, and a third finger link is bent interlocking with the second finger link when the second finger link is bent. A driving source for bending the finger is a motor or an actuator, such as a linear actuator. The driving source imparts driving force to the first finger link so that the first finger link is bent relative to the base section. When the first finger link is bent, the second finger link and the third finger link are sequentially bent. 
     A typical robot hand of conventional art is able to stably “grip” an object, however, suffers from a problem of difficulty in “manipulating” the object. To “grip” refers to that an object is firmly held, while to “manipulate” refers to that a machine, for example, is manipulated to bring it into action. For example, when a robot is assigned to a screw tightening job using an electric screwdriver, the robot hand is required to firmly hold (grip) the handle of the electric screwdriver and pull (manipulate) the trigger of the electric screwdriver. A typical robot hand of conventional art excels in firmly holding the handle of an electric screwdriver, however, suffers from a problem of not being good with pulling the trigger of the electric screwdriver. 
     As a robot hand that solves the problem, the applicant has proposed a robot hand having a finger in which a small actuator is incorporated into each joint of the finger (see Patent Literature 1). In this robot hand, a first actuator is incorporated into a first joint between a base section and a first finger link. A second actuator is incorporated into a second joint between the first finger link and a second finger link. A third actuator is incorporated into a third joint between the second finger link and a third finger link. The robot hand described in Patent Literature 1 is able to independently bend the first to third finger links, and hence is able to grip an object and manipulate the gripped object. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: JP 2002-113681 A 
       
    
     SUMMARY OF THE INVENTION 
     Technical Problem 
     However, the robot hand described in Patent Literature 1 suffers from a problem of difficulty in obtaining a fingertip force (torque) and a bending angle of a finger (stroke) similar to those of a human being, with an actuator of a size that can be housed in each joint of the finger. Further, since an actuator is provided to each joint, there is a problem of increasing the number of actuators. 
     In this regard, the present invention has an object of providing a robot hand which is capable of gripping an object and manipulating the gripped object like a human hand, and can reduce the number of actuators. 
     Solution to Problem 
     In order to solve the above problem, the present invention provides a robot hand that includes: abase section; a first finger link pivotably connected to the base section; a second finger link pivotably connected to the first finger link; a third finger link pivotably connected to the second finger link; an auxiliary link that interlocks pivoting of the second finger link relative to the first finger link with pivoting of the third finger link relative to the second finger link; a first actuator that imparts driving force to the first finger link so that the first finger link pivots relative to the base section; and a second actuator that imparts driving force to at least one of the second finger link and the third finger link so that the second finger link pivots relative to the first finger link and the third finger link pivots relative to the second finger link. 
     Advantageous Effects of the Invention 
     According to the present invention, (1) for example, when the second actuator is driven in a state where the first actuator is halted, a finger tip (the second finger link and the third finger link) alone can be bent without bending the base (the first finger link) of the finger. Further, (2) for example, when the first actuator and the second actuator are concurrently driven at substantially the same speed, the base (the first finger link) alone can be bent without bending the finger tip (the second finger link and the third finger link). In this case, torque that corresponds to two actuators acts on the finger. Further, (3) for example, when the first actuator and the second actuator are concurrently driven, with the speed of the second actuator being higher than that of the first actuator, the base (the first finger link) of the finger as well as the finger tip (the second finger link and the third finger link) can be bent. This enables an action with which an object is gripped and the gripped object is manipulated in the same way a human hand does. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating a state where a finger of a robot hand is extended according to an embodiment of the present invention; 
         FIG. 2  is a plan view of a robot hand according to an embodiment of the present invention; 
         FIG. 3  is a side view of a robot hand according to an embodiment of the present invention; 
         FIG. 4  is a side view of a robot hand according to an embodiment of the present invention; 
         FIGS. 5(A) to 5(F)  show motion diagrams of a robot hand according to the present embodiment; and 
         FIG. 6  shows another example of first and second actuators of a robot hand according to the present embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     With reference to the accompanying drawings, hereinafter is described a robot hand according to an embodiment of the present invention.  FIG. 1  is a perspective view illustrating a state where a finger of the robot hand of the present embodiment is extended.  FIG. 2  shows a plan view of the robot hand, while  FIGS. 3 and 4  show side views of the robot hand. The robot hand of the embodiment has three joints corresponding to those of a human finger and is capable of skillful and delicate manipulation of an object. Typically, the robot hand is used being combined with other fingers to configure an articulated multi-fingered hand. 
     First, a whole configuration of the robot hand is described. The robot hand is provided with a base section  1  corresponding to the back of a human hand, a first finger link  11  corresponding to a proximal phalange of a finger, a second finger link  12  corresponding to an intermediate phalange of a finger, and a third finger link  13  corresponding to a distal phalange of a finger. The first finger link  11  has a proximal portion which is pivotably connected to the base section  1  via a first shaft  21 . The second finger link  12  has a proximal portion which is pivotably connected to a distal portion of the first finger link  11  via a second shaft  22 . The third finger link  13  has a proximal portion which is pivotably connected to a distal portion of the second finger link  12  via a third shaft  23 . The first to third shafts  21 ,  22  and  23  correspond to a metacarpal interphalangeal joint, a proximal interphalangeal joint and a distal interphalangeal joint, respectively, of a human finger. The first to third shafts  21 ,  22  and  23  are parallel to each other. 
     An auxiliary link  2  has an end portion which is pivotably connected to the first finger link  11  via a connecting shaft  3 , and the other end portion which is pivotably connected to the third finger link  13  via a connecting shaft  4  (see  FIGS. 3 and 4 ). The auxiliary link  2  has a role of interlocking the pivoting of the second finger link  12  relative to the first finger link  11  with the pivoting of the third finger link  13  relative to the second finger link  12 . The first finger link  11 , the second finger link  12 , the third finger link  13  and the auxiliary link  2  configure a four-joint pivot chain in which the four links are all chained by turning pairs. Assuming that the first finger link  11  is fixed, the third finger link  13  is allowed only a certain restricted motion. 
     As shown in  FIG. 1 , a first actuator imparts driving force to the first finger link  11  so that the first finger link  11  pivots relative to the base section  1 . The first actuator is a first linear actuator  31  having a body  31   a  and a shaft  31   b  (see  FIG. 2 ) that linearly moves relative to the body  31   a . The body  31   a  of the first linear actuator  31  is pivotably supported by the base section  1  about a center line L 1 . The shaft  31   b  of the first linear actuator  31  is pivotably connected to the first finger link  11  so that driving force can be imparted to the first finger link  11 . When the first linear actuator  31  imparts driving force to the first finger link  11 , the first finger link  11  pivots relative to the base section  1 . With the pivoting of the first finger link  11  relative to the base section  1 , the body  31   a  of the first linear actuator  31  pivots about the center line L 1  relative to the base section  1 . 
     A second actuator imparts driving force to the second finger link  12  so that the second finger link  12  pivots relative to the first finger link  11 . The second actuator is a second linear actuator  32  having a body  32   a  and a shaft  32   b  that linearly moves relative to the body  32   a . The first linear actuator  31  has the same size as that of the second linear actuator  32 . The body  32   a  of the second linear actuator  32  is pivotably supported by the base section  1  about the center line L 1 . The shaft  32   b  of the second linear actuator  32  is pivotably connected to a proximal portion of a working link  5 . The working link  5  has a distal portion which is pivotably connected to the second finger link  12 . When the second linear actuator  32  imparts driving force to the second finger link  12 , the second finger link  12  pivots relative to the first finger link  11 . Interlocking with this, the third finger link  13  pivots relative to the second finger link  12 . Further, the body  32   a  of the second linear actuator  32  pivots about the center line L 1  relative to the base section  1 . 
       FIGS. 5(A) to 5(F)  show motion diagrams of the robot hand. According to the robot hand configured as described above, (1) for example, when the second linear actuator  32  is driven in a state where the first linear actuator  31  is halted, the finger tip (the second finger link  12  and the third finger link  13 ) alone can be bent without bending the base (the first finger link  11 ) of the finger ( FIG. 5(C)  to  FIG. 5(B)  to  FIG. 5(A) ). In other words, with the first finger link  11  retaining an angle relative to the base section  1 , the second finger link  12  can be pivoted relative to the first finger link  11 , and the third finger link  13  can be pivoted relative to the second finger link  12 . 
     Further, (2) for example, when the first linear actuator  31  and the second linear actuator  32  are concurrently driven at substantially the same speed, the base (the first finger link  11 ) alone can be bent without bending the fingertip (the second finger link  12  and the third finger link  13 ) ( FIG. 5(C)  to  FIG. 5(D)  to  FIG. 5  (E)). In this case, the finger can be applied with torque that is a sum of the torque of the first and second linear actuators  31  and  32 . 
     Further, (3) for example, when the first linear actuator  31  and the second linear actuator  32  are concurrently driven, with the speed of the second linear actuator  32  being higher than that of the first linear actuator  31 , the base (the first finger link  11 ) of the finger as well as the finger tip (the second finger link  12  and the third finger link  13 ) can be bent ( FIG. 5(C)  to  FIG. 5(F) ). 
     Hereinafter is described a structure of each of parts of the robot hand. As shown in  FIG. 1 , in the following description, a direction in which the extended finger extends is a front-back direction, and a direction perpendicular to the extended finger is a right-and-left direction. 
     The base section  1  includes a bottom  1   a  and a pair of support walls  1   b  and  1   c  vertically set up from the ends of the bottom  1   a  in the right-and-left direction. The pair of support walls  1   b  and  1   c  is provided therebetween with an intermediate wall  1   d . The body  31   a  of the first linear actuator  31  is pivotably supported between the support wall  1   b  and the intermediate wall  1   d . The body  32   a  of the second linear actuator  32  is pivotably supported between the intermediate wall  1   d  and the support wall  1   c . The center line L 1  for the pivoting of the first linear actuator  31  relative to the base section  1  is in alignment with the center line L 1  for the pivoting of the second linear actuator  32  relative to the base section  1 . 
     Using ball screws, the first and second linear actuators  31  and  32  allow the respective shafts to linearly move relative to the respective bodies. The shafts  31   b  and  32   b  have respective outer peripheral surfaces in which threads are formed. The bodies  31   a  and  32   a  are incorporated with ball screw nuts to be threadably engaged with the threads of the respective shafts  31   b  and  32   b . The bodies  31   a  and  32   a  are mounted with motors  31   c  and  32   c , respectively, for rotating and driving the ball screw nuts. When the ball screw nuts are rotated and driven by the motors  31   c  and  32   c , the shafts  31   b  and  32   b  are linearly moved in an axial direction. 
     The base section  1  is arranged with a first driver  33  and a second driver that supply electric power suitable for controlling the motors of the first linear actuator  31  and the second linear actuator  32  ( FIG. 1  only shows the first driver  33 , but the second driver is arranged below the second linear actuator  32 ). The first driver  33  and the second driver are each provided with a power converter, such as a PWM (pulse width modulation) inverter, that supplies electric power to the motor, and a controller that controls the power converter on the basis of the information from a higher-order command device, such as an operational manipulator, and sensors described later. The first driver  33  and the second driver carry out synchronous control with either of the first and second linear actuators  31  and  32  as being a main axis and the other as being a driven axis. 
     The shaft  31   b  of the first linear actuator  31  is pivotably connected to the first finger link  11  via a first adaptor  35 . The first adaptor  35  includes a body  35   a  fixed to the first finger link  11 , and a pair of shaft supports  35   b  diverged into two from the body  35   a . The pair of shaft supports  35   b  rotatably supports a connecting shaft  28 . The connecting shaft  28  is connected with the shaft  31   b  (see  FIG. 2 ) of the first linear actuator  31 . 
     The shaft  32   b  of the second linear actuator  32  is pivotably connected to the working link  5  via a second adaptor  36 . The second adaptor  36  includes a body  36   a  connected to the shaft  32   b  of the second linear actuator  32 , and a pair of connecting sections  36   b  projected forward from the ends of the body  36   a  in the right-and-left direction, being diverged into two. The pair of connecting sections  36   b  is provided with a connecting shaft  37 . The connecting shaft  37  is rotatably connected with a proximal portion of the working link  5 . 
     The base section  1  has a front end which has a U-shaped cross section. The front end of the base section  1  includes a pair of support walls  1   e  across which a first shaft  21  is bridged to pivotably support the first finger link  11 . The base section  1  is mounted with a sensor  38  (see  FIG. 3 ). The sensor  38  is configured, for example, by a six-axis force sensor which concurrently detects force and torque in X, Y and Z directions in real time. 
     As shown in  FIG. 1 , the first finger link  11  has a U-shaped cross section. The first finger link  11  includes a bottom and a pair of side walls  11   a  vertically set up from the ends of the bottom in the right-and-left direction. The pair of side walls  11   a  of the first finger link  11  is fitted between the pair of support walls  1   e  in the distal portion of the base section  1 . The pair of side walls  11   a  of the first finger link  11  has distal portions which are provided with the second shaft  22 . The second finger link  12  is pivotably supported by the second shaft  22  (see  FIG. 3 ). The first finger link  11  is mounted with a sensor  39  (see  FIG. 3 ) configured, for example, by a six-axis force sensor. 
     The second finger link  12  has a U-shaped cross section. The second finger link  12  includes a bottom and a pair of side walls  12   a  vertically set up from the ends of the bottom in the right-and-left direction. The pair of side walls  12   a  of the second finger link  12  is fitted between the pair of side walls  11   a  of the first finger link  11 . The pair of side walls  12   a  of the second finger link  12  has distal portions which are provided with the third shaft  23 . The third finger link  13  is pivotably supported by the third shaft  23 . The pair of side walls  12   a  of the second finger link  12  has proximal portions which are provided with a connecting shaft  6 . The connecting shaft  6  is connected to a distal portion of the working link  5  (see  FIG. 4 ). The pair of side walls  12   a  is formed with respective cuts  12   b  so as to avoid interference with the connecting shaft  4  (see  FIG. 4 ). 
     The third finger link  13  has a U-shaped cross section. The third finger link  13  includes a bottom and a pair of side walls  13   a  vertically set up from the ends of the bottom in the right-and-left direction. The pair of side walls  12   a  of the second finger link  11  is fitted inside the pair of side walls  13   a  of the third finger link  13 . The pair of side walls  13   a  of the third finger link  13  has proximal portions which are provided with the connecting shaft  4 . The auxiliary link  2  is pivotably connected to the connecting shaft  4 . The third finger link  13  is mounted with a sensor  40  (see  FIG. 3 ) configured, for example, by a six-axis force sensor. 
     The working link  5  is formed into a plate shape which is elongated in the front-back direction. The working link  5  has a proximal portion which is pivotably connected to the connecting shaft  37  of the adaptor  36 . The distal portion of the working link  5  is pivotably connected to the connecting shaft  6  of the second finger link  12 . 
     The auxiliary link  2  is formed into a plate shape which is elongated in the front-back direction. The auxiliary link  2  has a proximal portion which is pivotably connected to the connecting shaft  3  (see  FIG. 3 ) of the first finger link  11 . The auxiliary link  2  has a distal portion which is connected to the connecting shaft  4  (see  FIG. 3 ) of the third finger link  13 . 
     The configuration of the robot hand of the present embodiment has so far been described. The robot hand of the present embodiment has advantageous effects as follows. The bodies  31   a  and  32   a  of the first linear actuator  31  and the second linear actuator  32 , respectively, for moving the finger are arranged at the base section  1 . Accordingly, being imparted with a force (joint torque) of intensity similar to that of a human finger, the size of the finger can be reduced to a size equivalent to that of a human finger. Further, when the first to third finger links  11 ,  12  and  13  collide with an object or are immersed in water, the first and second linear actuators  31  and  32  can be protected. 
     The center line L 1  for the pivoting of the first linear actuator  31  relative to the base section  1  is arranged in alignment with the center line L 1  for the pivoting of the second linear actuator  32  relative to the base section  1 . This facilitates the control of the first and second linear actuators  31  and  32 . 
     The second linear actuator  32  imparts driving force to the second finger link  12  via the working link  5 . Accordingly, the second linear actuator  32  can be arranged at the base section  1  which is distanced from the second finger link  12 . 
     The auxiliary link  2  is pivotably connected to the first finger link  11  and the third finger link  13  to enable interlinkage of the pivoting of the first finger link  11  with the pivoting of the third finger link  13 . 
     The present invention is not limited to the foregoing embodiment, but may be modified into various embodiments as follows within a scope not changing the spirit of the present invention. 
     In the foregoing embodiment, the finger of the robot hand has three joints. However, the finger of the robot hand may have four joints. In this case, a fourth finger link is pivotably connected to a distal portion of the third finger link. Then, a second auxiliary link is pivotably connected to the second finger link and the fourth finger link so that the pivoting of the third link relative to the second link is interlocked with the pivoting of the fourth link relative to the third finger link. 
     In the foregoing embodiment, the first to third finger links  11 ,  12  and  13  and the auxiliary link  2  are chained by turning pairs to configure a four-joint pivot chain. However, at least one of the four turning pairs may be replaced by a sliding pair. 
     In the foregoing embodiment, driving force is imparted from the second linear actuator  32  to the second finger link  12  via the working link  5 . However, driving force may be directly imparted from the second linear actuator to the second finger link. Alternatively, driving force may be imparted from the second linear actuator to the auxiliary link via the working link. Alternatively, driving force may be imparted from the second linear actuator to the third finger link via the working link. 
     In the foregoing embodiment, the first and second linear actuators  31  and  32  provided to the base section  1  are used as a driving source for moving the finger. However, first and second rotary motors  41  and  42  having respective speed reducers as shown in  FIG. 6  may be used, being provided to the base section  1 . In this case, the first and second rotary motors  41  and  42  having speed reducers include output shafts  41   a  and  42   a  which are provided with a lever  43  being fixed thereto. The first rotary motor  41  having a speed reducer pivots the first finger link  11  via the lever  43 . The second rotary motor  42  having a speed reducer pivots the second finger link  12  via the lever  43 . 
     In the foregoing embodiment, the first and second linear actuators  31  and  32  provided to the base section  1  are used as a driving source for moving the finger. However, a first rotary motor may be provided at a position corresponding to the metacarpal interphalangeal joint of a human hand so that the first link is ensured to pivot relative to the base section. Alternatively, a second rotary motor may be provided at a position corresponding to the proximal interphalangeal joint of a human hand so that the second link is ensured to pivot relative to the first link. 
     The foregoing embodiment uses the first and second linear actuators  31  and  32  which use ball screws. However, instead of the first and second linear actuators  31  and  32  using ball screws, pneumatic or hydraulic cylinders, linear motors, artificial muscle actuators, or the like may be used. 
     In the foregoing embodiment, the first to third shafts  21 ,  22  and  23 , as well as the connecting shafts  3  and  4 , are fitted to respective bores that match the diameters of the shafts. However, the shafts may be fitted to respective long holes. In this case, there is a need of providing springs that urge the first to third shafts  21 ,  22  and  23 , as well as the connecting shafts  3  and  4 , to ends of respective long holes in a longitudinal direction so that the first to third finger links  11 ,  12  and  13  are enabled with only a restricted movement. 
     INDUSTRIAL APPLICABILITY 
     The robot hand of the present invention can be used as an end effector of a robot, such as a humanoid robot or an industrial robot. Besides, the robot hand of the present invention can be used as an artificial hand that can serve in place of a human hand. 
     The present specification is based on Japanese Patent Application No. 2012-250491 filed on Nov. 14, 2012. All the contents of the application are incorporated herein. 
     REFERENCE SIGNS LIST 
       1  . . . Base section,  2  . . . Auxiliary link,  5  . . . Working link,  11  . . . First finger link,  12  . . . Second finger link,  13  . . . Third finger link,  21  . . . First shaft,  22  . . . Second shaft,  23  . . . Third shaft,  31  . . . First linear actuator (First actuator),  31   a  . . . Body of first linear actuator,  31   b  . . . Shaft of first linear actuator,  32  . . . Second linear actuator (Second actuator),  32   a  . . . Body of second linear actuator,  32   b  . . . Shaft of second linear actuator, L 1  . . . Center line