Abstract:
An improved robotic thumb for a robotic hand assembly is provided. According to one aspect of the disclosure, improved tendon routing in the robotic thumb provides control of four degrees of freedom with only five tendons. According to another aspect of the disclosure, one of the five degrees of freedom of a human thumb is replaced in the robotic thumb with a permanent twist in the shape of a phalange. According to yet another aspect of the disclosure, a position sensor includes a magnet having two portions shaped as circle segments with different center points. The magnet provides a linearized output from a Hall effect sensor.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0001]    This invention was made with government support under NASA Space Act Agreement number SAA-AT-07-003. The government may have certain rights in the invention. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to robotic hands, and more particularly to robotic thumbs. 
       BACKGROUND OF THE INVENTION 
       [0003]    Typical robots are automated devices that are able to manipulate objects using a series of rigid links, which in turn are interconnected via articulations or motor-driven robotic joints. Each joint in a typical robot represents an independent control variable, also referred to as a degree of freedom (DOF). End-effectors are the particular links used for performing a task at hand, e.g., grasping a work tool or an object. Therefore, precise motion control of a robot may be organized by the level of task specification: object level control, i.e., the ability to control the behavior of an object held in a single or cooperative grasp of a robot, end-effector control, and joint level control. Collectively, the various control levels cooperate to achieve the required robotic mobility, dexterity, and work task-related functionality. 
         [0004]    Humanoid robots in particular are robots having an approximately human structure or appearance, whether a full body, a torso, and/or an appendage, with the structural complexity of the humanoid robot being largely dependent upon the nature of the work task being performed. The use of humanoid robots may be preferred where direct interaction is required with devices or systems that are specifically made for human use. Due to the wide spectrum of work tasks that may be expected of a humanoid robot, different control modes may be simultaneously required. For example, precise control must be applied within the different spaces noted above, as well as control over the applied torque or force, motion, and the various grasp types. 
       SUMMARY OF THE INVENTION 
       [0005]    According to a first aspect of the disclosure, a robotic hand assembly includes a base structure, first, second, third, and fourth phalanges, and first, second, third, and fourth joints. The first joint operatively connects the first phalange to the base structure such that the first phalange is selectively rotatable with respect to the base structure about a first axis. The second joint operatively connects the second phalange to the first phalange such that the second phalange is selectively rotatable with respect to the first phalange about a second axis. The third joint operatively connects the third phalange to the second phalange such that the third phalange is selectively rotatable with respect to the second phalange about a third axis. The fourth joint operatively connects the fourth phalange to the third phalange such that the fourth phalange is selectively rotatable with respect to the third phalange about a fourth axis. 
         [0006]    Five tendons are operatively connected to the phalanges to selectively exert force thereon and thereby generate torque at the joints. The tendons are configured such that the torque at each of the first, second, third, and fourth joints is independently controllable by the five tendons. 
         [0007]    According to a second aspect of the disclosure, a robotic hand assembly includes a robotic thumb including a first phalange and a second phalange, and a joint interconnecting the first phalange and the second phalange such that the first phalange is selectively rotatable with respect to the second phalange. A magnet is mounted with respect to the first phalange and has a first portion forming a first circle segment characterized by a first center point, and has a second portion forming a second circle segment characterized by a second center point. A Hall effect sensor is mounted with respect to the second phalange for rotation therewith with respect to the first phalange. The shape of the magnet provides linearized output of the Hall effect sensor, thereby providing accurate positional data to a control system for the robotic hand. 
         [0008]    According to a third aspect of the invention, a robotic hand assembly includes a base structure, first, second, third, and fourth phalanges, and first, second, third, and fourth joints. The first joint operatively connects the first phalange to the base structure such that the first phalange is selectively rotatable with respect to the base structure about a first axis. The second joint operatively connects the second phalange to the first phalange such that the second phalange is selectively rotatable with respect to the first phalange about a second axis. The third joint operatively connects the third phalange to the second phalange such that the third phalange is selectively rotatable with respect to the second phalange about a third axis. The fourth joint operatively connects the fourth phalange to the third phalange such that the fourth phalange is selectively rotatable with respect to the third phalange about a fourth axis. The third and fourth axes are substantially parallel to one another. The second phalange is characterized by a twist such that the second axis is not parallel to the third and fourth axes. The twist replaces one of the five degrees of freedom of a human hand with the twist in the shape of the second phalange. 
         [0009]    The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic perspective illustration of a dexterous humanoid robot having two hands; 
           [0011]      FIG. 2  is schematic perspective illustration of an upper arm for the dexterous humanoid robot of  FIG. 1 ; 
           [0012]      FIG. 3  is schematic perspective illustration of a lower arm for the dexterous humanoid robot of  FIGS. 1 and 2 ; 
           [0013]      FIG. 4  is a schematic, top view of one of the hands of  FIG. 1 ; 
           [0014]      FIG. 5  is a schematic, bottom view of the hand of  FIG. 4 ; 
           [0015]      FIG. 6  is a schematic, perspective view of a thumb of the hand of  FIGS. 4 and 5 ; 
           [0016]      FIG. 7  is another schematic, perspective view of a thumb of the hand of  FIGS. 4 and 5 ; 
           [0017]      FIG. 8  is yet another schematic, perspective view of a thumb of the hand of  FIGS. 4 and 5 ; 
           [0018]      FIG. 9  is a schematic, side view of a sensor assembly at a joint of the thumb of  FIGS. 6-8 ; 
           [0019]      FIG. 10  is a graph depicting the performance of the sensor assembly of  FIG. 9  as a function of the rotational position of the joint; 
           [0020]      FIG. 11  is a schematic, side view of the thumb of  FIGS. 6-8  depicting tendon routing; and 
           [0021]      FIG. 12  is a schematic, top view of the thumb of  FIGS. 6-8  depicting tendon routing. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0022]    With reference to the drawings, wherein like reference numbers refer to the same or similar components throughout the several views,  FIG. 1  shows a dexterous humanoid robot  10  adapted to perform one or more tasks with multiple degrees of freedom (DOF). 
         [0023]    The humanoid robot  10  may include a head  12 , torso  14 , waist  15 , arms  16 , hands  18 , fingers  19 , and thumbs  21 , with various joints being disposed within or therebetween. The robot  10  may also include a task-suitable fixture or base (not shown) such as legs, treads, or another moveable or fixed base depending on the particular application or intended use of the robot. A power supply  13  may be integrally mounted to the robot  10 , e.g., a rechargeable battery pack carried or worn on the back of the torso  14  or another suitable energy supply. 
         [0024]    According to one embodiment, the robot  10  is configured with a plurality of independently and interdependently-moveable robotic joints, such as but not limited to a shoulder joint assembly (arrow A), an elbow joint assembly (arrow B), a wrist joint assembly (arrow C), a neck joint assembly (arrow D), and a waist joint assembly (arrow E), as well as the various finger and thumb joint assemblies (arrow F) positioned between the phalanges of each robotic finger  19  and thumb  21 . 
         [0025]    The arm  16  is divided into an upper arm  22  and a lower arm (or forearm)  24 . The upper arm  22  extends from the shoulder joint assembly (arrow A) to the elbow joint assembly (arrow B). Extending from the elbow joint (arrow B) is the lower arm  24 , hands  18 , fingers  19 , and thumbs  21 . For the purpose of simplification, as described herein, the upward direction is toward the head  12  and the downward direction is toward the waist  15 . Those skilled in the art will appreciate that since the robot  10  is intended to simulate a humanoid, the robot will be substantially symmetrical about a vertical plane bisecting the torso and head, and essentially include an identical symmetrical structure on both the left and right sides. 
         [0026]    Referring to  FIG. 2 , the upper arm  22  is illustrated. Although only one upper arm  22  for the arms  16  is shown, both the left and the right arms  16  operate in the same manner as described below. The upper arm  22  has a shoulder joint assembly (arrow A) that includes a first shoulder joint S 1  providing a first DOF, and second shoulder joint S 2  providing a second DOF, and a third shoulder joint S 3  providing a third degree of freedom. Together the first through third shoulder joints S 1 , S 2 , S 3  perform the movements that represent the movements a human shoulder can perform. Specifically, rotation of the first shoulder joint S 1  about a first shoulder axis SA 1  moves a second shoulder axis SA 2  for the second shoulder joint S 2  into a desired position. Based upon the position of the first shoulder joint S 1 , rotation of the second shoulder joint S 2  about the second shoulder axis SA 2  then moves the arm  16  up and down relative to the torso  14 , or forward and backward relative to the torso  14 . The third shoulder joint S 3  rotates the upper arm  22  about a third shoulder axis SA 3 . Rotation of the third shoulder joint S 3  rotates the upper arm  22  axially, i.e. rotation of the third shoulder joint S 3  rotates the elbow joint assembly (arrow B) to face upwards or downwards. Therefore, together the first shoulder joint S 1 , the second shoulder joint S 2 , and the third shoulder joint S 3  form the motions of a shoulder joint assembly (arrow A). 
         [0027]    The upper arm  22  also includes an elbow joint assembly (arrow B) which includes a first elbow joint L 1  and a second elbow joint L 2 . The first elbow joint L 1  and second elbow joint L 2  each provide a degree of freedom. Together the first elbow joint L 1 , and the second elbow joint L 2  perform the movements that represent the movements a human elbow can perform. Rotation of the first elbow joint L 1  about a first elbow axis B 1  causes the upper arm  22 , below the elbow joint assembly (arrow B) to bend and straighten. Additionally, rotation of the second elbow joint L 2  about a second elbow axis B 2  causes the upper arm  22 , below the elbow joint assembly (arrow B) to rotate axially, i.e. rotation of the second elbow joint L 2  about the second elbow axis B 2  rotates the lower arm  24  and hand  18  ( FIG. 1 ) to face palm up or down. 
         [0028]      FIG. 3  illustrates the lower arm  24 , including the wrist joint assembly (arrow C), the hand  18 , the fingers  19 , and thumb  21 . The lower arm  24  includes a plurality of finger (and thumb) actuators  26  and a plurality of wrist actuators  28 . Additionally, a plurality of controls  30  for the finger actuators  26  and the wrist actuators  28  are also supported on the lower arm  24 . The lower arm  24  is attached to a load cell  32  which is used to connect the lower arm  24  with the upper arm  22 . The hand  18  includes a base structure  34  that defines the palm  36  of the hand  18 . Fingers  19  and thumb  21  are movably mounted to the palm structure  34  and selectively curl toward the palm  36  in order to grip an object, such as the one shown at  20  in  FIG. 1 . 
         [0029]    In the embodiment depicted, the thumb  21  is proportionately incorporated into a hand  18  that is comparable in size to that of a sixtieth to eight-fifth percentile human male hand. More specifically, in the embodiment depicted, the length of the hand  18  is 7.9 inches (eightieth percentile human); the breadth, or width, of the hand  18  is 3.6 inches (sixtieth percentile human); and the circumference of the hand (around the base structure) is 8.8 inches (eighty-fifth percentile human). 
         [0030]    Referring to  FIGS. 4 and 5 , the thumb  21  includes a plurality of rigid links, or phalanges  38 A-D, and a plurality of joints  42 A-D. Joint  42 A rotatably mounts phalange  38 A to the base structure  34  such that the phalange  38 A is selectively rotatable with respect to the structure  34  about axis A 1 . Joint  42 B rotatably mounts phalange  38 B to phalange  38 A such that phalange  38 B is selectively rotatable with respect to phalange  38 A about axis A 2 . Joint  42 C rotatably mounts phalange  38 C to phalange  38 B such that phalange  38 C is selectively rotatable with respect to phalange  38 B about axis A 3  Joint  42 D rotatably mounts phalange  38 D to phalange  38 C such that phalange  38 D is selectively rotatable with respect to phalange  38 C about axis A 4 . 
         [0031]    The thumb  21 , with four phalanges  38 A- 38 D and four independently controllable joints  42 A- 42 D, is therefore characterized by four degrees of freedom. A human thumb is most accurately modeled to have five independently controllable joints or degrees of freedom. The thumb  21  in the embodiment depicted is configured to closely approximate the poses achievable by a human thumb with only four degrees of freedom, thereby contributing to the compactness of the hand  18 . 
         [0032]    More specifically, one of the five degrees of freedom in the human thumb, namely, the dynamic twist between axes A 2  and A 3 , has been replaced in the robotic thumb  21  with a permanent, angular twist formed in the shape of phalange  38 B. That is, phalange  38 B is configured and shaped such that axis A 3  is linearly displaced and rotated approximately 40 degrees relative to axis A 2 . Axes A 4  and A 3  are parallel to one another. As shown in  FIGS. 5 and 7 , axes A 1  and A 2  do not intersect, but axis A 2  extends in directions that are orthogonal to the directions in which axis A 1  extends. Axis A 2  is neither parallel nor perpendicular to axes A 3  and A 4 . 
         [0033]    Referring to  FIGS. 6-8 , the thumb  21  includes at least two types of sensors, along with compact electronics  46  to read the sensors and transmit sensor data upstream. The functions of the electronics  46  include providing power to the sensors, collecting analog sensor data, converting analog signals to digital signals, multiplexing digital signals, and communicating data to upstream electronics. More specifically, the sensors of the thumb  21  includes tactile load cells  50 A,  50 B, each of which is mounted to a respective phalange  38 C,  38 D. The thumb  21  also includes a plurality of joint position sensor assemblies  54 A- 54 D, each of which is configured to measure the absolute angular position of a respective one of the joints  42 A- 42 D and the angular position of a phalange relative to a connecting phalange. 
         [0034]    Each of the joint position sensor assemblies  54 A- 54 D includes a respective magnet  58 A- 58 D and a respective Hall effect sensor  62 A- 62 D (Hall effect sensor  62 A is shown in  FIG. 4 ). Referring to  FIG. 9 , sensor assembly  54 D is representative of sensor assemblies  54 A- 54 C, and thus magnet  58 D and sensor  62 D are representative of magnets  58 A- 58 C and sensors  62 A- 62 C, respectively. Magnet  58 D is rigidly mounted with respect to phalange  38 C, and sensor  62 D is rigidly mounted with respect to phalange  38 D. Magnet  58 D is characterized by two portions  66 ,  70 . Portion  66  is a segment of a circle having a center point  74  on axis A 4 . Portion  70  is a segment of a circle having a center point at  78 . The north pole N of the magnet  58 D is disposed at one intersection of the portions  66 ,  70 , and the south pole S of the magnet  58 D is disposed at the other intersection of the portions  66 ,  70 . In the embodiment depicted, portion  66  has the same radius as portion  70 , and the concave sides of portions  66 ,  70  face one another. The magnet  54 D circumscribes both center points  74 ,  78 . 
         [0035]    Sensor  62 D is positioned on phalange  38 D such that, as phalange  38 D rotates with respect to phalange  38 C about axis A 4 , the sensor  62 D maintains a constant distance from portion  66  of the magnet  58 D. The shape of the magnet  58 D and the placement of the sensor  62 D provide a linear relationship between angular position of the phalange  38 D with respect to phalange  38 C and the change in magnetic field that is read by sensor  62 D. More specifically, and with reference to  FIG. 10 , line  82  depicts the signal generated by a Hall effect sensor as a function of angular position with respect to a conventional round magnet (not shown). As shown by line  82 , the signal is sinusoidal. Line  86  depicts the signal generated by Hall effect sensor  62 D as a function of angular position with respect to magnet  58 D. As shown by line  86 , sensor assembly  54 D generates an approximately linear signal over a 150-degree usable range of angular positions. 
         [0036]    Magnet  58 A is mounted with respect to phalange  38 A and sensor  62 A is mounted with respect to the base structure  34 , and thus sensor assembly  54 A measures the rotational position of phalange  38 A with respect to the base structure  34 . Magnet  58 B is mounted with respect to phalange  38 A and sensor  62 B is mounted with respect to phalange  38 B, and thus sensor assembly  54 B measures the rotational position of phalange  38 B with respect to phalange  38 A. Magnet  58 C is mounted with respect to phalange  38 B and sensor  62 C is mounted with respect to phalange  38 C, and thus sensor assembly  54 C measures the rotational position of phalange  38 C with respect to phalange  38 B. Magnet  58 D is mounted with respect to phalange  38 C and sensor  62 D is mounted with respect to phalange  38 D, and thus sensor assembly  54 D measures the rotational position of phalange  38 D with respect to phalange  38 C. 
         [0037]    Referring to  FIG. 11 , wherein like reference numbers refer to like components from  FIGS. 1-10 , movement of the phalanges  38 A- 38 D about joints  42 A- 42 D is accomplished by robotic tendons  90 A- 90 E, i.e., flexible members such as cables. Each of the tendons  90 A- 90 E is operatively connected to a respective actuator (shown at  26  in  FIG. 3 ) in the forearm (shown at  24  in  FIG. 3 ). In an exemplary embodiment, the actuators  26  are electric motors operatively connected to the tendons  90 A- 90 E by drive mechanisms configured to convert the rotary motion of the motors to linear motion to drive the tendons  90 A- 90 E. The placement of the actuators and drive mechanisms in the forearm  24  and/or wrist contributes to the compactness of the hand  18 . 
         [0038]    The routing of the tendons  90 A- 90 E with respect to the joints  42 A-D and the axes A 1 -A 4  enables the thumb  21  to be fully controlled through four degrees of freedom using only the five tendons  90 A- 90 E. Two opposing tendons  90 A,  90 B control the distal pitch joint  42 D, and two opposing tendons  90 C,  90 D control the medial pitch joint  42 C. One end of tendon  90 A is operatively connected to phalange  38 D on one side of joint  42 D and axis A 4  such that tension in tendon  90 A causes rotation of phalange  38 D with respect to phalange  38 C about axis A 4  in a first direction  94 . One end of tendon  90 B is operatively connected to phalange  38 D on the opposite side of joint  42 D and axis A 4  from tendon  90 A such that tension in tendon  90 B causes rotation of phalange  38 D with respect to phalange  38 C about axis A 4  in a second direction  98  opposite the first direction  94 . 
         [0039]    One end of tendon  90 C is operatively connected to phalange  38 C on one side of joint  42 C and axis A 3  such that tension in tendon  90 C causes rotation of phalange  38 C with respect to phalange  38 B about axis A 3  in the first direction  94 . One end of tendon  90 D is operatively connected to phalange  38 C on the opposite side of joint  42 C and axis A 3  from tendon  90 C such that tension in tendon  90 D causes rotation of phalange  38 C with respect to phalange  38 B about axis A 3  in the second direction  98 . Rotation of the phalanges in the first direction  94  causes the phalanges to rotate toward the palm  36 , and thus rotation of the phalanges in the first direction  94  enables the hand  18  to grip an object. Rotation of the phalanges in the second direction  98  causes the phalanges to rotate away from the palm  36 , and thus causes the thumb  21  to release a grip on the object. 
         [0040]    Tendon  90 A is routed on the palmar side of joints  42 B-D and axes A 2 -A 4 . Tendon  90 B is on the palmar side of joint  42 B and axis A 2 , and is on the non-palmar side of joints  42 C and  42 D and axes A 3  and A 4 . Tendon  90 C is routed on the palmar side of joints  42 B and  42 C axes A 2  and A 3 . Tendon  90 D is routed on the palmar side joint  42 B and axis A 2 . Tendon  90 E is routed on the non-palmar side of axis A 2 . 
         [0041]    The routing of tendons  90 A- 90 D on the palmar side of the axis A 2  of the proximal pitch joint  42 B enables tendons  90 A- 90 D to be used to close joint  42 B, i.e., to rotate phalange  38 B with respect to phalange  38 A about axis A 2 . The tension in each of these tendons  90 A- 90 D is summed to maximize gripping torque applied to the proximal pitch joint  42 B. Opening of the proximal pitch joint  42 B is controlled by tendon  90 E, which is routed to oppose the other four tendons  90 A- 90 D on the opposite side of axis A 2 . 
         [0042]    Referring to  FIG. 12 , wherein like reference numbers refer to like components from  FIGS. 1-11 , there are no tendons dedicated to controlling the position of the base roll joint  42 A. Instead, four of the five tendons  90 A- 90 D are routed on opposite sides of axis A 1  of the base roll joint  42 A, and the balance of tension in these four tendons  90 A- 90 D is manipulated to control the position of joint  42 A and, correspondingly, the angular position of phalange  38 A with respect to the base structure  34 . More specifically, tendons  90 A and  90 B are routed on one side of joint  42 A and axis A 1 , and tendons  90 C and  90 D are routed on another side of joint  42 A and axis A 1 . The balance of tensions between tendons  90 A and  90 B, and tendons  90 C and  90 D controls the angular position of phalange  38 A with respect to the base member (shown at  34  in  FIGS. 4-5 ). 
         [0043]    Given the tendon routing shown in  FIGS. 11 and 12 , it is possible to show how the four joint torques are independently controllable, as is the overall internal tension. Assuming that all of the moment arms are equal, then 
         [0000]    
       
      
       T 
       1 
       =A−B+C+D;  
      
     
         [0000]    
       
      
       T 
       2 
       =A+B+C+D−E;  
      
     
         [0000]        T   3   =A−B+C−D ; and 
         [0000]    
       
      
       T 
       4 
       =A−B,  
      
     
         [0000]    wherein A is the tension in tendon  90 A, B is the tension in tendon  90 B, C is the tension in tendon  90 C, D is the tension in tendon  90 D, E is the tension in tendon  90 E, T 1  is the torque at joint  42 A, T 2  is the torque at joint  42 B, T 3  is the torque at joint  42 C, and T 4  is the torque at joint  42 D. To get a commanded set of joint torques, the following equations apply: 
         [0000]        A=−T   1 /4 +T   2 /5 +T   4 /2 +t/ 4; 
         [0000]        B=−T   1 /4 +T   2 /5 −T   4 /2 +t/ 4; 
         [0000]        C=T   1 /4 +T   2 /5 +T   3 /2 −T   4 /2 +t/ 4; 
         [0000]        D=T   1 /4 +T   2 /5 −T   3 /2 −T   4 /2 +t/ 4; and 
         [0000]        E=−T   2 /5 +t,    
         [0000]    where t is an internal tensioning factor that is large enough to keep all tensions positive. Those skilled in the art will recognize how to modify these equations if the moment arms are not equal or if they change with the angle of rotation of the joints. 
         [0044]    It should be noted that, although the tendons  90 A-E are depicted in  FIGS. 11 and 12  as being external to the phalanges  38 A- 38 D, each of the tendons is routed through a respective internal guide channel formed in the phalanges  38 A- 38 D. Portions of the internal guide channels in phalange  38 B are shown at  102 A- 102 E in  FIG. 7 . Referring to FIGS.  7  and  11 - 12 , tendon  90 A is routed through guide channel  102 A; tendon  90 B is routed through guide channel  102 B; tendon  90 C is routed through guide channel  102 C; tendon  90 D is routed through guide channel  102 D; and tendon  90 E is routed through guide channel  102 E. The angular twist in the shape of phalange  38 B results in curved guide channels  102 A- 102 D; exemplary methods of forming the guide channels  102 A- 102 D include casting and Direct Metal Laser Sintering (DMLS). 
         [0045]    It should also be noted that, although axis A 2  appears to be parallel to axes A 3  and A 4  in  FIGS. 11 and 12 , axis A 2  is twisted relative to axes A 3  and A 4  as shown in  FIGS. 4 and 5 . 
         [0046]    In the embodiment depicted, the range of motion of joint  42 A (base roll) is 0° to 80°; the range of motion of joint  42 B (proximal pitch) is 0° to 100°; the range of motion of joint  42 C (medial pitch) is 0° to 80°; and the range of motion of joint  42 D (distal pitch) is −30° to 90°. 
         [0047]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.