GB2519993A

GB2519993A - Robotic hand

Info

Publication number: GB2519993A
Application number: GB1319455.0A
Authority: GB
Inventors: Daniel Greenwald; Matthew Paul Godden
Original assignee: Shadow Robot Co Ltd
Current assignee: Shadow Robot Co Ltd
Priority date: 2013-11-04
Filing date: 2013-11-04
Publication date: 2015-05-13
Anticipated expiration: 2033-11-04
Also published as: WO2015063523A3; WO2015063523A2; GB2519993B; GB201319455D0

Abstract

A robotic end effector comprising: a frame portion defining a base Cartesian coordinate reference frame, three finger members and a thumb member. The base portion represents the palm of a human hand. The finger members comprise distal, medial and proximal portions and the thumb member comprises distal and proximal portions. Each member is attached to the frame portion by its proximal portion. The finger members have two degree of freedom joints where the proximal portions join the palm region of the hand. These joints allow rotation around an axis coming out of the plane of the palm. This allows the fingers to splay out. The thumb member has a rotational joint, the axis of rotation of which is parallel to the plane of the palm, allowing the thumb to roll over towards the palm. Rotation around the axis of the thumbs proximal portion is also allowed. Where a digit has N joints, it is actuated by N+1 tendons, operating on a motor drive and capstan arrangement. A rotary position sensor is used to sense the position of the capstan.

Description

ROBOTIC HAND

Technical Field

The present invention relates to robotic hands. In particular, the invention relates to a robotic end effector with improved dexterity.

Background

It is a prime goal for designers and inventors in the technical field, to provide an artificial hand approximating the human hand as regards to form, size, strength and weight and above all, a hand which is substantially indistinguishable from the human hand as regards to dexterity, Le.

its manipulative ability.

There have, over the years, been numerous attempts made by various individuals and organizations, to provide such an artifact, and whilst considerable progress has been achieved to date, the hand designs have invariably fallen short of the above-mentioned characteristics in one respect or another. Even where the designs have provided an effector which is sufficient (in terms of mechanical flexibility) to allow the end to grasp any object a human hand can grasp, thereby allowing it to use standard tools, these end effectors are often expensive to manufacture and maintain, and are likely to not to be robust enough for use in an industrial environment.

In particular, the human thumb which incorporates ball and socket/saddle type joints is particularly difficult to design. To obtain the range of motion provided by a thumb, the artificial thumb may be designed with joints approximating those found in the human hand. However, it has been that these configurations not only require significant manufacturing complexity but it is also difficult to mount sensors at these joints, and without full and accurate sensing of movements at the joints, movements of the artificial thumb are difficult to control.

The present invention therefore aims to provide a robotic hand which more closely mimics a human hand, including providing improved dexterity. Additionally, the present invention aims to provide a robotic hand which affords more accurate control allowing an operator to tele-operate the end effector without inducing fatigue or confusion.

Sum ma iv This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

A robotic end effector comprising a frame portion defining a base Cartesian coordinate reference frame; three finger members and a thumb member, wherein each finger member comprises distal, medial and proximal portions, and wherein the thumb member comprises a distal and proximal portion; and wherein each member is attached to the frame portion by the proximal portion. By providing a robotic end effector having three fingers and a thumb, a user controlling the movement of the robotic end using a glove emulator or similar will have a spare finger which is not used for controlling the functionality or movement of the glove. This spare finger can be used to for example to turn the system, or the controller or emulator, off.

This is particularly advantageous as the little finger is not required to control or perform, and therefore is often not needed to emulate, the vast majority of functionalities provided by the human hand.

Preferably, the frame portion is substantially rectangular in shape; this is such that the frame portion emulates the palm region of the human hand. Preferably, the finger members are attached substantially along one edge of the frame portion, and even further preferably are spaced accordingly on said edge of the frame portion. Preferably, where the finger members are attached substantially along one edge of the frame portion, the attachment of one or more of the finger members to the frame portion may be such as to offset the one or more of the finger members from the plane the remaining finger members are attached to the frame portion.

Preferably, each of the finger members has substantially the same dimensions and/or configuration. By having three substantially identical finger members, the production/manufacturing costs are kept down. Alternatively, the finger members can have different dimensions and/or configurations; for example, to more closely mimic the differences between the various fingers of the human hand.

Preferably, the thumb member is attached to the frame portion substantially along an edge adjacent to (preferably, substantially orthogonal/perpendicular to) the edge on which the finger members are attached. This arrangement is such as to closely emulate the configuration of the human hand from both an aesthetic but also functional point of view.

A finger member for use in the robotic end actuator as hereinbefore described, wherein the finger member comprises a one-degree-of-rotation freedom joint coupling between one end of the distal portion and one end of the medial portion; a one-degree-of-rotation freedom joint coupling between the other end of the medial portion and one end of the proximal portion; and a two-degree-of-rotation freedom joint coupling the other end of the proximal portion to said frame portion with one of the rotational axes of the rotary part of said joint offset angularly with the reference to said base coordinate reference frame.

A thumb member for use in the robotic end actuator as hereinbefore described and/or along with the finger member as hereinbefore described, wherein the thumb member comprises: a one-degree-of-rotation freedom joint coupling between one end of the distal portion and one end of the proximal portion; and a one-degree-of-rotation freedom joint coupling between the other end of the proximal portion and the frame portion; wherein the frame portion comprises a first one-degree-of-rotation freedom joint coupling and a second one-degree of freedom joint, and wherein the first and second one-degree-of-rotation freedom joints are offset angularly with reference to said base coordinate reference frame.

The finger member as hereinbefore described, wherein said two-degree-of-rotation freedom joint comprises two single-degree-of-rotation freedom portions, the first portion having its rotational axis offset angularly with reference to the base coordinate reference frame, and the other portion having its rotational axis orthogonal to the rotation axis of said first portion.

The member or members as hereinbefore described, wherein each of the joints is actuated by N1 arrangement of tendons. The member or members as hereinbefore described, wherein the N1 arrangement actuates each joint by providing two tendons attached to each joint such that actuation of one tendon actuates the joint in one direction and actuation of the second tendon actuates the join in the opposed direction. The particular tendon based actuation, based on a N1 actuation paradigm arranged such that tendons co-operate in the direction where force exerted by certain joints are maximized, provides for greater control of the members.

An actuator system for use in the robotic end effector as hereinbefore described and/or along with the member or members as hereinbefore described, wherein the actuator comprises: a motor drive comprising a capstan; a string rotatably attachable to the capstan, the string configured to wind onto and off of the capstan in use; and a rotary position sensor for sensing the position of the capstan.

The actuator system as hereinbefore described wherein the actuator system further comprises an output roller with a position sensor through which the string exits the actuator system.

The actuator system as hereinbefore described wherein the actuator system further comprises a roller between the capstan and the output roller.

The actuator system as hereinbefore described, further comprising an elastic element arranged such that external forces on the string causes the elastic element to move and thus altering the total path length of the string between the capstan and the output roller.

A robotic hand comprising the end effector, finger member, thumb member and/or actuator as hereinbefore described.

An upper arm assembly comprising the robotic hand as hereinbefore described.

An artificial hand, finger member, thumb member and/or actuator substantially as hereinbefore described with reference to the accompanying drawings.

The preferred features may be combined as appropriate, as would be apparent to a skilled person, and may be combined with any of the aspects of the invention.

Brief Description of the Drawings

The invention is diagrammatically illustrated, by way of example, with reference to the following drawings, in which: Figure 1 illustrates an exemplary robotic end effector where the palm region is upwards facing; Figure 2 illustrates the exemplary robotic hand from Figure 1 from a different perspective wherein the palm region is downwards facing; Figure 3 illustrates schematically the components of the robotic end effector of Figures 1 and 2; Figure 4 illustrates schematically a side perspective of a digit of the robotic hand of Figure 3 in conjunction with the working joints and the tendons; Figure 5 illustrates schematically a rearward perspective of the digit of the robotic hand of Figure 4; Figure 6 illustrates a perspective view of a digit of the robotic hand as that shown in Figures 4 and 5; and Figures 7A to C illustrate schematically the actuator system for actuating movement in the robotic hand effector.

Common reference numerals are used throughout the figures to indicate similar features.

The kinematics of an anthropomorphic hand in accordance with the invention should be apparent from the Figures of the drawings. Throughout the ensuing description and in the accompanying claims, the expressions "x", "y", and "z", are employed in relation to axes about which angular displacements of the phalanges of the finger-or thumb-representing digits of the hand depicted are to occur. The terminology based on the Euler angles will be used in order to provide a satisfactory appreciation of the constructional features of hands in accordance with the invention without loss of any mathematical rigor in the application.

Detailed Description

Additional advantages and novel features of the invention will be set forth in part within the description which follows and will become apparent to those skilled in the art upon examination of the following and the accompanying figures, or may be learned by practice of the invention.

Figure 1 illustrates an exemplary robotic end effector where the palm region is upwards facing and Figure 2 illustrates the exemplary robotic hand from Figure 1 from a different perspective wherein the palm region is downwards facing. In this example, the robotic hand or end effector 10 of each of Figures 1 and 2 comprises three finger digits 102, 104, 106 and a thumb digit 108, which substantially imitate the ring, middle and index fingers and thumb of a human hand, respectively. The finger digits 102, 104, 106 are arranged on the palm region 150 substantially spaced along one edge of the palm region 150. The thumb digit 108 is arranged, in this example, on an edge adjacent to the edge finger digits 102, 104, 106 are arranged; such that the positioning of the thumb digit 108 substantially emulates the positioning of the human thumb on the human hand. In this example, the end actuator 10 appears to be a robotic hand emulating the right hand. However, it will be appreciated that an alternative arrangement can be provided to emulate the left hand.

Although not depicted in the figures, the end effector 10 may be attached to commercially available robot arms.

Figure 3 illustrates schematically exemplary components of the robotic end effector 10 of Figures 1 and 2. In this example, the robotic hand 10 comprises three finger digits 102, 104, 106 and a thumb digit 108, which substantially imitate the ring, middle and index fingers and thumb of a human hand, respectively. The digits 102, 104, 106, 108 are connected to frame 160, wherein frame 160 substantially forms the structure of the palm region 150. In particular, each finger digits 102, 104, 106 are attached to one end of three substantially planar and parallel bars forming frame 160. These three parallel bars represent the metacarpals of the human hand. The parallel bars in this arrangement each comprise two ends, the first end (opposed to the end attached to thefinger digits 102, 104, 106) being attached to a fourth bar, perpendicularly placed in respect of the parallel bars. The frame 160 thereby defines a substantially rectangular area which is intended to mimic the palm region of the human hand.

Although in this example, the frame 160 comprises three substantially parallel and planar bars attached on one end to a perpendicular bar and attached on the opposite end to the finger digits, it will be appreciated that alternative arrangements and component shapes are possible. In fact, it will be appreciated that the frame 160 need not be substantially planar nor does it need to have a substantially rectangular area. Also, the frame 160 does not need to comprise bars forming a hollow frame, but may be comprised out of a solid structure. In fad, any shape or configuration suitable for use as means for emulating a palm region or similar in an end effector, or at least means suitable for connecting the members in a particular arrangment, may be provided.

In this example, the frame 160 is substantially planer and defines a substantially rectangular area. Each of finger digits 102, 104, 106 is attached to the frame 160 on one edge and the thumb digit 108 is attached to an adjacent edge of the frame 160. Specifically, finger digits 102, 104, 106 are each attached to respective ends of the three substantially parallel bars forming the frame. The thumb digit 108 is secured to the edge of the frame 160 which is adjacent to the edge on which the finger digits 102, 104, 106 are secured.

Specifically, the thumb digit 108 is attached along substantially the length of one of the substantially parallel bars, the end of which is connected to one of finger digits 102, 104, 106.

In this example, the thumb digit 108 is attached to an outer one of the substantially parallel bars of frame 160; in this example, to the right exterior bar where the palm 150 is facing upwards so as to emulate the thumb positioning in a right hand. However, it will be appreciated that the thumb digit 108 need not be so attached and in fact can be attached at a multitude of positions on the frame 160, wherein each achieve different dexterity and results.

It will also be appreciated that in some embodiments, the thumb digit 108 may be releasably connectable to a plurality of locations on the frame 160 to allow for alternative configurations and functionalities to be made; this may be alternatively or additionally applicable with regards to the finger digits 102, 104, 106.

Each finger digit 102, 104, 106 preferably includes a distal finger portion 112, a medial finger portion 114 and a proximal finger portion 116. For the avoidance of doubt, although only the distal, medial and proximal finger portion 112, 114, 116 of finger digit 102, or the ring finger, are labeled in Figure 1, it is clear from Figure 1 that finger digits 104 and 106 also include finger portion 112, 114, 116. It will also be appreciated that although in this example each finger digit 102, 104, 106 is configured to comprise a substantially similar configuration with the same type of joints for each portion; this is not required and may be varied.

The distal finger portion 112 and the medial finger portion 114 are connected by a distal finger joint 118. The distal finger joint 118 enables the distal finger portion 112 to move about axis 4, illustrated in Figure 1, with respect to the medial finger portion 114. In this example, axis 4 is in the same plane as frame 160 when the end effector 10 is not in use. The medial finger portion 114 and the proximal finger portion 116 are connected by a medial finger joint 120. The medial finger joint 120 enables the medial finger portion 114 to move about axis Z3, also illustrated in Figure 1, with respect to the proximal finger portion 116. In this example, axis 4 is in the same plane as frame 160 when the end effector 10 is not in use and is substantially parallel to Z4. Finally, the proximal finger portion 116 is connected to the palm section 150 by a proximal finger joint 122. The proximal finger joint 122 enables the proximal finger portion 116 to move about an axis Z2 and about an axis Z1, both depicted in Figure 1, with respect to the palm section 150. Joint 122 can be thought of as essentially two separate joints. Proximal finger joint 122 comprises a first proximal finger joint enabling movement in a first direction about axis Z1, and a second proximal finger joint enabling movement in a second direction about axis Z2.

In this example, axis Z2 is in the same plane as frame 160 when the end effector 10 is not in use and is substantially parallel to Z3 and Z4. Axis Z1 is substantially orthogonal to axes Z2, Z3 and 4. Although only the distal, medial and proximal finger joints 118, 120, 122 of finger digit 102 are labeled in Figure 1, it is clear from Figure 1 that finger digits 104 and 106 also include finger joints similar to the finger joints 118, 120, 122. However, it will also be appreciated that each finger digit may not include the same configuration and/or type of finger joint(s). It will also be appreciated that where the fingers are kept substantially similar, manufacturing costs maybereduced.

In this example, finger digit 104 is positioned at a slightly greater distance from the substantially perpendicular bar adjoining the three parallel bars forming frame 160 as illustrated in Figure 1. This may be as a result of the bar attached to finger digit 104 being longer than the other parallel bars. Additionally or alternatively, finger digit 104 can itself be longer or generally have different dimensions than the other finger digits. By placing finger digit 104 further from the palm region 150, the offset emulates the position of the middle finger of the human hand. It will be appreciated that such offsets or other configurations may be provided for each of the finger digits.

The thumb digit 108 includes a distal thumb portion 128 and a proximal thumb portion 130.

The thumb digit 108 comprises: a one-degree-of-rotation freedom joint coupling between one end of the distal portion 128 and one end of the proximal portion 130 and a one-degree-of-rotation freedom joint coupling between the other end of the proximal portion 130 and the frame portion 160. The frame portion 160, along the edge of the palm region 150, comprises a first one-degree-of-rotation freedom joint coupling and a second one-degree of freedom joint. The first and second one-degree-of-rotation freedom joints are offset angularly with reference to said base coordinate reference frame.

Specifically, the distal thumb portion 128 and the proximal thumb portion 130 are connected by a distal thumb joint 134. The distal thumb joint 134 enables the distal thumb portion 128 to move about axis Z'4, illustrated in Figure 1, with respect to the proximal thumb portion 130.

The proximal thumb portion 130 and the metacarpal thumb portion 132 are connected by a proximal thumb joint 136. The proximal thumb joint 136 enables the proximal thumb portion to move about an axis Z'3, illustrated in Figure 1, with respect to the metacarpal thumb portion 132. In this example, palm joint 124 sits along one of substantially parallel bars of frame 160 to allow for movement about an axis Z1. Axes 14 and 13 are substantially parallel to one another. Axis 12 is substantially orthogonal to axes Z'4 and 13. Finally, axis Zi is substantially orthogonal to axes Z'2, Z'3 and 14.

This thumb and palm enables movement of the thumb about the palm section 150 or frame such that, for example, the thumb digit 108 can touch the base portion 126 of finger digits 102, 104, 106.

The configuration of the joints of the thumb digit 108 facilitates movement such that the thumb digit 108 in use can touch the side of the palm section, in particular the base portion 126 of the finger digit 106. The thumb digit 108 can advantageously also touch each of the distal finger portions 112, medial finger portions 114 and the proximal finger portions 116 of each finger digit. The thumb digit 108 arrangement further enables the distal thumb portion 128 and proximal thumb portion 130 to rest alongside the palm section 150 without obstructing the palm section 150.

The thumb digit 108 arrangement described herein provides a range of movements with revolute joints. In fact, the range of motion provided by the robotic end effector, particularly by the thumb digit 108, is a significant improvement over known robotic hands, previously the thumb digit was unable to touch the side of the palm and index finger.

The geometric movement of the thumb and finger digits will now be considered in more detail using the Denavit-Hartenberg (D-H) convention. As stated by Lopez and Foulc1, an P. Lopez and J.N. Foulc. "Introduction to Robotics volume I. Glentop. 1986 articulated mechanical system (AMS) is characterized by two parameters: structural parameters (constant) and articular variables (angles or lengths). Each link in the AMS has assigned a Cartesian coordinate system that can be expressed as a series of transformations from the main reference frame. According to the formalism of Eulerian angles, the relation between one reference frame and the next can be stated as three translations and three rotations, which correspond to the Eulerian angles (q, 0, cp).

The Denavit-Hartenberg 2 convention, allows us to express a reference frame relative to the previous one, by four parameters. These in turn represent the four specific transformations the reference frame must undergo in the order dictated. (First Z then X, the rotation and translation order within these is irrelevant). The parameters are: 0 > rotation in Z; r > translation in Z; a > translation in X; a > rotation in X. 1= Transformation = (Rot. in Z by 0) x (Trans. Z by r) x (Trans. in X by a) x (Rot. in X by ci) In matrix form we have: T= cos (0) -sin(0)cos(a) sin(0)cos(a) a cos(a) sin (0) cos(0)cos(a) -cos(0)sin(a) a sin(a) o sin(a) cos(a) r o o 0 1 Filling in each set of 4 parameters (each row in the parameter table) into the previous definition gives a transformation matrix that relates two adjacent frames of reference.

Repeating this procedure for the entire set, one gets a number of matrices equal to the degrees of freedom (DOF) of the AMS, and multiplying all these matrices in the appropriate order yields the position and orientation of the end-effector.

2 R.S. Harlenberg and J. Denavit. "A kinematic notation for lower pair mechanisms based on mathces", Journal of Applied Mechanics, vol. 71, Pp. 215-221, June 1955.

Many people are not aware that there are two different forms of D-H representation for serial-link manipulator kinematics: a) Classical as per the original 1955 paperof Denavit and Hartenberg. and used in textbooks such as by Paul Fu et al or Spong and Vdyasagar.

(This is the form being used for this description) orb) Modified form as introduced by Craig in his text book. P.1. Corke, A Robotics Toolbox for Matlab'. IEEE Robotics and Automation Magazine, vol.3, pp. 24-32. March 1996.

Identifying all the quartets of parameters uniquely defines the mechanics of the AMS. It is important to keep in mind however, that there are several different ways, using the D-H convention, to define the same AMS, and they are all equivalent with respect to the mechanics of the AMS.

It should be noted that three of the parameters are constant (r, a, a), and the controlled variable along which the joint moves is (e). The constant parameters (r, a, a) can be set at different values to improve the overall behavior.

The preferred values for the Denavit-Hartenberg parameters for each of the thumb and finger digits are set out in the tables below. Thumb Axis

0 r a a

Description

Origin to Joint 1 180 35 30 0 Joint I -Joint 2 281 15.665 5.812 242 Joint 2-Joint 3 293 33.341 0 270 Joint3-Joint4 0 0 45 0 Joint4-Thumb 0 0 22 0 Nominal Tip Centre First Finger (for example, pointer or index finger) Axis 9 r a a

Description

Origin to Joint 1 180 85 30 90 Joint 1 -Joint2 90 0 0 90 Joint2-Joint3 0 0 45 0 Joint3-Joint4 0 0 25 0 Joint4-Finger 0 0 16 0 Nominal Tip Centre Second Finger (for example, middle finger) Axis o r a a

Description

Origin to Joint 1 180 90 0 90 Joint 1 -Joint2 90 0 0 90 Joint2-Joint3 0 0 45 0 Joint3-Joint4 0 0 25 0 Joint4-Finger 0 0 16 0 Nominal Tip Centre Third Finger (for example, ring finger) Axis o r a a

Description

Origin to Joint 1 180 85 -30 90 Joint I -Joint2 90 0 0 90 Joint2-Joint3 0 0 45 0 Joint3-Joint4 0 0 25 0 Joint4-Finger 0 0 16 0 Nominal Tip Centre The values for U and a may fall within a specified range detailed in the table and may range from minus 25° of the value to plus 25° of the value. The values for rand a may fall within a specified range detailed in the table and may range from minus 15mm of the value to plus 15 mm of the value.

Figure 4 illustrates schematically an enlarged side perspective of a finger digit of the robotic hand in conjunction with the working joints and the tendons. Figure 4 illustrates schematically an arrangement for actuating the distal finger joint 118, medial finger joint 120 and proximal finger joint 122, as previously illustrated in Figure 3. Figures Sand 6 illustrate schematically different perspectives of Figure 4 to further the understanding of the tendon arrangement.

The robotic end effector 10 in this example includes a plurality of tendons. These tendons are used to actuate the various joints. It will be appreciated that the joints may be actuated by alternative means. Additionally, it will be appreciated that palm section 150 may be actuated by one or more actuation devices.

To actuate a finger or thumb digit in this example, as illustrated in Figure 4, two tendons are attached, at a first end, to each joint. The two tendons are also connected, at a second end, to an actuation device (not illustrated). This arrangement allows for each joint to be actuated in a first direction, and in a second direction, opposite to the first direction. One actuation device may be provided for each joint.

Additionally or alternatively, one tendon could be used to actuate each joint, wherein the tendon is attached around and connected to the joint. The first and second ends of the tendon of this example are connected to an actuation device in order to actuate the joint in a similar manner to that depicted in Figure 4.

Each tendon of the robotic hand section 10 preferably comprises its own actuation device.

For example, in the hand section 10 illustrated in Figure 4, each finger digit 102, 104, 106, comprises of four joints, and in accordance with the N1 configuration may require at least 5 actuation devices (not illustrated). In addition, the palm section 150 may comprise two actuation devices, which may comprise further actuation devices to emulate wrist movement where the robotic end effector lOis to be attached to a robotic arm. It will be appreciated that different arrangements may be provided which use a different number of actuation devices.

For example, the palm section 150 may not be required to move, or may only be required to have limited movement, in which case fewer actuation devices may be provided.

In addition, a human finger digit, in most instances, is not capable of moving the distal finger portion 112, without also moving the medial finger portion 114. Consequently, in order to realistically mimic a human hand, the distal finger joint 118 and medial finger joint 120 may be actuated together.

As can be seen in Figure 4, a first end of a tendon 202 is connected to the medial finger joint at medial connection point 120A. A second end of the tendon 202, opposite to the first end of the tendon 202, is connected to an actuation device (not illustrated). A first end of a tendon 204 is connected to the distal finger joint 118 at distal connection point 118A. A second end of the tendon 204, opposite to the first end of the tendon 204, is connected to an actuation device (not illustrated). A first end of tendon 206 is connected to the distal finger joint 118 at distal connection point 118B. A second end of the tendon 206, opposite to the first end of the tendon 206, is connected to the actuation device (not illustrated).

A first end of arch tendon 208 is connected to the proximal finger joint 122 at proximal connection point 122A. A second end of the arch tendon 208, opposite to the first end of the arch tendon 208, is connected to the actuation device (not illustrated). A first end of the second arch tendon 210 is connected to the proximal finger joint 122 at proximal connection point 122A. A second end of the second arch tendon 210, opposite to the first end of the second arch tendon 210, is connected to the actuation device (not illustrated) in order to actuate the joint in the first direction and in the second direction, opposite to the first direction.

The tendon 202 is firstly guided around the medial finger joint 120 and secondly guided around the proximal finger joint 122 as to induce movement of the medial finger joint 120 and proximal finger joint. The tendon 202 is not connected to the proximal finger joint 122 in this example. However, in another example, the tendon 202 may be guided through the proximal finger joint 122.

The tendon 204 and tendon 206 are firstly guided around the distal finger joint 118 such that the tendon 204 is guided towards the extensor side of the robotic hand 10 and the tendon 206 is guided towards the flexor side of the robotic hand 10. The tendon 204 and tendon 206 are then guided around the medial finger joint 120 towards flexor side of the robotic hand 10. The tendon 204 and tendon 206 are lastly guided around the proximal finger joint 120; the tendons are guided such that they are on the flexor side of the robotic hand 10. The tendon 204 and tendon 206 are not connected to the proximal finger joint 122. However in another embodiment of the invention the tendon 204 and tendon 206 may be guided through at least one of the distal finger joint 118, medial finger joint 120 and the proximal fingerjoint 122.

The arch tendon 208 and 210 are guided around the proximal finger joint 122 parallel to one another forming an arch shaped configuration on the flexor side of the robotic hand 10 as to not to hamper movement of the proximal finger joint 122. The arch tendons 208 and 210 are not connected to the proximal finger joint 122. However in another embodiment of the invention at least one arch tendon 208 and second arch tendon 210 may be guided through the proximal finger joint 122.

It will be appreciated that activation of the actuation device to which the tendon 202 and tendon 206 are connected results in the distal finger portion 112 moving about the distal finger joint 118 and the medial finger portion 114 moving about medial finger joint 120, such that the finger digit bends or straightens.

For example, in order to bend the finger digit, the tendon 206 is pulled in direction A resulting in the distal finger portion moving about the distal finger joint 118. Since the distal finger joint 118 is connected to the medial finger joint 120 by a medial finger portion 114, movement of the distal finger joint 118, results in movement of the medial finger portion, resulting in movement of the medial fingerjoint 120, ultimately bending the finger digit.

In order to straighten the finger digit, the tendon 202 is pulled in direction A, resulting in movement of the medial finger joint 120. In addition, the tendon 204 is moved in direction A ultimately straightening the finger digit. It will be appreciated that similar arrangements and functioning to actuate each of the joints may be provided.

There could be alternative arrangements for connecting a distal finger joint 118, a medial fingerjoint 120 and proximal finger joint 122 for actuation. A first end of an tendon 202 may be connected to the distal finger joint 118 at distal connection point 118A.

A second end of the tendon 202, opposite to the first end of the tendon 202, may be connected to the actuation device (not illustrated). A first end of tendon 204 may be connected to the distal finger joint 118 at distal connection point 11 8A. A second end of the tendon 204, opposite to the first end of the tendon 204, may be provided with a tendon nodule. A biasing device, a spring, may be provided on the tendon 204 between a tendon nodule and point 204. The tendon nodule and the biasing device 208 may be provided in a channel. Finally, a first end of a tendon 206 may be connected to the distal finger joint 118 at distal connection point 11 8A. A second end of the tendon 206, opposite to the first end of the tendon 206, maybe connected to the actuation device.

The tendon 202 and the tendon 206 may move substantially in the same distance in order to bend and straighten the finger digit. The tendon 206 may be arranged to move a substantially greater distance than the tendon 202 in order to bend and straighten the finger digit. Having both tendons 202 and 206 moving substantially the same distance results in increased accurate movement control and simpler actuation control.

The depicted tendon and joint arrangement permits the joints to be actuated independently whilst maximizing the amount of torque the medial finger joint 120 and medial thumb joint 136 can exert in the flexor direction. This is achieved by arranging the tendons such that the arch tendon 208 and the second arch tendon 210 acting differentially, cause proximal digit joint 122 to extend. Similarly, the loopback tendon 204 and the tendon 206 when acting in concert, combine to cause medial finger joint 120 to flex.

Generally, therefore, to actuate a chain of N degrees of freedom using tendon-like chords acting unidirectionally a minimum of N±1 tendon may be used to actuate all the degrees of freedom independently. Compared to the standard 2N actuation arrangement, where each degree of freedom has two tendons arranged in agonist/antagonist fashion, the invention effectively doubles the torque that proximal finger joints 122 and medial finger joints 120 can exert; particularly in a flexural direction (e.g. when closing the hand into a fist). Using the smallest number of tendons is preferred when decreasing mechanical complexity, at the cost of increasing the complexity of the control system. However, it will be appreciated that by arranging N1 tendon various further configurations, not depicted, are possible.

Figures 7A to C illustrate schematically the actuator system for actuating movement in the robotic hand actuator 10. The actuator system has a compact design whilst still being capable of exerting accurate force and position control with inexpensive motors and sensors.

Output force is unidirectional and exerted by winding a string onto a capstan.

Fig 7A illustrates the actuator system 1000 which comprises of motor 1001 attached to a gearbox 1002. Onto the output shaft of the gearbox 1002 is mounted a capstan 1003 onto which the string 1004 winds.

As the string 1004 moves (winding or un-winding onto the capstan 1003) its position may be accurately sensed through a rotation sensor on the output roller 1005. The string's 1004 position is similarly sensed accurately by sensing the rotation of the capstan 1003, onto which sensor 1006 is mounted.

Using the signal from either sensor 1006, alone or jointly, provides accurate position information for controlling the actuator. It will be appreciated that both signals may be used, as a double check or otherwise.

An elastic element, in this case spring 1007, may be positioned alongside the strings 1004 path in between the capstan sensor and the output sensor. Advantageously, the addition of the spring 1007 allows for energy to be stored onto the spring 1007 when an external load applies force to the string 1004 and for the magnitude of an external force applied onto the string 1004 to be calculated, via geometry and using Hooke's law in the case of a standard linear spring.

When an external force is exerted on the string 1004 and forces the spring 1007 to deform, a differential arises between the positional reading from the capstan's sensor and the output sensor. This occurs due to a deflection of roller 1008, which causes the string's 1004 path to become straighter and therefore change the overall length of the path of the string 1004 as measured between the capstan 1003 and the output roller 1005.

The spring 1007 therefore acts as an elastic element in between the output shaft of the gearbox 1002 and the load on the string 1004. However, a much simpler method, and one suitable for actuating a unidirectional string actuator, as well as sensing both force and position is created. Rotary sensors in general provide superior sensing accuracy relative to cost and therefore the invention benefits from lower manufacturing costs.

Additionally, a force actuator based on unidirectional string actuation for linear action benefits from lower weight and manufacturing costs as compared to linear motion systems which must make use of linear screws or rack and pinion mechanisms.

Those skilled in the art will appreciate that while the foregoing has described what is considered to be the best mode and, where appropriate, other modes of performing the invention, the invention should not be limited to the specific configurations and methods disclosed in this description of the preferred embodiment. Those skilled in the art will recognize that the invention has a broad range of applications in many different types of robotics and that the embodiments may take a wide range of modifications without departing from the inventive concept as defined in the appended claims.

Claims

CLAIMS1. A robotic end effector comprising: a frame portion defining a base Cartesian coordinate reference frame; three finger members and a thumb member, wherein the finger members comprise distal, medial and proximal portions; wherein the thumb member comprises distal and proximal portions; and wherein each member is attached to the frame portion by its proximal portion.
2. A finger member for use in the robotic end effector of claim 1, wherein the finger member comprises: a one-degree-of-rotation freedom joint coupling between one end of the distal portion and one end of the medial portion; a one-degree-of-rotation freedom joint coupling between the other end of the medial portion and one end of the proximal portion; and a two-degree-of-rotation freedom joint coupling the other end of the proximal portion to said frame portion with one of the rotational axes of the rotary part of said joint offset angularly with the reference to said base coordinate reference frame.
3. A thumb member for use in the robotic end effector of claim 1 and/or along with the finger member of claim 2, wherein the thumb member comprises: a one-degree-of-rotation freedom joint coupling between one end of the distal portion and one end of the proximal portion; a one-degree-of-rotation freedom joint coupling between the other end of the proximal portion and the frame portion; and wherein the frame portion comprises a first one-degree-of-rotation freedom joint coupling and a second one-degree of freedom joint, wherein the first and second one-degree-of-rotation freedom joints are offset angularly with reference to said base coordinate reference frame.
4. The member of claims 2 or 3, wherein said two-degree-of-rotation freedom joint comprises two single-degree-of-rotation freedom portions, the first portion having its rotational axis offset angularly with reference to the base coordinate reference frame, and the other portion having its rotational axis orthogonal to the rotation axis of said first portion.
5. The member of any preceding claim, wherein N is the number of joints of a digit, and wherein each of the digits is actuated by N+1 arrangement of tendons.
6. The member of claim 5, wherein the N+1 arrangement actuates each digit by providing N+1 tendons acting on N joints such that actuation of a subset of tendons moves some joints in one direction and others in the opposite direction.
7. An actuator system for use in the robotic end effector of claim 1 and/or along with the member of any of claims 2 to 6, wherein the actuator comprises: a motor drive comprising a capstan; a string rotatably attachable to the capstan, the string configured to wind onto and off of the capstan in use; and a rotary position sensor for sensing the position of the capstan.
8. The actuator system of claim 7, wherein the rotary position sensor is provided on an output roller through which the string exits the actuator system.
9. The actuator system of claim 8, wherein the actuator system further comprises a roller between the capstan and the output roller.
10. The actuator system of any of claims 8 to 9, further comprising an elastic element arranged such that external forces on the string causes the elastic element to move and thus altering the total path length of the string between the capstan and the output roller.
11. A robotic hand comprising the end effector, finger member, thumb member and/or actuator of any proceeding claim.
12. An upper arm assembly comprising the robotic hand of claim 11.
13. An artificial hand, finger member, thumb member and/or actuator substantially as hereinbefore described with reference to the accompanying drawings.