Robot hand with humanoid fingers

A robotic hand with finger assemblies to better simulate human hand form factors and gestures. For each finger assembly, the robotic hand includes a finger drive assembly that is operable to selectively apply tension to four elongated and flexible tension elements (e.g., steel cable). Each of the finger assemblies includes a set of links or link members that are actuated or moved by the selective tensioning/movement of the tension elements by the drive assembly. The links are interconnected with pivotal joints such that they have three degrees-of-freedom, and the finger assembly includes a set of pulleys that are supported on the links and that are arranged to provide support and to guide the tension elements through the finger assembly. The tension elements preferably extend only partially about any one of the pulleys, whereby the finger assembly utilizes “n+1” actuation with non-helical wrapping of the tension elements.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to robotics and, more particularly, to a robot hand that includes fingers designed to fit within a human form factor and to move and behave more like fingers of a human hand.

2. Relevant Background

In recent years, there has been an increasing demand for robots that more closely simulate or mimic humans. For example, animatronic figures are robotic systems that are designed to duplicate characters as closely possible, and many of these characters are human or human-like characters. Robots used to provide animatronic figures may be displayed as part of rides, attractions, theater shows, retail displays, and other entertainment venues. In these settings, there is desire for the animatronic figures or robots to mimic the character, such as a character from a movie or animated film, in terms of their shape, dexterity, and ability to produce motions and forces (e.g., dynamics of a mimicked character). In addition, it may be useful for a robot to be designed to reproduce physical abilities such as walking and manipulating objects such as with fingers of a robotic hand. Many characters are made to have human characteristics or features such as hands, fingers, and the like, even when they are not a human or human-like, e.g., ants, birds, monsters, and so on with human-like hands and fingers.

Increasingly, robot designers and manufacturers are being requested to design robotic systems with human-like or anthropomorphized features and capabilities to be used in non-entertainment applications. These uses may include a robot designed for patient care in a hospital or physical therapy setting, home care for a patient, or a robot for performing household tasks. In these applications, robotic systems are expected to interact with humans in a useful manner but also in an appealing manner. Robots are generally found more appealing when they look and behave in a manner familiar to humans, and it has generally been accepted that an effective human-robot interaction is provided by a human-like robotic system or a robot with human characteristics or features such as hands and fingers.

In entertainment and other applications, a challenging and important aspect is the design of the hands of the robot. For example, the hands of a robotic character, even if the character does not have human hands, are typically designed in an attempt to mimic the form, dexterity, dynamics, and functionality of human hands. Unfortunately, none of the existing robotic hand designs have successfully met all the design challenges in presenting a robotic human hand. There are numerous end-effector designs in existence, but these are generally variations of simplistic two-fingered grippers or jaws with a single degree-of-freedom that are used to grasp or clamp objects.

Several robotic “hands” have been produced, but some of these designs only bear a greater resemblance to human hands than the two-clawed gripper but typically are lacking in terms of dexterity and form. For example, a human finger has four degrees-of-freedom (DOF) (although only 3 DOF are typically controlled independently). However, robotic hands typically have much fewer DOF with some hands only providing one DOF per band, which significantly limits their dexterity and motion capability. Some will provide one DOF per finger such that each finger can be articulated independently. However, the finger motion may be a simplistic motion such as curling upon itself with no side-to-side motion of each finger or independent movement of parts or digits of the fingers as found in a human hand.

Existing robot hands that provide increased numbers of DOF often are very complex or fail to match a human form factor. For example, one existing hand design provides 24 DOF total for the hand with relatively good finger form factor compliance, but this hand design requires the number of cables (or “tendons”) and actuators to be up to twice the number of DOF or forty-eight in this case. This results in a large form factor at the wrist and forearm that is less human in appearance. An additional problem with this hand design is that the cables or tendons used to actuate the finger movements run over fixed, un-lubricated metal or plastic runners creating significant friction and wear issues.

Another hand provides two digits for each “finger” and utilizes a pulley and actuator mechanism that does not lend itself to being packaged with human form factor (e.g., thin elongated fingers, a relatively small wrist, and thin palm). Particularly, in this hand design, an “n+1” arrangement is used for the drive cables or tendons, which reduces the number of cables required, but the pulley arrangement is such that the cables each wrap about their supporting pulleys by more than 360 degrees, which requires that the pulleys be thick (e.g., generally twice the cable thickness) making it difficult to place in a finger form factor packaging. Also, the cables create additional friction and wear as they cross over one another and rub upon each other during operation of the hand. Further, this robot hand requires four motor drives per finger, which increases costs, complexity, form factor, and maintenance.

Yet other robotic hands may be designed to use a thicker cable and actuate the fingers with a push/pull arrangement. Motors are proximally mounted to the wrist that is used to support the hand. To transmit power through the wrist, flexible drive shafts are used, with rotary motion as opposed to linear motion being transmitted through the wrist. This rotary motion is converted to linear motion by means of lead screws mounted in the palm of the hand. This provides the advantage of passing a number of drive shafts equal to the number of DOF of the hand (e.g., twelve in one example of this design). However, one disadvantage of the rotary drive hand is that twelve lead screws must be packaged within the palm of the hand, resulting in a large (i.e., greater than human-sized) palm. Also, the use of a thick cable in a push/pull arrangement to actuate the finger DOF limits the amount of force that may be applied in the “push” direction, which may limit the uses of this robotic hand design.

Hence, there remains a need for hand design for a robot or robotic system that meets the challenges associated with a human form factor while achieving the functionality expected of a human hand. It is preferable that such a hand design would include fingers with a similar number of digits as found in a human hand and with dexterity and movement that is more human like (e.g., fingers that move with a similar number of DOF). It is also preferable that the robot hand design includes a relatively small number of components and addresses wear and maintenance issues associated with use of actuating cables (or tendons).

SUMMARY OF THE INVENTION

The present invention addresses the above problems by providing a design for a robot hand with fingers with three digits and human-like form and movement to provide a number of advantages over prior hand and/or finger designs. Embodiments of the robot hands described herein address factors including the ability to fit a human form factor, a desirable DOF (e.g., three DOF per finger provided on or supported within the robot hand), method of actuation, the ability to precisely control the joints, the ability to apply sufficient forces to grasp objects, and longevity (e.g., reduce tendon or cable friction and other wear that may otherwise cause early failure or force added maintenance).

As will become clear, some embodiments of the described robot hands use the minimum practical number of tension elements (e.g., cables, tendons, or the like) to actuate three DOF fingers (e.g., n+1 actuation using four cables or tension elements). This is a significant advantage when routing the cable or tendons through a two-jointed, flexible wrist, which provides a very constrained space when limited to a form factor of a human wrist. The robot hands of some embodiments may use a reduced or even a minimum number of motors to actuate the fingers. Motors have associated complexity, cost, and packaging constraints, and, hence, reducing the number of actuators or drive motors leads to a more desirable hand design. Additionally, hand embodiments use a pulley design that allows the finger design to fit within a human form factor. Many prior hand designs were not forced to comply with a human form factor constraint, but such a constraint is called for in many animatronic and non-entertainment robot applications. Further, the use of pulleys in the fingers themselves (e.g., pulleys supported upon finger digits or segments of each finger assembly of a hand), instead of sliding cables over or through un-lubricated elements, significantly reduces friction and decreases wear (i.e., increases longevity). Hand embodiments may use a passive tendon tension maintenance system to provide pre-tensioning of the finger drive or actuating cables/tendons. This is in contrast to an active approach that requires the use of additional motors along with their associated hardware, electronic and software complexity, and added cost. Yet further, embodiments of the robot hand described herein typically use fixed kinematic relationships between the actuator motion and finger joint motion.

More particularly, a robotic hand is provided with at least one finger assembly and, more typically, five finger assemblies may be included to better simulate a human hand. For each finger assembly, the robotic hand includes a finger drive assembly that is operable to selectively apply tension to four elongated and flexible tension elements (e.g., steel cable or the like). Each of the finger assemblies includes a set of links or link members that are actuated or moved by the selective tensioning/movement of the tension elements by the drive assembly. The links are interconnected with pivotal joints such that they have 3 DOF, and the finger assembly includes a set of pulleys that are supported on the links and that are arranged to provide support and to guide the tension elements through the finger assembly. The tension elements preferably extend only partially about any one of the pulleys (e.g., only a partial wrapping about each contacted pulley), whereby the finger assembly utilizes “n+1” actuation (where “n” is the DOF and the value is the number of tension elements) with non-helical wrapping of the tension elements.

In some cases, the pulleys may be about half the height of pulleys used in devices using helical wrapping. In helical wrapping systems, a pulley without any grooves or one wide, flat groove may be used so that a helix can form while in other applications a single, helically machined groove is used. In either case, the use of helical wrapping requires additional room for the cable wrap to “walk” across the face of the pulley. In contrast within some embodiments described herein, each of the cables or tension elements may wrap around less than half of the circumference of each contacted pulley, with some contacting on about a quarter wrap or 90 degrees. The set of links may include first, second, and third digits or digit links (e.g., to simulate the three digits or segments of a human finger). In such cases, the third digit link may be pivotally mounted to the second digit link, which in turn is pivotally connected to the first digit link. The first and second digit links may be independently actuated or operable by the drive assembly, with a pair of the tension elements or cables terminating on each of these two links. An additional coupler link may be included in the finger assembly to interconnect the third digit link to the second digit link such that the third digit link is actuated by movement of the second digit link (e.g., the third digit link may be passively actuated to behave as a follower or slave link to the second digit link).

The hand may also include a palm element or plate, a base link member, and a first digit mounting link member. The base link member is rigidly attached to the palm plate to support the finger assembly within the hand. The first digit mounting link member is pivotally mounted to the base link member for pivoting about a first axis (such as with a range of motion of about 40 degrees or 20 degrees or less in each rotation direction) while the first digit link is pivotally coupled to the first digit mounting link member for pivoting about a second axis that is transverse or even orthogonal to the first axis (such as with a range of less than about 15 degrees in a counterclockwise direction away from the palm plate and in the range of about 75 to 100 degrees in a clockwise direction toward the palm plate). In this manner, the range of motion of the first digit of the finger assembly is similar to a human finger with a side-to-side movement (e.g., plus or minus 13 degrees or the like relative to a vertical plane passing through the first axis) and with a small backward bending (such as less that about 15 degrees relative to a horizontal plane passing through second axis) but a large forward bending movement (such as more than 90 degrees). The third digit link is actuated by the second digit link such that it and the second digit link straighten with the backward bending similar to a human finger and it and the second digit link curl further inward with the forward bending or curling of the first digit link (such as for forming a fist or grasping an object). In some embodiments, the drive assembly is adapted to provide a passive tension maintenance system to maintain a desired tension on the four tension elements, and this and other features allow three actuators (e.g., drive motors) to actuate or drive the four tension elements rather than using at least four actuators.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Briefly, embodiments of the present invention are directed to robotic hand systems that address the longstanding demand to have improved performance with enhanced simulation of a human hand and human fingers. Prior robotic hands either had less joints and digits/segments than found in a human finger (i.e., three segments or digits) or were sized and/or designed such that the fingers, palm, wrist, or other portions would not fit or suit within human form factors. The robotic hand systems described herein provide a hand or hand assembly with fifteen degrees of freedom (DOF) (e.g., three DOF per finger) such that the hand and each finger can create a wide variety of gestures while still fitting within a human form factor. In each finger or finger assembly, a combination of tension elements (e.g., tendons or drive cables that may take the form of flexible steel cables or wires/wire ropes), linkages, and pulleys to actuate four joints per finger, which provides three DOF per finger, while remaining within human size constraints. The actuation uses “n+1” tension elements or tendons such that four tension elements are used to actuate three DOF in each finger. In this manner, each finger takes the form factor of a human finger in part due to the unique pulley and tension element/drive arrangement, and each finger is independently actuated with human-like dexterity, gestures, and ranges of movement of the three digits or segments of the fingers of the robotic hand.

FIG. 1illustrates a robotic hand system100in accordance with an embodiment of the invention shown in prototype arrangement (rather than with its motors or drivers sized and positioned into a human form factor arm, shoulder, or body). As shown, the system100includes a robotic hand or robotic hand assembly110, a wrist130, a forearm140, and a set of finger drive assemblies or mechanisms160. The drive assemblies (or motor drives)160are mounted on a support base or plate150, but, in practice, the drive assemblies160may be mounted on the forearm140, on an upper arm (not shown), or in/on the torso (not shown) of the robotic system100. Although not shown, a number of drive cables or tendons (also called tension elements) would be run from the drive assemblies160through the forearm140and wrist130for connection to portions of the hand assembly110(e.g., to independently actuate or drive the fingers of the hand110).

Components of the system100are described in more detail below, but, briefly, it can be seen that the hand assembly110, which is shown in more detail inFIG. 2, includes five fingers or finger assemblies112,114,116,118,120. The finger assemblies112,114,116,118,120are rigidly affixed to a plate124, which in turn is mounted to the wrist130to move with the wrist130and forearm140. The finger assemblies112,114,116,118,120are affixed at a base or initial link member (e.g., link l0in the following figures) with the next link member (e.g., link l1in the following figures) attached to the base or initial link member. The plate124may be configured to simulate a human palm such as with one of the finger assemblies120(e.g., the thumb) mounted out of plane relative to the other four finger assemblies112,114,116,118, which may be arranged in a semi-circle or other pattern (e.g., with their base link members not arranged perfectly parallel, for example) to, again, better match the arrangement of a human hand and facilitate a desired range of side-to-side and other motion of the finger assemblies112,114,116,118, and120. One drive assembly160is provided to independently (which may include concurrent operation, too) operate or actuate a paired or corresponding one of the fingers112,114,116,118, or120. Hence, in this 5-finger system100, five drive assemblies160are provided to drive the five fingers112,114,116,118,120of the hand assembly110.

The following provides a description of the design of a single one of the finger assemblies112,114,116,118, or120along with its associated drive assembly or motor drive mechanism160, and such teaching may be applied to any of the drive/finger pairings shown in the system100ofFIGS. 1 and 2to provide a more human-like robotic hand system100. Additionally, the system100would include one or more power supplies for powering the drive motors of assemblies160, and the assemblies160would be operated by one or more controllers to selectively operate and actuate the fingers112,114,116,118,120as well as the wrist130and other portions of the system100. Such power and control devices may take many forms to practice the invention, are well known by those skilled in the art, and are not considered limiting to the invention. The number of drive motors (e.g., three per finger), pre-tensioning of the tendons/drive cables, and other features are considered more significant to the present invention and are discussed in detail below.

FIG. 3illustrates a finger assembly300such as may be used in a robotic hand of an embodiment of the invention (such as the hand110of system100ofFIGS. 1 and 2). Generally, the finger assembly300is made up of a set of six links (labeled l0to l6in the figures) and eight shafts (or pivot pins/axles labels s0to s8in the figures often with a pivot axis drawn through or along the longitudinal axis of such shafts). In addition, there are nine pulleys (labeled p1to p9in the figures) that are mounted in the links or link members and are used to support tendons or tension elements (e.g., steel drive cables or the like), which are used to actuate the finger300during use including movement of the three digits with 3 DOF.

As shown inFIG. 3, the finger assembly300includes a base or initial link member (with link being used interchangeably with link member)310that would be mounted via mounting holes312, which may take the form of threaded holes, press fit receptacles, or the like, to a hand plate. The base link (i.e., link l0)310includes four cable guide channels or passageways314, and the assembly300is shown schematically to be actuated or driven with four cables321,322,323,324(shown as c1to c4in figures, too) that would extend through the passageways314to the next link member330(link l1) and its channels or passageways334. The link member330is pivotally mounted to the base link310via shaft or pin332that extends through hole333in link member330(and four pulleys as discussed with reference toFIG. 4). The link member330(link l1) and its pivotal mounting or joint with base link310simulates, in part, functionality of the knuckle of a human hand with side-to-side pivoting or motion about shaft332(or Axis1).

The finger assembly300further includes an elongated link member (link l2)340mimicking the first digit of a human finger. The link member340is pivotally mounted to the link member330at a first end via shaft336that extends through the link member340and a pair of holes337in the body of link member330, which is arranged to extend about both sides of the end of link member340. The link member (link l2)340pivots when actuated by tension elements about shaft336(Axis2). The link member340supports a set of pulleys344that pivot on the body of link member340about mounting/supporting shafts348(e.g., the set of pulleys344may include four pulleys as shown in the exploded view ofFIG. 4for guiding and supporting the tensioning elements used to actuate the finger assembly300).

At a second end of the link member340, the finger assembly300includes another link member (link l3)350that mimics the second digit of the human finger. The link member350is pivotally mounted to the link member340via pin or shaft356such that it may pivot about Axis3. Hence, when actuated by cables or tension elements321-324, the finger assembly300can produce independent movement of the digit/link member350relative to the digit/link member340about the shaft356(Axis3) (e.g., like a human finger the second digit may move with the first digit held stationary or as this digit is also moving at the knuckle). One or more pulleys354may be provided on or as part of link member350, withFIG. 4showing a single pulley (i.e., p9) formed as a part of the body of link member350. The finger assembly300further includes another link member370that represents the third digit of a human finger and is pivotally mounted to the second digit or link member350via pin364. The pivoting about Axis4or shaft364is tied to movement of link member350via link member360(link l5), which is pivotally attached to both link members340and370.

To better understand the design and operation of a finger assembly (such as assembled finger300), it may be useful to show one useful arrangement for a finger for use with a robotic hand assembly in an exploded manner.FIG. 4illustrates an exploded view of a single finger or finger assembly400as may be used in a hand assembly in accordance with the present invention (and used for finger300although other pulley arrangements, link member configuration, and design alterations may be used to provide the functionality of finger assembly300). The base link (link member l0)410of the finger400would be mounted to a palm plate (such as plate124ofFIGS. 1 and 2) with mounting holes418. The next link (link member l1)420may take the form of a double clevis as shown. This allows it to be pivotally linked via holes421and Axis1shaft (shaft or pin s1)416to the base link410at hole/passageway417while also being pivotally linked via holes422and Axis2shaft (shaft or pin s2)423to link or first digit (link member l2)430.

Link (link member l3)460may be constructed as a unitary body or in two halves as shown, and link460represents a second digit of a human finger. Link460is pivotally mounted to the first digit link430via the Axis3shaft (shaft or pin s5)452that extends through holes450and462in links430,460, respectively. The finger400further includes a link480(link member l4) that provides a third digit of the finger400similar to a human finger. The link480is pivotally mounted to Axis4shaft (shaft or pin s6)474that extends through hole488in third digit link480and hole472in the halves of second digit link460. There is an additional link (link member l5)468that is used to couple the motion of second digit link460and third digit link480. The link468is pivotally mounted via shafts458,482(shafts or pins s7and s8) that extend into holes454and484in lines430and480. The link468is also pivotally attached at its proximal end with pin or shaft458to the first digit link430via hole454(with its distal end attached to third digit link480via shaft482). As a result of this mounting arrangement, movement of the third digit link480is coupled to movement or motion of the second digit link460(e.g., the link480curls inward with the link460and straightens with the link460but not independent of this second digit link).

As discussed above, the fingers formed in accordance with embodiments of the invention are actuated with a set of pulleys and tension elements arranged to achieve a form factor that allows the pulleys and tension elements to be housed or positioned within the human form factor of a finger. The finger400, for example, typically would be actuated using tendons or cables that are tensioned and moved by a drive assembly (such as assembly160shown inFIG. 16). The cables are not shown inFIG. 4but would extend through the holes419in base link or mounting block410and over the pulleys shown as part of finger400for termination or attachment on the links (as will be discussed for each of the four cables with reference to the following figures). In the embodiment, steel cables (e.g., SAVA Industries2024SN or the like) are used for tension elements. The steel cables operate over pulleys in the finger400and terminate in either first digit link430or second digit link460.

With reference toFIG. 4, pulleys411,412,413, and414(pulleys p1to p4) are each single-groove idler pulleys that ride on Axis1shaft416(shaft or pin s1), which extends through base link410via hole or passageway417. Pulleys436and434(pulleys p5and p7) are supported on and rotate about Axis2shaft423(shaft or pin s2), which extends through a hole432in a first/proximal end of first digit link430. Pulley436is a double-groove idler pulley while pulley434is a single-groove idler pulley. Pulley438(pulley p6) is also a double-groove idler pulley, which is supported on and rotates about shaft440(shaft or pin s3) that extends through hole441in first digit link430proximate to pulley436. Pulley442(pulley p8) is a double-groove idler pulley that is supported by and rotates about idler pulley shaft448(shaft or pin s4) that extends through a hole446in a second/distal end of first digit link430. In this design, pulley p9is machined into a half of the body of second digit link460(but it could also be designed as a separate idler pulley in which case it may be supported and rotate about Axis3shaft452(shaft s5)). Retaining or guide plates444and470may be included to retain pulleys and/or cable on the first and second digit links430,460.

The robotic finger embodiments described herein are generally operated via four tendons or cables (e.g., tensioning elements that may take the form of steel cables or the like) in an “n+1” arrangement. That is, four tendons that remain in tension are used to actuate each finger's 3 degrees-of-freedom (DOF).FIGS. 5 to 7present partial views of a robotic finger assembly500illustrating the pulley set and the second digit link to explain exemplary tendon or cable routing and/or termination or attachment within the robotic fingers of the invention. The four cables or tendons are labeled c1to c4, and these may be the cables shown inFIG. 3used to actuate the finger300. As shown, the pulley set for the finger assembly500(which may be finger300or400for example) includes nine pulley elements514,518,520,526,530,540,554with some being single and some being double track pulleys to provide pulleys p1to p9as shown (e.g., pulley element or pulleys514represents two individual pulleys as does element518while elements520,526, and540are double-groove pulleys).

FIG. 5shows the cable or tendon510(or cable c1) and its routing in the pulley assembly of finger500as well as its termination point558on the body of second digit link550(link l3). From the termination point558in link550, the cable or tendon510passes around pulley554and makes an “S” shape to the opposite side of pulley540contacting one of the two tracks of this pulley540. It continues to pulley526(again, contacting one of its tracks) and then wraps in another “S” shape around to the opposite side of pulley520against one of its two tracks. It continues to pulley p2portion of pulley element514where it makes a slight bend towards the inside of the finger in order to maintain contact with pulley514. Note, the cable510uses the inside groove or track of pulleys520,526, and540. Also, significantly, the cable routing shown inFIG. 5does not require or create any helixes (a full wrap around a pulley) but, instead, only calls for the cable510to wrap part way (such as less than 180 degrees of contact and, often, less than about 90 degrees of contact between the pulley and the tendon510). This increases the number of pulleys required in the set of pulleys of finger500, but it reduces the amount of friction while allowing the finger to conform to a human finger form factor (e.g., facilitates miniaturization).

FIG. 6illustrates the finger assembly500with the tendon610(cable c2) routed through the pulley set. The tendon610is shown to terminate in second digit link550at termination or mounting point616on the opposite side of pulley554as did the tendon510(cable c1). It wraps partially around pulley554and makes an “S” shape to the opposite side of pulley540. The tendon610continues on its routing to pulley526and makes another “S” shape onto pulley520. It continues to pulleys518around which it makes a slight bend in order to maintain contact with pulley p3. As shown, the tendon610uses the outside grooves of pulleys520,526, and540, and the tendon610is not routed completely around any of the pulleys of finger assembly500(i.e., no helixes are formed) but only contacts a portion of each pulleys contact track or groove. Note, pulleys p1, p2, p3, and p4are individual pulleys that can rotate independently (and not four different grooves in two pulleys).

FIG. 7illustrates the finger assembly500with tendons720and740(cables c3and c4) routed through the pulley set. Tendon720terminates at726in the first digit link l2(not shown inFIG. 7for ease of illustrating cable routing but it may be link430of finger assembly400or link340of assembly300). The tendon720extends from link l2over a portion of pulley530. It continues onto pulley p4portion of pulley element518, where it makes a slight wrap towards the inside of the finger500in order to maintain contact with pulley element518. Tendon740(cable c4) also terminates on first digit link l2at746, but it continues onto the opposite side of pulley530as tendon720. Tendon740then is routed to pulley p1, where it makes a slight wrap or bend towards the inside of the finger500to maintain contact with pulley p1. Again, the cables are not wrapped in a helix shape about any of the pulleys of finger500, and none of the cables rub against themselves or each other, which limits friction and increases longevity of the finger500.

FIG. 8illustrates an orthogonal view of the finger assembly300ofFIG. 3(which may be designed with the arrangement of pulleys and the cable routing shown inFIGS. 3 and 4, respectively). The assembly300is shown to include the cables322,323extending into holes or passageways314in base link member310to contact pulleys in link member330(link l1) and then pulleys in first digit link340(i.e., pulleys p5and p7supported on link l2). As can be seen, the cable guide holes or passageways314in block or base link310are angled outward from the face or side of the link body310where the cables322,323are received so as to accommodate the slight wrap about pulleys p1, p2, p3, and p4made by tendons c1to c4(with only cables322,323being visible inFIG. 8). The angling assists in maintaining the desired contact between a portion of each of the pulleys p1to p4and cables c1to c4.

The fingers of embodiments in accordance with the invention, such as those adapted as shown with finger assembly300, may be designed to provide a range of motion of each of the finger digits/segments that is similar to that found or obtained with a human finger.FIGS. 9-14show the finger assembly300in a variety of positions or modes of operation that are achievable due to the arrangement of the joints and by actuation through movement by the drive assemblies of tension elements or cables over the included pulleys. Specifically,FIGS. 9 and 10illustrate the side-to-side range of motion provided for the finger assembly300as is found in the human finger at the knuckle. For example,FIG. 9shows the finger300in a first side position (left-most position) whileFIG. 10shows the finger300in a second side position (right-most position). These figures show the link330(link l1) as it fully pivots side-to-side on pin or shaft332or rotating about Axis1of the finger300.

FIG. 9shows the rotation to be at a maximum angle, θ, which may be less than about 20 degrees such as about 13 degrees as shown (negative or positive rotation depending on the orientation with the rotation appearing negative or counterclockwise inFIG. 9).FIG. 10shows the rotation to be at a maximum angle, α, in the other or opposite direction (e.g., clockwise or a positive angle of rotation relative to an orthogonal plane extending upward through Axis1). This may be about the same magnitude as the rotation in the other direction for symmetric side-to-side movement or it may differ some amount. In one example, the rotation angle, α, is also less than about 20 degrees or about 13 degrees as shown.FIGS. 9 and 10show the range of motion of link l1relative to link l0about Axis1to be about plus or minus 13 degrees. At the extremes of motion, contact may be made between the flats on link l1and link l0(e.g., a portion of the body of link330may abut or contact a proximate surface of block or base link310to act as a limit or stop to rotation of the link330about pin or shaft332).

FIGS. 11 and 12illustrate the finger assembly300in first and second vertical positions (e.g., positions relative to a horizontal plane passing through pin336in link330), withFIG. 11showing the finger300in bent back position (the first digit link340bent away from the palm plate) andFIG. 12showing the finger in a fully bent forward position (the first digit link340bent inward toward the palm plate). The fingers of the human hand do not extend very far backward or away from the palm, and, hence, the finger300is shown inFIG. 11to have a first vertical position associated with maximum backward bending with a relatively small angle of rotation, β, such as less than about 20 degrees (counterclockwise or negative rotation relative to pin336) and, in one example, about 13 degrees. Also, in this position, the digits of the finger300are generally straight or in a line with links340,350, and370generally aligned or with their longitudinal axes being planar but in some cases, second digit link350and third digit link370may arch backward further than first digit link340similar to the human finger. Travel to this vertical position may be limited with a stop on link330or link340or, in some cases, travel in this direction is limited by operation of the tension elements or cables (or by operation of drive motors).

In contrast, the human fingers can be curled inward toward the palm to form a fist or to grasp objects. With this in mind and as shown inFIG. 12, the finger assembly300is designed to allow the first digit link340(or link l2) to rotate through a relatively large angle of rotation, τ, about pin or shaft336(Axis2) such as a clockwise rotation to the second vertical position shown of at least about 75 degrees and more typically to at least about 90 degrees (with 93 degrees shown). When considered together,FIGS. 11 and 12show the range of motion of link l2relative to link l1about Axis2, and this range may be about negative 13 degrees (counterclockwise rotation) to about positive 93 degrees (clockwise rotation) or more.

As discussed above, the second digit link350(link l3) may be independently actuated relative to the first digit link340(link l2).FIG. 13shows the finger assembly300in a closed or fully curled inward position with the second digit link350rotated about pin356or Axis3to a positive rotation (clockwise) angle, α, of at least about 90 degrees and more typically at least about 100 degrees. In other words, the second digit link350has a range of motion about Axis3or shaft356of about 0 to 100 degrees.

In some embodiments, the third digit link370(link l4) is coupled to the second digit link340(link l3) as a slave linkage. It will be seen inFIG. 13that the third digit link370(link l4) is rotated relative to or with link340(link l3).FIG. 14illustrates the finger assembly300with the second digit link350or l3as a line to better show link360(link l5). This rotation is a passively coupled rotation and is a function of the rotation of the second digit link350(link l3) to the first digit link340(link l2). As will be understood fromFIG. 14, link360(link l5) pivots about third digit link370(link l4) at shaft or pin1412(shaft s8) and about first digit link340(link l2) at shaft1410(shaft s7). The distances between shaft1410(shaft s7) and Axis3on link340may be set to be about approximately 1.3 times less than the distance between shaft1412(shaft s8) and Axis4on link370. Note, this type of coupling may also be achieved using pulleys and cables.

The motion of each of the finger joints is related to the motion of each tendon. If each joint position is labeled q1, q2, q3corresponding to relative link motions about Axes1,2, and3, respectively. The velocities of each joint are given by qi, where the units would be radians/second. The velocities of each cable are given by ci, where the units would be meters/second. If the radius of each pulley is given in meters, then we have the following relationship:

(c.⁢1c.⁢2c.⁢3c.⁢4)=[r⁢⁢1-r⁢⁢3-r⁢⁢4r⁢⁢1r⁢⁢3r⁢⁢4·-r⁢⁢1r⁢⁢20-r⁢⁢1-r⁢⁢20]⁢(q.⁢1q.⁢2q.⁢3)
Note, that the motions of the tendons are not independent. That is, the three joint velocities define the velocities of all four tendons if they are to remain in tension. Stated otherwise, if any three of the four tendon velocities is commanded, the fourth tendon velocity is defined by the above equation. If velocities were to excessively vary from the relationships defined by the equation, the tendon would either stretch or lose tension.

As noted above, the motion of the tendons or cables is not independent. One way to operate the finger tendons would be to connect each tendon to an independent linear actuator. In this case, the motion of the four actuators would need to be coordinated to maintain the relation in the above equation and simultaneously maintain cable tension. Another approach is to use a mechanism to enforce this relation so that only three actuators or motors are required to drive each finger of the robotic hands described herein. Such a mechanism1500, which may be thought of as a passive tension maintenance mechanism, is shown schematically inFIG. 15. Here, tendons c1and c2form a loop that is supported by pulley p10. Tendons c3and c4are made to form a loop supported by pulley p11. The desired relationship is then enforced via a mechanism (not shown) that forces the axis of the pulleys p10and p11to travel parallel to the y-axis inFIG. 15. The velocities of each pulley along this axis, v1and v2, are equal and opposite (e.g., v1=−v2).

In this case, the kinematic relationship of the previous joint to tendon mapping equation will be satisfied, and only three of the four tendons need to be actuated via controlled actuators or drive motors in order to drive the finger. In the initial positions of pulleys p10and p11are set such that there is an initial tension in the cable, then that tension can be maintained passively. If the tendons c1, c3, and c4are driven using actuators m1, m2, and m3, where the direction of positive motion is the same, then the following relationship exists (with positions having units of meters and indicated without dots over the letters/symbols and velocities ({dot over (m)} i and {dot over (q)}, i) having units of meters/second with dots shown over the letters/symbols):

FIG. 16illustrates the finger drive assembly or mechanism160, and this mechanism160is adapted to implement the passive tension maintenance mechanism described above that allows three actuators (or drive motors in this example) to be used to operate or drive four tension elements or tendons/cables. The system or assembly160includes three actuators1617that may be provided with brushless DC motors or the like that are held in motor housing1619, which in turn may be affixed to a base plate1620. Each motor1617in some applications may have an encoder1618to record or determine rotary position for accurate control of a linked finger assembly. The output shaft of each motor1617is coupled to a lead screw1605via a flexible coupling1611, which may be adapted to accommodate misalignment between the drive shaft and the lead screw1605. The lead screw1605is supported by a front bearing1603and a rear bearing1610, which supports thrust loads on the lead screw1605.

The lead screw1605, which is supported or retained by collar1609, drives a nut1607, which is mounted in a block1606. This block1606is prevented from rotation by way of a “tongue” that rides in a grooved plate1604. In one embodiment, the grooved plate1604is made from acetal, which provides a low-friction sliding surface. Each block1606is mounted with a clamp plate1608that is used to secure a cable tendon through which linear motion is transmitted. The passive tension maintenance mechanism is provided with two pulleys1613and1614that are mounted to a pivoting arm1621via shafts1615and1616. The pivoting arm1621pivots on a link1622, which is constrained to slide in a slot in motor mount1619. The motion of link1622is constrained by a tensioning screw1623that is captured in a hole in motor mounting block1619. The pivoting action of arm1621very closely approximates the constraint in the equation v1=−v2over the range of motion of the finger.

FIG. 17shows the finger driving mechanism160with the tendons or cables1710,1720,1730,1740(or cables c1to c4) routed through the passive tension maintenance mechanism. The cables1710,1720,1730,1740are passed through holes in the bearing support block1601to pulleys1613and1614. By tightening the tensioning screw1623, the finger tendons1710,1720,1730,1740may be tensioned. Additional adjustments1602on bearing support block1601may be used to fine tune the position of the finger joints relative to the lead screw nuts1607.

In the prior description, it was generally assumed that the length of the tendons or cables between the finger assembly and the finger drive assembly remains constant. However, it is expected that the drive assembly and the finger assemblies may be mounted on opposite sides of a wrist joint and the length of the cables may not be constant. To support such an implementation, flexible tendon conduits may be used to maintain the constant length constraint. For example,FIG. 18shows a cable or tendon connection assembly1800with a flexible conduit1830mounted at one end to a bearing support block1810at the drive assembly and at another end to a base link1820(link l0of a finger assembly). The cable tendon1840then extends through this conduit1830. The conduit1830supports a compression load that is equal in magnitude to the tension in the tendon1840.FIG. 19illustrates one implementation of a flexible conduit1900, and, as shown, this embodiment utilizes a conduit1900that is formed from a square stainless steel wire or coil1910that provides the advantage of having smooth internal and external surfaces. The conduits1910are lined with a fiberglass fiber impregnated Teflon-liner tube or the like1920, which reduces friction between the steel tendons (such as tendon1840) and the conduit1910(or conduit1830). Further, the interface between these components may be lubricated using a Teflon or other lubricant.