Patent Description:
Prosthetic hands are provided to persons who lack natural hands owing to amputation because of trauma, illnesses, or congenital defects, to afford desirable capability in the performance of manual actions such as grasping and moving objects, if not the complete dexterity of natural hand movements. Typically or preferably, prosthetic hands are mechanically integral (not requiring an associated artificial arm), operated with a power supply rather than body powered, and configured to resemble a natural hand. As is well known in the art, present day prosthetic hands commonly are employed with myoelectric control.

At present, advanced electronic prosthetic hands, though achieving high dexterity, are very high in cost and therefore not accessible to many potential users.

<CIT> discloses an orientation controller, mechanical arm, gripper and components thereof.

An object of the present invention is to provide new and improved artificial hands, including hands suitable for prosthetic hands and hands suitable for robotic use. Additional objects are to provide a natural looking, motorized and electronically controllable prosthetic hand with a high level of dexterity, integral mechanism, good strength and low cost, capable of being articulated into many positions for grasping different objects and performing different functions and gestures, including most common motions, such as grip patterns that require all digits to wrap around an object as well as pointing and pinching, which require other digits to be pre-closed and thumb and pointer finger to align.

Further features and advantages of the invention will be apparent from the detailed description set forth below, together with the accompanying drawings.

For purposes of illustration, the invention will be described as embodied in an artificial hand, in particular suitable for use as a prosthetic hand <NUM> (here shown as a left hand) having four finger digits <NUM>, <NUM>, <NUM> and <NUM> respectively corresponding to the index, middle, ring and little fingers of a natural human hand, a thumb digit <NUM>, and a palm body <NUM> on which the finger and thumb digits are pivotally mounted in an arrangement simulating the positions of the four fingers, thumb and palm of the natural hand. These features are constituted of rigid elements conveniently or preferably fabricated of a suitable plastic by three-dimensional (3D) printing, as hereinafter further discussed (alternatively, the elements may be made using any other 3D printing or traditional manufacturing technology, such as CNC machines, casting, molding, etc.). The finger digits, thumb digit and palm body may have relative lengths generally conforming to their human hand counterparts. If desired, the prosthetic hand may be provided with a socket forearm <NUM> (<FIG>) also usable as a display stand.

Each of the finger digits comprises two phalange sections, viz. a proximal phalange section (corresponding to the proximal phalange of a human finger) and a distal phalange section (corresponding to the intermediate and distal phalanges of a human finger as if fused together with a slight bend between them to facilitate wrapping around objects). In the index finger digit, the proximal phalange section is designated 11a and the distal phalange section is designated 11b; in the middle finger digit, the proximal and distal phalange sections are 12a and 12b respectively; in the ring finger digit, the two phalange sections are respectively 14a and 14b; and in the little finger digit, the two phalange sections are respectively 15a and 15b. The combination of distal and middle phalanges in a single rigid distal phalange section serves to simplify the construction of the prosthetic hand and enhance durability, as it is found that a pivotal connection between distal and middle phalanges is not strictly necessary for satisfactory functioning of the finger digits. If desired, however, these fused distal phalange sections may be replaced with separate distal and middle phalange sections interconnected by a pivot joint.

In each finger digit, the distal end of the proximal phalange section and the proximal end of the distal phalange section are interconnected by a pivot pin <NUM>, which enables relative rotation of the two phalange sections about a pivot axis that is perpendicular to the long dimension of the finger digit when the latter is fully extended. Similarly, the proximal end of the proximal phalange section of each finger digit is connected to the distal end of the palm body <NUM> by a pivot pin <NUM> which enables rotation of the proximal phalange section relative to the palm body about a pivot axis parallel to the axis defined by pivot pin <NUM>. The proximal and distal phalange sections of each finger digit are, therefore, pivotally movable relative to each other and to the palm body in simulation of movement of a human finger between extended and inwardly curled positions relative to a human palm.

More particularly, in the described embodiment the proximal phalange sections 11a, 12a, 14a and 15a of the four finger digits are respectively mounted to the palm body through knuckle elements 11c, 12c, 14c and 15c. That is, the pivot pins <NUM> respectively connect the proximal phalange sections to the knuckle elements. Each knuckle element is connected by a pivot pin <NUM> to the palm body for rotation relative thereto in a plane parallel to the axis of rotation of the associated proximal phalange section about its pin <NUM> relative to the knuckle element. If the axes of rotation about pins <NUM> and <NUM> are horizontal, the axes of rotation about pins <NUM> are vertical.

Features such as mating surfaces of the phalange sections may be adjusted to generate different frictional forces upon application of pivotal forces such that the proximal phalange section of each finger digit pivots (relative to the palm body) before the distal phalange section, as is desired for object grasping and enhanced control (<FIG>). In addition, each digit has slightly different lengths for each section (<FIG>), for improved gripping effect and natural appearance. Optionally, soft rubber grip pads (not shown) may be added on the tips and internal faces of the digits, to help grip smooth objects.

As in some known prosthetic hands, the present invention provides tendons for the finger digits to retract or curl the digits from extended position. While other prosthetic hand designs have employed direct mechanical linkages to flex the digit joints, such arrangements are costly, difficult to incorporate in the structure without reduced flexibility, lessened gripping and holding strength, and vulnerability to damage, e.g. breakage of fingers.

In accordance with the invention, in the embodiment shown, as a tendon for each of the finger digits, there is provided an elongated flexible flat strap member <NUM> extending lengthwise through slots or channels <NUM> formed in the successive phalange sections (e.g. sections 11a and 11b of index finger digit <NUM>). As thus disposed, each strap member has major flat surfaces <NUM>, <NUM> substantially parallel to the axes of rotation about the pivot pins <NUM> and <NUM> of its associated finger digit (see <FIG>) but offset inwardly therefrom with respect to a direction of finger digit curling toward the palm face 18a of the palm body <NUM>, the strap member further having a distal end <NUM> anchored to the distal phalange section (e.g. section 11b). Specifically, strap member distal end <NUM> may be wrapped around an internal post <NUM> in the distal phalange section and anchored by a self-tapping retaining screw <NUM> which passes through the plastic of the latter phalange section and the strap.

Each finger digit may have a plate <NUM> (<FIG>) that may (for example) fit in a friction fit on the back of each phalange section, the end portion of this plate serving to cover the retaining screw <NUM>. The provision of plate <NUM> also facilitates 3D printing of the finger digits and may add a decorative effect if printed in a different color.

Owing to the inwardly offset position of each tendon or strap member with respect to the rotational axes defined by pins <NUM> and <NUM> in its associated finger digit, pulling of the strap member in a proximal direction from its proximal end causes the finger digit to curl or close on itself (<FIG>), since the length of the portion of the strap member distally of the pivot pin <NUM> is thereby decreased, forcing the phalange sections to rotate around the pivot pin axes to bring them closer together.

Illustrative but non-limiting examples of articles suitable for use as the strap members <NUM> of the invention are the currently commercially available products known as zip ties or cable ties made of nylon. These ties have a rectangular strap cross-section of such proportions that they are flexible primarily in one direction while being much more rigid laterally as well as in compression and tension; hence they can curl on themselves to actuate (bend inwardly) a finger digit <NUM>, <NUM>, <NUM> or <NUM> when pulled from their proximal (actuating driven) ends <NUM> (see <FIG>) and can also be pushed from their same ends <NUM> to straighten a bent finger digit. For instance, in a specific example for a typical adult-sized prosthetic hand, the strap members may be nylon zip ties or cable ties each having a length of about <NUM> (trimmed down after being secured), a transverse width of about <NUM> and thickness of e.g. about <NUM>.

Use of a strap member as a tendon thus enables the tendon to effect extension of a curled finger digit as well as curling of an extended finger digit, merely by having the proximal end of the strap member pushed longitudinally by the same actuator that curls the digits by pulling the same end of the strap member. This obviates the provision of spring-biasing means or other resilient arrangements for re-straightening a curled finger digit, as has heretofore been necessary with tendons made of string or the like. Not only is the structure of the prosthetic hand thereby simplified, but in addition the force required to retract (curl) an extended finger is reduced, because there is no extension-biasing force to be overcome, and the actuator need not be kept energized to maintain the finger digit in curled position.

The use of strap members as tendons for the finger digits also affords an advantageously wide surface area to spread the pressure of the forces being applied to the finger digit material along which the tendon slides when under tension, thereby reducing wear, in contrast to the concentrated and abrasive force of a tendon made of string. In the case of nylon zip ties, the nylon is a self-lubricating material which slides easily within the slots or channels of the phalange sections, as well as being one of the strongest polymers. Moreover, such tendons render the finger digits beneficially compliant in that they enable the digits to flex slightly when subjected to external forces while the actuator is fixed.

Each of the strap members <NUM> extends proximally past and beyond the knuckle element (e.g. element 11c) of its associated finger digit and into the palm body <NUM> for attachment to a linear actuator for that finger digit, i.e., an actuator that moves the strap member linearly along a path generally parallel to the associated finger digit. Stated with reference to the index finger digit <NUM>, in accordance with currently preferred embodiments of the invention a linear actuator <NUM> therefor is disposed within the palm body and connected to the proximal end <NUM> of the strap member <NUM> for moving the strap member longitudinally through the phalange sections 11a and 11b of the finger digit <NUM> in each of two opposed directions thereby to move the phalange sections pivotally relative to each other and to the palm body between positions respectively simulating fully extended and inwardly curled positions of the finger digit.

Each linear actuator <NUM> in the illustrated embodiment of the invention is shown as comprising a lead screw <NUM>, a DC motor <NUM> for rotating the lead screw in each of two opposed directions (e.g. a DC metal geared Common N20 Form factor motor), and a driver member <NUM> threaded on the lead screw for longitudinal movement therealong in each of two opposed directions (indicated by arrow <NUM>) dependent on the direction of rotation of the lead screw, the driver member being anchored to the proximal end <NUM> of the strap member <NUM> for moving the strap member longitudinally through the phalange sections.

The lead screw <NUM> of each linear actuator is mounted in a generally rectangular actuator housing <NUM> entirely within, and constituting part of, the palm body, for rotation about an axis generally parallel to the direction in which the finger digits extend (<FIG>). The driver member <NUM> threaded thereon is rectangular and constrained against rotation by the side walls of housing <NUM> so that rotation of the lead screw moves the driver member digitally or proximally depending on the direction of rotation. Through a slit <NUM> in the front of the actuator housing, the associated strap member <NUM> extends from the finger digit into the housing, and the proximal end <NUM> of the strap member overlies and is securely affixed to the driver member, for example utilizing the small rectangular plastic feature <NUM> conventionally formed at one end of zip ties; thus, the proximal end of the strap member is stacked above the lead screw, providing a compact assembly. Movement of the driver member, when the lead screw turns, pushes or pulls the strap member through the slit <NUM> to open or close the associated finger digit(s). The backlash of the lead screw holds the digit in any position to which it is moved without need to maintain power to the motor.

It is currently preferred to fabricate the lead screws <NUM> of plastic by 3D printing in order to facilitate customization of strength/travel distance/speed to actuate, for example in production of child-size devices which have reduced space for linear travel of the driver member but may also be less strong, or to accommodate the choice of individual users with respect to actuation speed vs. strength.

For various grip patterns as well as for determining whether a finger digit has reached its fully extended or fully curled position, each of the linear actuators <NUM> for the finger digits has a linear potentiometer <NUM> extending alongside it, to measure the position of the driver member along the lead screw (alternatively, each potentiometer may be disposed directly beneath its associated linear actuator). This feedback provides the absolute position of a wiper (carried by the driver member) along the length of a resistive path to the microcontroller for the hand. The microcontroller can use the supplied data to determine the digit position and if necessary instruct the actuator motor to rotate the lead screw so as to move the driver member to the currently required position for each digit independently. Other means for position sensing (e.g. soft potentiometers, to reduce the width of the device by, say, <NUM>, to accommodate the electronics on board), and other sensors such as force sensitive resistors in the distal phalange tips, may also be employed with the hand.

Although the described embodiment of the prosthetic hand has four finger digits it includes only three finger digit linear actuators <NUM>, arranged side by side in the palm body. There are separate linear actuators for each of the finger digits <NUM> and <NUM> respectively corresponding to the index and middle fingers, but the digits <NUM> and <NUM> respectively corresponding to the ring and little fingers (which are rarely used independently in a natural hand) share a common linear actuator 40a; the driver member 46a of the actuator 40a is made wide enough to accommodate the proximal ends of the strap members of both digits <NUM> and <NUM> mounted thereon. This saves space, reduces the total number of required components, and reduces the electronic control requirements while providing a full complement of finger digits for realistic appearance and grip. Alternatively, if desired, all four finger digits may provided with individual linear actuators so that the ring and little fingers are separately movable between open and closed positions.

An additional important feature of the present invention in the embodiment shown is the provision of an arrangement for spreading (splaying) the fingers laterally from closed (adducted) position to open (abducted) position, substantially in a common plane. This is enabled by the pivotal mounting of the knuckle elements 11c, 12c, 14c and 15c on the palm body <NUM> by the pins <NUM> for limited individual abduction-adduction rotation (up to a total angle of about <NUM>°), relative to the palm body, about axes perpendicular to the axes of rotation of the proximal phalange sections about the pins <NUM> relative to the knuckle elements. The pins <NUM> are located on the back of the prosthetic hand while the strap members <NUM> overlie the palm-facing surfaces of the knuckle elements so that the strap members pass from the proximal phalange sections of the finger digits above the knuckle elements (as seen in <FIG>) to their associated linear actuator driver members <NUM> without interference from pins <NUM>. The strap members <NUM> pass over the centerlines of (axes of knuckle rotation about) pins <NUM> and are guided into the linear actuators through slits <NUM>; hence abduction-adduction rotation of the finger digits does not change the longitudinal distance the strap members need to move in order to pull or push their associated finger digits and does not change the point at which the strap members enter the palm body to be actuated; also, although abductive pivoting of the finger digits requires slight lateral bending of the strap members forwardly of the linear actuators as indicated at <NUM> (see <FIG>), the above-described strap members have sufficient lateral flexibility to accommodate the limited extent of lateral bending involved and still be able to be pushed or pulled longitudinally through their associated slits <NUM> and phalange section channels <NUM>.

The finger digits are driven together between their adducted (<FIG> and <FIG>) and abducted (<FIG> and <FIG>) positions by a plate <NUM> mounted in guide grooves <NUM> on the back of the palm body <NUM> for sliding motion between a proximal position (<FIG>) and a distal position (<FIG>) on the palm body. Each of the knuckle elements 11c, 12c, 14c and 15c has a thin flat arm <NUM> extending proximally therefrom over the plate <NUM>. At the proximal end of each arm <NUM> is a thin flat peg <NUM> projecting toward the plate <NUM> and inserted in one of four diverging slots <NUM> formed in the plate such that the pegs of different finger digits are respectively received in different slots. A linear actuator <NUM>, similar to the linear actuators <NUM> and also mounted in the palm body, is connected to the plate <NUM> so as to move it between the aforesaid proximal and distal positions; as in the case of the finger digits and actuators <NUM>, the location of the plate between the limits of its proximal-distal travel (and thus the degree of abduction of the finger digits) is controlled by controlling the position of the linear actuator. <NUM>, the latter position being measured e.g. with a linear potentiometer <NUM> or other linear sensing means. It may be noted that the use of a single linear actuator <NUM> to curl and extend both the ring finger and the little finger digits facilitates the provision of space in the palm body for the linear actuator <NUM> that drives the adduction and abduction of the finger digits, although it is also possible to fit four separate linear actuators for fingers as well as the actuator <NUM> into the palm.

In the illustrated embodiment, the four slots <NUM> in plate <NUM> diverge in a distal direction. Consequently, when the plate <NUM> is at its proximal limit of travel (<FIG> and <FIG>), the four pegs <NUM> (respectively guided by the four slots <NUM>) are located at the distal, maximally separated ends of the slots, and the four knuckle elements 11c, 12c, 14c and 15c are pivoted about their respective pins <NUM> into positions where the four finger digits are parallel (adducted). Upon movement of plate <NUM> by linear actuator <NUM> to the distal limit of plate travel (<FIG> and <FIG>), the pegs <NUM> are located at the proximal, minimally separated slot ends, pivoting the four finger digits into their maximally separated (fully abducted) positions.

It is not necessary that each digit can be adducted and abducted. For example, the one or both of the central digits <NUM>, <NUM> may remain stationary. Accordingly, the above described mechanisms may only be present for those digits that are configured to be adducted and abducted.

In the described embodiment of the invention, the palm body has a rigid casing <NUM> for receiving and enclosing the finger-digit linear actuators <NUM>, the adductor-abductor linear actuator <NUM>, the adductor-abductor plate <NUM> and the knuckle arms <NUM>. The casing, which may have decorative features (not shown) is held in place by two screws <NUM>. Alternative arrangements may, for example, include additional guiding plates to reduce play of the actuators, and a removable palm face for ease of wire management and repair.

The artificial hand of the invention, in this embodiment, also includes a thumb digit <NUM> (<FIG>) mounted on the palm face of the palm body casing and extending laterally from the palm body. The thumb digit has a proximal thumb phalange section <NUM> with a proximal end <NUM> pivotally connected by a joint <NUM> to the palm body for rotation relative thereto about a first thumb axis, and a distal thumb phalange <NUM> section with a proximal end <NUM> pivotally connected by a pin <NUM> to the distal end of the proximal thumb phalange section <NUM> for rotation relative thereto about a second thumb axis non-parallel to the first thumb axis, such that the thumb phalange sections are pivotally movable relative to each other and to the palm body in simulation of movement of a human thumb relative to a human palm;.

As a tendon for the thumb digit, there is provided an elongated flexible flat thumb strap member <NUM> extending lengthwise through the successive thumb phalange sections <NUM>, <NUM> with major flat surfaces <NUM> and <NUM> offset inwardly from the aforesaid first and second thumb axes with respect to a direction of thumb bending, the strap member <NUM> having a distal end anchored to the distal thumb phalange section <NUM>. The successive thumb phalange sections cooperatively define a non-rectilinear path for guiding the thumb strap member longitudinally therethrough. This strap member <NUM> may be of the same type as the above-described strap members <NUM> of the finger digits, and thus may (for example) be a nylon zip tie or cable tie, having the same properties already discussed.

A thumb linear actuator <NUM> is mounted within a housing <NUM> secured by four screws <NUM> on the palm body (whereby the thumb digit is mounted on the palm body), and connected to a proximal end <NUM> of the thumb strap member <NUM> for moving the thumb strap member longitudinally through the thumb phalange sections in each of two opposed directions thereby to move the thumb phalange sections pivotally relative to each other and to the palm body between positions respectively simulating said extended and inwardly curled positions of a human thumb relative to a human palm. The thumb linear actuator, in the form shown, comprises a lead screw <NUM> extending transversely across the palm body (perpendicular to the rotational axis of pivot joint or pin <NUM>, a motor <NUM> for rotating the lead screw in each of two opposed directions, and a driver member <NUM> threaded on the lead screw for longitudinal movement therealong in each of two opposed directions dependent on the direction of rotation of the lead screw. The driver member <NUM> is anchored to the proximal end <NUM> of the thumb strap member <NUM> for moving the thumb strap member longitudinally through the thumb phalange sections as aforesaid. The structure and operation of the linear actuator <NUM> may be the same as that of the aforementioned linear actuators <NUM> and <NUM>, and for control purposes may be provided in like manner with a linear potentiometer <NUM>.

A significant difference between the thumb and finger digits is the need for the thumb to rotate along two non-parallel axes. That is to say, instead of rotating about parallel pivotal axes (as defined for the finger digit phalange sections by pivot pins <NUM> and <NUM>), the thumb proximal phalange section <NUM> pivots on an axis defined by joint <NUM>, perpendicular to the linear actuator screw axis, but the distal thumb phalange section <NUM> pivots about an axis which is not parallel to that of j oint <NUM>. The reason for this is that the thumb rotates through multiple axes to curl around objects and grip them. Accordingly, an internal channel <NUM> (<FIG>) guides the strap member from the linear actuator through the proximal thumb phalange member <NUM> to the distal thumb phalange member <NUM> which is not in line with the linear actuator. The properties of the strap member tendon, including useful though limited lateral flexibility as described above, allow for push-pull motion of the thumb digit through multiple pivots that are not aligned. This avoids any need for multiple motors to drive the thumb, as the single linear actuator and thumb-tendon strap member can first rotate the thumb into position about joint <NUM> and then close thumb about pin <NUM>, resulting in a relatively accurate and capable looking thumb assembly with minimal complexity.

As stated, it is currently preferred to use 3D printing to manufacture most of the components of the described prosthetic hand, apart from the motors, potentiometers and some other ancillary fittings and connections. 3D printing allows advantageous customization while achieving production at relatively low cost. The design of components and especially the orientation of parts has been selected to reduce the amount of support structures required in 3D printing and reduce printing time as well as increase strength and definition. For instance, as shown in the drawings, the lead screws in the linear actuators are configured with opposed longitudinal flat sides <NUM> (<FIG>) to allow them to print flat on a build plate along the strongest direction and make them easy to print with good definition along the layer lines. The inner palm support that houses all the components for the linear actuators has also been optimized to reduce support structures and give significant strength to hinges and other features. Finger digit sections have also been designed to print flat on their side which allows for stronger hinges (continuous line of filament). The decorative plates have been designed to be printed on the flat visible face to make it as aesthetic and clean as possible. The inner housing (palm body casing) has been designed to be printed with the wrist opening flat on the build surface to allow more organic shapes with less visible layering. Overall, objectives of the design are to reduce the cost of the devices, reduce print time, provide desired strength of printed parts and lower the number of parts and actuators.

The use of the hand will be readily apparent to persons skilled in the art, being effected by operation of the linear actuator motors, for example (in prosthetic use) under myoelectric control (through leads, not shown, extending externally of the hand) utilizing information supplied from the linear potentiometers and/or other sensors. The motors themselves may be powered by rechargeable batteries. Controlling electronics, microcontrollers and such that interpret the control signals and drive the motors based on positive sensors may also be provided. As stated, the hand structure of the invention may also be used in robotics, not just in prosthetics.

Claim 1:
An artificial hand (<NUM>), comprising:
(a) a palm body (<NUM>);
(b) at least two finger digits (<NUM>, <NUM>, <NUM>, <NUM>) extending distally from the palm body (<NUM>) and each having a knuckle element (11c, 12c, 14c, 15c) pivotally connected to the palm body (<NUM>), and characterised by further comprising:
(c) an adductor-abductor plate (<NUM>) mounted in the palm body (<NUM>) for sliding movement in distal and proximal directions and having diverging slots (<NUM>), and an adductor-abductor linear actuator (<NUM>) in the palm body (<NUM>) for effecting sliding movement of the plate as aforesaid, and wherein each of the knuckles (11c, 12c, 14c, 15c) has an arm (<NUM>) extending proximally from the knuckle over the palm body (<NUM>) and bearing a peg (<NUM>) inserted in one of the slots (<NUM>), such that sliding movement of the plate (<NUM>) causes the slots (<NUM>) to guide the pegs (<NUM>) divergently or convergently thereby to rotate the knuckles for adduction or abduction of the finger digits(<NUM>, <NUM>, <NUM>, <NUM>).