Artificial hand

An artificial hand has a stationary wrist and two fingers and a thumb pivotal from a horizontal axis in the wrist. The thumb may have two separable portions, one of which is pivotal away from the other along a generally vertical axis by manual prepositioning. This enables rounded objects such as doorknobs to be grasped by the curved main finger and the two thumb portions, making stable three-point contact. The two fingers are pivotal along the wrist axis in a fixed range of motion with respect to the thumb, and a spring urges the fingers toward a normal open position. Tension of a sheathed cable fitted to a standard body harness closes the fingers to the thumb, enabling a powerful grip. The second finger is straight and normally remains alongside the curved finger until, upon closure of the curved finger and contact to its tip with the thumb, further cable tension closes the straight finger against the thumb to grip small or flat, thin objects. A special link between the cable and the fingers is provided for this purpose.

BACKGROUND OF THE INVENTION 
The invention relates to artificial mechanical hands, and more particularly 
to an improved mechanical hand with multiple prehension capability, 
especially suitable for bilaterals, or double amputees. 
For unilaterals, or single amputees, a mechanical hand often takes the form 
of a simple split hook of the type shown, for example, in U.S. Pat. No. 
1,042,413. This type of artificial hand unusually has a spring or elastic 
band urging the two hook sections together to grasp objects between them, 
with the sections openable by the action of a cable attached to a body 
harness. Another example of this type of artificial hand is shown in U.S. 
Pat. No. 1,206,753. 
Bilaterals, with no natural hand for the more difficult grasping functions, 
need artificial hands with more complete prehension capability than is 
afforded by the hook described above. A number of more complex artificial 
hand mechanisms have been suggested, as shown for example in U.S. Pat. 
Nos. 2,422,530, 2,487,724, 2,409,884, 2,853,711, 3,413,658, and 4,016,607. 
The disadvantages of these prior art devices have been that they are either 
too complicated to be economically feasible, they have been difficult to 
learn to operate, they have failed to provide important types of 
prehension capability, or they have been oriented so much toward cosmetic 
appeal that they necessarily have been very limited in functional 
advantages. 
None of the devices shown in the prior patents provides the degree of 
prehensile versatility, with the simplicity of construction and operation, 
as does the present invention described below. 
SUMMARY OF THE INVENTION 
The artificial hand of the present invention facilitates a combination of 
important prehension functions in one relatively simple apparatus, 
operable by a standard sheathed cable connected to a body harness known in 
the prior art. The hand enables the user to grasp rounded objects such as 
doorknobs and to easily turn a doorknob, to grasp objects between a finger 
tip and a thumb, and to grip small or thin objects with an auxiliary 
finger which forms a line of contact with the flat surface of the thumb. 
The fingers are urged by a spring toward their open position away from the 
thumb, and cable tension is effective to close the fingers towards the 
thumb in a powerful grip. Many prior art mechanical hands worked 
oppositely, with a spring providing the pressure to close the gripping 
mechanism and the cable merely opening it. 
When cable tension is put to the hand of the invention, the finger tip of a 
main finger first comes into contact with the relatively stationary thumb. 
Continued additional tension brings the auxiliary, straight finger into a 
line of contact with the thumb; and still further cable retraction pivots 
the entire closed hand, fingers and thumb, downward along a wrist pivot 
axis, to a position where the hand would be usable for reaching into a 
breast pocket, for example. 
The thumb of the artificial hand preferably is split into two components, 
one of which is pivotable toward and away from the other. This is for 
prepositioning the openable thumb portion for functions such as gripping 
doorknobs, where three points of contact are desirable for a stable grip. 
In a preferred embodiment, an artificial hand according to the present 
invention comprises a support base for connecting to the arm of the user, 
with a wrist connected to the base and a pivot axis in the wrist. A 
pivotal main finger is connected along the pivot axis to the wrist, with a 
downwardly angled finger tip at its ends. Alongside the main finger is a 
generally straight pivotal finger, also connected along the pivot axis to 
the wrist and normally in a position spaced angularly back of the finger 
tip of the main finger, so that the finger tip leads the straight finger 
as the two fingers are moved downwardly. A thumb extends from the wrist, 
positioned to be contacted by the fingers in their downward, closed 
position. Means are provided in association with the main finger and the 
thumb for enabling grasping of rounded objects between them. There are 
provided a control cable and cable housing adapted for connection to 
typical harness apparatus worn on the body of the user, with means 
connecting the forward end of the cable housing to the thumb and means 
connecting the forward end of the cable, extending from the housing, to 
the fingers in such a way that retraction of the cable in the housing 
pulls the fingers toward the thumb, first contacting the main finger tip 
with the thumb and then bringing the straight finger toward contact with 
the thumb on further retraction of the cable. A means is provided for 
biasing the main finger and the straight finger away from the thumb to 
their normal open position. 
Accordingly, it is among the objects of the invention to provide an 
improved artificial, mechanical hand capable of fulfilling the needs of 
bilaterals and providing for multiple forms of prehension from a simple, 
single-cable actuation system. Other objects, advantages and features of 
the invention will be apparent from the following description of some 
preferred embodiments, considered in connection with the accompanying 
drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the drawings, FIG. 1 shows an artificial hand 10 according to the 
invention, preferably employed as a right hand because of the location of 
a cable and sheath 11 and 12 and the orientation of certain other 
components. 
The hand 10 includes a support base 13 with some form of connection such as 
a threaded stud 14 for securing to a prosthetic device 16 attached to the 
arm of the user. Preferably, the support base 13 has a forward extending 
flange or wrist 17 as shown, from which a main finger 18, a straight 
finger 19 and a thumb 21 are pivotally supported along a wrist pivot axis 
22. A threaded shaft 23 (see also FIG. 6) is advantageously used for 
supporting the fingers 18 and 19 and the thumb 21 along the axis 22, and 
nuts 24 at either end and may be employed to retain the assembly together. 
The position of the aritifical hand shown in FIGS. 1 and 2 is the normal 
position. The main finger 18 and the straight finger 19 are biased toward 
the open position by a spiral spring 26 on the left side of the hand (see 
FIGS. 2 and 6), secured to the threaded shaft 23 by a slot 23a shown in 
FIG. 6 and in engagement with a stud pin 27 which extends from the 
straight finger 19 through an elongated, slot-shaped opening or window 28 
of the main finger to its connection with the spring 26 as shown in FIG. 
2. The stud 27 and the window 28 are so positioned that both the fingers 
18 and 19 receive the force of the spring 26 when the fingers are both in 
the normal open position shown in FIGS. 1 and 2. However, the straight 
finger 19 is permitted a small degree of movement downward relative to the 
main finger 18, while still being under the influence of the spring 26, 
tending to urge it toward the full open position. The purpose and function 
of the arrangement will be explained below. 
Limitation of upward, opening movement of the fingers 18 and 19 is provided 
by a stud 29 forming a stop against which an abutment 31 engages (see 
FIGS. 2 and 6). This limits upward pivotal movement of the main finger 18, 
since the abutment 31 is on this finger, and also limits movement of the 
straight finger 19 in the same direction, since the stud 27 extends from 
the finger and is stopped by the boundary of the window 28 in the main 
finger. 
The cable 11 and sheath 12 are adapted for connection to a standard body 
harness (not shown) for operation of mechanical hands, with appropriate 
means connected to the shoulder for pulling the cable 11, retracting it 
within its sheath 12, which is braced at another point, such as the upper 
arm. Retraction of the cable moves the two fingers downwardly with respect 
to the thumb 21, to which the end of the sheath 12 is anchored as shown. 
The end of the cable 11 is attached to a link 32, which is pivotally 
connected at spaced locations 33 and 34 to each of the straight finger 19 
and the main finger 18, respectively. The link 32, and its connection 36 
with the end of the cable 11, are so positioned that retraction of the 
cable 11 first pulls the main finger 18 downwardly toward the thumb, until 
it reaches contact with the thumb as illustrated in dashed lines in FIG. 2 
with the main finger 18a and the straight finger 19a. The straight finger 
remains in its normal position with respect to the main finger during this 
retraction, and objects can be grasped between a tip 37 of the main finger 
and the thumb, or between a concavely curved portion 38 of the main finger 
and the thumb. 
However, if the cable 11 is retracted further when the fingers are in the 
positions 18a and 19a shown in FIG. 2, the straight finger 19a will be 
urged by the pivotal cable link 32 further downwardly, independent of the 
main finger, until it meets the thumb at a position 19b shown in dashed 
lines in FIG. 2. This enables the grasping of small, long objects, such as 
a pencil. In this position both the fingers are urged against the surface 
of the thumb 21 by the force applied by the cable 11 through the link 32. 
Only the straight finger 19 is acted upon by the spring 26 in this 
position, since the stud 27 extending from the straight finger will be at 
the lower end of the window 28. 
When the cable 11 is released, the spiral spring 26 would tend to pull the 
straight finger back to its position 19a shown in FIG. 2, before the main 
finger 18 leaves the position 18a shown in FIG. 2. However, in some 
circumstances it is desirable that the straight finger remain extended, 
substantially flush with the finger tip 37 of the main finger, during the 
initial part of the retraction. This is desirable, for example, when the 
hand is to be inserted in a pocket and the straight finger 19 might snag 
on the pocket if in its normal position with respect to the main finger 
18. Therefore, a tension spring 39 is positioned as shown on the left side 
of the hand 10, secured to the outside of the main finger 18 and connected 
to the stud 27 of the straight finger, tending to move the straight finger 
19 toward the position 19b shown in FIG. 2 relative to the main finger 18. 
The force of the spring 39 is considerably lighter than that of the spiral 
spring 26, but sufficient to partially counterbalance the spring 26 during 
the initial release of the cable 11, so that the two fingers 18 and 19 do 
not assume their normal positions relative to one another until they have 
both moved somewhat away from the thumb 21. 
The normal position of the thumb 21 on the wrist or flange 17 is shown in 
FIGS. 1 and 2 in solid lines. However, the thumb 21, like the fingers 18 
and 19, is pivotal along the axis 22. To hold it in the normal, generally 
straight forward position shown in the figures, a friction washer 41 is 
positioned between the thumb 21 and the wrist 17, as best seen in the 
exploded view of FIG. 6. Thus, with a prescribed degree of tightness of 
the nuts 24 on the threaded shaft 23, the thumb is held in its normal 
position while the fingers freely rotate along the axis 22. 
When desired, the thumb can be moved manually or "prepositioned" to a 
downwardly pivoted condition, as shown in dashed lines in FIG. 2, with the 
thumb shown at 21b. The user does this prepositioning by reaching his arm 
out beyond the point where the fingers contact the thumb, to retract the 
cable even further. This pulls the thumb to the downwardly pivoted 
position 21b. 
This positioning of the hand is desired, for example, when the user wishes 
to reach into a breast pocket. Once in this position the fingers and thumb 
can be used in the normal way, by retraction of the cable 11. When the 
thumb and fingers are to be returned, the thumb is simply pushed back to 
its normal position by pushing against a stationary object or against a 
part of one's body such as a leg, etc. The fingers stay in the same 
relative position with respect to the thumb (as in FIG. 1), because of the 
stop and abutment 29 and 31 acting between the thumb 21 and the main 
finger 18. The normal position is defined as shown in FIG. 1 by a rear 
portion 21a of the thumb engaging against a forward bottom surface 17a of 
the wrist 17. 
To aid in the manual return of the thumb to the normal position, there may 
be provided a second spiral spring 42 on the right side of the hand as 
shown in FIGS. 1 and 6. This spring engages against a stud 43 on the wrist 
flange 17 and acts on the threaded shaft 23 (via a slot 23b shown in FIG. 
6), which preferably is connected to the thumb 21 to urge the shaft 23 and 
thumb 21 toward the normal position. Friction between the wrist 17 and 
thumb 21 is preferably sufficient to maintain the thumb in whatever 
position the user prepositions it, but the spring enables it to be 
returned with a lighter force. 
FIG. 3 shows a resilient tip 44 on the finger tip 37, which may be a 
replacable element inserted into the finger tip as shown. This enables 
better grasping of objects between the finger tip and thumb. 
As shown in the drawings, particularly FIG. 6, the thumb 21 is made up of 
several components. A rearward or base portion 21c of the thumb is affixed 
to the threaded shaft 23, and this may be integral with a stationary 
portion 21d of the thumb, or it may be affixed thereto by fasteners 46, as 
shown. The thumb may also include a movable portion 21e, pivotal along a 
generally vertical axis 47 (FIG. 6) with respect to the remainder of the 
thumb. This enables the movable portion 21e to swing away from the 
stationary portion 21d as indicated in dashed lines in FIGS. 1 and 4. 
When the thumb portions 21d and 21e are closed, i.e. in their normal 
position, and the main finger 18 is brought down to the thumb, the finger 
tip 37 (i.e. the resilient insert 44) engages against the movable portion 
of the thumb 21e. The straight finger 19 comes down adjacently and engages 
against the surface of the stationary thumb portion 21d. When the movable 
thumb portion 21e is opened, by manual prepositioning, the main finger 18 
then converges toward the space between the two thumb portions. This 
provides a three-point set of gripping contacts for engaging thick or 
rounded objects, particularly those which are to be turned such as 
doorknobs. A rubber or resilient type surface 48 preferably is included on 
both thumb portions for better gripping of objects, and this aids 
considerably in the gripping of rounded objects. 
The movable thumb portion 21e may be connected to the thumb base portion 
21c by a threaded fastener 49, as best seen in FIGS. 4 and 6. It is 
maintained in the normal position or the open position by a ball and 
detent arrangement. As indicated in FIG. 6, this may include a spring 51 
urging a ball 52 downwardly from a bore (see FIG. 2) in the portion 21c, 
for engagement with either of two detents 53 and 54 in the upper surface 
of the movable thumb portion 21e. 
As indicated in broken lines in the bottom view of FIG. 4, a tension spring 
55 may be included to urge the movable thumb portion 21e toward the closed 
position, the spring not being sufficiently strong to overcome the holding 
action of the ball and detent. 
When the thumb portions 21d and 21e are separated, as shown in dashed lines 
in FIGS. 1 and 4, the hand is sometimes used to pick up heavy objects. For 
this purpose it is necessary to keep the thumb 21 in the normal position, 
preventing it from pivoting downwardly (as shown at 21b in FIG. 2). 
Therefore, a special feature is provided for acting between the movable 
thumb portion 21e and the wrist 17. As best seen in the bottom view of 
FIG. 4, this arrangement comprises a stud 56 extending downwardly from the 
bottom of the wrist 17 and a boss 57 which is clear of the stud 56 in the 
closed position of the thumb but directly in the path of the stud 56 when 
the movable thumb portion 21e is pivoted outwardly as shown in dashed 
lines in FIG. 4. This provides a stop against downward movement of the 
thumb assembly, even when heavy weights are lifted. 
There are several additional features which give the artificial hand of the 
invention additional versatility, particularly for bilaterals who have no 
natural hand to supplement the use of the mechanical hand. One such 
feature is a groove 60 in the side of the finger tip 37 of the curved main 
finger 18, as shown in FIGS. 2 and 6. The groove 60 can be used to catch 
an edge of a small object, and the narrow portion of the finger below the 
groove, between the groove and the tip, enables the user to lift the edge 
of a small object such as a pop top seal on a can of liquid refreshment, 
and from there he is able to grasp the object between the pliable finger 
tip pad 44 and the thumb 21. 
As shown in the bottom view of FIG. 4, grooves 61 or other textured 
surfacing preferably are included in the bottom surface of the movable 
thumb portion 21e, to aid the user in prepositioning the thumb to the open 
position. 
At the top surface of the movable thumb portion 21e as shown in FIGS. 1 and 
6, there may be included a metal corner area 62, in the surface otherwise 
covered with the resilient high-friction surface material 48. This is 
helpful in picking up small objects in instances where the resilient 
material 48 might actually hinder the grasping of the object between the 
finger tip 37 and the thumb portion 21e. 
As indicated in the drawings, the straight finger 19, which converges down 
onto the non-pivotal thumb portion 21d in a line of contact just adjacent 
to the separation of the two thumb portions 21d and 21e, may also include 
a resilient surface strip 63. This further aids in gripping objects or 
sheet materials such as papers. 
An additional feature that preferably is included in the artificial hand 10 
of the invention for both aesthetic and functional reasons is a pair of 
protective cups 65 appropriately secured to the outside of the wrist 17 on 
the one side and of the main finger 18 on the other side, as shown in 
FIGS. 1, 2, 4 and 6. These cups 65 improve the appearance of the hand, 
hiding the springs 42, 26 and 39 and the other hardware associated with 
them, and also cover these components to prevent their catching or 
snagging on clothing or other objects. 
It should be understood that other features of the artificial hand of the 
invention may be modified to present a more aesthetic appearance--the 
fingers may be modified to appear more like human fingers, and the thumb 
may also be made to appear more like the human. Preferably, these changes 
are made in such a way as to maintain the functionality of the hand and to 
avoid excessive cost of manufacture. 
It should also be understood that certain modifications can be made to the 
function of the hand shown in the drawings, without departing from the 
scope of the invention. For example, the principal purpose of the 
two-component pivotal thumb is to provide a three-point contact for 
certain types of gripping, such as doorknobs and other rounded or thick 
objects. This can be accomplished, for some applications, by simply 
providing a shaped thumb capable of providing two points of contact 
without any prior prepositioning movement, the third point of contact 
being made by the main finger 18. The illustrated split thumb, however, is 
preferred. 
Similarly, for some applications it may be desirable to eliminate the 
straight finger 19, including the main finger 18 as the only finger 
converging toward the thumb. For example, if the artificial hand is to be 
used by a unilateral amputee, rather than a bilateral, or if it is for a 
bilaterial having a complete artificial hand 10 as illustrated in the 
drawings as one hand, the other hand may be of a somewhat simplified 
version, perhaps without the straight finger 19. 
It should be further understood that the split thumb, as provided, can take 
other forms from that shown in the drawing. For example, it may be formed 
with the portions 21d and 21e both swingable away from one another, rather 
than the simpler arrangement illustrated wherein only one portion is 
movable. 
Other embodiments and variations to the illustrated preferred embodiment 
will be apparent to those skilled in the art and may be made without 
departing from the spirit and scope of the invention as defined in the 
following claims.