Note: Descriptions are shown in the official language in which they were submitted.
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~p~'R T~IM13 PROSTHEST_S
The present invention relates to upper limb prostheses and in
particular to such prostheses with mechanically (usually
electro-mechanically) operable pivoting wrist, elbow and/or
shoulder joints.
The design of such prostheses presents various problems in
relation to design flexibility and manufacturing cost,
cosmetic appearance, power, stability etc. It will be
appreciated that upper limb prostheses have relatively high
power and strength requirements due to, inter alia, the
considerable leverage forces exerted when, for example, using
the prosthesis to lift objects more or less at arm's length.
Thus previously known prostheses are essentially exoskeletal
in nature with a relatively substantial large diameter shell
structure shaped and finished to have the appearance of an
upper limb or part thereof. With this type of construction it
is necessary for a substantial part of the manufacture of the
prosthesis to be customised to each individual patient, and in
the case of children, to different developmental stages
thereof. As the customised shell is also used as the main
structural load bearing component and the support for the
various operating mechanisms of the upper limb this results in
relatively high costs and extended manufacturing processes.
In addition, where, as is usually desirable, a rotating wrist
is used, then the cosmetic appearance is compromised by the
visibility of the join or discontinuity between the rotating
and non-rotating parts of the prosthesis. In addition the
motors used require relatively complex gearing systems and
often the inclusion of secondary motors in order to provide
the required power, and the necessary locking of the joint
under load in a desired attitude, respectively. This in turn
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leads to increased weight, reduced design flexibility and
relatively high power consumption.
It is an object of the present invention to avoid or minimise
one or more of the above disadvantages.
It has now been found that by the use of a worm gear system
for mechanically operating the prosthesis, the construction
of upper limb prostheses can be very considerably simplified
whilst maintaining performance comparable with or better than
that of conventional externally powered upper limb prostheses.
In more detail the present invention provides an articular
endoskeletal prosthesis for providing a user with at least one
of a mechanically operable pivoting wrist, elbow and shoulder
joint, said prosthesis having at least one elongate
endoskeletal tube upper limb member with a proximal end
portion having a pivotal connection to a support body
therefor, one of said upper limb member proximal end portion
and said support body having a fixed worm gear wheel means and
the other a drive motor having a drive output worm extending
generally tangentially of said worm gear wheel means for
engagement with the gear teeth of said worm gear wheel means
so that when said drive motor is operated, in use of the
prosthesis, said upper limb member moves around said worm gear
wheel means so as to pivot said upper limb member about its
pivotal connection.
Thus with a prosthesis of the present invention construction
may be greatly simplified by using more or less plain
conventional lightweight tubing of relatively small diameter
(as compared with the limb diameter) and which can readily be
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cut to any desired length. The relatively simple and compact
form of drive mechanism also contributes to simplifying
construction and reducing the strength and size requirements
of the tubing and drive motor and power source requirements.
Thus the cosmetic personalisation of a prosthesis to a
particular patient can be substantially restricted to a non-
structural outer cladding for the prosthesis. The form of
construction used by the invention can moreover provide
improved cosmeticisation opportunities as further discussed
hereinbelow.
Another significant benefit of the present invention arises
from the fact that a worm gear system is inherently
substantially self-locking so that when the motor is switched
off and stops driving a limb member which is still under load,
the limb member is held in position and no additional
mechanism is required in order to retain the limb member in a
given position.
In general the drive motor means and any gearbox provided
therewith, have a generally cylindrical form with an axially
extending worm gear so that they can conveniently be mounted
inside the end of an endoskeletal tube member with the drive
output worm projecting axially outwardly therefrom. The power
source could also be mounted inside the endoskeletal tube
member but more conveniently could have a generally annular
form (with a greater or lesser angular extent e.g. two units
each having an angular extent of I80°) fitted around the
outside of the endoskeletal tube member.
As noted above the prostheses of the invention may have one or
more of a wrist joint, an elbow joint, and a shoulder joint,
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mechanically operable in accordance with the present
invention. It would also be possible though to use, for
example, an elbow joint according to the present invention in
combination with a conventional mechanically operable wrist
joint. Generally it will be more convenient to have the drive
motor with its drive output worm mounted down-limb of the
fixed worm gear wheel means. Thus in the case of a wrist
joint the drive motor would preferably be inside the hand
member and the fixed gear wheel means on the distal end of the
forearm member. It would also be possible though for the
drive motor to be inside the forearm member with the fixed
worm gear wheel means mounted on the hand member. Similarly
it would generally be preferred with an elbow joint for the
drive motor to be in the forearm or lower arm member and the
fixed worm gear wheels to be on the upper arm member; and with
a shoulder joint, for the former to be in the upper arm member
and the latter on a support body fitted in the shoulder of the
patient. An advantage of the alternative arrangement of
having the drive motor up-limb of the joint e.g. in the upper
arm for an elbow joint, is that it raises the centre of
gravity of the limb proximally thereby reducing the energy
consumption and power requirements of the drive motor for that
joint. It will of course be appreciated that, depending on
the extent of the prosthesis, the support body for any given
joint may comprise an endoskeletal tube member or some form of
stump adaptor.
The endoskeletal tube members may have a variety of different
forms and sizes depending , inter alia, on the materials used
and the requirements of the individual patient. Thus the tube
may be of polygonal e.g. square or hexagonal section, or could
have a rounded, e.g.oval or elliptical section. Conveniently
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though there is used a generally plain cylindrical section as
this is generally more easily available and more readily
interfaceable with the other components of the prosthesis.
The diameter may vary with strength and rigidity requirements
which would generally increase from a hand member to a forearm
member to an upper arm member. The tube wall thickness and
material and construction will also affect the tube diameter.
Advantageously the tubing is of woven and/or laminated carbon
fibre which combines considerable strength with lightness. In
this case the tubing could generally have a diameter in the
range from 10 to 50 mm, preferably 12 to 40 mm with a wall
thickness of from 0.5 mm to 5 mm, preferably from 1 to 2.S mm.
Thus for example in the case of a hand member there would
typically be used tubing with a diameter of from 15 mm to 20
mm and in a lower or upper arm member tubing with a diameter
of from 25 mm to 35 mm. Other materials could also be used
though, e.g. high strength lightweight metal alloys such as
duralumin (TM) .
Various suitable motors having a relatively high power-to-
weight ratio are known in the art including permanent magnet
DC motors which have a substantially linear relation between
torque and drive current over a reasonably wide range which
facilitates control of the driving of the finger member.
Particularly suitable motors are available from Minimotor SA
of Switzerland, especially their motors which have a diameter
of around 10 to 30 mm. A further advantage of this type of
motor is the availability of a modular gearbox system coupled
to the output shaft of the motor which allows different
torque-output drive speed ratios to be selected simply by
choosing from a range of gearboxes with different ratios.
This has the advantage of facilitating the provision, in a
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multi-joint prosthesis, of different operating characteristics
by simply using different gearboxes in different joints.
The use of cylindrical endoskeletal tube members also has the
advantage of facilitating the incorporation of a rotational
capability - especially in relation to wrist joints. This may
be provided in generally known manner but the use of an
endoskeletal form of construction has the additional advantage
of allowing the use of cosmetic cladding which extends
unbroken across the joint thereby avoiding the unsightly
discontinuities that are present in conventional rotating
wrist joints.
Further preferred features and advantages of the invention
will appear from the following detailed description given by
way of example of some preferred embodiments illustrated with
reference to the accompanying drawings in which:
Fig.l is a schematic sectional view of a multi-joint
prosthesis of the invention;
Fig.2 is a detailed partly cut-away and sectioned view of the
elbow joint of a prosthesis of the invention;
Fig.3 is a detailed partly cut-away and sectioned view of the
wrist joint of a prosthesis of the invention; and
Fig.4 is a detailed sectional view of the rotary actuator part
of the wrist joint of Fig.3.
Fig.l shows an upper limb prosthesis 1 comprising a.shoulder
stump adaptor support body 2 pivotally connected 3 to the
proximal, upper, end 4 of an upper arm member 5 whose distal,
lower, end 6 is in turn pivotally connected 7 to the proximal,
upper, end 8 of a forearm member 9 acting as a support body
therefor. The distal, lower, end 10 of the latter is in turn
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pivotally connected 11 to a hand member 12. The forearm is
covered in a flexible silicone rubber cosmetic cladding 13
prestretched,over an arm bearing.
As shown in Fig.2 into the upper end 8 of the forearm tube 9
is inserted a cylindrical housing end 14 of an adapter 15, the
other end 16 of which has a pair of parallel opposed flanges
17 which project laterally 18 of the forearm tube 9. The
projecting flange portions 18 receive therebetween a worm gear
wheel 19 to which they are connected pivotally by a pivot pin
20. The worm gear wheel 19 has at one side a radially
outwardly projecting cylindrical plug adapter 21 which is
inserted and fixedly held (e. g. bonded, push-fit gripped,
screwed in, clamped etc) inside the lower end 6 of the upper
arm tube member 5 thereby fixedly holding the worm gear wheel.
Inside the cylindrical housing end 14 of the adapter 15 is
mounted a drive motor 22 (which may be provided with an
integral epicyclic gearbox 23) having a drive output shaft 24
on which is provided a worm gear 25 which extends between the
flanges 17 for driving tangential inter-engagement with the
worm gear wheel 19. The drive motor 22 is connected via
electrical contact means 26 in the wall of the forearm tube 9,
to the power supply control circuitry 27 of an annular battery
pack 28 which fits closely around the tube 9. When the drive
motor 22 is operated, the worm gear 25 draws itself and the
forearm tube 9 around the fixed worm gear wheel 19 in a
clockwise or anti-clockwise direction thereby swinging the
forearm 9 up or down from the upper arm 5. In a particularly
preferred form of embodiment the mounting of the fixed worm
gear wheel 19 and the driven worm gear 25 with its drive
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motor, is reversed i.e. the former is mounted on the forearm 9
and the latter is mounted in the upper arm 5.
Fig. 3 shows a wrist joint 30 which is of generally similar
construction to that of the elbow joint of Fig.2 albeit that
in this case it will be appreciated that the hand tube 12 will
be significantly shorter and may be somewhat smaller in
diameter than the forearm tube 9 insofar as the strength
requirements will be lower and a smaller motor 31 may be used.
As described in more detail with reference to Fig.4, the
support body for the fixed worm gear wheel 32 on the lower end
10 of the forearm tube 9 is conveniently in the form of a
rotary actuator connection 33 mounted on said lower end 10 of
the tube 9.
In more detail the rotary connection 33 comprises a fixed
stump portion 34 fixedly mounted in the distal end l0 of the
forearm tube 9 and having at its distal end 35 a ring gear 36.
A generally tubular wrist flexor support body 37 has an open
end portion 38 rotatably mounted on the stump portion 34 via
annular bearings 39 and a closed end portion 40 mounting on
its outside face 41 the wrist flexor fixed worm gear wheel 32,
and on its inside face 43 a spur pinion gear drive unit 44.
The drive unit 44 extends parallel to but offset from the
central longitudinal rotational axis of said support body 37
for driving engagement of the spur pinion gear 45 thereof with
the ring gear 36 so that operation of the drive motor 46 of
said drive unit 44 causes the wrist flexor support body 37 to
rotate about said stump portion 34.
With this kind of arrangement the cosmetic hand cladding which
is usually in the form of a suitably tinted silicone rubber
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glove 140 may be extended well up above the wrist joint itself
where it can readily be concealed under a patient's clothing,
the upper end 141 of the cladding 140 being simply supported
via an annular bearing arrangement 142.
By using movable gripping fingers 143 in which the drive
motors and gear means are mounted in the finger members
themselves (as described in our earlier patent publication No
W095/24875) - rather than inside the body of the hand i.e. the
palm portion of the prosthesis as with conventional prostheses
- it is now for the first time possible to provide a
prosthesis with wrist flexion together with wrist rotation and
mechanically operable fingers.
