192 clutches and power-stop control – Clutches – Transversely engaged
Reexamination Certificate
2002-11-06
2004-12-28
Lorence, Richard M. (Department: 3681)
192 clutches and power-stop control
Clutches
Transversely engaged
C192S026000, C192S04100R
Reexamination Certificate
active
06834752
ABSTRACT:
TECHNICAL FIELD
This invention relates to a dynamic electromechanical orthotic or prosthetic device with a wrap spring clutch.
BACKGROUND
Many amputees and patients with partial or complete paralysis of the extremities require assistive technology such as, for example, prostheses or orthoses, respectively (referred to herein by the general term orthosis or orthotic device), to enhance mobility.
For example, to function efficiently, the lower extremity should have the ability to: (1) support body weight during the stance phase of the locomotion cycle (when the foot is in contact with the ground); (2) rotate and coordinate the joints to achieve forward progression; (3) adjust limb length by flexing the knee during the swing phase of gait (when the foot is not in contact with the ground); and (4) further smooth the trajectory of the center of gravity by slightly flexing the knee in mid-stance.
To provide efficient locomotion, a knee-ankle-foot orthotic (KAFO) must restrain knee joint flexion at heel strike though the stance phase of the gait while also permitting free knee flexion during the gait swing phase. KAFOs with electromechanical knee restraint components utilize a wide variety of electronically controlled mechanical clutch and brake designs to provide knee control during walking. One successful design includes a small, lightweight, electronically controlled knee lock mechanism that can be installed on a conventional KAFO. Referring to
FIG. 1
, the KAFO device
10
includes an orthotic with an upper portion
12
with a thigh cuff
14
and thigh retaining straps
16
, as well as a lower portion
18
with a lower leg/foot cuff
20
and corresponding foot retaining straps
22
. A medial thigh strut
24
and a medial shank strut
26
are connected by a conventional hinge
28
at the knee joint on the medial side of the device
10
. On the lateral side of the device, a lateral thigh strut
30
connects to the thigh cuff
14
and extends outwardly at a bend
32
to engage the output hub
36
of a knee hinge clutch mechanism
34
. The input hub
38
of the clutch mechanism
34
is connected to a generally straight lateral shank strut
40
joined to the lower leg/foot cuff
20
.
Referring to
FIG. 2
, the clutch mechanism
34
is a wrap spring clutch. Wrap spring clutches are a known class of overrunning clutches that allow torque to be transmitted from one shaft to another in only one direction of rotation. The clutch mechanism
34
includes a cylindrical input arbor
42
attached to the input hub
36
, a cylindrical output arbor
44
attached to the output hub
38
, and a cylindrical spring
46
having turns with a substantially square cross sectional shape. The input arbor
42
and the output arbor
44
are the same diameter and maintained end-to-end in an abutting relationship by a retaining clip (not shown), and rotate on a common axis. This rotational axis, referred to herein as the flexion extension axis
48
, is collinear with respect with the rotational axis of the medial hinge
28
(See FIG.
1
). The spring
46
is connected to the output arbor
44
, slips on the input arbor
42
and acts as self-engaging brake between them. If a torque is applied to the input hub
36
in the direction of arrow A, the spring
46
wraps down tightly onto the shaft formed by the abutting input arbor
42
and the output arbor
44
, which locks the input arbor
42
and the output arbor
44
together and locks the lateral electromechanical knee joint. Conversely, when torque is applied in a direction opposite arrow A, the spring
46
unwraps from the shaft formed by the input arbor
42
and the output arbor
44
, which permits the shaft to slip easily in the opposite direction and allows the electromechanical knee joint to swing freely. If the input arbor
42
and the output arbor
44
are under load and must be disengaged, a control tang
50
on the spring
46
may be moved in the direction of arrow B to release the spring
46
.
Referring again to
FIG. 1
, a circumferential control collar
52
around the spring
46
engages the control tang
50
. The control collar
52
is engaged via a turnbuckle
54
attached to the output member of an electrically actuated linear solenoid
56
mounted on the lateral thigh strut
32
. The linear solenoid
56
is controlled by an electronic control system
58
attached to the belt of the wearer. The control system
58
receives electrical input signals from an arrangement of two sets of foot contact sensors and, based on these signals, generates electrical output signals to control the solenoid
56
. The first set of sensors
60
,
62
are force sensitive resistors mounted on the underside of the lower leg/foot cradle
20
, and provide varying electrical input signals to the control module
58
dependent on the degree of contact between the cradle
20
and a walking surface. The second sensors are attached on the underside of the wearer's opposite foot (not shown in
FIG. 1
) and provide varying electrical input signals to the control module
58
dependent on the degree of contact between the opposite foot and the ground. A combination logic network in the electronic control module
58
monitors electrical output commands based on the inputs from the foot sensors on the orthotic and the opposite foot. Based on the input from the sensors, a controller algorithm generates an actuation signal that is sent to the solenoid
56
for release of the clutch mechanism
34
during the swing phase of the gait.
The prosthetic/orthotic device
10
shown in
FIGS. 1-2
provides an articulated knee joint system that reduces metabolic energy requirements during gait. The locking action of the clutch
34
provides knee stability during stance while allowing free knee motion during the swing phase of gait.
SUMMARY
The orthotic device illustrated in
FIGS. 1-2
provides significantly enhanced performance compared to a conventional fixed knee orthosis. However, the extremely wide lateral profile of the clutch
34
makes the device
10
unattractive and difficult to wear under clothing such as trousers or skirts. In addition, the offset between the lateral thigh strut
30
and the lateral shank strut
40
increases torsional loading at the joint compared to conventional in-line braces. The foot sensors attached to both the device
10
and the opposed foot of the wearer are both unattractive and inconvenient to connect/disconnect.
The invention provides a wrap spring clutch with a significantly reduced lateral profile, which makes an orthotic device using the clutch much more attractive to wear under clothing. The reduced lateral profile and adjacent input/output frames of the clutch also reduce torsion in the lateral knee joint region. The wrap spring clutch provides bi-directional rotation, multiple locking positions, self-engagement and simple disengagement under load with very little energy input from a power source such as a battery. The wrap spring clutch design also provides a fail-safe locking mechanism if power fails. The low profile clutch design makes the device easy to use, and, consequently, more patients requiring the assistance of an orthotic device would be more likely to actually wear it on a daily basis. The unilateral input from sensors on the orthotic device renders unnecessary the extra set of wires and sensors that previously encumbered the wearer's contralateral foot, and also greatly simplifies attachment and removal of the device.
In one aspect, the invention is a clutch including an output hub on an output frame, and an input shaft on an input frame, wherein the input shaft rotates within a bore in the output hub. An input hub is attached on an end of the input shaft, and a spring engages the input hub and the output hub. A circumferential spring clamp secures the spring to the input hub such that the input frame and the output frame are adjacent to one another on a side of the clutch opposite the input hub.
In another aspect, the invention is an orthotic joint control apparatus, including a clutch with an output hub on an output frame and
Irby Steven E.
Kaufman Kenton R.
Fish & Richardson P.C. P.A.
Lorence Richard M.
Mayo Foundation for Medical Education and Research
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