U.S. patent number 3,769,636 [Application Number 05/249,654] was granted by the patent office on 1973-11-06 for end point control of upper extremity orthotic brace using head orientation.
This patent grant is currently assigned to Iowa State University, Research Foundation. Invention is credited to Jon H. Friedman.
United States Patent |
3,769,636 |
Friedman |
November 6, 1973 |
END POINT CONTROL OF UPPER EXTREMITY ORTHOTIC BRACE USING HEAD
ORIENTATION
Abstract
An end-point control of an upper-extremity orthotic brace
employing head orientation is disclosed herein which is
particularly well suited for quadriplegics who are able to spend
some portion of their day in a wheel chair. A first gimbal is
detachably secured to the patient's head by means of a head strap
or the like and is interconnected by a shaft to a second gimbal
which is secured to the wheel chair. The first and second gimbals
have responsive means thereon such as single turn potentiometers
which are responsive to azimuth, elevational and range movements of
the patient's head. A control system is connected to the
potentiometers for driving a powered device such as an arm brace so
that the patient can control the operation of the arm brace through
coordinated head movements.
Inventors: |
Friedman; Jon H. (Mundelein,
IL) |
Assignee: |
Iowa State University, Research
Foundation (Ames, IA)
|
Family
ID: |
22944431 |
Appl.
No.: |
05/249,654 |
Filed: |
May 2, 1972 |
Current U.S.
Class: |
623/24; 623/57;
414/9; 601/23 |
Current CPC
Class: |
A61G
5/125 (20161101); A61F 4/00 (20130101) |
Current International
Class: |
A61F
4/00 (20060101); A61G 5/12 (20060101); A61G
5/00 (20060101); A61f 001/00 () |
Field of
Search: |
;3/1-1.2,12,12.8
;128/25R,26,77 ;214/1CM |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"Electrically Powered Orthotic Systems" by Vernon L. Nickel et al.,
The Journal of Bone & Joint Surgery, Vol. 51-A, No. 2, March
1969, pages 343-351..
|
Primary Examiner: Gaudet; Richard A.
Assistant Examiner: Frinks; Ronald L.
Claims
I claim:
1. In combination,
a chair means for supporting a patient therein;
a first gimbal means for detachable connection to the patient's
head,
a second gimbal means secured to said chair means,
interconnection means interconnecting said first and second gimbal
means for sensing movement of said first gimbal means in response
to head movement,
said first and second gimbal means having responsive means thereon
which is responsive to azimuth, elevational and range movements of
the patient's head,
a powered device,
and a control system connecting said responsive means and said
powered device to permit the patient to control the operation of
the device by head movements.
2. The combination of claim 1 wherein said powered device is an
orthotic brace.
3. The combination of claim 2 wherein said brace is an upper
extremity brace.
4. The combination of claim 1 wherein said chair means is a powered
wheel chair, said control system being mounted on said wheel
chair.
5. The combination of claim 1 wherein said interconnection means
comprises a shaft.
6. The combination of claim 1 wherein said responsive means
comprises potentiometers which are operatively secured to said
first and second gimbal means.
7. The combination of claim 5 wherein said first gimbal means
comprises first and second supports which are pivotally movable
with respect to each other, said responsive means on said first
gimbal means comprising first and second potentiometer means
connected to said first and second supports and being responsive to
relative movement of said supports.
8. The combination of claim 7 wherein said second gimbal means
comprises a third support secured to said chair means, a fourth
support pivotally secured about a horizontal axes to said third
support and a fifth support pivotally secured about a vertical axes
to said fourth support, said fifth support being secured to said
shaft and being movable therewith during the elevational and
azimuth movements of the patient's head, said responsive means
comprising third and fourth potentiometer means operatively secured
to said third and fourth supports, said third potentiometer means
being responsive to relative movements of said fourth support with
respect to said third support, said fourth potentiometer means
being responsive to relative movement of said fifth support with
respect to said fourth support.
9. The combination of claim 8 wherein a fifth potentiometer means
is operatively secured to said shaft which is responsive to
longitudinal movements thereof.
10. In combination,
a chair means for supporting a patient therein;
a first support means for detachable connection to the patient's
head,
a second support means secured to said chair means,
interconnection means interconnecting said first and second support
means for sensing movement of said first support means in response
to head movement,
said first and second support means having responsive means thereon
which is responsive to azimuth, elevational and range movements of
the patient's head,
a powered device,
and a control system connecting said responsive means and said
powered device to permit the patient to control the operation of
the device by head movements.
Description
In recent years an increasing number of people are surviving
accidents or neuromuscular diseases with extensive paralysis.
Typically such disability occurs in persons who have suffered
poliomyelitis, muscular dystrophy, cerebral palsy, or lesions in
the fourth or fifth cervical spinal cord region. Even though modern
medicine is conquering polio through vaccination, there are an
increasing number of paralysis victims resulting from automobile
accidents and hostilities such as Vietnam.
Quadriplegics, those experiencing paralysis of all four limbs, are
normally bedridden, but may spend some portion of their day wheel
chair bound. Generally, such patients while lacking function in
their upper-extremities do retain normal muscular control from
their shoulders upward including, in some cases, the ability to
raise and lower the shoulder girdle.
The problem of restoring limited function by means of external
mechanical devices, termed upper-extremity orthotics, is complex
for any such mechanism must be built to follow the anatomical
joints and support the flail extremity along with performing nearly
normal upper-extremity motion. The control of such an orthotic
device is particularly difficult for severely handicapped patients
requiring multi-degree of freedom assistive braces and possessing
few functional residuals for control signal sources.
The rehabilitation of upper-extremity function through orthotic
devices is doubly challenging for any solution must be both
technologically sound and psychologically acceptable to the
patient. Realistically, one must accept the fact that a mechanical
device will never satisfactorily substitute for a normally
functioning limb. However, the objective of the rehabilitation of a
patient is not to enable him to perform tasks more efficiently than
could be done by an attendant, but is to provide some degree of
functional independence and associated personal satisfaction. It is
of psychological advantage to allow the patient continuous
voluntary control over the system rather than merely initiating a
fully automated sequence even though its performance might be
superior. From a purely mechanical standpoint, it would be much
easier to design a manipulator which would execute a programmed
routine, but it is generally agreed that mobilizing an existing arm
and actively involving the quadriplegic in the control system are
beneficial in minimizing the feeling of being a "mechanical man"
and encouraging any possible increase in residual limb
function.
During the past decade researchers have developed numerous
upper-extremity orthotics to provide partial return of arm function
to severely paralyzed patients. Although designers have shown
awareness of control and feedback, their primary attentions have
been directed toward the powering and fitting of assistive devices.
Present state of the art is such that the necessary hardware can be
built; but there are serious problems involved in designing
effective control systems. At the present time such control systems
are in a rudimentary stage.
Investigations have been conducted in many areas including studies
regarding brace configuration, actuator types, modes of control,
and suitability of various control sites. It appears that the only
complete agreement among researchers concerning these topics is
that there is general disagreement regarding the correct approach
to the problem.
Arm function is extremely complex; in fact, there are eleven
degrees of freedom in the arm not including the hand. The trend in
the development of orthotic brace configurations has been to
increase the number of degrees of freedom in the hope of providing
a more flexible and functional brace. One of the latest devices,
the Rancho Electric Arm, has 7.degree. of freedom which is thought
by some investigators to be the minimum number required to restore
reasonable arm movement. These seven joints include two joints at
the shoulder, two at the elbow (one flexion/extension and the other
humeral rotation), forearm rotation, wrist flexion and hand
prehension. However, generally associated with an increase in the
number of degrees of freedom is an undesirable increase in the bulk
of the brace and complication of the control system.
The decision regarding whether to use pneumatic or electrical
actuators to operate an orthotic brace is not clear-cut even though
several studies have been conducted in this area. However, both
types of actuators have been used successfully and their
performance is comparable. The most widely used external-power
source has been CO.sub.2 gas in the pneumatic systems. The
actuators for these systems are pistons and McKibben artificial
muscles. More recently electrical systems have been used with
permanent magnet 24 volt D.C. motors as actuators.
Studies in the past have concentrated on two basic approaches:
first, to operate an orthotic brace completely by direct patient
control, and second, to make such control fully automatic. In
direct control schemes, the patient excercises continuous control
over the motion of the assistive device. Automatic control, once
initiated allows a movement to progress to its completion without
further conscious attention. There are obvious problems with both
methods.
Direct patient control is difficult because of the number of
degrees of freedom which must be controlled. Devices in this
category presently require separate sites or switches to control
each joint of the brace. The disadvantages of this type of system
are that coordinated motion of the brace is difficult since
multiple sites must be activated simultaneously and smooth
positioning of the brace is relatively unobtainable with an on-off
control system. The results of one study indicate that a polio
patient required 150 motions to take five bites of food and 45
motions to pick up a cup and drink from it using the direct type of
control. In general, presently developed systems require a degree
of mental attention that is excessive, particularly in terms of the
frequently unnatural motion that results.
On the other side of the spectrum is the completely automatic
device in which the patient simply selects which one of several
programmed motions will be performed. There are several problems
associated with this approach including reduced adaptability due to
a limited number of movement sequences, the expense of peripheral
equipment normally associated with such a system, and substantially
reduced patient participation.
In recent years, one of the most active areas of interest has been
in discovering anatomical sites which are suitable for generating
control signals. Many exotic control sources have been proposed for
severely paralyzed patients having limited effector sites. In
general, higher order quadriplegics have only the following control
sites available: relative motions of body parts above the
shoulders, electromyographic signals (EMG), electroneurographic
signals (ENG), electroencephalographic signals (EEG), and sound or
speech.
Investigators have considered several schemes for transforming
relative motion of parts of the body into usable signals. Included
among these studies have been attempts to use head motion to
actuate simple arrays of switches, a light source attached to
eyeglasses that may be directed to activate appropriate photocells,
and switches activated by eyebrow motion. One of the most commonly
used techniques has been the operation of a switch or strain gauge
array by means of the tongue. One of the latest approaches has been
an attempt to use eyeball motion as the signal source. This method
utilizes the fact that light shining on the eye is reflected back
toward the source in varying amounts depending on the eye
orientation. Eye motion will eventually be used to generate signals
for azimuth and elevation inputs to a coordinate converter.
Preliminary findings indicate that drift, blinks, and light
intensities will be a major source of problems.
Electromyographic signals, the electrical activity associated with
muscle activity, have been used in various control schemes. The
main problem with such systems has been the excessive amount of
effort required to activate multiple sites in comparison to the
minimal function provided. Electroneurographic signals, the
potential activity from the nerves, and electroencephalographic
signals, the potential activity of the central nervous sytem, have
been proposed as signal sources, but present techniques and signal
pattern recognition problems make them impractical. The use of
sound or speech to activate electrical circuits by using acoustical
filters appears feasible, but again the control of several
actuators by this method would be difficult and its operation would
limit communication of the patient during brace operation.
The state of the art is such that systems presently developed or
being developed provide limited restoration of upper-extremity
function, but either require extreme effort to generate coordinated
motion or totally lack active patient participation.
Therefore, it is a principal object of this invention to provide an
end-point control of an upper-extremity orthotic brace using head
orientation.
A further object of this invention is to provide a means for
controlling a powered device using head orientation.
A further object of this invention is to provide a gimbal which is
secured to the patient's head by a head strap and which is
interconnected by a shaft to a second gimbal which is secured to
the wheel chair, the gimbals and shaft permitting the reading of
azimuth, elevational and range changes in the head position.
A further object of this invention is to provide a device having
two sets of gimbals to measure the actual angles of azimuth and
elevation as referenced to the wheel chair.
A further object of this invention is to provide a control system
for operating an orthotic brace through vertical, horizontal and
rearward and forward head movement.
These and other objects will be apparent to those skilled in the
art.
This invention consists in the construction, arrangements and
combination of the various parts of the device, whereby the objects
contemplated are attained as hereinafter more fully set forth,
specifically pointed out in the claims, and illustrated in the
accompanying drawings, in which:
FIG. 1 illustrates the end-point coordinates;
FIG. 2 is a side view illustrating the end-point control of an
upper-extremity orthotic brace;
FIG. 3 is a top view of the gimbal arrangement;
FIG. 4 is a front view of the fixed gimbal;
FIG. 5 is a front view of the head mounted gimbal;
FIG. 6 schematically illustrates the manner in which the elevation
angle is measured;
FIG. 7 schematically illustrates the brace axes;
FIG. 8 is a schematic illustration of the control system;
FIG. 9 is a schematic illustration of the electrical circuitry of
the weighting circuit and comparator;
FIG. 10 is a schematic illustration of the electrical circuitry of
the pulse width modulating circuit; and
FIG. 11 is a schematic view of the electrical circuitry of the
motor drive circuit.
Based on the limitations of existing upper-extremity orthotic
systems, the design of an improved assistive device requires the
selection of a more suitable control site. The desire to initiate
movement of an orthotic device originates at some conscious level
in the central nervous system and takes the form of some voluntary
physical action. Head orientation is particularly suited as a
control site, since the head has its own vertical sensing element
and smooth control of head motion over a wide dynamic range is
possible.
Azimuth, elevation, and radius of action together generate a
vector-distance function that can serve to specify the end-point
coordinates or an orthotic brace. This end-point coordinate system,
shown in FIG. 1, is in the form of spherical coordinates. Positions
of the hand that are normally traversed in routine self-care
activities may be specified in terms of this vector-distance
function.
An array of transducers was designed and constructed to provide a
continuous measurement of the angular orientation of the head
together with a simulated signal of "desired range" based on head
position. This device is shown in FIG. 2 and is generally
identified by the reference numeral 10. Device 10 generally
consists of two gimbals 12 and 14 interconnected by a small
aluminum shaft 16 which senses movements of gimbal 12.
Gimbal 12 is strapped to the patient by an elasticized headband 18
and the second gimbal 14 is attachd to a mounting 20 on the back of
the wheel chair 22. The device allows the patient to rotate his
head approximately 100.degree. in the vertical plane and 80 degrees
in the horizontal plane with negligible restraint. The only
significant restriction is in the forward-backward motion of the
head which is limited to approximately two inches of travel by the
range transducer.
It is necessary to use two sets of gimbals to measure the actual
angles of azimuth and elevation as referenced to the wheel chair.
As shown in FIG. 6, the true elevation angle is obtained by adding
the corresponding angles of both gimbals. This same relationship
holds true for measuring azimuth. Thus, the gimbal 14 mounted on
the wheel chair measures the necessary correction to account for
the fact that the gimbal 12 strapped to the patient measures angles
with respect to the interconnecting shaft 16 rather than to a fixed
set of axes.
A radius of action or "desired range" is simulated by the patient's
relative forward-backward positioning of his head which is
converted from a linear displacement of the interconnecting shaft
16 to the rotation of potentiometers 24 and 24'. Minimum range is
selected by the patient moving his head to the most forward
position, a somewhat natural eating posture. Range is increased by
the patient moving his head backward.
More specifically, gimbal 12 comprises a U-shaped yoke 28 which is
strapped to the patient's head. The legs 30 and 32 of yoke 28 have
potentiometers P.sub.E mounted thereon respectively which are
operatively connected to the shafts 34 and 36 extending inwardly
from legs 30 and 32 respectively. The inner ends of shafts 34 and
36 are rigidly secured to sides 38 and 40 of block 42.
Potentiometers P.sub.A are mounted on the top and bottom portions
of block 42 and are operatively connected to the shafts 44 and 46
extending from block 42. The inner ends of shafts 44 and 46 are
rigidly secured to support 48 which is secured to shaft 16. Thus,
movement of the patient's head is an upwardly direction causes yoke
28 to rotate or pivot with respect to shafts 34, 36 and the block
42. Such movement of yoke 28 causes the shafts 34 and 36 to change
the resistance of the potentiometers P.sub.E due to their
connection with the shafts 34 and 36.
Movement of the patient's head in a sideway manner causes yoke 28
to in turn rotate or pivot block 42 with respect to support 48 and
shafts 44, 46. Such movement causes shafts 44 and 46 to change the
resistance in the potentiometers P.sub.A due to the connection
therewith. Forward or backward movement of the patient's head
causes shaft 16 to be correspondingly moved. The patient can
simultaneously control potentiometers P.sub.A and P.sub.E by moving
his head sideways and vertically.
Gimbal 14 comprises a U-shaped yoke 50 which is secured to the
wheel chair. The legs 52 and 54 of yoke 50 have potentiometers
P.sub.E mounted thereon respectively which are operatively
connected to the shafts 56 and 58 extending inwardly from legs 52
and 54 respectively. The inner ends of shafts 56 and 58 are rigidly
secured to sides 60 and 62 of block 64. Potentiometer P.sub.A is
mounted on the top of block 64 and is operatively connected to the
shaft 66 extending from block 64. A shaft 68 also extends from
block 64. The inner ends of shafts 66 and 68 are rigidly secured to
support 70. Shaft 16 slidably extends through support 70.
Rotational movement of shaft 16 causes pivotal movement of support
70 by means of a keyway arrangement. Support 70 has a pair of
rearwardly extending legs 72 and 74 having the range potentiometers
P.sub.R mounted thereon. The shafts 76 and 78 are connected to the
potentiometers P.sub.R and have a gear or roller 80 mounted thereon
which engages the shaft 16 to sense any longitudinal movement of
the shaft 16.
Thus, elevational movement of the patient's head causes shaft 16 to
pivot support 70 and block 64 with respect to yoke 50 so that the
resistance in the elevation potentiometers P.sub.E is changed.
Sideways movement of the patient's head causes shaft 16 to pivot
support 70 with respect to block 64 to change the resistance in the
azimuth potentiometers P.sub.A. Longitudinal movement of shaft 16
(range) causes the resistance to be changed in the range
potentiometers P.sub.R.
Head orientation is well suited as a control site because of the
ease in measuring a set of coordinates which fully specify the
desired end-point of an orthotic brace 26. This natural signal
source requires minimal concentration, effort, and training to
activate. It allows a patient to directly control the trajectory of
an assistive device through head motion, is cosmetically
acceptable, and places few restrictions on patient movement.
The orthotic brace 26 is shown in FIG. 2 and is readily available.
The brace 26 was originally designed as a pneumatically actuated
feeder but has been converted to electric motor drive. Electrical
actuators are preferred since there is a ready source of battery
power in the electric wheel chairs.
The orthotic brace 26 allows for three powered motions; a
horizontal displacement, a vertical displacement, and an elbow
flexion/extension. The horizontal and vertical displacements are
completely independent motions and together contribute to the
abduction/adduction and flexion/extension of the upper arm. A
coiled spring lessens the effects of gravity by assisting in the
vertical support of the brace and the arm. A telescopic rod and
tube connected to the elbow flexion/extension unit serves as an
attachment for the hand support. A molded elbow and forearm trough
is attached to this unit and acts as a support for the forearm
which is held secure in the trough by a Velcro strap. There are
several sites for adjustment of the orthosis to assist in the
fitting of patienls.
The exact power requirements of upper-extremity orthotics are
difficult to define, not only because of the wide age span of
patients, but also because of variations in size from an atropied
limb to a normal limb. To allow for this wide range of torque
requirements permanent magnet motors with linear load-speed curves
are utilized with adjustable gain drive circuitry. These 24 volt
D.C. motors have planetary ger heads with a 639:1 gear reduction
and provide the capability of 288 oz. in. torque under continuous
load conditions. This type of motor is particularly desirable
because of its relative compactness and light weight. Although
there is some noise associated with their opeation, it is not
distracting and may provide some useful function as an audible
feedback.
All joints of the orthotic brace, three driven and one free, are
continuously monitored by transducers. These small potentiometers
provide measurements of the brace angles and are mounted with
couplings which allow easy adjustment for proper reference.
The control system was designed to be "volitional", "proportional",
and "vectorial". "Volitional" means the patient can start, stop, or
modify the course of action. "Proportional" control means that by
varying his motion the patient can control the rate of action or
the force exerted. Finally, "vectorial" control means that a
particular motion can be achieved in a smooth direct fashion rather
than in a sequence of motions about different axes.
The overall scheme behind this design involves the theory of
end-point control in which the parameter to be specified is
position and the control signal is in terms of a desired end-point.
Most simply stated, this system allows a patient to regulate the
location of his hand through head orientation. To fulfill the
requirements of end-point control it is necessary to generate
control equations which fully express the relationship between the
head oriented coordinates and those of the orthotic brace.
FIG. 7 is a diagrammatic representation of both the brace and head
oriented coordinate systems. The brace angles include: F, the motor
driven brace angle in horizontal displacement; G, a motor driven
brace angle in the vertical plane; and J, a motor driven angle of
elbow flexion/extension. The axis of rotation for angle J is offset
40.degree. from the vertical thereby giving this motion both a
vertical and horizontal component.
The equations expressing the relationship between the head oriented
coordinate system and the orthotic brace coordinate system, in
terms of a desired end-point (x, y, z), are as follows:
x: RcosEsinA = d.sub.1 cosGsinF + d.sub.2 sin(F+H) + (d.sub.3
cos.theta.+ (d.sub.3 -d.sub.3 cos.theta.)sinJ)sin(F+H+J) +
K.sub.x
y: RcosEcosA = d.sub.1 cosGcosF + d.sub.2 cos(F+H) + (d.sub.3
cos.theta. + (d.sub.3 -d.sub.3 cos.theta.)sinJ)cos(F+H+J) +
K.sub.y
z: RsinE = d.sub.1 sinG + d.sub.3 sin.theta.cosJ + K.sub.z
where,
d.sub.1 = 7 1/2inches
d.sub.2 = 7 1/2inches
d.sub.3 = 18 inches
.theta. = 40.degree.
The K.sub.x, K.sub.y, and K.sub.z terms account for the respective
x, y, and z displacements between the two sets of axes and are
dependent upon the adjustment of the brace in fitting a
patient.
However, these exact equations are relatively complex trigonometric
expressions and their solution requires considerable computational
equipment or a costly series of resolver chains in place of the low
cost potentiometers. At the sacrifice of some accuracy, but with
considerable cost reduction, a simplified set of control equations
are used. These equations are based on the geometry of the brace
along with some consideration for the natural motion that is being
simulated. The result of this simplification is an algorithm of
weighting factors which can be optimized to satisfactorily
duplicate natural arm motions and to minimize the error in the
end-point positioning of the brace with respect to head
orientation.
The horizontal and vertical displacements of this assistive device
are completely independent motions, but actuation of the elbow
flexion/extension unit results in both horizontal and vertical
components. A straightforward way of relating the head generated
signals of azimuth, elevation, and range to the motorized angles of
the brace is to assume that the elbow flexion/extension actuator is
primarily involved in changing the "desired range" of the hand.
This assumption is reasonably valid in that the actuators
controlling horizontal and vertical displacements by themselves
have minor effects in changing the radius of action of the hand.
Based upon these approximations, the actuator for horizontal
displacement, angle F, and the actuator for vertical displacement,
angle G, are coupled to "desired range" signals to compensate for
the fact that elbow flexion/extension has components besides range
associated with its motions. These greatly simplified control
equations are as follows:
A = K.sub.1 (F+H)
E = K.sub.2 G
R = K.sub.3 (F+H) + K.sub.4 G - K.sub.5 J
where all K terms are experimentally determined weighting factors.
There are two major sources of error which limit the accuracy of
this approach. First, the horizontal and vertical components
associated with elbow flexion/extension are not linear functions of
angle J as assumed in the equations above. And second, motions
produced by the horizontal and vertical actuators do have
components of range involved with their displacements which are not
reflected in the control equations. However, despite these
limitations the expressions appear to be useable.
FIG. 8 is a block diagram of the overall control system for one
motorized component. Azimuth, elevation, range, and appropriate
brace angles are weighted together by a resistive network and the
result, a computed angle, is compared to the actual brace angle.
This is accomplished by the differential amplifier arrangement
shown in FIG. 9. The two outputs of this circuitry are directly
related to the magnitude of the error existing between the desired
and the actual brace angle, but are inversely related to each other
about a 6 volt D.C. reference. The next stage of the electronics
consists of a pair of pulse width modulating circuits, shown in
FIG. 10. If an output from the comparator stage exceeds a
prescribed level, which is adjustable, the pulse width modulating
circuit will generate a signal with a duty cycle which is a
function of the error. Both the "dead zone" and the gain of this
circuit are adjustable thereby allowing the control sensitivity,
motor speed, and "dead zone" to be matched to the limitations and
requirements for a particular direction and speed of an actuator to
drive the error within an allowable range. Each of these circuits
is mounted on an individual printed circuit board and inserted in a
rack mounted on the back of the wheel chair. Two 12 volt D.C.
batteries, connected in series, are used as a power source for both
the motors and the electronics.
This control system acts as a simple servomechanism by which a
signal, computed angle, is compared with the actual position of a
joint and this error signal serves to operate actuators to null or
minimize that error. This design depends to some extent on visual
feedback for correcting errors in the positioning of the brace
which are a result of simplifying the control equations and in the
fine positioning required for performing precision tasks. Audio
feedback from the electric motors may be useful in sensing the
external load and/or the velocity of the limb.
The system disclosed herein provides the severely paralyzed patient
with a simple, low cost assistive device which can be operated with
minimal effort, concentration, and training. The key feature in
this design is the use of head orientation as the controlling
signal. This natural site of independent motion in azimuth and
elevation is cosmetrically acceptable, allows the patient to
excercise direct control of the orthotic brace, and greatly
simplifies the control problem by expressing all parameters in
terms of the desired end-point.
While the gimbal arrangement has been described herein as being
well suited for controlling devices such as an orthotic brace, it
should be noted that the gimbal arrangement could be used to
control devices other than orthotic braces. Head orientation could
be used by any patients with upper extremity handicaps to operate
manipulators, typewriters, etc.
Thus it can be seen that a novel system has been provided which
permits the severely paralyzed patient to operate a device through
the use of head orientation. Thus it can be seen that the device
accomplishes at least all of its stated objectives.
* * * * *