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Claims  |
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The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. The method of tracing the movement of a minor body in space in relation
to a major body that is also movable in space where the minor body is
connected to, and supported by, the major body in such a way that movement
of the major body is imparted to the minor body while the minor body is
movable in relation to the major body, comprising the steps of:
positioning a first light detector and a second light detector in immovable
positions and in fixed, spaced-apart relation to each other, where said
first and second light detectors each has a planar light-sensitive surface
that has the capability of generating electrical signals indicative of the
physical location where said light is incident on said light-sensitive
surface and a lens system for focusing a beam of light onto the
light-sensitive surface;
defining a first planar two-dimensional coordinate system for said first
detector for indicating the position of an incident light spot on the
light-sensitive surface of the first detector, and defining a second
planar two-dimensional coordinate system for said second detector for
indicating the position of an incident light spot on the light-sensitive
surface of the second detector;
defining a system frame of reference in terms of a three-dimensional
coordinate system by positioning a plurality of calibraiton light-emitting
sources in fixed, precisely measured spatial relation to each other in the
field of vision of the first and second detectors, detecting the positions
of said calibration light-emitting sources with the first and second
detectors, and calibrating the image coordinate systems of said first and
second detectors to correspond with the measured spatial relationships of
the calibration light-emitting sources;
attaching at least three major body light-emitting sources in fixed
spaced-apart relation to each other on said major body, and attaching at
least three minor body light-emitting sources in fixed spaced-apart
relation to each other on said minor body;
detecting the locations of said major body light-emitting sources and of
said minor body light-emitting sources in the system frame of reference
with said first and second detectors, and calculating three-dimensional
image coordinate designations for each of those locations as a function of
the respective first and second two-dimensional coordinates of the
incident light spots on the respective light-sensitive surfaces of the
first and second detectors;
transforming said coordinate designations of said minor body light-emitting
sources to a local major frame of reference defined by the positions of
said major body light-emitting sources by defining a local major
coordinate system that is fixed in spatial relation to said major body
light-emitting sources, defining a local minor body coordinate system that
is fixed in spatial relation to said minor body light-emitting sources,
and offsetting the local minor coordinates of the minor body
light-emitting sources with the local major coordinate system; and
moving the minor body in relation to the major body for a period of time
while detecting positions of both the major body light-emitting sources
and the minor body light-emitting sources and transforming coordinates of
the positions detected to the local major coordinate system.
2. The method of claim 1, including the tracking of a selected individual
point on the minor body, comprising the steps of:
positioning at least three pointer light-emitting sources on a rigid
pointer that has a pointer tip;
measuring precisely the spatial relations of said pointer light-emitting
sources to each other and to said pointer tip;
positioning said pointer tip on a selected point on the minor body to be
tracked;
detecting the locations of said pointer light-emitting sources along with
detecting the locations of said major and minor body light-emitting
sources;
calculating three-dimensional image coordinates for each of those locations
of the detected pointer, major body, and minor body light-emitting sources
as functions of the respective first and second two-dimensional
coordinates of the incident light spots on the respective light-sensitive
surfaces of the first and second detectors focused thereon from the
light-emitting sources;
determining the coordinates of said selected point in the minor local
coordinate system as a function of the spatial relations of said pointer
tip to said pointer light-emitting sources and as a function said pointer
light-emitting sources to said minor body light-emitting sources;
transforming the coordinates of said selected point and of said minor body
light-emitting sources to said major coordinate system;
moving the minor body in relation to the major body for a period of time
while detecting sequential positions of both the major body light-emitting
sources and the minor body light-emitting sources;
determining the coordinates of said selected point as a function of its
fixed spatial relation to the minor body light-emitting sources in
sequential positions of the minor body light-emitting sources as the minor
body moves; and
transforming the local minor coordinates of said selected point to the
local major coordinate system.
3. The method of claim 2, including the step of displaying said selected
point on a visual display device as a function of its local major
coordinates as it moves.
4. The method of claim 2, including the steps of defining an anatomic frame
of reference in fixed spatial relation to permanent anatomic reference
points on said major body and transforming the three-dimensional
coordinates of said major and minor body light-emitting sources from said
local major coordinates system to three-dimensional anatomic coordinates
in fixed spatial relation to said anatomic frame of reference.
5. The method of claim 4, including the steps of:
positioning said pointer tip sequentially on three selected permanent
anatomic reference points on said major body, and, with the pointer tip
positioned at each of said selected anatomic reference points, detecting
the locations of said pointer light-emitting sources along with detecting
the positions of the major body light-emitting sources;
defining an anatomic coordinate system in a fixed spacial relationship to
the positions of said anatomic reference points; and
using the spatial relationships of said anatomic reference points to said
major body light-emitting sources, transforming said local major
coordinate system of reference to said anatomic coordinate system of
reference.
6. The method of claim 5, including the steps of transforming the local
major coordinates of said selected point on said minor body being tracked
into three-dimensional coordinates in terms of said anatomic coordinate
reference system.
7. The method of claim 6, including the steps of selecting and placing the
pointer tip on additional points on the minor body in sequence,
determining the coordinates of these additional points in the anatomic
reference system, and tracing and recording these points in relation to
the anatomical coordinates of the minor body light-emitting sources as
they move with the minor body.
8. The method of claim 7, including the steps of displaying the movements
of the selected points on the minor body on a visual display device as a
function of the sequential anatomic reference coordinates of the selected
points as they move with the minor body.
9. The method of claim 8, including the steps of video recording in digital
data format the minor and major bodies simultaneously as the movements of
the selected points are being detected and recorded, merging the data of
the video image with the coordinate data of the selected points, and
displaying the video image of the moving major and minor bodies together
with an image of the moving selected points superimposed on each other and
moving together at the same speeds.
10. The method of claim 9, including the steps of determining the axis of
rotation of the minor body from the anatomic coordinate data of the moving
selected points on the minor body, and recording the anatomic coordinates
of the axis of rotation.
11. The method of claim 10, including the step of physically locating the
axis of rotation on the minor body by positioning said pointer tip
adjacent the minor body and moving it on said minor body while
continuously detecting the pointer light-emitting sources and determining
the anatomic coordinates of the pointer tip as it moves on the minor body
and continuously comparing these anatomic coordinates of the moving
pointer tip with the anatomic coordinates of the axis of rotation, and
providing a signal perceptible to a human sense when the anatomic
coordinates of the pointer tip coincide with the antomic coordinates of
the point of rotation.
12. The method of claim 2, including the step of positioning four pointer
light-emitting sources on said pointer.
13. The method of claim 12, including the step of positioning one of said
pointer light-emitting sources immediately adjacent said pointer tip and
positioning the other three pointer light-emitting sources more remote
from said pointer tip.
14. The method of claim 1, including the steps of:
sensing photovoltages at four points on diametrically opposite peripheral
sides of said light-sensitive surface of each of said first and second
detectors;
amplifying each sensed voltage immediately adjacent said light-sensitive
surface; and
converting said four amplified voltage signals from analog to digital form,
and determining orthogonal X and Y planar two-dimensional coordinates of
the position of the focused light spot on the light sensitive surface as a
function of respective photovoltage magnitudes at each lead, distances
between leads, and distances from the position of the focused incident
light spot to the respective leads.
15. The method of claim 14, including the steps of switching on only one
light-emitting source one at a time in a predetermined sequence and in a
predetermined time cycle, and detecting the light emitted by each
light-emitting source one at a time with said first and second detectors,
determining the three-dimensional image coordinates of each light-emitting
source simultaneously with detecting the emitted light as the
light-emitting source is turned on, and storing said coordinates along
with the time of detection.
16. The method of claim 15, including the step of averaging the coordinates
for four sequential detections of each light-emitting source and storing
the averaged coordinates.
17. The method of claim 14, including the steps of delaying determination
of the X and Y planar coordinates for a sufficient time for the
photovoltage induced by the incident light to stabilize.
18. The method of claim 17, including the steps of continuously detecting
the photovoltage induced by each incident light spot on the
light-sensitive surface and determining the rate of change of the voltage,
and, when the rate of change of the voltage decreases to a predetermined
threshold rate of change, initiating the step of determining the X-Y
planar coordinates.
19. The method of claim 1, including the steps of attaching four major
light-emitting sources on said major body, and attaching four minor
light-emitting sources on said minor body.
20. The method of claim 19, including the steps of attaching said four
major light-emitting sources in at least two different planes that are
spaced different distances from the detectors, and attaching said four
minor light-emitting sources in at least two different planes that are
spaced different distances from the detectors.
21. Mandibular movement monitoring apparatus for detecting, monitoring, and
analyzing movement of a person's mandible in relation to the person's
cranium as the cranium and the mandible move in space, said apparatus
comprising:
two photo detector means for detecting light spots incident on
photo-sensitive surfaces in a manner indicative of the specific position
of the incident light spot on the photo detector surfaces, said
photodetector means including lens means for focusing incident light onto
said photo-sensitive surfaces, and signal output means for outputting data
signals;
processing means for processing said incident spot data signals from said
detector means to determine three-dimensional spatial coordinates of the
sources of the incident light spots;
four upper light source means for producing light to be detected by said
detector means;
four lower light source means for producing light to be detected by said
detector means;
harness means for mounting said upper light source means in immovable
relation to the person's cranium and for mounting the lower light source
means in immovable relation to the person's mandible, said four upper
light source means being mounted in at least two different planes that are
different distances from said detector means, and said four lower light
source means being mounted in at least two different planes that are
different distances from said detector means;
pointer means for establishing spacial relationships of selected points on
the person's mandible and cranium in relation to said upper and lower
light source means, said pointer means including a rigid body with a
designated pointer tip thereon, first pointer light-emitting means
positioned immediately adjacent said pointer tip for emitting light from a
location close to said tip, and second, third, and fourth pointer
light-emitting means positioned more remotely from said pointer tip and in
precisely measured spaced-apart relation to each other, to said first
pointer light-emitting means, and to said pointer tip; and
displaying means for displaying selected points in terms of
three-dimensional coordinate reference systems.
22. The apparatus of claim 21, including a calibration cube having a
plurality of calibration light-emitting means mounted thereon in precisely
measured spatial relations to each other for calibrating said detector
means and said data processing means to a predetermined spatial reference
system defined by the positions of said calibration light-emitting means
on said calibration cube.
23. Harness apparatus for mounting LED's on a person's head, some of which
LED's are mounted in immovable relation to the person's cranium and some
of which LED's are mounted in immovable relation to the person's mandible,
comprising:
an upper frame comprised of an elongated upper cross bar, a nose piece
attached to the upper cross bar for supporting the upper frame on the
person's nose, two elongated ear bow members, one of which extends
rearwardly from one end of the upper cross bar and the other of which
extends rearwardly from the other end of the upper cross bar;
a lower frame comprised of an elongated lower cross bar, and a chin cup
attached to the lower cross bar for positioning under the person's chin;
two spaced-apart left side elastic bands, one of which extends between the
proximal end of the left ear bow and the lower cross bar and the other of
which extends from the distal end of the left ear bow to the left rear
corner of the chin cup;
two spaced-apart right side elastic bands, one of which extends between the
proximal end of the right ear bow and the lower cross bar and the other of
which extends from the distal end of the right ear bow to the right rear
corner of the chin cup;
a first upper LED bracket extending upwardly and forwardly from the left
end of the upper cross bar, a second upper LED bracket extending upwardly
and forwardly from the right end of the upper cross bar, a third upper LED
bracket extending laterally outward from the left ear bow, a fourth LED
bracket extending laterally outward from the right ear bow, and an LED
mounted on the distal end of each of said first, second, third, and fourth
upper LED brackets; and
a first lower LED bracket extending forwardly from the left end of said
lower cross bar, as second lower LED bracket extending forwardly from the
right end of said lower cross bar, a third lower LED bracket extending
upwardly from the left end of said lower cross bar, a fourth lower LED
bracket extending upwardly from the right end of said lower cross bar, and
an LED mounted on the distal end of each of said first, second, third, and
fourth lower LED brackets. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of tracking,
monitoring, and analyzing movement of a rigid body in three dimensions in
relation to another body as they both move in relation to a motion
detector, and more specifically to the tracking, recording, monitoring,
analyzing, and displaying the movement of a mandible in relation to a
cranium.
2. State of the Prior Art
The field of dental occlusion (closure of the jaws) is many-faceted and has
many implications, some of which researchers and practitioners have only
recently become aware, and such awareness is still growing. For example,
disfunctions of the temporal mandibular joint (TMJ) can be manifested in
such a widely varying symptoms as pain or noise in the TMJ itself,
headache, backache, vision impairment, and others. Therefore, it has
become important to be able to classify TMJ disfunctions for more
effective analysis and treatment and to be able to monitor the effects of
TMJ treatment. Other applications in this field of dental occlusion
include rehabilitation of the occlusion by restorative, orthodontic,
and/or surgical means, as well as the construction of prosthetic devices.
The problem of measuring and analyzing the physical relationship between
the upper and lower jaws during the processes of speech, mastication
(chewing), and deglutition (swallowing) is crucial to this field and study
of dental occlusion. For example, the following relationships and motions
are significant to researchers and practitioners working in this field:
(1) Envelopes of motion of the mandible during normal speech and chewing,
and during maximum extension.
(2) Movement of the condyles within envelopes of possible movement as the
patient chews, speaks, or swallows.
(3) Similarities and differences in condyle displacement between rest
position and "centric relation" in different individuals.
(4) Mandibular velocities during various functions.
(5) Asymmetries of movement during functional activity.
(6) Changes in functional activity and border movement after various types
of therapeutic intervention.
Mechanical articulators have been used to advance knowledge of relative jaw
movement. See, e.g., B. B. McCollum, "Gnathology, A Research Report,"
Scientific Press, Pasadena, Calif. (1955), and by W. G. A. Bonwill, The
Scoentific Articulation of the Human Teeth as Founded on Geometrical,
Mathematical, and Mechanical Laws, 8 J. PROSTHETIC DENTISTRY 41 (1958). An
empirical approach published by N. G. Bennett, A Contribution to the Study
of the Movements of the Mandible, 21 DENT. ITEMS OF INTEREST 617 (1899),
was another important early step in this field. L. E. Kurth, Centric
Relations and Mandibular Movement, 50 JADA 309 (1955), B. Jankelsen,
Physiology of the Human Dental Occlusion, 50 JADA 664 (1955), and U.
Posselt, "Physiology of Occlusion and Rehabilitation", F. A. Davis Co.,
Blackwell Scientific Publication, Philadelphia, at 44 (1962), were more
functionally oriented studies of dental occlusion. A significant report in
which the limits of movements of the condyle heads were defined by using a
series of wax check bites with the teeth held in different positions of
opening and eccentricity is found in U. Posselt, Movement Areas of the
Mandible, 7 J. PROSTHETIC DENTISTRY 368 (1957).
While all of the developments described above represented significant
advances in the study and understanding of dental occlusion, they were
based on methods that used bulky intra-oral mechanical components to
acquire mandibular movement data. Such bulky, cumbersome instrumentation
introduced distortions into the masticatory (chewing) pattern resulting in
data that was somewhat skewed from a person's normal mandibular movement
patterns. Also, the data were not stored and were not available for
subsequent analysis.
Consequently, more recent efforts in this field have moved in the direction
of trying to gather more accurate data for occlusion analysis. One such
development utilizes a magnet mounted on a patient's tooth, and a system
of antennae positioned on either side of the patient's head pick up
signals indicative of the tooth. However, this type of system is limited
to tracking a single point. Therefore, three-dimensional movements of the
entire mandible cannot be determined.
Another type of system uses rigid stylii, attached to the mandible, which
move against a resistive foil recording surface. A variation of this kind
of system uses three styli attached to the teeth and three orthogonal
sensor surfaces. See S. Hobo & S. Mochizuki, A Kinematic Investigation of
Mandibular Border Movement by Means of an Electron Measuring System, Part
I: Development of the Measuring System, 50 J. PROSTHETIC DENTISTRY 368,
No. 3 (1983), and S. Hobo, A Kinematic Investigation of Mandibular Border
Movement by Means of an Electronic Measuring System, Part II: A Study of
the Bennett Movement, 51 J. PROSTHETIC DENTISTRY 642, No. 5 (1984). This
kind of system is quite constraining to the patient, and computation of
condylar paths is slow.
Researchers in this field are now recognizing that recording and display of
mandibular movements should be performed on a real-time basis in order to
have real clinical utility. The approach to the mandibular movement
problem considered to be the most flexible at the present time involves
the tracking of light emitting diodes (LED's) on the mandible using
various kinds of detectors. These LED tracking systems can produced
three-dimensional coordinates that can be plotted in various planes,
displayed graphically on a computer monitor, and stored for later
analysis.
There are a number of variations in the mean of attaching the LED's to the
mandible and in the types of detection and computing hardware employed.
For example, a single LED on a patient's mandible has been used. See T.
Jemt, Chewing Patterns in Dentate and Complete Denture Wearers Recorded by
Light Emitting Diodes, 5 SWED, DENT. J. 199 (1981), S. Karlsson, Recording
of Mandibular Movements by Intra-orally Placed Light Emitting Diodes, 35
ACTA. ODONT. SCAN. 111 (1977), and A. Ekfeldt, T. Jemt & L. Mansson,
Interocclusal Distance Measurement Comparing Chin and Tooth Reference
Points, 47 J. PROSTHETIC DENTISTRY 560, No. 5 (1982). Another approach
uses clutch-mounted (fastened to teeth) LED's and three linear array
detectors with 2,048 diodes on each detector, and three-dimensional
coordinates are computed by a specialized hardware interface and displayed
on a graphics screen. See F. Mesqui, F. Kaeser & P. Fisher, On-line
Three-dimensional Light Spot Tracker and Its Application to Clinical
Dentistry, PROCEEDINGS, BIOSTERIOMETRICS, at 310 (1985), and S. Palla, B.
Ernst & F. Mesqui, The Condylar Path of Clicking Joints, IADR ABSTRACT 145
(1986).
The present inventors also reported the use of a non-restraining head
harness comprises of an upper component mounted on the cranium and a lower
component mounted on the lower jaw and fastened together by elastic
connectors. Three LED's were mounted on the upper component, and three
LED's were mounted on the lower component. The LED positions were detected
by two detectors and computed in three dimensions using photogrammetric
techniques. See S. Curry & S. Baumrind, Real Time Monitoring of the
Movement of the Mandible, 4 PROCEEDINGS, AMERICAN SOCIETY OF
PHOTOGRAMMETRY 99 (1986). These developments, while significant in some
sense, also highlighted the substantial shortcomings of the then-existing
technology.
In spite of the work and studies described above, all of which have
incrementally advanced the state of this art prior to this invention,
there still remained a need for additional improvements to attain a system
that would monitor the movements of the human mandible more accurately and
more efficiently in three dimensions. For example, in order to obtain more
realistic, natural results, the patient needs to be allowed maximum
freedom of movement with a minimum of constraint on his/her natural head
movement activity, yet the detectors must be able to detect the mandibular
movement accurately, in spite of such freedom of movement. The LED's have
to be mounted in more secure, immoveable, and stable relation to the
patient's lower jaw and cranium, yet maintain maximum comfort and minimum
constraint against movement. More accurate and efficient data processing
and controls, as well as improved and useable displays of results, are
imperative for any feasible and useful application. Also, improved
tracking of individually selected points, as well as an ability to find or
pinpoint specific desired points in a predictable, repeatable manner were
still required prior to this invention, as well as an ability to repeat
measurements of specific points, axes of rotation, and the like, at a
later date, and compare them to prior data.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of this invention to provide an
efficient and accurate system for monitoring and displaying movements of a
plurality of solid objects in relation to each other as they also move
together in relation to a detector system.
A more specific object of the present invention is to provide an efficient
and accurate method and apparatus for monitoring and displaying movements
of a person's mandible in relation to the cranium as both are free to move
together in relation to a detector system.
Another specific object of the present invention is to provide a method and
apparatus for tracing the movement of any selected point or plurality of
points on one of two rigid objects moving in relation to each other, such
as on the mandible as it moves in relation to the cranium.
Still another specific object of the present invention is to provide a
method and apparatus for determining the center of rotation of one rigid
object at any instant in time and to display the movement of the center of
rotation in real time in relation to another object.
Yet another object of the present invention is to provide a method and
apparatus for guiding an external indicator to a preselected point on a
person's mandible in an accurate, repeatable manner for subsequent
monitoring of movement of that preselected point.
It is an object of the present invention to provide a method and apparatus
for superimposing a graphic representation of the movement of selected
points on a person's mandible in conjunction with a video image of the
person's face as he/she moves his/her jaw in speech, chewing, and
swallowing processes.
It is another object of this invention to provide an improved, more
comfortable harness apparatus for mounting LED's on a person's face in a
manner that secures the LED's in substantially immovable relation to
selected parts of the person's face, such as the cranium and mandible.
It is still another object of this invention to provide a more sensitive
and efficient detector system for monitoring and recording movement of
objects.
Additional object, advantages, and novel features of this invention are set
forth in part in the description that follows, and in part will become
apparent to those skilled in the art upon examination of the following
specification or may be learned by the practice of the invention. The
objects and advantages of the invention may be realized and attained by
means of the instrumentalities and in combinations particularly pointed
out in the appended claims.
To achieve the foregoing and other objects and in accordance with the
purposes of the present invention, as embodied and broadly described
herein, the method of this invention may comprise detecting the movements
of a plurality of LED's mounted on major and minor bodies that are
connected together to monitor and analyze movements of the minor body with
respect to the major body as they bodh move in space. The invention
includes steps of establishing and calibrating a three-dimensiional system
frame of reference, local three-dimensional frames of reference within the
system frame of reference for the LED's mounted on the major and minor
bodies, establishing an anatomic frame of reference having a permanently
fixed relation to the major body, and transforming local minor system
coordinates to local major system coordinates and to anatomic reference
system coordinates. The method of this invention also includes specific
steps utilized in the system to detect, process, monitor, and display
selected points and movements.
The apparatus of this invention may comprise a system of components to
perform the method of the invention, including specific improved harness
apparatus for mounting LED's on a person's head and an LED pointer for
establishing selected points to be detected, tracked, and utilized in the
method of this invention.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects of the present invention will become more readily
appreciated and understood from a consideration of the following detailed
description of the preferred embodiment when taken together with the
accompanying drawings, in which:
FIG. 1 is a perspective view of the mandibular motion analysis system
components according to the present invention with the harness shown
mounted on a patient and a researcher or practitioner at the keyboard of a
computer processing unit;
FIG. 2 is a schematic view of the mandibular motion analysis system of the
present invention;
FIG. 3 is a perspective view of an LED harness according to the present
invention;
FIG. 4 is a perspective view of an alternate embodiment LED harness
according to the present invention;
FIG. 5 is a diagrammatic representation of a detector utilized according to
the present invention to establish X-Y harness coordinates;
FIG. 6 is a diagrammetric illustration of non-linear coordinate position
response of a photo diode surface before calibration;
FIG. 7 is a diagrammetric illustration of the linear X-Y coordinate
response of the photo diode after calibration according to this invention;
FIG. 8 is a graphical representation of signal output of the photo diode in
relation to time;
FIG. 9 is an isometric view of the system frame of reference or coordinate
system with the detectors, an LED, and the initial calibration frame
positioned therein according to this invention;
FIG. 10 is a perspective view of an example anatomical frame of reference
utilized according to this invention;
FIG. 11 is a perspective view of a free position LED pointer utilized
according to the present invention;
FIG. 12 is a flow chart of data acquisition and transformations in the use
of an anatomical frame of reference.
FIG. 13 is an example time series plot of central incisor movements with
each dimension plotted separately in one dimension;
FIG. 14 is an example border movements plot of mandible movement in the
saggital plane in two dimensions;
FIG. 15 is an illustration of a three-dimensional line representation of
the patient's mandible superimposed on a three-dimensional video display
of the patient's photo image.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The mandibular motion analysis system 10 according to the present
invention, as shown in FIG. 1, comprises an LED harness 100 mounted on the
head of a patient P, a pair of light detectors 12, 14 positioned a spaced
distance in front of the patient P, a detector pre-amplifier unit 16, an
LED controller 18, a computer processing unit 20, and a graphics display
unit 22. An optional video camera recorder 15 is also shown for use in
superimposing a moving video image of the patient P on a representative
image of the patient's mandible for viewing together in action on a
separate video monitor 23. An operator O or clinician is shown operating
the keyboard of the computer 20. The operator O has the patient P perform
a series of mandibular movements, such as extreme border movements, as
well as normal speech, chewing, and swallowing movements, while the
detector and video equipment is turned on to collect mandibular motion
data. The data are then stored, processed, and displayed for research or
clinical analysis of the patient's mandibular movements as recorded by the
system 10. There can also be a patient database system to aid in storing
and retrieving data. A floppy disk containing the data collected on the
patient can be made part of the patient's records.
The mandibular motion analysis system 10 is illustrated in FIG. 2 in
schematic to facilitate a description of the principle components. The two
detectors 12, 14 are positioned a spaced distance apart from each other,
as well as a spaced distance in front of the head of the patient P. Both
detectors 12, 14 remain stationary in these fixed positions. The distance
between the detectors 12, 14 is arbitrary, but once it is chosen and set,
it remains fixed and is utilized by the computer 20 in calculating X-Y-Z
coordinates.
Each detector 12, 14 has a photo diode 30, 130, respectively, as shown in
FIGS. 5 and 9, that produces electric current or a photovoltage when any
part of it is exposed to light. It is preferred, although not necessary,
that the LED's emit infrared light radiation and that the photo diodes 30,
130 be infrared detectors. For example, the photo diode 30 of detector 12,
as illustrated in schematic in FIG. 5, has an infrared light-sensitive
surface about 1 cm.times.1 cm in size. It is wired to take off
photo-generated currents from its four sides, as shown at leads 31, 32,
33, 34. There are measurable photo-generated voltages V.sub.1, V.sub.2,
V.sub.3, V.sub.4 at the leads 31, 32, 33, 34, respectively, which are
preferably amplified immediately adjacent the photo diode 30 at the
detector 12 by amplifiers 35, 36, 37, 38, respectively. These signals are
also preferably conditioned even further at the detector 12 by filters 41,
42, 43, 44 to eliminate as much electronic noise as possible at the
detector location, and then they are fed to an analog to digital (A/D)
converter. The resulting digital signals of the amplified voltages
V.sub.1, V.sub.2, V.sub.3, and V.sub.4 are then fed to a microprocessor 50
for conversion to meaningful X-Y coordinates indicative of where infrared
light from LED's is incident on the photo diode 30.
The respective voltages V.sub.1, V.sub.2, V.sub.3, V.sub.4 in relation to
each other indicate the portions, or locations on the surface of the photo
diode 30 surface where light is incident or most intense. Specifically,
the higher the voltage on any lead 31, 32, 33, or 34, the closer the
incident light to that lead. Consequently, X-Y plane coordinates of a spot
of light incident on any part of the photo diode 30 surface can be
determined by a fairly straightforward calculation using the formula:
V.sub.s =V.sub.o sin h[.alpha.(L-S)]/sin h(.alpha.L) (1)
where V.sub.s is the measured current voltage at a specific contact or
lead, i.e., V.sub.s =V.sub.1, V.sub.2, V.sub.3, or V.sub.4 for leads 31,
32, 33, 34, respectively, V.sub.o is the total photo-induced current
voltages at all leads or contacts, i.e., V.sub.o =V.sub.1 +V.sub.2
+V.sub.3 +V.sub.4, L is the distance between leads or contacts, S is the
distance from the contact in question to the spot of light on the photo
diode 30 surface, and .alpha. is a fall off parameter characteristic of
the specific photo diode semiconductor material used. The photo-induced
signals can also be measures of photo-induced current at each lead 31, 32,
33, 34. Such currents can be converted to measurable voltage signals by
current-to-voltage converting operational amplifiers. In a good photo
diode, .alpha. should approach zero, thus reducing the effective formula
to:
V.sub.s =V.sub.o (L-S/L) (2)
and should be linear across the surface of the photo diode 30.
Since actual photo diodes 30 are less than perfect, the behavior of .alpha.
for any given photo diode can be modeled by collecting a dense grid of
accurately known points in X and Y planar coordinates on the photo diode
30, and computing parameters that can produce linear and orthogonal
coordinates from the above equation (2). Such parameters can be applied by
computer 20, or, preferably by the dedicated microprocessor 50, to the
output voltages V1, V2, V3, V4, of the photo diode 30 to eliminate
distortion and produce accurate linear and orthogonal X-Y position
coordinates of a light spot 40 incident on the photo diode 30 surface.
Once this calibration procedure is performed, i.e., the correction
parameters for a particular photo diode 30 are determined, it remains
valid for that particular photo diode. FIG. 6 illustrates the
characteristic non-linearity of the raw X-Y coordinate system produced by
the photo diode 30 before calibration, and FIG. 7 illustrates the
corrected X-Y coordinate linearity after calibration and application of
the correction parameters to the raw X-Y coordinates by the microprocessor
50.
It has also been found that the signals generated by the photo diode 30 are
typically somewhat erratic at first upon being exposed to the incident
light spot 40 from an LED. For example, as illustrated in FIG. 8, upon
being first exposed to the light spot 40, the output voltages V.sub.o
shoot upwardly quite rapidly and then, over a very short time interval,
decrease and ultimately settle into a more steady output at about a time
t.sub.1 until the LED is turned off at time t.sub.3. Therefore, in order
to eliminate noise and instability and to get a more accurate X-Y
coordinate signal indicative of the position of light spot 40 on photo
diode 30, it is necessary to only read the signals generated at some
appropriate time interval when the voltage output signals are steady, such
as the time interval t.sub.1 to t.sub.2 illustrated in FIG. 8. This goal
can be accomplished by setting some arbitrary t.sub.1 before the voltage
signal is read. However, it is preferable to use the microprocessor 50 to
constantly calculate and monitor the rate of voltage change and to find
the time t.sub.1 when the rate of change decreases to an acceptable
threshold. The output voltages V.sub.1, V.sub.2, V.sub.3, and V.sub.4 can
then be read in the time interval t.sub.1 to t.sub.2 beginning at t.sub.1
as determined by the microprocessor 50. This period will be on the order
of microseconds.
As mentioned above, the microprocessor 50 is also used to perform some or
all of the calculations according to equation (2). It may be preferable to
same some of this data for other analysis uses in the computer; therefore,
it has been found preferable to just perform the add/subtract functions of
equation (2) with the microprocessor for each X and Y coordinate. Thus,
FIG. 5 is illustrated as having essentially two very highly conditioned
add/subtract signals for the X and Y coordinates of the light spot 40
output by microprocessor 50 through leads 51, 52. If it is desired to
perform the complete formula (2) calculations in the microprocessor 50,
the signals output through leads 51, 52 would be highly conditioned
complete X-Y coordinate data for the position of light spot 40. The X-Y
image coordinates of the photo diode 30 of detector 12 have been
designated in FIGS. 2, 5 and 9 as X.sub.12 -Y.sub.12.
The second detector 14, as illustrated in FIG. 5, has similar components
and features as detector 12. For example, the detector has a photo diode
130 with four leads 131, 132, 133, 134, at which photo voltages are
produced. These voltage signals are amplified by amplifiers 135, 136, 137,
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