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BACKGROUND OF THE INVENTION
This invention relates to the field of pressure measurement. Specifically
this invention relates to an improvement in an optical technique for
pressure measurement used in the field of static and dynamic foot pressure
distribution measurements.
One prior art foot pressure measurement system is disclosed in R. P. Betts
and T. Duckworth, "A Device for Measuring Plantar Pressures Under the Sole
of the Foot," 7 Engineering in Medicine 223 (1978). As described therein,
this system comprises a glass or transparent plate illuminated along two
or more edges, with a thin sheet of reflective material on its upper
surface, as shown in FIGS. 1 and 2. The light shining into the plate
normally is internally reflected. The reflective material causes light to
escape through the top and bottom surfaces of the glass plate when
pressure is applied to the reflective material. The amount of light
escaping is proportional to the applied pressure. Viewing the underside of
the glass reveals the applied pressure distribution as a variation in
light intensity. The variation of light intensity and hence pressure are
conveyed to the observer by viewing the underside of the plate, either
directly or using a mirror, with a monochrome television camera. In an
alternative prior art embodiment, the reflected light is processed into
color bands for a display on a color monitor, each band representing a
specific pressure range.
A significant advance in this art was made by capturing the light intensity
data in a computer system. See. e.g., C. I. Franks, et al.,
"Microprocessor-based Image Processing System for Dynamic Foot Pressure
Studies," Medical & Biological Engineering and Computing 566 (Sept. 1983).
A typical configuration for such a system is shown in FIG. 3. In this
system data from the video camera is converted into digital format by a
microprocessor image capture and analysis system, and the data are stored
in digital memory. This system enables the observer to playback the
pressure distribution data from either a static or dynamic sequence of
samples and to perform further analysis of the data. With the development
of this system improved calibration techniques became possible and were
implemented by measuring the total vertical force applied to the top
surface of the plate each time light intensity distribution was measured
using force transducers. This provided the necessary data with which to
calibrate the light values in terms of applied pressures.
The prior art systems depend on distinguishing background light levels from
light levels caused by foot pressure by setting a threshold level, below
which all light values are considered to be background light. As there is
a certain amount of noise in the video data, and a degree of irregularity
in the evenness of background light escaping from the glass plate, setting
a threshold level can lead to loss of low levels of foot pressure data if
the threshold level is set too high and erroneous data if the threshold
level is set too low.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide an improved
foot pressure measurement system with a variable background threshold
level.
Another object of the present invention is to provide an improved foot
pressure measurement system in which background threshold levels may be
made to correspond to each element of the scanned view of the light
output.
Another object of the present invention is to enable detection of lower
pressure levels in a foot pressure measurement system than otherwise would
be possible.
A further object of the present invention is to eliminate or substantially
reduce interference caused by variations in the amount of light escaping
from the glass plate in a foot pressure measurement system.
A still further object of the present invention is to eliminate or
substantially reduce in a foot pressure measurement system the effect of
increased or decreased light value levels escaping from the glass plate as
a result of internally reflected images which may be seen through the
underside thereof.
Another object of the present invention is to compensate in a foot pressure
measurement system for increased or decreased light levels escaping from
the glass plate as a result of impurities within the glass.
A further object of the present invention is to compensate for increased or
decreased light values escaping from the glass plate in a foot pressure
measurement system as a result of foreign objects within the glass.
A still further object of the present invention is to capture and store in
a foot pressure measurement system variable background threshold data
immediately prior to capturing pressure data.
Another object of the present invention is to reduce the effect on the
emission of background light from the glass plate in a foot pressure
measurement system caused by changes in ambient temperature.
A further object of the present invention is to eliminate the effects of
long term fluctuations in light intensity from glass plate 2 of a foot
pressure measurement system.
A further object of the present invention is to eliminate the effects of
medium term fluctuations in light intensity from the glass plate of a foot
pressure measurement system.
Another object of the present invention is to eliminate calibration errors
caused by variations in background light levels from the glass plate of a
foot pressure measurement system.
A still further object of the present invention is to enable effective run
length encoding of data and hence reduced storage space requirements by
eliminating background light levels in a foot pressure measurement system.
Another object of the present invention is to provide an improved
reflective material in a foot pressure measurement system.
Briefly, in accordance with the preferred embodiment of this invention, the
foregoing objects are achieved by providing an improved foot pressure
measurement system in which a reference measurement is made of background
light intensity and distribution before pressure is applied to the
reflective material on the glass plate and this background light intensity
is subtracted from the light levels when pressure is applied. A
photographic paper is used as the reflective material on the top surface
of the glass plate to improve the reflectance characteristics of the
system.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram of the optical portion of the prior art foot pressure
measurement system which is incorporated in the present invention.
FIG. 2 is an enlarged view of the reflective material-to-glass interface of
the prior art foot pressure measurement system.
FIG. 3 is a diagram of the prior art microprocessor-based dynamic foot
pressure measurement system, with force transducers at the corners of the
glass plate.
FIGS. 4a-d are graphs of the light intensity versus applied pressure for
various types of reflective materials.
FIG. 5 is a block diagram of the microprocessor image capture and analysis
system of the present invention.
FIG. 6 is a flow chart showing data collection in the present invention.
FIG. 7 is a flow chart showing background reduction and data encoding in
the present invention.
FIG. 8 is a flow chart showing data calibration and display in the present
invention.
FIG. 9 is an illustration of output foot pressure printout of the present
invention showing some of the sequential frames of data.
FIG. 10 is a flow chart of the control program's primary functions of the
present invention.
FIGS. 11a-b are flow charts of the data capture functions in the control
program of the present invention.
FIG. 12 is a flow chart of the display and analysis functions in the
control program of the present invention.
FIG. 13 is a flow chart of the analysis functions in the control program of
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings wherein like referenced numbers designate
identical or corresponding parts throughout the several views, FIG. 1
illustrates the optical portion of the prior art foot pressure measurement
system incorporated in the present invention.
In the preferred embodiment, glass plate 2 is made of Pilkington clear
white plate glass, grade A, measuring approximately 22.5 inches by 19
inches by 1 inch. Other suitable materials are plexiglass and Dow Corning
Pyrex. The surfaces and edges of glass plate 2 are ground flat and
polished to ensure maximum transmission of light and to minimize spurious
reflections.
Conventional fluorescent strip lights 1 are mounted so as to allow light
only to penetrate the edge of glass plate 2. The strip lights are mounted
inside conventional reflectors 200. A sheet of reflective material 3 is
positioned on the top surface of glass plate 2. A mirror 4 is positioned
beneath glass plate at a 45.degree. angle thereto. The lens of monochrome
television camera 5 is focused on mirror 4 and is aimed along an axis
parallel to the surface of glass plate 2.
FIG. 2 illustrates the interface between glass plate 2 and reflective
material 3. In FIG. 2a, no pressure is applied to this material. Because
of the irregular surface of reflective material 3 there are numerous air
gaps separating it from glass plate 2. Since air has a lower refractive
index than glass, light passing through glass plate 2 from strip light 1
is internally reflected where air gaps exists between glass plate 2 and
reflective material 3. Where reflective material 3 comes into intimate
contact with glass plate 2, such as at point 201, internal reflection does
not occur because reflective material 3 has a higher refractive index than
glass. At these points of contact light is refracted out of the glass and
scattered back in all directions from the surface of reflective material
3. A portion of the scattered light is reflected through the bottom
surface of glass plate 2 to mirror 4 and into television camera 5.
Referring to FIG. 2b, when pressure is applied to reflective material 3,
such as by a person standing on the upper surface thereof, the deformable
surface of this material is forced into more intimate contact with the
upper surface of glass plate 2, the total area of such contact depending
on the applied pressure. Output light intensity versus applied pressure
for a variety of different reflective materials in shown in FIGS. 4a-d. In
each curve the 25th, 50th, 75th and 100th percentile curves are shown for
the corresponding reflective material. These percentiles refer to pixels
having a light intensity at the specified percentile level. For example,
the 75th percentile curve means that the pressure versus light intensity
curve is for pixels having a sufficiently high light intensity that 75% of
the total pixels have a lower light intensity while 25% have a higher
light intensity. FIG. 4a illustrates the pressure versus light sensitivity
curve for "Baromat" ridged surface silicone rubber manufactured by
Biomechanics of La Mesa, Calif. FIG. 4b illustrates the pressure versus
light sensitivity curve for white polyvinyl-chloride, trade named "Velbex"
manufactured by Storeys Industrial Products, Ltd. FIG. 4c illustrates the
pressure versus light sensitivity curve for natural latex rubber, grade
"S" manufactured by Four D Rubber Co., Ltd. FIG. 4d illustrates the
pressure versus light sensitivity curve for a resin coated photographic
paper, trade named "Ilfospeed," No. MG.44M, medium weight pearl finish,
manufactured by Ilford, S.A.
Baromat, PVC plastic and natural latex rubber, as shown in FIGS. 4a-c,
respectively, have been used in prior art foot pressure measurement
systems. As these figures show, the pressure versus light intensity curves
are nonlinear. Furthermore, in the case of PVC and natural latex rubber,
the pressure versus light intensity curves exhibit hysteresis, i.e., the
light intensity follows one curve when pressure is increased from zero to
a specified maximum level and then follows a different curve as pressure
is removed from the material. As shown in FIG. 4d, the resin coated
photographic paper exhibits an essentially linear pressure versus light
intensity curve and exhibits no hysteresis. This material also shows
little viscoelasticity, tackiness or other hesteresis-like effects and
exhibits no evidence of saturation over the pressure range studied.
Referring again to FIG. 1, the upper surface of reflective material 3 is
covered by an opaque material 6, such as a photographic dark room
rubberized fabric. The preferred reflective material is resin coated
photographic paper, such as the "Ilfospeed" photographic paper discussed
in connection with FIG. 4, which should be "fixed" by the normal
photographic developing process and placed white side down on the upper
surface of glass plate 2. The same type of photographic paper is also
manufactured by Kodak and is identified as "Poly Contrast" paper. An
alternative reflective material is trade named "White Colour Card," 0.013
inch thickness, manufactured by Slater-Harrison.
Referring to FIG. 3, glass plate 2 is mounted on force transducers 7 placed
at each of the four corners thereof. These transducers measure the overall
vertical force applied to glass plate 2, allowing a highly accurate
calibration of the relationship between light levels and pressure. In an
alternative embodiment, multi-component force transducers are used which
also measure shear forces and torques applied to glass plate 2. This
increases the versatility of the pressure measurement system of the
present invention in some applications. The optical axis of camera 5 is
parallel to glass plate 2. To reduce the overall height of the structure
of this system, mirror 4 and camera 5 may be rotated as a unit so that the
angle between mirror 4 and glass plate 2 is reduced to less than
45.degree.. It is essential, however, that the angular relationship
between mirror 4 and camera 5 remain constant to maintain the correct view
of the underside of glass plate 2.
For optimum results the entire structure shown in FIG. 1 (with the
exception of the top surface of glass plate 2 which is already covered by
reflective material 3, which is in turn covered by opaque material 6) is
enclosed in a light proof assembly to exclude extraneous light from glass
plate 2, mirror 4 and camera 5. Camera 5 may be positioned externally to
the light-proof assembly, with provision made for the camera lens to view
mirror 4 through an aperture in the light-proof assembly.
Using the resin coated photographic paper as the reflective material 3 of
the preferred embodiment, video camera 5 generates an output analog signal
whose magnitude is directly proportional to the pressure exerted on this
film.
Referring again to FIG. 3, the output signal from monochrome TV camera 5 is
input to microprocessor image capture and analysis ("MICA") system 8. MICA
system 8 is shown in block diagram form in FIG. 5. Also input to MICA
system 8 are the output signals generated by each of the force transducers
7. The video signal from video camera 5 is input to a conventional gain
and clamp circuit 9, such as the combination of an Analog Devices Model
No. AD711 operational amplifier (gain) and a Burr Brown Model No. SHC298
(sample and hold). Gain and clamp circuit 9 is controlled by a standard
video offset control ("VOC") circuit 11, such as an Analog Devices Model
No. AD558. CPU 23 provides data value to VOC 11, which is determined by
integrating the digital video signal from a single frame from camera 5 and
comparing this integrated light value to a preselected value. If the
integrated light value exceeds the preselected value, VOC 11 increases the
offset voltage fed to gain and clamp circuit 9; conversely, if the
integrated light value is less than the preselected value, VOC 11
decreases the offset voltage fed to gain and clamp circuit 9. The output
of gain and clamp circuit 9 is input to a conventional high-speed video
analog to digital converter ("ADC") 10, such as a Micro Power Model No.
MP7684.
The operation of MICA system 8 is controlled by a conventional central
processing unit ("CPU") 23, which may be an 8, 16 or 32 bit processor or
any other device capable of being programmed and of providing control
functions for the other components of the system. In the preferred
embodiment CPU 23 is a Harris Model No. 80C88 microprocessor. CPU 23
passes and receives data to and from the other elements of the system via
conventional CPU data bus 19. Similarly, device and memory addresses,
control signals, requests and acknowledgements are transmitted between CPU
23 and the other system elements via CPU address and control bus 20.
In the preferred embodiment, video ADC 10 converts the analog video signal
for each pixel in video camera 5 into an 8 bit digital value. The digital
output from video ADC 10 is fed onto a conventional video random access
memory ("video RAM") bus 12, as described below, by means of a signal from
CPU 23 on CPU address and control bus 20.
The digital values produced by video ADC 10 are stored in a conventional
video random access memory ("video RAM") 16, such as a Fujitsu Model No.
MB 8146115. Data is input to video RAM 16 on video RAM bus 12 under
control of a conventional video system controller 17, such as a Texas
Instruments Model No. TMS 34061. Video RAM 16 can store 1,048,576 bytes,
or 32 frames of video data, each of which measures 256 pixels by 128
pixels. Video system controller 17 provides video timing and synchronizing
signals 18 for the video elements of the system, such as horizontal and
vertical sync pulses and horizontal and vertical blanking pulses.
The 8-bit digital values produced by video ADC 10 are also input to a
conventional color lookup device 13, such as an Inmos Ltd. Model No. IMS
G170S50, which converts these values into three analog values to drive the
red, green and blue inputs 14 to a conventional analog color graphics
monitor 15 such as an NEC Multisync. This produces a color-coded display
of the pressure data seen by monochrome video camera 8. In this way the
pressure values are grouped into bands of colors for easier recognition by
the user of the present system. Color lookup device 13 is preset by CPU 23
to provide a selected range of colors at its output. It has 256,000 colors
to choose from, of which a palette of 256 may be selected at any one time.
For example, if the digital value 15 is input to color lookup device 13,
the color light blue is generated, while if the digital value 30 is input,
the color dark blue is generated.
Video RAM 16 is dual-ported to allow simultaneous access to its data by
video system controller 17 and CPU 23. In this way, CPU 23 may access the
digitized video data while it is being input to video RAM 16.
Programming information for CPU 23 is stored in a conventional 32 kilobyte
random access memory 22 ("CPU RAM"), such as an NEC Model No. D43256C-12L.
This memory contains the CPU control program and various constants such as
values for color lookup device 13 and VOC 11.
Referring again to FIG. 3, each of the force transducers 7 generates a
voltage directly proportional to the force exerted on glass plate 2. As
shown in FIG. 5, these signals are fed to a conventional analog to digital
converter ("ADC") 24, such as Analog Devices Model No. AD7828, which
converts these analog voltages into 8-bit digital format. The output of
ADC 24 is fed to CPU RAM 22. In the preferred embodiment four force
transducers are used so that four 8-bit digital channels are output from
ADC 24. It should be understood, however, that a larger number of force
transducers may be used in the instant invention.
In the preferred embodiment control programs, described below are
transferred from and data are transferred to and from a host computer 28,
such as an IBM Model PC/AT, via a conventional parallel interface 26, such
as an Advanced Micro Devices Model No. 82C55, communicating over bus 27.
This provides flexibility in programming and operation of the system. In
an alternative embodiment, the entire system of FIG. 5 is incorporated
into host computer 28 itself. In another alternative embodiment the entire
system of FIG. 5 (excluding host computer 28 and monitor 15) is
incorporated in a single integrated circuit board, such as the True Vista
Video Graphics board, Model AT Vista, made by True Vision, Inc.
A conventional "bootstrap" program is stored in eight kilobytes of a
conventional erasable programmable read-only memory ("EPROM") 21, such as
an Hitachi HN27C64G-15, to enable system operation to begin. On "power up"
the bootstrap program sends a reset pulse through the system to initialize
all of the component elements. This program then directs CPU 23 to input
or "download" the control program and certain system parameters, described
below, from host computer 28 through parallel interface 26.
In the preferred embodiment host computer 28 is programmed to calculate
calibration values from the force and video data, as described below. CPU
23 may also be programmed to modify the video data, as described below.
Host computer 28 interacts with CPU 23 providing it with information to
display, via video RAM 16 and color lookup 13, on a conventional analog
color monitor 15, such as an NEC "Multisync" monitor. Similarly, the
initiation of data collection from both video ADC 10 and 8-bit ADC 24 may
be ultimately controlled by host computer 28. Data collected by the
instant pressure measurement system may be stored and further processed,
if desired, by host computer 28.
Operation of the system is explained by reference to the flowcharts in
FIGS. 6-8. As shown by block 30 in FIG. 6, the system is initialized for
data collection by the "bootstrap" program which downloads program
instructions and constant data parameters, such as the video offset
control parameters, color lookup parameters and video system controller
parameters, from host computer 28. After initialization one frame of video
data is input from monochrome television camera 5 to MicaSystem 8, prior
to any pressure being applied to glass plate 2. This provides background
level data for each pixel sample. A video frame in the instant system
comprises a field of 128.times.256 pixels or 32,768 pixels per frame. The
video signal for each pixel is converted by video ADC 10 into an 8-bit
digital word and stored in video Ram 16, as shown by block 31 in FIG. 6.
After the video background frame has been stored, the voltages generated by
force transducers 7 are sampled and converted into 8-bit digital words by
ADC 24. This data is stored in CPU RAM 22 as baseline data, as shown by
block 32.
The program then enters a loop wherein the next frame of video data is
observed by video camera 5, digitized by video ADC 10 and stored in video
RAM 16, as shown by block 33. The force transducer data from force
transducers 57 are then sampled by ADC 24 during transmission of the first
video frame, as shown in block 34. The video data stored in video RAM 16
is compared with the previously stored video data for the background frame
by subtracting the digital value for each pixel in the background frame
from the digital value for the corresponding pixel in the video frame.
These differences are then summed. If the sum is greater than a specified
threshold value, input from host computer 28, it is assumed that pressure
has been applied to glass plate 2. Alternatively, the same type of
comparison is made between the stored baseline reference level of force
transducers 7 (block 32) with the new values for these transducers (block
34) and an increase in level above a specified threshold level indicates
an increase in pressure applied to glass plate 2. Block 35 illustrates
this step. This pixel-by-pixel comparison is carried out as pixel data for
the current frame is read into video RAM 16 by means of the dual port in
this device.
If there is no change in pressure levels (either by comparing the
background video frame against the current video frame or by comparing the
baseline force transducer data against the current force transducer data),
this process is reiterated. Thus, the next frame of video data is input to
video RAM 16 and compared with the background frame, and the next
corresponding set of force transducer data is input to CPU RAM 22 and
compared with the baseline data. During this repetitive sequence the data
in video RAM 16 for the current frame writes over the data for the
preceding frame and the current force transducer data in CPU RAM 22
corresponding to the preceding frame writes over the force transducer data
for the frame.
If the comparison between the background frame and the current frame
indicates a change in pressure level above the specified minimum, or if
the comparison between the baseline force transducer data and the current
force transducer data indicates a change in pressure level on glass plate
2, the system proceeds to the loop defined by blocks 36-38 in FIG. 6. The
first step, as shown by block 36, is to sample and save the current video
frame. This frame is stored in a separate location in video RAM 16.
Similarly, the current set of force transducer data, as shown in block 37,
is sampled and stored in a separate location in CPU RAM 22.
The system then interrogates to determine whether video RAM 16 is full,
i.e., whether it has stored 32 frames of video data, as shown by block 38.
If video RAM 16 is not full, the system returns to block 36 and repeats
this process for the next frame of video data and force transducer data.
This process continues until video RAM 16 is full, i.e., it contains 32
frames of video data. Since a footstep typically does not last for the
duration of all 32 frames, there will be one or more frames stored in
video RAM 16 which contain only background data and one or more
corresponding sets of force transducer data stored in CPU RAM 22
comprising baseline reference data.
Referring now to FIG. 7, the background video frame, which previously had
been used to determine initiation of a footstep and the first frame of
video data stored in video RAM 16 containing foot pressure data are read
by CPU 23 on a pixel-by-pixel basis, as shown in blocks 51 and 52. Each
background video frame pixel is subtracted from the corresponding first
frame pixel, as shown in block 53. This subtraction has the effect of
reducing background levels to very low digital values, such as 1 or 2,
depending on the short-term noise in the system. This step is followed by
subtracting a constant value, such as digital 3, from each pixel value, as
shown in block 54. If the resulting pixel value is negative, it is set to
zero, as shown in block 55. As a result of this step, a zero pixel value
indicates no pressure has been applied to the area in glass plate 2
corresponding to this pixel, while a non-zero pixel value indicates that
pressure has been applied to this area. The constant value used in block
54 is then added back to the non-zero pixel values, as shown in block 56.
The background-free video data is then written over the unmodified data in
video RAM 16. The result of this process is that the background signal
(corresponding to the absence of pressure from a footstep) is eliminated
from the video signal on a pixel-by-pixel basis.
The modified data in video RAM 16 may then be compressed, as shown at block
57, to reduce storage space requirements using standard data compression
techniques. For example, because the background data has been set to zero,
an effective method of data compression is to "run length encode" the
data. Using this technique two numbers are used to represent a stream of
constant values. The first number indicates the data value and the second
number indicates how many times the data value is repeated. In this way,
long streams of unchanging values are reduced to two data values for
storage. For example, if one line of the video frame had foot pressure at
locations on glass plate 2 corresponding to the first ten pixels of a
particular video scan line and there was no foot pressure at locations
corresponding to the remaining 118 pixels in that line, this data could be
run length encoded by storing the numbers "0" and "118."
The encoded data is then saved in CPU RAM 22, as shown by block 58. The
program then checks to see if all stored frames have been processed, as
shown in block 59. If additional frames must be processed, the system
loops back to block 52 and the next video frame is read and compared with
the background frame, in the same manner as above. If no further video
frames are to be processed, the system exits to the series of steps
illustrated in block diagram form in FIG. 8.
Referring now to FIG. 8, the video data is calibrated in host computer 28
following the encoding process. The first frame of encoded data is read
from CPU RAM 22 into host computer 28 through parallel interface 26, as
represented by block 70. The light values are then integrated over the
entire video frame, i.e., the digital values for all pixels are added
together for the entire frame, as represented by block 71. The integrated
value is then tested to determine if the frame contains any pressure data,
as shown by block 72. If the integrated value is zero (indicating that the
frame has no pressure data), the system skips to block 76, whose function
is described below. If the integrated value is non-zero (indicating that
the frame has pressure data), the frame data is calibrated.
The calibration factor for a frame is calculated from the following
equation, as represented in block 73:
##EQU1##
where L.sub.i light value (0-255) for the "i"th pixel,
N=number of pixels
A.sub.P =pixel area
F=total force on glass plate 2
C=calibration factor (same for all pixels)
Pixel area is calculated from the geometrical relationship between the
camera scan area and the dimensions of the viewed area of glass plate 2.
It may be found by applying points of pressure at known separations on
glass plate 6 and then identifying the corresponding pixels in the video
output. For example, if pressure is applied to two points on glass plate
2, separated by ten inches and this pressure generates increased light
values at pixels 20 and 120 on a particular scan line, the pixel
separation equals 100 and adjacent pixels correspond to a 0.1 inch
separation on glass plate 2.
Force in the foregoing calibration equation is determined by adding the
four digitized values for the output of force transducers 7 corresponding
to the video frame being calibrated. As described above, this data is
stored in CPU RAM 22.
Every pixel for the particular frame being calibrated is then multiplied by
the calibration factor, as shown by block 74. After the frame data has
been calibrated it is fed to color lookup device 13, which generates an
analog voltage corresponding to the calibrated digital value for each
pixel. Since the pixel value is encoded in an eight-bit word, color lookup
device 13 generates 256 different combinations of analog voltages on the
"R" (red), "G" (green) and "B" (blue) output lines 14. The output of color
lookup device 13 is fed on lines 14 to color monitor 15, which displays
the video frame in color from a palette of 256 colors, as represented by
block 75. Alternatively, as shown in FIG. 3, the output of color lookup
device 13 may be fed to a printer 204, a plotter 205, or stored on a hard
disk 202 or a diskette 205. An example of eight frames printed by printer
204 showing foot pressure at times 0.03, 0.10, 0.17, 0.23, 0.30, 0.37,
0.43 and 0.50 seconds are shown, respectively, in FIGS. 9a-h. As shown in
FIG. 9a, the foot begins exerting pressure at the heel. Pressure then is
applied to the ball of the foot (FIGS. 9b-d). As pressure is removed from
the heel, it begins to be applied to the smaller toes (FIGS. 9e-f) and
finally is applied to the large toe (FIGS. 9g-h).
Referring again to FIG. 8, the system interrogates to determine whether all
frames have been displayed, as shown by block 76. If additional frames
remain to be displayed the system loops back to block 70 and performs the
same sequence of steps for the next frame. When all frames have been
displayed, the system exits this loop.
Flow charts for a typical control program for CPU 23 are shown in FIGS.
10-13. Referring first to FIG. 10, the program is entered at 100. CPU 23
interrogates parallel interface 26 to see if the host computer 28 is
requesting action. If no action is requested the control program continues
to interrogate parallel interface 26. If host computer 28 requests action
the control program evaluates the request, as shown by block 102 to see if
it should enter the data capture routines in FIGS. 11a-b. If this action
is required, the data capture routines, described below, are entered as
shown at block 103. If the data capture routines are not required the
control program tests to see if it should enter the display and analysis
routines in FIGS. 12-13. If this action is required the display and
analysis routines, described below, are entered, as shown at block 105. If
neither of these actions is required, the control program returns to block
100 and monitors the parallel interface for further requests from host
computer 28.
A flow chart indicating the data capture functions is shown in FIGS. 11a-b.
This portion of the control program allows the operator to direct CPU 23
to carry out various functions, as described below.
Function 110 ("Set Display Cycle Speed?"): This function controls the
repetition rate for displaying the sequential samples of pressure data. As
shown in block 111, the operator inputs a value between 0 and 9 from host
computer 28. A value of 9 selects the highest possible display rate, while
progressively lower values slow the rate down. The value of 0 "freezes"
the display at the currently displayed frame.
Function 112 ("Display Next Frame?"): This function is selected by the
operator by inputting a space character from host computer 28. This
selects the next frame in sequence, as shown at block 113, allowing the
operator to step through the display of sequential pressure data (when
used in combination with the frame display rate value 0).
Function 114 ("Display Previous Frame?"): This function is selected by the
operator inputting the minus character from host computer 28. This causes
the displayed frame to be decremented (block 115), allowing the operator
to step backwards through the display of sequential pressure data (when
used in combination with the frame display rate value 0).
Function 116 ("Save Data on Disk?"): When the host computer requests this
function pressure data from video RAM 16 is transferred via parallel
interface 26 to host computer 28, which stores the data in a file on hard
disk 202 or diskette 205. The values for the force transducer data are
also transferred and saved, simultaneously.
Function 118 ("Capture Dynamic Sequence?"): When the host computer requests
this function the data capture routines previously described in FIG. 6 are
entered, and a sequence of pressure events is sampled and stored in video
RAM 16.
Function 120 ("Capture Single Frame?"): When host computer 28 requests this
function the data capture routines are entered but capture is limited to a
single frame of data from video camera 5.
Function 122 ("Set Offset D/A Automatically?"): When host computer 28
requests this function a routine is entered which sets video offset
control 11 as follows: Video offset control 11 is loaded with a default
value and one frame of video data is acquired and stored in video RAM 16.
This video data is then transferred to host computer 28 which integrates
the light values. The resulting integral is then compared with a
pre-defined target value. If the integral has a higher value than the
target value, video offset control 11 is reset with a new, increased value
to raise the video offset voltage. This voltage is applied to gain and
clamp circuit 9, which adjusts the level of video voltage applied to video
ADC 10, such that background video levels are reduced. If the integral has
a lower value than the pre-defined target level, video offset controller
11 is reset with a lower value. After the video offset voltage is reset a
new frame of video data is acquired and the process is repeated. This
procedure continues until the integrated light from the video field is
within a predetermined margin of the target value.
Function 124 ("Set Offset D/A Manually?"): This function allows the
operator to load video offset control 11 with a value from host computer
28. The level of video background may thus be preset directly by the
operator.
Function 126 ("Continuous Image?"): If this function is selected by host
computer 28, video ADC 10 will be turned on (block 127). This passes the
video data directly through to color monitor 15 via color lookup device
13. Data is not stored during this process, which is intended to allow the
operator to check for proper functioning of the video system. The control
program then interrogates for input of an escape character from the host
computer (block 128). If an escape character is received the control
program turns off (block 129) video ADC 10.
Function 130 ("Return to Main Menu?"): If this function is selected control
program starts over again by returning to block 100.
Referring to FIG. 12, a flow chart for the display and analysis functions
is shown. This part of the control program allows the operator to direct
CPU 23 to carry out various functions as follows:
Function 140 ("Set Display Cycle Speed?"): This function controls the
repetition rate for display of the sequential samples of pressure data.
This function is selected (block 141) by inputting a number between 0 and
9 from the host computer. A value of 9 selects the highest possible rate
for display. Progressively lower values will slow the rate down until a
value of 0 which "freezes" the display at the currently displayed frame.
Function 142 ("Display Next Frame?"): This function is selected by
inputting a space character from host computer 28. It causes the displayed
frame to be incremented (block 143), allowing the operator to step through
the display of sequential pressure data (in combination with selecting the
frame display rate value 0).
Function 144 ("Display Previous Frame?"): This function is selected by
inputting the minus character from host computer 28. It causes the
displayed frame to be decremented (block 145), allowing the operator to
step backwards through the display of sequential pressure data (in
combination with selecting the frame display rate value 0).
Function 146 ("Load Data from Host?"): This function instructs host
computer 28 to download (block 147) a file of previously collected
pressure data to video RAM 16. This data is calibrated by host computer 28
before downloading. Once in video RAM 16, the data is displayed on color
monitor 15 via color lookup table 13.
Function 148 ("Analysis Functions?"): When host computer requests this
function the control program enters the flow chart shown in FIG. 13 at
point 160. These functions are described below.
Function 150 ("Return to Main Menu?"): When host computer 28 requests this
function the control program returns to the beginning (block 100) of the
flow chart in FIG. 10. If this function is not requested, the control
program stays in the "Display and Analysis Functions" and continues
testing for requests.
Referring to FIG. 13, a flow chart illustrating the Analysis Functions is
shown. This part of the control program allows the operator to
interactively test areas of interest in the pressure data for further
analysis, as described below:
Function 160 ("Set Area Size?"): This function allows the operator to set
the size of the area of interest. This is done by incrementing or
decrementing the radius of area (block 161). Host computer 28 sends data
to video RAM 16 which produces an image of the circle of selected radius
on color monitor 15.
Function 162 ("Move to New Area?"): If this function is selected, host
computer 28 re-draws the circle for the area of interest in video RAM 16
at new co-ordinates. This allows the operator to reposition the area of
interest on the screen.
Function 164 ("Enter Area?"): This function allows host computer 28 to
re-draw the circle for the area of interest in a different color, and this
circle is then retained on the image. The circles position and radius are
saved (block 165) by host computer 28 for incorporation into the data
file.
Function 166 ("Set New Top Point?"): When host computer 28 selects this
function the pressure data in each frame of information is repositioned to
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