U.S. patent number 3,740,144 [Application Number 05/200,775] was granted by the patent office on 1973-06-19 for method and apparatus for optically detecting the presence of an element in a substance.
Invention is credited to Winston G. Walker.
United States Patent |
3,740,144 |
Walker |
June 19, 1973 |
METHOD AND APPARATUS FOR OPTICALLY DETECTING THE PRESENCE OF AN
ELEMENT IN A SUBSTANCE
Abstract
A system for detecting blood in eggs in which a beam of
substantially monochromatic light or at least light within a very
narrow wavelength band in the region of 578 nanometers (nm) is
passed through an egg to be tested. The band is continually shifted
in wavelength a number of times per second between substantially
the shortest and the mid-length wavelengths of the broader blood
absorption band, i.e. 578 to 573 nm. In a preferred embodiment,
this is effected by a Fabry-Perot type interference filter placed
in a light beam and oscillated about an axis by an electromagnetic
device. A photoelectric device senses the light transmitted by the
egg and the output signal derived therefrom is compared with an
oscillating signal transmitted in time with the oscillation of the
filter. If one phase relation exists between such signals, the egg
is rejected as having blood present therein and if an opposite
phase relation exists, the egg is retained as clear.
Inventors: |
Walker; Winston G. (Anaheim,
CA) |
Family
ID: |
22743131 |
Appl.
No.: |
05/200,775 |
Filed: |
November 22, 1971 |
Current U.S.
Class: |
356/53; 356/325;
359/578; 356/229; 356/332; 359/244 |
Current CPC
Class: |
G01J
3/433 (20130101); A01K 43/00 (20130101) |
Current International
Class: |
A01K
43/00 (20060101); G01J 3/42 (20060101); G01J
3/433 (20060101); A01k 043/00 () |
Field of
Search: |
;356/53,83,93,97,95,100,204,205,229 ;350/163,164,285,311 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wibert; Ronald L.
Assistant Examiner: Godwin; Paul K.
Claims
What is claimed is:
1. The method of detecting the presence of an element in a
substance wherein said element is effective to absorb radiant
energy within a particular band of wave lengths, comprising
the steps of passing a radiant energy beam of a narrow band of wave
lengths within said particular band through said substance,
oscillating the wave lengths of said narrow band between
predetermined limiting wave lengths within said particular
band,
converting that portion if said beam which passes through said
substance into a first signal which varies in accordance with the
intensity of said portion of said beam,
creating a second signal which varies in accordance with the wave
lengths of said narrow band, and
creating a third signal indicative of the presence of said element
in said substance when a predetermined phase relationship occurs
between said first signal and said second signal.
2. The method according to claim 1 wherein said limiting wave
lengths comprise substantially a mid-length wave length and a wave
length within and adjacent one end of said particular band.
3. The method of detecting eggs having blood therein comprising
the steps of passing a light beam of a narrow band of wave lengths
through an egg being tested,
oscillating the lengths of said wave lengths in said narrow band at
least substantially between 578nm and 573nm,
converting that portion of said beam which passes through said egg
into a first signal which varies in accordance with the density of
said portion of said beam,
creating a second signal which varies in accordance with the wave
lengths of said narrow band, and
creating a third signal only when said second signal varies
substantially in phase with said first signal to indicate the
presence of blood in said egg.
4. The method according to claim 3 which comprises
conveying said eggs past said beam, and
oscillating said wave lengths of said narrow band a plurality of
times while each of said eggs is in said beam.
5. Apparatus for detecting the presence of an element in a
substance wherein said element is effective to absorb radiant
energy within a particular band of wave lengths, comprising
means for directing a beam of radiant energy of a narrow band of
wave lengths within said particular band through said substance and
for oscillating the wave lengths of said narrow band substantially
between a mid-length wave length and a wave length within and
adjacent one end of said particular band,
photosensitive means for receiving that portion of said beam
passing through said substance and for creating a first signal
which varies with the intensity of the radiant energy contained in
said portion of said beam,
means controlled by said first mentioned means for creating a
second signal which varies with the wave lengths of said narrow
band,
a signal device for indicating the presence of said element in the
said substance, and
means for comparing the phase relationship between said first and
said second signals and for actuating said signal device when a
predetermined phase relationship exists between said first and
second signals.
6. Apparatus according to claim 5 wherein said limiting wavelengths
comprise substantially the shortest and the mid-length wavelengths
in said particular band.
7. Apparatus for detecting eggs having blood therein comprising
means for passing a light beam of a narrow band of wave lengths
within a particular band of wave lengths absorbed by blood through
an egg being tested and for oscillating the wave lengths of said
narrow beam between substantially the shortest and the midlength
wave length within said particular band,
photosensitive means for receiving that portion of said beam
passing through said egg and for creating a first signal which
varies with the intensity of the light contained in said portion of
said beam,
means controlled by said first mentioned means for creating a
second signal which varies with the wave lengths of said narrow
beam,
an egg ejecting device, and
means for comparing the phase relationship between said first and
second signals and for causing operation of said ejecting device
when said first and second signals are substantially in phase.
8. Apparatus according to claim 7 wherein said first mentioned
means comprises means including
a light source,
a dielectric band pass filter in said beam, and
means for oscillating said filter about an axis extending parallel
to the plane of said filter whereby to oscillate the wave lengths
of said narrow band.
9. Apparatus according to claim 8 comprising means supporting said
filter for adjustment about a second axis normal to said first axis
whereby to change the wave lengths passed by said filter at one end
of the oscillation thereof.
10. Apparatus according to claim 8 wherein said oscillating means
oscillates said filter equal amounts on opposite sides of a plane
normal to the length of said beam, and
said means for creating said second signal comprises means
controlled by said oscillating means for oscillating said second
signal at twice the frequency of oscillation of said filter.
11. Apparatus according to claim 7 wherein said first mentioned
means comprises means including
a light source; and a rotatable dielectric band pass filter in said
beam,
said filter oscillating said wave lengths of said narrow band
during rotation of said filter.
12. Apparatus according to claim 7 wherein said first mentioned
means comprises
a tunable laser,
oscillating means, and
means controlled by said oscillating means for tuning said laser to
change the wavelength of light emitted by said laser between
substantially said shortest and said mid-length wavelength.
13. Apparatus according to claim 7 comprising
means for conveying said eggs past said beam and wherein said first
mentioned means oscillates the lengths of said narrow band a
plurality of times while each of said eggs is in said beam.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and apparatus for optically
detecting certain properties of a substance by detecting
differences in color emitted by the substance without modifying or
affecting the substance itself.
2. Description of the Prior Art
Detecting devices of the above type have been used heretofore in
which the optical characteristics of a substance have been analyzed
photoelectrically in testing for a particular property or
ingredient. One particularly difficult application of this type of
analysis is the detection of small amounts of blood which are
occasionally found in eggs.
Automatic apparatus have been developed for detecting blood in eggs
by impinging on an egg a beam of colored light comprising a very
narrow band of wavelengths within that portion of the spectrum
which is absorbed by blood and employing a photosensitive device to
measure the light transmitted by the egg. Since the light falling
on the photo-sensitive device is attenuated appreciably when an egg
having blood therein is tested, due to absorption by the blood,
such measurement can be used to segregate blood eggs from clear
eggs.
However, the density of eggs varies considerably due to several
factors, such as the thickness of the shell, color of the shell,
color of the yolk, and age of the egg which affects the density of
the albumen in the egg. Because of such variations in density in
different eggs it is not feasible to use a fixed reference of light
values with which the amount of light transmitted by various eggs
being tested can be compared to indicate the presence of blood. For
example, the transmission of light in the 578 nm region through
non-blood eggs of various shell thicknesses, colors, etc., has been
found to vary from approximately 4 to 13 percent, whereas the
attenuation due to absorption of such light by blood present within
the egg may be less than 1 percent.
Accordingly, the most successful prior art devices generally
provide a reference obtained by passing light of a wavelength which
is not affected by the presence of blood, through the egg being
tested. Such reference standard is then compared with light of a
wavelength within the blood absorption band which has been
transmitted through the same egg. If the ratio between such two
different wavelengths is greater than a predetermined amount, the
egg is rejected as having blood present therein. As noted above,
only a small amount of available light is transmitted by an egg
and, of that, less than 1 percent may be absorbed by blood so that
the detecting device must be extremely sensitive and
discriminating. Heretofore, this has resulted in relatively complex
and expensive equipment which is not entirely reliable. For
example, analysis of eggs tested by currently available automatic
blood detecting equipment shows that at least 5 percent of all eggs
having blood present therein are allowed to pass undetected. Also,
blood detecting equipment commonly in use at present generally
requires multiple optical systems which may include relatively
expensive filters, lens systems, photo-sensitive devices and
associated electronic equipment to establish, on one hand, a
reference level for the average density of an egg being tested and,
on the other hand, a level of light in the blood absorption band
which is passed through the egg. Other equipment requires different
filters to be sequentially positioned in a light beam passed
through the egg to establish the reference and sample light
values.
Another problem in presently available blood detecting equipment is
that very narrow and, therefore, expensive band pass light filters
are required in order to obtain sufficient sensitivity to detect
small amounts of blood in eggs being tested. Also, such filters
require collimated light. However, the diffused light transmitted
by an egg can be collimated only by utilizing a small fraction of
such light, thereby reducing the total amount of light available to
the detecting device. Other systems using a prism or grating type
monochrometer require a very narrow beam restricting slit for
proper resolution of the blood absorption band and therefore the
total available light is relatively small, thus reducing the
sensitivity of the system.
SUMMARY OF THE INVENTION
The present invention provides a simpler, less expensive and yet
more reliable detecting apparatus. According to a preferred form of
this invention, only a single optical system including a single
narrow bandpass light filter is employed, in which the filter is
continually oscillated in the light beam in a manner to shift the
essential or peak wavelength a number of times a second between the
shortest and mid-length wavelengths of the blood absorption band,
such wavelengths normally being 578 nm and 573 nm, respectively.
The constantly changing filtered beam is passed through the egg and
the light transmitted thereby is collected onto a photo-sensitive
device. The output signal of the photo-sensitive device is compared
with an oscillating signal derived from the filter oscillating
means and, if blood is present, the signals will be found to be in
a particular phase relationship. If no blood is present, an
opposite phase relationship will exist. Phase comparing means is
employed to reject blood eggs. Since the result is dependent upon
the phase relationship of the signals and not upon the degree of
sensitivity of any part of the system or upon any measurements of
the amount of light transmitted by the egg being tested, the system
becomes entirely reliable regardless of such variables as the
quality of the light source or the quality of the components. Also,
since the system employs collimated light to pass through the
single filter onto the egg, all of the light passing through the
egg may be collected for detection, thus increasing the sensitivity
of the system far above the threshold of detection.
In the preferred embodiment of the invention, a collimated light
beam passes through a narrow bandpass filter of the dielectric or
Fabry-Perot interference type and the resulting essentially
monochromatic light in the 578 nm region is then passed through the
egg being tested and the transmitted light is focused onto a
photo-electric device. The filter is continuously oscillated about
an axis to vary the essential wavelength of the band between
approximately the shortest and mid-length wavelength in the blood
absorption band. Means are provided to adjust the filter so that
the highest wavelength limit may be precisely set. Therefore,
relatively inexpensive filters having wide spectral tolerances may
be employed since they can be readily adjusted to the desired
wavelength.
Also, according to the invention, the filter is oscillated on
opposite sides of its position of maximum wavelength transmission
during each oscillation cycle so that the frequency of oscillation
thereof is only one-half the frequency of optical scanning, thereby
reducing wear and vibration of the mechanical components and
improving the speed of test by having a higher frequency electrical
signal.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view showing waves depicting the percentage
of light transmission at different wavelengths by eggs having
different overall densities.
FIG. 2 is an enlarged view showing a curve representing a typical
dip in the light transmission at different wavelengths due to
absorption by blood within an egg.
FIG. 3 is a schematic view of a system embodying a preferred form
of the invention for rejecting blood eggs.
FIG. 4 is a perspective view of the filter support and
adjustment.
FIG. 5 is a view illustrating the phase relationship of the filter
drive signal and the output of the photo-sensitive device for blood
eggs and clear eggs.
FIG. 6 is a schematic view of a modified form of the invention
employing a wedge type rotary dielectric or interference
filter.
FIG. 7 is a developed view illustrating the relative change in
wavelength transmission and potentiometer voltage output around the
rotary filter of FIG. 6.
FIG. 8 is a schematic view of a modified form of the invention
employing a tunable laser.
FIG. 9 is a circuit diagram of the phase comparator.
FIG. 10 shows the signal waveforms developed at different points in
the phase comparator circuit.
DETAILED DESCRIPTION OF THE EMBODIMENTS
Referring to FIG. 1, line 11 illustrates the percentage of light
transmission for different wavelengths of light passed through a
typical day-old egg having a relatively thin white shell and
containing blood. Line 12 illustrates the percentage transmission
for light passed through a typical older egg having a colored shell
and also containing blood. It will be noted that the dip at 13,
caused by the absorption of blood in the region of 578 nm, effects
a much smaller change in light transmission than the variables
resulting from shell thickness, shell color, age, etc.
According to the present invention, and as shown in the magnified
curve of FIG. 2, the wavelength of the light transmitted through
the egg is oscillated between limits preferably representing
essentially the shortest and the mid-length of wavelengths within
the blood absorption band, i.e., between 578 nm and 573 nm. Thus,
if blood is present, the character of the light transmitted by the
egg will essentially correspond to that portion of the transmission
curve from a to b whereas if no blood is present, the character of
the light transmitted will essentially correspond to that portion
of the alternate transmission curve from b to c.
Referring to FIG. 3, the apparatus disclosed therein comprises a
light source 14 and a collimator lens 15 for projecting a
continuous collimated beam of light 16. A dielectric or Fabry-Perot
type interference filter 17 which passes a very narrow light band
in the 578 nm region is located in the beam.
Eggs, i.e., 18, to be tested are carried past the beam 16 on a
suitable conveyor 19. As each egg passes through the beam 16, a
lens 20 focuses the transmitted light onto a suitable photodiode
21, the output of which is amplified by amplifier 22 and fed over
line 70 to the lower input of a phase comparator 23. The filter 17
is mounted in a frame 24, FIG. 4, supported by trunnion bearings 25
in a support 26 for movement about a horizontal axis 27 passing
through the plane of the filter. The support 26 is pivotally
supported by a bearing 28 on a base 30 for movement about a
vertical axis 31 intersecting the axis 27. The support 26 may be
locked in different adjusted positions about axis 31 by a lock
screw 33 which extends through an arcuate slot 34 in the support
and is threaded into the base 30.
An arm 35 is attached to the frame 24 and is pivotally connected to
the armature 36 of a solenoid 37 suitably mounted on the support
26. By adjusting the point 39 of pivotal connection along the arm
35 the amplitude of oscillation of the filter may be changed. The
solenoid 37 is driven by an oscillator 38, preferably at the rate
of approximately 47 cycles per second so that the filter is
oscillated a number of times while each egg intercepts the beam 16.
Thus, a number of separate tests are made of each egg to further
insure reliable results. It should be noted that each cycle
involves an excursion of the filter 17 on opposite sides of a plane
normal to the axis of beam 16 and that the transmitted wavelength
decreases as the filter moves on either side of such normal plane
so that the resulting optical frequency of the wavelength shift is
twice that of the oscillation of the filter.
The output signal of the oscillator 38, as indicated by line 40 in
FIG. 5, is fed through a frequency doubler circuit 41 of
conventional construction and over line 71. The resulting signal,
as indicated by curve 42, is fed to the upper input of the
comparator circuit 23. The output of the latter is fed through an
amplifier 43 and over line 73 to the solenoid 44 of an egg rejector
device 45. The latter is effective, upon energization of the
solenoid 44, to eject an egg being tested off the conveyer 19 and
into a suitable receptacle (not shown) for blood eggs.
In operating the apparatus, the filter 17 is first adjusted about
its vertical axis 31 with the filter in a vertical plane as
depicted at 17a, 17c, or 17e (FIG. 5) until it passes a wavelength
of essentially 578 nm which represents the point of maximum
absorption of oxidized blood hemoglobin. The amplitude of the drive
signal developed by the oscillator 38 is preferably adjusted, as by
a potentiometer 47, so that the filter, when at the limits of its
excursion in either direction, as depicted at 17b and 17d, will
pass a wavelength of essentially 573 nm which represents the point
b at the lower end of the blood absorption curve of FIG. 2.
Now, when a blood egg intercepts the beam 16, the photodiode 21
will develop a signal represented by curve 48 of FIG. 5. That is,
when the beam 16 constitutes light at essentially 578 nm, the
signal developed by the photodiode 21 will be at a minimum, as
indicated at 51, due to the maximum absorption by the blood at such
wavelength. However, the developed signal will be at a maximum, as
indicated at 52, when the beam 16 constitutes light at essentially
573 nm. Thus, when the signals from the photodiode 21 and from the
frequency doubler circuit are in their relative positions shown by
curves 42 and 48, the phase comparator circuit 23 will apply a
drive signal through amplifier 43 to energize the solenoid 44 to
eject the blood egg.
On the other hand, when a clear egg intercepts the beam 16, the
photodiode 21 will develop a signal represented by line 53 which is
in direct phase relation to the shift in wavelength of the beam 16.
That is, when the beam 16 constitutes light at 578 nm, the signal
will be at a maximum, as indicated at 54. However, when the beam 16
shifts to the shorter wavelength of 573 nm, the signal will be at a
minimum, as indicated at 55. In this case, the comparator circuit
will not apply a drive signal to the ejecting means.
It will be noted from the foregoing that the rejection signal is
developed entirely independently of the overall density of the egg
and of any measurement of the amount of light attenuated by blood
present in the egg but, instead, is determined solely by whether
the response of the photodiode 21 follows the gradient represented
by the curve a-b of FIG. 2 or the gradient represented by the curve
b-c.
In order to improve the sensitivity of the system, a light
polarizing filter 56 may be inserted in the beam 16.
FIG. 6 illustrates a modified form of the invention in which
elements similar to those of FIG. 1 are identified by similar
reference numerals. In this case, the oscillating filter 17 of FIG.
3 is replaced by a rotating filter disc 57 of the dielectric or
Fabry-Perot interference type which is rotated at a constant speed
by a motor 58. The disc has an interference coating which gradually
changes through 360.degree. in order to shift the wavelength of the
narrow band beam passing therethrough from essentially 578 nm to
573 nm. The developed curve 60 of FIG. 7 illustrates the bandpass
characteristic of the disc through 360.degree. of rotation.
The motor 58 is mounted on a bracket 61 which, in turn, is mounted
on a base 62 for adjustment about a vertical axis 63. A lock screw
64 is effective to lock the motor in any adjusted position.
Preferably, when the disc 57 is in a rotated position in which it
passes the longest wavelength, the motor is adjusted about axis 63
until such wavelength is precisely 578 nm.
A rotary potentiometer 64 is driven by the motor and its output is
connected to the upper input of the phase comparator circuit 23.
The output of the potentiometer is indicated by the curve 65 in
relation to the wavelength curve 60. In other respects, the system
of FIG. 6 operates the same as that of FIG. 3.
The motor 58 is preferably operated at a speed such that the light
beam will be shifted between 578 nm and 573 nm a number of times
while each egg intercepts such beam. Thus, a number of independent
tests are made of each egg to further insure reliability.
FIG. 8 illustrates a further modified form of the invention in
which elements similar to those found in FIG. 1 are identified by
the same reference numerals. Here, the filter 17 of FIG. 1 is
replaced by a tunable laser 66 which is capable of varying the
wavelength of the emitted beam 67 from 578 nm to 573 nm under
control of oscillator circuit 38. In this case, the circuit 38 is
directly connected to the upper input of the phase comparator
circuit 23. Tunable lasers of this type are commercially available,
for example, from Synergistics, Inc. of Princeton, N.J.
A suitable diffuser 68 is located in the beam 67 to disperse the
beam over the projected area of the egg 18.
In other respects, the system of FIG. 8 operates the same as that
of FIG. 3.
The oscillator circuit 38 is preferably operated at such a rate
that the light beam 67 will be shifted between 578 nm and 573 nm a
number of times while each egg intercepts the dispersed component
of such beam.
FIGS. 9 and 10 illustrate a preferred form of the phase comparator
circuit and the resulting signal waveform.
The signal received over line 71 from the frequency doubler circuit
41 is squared by clipping diodes 73, 74 and shunted by diode 75 and
amplifier 76 (see C). Such signal is inverted by inverter circuit
77 (see c) and the direct and inverted components of the signal are
fed over lines 78 and 79 and through diodes 80 and 81, to control
field effect transistors 82 and 83, respectively.
The signal received over line 70 from the photodiode 21 is
amplified by amplifier circuit 84 (see B). Part of such signal is
controlled by transistor 83 and another part is inverted by
amplifier circuit 85 and controlled by transistor 82. The resulting
components of both the direct and inverted parts of the signal B
are combined at point 86 (see D) and are fed through an integrator
87 to a voltage comparator circuit 88 resulting in a waveform (see
E) which, if blood is present, becomes increasingly more positive
potential until, at the end of the test period, the control
threshold for the egg ejecting device is exceeded. If, on the other
hand, blood is absent, the resulting waveform becomes of
increasingly more negative potential and is therefore ineffective
to control the ejecting device.
The integrating comparator 90 across integrator 87 is shorted by a
switch 91 between eggs and when no eggs are being tested.
* * * * *