U.S. patent number 3,810,005 [Application Number 05/344,932] was granted by the patent office on 1974-05-07 for flaw detection system using microwaves.
This patent grant is currently assigned to Industrial Development Design. Invention is credited to Don U. Bennion, Leonard R. West.
United States Patent |
3,810,005 |
Bennion , et al. |
May 7, 1974 |
FLAW DETECTION SYSTEM USING MICROWAVES
Abstract
A method and apparatus for the detection of flaws in pieces of
lumber or like material in which there may be wide variations in
density within each piece, or among the pieces being examined.
Lumber being processed is moved past two adjacent microwave
detectors positioned to receive microwave radiation transmitted
through the moving lumber from a conventional microwave source, and
the outputs from the detectors are amplified and compared in a
differential amplifier, the presence of flaws resulting in
difference signals which are used to generate pulses for
controlling a lumber processing device or for storage in a memory
device and use in subsequent processing steps.
Inventors: |
Bennion; Don U. (Salt Lake
City, UT), West; Leonard R. (Salt Lake City, UT) |
Assignee: |
Industrial Development Design
(Salt Lake City, UT)
|
Family
ID: |
23352728 |
Appl.
No.: |
05/344,932 |
Filed: |
March 26, 1973 |
Current U.S.
Class: |
324/639; 73/104;
73/159; 73/596; 144/357; 324/647; 340/600 |
Current CPC
Class: |
G01N
22/02 (20130101) |
Current International
Class: |
G01N
22/02 (20060101); G01N 22/00 (20060101); G01r
027/04 () |
Field of
Search: |
;324/58.5A,58A,95,58.5B
;246/169D ;340/248 ;73/104,159 ;144/312 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Krawczewicz; Stanley T.
Attorney, Agent or Firm: Fulwider, Patton, Rieber, Lee &
Utecht
Claims
1. For use with a system for detecting flaws in non-conducting
material having at least one widely varying physical characteristic
affecting the attenuation of microwave radiation transmitted
through the material, the combination comprising:
at least two microwave detectors positioned to receive microwave
radiation transmitted through and consequently attenuated by the
material;
signal difference sensing means responsive to differences in output
signals from said microwave detectors and non-responsive to
variations in attenuation characteristics of the material affecting
said microwave detectors substantially equally; and
electrical means for coupling said signal difference sensing means
to means for controlling processing of the material, whereby a flaw
in the material produces a momentary difference in output signals
from said microwave detectors as the flaw passes said detectors,
and the difference signal is used to control processing of the
material in such a fashion as to avoid
2. A combination as set forth in claim 1, wherein there are two
microwave
3. A combination as set forth in claim 1, wherein said electrical
means include level sensing means for rejecting signal differences
below a
4. A combination as set forth in claim 3, wherein said electrical
means include trigger circuit means for generating control pulse
signals in
5. A combination as set forth in claim 4, wherein said electrical
means include absolute value generation means equally responsive to
positive and
6. A combination as set forth in claim 4, wherein there are two
microwave
7. Apparatus for detection of flaws in moving lumber of widely
varying density, said apparatus comprising:
a source of microwave radiation positioned to irradiate the moving
lumber;
at least two microwave detectors adjacently positioned to receive
the radiation after transmission through the lumber and consequent
attenuation and distortion by the presence of flaws;
differential amplifier means for detecting and amplifying
differences in output signals from said microwave detectors, said
differences being generated as a result of flaws passing across one
of said detectors and said differential amplifier means being
non-responsive to variations in the output signals due to
variations in lumber density affecting said microwave detectors
substantially equally; and
electrical means for coupling said differential amplifier means to
means for controlling processing of the lumber in such a fashion as
to avoid the
8. Apparatus as set forth in claim 7, wherein there are two
microwave
9. Apparatus as set forth in claim 8, wherein:
said source of microwave radiation generates electromagnetic
radiation having a wavelength greater than 1 centimeter; and
10. Apparatus as set forth in claim 7, wherein said differential
amplifier means include level sensing means for rejecting signal
differences below a
11. Apparatus as set forth in claim 10, wherein said electrical
means include trigger circuit means for generating control pulse
signals in
12. Apparatus as set forth in claim 11, wherein there are two
microwave
13. Apparatus as set forth in claim 12, wherein said electrical
means include absolute value generation means equally responsive to
positive and
14. Apparatus as set forth in claim 13, wherein:
said source of microwave radiation generates electromagnetic
radiation having a wavelength greater than 1 centimeter; and
15. Apparatus for detection of flaws in moving lumber of widely
varying density, said apparatus comprising:
a source of microwave radiation positioned to irradiate the moving
lumber;
first and second microwave detectors positioned adjacently in the
line of motion of the lumber to receive the radiation after
transmission through the lumber and consequent attenuation and
distortion by the presence of flaws;
first and second single-ended operational amplifiers for receiving
and amplifying corresponding output signals from said first and
second microwave detectors;
a differential operational amplifier for detecting and amplifying
signal differences between the output signals from said first and
second microwave detectors, said signal differences resulting from
flaws passing across one of said detectors and said differential
operational amplifier being non-responsive to variations in the
output signals from said first and second single-ended operational
amplifiers due to variations in lumber density affecting said first
and second microwave detectors equally;
absolute value generation means for inverting negative signal
differences but not positive signal differences;
signal level sensing means for rejecting those of said signal
differences below a selectable threshold level and thereby
rejecting variations in the output signals from said first and
second single-ended operational amplifiers due to variations in
lumber density affecting said first and second microwave detectors
substantially equally; and
trigger circuit means for generating control pulse signals in
response to
16. Apparatus as set forth in claim 15, wherein:
said source of microwave radiation generates electromagnetic
radiation having a wavelength greater than 1 centimeter; and
17. Apparatus as set forth in claim 15, wherein:
said level sensing means includes at least one unijunction
transistor; and
said trigger circuit means includes at least one silicon
controlled
18. A method for detecting flaws in moving lumber of widely varying
density, comprising the steps of:
transmitting microwave radiation through the lumber;
measuring received radiation at at least two adjacent positions
substantially equally affected by attenuation variations caused by
the widely varying lumber density;
sensing significant differences in the radiation measured at said
adjacent positions, said differences resulting only from the
presence of flaws in the lumber moving through said adjacent
positions; and
generating in response to said significant differences control
signals for
19. A method as set forth in claim 18, wherein said step of
sensing
20. A method as set forth in claim 19, wherein said step of sensing
significant differences includes sensing the absolute magnitude of
said differences and rejecting those of said differences below a
selectable
21. A method as set forth in claim 20, wherein said step of
generating control signals includes triggering generation of
control pulse signals in
22. A method for detecting flaws in lumber of widely varying
density, comprising the steps of:
transmitting radiation from a microwave oscillator source;
moving the lumber through the microwave radiation;
receiving the microwave radiation at two adjacent microwave
detectors after transmission through the lumber, the two detectors
being substantially equally affected by variations in attenuation
of the radiation due to the widely varying lumber density;
detecting significant difference signals between outputs from the
two detectors, said significant difference signals resulting only
from the presence of flaws in the lumber moving across one of the
detectors; and
generating in response to said significant difference signals
control
23. A method as set forth in claim 22, wherein:
said step of transmitting utilizes a wavelength greater than 1
centimeter; and
24. A method as set forth in claim 22, wherein said step of
detecting significant difference signals includes inverting all
negative ones of the signal differences, thereby generating
absolute values of the signal
25. A method as set forth in claim 24, wherein said step of
detecting significant difference signals includes sensing the
absolute values of the signal differences and rejecting those below
a selectable threshold level.
26. A method as set forth in claim 25, wherein said step of
generating control signals includes triggering generation of
control pulse signals in response to those of said significant
difference signals above the
27. A method for detecting flaws in lumber with widely varying
density, comprising the steps of:
transmitting microwave radiation from a microwave oscillator
source;
receiving the microwave radiation at two adjacent microwave
detectors after transmission through the lumber;
moving the lumber between the microwave oscillator source and the
two microwave detectors in a direction substantially at right
angles to the direction of radiation;
amplifying output signals from the two microwave detectors in two
corresponding single-ended operational amplifiers;
detecting and amplifying in an operational amplifier difference
signals representative of the difference between the two output
signals, said difference signals resulting from the momentary
presence of flaws in the lumber moving across one of the
detectors;
disregarding gradual fluctuations in lumber density, said
fluctuations resulting in practically equal effects on the
microwave radiation received at the microwave detectors;
inverting all negative ones of said difference signals, thereby
generating absolute magnitudes of said difference signals;
sensing the absolute magnitudes of said difference signals and
rejecting those of said difference signals below a selectable
threshold level; and
generating control pulse signals for use in processing the lumber,
in response to those of said difference signals above the threshold
level.
28. A method as set forth in claim 25, wherein:
said step of transmitting utilizes a wavelength greater than 1
centimeter; and
the flaws to be detected exceed 3 millimeters in diameter.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to systems for the detection of
flaws in lumber and, more particularly, to lumber flaw detection
systems using microwave radiation. Such systems are used to supply
information for automatically marking or cutting the lumber into
desired lengths free of flaws.
In the prior art, short-wave electromagnetic radiation, widely
known as microwave radiation, has been used to detect flaws or
non-homogeneous zones in electrically non-conducting material,
particularly glass. The microwave radiation is either transmitted
through or reflected from the material being examined, and a
microwave receiver is used to detect variations in the transmitted
or reflected radiation caused by flaws in the material as it is
moved past the receiver.
Common defects in lumber, such as knots, pitch, and wind shake, are
non-homogeneous zones which can be readily detected using a
microwave technique. However, because lumber is not, in general, as
homogeneous as many synthetic materials, such as glass, prior art
microwave techniques are not directly transferable to lumber flaw
detection systems. Because of the widely varying moisture content
of lumber, the density of the lumber may vary widely within a
single piece as well as from piece to piece. These density
variations show up as variations in the received microwave
radiation, making the detection of flaws in the lumber very
difficult, if not impossible, using prior art methods. One possible
solution to this problem is to filter out the density variations,
which will generally be more gradual than the variations due to
flaws, by employing, for example, some form of capacitance coupling
in circuitry associated with the receiver. This is not a completely
satisfactory solution, however, since the speed of the lumber with
respect to the receiver then becomes a critical factor in the use
of the technique.
Ideally, a flaw detection system for lumber should be insensitive
to normal variations in density of the lumber from piece to piece
and within single pieces, while still remaining sufficiently
sensitive to changes in density due to flaws in the lumber.
Furthermore, this insensitivity to normal density variations should
not be achieved at the expense of a lower processing speed. The
present invention meets all of these needs.
SUMMARY OF THE INVENTION
The present invention resides in an improved method and apparatus
for the detection and location of flaws in lumber and like
material, using microwave radiation. Basically, the apparatus of
the invention includes a source of microwave radiation, at least
two microwave detectors, a differential amplifier for detecting a
difference in output between the detectors, and a means for
coupling the differential amplifier to a control or storage device
used for subsequent processing of the lumber.
Normal variations in the density of the lumber, because of their
gradual nature, will generally have equal effects on adjacent
detectors and will produce very little difference signal. Small
flaws such as knots, on the other hand, will affect the output of
only one detector at a time, and will result in a momentary
difference signal which can be used to operate a lumber marking or
cutting device, or stored for subsequent use in processing the
lumber.
The method of the present invention basically includes the steps of
transmitting microwave radiation through the lumber, measuring
received radiation at at least two adjacent positions, sensing
differences in the measured radiation at the adjacent positions,
and generating therefrom control signals for use in processing the
lumber.
More specifically, in a presently preferred embodiment of the
invention, two microwave detectors are employed, the output of each
being amplified and fed to a variable gain differential amplifier,
the output of which is proportional to the difference between the
outputs of the two detectors. Since the detectors are positioned
close together, gradual variations in lumber density produce no
difference signal, or a negligibly small difference signal, but
small flaws in the lumber produce substantial difference signals at
the output of the differential amplifier. An absolute value circuit
is included, following the differential amplifier, in order that
both positive and negative difference signals will be detected.
Then, a level sensing circuit serves a filtering function by
rejecting difference signals below a certain level, and passing
others on to a trigger circuit which, in cooperation with the level
sensing circuit, produces pulse signals to be stored or used to
operate lumber processing equipment.
It can be readily seen that the invention provides a new and useful
tool for the detection and location of flaws in lumber. The
invention overcomes the disadvantages of prior art microwave flaw
detection systems as applied to lumber and like materials, in that
small flaws can be conveniently distinguished from normal
fluctuations in density without imposing any limitation on lumber
processing speed. Other aspects and advantages of the invention
will become apparent from the following detailed description taken
in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a flaw detection system embodying the
invention; and
FIG. 2 is a more detailed electrical schematic diagram of the
system shown in FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As shown in the drawings for purposes of illustration, the
invention is embodied in an improved system using microwave
radiation for the detection of flaws, such as knots, pitch, and
wind shake, in lumber. It will be understood that, while the
invention is particularly well suited for the detection of flaws in
lumber, it could also be used for the detection of flaws in other
like materials, lacking perfect homogeneity.
In accordance with the present invention, as illustrated in FIG. 1,
a piece of lumber 10 being examined for flaws is passed between a
microwave oscillator source 11 and two microwave detectors 12 and
13, the outputs of which are amplified by two corresponding
amplifiers 14 and 15, and connected to a differential amplifier 16,
which produces an output proportional to the difference between the
outputs of the two microwave detectors. Since the detectors 12 and
13 are disposed close together in the line of motion of the lumber
10, gradual density variations along the length of the lumber will
generally affect both detectors equally, and will result in a
negligibly small difference signal, if any, at the output of the
differential amplifier 16. A small flaw, on the other hand, such as
the one shown at 17, will affect the output of only one of the
detectors 12 and 13 at a time and will produce a relatively large
difference signal at the output of the differential amplifier 16.
Thus, the system is capable of detecting flaws in material having
normal inherent density fluctuations.
More specifically, the microwave oscillator 11 is a conventional
microwave source, of either the klystron or the solid state diode
variety, generating microwave radiation having a wavelength
typically in excess of one centimeter. Flaws detected by the system
are typically larger than one-eighth inch (approximately 3 mm) in
diameter. The microwave detectors 12 and 13 are positioned adjacent
to each other in the path of the radiation transmitted through the
lumber 10, and include microwave horns and diode detectors of
conventional design.
The amplifiers 14 and 15, to which the outputs of the detectors 12
and 13 are connected, are single-ended operational amplifiers.
Since these devices have a characteristically high input impedance
and low output impedance, they serve the dual function of
amplification and impedance transformation. The differential
amplifier 16 is also an operational amplifier, connected to have a
variable gain so that the sensitivity of the detection system may
be varied.
The output from the differential amplifier 16 is connected to an
absolute value circuit 18 providing a positive output signal equal
in magnitude to that of its input signal but without regard to the
sign of the input signal. The output from the absolute value
circuit 18 is, in turn, connected to a level sensing circuit 19,
which serves a filtering function in that it rejects difference
signals below a certain selectable threshold value. Difference
signals of sufficient magnitude to activate the level sensing
circuit 19 are conveyed to a trigger circuit 20, which, in
cooperation with the level sensing circuit, produces signals in
pulse form to operate a lumber marking device 21, or other lumber
processing device, or to be stored in computer memory and logic
elements 22 for subsequent use in processing the lumber 10.
Referring now to FIG. 2, there is shown by way of example and not
by way of limitation, a detailed schematic diagram of a presently
preferred embodiment of the invention. The amplifiers 14 and 15 and
the differential amplifier 16 each include an operational, or d.c.
amplifier having characteristically high gain, high input
impedance, and low output impedance. Such operational amplifiers
are typically available in integrated circuit form. In a presently
preferred embodiment of the invention, each of the three amplifiers
14, 15 and 16 utilizes one-half of a dual operational amplifier
integrated circuit chip, device type MC1437L, manufactured by
Motorola Semiconductor Products, Inc., Phoenix, Ariz.
The first operational amplifier 14 has an inverting input terminal
25, a non-inverting input terminal 26, an output terminal 27, a B+
power supply terminal 28, a B- power supply terminal 29, two input
lag terminals 30 and 31, and an output lag terminal 32. The second
operational amplifier 15 has an inverting input terminal 34, an
non-inverting input terminal 35, an output terminal 36, a B+ power
supply terminal 37, a B- power supply terminal 38, two input lag
terminals 39 and 40, and an output lag terminal 41. Similarly, the
differential amplifier 16 has an inverting input terminal 43, a
non-inverting input terminal 44, an output terminal 45, a B+ power
supply terminal 46, a B- power supply terminal 47, two input lag
terminals 48 and 49, and an output lag terminal 50.
Both the amplifiers 14 and 15 are connected in a non-inverting
configuration, i.e., the output has the same sign as the input. The
output of the first microwave detector 12 is applied between the
non-inverting input terminal 26 of amplifier 14 and ground, a
variable feedback resistor R51 connects the output terminal 27 to
the inverting input terminal 25, and another resistor R52 is
connected between the inverting input terminal 25 and ground. In
this configuration, the closed loop gain, i.e., the ratio of the
voltage at the output terminal 27 to the voltage at the
non-inverting input terminal 26 is positive and is determined
primarily by the values of the resistors R51 and R52. Power is
supplied to the amplifier 14 through the power supply terminals 28
and 29, and frequency compensation of the amplifier is provided by
a resistor R53 and a capacitor C54 connected in series between the
input lag terminals 30 and 31 and a further capacitor C55 connected
between the output terminal 27 and the output lag terminal 32.
The second amplifier 15 is connected in a similar fashion, i.e.,
the output from the second microwave detector 13 is applied between
the non-inverting input terminal 35 and ground, a variable feedback
resistor R56 is connected between the output terminal 36 and the
inverting input terminal 34, and another resistor R57, is connected
between the inverting input terminal 34 and ground. Again, power
supplied to the amplifier 15 through the power supply terminals 37
and 38, and frequency compensation is provided by a resistor R58
and a capacitor C59 connected in series between the input lag
terminals 39 and 40, and a further capacitor C61 connected between
the output terminal 36 and the output lag terminal 41.
Output from the amplifier 14 is connected from the output terminal
27 through a resistor R62 to the inverting input terminal 43 of the
differential amplifier 16, and output from the amplifier 15 is
connected from the output terminal 36 through a resistor R63 to the
non-inverting input terminal 44 of the differential amplifier. A
feedback resistance comprising two resistors R64 and R65 in series
is connected between the output terminal 45 and the inverting input
terminal 43. Another resistance consisting also of two resistors
R66 and R67 in series is connected between the non-inverting input
terminal 44 and ground, and a variable resistor R68 is connected
between the junction point of resistors R64 and R65, and the
junction point of resistors R66 and R67. In this configuration, the
differential amplifier 16 produces an output signal between its
output terminal 45 and ground which is proportional to the
difference between the output signals of amplifiers 14 and 15, and
the variable resistor R68 operates to vary the gain of the
differential amplifier. As in the other amplifiers, power is
supplied to the differential amplifier 16 through the power supply
terminals 46 and 47, and frequency compensation is effected by
means of a resistor R69 and a capacitor C71 connected in series
between the input lag terminals 48 and 49, and a further capacitor
C72 connected between the output terminal 45 and the output lag
terminal 50.
The absolute value circuit 18 utilizes an additional operational
amplifier 74, which, like the others, has an inverting input
terminal 75, a non-inverting input terminal 76, an output terminal
77, power supply terminals 78 and 79, input lag terminals 81 and
82, and an output lag terminal 83. A feedback resistor R84 is
connected between the output terminal 77 and the inverting input
terminal 75, and frequency compensation is provided by a resistor
R85 and a capacitor C86 connected in series between the input lag
terminals 81 and 82, and a further capacitor C90 connected between
the output terminal 77 and the output lag terminal 83.
The output of the differential amplifier 16 is connected to the
absolute value circuit through a network including three diodes 87,
88 and 89, two resistors R91 and R92, and a voltage divider
consisting of an additional resistor R93 connected to the B+
voltage, and a low-resistance potentiometer R94 connecting the
resistor R93 to ground.
The output terminal 45 of the differential amplifier 16 is
connected through the resistor R91 to the inverting terminal 75,
and is also connected to the anode of the first diode 87, the
cathode of which is connected to the anode of the second diode 88.
The cathode of the second diode 88 is, in turn, connected through
the resistor R92 to the inverting terminal 75. Finally, the sliding
contact of the potentiometer R94 is connected to the anode of the
third diode 89, the cathode of which is connected both to the
non-inverting input terminal 76 and to the junction point between
the first and second diodes 87 and 88.
In a presently preferred embodiment of the invention, the feedback
resistor R84 is 10k.OMEGA., and the resistors R91 and R92 are
10k.OMEGA. and 5k.OMEGA., respectively. With these values of
resistance, the absolute value circuit 18 acts as an inverter with
a gain of unity when negative signals are presented to it, and as a
unity-gain amplifier for positive signals. For negative input
signals, the only effective path is through the resistor R91 to the
inverting input terminal 75, since other possible paths are blocked
by the first diode 87. The non-inverting, or positive terminal 76
is held as close to ground potential as possible by adjustment of
the potentiometer 94, and, for negative input signals, the circuit
is effectively connected in a conventional inverting configuration
for operational amplifier, the closed loop gain being primarily
determined by the ratio of the resistances R84 and R91, i.e.,
-1.
For positive inputs, there are three possible paths: through the
resistor R91 to the inverting input terminal 75, through the first
diode 87 to the non-inverting input terminal 76, and through the
first and second diodes 87 and 88 and the resistor R92 to the
inverting input terminal 75. Using familiar principles of
superposition, the closed loop gain can be computed for each path
separately, and the values added to obtain the effective gain for
positive input signals. For the first path, through the resistor
R91 to the inverting terminal 75, the gain is -1, as was shown for
negative input signals. The second path, through the first diode 87
to the non-inverting input terminal 76, is effectively a
conventional non-inverting configuration for operational
amplifiers, with the input connected to the non-inverting input
terminal, and the inverting input terminal 75 having a resistance
to ground comprising the resistors R91 and R92 in parallel, i.e., a
value of 10/3k.OMEGA..
If the input voltage is designated e.sub.1 and the voltage drop
across the first and second diodes 87 and 88 are designated v.sub.1
and v.sub.2, respectively, then the voltage applied to the
non-inverting input terminal 76 through the second path is (e.sub.1
- v.sub.1) and the closed loop gain for this voltage is: 1 + (R84
.div. 10/3) = +4.
For the third path, through the first and second diodes 87 and 88
and the resistor R92, the effective input voltage is (e.sub.1 -
v.sub.1 - v.sub.2) and the closed loop gain is -R84/R92, or -2.
Thus, the overall closed loop gain sums to +1, if v.sub.1 = v.sub.2
; and the absolute value circuit 18 outputs to the level sensing
circuit 19 a positive signal equal in magnitude to that of the
input signal.
The level sensing circuit 19 (FIG. 1) and the trigger circuit 20
(FIG. 1) include, as shown in FIG. 2, two unijunction transistors
96 and 97, two silicon controlled rectifiers (SCR's) 98 and 99, a
NAND gate 101, and an npn transistor 102. The output signal from
the absolute value circuit 18 is applied from the output terminal
77 through diode 103 and a resistor R104 to the emitter terminal of
the first unijunction transistor 96, the base-one terminal of the
unijunction transistor 96 is connected to ground through a resistor
R105, and power is supplied to the base-two terminal of the
unijunction transistor 96 through a resistor R106. In a presently
preferred embodiment of the invention, the first unijunction
transistor 96 will be turned on when the output from the absolute
value circuit 18 is in the region of 50 to 80 per cent of the power
supply (B+) voltage.
Whenever the first unijunction transistor 96 is turned on by a
sufficiently high output voltage from the differential amplifier
16, the first SCR 98 is also turned on, since the base-one terminal
of the first unijunction transistor 96 is connected to the gate
terminal of the first SCR 98, the anode terminal of which is
supplied with power (B+) through a resistor R107, and the cathode
terminal of which is connected to ground through a resistor R108. A
capacitor C109 is connected between the anode terminal of the SCR
98 and ground, so that, when the SCR 98 is non-conducting, the
capacitor C109 is charged from the power supply. When the SCR 98 is
triggered, the capacitor C109 is discharged through the SCR 98 and
through the resistor R108 to ground.
The pulse generated by the discharge of the capacitor C109 is fed
through a coupling capacitor C111 to the emitter terminal of the
second unijunction transistor 97, which has its base-one terminal
connected to ground through a resistor R112 and its base-two
terminal connected to the power supply (B+) through a resistor
R113. In a voltage divider circuit consisting of a resistor R114
and a variable resistor R115 connected in series between the power
supply (B+) and ground, the junction between the resistors R114 and
R115 is connected to the emitter terminal of the second unijunction
transistor 97, and the variable resistor R115 is adjusted so that a
pulse from the capacitor C109 in the circuit of the first SCR 98
will, together with the voltage from the voltage divider circuit,
apply a high enough voltage to the emitter of the second
unijunction transistor 97 to momentarily turn that device on.
The second SCR 99 has its anode terminal connected to the power
supply (B+) through two resistors R116 and R117 in series, the
resistor R117 being variable and connected to the anode. A
capacitor C118 is connected between the junction of the two
resistors R116 and R117 and ground, the cathode of the SCR 99 is
connected to ground, and the base-one terminal of the second
unijunction transistor 97 is connected to the gate terminal of the
second SCR 99. Thus, when the second unijunction transistor 97 is
turned on, a pulse is applied to the gate terminal of the second
SCR 99, which is turned on by the pulse. The capacitor C118, which
is charged when the SCR 99 is non-conducting, is discharged through
the resistor R117 and the SCR 99 when the latter is triggered, thus
momentarily lowering the potential at the anode of the SCR 99.
The combination of the two unijunction transistors 96 and 97 and
the two SCR 98 and 99 is designed to provide one short pulse to the
NAND gate 101, which has one input connected to the anode terminal
of the second SCR 99 and the other input terminal grounded. The
logic of the NAND gate is such that ground voltage is a logical "1"
and a positive voltage is a logical "0." Thus, the inputs change
momentarily from "0" and "1" to "1" and "1," respectively, when the
anode potential of the SCR 99 falls, and the output of the NAND
gate 101 momentarily changes from "1" to "0," i.e., a positive
pulse is output. The output terminal of the NAND gate 101 is
connected to the base terminal of the npn transistor 102, the
emitter terminal of which is grounded and the collector terminal of
which is connected to the power supply (B+) through a relay 119.
When the NAND gate 101 is pulsed, the transistor 102 is momentarily
forward biased, and the resulting collector current operates the
relay 119. As shown by way of example in FIG. 2, the relay 119 may
operate a switch 121 in an a.c. circuit 122 connected to supply
power to the lumber marking device 21, or the operation of the
unijunction transistors 96 and 97 can be used to enter information
into computer memory and logic circuits 22 (FIG. 1).
Normally, the RC time constant of the trigger circuit 20 is
adjusted, using the variable resistor R117, to keep the transistor
102 switched on for long enough for a flaw to pass the second of
the two detectors 12 and 13. Thus, for a given maximum flaw size
and lumber speed, only one pulse would be generated during the
transition of one flaw past the detector system. For very large
flaws, a second pulse will be generated as the last portion of the
flaw passes the second detector. This will usually be a desirable
result, since a small flaw can be removed with a single cut of a
double-blade saw, while a large flaw will require two cuts.
In a presently preferred embodiment of the invention, the following
values of resistance and capacitance may be used. It will be
understood by those of ordinary skill in the electronics art that
the invention is not limited to circuitry using the specific values
set forth herein.
R51 10k.OMEGA. (max.) R105 100.OMEGA. R52 1k.OMEGA. R106 470.OMEGA.
R53 1.5k.OMEGA. R107 1M.OMEGA. R56 10k.OMEGA. (max.) R108 1k.OMEGA.
R57 1k.OMEGA. R112 100.OMEGA. R58 1.5k.OMEGA. R113 470.OMEGA. R61
10k.OMEGA. R114 30k.OMEGA. R63 10k.OMEGA. R115 50k.OMEGA. (max.)
R64 10k.OMEGA. R116 1M.OMEGA. R65 10k.OMEGA. R117 5k.OMEGA. (max.)
R66 10k.OMEGA. C54 100pfd R67 10k.OMEGA. C55 100pfd R68 10k.OMEGA.
(max.) C59 100pfd R69 1.5k.OMEGA. C61 100pfd R84 10k.OMEGA. C71
100pfd R85 1.5k.OMEGA. C72 100pfd R91 10k.OMEGA. C86 100pfd R92
5k.OMEGA. C90 100pfd R93 10k.OMEGA. C109 0.1.mu.fd R94 500.OMEGA.
C111 1.mu.fd R104 1k.OMEGA. C118 5.mu.fd
In the presently preferred embodiment, conventional components are
employed throughout. As mentioned above, the operational amplifiers
used in the embodiment are half-sections of dual operational
amplifier modules designated MC1437L. The SCR's employed are
designated 2N5060, the unijunction transistors 2N4891, the diodes
1N34A, the NAND gate MC673P, and the npn transistor 2N4921. Again
it will be understood that the invention is not limited to the use
of these specific components.
From the foregoing, it can be seen that the invention as described
in detail for purposes of illustration, provides a new and useful
tool for the detection and location of flaws in lumber and like
material. Small flaws in moving pieces of lumber can be reliably
detected and located, and can be conveniently distinguished from
normal fluctuations in lumber density without imposing any
limitation on processing speed. It will also be seen that, while a
particular form of the invention has been illustrated and
described, various modifications can be made without departing from
the spirit and scope of the invention. Accordingly, the invention
is not to be limited, except as by the appended claims.
* * * * *