U.S. patent number RE30,967 [Application Number 06/124,052] was granted by the patent office on 1982-06-15 for automatically controlled weigh feeding apparatus.
This patent grant is currently assigned to Acrison, Inc.. Invention is credited to Angelo Ferrara, Ronald J. Ricciardi, Alexander A. Urban.
United States Patent |
RE30,967 |
Ferrara , et al. |
* June 15, 1982 |
Automatically controlled weigh feeding apparatus
Abstract
Disclosed herein is an automatically controlled weigh feeding
system including a container prefilled with a substance, a device
for discharging the substance from the container at a controllable
rate, apparatus for weighing the container and its contents and for
producing an electrical signal proportional to that weight,
apparatus actuated by the electrical signal for controlling the
discharge of the substance from the container, and a detector
circuit actuated by the electrical signal for producing an output
which is responsive to predetermined excessive excursions of the
electrical signal for locking the discharge control apparatus
against deviation during the time of the excessive excursion.
.Iadd.
Inventors: |
Ferrara; Angelo (Fairfield,
NJ), Ricciardi; Ronald J. (Garfield, NJ), Urban;
Alexander A. (Park Ridge, NJ) |
Assignee: |
Acrison, Inc. (Moonachie,
NJ)
|
[*] Notice: |
The portion of the term of this patent
subsequent to June 17, 1992 has been disclaimed. |
Family
ID: |
27494516 |
Appl.
No.: |
06/124,052 |
Filed: |
February 25, 1980 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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345587 |
Mar 28, 1973 |
3889848 |
|
|
|
274844 |
Jul 25, 1972 |
|
|
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Reissue of: |
550639 |
Feb 18, 1975 |
03967758 |
Jul 6, 1976 |
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Current U.S.
Class: |
222/58;
700/240 |
Current CPC
Class: |
G01G
11/08 (20130101); G01G 15/00 (20130101); G01G
13/28 (20130101) |
Current International
Class: |
G01G
11/00 (20060101); G01G 11/08 (20060101); G01G
13/28 (20060101); G01G 13/00 (20060101); G01G
15/00 (20060101); G01G 011/14 () |
Field of
Search: |
;177/122,1,157
;222/58,36,55 ;318/345 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Tollberg; Stanley H.
Attorney, Agent or Firm: Davis, Hoxie, Faithfull &
Hapgood
Parent Case Text
This is a continuation-in-part of our copending application Ser.
No. 345,587, filed Mar. 28, 1973, which issued as U.S. Pat. No.
3,889,848 and which, in turn, is a continuation-in-part of a parent
application Ser. No. 274,844, filed July 25, 1972 (and later
abandoned). .Iaddend.
Claims
We claim:
1. A weigh feeding apparatus comprising a container for a prefilled
substance, means for discharging the substance from the container
at a controllable rate, means for weighing the container and its
contents and for producing an electrical signal proportional to the
weight, means actuated by said electrical signal for controlling
the discharge of the substance from the container, detector circuit
means actuated by said electrical signal for producing an output
which is responsive to predetermined excessive excursions of said
electrical signal, and means responsive to said output for locking
the discharge control means against deviation during the time of
said excessive excursion. .[.2. A weigh feeding apparatus according
to claim 1 wherein said detector circuit means
comprises an adjustable gain amplifier..]. 3. A weigh feeding
apparatus comprising a container for a prefilled substance; means
for discharging said substance from the container at a controllable
rate; means for weighing said container prefilled with said
substance; means coupled to said weighing means for producing an
electrical signal proportional to the weight determined by said
weighing means; first circuit means having an output terminal and
having an input coupled to said electrical signal means for
providing a rate signal at said output terminal which is
proportional to the discharge rate of said substance from said
container; control signal generating means having an output
terminal, and having an input terminal connected to said first
circuit means output terminal, wherein said control signal means is
for generating at its output terminal a discharge control signal
which is a function of said rate signal; and means coupled between
said control signal generating means output terminal and said means
for discharging said substance, for controlling the discharge rate
of said discharging means in response to said discharge control
signal, detector circuit means having an output terminal and having
an input coupled to said electrical signal means for producing an
output which is responsive to predetermined excessive excursions of
said electrical signal, means coupled between the output terminal
of said detector circuit means and said control signal generating
means for maintaining said control signal constant during the time
of said excessive excursions. .[.4. A weigh feeding apparatus
according to claim 3 wherein said detector circuit means comprises
an alternating current coupled, adjustable gain amplifier with
frequency response..]. .[.5. A weigh feeding apparatus according to
claim 3 wherein said detector circuit means comprises an
alternating current coupled amplifier, said amplifier having an
input terminal connected to the input of the detector circuit means
through an input capacitor and to ground through a resistor, a
feedback capacitor connected between an output terminal and a
second input terminal of said amplifier, said output terminal of
the amplifier being coupled to a feedback potentiometer disposed
between two resistors, the other terminal of one of said resistors
being connected to ground through a capacitor and resistor
connected in parallel, and the wiper arm of said potentiometer
being coupled to said second input terminal of said amplifier to
control the gain of the amplifier, and said output terminal of said
amplifier being coupled through an output capacitor to said
output
terminal of said detector circuit means..]. 6. Apparatus for
feeding particulate solid material comprising a container for a
quantity of said particulate solid material; means for discharging
said particulate solid material from the container at a
controllable rate; means for weighing said container prefilled with
said particulate solid material; means coupled to said weighing
means for producing .[.and.]. .Iadd.an .Iaddend.electrical signal
proportional in amplitude to the weight determined by said weighing
means; differentiator circuit means having an output terminal and
having an input coupled to said electrical signal means, wherein
said differentiator circuit means is for differentiating said
electrical signal to provide a rate signal at said output terminal
which is proportional in amplitude to the discharge rate of said
particulate solid material from said container; control signal
generating means having an output terminal, and having an input
terminal connected to said differentiator circuit means output
terminal, wherein said control signal means is for generating at
its output terminal a discharge control signal which is a function
of the amplitude of said rate signal; and means coupled between
said control signal generating means output terminal and said means
for discharging said particulate solid material for controlling the
discharge rate of said discharging means in response to said
discharge control signal, electrically actuatable means for
refilling said container, first detector means for detecting when
the quantity of said particulate .[.said.]. .Iadd.solid
.Iaddend.material in said container is less than a desired minimum
quantity, second detector means for detecting when the quantity of
said particulate solid material in said container is greater than a
desired maximum quantity, switching means coupled between said
first and second detector means and said means for refilling said
container for energizing said electrically actuatable refilling
means in response to detection by said first detector means
.[.to.]. .Iadd.of .Iaddend.said desired minimum quantity, and for
maintaining said refilling means in said energized state until
detection by said second detector means of said desired maximum
quantity, detector circuitry means having an output terminal and
having an input coupled to said electrical signal means for
producing an output which is responsive to predetermined excessive
excursions of said electrical signal means, means coupled between
the output terminal of said detector circuit means and said control
signal generating means for maintaining said control signal
constant during the time of said excessive excursions. 7. Apparatus
for feeding particulate solid material comprising a container for a
quantity of said particulate solid material; means for discharging
said particulate solid material from the container at a
controllable rate; means for weighing said container prefilled with
said particulate solid material; means coupled to said weighing
means for producing an electrical signal proportional in amplitude
to the weight determined by said weighing means; differentiator
circuit means having an output terminal and having an input coupled
to said electrical signal means, wherein said differentiator
circuit means is for differentiating said electrical signal to
provide a rate signal at said output terminal which is proportional
in amplitude to the discharge rate of said particulate solid
material from said container; control signal generating means
having an output terminal, and having an input terminal connected
to said differentiator circuit means output terminal, wherein said
control signal means is for generating at its output terminal a
discharge control signal which is a function of the amplitude of
said rate signal; and means coupled between said control signal
generating means output terminal and said means for discharging
said substance, for controlling the discharge rate of said
discharging means in response to said discharge control signal,
detector circuit means having an output terminal and having
.[.and.]. .Iadd.an .Iaddend.input coupled to said electrical signal
means for producing an output signal which is responsive to a
predetermined excessive excursion of said electrical signal,
voltage sensing circuit means coupled between the output terminal
of said detector circuit means and said control signal generating
means for maintaining said control signal constant during the
time of said excessive excursion. 8. Apparatus for feeding
particulate solid material, comprising a container for a quantity
of said particulate solid material; means for discharging said
particulate solid material from the container at a controllable
rate; means for weighing said container prefilled with said
particulate solid material; means coupled to said weighing means
for producing an electrical signal proportional in amplitude to the
weight determined by said weighing means; differentiator circuit
means having an output terminal and having an input coupled to said
electrical signal means, wherein said differentiator circuit means
is for differentiating said electrical signal to provide a rate
signal at said output terminal which is proportional in amplitude
to the discharge rate of said particulate solid material from said
container; control signal generating means having an output
terminal, and having an input terminal connected to said
differentiator circuit means output terminal, wherein said control
signal means is for generating at its output terminal a discharge
control signal which is a function of the amplitude of said rate
signal, and means coupled between said control signal generating
means output terminal and said means for discharging said
substance, for controlling the discharge rate of said discharging
means in response to said discharge control signal; said means for
producing said electrical signal being a linearly variable
differential transformer; said means coupled between said
discharging means and said control signal generating means
including an electric motor for driving said discharging means; and
said control signal generating means including a reference signal
source, a comparator having first and second inputs connected
respectively to said reference signal source and said
differentiator circuit means output terminal, and having an output
for providing a comparison signal in response to said signals from
said reference source and differentiator circuit means, and motor
drive signal generating means having an input connected to said
comparator output, and having an output which provides said
discharge control signal for controlling the speed of said motor;
detector circuit means having an input connected to said electrical
signal means for producing an output signal which is responsive to
a predetermined excessive excursion of said electrical signal,
voltage sensing circuit means having an input coupled to an output
terminal of said detector circuit means, .[.and.]. .Iadd.an
.Iaddend.indicating meter for providing a visual indication of the
discharge rate of said fluid substance as it is discharged from the
container, .Iadd.and .Iaddend.signal holding means having an input
coupled to the differentiator circuit means output to provide an
indicating signal to said indicating meter, said voltage sensing
circuit means having an output coupled to said signal holding means
and said comparator for completing feedback paths in said signal
holding means and comparator during the time that said detector
circuit means detects said excessive excursion for the purpose of
maintaining constant outputs from said comparator and signal
holding means during said time. .Iadd.9. A weigh feeding apparatus
comprising a container for a prefilled substance, means for
discharging the substance from the container at a controllable
rate, means for weighing the container and its contents for
producing an electrical signal proportional to the weight, said
electrical signal exhibiting excessive excursions in response to
disturbances impinging on said weighing means, means actuated by
said electrical signal for controlling the discharge of the
substance from the container, detector circuit means actuated by
said electrical signal for producing an output which is responsive
to predetermined excessive excursions of said electrical signal,
and means responsive to said output for locking the discharge
control means against deviation during the time of said
predetermined excessive excursions. .Iaddend. .Iadd.10. Weigh
feeding apparatus as in claim 9, wherein said detector means
produces an output for each excursion of said electrical signal
which has an acceleration or deceleration in excess of a
predetermined value, and said responsive means locks the discharge
control means against deviation while each said excessive excursion
continues. .Iaddend. .Iadd.11. Weigh feeding apparatus as in claim
10, wherein said discharge control means includes differentiator
circuit means actuated by said electrical signal for producing a
second electrical signal which is proportional to the actual rate
of discharge of said substance from said container, and wherein
said apparatus also includes a discharge rate indicator actuated by
said second electrical signal for displaying the actual rate of
discharge of the substance from the container, said discharge rate
indicator displaying a constant value while the predetermined
excessive excursion of the electrical signal continues. .Iaddend.
.Iadd.12. Weigh feeding apparatus as in claim 11, wherein said
discharging means includes a mechanism for moving said substance
and a motor for driving said mechanism, and wherein said discharge
control means also includes circuit means for establishing a third
electrical signal indicative of the desired discharge rate, a
comparison circuit for receiving and comparing said second and
third electrical signals to produce a fourth electrical signal
which is proportional to the difference between said second and
third signals, further circuit means for combining said fourth
signal with a fifth electrical signal representative of the
existing speed of said motor to produce a sixth electrical signal
having a value responsive to the relative values of said fourth and
fifth signals, and circuit means for delivering said sixth
electrical signal to said motor to control the speed thereof.
.Iaddend. .Iadd.13. A weigh feeding apparatus comprising a
container for a prefilled substance, means for discharging the
substance from the container at a controllable rate, first circuit
means for establishing a first electrical signal indicative of the
desired discharge rate, means for weighing the container and its
contents and for producing a second electrical signal proportional
to the weight thereof, means actuated by said second electrical
signal for differentiating said second signal to produce a third
electrical signal representative of the actual rate of discharge of
said substance from the container and for controlling the discharge
rate in accordance with the relative values of said first and third
electrical signals, said discharge control means supplying a
control signal to said discharging means, second circuit means for
detecting disturbances sensed by said weighing means which occur at
a rate which is faster than changes in said actual discharge rate,
said second circuit means including detector circuit means actuated
by said second electrical signal for producing an output signal
which is responsive to predetermined excessive excursions of said
second electrical signal, and means responsive to said output
signal for locking the discharge control means against deviation
during the time of said predetermined excessive excursions.
.Iaddend. .Iadd.14. A weigh feeding apparatus as in claim 13,
wherein, during the time of the predetermined excessive excursions,
said responsive means locks the discharge control means at the
discharge rate set by the immediately preceding control signal
supplied to the discharging means. .Iaddend. .Iadd.15. A weigh
feeding apparatus comprising a container for a prefilled substance,
means for discharging the substance from the container at a
controllable rate, means for weighing the container and its
contents and for producing an electrical signal proportional to the
weight, said electrical signal exhibiting excessive excursions in
response to disturbances impinging upon said weighing means, means
actuated by said electrical signal for controlling the discharge of
the substance from the container, sensing circuit means responsive
to said electrical signal for sensing when said weight reaches a
predetermined minimum and when it reaches a predetermined maximum,
refill means responsive to said sensing circuit means for
initiating a refill of said container, while the discharge of
substance from said container continues, when the weight has
reached said predetermined minimum, and for discontinuing the
refill operation when the weight has reached said predetermined
maximum, detector circuit means actuated by said electrical signal
for producing an output signal which is responsive to predetermined
excessive excursions of said electrical signal, and means
responsive to said sensing circuit means and to the output signal
from the detector circuit means for locking the discharge control
means against deviation during the refill operation and during the
time of said predetermined excessive excursions. .Iaddend.
.Iadd.16. Weigh feeding apparatus as in claim 15, wherein said
electrical signal exhibits excessive excursions in response to
disturbances impinging upon said weighing means which produce
forces other than the forces resulting from the weight of the
substance in the container, or from the changes in such weight,
wherein said detector circuit means produces an output signal for
each excursion of said electrical signal which has an acceleration
or deceleration in excess of a predetermined value, and wherein
said responsive means locks the discharge control means against
deviation while said excessive excursion continues. .Iaddend.
.Iadd.17. Weigh feeding apparatus as in claim 16, wherein said
discharge means constitutes a double auger mechanism for
maintaining a constant volumetric feeding of the substance while
said responsive means is operating to lock the discharge control
means against deviation. .Iaddend. .Iadd.18. A weigh feeding
apparatus comprising a container for a prefilled substance, means
for discharging the substance from the container at a controllable
rate, means for weighing the container and its contents and for
producing an electrical signal proportional to the weight, said
electrical signal changing in value as substance is discharged from
the container and the weight of its contents decreases, said
electrical signal changing in value more rapidly and exhibiting an
excessive excursion for each disturbance which is sensed by said
weighing means as a more rapid change in weight, means actuated by
said electrical signal for controlling the discharge of the
substance from the container, circuit means for providing
protection against excessive disturbances including detector
circuit means actuated by said electrical signal for producing an
output which is responsive to predetermined excessive excursions of
said electrical signal, and means responsive to said output for
locking the discharge control means against deviation during the
time of said excessive excursions. .Iaddend. .Iadd.19. Weigh
feeding apparatus as in claim 18, wherein said detector circuit
produces an output for each change of said electrical signal beyond
a predetermined amount, from one instant in time to the next, and
said responsive means is for locking said discharge control means
against deviation during the time such change occurs. .Iaddend.
Description
This invention relates to weigh feeding systems and it is
particularly applicable to apparatus for feeding particulate solid
material. Systems constructed according to the present invention
are particularly adapted among other possible uses for accurately
weigh feeding a wide variety of substances including dry materials
regardless of whether the material is free-flowing, sluggish, or
pressure sensitive, and ranging from amorphous powders to flakes,
pellets, chunks and even fibers, as well as liquids.
Various controlled weigh feeding systems have been known in the
past, as for example, the system disclosed in U.S. Pat. No.
3,494,507, wherein a weighing device is incorporated for providing
an output signal which is used as one of the parameters for
controlling the discharge rate of the system. Thus, in the
above-cited patent, the contents of a container are discharged onto
a conveyor moving at a known rate, and the weight of the conveyor
is detected, so that the numerical values corresponding to the
weight of the conveyor and the speed thereof can be combined to
provide a discharge rate signal to an indicator device. It has been
found, however, that the system as disclosed in the above-cited
patent is highly effective except where extremely low rates and
optimum accuracy are required, wherefore it is desirable to provide
a weigh feeding system having a discharge rate which can be
controlled to a high degree of accuracy, and which can be adjusted
from a fraction of a pound per hour upwards.
The present invention is closely related to U.S. Pat. No.,
3,889,848 issued June 17, 1975, and is directed to improvements of
the apparatus described and claimed therein. In accordance with
this application, there is provided a weigh feeding apparatus
wherein the discharge rate of a fluid substance from a container is
maintained at a predetermined constant value. The container and its
contents are weighed, and an electrical signal is produced which
signal has an amplitude proportional to the weight of the container
and its contents. This electrical signal, which varies as the
contents of the container are discharged, is differentiated and
applied to a comparator circuit together with a reference signal,
wherefore the output of the comparator circuit may be used to
control said discharge rate of the substance as it is fed from the
container. The comparator output is applied to a signal generator
for producing a motor drive signal for a DC motor having its output
shaft connected to drive a device for discharging the substance
from the container. That signal generator may comprise a pulsing
circuit for controlling a pair of SCR's which are disposed in a
rectifying bridge circuit connected between an AC voltage source
and the input of the DC motor. Accordingly, the speed of the motor
is controlled by the pulsing circuit, which, in turn, is controlled
by the algebraic sum of the output signal of a tachometer generator
which is coupled directly to the motor shaft, and the output signal
from the comparator. It can be seen that the above-described
apparatus provides an accurate weigh feeding system, whereby the
feeding rate may be maintained at a constant value, and wherein the
predetermined feeding rate may be adjusted by adjusting the value
of the reference signal source.
Additionally, the output of the weighing device may be applied to a
pair of differential amplifier circuits, along with a pair of
reference voltage inputs, for determining when the contents of the
container varies above and below desired maximum and minimum fill
levels for the container. That is, circuitry is provided for
automatically refilling the container when the weight of the
substance therein reaches the desired minimum weight, and for
terminating the filling process for the container when the fluid
substance therein reaches the desired maximum weight. Such
circuitry includes means for maintaining the discharge rate of the
container at the constant rate equal to the instantaneous rate
thereof immediately preceding energization of the filling device
for the container. Particularly, the pair of differential amplifier
circuits are coupled to a pair of relay driver circuits for
controlling a relay circuit to energize the filling device when the
substance in the container reaches the minimum weight, and for
maintaining that filling device in an energized state until the
container is refilled to its maximum desired level. The relay
circuit is also coupled to the comparator circuit, for controlling
the latter to produce a constant output during the refilling
process for the container, thereby maintaining the discharge rate
of the container at the value of the particular discharge rate
thereof immediately preceding energization of the filling
device.
As pointed out in said U.S. Pat. No. 3,889,848, in certain
installations there exists a possibility of physical forces
impinging upon the weigh feeder from an external source, such as
wind or air currents, physical contact with the weigh feeder by
operating personnel, or the like, for example. These forces cause
the weigh feeder to move at a rate that is other than that
resulting from the linear discharge of the contents of the
container. Because such additional movement, i.e. acceleration, is
an error and has no direct relationship to the actual discharge of
material from the container, the control system could continue to
perform its corrective function utilizing the erroneous output
signal for comparison with the fixed set point reference signal
derivative. The aforementioned patent application discloses one
means for preventing such excessive and abnormal movements of the
weigh feeder scale from grossly affecting or disturbing the normal
operation of the system to thereby prevent large excursions of the
output feed rate. The present invention is directed to a new
improved means for accomplishing this objective, which is of
simplified construction and, hence, more economical.
In accordance with the invention there is provided a weigh feeding
system comprising a container prefilled with a substance, a device
for discharging the substance from the container at a controllable
rate, and apparatus for weighing the container and its contents and
for producing an electrical signal proportional to that weight. In
addition, said system is further characterized by apparatus
actuated by said electrical signal for controlling the discharge of
the substance from the container, and detector circuit means
actuated by said electrical signal for producing an output which is
responsive to predetermined excessive excursions of the electrical
signal for locking the discharge control apparatus against
deviation during the time of the excessive excursion.
It will be appreciated that due to the double auger mechanism
employed in the system of the present invention, accurate
volumetric output is maintained even during the periods when the
electrical system is temporarily "locked out" due to some external
disturbance, or during a refill cycle. Such double auger mechanism
is disclosed in U.S. Pat. Nos. 3,186,602 and 3,439,836, for
example.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings illustrate several embodiments of the
invention. In such drawings:
FIG. 1 is a diagrammatic view of a combination of elements embodied
in the invention;
FIG. 2 is a block diagram of the control circuitry embodied in the
combination shown in FIG. 1;
FIG. 3 is a schematic diagram of the comparator circuitry shown in
block form of FIG. 2;
FIG. 4 is a schematic diagram of the motor drive signal generator
shown in block form in FIG. 2;
FIG. 5 is a schematic diagram of the signal holding circuit shown
in block form in FIG. 2;
FIG. 6 is a schematic diagram of the detector circuitry shown in
block form in FIG. 2; and
FIG. 7 is a schematic diagram of the relay circuit shown in block
form in FIG. 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The volumetric feeding apparatus of this invention, as shown
diagrammatically in FIG. 1, includes a container 10 for a quantity
of material, wherein the container has a discharge device 12
connected thereto for feeding the substance out of the container
and through the conduit 14. As illustrated, a motor 16 connected
through a gear-reduction device 18 is provided for driving the
discharge device 12, which, as illustrated in FIG. 1 may comprise
an auger mechanism as described in detail in U.S. Pat. No.
3,186,602, issued June 1, 1965. The entire feeding apparatus,
including the container, the discharge device, the motor, and the
gear-reduction device, is mounted on a scale 20, which may comprise
a structure as described in detail in U.S. Pat. No. 3,494,507,
issued Feb. 10, 1970.
In accordance with the invention there is provided a detecting
device as for example, a linearly variable differential transformer
(LVDT) 22, coupled to the scale for providing an electrical signal
having an amplitude which is proportional to the weight of the
container and its contents. That is, as the contents of the
container 10 are discharged, a relative movement occurs between the
windings and the core of the LVDT, thereby causing a varying output
voltage proportional to the varying weight of the container and its
contents. Thus, as the substance is discharged from the container
the .[.LDVT.]. .Iadd.LVDT .Iaddend.provides an electrical signal
which varies in response to such discharge. The electrical signal
from the LVDT is applied to control circuitry 24 by a conductor 26,
and the control circuitry also receives a tachometer signal from
the motor 16 as a second input thereto. The purpose of the control
circuitry 24 is to provide an output signal on a conductor 30 which
is used to control the speed of the motor 16, thereby controlling
the discharge rate of the substance from the container 10. In
particularly, the control .[. cicuitry.]. .Iadd.circuitry
.Iaddend.operates to maintain the motor speed at a value which
provides a desired specific discharge rate for the substance in
response to the detection of the actual discharge rate as derived
from the LVDT signal, and in response to the actual speed of the
motor as determined by the tachometer signal.
As illustrated in FIG. 1, the invention further comprises a second
volumetric feeding device 32, also having a container 34, and an
auger discharge mechanism 36 for operation to automatically refill
the container 10 in order to maintain the fill level of the
container 10 between predetermined desired levels. The discharge
device 36 is driven by a constant speed motor 38 which is energized
by an output signal from the control circuitry as coupled through a
conductor 40.
In the embodiment illustrated in FIG. 1, the containers 10 and 34
and discharge devices 12 and 36 are for all types of substances
comprising solid particles, but it is to be understood that the
combination as described above, may be used also for controlling
the discharge of liquid substances from a container, wherefore the
augers would be replaced by pumps.
FIG. 2 illustrates a block diagram of the control circuitry 24
which forms a part of the combination shown in FIG. 1, wherein the
LVDT output signal is applied to a rectifier 42 for converting the
AC signal from the LVDT into a DC signal, which DC signal is then
applied to an amplifier 44. The amplified DC signal is coupled
through a conductor 46 to a differentiator 48 which provides an
output signal directly proportional to the rate of discharge of the
substance from the container 10. That is, the LVDT output signal,
which comprises a linearly variable electrical signal when the
substance is discharged at a constant rate, is differentiated to
provide a steady state signal which is directly and linearly
proportional to said discharge rate.
The output of the differentiator 48 is coupled along a conductor 50
and through a signal holding circuit 52 to a flow rate indicator 54
for the purpose of providing a visual indication of the detected
flow rate of the substance being fed from the container 10.
The output of the differentiator 48 is also applied as an input to
a comparator circuit 56, such comparator circuit also having a
reference voltage signal as a second input 58 thereto, coupled from
a voltage source 60, for the purpose of providing a comparison
output signal as related to the two input signals. Thus, the
reference voltage signal may be set to correspond to the desired
discharge rate for the substance, whereby the output 62 from the
comparator circuit provides an error signal as determined by any
difference between the reference voltage signal and the actual
discharge rate as indicated by the differentiator output 50. Then,
the error signal provided by the comparator output 62 is applied to
a motor drive signal generator 64 algebraically with the tachometer
output signal 28, and the motor drive signal generator then
produces an output signal for application to the drive motor.
Accordingly, when the actual discharge rate of the substance varies
from the desired discharge rate thereof, the error signal from the
comparator 56 causes the motor drive signal generator 64 to
generate an output which alters the speed of the drive motor 16,
thereby changing the discharge rate until it corresponds with the
desired discharge rate.
The amplified DC signal corresponding to the LVDT signal is also
applied through the conductor 46 as a first input to a pair of
differential amplifiers 66 and 68, each of which has a second input
connected to different reference voltage source output circuits of
a second reference voltage source 70. The purpose of the pair of
differential amplifiers 66, 68 is to provide output signals
indicating when the quantity of substance within the container 10
falls below the desired minimum quantity, and when the quantity of
such substance exceeds a desired maximum quantity. Thus, the
reference voltage source 70 provides output signals corresponding
to these predetermined desired maximum and minimum quantities. The
outputs from the differential amplifiers are coupled through
conductors 66a and 68a, and through respective relay driver
circuits 72, 74 and applied as inputs to a relay circuit .[.76.].
.Iadd.76' .Iaddend.for controlling the operation of the motor 38 by
means of a signal coupled along conductor 40. As described above,
operation of the motor 38 causes the container 10 to be refilled
from the container 34. Accordingly, the relay circuitry is
connected to energize the motor 38 when the minimum detecting
differential amplifier 66 generates an output in response to the
indication of the minimum quantity of substance, and such relay
circuitry maintains the drive motor 38 in an energized state until
a signal is received from the maximum detecting differential
amplifier 68 indicating that the fill level of the container 10 has
reached the desired maximum level. Upon completion of the refill
process, the motor 38 is deenergized, but it is to be understood
that the discharge of the substance from the container 10 is
continuous throughout the period before, during, and after the
refill process.
An output 78 from the relay circuitry .[.76.]. .Iadd.76'
.Iaddend.is also coupled to the signal holding circuit for causing
that circuit to maintain the flow rate indication at the value
thereof immediately preceding initiation of the refilling process;
and a third output 80 from the relay circuitry .[.76.]. .Iadd.76'
.Iaddend.is applied to the comparator circuit 56 in order to
maintain the comparison output signal at the value thereof
immediately preceding such refill process. That is, the second and
third outputs from the relay circuit .[.76.]. .Iadd.76'
.Iaddend.prevent grossly erroneous readings on the flow rate
indicator 54, and prevent erratic control of the motor drive signal
generator 64 while the container 10 is being refilled.
The details of the comparator circuitry 56 are shown in schematic
form in FIG. 3, wherein the input 58 from the reference signal
source 60 is applied to one input terminal of a unity gain follower
amplifier 82, which, for example, may be provided by an integrated
circuit such as a Burr-Brown Model No. 3500 device. The connections
of the various terminals of the unity gain follower amplifier 82
are as shown in FIG. 3, wherein positive and negative voltage
sources V+ and V- are connected thereto, and wherein the output 82a
is fed back to one of the input terminals. The output 82a of the
unit gain follower amplifier is also connected to one end of a
potentiometer 84 which has its other end connected to the output of
a unity gain inverter amplifier 85 whose input is connected to the
output 50 of the differentiator circuit 48. The wiper arm 84a of
the potentiometer is connected to one input 86a of an operational
amplifier 86 connected in an inverting feedback mode. The device
forming the operational amplifier may comprise a Burr-Brown Model
No. 3267/12 C amplifier device. Then, the output of the operational
amplifier is connected through a set of relay contacts 88a to the
input 90a of an integrating circuit 90, which may comprise, for
example, a Burr-Brown operational amplifier Model No. 3308/12C
device.
In operation, if the reference voltage signal at 58 is greater than
the input signal from the differentiator, more current will flow
into the operational amplifier 86, thus causing the output thereof
to swing negative. A negative input to the integrator 90 causes its
output to go positive, and the time required to reach full output
is determined by the input RC network 92 of the integrator and the
amplitude of the voltage applied thereto. On the other hand, when
the differentiator output voltage is higher than the reference
signal, the amplifier output will swing positive thus causing the
integrator output to decrease in voltage. In this manner, an error
control voltage proportional to the comparison between the actual
and desired flow rates is generated by the comparator, and the
adjustable RC network 92, provided between the output of the
amplifier 86 and the input of the integrator 90, provides a fast
increase in the comparator output when a large error is introduced.
The zener diode 94 is for clamping the comparator output voltage
between a predetermined positive voltage and a voltage of about
-0.2 volts as determined by the diode 96.
When the relay contacts 88a are opened, the integrator maintains a
constant output voltage at the conductor 62 due to the feedback
capacitor 98, since the decay of that output voltage is primarily
determined by the leakage of the feedback capacitor and the input
impedance of the operational amplifier forming the integrator 90.
Thus, during normal operating conditions, the relay contacts 88a
remain closed so that a continuously corrected error voltage is
produced. However, during the period in which the container 10 is
being refilled, the relay contacts 88a are opened, as described
below, so that the output signal on the conductor 62 is maintained
at the value immediately preceding the opening of contacts 88a.
A difference signal derived from the tachometer output signal on
the line 28 and the comparison signal on the line 62 is applied to
a terminal 100 of an amplifier 102 connected to a uni-junction
pulsing circuit 104, as shown in FIG. 4. FIG. 4 also illustrates a
motor armature connection 106, and a field connection 108 for the
DC motor 16, wherein the armature and field are connected to a
rectifier circuit 110a, which in turn receives an output power
signal from an AC source, such as a 110 volt, 60 Hz. supply 112.
The AC source 112 is also coupled to a primary winding of a
transformer 114, the secondary of which is connected through a
unfiltered full-wave rectifier 116 to provide the supply voltage
for uni-junction pulse circuit 104 and amplifier 102. Thus, the
uni-junction pulser circuit 104 is synchronized with the AC source
applied to the rectifier circuit 110. The output of the
uni-junction pulser circuit is connected to the primary 118a of a
pulse transformer having a pair of secondaries 118b and 118c
connected respectively to the gate electrodes to a pair of SCR
devices 110b and 110c connected in the full wave bridge which
provides the rectifier circuit 110a.
Accordingly, the drive signal applied to the armature of the DC
motor is derived from the rectifier circuit 110a and is controlled
by the pulsing of the uni-junction transistor circuit 104, wherein
the timing of the uni-junction transistor circuit is dependent upon
the input 100 to the amplifier portion 102 thereof.
A commutating diode is connected across the rectifying bridge of
the circuit 110a to maintain a flow of armature current when the
SCR's 110b and 110c are turned off during the negative half cycle
of the line voltage. Also, the diodes 120a and 120b in the circuit
110a provide a constant DC voltage for the motor field connection
108.
Again, it is seen that by varying the timing pulses from the
uni-junction firing circuit 104, the SCR's 110b and 110c will be
controlled to turn on at a varying point with respect to the anode
voltages, thus providing a varying DC output for the motor
armature, in order to control the speed of the DC motor.
FIG. 5 illustrates an embodiment of the signal holding circuit 52,
which may comprise, for example, an operational amplifier such as a
Burr-Brown Model No. 3309/12C device, which provides a high input
impedance FET amplifier 122 having an extremely low leakage
capacitor 124 in its feedback loop. Relay contacts 88b connect the
negative input of the amplifier to the output 50 of the
differentiator 48, whereby the device 52 operates as a unity gain
invertor. That is, while the relay contacts 88b are closed, the
differentiator output at line 50 is coupled to the indicator 54 to
give an indication of the actual discharge rate. However, when the
relay contacts 88b are opened, the value of the output voltage for
the circuit 52 remains at the last value of the input level at 50
due to the presence of the low leakage capacitor 124 in the
feedback loop. Accordingly, when the relay circuit .[.76.].
.Iadd.76' .Iaddend.operates to initiate the refill process for the
container 10, the indicator device 54 is supplied with a constant
voltage equivalent to the output from the signal holding circuit 52
immediately prior to the initiation of such refilling process, and
such constant voltage is maintained until termination of the refill
process and the closing of relay contacts 88b.
FIG. 7 illustrates a representative relay circuit .[.76.].
.Iadd.76' .Iaddend.wherein a motor drive power source V is coupled
through the line 40 to the refill motor 38 through a set of relay
contacts 88c, which contacts are controlled by a relay coil 88
having one end connected to a common potential point, and having
its other end connected to the power source V through a pair of
normally opened contacts 126a of a relay having its coil 126
connected to the relay driver circuit 72 which is controlled by the
minimum detecting differential amplifier 66. The coil 88 is also
connected to the power source V through the relay contacts 128a of
a relay having its coil 128 controlled by the maximum detecting
differential amplifier relay driver circuit 74 and through a pair
of slave contacts 88d.
In operation, when the minimum detecting differential amplifier 66
provides an outut signal, the relay driver circuit 72 causes the
relay coil 126 to energize, thereby connecting the voltage source
to the coil 88 of the control relay, thus causing it to energize.
Accordingly, the refill process is initiated due to the closing of
the relay contacts 88c. When the fluid substance level in the
container rises sufficiently to cause deenergization of the minimum
detecting circuit relay 126, the control relay coil 88 remains
energized due to the slave contacts 88d. Also, the signal holding
circuit 52 and the comparator circuit 56 are locked in their
respective steady state conditions as described above due to the
actuation of the relay contacts 88a and 88b which are shown in
dotted lines in FIGS. 3 and 5, and which are connected by the
conductors 78 and 80 to the respective signal holding and
comparator circuit. However, when the maximum detecting
differential amplifier 68 generates an output signal through the
relay driver circuit 74 to the maximum detecting relay 128, then
the energization circuit for the control relay coil 88 is opened,
and the refill process is terminated due to the opening of the
relay contacts 88c.
It will be appreciated that the weigh feeder may be subject to an
external force impinging upon the weigh feeder system, thereby
altering the constant upward movement, or velocity, of the system.
This alteration results in either acceleration or deceleration of
the system, depending upon the direction of the impinging external
force. The present invention is directed to the elimination of
large excursions of the output feed rate.
As best seen in FIG. 2, there is provided detector circuitry 150
which receives the amplified DC signal corresponding to the LVDT
signal through the conductor 46. FIG. 6 illustrates an embodiment
of the detector circuitry 150, which comprises an alternating
current coupled, adjustable gain amplifier with frequency response
164, which, for example, may be provided by the National
Semiconductor Corp., Model No. LM324N. The amplifier 164 has an
input terminal 166 which is connected to the conductor 46 through
an input capacitor 168 and to ground through a resistor 170. A
feedback capacitor 172 is connected between the output terminal 174
and a second input terminal 176 of the amplifier 164. Also, the
output terminal 174 of the amplifier is coupled to a feedback
potentiometer 178 disposed between two resistors 180 and 182. The
other terminal of resistor 182 is connected to ground through a
capacitor 184 and a resistor 186 connected in parallel. The sliding
contact or wiper arm 188 of the potentiometer 178 is coupled to the
input terminal 176 to control the gain of the amplifier 164. Thus,
the wiper arm may be considered to be a reference signal source.
The output terminal 174 of the amplifier is coupled to a conductor
158 through an output capacitor 190.
Thus, any acceleration, deceleration or abnormal disturbance in the
weigh feeder system, as reflected by the signal received by the
detector circuitry causes it to emit an output signal 158. As seen
in FIG. 2, the output 158 from the detector circuitry 150 is
coupled through a relay driver circuit 160 to a relay circuit 76'.
This relay circuit is similar to relay circuit 76 .Iadd.of the
abovementioned patent 3,889,848, .Iaddend.but has added thereto a
relay coil 162, FIG. 7, which when energized opens normally closed
contacts 88a' and 88b'. Thus, in operation, when the detector
circuitry 150 provides an output signal, corresponding to an
excessive acceleration or deceleration of the weigh feeder system,
the relay driver circuit 160 causes the relay coil 162 to energize,
thereby opening relay contacts 88a' and 88b'. These contacts are
connected by the conductors 78 to 80 to the respective signal
holding and comparator circuits. Consequently, the output signal on
the conductor 62 is maintained at the value immediately preceding
the opening of contacts 88a' in the same manner as that described
hereinbefore in connection with contacts 88a. When the relay
contacts 88b' are opened, the value of the output voltage for the
circuit 52 remains at the last value of the input level at 50 and,
hence, the indicator device 54 is supplied with a constant voltage
equivalent to the output from the signal holding circuit 52
immediately prior to the initiation of the excessive deviation, and
such constant voltage is maintained until termination of the
excessive acceleration or deceleration condition and the closing of
the relay contacts 88b', thereby returning the system to normal
operation, in the same manner as that described hereinbefore in
connection with contacts 88b.
From the foregoing disclosure it can be seen that the instant
invention provides an improved weigh feeding apparatus, wherein the
discharge rate of a substance from a container may be maintained at
a constant value selected from a range of values, and wherein the
container may be automatically refilled during the continuous
discharge of the substance, and wherein excessive excursions of the
system are eliminated.
Although a specific representative structure has been described
herein for purposes of explanation, reference should be had to the
appended claims in determining the scope of this invention.
* * * * *