U.S. patent number RE32,102 [Application Number 06/586,660] was granted by the patent office on 1986-04-01 for weigh feeding apparatus.
This patent grant is currently assigned to Acrison, Inc.. Invention is credited to Angelo Ferrara, Joseph L. Hartmann, Ronald J. Ricciardi.
United States Patent |
RE32,102 |
Ricciardi , et al. |
April 1, 1986 |
**Please see images for:
( Certificate of Correction ) ** |
Weigh feeding apparatus
Abstract
Disclosed herein is an automatically controlled weigh feeding
apparatus including a container for prefilling with a substance, a
device for discharging the substance from the container at a
controllable rate, apparatus for weighing the substance being
discharged and for producing an electrical signal proportional to
that weight, a voltage to frequency converter connected to receive
the electrical signals, a digital computer, apparatus coupled to an
output of the voltage to frequency converter for inputting data
signals to the digital computer, the computer being adapted to
compute a corrective signal based on the input data signals
received, and coupling apparatus coupled between the computer and
the device for discharging the substance from the container for
controlling the rate of discharge responsive to the corrective
signal.
Inventors: |
Ricciardi; Ronald J. (Woodcliff
Lake, NJ), Ferrara; Angelo (Patterson, NJ), Hartmann;
Joseph L. (Jersey City, NJ) |
Assignee: |
Acrison, Inc. (Moonachie,
NJ)
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Family
ID: |
27494578 |
Appl.
No.: |
06/586,660 |
Filed: |
March 6, 1984 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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907960 |
May 22, 1978 |
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678391 |
Apr 19, 1976 |
4054784 |
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913203 |
Jun 6, 1978 |
4210963 |
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803251 |
Jun 3, 1971 |
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678391 |
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587869 |
Jun 18, 1975 |
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907960 |
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748397 |
Dec 7, 1976 |
4111272 |
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678391 |
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587869 |
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Reissue of: |
125370 |
Feb 28, 1980 |
04320855 |
Mar 23, 1982 |
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Current U.S.
Class: |
222/56; 177/185;
177/50; 222/58; 222/77; 700/240 |
Current CPC
Class: |
G01G
11/12 (20130101); G05D 7/0611 (20130101); G05D
7/0605 (20130101) |
Current International
Class: |
G01G
11/00 (20060101); G01G 11/12 (20060101); G05D
7/06 (20060101); B67D 005/08 () |
Field of
Search: |
;222/1,14,15,52,55,56,63,58,71,77 ;177/50,1,185,119-123
;364/468,469,478,479,550,551,567,570,571,579
;318/628,637,644,646 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2358100 |
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May 1975 |
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DE |
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86157 |
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Nov 1965 |
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FR |
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Other References
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Engineering, Sep., 1967, pp. 75-80. .
Considine, D. M., ed., Process Instruments and Control Handbook,
McGraw Hill Book Company, First Ed., 1957, Second Ed., 1974. .
Corbett, J. L., "Applications of digital computers to the long term
measurement of blood pressure and the management of patients in
intensive care situations", AFIPS Confl Proc., vol. 33, Pt. 2, 1968
Fall Joint Comput. Conf., pp. 1105-1114, reprinted in Schoeffler,
J. D., et al. eds., Mincomputers: Hardware, Software, and
Applications, IEEE Press, 1972. .
Crowley, P. W., "Metering Pumps and Liquid Proportioning", 39
Instruments and Control Systems, 119-121 (Jan. 1966). .
Flum, H. H., et al. "The Bunker-Ramo 335 for DDC Applications".
.
Gilmore Industries, Inc. Jun. 30, 1969 Newsletter A-36045, Gilmore
Model 710 Solves the Problem of Low Weight Rate Measurement. .
Lex, R. G., Jr. et al. "The Application of the SDS 92-I to Direct
Digital Control Through High Speed Computing". .
Liptak, B. G., ed., Instrument Engineer's Handbook, vol. 1,
"Process Measurement", Chilton Book Company, First Ed., 1969. .
Marhauer, H. H., "A new Batch Mass Flow Controller" Preprint No.
5.1-2-66, 21st Annual ISA Conference and Exhibit, New York, N.Y.,
Oct. 24-27, 1966. .
McEvoy, L. D., "Control Systems for Belt Feeders", Instrumentation
_Technology, Feb., 1968, pp. 41-45. .
Preliminary System Design Specification, Section 3-Functional
Description, SDS #3, prepared by General Electric for Merck &
Co., Inc., 5/26/67-7/19/67. .
Proceedings of the Computer in Control Systems Conference,
presented at Atlantic City, N.J., Oct. 16-18, 1957 and _sponsored
by Feedback Control Systems Committee, American Institute of
Electrical Engineering; Professional Group on _Automatic Computers,
Institute of Radio Engineers; Instruments and _Regulators Division,
American Society of Mechanical Engineers. .
Savas, E. S., "Application Objectives for Control Computers",
Conference Paper CP-63-1093, IEEE Summer General Meeting and
Nuclear Radiation Effects Conf., Toronto, Canada, Jun. 16-21, 1983.
.
Savas, E. S., "Computer Control Concepts", Process Control Seminar,
Poughkeepsie, N.Y., Mar. 28-Apr. 8, 1960. .
Savas, E. S., "Computer Control in the Paper Mill, Part II, Paper
Machine Monitoring:", Tappi 47(3): 149A-152A (Mar. 1964). .
Savas, E. S., Computer Control of Industrial Processes, McGraw
Hill, Inc. 1965. .
Specifications 111563, A Direct Digital Computer Control System,
Monsanto Chemical Corp., Revision 1, Feb. 14, 1964. .
Vannah, W. E., "DDC will improve Process Instrumentation". .
Williams, T. J., et al., eds. Progress in Direct Digital Control,
Instrument Society of America. .
The work done in the development of weigh feeding systems by
Thayer, including development of a system for the U.S. Navy. .
Howe-Richardson Scale Leaflet No. 351. .
BIF Industries Bulletin Ref. No. 31-12.201-1. .
BIF Industries Bulletin Ref. No. 31-01.201-1. .
Thayer-Scale Division, Cutler-Hammer Bulletin 5E01..
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Primary Examiner: Rolla; Joseph J.
Parent Case Text
This is a continuation of application Ser. No. 907,960, Filed May
22, 1978, .Iadd.now abandoned, .Iaddend.which is a continuation of
Ser. No. 748,397, Dec. 7, 1976 now U.S. Pat. No. 4,111,272.
.Iadd.This is also a continuation-in-part of application Ser. No.
913,203, filed Jun. 6, 1978 (now U.S. Pat. No. 4,210,963), which is
a continuation of application Ser. No. 803,251, filed Jun. 3, 1977
(now abandoned), which is a continuation of application Ser. No.
678,391 (now U.S. Pat. No. 4,054,784), which is a
continuation-in-part of application Ser. No. 587,869, filed Jun.
18, 1975 (now abandoned).
Claims
What is claimed is:
1. A weigh feeding machine comprising
a container for a substance;
discharge means for discharging the substance from the container at
a controllable feed-out rate;
means for producing a first electrical signal corresponding to the
desired feed-out rate;
means for sensing the weight of at least the substance in the
container and for producing a second electrical signal having a
characteristic which is proportional to the value of said
weight;
means for sampling said second electrical signal during each of a
succession of time intervals;
means for computing a feed-out rate from signals derived from said
sampling and for comparing an electrical signal representative of
said computed feed-out rate with the first electrical signal, and
for producing, as a result of said comparison, a control electrical
signal indicative of the desired changes, if any, in the feed-out
rate of the discharge means;
control means for controlling the discharging means in accordance
with said control electrical signal to thereby maintain the
feed-out of the substance from the container at the desired
feed-out rate; and
means for comparing a signal derived from at least one sample taken
during one of said time intervals with a signal derived from at
least one sample taken during another of said time intervals, for
repeating said comparison for successive time intervals, so that
the signal derived during each of said successive time intervals is
compared with a signal derived during a different time interval,
and for inhibiting the action of the control electrical signal on
the control means when said comparison shows a difference between
the compared signals beyond a predetermined limit.
2. A weigh feeding machine according to claim 1, wherein the
comparison and inhibiting means compares a signal derived during
each time interval with a signal derived during the immediately
preceding time interval.
3. A weigh feeding machine according to claim 2, wherein, when the
last-mentioned comparison produces a difference beyond said
predetermined limit, said inhibiting means inhibits the control
electrical signal so as to permit the feed-out rate to continue at
a rate established by at least one preceding control electrical
signal. .[.4. A weigh feeding machine comprising a container for a
substance;
discharge means for discharging the substance from the container at
a controllable feed-out rate;
storage means for storing a first electrical signal corresponding
to the desired feed-out rate;
means for sensing the weight of at least the substance in the
container and for producing a second electrical signal at a
frequency which corresponds to the value of said weight and changes
for the different values of weight sensed;
means for sampling the second electrical signal during each of a
succession of time intervals;
digital circuit means for comparing an electrical signal derived
from said sampling of said second electrical signal with an
electrical signal derived from said first electrical signal, for
producing, as a result of said comparisons, control electrical
signals indicative of the desired changes, if any, in the feed-out
rate of the discharge means;
control means for controlling the discharging means in accordance
with said control electrical signal to thereby maintain the
feed-out of the substance from the container at the desired
feed-out rate;
means for comparing a signal derived from at least one sample taken
during one of said time intervals with a signal derived from at
least one sample taken during another of said time intervals, for
repeating said comparison for successive time intervals, so that
the signal derived during each of said successive time intervals is
compared with a signal derived during a different time interval,
and for inhibiting the action of the control electrical signals on
the control means when said comparison shows a difference between
the compared signals beyond a predetermined limit..].
A weigh feeding machine comprising a container for a substance;
discharge means for discharging the substance from the container at
a controllable feed-out rate;
means for producing a first electrical signal corresponding to the
desired feed-out rate;
means for sensing the weight of at least the substance in the
container and for producing a second electrical signal proportional
to the value of said weight;
.Iadd.means for sampling said electrical signal during each of a
succession of time intervals; .Iaddend.
digital circuit means for comparing an electrical signal derived
from said sampling of said second electrical signal with an
electrical signal derived from the first electrical signal, for
producing, as a result of said comparison, a control electrical
signal indicative of the desired changes, if any, in the feed-out
rate of the discharge means;
control means for controlling the discharging means in accordance
with said control electrical signal to thereby maintain the
feed-out of the substance from the container at the desired
feed-out rate;
means for comparing a signal derived from said second electrical
signal during each of a succession of time intervals with a signal
derived from said second electrical signal during a different one
of said time intervals; and
means, responsive to said comparisons of signals derived from said
second electrical signal during successive time intervals, for
inhibiting the control means when said comparison shows a
difference between the compared signals beyond a predetermined
limit and for establishing a feed-out rate corresponding to the
value of at least one preceding control electrical
signal. 6. A weigh feeding machine according to claim 5 wherein
said sampling and comparing means compares a signal derived from at
least one sample taken during each time interval with a signal
derived from at least one sample taken during the immediately
preceding time interval. .[.7. A weigh feeding machine comprising a
container for a substance;
discharge means for discharging the substance from the container at
a controllable feed-out rate;
storage means for storing a first electrical signal corresponding
to the desired feed-out rate;
means for sensing the weight of the container and its contents and
for producing a second electrical signal at a frequency which
corresponds to the value of said weight;
digital circuit means for sampling the second electrical signal
during each of a succession of time intervals;
storage means for storing the frequency signals representative of
the samples of said second electrical signal during such succession
of time intervals;
digital computer means for computing a succession of feed-out rates
from the frequency signals corresponding to the samples taken
during said successive time intervals, and for comparing an
electrical signal representative of each said computed feed-out
rate with the first electrical signal representative of said
desired feed-out rate, for producing, as a result of said
comparisons, control electrical signals indicative of the desired
changes, if any, in the feed-out rate of the discharge means;
control means for controlling the discharging means in accordance
with said control electrical signals to thereby maintain the
feed-out of the substance from the container at the desired
feed-out rate; and
means for comparing a signal derived from at least one sample taken
during one of said time intervals with a signal derived from at
least one sample taken during another of said time intervals, for
repeating said comparison for successive time intervals, so that
the signal derived during each of said successive time intervals is
compared with a signal derived during a different time interval,
and for inhibiting the action of the control electrical signal on
the control means when said comparison shows a difference between
the compared signals beyond a predetermined limit..].
.[.8. A weigh feeding machine comprising a container for a
substance;
discharge means for discharging the substance from the container at
a controllable feed-out rate;
storage means for storing a first electrical signal corresponding
to the desired feed-out rate;
means for sensing the weight of the substance discharged from the
container and for producing a second electrical signal at a
frequency which corresponds to the instantaneous value of said
weight;
digital circuit means for sampling the second electrical signal
during each of a succession of time intervals;
storage means for storing the frequency signals representative of
the samples of said second electrical signal;
digital circuit means for comparing electrical signals derived from
said sampling of said second electrical signal with an electrical
signal derived from the first electrical signal, for producing, as
a result of said comparison, a control electrical signal indicative
of the desired changes, if any, in the feed-out rate of the
discharge means;
control means for controlling the discharging means in accordance
with said control electrical signal to thereby maintain the
feed-out of the substance from the container at the desired
feed-out rate;
means for comparing a signal derived from samples taken during each
of a succession of said time intervals with a signal derived from
said second electrical signal during a different one of said time
intervals; and
means, responsive to the last-mentioned comparisons, for inhibiting
the control means when said comparison shows a difference between
the compared signals beyond a predetermined limit and for
establishing a feed-out rate corresponding to the value of at least
one preceding control electrical signal..]. .[.9. A weigh feeding
machine comprising a container for a substance;
discharge means for discharging the substance from the container at
a controllable feed-out rate;
storage means for storing a first electrical signal corresponding
to the desired feed-out rate;
means for sensing the weight of at least the substance in the
container and for producing a second electrical signal at a
frequency which corresponds to the value of said weight and changes
for the different values of weight sensed;
digital circuit means for sampling the second electrical signal
successively, each sampling including a predetermined number of
periods of said second electrical signal;
said digital circuit means sampling said second electrical signal a
plurality of times during each of a succession of time
intervals;
storage means for storing the samples of said second electrical
signal during each such time interval;
digital computer means for computing a feed-out rate during each
such time interval, from the samples taken during such time
interval, and for comparing an electrical signal representative of
said computed feed-out rate with the first electrical signal
representative of said desired feed-out rate, for producing, as a
result of said comparison, a control electrical signal indicative
of the desired changes, if any, in the feed-out rate of the
discharge means;
control means for controlling the discharging means in accordance
with said control electrical signal to thereby maintain the
feed-out of the substance from the container at the desired
feed-out rate; and
means for comparing a signal derived from at least one sample taken
during one of said time intervals with a signal derived from at
least one sample taken during another of said time intervals, for
repeating said comparison for successive time intervals, so that
the signal derived during each of said successive time intervals is
compared with a signal derived during a different time interval,
and for inhibiting the action of the control electrical signal on
the control means when said comparison shows a difference between
the compared signals beyond a predetermined limit..].
.[.10. A weigh feeding machine according to claim 9, wherein,
during each sampling, said digital circuit means samples said
second electrical signal for a number of periods of said second
signal which varies inversely with the value of the desired
feed-out rate..]. .[.11. A weigh feeding machine according to claim
9, wherein,
during each time interval, said digital circuit means samples said
second electrical signal a number of times which varies inversely
with the desired feed-out rate..]. .[.12. A weigh feeding machine
according to claim 9, wherein
said means for comparing compares the signal representative of the
computed feed-out rate for each time interval with the signal
representative of the computed feed-out rate for at least one
preceding time interval..]. .[.13. A weigh feeding machine
according to claim 9, wherein the comparison means for the computed
feed-out rate compares the signal representative of each computed
feed-out rate with the signal representative of the computed
feed-out rate for the immediately preceding time interval..].
.[.14. A weigh feeding machine according to claim 9, wherein, when
the comparison between the signals for the computed feed-out rates
for different time intervals is beyond said predetermined limit,
said inhibiting means inhibits any control electrical signal from
being transmitted to the control means, so that the feed-out rate
continues at the rate to which it was last corrected..]. .[.15. A
weigh feeding machine according to claim 9, wherein,
the digital circuit means includes a high frequency oscillator
having an operating frequency at least an order of magnitude higher
than the frequency corresponding to the value of the weight being
sensed;
gating means coupled to said high frequency oscillator; and
second control means for enabling said gating means for a period of
time corresponding to a predetermined number of periods of the
frequency corresponding to the weight being sensed, to pass signals
from said high frequency oscillator during said period of time, to
thereby convert the frequency of the weight being sensed to said
high frequency..]. .[.16. A weigh feeding machine according to
claim 15, wherein said second control means enables the gating
means for a predetermined number of periods which varies inversely
with the value of the desired feed-out rate..]. .[.17. A weigh
feeding machine according to claim 15, further including
storage means for storing the signals from said high frequency
oscillator; and
multiplexing means coupled to said storage means for multiplexing
the different portions of the high frequency signal out of said
storage means in a predetermined sequence..]. .[.18. A weigh
feeding machine according to claim 15, wherein
said gating means includes a first gating means for the low
frequency second electrical signal and a second gating means for
the high electrical signal from said oscillator; and
said second control means enables said first and second gating
means simultaneously;
further including
a first counter coupled to said first gating means for counting the
periods of said low frequency second electrical signal,
a second counter coupled to said second gating means for counting
the periods of said high frequency electrical signal, and
disabling means responsive to said first counter reaching a
predetermined count for disabling said second gating means..].
.[.19. A weigh feeding machine according to claim 18, wherein said
disabling means includes a comparison circuit coupled to said first
counter for producing a disabling signal when said first counter
has reached a predetermined count, for disabling said first and
second gating means..]. .[.20. A weigh feeding machine comprising a
container for a substance;
discharge means for discharging the substance from the container at
a controllable feed-out rate;
storage means for storing a first electrical signal corresponding
to the desired feed-out rate;
means for sensing the weight of at least the substance in the
container and for producing a second electrical signal at a
frequency which corresponds to the value of said weight and changes
for the different values of weight sensed;
digital circuit means for sampling the second electrical signal a
plurality of times during a predetermined time interval, for a
succession of said time intervals;
said digital circuit means including circuit means for converting
the frequency of the sampled signal to a higher frequency which is
at least an order of magnitude higher than the frequency of the
sampled signal;
storage means for storing the higher frequency signals
representative of the samples of said second electrical signal
during each such time interval;
digital computer means for computing a feed-out rate during each
such time interval, from the higher frequency signals corresponding
to the samples taken during one such time interval, and for
comparing an electrical signal representative of said computed
feed-out rate with the first electrical signal representative of
said desired feed-out rate, for producing, as a result of said
comparison, a control electrical signal indicative of the desired
changes, if any, in the feed-out rate of the discharge means;
control means for controlling the discharging means in accordance
with said control electrical signal to thereby maintain the
feed-out of the substance from the container at the desired
feed-out rate; and
means for comparing the signal representative of the computed
feed-out rate for each such time interval with the signal
representative of the computed feed-out rate for at least one
preceding time interval; and
inhibiting means, responsive to said comparison of computed
feed-out rates, for inhibiting the action of the control electrical
signal on the control means when said comparison shows a difference
between the computed
feed-out rates beyond a predetermined limit..]. .[.21. A weigh
feeding machine according to claim 20 wherein said digital circuit
means samples said second electrical signal for a predetermined
number of its periods during each sampling, and produces a larger
number of periods at the higher frequency extending over
substantially the same time duration..]. .[.22. A weigh feeding
machine according to claim 20, wherein said digital circuit means
includes a high frequency oscillator having an operating frequency
at least an order of magnitude higher than the frequency
corresponding to the value of the weight being sensed;
gating means coupled to said high frequency oscillator; and
second control means for enabling said gating means for a period of
time corresponding to a predetermined number of periods of the
frequency corresponding to the weight being sensed, to pass signals
from said high frequency oscillator during said period of time, to
thereby convert the
frequency of the weight being sensed to said high frequency..]. 23.
A weigh feeding machine comprising a container for a substance;
discharge means for discharging the substance from the container at
a controllable feed-out rate;
storage means for storing a first electrical signal corresponding
to the desired feed-out rate;
means for sensing the weight of at least the substance in the
container and for producing a second electrical signal having a
characteristic which corresponds to the value of said weight;
.[.said.]. digital circuit means .Iadd.for .Iaddend.sampling said
second electrical signal a plurality of times during each of a
succession of time intervals;
storing means for storing the samples of said second electrical
signal during each such time interval;
digital computer means for computing a feed-out rate during each
such time interval, from the samples taken during one such time
interval, and for comparing an electrical signal representative of
said computed feed-out rate with the first electrical signal
representative of said desired feed-out rate, for producing, as a
result of said comparison, a control electrical signal indicative
of the desired changes, if any, in the feed-out rate of the
discharge means;
control means for controling the discharging means in accordance
with said control electrical signal to thereby maintain the
feed-out of the substance from the container at the desired
feed-out rate; and
means for comparing a signal derived from at least one sample taken
during one of said time intervals with a signal derived from at
least one sample taken during another of said time intervals, for
repeating said comparison for successive time intervals, so that
the signal derived during each of said successive time intervals is
compared with a signal derived during a different time interval,
and for inhibiting the action of the control electrical signal on
the control means when said comparison shows a
difference between the compared signals beyond a predetermined
limit. 24. A weigh feeding machine according to claim 23, wherein
the means for comparing the signals derived from samples taken in
different time intervals compares the signal representative of each
computed feed-out rate with the signal representative of the
computed feed-out rate for the
immediately preceding time interval. 25. A weigh feeding machine
according to claim 23, wherein, when comparison between the signals
derived from samples taken in different time intervals is beyond
said predetermined limit, said inhibiting means inhibits any
control electrical signal from being transmitted to the control
means, so that the feed-out rate continues at the rate to which it
was last corrected. .[.26. A weigh feeding device comprising
a container for a substance;
a discharge means for discharging the substance from the container
at a controllable feed-out rate;
storage means for storing a first electrical signal corresponding
to the desired feed-out rate;
means for sensing the weight of at least the substance in the
container;
first circuit means responsive to said sensing means for producing
a succession of second electrical signals, each at a frequency
which is responsive to the value of the weight sensed;
counting means for counting the cycles of each of said second
electrical signals to produce a succession of total counts, each of
which is a measure of the value of the weight sensed;
a digital circuit for storing said total counts and comparing an
electrical signal responsive to a plurality of said total counts
with the first electrical signal representative of said desired
feed-out rate, for producing, as a result of said comparison, a
control electrical signal indicative of the desired changes, if
any, in the feed-out rate of the discharge means; and
control means for controlling the discharge means in accordance
with said control electrical signal to thereby maintain the
feed-out of the
substance from the container at the desired feed-out rate..].
.[.27. A weigh feeding device according to claim 26, wherein
said digital circuit includes means for computing one or more error
limits in the form of deviations from the computed feed-out rate;
and
means operative in computing the feed-out rate, for excluding from
the computation thereof any total count values which fall beyond
said error limits..]. .[.28. A weigh feeding device comprising
a container for a substance;
discharge means for discharging the substance from the container at
a controllable feed-out rate;
storage means for storing a first electrical signal corresponding
to the desired feed-out rate;
a voltage source for producing an output voltage at a predetermined
number of cycles per second;
means for sensing the weight of at least the substance in the
container and producing a second electrical signal responsive to
said weight;
circuit means responsive to said second electrical signal for
gating a succession of cycles of said output voltage from said
voltage source for a period of time, the duration of which is
dependent upon the value of said weight;
counting means for counting the cycles gated from said source to
produce a total count which is a measure of the value of the weight
being sensed;
a digital circuit for comparing an electrical signal responsive to
said total count with the first electrical signal representative of
said desired feed-out rate, for producing, as a result of said
comparison, a control electrical signal indicative of the desired
changes, if any, in the feed-out rate of the discharge means;
and
control means for controlling the discharge means in accordance
with said control electrical signal to thereby maintain the
feed-out of the substance from the container at the desired
feed-out rate..]. .[.29. A weigh feeding device according to claim
28, wherein
said circuit means includes sampling means for repeatedly sampling
the second electrical signal from said sensing means;
each such sample controlling the period of time over which the
output from said voltage source is gated;
said counting means counting the cycles gated from said source for
each said sampling and producing a series of total counts, one for
each of said samplings;
storage means for storing all of said total counts; and
said digital circuit computing the feed-out rate from a plurality
of the total counts which occur during a predetermined time
interval..]. .[.30. A weigh feeding device comprising
a container for a substance;
discharge means for discharging the substance from the container at
a controllable feed-out rate;
storing means for storing a first electrical signal corresponding
to the desired feed-out rate;
means for sensing the weight of at least the substance in the
container and for producing a second electrical signal which
corresponds to the value of said weight;
a voltage source for producing an output signal at a predetermined
frequency;
counting means for counting the signals from said voltage
source;
a digital circuit for sampling the second electrical signal
successively and, for each such sampling, gating output signals
from said voltage source to said counting means for a period of
time which corresponds to a characteristic of said second
electrical signal;
storage means for storing a plurality of values corresponding to
the total counts of said counting means for all of said
samplings;
digital computer means for computing a feed-out rate from the total
counts for a plurality of said samples, and for comparing an
electrical signal representative of said computed feed-out rate
with the first electrical signal representative of said desired
feed-out rate, for producing, as a result of said comparison, a
control electrical signal indicative of the desired changes, if
any, in the feed-out rate of the discharge means; and
control means for controlling the discharge means in accordance
with said control electrical signal to thereby maintain the
feed-out of the
substance from the container at the desired feed-out rate..].
.[.31. A weigh feeding device according to claim 30, further
including
circuit means controlled by said digital computer for initiating
each successive period of time for which output signals from said
voltage source are gated to said counting means, and
said digital circuit terminating each such successive period of
time at a time which corresponds to the value of the characteristic
of the second electrical signal..]. .[.32. A weigh feeding device
comprising
a container for a substance;
discharge means for discharging the substance from the container at
a controllable feed-out rate;
means for establishing a first electrical signal corresponding to
the desired feed-out rate;
source means for producing an output signal at a predetermined
frequency;
counting means coupled to said source means for receiving and
counting the signals therefrom;
means for sensing the weight of at least the substance in the
container and for producing a second electrical signal having a
frequency which corresponds to the value of said weight;
digital circuit means for repeatedly sampling said second signal
and controlling the count of said counting means, during each such
sampling, to count to the frequency of said second signal at the
time of said sampling;
storage means for storing a plurality of values, each corresponding
to the count of said counting means for one of said samplings;
digital computer means for computing a feed-out rate for each of a
succession of time intervals, from the count samples during one
such time interval, and for comparing an electrical signal
representative of said computed feed-out rate with the first
electrical signal representative of said desired feed-out rate, for
producing, as a result of said comparison, a control electrical
signal indicative of the desired changes, if any, in the feed-out
rate of the discharge means; and
control means for controlling the discharging means in accordance
with said control electrical signal to thereby maintain the
feed-out of the
substance from the container at the desired feed-out rate..].
.[.33. A weigh feeding device comprising
a container for a substance;
discharge means for discharging the substance from the container at
a controllable feed-out rate;
means for establishing a first electrical signal corresponding to
the desired feed-out rate;
means for sensing the weight of at least the substance in the
container and for producing a second electrical signal having a
characteristic which corresponds to the value of said weight;
a source of signals at a predetermined frequency;
a counter for counting the signals from said source;
storage means for storing a succession of values corresponding to
counts of said counter;
digital circuit means for sampling the second electrical signal
successively and for transmitting from said counter to said storage
means, for each such sampling, a value corresponding to the count
of the counter for a period of time proportional to the weight
sensed;
digital computer means for computing a feed-out rate from a
plurality of said count values, and for comparing an electrical
signal representative of said computed feed-out rate with the first
electrical signal representative of said desired feed-out rate, for
producing, as a result of said comparison, a control electrical
signal indicative of the desired changes, if any, in the feed-out
rate of the discharge means; and
control means for controlling the discharge means in accordance
with said control electrical signal to thereby maintain the
feed-out of the substance from the container at the desired
feed-out rate..]. .[.34. A weigh feeding device according to claim
33 wherein
the sensing means produces an electrical signal whose frequency
corresponds to the value of the weight being sensed;
further including second counting means for counting the signals
from said sensing means; and
means responsive to the count in said second counting means for
controlling
said period of time for said first counting means..]. 35. A weigh
feeding machine comprising a container for a substance;
discharge means for discharging the substance from the container at
a controllable feed-out rate;
means for producing a first electrical signal corresponding to the
desired feed-out rate;
means for sensing the weight of at least the substance in the
container and for producing a second electrical signal having a
characteristic which is proportional to the value of said
weight;
digital circuit means for sampling said second electrical signal at
least once during each of a succession of time intervals;
means for computing a feed-out rate during each of said time
intervals from signals derived from said sampling and for comparing
an electrical signal representative of each such computed feed-out
rate with the first electrical signal representative, for
producing, as a result of said comparison, control electrical
signals indicative of the desired changes, if any, in the feed-out
rate of the discharge means;
control means for controlling the discharging means in accordance
with said control electrical signals to thereby maintain the
feed-out of the substance from the container at the desired
feed-out rate; and
means for comparing a signal derived from at least one sample taken
during one of said time intervals with a signal derived from at
least one sample taken during another of said time intervals, for
repeating said comparison for successive time intervals, so that
the signal derived during each of said successive time intervals is
compared with a signal derived during a different time interval,
and for inhibiting the action of the control electrical signal on
the control means when said comparison shows a
difference between the compared signals beyond a predetermined
limit. 36. A weigh feeding machine according to claim 35, wherein
the means for comparing the signals derived from samples taken in
different time intervals compares a signal representative of each
computed feed-out rate with a signal representative of the computed
feed-out rate for the immediately preceding time interval.
Description
BACKGROUND OF THE INVENTION
This invention relates to feeding systems and it is particularly
applicable to apparatus for feeding fluid-like material. Systems
constructed according to the present invention are particularly
adapted, among other possible uses, for accurately 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 control weigh feeding systems have been known in the past,
as for example, the system disclosed in U.S. Patent Application
Ser. No. 345,587, filed Mar. 28, 1973, which has issued as U.S.
Pat. No. 3,889,848. 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 weighted, 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. The 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 output signal from the comparator. It can
be stated 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 .[.or.].
.Iadd.of .Iaddend.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 a 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 discloses one means for
preventing such excessive and adnormal 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.
Disclosed in our patent application Ser. No. 678,391, which has
issued as U.S. Pat. No. 4,054,784, in one form thereof, is a new
and improved weigh feeding apparatus characterized by a container
for a prefilled substance having means for discharging the
substance therefrom at a controllable rate. A scale system is
provided for weighing the container prefilled with the substance
and an electrical circuit serves to produce a first electrical
signal proportional in amplitude to the weight, and a high gain
amplifier amplifies the electrical signal. An analog-digital
converter (ADC) is coupled to the amplifier and a digital computer
is adapted to receive pulse signals from the ADC for computing and
outputting a signal corresponding to the signal received.
Digital-analog converter ramp offset means which is controlled by
the computer outputs a controlled stepping signal, that is applied
as a second input to the amplifier means to algebraically combine
therewith. Each step corresponds to one time cycle of operation,
thereby maintaining the output of the amplifier in a given
preselected range of amplitude during one time cycle of operation.
The digital computer as another operation thereof computes a
corrective signal based on the signals received, and means coupled
between the computer and the means for discharging the substance
from the container, serve to control the rate of discharge
responsive to the corrective signal.
SUMMARY OF THE INVENTION
The present invention is directed to new, improved means for
accomplishing the foregoing objectives, as well as additional
objectives, as will become apparent as the description
proceeds.
One of the features of the present invention resides in the
provision of a new and improved weigh feeder system, which is
capable of controlling more operating parameters, which operates
faster, which provides a faster responsive action, and which is
more accurate as compared to the prior art systems. In addition,
the feeder system of the present invention has a memory and is
capable of taking into account past errors in the material flow
rate and taking corrective action with respect thereto.
Also, the system is capable of disregarding single or multiple
extraneous material flow rate readings, which may be caused by such
factors as noise, vibrations, or the like, for example.
To the accomplishment of the foregoing and other objectives, the
invention contemplates the provision of a new and improved weigh
feeder apparatus, which comprises a container for prefilling with a
substance, and means for discharging the substance from the
container at a controllable rate. Means are provided for weighing
the substance being discharged, and means coupled thereto serve to
produce electrical signals proportional in amplitude to the weight
determined. A voltage to frequency converter, which receives the
electrical signals, is coupled by electrical circuitry to a digital
computer for inputting data signals thereto. The digital computer
is adapted to compute a corrective signal based on the input data
signals received, and means are coupled between the computer and
the means for discharging the substance from the container for
controlling the rate of discharge responsive to the corrective
signal.
In one form of the invention, the means for weighing the substance
being discharged comprises a scale for weighing the container
prefilled with the substance, and in another form thereof the means
for weighing the substance being discharged comprises a moving belt
conveyor wherein the entire belt and its contents are weighed. In a
third form the means for discharging the substance comprises a
volumetric type auger feeder wherein the entire auger feeder and
its contents are weighed.
According to one aspect of the invention, the weighing means are
connected to the voltage to frequency converter by a linear
variable differential transformer and a differential DC amplifier
circuit.
In one embodiment of the invention, the means coupled to an output
of the voltage to frequency converter for inputting data signals to
the digital computer includes a first gating circuit, means
coupling this gating circuit to the voltage to frequency converter,
and a second gating circuit with an oscillator coupled thereto. A
first logic circuit is provided for receiving information from the
computer for selecting a predetermined time base period, and means
are provided for coupling this logic circuit to the gating circuits
for enabling them. A first counter is connected to the output of
the first gating circuit and a second counter is coupled to the
output of the second gating circuit. A second logic circuit is
provided for receiving information from the computer for selecting
a predetermined number of periods to be passed through the first
gating circuit. A comparator is interposed between the first
counter and the second logic circuit for determing when the first
counter has counted the predetermined number of periods. A bit data
latch or register is connected to an output of the second counter,
and means responsive to the comparator are provided for enabling
the bit data latch to receive bits of data from the second counter
and to disenable the gating circuits and to reset the first and
second counters the counter means. In addition, means are provided
for connecting an output of the bit data latch to the digital
computer. According to an aspect of the invention, the means
coupling the first logic circuit to the gating circuits for
enabling these circuits includes a time base generator driven by
the oscillator.
Further, in a form thereof, the invention includes means for
inputting into the digital computer a preselected feed rate. The
computer has programmed therein a calculation time cycle and is
adapted to store in memory a series of data signals received for
each calculation time cycle and computing the corrective signal by
comparing the signals received with the preselected feed rate. The
computer is adapted to maintain said corrective signal constant
during the time when a preselected number of the signals received
exceeds preselected upper of lower limits during one calculation
time cycle. Further, the computer is provided with means for
correcting the data signals received to compensate for errors due
to extraneous noise.
In still another form of the invention, the digital computer is
adapted to store in memory a series of data signals received for
each of the calculation time cycles and to compute the slope of the
actual feed line during each such calculation time cycle. It also
compares the computed slope during each time cycle with the
computed slope for the last preceeding calculation time cycle, and
determines the percentage variation therefrom, and if the variation
is within a predetermined range it proceeds to compute the
corrective signal corresponding to the variation, and if the
variation is in excess of the predetermined range it maintains the
corrective signal constant.
.Iadd.While the data signals as disclosed herein are derived from
the weight signal through a voltage to frequency converter,
frequency is not the only characteristic of the weight signal that
might be used to practice the present invention, and the present
application is not limited to the use of frequency. In contrast,
copending application Ser. No. 586,899 is directed to the use of a
signal having a frequency proportional to weight. .Iaddend.
According to another aspect of the invention, there is provided
under-weight limit input means and overweight input means to the
digital computer, and the computer is adapted to actuate an alarm
when the data signals received by the computer exceed one of said
limits. The computer may also be adapted to integrate the
preselected feed rate with respect to time and output a display
corresponding to the desired total feed commanded, and to integrate
the actual total weight of material fed as determined by the data
signals received and, by comparing said total feed commanded to the
actual weight of material fed, adjust said corrective signal.
In accordance with other forms of the invention, means are provided
for operating the system in a volumetric mode, and means are
provided for automatically refilling the supply container to
maintain the supply of material therein within preselected upper
and lower limits.
These features of the invention have been outlined in order that
the detailed description thereof that follows may be better
understood, and in order that the present contribution to the art
may be better appreciated. There are, of course, additional
features of the invention that will be described more fully
hereinafter. Those skilled in the art will appreciate that the
conception on which this disclosure is based may readily be
utilized as the basis of the designing of other structures for
carrying out the various purposes of the invention. It is
important, therefore, that this disclosure be regarded as including
such equivalent constructions and methods as do not depart from the
spirit and scope of the invention.
Several embodiments of the invention have been chosen for purposes
of illustration and description, and are shown in the accompanying
drawings forming a part of the specification, wherein:
FIG. 1 is a schematic side elevation and block diagram of a weigh
feeder assembly according to one embodiment of the invention;
FIG. 2 is a schematic side elevation and block diagram similar to
FIG. 1, but showing another embodiment of a weigh feeder
assembly;
FIG. 3 is a schematic side elevation and block diagram similar to
FIGS. 1 and 2, but showing still another embodiment of a weigh
feeder assembly;
FIGS. 4A and 4B cooperate to form a block diagram of the interface
circuitry for coupling any one of the feeder assemblies of FIGS. 1
to 3 to a computer or micro processor;
FIG. 5 is a block diagram of the inputs and outputs of the computer
or micro processor according to the invention;
FIG. 6 is a graphic representation of the output voltage which
respect to time of the differential amplifier circuit of the
present invention;
FIG. 7 is a graphic representation of the actual measured feed
curve as compared to the desired feed curve, using the feeder
assembly of FIG. 1;
FIG. 8 is a graphic representation of the positional relationship
of the shaft encoder with respect to the system noise;
FIG. 9 is a graphic representation of the output of the voltage to
frequency converter with respect to time, before it is corrected
for the induced system noise;
FIG. 10 is a graphic representation of the output of the voltage to
frequency converter with respect to time, after it has been
corrected for the induced system noise;
FIG. 11 is a graphic representation of the actual measured feed
curve as compared to the desired feed curve similar to FIG. 7, but
illustrating another mode of programming the computer;
FIG. 12 is a graphic representation of the actual measured feed
curve as compared to the desired feed curve using the feeder
assemblies of either .[.FIG. 1 or FIG. 2.]. .Iadd.FIG. 2 or FIG.
3.Iaddend.;
FIG. 13 is a flow chart showing the program start;
FIG. 14 is a flow chart of the background;
FIG. 15 is a flow chart of the timer routine of the computer;
FIG. 16 is a flow chart of the keyboard interrupts;
FIG. 17 is a flow chart of the calculation routine;
FIG. 18 is a flow chart for computing the scale weight and hopper
level; and
FIG. 19 is a chart specifying the subroutine description.
In the embodiment of the invention shown in FIG. 1, there is
illustrated diagrammatically a feeder assembly indicated generally
at 10, which comprises a container 12 with a discharge device
connected thereto for feeding a substance 14 from the container
through a discharge conduit 16. As illustrated, a variable speed DC
motor 18, connected to a gear-reduction device 20, is provided for
driving the discharge device. The feeder assembly may comprise an
auger mechanism as disclosed in detail in U.S. Pat. No. 3,186,602
issued June 1, 1965. The entire feeding assembly, including the
container, the discharge device, the motor, and the gear-reduction
device is mounted on a scale 22, 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 linear variable differential transformer
(LVDT) 24, 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 12 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 LVDT provides an electrical signal which varies in response to
such discharge, which may, for example, be a DC voltage with a
range of the order of from about plus or minus 3 volts to about
plus or minus 6 volts when the material in the container drops from
its upper level to its lower level.
In the embodiment of the invention illustrated in FIG. 2, there is
provided a feeder assembly indicated generally at 10 which
comprises a volumetric type feeder 26 having an upper inlet 28 for
receiving material to be processed and a lower dispensing outlet 30
for dispensing the material 32 onto a conveyor belt 34. A variable
speed DC motor 35 is provided for driving the discharge device. A
suitable type of volumetric feeder for this purpose is described in
detail in the aforesaid U.S. Pat. No. 3,186,602.
The conveyor belt 34 is carried by a pair of spaced rollers 36, one
of which is driven by drive means, such as a constant speed motor
and chain drive, for example (not shown). The rollers are mounted
on a conveyor support frame, not shown. In operation the material
32 passes from the feeder 26 through the outlet 30 to the conveyor
belt 34 and is discharged therefrom as at 40 into a receiving
hopper or container 42. Suitable scale means for the conveyor belt
are described in detail in the aforesaid U.S. Pat. No. 3,494,507.
Thus, the conveyor belt 34 is mounted in such a manner that the
entire belt and its contents can be "sensed" or weighed by a force
sensing load cell, such as the LVDT 24, described hereinbefore in
connection with the embodiment of FIG. 1.
In the embodiment of the invention illustrated in FIG. 3, there is
provided a feeder assembly indicated generally at 10, which also
comprises a volumetric auger type feeder 44, having an upper inlet
46 for receiving material to be processed and a lower enclosed
dispensing outlet 48. A particularly suitable type of volumetric
feeder for this purpose is described in detail in the aforesaid
U.S. Pat. No. 3,186,602. The feeder 44 employs an auger (not shown)
driven by a motor 50 for propelling the material through the outlet
48 into a downspout 52, as indicated by arrow 54. The dispensing
outlet and the downspout are mounted in fixedly sealed relationship
with respect to each other. The downspout leads to the inlet of an
enclosed auger type conveyor 56, which incorporates an auger 58
having a drive shaft 60 driven at substantially constant speed by a
motor, not shown, through a chain and pulley system 62. The auger
58 serves to move the material through a conveyor cylinder 64 to a
fixedly mounted discharge outlet 66 where it passes into a
discharge conduit 68, as indicated by arrow 70. The movable
conveyor cylinder 64 is flexibly connected in sealed relationship
to the fixed downspout 52, as by means of a downspout sleeve 72. In
addition, the movable cylinder .[.63.]. .Iadd.64 .Iaddend.is
flexibly connected in sealed relationship to the fixed discharged
conduit 68, by means of a sleeve clamping assembly 74. Accordingly,
it will be appreciated that the material being processed passes
through a completely closed system from inlet to outlet. A
particularly suitable system of this type is described in detail in
U.S. Pat. No. 3,804,298 issued Apr. 16, 1974. The conveyor 64 is
mounted in a scale-like manner so that the entire conveyor assembly
and its contents, but not including conduits 48 or 68, or the
equipment feeding those conduits, can be "sensed" or weighed by a
force sensing load cell, such as the LVDT 24, described
hereinbefore in connection with the embodiment of FIG. 1.
In the embodiments illustrated in FIGS. 1, 2 and 3, the feeder
assemblies 10, having containers and discharge conduits for all
types of substances, are particularly suitable for solid particles,
but it is to be understood that the combinations described above
may also be used for controlling the discharge of liquid substances
from the containers, wherefore the augers would be replaced by
pumps.
Referring next to FIGS. 4A and 4B, there is shown interface
circuitry for coupling the feeder assembly 10 to a micro processor
and memory or computer 76. It will be appreciated that any one of
the feeder assemblies 10 of the embodiments of FIGS. 1-3 may be
employed with this interface. The LVDT 24, FIG. 4A, is provided
with a rod 78, which is movable in response to the weight being
measured. A sine wave oscillator 80, which may, for example,
comprise a Burr-Brown Model No. 8692-1001, has outputs 82 and 84
which are coupled to inputs 86 and 88 of the LVDT for applying an
AC input thereto. The LVDT has outputs 90 and 92, the output 90
being coupled to an input 94 of a differential DC amplifier circuit
96 and the output 92 being connected to a summing junction 98
which, in turn, is connected to an input 100 of the differential DC
amplifier circuit 96. Also, applied to the summing junction 98 is
an offset circuit 102 controlled by an offset adjust 103. In
addition, the amplifier circuit 96 is provided with a gain adjust
106. In the embodiments illustrated, the LVDT signal, which is a DC
signal between about minus 3 and plus 3 volts depending on the
position of the movable rod 78, is fed into the differential DC
amplifier 96 along with the offset voltage. The offset adjust and
the gain adjust set the output 104 from the amplifier circuit for
plus 5 volts when the portion of the feeder system 10 mounted on
the scale is empty and for plus 10 volts when the feeder system is
full, as shown in FIG. 6. Any suitable amplifier circuit may be
employed such as two Model OPO5EJ units, as manufactured by
Precision Monolithics, Inc. for example. The first unit is a
differential amplifier circuit, which is followed by a variable
gain single-ended amplifier circuit. The output 104 of the
amplifier circuit 96 is coupled to an input 108 of a voltage to
frequency converter 110, which outputs a corresponding pulse train
output at 112 of from 5 KHz to 10 KHz. It will be appreciated that
the embodiment of FIG. 1 is a weight loss system wherein the weight
on the scale as sensed by the LVDT gradually diminishes until the
container 12 is empty, and thus the pulse train output gradually
moves from 10 KHz to 5 KHz. On the other hand, in the embodiments
of FIGS. 2 and 3, the weight on the scale as sensed by the LVDT
remains substantially constant so that the output of the voltage to
frequency converter 110 also remains constant. That is, if the
frequency outputted is at 5 KHz then the rate of flow would be
zero, and if the frequency is 10 KHz then the rate of flow would be
maximum. In normal operation, the frequency outputted would be at a
substantially constant value somewhere therebetween, such as at 6
KHz, for example. The voltage to frequency converter may be a
Burr-Brown Model VFC-12, for example. The pulse train is fed to the
input 114 of an optical isolator 116 which may comprise, for
example, a Monsanto Corporation Model No. MCL600. The optical
isolator 116 outputs to a differential line driver 118, which
drives a twisted pair cable 120. The pulse train is received by a
differential line receiver 122 coupled to the twisted pair
cable.
A 10 MHz. crystal oscillator, or clock, 124 has an output 126
coupled to an input 128 of a time base generator 130 for driving
the time base generator. Conword I circuit 132, which includes
logic circuitry, has an input 134 for receiving programmed
information from the computer 76 and an output 136 coupled to an
input 138 of the time base generator for selecting a particular
time base period, and responsive thereto the time base generator
generates a selected time period, i.e. 1, 0.5, 0.25, or 0.125
seconds the start of which is gated by a signal from the 10 MHz
oscillator. The time base generator has an output 140 which is
coupled to a start input 142 of gating circuit I, indicated at 144,
and to start input 146 of gating circuit II, indicated at 148, so
that when the time base generator generates a new period the gating
circuits I and II are enabled. The output 140 of the time base
generator is also coupled to the real time clock of the computer
76, via line 141. The output 126 of the crystal oscillator 124 is
coupled to an input 150 of the gating circuit II, which has an
output 152 coupled to an input 154 (FIG. 4B) of a high speed 24 bit
counter 156. The differential line receiver 122 has an output 158
coupled to an input 160 of the gating circuit I, and this gating
circuit has an output 162 coupled to an input 164 of a counter 166.
Now, when the gating circuits I and II are enabled, the 10 MHz.
pulse train from crystal oscillator 124 passes through the gating
circuit II to the high speed 24 bit counter 156, and 5 to 10 KHz
signal on the differential line receiver output 158 passes through
the gating circuit I to the counter 166.
As seen in FIG. 4B, there is provided a conword II circuit 168,
which includes logic circuitry and has an input 170 for receiving
information from the computer 76 indicating the number of periods,
outputted by the differential line receiver 122, to be measured,
i.e. 4000, 2000, 1000, or 500. .[.As.]. .Iadd.An .Iaddend.output
172 of the conword II circuit 168 is coupled to an input 174 of a
binary comparator 176. A second input 178 couples the comparator to
an output 180 of the counter 166. It will be appreciated that the
conword I and II circuits 132, 168 have previously been programmed
by the computer according to the ratio of the maximum feed rate to
the desired feed rate of the feeder assembly 10. A feeder assembly
with a high desired feed rate will have a relatively large change
in weight per unit of time and, once the rate is controlled, a
large change in the rate of change of the pulse train frequency
outputted from the voltage to frequency converter 110. This enables
measurements to be made more rapidly according to the following
schedule:
__________________________________________________________________________
NUMBER OF PERIODS RESULTANT TIME MAX. FEED RATE MEASURE TIME BASE
REQUIRED FOR RATIO DESIRED FEED RATE (CONWORD II) (CONWORD I)
MEASUREMENT
__________________________________________________________________________
1 TO 2 500 .125 sec. 0.05-0.1 sec.* 2 TO 4 1000 .250 sec. 0.1-0.2
sec.* 4 TO 8 2000 .500 sec. 0.2-0.4 sec.* 8 AND ABOVE 4000 1.000
sec. 0.4-0.8 sec.*
__________________________________________________________________________
*Depends on frequency of pulse train.
Thus, the number of periods designated by Conword II fixes the
number of periods that go through gate I, i.e. the number of
periods determines the gate cycle. The time base (Conword I) starts
the operation of the gates, such as every 0.125 seconds, for
example. The resultant time it takes to get n periods, such as 500
for example, through gate I is, for example, 0.05 seconds when the
frequency of the voltage to frequency converter 110 is 10 KHz and
0.1 seconds when the frequency of the voltage to frequency
converter is 5 KHz.
The comparator 176 has an output 182, which is coupled to an input
184 of a two phase one shot 186, having a first output 188 and a
second output 190. The first output 188 is coupled to an input 192
of a 24 bit data latch or register 194. The second output 190 of
the one shot is connected to an input 196 of the high speed 24 bit
counter 156 and is also coupled to an input 198 of the counter 166.
The output 182 of the binary comparator 176 is also coupled to an
input 200 of the gating circuit I and to an input 202 of the gating
circuit II.
In operation, the counter 166 outputs the number of pulses counted
to the comparator 176 and when the comparator indicates that the
number of pulses counted equals the preselected number, as
indicated by the conword II circuit 168, it outputs a signal from
its output 182 to the two phase one shot 186 which, in turn,
signals the 24 bit data latch 194 to receive 24 bits of data from
the high speed 24 bit counter 156 which is coupled thereto as by
coupling 204. The second output 190 of the two phase one shot
applies a signal at 196 to clear and reset the high speed 24 bit
counter 156 and a signal at 198 to clear and reset the counter 166.
At the same time the output 182 of the binary comparator 176
outputs a signal to the input 200 of the gating circuit I and the
input 202 of the gating circuit II, to open and reset these
circuits. These circuits now await the start of a new time base
generator output. In addition, the output 182 outputs a signal via
one shot 183 to the computer 76, indicating that the data is
ready.
Meanwhile, the computer 76 has a minimum of 75 milliseconds in
which to respond to the data ready signal. Still referring to FIG.
4B, the 24 bit data latch 194 has an output 206 coupled to an input
208 of a multiplexer 210. The multiplexer also has an input 212
coupled to conword III circuit 214, that receives signals from the
computer 76 indicating the timing and sequence in which the three 8
bit groups of the 24 bit latch will be selected to be outputted by
the multiplexer 210 on the line 216 to the computer for processing
in conjunction with the time base information furnished by line
141.
When the time base generator 130 initiates a new period, the
foregoing sequence is repeated.
A binary number system is employed as the code for information
handling because of certain advantages hereinafter brought out.
Thus, the weigh feeder system is provided with a digital computer
76, which includes processing, memory and control systems. Any
suitable digital computer may be employed such as a micro processor
Model IMP16C/300 and memory Model IMP16P/004P, as manufactured by
National Semiconductor Corp., or an LSI-11 as manufactured by
Digital Equipment Corp., for example.
As best seen in FIG. 5, a plurality of inputs are applied to the
processor to control the same. A conventional off-on switch 218
serves to control the main power supply to the processor. A switch
220 is provided whereby the refill sequence may be automatically
actuated (switch in "auto") when product level reaches low level,
or at any product level (switch in "manual"), or the refill
sequence may be bypassed (when switch is in "bypass"). The refill
sequence is a procedure wherein the motor speed will not lockout
for refill, thereby actuating the refill controller, until the
computer first senses that the scale is undisturbed by foreign
influences and secondly, senses that the feed rate agrees with the
set feed rate. Input switch 222 serves to convert the system
between gravimetric control and volumetric control, as desired.
This will be explained more fully hereinafter. A reset total push
button switch 224 serves to reset the processor for an entirely new
batch of data. Also, there is provided a scale weight switch 226,
that inputs into the processor the scale weight, S, which is
determined by the size or model of the feeder assembly 10 being
employed in the particular installation. This factor is set once
and is not adjusted unless a new model or size of feeder assembly
is installed.
A motor speed input switch 228 is provided, which is set by the
operators at a preselected percent in the range between 0% to 100%,
to input into the processor the desired operating speed of the
motor when operating volumetrically.
Input switch 230 is actuated by the operator to input the desired
feed rate R (LBS./HR) into the processor. This is a digital word,
stored in memory, that represents the desired slope of the feed
line, which for the embodiment illustrated in FIG. 1 is indicated
by curve 232, FIG. 7, for example. Input switch 234 is also
actuated by the operator to input the under weight set point into
the processor memory. It represents the selected minimum limit of
the feed rate range, as is indicated by the dotted line 236 in FIG.
7. This limit is expressed as a percentage of from 0 to 9.99% below
the desired feed rate R. Input switch 238 inputs the overweight set
point into memory. It represents the selected maximum limit of the
feed range, as is indicated by the dotted line 240 in FIG. 7. This
limit also is expressed as a percentage of from 0 to 9.99% above
the desired feed rate R.
Still referring to FIG. 5, digital switch 242 is an operator
activated switch into the memory, the desired minimum or low level
of the material in the container 12, FIG. 1, or container 28, FIG.
2, or container 46, FIG. 3. The range of this switch is from 0 to
99.9%. Thus, for example, if the operator desires the system to
shift into its refill mode when the container 12 or 28 or 46 is
down to 5% of its capacity, he sets the low level switch 242 at
05.0%. Digital input switch 244 is an out of low level switch with
a range of from 0 to 99.9% so that the operator can input into
memory the desired level for the system to shift out of its refill
mode to its normal operative mode. Thus, for example, the operator
could set this switch for 90.0%, whereby when the container 12 or
28 or 46 reaches 90% of its capacity, the system would shift out of
its refill mode to its normal operative mode.
In addition, the processor also receives a signal from a shaft
encoder 246, FIGS. 1-3. This allows a correlation to be made
between the shaft angle and system noise induced by the movement of
the material and machinery mounted on the scale or, in the case of
FIG. 1, the movement of the product in the storage hopper. This
correlation may then be used as a correction factor, subtracting
out noise components due to moving machinery on the scale such as
for example, the motor, gear box, augers, as well as movement of
the material in the container. The processor 76 is provided with a
learn mode input switch 248, which is shiftable between normal
operation and learn mode operation. When a new material is going to
be processed by the system or when the system is first installed,
the system is set in operation, but instead of discharging the
substance 14, FIG. 1, out of the system, it is collected in a small
container, not shown, and retained on the scale 22 so that there is
no net loss of weight from the scale. The switch 248 is shifted to
its learn mode position. The motor 18 is run throughout its speed
range and the shaft encoder 246 senses the shaft angle, while the
input circuit to the computer 76, including the LVDT, picks up the
noise corresponding to the rotational position of the drive shaft
and sends out digital signals to the processor, which are stored in
memory. After this information has been stored in memory, the small
container is removed from the scale and the switch 248 is shifted
to its normal operation. This same technique is applicable to the
feeder assemblies of FIGS. 2 and 3, using a container on the
respective scales to receive the material being discharged.
FIG. 8 illustrates the positional relationship of the shaft encoder
246 with respect to the system noise detected for a particular
shaft speed during the learn mode operation. FIG. 9 illustrates the
output of the voltage to frequency converter 110 with respect to
time, before it is corrected for the induced system noise.
Processor 76, as another operation thereof, subtracts the stored
system noise data from the data received from the voltage to
frequency converter, through the multiplexer 210, to present
connected values of this information for processing. FIG. 10
illustrates the corrected output from the voltage to frequency
converter 110 with respect to time. Any suitable type of shaft
encoder may be employed such as a Series 2500, Optical Encoder, as
manufactured by Renco Corporation.
The microprocessor 76 has, as an output, a display device 250 which
indicates the total feed commanded. This device indicates the total
feed asked for by the operator over a relatively long period of
time. Thus, the processor, as one operation thereof, receives the
selected feed rate R from the input switch 230 and integrates it
with respect to the elapsed time and continuously displays the
total feed commanded, in pounds. As another output there is
provided a display device 252 which indicates the actual total feed
discharged from the feeder assembly 10. Thus, the processor, as one
operation thereof, receives a signal from the multiplexer 210
corresponding to the total scale weight, which, in the FIG. 1
apparatus, indicates the quantity of material remaining in the
container. This signal represents the weight of the material in the
bin 12. Any change in this signal, except during refill, represents
the amount of material fed. These changes are totalled by the
processor to give the actual total feed, in pounds. During refill,
in the FIG. 1 apparatus, the amount of material fed is computed by
the processor from the reading of the feed rate meter and the time
it takes to refill. When refill is completed the signal from the
multiplexer 210 is again used to compute the total amount of
material fed. In the FIG. 2 and FIG. 3 apparatus the total feed
discharged can be determined directly from the measured weight of
the material being delivered. The operators can compare the actual
total feed, as displayed at 252, with the total feed commanded, as
displayed at 250, to determine how the system is functioning and,
if necessary, take corrective action.
A feed rate display device, such as a four digit meter, 254, for
example, shows the actual feed rate in pounds per hour of the
feeder assembly. Thus, the processor, as another operation thereof,
receives the scale weight signal from the multiplexer 210 and
corrects this signal, as pointed out hereinbefore, and then
differentiates the signal with respect to time to produce a signal
indicative of the present rate of feed. This can be visually
compared to the desired feed rate as set by the input switch 230 to
determine possible malfunctions in the system.
A scale weight display device, such as a three digit meter 256, for
example, is provided to indicate the actual percentage of product
remaining in the container 12 on the scale 22 of FIG. 1. Thus, the
processor, as still another operation thereof, receives a signal
from the multiplexer 210 corresponding to the weight on the scale
22 and computes the actual percentage of material remaining in the
container 12. Next, there is provided, as another output of the
processor 76, a three digit motor speed meter 258 which indicates
the actual speed of the motor 18. That is, the processor receives a
signal from a tachometer 260, indicating the speed of the motor 18,
by a conductor 262 through a conventional analog-digital converter
264, and outputs a motor speed on meter 258. While this speed is
usually relatively constant, it may vary to some extent over a long
period of time. It is advantageous for the operator to know, as any
sudden variations may indicate a blockage of material in the
system.
In addition, there are provided operational and warning indicators,
such as lights, buzzers, or the like, for example, for purposes of
keeping the operators informed. An underweight light 266 indicates
when the actual feed rate, as indicated by the meter 254, falls
below the underweight set point 234, and overweight light 268
indicates when the actual feed rate exceeds the overweight set
point 238. That is, when the actual feed rate falls below the line
236, FIG. 7, which is set by the underweight set point switch 234,
the underweight light 266 is actuated, and when the actual feed
rate is above the line 240, FIG. 7, which is set by the overweight
set point switch 238, the overweight light 268 is actuated.
Preferably, there is a preselected time delay period of from about
0 to about 3 minutes delay after the feed rate meter 254 indicates
an overweight or an underweight condition before the warning lights
are actuated. Light 270 shows when the system is in its refill
mode, i.e. when the container 12 is being refilled. The light 272
indicates that the system is in its ACRILOK mode. This mode of
operation will be explained more fully hereinafter. Run light 274
indicates that the system is in operation and standby light 276
indicates that the system power has been applied, but all machinery
is stopped. The light 278 indicates that the bin 12 is in its low
level condition.
A control output 280 from the processor 76 is applied to a
digital-analog converter (DAC) 282. Any suitable type of DAC may be
employed, such as a 10 bit Model AD7520L, as manufactured by Analog
Devices, Inc., for example. In the DAC, the digital word is
converted to an analog signal, which is applied to the tachometer
260 and an SCR motor control 284. Any suitable type of motor
control may be employed such as Acrison, Inc.'s Model ACR100BTG,
for example. This controller produces an output which is applied to
the motor 18 to control the speed thereof, and thereby control the
discharge rate of the material from the feeder assembly 10.
In operation, the operator must determine whether he wishes to
operate in the volumetric mode or the gravimetric mode. If the
volumetric mode is selected, then the operator sets the motor speed
switch 228 to the desired motor speed. In this mode of operation,
the output of the processor is a digital word conveyed by conductor
280 to the DAC 282. The DAC causes a voltage from 0 to 6 volts to
appear on conductor 286 and the SCR motor control adjusts the speed
of the DC motor 18 until the output of the tachometer 260 exactly
equals the voltage on the conductor 286. While this mode of
operation is desirable at certain times, it does not provide as
high a degree of accuracy as the gravimetric mode and,
consequently, the gravimetric mode is predominantly employed.
In operation, when employing the embodiment of FIG. 1, when the
operator sets the switch 222 to the gravimetric mode of operation,
the operator then sets the feed rate switch 230 to the desired feed
rate R (LBS./HR.), which, as discussed hereinbefore, determines the
slope of the feed curve or line 232, FIG. 7. Samples are taken and
stored in the computer memory. The samples, generally illustrated
in FIG. 7 by dots, form the actual feed curve 288. It is noted that
for each point or sample the gating circuits I and II open and
close. The computer has programmed therein a calculation time
cycle, during which cycle the computer receives and stores a number
of samples. The calculation time cycle, as well as the number of
samples taken during such a cycle is a function of the feed rate of
the machine. For example, if the machine has a high feed rate four
samples may be taken for each calculation time cycle and if the
machine has a low feed rate sixty samples may be taken for each
calculation time cycle. The calculation time cycle may range from
about 1/2 second to about 60 seconds, for example, depending on the
feed rate. Once during each calculation time cycle the processor
computes a regression on these samples with respect to time, and
thence computes the RMS error of the slope.
FIG. 7 illustrates an upper 3 RMS error line at 290 and a lower 3
RMS error line at 292. If less than two, for example, sample data
points exceed 3 RMS error in either direction, as indicated at 294
in FIG. 7, regression on time is recomputed with the data points
exceeding 3 RMS, as indicated at 296, excluded. Thence, the
computed slope of the actual feed curve is compared with the slope
of the desired or set point feed line, and a corresponding
correction command is outputted at 280 to adjust the motor control
284, thereby to adjust the actual rate of discharge of the material
from the feeder assembly 10. This calculation time cycle is
continuously repeated to continuously adjust the motor control
284.
If more than two, for example, sample data points exceed 3 RMS
error in either direction, as indicated at 298 in FIG. 7, the
system is changed into its ACRILOK mode. That is, the ACRILOK light
272 is energized and the output command 280 to the DAC 282 and
motor control 284 is not updated, but continues in its present
state. That is, the processor continues to receive sample signals
from the multiplexer 210 and computes the regression analysis
thereof, but no correction command is outputted at 280. The feed
rate meter 254 is also locked at the last control data point. The
feed system remains in a locked condition until a subsequent
calculation time cycle of operation .Iadd.in which .Iaddend.less
than two data points exceed 3 RMS error, and then the system is
returned to its normal operating mode and the correction command is
again outputted at 280.
In the alternative, as illustrated in FIG. 11, the computer may be
programmed in a second manner for outputting correction commands at
280 to adjust the motor control 284. In operation, the operator
sets the feed rate switch 230, FIG. 5, to the desired feed rate R
(LBS./HR.) which, as discussed hereinbefore, determines the slope
of the desired feed curve or line 306, FIG. 11. As pointed out in
connection with the computer program illustrated in FIG. 7, samples
are taken and stored in the computer memory. The samples, generally
illustrated in FIG. 11 by dots 307, form the actual feed curve in
segments, as indicated at 308, 310, 312, 314 and 316. It is noted
that for each point or sample the gating circuits I and II open and
close. As pointed out hereinbefore, the computer has programmed
therein a calculation time cycle, during which cycle the computer
receives and stores a number of samples. The calculation time
cycle, as well as the number of samples taken during such a cycle,
is a function of the feed rate of the machine. For example, if the
machine has a high feed rate four samples may be taken for each
calculation time cycle and if the machine has a low feed rate sixty
samples may be taken for each time cycle. In FIG. 11 eight samples
are shown for each calculation time cycle, for example. The
calculation time cycle may range from about 1/2 second to about 60
seconds, for example, depending on the feed rate. Once during each
calculation time cycle the processor computes a regression on these
samples with respect to time to determine the slope of the actual
feed line during such calculation time cycle. The slope of one
calculated time period or segment is compared to the last derived
slope to determine the deviation thereof. Thus, the percentage
variation of the slope of segment 310 is compared to that of
segment 308. If the variation is within an acceptable range, then
the slope is adjustable, and a corresponding correction command is
outputted at 280 of the computer to adjust the motor control 284,
thereby to adjust the actual rate of discharge of the material from
the feeder assembly 10. The aforesaid acceptable range is
predetermmined and it may be constant or it may be variable. As an
example, it may be within about 5 to 10% of the absolute value.
However, if the percentage variation of the slope segment, such as
that indicated for segment 312, is beyond the acceptable range, the
system is changed into its ACRILOK mode. That is, the ACRILOK light
272 is energized and the output command 280 to the DAC 282 and
motor control 284 is not updated, but continues in its present
state. Thus, the processor continues to receive sample signals from
the multiplexer 210 and compute the regression analysis thereof,
but no correction command is outputted at 280. The feed rate meter
254 is also locked at the last control data point. The feed system
remains in a locked condition until in a subsequent calculation
time cycle of operation the variation of the slope is within an
acceptable range, and then the system is returned to its normal
operating mode and the correction command is again outputted at
280.
As indicated above, the embodiment of FIG. 1 is a weight loss
system wherein the weight on the scale as sensed by the LVDT
gradually diminishes until the container 12 is empty. On the other
hand, in the embodiments of FIGS. 2 and 3, the weight on the scale
as sensed by the LVDT remains substantially constant. Thus, the
output of the voltage to frequency converter 110 is also
substantially constant at some frequency, such as 6 KHz., for
example. That is, if the frequency outputted from the voltage to
frequency converter 110 is constant at 5 KHz. then the rate of flow
is zero, and if the frequency is 10 KHz, there would be maximum or
full flow of the machine. The computer receives signals from the
multiplexer 210 corresponding to the output of the voltage to
frequency converter 110 in the same manner as that described
hereinbefore. FIG. 12 illustrates the manner in which the computer
is programmed for this mode of operation. In this mode of
operation, the desired feed curve 318 is a straight horizontal
line. Samples as indicated by dots 320 are taken and stored in the
computer memory in the same manner as that described hereinbefore
in connection with the mode of operation of FIG. 11. Thus, the
samples form the actual feed curve in segments, as indicated at
322, 324, 326, 328 and 330. As indicated before, once during each
calculation time cycle the processor computes a regression on these
samples with respect to time to determine the slope of the actual
feed line during such calculation time period cycle. The slope of
one calculation time period or segment is compared to the last
derived slope to determine the deviation thereof. Thus, the slope
of segment 324 is compared to that of segment 322, and if the
variation is within an acceptable range, then the slope is
adjustable, and a corresponding correction command is outputted at
280 of the computer to adjust the motor control 284, thereby to
adjust the actual rate of discharge of the material from the feeder
assembly 10. The aforesaid acceptable range is predetermined as
described above in connection with FIG. 11. If the percentage
variation of the slope segment such as that indicated for segment
328, is beyond the acceptable range, the system is changed into its
ACRILOK mode. As before, the system remains in the ACRILOK mode
until in a subsequent calculation time cycle of operation the
variation of the slope is within an acceptable range of the last
slope that was acceptable, and then the system is returned to its
normal operating mode and the correction command is again outputted
at 280.
As still another operation of the processor, the total feed
commanded, as indicated at 250, is compared to the actual total
feed, as indicated at 252, periodically, such as every 5 or 10
minutes, for example. If there is a deviation exceeding
predetermined limits, the processor modifies the aforementioned
command output at 280 to gradually correct the actual feed to the
total feed. This is programmed to take from about 5 minutes to
about 10 minutes, thereby to avoid sharp fluctuations in the feed
rate command, but nevertheless, obtain as close as possible the
total feed selected over a long period of time. This is, in effect,
an override command and modifies the correction command, described
hereinbefore, as outputted at 280 of the computer. It is applicable
to all of the gravimetric modes of operation described above,
including the embodiments of FIGS. 1, 2 and 3.
A further operation of the processor, in the embodiment of FIG. 1,
is to determine when the scale weight, as indicated by the meter
256, drops to a predetermined low level, as set by the low level
switch 242, and then search for an "on rate" condition. In the
embodiments of FIGS. 2 and 3 a sensor 299 is provided for sensing
the level of the material in the containers 28 and 46,
respectively, and when the level thereof drops to a predetermined
low level, as set by the low level switch 242, the processor
searches for an "on rate" condition. That is, the output signal
outputted at 254 is monitored until the difference between it and
the feed rate switch 230 is less than a predetermined error limit.
Thence, the system is changed into its refill mode wherein the
output command 280 and feed rate meter 254 are not updated, but are
retained in their present state, similar to their operation as
described hereinbefore in connection with the ACRILOK mode. At the
same time, a command is outputted to a refill cicuit 300, which
sends a signal to a refill controller 302 that controls the flow of
material from a refill source 304 to the container 12, FIG. 1,
container 28, FIG. 2, and container 46, FIG. 3. The controller 302
could be an AC motor when handling dry particulate material or
could be a value when handling liquids.
The system remains in the refill mode until, in the embodiment of
FIG. 1, the processor detects that the container 12 is refilled, as
indicated by the scale weight meter 256, and as selected by the out
of low level switch 244. In the embodiments of FIGS. 2 and 3, the
sensor 299 detects when the containers 28 and 46 are refilled to
the extent, as selected by the out of low level switch 244. At this
time, the processor outputs a signal to the refill circuit 300
which, in turn, directs the refill controller 302 to discontinue
refilling the container 12, FIG. 1, container 28, FIG. 2, and
container 46, FIG. 3. The processor then returns the system to its
normal operational mode.
FIGS. 13 to 19 are flow charts of the computer 76. Thus, FIG. 13 is
a flow chart showing the program start, and FIG. 14 is a flow chart
of the background routine. FIG. 15 is a flow chart of the timer
routine and FIG. 16 shows the keyboard interrupts. FIG. 17 is a
flow chart of the calculation routine, and FIG. 18 computes the
scale weight and hopper levels, while FIG. 19 gives the subroutine
description. Appendix A is a program with descriptive comments for
carrying out the basic operations of the computer 76.
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 preselected constant value, wherein the container may be
automatically refilled during the continuous discharge of the
substance, wherein excessive excursions of the system are
eliminated, wherein extraneous data recordings are eliminated when
calculating the flow rate, and wherein past flow rate values may be
stored in memory and compensated for at a later point in time.
Although certain particular embodiments of the invention have been
herein disclosed for purposes of explanation, various modifications
thereof, after study of the specification, will be apparent to
those skilled in the art to which the invention pertains.
* * * * *