U.S. patent application number 09/870919 was filed with the patent office on 2001-09-27 for apparatus and control method for feeder system for flowable material.
Invention is credited to Flesher, James L., Moran, Robert L..
Application Number | 20010024096 09/870919 |
Document ID | / |
Family ID | 26744918 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010024096 |
Kind Code |
A1 |
Moran, Robert L. ; et
al. |
September 27, 2001 |
Apparatus and control method for feeder system for flowable
material
Abstract
An apparatus for precisely controlling the feed rate of a feeder
comprises: a motor operatively connected to the feeder to cause
dispensing of the feeder when the motor is driven; a control
circuit for supplying, when actuated, an AC voltage supply to the
motor for driving of the motor; a counter disposed in communication
with the control circuit for actuation thereof when an overflow
signal is generated by the counter; a latch controller disposed in
communication with the counter for enablement and disablement of
the counter, the latch controller disabling the counter when the
overflow signal is generated by the counter; a detector connected
to the AC voltage supply for detecting when the AC voltage crosses
over a median voltage thereof, the detector further disposed in
communication with the latch controller for enablement of the
counter when the median voltage is detected; and a fuzzy logic
controller disposed in communication with the counter for
generating an output to the counter that loads a determined count
into the counter such that the counter generates an overflow signal
within a time interval equal to a determined percentage of the half
period of the AC voltage. The control circuit includes a pair of
silicon control rectifiers disposed in parallel but reversed to one
another resulting in each silicon control rectifier being able to
supply the AC voltage to the motor during opposite half periods of
a time period of the AC voltage if continuously actuated.
Inventors: |
Moran, Robert L.; (Tega Cay,
SC) ; Flesher, James L.; (Charlotte, NC) |
Correspondence
Address: |
KENNEDY COVINGTON LOBDELL & HICKMAN, LLP
100 N TRYON STREET
BANK OF AMERICA CORPORATE CENTER
CHARLOTTE
NC
282024006
|
Family ID: |
26744918 |
Appl. No.: |
09/870919 |
Filed: |
May 31, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
09870919 |
May 31, 2001 |
|
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|
09188402 |
Nov 6, 1998 |
|
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60064812 |
Nov 7, 1997 |
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Current U.S.
Class: |
318/560 |
Current CPC
Class: |
G05B 13/027
20130101 |
Class at
Publication: |
318/560 |
International
Class: |
G05B 011/01 |
Claims
What is claimed is:
1. A method of determining an appropriate change to a regulator
that controls an outflow of a flowable material from a supply of
the flowable material, comprising the steps of: for a plurality of
small time intervals during the outflow, (a) calculating values
representative of a rate of weight change of the supply of the
flowable material based on weight measurements taken over said
small time intervals; (b) calculating values representative of a
rate error based on said calculated values for the rate of weight
change and based on a setpoint value for the rate of weight change;
(c) determining a value representative of an appropriate change to
the regulator for maintaining the outflow at the setpoint value for
the rate of weight change by applying fuzzy logic control to said
calculated values representative of the rate error.
2. The method of claim 1, further comprising calculating values
representative of the change in the rate error based on said
calculated values for the rate error, and applying fuzzy logic
control to said calculated values representative of the change in
the rate error.
3. The method of claim 1, wherein said calculated values
representative of a rate of weight change are average values.
4. The method of claim 1, wherein said calculated values
representative of a rate error are average values.
5. The method of claim 1, further comprising weighing the supply of
the flowable material during the plurality of small time
intervals.
6. The method of claim 1, further comprising determining the
setpoint value by weighing the outflow of the flowable material
from the supply of the flowable material.
7. An apparatus for precisely controlling the driving of a motor,
comprising: (a) a control circuit operatively connected to the
motor which provides a voltage supply to the motor for driving the
motor when the control circuit is actuated; (b) a timing circuit
disposed in communication with said control circuit for actuating
said control circuit after a determined time interval; (c) a fuzzy
logic controller disposed in communication with said timing circuit
for determining said time interval; and (d) a sensor disposed in
communication with said fuzzy logic controller for measuring a rate
of a supply of flowable material that is dispensed by the feeder.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is entitled to the benefit of, and claims
priority to, U.S. Provisional Patent Application Ser. No.
60/064,812, filed Nov. 7, 1997, by Moran et al., and entitled
"CONTROLLER FOR VIBRATORY FEED SYSTEM FOR BULK SOLIDS" and U.S.
patent application Ser. No. 09/188,402, filed Nov. 6, 1998, by
Moran et al., and entitled "APPARATUS AND CONTROL METHOD FOR FEEDER
SYSTEM FOR FLOWABLE MATERIAL," the entirety of which is
incorporated herein by reference.
BACKGROUND OF THE PRESENT INVENTION
[0002] The present invention relates broadly to bulk material
supply systems and, more particularly, to a feed system for bulk
solids and its associated controller wherein the controller employs
fuzzy logic for rapid reactions to changes in weight.
[0003] Bulk solids appear throughout industry and must be handled
or processed in a manner which will provide consistent results
without waste. Examples of industries which utilize bulk solids
include food, lumber, paper, chemical, petroleum refining, rubber,
stone, clay, glass, and concrete. The bulk solid materials may
include such diverse items as cabbage flakes, bleach, bauxite,
baking soda, fiberglass, flour, grass seed, iron ore, starch,
sugar, raisins, parsley, noodles, nylon, mineral fiber, mica, lime,
and detergent. All of these materials share a common feature in
that they are flowable solids. They are fungible materials which
may be poured for filling into containers or otherwise metered
under flow conditions for processing.
[0004] Typically, such processing includes providing a hopper
filled with the bulk material with some form of regulator or
metering device providing the necessary flow control for
processing.
[0005] One method of determining how much bulk solid material has
been dispensed during any given dispensing operation is by using
the so-called loss-in-weight method. There, the hopper containing
the bulk material is continually weighed and the reduction in
weight is indicative of the material dispensed.
[0006] Further, the reduction in weight-per-unit time is indicative
of the rate at which a predetermined amount of the bulk material is
dispensed. Therefore, by precisely determining the change in weight
of the hopper, a precise indication of the amount of material
dispensed is realized. This information can be used for controlling
the feed process. Furthermore, while the present invention is
described for operation with a vibratory feeder, it should be noted
that it is equally effective with screw feeders or belt feeders.
The focus of the present invention lies in its applicability to
loss-in-weight feeders.
[0007] A common method which is used to control dispensing of bulk
solids is the proportional method used throughout the industry. The
setpoint for such control method is a desired rate of change of
weight for a supply of the bulk solid. However, because the control
variable (the weight change) is the integral of the rate of weight
change and not the rate of weight change itself, the proportional
control method currently used in the industry, while reliable, is
clumsy and lacks a certain amount of precision.
[0008] Several methods may be used to control the actual feed of
the bulk solid material. Valves may be used which are open
proportionally or open for a certain time period. Other methods
include the use of a belt feeder or a screw feeder. A vibratory
feeder is disclosed in Peschl U.S. Pat. No. 3,973,703. There, a
vibrating tray is disclosed containing a number of plates in an
angular relationship to one another. According to this method, the
bulk material will not flow unless the feeder is vibrated or
otherwise agitated in some manner. Such feeders allow for precise
flow with the flow rate being based on the amplitude of vibration
or agitation. This type of feeder can provide accurate flow
characteristics and can respond rapidly to changing inputs from an
associated excitation motor. The motor is driven responsive to a
control variable. As discussed above, the current proportional
controllers are slow to respond to changes in demand or process
changes and, therefore, the precision and rapid changing
characteristics of any loss in weight type feeders including the
vibratory feeder are not fully realized using a proportional
controller.
SUMMARY OF THE PRESENT INVENTION
[0009] It is accordingly an object of the present invention to
provide a feed control system which precisely controls a vibratory
feeder and offers rapid response to a change in demand.
[0010] Briefly summarized, the method of the present invention
includes determining an appropriate change to a regulator that
controls an outflow of a flowable material from a supply of the
flowable material. The method includes the steps of, for a
plurality of small time intervals during the outflow, (a)
calculating average values representative of a rate of weight
change of the supply of the flowable material; (b) calculating
average values representative of a rate error based on the
calculated average values for the rate of weight change and based
on a setpoint value for the rate of weight change; (c) calculating
values representative of the change in the rate error based on the
calculated average values for the rate error; and (d) determining a
value representative of an appropriate change to the regulator for
controlling the outflow by applying fuzzy logic control to the
calculated average values representative of the rate error and the
calculated values representative of the change in the rate
error.
[0011] Preferably, the method further comprises weighing the supply
of the flowable material during the plurality of small time
intervals as well as determining the setpoint value by weighing the
outflow of the flowable material.
[0012] The apparatus of the present invention precisely controls
the feed rate of the feeder and itself includes: (a) a motor
operatively connected to the feeder which causes dispensing of a
flowable material by the feeder when the motor is driven; (b) a
control circuit operatively connected to the motor which provides a
voltage supply to the motor for driving the motor when the control
circuit is actuated; (c) a counter disposed in communication with
the control circuit for actuating the control circuit after a
determined time interval; and (d) a fuzzy logic controller disposed
in communication with the counter for determining the time
interval.
[0013] Preferably, the voltage supply is AC voltage and the
determined time interval ranges between zero and one-half of a time
period of the AC voltage. Furthermore, the apparatus preferably
includes a sensor disposed in communication with the fuzzy logic
controller for measuring a weight of a supply of flowable material
that is dispensed by the feeder.
[0014] In a feature of the present invention, the control circuit
deactuates at a recurring point in time. Preferably, the recurring
point in time is a crossover of a median voltage of the AC voltage
supply. Furthermore, the counter preferably restarts at the
recurring point in time as well.
[0015] The preferred embodiment of the apparatus of the present
invention includes: (a) a motor operatively connected to the feeder
to cause dispensing of the feeder when the motor is driven; (b) a
control circuit for controlling the driving of the motor, the
control circuit including a pair of silicon control rectifiers
disposed in parallel but reversed to one another with each silicon
control rectifier operatively connected to the motor such that,
when each silicon control rectifier is fired, an AC voltage is
supplied to the motor and the motor is driven, the parallel and
reversed disposition of the silicon control rectifiers in the
control circuit resulting in each silicon control rectifier being
able to supply the AC voltage to the motor during opposite half
periods of a time period of the AC voltage; (c) a counter disposed
in communication with each of the silicon control rectifiers for
actuation thereof when an overflow signal is generated by the
counter; (d) a latch controller disposed in communication with the
counter for enablement and disablement of the counter with the
latch controller disabling the counter when the overflow signal is
generated by the counter; (e) a detector connected to the AC
voltage for detecting when the AC voltage crosses over a median
voltage thereof with the detector being further disposed in
communication with the latch controller, with the detector
generating a signal to the latch controller for enablement of the
counter when the median voltage is detected; (f) a fuzzy logic
controller disposed in communication with the counter for
generating an output to the counter that loads a determined count
into the counter such that the counter generates an overflow signal
within a time interval equal to a determined percentage of the half
period of the AC voltage, whereby each silicon control rectifier is
fired for the determined percentage of the half period of the AC
voltage, the counter retaining the determined count until a
different determined count is loaded into the counter by the fuzzy
logic controller; (g) a sensor that measures a weight of a supply
of flowable material that is dispensed by the feeder for
calculation of a rate of weight change of the supply of flowable
material; and (h) a second sensor disposed for measurement of a
weight of the flowable material dispensed by the feeder and a time
interval of the dispensing for calculation of a setpoint value.
[0016] Furthermore, the fuzzy logic controller includes an
analog-to-digital converter, a moving average filter, and a fuzzy
logic processor including a predetermined rule base, whereby the
fuzzy logic controller compares the rate of weight change of the
supply of flowable material and the setpoint value for
determination of the percentage of the half period of the AC
voltage before the controller generates the overflow signal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is diagrammatic view of a bulk material handling
system employing a controller according the preferred embodiment of
the present invention;
[0018] FIG. 2 is a block diagram of the external components of the
feeder control system; and
[0019] FIG. 3 is a block diagram of the fuzzy logic processor.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0020] According to the present invention, a controller is provided
which uses fuzzy logic reasoning to provide control signals to
silicon control rectifiers (SCRs) which drive an electric motor
that causes vibration of the feeder for dispensing bulk solids.
[0021] To that end, the present invention provides a fuzzy logic
based processor which produces an output signal for controlling the
firing of a pair of SCRs which control through a motor the
excitation of a vibratory feeder for feed rate control when
dispensing bulk solid material. The system employs a hopper which
is suspended on load cells. The hopper contains a predetermined
amount of bulk solid material for dispensing and is replenished
from a material supply in a controlled manner. In reality, the
combined weight of the electromagnetic drive motor, feed tray,
hopper, suspended components and material is weighed using the load
cells with all weight except for the material "zeroed out"
electronically.
[0022] The output from the load cells is sent to the controller
and, initially, to an anti-aliasing filter. High frequencies, which
in analog controllers normally are effectively eliminated by the
low pass filtering, may because of "aliasing" appear as low
frequency signals in the bandwidth of the sample control system.
The anti-aliasing filter effective eliminates all signal components
with frequencies above half the sampling frequency. From there, the
signal is fed to an analog to digital converter which is Preferably
an oversampling sigma-delta type of charge balancing converter. The
output of the converter enters a programmable digital filter with
notch frequencies of the filter set to 5, 10, 25, 30, 50, or 60
hertz depending on the controller. Analog to digital conversion
occurs at a rate that is a function of notch frequency. The rate
may be expressed as time=1/notch frequency. The output code from
the filter results in a converted signal of 24 bits with no missing
codes and 0.0015% nonlinearity. This corresponds to a full-scale
count of 16,777,216 before post filtering. The software reads a
24-bit word at a rate equal to the notch frequency for which the
programmable filter has been set. The software then places this
count into two moving average filters, one for use by the display
and one to be used by the control algorithm. A number of averages
for each post filter is entered independently. In general, a small
number of averages in the control filter allows for fast, tight
control and a larger number in the display filter allows for more
readable display of rate output.
[0023] Analog to digital conversion occurs every 100 milliseconds
provided the notch frequency is 10 Hz, with a digital count
representing the combined weight of the hopper, feeder, and
material being dispensed. A 5 Hz notch frequency will result in a
conversation rate of 200 milliseconds. The digital count is stored
in a circular ring buffer which is used to average the weight. The
number of counts to be averaged equals the number of filter
samples. The ring buffer stores a predetermined number of samples.
As each new sample is introduced, the oldest sample in residency is
subtracted from the running total and the newest sample is added to
the running total with the average count being computed by dividing
the running total by the number of filter samples.
[0024] This average count is then converted to a weight value by
subtracting the tare count, which amounts to deducting the weight
of the container and everything supported by the load cells except
for the material, and then multiplying the difference by the weight
to count ratio which was predetermined during calibration. The
change in weight is computed by subtracting the current weight from
the previously measured weight, with the current weight being
stored as the new previous weight. Rate is computed by multiplying
the change in weight value by the rate per minute factor. The rate
is stored in a circular ring buffer which is used to provide an
average in a manner discussed previously.
[0025] The computer then undertakes fuzzy logic processing based on
the change in weight and the rate of weight change. The frequency
of performing the fuzzy logic processing is controlled by an update
value which is entered by the operator and is a multiple of 100
milliseconds. This time period is also a function of the notch
frequency. As is known with fuzzy logic, a rule base is provided
and appears as follows:
[0026] The fuzzy logic rule base has two inputs. One is the rate
error and the other is the change in rate error since last
processing cycle. The rate error is determined by subtracting the
calculated change in weight from the measured change in weight with
the calculated change in weight being computed from the rate
setpoint, the rate per minute factor, and the frequency of the
fuzzy logic processing cycle. The change in rate error is computed
by subtracting the previous rate error from the current rate error.
The current rate error is then stored as the new previous rate
error.
[0027] Basically, the analysis of the rate error and the change in
rate error proceeds in four steps. Under fuzzification, the
membership functions defined on the input variable are applied to
their actual values, to determine the degree of truth for each rule
premise. Under inference, the truth value for the premise of each
rule is computed, and applied to the conclusion parity of each
rule. This results in one fuzzy subset to be assigned to each
output variable for each rule. The output membership function is
scaled by the rule premise's computed degree of truth.
[0028] Under composition, all of the fuzzy subsets assigned to each
output variable are combined together to form a single fuzzy subset
for each output variable. Using MAX-DOT inference, the combined
output fuzzy subset is constructed by taking the pointwise maximum
over all of the fuzzy subsets assigned to variables by the
inference rule. Finally, the present invention employs centroid
defuzzification, which is used to convert the fuzzy output set to a
crisp number. The crisp number may then be employed to control the
vibration of the feeder. In the centroid method, the crisp value of
the output variable is computed by finding the variable value of
the center of gravity of the membership function for the fuzzy
value. The present fuzzy logic rule base produces an output which
is a percentage value. The output is then multiplied by the gain
value. The resulting value is algebraically added to the SCR
percent value by the computer, which directly controls the firing
of the SCRs. The firing of the SCRs controls the electromagnetic
drive motor.
[0029] The membership functions are as follows:
[0030] Membership Function--Rate Error:
[0031] Range of input is -1 to +1.
[0032] Member negative points are -1,1 -0.5,1 0,0
[0033] Member zero points are -0.5,0 0,1 0.5,0
[0034] Member positive points are 0,0 0.5,1 1,1
[0035] Membership Function--Change in Rate Error:
[0036] Range of input is -1 to +1.
[0037] Member negative points are -1,1 -0.5,1 0,0.
[0038] Member zero points are -0.5,0 0,1 0.5,0
[0039] Member positive points are 0,0 0.5,1 1,1
[0040] Membership Function--Output Change Percentage:
[0041] Range of output is -1000 to +1000.
[0042] Membership negative points are -1000,0 -833.33,1
-666.66,0
[0043] Membership zero points are -166.66,0 0,1 166.66,0
[0044] Membership positive points are 666.66,0 833.33,1 1000,0
[0045] The rule base contains nine rules which follow:
[0046] 1. If rate error is N and change in rate error is N, then
output change percentage is P.
[0047] 2. If rate error is N and change in rate error is Z, then
output change percentage is P.
[0048] 3. If rate error is N and change in rate error is P, then
output change percentage is N.
[0049] 4. If rate error is Z and change in rate error is N, then
output change percentage is P.
[0050] 5. If rate error is Z and change in rate error Z, output
change percentage is Z.
[0051] 6. If rate error is Z and change in rate error is P, then
output change percentage is N.
[0052] 7. If rate error is P and change in rate error is N, then
output change percentage is P.
[0053] 8. If rate error is P and change in rate error is Z, then
output change percentage is N.
[0054] 9. If rate error is P and change in rate error is P, then
output change percentage is N.
[0055] In the above rule base, P represents positive, N represents
negative, and Z represents zero.
[0056] The main algorithm for the MAX-DOT centroid method for fuzzy
interfacing is as follows: 1 V = i = 1 n 1 M 1 / i = 1 n 1 A 1 W
1
[0057] where:
[0058] V is the variable value at the centroid of the fuzzy
set,
[0059] .alpha..sub.i: is the degree of membership computed for the
premise of rule i,
[0060] W.sub.1 is the weight assigned to the rule i,
[0061] M.sub.1 is the moment of the membership function assigned to
V in rule i around zero, and
[0062] A.sub.1 is the area of the membership function assigned to V
in rule i.
[0063] The electromagnetic drive motor, which controls the
vibration of the feeder, requires an input of between 0 and 115 VAC
for corresponding amplitudes of vibration between 0% and 100%
(corresponding to 0.000 inches to 0.060 inches). The SCR drive
control works by turning on the SCRs for a percentage of each half
cycle of the AC line voltage. In full wave control an SCR is needed
for each polarity of a line, this being accomplished by placing two
SCRs in parallel with one reverse from the other. If each SCR
conducts for half of its corresponding half cycle, 50% of the line
voltage is the average voltage sent to the load. Once an SCR is
turned on, the SCR stays on until the current flowing through it
drops to 0, i.e., when the AC line reverses polarity.
[0064] The control circuit includes a "zero crossing detector".
This circuit generates a narrow pulse at each crossing of zero
volts of the AC line voltage. This occurs every 8.33 milliseconds
for a 60 cycle line. When the zero crossing pulse occurs, it sets a
latch whose output enables the 16 bit counter to count. The counter
is clocked by a crystal oscillator at 7.3728 MHz. If the counter
had a net count of zero when it was enabled, it would take 65536
counts of the clock to fill the counter and generate an overflow.
With a clock of 7.3728 MHz, each cycle is 135 nanoseconds.
Therefore, the 65536 counts.times.135 nanoseconds=8.888
milliseconds or little more time than one-half of the AC cycle. If
a small count of 4500 is loaded into the counter, the first clock
pulse after zero crossing enables the counter and it will take
almost the entire half cycle for an overflow to occur. This
overflow signal does two things. Initially, it triggers the SCRs.
It also resets the control latch disabling the counter until the
next zero crossing. The firing of an SCR just before zero crossing
results in an average output voltage of almost zero volts. This
happens every 8.333 milliseconds without any intervention from the
software. If a large count is loaded into the counter, e.g.,
64,000, the SCRs are turned on just after the zero crossing and the
output voltage will approximate the line voltage. These minimum and
maximum counts are scaled in the software to be 0% to 100% output.
Using this method of triggering the SCRs, minimum software
intervention is required because if the output does not need to
change the software need do nothing. The circuit runs by itself. If
the output needs to change, the software writes the new number once
and the output is changed at the next zero crossing.
[0065] By employing the fuzzy logic controller in combination with
the zero crossing detector, the software can cooperate with the
zero crossing detector to rapidly change the firing rate of the
SCRs thereby controlling the feeder in a precise manner.
[0066] Turning now to the drawings and, more particularly to FIG.
1, a bulk material handling system is generally indicated at 10 and
includes a skeletal frame 12 supporting the components of the
system. A product conveyor 16 is formed as a driven, endless belt
system for carrying a fungible, flowable product P (such as
strawberries) on the top flight thereof. The product P is emitted
from a feeder conveyor 14 disposed at one end of the product
conveyor 16. A series of idlers 38 supports the top flight of the
conveyor 16. The product conveyor 16 conveys the product P through
the handling system. A 5 hopper 18 is formed as an inverted,
frusto-conical member having a replenishment feeder 23 at an open,
upper end thereof. A vibrational distribution feeder 30 is disposed
at the lower, open end of the hopper 18 at a position spaced a
predetermined distance from the product conveyor 16 for depositing
bulk material B (such as sugar) on the product P on the conveyor
16. The vibrational feeder 30 includes an electromagnetic drive
motor 32 being controlled by two silicon controlled rectifiers
(SCRs) contained within a SCR controller illustrated generally at
34. The replenishment feeder 23 is controlled by a refill gate 24
operationally attached thereto. The hopper 18 is suspended on load
cells 20 by cables 22.
[0067] The present invention also includes two microprocessor or
computer-based controls. Initially, a weight speed multiplier 44 is
mounted to the frame 12 and operatively connected to a load cell 45
associated with one of the idlers 38 in contact with the product
conveyor 16 to determine the amount of bulk material dispensed and
time of the dispensing.
[0068] A second computer-based control is the rate controller 40
and receives input from the operator and, through other various
other inputs as will be discussed in greater detail hereinafter,
controls firing of the SCRs to excite the electromagnetic drive
motor 32 to control the vibrational feeder 30. The rate controller
40 receives input from the weight speed multiplier 44 to coordinate
the operation of the vibrational feeder 30 with the operation of
the product conveyor 16. An electrical output signal is supplied
through control lines 26 from the rate controller 40 to the refill
gate 24 to replenish the hopper 18 when the bulk material supply
gets low. The rate controller 40 receives an electrical signal from
the load cells 20 through electric line 28 from which the rate
error and change in rate error are determined. An output line
extends from the rate controller 40 to the SCR controllers 34 for
controlling the vibrational feeder 30.
[0069] The external arrangement can also be seen in FIG. 2. There,
in a block form, it can be seen that controller 40 is operationally
connected to the load cells 20 through control line 28. The load
cells 20 are physically connected to the hopper 18. The hopper/load
cell arrangement provides the primary input to the fuzzy logic
controller 40. Additionally, the weight speed multiplier 44
supplies a coordinating signal (the setpoint) through electric line
43 to the rate controller 40. The output of the rate controller 40
is transmitted through electrical line 36 to the SCR controller 34
including two SCRs 46,48 which excite the drive motor 32 for
operating the vibrating feeder 30.
[0070] Turning now to FIG. 3, the internal processor is illustrated
generally in broken lines at 50. The output from the load cells 20
is administered to an anti-aliasing filter 54 which acts to remove
aliases of the primary frequency of interest. The anti-aliasing
filter 54 sends its output signal to an analog/digital converter 56
which provides a digital output for processing by the fuzzy logic
controller. The digital output signal is fed to the ring buffers 58
and the output of these is the rate error 60 and the change in rate
error 62 which are fed to the fuzzy logic rule base 52 for
processing with the output appearing on output signal line 64.
[0071] In operation, the conveyor 16 is moved under the vibratory
feeder 30 and receives bulk material from the hopper according to
controlled vibrations of the vibrating feeder 30. The load cells 20
monitor the change in weight and continually feed this information
along lines 28 to the main controller 40. Meanwhile, the weight
speed multiplier 44 is receiving input from the load cell 45
associated therewith regarding speed and weight carried on the top
flight of the conveyor 16. The output of the main load cells 20 is
processed using the anti-aliasing filter 54, the analog to digital
converter 56, and the ring buffers 58 to arrive at a value for the
rate error 60 and a value for the rate of change of the weight
error 62. Mapping of these values 60,62 are made according to fuzzy
logic membership functions and the results are applied to a fuzzy
logic controller comprising a rule base 52 within the rate
controller 40, and the output variable appears as a control signal
64 which controls the firing of the SCRs which, in turn, controls
the rate at which the vibrational feeder dispenses bulk material
product.
[0072] The above system provides a rapid and precise apparatus for
controlling the amount of bulk solid material distributed during a
process.
[0073] Moreover, it is contemplated within the scope of the present
invention that, while less precise, a single SCR could be used in
the control circuit, whereby dead time would occur during each
cycle when no voltage could be applied to the motor. Furthermore,
it is also contemplated that, while the control circuit described
in the preferred embodiment includes two SCRs disposed in parallel,
reversed configuration, other electronic components can be used
such as diodes and transistors with the desired result.
[0074] It will therefore be readily understood by those persons
skilled in the art that the present invention is susceptible of
broad utility and application. Many embodiments and adaptations of
the present invention other than those herein described, as well as
many variations, modifications and equivalent arrangements will be
apparent from or reasonably suggested by the present invention and
the foregoing description thereof, without departing from the
substance or scope of the present invention. Accordingly, while the
present invention has been described herein in detail in relation
to its preferred embodiment, it is to be understood that this
disclosure is only illustrative and exemplary of the present
invention and is made merely for purposes of providing a full and
enabling disclosure of the invention. The foregoing disclosure is
not intended or to be construed to limit the present invention or
otherwise to exclude any such other embodiments, adaptations,
variations, modifications and equivalent arrangements, the present
invention being limited only by the claims appended hereto and the
equivalents thereof.
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