U.S. patent application number 11/895421 was filed with the patent office on 2008-02-07 for control system for and method of combining materials.
Invention is credited to Jon Kevin McLaughlin, Roger Phillip Williams.
Application Number | 20080031085 11/895421 |
Document ID | / |
Family ID | 46329218 |
Filed Date | 2008-02-07 |
United States Patent
Application |
20080031085 |
Kind Code |
A1 |
McLaughlin; Jon Kevin ; et
al. |
February 7, 2008 |
Control system for and method of combining materials
Abstract
An apparatus and method for combining multiple materials. The
multiple materials may include both a major material and one or
more minor materials. The major and minor materials are added at
transient or steady state flow rates, depending upon a command from
a control signal. The actual flow rates track the commanded flow
rates, but deviate by an error. The claimed arrangement provides an
instantaneous and time-based error believed to be unobtainable in
the prior art.
Inventors: |
McLaughlin; Jon Kevin; (West
Chester, OH) ; Williams; Roger Phillip; (Cincinnati,
OH) |
Correspondence
Address: |
THE PROCTER & GAMBLE COMPANY;INTELLECTUAL PROPERTY DIVISION - WEST BLDG.
WINTON HILL BUSINESS CENTER - BOX 412
6250 CENTER HILL AVENUE
CINCINNATI
OH
45224
US
|
Family ID: |
46329218 |
Appl. No.: |
11/895421 |
Filed: |
August 24, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11217802 |
Sep 1, 2005 |
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11895421 |
Aug 24, 2007 |
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11217273 |
Sep 1, 2005 |
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11895421 |
Aug 24, 2007 |
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Current U.S.
Class: |
366/162.1 |
Current CPC
Class: |
B01F 15/042 20130101;
B01F 5/0456 20130101; G05D 11/132 20130101; B01F 13/1055 20130101;
F04B 13/02 20130101; B01F 5/0453 20130101 |
Class at
Publication: |
366/162.1 |
International
Class: |
B01F 15/04 20060101
B01F015/04 |
Claims
1. A method for combining materials comprising at least one major
material and at least one minor material, said at least one major
material and at least one minor material combining to make a total,
said method comprising the steps of: providing a confluence region;
supplying at least one major material into said confluence region;
adding at least one minor material to said confluence region in the
vicinity of said major material, whereby said major material and
said at least one minor material come into contacting relationship
in a first proportion and are maintained within said confluence
region; and changing the amount of said at least one major material
and said at least one minor material added to said confluence
region throughout a first period of time, while maintaining said
first proportion of said at least one major material to a
respective setpoint and said first proportion of said at least one
minor material to a respective setpoint within an instantaneous
error of not more than .+-. about five percent of full scale flow
rate, said first period of time being less than one second.
2. A method according to claim 1, wherein said instantaneous error
is not more than about .+-.3 percent.
3. A method according to claim 2, wherein said first period of time
is not more than about one-half second.
4. A method according to claim 1 wherein said step of adding at
least one minor material to said confluence region comprises of the
step of continuously adding the at least one minor material.
5. An apparatus for combining at least two materials together, said
apparatus being able to undergo a transient whereby the amount of
said materials blended per unit time is varied either to be greater
than or less than a prior rate of blending said materials, whereby
said transient produces an instantaneous error and a cumulative
error between a command signal having a setpoint which is changed
at time T=0 and a measured flow rate, said instantaneous error
being not more than: IE<A*M*exp(-t/.tau.) where IE is the
instantaneous error in volume per unit time, and A is the magnitude
of the setpoint change at time zero, normalized to unity, M is a
scale factor ranging from about 0.1 to about 0.5, t is the
instantaneous time in seconds, not to exceed about 1.5 *.tau.,
.tau. is a time constant ranging from about 0.1 to about 1.0
seconds.
6. An apparatus according to claim 5, wherein .tau. is 1 and t
ranges from 0 to about 0.5*.
7. An apparatus according to claim 5, wherein .tau. is 0.5 and t
ranges from 0 to about 3*.tau..
8. An apparatus according to claim 5 wherein M is 0.5, .tau. is 1
and t ranges from 0 to about 2.0*.tau..
9. An apparatus according to claim 5 wherein M is 0.5, .tau. is 0.5
and t ranges from 0 to about 2*.tau..
10. An apparatus according to claim 5 wherein M is 0.25, .tau. is 1
and t ranges from 0 to about 1.5*.tau..
11. A control system for blending at least two fluids materials
together, said control system being able to undergo a transient
lasting not more than one second, whereby the amount of materials
added per unit time is varied either to be greater than or less
than a rate of adding said materials prior to said transient,
whereby said transient produces an cumulative error over a period
of time given by the formula: IE.sub.k=[Command Signal for Flow
Rate].sub.k-[Actual Flow Rate].sub.k wherein Command Signal for
Flow Rate is the desired flow rate, Actual Flow Rate is the
resulting flow rate in the system, and a transition between a
continuous time t, and a discrete time is given by the formula
t=k*.DELTA.T, wherein k is an index for a discrete time period
.DELTA.T, and t and .DELTA.T are measured in seconds; and wherein
for a transient command signal of normalized magnitude equal to one
said cumulative error for the period from t=0 to t=T.sub.final, for
T.sub.final up to about 5 seconds or less is given by the formula:
CE.sub.Tfinal<0.50.
12. An apparatus according to claim 11, wherein said cumulative
error is given by the formula CE.sub.Tfinal<0.37.
13. An apparatus according to claim 11, wherein T.sub.final is up
to about 4 seconds.
14. An apparatus according to claim 11, wherein T.sub.final is up
to about 3 seconds.
15. An apparatus according to claim 12, wherein T.sub.final is up
to about 4 seconds.
16. An apparatus according to claim 12, wherein T.sub.final is up
to about 3 seconds.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. Nos. 11/217,273 and 11/217,802, both filed Sep. 1,
2005.
FIELD OF THE INVENTION
[0002] The present invention relates to a method and control system
for combining materials.
BACKGROUND OF THE INVENTION
[0003] Many methods are known in the art for combining fluid
materials. Typically, the materials are combined upstream of a mix
tank. Such materials are then jointly added to the mix tank and
stirred until a homogenous blend is achieved. Further processing
steps downstream of the confluence region may include the addition
of more material(s), the addition or removal of energy, such as
thermal energy, etc.
[0004] Additionally or alternatively, such materials can be mixed
in a dynamic mix tank using mechanical agitation and/or alternative
forms of agitation, such as ultrasonic vibration. The combined
materials, or blend, may then be transported downstream and become
an intermediate for further processing. Alternatively, these
materials may be added to a container for ultimate sale or use.
[0005] The prior art methods and systems have several
disadvantages. If such a mix tank is used, it can require
considerable energy to achieve the desired mixing. If one desires
to change the formulation, or even the minor materials, this change
usually entails cleaning the entire tank and associated system.
Cleaning the entire system can be time-consuming and laborious.
Then new materials are added and the process begins again.
Considerable waste of time and materials can occur.
[0006] Transients from no production or low rate production to full
production rates are inevitable when changes between different
products occur, etc. It is generally desirable that such a
transient be over and steady state operation resume as quickly as
possible. This is because one typically desires reaching steady
state production rates as soon as reasonably practicable.
Furthermore, product manufactured out of specification during
transients may be wasted. If one were to accept a slower transient,
then it is likely greater accuracy in the products manufactured
during the transient can occur and less product may be wasted by
having a slower transient. Thus a tradeoff is present in the
art.
[0007] Often, the speed in which a system and respond to transients
is limited by the hardware. For example, a flow meter which is
intended to provide actual flow rate at a particular point in time
may not follow and/or indicate a change in flow rate as quickly as
one would like for the rate of change of the transient. For
example, valves which provide flow control and ultimately the rate
of material addition may not respond as quickly as one would
desire. Furthermore, different sizes of valves, different operators
used in conjunction with the valves, and even valves from different
manufacturers may respond at different rates once a command signal
is received. Yet further, the same valve may respond at different
rates over different portions of the open/close cycle.
[0008] Accordingly, what is needed is an apparatus, and process of
using such apparatus, which allows for quickly changing the
formulation of a blend, accurately follows transients, minimizes
wasted materials, and rapidly provides for homogeneity in the
blend. Unless otherwise stated, all times expressed herein are in
seconds, proportions and percentages herein are based on volume.
Optionally, the invention may use proportions and percentages based
on mass.
SUMMARY OF THE INVENTION
[0009] The invention comprises a method and apparatus for blending
together two or more materials in a predetermined proportion. The
materials may be combined at various flow rates with various ramps
therebetween, while maintaining the predetermined proportion within
a relatively tight error band, considering either the instantaneous
error at a point in time or the cumulative error over a period of
time.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic view of an exemplary system according
to the present invention, shown partially in cutaway and providing
for eight minor materials.
[0011] FIG. 2 is an instantaneous vertical sectional view of an
exemplary system according to the present invention, schematically
pumps for supplying the minor materials to the confluence region
and a circumferential clamp therearound.
[0012] FIG. 3 is a graph showing the performance curve of an
illustrative system according to the prior art for a command signal
having a step input.
[0013] FIG. 4 is a graph showing a transient response curve of an
exemplary system according to the present invention for a step
input, as compared to an idealized theoretical response of the
prior art for the same step input.
[0014] FIG. 5 is a graph of transient response curves of a system
for a 0.2 second ramp input showing the command signal and certain
process variables for one major and two minor materials.
[0015] FIG. 6 is an enlarged graph of the transient response curve
of one of the minor materials in FIG. 5.
[0016] FIG. 7 is a graph showing the instantaneous error of the
system of FIG. 4.
[0017] FIG. 8 is a graph showing the cumulative error of the system
of FIG. 4.
[0018] FIG. 9 is a schematic diagram of a flow rate feedback
control system, according to the prior art.
[0019] FIG. 10 is an exemplary schematic diagram of a motor
position feedback control system usable with the present invention,
showing optional components in dashed.
DETAILED DESCRIPTION OF THE INVENTION
[0020] Referring to FIGS. 1-2, the invention comprises an apparatus
10 and process for combining, blending or mixing two or more
materials. Combining refers to adding materials together with or
without substantial mixing towards achieving homogeneity. Mixing
and blending interchangeably refer to combining and further
achieving a relatively greater degree of homogeneity
thereafter.
[0021] The resulting combination of materials may be disposed in a
container (not shown). The container may be insertable into and
removable from the apparatus 10. The apparatus 10 comprises
apparatus 10 hardware for adding at least one major or first
material to the container and for adding at least one minor or
second through nth materials to the container. The apparatus 10 for
adding the major material(s) and minor material(s) provides for
some or all of these materials to come together in a confluence
region 12. The confluence region 12 is the region or point where
the major material(s) and at least one, and likely each, of the
minor material(s) initially come into contacting relationship with
one another and is where mixing may occur. Mixing of the major
material(s) and minor material(s) may occur at the confluence
region 12, downstream thereof, or both.
[0022] The confluence region 12 may comprise one or more inlets
14A, which may be referred to as a major material inlet 14A, for
supplying one or more major materials, and at least one inlet 14I,
each of which may be referred to as a minor material inlet 14I, for
supplying one or more minor materials. The confluence region 12 may
further comprise at least one common outlet 16 for discharging the
major material(s) and minor material(s) from the confluence region
12, and optionally directly into the container or optionally to the
container after further processing. It is understood that after the
materials leave the confluence region 12 through the common outlet
16, a single container may be filled or plural containers having
equal or unequal volumes and flow rates thereinto may be filled in
parallel.
[0023] The apparatus 10 for supplying the minor material(s) may
comprise one or more inlet tube(s) 14I inserted into the apparatus
10 for supplying the minor material(s) directly to the confluence
region 12. Each minor material may have a dedicated inlet tube 14I
or, alternatively, plural minor materials may be inserted through a
single inlet tube 14I. Of course, if desired, the same minor
material may be added through more than one inlet tube 14I, in
various combinations of like or different materials, quantities,
feed rates, flow rates, concentrations, temperatures, etc.
[0024] The inlet 14I for each of the minor materials terminates at
an inlet discharge 18. The inlet discharges 18 may lie in a common
plane, as shown. The inlet discharge 18 defines the beginning of
the confluence regions 12, as noted above. The inlet discharge 18
is the point a minor material leaves a respective inlet 14I and
enters the confluence region 12. The inlet discharge 18 may be
closely juxtaposed with an inline mixer, so that mixing of the
materials occurs almost immediately in the confluence region
12.
[0025] While apparatus 10 having eight inlet tubes 14I, each
equally spaced from the other, are illustrated, one of skill will
recognize the invention as not so limited. More or less inlet tubes
14I may be provided and be equally or unequally spaced
circumferentially, radially, and/or longitudinally. Further, the
inlet tubes 14I may have equal or unequal cross sectional areas,
shapes, lengths and flow rates therethrough. The minor materials
may be supplied to the inlet tubes 14I from one or more common
sources or from different sources.
[0026] If desired, the volume of the inlet tubes 14I for the minor
materials may be relatively small relative to the total volume of
the entire apparatus 10. This relative sizing provides the benefit
that less hysteresis in the system might occur, due to the small
volume of the inlet tubes 14I between the pump 20, and the
confluence region 12.
[0027] The apparatus 10 may comprise a plurality of supply lines
for the minor materials. Each supply line may extend from the
source of at least one major material or at least one minor
material to a respective inlet discharge 18 within the confluence
region 12.
[0028] The inlet discharge 18 may occur at the distal end of an
inlet tube 14I. Each supply line thereby defines a volume from its
respective material supply to its respective discharge within the
confluence region 12. The at least on supply for adding at least
one major material subtends a first volume extends from that
material source to the common plane where the inlet discharges 18
occur. Each supply for adding each of said minor materials subtends
a sub-volume. The sub-volumes are combined to yield a second
volume. The first volume and the second volume are summed to yield
a total volume. The second volume may comprise less than 20
percent, less than 10 percent, less than 5 percent or less than 3
percent of the total volume.
[0029] The first material may be injected into the confluence
region 12 at a first velocity. The second through Nth materials may
be injected into the confluence region 12 at a second velocity, a
third velocity, . . . up to N velocities for N minor materials. The
second through Nth velocities may be matched to, substantially the
same as, or may be slightly different than the first velocity and
each other. One or more of the minor materials may generally
correspond with or be matched in flow velocity at the time of entry
into the confluence region 12 to the velocity of the at least one
major material(s) at that same cross-section of the confluence
region 12. In one embodiment of the invention, any or all of the
second through Nth velocities of the minor materials may be within
.+-.50 percent, and may even be more closely matched to within
.+-.25 percent, and may even be more closely matched to .+-.5
percent of the first velocity of the major material(s). This
arrangement allows the minor materials to enter the flow as a
continuous stream, without dribbling, and thereby promote better
mixing. The discharge speed of the minor material into the flow
stream is determined by a combination of the discharge orifice (if
any) and the Output of the pump 20 supplying that minor material.
In a degenerate case, the first velocity may be identically matched
to any or all of the second through Nth velocities.
[0030] If desired the apparatus 10 and method including the present
invention may utilize plural confluence regions 12. The plural
confluence regions 12 may be disposed in series, in parallel, or a
combination thereof. The plural confluence regions 12 may be
identical or different in any or all of their major materials,
minor materials, proportions, flow rates, command signals, etc.
Certain plural confluence regions 12 may be used to premix minor
materials, major materials, or any combination thereof to be mixed
with other materials in later-occurring in confluence regions
12.
[0031] The container may be the final receptacle for the
combination of the major and minor materials after they are blended
together and leave the confluence region 12. The container may be
ultimately shipped and sold to the consumer, or may be used for
transport and storage of the blend of major materials and minor
materials as an intermediate.
[0032] The container may be moved into and out of the apparatus 10
under its own power, as occurs with a tanker truck container, may
be moved by the apparatus 10 itself, or by an outside motive force.
In a degenerate case, all of the minor materials are added to one
major material at the same point, thereby defining the beginning of
the confluence region 12. The end of the confluence region 12 is
defined as the common outlet 16 therefrom. In a degenerate case,
the common outlet 16 may be into atmospheric pressure conditions,
such as into a container filled with air, into a vacuum, such as an
evacuated container, or even into a pressurized container. The
blend or other combination of materials may be held above
atmospheric pressure from the confluence region 12 to the point of
discharge into the container.
[0033] The container may be of any suitable size, geometry,
configuration, number, etc. The volume of the container may range
from a few cubic centimeters to at least the size of a railroad
tanker. The container may be provided with a frangible or
resealable closure as are well known in the art, and be made of any
material suitable for containing the materials combined according
to the present invention.
[0034] The end of the confluence region 12 can also be defined as
that point at which substantial homogeneity is obtained and
additional intermixing of the materials is insubstantial. Such a
point may occur prior to discharge into a container. The length of
the confluence region 12 is defined as the distance from the
beginning of the confluence region 12 to the aforementioned common
outlet 16. The volume of the confluence region 12 is the length
multiplied by the cross-sectional area of the confluence region 12
therein. The length of the confluence region 12 may be relatively
short compared to the inlet tubes 14I and other geometries in the
system.
[0035] While a confluence region 12 of constant cross section is
shown, one will realize the invention is not so limited. The
invention may be of variable cross section, such as convergent,
divergent, barrel-shaped Venturi-shaped, etc.
[0036] As used herein, a major material is the largest single
material in the final combination and may refer to any one material
which comprises more than 33 percent, and, in another embodiment,
even more than 50 percent, and may even comprise more than 67
percent of the total composition. Equal volumes for plural major
and minor materials are contemplated herein. In contrast, a minor
material is any one material which may comprise less than or equal
to 50 percent, in another embodiment 10 percent, in another
embodiment less than 5 percent, and in still another embodiment
less than 1 percent of the total composition. The invention also
contemplates plural materials in equal and/or relatively equal
proportions and/or flow rates.
[0037] The apparatus 10 for supplying the major material may
comprise a pipe, conduit, open channel, or any other suitable
apparatus 10 through which the materials may flow. While a round
pipe is illustrated, the invention is not so limited. Any desired
cross section, constant or variable, may be utilized.
[0038] The apparatus 10 and method described and claimed herein do
not require a dynamic mix tank. As used herein, a mix tank refers
to tanks, vats, vessels and reactors and is inclusive of the batch
and continuous stir systems which use an impeller, jet mixing
nozzle, a recirculating loop, gas percolation, or similar means of
agitation to combine materials therein. It can be difficult to
quickly and accurately follow and achieve desired transient flow
rates using a dynamic mix tank. This is because flow stagnation and
interruption may occur while materials are being combined in a
dynamic mix tank. Different proportions of flow rates can occur and
prevent the desired product formulation from being achieved. If the
desired formulation is not achieved, product is wasted.
Furthermore, the residence time often necessary to achieve mixing
and axial dispersion of the materials requires energy and may be
difficult to achieve with multiple additions of minor
materials.
[0039] The apparatus 10 described and claimed herein may utilize an
inline mixer. As used herein an inline mixer refers to a mixing
device which does not impute macro-scale flow stagnation, or
prevent a continuous flow through portion of the apparatus 10
having the inline mixer from occurring. One non-limiting type of
inline mixer is, for example, an ultrasonic or cavitation type
mixer. One such system is a Sonolator homogenizing system available
from Sonic Corporation of Stratford, Conn. Another non-limiting
type of inline mixer is a static mixer as known in the art and
disclosed in U.S. Pat. No. 6,186,193 B1, issued Feb. 13, 2001 to
Phallen et al. and in commonly assigned U.S. Pat. Nos. 6,550,960
B2, issued Apr. 22, 2003 to Catalfamo et al.; 6,740,281 B2, issued
May 25, 2004 to Pinyayev et al.; 6,743,006 B2, issued Jun. 1, 2004
to Jaffer et al.; and 6,793,192 B2, issued Sep. 21, 2004 to
Verbrugge. Further, if desired, static mixers or other inline
mixers may be disposed in or with one or more of the inlet tubes
14A or upstream of the confluence region 12. Additionally, surge
tanks may be used to provide more constant flow for materials
combined by the apparatus 10 and method described and claimed
herein. Additionally or alternatively a Zanker plate may be
utilized.
[0040] The major and/or minor material(s) may comprise a fluid,
typically a liquid, although gaseous major and minor materials are
contemplated. The major and/or minor material(s) may include, but
are not limited to suspensions, emulsions, slurries, pastes, gels,
aqueous and nonaqueous materials, pure materials, blends of
materials, etc.
[0041] Optionally, at least one of the major material(s) and one or
more of the minor material(s) may comprise a solid, such as a
granular or particulate substance. Granular or particulate
materials may be added in any known fashion, including but not
limited to that disclosed in commonly assigned U.S. Pat. No.
6,712,496 B2, issued Mar. 30, 2004 to Kressin et al.
[0042] While the invention is described below in non-limiting,
exemplary terms of pumps 20 and servomotors, the invention is not
so limited and may use any motive force or similar means for
supplying the major and minor materials. A used herein motive force
refers to any force used to provide energy which, in turn, is used
to supply materials to the confluence region 12 and may include,
without limitation, electric motors, gravity feeds, manual feeds,
hydraulic feeds, pneumatic feeds, etc.
[0043] The at least one major material(s) and/or at least one minor
material(s) may be supplied from a hopper, tank, reservoir, pump
20, such as a positive displacement pump 20, or other supply or
source to the pipe, or other supply devices, as are known in the
art and provide the desired accuracy for dosing such materials. The
major material(s) and/or minor material(s) may be supplied via a
pump 20, auger feed, or any other suitable means.
[0044] The apparatus 10 for providing the major and/or minor
materials may comprise a plurality of positive displacement pumps
20. Each pump 20 may be driven by an associated motor, such as an
AC motor or a servomotor. Each servomotor may be dedicated to a
single pump 20 or optionally may drive plural pumps 20. This
arrangement eliminates the necessity of having flow control valves,
flow meters and associated flow control feedback loops as are used
in the prior art.
[0045] As used herein, a flow control valve refers to a valve
quantitatively used to allow a specific quantity or flow rate of
material to pass thereby and is used to modulate actual flow rate.
A flow control valve does not include an on-off valve which allows
the process according to the present invention to qualitatively
start or stop.
[0046] Referring to FIG. 9, an illustrative flow control feedback
loop according to the prior art is illustrated. A flow control
feedback loop compares a flow rate set point, or command signal, to
a measured flow rate. A subtraction is performed to determine an
error. The error, in turn, is used to adjust or correct the
velocity drive control. The velocity drive control is associated
with a motor operatively connected to the pump 20 from which the
actual flow rate is measured. This system has the disadvantage that
the system response may be dictated by and constrained by the
accuracy and response time of the flow meter.
[0047] Referring to FIG. 10, a nonlimiting, exemplary motor control
loop according to the present invention, is shown. Such a motor
control loop may or may not comprise at least one of a feedforward
loop and/or feedback loop, so long as the control system does not
have zero gain in the position control or velocity control if the
appropriate feedforward loops are not utilized.
[0048] If desired, the motor control loop may comprise nested
control loops. The innermost of these loops may be a torque control
feedback loop, which is shown as a single box scaling both torque
and current. A torque command is input to the torque control. The
torque control converts the torque command to an equivalent current
command, which is input to the current controller for the motor.
The current controller, in turn, provides a current feedback signal
to the current control. However a torque control may be utilized,
recognizing there it is a mathematical relationship between torque
and current, which may be determined using a scaler. The torque
control loop may be surrounded by a velocity control feedback loop,
which, in turn, may be surrounded by a position control feedback
loop. The velocity feedback control loop, the position feedback
control loop and/or a feedforward path for velocity and/or
acceleration are optional features for the present invention. The
velocity and acceleration feed forward loop may utilize respective
gains K.sub.vff and K.sub.aff, as shown.
[0049] The derivative of the motor position with respect to time
may be taken to yield motor velocity, or oppositely, the velocity
feedback may be integrated with respect to time to yield motor
position. The motor position control loop may use a motor position
command signal and compare this set point or command signal to the
motor position feedback to calculate position error. A velocity
setpoint can be derived from the position error using the position
controller.
[0050] The velocity setpoint may be compared to actual motor
velocity to also determine a velocity error. This velocity error
may be used to adjust the actual velocity of the motor, using known
techniques. The motor velocity may then be correlated to pump 20
output, as is known in the art.
[0051] Optionally, the position setpoint may have its derivative
taken with respect to time, to yield a feedforward velocity. The
feedforward velocity may be input to the velocity setpoint summer
and used in conjunction with the output of the position loop
control to generate a velocity loop command signal. The feedforward
velocity may also be used without taking into account the position
loop control signal, in order to generate the velocity loop command
signal. Optionally, the feedforward velocity may have its
derivative taken to yield a feedforward acceleration. Likewise, the
feedforward acceleration may be used in conjunction with, or
without, the output of the velocity loop controller to determine
the acceleration profile of the motor, which is proportional to the
torque command signal issued to the motor.
[0052] The setpoints of the major and minor materials may be
generated as a fraction or percentage of a master volumetric
setpoint or command signal. The master volumetric setpoint may be
defined in terms of total flow volume, flow rates, and/or time rate
of change of flow rates.
[0053] While the foregoing discussion is directed to a motor
control loop based on motor position, one of the skill will
recognize the invention is not so limited. The motor control loop
may be based on motor position, motor velocity, motor acceleration,
motor current, motor voltage, torque etc. Such a control system and
method may be used to define a master setpoint in terms of
torque/current, position, velocity, and/or acceleration, providing
there is a direct relationship between flow and
torque/current/position/velocity/acceleration, as occurs with the
present invention. The major and minor material setpoints may be
input to the individual motive force systems as a command position
and/or velocity and/or torque setpoint.
[0054] The motor position setpoint, or command signal, may be sent
to one or more servomotors. According to the present invention, all
of the major materials and minor materials may be driven in unison
through such servomotors, each of which may be coupled to one or
more pumps 20. Instead of or in addition to the pump 20/servomotor
combination, one of ordinary skill may use a variable frequency
drive to vary the voltage supplied to an AC motor-driven pump 20.
Alternatively, or additionally, pump 20 output can be changed using
various other means, as are known in the art. For example, to vary
pump 20 output for a given motor, one could use a mechanical
variable speed/adjustable speed drive, a multi-speed
transmission/gearbox, and/or a hydraulic adjustable speed
drive.
[0055] This arrangement provides the benefit that the flow rates of
some or all of the major materials and minor materials can be
ramped up or down in unison without requiring a common drive or
flow control valves, providing greater fidelity to the desired
formulation of the final blend of all materials. Thus, if one
desires to have a step change, a ramp change either up or down, or
even a start/stop in one or more flow rates, this transient can be
accommodated more quickly than according to the prior art known to
the inventors. Thus, the proportion of major and minor materials
remains within a relatively tight tolerance of the desired
formulation without unduly disrupting or unduly decreasing a flow
rate usable for production quantities.
[0056] As noted above, this arrangement provides the benefit that
it is not necessary to have a control loop directly monitoring flow
rates. Instead, the flow rates for the major and minor materials
may be determined by knowledge of the pump 20 characteristics for a
given fluid viscosity, pump 20 type, and inlet/outlet pressure
differential. Based on a desired flowrate, pump 20 compensation
algorithms may be used to achieve accurate flow rate delivery
without requiring direct flow measurement. Direct flow measurement
may introduce delays and inaccuracies during high-speed transient
response due to limitations inherent in the instrumentation, system
hysteresis, etc.
[0057] The pump 20 may be driven to its desired rotational speed
depending upon pump 20 capacity, including any motor or pump 20
slip factor to account for the pump 20 operating at less than 100
percent efficiency. If desired, the apparatus 10 and method
according to the present invention may monitor torque, position,
velocity and/or acceleration of the motor shaft.
[0058] Thus, an apparatus 10 and method according to the present
invention might not have a flow feedback loop to compensate for
variations in flow rate or even a flow meter to monitor the
addition and/or rate of addition of the individual major or minor
materials, for example, as they are added to the confluence region
12. Such a control system provides a relatively high degree of
fidelity to the desired, i.e. commanded, response.
[0059] The apparatus 10 and method claimed herein may be controlled
by a command signal as is known in the art. The command signal may
be considered to be a dynamic setpoint, and is the target rate of
material addition for each material at a given point in time. The
command signal may be sent from a computer, such as a PLC. The
signal from the PLC may be sent to a motor drive system. The PLC
and drive system may be internal or external to the system under
consideration.
[0060] If desired, each motor may have a dedicated drive
controller. The command signal(s) is/are sent from the computer to
the drive controller and then to the motor, which may be a
servomotor. Of course, one of skill will recognize that other
apparatus 10 and means for adding the materials may be utilized and
the command signal sent from the controller to such apparatus 10 or
means of material addition. Upon receipt of the command signal, the
servomotor accelerates or decelerates to the specified rotational
speed for its associated pump 20 or other apparatus 10 or means of
material addition. The rate of material addition is thereby
controlled from the command signal.
[0061] Two types of tracking error may be considered with the
present invention. Tracking error is the difference between the
value of a command signal and a process variable. The first is the
instantaneous tracking error given in volume of material
transferred per unit time. The instantaneous error measures the
difference between any process variable and the command signal at a
specific point in time.
[0062] The second tracking error one may consider the cumulative
error. The cumulative error is the sum of each instantaneous error
for each material under consideration throughout a specific period
of time and is measured in volume. The period of time under
consideration will depend upon the length of the transient.
[0063] Referring to FIGS. 3 and 4, the tracking error shown is the
difference between the command signal and a feedback process
variable. In FIG. 3, the particular feedback process variable is
the actual flowrate measured by a flowmeter for purposes of
benchmarking. However, according to the present invention, a
flowmeter is not necessary for production of material combinations,
mixtures or blends.
[0064] FIG. 3 particularly shows the performance of one system
according to the prior art. This system had a pipe with a nominal
diameter of 5.1 cm. Flow was controlled by a flow control ball
valve available from Fisher Controls, a division of Emerson of St.
Louis, Mo. The valve was controlled by an Allen-Bradley ControLogix
1756-5550 controller. The controller relayed signals to the control
valve based upon measured flow rate. Flow rate was measured by a
Micro Motion CMF100 ELITE mass flow meter with an RFT 9739
transmitter, also available from Emerson. The system used water at
a pressure of approximately 10 bar in response to a step input.
Examination of FIG. 3 shows that the system took approximately 40
seconds to reach steady state conditions.
[0065] FIG. 4 shows the ideal theoretical response to a step input
using a control valve. The command signal shows a step input. The
response is calculated according to the formula:
g(t)=1-e.sup.-t/.tau. using a one second time constant (.tau.).
Even under such favorable theoretical conditions, FIG. 4 shows that
it may take approximately four time constants, and therefore four
seconds in this example, to reach steady state conditions.
[0066] FIG. 4 also shows that for a step input, steady state
conditions according to the present invention may be reached in
less than 0.1 seconds. The system according to the present
invention in FIG. 4 utilized a command signal from an Allen Bradley
ControlLogix 1756-L61 processor communicating via a Sercos
1756-M16SE communication card to an Allen Bradley Kinetix 6000
drive system for the minor material. The minor material, a dye
solution, was supplied by a Zenith C-9000 pump available from the
Colfax Pump Group of Monroe, N.C. and driven by an Allen Bradley
MPF-B330P servomotor. The servomotor had a dedicated Sercos Rack
K6000 drive. The servo motor and the pump 20 were connected through
an Alpha Gear SP+ drive available from Alpha Gear of Alpha Gear
Drives, Inc. of Elk Grove Village, Ill.
[0067] As shown in FIGS. 3-4, in the prior art, low tracking error
and relatively constant proportions of materials were difficult to
achieve with a step change or with a sharp ramp change. This is
because not all of the valves, actuators, etc., could respond
simultaneously, in synchronization, and in the same proportion
during these rapid change conditions. However, with the present
invention and the absence of valves, particularly flow control
valves, dynamic mix tanks, the associated hysteresis, etc., greater
fidelity of response to the command signal can be achieved.
[0068] One transient which may be considered is from the start of
flow, or the start of a change in flow rate command, to the point
at which steady state operation is achieved. Such a transient is
shown in FIGS. 5-6. FIGS. 5-6 were generated with a system
according to the present invention. This system had a horizontally
disposed, 5.1 cm diameter confluence region 12 with a constant
cross section. The confluence region 12 had eight inlets 14I, each
with an inner diameter of 3 mm, disposed on a diameter of 1.5 cm as
shown in FIGS. 1-2, although only two inlets 14I were utilized for
this example.
[0069] The major material comprised a liquid soap mixture. The
first and second minor materials comprised two different dye
solutions. The major material, first minor material and second
minor material were set to the desired proportions of 98.75, 0.75,
and 0.5 percent respectively. The actual command signal issued to
the servomotor control may be adjusted in accordance with known
pump 20 compensation algorithms to account for the common pump 20
inefficiencies and irregularities.
[0070] The major material was supplied by a Waukesha UII-060 pump
available from SPX Corp. of Delavan, Wis. and driven by an Allen
Bradley MPF-B540K servomotor. Each minor material was supplied by a
Zenith C-9000 pump available from the Colfax Pump Group of Monroe,
N.C. and driven by an Allen Bradley MPF-B330P servomotor. Each
servomotor had a dedicated Sercos Rack K6000 drive and was
connected through an Alpha Gear SP+ drive available from Alpha Gear
of Alpha Gear Drives, Inc. of Elk Grove Village, Ill. The system
was controlled by an Allen Bradley ControlLogix 1756-L61 processor
communicating via a Sercos 1756-M16SE communication card to an
Allen Bradley Ultra 3000 or Allen Bradley Kinetix 6000 drive system
for the major and minor materials, respectively.
[0071] A fourteen element SMX static mixer available from Sulzer
was disposed within approximately one mm of the start of the
confluence region 12. A twelve element SMX static mixer was
disposed approximately 46 cm downstream of the first static mixer.
The materials were considered to be adequately mixed after the
second static mixer.
[0072] As shown by FIGS. 5-6 the present invention may be used with
transients having various increasing flow rates, various decreasing
flow rates, or with steady state operation at various constant
rates. The curve illustrated in FIG. 5 can be divided into three
generally distinct segments. The first segment of the curve is the
ramp-up where flow rates of each of the materials increases from
zero to a predetermined value for each material. The second portion
of the curve is the steady state flow, wherein the flow rates are
maintained relatively constant and may be usable for production
quantities. The third portion of the curve shows the ramp-down from
the steady state flow rate to a lesser flow rate. The lesser flow
rate may be zero, in the degenerate case, or it may be a flow rate
which is simply less than that shown in the other portions of the
curve. Throughout all three portions of these curves the proportion
of each material to the total of the blend of all materials in the
feed is maintained substantially constant.
[0073] In one embodiment the command signal may be for a transient
to go from a no flow or zero flow signal to a signal of 100 percent
of full scale flow in a single transient although steady state flow
rates of less than 100 percent may be utilized. The transient may
be commanded to occur in not more than 2 seconds, not more than one
second, not more than one-half second or less. During such a
transient, according the present invention, each major or minor
material, i.e. first, second third . . . nth material, may remain
within .+-.10 percent, 5 percent, 3 percent or measured full scale
flow throughout the transient. The percentage may be based on the
instantaneous error, described below.
[0074] Of course, one of ordinary skill will realize the invention
is not limited to transients with only three different flow rates.
The transition from a first steady state flow may be to a greater
or lesser steady state flow rate. Multiple transitions, both
increasing and decreasing in any combination, pattern, of equal or
unequal time periods, ramps, etc., may be utilized as desired.
[0075] According to the present invention, the at least one first
material and at least one second material occur in a generally
constant proportion, i.e., constant flow relative rates into the
confluence region 12 throughout the steady state operating period.
Likewise, the substantially constant proportion is maintained
throughout the transitional flow rate periods as well. The
substantially constant proportion is maintained both as flow rates
increase and decrease, so long as the flow rate is greater than a
near zero, nontrivial value.
[0076] While a first order, linear rate of change throughout the
transition regions is illustrated in FIGS. 5-6, the invention is
not so limited. A second order, third order, etc., rate of change
may also be utilized, so long as the substantially constant
proportion is maintained. It is only necessary that the pumps 20,
or other motive forces, be controlled in such a way that generally
constant proportionality is maintained. While constant proportion
may be more readily envisioned, and easier to execute and program
utilizing a linear rate of change, one of skill will recognize
other options are available to maintain the constant proportion
throughout the transitions.
[0077] Referring back to the systems of FIGS. 3-4 and as
illustrated by Table 1, which tabulates the data illustrated in
FIG. 4, the instantaneous error according to the prior art
decreases throughout the duration of the transient. However, this
error never reaches the relatively low value of the present
invention within the 5 second time period illustrated in Table 1.
Table 1 also illustrates the cumulative error for both the prior
art and present invention systems. TABLE-US-00001 TABLE 1 Time in
seconds from start of command signal step. Tracking Error Command
signal issued at T = 1 second. INSTANTANEOUS 0.1 sec. 0.25 sec.
0.50 sec. 1 sec. 5 sec. ERROR (volume/ sec) Prior Art 0.905 0.779
0.607 0.369 0.009 Present 0.002 0.002 0.002 0.002 0.002 Invention
CUMULATIVE 0.1 sec. 0.25 sec. 0.50 sec. 1 sec. 5 sec. ERROR
(volume) Prior Art 0.089 0.215 0.386 0.624 0.990 Present 0.006
0.006 0.006 0.007 0.015 Invention
[0078] FIG. 7 illustrates that the instantaneous error can be
approximated by the first order exponential equation:
IE=A*M*exp(-t/.tau.) [0079] Where IE is the instantaneous error in
volume per unit time, and [0080] A is the magnitude of the setpoint
change, normalized to unity for the present invention, [0081] M is
a coefficient of the amplitude which reduces the value of the
amplitude from the normalized unity setpoint magnitude to any value
from 0 to 1, or from 0.1 to 1, or from 0.2 to 1 or from 0.3 to 1 or
from 0.4 to 1 or from 0.5 to 1, as desired, [0082] t is the
instantaneous time in seconds, [0083] .tau. is the time constant in
seconds.
[0084] This approximation is particularly suitable for prior art
transients lasting up to 1 second, 2 seconds, 3 seconds, 4 seconds
and even 5 seconds. Illustrative, non-limiting combinations of the
coefficient, time constant and time period under consideration are
set forth in Table 2. TABLE-US-00002 TABLE 2 M Tau t(sec) 0.5 1.0
0-0.5*.tau. 0.5 0.75 0-1.33*.tau. 0-1*.tau. 0-0.5*.tau. 0.5 0.5
0-3*.tau. 0-2*.tau. 0-1*.tau. 0.5 0.25 0-8*.tau. 0-4*.tau.
0-2*.tau. 0.25 1.0 0-1.5*.tau. 0-1*.tau. 0.25 0.75 0-2*.tau.
0-1*.tau. 0.25 0.5 0-3*.tau. 0-1.5*.tau. 0.25 0.25 0-4*.tau.
0-2*.tau.
[0085] FIG. 7 further shows that the present invention may achieve
an instantaneous error given by the following exemplary
inequalities, although any of the combinations set forth in Table 2
or otherwise may be utilized.
[0086] IE<A*M*exp(-t/.tau.) for values of M=0.5, .tau.=1,
evaluated from time t=0 to 0.5*.tau. or more particularly
[0087] IE<A*M*exp(-t/.tau.) for values of M=0.5, .tau.=0.5,
evaluated for t from 0 to 3.0*.tau. or more particularly
[0088] IE<A*M*exp(-t/.tau.) for values of M=0.25, .tau.=1.0,
evaluated for t from 0 to 1.5*.tau..
[0089] The instantaneous error can be integrated over a desired
time period to yield a cumulative error for that period according
to the formula t 2 .times. CE = .intg. t 1 .times. IE .times.
.times. d ( t ) ##EQU1##
[0090] Where CE is the cumulative error,
[0091] t.sub.1 is the starting time and set to 0 for the degenerate
case, and
[0092] t.sub.2 is the end of the time period under
consideration.
[0093] FIG. 8 illustrates that the cumulative error according to
the prior art can be approximated by the equation
CE.sub.k=(0.5*(IE.sub.k-1+IE.sub.k)*.DELTA.T)+CE.sub.k-1
[0094] Where CE is the cumulative error in volume,
[0095] k is the index for the specific discrete time period,
[0096] .DELTA.T is the discrete time sampling and period, in
seconds, and
[0097] IE remains as previously defined.
[0098] However, one of skill will recognize that the instantaneous
error approaches zero as time continues towards steady state flow.
Since the cumulative error is dependent upon instantaneous error,
the cumulative error will not significantly increase as the
instantaneous error approaches zero. One of ordinary skill will
recognize that any combination of values set forth in Table 2 may
be utilized with the present invention, so that the invention is
not limited to the above inequalities for instantaneous error or
associated cumulative error.
[0099] If desired, one may utilize a piston pump with the present
invention. A piston pump may provide more versatility with certain
fluids which may be used in conjunction with the present invention,
and also has a pulsating output which provides repeating
fluctuations in the flow rate. If desired, one may program the
servomotor to have a negative superposition with the actual pump
output so that the fluctuations are dampened by using camming of
the motor, as is known in the art. This provides the advantage that
no dampener is necessary in the system downstream of the piston
pump. The dampener may add hysteresis or other undesirable affects
which are avoided according to the present invention.
[0100] An alternative embodiment of the invention is presented. In
this embodiment, a small portion, which may be a minority portion,
of the product stream is diverted. The diverted portion of the
product may have all of the materials of the final product as
desired. Alternatively, the diverted minority portion may be
missing one or more materials.
[0101] The diverted minority portion of the product stream may have
at least one material added using the apparatus 10 and method
disclosed herein. The minor material may be added to the diverted
stream immediately upstream of an ultrasonic horn, static mixer,
etc. This portion of the stream is then usable as an intermediate
or final product. This minority portion, having thus been
completed, is then discharged into the container for ultimate
use.
[0102] The majority portion of the stream may continue through the
process unabated, without the further addition of a minor material,
and without diversion. Alternatively, additional minor materials
may be added to the major portion of the product stream. The major
portion of the product stream is then sent to a container for
ultimate use, as disclosed above.
[0103] This arrangement provides the benefit that parallel
manufacture of a major product and a minor product may be
simultaneously accomplished. For example, the major portion of the
product may comprise a first die, perfume, additive, etc. A less
popular or less often used minor portion of the product stream may
be diverted and have a second die, perfume, or other additive
included in the final product. Alternatively, this arrangement
provides the benefit that the major portion of the product may be
produced without a particular dye, perfume, additive, etc., while a
desired dye, perfume, or other additive is included in the diverted
stream of the minority product, or vice versa. This arrangement
provides the benefit that both products may be produced in any
desired proportion without costly shutdown, cleaning, etc.
[0104] Of course, one of skill will recognize that more than a
single minority product stream may be diverted. Plural minority
streams may be diverted, each producing a relatively small quantity
of the final product with or without specific and other additives.
This arrangement provides flexibility in the manufacturing process
for producing a large or majority first quantity of a blend of
materials and one or more relatively small, even very small,
minority quantities of materials, all without shutting down and
recleaning the apparatus 10 and associated systems.
[0105] The dimensions and values disclosed herein are not to be
understood as being strictly limited to the exact numerical values
recited. Instead, unless otherwise specified, each such dimension
is intended to mean both the recited value and a functionally
equivalent range surrounding that value. For example, a dimension
disclosed as "40 mm" is intended to mean "about 40 mm."
[0106] All documents cited in the Detailed Description of the
Invention are, in relevant part, incorporated herein by reference;
the citation of any document is not to be construed as an admission
that it is prior art with respect to the present invention. To the
extent that any meaning or definition of a term in this written
document conflicts with any meaning or definition of the term in a
document incorporated by reference, the meaning or definition
assigned to the term in this written document shall govern.
[0107] While particular embodiments of the present invention have
been illustrated and described, it would be obvious to those
skilled in the art that various other changes and modifications can
be made without departing from the spirit and scope of the
invention. It is therefore intended to cover in the appended claims
all such changes and modifications that are within the scope of
this invention.
* * * * *