U.S. patent application number 13/803576 was filed with the patent office on 2014-09-18 for pump stand with improved pump control.
This patent application is currently assigned to USC, L.L.C.. The applicant listed for this patent is USC, L.L.C.. Invention is credited to Timothy A. Craft, Lynn E. Strahm, Daniel M. Tramp.
Application Number | 20140271243 13/803576 |
Document ID | / |
Family ID | 50001763 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140271243 |
Kind Code |
A1 |
Craft; Timothy A. ; et
al. |
September 18, 2014 |
PUMP STAND WITH IMPROVED PUMP CONTROL
Abstract
Integrated, stand-alone, multiple-purpose pump stands are
provided for controlled pumping of different liquids from a
stand-mounted tank to a downstream use location, e.g., a seed
treating device. The pump stands are equipped with an operating
assembly including a liquid tank, a powered pump, a liquid flow
line equipped with a flow meter from the tank and pump to the use
location, and a programmable digital control device. During
operation, the control device serves to approach and maintain the
flow rate from the pump stand at or about a desired setpoint flow
rate.
Inventors: |
Craft; Timothy A.; (Holton,
KS) ; Tramp; Daniel M.; (Sabetha, KS) ;
Strahm; Lynn E.; (Sabetha, KS) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
USC, L.L.C. |
Sabetha |
KS |
US |
|
|
Assignee: |
USC, L.L.C.
Sabetha
KS
|
Family ID: |
50001763 |
Appl. No.: |
13/803576 |
Filed: |
March 14, 2013 |
Current U.S.
Class: |
417/53 ;
417/300 |
Current CPC
Class: |
Y10T 137/0357 20150401;
A01C 1/06 20130101; Y10T 137/5409 20150401; Y10T 137/0363 20150401;
G05D 7/0676 20130101; F04D 15/0066 20130101; Y10T 137/7303
20150401 |
Class at
Publication: |
417/53 ;
417/300 |
International
Class: |
F04D 15/00 20060101
F04D015/00 |
Claims
1. (canceled)
2. (canceled)
3. (canceled)
4. (canceled)
5. (canceled)
6. (canceled)
7. (canceled)
8. (canceled)
9. (canceled)
10. (canceled)
11. (canceled)
12. An integrated pump stand operable to deliver liquid at a
controlled flow rate, comprising: a supporting frame assembly; an
operating assembly supported by the frame assembly and including--
a tank operable to hold a liquid to be delivered; a powered pump; a
flow line operably coupled with said tank and pump for delivery of
liquid from the tank; a flow meter operably attached to said flow
line to determine the flow rate of liquid through said flow line;
and a controller device operably coupled with said pump and flow
meter in order to deliver liquid from said flow line at or about a
preselected setpoint flow rate.
13. The pump stand of claim 12, said controller device being a
digital device programmed to continually monitor and adjust the
flow rate of said liquid by control of said pump, to maintain the
liquid flow rate at or about said setpoint flow rate.
14. The pump stand of claim 12, said controller device being a
digital device programmed to: (a) control the operation of said
powered pump so as to pump the liquid at a flow rate at or about
said setpoint flow rate, by periodically comparing the determined
flow rate of the liquid from said source with said setpoint flow
rate, and: (i) if the difference between the determined flow rate
and the setpoint flow rate is at or above a first predetermined
magnitude, operating said pump so as to alter the operation of the
pump at a relatively high aggressive first correction rate, so that
the determined flow rate approaches said setpoint flow rate at the
aggressive first correction rate; (ii) if the difference between
the determined flow rate and the setpoint flow rate is at or above
a second predetermined magnitude but below said first predetermined
magnitude, operating said pump so as to alter the operation of the
pump at a relatively low moderate second correction rate lower than
said first correction rate, so that the determined flow rate
approaches said setpoint flow rate at the moderate second
correction rate; and (iii) continuing said controlling step (a)(i)
and (a)(ii) throughout the flow of liquid from said liquid
source.
15. The pump stand of claim 14, said digital device also programmed
to control the operation of said powered pump such that if the
difference between the determined flow rate and the setpoint flow
rate is at or above a third predetermined magnitude but below said
second predetermined magnitude, and to operate said pump so as to
alter the operation of the pump at a relatively lower conservative
third correction rate lower than said second correction rate, so
that the determined flow rate approaches said setpoint flow rate at
the conservative third correction rate.
16. The pump stand of claim 12, including a human operator
interface operably coupled with said controller device permitting
entry of said setpoint flow rate.
17. The pump stand of claim 12, including calibration apparatus
operable to determine the actual flow rate of said liquid.
18. (canceled)
19. The pump stand of claim 12, said controller device having
memory operable to store a plurality of flow rate correction
factors for a corresponding plurality of different liquids.
20. The pump stand of claim 12, said controller device being
programmable and operable to apply a feedback control loop
according to a tiered control scheme.
21. The pump stand of claim 20, said controller programmed to
employ a multi-tiered proportional-integral-derivative (PID)
control loop.
22. (canceled)
23. The pump stand of claim 12, said tank operable to hold a seed
coating liquid.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention is broadly concerned with improved,
stand-alone pump stands for controlling the flow rate of a liquid
from a liquid source. More particularly, the invention is concerned
with such pump stands, and corresponding methods, wherein the flow
rate of liquid is rapidly approached and maintained at or about a
preselected setpoint flow rate.
[0003] 2. Description of the Prior Art
[0004] In many agricultural applications, seeds are coated with
various liquid chemicals prior to planting. Such liquids may
include pesticides, growth stimulants, or plant nutrients, and
these liquids have a variety of different physical characteristics
such as viscosities and drying rates. Seed treaters have been
developed for coating large volumes of seed on an industrial basis.
Generally, such treaters include a seed inlet, a sprayer or other
device for applying coating liquids to the surfaces of the seeds,
and some sort of rotating drum or the like to assure uniform seed
coating. As such, it is necessary to deliver the treating liquids
to the application device at a uniform flow rate. That is to say,
if the liquids are delivered at variable flow rates, then the seeds
will be differentially coated, depending upon the instant at which
the seeds were treated with the liquid.
[0005] There are two basic types of pumping systems for handling
and pumping of seed treating liquids delivered to downstream seed
treaters. Most often, these systems are mounted on a stand or other
support structure separate from the seed treaters. These systems
include mix tank(s), pump(s), tubing system(s), and various types
of monitoring and control equipment.
[0006] The first type is a "manual" system that uses a controller
of some type to drive the pump motor(s) based upon a proportional
signal. For example, the pump motor(s) can be operated at 50% of
the maximum speeds thereof. If the operator needs to adjust the
liquid flow rate exiting the pump, the flow rate must be manually
adjusted using the controller. In these types of systems, the flow
rate is typically determined either by an in-line flow meter, or a
"catch and time" technique wherein the volume of liquid delivered
over a selected period of time is measured, and the flow rate is
thus determined. Some of these manual systems also have the ability
to read a signal from a downstream seed treater to either turn on
the pump(s), or to terminate the operation thereof. However, none
have the ability to automatically adjust liquid flow rate over
time. Furthermore, these systems do not have any means of
automatically reporting the volume of liquids pumped, so the
operator must either use a flow meter totalizer or some sort of
mass balancing to calculate the total chemical usage for a given
time period.
[0007] The second type of system is an automated or automatic
system, and is generally plug-connected to a PLC-based controller
that performs all of the logical steps for pumping operations. In
these systems, an operator may set a desired flow rate, and the
pump speed will automatically adjust to meet that desired flow
rate, based upon information received by the PLC from a connected
flow meter. This is generally done via a PI (proportion-integral)
or PID (proportion-integral-derivative) software control loop.
These systems also have automatic reporting capabilities that show
total chemical usage.
[0008] In many instances, upgrades are available for the manual and
automatic systems, which allow adjustment of the liquid flow rate
during operation. These upgrades allow an operator to offset via a
multiplier any consistent inaccuracies that the flow meter may
display. Such inaccuracies occur quite often with the use of
standard volumetric/electromagnetic flow meters normally employed.
All of the known manual system upgrades provide only a display
device, and do not provide any control function. Moreover, they
have only one adjustable offset or multiplier per flow meter.
[0009] As such, there are presently no "stand-alone" liquid pump
stands which allow the operator to choose a desired setpoint flow
rate, with the on-board controllers serving to automatically
maintain the set point flow rate via adjustment of pump speeds.
Moreover, none of the known "automatic" pump stands makes use of
multiple PI or PID control loops to accomplish fast pump speed
changes and steady pump speed control. Additionally, all adjustable
flow rate displays for "stand-alone" pump stands have only one
available adjustment for each flow meter. This means that if an
operator wishes to run a different liquid through the same flow
meter, then the operator must recalibrate the display of the flow
meter, without the capacity to retain previously used calibration
settings.
SUMMARY OF THE INVENTION
[0010] The present invention overcomes the problems outlined above
and provides a movable stand-alone pump stand, which can be used to
good effect with seed treater(s) so as to properly coat
agricultural seeds with specified and essentially identical amounts
of liquid chemicals. The pump stands of the invention generally
include a supporting frame assembly (preferably of generally
L-shaped design), which supports a complete operating assembly.
That is to say, the operating assembly includes a liquid chemical
tank, a powered pump, a flow line coupled with the tank and pump
for delivery of liquid from the tank to a downstream seed treater,
a flow meter operably attached to the flow line to determine the
flow rate of liquid through the flow line during operation, and a
programmable digital device operably coupled with the pump and flow
meter in order to deliver liquid from the flow line at or about a
preselected setpoint flow rate. The modular, stand-alone design of
the pump stands greatly facilitates seed coating operations, and
allows an operator to easily control all steps associated with such
coating practices.
[0011] The digital device controller can be used to control the
various pump stand operations described previously. However, from
an operational standpoint, the ability to quickly approach and
maintain a setpoint flow rate of liquids is of prime importance. As
used herein, "at or about a setpoint flow rate" refers to the
ability of the pump stands of the invention to maintain a
preselected setpoint flow rate over time, with a relatively small
plus or minus variance from the exact set point flow rate, e.g.,
plus or minus about 1-10%. It will be appreciated that the "plus or
minus" variance is largely determined by the program variables
described herein.
[0012] Thus, the invention further includes a method for
controlling the flow rate of a liquid from a liquid source, which
is applicable to fluids in general, but which is especially
designed for seed-coating operations. The method broadly comprises
the steps of:
[0013] (a) establishing a desired setpoint flow rate for the liquid
from the source;
[0014] (b) pumping the liquid from the source using a powered pump,
and determining the flow rate of the pumped liquid from the
pump;
[0015] (c) controlling the operation of the powered pump to pump
the liquid at a flow rate at or about the setpoint flow rate, by
periodically comparing the determined flow rate of the liquid from
the source with the setpoint flow rate, and: [0016] (i) if the
difference between the determined flow rate and the setpoint flow
rate is at or above a first predetermined magnitude, operating the
pump so as to alter the operation of the pump at a relatively high
aggressive first correction rate, so that the determined flow rate
approaches the setpoint flow rate at the aggressive first
correction rate; [0017] (ii) if the difference between the
determined flow rate and the setpoint flow rate is at or above a
second predetermined magnitude but below the first predetermined
magnitude, operating the pump so as to alter the operation of the
pump at a relatively low moderate second correction rate lower than
the first correction rate, so that the determined flow rate
approaches the setpoint flow rate at the moderate second correction
rate; and [0018] (iii) continuing the controlling steps (c)(i) and
(c)(ii) throughout the flow of liquid from the liquid source.
[0019] In preferred forms, the method includes a further step if
the difference between the determined flow rate and the setpoint
flow rate is at or above a third predetermined magnitude but below
the second predetermined magnitude, operating the pump so as to
alter the operation of the pump at a relatively lower conservative
third correction rate lower than the second correction rate, so
that the determined flow rate approaches the setpoint flow rate at
the conservative third correction rate.
[0020] As noted previously, these method steps are carried out
using a programmable digital device. The digital device may be
user-operated where an operator inputs the setpoint flow rate and
mode of operation, or such information may be electronically
communicated to the digital device. During operation, the flow
meter may be calibrated to ensure that the determined flow rate
reported by the meter is the actual flow rate of the liquid. Such
calibration may be carried out by measuring the flow of liquid
through the flow meter for a selected period of time to give an
actual flow rate for the liquid, comparing the measured flow rate
with the flow rate reported by the flow meter, determining a
correction factor unique to the flow meter and liquid, and storing
the correction factor in electronic memory. A useful feature of the
present invention is that the pump stand is equipped with
electronic memory so that a plurality of correction factors may be
stored for a corresponding plurality of different liquids. Hence,
once the flow meter is calibrated and stored for a particular
liquid, that calibration information can be retrieved when the
corresponding liquid is again used with the pump stand.
[0021] In order to rapidly approach and maintain the flow rate of
liquid from the pump stand at or about the setpoint flow rate, the
digital control device is preferably programmed to apply a feedback
control loop according to a tiered control scheme in order to carry
out the steps (c)(i) through (c)(iii) described above. To this end,
a multi-tiered proportional-integral-derivative (PID) control loop,
or a multi-tiered proportional-integral (PI) control loop, is
employed carry out these steps.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a front perspective view of a pump stand in
accordance with the invention;
[0023] FIG. 2 is a rear perspective view of the pump stand depicted
in FIG. 1; and
[0024] FIG. 3 is a schematic flow diagram illustrating the
preferred digital processor control of the pump stand.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Pump Stand
[0025] Turning now to FIGS. 1-2, a pump stand 10 is illustrated.
The stand 10 broadly includes a supporting frame assembly 12, a
tank assembly 14, a first valve and conduit assembly 16, a pump and
conduit assembly 18, a second valve and conduit assembly 20 with an
in-line flow meter 22, a calibration tube 24, and control assembly
26. The pump stand 10 is designed to hold liquid chemical(s),
typically used for seed coating, and to deliver calibrated amounts
of the chemical(s) to a seed treater or the like. The pump stand 10
is completely self-contained, and has a number of features greatly
facilitating accurate dispensing of chemical(s).
[0026] In more detail, the frame assembly 12 includes a box-like,
quadrate base 28 presenting an uppermost mounting plate 30 and
having a pair of upstanding, opposed frame arms 32 and 34 secured
to the rear end of base 28. An equipment mount plate 36 extends
between the arms 32, 34, and an uppermost rigidifying cross-brace
38 interconnects the arms 32, 34 at their uppermost ends. A
generally U-shaped bumper 40 is secured to the arms 32, 34 and
extends rearwardly therefrom.
[0027] The tank assembly 14 includes a triangular tank base 42
comprising three upstanding legs 44 secured to the mounting plate
30 with a generally triangular, intermediate apertured support
plate 46 secured to the legs 44 above mounting plate 30. The upper
end of the base 42 includes the generally circular hoop 48 likewise
supported by the legs 44 adjacent the upper ends thereof. The base
42 is designed to support a conical-bottom liquid tank 50 including
a generally circular upper wall 52 and a substantially
frustoconical lower wall 54 having a lowermost liquid outlet 56. An
upper tank cover 58 is positioned atop the circular wall 52 in
order to close the tank 50 and to allow filling thereof through the
ports 60. The cover 58 also supports an agitator drive motor 62
with an associated gear box 64. A central agitator shaft (not
shown) is operably coupled with gear box 64 and extends into the
confines of tank 50. The agitator shaft has conventional mixing
elements so that the chemical(s) within tank 50 may be agitated to
ensure proper mixing thereof.
[0028] The first valve and conduit assembly 16 includes a delivery
pipe 66 operably coupled with tank outlet 56 and equipped with a
diverter valve 68. The output end of pipe 66 is equipped with a tee
70. A drain conduit 72 is secured to one end of the tee 70, whereas
a liquid delivery conduit 74 is secured to the opposite end of tee
70. The drain conduit 72 is also equipped with a two-way diverter
valve 76. The assembly 16 also includes a two-way diverter valve 78
supported on a forwardly extending plate 80. The delivery conduit
74 is secured to the input of valve 78. A pair of output conduits
82 and 84 are also coupled with valve 78. Output conduit 82 extends
to and is coupled with calibration tube 24, whereas output conduit
84 extends to and is connected with a liquid filter 86 secured to
the rear face of mounting plate 36.
[0029] The pump and conduit assembly 18 includes a lower manifold
block 88 secured to the rear face of equipment mounting plate 36,
an intermediate pumping assembly 90, and an upper manifold block
92. The filter 86 is coupled to lower manifold block 88 for
delivery of filtered chemicals to a pair of outputs 96, each
equipped with a short conduit 98. The intermediate pumping assembly
90 includes an electrical drive motor 100 and a pair of pumping
heads 102 and 104. The output of the head 104 is delivered through
short conduits 106 to upper manifold block 92, which delivers the
pumped liquid through output pipe 108 equipped with an upstanding
turbulence-minimizing pipe 110.
[0030] The second valve and conduit assembly 20 includes a liquid
conduit 112 coupled with the end of pipe 108 and equipped with the
in-line flow meter 22, and a dual valve assembly 114 mounted on an
upstanding plate 116 and having upper and lower valves 118 and 120.
The upper end of conduit 112 is coupled with the lower valve 120,
and the outputs thereof are respectively coupled with a coiled
liquid delivery line 122, which is coupled to a downstream seed
treater or other device, and to the input of upper valve 118. The
outputs of valve 18 are respectively coupled with a recirculation
conduit 124 leading to tank 50, and a calibration tube conduit
126.
[0031] The calibration tube is in the form of an elongated upright
tube 127 equipped with upper and lower end caps 128 and 130, and a
volumetric scale (not shown) imprinted on the body of the tube 127.
As illustrated, the conduit 126 is secured to the upper end cap
128, whereas output conduit 82 is secured to lower end cap 130.
[0032] The control assembly 26 includes a conventional electrical
junction box 132 and a controller 134 equipped with a touch pad
output 136. The sequential operation of the pump stand 10 is
governed and controlled by the controller 134, and this operation
will be described in detail in connection with FIG. 3.
[0033] In alternative forms of the pump stand 10, a weigh scale
(not shown) may be used in lieu of mounting plate 30 in order to
provide continuous monitoring of the weight of chemical(s) within
the tank.
Operation of the Pump Stand
[0034] There are four basic modes of operation for the pump stand
10, namely initial recirculation of liquid, pump calibration,
normal calibrated delivery of liquids to the downstream seed
treater or other device, and a reverse or flush operation.
[0035] The recirculation mode would typically be used during
startup of the pump stand in order to ensure that the liquid
chemicals within the tank 50 are uniformly mixed. In order to
recirculate, the agitation drive motor is operated to mix the
chemicals within tank 50. Also, the valve 68 is open to prevent
delivery of liquid through outlet 56 and pipe 66, the valve 76 is
closed, and the valve 78 is opened to deliver liquid through filter
86, lower manifold block 88, and pumping heads 102, 104. The lower
valve 120 is set to deliver the pumped liquid to upper valve 188,
which is set to deliver through recirculation conduit 124, back to
tank 50. It will thus be seen that operation of the pump assembly
90 draws liquid front the tank 50 and ultimately recirculates this
fluid back to the tank.
[0036] After adequate circulation is achieved, the stand 10 may be
used if needed to calibrate the flow rate of the pumping assembly
90 in order to deliver consistent volumes of liquid per unit time
through the delivery line 122. Specifically, in this mode of
operation, the upper valve 118 is positioned so as to deliver
liquid through the calibration tube conduit 126. This continues for
a predetermined period of time (e.g., one minute), and the amount
of liquid collected with calibration tube 24 is determined using
the volumetric scale markings on tube 127. If the target output of
the pumping assembly 90 is 50 ounces/minute, this can be determined
using the collected amount of liquid. If the flow rate is either
too high or too low relative to the desired output rate, the
controller 134 can be operated to compensate for the difference. In
this operation, the touch screen is tapped until a calibration
screen appears, whereupon the underage or overage flow rate is
adjusted to the target rate. The controller 134 thus provides a
signal u(t) to the pumping assembly 90 to speed up or slow down, as
the case may be, so as to deliver a consistent flow rate output to
the downstream seed treater or the like. The controller 134 is also
provided with continuous flow rate data owing to the presence of
the in-line flow meter 22. Once calibration is achieved, the valve
78 is manipulated so that the pumping assembly 90 removes the
liquid from the calibration tube 24, which is diverted through the
pumping assembly 90, as described previously.
[0037] After optional calibration, the pump stand 10 is typically
used in a normal delivery mode. This requires only that the valve
78 be manipulated after emptying of the calibration tube 24 so that
the pumping assembly 90 draws liquid from the tank 50, and
manipulation of lower valve 120 so that the pumped liquid is
directed to the delivery line 122 for downstream use.
[0038] At the end of a given run, it may be necessary to change the
liquid chemical(s) within tank 50 in order to deliver different
chemical(s) for a subsequent run. In such a case, the valve 76 is
opened to deliver liquid to the drain conduit 72, and the pump
drive motor 100 is reversed. This serves to remove all liquids
within the pump assembly and other conduits, while the material
remaining in tank 50 is allowed to flow by gravitation through the
conduit 72.
[0039] Before a fresh batch of liquid chemical(s) is delivered to
tank 50, it may be desirable to flush the entire system. Water or
other cleaning fluids are directed to tank 50, whereupon the pump
stand 10 is operated in recirculation mode, as described above,
followed by a second flush operation. The tank 50 can then be
refilled with the necessary liquid chemical(s) for the subsequent
run.
Automated Control of Pump Stand
[0040] As mentioned above, the controller 134 governs operation of
the pump stand 10. The controller 134 is preferably a digital
integrated circuit and may be a general use, commercial
off-the-shelf computer processor, a programmable logic device
configured for operation with the pump stand 10, or an application
specific integrated circuit (ASIC) especially manufactured for use
with the pump stand 10. The controller 134 may include two or more
separate integrated circuits cooperating to control operation of
the pump stand 10, and may include one or more analog elements
operating in concert with or in addition to the digital circuit or
circuits. The controller 134 may include or communicate with a
memory element configured to store data, instructions, or both for
use by the controller 134. The controller 134 is also referred to
herein a programmable logic controller or PLC.
[0041] An exemplary sequence of control steps performed by the
controller 134 is illustrated in the flow diagram of FIG. 3.
Operation of the controller 134 may begin manually in response to a
user input or automatically in response to a start signal received
from an external device such as a seed treater. A user may manually
launch a treatment application process by engaging a button or
other user interface element designated for that purpose, as
depicted in block 200, or may place the controller 134 in automatic
start mode, as depicted in block 202. When the controller 134 is in
the automatic start mode it automatically launches the process upon
receiving the start signal, as indicated in block 204.
[0042] Whether the controller 134 begins the process in response to
a manual input from a user or in response to a start signal, it
first determines a mode of operation, as depicted in block 206. The
controller 134 may determine the mode of operation by, for example,
prompting the user to select the mode or by retrieving a
previously-stored setting indicating the mode of operation. If a
pump percentage mode is selected, as depicted in block 208, the
controller 134 prompts the user to enter a desired percentage, as
depicted in block 210, corresponding to a percentage of the maximum
output or speed of the motor. The controller 134 then communicates
the control signal u(t) to the pump motor to cause the pump motor
to operate at the desired percentage, as depicted in block 212,
until the user stops the motor. The pump percentage mode may be
used, for example, during initial recirculation, while the target
rate mode may be used during pump calibration and normal calibrated
delivery.
[0043] If the controller 134 operates in the target rate mode 214
the controller 134 determines a flow rate setpoint, as depicted in
block 216. The flow rate setpoint is the desired or target
application flow rate. The controller 134 may prompt the user to
submit the setpoint, for example, or may retrieve it from memory or
receive it from an external device. The flow rate setpoint may
change during operation, as explained below.
[0044] When the controller 134 has determined the flow rate
setpoint, it then controls the pump motor to apply treatment as
closely as possible to the setpoint. More specifically, the
controller 134 determines a flow rate error e(t) corresponding to a
difference between the actual flow rate (as indicated by the
in-line flow meter 22) and the setpoint and uses a feedback control
loop function to modify the actual flow rate to minimize the error.
The value of e(t) may be expressed in various ways, including as a
raw difference or as a percentage of the setpoint. The controller
134 applies a feedback control loop to control the pump motor
according to a tiered control scheme wherein a more aggressive
(faster) response is applied to greater values of e(t) and a more
conservative (slower and more stable) response is applied to
smaller values of e(t). More particularly, the controller 134 uses
a multi-tiered proportional-integral-derivative ("PID") or
proportional-integral ("PI") control loop to manipulate process
control inputs (e.g., a motor control signal) to minimize e(t). In
some embodiments, the controller 134 generates a pump motor control
signal according to the following control equation:
u ( t ) = K p [ e ( t ) + 1 T n .intg. 0 t e ( .tau. ) ( .tau. ) +
T v t e ( t ) ] + U Offset ##EQU00001##
wherein-- [0045] u(t) is the pump motor control signal; [0046] e(t)
is the error function defined above; [0047] K.sub.P is a
proportional coefficient; [0048] T.sub.n is an integral
coefficient; [0049] T.sub.v is a derivative coefficient; and [0050]
U.sub.Offset is an offset variable for the motor control
signal.
[0051] The controller 134 is configured to manipulate the values of
K.sub.p, T.sub.n and T.sub.v to shift the PID control function
between a more aggressive response and a more conservative
response. Generally, increasing the value of K.sub.p increases the
aggressiveness of the control loop while increasing the value of
T.sub.n decreases the aggressiveness of the control loop. The
values of K.sub.p and T.sub.n will depend on other,
implementation-specific variables such as the number of pump heads
associated with the pump motor. The value of U.sub.Offset may be
specific to particular application chemicals and/or particular
application processes.
[0052] In one preferred embodiment, the variable T.sub.v is set to
zero to entirely eliminate the derivative term from the equation
such that the controller 134 implements a PI control function.
Alternatively, the value of T.sub.v may be set to a very low number
to minimize the influence of the derivative term on the output. By
way of example, for aggressive operation, the value of K.sub.p may
be within the range of from about 0.8 to about 0.5, for moderate
operation may be within the range of from about 0.05 to about 0.2,
and for conservative operation may be within the range of from
about 0.02 to about 0.5. For aggressive operation, the value of
T.sub.n may be within the range of from about 1.0 to about 4.0, for
moderate operation may be within the range of from about 2.0 to
about 5.0, and for conservative operation may be within the range
of from about 4.0 to about 6.0. Table 1 illustrates exemplary
values of K.sub.p and T.sub.n for aggressive, moderate and
conservative loops when the pump motor is driving one pump head,
two pump heads and three pump heads.
TABLE-US-00001 TABLE 1 1 Pump Head 2 Pump Heads 3 Pump Heads
Aggressive Loop K.sub.p = 0.2 K.sub.p = 0.15 K.sub.p = 0.1 T.sub.n
= 2.0 T.sub.n = 2.5 T.sub.n = 3.0 Moderate Loop K.sub.p = 0.1
K.sub.p = 0.085 K.sub.p = 0.075 T.sub.n = 3.0 T.sub.n = 3.5 T.sub.n
= 4.0 Conservative Loop K.sub.p = 0.01 K.sub.p = 0.01 K.sub.p =
0.01 T.sub.n = 5.0 T.sub.n = 5.0 T.sub.n = 5.0
[0053] Returning again to FIG. 3, the controller 134 begins
operation by entering the aggressive control loop and communicating
the control signal u(t) to the pump motor, as depicted in block
218. The controller 134 periodically compares the actual flow rate
with the setpoint to determine if e(t) has fallen below an
aggressive threshold, as depicted in block 220. The aggressive
threshold may be, for example, between about 20% and about 40%, and
may particularly be about 25%, about 30% or about 35%. If the
actual flow rate has fallen below the aggressive threshold, the
controller 134 shifts to the moderate control loop and continues
communicating the control signal u(t) to the pump motor, as
depicted in block 222. The controller 134 periodically compares the
actual flow rate with the setpoint to determine if e(t) has fallen
below a moderate threshold, as depicted in block 224. The moderate
threshold may be, for example, between about 10% and about 20%, and
may particularly be about 12%, about 15% or about 18%. If e(t) has
fallen below the moderate threshold, the controller 134 shifts to
the conservative control loop and continues communicating the
control signal u(t) to the pump motor, as depicted in block 226. If
e(t) has not fallen below the moderate threshold, the controller
134 returns to block 220 to determine if e(t) is below the
aggressive threshold.
[0054] When the controller 134 is operating in the conservative
control loop, it remains in the conservative control loop until the
user presses a stop button, until the setpoint changes as depicted
in block 228, or until e(t) exceeds the moderate threshold. If the
setpoint changes the controller 134 shifts back into the aggressive
control loop to bring the actual flow rate near the setpoint as
quickly as possible, then shifts back into the moderate and
conservative control loops as e(t) decreases, as explained
above.
[0055] The user may initiate the reverse or flush operation set
forth above by engaging a button or other user interface element
designated for that purpose, as depicted in block 230, wherein the
controller 134 drives the pump motor in reverse, as depicted in
block 232. The controller 134 continues driving the pump motor in
reverse until the user presses a stop button.
[0056] The controller 134 may store operational parameters
associated with particular chemical mixtures and/or particular
processes so that when a user reinitiates a process that was
previously run the controller 134 recalls the parameters associated
with that process, thus relieving the user of the burden of
recalibrating the pump stand 10 each time a process is run. Using
the touch pad 136, for example, the user may calibrate the pump
stand 10 for use with a first chemical mixture. First calibration
information specific to the first chemical mixture is created and
used, for example, to adjust the output of the flow meter 22. The
controller 134 stores the first calibration information in the
memory. When the pump stand 10 is subsequently used with a
different process that involves a second chemical mixture the user
calibrates the pump stand 10 for the second mixture. The controller
134 associates second calibration information with the second
mixture and stores the second calibration information in memory.
This process may be repeated for multiple chemical mixtures,
wherein the controller 134 stores separate calibration information
for each of the chemical mixtures.
[0057] Thereafter, each time the user desires to use the first
chemical mixture he or she simply selects the first mixture via the
touch pad 136 wherein the controller 134 retrieves the first
calibration information from memory. In this manner, the controller
134 may retrieve and use operational parameters associated with any
of the previously used chemical mixtures. While the discussion
above has focused on the use of calibration information used to
adjust the output of the flow meter 22, the operational parameters
stored in memory and retrieved by the controller 134 may also be
associated with any of the variables K.sub.p, T.sub.n, T.sub.v,
U.sub.Offset.
* * * * *