U.S. patent application number 15/590860 was filed with the patent office on 2018-10-25 for zero pulsation pump.
The applicant listed for this patent is Wanner Engineering, Inc.. Invention is credited to Richard HEMBREE.
Application Number | 20180306179 15/590860 |
Document ID | / |
Family ID | 63853713 |
Filed Date | 2018-10-25 |
United States Patent
Application |
20180306179 |
Kind Code |
A1 |
HEMBREE; Richard |
October 25, 2018 |
ZERO PULSATION PUMP
Abstract
A positive displacement pump includes at least two pumping
chambers and associated plungers. Each plunger is driven by an
associated variable speed motor, such as a stepper motor, in a
reciprocating motion. The stepper motor varies speed during each
stroke of the plunger. A controller controls speed and direction of
each stepper motor. Each stepper motor is coupled to a leadscrew
having an associated guide rod mounted on the leadscrew to move
along the leadscrew as the leadscrew rotates and actuate an
associated plunger. The controller varies the speed, displacement
and duration of the stepper motors' steps to maintain a constant
outflow without pulses.
Inventors: |
HEMBREE; Richard; (Port
Coquitlam, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Wanner Engineering, Inc. |
Minneapolis |
MN |
US |
|
|
Family ID: |
63853713 |
Appl. No.: |
15/590860 |
Filed: |
May 9, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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62489244 |
Apr 24, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04B 49/12 20130101;
F04B 2203/0214 20130101; F04B 17/04 20130101; F04B 23/06 20130101;
F04B 53/14 20130101; F04B 35/04 20130101; F04B 27/005 20130101;
F04B 11/0058 20130101; F04B 49/065 20130101; F04B 49/20
20130101 |
International
Class: |
F04B 49/20 20060101
F04B049/20; F04B 27/00 20060101 F04B027/00; F04B 35/04 20060101
F04B035/04; F04B 49/06 20060101 F04B049/06; F04B 53/14 20060101
F04B053/14 |
Claims
1. A positive displacement pump, comprising: a plurality of pumping
chambers; a plunger associated with each pumping chamber, each of
the plungers moving in a reciprocating motion; a variable speed
motor driving each plunger, the variable speed motor varying speed
during each stroke; and a controller controlling speed and
direction of each variable speed motor.
2. The pump according to claim 1, the variable speed motor being
coupled to a leadscrew having a guide rod threadably mounted on the
leadscrew to move along the leadscrew as the leadscrew rotates.
3. The pump according to claim 2, wherein the guide rod is
connected to the plunger.
4. The pump according to claim 3, further comprising a position
sensor in communication with the controller.
5. The pump according to claim 1, wherein the variable speed motor
comprises a stepper motor.
6. The pump according to claim 5, wherein the stepper motors have
variable rotation in one direction for a pressure stroke and in an
opposite direction for the suction stroke and the controller is
adapted to change speeds of each motor during the stroke so that
the combined output of the plungers produce a constant flow.
7. The pump according to claim 1, wherein the pump comprises two
plungers, wherein a speed profile for a pressure stroke includes a
pressure ramp portion at a beginning of the stroke and at an end of
the stroke, wherein pressure builds up to a discharge pressure at a
start of the stroke and decays at an end of the stroke, but no flow
exits a first one of the plungers, and wherein the other one of the
plungers produces full flow during periods of pressure ramping.
8. The pump according to claim 1, further comprising a pressure
input.
9. The pump according to claim 1, further comprising a load
input.
10. The pump according to claim 1, further comprising a pressure
input or a load input.
11. The pump according to claim 1, further comprising a pressure
input and a load input.
12. The pump according to claim 1, wherein the controller is
adapted to slow the motor to slow rotation speed of the leadscrew
as the plunger nears top dead center and stops at top dead center
first direction.
13. The pump according to claim 1, wherein the controller is
adapted to slow the motor to slow rotation speed of the leadscrew
as the plunger nears bottom dead center and stops at bottom dead
center second direction.
14. The pump according to claim 1, wherein the pump comprises three
plungers and wherein the guide rods have 1/3 of cycle different
from each other.
15. The pump according to claim 1, wherein the variable speed motor
comprises a servo motor.
16. A method for controlling a pump, the pump having a first
pumping chambers and an associated first plunger, and a second
pumping chamber and an associated second plunger, each plunger
being driven by an associated variable speed motor, and a
controller; the method comprising: controllably driving a first
variable speed motor to vary displacement and speed of the
associated first plunger; controllably driving a second variable
speed motor to vary displacement and speed of the associated second
plunger; the speed of displacement of each variable speed motor
being varied as the plungers approach top dead center and bottom
dead center and coordinated so that pump outflow is substantially
constant.
17. The method according to claim 16, wherein determines flow by a
controller with the formula: dV=P*V/K where: K and V are constants
stored in the microcontroller for the pump. P=the output pressure
and can be entered by the operator or input from a transducer.
K=the combined bulk modulus of the system which includes the fluids
and components that deflect during the pressure stroke. V=pumping
chamber volume dV=the change in volume due to compression of the
fluids and expansion of the pumping chamber.
18. The method according to claim 16, wherein the variable speed
motors comprise stepper motors.
Description
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention is directed to a pump producing a
constant outflow and avoiding pulses in the output flow.
Description of the Prior Art
[0002] Conventional positive displacement pumps use pistons or
plungers to displace fluid. However, the reciprocating motion
produces pulses or surges in the output flow. It can be appreciated
that single cylinder pumps generally produce the greatest pulsation
as the one cylinder alternates from suction to discharge. To
overcome this problem, more cylinders may be added that utilize an
overlapping output that is timed to greatly decrease the
pulsations. However, even with multiple cylinders, such as
Quintuplex pumps, there are still small pulses.
[0003] Attempts have been made to reduce the pulsations by
modifying the stroke of the plungers to reduce the pulsation. Such
a pump is shown for example in U.S. Pat. No. 5,145,339 to Lehrke,
which is directed to a two cylinder pump using cams to produce a
pulseless output. Although the pump design in the Lehrke patent
does reduce the pulsation, Lehrke's use of cams with complex cam
shapes and related mechanisms are relatively complex and expensive.
The design also has a fixed stroke profile that can't be varied
with pumping conditions that affect the output per stroke, such as
the compressibility of fluid. A design utilizing cams does not
provide flexibility to alter the stroke profile while the pump is
running. For high pressure metering applications, the displacement
is small compared to the system bulk modulus and a portion of the
stroke is needed to build pressure in the pumping chamber before
any fluid leaves the discharge valve. With such a design, the cam
profile for such an application would only be effective at one
pressure. Different cams with different profiles would be required
to be effective at different pressures.
[0004] It can therefore be seen that a simple and inexpensive
positive displacement pump is needed that substantially eliminates
pulses in the output flow. Such a pump should be simple and operate
with a minimum number of pumping chambers and plungers to minimize
cost. Moreover, such a pump should be effective even with two
pumping chambers. It should also be possible to change the stroke
profile and to change the profile while the pump is running. Such a
pump should also be able to adapt to different operating conditions
including different pressures. The present invention addresses
these problems as well as others associated with eliminating pulses
from positive displacement pumps.
SUMMARY OF THE INVENTION
[0005] The present invention is directed to a pulseless positive
displacement reciprocating pump, such as a piston type pump or a
diaphragm pump. In place of a conventional cylinder and piston
arrangement, the pump preferably has two or more guide bores with
associated guide rods reciprocating back and forth within the bore.
The guide rod threadably connects to a lead screw, such as a
recirculating ball type lead screw. An associated variable speed
motor, such as a stepper motor or a servo motor, actuates each lead
screw in both directions. The lead screw includes threads that mate
with complementary threads of the guide rod so that as the lead
screw rotates, the guide rod is moved axially along the lead screw
to extend and retract the plunger into and out of the pumping
chamber. The stepper motors can be precisely rotated in miniscule
discrete stepped movements and are able to precisely control
rotation of the lead screw and therefore the axial position of the
guide rod to closely control the position of the plunger and its
movements into and out of the pumping chamber.
[0006] In operation, to start the pump, with the plunger at bottom
dead center, the controller would actuate a first one of the
stepper motors to rotate a respective leadscrew in a first
direction, which causes the guide rod to travel axially. The
controller would communicate to the first stepper motor to increase
the rotation speed up to the maximum that produces the full output
of the guide rod and guide bore. For most of the stroke, the
stepper motor rotates at a constant speed. However, as the plunger
nears top dead center, the stepper motor is slowed by the
controller until the plunger stops at top dead center. The stepper
motor would then start turning in the opposite direction and
increasing to a maximum speed and then decreasing again near bottom
dead center until coming to a stop at bottom dead center.
[0007] In a two pumping chamber pump, duration of the pressure
stroke is slightly longer than the suction stroke so that the ramp
up portion and ramp down portion of the two plunger strokes
overlap. This overlap produces the continuous combined flow at the
pump discharge. As the plunger proceeds forward from bottom dead
center, there is a portion of the stroke that is compressing the
fluid and expanding the pressure containing components. During this
period of the stroke, no flow exits the pumping chamber while the
other guide rod and plunger assembly is still producing full flow.
The controller can determine the number of steps that the stepper
motor must move before beginning to slow the other guide rod and
associated plunger. It can be appreciated that operation of a
diaphragm pump would be substantially the same as for a piston type
pump, but acting through a diaphragm.
[0008] For a pump with three pumping chambers, the pump stroke
cycle can be timed with the overlap similar to a shaft driven pump
where the strokes have a phase difference 120 degrees apart or 1/3
of a pump cycle apart. Therefore, there is overlap timing on both
the pressure and suction strokes of each plunger. The speeds during
the overlaps are calculated in the same manner for both the
pressure and suction strokes and the displacement of and duration
are precisely controlled by the controller and the stepper
motors.
[0009] These features of novelty and various other advantages that
characterize the invention are pointed out with particularity in
the claims annexed hereto and forming a part hereof. However, for a
better understanding of the invention, its advantages, and the
objects obtained by its use, reference should be made to the
drawings that form a further part hereof, and to the accompanying
descriptive matter, in which there is illustrated and described a
preferred embodiment of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Referring now to the drawings, wherein like reference
letters and numerals indicate corresponding structure throughout
the several views:
[0011] Referring now to the drawings, wherein like reference
letters and numerals indicate corresponding structure throughout
the several views:
[0012] FIG. 1 is a side sectional view of a reciprocating pump
according to the principles of the present invention;
[0013] FIG. 2 is a detail view of a conventional recirculating ball
type leadscrew and nut;
[0014] FIG. 3 is a perspective view of the pump shown in FIG. 1
with a portion of the housing removed for clarity;
[0015] FIG. 4 is a top sectional view of the pump shown in FIG.
3;
[0016] FIG. 5 is a side sectional view of a diaphragm pump
according to the principles of the present invention;
[0017] FIG. 6 is a graph showing the output for the pump shown in
FIG. 3 operating at high pressure;
[0018] FIG. 7 is a graph showing the output for the pump shown in
FIG. 3 operating at low pressure with insignificant fluid
compression;
[0019] FIG. 8 is a graph showing the output for a three pumping
chamber pump operating at low pressure;
[0020] FIG. 9 is a graph showing the output for a three pumping
chamber pump operating at high pressure; and
[0021] FIG. 10 is a flow diagram for the method for controlling the
pump shown in FIG. 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0022] Referring now to the drawings and in particular to FIGS. 1,
3 and 4, there is shown a positive displacement reciprocating pump,
generally designated (100). The pump (100) includes a pump housing
(102) and a manifold (104). The pump (100) includes at least one
guide bore (106) and preferably two or more guide bores (106). Each
guide bore (106) includes an associated guide rod (108)
reciprocating longitudinally back and forth within the guide bore.
The manifold (104) includes a hydraulic chamber (110) as well as an
inlet check valve (112) and outlet check valve (114). A plunger
(130) connects to the guide rod (108) and moves back and forth into
the hydraulic chamber (110).
[0023] The guide rod (108) threadably connects to a lead screw,
such as a recirculating ball type lead screw (122). A variable
speed motor, such as a servo motor or a stepper motor (120),
depending on the size an application of the pump, actuates the lead
screw (122) in both directions. As shown in FIG. 2, a conventional
lead screw (122) includes threads (124) that mate with
complementary threads of a nut (126). The nut (126) may include a
threaded portion (128). The lead screw (122) and nut (126) may be
configured as a ball screw with a recirculating ball nut to reduce
friction. It can be appreciated that the guide rod (108) may be
directly driven by a lead screw as shown in FIG. 1 or mounted to
the nut (126) shown in FIG. 2. Referring again to FIG. 1, a tab
(132) extends from the guide rod (108) and passes through a
position sensor, such as a slot detector (134) that communicates to
a microcontroller (150) when the plunger (130) is at bottom dead
center. The guide rod (108) includes a second tab (140) that moves
in a slot (142) to prevent free rotation of the guide rod (108).
Therefore, as the lead screw (122) rotates, the guide rod (108)
will move axially along the lead screw to extend and retract the
plunger (130) into and out of the pumping chamber (110), which is
filled with fluid. It can be appreciated that the stepper motors
(120) can be precisely rotated in miniscule discrete stepped
movements and are able to precisely control rotation of the
associated lead screws (122) and therefore the axial position of
the guide rod (108) to closely control the position of the plunger
(130) and its movements into and out of the pumping chamber
(110).
[0024] Referring now to FIG. 5, there is shown another embodiment
of a pump system (200) according to the principles of the present
invention. In the embodiment shown, the pump (200) is a diaphragm
type pump. The diaphragm pump (200) preferably includes at least
two guide bores (206), but more typically includes three or five
guide bores. The pump (200) includes a pump housing (202) and a
manifold (204). The manifold includes a pumping chamber (218), an
inlet check valve (212) and outlet check valve (214). The guide
bore (206) includes a reciprocating guide rod (208) that connects
to a plunger (230) that pumps hydraulic fluid into the hydraulic
chamber (210). The hydraulic fluid acts against a diaphragm (216)
to force pumped fluid from the pumping chamber (218) to the outlet
valve (214). Each of the guide bores (206) is driven by a variable
speed motor, such as a servo motor or a stepper motor (220) in a
manner similar to that for the embodiment shown in FIG. 1. The pump
(200) also includes a lead screw (222), a plunger (230), a position
sensor including a tab (232) and corresponding slot detector (234),
tab (240) and slot (242) to prevent free rotation, and a bearing
(244). Moreover, valves (236) control the hydraulic fluid within
the housing (202) as the fluid moves between suction and power
strokes. Actuation of a stepper motor (220) rotates the associated
lead screw (222) and moves the guide rod (208) into and out of a
receiving portion of the guide bore (206). A microcontroller (250)
controls each of the stepper motors (220) to achieve a varied speed
and precise displacement to achieve a substantially pulse free
output flow.
[0025] In operation, to start the pump (100), with the plunger
(130) at bottom dead center, the controller (150) would drive a
first stepper motor (120) to rotate the leadscrew (122) in a first
direction, which causes the guide rod (108) to travel axially
forward and therefore to the right towards the manifold as depicted
in FIG. 1. The controller (150) would communicate to the stepper
motor (120) to increase the rotation speed up to the maximum that
produces the full output of the guide bore (108) and plunger (130)
assembly. For most of the stroke, the stepper motor (120) rotates
at a constant speed. However, as the plunger (130) nears top dead
center, the stepper motor (120) is slowed by the controller (150)
until it stops at top dead center. The stepper motor (120) would
then start turning in the opposite direction and increasing to a
maximum and then decreasing again near bottom dead center until
coming to a stop at bottom dead center.
[0026] In a two pumping chamber pump with two plungers, duration of
the pressure stroke is slightly longer than the suction stroke so
that the ramp up portion and ramp down portion of the two plunger
strokes overlap. This overlap produces continuous combined flow at
the pump discharge. As the first plunger (130) proceeds forward
from bottom dead center, there is a portion of the stroke that is
compressing the fluid and expanding the pressure containing
components. During this period of the stroke, no flow exits the
pumping chamber (110) of the first plunger (130) while the other
plunger is still producing full flow. The controller (150) can
determine the number of steps that the stepper motor (120) must
move before beginning to slow the other guide rod/plunger. It can
be appreciated that operation of a diaphragm pump (200) would be
substantially the same as for a piston type pump (100).
[0027] The controller utilizes a formula of
Dv=P*V/K
where: [0028] K and V are constants stored in the microcontroller
for the pump. [0029] P=the output pressure and can be entered by
the operator or input from a transducer. [0030] K=the combined bulk
modulus of the system which includes the fluids and components that
deflect during the pressure stroke. This can be determined
experimentally for the pump being controlled. [0031] V=pumping
chamber volume [0032] dV=the change in volume due to compression of
the fluids and expansion of the pumping chamber.
[0033] Example using values for a small metering pump operating at
3000 psi. [0034] P=3000 psi [0035] V=0.4 cubic inches [0036]
K=250,000 psi [0037] dP=3000*0.4/250000=0.0048 cubic inches.
[0038] dP divided by the plunger diameter will give the stroke
travel to build up to system pressure from 0.
[0039] The controller (150) calculates the number of steps that the
stepper motor (120) moves to advance the plunger (130) from bottom
dead center before the fluid starts leaving the pumping chamber
(110) and the other plunger (130) can start slowing down. Stepper
motors have a fixed number of steps per revolution. A typical motor
uses 200 steps per revolution. However, drivers can increase this
number to a much higher number of steps per revolution using
microsteps for each full step. Stepper motors may commonly have as
many as 3200 steps per revolution for certain applications. As each
step is a fixed amount of rotation and the lead screw (122) moves
the guide rod (108) a constant linear travel distance per
revolution, each step will correspond to a fixed axial displacement
and therefore a fixed volume of displaced fluid. Therefore, the
time for each step determines the output flow rate of the
corresponding plunger and pumping chamber. With these parameters
being known, the constant output per step makes an algorithm for
flow rate and combining flows from multiple pumping chambers and
associate guide rods and plungers can be calculated as follows:
[0040] The flow rate for one plunger is governed by the
formula:
Q=Vs/T [0041] Where: [0042] Q is the volume of fluid per step Vs
divided by the duration for the step T.
[0043] The microcontroller 150 controls the stepper motor speed by
varying the duration T. The controller varies the duration T
continuously during the ramp pressure or combined flow periods of
the stroke.
[0044] When multiple plungers are producing flow the total flow Qt
is calculated as follows:
T=T1+T2 for a two plunger pump
[0045] Where: [0046] T1 and T2 are the duration of the step for
motors 1 and 2.
[0047] Therefore, the volume of fluid can be shown as:
Qt=Vs/(T1+T2)
[0048] It can therefore be appreciated that when only one guide
rod/plunger is operating, T1=T, and T2=0. When a first plunger
starts to slow as it reaches the end of the stroke, the second
plunger starts moving at a speed determined by the step time
calculation:
T2=T-T1
[0049] Therefore, these durations T are active only when the motors
(120) are moving in the same direction, since the pump's check
valves (112 and 114) combine flows when the plungers (130) move in
the same direction. It can be appreciated that the controller (150)
stores pump specific constants that may include a system stiffness
factor. The controller (150) also has pump specific characteristics
including displacement per step and the number of steps per stroke
as well as acceleration rates for the rate of change of step
durations. The controller (150) also includes a desired output flow
rate that may be constant or may be programmable and an output
pressure that may be constant or programmable.
[0050] Examples of typical components for an exemplary metering
pump include: a Hetai Stepper Motor model #57BYGH603; a
McMaster-Carr Ball Screw model #; and a McMaster-Carr model
#5966K16 Ball Nut.
[0051] Referring now to FIGS. 6 and 7, there are shown graphs for
the output of the two pumping chambers and two plungers. FIG. 6
shows the outputs of each plunger and the combined output for a
pump operating at high pressure.
[0052] Zone 1 is the beginning of Plunger 1 pressure stroke. During
Zone 1 the plunger of Plunger 1 is moving forward and building
pressure while the fluids compress and the chamber expands. During
this period, there is no flow exiting the chamber, so the Plunger 2
continues at the maximum output. As soon as Plunger 1 pressure
reaches the output pressure at the end of Zone 1, Plunger 2 slows
its flowrate rapidly to offset the flow starting from Plunger 1. In
Zone 2 Plunger 2 continues to lower its flow to zero while Plunger
1 increases at rates that result in a constant combined flow. The
plunger velocities at the start of Zone 2 can be adjusted to match
the change in flow when check valve the pumping chamber of Plunger
1 opens. When Plunger 2 stops at top dead center Plunger 1 is
producing full flow. Plunger 1 continues output at a constant rate
for the duration of Zone 3. During Zone 3 Plunger 2 makes its
suction stroke, traveling to bottom dead center and then starts
moving forward to build pressure by the end of Zone 3.
[0053] Referring now to FIG. 7, there are shown the outputs of each
plunger and the combined output for a pump operating with low
pressure where fluid compression is insignificant. It will be
appreciated that such conditions are a special case of the graph in
FIG. 6 where Zone 1 has a length of zero because there is no
pressure build up. Zone 2 begins where Plunger 1 starts increasing
plunger speed up to the maximum output. At the same time in Zone 2
Plunger 2 is decreasing so the combined output is constant. Zone 3
is where Plunger 1 is producing full flow and Plunger 2 is
producing no flow while it is in its suction stroke.
[0054] The present invention has been described with stepper motors
(120, 220), which deliver a fixed displacement per step and are
very simple to control. However, stepper motors are relatively
inefficient for certain applications. In small metering pumps this
is not a big factor, but in larger pumps energy losses could make
stepper motors impractical. In such applications a servo motor
system could be used. A system using servo motors would include
variable speed control of the motor and position encoders to
communicate to the microcontroller how fast to run the motor in the
various ramp zones.
[0055] It can be appreciated that a minimum of two pumping chambers
and associated plungers are required to take advantage of the
overlap and modified control to produce a steady output flow. This
is also the simplest configuration and typically the least
expensive. However, in order to have the pressure strokes overlap,
the intake strokes of a two plunger pump would not overlap, which
may result in a moment of zero flow. For most metering
applications, this is negligible and not important. However, for
some applications, this may be important and require a different
approach. Applications that have a sensitive or viscous fluid may
require a smooth inlet flow. For such applications, a three pumping
chamber pump may be used in which three of the plungers such as
shown in FIG. 1 or FIG. 4 are utilized to create a pulseless inlet
flow as well as a pulseless discharge. Moreover, it can be
appreciated that many pumps may include a larger number of pumping
chambers and associated plunger including five pumping chambers and
plungers to replace conventional five cylinder pumps. For a pump
with three plungers, the pump stroke cycle can be timed with the
overlap similar to a shaft driven pump where the strokes have a
phase difference 120 degrees apart or 1/3 of a pump cycle apart.
Therefore, there is overlap timing on both the pressure and suction
strokes of each plunger. The speeds during the overlaps are
calculated in the same manner for both the pressure and suction
strokes.
[0056] As shown in FIGS. 8 and 9, the flow outputs for a three
plunger pump overlap. As shown in FIG. 8, the horizontal axis of
the graph represents 300 time units for one pump cycle. The
vertical axis is output or plunge velocity. All positive velocities
are pressure strokes and all negative velocities represent suction
strokes. In FIG. 8, the pump is operating at a low pressure so
there is no pressure building zone. The overlap zones for two
plungers are spaced so that they occur during the time that the
third plunger is operating alone on the opposite stroke. When
Plunger 1 is providing full output, Plunger 2 and Plunger 3 are
combining their intake strokes.
[0057] Referring now to FIG. 9, a pump cycle for a three plunger
pump is shown operating at high pressure. It can be appreciated
that Zones 1, 2 and 3 are the same as the Zones for the two plunger
pump shown in FIG. 6 in which Zone 1 is the pressure build zone,
Zone 2 is the combined flow zone and Zone 3 is the portion of the
stroke in which one plunger is providing full flow. It can also be
appreciated that FIG. 9 shows that shorter Zones 1 and 2 can be
used followed and then a dwell period can be added following Zones
1 and 2 at the top and bottom of the strokes. This is shown at the
zero velocity line in FIG. 9 where the plungers would be at top
dead center or bottom dead center. In a manner similar to that
shown in FIG. 6 for a two plunger pump, each of the constant speed
zones are extended to cover the pressurization zone of the next
plunger. This can also be seen on the suction side of the stroke
where the constant negative velocity is extended on each plunger
while the next plunger is lowering its pressure as it retracts from
top dead center. It can be appreciated that the combined total flow
therefore is substantially pulseless and provides improved control
relative to what is possible with the prior art or any combination
thereof.
[0058] In operation, the controller would include various constants
and parameters related to the particular pump being controlled and
the desired output flow and operating flow and pressure. The
controller would calculate: [0059] Step duration for output flow
(Tf) [0060] Number of steps for pressure build during Zone 1 (N11)
(decreasing step duration) [0061] Time for zone 1 (Tz1) based on
N11 and acceleration rate [0062] Number of steps for the flow
producing plunger during Zone 1 (N21) N21=Tz1/Tf (at constant step
duration (Tf). [0063] Number of steps for overlap Zone 2 (N2)
[0064] Time for Zone 2 (Tz2) [0065] Number of steps for the flow
producing plunger during Zone 3 (N13)=Nf-(N11-N2)
[0066] Once the operating parameters have been calculated, the
controller is able to operate the pump for a desired flow rate and
pressure. Referring to FIG. 10, the operation begins by starting
the pump and moving both plungers to bottom dead center. The second
plunger is moved at a Tf step duration for Ns-(N2+N12) steps. This
represents the start of Zone 1. A stroke begins by moving the
plunger 1 with decreasing step duration (T1) for N11 steps. Then,
at each step of plunger 1, T2 is calculated using the formula
T2=Tf-T1. The controller communicates to the stepper motor to
continue moving plunger 2 with the increasing T2 step durations
until top dead center at the end of Zone 2.
[0067] When plunger 1 reaches the end of Zone 2, the controller
instructs the stepper motor to continue for N13 steps at Ts step
duration to the end of Zone 3. Then, when plunger 2 reaches the end
of Zone 2, plunger 2 is at top dead center. As the controller
detects plunger 2 reaching top dead center, the controller
instructs the stepper motor to reverse its direction to arrive at
bottom dead center at a time to start its pressure stroke before
plunger 1 finishes its pressure stroke. These strokes are repeated
alternating plunger 1 and plunger 2. The resulting flow is
substantially pulse free and achieves the desired flow rate and
output pressure.
[0068] It is to be understood, however, that even though numerous
characteristics and advantages of the present invention have been
set forth in the foregoing description, together with details of
the structure and function of the invention, the disclosure is
illustrative only, and changes may be made in detail, especially in
matters of shape, size and arrangement of parts within the
principles of the invention to the full extent indicated by the
broad general meaning of the terms in which the appended claims are
expressed.
* * * * *