DISPLACEMENT PUMP AND CONTROL SYSTEM

POMPE VOLUMETRIQUE ET SYSTEME DE COMMANDE

English Abstract

A pump system includes: a positive displacement pump (20), such as a diaphragm pump; an electric motor (12) directly coupled to the positive displacement pump; and a programmable controller (16) configured to sense the current to the electric motor and to maintain constant a desired current value, so that a constant torque is provided which achieves a constant fluid discharge pressure from the pump.

French Abstract

Un système de pompe comprend une pompe à variation de volume, telle qu'une pompe à membrane, un moteur électrique directement accouplé à la pompe à variation volume, et un dispositif de commande programmable configuré pour maintenir un courant souhaité appliqué au moteur électrique. Le dispositif de commande programmable est conçu pour détecter le courant vers le moteur et pour maintenir un courant constant. Il a été observé qu'un courant constant fournit un couple constant et qu'un couple constant produit une pression de refoulement de fluide constante à partir de la pompe. Le dispositif de commande programmable utilise une formule de puissance absorbée pour déterminer le courant correct pour obtenir le couple nécessaire pour une pression de refoulement de fluide souhaitée. Le dispositif de commande programmable comprend un mode d'économie d'énergie à courant minimal et la pompe se trouve dans un état « débit nul », sans écoulement. Le système est utilisé au moyen d'un procédé qui maintient une pression de refoulement de fluide constante ainsi qu'un mode d'économie d'énergie.

Claims

CLAIMS
1. A pump system (10), comprising:
a positive displacement pump (20);
an electric motor (12);
said pump system being characterized by:
a programmable controller (16) configured to maintain a desired current to the
electric motor (12); and
the electric motor (12) being directly coupled to the positive displacement
pump
(20).
2. The pump system (10) according to claim 1, wherein the programmable
controller
(16) comprises a current sensor.
3. The pump system (10) according to claim 1 or claim 2, wherein the
positive
displacement pump (20) comprises a diaphragm pump (20).
4. The pump system (10) according to any preceding claim, comprising an
inverter
(14) including the programmable controller (16).
5. The pump system (10) according to any preceding claim, wherein the
programmable controller (16) controls current according to an absorbed power
formula.
6. The pump system (10) according to any preceding claim, wherein the
programmable controller (16) comprises a power saving mode.
7. The pump system (10) according to claim 6, wherein the programmable
controller
(16) detects acceleration from the power saving mode and is operably
configured to apply
the desired current.
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8. The pump system (10) according to any preceding claim, wherein the
controller
(16) comprises a variable frequency drive controller (16).
9. The pump system (10) according to any preceding claim, wherein the
system is
configured for connecting to a fluid system solely with a current connection
to the motor
(12) and a fluid connection to the pump (20).
10. A method for controlling a positive displacement pump (20) with a
system (10)
including an electric motor (12) and a programmable controller (16) to achieve
a desired
constant fluid discharge pressure, the method comprising:
determining current and torque requirements for the desired constant fluid
discharge pressure;
said method being characterized by:
programming the controller (16) to control the system (10) in a power saving
mode with minimum current and torque with the pump (20) having no flow;
providing constant current to the motor (12) corresponding to a torque for the
desired constant fluid discharge pressure;
maintaining the current for the corresponding torque and fluid discharge
pressure.
11. The method according to claim 10, further comprising returning the
system (10)
to a power saving mode when demand ends.
12. The method according to claim 10 or claim 11, wherein the torque
automatically
accelerates when there is demand on the pump (20) and wherein the programmable
controller (16) senses the acceleration and adjusts the current for the
desired constant
fluid discharge pressure.
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Description

CA 03040627 2019-04-15
WO 2018/051192 PCT/IB2017/001471
DISPLACEMENT PUMP AND CONTROL SYSTEM
Background of the Invention
This application is being filed on September 15, 2017, as a PCT International
Patent application and claims the benefit of priority to U.S. Provisional
patent
application Serial No. 62/395,568 filed September 16, 2016, the entire
disclosure of
which is incorporated by reference in its entirety.
Field of the Invention
The present invention is directed to a control system for pumps and in
particular to a control system to a controller using current to maintain a
constant
fluid pressure.
Description of the Prior Art
Diaphragm pumps are used for a variety of purposes and applications and
often require maintaining constant fluid pressure even under varying load
conditions. Diaphragm pumps generally include a diaphragm, a pumping chamber,
and a piston acting on hydraulic fluid on a first side of the diaphragm and
separated
from the pumping chamber by the diaphragm. The piston assembly is adapted to
reciprocate and move between a first position and a second position to actuate
the
diaphragm. As the piston moves away from the diaphragm, the diaphragm flexes
away from the pumping chamber allowing the pumping fluid to be drawn into the
pumping chamber through an inlet passage. As the piston moves towards the
diaphragm, the diaphragm flexes toward the pumping chamber and causes the
fluid
of the pumping chamber to be discharged through a discharge passage.
Often, such pumps are operated to maintain a constant fluid pressure. To
control the fluid pressure even as the load changes, it is necessary to
increase or
decrease the pump speed. Generally controlling of the pump requires pressure
sensors to provide feedback to increase or decrease the pumped fluid being
discharged to maintain a fluid discharge pressure as pumping conditions may
vary.
Moreover, it can be appreciated that such controls typically require special
connections, including wiring, as well as additional pressure sensors and may
include a complicated controller with formulas to control the pump speed.
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Moreover, it may be difficult or even impossible to retrofit an existing pump
so that
it can achieve such constant fluid discharge pressure.
It can be seen then that a new and improved pump control system is needed.
Such a system should control a pump to maintain a constant fluid pressure even
under varying load conditions. Moreover, such a system should be reliable,
simple
and inexpensive. Such a system should be easy to adapt to existing
installations
without special fittings or attachment. The present invention addresses these,
as
well as others associated with pumps, pump control systems and maintaining
constant fluid pressure.
Summary of the Invention
The present invention is directed to a pump system includes a positive
displacement pump, such as a diaphragm pump, an electric motor directly
coupled to
the positive displacement pump, and a programmable controller configured to
maintain a desired current to the electric motor. The programmable controller
is
adapted to sense the current to the motor and to maintain constant current.
The
controller may be a variable frequency drive controller. It has been found
that
constant current provides constant torque and constant torque achieves
constant fluid
discharge pressure from the pump. The programmable controller utilizes an
absorbed power formula to determine the correct current to achieve the
necessary
torque for a desired fluid discharge pressure. The programmable controller
includes
a power saving mode with minimal current and the pump is "dead headed" with no
flow. When demand resumes from the power saving mode, the programmable
controller detects acceleration from the power saving mode and is operably
configured to apply the desired current. The system is configured for
connecting to
an external application solely with a current connection to the motor and a
fluid
connection to the pump.
A method for controlling the system includes programming the controller to
control the system in a power saving mode with minimum current and torque with
the pump having no flow. Using an absorbed power formula and setting a desired
pump fluid discharge pressure, the current and torque requirements for the
desired
constant fluid pressure are determined. The controller then provides constant
current to the motor corresponding to the torque for the desired constant
fluid
pressure. The controller maintains the current for the corresponding torque
and fluid
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discharge pressure. The controller may be programmed to return the system to a
power saving mode when demand ends. Moreover, as the torque automatically
accelerates from the power saving mode when there is demand on the pump, the
programmable controller senses the acceleration and returns to the current for
the
desired constant fluid discharge pressure.
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
Referring now to the drawings, wherein like reference letters and numerals
indicate corresponding structure throughout the several views:
Figure 1 is a perspective view of a pump, motor and control system
according to the principles of the present invention;
Figure 2 is a flow diagram for operating the system shown in Figure 1;
Figure 3 is a side sectional view of a diaphragm pump for the system shown
in Figure 1; and
Figure 4 is a graph of torque versus current.
Detailed Description of the Preferred Embodiment
Referring now to the drawings and in particular to Figure 1, there is shown a
pump, drive and control system, generally designated (10). The system (10)
includes a positive displacement pump, such as a diaphragm pump (20). The pump
is driven by an electric motor (12). An inverter (14) with a programmable
logic
controller (16) provides overall control of the system (10). The controller
(16) may
be a variable frequency drive controller. It can be appreciated that the
system (10) is
particularly suited for providing and maintaining constant fluid pressure.
It can also be appreciated that the components have a modular configuration
and may be adapted to a larger fluid system and provides "plug and play"
connections with such connections only needed for power for the motor (12) and
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liquid for the pump (20). Therefore, the system (10) of the present invention
is
easily adapted and retrofitted to existing systems. It can also be appreciated
that the
motor (12) may include forced cooling for advantageous operation. The system
may
be adapted to multiple different systems such as providing constant pressure
for
tools without requiring special modifications to the system receiving the
pumped
fluid.
Referring now to Figure 3, there is shown a positive displacement fluid
pump such as a hydraulically driven diaphragm pump, generally designated (20).
The diaphragm pump (20) is driven by a crankshaft (36) mounted in a crankcase
(22). The manifold (26) includes an inlet passage (76) and a discharge passage
(74).
The manifold (26) also includes one or more inlet check valves (72) and one or
more
discharge check valves (70).
In the embodiment shown, the pump (20) is a diaphragm pump and includes
a diaphragm (46) mounted on a valve stem (44). The diaphragm pump (20) may be
a metering pump with very low flows that requires reliable precision inlet and
discharge valves to achieve precise flow rates. However, it can be appreciated
that
the present invention is usable with many different types of pumps that use
check
valves. The diaphragm (46) is hydraulically driven by a plunger (42) connected
to a
slider (40) on connecting rod (38) to the crankshaft (36). The diaphragm
system
includes an overfill check valve (48) and an underfill check valve (50).
The diaphragm (46) receives fluid in a pumping chamber (34) and the fluid is
pumped while the diaphragm deflects back and forth between an extended
position
and a fully retracted position. The manifold (26) includes separate inlet
check
valves (72) and discharge check valves (70).
Referring to Figure 4, the torque at the pump shaft is controlled by motor
current. Absorbed power formulas are utilized to measure the torque in
relation to
different electric currents. It has been found that the torque is directly
proportional
to the discharge pressure. Therefore, as torque is also linearly proportional
to
current, simple and reliable control is attained by providing a constant
current to the
motor (12), constant discharge fluid pressure may be achieved.
Referring to Figure 2, achieving a constant discharge pressure may begin
with the pump in a "dead headed" operating state. In such a mode, there is
only a
very small current provided and it is envisioned that the system (10) will
require
only 150 watts in this mode. To achieve a constant fluid discharge pressure,
the
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torque required and therefore the current required is calculated. After these
parameters are input, the controller (16) applies the current to the motor
(12) to drive
the pump (20) at the desired torque to achieve the constant discharge fluid
pressure.
The logic controller (16) then maintains the proper current to achieve the
fluid
pressure. When pumping operation is over, the programmable controller (16)
again
decreases the current so that a very slight trickle current is utilized.
The present invention utilizes direct drive of the motor (12) to the pump (20)
without a gearbox. Moreover, no pressure sensors are required after initial
parameters and relationships are determined. The constant fluid pressure is
maintained with simple operation of the programmable logic controller (12).
It can be appreciated that the programmable logic controller (12) also
provides for a metering/dosing control with different control software. The
logic
controller (12) is able to operate with the pump (20) dead headed, in which
there is
no flow, and is able to enter the sleep or power saving mode where current is
reduced to a bare minimum for energy savings. Moreover, it can be appreciated
that
when there is flow demand, the minimal torque causes an acceleration, which is
automatically detected and torque is therefore again applied at the desired
level by
the controller (16). The controller (16) generally utilizes an absorbed power
formula
to set and maintain the motor (12) to drive the pump (20) to achieve the
desired flow
rate.
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.
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Representative Drawing