U.S. patent application number 13/514449 was filed with the patent office on 2013-02-14 for system and method for controlling linear pump system.
This patent application is currently assigned to GRACO MINNESOTA INC.. The applicant listed for this patent is Christopher R. Blackson, Roger D. Blough, Nicholas D. Long. Invention is credited to Christopher R. Blackson, Roger D. Blough, Nicholas D. Long.
Application Number | 20130039778 13/514449 |
Document ID | / |
Family ID | 44146097 |
Filed Date | 2013-02-14 |
United States Patent
Application |
20130039778 |
Kind Code |
A1 |
Blackson; Christopher R. ;
et al. |
February 14, 2013 |
SYSTEM AND METHOD FOR CONTROLLING LINEAR PUMP SYSTEM
Abstract
Systems and methods for operating a linear pump system involve
operating a linear motor system; reciprocating a linear pump and a
motor control module that issues commands and a control logic input
to the linear motor system. The linear motor system is operated to
reciprocate an output shaft between first and second reversal
positions. The linear pump is reciprocated with the output shaft to
produce a flow of material. A pump reversal command reverses
direction of the output shaft. A torque command controls speed of
the output shaft. The control logic input reciprocates the output
shaft at speeds to produce a constant output condition of the flow
of material. The motor control module adjusts the torque command to
operate the output shaft at an increased speed above what is
necessary for the constant output condition for a temporary time
period beginning when the reversal command is issued.
Inventors: |
Blackson; Christopher R.;
(Uniontown, OH) ; Long; Nicholas D.; (Broadview
Heights, OH) ; Blough; Roger D.; (Canal Fulton,
OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Blackson; Christopher R.
Long; Nicholas D.
Blough; Roger D. |
Uniontown
Broadview Heights
Canal Fulton |
OH
OH
OH |
US
US
US |
|
|
Assignee: |
GRACO MINNESOTA INC.
Minneapolis
MN
|
Family ID: |
44146097 |
Appl. No.: |
13/514449 |
Filed: |
December 8, 2010 |
PCT Filed: |
December 8, 2010 |
PCT NO: |
PCT/US10/03120 |
371 Date: |
August 29, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61267509 |
Dec 8, 2009 |
|
|
|
Current U.S.
Class: |
417/44.1 |
Current CPC
Class: |
F04B 9/113 20130101;
F04B 23/02 20130101; F04B 49/20 20130101; F04B 17/04 20130101; F04B
11/0058 20130101 |
Class at
Publication: |
417/44.1 |
International
Class: |
F04B 49/06 20060101
F04B049/06 |
Claims
1. A linear pump system comprising: a linear motor system that
produces a reciprocating movement of an output shaft between first
and second reversal positions; a linear material pump connected to
the output shaft to produce a flow of material; and a motor control
module that: issues a reversal command to the linear motor system
to reverse direction of the output shaft; issues a torque command
to the linear motor system to control speed of the output shaft;
and issues a control logic input to the linear motor system to
reciprocate the output shaft at speeds to produce a constant output
condition of the flow of material; wherein the motor control module
adjusts the torque command to operate the output shaft at an
increased speed above what is necessary for the constant output
condition for a temporary time period beginning when the reversal
command is issued.
2. The linear pump system of claim 1 wherein the linear motor
system further comprises: a linear hydraulic motor that includes
the output shaft; an electric motor that receives the torque
command from the motor control module; a rotary hydraulic pump
driven by the electric motor that provides a flow of pressurized
hydraulic fluid commensurate with speed of the electric motor to
control speed of the output shaft; and a hydraulic dual output
reversing valve coupled to the linear hydraulic motor and that
receives the flow of pressurized hydraulic fluid from the rotary
hydraulic pump to hydraulically reverse direction of the output
shaft in response to receiving the reversal command from the motor
control module.
3. The linear pump system of claim 1 wherein the motor control
module turns off the control logic input in response to adjusting
the torque command and while operating the output shaft at speeds
above what is necessary for the constant output condition.
4. The linear pump system of claim 3 wherein the linear motor
system further comprises: a position sensor connected to the linear
hydraulic motor that issues a position signal in response to the
output shaft moving away from one of the reversal positions;
wherein the motor control module alters the adjusted torque command
to reduce the increased speed of the output shaft in response to
receiving the position signal.
5. The linear pump system of claim 3 wherein the motor control
module turns on the control logic input after the temporary time
period terminates.
6. The linear pump system of claim 5 wherein the temporary time
period terminates when a reset condition is detected.
7. The linear pump system of claim 5 wherein the linear motor
system further comprises: a pressure sensor for sensing pressure in
the flow of material; wherein the reset condition comprises a
sensed pressure rise.
8. The linear pump system of claim 1 wherein the constant output
condition comprises either constant pressure output or constant
flow output.
9. A method for operating a linear pump system comprising:
operating a linear motor system to reciprocate an output shaft
between first and second reversal positions; reciprocating a linear
pump with the linear motor system output shaft to produce a flow of
a material; driving the linear motor system at rates to provide a
constant output condition of the flow of material; initiating a
reversal in direction of the output shaft; and driving the linear
motor system at an increased rate above what is necessary for the
constant output condition for a temporary time period beginning
when the reversal in direction of the output shaft is
initiated.
10. The method for operating a linear pump system of claim 9 and
further comprising: operating a linear hydraulic motor having the
output shaft; operating an electric motor; operating a rotary
hydraulic pump with the electric motor to provide a flow of
pressurized hydraulic fluid to the linear hydraulic motor to
control speed of the output shaft; and operating a hydraulic dual
output reversing valve coupled to the linear hydraulic motor and
that receives the flow of pressurized hydraulic fluid to reverse
direction of the output shaft.
11. The method of operating a linear pump system of claim 10 and
further comprising: a motor control module that coordinates
operation of the electric motor and the hydraulic dual output
valve, wherein: the linear motor system is driven at rates to
provide the constant output condition in response to receiving a
control logic input from the motor control module; the reversal in
direction of the output shaft is initiated in response to the
hydraulic dual output valve receiving a reversal command from the
motor control module; and the linear motor system is driven at the
increased rate in response to the electric motor receiving a torque
command from the motor control module.
12. The method of operating a linear pump system of claim 11 and
further comprising: turning off the control logic input when the
torque command is issued while operating at the increased rate.
13. The method of operating a linear pump system of claim 12 and
further comprising: detecting a position of the output shaft at a
reversal position; and altering the torque command to reduce the
increased rate in response to detecting the reversal position.
14. The method of operating a linear pump system of claim 12 and
further comprising: turning on the control logic input after the
temporary time period terminates.
15. The method of operating a linear pump system of claim 14 and
further comprising: sensing a pressure of the output flow material;
and terminating the temporary time period when a pressure rise is
sensed.
16. The method of operating a linear pump system of claim 9 wherein
the constant output condition comprises either constant pressure
output or constant flow output.
17. A method of operating a linear pump system comprising:
operating a linear motor system to reciprocate an output shaft
between first . and second reversal positions; reciprocating a
linear pump with the linear motor system output shaft to produce a
flow of a material; driving the linear motor system at rates to
provide a constant output condition of the flow of material; and
temporarily driving the linear motor system at an increased rate
above what is necessary for the constant output condition when the
output shaft reverses direction.
18. The method of claim 17 wherein the step of driving the linear
pump comprises: reversing direction of the output shaft;
controlling speed of the output shaft; and wherein the direction
and speed of the output shaft are controlled with control logic to
provide the constant output condition, the control logic being
suspended when the linear pump is temporarily driven at the
increased rate.
19. The method of claim 18 and further comprising: detecting a
position of the output shaft; and reducing the increased rate when
the output shaft is detected moving away from a reversal
position.
20. The method of claim 19 and further comprising: sensing a
pressure in the flow of material; and initiating the control logic
when a pressure rise is sensed.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application claims priority under 35 U.S.C. .sctn.120
to U.S. provisional application Ser. No. 61/267,509, entitled
"MINIMIZING PRESSURE DROP DURING PUMP REVERSAL IN A LINEAR PUMP
SYSTEM," filed Dec. 8, 2009 by inventors Christopher Blackson, Nick
Long and Roger Blough, the contents of which are incorporated by
this reference.
[0002] This application claims priority under 35 U.S.C. .sctn.119
to PCT application Serial No. PCT/2010/______, entitled "SYSTEM AND
METHOD FOR CONTROLLING LINEAR PUMP SYSTEM," filed Dec. 8, 2010 by
inventors Christopher Blackson, Nick Long and Roger Blough, the
contents of which are incorporated by this reference.
BACKGROUND
[0003] The present invention relates generally to pump control
systems. More particularly, the present invention relates to
reducing pressure drop in linear pumps.
[0004] Linear pumps include a piston that reciprocates in a housing
to push fluid through the housing. Conventional linear pumps draw
fluid into the housing on a backward stroke and push the fluid out
of the housing on a forward stroke. Valves are used to prevent
backflow through the pump. The valves can also be configured to
draw in fluid and pump fluid on opposite sides of the piston during
each of the backward stroke and forward stroke in order to provide
a steady flow of fluid from the pump. There is, however, an
inherent drop in pump pressure when the piston reverses direction,
which results in variation of the volume of dispensed fluid. This
variation is particularly undesirable when precisely metered flow
is needed. In dual component metering systems, for example, a resin
material and a catalyst material are simultaneously discharged from
a mixing head of a dispensing gun. Mixing of the two materials
produces a chemical reaction that begins a solidification process
resulting in a hardened material after full curing. It is
advantageous to provide even flow of the resin material and the
catalyst material throughout the dispensing process to ensure a
proper ratio of resin to catalyst such that the mixture properly
cures. There is, therefore, a need for reducing the pressure loss
associated with linear pumps used in single and dual component
metering systems.
SUMMARY
[0005] The present invention is directed to methods and systems for
operating a linear pump system.
[0006] A method of operating a linear pump system comprises
operating a linear motor system and reciprocating a linear pump.
The linear motor system is operated to reciprocate an output shaft
between first and second reversal positions. The linear pump is
reciprocated with the linear motor system output shaft to produce a
flow of material. The linear motor system is driven at rates to
provide a constant material flow output condition. The linear motor
system is temporarily driven at an increased rate above what is
necessary for the constant output condition when the output shaft
reverses direction.
[0007] A linear pump system comprises a linear motor system, a
linear material pump and a motor control module. The linear motor
system produces a reciprocating movement of an output shaft between
first and second reversal positions. The linear material pump is
connected to the output shaft to produce an output flow of
material. The motor controller issues a reversal command, a torque
command and a control logic input to the linear motor system. The
reversal command is issued to reverse direction of the output
shaft. The torque command is issued to control speed of the output
shaft. The control logic input is issued to reciprocate the output
shaft at speeds to produce a constant output condition of the flow
of material. The motor control module adjusts the torque command to
operate the output shaft at an increased speed above what is
necessary for the constant output condition for a temporary time
period beginning when the reversal command is issued.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 shows a dual-component pump system having a pumping
unit, component material containers and a dispensing gun.
[0009] FIG. 2 shows a schematic of the dual-component pump system
of FIG. 1 having individually controlled linear component
pumps.
[0010] FIG. 3 shows a flow chart for a method of controlling a
linear component pump of FIG. 2.
DETAILED DESCRIPTION
[0011] FIG. 1 shows dual-component pump system 10 having pumping
unit 12, component material containers 14A and 14B and dispensing
gun 16. Pumping unit 12 comprises hydraulic power pack 18, display
module 20, fluid manifold 22, first linear pump 24A, second linear
pump 24B, hydraulic fluid reservoir 26 and power distribution box
28. As shown in FIG. 2, an electric motor, a dual output reversing
valve, a hydraulic linear motor, a gear pump and a motor control
module (MCM) for each of linear pumps 24A and 24B are located
within hydraulic power pack 18. Dispensing gun 16 includes dispense
head 32 and is connected to first linear pump 24A and second linear
pump 24B by hoses 34A and 34B, respectively. Hoses 36A and 36B
connect feed pumps 38A and 38B to linear pumps 24A and 24B,
respectively. Compressed air is supplied to feed pumps 38A and 38B
and dispensing gun 16 through hoses 40A, 40B and 40C,
respectively.
[0012] Component material containers 14A and 14B comprise drums of
first and second viscous materials that, upon mixing, form a
hardened structure. For example, a first component comprising a
resin material, such as a polyester resin or a vinyl ester, is
stored in component material container 14A, and a second component
comprising a catalyst material that causes the resin material to
harden, such as Methyl Ethyl Ketone Peroxide (MEKP), is stored in
component material container 14B. Electrical power is supplied to
power distribution box 28, which then distributes power to various
components of dual-component system 10, such as the MCM within
hydraulic power pack 18 and display module 20. Compressed air from
a separate source (not shown) is supplied to feed pumps 36A and 36B
through hoses 40A and 40B to supply flows of the first and second
component materials to linear pumps 24A and 24B, respectively.
Linear pumps 24A and 24B are hydraulically operated by the gear
pump in hydraulic power pack 18. The gear pump is operated by the
electric motor in power pack 18 to draw hydraulic fluid from
hydraulic fluid reservoir 26 and provide pressurized hydraulic
fluid flow to the dual output reversing valve, which operates the
linear motor, as will be discussed in greater detail with reference
to FIG. 2.
[0013] When a user operates dispense gun 16, pressurized component
materials supplied to manifold 22 by linear pump 24A and linear
pump 24B are forced to mixing head 32. Mixing head 32 blends the
first and second component materials to begin the solidification
process, which completes when the mixed component materials are
sprayed into a mold, for example. The first and second component
materials are typically dispensed from gun 16 at a constant output
condition. For example, a user can provide an input at display
module 20 to control the MCM to dispense the component materials at
a constant pressure or at a constant flow rate. The MCM uses
control logic inputs and outputs in conjunction with the electric
motor and the dual output reversing valve, among other components,
to provide the constant output condition. However, because linear
pumps 24A and linear pump 24B include pistons that must reverse
direction, there is a slight variation in the constant output
condition as pressures in the pumps drop at the reversal point. The
present invention provides a control system and method for reducing
variations in the pressures of the dispensed component materials
that arise from pressure drops produced at reversal positions of
linear pump 24A and linear pump 24B.
[0014] FIG. 2 shows a schematic of dual-component pump system 10 of
FIG. 1 having individually controlled linear component pumps 24A
and 24B. Pump system 10 includes pumping unit 12, dispensing gun
16, first linear pump 24A, second linear pump 24B, hydraulic fluid
reservoir 26A, second hydraulic fluid reservoir 26B, motor control
modules (MCMs) 42A and 42B, electric motors 44A and 44B, gear pumps
46A and 46B, dual output reversing valves 48A and 48B, hydraulic
linear motors 50A and 50B, output pressure sensors 52A and 52B and
velocity linear position sensors 54A and 54B. Hydraulic reservoirs
26A and 26B also include pressure relief valves 56A and 56B,
filters 58A and 58B, level indicators 60A and 60B, and pressure
sensors 62A and 62B, respectively.
[0015] Hydraulic fluid reservoir 26A, MCM 42A, electric motor 44A,
gear pump 46A, dual output reversing valve 48A and hydraulic linear
motor 50A are located within hydraulic power pack 18 and comprise
first linear motor system 64A. Likewise, hydraulic fluid reservoir
26B, MCM 42B, electric motor 44B, gear pump 46B, dual output
reversing valve 48B and hydraulic linear motor 50B are located
within hydraulic power pack 18 and comprise second linear motor
system 64B. In other embodiments of the invention, the linear motor
systems share components, such as an electric motor, gear pump and
hydraulic fluid reservoir.
[0016] With pumping unit primed and activated, pressurized first
and second component materials are provided to linear pumps 24A and
24B, respectively by feed pumps 38A and 38B (shown in FIG. 1),
respectively. Feed pumps 38A and 38B are operated with pressurized
air. Linear pumps 24A and 24B are operated by first and second
linear motor systems 64A and 64B to provide pressurized first and
second component materials to dispensing gun 16. Also, pressurized
air is provided to dispensing gun 16 to operate a pump or valve
mechanism to release the pressurized component materials into mix
head 32 and out of gun 16.
[0017] Linear motor systems 64A and 64B are controlled by motor
control modules (MCM) 42A and 42B, respectively. MCMs 42A and 42B
operate linear motor systems 64A and 64B in equal and identical
manners so that proportional amounts of component material are
provided to dispensing gun 16. Description of the operation linear
motor systems 64A and 64B will be directed to linear motor system
64A, with operation of linear motor system 64B operating in a like
manner, with like components being numbered accordingly.
[0018] Electric motor 44A receives electric power from power
distribution box 28 (FIG. 1). In one embodiment, electric motor 44A
comprises a direct current (DC) motor. MCM 42A issues torque
command C.sub.T, which is received by motor 44A to control the
speed of drive shaft 66A. Drive shaft 66A is coupled to gear pump
46A, which is submerged in hydraulic fluid within hydraulic fluid
reservoir 26A. Gear pump 46A utilizes the rotary input from motor
44A to drawn in fluid from reservoir 26A and produce a flow of
pressurized hydraulic fluid in line 68A. Hydraulic fluid reservoir
26A includes level indicator 60A, which is used to determine the
amount of fluid within reservoir 26A. Pressure sensor 62A can be
used to determine under-fill conditions within reservoir 26A. In
other embodiments, drive shaft 66A is used to drive other types of
positive displacement pumps that convert rotary input into
pressurized fluid flow, such as rotary vane pumps or peristaltic
pumps.
[0019] Pressurized hydraulic fluid from pump 46A flows past
pressure relief valve 56A and to dual output reversing valve 48A.
Relief valve 56A provides a means for allowing excess pressurized
hydraulic fluid to return to reservoir 26A when excessive pressure
conditions exists. As will be discussed below, reversing valve 48A
uses the pressurized hydraulic fluid to reciprocate linear motor
50A. Pressurized hydraulic fluid returns to reservoir 26A from
reversing valve 48A in line 70A after passing through filter 58A.
Filter 58A removes impurities from the hydraulic fluid. Thus, a
closed circuit flow of hydraulic fluid is formed between reservoir
26A, gear pump 46A, reversing valve 48A and linear motor 50A.
[0020] Dual output reversing valve 48A is constructed according to
conventional reversing valve designs, as are known in the art. Dual
output reversing valve 48A receives a continuous flow of
pressurized hydraulic fluid and diverts the flow of fluid to linear
motor 50A. Specifically, reversing valve 48A includes an input
connected to line 68A, an output connected to line 70A and two
ports connected to lines 72A and 74A. Pressurized fluid is
alternately supplied to lines 72A and 74A, which is used to actuate
linear motor 50A.
[0021] Linear motor 50A includes piston 76A, which slides within
housing 78A between two fluid chambers. Each fluid chamber receives
a flow of pressurized fluid from lines 72A and 72B, respectively.
For example, with reversing valve 48A in a first position, line 72A
provides pressurized fluid to a first chamber in housing 78A to
move piston 76A downward (with respect to FIG. 2). Simultaneously,
fluid within the other chamber in housing 78A is pushed out of
linear motor 50A and back into reversing valve 48A through line 74A
and out to line 70A. MCM 42A issues reverse command C.sub.R, which
is received by reversing valve 48A to control when linear motor 50A
begins reversing direction. After reverse command C.sub.R is
received, reversing valve 48A switches to a second position such
that pressurized fluid is supplied to housing 78A through line 74A
and fluid from housing 78A is removed through line 72A. Thus,
operation of reversing valve 48A reciprocates piston 76A within
housing 78A between two reversal positions, which also reciprocates
output shaft 80A. Velocity linear position sensor 54A is coupled to
shaft 80A and provides MCM 42A an indication of the position and
speed of piston 76A based on the rate at which piston 76A is
moving. In particular, position sensor 54A provides position signal
S.sub.Po to MCM 42A when output shaft 80A is moving away from one
of the reversal positions.
[0022] Output shaft 80A of linear motor 50A is directly
mechanically coupled to piston shaft 82A of linear pump 24A. Shaft
82A drives piston 84A within housing 86A. Piston 84A draws into
housing 86A a component material from container 14A, as provided by
feed pump 38A (FIG. 1). Linear pump 24A comprises a double action
pump in which component material is pushed into line 88A on an up
stroke (with reference to FIG. 2) and pushed into line 89A on a
down stroke (with reference to FIG. 2). Specifically, on an up
stroke, valve 90A opens to draw component material from feed pump
38A through manifold 22 (shown in FIG. 1) and into housing 86A, and
valve 92A opens to allow piston 84A to push material into
dispensing gun 16 through line 88A, while valves 94A and 96A are
closed. On a down stroke, valves 90A and 92A close, while valve 94A
opens to draw component material from feed pump 38A through
manifold 22 (shown in FIG. 1) and into housing 86A, and valve 96A
opens to allow piston 84A to push material into dispensing gun 16
through line 89A. The dual action of linear pump 24A maintains a
continuous and near constant supply of component material during
operation. As mentioned, however, at the reversal point of piston
shaft 82A a slight pressure drop occurs. The present invention
alleviates some of the experienced pressure drop by accelerating
piston shaft 82A near the reversal point.
[0023] Component material from lines 88A 89A is pushed into
dispensing gun 16 by pressure from linear pump 24A, where it mixes
with component material from linear pump 24B within mix head 32
before being sprayed from gun 16. Pressure sensor 52A senses
pressure of the component material within line 88A and sends
pressure signal S.sub.Pr to MCM 42A. Optional heater 98A can be
attached to line 88A to heat the component material before
dispensing from mix head 32 to, for example, reduce the viscosity
of the component material or to facilitate reacting and curing with
the other component material.
[0024] MCM 42A receives position signal S.sub.Po and pressure
signal S.sub.Pr and issues reverse command C.sub.R and torque
command C.sub.T. Using position signal S.sub.Po and pressure signal
S.sub.Pr, MCM 42A coordinates reverse command C.sub.R and torque
command C.sub.T to control linear motor system at a constant output
condition. For example, an operator of dual-component pump system
10 can specify at an input in display module 20 (FIG. 1) that
pumping unit 12 will operate to provide a constant pressure of the
first and second component materials to manifold 22 (omitted from
FIG. 2, shown in FIG. 1) or a constant flow output of the component
materials to manifold 22. MCM 42A operates control logic that
continuously adjusts reverse command C.sub.R and torque command
C.sub.T to maintain the constant output condition. Torque command
C.sub.T determines how fast motor 44A rotates shaft 66A, which
directly relates to how fast the chambers within housing 78A of
linear motor 50A will fill with fluid. Reverse command C.sub.R
determines when reversing valve 48A switches position. Issuance of
reverse command C.sub.R is coordinated with how fast the chambers
within housing 78A fill so that reversing valve 48A can switch the
direction of fluid flow into housing 78A. The control logic
maintains the speed of motor 44A and the switching rate of
reversing valve 48A in concert to maintain the desired constant
output condition. As will be discussed with reference to FIG. 3,
the present invention operates linear motor system 64A to minimize
pressure drops when piston shaft 82A reverses direction.
[0025] FIG. 3 shows a flow chart diagramming instructions for a
method of controlling linear component pumps 24A and 24B of FIG. 2.
At first step 100, motor control module (MCM) 42A operates linear
pump system 64A using control logic inputs, e.g. programmed inputs
or inputs entered at display module 20, such that linear pump 24A
is operated at a constant output condition. Specifically, MCM 42A
adjusts torque command T.sub.C to electric motor 44A to control the
speed of shaft 66A.
[0026] When pump shaft 82A gets to the end of its travel at a
reversing point, MCM 42A issues control logic output in the form of
reverse command C.sub.R to reversing valve 48A as part of the
control logic at step 110. Next, at step 120, MCM 42A turns off the
control logic such that MCM 42A is no longer continuously updating
torque command C.sub.T and reverse command C.sub.R to produce a
constant output condition. At step 130, MCM 42A issues torque
command C.sub.T to motor 44A to increase the speed of shaft 66A,
thereby increasing the output of pressurized fluid flow to dual
output reversing valve 48A. Correspondingly, MCM 42A issues reverse
commands C.sub.R to reversing valve 48A to reverse the direction of
pump output shaft 80A commensurate with the flow of pressurized
hydraulic fluid. Specifically, reversing valve 48A must be operated
to allow the chambers within housing 78A in linear motor 50A to be
filled and evacuated at a flow rate equal to that provided by pump
46A. As such, after step 130 is performed, velocity of output shaft
80A is momentarily increased beyond what was previously being
performed at step 100 to achieve the constant output condition.
Output shaft 80A thus operates shaft 82A of linear pump 24A at an
increased rate to reduce pressure drop in linear pump 24A when
shaft 82A is at a reversal position within housing 86A. Output
shaft 80A and piston shaft 82A thereby reverse direction more
quickly than what would have occurred under the control logic
regime.
[0027] At step 140, the control logic detects from linear position
sensor 54A a reversal in direction of output shaft 80A.
Subsequently, at step 150 torque command C.sub.T to motor 44A is
reduced below the levels instructed at step 130 by altering torque
command C.sub.T. Typically, the speed is maintained some amount
higher than what was being commanded under the control logic. The
speed can, however, be reduced below speeds at step 100 in order to
minimally disrupt the constant output condition if needed. At step
160, a reset condition is detected such that the control logic can
be turned on at step 170. For example, a reset condition can be
determined when the pressure in line 88A is sensed as increasing,
indicating that shaft 82A and shaft 78A have completed the reversal
process. Step 170 may occur immediately after a predetermined
period of time, typically a few tens of milli-seconds so as to
minimize disruption of the constant output condition. Thus, when
MCM 42A receives pressure signal S.sub.Pr from pressure sensor 52A,
the control logic can be reestablished such that motor 44A and
reversing valve 48A are again operated under the constant output
condition, as is done at step 100. In other embodiments, the reset
condition can be established based on a predetermined amount of
time, such as a predicted time it takes for linear motor 50A to
complete a reversal process based on the pump speeds of steps 130
and 150.
[0028] The present invention provides a system and method for
reducing pressure variations during operation of a linear pump
system. As discussed above, linear pumps inherently produce a
reduction in output pressure when the piston reverses direction.
With respect to the disclosed embodiment, the output pressure of
the pump is directly proportional to the speed at which the piston
moves, which is determined by the speed at which an electric motor
drives the linear motor actuating the linear pump. Thus, when the
piston stops to reverse direction, the pump pressure drops. The
drop in pump pressure is particularly disadvantageous when constant
output conditions are desired. Furthermore, under constant output
conditions, input speeds to the electric motor driving the linear
motor remain generally constant such that, even under constant
pressure output conditions, the pressure output of the linear pump
exhibits a slight waveform pattern. In one embodiment of the
present invention, the speed of the electric motor is momentarily
increased near the reversal point of the linear motor over the
speed necessary to provide the constant output condition. As such,
the slight waveform pattern of the output pressure is reduced.
[0029] Although the present invention has been described with
respect to controlling a linear pump system based on speed or
torque control of electric motors, the invention can be applied to
other types of linear pump systems or can be used to control the
described system in other ways. Rather than controlling the speed
of the electric motor, the hydraulic fluid pressure can be
controlled using a programmable hydraulic pressure regulator that
controls speed of the linear motor in place of reversing valve 48A.
Specifically, the pressure regulator would be fed with pressurized
hydraulic fluid from the electric motor and gear pump combination
and would feed fluid to either the linear motor or back to the
fluid reservoir. The pressure regulator would then be programmed or
controlled to alter the ratio of hydraulic fluid entering the
linear motor and being fed back to the reservoir. Normally, control
logic would be used to control a constant output condition with the
pressure regulator. However, the control logic could be temporarily
suspended and the output of the pressure regulator to the liner
motor would be increased when the linear motor is at or near the
reversal position. Alternatively, the hydraulic system and
hydraulic pressure regulator of the described embodiment could be
replaced with a pneumatic system and a pneumatic pressure
regulator.
[0030] While the invention has been described with reference to an
exemplary embodiment(s), it will be understood by those skilled in
the art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment(s) disclosed, but that the invention will
include all embodiments falling within the scope of the appended
claims.
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