U.S. patent application number 12/040444 was filed with the patent office on 2009-09-03 for method and device for monitoring and controlling a hydraulic actuated process.
Invention is credited to Peter T. Carstensen.
Application Number | 20090220352 12/040444 |
Document ID | / |
Family ID | 40651402 |
Filed Date | 2009-09-03 |
United States Patent
Application |
20090220352 |
Kind Code |
A1 |
Carstensen; Peter T. |
September 3, 2009 |
Method and Device for Monitoring and Controlling a Hydraulic
Actuated Process
Abstract
A method and system for monitoring and controlling a hydraulic
pump condition. More specifically, the invention relates to a
method and device for monitoring and controlling a hydraulic
actuated process indirectly by monitoring and controlling an
electric motor driving a positive displacement hydraulic pump. This
invention also relates to a precision hydraulic energy delivery
system. Direct coupling of the pump to a primary mover (motor) and
related motor control allows for complete motion control of a
hydraulically driven machine without the use of any downstream
devices. By employing motion control algorithms in the motor
control, the hydraulic output at the pump head is controlled in a
feed forward method.
Inventors: |
Carstensen; Peter T.;
(Adirondack, NY) |
Correspondence
Address: |
FROMMER LAWRENCE & HAUG
745 FIFTH AVENUE- 10TH FL.
NEW YORK
NY
10151
US
|
Family ID: |
40651402 |
Appl. No.: |
12/040444 |
Filed: |
February 29, 2008 |
Current U.S.
Class: |
417/44.11 |
Current CPC
Class: |
F04B 2205/05 20130101;
F04B 2205/09 20130101; F04B 2201/1208 20130101; F04B 2203/0201
20130101; F04B 2201/1202 20130101; F04B 17/03 20130101; F04B
2203/0207 20130101; F04B 2205/13 20130101; F04B 49/065 20130101;
F04B 2203/0209 20130101 |
Class at
Publication: |
417/44.11 |
International
Class: |
F04B 49/06 20060101
F04B049/06 |
Claims
1. A method for monitoring and controlling a hydraulic actuated
process, comprising the steps of: monitoring and controlling an
electric motor driving a positive displacement hydraulic pump
driving said hydraulic actuated process, said monitoring and
controlling being carried out by utilizing an algorithm programmed
into the electric motor drive control that systematically measures
and corrects for any combination of or all three physical
parameters of the motor, pump and hydraulic fluid, thereby
optimizing an applied torque and resultant pump pressure, and
wherein said three physical parameters are windage torque, viscous
torque and coulomb torque, respectively.
2. The method according to claim 1, wherein a plurality of drives,
motors and pumps are electronically line-shafted together providing
precise and stable control of pressure and flow being fed to a
common output header regardless of individual pump characteristics
or fluid condition variations.
3. The method according to claim 1, wherein a precise measurement
and control of press-ram position, and/or ram velocity is
achieved.
4. The method according to claim 1, wherein said method monitors
and/or controls hydraulic pressures created by the pump, which
after mathematical correction for line losses at various flow
rates, mimics load at the press ram.
5. The method of claim 1, wherein the algorithm includes a
subroutine for eliminating a pressure spike; wherein any excess
hydraulic output is used to generate electrical energy when a
pressure spike occurs; the electrical energy being stored in an
energy storage means.
6. The method of claim 1, wherein the algorithm includes a
subroutine for eliminating a pump pressure droop; wherein an input
signal overrides the existing hydraulic output settings when a
pressure droop occurs.
7. The method of claim 1, wherein said drive motor is used both for
delivering energy and for reclaiming energy from the hydraulic
output.
8. The method of claim 1, wherein the algorithm includes a
subroutine for measuring pump shaft torque output and translating
the measured torque output into a pressure delivered signal.
9. The method of claim 1, wherein the algorithm includes a
subroutine for maintaining a constant horsepower from the drive
motor, thereby limiting hydraulic output to the application
similarly.
10. The method of claim 1, further comprising means for storing
electrical energy including reclaimed energy from regeneration, and
for providing for the requirements of high energy applications
typically requiring a hydraulic accumulator.
11. The method of claim 1, wherein the algorithm includes a
subroutine such that a volumetric pulse correlated with the
hydraulic output is used to position the pump cylinders.
12. The method of claim 1, wherein the algorithm includes a
subroutine for detecting a pump leakage rate and outputting an
alarm when a predetermined leakage limit is exceeded.
13. The method of claim 1, wherein the algorithm includes a
subroutine for assessing a pump output level and applying a profile
of torque vs. velocity corresponding to the assessed output
level.
14. A hydraulic pump system comprising: a hydraulic pump; a drive
motor directly coupled to said pump; and a motor control coupled to
said pump for controlling said drive motor; said motor control
employing a motion control algorithm to control a hydraulic output
of the pump, wherein said algorithm measures and corrects for any
combination of or all three physical parameters of the motor, pump
and hydraulic fluid, thereby optimizing an applied torque and
resultant pump pressure, and wherein said three physical parameters
are windage torque, viscous torque and coulomb torque and
application items REDUX V and REDUX P, respectively.
15. The system according to claim 14, wherein a plurality of
drives, motors and pumps are electronically line-shafted together
providing precise and stable control of pressure and flow being fed
to a common output header regardless of individual pump
characteristics or fluid condition variations.
16. The system according to claim 14, wherein a precise measurement
and control of press-ram position, and/or ram velocity is
achieved.
17. The system according to claim 14, wherein said system monitors
and/or controls hydraulic pressures created by the pump, which
after mathematical correction for line losses at various flow
rates, mimics load at the press ram.
18. The system of claim 14, wherein the algorithm includes a
subroutine for eliminating a pressure spike; wherein any excess
hydraulic output is used to generate electrical energy when a
pressure spike occurs; the electrical energy being stored in an
energy storage means.
19. The system of claim 14, wherein the algorithm includes a
subroutine for eliminating a pump pressure droop; wherein an input
signal overrides the existing hydraulic output settings when a
pressure droop occurs.
20. The system of claim 14, wherein said drive motor is used both
for delivering energy and for reclaiming energy from the hydraulic
output.
21. The system of claim 14, wherein the algorithm includes a
subroutine for measuring pump shaft torque output and translating
the measured torque output into a pressure delivered signal.
22. The system of claim 14, wherein the algorithm includes a
subroutine for maintaining a constant horsepower from the drive
motor, thereby limiting hydraulic output to the application
similarly.
23. The system of claim 14, further comprising means for storing
electrical energy including reclaimed energy from regeneration, and
for providing for the requirements of high energy applications
typically requiring a hydraulic accumulator.
24. The system of claim 14, wherein the algorithm includes a
subroutine such that a volumetric pulse correlated with the
hydraulic output is used to position the pump cylinders.
25. The system of claim 14, wherein the algorithm includes a
subroutine for detecting a pump leakage rate and outputting an
alarm when a predetermined leakage limit is exceeded.
26. The system of claim 14, wherein the algorithm includes a
subroutine for assessing a pump output level and applying a profile
of torque vs. velocity corresponding to the assessed output level.
Description
INTRODUCTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for monitoring and
controlling a hydraulic pump. More specifically, the invention
relates to a method and device for monitoring and controlling a
hydraulic actuated process indirectly by monitoring and controlling
an electric motor driving a positive displacement hydraulic
pump.
[0003] This invention also relates to a precision hydraulic energy
delivery system. Direct coupling of the pump to a primary mover
(motor) and related motor control allows for complete motion
control of a hydraulically driven machine without the use of any
downstream devices. By employing motion control algorithms in the
motor control, the hydraulic output at the pump head is controlled
in a feed forward method.
[0004] 2. Background of the Invention
[0005] In the prior art, it is well known that in situations where
higher pressures of fluid movement are desired, a positive
displacement pump is commonly used. A positive displacement pump is
usually a variation of a reciprocating piston and a cylinder, of
which the flow is controlled by some sort of valving. Reciprocal
machinery, however can be less attractive to use than rotary
machinery because the output of a reciprocal machine is cyclic,
where the cylinder alternatively pumps or fills, therefore there
are breaks in the output. This disadvantage can be overcome to a
certain extent by: using multiple cylinders; bypassing the pump
output through flow accumulators, attenuators, dampers; or waste
gating the excess pressure thereby removing the high pressure
output of the flow.
[0006] In addition to uneven pressure and flow output,
reciprocating pumps have the disadvantage of uneven power input
proportional to their output. This causes excessive wear and tear
on the apparatus, and is inefficient because the pump drive must be
sized for the high torque required when the position of the pump
connecting rod or cam, in the case of an axial (wobble plate) pump,
is at an angular displacement versus the crankarm dimension during
the compression stroke that would result in the highest required
input shaft torque.
[0007] Moreover, if the demand of the application varies,
complicated bypass, recirculation, or waste gate systems must be
used to keep the system from "dead-heading." That is, if flow
output is blocked when the pump is in operation, the pump will
either breakdown by the increased pressure or stall. If stalling
occurs, a conventional induction electric motor will burn out as it
assimilates a locked rotor condition with full rated voltage and
amperage applied. Typically systems with fixed displacement pumps
use a relief valve to control the maximum system pressure when
under load. Therefore, the pump delivers full flow at full pressure
regardless of the application thus wasting a large amount of
power.
[0008] In this regard, certain prior art that attempts to correct
the problems associated with torque output of a pump motor should
be noted.
[0009] In U.S. Pat. No. 5,971,721, an eccentric transmission
transmits a torque demand from a reciprocating pump, which varies
with time, to the drive motor such that the torque demand on the
drive motor is substantially constant. The result is the leveling
of torque variation required to drive a positive displacement pump
at the transmission input shaft with the effect of constant pump
output pressure. This is accomplished by means of eccentric pitch
circle sprocket sets with gear belts or eccentric pitch circle
matched gear sets.
[0010] The use of an eccentric gear or sprocket set has a
significant effect on the overall torque requirement and the
magnitude of the discharge pulse of the pump. But, because most
pumps are of a multi-cylinder or are vane or gear types, the pump
input shaft torque requirement would not be perfectly counter-acted
(leveled) by using the reduction pattern developed by eccentrically
matched transmission components.
[0011] In U.S. Pat. No. 5,947,693, a position sensor outputs a
signal by sensing the position of a piston in a linear compressor.
A controller receives the position signal and sends a control
signal to control directional motion output from a linear
motor.
[0012] In U.S. Pat. No. 4,726,738, eighteen or nineteen torque
leads are measured along the main shaft in order to maintain
constant shaft velocity revolution and are translated to a required
motor torque for particular angles of the main shaft.
[0013] U.S. Pat. No. 4,971,522 uses a cyclic lead transducer input
and tachometer signal input to a controller to signal varied cyclic
motor input controls to provide the required motor torque output. A
flywheel is coupled to the motor in order to maintain shaft
velocity. However, the speed of the motor is widely varied and the
torque is varied to a smaller extent.
[0014] U.S. Pat. No. 5,141,402 discloses an electrical current and
frequency applied to the motor which are varied according to fluid
pressure and flow signals from the pump.
[0015] U.S. Pat. No. 5,295,737 discloses a motor output which is
varied by a current regulator according to a predetermined cyclic
pressure output requirement. The motor speed is set to be
proportional to the volume consumed and inversely proportional to
the pressure.
[0016] It is seen from the foregoing that there is a need for
electronic attenuation of the torque profile in a pump. When the
torque profile is compared with the input shaft displacement and
other known factors such as system inertia and response time of the
pump drive etc., a pump can produce constant pressure and therefore
constant flow without the typically associated ripple common to
power pumps for the full range of the designed volumetric delivery,
by driving them in a feed forward method.
[0017] It should be noted that the foregoing hydraulic pumping
systems control output pressure and flow in the micro sense. These
concepts examine modulating the input shaft torque and speed to
provide a constant hydraulic output, whether it is pressure or flow
limited. See U.S. Pat. No. 5,971,721, U.S. Pat. No. 6,494,685, and
U.S. Pat. No. 6,652,239, the entire contents of which are hereby
incorporated by reference.
[0018] It should be further noted that attempts to provide a high
dynamic range of hydraulic flow and pressure during operation of
prior pumping systems required placement of downstream devices in
the liquid path to modulate the hydraulic output. With such
systems, the pump provides the maximum hydraulic flow (as the prime
mover) and the downstream devices adjust the output to match the
application requirements.
[0019] The prime mover in such systems is typically a constant
speed induction motor. In to order to control the hydraulic output,
feedback devices, a processor (be it mechanically balanced or
electronic) and hydraulic servo valves must be placed into the
hydraulic stream for flow and pressure regulation. This treatment
of hydraulic delivery places the "smarts" of the system in the
hydraulic output portion of the system. Disadvantageously, these
systems require many hydraulically driven devices, are mechanically
(geometry) limited, are energy inefficient when total system
performance is scrutinized and have a small range of dynamic
response (typically 10-1). Typical examples of a command-response
curve of a small servo valve and a large servo valve are shown in
FIGS. 9 and 10, respectively.
[0020] Moving the "smarts" directly into the prime mover--by
incorporating variable speed (VFC) controlled motors--has been
attempted. However, this provides limited torque delivery potential
at low speeds, and many feedback devices are required for its
operation. Further, the response of such a system is only generally
higher than the 150 ms range and the energy savings potential is
only in the 50% range.
[0021] These approaches address--in the macro sense--the need for a
prime mover coupled to a power pump that controls the energy, and
therefore the flow (velocity) and pressure (torque) at the input
shaft of the pump. Moreover, the desired system must replicate the
motion control capabilities of existing systems without requiring
the use of downstream flow control devices and feedback
circuits.
[0022] An example of another hydraulic process, also to which one
embodiment of the present invention is directed to, would be
presses (such a metal forging presses and laminating presses)
driven by hydraulic cylinders. In critical applications, valves and
feedback controls are used to control the critical process
variables of applied force and the rate of actuation. A variety of
transducers are employed both to facilitate control and to monitor
the process.
[0023] Additionally, level switches, pressure transducers and flow
switches are often employed to monitor system conditions such as
low oil levels, plugged pump inlet filters and burst hoses. Use of
such transducers adds to the system cost and complexity and is
prone to failure particularly in hostile environments.
[0024] Yet another example of a prior art implementation are
computer controlled servo valves relying on feedback from pressure
transducers, linear position transducers, and flow meters. The
limitations of traditional systems include reliability, slow
response time and control precision. A recent research paper in the
Journal of Materials titled: Modeling and Simulating Metal-Forming
Equipment, by Frazier, Medina, Mullins and Irwin describes the
current art as it is applied to forging presses. The paper
described a metal forging process, which included a cylindrical
upsetting of plain carbon steel. The press was programmed to forge
at a constant velocity of 1.27 cm/sec. A plot of an experimental
and simulated ram velocity profile is shown in FIG. 12. The data
clearly reveals the ramping up and overshoot of the desired
velocity. A brief change in velocity due to impact with the
workpiece is observed near 3.5 seconds.
[0025] FIG. 13 shows an experimental and simulated result for the
ram load as derived from the ram pressure measurement. The plot
reveals that approximately 88.96 kN are needed to overcome the
counter-balance and frictional forces. The load increases rapidly
beginning at approximately 3.5 seconds. This corresponds to impact
with the workpiece. Beginning at approximately 4 seconds, elastic
deformation of the workpiece and tooling ceases and plastic
deformation of the workpiece begins. It is clear from the data that
the press was able to maintain the desired velocity under load, as
long as the load did not increase too rapidly, but as soon there
was a sudden increase in load, the desired velocity is lost.
[0026] It is to be noted that a particular valve command does not
always result in the same flow rate. This is due to the changing
pressure across the servo manifold, clearly revealing that the flow
rate can decrease even as the command for higher velocity
increases.
[0027] As the need for precise control of ram velocity, as well as
position, increases, the need for direct measurement of velocity as
a feedback control signal will become more acute. Therefore,
current techniques for controlling velocity (inversion of
servovalve flow models combined with pressure measurements and
numerical differentiation of displacement measurements) are not
adequate for high performance over a broad range of forging
conditions.
[0028] Experience shows the need for press operators to customize
the press control law in order to achieve the desired velocity
profile for different forming operations. Having a custom control
law for equipment that repeatedly makes the same part for several
weeks or more is satisfactory, but as the need to use the same
equipment for several different parts in a day or custom small lots
increases, having to repeatedly tune the control law can waste
significant time. Control laws, therefore, need to be designed to
be robust so that different loading conditions and velocity
profiles can be handled successfully without the need for
customized tuning.
[0029] The paper's conclusion includes the following statement:
[0030] Current techniques for controlling velocity (inversion of
servovalve flow models combined with pressure measurements and
numerical differentiation of displacement measurements) are not
adequate for high performance over a broad range of forging
conditions.
[0031] Accordingly, there is a need for a system and method of
eliminating the need for servovalves and transducers while
providing more precise control of both hydraulic press ram force
and displacement. There is also a need for a pump and motor
assembly with constant pressure output and a motor controller with
electrical regeneration. With the possibility of directly sensing
workpiece conditions during forming operations, it is demonstrated
that these measurements could be fed back to the metal-forming
equipment for computer control of the forming equipment, thereby
enabling real-time compensation for variations in initial workpiece
and equipment conditions. From a process control perspective, this
approach enables the highest level of robustness and repeatability
in production. Common to each of these factors is the need for
improved control and predictability of the equipment's behavior,
which itself is based on the desire to achieve near-net shapes,
higher-quality end products, higher yields, and better control of
microstructure, especially for hard-to-form materials in metal
forging process.
[0032] More specifically, the current synchronized motion control
methods used in hydraulic applications are not designed to possess
the dynamic hydraulic properties which affect each axis
independently that are responsible for coordinating force inherent
in classical multi-axis, hydraulic machinery, such as for example
shown in FIG. 15. Consequently, these controllers cannot easily
maintain coordination for all operating conditions without
expensive and complicated feedback devices and control loops.
SUMMARY OF THE INVENTION
[0033] It is therefore an object of the invention to device a
control method for use in hydraulic applications that possesses the
dynamic hydraulic properties affecting each axis independently that
are responsible for coordinating force inherent in classical
multi-axis and multi-prime mover, hydraulic machinery.
[0034] A further objective of the invention is to provide
controllers that maintain coordination for all operating conditions
without expensive and complicated feedback devices and control
loops.
[0035] Another object of the present invention is to provide a
method for electronic attenuation of pump torque variation
requirements in order to produce a matched motor torque output that
will result in constant output pressure from a pump.
[0036] Yet another object of the present invention is to provide
monitoring and control factors which vary the power and torque
output of a pump motor based on calculated torque variation
requirements.
[0037] Yet another object of the present invention is to increase
the energy efficiency of a pump system, by providing a force
balanced relationship between the motor output and the
application's hydraulic requirement, thus allowing the use of
energy saving torque drives without incurring the pressure
variations associated with their use.
[0038] Yet another object of the present invention is to decrease
the wear and tear on the pump by providing a substantially constant
force output from the motor of the pump and reduce the amount of
cycles of the pump to the application's requirement.
[0039] Yet another object of the present invention is to provide a
method for electronic attenuation of pump torque variation by
supplying information for design of an electronic transmission
system that can achieve a modulated torque output from the motor to
the pump.
[0040] Yet another object of the present invention is to achieve
precise control of flows and pressures, thus precise control of
press ram velocities, force and position.
[0041] Yet another object of the invention is to create precise
hydraulic output from the pump utilizing an algorithm programmed
into the drive control that systematically measures and corrects
for three key physical parameters of the motor, pump and hydraulic
fluid combination. The three parameters being windage torque,
viscous torque and coulomb torque. One advantage provided by this
aspect of the invention is that the resultant precision allows
multiple (two or more) drive, motor and pump combinations to be
electronically "line-shafted" together while providing precise and
stable control of pressure and flow being fed to a common output
header regardless of individual pump characteristics or fluid
condition variations.
[0042] The invention also provides for development of an empirical
understanding of the positive displacement pump in regards to
slippage (variation from theoretical displacement) throughout the
full pressure/flow delivery range of the pump. This understanding
combined with the drive controller's precise measurement of motor
rpm gives an extremely precise measurement and control of hydraulic
fluid flow rate.
[0043] In turn, knowing the displacement volumes of the cylinder
being actuated and mathematically correcting for elasticity of the
piping system allows for very precise control and or measurement of
press-ram position, and/or ram velocity than may be achieved with
prior art.
[0044] The invention employs the feed forward torque control
aspects of the drive system to precisely monitor and/or control
hydraulic pressures created by the pump which after mathematical
correction for line losses at various flow rates, mimics load at
the press ram. The invention also provides both a more precise and
a more robust method than does the prior art.
[0045] To attain the objects described, there is provided a method
for obtaining a polar map for process control within the electronic
drive of a targeted pump. This polar map is calculated by a
processor or is externally calculated then input into a processor.
Once the torque profile of the pump is obtained and translated into
a polar map, the processor can compare the shaft displacement angle
of the pump input shaft to the reference polar map. The processor
can also take into account selected factors such as the response
time of the pump drive, the motor inductive reactance, system
inertia, application characteristics of the pump, and regenerative
energy during deceleration of the pump.
[0046] Using selected factors and the comparison results, the
processor signals the motor controller to vary the amperage,
voltage, and frequency applied to the motor in order to regulate
the torque output of the pump motor. With an accurately modulated
motor torque output in concert with the established polar map (for
the targeted pump), the pump output pressure will remain constant
regardless of the pump's crank arm location or the velocity of
fluid flow.
[0047] It is also an object of the present invention to provide a
hydraulic energy delivery system that allows for complete motion
control of a hydraulically driven machine with the use of minimal
or no downstream feedback devices.
[0048] It is therefore a further object of the present invention to
provide control factors which vary the power and torque output of a
pump motor by employing motion control algorithms.
[0049] To attain the objects described, there is provided direct
coupling of a positive displacement pump to a pump drive motor and
related controls. By employing motion control algorithms into the
motor control, the hydraulic output at the pump head will
simultaneously follow. Control features listed herein may be
integrated into the system by developing algorithms and subroutines
for the control system coupled to the pump.
[0050] These and other objects and advantages are provided by the
present invention, preferred embodiments of which are described in
the paragraphs below.
[0051] All features listed herein may be integrated into the system
by developing algorithms and subroutines for monitoring and
controlling the system coupled to the hydraulic pump.
[0052] The present invention will now be described in more complete
detail with reference being made to the figures identified
below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0053] The following detailed description, given by way of example
and not intended to limit the present invention solely thereto,
will best be appreciated in conjunction with the accompanying
drawings, wherein like reference numerals denote like elements and
parts, in which:
[0054] FIG. 1 is a block diagram of the steps required for a method
of electronic attenuation of torque profile and the resulting
control of the pump;
[0055] FIG. 2 is a graph depicting individual input torque
variation for each node of a triplex pump based upon pump input
shaft rotational degrees;
[0056] FIG. 3 is a graph depicting a percentile summation of input
torque variation compared to angular displacement of the input
shaft of a triplex pump;
[0057] FIG. 4 is a table depicting variations of input torque above
and below the mean for triplex pumps in relation to the linear
distance between the plunger/piston pivot point and the throw pivot
point multiplied by the throw radius;
[0058] FIG. 5 is a graph depicting a plotting of geometric distance
variation points based upon the summation of total torque variation
for a triplex pump;
[0059] FIG. 6 is a polar map depicting the torque profile versus
angular displacement of a pump input shaft;
[0060] FIG. 7 is a diagram illustrating a precision hydraulic
delivery system according to the present invention;
[0061] FIG. 8 is a graph depicting a profile of torque vs. velocity
for an exemplary hydraulic system in accordance with the present
invention;
[0062] FIG. 9 is a graph depicting command, response curves of a
small servo valve;
[0063] FIG. 10 is a graph depicting command, response curves of a
large servo valve;
[0064] FIG. 11 is a schematic of a hydraulic press system according
to one embodiment of the invention;
[0065] FIG. 12 is a graph depicting commanded, simulated and
experimental ram velocity profiles not within normal
boundaries;
[0066] FIG. 13 is a graph depicting simulated and experimental ram
load profiles not within normal boundaries;
[0067] FIG. 14 is a diagram of "electronic line-shafting" with a
master/slave configuration of multi-drop positive displacement
hydraulic pumps, according to one embodiment of the invention;
[0068] FIG. 15 is a schematic of a typical non-compensated
electronic line-shafting in a multi-axis hydraulic machinery;
and
[0069] FIG. 16 is a diagram of a system incorporating the Learn TQ
items: Coulomb torque, Windage, viscous coefficient and application
characteristics: Redux P, Redux V feed-forward compensation
algorithm, according to one embodiment of the invention.
[0070] The description of the various elements of the invention
will be discussed in detail in the following sections.
DETAILED DESCRIPTION OF THE INVENTION
[0071] The instant invention will now be described more fully
hereinafter with reference to the accompanying drawings, in which
preferred embodiments of the invention are shown. This invention
may, however, be embodied in many different forms and should not be
construed as limited to the illustrated embodiments set forth
herein. Rather, these illustrated embodiments are provided so that
this disclosure will be thorough and complete, and will fully
convey the scope of the invention to those skilled in the art.
[0072] Referring now to the drawings in detail wherein like
numerals refer to like elements throughout the several views where
Blocks 1-5 of FIG. 1 depict the development of a baseline polar
guide of the torque profile for the targeted pump.
[0073] In Block 1 of FIG. 1 and graphically depicted in FIG. 2, the
output characteristic of volumetric displacement would directly
relate to the input torque variations above 10 and below 12 the
comparative mean 14. The processor identifies the output discharge
characteristics such as the number of plungers, pistons in a piston
pump, or vane/gear in a rotary pump. The processor also utilizes a
comparative mean where, the comparative mean is representative of
the basic torque requirement of the pump input shaft rated at a
specific output pressure of the pump. A pulsation pattern 16 would
be repeated at the same rate per revolution as the number of the
pump's volumetric displacement cavities. As illustrated in FIG. 2,
a triplex positive displacement pump would repeat a pulsation
pattern 16 every 120 degree rotation of the pump input shaft. These
torque variations above 10 and below 12 the mean 14 are calculated
and recorded for Block 1 of FIG. 1.
[0074] For other pumps such as a quintaplex plunger pump, which
incorporates five plungers, a pulsation pattern would be produced
five times per revolution of the pump input shaft, repeating every
72 degrees if the output pressure is to remain constant; and for a
rotary vane pump with nine vanes selected, the pulsation pattern
would repeat every 40 degree rotation of the pump input shaft if
the output pressure is to remain constant.
[0075] In Block 2 of FIG. 1 and depicted graphically in FIG. 3, the
torque profile versus displacement angle of the targeted pumping
system is the summation of the torque requirement for each
volumetric displacement component, depicting a percentage above
mean 18 and the percentage below mean 20.
[0076] In Block 3 of FIG. 1, the magnitude of the input torque
variation for the power pump is determined by the processor, where
the magnitude of the torque variation is the number of volumetric
displacement cavities activated in one revolution and the
relationship "Q". The calculation "Q" is the linear distance "L"
between the plunger/piston pivot point and the throw pivot point
multiplied by the throw radius "R"; "Q=LR". FIG. 4 in table form,
depicts the percentile variations of input torque above and below
the mean for triplex pumps with various "Q".
[0077] FIG. 5 graphically depicts the total torque variation to
show a torque profile for a triplex pump (three volumetric
displacements per revolution) with a "Q" at 4:1 with variations
shown above and below the mean. The mean is representative of the
basic rms (root mean squared) torque requirement of the pump input
shaft rated at a specific output pressure of the pump versus the
angular displacement of the pump crank shaft. The relationship of
"Q" and the effect it has on torque variation would also apply to
rotary pumps. A plotted geometric distance variation using t1-t15
(as plotting points) is then imposed on the torque profile.
[0078] In Block 4 of FIG. 1 and graphically depicted in FIG. 6, a
pump polar map is determined based on the torque profile and the
input shaft angular displacement of the pump. The center 34 of the
polar map is to represent zero torque. The incremental lines 36
depicted orbitally are the angular displacement of the targeted
pump's input shaft. The plotted pump torque variation curve 38 that
occurs above and below the mean 40 is to be considered a geometric
percentage of the summation of the torque requirement of each of
the volumetric displacement components of the targeted pump.
[0079] The distance of each point plotted on the polar map's center
from the base diameter's center is the geometric distance variation
(over or under) of the base radii percentile established from
torque versus the pump input shaft displacement angle (t1 thru
t15). The geometric distance variations are the plotting points
determined in FIG. 5. The torque versus angular displacement
profile of the pump system selected is to become the reference
polar guide for the comparitor algorithm in the processor in Block
5 of FIG. 1. The reference polar guide determined by the processor
in Blocks 1-5 can also be determined externally from the processor
and then input into the processor.
[0080] Blocks 6-10 of FIG. 1 are the operating steps from
electronic attenuation of the torque profile to provide a constant
output pressure at the pump, wherein Block 6 indicates the
transmission of the angular displacement of the input shaft of a
pump in operation. A pulse transmitter mounted on the input shaft
relays to a counter--which is part of the processor--the angular
position of the pump drive.
[0081] In Block 7 of FIG. 1, an electronic processor gathers this
output shaft orientation feedback information, and processes the
angular displacement data. The processor then attenuates from the
peak requirement of the pump, the output torque of the drive
compared to the predetermined reference polar map of Block 5. A
corresponding torque command value is then selected.
[0082] In Block 8 of FIG. 1, other inputs of system readings such
as system inertia, parasitic leads, off throttle friction, response
time of the pump, motor inductive reactance, application
characteristics of the pump, regenerative energy during
deceleration of the pump, and translation speed can be selectively
factored into the processor algorithm for changes in process
control.
[0083] In Block 9 of FIG. 1, based upon the inputs of Blocks 7 and
8, the processor of the electronic drive signals the motor
controller to apply the correct amperage, voltage, and frequency to
the motor which then provides the correct torque according to the
angular displacement of the pump input shaft.
[0084] In Block 10 of FIG. 1, the resultant signal to the motor
controller and motor will drive the pumping system to produce
constant pressure at the full range of the designed system flow
volume regardless of pump radial crankshaft location and the
velocity of the fluid pumped.
[0085] Block 11 of FIG. 1, depicts the use of this method in future
systems where information gathered from pump operation by this
method can be used to design more responsive components such as
transmissions and electronic drives. More responsive components
would decrease the time increments between Blocks 6-10. As response
times are decreased, the torque output produced for indicated
angular displacements will increase in efficiency.
[0086] FIG. 7 depicts a precision hydraulic delivery system 71
according to the present invention. Advantageously, this system
provides direct coupling of a positive displacement pump 72 to a
prime mover 73 and related motor drive control 74. The prime mover
73 in the pump system shown is, for example, a constant speed
induction motor. The motor has, for example, a 1000-1 (torque) turn
down ratio. The motor control 74 may be, for example, an electronic
servo or hydraulic type motor control. Direct coupling of the pump
72 to the motor 73 and motor control 74 allows for complete motion
control of the pump 72 without requiring any of the downstream flow
control devices, feedback devices, hydraulic energy storage devices
(accumulators) or energy dissipation devices normally used in
conventional pump systems.
[0087] The system in FIG. 7 employs motion control algorithms in
the electronic motor control so that the hydraulic output at the
pump head will simultaneously follow the control signals generated
by the algorithms and sent to the motor. This ability allows a
large dynamic range of hydraulic energy to be delivered by placing
the "smarts" of the system directly into the electrical handling
capabilities of the prime mover circuit. The modulation of torque
(resulting in hydraulic pressure) and velocity (resulting in
hydraulic flow) are most efficiently handled within the electronic
servo or hydraulic type control of the primary mover.
[0088] The teachings of U.S. patent application Ser. No. 09/821,603
and U.S. Pat. No. 5,971,721, which are hereby incorporated by
reference, may be incorporated into the macro motion control
capabilities described herein to provide improved system response,
"keypad" tuning of a hydraulic application, very high systemic
efficiency characteristics and simplified hydraulic circuitry.
[0089] Several exemplary control features of the present invention
are described in greater detail below. These features represent
only a fraction of the possible features that may be electronically
integrated into a hydraulic delivery system by control algorithms
and subroutines for a prime mover servo control system coupled to a
pump.
[0090] "SLAM Absorption" Feature
[0091] The "SLAM" subroutine is an energy absorbing function that
provides hydraulic component protection by eliminating pressure
spikes. In some applications, a "spike" in pressure occurs when
flow volume is rapidly reduced. This normally occurs when, for
example, a directional control valve is shut, and is typically
followed by the pressure relief valve waste-gating the excess flow
to a tank until the system flow returns to normal.
[0092] This condition is undesirable, and to eliminate it the
present invention has a discrete input that activates the "SLAM"
function when such an event occurs. A determination as to the
likelihood of such an event is made during commissioning. Use of
the "Position Sensing" feature (described below) allows the "SLAM"
subroutine to be invoked when necessary. The "SLAM" feature causes
the electronic drive to capture the inertial energy of the system
via the regenerating capabilities of the prime mover (turning the
motor into a generator), and to store this captured electrical
energy in the electronic drive (see "energy storage system" below).
The normally waste-gated energy is thus captured by the drive
during this function, thereby saving energy and reducing wear on
the hoses and hydraulic system.
[0093] "JAB Applied" Feature
[0094] The "JAB" feature eliminates pressure "droop" by invoking a
rapid pump acceleration feature of user defined time and amplitude,
that is applied over and above the normal flow or pressure input
commands. In some instances, a rapid increase in flow volume
required by the application will cause the pressure to droop until
high inertia components in the pumping system are accelerated to
the required delivery velocity. If this droop is undesirable in a
specific application, a discrete input can be used to activate this
"JAB" rapid acceleration feature that is applied over and above the
normal flow or pressure input commands that are controlling the
pump.
[0095] Dual Function Pump/Motor Feature
[0096] This feature provides for single unit hydraulic motor/pump
functions from the same hydraulic device for energy delivery and
reclamation (regeneration and storage).
[0097] "Pressure Loop" Feature
[0098] This feature provides a pump shaft torque output measurement
method which is translated into a pressure delivered signal.
[0099] "Constant HP System" Feature
[0100] This feature provides a constant horse power electrical
drive system for maintaining an energy ceiling regardless of the
delivered flow volume.
[0101] "Energy Storage System" Feature
[0102] This feature provides an electrical energy storage device in
the drive system for reclamation of energy from regeneration (see
"Dual function pump/motor" and "SLAM" function), or for high output
energy spikes typically provided by a hydraulic accumulator.
"Position Sensing" feature
[0103] According to this feature, a volumetric pulse correlates to
a pump output volume that will cause an incremental pulse to occur.
This volumetric pulse (output by the electronic drive module
inclusive of compensation factors Pump TQ Learn and application
items REDUX V and REDUX P) is used for the positioning of known
hydraulic cylinders and their corresponding volumetric
displacements.
[0104] "Leakage Detection" Feature
[0105] This subroutine is used to detect user defined excessive
hydraulic leakage rates. This feature compares the output of the
"Position Sensing" function to a known limit during a move, and if
there is a discrepancy beyond a predetermined amount, an alarm
output results.
[0106] "Output Gain Offset" Feature
[0107] This feature allows the user to assess the output gain
levels of the hydraulic delivery (pressure vs. flow) in order to
overcome any application flow restrictions or mechanical variation.
The assessment results in a profile of torque vs. velocity for the
desired hydraulic output.
[0108] FIG. 8 shows an example 5 point torque profile,
including:(1) Gain Zero 801, (2) Gain Lo 802, (3) Gain Mid 803, (4)
Gain Hi 804, and (5) Gain Max 805. The five gain points plotted on
the graph are described below.
[0109] 1. Gain Zero: For "pressure delivered" vs. "zero velocity"
(the RPM of this point is always anchored at zero RPM), the Gain
Zero corrects the pressure reference command as the velocity
decreases to "0" to compensate for systemic "sticktion".
[0110] 2. Gain Low: For "pressure delivered" vs. "velocity," the
Gain Low corrects the pressure reference command as the velocity
increases/decreases to compensate for system losses. Gain Low RPM:
Applies the "GAIN LOW" value when the pump system is operating
within a user defined RPM range (typically, 0 to 50 RPM). The gain
is applied as a tapered offset beginning with the "GAIN ZERO" value
at 0 RPM, and ending with the "GAIN LOW" value at the "GAIN LOW
RPM." Any operation above this speed is ramped to the "GAIN MID"
point.
[0111] 3. Gain Mid: For "pressure delivered" vs. "velocity," the
Gain Mid corrects the pressure reference command as the velocity
increases/decreases to compensate for system losses.
[0112] Gain Mid RPM: Applies the "GAIN MID" value when the pump
system is operating within a user defined RPM range (typically, 50
to 700 RPM). The gain is applied as a continued offset beginning
with the "GAIN LO" value at the "GAIN LO RPM" and ending with the
"GAIN MID" value at the "GAIN MID RPM." Any operation above this
speed is ramped to the "GAIN HI" point.
[0113] 4. Gain High: For "pressure delivered" vs. "velocity," the
Gain High corrects the pressure reference command as the velocity
increases/decreases to compensate for system losses.
[0114] Gain High RPM: Applies the "GAIN HIGH" value when the pump
system is operating within a user defined RPM range (typically, 701
to the maximum RPM). The gain is applied as a continued offset
beginning with the "GAIN MID" value at the "GAIN MID RPM" and
ending with the "GAIN HIGH" value at the "GAIN HIGH RPM." Any
operation above this speed is ramped to the GAIN MAX RPM point.
[0115] 5. Gain Max: For pressure delivered vs. DRIVE SPEED MAX
velocity (the RPM of this point is always anchored at the drive
speed max RPM), the Gain Max attenuates the pressure reference
command as the velocity increases/decreases to compensate for
system losses.
[0116] The invention according to one embodiment of the invention
is a method for monitoring and controlling a hydraulic pump driving
a metal forging press. A simplified block diagram of a hydraulic
press system 110, for example a metal forging press, is shown in
FIG. 11. The system 110 is powered by an electric motor that drives
a hydraulic pump 118. Transient demands for high ram speeds are met
by an accumulator system 120. A counter-balance is employed to
support and return the main ram 112 to the top of its stroke after
the completion of a forging operation. The hydraulic manifold 114
controls the flow of fluid to the main ram cylinder 116 and to the
tank 122. The metal forging can be a cylindrical upsetting of, for
example, plain carbon steel. The press can be programmed to forge
at any constant velocity, for example at 1.27 cm/sec.
[0117] One embodiment of the invention is an application of an
"electronic line-shafting" control technique which serves to
replicate and even improve the historical, hydraulic multi-axis
coordinated motion control techniques. This technique incorporates
a method of servo-driven hydraulic prime-mover control on
multi-axis hydraulic applications with the Learn TQ, Redux V, and
Redux P compensation factors incorporated for direct feed forward
precise hydraulic output without the need for external feedback
devices. Redux P relates to the compensation or reduction or
compression of a fluid or system capacitance, while Redux V relates
to the restrictive flow of the pump. The result demonstrates that
the "electronic line-shafting" technique significantly improves the
coordination, robustness, and overall stability of hydraulic power
output subjected to realistic physical limitations.
[0118] Therefore, key aspects of the present invention include
precise control of press ram velocities, force and position
requires precise control of flows and pressures. To create precise
hydraulic output from the pump, the invention utilizes an algorithm
programmed into the drive control named Pump Torque Learn
(abbreviated Learn TQ) that systematically measures and corrects
for three key physical parameters of the motor, pump and hydraulic
fluid combination. These three factors are accounted for to
understand the relationship between applied torque and resultant
pump pressure; a relationship that changes over the range of
operating speeds of the pump. These parameters are windage torque,
viscous torque and coulomb torque, respectively. A separate
advantage provided by this aspect of the invention is that the
resultant precision allows multiple (two or more) drive, motor and
pump combinations 125 to be electronically "line-shafted" together
while providing precise and stable control of pressure and flow
being fed to a common output header 130 regardless of individual
pump characteristics or fluid condition variations. A multi-drop
set-up for positive displacement hydraulic pumps used in
"line-shafting" hydraulic supplies, according to one embodiment of
the invention is shown in FIG. 14. A further example of a system
150 incorporating the Learn TQ, Redux P, Redux V feed forward
compensation algorithm according to one embodiment of the invention
is shown in FIG. 16.
[0119] The invention also incorporates development of an empirical
understanding of the positive displacement pump in regards to
slippage (variation from theoretical displacement) throughout the
full pressure/flow delivery range of the pump. This understanding
combined with the drive controller's precise measurement of motor
rpm gives an extremely precise measurement and control of hydraulic
fluid flow rate. In turn, knowing the displacement volumes of the
cylinder being actuated and mathematically correcting for
elasticity of the piping system allows for very precise control and
or measurement of press-ram position, and/or ram velocity than may
be achieved with prior art.
[0120] As explained above, one embodiment of the invention employs
the feed forward torque control aspects of the drive system to
precisely monitor and/or control hydraulic pressures created by the
pump which after mathematical correction for line losses at various
flow rates, mimics load at the press ram. The invention therefore
provides both a more precise and a more robust method than does
prior art.
[0121] Accordingly, some of the benefits derived from the present
invention are:
[0122] 1. More precise control of ram velocity profile than prior
art.
[0123] 2. Without relying on external sensors mounted at the
process but rather using motor current signature analysis combined
with motor shaft encoder data, the drive controller may be taught
to recognize, report, and/or take action against process anomalies.
Such anomalies would show themselves as velocity (flow rates),
current draws and torques (pressures) that are deemed to be outside
normal process parameters. Examples include:
[0124] a) A plugged inlet filter would cause a low current
signature combined with a high velocity (motor rpm) than would be
expected for the flow and pressure being delivered.
[0125] b) A burst hydraulic hose would result in an abrupt shift to
an abnormally high flow rate.
[0126] c) Metal being forged that was not within proper metallurgy
specifications or a billet not heated to the desired temperature
would produce ram speed, displacement and force characteristics
that the computer could recognize or simply log as being not within
normal boundaries (such as shown in FIGS. 12 and 13).
[0127] The ability to "electronically line-shaft" two or more pump,
motor, and drive systems to feed a common hydraulic output header
while maintaining precise and stable control of both total flow and
common pressure.
[0128] Thus, while fundamental novel features of the invention are
shown and described and pointed out, it will be understood that
various omissions and substitutions and changes in the form and
details of the devices illustrated, and in their operation, may be
made by those skilled in the art without departing from the spirit
of the invention. For example, it is expressly intended that all
combinations of those elements and/or method steps which perform
substantially the same function in substantially the same way to
achieve the same results are within the scope of the invention.
Moreover, it should be recognized that structures and/or elements
and/or method steps shown and/or described in connection with any
disclosed form or embodiment of the invention may be incorporated
in another form or embodiment. It is the intention, therefore, to
be limited only as indicated by the scope of the claims appended
hereto.
* * * * *