U.S. patent application number 11/977471 was filed with the patent office on 2008-05-01 for valve, controller, system and method providing closed loop current control of a voice coil using pulse width modulation drive elements.
This patent application is currently assigned to Enfield Technoloties, LLC. Invention is credited to Daniel S. Cook.
Application Number | 20080099090 11/977471 |
Document ID | / |
Family ID | 39474993 |
Filed Date | 2008-05-01 |
United States Patent
Application |
20080099090 |
Kind Code |
A1 |
Cook; Daniel S. |
May 1, 2008 |
Valve, controller, system and method providing closed loop current
control of a voice coil using pulse width modulation drive
elements
Abstract
A linear voice coil actuator is described, specifically applied
to a fluid power valve. The valve includes at least one inlet port
and at least one outlet port. A spool controls fluid flow between
the inlet port and outlet port. At least one counter-acting spring
asserts a force on the spool. The valve also includes a linear
voice coil to regulate movement of the spool. The linear voice coil
responds to a pulse width modulated signal, wherein the pulse width
modulated signal is based on a determined current in the linear
voice coil. Electromagnetic interference filtering may also be
used. A controller, system and method are also described.
Inventors: |
Cook; Daniel S.;
(Terryville, CT) |
Correspondence
Address: |
HARRINGTON & SMITH, PC
4 RESEARCH DRIVE
SHELTON
CT
06484-6212
US
|
Assignee: |
Enfield Technoloties, LLC
|
Family ID: |
39474993 |
Appl. No.: |
11/977471 |
Filed: |
October 25, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60854562 |
Oct 25, 2006 |
|
|
|
Current U.S.
Class: |
137/625.65 ;
251/129.09; 332/109; 360/78.12 |
Current CPC
Class: |
F16K 31/04 20130101;
Y10T 137/87217 20150401; Y10S 251/905 20130101; F15B 13/0446
20130101; F16K 11/07 20130101; F16K 37/0041 20130101; Y10T
137/86622 20150401; H01F 7/1844 20130101; F15B 13/0402 20130101;
Y10T 137/86614 20150401; Y10T 137/7761 20150401; F16K 31/02
20130101; Y10T 137/0396 20150401; F16K 27/048 20130101; F16K
31/0613 20130101; Y10T 137/2529 20150401; F16K 27/041 20130101 |
Class at
Publication: |
137/625.65 ;
251/129.09; 332/109; 360/78.12 |
International
Class: |
F15B 13/044 20060101
F15B013/044 |
Claims
1. A valve comprising: at least one inlet port; at least one outlet
port; a spool configured to control fluid flow between the inlet
port and outlet port; at least one counter-acting spring configured
to assert a force on the spool; and a linear voice coil configured
to regulate movement of the spool; wherein the linear voice coil is
configured to respond to a pulse width modulated signal, wherein
the pulse width modulated signal is based on at least a determined
current in the linear voice coil.
2. The valve of claim 1, wherein the pulse width modulated signal
minimizes voltage and current ripples in the linear voice coil.
3. The valve of claim 1, wherein providing the pulse width
modulation drive signal uses an H-bridge topology that allows for
bi-directional drive currents.
4. The valve of claim 1, wherein a switching frequency of the pulse
width modulation drive signal is between about 20 kHz and about 1
MHz.
5. A controller comprising: a receiver configured to receive a
current signal based upon a determined current through a linear
voice coil; and a processor configured to produce a control signal
based on at least the received current signal, wherein the control
signal is to be used by a pulse width modulation driver to generate
a pulse width modulation drive signal to be applied to the linear
voice coil.
6. The controller of claim 5, further comprising electromagnetic
interference filter circuitry configured to minimize voltage and
current ripples in the linear voice coil.
7. The controller of claim 5, wherein generating the pulse width
modulation drive signal uses an H-bridge topology that allows for
bi-directional drive currents.
8. The controller of claim 5, wherein a switching frequency of the
pulse width modulation drive signal is between about 20 kHz and
about 1 MHz.
9. A system comprising: a linear voice coil actuated valve
comprising: a spool; at least one counter-acting spring configured
to apply a force on the spool; and a linear voice coil configured
to regulate a fluid flow through the valve by moving the spool; a
sensor configured to determine a current in the linear voice coil;
a processor configured to produce a control signal based at least
on the determined current; and a pulse width modulation driver
responsive to the control signal configured to generate a pulse
width modulation drive signal to be applied to the linear voice
coil.
10. The system of claim 9, further comprising electromagnetic
interference filter circuitry configured to minimize voltage and
current ripples in the linear voice coil.
11. The system of claim 9, wherein the sensor comprises at least
one of a Hall Effect current sensor, a toroidal Hall Effect sensor,
current sense resistors, and transformers.
12. The system of claim 9, wherein the sensor further comprises a
difference amplifier circuit.
13. The system of claim 13, wherein the difference amplifier
circuit has a common mode rejection ratio of at least -40 dB.
14. The system of claim 13, wherein common mode rejection ratio
limits are applied at least to a fifth harmonic of the pulse width
modulation drive signal.
15. The system of claim 9, wherein generating the pulse width
modulation drive signal uses an H-bridge topology that allows for
bi-directional drive currents.
16. The system of claim 9, wherein a switching frequency of the
pulse width modulation drive signal is between about 20 kHz and
about 1 MHz.
17. A method comprising: providing a pulse width modulation drive
signal to a linear voice coil of a linear voice coil actuated
valve; determining a current through the linear voice coil; and
adjusting the pulse width modulation drive signal based at least
upon the determined current; wherein the linear voice coil is used
to move a spool having a force applied to the spool by at least one
counter-acting spring.
18. The method of claim 17, further comprising an electromagnetic
interference filter designed to minimize voltage and current
ripples in the linear voice coil in order to produce less
electromagnetic radiation.
19. The method of claim 17, wherein determining the current
comprises using at least one of a Hall Effect current sensor, a
toroidal Hall Effect technique, current sense resistors, and
transformers.
20. The method of claim 17, wherein providing the pulse width
modulation drive signal uses an H-bridge topology that allows for
bi-directional drive currents.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application claims priority under 35 U.S.C.
.sctn.119(e) from Provisional Patent Application No. 60/854,562,
filed Oct. 25, 2006, the disclosure of which is incorporated by
reference herein in its entirety.
TECHNICAL FIELD
[0002] This invention relates generally to control systems and,
more specifically, relates to controllers and systems using
electronically controlled valves, electronically controlled valves,
and portions thereof.
BACKGROUND
[0003] Control systems for electronically controlled valves control
many different types of fluids for many different purposes. While
control systems, their controllers, and the associated
electronically controlled valves have many benefits, these control
systems, controllers, electronically controlled valves and portions
thereof may still be improved.
[0004] It is desirable, in some high performance pneumatic
proportional and servo-valve applications, to be capable of moving
the valve element (e.g., the spool) quickly and accurately. It is
also desirable to locate the main drive elements close to the
valve; this may be considered important enough that the drive
elements are typically located within the primary envelope of the
valve body or case.
[0005] A common classical approach to driving a voice coil is to
apply voltages to the coil without controlling the coil current
directly. This method results in poorer performance of the voice
coil mechanical system due to inductance and generator effects of
the coil.
[0006] To overcome these problems, a trans-conductance amplifier
which will automatically control the current through the coil with
high fidelity and bandwidth may be implemented. A common approach
is to construct a `totem pole` dual transistor pair linear drive
amplifier (e.g., similar to a Class AB drive stage). This method of
power drive is inherently inefficient, especially for high currents
or power supply voltages. High thermal power dissipation limits or
prevents efficient application of a linear drive element internal
to an electronic or electromechanical element (e.g., voice coil
valve body, DC motor, heater element, etc).
SUMMARY
[0007] An exemplary embodiment in accordance with this invention is
a valve (e.g., a linear voice coil actuated fluid power valve). The
valve includes at least one inlet port and at least one outlet
port. A spool controls fluid flow between the inlet port and outlet
port. At least one counter-acting spring asserts a force on the
spool. The valve also includes a linear voice coil to regulate
movement of the spool. The linear voice coil responds to a pulse
width modulated signal, wherein the pulse width modulated signal is
based on a determined current in the linear voice coil.
[0008] Another exemplary embodiment in accordance with this
invention is a controller to control a pulse width modulation
driver for a linear voice coil. The controller includes a receiver
to receive a current signal based upon a determined current through
a linear voice coil. A processor produces a control signal based on
the received current signal. The control signal is to be used by
the pulse width modulation driver to generate a pulse width
modulation drive signal to be applied to the linear voice coil to
move a spool having a force applied to the spool by at least one
counter-acting spring.
[0009] A further embodiment in accordance with this invention is a
system. The system includes a linear voice coil actuated fluid
power valve. The valve has a spool. At least one counter-acting
spring applies a force on the spool. A linear voice coil regulates
a fluid flow through the valve by moving the spool. The system also
includes a sensor to determine a current in the linear voice coil.
A processor produces a control signal based at least on the
determined current. A pulse width modulation driver generates a
pulse width modulation drive signal to be applied to the linear
voice coil in response to the control signal.
[0010] Another exemplary embodiment in accordance with this
invention is a method. The method includes providing a pulse width
modulation drive signal to a linear voice coil of a linear voice
coil actuated fluid power valve. The current in the linear voice
coil is determined. The pulse width modulation drive signal is
adjusted based at least upon the determined current. The linear
voice coil is used to move a spool having a force applied to the
spool by at least one counter-acting spring.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The attached Drawing Figures include the following:
[0012] FIG. 1 is a block diagram of a system including a portion
for controlling an electronically controlled valve and the
electronically controlled valve;
[0013] FIG. 2 is a cutaway, perspective view of an exemplary
pneumatic valve;
[0014] FIG. 3 is a view of the motor housing retainer coupled to
the motor housing and also of the coil header assembly and
spool;
[0015] FIG. 4 is a circuit diagram of a first exemplary valve
controller;
[0016] FIG. 5 is a circuit diagram of a second exemplary valve
controller;
[0017] FIG. 6 is a block diagram illustrating another system for
controlling an electronically controlled valve;
[0018] FIG. 7 is a block diagram illustrating circuitry for power
and indication for use with valve controllers;
[0019] FIG. 8 is a block diagram illustrating circuitry for analog
signal interfaces for use with valve controllers;
[0020] FIG. 9 is a block diagram illustrating of a connector and
indication interface circuitry for use with valve controllers;
and
[0021] FIG. 10 shows a logic flow diagram of a method in accordance
with an embodiment of this invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0022] Referring now to FIG. 1, a block diagram is shown of an
exemplary system 100 having a portion for controlling an
electronically controlled valve 120. System 100 also includes in
this example the electronically controlled valve 120. FIG. 1 is a
simplistic, high-level view of a system 100 that includes a control
input 105, an adder 110, a spool position controller 115, the
electronically controlled valve 120, and a feedback sensor module
150 that takes an input from one or more feedback sensors (not
shown) and that produces one or more feedback signals 151. A valve
controller 160 includes the adder 110, the spool position
controller 115, and the feedback sensor module 150. The
electronically controlled valve 120 includes a spool actuator 125,
such as a voice coil, a spool 130, a body 135, an input 140, and an
output 145.
[0023] The electronically controlled valve 120 controls fluid
(e.g., air, gas, water, oil) 141 flow through the electronically
controlled valve 120 by operating the spool 130. The spool actuator
125 controls movement of the spool 130 based on one or more control
signals 116 from the spool position controller 115. The spool
position controller 115 modifies the one or more control signals
116 based on the one or more input signals 111, which include
addition of the control input signal 105 and the one or more
feedback signals 151. The feedback sensor module 150 can monitor
the spool actuator 120 (e.g., current through the spool actuator),
a sensor indicating the position of the spool 130, or sensors
indicating any number of other valve attributes (e.g., pressure or
flow rate of the fluid 141). Aspects of the present invention are
related to a number of the elements shown in FIG. 1.
[0024] Now that an introduction has been given with regard to an
exemplary system 100, descriptions of exemplary aspects of the
invention will now be given.
[0025] Turning to FIG. 2 in addition to FIG. 1, a cutaway,
perspective view is shown of an exemplary pneumatic valve 200. The
pneumatic valve 200 includes an electronics cover 205, a motor
housing retainer 207, a motor housing 210, an upper cavity 215, a
lower cavity 216, a coil header assembly 220, a spool 230, a sleeve
260, a lower spring 240, an upper spring 245, external ports 270,
271, 280, 281, and 282, circumferentially spaced internal ports
270a, 271a, 280a, 281a, and 282a, and a valve body 290. Coil header
assembly 220 includes a voice coil portion 222 having a voice coil
221 and an overlap portion that overlaps a portion of the spool 230
and connects the spool 230 to the coil header assembly 220. The
spool actuator 125 of FIG. 1 includes, in the example of FIG. 2,
motor housing 210, coil header assembly 220, upper spring 245, and
lower spring 240. It is noted that a view of the motor housing 210
is also shown in, e.g., FIG. 3 and that at least a portion of the
motor housing 210 is magnetized in order to be responsive to the
voice coil 221. A cable 1720 couples the motor housing retainer 207
to the voice coil 221.
[0026] In this example, a top surface 211 of the motor housing 210
contacts a bottom surface 208 of motor housing retainer 207. The
motor housing 210 is therefore held in place by the motor housing
retainer 207, and the motor housing retainer 207 is a printed
circuit board. The motor housing retainer 207 serves multiple
purposes.
[0027] Patent application Ser. No. ______, filed on Sep. 19, 2007
and titled "Retaining Element for a Mechanical Component" describes
the motor housing retainer 207 in further detail. Patent
application Ser. No. ______ is assigned to the assignee of the
present application, and is hereby incorporated by reference in its
entirety.
[0028] The spool 230 includes in this example a passage 265. The
passage 265 has a number of purposes, including equalizing pressure
between the upper cavity 215 and the lower cavity 216, as described
in more detail below. The passage 230 is included in an exemplary
embodiment herein, but the spool 230 may also be manufactured
without passage 265.
[0029] As also described below, the electronics cover 205 includes
a connector 206 used to couple a spool position controller 115 to
the voice coil 221 on voice coil portion 222. The electronics cover
205 is one example of a cover used herein. Other examples are shown
below.
[0030] A description of exemplary operation of the valve 200 is
included in U.S. Pat. No. 5,960,831, which is assigned to the
assignee of the present application and is hereby incorporated by
reference in its entirety. U.S. Pat. No. 5,960,831 describes, for
instance, airflow through the external ports 270, 271, 280, 281,
and 283 and the circumferentially spaced internal ports 270a, 271a,
280a, 281a, and 283a. It is noted that the springs 240, 245 along
with the coil header assembly 220, motor housing 210, and spool
230, are configured such that the spool 230 blocks the ports 281A
when no power is applied to the voice coil 221. Other portions of
pneumatic valve 200 are also described in U.S. Pat. No.
5,960,831.
[0031] The use of pulse width modulation (PWM) is widely known in
open loop voltage applications (such as solenoids, TEC, audio
speaker drivers, etc.). In PWM the width of pulses in the signal is
adjusted thereby changing the average value of the wave. This
method could be adapted to voice coils used for pneumatic valve
applications to gain the efficiency advantage, however, they would
suffer the same consequences as a linear voltage output driver.
[0032] In order to provide an adequate output driver that will meet
the requirements of size, weight, current/voltage drive capability,
efficiency, and response/bandwidth, one must first consider the
basic elements required. The elements to be driven are a voice coil
pneumatic valve such as the pneumatic valve 200; a PWM H-Bridge
drive stage; a sensing element and circuitry to accurately and
quickly report the coil current; and a closed loop controller of
sufficient accuracy and bandwidth.
[0033] Referring to FIGS. 4 and 5, these figures show two different
exemplary valve controllers according to an exemplary embodiment of
the present invention. The circuits shown in FIGS. 4 and 5
correspond to the adder 110, the spool position controller 115, and
the feedback sensor module 150 of FIG. 1. The TB6 connection in
FIG. 4 and the J6 connection in FIG. 5 are used to carry the
control signal(s) 116. The current sense circuit (including an
INA145) in FIG. 4 and current sense circuit (including an INA157)
of FIG. 5 are non-limiting examples of a feedback sensor module
150. The current sense circuit in FIG. 4 uses an INA145 to sense
voltage across resistor R9 and to determine current flow through
the voice coil using the sensed voltage. Similarly, the current
sense circuit in FIG. 5 uses an INA157 to sense voltage across
resistor R21 and to determine current flow through the voice coil
using the sensed voltage.
[0034] FIG. 6 is a block diagram illustrating another system 2700
for controlling an electronically controlled valve. System 2700 is
similar to the system shown in FIG. 1. System 2700 includes an
adder 2710, a closed loop controller 2730, a PWM drive circuit 2720
(including an H-Bridge drive), a "plant" to be controlled 2720
(e.g., a voice coil pneumatic valve such as valve 200 of FIG. 2),
and a feedback sensor 2750 (including a current sensing circuit).
The blocks of system 2700 are shown in FIGS. 4 and 5, except for
block 2730. The input 2705 is X(s). The feedback sensor 2750
produces one or more feedback signals 2751, which are added by
adder 2710 to produce an input signal 2711. The output 2721 is the
Y(s) output, which may represent the valve position, the pressure
or some other controlled variable. The controller 2730 may include
an electromagnetic interference filter.
[0035] In terms of FIG. 1, the spool position controller 115
includes the closed loop controller 2730 and the PWM drive circuit
2740, the plant to be controlled includes the electronically
controlled valve 120, which produces the Y(s) (output 2721), the
feedback sensor module 150 includes the feedback sensor 2750, and
the adder 110 includes the adder 2710. Feedback sensor 2750 could
include, for instance, one or more of the following: dedicated Hall
Effect Current Sensors (e.g. Allegro ACS705), toroidal Hall Effect
techniques, current sense resistors, transformers, etc. In FIGS. 4
and 5, CMD is the input. The FBK and AUX signals are optional. This
circuit in particular is provided to show techniques for PWM closed
loop control. It is noted that dead band modification circuitry
1010 and block 1020 (e.g., variable frequency and amplitude dither
control circuitry) are not necessary but are beneficial.
[0036] FIG. 7 contains an exemplary diagram of circuitry for power
and indication for use with the exemplary valve controllers of
FIGS. 4 and 5; FIG. 8 contains an exemplary diagram of circuitry
for analog signal interfaces for use with the exemplary valve
controllers of FIGS. 4 and 5; and FIG. 9 contains an exemplary
diagram of connector and indication interface circuitry for use
with the exemplary valve controllers of FIGS. 4 and 5.
[0037] It is noted that FIGS. 4 and 5 perform similar functions,
including an ability to control the voice coil of a pneumatic valve
(e.g., a linear voice coil actuated fluid power valve) with a high
degree of accuracy and at a high speed. The two circuits in FIGS. 4
and 5 utilize similar techniques, but are different circuits: FIG.
4 is analog and FIG. 5 has a digital component. FIGS. 4 and 5 show
two different methods in accordance with the exemplary embodiments
of this invention. Both methods have certain advantages described
below. Each implementation also has certain benefits and detriments
that are particular to that implementation.
[0038] Regarding FIG. 4, information about the DRV593 may be found
in the data sheet SLOS401A, September 2002 (revised October 2002)
for the DRV593/DRV594, from Texas Instruments; information about
the INA145 may be found in the data sheet SBOS120, entitled
"INA145" and subtitled "Programmable Gain Difference Amplifier"
(March 2000 printing date), from Burr-Brown. Regarding FIG. 5,
information about the PIC16F818 is described in the data sheet
DS39598E, entitled "PIC16F818/819 Data Sheet" and subtitled
"18/20-Pin Enhanced Flash Microcontrollers with nanoWatt
Technology" (2004), from Microchip; information about the A3959 is
described in data sheet 29319.37H, entitled "3959" and subtitled
"DMOS Full-Bridge PWM Motor Driver (no date given), from Allegro
Microsystems, Inc.; information about the INA157 may be found in
the data sheet SBOS105, entitled "INA 157" and subtitled
"High-Speed, Precision Difference Amplifier", (March 1999 printing
date), from Burr-Brown. It is noted that other suitable products
may also be chosen for these functions and that these are merely
non-limiting examples.
[0039] A. PWM Drive Stage
[0040] A PWM drive stage is commonly an H-Bridge topology to allow
for bi-directional drive currents. Exemplary PWM drive stages are
shown primarily at the right side of FIGS. 4 and 5 and implemented
by the DRV593 and A3959, respectively. The selection criteria for
this functional element (e.g., DRV593 and A3959) include adequate
voltage and current capability of the semi-conductor element, high
switching frequency, low latency, and on-state resistance of drive
elements. The DRV593 and A3959 are examples of PWM drive stages
that meet these criteria.
[0041] Regarding adequate voltage and current capability of the
semi-conductor element: the voltage and current requirements depend
on the particular voice coil motor being driven. Typical values of
voltage may range from about 3V to around 48V and a preferred range
may be between around 12V to about 24V. Typical voice coil currents
may range from approximately 100 mA to greater than about 5A. The
non-limiting exemplary designs shown are intended for coil currents
between around 500 mA and approximately 2A.
[0042] High switching frequency is dependant on the coil inductance
and supply voltage. Typical values are around 20 kHz to about 1
MHz. The non-limiting exemplary designs use approximately 40 kHz
[A3959] and approximately 500 kHz [DRV593]. Higher switching
frequencies may result in higher losses which in turn result in
lower thermal efficiency. Generally, higher switching frequency
with sufficient circuit design may be preferred over lower
switching frequency.
[0043] Low latency refers to input to output delay. Typically an
acceptable latency is around 1 usec, however, it may be preferred
to achieve the lowest latency possible in order to optimize
performance.
[0044] Typically MOSFETs will provide less than 0.1 ohm of on-state
resistance thereby minimizing the power dissipation. The minimum
on-state resistance is 0 [zero] Ohm, however, this is practically
unachievable. It is possible to find commonly produced MOSFET's
with an on-state resistance of approximately 0.005 ohm. The maximum
on-state resistance will depend heavily on the drive current of the
particular design, the particular PWM drive elements selected and
their power dissipation capacity. An on-state resistance of greater
than about 100 Ohms may render the design nearly useless by
resulting in more than desired power dissipation.
[0045] B. Current Sense Element and Circuit
[0046] The functional requirements of a coil current sense element
circuit (shown primarily at the right side of FIG. 5) are that the
element and circuit should have high bandwidth to accurately
measure currents from DC to >50 kHz, linear relationship between
coil current and output over complete bi-polar range, and
insensitivity to coil drive artifacts (e.g., voltage, frequency,
etc) and insensitive to coil artifacts (e.g., resistance,
inductance). It is preferable to measure the current in the coil
circuit rather than the low or high side due to the linear
relationship of the current in the coil circuit. Some available
methods include a series sense resistor, transformers, and a
hall-effect current sensor (e.g., two varieties of such). Hall
Effect methods may suffer from noisy output signals, may present
hysteretic performance, and are susceptible to external magnetic
fields (fixed or varying). A series sense resistor suffers from
insertion loss; however, an adequately small sense resistor and
accurate sensing circuitry will minimize this impact.
[0047] A formidable issue to be resolved when implementing coil
current sensing techniques is the sensing circuit itself. Since
most methods of PWM generation involve pulsing one side of the
H-Bridge or the other (depending on desired direction of current
flow), the sense resistor and sensing electronics will be subjected
to high frequency, high amplitude pulses at the sense resistor.
Assuming a 0.1 ohm resistor with a 24V supply driving 1A, the
signal will be 100 mV amongst high frequency square wave pulses of
0V to 24V at frequencies >40 kHz. Specialized sensing circuitry
can help to discriminate this low level signal from the drive power
applied; especially when the current controller bandwidth is
expected to be approximately of the PWM frequency.
[0048] A common and classical approach is to use a difference
amplifier circuit across the sense resistor. Some difference
amplifiers or instrumentation amplifiers will not be suitable due
to low common mode rejection, poor common mode limits, or slow
response among other short comings. By contrast, a difference
amplifier as used herein should have high common mode voltage
limits up to the drive supply and have high common mode rejection
ratio (CMRR) due to the frequency composition of the sense resistor
signal during pulsing of the associated PWM output.
[0049] The minimum acceptable CMRR is around about -40 dB and the
maximum is limitless based on available technology. A CMRR of
around -160 dB may function better than the exemplary design shown
in FIG. 5. The CMRR limits should apply to at least the 5.sup.th
harmonic of the fundamental switching frequency (for example, a 40
kHz switching frequency would have a CMRR of -40 dB or lower at the
5.sup.th harmonic, which is 200 kHz) while having constant gain up
to at least the bandwidth of the current to be controlled (e.g., at
least 100 Hz)
[0050] The sense resistor should be selected to minimize the
percentage of power loss while maximizing the output signal level
from the sense element. A `home grown` sense amplifier could be
constructed using specialized equipment or statistical component
sorting that could possess the common mode rejection necessary at
the frequencies necessary to provide a clean signal; however, this
may not be feasible in large scale production. A dedicated
instrumentation amplifier or difference amplifier with laser
trimmed resistors will provide adequate signaling capabilities.
Some such amplifiers, meeting the criteria given above, are
included in the INA145 shown in FIG. 4 and in the INA157 shown in
FIG. 5.
[0051] C. Closed Loop Current Controller
[0052] Any servo system must incorporate a controller to monitor
command and feedback and generate an actuator drive signal (in this
case, it is a PWM duty cycle and direction command). The coil
dynamics can be described by the transfer characteristic:
Y ( s ) U ( s ) = G V 15 ( s ) = [ ( K Motor m L Coil ) s 3 + ( R
Coil L Coil + B m ) s 2 + ( B R Coil + k L Coil + K Motor K E m L
Coil ) s + ( k R Coil m L Coil ) ( K Motor m L Coil ) s s 3 + ( R
Coil L Coil + B m ) s 2 + ( B R Coil + k L Coil + K Motor K E m L
Coil ) s + ( k R Coil m L Coil ) ( 1 L Coil s 2 + B m L Coil s + k
m L Coil ) s 3 + ( R Coil L Coil + B m ) s 2 + ( B R Coil + k L
Coil + K Motor K E m L Coil ) s + ( k R Coil m L Coil ) ] ,
##EQU00001##
where the top transfer function represents the coil position, the
middle transfer equation represents the velocity, and the final
transfer equation represents the coil current. It has been shown
that a high gain, high bandwidth (e.g., gain >70,000 and
BW>10 kHz) `P` type current controller (e.g., implemented as a
trans-conductance amplifier) will properly control current with
high accuracy and fidelity. PWM systems are likely to possess some
time lag or other system lag that will inhibit the use of a similar
system with similar gains (e.g., the time lag or signal lag will
invariably reduce the bandwidth of the system and degrade
performance, likely creating an oscillatory system). As a
consequence, a more robust controller was needed.
[0053] The variables to be controlled affect the controlled
variable as well as how quickly these variables will change with
respect to the controller's ability to compensate for the
variables. In a voice coil, the coil motion in a static magnetic
field and the coil inductance have dramatic impact on the voltage
required to generate and control a current though that coil:
V Coil = k e v + L i t + i R . ##EQU00002##
[0054] Since the coil is rigidly attached to a mechanical system,
the electrical effects due to the mechanical elements will respond
much slower than the electrical elements of the coil (e.g., the
velocity of the coil will cause voltage to change much slower than
the inductive effects would by nearly a factor of 10). For this
reason, the model to control only the inductive elements of the
system can be simplified, thereby assuming that a controller that
can control the much more responsive electrical elements can
compensate for effects from slower mechanical elements:
V Inducter = L i t + i R . ##EQU00003##
[0055] This is a simple first order plant, and much classical
control systems development has been done on similar ideal systems.
It can be shown that a suitable controller for this type of system
is a P-type (proportional-type) or PI-type
(proportional-integral-type) controller (the I can be implemented
based on the acceptable P gain and the necessity for high steady
state (SS) accuracy).
[0056] D. Output EMI Filter
[0057] The PWM output drive may generate a significant quantity of
EM (electromagnetic) radiation due to the square edge pulses of the
output drive elements. An EMI (electromagnetic interference) output
filter is often implemented to minimize the radiated energy and
contain the higher frequency components to a local area on the PCB.
While output filter design is typically a straightforward process;
in this particular case (e.g., powering a voice coil), the load is
not resistive as assumed, it is inductive which dramatically
impacts the transfer characteristic for filter design. A new
`minimum emissions` EMI filter design approach is taken to minimize
the radiated emissions from the output of the driver. In FIG. 4
(which shows an exemplary controller) an output EMI filter 410 is
shown which includes L1, R54, and C27. The components and
corresponding values may be selected by examination of the transfer
characteristics of the filter and load component in order to
minimize the voltage and current ripple in the load (and thereby,
the radiated emissions). It is noted that the EMI filter is
optional.
[0058] FIG. 10 shows a logic flow diagram of a method in accordance
with an embodiment of this invention. In block 810 a pulse width
modulation drive signal is provided to a linear voice coil of a
linear voice coil actuated fluid power valve. The current in the
linear voice coil is determined in block 820. In block 830, the
pulse width modulation drive signal is adjusted based at least upon
the determined current. The linear voice coil is used to move a
spool having a force applied to the spool by at least one
counter-acting spring.
[0059] Certain embodiments of the disclosed invention may be
implemented by hardware (e.g., one or more processors, discrete
devices, programmable logic devices, large scale integrated
circuits, or some combination of these), software (e.g., firmware,
a program of, executable instructions, microcode, or some
combination of these), or some combination thereof. Aspects of the
disclosed invention may also be implemented on one or more
semiconductor circuits, comprising hardware and perhaps software
residing in one or more memories. Aspects of the disclosed
invention may also include computer-executable media tangibly
embodying one or more programs of computer-readable instructions
executable by one or more processors to perform certain of the
operations described herein.
[0060] The foregoing description has provided by way of exemplary
and non-limiting examples a full and informative description of the
best techniques presently contemplated by the inventors for
carrying out embodiments of the invention. However, various
modifications and adaptations may become apparent to those skilled
in the relevant arts in view of the foregoing description, when
read in conjunction with the accompanying drawings and the appended
claims. All such and similar modifications of the teachings of this
invention will still fall within the scope of this invention.
[0061] Furthermore, some of the features of exemplary embodiments
of this invention could be used to advantage without the
corresponding use of other features. As such, the foregoing
description should be considered as merely illustrative of the
principles of embodiments of the present invention, and not in
limitation thereof.
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