Title:
Valve, controller, system and method providing closed loop current control of a voice coil using pulse width modulation drive elements
Kind Code:
A1


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, US)
Application Number:
11/977471
Publication Date:
05/01/2008
Filing Date:
10/25/2007
Assignee:
Enfield Technoloties, LLC
Primary Class:
Other Classes:
332/109, 360/78.12, 251/129.09
International Classes:
F15B13/044
View Patent Images:
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Primary Examiner:
FRISTOE JR, JOHN K
Attorney, Agent or Firm:
Harrington & Smith, Attorneys At Law, LLC (SHELTON, CT, US)
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

This patent application claims priority under 35 U.S.C. §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

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

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.

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.

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.

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

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.

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.

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.

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

The attached Drawing Figures include the following:

FIG. 1 is a block diagram of a system including a portion for controlling an electronically controlled valve and the electronically controlled valve;

FIG. 2 is a cutaway, perspective view of an exemplary pneumatic valve;

FIG. 3 is a view of the motor housing retainer coupled to the motor housing and also of the coil header assembly and spool;

FIG. 4 is a circuit diagram of a first exemplary valve controller;

FIG. 5 is a circuit diagram of a second exemplary valve controller;

FIG. 6 is a block diagram illustrating another system for controlling an electronically controlled valve;

FIG. 7 is a block diagram illustrating circuitry for power and indication for use with valve controllers;

FIG. 8 is a block diagram illustrating circuitry for analog signal interfaces for use with valve controllers;

FIG. 9 is a block diagram illustrating of a connector and indication interface circuitry for use with valve controllers; and

FIG. 10 shows a logic flow diagram of a method in accordance with an embodiment of this invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

A. PWM Drive Stage

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.

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.

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.

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.

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.

B. Current Sense Element and Circuit

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.

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.

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.

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 5th harmonic of the fundamental switching frequency (for example, a 40 kHz switching frequency would have a CMRR of −40 dB or lower at the 5th 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)

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.

C. Closed Loop Current Controller

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)=GV15(s)=[(KMotormLCoil)s3+(RCoilLCoil+Bm)s2+(BRCoil+kLCoil+KMotorKEmLCoil)s+(kRCoilmLCoil)(KMotormLCoil)ss3+(RCoilLCoil+Bm)s2+(BRCoil+kLCoil+KMotorKEmLCoil)s+(kRCoilmLCoil)(1LCoils2+BmLCoils+kmLCoil)s3+(RCoilLCoil+Bm)s2+(BRCoil+kLCoil+KMotorKEmLCoil)s+(kRCoilmLCoil)],

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.

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:

VCoil=kev+Lit+iR.

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:

VInducter=Lit+iR.

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).

D. Output EMI Filter

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.

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.

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.

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.

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.