Electro-hydraulic servovalve control with input

The subject matter of this specification can be embodied in, among other things, a controller apparatus that includes a digital controller configured to provide a digital position signal based on a setpoint and a differential analog feedback signal, and a converter circuit configured to provide a differential analog electrohydraulic servo valve position control signal based on the digital position signal, and provide the differential analog feedback signal based on the differential analog electrohydraulic servo valve position control signal.

TECHNICAL FIELD

This specification relates to control systems for electro-hydraulic servo valves.

BACKGROUND

Electro-hydraulic servo valves (EHSV) are used for electro-hydraulic control of components such as fuel valves, actuators, or switching valves. In some applications, EHSVs can be configured to provide hydraulic power to translate the position of linear or rotary actuators. With position feedback, the EHSV can be configured to drive the position of an actuator.

Aircraft vehicles include hydraulic servo control systems that control one or more adjustable surface components such as, for example, the ailerons, rudders, and elevators. Conventional hydraulic servo control systems are based on an analog electronic topology comprising various analog electronic devices to measure one or more analog signals that indicate a current position of the surface components. The analog signal is then compared to an analog set point value. The error between the analog signal and the analog set point value is determined, and the surface components are actively adjusted to maintain a minimum error.

SUMMARY

In general, this document describes control systems for electro-hydraulic servo valves.

In a first aspect, a controller apparatus includes a digital controller configured to provide a digital position signal based on a setpoint and a differential analog feedback signal, and a converter circuit configured to provide a differential analog electrohydraulic servo valve position control signal based on the digital position signal, and provide the differential analog feedback signal based on the differential analog electrohydraulic servo valve position control signal.

Various embodiments can include some, all, or none of the following features. The digital controller can be further configured receive an electrohydraulic servo valve spool position signal, and the digital position signal can be further based on the electrohydraulic servo valve spool position signal. The electrohydraulic servo valve spool position signal can be based on a linear position of a spool of an electrohydraulic servo valve. The electrohydraulic servo valve spool position signal can be a linear variable differential transformer signal. The digital controller can be further configured receive an output position signal, and the digital position signal can be further based on the output position signal. The output position signal can be based on a position of an actuator. The actuator can be a hydraulic rotary piston actuator. The output position signal can be a variable differential transformer signal.

In another aspect, a method of position control includes receiving a predetermined setpoint, receiving a differential analog feedback signal, determining a digital position signal based on the received predetermined setpoint and the received differential analog feedback signal, providing the determined digital position signal, determining a differential analog electrohydraulic servo valve position control signal based on the digital position signal, and providing the differential analog electrohydraulic servo valve position control signal.

Various implementations can include some, all, or none of the following features. The method can also include receiving an electrohydraulic servo valve spool position signal, where the digital position signal is further based on the electrohydraulic servo valve spool position signal. The electrohydraulic servo valve spool position signal can be based on a linear position of a spool of an electrohydraulic servo valve. The electrohydraulic servo valve spool position signal can be a linear variable differential transformer signal. The method can also include receiving an output position signal, wherein the digital position signal is further based on the output position signal. The output position signal can be based on a position of an actuator. The actuator can be a hydraulic rotary piston actuator. The output position signal can be a variable differential transformer signal.

In another aspect, a control system includes a controller configured to provide a predetermined setpoint and receive a first differential analog feedback signal, an electrohydraulic servo valve configured to receive a differential analog electrohydraulic servo valve position control signal, and a conversion apparatus comprising circuitry configured to perform operations including receiving the predetermined setpoint, receiving a second differential analog feedback signal, determining a digital position signal based on the received predetermined setpoint and the second differential analog feedback signal, determining the differential analog electrohydraulic servo valve position control signal based on the determined digital position signal, providing the differential analog feedback signal based on the differential analog electrohydraulic servo valve position control signal to the electrohydraulic servo valve, determining the first differential analog feedback signal based on the second differential analog feedback signal, and providing the first differential analog feedback signal to the controller.

Various embodiments can include some, all, or none of the following features. The control system can also include a position sensor configured to sense a position of a valve spool of the electrohydraulic servo valve and provide an electrohydraulic servo valve spool position signal representative of the position, wherein the controller is further configured receive the electrohydraulic servo valve spool position signal, and the digital position signal is further based on the electrohydraulic servo valve spool position signal. The control system can also include a hydraulic actuator configured to be actuated by a hydraulic output of the electrohydraulic servo valve, and a position sensor configured to sense a position of hydraulic actuator and provide an actuator position signal representative of the position, where the controller is further configured receive the actuator position signal, and the digital position signal is further based on the actuator position signal. The conversion apparatus can also include an amplifier configured to selectably amplify the differential analog electrohydraulic servo valve position control signal based on an amplification signal provided by the controller.

The systems and techniques described here may provide one or more of the following advantages. First, a system can provide position control in harsh operational environments. Second, the system can operate with greater immunity to, and reduced emission of, electromagnetic interference. Third, the system can operate with greater immunity to the effects of temperature changes. Fourth, the system can operate with lower power requirements and greater power efficiency.

DETAILED DESCRIPTION

This document describes control systems for electro-hydraulic servo valves. The analog devices used in previous designs to generate and measure analog signals are susceptible to temperature changes. Consequently, in some implementations such as aircraft applications, these components are subjected to different temperatures during operation, and various characteristics of the analog devices (e.g., gain, error, and phase margin) can vary, thereby reducing the accuracy of such analog control systems. Some such previous designs have also required the use of multiple power sources to power the individual analog components and to define the analog set point values. Consequently, such previous analog control systems have required increased power, such that the overall power efficiency of the aircraft is reduced.

In general, the control systems described in this document implement closed loop control that remains in the digital domain, and uses position feedback systems that are resistant to the effects of temperature changes and other adverse operational conditions that can be experienced in some applications (e.g., aircraft control). The control systems described in this document also implement analog control signals instead of the pulse-width-modulated (PWM) control signals used in some previous designs. By using analog signals instead of PWM, the electromagnetic interference that can be caused by PWM signals can be avoided.

FIG. 1is a schematic diagram that shows an example of a system100for hydraulic position control. The system100includes an electro-hydraulic servo valve (EHSV)102. The EHSV102is configured to move to multiple bi-polar positions that are sensed by a sensor104. In some implementations, the sensor104can be a resolver. In some implementations, the sensor104can be a variable differential transformer (VDT), such as a rotary VDT or a linear VDT. For example, VDTs have very few or no internally contacting parts that could experience temperature-related problems, and as such VDTs can be used in operational environments that have wide operational temperature ranges that could damage, degrade, or destroy other types of position sensors (e.g., in proximity to engines). VDTs are also mechanically robust, with few or no moving parts in frictional contact to wear out due to mechanical cycling and/or vibration.

The EHSV102controls flows of hydraulic fluid to an actuator106(e.g., a linear hydraulic piston, a hydraulic rotary piston actuator) through one or more hydraulic lines105. The actuator106is configured to drive the position of a physical or mechanical load (e.g., an aircraft flight control surface, a valve). The position of the actuator106is sensed by a sensor108. In some implementations, the sensor108can be a VDT or resolver.

A controller110(e.g., a digital controller, a processor, a field-programmable gate array) is configured to provide a digital control signal112to a digital-to-analog converter (DAC)120. The digital control signal112represents a target (e.g., desired) configuration or position of the EHSV102and/or the actuator106. The DAC120converts the digital control signal112into a differential analog control signal that includes an analog control signal122aand an analog control signal122b. In some embodiments, the digital control signal112can be transmitted and received as a serial peripheral interface (SPI) signal (e.g., the controller110and the DAC120can communicate with each other through SPI ports). The digital control signal112is based in part on a received (e.g., user or automatically provided) or determined (e.g., calibrated, calculated) setpoint111, and on one or more feedback signals that will be described in subsequent paragraphs.

The system100includes a power stage101that includes an amplifier130aand an amplifier130b. The analog control signal122ais amplified by the amplifier130ato provide an amplified analog control signal132a. The analog control signal122bis amplified by the amplifier130bto provide an amplified analog control signal132b. The amplified analog control signals132aand132bform an amplified differential analog control signal that is provided to drive the configuration of the EHSV102. In some embodiments, the analog output current needed to drive the motor of the EHSV can be about +/−10 mA. In some implementations, a DAC with an op-amp buffered output can provide a tight, digitally controlled analog output that is differential. The DAC approach is inherently less noisy (e.g., EMC) as compared to a PWM approach.

A portion142aof the amplified analog control signal132ais amplifier by an amplifier140ato provide a buffered analog control signal144a. A portion142bof the amplified analog control signal132bis amplifier by an amplifier140bto provide an amplifiedanalog control signal144a. The amplified analog control signals144aand144bform an amplified differential analog control signal that is provided to receiver150. The receiver150is an analog-to-digital converter (ADC). The receiver150converts the amplified differential analog signal provided by the amplified analog control signals144aand144binto a digital signal that can be processed by the controller110. In use, the amplified analog control signals144aand144bprovide feedback that is used in a control loop that can be used for determining the digital control signal112. In the illustrated example, the receiver150is integrated with the controller110, but in some embodiments, the receiver150can be a separate module in communication with the controller110.

The sensor104provides a position signal162to a signal demodulator160, and the signal demodulator160provides a demodulated signal164based on the position signal162. A receiver170is configured to receive the position signal162. In some embodiments, the receiver can be configured to receive analog and/or digital signals and convert or otherwise provide them in a format that can be used by the controller110. For example, the sensor104can be a VDT, and the position signal162can be an analog differential output signal of the VDT that varies with the position or configuration of the EHSV102. In such an example, the signal demodulator160can be an ADC that is configured to convert the VDT signal to a digital signal that can be received by the receiver170. In another example, the sensor104can be a resolver, and the position signal162can be a digital signal that varies with the position or configuration of the EHSV102. In such an example, the signal demodulator160can be a protocol converter that is configured to convert the digital signal to a format that can be received by the receiver170.

In use, the demodulated signal164provides feedback that is used in a control loop that can be used for determining the digital control signal112. In the illustrated example, the receiver170is integrated with the controller110, but in some embodiments, the receiver170can be a separate module in communication with the controller110.

The sensor108provides a position signal182to a signal demodulator180, and the signal demodulator180provides a demodulated signal184based on the position signal182. A receiver190is configured to receive the position signal182. In some embodiments, the receiver190can be configured to receive analog and/or digital signals and convert or otherwise provide them in a format that can be used by the controller110. For example, the sensor108can be a VDT, and the position signal182can be an analog differential output signal of the VDT that varies with the position or configuration of the EHSV102. In such an example, the signal demodulator180can be an ADC that is configured to convert the VDT signal to a digital signal that can be received by the receiver190. In another example, the sensor108can be a resolver, and the position signal182can be a digital signal that varies with the position or configuration of the EHSV102. In such an example, the signal demodulator180can be a protocol converter that is configured to convert the digital signal to a format that can be received by the receiver190.

In use, the demodulated signal184provides feedback that is used in a control loop that can be used for determining the digital control signal112. In the illustrated example, the receiver190is integrated with the controller110, but in some embodiments, the receiver190can be a separate module in communication with the controller110. In some embodiments, the controller110can be an FPGA or a microprocessor. For example, both FPGAs and microprocessors can be well suited to read the feedback from the sensors104and/or108(e.g., VDT or resolver signals) and drive a digital control signal. The controller110closes the current control loop and the position control loop, allowing for configurability in ranges, Ki/Kp values, and software imposed limits.

An advantage of this approach is that the closed loop control can remain in the digital domain. Current control in the digital domain allows for configurability, for example, if a different motor is connected. The power stage can remain analog, and the absence of PWM switching provides the advantage of the inherently low radiated emissions. The DAC120with differential analog outputs allows for precise control in the low current domain. The differential voltages of the amplified analog control signals144aand144ballow for analog-to-digital conversion within the receiver150to be sampled at substantially any time, with substantially no timing constraints to sense the current.

The system100can be used in harsh operational environments (e.g., environments that would degrade, destroy, or otherwise negatively affect the longevity and/or performance of previous control systems). In some implementations, the controller110can be located remotely from other components of the system100. For example, the controller110can be located in or near an aircraft cockpit, and the actuator106can be in an aircraft wing or engine. In such an example, the digital nature of the digital control signal112can allow the digital control signal112to be transmitted from near the cockpit to near the actuator106with relatively greater immunity to noise and/or signal degradation that could negatively affect an analog control signal. In another example, and as described in previous paragraphs, the sensors104and/or106can be ratio metric VDTs or resolvers, which are robust absolute position sensors that are inherently frictionless, have virtually infinite cycle life, and can operate in harsh environments.

In some implementations, the EHSV102can be located remotely from the DAC120. For example, since the analog control signals122aand122b, and the amplified analog control signals132aand132bare differential analog signals, they are substantially immune to electrical noise over a distance (e.g., unlike non-differential signals). In another example, since the analog control signals122aand122b, and the amplified analog control signals132aand132bare differential analog signals, these signals can emit substantially less electromagnetic interference over long interconnections than the PWM signals used in other designs.

In some implementations, the actuator106can be located remotely from the EHSV102. For example, the fluidic connection provided by the hydraulic lines105between the EHSV102and the actuator106is immune to electrical noise, and can be tolerant of high temperatures that might otherwise damage electrical connections (e.g., melt insulation on wires).

In some implementations, the sensor104can be located remotely from the controller110and/or the signal demodulator160. For example, the sensor104can be a VDT and the position signal162can be a VDT signal. Some types of VDT signals are differential analog signals that vary as the sensed position changes. Differential signals are highly immune to the effects of electrical noise and signal degradation that may otherwise occur over long transmission distances. In some implementations, the sensor108can be located remotely from the controller110and/or the signal demodulator180for similar reasons.

In some embodiments, the power stage101can be replaced or modified based on the particular application and/or user needs. For example, power to the amplifiers130aand130bcan be controlled based on the current demand. In such an example, if the current is low the rail can be dropped, and if high current is needed, then the rail can be increased. In another example, more output drive current can be achieved by connecting two amplifiers in parallel with a higher supply voltage to the amplifier. In such examples, the second op-amp could be changed to a difference voltage follower. A follower configuration can allow a single DAC output to drive the differential current, reducing the complexity of the digital control. In another example, the amplifier configuration can also be replaced by an H-bridge topology for higher power currents.

FIG. 2is a block diagram that shows an example power stage200. In some embodiments, the power stage200can be a variant of the example power stage101of the system100ofFIG. 1. In general, the power stage200is configured such that power to the amplifiers130aand130bcan be controlled, and includes parallel amplifiers to drive the amplified analog control signals132aand132b.

The power stage200includes the amplifiers130aand130b, and the EHSV102in the illustrated view. The analog control signal122aand the analog control signal122bare received from the DAC120(not shown in this view), and the portions142aand142bare provided to the amplifiers140aand140b(not shown in this view).

Power to the amplifiers130aand130bis controlled by a power control circuit210. Constant power is supplied to the amplifiers130aand130bby a power supply212. Additional power from a power supply214is supplied to the amplifiers130aand130bbased on an amplification control signal216(e.g., provided by the controller110). When the signal216is brought high, a switch218aand a switch218ballow the additional power from the power supply214to flow to the amplifiers130aand130b. When the signal216is brought low, the switch218aand the switch218bprevent additional power from the power supply214to flow to the amplifiers130aand130b.

Output drive current, in addition to the current provided by the amplifier130a, is provided to the EHSV102by an amplifier230a. The amplifier230ais configured to follow the amplified analog control signal132aoutput by the amplifier130a, and provide its output in parallel with the amplified analog control signals132ato form an amplified analog control signal232athat is provided to the EHSV102. Similarly, the amplifier230bis configured to follow the amplified analog control signal132boutput by the amplifier130b, and provide its output in parallel with the amplified analog control signals132bto form an amplified analog control signal232bthat is provided to the EHSV102. Together the amplified analog control signals232aand232bform a differential analog control signal that drives the operation of the EHSV102.

FIG. 3is a flow chart that shows an example of a process300for hydraulic position control. The process may be performed, for example, by a system such as the example system100ofFIG. 1. For clarity of presentation, the description that follows uses the system100and the power stage200as examples for describing the process. However, another system, or combination of systems, may be used to perform the processes.

At310, a predetermined setpoint is received. For example, the example controller110can receive the setpoint111from a human operator (e.g., a pilot) or from another circuit (e.g., an autopilot) that represents a desired configuration of the EHSV102, the actuator106, or mechanical loads that are actuated by the actuator106.

At320, a differential analog feedback signal is received. For example, controller110can receive the amplified differential analog signal provided by the amplified analog control signals144aand144b.

At330, a digital position signal is determined based on the received setpoint and the received differential analog feedback signal. For example, the controller110can determine the digital control signal112based on the setpoint111and the amplified analog control signals144aand144b.

At340, the determined digital position signal is provided. For example, the digital control signal112can be provided from the controller110to the DAC120.

At350, a differential analog electrohydraulic servo valve position control signal is determined based on the digital position signal. For example, the DAC120provides the amplified analog control signals132aand132b, which together form the amplified differential analog control signal.

At360, the differential analog electrohydraulic servo valve position control signal is provided. For example, the amplified differential analog control signal formed by the amplified analog control signals132aand132bis provided by the DAC120.

In some implementations, the process300can also include receiving an electrohydraulic servo valve spool position signal, where the digital position signal is further based on the electrohydraulic servo valve spool position signal. For example, the controller110can receive the demodulated signal164based on the position signal162, and the controller110can determine the digital control signal112based on the demodulated signal164.

In some implementations, the electrohydraulic servo valve spool position signal can be based on a linear position of a spool of an electrohydraulic servo valve. For example, the position signal162can be provided by the sensor104, which is configured to sense the linear position of the EHSV102. In some implementations, the electrohydraulic servo valve spool position signal can be a variable differential transformer signal. For example, the sensor104can be a linear or rotary VDT.

In some implementations, the process300can also include receiving an output position signal, wherein the digital position signal is further based on the output position signal. For example, the controller110can receive the demodulated signal184based on the position signal182, and the controller can determine the digital control signal112based on the demodulated signal184. In some implementations, the output position signal can be a variable differential transformer signal. For example, the sensor108can be a linear or rotary VDT that can provide the position signal182as a VDT signal.

In some implementations, the output position signal can be based on a position of an actuator. For example, the position signal182is provided by the sensor108, which is configured to sense the position of the actuator106or a load that is positioned or otherwise controlled by the actuator106. In some implementations, the actuator can be a hydraulic rotary piston actuator (RPA). For example, the actuator106can be a hydraulic RPA.

FIG. 4is a schematic diagram of an example of a generic computer system400. The system400can be used for the operations described in association with the process300according to one implementation. For example, the system400may be included as part or all of the example controller110ofFIG. 1.

The system400includes a processor410, a memory420, a storage device430, and an input/output device440. Each of the components410,420,430, and440are interconnected using a system bus450. The processor410is capable of processing instructions for execution within the system400. In one implementation, the processor410is a single-threaded processor. In another implementation, the processor410is a multi-threaded processor. The processor410is capable of processing instructions stored in the memory420or on the storage device430to display graphical information for a user interface on the input/output device440.

The storage device430is capable of providing mass storage for the system400. In one implementation, the storage device430is a computer-readable medium. In various different implementations, the storage device430may be a floppy disk device, a hard disk device, an optical disk device, or a tape device.

The input/output device440provides input/output operations for the system400. In one implementation, the input/output device440includes a keyboard and/or pointing device. In another implementation, the input/output device440includes a display unit for displaying graphical user interfaces.

To provide for interaction with a user, the features can be implemented on a computer having a display device such as a CRT (cathode ray tube) or LCD (liquid crystal display) monitor for displaying information to the user and a keyboard and a pointing device such as a mouse or a trackball by which the user can provide input to the computer. User interaction can be command line-based, or by using register reads and writes to get the information in and/or out of the system.