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

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. An example feedback control system of EHSVs can be found in the publication <NPL>.

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.

In general, this document describes control systems for electro-hydraulic servo valves. A controller apparatus according to the present invention is set out in claim <NUM>. A method according to the present invention is set out in claim <NUM>. A control system according to the present invention is set out in claim <NUM>. Further advantageous developments of the present invention are set out in the dependent claims.

In a general 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.

The digital controller can be further configured to 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 to 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 general 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.

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 general 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.

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 to 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 to 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.

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> is a schematic diagram that shows an example of a system <NUM> for hydraulic position control. The system <NUM> includes an electro-hydraulic servo valve (EHSV) <NUM>. The EHSV <NUM> is configured to move to multiple bi-polar positions that are sensed by a sensor <NUM>. In some implementations, the sensor <NUM> can be a resolver. In some implementations, the sensor <NUM> can 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 EHSV <NUM> controls flows of hydraulic fluid to an actuator <NUM> (e.g., a linear hydraulic piston, a hydraulic rotary piston actuator) through one or more hydraulic lines <NUM>. The actuator <NUM> is configured to drive the position of a physical or mechanical load (e.g., an aircraft flight control surface, a valve). The position of the actuator <NUM> is sensed by a sensor <NUM>. In some implementations, the sensor <NUM> can be a VDT or resolver.

A controller <NUM> (e.g., a digital controller, a processor, a field-programmable gate array) is configured to provide a digital control signal <NUM> to a digital-to-analog converter (DAC) <NUM>. The digital control signal <NUM> represents a target (e.g., desired) configuration or position of the EHSV <NUM> and/or the actuator <NUM>. The DAC <NUM> converts the digital control signal <NUM> into a differential analog control signal that includes an analog control signal 122a and an analog control signal 122b. In some embodiments, the digital control signal <NUM> can be transmitted and received as a serial peripheral interface (SPI) signal (e.g., the controller <NUM> and the DAC <NUM> can communicate with each other through SPI ports). The digital control signal <NUM> is based in part on a received (e.g., user or automatically provided) or determined (e.g., calibrated, calculated) setpoint <NUM>, and on one or more feedback signals that will be described in subsequent paragraphs.

The system <NUM> includes a power stage <NUM> that includes an amplifier 130a and an amplifier 130b. The analog control signal 122a is amplified by the amplifier 130a to provide an amplified analog control signal 132a. The analog control signal 122b is amplified by the amplifier 130b to provide an amplified analog control signal 132b. The amplified analog control signals 132a and 132b form an amplified differential analog control signal that is provided to drive the configuration of the EHSV <NUM>. In some embodiments, the analog output current needed to drive the motor of the EHSV can be about +/-10mA. 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 portion 142a of the amplified analog control signal 132a is amplified by an amplifier 140a to provide a buffered analog control signal 144a. A portion 142b of the amplified analog control signal 132b is amplified by an amplifier 140b to provide an amplified analog control signal 144a. The amplified analog control signals 144a and 144b form an amplified differential analog control signal that is provided to receiver <NUM>. The receiver <NUM> is an analog-to-digital converter (ADC). The receiver <NUM> converts the amplified differential analog signal provided by the amplified analog control signals 144a and 144b into a digital signal that can be processed by the controller <NUM>. In use, the amplified analog control signals 144a and 144b provide feedback that is used in a control loop that is used for determining the digital control signal <NUM>. In the illustrated example, the receiver <NUM> is integrated with the controller <NUM>, but in some embodiments, the receiver <NUM> can be a separate module in communication with the controller <NUM>.

The sensor <NUM> provides a position signal <NUM> to a signal demodulator <NUM>, and the signal demodulator <NUM> provides a demodulated signal <NUM> based on the position signal <NUM>. A receiver <NUM> is configured to receive the position signal <NUM>. 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 controller <NUM>. For example, the sensor <NUM> can be a VDT, and the position signal <NUM> can be an analog differential output signal of the VDT that varies with the position or configuration of the EHSV <NUM>. In such an example, the signal demodulator <NUM> can be an ADC that is configured to convert the VDT signal to a digital signal that can be received by the receiver <NUM>. In another example, the sensor <NUM> can be a resolver, and the position signal <NUM> can be a digital signal that varies with the position or configuration of the EHSV <NUM>. In such an example, the signal demodulator <NUM> can be a protocol converter that is configured to convert the digital signal to a format that can be received by the receiver <NUM>.

In use, the demodulated signal <NUM> provides feedback that is used in a control loop that can be used for determining the digital control signal <NUM>. In the illustrated example, the receiver <NUM> is integrated with the controller <NUM>, but in some embodiments, the receiver <NUM> can be a separate module in communication with the controller <NUM>.

The sensor <NUM> provides a position signal <NUM> to a signal demodulator <NUM>, and the signal demodulator <NUM> provides a demodulated signal <NUM> based on the position signal <NUM>. A receiver <NUM> is configured to receive the position signal <NUM>. In some embodiments, the receiver <NUM> 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 controller <NUM>. For example, the sensor <NUM> can be a VDT, and the position signal <NUM> can be an analog differential output signal of the VDT that varies with the position or configuration of the EHSV <NUM>. In such an example, the signal demodulator <NUM> can be an ADC that is configured to convert the VDT signal to a digital signal that can be received by the receiver <NUM>. In another example, the sensor <NUM> can be a resolver, and the position signal <NUM> can be a digital signal that varies with the position or configuration of the EHSV <NUM>. In such an example, the signal demodulator <NUM> can be a protocol converter that is configured to convert the digital signal to a format that can be received by the receiver <NUM>.

In use, the demodulated signal <NUM> provides feedback that is used in a control loop that can be used for determining the digital control signal <NUM>. In the illustrated example, the receiver <NUM> is integrated with the controller <NUM>, but in some embodiments, the receiver <NUM> can be a separate module in communication with the controller <NUM>. In some embodiments, the controller <NUM> can be an FPGA or a microprocessor. For example, both FPGAs and microprocessors can be well suited to read the feedback from the sensors <NUM> and/or <NUM> (e.g., VDT or resolver signals) and drive a digital control signal. The controller <NUM> closes 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 DAC <NUM> with differential analog outputs allows for precise control in the low current domain. The differential voltages of the amplified analog control signals 144a and 144b allow for analog-to-digital conversion within the receiver <NUM> to be sampled at substantially any time, with substantially no timing constraints to sense the current.

The system <NUM> can 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 controller <NUM> can be located remotely from other components of the system <NUM>. For example, the controller <NUM> can be located in or near an aircraft cockpit, and the actuator <NUM> can be in an aircraft wing or engine. In such an example, the digital nature of the digital control signal <NUM> can allow the digital control signal <NUM> to be transmitted from near the cockpit to near the actuator <NUM> with 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 sensors <NUM> and/or <NUM> can 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 EHSV <NUM> can be located remotely from the DAC <NUM>. For example, since the analog control signals 122a and 122b, and the amplified analog control signals 132a and 132b are 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 signals 122a and 122b, and the amplified analog control signals 132a and 132b are 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 actuator <NUM> can be located remotely from the EHSV <NUM>. For example, the fluidic connection provided by the hydraulic lines <NUM> between the EHSV <NUM> and the actuator <NUM> is 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 sensor <NUM> can be located remotely from the controller <NUM> and/or the signal demodulator <NUM>. For example, the sensor <NUM> can be a VDT and the position signal <NUM> can 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 sensor <NUM> can be located remotely from the controller <NUM> and/or the signal demodulator <NUM> for similar reasons.

In some embodiments, the power stage <NUM> can be replaced or modified based on the particular application and/or user needs. For example, power to the amplifiers 130a and 130b can 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> is a block diagram that shows an example power stage <NUM>. In some embodiments, the power stage <NUM> can be a variant of the example power stage <NUM> of the system <NUM> of <FIG>. In general, the power stage <NUM> is configured such that power to the amplifiers 130a and 130b can be controlled, and includes parallel amplifiers to drive the amplified analog control signals 132a and 132b.

The power stage <NUM> includes the amplifiers 130a and 130b, and the EHSV <NUM> in the illustrated view. The analog control signal 122a and the analog control signal 122b are received from the DAC <NUM> (not shown in this view), and the portions 142a and 142b are provided to the amplifiers 140a and 140b (not shown in this view).

Power to the amplifiers 130a and 130b is controlled by a power control circuit <NUM>. Constant power is supplied to the amplifiers 130a and 130b by a power supply <NUM>. Additional power from a power supply <NUM> is supplied to the amplifiers 130a and 130b based on an amplification control signal <NUM> (e.g., provided by the controller <NUM>). When the signal <NUM> is brought high, a switch 218a and a switch 218b allow the additional power from the power supply <NUM> to flow to the amplifiers 130a and 130b. When the signal <NUM> is brought low, the switch 218a and the switch 218b prevent additional power from the power supply <NUM> to flow to the amplifiers 130a and 130b.

Output drive current, in addition to the current provided by the amplifier 130a, is provided to the EHSV <NUM> by an amplifier 230a. The amplifier 230a is configured to follow the amplified analog control signal 132a output by the amplifier 130a, and provide its output in parallel with the amplified analog control signals 132a to form an amplified analog control signal 232a that is provided to the EHSV <NUM>. Similarly, the amplifier 230b is configured to follow the amplified analog control signal 132b output by the amplifier 130b, and provide its output in parallel with the amplified analog control signals 132b to form an amplified analog control signal 232b that is provided to the EHSV <NUM>. Together the amplified analog control signals 232a and 232b form a differential analog control signal that drives the operation of the EHSV <NUM>.

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

At <NUM>, a predetermined setpoint is received. For example, the example controller <NUM> can receive the setpoint <NUM> from a human operator (e.g., a pilot) or from another circuit (e.g., an autopilot) that represents a desired configuration of the EHSV <NUM>, the actuator <NUM>, or mechanical loads that are actuated by the actuator <NUM>.

At <NUM>, a differential analog feedback signal is received. For example, controller <NUM> can receive the amplified differential analog signal provided by the amplified analog control signals 144a and 144b.

At <NUM>, a digital position signal is determined based on the received setpoint and the received differential analog feedback signal. For example, the controller <NUM> can determine the digital control signal <NUM> based on the setpoint <NUM> and the amplified analog control signals 144a and 144b.

At <NUM>, the determined digital position signal is provided. For example, the digital control signal <NUM> can be provided from the controller <NUM> to the DAC <NUM>.

At <NUM>, a differential analog electrohydraulic servo valve position control signal is determined based on the digital position signal. For example, the DAC <NUM> provides the amplified analog control signals 132a and 132b, which together form the amplified differential analog control signal.

At <NUM>, 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 signals 132a and 132b is provided by the DAC <NUM>.

In some implementations, the process <NUM> 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. For example, the controller <NUM> can receive the demodulated signal <NUM> based on the position signal <NUM>, and the controller <NUM> can determine the digital control signal <NUM> based on the demodulated signal <NUM>.

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 signal <NUM> can be provided by the sensor <NUM>, which is configured to sense the linear position of the EHSV <NUM>. In some implementations, the electrohydraulic servo valve spool position signal can be a variable differential transformer signal. For example, the sensor <NUM> can be a linear or rotary VDT.

In some implementations, the process <NUM> can also include receiving an output position signal, wherein the digital position signal is further based on the output position signal. For example, the controller <NUM> can receive the demodulated signal <NUM> based on the position signal <NUM>, and the controller can determine the digital control signal <NUM> based on the demodulated signal <NUM>. In some implementations, the output position signal can be a variable differential transformer signal. For example, the sensor <NUM> can be a linear or rotary VDT that can provide the position signal <NUM> as a VDT signal.

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

<FIG> is a schematic diagram of an example of a generic computer system <NUM>. The system <NUM> can be used for the operations described in association with the process <NUM> according to one implementation. For example, the system <NUM> may be included as part or all of the example controller <NUM> of <FIG>.

The system <NUM> includes a processor <NUM>, a memory <NUM>, a storage device <NUM>, and an input/output device <NUM>. Each of the components <NUM>, <NUM>, <NUM>, and <NUM> are interconnected using a system bus <NUM>. The processor <NUM> is capable of processing instructions for execution within the system <NUM>. In one implementation, the processor <NUM> is a single-threaded processor. In another implementation, the processor <NUM> is a multi-threaded processor. The processor <NUM> is capable of processing instructions stored in the memory <NUM> or on the storage device <NUM> to display graphical information for a user interface on the input/output device <NUM>.

The features described can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. The apparatus can be implemented in a computer program product tangibly embodied in an information carrier, e.g., in a machine-readable storage device for execution by a programmable processor; and method steps can be performed by a programmable processor executing a program of instructions to perform functions of the described implementations by operating on input data and generating output. The described features can be implemented advantageously in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. A computer program is a set of instructions that can be used, directly or indirectly, in a computer to perform a certain activity or bring about a certain result.

The processor and the memory can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits) and/or field programmable gate arrays (FPGA).

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.

Claim 1:
A controller apparatus, comprising:
a digital controller (<NUM>) configured to provide a digital position signal (<NUM>) based on a setpoint (<NUM>) and a differential analog feedback signal (144a, 144b); and
a converter circuit (<NUM>, <NUM>) configured to provide a differential analog electrohydraulic servo valve position control signal (132a, 132b) to an electrohydraulic servo valve (<NUM>) based on the digital position signal (<NUM>), and provide a portion of the differential analog electrohydraulic servo valve position control signal (132a, 132b) as the differential analog feedback signal (144a, 144b).