Patent Description:
This instant specification relates to ultrasonic position sensors.

Position measurement devices are used for the characterization and operation of fluid control systems. Traditionally, effector (e.g., valve body, piston head) position tracking is achieved through the use of linear variable differential transformers (LVDTs). LVDTs drive system sizing and introduce accuracy and sizing constraints. Specifically, actuation devices generally require the LVDT be installed through the piston rod, driving actuator sizing.

Ultrasonic position sensors are a proven industrial technology that can be leveraged for position detection. Existing time of flight ultrasonic position sensors emit acoustic pings and measure the amount of time until reflected echoes of the pings return. The amount of time between the transmission and return of the pings is generally dependent upon the distance between the transceiver and the object being measured, and the speed of sound in the medium through which the pings are being transmitted. That speed of sound is dependent upon the characteristics of the medium, such as its density, temperature, and/or acoustic impedance. Existing time of flight ultrasonic position sensors depend upon on predetermined knowledge or determination of the speed of sound through the medium through which the pings are being transmitted in order to function. In applications such as fuel valves and pressure regulators, the temperatures and types of fuels used can vary, which can cause the speed of sound to vary dynamically during operation. The speed of sound of a medium can be sensed, but the inclusion of these additional sensors adds to the complexity, size, cost, and weight of such systems.

<CIT> describes a method for measuring movement information with respect to a piston linearly movably accommodated in a housing, defining a first and a second cylinder chamber from each other, the first and/or the second cylinder chamber are at least partially filled with a pressure fluid, wherein a first ultrasonic source is attached to the cylinder, which can convert a first input signal into pressure fluctuations in the pressure fluid, so that sound waves propagate in the pressure fluid, which are at least partially reflected by the piston, wherein a first ultrasonic receiver is attached to the housing, which can convert pressure fluctuations in the pressure fluid into a first output signal. A first frequency difference between the first input signal and the first output signal is measured.

In general, this document describes ultrasonic positon sensors.

A position sensor 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.

According to the present disclosure, a position sensor system includes a fluid effector that includes a housing having an inner surface defining a cavity, and a moveable body having a first face and a second face opposite the first face and configured for reciprocal movement within the housing and configured to contact the inner surface and subdivide the cavity to define a first fluid chamber at the first face and define a second fluid chamber at the second face, an acoustic transmitter system configured to emit a first emitted acoustic waveform in a first direction toward the first face, and emit a second emitted acoustic waveform in a second direction opposite the first direction toward the second face, and an acoustic receiver system configured to detect a first reflected acoustic waveform based on a first reflection of the first emitted acoustic waveform based on the moveable body, and detect a second reflected acoustic waveform based on a second reflection of the second emitted acoustic waveform based on the moveable body.

Various implementations can include some, all, or none of the following features. The position sensor system can include a timer configured to determine a first time of flight of the first emitted acoustic waveform and the first reflected acoustic waveform, and determine a second time of flight of the second emitted acoustic waveform and the second reflected acoustic waveform. The position sensor system can include a processor system configured to determine a position of the moveable body within the cavity based on the first time of flight and the second time of flight. The acoustic transmitter system can be configured to emit one or both of the first emitted acoustic waveform and the second emitted acoustic waveform through a fluid in the cavity, and the acoustic receiver system can be configured to receive one or both of the first reflected acoustic waveform and the second reflected acoustic waveform from the fluid in the cavity. The acoustic transmitter system can be configured to emit one or both of the first emitted acoustic waveform and the second emitted acoustic waveform through the housing, and the acoustic receiver system can be configured to receive one or both of the first reflected acoustic waveform and the second reflected acoustic waveform from the housing. The housing can include an acoustic impedance based on a position of an acoustic interface defined by contact between the moveable body and the housing, and at least one of the first reflected acoustic waveform and the second reflected acoustic waveform can be at least partly reflected based on the acoustic impedance. The acoustic transmitter can be configured to transmit the first emitted acoustic waveform at a predetermined emitted frequency, and the acoustic receiver can be configured to determine a reflected frequency of the first reflected acoustic waveform. The position sensor system can include a processor system configured to determine a speed of the moveable body based on the predetermined emitted frequency and the reflected frequency. The fluid effector can be a linear piston effector, the cavity can be a tubular cavity having a first longitudinal end and a second longitudinal end opposite the first longitudinal end, the moveable body can be a piston head configured for longitudinal movement within the tubular cavity, the acoustic transmitter system can include a first acoustic transmitter arranged at the first longitudinal end and a second acoustic transmitter arranged at the second longitudinal end, and the acoustic receiver system can include a first acoustic receiver arranged at the first longitudinal end and a second acoustic receiver arranged at the second longitudinal end. The fluid effector can be a rotary fluid effector, the cavity can be a cylindrical cavity defining a central axis, the moveable body can be a piston head configured for semi-elliptical movement within the cylindrical cavity about the central axis and can define an acoustic interface in a first portion of the housing proximal an axial position of the piston head within the cylindrical cavity, the acoustic transmitter system can be configured to emit the first emitted acoustic waveform elliptically through a second portion of the housing about the central axis in a first direction toward the first portion, and can be configured to emit the second emitted acoustic waveform elliptically through a third portion of the housing about the central axis in a second direction opposite the first direction toward the first portion, and the acoustic receiver system can include a first acoustic receiver arranged proximal the acoustic transmitter and configured to receive the first reflected acoustic waveform, and a second acoustic receiver arranged proximal the acoustic transmitter and configured to receive the second reflected acoustic waveform. The position sensor system can include a phase detector configured to determine a difference between at least one of (<NUM>) a first emitted phase of the first emitted acoustic waveform and a first reflected phase of the first reflected acoustic waveform, and (<NUM>) a second emitted phase of the second emitted acoustic waveform and a second reflected phase of the second reflected acoustic waveform.

According to the present disclosure, a method of position sensing includes emitting a first emitted acoustic waveform in a first direction through an acoustic medium having a first acoustic impedance toward a first side of an acoustic interface, emitting a second emitted acoustic waveform in a second direction, opposite the first direction, through the acoustic medium toward a second side of the acoustic interface opposite the first side, reflecting, by the acoustic interface, a first reflected acoustic waveform in the second direction based on the first emitted acoustic waveform, reflecting, by the acoustic interface, a second reflected acoustic waveform in the first direction based on the second emitted acoustic waveform, and determining a first position of the acoustic interface based on the first reflected acoustic waveform and the second reflected acoustic waveform.

Various implementations can include some, all, or none of the following features. The method can include determining a first time of flight based on the first emitted acoustic waveform and the first reflected acoustic waveform, and determining a second time of flight based on the second emitted acoustic waveform and the second reflected acoustic waveform, where determining a first position of the acoustic interface can be based on the first time of flight and the second time of flight. Determining the first position of the acoustic interface based on the first time of flight (t<NUM>) and the second time of flight (t<NUM>) can be given by an equation: (t<NUM>-t<NUM>)/(t<NUM>+t<NUM>). The method can include determining a second position of the acoustic interface, and determining a speed of the acoustic interface based on the first position and the second position. The method can also include determining a reflected acoustic frequency based on one or both of the first reflected acoustic waveform and the second reflected acoustic waveform, and determining a speed of the acoustic interface based on the determined reflected acoustic frequency and a predetermined emitted acoustic frequency of one or both of the first emitted acoustic waveform and the second emitted acoustic waveform. The acoustic medium can be a fluid having a first acoustic impedance, the acoustic interface can be defined by a moveable body within a fluid effector and having a second acoustic impedance that is different than the first acoustic impedance, the first emitted acoustic waveform can be emitted toward a first face of the moveable body through the fluid, the second emitted acoustic waveform can be emitted toward a second face of the moveable body, arranged opposite the first face, through the fluid, the first reflected acoustic waveform can be based on a first reflection of the first emitted acoustic waveform by the first face, and the second reflected acoustic waveform can be based on a second reflection of the second emitted acoustic waveform by the second face. The acoustic medium can be a housing of a fluid effector, the housing having a first acoustic impedance and defining a cavity, and can include contacting a portion of the housing with a moveable body configured for movement within the cavity, and modifying, based on the contacting, the first acoustic impedance of the contacted portion of the housing to define a portion of the housing having a second acoustic impedance that is different from the first acoustic impedance, wherein the contacted portion of the housing can define the acoustic interface. The method can include determining a phase difference between at least one of (<NUM>) a first emitted phase of the first emitted acoustic waveform and a first reflected phase of the first reflected acoustic waveform, and (<NUM>) a second emitted phase of the second emitted acoustic waveform and a second reflected phase of the second reflected acoustic waveform, wherein determining a first position of the acoustic interface can be further based on the determined phase difference.

According to the present disclosure, a non-transitory computer storage medium is encoded with a computer program, the program comprising instructions that when executed by data processing apparatus cause the data processing apparatus to perform operations including emitting a first emitted acoustic waveform in a first direction through an acoustic medium having a first acoustic impedance toward a first side of an acoustic interface, emitting a second emitted acoustic waveform in a second direction, opposite the first direction, through the acoustic medium toward a second side of the acoustic interface opposite the first side, detecting a first reflected acoustic waveform, based on the first emitted acoustic waveform, reflected in the second direction by the acoustic interface, detecting a second reflected acoustic waveform, based on the second emitted acoustic waveform, reflected in the first direction by the acoustic interface, and determining a first position of the acoustic interface based on the detected first reflected acoustic waveform and the detected second reflected acoustic waveform.

The systems and techniques described here may provide one or more of the following advantages. First, a system can determine a position and/or speed of a target object though an acoustic transmission medium. Second, the system can operate without determining the acoustic properties of the transmission medium. Third, the system can have a more efficient and/or economical mechanical design compared to existing mechanical position measurement solutions such as variable differential transformers (VDTs). Fourth, the system can have a more efficient and/or economical electronic design compared to existing ultrasonic position measurement solutions. Fifth, the system can provide a more space efficient option for system sizing. Sixth, the system can improve weight, pump demand, thermal loads, and measurement accuracy.

This document describes systems and techniques for ultrasonic position sensing, more particularly, for sensing the position of moveable members in fluid environments, such as valve bodies and piston heads. In general, the ultrasonic position sensing systems and techniques described in this document measure the distance from a moveable object to each end of its length of travel to determine a ratiometric position value that can be determined without needing to know or otherwise determine the speed of sound in the medium in which the ultrasonic signals are being transmitted.

<FIG> is a schematic diagram that shows an example of a system <NUM> for ultrasonic position measurement (e.g., a position sensor system). The system <NUM> includes a fluid effector <NUM>. The fluid effector <NUM> includes a housing <NUM> having an inner surface <NUM> defining a cavity <NUM> (e.g., a cylindrical cavity), and a moveable body <NUM>. The moveable body <NUM> has a face <NUM> and a face <NUM> opposite the face <NUM>, and is configured for reciprocal movement within the housing <NUM>. The moveable body <NUM> is configured to contact the inner surface <NUM> and subdivide the cavity <NUM> to define a fluid chamber <NUM> at the face <NUM> and define a fluid chamber <NUM> at the face <NUM>, and is configured for longitudinal movement within the cavity <NUM>.

The fluid effector <NUM> includes an acoustic transceiver 130a. The acoustic transceiver 130a includes an acoustic transmitter system configured to emit an emitted acoustic waveform 132a in a first direction toward the face <NUM>. The acoustic transceiver 130a also includes an acoustic receiver system configured to detect a reflected acoustic waveform 133a based on a first reflection of the emitted acoustic waveform 132a based on the moveable body <NUM>. In some embodiments, a single transducer (e.g., a piezo element) can perform the functions of both the acoustic transmitter and the acoustic receiver. In some embodiments, the acoustic transmitter and the acoustic receiver can be discrete components.

The fluid effector <NUM> also includes an acoustic transceiver 130b. The acoustic transceiver 130b includes an acoustic transmitter system configured to emit an emitted acoustic waveform 132b in a second direction opposite the first direction toward the face <NUM>. The acoustic transceiver 130a also includes an acoustic receiver system configured to detect a reflected acoustic waveform 133b based on a second reflection of the emitted acoustic waveform 132b based on the moveable body <NUM>. In some embodiments, a single transducer (e.g., a piezo element) can perform the functions of both the acoustic transmitter and the acoustic receiver. In some embodiments, the acoustic transmitter and the acoustic receiver can be discrete components.

A signal processor <NUM> is configured to process signals from the acoustic transceiver 130a and the acoustic transceiver 130b to determine the position of the moveable body <NUM> within the cavity <NUM>. A controller <NUM> (e.g., a computer) is configured to receive position information from the signal processor <NUM> and perform functions based on the position information (e.g., control a process, present information to a user, transmit information to another system, record a log). In some embodiments, the signal processor <NUM> can include a timer (e.g., to measure the times of flight of emitted and reflected signals). In some embodiments, the signal processor <NUM> can include a phase detector (e.g., to determine phase and/or Doppler shifts in reflected signals).

In general, the fluid effector <NUM> is configured as a ratiometric position-sensing device. A transmit-receive transducer is located on either end of the effector. Both transmitters can send a pulse echo and receive an echo upon reflection from the effector piston. Time measurements of the two transducers can independently determine the position of a moveable body when sound speed is known. However, when coupling two transducers into a system, sound speed is cancelled and a ratiometric ultrasound position sensor is obtained. In some implementations, if either transducer fails, redundancy can be obtained through measurement or approximation of sound speed. The techniques for processing the signals, and several examples of the fluid effector <NUM>, will be discussed in the descriptions of <FIG>.

<FIG> is an internal view of an example of a linear fluid effector <NUM>. In some implementations, the linear fluid effector <NUM> can be the example fluid effector <NUM> of <FIG>.

The fluid effector <NUM> includes a housing <NUM> having an inner surface <NUM> defining a cavity <NUM> (e.g., a tubular cavity), and a moveable body <NUM>. The housing <NUM> is generally tubular, having a first longitudinal end 213a and a second longitudinal end 213b opposite the first longitudinal end 213a, and a length represented by arrow <NUM>.

The moveable body <NUM> has a face 220a and a face 220b opposite the face 220a. The moveable body <NUM> is configured for reciprocal movement within the housing <NUM>. The moveable body <NUM> is configured to contact the inner surface <NUM> and subdivide the cavity <NUM> to define a fluid chamber 224a on the side of the face 220a and define a fluid chamber 224b on the side of the face 220b.

In some examples, the fluid effector <NUM> can be configured as a valve. For example, the housing <NUM> can be a valve housing and the moveable body <NUM> can be a valve body configured to slide longitudinally within the valve housing to control fluid flow. In some examples, the fluid effector <NUM> can be configured as a pressure regulator or sensor, in which fluid pressure in one or both of the fluid chambers 224a-224b can urge movement of the moveable body <NUM> within the housing. In some examples, the fluid effector <NUM> can be configured as a fluid actuator. For example, the housing <NUM> can be a hydraulic cylinder and the moveable body <NUM> can be a piston head that can be moved within the cavity <NUM> to urge a fluid flow, or a piston head that can be moved within the cavity <NUM> by fluid pressure within the fluid chambers 224a-224b. In some examples, the fluid effector <NUM> can be configured as any appropriate form of device in which a moveable body moves linearly within a fluid-filled cavity.

The fluid effector <NUM> includes an acoustic transceiver 230a. The acoustic transceiver 230a includes an acoustic transmitter system configured to emit an emitted acoustic waveform 232a toward the face 220a through a medium (e.g., a fluid) filling the fluid chamber 224a. The acoustic transceiver 230a also includes an acoustic receiver system configured to detect a reflected acoustic waveform 233a based on a reflection of the emitted acoustic waveform 232a off the moveable body <NUM>.

The fluid effector <NUM> includes an acoustic transceiver 230b. The acoustic transceiver 230b includes an acoustic transmitter system configured to emit an emitted acoustic waveform 232b toward the first face 220b through a medium filling the fluid chamber 224b. The acoustic transceiver 230b also includes an acoustic receiver system configured to detect a reflected acoustic waveform 233b based on a reflection of the emitted acoustic waveform 232b off the moveable body <NUM>. In some embodiments, a single transducer (e.g., a piezo element) can perform the functions of both the acoustic transmitter and the acoustic receiver. In some embodiments, the acoustic transmitter and the acoustic receiver can be discrete components.

The acoustic transceivers 230a-230b are configured to be activated by an external system such as the example signal processor <NUM> of <FIG>, and provide signals based on the reflected acoustic waveforms 233a-233b to the external system for processing. In some embodiments, a single transducer (e.g., a piezo element) can perform the functions of both the acoustic transmitter and the acoustic receiver. In some embodiments, the acoustic transmitters and the acoustic receivers can be discrete components.

The medium through which the acoustic waveforms 232a and 233a travel has a speed of sound (C<NUM>). In the illustrated example, the measured time (t<NUM>) (e.g., a first time-of-flight) in conjunction with the sound speed (C<NUM>) defines a distance L<NUM> (represented by arrow 260a) from the acoustic transceiver 230a to the face 220a of the moveable body <NUM>: <MAT>.

The medium through which the acoustic waveforms 232b and 233b travel has a speed of sound (C<NUM>). In the illustrated example, the measured time (t<NUM>) (e.g., a second time-of-flight) in conjunction with the sound speed (C<NUM>) defines a distance L<NUM> (represented by arrow 260b) from the acoustic transceiver 230b to the face 220b of the moveable body <NUM>: <MAT>.

The acoustic transceivers 230a and 230b and the moveable body <NUM> can be configured such that the signals are used to determine a ratiometric value for the position of the moveable body <NUM> within its range of motion (e.g., the distance L<NUM>+L<NUM>, or the length <NUM> minus the longitudinal thickness of the moveable body <NUM>): <MAT>.

In use, the speed of sound in the fluid that fills the cavity <NUM> does not need to be known or determined. Since both sides of the cavity <NUM> are filled with the same type of fluid under substantially the same conditions (e.g., temperature), the speed of sound in the fluid will be the same on both sides of the cavity <NUM>, and the speed of sound becomes cancelled out of Equation <NUM>. And since the speed of sound drops out of Equation <NUM>, the relative position of the moveable body <NUM> within the cavity <NUM> becomes a unitless ratiometric value. An absolute position of the moveable body <NUM> can be determined, if needed, based on the ratiometric value and a predetermined value for the range of motion (e.g., L<NUM> + L<NUM>). For example, if the range of motion is known to be <NUM>, and the position is determined to be <NUM> (e.g., based on t<NUM> and t<NUM>), then the absolute position of the moveable body <NUM> within the cavity <NUM> can be determined.

For example, the transducers may sit flush with the bore of the cylinder on both ends (e.g., if the piston head sits on the wall time is zero on the face). In this example, if the piston is precisely in the middle, then t<NUM> = t<NUM>, which is <NUM>% of stroke. However, Equation <NUM> is Position ~ (t<NUM>-t<NUM>)/(t<NUM>+t<NUM>) → (t<NUM> = t<NUM>) (e.g., the numerator goes to zero). As the piston strokes in one direction, t<NUM> decreases and t<NUM> increases, driving the ratio negative. Conversely, as the piston strokes in the opposite direction, the ratio increases. So at one stop the position output is -<NUM> in this example, and at the opposite stop the position output is +<NUM>. In another example, for an Equation <NUM> measurement of <NUM> this would fall between -<NUM> (e.g., retract) and +<NUM> (e.g., extend). The percentage of total stroke here becomes (. <NUM>-(-<NUM>))/(<NUM>-(-<NUM>)) → <NUM>/<NUM> → <NUM>% of total stroke. For a piston configuration having a total stroke of <NUM>, the actual position from the housing stop would be (L<NUM>+L<NUM>)*<NUM>%=<NUM>*<NUM>%=<NUM>, and the distance from the opposing stop would be <NUM>-<NUM>=-<NUM>.

Since the ratiometric value is based on the distances between the acoustic transceivers 230a and 230b and the faces 220a and 220b, the thickness of the moveable body <NUM> (e.g., the distance between the faces 220a and 220b) does not directly affect the ratiometric value. In some implementations, the absolute positions of the faces 220a and 220b can be determined based on a determined absolute position of the moveable body <NUM> and the predetermined thickness of the moveable body <NUM> (e.g., the absolute position of the face 220a-220b can be offset from the absolute position of the center of the moveable body <NUM> by plus or minus one-half the distance between the faces 220a and 220b or another predetermined offset distance).

The described technique can be extended to perform additional functions. For example, by pinging the two sides of the moveable body <NUM>, the position of the moveable body <NUM> can be determined. By pinging the two sides of the moveable body <NUM> again to determine a second position of the moveable body, the difference in the two positions and the amount of time between the two measurements can be used to determine a speed of the moveable body <NUM>. The determined speed of the moveable body <NUM> and predetermined knowledge of the mechanical configuration of the fluid effector <NUM> can be used to determine a linear velocity of the moveable body <NUM> (e.g., the speed can be determined, and the moveable body <NUM> is known to move linearly). In another example, multiple positions and/or velocities can be measured and/or determined, and such information can be used to determine an acceleration of the moveable body <NUM>.

In the example fluid effector <NUM>, the acoustic waveforms 232a and 232b are reflected off the faces 220a and 220b. The reason that the acoustic waveforms 232a and 232b are reflected is because the moveable body <NUM> defines an acoustic interface at the faces 220a and 220b. The fluid in the fluid chambers 224a and 224b has an acoustic impedance, and the moveable body <NUM> has a different acoustic impedance. As in many types of signal transmission systems, an impedance mismatch can cause a transmitted signal to be reflected. In the illustrated example in which ultrasonic signals are being transmitted, the locations of these impedance mismatches define the locations of acoustic interfaces. In the illustrated example, the face 220a and the face 220b define the locations of the acoustic impedance mismatches and their corresponding acoustic interfaces. Other examples of using acoustic interfaces for determining the location of a moveable body are discussed in further detail in the descriptions of <FIG>.

<FIG> is an internal view of another example of a linear fluid effector <NUM> (e.g., a linear piston effector). In some implementations, the linear fluid effector <NUM> can be the example fluid effector <NUM> of <FIG>. In general, this example also relies on time of flight, but uses transverse waves propagating within the cylinder wall of the actuator instead of the hydraulic working fluid.

The linear fluid effector <NUM> includes a housing <NUM> having an inner surface <NUM> defining a cavity <NUM>. A moveable body <NUM> (e.g., a piston head in the illustrated example) is configured to move longitudinally within the cavity <NUM> to actuate a piston rod <NUM>. The housing <NUM> is generally tubular, having a first longitudinal end 313a and a second longitudinal end 313b opposite the first longitudinal end 313a.

The moveable body <NUM> has a face 320a and a face 320b opposite the face 320a. The moveable body <NUM> is configured for reciprocal movement within the housing <NUM> with a total stroke (represented by arrow <NUM>). The moveable body <NUM> is configured to contact the inner surface <NUM> and subdivide the cavity <NUM> to define a fluid chamber 324a on the side of the face 320a and define a fluid chamber 324b on the side of the face 320b.

The linear fluid effector <NUM> includes an acoustic transceiver 330a. The acoustic transceiver 330a includes an acoustic transmitter system configured to emit an emitted acoustic waveform 332a through the housing <NUM> toward a first side 320a of an acoustic interface <NUM>. The acoustic transceiver 330a also includes an acoustic receiver system configured to detect a reflected acoustic waveform 333a based on a reflection of the emitted acoustic waveform 332a off the acoustic interface <NUM>.

The linear fluid effector <NUM> includes an acoustic transceiver 330b. The acoustic transceiver 330b includes an acoustic transmitter system configured to emit an emitted acoustic waveform 332b through the housing <NUM> toward a second side 320b of the acoustic interface <NUM>. The acoustic transceiver 330b also includes an acoustic receiver system configured to detect a reflected acoustic waveform 333b based on a reflection of the emitted acoustic waveform 332b off the acoustic interface <NUM>.

The acoustic transceivers 330a-330b are configured to be activated by an external system such as the example signal processor <NUM> of <FIG>, and provide signals based on the reflected acoustic waveforms 333a-333b to the external system for processing. In some embodiments, a single transducer (e.g., a piezo element) can perform the functions of both the acoustic transmitter and the acoustic receiver. In some embodiments, the acoustic transmitter and the acoustic receiver can be discrete components.

Transverse waves and/or surface acoustic waves are generated by acoustic transceivers 330a-330b located on opposing ends of the cylinder wall in intimate acoustic contact with the housing <NUM>. In some embodiments, the acoustic transceivers 330a-330b can be formed of bonded bulk ceramic, bulk single-crystal, or deposited piezoelectric layers, material films, or any other appropriate material that can form an integral part of the housing <NUM>. The acoustic transceivers 330a-330b are configured to generate a hoop stress in the housing <NUM> which propagates in the axial direction along the housing <NUM>. Transverse waves and surface acoustic waves cannot propagate within fluidic masses, substantially eliminating the effects of reverberation and cross coupling within the fluid that may otherwise interfere with measurement accuracy. The waves are reflected when they reach the moveable body <NUM>, being in intimate contact with the housing <NUM>, produces an abrupt acoustic impedance change in the propagation path.

In some implementations, this example can be used in applications that cannot accommodate transducers in contact with the hydraulic fluid medium, cannot accommodate the required pressure ports into the hydraulic cylinder, would otherwise benefit from reduced size and location of the transducers, or require higher measurement accuracy than previous position indicators. In some implementations, sensor accuracy may not be substantially impacted compared to the echoes in the fluid. The acoustic transceivers 330a-330b may further be located within the inner diameter of the housing <NUM> in contact with the fluid, or externally on the outside of housing <NUM>. In some embodiments, the acoustic transceivers 330a-330b can be fashioned as removable transducers. For example, the use of removable transducers can enable the techniques described in this document to be applied or retrofitted to hydraulic or pneumatic fluidic actuators not originally designed or conceived to possess position sensing functionality at the time of manufacture.

The process of determining the position of the moveable member <NUM> is similar to that of the process described in relation to the example fluid effector <NUM> of <FIG>, except that instead of transmitting and receiving the acoustic waveforms 232a, 232b, 233a, and 233b though fluid in the fluid chambers 224a and 224b as in the example fluid effector <NUM>, the acoustic waveforms 332a, 332b, 333a, and 333b are transmitted through the housing <NUM>. The emitted acoustic waveforms 332a and 332b are reflected by the acoustic interface <NUM> as the reflected acoustic waveforms 333a and 333b.

In use, the times of flight of the emitted acoustic waveforms 332a and 332b, and their return as the reflected acoustic waveforms 333a and 333b can be measured (e.g., times-of-flight) and used to determine the ratiometric position (and by extension, the absolute position) of the moveable member <NUM> and the piston rod <NUM>. For example, equations <NUM>-<NUM> discussed above can also be used with the times-of-flight determined from the linear fluid effector <NUM>.

<FIG> is a sectional view of an example of an acoustic interface <NUM>. In some examples, the acoustic interface <NUM> can be the example acoustic interface <NUM> of <FIG>. In the illustrated example, a housing <NUM> includes an inner surface <NUM> that defines a cavity <NUM>. A seal <NUM> is configured to contact the inner surface <NUM> and a moveable body <NUM> to subdivide the cavity <NUM> into a fluid chamber 424a and a fluid chamber 424b. The seal <NUM> contacts the housing <NUM> at a contact area <NUM>.

Acoustic impedance is defined as Z=ρBVP, where ρB is the bulk density of the medium and is the longitudinal velocity of the wave in the medium. The housing <NUM> is made out a material that has a natural acoustic impedance, for example, due to the temperature, density, and other properties of the material from which the housing <NUM> is formed. In the illustrated example, the regions of the housing <NUM> having the natural acoustic impedance are represented by a light dither pattern and the identifier <NUM>. For example, the acoustic impedance of aluminum is about <NUM>/cm<NUM>-sec x10<NUM>, and the acoustic impedance of <NUM> stainless steel is about <NUM>/cm<NUM>-sec x10<NUM>. These are just two examples of acoustic impedances for two different materials. The techniques described in this document make it unnecessary to know, determine, or estimate the acoustic impedance of a material.

The housing <NUM> also includes a region of modified acoustic impedance represented by a denser dither pattern and the identifier <NUM>. In some embodiments, the effective acoustic impedance of a material can be affected by mechanical contact with or proximity to another object at or around the point of contact or proximity. For example, mechanical contact between the seal <NUM> and the housing <NUM> can acoustically dampen the housing <NUM> at or around the contact area <NUM> and increase the acoustic density of the housing <NUM> at or near the contact area <NUM>. In such examples, the region <NUM> can have a relatively higher acoustic impedance than the regions <NUM>. In another example, the seal <NUM> may have a lower acoustic impedance than the housing <NUM>, and mechanical contact between the seal <NUM> and the housing <NUM> can provide a path of lesser acoustic impedance for acoustic vibrations travelling along the housing <NUM> at or near the contact area <NUM>, effectively lowering the acoustic impedance of the acoustic transmission pathway in the region <NUM> relative to the regions <NUM>.

In general, when two sections of a transmission medium have different impedances, an impedance mismatch is presented. The boundaries between differing acoustic impedances define the locations of acoustic impedance mismatches, which are also called acoustic interfaces. In the illustrated example, acoustic waves traverse at the interface of the fluid and the housing (e.g., along the inner surface <NUM>). The mismatch in impedance occurs when the fluid becomes the seal. The junctions where the inner surface <NUM>, the fluid, and the seal <NUM> coincide one another define an acoustic interface 470a and an acoustic interface 470b.

As in many types if signal transmission processes, a signal that propagates along a transmission pathway and then encounters an impedance mismatch can result in at least a portion of the signal to be reflected back along the transmission pathway. Similarly, acoustic signals (e.g., the emitted acoustic waveforms 332a and 332b) can be reflected back toward their sources by acoustic interfaces.

In the illustrated example, the locations of the acoustic interfaces 470a and 470b within the housing <NUM> are defined by the location of the moveable body <NUM> within the cavity <NUM> (e.g., the moveable body <NUM> defines the location of the seal <NUM>, which defines the location of the region <NUM>, which defines the locations of the acoustic interfaces 470a and 470b). Movement of the moveable body <NUM> causes the acoustic interfaces 470a and 470b to move as well.

Returning briefly to <FIG>, movement of the moveable body <NUM> causes corresponding movements of acoustic interfaces (e.g., the acoustic interfaces 470a and 470b) within the housing <NUM>. As the moveable body <NUM> moves, the distances between the acoustic transceivers 330a and 330b and their respective acoustic interfaces change as well, which causes proportional changes in the times-of-flight of the emitted acoustic waveforms 332a and 332b and the reflected acoustic waveforms 333a and 333b. As discussed above, the times of flight can be used to determine the ratiometric position of the acoustic interfaces along the housing <NUM>, and therefore determine the position of the moveable member <NUM> within the cavity <NUM>. As also discussed above, these locations can be determined without knowing or determining the acoustic properties of the housing (e.g., the acoustic impedances of the housing or of regions of modified acoustic impedance, which can change dynamically with temperature).

<FIG> is a sectional view of an example of a rotary fluid effector <NUM>. In some implementations, the rotary fluid effector <NUM> can be the example fluid effector <NUM> of <FIG>. The rotary fluid effector <NUM> includes a housing <NUM> having an inner surface <NUM> defining a cavity <NUM> that is generally cylindrical. A moveable body <NUM> (e.g., a rotary vane in the illustrated example) is configured to move semi-elliptically (e.g., rotate, pivot) about a central axis <NUM> of a shaft <NUM> within the cavity <NUM>. In some embodiments, the moveable body <NUM> can be configured to urge rotation of the shaft <NUM>.

The moveable body <NUM> is configured to contact the inner surface <NUM> (e.g., directly or through a seal) along a contact area <NUM> at or along an axial position of the generally cylindrical housing <NUM>. The materials used to form the housing <NUM> have an acoustic impedance, and the contact between the moveable body <NUM> and the housing <NUM> modified the acoustic impedance of the housing <NUM> at or around the contact area <NUM> to define a region <NUM> having a modified acoustic impedance. The region <NUM> presents an acoustic impedance mismatch within the housing <NUM>, having an acoustic interface 570a and an acoustic interface 570b.

The rotary fluid effector <NUM> includes an acoustic transceiver <NUM>. The acoustic transceiver <NUM> includes an acoustic transmitter system configured to emit an emitted acoustic waveform 532a through the housing <NUM> toward the acoustic interface 570a. The acoustic transceiver <NUM> also includes an acoustic receiver system configured to detect a reflected acoustic waveform 533a based on a reflection of the emitted acoustic waveform 532a off the acoustic interface 570a.

The acoustic transceiver <NUM> is also configured to emit an emitted acoustic waveform 532b through the housing <NUM> toward the acoustic interface 570b of the region <NUM>. The acoustic transceiver <NUM> also includes an acoustic receiver system configured to detect a reflected acoustic waveform 533b based on a reflection of the emitted acoustic waveform 532b off the acoustic interface 570b. In the illustrated example, the acoustic transceiver <NUM> is configured to perform the transmission and receipt of the acoustic waveforms 532a, 532b, 533a, and 533b (e.g., by "ringing" the housing <NUM> at a single location and having the emitted waveforms 532a-532b propagate away from both sides), but in some embodiments separate acoustic transceivers can be used (e.g., one configured to ring the periphery of the housing <NUM> in a clockwise direction and another configured to ring the periphery in a counterclockwise direction).

The acoustic transceiver <NUM> is configured to be activated by an external system such as the example signal processor <NUM> of <FIG>, and provide signals based on the reflected acoustic waveforms 533a-533b to the external system for processing. In some embodiments, a single transducer (e.g., a piezo element) can perform the functions of both the acoustic transmitter and the acoustic receiver. In some embodiments, the acoustic transmitter and the acoustic receiver can be discrete components.

The process of determining the position of the moveable body <NUM> is similar to that of the process described in relation to the example linear fluid effector <NUM> of <FIG>, except that instead of transmitting and receiving the acoustic waveforms 332a, 332b, 333a, and 333b along the longitudinal length of the housing <NUM> as in the example linear fluid effector <NUM>, the acoustic waveforms 532a, 532b, 533a, and 533b are transmitted circumferentially (e.g., orbitally) about the housing <NUM>. The emitted acoustic waveforms 532a and 532b are reflected by the acoustic interface <NUM> as the reflected acoustic waveforms 533a and 533b.

In use, the times of flight of the emitted acoustic waveforms 532a and 532b, and their return as the reflected acoustic waveforms 533a and 533b can be measured (e.g., times-of-flight) and used to determine the ratiometric position (and by extension, the absolute position) of the moveable body <NUM> and the shaft <NUM>. For example, equations <NUM>-<NUM> discussed above can also be used with the times-of-flight determined from the rotary fluid effector <NUM>.

In some embodiments, the rotary fluid effector <NUM> can be a rotary vane actuator (RVA) or a rotary valve. In some embodiments, the rotary fluid effector can be modified to be a rotary piston actuator (RPA). For example, emitted waveforms can be transmitted circumferentially about a tubular housing toward the end of a rotary piston that is configured to move about the axis of the housing and define an acoustic interface within a portion of the housing, and the acoustic interface can reflect a portion of the waveforms for use in determining the rotary position of the rotary piston.

<FIG> is a conceptual diagram <NUM> of a transmitted acoustic waveform <NUM>. <FIG> is a graph <NUM> showing examples of phase shifts in acoustic waveforms. In addition to time based measurement (e.g., as discussed above), time and phase are related to one another as a function of frequency and wavelength. In the illustrated example, the transmitted acoustic waveform <NUM> is transmitted by an acoustic transceiver <NUM> as a continuous wave of single frequency f. The transmitted acoustic waveform <NUM> is broadcast toward a moveable reflector <NUM> positioned at some distance D from the reflector. The transmitted acoustic waveform <NUM> is reflected back toward the acoustic transceiver <NUM>, and reaches the acoustic transceiver <NUM> after making a round trip of length L = 2D.

The acoustic transceiver <NUM> travels some whole number n of wavelengths plus a fraction, where wavelength is given by: <MAT>.

Using Equation <NUM>, the round trip distance to target can be written as: <MAT> <MAT> <MAT> <MAT> <MAT>.

Where the ϕ/2π term is equivalent to time as shown in Equations <NUM> and <NUM>. If n<NUM> = <NUM>, Equation <NUM> is unambiguous and since the frequency f and fluid sound speed are known apriori, D can be determined by direct measurement of the phase of the received signal relative to the transmitted signal.

When n<NUM>><NUM>, D is ambiguous as the measured phase values repeat at intervals of 2πf. The value n<NUM> can be extracted from the measured data based on the idea that the differential phase shift of two simultaneously propagating waves of differing frequencies will generate progressively larger phase shifts; the value of the increase is a constant φd as the travel time increases. This is shown in <FIG>. Detecting the two signals at some distance D and knowing they began traveling at the same time the measured phase can be divided by φd to extract the number of complete wave periods that occurred to generate the measured phase difference. Mathematically: <MAT>.

The phase difference embodiment modifies the time difference embodiment by applying a fixed frequency f<NUM> to the phase measurement in one of the fluid chambers, and another fixed frequency f<NUM> to the other fluid chamber. The exact frequency values of f<NUM> and f<NUM> are not critical to the function of the invention, however it is critical that the frequencies are selected to ensure that n<NUM> = n<NUM> or n<NUM> = n<NUM> +<NUM>. This relationship ensures that the value of φd remains constant over the entire measurement range.

Rewriting Equation <NUM>, using Equations <NUM> and <NUM>: <MAT>.

The phase embodiment maintains the same ratiometric benefits of mechanical length and sound speed insensitivity as the time of flight embodiment. The frequency f<NUM> is related to f<NUM> by a fixed ratio. This condition ensures the relative phase difference remains constant with circuit aging and temperature change. Other embodiments can remove this restriction with the result of reduced aging performance and temperature compensation without substantively altering the method.

Ultrasonic pulses are emitted periodically as is prescribed for position measurement. Following each emission, the returned echo signal is sampled at a fixed delay after the emission. From Equations <NUM> and <NUM>, this delay defines the depth.

As the actuator moves between the successive emissions the sampled values taken at time Ts will change over the time. As the speed information is available only periodically, the technique is limited by the Nyquist theorem. This means that a maximum speed exists for each pulse repetition frequency (Fprf): <MAT>.

The maximum measurable depth is also defined by the pulsed repetition frequency: <MAT>.

Therefore the product of Pmax and Vmax is constant, and is given by: <MAT>.

<FIG> is a flow diagram of an example process <NUM> for ultrasonic position sensing. In some implementations, the process <NUM> can be performed by all or part of the example system <NUM> of <FIG>, the example fluid effector <NUM>, the example linear fluid effector <NUM> of <FIG>, the example linear fluid effector <NUM> of <FIG>, or the example rotary fluid effector <NUM> of <FIG>.

At <NUM>, a first emitted acoustic waveform is emitted in a first direction through an acoustic medium having a first acoustic impedance toward a first side of an acoustic interface. For example, the acoustic transceiver 130a can emit the emitted acoustic waveform 132a toward the face <NUM> of the moveable body <NUM> through a fluid in the cavity <NUM>. In another example, the acoustic transceiver <NUM> can emit the emitted acoustic waveform 532a toward the acoustic interface 570a of the moveable body <NUM> through the housing <NUM>.

At <NUM>, a second emitted acoustic waveform is emitted in a second direction, opposite the first direction, through the acoustic medium toward a second side of the acoustic interface opposite the first side. For example, the acoustic transceiver 130b can emit the emitted acoustic waveform 132b toward the face <NUM> of the moveable body <NUM> through a fluid in the cavity <NUM>. In another example, the acoustic transceiver <NUM> can emit the emitted acoustic waveform 532b toward the acoustic interface 570b through the housing <NUM>.

At <NUM>, a first reflected acoustic waveform is reflected by the acoustic interface in the second direction based on the first emitted acoustic waveform. For example, the face <NUM> can reflect the reflected acoustic waveform 133a back toward the acoustic transceiver 130a. In another example, the acoustic interface 570a can reflect the reflected acoustic waveform 533a back toward the acoustic transceiver <NUM>.

At <NUM>, a second reflected acoustic waveform is reflected by the acoustic interface in the first direction based on the second emitted acoustic waveform. For example, the face <NUM> can reflect the reflected acoustic waveform 133b back toward the acoustic transceiver 130b. In another example, the acoustic interface 570b can reflect the reflected acoustic waveform 533b back toward the acoustic transceiver <NUM>.

At <NUM>, a first position of the acoustic interface is determined based on the first reflected acoustic waveform and the second acoustic waveform. For example, measurements based on the acoustic waveforms 132a, 132b, 133a, and 133b, or the acoustic waveforms 532a, 532b, 533a, and 533b can be used with Equations <NUM>-<NUM> to determine the positions of the moveable bodies <NUM> or <NUM>.

In some implementations, the process <NUM> can also include determining a first time of flight based on the first emitted acoustic waveform and the first reflected acoustic waveform, and determining a second time of flight based on the second emitted acoustic waveform and the second reflected acoustic waveform, where determining a first position of the acoustic interface is further based on the first time of flight and the second time of flight. In some implementations, determining the first position of the acoustic interface based on the first time of flight (t<NUM>) and the second time of flight (t<NUM>) is given by an equation: (t<NUM>-t<NUM>)/(t<NUM>+t<NUM>). For example, Equation <NUM> shows an example of how times of flight of reflected acoustic waveforms can be used to determine a ratiometric position of the acoustic interface that caused the reflections.

In some implementations, the process <NUM> can also include determining a second position of the acoustic interface, and determining a speed of the acoustic interface based on the first positon and the second position. For example, by determining a first position of the moveable body <NUM>, a second position of the moveable body <NUM>, and the amount of time between the two positions, a speed at which the moveable body <NUM> is moving can be determined.

In some implementations, the process <NUM> can include determining a reflected acoustic frequency based on one or both of the first reflected acoustic waveform and the second acoustic waveform, and determining a speed of the acoustic interface based on the determined reflected acoustic frequency and a predetermined emitted acoustic frequency of one or both of the first emitted acoustic waveform and the second emitted acoustic waveform. For example, the emitted acoustic waveforms 132a and 132b can be emitted at a predetermined emitted frequency, and movement of the example moveable body <NUM> can cause a Doppler shift in the reflected acoustic waveforms 133a and 113b. The degree of the Doppler shift can be measured to determine a speed of the moveable body <NUM> relative to the acoustic transceivers 130a and 130b.

In some implementations, the acoustic medium can be a fluid having a first acoustic impedance, the acoustic interface can be defined by a moveable body within a fluid effector and having a second acoustic impedance that is different than the first acoustic impedance, the first emitted acoustic waveform can be emitted toward a first face of the moveable body through the fluid, the second emitted acoustic waveform can be emitted toward a second face of the moveable body, arranged opposite the first face, through the fluid, the first reflected acoustic waveform can be based on a first reflection of the first emitted acoustic waveform by the first face, and the second reflected acoustic waveform can be based on a second reflection of the second emitted acoustic waveform by the second face. For example, the emitted acoustic waveforms 132a and 132b can travel through a fluid in the cavity <NUM> to the face <NUM> and the face <NUM>, and be reflected back through the fluid to the acoustic transceivers 130a and 130b.

In some implementations, the acoustic medium can be a housing of a fluid effector, the housing having a first acoustic impedance and defining a cavity, and also including contacting a portion of the housing with a moveable body configured for movement within the cavity, and modifying, based on the contacting, the first acoustic impedance of the contacted portion of the housing to define a portion of the housing having a second acoustic impedance that is different from the first acoustic impedance, where the contacted portion of the housing defines the acoustic interface. For example, contact between the example seal <NUM> and the example housing <NUM> can develop the region of modified acoustic impedance <NUM>.

In some implementations, the process <NUM> can also include determining a phase difference between at least one of (<NUM>) a first emitted phase of the first emitted acoustic waveform and a first reflected phase of the first reflected acoustic waveform, and (<NUM>) a second emitted phase of the second emitted acoustic waveform and a second reflected phase of the second reflected acoustic waveform, wherein determining a first position of the acoustic interface is further based on the determined phase difference. For example, the differences in phase between the emitted acoustic waveform 132a and the reflected acoustic waveform 133a can be used (e.g., in the example Equations <NUM>-<NUM>) to determine a position of the moveable body <NUM>.

All of the embodiments described can provide, in addition to position, direct measurement of actuator speed by the incorporation of signal processing to extract Doppler shift information (e.g., reflected frequency) from the transducer(s) signals. While only one of the plurality of transducers is required to be processed, Doppler processing of two transducers can provide higher accuracy by a factor of about <NUM>. 4x over the use of a single channel.

<FIG> is a schematic diagram of an example of a generic computer system <NUM>. The system <NUM> can be a data processing apparatus (e.g., processor system) used for the operations described in association with the process <NUM> according to one implementation. For example, the system <NUM> may be included in either or all of the signal processor <NUM> or the controller <NUM>.

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>.

In another implementation, input/output device <NUM> includes a serial link, (e.g., Ethernet, CAN, RS232, RS485, optical fiber), for example, to interface to a remote host and/or to send measurement results, either in a command/response protocol, or at some periodic update rate after a short initialization period (e.g., <<NUM> sec). In another implementation the input/output device <NUM> includes a data bus connection to a second computer system or processor.

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.

Although a few implementations have been described in detail above, other modifications are possible. In addition, the logic flows depicted in the figures do not require the particular order shown, or sequential order, to achieve desirable results. In addition, other steps may be provided, or steps may be eliminated, from the described flows, and other components may be added to, or removed from, the described systems. Accordingly, other implementations are possible as long as they are within the scope of the following claims.

Claim 1:
A position sensor system (<NUM>), comprising:
a rotary fluid effector (<NUM>) comprising
a housing (<NUM>) having an inner surface (<NUM>) defining a cylindrical cavity (<NUM>) defining a central axis (<NUM>), and
a moveable body (<NUM>) having a first face and a second face opposite the first face and configured for reciprocal movement within the housing and configured to contact the inner surface and subdivide the cylindrical cavity to define a first fluid chamber at the first face and define a second fluid chamber at the second face, the moveable body being a piston head configured for semi-elliptical movement within the cylindrical cavity about the central axis and defining an acoustic interface (570a, 570b) in a first portion of the housing proximal an axial position of the piston head within the cylindrical cavity;
an acoustic transmitter system configured to emit a first emitted acoustic waveform (532a) elliptically through a second portion of the housing about the central axis in a first direction toward the first portion, and emit a second emitted acoustic waveform (532b) elliptically through a third portion of the housing about the central axis in a second direction opposite the first direction toward the second portion; and
an acoustic receiver system comprising i) a first acoustic receiver arranged proximal the acoustic transmitter system and configured to detect a first reflected acoustic waveform (533a) based on a first reflection of the first emitted acoustic waveform based on the moveable body, and ii) a second acoustic receiver arranged proximal the acoustic transmitter system and configured to detect a second reflected acoustic waveform (533b) based on a second reflection of the second emitted acoustic waveform based on the moveable body;
wherein the position sensor system (<NUM>) is configured to determine a first position of the acoustic interface based on the first reflected acoustic waveform and the second reflected acoustic waveform.