Patent Description:
Flow angle sensors, such as angle of attack sensors or side slip angle sensors, are installed on aircraft to generate air data parameters. Angle of attack sensors with rotatable vanes are installed on the exterior of an aircraft to measure the aircraft angle of attack, the angle between oncoming airflow and the aircraft zero line (a reference line of the aircraft, such as a chord of a wing of the aircraft). The angle of attack sensor is mounted to the aircraft such that the rotatable vane protrudes outside the aircraft and is exposed to oncoming airflow. Aerodynamic forces acting on the rotatable vane cause the vane to align with the direction of the oncoming airflow. Rotational position of the vane is sensed and used to determine the aircraft angle of attack. It can be difficult to measure the angle of attack under certain conditions. <CIT> discloses an angle measurement probe on board an aircraft and aircraft implementing at least one such probe. <CIT> relates to an angle of attack detection and indication system. The angle of attack detection systems of these documents use photo-electrical barriers with LEDs and photo-transistors to detect the rotation of disks with apertures. <CIT> discloses an angle-of-attack sensor with rotatable airfoil.

A flow angle sensor includes a sensing element, a background component connected to and movable with the sensing element, the background component having a marker, a lens adjacent the disk, an image sensor axially aligned with the lens to capture an image of the marker, a light source positioned to illuminate the disk, and an image processing system connected to the image sensor. The image processing system provides an angle of attack output based on a location of the marker sensed by the image sensor.

The flow angle sensor is an angle of attack sensor including a housing, a faceplate positioned on the housing, a vane assembly adjacent the faceplate, the vane assembly including a vane connected to a vane shaft, a rotatable disk connected to the vane shaft opposite the vane, the disk having a marker, a lens adjacent the disk, an image sensor axially aligned with the lens, a light source within the housing and positioned to illuminate the disk, and an image processing system connected to the image sensor.

In general, the present disclosure describes an angle of attack sensor that has an image sensor connected to an image processing system to measure angle of attack using optical sensing technology. The image sensor determines the locations of a marker on a rotating disk connected to a rotating vane by continuously capturing images of the marker using a lens and a light source. The image processing system uses the locations of the marker to determine the angular displacement of the vane and subsequently the local flow angle.

<FIG> is a perspective view of angle of attack sensor <NUM>. Angle of attack sensor <NUM> includes faceplate <NUM> (which includes mounting plate <NUM> and chassis <NUM>), housing <NUM>, and vane assembly <NUM> (which includes vane <NUM>).

Angle of attack sensor <NUM> is a flow angle sensor. Faceplate <NUM> is a multi-piece faceplate that includes mounting plate <NUM> and chassis <NUM>. Mounting plate <NUM> has an opening at a center of mounting plate <NUM>. Chassis <NUM> is adjacent mounting plate <NUM> and may be heated. Mounting plate <NUM> is positioned on chassis <NUM> such that chassis <NUM> is located inward from or interior to mounting plate <NUM> with respect to housing <NUM>. In alternate embodiments, faceplate may be a single-piece faceplate that does not include chassis <NUM>. Housing <NUM> is cylindrical with an annular sidewall between an open first end and a closed second end. In alternate embodiments, housing <NUM> may be any suitable shape. Faceplate <NUM> is positioned on housing <NUM> adjacent to the open first end of housing <NUM>. Mounting plate <NUM> is an outer piece of faceplate <NUM>, and chassis <NUM> is an inner piece of faceplate <NUM>. Vane assembly <NUM> is adjacent faceplate <NUM>. Vane assembly <NUM>, which includes vane <NUM>, has a portion that is positioned in chassis <NUM> and extends through the opening of mounting plate <NUM>. Vane <NUM> extends through mounting plate <NUM>.

Angle of attack sensors <NUM> are installed on an aircraft and mounted to the aircraft via fasteners, such as screws or bolts, and mounting holes on mounting plate <NUM>. As a result, mounting plate <NUM> is about flush with the skin of the aircraft and housing <NUM> extends within an interior of the aircraft. Vane <NUM> extends outside an exterior of aircraft and is exposed to external airflow, causing vane <NUM> to rotate with respect to mounting plate <NUM> and chassis <NUM> via a series of bearings within angle of attack sensor <NUM>. Vane <NUM> rotates based on the local flow angle. Vane <NUM> causes rotation of a vane shaft, and a disk within housing <NUM>. Rotation of the rotatable vane is determined and used to measure the angle of attack. The measured angle of attack is communicated to a flight computer or other aircraft systems, such as avionics, air data inertial reference units (ADIRUs), flight control computers, or air data computers, and can be used to generate air data parameters related to the aircraft flight condition.

<FIG> is a schematic view of angle of attack sensor <NUM>. <FIG> is a schematic top view of disk <NUM> showing marker <NUM>. <FIG> is a schematic top view of disk <NUM> showing marker <NUM> after disk <NUM> has been rotated. <FIG> is a schematic view of angle of attack sensor <NUM> showing variables used for calculating angle of attack. <FIG> is a schematic view showing movement of marker <NUM> along pixels <NUM> of image sensor <NUM>. <FIG> is a flowchart showing method <NUM> for image processing. <FIG> will be discussed together. Angle of attack sensor <NUM> includes faceplate <NUM>, housing <NUM>, vane assembly <NUM> (which includes vane <NUM>), vane shaft <NUM>, disk <NUM>, marker <NUM>, lens <NUM>, image sensor <NUM>, image processing system <NUM>, and light source <NUM>. Image sensor <NUM> includes pixels 40A-40N ("N" is used herein as an arbitrary integer), first marker location M1, second marker location M2, and pitch <NUM>. Method <NUM> (shown in <FIG>) includes step <NUM>, step <NUM>, step <NUM>, step <NUM>, step <NUM>, step <NUM>, step <NUM>, step <NUM>, and step <NUM>.

Faceplate <NUM> is positioned on housing <NUM>. Vane assembly <NUM>, which includes vane <NUM>, extends through faceplate <NUM>. Vane <NUM> projects into the airstream that is aligned with the external airflow. Vane <NUM> is a sensing element. An end of vane <NUM> may be positioned in an opening of faceplate <NUM>. Vane <NUM> is connected to a first end of vane shaft <NUM>. Vane shaft <NUM> extends into housing <NUM>. A second end of vane shaft <NUM> is internally connected to rotating cylindrical disk <NUM>. As such, vane <NUM> is connected to disk <NUM> via vane shaft <NUM>. Vane <NUM>, vane shaft <NUM>, and disk <NUM> move, or rotate, together. Disk <NUM> is a background component for marker <NUM>. Marker <NUM> is positioned in disk <NUM>. Marker <NUM> may be a dot or any other suitable shape. Marker is in a fixed position within disk <NUM>. As shown in <FIG>, as disk <NUM> rotates, the location of marker <NUM> changes. Lens <NUM> is adjacent disk <NUM>. Lens <NUM> is a converging lens. Image sensor <NUM> is also placed along an axis of vane shaft <NUM> and is axially aligned with disk <NUM> and lens <NUM>. Image sensor <NUM> is a complementary metal-oxide-semiconductor (CMOS) based image sensor. In alternate embodiments, image sensor <NUM> may be any other suitable image sensor chip or image sensor. Image processing system <NUM> is connected to image sensor <NUM>. Image processing system <NUM> may be electrically or wirelessly connected to image sensor <NUM>. Light source <NUM> is within housing <NUM> and positioned to illuminate disk <NUM> for proper detection by image sensor <NUM>.

As seen in <FIG>, field of view FOV is equal to the diameter of disk <NUM>. In alternate embodiments, field of view FOV may be greater than or less than the diameter of disk <NUM> depending on desired resolution. Length X is the diagonal length of image sensor <NUM>. Focal length f of lens <NUM> is the distance between lens <NUM> and image sensor <NUM>. Working distance WD is the distance between disk <NUM> and lens <NUM>. Focal length f and working distance WD determine the magnification for image processing system <NUM>. Focal length f divided by working distance WD is equal to length X divided by field of view FOV (f/WD = X/FOV). As such, field of view FOV, length X of image sensor <NUM>, focal length f, and working distance WD are variables used by image processing system <NUM> in calculating angle of attack.

As seen in <FIG>, image sensor <NUM> includes pixels 40A-40N. Image sensor <NUM> has a two-dimensional fixed array of pixels 40A-40N. <FIG> shows pixels 40A-40N. In alternate embodiments, image sensor <NUM> may include any number of pixels. Pixels 40A-40N relate to the resolution of image sensor <NUM>. First marker location M1 designates a first location of marker <NUM> determined from a first image of marker <NUM> within image sensor <NUM>. First marker location M1 corresponds to a first location of disk <NUM> and vane <NUM>. Second marker location M2 designates a second location of marker <NUM> determined from a second image of marker <NUM> within image sensor <NUM>. Second marker location M2 corresponds to a second location of disk <NUM> and vane <NUM>. As marker <NUM> moves, images of marker <NUM> move among pixels 40A-40N. Pitch <NUM> is the distance between first marker location M1 and second marker location M2, or the distance between pixels 40A-40N corresponding to first marker location M1 and second marker location M2, on image sensor <NUM>. As marker <NUM> rotates, it moves along an arc on image sensor <NUM> to determine rotation of vane <NUM>, resulting in movement in, or a change in position within, pixels <NUM> in both horizontal and vertical (or x-axis and y-axis) directions.

Disk <NUM> captures movement of vane <NUM>. As vane <NUM> rotates, vane shaft <NUM> and disk <NUM> rotate. Marker <NUM> is utilized for angle indication. Light source <NUM> illuminates disk <NUM> so that image sensor <NUM> can capture marker <NUM> in disk <NUM> with the use of lens <NUM>. Image sensor <NUM> captures the position of marker <NUM>. Image sensor <NUM> continuously senses the position of marker <NUM> in disk <NUM> and transmits marker <NUM> position information to image processing system <NUM>. The location of marker <NUM> is used to determine if and where marker <NUM> is moving within image sensor <NUM> to measure angular displacement of vane <NUM>. As such, angle of attack sensor <NUM> uses image processing system <NUM> to capture the movement of disk <NUM> by calculating the angular movement of marker <NUM>, which is directly proportional to the angle of vane <NUM>, based on tracking the position of marker <NUM> on images captured by image sensor <NUM> and calculating pitch <NUM>. Image processing system <NUM> uses the positions and number of pixels 40A-40N occupied by marker <NUM> to calculate an angle of attack via an image processing algorithm.

For example, vane <NUM> begins in an initial position of zero degrees. When vane <NUM> is at zero degrees, an image of marker <NUM> is captured, and the location of marker <NUM> corresponds to first marker location M1. As such, first marker location M1 corresponds to a zero angle or default position. As vane <NUM> rotates, the movement of circular disk <NUM> causes the location of marker <NUM> to change from its default position. Image sensor <NUM> captures a new image of marker <NUM> in a new location, which corresponds to second marker location M2. The change in position of marker <NUM>, identified using second marker location M2 and the default position, or first marker location M1, is equal to pitch <NUM>, which is used to compute an angle via digital processing techniques. First marker location M1 and second marker location M2 may correspond to any two positions of vane <NUM>. First marker location M1 and second marker location M2 information is transmitted to image processing system <NUM>, which uses an image processing algorithm that correlates the marker locations M1, M2 to an aircraft angle of attack. For example, motion of marker <NUM> can be determined by the percentage of pixels <NUM> the image of marker <NUM> has moved across. As such, image processing system <NUM> provides an angle of attack output based on a location of marker <NUM> sensed by image sensor <NUM>.

<FIG> shows method <NUM> for image processing by image processing system <NUM>. Step <NUM> includes starting image capture. Image sensor <NUM> captures an image of marker <NUM> on disk <NUM>. Step <NUM> includes image enhancement by removing noise. Image processing system <NUM> receives the image captured by image sensor <NUM>. Image processing system <NUM> removes noise, thereby enhancing the image. Step <NUM> includes identifying marker <NUM> in the captured image. Image processing system <NUM> identifies marker <NUM> on the enhanced image. Step <NUM> includes locating marker <NUM> position using details of pixels 40A-40N. Image processing system <NUM> locates the position of marker <NUM> on the image. Step <NUM> includes identifying the angle of marker <NUM> based on the pixel number. Image processing system <NUM> uses pixels 40A-40N to identify the angle of marker <NUM> by identifying in which of pixels 40A-40N image is located. Step <NUM> includes computing the center point in the image. Image processing system <NUM> determines the center point in the image of marker <NUM>, generating first marker location M1. Step <NUM> includes providing the angle value to image processing system <NUM>. Image sensor <NUM> transmits information corresponding to the pixel <NUM> in which the center point of the image of marker <NUM> is located to image processing system <NUM>. Step <NUM> includes capturing and storing the position of marker <NUM>. Image processing system <NUM> receives location information from image sensor <NUM> and stores such information. Step <NUM> includes capturing a new image in a predefined time. Image sensor <NUM> captures a new image of marker <NUM> after a set amount of time to determine whether marker <NUM> has moved. The new position of marker <NUM> correlates to the angle at which vane <NUM> has moved. Method <NUM> is continuously repeated, with image sensor <NUM> constantly capturing images to track the position of marker <NUM> in corresponding pixels <NUM> to determine corresponding movement of vane <NUM>, which produces angle of attack.

Traditional angle of attack sensors, or other flow angle sensors, use resolvers, rotatory variable differential transformers (RVDTs), and potentiometer-based concepts for angle of attack measurement. As such, the sensor may rely on electromagnetics to measure local physical angular displacement with respect to the air stream. Accuracy of the angle of attack measurement varies with temperature, and the sensing element can cause increased friction, which is undesirable. For example, angle accuracy decreases with respect to temperature. Further, the angle is limited with RVDT and potentiometer-based systems of sensors, resulting in a limitation in measurement capabilities. The relative measurement of traditional systems is also dependent on mechanical properties of the vane shaft, such as friction, weight, and tolerance and additional gears that may be present in the system. Additional excitation is also required for the sensor, which cannot be completely isolated from the system. Excitation connections through wires to the vane shaft and resolver or potentiometer are prone to electromagnetic interference (EMI). Changes in electrical parameters, like wire inductances and resistances, cause accuracy variations. As a result, an offset error to the measured value needs to be corrected by calibration. Only relative measurement is possible, and losses will require calibration. Additionally, measured angle accuracy varies with angular displacement when using certain traditional technologies.

Because angle of attack sensor <NUM> does not require contact, friction and hysteresis are reduced, resulting in an increase in reliability and accuracy of absolute angle of attack. The accuracy of angle of attack sensor <NUM> is less affected by temperature variations than traditional sensors because only the image is monitored. Further, angle of attack sensor <NUM> is immune to EMI noise as angle of attack sensor <NUM> uses optical image sensing and image processing to generate angle of attack measurements. Additionally, because angle of attack sensor <NUM> is an optical-based system that does not require contact, angle of attack sensor <NUM> is less prone to effects of direct and indirect lightning strike. Angle of attack sensor <NUM> is also capable of high-resolution encoding. Angle of attack sensor <NUM> achieves the same high level of accuracy as traditional systems for the complete range of angular displacement. Increased magnification is balanced against decreased focal length f to result in a reasonably-sized angle of attack sensor <NUM> with optimal angular resolution. As such, angle of attack sensor <NUM> produces angle of attack measurements that are as accurate or more accurate than traditional angle of attack sensors.

<FIG> is a schematic view of angle of attack sensor <NUM>. Angle of attack sensor <NUM> includes faceplate <NUM>, housing <NUM>, and vane assembly <NUM> (which includes vane <NUM>), vane shaft <NUM>, disk <NUM>, marker <NUM>, lens <NUM>, image sensor <NUM>, image processing system <NUM>, light source <NUM>, and second location <NUM>.

Angle of attack sensor <NUM> has the same structure and function as described with respect to <FIG>. However, angle of attack sensor <NUM> has image processing system <NUM> positioned in second location <NUM> rather than housing <NUM>. Second location <NUM> is a location separate from angle of attack sensor <NUM>. Second location <NUM> may be the flight controls, another remote module, or any other suitable location. Image processing system <NUM> in second location <NUM> is electrically or wirelessly connected to image sensor <NUM> of angle of attack sensor <NUM>. Positioning image processing system <NUM> in second location <NUM> allows angle of attack sensor <NUM> to have a smaller size.

While angle of attack sensors <NUM> and <NUM> have been described with respect to rotatable vanes <NUM> and <NUM> as the sensing elements and rotatable disks <NUM> and <NUM> as background components, angle of attack sensors with various types of sensing elements influenced by airflow external to the aircraft and various background components, including those that move side-to-side or up-and-down, (such as a flipper or cone-based system) can use image sensors (such as image sensors <NUM> and <NUM>), lenses (such as lenses <NUM> and <NUM>), light sources (such as light sources <NUM> and <NUM>), and image processing systems (such as image processing systems <NUM> and <NUM>) to measure angle of attack via optical sensing technology. Additionally, while such technology has been described with respect to angle of attack sensor <NUM> and <NUM>, it may also be used on other types of flow angle sensors, such as a side slip sensor.

Claim 1:
A flow angle sensor (<NUM>; <NUM>) comprising:
a sensing element (<NUM>; <NUM>);
a background component (<NUM>; <NUM>) connected to and movable with the sensing element, the background component having a marker (<NUM>);
a lens (<NUM>) adjacent the background component;
an image sensor (<NUM>) axially aligned with the lens to capture an image of the marker;
a light source (<NUM>) positioned to illuminate the background component; and
an image processing system (<NUM>) connected to the image sensor, wherein the image processing system provides an angle of attack output based on a location of the marker sensed by the image sensor.