Patent Application
20090184862
1. Field of the Invention
The present invention relates to collision avoidance systems and, more particularly, to collision avoidance systems and methods that employ multiple sensors to provide collision avoidance.
2. Background of the Invention
A Traffic Alert and Collision Avoidance System (“TCAS”) is a computerized avionics system that is designed to reduce the danger of mid-air collisions between aircraft. TCAS is an implementation of the Airborne Collision Avoidance System mandated by the International Civil Aviation Organization to be fitted on all aircraft over 5700 kg or authorized to carry more than 19 passengers. TCAS tracking is typically accomplished by separately tracking each of the parameters of range, altitude, and bearing for each aircraft that has a transponder capable of responding to TCAS track interrogations. TCAS monitors the airspace around an aircraft, independent of air traffic control, and warns pilots of the presence of other aircraft which may present a threat of mid air collision. In certain situations, a TCAS provides a pilot with a Resolution Advisory (“RA”) that suggests a flight maneuver for the pilot to execute to avoid a collision.
TCAS tracking, however, is not error-proof, and as such, pilots may perform a visual inspection to confirm the accuracy of an RA. Visual confirmation too, is prone to error. Furthermore, in the case of an unmanned aerial vehicle (“UAV”), no human pilot is present to perform a visual inspection to confirm the accuracy of any recommended maneuver, assuming such a collision avoidance maneuver was recommended for a UAV. As such, UAVs may not currently fly in commercial airspace.
In view of the foregoing, embodiments of the present invention provide collision avoidance systems and methods that employ multiple sensors to provide collision avoidance advisories.
Systems and methods consistent with embodiments of the present invention may provide means to use TCAS tracking data and optical tracking data to provide an automated advisory, such as an RA. The TCAS tracking data may be determined to be correlated or uncorrelated to the optical tracking data in order to determine what type of advisory to provide, if any. TCAS tracking data and optical tracking data are considered to be “correlated” when it is determined that they are both tracking the same object (e.g., another aircraft) and are considered to be “uncorrelated” when it is determined that they are not both tracking the same object.
Systems and methods consistent with embodiments of the present invention are not limited to employing TCAS tracking data and optional tracking data. More generally, systems and methods consistent with embodiments of the present invention may employ tracking data from any two or more sensors, attempt to correlate the tracking data, and based on such correlation of failure to correlate, determine what type of advisory to provide, if any. For example, sensors providing tracking data may comprise any two or more of the following: IR (Infrared), optical, LIDAR (Light Detection and Ranging), radar, secondary surveillance (independent of TCAS), TCAS, ADS-B (Automatic Dependent Surveillance-Broadcast), aural, Doppler radar or any other sensor now known or later developed for providing tracking data. Moreover, embodiments of the present invention may provide any desired advisory, such as a Traffic Advisory (“TA”), an RA or any other type of advisory now known or later envisioned.
Systems and methods consistent with embodiments of the present invention can be used for, but are not limited to UAV's to provide an automated collision avoidance maneuver that can be executed safely within the ATC environment, i.e., anywhere within restricted or controlled airspace, or also outside of the ATC environment. In the UAV context, for example, an optical system, as described below, may provide the “see-and-avoid” function normally provided by a pilot as a means of determining whether a TCAS RA maneuver can be safely executed.
Systems and methods consistent with embodiments of the present invention may provide a collision avoidance system for a host aircraft comprising a plurality of sensors for providing data about other aircraft that may be employed to determine one or more parameters to calculate future positions of the other aircraft, a processor to determine whether any combinations of the calculated future positions of the other aircraft are correlated or uncorrelated, and a collision avoidance module that uses the correlated or uncorrelated calculated future positions to provide a signal instructing the performance of a collision avoidance maneuver when a collision threat exists between the host aircraft and at least one of the other aircraft.
It is to be understood that the descriptions of this invention herein are exemplary and explanatory only and are not restrictive of the invention as claimed.
Reference will now be made in detail to the exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings.
Embodiments of the present invention provide systems and methods that employ multiple sensors to provide collision avoidance advisories, such as RAs. One embodiment of the present invention provides means to use TCAS tracking data and optical tracking data to provide an automated resolution advisory. The TCAS tracking data may be determined to be correlated or uncorrelated to the optical tracking data in order to determine what resolution advisory to provide, if any. TCAS tracking data and optical tracking data may be considered to be “correlated” when it is determined that they are both tracking the same object (e.g., another aircraft) and may be considered to be “uncorrelated” when it is determined that they are not both tracking the same object.
Referring back to graph 10, the TCAS-calculated elevation angles (θe) are compared with a correlation window 15 to the elevation angles of the optical data (21, 22, 23, 24 and 25) on a correlated scan-by-scan basis. In other words, at time t1 for update 1, the TCAS-calculated elevation angle (θe) is the entering argument for the correlation window 15 to see if there is a correlated contact from the optical data. For example, as shown in graph 10, the TCAS-calculated elevation angle (θe) at time t3 for update 3 places the correlation window 15 such that it intersects with the optical update 23, and as such, the optical update 23 is correlated with the TCAS data track at time t3 for update 3. The size of the window 15 may be based on the accuracy of the range and altitude measurements of the TCAS system. TCAS range accuracy is generally within about 200 ft. and altitude errors are generally within about 300 ft. For example, for an intruder aircraft having a one nautical mile TCAS slant range from and an altitude of 300 feet above own aircraft, the worst case elevation angle (θe) error is approximately Sin−1 600′/5876′−Sin−1 300′/6076′=5.86 degrees−2.83 degrees=3.03 degrees. In general, an error limit of approximately ±3 degrees is expected and can be used for an initial correlation window for the tracking algorithm. For example, the correlation window 15 may be centered on a TCAS-calculated elevation angle and cover approximately ±3 degrees on both sides of the TCAS-calculated elevation angle, or it could be based on the optical position prediction for the next update based on a derived optical elevation rate with a window expanded ±3 degrees relative to the predicted optical elevation angle.
Not shown is a technique for changing the position of own aircraft to create a baseline distance from which to triangulate a range estimate for the optical sensor. This range can then be used to also correlate with TCAS range tracks for aircraft within the environment. For example, one method is to fly to a new lateral position in space so that at least one of the initial or final positions is directly in line with the longitudinal axis of own aircraft. This establishes a right triangle with a baseline length equal to the initial position minus the final lateral position. Positions in space could be determined by a GPS position sensor. If the measurements are taken within a relatively short predetermined period of time, e.g., a few seconds, of one another, an approximate range may be determined by triangulation. For example, for a 650 ft. baseline and an azimuth angle change of 3 degrees, the following can be used to approximate range: Range=650 feet/cosine (90 degrees−3 degrees)=12,420 feet (or approximately 2.0 nautical miles).
Thus, any sensor or set of sensors can be used to correlate with TCAS range, altitude, and/or bearing, to determine if an aircraft detected by another sensor or sensors is the same aircraft that TCAS is also tracking. Determining when another sensor track is the same aircraft that TCAS is tracking is known as track correlation.
TCAS uses the detected range and bearing of an intruder, as well as a data-link-reported altitude for the intruder to determine if a TCAS RA is required. These RA's consist of Climb, Descend, Maintain Vertical Rate and other similar vertical rate commands, as prescribed in RTCA DO-185A to prevent collision of own aircraft with other aircraft in proximity to own aircraft. The detailed operation of TCAS is further discussed in Radio Technical Commission for Aeronautics (RTCA) DO-185A, “Minimum Operational Performance Standards for Traffic Alert and Collision Avoidance System II (TCAS II) Airborne Equipment,” 1997 and Radio Technical Commission for Aeronautics (RTCA) DO-185, “Minimum Operational Performance Standards for Traffic Alert and Collision Avoidance System (TCAS) Airborne Equipment,” 1983, both of which are incorporated herein by reference in their entirety.
Other sensors can use various logic to determine if a collision between own aircraft and another aircraft is imminent. For instance, in the example shown using an optical sensor, an azimuth rate less than a set threshold can be used to indicate that another aircraft is headed towards own aircraft. This is because an azimuth rate of zero, for example, indicates that an aircraft may be moving towards own aircraft. An exception to this scenario is when an intruder aircraft is maintaining position with respect to own aircraft at a range less than a predetermined amount, such as less than 2 nautical miles. This exception can be tested for by changing own aircraft speed to see if a bearing rate greater than the collision avoidance threshold can be generated. This technique is typically used by ships at sea when radar tracking information is absent. This rate can be used to determine if and, if so, how own aircraft should maneuver to avoid an on-coming aircraft.
Track correlation between TCAS tracks and other sensor tracks, as well as TCAS RA and other sensor collision prediction information, may then be used by embodiments of the multi-sensor collision avoidance logic of the present invention to determine which maneuver signal to send, if any, to the pilot or autonomous control device.
Embodiments of the present invention need not be carried out by modules contained within an existing TCAS, but may be handled by any processor and memory combination adapted to receive the necessary inputs. In the case of the embodiment shown in
Suitable processors may include any circuit that can perform a method that may be recalled from memory and/or performed by logic circuitry. The circuit may include conventional logic circuit(s), controller(s), microprocessor(s), and/or state machine(s) in any combination. Embodiments of the present invention may be implemented in circuitry, firmware, and/or software. Any conventional circuitry may be used (e.g., multiple redundant microprocessors, application specific integrated circuits). For example, the processor may include an Intel PENTIUM® microprocessor or a Motorola POWERPC® microprocessor. The processor may cooperate with any memory to perform methods consistent with embodiments of the present invention, as described herein.
Memory may be used for storing data and program instructions in any suitable manner. Memory may provide volatile and/or nonvolatile storage using any combination of conventional technology (e.g., semiconductors, magnetics, optics) in fixed and/or replaceable packaging. For example, memory may include random access storage for working values and persistent storage for program instructions and configuration data. Programs and data may be received by and stored in the system in any conventional manner.
Step A starts the multi-sensor collision avoidance logic, which may be performed by multi-sensor resolution advisory logic 270, as shown in
Step B determines if a TCAS RA is called for according to the TCAS collision avoidance logic, as described in RTCA DO-185A. If a TCAS RA is called for, then step C determines if other sensor tracks exist. In the case of the embodiment of
For each track that correlates, step E determines if a potential collision has been determined by another sensor. It is often the case that the other sensors detect a track of another aircraft, but no collision is predicted. If a potential collision has been determined by another sensor, step F looks at the predicted vertical separation, and if it is enough separation then the TCAS RA signal is continuously sent in step G. Vertical separation may be determined based on a exemplary pilot response to a TCAS RA (e.g., a 5 second delay), an assumed vertical rate (e.g., 1500 feet/minute) and a time to closest point of approach (e.g., 20 to 30 seconds) per RTCA DO-185/DO-185A. If a potential collision has not been determined by another sensor in step E, then step I sends a signal to perform a TCAS RA. If a potential collision has been determined by another sensor in step E and step F determines insufficient vertical separation, then the multi-sensor resolution advisory logic 270 commands an enhanced maneuver in step J, such as Increase Climb or Increase Descent, and a horizontal maneuver which are both transmitted to the pilot or autonomous control device.
Returning to step B, if a TCAS RA does not exist, then step K determines if any other sensor track(s) are predicting a collision. If the other sensor track(s) predict a collision, then step L checks to see if a TCAS track correlates with the other sensor track(s). If the other sensor track(s) do not predict a collision, then in step Q no signal is sent for any corrective action. If a correlation between a TCAS track and the other sensor track(s) exists, then step M does not send a signal for any maneuver to the pilot or autonomous control device (this is because TCAS “sees” the target and has determined that there is enough vertical clearance to prevent a collision).
If there is no correlation between a TCAS track and the other sensor track(s), then a further check in step R is done to see if there is more than one other sensor track prediction for a collision, and if the required horizontal maneuvers are in conflict with one another, i.e. one track requires a turn right maneuver and the other track requires a turn left maneuver, then step S does not send a signal for any maneuver to the pilot or autonomous control device (this is because there is no clear choice as to which of the two conflicting horizontal maneuvers to pick, so the only choice is to continue flying on the current flight path, since TCAS has also not provided a vertical sense maneuver). If the horizontal maneuvers are not conflicting with one another, then in step U a horizontal maneuver signal is sent to the pilot or autonomous control device.
Step H is used for the case where step C has determined that there are no other sensor tracks in proximity and that the TCAS RA signal of step H can be sent.
Step N is used when step D does not detect that another sensor track correlates to a TCAS RA track. In step N, the system determines whether other sensor track(s) predict a collision, and if so, in step O, the system determines whether the vertical separation prediction to both tracks is beyond a “safe threshold” (e.g., 400 ft.). Then, if the vertical separation prediction to both tracks is sufficient, a TCAS vertical RA can be safely performed, so step P sends a TCAS RA signal to the pilot or autonomous control device. If step O does not determine that there is enough vertical separation to both tracks, then step V sends a TCAS RA and horizontal maneuver to the pilot or autonomous control device. If step N does not determine that another sensor predicts a collision, then step T sends a TCAS RA signal to the pilot or autonomous control device.
Step 501 starts the multi-sensor collision avoidance logic of
Step 502 determines when a potential collision with own vehicle exists. This can be a calculation based on range rate and altitude rate convergence toward own vehicle, as is the case for TCAS. Alternatively, the determination can be based on a bearing rate and calculated altitude and altitude rate closure with respect to own aircraft, or any other means of determining that two vehicles are converging on the same point in space (with some degree of tolerance such as in ATC airspace where a 500 ft. vertical clearance and 1000 ft. horizontal clearance is allowed in the worst case) at the same time such as to potentially cause a collision.
Step 503 compares each collision threat to determine the best composite resolution of the collision threats that may exist at the same time that are not conflicting with one another, or in the case of only one collision threat, determines that another sensor of greater accuracy, reliability or other measure of priority has determined that the other vehicle is not a threat (and thus inhibiting any resolution selection), or the sensor determining the potential collision has sufficient accuracy, reliability or other measure of priority to cause a non-composite maneuver to be selected.
Step 504 is the logic interface that formats the collision resolution signal to send to the autonomous control device or pilot.
Step 505 is the logic that causes a repetitive evaluation of all sensor tracks through steps 502-504 until the entire number of tracks have been evaluated for each scan, where a scan is a time interval that can occur randomly, uniformly, jittered, triggered or any other method of causing the complete execution of the multi-sensor collision avoidance logic for every sensor track generated within the system.
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Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and embodiments disclosed herein. Thus, the specification and examples are exemplary only, with the true scope and spirit of the invention set forth in the following claims and legal equivalents thereof.
