Patent Description:
An unmanned vehicle, which may also be referred to as an autonomous vehicle, is a vehicle capable of travel without a physically-present human operator. An unmanned vehicle may operate in a remote-control mode, in an autonomous mode, or in a partially autonomous mode.

When an unmanned vehicle operates in a remote-control mode, a pilot or driver that is at a remote location can control the unmanned vehicle via commands that are sent to the unmanned vehicle via a wireless link. When the unmanned vehicle operates in autonomous mode, the unmanned vehicle typically moves based on pre-programmed navigation waypoints, dynamic automation systems, or a combination of these. Further, some unmanned vehicles can operate in both a remote-control mode and an autonomous mode, and in some instances may do so simultaneously. For instance, a remote pilot or driver may wish to leave navigation to an autonomous system while manually performing another task, such as operating a mechanical system for picking up objects, as an example.

Various types of unmanned vehicles exist for various different environments. For instance, unmanned vehicles exist for operation in the air, on the ground, underwater, and in space. Unmanned aerial vehicles (UAVs) are becoming more popular in general. Their use over populated areas, such as suburban and urban localities, means that controlling the noise generated by these vehicles is increasingly important.

<CIT> is directed to monitoring a noise signature of an unmanned aerial vehicle (UAV) and varying the speed of the motors of the UAV to reduce unwanted sound (i.e., noise) of the UAV based on the noise signature. The noise signature of the UAV may be measured by an audio sensor of a vibration sensor, and feedback may be provided to the UAV. The UAV may generate noise during flight, which may include a number of noise components such as tonal noise (e.g., a whining noise such as a whistle of a kettle at full boil) and broadband noise (e.g., a complex mixture of sounds of different frequencies, such as the sound of ocean surf). By measuring the noise signature of the UAV, and varying the motor revolutions per minute (RPM) during flight operations, the UAV may reduce tonal components of the UAV noise signature.

<CIT> discloses that sounds are generated by an aerial vehicle during operation. For example, the motors and propellers of an aerial vehicle generate sounds during operation. Disclosed are systems, methods, and apparatus for actively adjusting the position and/or configuration of one or more propeller blades of a propulsion mechanism to generate different sounds and/or lifting forces from the propulsion mechanism.

<CIT> discloses that aerial vehicles may be operated with discrete sets of propellers, which may be selected for a specific purpose or on a specific basis. The discrete sets of propellers may be operated separately or in tandem with one another, and at varying power levels. For example, a set of propellers may be selected to optimize the thrust, lift, maneuverability or efficiency of an aerial vehicle based on a position or other operational characteristic of the aerial vehicle, or an environmental condition encountered by the aerial vehicle. At least one of the propellers may be statically or dynamically imbalanced, such that the propeller emits a predetermined sound during operation. A balanced propeller may be specifically modified to cause the aerial vehicle to emit the predetermined sound by changing one or more parameters of the balanced propeller and causing the balanced propeller to be statically or dynamically imbalanced.

Embodiments of a system, apparatus, and method of operation of an unmanned aerial vehicle (UAV) for controlling tonal noise output from the rotor units of the UAV are described herein. In the following description numerous specific details are set forth to provide a thorough understanding of the.

As UAV become more common in the skies over populated environments, controlling the tonal noises that emanate from their rotor units (also referred to as multi-rotor tonal noise) is becoming increasingly important. Multi-rotor tonal noise can be perceived as a nuisance to bystanders, particularly when regularly subjected to this noise. The perceived annoyance of multi-rotor tonal noise can be abated by spreading out the tonal noises. This spreading can be achieved spectrally by spreading component frequencies generated by the rotor units of a UAV, can be achieved temporally by offsetting phases of peak amplitudes of the tonal noises, or can be done using a combination of these two spreading techniques. Additional techniques that spread out tonal noises to reduce the perceived nuisance of multi-rotor tonal noise, and in some cases even generate pleasant sounds, include generating chords, melodies, or beat frequencies from the tonal noises generated by the rotor units of a UAV.

Embodiments described herein include a UAV, which refers to any autonomous or semi-autonomous vehicle that is capable of performing some functions without a physically present human pilot. A UAV can take various forms. For example, a UAV may take the form of a fixed-wing aircraft, a glider aircraft, a tail-sitter aircraft, a jet aircraft, a ducted fan aircraft, a lighter-than-air dirigible such as a blimp or steerable balloon, a rotorcraft such as a helicopter or multicopter, and/or an ornithopter, among other possibilities. Further, the terms "drone," "unmanned aerial vehicle system" (UAVS), or "unmanned aerial system" (UAS) may also be used to refer to a UAV.

<FIG> is a perspective view illustration of a UAV <NUM>, according to an embodiment of the disclosure. The illustrated embodiment of UAV <NUM> is a fixed-wing UAV, which may also be referred to as an airplane, an aeroplane, a glider, or a plane, among other possibilities. The fixed-wing UAV <NUM>, as the name implies, has a wing assembly <NUM> that generates lift based on the wing shape and the vehicle's forward airspeed. For instance, wing assembly <NUM> may have an airfoil-shaped cross section to produce an aerodynamic lift force on the UAV <NUM>. Although UAV <NUM> is illustrated as a fixed-wing UAV, it should be appreciated that the multi-rotor noise control techniques described herein are also applicable to other types of multi-rotor UAVs as described above.

The illustrated embodiment of UAV <NUM> includes a fuselage <NUM>. In one embodiment, fuselage <NUM> is modular and includes a battery module, an avionics module, a mission payload module, and a fuselage cover. These modules are detachable from each other and mechanically securable to each other to contiguously form at least a portion of the fuselage or UAV main body.

The battery module may house one or more batteries for powering UAV <NUM>. The avionics module houses flight control circuitry of UAV <NUM>, which may include a processor and memory, communication electronics and antennas (e.g., cellular transceiver, wifi transceiver, etc.), and various sensors (e.g., global positioning sensor, an inertial measurement unit (IMU), a magnetic compass, etc.). The mission payload module houses equipment associated with a mission of UAV <NUM>. For example, the mission payload module may include a payload actuator for holding and releasing an externally attached payload. In another embodiment, the mission payload module may include a camera/sensor equipment holder for carrying camera/sensor equipment (e.g., camera, lenses, radar, lidar, pollution monitoring sensors, weather monitoring sensors, etc.). Of course, the mission payload module may provide mixed use payload capacity (e.g., additional battery and camera equipment) for a variety of mix-use missions.

The illustrated embodiment of UAV <NUM> further includes forward propulsion units <NUM> (also referred to as rotor units) positioned on wing assembly <NUM>, which can each include a motor, shaft, and propeller, for propelling UAV <NUM>. The illustrated embodiment of UAV <NUM> further includes two boom assemblies <NUM> that secure to wing assembly <NUM>. In one embodiment, wing assembly <NUM> includes a wing spar disposed within a wing foil.

The illustrated embodiments of boom assemblies <NUM> each include a boom housing <NUM> in which a boom carrier (not illustrated) is disposed, vertical propulsion units <NUM>, printed circuit boards <NUM>, and stabilizers <NUM>. Boom carriers are structural members (e.g., tubular rods) that provide the main structural support to which the wing spar and vertical propulsion units <NUM> are mounted. Vertical propulsion units <NUM> (also referred to as rotor units) can each include a motor, shaft, and propeller, for providing vertical propulsion. Vertical propulsion units <NUM> may be used during a hover mode where UAV <NUM> is descending (e.g., to a delivery location) or ascending (e.g., following a delivery). Stabilizers <NUM> (or fins) may be included with UAV <NUM> to stabilize the UAV's yaw (left or right turns) during flight. In some embodiments, UAV <NUM> may be configured to function as a glider. To do so, UAV <NUM> may power off its propulsion units and glide for a period of time.

During flight, UAV <NUM> may control the direction and/or speed of its movement by controlling its pitch, roll, yaw, and/or altitude. For example, the stabilizers <NUM> may include one or more rudders 1108a for controlling the UAV's yaw, and wing assembly <NUM> may include elevators for controlling the UAV's pitch and/or ailerons 1102a for controlling the UAV's roll. As another example, increasing or decreasing the speed of all the propellers simultaneously can result in UAV <NUM> increasing or decreasing its altitude, respectively.

Many variations on the illustrated fixed-wing UAV are possible. For instance, fixed-wing UAVs may include more or fewer rotor units (vertical or horizontal), and/or may utilize a ducted fan or multiple ducted fans for propulsion. Further, UAVs with more wings (e.g., an "x-wing" configuration with four wings), are also possible. Although <FIG> illustrates one wing assembly <NUM>, two boom assemblies <NUM>, two forward propulsion units <NUM>, and six vertical propulsion units <NUM> per boom assembly <NUM>, it should be appreciated that other variants of UAV <NUM> may be implemented with more or less of these components. For example, UAV <NUM> may include two wing assemblies <NUM>, four boom assemblies <NUM>, and more or less propulsion units (forward or vertical).

It should be understood that references herein to an "unmanned" aerial vehicle or UAV can apply equally to autonomous and semi-autonomous aerial vehicles. In an autonomous implementation, all functionality of the aerial vehicle is automated; e.g., pre-programmed or controlled via real-time computer functionality that responds to input from various sensors and/or pre-determined information. In a semi-autonomous implementation, some functions of an aerial vehicle may be controlled by a human operator, while other functions are carried out autonomously. Further, in some embodiments, a UAV may be configured to allow a remote operator to take over functions that can otherwise be controlled autonomously by the UAV. Yet further, a given type of function may be controlled remotely at one level of abstraction and performed autonomously at another level of abstraction. For example, a remote operator could control high level navigation decisions for a UAV, such as specifying that the UAV should travel from one location to another (e.g., from a warehouse in a suburban area to a delivery address in a nearby city), while the UAV's navigation system autonomously controls more fine-grained navigation decisions, such as the specific route to take between the two locations, specific flight controls to achieve the route and avoid obstacles while navigating the route, and so on.

As mentioned above, the perceived annoyance of multi-rotor tonal noise can be abated by spreading out the tonal noises. <FIG> is a chart illustrating example tonal noise from rotor units of a UAV that is spectrally concentrated about two frequencies F1 and F2. Spectrally distinctive or spectrally concentrated tonal noises are often perceived as a greater nuisance relative to spectrally dispersed noise (e.g., such as white noise, pink noise, pseudo-random noise, etc.). By spectrally spreading out multi-rotor tonal noises (e.g., as illustrated in <FIG>), the perceived annoyance of the multi-rotor tonal noises can be reduced, in accordance with embodiments described herein.

Another form of concentrated or distinctive multi-rotor tonal noise is phase aligned tonal noise (also referred to as temporally aligned tonal noise), as illustrated in <FIG>. With phase aligned multi-rotor tonal noise, the constituent tonal noises S1, S2, S3 from the various rotor units constructively interfere generating high amplitude, pulsating noises. Again, these phase aligned tonal noises are typically perceived as being a greater nuisance than phase offset (or temporally dispersed) multi-rotor tonal noise. For example, <FIG> illustrates constituent tonal noises S4, S5, and S6 generated by various rotor units of a UAV that are offset in phase relative to each other. The phase dispersed tonal noises illustrated in <FIG> are more evenly dispersed in time and generate less peaky or pulsating noise relative to the phased aligned tonal noise illustrated in <FIG>. Accordingly, the multi-rotor tonal noises can be spread spectrally (dispersing frequency components), can be spread temporally (offsetting phase delays), or a combination of both to reduce perceived audible annoyance.

<FIG> is a functional block diagram illustrating a control system <NUM> for modulating phases and/or rotation rates of rotor units of UAV <NUM>, in accordance with an embodiment of the disclosure. The illustrated embodiment of control system <NUM> includes a controller <NUM> and motor drivers <NUM>. Motor drivers <NUM> drive rotor units <NUM>, which include a motor, a shaft, and a bladed rotor <NUM>. Bladed rotors <NUM> may be mounted in a vertical orientation to generate vertical thrust (e.g., vertical rotor units) or a horizontal orientation to generate horizontal thrust (e.g., horizontal rotor units).

Controller <NUM> operates to choreograph the operation of rotor units <NUM> to control their rotation speed and relative phase delays. Controller <NUM> may be implemented as a general purpose processor or microcontroller executing software/firmware logic (e.g., instructions) or a hardware controller executing hardware logic (e.g., application specific integrated circuit, field programmable gate array, etc.). In the illustrated embodiment, controller <NUM> outputs pulse width modulated (PWM) control signals to motor drivers <NUM>. The duty cycle, frequency, and/or phase of the PWM control signals can be modulated to control the rotation rates and phase delays of rotor units <NUM>. Motor drivers <NUM> receive the PWM control signals and generate the drive current/voltage for driving the motors of rotor units <NUM>. In one embodiment, motor drivers <NUM> modulate battery power based upon the PWM control signals to drive the motors of rotor units <NUM>.

In one embodiment, feedback sensor signals are provided to controller <NUM>. In one embodiment, the feedback sensor signals are based upon real-time monitoring of the voltage and/or current that is driving each rotor unit <NUM>. In one embodiment, the feedback sensor signals are based upon an encoder that provides actual rotation speed (e.g., rotational frequency or rotational period) or actual rotational position (e.g., rotational phase). Controller <NUM> may use the feedback signals to adjust the PWM control signals in real-time to achieve a desired rotation rate or phase delay of each rotor unit <NUM> or groups of rotor units <NUM>. Of course, other control system architectures may be implemented. Similarly, other feedback sensor system may be provided to monitor rotational rate and/or phase in real-time (e.g., audio sensor, optical sensor, etc.).

The rotation rate or rotational frequency of each rotor unit <NUM> directly correlates to the spectral content of the tonal noises generated by each rotor unit <NUM>. Accordingly, by independently adjusting the rotation rate of a given rotor unit <NUM> the component frequencies of the tonal noise generated by that rotor unit <NUM> can be independently controlled. By collectively varying the rotation rates of rotor units <NUM> relative to each other, the collective component frequencies generated by UAV <NUM> can be spectrally spread out to reduce the perceived nuisance of the tonal noises. Similarly, rotational phase of each rotor unit <NUM> directly correlates to the temporal position of the peak amplitude of the tonal noises generated by each rotor unit <NUM>. By offsetting the phase delays applied to each rotor unit <NUM> (or groups of rotor units <NUM>), the peak amplitudes of the tonal noises are offset relative to each other thereby also reducing the perceived nuisance of the tonal noises collectively output from UAV <NUM>.

One technique for spectrally spreading out component frequencies of tonal noise is to vary the physical geometries of bladed rotors <NUM>. Changing the physical geometries of bladed rotors <NUM> enables different rotation rates of rotor units <NUM> to achieve a similar or same thrust. Accordingly, changing the physical geometries of bladed rotors relative to each other (or in groups relative to each other) enables constant thrust for stable flight while varying the component frequencies output from one rotor unit <NUM> to the next. This serves to spectrally spread out the component frequencies of the tonal noises collectively generated by the rotor units of UAV <NUM>.

Varying the physical geometries between the rotor units of UAV <NUM> may include varying one or more of a diameter of bladed rotors <NUM>, a surface area of bladed rotors <NUM>, a pitch of bladed rotors <NUM>, or a number of blades on a bladed rotor <NUM>. For example, as illustrated in <FIG>, UAV <NUM> may include one or more bladed rotors <NUM> having three blades <NUM>, may include one or more bladed rotors <NUM> having four blades <NUM> (e.g., see <FIG>), may include one or more bladed rotors <NUM> having five blades <NUM> (e.g., see <FIG>), may include one or more bladed rotors <NUM> having six blades <NUM> (e.g., see <FIG>), may include one or more bladed rotors <NUM> having seven blades <NUM> (e.g., see <FIG>), etc. In one embodiment, each rotor unit of UAV <NUM> may have a different physical geometry to achieve variable rotation rates for a given thrust. In yet other embodiments, the rotation rates of the rotor units may be varied in groups.

<FIG> is a plan view illustration of UAV <NUM> depicting how rotor units A-M may be logically grouped and their rotation rates varied in groups to spectrally spread out the component frequencies of tonal noise, in accordance with an embodiment of the disclosure. For example, <FIG> illustrates the vertical lift rotor units A-L logically organized into six groups <NUM>-<NUM> with each group including two rotor units. Because rotor units A-L are paired in a symmetrical manner, their rotation rates can be varied on a group-wise basis. For example, groups <NUM> and <NUM> may be assigned a common rotation rate R1, while groups <NUM> and <NUM> may be assigned a common rotation rate R2, and groups <NUM> and <NUM> may be assigned yet another common rotation rate R3, where R1, R2, and R3 are different rotation rates that generate different, spectrally spaced tonal noises. Additionally, the geometries of the bladed rotors may also be varied within a group to provide further rotational rate diversity, while achieving common thrust output from rotor units within a given group. In one embodiment, forward thrust rotor units M and N may form another logical group that is independently varied.

<FIG> is a plan view illustration of UAV <NUM> depicting yet another technique for varying rotation rates of vertical lift rotor units A-L to spectrally spread out the component frequencies of the tonal noises. In <FIG>, the rotation rates of rotor units A-L are dynamically modulated in a sequential pattern or circuit (e.g., A-B-C-D-E-F-L-K-J-I-H-G and repeat). For example, each rotor unit may rotate at different rotation rate from the other rotor units, but hand off its current rotation rate to the next rotor unit in the circuit and receive a new rotation rate from a previous rotor unit in the circuit. The rotation rate exchange may then cycle through the circuit (e.g., A-B-C-D-E-F-L-K-J-I-H-G and repeat). Of course, other circuit paths and dynamic modulation schemes may be implemented. In some embodiments, this sequential pattern of dynamic modulation may introduce a gyroscopic wobble about a stabilized center of UAV <NUM>. In other embodiments, the rotation rates may be sequentially modulated in geometrically opposing pairs or groups of rotor units to reduce or offset any gyroscopic wobble.

As mentioned above, in addition (or alternatively) to varying the relative rotation rates of rotor units of UAV <NUM> to spectrally spread out component frequencies, the tonal noises generated by UAV <NUM> may also be spread out by introducing phase delays between the rotor units. In one embodiment, the phase delays of the rotor units are offset relative to each other to offset phases of peak amplitudes of the tonal noises generated by different ones of the rotor units from each other (e.g., see <FIG>).

<FIG> is a flow chart illustrating a process <NUM> for phase delaying rotor units <NUM> of UAV <NUM> to spread out tonal noises in time and phase, in accordance with an embodiment of the disclosure. The order in which some or all of the process blocks appear in process <NUM> should not be deemed limiting. Rather, one of ordinary skill in the art having the benefit of the present disclosure will understand that some of the process blocks may be executed in a variety of orders not illustrated, or even in parallel.

In a process block <NUM>, the revolution frequency of one or more rotor units <NUM> is monitored to determine a rotation period, which is the inverse of the revolution frequency. In one embodiment, a single rotor unit <NUM> is selected for monitoring the revolution frequency. In other embodiments, rotor units <NUM> may be logically grouped and the revolution frequency of a selected member from each group is monitored to determine a group wise revolution frequency. In yet other embodiments, the revolution frequency of all rotor units (or groups of rotor units) may be monitored and averaged to determine a rotation period.

With a rotation period determined, process <NUM> continues to a process block <NUM> where the rotation period is divided by a number N to generate a phase delay value (measured in seconds). The number N may represent a total number of all rotor units <NUM> on UAV <NUM> or a number of rotor units <NUM> that are members of a sub-group. With the phase delay value determined, controller <NUM> phase delays each rotor unit <NUM> by a different integer multiple of the phase delay value (process block <NUM>). When the revolution frequency of the monitored rotor unit <NUM> changes (decision block <NUM>), the rotation period changes and a new phase delay value is recalculated and applied in real-time. By dividing the rotation period of rotor units <NUM> by the number N of rotor units <NUM>, the phase delays can be evenly distributed in time. Process <NUM> can be applied to all rotor units <NUM> of UAV <NUM> as a single group, or applied on a sub-group basis as described below.

<FIG> is a flow chart illustrating a process <NUM> for phase delaying rotor units <NUM> of UAV <NUM> in groups to spread out tonal noises in time and phase, in accordance with an embodiment of the disclosure. The order in which some or all of the process blocks appear in process <NUM> should not be deemed limiting. Rather, one of ordinary skill in the art having the benefit of the present disclosure will understand that some of the process blocks may be executed in a variety of orders not illustrated, or even in parallel.

In some embodiments, the acoustical wavelengths generated by the rotor units may range between <NUM> to <NUM>. Accordingly, depending upon the overall size of UAV <NUM> and how far the rotor units are separated from each other, it may produce improved results to group closely located rotor units into noise generating subgroups. In a process block <NUM>, rotor units of UAV <NUM> are logically associated into noise generating subgroups (i) based upon proximity. For example, referring to <FIG>, rotor units A, B, and C mounted on boom assembly 1110A fore of wing assembly <NUM> are logically associated into a first noise generating subgroup (<NUM>), rotor units D, E, and F mounted on boom assembly 1110A aft of wing assembly <NUM> are logically associated into a second noise generating subgroup (<NUM>), rotor units G, H, and I mounted on boom assembly 1110B fore of wing assembly <NUM> are logically associated into a third noise generating subgroup (<NUM>), and rotor units J, K, and L mounted on boom assembly 1110B aft of wing assembly <NUM> are logically associated into a fourth noise generating subgroup (<NUM>). Of course, other logical groupings based upon proximity may also be implemented.

In a process block <NUM>, phase delay values d(i) for each noise generating sub-group (I) are generated. Each phase delay value d(i) is calculated by monitoring a revolution frequency for the particular noise generating sub-group (i) and dividing the rotation period by a number n(i) of rotor units within the given noise generating sub-group (i). In the illustrated embodiment, n(i) = <NUM> for each noise generating sub-group (i), which corresponds to a phase delay of a <NUM> degrees; however, in other embodiments n(i) may vary between different noise generating sub-groups. Finally, Once the phase delay values d(i) are calculated, each rotor unit with a given noise generating subgroup (i) is phase delayed relative to the other rotor units within the given noise generating subgroup (i) by a different integer multiple of the phase delay value d(i) (process block <NUM>).

In addition to adjusting the rotation rates or phase delays of rotor units <NUM> of UAV <NUM> to spread out tonal noises, the rotation rates and/or phase delays may be dynamically modulated to generate chords or even melodies. The generation of chords or melodies can also reduce the perceived nuisance of a UAV. Accordingly, in one embodiment, the rotation rates and/or phase delays are dynamically modulated by controller <NUM> to generate chords or melodies with the tonal noises emanating from rotor units <NUM>. In one embodiment, controller <NUM> may be programmed to associate a particular melody (or chord) with a particular flight phase of UAV <NUM> and modulate the PWM control signals in a manner that generates that melody (or chord) while UAV <NUM> is operating in that flight phase. For example, controller <NUM> may generate one melody (or chord) during an arrival phase, generate another melody (or chord) during a departure phase, and generate yet another melody (or chord) during a transit phase. Example chords that may be generated by modulating the rotation rates of different rotor units <NUM> may include one or more of a perfect <NUM>th, a perfect <NUM>th, a major <NUM>rd, a minor <NUM>rd, a major triad, or otherwise.

Another technique that can increase the perceived desirability of the noise emanating from rotor units of UAV <NUM> is to use controller <NUM> to slightly offset or spread out the rotational frequencies of rotor units <NUM> from each other to generate a more pleasant sounding beat frequency. This beat frequency is a generated as an interference pattern between the tonal noises generated by multiple rotor units <NUM>. A perceived modulation or acoustical beat could be achieved by having controller <NUM> shift rotational frequencies of rotor units by approximately <NUM>-<NUM>% relative to each other (e.g., relative to their neighbors). In one embodiment, the rotor units <NUM> may be grouped into quadrants, as illustrated by the noise generating sub-groups in <FIG>, with the rotor units in each quadrant rotating at the same frequency, but each quadrant group of rotor units having a frequency that slightly deviates from their neighbor quadrant. This slight offset in rotational frequencies can be selected to generate a desirable interference pattern or beat frequency, which may be perceived as a more pleasant sound.

<FIG> is a functional block diagram illustrating subsystems of a demonstrative UAV <NUM>, in accordance with an embodiment of the disclosure. UAV <NUM> may take the form of UAV <NUM> illustrated in <FIG>. However, UAV <NUM> may also take other forms.

UAV <NUM> may include various types of sensors, and may include a computing system configured to provide the functionality described herein. In the illustrated embodiment, the sensors of UAV <NUM> include an inertial measurement unit (IMU) <NUM>, ultrasonic sensor(s) <NUM>, and a GPS <NUM>, among other possible sensors and sensing systems.

In the illustrated embodiment, UAV <NUM> also includes one or more processors <NUM>. A processor <NUM> may be a general-purpose processor or a special purpose processor (e.g., digital signal processors, application specific integrated circuits, etc.). The one or more processors <NUM> can be configured to execute computer-readable program instructions <NUM> that are stored in the data storage <NUM> and are executable to provide the functionality of a UAV described herein.

The data storage <NUM> may include or take the form of one or more computer-readable storage media that can be read or accessed by at least one processor <NUM>. The one or more computer-readable storage media can include volatile and/or nonvolatile storage components, such as optical, magnetic, organic or other memory or disc storage, which can be integrated in whole or in part with at least one of the one or more processors <NUM>. In some embodiments, the data storage <NUM> can be implemented using a single physical device (e.g., one optical, magnetic, organic or other memory or disc storage unit), while in other embodiments, the data storage <NUM> can be implemented using two or more physical devices.

As noted, the data storage <NUM> can include computer-readable program instructions <NUM> and perhaps additional data, such as diagnostic data of the UAV <NUM>. As such, the data storage <NUM> may include program instructions <NUM> to perform or facilitate some or all of the UAV functionality described herein. For instance, in the illustrated embodiment, program instructions <NUM> include a navigation module <NUM> and a tether control module <NUM>.

In an illustrative embodiment, IMU <NUM> may include both an accelerometer and a gyroscope, which may be used together to determine an orientation of the UAV <NUM>. In particular, the accelerometer can measure the orientation of the vehicle with respect to earth, while the gyroscope measures the rate of rotation around an axis. IMUs are commercially available in low-cost, low-power packages. For instance, an IMU <NUM> may take the form of or include a miniaturized MicroElectroMechanical System (MEMS) or a NanoElectroMechanical System (NEMS). Other types of IMUs may also be utilized.

An IMU <NUM> may include other sensors, in addition to accelerometers and gyroscopes, which may help to better determine position and/or help to increase autonomy of the UAV <NUM>. Two examples of such sensors are magnetometers and pressure sensors. In some embodiments, a UAV may include a low-power, digital <NUM>-axis magnetometer, which can be used to realize an orientation independent electronic compass for accurate heading information. However, other types of magnetometers may be utilized as well. Further, note that a UAV could include some or all of the above-described inertia sensors as separate components from an IMU.

UAV <NUM> may also include a pressure sensor or barometer, which can be used to determine the altitude of the UAV <NUM>. Alternatively, other sensors, such as sonic altimeters or radar altimeters, can be used to provide an indication of altitude, which may help to improve the accuracy of and/or prevent drift of an IMU.

In a further aspect, UAV <NUM> may include one or more sensors that allow the UAV to sense objects in the environment. For instance, in the illustrated embodiment, UAV <NUM> includes ultrasonic sensor(s) <NUM>. Ultrasonic sensor(s) <NUM> can determine the distance to an object by generating sound waves and determining the time interval between transmission of the wave and receiving the corresponding echo off an object. A typical application of an ultrasonic sensor for unmanned vehicles or IMUs is low-level altitude control and obstacle avoidance. An ultrasonic sensor can also be used for vehicles that need to hover at a certain height or need to be capable of detecting obstacles. Other systems can be used to determine, sense the presence of, and/or determine the distance to nearby objects, such as a light detection and ranging (LIDAR) system, laser detection and ranging (LADAR) system, and/or an infrared or forward-looking infrared (FLIR) system, among other possibilities.

In some embodiments, UAV <NUM> may also include one or more imaging system(s). For example, one or more still and/or video cameras may be utilized by UAV <NUM> to capture image data from the UAV's environment. As a specific example, charge-coupled device (CCD) cameras or complementary metal-oxide-semiconductor (CMOS) cameras can be used with unmanned vehicles. Such imaging sensor(s) have numerous possible applications, such as obstacle avoidance, localization techniques, ground tracking for more accurate navigation (e,g. , by applying optical flow techniques to images), video feedback, and/or image recognition and processing, among other possibilities.

UAV <NUM> may also include a GPS receiver <NUM>. The GPS receiver <NUM> may be configured to provide data that is typical of well-known GPS systems, such as the GPS coordinates of the UAV <NUM>. Such GPS data may be utilized by the UAV <NUM> for various functions. As such, the UAV may use its GPS receiver <NUM> to help navigate to the caller's location, as indicated, at least in part, by the GPS coordinates provided by their mobile device.

The navigation module <NUM> may provide functionality that allows the UAV <NUM> to, e.g., move about its environment and reach a desired location. To do so, the navigation module <NUM> may control the altitude and/or direction of flight by controlling the mechanical features of the UAV that affect flight (e.g., its rudder(s), elevator(s), aileron(s), and/or the speed of its propeller(s)).

In order to navigate the UAV <NUM> to a target location, the navigation module <NUM> may implement various navigation techniques, such as map-based navigation and localization-based navigation, for instance. With map-based navigation, the UAV <NUM> may be provided with a map of its environment, which may then be used to navigate to a particular location on the map. With localization-based navigation, the UAV <NUM> may be capable of navigating in an unknown environment using localization. Localization-based navigation may involve the UAV <NUM> building its own map of its environment and calculating its position within the map and/or the position of objects in the environment. For example, as a UAV <NUM> moves throughout its environment, the UAV <NUM> may continuously use localization to update its map of the environment. This continuous mapping process may be referred to as simultaneous localization and mapping (SLAM). Other navigation techniques may also be utilized.

In some embodiments, the navigation module <NUM> may navigate using a technique that relies on waypoints. In particular, waypoints are sets of coordinates that identify points in physical space. For instance, an air-navigation waypoint may be defined by a certain latitude, longitude, and altitude. Accordingly, navigation module <NUM> may cause UAV <NUM> to move from waypoint to waypoint, in order to ultimately travel to a final destination (e.g., a final waypoint in a sequence of waypoints).

In a further aspect, the navigation module <NUM> and/or other components and systems of the UAV <NUM> may be configured for "localization" to more precisely navigate to the scene of a target location. More specifically, it may be desirable in certain situations for a UAV to be within a threshold distance of the target location where a payload <NUM> is being delivered by a UAV (e.g., within a few feet of the target destination). To this end, a UAV may use a two-tiered approach in which it uses a more-general location-determination technique to navigate to a general area that is associated with the target location, and then use a more-refined location-determination technique to identify and/or navigate to the target location within the general area.

For example, the UAV <NUM> may navigate to the general area of a target destination where a payload <NUM> is being delivered using waypoints and/or map-based navigation. The UAV may then switch to a mode in which it utilizes a localization process to locate and travel to a more specific location. For instance, if the UAV <NUM> is to deliver a payload to a user's home, the UAV <NUM> may need to be substantially close to the target location in order to avoid delivery of the payload to undesired areas (e.g., onto a roof, into a pool, onto a neighbor's property, etc.). However, a GPS signal may only get the UAV <NUM> so far (e.g., within a block of the user's home). A more precise location-determination technique may then be used to find the specific target location.

Various types of location-determination techniques may be used to accomplish localization of the target delivery location once the UAV <NUM> has navigated to the general area of the target delivery location. For instance, the UAV <NUM> may be equipped with one or more sensory systems, such as, for example, ultrasonic sensors <NUM>, infrared sensors (not shown), and/or other sensors, which may provide input that the navigation module <NUM> utilizes to navigate autonomously or semi-autonomously to the specific target location.

As another example, once the UAV <NUM> reaches the general area of the target delivery location (or of a moving subject such as a person or their mobile device), the UAV <NUM> may switch to a "fly-by-wire" mode where it is controlled, at least in part, by a remote operator, who can navigate the UAV <NUM> to the specific target location. To this end, sensory data from the UAV <NUM> may be sent to the remote operator to assist them in navigating the UAV <NUM> to the specific location.

As yet another example, the UAV <NUM> may include a module that is able to signal to a passer-by for assistance in either reaching the specific target delivery location; for example, the UAV <NUM> may display a visual message requesting such assistance in a graphic display, play an audio message or tone through speakers to indicate the need for such assistance, among other possibilities. Such a visual or audio message might indicate that assistance is needed in delivering the UAV <NUM> to a particular person or a particular location, and might provide information to assist the passer-by in delivering the UAV <NUM> to the person or location (e.g., a description or picture of the person or location, and/or the person or location's name), among other possibilities. Such a feature can be useful in a scenario in which the UAV is unable to use sensory functions or another location-determination technique to reach the specific target location. However, this feature is not limited to such scenarios.

In some embodiments, once the UAV <NUM> arrives at the general area of a target delivery location, the UAV <NUM> may utilize a beacon from a user's remote device (e.g., the user's mobile phone) to locate the person. Such a beacon may take various forms. As an example, consider the scenario where a remote device, such as the mobile phone of a person who requested a UAV delivery, is able to send out directional signals (e.g., via an RF signal, a light signal and/or an audio signal). In this scenario, the UAV <NUM> may be configured to navigate by "sourcing" such directional signals - in other words, by determining where the signal is strongest and navigating accordingly. As another example, a mobile device can emit a frequency, either in the human range or outside the human range, and the UAV <NUM> can listen for that frequency and navigate accordingly. As a related example, if the UAV <NUM> is listening for spoken commands, then the UAV <NUM> could utilize spoken statements, such as "I'm over here!" to source the specific location of the person requesting delivery of a payload.

In an alternative arrangement, a navigation module may be implemented at a remote computing device, which communicates wirelessly with the UAV <NUM>. The remote computing device may receive data indicating the operational state of the UAV <NUM>, sensor data from the UAV <NUM> that allows it to assess the environmental conditions being experienced by the UAV <NUM>, and/or location information for the UAV <NUM>. Provided with such information, the remote computing device may determine altitudinal and/or directional adjustments that should be made by the UAV <NUM> and/or may determine how the UAV <NUM> should adjust its mechanical features (e.g., its rudder(s), elevator(s), aileron(s), and/or the speed of its propeller(s)) in order to effectuate such movements. The remote computing system may then communicate such adjustments to the UAV <NUM> so it can move in the determined manner.

In a further aspect, the UAV <NUM> includes one or more communication systems <NUM>. The communications systems <NUM> may include one or more wireless interfaces and/or one or more wireline interfaces, which allow the UAV <NUM> to communicate via one or more networks. Such wireless interfaces may provide for communication under one or more wireless communication protocols, such as Bluetooth, WiFi (e.g., an IEEE <NUM> protocol), Long-Term Evolution (LTE), WiMAX (e.g., an IEEE <NUM> standard), a radio-frequency ID (RFID) protocol, near-field communication (NFC), and/or other wireless communication protocols. Such wireline interfaces may include an Ethernet interface, a Universal Serial Bus (USB) interface, or similar interface to communicate via a wire, a twisted pair of wires, a coaxial cable, an optical link, a fiber-optic link, or other physical connection to a wireline network.

In some embodiments, a UAV <NUM> may include communication systems <NUM> that allow for both short-range communication and long-range communication. For example, the UAV <NUM> may be configured for short-range communications using Bluetooth and for long-range communications under a CDMA protocol. In such an embodiment, the UAV <NUM> may be configured to function as a "hot spot;" or in other words, as a gateway or proxy between a remote support device and one or more data networks, such as a cellular network and/or the Internet. Configured as such, the UAV <NUM> may facilitate data communications that the remote support device would otherwise be unable to perform by itself.

For example, the UAV <NUM> may provide a WiFi connection to a remote device, and serve as a proxy or gateway to a cellular service provider's data network, which the UAV might connect to under an LTE or a <NUM> protocol, for instance. The UAV <NUM> could also serve as a proxy or gateway to a high-altitude balloon network, a satellite network, or a combination of these networks, among others, which a remote device might not be able to otherwise access.

In a further aspect, the UAV <NUM> may include power system(s) <NUM>. The power system <NUM> may include one or more batteries for providing power to the UAV <NUM>. In one example, the one or more batteries may be rechargeable and each battery may be recharged via a wired connection between the battery and a power supply and/or via a wireless charging system, such as an inductive charging system that applies an external time-varying magnetic field to an internal battery.

The UAV <NUM> may employ various systems and configurations in order to transport and deliver a payload <NUM>. In some implementations, the payload <NUM> of a given UAV <NUM> may include or take the form of a "package" designed to transport various goods to a target delivery location. For example, the UAV <NUM> can include a compartment, in which an item or items may be transported. Such a package may one or more food items, purchased goods, medical items, or any other object(s) having a size and weight suitable to be transported between two locations by the UAV. In other embodiments, a payload <NUM> may simply be the one or more items that are being delivered (e.g., without any package housing the items).

In some embodiments, the payload <NUM> may be attached to the UAV and located substantially outside of the UAV during some or all of a flight by the UAV. For example, the package may be tethered or otherwise releasably attached below the UAV during flight to a target location. In an embodiment where a package carries goods below the UAV, the package may include various features that protect its contents from the environment, reduce aerodynamic drag on the system, and prevent the contents of the package from shifting during UAV flight.

For instance, when the payload <NUM> takes the form of a package for transporting items, the package may include an outer shell constructed of water-resistant cardboard, plastic, or any other lightweight and water-resistant material. Further, in order to reduce drag, the package may feature smooth surfaces with a pointed front that reduces the frontal cross-sectional area. Further, the sides of the package may taper from a wide bottom to a narrow top, which allows the package to serve as a narrow pylon that reduces interference effects on the wing(s) of the UAV. This may move some of the frontal area and volume of the package away from the wing(s) of the UAV, thereby preventing the reduction of lift on the wing(s) cause by the package. Yet further, in some embodiments, the outer shell of the package may be constructed from a single sheet of material in order to reduce air gaps or extra material, both of which may increase drag on the system. Additionally or alternatively, the package may include a stabilizer to dampen package flutter. This reduction in flutter may allow the package to have a less rigid connection to the UAV and may cause the contents of the package to shift less during flight.

In order to deliver the payload, the UAV may include a winch system <NUM> controlled by the tether control module <NUM> in order to lower the payload <NUM> to the ground while the UAV hovers above. As shown in Figure <NUM>, the winch system <NUM> may include a tether <NUM>, and the tether <NUM> may be coupled to the payload <NUM> by a payload coupling apparatus <NUM>. The tether <NUM> may be wound on a spool that is coupled to a motor <NUM> of the UAV. The motor <NUM> may take the form of a DC motor (e.g., a servo motor) that can be actively controlled by a speed controller. The tether control module <NUM> can control the speed controller to cause the motor <NUM> to rotate the spool, thereby unwinding or retracting the tether <NUM> and lowering or raising the payload coupling apparatus <NUM>. In practice, the speed controller may output a desired operating rate (e.g., a desired RPM) for the spool, which may correspond to the speed at which the tether <NUM> and payload <NUM> should be lowered towards the ground. The motor <NUM> may then rotate the spool so that it maintains the desired operating rate.

In order to control the motor <NUM> via the speed controller, the tether control module <NUM> may receive data from a speed sensor (e.g., an encoder) configured to convert a mechanical position to a representative analog or digital signal. In particular, the speed sensor may include a rotary encoder that may provide information related to rotary position (and/or rotary movement) of a shaft of the motor or the spool coupled to the motor, among other possibilities. Moreover, the speed sensor may take the form of an absolute encoder and/or an incremental encoder, among others. So in an example implementation, as the motor <NUM> causes rotation of the spool, a rotary encoder may be used to measure this rotation. In doing so, the rotary encoder may be used to convert a rotary position to an analog or digital electronic signal used by the tether control module <NUM> to determine the amount of rotation of the spool from a fixed reference angle and/or to an analog or digital electronic signal that is representative of a new rotary position, among other options.

Based on the data from the speed sensor, the tether control module <NUM> may determine a rotational speed of the motor <NUM> and/or the spool and responsively control the motor <NUM> (e.g., by increasing or decreasing an electrical current supplied to the motor <NUM>) to cause the rotational speed of the motor <NUM> to match a desired speed. When adjusting the motor current, the magnitude of the current adjustment may be based on a proportional-integral-derivative (PID) calculation using the determined and desired speeds of the motor <NUM>. For instance, the magnitude of the current adjustment may be based on a present difference, a past difference (based on accumulated error over time), and a future difference (based on current rates of change) between the determined and desired speeds of the spool.

In some embodiments, the tether control module <NUM> may vary the rate at which the tether <NUM> and payload <NUM> are lowered to the ground. For example, the speed controller may change the desired operating rate according to a variable deployment-rate profile and/or in response to other factors in order to change the rate at which the payload <NUM> descends toward the ground. To do so, the tether control module <NUM> may adjust an amount of braking or an amount of friction that is applied to the tether <NUM>. For example, to vary the tether deployment rate, the UAV <NUM> may include friction pads that can apply a variable amount of pressure to the tether <NUM>. As another example, the UAV <NUM> can include a motorized braking system that varies the rate at which the spool lets out the tether <NUM>. Such a braking system may take the form of an electromechanical system in which the motor <NUM> operates to slow the rate at which the spool lets out the tether <NUM>. Further, the motor <NUM> may vary the amount by which it adjusts the speed (e.g., the RPM) of the spool, and thus may vary the deployment rate of the tether <NUM>.

In some embodiments, the tether control module <NUM> may be configured to limit the motor current supplied to the motor <NUM> to a maximum value. With such a limit placed on the motor current, there may be situations where the motor <NUM> cannot operate at the desired operate specified by the speed controller. For instance, as discussed in more detail below, there may be situations where the speed controller specifies a desired operating rate at which the motor <NUM> should retract the tether <NUM> toward the UAV <NUM>, but the motor current may be limited such that a large enough downward force on the tether <NUM> would counteract the retracting force of the motor <NUM> and cause the tether <NUM> to unwind instead. And as further discussed below, a limit on the motor current may be imposed and/or altered depending on an operational state of the UAV <NUM>.

In some embodiments, the tether control module <NUM> may be configured to determine a status of the tether <NUM> and/or the payload <NUM> based on the amount of current supplied to the motor <NUM>. For instance, if a downward force is applied to the tether <NUM> (e.g., if the payload <NUM> is attached to the tether <NUM> or if the tether <NUM> gets snagged on an object when retracting toward the UAV <NUM>), the tether control module <NUM> may need to increase the motor current in order to cause the determined rotational speed of the motor <NUM> and/or spool to match the desired speed. Similarly, when the downward force is removed from the tether <NUM> (e.g., upon delivery of the payload <NUM> or removal of a tether snag), the tether control module <NUM> may need to decrease the motor current in order to cause the determined rotational speed of the motor <NUM> and/or spool to match the desired speed. As such, the tether control module <NUM> may, based on the current supplied to the motor <NUM>, determine if the payload <NUM> is attached to the tether <NUM>, if someone or something is pulling on the tether <NUM>, and/or if the payload coupling apparatus <NUM> is pressing against the UAV <NUM> after retracting the tether <NUM>. Other examples are possible as well.

During delivery of the payload <NUM>, the payload coupling apparatus <NUM> can be configured to secure the payload <NUM> while being lowered from the UAV by the tether <NUM>, and can be further configured to release the payload <NUM> upon reaching ground level. The payload coupling apparatus <NUM> can then be retracted to the UAV by reeling in the tether <NUM> using the motor <NUM>.

In some implementations, the payload <NUM> may be passively released once it is lowered to the ground. For example, a passive release mechanism may include one or more swing arms adapted to retract into and extend from a housing. An extended swing arm may form a hook on which the payload <NUM> may be attached. Upon lowering the release mechanism and the payload <NUM> to the ground via a tether, a gravitational force as well as a downward inertial force on the release mechanism may cause the payload <NUM> to detach from the hook allowing the release mechanism to be raised upwards toward the UAV. The release mechanism may further include a spring mechanism that biases the swing arm to retract into the housing when there are no other external forces on the swing arm. For instance, a spring may exert a force on the swing arm that pushes or pulls the swing arm toward the housing such that the swing arm retracts into the housing once the weight of the payload <NUM> no longer forces the swing arm to extend from the housing. Retracting the swing arm into the housing may reduce the likelihood of the release mechanism snagging the payload <NUM> or other nearby objects when raising the release mechanism toward the UAV upon delivery of the payload <NUM>.

Active payload release mechanisms are also possible. For example, sensors such as a barometric pressure based altimeter and/or accelerometers may help to detect the position of the release mechanism (and the payload) relative to the ground. Data from the sensors can be communicated back to the UAV and/or a control system over a wireless link and used to help in determining when the release mechanism has reached ground level (e.g., by detecting a measurement with the accelerometer that is characteristic of ground impact). In other examples, the UAV may determine that the payload has reached the ground based on a weight sensor detecting a threshold low downward force on the tether and/or based on a threshold low measurement of power drawn by the winch when lowering the payload.

Other systems and techniques for delivering a payload, in addition or in the alternative to a tethered delivery system are also possible. For example, a UAV <NUM> could include an air-bag drop system or a parachute drop system. Alternatively, a UAV <NUM> carrying a payload could simply land on the ground at a delivery location.

Claim 1:
A method of controlling tonal noises produced by an unmanned aerial vehicle, UAV (<NUM>), the method comprising:
generating thrust with a plurality of rotor units (<NUM>) mounted to the UAV to propel the UAV into flight, each of the rotor units including a bladed rotor (<NUM>); and
adjusting at least one of a rotation rate or a phase delay of at least one of the rotor units relative to one or more others of the rotor units, wherein adjusting the at least one of the rotation rate or the phase delay causes a spread in the tonal noises generated by the rotor units,
wherein adjusting at least one of the rotation rate or the phase delay comprises varying rotation rates of the rotor units relative to each other to spectrally spread out component frequencies of the tonal noises collectively generated by the rotor units,
wherein one or more of the rotor units have different physical geometries relative to each other such that different rotation rates for different ones of the rotor units produce a common amount of thrust.