U.S. patent application number 15/245546 was filed with the patent office on 2018-03-01 for unmanned aerial vehicle.
The applicant listed for this patent is PRINCESS SUMAYA UNIVERSITY FOR TECHNOLOGY. Invention is credited to Hamzeh Mahmoud Alzu'bi, Osamah Ahmad Rawashdeh, Belal Hussein Sababha.
Application Number | 20180057163 15/245546 |
Document ID | / |
Family ID | 61240361 |
Filed Date | 2018-03-01 |
United States Patent
Application |
20180057163 |
Kind Code |
A1 |
Sababha; Belal Hussein ; et
al. |
March 1, 2018 |
UNMANNED AERIAL VEHICLE
Abstract
A vertical take-off and landing ("VTOL") unmanned aerial vehicle
("UAV") system and a method of controlling the same, wherein such
method controls the stability and maneuverability of the VTOL UAV
by manipulating the speeds of the propellers at each rotor. The
VTOL UAV includes a body with three extending arms, wherein each of
such arms is aligned and fixed at a certain angle from a central
axis passing through the body. Each extending arm is equipped with
a rotor with propellers. The rotors are sufficient to control the
yaw of the UAV, and there is no need for coaxial rotors or an extra
servo-motor in order to control the yaw of the UAV, thus reducing
the cost and the weight of the UAV.
Inventors: |
Sababha; Belal Hussein;
(Amman, JO) ; Alzu'bi; Hamzeh Mahmoud; (Amman,
JO) ; Rawashdeh; Osamah Ahmad; (Rochester Hills,
MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PRINCESS SUMAYA UNIVERSITY FOR TECHNOLOGY |
Amman |
|
JO |
|
|
Family ID: |
61240361 |
Appl. No.: |
15/245546 |
Filed: |
August 24, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B64C 2201/14 20130101;
B64C 2201/027 20130101; B64C 2201/108 20130101; B64C 39/024
20130101 |
International
Class: |
B64C 39/02 20060101
B64C039/02; B64C 27/08 20060101 B64C027/08; B64C 17/06 20060101
B64C017/06 |
Claims
1. An unmanned aerial vehicle ("UAV") comprising: a main body
having a front portion and a rear portion, wherein said main body
is bifurcated by a line of symmetry; first, second, and third
similar arms extending radially from said main body, wherein said
first and second arms extend from said front portion and are
positioned relative to each other on opposite sides of said line of
symmetry, and wherein said third arm extends from said rear portion
along said line of symmetry; and a single rotor positioned on each
of said first, second, and third arms.
2. The unmanned aerial vehicle as recited in claim 1, wherein said
single rotors positioned on said first and second arms rotate in a
similar direction, and wherein said single rotor positioned on said
third arm rotates in an opposite direction.
3. The unmanned aerial vehicle as recited in claim 1, wherein said
UAV is configured to achieve maneuverable flight with only said
single rotors positioned on said first, second, and third arms.
4. The unmanned aerial vehicle as recited in claim 2, wherein said
single rotors positioned on said first and second arms produce
similar amounts of torque and lift while said rotor positioned on
said third arm produces twice the amount of torque produced by
either of said other two single rotors.
5. The unmanned aerial vehicle as recited in claim 1, further
comprising a DC motor coupled to each single rotor and positioned
on said first, second, and third arms.
6. The unmanned aerial vehicle as recited in claim 1, further
comprising a plurality of ("PID") controllers configured to control
a set of parameters, including altitude, roll, pitch, and yaw, of
said UAV system.
7. The unmanned aerial vehicle as recited in claim 6, wherein said
plurality of PID controllers are four, each configured to control
at least one parameter of said set of parameters with equivalent
execution rates of roll and pitch control loops, and a higher
execution rate of a yaw control loop than said execution rates of
said roll and pitch control loops.
8. The unmanned aerial vehicle as recited in claim 1, further
comprising three command mixers configured to mix outputs of said
PID controllers, wherein said mixed outputs are sent to a plurality
of rotor controllers.
9. The unmanned aerial vehicle as recited in claim 1, wherein said
UAV does not include any servo-motors coupled to said single rotors
so that said single rotors are attached to said arms in a fixed
manner.
10. The unmanned aerial vehicle as recited in claim 1, wherein said
single rotors are not coaxial rotors.
11. A method for controlling a UAV system comprising: comparing, by
at least one controller, a plurality of actual parameters versus a
plurality of desired parameters; identifying, by the at least one
controller, correction values for the compared parameters; mixing,
by at least one command mixer, the correction values; and
communicating the mixed values at the at least one command mixer to
a corresponding rotor controller of said UAV system.
12. The method as recited in claim 11, wherein said parameters
include altitude, roll, pitch, and yaw of said UAV system.
13. The method as recited in claim 11, wherein said actual
parameters are obtained from a plurality of sensors selected from a
group consisting of gyroscopes, accelerometers, sonar, and pressure
sensors.
14. The method as recited in claim 11, wherein said correction
values are a result of a difference between values of said desired
and actual parameters after being subjected to a PID control
loop.
15. The method as recited in claim 11, wherein a first command
mixer adds an altitude correction value and subtracts roll, pitch,
and yaw correction values to send to a first one of the rotor
controllers.
16. The method as recited in claim 15, wherein a second command
mixer adds said roll and altitude correction values but subtracts
said pitch and yaw correction values to send to a second one of the
rotor controllers.
17. The method as recited in claim 16, wherein a third command
mixer adds said pitch, yaw, and altitude correction values and
disregards said roll correction value to send to a third one of the
rotor controllers.
18. The method as recited in claim 17, wherein said UAV system
comprises: a main body having a front portion and a rear portion,
wherein said main body is bifurcated by a line of symmetry; first,
second, and third similar arms extending radially from said main
body, wherein said first and second arms extend from said front
portion and are positioned relative to each other on opposite sides
of said line of symmetry, and wherein said third arm extends from
said rear portion along said line of symmetry; and a single rotor
positioned on each of said first, second, and third arms; wherein
said first one of the rotor controllers is configured to control
rotational speed of said single rotor positioned on said first arm,
wherein said second one of the rotor controllers is configured to
control rotational speed of said single rotor positioned on said
second arm, and wherein said third one of the rotor controllers is
configured to control rotational speed of said single rotor
positioned on said third arm.
19. An unmanned aerial vehicle ("UAV") consisting of first, second,
and third single rotors, wherein the UAV further comprises: a main
body having a front portion and a rear portion, wherein said main
body is bifurcated by a line of symmetry; first, second, and third
similar arms extending radially from said main body, wherein said
first and second arms extend from said front portion and are
positioned an equal radial distance from said line of symmetry, and
wherein said third arm extends from said rear portion along said
line of symmetry; wherein said first single rotor is positioned on
said first arm; wherein said second single rotor is positioned on
said second arm; and wherein said third single rotor is positioned
on said third arm.
20. The UAV as recited in claim 19, further comprising a fixed
blade propeller attached to each rotor such that all three
propellers are aligned on a common plane in a fixed manner.
Description
TECHNICAL FIELD
[0001] The present disclosure relates in general to an Unmanned
Aerial Vehicle ("UAV") and in particular to a UAV in which the
stability and maneuvering is achieved by manipulating the
rotational speeds of a plurality of propellers.
BACKGROUND
[0002] An unmanned aerial vehicle ("UAV") is an aircraft that
manipulates aerodynamic forces to provide lift without an onboard
human operator. Generally, UAVs can be flown autonomously or
piloted remotely. UAVs are able to carry payloads depending on
their power plant. A vertical takeoff and landing ("VTOL") UAV is
an aircraft that is capable of VTOL from a static or dynamic
position. VTOL aircraft have the ability to transition between
movement phases including vertical takeoff, hover, lateral
movement, and landing. Multi-rotor UAVs are VTOLs that have
recently emerged. Such UAVs make use of more than one rotor to
function. Tricopters (a.k.a. tri-rotors) are a special version of
multi-rotor UAVs that engages three rotors. Tri-rotor VTOL UAVs
fall mainly into two categories. In the first, UAVs are equipped
with three coaxial rotors. Each motor in every coaxial rotor in
this configuration rotates in the opposite direction of the other
to cancel the yaw moment generated by every motor within the
coaxial rotor assembly. In the other category, UAVs have three
single rotors with a single servo-motor for one of the rotors. The
servo-motor is used to change the lifting angle of one of the three
single rotors. Turning the rotor clockwise or counterclockwise by
the control loop will change the yaw of the vehicle. In both
configurations, the main goal is to stabilize the yaw moment of the
vehicle.
[0003] The coaxial and tilting servo-motor configuration
approaches, however, require additional precision moving parts that
increase the complexity of the mechanical design. In addition,
these extra mechanical components (i.e., coaxial rotors or
servo-motor) add overhead cost and weight.
[0004] Kataoka et al. studied a tri-rotor UAV system with only
three motors that are all mounted on the three arms of the UAV with
fixed tilt angles (Kataoka et al., "Nonlinear Control and Model
Analysis of Trirotor UAV Model," 18th IFAC World Congress, Aug.
28-Sep. 2, 2011). The authors showed that the hovering control of a
system with only three inputs (the three motors, in this case) is
impossible.
SUMMARY
[0005] Embodiments of the present disclosure provide an Unmanned
Aerial Vehicle ("UAV") using only three propellers, which may be a
Vertical Take-off and Landing ("VTOL") UAV.
[0006] Embodiments of the present disclosure provide a UAV system
in which yaw is adjusted to enable lateral maneuvering with minimal
pitch alternation that does not affect the UAV's stability.
[0007] Embodiments of the present disclosure provide a method for
controlling the stability and maneuvering ability of a UAV by
manipulating the speeds of the three installed propellers.
[0008] Aspects of the present disclosure provide a low cost and low
weight UAV compared to the conventional solutions.
[0009] Aspects of the present disclosure provide a method for
controlling the balance (roll, pitch, and yaw) of a UAV and making
such UAV capable of hovering and lateral maneuvering.
[0010] Aspects of the present disclosure provide a tri-rotor UAV
system having a front portion and a rear portion separated by a
line of symmetry, wherein the main body has three horizontal arms
extending radially therefrom, wherein two of the arms extend in a
front portion, and one of the arms extends in a rear portion, and
wherein each of the arms has at an end a rotor containing a DC
motor, a propeller, and a base, and wherein the main body encloses
a plurality of Proportional-Integral-Differential ("PID")
controllers, and a plurality of command mixers.
[0011] In aspects of the present disclosure, the rotors extending
in the front portion rotate in a similar direction, while the rotor
extending in the rear portion rotates in an opposite direction,
such that adverse torque forces and gyroscopic moment forces are
reduced or even cancelled. This leads to yaw moment control. The
rotational speed difference between the two front rotors produces
the roll moment, while the pitch moment is created due to the
variation of speed between the rear rotor and the front two rotors
collectively.
[0012] In aspects of the present disclosure, the rotors have
equivalent initial rotational speeds.
[0013] In accordance with aspects of the present disclosure, the
rotors in the front portion produce a similar amount of torque and
lift while the rotor in the rear portion produces twice the amount
of torque produced by either rotor in the front portion.
[0014] According to aspects of the present disclosure, the base
fixes the DC motor to the arm.
[0015] In aspects of the present disclosure, the plurality of PID
controllers control a set of parameters including altitude, roll,
pitch, and yaw of the system.
[0016] In accordance with aspects of the present disclosure, the
plurality of PID controllers are four, each controlling at least
one parameter of a set of parameters, and wherein execution rates
of roll and pitch control loops are equivalent, and have higher
rates than a yaw control loop.
[0017] According to aspects of the present disclosure, the command
mixers are three, and mix outputs of the PID controllers, wherein
the mixed outputs are transmitted to a plurality of rotor
controllers.
[0018] Aspects of the present disclosure provide a method for
controlling a UAV system include comparing, by at least one
controller, a plurality of actual parameters versus a plurality of
desired parameters; identifying, by the at least one controller,
correction values for the compared parameters, mixing, by at least
one command mixer, the correction values; and communicating the
mixed values at the at least one command mixer to a corresponding
rotor controller.
[0019] In aspects of the present disclosure, the parameters include
altitude, roll, pitch, and yaw of the system.
[0020] According to aspects of the present disclosure, the actual
parameters are obtained from a plurality of sensors comprising
gyroscopes, accelerometers, sonar, and pressure sensors.
[0021] In accordance with aspects of the present disclosure, the
desired parameters are pre-set by an operator (for example, remote
pilot, or autopilot).
[0022] In aspects of the present disclosure, the correction values
are a result of a difference between values of the desired and
actual parameters after being subjected to a PID control loop.
[0023] According to aspects of the present disclosure, a first
command mixer adds an altitude correction value and subtracts roll,
pitch, and yaw correction values.
[0024] In aspects of the present disclosure, a second command mixer
adds up roll and altitude correction values but subtracts pitch and
yaw correction values.
[0025] In aspects of the present disclosure, a third command mixer
adds up pitch, yaw, and altitude correction values and disregards a
roll correction value.
[0026] In embodiments of the present disclosure, the UAV is
configured to achieve maneuverable flight using only three single
rotors each positioned on arms of the UAV that extend from a main
body of the UAV. The three single rotors are not coaxial rotors.
Such a UAV may also be configured to achieve maneuverable flight
without the use of any servo-motors to control the yaw of the UAV.
The yaw moment control is achieved by only manipulating the
rotational speeds of the propellers at each rotor, without the use
of any conventional mechanical components for dynamically tilting
motor(s) (e.g., a servo-motor).
[0027] Such a UAV may be configured with no servo-motors coupled to
any of the single rotors.
[0028] Embodiments of the present disclosure provide UAV design
that only employs three brushless DC motors with three fixed pitch
propellers for propulsion and flight control. The design of the UAV
in accordance with embodiments of the present disclosure is
different than the one presented in Kataoka et al. (previously
referenced herein) by not having the fixed tilt angles for any of
the three rotors. No additional mechanics for dynamically tilting
motor(s), found on existing tricopters, are used. A control
strategy to control the stability and maneuvering of the UAV is
achieved by only manipulating the rotational speeds of the
propellers at each rotor. Two of the rotors rotate in the same
direction while the third rotates in the opposite direction. The
control methodology is novel compared to other systems that require
either coaxial rotors or an extra servo-motor to control the yaw of
the UAV. Results show that the UAV design achieved stable flight
with minimal position-attitude cross control effect. The fixed
nature of the rotors in the UAV design, reduced mechanical
requirements and cost compared to existing vehicles of its
type.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The disclosure will now be described with reference to the
accompanying drawings without restricting the scope of the
disclosure thereof, and in which:
[0030] FIG. 1 illustrates a top view of a UAV system configured in
accordance with embodiments of the present disclosure.
[0031] FIG. 2 illustrates a perspective view of a UAV system
configured in accordance with embodiments of the present
disclosure.
[0032] FIG. 3A illustrates a block diagram showing inputs and
outputs of controllers of a UAV system configured in accordance
with embodiments of the present disclosure.
[0033] FIG. 3B illustrates a block diagram showing inputs and
outputs of command mixers of a UAV system configured in accordance
with embodiments of the present disclosure.
[0034] FIG. 4 illustrates a flowchart of a method for controlling a
UAV system configured in accordance with embodiments of the present
disclosure.
DETAILED DESCRIPTION
[0035] FIGS. 1, 2, 3A, and 3B illustrate a UAV system, configured
according to embodiments of the present disclosure. The UAV system
in embodiments of the present disclosure includes a main body 1
enclosing a cavity (not shown). The main body 1 has a front portion
10 and a rear portion 11; the front and rear portions 10, 11 are
illustrated in FIG. 1 as being separated by a central axis Y-Y.
Three arms 100, 101, and 102 (which may be configured substantially
identical to each other) extend radially outwardly from the main
body 1, wherein the arms 100, 101, and 102 are aligned and fixed at
one or more certain angles from a central axis X-X (axis X-X
represents a line of symmetry bifurcating the main body 1 of the
UAV). Two arms 100, 101 extend from the front portion 10 of the
main body 1, and one arm 102 extends from the rear portion 11 of
the main body 1. In embodiments of the present disclosure, each of
the arms 100, 101, 102 is equipped with a rotor 100a, 101a, 102a,
respectively, wherein each of the rotors 100a, 101a, 102a includes
a DC motor 100b, 101b, 102b, respectively, wherein each motor 100b,
101b, 101b operates rotation of a propeller 100c, 101c, 102c,
respectively. Each rotor 100b, 101b, 102b is connected to each of
the arms 100, 101, 102 by a base 100d, 101d, 102d, respectively.
The propellers 100c, 101c, 102c may each have two or more blades.
In embodiments of the present disclosure, each of the propellers
100c, 101c, 102c may be a fixed blade propeller attached to each
rotor 100a, 101a, 102a, respectively, such that all three
propellers are aligned on a common plane.
[0036] FIGS. 3A and 3B illustrate an avionics control system of the
UAV. The avionics control system may include two components: the
PID controllers 2, 3, 4, 5 and the three motor command mixers 6, 7,
8. Each PID controller calculates the difference between the
feedback and the reference and tries to eliminate error. The output
of each controller is mixed in the command mixers 6, 7, 8 to
produce the desired pulse width modulation ("PWM") signals and send
them to the motor controllers to achieve the desired motor speed
for each of the motors for the rotors.
[0037] Referring to FIG. 3A, embodiments of the present disclosure
further include a plurality of Proportional-Integral-Differential
("PID") controllers (for example, four controllers 2, 3, 4, 5),
wherein such controllers are responsible for controlling the
system's roll, pitch, yaw, and altitude, respectively. As
illustrated in FIG. 3B, the UAV system, in embodiments of the
present disclosure, includes a plurality of command mixers (for
example, three command mixers 6, 7, 8), wherein the mixers 6, 7 mix
the outputs of the controllers 2, 3, 4, 5, respectively, while the
mixer 8 mixes the outputs of the controllers 3, 4, 5.
[0038] Embodiments of the present disclosure also include a
plurality of rotor speed controllers (for example, three
controllers 12, 13, 14 to control the rotors 100a, 101a, 102a,
respectively). The controllers 12, 13, 14 may include
microcontrollers.
[0039] In the UAV system in embodiments of the present disclosure,
yaw is adjusted to enable lateral maneuvering with minimal pitch
alternation that does not affect the UAV's stability, since the
torque produced by the rear rotor 102a is double the torque
produced by either of the rotors 100a, 101a, and the execution rate
of the pitch PID controller 3 is higher than the yaw PID controller
4.
[0040] In embodiments of the present disclosure, the arms 100, 101
may be substantially aligned by the same angle (.theta.) with
respect to the axis X-X, while the arm 102 may be substantially
parallel to the axis X-X.
[0041] In the UAV system of embodiments of the present disclosure,
the DC motors 100b, 101b, 102b may be brushless out runner type DC
motors, wherein such motors have a substantially high frequency
response.
[0042] As illustrated in FIG. 2, each of the propellers 100c, 101c,
102c rotates about a corresponding axis, c1-c1, a1-a1, b1-b1,
respectively, wherein such axes represent central lines of the DC
motors 100b, 101b, 102b, respectively.
[0043] In embodiments of the present disclosure, the propellers
100c, 101c rotate in a similar direction (i.e., clockwise or
counterclockwise), while the propeller 102c rotates in an opposite
direction to propellers 100c, 101c, such that the adverse torque
forces and gyroscopic moment forces are reduced or even cancelled.
This leads to yaw moment control.
[0044] In the UAV system of embodiments of the present disclosure,
the propellers 100c, 101c, 102c may rotate initially at
substantially equivalent rotational speeds, wherein such speeds are
controlled by the controllers 2, 3, 4, 5. However, the relative
rotational speeds of the propellers 100c, 101c, 102c can be varied
by the controllers 2, 3, 4, 5 in order to maintain altitude and
attitude stability. In embodiments of the present disclosure, the
rotational speeds of the propellers 100c, 101c, 102c are variable
in order to increase or decrease thrust or propulsion of the UAV
and to improve stability.
[0045] The UAV system of embodiments of the present disclosure
achieves yaw stability control by manipulating the rotational
speeds of the propellers at each DC motor 100b, 101b, 102b to
control the attitude of the UAV and to make it capable of hovering
and lateral maneuvering, thus eliminating the need for using
coaxial rotors or an additional servo-motor. In embodiments of the
present disclosure, since the rotor 102a may be configured to
produce about double the torque produced by either of the rotors
100a and 101a, and since the execution rate of the pitch PID
controller 3 is higher than the execution rate of the yaw PID
controller 4, a pitch angle may be updated more rapidly than a yaw
angle drift. A result will be a portion of a degree pitch
oscillation and a portion of a degree yaw drift that is corrected
by the control system less occasionally than the pitch correction.
In embodiments of the present disclosure, the mechanical
specifications, propeller dimensions, motor dimensions, and power
requirements of rotor 102a are higher than those of rotor 101a and
rotor 100a in order to achieve the required torque of rotor
102a.
[0046] In order to stabilize the UAV of embodiments of the present
disclosure, the thrust (T) obtained from rotor 102a relates to the
angle 20 between the arms 100 and 101 according to the formula:
T.sub.102a=(F.sub.101a+T.sub.100a)*COS(.theta.)
[0047] where .theta. is the angle between either of the arms 100 or
101 with the central axis X-X.
[0048] In embodiments of the present disclosure, the feedback
signals regarding the system's actual roll, yaw, and pitch may be
obtained from well-known gyroscopes and accelerometers (not shown),
wherein such gyroscopes and accelerometers may be operably
connected to the controllers 2, 3, 4.
[0049] In embodiments of the present disclosure, the feedback
signal related to the system's actual altitude relative to the
ground may be provided by a well-known sonar sensor (not shown) if
the operating altitude of the system is less than a predetermined
distance (for example, 6 meters). But, if the operating altitude of
the system is equal to or greater than the predetermined distance,
then a well-known pressure sensor (not shown) may be used to
provide feedback on the altitude. The sonar or the pressure sensors
may be operably connected to the controller 5.
[0050] In embodiments of the present disclosure, a power source for
the system, the controllers 2, 3, 4, 5, the command mixers 6, 7, 8,
as well as the gyroscopes, accelerometers, and pressure sensors,
may be enclosed in the cavity of the main body 1. The sonar sensor
may be installed on a bottom surface of the main body 1.
[0051] Reference is now being made to FIG. 4, which represents a
flowchart of a method for controlling a UAV, configured in
accordance with embodiments of the present disclosure, which makes
the UAV capable of hovering and lateral maneuvering at adjustable
altitudes.
[0052] In process block 40, one or more of the controllers 2, 3, 4,
5 compares its respective actual parameter versus a desired
parameter. In process block 41, the one or more of the controllers
2, 3, 4, 5 identifies correction values for the parameters. In
process block 42, one or more of the command mixers 6, 7, 8 mixes
the identified correction values. In process block 43, the mixed
values are communicated by the one or more command mixers 6, 7, 8
to a corresponding rotor controller 12, 13, 14.
[0053] In embodiments of the present disclosure, the comparison
between the actual and desired parameters may take place at the
controllers 2, 3, 4, 5, wherein each controller may compare actual
and desired values for one parameter only. The parameters may
include the UAV roll, pitch, yaw, and altitude.
[0054] The UAV system of embodiments of the present disclosure may
be autonomous, semi-autonomous, or remotely piloted in any suitable
well-known manner. In embodiments of the present disclosure, values
of the desired parameters may be pre-set by an operator (for
example, a remote pilot or autopilot). For example, a desired
parameter may originate from an operator's controller, such as a
well-known remote controller, wherein such parameters are produced
as a result of a manual manipulation of one or more joysticks, or
equivalent activators. Alternatively, such desired parameters may
be generated within such a remote controller as a result of a
preprogrammed flight plan for the UAV. The UAV may therefore
include well-known circuitry and electronics (which may be encased
within the cavity of the main body 1) for wirelessly communicating
with the remote controller. Or, a preprogrammed flight plan may be
stored in a memory device within the UAV for operation by
well-known circuitry and electronics communicating such desired
parameters to the controllers 2, 3, 4, 5.
[0055] Referring to FIG. 3A, in embodiments of the present
disclosure, the correction values may include roll correction,
pitch correction, yaw correction, and altitude correction, wherein
such correction values may be obtained from the difference (error)
between the actual and the desired values (i.e., the error value)
after being subjected to PID control algorithms implemented within
the controllers 2, 3, 4, 5. As an example, for the pitch, roll, and
yaw, the error may be:
error=desired angle-actual angle,
[0056] where the desired angle may be set by the remote pilot or
auto pilot, and the actual angle is read by a sensor on the UAV.
The angles could be roll angle, pitch angle, and/or yaw angle. In
the case of altitude, the error may be:
error=desired altitude-actual altitude,
[0057] wherein the desired altitude is set by the remote pilot or
auto pilot, and the actual altitude is read by a sensor.
[0058] In the PID control algorithms, the error value may be
multiplied by a proportional gain Kp (P controller) to get a "P"
correction (P correction=Kp*error value), differentiated and
multiplied by a differential gain Kd (D controller) to get a "D"
correction (D correction=Kd*derivative of the error value), and
integrated and multiplied by an integral gain Ki (I controller) to
get an "I" correction (I correction=Ki*integration of the error
value). Then, these P, I, D corrections are added to obtain the
required overall correction values for each of the parameters.
[0059] For example, repeated control loops (i.e., a control loop
may be a set of computer executable software program code
instructions performed in order to compute the P, I, D correction
values) of the PID control algorithm are configured to continuously
calculate the corrections reading the desired angle, reading the
actual angle, calculating the error value, integrating the error
value, differentiating the error value, multiplying the error value
with a Kp gain to produce a P correction, multiplying the
integrated error value with a Ki gain to produce an I correction,
multiplying the differentiated error value with a Kd gain to
produce a D correction, and adding up all three corrections (P, I,
and D corrections) to produce the correction for each of the
control loops, wherein the correction of each of the control loops
is the pitch, roll, yaw, or altitude correction, as the case may
be. Then, the corrections are sent to the mixers. A frequency of
the control loops is how many times each control loop is repeated
during a unit of time.
[0060] As shown in FIG. 3A, the correction values may be the output
of the controllers 2, 3, 4, 5, while the desired and the actual
values may be the inputs of such controllers 2, 3, 4, 5.
[0061] In embodiments of the present disclosure, the command mixer
6 may add the altitude correction value, but subtract the roll,
pitch, and yaw correction values in order to produce its output
value. The output value of the command mixer 6 may be transmitted
to the controller 12.
[0062] In embodiments of the present disclosure, the command mixer
7 may add up the roll and altitude correction values, but subtract
the pitch and yaw correction values in order to produce its output
value. The output value of the command mixer 7 may be transmitted
to the controller 13.
[0063] In embodiments of the present disclosure, the command mixer
8 may add up the pitch, yaw, and altitude correction values, and
disregard the roll correction value in order to produce its output
value. The output value of the command mixer 8 may be transmitted
to the rotor 102a controller 14. The command mixer 8 may disregard
the roll correction value since the rotor 102a has no effect on the
system's roll.
[0064] In embodiments of the present disclosure, the altitude
correction value may be added to the mixers 6, 7, 8, since the
altitude correction value affects the motors 100b, 101b, 102b
substantially equally by increasing or decreasing rotational speed
(rpm) to increase or decrease altitude.
[0065] In embodiments of the present disclosure, the roll
correction value may be added to the controller 12 and subtracted
from the controller 13 to increase the rotational speed (rpm) of
the rotor 100a and decrease the rotational speed (rpm) of the rotor
101a. Having such variation in speeds may make the rotor 100a of a
higher elevation than the elevation of the rotor 101a, wherein such
variation may result in rolling the UAV about the axis X-X and
start moving in the direction of the rotor 100a (if the roll
correction was negative, the UAV will move to the direction of the
rotor 101a).
[0066] In embodiments of the present disclosure, the pitch
correction value may be added to the controller 14 and subtracted
from the controllers 12, 13 to result in pitching the UAV downwards
or upwards causing a forward or backward movement of the UAV,
respectively.
[0067] In embodiments of the present disclosure, the yaw correction
may be added to the controller 14 while subtracted from the
controllers 12, 13. Given that yaw control loop will produce such a
correction less frequently than the pitch correction of the pitch
control loop, and given that the torque of the rotor 102a is twice
the torque of either of the rotors 100a, 101a, this may result in
making the UAV to yaw around itself clockwise or counter-clock
wise, depending upon the sign (positive or negative) of the yaw
correction.
[0068] In embodiments of the present disclosure, the output values
of the command mixers 6, 7, 8 may be a set of desired Pulse Width
Modulation ("PWM") commands in order to adjust the rotational
speeds (rpm) of the rotors 100a, 101a, 102a.
[0069] In embodiments of the present disclosure, the frequencies
(i.e., the number of times the aforementioned control loop is
executed during a unit of time) for executing the roll and pitch
control loops may be substantially equal, but may be substantially
higher than the frequency for executing the yaw control loop.
[0070] In certain embodiments of the present disclosure, the
execution rate of the pitch control loop is higher than the
execution rates of both roll and yaw control loops. Also, the
execution rate of the roll control loop may be higher than the
execution rate of the yaw control loop.
[0071] The following example illustrates embodiments of the present
disclosure without, however, limiting the scope thereof.
[0072] A simulation was performed using the model parameters and
the PID gain values shown in Tables 1 and 2, respectively.
TABLE-US-00001 TABLE 1 Tri-rotor model parameters. Parameters
Values Mass (m) 2.375 kg Moment of inertia (I.sub.xx)
51.2*10.sup.-3 kg m.sup.2 Moment of inertia (I.sub.yy)
44.1*10.sup.-3 kg m.sup.2 Moment of inertia (I.sub.zz)
3.8*10.sup.-3 kg m.sup.2 Arm length (l) 0.288 m Gravitational
acceleration (g) 9.81 m/s.sup.2 Rotor inertia (J.sub.r) 6*10.sup.-5
kg m.sup.2 Thrust coefficient (b.sub.1) 7.8*10.sup.-5 N s.sup.2
Thrust coefficient (b.sub.2) 13.3*10.sup.-5 N s.sup.2 Drag
coefficient (d.sub.1) 7.5*10.sup.-7 N s.sup.2 Drag coefficient
(d.sub.2) 15*10.sup.-7 N s.sup.2
[0073] The six degree of freedom rigid body motion equations are
expressed as follows:
.phi.=p+tan .theta.(q sin .phi.+r cos .phi.),
.theta.=q cos .phi.-r sin .phi.,
.psi.=(q sin .phi.+r cos .phi.)sec .theta., Kinematic
equations:
U.sub.x=b.sub.1(.OMEGA..sub.1.sup.2-.OMEGA..sub.2.sup.2)l,
U.sub.T=b.sub.1(.OMEGA..sub.1.sup.2+.OMEGA..sub.2.sup.2)+b.sub.2.OMEGA..-
sub.3.sup.2,
U.sub.y=b.sub.1(.OMEGA..sub.1.sup.2+.OMEGA..sub.2.sup.2)l cos
.beta.-b.sub.2.OMEGA..sub.3.sup.2l,
U.sub.z=ld.sub.1(.OMEGA..sub.1.sup.2+.OMEGA..sub.2.sup.2)-ld.sub.2.OMEGA-
..sub.3.sup.2, Tri-rotor moment inputs: [0074] U.sub.T, U.sub.x,
U.sub.y, U.sub.z are the total thrust, rolling moment, pitching
moment and yawing moment, respectively, and b, d are the thrust
factor and the drag factor, respectively.
[0074]
I.sub.xx.phi.=.theta..psi.(I.sub.yy-I.sub.zz)+J.sub.r.theta..OMEG-
A..sub.r+U.sub.x,
I.sub.yy.theta.=.theta..psi.(I.sub.zz-I.sub.xx)-J.sub.r.phi..OMEGA..sub.-
r+U.sub.y,
I.sub.zz.psi.=.theta..phi.(I.sub.xx-I.sub.yy)+J.sub.r.OMEGA..sub.r+U.sub-
.z,
mz=mg-(cos .psi. cos .phi.)U.sub.T,
mx=(sin .psi. sin .phi.+cos .psi. sin .theta. cos
.phi.)U.sub.T,
my=(-cos .psi. sin .phi.+sin .psi. sin .theta. cos .phi.)U.sub.T,
Equations of motion:
TABLE-US-00002 TABLE 2 PID controller gain values. K.sub.p K.sub.d
K.sub.i Roll 6.6667 3.2456 0.02 Pitch 13.3334 11.18075 0 Yaw 0.5
0.147225 0 Altitude 10.5409 9.1423 0.01
[0075] In embodiments of the present disclosure, each of the motors
has a high frequency response. Higher motor frequency response may
result in lower oscillation in the pitch angle due to the
interdependencies of pitch and yaw controllers during command
signal mixing. Two values of frequency response were simulated, the
first value was 12 Hz, and the second value was 50 Hz. During such
a simulation, the position (X, Y) and altitude (Z) of the tri-rotor
system were held constant. The results indicated that the system
stability and behavior were better at the higher motor frequency
response of 50 Hz. Moreover, the amount of drift in X and Y
Cartesian coordinates as well as the oscillation in the roll,
pitch, and yaw angles were less at the higher motor frequency
response (the motor frequency response relates to how fast the PWM
commands may be sent to a motor to change its rotational speed and
how fast the motor will respond accordingly).
[0076] As noted herein, aspects of the present disclosure may be
embodied as various processes, methods, algorithms, etc. for
performing the various functions described herein, including with
respect to FIGS. 3A, 3B, and 4, wherein such various processes,
methods, algorithms, etc. may be implemented in hardware, software,
or a combination thereof. As such, aspects of the present
disclosure may be a system, a method, and/or a computer program
product at any possible technical detail level of integration. The
computer program product may include a computer readable storage
medium (or media) having computer readable program instructions
thereon for causing a processor to carry out aspects of the present
disclosure.
[0077] The computer readable storage medium can be a tangible
device that can retain and store instructions for use by an
instruction execution device, such as the aforementioned
microcontrollers or microprocessors, which may implement any one or
more of the controllers 2, 3, 4, 5, command mixers 6, 7, 8, and/or
the controllers 12, 13, 14. The computer readable storage medium
may be, for example, but is not limited to, an electronic storage
device, a magnetic storage device, an optical storage device, an
electromagnetic storage device, a semiconductor storage device, or
any suitable combination of the foregoing. A computer readable
storage medium, as used herein, is not to be construed as being
transitory signals per se, such as radio waves or other freely
propagating electromagnetic waves, electromagnetic waves
propagating through a waveguide or other transmission media (e.g.,
light pulses passing through a fiber-optic cable), or electrical
signals transmitted through a wire.
[0078] Computer readable program instructions described herein can
be downloaded to respective computing/processing devices from a
computer readable storage medium or to an external computer or
external storage device via a network, for example, the Internet, a
local area network, a wide area network, and/or a wireless network.
The network may comprise copper transmission cables, optical
transmission fibers, wireless transmission, routers, firewalls,
switches, gateway computers, and/or edge servers. A network adapter
card or network interface in each computing/processing device
receives computer readable program instructions from the network
and forwards the computer readable program instructions for storage
in a computer readable storage medium within the respective
computing/processing device.
[0079] Computer readable program instructions for carrying out
operations of aspects of the present disclosure may be assembler
instructions, instruction-set-architecture ("ISA") instructions,
machine instructions, machine dependent instructions, microcode,
firmware instructions, state-setting data, configuration data for
integrated circuitry, or either source code or object code written
in any combination of one or more programming languages, including
an object-oriented programming language such as Smalltalk, C++, or
the like, and procedural programming languages, such as the "C"
programming language or similar programming languages. The computer
readable program instructions may execute entirely on the UAV
system, partly on the UAV system, as a stand-alone software
package, partly on the UAV system and partly on a remote computer,
or entirely on the remote computer or server. In the latter
scenario, the remote computer may be connected to the UAV system
through any type of network, including a wireless network, a local
area network ("LAN") or a wide area network ("WAN"), or the
connection may be made to an external computer (for example,
through the Internet using an Internet Service Provider). In some
embodiments, electronic circuitry including, for example, a
microcontroller, programmable logic circuitry, field-programmable
gate arrays ("FPGA"), or programmable logic arrays ("PLA") may
execute the computer readable program instructions by utilizing
state information of the computer readable program instructions to
personalize the electronic circuitry, in order to perform aspects
of the present disclosure.
[0080] Aspects of the present disclosure are described herein with
reference to a flowchart and block diagrams of methods, apparatus
(systems), and computer program products according to embodiments
of the disclosure. It will be understood that each block of the
flowchart and/or block diagrams, and combinations of blocks in the
flowchart and/or block diagrams, can be implemented by computer
readable program instructions.
[0081] These computer readable program instructions may be provided
to a processor of a microcontroller, general purpose computer,
special purpose computer, or other programmable data processing
apparatus to produce a machine, such that the instructions, which
execute via the processor of the computer or other programmable
data processing apparatus, create means for implementing the
functions/acts specified in the flowchart and/or block diagram
block or blocks. These computer readable program instructions may
also be stored in a computer readable storage medium that can
direct a computer, a programmable data processing apparatus, and/or
other devices to function in a particular manner, such that the
computer readable storage medium having instructions stored therein
comprises an article of manufacture including instructions which
implement aspects of the function/act specified in the flowchart
and/or block diagram block or blocks.
[0082] The computer readable program instructions may also be
loaded onto a microcontroller, computer, other programmable data
processing apparatus, or other device to cause a series of
operational steps to be performed on the microcontroller, computer,
other programmable apparatus, or other device to produce a computer
implemented process, such that the instructions which execute on
the microcontroller, computer, other programmable apparatus, or
other device implement the functions/acts specified in the
flowchart and/or block diagram block or blocks.
[0083] The flowchart and block diagrams in the Figures illustrate
the architecture, functionality, and operation of possible
implementations of systems, methods, and computer program products
according to various embodiments of the present disclosure. In this
regard, each block in the flowchart or block diagrams may represent
a module, segment, or portion of instructions, which comprises one
or more executable instructions for implementing the specified
logical function(s). In some alternative implementations, the
functions noted in the blocks may occur out of the order noted in
the Figures. For example, two blocks shown in succession may, in
fact, be executed substantially concurrently, or the blocks may
sometimes be executed in the reverse order, depending upon the
functionality involved. It will also be noted that each block of
the block diagrams and/or flowchart, and combinations of blocks in
the block diagrams and/or flowchart, can be implemented by special
purpose hardware-based systems that perform the specified functions
or acts or carry out combinations of special purpose hardware and
computer instructions.
[0084] While the disclosure has been described in details and with
reference to embodiments thereof, it will be apparent to one
skilled in the art that various additions, omissions, and
modifications can be made without departing from the spirit and
scope thereof.
[0085] Although the above description contains much specificity,
these should not be construed as limitations on the scope of the
disclosure but is merely representative of the embodiments thereof.
The above described embodiments are intended to be exemplary
only.
LIST OF SYMBOLS
[0086] .theta. Pitch angle [0087] .phi. Roll angle [0088] .psi. Yaw
angle [0089] l Horizontal distance from center of propeller to
center of gravity [0090] I.sub.xx,yy,zz Moments of inertia [0091] J
Rotor inertia [0092] m Overall mass [0093] g Gravity acceleration
[0094] x, y, z Position in body coordinate frame [0095] X, Y, Z
Position in earth coordinate frame [0096] .OMEGA. Propeller angular
rate [0097] .OMEGA..sub.r Overall residual propeller angular speed
[0098] .beta. The angle between x body axis and rotor one arm
[0099] p, q, r Body angular rates [0100] C Friction coefficient
[0101] .tau. Time constant
* * * * *