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Organic Air Vehicle (OAV) Flight Control
An Application of
Multi-Application Control (MACH)
Dale Enns
Honeywell
4 March 2005
SAE AEROSPACE CONTROL AND GUIDANCE SYSTEMS COMMITTEE
Salt Lake City, Utah
AES Technology Centers of Excellence
DE/kv 12/1/03
Introduction
Vehicle
Missions
Takeoff, ascend, hover, rotate, translate, descend, land
autonomously and with pilot in the loop
AES Technology Centers of Excellence
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Design Theory
x = States incl. p, q, r, u, v, w, …
u = Control Surfaces
True Aircraft Model (TRAC)
x f x,u
Controlled Variable (CV)
y = p, q, r
y hx
Calculus and On-board Aircraft Model
(OBAC)
h
y
x ax bx u
x
Dynamic Inversion
u binv x y des ax
Feedback Controls
y des Kyc y
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y des
K
b
inv
x
x
x
x
X TRAC
OBAC
x
u
(x)
C
x
yc
C
f(x,u)
x 1
x
y
h(x)
s
a(x)
DE/kv 12/2/03
Basic Feedback Loop
fc
yc
_
1
s
fi K b
_
1
s
Kb
y
_
fa
Proportional Gain = K b 4
Integral Gain = fi
rad
sets bandwidth
sec
1
needed for desensitization and disturbance rejection
4
1
Command Gain = fc needed for closedloop response tailoring
2
Anti-Integral Windup Gain = fa 3 needed when actuator commands are limited
Kb
K
s b
ys
2
2
2
2
Closed Loop Transfer Function =
2
y c s s K bs fiK b s 2
Loop Transfer Function (at y) =
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Ls
K b s fiK b 4s 1
s2
s2
DE/kv 12/2/03
Control Law Structure
Inner loop pair
Outer loop pair
Position
Commands
Kpos s
Throttle
Command
Velocity
Commands
K vel s
Attitude
Commands
Katt s
Angular
Rate
Commands
Kpqr s
Vane
Commands
Heading
Command
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DE/kv 12/2/03
Control Allocation Approach
Given B and d find u to minimize
|| Bu – d ||2
Subject to constraints
umin < u < umax
Constraints include worst case of
Position and rate limits
Desired d is unachievable so find
Closest approximation with axis prioritization
u2
d2
d=Bu
u1
d1
Solution involves finding the intersection of two ellipsoids
AES Technology Centers of Excellence
DE/kv 12/2/03
Unique Inverse
We require that the Jacobian not change sign over the region of interest
Jacobian = det f
u
Such that the solution to f u d has a unique solution for a given d
Montontonicity for scalars
f(u)
f (u)
Example for 2 dimensions
Solution 1
Solution 2
u
d
Jacobian > 0
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Jacobian < 0
DE/kv 12/2/03
2x2 Example of Non-Unique Inverse
f(u) is piecewise linear, continuous
Slopes of diagonal are equal to 1
Off-diagonal slopes change at the origin
3
In Quadrant 1
2
f2 = 1/3 u1 + u2
In Quadrant 2
f1 = u1 + 3/2 u2
f2 = u 1 + u 2
In Quadrant 3
f1 = u1 + 1/2 u2
f2 = u 1 + u 2
Jacobian = 1/2
1
0
f2
f1 = u1 + 3/2 u2
Mapping of
-2 < u1 < 2
-2 < u2 < 2
Jacobian = -1/2
-1
quadrant
quadrant
quadrant
quadrant
-2
Jacobian = 1/2
1
2
3
4
-3
In Quadrant 4
f1 = u1 + 1/2 u2
f2 = 1/3 u1 + u2
Jacobian = 5/6
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-4
-3
-2
-1
0
1
f1
2
3
4
5
DE/kv 12/2/03
Closed Loop Poles = Open Loop Zeros
Open Loop
x Ax Bu
y Cx
zI A B
det
0
C
0
for z zeros of Gs where
Gs CsI A B
1
Dynamic Inversion
u CB
1
y d CAx
Theorem
If z zero of Gs
then A BCB CA z, 0
1
Closed Loop for y d 0
x Ax BCB CAx
1
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OAV Integrated Avionics – AV2
+3.3V
GPS Rcvr
Base Station
µHard Modem
WOW
+15V -15V
Serial
Serial
+5V
GND
+5V
Interim Radio
Receiver
Serial
+5V
CMOS Camera
Engine Speed
FMU
Pulse Train
InfraRed Camera
2.4GHz Video
Transmitter
IMU
I2C Serial
GND
+5V
GND
+5V
GND
Altimeter
1
2
Air Data
PWM
A/D
FMU H/W
x-axis
+V
GND
Magnetometer
y-axis
z-axis
3
Servo 1
4
5
External H/W
Servo 2
Temperature
6
Servo 3
Battery State
7
Servo 4
Payload H/W
Comm. H/W
8
Engine Temp
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Engine Throttle
DE/kv 12/2/03
OAV Avionics
Flight Management Unit
IMU
– MEMS IMU HG-1900
– GPS
– Blended GPS/Inertial Nav & Attitude
information
– Flight Control Laws
– Actuation commands
Flight Control Surfaces
Engine Throttle
Commonality of hardware leads to
lower cost - common gun-launched
IMU entering high volume production
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FMU
– Payload selection
– Payload pointing
Honeywell Intl. Proprietary
DE/kv 12/2/03
Flight Controls Adverse Weather Issues
Hover in steady wind
– Vehicle will tilt into the wind
– More tilt for more wind
Gusting winds
– Vehicle will tilt back and forth to adjust to changing wind
– Non-minimum phase response
Measurements of airspeed relative to vehicle lead to improved
performance
– Direct sensing
– Estimation
– 3 components of relative wind
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Hover in Steady Wind
Force Balance
Tilt from Vertical
Moment Balance
T
L
Wind
D
M 0
CG
Duct Nose Up
Vanes Nose Down
a
Vane
Deflection
for
Trim
(Degrees)
Wind Along
Pitch Axis
Roll Axis
e
10
20
mg
Large
Roll Vane Deflection
Required for Trim
at Intermediate Speeds
30
40
Horizontal Wind Speed (Knots)
AES Technology Centers of Excellence
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OAV Specifics
On-board Aircraft Model (OBAC)
– 3 Forces and 3 Moments are Dependent Variables
– V , , , a , e , r , rpm are Independent Variables
– Combine table lookup and analytical expressions for forces and
moments
– Rigid body with propeller/engine momentum equations of motion
Accels
Wind Estimator
Estimation
Gains
Modeled Accels
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1
S
OBAC
Wind Estimate
Measurements
DE/kv 12/2/03
Robust Stability Analysis
Control Law
Introduce
Multiplicative
Perturbations
at all interfaces
between Plant &
Control Law
w a
w
s
a
0
0
s
Plant
za
_
a
wa
Gi
K
ws
s
zs
Unacceptable
log 10
log M
za
z
s
Negotiable
log 10
Satisfactory
M
1
0
log
logbw
1
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DE/kv 12/2/03
MOVIE OF OAV FLIGHT TEST
1 July 2004
Ft. Benning, Georgia
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DE/kv 12/2/03
Conclusions
Multi-Application Control (MACH)
– Reusable control law
– Robust, versatile, modular, nonlinear,
multivariable design
Other Applications of Dynamic Inversion
– X-35 Lockheed Martin Joint Strike Fighter
– X-38 Prototype Crew Return Vehicle
AES Technology Centers of Excellence
DE/kv 12/2/03