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Improving autonomous orchard vehicle trajectory tracking performance via slippage compensation
Dr. Gokhan BAYAR
Mechanical Engineering Department of Bulent Ecevit University
Zonguldak, Turkey
This study was conducted under the Supervision of Dr. Marcel Bergerman in the Field Robotics Center of Robotics Institute of Carnegie Mellon University,
Pittsburgh, PA, USA.
Development of a slippage estimation procedure and performing a desired trajectory tracking control.
Objective of the Research
1
a single set of controller parameters or a unique equation of motion
to guarantee a desired performance and accuracy
Due to changing the characteristics Of wheel-ground interaction
2
the simple assumptions which are generally used in the mobile robot / autonomous vehicle applications:• ideal transmission• ideal rolling• no slippage• no lost of traction control• no external wheel forces• no surface change behavior• no disturbance, etc.
3
Surface Information
<Mobile Robot> Unmanned
Ground Vehicle
Desired task
[f(x,y,t)]
[f(x,y)]
Vehicle Model
Controller
Forward Velocity
Steering Angle
x,y,θ,V,δ
Wheel-Ground Interaction
4
Trajectory Tracking Control of an Autonomous Vehicle
f(X,Y,t)desired
f(X,Y,t)actual
Vehicledesired(t)
XError(t)= |XDesired(t) - XActual(t)|
YError(t)= |YDesired(t) - YActual(t)|
θError(t)= |θDesired(t) - θActual(t)|
X
Y
Vehicleactual(t)
5
Dynamic approachesKinematic/Car‐like robot approachPoint mass modelDubins curves
Desired Trajectory Generator
6
Car‐like robot model
7
8
Desired trajectory tracking controller
ΣXdesired
XPS
Σ
YPS
Ydesired
Controller
Σ
θPS
θdesired
Vehicle
Vc
Xe
Ye
θe
+
+
+
-
-
-
V
V
x, y
Φc
Φ
Φ
9
Lyapunov Functions
10
trees
Working Environment of an Orchard Robot Vehicle
w1
w2
11
-40 -20 0 20 40 60 80 100 120-20
0
20
40
60
80
100
120
Reference Trajectory
12
Turning Geometry
13
14
Experimental Orchard
15
1. Experiments to test the behaviour of the proposed model
Slippage information is not taken into consideration.
RTK-GPS is used for position feedback.
16
4 km autonomous drive achieved in the orchard
17
Desired and actual steering angles for 4 km autonomous drive
18
Video
19
2. Experiments to test the behaviour of the proposed model.
Slippage information is not taken into consideration.
Row Detection System (via Laser Scanning RangeFinder) is used.
20
21
22
23
24
25
Experimental results obtained in the first row of the orchard
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Experimental results obtained in the first row. Width = 4.44 m, Length = 52.95 m.
(a) Steering angles, (b) Lateral errors
Video ‐ First Row
Width = 4.44 m, Length = 52.95 m
0.5 m/s Forward Velocity
Forward Camera Front Camera
27
3. Experiments to test the behaviour of the proposed model.
Slippage information is taken into consideration.
RTK-GPS is used for position feedback.
28
RTK-GPSOdometer Steering System
29
30
Car Like Robot Model Without Slippage
Car Like Robot Model With Slippage
It is assumed that 31
Slippage Experiments on Snow
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0 5 10 15 20-10
-8
-6
-4
-2
0
2
4
6
X-Direction [m]
Y-D
irect
ion
[m]
DesiredReal
0 5 10 15 20-10
-8
-6
-4
-2
0
2
4
6
X-Direction [m]
Y-D
irect
ion
[m]
DesiredReal
Reference Trajectory Tracking Control on Snow
Vehicle Control
Without Slip Estimation
Vehicle Control
With Slip Estimation
33
0 20 40 60 800
0.2
0.4
0.6
0.8
1
1.2
1.4
Time [s]
Forw
ard
Spee
d [m
/s]
w/o Estimationw/ Estimation
0 20 40 60 80-50
-40
-30
-20
-10
0
10
20
30
Time [s]
Stee
ring
Ang
le [d
eg]
w/o Estimationw/ Estimation
34
4. Orchard Experiments.
Slippage information is taken into consideration.
Row Detection System (via Laser Scanning RangeFinder) is used.
35
36
37
E1 results obtained by using RTK GPS feedback without using slippage estimation. E2 results obtained by using the slippage estimation procedure that uses RTK GPS feedback. E3 results obtained by using feedback information coming from dead reckoning algorithm. No slippage estimation procedure is adapted into the system model.E4 results obtained by using the slippage estimation process that uses the dead reckoning feedback information. 38
Video ‐ Turning control without slippage estimation
39
Video ‐ Turning control withslippage estimation
40
1Field Robotics Center, Robotics Institute, Carnegie Mellon University, Pittsburgh, PA, USA2Mechanical Engineering Department, Middle East Technical University, Ankara, Turkey
Special thanks to the co-authors of the paper:
Gokhan Bayar*, Marcel Bergerman1, E. ilhan Konukseven2, A. Bugra Koku2, “Improving the trajectory tracking performance of autonomous orchard vehicles using wheel slip compensation”, Biosystems Engineering, vol. 146, pp. 149-164, 2016.
Thanks for your attention
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