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

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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

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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.

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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

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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)

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Dynamic approachesKinematic/Car‐like robot approachPoint mass modelDubins curves

Desired Trajectory Generator

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Car‐like robot model

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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

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-40 -20 0 20 40 60 80 100 120-20

0

20

40

60

80

100

120

Reference Trajectory

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Turning Geometry

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Experimental Orchard

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1. Experiments to test the behaviour of the proposed model

Slippage information is not taken into consideration.

RTK-GPS is used for position feedback.

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4 km autonomous drive achieved in the orchard

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Desired and actual steering angles for 4 km autonomous drive

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Video

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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.

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21

22

23

24

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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

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3. Experiments to test the behaviour of the proposed model.

Slippage information is taken into consideration.

RTK-GPS is used for position feedback.

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RTK-GPSOdometer Steering System

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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

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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

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4. Orchard Experiments.

Slippage information is taken into consideration.

Row Detection System (via Laser Scanning RangeFinder) is used.

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36

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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 

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Video ‐ Turning control withslippage estimation 

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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