[PPT] - Guidance of Autonomous Tractor With Four Wheel Steering Tim o PowerPoint Presentation

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Guidance of Autonomous Tractor With Four Wheel Steering

Tim o Oksanen

Doctor of Science (technology) ( gy) Docent (agricultural engineering) Senior Research Scientist Senior Research Scientist

Aalto University, Finland

Dept of Automation and Systems Technology

Dept. of Automation and Systems Technology

IEEE RAS AgRobots TC IEEE RAS AgRobots TC Webinar #11 September 26, 2013

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The presentation The presentation

Most of the slides related to presentations in:

p

– Oksanen, T., Backman, J. 2013. Guidance system for agricultural tractor with four wheel steering. IFAC Bio-Robotics Conference, Sakai Japan 27 29 March 2013 Sakai, Japan, 27-29 March 2013. – Oksanen, T. 2012. Embedded control system for large scale unmanned tractor. 5th Automation Technology for Off-road Equipment Conference (ATOE), Valencia, Spain, July 8 - July 12, 2012. pp. 3-8. – Oksanen, T. 2012. Path following algorithm for four wheel independent steered tractor 5th Automation Technology for Off-road independent steered tractor. 5th Automation Technology for Off-road Equipment Conference (ATOE), Valencia, Spain, July 8 - July 12, 2012.

pp. 9-14.

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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Part 1: The tractor "APU Module" Part 1: The tractor APU-Module

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The Autonomous Tractor "APU Module"

165 hp turbodiesel ~6000 kg

APU-Module

g Hydraulic drivetrain Each wheel (4WD)

Steering

Steering

Drive

3p-hitch in both ends PTO in both ends PTO in both ends Up to 9 aux valves 12V DC electric Built originally 1990-1992 by a Finnish company. E&E refurbished 2011-2012 2011 2012 Originally designed for unmanned use unmanned use (autonomous)

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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Drivetrain Drivetrain

Four variable displacement hydraulic pumps attached to

shaft of diesel engine

Constant displacement motors in each wheel hub
One pump drives one motor, independent control of

wheel drive (coupled only by ground contact)

– ”differential” needs to be realized in electronic control system

Encoder in each wheel to measure speed
Each wheel has independent hydraulic actuator for

steering with position sensor; no track rods used

k it ibl t hi t A k t i – makes it possible to achieve accurate Ackermann geometry in four wheel steering

4 wheel drive + 4 wheel steering

4 wheel drive + 4 wheel steering

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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Drivetrain Drivetrain

Original design of tractor did not contain brakes at all

g g

– Hydrostatic system is able to do deceleration – When the tractor is stationary, a small drift happens Parking brake implemented in rear wheels

For implements the original hydraulic system provides

p g y y p 180 l/min @ 200 bar hydraulic flow

– up to 9 auxiliary hydraulic valves available in both ends – analogue proportional heads in the directional valves

The diesel engine is from 1990 (Perkins 1006-6T)

g ( )

– No built-in ECU – Monitoring and control of engine needs to be realized

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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Requirements for Electronic control system Requirements for Electronic control system

System

y

– Real-timeness – Safety

Control interfaces

– Interface to autonomous navigation system g y – Wireless manual control (safety)

Functions

– Cruise control – Coupled steering & drive p g – Brake control – Engine control – Hitch and PTO control

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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Materials Materials

The tractor has plenty of I/O; altogether ~80, of which 34

d t b PWM ( 2A) f h d li need to be PWM (>2A) for hydraulic propos

A control module Parker/Mitron MCC2212 was selected

due to several reasons

– Plenty of power outputs (12 DO + 10 PWM) – Programming with C language – Pretty mature product, more than 10 years (th i it lf i td t d) – (the microprocessor itself is outdated) – CAN bus

≥4 of these are needed (I/O)

≥4 of these are needed (I/O)
Communication

– adapted from SAE J1939, mainly 100ms

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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Control system Control system

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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Part 2: Guidance & four wheel steering Part 2: Guidance & four wheel steering

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Introduction Introduction

The presentation shows how to keep a vehicle with 4WS

p p

n track on the field
Later the results in real field operation

Later the results in real field operation

Four wheel steering is used in some commercial

tractors: tractors:

Case 4894 Claas Xerion series

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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Seed drill (combined) Seed drill (combined)

Tume KL-2500 (1987)

125 mm seed coulters
250 mm fertilizer coulters
0.46 m3 fertilizer
0.31 m3 seeds
Cat2 hitch mounting

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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Materials Materials

Constraints

– Steering angle (~20 deg) – Steering rate (8-12 °/s @1500rpm) St i d i (d l 400 ) – Steering dynamics (delay ~400ms)

limits the driving speed vs. tracking accuracy

V hi l d b ili d (40 k /h) – Vehicle max. speed cannot be utilized (40 km/h)

Positioning devices a.k.a. "HighDock"

– RTK-GPS (VRS), Trimble 5700 – Fiber-optic gyroscope, KVH DSP-3000 (for heading) I li t I ti l Li k 3DM GX2 (i l MEMS ) – Inclinometer, Inertial-Link 3DM-GX2 (incl. MEMS gyros) – Low-level sensor fusion in heading estimation

C i ti 2 250kb CAN b 100 l ti

Communication: 2x 250kbps CAN-bus, 100 ms cycle time

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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Path tracking Path tracking

Route planner gives waypoints five seconds ahead

p g yp

– Polyline (x, y), speed, acceleration limit, working position, heading offset – The polyline is feasible (e.g. turning radius)

Error variables in tracking

– Lateral error – Angular error

While navigating, the waypoints

are removed as soon as they are passed

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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Prediction Prediction

The state of robot predicted over finite time horizon
Constant velocity and zero steering assumed

– Through dynamic model

Path error calculated for each

predicted state p vector of errors

Weighted average

Weighted average to form errors for navigation

a ga o

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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Structure of inverse kinematic path tracker Structure of inverse kinematic path tracker

Path Error

x

Path Error Calculation Lateral Controller Inverse

αF x v

Approach Filter Angular Controller Kinematics

αR

Feed- forward forward Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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The Approach Filter The Approach Filter

The regulators are minimizing angular error and lateral

g g g error, separately

In case the lateral error is (very) large, ”using” only the

In case the lateral error is (very) large, using only the crab steering manner for getting on the track would take a long way (as the steering angle is limited) g y ( g g )

When lateral error is large, the Approach Filter modifies

angular error signal angular error signal

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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Part 3: Field experiments Part 3: Field experiments

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Field experiment plan (autumn 2012) Field experiment plan (autumn 2012)

Preplanned route

p

2.4 ha winter wheat
Strategy
Strategy
1. six times around

the field; CCW, the field; CCW, reversing in corners

2. looping the rest,

skipping 5-6 swaths

Refilling tanks

manually

Latitude 60.45°

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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Accuracy

the path is linear piecewise (not smooth)

Accuracy

5

5

5 gle (deg) 1 2 0 0 1 2 5 0 1 3 0 0 1 3 5 0 1 4 0 0

1 0

ang 1 2 0 0 1 2 5 0 1 3 0 0 1 3 5 0 1 4 0 0 0 . 5 teral (m) 1 2 0 0 1 2 5 0 1 3 0 0 1 3 5 0 1 4 0 0

1
0 . 5

lat 1 2 0 0 1 2 5 0 1 3 0 0 1 3 5 0 1 4 0 0 t im e (s )

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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Accuracy Accuracy

1 . 5 0 . 5 1 gle (deg) 1 2 0 0 1 2 5 0 1 3 0 0 1 3 5 0 1 4 0 0

1 . 5
1
0 . 5

ang 1 2 0 0 1 2 5 0 1 3 0 0 1 3 5 0 1 4 0 0 0 . 0 5 eral (m) 1 2 0 0 1 2 5 0 1 3 0 0 1 3 5 0 1 4 0 0

0 . 0 5

late 1 2 0 0 1 2 5 0 1 3 0 0 1 3 5 0 1 4 0 0 t im e (s )

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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Accuracy in sowing Accuracy in sowing

2000 2500 1000 1500

2
1.5
1
0.5

0.5 1 1.5 2 500

Angular error (deg)

angular error (m) 2500 1500 2000 500 1000

Lateral error (m)

0.2
0.15
0.1
0.05

0.05 0.1 0.15 0.2 lateral error (m)

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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Three weeks after Three weeks after...

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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Three weeks after Three weeks after...

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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About positioning About positioning

RTK-GPS signal was under quality tolerances numerous

g q y times

Reasons

Reasons

– North location of the field (southern Finland, >60° latitude) – Trees around the field, especially south side , p y – Correction signal communication errors (GPRS)

Stats

Stats

– Signal availability 85% of time – Longest continuous period: 18 minutes g p – Average period: 5 minutes

When signal bad, the vehicle waits stationary

g , y

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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About GPS About GPS

GPS signal availability may be under tolerances

– GPS fix – Number of satellites HDOP – HDOP – Standard deviation of the major axis (pseudorange stats)

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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The tests continued spring 2013 (6 1ha) The tests continued spring 2013 (6.1ha)...

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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After recalibration of wheel angles After recalibration of wheel angles...

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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Summary and Conclusions Summary and Conclusions

Autonomous tractor was developed 2009-2013

p

Guidance algorithm for 4WS
GPS positioning unreliable in practice (shadows etc)
GPS positioning unreliable in practice (shadows etc)

– Lowers operational efficiency; 15% just for waiting – Additional equipment would be necessary Additional equipment would be necessary

Calibration important in 4WD steering system

C th l i t hi hli ht d h

Coverage path planning was not highlighted here

– but it was working too

I Y T b

In YouTube:

http://www.youtube.com/watch?v=8b4dBFMLDiI j t h " d l " ...or just search "apu-module"

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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Acknowledgements Acknowledgements

Academy of Finland

y

– funding the Postdoctoral Researcher's project (2011-2013)

Modulaire Oy

Modulaire Oy

– Original author of the tractor (mechanics & hydraulics) ~1992

MTT Agrifood Research Finland

MTT Agrifood Research Finland

– The refurbishment was done together with Mr. Raimo Linkolehto – In early phases Mr. Antti Hurme studied hydraulics In early phases Mr. Antti Hurme studied hydraulics – The sowing trials were carried out in their production fields

Aalto University

Aalto University

– "HighDock" was prepared with Mr. Juha Backman – Prof. Arto Visala provided infrastructure p

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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References References

Oksanen, T. 2012. Embedded control system for large scale unmanned

tractor 5th Automation Technology for Off-road Equipment Conference

tractor. 5th Automation Technology for Off road Equipment Conference

(ATOE), Valencia, Spain, July 8 - July 12, 2012. pp. 3-8.

Oksanen, T. 2012. Path following algorithm for four wheel independent

f Off steered tractor. 5th Automation Technology for Off-road Equipment Conference (ATOE), Valencia, Spain, July 8 - July 12, 2012. pp. 9-14.

Oksanen T 2012 Modeling and control of hydraulic drivetrain in

Oksanen, T. 2012. Modeling and control of hydraulic drivetrain in agricultural tractor with Position backlash in speed sensor feedback. IFAC Workshop on Dynamics and Control in Agriculture and Food Processing (DYCAF2012) Plovdiv Bulgaria Jun 13 Jun 16 2012 pp 13 17 (DYCAF2012), Plovdiv, Bulgaria, Jun 13 - Jun 16, 2012. pp. 13-17.

Oksanen, T., Backman, J. 2013. Guidance system for agricultural tractor

with four wheel steering. IFAC Bio-Robotics Conference, Sakai, Japan, 27- 29 March 2013.

Oksanen, T., Linkolehto, R. 2013. Control of four wheel steering using

independent actuators Fourth IFAC International Conference Agricontrol independent actuators. Fourth IFAC International Conference Agricontrol 2013, Espoo, Finland, 28-30 August 2013.

Timo Oksanen 26.9.2013

IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011

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