guidance of autonomous tractor with four wheel · pdf file• the diesel engine is from...

Guidance of Autonomous Tractor With Four Wheel Steering

Timo OksanenDoctor of Science (technology)( gy)Docent (agricultural engineering)

Senior Research ScientistSenior Research Scientist

Aalto University, FinlandDept of Automation and Systems TechnologyDept. of Automation and Systems Technology

IEEE RAS AgRobots TCIEEE RAS AgRobots TCWebinar #11September 26, 2013

The presentationThe 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 2013Sakai, 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-roadindependent steered tractor. 5th Automation Technology for Off-road Equipment Conference (ATOE), Valencia, Spain, July 8 - July 12, 2012. pp. 9-14.

Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation

Webinar #011slide 2

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

slide 3

The Autonomous Tractor"APU Module"

165 hp turbodiesel~6000 kgAPU-Module gHydraulic drivetrainEach wheel (4WD)

• SteeringSteering• Drive

3p-hitch in both endsPTO in both endsPTO in both endsUp to 9 aux valves12V DC electric

Built originally1990-1992 by a Finnish company.E&E refurbished2011-20122011 2012

Originally designed for unmanned useunmanned use(autonomous)


Webinar #011slide 4

DrivetrainDrivetrain• 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 usedk 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 steering4 wheel drive + 4 wheel steering


Webinar #011slide 5

DrivetrainDrivetrain• Original design of tractor did not contain brakes at allg 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 providesp g y y p180 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


Webinar #011slide 6

Requirements for Electronic control systemRequirements for Electronic control system

• Systemy– Real-timeness– Safety

• Control interfaces– Interface to autonomous navigation systemg y– Wireless manual control (safety)

• Functions– Cruise control– Coupled steering & drivep g– Brake control– Engine control– Hitch and PTO control


Webinar #011slide 7

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

d t b PWM ( 2A) f h d lineed 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


Webinar #011slide 8

Control systemControl system


Webinar #011slide 9

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

slide 11

IntroductionIntroduction• The presentation shows how to keep a vehicle with 4WS p p

on track on the field• Later the results in real field operationLater the results in real field operation• Four wheel steering is used in some commercial

tractors:tractors:

Case 4894 Claas Xerion series


Webinar #011slide 12

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



MaterialsMaterials• 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 accuracyV 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



Path trackingPath tracking• Route planner gives waypoints five seconds aheadp 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 waypointsare removed as soon as theyare passed



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

– Through dynamic model

• Path error calculated for eachpredicted statep

vector of errors• Weighted averageWeighted average

to form errorsfor navigationo a ga o



Structure of inverse kinematic path trackerStructure of inverse kinematic path tracker

Path Errorx Path Error Calculation

Lateral Controller

Inverse αF

x v

Approach Filter

Angular Controller

Kinematics αR

Feed-forwardforward



The Approach FilterThe Approach Filter• The regulators are minimizing angular error and lateralg g g

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

crab steering manner for getting on the track would takea long way (as the steering angle is limited)g y ( g g )

• When lateral error is large, the Approach Filter modifiesangular error signalangular error signal



Part 3: Field experimentsPart 3: Field experiments

slide 19

Field experiment plan (autumn 2012)Field experiment plan (autumn 2012)• Preplanned routep• 2.4 ha winter wheat• Strategy• Strategy

1. six times aroundthe field; CCW,the field; CCW,reversing in corners

2. looping the rest,skipping 5-6 swaths

• Refilling tanksmanually

• Latitude 60.45°



Accuracy the path is linear piecewise (not smooth)Accuracy5

-5

0

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

0

tera

l (m

)

1 2 0 0 1 2 5 0 1 3 0 0 1 3 5 0 1 4 0 0-1

-0 . 5lat

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



AccuracyAccuracy1 . 5

0

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 . 5ang

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



Accuracy in sowingAccuracy in sowing2000

2500

1000

1500

-2 -1.5 -1 -0.5 0 0.5 1 1.5 20

500

Angular error (deg)angular error (m)

2500

1500

2000

500

1000

Lateral error (m)-0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.20

lateral error (m)



Three weeks afterThree weeks after...



About positioningAbout positioning• RTK-GPS signal was under quality tolerances numerousg q y

times• ReasonsReasons

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

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

• When signal bad, the vehicle waits stationaryg , y



About GPSAbout GPS• GPS signal availability may be under tolerances

– GPS fix– Number of satellites

HDOP– HDOP– Standard deviation of the major axis (pseudorange stats)



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



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



Summary and ConclusionsSummary and Conclusions• Autonomous tractor was developed 2009-2013p• 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 necessaryAdditional equipment would be necessary

• Calibration important in 4WD steering systemC 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"



AcknowledgementsAcknowledgements• Academy of Finlandy

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

• Modulaire OyModulaire Oy– Original author of the tractor (mechanics & hydraulics) ~1992

• MTT Agrifood Research FinlandMTT Agrifood Research Finland– The refurbishment was done together with Mr. Raimo Linkolehto– In early phases Mr. Antti Hurme studied hydraulicsIn early phases Mr. Antti Hurme studied hydraulics– The sowing trials were carried out in their production fields

• Aalto UniversityAalto University– "HighDock" was prepared with Mr. Juha Backman– Prof. Arto Visala provided infrastructurep



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

tractor 5th Automation Technology for Off-road Equipment Conferencetractor. 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 Offsteered 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 inOksanen, T. 2012. Modeling and control of hydraulic drivetrain in

agricultural tractor with Position backlash in speed sensor feedback. IFACWorkshop 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 Agricontrolindependent actuators. Fourth IFAC International Conference Agricontrol2013, Espoo, Finland, 28-30 August 2013.



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