guidance of autonomous tractor with four wheel...
TRANSCRIPT
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
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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 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)
Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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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
Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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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
Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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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
Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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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
Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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Control systemControl system
Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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Part 2: Guidance & four wheel steeringPart 2: Guidance & four wheel steering
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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
Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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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 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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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
Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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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
Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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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
Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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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
Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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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
Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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Part 3: Field experimentsPart 3: Field experiments
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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°
Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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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 )
Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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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 )
Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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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)
Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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Three weeks afterThree weeks after...
Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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Three weeks afterThree weeks after...
Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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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
Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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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)
Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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The tests continued spring 2013 (6 1ha)The tests continued spring 2013 (6.1ha)...
Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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After recalibration of wheel anglesAfter recalibration of wheel angles...
Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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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"
Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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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
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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.
Timo Oksanen 26.9.2013IEEE RAS TC on Agricultural Robotics and Automation
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