Active Driver Assistance for Vehicle Lanekeeping

Transcription

1 Active Driver Assistance for Vehicle Lanekeeping Eric J. Rossetter October 30, 2003 D D L ynamic esign aboratory

2 Motivation In 2001, 43% of all vehicle fatalities in the U.S. were caused by a collision with a fixed obstacle (NHTSA) This accounted for over 18,000 fatalities in 2001 Stanford University Active Driver Assistance for Vehicle Lanekeeping - 2 Dynamic Design Lab

3 Spectrum of Lanekeeping Assistance PASSIVE ACTIVE Stanford University Active Driver Assistance for Vehicle Lanekeeping - 3 Dynamic Design Lab

4 Spectrum of Lanekeeping Assistance PASSIVE ACTIVE Lane Departure Warning These systems warn the driver of an imminent lane departure (Suzuki and Jansson (2003), Feng et al. (2000), Lee et al. (1999)) Visual, Auditory, or Haptic Lanekeeping is still the drivers responsibility Stanford University Active Driver Assistance for Vehicle Lanekeeping - 4 Dynamic Design Lab

5 Spectrum of Lanekeeping Assistance PASSIVE ACTIVE Lane Departure Warning Fully Autonomous Completely autonomous systems remove the driver entirely from the lanekeeping task (Fenton and Mayhon (1991), Shladover et al. (1991)) Requires an extremely high level of robustness Stanford University Active Driver Assistance for Vehicle Lanekeeping - 5 Dynamic Design Lab

6 Spectrum of Lanekeeping Assistance PASSIVE ACTIVE Lane Departure Warning Fully Autonomous Active Assistance Active assistance combines driver and controller commands to aid in lanekeeping Stanford University Active Driver Assistance for Vehicle Lanekeeping - 6 Dynamic Design Lab

7 Design Challenge for Active Assistance Design objectives for a lanekeeping assistance system: Provide lanekeeping ability without driver inputs Must not hinder normal driving These are often competing objectives How do we design the lanekeeping controller to satisfy both these objectives? Stanford University Active Driver Assistance for Vehicle Lanekeeping - 7 Dynamic Design Lab

8 Talk Outline Enabling Technologies Spring Analogy for Lanekeeping Stability Conditions Spring attachment point Sensing location Sizing the Spring Experimental Results Conclusions Stanford University Active Driver Assistance for Vehicle Lanekeeping - 8 Dynamic Design Lab

9 Enabling Technologies The ability to determine lane position Vision Systems (Gehrig et al. (2002), Franke et al. (1997)) GPS combined with Precision Road Maps (Omae & Fujioka (1999), Farrell & Barth (2000), Alban (2002)) Control of steering, braking, and throttle Brake- and Throttle-by-Wire Steer-by-Wire Source: Delphi Automotive Stanford University Active Driver Assistance for Vehicle Lanekeeping - 9 Dynamic Design Lab

10 Steer-by-Wire Corvette 1997 Corvette was modified to a steer-by-wire format No mechanical connection between the steering wheel and front road wheels handwheel steering column intermediate shaft belt drive handwheel angle sensor handwheel feedback motor steering actuator universal joints power assist unit pinion angle sensor gear assembly pinion rack Conventional Steering System Steer-by-Wire System Stanford University Active Driver Assistance for Vehicle Lanekeeping - 10 Dynamic Design Lab

11 Global Positioning System The Global Positioning System (GPS) is a worldwide positioning system consisting of over 24 satellites that broadcast ranging information Stanford University Active Driver Assistance for Vehicle Lanekeeping - 11 Dynamic Design Lab

12 Position Using GPS Distance from each satellite is determined by the time of flight of the satellite signal ρ = c t Satellite 2 Satellite 1 Satellite 3 ρ 1 Stanford University Active Driver Assistance for Vehicle Lanekeeping - 12 Dynamic Design Lab

13 Position Using GPS Distance from each satellite is determined by the time of flight of the satellite signal ρ = c t Satellite 2 Satellite 1 ρ Satellite 3 2 ρ 1 Stanford University Active Driver Assistance for Vehicle Lanekeeping - 13 Dynamic Design Lab

14 Position Using GPS Distance from each satellite is determined by the time of flight of the satellite signal ρ = c t Satellite 2 Satellite 1 ρ Satellite 3 2 ρ 1 ρ 3 Stanford University Active Driver Assistance for Vehicle Lanekeeping - 14 Dynamic Design Lab

15 Differential GPS A base station and vehicle see the same atmospheric errors Centimeter level accuracy is obtained with differential corrections Ionosphere ~20,000 km Troposphere ~1 km Stanford University Active Driver Assistance for Vehicle Lanekeeping - 15 Dynamic Design Lab

16 Control Concept Make vehicle behave as though it is attached to the road with a mechanical spring Road Centerline Force = k e Spring does not have to be extremely stiff Control force smoothly assists the driver Energy interpretation is useful for analysis Lateral Error: e Stanford University Active Driver Assistance for Vehicle Lanekeeping - 16 Dynamic Design Lab

17 Realizing this Control Concept With by-wire technology the steering, braking, and throttle are controlled to create the equivalent spring force F yl (δ) F yr (δ) F x F xlf F xrf F x x cf F y M F y F xlr F xrr Physical System Equivalent Control Force Stanford University Active Driver Assistance for Vehicle Lanekeeping - 17 Dynamic Design Lab

18 Realizing this Control Concept With control of only the front steering the control force is constrained at the front axle F yl (δ) F yr (δ) F x F y F x a M F y Physical System Equivalent Control Force Stanford University Active Driver Assistance for Vehicle Lanekeeping - 18 Dynamic Design Lab

19 Vehicle Behavior How does the vehicle behave under this control concept? Perform a linear analysis of the system dynamics: Model the vehicle dynamics with the lanekeeping controller Linearize the vehicle dynamics Look at eigenvalues (tell us about the system behavior) Lanekeeping behavior is related to the spring attachment point Stanford University Active Driver Assistance for Vehicle Lanekeeping - 19 Dynamic Design Lab

20 Attachment Point Condition Intuitively, creating the effect of a spring attached near the front of the vehicle will rotate the vehicle in the direction of the applied force Desired Location Stanford University Active Driver Assistance for Vehicle Lanekeeping - 20 Dynamic Design Lab

21 Attachment Point Condition Intuitively, creating the effect of a spring attached near the front of the vehicle will rotate the vehicle in the direction of the applied force Desired Location Stanford University Active Driver Assistance for Vehicle Lanekeeping - 21 Dynamic Design Lab

22 Attachment Point Condition Intuitively, creating the effect of a spring attached near the front of the vehicle will rotate the vehicle in the direction of the applied force Desired Location Stanford University Active Driver Assistance for Vehicle Lanekeeping - 22 Dynamic Design Lab

23 Attachment Point Condition What if the attachment point moves too far back? Desired Location Stanford University Active Driver Assistance for Vehicle Lanekeeping - 23 Dynamic Design Lab

24 Attachment Point Condition What if the attachment point moves too far back? Desired Location Stanford University Active Driver Assistance for Vehicle Lanekeeping - 24 Dynamic Design Lab

25 Attachment Point Condition What if the attachment point moves too far back? Desired Location Vehicle moves away from desired location! Stanford University Active Driver Assistance for Vehicle Lanekeeping - 25 Dynamic Design Lab

26 Neutral Steer Point Critical point is called the neutral steer point Neutral steer point is the location on a vehicle where an external force creates no rotation (yaw rate) Neutral Steer Point UNSTABLE STABLE Location of the neutral steer point depends on vehicle properties Tires and weight distribution Stanford University Active Driver Assistance for Vehicle Lanekeeping - 26 Dynamic Design Lab

27 Neutral Steer Point This point is used in vehicle design to ensure appropriate responses to physical disturbances Side-wind or gravity force on banked roads What is the implication for the design of a lanekeeping control system? Must coordinate the steering, braking, and throttle commands to ensure that the resultant force is in front of the neutral steer point With only front steering the control force is always in front of the neutral steer point Stanford University Active Driver Assistance for Vehicle Lanekeeping - 27 Dynamic Design Lab

28 Simulation 2 Lateral Error of Vehicle Lateral Position (m) Force behind neutral steer point Force in front of neutral steer point Time (s) Stanford University Active Driver Assistance for Vehicle Lanekeeping - 28 Dynamic Design Lab

29 High Speed Oscillations Satisfying the neutral steer point condition is not sufficient for high speed lanekeeping 8 Lateral Error Also need to look at sensing location Drivers look forward while driving Lateral Position (m) Time (s) Stanford University Active Driver Assistance for Vehicle Lanekeeping - 29 Dynamic Design Lab

30 Sensing Location Controller must use a certain amount of lookahead for high speed stability Base spring compression/extension on the lateral error in front of the vehicle Sensing at C.G. 8 6 No Lookahead 15 m Lookahead 4 Using Lookahead lateral position (m) time (s) Stanford University Active Driver Assistance for Vehicle Lanekeeping - 30 Dynamic Design Lab

31 Sizing the Spring Control force must be large enough to keep the vehicle in the lane without driver commands Most important factor for sizing the control force (or spring) is the road curvature Spring force must provide the necessary centripetal force for the turn Stanford University Active Driver Assistance for Vehicle Lanekeeping - 31 Dynamic Design Lab

32 Sizing the Spring: Basic Concept Centripetal force needed to go around a turn of radius R at a velocity V is: F c = m V 2 R Recall that the spring force is: F s = ke Equate the two forces and solve for the spring stiffness k = m V 2 Re Road Edge R Stanford University Active Driver Assistance for Vehicle Lanekeeping - 32 Dynamic Design Lab

33 Sizing the Spring In reality it is a little more complicated Curvature is not constant Vehicle dynamics influence motion Transient effects Basic spring analogy and concept of energy storage is used to scale the gain of the controller (or spring) Lyapunov theory Stanford University Active Driver Assistance for Vehicle Lanekeeping - 33 Dynamic Design Lab

34 Lyapunov Approach Create an energy-like function of the states with the properties: L(x) > 0 L(x) < 0 x(0),x(0) x max Energy Bowl 10 8 Sublevel Sets Energy Velocity Initial Condition Max Position Velocity Position Position Stanford University Active Driver Assistance for Vehicle Lanekeeping - 34 Dynamic Design Lab

35 Experimental System Test vehicle is a 1997 Corvette Modified to include steer-by-wire DC-DC Converters GPS Receivers Inertial Sensors Control Computer Motor Amplifier Stanford University Active Driver Assistance for Vehicle Lanekeeping - 35 Dynamic Design Lab

36 Video Stanford University Active Driver Assistance for Vehicle Lanekeeping - 36 Dynamic Design Lab

37 Experiment vs. Simulation 100 Map 2 Lateral Error Simulation Experimental North (m) Lateral Error (m) East (m) Time (s) Experimental results show one loop at 11m/s (25mph) without driver steering inputs Guarantee the lanekeeping ability of the system Stanford University Active Driver Assistance for Vehicle Lanekeeping - 37 Dynamic Design Lab

38 Lanekeeping Bounds 100 Map 2 Lateral Error Simulation Experimental North (m) Lateral Error (m) Reachable Set East (m) Time (s) Experimental results show one loop at 11m/s (25mph) without driver steering inputs Guarantee the lanekeeping ability of the system Stanford University Active Driver Assistance for Vehicle Lanekeeping - 38 Dynamic Design Lab

39 Conclusions Lanekeeping system works remarkably well Two important conditions for a well-behaved lanekeeping system Neutral steer point condition Sensing location (lookahead) Quantitative guarantee on the lanekeeping performance Stanford University Active Driver Assistance for Vehicle Lanekeeping - 39 Dynamic Design Lab

40 The End Questions? Stanford University Active Driver Assistance for Vehicle Lanekeeping - 40 Dynamic Design Lab