Achieving accurate, real-time lane-keeping control during high-speed cornering on large-curvature roads while ensuring robust vehicle stability is a critical challenge in autonomous driving. To address this challenge, this study developed a robust offset-free model predictive control (OF-MPC) framework for vision-based autonomous vehicle lane-keeping. The regulation problem in this framework is solved using several algorithms. Numerical simulation results indicated that the interpolation-tube-based constrained iterative linear quadratic regulator (itube-CILQR) algorithm outperformed solvers based on the standard Interior Point Optimizer (IPOPT) and Operator Splitting Quadratic Program (OSQP), achieving a mean computation time of less than 5 ms. The itube-CILQR algorithm was then used for vehicle control in vision-based lane-keeping experiments in a simulation environment to quantify the perceptual uncertainty of a visual perception model (multitask UNet). This quantification was performed using the OF-MPC framework for traffic scenes that were not encountered during model training. Overall, the developed OF-MPC framework and the proposed method for characterizing the perceptual uncertainty of a visual perception system in unseen environments can contribute to the future development of advanced autonomous driving systems.
Figures & tables
Symbol
Values
Symbol
Values
dt
0.01 s
Cαf
80000 N/rad
vx
{20.0, 21.1} m/s
Cαr
80000 N/rad
Iz
2000 kgm 2
lf
1.27 m
m
1150 kg
lr
1.37 m
TABLE I: Model and Vehicle Parameters Used in This Study
Symbol
Values
Symbol
Values
N
30
Q
diag([20, 1, 20, 1])
Δ
[-2.0, 2.0] m
R
60 I
Δ˙
[13.0, 13.0] m/s
Q′
diag([1, 1])
θ
[- π/2 , π/2 ] rad
R′
60 I
θ˙
[-10.0, 10.0] rad/s
S
50 I
δ
[- π/6 , π/6 ] rad
qs
100
TABLE II: Ranges of the Control Parameters Considered in This Study
Fig. 1: Architecture of the proposed OF-MPC framework for closed-loop testing of the controlled system.
Fig. 2: Outer boundaries of sets X′ , Xˉ′ , Se , and Sx when vx = 21.1 or 20.0 m/s and κ = ± 0.1 or ± 0.05 1/m. Here, x1≡Δ˙ and x3≡θ˙ .
Fig. 3: Outer boundaries of sets Tˉ02 and Tˉ13 when vx = 20.0 or 21.1 m/s and ci = 10−16 or 20.0. Here, x0≡Δ , x1≡Δ˙ , x2≡θ , and x3≡θ˙ .
Fig. 4: Numerical simulation results obtained with different IPOPT- and OSQP-based solvers under tightened constraints when vx = 20.0 m/s, ∣x1∣≤ 13.0 m/s, and ∣x3∣≤ 10.0 rad/s: (a) trajectory of the actual system state x0 ( Δ ); (b) trajectory of the system control input u = δ ; and (c) trajectories of the estimated road curvatures obtained with the tube-OSQP-X algorithm, which were obtained by dividing the estimated disturbance vectors d^0 and d^1 by γ0 and γ1 , respectively.
Fig. 5: Numerical simulation results obtained with different itube-CILQR-based solvers when vx = 20.0 m/s, ∣x1∣≤ 13.0 m/s, and ∣x3∣≤ 10.0 rad/s: (a) trajectory of the actual system state x0 ( Δ ); (b) trajectory of the system control input u = δ ; and (c) trajectories of the estimated road curvatures obtained with the itube-CILQR-T-0 algorithm, which were obtained by dividing the estimated disturbance vectors d^0 and d^1 by γ0 and γ1 , respectively.
Fig. 6: Numerical simulation results obtained with the itube-CILQR solver when vx = 20.0 m/s, ∣x1∣≤ 13.0 m/s, and ∣x3∣≤ 10.0 rad/s: trajectories of the actual system states (a) x1 , (b) x2 , and (c) x3 .
Method
tube-IPOPT-X b
tube-OSQP-X b
itube-CILQR-X
itube-CILQR-T-20
itube-CILQR-T-0
Max. Δ (m)
0.024333
0.024268
0.023162
0.022097
0.021675
Latency (ms)
6.45
0.84
1.10
4.21
7.35
a All algorithms were implemented in C++.
b The tube-IPOPT-T-0/20 and tube-OSQP-T-0/20 algorithms could not achieve convergence for the considered optimization problem.
TABLE III: Maximum Lateral Offsets and Average Computation Times Achieved by the tube-IPOPT-X, tube-OSQP-X, itube-CILQR-X, itube-CILQR-T-20, and itube-CILQR-T-0 Algorithms a
Fig. 7: Example traffic scene and maps of track A (left) and track B (right) in TORCS. The input of the adopted deep neural network model was an RGB image with a resolution of 228 × 228 pixels.
Fig. 8: Curvature profiles of tracks A and B.
Fig. 9: Dynamic performance of the itube-CILQR-T-20 algorithm in lane-keeping maneuvers within the central lanes of tracks A and B at a vehicle speed of 72 km/h when the noise level ( σ ) was set to 0 and the friction coefficient ( fr ) was set to 1.0.
Fig. 10: Dynamic performance of the itube-CILQR-T-20 algorithm in lane-keeping maneuvers within the central lanes of tracks A and B at a vehicle speed of 72 km/h when σ = 1.8 % and 2.0 % and fr = 1.0.
σ
track-A
track-B
fr
Avg
SD
fr
Avg
SD
1.0
0.9
0.8
1.0
0.9
0.8
0.5 %
0.9941
0.9159
0.9324
0.9474
0.0412
0.8604
0.8616
0.8720
0.8646
0.0063
0.8 %
1.4989
1.4021
1.4266
1.4425
0.0503
1.3625
1.3294
1.2987
1.3302
0.0319
1.0 %
1.7393
1.6674
1.6334
1.6800
0.0540
1.5741
1.6156
1.4961
1.5619
0.0606
1.3 %
1.9226
1.9093
1.9523
1.9280
0.0220
1.8943
1.8633
1.6802
1.8126
0.1157
TABLE IV: Average and Standard Deviation Values of the κ -Score During Lane-Keeping Maneuvers Conducted Using the itube-CILQR-T-20 Solver at Different σ and fr Values
Autonomous driving develops vehicles that perceive road scenes, predict interactions, and plan and control safe movement with limited or no human input.