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Page 239                           Li et al. Intell Robot 2024;4(3):230-43  I http://dx.doi.org/10.20517/ir.2024.15

                                    3.0      Sobriety
                                   Angular velocity of pendulum  -1.5
                                             Fatigue
                                    1.5
                                             Very fatigue

                                    0.0





                                    -3.0
                                                         Time length (60s)


                                 Figure 9. Waveform of transverse angular velocity (adapted from Li et al., 2023  [24] ).

                                    120
                                             Sobriety
                                   Vehicle speed(Km/h)  100
                                             Fatigue
                                    110
                                             Very fatigue


                                     90

                                     80

                                     70
                                                        Time length (400s)

                                     Figure 10. Waveform of vehicle speed (adapted from Li et al., 2023  [24] ).


                                    0.20
                                              Sobriety
                                              Fatigue
                                    0.15
                                   Lateral acceleration  0.10
                                              Very fatigue

                                    0.05

                                    0.00

                                    -0.05
                                                         Time length (58s)

                                   Figure 11. Waveform of lateral acceleration (adapted from Li et al., 2023  [24] ).


               In the experimental results, the prediction accuracy for the fatigue state is indeed significantly lower than for
               the awake and very fatigued states. This discrepancy can be attributed to the subtler behavioral indicators as-
               sociated with the fatigue state, which makes it more challenging to distinguish compared to the more distinct
               characteristics of alertness and extreme fatigue. The awake state is characterized by highly responsive and con-
               sistent driving behaviors, while the very fatigued state exhibits more pronounced deviations and irregularities
               due to extreme tiredness. In contrast, the fatigue state presents less obvious signs, such as slight deviations
               or minor lapses in attention, which can be harder to detect accurately. Additionally, individual differences
               in how drivers exhibit fatigue can contribute to this challenge. While some drivers may show clear signs of
               fatigue, others may have more subtle or varied manifestations, making it difficult for the model to generalize
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