Influence of Road Heeling Angle on Human Stepping Friction

Walking is the most common way of movement in human daily life, and slip and fall accidents frequently happen in the process of human walking. It not only seriously affects physical and mental health of the human body, but also causes huge economic losses to the society. At present, the prevention of slip and fall is the main research direction of human stepping friction. The existing researches mainly focus on the dynamics and kinematics of human body when walking on the horizontal and slope pavements, studies dealing with heeling pavement have been limited. In this paper, ten healthy male subjects (age 22.3±1.85 years, height 175.4±3.3 cm, weight 65.1±5.8 kg) were selected for this study. The outsole material was rubber with density 1.18 g/cm3, and the angle, interval and height of sole pattern were 95°, 2.25 mm and 1.03 mm, respectively. A self-made stepping friction test platform, which was composed of a electromechanical motion platform with six degree of freedom, two force plates (Bertec FP4060-08-2000, size 0.6 m×0.4 m, sampling frequency 1 kHz, Bertec Corporation, U.S.), one plantar pressure plate (Podomed UP18, size 1.8 m×0.5 m, measurement error≤±1%, time lag≤0.1%, acquisition frequency 200 Hz, Sensor medica, Italy), and a motion capture system with six cameras (Miqus M3, displacement error≤0.1 mm, acquisition frequency 340 fps, system delay≤5 ms, Qualisys, Sweden), was used to test the mediolateral friction F_x, anterior-posterior friction F_y, normal pressure F_z, toe out angle and gait cycle of human body when walking on heeling pavement, and the required friction coefficient was calculated. The heeling angles of α between the platform and horizontal plane were −20°, −15°, −10°, −5°, 0°, 5°, 10°, 15° and 20°, respectively. The results showed that the extreme values of mediolateral friction and required coefficient of friction increased with the increase of pavement heeling angle, while the extreme values of anterior-posterior friction force and required coefficient of friction did not change significantly. The anterior-posterior coefficient of friction was similar to the overall coefficient of friction, the anterior-posterior coefficient of friction played a major role in the overall coefficient of friction, and risk of sideslip increased. The human body could adjust the center of gravity to lower side to reduce the required coefficient of friction, so as to reduce the risk of sliding. With the increased of heeling angles, the toe out angle of lower foot decreased, and the toe out angle of higher foot increased. The human body could increase the dynamic stability region by increased the toe out angle of lower side foot to improve the stability of walking on heeling pavement. The adaptive balancing mechanism of human body slowed down the walking speed on heeling pavement, shorted the dangerous single support phase and prolonged safe double support phase to prevent slip and fall, because heeling angle increased the risk of sideslip.