Verification of damped bipedal inverted pendulum model against kinematic and kinetic data of human walking on rigid-level ground

Abstract

In this study, kinematic and kinetic data for 14 test subjects walking on a treadmill were recorded to verify a damped bipedal inverted pendulum (DBIP) model. The verification aim was for the DBIP model to match the step frequency and first harmonic dynamic load factor (DLF1) extracted from the measured data, as these are key parameters of interest in civil engineering applications. The verification was conducted in several phases. First, kinematic data from 39 markers attached to the human body were used to get the trajectory of body’s centre of mass (BCoM). This trajectory, in conjunction with the vertical and longitudinal ground reaction forces (GRFs) were then used to plot the leg force – leg length relationship. Linear curve fitting yielded the spring stiffness and spring length parameters. These parameters, together with the body mass and damping coefficient, were fed into the DBIP model to identify initial conditions for the motion of BCoM leading to the stable periodic gait. For the 14 test subjects, the model produced excellent agreement with the measured step frequency and DLF1, while relative error for the walking speed was between -12.6% and 2.0%. The simulated waveform of the vertical BCoM displacement was found to match the measured signal well. In addition, match between simulated and measured GRF profiles was satisfactory except for one test subject. Regression functions have been established for estimating model parameters, based on which step-by-step procedures have then been proposed for modelling a pedestrian within the population. The results suggest that the DBIP succeeds in modelling pedestrians walking on rigid level surfaces. In the next step the model should be considered for modelling pedestrians on vibrating civil engineering structures.