Quantitative study on SLIP model parameters based on multi-rigid-body dynamics

The spring-loaded inverted pendulum (SLIP) model is often used to describe the interaction between hindlimbs and the ground during the locomotion of animals or humans. This model is frequently adopted to qualitatively explain the flexible deformation of legs and feet and the trajectory change of center of mass (COM), caused by the impact between hindlimbs and the ground. However, such research cannot provide precise reference on the structural parameters, spring and damper selections and their collocations for the design of robotic legs and feet. In this study, an SLIP model was established on the multi-rigid-body dynamics software Adams. The main influence factors on the SLIP model were determined by targeting at the touchdown-phase duration of animal or human locomotion. Then the main factors were quantitatively studied by combining a multivariate orthogonal polynomial regression design. Simulation showed that spring stiffness coefficient (Z1), damping coefficient (Z2), swing angular velocity (Z3) and initial swing position (Z4) were the main factors affecting the trajectory of COM. Multivariate orthogonal polynomial regression analyses showed the relationship between the COM fluctuation (y) and the main factors satisfied the following equation: y = 217.33 - 16.25 Z1 + 0.3975 Z12 - 194.6 Z2 - 0.953 Z3 + 0.755 Z4 + 8.1 Z1 Z2 + 0.043 Z1 Z3 + 0.6 Z2 Z3 - 0.0055 Z3 Z4.