Walking and jogging at similar speeds with a passive SLIP model based compliant biped

This paper studies a 2D, spring-loaded inverted pendulum (SLIP) passive dynamic biped with two degrees of freedom (stance leg only) to find the existence of symmetric periodic walking and jogging gaits. These gaits are differentiated by vertical ground reaction force (vGRF) patterns. The double-support phase is considered to be instantaneous, and jogging has no airborne phase. We consider the initial leg compression an additional model parameter compared to earlier studies with symmetric gaits. Different gaits are obtained through numerical optimization with various combinations of model parameters -- initial leg compression, spring stiffness, and touchdown angle; with the gait speed as the resultant parameter. Initial compression of the leg spring is found to be an important parameter in transitioning between walking and jogging gaits. This approach can capture the vertical ground reaction force and center of mass (CoM) trajectories of human gaits for both walking and jogging while providing additional control over peak vGRF and the amplitude of CoM oscillation. In comparison, existing SLIP walking models employ an asymmetric single support phase (SSP), and jogging gaits incorporate an aerial phase. Overall, we present a common approach to finding both slow walking and jogging gaits without significant changes in resulting gait speeds.