Applying swing-leg retraction on an actuated spring loaded inverted pendulum model

The planar spring-mass model is frequently used to describe bouncing gaits (running, hopping, trotting, galloping) in animal and human locomotion and robotics. Many approximate solutions have been suggested by researchers to predict center of mass trajectory during stance, some of them even proposed models including damping losses. Over the years, many improvements to the model have been suggested with various actuators to take care of non-linearities of the system. But the control laws for those models often require computation after each step. We have used one such model and implemented swing-leg retraction to it, which is an early control method to improve stability of the model. Though a deadbeat control strategy is better, swing leg retraction reduces computation at each step and also the need for precise actuators. We have compared and presented results for the model with and without swing-leg retraction, with control parameters fixed at beginning.