Influence of Leg Elasticity on the Locomotion Behavior of a Quadrupedal Robot

Kurzfassung

Different quadrupedal template models with fixed parameters have been introduced to facilitate the analysis of limit-cycle motions for this type of locomotion. However, biology shows that animals use a leg stiffness that changes with the locomotion velocity, and other studies show that the stability of the gait is dictated by the parameters choice. The research question of this thesis is: How does variable leg elasticity influences the stability of a quadrupedal gait? To answer that question, a detailed characterization of the emerging gaits from a model with compliant legs and shoulder joints represented as torsional springs is carried out. This model can be used to characterize the most common quadrupedal gaits observed in nature. A detailed analysis of the stability, which helps to understand the influence of perturbations on the locomotion, is performed for the obtained gaits. Furthermore, a parametric optimization has been implemented to search for the system parameters that guarantee maximum gait stability. The analysis shows that the adoption of a leg stiffness that increases with the speed of locomotion, together with the highest feasible leg swing frequency, noticeably increases the gait stability over a wide range of horizontal velocities while reducing the oscillations of the trunk. This insight can be applied in the design of novel elastic quadrupedal robots, where constant stiffness actuators could be replaced with variable stiffness actuators to improve the overall locomotion behavior.