Passive Walking Biped Robot Model with Flexible Viscoelastic Legs

To simulate the complex human walking motion accurately, a suitable biped model has to be proposed that can significantly translate the compliance of biological structures. In this way, the simplest passive walking model is often used as a standard benchmark for making the bipedal locomotion so natural and energy-efficient. This work is devoted to a presentation of the application of internal damping mechanism to the mathematical description of the simplest passive walking model with flexible legs. This feature can be taken into account by using the viscoelastic legs, which are constituted by the Kelvin–Voigt rheological model. Then, the update of the impulsive hybrid nonlinear dynamics of the simplest passive walker is obtained based on the Euler–Bernoulli’s beam theory and using a combination of Lagrange mechanics and the assumed mode method, along with the precise boundary conditions. The main goal of this study is to develop a numerical procedure based on the new definition of the step function for enforcing the biped start walking from stable condition and walking continuously. The study of the influence of various system parameters is carried out through bifurcation diagrams, highlighting the region of stable period-one gait cycles. Numerical simulations clearly prove that the overall effect of viscoelastic leg on the passive walking is efficient enough from the viewpoint of stability and energy dissipation.

Semi-Passive Walk and Active Walk by One Bipedal Robot: Mechanism, Control and Parameter Identification

We developed a bipedal robot equipped with brake and clutch mechanisms to change the number of active and passive joints, thereby enabling various types of movements including normal active walking using 12-dof joints, under-actuated walking using brake, and passive-based walking using clutch and passive joints. In this paper, we describe three technologies to achieve the proposed system and show experimental results on active and semi-passive walking. The first technology comprises a small and high-strength clutch mechanism to sustain the massive weight of life-sized robots using actuators for joint and dog clutch control. The second technology comprises a walking controller using a simulation-based optimization technique to consider passive joint dynamics instead of depending on the inverse kinematics problem, thereby enabling the control of the under-actuated leg. The last technology is model parameter identification to achieve unstable passive-based walking in real-world considering the body as well as environmental parameters such as ground slope. To the best of our knowledge, the proposed robot is the first to achieve both active and passive-based walking using a bipedal body. This enables the implementation of the passive-walking technology to active-joint robots and expands the application possibility of passive joint for bipedal robots.