To date, most passive walkers have been designed with arc-shaped feet rigidly attached to the legs. We developed a simple 3D straight-legged passive walker with flat feet and ankle springs. The flat feet are connected to the legs with springs at the ankles that produce torsional force while the stance leg is on the ground, mimicking the motion of simple 3D passive walkers with arc-shaped feet. This helps to prevent slipping and to handle the disturbance behavior of the robot. Flat feet are particularly advantageous for yaw stability. Our 3D passive-walker robot with a 0.84-m leg can walk the full length of a 1.8-m slope at about 0.44 m/s.

This study presents a design technique of an efficient biped walking robot on level ground with a simple mechanism based on passive-dynamic walking. A torso is used to generate active power replacing gravity used in passive walk. Swing-leg control is introduced to create a steady gait. Numerical simulations show that a biped robot with knees and a torso can walk efficiently on level ground. When we choose an appropriate parameter of the swing-leg control, the biped robot can walk stably over a wide range of speed. Furthermore, the walking performance of the robot increases with the increase of the radius of circular feet.

This study aims at finding active biped robot designs with efficiency and simplicity of passive-dynamic walking. In this paper, it is shown that a biped robot with torso can walk efficiently on level ground over a wide range of speed by using torso and swing leg control based on passive-dynamic walking. A torso is used to generate active power replacing gravity, proposed by McGeer. The biped robot can exhibit a stable gait not planed in advance, and a period-doubling bifurcation is demonstrated in numerical simulations. Furthermore, when we choose carefully a swing leg control gain, a reverse period-doubling bifurcation from chaotic gaits to period-one gaits is demonstrated, which is not found in the passive-dynamic walking.

This study aims at establishing a new control strategy for more natural and efficient bipedal locomotion. In this study, the robot is modeled as a planar biped model composed of a torso, hips, and two different legs with knees, but without ankles. The proposed method consists of central pattern generator (CPG) for legged locomotion and torso attitude control. It is well known that the CPG controller copes with environmental changes by mutual entrainment of the oscillatory activities of the CPG and the body. Therefore, the biped robot can walk on both a level ground and a slope, and has the robustness for environmental changes. Moreover, the torso attitude control is executed concurrently with CPG controller for legged locomotion in the method. By utilizing the interaction between torso and legs, the biped robot with the torso can walk on the level ground over a wide range of speed. This paper presents a systematic control design method of the proposed strategy by using the genetic algorithm. In order to verify the effectiveness of the proposed method, computational simulations were carried out. As a result, it was demonstrated that the biped robot can walk on the level ground at a variable pace according to the desired torso angle given as an external command. Moreover, it was confirmed that the proposed controller has the robustness for environmental changes and external disturbance, and the biped robot can walk naturally on the uphill and downhill slopes.