Dynamics, stability, and actuation methods for powered compass gait walkers

In this paper, methods to achieve actively powered walking on level ground using a simple 2-dimensional walking model (compass-gait walker) are explored. The walker consists of 2 massless legs connected at the hip joint, a point mass at the hip, and an infinitesimal point mass at the feet. The walker is actuated either by applying equal joint torques at the hip and ankle, by an impulse applied at the toe off, immediately before the heel strike, or by the combination of both. It is shown that actuating the walker by equal joint torques at the hip and ankle on level ground is equivalent to the dynamics of the passive walker on a downhill slope. The gait cycle for the simplified walker model is determined analytically for a given initial stance angle. Stability of the gait cycle by an analytical approximation to the Jacobian of the walking map is calculated. The results indicate that the short-period cycle always has an unstable eigenvalue, whereas stability of the long-period cycle depends on selection of the initial stance angle. The effect of the torso mass by adding a third link attached at the hip joint is investigated. The torso link is kept in the vertical position by controlling the torque applied to it. The proportional-derivative control law is utilized to regulate the angular position error of the torso link. Using linearized dynamics for this walker, active control is applied to the ankle, which reduces the dynamics of the walker to the passive walker without the torso. The proposed walker is capable of producing stable walking while keeping the torso in an upright position.

Anahtar Kelimeler:

Robot dynamics, bipeds, legged robots, passive walking, stability

Dynamics, stability, and actuation methods for powered compass gait walkers

Keywords:

Robot dynamics, bipeds, legged robots, passive walking, stability,

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torso mass and its distance from the hip joint. For torso moment of an inertia greater than zero, the walking speed does not strongly depend on α and r (Figures 7g–7i). 6. Conclusions
In conclusion, the findings presented in this study can shed light on the design and development of walking-related mechanisms such as legged robots or walk assist devices. Analysis of passive walking devices such as the ones presented in this paper can also lead to a better understanding of the principles of natural walking.
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