Various bipedal robots have been developed.
What has been lacking, however, are bipedal robots that can perform
``non-stationary motion''.
``Non-stationary motion'' means sitting down, standing up,
moving limbs, and so on.
We have constructed a legged robot that can perform these movement
without using the ankle-torque.
Though it is natural to use ankle-torque for non-stationary motions,
the usable amount of torque is restricted.
We have to consider this input constraint when we design a control
scheme to use ankle-torque for non-stationary motions.
Since it is difficult to design a control scheme to use ankle-torque
for general non-stationary motion, we focus on standing upright that
is a special non-stationary motion.
Concretely, we gave an invariant set where ankle-torque is effective,
and designed a hybrid control scheme that alternates between non-linear
and LQ control schemes on the surface of the invariant set.
We also discovered stability of the controlled system with constrained
ankle-torque.
Moreover, simulations demonstrated the effectiveness of the control
scheme.
We expect that it can also be applied to non-stationary motions in general.
Proc. IEEE/RSJ Int. Conf. on Intelligent Robots and Systems '99, pp.1804-1809
