By contrast with the wheeled Pioneer robot, a number of laboratories have designed and built legged robots with two, four, six and even eight legs.Clearly, the broad architecture of these machines is based on iological prototypes, but the robots generally have fewer degrees of freedom and hence are much less complex than the animals on which they are based.TITAN VIII, with TITAN standing for Tokyo Institute of Technology Aruku Norimono [walking vehicle]), was constructed in the Hirose-Yoneda Laboratory of the Tokyo Institute of Technology. Shigeo Hirose is one of the best robot designers in the world at the present time. He developed the theory of stability for legged locomotion machines and has built a series of increasingly sophisticated quadruped robots.
This robot is equipped with adaptive feet, enabling it to walk on uneven terrain; it also has the ability to recover from falls and can climb stairs autonomously. One of the most interesting features of this robot is that it can stand on three legs and use the fourth leg,equipped with an adjustable gripper,as a manipulator.
Two types of control problems appear in connection with quadruped robots,involving static and dynamic stability. Static stability refers to the ability of the robot to maintain an upright posture while standing (or while moving very slowly, so that dynamic e¤ects are negligible). With quadrupeds (also known as tetrapods), this means that when one leg is o¤ the ground, the projection of the system’s center of gravity must lie within the triangle formed by the three legs on the ground. It is evident that if the center of gravity is outside of this triangle, it will exert torque and cause the animal or robot to fall. Animals adjust their center-of-gravity position as they walk to ensure static stability. In robots this may require an active control system.
The situation is more complex when the animal moves rapidly, for example, a horse in gallop. In this case all four legs may be o¤ the ground for brief periods, and dynamic stability requires the consideration of inertial forces due to the motion as
well as gravity.
