When the sole of the foot of one of the leg sections of the robot leaves
or touch the floor, the angular velocity of the joint angle .theta. of
each of the joints of the leg section of the robot becomes infinitely
large and excessive loads are applied to the respective joints if the leg
section is stretched out or the robot takes some other peculiar attitude.
Therefore, when the sole of the foot section of a leg section leaves or
touches the floor, the constraining conditions are defined for the foot
section relative to the floor surface that the foot section touches
according to the degree of operability of the leg section in order to
reduce the loads that are applied to the respective joints of the leg
section. Additionally, the attitude of the foot section is determined so
as to minimize or reduce the potential energy attributable to a minute
quantity of positional changes of the joints of the leg section.
