Figure 2. Examples of motions generated by the stack of task.
Left column: The stack of tasks is composed
of three constraints (both feet and center of mass
should remain at a fixed position; all of them
are always feasible and satisfied) and two tasks
to control the gaze and the right hand. At the final
configuration (e), the robot has reached the ball
with its right hand and the ball is centered in
the robot field of view. The left hand had moved
only to regulate the position of the center of
mass. Right column: The motion is similar
but a task has been added to control the position
of the left hand: the desired position imposed
to the left hand is the final position reached
by the left hand in the previous movement.
The two motions look very similar, but their
“meanings” are different. In the right motion
(a–e), the left hand moves to regulate the
balance; in the right motion (f–j), the left hand
moves to reach a specific position.
The motions of the left hand look similar but
they are not exactly the same. The curves show
the distance function for the left hand going
from its initial position to its final position
in both cases. The curves are different. The
exponential decreasing of the distance function
(red curve) ‘’signs” the presence of the left-hand
Right-hand reaching while enforcing the
balance: the left hand has moved only to
correct the balance.
Simultaneous right-hand and left-hand
reaching: the target imposed to the left hand
is the final position reached in the previous
(right-hand only) movement.
0.0 0.5 1.0 1. 5
Right-hand reaching only
Right-hand and left-hand
2.0 2. 5 3.0