1) Step 1 (Approach): The robot hand holds a ring firmly
and takes its initial posture, where the angle between the central
axis of the ring and the shaft is θinit
x , and the lowest point of the
ring is located in the lower portion by zinit with respect to the top
surface of the shaft. When the robot hand moves to the shaft, the
ring contacts the shaft first in its inner edge (Jrs) but outer edge
by virtue of initial posture. When the force sensor value meets
the condition |Fy| ≥ Fconst
y , the system detects contact and starts
compriance control. At this stage, there is a positioning error δx
in the x-axis direction. The acceptable range of θinit
x and zinit are
calculated in Section III-C.