4MELFA-BASIC IV
Detailed explanation of command words 4-226
(9) Description of singular points.
<In the case of a vertical 6-axis robot>
Movement from posture A, through posture B, to posture C can-
not be performed using the normal linear interpolation (Mvs).
This limitation applies only when J4 axis is at zero degrees at all
the postures A, B, and C. This is because the structure flag of axis
J5 (wrist axis) is FLIP for posture A and NONFLIP for posture C.
Moreover, in posture B, the wrist is fully extended and axes J4
and J6 are located on the same line. In this case, the robot cannot
perform a linear interpolation position calculation.
The 3-axis XYZ (TYPE 0, 1) method in the command option of
Mvs should be used if it is desired to perform linear interpolation
based on such posture coordinates. Note that, strictly speaking,
this 3-axis XYZ method does not maintain the postures as it
evenly interpolates the joint angle of axes J4, J5, and J6 at pos-
ture A and C. Therefore, it is expected that the robot hand's pos-
ture may move forward and backward while moving from posture
A to posture C.
In this case, add one point in the middle to decrease the amount
of change in the hand's posture.
Another singular point is when the center of axis J5 is on the Z
axis of the base coordinates and the wrist is facing upward. In this
case, J1 and J6 are located on the same axis and it is not possi-
ble to calculate the robot position.
Fig.4-16:Singular point 1
About singular points of vertical 6-axis robots
1) Posture A
Posture at which the
flag changes status
2) Posture B
3) Posture C
NONFLIP
FLIP
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