Under what condition does singularity occur in FANUC robots?

• A. Occurs when all axes are aligned at zero degrees.
• B. Occurs when XYZ/Cartesian coordinate axes 4 and 6 are aligned and axis 5 approaches 0 degrees.
• C. Occurs when joint 2 is at 90 degrees.
• D. Occurs when axis 1 is at 180 degrees.

Answer: (B)

Singularity happens when the robot’s joints align in a way that the end effector loses one independent motion, because the Jacobian becomes rank-deficient. For a 6‑axis FANUC, the wrist joints (the last three) control orientation. When the wrist is positioned so that the axis 4 and axis 6 lines up (they become collinear) and the wrist pitch axis (axis 5) is near 0 degrees, those rotations cease to be independent. That means rotating around one wrist axis inevitably affects the others, and small joint moves can produce large or unpredictable changes in orientation. This wrist-alignment condition—where the fourth and sixth axes align with the fifth near zero degrees—is exactly the situation described, and that’s why it’s identified as the singular configuration.

Other listed poses don’t produce that specific loss of independence in the wrist joints. They may be awkward or near joint limits, but they do not define the standard wrist singularity that arises from the alignment of wrist axes with the wrist pitch near zero.