In SCARA robots, which statement describes the joints providing horizontal compliance for insertion tasks?

• A. The wrist joint provides horizontal compliance.
• B. The base joint provides horizontal compliance.
• C. The elbow joint provides vertical compliance on its own.
• D. The shoulder and elbow joints use vertical axes to be compliant in the horizontal direction.

Answer: (B)

In SCARA robots, tasks that involve inserting a part rely on being able to adjust position in the horizontal plane without changing height. The base joint, which rotates about a vertical axis, is responsible for that in-plane motion and, therefore, provides the horizontal compliance needed during insertion. It lets the end-effector drift slightly or be controlled with impedance in the horizontal direction as the part aligns with its receptacle, reducing insertion forces and binding.

The other joints don’t provide this same direct horizontal flexibility. The elbow and shoulder contribute to reach within the plane, but their motion is not the primary source of horizontal compliance, and the idea that vertical-axis motion at those joints enables horizontal compliance isn’t aligned with how a SCARA is typically arranged. The wrist mainly handles orientation and finer positioning, not a standalone source of horizontal permissiveness for insertion.