Which feature distinguishes a SCARA robot from a Cartesian manipulator?

• A. It uses spherical joints for rotational axes.
• B. It lacks any rotational joints and only translates.
• C. It uses vertical axes for shoulder and elbow joints to provide horizontal compliance for vertical insertion tasks.
• D. It has four translational joints in a plane.

Answer: (C)

SCARA robots achieve planar reach through rotary joints: the shoulder and elbow rotate about vertical axes, letting the arm sweep in the horizontal plane, while a separate vertical axis handles up-and-down motion. This arrangement provides horizontal reach with some compliance in the plane, which is especially useful for vertical insertion tasks where alignment and guidance happen in x–y as parts are moved into place from above. A Cartesian manipulator, on the other hand, moves primarily with linear actuators along orthogonal x, y, and z axes and typically lacks these planar rotary joints, so it performs straight-line motion rather than sweeping a plane with rotating joints. The described feature—vertical-axis rotation at the shoulder and elbow enabling horizontal reach for vertical insertion—is what distinguishes SCARA from a Cartesian system.