Which frame remains stationary in space as the robot arm moves?

• A. Base frame.
• B. Tool frame.
• C. User frame.
• D. World frame.

Answer: (A)

In robotic kinematics, frames of reference are attached to different parts of the system. The base frame is fixed to the robot’s base and serves as the stationary reference in space. Since the base is anchored to the environment, it does not move when the arm’s joints articulate. The tool frame, on the other hand, is attached to the end effector and moves with the arm, so it changes position and orientation as the arm moves. While a world frame can also be defined as a fixed reference, the frame that remains stationary relative to space while the arm moves is the base frame.