What are linear and circular interpolation in robot motion, and when would you use each?

• A. Linear interpolation moves end-effector along straight lines; circular interpolation follows arcs between points; use linear for welding or pick-and-place, circular for arcs.
• B. Linear interpolation uses curved paths; circular uses straight lines.
• C. Both are used for same tasks; no difference.
• D. Linear interpolation is only for 2D tasks; circular is 3D.

Answer: (D)

The key idea is how the path is defined between two points. Linear interpolation makes the end effector move along a straight line from the start pose to the end pose in Cartesian space. Circular interpolation makes the motion follow a circular arc, defined by an arc center (or radius) and the plane in which the arc lies, between the two poses.

Use linear interpolation when you need a straight, direct move. This is common for welding beads, straight-line machining, or fast pick-and-place where the tool must stay on a straight path with consistent orientation or controlled orientation along that line.

Use circular interpolation when you need a smooth curved motion. This comes up for tracing arcs, following a contour on a curved surface, drilling or milling along a circular path, or connecting straight segments with a rounded transition to avoid sharp corners. You’ll define the arc plane and center, and the controller will keep the tool on that arc while typically managing the appropriate orientation along the path.

It’s worth noting that both capabilities aren’t limited to a single plane or dimension: linear moves can occur in 3D space, and circular moves are defined within a plane but can be oriented in 3D space. The idea that linear is only 2D and circular only 3D isn’t accurate.