External Axis
An external axis is a motor-driven turntable, rail, or positioner coordinated by the robot controller to extend reach or reorient the part during a path.
An external axis (or auxiliary axis) is a servo-driven mechanism — a linear rail, rotary positioner, or turntable — that the robot controller commands in coordination with the arm's own axes. It extends the system beyond what the arm alone can reach or orient.
A linear rail (7th axis) moves the robot along a line to serve multiple stations or long parts; a positioner rotates the workpiece so a welding torch can reach all sides. Coordinated motion keeps the tool path continuous as both robot and external axis move.
External axes are common in welding and large-part handling. When sourcing a used system, confirm the controller has the spare axis channels and software to drive the positioners or rail you need.