Coordinates
Base Frame
The base frame is the Cartesian coordinate system fixed at the robot's mounting base, serving as the reference origin from which the arm's motion and other frames are measured.
What it is
The base frame is the coordinate system anchored to the physical base of the robot, the plate or casting where the arm is bolted to the floor, pedestal, or fixture. Its origin sits at the mounting base and it doesn't move when the arm moves, which makes it the stable reference everything else hangs off.
On many FANUC systems the world frame coincides with the base frame unless you deliberately offset it. That's why people use the two terms loosely. They stay separate concepts: the base frame is tied to hardware, the world frame is the software reference that may or may not sit on top of it.
How it actually works
The base frame is three axes at the mounting flange: X and Y in the plane of the base plate, Z pointing straight up along the axis of rotation of the first joint. When you jog the robot in Cartesian mode relative to this frame, +Z moves the tool straight up regardless of how the arm is folded, because the frame stays put while the joints solve the pose.
User frames and the tool center point are all defined relative to this reference. Set up a 3-point user frame on a fixture and the controller stores that frame as an offset from the base/world origin, so a base that's been surveyed or shimmed out of level shifts every downstream frame with it. Get the base reference wrong and every taught position inherits the error.
How it differs
- World Frame · The base frame is fixed to the robot's physical mounting base; the world frame is the software reference that, on many FANUC controllers, coincides with the base frame by default but can be offset from it (for example to line up multiple robots or a shared cell origin).
- User Frame · A user frame is an application-specific coordinate system a technician defines on a fixture or workpiece, expressed as an offset from the base/world frame. The base frame is the fixed origin those user frames are measured against.
- Tool Frame (TCP) · The tool frame rides on the faceplate and moves with the wrist; the base frame stays anchored to the floor. Jog in base and the origin never moves; jog in tool and the reference travels with the end-of-arm tooling.
Where you meet it in the field
- FANUC M-20iD/25 · The base frame origin sits at this arm's mounting base, where it bolts to the floor or pedestal.
- 3-point user frame setup · User frames are taught as offsets from the base/world frame, so the base reference is what your three points are ultimately measured against.
Common questions
- Are the base frame and world frame the same thing?
- On many FANUC systems they coincide out of the box, so people treat them as one. They stay distinct concepts: the base frame is tied to the physical mounting base, while the world frame is a software reference you can offset from the base, which matters when you're aligning multiple robots to a shared cell origin.
- If I mount the robot on a tilted surface, does the base frame stay level?
- No. The base frame is fixed to the robot's base, so it tilts with the mounting. Its Z axis follows the first joint's axis of rotation rather than gravity. If you need a level reference on a tilted mount, that's what an offset world frame or a taught user frame is for.
- Do my taught points move if I re-survey the base?
- Points taught relative to a user frame follow that frame if you redefine the base or world reference under it. Points taught in a fixed frame don't automatically shift, so re-establishing the base reference after a move is a real chance to introduce error across every downstream position. Confirm your frames before running production.