Performance
Reach
Reach is the maximum horizontal distance a robot arm can extend from its axis 1 centerline to the wrist center.
What it is
Reach is a single number that tells you how far an arm can stretch: the horizontal distance from the axis 1 rotation centerline out to the wrist center at full extension. It's the headline spec on almost every arm datasheet because it's the first thing that decides whether a robot can physically touch the parts you need it to touch.
It's measured to the wrist center. Whatever you bolt on the faceplate, gripper, weld torch, dispense nozzle, extends past that point, so your usable working distance is reach plus the tool offset. Plan around the wrist center and add the tool separately.
How it actually works
An articulated arm builds its reach from the link lengths between axes 2, 3, and the wrist, swept around by axis 1. Fully extended, those links line up to give the maximum radius; folded in, the arm can't work below a certain minimum radius near its own base. So reach describes the outer edge of an annular region.
The number is comparable across arms of the same class. The FANUC M-710iC/70 is a long-reach arm built to cover large fixtures and multi-station cells, while the M-20iD/25 is a mid-reach arm sized for tighter, faster work close in. Pick the reach that lets the wrist center land on your farthest point without the arm hitting full extension, because motion quality and stiffness both fall off as you approach the limit.
How it differs
- Work envelope · Reach is one distance: the maximum horizontal radius to the wrist center. The work envelope is the full 3D volume the wrist center can actually occupy, shaped by every axis limit together. Two arms can share the same reach number and still have very different envelopes because of how high, how low, and how far behind the base each can swing.
- Payload · Reach is how far the arm goes; payload is how much it can hold at the faceplate. They trade against each other. A long-reach arm carrying a heavy tool at full extension puts far more torque on the lower axes than the same load held in close, which is why manufacturers publish load-moment limits alongside the reach and payload headline.
Where you meet it in the field
- FANUC M-710iC/70 · A long-reach articulated arm, the case where reach is the deciding spec for covering large fixtures and spread-out stations.
- FANUC M-20iD/25 · A mid-reach arm sized for tighter, faster work close to the base, the other end of the reach-versus-agility trade.
Common questions
- Is reach measured to the tool tip or to the wrist?
- To the wrist center. Anything you mount on the faceplate extends beyond that, so your real working distance is the published reach plus your tool offset. Size the arm to the wrist center, then add the tool.
- Can the robot reach anything within that radius?
- No. Reach is the outer horizontal limit, but the arm also has a minimum radius it can't work inside, near its own base, plus height and swing limits. The reachable space is the work envelope, a shell shaped by all the axis limits.
- Should I just buy the longest reach I can afford?
- Not for its own sake. Longer arms tend to be slower, less stiff, and lose effective payload at full extension. Match the reach to your farthest work point with a little margin, so the arm isn't operating at the edge of its extension where accuracy and rigidity are worst.