Portable Measuring Arms
Articulated portable CMMs for on-machine, on-fixture and shop-floor inspection - contact probing and integrated laser scanning brought to the part.
How it works
A portable measuring arm uses six or seven encoded rotary joints to give the 3D position (and orientation) of a probe at the end of the arm. Working volumes are spherical, typically 1.2 to 4.5 metres in diameter. Modern arms accept both touch-trigger / hard probes and integrated laser-line scanners on the same wrist.
Typical accuracy
Single-point repeatability on a 2.5-metre 7-axis arm is typically 25-50 microns; volumetric accuracy 40-90 microns. Integrated laser-line scanners add 25-60 microns to the arm uncertainty depending on the model.
Applications
- On-machine part checks between operations
- Fixture and jig proving on the shop floor
- Reverse engineering of legacy tooling and castings
- Weld and fabrication inspection where the part cannot move
- Field service and remote-site inspection
Strengths
- • Truly portable - single-case transport, no forklift
- • Contact and scanning on the same tool
- • Fast setup - minutes, not hours
- • Cost-effective compared with a large fixed CMM
Limitations
- • Operator technique dominates real-world uncertainty
- • Not suitable for sub-10 micron tolerances
- • Sphere-of-reach limits large-part coverage without leapfrogging
- • Battery life and cable management on shop-floor work
6-axis vs 7-axis - and why it matters
A 6-axis arm gives position only; a 7-axis arm adds a redundant infinite-rotation wrist that allows the operator to rotate a laser scanner without moving the arm base. Every serious scanning-arm application uses 7-axis. For pure contact probing, 6-axis is still viable but less ergonomic.
Where arms replace a CMM - and where they don't
Portable arms are the right tool when parts cannot practically be brought to a fixed CMM: large weldments, tooling on the machine, fixtures bolted to a jig table. They are not a replacement for a bridge CMM on precision-machined parts under 300 mm at 5-10 micron tolerances - the physics of a cantilevered arm cannot compete with a granite base.
Buying considerations
- Reach and 6-axis vs 7-axis (scanning always needs 7-axis)
- Integrated laser scanner throughput and stand-off
- Certified per ISO 10360-12 for arms with scanners
- Software: PolyWorks, Verisurf, CAM2, Spatial Analyzer
- Battery, wireless and case robustness for real shop-floor use
FAQs
How accurate is a portable arm in real use?+
Volumetric accuracies of 40-90 microns are typical on a 2.5 metre arm in a stable environment. Add operator variability, thermal drift and fixturing and 100-150 microns is a realistic uncertainty budget for shop-floor use.
Can we use one arm for both probing and scanning?+
Yes - integrated laser scanners on the FARO Quantum, Hexagon Absolute Arm and Kreon Ace share the same wrist as the hard probe, with the arm auto-detecting which is fitted.