Robot repeatability is not process capability

A repeatability number answers a narrower question

A robot's pose-repeatability figure describes consistent return under a defined robot test. It does not by itself say how close the robot comes to a programmed target, how accurately it follows a path or whether the configured process produces an acceptable part or result.

The buyer's requirement should begin with the end output: the feature, position, path, assembly, inspection result or quality characteristic that must pass, its tolerance and reference, and the conditions in which it must be achieved. Robot repeatability is one evidence input to that requirement—not a substitute for it.

Pose and path measures are not substitutes

ISO 9283:1998 remains the current published international standard for industrial-robot performance criteria and related test methods, although ISO's page shows that the edition is under review in 2026. Its public catalogue establishes the standards scope; the full paid text was not reviewed for this article.

ABB's current IRB 6760 specification separately reports pose accuracy, pose repeatability, path accuracy, path repeatability and stabilization time. ABB claims pose repeatability of 0.06 mm and 0.08 mm for its two documented variants while reporting path accuracy of 1.4 mm and 1.1 mm. Those different figures are a manufacturer-specific illustration of why the measures cannot be exchanged.

• Pose repeatability concerns repeated arrival around a position; it is not automatically closeness to the programmed position.
• Pose accuracy concerns position relative to the programmed target; it is not automatically the result along a continuous process path.
• Path accuracy and path repeatability concern motion along a path and may matter more for cutting, dispensing, welding, scanning or finishing.
• The finished output adds the tool, fixture, object, sensing, calibration, process and measurement system to the robot's motion.

Start with the customer's output tolerance

This makes the requirement comparable across proposed solutions. It also prevents a provider from answering an end-process question with the most favourable motion figure on a data sheet.

• Name the characteristic that will be accepted: for example placed-part pose, hole position, assembled gap, bead or cut path, surface result or inspection reading.
• State the nominal value, tolerance, unit, datum or coordinate frame, measurement location and consequence of a failed result.
• Identify whether the task depends on a point, a continuous path, stabilization time, force or process behaviour, or several of these together.
• Record part presentation, object variation, fixtures, calibration, vision correction and every material operating condition instead of assuming an ideal input.

Keep the complete error budget visible

Separate the robot's motion from base and mounting deflection, tool-centre-point calibration, end-effector compliance, fixture and workpiece variation, sensing and coordinate transforms, process forces, thermal effects, wear and measurement uncertainty. Mark an unknown contributor as unknown rather than assigning the entire tolerance to the robot figure.

Attach each input to the exact load state, speed, path, workspace region, approach direction, environment and software mode. ABB says its own ISO 9283 results can vary with position in the working range, velocity, arm configuration, approach direction, load direction and gearbox backlash. That is ABB manufacturer guidance for the named product, not an independently verified rule or result for another application.

Ask for evidence with its conditions attached

Universal Robots' current UR20 technical page, for example, lists ±0.1 mm pose repeatability per ISO 9283. That is a manufacturer rating for the documented UR20, not evidence that a configured gripper, fixture, vision system and process will hold an end-output tolerance of ±0.1 mm.

• Name the exact robot variant, controller, software and performance mode proposed.
• For every figure, state the performance criterion, standard edition, load, offset, speed, test plane, workspace and other material test conditions.
• Keep rated, typical, sample-average, simulated, trial-observed and production-observed values as different claim types.
• Record the configuration or operating changes that can alter the result and the recalibration or retesting they require.
• Do not subtract a brochure repeatability figure from the process tolerance and call the remainder a verified engineering margin; the measures and conditions may differ.

Test the configured process, not the brochure

Freeze the robot, controller, software, tool, fixture, sensor, program, workpiece range and measurement method before an acceptance run. Use representative positions, paths, speeds, loads, approach directions, part variation, shifts and environmental conditions, and preserve raw results, rejected outputs, interventions, measurement uncertainty and the approval decision.

ISO 22514-2:2026 addresses statistical procedures for capability or performance using measured continuous quality characteristics. ISO 22514-3:2020 addresses short-term studies on consecutively produced discrete parts and carries important limits: its public abstract says it is not suitable below 30 observations or where tool-wear patterns or autocorrelation are present. These are process-study scopes, not universal robot acceptance rules. A qualified quality or process owner should choose a method that fits the output and evidence available.

Keep short-term and lifecycle evidence separate

A short acceptance study cannot automatically establish performance across tool wear, thermal drift, maintenance, changeovers, recalibration loss, material variation or every future production condition. Define which longer-term observations matter and what threshold triggers correction or renewed testing.

Reopen the affected evidence after a material change to the robot or controller, software mode, tool, fixture, payload, tool centre point, calibration, sensor, program, speed, path, workpiece, process consumable, mounting or environment. Preserve the earlier result as version-specific history rather than carrying its pass into a changed configuration.

Keep manufacturer claims and verification distinct

ABB and Universal Robots are authoritative for what they publish about their named products and stated conditions. Their ratings are manufacturer-provided evidence, not independent verification of a buyer's configured process. ISO is authoritative for the public scope and status of its standards, but the cited ISO pages do not verify a named robot or deployment.

RobotAtom records the required output, exact source, claim type, test conditions, configured-process evidence and unknowns. It does not certify robot accuracy, process capability, safety or compliance, and a performance test does not replace applicable safety, metrology, quality or sector review.