Accuracy vs Repeatability in Robot Arms and Vision Systems: What the Numbers Actually Mean

When manufacturers evaluate robot arms and 3D vision cameras, two specifications appear on nearly every datasheet: accuracy and repeatability. They sound similar. They are often used interchangeably in casual conversation. In engineering terms, they measure entirely different things, and confusing them leads to real consequences when building an automation cell.

A robot arm or camera can be highly repeatable but inaccurate. It can be accurate but not particularly repeatable. Understanding the difference determines whether the specification you are reading is actually relevant to your application.

What Repeatability Means

Repeatability is the ability of a system to return to the same position or produce the same measurement result, cycle after cycle, under the same conditions.

For a robot arm, repeatability is measured by commanding the arm to move to a specific taught position many times and measuring how much the actual endpoint varies between cycles. If the arm returns to within 0.1 mm of the taught position on every cycle, it has ±0.1 mm repeatability. It does not matter where that position is in absolute space. The arm just needs to come back to the same place consistently.

For a 3D vision camera, repeatability is how stable the depth readings are across repeated scans of the same static scene. A camera with high Z repeatability produces depth values that barely change from scan to scan under the same conditions, which means the robot receives consistent pick coordinates cycle after cycle.

Repeatability is what matters most for production automation. A robot arm executing the same pick cycle thousands of times per shift needs to arrive at the same position consistently. A 3D vision camera detecting the height difference between two layers of parts needs to produce stable depth readings between scans. Both are repeatability problems.

What Accuracy Means

Accuracy is the closeness of a measurement to the true value. It answers a different question: not "does the system return to the same place every time" but "does the system go to the correct place."

For a robot arm, accuracy refers to how close the arm's actual endpoint position is to the programmed target position in absolute space. A highly accurate arm goes where it is told to go in absolute coordinates. A highly repeatable arm returns to the same place it went before, whether or not that place is exactly where it was commanded.

For a 3D vision camera, accuracy refers to how close measured values are to the physical reality of the objects being scanned. An accurate camera measures a part that is 50.00 mm tall and returns a value close to 50.00 mm. A repeatable camera measures that same part consistently on every scan, even if its readings are consistently offset from the true value.

These are distinct quantities. High repeatability does not guarantee high accuracy, and high accuracy does not guarantee high repeatability. A production-grade vision and robot system needs both, but for different reasons depending on the application.

Why the Distinction Matters in Practice

For most robotic automation applications, repeatability matters more than accuracy, and understanding why helps clarify which specification to prioritize when evaluating hardware.

Consider a robot arm doing pick and place. The arm is taught a pick position by physically moving it to the correct location and recording that position. The robot then returns to that taught position cycle after cycle. What matters is that it comes back to exactly where it was taught, not that the absolute coordinates in space are perfectly correct. The teaching step absorbs any absolute accuracy error. Repeatability determines whether the pick is reliable over thousands of cycles.

This is why cobot datasheets emphasize repeatability rather than accuracy. The Fairino FR5 specifies ±0.02 mm repeatability. That figure tells you how reliably the arm returns to a taught position in production, which is the specification that actually determines whether your automation cell works consistently.

For 3D vision cameras the distinction plays out differently depending on the application. For robot guidance where the camera provides pick coordinates, repeatability determines whether the system produces consistent results cycle after cycle. For dimensional inspection where the camera measures actual part dimensions and those measurements are compared against design tolerances, accuracy matters directly. A camera with excellent repeatability but poor accuracy produces consistent measurements that are consistently wrong relative to the true dimension.

The practical test: if you are teaching positions by demonstration and the robot is picking parts it was shown, repeatability is your primary specification. If you are measuring parts against a defined tolerance and the measured value needs to be close to the physical truth, accuracy is what you are evaluating.

Reading the Specifications on Blue Sky Robotics Arms

Every arm in the Blue Sky Robotics lineup lists repeatability as the primary precision metric, which is the correct specification for evaluating production suitability.

The UFactory Lite 6 ($3,500) achieves ±0.1 mm repeatability, sufficient for most light-duty pick and place and inspection tasks. The Fairino FR5 ($6,999) and Fairino FR10 ($10,199) both deliver sub-millimeter repeatability suited for production-grade vision-guided automation.

For vision-guided cells where the camera layer also needs to meet precision requirements, Blue Sky Robotics' Blue Argus platform ships camera hardware, compute, and vision software as a tested, pre-configured system. Because the hardware and software are validated together before shipping, the repeatability of the full sensing pipeline is known rather than estimated from individual component specs.

Getting Started

Use our Cobot Selector to find the right arm for your precision requirements. Browse our full UFactory lineup and Fairino cobots with current pricing, or book a live demo to discuss your specific tolerance requirements.

FAQ

What is the difference between accuracy and repeatability in a robot arm?Repeatability is how consistently the arm returns to the same position cycle after cycle. Accuracy is how close the arm's actual position is to the commanded position in absolute space. For most production automation where positions are taught by demonstration, repeatability is the more relevant specification.

Which matters more for vision-guided robot automation: camera accuracy or repeatability?

For robot guidance where the camera provides pick coordinates, repeatability determines cycle-to-cycle consistency. For dimensional inspection where measured values are compared to design tolerances, accuracy matters directly. Most production applications require both, but repeatability is typically the primary concern for guidance tasks.

What does ±0.02 mm repeatability mean on a cobot datasheet?

It means the robot arm returns to within 0.02 mm of the taught position on repeated cycles under standard conditions. For context, 0.02 mm is 20 micrometers, which is sufficient for precision assembly, tight-tolerance pick and place, and most vision-guided inspection tasks in manufacturing.