What is the difference between accuracy and repeatability in a robotic arm?
Accuracy describes how closely a robot reaches a commanded position relative to the intended reference. Repeatability describes how consistently it returns to the same position over repeated attempts. A robot can return to the same slightly incorrect location very consistently, so these specifications answer different questions.
What this means in practice
Repeatability is often useful for taught pick-and-place tasks where positions are established on the real cell. Absolute positioning matters when paths come from CAD data, measurement systems, or offline programming. The complete process also depends on fixture consistency, tool calibration, temperature, loading, and part variation.
Build an application error budget
The finished result combines robot behavior with tool calibration, fixture placement, part tolerances, and environmental effects. For contact processes, structural compliance can also matter. A robot specification represents one contribution to the total, not a guarantee of finished-product tolerance.
Measure the characteristic the process actually requires: point placement, orientation, path quality, or final assembly dimensions. Use representative loads and operating conditions. If the robot returns consistently but always misses the intended location, investigate reference and calibration errors before attributing the problem to repeatability.
Key points
Compare like-for-like specifications and their stated test conditions.
Include angular and path performance when the process requires them.
Measure the finished process result rather than relying only on a robot datasheet.
Practical example and next step
For example, repeatable motion cannot compensate for a loose fixture that shifts each component. Define the required product tolerance, allocate an error budget across the cell, and demonstrate performance using representative parts and operating conditions.