Intro
Positioning accuracy and repeatability are two different concepts.
In the industrial field, it is often used to describe the performance of mechanical systems.
Repeatability is higher than positioning accuracy.
Positioning accuracy
Positioning accuracy is a definite value, not a range; while repeatability accuracy is a range.
Positioning accuracy refers tothe degree of deviation between the target position and the actual position that a mechanical system can achieve in a single movement.
It reflects the accuracy with which a mechanical system reaches its target position in a single motion.
In layman’s terms: it refers to the difference between the actual position the machine or equipment reaches when it stops and the position you require it to reach.
Positioning accuracy is a fixed value (e.g., 0.01 mm) and not a range (e.g., ±0.02 mm).
The positioning accuracy error depends on the manufacturing error of the transmission components.
For example: If a shaft is required to travel 100mm, it actually travels 100.01mm. The extra 0.01mm is the positioning accuracy.
For example: If the lead screw travel distance is set to 100mm, the actual travel distance of 100 lead screws will be between 99.99mm and 100.01mm, and the positioning accuracy will be 0.02mm (100.01-99.99=0.02).
Repeatability
Repeatability refers to the accuracy with which a mechanical system can repeatedly reach the same target position in multiple movements. It reflects the consistency and repeatability of the mechanical system in reaching the same target position in multiple movements. Repeatability is very important for applications that require multiple repetitive movements.
In layman’s terms, it refers to the error that occurs when the same location is located multiple times.
Repeatability is a range (e.g., ±0.02).
Repeat position error is related to the clearance of transmission components.
In addition, repeatability accuracy is not only related to the accuracy and resolution of the grating ruler (displacement sensor), but also to the errors of the mechanical system , such as the guiding system, transmission system and structural rigidity.
These factors can reduce positioning accuracy and, to some extent, affect repeatability accuracy.
For example: A shaft is required to travel 100 mm.
As a result, the first time it actually moved 100.01mm, and when the same action was repeated , it moved 99.99mm. The error between these two is 100.01-99.99=0.02mm, which is the repeatability accuracy.
Repeatability representation: denoted by ±x, where the error above is represented as ±0.01mm, or ±(0.02/2).
For example: if the lead screw travel distance is set to 100mm, the actual travel distance after 100 cycles will be between 99.988mm and 99.992mm, and its repeatability is ±0.002mm.
