In a description for ballscrews on a CNC, I saw two types of error listed:
- Incremental error: < 0.0006"/ft
- Cumulative error: < 0.0008" at 35"
What are these types of error measuring? What is the difference between them?
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Sign up to join this communityIn a description for ballscrews on a CNC, I saw two types of error listed:
What are these types of error measuring? What is the difference between them?
The "incremental error" is the relative error in moving between two positions. (But only the USA would think of specifying a dimensionless quantity in "inches per foot" just to confuse people.)
If the screw is commanded to move a distance $x$ (in any length unit!) the distance actually moved will be between 0.99995$x$ and 1.00005$x$ (because 0.0006/12 = 0.00005)
But the cumulative error after several movements (or one long movement) is less than this: the above formula would give between 34.99825" to 35.00175" for a commanded total movement of 35", but the second specification says the actual distance moved will be between 34.99920" and 35.00080", which is about half the worst incremental error.