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Ball screw precision how to understand?

The Ball Screw is a high-efficiency feed screw with the ball making a rolling motion between the screw axis and the nut. Compared with a conventional sliding screw, this product has drive torque of one-third or less, making it most suitable for saving drive motor power.

 Accuracy of the Ball Screw
Lead Angle Accuracy
The accuracy of the Ball Screw in the lead angle is controlled in accordance with the JIS standards
(JIS B 1192 - 1997).
Accuracy grades C0 to C5 are defi ned in the linearity and the directional property, and C7 to C10 in
the travel distance error in relation to 300 mm. 

[Actual Travel Distance]
An error in the travel distance measured with an actual Ball Screw.
[Reference Travel Distance]
Generally, it is the same as nominal travel distance, but can be an intentionally corrected value of the nominal travel distance according to the intended use.
[Target Value for Reference Travel Distance]
You may provide some tension in order to prevent the screw shaft from runout, or set the reference travel distance in “negative” or “positive” value in advance given the possible expansion/contraction from external load or temperature.
In such cases, indicate a target value for the reference travel distance. 
[Representative Travel Distance]
It is a straight line representing the tendency in the actual travel distance, and btained with the least squares method from the curve that indicates the actual travel distance.
[Representative Travel Distance Error (in )]
Difference between the representative travel distance and the reference travel distance.
The maximum width of the actual travel distance between two straight lines drawn in parallel with the representative travel distance.
Indicates a fluctuation against a given thread length of 300 mm.
A fl uctuation in one revolution of the screw shaft. 
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