Specialized Concentrated Focused
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Advantageous Functions
6. Advantageous Functions
6.1. Lead Screw Error Compensation
6.1.1. Causes of Lead Screw Error
Lead screw error consists of screw pitch error and errors caused by backlash.
Screw Pitch Error
Pitch error is caused by defect in manufacturing of lead screw and long-term wear, etc. In order to
improve precision, pitch compensation is needed to meet the requirement. The sketch of lead screw is
shown in Fig. 6-1. A coordinate system is established, based on point
―O‖ on the lead screw as the
reference point, nominal value as X-coordinate, and actual value as Y-coordinate. Then ideal moving
curve is as curve ―1‖ in Fig. 6-2 however, actual curve will be curve ―2‖ due to pitch error. That is to say,
the Actual value is not the same as its corresponding Nominal value, actual moving curve deviating
from the ideal one, and their difference is called error, i.e.:
Error = nominal mechanical coordinate
– actual mechanical coordinate
A Sketch of lead screw
B Moving curve
Reference point
0
5
1
Ideal move(without screw error)
S(nominal value)
2
Actual move(with screw error)
L(actual value)
Fig. 6-1 Screw error principle illustration
Backlash Error
Hysteresis feature is caused by forward and reverse clearance. Assume that the driving shaft drives
the driven shaft in negative (CW) rotation, the servo motor will be idling without moving worktable
because of mechanical driving chain backlash when the driving shaft suddenly begins CCW rotation
(positive motion). After staying at a certain position for some time, the worktable will move backward
with the driving shaft. When the direction of driving shaft changes again, the situation is the same,
which is called Hysteresis
. If pitch error doesn‘t exist, under ideal condition, the moving curve of
