Specialized Concentrated Focused
Operation
「
51
」
(A) Sketch of Screw
(B) Picture of Moving Curve
Reference Point
0
5
1
Ideal Move (Without Pitch Error)
S (Nominal Value)
2
Actual Move (With Pitch Error)
L (Actual Value)
Fig. 3-37 Analysis of Pitch Error
Pitch Error Compensation Method
In pitch compensation, generally pitch error v
alue isn‟t related to feed direction. That is, when the pitch is
too small in positive feed, additional pulse is needed, and thus, when negative feed passes the same
position, the same amount of feed pulse should be added. But if the pitch is large, deduction of pulse is
needed, and neither is the reducing amount related to feed direction. In software compensation,
correction of each point on the error curve should be tabulated and saved to the system memory. Then
auto compensation for coordinates of each point is available in running, so as to improve machine
precision.
Backlash Compensation
Hysteresis feature is caused by forward and reverse clearance. Assume that driving shaft drives driven
shaft in negative (CW) rotation, 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 the 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 worktable is
shown in Fig. 3-38(A), in which the curve of horizontal section is during the idling of servo motor without
worktable movement. The actual moving curve of worktable is shown in Fig. 3-38(B).
(A) Hysteresis Feature
(B) Actual Moving Curve
L (Actual Value)
S (Nominal Value)
L (Actual Value)
S (Nominal Value)
Fig. 3-38 Analysis of Backlash
The popular explanation is: because spindle is generally fixed on the screw whose outer wire and the
inner wire on the outer wire cannot be completely matched, backlash compensation compensates the
