Stiction - HEIDENHAIN TNC 415 Technical Manual

1.6.6 Stiction

Guideways with a relatively high level of stiction can cause servo lag at low feed-rates, even when
using feed precontrol. A servo lag can be detected using, for example the TNC's integral
oscilloscope, and the TNC can also compensate the error. This is done by entering an axis-specific
factor to compensate the stiction in machine parameter 1511 (guideline factor: 5 000 to 10 000). A
higher nominal value based on this factor is then output while traversing.
∆ s
× k × MP1511
a
F =
add v
t
C
MP1050
× F
V =
add add
MP1010
This increase in nominal value is limited by MP1512. If this limit is set too high then the machine will
oscillate at standstill (guideline: < 50). MP 1512 limits the value ∆s
∆s
×
256
a lim it
MP1512 =
GP
Compensation may only be active at low feed rates as the increased nominal value would cause
oscillation at high speed. The feed-rate limit for stiction compensation is defined in MP1513.
Stiction compensation is effective only during operation with feed precontrol. If stiction
compensation is to be in effect in the manual operating modes as well, feed precontrol (MP1391)
must be activated for manual operation in each axis.
MP1511 Factor for stiction compensation
Entry: 0 to 16 777 215 [µs]
MP1511.0 X axis
MP1511.1 Y axis
MP1511.2 Z axis
MP1511.3 4th axis
MP1511.4 5th axis
01.98 TNC 407/TNC 415/TNC 425
F = Additional feed rate [
add
∆s
= Servo lag difference after one control loop cycle [mm]
a
t = Control loop cycle time [µs]
C
k = Position loop gain [
v
MP1511 = Factor for stiction compensation [µs]
V = Additional analog voltage [V]
add
MP1050 = Analog voltage for rapid traverse [V]
MP1010 = Rapid traverse [
MP1512 = Limit to the amount of stiction compensation
[counting steps]
∆s Limit value for ∆s
=
alimit
GP = Grating period of the measuring system [µm]
1 Machine axes
m
]
min
m/min
]
mm
m
]
min
in the above formula.
a
[µm]
a
4-33