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6.4.6 Compensation of Static Friction
Calculations
6 – 48
On guideways with high static friction (stick-slip friction), a following error can
occur at low feed rates during operation with velocity feedforward control.
This error can be compensated by the TNC. You can measure following error
by using, for example, the integrated oscilloscope of the TNC.
Compensation of static friction works only under velocity feedforward control.
If it is also to work in manual operating modes, you must activate velocity
feedforward control in each axis with MP1391.x for manual operation.
For compensation of static friction, an additive nominal velocity is output
whose value F
is calculated from the factor for static friction compensation:
zus
∆
s
------- -
a
⋅
⋅
F
=
k
MP1511
zus
v
t
R
F
= additional feed rate [m/min]
zus
∆s
= following error difference after one control loop cycle [mm]
a
t
= control loop cycle time [µs]
R
k
= control loop gain [(m/min)/mm]
v
MP1511.x = factor for static friction compensation [µs]
This additive nominal value is limited with MP1512.x. If this limit is too high,
the machine vibrates at a standstill:
⋅
s
256
agrenz
------------------------------ -
MP1512.x
=
TP
MP1512.x = limitation of the amount of the static friction compensation
[counting steps]
= limit value for ∆s
s
agrenz
TP = grating period of the encoder [µm]
[µm]
a
HEIDENHAIN Technical Manual TNC 426, TNC 430
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