Servo Resolution; Calculation Of The Smallest Voltage Step - HEIDENHAIN TNC 415 Technical Manual

Servo resolution:

The internal calculating resolution of the control is always 0.1 µm. However the display step can be
set with MP7290. The rounding up or down is only in display (see section "Display and operation").
Normally a servo resolution of 1 µm is sufficient, i.e. the control must be able to generate at least
one voltage step per 1 µm positional deviation. For 0.1 µm servo resolution at least one potential
step must be generated per 0.1 µm.

Calculation of the smallest voltage step:

The controls produce an analogue voltage 0 to 10 V. This 10 V is divided by the TNC 415 with a 16
Bit A/D-converter to give 65 536 divisions. As a result, the smallest potential step is 0.15 mV.
In the TNC 407 the 10 V analogue potential is produced by a 14 Bit A/D converter, giving 16 384
divisions. The resulting smallest potential step is 0.6 mV.
Potential steps per µm (0.1 µm) positional deviation:
As described above, moving with the rapid traverse (MP1010) results in a certain lag distance s
The rapid traverse rate is reached at a definite voltage (MP1050). So one can calculate a definite
potential ∆U per µm of positional deviation (lag).
MP1050 [mV]
∆U =
s a [µm]
If ∆U is divided by the smallest voltage step which can be produced (0.15 mV for TNC 415 or 0.6 mV
for TNC 407), the result is the number of voltage steps which are produced per µm or 0.1 µm
positional deviation.
for TNC 415:
∆U [mV]
n =
0.15 [mV]
Example:
m/min
k = 2 rapid traverse 5 000 [mm/min], U = 9 [V]
v
mm
5 000 [mm / min]
Ve
s = =
a
k
v
2
9 000 [mV]
∆U =
2 500 [µm]
3.6 [mV / mm]
n =
TNC 415
0.15 [mV]
3.6 [mV / mm]
n =
TNC 407
0.6 [mV]
01.98 TNC 407/TNC 415/TNC 425
= 2 500 [µm]
m / min
mm
= 3.6 [mV/µm]
= 24 steps/µm positional deviation
= 6 steps/µm positional deviation
3 Servo positioning of the NC-axes
for TNC 407:
∆U [mV]
n =
0.6 [mV]
.
a
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