Detailed Description
2.6 Referencing with absolute value encoders
Reference Point Approach (R1)
2-40 Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0
2.6.8 Enabling the measurement system
The measuring system of a machine axis is activated in the following cases:
• Power up of the control (POWER ON)
• Activation of the measuring system via interface signal (deselection of "Parking"):
DB31, ... DBX1.5/1.6 (position measuring system 1/2)
DB31, ... DBB2.1 (servo enable)
• Violation of the assigned encoder limit frequency (spindles):
MD36300 $MA_ENC_FREQ_LIMIT
When the measuring system is activated, the NC synchronizes the actual value system of
the machine axis with the current absolute value. Axis travel movements are disabled during
synchronization. Spindle travel movements are not.
Parameterizing the encoder limit frequency (spindles)
The EQN 1325 absolute encoder made by Heidenhain has an incremental track and an
absolute track.
If a spindle operates at rotational speeds above the encoder limit frequency of the
incremental track, a significantly lower limit frequency of the absolute track must be assigned
as the encoder limit frequency:
MD36300 $MA_ENC_FREQ_LIMIT
Otherwise an incorrect absolute position would be read because the parameterized encoder
limit frequency is not reached when the measuring system is activated. This would cause a
position offset in the actual value system of the machine axis.
Determining the encoder limit frequency
The encoder limit frequency to be parameterized is derived from the smaller of the two
following limit speeds:
• Encoder
The limit speed or encoder limit frequency is listed in the data sheet of the encoder
(e.g., limit speed = 2000 [rpm])
• NC
Due to the NC-internal evaluation process, the maximum limit speed for which error-free
calculation of the absolute value by the NC is possible is 4 encoder revolutions per
interpolation cycle.
For an interpolation cycle of, for example, 12 ms: Limit speed = 4/12 ms = 20,000 rpm
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