Secondary Conditions For Absolute Encoders - Siemens SINUMERIK 808D Function Manual

Reference cam adjustment
The reference cam must be calibrated exactly. The following factors influence the response time of the control when
detecting the reference cam ("Reference point approach delay" interface signal):
● Switching accuracy of the reference cam switch
● Delay of the reference cam switch (NC contact)
● Delay at the PLC input
● PLC cycle time
● Internal processing time
Practice has shown that the signal edge of the reference cam, which is required for synchronizing, is aligned between two
synchronized pulses (zero marks). This can be achieved by:
● Set MD34080 REFP_MOVE_DIST = MD34090 REFP_MOVE_DIST_CORR = MD 34100 REFP_SET_POS = 0
● Reference axis
● In "JOG" mode, traverse the axis to half the path length between the two zero marks. This path is independent of the
pitch of the leadscrew S and the gear ratio n (e.g. S=10 mm/rev, n=1:1 produces a path of 5 mm).
● Calibrate the cam switch so that switching is done at exactly this position (IS "Reference point approach delay"
(DB380x.DBX1000.7))
● Alternatively, the value of MD34092 REFP_CAM_SHIFT can be changed instead of moving the cam switch.
WARNING
Unable to protact the machine due to the incorrectly calibrated reference cam
If the reference cam is not calibrated precisely, an incorrect synchronizing pulse (zero mark) may be evaluated. In this
case, the control assumes an incorrect machine zero and moves the axes to incorrect positions. Software limit switches
act on incorrect positions and are therefore not able to protect the machine.
16.3

Secondary conditions for absolute encoders

Calibration time
The calibration process determines the offset between the machine zero and the encoder zero and stores it in a non-volatile
memory. Normally, calibration need only be performed once, i.e. during first commissioning. The control then knows the
value and can calculate the absolute machine position from the encoder absolute value at any time. This status is identified
by MD34210 ENC_REFP_STATE=2.
The offset is stored in MD34090 REFP_MOVE_DIST_CORR.
The calibration process must be repeated in the following situations:
● After mounting/removal or replacement of encoder or of motor with built-in encoder.
● After change of an existing gear unit between motor (with absolute encoder) and load.
● Generally speaking, every time the mechanical connection between the encoder and load is separated and not
reconnected in exactly the same way.
Note
The control may not always recognize the need for recalibration. If it detects such a need, it sets MD34210 to 0 or 1. The
following is detected: changeover to another gear speed with a different gear ratio between the encoder and load.
In all other cases, the user must overwrite MD34210.
Data backup
When machine data is backed up, the status of MD34210 ENC_REFP_STATE is also saved.
By loading this data set, the axis is automatically deemed calibrated!
WARNING
If the data set has been taken from another machine (e.g. series startup), calibration must still be carried out after loading
and activating the data.
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Function Manual
01/2017