Siemens SINUMERIK 840D sl Programming Manual page 38
Measuring cycles
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Description
2.8 Measurement principle
The resulting maximum measuring position is available in the result parameters _OVR[ ] and
_OVI[ ] of the measuring cycle.
At the instant the switching signal is output by the probe, the current actual position is stored
internally "on-the-fly" as the actual value, the measuring axis is stopped and then the "Delete
distance-to-go" function is executed.
The distance-to-go is the path not yet covered in the measuring block. After deletion, the next
block in the cycle can be processed. The measuring axis travels back to the starting position.
Any measurement repetitions selected are restarted from this point.
Measurement path DFA
Measurement path DFA defines the distance between the starting position and the expected
switching position (setpoint) of the probe.
Measuring velocity
As measuring feedrate, all of the measuring cycles use the value saved in the general setting
data SD54611 after the calibration of the workpiece probe. A different measuring feedrate can
be assigned for each calibration field [n].
To calibrate the measuring probe, either the measuring feedrate from the channel-specific
setting data SD55630 $SCS_MEA_FEED_MEASURE is used (default value: 300 mm/min) or
the measuring feedrate can be overridden in the input screen form at the calibration instant.
To do this, bit 4 must be set to 1 in the general setting data SD54760
$SNS_MEA_FUNCTION_MASK_PIECE .
The maximum permissible measuring velocity is derived from:
● The deceleration behavior of the axis.
● The permissible deflection of the probe.
● The signal processing delay.
Deceleration distance, deflection of probe
NOTICE
Safe braking of the measuring axis
Safe deceleration of the measuring axis to standstill within the permissible deflection path of
the probe must always be ensured. Otherwise damage will occur!
A delay t, typical for the control, is taken into account in signal processing (IPO cycle) for the
time between detection of the switching signal and output of the deceleration command to the
measuring axis: general machine data MD10050 $MN_SYSCLOCK_CYCLE_TIME and
MD10070 $MN_IPO_SYSCLOCK_TIME_RATIO). This gives the braking distance component.
The following error of the measuring axis is reduced. The following error is velocity dependent
and at the same time dependent on the control factor of the measuring axis (servo gain of the
associated machine axis: servo gain factor).
38
Programming Manual, 12/2017, 6FC5398-4BP40-6BA1
Measuring cycles
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