Measuring Strategy For Measuring Workpieces With Tool Offset - Siemens SINUMERIK 840D sl Programming Manual

1.9

Measuring strategy for measuring workpieces with tool offset

The actual workpiece dimensions must be measured exactly and compared with the setpoint
values to be able to determine and compensate the actual dimensional deviations on the
workpiece. An offset value can then be ascertained for the tool used for machining.
Function
When taking measurements on the machine, the actual dimensions are derived from the
path measuring systems of the position-controlled feed axes. For each dimensional deviation
determined from the set and actual workpiece dimensions there are many causes which
essentially fall into three categories:
● Dimensional deviations with causes that are n o t subject to a particular trend, e.g.
● Dimensional deviations with causes that a r e subject to a particular trend, e.g. tool wear
● Accidental dimensional deviations, e.g. due to temperature fluctuations, coolant or slightly
Mean value calculation
Mean value calculation in conjunction with measurement weighting has proven a suitable
method.
When correcting a tool, it can be selected whether a correction is made based on the actual
measurement, or whether an average value of the measurement differences should be
generated over several measurements which is then used to make the correction.
The formula of the mean value generation chosen is:
Mi
Mv
new
Mv
old
k
D
i
Measuring cycles
Programming Manual, 02/2011, 6FC5398-4BP40-0BA0
positioning scatter of the feed axes or differences in measurement between the internal
measurement (probe) and the external measuring device (micrometer, measuring
machine, etc.).
In this case, it is possible to apply empirical values, which are stored in separate
memories. The set/actual difference determined is automatically compensated by the
empirical value.
or thermal expansion of the leadscrew.
soiled measuring points.
Assuming the ideal case, only those dimensional deviations that are subject to a trend
can be taken into account for compensation value calculation. Since, however, it is hardly
ever known to what extent and in which direction accidental dimensional deviations
influence the measurement result, a strategy (sliding averaging) is needed that derives a
compensation value from the actual/set difference measured.
-
Mi D
= -
Mi alt
neu alt
k
Mean value new = amount of compensation
Mean value prior to last measurement
Weighting factor for mean value calculation
Actual/set difference measured (minus any empirical value)
1.9 Measuring strategy for measuring workpieces with tool offset
i
Description
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