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

General

1.9 Measuring strategy for measuring workpieces with tool offset

Measuring accuracy
A delay occurs between detection of the switching signal from the probe and transfer of the
measured value to the control. This is caused by signal transmission from the probe and the
hardware of the control. In this time a path is traversed that falsifies the measured value.
This influence can be minimized by reducing the measuring speed.
The rotation when measuring a mill on a rotating spindle has an additional influence. This
can be compensated for by compensation tables. (see Section 5.2.2 CYCLE971
"Measurement and correction strategy").
The measurement accuracy that can be obtained is dependent on the following factors:
• Repeat accuracy of the machine
• Repeatability of the probe
• Resolution of the measuring system
1.9 Measuring strategy for measuring workpieces with tool offset
1.9
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 3 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
1-24
Note
Repeat accuracy
A test program for determining the overall repeatability of a machine is described in
Section 10.4.
positioning scatter of the feedforward axes or differences in measurement between the
internal measurement (measuring 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.
Programming Manual, Release 04/2006, 6FC5398-4BP10-0BA0
Measuring cycles