Calibrating The Ots - Renishaw OTS Installation Manual

Calibrating the OTS

Why calibrate a probe?
A probe is just one component of the
measurement system which communicates with
the machine tool. Each part of the system can
introduce a constant difference between the
position that the stylus touches, and the position
that is reported to the machine. If the probe is
not calibrated, this difference will appear as an
inaccuracy in the measurement. Calibration
of the probe allows the probing software to
compensate for this difference.
During normal use, the difference between the
touch position and the reported position does
not change but it is important that you calibrate
your probe in the following circumstances:
•
when a probe system is to be used for the
first time;
•
when a new stylus is fitted to the probe;
•
when it is suspected that the stylus has
become distorted or that the probe has
crashed;
•
at regular intervals to compensate for
mechanical changes of your machine tool.
When your probe is assembled and mounted
on the machine table, it is necessary to align
the stylus faces with the machine axes to avoid
probing errors when setting tools. It is worth
taking care with this operation – you should
try to get the faces aligned to within 0.010 mm
(0.0004 in) for normal use. This is achieved by
manually adjusting the stylus with the adjusting
screws provided, and using a suitable instrument
such as a DTI clock mounted in the machine
spindle.
When the probe has been correctly set up on
the machine, it is time to calibrate the probe.
Calibration cycles are available from Renishaw
for this task. The purpose is to establish the
probe stylus measuring face trigger point values
under normal measuring conditions.
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The calibration values are stored in macro
variables for computation of the tool size during
tool setting cycles.
Values obtained are axis trigger positions
(in machine co-ordinates). Any errors due to
machine and probe triggering characteristics
are automatically calibrated out in this way.
These values are the electronic trigger positions
under dynamic operating conditions, and
not necessarily the true physical stylus face
positions.
NOTE:
Poor repeatability of probe trigger point values
indicates that either the probe/stylus assembly
is loose or a machine/probe fault exists. Further
investigation is required.
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