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ABOUTtooling
As a result, aligning a workpiece on a 3-axis
machine requires just one tedious operation.
Relational measurement
After determining the position of the tool
with respect to the tool setter and the position
of the workpiece in relation to the
workpiece probe, the position of the tool
setter with respect to the workpiece probe
must be determined. This will close the
measurement loop and provide the position
of the tool with respect to the workpiece
(see diagram on page 17).
The simplest approach is to measure the
spherical probe directly with the tool setter.
Shining a laser beam at a ruby sphere,
which most touch probes incorporate, results
in accuracy errors because the ruby
is transparent. This results from the light
beam continuing to the sensor even when
the probe is in the path. Probe manufacturers
offer alternative, nontransparent probe
materials, such as alumina and carbide, which can avert this
problem.
As the tool is traversed from the tool setter to the workpiece,
errors accumulate due to geometry and encoder accuracy.
The same situation occurs as the workpiece probe is
moved from the tool setter to the workpiece. While both of
these displacements may be precise, or repeatable, the positional
accuracy can vary by several microns.
This accuracy problem can be minimized by placing
the machine probe as close to the cutting tool as possible
and by placing the tool setter as close to the workpiece as
possible. In many instances, machine tool probes can be
placed directly in the spindle taper and be operated via
infrared or radio signals. This allows wireless communication,
which, in turn, permits probe mounting with regular
tool changes.
Unfortunately, machine tool probes are not available for
the small tapers in many high-speed micromachine spindles.
Mounting the probe near the spindle on the machine tool
stage, however, can be adequate for most applications, and
help compensate for errors.
As micromachinists attempt to effectively apply smaller
microtools, these tools must be in registration with the workpiece.
Employing measurement strategies designed specifically
for micromachining can go a long way toward reaching
this goal. µ
About the author: Chris Morgan is chief technology offi cer
for Advanced Machine Technologies LLC, Crestwood, Ky. The
company is a tool and die shop for the micromanufacturing
fi eld. It performs micromilling, microEDMing and microgrinding;
machining of diffi cult-to-machine materials; and manufactures
Microlution
A Renishaw touch probe and System 3R pallet mounted on a Microlution 5100-S
machine tool.
cutting tools for micromachining. Telephone: (502) 243-0263.
E-mail: cmorgan@amtech.us.com. Web: www.amtech.us.com.
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