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c.
Accuracy considerations. Deals with factors affecting the ultimate measuring accuracy
of the Laser Transducer System. Centers on the effect of the environment under which
the measurement is made along with techniques for compensating for these effects.
Specific types of measurement errors, including the effect of thermal expansion of the
part being measured or cut, are discussed. Consideration i s also given to cosine error
or errors due to misalignment.
d.
System installation. Discussion of how to install the measurement components in
actual measurement applications. Consideration of possible combinations to split and
direct the laser beam to the measurement location. Also discussed is how to route the
laser beam to the measurement location with emphasis on minimizing possible mea-
surement errors. This will include the effect of Abbe errors and thermal instabilities
on the measurement process. Techniques for protecting the beam from disruptions
such a s thermal effects, cutting fluid, and chips which could interrupt the measure-
ment are also discussed.
e.
Alignment procedure. General rules for the actual alignment of the Laser Transducer
System after it is installed on a machine are discussed. Different techniques of align-
ing the components, depending upon the installation and accuracy requirements are
also covered. Specific examples including a 3-axis measurement application utilizing
the linear interferometer and an X-Y stage application using plane mirror interfero-
meters illustrate fundamental techniques which can be applied to most installations.
2.2
OVERVIEW
O F
LASER
A N D
OPTICS
The
Laser
Transducer
System
is
a
high
accuracy,
high
resolution
measuring system
and
improper
installation
or
use
can
degrade
measurement
accuracy.
An
understanding
of
the
basic
measurement
capabilities
of
the
system
along
with
the
proper
considerations
of
pos-
sible
sources
of
errors
prior
to
installation
of
the
equipment
will
greatly
minimize
problems
both
during
installation
and
during
operation.
There are a wide variety of possible configurations for the laser and optics, but all multiaxis
configurations have four basic parts in common:
a.
A two-frequency laser source (5501A Laser Transducer).
b.
A set of splitting and bending optics (10700 series).
c.
A set of measurement optics (10700 series).
d.
A set of receivers (10780A Receiver).
In addition, an adjustable mount (10710A) is available to facilitate the location and alignment
of the splitting and bending optics and the single beam interferometer. Another adjustable
mount (10711A) is available for the linear interferometer and the plane mirror interferometer.
2.3
FUNDAMENTAL
MEASUREMENT
CONCEPTS
To
explain
some
of
the
basic
measurement
principles
we
will
start
with
a
single
axis
measure-
ment
system
(Figure
2-7).
The
5501A
Laser
Transducer
(laser
head)
is
the
reference
upon
which
all
measurements
are
based.
Also
required
i s
some
type
of
interferometerhetroref
lec-
tor
combination.
This
can
be
the
10702A
Linear
l
nterferometer
and
10703A
Retroreflector;
the
10705A
Single
Beam
l
nterferometer
and
the
10704A
Retroreflector;
or
the
10706A
Plane
Mirror
l
nterferometer
and
a
flat
mirror
(user
supplied)
a s
the
retroreflector.
The
10780A
Receiver
is
the
only
other
component
required
in
the
basic
measurement
system.
The
10780A
Receiver
detects
the
displacement
of
either
the
interferometer
or
retroreflector
with
respect
to each other
and
generates
a
measurement
signal
which
is
sent
to
the
electronics.
There
the
measurement
signal
i s
compared
to
the
reference
signal
generated
by
the
5501A
Laser
Trans-
ducer.
The
comparison
of
the
reference
and
measurement
signals
is
done
by
the
electronics
in
order
to
generate
displacement
information
appropriate
to
the
specific
application.
Refer
to
SECTION
Ill
for
a
description
of
the
various
system
electronics
configurations.
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