HP 5528A User Manual

Model 5528A
Distance Measurements
6-26
Misalignment Between Machine Travel Axis and Laser Measurement
Axis (Cosine Error)
Description
If the Laser beam's path doesn't duplicate the machine's travel path you won't be measuring the
actual
path, but" path offset by some angle. The resulting error is called "Cosine Error" and
depends on the true path length and the cosine of the offset angle. (See Figure 6-13)
Minimizing Effects
Cosine error is reduced by making the Laser beam parallel to the Optics' travel path. Parallelism is
Indicated by the absence of motion between the return dots from I he Int erferometer Assembly
and the Retroreflector al the laser H ead's bottom port, as the Optics are moved along the
measurement axis .
The " OVERLAPPING DOTS" alignment method. described in Section 15 of this User's Guide.
describes how to minimize
Ihe mol ion between the return dots and, therefore, minimize the
cosine error.
In special sha ri -distance. high-accuracy, measurement situalion s. lack of motion betwccn the
return dots is not a stro ng enough assurance of minimal cosine error. In these cases, you should use
the
"Maximum Measurement Reading" technique. described in Section lS, to reduce cosine error
to
CI negligible level.
LASER
BEAM
-1 r- LASER WAVELENGTH
~'i-"
~~t'
,~'i-
p'
.. d' II
I "' , I III
, I I I", LASER BEAM DIRECTION p"
Figure 6-13. Cosine Error

HP 5528A Specifications

General

Brand	HP
Model	5528A
Category	Measuring Instruments
Language	English