HP 5528A User Manual

Model 5528A
Velocity Measurements
7-8
Misalignment Between Machine Travel Axis and
Laser Measurement Axis
D esc ription
If the laser beam's path doesn't dup licate the ma chine's travel pilth, you won' t be mea suring the
aQual Velocity, but a Velocity that is slightly les~ . ( See "C OS I NE ERROR" material in Section 6, and
Figure 6- 13 .)
Minimizing Effects
The error is reduced by making the l ase r beam parallel to the Optics' travel path. Parallelism is
indicated by the absence of motion between the return dots from the Interferometer Assembly and
the Retroreflector at the Laser Head 's bottom port, as the Op ti cs are moved along the measurement
axi s.
The "OV ERLAPPING DOTS" alignment method, described in Seaion 15 of t hi s User 's Guide,
des cribes how 10 minimize the motion between the return dots and, therefore, minimize Ihe cosine
error.
Uncompensated Measurement Path Length (Dead path Error)
D es cription
This is a complication of the " Velocity- at-light " error.
Compensation for velocity- of- light error is applied only in proportion to the di st anc e measu red.
The error, however. exists over the whole path between the Optics, including those pa rts not
measured. Any lime the laser Measurement System is reset with some distance existing between
the optics, the length of the " open" distance will be uncompensated, and will result in an error. The
name for th is kind of error is "Oeadpath Error".
Minimizing Effects
To minimize the amount of Ihis error, Ihe on ly time you should reset the Laser Measurement System
is when the Opti cs are as dose together ilS possibl e.
The only way this error can be eliminated is to reset the Laser Measurement Sys tem when theoptics
(not their bases ) ilre aaually touc hins . For most app lications, r ese lling when the optics are within
five centimet res (2 Inches) will be enough to nullify the error.

HP 5528A Specifications

General

Brand	HP
Model	5528A
Category	Measuring Instruments
Language	English