4. DESIGNING THE FIXTURES
・ Size of reference pins
L
φD
The diameter of the reference pin should be such
that it can block the laser beam by more than 2
mm and the beam will not cross the pin. A pin of
about 10 mm diameter would meet such a
requirement.
The setup must also be fairly robust so that the
gap between the reference pins will not change
while in service.
(2) Parallelism adjustment
Set up two measuring units integrating the emission unit and the reception unit so
that the parallelism of the two measuring units can be adjusted.
First align the optical axis of each measuring unit, then adjust the parallelism
between the two measuring units.
If the parallelism adjustment is inadequate, errors will generate when the
workpiece is shifted in the optical axis direction.
The degree of accuracy to which the adjustment should be made depends on user
requirements. For reference, three example accuracy ranges are given below:
a. Should be ±20 to ±50 μm with the gage shifted within ±50 mm from the
measuring point.
b. Should be ±5 to ±10 μm with the gage shifted within ±10 mm from the
measuring point.
c. Should be ±5 to ±10 μm with the gage shifted within ±5 mm from the
measuring point.
Generally, the larger the amount of shift of the gage, the easier will be the
adjustment.
The most appropriate size of the gage would be the median value of the
measuring range.
Measuring position
Gage shift
Gage shift
direction
direction
Reception unit
Emission unit
Reception unit
Emission unit
No. 99MCA094A
4-9
