The document discusses using a laser micrometer to measure dimensional changes in clear polymer contact lens samples while they are submerged in saline solution during testing. The laser micrometer can distinguish between the glass enclosure, saline solution, and polymer samples using multi-segment mode and a programmable threshold. It offers accuracy of 1 micron, resolution of 0.2 microns or better, and a measurement speed of 2300 per second, making it suitable for measuring the challenging target of transparent materials submerged in liquid.

1. A167 en
Laser high-speed micrometer
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Contact lens measurement
In their quest for better materials, Research and Develop-
ment teams at contact lens manufacturers have a need to
conduct various material tests on clear, flexible polymer
samples. The material samples must be submerged du-
ring testing in a saline solution for hydration, as they have
completely different properties in their dry state as in their
hydrated state. The challenge is to find a way to measure
dimensional changes in the samples while stretched, hea-
ted, etc. while inside small hydration enclosures. Since
contact sensors could easily influence the measurements,
a non-contact method is preferable. Also, since the plas-
tic is almost invisible when submerged, most optical mea-
surement technologies would fail in this application. Tra-
ditional thru-beam sensors cannot adequately distinguish
the sample from the surrounding fluid, and vision cameras
are too dependent on external lighting conditions to be
reliable.
Measurement system requirements
The highly sophisticated thru-beam model ODC2600-40 Accuracy: 1 micron target
is uniquely capable of making these dimensional measu- Resolution: 0.2 microns or better
rements with high accuracy and speed. A curtain of LED Target: Must measure dimensions of a clear polymer
light is transmitted across the sample through the walls of strip submerged in saline bath, measured through a glass
the enclosure. The sensor is used in segment mode, easi- enclosure
ly distinguishing between the enclosure walls, saline bath,
and test sample edges. The unique dynamic threshold
feature allows the user to fine tune the sensor such that Reason for System selection:
it sees the polymer sample’s edges with optimum clarity. Multi segment mode and programmable threshold allow
Also, as the threshold setting is adjusted, it functions as a
for accurate measurement of such a challenging target.
calibration of the sensor to the material being tested (the
threshold can be adjusted until the known width value is
Advantages:
displayed.
- Dynamic adjustable threshold
Sensor accuracies of 1 micron are achieved using high - Intelligent multi segment mode
quality telecentric optics and a proprietary, high resolu- - Measures through glass enclosure and clear liquid
tion CCD receiving array. This technology also allows for - High speed helpful in material test applications
measurement at a far higher rate (2300 per second) than
traditional scanning micrometers, allowing for plenty of
horizontal resolution in potentially high-speed tests.
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2. application
Ambient conditions
- Test lab
- Room temperature
System structure
ODC 2600-40
Reasons for the system selection
Multi segment mode and programmable threshold allow
for accurate measurement of such a challenging target.
Technology advantage
- Dynamic adjustable threshold
- Intelligent multi segment mode
- Measures through glass enclosure and clear liquid
- High speed helpful in material test applications
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