Download Chapter 15 Accuracy and Repeatability

Chapter 15 Accuracy and Repeatability
Achieving Optimum System Accuracy and Repeatability
Achieving Optimum System Accuracy and
Repeatability
To achieve the best measurement accuracy and repeatability from a
laser interferometer system in your application:
1. Whenever possible, make the measurements in a tightly-controlled,
stable environment. Also, use the appropriate compensation
methods to correct for atmospheric and material temperature
effects.
2. When designing a machine to use a laser interferometer system,
minimize both deadpath distances and Abbé offsets. If a deadpath
exists on the machine, correct for it during measurements.
3. For each measurement axis, be sure to properly align optical
components during installation to minimize the amount of cosine
error.
4. Use the proper components for the particular application. If
significant changes in environmental conditions are expected, use
automatic compensation and interferometers with minimal
thermal drift.
Additional details are presented below.
Minimizing environmental effects
The relative importance of typical atmospheric effects and material
temperature errors is shown in Figure 15-19. Measurement errors due
to material temperature errors are especially important in many
applications. Ideally, all distance measurements with the laser system
would be made in a temperature-controlled room held at exactly 20°C
(68° F), the standard temperature. Then the machine or part would be
at its “true” size and the wavelength compensation number determined
earlier could be used directly.
15-44
User’s Manual