Kinematic Mount Selection for Optical Scanning Assemblies
Kinematic mount selection for optical scanning assemblies isolates substrates from thermal and dynamic distortions while maintaining sub-microradian repeatability.
Thermal Expansion Matching
Meaning
Coordination of material properties within an assembly prevents mechanical stress and misalignment during temperature changes. Thermal expansion matching involves choosing components with identical or complementary coefficients of thermal expansion to maintain critical dimensions. This practice is essential for optical systems where even a few microns of shift can cause a loss of focus.
Material Selection
Bonding a glass lens to a metal mount requires an adhesive or a mechanical interface that can absorb the difference in growth rates. Using invar or other low expansion alloys for the structure provides a stable platform for sensitive components. Effective thermal expansion matching reduces the need for active cooling or complex athermalization designs.
Interface Stress
Differences in expansion rates create significant forces at the mounting points of a rigid assembly. These stresses can cause the optical elements to warp or the structural bonds to fail over time. Proper design ensures that the parts can expand and contract without losing their relative alignment.
Operational Verification
Systems are cycled through the expected temperature range of the factory floor to ensure they remain within tolerance. If the thermal expansion matching is poor, the device will require frequent recalibration as the seasons change. The cost of failing this requirement is a significant increase in the total cost of ownership for the end user.