In AOI optical inspection, 2D video measuring, laser contour detection, X-ray inspection and other optical equipment applications, imaging clarity, measurement repeatability and long-term operational stability are directly determined by the base benchmark. Optical inspection relies on stable optical paths. Tiny base deformation, vibration or flatness deviation will lead to image distortion, focal shift and jumping detection data. As the load-bearing benchmark of the complete optical system, granite air bearing base cannot be selected merely by external dimensions. It is essential to verify multiple core parameters combined with the working principle of optical equipment.
Many equipment manufacturers only focus on overall size and price during selection, ignoring substrate properties, stress status, matching of air bearing structures and environmental adaptability indicators. After delivery and commissioning, the equipment suffers from measurement drift with room temperature fluctuation, air film jitter and long-term precision degradation, greatly reducing the yield of optical inspection. As a professional manufacturer of ultra-precision components worldwide, UNPARALLELED Group (Brand: UNPARALLELED®) serves numerous optical inspection equipment manufacturers and has accumulated abundant practical experience in projects supporting granite air bearing bases for AOI, XRAY and optical profilometers. We recommend that optical equipment manufacturers verify parameters item by item from six dimensions: substrate indicators, geometric accuracy, air bearing unit parameters, stress aging, environmental resistance and installation matching.
Substrate parameters are the first checkpoint for selection, with priority given to density and thermal expansion coefficient. Optical inspection is extremely sensitive to temperature changes. Thermal expansion and contraction of the base material will directly alter the relative position between optical lenses and workpieces under test. It is critical to distinguish granite from marble during selection. Marble contains many mineral impurities with low density and poor thermal stability. It is prone to uneven deformation under temperature fluctuation and is completely unsuitable for high-precision optical inspection scenarios. UNPARALLELED® exclusive black granite features dense and uniform crystal structure, stable density and excellent thermal expansion performance, which can minimize benchmark deformation caused by temperature gradients. Meanwhile, confirm whether the substrate has undergone multiple rounds of aging treatment combining natural aging and constant-temperature stress relief to eliminate inherent internal stone stress and prevent slow base deformation after long-term equipment operation, which would trigger optical benchmark drift.
The second set of core selection parameters refers to geometric accuracy indicators that must match the inspection grade of optical equipment. Optical inspection equipment imposes far stricter requirements on working surface flatness, straightness and parallelism than ordinary mechanical processing platforms. Instead of only checking static factory precision, confirm the international metrology standards adopted for accuracy evaluation, such as DIN, ASME and JIS. Apart from working surface flatness, base thickness and rigidity matching cannot be overlooked. Thin bases lack sufficient self-weight and tend to produce micro-deflection under air bearing thrust or workpiece load, tilting the optical imaging plane. When designing air bearing bases dedicated to optical equipment, UNPARALLELED Group optimizes section thickness and internal rib layout to control deflection at sub-micron levels under rated load. Position tolerance of threaded holes, dowel pin holes and installation reference surfaces on the base also needs verification, as hole deviation will impair the coaxiality of assembled optical modules.
Third, supporting parameters of air bearing units are what differentiate air bearing bases from ordinary granite surface plates. During selection, confirm air pad layout, load capacity of single air pad, recommended air supply pressure and air film thickness. Optical inspection equipment mostly requires smooth movement without crawling. The air film thickness must stay within a stable micron range, and air pads should be evenly arranged to cover stressed areas of the base and avoid tilting caused by insufficient local load capacity. In addition, check the internal airway machining quality of the base; airway inner walls should be smooth and free of sand holes to prevent air film jitter induced by pressure fluctuation during gas supply. The air pressure window and gas consumption must also match the equipment's own gas source system. UNPARALLELED® can customize airway and air pad layout according to the travel range of optical equipment and the weight of optical modules. Even with minor pressure fluctuations of the gas source, stable air film can be maintained to avoid image noise and distorted edge detection.
Fourth, environmental adaptability parameters to fit actual working conditions in optical workshops. Although optical inspection workshops are usually air-conditioned, diurnal temperature differences and local temperature rise generated by equipment heat still exist. Pay close attention to the allowable operating temperature range of the base and its deformation rate under temperature variation. For equipment requiring long continuous online inspection, evaluate the precision drift of the base after 8 consecutive hours of operation. Vibration attenuation capacity is also critical, as optical inspection is highly sensitive to micro-vibration from the ground. Drawing on years of R&D experience in constant-temperature and vibration-isolated workshops at UNPARALLELED Group, we assess the damping characteristics of the base in the design phase. Vibration isolation structures can be equipped if needed to block vibration transmitted from workshop production lines, air compressors and surrounding machine tools, preventing vibration from reaching optical lenses and blurring images.
Fifth, load and dynamic working condition parameters. Load calculation should not only rely on workpiece weight. It is necessary to sum the total static load of all upper assemblies including optical modules, linear motors, sliding tables and cables, and reserve allowance for dynamic impact. The rated load and overload threshold of the air bearing base must be clearly defined. High-speed optical scanning equipment with frequent start-stop cycles generates dynamic inertial force. It is required to verify the deformation indicators of the base under dynamic load to avoid instantaneous benchmark offset during high-speed scanning and inconsistent continuous inspection data. Engineers from UNPARALLELED® will evaluate the dynamic load curve of the whole optical system in advance and recommend appropriate base specifications for customers. 
Last but not least, metrology traceability and factory inspection parameters. High-precision optical inspection equipment requires regular calibration, and the base serves as a reference component, so factory inspection data is critical. Confirm all inspection items of the base are completed with traceable measuring instruments and accompanied by valid calibration certificates, covering key indicators including flatness, parallelism and roughness. All measuring instruments of UNPARALLELED Group are traceable to national metrology institutes. Precision machining is completed by senior lapping craftsmen. The manually lapped surface quality directly ensures uniform and stable air film and extends the service life of air pads.
Beyond parameter selection, pay attention to post-delivery supporting services such as pre-placement commissioning and installation leveling of the base inside constant-temperature workshops. An optical inspection system is an integrated optical, mechanical and electrical solution. The granite air bearing base is not an independent component; all its parameters must coordinate with optical modules, motion platforms and gas source systems. UNPARALLELED® maintains continuous project cooperation with many optical equipment enterprises and research institutes, delivering customized granite air bearing base solutions for AOI, video measuring, XRAY inspection and other scenarios.
In summary, purchasing granite air bearing bases for optical inspection equipment cannot be done simply by size. Substrate thermal stability, geometric accuracy, air bearing unit parameters, load rigidity, anti-vibration and temperature drift indicators, and metrology traceability certificates need to be evaluated one by one. A properly selected granite air bearing base can stabilize the benchmark of optical inspection, reduce imaging errors caused by temperature and vibration, and guarantee reliable long-term inspection data for AOI, video measuring, laser inspection and other equipment.