CASE STUDY
Precision Motion for X-Ray Mirror Metrology With
OAV Air Bearings
NSRRC researchers developed a multi-axis white light interferometer stitching stage using OAV Air Bearings to achieve micron-level linear positioning and precise angular control for X-ray mirror metrology.
CUSTOMER
NSRRC
INDUSTRY
Research & Academics
APPLICATION
X-Ray Mirror Metrology
PRODUCTS USED
Open Block, Thrust, and Flat Bearings
BENEFIT
Frictionless Precision Motion
THE CHALLENGE
Measuring the surface figure of X-ray mirrors requires extremely precise positioning. At the National Synchrotron Radiation Research Center (NSRRC) in Taiwan, researchers developed a white light interferometer stitching measurement system capable of capturing multiple high-resolution surface images and combining them to evaluate large X-ray mirrors.
The measurement stage needed to accommodate mirrors up to 1200 mm in length while providing precise motion across multiple linear and rotational axes. The X-axis required 1200 mm of travel, the Y-axis 390 mm, and the measurement head 390 mm of Z-axis travel. The system also required ±1.5° of rotation about both the X- and Y-axes to support the measurement of curved mirror geometries such as toroidal mirrors.
Maintaining positioning accuracy across these ranges was critical. The interferometer used in the system provided approximately 8.69 µm spatial resolution per pixel with its 1X objective. To reliably stitch individual measurements together, the motion platform therefore needed positioning performance substantially finer than the imaging resolution while maintaining precise, repeatable motion across the measurement area.
THE SOLUTION
To provide precision linear guidance across the large measurement area, the NSRRC team incorporated OAV Air Bearings throughout the multi-axis stage. The X-axis used three 25 mm diameter stainless steel shafts supported by twelve OAV 25 mm open-pillow block air bearings, while the Y-axis used four 25 mm diameter stainless steel shafts supported by eight additional OAV 25 mm open-pillow block air bearings.
Combined with high-precision optical encoders and linear scales, the system provided linear scale accuracy of ±1 µm over distances up to 1 m, with encoder resolution reaching 50 nm. The X- and Y-axis drive systems provided motion increments of 0.8 µm and 0.4 µm per motor step, respectively—supporting positioning performance finer than the approximately 8.69 µm spatial resolution per pixel of the interferometer.
Precision rotational motion required additional OAV Air Bearing configurations. For X-axis tilt, the researchers used two OAV 60 × 20 mm 3-way frictionless ID thrust air bushings operating on 20 mm diameter stainless steel shafts. A wedge-driven mechanism provided ±1.5° of X-axis tilt, while the optical encoders measurd the angular position.
Figure 1. Multi-axis white light interferometer stitching measurement stage for X-ray mirror measurement.
The Y-axis rotation system used an OAV 150 × 75 mm 3-way frictionless ID thrust air bushing together with four OAVF20L40 flat air bearings. The thrust air bushing provided the push force on the rotation plate while the flat air bearings provided the opposing pull force, maintaining precise positioning throughout rotation. Together with the optical encoder system, the rotational stages achieved an angular measurement accuracy of 2.87 × 10⁻³ degrees across a ±1.5° range.
By combining the open-pillow block air bearings for long-travel linear guidance with thrust and flat air bearings for rotational control, the researchers created a multi-axis motion platform capable of supporting the precise positioning required for white light interferometer stitching of X-ray mirror surfaces.
Figure 2: The mechanical design of the rotation X-axis stage. The 3-way frictionless ID OAV thrust air bushings and optical encoders to measurement tilt degree in X-axis.
Figure 3. Y-axis rotation stage using an OAV 3-way thrust air bushing and flat air bearings to provide opposing push and pull forces during precision rotation.
THE RESULTS
The completed stage design achieved the positioning performance required for white light interferometer stitching of X-ray mirror surfaces. Linear scale accuracy reached ±1 µm over distances up to 1 m, while the optical encoder system provided resolution down to 50 nm. The X- and Y-axis positioning performance was therefore finer than the approximately 8.69 µm spatial resolution per pixel of the interferometer used in the study.
For curved-mirror measurements, the two rotational axes provide ±1.5° of travel with angular accuracy reaching 2.87 × 10⁻³ degrees. By integrating OAV Air Bearings throughout both the linear and rotational stages, the researchers created the precision motion architecture needed to support multi-position image acquisition and stitching.
±1 µm linear scale accuracy over distances up to 1 m
50 nm optical encoder resolution
±1.5° rotational measurement range
2.87 × 10⁻³° angular accuracy
With positioning performance finer than the approximately 8.69 µm spatial resolution per pixel of the interferometer, the stage provided the motion control required to capture and align multiple surface measurements for stitching. The combination of the OAV open-pillow block, thrust air bushings, and flat air bearings supported precision linear and rotational motion across the multi-axis platform used for advanced X-ray mirror metrology.
REFERENCES
Ming-Ying Hsu et al. (2025). The White Light Interferometer Stitching Measurement Stage Design for the X-Ray Mirror. Journal of Physics: Conference Series, 3010, 012088. DOI: 10.1088/1742-6596/3010/1/012088