Laser Interferometer Inspection of Granite Platform Flatness: Easy-to-Understand Principles
I. Core Principle
Utilizing the extremely high stability of laser wavelength, it precisely calculates the deviation of height undulations at every point on the platform through changes in interference fringes caused by optical path differences, and three-dimensionally fits the true flatness.
The laser wavelength itself serves as a natural benchmark ruler at the micron and nanometer level, unaffected by temperature or human reading errors.
II. Simple Working Process
The laser transmitter emits a single-frequency, stabilized laser beam. One beam is directed towards a fixed reference mirror, while the other is directed towards a moving mirror placed on the granite platform.
The mirror moves with the bridge along the longitudinal, transverse, and diagonal lines of the platform.
Where the platform is high or low → the mirror tilts up or down.
The two laser beams converge to produce changes in bright and dark interference fringes.
The instrument automatically converts: fringe change quantity → vertical height difference.
III. How is Flatness Calculated?
Following a grid path: scanning the entire table surface row by row along the longitudinal, transverse, and two diagonal lines.
Collecting the height coordinate Z value at every point.
The software uses the least squares method to fit an ideal standard plane.
Highest measured point – Lowest measured point
= Granite platform flatness error
IV. Other Precisions Measurable Simultaneously
Прямолинейность
Planar distortion (warping)
Perpendicularity (granite right-angle reference surface)
Параллелизм
Positional tolerance of holes, straightness of guides
V. Advantages of Laser Interferometer Compared to Spirit Level
Higher precision: up to 0.001μm level
Unaffected by bridge length or human reading errors
No cumulative error on long tables
Directly outputs a 3D error cloud map, making high and low spots immediately visible
Long-term traceability to national length standards in a constant temperature environment, arbitration-level precision
VI. One-sentence Summary
Laser Interferometer = using light as a ruler to precisely measure the height difference at every point on the granite surface, fitting the entire plane through a computer to calculate the true, high-precision flatness error.
