The machine qualification product portfolio of IBS Precision Engineering includes the Spindle Error Analyzer (SEA), a system designed to measure and analyse the dynamic and thermal error motions of high-precision spindles. The SEA enables detailed characterisation of spindle behaviour under realistic operating conditions, supporting both machine qualification and process optimisation.
The SEA configuration consists of three displacement sensors that measure the radial (X/Y) and axial (Z) error motions of a target mounted on the rotating spindle. When the target geometrical error is significantly smaller than the spindle error motion, the measured variation can be reliably attributed to the spindle, making the SEA highly effective for machine qualification, condition monitoring and performance verification.
Advances in spindle technology have significantly reduced error motion levels in specific high-accuracy spindle applications. In high-precision manufacturing with e.g. high-quality bearings and improved thermal and structural stability, the typical error motion averages about 1–3 µm. In ultra-precision machining with e.g. air bearings and metrology spindles, the typical spindle error motion is <0.1 µm.
At these levels of precision, the relationship between spindle error motion and target form error changes. The target geometrical error is no longer negligible and becomes a significant component in the measurement, contributing directly to the overall uncertainty. As the error magnitudes grow closer, the need to distinguish between the individual contributions of spindle motion and target geometry increases.
For ultra-precision applications requiring deeper analysis, IBS Precision Engineering developed the Multi-Probe Analyzer (MPA) extension kit. Designed for spindles with error motions of 500 nm and below, the MPA separates target geometry from the measurement, revealing true spindle performance at nanometer level.
The Multi-Probe Analyzer (MPA) is an extension-kit for the SEA system. The key innovation is the implementation of the multi-probe method, enabling separation of spindle error motion and target geometrical error within the measured signal. This allows accurate spindle characterisation, when both contributions are approaching the same order of magnitude.
The MPA uses the same probe nest base, sensors and measurement software as the SEA plus a further MPA app. The system operates with three displacement sensors mounted in the MPA ring around the rotating target at optimised angular positions. These sensor positions make it possible to separate the target geometrical errors from the spindle error motion.
Although the hardware, software and measurement setup are largely shared with the SEA, the underlying data analysis approach is fundamentally different. By processing the measurement data in the MPA software, the individual contributions of spindle error motion and target geometry can be separated. This enables reliable extraction of harmonic content up to 150 UPR, well beyond the range typically encountered in practical spindle applications.
By combining multi-probe measurement with advanced signal processing, the MPA provides several key advantages:
This enables precise characterisation of ultra-precision spindle performance under realistic operating conditions. The separated MPA data can subsequently be imported back into the Spindle Error Analyzer software for further in-depth spindle analysis.
A typical SEA measurement uses two probes in the same plane, positioned 90° around the target. This results in a combined error of spindle and target, meaning the observed behavior does not represent the true spindle behavior.
By placing three probes in the same plane at optimised angles, spindle error motion can be separated from the target error. Harmonic content up to 150 UPR can be extracted.
The separated signal from the spindle and target reveal the significant impact of target errors to the measured error. This means in our example above, SEA measures 238 nm of spindle error, MPA reveals a true spindle error of 202 nm.
Multi-probe error separation enables independent determination of target geometry and spindle error motion from a single measurement. As spindle technologies advance, this method provides a robust way to maintain measurement accuracy in ultra-precision machine environments.
Read more: MPA webpage