TL;DR
Linear scale errors cause systematic dimensional errors on all measured features. Clean the scale reader heads and verify the scale strip is free of oil film before concluding a scale or encoder failure.
What you might see
- all measurements on one axis shifted by a consistent offset
- length measurement error on a calibration artifact
- encoder position jumps on slow axis motion
- CMM performance qualification fails on the affected axis
Likely causes
Scale reader head contaminated with oil aerosol or dust from the measuring environment
Scale strip thermal expansion from inconsistent room temperature causing apparent length error
Reader head gap changed from vibration or mechanical contact
Scale strip physically damaged or scratched in one area
Required tools
- Lint-free cloths and isopropyl alcohol
- Calibrated length reference artifact (gauge block or ball bar)
- CMM room thermometer
Safety first
- Do not touch the linear scale strip with bare hands. Fingerprint contamination causes reading errors.
- Do not attempt to realign the reader head without OEM guidance. Incorrect gap spacing causes irreversible scale damage.
Procedure
- 1
Confirm the CMM room temperature is stable and within the Zeiss specification before measuring or diagnosing a scale error. Thermal errors mimic scale errors.[1]
- 2
Locate the scale reader head for the affected axis according to the CMM service documentation. Inspect it for visible contamination.[1]
- 3
Clean the reader head window with a lint-free cloth moistened with isopropyl alcohol. Do not touch the scale strip with the cloth.
- 4
Inspect the scale strip for any oil film, fingerprints, or physical damage over the full axis travel length.
- 5
After cleaning, run the CMM performance qualification routine and compare the results to the previous record.
- 6
If the error persists after cleaning and is confined to one region of the axis, suspect a physical scratch or chip on the scale strip in that region. Contact Zeiss service for scale strip inspection and replacement.
Sources
Zeiss Zeiss CONTURA / PRISMO Coordinate Measuring Machine (CMM) general technical documentation, Zeiss
Zeiss CONTURA / PRISMO CMM maintenance documentation, linear scale maintenance and performance qualification (general)
More guides for Zeiss Zeiss CONTURA / PRISMO
How to diagnose air bearing contamination on a Zeiss CONTURA / PRISMO CMM
CMM air bearing contamination causes drag, axis sticking, or erratic motion. Verify the compressed air supply is clean and dry, and check the air filtration before suspecting internal bearing damage.
How to fix probe qualification failure on a Zeiss CONTURA / PRISMO CMM
Probe qualification failure means the CMM cannot establish a reliable stylus reference and should not be used for inspection until resolved. Clean the reference sphere and inspect the stylus before re-qualifying.
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