Observed failure mode
Installed problem statement
Reported angle drift originated in the encoder mounting stack rather than the control loop because the cover-mounted sensing reference moved relative to the bearing-supported output under heat.
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Encoder datum review summary
Output-angle drift traced to encoder stack alignment and thermal movement at the cover interface
Engineering response
Corrective design move
The encoder reference was re-tied to the bearing-supported structure, spacer growth was reviewed, and thermal drift was separated from backlash and servo tuning effects.
Review inputs
Thermal-soak repeatability data before and after service access.
Encoder-carrier support geometry, spacer stack, and cover-interface motion.
Evidence separating drivetrain backlash from sensing-reference movement.
Expected outputs
Sensor datum relocation strategy tied to the bearing-supported structure.
Thermal-soak verification plan for repeatability and service access.
Interface map showing where sensing-reference motion enters the stack.
Engineering interventions
Separated encoder-reference motion from drivetrain motion by tracing every interface between the sensor carrier and the output datum.
Revised the carrier support so the measurement reference followed the bearing-controlled structure rather than the thermally active cover.
Added thermal-soak verification with angle repeatability checks before and after service removal.
Critical watch items
Cover-mounted sensor references moving independently from the output datum.
Spacer growth reintroducing drift after reassembly.
Controls debugging masking a mechanical sensing-stack problem.
| Review dimension | Observed result |
|---|---|
| Primary failure mode | Encoder reference drift under thermal growth |
| Critical change | Sensor datum moved to bearing-supported structure |
| Verification effect | Repeatability stabilized across thermal soak and service access |
Design lessons
Apparent control drift can originate in the measurement stack when the sensor datum is not tied to the controlled output structure.
Thermal behavior must be reviewed across covers, spacers, and support members, not only the drivetrain core.
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