By Dovydas Kersys · Chapter 56 of 58 in Machine Commissioning.
Before you begin: Follow the machine documentation, risk assessment, site procedures and lockout/tagout requirements. Commissioning can expose personnel to electrical energy, stored pressure and unexpected motion. Never defeat a safety function merely to make a test easier. Examples and diagrams are generic and must be checked against the actual machine.
Symptom
A servo axis oscillates around position as soon as it is enabled.
Diagnostic approach
The team considers reducing gains, but commissioning rules say to prove mechanics and feedback direction first.
What the team found
A small manual rotation shows encoder position changes in the opposite sign expected by the drive configuration. The feedback orientation parameter is corrected, the axis is retested with conservative gains, and only then is tuning performed.
Commissioning lesson
Never tune around incorrect feedback polarity.
Use the same layered isolation method even when the symptom seems to point at software.
FIELD RULE: Preserve evidence before making changes: values, states, diagnostics, timestamps and the exact machine condition.
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Adapted from Machine Commissioning for Maintenance and Automation Technicians, by Dovydas Kersys. © 2026 Dovydas Kersys. Featured cover image is an AI-generated editorial illustration.