Servo Says Homed but the Machine Zero Is Wrong? Check the Reference Chain
A homed status indicates that the configured referencing operation completed under its rules. It does not independently prove that machine zero is physically correct. Compare the reference sensor, encoder event, offset, and coordinate definition before adjusting production positions.
Original reference-chain example; homing and position validation are machine-specific.
What is happening?
Homing establishes a relationship between feedback and the machine coordinate system through a configured method. Active, passive, switch, marker, and immediate reference operations have different meanings. An incorrect offset or reference event can produce a repeatable but wrong zero.
Check these five things
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Record the axis type, homing method, offset, and accepted commissioning configuration.
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Identify the physical reference event and compare it with the configured switch or feedback source.
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Review any position redefinition performed after homing by application logic.
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Use the approved controlled homing procedure and measure the resulting reference position.
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Test repeatability from the allowed starting conditions and record deviations.
Worked example
A training axis repeats its home sequence consistently, but a copied offset shifts machine zero by 20 millimeters. Repeating homing does not remove the offset because the sequence is applying it as configured.
Quick diagnostic reference
| Layer | Evidence |
|---|---|
| Reference event | Correct physical switch or marker |
| Offset | Approved coordinate relationship |
| Application | No unintended later redefinition |
The mistake to avoid
Do not compensate every recipe position for a wrong home reference. That spreads the same coordinate error through the application.
How to verify the fix
Confirm machine zero against the approved physical reference and verify relevant limits and positions after any accepted correction.
Field-work boundary: These are educational diagnostic guides. Use the exact equipment manuals and approved site procedures. Electrical testing and machinery changes belong to qualified, authorized personnel; control hazardous energy and validate affected functions before release.
Technical reference
Rockwell Automation: Motion Axis Home. The examples and diagnostic tables above are original teaching material; they do not replace the product manual.