LGDiMaggio Gear Fault Diagnosis
Detect gear faults through spectral analysis of vibration signals, focusing on gear mesh frequency (GMF) harmonics, sidebands, and modulation patterns. This workflow supports expert judgment — it never replaces it.
Prerequisite: The predictive-maintenance-mcp MCP server must be connected.
Background
Gear faults produce characteristic vibration patterns:
- Gear Mesh Frequency (GMF) = number_of_teeth x shaft_RPM / 60
- Healthy gears show GMF and low-level harmonics
- Faulty gears show increased GMF harmonics, sidebands spaced at the shaft frequency, and broadband noise
Workflow
Step 1 — Signal Selection and Parameters
Load the signal with load_signal(filepath="gearbox_run1.csv", signal_unit="g")
or pick a loaded one from list_signals(scope="memory"). Verify sampling rate
and metadata with get_signal_info(signal_id="<id>"). For raw binary files
(.bin/.raw/.dat), also declare sample_format and sampling_rate (or
provide a companion <stem>_metadata.json) — see the signal-management skill.
Gather from the user (do NOT guess):
- Shaft RPM (or shaft frequency in Hz)
- Number of teeth on the gear of interest
- Gear ratio (if analyzing a gear pair)
Calculate:
- GMF = teeth x RPM / 60
- Shaft frequency = RPM / 60
Step 2 — Statistical Screening
Call analyze_statistics(signal_id="<id>").
Gear fault indicators (screening only, never diagnostic alone):
- Kurtosis > 3: impulsive content (possible tooth damage)
- Crest Factor > 5: localized damage
- RMS increase: overall vibration energy rise
Step 3 — FFT Analysis
Call analyze_fft(signal_id="<id>").
Inspect the spectrum for:
| Pattern | Indicates |
|---|---|
| GMF with low harmonics, no sidebands | Normal gear operation |
| Increased GMF harmonics (2x, 3x, 4x GMF) | Gear wear or misalignment |
| Sidebands around GMF at shaft frequency spacing | Localized tooth damage |
| Broadband noise increase | Advanced wear or pitting |
| Ghost frequencies (non-harmonic peaks) | Manufacturing defects |
Systematic check of the expected GMF against the envelope spectrum:
Call check_bearing_faults(signal_id="<id>", rpm=1500, frequencies={"GMF": 800.0})
(The frequencies route accepts any labeled frequency — it is the
out-of-catalog / gearbox path.)
Step 4 — Envelope Analysis (for Modulation)
Call analyze_envelope(signal_id="<id>", filter_low=500, filter_high=5000).
Center the demodulation band around GMF or its harmonics (keep it below Nyquist) to extract amplitude modulation. Sidebands in the envelope spectrum at shaft-frequency spacing corroborate gear fault modulation.
Step 5 — Advanced Spectral Analysis
Call compute_spectrogram_stft(signal_id="<id>") to check for time-varying
patterns — localized tooth damage shows periodic energy bursts at the shaft
rotation rate.
Call compute_power_spectral_density(signal_id="<id>") for a smoothed
spectral view that highlights persistent gear-mesh patterns.
Step 6 — ISO Severity Context
Call assess_severity(signal_id="<id>", machine_group=2, support_type="rigid").
Report the zone (A/B/C/D) and urgency. The verdict requires a DECLARED signal
unit — if refused, confirm the unit with the user and re-load with
load_signal(filepath="<file>", signal_unit="mm/s", overwrite=True).
Step 7 — Diagnosis Summary
Classification rule (choose exactly one, cite the evidence):
- Gear tooth fault — strong evidence: GMF harmonics present AND at least one clear sideband pair spaced at the shaft frequency AND a supporting statistic (Kurtosis > 3 or CF > 4)
- Possible localized tooth damage: partial sidebands or ambiguous spacing — list the missing evidence needed for confirmation
- Uniform wear / increased load: elevated GMF amplitude WITHOUT sidebands and normal impulsiveness
Each conclusion MUST cite: tools used, specific peaks (frequency and magnitude), sideband spacing vs the expected shaft frequency, and supporting statistics.
Step 8 — Report Generation
Call generate_fft_report(signal_id="<id>", max_freq=5000, num_peaks=15, rpm=1500)
and optionally generate_diagnostic_report_docx(signal_id="<id>", sections={"summary": "..."}).
Important Notes
- GMF calculation requires an accurate tooth count and RPM — ask, never assume
- Multi-stage gearboxes: analyze each stage separately
- Gear and bearing faults can coexist; if bearing frequencies also appear, recommend the bearing-diagnosis skill as well
- Use cautious language for all diagnoses; the final call rests with a qualified engineer
- All processing is local — no data leaves the machine