Unplanned downtime of lifting equipment is costly – it stops production, increases risk and accelerates wear. Predictive maintenance turns reactive repairs into planned interventions by constantly monitoring the „health“ of the mechanics and electrical drives: vibrations, temperature, current peaks, cycles and loads.

What we observe and why

Vibration (ISO frequency bands): bearing defects, misalignment, imbalance, loose connections, worn gears.
Temperature: overheating of motors/gearboxes/brakes; load and environmental trends.
Electrical parameters: current, voltage, distortion, inrush peaks – indicator for mechanical load and profile setting.
Operational metrics: number of lifts, ton-meters, time in different modes, brake counter, overloads.

Sensors and architecture

Vibration sensors: accelerometers (ICP/IEPE) on motor and gearbox bearings; measurement points on X/Y/Z axes, fixed bases.
Temperature: built-in Pt100/thermistors in windings and bearings, infrared points for housings and brakes.
Current sensors: current clamps/inverter modules; log for starts, peaks and stops.
Gateway/IIoT: local collection (edge) + periodic upload; buffer in case of no connectivity; secure access for diagnostics.

Analytics: from data to solutions

Spectral analysis (FFT): unbalance (1×RPM), misalignment (2×RPM), bearing defects (BPFO/BPFI), gears (mesh frequency).
Trend lines: „A “slow” degradation is more valuable than a one-time peak – use moving averages and trend slope alarms.
Temperature profiles: corrected for ambient temperature; alarms by absolute value and by ΔT relative to baseline.
Event correlation: associate vibration/temp. with a specific route/load/operator mode; remove „false“ alarms.

Alarm thresholds and logic

Static thresholds: ISO 10816/20816 for general vibration; temperature limits from manufacturer.
Dynamic thresholds: speed/load thresholds (heavier load → lower speed/acceleration limit); seasonal/environmental adjustments.
Alarm levels:
- Warning – increased vibration or ΔT; schedule an inspection.
- Action – critical trend reached; prepare parts/time window.
- Shutdown (safety interlock) – protective shutdown at dangerous values (e.g. brake overheating).
HMI/notifications: clear messages "where/what/what to do", not just codes; email/mobile push notifications for Action/Shutdown.

Implementation plan (phased)

Baseline: single spectrum and thermal profile at nominal modes; cycle/load recording.
Pilot of a mechanism: lifting motor and main gearbox; sampling frequency and thresholds adjustment.
Fine tuning: filtering of structural resonances, masks for specific speeds/positions, alarm adaptation.
Procedures: checklist "what we do in case of Warning/Action"; response time and responsible persons.
Scaling: adding axles (bogie/axle), brakes, energy measurement; uniform mounting points and labels.

Condition-based routine maintenance

Bearings/gearboxes: lubrication by condition (temp./vibration), not just by calendar; oil analysis (ferrowear, water).
Brakes: operation counter, pad/coil temp., electric brake adjustment for gentle operation.
Ropes/Chains: correlation of vibration peaks with wear; view of Action alarms.
Electric drive: review of start-up profiles (S-curves/jerk) to reduce shocks and peaks.

KPIs for a predictive program

Unplanned downtime (h/month) and share of total stay.
MTBF/MTTR by mechanism (lift/trolley/bridge).
Share of interventions "by condition"„ against "emergency" (target: >70% by condition).
Average vibration amplitude and ΔT compared to baseline.
kWh/cycle and peak currents (an indirect measure of smoothness and profile tuning).

The Bulgarian context: practical notes

Mixed park and different ages: Start with the critical taps; full coverage is not necessary from day one.
Environment (dust/temperature): IP65 industrial housings, shielded cables, fastenings with protection against vibration loosening.
Resources: train 1–2 „champions“ for basic measurements and spectrum reading; external expertise for complex cases.

Final accent

Predictive maintenance is an investment in predictability: early warning, reduced risk of sudden failures and better planning of parts and service windows. The combination of vibration analysis, temperature monitoring and sensible alarm thresholds extends the life of mechanisms, stabilizes the cycle and reduces the total cost of ownership.

The most important thing is discipline: uniform measurement points, consistent intervals, and short KPI reviews. This way, the „health“ of the cranes becomes visible, and decisions are timely and data-based.