Drive complaints sound alike – rough ride, wrong levelling, noise, tripping on acceleration – but the cause is usually mechanical, electrical or a mismatch between the two. Knowing which machine type you are standing in front of removes most of the guesswork.
Machine types
| Type | Character | Typical faults |
|---|---|---|
| Geared traction (worm or helical) | Motor runs fast, gearbox reduces to the sheave | Oil leaks and level, bearing noise under load, worn worm, sheave groove wear |
| Gearless permanent magnet | Low-speed, high-torque, compact machine room or MRL | Brake pick-up, encoder coupling runout, magnet temperature limits, drive parameter mismatch |
| Hydraulic | Jack, pump and valve; no counterweight | Oil temperature, jack seal weep, valve drift, pump coupling and starter faults |
| Drum / winding drum (legacy) | Rope wound on a drum | Rope spooling, drum wear, outdated safety devices |
Control of the motor
- VVVF (inverter): the drive controls torque and speed directly and expects accurate feedback. Symptoms point at the drive only after feedback is proven good.
- Resistor / two-speed AC or DC: contactors, resistors and a motor with a known slip. Symptoms point at contacts, resistor banks and motor windings.
- Soft starter on hydraulic: acceleration is set electronically; a sagging supply looks exactly like a bad starter.
The four measurements that separate drive from mechanics
- Current per phase under load. An unbalanced or high phase current on a smooth-running car points at the motor or supply, not the gearbox.
- Encoder feedback vs actual travel. If the drive sees movement that does not match the car, the fault is feedback, coupling or slip – not the control algorithm.
- Brake timing and gap. Late brake pick-up causes roll-back and rough starts; a dragging brake causes heat, noise and levelling drift.
- Temperature after a duty cycle. Hot-only faults in hydraulic units are almost always oil or valve related; hot-only faults in traction units point at the brake or the machine bearings.
Noise: reading it correctly
Noise that follows car speed but not direction is usually machine or sheave related. Noise that appears only in one direction is often rope or guide related. Noise that appears only at one landing is neither – look at the rail joints and the door equipment at that landing.
Parameters are not portable. Drive parameter sets are specific to machine, encoder, rope ratio and car weight. Copying a “known good” set between units of the same model is a common cause of rough running and nuisance faults.
See also control systems for feedback types, and forum threads on drive faults.