Inspection Points for Front-Rear Dual Encoder Signal Faults

In general, an encoder converts changes in motor shaft rotation into electrical signals and transmits them to the controller. Based on these signals, the controller performs speed control, determines position, and controls stopping.

The front-rear dual encoder structure obtains rotational information from both sides of the Traction Machine. Compared with relying on only one encoder signal, it provides more scope for signal comparison and fault detection.

However, a dual structure does not make field inspections simpler. Instead, the wiring condition, mounting condition, and signal quality of both encoders must be checked together for consistency.

D&D has a history of developing a front-rear dual encoder Traction Machine in 2021. At sites using Traction Machines such as the MCK500 [Ø480] 2:1 and MCK520 [Ø650] 1:1, the encoder should be regarded not merely as an accessory but as part of the sensing system used to assess drive stability.

Signal Faults First Appear as Operating Symptoms

Encoder faults do not always appear only as clear fault codes. In their early stages, they may first become apparent as slight vibration during operation or changes in stopping feel.

Maintenance technicians should watch for the following symptoms.

These symptoms may also be related to the brake, rope tension, or control settings. Therefore, rather than concluding that the encoder alone is the cause, it is advisable to inspect it as one part of the Traction Machine’s rotation detection system.

Wiring and Connectors Should Be Checked First

Because encoder signals are transmitted as weak electrical signals, they are greatly affected by wiring conditions. Even when no visible wire break is present, compressed insulation, repeated bending, or connector play may cause intermittent signal faults.

First, check that each connector is fully engaged. If a connector has a locking mechanism, the locking section must be completely secured. Oil, dust, or metal particles around a connector may cause contact resistance or signal instability.

Cables should be arranged so that they do not move with Traction Machine vibration. Securing them too tightly with cable ties may place stress on the internal conductors, while leaving them too loose may create a risk of contact with rotating parts or sharp edges.

It is also necessary to check whether encoder signal cables run closely alongside power supply, brake, or power cables over long distances. Even if complete separation is difficult under site conditions, unnecessary close contact and twisting should be minimised.

Check the Mounting Condition and Axial Movement

Because an encoder reads the movement of a rotating shaft, its mounting position is important. If the mounting bracket is loose or the encoder body moves slightly, even normal rotation may be converted into an unstable signal.

For a front-rear dual encoder Traction Machine, both encoders must be checked using the same criteria. If one side is firmly secured while the other is exposed to vibration, the compared signals may differ.

Check the following items during inspection.

• Whether the encoder body fasteners are loose
• Whether the bracket is deformed or cracked
• Whether the shaft connection is eccentric, loose, or subject to interference
• Whether the cable is pulled during rotation
• Whether the cable is compressed after the cover is secured

In particular, cables may become compressed when the cover is closed again after maintenance. It is important to make a habit of checking whether the cable position around the cover has changed before and after operation.

Contamination and Abnormal Noise Provide Clues to Signal Quality

Dust, oil mist, moisture, and metallic foreign matter may occur in the Traction Machine room or upper Hoistway environment. If contamination accumulates around the encoder, it may affect connector contact and sensor stability.

When cleaning, it is safer to follow the manufacturer’s inspection procedure than to use strong compressed air or solvents excessively. If foreign matter enters the connector or a sealed area is damaged while contamination is being removed, the problem may worsen.

Abnormal noise is also an important clue. If scraping, interference, or repeated clicking is heard around the encoder, check the clearance between rotating and fixed parts, cover interference, and the shaft connection condition.

These noises must be distinguished from bearing noise in the Traction Machine body, brake operating noise, and noise around the Sheave. When narrowing down the source of a noise, recording whether it changes according to travel direction, speed changes, and load conditions can help identify the cause.

Maintenance Records Provide a Basis for Finding Recurring Faults

Encoder signal faults are often intermittent. Even if the cause is not found during a single inspection, a record must be kept if the same symptom recurs.

It is advisable to record the travel direction, floor where the fault occurred, time of occurrence, load condition, control panel indication, whether the encoder connector was reconnected, and whether cleaning was performed. Simply writing “encoder checked” does not provide enough information for the next maintenance technician to make an assessment.

For a front-rear dual encoder structure, the record must also distinguish whether the front or rear encoder was inspected. Subsequent assessments will differ depending on whether both sides were checked or action was taken on only one side.

The decision to replace a component should not be based on a single symptom. The signal condition, mechanical mounting, wiring condition, reproducibility, and manufacturer’s criteria should be considered together. Rapid recovery is important in the field, but replacing components without identifying the cause may allow the same problem to recur.

The front-rear dual encoder Traction Machine is designed to improve the reliability of rotation detection. To retain this advantage, signals from both encoders must be transmitted stably to the controller. It is important for maintenance technicians to establish an inspection system focused on wiring, fastening, contamination, abnormal noise, and records so that minor signs are not overlooked.