Recurring MR-JE-A encoder cable faults: check cable-carrier routing and connector stress

When feedback abnormalities recur near a particular machine position and still require observation after cable replacement, include the cable's motion path in the inspection. This does not mean that every position-dependent alarm is caused by a cable; it means retaining sufficient information about the mechanical routing. This article is limited to the cable-stress requirements in the MR-JE-A manual.

Which stresses the manual addresses

Section 2.3 of SH-030128ENG-J requires preventing the cable's own weight and bending stress from being transmitted to the connection. When a motor moves with a mechanism, provide appropriate slack at the connection, consider cable flexing life, and prevent damage from chips, machine edges or being stepped on. Check permissible bending conditions for the specific compatible cable; one radius cannot be prescribed for every cable.

Photograph the entire motion path first

After stopping the machine and implementing safety measures, photograph the motor connection, retaining clamps, cable-carrier entry and exit, and existing abrasion marks. Include adjacent parts as location references rather than photographing only a small damaged section of sheath. Record the actual movement during which the fault occurred. If historical observations suffice, there is no need to run the machine again to provoke an alarm.

An intact outer sheath does not establish that the internal conductors are sound. If wear is found, retain information about its location and surrounding structure. Qualified personnel should decide whether electrical testing is needed using the applicable cable and equipment documentation. Do not treat an encoder circuit as an ordinary power cable and apply arbitrary test voltages.

Four points to establish before replacing a cable

• Which compatible cable is actually installed, and whether its model, length and connection ends can be confirmed.
• Whether the cable bends with moving components and whether fixed points and moving sections are clearly identified.
• Whether the old cable's damage coincides with the cable-carrier exit, a fastening point or a machine edge; photographs should show the relationship.
• Whether previous replacement records describe routing and clamping changes or only the new cable model.

The follow-up must cover routing

Installing a new cable without investigating the original stress locations may still leave insufficient evidence to understand recurring faults. After repair, retain the new routing and actual inspection results, and verify the movement range and relevant functions according to the machine-level plan. Do not pull or shake connectors while the machine is running to reproduce the problem, and do not leave temporary loose wiring as a permanent repair.

Our FANUC serial-data error record (Chinese) concerns alarms from another brand. Its approach to organizing cable and connection information can be useful, but alarm definitions are not interchangeable. Providing the drive, encoder and cable models together helps identify the appropriate manual.

Reference: MR-JE-_A Servo Amplifier Instruction Manual, SH-030128ENG-J, §2.3 Encoder cable stress, printed page 2-4. This article explains applicability and suggests how to organize site information. Perform specific work according to the documentation for the actual equipment and its machine builder.