Industrial Robot Motor Overload Alarm: Cable, Encoder & Signal System Diagnostic Guide

Motor overload alarms in industrial robots are not always caused by real mechanical overload.

In many field cases, the alarm is triggered by incorrect load estimation inside the servo system, usually caused by encoder feedback issues, cable degradation, or signal instability rather than actual motor stress.

What Is a “Ghost Overload”?

A Ghost Overload refers to a situation where:

• Mechanical load is normal
• Motor is functioning correctly
• No physical obstruction exists
• Yet the controller reports overload

This happens when the control system misinterprets feedback signals and overcompensates torque output.

In practice:

Correct motion + incorrect system interpretation = false overload alarm

Core Control Principle

Motor load calculation is based on a closed-loop system:

Encoder Feedback → Servo Controller → Current / Torque Output

When any part of this loop becomes unstable:

• Controller misjudges load conditions
• Torque output increases abnormally
• Current spikes appear without real resistance

Result: Motor overload alarm without mechanical failure

Quick Symptom Diagnos is Matrix

Root Cause Breakdown

1. Encoder Feedback Instability (Primary Cause)

Encoder signals define real-time position and load interpretation.

When unstable:

• Position feedback fluctuates
• Servo loop overcorrects torque
• Current increases artificially

This leads to false overload detection.

2. Brake System Signal Issues

Brake behavior directly affects startup load calculation.

Typical failure behavior:

• Axis remains partially locked
• Brake release delay occurs
• High initial current spike appears

Result:

→ Controller interprets it as excessive load

3. Power Cable Degradation

Power delivery instability affects motor efficiency.

Common symptoms:

• Voltage drop under load
• Rising current demand
• Heat-related overload triggers

Mechanism:

Reduced power efficiency → higher current draw → overload alarm

4. Cable Harness Fatigue (Intermittent Faults)

High-flex robot cables degrade over time.

Typical field behavior:

• Random overload alarms
• Dependence on robot posture
• Temporary recovery after reboot or motion change

Root cause:

Internal conductor micro-fractures → unstable signal transmission

Advanced Failure Mode: Flex Fatigue

In high-motion axes (especially wrist joints):

• Continuous torsional stress
• Repeated bending cycles
• Copper strand fatigue

Over time:

• Resistance becomes unstable
• Signal quality fluctuates
• Feedback becomes inconsistent

Result:

→ Intermittent “ghost overload” with no mechanical fault

Cross-Brand Pattern (Universal Behavior)

Although alarm codes differ across manufacturers, failure logic is consistent:

• ABB → torque deviation / motion supervision
• FANUC → servo / collision detection alarms
• KUKA → velocity / command limit deviation
• Yaskawa → position deviation / overcurrent alarms

Shared root mechanism:

Encoder instability + cable degradation = false overload across all platforms

Diagnostic Workflow (Field Method)

Step 1 — Confirm Mechanical Condition

• Axis moves freely
• No physical obstruction
• No abnormal friction

Step 2 — Check Brake Behavior

• Confirm proper release at startup
• Check for initial axis locking

Step 3 — Inspect Cable System (Critical Step)

Focus on:

• Wrist and high-flex axes
• Connector oxidation or looseness
• Visible bending fatigue

Step 4 — Evaluate Encoder Stability

• Position fluctuation during motion
• Intermittent signal loss
• Cold vs warm behavior difference

Step 5 — Thermal Pattern Check

• Overload appears after heating
• Cable or motor temperature abnormal

Pro Diagnostic Insight

Cable or encoder-related overload cases typically show:

• Intermittent alarm behavior
• Strong dependence on robot posture
• Temporary recovery after reboot
• No improvement after motor replacement

If two or more conditions match:

→ Prioritize cable + encoder system inspection

Cost of Misdiagnos is

Recommended Repair Strategy

Core Fix: Signal Integrity Restoration

If overload is not mechanical:

• Stabilize encoder signal path
• Restore power cable integrity
• Verify brake signal consistency

Outcome:

• Correct torque calculation restored
• False overload eliminated
• System stability improved

Supporting Layer: Encoder Cable System

Improves:

• Motion consistency
• Feedback stability
• Noise resistance

Extended Layer: Power & Brake System

Includes:

• Motor power cables
• Brake control circuits
• Internal harness wiring

Key Engineering Insight

Motor overload is often not a motor problem.

It is usually a signal interpretation problem inside the servo loop.

Once feedback becomes unstable, the controller will continuously “correct a problem that does not exist”.

FAQ

1. Does motor overload mean motor damage?
No. Most cases are caused by incorrect feedback interpretation.

2. What is a Ghost Overload?
A false overload triggered by unstable signal or encoder feedback.

3. Can cables really cause overload alarms?
Yes. Signal instability leads to incorrect torque compensation.

4. Why does reboot sometimes help?
 It temporarily resynchronizes signals, but does not fix hardware degradation.