1. Problem Description & Scope

This guide addresses common issues leading to servo drive following errors and position loss in industrial automation systems. These problems are frequently encountered in motion control applications across the automotive, aerospace, and food processing sectors. Symptoms include erratic motion, loss of position, encoder feedback errors, and abnormal motor behavior. The severity classification is as follows: Critical (complete loss of position control), Major (intermittent position loss or encoder errors), and Minor (slight deviation or minor feedback issues).

2. Safety Precautions

Lockout/Tagout (LOTO) is mandatory before servicing any motion control system. Ensure all energy sources are disconnected and the system is de-energized. Use appropriate PPE, including insulated gloves, safety glasses, and protective footwear. Do not attempt to operate or test the system while it is under load or with stored energy.

3. Diagnostic Tools Required

4. Initial Assessment Checklist

5. Systematic Diagnosis Flowchart

1. Check for drive error codes
   1. If error code is 0x1200 (Encoder Feedback Error), proceed to Step 5.2
   2. If error code is 0x1201 (Position Loss), proceed to Step 5.3
   3. If error code is 0x1202 (Tuning Parameter Error), proceed to Step 5.4
2. Step 5.2: Encoder Feedback Error
   1. Verify encoder wiring connections (check for loose, damaged, or reversed connections)
   2. Use a multimeter to check for continuity and resistance in the encoder signal lines
   3. Test encoder signal with an oscilloscope (0-5 V DC, 1 kHz to 100 kHz)
   4. If signal is unstable or out-of-range, check encoder health and mounting
3. Step 5.3: Position Loss
   1. Inspect mechanical coupling for misalignment, wear, or damage
   2. Use a vibration analyzer to check for excessive vibration (alarm threshold: > 10 mm/s RMS)
   3. Verify motor shaft alignment with laser alignment tool (tolerance: ±0.05 mm)
   4. Check for backlash or play in the mechanical system
4. Step 5.4: Tuning Parameter Error
   1. Review PID tuning parameters (proportional gain: 1–10, integral time: 0.1–10 sec, derivative time: 0.01–1 sec)
   2. Check for incorrect motor inertia or load inertia values
   3. Verify acceleration/deceleration rates (alarm threshold: > 5000 rpm/sec)
   4. Perform a motor parameter identification test using a motor tuning tool

6. Fault-Cause Matrix

7. Root Cause Analysis for Each Fault

7.1 Encoder Feedback Error

Encoder feedback errors typically occur due to poor signal integrity, mechanical issues, or electronic faults. The encoder signal is a critical feedback loop for position and speed control. If the signal is unstable or out-of-range, the drive cannot accurately determine the motor’s position, leading to erratic motion or complete loss of control.

How to Confirm: Use an oscilloscope to measure the encoder signal. A healthy signal should be within 0–5 V DC and show consistent pulses. If the signal is noisy, clipped, or intermittent, it indicates a wiring or mechanical issue. A damaged encoder may show erratic or missing pulses.

Damage if Left Unresolved: Continuous encoder feedback errors can lead to system shutdowns, loss of position accuracy, and potential mechanical damage due to uncontrolled motion.

7.2 Position Loss

Position loss is often caused by mechanical misalignment, excessive vibration, or backlash in the system. When the mechanical coupling is not aligned, the drive may not receive accurate feedback, causing the motor to lose position. Excessive vibration can also introduce errors in the encoder signal, leading to position loss.

How to Confirm: Use a laser alignment tool to check coupling alignment (tolerance: ±0.05 mm). Measure vibration using a vibration analyzer (alarm threshold: >10 mm/s RMS). If vibration is above threshold, the system is likely experiencing mechanical resonance or imbalance.

Damage if Left Unresolved: Position loss can result in product defects, safety hazards, and reduced system uptime due to frequent shutdowns and recalibration.

7.3 Tuning Parameter Error

Tuning parameter errors occur when PID gains are set incorrectly or the system’s inertia values are not properly accounted for. Incorrect tuning can lead to instability, overshoot, or underperformance of the motor, causing position loss or erratic behavior.

How to Confirm: Review the PID parameters in the drive configuration. Proportional gain should be between 1 and 10, integral time between 0.1 and 10 seconds, and derivative time between 0.01 and 1 second. Verify that the inertia values match the motor and load specifications. Acceleration/deceleration rates should not exceed 5000 rpm/sec.

Damage if Left Unresolved: Incorrect tuning can lead to motor overheating, premature wear, and system instability, reducing the overall reliability and lifespan of the drive and motor.

8. Step-by-Step Resolution Procedures

8.1 Encoder Feedback Error

1. Verify all encoder wiring connections for tightness and integrity. Replace any damaged or frayed cables.
2. Use a multimeter to test continuity and resistance in the encoder signal lines (expected resistance: 100–500 ohms). Ensure no short circuits or open circuits.
3. Test the encoder signal with an oscilloscope (0–5 V DC, 1 kHz to 100 kHz). Ensure signal is stable and within range.
4. Inspect the encoder for physical damage, such as cracks or wear. Replace if necessary.
5. Reconfigure the drive to match the encoder’s signal type and resolution.
6. Verify the system’s operation and check for residual errors.

8.2 Position Loss

1. Use a laser alignment tool to align the mechanical coupling within ±0.05 mm.
2. Check for wear or damage in the coupling and replace if necessary.
3. Measure vibration with a vibration analyzer (alarm threshold: >10 mm/s RMS). If vibration is excessive, identify and resolve the source of resonance or imbalance.
4. Inspect the gear or belt system for backlash or play. Adjust or replace components as needed.
5. Perform a system calibration and verify motion accuracy.

8.3 Tuning Parameter Error

1. Review and adjust PID parameters (proportional gain: 1–10, integral time: 0.1–10 sec, derivative time: 0.01–1 sec).
2. Verify the motor and load inertia values against the motor datasheet and system specifications.
3. Adjust acceleration/deceleration rates to ensure they do not exceed 5000 rpm/sec.
4. Perform a motor parameter identification test using a motor tuning tool.
5. Reconfigure the drive and test the system for stability and accuracy.

9. Preventive Measures

10. Spare Parts & Components

Visit UNITEC-D e-Catalog for spare parts and components

11. References

• ANSI/ASME B5.54-2013: Mechanical Power Transmission – Couplings
• ISO 10816-1: Mechanical vibration – Measurement and evaluation of machine vibration
• NFPA 70: National Electrical Code (NEC)
• IEEE 1588: Precision Clock Synchronization for Networked Measurement and Control Systems
• UNITEC-D Maintenance Guide: Servo Drive Troubleshooting

1. Problem Description & Scope

This troubleshooting guide addresses servo drive systems experiencing following error and position loss in industrial automation applications. The symptoms include erratic motion, failure to maintain position, and system shutdowns. These issues can occur in a variety of equipment types including CNC machines, robotic arms, and automated assembly lines.

The severity classification is as follows: Critical if the system failure results in production stoppage or safety risk, Major if it causes partial system failure or frequent downtime, and Minor if it results in intermittent performance issues without significant impact on operations.

2. Safety Precautions

Warning: Always ensure the system is de-energized and locked out before performing any diagnostic or repair work. Use appropriate PPE, including insulated gloves, safety glasses, and hearing protection when working near high-speed or high-voltage systems.

Warning: Verify that all stored energy (e.g., in capacitors, compressed air, or springs) has been fully dissipated before beginning any inspection or maintenance procedure.

3. Diagnostic Tools Required

4. Initial Assessment Checklist

5. Systematic Diagnosis Flowchart

1. Symptom: Following Error and Position Loss
1. Check Encoder Feedback
1. Use the encoder test unit to verify signal integrity and accuracy
2. If signal is weak, inspect wiring, connector, and encoder itself
2. Inspect Mechanical Coupling
1. Use a vibration analyzer to check for misalignment or imbalance
2. Measure radial and axial runout using a dial indicator
3. Review Servo Tuning Parameters
1. Check gain settings, velocity, and acceleration limits
2. Verify that parameters match the system load and application requirements
4. Analyze Load Conditions
1. Measure torque and power consumption using a multimeter
2. Use a thermal imaging camera to identify overheating components
2. If Encoder Feedback is Faulty
1. Verify signal voltage and current levels
2. Check for interference or grounding issues
3. If Mechanical Coupling is Faulty
1. Measure runout within acceptable limits (≤0.05 mm)
2. Replace worn or damaged couplings
4. If Tuning Parameters are Incorrect
1. Adjust gain and velocity settings based on load and application
2. Test system performance after adjustment
5. If Load Analysis Indicates Overload
1. Reduce load or increase motor power rating
2. Ensure proper cooling and ventilation

6. Fault-Cause Matrix

7. Root Cause Analysis for Each Fault

7.1 Encoder Feedback Failure

Root Cause: Encoder feedback failure is typically caused by damaged wiring, poor grounding, or internal encoder failure. This can lead to inconsistent or no feedback signal, causing the drive to lose position and trigger a following error.

Diagnostic Confirmation: Use a multimeter to verify signal voltage and current. Check for continuity and resistance across the encoder wiring. If no signal is detected, inspect the encoder for physical damage.

Damage if Left Unresolved: Continuous feedback failure can cause the drive to shut down, leading to unplanned downtime and potential safety hazards.

7.2 Mechanical Coupling Misalignment

Root Cause: Mechanical coupling misalignment results from wear, improper installation, or environmental factors. This causes vibration, uneven load distribution, and reduced positional accuracy, leading to following errors and position loss.

Diagnostic Confirmation: Use a dial indicator to measure radial and axial runout. If runout exceeds 0.05 mm, the coupling is misaligned and requires adjustment or replacement.

Damage if Left Unresolved: Prolonged misalignment can lead to bearing failure, shaft damage, and reduced system lifespan.

7.3 Incorrect Servo Tuning Parameters

Root Cause: Incorrect tuning parameters, such as improper gain or velocity limits, can cause the drive to respond inadequately to load changes, leading to position loss and following errors.

Diagnostic Confirmation: Review the drive’s tuning parameters and compare them with manufacturer recommendations. Use a vibration analyzer to check for excessive vibration after parameter adjustments.

Damage if Left Unresolved: Poor tuning can result in inefficient operation, increased wear, and potential system failure.

7.4 Excessive Load or Overheating

Root Cause: Excessive load or overheating can cause the drive to lose control of the motor, leading to position loss and following errors. This is often due to improper motor selection, inadequate cooling, or overload conditions.

Diagnostic Confirmation: Measure torque and power consumption with a multimeter. Use a thermal imaging camera to identify components exceeding 70°C.

Damage if Left Unresolved: Overheating can damage internal components, leading to permanent system failure.

8. Step-by-Step Resolution Procedures

8.1 Encoder Feedback Failure

1. Inspect encoder wiring for damage or corrosion. Replace any faulty cables.
2. Verify grounding connections and ensure they are secure and free from interference.
3. Test the encoder signal using a multimeter. Ensure voltage and current are within acceptable limits (0–10 V, 0–20 mA).
4. If the encoder is faulty, replace it with a compatible model from UNITEC-D’s catalog.
5. Reboot the system and verify that the drive resumes normal operation.

8.2 Mechanical Coupling Misalignment

1. Use a dial indicator to measure radial and axial runout. If exceeding 0.05 mm, the coupling is misaligned.
2. Adjust the coupling using a torque wrench to ensure proper alignment. Apply torque within manufacturer specifications (e.g., 15–25 Nm).
3. Replace any worn or damaged couplings with a new, compatible model.
4. Recheck alignment and ensure runout is within acceptable limits.
5. Test the system for smooth operation and absence of vibration.

8.3 Incorrect Servo Tuning Parameters

1. Review the drive’s tuning parameters (gain, velocity, acceleration) and compare them with manufacturer recommendations.
2. Adjust gain settings to match load requirements. Start with recommended values and incrementally increase as needed.
3. Use a vibration analyzer to monitor system performance after parameter changes. Ensure vibration levels are within acceptable limits (≤5 mm/s).
4. Test the system under load to confirm proper operation and position accuracy.

8.4 Excessive Load or Overheating

1. Measure torque and power consumption with a multimeter. Ensure values are within motor rating limits.
2. Use a thermal imaging camera to identify overheating components. Replace any components exceeding 70°C.
3. Ensure proper cooling and ventilation for the system. Install additional cooling if necessary.
4. Verify that the motor and drive are appropriately rated for the application load.
5. Test the system under full load to confirm stability and performance.

9. Preventive Measures

10. Spare Parts & Components

Visit UNITEC-D E-Catalog for a complete selection of spare parts and components for servo drive systems.

11. References

• ANSI/IEEE C57.91-2011 — IEEE Guide for the Application of Power Transformers
• ASME B5.54-2020 — Specification for Servo Motors and Servo Systems
• NFPA 70E — Standard for Electrical Safety in the Workplace
• UL 508A — Standard for Industrial Control Equipment
• CE Marking for Machinery Directive 2006/42/EC
• UNITEC-D Maintenance Guide: Servo Drive Troubleshooting