Troubleshooting Guide: Tracking Error and Loss of Position in Servo Drives

1. Description and Scope of the Problem

This diagnostic guide focuses on identifying and resolving faults related to excessive following error (following error) and loss of position in servo drives, critical issues that compromise the accuracy and efficiency of machine tools. The main symptoms include:

• following error (following error) or anomalous position alarms in the control system (PLC/CNC).
• Deviations or inaccuracies in the positioning of the axis.
• Vibrations, abnormal noise or jerky movements during operation.
• Unexpected machine stops with positioning error messages.

These problems can occur on servo drives, brushless motors, rotary or linear encoders, gearboxes and mechanical couplings in various applications, typically in the machine tool sector (CNC machining centers, lathes, milling machines, industrial robots, precision axis movement systems). The severity of the problem can be classified as:

• Critical: The machine is stopped or operates with a risk of collision or damage to the piece/tool. Requires immediate intervention.
• Major: Significant performance degradation, reduction in machining quality, increase in cycle times. Requires priority intervention.
• Minor: Sporadic alarms or slight inaccuracies that do not stop production but indicate an anomalous condition that could evolve. Requires intervention planning.

2. Safety Precautions

!WARNING! Diagnosing and repairing power-assisted systems poses significant electrical and mechanical risks. Always follow standard safety procedures.

• Lockout/Taglet (Lockout/Tagout): Before any mechanical or electrical intervention, scrupulously apply the lockout/taglietto procedures compliant with the UNI EN ISO 14118 standard to prevent unexpected starting.
• Discharge Stored Energy: Servo drives contain high-capacity capacitors that can maintain a dangerous voltage even after disconnecting from power. Wait the time specified by the manufacturer (usually 5-10 minutes) and verify the absence of voltage on the DC bus with a certified multimeter EN 61243-3 before touching any component.
• Personal Protective Equipment (PPE): Always wear suitable PPE, including insulating gloves compliant with UNI EN 60903, safety glasses compliant with UNI EN 166, and safety shoes compliant with UNI EN ISO 20345.
• Verify No Voltage: Always use a CAT III 1000V or higher digital multimeter to confirm the absence of voltage on all circuits before proceeding.
• Unexpected Movement Hazard: During functional tests, maintain a safe distance from moving axes.

3. Necessary Diagnostic Tools

The effectiveness of the diagnosis depends on the use of adequate instrumentation. Below is a table of essential tools:

4. Initial Assessment Checklist

Before starting any in-depth diagnosis, it is crucial to gather information and observe operating conditions. This helps target the investigation correctly.

5. Systematic Diagnosis Flow

This logical flowchart guides the technician through a diagnostic path based on observed symptoms, to isolate the root cause of the problem.

1. Initial Symptom: Following Error or Loss of Position alarm.
   1. Check the alarm registers of the drive and control system (PLC/CNC).
      • If the alarm specifically indicates a problem with the encoder (e.g. 'Encoder Fault', 'Feedback Error'): Proceed to the “Encoder Diagnosis” section (Step 2).
      • If the alarm indicates excessive current or motor overload (e.g. 'Overcurrent'): Proceed to the “Mechanical Load Analysis” section (Step 4).
      • If the alarm is related to tuning or stability (e.g. 'Tuning Error', 'Instability'): Proceed to the “Verify Tuning Parameters” section (Step 5).
      • If there are no specific alarms, but the machine shows a clear loss of position or excessive tracking error (e.g. deviation > 100 encoder counts under load): Proceed to the “Encoder Diagnosis” section (Step 2) as the most likely starting point.
   2. Encoder diagnosis.
      1. Visual inspection of the encoder and related wiring.
         • Is the cable damaged (crushed, stripped) or are the connectors loose/disconnected?
           • Probable Cause: Damaged encoder wiring or loose connection.
           • Resolution: Restore or replace the wiring. (See Section 8.1)
         • If the wiring is intact:
      2. Check the encoder power supply (usually 5V or 24V DC) with a multimeter.
         • Is the voltage out of specification (e.g. ±5% of nominal voltage)?
           • Probable Cause: Encoder or drive power supply problem.
           • Resolution: Check the drive's DC power supply or auxiliary power supply. (See Section 8.8)
         • If the power supply is correct:
      3. Check the encoder output signals (A, B, Z for incremental; serial for absolute) with an oscilloscope.
         • Are the signals distorted, noisy (>20mVpp of noise), absent or with unclear transitions?
           • Probable Cause: Defective encoder or electrical interference.
           • Resolution: Replace the encoder or improve the shielding/grounding. (See Section 8.2)
         • If the signals are correct and clean: Proceed to the “Check Mechanical Coupling” section (Step 3).
   3. Check Mechanical Coupling.
      1. Inspect the coupling between motor and load (or motor and gearbox, or gearbox and axis).
         • Is there excessive backlash, misalignment or wear on the coupling?
           • Probable Cause: Defective mechanical coupling.
           • Resolution: Replace and realign the coupling. (See Section 8.3)
         • If the coupling is intact:
      2. Check the tightening of all the fixing screws of the motor, gearbox, encoder and load.
         • Loose screws?
           • Probable cause: Mechanical loosening.
           • Resolution: Tighten the screws to the torques specified by the manufacturer. (See Section 8.3)
         • If the tightenings are correct:
      3. Manually test the axial and radial play on the motor shaft, encoder shaft and at the gearbox input/output (if present), using a comparator.
         • Excessive play (>0.01mm radial, >0.02mm axial)?
           • Probable Cause: Worn motor, gearbox or encoder bearings.
           • Resolution: Replace the bearings or the defective component. (See Section 8.3)
         • If no play is detected: Proceed to the “Mechanical Load Analysis” section (Step 4).
   4. Mechanical Load Analysis.
      1. Decouple the motor from the load (if possible and safe) and move the axis manually.
         • Do you perceive excessive friction, irregular resistance or "hardness" in the movement?
           • Probable Cause: High mechanical friction in the system (guides, screws, etc.).
           • Resolution: Lubricate, clean, or replace worn components. (See Section 8.4)
         • If the manual movement is smooth:
      2. Monitor the current drawn by the motor via the drive software during a typical duty cycle.
         • Is the peak current regularly high (e.g. >150% of the rated current) or does the RMS current consistently exceed 15% of the rated value of the motor?
           • Probable Cause: Motor overload.
           • Resolution: Reduce load, optimize motion profiles or consider a more powerful motor/gearbox. (See Section 8.6)
         • If the load seems normal: Proceed to the “Verify Tuning Parameters” section (Step 5).
   5. Check Tuning Parameters.
      1. Access the drive diagnostic software and check the tuning parameters (P, I, D gains, notch filter, inertia).
         • Have the parameters been changed recently or are they inconsistent with the application?
           • Probable Cause: Parameters of suboptimal tuning.
           • Resolution: Perform auto-tuning or manually adjust the gains. (See Section 8.5)
         • If the parameters seem correct:
      2. Perform a step response test and analyze the curve.
         • Is the response slow, has excessive overshoot (>15%), oscillations or a settling time (>100ms) that is too long?
           • Probable cause: Tuning not optimal.
           • Resolution: Optimize tuning to improve stability and responsiveness. (See Section 8.5)
         • If the tuning is validated as correct: Proceed to the “Servo Drive (Drive) Verification” section (Step 6).
   6. Check Servo Drive (Drive).
      1. Visually inspect the servo drive unit for damage (swollen capacitors, burn marks, damaged components).
         • Obvious damage?
           • Probable Cause: Defective drive.
           • Resolution: Replace the drive. (See Section 8.7)
         • If there is no visible damage:
      2. Check the DC bus voltage with a multimeter after waiting for the capacitors to discharge.
         • Is the voltage abnormal or fluctuating?
           • Probable Cause: Problem internal to the drive or power supply.
           • Resolution: Replace the drive or check the power supply. (See Section 8.7, 8.8)
         • If the voltages are correct:
      3. If available, try with a replacement drive known to be functional (ensuring compatibility and correct parameter loading).
         • Is the problem resolved?
           • Probable Cause: Defective drive.
           • Resolution: Replace the drive. (See Section 8.7)
         • If the problem persists with a replacement drive, or if one is not available: the problem may be intermittent or of a complex nature that cannot be isolated with previous tests. Consider a deeper analysis with OEM support.

   6. Cause-Fault Matrix

   This matrix summarizes symptoms, most likely causes, diagnostic tests and expected results for quick reference.

   Symptom	Probable Causes (ranked by probability)	Diagnostic Test	Expected Result if Cause Confirmed
   Following Error / Loss of Position / Inaccuracy alarm	1. Damaged/loose encoder wiring	Visual inspection, continuity check (multimeter)	Interruption, abnormal resistance (>1Ω), loose connectors
   	2. Defective encoder	Oscilloscope on encoder signals (A, B, Z or serial)	Distorted, absent signals, excessive noise (>20mVpp)
   	3. Excessive mechanical play (coupling, gearbox, bearings)	Visual inspection, manual clearance test, dial indicator (max radial clearance 0.01mm, axial 0.02mm)	Anomalous free movement, eccentricity, hysteresis during motion reversal
   	4. High mechanical friction	Manual movement of decoupled axis, motor current monitoring (drive software)	High resistance, peak current >150% nominal during movement
   	5. Suboptimal tuning parameters	Auto-tuning drive, step response analysis (software drive)	Overshoot >15%, oscillations, settling time long (>100ms), following error > ±5 counts moving encoder
   	6. Motor overload	Motor current monitoring (drive software)	RMS current > 15% of rated motor current for extended periods
   	7. Defective servo drive unit	Visual inspection, DC bus voltage check, drive exchange	Visible damage (swollen capacitors), problem solved with replacement drive
   	8. Unstable drive/encoder power supply	Multimeter/Oscilloscope on power supplies (e.g. 5V/24V encoder, DC bus drive)	Voltage/current out of specification (e.g. ripple >5% nominal voltage), fluctuations
   Vibrations / Abnormal Noise	1. Coupling misalignment	Vibration analyzer, alignment check with comparator	High radial vibrations (1x, 2x RPM), radial misalignment >0.05mm
   	2. Worn motor/load bearings	Vibration analyzer, thermal imaging camera	Vibration spectrum with bearing defect frequencies, local overheating >70°C

   7. Root Cause Analysis for Each Fault

   Understanding the “why” of a failure is essential for prevention and effective resolution.

   7.1 Damaged or Loose Encoder Wiring

   • Why it happens: Encoder cables are often subject to repeated mechanical stress (bending in cable chains), machine vibrations, accidental crushing during maintenance or installation. Contact corrosion in humid or dirty environments, or broken shielding, can degrade signal quality. Bending radii not respected can lead to internal breakages of the conductors.
   • How to confirm: In addition to visual inspection for breaks or stripping, using a multimeter in continuity mode allows you to check each individual conductor (pin-to-pin). A cable flex test during measurement may reveal intermittent interruptions. The resistance between the contacts should be <1 Ohm.
   • Damage if unresolved: Intermittent loss of position feedback can cause jerky movements, unpredictable machine stops, following error alarms or, in more severe cases, potential damage to the drive or motor due to abnormal start/stop cycles and high inrush currents.

   7.2 Defective Encoder

   • Why it happens: Mechanical wear of the encoder's internal bearings can generate backlash and inaccuracy in reading. Contamination (dust, oil, moisture) can clog optical discs or damage magnetic sensors. Power or signal line surges, or aging electronic components, can degrade signal integrity.
   • How to confirm: Analyzing the A/B/Z signals (for incremental encoders) or the serial signal (for absolute encoders) with an oscilloscope is the most effective method. A signal without sharp transitions, with excessive noise (>20mVpp), or with an amplitude reduced compared to specifications, is indicative of a malfunction.
   • Damage if unresolved: Impossibility of precise positioning, uncontrolled axis movements (runaway), machine collisions, accelerated wear of mechanical components due to abnormal stresses.

   7.3 Excessive Mechanical Play

   • Why it happens: Natural wear of the couplings (elastic or rigid) between motor, gearbox and load is a common cause. Worn motor, gearbox or ball screw bearings introduce play. The fixing screws of these components can loosen due to prolonged vibrations or insufficient initial tightening. Backlash in the reduction gears (backlash) may increase with wear.
   • How to confirm: Carry out a manual test: block the motor and try to move the axis by hand, then vice versa. The use of a dial gauge, with a resolution of 0.001mm, to measure radial and axial play (e.g. on the crankshaft, gearbox shaft, ball screw end) is crucial. Tests with reverse motion under light load can reveal system hysteresis.
   • Damage if unresolved: Positioning inaccuracy, vibration and excessive noise during movement, increased dynamic stresses on motor and drive, accelerated wear of other mechanical components and potential structural failure.

   7.4 High Mechanical Friction

   • Why it happens: Insufficient or no lubrication of linear guides, ball screws or bushings is the main cause. Excessive wear of guides or ball slides, accumulation of dirt or foreign objects in the motion system, or excessive preload on bearings can significantly increase friction.
   • How to confirm: Uncouple the motor and move the axis manually to feel the resistance. Monitor the peak current absorbed by the motor during the acceleration and deceleration phases. The current should be proportional to the load; abnormal and repeated peaks (>150% of rated current) indicate high or irregular friction.
   • Damage if unresolved: Excessive motor overheating, high power consumption, accelerated wear of mechanical components (especially guides and screws), reduction in servo drive life, and potential blocking of motion.

   7.5 Non-Optimal Tuning Parameters

   • Why it happens: The tuning parameters (proportional, integral, derivative gains - Kp, Ki, Kd) establish how the drive reacts to position errors. Significant changes in uncompensated machine load, replacement of mechanical or motor components without inertia recalculation, or errors during manual tuning are common causes. An outdated tuning may no longer be suitable due to mechanical wear.
   • How to confirm: Perform a command step response test (step response) via the drive software and analyze the response curve (overshoot, settling time, oscillation frequency). Tuning that is too "aggressive" can cause instability and vibrations, while tuning that is too "soft" results in slowness and excessive following error. The moving following error should be within ±5 encoder counts.
   • Damage if unresolved: Positioning inaccuracy, jerky movements, vibrations, anomalous overheating of the motor and drive (due to continuous corrections), accelerated mechanical wear.

   7.6 Motor Overload

   • Why this happens: The mechanical workload consistently exceeds the rated capacity of the engine. This may be due to incorrect initial design, adding mass to the load, increased duty cycles (high frequency of acceleration/deceleration which increases the RMS current), excessive mechanical friction (as described in 7.4) or incorrectly calculated load inertia in tuning.
   • How to confirm: Monitor the RMS (Root Mean Square) current and peak motor current in the drive diagnostic software. Compare these values ​​with the rated (IRMS) and peak (IPeak) current specified on the motor nameplate. If the RMS current exceeds 15% of the nominal value for prolonged periods, you are in an overload condition. Monitoring engine temperature with a thermal imager is a direct indicator (surface temperature >90°C is critical).
   • Damage if unresolved: Excessive motor overheating leading to degradation of winding insulation (compliant with CEI EN 60034-1), loss of magnetization in permanent magnet synchronous motors, and ultimately blockage or total failure of the motor.

   7.7 Servo Drive Unit Defective

   • Why it happens: Internal electronic components, especially electrolytic capacitors on the DC bus, have a limited useful life and can degrade with time, overheating, or voltage fluctuations. Current overloads, power line surges, manufacturing defects, or insufficient ventilation leading to prolonged overheating can cause failure of IGBTs, control circuits, or the internal power supply.
   • How to confirm: Internal visual inspection for swollen or leaking capacitors, burn marks, charred components, or blown fuses. Checking the DC bus voltage with a multimeter may reveal anomalous values. Testing with a working replacement drive (if available and compatible) is the definitive proof.
   • Damage if unresolved: Erratic or intermittent motor operation, inability to control, complete failure of the drive and potential irreversible damage to the motor if the drive sends incorrect signals or currents.

   7.8 Drive/Encoder Power Supply Unstable

   • Why it happens: DC power supply problems (e.g. degraded switching PSU generating excessive ripple, voltage drops due to line overload), undersized or damaged power supply wiring. Electromagnetic disturbances (EMI) coming from other devices (e.g. welding machines, motors, inverters) can induce noise on the power and signal lines, interfering with the correct operation of the drive and encoder.
   • How to confirm: Measure the supply voltage of the drive and encoder with a multimeter to verify the RMS value and with an oscilloscope to analyze the ripple. Ripple should be less than 5% of the rated voltage (e.g. <0.25V for 5V DC). Sudden voltage/current fluctuations or spikes can be detected with the multimeter's Min/Max function.
   • Damage if unresolved: Unstable and unpredictable operation of the drive, sudden resets, incorrect or intermittent readings of encoder signals, significant reduction in the useful life of the electronic components of the drive and encoder.

   8. Step-by-Step Resolution Procedures

   The following procedures are numbered and detailed to guide the technician through correcting the identified root causes.

   8.1 Encoder Wiring Resolution

   1. !WARNING! Perform the complete blocking/cutting procedure on the machine. Check the absence of voltage.
   2. Visually inspect the entire route of the encoder cable, from the motor (or encoder) junction box to the drive, looking for pinches, cuts, abrasions, peeling, or loose connectors.
   3. With a multimeter, check the continuity of each individual conductor of the encoder cable (pin-to-pin on both connectors). The resistance for an intact conductor should not exceed 1 Ohm. Also check the continuity of the shielding.
   4. Clean and tighten all connectors. Use industrial, non-residue electrical contact spray to remove oxidation and improve conductivity.
   5. If the cable is damaged at any point or shows intermittent breaks, replace it with a new cable of identical specifications (type of shielding, conductor cross-section, insulation material) and adequate length. Respect the minimum bending radii indicated by the manufacturer (typically 10x the diameter of the cable for fixed installations, 20x for cables in drag chains or in movement).
   6. Make sure that the cable shield is correctly earthed on both ends (if specified by the manufacturer) or on only one, to avoid ground loops, according to the CEI EN 61000-6-4 regulations for electromagnetic compatibility.
   7. Restore power to the machine and test the movement of the axis in all its excursions and at different speeds.

   8.2 Troubleshooting Defective Encoder

   1. !WARNING! Perform complete blocking/cutting procedure. Check the absence of voltage.
   2. Check the encoder power supply. If it is incorrect, consult procedure 8.8.
   3. Disconnect the faulty encoder. Be sure to note the pin wiring.
   4. Install a new encoder with the same model, resolution (PPR or bit), output type (TTL, HTL, Sin/Cos, serial) and interface (e.g. SSI, EnDat, Hiperface) as the original one.
   5. Make sure of the correct mechanical coupling on the crankshaft. The tightening of the lock screw or joint should comply with the manufacturer's specifications (e.g. 2Nm for M3 screws). Avoid mechanical tension on the encoder body.
   6. Reconnect the encoder wiring, respecting the pin order.
   7. Restore power. In the drive software, check the encoder orientation (the pulse count should increase or decrease correctly based on the direction of rotation of the motor shaft). It may be necessary to perform a reset (homing) or recalculation of the position offsets.
   8. Perform motion tests at low speed, monitoring the following error, and then gradually increase the speed and load.

   8.3 Resolving Excessive Mechanical Play

   1. !WARNING! Perform complete blocking/cutting procedure. Check the absence of voltage.
   2. Identify the exact source of the play using a dial gauge or micrometer:
      • Coupling: Check the play between the crankshaft and the coupling, and between the coupling and the load/reducer shaft.
      • Bearings: Check the radial and axial play on the motor, gearbox and ball screw bearings. Radial clearance should not exceed 0.01mm and axial clearance 0.02mm for precision applications.
      • Reducer: Check the backlash (backlash) of the reducer by moving the output shaft while the input is blocked.
   3. For worn couplings: Replace the coupling with a new component of the same characteristics (material, size, torque capacity). Make sure the correct alignment of the shafts; a maximum acceptable misalignment is typically 0.05mm radial and 0.1mm angular, verifiable with a comparator or laser alignment system.
   4. For worn bearings: Replace the motor, gearbox or axle bearings. Use specific tools for extraction and installation to avoid damage. Lubricate the new bearings with the grease specified by the manufacturer.
   5. For loose tightenings: Tighten all the motor, gearbox, coupling and load fixing screws to the torques indicated in the OEM manuals (e.g. M8 screws with 25Nm, M10 screws with 49Nm). Use a UNI EN ISO 6789 certified torque wrench.
   6. For backlash in gearbox: If gearbox backlash exceeds OEM specification (e.g. > 5 arcmin for precision gearboxes), consider replacing the gearbox. Attempt to adjust the backlash only if provided for by the manufacturer.
   7. Restore power and test the movement of the axis, monitoring the following error and the absence of abnormal noises or vibrations.

   8.4 Resolution of High Mechanical Friction

   1. !WARNING! Perform complete blocking/cutting procedure. Check the absence of voltage.
   2. Decouple the motor from the axis (if possible and safe) and move the axis manually to identify the points of greatest resistance or friction (linear guides, ball screws, support bearings).
   3. Clean the linear guides and ball screws thoroughly. Remove chips, dust, oxides or metal debris that may impede movement.
   4. Lubricate the guides and screws with the lubricant specified by the manufacturer (e.g. ISO VG 68 oil, NLGI 2 grease). Observe the lubrication points and intervals.
   5. Inspect the linear guide pads and ball screw nuts; replace if they have excessive wear, grooves or damaged surfaces.
   6. Check the alignment of the guides. Excessive misalignment can cause significant friction and non-uniform loads. Correct the alignment if necessary.
   7. Restore the motor-axis coupling.
   8. Restore power and monitor the motor current during movement to verify that it is within normal limits and that there are no abnormal spikes.

   8.5 Resolution of Non-Optimal Tuning Parameters

   1. Access the drive diagnostics and tuning software.
   2. If available, perform the drive auto-tuning function. This function automatically calculates the load inertia and sets appropriate initial gains. Record the parameters obtained.
   3. Perform a step response test (step response). Analyze the curve obtained:
      • If the response is too slow or with following error high: Gradually increase the proportional (Kp) and integral (Ki) gains.
      • If the response exhibits overshoot, oscillations or is unstable: Reduce Kp or increase the derivative gain (Kd) to dampen oscillations. Add or adjust notch filters if mechanical resonances are present.
   4. Adjust gains carefully, making small increments and monitoring the response to each change. The objective is to minimize static and dynamic following error, maintain a fast settling time (e.g. <50ms) and a stable response without oscillations. The following error during nominal motion should not exceed ±5 encoder counts.
   5. Save the new tuning parameters in the drive and make a backup on your PC.
   6. Perform machine operation tests under different load conditions, speeds and movement profiles to validate the new tuning.

   8.6 Motor Overload Resolution

   1. !WARNING! Perform complete blocking/cutting procedure. Check the absence of voltage.
   2. Determine the precise cause of the overload:
      • If due to excessive friction, see procedure 8.4.
      • If the payload (mass or resisting force) exceeds the capacity of the motor or gearbox, consider redesigning the mechanical system.
   3. If the payload is intrinsically high, consider replacing the engine with one of higher power and torque. Alternatively, if a gearbox is present, implement one with a higher reduction ratio to increase the torque available to the axis.
   4. Check that the load inertia value set in the drive corresponds to the real one. If the inertia was calculated incorrectly, recalculate and update the parameter.
   5. Optimize the motion profiles (acceleration/deceleration, cruise speed) in the PLC/CNC program to reduce peak currents and average RMS current, while respecting the thermal limits of the motor.
   6. Restore power and monitor the motor's RMS and peak current to ensure they are within rated limits throughout the duty cycle. Check the engine temperature with the thermal imaging camera.

   8.7 Resolution Defective Servo Drive Unit (Drive).

   1. !WARNING! Perform complete blocking/cutting procedure. Check the absence of voltage and wait for the capacitors to discharge (typically 5-10 minutes).
   2. Visually inspect the inside of the drive, if accessible. Look for swollen or leaky capacitors, burn marks on circuit boards, charred components, or blown fuses.
   3. If you suspect a faulty drive and there is no visible damage, proceed with replacement. Make sure you have an identical or fully compatible replacement drive.
   4. Before replacement, make a complete backup of the drive parameters (if possible) and the firmware. Load the correct firmware and saved parameters into the new unit.
   5. Install the new drive, making sure that all connections (power supply, motor, encoder, I/O, fieldbus) are correct and tightened adequately.
   6. Dispose of the defective unit according to local regulations and Directive 2012/19/EU (WEEE).
   7. Restore power and test the servo-assisted system in all its functions.

   8.8 Unstable Drive/Encoder Power Resolution

   1. !WARNING! Perform complete blocking/cutting procedure. Check the absence of voltage.
   2. Check the drive's DC power supply or the auxiliary power supply for the encoder. Measure the output voltage and ripple with a multimeter and oscilloscope. Ripple should be less than 5% of rated voltage. Replace power supply if out of specification.
   3. Check the power cables (both AC and DC) of the drive and encoder. Make sure that the cable sections are sized correctly for the maximum absorbed current. Undersized cables can cause significant voltage drops under load.
   4. Check the integrity of the earth connection of all components. Effective grounding is critical for EMI noise suppression.
   5. Consider installing line EMI filters (e.g. compliant with CEI EN 61000-6-4) to mitigate disturbances on the power line that can affect the drive and encoder signals.
   6. Restore power and monitor system voltages and operation for fluctuations or noise.

   9. Preventive Measures

   Implementing preventative measures is critical to ensuring reliability and extending the life of servo drives and associated components.

   Root Cause	Prevention Strategy	Monitoring Method	Recommended Interval
   Damaged Encoder Wiring	Adequate cable fixing (cable clips, cable chains), mechanical protection against crushing, compliance with minimum bending radii.	Periodic visual inspection of the cable route, cable continuity test (resistance <1Ω).	Annually or at each major preventive maintenance intervention.
   Defective encoder	Periodic cleaning of the surrounding environment, protection from contaminants (dust, oil, liquids), check the integrity of the seals.	Encoder signal quality monitoring with oscilloscope, surface temperature control with thermal imager.	Biennial or 8000 hours of operation.
   Excessive Mechanical Game	Regular lubrication program (guides, screws, bearings), check tightening of fixing screws (motor, gearbox, coupling).	Visual inspection and manual testing of the game, use of comparator for precision measurements.	Every six months or 4000 hours of operation.
   High Mechanical Friction	Periodic cleaning and lubrication of guides and ball screws, inspection of slides and nuts.	Motor current trend monitoring (RMS and peak) via drive software, manual measurement of the decoupled axis dragging force.	Monthly (software monitoring), Quarterly (cleaning/lubrication).
   Non-Optimal Tuning Parameters	Regular backup of drive parameters, auto-tuning after significant changes to load or mechanical components.	Analysis of the step response (step response) via drive software, monitoring of the following error in production.	After changes, Annual (verification).
   Motor Overload	Analysis and correct sizing of the motor/gearbox for the application, optimization of movement profiles (reduction of extreme accelerations).	Continuous monitoring of motor current (RMS and peak) and motor surface temperature (integrated thermal imaging camera/sensor).	Continuous (software drive), Quarterly (thermal imaging camera).
   Defective Servo Drive Unit	Installation in a controlled environment (temperature, humidity), internal cleaning of dust, verification of cooling fan efficiency.	Internal visual inspection (capacitors, components), internal drive temperature monitoring (if available).	Annual.
   Unstable power supply	Preventive maintenance of DC power supplies (ripple check), integrity check and wiring sizing, installation of EMI filters.	Voltage and ripple monitoring on DC bus and auxiliary supplies with multimeter/oscilloscope.	Annual.

   10. Spare parts and components

   Having an adequate inventory of critical parts significantly reduces downtime. UNITEC-D offers a wide range of components for servo drives and mechanical systems.

   Part Description	Key Specification	When to Replace	UNITEC category
   Incremental/Absolute Encoder	Resolution (e.g. 1024 PPR, 23 bit), Output type (TTL, HTL, Sin/Cos, SSI, EnDat), Power supply voltage.	Anomalous signals, mechanical play on the shaft, excessive noise, exceeding the operating hours recommended by the manufacturer (e.g. 20,000 hours).	Industrial sensors
   Encoder cable	Length, Number of conductors, Section, Type of shielding, Connectors (e.g. M12, D-sub).	Physical damage (cuts, crushing), interruptions in continuity, degradation of insulation, persistent EMI problems.	Industrial Wiring
   Motor/Gearbox Coupling	Shaft diameter (e.g. ⌀14mm, ⌀19mm), Nominal torque (e.g. 50 Nm), Material, Type (elastic, bellows).	Excessive play, wear of the slats/elastic elements, deformations, breakage. Inspect every 2000 hours.	Transmission Components
   Motor/Axle/Gearbox Bearings	Type (radial, oblique), Dimensions (internal/external diameter, width), Accuracy class (e.g. P5, P4).	Excessive noise (squealing, rolling), abnormal vibrations, radial/axial clearance out of specification (e.g. >0.01mm), local overheating. Inspect every 4000 hours.	Precision Mechanics
   Servo Drive Unit (Drive)	Rated power (e.g. 1.5 kW, 5 kW), Supported motor type (synchronous, asynchronous), Fieldbus interface (e.g. Profinet, EtherCAT).	Internal drive diagnosis (critical alarms that cannot be resolved), visible damage (e.g. swollen capacitors, traces of burns), erratic operation or total failure.	Power Electronics
   Auxiliary DC power supply	Output voltage (e.g. 24V DC), Maximum current (e.g. 5A, 10A), Stability (ripple <5%).	Unstable voltage, excessive ripple, complete failure. Check every 8000 hours.	Power Electronics
   EMI filter (for drives)	Rated current (e.g. 10A, 20A), Rated frequency, Degree of protection (e.g. IP20).	Persistent EMI problems not solvable with shielding/grounding, physical damage.	Electrical Components
   Brushless Motor (Servo)	Rated Power (kW), Rated Torque (Nm), Maximum Speed (RPM), Mounting Flange, Compatible Feedback Type.	Repeated thermal overload, burnt windings (insulation resistance measurement <0.5MΩ at 500V DC), shaft breakage, excessive noise from internal bearings.	Industrial motorization

   To find the specific spare parts for your needs and guarantee maximum compatibility and reliability, visit our e-catalog: www.unitecd.com/e-catalog/. Our technical team is available to support you in your choice.

   11. References

   For further information and consultation of current regulations, please refer to the following standards and documents:

   • UNI EN ISO 13849-1: Safety of machinery – Safety-related parts of control systems – Part 1: General principles for design.
   • UNI EN ISO 14118: Machinery safety – Prevention of unexpected starting.
   • UNI EN ISO 12100: Machinery safety – General design principles – Risk assessment and reduction.
   • CEI EN 61800-3: Variable speed electric drive systems – Part 3: Electromagnetic compatibility (EMC) requirements and specific test methods.
   • CEI EN 60034-1: Rotating electrical machines – Part 1: Nominal characteristics and performances.
   • OEM (Original Equipment Manufacturer) Technical Manuals of the servo drives, servomotors and encoders used.
   • Related UNITEC Maintenance Guides: “Vibrational Diagnostics for Machine Tools”, “Precise Alignment of Couplings”.