Optimizing Maintenance on Packaging Lines: Guide for Servo Controllers, Pneumatic Actuators and Sensors

1. Introduction: The Importance of Maintenance on Packaging Lines

Operational efficiency in modern manufacturing depends critically on the reliability of production lines, especially in the packaging sector. An unexpected failure can lead to significant losses through downtime, product rejection, and urgent repair costs. This technical guide details maintenance strategies for key components in packaging lines: servo controllers, pneumatic actuators and sensors. The objective is to provide a framework to ensure production continuity, product quality and safety, in compliance with standards such as the UNE-EN ISO 13849 series on machinery safety and the CE directive.

A well-structured maintenance program not only prevents breakdowns, but also optimizes performance and prolongs the useful life of equipment. The application of condition monitoring techniques and effective spare parts management are essential to achieve these objectives.

2. System Architecture: Packaging Line

A typical packaging line comprises interconnected subsystems that perform functions such as feeding, dispensing, filling, sealing, labeling and palletizing. The precision and speed of these operations are critical, controlled by a combination of technologies:

• Servo Controllers and Servo Motors: Provide high-precision motion control for tasks such as exact positioning of containers, synchronized manipulation or material cutting. They allow dynamic adjustments of speed and torque, essential for different product formats. A representative example is the DANFOSS 132F0020 servo controller, a VLT AutomationDrive FC 302 drive designed for demanding industrial applications, with a nominal power of 0.37 kW at 3x380-480V, offering flux vector control and integrated safety functionalities according to EN 61800-5-2.
• Pneumatic Actuators: They are used for linear or rotary movements of controlled force, such as clamping, pushing, lifting or opening/closing valves. Their robustness and simplicity make them ideal for industrial environments. They include pneumatic cylinders (ISO 15552, ISO 6432), directional valves (ISO 5599-1) and air handling units (FRL - filter, regulator, lubricator).
• Sensors: They constitute the nervous system of the line, detecting the presence, position, orientation and characteristics of the product or container. Common types include proximity sensors (inductive for metals, capacitive for non-metals, photoelectric for opaque/transparent objects), encoders for position feedback in servo motors, and pressure/temperature sensors. Compliance with EN 60947-5-2 is essential for the reliability of proximity sensors.

3. Inventory of Critical Components and Specifications

4. Preventive Maintenance Plan

A rigorous maintenance schedule is essential for the reliability of the line. Intervals are based on an average operating cycle of 16 hours/day, 5 days/week.

Daily Tasks (Before or After the Production Shift)

• General Visual Inspection: Check for air leaks, abnormal noises, excessive vibrations in servomotors, loose or damaged cables, and dirt accumulation in sensors.
• Pneumatic Pressure Verification: Confirm that the working pressure is maintained between 6-7 bar in the FRL unit and at critical points in the system.
• Surface Cleaning of Sensors: Ensure that the optical windows or active surfaces of the sensors are free of dust, product residues or moisture.

Weekly Tasks (Every 80 Hours of Operation)

• Purge of FRL Units: Empty the condensate drains on the compressed air filters.
• Cable Fastening Check: Check the tightness of cable glands and connections of power, control and feedback cables in servo controllers and servo motors. Ensure the correct bend radius in energy chain cables.
• Lubrication of Pneumatic Components: If the system uses in-line lubricators, check the oil level and adjust the drip rate according to the manufacturer's specifications (generally 1-3 drops/min for every 1000 l/min of flow).
• Photoelectric Sensor Alignment Verification: Adjust if necessary to ensure reliable product detection.

Monthly Tasks (Every 320 Hours of Operation)

• Inspection of Pneumatic Gaskets and Seals: Look for signs of aging, cracks or leaks. Consider preventive replacement sealing kits on actuators with high duty cycle.
• Servo Controller Parameter Review: Connect to the software interface (Danfoss Drive Composer, for example) and verify that the key operating parameters (current limits, PID gains, ramps) are within the defined ranges and have not suffered deviations.
• Calibration of Critical Sensors: Perform a functional verification or zero calibration on weight, pressure or temperature sensors if applicable, using certified standards.
• Cleaning Servo Controller Fans and Heatsinks: Ensure adequate air flow to avoid overheating.

Annual Tasks (Every 4000 Hours of Operation or Annually)

• Complete Servo Controller Diagnostics: Includes motor insulation testing, verification of DC-Link capacitors (discharging and reforming if they have been stored or inactive for a long time), and input power quality analysis (EN 50160).
• Preventive Replacement of Sealing Kits in Pneumatic Actuators: Especially in high cycle frequency cylinders.
• Inspection of Servomotor Bearings: Vibration measurement (UNE-EN ISO 13443-1) and, if necessary, replacement of bearings. A bearing failure can result in downtime of 6-8 hours and an approximate cost of €300-€800 in labor alone.
• General Audit of the Pneumatic System: Leak detection with ultrasonic equipment (significant energy savings), review of air quality (dew point, particle and oil content).

5. Common Failure Modes

Identifying and understanding the most frequent failure modes is a pillar of the predictive maintenance strategy:

1. Servo Controller Failure due to Overheating:
   • Cause: Obstruction of fans, high ambient temperature, continuous motor overload.
   • Effect: Disconnection due to thermal protection, reduction in the useful life of electronic components (capacitors), catastrophic failure of the power module.
   • Impact: Complete stoppage of packaging section, estimated downtime: 2-4 hours.
2. Leaks in Pneumatic Actuators:
   • Cause: Wear of seals (seals, O-rings), mechanical damage, contamination of compressed air.
   • Effect: Loss of pressure, erratic or slow movement of the actuator, increased energy consumption of the compressor.
   • Impact: Reduced line speed, increased operating costs, downtime for repair: 1-2 hours.
3. Misalignment or Contamination of Sensors:
   • Cause: Mechanical impacts, accumulation of dust, dirt or product, excessive vibrations.
   • Effect: Erroneous detection or lack of detection, lost cycles, product jams.
   • Impact: Product quality failures (empty, poorly sealed containers), intermittent line stoppages. Downtime: 0.5-1 hour.
4. Bearing Failure in Servomotors:
   • Cause: Inadequate lubrication, misalignment, excessive vibrations, overload.
   • Effect: Abnormal noise, motor vibration, temperature increase, eventual seizure.
   • Impact: Damage to servomotor, possible damage to attached mechanical transmission. Downtime: 6-8 hours.
5. Connection or Wiring Problems in Servos/Sensors:
   • Cause: Bending wear on cable chains, loose connections, damage from rodents or impacts.
   • Effect: Intermittent signals, loss of communication, emergency stops.
   • Impact: Sporadic arrests that are difficult to diagnose. Variable accumulated downtime.

6. Troubleshooting Guide

The following guide presents a structured approach to diagnosing common faults:

Problem: Servomotor does not start or produces a fault alarm

Step 1: Check the alarm on the servo controller display. Is it an overcurrent, overvoltage, undervoltage, overtemperature or encoder fault?

• If it is overcurrent/overload:

  a. Disconnect the motor from the mechanical load. Try to start the engine alone. If it starts, the problem is mechanical (excessive load, jamming, friction). Review the mechanics of the line.

  b. If the motor does not start without load either, check the resistance of the motor phases (U-V, V-W, W-U) with a multimeter. They must be similar and within nominal values. Also measure the insulation resistance of the motor to ground. A low value indicates an insulation fault.

  c. Confirm that the current limiting parameters in the servo driver are correct for the installed motor.

• If it is overvoltage/undervoltage:

  a. Check the mains supply voltage at the servo controller input. It must be within the nominal range (380-480V ±10%).

  b. In overvoltage, check the state of the braking resistor if applicable.

• If it is overtemperature:

  a. Clean the fans and heatsinks of the servo controller and servo motor.

  b. Verify that the motor load does not exceed 80-90% of its nominal capacity during continuous operation.

  c. Check the ambient temperature of the electrical cabinet and motor area. Ensure correct ventilation.

• If it is an encoder failure:

  a. Check the encoder cable for physical damage (cuts, crushes) or loose connections.

  b. Check the encoder power supply. If possible, use an oscilloscope to check the encoder output signals.

Problem: Pneumatic actuator slow, weak or not moving

Step 1: Check the air pressure at the actuator inlet. Is it within the operating range (e.g. 6 bar)?

• If the pressure is low:

  a. Check FRL unit: filter (clean/replace), regulator (adjust to desired pressure).

  b. Inspect the compressed air line from the FRL to the actuator for leaks (use leak detector or soap solution) or restrictions (crushed tubes, defective fittings).

• If the pressure is correct:

  a. Activate the valve that controls the actuator. Can you hear the click of the coil? Does air pass through the valve?

  • If the click is not heard, check the electrical supply to the valve coil.
  • If you hear but no air movement, the valve coil or spool may be stuck or damaged.

  b. If the valve is working correctly, the problem may be the actuator itself: worn internal seals, bent or seized stem. Consider replacing the actuator or its repair kit.

Problem: Sensor does not detect the object or generates false detections

Step 1: Clean the active surface or sensor lens. Ensure that there are no physical obstacles.

Step 2: Check the alignment of the sensor with respect to the object to be detected (in photoelectric sensors, ensure that the beam is correctly interrupted or reflected).

Step 3: Check the sensor wiring. Is it properly connected (power, signal) and undamaged?

Step 4: Check the sensor power supply (generally 10-30V DC). Is it stable?

Step 5: For sensors with sensitivity adjustment (e.g. capacitive, photoelectric), adjust based on material and object distance. Make sure there are no sources of electromagnetic interference nearby.

7. Spare Parts Strategy

Efficient spare parts management minimizes downtime and associated costs. It is recommended to classify spare parts as critical or non-critical.

Critical Spare Parts (High Downtime Impact, Long Delivery Time)

• Servo controllers: Complete units (e.g. DANFOSS 132F0020). Estimated downtime per failure: 2-4 hours. Downtime cost for a packaging line: €800-1500/hour (based on a production of 20,000 units/hour at €0.05-0.075/unit). Recommended stock: 1 unit in stock.
• Servomotors: Complete units of the most common type. Recommended stock: 1 unit.
• Complex Pneumatic Valves: Proportional or safety valves with special functions. Recommended stock: 1 unit of each critical type.
• Special Pneumatic Cylinder Assemblies: Cylinders with non-standard characteristics or dimensions. Recommended stock: 1 unit of each critical type.

Non-Critical Spare Parts (Low Downtime Impact, Short Delivery Time)

• Pneumatic Actuator Repair Kits: Seals, retainers, etc. Recommended stock: 2-3 kits for each common actuator type.
• Standard Proximity Sensors: Inductive, capacitive, photoelectric. Recommended stock: 3-5 units of each most used type/model.
• Pneumatic Fittings and Tubes: Connections, elbows, splices, tube segments. Recommended stock: Variety of common sizes.
• Servomotor/Encoder Cables: Pre-assembled segments or material to make. Recommended stock: 1-2 common lengths.

For the acquisition of original and compatible spare parts, UNITEC-D offers an efficient platform. We recommend maintaining a spare parts inventory based on criticality analysis and average lead times (2-4 weeks for specialized components, 1-3 days for consumables). A failure of a critical component such as a servo controller with no spare part available can incur downtime costs of up to €12,000 for one day of downtime, excluding loss of production and penalties for late deliveries.

8. Condition Monitoring Integration

The implementation of condition monitoring techniques is an advanced predictive maintenance strategy that aligns with the principles of Industry 4.0. It allows you to detect anomalies and predict failures before they occur, transforming maintenance from reactive to proactive.

• Servo Controllers and Servomotors:
  • Vibration Analysis (UNE-EN ISO 13443-1): Continuous or periodic monitoring of vibrations in servomotors and mechanical transmissions to detect imbalances, misalignments, bearing or gear failures.
  • Infrared Thermography: Temperature measurement in hot spots (terminals, heatsinks, bearings) to identify overloads or incipient insulation failures.
  • Motor Current Analysis: Detection of abnormal patterns in the current spectrum that may indicate mechanical or electrical failures.
  • Power Quality Monitoring (UNE-EN 50160): Evaluation of harmonics, voltage drops and peaks that may affect the useful life of the servo controller.
• Pneumatic Actuators:
  • Pressure and Flow Sensors: Monitoring of pressure fluctuations and air consumption in the actuators and pneumatic lines. A sustained increase in flow or a drop in pressure may indicate internal or external leaks.
  • Acoustic Leak Detection: Use of ultrasonic detectors to accurately identify small compressed air leaks, which contributes to significant energy savings (up to 30% of compressed air consumption).
• Sensors:
  • Self-Diagnostic Functions: Many modern sensors incorporate diagnostic outputs that indicate their operating status or the need for cleaning/resetting.
  • Output Signal Monitoring: Monitor the stability and reliability of the output signal to detect performance degradation.

9. Conclusion

The reliability of packaging lines is a differentiating factor in industrial competitiveness. A comprehensive maintenance approach, combining preventive strategies with condition monitoring and strategic spare parts management, is essential. The implementation of the protocols described here, together with the use of certified and high quality components, such as those offered by UNITEC-D, minimizes unplanned downtime, prolongs the useful life of assets and ensures compliance with safety and quality standards (CE, AENOR).

To explore our wide range of servo controllers, pneumatic actuators and sensors, and to optimize your spare parts strategy, visit the UNITEC-D E-Catalog.

10. References

• UNE-EN ISO 13849-1: Machine safety. Parts of the command systems related to safety. Part 1: General principles for design.
• UNE-EN ISO 13443-1: Mechanical vibrations. Measurement and evaluation of vibrations in machines.
• UNE-EN 60947-5-2: Low voltage switchgear. Part 5-2: Control devices and switches. Proximity detectors.
• UNE-EN 61800-3: Variable speed electric power drive systems. Part 3: Electromagnetic compatibility (EMC) requirements and specific test methods.
• UNE-EN 61800-5-2: Variable speed electric power drive systems. Part 5-2: Security requirements. Functional.
• UNE-EN 50160: Characteristics of the voltage supplied by the general distribution networks.
• ISO 15552: Pneumatic rod cylinders.
• ISO 6432: Pneumatic rod cylinders. Small dimensions.
• ISO 5599-1: Pneumatic control valves. Part 1: Basis for the selection and designation of valve characteristics.