Maintenance instructions for automated guided vehicles (AGVs) and autonomous mobile robots (AMR): wheel replacement, sensor calibration, battery conditioning and charging system testing

1. Scope & Purpose

This comprehensive maintenance guide is designed to ensure the reliable and safe operation of automated guided vehicles (AGVs) and autonomous mobile robots (AMR) in industrial environments. It focuses on critical aspects of preventive maintenance that are essential for the availability and lifespan of your AGV/AMR fleet. The guide covers detailed wheel changing procedures, precise sensor calibration, proper battery conditioning, and a thorough charging system check. Carrying out this maintenance work regularly minimizes downtime, optimizes operational efficiency and guarantees compliance with relevant safety standards in manufacturing and logistics facilities.

2. Safety precautions

WARNING: Always observe the general occupational safety regulations and the specific manufacturer instructions for the respective AGV/AMR. Work on electrical systems and batteries may only be carried out by qualified specialist personnel. Failure to observe this can result in a risk of fatal injury due to electrical voltage, chemicals or mechanical crushing hazards.

Energy insulation (Lockout/Tagout - LOTO): Before starting any work on the AGV/AMR, the machine must be completely isolated from all energy sources (electrical, hydraulic, pneumatic, kinetic) in accordance with DIN EN ISO 14118 (Safety of Machines - Avoiding Unexpected Start-Up) and secured against being switched on again unintentionally. To do this, use a LOTO kit.

Personal Protective Equipment (PPE): Always wear appropriate PPE during all maintenance work. These include:

• Safety shoes (category S3 according to DIN EN ISO 20345)
• Protective gloves (cut-resistant, chemical-resistant for batteries)
• Safety glasses (according to DIN EN 166)
• Hearing protection (if required)
• When working on batteries: face shield and acid-proof protective clothing

Battery Dangers: Lithium-ion and lead-acid batteries pose risks from short circuits, fire, explosion, chemical burns and the release of gases. Ensure good ventilation and avoid sparks.

3. Tools & Materials Required

4. Pre-inspection checklist

Perform this visual and functional inspection before beginning detailed maintenance to assess the overall condition of the AGV/AMR and identify any obvious defects.

5. Step-by-step instructions

5.1. Wheel change

1. Provide safety:

   Shut down the AGV/AMR in a safe area. Press the emergency stop button.

   WARNING: Completely disconnect the AGV/AMR from the power supply and secure it against unintentional switching on according to the LOTO procedure (DIN EN ISO 14118). Disconnect the main battery connector or operate the battery circuit breaker.

   Raise the AGV/AMR using a suitable lifting tool (e.g. hydraulic lifting table or workshop crane) until the wheels to be changed hang freely in the air. Additionally secure the AGV/AMR against falling with support stands. Error: Inadequate securing can result in serious injury.

2. Dismantle the old wheel:

   Loosen the fastening screws (e.g. M12, quality 8.8) of the wheel with a suitable socket wrench. Carefully remove the wheel from the axle.

   Error: Using an impact wrench that is not calibrated or incorrectly adjusted can damage threads on the axle or screws.

3. Clean the axle and wheel hub:

   Thoroughly clean the wheel axle and the wheel mount on the chassis from dirt, rust and old grease residue. Use suitable cleaning cloths and, if necessary, isopropyl alcohol (IPA). Check the axle for damage.

4. Mount new wheel:

   Place the new wheel flush on the axle. Make sure the alignment is correct if the wheel is directional. Lightly grease the contact surfaces of the screw heads with the recommended lithium soap grease KP2K-20.

   Insert the fastening screws and first tighten them hand-tight.

5. Tighten torque:

   Tighten the screws using torque wrench 1 (20-100 Nm range) in a criss-cross pattern to the manufacturer's specified torque. Typical values ​​are 80 Nm ± 5 Nm for steel wheels or 45 Nm ± 3 Nm for plastic wheels (e.g. Vulkollan).

   Check: Visually check that all screws are flush and that the wheel contact surfaces are completely in contact. Repeat the torque tightening after a short operating time (approx. 10 hours) to check the setting behavior.

6. Functional test:

   Carefully lower the AGV/AMR and remove the lifting tool and the safety brackets. Check the freedom of movement of the new wheels by turning them manually. There should be no grinding noises or blockages.

5.2. Sensor calibration

1. Preparation and cleaning:

   Place the AGV/AMR on a flat, defined calibration surface (e.g. in the maintenance area). Press the emergency stop and secure the device against unintentional starting. Thoroughly clean all sensor surfaces (laser, camera, ultrasound) with lint-free cloths and IPA. Error: Contamination on the sensor optics leads to incorrect measurement results and incorrect calibrations.

2. Laser scanner (e.g. Sick S300 / Leuze RSL):

   Start the manufacturer-specific calibration software of the laser scanner. Place reference points or calibration targets (e.g. reflective plates according to ISO 13482) at the distance and angle to the scanner specified by the manufacturer.

   Adjust the offset values ​​and angle corrections in the software until the measured distances to the reference points are within the tolerance (e.g. ± 2 mm at 5 m distance). The typical scanning resolution should be 0.1°.

   Check: Check the displayed scan area in the software for plausibility and correct recognition of the reference points.

3. Camera systems (e.g. Basler Ace / Cognex In-Sight):

   Use the camera system's calibration software. Position a defined calibration board (e.g. checkerboard pattern with known dimensions) in the camera's field of view. Make sure the lighting is even.

   Perform calibration to determine distortion corrections and the intrinsic (focal length, main point) and extrinsic (position, orientation of the camera in space) parameters. Save the calibration data.

   Check: Take a test image of the calibration board and analyze it for image quality, geometric fidelity and correct dimensional accuracy.

4. Ultrasonic sensors (e.g. Baumer UNDK / ifm efector):

   Check the distance measurement of the ultrasonic sensors on defined reference objects with a known distance (e.g. a wall 1 m away). Compare the sensor reading with the actual distance. The tolerance should be ± 5 mm at 1 m distance.

   If necessary, adjust the sensitivity or switching points using the parameterization software. Error: Ambient temperature and humidity can affect ultrasonic measurements. Take this into account when calibrating.

5. Save and Document:

   Save all calibrated parameters in the AGV/AMR control system. Create a detailed calibration report with date, time, technician name and achieved values. This is important for traceability and compliance with machine safety (DIN EN ISO 3691-4).

5.3. Battery conditioning

1. Battery Safety:

   WARNING: Working on battery systems requires special training and PPE (face protection, acid-resistant gloves, fire-resistant clothing). There is a high risk of short circuits, chemicals (for lead-acid batteries), thermal runaway (for Li-ion batteries) and the release of flammable gases. Ensure adequate ventilation.

   Disconnect the AGV/AMR from the charging station and place it in a well-ventilated area. Turn off the FTS/AMR completely.

2. Diagnostics of the battery management system (BMS):

   Connect the diagnostic device to the BMS of the AGV/AMR. Read the data from individual cells. Pay attention to:

   • Cell voltage deviations: Should not be more than 50 mV between individual cells.
   • Temperature imbalances: Max. 5°C difference between cells.
   • Internal resistance of the cells: Compare the values ​​with the manufacturer's specifications. Elevated values ​​indicate cell aging.
   • Number of charging cycles and the state of health (SoH).

   Error: Neglecting BMS data can lead to premature battery failure and safety risks.

3. Controlled Discharge Cycle:

   Connect the battery to an external battery conditioning or discharging device. Discharge the battery in a controlled manner up to an SoC of approx. 20%. For lead-acid batteries, the discharge current (C rate) should be approximately C/10, for lithium-ion batteries up to C/5 to avoid damage. Pay attention to the manufacturer's instructions.

   Error: A deep discharge below the minimum voltage specified by the manufacturer can lead to irreversible damage and loss of capacity.

4. Charging cycle (equalization charging/balancing):

   Fully charge the battery with the conditioning device. The device should have a balancer function, especially with lithium-ion batteries, to balance the voltages of the individual cells. Monitor the overall voltage and current while charging. For lead-acid batteries, equalization charging is important to reduce sulfation.

   Check: After charging, the cell voltages should be within the tolerance of ± 20 mV again.

5. Capacity test:

   After conditioning, carry out a capacity test by discharging the fully charged battery in a controlled manner with a defined current and measuring the capacity removed. Compare this value with the rated capacity of the battery. As a rule, >80% of the nominal capacity is acceptable.

6. Documentation:

   Document the battery condition, the measured capacity, the charging and discharging cycles carried out and any anomalies in the maintenance log.

5.4. Charging system check

1. Visual inspection of the charging infrastructure:

   Check the charging station or the charging contacts on the floor for mechanical damage, deformation, heavy contamination, corrosion or tarnishing marks. Check all visible cables and lines for chafing, cracks or kinks.

2. Electrical testing of the charging station (according to VDE 0100-600, VDE 0113-1, DGUV regulation 3):

   WARNING: Danger to life due to electrical voltage! These measurements may only be carried out by a certified electrician and require compliance with all safety regulations and the use of suitable, insulated measuring devices (multimeter CAT III 600V).

   • Output voltage measurement: Measure the output voltage of the charging station without an FTS/AMR connected. The value should be within the tolerance range (e.g. 48V DC ± 0.5V).
   • Charging current measurement: Measure the charging current with a clamp ammeter while an AGV/AMR is charging. The current should be high at the beginning of the charging cycle (e.g. 50A) and decrease as the state of charge increases.
   • Protective conductor test: Check the continuity of the protective conductor (RPE) from the charging station to the AGV/AMR. The resistance must be < 0.1 Ohm.
   • Insulation resistance measurement: Carry out an insulation resistance measurement between the active conductors and the protective conductor. The value must be > 1 Mohm.

   Errors: Incorrect electrical parameters can lead to inefficient charging, overheating or even fires.

3. Communication check:

   Check the communication interface (e.g. CAN bus, Ethernet, WLAN) between the AGV/AMR and the charging station. Check the control system or the AGV/AMR diagnostic software for communication errors or timeouts during the charging process.

   Check: The AGV/AMR must be able to drive independently to the charging station, start the charging process and end it after reaching the target SoC.

4. Mechanical testing of the contact:

   Check the precise alignment of the charging contacts of the AGV/AMR and charging station. Make sure that there is sufficient pressure on the contacts to ensure low contact resistance.

6. Post-maintenance checklist

After completing all maintenance work, perform these checks to ensure the correct function and safety of the AGV/AMR.

7. Troubleshooting Guide

This manual provides typical symptoms, their likely causes, and recommended corrective actions to quickly resolve AGV/AMR system malfunctions.

8. Recommended maintenance schedule

This plan provides a preventive maintenance policy for your AGV/AMR fleet. Frequency and duration may vary depending on operating intensity and environmental conditions.

9. Spare parts reference

A selection of common spare parts for AGV/AMR systems that you should have on hand to ensure operational availability. The specifications mentioned here are typical examples; Precise information can always be found in the manufacturer's documents.

For additional spare parts and specific components, visit our e-catalog at www.unitecd.com/e-catalog/.

10. References

• DIN EN ISO 14118: Machine safety – avoiding unexpected start-ups.
• DIN EN ISO 3691-4: Industrial trucks - Safety requirements and verification - Part 4: Driverless industrial trucks and their systems.
• DIN EN ISO 13849-1: Safety of machines - Safety-related parts of controls - Part 1: General design principles.
• DIN EN ISO 20345: Personal protective equipment – ​​safety shoes.
• DIN EN 166: Personal eye protection – requirements.
• VDE 0100-600: Setting up low-voltage systems – testing.
• VDE 0113-1 (EN 60204-1): Safety of machines - Electrical equipment of machines - General requirements.
• DGUV regulation 3 (formerly BGV A3): Electrical systems and equipment.
• DIN ISO 6789: Micrometer screws with non-digital display - requirements and tests.
• Manufacturer documentation: Specific maintenance and operating instructions for the AGV/AMR systems used (e.g. Kuka, Omron, Grenzbach, Agilox).