Practical Guide to AGV/AMR Fleet Maintenance: Wheels, Sensors, Batteries and Chargers

1. Scope and Purpose

This practical guide details the essential procedures for preventive and corrective maintenance of autonomous guided vehicles (AGV) and autonomous mobile robots (AMR) used in manufacturing environments. It specifically covers wheel replacement, sensor calibration, battery conditioning and charging system checks. The objective is to guarantee maximum operational availability of the fleet, optimize performance and extend the useful life of equipment, minimizing unscheduled stops and maintenance costs.

This maintenance must be carried out according to the recommended schedule or whenever there are signs of performance degradation, such as route deviation, communication failures or reduced battery autonomy. Strict adherence to this guide directly contributes to operational safety and production line efficiency.

2. Safety Precautions

WARNING: Failure to follow these safety instructions could result in serious injury or damage to equipment.

Always use appropriate Personal Protective Equipment (PPE): safety glasses, protective gloves (anti-cut and insulating for electrical work), safety shoes with steel toecaps.

BEFORE starting any intervention, carry out the Lockout/Tagout procedure (LOTO - Lockout/Tagout) in accordance with standard NR-10 for electrical systems and NR-12 for machines and equipment. Disconnect and lock out all power sources (electrical, hydraulic, pneumatic) and ensure that the equipment cannot be accidentally restarted. Check the absence of voltage with a calibrated multimeter.

Suspended loads: When lifting the AGV/AMR, only use designated lifting points and lifting equipment with adequate capacity and inspected. Stay away from the suspended load operating area.

Batteries: Handling batteries requires special attention. They may contain corrosive chemicals (acid) and release flammable gases. Avoid short circuits. In case of leakage, neutralize the acid with baking soda and dispose of properly.

Unexpected Movement: Ensure that the AGV/AMR is immobilized and locked before any intervention, even with the power off, to avoid accidental movements on ramps or uneven surfaces.

3. Tools and Materials Required

The following tools and materials are mandatory for carrying out maintenance tasks:

4. Pre-Maintenance Inspection Checklist

Perform this inspection before beginning any maintenance procedures to identify obvious problems and ensure safety.

5. Step by Step Procedure

5.1. Wheel Replacement

1. Immobilization and Locking:
   1. Position the AGV/AMR on a flat, firm surface, away from the workflow.
   2. Press the emergency stop button.
   3. Perform the full LOTO procedure, isolating all power sources.
   4. Check the absence of voltage with the multimeter on the power interfaces.
   5. Use chocks on unworked wheels to ensure stability.
   6. Do not start work before confirming the power lock and complete immobilization of the vehicle.
2. Lifting and Support:
   1. Use the hydraulic jack to raise the AGV/AMR using the lifting points designated by the manufacturer, until the wheel to be replaced is free from the ground.
   2. Place safety stands under the chassis, close to the lifting points, to support the AGV/AMR. Make sure equipment is stable on stands.
   3. Lower the jack slightly until the weight is supported by the jack stands.
   4. Never work under an AGV/AMR supported only by the jack. Always use safety stands.
3. Removing the Old Wheel:
   1. Using the torque wrench, loosen the wheel fixing bolts. If the wheel has a cover, remove it first.
   2. Remove the screws and washer (if present).
   3. Remove the wheel from the axle, observing the presence of spacers or additional components.
   4. Inspect the wheel axle and hub for wear, damage or dirt. Clean them if necessary.
   5. Do not discard old screws and washers before checking whether the new ones are compatible or will be reused.
4. New Wheel Installation:
   1. Check that the new wheel is the correct type and specification (hardness, diameter, material, bearing) according to the manufacturer's manual and the spare part code.
   2. Apply a thin coat of high-performance grease to the shaft if recommended by the manufacturer.
   3. Position the new wheel on the axle, aligning the bolt holes.
   4. Insert the fixing screws (use new screws if the manufacturer specifies or if the old ones are worn).
   5. Apply medium resistance chemical lock (e.g. Loctite 243) to the screw threads.
   6. Tighten the screws by hand until they stop.
   7. Using a torque wrench, tighten the screws in a star or cross pattern (if there are more than 4 screws) to the torque specified by the manufacturer. Illustrative torque for M10 screws: 50 Nm. M8 screws: 28 Nm.
   8. Do not exceed the specified torque as this may damage the bolts or wheel hub. Insufficient torque may cause loosening.
5. Finishing:
   1. Slightly lift the AGV/AMR with the jack, remove the safety stands and gently lower the equipment to the ground.
   2. Remove the shims.
   3. Remove the LOTO device and re-energize the AGV/AMR.
   4. Perform a straight-line motion test to verify alignment and absence of vibrations.

5.2. Sensor Calibration

Sensors (LIDAR, ultrasonic, proximity, encoders) are critical for the navigation and safety of the AGV/AMR. Calibration ensures the accuracy of your readings.

1. Preparation:
   1. Position the AGV/AMR in a designated calibration area, free from obstructions and with reference markings.
   2. Activate the LOTO according to the standard procedure.
   3. Carefully clean the lenses and sensor surfaces with a clean cloth and electronic contact cleaner, if necessary, or dry compressed air (at low pressure).
   4. Dirt on sensors is the most common cause of calibration failures.
2. Calibration of Distance Sensors (LIDAR/Ultrasonic):
   1. Access the AGV/AMR manufacturer's diagnostic/calibration software via service interface (Ethernet/USB).
   2. Position calibrated reference plates at known distances (e.g. 500 mm, 1000 mm, 2000 mm) from the sensor.
   3. Adjust the sensor's physical position (if adjustable) or software parameters until digital readings match actual distances.
   4. The expected accuracy for modern LIDAR sensors is +/- 5 mm at distances up to 10 meters. Ultrasonic sensors may have a larger tolerance of +/- 10 mm.
   5. Check the fixation of the sensors after calibration. The illustrative torque for M5 sensor fixing screws is 8 Nm.
   6. Reading deviations can be caused by vibration, physical misalignment or incorrect software parameters.
3. Calibration of Proximity/Line Sensors:
   1. Use the calibration kit with tapes or reference objects.
   2. Adjust the detection distance according to the manual, normally between 1 mm and 5 mm from the target object for inductive or capacitive sensors.
   3. For optical line sensors, use the system guide tape and adjust the sensitivity until the sensor reliably detects the line.
   4. Make sure there is no electromagnetic interference (EMI) or excessive ambient light that could affect the reading.
4. Calibration of Wheel Encoders:
   1. Generally, the encoders are automatically calibrated by the system or require a 'teach-in' procedure via software, where the AGV/AMR travels a known distance.
   2. Check the diagnostic software for correct number of pulses per revolution and for counting errors.
   3. Dirty or damaged encoders can cause significant route deviations. Clean them carefully if accessible.

5.3. Battery Conditioning and Inspection

Regular conditioning of batteries, especially lead-acid and lithium-ion batteries, is essential to their longevity and performance.

1. Battery Safety:
   1. (SAFETY WARNING) Wear insulated gloves and protective glasses when handling batteries, especially lead-acid.
   2. Check the battery casing for swelling, leaks, cracks or corroded terminals.
   3. Clean the battery terminals with a terminal brush and apply protective grease to prevent oxidation.
   4. Corroded terminals increase resistance and generate excessive heat, reducing efficiency.
2. Voltage and Temperature Check:
   1. With the AGV/AMR turned off (LOTO applied), use the multimeter on the DC voltage scale to measure the total battery voltage. For 24V systems, a fully charged battery should read approximately 25.2V to 25.8V. For 48V, about 50.4V to 51.6V.
   2. Use the infrared thermometer to check the battery surface temperature. The ideal operating temperature is between 20°C and 30°C. Temperatures above 40°C during charging indicate a problem.
   3. Significant voltage variations between cells (for multi-cell batteries) or high temperatures may indicate defective cells or overcharging.
3. Conditioning (for Lead-Acid batteries):
   1. If the battery is lead-acid, check the electrolyte level in each cell (if applicable). Refill with distilled water to the indicated level, NEVER with acid.
   2. Schedule an equalization or conditioning cycle through the battery management system (BMS) or smart charger, if available. This process applies a controlled charge to balance cell voltage.
   3. Lack of distilled water or uneven equalization drastically reduces lead-acid battery life.
4. BMS (Battery Management System) Inspection:
   1. Access BMS logs and status via diagnostic software. Check errors, overcharge/undercharge history and cell balancing (for Lithium-Ion).
   2. Confirm that the BMS is reporting remaining capacity accurately.
   3. A failed BMS may not protect the battery against dangerous conditions or provide inaccurate readings.

5.4. Charging System Check

An efficient charging system is critical to fleet autonomy.

1. Visual Inspection of Charging Station:
   1. Check the station's power cord for physical damage, abrasions, or signs of overheating.
   2. Inspect the charging contacts (pins, plates) on the AGV/AMR and station for dirt, corrosion, wear or misalignment.
   3. Clean the contacts with electrical contact cleaner and an anti-static brush.
   4. Dirty or damaged contacts can cause charging failure and electrical arcing.
2. Checking the Charger Output Voltage:
   1. With the AGV/AMR disconnected from the station, use the multimeter on the DC voltage scale to measure the charger output voltage at the contact terminals.
   2. For a 24V charger, the voltage should be around 28V to 29.2V (float or absorption voltage). For a 48V charger, expect between 56V and 58.4V. Consult the charger manual for exact values.
   3. Voltages outside the specified range may damage the battery or prevent charging.
3. Charging Test:
   1. Connect the AGV/AMR to the charging station and observe the beginning of the charging cycle.
   2. Monitor the AGV/AMR display or diagnostic software to confirm that the “charging” status is active.
   3. Use a clamp meter (if available and applicable) to check the charging current. A typical current for AGV/AMR batteries ranges from 20A to 50A, depending on battery capacity and charger.
   4. Check the temperature of the charging connectors and battery during the cycle with the infrared thermometer. No area should be overheated (above 45°C at the connectors).
   5. Slow or ineffective charging may indicate damaged cables, a faulty charger or a communication failure between the AGV/AMR and the station.
4. Communication Check:
   1. Many smart charging systems communicate with the AGV/AMR. Check communication logs in the software.
   2. Communication failures can prevent optimized charging or even start the cycle.

6. Post-Maintenance Verification Checklist

Upon completion of maintenance procedures, perform the following tests to ensure correct and safe operation of the AGV/AMR.

7. Troubleshooting Guide

This guide helps you identify and fix common problems.

8. Recommended Maintenance Schedule

9. Spare Parts Reference

To ensure operational continuity, always use quality and compatible replacement parts. Consult the UNITEC-D e-catalog for availability and specifications.

See our full e-catalog for details and ordering: https://www.unitecd.com/e-catalog/

10. References

• ABNT NBR 5410: Low Voltage Electrical Installations.
• ABNT NBR 14136: Plugs and Sockets for Domestic and Similar Use – Brazilian Standard.
• NR-10: Safety in Electricity Installations and Services (Ministry of Labor and Employment).
• NR-12: Occupational Safety in Machinery and Equipment (Ministry of Labor and Employment).
• Technical documentation from the AGV/AMR Manufacturer (Service Manual, Electrical Diagrams, etc.).
• Technical Documentation from the Battery Charger Manufacturer.
• ISO 3691-4: Industrial trucks - Safety requirements and verification - Part 4: Driverless industrial trucks and their systems.