In the automotive manufacturing logistics system, AGVs serve as key equipment for material transportation, and the stability of their mechanical systems directly affects the continuity of production takt. This article focuses on three core modules - the towing mechanism, the drive system, and the AGV body operation - and systematically analyzes the causes and solutions of typical mechanical failures under the high-load and high-takt characteristics of automotive logistics.
1. Towing Mechanism: Structural Principle and Typical Failure Analysis
The towing mechanism is the core unit enabling the AGV and the material cart to "lock–unlock." With a daily operating frequency exceeding 500 cycles and a load capacity of 500–3000 kg, long-term operation often leads to mechanical failures.
Its operating principle is based on converting rotational motion into linear motion: the towing motor drives the rotating disk through a coupling, and the cam follower converts circular motion into the linear movement of the lifting rod. During upward motion, the compressed spring provides the restoring force; during downward motion, the cam forces the rod to descend. The slotted photoelectric sensor keeps positioning accuracy within ±1 mm.
Lifting-rod jamming is the most frequent failure and mainly originates from four aspects: first, foreign objects such as iron filings or oil contamination on the ground intrude into the mechanism, causing the friction coefficient to rise sharply from 0.15 to above 0.4; second, spring fatigue exceeds 20%, making the restoring force insufficient to overcome the rod's own weight; third, wear of the cam follower bearing converts rolling friction into sliding friction; fourth, insufficient or loose set-screw length leads to transmission misalignment. Solutions include replacing bearings with PA66 + glass-fiber materials, using 50CrVA alloy spring steel, selecting sealed-type cam followers, and increasing the set-screw length to 16 mm combined with thread-locking adhesive.
Motor burnout is typically a chain reaction of mechanical jamming. The stall current may reach 5–8 times the rated value, causing coil temperature to exceed 250°C within 3–5 minutes, leading to insulation failure. Preventive measures include checking winding insulation resistance (>0.5 MΩ required), adding a stall protector, and configuring a lifting-timeout alarm.
2. Drive Mechanisms: Failure Differences and Troubleshooting Across Three Drive Types
Differential drive is suitable for straight-line motion or small-radius turns, achieving steering through speed differences between the left and right motors. Common failures include undesired deviation or derailment due to missing keys or excessive keyway clearance. The standard fit clearance is 0.01–0.03 mm. Troubleshooting includes dismantling the drive shaft to check the key; install a new one if missing, and replace with a 45-steel key if the clearance is excessive. Cable wear requires replacing with high-temperature-resistant ties, with fixing points every 300 mm, and adding nylon drag chains at contact points between cables and chassis. Insufficient traction requires inspecting deformed drive springs, stroke deviation of the push-rod motor, and wear of oil-free bushings.
Differential-rotation drive is suitable for in-place rotation and complex paths and, with independent modular design, enables steering in narrow aisles. Under no-load conditions, S-shaped deviation primarily results from asymmetry between the left and right drives; checks include key installation, loose driver wiring, and consistency of damping-spring compression. Under loaded conditions, S-shaped deviation is directly related to load distribution; troubleshooting includes checking spring deformation, structural bending, and load offset. A square ruler is used to measure the verticality of the drive mounting base, with an allowable error ≤0.5 mm/m. The cart's center of gravity should not deviate from the AGV center by more than 100 mm.
AGV drive wheel (steering-wheel) drive is used in bi-directional latent-type or top-carry AGVs, typically supporting loads ≥1500 kg. Slippage essentially arises from insufficient driving force, mainly caused by spring failure that reduces ground-contact pressure or by guide-bushing wear exceeding 0.15 mm, leading to radial displacement. Solutions include replacing rectangular-section springs and adjusting the nut to maintain a compression range of 8–12 mm; inspecting the inner wall of the copper guide bushing, and replacing it with a tin-bronze bushing if wear exceeds 0.2 mm, followed by applying lithium-based grease.
3. AGV Body Operation: Systematic Troubleshooting Methods
Derailment is often caused by excessive steering resistance. For differential drive, the oil-free bushing on the connecting flange should be checked for wear. For AGV drive wheel (steering-wheel) drive, the rotational resistance of the slewing bearing should be inspected. Universal-wheel design defects - including an undersized wheel diameter, overly wide wheel surface, or overly soft material - also increase steering resistance. External factors include excessive turning speed, overly long carts, and load offset. When the magnetic tape's turning radius is below 500 mm, the AGV speed must be ≤20 m/min, and load-offset ratio should be controlled within 10%.
Slippage requires quantitative checks from three aspects: pressure, friction coefficient, and load. Drive-spring compression should be ≥5 mm, and the AGV's own weight should not be less than one-third of the cart's weight; otherwise, counterweights must be added. A reduced friction coefficient may result from drive-wheel surface wear exceeding 5 mm or from floor oil contamination; solutions include replacing the polyurethane tread or cleaning the floor. Load offset reduces ground contact pressure on one drive wheel, requiring adjustment of the cart's center of gravity.
Path-deviation issues involve path accuracy errors. If the directional wheel is misaligned, the angle between it and the AGV's centerline should be ≤1°, requiring laser alignment calibration. Magnetic-navigation errors may arise from misaligned magnetic tape installation or inconsistent spacing and require recalibration. A center-of-gravity deviation exceeding 50 mm results in uneven load distribution between the two drive wheels; a center-of-gravity measuring device should be used to correct this with counterweights.
4. Conclusion: A Preventive System for Mechanical Failures in Automotive-Logistics AGVs
Based on the above failure analysis, automotive-logistics AGVs require a three-level preventive system. First-level prevention (design stage) involves selecting components suitable for automotive logistics, reserving 10–20% performance redundancy, and enhancing protective structures (anti-collision blocks, drag chains, dust covers). Second-level prevention (operation and maintenance) requires establishing daily, weekly, and monthly inspections: daily inspection of lifting-rod jamming and drive-wheel wear; weekly inspection of spring force and cable fixation; monthly inspection of motor insulation and bearing clearance. At the same time, a fault database should be built to track high-frequency failures. Third-level prevention (post-failure) requires full-load testing after repairs (e.g., ten full-load operating cycles) and specialized training for maintenance personnel. Through closed-loop management of "principle–failure–troubleshooting–prevention," AGV mechanical downtime can be reduced to less than one hour per month, ensuring continuous and efficient operation of the automotive manufacturing logistics system.
