In the automotive manufacturing logistics automation system, the stable operation of AGVs (Automated Guided Vehicles) directly determines the efficiency and accuracy of the SPS (Set Parts Supply) model. In a certain SPS project, three key technical issues frequently occurred in AGV equipment: lifting plate clearance, load derailment, and pallet pin positioning deviation. This paper analyzes the root causes from the perspectives of mechanical calculation, structural design, and transmission principles, and proposes practical, system-level solutions to provide technical reference for the reliable application of AGVs in automotive manufacturing logistics.
1. Excessive Clearance After Lifting Plate Braking: Dual Optimization of Transmission and Gear Meshing
As the core component for carrying material carts, the lifting plate still has a manually movable clearance even when the brake is fully engaged. Under load, the material cart can still be rotated counterclockwise, seriously affecting positioning accuracy and creating risks of material deviation.
(1) Root Cause Analysis: Transmission Connection and Gear Meshing Defects
Through teardown and analysis of the AGV lifting plate transmission system, the problems were found to originate mainly from the following aspects:
Failure of the motor–gearbox transmission connection
The connection between the motor and gearbox uses a clamping collar with screws. The original tightening torque was insufficient. Under load, micro angular displacement occurred between the gearbox and motor, creating a "free rotation clearance."
Excessive meshing clearance in the gear pair
The meshing clearance between the large slewing bearing gear (180 teeth) and the gearbox output pinion (20 teeth) exceeded the design tolerance, further amplifying the amount of rotational free play in the lifting plate.
(2) Mechanical Boundary Calculation: Quantifying the External Force Required to Rotate the Plate
Based on torque transmission principles, the total resisting torque model required to rotate the plate is established:
FL ≥ T × i₁ × η₁ × η₂ × i₂
F: Force required to rotate the plate (N)
L: Distance from force application point to plate center (m)
T: Brake holding torque (1.5 Nm)
i₁: Gearbox reduction ratio (40)
i₂: Gear transmission ratio (190/20 = 9)
η₁: Gearbox efficiency (0.98)
η₂: Gear efficiency (0.95)
The calculation shows that when the force arm is 0.6 m, 1.0 m, and 1.5 m, the required forces are 873.8 N, 502.7 N, and 335.0 N, corresponding to equivalent masses of 87.4 kg, 50.3 kg, and 33.5 kg. The results indicate that mechanical structure alone cannot fully eliminate the clearance; control-system compensation is required.
(3) Systematic Rectification Solutions
Transmission connection upgrade
Replace the original clamp connection with a keyed NORD gearbox. The key structure prevents relative rotation between the motor and gearbox, completely eliminating rotational free play.
Gear meshing optimization
Center distance adjustment: Mill the gearbox mounting holes to control meshing clearance within 0.1–0.15 mm.
Material and process upgrade: Use 20CrMnTi with carburizing and quenching to reach Grade 6 accuracy (GB/T 10095.1-2008).
Add a parallel key connection: Optimize H9/h8 tolerance to reduce rotational clearance between gear and shaft.
Control-system compensation
A clearance compensation algorithm is embedded in the AGV controller. After braking, the encoder checks residual deviation; if above 0.5°, the system performs automatic fine adjustment to keep the final deviation within ±0.1°.
2. AGV Load Derailment: System Improvements in Load Distribution and Track Adaptability
The AGV frequently derailed when transporting a 1000 kg air-storage tank. Routine hardware validation found no abnormalities, requiring deeper analysis from load distribution and dynamic behavior perspectives.
(1) Hardware Capability Verification
Verification of drive power, output torque, and spring pressing force confirmed that all parameters theoretically satisfy load requirements, ruling out insufficient power as the cause.
(2) Root Causes of Derailment
Load eccentricity resulting in uneven wheel pressure
The cylindrical air tank caused the center of gravity to deviate 150–200 mm from the AGV center, significantly increasing wheel pressure on one side and reducing it on the other. During steering or passing track joints, derailment becomes more likely.
Insufficient track interface accuracy
Some track joints had height differences of 0.5–0.8 mm (specification ≤0.3 mm). Heavy-load AGVs produce impact forces when passing such joints, increasing derailment probability.
Steering control algorithm not adapted to heavy-load conditions
The fixed angular velocity steering mode does not consider increased inertia under heavy loads, amplifying impact forces at track joints.
(3) Comprehensive Rectification Measures
Load control and monitoring
Short-term: Reduce single-load to 800 kg; limit center-of-gravity deviation to ≤50 mm.
Long-term: Add load-eccentricity sensors; prohibit AGV startup when exceeding limits.
Track joint accuracy restoration
Grind and level joints to ensure ≤0.3 mm height difference.
Add polyurethane buffers to reduce impact vibration.
Steering control algorithm upgrade
Establish a load–angular velocity matching table to limit steering speed under heavy load.
Use vision to identify track joints and pre-emptively reduce speed.
3. Pallet Pin Positioning Deviation: System Compensation Across Multiple Error Sources
When the lifting AGV executes pin insertion, it often fails to engage the material cart's locking holes. The root cause is the accumulation of errors across multiple stages: manual placement, cart movement, structural design, and AGV rotation.
(1) Error Source Analysis
Manual alignment error: Initial placement deviation can reach ±20 mm.
Cart drift: Floor slope causes secondary drift of ±10 mm.
Defective hole structure: Thin steel plate and straight-hole design cannot absorb deviation.
Rotational plate error: Micro-movement during lifting introduces coaxiality deviation.
(2) Full-chain Error Control Solutions
Rigid alignment system
Install L-shaped ground stops combined with laser alignment sensors to reduce initial deviation to within ±3 mm.
Anti-drift design for carts
Add ratchet brake casters to prevent movement on slopes ≤1°.
Upgrade of positioning hole structure
Replace 1.5 mm thin plate with 8 mm Q345 steel.
Change straight hole to a composite hole with a 60° chamfer; entrance diameter φ15 mm; guide section length 10 mm.
Hone inner wall to reduce friction.
Vision-based compensation system
A vision camera identifies the actual hole position and drives X/Y/θ compensation of the rotating plate to keep coaxial deviation ≤2 mm.
4. Summary
The AGV issues discussed in this paper essentially reflect insufficient system matching among mechanical structures, control algorithms, and field conditions. Through the systematic engineering approach of "quantitative analysis, full-chain coordination, and dynamic–static combined compensation," the implemented solutions achieved remarkable results: the lifting plate clearance issue was completely resolved, AGV derailment frequency dropped to zero, and pin insertion success rate increased to 99.5%. These solutions provide valuable reference for improving AGV system stability in high-throughput logistics scenarios such as automotive manufacturing.
