Investigation of Countermeasures for AGV Start-Up Wheel Slip

Premise

• Target: indoor AGV
• Floor: epoxy, coated flooring, smooth concrete
• Speed range: low speed
• Phenomenon: slip occurs only at the instant of start-up
• Start-up stability prioritized over wear

At start-up, the governing factor is the static friction limit before transition to dynamic friction.
Required condition: Drive torque ＞ μs × N × r

μs: coefficient of static friction
N: drive wheel load
r: tire radius

Slip occurs when any of the following apply:
• Insufficient μs
• Insufficient N
• Excessive r
• Excessive peak torque

Causes

Material side

• PU hardness too high
• Insufficient hysteresis
• Surface too smooth
• Localized contact pressure distribution

Geometric side

• Large tire diameter
• Narrow width
• Short contact length

Vehicle side

• Low drive wheel load
• Excessive caster load on non-driven wheels
• Center of gravity biased toward non-driven side

Control side

• High peak torque at start-up
• No current limit setting
• No slip feedback

Countermeasures

Tire Side

• Lower PU hardness
Higher hysteresis orientation. Initial μ increase. Wear tends to increase.

• Shallow grooves, micro-sipes
Create initial shear response. May be counterproductive in dusty environments.

• Reduce tire diameter
Lower required start torque. Reduced step-climbing ability. Increased heat density.

• Increase tire width
Change contact condition. Lower contact pressure. Potential improvement in initial μ build-up.

• Vulcanized rubber tread
Designed for epoxy floors. High μ. Replacement-oriented wear concept.

• TPS-based TPE
For limited floor materials. Durability evaluation not fully organized.

Non-Tire Measures

• Increase vehicle weight
Particularly increasing drive wheel load. N rises and slip limit expands. Energy consumption worsens.

• Add drive wheels
From 2WD to 4WD. Total driven-wheel N increases. Control becomes more complex.

• Limit start-up torque
Soft start. Suppress peak torque. Acceleration time increases.

• Slip control
Slip ratio feedback. Automatic torque reduction. Additional sensors required.

Structural Organization

Short-term response

• Start-up torque limitation
• Software control

Mid-term response

• Hardness optimization
• Micro-pattern design

Long-term response

• Redesign of vehicle architecture and load distribution
• Differentiated tire lines by floor condition

Constraints

• Wear and μ tend to be inversely correlated
• Heat generation correlates with hysteresis
• Floor material differences are dominant variables
• Groove effectiveness declines in dusty environments

Points for Consideration

Design to eliminate slip by accepting wear.
Design to tolerate limited slip and suppress via control.
Specialization by floor type or general-purpose solution.
In AGV applications, “failure mode” and “start-up stability” may dominate over absolute wear volume.
Consideration of whether performance indices should be redefined.