In previous articles, we explored various aspects of AGV technology. Now, we delve deeper into one of the most critical components of AGV systems: the suspension system. The primary function of a suspension system is to adjust the normal force applied to the steering wheels, ensuring that it is neither too low (which could cause slippage and traction failure) nor too high (which could lead to excessive current draw and a range of issues, including wheel overload).
Role of Springs in AGV Suspension
Springs are the most commonly used components in suspension systems. By leveraging the elasticity of compressed springs, the suspension automatically adjusts the normal force on the steering wheels, ensuring stable AGV operation.
Most suspension mechanisms are equipped with devices that allow the adjustment of the initial or pre-compression amount of the spring, significantly increasing the design margin and facilitating later-stage adjustments. The type of suspension structure and the parameters of spring selection are critical to AGV performance. A well-designed suspension system can enhance the adaptability of AGVs to different environments and improve operational stability.
Example: A Typical 4-Auxiliary-Wheel and 2-Steering-Wheel System
To illustrate, let's consider a typical wheel configuration with four auxiliary wheels and two steering wheels. Before performing calculations, we need to define two parallel reference planes:
A reference plane based on the ground level.
A reference plane based on the vehicle frame where the wheel system is mounted.
For simplicity, we assume the height of the two auxiliary wheels and the steering wheel on one side of the AGV is the same, and the ground surface may be either symmetrical or asymmetrical with respect to the ground reference plane.
The simplified schematic is shown below (not included).
As depicted, the steering wheel moves up and down relative to the ground plane during operation. The spring's stiffness (denoted as KKK) and pre-compression amount (denoted as LLL) must meet the following conditions:
When the AGV is fully loaded and the steering wheel is on a concave surface (-10 mm), the wheel must not slip.
When the AGV is fully loaded and the steering wheel is on a convex surface (+10 mm), the wheel must not be overloaded.
When the AGV is empty and on a flat surface (0 mm), the auxiliary wheels must not lose contact with the ground.
Case Study: Parameter Calculation
Suppose an AGV weighs 3 tons, with a payload capacity of 5 tons (centered on the vehicle's center of gravity). The steering wheel has a maximum load capacity of 2 tons, with a sliding friction coefficient of 0.3 and a rolling friction coefficient of 0.03. The AGV must operate smoothly on a ground surface with a flatness tolerance of ±10 mm.
Assuming the spring's pre-compression amount is LLL, the spring is compressed by L−10L-10L−10 mm on concave surfaces and L+10L+10L+10 mm on convex surfaces. The stiffness of the spring is denoted as KKK.
1. Full Load, Concave Surface (-10 mm)
When the AGV is fully loaded and one side of the vehicle bears a weight of 4 tons, to ensure sufficient traction:
2. Empty Load, Flat Surface (0 mm)
When the AGV is empty and one side bears a weight of 1.5 tons, to ensure no auxiliary wheel loses contact:
3. Full Load, Convex Surface (+10 mm)
When the AGV is fully loaded and one side bears a weight of 4 tons, to avoid overloading the steering wheel:
Results and Recommendations
Based on the calculations, the spring stiffness and pre-compression amount must satisfy the following constraints:
This combination satisfies the requirements under all three conditions. It highlights the importance of having an adjustable pre-compression device in the suspension system, enabling fine-tuning during design and operation.
Conclusion
This article introduces the key requirements for AGV suspension design and provides a detailed method for quickly calculating spring stiffness and pre-compression. In practical applications, these results can guide the selection of optimal spring parameters, ensuring stable and reliable AGV operation.
