Wear Behavior of Steel Wheels on Stacker Cranes

Stacker cranes (de: Regalbediengerät, RBG) are an important part of modern intralogistics concepts. They enable the automatic storage and retrieval of various goods in both automatic pallet warehouses and automatic small parts warehouses. A stacker crane consists of the main components: supporting structure, lifting mechanism, load handling device, and travel drive. The wheel-rail system holds particular significance as damage to this subsystem often and quickly leads to a failure of the entire system, resulting in the stacker crane coming to a standstill. Due to the high level of automation and the substantial throughput in logistics, the stress on the wheel-rail system, especially in pallet stacker cranes, is significant. This results in high dynamic forces and consequently wear on the wheel-rail system.

The design of wheel-rail systems has traditionally been carried out using standards such as DIN 15070 or the FEM guideline FEM 1.001. However, these regulations provide calculation foundations for crane wheels and were not originally intended for the requirements of steel wheels in pallet stacker cranes. Despite norm-compliant design, damages to the wheel-rail system of pallet stacker cranes have increased for various reasons. This is attributed, among other factors, to methodological weaknesses in DIN 15070 that fail to accurately account for all influencing factors.

A practical and simultaneously reliable design method for the wheel-rail system of pallet stacker cranes is lacking. While the norm DIN EN 13001-3-3 now offers a new calculation approach, primarily designed for the design of crane wheel-rail systems, it has addressed many of the weaknesses present in DIN 15070. During the research project "Methodology for Practically Oriented Design of the Wheel-Rail System of Stacker Cranes (MARS)" conducted at the Chair of fml from 2018 to 2021, the creation of prediction models for the load collective and total number of wheel-overruns calculated in DIN EN 13001-3-3 enabled a practical application of this standard for RBG.

However, it is important to note that when applying DIN EN 13001-3-3, the focus is on proving static strength and fatigue resistance, and it does not allow for quantification of sliding wear occurring over the system's lifespan.

The goal of this research project is to expand the design procedure developed in the previous project, allowing for the consideration of the expected wear behavior of the wheel-rail contact during the system's lifespan. The wear behavior of the wheel-rail system in pallet stacker cranes (RBG) will be numerically investigated to establish a scientifically grounded design specification for wear rate. The developed method will complement the design calculation with proof of wear resistance, thereby enhancing safety in the dimensioning of the RBG's wheel-rail system.

Due to the wide range of applications for RBG, a multitude of parameters and influences must be considered. A methodical approach ensures that each design parameter is scrutinized for its relevance and that the varying impacts of these parameters are identified. Predictive models are then developed to incorporate these influences into the design method. Following the creation of these predictive models, the software demonstrator developed in the MARS project is expanded. This ensures the practicality and applicability of the enhanced procedure. A scholarly treatment of the topic also forms the basis for transferring the acquired insights into relevant guidelines (e.g., VDI guideline, FEM guideline) after the research project, making them accessible to a broad audience.

In the first work package, all relevant influencing factors of stacker cranes (RBG) and storage racks are identified, which could potentially affect the wear behavior. In the next step, a suitable target variable is defined to assess the wear condition and behavior of the wheel-rail system of RBG. To identify the influence of the parameters determined in work package 1 on wear behavior, a suitable multibody simulation model (MKS model) is created in work package 2. To automate the simulation process, it is controlled using co-simulation in conjunction with MATLAB/Simulink. The MKS model created in work package 2 is used in work package 3 to establish a database for the development of prediction models. Meaningful variation intervals for the input variables identified in work package 1 must be defined for this purpose. Subsequently, experimental plans are created using statistical methods to achieve a high information density regarding the relationships between the input and target variables with the fewest possible simulation runs. In work package 4, based on the datasets created in work package 3, models using machine learning methods are developed to predict the target variable defined in work package 1. Suitable types of prediction models must first be selected for this purpose. Using these prediction models, a wear resistance proof, analogous to the proofs of static strength and fatigue strength from DIN EN 13001-3-3, is created in work package 5. The wear resistance proof thus developed is integrated into the software demonstrator developed in the MARS project. This adds another type of damage, wear, to the demonstrator. Finally, the developed design method is evaluated in collaboration with the companies from the project-accompanying committee. The method is retrospectively tested using data from real cases of wear on steel wheels

This research project was carried out on behalf of the Research Association for Intralogistics/Material Flow and Logistics Systems (FG IFL) and was funded by the Federal Ministry for Economic Affairs and Technology through the Working Group of Industrial Research Associations "Otto von Guericke" e.V. (AiF).