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Model-based design of large-scale mining equipment

27 May 2016

FLSmidth approached Maplesoft’s Engineering Solutions team to provide a platform for examining the dynamic behaviour of a Lifted Radial Stacker - a complex mechanical machine used for material handling in mines.

The Lifted Radial Stacker is an extendable structure that travels on a system of two crawlers. One crawler is stationary and provides the centre of rotation, while the other is driven by an onboard operator. The conveyor system on the structure moves overburden from the mining process to the stockyard.

Because of its long arm, multiple centre-of-gravity points, and a moving crawler that traverses uneven terrain, stability and weight distribution are key considerations in its design. Therefore, engineers at FLSmidth required a multidomain dynamic model of the Lifted Radial Stacker, which can be used as a platform to assess its stability, and investigate its dynamic response under varying conditions such as operator behaviour, load distribution, and terrain unevenness.

Maplesoft’s Engineering Solutions team developed a model of the Lifted Radial Stacker using MapleSim. The MapleSim model consists of the main frame, the extendable frame, the moving and passive crawlers, suspension assembly, frame lift assembly, leveling hydraulics, and the masses of the external assemblies attached to the main frame. 

The main frame was modeled using dimensions and attributes from the CAD design of a reference Lifted Radial Stacker in service at a client’s site. The frame has a number of assemblies attached to it including the cab, generator, belt, and hopper. The location and mass of each assembly in the model are parameterised and can be altered, and more assemblies can be added if desired. Some of the assemblies are off-centre, affecting the centre of gravity of the main frame, and subsequently, the stability of the entire Lifted Radial Stacker. The extendable frame extends and retracts at a user-defined rate, representing another factor affecting the dynamics of the system. 

Other subsystems in the MapleSim model include a frame lift assembly, the gimbal which contains hydraulic cylinders that level the structure and a lengthwise roller that connects the track and gimbal to the main frame. The model encapsulates the motion of the main and extendable frames, the behaviour of the lifting cylinders, the control of the hydraulics, and travel across terrain.

The multidomain system-level model of the Lifted Radial Stacker, together with MapleSim and Maple, provides engineers at FLSmidth with a virtual environment to apply multiple approaches to evaluate the dynamic response of the system. They can examine the maximum loading on parts such as the rollers, and investigate the maximum sway of the structure under extreme acceleration or deceleration, such as when performing an emergency stop. 

The model can also be used to examine the quality of terrain the system can traverse, in order to determine the maximum height of mounds and troughs it can safely navigate without tipping over, and to analyse the design parameters affecting the stability of the gimbal, such as cylinder diameters, stroke, and controller gain and deadband. The dynamics of the hydraulic system can also be examined, and weight distribution across the system can be analysed, to determine the parameters that affect the stability of the structure. 

Engineers at FLSmidth can also perform numerous types of further analysis. For example, they can use Maple to develop a design tool to evaluate subsystem loading across the Lifted Radial Stacker, either to validate existing implementations, or for part sizing for a new design. Or, for a given terrain profile, they can create an analysis tool to determine the operational safety limits of the Linear Radial Stacker such as the maximum speed it should travel at, and its maximum load and capacity.

The MapleSim model of FLSmidth’s Lifted Radial Stacker is fully parametric, which enables it to serve multiple purposes. It can be configured to represent an existing installation of a Lifted Radial Stacker, and used to investigate operational safety limits, test design changes, and validate proposed improvements. The model can also be configured with the dimensions and properties of a potential new design, and used to assess its viability early on in the development cycle, before expensive commitments are made.

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