Wheel loader trajectories between loading and unloading positions in a repetitive loading cycle are studied. A wheel loader model available in the literature is improved for better fuel estimation and optimal control problems are formulated and solved using it. The optimization results are analyzed in a side to side comparison with measurement data from a real world application. It is shown that the trajectory properties affect the operation productivity. However, efficient trajectories are not the only requirement for high productivity operation and all major power consuming sources such as vehicle dynamics, lifting and steering have to be included in the optimization for productivity analysis. The effect of operator steering capability is also analyzed showing that development of autonomous vehicles can be envisaged especially for repetitive cycles.

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The purpose of earth-moving equipment like wheel loaders is to engage with the ground or other material. It is therefore obvious that the bucket filling phase must be included when studying optimal machine control over a complete working cycle because total productivity and efficiency of the machine are to a large extent determined by it. This paper reports and discusses the results of research into how to utilize Discrete Element Method simulations in combination with Optimal Control to find the optimal bucket filling strategy and what has been learned regarding preparing and conducting both simulations of bucket filling and physical testing for verification. This paper also discloses which bucket filling strategy appears to be optimal, based on the results so far-and why we cannot be completely certain.

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