Quantifying Operability of Working Machines

Abstract: In working machines the human operator is essential for the performance of the total system. Productivity and energy efficiency are both dependent not only on inherent machine properties and working place conditions, but also on how the operator manoeuvres the machine. In order to operate energy-efficient the operator has to experience the machine as harmonic. This is important to consider during the development of such working machines.It is necessary to quantify operability and to include this interaction between the human operator and the machine in both the later stages of a development project (where physical prototypes are evaluated by professional test operators) as well as in the earlier stages like concept design (where only virtual prototypes are available).The influence of the human operator is an aspect that is traditionally neglected in dynamic simulations conducted in concept design, because the modelling needs to be extended beyond the technical system. The research presented in this thesis shows two approaches to rule-based simulation models of a wheel loader operator. Both operator models interact with the machine model just as a human operator does with the actual machine. It is demonstrated that both operator models are able to adapt to basic variations in workplace setup and machine capability. A “human element” can thus be introduced into dynamic simulations of working machines, providing more relevant answers with respect to operator-influenced complete-machine properties such as productivity and energy efficiency.While the influence of the human operator is traditionally ignored when evaluating machine properties in the early stages of the product development process, later stages are very reliant on professional test operators using physical prototypes. The presented research demonstrates how the traditional subjective evaluation of a machine’s operability can be complemented by a calculated measure for the operator’s control effort, derived from the recorded control commands of the machine operator. This control effort measure can also be calculated from the control commands of an operator model in a simulation, such as those presented in this thesis. It thus also allows for an assessment of operability already in the concept design phase.In addition, the results of a study of quantifying operator workload by means of measuring psycho-physiological data such as heart rate variability and respiration rate are presented as the first step towards realising workload-adaptive operator assistance functions. Once fully developed, the method itself can also be used as another complement to the traditional subjective evaluations of operability. This approach can then be applied not only in testing of physical prototypes, but also earlier in the product development process in studies on human-in-the-loop simulators.