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Multi-purpose controls are increasingly being used on earthmoving machinery for the control of safety-related functions. In addition to the basic functions, a number of auxiliary functions may be operated for example by buttons or switches on the joystick, or the basic functions on the multi-purpose control may be switched to other functions by further control elements such as switches on the multi-purpose control itself or on the operator panel. The result is that an increasing number of discrete functions, which are grouped to form units and may be accommodated on several layers, are assigned to the controls. The key objective of the project was to establish the number of function units which can be assigned to a multi-purpose control and which a trained machine operator may cope with whilst still being able to operate the machine safely and reliably, even under critical conditions. The project, which was interdisciplinary in nature, was implemented in a number of stages: a survey of standards, statutory regulations, the results of other research projects, and studies by the Berufsgenossenschaften, recordings of the tasks of earthmoving machinery operators on video, and a survey of machine operators. The study failed to provide a direct answer to the key question, that of the maximum number of function units which an operator can cope with, since an earthmoving machine with a greater number of function units than operators were capable of handling was not available during the test phase. The chief results of the study can however be summarized in the following recommendations: The function units should be restricted in number to the basic movements and a maximum of four further function units per multi-purpose control. The function on the multi-purpose control should be designed for maximum compatibility with the machine's response. The multi-purpose control itself and the control elements accommodated on it should be of ergonomic design, for example with adaptation of the geometry to the fingers and hand by the provision of a rest for the edge of the hand and/or forearm. The arrangement of the control elements on the multi-purpose control and the assignment of functions to them should be standardized in consideration of frequency of use and the risk potential presented by the function units. |