Arm Movements in Operating
Rotary Controls

By A.J.M. van der Vaart, 1995
Delft University Press
ISBN: 90-407-1131-3
168 pages
$51.00 paper

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Using daily life equipment often means grasping, holding or moving knobs to control a mechanism. Little is known of the interplay between the technical characteristics of these controls, the anatomical possibilities of users, and the nature of the controlling tasks. In this series of experimental studies three forms of rotary controls (O-, T- and L-shaped) were chosen and to be handled by the arm. Rotation can be effected forearm-rotation (supination), or by whole arm rotation (CAR) - or a combination -, leaving one degree of freedom extra for the task and to individual choice. Theoretically, this allows for an infinity of ways to handle the control, though it can be expected that individuals develop a more or less constant way. Can these constancies be explained by characteristics of subjects, objects and tasks?

Arm motions were opto-electrically measured and analysed. Indeed, constancies were found, the intra-individual ones proving to be more outspoken than the inter-individual similarity. With the O-knob, offering least constraints to grasping, three different tactics could be distinguished.

The findings led to a new theoretical explanations of an ergonomic nature, inclusive some practical hints concerning design and choice of rotary controls. To be recomended to researchers in the field of movement sciences, ergonomics and equipment design.

Technology
Series Physical Ergonomics

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