Evaluating Operator-Machine Interactions in Comparative Time Studies

Abstract

Comparative experimental studies offer possibilities for reducing the uncontrolled variation in time studies of forest work. However, the factor “Operator” has often been found to be very difficult to keep constant when working with different machines. Analysis of variance often indicates that an interaction between operator and machine reduces opportunities to make generalizations.

The objective of this study was to develop and test a method for analysing and correcting for operator-machine interaction effects in comparative time studies encompassing few operators.

A new variable “Adaptation” was introduced to describe differences in the operators’ degree of adaptation to various machines. In the present study the numeric value of the variable was estimated from (a) previous experience, (b) the subjective feeling of adaptation by the operator, and (c) a standardized time study of loading from a pile.

Analysis of variance showed that differences in adaptation could explain the interaction effects in both loading and unloading. The remaining effects of the interaction between operator and machine were not significant.

The method seems to offer more possibilities to generalize and statistically validate differences, even when the number of operators is limited.

Keywords:

• work science
• grapple loading
• forwarder
• farm tractor
• logging
• short-wood