Shape-Coding and Length-Coding as a Measure to Reduce the Probability of Selection Errors During the Control of Industrial Equipment

OCCUPATIONAL APPLICATIONS

Shape-coding and length-coding of control levers may have limited benefits for the prevention of selection errors during operation of roof-bolting machines and other industrial equipment. Any benefits of arbitrary shape-coding or length-coding for reducing selection errors are likely to be restricted to situations in which the arrangement of controls in relation to the participant is subsequently altered in some way, such as the operator moving from one machine to another with a different control layout. If shape-coding is employed, measures should be taken to ensure that the relationship between shape and function remains consistent across similar equipment and that the relationship between shape and function cannot be altered in error during maintenance.

TECHNICAL ABSTRACT

Rationale: Underground coal mining is one of the most hazardous industrial environments, and roof-bolting machine operators are the most at-risk occupation in underground coal mining. Many examples of industrial equipment, including bolting machines used in underground coal mines, are operated via a bank of levers that control different machine functions and movements. Errors in the use of these controls are a cause of serious injuries. Purpose: A recent design guideline for underground bolting equipment has specified the use of arbitrary shape-coding for principal equipment functions with the aim of reducing injuries caused by operators inadvertently operating the wrong lever (a selection error). Three experiments were conducted to provide further insight to the use of control-coding. Methods: Sixty-four individuals participated in three experiments. Each participant operated a physical simulation of a single-boom roof-bolter machine via five levers in either shape-coded, length-coded, or identical handle conditions. In two experiments, the location of the controls was changed half-way through the experiment. Selection error rate data were collected. Results: When operators are not under time pressure, their attention is not divided, and they are able to view the controls they are manipulating, any benefits of arbitrary shape-coding or length-coding for reducing selection errors are likely to be restricted to situations in which the arrangement of controls in relation to the participant is subsequently altered. Conclusions: If shape-coding is employed, measures should be taken to ensure that the relationship between shape and function remains consistent and that maintenance errors, such as reversing handle shapes, are prevented.

KEYWORDS:

• Man–machine interface
• controls design
• mining

ACKNOWLEDGMENTS

The authors wish to thank Tim Matty, Al Cook, Joe DuCarme, and Mary Ellen Nelson for building the testing arm and physical set up and to Bill Porter for the MATLAB programming. Big thanks are extended to David Beshero and Patrick Roth for their illustrations of the roof-bolting controls and experimental setup. Finally, the help and cooperation of Fletcher Mining Equipment, including the use of their Roof Ranger II roof-bolting machine, are greatly appreciated.

The findings and conclusions in this article are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health. Mention of any company or product does not constitute endorsement by the National Institute for Occupational Safety and Health.