Chapter 5 

 THE DESIGN OF CONTROLS 



D. R. CRAIG AND D. G. ELLSON 



Indiana University 



Introduction 



This chapter is intended as a general 

 treatment of the relationships between con- 

 trol design variables and the operating char- 

 acteristics of man-machine combinations. 

 It is not the purpose of this chapter to 

 present a complete catalogue of information 

 concerning the known effects of manipulating 

 the numerous variables of control design. 

 Much of this information is available in an 

 annotated bibliography by Macmillan and 

 Lawrence (18), in an extensive review by 

 Jenkins (17), and in a less exhaustive treat- 

 ment by Channell (4). These reviews may 

 be supplemented by a very practical check 

 list for the evaluation of equipment design 

 (21) in those cases where immediate applica- 

 tion of current information is desired. In 

 addition, much of the material in the next 

 two chapters applies directly or indirectly to 

 the design of controls. Rather, it is the 

 purpose of this chapter to present a systema- 

 tic approach to the problems in this area in 

 the hope that it will lead eventually to the 

 basic research which is necessary to relate 

 and reconcile many of the facts brought forth 

 by the recently accelerated interest in equip- 

 ment design. 



Historical Approaches to the Problems of 

 Control Design 



The literature pertinent to the design of 

 manual (and pedal) controls is not very ex- 

 tensive, but the heterogeneity of the subject- 

 matter and the specificity of most of the 

 research make summarization difficult and of 

 questionable value. The implied definition 

 of "controls" has embraced any and all 



devices manipulated by the operator of a 

 machine or instrument. It is obvious that 

 the problems involved in the design of the 

 knob on a range-selector switch have little 

 in common with the problems involved in 

 the design of a remote control gunsight. 

 Both devices, however, qualify as "con- 

 trols" and usually enter into discussions of 

 control design on fairly even terms. Like- 

 wise, there has been a failure to distinguish 

 between design problems related to the 

 nature of the operator's total task and design 

 problems related to the operating char- 

 acteristics of the control device. As a 

 result, in discussions of control design one 

 finds such factors as the color coding of con- 

 trol knobs grouped together with such factors 

 as gear ratios and inertia. The types of 

 problems and classes of variables considered 

 by any one group of investigators have been 

 determined simply by the interests and re- 

 sponsibilities of that group, rather than by 

 the demands of a systematic approach. 



During and immediately following World 

 War II, a considerable amount of research 

 was performed on the effects of the char- 

 acteristics of the task on control operations 

 involving a human operator. It was stimu- 

 lated largely by requests for data from en- 

 gineers and designers of military, aviation, 

 and other types of complex equipment which 

 require highly skilled performance for effi- 

 cient and accurate operation. It included 

 the determination of the effects on speed and 

 accuracy of control operations of such vari- 

 ables as size, shape, and location of control 

 knobs; friction, damping, and inertia of 

 controls; operating radii of controls; and 

 gear ratios. Much of this work was neces- 



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