150 



DESIGN OF CONTROLS 



and experiment wdth specific machines and 

 particular operations. Little generalization 

 is possible. This condition is largely due to 

 inadequacies in the approaches to the prob- 

 lems of equipment design in general. Tradi- 

 tional attempts to link a better man to the 

 machine and, through changes in existing 

 equipment, to provide a better link between 

 man and machine, have masked the fact that 

 the operator and his controls are transmis- 

 sion elements in a control system, that the 

 control task is performed by the control sys- 

 tem as a whole, and that the design of its 

 elements must logically be conceived in 

 terms of the design of the system. The rela- 

 tionships between facts obtained from differ- 

 ent systems and control situations can be 

 understood only after system differences are 

 clarified. 



In attempting a systematic approach from 

 this point of view we have first classified con- 

 trol design problems according to their source 

 and control tasks according to their sensi- 

 tivity to the transmission characteristics of 

 the operator. Problems arising from the 

 suitability of the transmission characteristics 

 of control systems and control tasks in which 

 operator characteristics play a critical role 

 were selected for further analysis. 



An evaluation of the information currently 

 available to the designer who attempts to 

 include the operator in the original design 

 layout leads to the conclusion that a different 

 sort of information is needed than that which 

 has been provided thus far. The designer 

 needs to know the transmission character- 

 istics of the operator, his operating ranges, 

 and his susceptibility to expected operating 

 conditions. The designer especially needs 

 to be aware of the fact that "the operator" as 

 an element in the design of the system is an 

 abstraction from the operator who, as an 

 individual, is the embodiment of a multi- 

 plicity of transmission systems. The details 

 of his role thus differ from system to system 

 and, to a large extent, determine the classi- 

 fication of the system. It is necessary to 



analyze the ways in which his roles may differ 

 before effective use can be made of his char- 

 acteristics, before system differences may be 

 accurately appraised, and before results of 

 system modifications may be properly in- 

 terpreted. The differences between sys- 

 tems with respect to the role of the operator 

 may be considered separately as input vari- 

 ables, operator variables, and manipulative 

 device variables, but their interrelationships 

 must be considered in any research or practi- 

 cal application. 



Research in the future should be oriented 

 toward providing answers to the following 

 questions: What are the transmission pos- 

 sibihties of the operator? What are his 

 transmission possibilities and characteristics 

 in each of his various roles? How best may 

 his transmission possibilities and character- 

 istics be exploited for a given type of control 

 task? Operational analysis, the technique 

 which has proved so useful to the designers 

 of complex transmission systems and servo- 

 mechanisms, may be a ready-made method 

 for use in the search for the necessary an- 

 swers. 



References 



1. Barnes, R. M. Motion and time study. 



London: John Wiley & Sons, Inc., 1946. 



2. Brown, J. S., & Jenkins, W. O. A pre- 



liminary analysis of human motor abilities 

 in relation to the design of equipment and a 

 suggested program of research. In: P. M. 

 FiTTS (Ed.), Psychological Research on 

 Equipment Design, A.A.F. Aviation Psy- 

 chology Program Research Reports, 1947, 

 19, 35-63. 



3. Brown, J. S., Knauft, E. B., & Rosenbaum, 



G. The accuracy of positioning reactions as 

 a function of their direction and extent. 

 Amer. J. Psychol., 1948, 41, 167-182. 



4. Channell, R. C, & ToLcoTT, M. A. The 



use of human engineering data in equipment 

 design problems. Office of Naval Research, 

 Special Devices Center, Navy Department, 

 Contract N6-ori-151, Project 20-F-2, Report 

 151-1-16, 20 May 1948. 



5. Chapanis, a.. Garner, W. R., Morgan, C. T., 



& Sanford, F. H. Lectures on men and 

 machines. Office of Naval Research, Special 



