140 



DESIGN OF CONTROLS 



tive to the operator's movement characteris- 

 tics. It is in this area that further research 

 is most sorely needed. It is also in this 

 area that the need for a consideration of 

 operator characteristics has been demon- 

 strated most critically to those who are 

 responsible for the development of equip- 

 ment intended for human operation. 



An Evaluation of Current Information 

 ON Problems Relative to the Design 

 of Controls for Human Use 



The shift of emphasis from ignoring the 

 operator in equipment design to the inclusion 

 of operator characteristics and operating 

 conditions in the original design layout has 

 resulted in a need for a great deal of informa- 

 tion about the operator. As was stated 

 earlier, the designer needs to know the move- 

 ment and transmission characteristics of the 

 operator, he needs to know his operating 

 limits, and he needs to know his susceptibil- 

 ity to expected operating conditions. As 

 was also stated earlier, the designer needs 

 to be aware of the principles by which the 

 operating conditions arising from the over- 

 all task design may be modified. 



The detailed treatment of operating con- 

 ditions is not strictly within the scope of the 

 present chapter. The chapters on panel 

 layout and arrangement of equipment are 

 concerned with the principles of over-all 

 task design. Other chapters deal with the 

 effects on the operator's performance rela- 

 tive to environmental factors, stress, fatigue, 

 etc. Problems arising from these sources 

 were classified as Class I and Class II. 

 They have been included in the discussion 

 thus far partly to provide perspective for the 

 problems of Class III and partly because a 

 control system originally designed or later 

 modified in isolation is very likely to possess 

 features which are unsatisfactory in terms of 

 actual operating conditions. The design of 

 a control system may increase the diflBculty 

 of the over-all task as well as the diflBculty 

 of the control operation. Increased diflB- 

 culty complicates the problems of selection 



and training. The design of a control 

 system may demand unnecessary effort on 

 the part of the operator. Even though this 

 added increment of effort is not in itself 

 significant, it becomes significant when con- 

 sidered in terms of the total demands made 

 on the operator by the over-all task. The 

 design of a control system may also demand 

 more of the operator's attention and abilities 

 than is necessary. Such demands may re- 

 strict unfavorably the scope of the over-all 

 task which may be assigned to the operator. 

 It is for these reasons that the problems 

 related to operating conditions have been 

 included in the preceding discussion. How- 

 ever, the rest of the chapter will be con- 

 cerned primarily with the problems of Class 

 III. 



The restriction of the discussion to prob- 

 lems of Class III also operates as a restriction 

 on the types of adjustment to be considered. 

 For adjustments of Types A-1 and A-2 a 

 consideration of the manner in which the 

 demands of the system fit into the operating 

 conditions far outweighs the influence of 

 operator characteristics on the adequacy of 

 the adjustment. We will therefore be deal- 

 ing, for the most part, only with adjustments 

 of Type B and Type C. 



The problems of Class III relate to the 

 suitability of the transmission characteristics 

 of the control system. In respect to the 

 human element in the system, the response 

 which the operator makes to the control 

 data which he receives must result in a 

 movement of the control device that is ade- 

 quate for the accomplishment of the re- 

 quired adjustment. In general, the opera- 

 tor is the potential source of innumerable 

 movement patterns. He is also capable of 

 receiving control data in many forms. 

 What are the transmission possibilities of 

 the operator? What are his transmission 

 characteristics? How best may his trans- 

 mission possibilities and characteristics be 

 exploited for a given type of control task? 

 Unfortunately the answers to these questions 

 are not readily available. 



