RELATIONSHIPS OF DESIGN PROBLEMS TO DESIGN CRITERIA 



137 



to illustrate some of the relationships be- 

 tween the problems which arise in the design 

 of controls. Specifically, we will consider 

 the placement of a handwheel in respect to 

 the operator for a task in which manipula- 

 tion of the handwheel is an intermittent 

 operation. It will be assumed that the 

 handwheel is the proper device for the re- 

 quired adjustment. In the process of evalu- 

 ating a tentative position of the handwheel, 

 three pertinent questions may be asked. 



1. Does the location of the handwheel 

 avoid waste motion or uncomfortable posi- 

 tions for its operation? 



2. Is the handwheel placed so that the 

 operator can grasp it quickly and accurately 

 without excessive attention to its exact 

 location? 



3. Does the position of the handwheel 

 allow for the optimal range and type of 

 movement which the adjustment requires? 



In attempting to answer these questions 

 several important implications become evi- 

 dent. It is obvious that in many cases the 

 answer could not be an unqualified ''yes" 

 to all three questions. Yet, in so far as 

 they are all three pertinent questions they 

 would all need to be considered and some 

 compromise effected. 



In addition, it should be noted that each 

 of the three questions is based on a different 

 set of criteria for evaluating a single design 

 variable. The criteria giving rise to ques- 

 tion (1) emphasize the effects of the design 

 on the over-all efficiency and welfare of the 

 operator. Question (2) is stimulated by a 

 set of criteria which emphasize the speed and 

 accuracy with which the operator may con- 

 tact his controls. Question (3) is based on 

 criteria which emphasize the effects of the 

 design on the adequacy with which the con- 

 trol may be manipulated relative to the 

 adjustment required. 



Again, it should be noted that the relative 

 weight given to the three sets of criteria will 

 depend upon the relation of the control 

 operation to the expected operating condi- 

 tions and upon the type of adjustment for 



which the control is used. If the control is 

 operated very infrequently and for only 

 brief periods, then the answer to the first 

 question is not very critical. If the con- 

 trol normally is operated at a time when 

 other demands of the task are minimal and 

 is not involved in necessary adjustments to 

 "emergency conditions," then the answer to 

 the second question is relatively unimpor- 

 tant. Finally, if the necessary adjustment 



TABLE I 

 Classification of Equipment Design Problems 



of the control is of the "on-off" type requir- 

 ing a single initiating movement, then the 

 answer to the third question is greatly re- 

 duced in significance. 



Also, it should be pointed out that the 

 considerations which prompt the first two 

 questions are based upon evaluation of the 

 design variable in respect to its relationship 

 to various operating conditions, whereas the 

 third question is concerned solely with the 

 effect of the variable on the required ad- 

 justment. 



The problems cited in the above example 



