144 



DESIGN OF CONTROLS 



tant not only to the designers of control 

 systems but also to the research worker who 

 must evaluate the role of the operator in 

 appraising the similarities and differences 

 between systems. 



In the following paragraphs some of the 

 more important system variables are listed 

 together with brief orientative comments. 



Input Variables 



Sense Modality. It was stated above that 

 control data may be furnished to the opera- 

 tor in several forms because of the differen- 

 tial sensitivity of his sense organs. The 

 sense modality through which the data are 

 transmitted determines certain relation- 

 ships relative to the operating conditions as 

 well as to the control operations. Very 

 often the selection of sense modality is not 

 a matter of choice for the designer. How- 

 ever, it is sometimes possible to solve many 

 problems caused by auditory data presented 

 in a noisy situation by switching to visual 

 presentation. It is also possible in some 

 tasks to relieve the load on the operator's 

 visual equipment by switching the presenta- 

 tion of data to another modality. The 

 development of "Flybar" is an interesting 

 example (5). In order to carry out such 

 design manipulations it is necessary to know 

 the characteristic differences which ob- 

 tain between the several modes of input 

 presentation. 



Number of sense modalities employed. 

 ■More than one sense modality usually is in- 

 volved in a single control system. Tactual 

 and kinaesthetic data in the form of feed- 

 back are often important accompaniments 

 of the visual or auditory data received from 

 the primary display. The feedback may 

 be from the manipulative devices (the "feel" 

 of the controls) or from the motion effects 

 which the operation causes (the "seat of the 

 pants" data to which the aircraft pilot 

 refers) . The possible provision of additional 

 control information by tactual or kinaes- 

 thetic feedback should be considered in origi- 

 nal system designs. The recognition of these 



feedback inputs is important also when modi- 

 fications are considered which distort or 

 exclude these data. For example, the in- 

 troduction of booster systems between the 

 pilot's controls and the control surfaces of 

 the aircraft has led to a need to impart "arti- 

 ficial feel" to the controls (19). The con- 

 tribution of these feedback data must also 

 be considered in connection with experi- 

 mental adjustment of inertia, damping, 

 friction, etc., in manipulative devices. The 

 "fatigue" effects of prolonged operations 

 also may involve the distortion of these feed- 

 back data through "numbness" or the adap- 

 tation of the sense organs involved, although 

 information on this point is lacking. 



For convenience of exposition the com- 

 ments concerning other input variables will 

 be in reference to visual inputs only. How- 

 ever, these variables apply generally to in- 

 puts in all sense modalities. 



Directness of data. This variable may 

 best be described by example. In a Type 

 B adjustment involving the linear position- 

 ing of a pointer the data may be furnished 

 by displaying verbally or visually a value 

 corresponding to a scale reading. By re- 

 ferring this data to the scale the operator 

 "sets up" the new position which is required. 

 The rest of the operation consists of aligning 

 the pointer with the new position. The 

 indirectness of this input system may be 

 compared with a display of the data in a 

 manner which "sets up" the new position 

 directly. This may be done by signal lights 

 behind or above the scale divisions. Or a 

 movable marker such as a pointer or spot 

 of light may be used. The differences be- 

 tween these display techniques may affect 

 total response time as well as the number of 

 sources of error in the total operation. 



Continuity of data. The input for Type B 

 adjustments is characteristically intermit- 

 tent, but the input for Type C adjustments 

 is generally intended to be continuous. 

 However, physically continuous data may 

 be effectively intermittent. If the velocity 

 of pointer movement constitutes a portion 



