148 



DESIGN OF CONTROLS 



port involves these same characteristics. 

 The development of equivalent one-handed 

 and.two-handed systems may require special 

 attention to this relationship. 



Provision of Proprioceptive Cues. Feed- 

 back inputs from the manipulative device 

 were mentioned in connection with input 

 variables. This variable is closely related 

 not only to load characteristics as mentioned 

 above, but also the operating range of move- 

 ment variables. The relative magnitude of 

 input dimensions and movement dimensions 

 may be such that the adjustment required 

 for some inputs involves changes in position, 

 rate, or acceleration which are too small to 

 provide discriminable cues. 



operator must position the handle at zero, to 

 match a constant target rate he must achieve 

 and hold the correct handle displacement 

 from zero, etc. Acceleration tracking equip- 

 ment has also been developed. Table III 

 shows the relationships between certain in- 

 put characteristics and the correlated re- 

 sponse characteristics for three different 

 tracking techniques. 



Table III is based on constant movement 

 dimensions, although most target courses 

 have constant dimensions only momentarily. 

 The implications in these relationships with 

 respect to the role of the operator are readily 

 discernible if the tracking task is analyzed. 

 We will first consider pursuit tracking of a 



TABLE III 



Target Movement — Handle Movement Relationships for Three Different Tracking 



Techniques 



Transformation of Operator Output. The 

 manipulative device and its succeeding 

 stages may amplify or reduce the operator's 

 movement to a system output movement of 

 the same form. His movements also may 

 be transformed into movements of a different 

 form, voltages, pneumatic pressures, etc. 

 It is also possible to transform his move- 

 ments in such a way that they are not direct 

 counterparts of inputs presented in the form 

 of movement. In rate tracking the position 

 of the control handle imparts a constant 

 velocity to the reticle. A change of direction 

 is accomplished by moving the handle across 

 a zero position. Thus, reticle rate corre- 

 sponds to handle position and reticle ac- 

 celeration corresponds to handle rate. To 

 match a constant position of the target the 



variable speed course in one dimension with 

 constant acceleration. (Restriction to one 

 dimension is a common feature of experi- 

 mental designs although such a restriction 

 prevents the operator from "anticipating" 

 acceleration changes.) Because of reaction 

 time, errors will immediately develop even 

 if the task is started with reticle and target 

 aligned. These errors are errors in accelera- 

 tion, rate, and position. Perfect correction 

 of all three types of error simultaneously will 

 bring the reticle back on target. Correc- 

 tions are made by acceleration adjustments 

 of the reticle movement. The development 

 of further error is suppressed by the main- 

 tenance of the correct acceleration. The 

 column on the right in Table III indicates 

 the handle-movement dimension in which 



