ROLE OF OPERATOR IN MANUALLY OPERATED CONTROL SYSTEMS 



147 



tion, extent, rate and force. The effective 

 operating range for each of these movement 

 characteristics differs according to the sys- 

 tem variables employed in the design of the 

 operator. Likewise, the distribution of 

 changes in the values of these characteristics 

 as a function of time during the movement 

 and the relationships between successive 

 movements and coincident movements de- 

 pend on operator design variables. 



Like the design of the input, the design of 

 the operator has been given little attention. 

 Separate discussion of the variables is not 

 warranted, but the listing of some of those 

 which have received at least exploratory 

 investigation may be profitable. They are: 

 the bodily member (or members) employed 

 in operating the control device; the operating 

 position, the point of support, the degree of 

 flexion, and the plane of action of the bodily 

 member used; the kind of movement, 

 whether translatory, rotary, or static, dis- 

 crete or continuous, cyclic or irregular; the 

 direction of the movement relative to the op- 

 erator, to indicator movements, and to move- 

 ments of other bodily members coincidently 

 employed. Bro^vn and Jenkins (2) have 

 classified movements and outlined a program 

 of research designed to elicit much of the in- 

 formation which is needed. Henschke and 

 Mauch (14), Brown et al. (3), and others 

 have made beginnings in the direction of in- 

 vestigating these variables. Studies by 

 Montpellier (8), Barnes et al. (1), Hill and 

 EUson (10), Taylor et al. (22), and Fenn (13) 

 have contributed to the knowledge concern- 

 ing the characteristic pattern of movements. 

 But the surface has only been scratched. 

 Ultimately the manipulation of such varia- 

 bles may be used in two ways: (1) to provide 

 those movement characteristics which are 

 desired as input to the controls, and (2) to 

 eliminate those movement characteristics 

 which are undesirable. 



Manipulative Device Variables 



The device which the operator manipu- 

 lates may constitute the only unit between 

 the operator and the output of the system. 



This is the case, for example, when the ma- 

 nipulative task of the operator consists of 

 sliding a pointer along a scale to accomplish 

 the required settings. More often there are 

 a number of transmission stages between the 

 manipulative device and the output of the 

 system. For purposes of the present discus- 

 sion the device and any succeeding stages 

 will be considered as a unit. 



There are four important operator-device 

 relationships which may vary from system 

 to system: (1) facilitation or inhibition of de- 

 sired operator design, (2) dynamic modifica- 

 tion of operator output, (3) provision of pro- 

 prioceptive cues, and (4) transformation of 

 operator output. 



Facilitation or Inhibition of Operator De- 

 sign. The relationship between the place- 

 ment and motion potentialities of the device 

 on the one hand and such operator variables 

 as mean limb flexion, plane of action, type 

 of movement, etc., on the other is obvious. 

 Especially to be noted is the function of de- 

 vice characteristics as motion or position 

 guides in maintaining consistency of move- 

 ment patterns. 



The relative magnitude of input changes 

 and required operator movements is a func- 

 tion of the amplification or reduction charac- 

 teristics of that part of the system which 

 intervenes between the operator and the 

 mechanism or process which he controls. 

 The importance of this relationship to the 

 maintenance of operator design may be il- 

 lustrated by considering the control-indica- 

 tor ratio in a compensatory tracking task. 

 A one-to-one ratio will require very slight 

 movements on the part of the operator in the 

 case of small deviations of the pointer from 

 the null position. The over-all operating re- 

 lationship between input and operator out- 

 put may be destroyed in this portion of the 

 input range. 



Dynamic Modification of Operator Output. 

 This variable encompasses the load charac- 

 teristics of the device, friction, inertia, and 

 damping. Relative to this variable it may 

 be well to point out that the choice of limb, 

 the number of limbs, and the point of sup- 



