This article throws light upon the four main factors to be considered in the design of control. The factors are: 1. Control Display Ratio (C/D Ratio) 2. Directional Relation in Control and Display 3. Control Resistance 4. Operational Coding of Controls.
Design of Controls: Factor # 1. Control Display Ratio (C/D Ratio):
The CD ratio is known as the ratio of the control system movement to the moving element of the display that shows or represents the control movement. It should be obvious to the operator operating the power, that this relationship is significant.
This term is meaning full only in case of continuous controls. An optimum C/D ratio will reduce the operation time. In the rapid or slowing movement any increase in C/D ratio would increase the time but in case of fine adjustment movement increased C/D ratio will reduce the time. The C/D ratio is illustrated in Fig. 36.12.
Design of Controls: Factor # 2. Directional Relation in Control and Display:
If control and moving element of the display are the correct relationship should exist between the motion direction. If the control moves in the direction of the clock the pointer must also move in the clock direction. The operator may be confused with reverse motion.
An appropriate control and display motion relation reduces time of reaction, facilitates quick decision making, speeds up movements, eliminates reversal mistakes and helps to decrease time of learning, is essential in a complex work and an irregular control motion sequence.
Design of Controls: Factor # 3. Control Resistance:
The control force offered to the intended movement is known as control resistance; it is provided by control and maintains a relationship to the resistance of the controlled device. Controls offer a wide range of resistances.
Some are negligible in terms of ph ysical forces where as other are significant. The main types are as follows:
(i) Inertia Force.
(ii) Static and Dynamic Friction.
(iii) Elastic or Spring Force.
(iv) Viscous Damping Force.
These resistances have the following effects on the operational performance of the control:
(a) The smoothness of search service is affected.
(b) Control movement accuracy and speed are affected.
(c) A very little control resistance, due to unintended load situations such as gravity and shock, can lead to a fortuitous activation.
Both types of resistance have its benefits, and limitations, which the designer spring or elastic resistance allows to reverse the control movement, as it is always directed at zero places. It can not easily be operated by accident other than by accident. It gives the user a sense of control.
Inertia intensity counteracts abrupt velocity shifts there by reducing the risk of unintended activation. Viscous damping force decreases risks of unintended activation against rapid control movement and thus helps the operator in carrying out smooth control motion. The operator's movement is actually perceived, however, difficult to precisely adjust.
In fluid and static situations, factional opposition play different roles. This falls when the power is active, but in static situations, this continues to hold the control role.
Design of Controls: Factor # 4. Operational Coding of Controls:
Coding ensures that controls must be coded to define the information transport technique easily by color numbers or literatures etc. to reduce the total running time. Controls of scale, shape, operating system, color position and labels are effective for regulating and monitoring their control.
The following rules in this regard should be followed:
(i) Shape Coding:
It should be connected with the desired control intent. It serves both as a visual display and as an input to communication. In many businesses and states, many methods are standardized for control coding.
(ii) Size Coding:
It is not as effective as type encoding, but in many cases can be used by industries in particular.
(iii) Position Coding:
It is useful for the formation of habits. Example is that electrical light bulbs are normally installed at shoulder height near doors or at other convenient places.
(iv) Method of Operation Coding:
This rule concerns that control should be designed so that it is not operated in the wrong direction.
(v) Colour Coding:
It is a type of visual coding that can be combined with other codes such as shape and degree, etc. It is very successful.
(vi) Labeling:
It is also an effective control coding method. A good level in notation and should be placed on or close to control should be accurate, complete and standard. However, all this can be achieved if room is available for leveling and illumination as visual aid.
