What is a control?
A control is a device that allows you to 'communicate' with objects and to manipulate them. Controls can enable you to direct equipment or machinery that can help you to generate more power, more reach and to reduce effort and risk. In some cases, the control also provides the force to make an action happen, for example, a foot pump pedal.
Mobile phoneThe controls on your mobile phone allow you to make calls, send text messages and set your favourite ring tone. The keys on your keyboard and your mouse buttons are all controls that enable you to view this page!
The main function of a control is to transmit information to an object. When you use a control, information is flowing from you to the object (brain signals pass to the muscles in your hands which move to activate the control). You gather information from the object via feedback, for example, in the form of a change in a visual display when you press a key on your keyboard, or illumination of a room when you operate the light switch, etc.
Types of controls
The type of information that is transmitted by a control can be discrete (separate) or continuous. Discrete controls use a limited number of conditions, for example, a light switch, which is either on or off. Continuous controls use any value between the outer limits, for example, the gas control knob on a cooker hob can regulate the flow of gas anywhere between the minimum and maximum flows.
Controls often have an associated display to provide you with information about the results of your control actions. These displays can also show discrete or continuous information. Read more on displays.
Another major difference between controls is the amount of force needed to use them. Some controls may require a light touch with fingertip operation, for example, keyboard push buttons or lighting toggle switches. Others need more force using the strength and grip of the whole hand or foot, for example, door knobs, gear levers, brake pedals. Can you think why there should be a difference? See the Effective controls information below to find out.
Effective controls
To be effective, controls must be accessible, identifiable and usable.
Accessibility - since almost all controls require physical contact to be operated, they must be able to be reached comfortably and efficiently. You must consider the body size of the user - it's no use putting an emergency button out of reach!
Identifiability - a control needs to be able to be identified in terms of what it does in order to operate (twist, lift etc.), what it controls and what state it is in (on, off, partially open, etc.). This is especially true for groups of controls that may have similar functions. For example, the controls on the cooker at home probably look almost identical, but the labelling, and often the position of the control, enable you to tell them apart. The controls on a cooker rotate when operated to give you an idea of their state. Feedback is given by the oven, grill, burners or plates as they produce heat. Feedback is an important element of controls, giving you confirmation of your actions.
Usability - a control must be able to be used! You should be able to operate it with the required force, speed and accuracy. For example, it would be difficult to operate a foot pump with your hand because you need a lot of force to push air into a tyre. Using your foot for this enables you to put your weight behind it and use the large leg muscles to push. However, you don't need to be precise, unlike setting a rotary central heating control. The control knob is designed to be operated with the fingers and does not require force.
Guidelines for design
Control compatibility
The control should operate in the way that people expect it to operate. There are certain directions of control movement which are expected by the majority of people. They are called population stereotypes and control movements which conform to these stereotypes are said to be compatible. In western Europe, for example, a movement to the right, a movement forwards and away from the body, or a clockwise rotation, instinctively suggests a start or increase in operation.
People learn how to use controls more quickly if compatible control movements are used. Compatible controls are safer to use in emergencies. When people are under stress, they tend to use the 'expected' direction of movement. Control movements that seem 'natural' to the operator are more efficient and less tiring because there is less need for thought and assessment, and therefore operation is faster.
The use of force
The maximum force (and speed, accuracy, or range of body movement) required to operate a control should not exceed the limits of the least capable operator. 'Normal' requirements for control operation should be a lot less than the capabilities of most operators.
Control movements should be as short as possible.
Controls should have enough resistance so that they can't be accidentally operated, especially where the consequences are serious. For example, the emergency stop button on an escalator should resist an accidental light touch. For controls like emergency stop buttons, requiring a single application of force, or short periods of continuous force exertion, a reasonable maximum resistance is half of the operator's maximum strength. For controls operated continuously, or for long periods, the resistance should be lower.
Power-assisted, or fully powered controls should be applied in some types of equipment where the operator cannot apply enough force unaided e.g. electric garage door controls.
Coding of controls
Controls that are different (coded) in terms of either shape, size, mode of operation, labelling, or colour are easier to identify than controls which are similar in these respects.
Shape coding - the use of a distinctive shape for controls improves their visual and tactile (touch) identification. Standardised shapes should be used and sharp edges should be avoided on the parts of the control that are grasped.
Size coding - where size is used to distinguish controls (usually control knobs), the larger control should always be at least 20% larger than the smaller one for controls ranging from 15-150mm in diameter, in order to avoid confusion in selection.
Colour coding - colour should not be used as the sole method of coding of the control. It is more effective when combined with other methods. Use red, orange, yellow, green and blue as they are the only colours that are effectively identified and recognised. However about 7% of men and under 1% of women suffer from red-green colour blindness - they are unable to differentiate reds and greens and tend to see these colours as shades of greyish-yellow. Therefore, in situations where colour coding and recognition are vital, you should check that all operators can distinguish the colours used.
Labelling Labelling
If controls are to be labelled, adequate space and lighting must be provided to enable the labels to be clearly visible. Labels should be either on the control or immediately adjacent to it. They should not obscure the control and should be difficult to remove. Letters and numbers used should be standard.
Hand controls
You should use hand controls in preference to foot controls if:
- accuracy of control positioning is important;
- speed of control positioning is important;
- continuous or prolonged application of force is not necessary.
You should use:
Push buttons or toggle switches for tasks involving speed of operation.
Fingertip or hand-operated rotary knobs for fine adjustment and small forces, e.g. radio tuning.
Control sticks or levers when you need to apply moderate to large forces intermittently, e.g. gear changing or using the hand brake in a car.
Sticks, levers or wheels for continuous adjustment or tracking tasks.
Controls that use one handed operation for precision and speed.
Controls that use two handed operation for larger forces.
A hand control should offer some resistance to movement or accidental operation, for example, the keys on your keyboard need a definite push to operate them (try pushing a key gently - you should feel a slight but definite resistance).
A hand control should allow you to get a good grip. You should make sure that the control material is suitable for the environment where it will be used. For example, if the control is to be used outdoors, it may need a more textured surface to allow good grip in the wet, or it may need to be insulated so that it is not too cold or hot to touch. Materials for hand controls should be poor conductors of heat and electricity. They should be non-porous so that they will not soak up liquids. They should be strong enough not to chip or crack and injure your hand.
Foot controls
You should use foot controls in preference to hand controls if:
- continuous control of the task is required but the precision of the position of the control is not important.
- large forces need to be applied.
If a large force is needed, you should use a pedal on which pressure is applied by the whole leg, e.g. car brake pedal.
If a smaller force and continuous control is needed, you should use a pedal on which pressure is applied mainly from the ankle, e.g. car accelerator pedal.
For all foot controls, the direction of movement should be down or away from the body and in line with the centre of the body.
The angle at which the pedal is positioned should allow the foot to be placed on the pedal surface with the ankle at an angle of 90º. This angle should increase with operation of the pedal, that is, the pedal should be pushed away from the body to operate.
A pedal should be flat and have a large enough contact area so that the foot does not slip off (a width of at least 90mm). A textured surface also helps to keep the foot in position.
Foot controls should only be used if you are seated, or for very short standing times. It can place strain on the other leg/foot if you operate a foot pedal while standing.
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