The keyboard is still the most common computer input device. The design of the keyboard has a significant effect on the operator’s performance in terms of speed and accuracy. The most common keyboard layout is the QWERTY layout. Where two hands are used on the keyboard, 57% of the workload is on the left hand, even though 80% of the population is right-handed. This is advantageous for the type of job where the right hand alternates between handwriting and typing. It is also important to have one standard keyboard layout. Although the QWERTY layout is not the most efficient (it is said to have been designed for slowness, so that the keys on early mechanical typewriters did not become overloaded and snag), it is now the best compromise as it has become the standard keyboard.
Keyboards are usually designed so that the alphanumeric section is in the centre, with the cursor, editing keys, and numeric keypad to the right. Function keys may be placed anywhere on the keyboard, but in order to give an aesthetically pleasing design they are often placed on the left-hand side. Lateral hand movements also require less energy than longitudinal (front to back) movements.
There are no specific recommendations for keyboard layout, as their design is extremely sensitive to the task being carried out. However, a degree of flexibility must be incorporated in their design to cater for all variations in user requirements. One solution to this would be to develop a modular keyboard consisting of several units. Each unit would be made up of a different set of keys. The units could be arranged in the desired layout based on the results of the task analysis. However, care must be taken in using a flexible keyboard configuration due to the risk of a negative transfer of training. For example, if an operator carries out a number of different tasks, and different keyboards are used for each of the different tasks, then high error rates must be expected.
Chord keyboards are a combination of a keyboard and a coding system. In a similar way to keys on a piano, one can press several keys at the same time. The advantage of this type of keyboard is that key-pressing speed compared with a standard typewriter is considerably better than 50% faster. There are, however, no special design recommendations for this type of keyboard. In general, it may be said that this type of keyboard needs further research before any firmer recommendations can be given regarding suitable areas of use and suitable design. Its main application is a kind of stenographic keying which allows direct imputing of text at the same speed as it is spoken. However, this demands a rather long period of training and operators need a particular aptitude of sensor-motor skills of their hands. The application in industrialised control rooms is probably very limited; however, there might be some use for this type of keyboard in special emergency situations. In other more administrative control situations, there might be other possible areas of use. One example could be stock market trading where success depends on speed of decision and action in sending complex messages.
The numeric keyboard appears in two different designs. The accepted layout is a 3 x 3 + 1 key set, but there are two alternatives within this. Adding machines have the 7, 8, and 9 keys on the top row while push-button telephones have the 1, 2, and 3 keys at the top (see Figure 5.4). In the future, all telephones will use the 1-2-3 keypad. Once this happens, it will be recommended that all numeric keyboards are of this design. Uniformity is important, and the user should not have to switch from one keyboard design to the other (with concomitant need to shift learned skills of keyboard usage).
The height of the keyboard is largely determined by its physical design, for example, electrical contacts and activating mechanism. Thicker keyboards (greater than 30 mm thick) should be lowered into the table surface to ensure a correct user posture. Unfortunately, this does not allow for flexible workplace design. Ideally, keyboards should be as thin as possible (less than 30 mm thick from the desk surface to the top of the second key row (ASDF…) and not need to be lowered into the
Layout of a numerical keyboard.
FIGURE 5.4 surface. Product development, particularly by Ergolab in Sweden, has resulted in thinner keyboards, and this allows for a more flexible workplace design.
Keyboards can be stepped, sloped, or dished. There is no evidence on the relative advantages of any of these profiles. The most important factor is for the keyboard to be able to be angled between 0 and 15 degrees up at the back and, if the keyboard operator is standing, it is advantageous if it can be raised at the front from 0 to 30 degrees.
The size of the key tops is a compromise between producing enough space for the finger on the key, while at the same time keeping the total size of the keyboard as small as possible. Key tops should be square and 12 to 15 mm in size. This size is quite sufficient for touch typing, but in cases where keyboards are used for other tasks—for example, on the shop floor—key sizes can be larger. The spacing of keys is standardised to 19.05 mm between key top centres. This is within the ergonomic recommendations of between 18 and 20 mm. The force required for key displacement should be the same on all keys. For skilled users, the actuating force should be
0. 25 to 0.5 N, and the key displacement (travel) 0.8 to 1.0 mm (from rest to activation of system). For unskilled users the force should be 1 to 2 N and the displacement 2 to 5 mm. The user requires feedback to indicate that the system has accepted the keystroke. This is an important keyboard characteristic, although the exact requirements vary according to the individual levels of user skill.
In normal typing and other key-pressing tasks, there is kinaesthetic (muscle) and tactile (touch) feedback from the actual depression of the key, auditory feedback from the key press and/or activation of the print mechanism, and visual feedback from the keyboard or from the output display. For skilled operators, feedback from the keyboard (sound and pressure change) is of little importance. When learning, and for unskilled operators, this feedback is important. The operator should be able to remove the acoustic feedback.
The colour of the keys is not generally regarded as important. A dark keyboard with light lettering is preferable when used in conjunction with light-on-dark image displays, and care should be taken not to cause any distracting reflections on the screen by light key colours. Matt finishes should be used where possible. The recommended reflectance factors for keyboards used in conjunction with negative-image (light on a dark background) VDUs are:
1. The lettering on the keys should be light and clearly defined. Its minimum height should be 2.5 mm in good lighting conditions. In the case of function keys, certain abbreviations may be required. These must follow a clear, logical pattern and be easily identifiable by the operator.
2. Keyboards used with positive image (black on white) VDUs should be lighter in colour with darker text. All key top surfaces should have a matt finish.
Care should be taken when using colours to code various function keys. Attention should not be drawn to a red key or a group of red keys if their importance in the system is minimal. These principles concerning colour may also be applied to any information lights found on the keyboard. There are international colour standards (IEC 1975, Publication 73: Colours of Indicator Lights and Push-Buttons) that can apply to both keys and information lights. These standards should be adhered to wherever possible.