ANATOMICAL AND ANTHROPOMETRICAL ASPECTS OF CONTROL DESIGN

Some of the principal anatomical and anthropometric aspects will be considered. For detailed specifications, some excellent handbooks are to be recommended (for example, Morgan et al., 1963; Grandjean, 1988). One important limitation of the recommendations available today is that they are based on the body measurements of Caucasians. For other ethnic groups, the measurements must be adapted for their proportionally shorter or longer leg lengths.

The following rules can be applied in the design of all types of control:

1. The maximum strength, speed, precision, or body movement required to operate a control must not exceed the ability of any possible operator.

2. The number of controls must be kept to a minimum.

3. Control movements which are natural for the operator are the best and the least tiring.

4. Control movements must be as short as possible, while still maintaining the requirement for ‘feel’.

5. The controls must have enough resistance to prevent their activation by mistake. For controls that are only used occasionally and for short peri­ods, the resistance should be about half the maximum strength of the operator. Controls that are used for longer periods must have a much lower resistance.

6. The control must be designed to cope with misuse. In panic or emergency situations, very great forces are often applied, and the control must be able to withstand these.

7. The control must give feedback so that the operator knows when it has been activated, even when this has been done by mistake.

8. The control must be designed so that the hand/foot does not slide off or lose its grip.

Table 5.1 gives a summary of the areas of use and the design recommendations for different controls. The controls are discussed in more detail later. Figure 5.1a, Figure 5.1b, and Figure 5.1c give the optimal areas for the different controls.

Stepwise Adjustments Continuous Adjustments

	Rotary Switch	Hand Push-Button	Foot Press-Button	Toggle Switch	Small Wheel	Wheel	Crank	Pedal	Lever
Large forces can be developed	—	—	—	—	No	Yes	No	Yes	Yes
Time constraint for adjustment	Medium	Fast	Fast	Very fast	—	—	—	—	—
Recommended number of	3-24	2	2	2-3	—	—	—	—	—
positions
Space requirements for placing and using	Medium	Small	Large	Small	Small to medium	Large	Medium to large	Large	Medium to large
Activation by accident	Small	Medium	Large	Medium	Medium	Large	Medium	Medium	Large
Limits of control movements3	270°	3.2 x 38 mm	12.7×100 mm	120°	None	±60°	None	Small3	±45°
Legibility	Good	Acceptable	Bad	Acceptable	Badd	Acceptable	Acceptable	Bad	Good
Visual identification of control position	Acceptable	Badb	Bad	Acceptable	Acceptable0	Bad to acceptable	Bad	Bad	Good
Checking control position on	Good	Badb	Bad	Good	Good	Bad	Bad	Bad	Good
panel together
Usability as part of a combination	—	Good	Bad	Good	Good	Good	Bad	Bad	Good
of controls

TABLE 5.1 Recommendations for Controls

a The exception is “cycle ” pedals, which have no limit.

b The exception is when the control is back-lit and the light goes off when the control is activated. c Only usable when control cannot be turned more than one revolution. Round wheels/knobs must be marked. d Assuming that control can be rotated more than one turn.

Reference point is at the angle between seat and backrest

I_____ I_____ I_____ I_____ I_____ I_____ I_____ L

0 10 20 30 40 50 60 70

Forward from Reference Point, cm

(a)

-20 -15 -10 -5 0 5 10 15 20 Distance to the Right and Left of Seat Reference Point, cm (b)

FIGURE 5.1 (a and b) Preferred vertical surface areas and limits for different classes of manual controls. (Modified from McCormick and Sanders, 1982. With permission.)