Allocation of functions can be done in more or less detail. If ergonomically-orientated function allocation is used, it is relatively simple to specify the level of detail at which the functions allocation should be carried out. In the function allocation stage that follows function analysis, the functions are allocated between humans and machines/personnel technology. In this way, one can specify which functions are to be performed by the human element and which by a technical component. It is therefore not meaningful for a function allocation to be written in terms that are too abstract. This can result in all the functions following function analysis needing a combination of both human and technical solutions.
An allocation of functions according to Figure 13.2 is thus far too general. It probably requires both human and technical work in the form of controlling and at the same time it requires technical equipment for water. One should therefore
|
FIGURE 13.2 Simplified system for cleaning textiles. |
divide up the functions into considerably smaller units. Ergonomic allocation of functions is concerned primarily with the distribution of functions between human and machine. This later stage is the first time that a further allocation is carried out, between the different technical solutions on the one hand, and the allocation of different tasks between different job holders on the other. In the textile cleaning system discussed above, therefore, the question is then asked whether the sorting of dirty textiles should be done with technical aids, and whether feeding-in should be done by hand or by technical means. The various sections in the process can be covered in the same way.
Function allocation is carried out on the basis of certain criteria. In the United States, various forms of productivity criteria are used in function allocation in the development of technical systems and methods for product development. The attempt is made to determine which is the more efficient at carrying out a particular function, a human or a machine. Special tables have been worked out that allow one to read off when man is more suitable or when one should use a machine. One such table is the well-known ‘Fitts’ List’, which is reproduced in Table 13.1. This narrow selections method is much too limited today to fulfil any practical function. Such efficiency criteria are, of course, important, but considerably more detail than that given in Fitts’ list is required. However, Fitts’ list can be used for a rough classification.
It is also important to take economic criteria into account but this is beyond the scope of this book. The most important factor we are concerned with is to create meaningful work that does not cause injury or fatigue to people; that is, we are concerned with the various forms of human criteria. The criteria should be decided at the same time as defining the system goal. The criteria are used in the evaluation of the human versus the technical alternative for the performance of different functions. We now look at some examples of how this form of discussion may be carried out in an allocation of functions.
Machines are often best at performing certain types of physical activities. This is particularly true of very simple operations with no fine manipulation, and where the work is monotonous and repetitive. The machine is almost always to be preferred over human beings for heavy physical lifting tasks, both from the efficiency and the human viewpoints. The technical solution, however, can be very costly if operations involve more complex and fine manipulations. In our example of textile cleaning, the feeding-in, unloading, and transport tasks should preferably be done mechanically, especially if the system is also to be suitable for an older population.
The human sense organs are in all cases superior to technical equivalents, particularly if the cost aspect is taken into account. In addition, different types of control work—where the person needs to use vision and hearing, for example—usually also involve important operations that people prefer to control themselves. For certain simpler types of sensory work, however, technical aids can be the best alternative. For simpler decision making, it is relatively easy and cheap today to use technical devices as an alternative to human inputs. But even here it is important to remember that human beings get satisfaction from controlling a process. In addition, a human being has considerable advantages when it comes to making simple decisions. For example, a person can make small adjustments to the decision process without having to use programmed information. A washing drum can be allowed to rotate a few
|
TABLE 13.1 Relative Advantage of Man and Machines
Source: Modified from Fitts and Posner (1967). |
minutes longer if the human operator sees (from sensory inputs) this as desirable, for example, due to the quality of the textiles being processed. It would be very costly to get a technical device to make such small modifications automatically. In complex decision making in systems with high inertia (for example, manoeuvring large ships, administrating parts of financial systems, or energy systems), operators obtain great benefits from using simulators and mathematical modelling of systems.
In general, it may be stated that a human being is a very poor monitor, and therefore should not be given the job of monitoring technical systems. On the other hand, a machine often makes a tireless monitoring device.
A good allocation of functions between humans and machines for the job of cleaning textiles may be as follows. The operator sorts the textiles according to quality and dirtiness and puts them into different bins. The machine is preprogrammed to handle the material from the different bins in different ways. Depending on the type of textile and type of water, the machine itself regulates the temperature, water quantity, and type and quantity of the various cleaning chemicals. After the textiles have been processed with water and chemical additives and centrifuged to remove excess moisture, they are transported down into a drum for drying. Removal of the dried textiles is done manually.
The different forms of function allocation can be discussed in a preliminary stage in this way. One can then analyse the different alternatives in more detail in order to find the ‘optimal’ solution. It is clear that, for the parameters in this case, it is very difficult to make any sort of quantification that would allow an exact form of optimisation procedure to be produced. This may be possible in certain cases, while in others it is considerably more difficult. Efficiency criteria can often be viewed in economic terms and thus allow a certain degree of comparability with other criteria. The result is a quantifiable evaluation system.
It is considerably more difficult to measure the human criteria (in terms of comfort, fatigue, and accident risks, for example) in such a way as to be comparable with other criteria. The difficulty of taking account of the human criteria in a more quantifiable way during function allocation must not result in their being dismissed altogether, as these aspects are often of the utmost importance. Within the field of technical production research, an attempt is made to translate the various forms of working efficiency into economic terms. However, it is not generally an easy method, and it is important to create a method in the future where other than just the economic criteria are taken into account. Only under these circumstances will we be able to build up a technology that is suited to people. In other words, it is important that a methodology for product development is used that allows us to steer the technology in the required direction, whilst also taking full account of what is best for the operator.
