The dramatic effect computer numerical control has already had on traditional engineering production techniques is now well appreciated. Machines controlled in this way
are capable of working for many hours every day virtually
unsupervised. They are readily adaptable to facilitate production of a wide
range of components. Every function traditionally performed by the operator of
a standard machine tool can be achieved via a computer numerical control
To appreciate just how versatile computer
numerical control can be, it is only necessary to examine very briefly the
human involvement in the production of a simple component such as the one
shown in Figure 1.3. The hole only is to be produced by drilling on a
conventional vertical milling machine. The activities of the operator in
producing the component would be as follows:
From this list it can be seen that even the simplest of machining operations involves making a considerable number of decisions that influence the resulting physical activity. A skilled machinist operating a conventional machine makes such decisions and takes the necessary action almost without thinking. Nevertheless, the decisions are made and the action is taken.
It is not possible to remove the human involvement totally
from a machining process. No automatic control system is yet capable of making
a decision in the true sense of the word. Its capability is restricted to
responding to a manually or computer- prepared program, and it is during the
preparation of the program that the decisions are made. Via that program the
machine controller is fed with instructions that give effect to the decisions.
In this way all the functions listed above, and many others not required in
such a simple example of machining, may be automatically and repeatedly controlled.
Figure 1.4 lists the elements of total machine control.