Functional modelling is one of the most efficient methods of analysing technical devices since it provides an opportunity to get a complete idea of the composition, structure, and connections among the components.
The functional model is a simplified diagrammatic model of the technical device. Each component of the device is represented as a rectangle, and the effect of this component on the other is represented as an arrow in it. The component name is written in the rectangle, and the verb denoting the action is written above the arrow.
Conventional functional model
The sequence of developing a functional model is as follows:
the main function of a machine or its part selected for analysis is determined;
the components are listed;
the relations among the components are indicated;
the functions of each component are calculated;
the model is synthesised;
the machine (or its part) connections to the environment are clarified.
If it is required to develop the machine model as a whole, its main function can be determined via the main product. It is usually specified in the issue description. If we examine any part of the machine, it is necessary to understand which useful product this part produces and to determine the main function via the product.
The information about the components of which the machine consists can be obtained from different sources: observing the machine itself; studying drawings, photos or drawings; from the physical model (layout).
Once the system components are determined, all interactions among them should be discovered. To that end, it is convenient to use the “interaction matrix”: it is a table the number of which columns and lines equals the number of the system components. The names of the components are written vertically and horizontally. Then each component is sequentially checked: if component A interacts with component B, then a mark is placed in the cell at the intersection.
Conventional interaction matrix
Then, it is required to determine for each pair which component is the tool (affects) and which is the object worked (is affected). Each effect is given a name. A verb accurately defining the essence of the action should be selected.
What is left is to combine functional pairs into a single arrangement. It is possible to begin developing the model from any point, the key point is for no significant component to be forgotten.
It is required to take into account the branching of actions from one component, addition of effects on one component etc. Upon developing the initial variant of the model, it is required to thoroughly check it and to analyse it for consistency and completeness. It should be corrected, if necessary.
It is possible to include significant components of the environment in the functional model. It is worth doing this when the external environment significantly affects any components of the machine being studied or it depends on the environment whether the machine will function in principle. For example, the loudspeaker can only operate in the atmospheric environment, and its sound will not spread in the vacuum.
Example. Electric flashlight
The pocket electric flashlight does not provide enough light. We should study this device, the flashlight, to understand where the issue occurs.
Electric flashlight arrangement
Main function: “expose objects to light”.
The material components of the flashlight: a lamp, a reflector, a light beam, protective glass, a body, a switch, electric current, a cable, and a battery.
Let us make the matrix of the component interactions:
The matrix of interactions of the electric-flashlight components
Let us determine the nature of interactions.
The light beam is processed by the lamp and the reflector: the lamp emits light, the reflector directs light.
The lamp is processed by the cable: the cable powers the lamp.
The battery powers the cable.
The switch controls the cable: it breaks and closes the electric circuit.
The body processes a lot of components, it holds the battery, the cable, the switch, the lamp, the reflector, and the protective glass.
The protective glass protects the lamp and the reflector from damage.
Generation of functional pairs
Functional pairs are summarised in a functional model.
The main sequence is as follows: the battery produces electric current and powers the cable – the cable carries electric current – electric current powers the lamp – the lamp emits the light beam – the light beam exposes the object to light.
The control is carried out as follows: the switch controls the cable, the reflector directs the light beam.
Besides, the functional model includes the body and the protective glass which hold and protect the device components while performing auxiliary functions.
Which components of the environment are required for the flashlight to operate? Assume the flashlight lies on a table on its own. Will it function?
Probably, somebody is required to turn on the flashlight, to hold it, and to direct the beam to the necessary object. It means that we should include the human – the flashlight “operator” – in the model. Besides, the properties of the air can affect the flashlight operation – e.g., it will give less light in the fog.
