Lecture
Functional analysis is the most general and universal approach to solving various problems. As a method for studying technical systems, it can be carried out in various aspects, and involves the use of various models and approaches (Fig. 9 .1).
Fig. 9.1 The main aspects, approaches and techniques of functional analysis
Functional analysis can be applied at various stages of the creation of technical systems (Fig. 9 .2).
The creation of any technical object (TO) begins with an analysis of needs and the formulation of the functions it must perform in order to satisfy these needs.
At the initial stage of creating a technical object, together with the formulation of the need, a list of functional requirements is drawn up to ensure that this need is satisfied.
Fig. 9.2 The main stages of creating a TO
The formulated functions are an integral part of the technical specification for developing the technical object. Therefore, at this stage it is important to understand:
1. Which functions need to be implemented;
2. Whether all these functions are necessary, or only some of them;
3. Whether these functions, or some of them, can be transferred to the supersystem.
When a technical object has been created in the form of certain models — for example, its physical operating principle has been synthesized, its structural diagram has been developed and a technical solution obtained (see Error: Reference source not found), drawings and a technological process have been developed — it becomes very important to assess how successful the solution turned out to be.
Then the purpose of functional analysis is to check the resulting solutions for compliance with the principles of the structure and functioning of the TS and the laws of their development, and, above all, from the standpoint of the principle of correspondence between function and structure.
A similar task arises when a prototype exists. The functional approach makes it possible to identify its main shortcomings and to set tasks for its improvement.
The functional approach involves analysing the functions both of the technical object as a whole and of its components and connections (see Error: Reference source not found).
A technical object is created to satisfy certain needs. To do this, it must perform certain functions. This may be one function or several.
If there are several functions, they may be independent or mutually complementary. For example, the function of a pencil – is to leave a mark on paper. If it has an eraser for erasing, that is its second function; if it has a bright cap that can be used as a pointer, that is its 3rd function; if it has a clip for attaching it, for example, in a pocket, that is its 4th function.
A TO can perform several mutually complementary functions. For example, a television – converts electromagnetic waves into image and sound, and allows the selection of the programmes received.
The set of functions that reflect the purpose of a technical object, the goal of its creation, and that determine its consumer properties, is customarily called the main useful function (MUF).
The MUF is realized through the working organ (WO), which interacts with the object toward which the action of the MUF is directed. The WO can perform its functions if energy and control are supplied to it. That is, in general, the working organ can function successfully if its operation is provided by the main components of the technical system (TS): the PE, the OU, and the Tr, which perform the main functions (MF). This, of course, holds if the technical system is complete (see Error: Reference source not found). If these components are absent from the TS, their function is performed by components of the supersystem.
To ensure the functioning of the WO, it is necessary to organize the performance of the main functions: the conversion of energy, the generation of control signals, and the transfer of substances and energy to the working organ.
Thus, the main functions ensure the performance of the MUF and are subordinate to it (Fig. 9 .3).
Fig. 9.3 Hierarchical representation of the relationship between the functions of a TO
For the technical system to operate well, auxiliary functions can be introduced into it that ensure the performance of the main functions. For example, generating a signal (command) to implement an MF (measuring transducers), switching (plug connectors); converting the properties of substances or fields (temperature, pressure, position) into electrical signals needed for the operation of the main components; coordinating the operation of the main functional components.
For the high-quality performance of the main and auxiliary functions, additional functions may be introduced.
Additional functions, together with the main one, provide the consumer properties of the technical object, improve the performance of the functions of the technical object as a whole or of its components, and extend its scope of application. A common feature of additional functions is that they increase comfort in performing the MUF and improve the operation of the corresponding functional component.
Additional functions include: measuring parameters (temperature, pressure, position) to monitor ongoing processes; ensuring human safety (protective devices); protecting the device from overloads (fuses); preventing the self-loosening of threaded connections (for example, Grower washers); increasing the stability of the device's operation (negative feedback); ensuring the manufacturability of the design and the maintainability of the technical object, for example, the possibility of adjusting and regulating the device's operating modes (trimmer capacitors, technological compensators used in assembly work, technological joints and connectors); diagnosing the operation of the device (indicators).
A distinguishing feature of auxiliary functions is that the main function cannot be performed without performing these functions. If, on the other hand, an additional function is not performed, the MUF can still be performed, but the quality will be low.
For example, damping vibrations during cutting (vibration dampers) helps to improve the quality of the resulting surface. Automatic lathes are equipped with chip breakers, otherwise the flowing chips would require the presence of a turner to remove them. Cutting fluid reduces friction during cutting and provides the required thermal regime during machining.
It should be noted that the division of functions into auxiliary and additional ones can, in some cases, be rather arbitrary. This division is of a purely methodological nature. Many components can perform both types of function at the same time. Designers always strive for this. For example, they try to combine structural joints with technological ones. But sometimes it is necessary to make special connectors for adjustment or repair work during operation.
For example, bellows in pipelines perform two functions: an auxiliary one – to reduce internal stresses under uneven heating during operation, and at the same time an additional one – to reduce installation stresses during assembly (the requirements for dimensional accuracy are reduced).
A simple example of an additional function is a resistive mosaic in thin-film microelectronics, which makes it possible to select the required resistance value. A set of film resistors of different ratings is created on the substrate of the microchip, and only individual sections are soldered into the circuit (Fig. 9 .4 b). It is also possible to create a bi-system, in which a shunting resistor is added to the main one (Fig. 9 .4 c), in which cuts are made to increase the resistance, performing trimming.
Fig. 9.4 Some types of resistors: a – ordinary resistor; c – bi-system; b – trimmer resistor.
Thus, the main and auxiliary functions form a certain hierarchy, a subordination that can be represented as a graph-tree (Fig. 9 .3). Additional functions, on the other hand, are subordinate to those functions whose operation they improve.
The rank of an auxiliary function – is the significance of the function, which determines its place in the hierarchy of functions that ensure the performance of the main function. The closer the function under consideration is to the MUF, the higher its rank.
First-rank auxiliary functions ensure the performance of the main function; second-rank auxiliary functions ensure the performance of first-rank auxiliary functions, and so on.
There may be several additional, main, and auxiliary functions.
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