Updated on January 12, 2025

Function rank

Function rank is a dimensionless measure that determines the importance of the useful function.

Overview

Function ranking is conducted when it is necessary to develop an innovation strategy.

Usually, it is calculated for components of the engineering system only; components of the supersystem are not ranked.

Ranking involves identifying the type of the function and then assigning it an appropriate number of points based on that type. The purpose of the scoring system is to establish relative importance among functions. The total points of all functions performed by a given component allow for calculating its functional index, which is essential for estimating the component’s value to the system. During the ranking only useful functions are considered, harmful functions are ignored. The level of performance is also not taken into account.
Functions are ranked for both devices and processes, but different criteria applied for them.

Function ranks for devices

The evaluation criterion here is the status of the component that is the object of the function. The function with the highest value (basic) is the one performed on the target component, i.e., the object of the main function. Functions performed on other components of the supersystem (additional) have a lower value. The least valued are the functions performed on the components of the system (auxiliary) since the primary concern is about interactions between the system and its supersystem components.
Functions for devices have three ranks, which are usually based on the following scoring system:

Function ranks for processes

Applying the same criteria used for devices to functions performed in processes turns out to be impossible. In this context, neither the target component nor the supersystem components are actively utilized, even though they technically exist.

For processes, functions have ranks, which are usually based on the following scoring system:

The most valued are functions directly resulting with an irreversible change in the final product of the process (productive). Functions that help perform other functions but are not resulting with an irreversible change at the end of the process (providing) are slightly less important. Corrective functions have the lowest rank.

The algorithm for function ranking for processes can be presented in the form of the following diagram:

In the function analysis of processes, the ranking is particularly important because what happens to a function during trimming depends closely on its rank. For devices, any rule can be applied to functions of any rank (except Rule A, which is not recommended if the removed component performs a basic function). However, for processes, there is no universal set of rules. A trimmed operation typically includes a broad set of functions, and each of them must be appropriately addressed based on its rank.

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