Function index

Function index is a dimensionless measure of the overall functional contribution of the component to the overall performance of the engineering system.

Overview

The function index is used to calculate a component’s value in the value analysis.

It usually depends on the number of useful functions the component performs and ranks of these functions. Originally, harmful functions were also included in the calculation, with points subtracted for their presence. Different factors were also applied to useful functions, depending on their level of performance. Some TRIZ specialists still follow this classical approach.

The method of calculation presented below is one of the simplest.

Calculating the function index

Both for devices and for processes, the following steps should be performed to calculate the function index of a component:

identify all functions performed by the component / within the operation,
determine their category,
rank each useful function (eg. basic / productive – 3pts, additional / providing – 2pts, auxiliary / corrective – 1pt),
sum up the function points of all functions performed by the component / in th operation,
normalize the function score.

Since harmful functions are not scored, they are not included in the calculations.

Let’s consider the fllowing example for a device: one of the components (component A) performs 1 harmful function and 3 useful functions:

1 basic function (3pts), and
2 auxiliary functions (2 x 1pts = 2pts).

The harmful function is ignored, so the total score of the component is 5pts. Let us assume that the sum of point scores for all components of the system equals 41pts. The total function index of component A equals 5/41.

In the same way, the function index for operations in processes can be calculated. For example, the sum of point scores for all operations in the process equals 132pts. Within operation X, the following useful functions are performed:

2 productive functions (2 x 3pts = 6pts),
3 providing function (3 x 2pts = 6 pts), and
1 corrective function (1pt).

The total score of the operation X is 13pts; therefore, its functionality index equals 13/132.