Design for usage: Function

The ‘design for usage’ part of the product life cycle can be broken down into four broad areas:

• function
• ease of use
• safety and reliability
• economic operation.

This step will examine the first of these: function.

It goes without saying that a product is expected to provide one or more functions. Simple products, such as a can opener, can have one or two functions. Complex ones, such as computers, may have tens, hundreds or even thousands of functions. Therefore, designers must recognise all of the functions required in a certain product and make sure that their designs provide these functions.

Essential and nonessential functions

The functions of any product can be divided into essential or nonessential functions. Designers must incorporate all essential functions in the design of a product, but can choose to omit some of the non-essential ones if they prove to be too difficult or costly. In some cases, non-essential functions may be included in high end, more expensive versions of a product to meet the desires of certain customers.

These functions are usually recognised, analysed and documented at an early stage of the design process. When the design requirements are set out, designers then make sure that the end product provides all these functions to a satisfactory standard.

Essential functions are those that every product should provide. For example, a food mixer should have a function for thoroughly mixing various kinds of food. If a mixer fails to provide this essential function, it is considered unfit for purpose.

Nonessential or desirable functions, on the other hand, are those that users prefer to have. But if a product fails to provide them, it’s still considered usable. For example, people expect a food mixer to have a function for changing the mixing speed. If a mixer does not have this function, it can still be used but in this case, it may be less attractive to users.

The number of functions that a product should have differs from one type of product to the other. A fairly complex engineering product, such as a car, will have dozens of essential functions and many nonessential, or desirable ones. For example, every car must have a functional unit to provide power to drive its wheels. The unit that provides this function is called the powertrain. A car must also have a functional unit that allows it to decelerate and stop safely. The unit that provides this function is called the braking system. Also, a car must have another functional unit to absorb the shocks and vibrations that occur when riding over rough road surfaces. The unit that provides this function is called the suspension system. These are just a few of the essential functions that every car must have. On the other hand, a car may have an active suspension system that provides a softer ride over rough road surfaces. Not all cars have this feature today as it is considered a desirable function.

It’s important to note that many functions were not considered essential in the past, but have become an essential and sometimes legally required one today. For example, cars sold in the UK were not required to have seatbelts until 1966. Before that, seatbelts were considered a desirable feature.

In the next step, you will see that it’s not enough for a product to provide all functions. It should also be easy and comfortable to use by all types of users, regardless of their physical, sensory or mental capacities.