Robust Design: Disposable Design Principle

Wednesday, May 19th, 2010 by Robert Cravotta

[Editor's Note: This was originally posted on the Embedded Master]

The disposable design principle focuses on short life span or limited use issues. At first glance this principle may make you think these principles only apply to cheap systems, but that would be incorrect. An example of an expensive system that can embody the disposable design principle is an expendable vehicle or component such as a rocket engine. These systems are in contrast to a reusable space vehicle, such as the Space Shuttle, which require a heavier mechanical structure and a recovery system, such as wings, thermal protection system and wheels that result in a lower overall payload capacity. In practice, using the single-use systems are less expensive, support a shorter time to launch, and are considered low risk for mission failure for many types of missions, including launching satellites into orbit.

Limited-use or disposable embedded systems can enjoy similar advantages over reusable versions. Limited-use systems are being embedded into all types of applications, such as inventory tracking tags, medical appliances, fireworks, environmental tracking pads for agriculture, security tags on retail items, and authentication modules to ensure that consumable subsystems are not matched with unsupported end-systems.

The disposable design principle also applies to systems that enforce an end-of-life. The plight of CFLs (Compact Fluorescent Lights) is a good example of a product industry that is responding to the consequences of adopting or ignoring the disposable principle. When a CFL reaches its end-of-life, it can manifest a (purportedly) rare failure mode where a fuse on the control board will burn out. I say purportedly rare because every CFL I have used to end-of-life (even on different lamps) has failed the same way with a small fire, smoke that smells like burning plastic, and burnt plastic on the base of the bulb. The CFL industry has taken notice of the consumer concern about unsettling end-of-life behaviors and is setting standards for handling end-of-life for CFLs. Enforcing an end-of-life mechanism can simplify the complexity the designers must accommodate because the system will shut itself down before the probability of key failure modes manifesting crosses some threshold.

Disposable or limited-use does not necessarily mean lower quality of the components, but it can mean that the system can take meaningful optimizations that drastically drop the cost of the system and improve the delivered quality of the end system. Disposable contact lenses are available in many styles, from daily, weekly, and monthly wear. Each type of lens makes different trades in the materials for durability and sterility that allows each to deliver superior quality at each price point.

Disposable hearing aids use a battery or cell that is fitted permanently within the system; there is no way to replace the battery with a new one. Using a permanent battery allows the disposable hearing aid to last longer on the same charge store than traditional hearing aids. The permanent battery also eliminates the need for the designer to implement a battery door and a mechanism for removing and placing batteries into the hearing aid. In fact, some disposable hearing aid designs are able to make use of a larger microphone area that would normally be consumed by a battery replacement door and hinge.


2 Responses to “Robust Design: Disposable Design Principle”

  1. Print Online says:

    Hey this a very insightful article! Thanks! I learned permanent battery allows disposable hearing aid to last longer on the same charge store than traditional hearing aids. This information is helpful because my father uses hearing aids.

  2. Joyce says:

    I feel far more folks should be required to read this, incredibly beneficial info.

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