Machine damage: A production line was designed to operate with coolant valve open. Due to a transient power failure of the controller, the controller invoked an unusual command sequence, and the production line started with the coolant valve closed.
This is an example of an interaction fault due to procedural disorder. Each of the units worked according to the specifications. However, the designers wrongly assumed that the first unit will never deviate from the specified command sequence. The system was not designed to detect and protect from deviations from this sequence. This kind of interaction faults can be avoided by implementing standards for scenario-based interaction protocols.
Production waste. A graphical user interface (GUI) enabled the operator
of a manufacturing system to control various parameters of several production lines.
The design was based on the service-oriented architecture (SOA) paradigm, in
which machines and other components are represented by objects, the parameters are
represented by properties and the machine operation is implemented by methods
that define the system services. A dedicated screen was designed for each
object, enabling the operator to set any of the object properties and to actuate
any of the methods.
Many operators found this design
logical. Sometimes, however, when they changed a production line, they forgot
to change all the settings. To work around this problem they developed a
verification test, to make sure that all the parameters were set correctly. Subsequently,
they prepared check lists of parameters that should be set or reset for each
production line. The check lists were implemented in the GUI next version,
shortening the pre-production verification cycles significantly.
A simple usability test at the prototype stage
could have revealed the design mistake, which should then have triggered a
redesign based on usability guidelines for scenario-based information
visualization, based on operator task analysis. Such redesign should have
guaranteed that the operator would set all the parameters relevant for each
production line.