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Design for UsabilityBased on Chapter 14, Blanchard, B.S. & Fabrycky, W.J. (2011) Systems Engineering and Analysis, Pearson.
CookMyProjectIntroductionFor a system to be effective and robust during service, the human element needs to be addressed from both a usability and an operability perspective.This requires a detailed understanding of Human Factors and the way in which an operator/user interacts with the system and its environment operator/user and the system/subsystems. These interactions will be detailed in the interface specifications included in the Product Baselinewill be traceable upwards to usability requirements and needs.Note that usability/operability applies not only to normal system use, but misuse and abuse. In this regard, Murphy’s Law is pertinent:
“If there are two ways to do something and one of those results in a catastrophe, then someone will do it that way”From a design perspective, think of power plugs and sockets:
Note that “Anything that can go wrong, will go wrong” (commonly referred to as Murphy’s Law) is in fact Finagle’s Law. Murphy was an aeronautical engineer and his law was meant as serious advice to practitionersDefinitionsUsability is the ease of use and learnability of a human-made object such as a tool or device (https://en.wikipedia.org/wiki/Usability)Operability is the ability to keep an equipment, a system or a whole industrial installation in a safe and reliable functioning condition, according to pre-defined operational requirements. (https://en.wikipedia.org/wiki/Operability)Human factors and ergonomics (commonly referred to as human factors) is the application of psychological and physiological principles to the (engineering and) design of products, processes, and systems. The goal of human factors is to reduce human error, increase productivity, and enhance safety and comfort with a specific focus on the interaction between the human and the thing of interest. (https://en.wikipedia.org/wiki/Human_factors_and_ergonomics)Human Factors RequirementsHuman Factors requirements relate to the tasks that a human is required to perform in the operation or use of a system. These tasks need to be Identified andFormulated with due consideration to human factorsThese activities form a key part of the functional analysis and allocation activities in the Preliminary Design Phase.The allocation of requirements is most commonly achieved using process called function allocation (also known as task allocation) Function allocation is a classic human factors method for deciding whether a particular function will be accomplished by a person, technology (hardware or software) or some mix of person and technology. To do this, the investigator considers error rates, fatigue, costs, hazards, technological feasibility, human values, ethical issues, and the desire of people to perform the function. (https://www.usabilitybok.org/function-allocation)
Environmental ConsiderationsInput to Functional Analysis and Requirements AllocationThe dominant considerations relate to technology and economicsTechnological: Can the function be automated?Economic: If the function can be automated, is it cost-effective to do so?There may also be political/societal considerations, such as whether or not to outsource
Personnel FactorsInput to Functional Analysis and Requirements AllocationThe following factors may need to be taken into determining whether a function should be allocated to an operator/user:Anthropomorphic factorsThese relate to the physical dimensions and capabilities of the human body.Human Sensory factorsThese relate predominantly to vision (sight) and hearing (noise).Physiological factorsThese relate to environmental stresses such as temperature, humidity, vibration and noise.Psychological factorsThese relate to personal attitudes such as initiative and motivation.Hierarchy of Human ActivityFor requirements allocated to humans, determine the level of allocationDepending on the granularity/complexity of the functional requirement (job) being allocated to the operator(s)/user, allocation at the level of Job operationsdutiestaskssubtasks or task elementsmay occur.
Job operation: Completion of a function normally includes a combination of duties and tasks. A job operation may involve one or more related groups of duties.Duty: Defined as a set of related tasks within a given job operation.Task: Constitutes a composite of related activities (informational, decision, and control activities) performed by an individual in accomplishing a prescribed amount of work in a specified environmentSubtask: Depending on the complexity of the situation, a task may be broken down into subtasks to cover discrete actions of a limited nature. Task element: Task elements may be categorised as per the smallest logically definable facet of activity (based on perceptions, decisions and control actions) that requires individual behavioural responses in completing a task or a subtask.(Blanchard& Fabrycky, 2011)Human Factors AnalysisFor each requirement allocated to a human, do human factors analysis. This involvesOperator Task AnalysisDevelopment of Operational Sequence DiagramsError Analysis andSystem safety/hazard analysisHuman Factors AnalysisOperator Task AnalysisInvolves a systematic study of the human behaviour characteristics associated with the completion of system tasks Operational Sequence Diagram
Refer to Fabrycky and Blanchard for Error Analysis and Safety/Hazard AnalysisCommon MeasuresLabour hours required per hour of system operation / maintenance:Time taken to accomplish a functionNumber of errors committed in a time period or while performing a functionCost of operators / maintenance personnel per hour of operation / maintenance
Human Factors in the System Life CycleReferencesBlanchard, B.S & Fabrycky, W.J. (2011) Systems Engineering and Analysis 5th. Edition, Pearson.
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