HUMAN FACTORS AND ERGONOMICS

There are various applications and sub-disciplines of human factors and ergonomics according to:

     - General requirements for the product; manufacturing costs, marketing aims, safety issues…etc.

     - Interface of the user with the product; will it be carried, used at hand, used at standing position…etc.?

     - Applications of product; work done by the user, does the user need instructions during usage, need feedback from the product during application…etc.?

     - Any other former versions of the product; traditional applications, customer habits, familiarization of the user to similar products…etc.

2 or 3 sub-disciplines of human factors and mostly combinations of them shall be studied with each criteria the design or the product has. Although basic principles of each sub-discipline application are almost the same, the content and the aim of the study are different.

Some applications of human factors and ergonomics studies are:

     • Human-Machine Interface: This discipline of human factors and ergonomics is basically interested in layout of the product if it contains any system design. It determines whether the layout of system components (buttons, screens, handles, seats…etc.) is designed suitable enough for the customer to perform his tasks or not. Basic analyses concerning human-machine interface are:

          1. Reach Envelope Analysis: It defines whether the user population is able to reach and activate system components due to his movement limitations in a task based order or not. Anthropometric data of the user population is highly important as an input. The limit body type is generally taken is %3 percentage slice of the anthropometric data if the system does not contain any emergency application. By related CAD tools, 3 D model of %3 percentage body type is created in the system environment and reach envelope is simulated according to the requirements. It is vital to reevaluate the system with field applications with mock-up of the product and mixed user body subjects.

          2. User View Analysis: This discipline also uses anthropometric data to figure out whether the geometric or location based layout of the system components are visible for the user in defined posture of the user or not. Head and eye movement limitations defined by the standards shall also be applied. It aims detection of view area of the user in normal head position and relocate the task critical system components in this area where user can focus comfortably in his work environment. %98 body type of the user population may be used if it is not clear that the posture of the user cause his limbs to create an obstacle or shade in vision around the system components or not. Visibility can be simulated with HMI CAD programs, system and user model and field tests with mockup and subjects shall be used for confirmation and correction.

          3. Work Load Analysis: Order and complexity of the tasks to be performed over the system by the user are evaluated with this discipline. This analysis mostly based on cognitive behavior of user and field tests containing careful observations on the subject’s cognitive behavior. Analyst should master the requirements of the system and tasks that can be performed and create scenarios based on these with ascending complexity order to observe the user while performing according to these scenarios. Subjects shall be also recorded with a camera for reevaluation and should also give feedback about their level of performance during the scenarios.

          4. Human Error Analysis: This discipline of human factors and ergonomics is also highly related with cognitive behavior of user and observations of these behaviors on field tests aiming to detect human error sources in the designed system. Other than studies in work load analysis, subjects for field studies should better be selected from the people less familiar with the system or product at first on purpose. This selection will prevent the analyst from overlooking any sources error which can be handled by more experienced people with the system. For example a person working with computers will sense that this symbol “Ф” will shut the system down even if there isn’t a “POWER OFF” placard or nameplate on a button. But a well-defined symbol or clear wording must be applied to create a user friendly system.

      • Task and Task Profile Analysis: This study mostly evaluates and constructs conceptual design inputs, major decisions and general layout of the tasks and task profiles related with the product. Task and action relation or connection is determined in workflow. System elements according to the task-action relation are also defined. Analyst creates task scenarios for other ergonomics studies.

      • Predetermined Time Standards: The main aim of this discipline of human factors and ergonomics is to calculate the time for complex process due the task requirements and analyze time motion concept to increase efficiency. A well-defined model of the task and the system should be achieved. Some commercial techniques like Work-Factor or Mento-Factor is mostly used.

      • Cognitive Task Analysis: This discipline of human factors and ergonomics is vital to determine the cognitive abilities for a task to be done with a system. Human behavior is analyzed in complex, realistic, variant, uncertain and stressful due to reaction time cases and this analysis is mostly achieved with high experience and costs.

      • Critical Decision Analysis: This study is based on collecting data from technically experienced users by using interviewing techniques. Critical decision analysis is extremely hard to achieve and it is recommended that analyst should be highly experienced in this field.

Reference:
  • Pheasant, S. , Haslegrave, C. M. (2006) . Bodyspace: Anthropometry, Ergonomics and the Design of Work . (3rd edition), CRC Press
  • MIL-STD-46855 Human Engineering Requirements for Military Systems, Equipment, and Facilities (2011)
  • MIL-HDBK-759 Human Engineering Design Guidelines (2012)
  • MIL-STD-1472 Human Engineering (2012)
  • MIL-HDBK-1908 Definitions of Human Factors Terms (1999)