The Human-Machine System Development Process

Ken Funk

9 January 1996

A human-machine system (HMS) is an integrated set of humans and machines that work together to accomplish some set of goals. HMSs include a mechanic with a wrench, a user and video cassette recorder, an airliner (including its flightcrew), a factory (including its workers), and an electric power generation/distribution system (including its operators, maintenance technicians, and other personnel).

Following is an outline of the human-machine system (HMS) development process that emphasizes the human-machine interface. It describes the responsibilities of the human factors engineering team as they work with mechanical, electrical, software, nuclear, aeronautical, civil, and other engineers to develop the overall system.

Though this outline may imply a rigid, sequential process, such is not the case. Not all of these activities are performed in any given system development project and some projects may involve other steps. They are often completed in a different order and in parallel. The process is inherently iterative in nature.

Overview

• Perceive need.
• Develop HMS Objectives and performance specifications.
• Perform HMS Analysis.
  • Perform system analysis.
  • Define users, operators, and maintainers.
  • Perform mission analysis.
  • Perform function analysis.
  • Allocate functions.
  • Perform task analysis.
• Perform HMS design.
  • Design work modules and jobs.
  • Perform preliminary HMS design.
  • Perform detailed HMS design.
  • Design facilitators.
    • Design instructional materials.
    • Design performance aids.
    • Design selection process.
    • Design placement process.
    • Design training program.
• Test and evaluate the HMS.
• References

The HMS Development Process

Perceive need.

• Synopsis: Identify need for new system/workstation(s).
• End product: Statement of Need (SON).

Develop HMS objectives and performance specifications.

• Define HMS objectives.
  • Synopsis: Define HMS objectives, purpose: what the HMS is to accomplish.
  • End product: Statement of HMS objectives, purpose.

• Identify HMS requirements.
  • Synopsis: Identify general requirements for and constraints or limitations on the use, operation, and maintenance of the HMS.
  • End product: List of HMS requirements and constraints.

• Describe HMS operating environment.
  • Synopsis: Define environment(s) which the HMS must operate in, including such considerations as
    • location(s).
    • atmospheric conditions (including weather).
    • illumination conditions.
    • other systems the HMS must interact with.
    • potential hazards.
    • stresses HMS will be subject to.
    • resources needed for operation.
    • etc.
  • End product: Description of the environment in which the HMS must operate.

• Define HMS performance specifications.
  • Synopsis: Define HMS performance measures, such as
    • accuracy, precision
    • speed
    • production rate, throughput.
    • safety and health
    • operator, user, and/or customer satisfaction
    • cost/profitability
    • etc.
  • End product: List of defined HMS performance measures including what they are and how they are to be measured.

• Identify alternatives.
  • Synopsis: Identify major technological options or alternative approaches.
  • End product: List of major technologocal options.

Perform HMS Analysis.

• Perform system analysis.
  • Synopsis: Define the HMS and its subsystems from the perspective of the system’s operators, users, and maintainers. Start with the whole system and decompose to an appropriate level. For each system/subsystem specify relevant attributes, including
    • name.
    • purpose/primary function.
    • inputs (especially control inputs).
    • outputs.
    • state variables (especially those of interest to the operators/users).
    • etc.
  • End product: Formal description of the HMS and its important subsystems.
  • Tools and techniques:
    • block diagrams.
    • hierarchical lists.
    • supplemental specification sheets.

• Define users, operators, and maintainers.
  • Synopsis: Characterize humans who will use, operate, and/or maintain the HMS, considering such attributes as
    • physical characteristics, capabilities, and limitations.
    • sensory capabilities and limitations.
    • cognitive capabilities and limitations.
    • education, training.
    • level of experience.
    • etc.
  • End product: List of typical operator, user, and/or maintainer characteristics.

• Perform mission analysis.
  • Synopsis: Describe the mission(s) the system is to accomplish.
  • End product: Detailed descriptions of HMS missions including normal and abnormal scenarios.
  • Tools and techniques:
    • mission profiles.
    • mission scenarios.

• Perform function analysis.
  • Synopsis: Identify functions that must be performed for the HMS to achieve its objectives. Start with the overall system function and decompose to appropriate level. For each function identified, specify important attributes, including
    • name of function.
    • goal to be accomplished.
    • constraints (time, space, resources, policies and procedures, etc.).
    • inputs (initial conditions).
    • outputs (final conditions).
    • etc.
  • End product: Description of all important system functions.
  • Tools and techniques:
    • hierarchical function lists.
    • functional flow diagrams.
    • IDEF0 models.
    • supplemental specification sheets.

• Allocate functions.
  • Synopsis: Assign system/subsystem functions to humans, machines, or to human/machine combinations considering
    • accuracy and precision requirements.
    • timing and speed requirements.
    • force and displacement requirements.
    • reliability requirements.
    • complexity of operations.
    • duration of function.
    • relationships to other functions.
    • human safety and health.
    • human comfort and satisfaction.
    • etc.

    Note: This is actually a design activity, but it is a necessary step before HMS analysis can be completed

  • End product: List of function allocations.
  • Tools and techniques:
    • Fitts lists.
    • Design evaluation matrices.

• Perform task analysis.
  • Synopsis: A task is a function that has been allocated to a human. For each task, define important attributes, including
    • name of task (i.e., name of function).
    • information required by operator/user/maintainer, including cues for initiation.
    • evaluation process.
    • decision reached after evaluation
    • action taken
    • frequency of task
    • time requirements (minimum, maximum, typical)
    • feedback required
    • communications required (what and who)
    • etc.
  • End product: Descriptions of all tasks.
  • Tools and techniques:
    • hierarchical task lists.
    • IDEF0 models.
    • supplemental specification sheets.

Perform HMS design.

• Design work modules and jobs.
  • Synopsis: Combine tasks into work modules. Combine work modules into jobs. Determine how many operatorss and/or maintainers are required and what each will do.
  • End product: List of operators and/or maintainers and the tasks each is responsible for.
  • Tools and techniques:
  • timelines.
  • man-machine charts.

• Perform preliminary HMS design.
  • Synopsis: Identify required workstations. For each workstation, identify major components and features and design its overall geometry and approximate layout. Specify such attributes as
    • type and location of doors, hatches, passageways, etc..
    • type and location of windows, ports, etc..
    • type and location of seating (if any).
    • type, location, and orientation of work surfaces.
    • location and orientation of display/control panels.
    • type and location of displays.
    • type and location of controls.
    • type and location of tools and other equipment
    • type and location of storage.
    • etc.
  • End product: Design documents (sketches, descriptions, etc.) specifying types of components, overall geometry, and approximate layout.
  • Tools and techniques:
    • design guidelines.
    • design criteria checklists.
    • human factors engineering handbooks.
    • sketches.
    • Computer-Aided Drafting (CAD) programs.
    • etc.

• Perform detailed HMS design.
  • Synopsis: Select specific components and specify details of each workstation, including
    • exact locations of components.
    • dimensions of components.
    • display formats.
    • control parameters (displacements, gains, resistances, etc.).
    • interface software specifications.
    • operating procedures.
    • etc.
  • End product: Design documents (drawings, descriptions, etc.) giving detailed specifications for all aspects of workstation.
  • Tools and techniques:
    • design guidelines.
    • design criteria checklists.
    • human factors engineering handbooks.
    • anthropometric data tables.
    • reach envelopes.
    • visibility diagrams.
    • drawings.
    • CAD programs.
    • manikins.
    • models.
    • mockups.
    • functional prototypes.

• Design facilitators.
  • Design instructional materials.
    • Synopsis: Design appropriate instructional materials, such as
      • operating instructions.
      • maintenance instructions.
    • End product: Instructional materials.

  • Design performance aids.
    • Synopsis: Develop appropriate performance aids, such as
      • operations manuals.
      • maintenance manuals.
      • checklists.
      • quick reference cards.
      • computer-based performance aids.
    • End product: Performance aids.

  • Design selection process.
    • Synopsis: Develop criteria and methods for selecting personnel based on such factors as
      • physical characteristics, capabilities, and limitations.
      • sensory characteristics, capabilities, and limitations.
      • mental characteristics, capabilities, and limitations.
      • educational background.
      • experience.
    • End product: Criteria and methods for selecting personnel.

  • Design placement process.
    • Synopsis: Develop criteria and methods for placing personnel in specific jobs.
    • End product: Criteria and methods for placing personnel in specific jobs.

  • Design training program.
    • Synopsis: Design training program including
      • training curriculum.
      • training materials.
      • evaluation procedures.
    • End product: Training programs.

Test and evaluate the HMS.

• Perform static evaluation.
  • Synopsis: Evaluate design documents to identify human factors problems and areas for improvement.
    • End product: List of deficiencies and suggestions for correction.
    • Tools and techniques:
      • design criteria checklists.
      • timelines.
      • man-machine charts.
      • workload analysis.
      • link analysis.
      • predetermined time standards.
      • biomechanical analysis.
      • simulation.
      • etc.

    • Perform dynamic evaluation.
    • Synopsis: Use mockup/prototype with representative operators/users/maintainers to identify human factors problems and areas for improvement. A procedure such as the following is often used:
      • develop scenarios.
      • develop performance measures.
      • simulate scenarios in mockup/prototype.
      • record results.
    • End product: List of deficiencies and suggestions for correction.
    • Tools and techniques:
      • role playing.
      • man-in-the-loop simulation.
      • direct observation.
      • audio/video recording.
      • eye movement apparatus.
      • verbal protocol analysis.
      • questionnaires.
      • etc.

References

Anonymous (1979). Military Specification: Human Engineering Requirements for Military Systems, Equipment, and Facilities, MIL-H-46855B, Redstone Arsenal, AL: US Army Missile R&D Command.

Anonymous (1987). Military Handbook: Human Engineering Procedures Guide, DOD-HDBK-763, Washington: Department of Defense.

Bailey, R.W. (1989). Human Performance Engineering, second edition, Englewood Cliffs, NJ: Prentice-Hall, pp.173-186.

Kearns, J.H. (1981). A Systems Approach for Crew Station Design, AFWAL-TR-81-3175, Wright-Patterson Air Force Base, OH: Air Force Wright Aeronautical Laboratories.