HumanMachine System: Controls

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HumanMachine System Controls

• The boundary between the human and the machine is
  the user interface.
• Information flows from human to machine through
  controls.

Physical Environment
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Guideline 1 Select the Proper Type of Control

• Types of systems
• Open-loop
• Closed-loop
• Discrete vs continuous
• Select part of the body to implement mental
  command
• Choose mechanical interface between human body
  and machine interior
• Consider amount of human power required
• Consider errors and speed

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Guideline 2 Select the Proper Control
Characteristics

• Force
• People variables
• Muscles used
• User population
• Percentile designed for
• Control variables
• Control options
• Keys and pushbuttons
• Knobs
• Cranks

• Control variables
• Purpose
• Design
• Hand wheels
• Foot/leg controls

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Control Options

• Keys and Pushbuttons
• Keys should be non-round, concave on top, and
  consistently displaced.
• Use key interlocks.
• Feed back activation to operator.
• Use shape to indicate function.
• Avoid palm buttons.
• Knobs
• Circular knobs depend on hand friction on
  circumference.
• Knob shape can compensate for slippery grip.
• Increasing diameter increases torque.

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Control Options (cont.)

• Cranks
• Provide high coefficient of friction.
• Allow grip to rotate on crank.
• Consider a sphere.
• Hand Wheels
• For valve control, increase radius to reduce
  tangential force.
• Use recommended heights.
• Rim diameter should be 2050 mm.
• For vehicle control, follow diameter and
  orientation recommendations.
• Consider permitting angle adjustment.

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Control Options (cont.)

• FootLeg Controls
• Provide greater force and free the hands.
• May be switches or pedals.
• Consider friction problems (shoe sole, dirt,
  debris).
• For continuous control, bend the ankle by
  depressing the toe.
• Consider knee switches.

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Guideline 3 Prevent Unintended Activation

• More severe consequences require greater
  precautions.
• Consider that operators may bypass the guard if
  it makes operation difficult.
• All equipment should have an emergency stop
  control.
• Consider two reaction times
• Human (sensing, deciding, carrying out)
• Machine

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Methods of Reducing Accidental Activation

• Key or special tool activation (locks)
• Interlocks
• Barriers or covers
• Recessing
• Spacing
• Resistance
• Direction

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Guideline 4 Prevent Incorrect Identification

• Labeling
• Color
• Shape
• Size
• Mode of operation
• Location

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• Labels should be
• Legible
• Located properly
• Understandable
• Color
• 8 of males, 0.4 of females have color
  perception problems
• Use 8 or fewer colors.
• Consider lighting requirements.
• Consider color stereotypes.
• Consider cultural differences in color stereotypes

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• Shape
• Can be a visual signal.
• Can be identified in the dark.
• Use up to 9 different shapes.
• Tactual shape coding is slower than color coding.
• Tactile signals (e.g. pimple, ridges) can help.

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• Size
• Only 2 or 3 different sizes can be
  differentiated.
• Larger sizes give mechanical advantage.
• Use larger sizes in cold environments.
• Mode of Operation
• Consider push/pull vs. rotate vs. slide.
• Mode of operation may be a backup for
  identification methods.
• Location can identify controls and groups of
  controls.

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Guideline 5 Make Accomplishments Equal Intentions

• Require verification of critical commands.
• Make complex sequences of actions user-friendly.
• Use more care and testing for actions with
  multiple steps.
• Check input for validity.
• For continuous controls, consider
  control/response ratio.
• Control positions often act as displays.

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Population Stereotypes

• Engineers habit patterns may not be the users
  habit patterns.
• Stereotypes are often country-specific (light
  switches, water faucets, car blinkers).
• See table 17.9, pg. 323 for US conventional
  control movements
• Consider labeling.

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Guideline 6 Properly Locate and Arrange the
Controls

• Arrangement of Controls
• Group related controls and displays together.
• Minimize layout complexity.
• Have blank space on the panel.
• Hand Controls
• Keyboards
• Manipulative controls
• Knobs
• Switches
• Force controls

• Foot Controls
• Avoid foot controls for standing operators.
• For continuous control, leg should fully extend
  at bottom of stroke.
• For discrete control, use one leg.
• Have straight line between pedal and back
  support.
• Comfort may be more important than force
  capability.
• Design to avoid fatigue.

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HumanMachine System Displays

• Displays include instruments, labels, and
  accompanying printed instructions and warnings.

Physical Environment
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Causes of Failure

• Legibility or detectability
• Understanding

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Displaying Information
Display
Information
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Guideline 1 Select Legible Characters

• Font
• Use printed characters
• Avoid Roman numerals
• Upper/lower case
• For short messages, use all caps
• For text or longer messages, use mixed-case with
  large open spaces in letters
• For VDT, use more pixels and lower dot pitch
• Size
• Character height K Distance from eye
• K 0.004, 0.006, 0.0017, 0.0073 radians
• Visual angle should be 1525 min of arc
• 1 min of arc 0.00029 rad

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Guideline 2 Arrange Characters Symbols

• Text clear and legible
• Print text in columns
• 10 -11-point type minimum
• Use space between number and unit
• Use double-spacing
• Do not justify right side
• Use headings for organization

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Guideline 2 (cont.)

• Codes dont rely on memory
• Automate the code transfer
• Make codes checkable
• Use short codes
• Make the code meaningful
• Abbreviations use with caution
• Use rules to form abbreviations
• Rules best for encoding are not necessarily the
  best for decoding
• Truncating works better than vowel deletion in
  testing, but best rule of thumb is to be
  consistent!
• Do not include period

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Guideline 3 Decide on Type of Display

• General Considerations
• Task/job whats the purpose of the display?
• User characteristics
• language, education, culture, expectations, etc.
• Standardization (see examples, next slide)
• Menus lists of options
• Deep vs Shallow
• Structure according to how information is used
• Minimize complexity / maximize understanding
• Avoid multiple pages
• Highlight options
• Use blank space and grouping

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Guideline 3 (cont.)

• Tables make the information easy to find
• Round data to 2 significant digits
• Use explicit tables
• Avoid matrix tables
• Make the primary comparison down the column
• Reduce row alignment errors and column selection
  errors
• Formulas simplify calculations
• Use to permit exact calculations
• Present in units that the user will enter
• Decide on significant digits necessary

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Guideline 3 (cont.)

• Graphs make relationships visible
• Use to compare complex relationships
• Use instead of tables when
• Displayed data have inherent structure
• Structure is relevant to the task
• Provide titles, labels, units
• Place close to the text it illustrates
• Guidelines for Good Graphs, for example
• Make graphs wider than tall
• Show scale subdivisions with tick marks
• Avoid hatching
• Use only a few curves on a single graph
• Indicate data points with open symbols

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Guideline 3 (cont.)

• Symbolic Messages be sure theyre understood
• Include shapes and colors, diagrams, pictographs
• Use color to identify categories
• makes navigation easier
• but use ONLY as a redundant code
• Use icons with care
• Weigh benefits vs. costs
• Maps locate in space and time
• Can show data distributions and location
  relationships
• May be scaled to distance or time
• May be not to scale

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Guideline 4 Project Your Message

• Slides
• 35 mm slides
• Computer projection
• Transparencies
• Video

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Guideline 5 Select the Instrument Display

• Discrete finite choice of options
• Continuous point on a scale
• Analog
• Digital
• Representational provide diagram or picture
• Video

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Warning Messages

• Type of failure
• False signals
• Missing signals
• Multiple signals
• Should be both visual and aural
• Should be within primary field of view
• Should provide guidance information
• Urgency / immediacy of warning should match
  severity of danger

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Guideline 6 Locate/Arrange the Display

• Location
• Locate to be seen easily
• Provide appropriate lighting
• Consider eye height and head orientation
• Keep data within a 20º cone of line of sight
• Angle should be about 30º below the Frankfurt
  Plane
• Arrangement
• Determine what the operator is required to do
• Maintain consistency on panel and within facility
• Decide on grouping logic
• Consider computer simulation