Human–Machine System: Controls
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Transcript of Human–Machine System: Controls
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Human–Machine System: Controls The boundary between the human and the
machine is the “user interface.” Information flows from human to machine
through controls.
MAN
CONTROLS
MACHINE
DISPLAYS
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 OptionsKeys 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 20–50 mm. For vehicle control, follow diameter
and orientation recommendations. Consider permitting angle adjustment.
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Control Options (cont.)
Foot–Leg 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 Engineer’s habit patterns may not be the user’s
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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Human–Machine System: Displays Displays include instruments, labels, and
accompanying printed instructions and warnings.
MAN
CONTROLS
MACHINE
DISPLAYS
Physical Environment
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Causes of Failure Legibility or detectability Understanding
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Displaying InformationInform
atio
nDisplay
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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 15–25 min of arc
1 min of arc = 0.00029 rad
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Guideline 2: Arrange Characters & SymbolsText – 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 – don’t 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 DisplayGeneral Considerations Task/job – what’s 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 they’re 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