1. Copyright Catherine M. Burns
CONTROLS
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2. Copyright Catherine M. Burns
Control Model
Controls enable an operator to take action
A. action on the interface
B. control signal to the machine
C. action on the world
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3. Copyright Catherine M. Burns
Controls as Displays
Controls must be visible and understandable. All guidance on information displays holds here as well.
Controls are also displays:
must be visible
must be understandable what they control
actions on them must be visible - give feedback!
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4. Exercise 1: Picking something for lunch
With a partner, examine the following menus. Make a decision on what to order.
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Basic Principles
Hick-Hyman Law:
Reaction time increases logarithmically as number of possible responses increases
(2 options faster than 8)
(or RT is a linear function of log2(n), suggesting people process information at a constant rate) RT N
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Basic Principles
Decision Complexity Advantage:
But given same amount of information to transmit, smaller # of complex decisions is faster than more simple decisions
Shallow menus faster than deep menus
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7. Resolving HH Law and Decision Complexity Advantage
Given 1 message
It will be faster to type it than to use Morse Code
Fewer keystrokes, but each keystroke carries more information
Morse Code keystrokes will be faster than typewriter keystrokes
HH Law (2 choices vs 26)
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Basic Principles
Response Expectancy: better select actions that are expected
Compatibility: to mental model of the user and physical compatibility
location compatibility (close to display)
movement compatibility (congruent with feedback)
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Exercise 2
With a partner
Draw a dot on a sheet of blank paper.
Have your partner try to hit the dot
1. As many times as possible in 1 minute
2. As accurately as possible 10 times.
Reverse roles.
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Exercise 3
With a partner
Take a sheet of blank paper
Draw a large circle on it and a small circle on it.
Hold the paper arm’s length away from your partner.
Have your partner touch the large circle 10 times, then the small circle 10 times
Which is easier?
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Basic Principles
Speed-Accuracy Trade-off: faster behaviour is generally less precise
Fitts Law: MT = a + blog2(2A/W) where A = amplitude, W = target width (Further target or decreased size, increases MT)
Feedback of control state: Can you tell when the control has been activated, or when the control signal has been sent?
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Fitts Law
MT is proportional to 2A/W
Log2(2A/W) is called the index of difficulty
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Software Controls
Usually 2 controls (input device) and on screen “soft control”
Input devices are highly task dependent.
Touch screen not precise, parallax issues, but direct input, easy to understand, no peripheral (Table 9.1, 9.2, 9.3)
Slide pad: Any comments?
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15. Continuous Control and Tracking
following a moving target
driving the most common example
generally based on controlling the error signal e(t)
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Exercise 4
Finger Tracking exercise
One partner is the leader the other the tracker. Then reverse roles.
How do you make it difficult for your partner to follow you?
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Types of Control
Zero order (Position x Control): position of control device = position of output.
computer mouse, drawing a line, analog tuning
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Velocity Control
First order (Velocity dx/dt Control): activation of control yields a velocity. Control must be moved back to stop movement..
car steering wheel
Joystick
Radio scan button (1 push sets up scan velocity, push to stop)
Control needs to have a “neutral” point where response stops
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19. Second Order or Acceleration Control
Spacecraft maneuvering
Each input produces an acceleration
Hard to control, sluggish and unstable
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Control Order
Zero Order
First Order
Second Order
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21. Copyright Catherine M. Burns
Control Problems
Time delays
Gain
Called “closed loop” or sometimes “negative feedback loop” instability
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22. Copyright Catherine M. Burns
Time delays
People tend to over command
Handling the lag requires anticipating the results of control movements
People correct too rapidly, or to tiny deviations
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23. Copyright Catherine M. Burns
Gain
Large system output to small input
Gain=DO/DI
Proper gain is somewhat task dependent
High gain good for large changes
High gain can cause overshooting and instability for small deviations
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24. Copyright Catherine M. Burns
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25. Controls on the Space Shuttle
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26. Death Star Gunner’s Helmet
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Lightsabers
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28. Darth Vader Control Accessibility?
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Close-up
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30. Copyright Catherine M. Burns
Control – Finger match
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