# 10 controls

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CONTROLS

Text p. 218-242

04/11/2012             Burns            1
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

04/11/2012            Copyright Catherine M. Burns   2
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!

04/11/2012            Copyright Catherine M. Burns          3
Exercise 1: Picking something
for lunch
 With a partner, examine the following
menus. Make a decision on what to order.

04/11/2012       Copyright Catherine M. Burns   4
Basic Principles

 Hick-Hyman Law:
 Reaction time increases
logarithmically as number of
possible responses increases     RT
 (2 options faster than 8)
 (or RT is a linear function of                 N
log2(n), suggesting people process
information at a constant rate)

04/11/2012        Copyright Catherine M. Burns       5
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

04/11/2012        Copyright Catherine M. Burns         6
Resolving HH Law and Decision

 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)

04/11/2012                   Copyright Catherine M. Burns            7
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)

04/11/2012            Copyright Catherine M. Burns   8
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.

04/11/2012      Copyright Catherine M. Burns   9
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?

04/11/2012             Copyright Catherine M. Burns            10
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?

04/11/2012      Copyright Catherine M. Burns   11
Fitts Law

 MT is proportional to 2A/W
 Log2(2A/W) is called the index of difficulty

04/11/2012      Copyright Catherine M. Burns     12
W1

Assume A1=4, W1=1
ID=log2(2A/W)=log2(8)=3
A1

ID=log2(2*2A1/W)=log2(16)=4
W1

A2=2A1

W2=1/2W1 ID=log2(2*2A1/W)=log2(16)=4

A1

04/11/2012         Copyright Catherine M. Burns               13
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)

04/11/2012      Copyright Catherine M. Burns   14
Continuous Control and
Tracking
 following a moving target
 driving the most common example
 generally based on controlling the error
signal e(t)

04/11/2012       Copyright Catherine M. Burns   15
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

04/11/2012      Copyright Catherine M. Burns   16
Types of Control

 Zero order (Position x Control): position of
control device = position of output.
   computer mouse, drawing a line, analog tuning

04/11/2012            Copyright Catherine M. Burns       17
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

04/11/2012              Copyright Catherine M. Burns                18
Second Order or Acceleration
Control
 Spacecraft maneuvering
 Each input produces an acceleration
 Hard to control, sluggish and unstable

04/11/2012          Copyright Catherine M. Burns   19
Control Order

Zero Order                      First Order

Second Order

04/11/2012              Copyright Catherine M. Burns   20
Control Problems

 Time delays
 Gain

 Called “closed loop” or sometimes “negative
feedback loop” instability

04/11/2012      Copyright Catherine M. Burns   21
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

04/11/2012      Copyright Catherine M. Burns   22
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

04/11/2012     Copyright Catherine M. Burns   23
STABLE EFFECTIVE
CONTROL

STABLE, BUT
OSCILLATING CONTROL

UNSTABLE CONTROL

UNSTABLE HIGH GAIN

04/11/2012   Copyright Catherine M. Burns   24
Controls on
the Space
Shuttle

04/11/2012   Copyright Catherine M. Burns                 25
Death Star Gunner’s Helmet

04/11/2012         Copyright Catherine M. Burns   26
Lightsabers

04/11/2012   Copyright Catherine M. Burns   27
Control
Accessibility?

04/11/2012   Copyright Catherine M. Burns   28
Close-up

04/11/2012   Copyright Catherine M. Burns   29
Control
–
Finger
match

04/11/2012   Copyright Catherine M. Burns             30

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