Lecture8

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14 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

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Control

Chapter 9

Defining Control


Chapter 6 (human information
processing)


knowing the state of
affairs, knowing what to do, and doing
it. Control is the doing part of the
process. It is both a noun and a verb
(to control). In information
processing, it involves the selection
and execution of responses or the last
two stages of the model.

Information Processing Model

Principles of Response Selection


Decision Complexity


speed of action
selection affected by complexity


Response Expectancy


perceive rapidly &
effectively info that we expect


Compatibility


location & movement
expectency


The Speed
-
Accuracy Tradeoff


not always
positive correlation between speed &
accuracy (e.g. severe time constraints)


Feedback


visual, tactile, & auditory

Discrete Control Activation


Physical Feel


feed back is positive feature
of discrete controls (toggle switch state
(visual), click (auditory), & snap (tactile).


Size


size of keys/controls represents the
trade
-
offs between available space and
usability


Confusion & Labeling


when controls are
unlabeled or poorly labeled confusion results

Positioning Control Devices


Movement time (figure 9.2)


Device characteristics


Direct position (light pen, touch screen)


Indirect position (mouse, pad, tablet)


Indirect velocity (joy stick, arrow keys)


Isotonic, isometric, spring loaded


Gain control (sensitivity)


Task performance dependence (figure 9.3)


The work space (table 9.3)


The environment (figure 9.4)

Verbal & Symbolic Input Devices


Numerical Data Entry (figure 9.4)


Linguistic Data Entry


Type writer/keyboard


Direct writing input (technical challenges)


Chording keyboard (figure 9.5)


Fast transcribing (court recorders)


Less fatigue and muscular/skeletal stress


Requires extensive learning

Voice Input


Benefits


Natural communications channel


Advantageous in dual task situations (dialing cell
phone while driving)


Allows dual input


Costs


Confusion & limited vocabulary


Speed constraints


Acoustic quality & noise/stress


Compatibility


less suitable for controlling
continuous movement

Continuous Control & Tracking

The tracking loop elements


standard,
actual, difference, & corrective action


Continuous Control & Tracking (cont.)


Input task


varies with frequency of
corrective actions


Control order


Position (0 order control)


Velocity (1
st

order control)


Acceleration (2
nd

order control)


Time delays & transport lags (e.g.
controlling robot on mars)

PROPORTIONAL CONTROL

Magnitude of correctvie action is proportional to magnitude of “error”

C
P

(t) = K
P

e(t)

15

10

Old Set
-
Point

New Set
-
Point

Proportional Cont Action tapers off as process


approaches new set
-
point but over shoots

Time

DERIVATIVE CONTROL

15

10

Old Set
-
Point

New Set
-
Point

Time

Proportional & Integral Control are

pushing the process down.

Derivative Control is anticipating over
-

shoot & is pushing the process up.





C
t
K
de
t
dt
d
d

INTEGRAL CONTROL

Keeps history of the accumulated error and attempts to correct any imbalance



dT
T
e
K
t
C
t
i
i


0
)
(
15

10

Old Set
-
Point

New Set
-
Point

Time

Continuous Control & Tracking (cont.)


Gain control (proportional to amount of
correction required)


Stability


instability is result of lags, gain to
high, & human trying to correct too fast


Open
-

versus closed
-
loop systems


Previous discussion was closed
-
loop


Open loop would be when operator notes
correction needed and simply puts switch to new
position regardless of correction needed

Remote Manipulation or
Telerobotics


Time delay


Depth perception & image quality
-

problem of accuracy in 3
-
D settings.
Limited bandwidth may also affect
image quality


Proprioceptive

feedback


Sense of
tactile feedback to prevent crushing of
fragile object being manipulated