ControlControlChapter 9Chapter 9

Defining ControlDefining Control Chapter 6 (human information Chapter 6 (human information

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

Information Processing Information Processing ModelModel

Principles of Response Principles of Response SelectionSelection

Decision Complexity – speed of action Decision Complexity – speed of action selection affected by complexityselection affected by complexity

Response Expectancy – perceive rapidly Response Expectancy – perceive rapidly & effectively info that we expect& effectively info that we expect

Compatibility – location & movement Compatibility – location & movement expectencyexpectency

The Speed-Accuracy Tradeoff – not The Speed-Accuracy Tradeoff – not always positive correlation between always positive correlation between speed & accuracy (e.g. severe time speed & accuracy (e.g. severe time constraints)constraints)

Feedback – visual, tactile, & auditoryFeedback – visual, tactile, & auditory

Discrete Control Discrete Control ActivationActivation Physical Feel – feed back is positive feature Physical Feel – feed back is positive feature

of discrete controls (toggle switch state of discrete controls (toggle switch state (visual), click (auditory), & snap (tactile).(visual), click (auditory), & snap (tactile).

Size – size of keys/controls represents the Size – size of keys/controls represents the trade-offs between available space and trade-offs between available space and usabilityusability

Confusion & Labeling – when controls are Confusion & Labeling – when controls are unlabeled or poorly labeled confusion unlabeled or poorly labeled confusion resultsresults

Positioning Control Positioning Control DevicesDevices Movement time (figure 9.2)Movement time (figure 9.2) Device characteristics Device characteristics

– Direct position (light pen, touch screen)Direct position (light pen, touch screen)– Indirect position (mouse, pad, tablet)Indirect position (mouse, pad, tablet)– Indirect velocity (joy stick, arrow keys)Indirect velocity (joy stick, arrow keys)

Isotonic, isometric, spring loadedIsotonic, isometric, spring loaded– Gain control (sensitivity)Gain control (sensitivity)

Task performance dependence (figure Task performance dependence (figure 9.3)9.3)

The work space (table 9.3)The work space (table 9.3) The environment (figure 9.4)The environment (figure 9.4)

Verbal & Symbolic Input Verbal & Symbolic Input DevicesDevices Numerical Data Entry (figure 9.4)Numerical Data Entry (figure 9.4) Linguistic Data EntryLinguistic Data Entry

– Type writer/keyboardType writer/keyboard– Direct writing input (technical Direct writing input (technical

challenges)challenges)– Chording keyboard (figure 9.5)Chording keyboard (figure 9.5)

Fast transcribing (court recorders)Fast transcribing (court recorders) Less fatigue and muscular/skeletal stress Less fatigue and muscular/skeletal stress Requires extensive learningRequires extensive learning

Voice InputVoice Input BenefitsBenefits

– Natural communications channelNatural communications channel– Advantageous in dual task situations Advantageous in dual task situations

(dialing cell phone while driving)(dialing cell phone while driving)– Allows dual inputAllows dual input

CostsCosts– Confusion & limited vocabularyConfusion & limited vocabulary– Speed constraintsSpeed constraints– Acoustic quality & noise/stressAcoustic quality & noise/stress– Compatibility – less suitable for controlling Compatibility – less suitable for controlling

continuous movementcontinuous movement

Continuous Control & Continuous Control & TrackingTracking

The tracking loop elements – The tracking loop elements – standard, actual, difference, & standard, actual, difference, & corrective actioncorrective action

Continuous Control & Tracking Continuous Control & Tracking (cont.)(cont.)

Input task – varies with frequency Input task – varies with frequency of corrective actionsof corrective actions

Control orderControl order– Position (0 order control)Position (0 order control)– Velocity (1Velocity (1stst order control) order control)– Acceleration (2Acceleration (2ndnd order control) order control)

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

PROPORTIONAL CONTROLPROPORTIONAL CONTROLMagnitude of correctvie action is proportional to magnitude of “error”

CP (t) = KP 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 CONTROLDERIVATIVE CONTROL

15

10

Old Set-Point

New Set-Point

Time

Proportional & Integral Control arepushing the process down.

Derivative Control is anticipating over-shoot & is pushing the process up.

C t K

de tdtd d

INTEGRAL CONTROLINTEGRAL CONTROLKeeps history of the accumulated error and attempts to correct any imbalance

dTTeKtCt

ii 0

)(

15

10

Old Set-Point

New Set-Point

Time

Continuous Control & Tracking Continuous Control & Tracking (cont.)(cont.)

Gain control (proportional to amount of Gain control (proportional to amount of correction required)correction required)

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

Open- versus closed-loop systemsOpen- versus closed-loop systems– Previous discussion was closed-loopPrevious discussion was closed-loop– Open loop would be when operator notes Open loop would be when operator notes

correction needed and simply puts switch to correction needed and simply puts switch to new position regardless of correction needednew position regardless of correction needed

Remote Manipulation or Remote Manipulation or TeleroboticsTelerobotics

Time delayTime delay Depth perception & image quality - Depth perception & image quality -

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

Proprioceptive feedback – Sense of Proprioceptive feedback – Sense of tactile feedback to prevent crushing tactile feedback to prevent crushing of fragile object being manipulatedof fragile object being manipulated