King Saud University. College of Engineering. IE 341: Human Factors Engineering

Transcription

1 King Saud University Cllege f Engineering IE 341: Human Factrs Engineering Fall 2016 (1 st Sem H) Chapter 10. Human Cntrl f Systems Tracking (Part 1) Prepared by: Ahmed M. El-Sherbeeny, PhD 1

2 PART I Cntents Inputs and Outputs in Tracking Pursuit and Cmpensatry Displays in Tracking Cntrl Order f Systems Cntrl Respnses with Varius Cntrl Orders Human Limitatins in Tracking Tasks PART II Factrs that Influence Tracking Perfrmance Prcedures fr Facilitating Tracking Perfrmance 2

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6 Inputs and Outputs in Tracking What is tracking? Invlves cntinuus cntrl f smething Examples: driving a vehicle, pilting a plane, tracing a line n a paper Requirements f Tracking Make crrect mvements at right times Task is paced by persn ding it (e.g. when driving a car) Task can be externally paced, i.e. persn has n cntrl n task rate (e.g. fllwing a racehrse with binculars) Tpics t be cvered here: Sme backgrund n certain cncepts in tracking Sme backgrund n many variables invlved with tracking perfrmance 6

7 Cnt. Inputs and Outputs in Tracking In tracking: Input specifies desired utput f system Example: curves in rad (input) specify desired path t be fllwed (utput) Inputs Types f input: Cnstant(e.g. steering a ship t specified heading, flying a plane t an assigned altitude), r Variable (e.g. fllwing winding rad, chasing a maneuvering butterfly with a net) Received directly frm envirnment Sensed by: Peple Mechanical sensrs (then presented n display as signals) Other classificatin f input: Signal smetimes called: target(r it really is a target) Mvement f signal called: curse Input signal can be described mathematically and shwn graphically These graphs can be used t characterize input 7

8 Cnt. Inputs and Outputs in Tracking Input Patterns Output Types f elementary patterns (input) that can be distinguished (next slide): Sine input (characterized by a sine wave) Step input: Specifies discrete change in value e.g. instructin frm cntrl twer fr plane t change altitude Ramp input: Specifies cnstant rate f change f sme variable e.g. maintaining cnstant velcity (since = /) Frequently called the cntrlled element Outputs are brught by: Physical respnse with a cntrl mechanism r Transmissin f sme frm f energy Output is reflected by: Indicatin n display, smetimes called fllwer r cursr, r: Observed by utward behavir f system (e.g. mvement f car) 8

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10 Pursuit & Cmpensatry Displays in Tracking Types f tracking displays (see next slide): Pursuit display Cmpensatry display Displays are shwn as: 1-D: relative mvement f 2 elements: represented by single value (tp fig.) 2-D: relative mvement in 2-D (e.g. chasing a mving aircraft) (bttm fig.) Pursuit display: Target and cursr (i.e. cntrlled element) mve Each indicatr shws its wn lcatin in space Task f the peratr: align mving cursr with mving target Cmpensatry display: One f the tw indicatrs mves (cntrlled element); ther is fixed (target) Task f the peratr: get the mving cursr t align with the target 10

11 Cnt. Pursuit & Cmpensatry Displays 11

12 Pursuit & Cmpensatry Displays in Tracking Errr cntrl: When indicatrs superimpsed: cntrlled element is n target Difference represents: errr, which shuld be minimized/eliminated Errr in pursuit display: Operatr can determine if errr is due t target r cntrlled element Operatr can see target independent f any mvement Errr in cmpensatry display: Only abslute errr/difference between target and cntrlled element If errr increases, display des nt shw what has mved (i.e. target, r cntrlled element, r bth) Advantage f cmpensatry display: saves space n instrument panel since n need t shw entire range f pssible values f 2 elements 12

13 Cntrl Order f Systems Cntrl rder: It is the hierarchy f cntrl relatinships between: mvement f cntrl, and utput it cntrls Objective f tracking task: cntrl system s that utput crrespnds t input as clsely as pssible Psitin (Zer-Order) tracking tasks: Mvement f cntrl device cntrls psitin directly e.g. mving a sptlight t keep it n an actr n a stage e.g. fllwing mvement f athlete with a camera Rate (Velcity r First-Order) cntrl tasks: Operatr mvement cntrls rate at which utput is being changed e.g. acceleratr (i.e. gas pedal) f car which cntrls speed (/) als e.g. peratin f machine gun that is cntrlled by hand cranks 13

14 Cntrl Order f Systems Acceleratin (secnd-rder) cntrl: Acceleratin: rate f change in rate f mvement e.g. steering wheel f car angle at which wheel is turned cntrls angle f frnt wheels this determines rate at which car turns i.e. rtatin f steering wheel accelerates car twards turning directin (i.e. angular acceleratin) Higher rder cntrl: i.e. third- r furth-rder cntrl e.g. third-rder cntrl invlves: direct cntrl f rate f change in acceleratin (aka jerk ) which then cntrls rate (i.e. velcity) which finally cntrls psitin f whatever is cntrlled e.g. cntrl f a large ship Cnsidered 3-rd r even 4 th rder cntrl since invlves many variables: Persn steering and actual mvement, psitin, mass f ship Cntinuus cntrl can be described as chain-reactin effects: i.e. change in psitin changes velcity (rate) changes acceleratin, etc. 14

15 Cntrl Respnses with Varius Cntrl Orders Operatr Cntrl: Expected t make cntrl respnses This brings abut desired peratin f system (that is implied by input) e.g. rad t be fllwed, r flight path f plane Effect f cntrl rder n tracking perfrmance Absence f help t peratr makes cntrl harder, esp. with higher-rder e.g. apprpriate respnse fr ramp, step, and sine inputs with: psitin, rate, and acceleratin cntrl systems (Figure 10-11) Dtted line: is respnse ver time needed fr satisfactry tracking f input With higher rder f cntrl # f cntrlled mvements peratr needs t make in respnse t single change in input Peple d well in 0-rder and 1 st rder cntrl systems But perfrmance with 2 nd rder cntrl system Tracking errr frm 40t 100% 15

16 Cntrl Respnses with Varius Cntrl Orders Example f deteriratin f cntrl Cnsider step input: (middle clumn in Figure 10-11) Target: jumps frward, then stps Respnses: made by jystick 0-rder cntrl: Simply mve stick frward t prper distance and hld 1-st rder (rate) cntrl: Mve stick frward t give certain velcity t cntrlled element As cntrlled element appraches psitin f target return stick t null psitin befre vershting target psitin 2 nd rder cntrl: Mre cmplicated prcedure here Cntrl is first mved frward this gives acc. t cntrlled element Stick must then be brught t null psitin (i.e. 0 acc. r cnst. vel.) Stick must then be mved in ppsite directin (i.e. deceleratin r slwing dwn cntrl) this avids vershting target Finally, return stick t null psitin this avids stpping and ging t ther directin Nte, this is all t mve cntrlled element frward and stpping it! Thus, perfrmance here clearly deterirates 16

17 Human Limitatins in Tracking Tasks Humans: Nt very gd at tracking tasks Especially with higher-rder cntrl parameters (see last slide) Wickens(1984): limitatins affecting tracking: 1. Prcessing time 2. Bandwidth 3. Anticipatin 1. Prcessing time Peple dn t prcess infrmatin instantaneusly there is time delay bet. target change and start f respnses t track it Magnitude f time delay is dependent n rder f cntrlled system: 0 and 1 st -rder: nd rder: Delays are harmful t tracking perfrmance since: Operatr is always chasing target, and Operatr is always behind (unless help is prvided t peratr) 17

18 Human Limitatins in Tracking Tasks 2. Bandwidth: This is upper limit f freq. with which crrective decisins can be made It is the max. freq. f randm input that can be successfully tracked Typical values: (nrmally) Nte, since 2 crrectins/cycle required / Peple can predict curses as high as Anticipatin: Often peratrs track targets using time lagged/sluggish systems e.g. ships r planes peratr must: a) Anticipate future errrs based n present cnditins b) Then make cntrl respnses that may reduce anticipated future errr Prblem: peple are nt gd at anticipating future utputs (esp. with slw systems) due t limitatins f wrking memry Nte, this is true even with experienced peratrs 18