고려대학교 산업공학과 ind641 engineering psychology chapter 10. manual control overview ...

고려대학교 산업공학과

IND641 Engineering Psychology

Chapter 10. Manual Control

OVERVIEW the analog form or the time-space trajectory of the response – the domain of continuous control human performance in manual control

skills approach primarily involves analog motor behavior, in which the operator must produce or

reproduce a movement pattern from memory with little environmental uncertainty with little environmental uncertainty, skills in theory may be performed perfectly and

identically from trial to trial open-loop control because once the skill has developed there is little need to process

the visual feedback from the response focuses on skill acquisition and practice

dynamic systems examines human abilities in controlling or tracking dynamic system to conform with

certain time-space trajectories in the face of environmental uncertainty because of the need to process error signals closed-loop control focuses on mathematical representations of the human’s analog response when

processing uncertainty generally addresses the behavior of the well-trained operator



OPEN-LOOP MOTOR SKILLS Discrete Movement Time

Fitts’ Law when movement amplitude (A) and target width (W) were varied, their joint effects were

summarized by a simple equation (Fig 10.1; Fig 10.2):

speed-accuracy trade-off in movement: movement time and accuracy reciprocally related index of difficulty (ID) of the movement higher b indicates less efficient movements, “a” reflects the start-up time for a movement

Models of Discrete Movement typical trajectory or time history as the stylus approaches the target (speed-accuracy tradeoff)1. an exponential approach to the target with an initial high-velocity approach(initial ballistic)

followed by a smooth, final, homing phase (current control)2. velocity profile control is not continuous but discrete corrections, acceleration and deceleration feedback processing assumption (Fig 10.3) – sample-and-correct process until the target

boundary is crossed – closed loop behavior -- generally exponential approach Motor Schema

with highly learned skills under minimal environmental uncertainty, visual feedback is not necessary open-loop fashion visual feedback may be harmful

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general characteristics of well-learned motor skills1. they may well depend on feedback, but the feedback is proprioceptive2. the patterns of desired muscular innervation may be stored centrally in LTM and executed as an

open-loop motor program without visual feedback correction or guidance motor program and motor schema

highly overlearned skills that do not depend on guidance from visual feedback low attention demand, single-response selection, and consistency of outcome

Low Attention Demand the motor program tends to be automated Single-Response Selection single-response selection required to activate or “load” a single motor program even with a

number of separate, discrete responses resources are demanded only once, at the point of initiation, when the program is selected

Consistency of Outcome: Programs Versus Schemata a motor program is assumed to generate very consistent space-time trajectories from one

replication to another what is consistent is not the process of muscular innervation but the product of response signature of one’s name meets the criteria of motor program

certain characteristics of the time-space trajectories remained invariant whatever is learned and stored in LTM cannot be a specific set of muscle commands but must represent a more generic or general set of specifications of how to reach the desired goal – motor schema

once a schema is selected, the process of loading requires the specific instance parameters to be specified to meet the immediate goals at hand



TRACKING OF DYNAMIC SYSTEMS when describing human operator control of physical systems, research moves from the domain of

perceptual motor skills and motor behavior to the more engineering domain of tracking this shift in domain from three nonhuman elements on the performance

1. the dynamics of the system itself2. the input to the operator3. the display

The Tracking Loop: Basic Elements (Fig 10.4) control dynamic – the relationship between the force, f(t), applied and the steering wheel

movement, u(t) system dynamic – the relationship between control position, u(t) and system response, o(t) error sources

1. command inputs, ic(t) – changes in the target to be tracked2. disturbance inputs, id(t) – applied directly to the system

input (Fig 10.5) – may be transient or continuous (predictable, periodic, random) display – the source of all information necessary to implement the corrective response

pursuit display – independent movement of both the target and the cursor compensatory display – only movement of the error relative to a fixed 0-error reference

tracking performance in terms of error



Transfer Functions the mathematical relationship between the input and the output of a system (Fig 10.6) Pure Gain -- (the output)/(the input) -- low-gain system – sluggish Pure Time Delay – transmission lag

delays the input but reproduce it in identical form T seconds later no effect on gain, nor does gain have any effect on time delay

Experimental Lag gradually “home in” or stabilize on the target input defined by time constant Ti: the time the output reach 63 % of its final value

Velocity-Control, Integrator, or First-Order System constant velocity, time integral of the output closely related to exponential lag

Acceleration-Control, Double-Integrator, or Second-Order System combines two integrators in series – constant acceleration unstable, or difficult to control – inertia

Differentiator minus-first-order: produce an output position of a value equal to the rate of change of the

input theoretically step response is a “spike”

Frequency-Domain Response



Human Operator Limits in Tracking Processing Time effective time delay – perceived error translated by operator after a lag zero and first-order system – 150 to 300 msec: second-order – 400 to 500 msec time delays due to human processing or system lag are harmful to tracking (Fig 10.7)1. any lag will cause output to no longer line up with input2. with periodic or random inputs, delay produce instability, oscillatory behavior Bandwidth tracking involves the transmission of information – common or disturbance-induces error the limit of information transmission in tracking is between 4 to 10 bits/sec (preview) frequency limit determines the maximum bandwidth of random inputs -- 0.5 to 1.0 Hz max. frequency with which corrections are exerted in tracking – 2times/sec Prediction and Anticipation must anticipate future errors on the basis of present values to make control correction after a

considerable lag Processing resources difficulty in anticipation related to the resource demands of spatial working memory mental model of the system’s dynamics working memory disrupted by concurrent tasks Compatibility tracking is primarily a spatial task -- spatial compatibility affects tracking performance



Effect of System Dynamics on Tracking Performance Gain

U-shaped function of system gain (system output / control input) intermediate gain – the lowest error and easiest to track high gain

minimal control effort to produce large corrections overcorrections and oscillations instability resulted in lags in system

optimal gain – the crossover point of the instability at high gain and effort at low gain Time Delay

pure time delay harmful in tracking worse tacking performance with greater delays

System Order zero-order and first order – roughly equivalent – successful tracking requires position

and velocity to be matched (Fig 10.8); economy of movement and space the orders above first – error and subjective workload increase dramatically second order control – unequivocally worse

generating lead – higher order derivatives be perceived as a basis for correction longer effective time delay increased lag respond smoothly bang-bang – double impulse or time-optimal control – optimal control (Fig 10.9)



Instability oscillatory and unstable behavior positive feedback systems

once an error is in existence, feedback works to add the error in the same direction

negative feedback systems more typical humans and systems function to reduce rather than increase detected error

high gain and long phase lag – instability Tracking Displays

Preview command input and system output determine the future error the future input will be most accurately available when there is preview – it enables the

operator to compensate for processing lags in the tracking loop no preview – predict the future course of the input (Fig 10.10) precognition mode – the input is nonrandom or contains periodicities – easier prediction Output Prediction and Quickening output prediction – a combination of its present position and its higher derivatives displays in

which a computer estimates error derivatives and future position predictive display (Fig 10.11; Fig 10.12) accuracy of any prediction – sluggishness (inertia) of the system and the frequency of control

or disturbance inputs



quickening – where the system error likely to be in the future if is not controlled --no indication of current error because current error provides no information that is useful for correction

Pursuit Versus Compensatory Displays the goal of tracking – to match the output to the input, or minimize error pursuit display – views the command input and the system output moving separately generally superior performance to compensatory one for two major reasons -- ambiguity of

compensatory information and the compatibility of pursuit displays cannot distinguish among the three potential causes of error: command input, disturbance

input, and the operator’s own incorrect control actions -- error is ambiguous and control is more difficult

a changing command input – advantage with greater S-R compatibility compensatory display

CONTROL DEVICES the light pen, touch screen, trackball, mouse, cursor keys, or joysticks implication of different control devices for simple positioning tasks, characterized by Fitts’s law Manual Control

manual control devices – anthropometric and biomechanical factors The Speed-Accuracy Trade-off

direct point devices (light pen or touch screen) -- very rapid but less accurate than indirect devices (mouse)

the slope of the Fitts’s law – the overall effectiveness of a control device, (lower, better) the slope by the mouse – lower than other control devices



Control Order Compatibility most control devices – displacement produce a constant displacement (zero-order) or

constant rate of movement (first-order) of the cursors across the screen only the light pen and touch screen must be zero-order controllers natural “affinities” or “compatibilities” – mice for zero-order control dynamics, and joysticks

for first-order control dynamics mouse

best captures the natural eye-hand coordination the optimal gain is between one and three – the cursor should travel between one

and three times the distance traveled by the hand if first-order control – abandons the natural eye-hand coordination and the zero-

velocity resting place spring-loaded joysticks

spring loading maximize proprioceptive and kinesthetic feedback natural resting state by “snap back” – automatically recovered problems as a zero-order device: the lack of precision with which any position off of

the center can be maintained, lack of available movement range

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