Szpytko J., Jaźwiński J., Woźniak D.A. Reliability shaping aspects of man – automated device set.

RELIABILITY SHAPING ASPECTS

OF MAN – AUTOMATED DEVICE SET

Szpytko J., Jaźwiński J., Woźniak D.A.

AGH University of Science and Technology, Mickiewicza Ave. 30, PL 30059 Cracow, Poland Air Force Institute of Technology, Ksiecia Boleslawa 6, Warszawa, Poland

UMWM, Cracow, Poland

Abstract: The paper is focusing on model of an man-machine set for shaping his critical and

reliability levels. The meaning of stress, possibility of reliability shaping and assessment indicators of operator operation has been formulated.

1. Introduction

The paper object is man – automated technical device dedicated to realisation particular operation. In the end of last century the designers of technical devices great attention have been paid at problem of automation. Following the automated devices was improved with use of information technology IT. The new more automated devices are in the making supported with artificial intelligence. Still the important and key position in practice is performing man – operator, with is playing the decision making functions, as well as supervisory. Today evolution of technical devices is driving at improvement not only devices, but also sets of man/ operator – automated devices (anthropocentric sets).

Development of anthropocentric sets is forcing greater attention at their identification (with taken into consideration property and critically), as well as shaping and designing possibilities of adequate information type connections for decision-making needs. The important problem of anthropocentric set (from reliability point of view) is their resistance at surroundings (external) actions that have weaken and deformation impact at decision-making process. Equivalent of device safety losing (e.g. offence of critical stress of the construction) is losing of operation capacity of the operator (e.g. health, as the result of stressors impact, mostly time type during decision making activities so called controls). Stress is a condition of the organism, which is independent or dependent on a human being [Cooper et al., 2001], and a result of a process with changeable relationship [Davis & Gibson, 1994] between a human and the environment [Cox, 1985]. The problem of stress identification at operator of transport means is described in paper [Woźniak,

Jaźwiński, Szpytko, 2003]. Simulation methods of investigations of aircraft safety flight in particular under stress are an object of work [Borgoń et al., 1998].

Paper is describing model of an anthropocentric set for shaping his critical and reliability. The meaning of stress, possibilits of reliability shaping and assessment indicators of operator operation has been formulated.

2. Model of operator – technical device set

Model of operator – technical device set is presented on Figure 1. The key positions in model are playing actors of operator C type and device OT type oriented at activity in specific environment. The activity is a object of monitoring, and then assessment M both qualitative and quantity. In systems equipment with automated supported devices the result of monitoring is directly addressed to the technical device.

Distinguish actors owning activity realisation possibilities expressed by their potential PO (PO1 - operator, PO2 – device) and characteristic attributes ZW. Between distinguish actors oriented at activities the impacts of i-th type are possible: energetic supply ZE, information supply ZI, surrounding influences ZO, device influences ZU.

Activities are object of controls ST: man with use adequate subsystems of the device (ST1) and then a device internal controls (ST2) that are addressed to do specified sequence of useful activities. During controls realisation the time delays Δt are possible (deviation, inertia) with consideration of operator Δt1 and device Δt2 attributes.

Fig.1. Integrated model of man- device – surrounding set

activity device OT Monitoring Automat man C ZI3 ZI1 ZO2 ZO1 ZU1 ZU2 ST2 (Δt2) ST1(Δt1) ZI2 ZE1,2

achievement of activity target, M0 ZW3

PO1 PO2

activity assessment of set C-OT M1

3. Shaping possibilities of anthropocentric set

The exploitation potential of anthropocentric set can be expressed with dependence: PO = PO1



device PO2 are time variable. For anthropocentric set operated in specified environment conditions the nominal potential PON is possible to define, and PON



The attribute ZW is a object of reinforcement or attenuation:

PO = f2(ZWij  Wij) (2)

where:

Wij – weight of j-th attribute of i-th actor.

Reinforcement of the system is possible as a result of re-dimensioning of the system, use of excess elements or with higher reliability (for devices) or as the result of training, education and supporting with engineering techniques (for operators). Attenuation is a result of unit or cumulated load substitute, unsatisfactory (too small, too high) or lack of energetic and/or informatics supplies, as well as disturbances. Between operator and device attributes’ exists several correlations, for example: perception – information visualization, knowledge – monitoring, skills – operation realization ability, decision making ability – corrective auto-activity, reaction on external stimulus – safety device and strength.

Fundamental factor that disturbs operator activities are stressors, which have situation and time characters. For operators of technical devices the essential is time stressor, which have strengthening or attenuation character of their attributes. Quantitative time stress model S was presents as follows [Siegel, Wolf, 1963]:

* T ] T [ E S (3) where:

S - time type stress,

E[T] - expected value of time which operator dispose to make decisions and actions beginning,

T* - realization of random variable T.

Controls ST2 of executed subsystems of anthropocentric set (which are responsible for particular activities) are resulting with conscious and advisable operator impacts (controls ST1) at the control devices of the system. Realisation of sequence of actions in time t by the system (device) achieved as the result of controls ST is described by the dependence:

ST = f3 [ST1(Δt1), ST2(Δt2), PO, t] (4)

The possible time delay Δt during device control is a consequence of possible attributes weights W changes of actors. The automated supporting unit can replace controls, which have been realized by the man.

The measure of man-device effectiveness (with total potential PO) is possible to express through the reliability P(ST) of controls (decision making) specified by the dependence:

P(ST/PO) = P(ST1/PO1)∙ P(ST2/PO2),

or P(ST/PO) = R(S)∙ R(W) (5) where:                           1 M S , 1 R 2 1 M S M , ) M S ( ) R 1 ( R M S 1 , 1 M ) 1 S ( ) R 1 ( R ) S ( R 0 0 0 0 0       U 5 4(U)( f (u))dU f R(U)

R(S) - probability of committing errors by operator as the result of stress S, R0 - probability of not committing errors by operator,

M - stress limit value,

R(U) - probability of non failure of the device and his controlling elements,

U, u - random variables assigned in example to strength and stress of the device/ element,

f4, f5 - probability density of strength and stress.

4. Operators’ activity assessment indicator

Reliability P(ST) of device controls is possible to express by the possible number of incorrect decisions of the anthropocentric set (errors of I and II type). The error of I type α is occurring, when the potential of the man-machine set is satisfactory and operator (or

automat) is making activity mistake/ error. The error of II type β is occurring when the potential of the set is not satisfactory and a operator is not making error of activity. Reliability P(Ai/B) of occurring the incorrect i-th type decision Ai of the operator

(automat), under a condition of degradation of operator potential B and possible errors of I and II type, is described by the dependence:



P(Ai) - probability of occurring the incorrect i-th type decision Ai of anthropocentric set

(i = 1...n),

P(B) - occurring probability of potential PO degradation of anthropocentric set expressed by m - th number of his attributes (j = 1...m, B = B1∩B2∩...Bm),

P(B/Ai) - probability of occurring m-th type attribute degradation of anthropocentric set

potential B (which condition occurring of incorrect i-th type decision Ai, monitored

as the result of investigation with taken into consideration possible errors of I and II type).

5. Final remarks

Work out model of the anthropocentric set is possible to use into rapid prototyping (in virtual environment) applications and oriented to critical and reliability shaping of complex systems composite with man and technical devices. The attention has been concentrated at man-operator that is endangered at external influences with stress character. The meaning of stress has been formulated, as well as possibilities of reliability shaping of anthropocentric set with use of assessment indicators of operator actions. The example algorithm of operation aircraft engine re-starting under the time stress influence is presented at work [Borgoń et al., 1998]. The problem of critical and reliability aspects shaping of man – automated device set is an object of running work.

The research project is financed from the Polish Science budget for the years 2005-08.

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