A GENERAL APPROACH FOR MAN-MACHINE SYSTEMS DESIGN

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1 Copyrght 2002 IFAC 5th Trennal World Congress, Barcelona, Span A GENERAL APPROACH FOR MAN-MACHINE SYSTEMS DESIGN A.Skaf,2, B.Davd 2, Z.Bnder, B. Descotes-Genon Laboratore d'automatque de Grenoble (LAG) ENSIEG-INPG, B.P. 46, Sant Martn d'hères Cedex, FRANCE Tel: ++33 (0) , Fax: ++33 (0) skaf@lag.enseg.npg.fr 2 Laboratore ICTT, ECOLE CENTRALE DE LYON, B.P Ecully Cedex, FRANCE Tel: ++33 (0) ; Fax: ++33 (0) Ahmad.Skaf@ ec-lyon.fr / Bertrand.Davd@ec-lyon.fr Abstract: The man-machne systems desgn s a major concern for the computer scentst, the control engneer and the ergonomcst. An adequate desgn for such systems means optmsaton of ther performance, whch s the result of takng nto account the human element snce the desgn stage. Human ntegraton, n the desgn stage, can strengthen the stablty and optmalty of all system functons. Ths paper deals wth the problem of man-machne systems desgn by proposng a general approach based on system analyss methodology, acton dentfcaton and acton specfcaton. All those aspects wll be treated n ths paper. Copyrght 2002IFAC Keywords: man/machne nteracton, soco-techncal system, desgn, methodology, ergonomc, co-operaton.. INTRODUCTION Generally, n the actvty s space of all semautomatc systems three areas of actvty can be dentfed: completely automated actvtes (realsed by machne), completely manual actvtes (performed by man) and actvtes whch can be performed by man (or machne) wth the machne s assstance (man s assstance). The last zone s called "the zone of man-machne actvtes". Fgure shows a graphc representaton of these three zones. From ths fgure, t can be seen that the zone of man-machne actvtes s stuated around a vrtual lne whch dvdes actvty s space nto automatc and manual zones. The dentfcaton of ths zone consttutes the prncpal dea of man-machne system desgn. Before explanng the methodology of dentfcaton, t s necessary to defne four terms used throughout the paper : Man actvtes Man-machne actvtes zone Dvdng lne (Automatc-Manuel) Man actvtes supported by machne Machne actvtes supported by the man Machne actvtes Fg.. Actvty zones of man-machne system

2 Acton: represents the effort made to reach a transtory target. One acton can be only performed by man or machne. Actvty: represents a set of actons whch lead to the achevement of a sub-objectve. Task: represents a set of actvtes whch lead to the achevement of an objectve. Msson: s a set of tasks leadng to the achevement of a global objectve. 2. SOCIO-TECHNICAL DESIGN: GLOBAL APPROACH (Mllot, 996) proposed a desgn methodology for a man-machne system. Ths methodology s based on two approaches: Descendant approach: ths approach consders the techncal characterstcs and the objectve of the system to acheve a prototype of a manmachne system. Ascendant approach: ths approach ams to gve a better defnton of tasks whch can be attrbuted to humans. Ths defnton s based on human crtera on the one hand, and on system performance on the other. 2.. Global approach As s shown n fgure 2, the global man-machne system desgn approach conssts of: Analyss of control and controlled system: ths conssts of dentfyng all actons whch have to be performed to reach the system goal. The analyss s accomplshed on two functonal modes: normal and abnormal. Obvously, ths stage become more dffcult f we desgn a new system (based only on specfcaton and techncal documentaton). Actons Analyss: ths conssts of dentfyng the actons performed by man and/or by machne. The am of ths analyss s to determne the need of assstance to perform man s acton ( eventually the need of assstance to perform machne s actons). Ths analyss s prncpally based on human crtera (mental and physcal capacty) and on techncal specfcaton of machne (n general meanng of term ncludng nformaton entty). Defnton of assstance and automaton tools: t s a matter of verfcaton f the realsaton of acton needs some assstance, and specfyng an adequate tool for ths assstance. Ths approach results n three types of desgn beng consdered: ergonomc desgn of post (work post), techncal desgn and man-machne nterface desgn (choce of co-operaton modes). Each type of desgn leads the defnton of a category of actvtes, respectvely: man's actvtes, machne's actvtes and man-machne actvtes. Defnton of man, machne and man-machne tasks (mplementaton stage): ths s a formulaton from the set of all actvtes (man, machne and man-machne actvtes) the correspondng tasks. After regroupng those tasks n the msson, t wll be mplemented ether n the executon level of soco-techncal systems or n ther supervson level (skaf, 999). As can be seen from ths descrpton and from fgure 2, the proposed approach s of a general nature. Ths means that t can gve the stages of man-machne system desgn, wthout, however, gvng the conceptual detals for each stage. Techncal desgn Contexts - normal functonng -Abnormal functonng Defnton of automaton tool No needs Human Model -lmts -resources Machne s actvtes Machne s tasks msson Soco-techncal system -objectves Machne s actons Human assstance need Executon level of soco-techncal system Analyse of control system and controlled system Actons Analyse Man-machne actvtes actons to carry out Desgn and specfcaton of manmachne nterface Man-machne tasks Man s actons Machne assstance need Ergonomc crtera Man-machne system s realsaton on real ste or smulated Characterstc of techncal system -nomnal techncal characterstc Man s actvtes Man s tasks Defnton of assstance tool Ergonomc desgn Supervson level of soco-techncal system No needs Fg. 2. Global approach for man-machne system desgn In ths paper, the methodology of acton specfcaton wll be detaled. Ths methodology descrbes the most mportant stage n global approach called "acton analyss". Before begnnng to descrbe the methodology of specfcaton, t s assumed that analyss of socotechncal systems (usng SADT, UML, ) resulted n dentfyng all actons that lead to acheve system objectves.

3 2.2. Ergonomc and techncal specfcatons of actons The am of specfcaton s to defne the actons whch have to be acheved by man and, respectvely, by machne. Ths smplstc dea masks a very complcated problem wthn the analyss method. Thus, the queston s: how can a reference model be created to specfy the acton? To deal wth ths problem, the method of specfcaton has to propose a set of ergonomc and techncal crtera. Accordng to these crtera, each acton wll be referenced to decde f ts realsaton wll be acheved by man or by machne. Before startng the descrpton of specfcaton methodology, t s advsable to note that the proposed method s approxmate because of ntegraton of human aspects. Assume that there s a set of actons to be specfed (to be marked as man or machne acton). For ths purpose, each acton should be consdered as a functon of two functons, thus a gven acton called Acton can be expressed lke: Acton(x=f(u),y=f(v)). It s assumed that ths functon s defned on [0,]. 0.5 y II : Actons realsed by machne V Actons realsed by machne wth human s assstance 0.5 III IV I : Actons realsed by human.0 Actons realsed by human wth machne s assstance Fg. 3. Graphcal representaton of sectors to whch actons belong. The functon x=f(u) [0,] represents a sutable degree of realsaton (for the correspondng acton) consderng a gven human model. Lkewse, the functon y=f(u) [0,] represents sutable degree of realsaton (for the correspondng acton) consderng a gven machne model (a set of techncal data). Thus, the values of x and y determne the sector to whch an acton consdered belongs. Fgure 3 shows the fve sectors to whch any acton has to belong to (n ths fgure the x-axs represents man and the y-axs represents the machne): Sector I: all actons belongng to ths sector are x consdered to be man s actons (.e. ther realsaton by man s more advantageous). Ths case s vald when the values of y belongng to [0,0.5[ and the values of x [0.5,] (see fgure 3). Sector II: all actons belongng to ths sector are consdered to be machne actons (.e. ther realsaton by machne s more advantageous). Ths case s vald when the values of x belongng to [0,0.5[ and the values of y [0.5,] (see fgure 3). Sector III: ths sector contans all actons performed by machne wth human assstance. In ths sector, for y values belongng to [0.5,] the values of x [0.5,] (consderng y x ) represent the assstance degree (level) contrbuted by man to accomplsh the realsaton of the correspondng acton. For example, x =0.5 of the gven acton shows that human assstance, for ts realsaton, s not really requred ( the acton s nearly automated). However, f x = ths means that human assstance really s necessary (nearly shared realsaton). Sector IV: Ths sector contans all actons performed by man wth machne assstance. In ths sector, for x values belongng to [0.5,] the values of y [0.5,] (consderng x y ) represent the assstance degree (level) contrbuted by the machne to accomplsh the realsaton of the correspondng acton. For example, y =0.5 of the gven acton shows that machne assstance, for ts realsaton, s not really requred ( the acton s nearly manual). However, f y =, ths means that machne assstance really s necessary (nearly shared realsaton). Sector V: represents all actons wth x and y [0,0.5] at the same tme (.e. for x [0,0.5]: y [0,0.5] and vce versa). The actons belongng to ths sector are consdered to be non specfable actons (.e. there s nsuffcent nformaton to decde f they can belong to one of another sector: I, II; II and IV). In ths paper, t s assumed that all studed actons belong to sector I, II, III and IV. Thus, to specfy the actons, t s suffcent to fnd x and y for each one. Consequently, the queston becomes: how can the values of x and y be found?. Before answerng ths queston, two remarks have to be consdered:. The am of acton specfcaton s to be able to judge the realsaton aspects of the acton (how?, what effort?, what means, for what prce? etc..). Ths makes t possble to decde whch actor can perform t, and also to defne the form of assstance f necessary. Therefore, t can be concluded that the context of the

4 analysed system (envronment, evoluton, means) affects the judgement. Ths fact makes the specfcaton method an approxmate one. 2. The numbers used to express an approxmate defnton have a symbolc meanng (.e. n ther place the symbols can be used). Usng numbers merely smplfes the reasonng. To deduce the expresson of functon x=f(u) t s assumed that the ntal value of x equals x 0 =, that means (see above) the acton can be performed by man. On another hand, assume the set of crtera (A, B, C,...N) whch affects the value of x by reducng t by Ω proportonal to ts ntal value. Thus, after applcaton of the crtera, the value of x becomes: x = x 0 (-Ω) () where s Ω less than or equal to. Assume that each crteron affects ndependently x, the expresson of Ω wll be: Ω = = N = A γ (2) where γ [0, ] s the nfluence of crteron (A, B, C,...N). Ths nfluence reduces x by : τ = γ x 0 (3) To keep the value of Ω wthn the nterval [0,] reservng the nfluence percent of each crteron, an coeffcent α wll be ntroduced : α = mn, = N = A γ Takng nto account ths coeffcent, the expresson () wll be wrtten as : x = x 0 (-α.ω) (4) Replacng the expressons of Ω and α n (4), the expresson of x becomes: = N = x mn,. γ = N = A γ = A x 0 (5) γ are the coeffcents whch translate the nfluence of each crteron on x value by reducng t by γ percent of ts ntal value. Thus, to fnd the value of x for a gven acton (n a gven context and for a gven human model) t s enough to fnd those coeffcents. The same reasonng for the functon y=f(v) leads to determnaton of the value of y : y = y 0 (-Ψ) (6) where y 0 = s the ntal value of y. Ψ s the nfluence of a set of techncal crtera (a, b, c,...,n). Assume that each crteron affects ndependently y, the expresson of Ψ wll be: Ψ = = n ζ = a (7) where ζ [0, ] s the nfluence of crteron (a, b, c,...,n). Ths nfluence reduces y by: σ = ζ y 0 (8) To retan the value of Ψ wthn the nterval [0,] reservng the nfluence percent of each crteron, an coeffcent β wll be ntroduced : β = mn, = n = a ζ Takng nto account ths coeffcent, the expresson (6) wll be wrtten as : y = y 0 (-β.ψ) (9) Replacng the expressons of Ψ and β nto (9), the expresson of y becomes : = n = y mn,. ζ = n = a ζ = a (0) y 0 ζ are the coeffcents whch translate the nfluence of each crteron on the value of y by reducng t by ζ percent of ts ntal value. Thus, to fnd the value of y of a gven acton (n a gven context and for a gven machne model) t s enough to fnd these coeffcents. To fnd ether γ or ζ a reference model of data for each crteron s needed. In ths paper fve crtera only are consdered: work load, securty and relablty as ergonomc crtera. Cost and feasblty as techncal crtera. Next, references data models for these crtera wll be establshed.

5 2.3. Work load Accordng to work psychologsts, work load s a relable ndex for estmatng the moblsaton state of an ndvdual. Thus, ths ndex can be used to decde f an acton can be easly performed by man. To reach ths goal, the modfed scale of Cooper Harper (quoted n Mllot,988) can be used n the way shown n fgure 4. Human model : mental & physque Key : WL: Work Load Acton Can acton be accomplshed yes Does acton requre a hgh WL non Does acton requre a low WL non yes yes non Dffculty level Impossble Heavy major dffculty Average major dffculty Low major dffculty Heavy mnor dffculty Average mnor dffculty Low mnor dffculty Not so easy easy Very easy Fg. 4. Modfed scale of Cooper Harper adopted for acton specfcaton So, to fnd the coeffcent γ wl, each acton wll be compared (from ts realsaton pont of vew) to 0 levels of dffculty (consderng a mental and/or physcal human model). Each level s ndcated by an ndex γ wl Securty Securty s a very mportant crteron n decdng whether a human can perform a gven acton or whether ths acton must be performed exclusvely by machne. For ths crteron, a smplfed model of reference has been adopted. Ths model s shown n table, where an acton can be ether dangerous or not. If not, protecton may or may not be provded when t s performed. Accordng to the case, the coeffcent γ s can take one of the followng arbtrary values:.0, 0.2, 0.0. (see table ). Table : Estmated values of nfluence coeffcent γ s of the securty crteron Acton Dangerous Non Non Acton dangerous dangerous affects Acton wth Acton wthout protecton protecton x functon γ S Index Relablty In ths paper, relablty s consdered as an antcpatory estmaton of achevement result. So, t can show ndvdual apttude to be nvolved n the realsaton of acton. For ths crteron, a smplfed model of reference has been adopted. Ths model s shown n table 2. Accordng to ths model, the coeffcent γ R can take one of the followng arbtrary values : 0. (very relable), 0.3, 0.5, 0.7, 0.9 (not relable). (see table 2). Table 2: Estmated values of nfluence coeffcent γ R of the relablty crteron Relablty of acton realsaton Correspondng sub-ntervals Estmated value of γ R Non relable [0.8-.0] 0.9 A lttle relable [ [ 0.7 Average relable [ [ 0.5 relable [ [ 0.3 Very relable [ [ Feasblty and cost Feasblty and cost are the techncal crtera consdered to answer the queston: can a machne perform the acton?, and how much wll that cost?. The reference models of both these crtera are shown n tables 3 and 4. Accordng to machne model, each acton can be ether automated, automated wth human assstance or not automated. Thus, the values of coeffcent ζ F can be 0.0, 0.5 or.0 (see table 3). Table 3: Estmated values of nfluence coeffcent ζ F of the feasblty crteron Nature of acton Estmated value of ζ F Automated 0.0 Automated wth assstance 0.5 Not automated.0 In the same way, accordng to the prce of automaton (whch can be determned accordng to the economcal and envronmental context), an acton can be fully automated, sem-automated or not at all automated. The correspondng values of ζ C are 0.0, 0.5 and.0. (see table 4). Table 4 : Estmated values of nfluence coeffcent ζ F of the cost crteron Choce of acton realsaton Estmated cost Estmated value of ζ C Automatc low 0.0 Free average 0.5 Not automatc hgh.0

6 3. CASE STUDY To llustrate the specfcaton method, a man-tap system (quoted n (Coutaz,990)) wll be consdered. The am of ths system s to fll a bath wth tepd water havng two taps (one for hot water and another for cold water). Modellng ths system usng the well-known method SADT leads us to determne the man actons to carry out (we only consder the normal functonng mode) whch are: To pour: ths acton can be supported by man, and/or by the control system (automata). The outputs are the hot water flow rate Fh and the cold water flow rate Fc. To measure: ths acton can be supported by man and/or temperature detector. The output s tepd water. So, our am s to desgn a man-tap system, where human lmts and needs are respected and the techncal and economcal aspects of the system are taken nto consderaton. From the human pont of vew, ths system s presented by the hot water rate flow Fh, cold water rate flow Fc and temperature T. These three varables are psychologcal varables whch express the am of the system (to obtan tepd water). Therefore, man can control T by actng on Fh and Fc (open/close the taps for hot water and cold water). Thus, he performs the actons to pour, and to measure. On another hand, today technology allows ths system to be fully automated, but at what prce? To specfy these two actons, or to properly desgn ths system, we wll calculate x and y for each acton takng nto account only two ergonomc crtera: safety and relablty and only two techncal crtera: feasblty and cost. Thus, by applyng the method descrbed above, the followng result can be obtaned: - It s too hard to control temperature usng two taps (one for hot water and one for cold water). For ths purpose, the nfluence (γ R ) of relablty on x assume take a hgh value (the approxmately estmated value for a person wth good mental and physcal capacty s 0.3). On the contrary, the nfluence of safety γ s s zero (there are no major rsks nvolved when usng taps). When fully automated, ths acton demands nstallaton of automata. Ths decson s feasble (ζ F =0.0) but the cost s too hgh (ζ C =.0), that means (applyng the equaton 0) ths acton s a human one (y=0). As t s dffcult (for man) to control T usng two taps, anther soluton can be proposed. Ths soluton conssts of nstallng a mxer tap. Ths soluton s feasble (ζ F =0.0) and the nfluence of cost ζ C s zero (general case). Therefore, applyng equatons 5 and 0, the x and y of acton to pour wll be : x= -( )=0.7 ; y= -( )=, whch means ths acton (to pour) wll be performed by machne (mxer tap) wth human assstance (open/close) (see fgure 3). 2- It s not easy to measure temperature (t mght be panful), thus the acton to measure can be consdered as a non dangerous acton wth protecton (coeffcent γ S wll be 0.2). Ths acton s relable (the hand s always used to check f the water s tepd) whch leads to consderng the coeffcent γ R =0.3. On another hand, t s not dffcult to nstall a detector (coeffcent ζ F =0.0), but the nfluence of cost ζ C could be 0.5. Therefore, f we apply equatons 5 and 0, the x and y of acton to measure wll be: x= - ( )=0.5; y=-( )=0.5. Ths leads us to conclude that ths acton can be automated (nstallaton of a temperature detector), but consderng prce, ths acton wll be performed by man. (usng a hand s cheaper than a detector) (fg.3). 4. CONCLUSION In ths paper, a general approach of man-machne system desgn was proposed. The methodology of acton specfcaton was descrbed, focussng on ergonomc and techncal acton specfcaton. A set of reference models for consdered crtera (techncal and ergonomc) was proposed. Fnally, an llustratve example was dscussed. The proposed desgn method s based on an approxmate estmaton to dentfy man and machne actons. One of the future drectons for ths work s to mprove ths approxmate methodology. Another perspectve would be to enhance and complete crtera reference models. Also, further work should study the remanng aspects of the general approach of soco-techncal system desgn such as defnton of assstance tools, automated tools,..etc. REFERENCES Coutaz, J. (990). Interface Homme-Machne : Concepton et Réalsaton. Dunod Informatque ISBN France. Mllot P. (988). Supervson des procédés automatsés et ergonoms. Edtons Hermès. Pars, France Mllot, P. (996). De la survellance à la supervson : l ntégraton des opérateurs humans, Ecole d été, Grenoble, France. Skaf A., Tan H, Davd B., Descotes-Genon B., Bnder Z. (999). Actons and actvtes n manmachne dsassemblng systems, n Human Centrered Processes HCP'99, septembre, France. Skaf A., Davd B., Descotes-Genon B., Bnder Z. (2000). Ergonomc and techncal specfcaton of actons n man-machne systems. In Europe Chapter of the Human Factors and Ergonomcs Socety Annual Conference Human-System Interacton. November, Maastrcht, Netherlands.

TECHNIQUE OF FORMATION HOMOGENEOUS SAMPLE SAME OBJECTS. Muradaliyev A.Z.

TECHNIQUE OF FORMATION HOMOGENEOUS SAMPLE SAME OBJECTS Muradalyev AZ Azerbajan Scentfc-Research and Desgn-Prospectng Insttute of Energetc AZ1012, Ave HZardab-94 E-mal:aydn_murad@yahoocom Importance of