5.4.1 Process of Work System Design
The implementation of ergonomic insights in concrete solutions of work system design is carried out in different operational functions. The individual divisions approach their task of work system design with different areas of interest. Regarding the systematization of such design interests Fu¨rstenberg (1983) developed a conception from a personal view. He differentiates interests of preservation, interests of design, and interests of utilization of human work. In reference to the interest of preservation of the human work ability the occupational safety was developed, which in turn endues own systematic pro- cedures, for example, the TOP model (Compes, 1970). Work technology is referred to, regarding the general interest of the function of work systems. The work technology is essentially affected by systema- tics of the technological determinism in its design procedure. In direction of the interest of utilization of the human work, the labor economics and the industrial organization are to be identified, which developed their systematics, for example, towards types of work processes (concerning humans, equipment, and work object) and towards types of requirements (e.g., for the job evaluation and remuneration).
The framework of a comprehensive ergonomic design process contains design interests, which can be related to Fu¨rstenberg and proceeds from the system ergonomic procedure (Kirchner, 1972; Do¨ring, 1986; Kraiss, 1986). The approach proceeds from a hierarchical-sequential procedure with feedback pos- sibilities during the design process. Thereby, the design areas of the technological, technical, organiz- ational, and ergonomic design are covered (Figure 5.9).
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In this context, technology should be understood as a describing level of technique. Technology deals with the systematics and analysis of concrete techniques. Technologies in this sense are, for example, manufacturing processes (Section 5.2.4 and Section 5.3.2). For instance, the manufacturing process
“turning” (technology) is to be carried out with a corresponding technique (turning machine, control program, etc.).
5.4.1.1 Technological Design
The technological design is mainly determined with the construction process of a product. For instance, necessary exactitudes (e.g., fits), stabilities (basic material, geometry, heat treatment), and surface properties (surface roughness, corrosion protection, etc.) in this process are determined in consideration of existing technologies (Section 5.3.2: Ropohl’s scheme). From an ergonomic point of view the technological design must consider the effects a decision for a specific technology can have on the conditions of work (e.g., stress caused by certain work environmental conditions, degree of the simplicity of assembly task).
5.4.1.2 Technical Design
In a second stage in the context of the technical design the degree of mechanization and automation, that is, the division of labor between working person, on the one hand, and working equipment and operating resources, on the other hand, are discussed. Thereby, human weaknesses and evolution-caused limit- ations of humans are adjusted by mechanization and automatization. Besides, remainder functions for people, for example, as automation gaps, are to be equally avoided.
Referring to the degree of mechanization and automatization, according to Figure 5.10, three levels can roughly be distinguished, namely, the manual activities, the mechanized fulfillment, and the automated fulfillment (Kirchner, 1972).
The manual fulfillment of a task may take place with the help of tools. The energy, however, which is necessary for the purposeful modification of the work object is mustered with the physical strength of a working person. Thereby, the human being poses as a regulator (Section 5.2.1), that is, he gathers infor- mation concerning the actual condition of the work object and processes it as long as the desired work result is available. The informational effort of the working persons can be reduced with the help of working equipments like templates or apparatuses. Mechanization means the substitution of human energy with technical forms of energy. In comparison with the manual fulfillment, however, the informa- tional effort can be further reduced, but no complete substitution of human information processing in the sense of a technical control or regulation takes place. The automation is characterized by the fact that — beyond the mechanization — the regulation of the process also takes place within the technical
idea of the work system
accomplishment of purpose
system performance
situation of a working person target areas
determination of work system purpose
and work object
technological design
technical design
ergonomic design organizational
design
alternative concepts of work system design basic influence
varying influence
1. design area 2. design area 3. design area 4. design area initial situation
FIGURE 5.9 System ergonomic procedure according to the principle of sequential designing.
Humans in Work System Environment 5-19
system. The working person solely has a monitoring function. The individual levels of mechanization and automation can be distinguished further (Kirchner, 1972).
The concept of supervisory control supplies basic design indications, referring to the degree of mechanization and automation. “The term supervisory control derives from the close analogy between a supervisor’s interaction with subordinate people in a human organization and a person’s inter- action with intelligent automated subsystems” (Sheridan, 2002). A supervisor gives instructions to the subordinates who have to understand and transform them into detailed actions. The subordinates, again, present their results to the supervisor. The supervisor has to compare his goals — in analogy to the cybernetic system approach (Section 5.2.1) — with the results presented by the subordinates.
Then he has to decide on the further action to be taken. The same sort of interaction occurs between a human supervisor and the automation (Sheridan, 1992). Thus, the automation can be compared to a subordinate, but with less intelligence. Five roles can be cited for the human supervisor: he has to plan, to teach, to monitor, to intervene, and to learn.
To find out whether it is better to carry out a task manually or supervisory, Figure 5.11 can be used.
The dashed line in the figure represents the time required for direct manual control. It is assumed that the more complex a task is, the more time it takes to carry out. The thin curve in the figure shows how much time someone needs to plan and teach a task. If the task execution time is required, a slice between the thin curve and the heavy solid curve is needed. The sum of these two values is shown by the heavy solid curve. The heavy solid curve intersects the dashed line in two places. On the one hand, the left end of the scale demonstrates that it is better to do simple tasks on your own, because this is much quicker than to explain it to a computer or another person. On the other hand, the right end represents that very complex tasks are too hard to figure out how to program and so it is faster to do them manually. If a task is to be repeated many times and the environmental conditions do not change, it is better to program it. In this case this automation (and supervisory control) is the fastest way.
5.4.1.3 Organizational Design
In the third stage the organizational design mainly deals with the division of labor between humans.
Different activity elements are combined to a whole task, which supports the motivation of the working person. The principle of the completeness of activities should have priority over principles of Taylorism and Fordism. Basic principles, which are formulated in the context of the socio-technical
degree of mechanization and automatization
manual fulfillment
mechanized fulfillment
automated fulfillment
subfunctions of a work system
acting on work object steering controlling
human
human
human human
human human
technique
technique technique
FIGURE 5.10 Levels of functional division between human and technique in a work system.
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system approach (Section 5.2.2) are to be considered with the task design. Moreover, regarding the implementation of group work, important organizational design fundamentals are described in Section 5.5.6.
5.4.1.4 Ergonomic Design
In the fourth stage of the ergonomic design the “division of labor between segments of the organism” is designed. On the basis of anthropometric and physiological and also information- and cognition- psychological realizations, activity elements and working equipment are improved for the functions of energy and power generation and the functions of the information absorption, processing, and delivery.
The model of user – computer interface, which is described in the following exemplifies the stage of ergonomic design. This model is based on the language model, which derives from Foley and van Dam (1982). The model supports the process of designing the user – computer interface and consists of four steps (Figure 5.12).
1. In the first step (conceptual design), the user has to clarify how a task can be carried out with the help of a computer. At this level the structure of the fulfilment of a task is partially determined by the analysis of the task.
2. In a second step, the software functions are defined. The functions influence the activities of the working person (semantic design).
3. In the next level, the user has to find a way to solve the function. Therefore, thesyntactic design defines the sequence of input and output. “For input, sequence is grammar — the rules by which sequences of tokens (words) in the language are formed into proper. . .sentences.” These input sentences are, for example, commands, names, coordinates, etc. The output tokens are often symbols and drawings.
completion time
direct manual control
supervisory control
execution time
planning and teaching time
measure of task complexity
manual better supervisory better manual better
manual better -example:
It takes less time to write a few words by hand than to type it in a
writing program on a computer.
supervisory better -example: In manufacturing automation is more economical than doing it by hand (large-batch operation).
manual better- example:
It seems impossible to teach a computer
to takecare of children, or write
symphonies.
sum of planning and teaching time and execution
time
the task is too complex to be programmed computer execution
speed compensates the time for planning and
teaching overhead
FIGURE 5.11 Range in which supervisory control outperforms manual control (in modification of Sheridan, T.B., Humans and Automation — System Design and Research Issues, John Wiley & Sons, Santa Monica, 2002. With Permission).
Humans in Work System Environment 5-21
4. In the last step (lexical design), it is determined how these input and output tokens are formed from the available hardware components. “We see, then, that lexical design represents the binding of hardware capabilities to the hardware — independent tokens of the input and output languages.”
General strategies of the work system design, apart from this systematic, sequential proceeding, can be differentiated further and are described in the following.
5.4.2 Corrective and Conceptive Work System Design In general, the design process of a work system has two variables:
. The changes (modernization, extension, etc.) of existing work systems
. The development of new work systems
From an ergonomic view the meaning of former type of design process is important, because existing work systems are frequently adapted to the (changed) requirements of human work (humanization measures). Such corrective measures of the work system design usually concentrate on ergonomic and/or organizational aspects (e.g., change of control elements, additional sound insulation, job enrich- ment, job enlargement).
The importance of the conceptive work system design increases in connection with the introduction and establishment of the concurrent engineering approach or related concepts for the parallelism and/or integration of a product-, process-, and production system design (Hacker refers also to the term of
“activity project planning,” [1991]). One of the objectives is to consider the requirements of human work in the draft stage and/or to anticipate the effects of design decisions.
Ulich (1993) differentiates between two kinds of conceptive work designs: “Preventive work design” as the mental anticipation of possible harming of the health and psychosocial impairment, and “prospective work design” as the conscious anticipation of possibilities of the personality development by the creation of scopes of activity, which can be used by employees in different ways. A prospective work design should result in motivation and enable learning through activities and tasks, which offer the potential for per- sonal expansion and development.
It has been indicated that although the conceptive (anticipated) work design can noticeably reduce the time and cost for the corrective work design, it does not eliminate these completely. An evaluation
organizational system
functionality task
dialogue methods
execution
conceptual design
semantic design
syntactic design
lexical design
user model of application
tool manager
dialogue manager display and input/output
manager
user computer
FIGURE 5.12 Model of user – computer interface (in modification of Foley, J.D., and Van Dam, A.,Fundamentals of Interactive Computer of graphics, Addison Wesley, Menlo Park, CA, 1982. With Permission).
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of the realized work system, however, is still necessary; the correctness of the obtained assumptions and forecasts must be verified with consideration of the individual characteristics of the working persons (see also for this stress-strain concepts in Luczak and Rohmert, 1997).
5.4.3 Sequential and Integrated Work System Design
Concerning the temporal reference with which the individual design range of technology, technique, ergonomics, and organization are processed two further strategies can be differentiated: the sequential and the integrated work system design (see Kirchner, 1972). The characteristic of the sequential work system design mentioned earlier — is that the design ranges are worked on gradually in a phase con- ception. (A conceptive design presupposes naturally that all phases will go through the thought process first before the work system is realized.) A fundamental problem consists, however, of the fact that the design levels are not independent of each other. Generally the decision made in a planning phase for a design condition limits the decision range of the following planning phases. The advantage of the transparent planning process, which limits the complexity is always faced with the disadvantage that interdependences between the design ranges are not considered necessary. It is criticized further that sequential concepts usually begin with the technological work system design and the following decisions are a subordinate of the selected technological concept (technological determinism).
This determinism can at least be partly avoided by iterative procedures, that is, by the installation of feedbacks and presumptions:
. Feedbacks:if no satisfying solutions can be found in a design phase, completed phases are repeated in the form of a loop and new insights can be integrated
. Presumptions:in each design phase the consequences are anticipated, which leads to a respective decision in the following stages of the design
The iterative design represents the transition towards integrated work system designs. The concept of the integrated work system design provides for a simultaneous processing of the four design stages, in contrast to the sequential work system design (Kirchner, 1972, 1993, 1997). Ergonomic problems and aspects of the work organization are to be considered in particular with reference to technological and technical determinations. A goal is to consider reciprocal effects from the beginning and avoid the com- pensatory measures, which are accomplished in the sequential design process. Compensatory measures abolish unwanted secondary conditions of proceeding decisions (Luczak, 1998). Due to the complexity of the planning process interdisciplinary planning teams are necessary for the realization of such an inte- grated approach (Luczak, 1996).
5.4.4 Technocentric and Anthropocentric Work System Design
Every decision made concerning the mechanization degree of a work system also means a determination of the function division between humans and operating resources. This allocation process can orientate itself towards different criteria. The spectrum of design strategies is clarified on the basis of two typical conceptions: the technocentric and the anthropocentric design strategies (Bro¨dner, 1986).
The aim of a technocentric design is to attain an operating goal (production of goods or services) poss- ibly independent of the requirements of manpower. The intention of the approach is to reach a high degree of mechanization and automation. The remaining work carried out by humans is characterized by a large amount of division in labor, in order to reach a high exchangeability in the workforce. Human work itself is a subordinate of technical requirements (e.g., cycle time) and is regarded in principal as a potential interference factor. A goal, in the long run, is a fully automated production.
In contrast, an anthropocentric design proceeds from the requirements of the workforce. Humans are perceived as a complex nature whose needs are to be considered during the work system design. Activity elements, which are helpful to this idea of man are carried out by humans, all others are transferred to the technical system. The goal is that the technology subordinates to the human (in particular also the
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individual human) requirements. Both strategies are faced with limitations in technical and economic basic conditions, as long as they are represented in a true form.