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J. Y. S. Luh, "An anatomy of industrial robots and their controls," IEEE Trans. Auto. Control, vol. AC-28, no. 2, Feb. 1983, pp. 133-153. C. P. Neuman and J. J. Murray, "Computational robot dynamics: Foundations and applications," J. Robotic Syst., vol. 2, no. 4, 1985. K. J. Astrom and B. Wittenmark, Computer-Controlled Systems: Theory and Design. Englewood Cliffs, NJ: Prentice-Hall, 1984. J. R. Rice, Numerical Methods, Software and Analysis. New York: McGraw-Hill, 1983. V. D. Tourassis and C. P. Neuman, "The inertial characteristics of dynamic robot models," Mechanism and Machine Theory, vol. 20, no. 1, pp. 41-52, 1985. E. Freund, "Direct design methods for the control of industrial robots," Computers in Mechanical Engineering, vol. 1, no. 4, pp. 71-79, Apr. 1983. C. P. Neuman, and V. D. Tourassis "Robot control: Issues and insight," in Proc. Third Yale Workshop on Applications of Adaptive Systems The-ory, K. S. Narendra, Ed. New Haven, CT: Yale University, pp. 179-189, 1983. R. G. Seippel, Transducers, Sensors, and Detectors. Reston, VA: Re-ston, 1983. C. S. G. Lee and B. H. Lee, "Planning of straight line manipulator trajectory in Cartesian space with torque constraints," in Proc. 23rd IEEE Conf. Decision and Control, pp. 1603-1609, 1984. J. Y. S. Luh and C. S. Lin, "Optimum path planning for mechanical manipulators," J. Dynamic Systems, Measurement, and Control, vol. 103, no. 3, pp. 142-151, June 1981. C. S. Lin, P. R. Chang, and J. Y. S. Luh, "Formulation and optimization of cubic polynomial joint trajectories for mechanical manipulators," IEEE Trans. Auto. Control, vol. AC-28, no. 12, pp. 1066-1074, Dec. 1983. V. D. Tourassis and C. P. Neuman "Robust nonlinear feedback control for robotic manipulators," Proc. IEE-D: Control Theory and Applica-tions, vol. 132, no. 4, pp. 134-143, July 1985. M. I. Zeldman, What Every Engineer Should Know About Robots. New York: Marcel Dekker, 1984. V. D. Tourassis, Dynamic Modeling and Control of Robotic Manipula-tors, Ph. D. dissertation, Department of Electrical and Computer En-gineering, Carnegie-Mellon University, Pittsburgh, PA, 1985. M. S. Pfeifer and C. P. Neuman, "VAST: A versatile robot arm dynamic simulation tool," Computers in Mechanical Engineering, vol. 3, no. 3, pp. 57-64, Nov. 1984. Uni mate Puma Robot, vol. 1, Unimate Inc., Shelter Rock Lane, Danbury, CT 06810, USA, 1980. H. W. Stone and C. P. Neuman, "Dynamic modeling of a three-degree-of-freedom robotic manipulator," IEEE Trans. Syst., Man, Cybern.,νοΐ. SMC-14, no. 4, pp. 643-654, July/August 1984. B. C. Kuo, Automatic Control Systems. Englewood Cliffs, NJ: Prentice-Hall, 1982. M. Vukobratovic and N. Kircanski, "New method for real-time manipu-lator dynamic model forming on microcomputers," in Proc. First Yugo-slavia-Soviet Symp. Applied Robotics, Feb. 1983. A. K. Bejczy, "Dynamic analysis for robot arm control," Proc. 1983 American Control Conf., pp. 503-504, 1983. M. Vukobratovic and N. Kircanski, "A method for computer-aided construction of analytical models of robotic manipulators," in Proc. First Int. Conf. Robotics, pp. 519-528, 1984. J. J. Murray and C. P. Neuman, "ARM: An algebraic robot dynamic modeling program," in Proc. First Int. Conf. Robotics, pp. 103-114, 1984. P. K. Khosla and C. P. Neuman "Computational requirements of cus-tomized Newton-Euler Algorithms," J. Robotic Systems, vol. 2, no. 1, 1985. Marinco APB-3024M Array Processor Board, Marinco, Inc., 3878-A Ruffin Road, San Diego, CA 92123, 1983. A. K. Bejczy and S. Lee, "Robot arm dynamic model reduction for control," in Proc. 22nd IEEE Conf. Decision and Control, pp. 1466-1476, 1983. C. P. Neuman, "Presentation of ARM: An algebraic robot dynamic modeling program," First Int. Conf. Robotics, Atlanta, GA Mar. 13, 1984. B. K. Kim and K. G. Shin "Minimum-time path planning for robot arms with their dynamics included," IEEE Trans. Syst., Man, Cybern., vol. SMC-15, no. 2, pp. 213-223, Mar. 1985. J. M. Hollerbach, "Dynamic scaling of manipulator trajectories," J. Dynamic Systems, Measurement, and Control, vol. 106, no. 1, pp. 102-106, Mar. 1984Ì J. M. Hollerbach and G. Sahar "Wrist partitioned inverse kinematic accelerations and manipulator dynamics," in Proc. First Int. Conf. Robotics, pp. 152-161, 1984. W. A. Wolovich and H. Elliott "A computational technique for inverse kinematics," in Proc. 23rd Conference on Decision and Control, pp. 1359-1363,1984.

Organizational Outcomes of Creativity

MARY ANN VON GLINOW AND STEVEN KERR

Abstract—While considerable research has been conducted on creativity, almost no research has been aimed at identifying creative behaviors and outcomes in ongoing organizations. In this study, organizational outcomes of creativity were explored for a sample of 182 scientific and technical employees of a large oil and gas firm. Results indicated that respondents were able to identify key behaviors as indicative of creativity and could identify organizational outcomes of those behaviors reasonably well. A comment on method is made and some practical implications offered.

INTRODUCTION

Creativity is one of the most popular buzzwords of our time. Nearly everyone agrees that it is an exceptionally valuable com-modity with almost irresistible allure to people in and out of organizations. Considerable effort has been spent to foster em-ployee creativity so that organizations can reap the presumably rich rewards of having a creative work force.

A great deal has been learned about how to measure creativity. Measurement most often emphasizes creativity's cognitive ele-ments, " . . . consisting of such phases as inspiration, elaboration, and communication" [6] or "hypothesis formation, hypothesis testing, and communication of results" [10]. Specific tests such as the Remote Associates Test (RAT) and the Torrance Tests of Creativity Thinking have been developed to assess creative ability [1]-

Quite a bit has also been gleaned about the biographical, psychological, and environmental correlates of creativity [5], [7], [3], [12], [9]. As has been noted elsewhere [2, p. 358], " . . . em-pirical creativity research has long been dominated by a trait approach, an attempt to precisely identify the personality dif-ferences between creative and noncreative individuals... ." Such research may be said to be conducted from the inside out, insomuch as an individual rather than his or her employing organization is the focus of attention. An implicit assumption is made that once an individual is identified as creative, or has been made more creative, his or her organization is bound to benefit. A few authors have gone so far as to suggest how organizations might benefit, but these suggestions are usually general, typically including such qualities as improved problem solving capacity, increased divergent thinking, increased tolerance for ambiguity, and "an ability to go beyond received patterns and rules" [4]. Techniques designed to foster creative output include the Gordon technique, synectics, brainstorming, retroduction and self-interro-gation [1], and a host of other techniques [13].

What Do People Mean by "Creativity?"

In view of the generality in most descriptions of the outcomes of creativity, we wondered whether most people have anything particular in mind when they speak of an organization's need for creativity, or when they refer to someone as creative. Some people use a word because it has a pleasant ring, evoking sensa-tions independent of specific meaning. Thus practitioners may nod with approval when told that some manager has the ability to "make tough decisions," and academics at a doctoral examina-tion may frown with dismay upon hearing a colleague remark that a student "didn't integrate well." We wondered if the word

Manuscript received July 9, 1984; revised January 27, 1985 and June 22, 1985. Research was supported by the Office of Naval Research under contract N00014-81-K0048.

The authors are with the Department of Management and Organization, Graduate School of Business Administration-1421, University of Southern California, Los Angeles, CA, 90089-1421.

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creativity has a capacity to evoke particular meanings, or whether the word evokes responses virtually independent of specific con-tent.

What are the Organizational Outcomes of Creativity?

While it is reassuring to know that creative people are intelli-gent, original, flexible, conceptually fluent, and adept at work inversions, not many organizations are not in the word-inversion business. Despite Steiner's [11, p. 51] claim that "there is consid-erable evidence that creative solutions are highly productive," virtually none of the many studies in creativity have shown that the skills and aptitudes attributed to creative people are linked to any favorable organizational outcomes.1 Steiner went on to claim, "If an organization is to survive, let alone prosper, then to a certain extent some of the managerial staff—in fact, the organi-zation as a whole—must be creative." While intuitively appeal-ing, such claims are empirically unsupported in the research literature. Of the approximately 32 descriptors of Steiner's "crea-tive organization" [11], not one describes what would commonly be considered a "bottom-line variable" (though the statement "subordinates have fun" might be said to reflect high morale). Of course, Steiner should not be criticized for the book he didn't write. However, the fact remains that it is only an assumption that creative individuals and creative organizations are more productive in terms of commonly used financial and productivity criteria. We were therefore interested to learn whether the mem-bers of an organization could be specific about the organizational outcomes of creativity.

METHOD

If employees are asked to consider an aspect of work unrelated to their daily jobs, the resulting divergence of responses will be less a tribute to the inherent vagueness of the term than to the fact that respondents have not thought much about it. We therefore sought respondents who actually made a serious at-tempt to think in terms of creativity: those who were expected to be creative as a regular part of their daily jobs.

Respondents were drawn from a large oil and gas firm. The firm employs technicians, engineers, and research and develop-ment ( R & D ) personnel, who all were engaged in the highly technical aspects of oil exploration and production. The 182 respondents represented such specialties as computer technology, all engineering subspecialties, and scientific personnel such as geologists and geophysicists.

All questions were screened by company employees, who re-jected questions judged inappropriate to their operations. Questions regarding creativity, as well as other issues, were ad-ministered on site by the research team. The anonymous questionnaire took approximately 45 minutes to complete and was then handed directly to a member of the research team (not an employee of the organization).

Measures

Three question about creativity were asked. 1) In order to maximize the possibility that respondents could anchor the con-cept of creativity in operational terms, they first were asked to think for a moment about the two most creative people in the company and identify them. 2) The respondents were then asked to describe the specific behavior or actions which caused them to believe that the individuals they identified are creative. 3) Finally, they were asked to describe the outcomes and result of this behavior.

The open-ended nature of these questions constrained our ability to analyze the data statistically and caused us to rely heavily on content analysis.

l \ noteworthy exception to this statement, which shows that it is possible to demonstrate linkage to favorable organizational outcomes, is provided by Walter [14]. In his controlled experiments with the AC Spark Plug Division of General Motors, significant changes occurred after creativity training in the number of usable and profitable suggestions made by engineers.

RESULTS

Two members of the research team analyzed separately, and then jointly, each response to questions 2 and 3 listed above. To the extent that both researchers were in agreement, subject re-sponses were grouped into categories. In the few cases where researchers were not in initial agreement, responses were cate-gorized after discussion.

Of the 182 who responded to this questionnaire, 76 (42 per-cent) were able to name two people as creative. Thirty-seven (an additional 20 percent) named one individual. The most common reason for declining to respond was that the respondent had not been with the company long enough to judge creative behavior. Virtually no one responded to question 2 or without indicating a name for question 1. Thus almost all respondents had someone specifically in mind when answering subsequent questions.

Creative Behavior or Actions

In response to the query "Describe the specific behavior or actions which caused you to believe that these individuals are creative," 108 respondents (59 percent) described at least one focal person behavior, for a total of 163 descriptions. Of these 163, 114 responses may be said to be consistent with the research literature on creativity [11], [8]. These behaviors include

1) Problem Formulation: A typical finding from research on creativity is that creative people tend to spend more time on problem formulation and are able to see problems from many different angles. Our data produced 20 responses that supported this finding; that is, the creative individual creates/develops method (seven responses); seeks new ways (six responses); and develops alternative/multiple solutions to problems (2). There were five other responses of this type to round out the 20.

2) Idea / Product Generation: Twelve responses dealt specifi-cally with idea or product generation as typical of creative individuals. Typical of these comments are the following

• "They are devising new training techniques and procedures and constantly are coming up with new ideas to improve our work procedures."

• "They have produced innovative (creative) pricing pro-posals."

• "Has developed numerous innovative ideas for service sta-tion design and promotions."

• " Development of new products showing new ideas and high degree of professional software development skills."

3) Complexity: Many researchers have reported that divergent thinking and dealing with complexity are characteristic of crea-tive individuals. Five responses state that the individual quickly solves complex problems (two responses); has the ability to absorb/retain/use much information (one response); can sense what is needed even when requests are "fuzzy" (1); and integrates information from many aspects of life to solve problems" (one response).

4) Behavioral Flexibility: Another important oft-cited correlate of creativity is flexibility, which is usually considered as an individual's behavioral response to a given stimulus. Two respon-dents described their focal person as being flexible.

5) Using Knowledge and Intelligence: Most researchers agree that intelligence plays some role in creativity. For example, Amabile [2] found in reviewing the literature that at low levels of intelligence, creativity levels are almost always low. Fourteen respondents described some aspect of intelligence in the focal person as evidence of creativity. Two additional responses men-tioned common sense, and one interesting comment described the focal person's ability to combine theory and practice.

6) Enthusiasm for Work: Several respondents suggested that enthusiasm is an indication of creativity. Four mentioned that the creative individuals loved their occupation and/or their work.

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Another described the creative individual as working hard, and another mentioned "high energy" as an indication of creativity.

7) Communication: Descriptors in this category state that the creative individual helps others learn and gives advice (seven responses); is articulate; displays ability with language (two re-sponses); provides feedback (one response); and is able to make esoteric systems understandable to others (1).

8) Displaying Creativity in Getting the Job Done: Some re-sponses, while clearly honest attempts to answer the question, border on the tautological and therefore do not teach us very much. These responses describe the creative individual as trying to improve programs, materials, etc. (nine responses); innovative with respect to methods or solutions (three responses); inventive and successful at performing tasks (two responses).

9) Use of Humor: Four respondents described their focal per-son's use of humor as indicative of creativity.

10) Trait-Based Aspects of Creativity: Though our question asked respondents to describe actions or behavior, many respon-dents replied in terms of traits or personality characteristics. Many of these responses were consistent with laboratory studies on creativity, including stubborn/assertive/determined (seven responses); imaginative (three responses); and miscellaneous other traits (five responses).

11) Absence of Fear: The most oft-described trait was fearless-ness. Specifically, five respondents described their focal person as " unafraid to take risks," " unafraid to express views," " unafraid to make mistakes," and " unafraid to tackle the unknown," which were each cited by one respondent.

Other Descriptions

49 responses do not fit traditional research notions of creativ-ity. Most of these were mentioned by only one or a few respon-dents and are not included here. However, a few descriptors were mentioned by several respondents.

12) People Orientation: Seven responses focus on the human-relations orientation of the focal persons as evidence that they were creative.

13) Job / Business Knowledge: Three responses describe the fact that the creative individual possessed good job or business knowledge.

14) Getting the Job Done: This category is included here, though it is hard to say to what extent it relates to creativity, because 14 respondents mentioned it as the key behavior that led to the focal person's being labeled creative.

15) Other Personality Characteristics: A variety of personality characteristics not usually found in the literature on creativity were cited by respondents. These included the following, none being mentioned more than twice. Accordingly, the responses describe the creative individual as dedicated; charismatic; percep-tive/insightful; alert; outgoing; takes initiative; high moral/ethi-cal standards; and politically savvy.

Outcomes of Creative Behavior

Many respondents appeared to have difficulty in describing the outcomes of creative behavior. Only 99 (54 percent) were able to city at least one specific outcome of a creative behavior. Of these, ten respondents were unable to distinguish behaviors from out-comes, virtually or literally repeating the answer they gave to question 2.

Responses to question 3 are shown in the bottom half of Table I. Responses to question 2, which were discussed earlier, are shown in the top half of the table. Table I is constructed along the lines suggested by Amabile [2], who argued that creative production is the result of three components: creative-relevant skills; domain-relevant skills (familiarity with factual knowledge of the particular setting); and task motivation. While certainly not a complete overlap with Amabile's model, our results con-form reasonably well to her categorization schema as shown in Table I.

In general, responses to question 3 divide fairly evenly into specifically anchored effectiveness outcomes for the organization; general statements about organizational effectiveness; statements about the morale, loyalty, satisfaction, and teamwork of organi-zation members; and specific outcomes that affected the creative person. The number of responses falling into each of these categories is also shown in Table I.

DISCUSSION

This research, in common with only a few other studies, sought answers related to creativity in an organizational setting; specifi-cally, in an organization that values creativity and is self-con-sciously trying to improve the creativity of its employees. This is in sharp contrast to most research on creativity, in which people are given creativity tests as the RAT. The approach taken in this research is analogous to early research on leadership, where people were identified as good or poor leaders by virtue of their records or the opinions of their colleagues. Only then were they tested for the presence or absence of particular traits and behav-iors. It would have made little sense for leadership researchers to have simply subjected people to paper and pencil tests, and on the basis of test results to have pronounced them good or poor leaders. Similarly, in studying creativity we are arguing for re-search that considers creative behaviors in the field.

Having sniped at previous research on creativity, let us now pay tribute to what was learned from that research. The fact is that many of the behavioral indicators of creativity supplied by respondents in our study are quite consistent with the existant research literature. This suggests to us that correlates of creativity identified primarily in the laboratory do have operational mean-ing in the field and are observable to organization members. Although it is unlikely that many of our respondents are familiar with the literature on creativity, most described behaviors con-sistent with that literature. With respect to descriptions of "crea-tive behavior" that have no counterpart in the creativity litera-ture, it is impossible for us to tell from this study whether respondents were in error, or whether some creative behaviors show up only in true-life situations.

As previously mentioned, respondents found it easier to de-scribe the behaviors of creative people than to describe the outcomes of these behaviors. Only two respondents claimed that the creative behavior they observed led to improvements in profits or revenue. When to these two responses are added all others relating to improvements in productivity, quality, turnover, production of new products, new business, and improved com-pany reputation in the marketplace— all of which might be considered to be specific "bottom-line indicators"—the total is still only 37 responses out of a possible 189. Of course, such a response pattern is understandable from the standpoint that creativity may be necessary but insufficient to cause such im-provements in the absence of other factors.

This last point seems worthy of elaboration. One important implication of Amabile's [2] model of creative production is that "domain-relevant" skills are as important as "creativity-relevant" skills in yielding creative product. This point has often been ignored both by creativity researchers and practitioners. Re-searchers have ignored this by designing studies in which depen-dent variables focus on such creativity-relevant skills as divergent thinking, conceptual fluency, originality, and variety and exclude organizational outcomes of the kind identified by our respon-dents. In light of the outstanding computer simulations and management games available today, such an exclusion is no longer necessary, if indeed it ever was. It should be possible, and is certainly desirable, for future researchers to test hypotheses germaine to creativity without ignoring realistic and important outcome variables.

With respect to organizational practice too, the question may be asked whether organizations seeking creativity have over-attended to creativity-relevant skills. Placing R & D labs in re-mote locations cut off from the head office, for example, and

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TABLE I CREATIVE BEHAVIOR, TRAITS, AND OUTCOMES1

Skills and Behavior Traits

A) Creativity-relevant (75)

B) Domain-relevant (49)

C) Task motivation (6)

Problem formulation (20) Idea/product generation (12) Complexity (5) Behavioral flexibility (2) Knowledge and Intelligence (16) Use of humor (2)

Communication (11) Creativity in getting the job

done (14) People orientation (7) Job and business knowledge (3) Getting the job done (14)

Enthusiasm for work (6)

Stubborness (7) Assertiveness/

determination/ imagination (3)

Absence of fear (8)

Outcomes

A) Effectiveness-related, specifically anchored (37)

B) Effectiveness-related, general (23)

C) Related to ambience and environment (26)

D) Related to favorable out-comes for the creative indi-v i d u a l ^ responses)

Increased profits (1) Increased revenues (1) Increased customer awareness and satis-

faction, and company reputation (5) Increased quality (4) Increased productivity (4) Man hours saved (4) New business obtained (2) Decreased turnover (1) New products produced (1) New/improved methods, applications,

and designs (12) Installed systems successfully (2)

Get's the job done/obtains goals/solves problems (23)

Better working environment (5) Taught others (4) Sets examples/lays foundations for others (3) Increased others' motivation (3) Improved teamwork by employees (2) Increased loyalty by peers and sub-

ordinates (3) Increased morale and job satisfaction (2) Gave others a more global view of

activities (2) Developed strategies to solve problems (1) Enabled the company to address im-

portant issues (1)

Became better liked (3) Gained informal recognition (6) Was promoted (7) Gained awards/formal recognition (3) Was sought after for advice or talents (3) Received pay raises (1)

1 The figures in parentheses indicate the number of responses.

situating high-tech employees in dual ladders or otherwise remov-ing them from the manager's world of budgetary and other constraints, are often recommended as ways to increase creative personnel 's motivation and, presumably, productivity. To what extent, however, are such gains in pure creativity purchased at the expense of the kinds of domain-relevant skills identified by Amabile?

With respect to our earlier question of whether the word "creat ivi ty" creates an affective response in people, it is note-worthy that no respondents described any negative organiza-tional consequences of creative employee behavior.

F r o m the organizational behavior literature, we might suppose that creative employees would be more tempermental, less re-sponsive to rules and authority, and more difficult and expensive to manage. Fur thermore, the awards, recognition, pay raises, and advancement described by many of our respondents as accruing to their focal person might have been expected to provoke feelings of jealously and inequity among other employees. However, to the extent that creativity in this organization— admittedly an atypical firm in its value and pursuit of creativity — c a m e wrapped in costs and hard feelings, not a single respon-dent elected to discuss these in response to our third question

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(though several respondents did contribute the opinion that the outcome of the creative behaviors they described was nil, as hierarchy or time pressure kept it from being effective).

It should be clear to the reader that the research described in this paper is primitive and exploratory. Nonetheless, we hope we have shown that it is possible for participants in an ongoing organization to operationally define creative behavior and to identify with some success the organizational outcomes of creativ-ity.

REFERENCES

[1] A. P. Brief and R. Aldag, Managing Organizational Behavior. St. Paul, MN.: West, 1981.

[2] T. M. Amabile, "The social psychology of creativity: A componential conceptualization," / . Personality and Social Psychol. vol. 45, pp. 357-376,1983.

[3] J. A. Chambers, "Relating personality and biographical factors to scien-tific creativity," Psychological Monographs 78, vol. 7, whole no. 584, 1964.

[4] Council of Scholars of the Library of Congress, Creativity: A Continuing inventory of Knowledge, Library of Congress, Washington, D.C., 1980.

[5] P. N. Khandwalla, Fourth Eye: Excellence Through Creativity. Al-lahabad: A. H. Wheeler, 1984. "

[6] E. Kris, Psychoanalytic Explorations in Art. New York: International Universities Press, 1952.

[7] D. W. MacKinnon, "What makes a person creative?" in Costello and Zalkind, Eds., Psychology in Administration: A Research Orientation. Englewood Cliffs, NJ: Prentice-Hall, 1963, pp. 414-425.

[8] H. J. Reitz, Behavior in Organizations. Homewood, IL: Richard D. Irwin, 1981.

[9] S. M. Segal, T. V. Busse, and R. S. Mansfield, "The relationship of scientific creativity in the biological sciences to predoctoral accomplish-ments and experiences," Amer. Educ. Res. Journal, vol. 17, no. 4, pp. 490-502, 1980.

[10] N. L. Smith, "The creative process: A study of its characteristics in R & D knowledge production," Knowledge: Creation, Diffusion, Utiliza-tion, vol. 3, no. 3, pp. 371-380, Mar. 1982.

[11] G. Steiner, "The creative organization," in Stanley Young, Ed., Manage-ment: A Decision-Making Approach. Belmont, CA: Dickenson, 1968, pp. 51-62.

[12] C. W. Taylor and R. L. Ellison, "Biographical predictors of scientific performance," Science, vol. 155, pp. 1075-1080, 1967.

[13] D. J. Treffinger and G. J. Gowan, "An updated representative list of methods and educational programs for stimulating creativity," Journal of Creative Behavior, vol. 5, pp. 127-139, 1971.

[14] J. W. Walter, Research Management: Principles and Practices. Washing-ton, D. C : Spartan Books, 1965, pp. 143.

A Dynamic Model of Mass and Energy Flow in Production Systems: Material

Recycling and Stability

HIRONORI HIRATA, SENIOR MEMBER, IEEE

Abstract—A mass-energy flow model of production systems consisting of a production process, a decomposition process, a control center, natural resources, consumers, and a scrap sector, is proposed. The key to the central control process is self-regulation, e.g., as mass increases in each production level, less energy is supplied and vice versa. Saving resources

Manuscript received September 15, 1983; revised December 8, 1984 and June 11, 1985.

The author is with the Department of Electronics, Chiba University, 1-33, Yayoi-cho, Chiba-shi 260, Japan.

through mass reutilization and decrease in waste plays an important role in the stability (local stability of an equilibrium) of the production system. Saving resources should be considered seriously, not only for economic benefits but for stability as well.

I. INTRODUCTION

The flow-based modeling method [1] makes a mass-energy flow (ME) model of production systems, controlled by the demand by consumers for the product. This type of modeling method is indispensable for the following reasons.

1) The modeling of large-scale systems like production systems typically encounters the following difficulties: very few quantita-tive observations of the systems are available, and very little a priori information about true system structure is known. Assum-ing that one can know the topology of the flows, i.e., the origins and terminal points, it becomes possible to compensate for the lack of data about mass with the available information on energy.

2) Total economic-ecological (EE) models, which consist of ecological subsystems, production subsystems, etc., are necessary to discuss problems that result from the interactions between socioeconomic and natural systems for environmental and re-source policy and management [2]-[4]. It is not enough to con-sider either mass or energy to make such a model. As in the ME model, the EE model should consist of both mass and energy, and the control process and the information should be considered as well.

A simple macromodel of mass and energy flow in production was proposed in [5] based on a model of mass and energy flow in ecosystems [6]. There are three forms of energy required to carry out each material transformation: human energy (labor), solar energy (land), and energy resources [3], [7], [8]. It is assumed that the energy used for transformation, i.e., energy value, is attri-buted to the transformed materials [5].

The previous model of production [5] operated according only to the amount of material in it. Human control and the relation to consumers had not been taken into account. The proposed ME model is controlled by the demand by consumers for the product. This model consists of several sectors: a production process, a decomposition process, a control center, natural resources, con-sumers, and a scrap sector. The control center regulates the amount of energy supplied to the production sector according to the information on the amount of mass in each production level and on the demand for the product by consumers.

Although the energy supplied to carry out material transforma-tion was linear in the previous model [5], it can be fundamentally nonlinear in the ME model. Nonlinearity of the processing en-ergy is necessary for showing the self-regulation in production systems.

There are two types of feedback that were not considered in the previous model: one represents waste during processing, and the other expresses loss of the product after processing. In maintaining the local stability of an equilibrium, mass reutiliza-tion and decrease in production waste are important. Positive equilibrium means constant operation of the production system. If the stability of the equilibrium is guaranteed, one can maintain constant operation or slow economic growth by controlling the parameters of the production system in order that the positive equilibrium gradually moves to a higher value.

II. MODEL

A. Production System

The production system shown in Fig. 1 consists of the follow-ing six sectors:

Sector 1) production process Sector 2) decomposition process

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