Design tactics = methods + working principles for design engineers

Design tactics = methods + working principles for design engineers

Design tactics = methods + working principles for design engineers V HUBKA Institut for Grundlagen der Maschinenkonstruktion, ETH, Zurich, Switzerland...

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Design tactics = methods + working principles for design engineers V HUBKA Institut for Grundlagen der Maschinenkonstruktion, ETH, Zurich, Switzerland

Every design process may be structured into more or less complex partial processes, phases, and detailed design steps with the help of a general procedural model. The resulting procedural elements are also processes, within which the states of information are changed. Each element has an accurately formulated goal that may be extracted from the general procedural model. If these processes are to progress in a planned and methodical way towards their goals within the given boundary conditions, corresponding rules of behaviour and methodical directions must exist. These are either contained in specific methods, or in the working principles, and serve to regulate design work as an ideal setpoint. The system of design methods and working principles is termed 'design tactics', the basic structuring mentioned above is termed 'design strategy'. Design tactics and strategy together comprise the fundamental area of design methodology. When considering methods, the relationship between technical knowledge and methodical procedure must be emphasized. Even the best method is not able to substitute for gaps in technical knowledge and expertise. Methods ari} merely one dimension in design work. They form one of the prerequisites for successful work, together with technical knowledge, experience, talent, ability, perseverance, and other personal properties.

First published as: Konstruktionstaktik = Methoden + Grunds~itze des Konstrukteures; Schweizer Maechinenmarkt, 9403 Goldach, Nr 11/1982, pp 42-5, and Nr 14/1982, pp 50-3, translated by W E Eder, RMC, Kingston, Ontario, Canada

188

METHODS, METHODOLOGY, PROCEDURAL PLAN, PERSONAL WORKING MODE, AND WORKING PRINCIPLE Use of the term 'method' to designate 'a particular path to reach a desired goal' is not uniform in science, and especially not in real life. On the one hand, the term is applied to complicated systems of instructions that almost deserve the name 'methodology', such as value analysis, or modelling. The term is also applied to simple rules of behaviour such as 'systematic field search'. For our purposes we will restrict the use of the term 'method' to those operations or activities that change one state of the operand with respect to one of its properties. Similar content is frequently implied by other terms, such as 'technology'. Such a use of this word does not aid understanding in communication; it has other meanings in various contexts. We will define as a 'design method' any system of methodical rules and directives that aims to determine the designer's manner of proceeding to perform a particular design activity, and to regulate the collaboration with available technical means, assuming a 'normal' engineering designer, 'normal' technical knowledge, and certain 'normal' Factors :

Design engineers

environment conditions. A model that reflects these factors is shown in Figure 1, as a process-model of a design activity. A set (in the mathematical sense) of methods constitutes a methodology. Various such sets can be recog n ized, for i nsta nce for a pa rticular area of activity, or technical speciality, eg a product family. A single element of any method may be considered as a working principle. This usually gives instructions that are generally valid for appropriate conduct in certain defined situations. For instance, the principle of 'equal wall thickness' in form-design, or the 'desire for minimum manufacturing costs in all design activities' are typical working principles. Viewed as a hierarchy, a system of working principles plus further directives constitute a method, and a set of methods constitutes a methodology. Ifa general method exists, then a particular methodical proceduralplan can be set up to determine the designer's conduct in a design activity for a particular case. A method may be the starting point for a number of procedural plans, and these can be modified to suit different problem assignments (technical specialities and types of design), as well as deviations from 'normal' technical knowledge and organizational conditions for the problem.

Technical means

Knowledge Environment Space time

Operand :

Design 0ctivity =

Information

change of state of information based on o

state I

method

Ouestion :

methodology

Information state 2

Answer:

problem

result

from the area of operonds

from the area of operonds

Figure 1. Process-model of design activity

0142-694X/83/03001-08 $03.00 (~) 1983 Butterworth & Co (Publishers) Ltd

DESIGN STUDIES

The individual way (taken by a particular designer) in which a design task is performed is termed a persona/working mode. It may be derived from a method or a procedural plan, with respect to the g reater or lesser deviation of the particular engineering designer from the 'normal'. The measure of existing design ability, or of tiredness and other similar factors, has an influence on the chosen personal working mode.

CHARACTERISTICS OF METHODS Every method has a number of characteristics that describe it from various viewpoints. Some of these may also be used as classifying aspects, to assist in placing characteristics in ordered relationships. The characteristics of methods may be placed into two general classes: • characteristics that describe the method as a tool in use • characteristics that describe the method as information

Characteristics of use Characteristics of use may be obtained with the help of the following keywords or questions: • What goal (aim) should the method serve? For which of the designer's ranges of activity is it usable? • How widely can it be employed with respect to product families? Can it only be used in one technological context, or in more than one? • Can itonly be used undercertain conditions, or does it require fulfillment of certain prerequisites? What aids are necessary? • Forwhom isthe method intended (type of operator)? For a single person orfor a group? What preconditions must these persons fulfill? • What isthe origin of the method? In what technological area, science, or discipline was it generated? • How does the method function? On what phenomena is it based? What is the 'mechanism' of that method? • What time does the use of the method demand?

Method as information This can be described with the help of questions related to informational properties 1: vol 4 no 3 july 1983

• Are the contents correct? • Isthe effectverifiable (sources, experiences)? • Are the contents complete, not merely excerpts? Can further details be obtained? • Isthe description clear and uniquely understandable? • Howold isthe information about this method? Is it still current and in its most recent form? • Is the method freely usable? Is its use (or that of proformae) unrestricted by protection or regulation? • Who is the author, and the publisher?

APPLICATION OF METHODS AND CONTINGENCIES We have defined the term 'method' and formulated a system model of design activity (Figure 1) with the purpose of obtaining an overview of the relationships that exist in the use of methods. Let us now systematically analyse the elements of this system, with the goal of obtaining as accurate a description as possible of its influences on the use of methods. Only in this way is it possible to determine the factors involved in using methods, and to consider the optimal use of individual methods. First we will summarize the goals set for the application of methods: • to enable attainment of an otherwise unattainable result • to obtain a best (optimal) result for the given boundary conditions, by finding and evaluating a number of solution variants • to perform the search process in the most effective way, with optimal use of technical means (equipment, etc) • to prepare the field for application of computers

The operand of design activity: machine systems and their properties The input and output of every design activity is comprised of information from a particular area of technology. For instance, for a designer of internal combustion engines, the motors, their parts, and specific problems are subjected to the designer's work; for a different designer, another product family and its problems are the subject of activity. As soon as we consider mechanical engineering, the object is represented by machine systems 2. In civil engineering, the

equivalent would be a constructional system, such as every house, or every bridge. It is understandable that the object that is being processed in engineering design exerts a substantial influence on the problem formulation for the design activity, and thereby also for the method. In spite of certain similarities, the problems involved in the design of an internal cumbustion engine, a crane, or a house, are different, and depend on that object. As the individual products get more similar, so also does the range of problems become similar. Thus the problems within the areas of fluid flow equipment, or of machine tools, are very closely linked, in spite of the range of differences between individual products within each area. A machine system is the representative of all kinds of machines, without differentiating between them with respect to function, form, size, complexity, or intricacy. When we speak about design methods used within engineering design, the operand (item to be subjected to change) of the design activity (process) is the machine system. Design methods for mechanical engineering must therefore consider the individuality and reg u la rity of this artificial system. The machine system is discussed from this viewpoint in the Theory of machine systems 2, which constitutes an essential foundation for the development (and design) of methods. One of the very important points in this theory is the concept of the machine system as 'carrier' of certain properties and characteristics. This concept connects all machine systems. A series of other commonalities also exists, for instance the stages of origination, systematics, graphical and other representation, and many others 2'3. The use of design methods is particularly influenced by the following charactertistics of the machine system: • degree of abstraction of the machine system, which can be defined in (eg)six levels: machine system, phylum, class, family, genus, and type • degree of originality of the machine system to be designed, which can be related to a scale consisting of: new, further developed (changed, or adapted), or re-used existing machine systems • degree of complexity of the machine system, in four basic steps: plant, machines, machine 189

sub-assemblies, and parts; each of these could be further sub-divided • degree of design difficulty of the machine system, which can be defined with respect to selected criteria regarding difficulty (eg of manufacture 2) at each level of complexity of the machine system • individual design characteristics and properties

to solve a partial problem. From the point of view of the engineering designer, the basic ways in which problem assignments (whether simple or complicated) are answered in appropriate design activities are as follows: • He formulates his answer on the basis of his knowledge and ability (know-how), immediately, or after a suitable expansion of his knowledge (in a learning process). The so-called intuitive procedures are included in this group. HLirlimann 4 uses the term 'receptive methods' for this general procedure, which works by reactions to an external stimulus or collection of relevant knowledge and experience. The range of problems for which this procedure can be used is restricted to simple problems, and is in particular unsuitable if an optimal solution tothe problem is desired. • The indirect way leads to the goal in such intermediate stages as are envisaged in an applicable method, while observing certain basic principles and procedural manners. This path is thus prescribed bya method, or in a more concrete case by a procedural plan and the procedural manner.

Design activities The design process is comprised of various partial processes, (which in turn are sub-divided into operations) that reside at different levels of a hierarchy. The sequence of design activities-- design s t e p s - - is established in a generalproceduralmodel. A designer may, as a partial task of design, need (for example) to establish a technical process, or a functional structure, orto deliver a strength verification ('stressing') for a component, or to select a material, or a tolerance or surface quality, orto represent (draw) a component. These partial tasks are performed within the framework of designing a particular machine system. These are the actual design activities in the narrower sense. In the model of the design process, Figure 2, they constitute the central stream, the working processes. A detailed hierarchy of these working steps is shown in Figure 3. In addition to these design steps, a large number of auxiliary processes must be performed, such as experimenting, standardization, etc, and some management processes as shown in Figure 2. All design activities are aimed at answering a very definite question, in other words

The conclusion to be drawn is that every designer should have a method available in his practical work for each of his activities, and this should give him the basis to derive a suitable procedural plan and personal procedural manner, to thus reach his goal. A useful overview of the types of design activities with respect to the use of methods is contained in Figure

3 as the third level (Basic Operations), and this scheme seems to be advantageous for a first organization of types of methods. Expansion of these considerations to the design operations and stages (levels 1 and 2) must wait until later. We will use the task of 'evaluation' as an example to better explain the above opinion. Evaluation appears as a partial operation in many design activities (as do the other basic operations in Figu re 3, level 3). The manner of use and mode of operation of the task 'evaluation' is given bythe general evaluation methods and theory. These must subsequently be fitted to the special tasks of evaluation that exist in each of the phases of 'conception', 'layout', or 'search for a particular problem formulation'. Similar adaptations must be performed for each of the basic operations, and this helps to explain the advantages of organizing the overview of methods into categories of the basic operations. Typical design activities are those that aim to establish the design characteristics and properties, and also those contained in the auxiliary and management processes (Figure 2). If these two types of design activity are plotted as the dimensions of a matrix (Table 1 ),the individual cells rep resent very typical desig n activities that can be used to describe the topology of the design process. Not all of these cells are highly significant for design, but that they exist is certain, and the questions about suitable methods for each cell or group of cells seems sensible.

Factors of design activities

Design process factors

Every design activity (process) is influenced by the effects of factors (operators), Figure 2. The possible factors in designing are:

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Management processes Information

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Optimization using means

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Figure2. General model of the design process

190

Description of the MS q>

I I I I

Information ~___

• the designer alone (self-solution) • the specialist in his speciality area (expertise) • a group, with varying composition (group solution) • technical means, eg computers (solution with the aid of technical means) • combinations of the above Most of the methods are intended for a single operator. A semantic question in the use of methods concerns the terminology, eg 'method of selfsolution, or expertise', and whether it is really appropriate for these contents. DESIGN STUDIES

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L ManagingI 1 Design stages:

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Discussing

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Communicating solution

Experimenting

Leading discussions (chairmanship)

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5 Elementary operations:

I O1 02 03 04 08

Seeing= observing Reading Listening Measuring Remembering (keepingin mind)

I 11 12 13 14 15 16

Speaking Writing (report) Sketching

22 23

Noting, annotating Ordering (classifying)

Drawing Dimensioning Setting up parts list

31 32 33 34 35 36

Comparing Combining Analysing, synthesising Abstracting, concretizing Establishing analogy, inversion Inducing, deducing

Figure3. Structural parts of the design process

The survey of methods shown in Table 2 concerns itself exclusively with methods that can be applied by a single operator or a group.

DESCRIPTION OF DESIGN METHODS For a method to become a successful instrument, its mode of operation must be sufficiently clearly and completely described. This description can still allow adequate freedom for an individual's procedural manner to unfold. Descriptions should cover the following points: vol 4 no 3 july 1983

• goal, input, output: forthe purpose of design, this includes the states of the information to be processed, and any significant intermediate stages that are characteristic of that method • description of the path (technology) from input to output, namely the sequence of relevant cohesive working activities and situations (working procedure, execution, and system of steps) • behaviourofthe engineering designer in the individual activities, with instructions as accurate as possible, particular reference to decisions, considerations for

formation of variants, or possibilities for self-checking and verification, etc. These instructions are directed to an assumed 'normal' person • specification of the prerequisites for a normal person (knowledge, abilities, skills), including information about training, and also possibilities for deviations for the working persons based on their individuality • references to technical means and aids that belong to the method or can support it (including proforma) • comments on the introduction of the method into practice, particu191

Table 1. Topology of design operations Establishing:

Execution of:

Design characteristics

Design properties

Auxiliary activities

Management activities

Anatomical structure

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General

O

Elaborating assigned problem statement

A

Searching for solutions

B

Evaluating, deciding, optimizing

C

Solution, communicating answers

D

Providing and preparing information

E

Verifying, checking

F

Representing

G

larly preparation work, schooling, but also problems and timetables • bibliography about the method, details of previous use, and encountered difficulties • area of origin of the method, and other characteristic aspects • basic evaluation of the method, its advantages and disadvantages

TYPES OF DESIGN METHODS The previous sections dealt with the general characteristics of methods and their particular states of embodiment. One could theoretically use each of the characteristics to classify the methods. The literatu re provides many different classifications, a number of them were described by HLirlimann 4 . The design literature tendsto proceed in a more pragmatic fashion, and prescribes the methods directly for a given problem type. If any classification is attempted, this is usually only from one aspect of methods, eg the differentiation between discursive and intuitive methods 5'6. To date the only complete treatment of the area of methods for design is found in Jones 7. Approximately 35 design methods are presented, and they a re classified into six categories according to a mixture of aspects. 192

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The general difficulty consists of the lack of a theory as basis for the classification, and consequently that a large number of characteristics are available as classifying aspects. For the designer, the following aspects are important: • range of use, or application possibilities • effectsofthe method • requirementsforthestatesofthe factors (operators)

Classification from range of use of methods As may be seen from the above listing of characteristics, the application of each method must be considered with respect to two regions: • range of activity, and functions to be performed bythe designer • area of technology or specialization in which the activity takes place (the operand to be changed by the effects of the designer) Both of these regions were analysed above, and their ranges of embodiment demonstrated. In particular, Table I describes and structures the designer's functions, and thereby perm its a n accu rate deft n itio n of the range of application for each method.

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Classification according to type of effects of the method Each method uses different phenomena, or different areas of the system shown in Figure 1,to achieve the desired goals. In this way, the following types of method can be generated (with no claims for completeness): • methods that are intended to provide basic improvements in the manner of working, their effectiveness for the human being as operator, such that the method forces him to work in a scientifically correct way, and to eliminate certain errors of thought (eg mental blocks) • methods that act on the creative characteristics of the human being, on his sub-conscious, frequently via formation of analogies, associations, motivation, or generation of advantageous situations (conflict, sociability, competition, challenge, stimulation, group interaction) • methods that attempt to describe and master the problem situation by means of strict logic and mathematics. This constitutes part of the so-called discursive methods, and particularly algorithms. This group also contains for instance the methods of dimenDESIGN STUDIES

Table 2. Design tactics: survey of methods. Comments: some methods are listed as basic principles, because the boundary between these two categories is indistinct. The methods are named by reference to commonly used terms

Name of Method

Characteristics

Objectives

Aggregation

Combination of machine subsystems into a single system, or of functions of a number of organs into one organ Modifying or partial transformation of an existing MS for different conditions Application of an existing MS for new functions Technical and economic properties of the MS are brought into a mathematical relationship and extremes values found Find technical and economic valuation by point counting Collect ideas in free discussion without criticism Four principles: criticism, division, ordering, create overview Thorough analysis of every property of the MS Procedure of invention, applied to design work Research all directions starting from fixed points of the region By applying a system of questions, find gapless information or product mental stimulation (eg six work-study questions) Observe an idealized mental model at work Starting from assumed values, obtain progressively closer approximation of all values After thorough preparation of the problem, take a break Combining of M S o r o f properties to obtain new and higher (more complicated) effects Systematic working in every situation requiring a solution or decision Systematic collection and classification of market information Representation of the TS for various purposes Enumeration of functioncarriers to solve partial functions, in matrix form Graphic representation of activities and their duration

New properties Simplified structure

Adaptation Application Dimensional investigation

Evaluation Brainstorming D6scartes Analysis of properties (attribute listing) Method of invention Systematic search of field Questioning

Mental experiment Iteration

Incubation Combinations with interactions Systems approach Market research Modelling technique Morphological matrix Critical path network Experimentation Synectics Techno-economic design

Step forwa rds/backwa rds Value analysis or engineering Division of totality

Methodical doubt (scientific scepticism) Method '6-3-5'

vol 4 no 3 july 1983

By measuring and testing, obtain desired values Team analyses problem and searches for new solutions through analogies Bytechnical and economic evaluation, find and improve the strong features of the design Attempt both solution directions, from 'is' to 'should be' and reverse Analysis and criticism of the existing solution from the viewpoint of economics Tactical procedure based on division of a whole concept or problem into component parts By systematic negation of existing solutions, search for new solution paths 6 participants, each write down 3 ideas within 5 minutes, then pass on to next person for similar 3 ideas

Reliable solution for new conditions Application of proven MS to new areas of use Find optimal solution

Find best variant among a few Find many solutions to a problem Correctness and effectiveness of the thought process Improvement of the existing MS Find new solutions Obtain completest possible information Obtain completest possible information

Testing of an idea, determination of behaviour Solution of a system with complicated interactions Find solutions by intuition Derive new solutions from existing MS As far as possible complete investigation of an area Establishing marketing conditions Determination of behaviour and other properties oftheTS Newsolutions by combinations of function carriers Create an overview of sequence and timing and find the critical path Determination of the properties of the MS Discover new solutions Determine one best solution from among a number Find the most favourable path to a solution Improvement of the economic properties of the MS Create overview, generate partial solutions

sioning and optimization • methodsthat prescribe methodical rules and regulations that do not necessarily result in reaching the goal, but significantly increase the overall probability of success. This type is labelled the heuristic method (after M011er8) • methods based particularly on the knowledge of the object as operand of the activity (eg theory of machine systems), and on the particular properties in question (eg solid mechanics and strength) • methods that encourage the use of technical means and aids, and aim towards automation of that part of the design process • combinations of the above methods appropriate to the existing situation The alert reader has no doubt discovered that these groups of methods at the same time represent possible areas and directions of rationalization.

Classification from the requirements of states of factors Some methods are restricted in their application because they dictate certain defi n ite states of t h e facto rs (operators). The following cases are typical for the existing methods: • The method is directed attheindividual designer, or at a group (either fully prescribed, or freely collected), or has no restrictions with respect to the solving personalities. In some cases the knowledge, skills, or abilities of the designer are also prescribed. • The method is conditional on availability of certain technical or working means (typically methods for computer application). In addition, the technical means may be generally or accurately specified (eg by type and make of computer). • The method prescribes certain definite working conditions, which may make general application of the method impossible.

Universal and specialized methods

Find new solutions Find many solutions

One hears frequently the terms 'universal or specialized methods', referring usuallyto the breadth of the range of applications. If we consider all the possibilities described above, it is seen that this terminology is in193

accurate unlessthe relevant classifying a s p e c t is a l s o s t a t e d . T h e s t a t e m e n t is o n l y c l e a r if it i n c l u d e s a d d i t i o n a l i n f o r m a t i o n , eg t h a t a c e r t a i n

m e t h o d is ' u n i v e r s a l w i t h r e s p e c t t o a r e a o f e x p e r t i s e ' , i m p l y i n g t h a t it is u s a b l e in a n u m b e r o f d i f f e r e n t t e c h nical b r a n c h a r e a s .

Table 3. Working principles for the designer

A: General Principles 1 Critical acceptance of all given information: do not accept any information without examination and verification 2 Controlprinciple: every result must be examined. Use an advantageous control strategy and tactics, and examine important requirements, eg function, realizability, economics 3 Principleofeffectiveness: in every process one should strive for maximum effectiveness 4 Principle of economy: economy is the first requirement for design. The function of the MS should be attained in the cheapest fashion. Depending on company policy, and on ethical considerations for the design engineer, this 'cheapest fashion' could be cheapest first cost, or cheapest running cost, or preferably cheapest whole-life cost 5 Optimization principle: aimforoptimum solution or best compromise solution for the given conditions, in optimum design time, with optimum care and accuracy 6 Systemandtotalityprinciple: everyobject and every process is simultaneously a system and a system element in ala rger system. All connection, interactions and relationships shold be considered 7 Principleofrecording information: human memory is unreliable. Every important item of information should be recorded (eg written down) and classified (catalogued) in an economic fashion 8 Ordering principle: every area of knowledge should be classified (eg Dewey decimal classification system) 9 Overview principle: create a usable and comprehensive survey 10 Principle of methodical and planned procedure: guide the progress of activities in a methodical and planned way. Use at least one solution path, and a different control or checking path B: General principles during search for solutions 1 Orientation principles: carefully determine the state of the art in the relevant area. It may be useful to attempt to think of possible solutions to the problem, using intuition and imagination, before applying.this orientation principle. The search for the state of the art can then proceed with better knowledge of the questions relevant to the specific problem, and with less danger of mental set, or fixation; but consider also the opposing danger of 'jumping to a conclusion', and defaulting on this orientation principle 2 Accept good existing solutions, but only after critical examination 3 Principleofaccurateproblemformulation: for each sub-division of the problem, formulate each step of the problem assignment 4 Principleofabstraction: formulate abstractions from the existing concrete circumstances to find new paths 5 Division principle: divideeverycomplex problem in sensible sub-divisions

194

6 Variations- combinations principle: combine suitable elements into a totality, vary the elementsthat can perform equivalent functions 7 Incubation principle: permitthe subconscious to work. Alternate productive phases with rest periods C: Principles concerning quality of the TS 1 Design with respect for function: then 'design follows function' (Walter Gropius), ie if it is rig ht, it also looks right, but not necessarilythe converse 2 Design forthe market: fulfil all customer requirements 3 Designforoperation: consideroperational safety and hi, man operator conditions, minimum space consumption, minimum dimensions 4 Design for the human being: offer maximum protection for the human, avoidance of difficult or monotonous human work, aim for minimal human fatigue 5 Design for appearance: keep in mind the aesthetic effect of the product 6 Design for packaging, storage and transport: create favourable conditions 7 Design in accordance with regulations: take into account all standards, codes, laws. Do not copy products protected by patents, trade marks, design registration, etc 8 Designformanufacturability: achievethe most economic realizability of the product with available manufacturing systems, aim for optimal manufacturing methods 9 Design for ease of assembly and maintenance: examine assembly methods for the TS, avoid special tooling 10 Aim for minimum manufacturing and running costs 11 Design for adequate strength: ensure appropriate strength and stiffness of the TS, considering also fatigue, creep, fracture mechanics, resonances, wear, and other modes of failure or deterioration 12 Design againstcorrosion: ensure appropriate resistance to corrosion for the TS 13 Consider thermal expansion of the system and its elements (steady-state and transient) 14 Provide adequate lubrication 15 Professionalism in design: simple structure, simple form, optimal dimensions, suitable materials, surface structure as coarse as permissible, largest possible tolerances

T h e a d v a n t a g e s a n d disadvantages of the universal and specialized methods are equivalent to those of the machines. A specialized method leads reliably and effectively to the desired result. Therefore each system and each school of design methodology must describe specialized m e t h o d s t h a t s u p p o r t t h e p r o c e d u r a l p l a n in its i n d i v i d u a l s t e p s , n a m e l y m e t h o d s s u c h as a r e des c r i b e d in A n d r e a s e n 9 a n d ML~ller B.

Time wasting and time saving methods It c a n n o t be d e n i e d t h a t s o m e m e t h o d s set g r e a t d e m a n d s o n t i m e , a n d o t h e r s set less d e m a n d s . T h e c h a r a c t e r i s t i c o f t i m e ( e v e n if it is o n l y r e l a t i v e ) is a l w a y s i m p o r t a n t f o r t h e designer suffering under pressure of deadlines.

SURVEY OF METHODS AND METHOD SELECTION The designer, and every user of methods, should know the answers to two questions: • W h i c h m e t h o d s e x i s t f o r his a r e a o f a c t i v i t y in g e n e r a l , a n d h o w a r e they described? • How should he select the most suitable method from among the e x i s t i n g o n e s in a p a r t i c u l a r p r o b lem situation?

Catalogue of methods T h e a n s w e r t o t h e f i r s t q u e s t i o n is represented by a catalogue of m e t h o d s t h a t m a y b e m o r e o r less c o m p l e t e . It can b e v e r y s i m p l e , f o r i n s t a n c e s i m i l a r t o T a b l e 2, a n d c o n t a i n a f e w k n o w n m e t h o d s in alphabetic order with short characterizations. Further details could be added, but nevertheless a satisfact o r y r e s u l t is n o t e x p e c t e d . A b e t t e r s o l u t i o n a l s o respects the second question, and c o u l d c o n s i s t o f a c a t a l o g u e in t w o parts: •

D: Principles concerning representation

techniques 1 Aim for clear, complete, unique and unambiguous representation of the TS 2 Economic, optimal representation 3 Purposeful representation (consideringthe receiver of the com m u n icatio n) 3 Purposeful representation (considering the receiver of the communication) 4 Considermanipulation, handling and archiving (filing) of documentation

d e s c r i p t i o n s o f m e t h o d s , as described above, (the collection should permit addition of further descriptions) • a r e g i s t e r in w h i c h t h e i n d i v i d u a l m e t h o d s a r e c l a s s i f i e d in s e l e c t e d ways described above. This register must definitely and minimally showthe relationship between the method and the appropriate activity (basic and design operations) and the area of expertise

DESIGN STUDIES

With the help of such a catalogue the designer can start by referring to the register, then check the description, and evaluate the method for his problem. An additional problem area is opened as soon asthe existing methods do not adequately cover the range of activity of the designer. This reveals a gap that justifies the demands for generation of new methods.

CREATION OF NEW METHODS, AND DERIVATION OF PROCEDURAL PLANS FROM THE METHODS In practice it will always be necessary to formulate one's own methods for missing ranges of activity and/or areas of expertise, and to derive procedural plans from the existing methods. Within the confines of this article it is not possible to present a procedure for formulating a method. The previous sections contain enough references to permit such work. Similar considerations are valid for deriving procedural plans by concretizing the general statements within the methods for a definite problem.

APPLICATION OF METHODS IN PRACTICE It is not possible to give a reliable indication of how the new methods are being used. The resdlts of the few investigations that exist are not suffi-

vol 4 no 3 july 1983

ciently representative. Even if only the best-known methods are considered, their use and degree of familiarity in the engineering community are relatively small. The not unexpected fact is that design methodology has not found the response it deserves. It is also necessary to warn against over-methodizing. The application of a method should be carefully considered, not only in general, but also in each particular case. It should contribute to improving the solution and/or makethe procedure more effective, and avoid too much formality. We must also distinguish between methods that have been tested, and those that are in an introductory phase. Time penalties must be considered here.

WORKING PRINCIPLES FOR THE DESIGNER We have already defined the working principle for the designer as an element ofthe area of methods. The instructions given in these principles are usually of general validity with respect to most areas of expertise, and also for many activities, eg the principle concerning minimum cost, or minimum space requirements. Other principles are used only in certain activities, eg the principle of uniform wall thickness is only applicable in the stages of form-design and verification. An impression of the range of principles may be obtained from Table 3 with respect to four areas.

In a similar fashion to the methods, where it is useful to derive personal working and procedural plans for the individual use of the designer, it is recommended that each designer should also develop a personal list of such working principles, and to augment it periodically with new ideas.

REFERENCES 1 Hubka, VDerKonstrukteuralslnformationsverbraucher SchweizerMaschinenmarkt,

Vo173Nos38,40and 42 (1973) 2 Hubka,V TheoriederMaschinensysteme Springer-Verlag,Berlin,FRG(1974) 3 Hubke, VPrincip/esofEngineeringDesign

ButterworthScientific,UK(1982)(translated and editedby Eden,W E, fromAIIgemeines Vorgehensmodell, WDK 1, FachpresseGoldach (1980)) 4 Hr.rlimann, WMethodenkata/og Lang,Bern, Switzerland(1981) 5 Conred, PErfo/gdurchmethodischesKonstruieren Lexika-Verlag,Grafenau(1978) 6 PehI, GandBeitz, WKonstruktions/ehre

Springer-Verlag,Berlin,FRG(1977) 7 Jones, JCDesignmethods:seedsofhuman futuresWiley, NewYork,NY,USA(1980)

secondedition M.',llm',J Methoden muss man anwenden ZIS, Halle(1980) Andreasen, M M Methods in the WDK-System

WDK5, Heurista,Z~irich,Switzerland(1981)

BIBLIOGRAPHY Chestnut, H System engineering methods

Wiley,NewYork,NY,USA(1967) Hubka, V Theorie der Konstruktionsprozesse

Springer-Verlag,Berlin,FRG(1977)

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