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    Chapter14 quality Chapter14 quality Document Transcript

    • The University of New South Wales School of Electrical Engineering and Telecommunications ELEC3017 ELECTRICAL ENGINEERING DESIGN CHAPTER 14: DESIGN FOR QUALITY Lecture Notes Prepared by Mr Leon Dearden CLD Quality Services Pty Ltd [with minor edits by D. Taubman]ELEC3017 Electrical Engineering Design -1- Design for Quality
    • 1. INTRODUCTIONThroughout the industrialised world, more and more organisations are embracing aTotal Quality Management (TQM) philosophy in their operations. A significant andearly step in this process is, usually, to achieve certification of their QualityManagement Systems (QMS) to one of the series of international quality standardsincluded in the ISO 9000 series.As future designers in electronics or software, you may well end up working in one ofthese organisations, thus you will need to understand the impact that QMS will have onyour design activities. Even if you work for yourself or in a “quality unaware”organisation, you will benefit from knowledge of the valuable contributions to thedesign process that can be made by applying quality management principles andapplying them whenever you can.The purpose of this chapter is to explore the treatment of design activities as one of anumber of “quality processes” included in a Quality Management System and to definethe attendant benefits.The subject matters discussed in general refer equally well to hardware and softwaredesign and development activities. Where there may be particular differences inapplication then such distinctions will be indicated.2. WHAT IS MEANT BY QUALITYThere are many definitions of quality, e.g. [1]; for myself, I prefer the followingdefinition: “The totality of product (or service) features and characteristics which satisfy customer needs at an affordable cost”This definition was constructed to show the important relationship between “CustomerNeeds”, “Product (or Service) Features” and “Cost”.There can be a difference between what the customer says they want (“theRequirement”) and what they really expect to get (the often unstated “expectations”).The “quality aware” designer needs to ensure that they understand and define thecustomer’s “needs” as the sum of stated “requirements” and unstated “expectations”.Unstated expectations can be as simple as screen layouts or fonts in software designs,adherence to corporate colour schemes for hardware items etc. or as important asgraceful degradation under failure conditions for safety critical systems such as aircraftor nuclear reactors.In other words the quality of the product is judged (by the customer ) in accordancewith the degree to which it meets their real needs (however poorly or inappropriatelythey may specify them). The aware designer looks beyond the written specification ofrequirements and seeks to understand the nature of the customer’s “reality”.ELEC3017 Electrical Engineering Design -2- Design for Quality
    • If you want examples of how important this factor can be, then I recommend you readProf. Nancy Leveson’s paper [2].Note also that we do not want to confuse “reliability” with “quality”. A product can behighly reliable in performing functions that a customer does not want or value.In all of the above, we must not lose sight of costs. The product or service must beprovided to the customer at a price they can afford and will regard as “value formoney”, while at the same time offering an acceptable profit to the supplier.3. QUALITY ASSURANCE STANDARDSOf the range of standards in the ISO 9000 series, one is of immediate interest todesigners:- AS/NZS ISO 9001:1994-Quality Systems- Model for design, development,production, installation and servicing.”.It is interesting to look at the scope and field of application stated for this standard.In its scope statement, the standard talks about: • “specifying quality system requirements for use where a supplier’s capability to design and supply conforming product needs to be demonstrated” • “The requirements specified are aimed primarily at achieving customer satisfaction by preventing nonconformity at all stages of design through to servicing”The standard goes on to define its applicability where: • “design is required and the product requirements are stated principally in performance terms, or they need to be established” • “confidence in product conformance can be obtained by adequate demonstration of a supplier’s capabilities in design, development, production, installation and servicing”There are significant differences in some aspects of design between software andhardware.In 1987, Australia initiated its own standard AS 3563 for Software Quality ManagementSystems (subsequently updated in 1991) in order to achieve the same aims as forhardware with the original 1987 version of AS 3901/ISO 9001(subsequently updated in1994). For a software development environment AS 3563 competently replaced AS3901/ISO 9001. This standard was adopted by the IEEE in the USA and was offered foradoption internationally by the ISO.However, with the revision made to ISO 9001 in 1994, it became more suitable forsoftware developers, so that software developers are now being certified to ISO 9001and AS 3563 has been relegated to a guidance role. In 1996, a further guidancestandard AS 3905.8 (Ref. B7) was released to assist software developers interpret ISO9001 and this is tending to take precedence over AS 3563.ELEC3017 Electrical Engineering Design -3- Design for Quality
    • The underlying philosophy is that by analysing, understanding, defining and controllingthe organisational processes involved in design, development, production, installationand servicing, then quality is designed in and built in to the product (hardware orsoftware). No longer are we so reliant, as in the past, on inspection and testing to try toeliminate faulty product (or software).These standards also emphasize design requirements. Reference is again made toNancy Leveson’s paper [2] on the difficulty, if not impossibility, of fully testing morethan very elementary software and hardware systems. Thus the definition andmanagement of design processes as a tool to enhance software and hardware quality(i.e. freedom from undesired performance modes) assumes a major importance.4. UNDERSTANDING THE DESIGN ACTIVITY AS A PROCESSIt is instructive to look at the elements of ISO 9001 as interpreted using AS 3905.8(AS 3563 used for background guidance):Clause ISO 9001 covers: AS 3905.8 covers: 4.1 Management responsibility Management responsibility 4.2 Quality system Quality system 4.3 Contract review Contract review, planning and requirements control 4.4 Design control Design, programming and user documentation control 4.5 Document and data control Document and data control 4.6 Purchasing Purchasing 4.7 Customer supplied product Customer supplied information and material 4.8 Product identification and Configuration management (including traceability product identification and traceability) 4.9 Process control Usually covered by Clauses 4.4; 4.14 & 4.19, however ‘Control of development environment’ can be covered here 4.10 Inspection and testing Inspection and testingELEC3017 Electrical Engineering Design -4- Design for Quality
    • 4.11 Inspection, measuring and test No direct equivalent unless associated equipment hardware is involved, however -may apply to Test Software if used 4.12 Inspection and test status Usually covered by Clauses 4.8; 4.10 & 4.15 4.13 Control of non conforming Usually covered by Clauses 4.8; 4.10 & product 4.14 4.14 Corrective and preventive action Corrective and preventive action 4.15 Handling, storage, packaging Handling, storage, packaging preservation preservation and delivery and delivery 4.16 Quality records Quality records 4.17 Internal quality audits Internal quality audits 4.18 Training Training 4.19 Servicing Software maintenance 4.20 Statistical techniques Statistical techniquesWhile we are going to concentrate on those elements of the process that mostparticularly represent design activities, it is important to realise that design activitiesimpact on or are impacted by almost all other organisational processes.For example: • Limitations of the production/inspection/testing process. Manufacturing engineers will want to constrain the design so that it can be economically manufactured using existing production tooling and work force capability. Alternatively, if the design requirements preclude this, then they will need time and resources to upgrade production capabilities and acquire and train staff. • Limitations of engineering resources or know-how. It may be necessary for Personnel to recruit more designers or arrange specialist training. • Requirements for special components or other materials. Purchasing may need to be involved at an early stage to source required materiel or negotiate acceptable alternatives. • Impact on service/maintenance operations. Training of service technicians and/or new equipment may be required. If ease of service/maintenance is a vital factor then such requirements may constrain the design process.ELEC3017 Electrical Engineering Design -5- Design for Quality
    • 4.1. DESIGN AS A “SPECIAL PROCESS”Special processes are specifically mentioned in the standards. Special processes arecharacterised by: • performance which is unable to be completely verified by inspection and testing of the product after it is completed; • performance defects which may become apparent only after the product has been in service for some time; or • the need for continuous monitoring of the process, or compliance with documented procedures, or both, in order to ensure that the desired product performance is “built in”When you think about it, some mechanical design, most electronic design and nearly allsoftware design fits this definition of a special process.This is why in a well managed design environment there are such things as: • Design methodologies • Design Standards • Design procedures • Design documentation standards • Test methodologies etc. etc.Based on the collective wisdom and experience of the designers, past and present, theorganisation has developed design techniques that minimise the chance of error inmeeting requirements. What the Quality Management System does in responding to theappropriate quality standards is ensure that this hard won knowledge is documented inprocedures so that conformance to the required processes can be verified. Also, withthis knowledge available in printed form, training of new employees is facilitated.5. ELEMENTS OF THE DESIGN PROCESSLet us now look at what the Standard (ISO 9001) says about design control.Requirement for proceduresAn organisation is required to establish and maintain documented procedures tocontrol and verify the design of the product in order to ensure that the specifiedrequirements are met.In view of our past discussion, this is reasonable. You verify where you can control theprocess and its methodologies to minimise the risk of error where verification isdifficult or even impossible.Remember, however, to check that the “specified requirements” are complete, andaugment them as necessary to specify the context of operations or assumptions beingmade by the writer of the requirements document. Also note that the writer of theELEC3017 Electrical Engineering Design -6- Design for Quality
    • specifications document may not be the end-user but only his agent, so that anotherlayer of assumptions may need to be identified.The process of requirements specification for minor design tasks can be as simple asvisiting with the customer to observe his environment and getting him to state what hewants to achieve in terms of outcomes. You the designer, can then create your own“design requirement” document, perhaps as simple as a page of notes, secure in theknowledge that you have a good understanding of the customer’s real “needs”.For extremely large and complex design tasks, with critical reliability and safety issues,creating a requirement specification (and in fact the whole design activity) is a muchmore demanding process.For moderately sized and moderately complex design activities, direct access to theend-user may not be possible for all members of a design team so that a reasonableamount of effort should be expended in creating requirements documents in order toprovide a credible and realistic definition of desired design outcomes in performanceterms.The requirements definition activity is often accomplished under the umbrella of anoverall design project management program. A very readable document covering thistopic as part of project management is the IEEE Standard for “Software ProjectManagement Plans” 1 . While this document is aimed at software design, itsmethodology is almost wholly applicable to hardware design as well. At the minimumlevel it can be used as a check list to ensure as a designer that you ask all the rightquestions before you start your design; in its intended application it provides amethodology for managing the whole design process.This phase of the design process, before any actual design work is done is perhaps themost critical of all. If the “requirement specification,” however expressed, is flawed orincomplete, then the design outcome must surely fail to meet the end-user’s requirementand will again just as surely cost an excessive amount of time and money to put right(assuming that recovery is possible!).There have been numerous studies done to quantify such penalties, one of theseillustrated in Figure 1, relates to software in which the cost to correct an error is relatedto the phase in a project that the error is found. Similar considerations apply tohardware.1 See the list of quality standards at the end of this document.ELEC3017 Electrical Engineering Design -7- Design for Quality
    • Relative Cost ($) Preliminary Detailed Code & Integrate Acceptance Operation Design Design Debug Phase Error Detected Figure 1. Relative Cost to Correct Errors-Software Testing.6. REQUIREMENT FOR DESIGN AND DEVELOPMENT PLANNING • required are plans that identify the responsibility for each design and development activity • these plans are to define all design activities and must be updated where necessary as changes are made to the design • design and verification activities are planned • these tasks are assigned to qualified personnel • adequate resources are provided to designers. • organisational and technical interfaces between different groups are to be identified • required design information is to be documented, transmitted and regularly reviewedWhat the Standard is trying to achieve here in terms of making sure that the designprocess is under control and given the best possible chance to succeed in achieving itsgoals, is: • plan the activities so that nothing is overlooked • assign qualified designers to individual tasks • give them the tools and support to do the job • make sure that interfaces with other designers are clearly defined • make sure that inter-group communications are effectiveELEC3017 Electrical Engineering Design -8- Design for Quality
    • 7. REQUIREMENTS FOR DESIGN INPUT • design input requirements are to be identified and documented • they must be reviewed by the supplier for completeness. • any incomplete, ambiguous or conflicting requirements must be resolved at this stageWe have already discussed this in some detail in Section 5 above.8. REQUIREMENTS FOR DESIGN OUTPUT • design output requirements are to be documented • they should be expressed as far as possible in terms of the original design input requirements ∗ design outputs should contain or reference acceptance criteria; ∗ they should conform to appropriate regulatory requirements ∗ they should identify any design characteristics affecting the safe use of the productTo meet this requirement it is important to ensure that the outcomes of the designprocess are expressed in a quantifiable fashion, i.e. : • number of requirement features met • number of calculations/analyses performed • number of defined acceptance criteria met • number of regulatory requirements identified and met • number of design characteristics or limitations) crucial to safe or proper functioning identifiedIn other words if you can tick off the lists as complete (and get your customer/end-userto agree) then the design task is complete! In order to achieve this desirable result thenthe required design outputs must have been defined at the beginning or at least early inthe design process and managed along with all the other activities.9. REQUIREMENTS FOR DESIGN VERIFICATION • verification activities should be planned and documented • competent people should be assigned to the verification task • design verification is required to establish that design output meets the design input requirement • this can be done using design control measures like: a) undertaking design reviews and documenting the resultsELEC3017 Electrical Engineering Design -9- Design for Quality
    • b) undertaking qualification tests as appropriate c) making design comparisons with similar proven designsUnderstand that design verification is more that just seeing if it works and running afew tests. For the reasons outlined before, it is often impractical or impossible to fullytest a design i.e. prove it is fully competent by testing alone.For that reason control of the design process is important and one element in achievingthat control is assessing the state of “soundness” of the process through design reviews.Design reviews for major projects can involve a significant amount of time and effortinvolving teams of independent experts. For minor design tasks it can be as simple asreviewing the design process and results to date with a colleague or supervisor. Theimportant thing is that it should be a planned activity that occurs at regular intervals sothat if problems are identified, they can be overcome or alternative courses of actionplanned and accomplished so as not to compromise the desired outcome of the overalldesign project.For more information on ways of conducting the design review process read BS7000 2 .10. REQUIREMENTS FOR DESIGN CHANGES • the requirement is to create and maintain procedures for the identification, documentation, review and approval of all changes and modificationsChange is an integral part of the design process and as such has to be managed.For the most part, particularly in electronics or software, each new design attempts tocreate something that has not been achieved before. While new designs may be similarto what has been done before, there is usually no exact step by step plan that willguarantee the outcome is correct at the first try.So at points along the design path, the designer will realise that the design is notperforming as required and that changes are necessary. Because human memory is soimperfect, it is vital to be systematic in making changes to designs and to record thechange details in some appropriate fashion. Without this the probability of performanceerrors being built into the design is very high. A systematic process to minimise thechance of errors when making design changes is even more vital when more than oneperson or group is involved in the design process.The change management process can vary from the simple to very complex dependingupon the nature and scale of the design project.2 See the list of quality standards at the end of this document.ELEC3017 Electrical Engineering Design - 10 - Design for Quality
    • 11. DESIGN PROGRAM MANAGEMENTWe have touched on the need to manage the design process closely in order to achievedesired outcomes, technically, timewise and financially. Program Management is asubject in itself and beyond the scope of this paper.12. COSTSISO 9001 does not explicitly deal with costs and this is perhaps a failing. Cost and timescale are vital factors in all design activities; ultimately to a significant extent, timescale problems can also be related to costs.Unless a designer is independently wealthy and undertaking design activities for the joyof it, he is ultimately responsible to the financier of the project for achieving a desiredamount of product performance for a defined overall cost. This measure of the designoutcome can also be more crudely defined as “bangs per buck”.Thus financial limitations are an ever-present constraining influence on the design,production, installation, operational, servicing and where relevant, retirement processesfor any product.The actions of the designer have an influence on all these costs. In the real world,technical performance is evaluated against these costs. Trade-offs or compromises aremade to achieve, hopefully an optimum, but at least an acceptable balance betweenthese conflicting requirements.Ideally at the requirements stage, cost specifications for all phases of a products life areset as design goals e.g.: • Design must complete within budget and time scale or the project may become financially non viable or miss its market opportunity. • The designed product must be able to be manufactured for less than a defined amount; otherwise sales, and hence profits, or adequate return on investment will not be realised. • Installation and servicing/maintenance costs should be designed to be low so as not to erode profitability. • Operating costs to the customer should be designed to be at acceptable levels so as to maintain customer satisfaction and hence sales. • Increasingly with the “greening” of industry, products must not degrade the environment and may need to be economically recycled or disposed of at the end of their useful life.These “Life-Cycle Costs” can be modelled and monitored prior to, throughout andbeyond the design stage. While the modelling relies on a lot of economic, technical,environmental and political factors which abound with assumption difficulties, theoutput of the process is a useful indicator of the overall cost-effectiveness or worth of aproduct or project. If the cost effectiveness becomes doubtful at any stage during thedesign process then the project may be cancelled or may need to be severelyELEC3017 Electrical Engineering Design - 11 - Design for Quality
    • restructured to align design goals with the perceived fiscal and political realities of thetime.13. CONCLUSIONIn presenting this paper on “Quality in Design” I hope I have achieved the goal ofdemonstrating that there is a lot more to the process of achieving quality in design thanundertaking the core design processes themselves, important though they may be.It is important to understand that: • There must be a clearly defined starting point for the design process. The “Design Requirement” must be established and understood: not only what is written, but what is unwritten (i.e. assumed to be known by the end-user). • For other than the most trivial of designs, complete testability is almost always impossible or at least uneconomical; therefore, control of the design processes and its methodologies is also vital to ensure the best possible chance of meeting design requirements. • Planning of design activities and clear allocation of responsibilities for activities is required. Designer capabilities must be equal to the tasks to be performed. • Organisational and technical interfaces must be recognised and systems set up to control interaction and communication. • Progress on design activities and technical outcomes should be formally reviewed at planned intervals during the design phase. Planned changes (involving re-design, alternative studies, additional resources etc.) may need to be put into effect to overcome any technical difficulties that become evident through the review process. • Desired design outcomes should be quantified i.e. there should be a countable number of defined outcomes established to delineate the completion of the design task. • The inevitability of change should be recognised and a competent system set up to manage design changes. • Above all this in, order to survive, the design or project must be managed to remain viable in terms of overall long term costs and time scales.ELEC3017 Electrical Engineering Design - 12 - Design for Quality
    • REFERENCES[1] W.R. (Bill) Chestnut, Quality Assurance: An Australian Guide to ISO9000 Certification. Melbourne: Addison Wesley Longman, 1997.[2] N.G. Leveson, Software Safety: Why, What, and How. University Of California.STANDARDS 1. AS/NZS ISO 9001:1994 “Quality systems- Model for quality assurance in design, development, production, installation and servicing” 2. “AS3904.1/ISO 9004 -1987 -Quality management and quality system elements - Guidelines” 3. “AS 3563.1 -1991 -Software Quality Management System Part 1: Requirements” 4. “AS 3563.2 -1991 -Software Quality Management System Part 2: Implementation Guide” 5. “British Standard BS 7000:1989 - Guide to managing product design” 6. “IEEE Standard for Software Project Management Plans -Std 1058.1-1987” 7. “AS/NZS 3905.8:1996” Quality system guidelines Part 8: Guide to AS/NZS ISO 9001:1994 for the software industry.ELEC3017 Electrical Engineering Design - 13 - Design for Quality
    • SUMMARY A coordinated program for the achievement of quality involves all phases of a product’s life cycle, from the initial concept through to design, development, pilot production, full production, transport, installation and ultimate use. Quality can be achieved only if management is actively involved in all phases. This chapter lists the many tasks which form part of such a coordinated program during the concept, design, development and pilot production phases, with major emphasis on the achievement of a product of high reliability. The importance of formal design reviews, of developmental testing of prototypes and of having an efficient Failure Reporting, Analysis and Corrective Action System (FRACAS) is stressed.ELEC3017 Electrical Engineering Design - 14 - Design for Quality