- Email: [email protected]
Method for the specification of tool management information systems
Method for the specification of tool management information systems D F KEHOE, D LITTLE, I AL-MALIKI and T M WYATT
Abstract: Structured systems analysis and design methods have been widely used in recent years in the specification of requirements for information systems. The development of techniques such as data flow diagramming and entity modelling and the supporting Computed Aided Software Engineering (CASE) tools have been applied since the 1970s in data processing environments. More recently, such methodologies have been applied to manufacturing systems through pro#famines such as IDEF. A research project is detailed which has identified the development needs for the application of structured methods to flexible manufacturing. A structured methodolooy for tool management information systems is outlined, together with the role of supporting CASE tools. The methodology models the current information systems associated with tool management, and guides the user in the generation of a requirements specification. The main stages in the implementation of the methodology are described, together with examples of an industrial application within a collaborating advanced manufacturin# company. Keywords: information systems, manufacturing systems, tool management, CASE, FMS, manufacturing strategy
'anufacturing developments since the 1970s have successively led to an increase in the .application of computers to process automation, production control and flexible manufacture. Manufacturing strategy has focused upon the reduction of labour and material costs and improving market responsiveness through the reduction of batch sizes. The manufacturing challenge of the 1990s is one of integration. Improving the degree of coordination between manufacturing subsystems requires effective information systems providing business decision support. Manufacturing integration is increasingly becoming the basis of competitive performance. The importance of effective manufacturing information
M
Advanced Manufacturing Systems Research Group, University of Liverpool, UK Paper received." 12 July 1990. Accepted 14 October 1990
systems is not matched, however, with established methods for defining the requirements specifications. Lack of clear, user-led specification methodologies are compounded by the inherent complexity of existing information systems which are often informal and poorly structured. In response to this, many manufacturing companies have adopted vendor-led solutions selected on the basis of comparing available alternatives rather than based upon a definition of user requirements. The advent of flexible manufacturing systems (FMS) has further increased the complexity and the importance of manufacturing information systems. Illustrative of the problems faced by manufacturing systems engineers is the provision of tool management systems within FMS. Initially, tool management was viewed as a secondary issue to the operational requirements of the machine tools and part transportation (the automation stage). Increasingly, companies became aware of the inventory costs associated with tooling, and therefore began to introduce computer-based stock control systems for tools (material control stage). Finally, the facilities for tool requirement planning are required as an integrated part of factory scheduling, and for improving manufacturing response (the integration stage). Research at the University of Liverpool has focused upon the application of structured methods to enable manufacturing systems engineering to define information system requirements, and to provide a mechanism for communication between user-based needs and vendorled solutions.
Defining information systems requirements for flexible manufacturing A major development in the management of flexible manufacturing has been the formal acceptance of the value and importance of information as a company resource. Further improvements in manufacturing performance are dependent upon the effective use of
0951-5240/91/010018-08 © 1991 Butterworth-Heinemann Ltd
18
Computer-Integrated Manufacturing Systems
information systems, and full integration can only be achieved through a coordinated application of available data. To define information system requirements, the key elements of such systems need to be identified. The primary 'views' of an information system are: • data flow (information transfer); • data structure (information relationships); • and data dynamics (information processing). In the manufacturing context, the requirements of each of these dimensions should be precisely established to correctly convey to the system vendor the required functionality of any proposed information system. To provide this definition, methods are required to communicate the requirements in terms of: • data flow diagrams; • logical data structures; • and entity life histories. Effective information system requirement specifications should provide a common language between user and vendor which will enable solutions to match needs. Too often, users have selected information systems such as scheduling, material control, maintenance management or tool management on the basis of comparing the merits of available commercial systems rather than on the basis of clearly defined user requirement. For flexible manufacture a further key requirement of an information system analysis method is that it should provide facilities for identifying interfaces with other factory systems, and for maintaining the detail and integrity of these interfaces through the successive detailed decomposition of the analysis. Here again the techniques associated with structured systems analysis methods enable requirements to be defined at successive levels of detail while maintaining the overall context of the system to be specified.
the most notable of these are the American IDEF and the French GRAI programmes 1°'11 IDEF was developed in the early 1980s within the US Air Force research laboratories, primarily for the benefit of associated aircraft production facilities. It consists of three integrated parts: IDEF-0 is for modelling the systems' functions, based upon the techniques proposed by RossS; IDEF-1 is for describing the data structures using the entity modelling approach at Bachman9; and IDEF-2 is for representing the dynamics of manufacturing systems with a view to building a simulation model 1°. The GRAI method ~1'~2 has been developed at the University of Bordeaux, France in a R&D project which began in 1971. The method consists of five phases, starting with the formation of a conceptual view and applying a set of graphic and tabular tools to gradually obtain a more detailed picture of the system's functionality in terms of real-time processes, activity sequences and decision centres. The focus of the GRAI method is on the analysis and definition of critical decision points in the management of manufacturing systems. Current methods tend to be'either too wide in scope, thus demanding extensive ~raining prior to application, or are too narrow, focusing on the representation of one aspect of the system and neglecting the integrated running of the organization as a whole. Our research has identified the need for a method which: (a) Exploits the modelling power of those techniques used by information systems methodologies; (b) deals with a specific element of the manufacturing system yet it (c) clearly defines the interfaces between this element and other parts of the organization with which it interacts and (d) be readily applicable by manufacturing engineers. Following detailed evaluation, SSADM* (Structured System Analysis and Design Method) was selected and used as a basis for developing a requirement specification method for tool management. Further methods are in the process of development for scheduling and material management systems.
Structured methods development The evolution of methods and techniques concerned with the development of information systems has taken place in parallel with technological developments in the computer industry as a whole. The emergence of application generators and computer-aided software engineering (CASE) tools, coupled with hardware sophistication, has encouraged the development of new methods such as YSM 1, LSDM 2, MASCOT 3, OAM 4 and SSADM 5. Many of these are based on older techniques such as those proposed by Gane and Sarson 6, James Martin 7, Ross 8 and Bachman 9. Whereas structured methods for information systems development are widespread and well advanced, efforts which have produced similar methods for manufacturing information systems are few and far between. Perhaps
Vol 4 No 1 February 1991
Liverpool University Method for Tool Management overview LUM-TM has been developed within the Department of Industrial Studies, University of Liverpool, and is aimed at specifying the requirements of plant-wide tool management information systems in flexible manufacturing environments. LUM-TM can be implemented by a small project team assisted by those involved in tool management within the user company. It can also be used by tool management software vendors to improve communication with customers, facilitate product justification on the *SSADM is currently the UK Government's standard for all informationtechnologyprojects.
19
THF
I TFP/IPl?l)l
P/~/7
I/Yl-llplZglPK IdPTllf)fff)IA R K
Pflf21 N A IVAP,FWf'AIT
•q K 9 TFIL
.9PFK l ' F TKA T T n 41 Z a~-¢llt3~r
DEFINE PROJECT OBJECTIVES G BOUNDARIES
PROJECT
;~:~°' [C,EATE "---~ACTIVITY
~o~
l MODEL
r
CURRENTSYS /
,, /,
.emt/Nn
LO6ICitL OFDROOEL -
-
-
sPoo
-
-
-
~C,EATE
,OATA ST,UCTURE tNODEL CUR Sys
.oJEo, ?
~
OEFINE. CLASSIFY
anal.Ys.td o/ cunnenL s,YsLeT~
~ D A T A
IclanIEIEO lIT US~BL~I IDENTIFY G CLASSIFY SOLUTIONS $OLLITIION IDEAS
USE•n
I PREPARE RATIONALISATION PROGRANNE
~
EVALUATE
x__.l six
"HOU~-~-~SEOPTIONS IN-ROUSE L_~ SIS OEVELOPNENT RESIIRCES
"-defJnlLJon o/ pequine,~enLs
CREATE REQUIBENENTS LIST
NEHLEY-IDEHTIFIEDRESTS
l
f
a
2-4 OPTIONS [ L,.... .,I
EVALUAT~ SHORT-LISTED OPTIONS
] ONE OPTION
,aIuateon o f solutions
~, N E Nj .T. S. . . . . /
--
ON
FE~SInILITTREPORT
•
~REOUIRENENTS
Fioure 1. Outline of LUM-TM Phase 1 basis of the customer's true requirements, and to introduce order to the implementation of tool management systems. The method consists of two phases, each comprising a number of stages. Stages include steps which are in turn divided into tasks. Some tasks are further decomposed into subtasks to clarify their method of application. The overall content of the method is as follows:
Phase 1: requirements analysis Stage 1--Analysis of current system 1.1. Create a physical model of current tool management. 1.2. Derive functional model of current system. 1.3. Compile problem-causes list (PCL).
Stage 2--Definition of requirements 2.1. Define functional solution(s) to each problem. 2.2. Create overview tool rationalization measures. 2.3. Create functional requirements list (FRL).
Stage 3--Evaluation of solutions 3.1. 3.2. 3.3. 3.4.
Identify options. Assess each option using FRL, and update FRL. Evaluate short-listed option in detail. Prepare feasibility report.
Phase 2: requirements solution Stage 4--Specification of physical system Stage 5---System implementation plan
20
The two phases of the method are respectively concerned with: (a) Identifying and analysing the problems of existing tool management procedures in the company. (b) Specifying ways of solving these problems. LUM-TM addresses these issues by building models of the activities, data flows and data structures associated with tool management. Figure 1 shows the overall structure of Phase 1 of LUM-TM, 'requirements analysis', illustrating the interfaces between its stages and steps. Stage 1, 'analysis of current system', begins with the definition of project prerequisites. These include defining the objectives, boundaries and scope of the project, as well as establishing an interviewing procedure and forming the project team. The process of creating a physical model (step 1.1.) demands investigation of existing tool management activities, as well as the information flows necessary for performing these activities. This is achieved through the use of data flow diagrams (DFD). Next, the existing tool management data structure is established with the use of a technique originally proposed by Bachman 9, and commonly referred to as an entity relationship diaaram. To remove the anomalies of the current system from the DFD model developed above, a functional D F D model is evolved in step 1.2. This attempts to identify the underlying functionality of tool management,
Computer-Integrated Manufacturing Systems
independent of how things are currently implemented. Therefore, it eliminates duplicated information flows, and data stores and employs a language which exposes the content of documents and the essence of activities, more clearly. Step 1.3 is concerned with drafting a list of tool management problems revealed from the analysis thus far. An attempt is also made to identify the causes of each problem. LUM-TM relies on the premise that clearly identifying the causes of a problem is a significant step towards defining pertnent solutions. The problemcause list (PCL) is then prioritized and classified according to the tool management personnel most closely associated with them. In step 2.1 the causes of each problem are further examined to identify potential solution requirements. At this stage, requirements are 'functional', i.e. expressed in terms of 'what' needs to be done to solve the problem, as opposed to 'how' they should be solved. Some of these requirements can be met by the tool management software system, others, however, will need to be dealt with irrespective of the software system. The latter category of requirements are used to prepare a tool rationalization program. Guidelines for this are provided in step 2.2. Software dependent requirements on the other hand are further analysed in step 2.3, and classified into eight types using the following criteria: • • • • • • • •
basic tool data management; tool inventory flow control & identification; tool requirements planning; tool specification for process planning; tool preparation & assembly; tool life monitoring; systems integration & system security; performance monitoring & management reporting.
A check-list is then produced of all the functions required of a tool management software system. The list also takes into account those features of the existing tooling procedures which are still desirable in the proposed implementation. New requirements identified during rationalization can also be added to the check-list at this point. Armed with the check-list and the data flow model, the user company can set out to identify ways of meeting its requirements. Initially, the option of bespoke software development is explored. Should this prove unfeasible, existing commercial implementations are evaluated, and an appropriate option is finally selected. Stage 3 of LUM-TM provides a detailed procedure for carrying out this evaluation, as well as for specifying the prerequisites to commissioning the selected option. It also states the long-term financial and operational implications of adopting this option. On completion of Phase 1, the results are presented in a feasibility report whose content is clearly prescribed in the method. Should the software development approach be adopted, then a procedure for translating the 'functional'
Vol 4 No 1 February 1991
specification into software modules is needed. Phase 2 of LUM-TM provides a two-stage method for such a project. Work is currently underway to develop the tasks of Phase 2. Each step of LUM-TM includes details on how the outputs should be documented and their accuracy checked. A record, labelled project monitor document, is created at the outset and updated at predefined intervals, to contain information on the project's progress. The method is presented in two media; a printed manual and a software support tool. The manual states and describes the tasks of the method, and explains with examples how they should be carried out. The software tool, on the other hand, supports the project planning, control and monitoring activities involved in implementing LUM-TM. Implementation of LUM-TM also involves the use of a CASE tool to assist in documenting, linking and updating the necessary models. Three project teams are required: a steering committee; quality assurance team; and a group of analysts. Their role and communication procedures are prescribed in the handbook in detail. The method was developed bearing in mind that the project team is not likely to have experience in techniques such as data flow and entity relationship modelling, and is therefore presented in such a way as to minimize the need for formal training. Project teams should be small, and drawn from existing personnel resources, and the method places strong emphasis on project management. The current version of LUM-TM has been developed on the basis of experience with FMSs gained by the Advance Manufacturing Systems Research Group at Liverpool University. This experience has been centred around medium-size FMSs. Therefore, the method is tailored to environments where the following features are dominant: • Large variety of parts produced in small batches. • The relationships between parts and tools on the one hand, and tools and tool-components on the other, are many-to-many, i.e. a part uses several tools and a tool is normally used to make several parts. • Modern CNC machine tools are in use with automatic tool changing facilities between magazine and spindle head. A cutting tool consists of a number of tool components, some of which may be standard (or durable) such as the holder; others are subject to wear (consumables) such as inserts, drills and carbides. • The cost of tools and the indirect cost associated with their management forms a significant portion of the overall production cost of a part.
Industrial application of LUM-TM LUM-TM has been tested through application in a major British FMS user company. The FMS installation consists of ten advanced CNC machining centres, each with a magazine capacity of 80 tools. In total, over 2000 cutting tools are used in making a variety of prismatic
21
parts belonging to four families of axles and gearboxes. The company has experienced a considerable growth in business over the last five years, a factor which has resulted in a significant increase in the number of tools required and the complexity of their management. The management had identified the need for improving existing tooling procedures, and had negotiated with a number of tool management software suppliers, but found it difficult to properly match the facilities offered by these packages against those which are specifically needed by their environment. The management's tttt
/
FtS
-,;j l
lllllfl
roqulrimento
illS)
1 Effective management of all FMS tooling functions, including tool requirement planning. 2 Evaluation of design changes, which may be dictated by customers or market demand. 3 Control over tooling flow on the shopfloor. 4 Performance monitoring and management reports generation.
~l.t e,..lill
i,,,~inl n l tool ordm,
preferred approach was to conduct the investigation and generate requirement specification in-house. LUM-TM was used for this purpose. A project team was formed in accordance with the instructions prescribed in step 1.1. The project's objectives were stated at the outset. These stipulated the development of detailed specification for a system, in terms of the necessary software functions, manual procedures, and operating policies, that facilities meeting the following criteria:
)
The company has a number of stand-alone CNC machines and other automated calls in addition to the FMS. However, the majority of the output is attributable to the FMS, and so are most of the tooling problems. The project boundary was defined as follows:
driving
• the project is to concern FMS tooling only; • a purchase order processing system for tool consumable is in place and operating satisfactoril;y • tooling specification for new and modified part designs is to be included; • specification of the geometry, bill of material assembly instructions, etc., for new tools is to be excluded, as this information is provided by the respective tool
~ ~ C O N S tool U coeP~mnt I I A requests O L E S coloonel~ dipitch note
Figure 2. Example of data lTow overview diagram (DFOD) for tool management
CUlli~' Plf~r,~ lllIS
11P~-
TmTATZVI[PJATO n ~
M t ~ Iq6 U
~RS/U/UII-.1WIle
,@
HmO.y PARTgOUTPL&N HC-PROO-I~ L2ST0
\ IEmli~l~ Eszm xo0~
Jll TOOLA Y A ~
Nr~llDOI. I . ~ 1
' ~on u ~Bzm6
. NC-PROOTm.L~BT 2
,--- 7--,11T
\.
!
. lllllll'llt',lI m
\ "-'/1 TO0. ~TA g l ~
lOi.
Olll.fillllTIll
Figure 3. Example of data flow diagram (DFD) for existhig tool management system 22
Computer-Integrated Manufacturing Systems
t i
"
I
1 °1
I
Figure 4. Entity relationship diagram (ERD) for tool management data structure vendors. However, the use and management of such information is to be covered by the project. The creation of an activity model began with identifying all existing documents and informal information transfers with respect to tool management, together with their sources, destinations and purposes. All relevant personnel were interviewed. They included product designers, industrial engineers, FMS control staff and presetters. Information obtained was documented using forms provided by LUM-TM. Using this information a data flow overview diagram (DFOD) for current tool management was developed (shown in Figure 2). The DFOD was then used as a basis for creating a DFD model. After several modifications, resulting from the model's content being reviewed by participating staff, a three-level DFD model was developed, and subsequently checked for consistency using the Automate Plus CASE tool 13. Figure 3 shows the top level of this model. The data structure was then investigated using the procedure provided within step 1.1. The entity
Vol 4 No 1 February 1991
relationship diagram developed can be seen in Figure 4. This was cross-referenced with the DFD model to validate the contents of both models, again with the aid of Automate Plus. The next step, 1.2, involved converting the DFD model into a functional one. Physical references such as 'tool data sheet' in Figure 3 were replaced with the actual information needed for transfer or storage, such as 'part-tool list' and 'tool cost data'. The activities were rearranged and renamed to reflect how things would be done had the current functions been performed by software modules. As a result, new data inputs, outputs and stores were identified. Again, a number of iterations were necessary before a final functional DFD model was agreed upon. Figure 5 shows the top level diagram of the functional model. Throughout the implementation of steps 1.1 and 1.2, problems were recorded as they were expressed by staff or revealed from the models. They were also reviewed on two occasions by the groups concerned. In step 1.3. a formal, more detailed problem-causes list (PCL) was
23
FORCTIONALOPD FOR INS -
TOP LEVEL- ~NAGE FNS TOOLIN6
-
LIVERPOOL LINIYERSITy Ak~/IA/LUN-TN/Bg
\
n l
ORDERNEN TI)~I.S REOUIREO
AI.LOCATI{~ PJ~T-T'L REel" LIST
/
@
\
\
~t
~lqmff lutm~m
C~T DATA
~
Figure 5. Example of functional data flow diagram .for tool management information system
constructed, and a degree of significance (1 to 5} was allocated to each problem. They were then classified into five sub-lists, each with specific relevance to a group of staff within the company (designers, process planners, FMC controllers, tool preparation and inventory control staff, and tool schedulers). Implementation of the rationalization exercise (step 2.2) involved establishing and analysing historical data associated with over 20 predefined parameters, including tool changing frequency per machine, tool expenditure pattern, and variations in machine tool load. A more detailed rationalization program is currently being carried out by the company with the aid of a relational database system. Following detailed discussions on the PCL developed above - with particular focus on examining the causes identified - the functional requirements were agreed upon. These were then classified under eight headings as prescribed in step 2.3 of LUM-TM. The content of one of these headings is shown in the Appendix. The functional requirements were then summarized and expressed in the form of a check-list containing 62 specific required features. Against these features, three commercial tool management software packages were assessed and a feasibility report produced. A more detailed evaluation of these packages is proposed pending completion of the extended tool rationalization exercise. In addition, application of LUM-TM in the collaborating firm has resulted in identification of significant improvements to the operational procedures associated with tool management.
24
Conclusion This paper outlines a structured methodology for the specification of the information system requirements for tool management. The methodology proposed is based upon formalized SSADM, and has been developed for the manufacturing context together with the application of associated CASE tools. Application of the structured methodology within an advanced manufacturing company illustrates the benefits of adopting information systems which have been based upon clearly defined user requirements rather than available vendor solutions.
References 1 Yourdon, E Modern Structured Analys& Prentice Hall, UK (1989) 2 Learmouth and Burchet Management Systems: LSDM Manual (V.3.5 Parts 1 and 2), London (March 1988) 3 Simpson, H R The MASCOT Approach to Software Design and Implementation Phd Thesis, Department of Computing and Control, Imperial College of Science and Technology, London, UK (1975) 4 Sirlon, Marvin, Sehoiehet, Kunin and Hammer 'OAM: an office anslysis methodology' Computer Science (October 1981) 5 SSADM Version 3 Manuals (Vols 1/2) National Computer Centre Ltd, Manchester, UK (1986) 6 Gane, C and Sarson, T Structural Systems Analysis
Computer-Integrated Manufacturing Systems
Tools and Techniques Prentice Hall, USA (1978) 7 Martin, J Design of Real-Time Computer Systems Prentice-Hall, USA (1967) 8 Ross, D T and Schoman, K E (Jr) 'Structured analysis for requirements definition' IEEE Trans. Softw. Eng. Vol SE-3 No 1 (January 1977) 9 Bachman, C W 'Data structure diagrams' Data Base Vol 1 No 2 (1969) 10 [CAM Modelling Manuals, IDEFO, IDEF1, IDEF2 ICAM Programme Library, AFWAR/MLTC, Wright Paterson Air Force Base, OH USA (1981) 11 Doumeingts, G and Vailespix, B 'Design methodology for advanced manufacturing systems' Comput. Ind. Vol 9 (1987) pp 271-296 12 Wyatt, T and AI-Maliki, I 'Methodologies the background' J. Inte9 r. Manuf. Syst. Vol 1 No 2 (April 1990) 13 Learmouth & Burchett Management Systems: AutoMate Plus User Guide (Vol 1/2/3) London, UK (1987)
Appendix: Sample tool management systems functional requirements specified through application of LUM-TM Performance monitorin 9 and management reportin9 The system should be able to retrieve and relate data as
Vol 4 No 1 February 1991
necessary for the generation of the following user reports on request: • For tools which have been fully used, produce a report which compares actual life values with the nominal values prescribed when tool was first used. • Tool breakage frequencies, together with reasons and statistics. • Tooling items usage reports based upon issues and returns of kits, tools and components. • Cost variations for tools and components, and item purchase histories. • Where-used variations in order to show part-tool relationships. • Where-stocked (for those tools that can be reconfigured into others.) • Stock levels, to show variation in quantities stocked against time, for a given range of tools. • Active/inactive tools report, listing the number of usages of a tool in a specified period. • Tool source variation (suppliers), over a given period of time. • Tool-machine relationships, that is which tools were used on a given machine during a specified period of time.
25
Abstract: Structured systems analysis and design methods have been widely used in recent years in the specification of requirements for information systems. The development of techniques such as data flow diagramming and entity modelling and the supporting Computed Aided Software Engineering (CASE) tools have been applied since the 1970s in data processing environments. More recently, such methodologies have been applied to manufacturing systems through pro#famines such as IDEF. A research project is detailed which has identified the development needs for the application of structured methods to flexible manufacturing. A structured methodolooy for tool management information systems is outlined, together with the role of supporting CASE tools. The methodology models the current information systems associated with tool management, and guides the user in the generation of a requirements specification. The main stages in the implementation of the methodology are described, together with examples of an industrial application within a collaborating advanced manufacturin# company. Keywords: information systems, manufacturing systems, tool management, CASE, FMS, manufacturing strategy
'anufacturing developments since the 1970s have successively led to an increase in the .application of computers to process automation, production control and flexible manufacture. Manufacturing strategy has focused upon the reduction of labour and material costs and improving market responsiveness through the reduction of batch sizes. The manufacturing challenge of the 1990s is one of integration. Improving the degree of coordination between manufacturing subsystems requires effective information systems providing business decision support. Manufacturing integration is increasingly becoming the basis of competitive performance. The importance of effective manufacturing information
M
Advanced Manufacturing Systems Research Group, University of Liverpool, UK Paper received." 12 July 1990. Accepted 14 October 1990
systems is not matched, however, with established methods for defining the requirements specifications. Lack of clear, user-led specification methodologies are compounded by the inherent complexity of existing information systems which are often informal and poorly structured. In response to this, many manufacturing companies have adopted vendor-led solutions selected on the basis of comparing available alternatives rather than based upon a definition of user requirements. The advent of flexible manufacturing systems (FMS) has further increased the complexity and the importance of manufacturing information systems. Illustrative of the problems faced by manufacturing systems engineers is the provision of tool management systems within FMS. Initially, tool management was viewed as a secondary issue to the operational requirements of the machine tools and part transportation (the automation stage). Increasingly, companies became aware of the inventory costs associated with tooling, and therefore began to introduce computer-based stock control systems for tools (material control stage). Finally, the facilities for tool requirement planning are required as an integrated part of factory scheduling, and for improving manufacturing response (the integration stage). Research at the University of Liverpool has focused upon the application of structured methods to enable manufacturing systems engineering to define information system requirements, and to provide a mechanism for communication between user-based needs and vendorled solutions.
Defining information systems requirements for flexible manufacturing A major development in the management of flexible manufacturing has been the formal acceptance of the value and importance of information as a company resource. Further improvements in manufacturing performance are dependent upon the effective use of
0951-5240/91/010018-08 © 1991 Butterworth-Heinemann Ltd
18
Computer-Integrated Manufacturing Systems
information systems, and full integration can only be achieved through a coordinated application of available data. To define information system requirements, the key elements of such systems need to be identified. The primary 'views' of an information system are: • data flow (information transfer); • data structure (information relationships); • and data dynamics (information processing). In the manufacturing context, the requirements of each of these dimensions should be precisely established to correctly convey to the system vendor the required functionality of any proposed information system. To provide this definition, methods are required to communicate the requirements in terms of: • data flow diagrams; • logical data structures; • and entity life histories. Effective information system requirement specifications should provide a common language between user and vendor which will enable solutions to match needs. Too often, users have selected information systems such as scheduling, material control, maintenance management or tool management on the basis of comparing the merits of available commercial systems rather than on the basis of clearly defined user requirement. For flexible manufacture a further key requirement of an information system analysis method is that it should provide facilities for identifying interfaces with other factory systems, and for maintaining the detail and integrity of these interfaces through the successive detailed decomposition of the analysis. Here again the techniques associated with structured systems analysis methods enable requirements to be defined at successive levels of detail while maintaining the overall context of the system to be specified.
the most notable of these are the American IDEF and the French GRAI programmes 1°'11 IDEF was developed in the early 1980s within the US Air Force research laboratories, primarily for the benefit of associated aircraft production facilities. It consists of three integrated parts: IDEF-0 is for modelling the systems' functions, based upon the techniques proposed by RossS; IDEF-1 is for describing the data structures using the entity modelling approach at Bachman9; and IDEF-2 is for representing the dynamics of manufacturing systems with a view to building a simulation model 1°. The GRAI method ~1'~2 has been developed at the University of Bordeaux, France in a R&D project which began in 1971. The method consists of five phases, starting with the formation of a conceptual view and applying a set of graphic and tabular tools to gradually obtain a more detailed picture of the system's functionality in terms of real-time processes, activity sequences and decision centres. The focus of the GRAI method is on the analysis and definition of critical decision points in the management of manufacturing systems. Current methods tend to be'either too wide in scope, thus demanding extensive ~raining prior to application, or are too narrow, focusing on the representation of one aspect of the system and neglecting the integrated running of the organization as a whole. Our research has identified the need for a method which: (a) Exploits the modelling power of those techniques used by information systems methodologies; (b) deals with a specific element of the manufacturing system yet it (c) clearly defines the interfaces between this element and other parts of the organization with which it interacts and (d) be readily applicable by manufacturing engineers. Following detailed evaluation, SSADM* (Structured System Analysis and Design Method) was selected and used as a basis for developing a requirement specification method for tool management. Further methods are in the process of development for scheduling and material management systems.
Structured methods development The evolution of methods and techniques concerned with the development of information systems has taken place in parallel with technological developments in the computer industry as a whole. The emergence of application generators and computer-aided software engineering (CASE) tools, coupled with hardware sophistication, has encouraged the development of new methods such as YSM 1, LSDM 2, MASCOT 3, OAM 4 and SSADM 5. Many of these are based on older techniques such as those proposed by Gane and Sarson 6, James Martin 7, Ross 8 and Bachman 9. Whereas structured methods for information systems development are widespread and well advanced, efforts which have produced similar methods for manufacturing information systems are few and far between. Perhaps
Vol 4 No 1 February 1991
Liverpool University Method for Tool Management overview LUM-TM has been developed within the Department of Industrial Studies, University of Liverpool, and is aimed at specifying the requirements of plant-wide tool management information systems in flexible manufacturing environments. LUM-TM can be implemented by a small project team assisted by those involved in tool management within the user company. It can also be used by tool management software vendors to improve communication with customers, facilitate product justification on the *SSADM is currently the UK Government's standard for all informationtechnologyprojects.
19
THF
I TFP/IPl?l)l
P/~/7
I/Yl-llplZglPK IdPTllf)fff)IA R K
Pflf21 N A IVAP,FWf'AIT
•q K 9 TFIL
.9PFK l ' F TKA T T n 41 Z a~-¢llt3~r
DEFINE PROJECT OBJECTIVES G BOUNDARIES
PROJECT
;~:~°' [C,EATE "---~ACTIVITY
~o~
l MODEL
r
CURRENTSYS /
,, /,
.emt/Nn
LO6ICitL OFDROOEL -
-
-
sPoo
-
-
-
~C,EATE
,OATA ST,UCTURE tNODEL CUR Sys
.oJEo, ?
~
OEFINE. CLASSIFY
anal.Ys.td o/ cunnenL s,YsLeT~
~ D A T A
IclanIEIEO lIT US~BL~I IDENTIFY G CLASSIFY SOLUTIONS $OLLITIION IDEAS
USE•n
I PREPARE RATIONALISATION PROGRANNE
~
EVALUATE
x__.l six
"HOU~-~-~SEOPTIONS IN-ROUSE L_~ SIS OEVELOPNENT RESIIRCES
"-defJnlLJon o/ pequine,~enLs
CREATE REQUIBENENTS LIST
NEHLEY-IDEHTIFIEDRESTS
l
f
a
2-4 OPTIONS [ L,.... .,I
EVALUAT~ SHORT-LISTED OPTIONS
] ONE OPTION
,aIuateon o f solutions
~, N E Nj .T. S. . . . . /
--
ON
FE~SInILITTREPORT
•
~REOUIRENENTS
Fioure 1. Outline of LUM-TM Phase 1 basis of the customer's true requirements, and to introduce order to the implementation of tool management systems. The method consists of two phases, each comprising a number of stages. Stages include steps which are in turn divided into tasks. Some tasks are further decomposed into subtasks to clarify their method of application. The overall content of the method is as follows:
Phase 1: requirements analysis Stage 1--Analysis of current system 1.1. Create a physical model of current tool management. 1.2. Derive functional model of current system. 1.3. Compile problem-causes list (PCL).
Stage 2--Definition of requirements 2.1. Define functional solution(s) to each problem. 2.2. Create overview tool rationalization measures. 2.3. Create functional requirements list (FRL).
Stage 3--Evaluation of solutions 3.1. 3.2. 3.3. 3.4.
Identify options. Assess each option using FRL, and update FRL. Evaluate short-listed option in detail. Prepare feasibility report.
Phase 2: requirements solution Stage 4--Specification of physical system Stage 5---System implementation plan
20
The two phases of the method are respectively concerned with: (a) Identifying and analysing the problems of existing tool management procedures in the company. (b) Specifying ways of solving these problems. LUM-TM addresses these issues by building models of the activities, data flows and data structures associated with tool management. Figure 1 shows the overall structure of Phase 1 of LUM-TM, 'requirements analysis', illustrating the interfaces between its stages and steps. Stage 1, 'analysis of current system', begins with the definition of project prerequisites. These include defining the objectives, boundaries and scope of the project, as well as establishing an interviewing procedure and forming the project team. The process of creating a physical model (step 1.1.) demands investigation of existing tool management activities, as well as the information flows necessary for performing these activities. This is achieved through the use of data flow diagrams (DFD). Next, the existing tool management data structure is established with the use of a technique originally proposed by Bachman 9, and commonly referred to as an entity relationship diaaram. To remove the anomalies of the current system from the DFD model developed above, a functional D F D model is evolved in step 1.2. This attempts to identify the underlying functionality of tool management,
Computer-Integrated Manufacturing Systems
independent of how things are currently implemented. Therefore, it eliminates duplicated information flows, and data stores and employs a language which exposes the content of documents and the essence of activities, more clearly. Step 1.3 is concerned with drafting a list of tool management problems revealed from the analysis thus far. An attempt is also made to identify the causes of each problem. LUM-TM relies on the premise that clearly identifying the causes of a problem is a significant step towards defining pertnent solutions. The problemcause list (PCL) is then prioritized and classified according to the tool management personnel most closely associated with them. In step 2.1 the causes of each problem are further examined to identify potential solution requirements. At this stage, requirements are 'functional', i.e. expressed in terms of 'what' needs to be done to solve the problem, as opposed to 'how' they should be solved. Some of these requirements can be met by the tool management software system, others, however, will need to be dealt with irrespective of the software system. The latter category of requirements are used to prepare a tool rationalization program. Guidelines for this are provided in step 2.2. Software dependent requirements on the other hand are further analysed in step 2.3, and classified into eight types using the following criteria: • • • • • • • •
basic tool data management; tool inventory flow control & identification; tool requirements planning; tool specification for process planning; tool preparation & assembly; tool life monitoring; systems integration & system security; performance monitoring & management reporting.
A check-list is then produced of all the functions required of a tool management software system. The list also takes into account those features of the existing tooling procedures which are still desirable in the proposed implementation. New requirements identified during rationalization can also be added to the check-list at this point. Armed with the check-list and the data flow model, the user company can set out to identify ways of meeting its requirements. Initially, the option of bespoke software development is explored. Should this prove unfeasible, existing commercial implementations are evaluated, and an appropriate option is finally selected. Stage 3 of LUM-TM provides a detailed procedure for carrying out this evaluation, as well as for specifying the prerequisites to commissioning the selected option. It also states the long-term financial and operational implications of adopting this option. On completion of Phase 1, the results are presented in a feasibility report whose content is clearly prescribed in the method. Should the software development approach be adopted, then a procedure for translating the 'functional'
Vol 4 No 1 February 1991
specification into software modules is needed. Phase 2 of LUM-TM provides a two-stage method for such a project. Work is currently underway to develop the tasks of Phase 2. Each step of LUM-TM includes details on how the outputs should be documented and their accuracy checked. A record, labelled project monitor document, is created at the outset and updated at predefined intervals, to contain information on the project's progress. The method is presented in two media; a printed manual and a software support tool. The manual states and describes the tasks of the method, and explains with examples how they should be carried out. The software tool, on the other hand, supports the project planning, control and monitoring activities involved in implementing LUM-TM. Implementation of LUM-TM also involves the use of a CASE tool to assist in documenting, linking and updating the necessary models. Three project teams are required: a steering committee; quality assurance team; and a group of analysts. Their role and communication procedures are prescribed in the handbook in detail. The method was developed bearing in mind that the project team is not likely to have experience in techniques such as data flow and entity relationship modelling, and is therefore presented in such a way as to minimize the need for formal training. Project teams should be small, and drawn from existing personnel resources, and the method places strong emphasis on project management. The current version of LUM-TM has been developed on the basis of experience with FMSs gained by the Advance Manufacturing Systems Research Group at Liverpool University. This experience has been centred around medium-size FMSs. Therefore, the method is tailored to environments where the following features are dominant: • Large variety of parts produced in small batches. • The relationships between parts and tools on the one hand, and tools and tool-components on the other, are many-to-many, i.e. a part uses several tools and a tool is normally used to make several parts. • Modern CNC machine tools are in use with automatic tool changing facilities between magazine and spindle head. A cutting tool consists of a number of tool components, some of which may be standard (or durable) such as the holder; others are subject to wear (consumables) such as inserts, drills and carbides. • The cost of tools and the indirect cost associated with their management forms a significant portion of the overall production cost of a part.
Industrial application of LUM-TM LUM-TM has been tested through application in a major British FMS user company. The FMS installation consists of ten advanced CNC machining centres, each with a magazine capacity of 80 tools. In total, over 2000 cutting tools are used in making a variety of prismatic
21
parts belonging to four families of axles and gearboxes. The company has experienced a considerable growth in business over the last five years, a factor which has resulted in a significant increase in the number of tools required and the complexity of their management. The management had identified the need for improving existing tooling procedures, and had negotiated with a number of tool management software suppliers, but found it difficult to properly match the facilities offered by these packages against those which are specifically needed by their environment. The management's tttt
/
FtS
-,;j l
lllllfl
roqulrimento
illS)
1 Effective management of all FMS tooling functions, including tool requirement planning. 2 Evaluation of design changes, which may be dictated by customers or market demand. 3 Control over tooling flow on the shopfloor. 4 Performance monitoring and management reports generation.
~l.t e,..lill
i,,,~inl n l tool ordm,
preferred approach was to conduct the investigation and generate requirement specification in-house. LUM-TM was used for this purpose. A project team was formed in accordance with the instructions prescribed in step 1.1. The project's objectives were stated at the outset. These stipulated the development of detailed specification for a system, in terms of the necessary software functions, manual procedures, and operating policies, that facilities meeting the following criteria:
)
The company has a number of stand-alone CNC machines and other automated calls in addition to the FMS. However, the majority of the output is attributable to the FMS, and so are most of the tooling problems. The project boundary was defined as follows:
driving
• the project is to concern FMS tooling only; • a purchase order processing system for tool consumable is in place and operating satisfactoril;y • tooling specification for new and modified part designs is to be included; • specification of the geometry, bill of material assembly instructions, etc., for new tools is to be excluded, as this information is provided by the respective tool
~ ~ C O N S tool U coeP~mnt I I A requests O L E S coloonel~ dipitch note
Figure 2. Example of data lTow overview diagram (DFOD) for tool management
CUlli~' Plf~r,~ lllIS
11P~-
TmTATZVI[PJATO n ~
M t ~ Iq6 U
~RS/U/UII-.1WIle
,@
HmO.y PARTgOUTPL&N HC-PROO-I~ L2ST0
\ IEmli~l~ Eszm xo0~
Jll TOOLA Y A ~
Nr~llDOI. I . ~ 1
' ~on u ~Bzm6
. NC-PROOTm.L~BT 2
,--- 7--,11T
\.
!
. lllllll'llt',lI m
\ "-'/1 TO0. ~TA g l ~
lOi.
Olll.fillllTIll
Figure 3. Example of data flow diagram (DFD) for existhig tool management system 22
Computer-Integrated Manufacturing Systems
t i
"
I
1 °1
I
Figure 4. Entity relationship diagram (ERD) for tool management data structure vendors. However, the use and management of such information is to be covered by the project. The creation of an activity model began with identifying all existing documents and informal information transfers with respect to tool management, together with their sources, destinations and purposes. All relevant personnel were interviewed. They included product designers, industrial engineers, FMS control staff and presetters. Information obtained was documented using forms provided by LUM-TM. Using this information a data flow overview diagram (DFOD) for current tool management was developed (shown in Figure 2). The DFOD was then used as a basis for creating a DFD model. After several modifications, resulting from the model's content being reviewed by participating staff, a three-level DFD model was developed, and subsequently checked for consistency using the Automate Plus CASE tool 13. Figure 3 shows the top level of this model. The data structure was then investigated using the procedure provided within step 1.1. The entity
Vol 4 No 1 February 1991
relationship diagram developed can be seen in Figure 4. This was cross-referenced with the DFD model to validate the contents of both models, again with the aid of Automate Plus. The next step, 1.2, involved converting the DFD model into a functional one. Physical references such as 'tool data sheet' in Figure 3 were replaced with the actual information needed for transfer or storage, such as 'part-tool list' and 'tool cost data'. The activities were rearranged and renamed to reflect how things would be done had the current functions been performed by software modules. As a result, new data inputs, outputs and stores were identified. Again, a number of iterations were necessary before a final functional DFD model was agreed upon. Figure 5 shows the top level diagram of the functional model. Throughout the implementation of steps 1.1 and 1.2, problems were recorded as they were expressed by staff or revealed from the models. They were also reviewed on two occasions by the groups concerned. In step 1.3. a formal, more detailed problem-causes list (PCL) was
23
FORCTIONALOPD FOR INS -
TOP LEVEL- ~NAGE FNS TOOLIN6
-
LIVERPOOL LINIYERSITy Ak~/IA/LUN-TN/Bg
\
n l
ORDERNEN TI)~I.S REOUIREO
AI.LOCATI{~ PJ~T-T'L REel" LIST
/
@
\
\
~t
~lqmff lutm~m
C~T DATA
~
Figure 5. Example of functional data flow diagram .for tool management information system
constructed, and a degree of significance (1 to 5} was allocated to each problem. They were then classified into five sub-lists, each with specific relevance to a group of staff within the company (designers, process planners, FMC controllers, tool preparation and inventory control staff, and tool schedulers). Implementation of the rationalization exercise (step 2.2) involved establishing and analysing historical data associated with over 20 predefined parameters, including tool changing frequency per machine, tool expenditure pattern, and variations in machine tool load. A more detailed rationalization program is currently being carried out by the company with the aid of a relational database system. Following detailed discussions on the PCL developed above - with particular focus on examining the causes identified - the functional requirements were agreed upon. These were then classified under eight headings as prescribed in step 2.3 of LUM-TM. The content of one of these headings is shown in the Appendix. The functional requirements were then summarized and expressed in the form of a check-list containing 62 specific required features. Against these features, three commercial tool management software packages were assessed and a feasibility report produced. A more detailed evaluation of these packages is proposed pending completion of the extended tool rationalization exercise. In addition, application of LUM-TM in the collaborating firm has resulted in identification of significant improvements to the operational procedures associated with tool management.
24
Conclusion This paper outlines a structured methodology for the specification of the information system requirements for tool management. The methodology proposed is based upon formalized SSADM, and has been developed for the manufacturing context together with the application of associated CASE tools. Application of the structured methodology within an advanced manufacturing company illustrates the benefits of adopting information systems which have been based upon clearly defined user requirements rather than available vendor solutions.
References 1 Yourdon, E Modern Structured Analys& Prentice Hall, UK (1989) 2 Learmouth and Burchet Management Systems: LSDM Manual (V.3.5 Parts 1 and 2), London (March 1988) 3 Simpson, H R The MASCOT Approach to Software Design and Implementation Phd Thesis, Department of Computing and Control, Imperial College of Science and Technology, London, UK (1975) 4 Sirlon, Marvin, Sehoiehet, Kunin and Hammer 'OAM: an office anslysis methodology' Computer Science (October 1981) 5 SSADM Version 3 Manuals (Vols 1/2) National Computer Centre Ltd, Manchester, UK (1986) 6 Gane, C and Sarson, T Structural Systems Analysis
Computer-Integrated Manufacturing Systems
Tools and Techniques Prentice Hall, USA (1978) 7 Martin, J Design of Real-Time Computer Systems Prentice-Hall, USA (1967) 8 Ross, D T and Schoman, K E (Jr) 'Structured analysis for requirements definition' IEEE Trans. Softw. Eng. Vol SE-3 No 1 (January 1977) 9 Bachman, C W 'Data structure diagrams' Data Base Vol 1 No 2 (1969) 10 [CAM Modelling Manuals, IDEFO, IDEF1, IDEF2 ICAM Programme Library, AFWAR/MLTC, Wright Paterson Air Force Base, OH USA (1981) 11 Doumeingts, G and Vailespix, B 'Design methodology for advanced manufacturing systems' Comput. Ind. Vol 9 (1987) pp 271-296 12 Wyatt, T and AI-Maliki, I 'Methodologies the background' J. Inte9 r. Manuf. Syst. Vol 1 No 2 (April 1990) 13 Learmouth & Burchett Management Systems: AutoMate Plus User Guide (Vol 1/2/3) London, UK (1987)
Appendix: Sample tool management systems functional requirements specified through application of LUM-TM Performance monitorin 9 and management reportin9 The system should be able to retrieve and relate data as
Vol 4 No 1 February 1991
necessary for the generation of the following user reports on request: • For tools which have been fully used, produce a report which compares actual life values with the nominal values prescribed when tool was first used. • Tool breakage frequencies, together with reasons and statistics. • Tooling items usage reports based upon issues and returns of kits, tools and components. • Cost variations for tools and components, and item purchase histories. • Where-used variations in order to show part-tool relationships. • Where-stocked (for those tools that can be reconfigured into others.) • Stock levels, to show variation in quantities stocked against time, for a given range of tools. • Active/inactive tools report, listing the number of usages of a tool in a specified period. • Tool source variation (suppliers), over a given period of time. • Tool-machine relationships, that is which tools were used on a given machine during a specified period of time.
25