An expert system for machine screws selection in engineering design

Expert Systems With Applications, Vol. 4, pp. 141-146, 1992 0957--4174/92 $5.00 + .00 Printed in the USA. © 1991 Pergamon Press plc

An Expert System For Machine Screws Selection in Engineering Design

JAHAU LEWIS CHEN AND HONG-SEN YAN

National Cheng Kung University, Tainan, Taiwan 70101, Republic of China

GE-YAN SHINE

Electronics Research & Service Organization, Industrial Technology Research Institute, Hsinchu, Taiwan 3 l015, Republic of China

AbstractuThis article describes an expert system for selecting machine screws in engineering design. This expert system is intended as an on-line consultant to give the designer interactive assistance in the selection of machine screws for designing industrial products. A rule-based microcomputer expert system development tool PC-PLUS provides the framework for this development. The details of knowledge organization, rule representation, inference reasoning process, and peoCormance of this expert system are demonstrated with two industrial design examples.

1. INTRODUCTION

MACHINE SCREWS are an important machine element used for fastening components in many machines. Al- though the unit price is very low, the quantity of machine screws being used is tremendous. The screws also affect the assembly reliability of full machine systems. Therefore, nearly all engineers are concerned with the selection and use of machine screws and thus need to be somewhat knowledgeable of the choices available and the factors governing their selection and use.

With the growth of expert system technology, the development of intelligent systems for engineering di- agnosis, maintenance, and design tasks is receiving in- creasing attention. For engineering design, the selection of engineering components and products from cata- logues often requires some level of knowledge for making decisions. Therefore, it is an ideal domain for de- veloping an expert system to aid the less experienced engineer performing component selection tasks (Vog- well, 1990). In the field of fastener selection, there are some expert systems that have been developed to aid the engineer selecting suitable fasteners. An expert system (Long, Bailey, & Shawver, 1988) was developed to aid and evaluate the design of a mechanically fastened joint and make a fastener selection recommendation. A prototype expert system for an automobile fastener selection (Krishnamurthi, Underbrink, Wells,

Requests for reprints should be sent to Jahau Lewis Chen, As- sociate Professor, Department of Mechanical Engineering, National Cheng Kung University, Tainan, Taiwan 70101, Republic of China.

141

& Mayer, 1987) and the Joint Design Assistant (JDA) expert system (Bonenberger & Brooks, 1990) have been developed to assist the automobile engineer performing the fastener selection task.

This article describes the development of an expert system for assisting the engineer in machine screws selection. PC-PLUSma rule-based microcomputer expert system development tool--provides the framework for this development.

2. MACHINE SCREW SELECTION IN ENGINEERING DESIGN

Today, the use of screw-thread fasteners remains the basic assembly method in the design and construction of products despite advances in other methods of join- ing. To be effective, each application must be properly engineered and installed, since failure of a single fastener can be destructive or even catastrophic. There- fore, the engineers must select standard fasteners of the type and size that will most adequately suit the application at hand.

Machine screws are one kind of fasteners used to fasten and hold things together. They are similar to cap screws that can be tightened exclusively by a screwdriver. Machine screws are usually used for smaller parts and used primarily to fasten a plate with thin sections to another component. They are available with a wide variety of head shapes (such as fillistcr head, oval head, flat head, or round head) to suit various design conditions.

Recently, with the development of the electronics and computer industry, the function of machine screws

142 J. L. Chen et al.

has been extended from fastening to ground path, thermal path, and electromagnetic shielding. For example, the selection of machine screws in electronics packing design, in addition to considering the strength of fastening and size, factors of corrosion resistance, magnetic properties, electric conductivity, thermal conductivity, thermal expansion, safety, cost, and appearance, also merit consideration. Furthermore, for saving the material stock cost, the standardization of machine screws selection for designing industrial products be- comes a very important task. The factors that must be considered during the selection of machine screws are summarized in Figure I.

The foregoing discussion indicates that the machine screws selection problem is a never-ending challenge to the engineer. There is an urgent need to have the machine screws selection expertise available in the design community. This situation provides an excellent opportunity for application of expert system techniques.

3. EXPERT SYSTEM APPROACH

Expert systems are computer programs that capture specialized knowledge about a narrow and well-defined domain and can simulate the reasoning process of a human expert to provide knowledgeable advice about a difficult task. Expert systems should typically consist of four components: a knowledge base, an inference engine, a knowledge acquisition facility, and an input- output interface with an explanation facility (Dym, 1985; Liebowitz, 1988). Currently, most expert systems lack a good knowledge acquisition facility. In most expert systems, it is desirable to separate the knowledge

base and the inference engine. With this separation, the knowledge can be modified as the domain is better understood. Such an approach also allows the same inference engine to deal with knowledge bases pertain- ing to different problem domains.

A knowledge base consists of domain facts and heu- ristic knowledge associated with the problem. In the representation of knowledge within the knowledge base, the rule-based knowledge representation is the most popular scheme in current expert systems. In this approach, the knowledge is represented as IF-(condition)-THEN-(action) rules. The (action) part is exe- cuted if the (condition) part provides a match with the available facts. Another scheme is frame-based knowledge representation. This is a network data structure to represent the relations between concepts and their attributes. Semantic networks and frames are included in this scheme. This approach allows more relations between the facts. The logic-based scheme uses a first- order predicate logic--a special subset of mathematical logic--to represent knowledge. This scheme has the feature of both representing and making inferences on knowledge by using one logical formulation.

The inference engine, which contains the reasoning technique, executes the program by matching the known input facts with the knowledge in the knowledge base to draw conclusions. The backward-chaining reasoning starts from a hypothesis or goal to check if the hypothesis can be supported by the available facts. On the other hand, the system that works from known facts to the conclusions is called forward-chaining reasoning. The mixed reasoning technique combines both forward chaining and backward chaining. Many inference engines can handle incomplete knowledge by as-

MACHINE SCREW SELECTION

I NECH&HIC&L

PROPERTY

i= MATERIAL :• STRENGTH • WEIGHT • ELECTRICAL

CONDUCTIVITY • THERMAL

CONDUCTIVITY i THERMAL

EXPANSION CORROSION

l RESISTANCE • WEAR AND

ABRASION • APPEARANCE

I HE&D STYLE

• HEX SQUARE BINDING OVAL WASHER PAN FLAT 12-POINT

T H R E A D TYPE

• UNC I

I TAPPgHG

SCREW TYPE

STANDARD POINTS THREAD FORMING SCREW THREAD CUTTING SCREW THREAD ROLLING SCREW

FIGURE 1. The factors of machine screw select ion.

I S I Z E

• HEAD DIMENSION

• THREAD DIMENSION

• BODY DIMENSION

An Expert System for Machine Screws Selection 143

soeiating confidence levels with the facts. The conclu- sion from the inference engine is one that has the high- est certainty associated with it.

During the development of an expert system, the primary bottleneck is in the acquisition of the expert knowledge for the knowledge base. Currently, this process is performed by the knowledge engineer who builds the expert system. The sources of expert knowledge are the domain expert and the experiences of domain experts that are documented in the available literatures. Naturally, an interview with the domain expert is one way in which a knowledge engineer can extract the knowledge from the domain expert. The difficulty of this approach is that the domain expert may not know how to describe the decision process, or may simply misunderstand the questions.

In recent years, several commercial expert system tools have been developed for building expert systems. These tools contain a domain independent inference engine, an empty knowledge base, and a user-friendly interface. With these tools, the expert system builder can concentrate more on the knowledge representation and less on the complex inference engine strategies. However, the choice of a suitable knowledge representation scheme and inference reasoning technique is an important ingredient to the success of an expert system. The available tools should be used carefully.

system. This tool offers forward and backward chaining, frame-based representation, meta-knowledge con- trol, graphics displays, a broad interface to Scheme. LISP language, and the capability to execute outside program.

In PC-PLUS, knowledge bases are organized in terms of frame trees. The subframe partitions a knowledge base into a number of related subproblems. A frame representation is used to partition knowledge into distinct groups of rules and parameters. This ar- rangement provides for a type of inheritance in which subframes inherit rules and parameters from their parent frames. The knowledge representation scheme is a mixed representation type which the rules are placed in frames and the parameters are placed in either the parameter group of that frame or that of a parent frame.

4.1. Architecture of the SCREW Expert System

The current structure of the SCREW expert system is illustrated in Figure 2. It contains a knowledge base, an inference engine with an explanation facility and a capability to execute outside programs, and an input- output facility that contains a knowledge base editor and a graphical display capability. This system is pres- ently operational on an IBM PC-AT-compatible personal computer,

4. A MACHINE SCREW SELECTION EXPERT SYSTEM

A rule-based microcomputer expert system development tool, Personal Consultant Plus (PC-PLUS) (Texas Instruments Inc., 1987), was selected as environment for the development of machine screw selection expert

4.2. Knowledge Base Organization and Knowledge Representation

Currently, the prototype machine screws selection expert system only has the SCREWS frame that contains rules about the mechanical properties and head style of machine screws.

The slots of the SCREWS frame are as following:

Frame :: SCREWS IDENTIFER :: "SCREWS-" TRANSLATION :: (MACHINE SCREW) GOALS :: (SCREW) PROMPTEVER :: (LINE : LEFT 20 :TAB :ATTR

(YELLOW) MACHINE SCREWS SELECTION PROGRAM :LEFT 17 :RIGHT 70 :ATTR (WHITE) :LINE 4 This program helps you select a machine screw.)

DISPLAYRESULTS :: YES PARMGROUP :: SCREWS-PARMS RULEGROUPS :: (SCREWS-RULES) SCREWS-PARMS :: (BIND CONDUCTIVITY CORROSION

FLAT LIGHTWEIGHT MAGNETIC SCREW STRENGTH TOOL)

SCREWS-RULES :: (RULE001 RULE002 RULE003 RULE004 RULE005 . . . . . . )

144 J . L . Chen et al.

KNOWLEDGE BASE I INFERENCE ENGINE

EXPLANATION FACILITY

I I i

KNOWLEDGE BASE I USER EDITOR ~. . [ (DESIGNER, EXPERT)

FIGURE 2. The architecture of the SCREW expert system.

A typical example of rule is as follows:

RULE036 SUBJECT :: SCREWS-RULES If 1) the force you applied is MIDDLE, and

2) material magnetic property is NO, and 3) the screw needs good electrical and

thermal conductivity is YES, and 4) the screw needs lightweight requirement

is YES, and 5) the screw driver is PLAIN,

Then it is definite (100%) that A machine crew is Aluminum-alloy, hexagon head screw.

The knowledge base for this system includes rules for type classification of machine screws, machine screws assembly techniques, and the characteristics of material. Furthermore, in addition to considering the strength of fastening, factors of corrosion resistance, magnetic properties, electric conductivity, thermal conductivity, thermal expansion, safety, cost, and appearance are also considered in the rules to improve the quality of selection.

4.3. Inference Engine

The type of rules in this system are consequent rule type. Therefore, the inference engine uses the backward-chaining approach to execute the reasoning process. The inference engine in PC-PLUS has 12 special functions to deal with the DBASE database manage- ment system for operating information in a database. With these special functions, the inference engine in this system can reason the machine screw selection problem by matching the design situations with rules in the knowledge base and the data of machine screws in a database.

4.4. Knowledge Acquisition

The sources of knowledge includes domain experts (electronic engineers) and experiences of domain experts that are documented in the available literature, such as design handbooks and design computer soft-

ware. Both interview and protocol analysis techniques were used to elicit knowledge for the knowledge base. During the SCREW expert system development, the knowledge acquisition process is recognized as the most difficult task.

5. EXAMPLES

Two industry design cases are studied to demonstrate the capability of this expert system. The first is the personal computer power supply system's internal connection machine screws as shown in Figure 3. The critical considerations for selecting this machine screw are as follows: (1) try to avoid cutting the electrical lines, (2) use magnetic material for easy assembly, and (3) assembly line uses a cross-recessed, air-powered screwdriver. The suggestion from the expert system is shown in Figure 4.

Another example is the machine screws on the outside plate of the electrical cabinet as shown in Figure 5. The outside plate of the cabinet needs to resist the impulse force. The machine screw will be used in an industrial environment that contains corrosive material. The advice of selecting the machine screw from the expert system is shown in Figure 6.

POWER SUPPLy CHASSIS

GROUND HACHINE SCREWS

FIGURE 3. Personal computer power supply system's internal connection machine screws.

An Expert System for Machine Screws Selection 145

C o n c l u s i o n s :

HACItIHE SCREWS SELECTOR

i i

A m a c h i n e s o r e u iB a s f o l l o u s ! B r a e s , S l o t t e d b i n d i n g h e a d s e r e .

A m a c h i n e s e r e , : : ( " B r a s s . S l o t t e d b i n d i n g head s o r e u " tOO RULE058).

D e t e r m i n e d t o b e : B r a s s , S l o t t e d b i n d i n g head s c r e . . . . by u s i n g RULEO5B

I f I ) t h e f o r c e you a p p l i e d i s LOg, end 2) m e t e r l a l . m a g n e t t c p r o p e r t y i s HO, and 3) a c r e , d r i v e r i s SLOTTED. end 4) Used i n e l e c t r i c a l c o n n e c t i o n i s YES,

Then i t i s d e f i n i t e ( 1 0 0 X ) t h a t A m a c h i n e s c r e u i s B r a s s , S l o t t e d ~ l n d i q g head s c r e u .

** End - RETURH/EHTER t o c o n t i n u e i n

** End - RETURH/EHTER t o c o n t i n u e

FIGURE 4. The mconvnendation from the expert system for power supply system's internal connection machine screws.

6. C O N C L U S I O N S

This article described a prototype machine screws selection expert system. This system can give the less experienced engineer advice in selecting the suitable

machine screws for their product designs. Preliminary testing of this SCREW expert system gives satisfactory results. It is believed that a system like this would en- hance the reliability of engineering designs.

Additional development work is on the subject of

MACHINE SCREWS FIGURE 5. The mmch~e Icmvm on the out,de p~ of lhe __~qskml cannot

146 J. L. Chen et aL

H A C I l I H E SCREWS S E L E C T O R

~ o n c l g s i o n s : ' - ' J

A m a c h i n e s c r e w i s a s f o l l o u s ~ S t a l n l a s s - a a r t e n s l t i c . C r o s s - r e c e s s e d f l a t Head S c r e w

^ m a c h i n e s c r e ~ :~ ( ' S t a i n l e s s - m a r t e n e l t l o , C r o s s - r e c e s s e d f l a t H e a d S c r . . . by u s i n g R U L E 0 2 0

I f 1 ) t h e f o r c e y o u a p p l i e d i s IIIGH, a nd 2) m a t e r i a l m a g n e t i c p r o p e r t y i s YES, and 3 ) m a c h i n e s c r e w n e e d h i g h c o r r o s i o n r e s i s t a n c e i s YES, end 4) s c r e w d r i v e r I s CROSS-RECESSED, and 5) U s e d i n e l e c t r i c a l . c o n n e c t i o n i s HO, and 6 ) S o r e ~ a s s e m b l y ~ l t h w e l l f a s t e n e r c e n t e r and f l u s h s u r f a c e I s

Y E S , Then i t is d e f l n l t e (IOOX) t h a t A machine s e r e . Is S t a i n l e s s - m a r t e n s l t l c , C r o s s - r e c e s s e d f l a t l lead S c r e w .

*~ End - RETUR/t/E~tTER to e o n t t n u e | a | . | I

** End - R E T U R H / E H T E R t o c o n t i n u e i

FIGURE 6. The recommendation from the expert system for the machine screws on the outside plate of the electrical cabinet.

utilizing the existing capability of commun ica t i ng with the database m a n a g e m e n t program and the CAD graphical program in the PC-PLUS env i ronment . An- other research work is to development such a system on a Chinese expert system development tool for the industry applicat ion requi rement in Taiwan.

Acknowledgments--The authors wish to express their sincere grati- tude and appreciation to the Tjing-Ling Manufacturing Technology Research and Development Center, National Cheng Kung University for kindly providing the PC-PLUS expert system development tool during this study.

R E F E R E N C E S

Bonenberger, P.R., & Brooks, R.S. (1990). JDA, An expert assistant for bolted joint design. Proceedings of the Fourth Annual ESD

Expert Systems Conference (pp. 77-91). Detroit, MI: Engineering Society of Detroit.

Dym, C.L. (1985). Expert systems: New approaches to computer- aided engineering. Engineering with Computers, 1, 9-25.

Krishnamurthi, M., Underbrink, Jr., A.J., Wells, M.S., & Mayer, R.J. (1987). A prototype expert system for automobile fastener selection. Proceedings of the First Annual ESD/SMI Expert Sys- tems Conference for Advanced Manufacturing Technology (pp. 347-361). Detroit, MI: Engineering Society of Detroit.

Liebowitz, J. (1988). Introduction to expert systems. Watsonville, CA: Mitchell Publishing.

Long, M.W., Bailey, S.G., & Shawver, W.R. (1988). An expert system for mechanically fastened joint design. Proceedings of the 1988 ASME International Computers in Engineering Conference (Vol. 1, pp. 97-102). New York: ASME.

Texas Instruments Inc. (1987). Personal consultant plus manuals. Austin, TX: Texas Instruments.

Vogwell, J. (1990). Computer-aided component selection: A new and expanding research activity. Computer-Aided Design, 22(5), 308- 310.

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An expert system for machine screws selection in engineering design