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Journal of Intelligent Manufacturing (1994) 5, 47-54 Object-oriented design support system for machine tools TOSHIMICHI MORIWAKI and MASAYUKI NUNOBIKI Faculty of Engineering, Kobe University, Rokko, Nada, Kobe, 657, Japan Received March 1992 and accepted January 1993 This paper deals with an object-oriented intelligent design support system which is intended to assist in the basic design of machine tools, in particular machining centres. The machine tools design process is analysed through interviews with experienced designers, and an object-oriented model is established to represent the design process. Software modules named design objects are proposed, which are basic components for the implementation of an intelligent design support system for machine tools. A prototype of the design support system for machining centres is developed based on the design objects, and some case studies are carried out to verify the effectiveness of the methods proposed. Keywords: Object-oriented, design support system, machine tools, design process, design object I. Introduction Presently, various types of machine tools are required to cope with the small-batch manufacture of a wide variety of products. It is therefore necessary to establish a design support system which can assist the designers of machine tools, in the logical and systematic design of various types of machine tools. The machine tools design process is a very complicated decision-making process which requires the know-how of experienced designers. It is, therefore, very important to develop an intelligent design support system for the machine tools which utilizes the know-how of the experienced designers effectively. There are various intelligent CAD systems and expert systems to carry out routine design of machine products in which the structures of the products are fixed and the standard methods for designing various parts are known. Brown and Chandrasekaran have developed the AIR- CYL system which assists the design of various air cylinders (Brown et al., 1986). Mittal et al. (1986) have proposed the PRIDE system which designs paper-hand- ling systems. The products dealt with in these cases are mainly the components of products, and their structural configurations are almost fixed. This paper deals with the design of machine tools, especially machining centres, which are typical examples 0956-5515 ) 1994 Chapman & Hall of complicated machine products. The machine tools have various structural configurations to cope with the wide range of machining functions. Some research on the design of machine tools has already been carried out. Systematic methods have been proposed in order to develop basic design systems for machine tools based on analysis of the shape generation process (Salje and Redeker, 1980; Iwata et al., 1990). Some structural design systems have also been developed, which deal with the design of basic structures of modular type machine tools (Shinno and Ito, 1984; Shinno and Ito, 1986). A knowledge based system has been developed to determine the types of machining centres from the functional requirements (Moriwaki and Nunobiki, 1990). However, most of the systems deal mainly with design problems in which the design parameters of the machine tools are predetermined at the beginning of the design stage. The objective of the present research is to develop an intelligent design support system which assists the basic design of machine tools, in particular machining centres. The design process of machine tools is analysed through interviews with experienced designers, and an object- oriented model is established to represent the design process. Software modules, named design objects, are proposed, which are basic components for the imple- mentation of an intelligent design support system for 48 Moriwaki and Nunobiki machine tools. A prototype design support system for the machining centres is developed based on the design objects, and some case studies are carried out to verify the effectiveness of the methods proposed here. 2. Object-oriented design process model for machine tools 2.1. Analysis of design process The machine tools design problem is recognized as an ill-structured problem, since the design parameters of the machine tools cannot be clarified without information concerning the configurations of the machine tools. The following are clarified through interviews with experi- enced designers, taking the machining centres as exam- ples of machine tools to be designed: (1) The designers first select a suitable machining centre configuration based on the requirements; (2) Two methods are applied to select a suitable configuration: specialization of the configurations and division of the configuration into the components; (3) When a suitable configuration is selected, the design parameters to be determined are clarified. These parameters can be determined systematically and logical- ly based on the requirements. The machining centres design process is represented by a series of phases, each of which consists of two steps, selection and design, as shown in Fig. 1. In the figure, the machine products are the objects to be designed. The machine products include such objects as the machines, units, components and parts, which should be designed. All the machine products are called pro- ducts, hereafter. Each step may be described as follows: STEP 1: selection of a suitable type of product A suitable configuration of the product is selected based on the requirements of the product. When a particular configuration is selected, a set of design parameters of the product is given. STEP 2: design of selected type of product The product is designed by determining all the design parameters of the selected type of product based on the requirements. Steps 1 and 2 are repeated until the geometric and technological information on the products is determined. 2.2. Design process model with design objects Software modules named design objects are proposed here to carry out the design of individual types of products, such as machining centres and components of / Product model 1 t / Selection of type of product Specialization I Type of product to be designed I , Design of product r Product model 2 - Selection of type of product g Specialization Type of product to be designed I i , Design of product , s Product model 3 Fig. 1. Design process. machining centres. The individual design objects have one-to-one correspondence with the individual types of products. The design objects are equivalent to the class objects in the object-oriented paradigm. The design objects represent the information and processes concern- ing the design parameters of the individual products to be designed. The products include both the machining centres and their components, such as spindle units, ATC (automatic tool changer) units and feed units. The tasks of the design objects are to determine the design parameters of the products to be designed and to select suitable design objects for the products to be activated in the next design phase. Figure 2 shows an example of the design process model expressed by design objects. The classification schema shown here is obtained through interviews with experi- enced designers of conventional machining centres. In the figure, the ellipses represent the design objects, which are connected by a set of generalization-specializa- tion links. The design object for the machining centre is first activated by a message to start the design process. The design object determines the parameters of the machining centre and generates its instance, which is represented by a box in the figure. Following this, the design object for the machining centre tries to select a design object in order to specialize the instance. In the case of Fig. 2, the design object for the vertical machin- ing centre is selected to determine the detailed design parameters of the instance. Thus, the selection of a suitable design object is equivalent to the selection of a specialized type of product, and the design of a selected type of product is Object-oriented design support system machine ) . tls Jis_ a sign for ,. en;res ) y lathes ) Design of a - machine tool t . Product model? is_a -.La of machine tool I Selection of a type is_a ecilia - - of machine tool Spvtin Design of a I Pro0ootmo0el o, machine too, 1 . , Selection of a type I 7 . of maclinltil Specialization 7 Design o .,= machine tool I Product model 3 I of machine tool Fig. 2. Design process model using design objects. () Design object; - instance. 49 equivalent to the generation of an instance of that design object. The detailed information on the instance is determined as the design progresses according to the generalization- specialization links, until all the parameters needed are determined. The instance specialized here in the figure is VMC type 1, which is one type of vertical machining centre. Most of the machining centres can be designed by activating the design objects according to the generaliza- tion-specialization links as shown in Fig. 2. However, the design objects may not find any conceived design objects suitable for the requirements in some cases. For instance, neither the vertical machining centre nor the horizontal machining centre satisfies the requirements for simul- taneous five-axis machining. In such cases, the designers generally divide the machining centre into such compo- nents as spindle units, ATC units and feed units, for example, and the detailed information on these compo- nents is determined in the next phase. The design objects for the components are needed to carry out the design. The design process model of the machining centres is summarized in Fig. 3 based on the design objects proposed here. The nodes and the links show the design objects and their relations, respectively. Two types of links are considered here-the generalization-specializa- tion links, which are the same as those presented in Fig. 2, and the whole-part links describing the relations between the whole products and their components. The design of the machining centres is carried out based on the model shown in Fig. 3 as follows. The design object of the machining centre is firstly activated, and the design parameters are determined. Following this, one of the design objects connected to the design object for the machining centre is activated in order to advance the design process. The design object activated here is either a design object for a specialized product or a design object for a component. The design process is advanced by activating the design objects according to the generalization-specialization links and the whole- part links. 3. Design objects for machining centres The contents of the design objects for the products are summarized as follows: (1) Attributes representing the products to be de- signed; (2) Knowledge needed to determine the attributes; (3) Knowledge needed to select specialized products and components. 50 Moriwaki and Nunobiki Machine tools 1 / Machine tool feed unit design VMC r V.T. spindle MC ; Feed unit with tool spindle, work table Work table feed unit ) ,/ Feedwithunit X) . V.W. table, ( TOOl spindle feed unit V.T. spindle feed unit Linear feed mechanism Fig. 3. Design objects and their relations for the design of machining centres. whole-part link. - Generalization-specialization link; - The design objects determine the attributes of the products using their own knowledge. A schema shown in Fig. 4 is proposed to represent knowledge of the design objects. This consists of three sections-the ID section, the attribute section and the method section The name of the design object and the relations to the other design objects are specified in the ID section. The attribute section defines the attributes of the instances, which are basically classified into the specifica- tions and the design parameters. The specifications give the functions and the performances required of the products to be designed, and the design parameters are the attributes to be determined based on the specifica- tions. The procedures and the knowledge needed to determine the values of design parameters are attached as the demons. An individual piece of information is represented as a tuple of AttributeName, Facet, Value. Some attributes have several facets, such as value, type, range, default, if_needed and so on. The last section gives the methods, which are executed when the messages from the other design objects are received. The design objects use the following methods to control the design process: (1) Determination: the method for determining the design parameters of the instances; ID Section Name of Design Object : * Type of Object : class Super Class : * Attribute Section Attributes : Attributel,value,* Attribute2,range,* Attribute2,default,* AttributeN,value,* Method Section Method for determination of design parameters Method for selection of design object Method for specialization of design object Method for division of design object Methodl,method,* Methodl,rule,* Methodl,table,* Fig. 4. Schema of design object. Object-oriented design support system 51 Message Message (with design constraints) Determination of design parameters Backtrack Specialization specialized object I Division I Selection of Selection of I subobjects Seodmessagoto 1 Sed messages to I specialized object subobjects Message Messages Fig. 5. Design process of a design object (2) Specialization: the method for specializing the configurations of the instances and for selecting suitable specialized design objects; (3) Division: the method for dividing the instances into components and for selecting suitable design objects of the components Figure 5 shows the design process of the individual designs. The values of the design parameters of an instance are firstly determined based on the specifications sent to the instance. Secondly, the designers examine whether or not the instance generated by the design object suits the spe- cifications. The designers can modify the contents of the instance if necessary. Thirdly, suitable design objects are selected to advance the design of the instance The design objects selected here are either a design object for a specialized product or a set of design objects for the components. In the selection of a design object for a specialized product, alternative structural configurations may be obtained. The most suitable configuration among the alternatives is selected as follows: the priorities among the alternatives are determined by referring to the tables, which deter- mine the rank of all the alternatives from several viewpoints, such as the machining accuracy, the cutting performance, the operability and the reliability. The most suitable configuration is then selected by the designers based on the ranks of alternatives Fourthly, the instances of the selected design objects are generated Finally, the messages are transmitted to the specialized instances or the instances of the components The mes- sages include information on the specifications and the constraints on the generated instances. Figure 6 shows examples of the execution of methods and demons In the figure, message determination is sent to prototype, which is an instance of vertical machining centre The instance named prototype then searches for a suitable method, and the method deter- mination of the design object for the vertical machining centre is activated consequently. The method determina- tion refers to the design parameters needed to define the instance named prototype, and activates if_needed de- mons. Each demon determines the value of the design parameters, and puts the result in the instance named prototype. 4. Object-oriented intelligent design support system A prototype intelligent design support system for machining centres has been developed based on the design objects. The basic structure of the system is schematically illustrated in Fig. 7. The system consists of five subsys- tems-the design object base, the object manager, the inference engine, the procedure base and the man- machine interface The contents and the functions of individual subsystems are summarized as follows. (1) Design object base. This subsystem stores all the design objects concerning the machining centres and Class : VMCType4 (Method Name) (Procedure) division divide . makeComponents : oo mkWP Link(Prototype) maomponents I Class: TiSpindle I Instance : Prototype / consist_of : txgolSpindle, oompol, Instanoe : Compol I flatTable, compo2 protOty- Fig. 6. Execution of methods and demons 52 Moriwaki and Nunobiki Object manager I Inference engine User Man-machine interface I Fig. 7. Structure of design support system. determine the design parameters and to select suitable design objects; (4) Procedure base. The procedure base is a collection of procedures which can be used directly by the design objects; (5) Man-machine interface. This subsystem provides the designers with the interactive methods to input the data, and also the methods to monitor the status of the designed products and the inference process. A prototype intelligent design support system has been implemented in K-PROLOG on a 32 bit engineering workstation (SONY NEWS model NWS-831). The indi- vidual design objects are represented by a set of clauses each of which has the same heading shown in Fig. 8. The identifier of the object is a functor which has the name of the object and four arguments. These arguments are slot, facet, value and unspecified argument. Each of these clauses declares a piece of information about the object to be designed. The attributes are represent

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