夾具類外文翻譯-基于事例推理的夾具設(shè)計研究與應用【中文4050字】【PDF+中文WORD】,中文4050字,PDF+中文WORD,夾具,外文,翻譯,基于,事例,推理,設(shè)計,研究,應用,中文,4050,PDF,WORD Journal of Southeast University ( English Edition) Vol. 20 No. 2 June 2004 ISSN 1003 ) 7985 Application and development of case-based reasoning in fixture design Wang Qi1, 2 Liao Wenhe1 ( 1College of M echanical and Electrical Engineering , N anjing U niversity of A er onautics and Astronautics, Nanjing 210016, China) ( 2 Department of M echanical Eng ineering, Y ancheng Institute of T echnology , Yancheng 224002, China) Abstract: Based on the case-based designing ( CBD) methodology, the fixture similarity is in two respects: the funct ion and the structure information. T hen, the computer-aided fixture design system is created on case- based reasoning ( CBR) , in which the att ribut es of the main features of workpiece and struct ure of fixture as case index code are designed for the ret rieve of the similar cases, and the structure and hierarchical relation of case library are set up for st ore. M eanw hile, the algorithm based on the knowledge- guided in the retrieve of the similar cases, the strategy of case adaptation and case storage in which the case identificat ion number is used to dist inguish from similar cases are presented. The applicat ion of the system in some projects improves the design efficiency and gets a good result. Key words: case-based reasoning; f ixture design; computer aided design ( CAD) Fix tures are dev ices that serve as the purpose of holding the w orkpiece securely and accurately, and maintaining a consistent relationship w ith respect to the tools w hile machining. Because the fixture structure depends on the feature of the product and the status of the process planning in the enterprise, it s design is the bottleneck during m anufacturing, w hich restrains to im prove the ef ficiency and lead- time. And fixture design is a com plicated process, based on ex perience that needs comprehensive qualitative know ledg e about a number of desig n issues including w orkpiece conf iguration, manufacturing processes involved, and machining environment. This is also a very t ime- consum ing w ork w hen using traditional CAD tools ( such as Unigraphics, CATIA or Pro/ E ) , which are good at perform ing detailed design tasks, but prov ide f ew benefits for taking advantage of the prev ious design ex perience and resources, w hich are precisely the key factors in improving the efficiency. T he m ethodology of case- based reasoning ( CBR) adapts the solution of a previously solved case to build a solution for a new problem w ith the f ollow ing four steps: retrieve, reuse, revise, and retain[ 1] . This is a more useful method than the use of an expert system to simulate hum an thought because proposing a similar case and applying a few modifications seems to be sel-f Received 2003-10-22. Foundation items: The Nat ional H igh Technology Research an d Development Program of C hina ( 863 Program ) ( No. 2002AA 411030) , the Natural S cientific Research Program College of University of Jiangsu Province ( No. 03KJD520246) . Biographies: Wang Qi ( 1962 ) ) , male, doctor, associate prof essor, w qi003 @ sohu. com; Liao W enhe ( corresponding author) , male, doctor, professor, cnw ho@ nuaa. edu. cn. ex planatory and more intuitive to humans. So various case- based design support tools have been developed for numerous areas[ 2- 4] , such as in injection molding and design, architectural design, die- casting die design, process planning, and also in f ix ture design. Sun used six digitals to compose the index code that included w orkpiece shape, machine portion, bushing, the 1st locating dev ice, the 2nd locating device and clamping device[ 5] . But the system cannot be used for other f ixture types except for drill fixtures, and cannot solve the problem of storage of the same index code that needs to be retained, w hich is very important in CBR[ 6] . 1 Construction of a Case Index and Case Library 1. 1 Case index The case index should be composed of all f eatures of the w orkpiece, which are distinguished f rom dif- ferent f ix tures. Using all of them would make the op- eration in convenient. Because the f orms of the parts are diverse, and the technology requirements of m an- ufacture in the enterprise also develop continuously, lots of features used as the case index w ill m ake the search rate slow , and the main feature unimportant, for the reason that the relative weig ht w hich is allot- ted to every feature must diminish. And on the other hand, it is hard to include all the features in the case index. Therefore, considering the practicality and the demand of rapid design, the case index includes both the major feature of the w orkpiece and the structure of fixture. The case index code is m ade up of 16 dig- Application and development of case- based reasoning in fixture design 175 its: 13 digits for case features and 3 dig it s for case -i dentification number. T he first 13 digits represent 13 features. Each dig it is corresponding to an at t ribute of the feature, w hich m ay be one of / * 0, / ?0, / 10, / 20, ,, / A0, / B0, ,, / Z0, ,, etc. In w hich, / * 0 means anyone, / ?0 uncertain, / 00 nothing. T he system rules: fixture type, w orkpiece shape, locating model cannot be / * 0 or / ?0. When the system is designed, the at tribute information of the three it ems does not have these options, w hich means the certain at t ribute must be selected. And the default of the other at tributes of the feature is w orkpiece material as / 30 ( m iddle carbon steel) , batch size as / 20 ( middle batch ) , w orkpiece scale / 30 ( medium ) , workpiece w eight / 30 ( m iddle ) , w orkpiece toughness / 10 ( much stiff er) , machining content / 9 0 ( relative ) , process property / 3 0 ( finished machining ) , clamping method / ?0 ( uncertain) , and others ( They are degree, profile modeling, etc. ) / 00 ( nothing ) . And the default v alues can be changed by the system administrator. For / * 0 and / ?0, w hen in retrial, / * 0 means matching anyone, / ?0 means matching none of them, and w hen saved, the certain means of / * 0 and / ?0 must be g iven. The last three digits are the case identif ication number, w hich means the 13 digits of the case feature are the same, and the number of these three digits is used for distinguishing them, and saving them in the same case family if needed. The system also rules: / 0000 is a prototype case, which is used for retrieval, and other cases are / 0010, / 0020, ,, which are used for reference cases to be searched by designers. If occasionally one of them needs to be changed as the prototype case, f irst it must be required to apply to change the one to / 0000, and the former is changed to referential case automatically. The construction of the case index code is show n in Fig. 1. 1. 2 Case library The case library consists of lots of predefined cases. Case representation is one of the most important issues in case- based reasoning . So compounding w ith the index code, the structure of case library is show n in Tab. 1. Fig. 1 Construction of case index code Tab. 1 Structure of case library Field name Data type Description Case ID Auto number Specify the case. s place in case l ibrary Case index Verchar Case index code: * * * * * * * * * * * * * - * * * Fixture type Verchar 1) Lathe f ixt ure; 2) Drilling jig; 3) M illing fixture; 4) Boring fixture; , Workpiece shape Verchar 1) Box; 2) Shaft; 3) Round; 4) Sheat h; 5) Seat ; 6) Piston rod; 7) Frame; 8) Plate-shel; 9) Block; A) Compound; , 5) M iddle hardness aluminum; , Batch size Verchar * ) Random; 1) Large batch; 2) M iddle batch; 3) Low batch; 4) Few Workpiece scale Verchar 1) M uch bigger; 2) Bigger; 3) M edium; 4) Less bigger; 5) Small Workpiece w eight Verchar 1) M uch heavier; 2) Heavier; 3) M iddle; 4) Less heavy; 5) Light Workpiece toughness Verchar ?) Uncertain ; 1) M uch stif fer; 2) Stiff er; 3) M iddle; 4) Les st iff er; 5) W eak M achining content Process property Verchar Verchar 1) Cylinder; 2) End face; 3) H ole; 4) Plane; 5) Step plane; 6) Slot; 7) Pocket; 8) Hole of dril-l ream; 9) Relative; A) Compounding 1) Blank; 2) Unfinishing machining; 3) Finish machining Workpiece material Verchar * ) Anyone; 1) Cast iron; 2) Low carbon steel; 3) M iddle carbon steel; 4) Alloy steel; Locating method Verchar 1) 3plane; 2) 1plane+ 2pin; 3) Big plane+ short pin; 4) Long V+ plane; 5) Double V+ plane; 6) Long pin+ little plane; 7) Small taper shaft; 8) centred ?) Uncertain ; 0) Nothing; 1) T op clamping; 2) T op+ side clamping; 3) S ide clamping; 4) Tilted Clamping method Verchar clamping; 5 ) M ult-i point top clamping; 6) Compounded clam ping; 7 ) Centred clamping; 8 ) Vacuum clamping; , Fixture body Verchar ?) Uncertain; 1) Plan e; 2) Cast ing; 3) W elding; 4) Compounding Others Verchar ?) Uncertain ; 0) Nothing; 1) Horizon-move-divided degree; 2) Horizon-round- divided degree; 3) Radia-l round-divided degree; 4) Profile modeling; , Case identification number Verchar Case identificat ion number: 000; 001; , Case mapping Verchar T he location of case modeling stored in hard disk of com puter 1. 3 H ierarchical f orm of Case T he structure similarity of the f ix ture is represented as the w hole fixture similarity, components sim ilarity and component similarity . So the w hole f ix ture case library, com ponents case library, component case library of f ix ture are f ormed corresponding ly. Usually design information of the w hole fix ture is composed of workpiece information and w orkpiece procedure information, w hich represent the fixture satisfying the specifically designing function demand. The w hole f ix ture case is made up of function components, w hich are described by the function components. names, numbers, and relationship to object- workpiece which are the body of the knowledge. The com ponents case represents the members. ( function component and other structure components) main- driven parameter, the number, and their constrain relations. The component case ( the low est layer of the f ixture) is the structure of function component and other components. In the modern f ix ture design there are lots of parametric standard parts and common non- standard parts. So the component case library should record the specif ication parameter and the w ay in w hich it keeps them. The hierarchical form of the f ix ture case library is show n in Fig. 2. cut dow n the t im e of adaptation. According to the requirement of fixture design, the strategy of case retrieval combines the w ay of the nearest neighbor and know ledge- guided. That is, first search on depth, then on breadth; the knowledge- guided strategy means to search on the know ledge rule f rom root to the object, w hich is f irst ly searched by the f ix ture type, then by the shape of the workpiece, thirdly by the locating method. For ex ample, if the case index code includes the m illing fixture of f ix ture type, the search is just for all milling fixtures, then for box of w orkpiece shape, the third f or 1plane+ 2pine of locating method. If there is no match of it, then the search stops on depth, and returns to the upper layer, and retrieves all the relative cases on breadth. Retrieval algorithms: 1 According to the case index information of f ix ture case library, search the relevant case library; o M atch the case index code w ith the code of each case of the case library, and calculate the value of the sim ilarity measure; ? Sort the order of similarity measure, the biggest value, w hich is the most analogical case. Sim ilarity betw een two cases is based on the similarity between the two cases . features. T he calculation of similarity measure depends on the type of the feature. The value of similarity can be calculated for num erical values, for example, compare w orkpiece with the w eight of 50 kg and 20 kg . T he value can also be calculated betw een non- numerical values, for example, now the first 13 digits index code is all non- numerical values. It is important that a CBR system supports a multitude of sim ilarity measure, and, ideally, allows the definition of new types. The sim ilarity measure of a f ix ture is calculated as follow s: n E ( w i si ( f ai , f bji ) ) i= 1 S = n E w i i= 1 i = 1, 2, ,, n Fig. 2 Hierarchical form of fix ture case library 2 Strategy of Case Retrieval In the case- based desig n of fixtures, the most important thing is the retrieval of the similarity, w hich can help to obtain the most sim ilar case, and to w here S is the similarity measure of current fixture, n is the number of the index feature, w i is the w eight of each f eature, si ( f ai , f bji ) is the sim ilarity measure of the at tribute f ai of the i- th feature w ith the attribute f bj i of relative feature of the j- th case in the case library . At the same t ime, 0 [ si ( f ai , f bji ) [ 1, the value counts as follows: If ( f ai and f bji are non- numerical values) If ( f ai = f bji ) si ( f ai , f bji ) = 1; Else si ( f ai , f bj i ) = 0; If ( f ai and f bj i are numerical values) f ai - f bj i so the case is not saved because it is represented well by the prototype case. Or is just saved as a reference case ( the last 3 digits are not / 0000, and not the same with si ( f ai , f bj i ) = 1- max( f ai , f bj i ) . others) in the case library. w here f ai is the value of the index at t ribute of the i- th feature, and f bj i is the value of at tribute of the relative i- th f eature of the j- th case in case library. So there are two methods to select the analogical fixture. One is to set the value. If the values of similarity measure of current cases were less than a given value, those cases would not be selected as analogical cases. When the case library is init ially set up, and there are only a few cases, the value can be set smaller. If there are lots of analogical cases, the value should get larger. The other is just to set the number of the analogical cases ( such as 10) , which is the largest value of similarity measure from the sorted order. 3 Case Adaptat ion and Case Storage 3. 1 Case adaptation The modification of the analog ical case in the fixture design includes the f ollowing three cases: 1) T he substitution of components and the component; 2) Adjusting the dimension of components and the component w hile the form rem ains; 3) T he redesig n of the model. If the components and component of the fixture are com mon objects, they can be edited, substituted and deleted with tools, w hich have been designed. 3. 2 Case storage Before sav ing a new fixture case in the case library, the designer must consider w hether the saving is valuable. If the case does not increase the know ledge of the system, it is not necessary to store it in the case library . If it is valuable, then the designer must analyze it before sav ing it to see w hether the case is stored as a prototy pe case or as reference case. A prototy pe case is a representation that can describe the main features of a case f amily. A case family consists of those cases w hose index codes have the same f irst 13 digits and different last three dig it s in the case library. The last three digits of a prototy pe case are alw ays / 0000. A reference case belongs to the same family as the prototype case and is distinguished by the different last three digits. From the concept that has been ex plained, the follow ing strategies are adopted: 1) If a new case mat ches any existing case family, it has the same first 13 digits as an existing prototype case, 2) If a new case matches any existing case family and is thought to be better at representing this case family than the previous prototype case, then the prototype case is substit uted by this new case, and the previous prototype case is saved as a reference case. 3) If a new case does not match any existing case f amily, a new case family w ill be generated automatically and the case is stored as the prototype case in the case library. 4 Process of CBR in Fixture Design According to the characteristics of f ix ture design, the basic information of the fixture design such as the name of f ix ture, part, product and the designer, etc. must be input first . T hen the f ix ture f ile is set up autom at ically, in which all components of the fixture are put together. Then the model of the w orkpiece is input or desig ned. The detailed information about the workpiece is input, the case index code is set up, and then the CBR begins to search the analogical cases, relying on the sim ilarity measure, and the most analog ical case is selected out. If needed, the case is adapted to satisfy the current design, and restored into the case library. T he f low chart of the process is show n in Fig. 3. Fig. 3 Flowchart of case- based reasoning for fixture deign 5 Illustrating for Fixture Design by CBR This is a workpiece ( see Fig. 4) . Its material is 45# steel. Its name is seat. Its shape is block, and the product batch size is middle, etc. A f ix ture is turning fixture that serves to turn the hole, w hich needs to be designed. The value of f eature, at tribute, case index code and w eight of the w orkpiece is show n in Tab. 2. The similarity is calculated as follow s: S= 1@ 100+ 1 @ 90+ 2 @ 1 @ 70+ 5 @ 1@ 60+ 2 @ 1@ 80+ 0 @ 100+ 0 @ 90 100+ 90+ 70+ 60+ 60+ 60+ 60+ 80+ 70+ 100+ 90+ 80+ 60 = 790= 0. 806 980 Fig. 4 A workpiece requested to design a fix ture ( M aximum size is 80 mm @ 49 mm @ 22 mm) Tab. 2 T he case index code and w eight of workpiece Feature name At tribut e value Index code We ig ht Fix ture ty pe La the fixt ure 1 100 Workpiece shape Block 9 90 Workpiece ma terial M iddle carbon steel 3 70 Bat ch size M iddle 2 60 Workpiece scale Small 5 60 Workpiece weight L ig ht 5 60 Workpiece toughness M uch stiffer 1 60 Machining content Hole 3 80 Pro cess propert y F inish machining 3 70 L ocating method 3plane 1 100 Clam ping method Uncert ain ? 90 Fixt ure body Compounding 4 80 Others No thing 0 60 T hrough searching, and calculating the similarity, the case index code of the most similar case is 1932551332140- 000, and the detailed information is shown in Tab. 3. Feature name Attribute value Index code Fixture type Lathe f ixture 1 W orkpiece shape Block 9 W orkpiece material M iddle carbon st eel 3 Batch size M iddle 2 Workpiece scale Small 5 W orkpiece w eight Light 5 W orkpiece toughn ess M uch st if fer 1 M achining content Hole 3 Process property Finish machining 3 Locating method 3plane 2 Clamping m ethod Uncertain 1 Fixture body Compounding 4 Others Nothing 0 Tab. 3 Case index code of t he most similar case So the value of similarity measure of the f ix ture w hich needs to be designed w ith the most analog ical case in case library is 0. 806, and the structure of the most analogical case is show n in Fig. 5. Fig. 5 M ost analogical fixture After having been substituted the com ponent, modified the locating model and clamp model, and adjusted the relative dimension, the new fix ture is designed, and the fig