1 / 25

KP3213 CAD/CAM

This lecture focuses on the principles of constraint-based modeling in CAD/CAM, emphasizing how user-defined constraints can reflect design intent, allowing for automatic geometry regeneration. It covers the concepts of parametric and variational modeling, explaining the differences in how constraints are applied and solved. Additionally, the lecture highlights various types of constraints—including ground, dimensional, and geometric—and discusses the importance of CAD standards such as IGES, DXF, and STEP for effective communication in CAD environments.

sigourney
Télécharger la présentation

KP3213 CAD/CAM

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. KP3213 CAD/CAM • Snapshot Lecture 5 • Objective of Lecture 6 • Understand constraint modeling • Learn CAD Standard • Lecture 6

  2. Constraints and Variational Modelling

  3. Constraint-based Modelling • User constrains geometry based on Design Intent • Design variations can be generated by changing a few key dimensions • Geometry is automatically regenerated based on constraints

  4. D5 D1 D2 D4 D3 Example

  5. Design Intent • The part should be twice as long as it is wide • The hole should be centred in both directions • The hole diameter should be 50mm

  6. Parametric and Variational Modelling • Parametric modelling • constraints defined sequentially • each constraint calculated based on previously defined constraints • order of constraint specification is important • Variational modelling • constraints solved simultaneously • order of constraint specification doesn’t matter

  7. Parametric Definition User specifies dimension D1, other dimensions calculated sequentially

  8. Variational Definition Solve system of simultaneous equations:

  9. Constraint Types • Ground constraints • Dimensional constraints • Geometric constraints

  10. Ground Constraints • Horizontal • Vertical • Both ends fixed • Point location • X of point • Y of point • Angle of line

  11. Dimensional Constraints • Horizontal dimension • Vertical dimension • Linear dimension • Angular dimension • Radial dimension

  12. Geometric Constraints • Parallel • Perpendicular • Tangent • Collinear, coincident, coplanar

  13. Modelling Approach • Sketch approximate geometry • Generate solids and features • Add constraints and dimensions afterwards

  14. Smart Sketching • Most CAD systems use “smart” sketching tools • Design intent is inferred, and constraints added automatically • For example, two lines that are nearly perpendicular “snap” perpendicular, with a constraint

  15. CAD Standard

  16. CAD Standard • Too many ways, need for standardization • Understand the graphic kernel system and its extension for developing graphic software system • Understand IGES, DXF and STEP • Dimensional measurement interface specs for communication between coordinate measuring machine and CAD data

  17. Standardization • GKS Graphical Kernel System • PHIGS Programmer’s Hierarchical Interface for Graphics • IGES Initial Graphics Exchange Specification • DXF Drawing Exchange Format • STEP Standard for the Exchange of Product Model Data • DMIS dimensional Measurement Interface Specification • VDI Virtual Device Interface • VDM Virtual Device Metafile • GKSM GKS Metafile • NAPLPS North American Presentation Level Protocol Syntex

  18. GKS Graphical Kernel System • It is very difficult for a program developed for a particular system to run on different system • However, substantial portions of it is similar • Same codes are rewritten many times • Program interchangeable is created • ISO has standardized GKS for 2D in 1982 with objectives: • Complete range of 2D facilities including interactive • Control graphics devices such as plotter and display devices • Small enough for variety of program • GKS 3D standards developed to cover which were not covered by GKS • GKS has been enhanced to provide separate stand for 3D

  19. PHIGS Programmer’s Hierarchical Interface for Graphics • Accepted by CAD vendors as system capable of 3D • Features in PHIGS not covered by GKS is as follows: • Very high interactivity • Hierarchical structuring of data • Real time modification pf graphics data • Support of geometry animation • Adaptability to distributed user environment

  20. NAPLPS North American Presentation Level Protocol Syntex • Presentation standard developed by the Canadian government with AT&T and other telcos • Basis of transferring data from computer to video displays systems such as tele-text and other video presentations systems • Is a means of encoding graphic data and text in electronically transferable format (ASCII) • Features: • Very compact (10% more compared with other format) • Resolution will be clearer • Integrated with communication networks • Large range of colors

  21. IGES Initial Graphics Exchange Specification • Most comprehensive standards and is designed to transmit the entire product definition including that of manufacturing and any other associated information • IGES file contains 6 sub-sections • Flag Section – ASCII format. Version 3 onward standardized as follows (ASCII default, binary form and compressed ASCII) • Start Section – man-readable prologue. Information contain is essentially for the person who would be processing this for other application. • Global Section – Contains info. about detail of the product, originator, company , date, drafting standards etc. • Directory Entry Section – Each entiry present is fixed in size contains 20 fields and 8 character each. To provide an index for the file and to contain attribute information such as color, line type transformation matrix etc. • Parameter Data Section – contains data associated with entities. A free format is allowed for maximum convenience. Also contains pointers. • Terminate Section – Contains the sub-totals of the records present. This would always contains a single records. It is possible that some design technique is lost.

  22. STEP Standard for the Exchange of Product Model Data • ISO standard 10303 (Product Data Representation and Exchange) • Able to share data across application, vendor platform between contractor, suppliers and customers • Scope: • Standard method representing info. Necessary for completely defining a product throughout the entire life cycle • Standard method for exchanging data electronically between two different systems • Overview – general introduction and overview part one of standard 10303 • Description methods - the application protocols planned in STEP are far-reaching compared to existing standards • Implementation methods – Specifications how STEP information physically represented for exchange environment. Refer to actual implementation levels.

  23. STEP Standard for the Exchange of Product Model Data • Conformance and tools – Provide specifications and conformance testing of the processors used for STEP information. • Integrated generic resources – Contains the specifications of the information models that support various application areas. Includes geometric and topological representation, product structure organization, material, visual representation, etc. • Application information models – These specify the information models to be used for specific application • Application protocols – Defines the context for the use of product data for a specific industrial needs.

  24. DXF Drawing Exchange Format • DXF has been developed and and supported by AutoDesk for use with the AutoCAD files • The drawing interchange file is ASCII • Overall organization: • HEADER section – contains general information about the drawing similar to the global section of IGES. Consists of AutoCAD database version number of system variables. • CLASSES section – Holds information for the application-defines classes. • TABLES section – contains definition of symbol tables such as line-tables, layer table text style table etc. • BLOCK section – contains symbols • ENTITIES section – contains graphical objects • OBJECTS section – Contains non-graphical. Examples are dictionaries that contain mline (multiple line styles and groups.

  25. Book Review for Week 3 • CAD/CAM Principles and Application 2nd edition by PN Rao Published by Mc Graw Hill • Chapter 8 Finite Element Analysis. Find other books that is relevant to FEM because we will do some detailed calculation

More Related