«Parametrics REFERENCE GUIDE All rights reserved. No part of this documentation may be reproduced in any manner (print, photocopy ...»
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TABLE OF CONTENTS
Please note: Illustrations showing menus and forms are taken from a window system.
The display for other platforms can differ slightly.
Online User Documentation (HTML) Online documentation for each book is provided in HTML format. You can view this online documentation in the MEDUSA installation directoryand directly by calling it up within the MEDUSA user interface.
1. Navigate to the directory where MEDUSA is installed.
MEDUSA installation directory/meddoc/doc/language/ (Unix) MEDUSA installation directory\meddoc\doc\language\ (Windows) where language is either english, german or french.
2. Click on the file mainmenu.htm.
3. Click the book title you want to view.
1. Click left on the entry Help inside the main menu.
2. Choose MEDUSA Documentation from the pulldown menu.
A browser opens showing the mainmenu.htm listing all available documents.
Printing Version of the Documentation (PDF) A PDF (Portable Document Format) file is included for each online book. You must have Acrobat Reader installed to view and print PDF files. If you don‘t have the Acrobat Reader, you
can download it for free from the Adobe homepage:
http://www.adobe.com/products/acrobat/readstep.html In order to search for a keyword across PDF files you can use Acrobat Reader. Therefor Acrobat Reader Version 6.0 or higher has to be installed. The Reader provides a multiple search function, i.e. you can specify complete directories containing several PDF files for searching.
This chapter describes the general principles of the MEDUSA Parametric Design system.
• Preparing a Drawing for Parameterization
• Parameterizing Object Geometry
• Advanced Features of Parametric Design
• Giving Commands in Parametric Design
Preparing a Drawing for Parameterization To parameterize geometry using the MEDUSA Parametric Design system you must prepare the geometry in a special way. In addition to the geometry that is to be parameterized the sheet
must contain the following:
• A parametric viewbox
• A datum or reference point
• Dimensioning The system uses a parametric grid to move points in the object geometry. You place some or all of the points in an object onto intersections on the grid. You then supply new parameters for the object geometry and the system uses these parameters to calculate the new position of each grid intersection when you give the PARS command. During parameterization, each point in the object geometry is positioned at the new grid intersection.
Any geometry that you want to parameterize must be inside a Parametric viewbox. A viewbox can be any shape, but must consist of straight line segments of line type LPV. The following figure shows a drawing of a rivet, enclosed in a rectangular parametric viewbox.
Figure 1 Parametric Viewbox Containing Definition of a Rivet
Reference Points Inside every parametric viewbox you must place a reference point or datum. The reference
• Provides a static point of reference for all moving points during parameterization
• Can be anywhere inside the viewbox: it does not have to be a physical point on the object geometry.
Points of object geometry move during parameterization in relation to the position within the viewbox of the reference point. The reference point does not move during parameterization.
Creating a reference point: Use either a special prim or a pair of intersecting static baselines, line type LBL to create a reference point. In the following figure, a pair of static baselines define a reference point for the rivet drawing. In this example, the reference point does not coincide with a point on the object geometry but is at a center of symmetry.
Figure 2 Rivet With Reference Point Please note: A grid line intersection is generated at the point on the sheet where you create a reference point. This is the starting point for the parametric grid.
For more information about using reference points see “Reference Points” on page 19.
Parametric Grid Lines Parametric Design works not by moving individual points but by moving a grid upon which all movable points are placed. Grid lines are line type STK, and can be oriented at any angle and spacing. To display parametric grid lines, use the PAR GRIS command. “The Parametric Grid” on page 59, describes the commands available for looking at different types of parametric grid lines.
The following figure shows the result of a PAR GRIS command. The static baselines generate two grid lines.
Reference points and the grid: A grid line intersection is created at the point where you place the reference point. This is the starting point for the rest of the parametric grid. To build the grid outwards from the reference point, you must dimension the object points.
Dimensioning the Object Points Dimensions are necessary to build up the grid. To place a point on the grid you must dimension it using one of the standard MEDUSA dimensioning commands. Each dimension requires one or more existing grid lines to support it, so you usually begin dimensioning from the reference point.
Figure 4 Rivet With Dimensioning and Grid Each time you add a new dimension clump, you can use the PAR GRIS command to check that the point you have dimensioned has been placed onto a grid intersection successfully. When you have dimensioned the object adequately, all moveable points will be at grid intersections, as in the above figure. You can now define a new set of object parameters. “Dimensioning” on page 27, explains some useful dimensioning techniques.
Defining your Own Parameters
To define new object parameters, you edit the dimension clump and replace the original dimension value with one of the following:
• Another numeric value
• A variable or an expression The following figure shows the rivet with new parameters, before parameterization.
Figure 5 Original Rivet Definition with New Parameters
Parameterizing Object Geometry When you have checked that the object points are at grid intersections and you have defined some new object parameters, the geometry is ready for parameterization.
Parameterization Commands You have to give just one command to parameterize geometry. This is the PARS command.
When you give this command, the system tries to parameterize all geometry which is inside a parametric viewbox. The new parameters you have defined are used to calculate new positions for each grid intersections. The object points are then moved to the new grid intersection positions.
The following figure shows the rivet after parameterization with new dimension values.
Figure 6 Rivet After Parameterization
Parameterizing a Drawing Using Parametric Design
To create parameterized versions of a drawing using Parametric Design, follow this procedure:
1. Draw a parametric viewbox around the object you want to parameterize.
2. Choose a datum or reference point that will remain static.
3. Decide if all or part of the object is to be parameterized.
4. Dimension the object to put all the relevant points onto the parametric grid.
5. Check that all movable points of the object lie at grid intersections.
6. Exclude some parts from parameterization, if desired.
7. Replace dimension values with your own parameters.
8. Parameterize the object using the PARS command.
9. Check the result.
Advanced Features of Parametric Design The following features enable you to perform more complex parameterization operations.
Parametric symbols Parametric symbols enable you to parameterize complex assemblies using several simple part definitions. For example, the parameterized drawing of a crankcase may refer to a number of standard fittings such as bolts and washers. You can define each fitting as a parametric symbol which includes the part geometry and a reference to the values needed to provide the correct size of fitting. The whole range of symbols is then derived simply by supplying different parameters when loading the symbol onto a sheet. See “Parametric Symbols” on page 111, for information on how to create and use parametric symbols.
Tables allow you to easily set several parameters of an object at the same time. After drawing and dimensioning a single part pattern and supplying variable dimension values, you can then place a table on the sheet with all the parameter values of that range of parts. During parameterization, the system reads the appropriate values from the correct line in the table and uses these values to parameterize the standard part definition.
The use of tables for parameterization is described in “Tables” on page 129.
Only geometry that is inside a parametric viewbox will be transformed during parameterization.
Geometry that is outside the viewbox will not be affected by any Parametric Design commands.
You can change the way that parts of geometry within a viewbox are transformed with parametric groups. Using parametric groups you can:
• Completely exclude parts of the drawing from parameterization
• Parameterize parts of a drawing without having to dimension them fully Geometry within a parametric group is treated as a single entity. Parametric groups can remain static or can be moved, magnified and rotated as a whole during parameterization. This allows you to handle details such as shaft ends and bolt holes simply.
See “Parametric Groups” on page 139, for more information.
Mechanisms You can use Parametric Design to study the movement of mechanisms. By repeatedly parameterizing a dimensioned drawing of a mechanism you can simulate its movement as it is redrawn on the screen at regular intervals. Whenever the mechanism is redrawn in a new position, its
previous positions remain visible, enabling you to investigate potential clashes between different parts of the mechanism.
See “Mechanisms” on page 159, for more information on using Parametric Design to simulate the movement of mechanisms.
Giving Commands in Parametric Design
There are two ways of giving MEDUSA commands:
• By typing the command at the keyboard (interactively)
• By placing in-sheet command text, text type TCO, on the sheet You can give any of the Parametric Design commands described in this manual (except the VER FULL command) both interactively and as in-sheet commands. When you enter a command interactively, the command is executed immediately. In-sheet commands are executed when you give the PARS command.
Why Use In-sheet Commands?
The advantage of using in-sheet commands is that they are stored with the sheet, so that, for example, special switch or layer settings or variable values are always used with a particular drawing. In-sheet commands only affect the viewbox in which you place them, so other viewboxes and other sheets are not affected by the commands in any one viewbox. After parameterization, parameters set with in-sheet commands are restored to the values held before parameterization. When you use Parametric Design, use in-sheet commands rather than interactive commands where the effects are global rather than local.