Catia

Mechanism Design & Animation
(Releases 14 & 15)

CATIA V5 Tutorials

Nader G. Zamani
University of Windsor

Jonathan M. Weaver
University of Detroit Mercy

PUBLICATIONS

Schroff Development Corporation www.schroff.com
www.schroff-europe.com

SDC

CATIA V5 Tutorials in Mechanism Design and Animation

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Chapter 4 Copyrighted Slider Crank Mechanism Material

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CATIA V5 Tutorials in Mechanism Design and Animation

Introduction

In this tutorial you create a slider crank mechanism using a combination of revolute and cylindrical joints. You will also experiment with additional plotting utilities in CATIA.

1 Problem Statement

A slider crank mechanism, sometimes referred to as athree-bar-linkage, can be thought of as a four bar linkage where one of the links is made infinite in length. The piston based internal combustion is based off of this mechanism. The analytical solution to the kinematics of a slider crank can be found in elementary dynamics textbooks. In this tutorial, we aim to simulate the slider crank mechanism shown below for constant crank rotation and to generateplots of some of the results, including position, velocity, and acceleration of the slider. The mechanism is constructed by assembling four parts as described later in the tutorial. In CATIA, the number and type of mechanism joints will be determined by the nature of the assembly constraints applied. There are several valid combinations of joints which would produce a kinematically correct simulationof the slider crank mechanism. The most intuitive combination would be three revolute joints and a prismatic joint. From a degrees of freedom standpoint, using three revolute joints and a prismatic joint redundantly constrains the system, although the redundancy does not create a problem unless it is geometrically infeasible, in this tutorial we will choose an alternate combination of joints bothto illustrate cylindrical joints and to illustrate that any set of joint which removes the appropriate degrees of freedom while providing the capability to drive the desired motions can be applied. In the approach suggested by this tutorial, the assembly constraints will be applied in such a way that two revolute joints and two cylindrical joints are created reducing the degrees of freedom arereduced to one. This remaining degree of freedom is then removed by declaring the crank joint (one of the cylindrical joints in our approach) as being angle driven. An exercise left to the reader is to create the same mechanism using three revolute joints and one prismatic joint or some other suitable combination of joints. We will use the Multiplot feature available in CATIA is used to create plotsof the simulation results where the abscissa is not necessarily the time variable.

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Cylindrical Revolute Revolute

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Cylindrical

Slider Crank Mechanism

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2 Overview of this Tutorial

In this tutorial you will: 1. Model the four CATIA parts required. 2. Create an assembly (CATIA Product)containing the parts. 3. Constrain the assembly in such a way that only one degree of freedom is unconstrained. This remaining degree of freedom can be thought of as rotation of the crank. 4. Enter the Digital Mockup workbench and convert the assembly constraints into two revolute and two cylindrical joints. 5. Simulate the relative motion of the arm base without consideration to time (in otherwords, without implementing the time based angular velocity given in the problem statement). 6. Add a formula to implement the time based kinematics associated with constant angular velocity of the crank. 7. Simulate the desired constant angular velocity motion and generate plots of the kinematic results.

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