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Synthesis of Planar Mechanisms Using a Constraint-Based Design Tool

Abstract

This paper discusses the use of a constraint-based design tool to design planar mechanisms. The technique has been developed for the synthesis of four-bar mechanisms and other more complex mechanisms based on the graphical approach. The constraint network provided by the 3D CAD software is used to impose relations between different members in a mechanism. In addition, the dimension animation is used to animate the skeleton form of a mechanism to study the motion. The technique developed in this study, which was proven effective in a senior-level class, will enable a designer to tackle the synthesis of planar mechanisms more quickly and accurately.

Introduction

A mechanism is a combination of two or more machine parts such as linkages, cams, and gears, which function together to perform a specific motion1, 2. A machine usually consists of one or more mechanisms, which must transmit and convert energy into work. Since the majority of common mechanisms are planar mechanisms that have parts moving in parallel planes3, the focus of this study is primarily on planar mechanisms. Nowadays, 3D CAD software packages are becoming an integrated part of the engineering world as the computer technology becomes more sophisticated 4, 5. They are widely used to perform design and engineering analysis based on solid model data6. With such a design tool, the synthesis of mechanisms can be quickly and accurately achieved using proper constraints provided by the software.

The constraints utilized in this study include two different groups: geometric and dimensional. The geometric constraints include those of coincidence, parallelism, perpendicularity, and location in space; the dimensional constraints include both linear and angular dimensions. With a constraint-based design tool, a designer can examine different situations quickly without the need to manually rework the graphical construction. A large number of design revisions can be made, because it’s easy to change a few dimensions and watch others change accordingly. In addition, one of the applied dimensional constraints can be set as the controlled factor to animate the mechanism using a dimension animation function provided by the software7. Thus, it’s easy to observe the motion of one member relative to others and their interference. A similar application of a constraint-based design tool had been proven effective in dealing with velocity and acceleration analysis of mechanisms8.

The purpose of this study is to develop a constraint-based technique for the synthesis of planar mechanisms. All the synthesis in this study was completed utilizing I-DEAS on the Unix-based Sun workstation. However, the synthesis can be as effective and efficient using any 3D CAD software such as Mechanical Desktop, Pro-Engineer, Solidworks or Unigraphics on a PC, as long as it is constraint-based. In an engineering technology program that incorporates a constraint-based design tool like I-DEAS, students can learn the technique without difficulty. This technique was introduced to a computer-aided design class at Central Michigan University. Students learned to deal with the synthesis of a number of planar mechanisms using I-DEAS.

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Chen, M. (2006, June), Synthesis Of Planar Mechanisms Using A Constraint Based Design Tool Paper presented at 2006 Annual Conference & Exposition, Chicago, Illinois. 10.18260/1-2--124