Up and Running with Autodesk Inventor Simulation 2011: A Step-by-Step Guide to Engineering Design Solutions

By Wasim Younis

Up and Running with Autodesk Inventor Simulation 2011 provides a clear path to perfecting the skills of designers and engineers using simulation inside Autodesk Inventor. This book includes modal analysis, stress singularities, and H-P convergence, in addition to the new frame analysis functionality.

The book is divided into three sections: dynamic solution, stress analysis, and frame analysis, with a total of nineteen chapters. The first chapter of each section offers an overview of the topic covered in that section. There is also an overview of the Inventor Simulation interface and its strengths, weaknesses, and workarounds. Furthermore, the book emphasizes the joint creation process and discusses in detail the unique and powerful parametric optimization function.

This book will be a useful learning tool for designers and engineers, and a source for applying simulation for faster production of better products.

• Get up to speed fast with real-life, step-by-step design problems—3 new to this edition!
• Discover how to convert CAD models to working digital prototypes, enabling you to enhance designs and simulate real-world performance without creating physical prototypes
• Learn all about the frame analysis environment—new to Autodesk Inventor Simulation 2011—and other key features of this powerful software, including modal analysis, assembly stress analysis, parametric optimization analysis, effective joint creation, and more
• Manipulate and experiment with design solutions from the book using datasets provided on the book's companion website (http://www.elsevierdirect.com/v2/companion.jsp?ISBN=9780123821027) and move seamlessly onto tackling your own design challenges with confidence
• New edition features enhanced coverage of key areas, including stress singularities, h-p convergence, curved elements, mechanism redundancies, FEA and simulation theory, with hand calculations, and more

• Language: English
• Publisher: Elsevier Science
• Release date: Apr 15, 2010
• ISBN: 9780123821034

Wasim Younis

Wasim Younis is an Autodesk Simulation consultant with over 15 years' experience in the manufacturing sector and Director of VDS Solutions (www.vdssolutions.co.uk), a leading Autodesk Inventor Simulation training, support and consultancy provider. He is well known within Autodesk Inventor Simulation community worldwide and is a regular contributor of Simulation tips, tricks and articles to Experience Manufacturing, the magazine dedicated to Autodesk Inventor users.

Book preview

chapters.

Chapter 1

The Dynamic Simulation Environment

Publisher Summary

This chapter provides an overview of simulation, as it enables understanding of the kinematics and dynamic behavior of mechanisms. Kinematics refers to the motion of the mechanism, including determining position, velocity, and acceleration, whereas dynamics is the study of masses and inertial forces acting on the mechanism. During a typical design process, designers go through a series of typical questions: Do the parts fit together or do the parts move well together? Is there interference? A cost-effective method is to create a working virtual prototype by using the Inventor simulation suite. The Inventor simulation suite allows the designer to convert assembly constraints automatically to mechanical joints, provides the capability to apply external forces including gravity, and allows the effects of contact friction, damping, and inertia to be taken into account. The simulation suite provides reaction forces, velocities, acceleration, and much more. With this information, the designer can reuse reaction forces automatically to perform finite element analysis, hence reducing risks and assumptions. There are four steps involved in creating a dynamic simulation as follows: grouping together all components and assemblies with no relative motion between them, creating joints between components that have relative motion between them, creating environmental conditions to simulate reality, and analyzing results.

Simulation overview

During a typical design process, designers go through a series of typical questions, such as: do the parts fit together? Do the parts move well together? Is there interference? Do the parts follow the right path? Even though most of these questions can be catered for by 3D CAD and rendering software, there may be other questions that cannot. For example, designers may want to know the machinery time cycle. Is the actuator powerful enough? Is the link robust enough? Can we reduce weight? All these questions can only be answered by building a working prototype or a series of prototypes. The major issues with this method are that it is timely and costly. An alternative cost-effective method is to create a working virtual prototype by using the Inventor simulation suite. The Inventor simulation suite allows the designer to convert assembly constraints automatically to mechanical joints, provides the capability to apply external forces including gravity, and allows the effects of contact friction, damping, and inertia to be taken into account. As a result of this, the simulation suite provides reaction forces, velocities, acceleration, and much more. With this information, the designer can reuse reaction forces automatically to perform finite element analysis, hence reducing risks and assumptions. Ultimately all this information helps the designers to build an optimum product, as illustrated by the following example.

Simulation – Basic Theory

Simulation enables understanding of the kinematic and dynamic behavior of mechanisms. 'Kinematics' simply refers to the motion of the mechanism, including determining position, velocity, and acceleration, whereas 'dynamics' is the study of masses and inertial forces acting on the mechanism.

where

F = external force

M = mass

a = acceleration

This is Newton's Law of Motion, which can also be expressed as

From both equations we can determine acceleration as a function of velocity

By integrating acceleration we can determine velocity

By integrating velocity we can determine position

Inventor Simulation 2011 calculates acceleration, velocity, and the position of the component/assemblies at each time step, referred to as image frames within the user interface.

Open-and Closed-Loop Mechanisms

A mechanism can, furthermore, be conceptually viewed as a set of rigid bodies interconnected to each other by joints that constrain, but not restrict, relative motion between any two bodies. Common joints used in mechanisms include revolution, cylindrical, prismatic, and spherical; a complete list of joints is given on page 17. The slider mechanism below comprises three revolutions, one prismatic, and one fixed (grounded) joint.

In addition, mechanisms can be generally categorized into open-loop mechanisms and closed-loop mechanisms. The difference is that the joint degrees of freedom (DOF) in open-loop mechanisms are independent of one another whereas in closed-loop mechanisms they are not independent. Extensive information on open- and closed-loop mechanisms is available from standard engineering books; theoretical technical information is beyond the scope of this book. The above slider mechanism is an example of closed loop; another example would be a Whitworth Return Mechanism. On the other hand, the following robot manipulator is an example of an open-loop mechanism, with one spherical, two revolution, and one fixed joint.

Redundant Mechanisms

Key pieces of information required from a mechanism analysis are the reaction forces and moments, due to acceleration, and inertial and external forces. These reaction forces are unique for a non-redundant model, whereas for a redundant model the reaction forces will not be unique, as explained by the simple shaft bearing example below.

For equilibrium, applied force (F) should be equal to the sum of all reactions at the bearings (RL)

Also, for equilibrium, the sum of all moments should be equal to zero

For a 1 m shaft this becomes

Substituting the value of R1 into the force equation gives us

Now substituting R2 into the force equation gives us

For a shaft with two bearings we have two unknowns and two equations, giving us one unique result, as

Now let us consider the same shaft with another bearing in the middle.

Again, for equilibrium, ∑F = 0 and ∑M = 0.

This creates three unknowns and two equations. To determine the reactions, we need to make some