Pro-Mechanism

COMPONENTS OF MECHANISM

In addition to being able to assemble components using realistic degrees of freedom, mechanism also does a lot more.  The typical progression to using mechanism is as follows.

Step 1 – Assemble Components

Create your assembly using mechanism connections to capture realistic degrees of freedom.  These connections are covered in great detail in the upcoming lessons.

Step 2 – Modify Joint Axis Settings

Control your connections by modifying the joint axes created by the connection.  This is explained in greater detail in the connection lessons individually.

Step 3 – Create Slots, Cams or Gear Pairs

Slots, Cams and Gear Pairs are special tools in mechanism that capture complex interactions between components.  These will each have their own lesson.

Step 4 - Drag Components and Create Snapshots

Dynamically pull or push on components that have open DOF to see them move in the assembly.  Take snapshots of your assembly at different states of motion to use in drawings or to come back to for reference.

Step 5 – Create Servo Motors or Force Motors

Servo motors and Force Motors are used to drive analysis and move your assembly on their own without using drag tools.  Each of these topics will be covered in great detail in their own lessons.

Step 6 – Create and Run Analyses

Start your animations to calculate the results you are looking for.  With servo motors in your assembly, you will be able to produce motion animations.  With Force motors, you will be able to calculate resultant forces and other measures while the animation is running.

Step 7 – View Results and Take Measurements

Run the animation to create MPEG movies, or to calculate interference along the path of the moving objects.  Create and view graphs that measure certain factors over time, such as position or force.

CONNECTION TYPES

The table at the top of the next page lists the different connections available through the component placement window at the time you assemble in a component.  In addition, the number of translational and/or rotational degrees of freedom are shown for each connection type.

Connection Type	Translational DOF	Rotational DOF	References Needed
Pin	0	1	2 Axes or Edges & 2 Planes, Planar Surfaces, Datum Points or Vertices
Slider	1	0	2 Axes or Edges & 2 Planes or Planar Surfaces
Cylinder	1	1	2 Axes or Edges
Planar	2	1	2 Planes or Planar Surfaces
Ball	0	3	2 Datum Points or Vertices
Bearing	1	3	1 Datum Point and 1 Axis or Edge
Weld	0	0	2 Coordinate Systems

There are two additional connection types in the list, but they don’t fit into the categories above.  These are the Rigid and General connections, and they allow you to use standard assembly placement constraints, such as Align, Mate, Insert, Tangent, etc.  We will see its usage in Mechanism later.

Ref - http://www.sharptechdesign.com/Tutorials/Mechanism_WF2/MDX_WF2_Lesson01.htm

Top Down Design

TOP-DOWN DESIGN

The idea behind Top-Down design is to try to build in intelligence between the fit, form and function of parts that reside in an assembly.  You try to capture this fit, form and function into the assembly first, and then pass the appropriate information down to the part level so that a change made at the assembly level or to one component in the assembly can drive updates to the rest of the critical parts.

In this method, many of the components are created in the assembly, instead of being assembled into the assembly.

SKELETON MODELS

The best way to capture fit, form and function for the assembly is to create a special kind of component called a Skeleton Model.  A Skeleton model is similar to a regular part, but it is treated specially in the assembly.  For example, a skeleton model is automatically excluded from the Bill of Material, where if you just created a regular part and used it like a skeleton, it would still be reported.

There are also restrictions that can be placed on regular parts that skeleton models are exempt from, or get special rights to deal with.  For example, you can make it so you are not allowed to copy surfaces from a regular part to another regular part, but you can still pass surfaces from the skeleton model to a regular part.  In defining such restrictions, you avoid creating parent-child relationships between individual part files, making the model more robust.

To demonstrate this principal, we will first create a new assembly file called Stacker.  Be sure to use a Design sub-type for this assembly, just as we did for the last lesson.  Also, once you have the assembly started, be sure to turn on the features in the model tree.