mechanisims

Design & Tech CAD

Mechanisms

Before you proceed with the mechanism extension you need to fully understand assemblies and Degrees of Freedom (DoF). Be careful with your reference selection - generally only choose references from two parts to make a connection.

The mechanism extension allows you to simulate and analyse a mechanism which has sliding and rotating joints. Once the assembly has been created it can be simply dragged on screen or motors can be attached to the joints which will simulate a controlled movement through an analysis.

Joints can be limited in their range of movement and a motors characteristics need to be carefully considered. An analysis can then show any interference between parts, trace a curve of the mechanism motion or create a movement envelope.

Some steps are carried out in the standard Assembly environment, some in the Mechanism extension - Assembly > Application > Mechanism

The fundamentals steps are:

Assemble and connect/constrain base part as ground
Assemble moving parts with Connections, fixed parts with Constraints
Set connections limits where needed
Move into the Mechanism extension
Create Mechanism specific connections - gears etc.
Apply and setup Servo Motors to driven Connections
Set up Analysis
Run Analysis
If required - Replay Analysis checking for interference

Tips

If you want the base part to move out of the scene, connect it to the assembly csys using the weld connection – this can then be disconnected
Be careful how you connect subassemblies – ie. if you have an arm pivoting on a body and then an entity constrained/connected to that arm - if that entity is related to anything other than the arm it may not allow the arm to move
Always consider your Limit Settings
When defining/editing a Motion Analysis consider how the initial configuration (through the analysis or motor settings) of an entity is controlled – this will stop parts flipping to an inappropriate configuration when the analysis starts
Create a ‘start position’ Snapshot

Common Connections and use:

Weld - aligns two coordinate systems - allows disconnection for animation

Slider – one axis/edge sliding along another axis/edge with no rotation around the axis/edge.

Pin – axis/edges aligned allowing rotation around the axis/edge but no translation along it.

Cylinder – either - to allow rotation and translation on an axis – rotational and slider motors can be attached to the connection – or – in combination with a separate but parallel pin connection to avoid conflicts.

Limits

Most connections have the facility to limit the movement of a joint and set a zero and regeneration position. You will need to specify a zero reference on each of the parts to enable this function.

Servo Motor Profile

For constant motion in a single direction choose make the Specification velocity and the Magnitude constant.

For a reciprocating motion make the Specification position and the Magnitude cosine. Consider the Graph to determine the effect of variables A, B, C and T. Use the Initial Position preview to determine where your zero point is.

A = amplitude – the distance the motor will reciprocate through

T = period – time through a full cycle

B = phase – degrees - offsets the cycle along the time line

C = offset – mm - offsets the cycle along the amplitude line

Tips

If you want the base part to move out of the scene, connect it to the assembly csys using the weld connection – this can then be disconnected