Step 6A1.3: Add a Transforming Mechanism

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Step 6A1.3: Add a Transforming Mechanism

Terminology:

Cam Terminology :

Descriptions and Definitions

Transforming Mechanism :

a Derived-Name for the Parts (dyad) in a kinematic-chain that transforms the motion of a Tool to a different motion for a Cam-Follower, usually located at a more convenient place in the machine.

Inverse-Kinematics :

the motion of Parts in a Transforming Mechanism are calculated from a Tool-Part that has its motion defined directly with FBs and MotionDesigner.

Dyad :

a kinematic-term for two Parts and three Joints that combine as a Transforming Mechanism.

Summary of this Step

Add a Transforming-Mechanism to the Tool-Part.

Notes on dyads:

Dyad is the kinematic term for the connection of:

•Two Parts

•Three Joints

We can describe a dyad with a three-letter acronym. Each letter represents a joint:

•Pin-Joint is a Revolute-Joint. It has the letter R

•Slide-Joint is a Prismatic-Joint. It has the letter P

•Ball-Joint is a Spherical-Joint. It has the letter S

E.g. The R-R-P dyad has two Parts and two Revolute-Joints (Pin-Joints) and one Prismatic-Joint (Slide-Joint)

There are 5 Planar dyads, and, in MechDesigner, there are 2 Spatial dyads.

Video of this Step

Video: Add the RRR Dyad ('Transforming' Mechanism)

tog_minusEdit the Base-Part

Why edit the Base-Part?

We need to add a Pin-Joint between a Part in a dyad and the Base-Part.

We must also, later in Step 6A.5, add a rotating-Part that will be the Cam-Shaft.

Thus, we must edit the Base-Part to add Point sketch-elements for the two Pin-Joints. However, there are a number of advantages if we add Lines. In time, these advantages become clear.

STEP 1: Edit the Base-Part

1.Double-click the Part-Outline of the Base-Part to open the Part-Editor

or

2.see also How to open the Part-Editor

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STEP 2: Add two Lines to the Base-Part.

1.Geometry toolbar > Add 2 × LinesRed-14-1bRed-14-2 - see image to the left.

2.Constraints toolbar > Add Horizontal | Click the Lines.

3.Geometry toolbar > Add Dimension | Click each Line to edit its length

Locate the two Lines with Dimensions. For each Line:

4.Geometry toolbar > Add Dimension | Click the start-Point and the X-axis. Also, do Add Dimension between the start-Point and the Y-axis.

5.Exit the Part-Editor
tog_minusAdd two Parts and three Pin-Joints  – the Transforming Mechanism

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STEP 1: Add two Parts

1.Click Kinematic-elements toolbar > Add Part ( Shortcut : Insert key on your keyboard )

2.Mouse-button-down, drag in the graphic-area, mouse-button up. to add PartRed-14-1b

3.Do Steps 1 and 2 again to add PartRed-14-2

The PartsRed-14-1bRed-14-2 are free Parts, or Blue Parts.

They are not kinematically-defined.

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STEP 2: Add three Pin-Joints

1.Click Kinematic-elements toolbar > Add Pin-Joint

2.Pin-JointRed-14-3: Click the start-Point of PartRed-14-1b and a Point in the Base-Part

3.Pin-JointRed-14-4: Click the start-Point of PartRed-14-2 and the start-Point in the Slider

4.Pin-JointRed-14-5: Click the end-Point of PartRed-14-2 and the end-Point of PartRed-14-1b

<<< we are about to click the end-Point of the PartRed-14-2 to add the Pin-JointRed-14-5

When you complete STEP 2, (above) the Parts in the transforming-mechanism become Green Parts.

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It is possible that the dyad will move to a closure that you do not want. The R-R-R dyad has two closures.

Note: Closures are explained in detail in Tutorial 2 Step 2.4

STEP 3: Change Dyad Closure

GST-Icon-ChangeDyadClosure

1.Click Kinematic-elements toolbar > Change Dyad Closure

2.Click the Part-Outline of PartRed-14-1b or PartRed-14-2

3.Click OK-tiny-11-15 in the Command-Manager

The two Parts in the dyad move to a different closure.

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STEP 4: Cycle the Model with the Transforming Mechanism

1.Mechanism-Editor: Click Run menu > Cycle

You will see that the Transforming Mechanism (dyad) moves with the Slider. A joint brakes (moves apart) if the Parts cannot move for the complete range of the Slider's motion!

If, as you cycle the model, the joints move apart, you can:

•Edit the length of the Parts in the dyad - in the image the lengths of the two Parts are 160mm and 110mm)

•Edit the Base-Part to move the position of the Pin-Joint in the ground.

•Edit the Tool-Motion (in MotionDesigner) to reduce the distance the Tool-Part moves.

•Edit the Base-Value in the Motion-Dimension dialog for the Slider.

Save you Mechanism