Summary of this Step

A Transforming Mechanism is a term we use for the Parts we add to the Motion-Part to make available to the Power-Source* a convenient location in the machine.

A Transforming Mechanism introduces the concept of Inverse-Kinematics.

*Power Source - the device or element that provides the input power to the kinematic-chain. In this case, the Power Source will be the 2D-Cam.

Dyad is a kinematic term for the connection of:

Two Parts
Three Joints

The Dyad is identified by its combinations of Pin-Joints, Slide-Joints and Ball-Joints.

However, Dyads use different terms for these Joints.

Pin-Joint has the term Revolute-Joint. It has the letter R
Slide-Joint has the term Prismatic-Joint. It has the letter P
Ball-Joint has the term Spherical-Joint. It has the letter S

E.g.: An R-R-R Dyad is a dyad that joint two Parts with three Revolute-Joints.

Note 2: In MechDesigner, there are 5 Planar Dyads, and 2 Spatial Dyads.

btn_delkeywordVideo of this Step


Tutorial 6A-3

Add the Transforming Mechanism


btn_delkeywordEdit the Base-Part

Why Edit the Base-Part?

In this Tutorial Step, we must add a Pin-Joint between one of the Parts in the Transforming-Mechanism and the Base-Part. (In Tutorial Step 6A.5, we must join the Cam-Shaft to the Base-Part).

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: Add two Lines to the Base-Part.
1.Edit the Base-Part : Double-click on the Part-Outline of the Base-Part to open the Part-Editor - see also How to open the Part-Editor
2.Part-Editor: Geometry toolbar > Add two LinesRed-14-1bRed-14-2 - see image to the left.
3.Part-Editor: Constraints toolbar > Add Horizontal | Click the Lines.
4.Part-Editor: Geometry toolbar > Add Dimension | Click each Line to edit its length
5.Part-Editor: Geometry toolbar > Add Dimension | Click the start-Point and the X-axis, then the start-Point and the Y-axis of each Line.
6.Exit the Part-Editor
btn_delkeywordAdd two Parts and three Pin-Joints  – the Transforming Mechanism


STEP 1: Add two Parts
1.Mechanism-Editor: Click Kinematic-elements toolbar > Add Part (Shortcut : Insert key on your keyboard)
2.Mechanism-Editor : Mouse-button-down, drag in the graphic-area, mouse-button up. to add PartRed-14-1b
3.Mechanism-Editor: 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.


STEP 2: Add three Pin-Joints
1.Mechanism-Editor: Click Kinematic-elements toolbar > Add Pin-Joint
2.Mechanism-Editor: Pin-JointRed-14-3: Click the start-Point of PartRed-14-2 and a Point in the Base-Part
3.Mechanism-Editor: Pin-JointRed-14-4: Click the start-Point of PartRed-14-1b and the start-Point in the Slider
4.Mechanism-Editor: Pin-JointRed-14-5: Click the end-Point of PartRed-14-2 and the end-Point of PartRed-14-1b

<<< the image shows we will now click the end-Point of the PartRed-14-1b to add the Pin-JointRed-14-5

When we complete STEP 3, the Parts in the transforming-mechanism become Green Parts.

Note: I have changed the Background colour to light-grey (RGB 192,192, 192).


STEP 3: Change Dyad Closure

It is possible that the new dyad (two Parts, three Joints) 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


1.Mechanism-Editor: Click Kinematic-elements toolbar > Change Dyad Closure
2.Mechanism-Editor: 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 move to a different closure.


STEP 4: Cycle the Model with the Transforming Mechanism.
1.Mechanism-Editor: Click Run menu > Cycle

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

To stop the joints moving apart, you can:

Edit the length of one or two of the Parts (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
Edit the Tool-Motion to reduce the distance it Tool-Part moves.

Save you Mechanism

Tutorials and Reference Help Files for MechDesigner and MotionDesigner 14.2 + © Machine, Cam, Mechanism, and Motion Design Software by PSMotion Ltd