Step 6A.3: Add a Transforming Mechanism

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Step 6A.3: Add a Transforming Mechanism

Summary of this Step

A Transforming Mechanism is the term we use for the Parts we add to the Motion-Part so that we can locate the Power-Source* more conveniently in the machine.

A Transforming Mechanism introduces the concept of Inverse-Kinematics.

*Power Source - the device or element that provides the 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.

tog_minusVideo of this Step

 

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

 
tog_minusEdit 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.

GST-6A3-001

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 - or see also How to open the Part-Editor

2.Part-Editor: Geometry toolbar > Add 2 × 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

Locate the two Lines with Dimensions. For each Line:

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

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

GST-6A3-002

We will add a Dyad - two Parts and three Joints.

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.

GST-6A3-003

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

 

GST-6A3-004

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

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

It is possible that the new dyad (two PartsRed-14-1bRed-14-2, 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

STEP 3: Change Dyad Closure

GST-Icon-ChangeDyadClosure

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.

GST-6A3-005

STEP 4: Cycle the Model with the Transforming Mechanism

1.Mechanism-Editor: Click Run menu > Cycle

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

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 the joints move apart, you can:

•Edit the length of one or two 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-box for the Slider.

Save you Mechanism