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:
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.
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.
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| STEP 1: | Add two Lines to the Base-Part. |
| 2. | Part-Editor:   - see image to the left. |
| 3. | Part-Editor Click the Lines. |
| 4. | Part-Editor: | Click each Line to edit its length |
| 5. | Part-Editor: | Click the start-Point and the X-axis, then the start-Point and the Y-axis of each Line. |
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| 1. | Mechanism-Editor: Click (Shortcut : Insert key on your keyboard) |
| 2. | Mechanism-Editor : Mouse-button-down, drag in the graphic-area, mouse-button up. to add Part |
| 3. | Mechanism-Editor: Do Steps 1 and 2 again to add Part |
The Parts are free Parts, or Blue Parts.
They are not .
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| STEP 2: | Add three Pin-Joints |
| 1. | Mechanism-Editor: Click |
| 2. | Mechanism-Editor: Pin-Joint : Click the start-Point of Part and a Point in the Base-Part |
| 3. | Mechanism-Editor: Pin-Joint : Click the start-Point of Part and the start-Point in the Slider |
| 4. | Mechanism-Editor: Pin-Joint : Click the end-Point of Part and the end-Point of Part |
<<< the image shows we will now click the end-Point of the Part to add the Pin-Joint
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).
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| 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
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| STEP 4: | Cycle the Model with the Transforming Mechanism. |
| 1. | Mechanism-Editor: Click |
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
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