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.
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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. 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 Lines 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 |
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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 Part 3.Mechanism-Editor: Do Steps 1 and 2 again to add Part The Parts They are not kinematically-defined. |
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STEP 2: Add three Pin-Joints 1.Mechanism-Editor: Click Kinematic-elements toolbar > Add Pin-Joint 2.Mechanism-Editor: Pin-Joint 3.Mechanism-Editor: Pin-Joint 4.Mechanism-Editor: Pin-Joint <<< the image shows we will now click the end-Point of the Part When we complete STEP 3, the Parts in the transforming-mechanism become Green Parts. Note: I have changed the Background color 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 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 |
