<< Click to Display Table of Contents >> Navigation: Getting Started Tutorials - MechDesigner > Tutorial 2A: Four-bar Kinematic-Chains > Step 2.3: Reconfigure as Crank-Slider |
To use different procedures to delete an element. In this case, we will delete a Pin-Joint.
To replace a Pin-Joint with a Slide-Joint.
Introduce, the R-R-P Dyad
➢Delete a Pin-Joint using the Selection-Window, Assembly-Tree, and the Kinematics-Tree
➢Add a Slide-Joint
In the Kinematics-Tree, the R-R-R Dyad changes to an R-R-P Dyad.
In this STEP 2.3, we will reconfigure the mechanism.
At the end of STEP 2.1, we had assembled a four-bar mechanism. If the input can rotate continuously, it is called a Crank-Rocker.
At the end of STEP 2.3 , we will reconfigure the Crank-Rocker to be a Crank-Slider. Because the rotation axis of the Crank is not on the same Plane as the sliding-axis of the Slider, it is also an Offset Crank-Slider.
The motion input to the Crank-Slider is the Crank.
In STEP 2.5, we will move the motion input from the Crank to the Slider. We will then call the mechanism a Slider-Crank.
Video: How to delete elements
Video: Add a Slide-Joint
We will delete a Pin-Joint, using contextual-menus, form the:
Note: It is also possible to delete joints in the graphic-area if you click it and the press with the 'delete' key on your keyboard.
When you click one or more elements in the graphic-area, Assembly-Tree or Kinematics-Tree, they show in the Selection-Window. You can delete the element using the Selection-Window. Here, the element we will delete is a Pin-Joint. |
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STEP 1: Delete the Pin-Joint 1.Mechanism-Editor: Click the Pin-Joint Look in the Selection-Window. |
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It is possible, and even likely, that you will select more than one element. In this case, we have clicked the Pin-Joint and a CAD-Line. 2.Selection-Window: Right-click the Pin-Joint in the Selection-Window. A contextual-menu shows. 3.Selection-Window: Click Delete in the contextual menu You will delete the Pin-Joint. |
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After you delete the Pin-Joint, you will see that the Part-Outlines of the Parts become Blue. Blue Parts are not kinematically-defined. Notes: MechDesigner will also delete the Motion-Dimension FB - it is bug!
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Because we delete the Motion-Dimension FB when we delete the Pin-Joint - which is a bug - we will add it again now. STEP 2: Re-add the Motion-Dimension FB 1.Mechanism-Editor: Click Kinematic-FB toolbar > Add Motion-Dimension FB
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First, we will replace the Pin-Joint that we deleted above. Note: Occasionally, you can only make a Part-Outline red if you hover above the arc near the start-Point of the Part. |
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STEP 1: Replace the Pin-Joint 1.Mechanism-Editor: Click Edit menu > Undo, or the Edit Toolbar > Undo icon - or - 1.Mechanism-Editor: : Do CTRL + Z key combination - or - 1.Mechanism-Editor: Click Kinematic elements toolbar > Add Pin-Joint, | Click the two Points again again In the graphic-area, you can see the Pin-Joint is in the model again. The Parts are Green Parts again. Parts with Green Part-Outlines are Kinematically Defined. STEP 2: Delete the Pin-Joint - again! 1.Click to the left of the graphic-area - the Assembly tab 2.Explore the Assembly-Tree to find the Pin-Joint that you want to delete - Here Pin-Joint7 - see Note 2 below.
3.Right-click the Pin-Joint in the Assembly-Tree - 4.Select Delete in the contextual-menu. In the image to the left, we can see the Part-Outlines of the Parts have become Blue. The Parts are now not kinematically-defined.
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Because we delete the Motion-Dimension FB when we delete the Pin-Joint - which is a bug - we will add it again now. STEP 3: Re-add the Motion-Dimension FB 1.Click Kinematic-FB toolbar > Add Motion-Dimension FB
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STEP 1: Re-add the Pin-Joint 1.Use Edit menu > Undo, or the Edit Toolbar > Undo icon - or - 1.Use the CTRL + Z key combination. The Parts-Outlines are now Green, again, as they are now kinematically-defined. |
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STEP 2: Delete the Pin-Joint - again! 1.Click on the Kinematics tab in the Project-Explorer to open the Kinematics-Tree. 2.Expand the R-R-R dyad. You can see the list of three Pin-Joints and two Parts.
3.Click the Pin-Joint that has the Grounded Pin-Joint Symbol
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The Pin-Joint is in the Selection-Window.
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Again, you will see, as in the image to the left, the Part-Outlines are Blue (see Step 2.1A) Blue Parts are not kinematically-defined.
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Because we delete the Motion-Dimension FB when we delete the Pin-Joint - which is a bug - we will add it again now. STEP 3: Re-add the Motion-Dimension FB 1.Click Kinematic-FB toolbar > Add Motion-Dimension FB
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The kinematic-chain in the model has Pin-Joints only. To remind us: •A Pin-Joint is between two Points •Each Point must be a child to a different Part Imagine Point 1 is the Bearing Shaft (on Part 1), and Point 2 is the Bearing Housing (on Part 2). Introducing the Slide-Joint •A Slide-Joint is a joint between two Lines •Each Line must be a child to a different Part Imagine Line 1 is a Slide-Rail (on Part 1), and Line 2 is a Slide-Block (on Part 2) |
To add a Slide-Joint, we need a Line in two different Parts. We are going to add a Slide-Joint between an Added-Part and the Base-Part. We will use: •The CAD-Line along the center of an added Part. •A new Line in the Base-Part, Note: We can use any Line we add to a Part and the Base-Part. |
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STEP 1: Add a Slide-Rail to the Base-Part. We will edit the Base-Part to add a new Line
Some Rules
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STEP 1: Add a Slide-Joint |
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1.Mechanism-Editor: Click Kinematic-elements toolbar > Add Slide-Joint A Slide-Joint needs two Lines. 2.Mechanism-Editor: Click the CAD-Line 3.Mechanism-Editor: Click the Line See the mouse-pointer in the image to the left. When you complete Add Slide-Joint, the Lines are now collinear. There is a Slide-Joint (see below: The Slide-Joint in the Graphic-Area) The Slide-Joint has replaced the Pin-Joint. |
STEP 2: If needed: Change the Dyad-Closure We look at Dyad Closures in much more detail in the next STEP 2.4 Dyad Closures There are four possible closures when you add the Slide-Joint: •The Parts may jump to a different position •AND / OR when you use Run menu (or toolbar) > Cycle, the Parts in the Dyad do not move as the Rocker moves. 1.Mechanism-Editor: Click Kinematic-element toolbar > Change Dyad Closure 2.Mechanism-Editor: Click on of the two Parts in the Dyad 3.Click Do 1-3 again, and again, until the Parts are in the same position as the image to the left. |
STEP 3: Expand the Kinematics-Tree The Parts that were in the R-R-R Dyad are now in an R-R-P Dyad. The three Joints in the R-R-P Dyad are: •Two Revolute-Joints, (R-R-P), - or two Pin-Joints •One Prismatic-Joint (R-R-P) - or one Slide-Joint |
There are a three symbols to represent a Slide-Joint. In the image we can see:
The arrow-head shows the Positive Direction of the Slide-Joint. The Positive Direction is important if you want to add a Motion-Dimension with the Slide-Joint. |