A Motion-Dimension Function-Block
See also Motion-Dimension dialog-box
Terminology and Definitions
Rocker : |
A Part whose Angle, relative to another Part, is specified by Motion-Dimension FB. |
Slider : |
A Part whose Distance, relative to another Part, is specified by Motion-Dimension FB. |
Motion-Dimension FB : |
A Motion-Dimension FB removes one degree-of-freedom from a Part so that it becomes a Motion-Part and a Part that is kinematically-defined. |
Motion-Part : |
The generic term for a Part whose position, relative to another Part, is specified by Motion-Dimension FB. A Motion-Part is a Rocker or a Slider. |
Kinematic states of Parts
Not kinematically-defined : |
The state of a Part when it has one or more degrees-of-freedom. |
kinematically-defined : |
The state of a Part when it has zero degrees-of-freedom. Its position, velocity, and acceleration are fully specified. |
All Parts in the model must be KINEMATICALLY-DEFINED before you should analyse any motion and force data. |
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Motion-Dimension FB function
A Motion-Dimension FB identifies a Motion-Part. A Motion-Dimension FB can specify, relative to a different Part, the: •Angle of a Part - which we call a Rocker - or - •Distance to a Part - which we call a Slider |
Motion-Dimension FB - Rocker
Prepare the model with these elements. The kinematic state of each element before you add a Motion-Dimension FB.
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Preparation: Motion-Dimension - Rocker (typical)
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Preparation example: •Two(2) Parts. In this case the Base-Part •Lines •Pin-Joint •Part •Part See Add Line, Add Part, Add Pin-Joint |
Add Motion-Dimension FB (Rocker)
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STEP 1: Select the Add Motion-Dimension FB command
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STEP 2: Select the three elements in the graphic-area (or Assembly-Tree)
STEP 3: Complete the Command
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Result: |
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Note: In the graphic-area: •To move the Motion-Dimension •To move the Motion-Dimension FB |
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To edit: |
STEP 3: Open the dialog-box - See Motion-Dimension dialog-box |
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Kinematics Tree - Motion-Dimension (Rocker)
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When we add a Motion-Dimension FB to a Pin-Joint, we identify it as a Rocker in the Kinematics-Tree. The kinematic elements are: Part + Pin-Joint + Motion-Dimension = ROCKER |
Motion-Dimension FB and Slider
Prepare the model with these elements. The kinematic state of the elements before you add the Motion-Dimension FB.
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Preparation: Add Motion-Dimension - Slider (typical)
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Preparation example: 1.Two(2) Parts One is a kinematically-defined Part ...the Base-Part The other is a free Part 2.The Parts are Joined... with a Slide-Joint 3.Start Point 4.start-Point The Lines are those that you select for the Slide-Joint See Add Line, Add Part, Add Pin-Joint |
Add Motion-Dimension FB (Slider)
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STEP 1: Add the Motion-Dimension FB
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STEP 2: Select three elements in the graphic-area (or Assembly-Tree)
STEP 3: Complete the Command
Result :
Note: To drag in the graphic-area the: •Motion-Dimension : CTRL+ Drag the FB icon •Motion-Dimension FB : Drag the FB icon STEP 4: Open the dialog-box - See Motion-Dimension dialog-box |
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Kinematics Tree - Motion-Dimension (Slider)
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When we add a Motion-Dimension FB to a Slide-Joint, we identify it as a Slider in the Kinematics-Tree. The kinematic elements are: •Part + •Slide-Joint + •Motion-Dimension = SLIDER |
Videos: Add Part, Add Joint, Add Motion-Dimension FB:
Add Motion-Dimension FB to a Pin-Joint
Video: Add Motion-Dimension FB - Rocker
Add Motion-Dimension FB to a Slide-Joint
Video: Add Motion-Dimension FB - Slider
Video: Add Motion-Dimension FB - Slider
Special Methods
Frequently, in a machine, joints are coincident (co-axial).
For example, there are two or more rotating-Parts that rotate about one center, or two or more sliding-Parts that slide along one axis.
Special Method: Coincident Pin-Joints
If you want to specify the motion of each rotating-part with a different Motion-Dimension FB, you must carefully plan as to which Points you select when you add the Pin-Joints,
Then, when you add the Motion-Dimension FBs, the Motion-Dimensions can reference the correct Parts.
Special Method: Coincident Slide-Joints
If you want to specify the motion of each sliding-part with a different Motion-Dimension FB, you must carefully plan as to which Lines you select when you add the Slide-Joints,
Then, when you add the Motion-Dimension FBs, the Motion-Dimensions can reference the correct Parts.
The Lines you select when you add the Slide-Joint determine between which two Parts you can specify the Motion-Dimension FB.
Special Method 1
The methods and principles described below apply to Rockers and Sliders. However, the descriptions below are given for Rockers only.
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Result of Special Method 1: The model shows •Two Motion-Dimension FBs •They reference the same Line in the Base-Part. You can see the dimension of the two Motion-Dimensions FBs start at the green horizontal Line. |
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There are two added Parts Each added Part, as always, has a CAD-Line, with a start-Point and an end-Point. There is a Line. This Line is in the Base-Part, which you cannot see. There are three(3) Lines in three(3) Parts in total. The start-Points in each line are 5, 7 and 11. Note: We can use the start-Points and/or the end-Points. |
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Add Pin-Joint #1 In the image to the left, Pin-Joint #1 is between point 7 and 5 Now we will add a Pin-Joint. #2 ADD Pin-Joint #2 We will add the Pin-Joint #2 between Points 11 and 5. Q: Why 11 and 5 and not 11 and 7 ? A: The Motion-Dimensions will reference the horizontal Line in the Base-Part. |
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Add Pin-Joint : Click Point 11 and then try to click Point 5. Because Point 5 and Point 7 are at the same position, MechDesigner does not know which Point to select. There is ambiguity between Point 5 and Point 5. Hence, the Select Elements dialog-box opens. The Select Elements dialog-box: •Gives ALL of the elements to complete the command are available •The element you had selected first is at the top of the list. •None of the elements are selected. |
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CTRL + Click ALL of the elements you need to complete the command. In this image, we select Point 11 and Point5 1.CTRL + CLICK Point11 AND Point5 2.Click
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Now, the each Part is joined with a Pin-Joint to the Point at the left end of the Line in the Base-Part. |
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The two Parts are now joined to the Base-Part with two Pin-Joints Now, use the Motion-Dimension FB two times Add Motion-Dimension 1 1.Click Function-Block toolbar > Add Motion-Dimension FB. |
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The Command-Manager show that we must select three elements
The first-element must be a Pin-Joint or Slide-Joint. We have two Pin-Joints! |
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When we click the Pin-Joints in the graphic-area the Select-Elements dialog-box opens as there are two Pin-Joints. In the Select-Elements dialog-box: Click the Pin-Joint5 - the one with the lower Element-Number if the names are different to those in the image. |
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Now we must select two Lines.
Click the horizontal Line Click the CAD-Line |
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This image shows the three elements in the Command-Manager boxes. |
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The first Rocker Motion-Dimension FB.
Add Motion-Dimension #2
We must now select another three elements, |
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Function-Block Toolbar > Motion-Dimension FB again. These are the elements.
Now, there is no ambiguity. There is only one Pin-Joint available.
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Here, you can see the result. Both Motion-Dimensions FBs use the Horizontal Line in the Base-Part as a reference for the motion-dimension. Note: When you add two Motion-Dimensions, the FBs may be on top of each other. Drag each FB so you can see them. |
Special Method 2:
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Result of Special Method 2 We want the two Motion-Dimensions FBs: •Motion-Dimension 1: From the Line in the Base-Part To a Line in 'Part 1' •Motion-Dimension 2: From the Line in 'Part 1' To the Line in 'Part 2' |
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Again, there are two Parts and a Line in the Base-Part. The Points at the ends of the lines are 5, 7 and 11. We want to: •Add a Pin-Joint between 'Point7' and 'Point5', and •Add a Pin-Joint between 'Point11' and 'Point7'. |
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In the image to the left, Point7 is joined to Point5 CONDITION 2 Add the second Pin-Joint between Point11 to Point7. •Q: Why Point7 and not Point5 ? •A: Because Point7 is a child to CAD-Line •We do not want the Motion-Dimension to reference the Line in the Base-Part. That was Method 1, above. |
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Select Point11. Then try to select Point7 There is ambiguity between Point5 and Point7. Hence, the Select Elements dialog-box opens. •ALL the elements you need for the command are made available to you •The first element you select is at the top of the list. |
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In the image to the left, we have selected Point11 and Point7. 1.CTRL + CLICK Point11 AND Point7 2.Click |
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The two Parts become joined with a Pin-Joint.
Do Add Motion-Dimension FBs two times.
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You must select three elements to do each Add Motion-Dimension FB |
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Element 1: A Joint. There is NO ambiguity when we select the Pin-Joint, There is only ONE Pin-Joint that is a joint between two Points with one Point in a kinematically-defined Part and the other Point in a free Part. The Select Elements dialog-box does NOT open. |
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Elements 2 & 3: Two Lines – a Solved Line Select the Horizontal Line |
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The three elements in the Command-Manager Click |
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You can see the First Motion-Dimension FB. Add the second Motion-Dimension. We must select three elements, |
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These are the elements: 1.Joint: when we select the Pin-Joint5, there is no ambiguity because the existing Motion-Dimension FB uses Pin-Joint2. 2.CAD-Line10: you must select this CAD-Line because it is a child to a Green Part and its start-Point is referenced by Pin-Joint6 3.CAD-Line11: you must select this CAD-Line because it is a child to a Blue Part and its start-Point is referenced by Pin-Joint6 |
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This image shows the end result. Motion-Dimension FB #1: uses the Horizontal Line that is a child to the Base-Part as a reference Line. Motion-Dimension FB #2: uses the CAD-Line along the center of the added Part as the reference Line. The CAD-Line is kinematically-defined after we add Motion-Dimension FB #1 - see Method 1 Note: When you add two Motion-Dimensions, the FBs may be on top of each other. DRAG each FB so you can see them. |
The nursery rhyme : She swallowed a cat, that swallowed a mouse, that swallowed a spider, that swallowed a fly... will come to mind.
A Slider To add a Motion-Dimension FB (for a Slider) you must select a Slide-Joint, and then one Point from each of the two Lines that define the Slide-Joint. •The properties of the Motion-Dimension FB are determined by the properties of the Slide-Joint. •The properties of the Slide-Joint are determined by the properties of the Lines you select to add the Slide-Joint. •The properties of the Lines are determined by the properties their start-Points and end-Points. Therefore, the positive-direction of the Motion-Dimension is defined by the start-Point and end-Point of the two Lines in the Slide-Joint. If the positive-direction of the Motion-Dimension is not as you want, you will need to add the Slide-Joint, and the Lines again.
Always, the positive-direction of a Motion-Dimension for a Slider : '...the positive direction of the Line, or CAD-Line, that is kinematically-defined before you add the Motion-Dimension FB to the Slide-Joint. What is the Positive-Direction of a Line, CAD-Line, or Part? The direction in which you drag - from its start-Point to its end-Point - when you add the Line, CAD-Line, or Part. Example Sliders •Line 1 is Green Part – it belongs to a kinematically-defined part. •Line 2 the Free Blue Part – it becomes a Slider after you add the Motion-Dimension FB I have used the red arrow-heads to show the direction in which I 'dragged' to add the Lines and Parts |
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•Line 1 – L1- Drag to the right •CAD-Line/Part 2 – L2 - Drag to the right The Motion-Dimension is 11.9. Increasing the value, will move the Slider to the up-right. The small Green arrowhead at the start-Point of Line 1 shows the positive direction of the Line and the Slider. |
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•Line 1 – L1 - Drag from Left to the Right •CAD-Line/Part 2 – L2 - Drag from Right to the Left The Motion-Dimension is '20'. Increasing the value will move the Slider to the right. The small arrowhead shows the positive direction |
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•Line 1 – L1 - Drag from Right < Left •CAD-Line/Part 2 – L2 - Drag from Left > Right The Motion-Dimension is 23'. Increasing the value will move the Motion-Part(Slider) to the left. The small arrowhead shows the positive direction |
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•Line 1 – L1 - Drag from Right to Left •CAD-Line/Part 2 – L2 - Drag from Right to Left The Motion-Dimension is -20'. Increasing the value will move the Motion-Part(Slider) to the left. The small arrowhead shows the positive direction. |
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