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Dyad : Assur Group : |
A Dyad is combination of two Parts and three joints. One joint joins the two Parts together. The other two joints join the two Parts to different kinematically-defined Parts. A Dyad is the smallest kinematic chain which when added to, or subtracted from, a mechanism results in a mechanism that has the same mobility (degrees-of-freedom) as the original mechanism. |
Assur Groups : |
Another name for a Dyad |
Dyad Closure : |
It is one arrangement, or assembly, of the two(2) parts in the Dyad. |
Configuration of Dyad's Assembly = another way of expressing 'Dyad Closure'. |
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Types of Dyad : |
Planar Dyads: RRR, RRP, RPR, RPP, PRP Spatial Dyads: SSR, SSP |
R : |
Revolute Joint = Pin-Joint |
P : |
Prismatic Joint = Slide-Joint |
S : |
Spherical Joint = Ball-Joint |
See more: Dyads |
![]() RRR Dyad ![]() RRR Dyad |
STEP 1: Do Change Dyad Closure
STEP 2: Select a Part
STEP 3: Complete the Command
The configuration of the assembly should now have changed. Compare the bottom image with the top image. STEP 4: Do again, if needed
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Top-Tip: If there are many Dyads in the model, you can use the Kinematics-Tree to help you identify each Dyad. In the Kinematics-Tree 1.Click and explore each Kinematic-Chain in the Kinematics-Tree 2.Click each Dyad The Parts and Joints of each Dyad become red in the graphic-area |
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The image below shows an Offset-Slider-Crank mechanism. |
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![]() Assembly Configurations of an Offset-Crank-Slider |
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Refer to the image above. Part The two Parts in the R-R-P dyad are Parts Part This means the Pin-Joint (x-R-x) can ONLY be on the red circle at the end of Part Part Important: The Point in Part This means the middle Pin-Joint (x-R-x) in Part This means the Pin-Joint (x-R-x) can ONLY be on the red lines There are 4 places the red circle intersects the red lines. Thus, the Pin-Joint R2 can ONLY be at 4 places. Therefore, the Offset Slider-Crank has 4 possible assembly configurations. |