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<< Click to Display Table of Contents >> Navigation: Getting Started Tutorials - MechDesigner > Tutorial 2B: Six-bar Kinematic-Chains |
To learn more about dyads (Also called Assur Groups)
To learn how to add dyads to a kinematically-defined chain.
To learn that a dyad does not change the degrees-of-freedom (DOF) of a kinematic-chain.
IMPORTANT concepts about DYADS
All Dyads have two Parts and three Joints.
If a kinematic-chain is a kinematically-defined chain before you add a new dyad, it will also be a kinematically-defined chain after you add a dyad.
In this tutorial, we will:
1.Add R-R-R and R-R-P dyads to build slightly more complex kinematic-chains.
oR Joints are Revolute-Joints. They are identical to Pin-Joints.
oP Joints are Prismatic-Joints. They are identical to Slide-Joints.
2.Demonstrate that a:
a.Slide-Joint is not always between the CAD-Lines along the X-axes of Parts.
b.Pin-Joint is not always at the start-Point or end-Point of the CAD-Line of Parts.
3.Learn a little about six-bar* kinematic-chains.
* The term bar is used more frequently than Part when we apply the term to mechanisms. For example four-bar, six-bar, eight-bar, ...
Dyad : |
See also Kinematics-Tree. A dyad does not change the number of degrees-of-freedom (DOF) of a kinematic-chain. Why? Each dyad has two Parts and three Joints: •Each Part adds 3 DOF*. Two Parts: 2 × +3.DOF = +6.DOF •Each Joint removes 2 DOF. Three Joints: 3 × – 2.DOF = – 6.DOF Thus, the total DOF = +6 + (– 6) = 0. *Parts on the Mechanism-Plane |
Motion-Parts : |
See the Rockers or Slider in the Kinematics-Tree A Motion-Part does not change the degrees-of-freedom (DOF) of a kinematic-chain. Why? A Motion-Part is one Part, one Joint, and one Motion-Dimension (a defined coordinate). •Each Part adds 3 DOF. One Part: 1Part × +3.DOF = +3.DOF •Each Joint removes 2 DOF. One Joint: +1Joint × –2.DOF = –2.DOF •A Motion-Dimension removes 1 DOF : +1MD × –1DOF = –1 DOF Thus, the change to the total Degrees-of-Freedom = +3 +(–2) + (–1) = 0(Zero). |
Add more Dyads➢6-bar Kinematic-Chains: Crank + R-R-R + R-R-R - only Pin-Joints. ➢6-Bar Kinematic-Chains: Crank + R-R-R + R-R-P - Pin-Joints and one Slide-Joint. Experiment with different possibilities of the three joints in a Dyad: R-R-R, R-R-P, RPR, RPP, PRP Also, change the driven Part from a Rocker to a Slider. |