Tutorial 2B: Six-bar Kinematic-Chains
Contents
Six-bar Kinematic-Chains
Objectives of this Tutorial
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. |
| o | R Joints are Revolute-Joints. They are identical to Pin-Joints. |
| o | P 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, ...
Terminology: Degrees-of-Freedom(DOF) : Dyads & Motion-Parts
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:
Thus, the total DOF = +6 + (– 6) = 0. *Parts on the Mechanism-Plane |
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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).
Thus, the change to the total Degrees-of-Freedom = +3 +(–2) + (–1) = 0(Zero). |
Step by Step Instructions
Add more Dyads
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. |