In this Step, we add two kinematic Dyads between the Piggyback Sliders and the machine frame (Base-Part).
It is then possible to drive one of the Parts in each Dyad, and thus drive the Piggyback Sliders, with cams or servomotors. The cams and servomotors are fixed to the machine frame.
Dyads that we can use.
We can use any of the five Dyads. To keep the principle very simple, we will add in this tutorial two R-R-R Dyads.
1. | First R-R-R Dyad: Connects the X-Slider to the Machine Frame. |
2. | Second R-R-R Dyad: Connects the Y-slider to the Machine Frame. |
(Note: Below, we have changed the X and Y Motions. Now, the motions include a constant velocity segment so that the motion follows 'something'. Hence, below, the XY-Path is different to the XY-Path in Step 11.1.)
We can now add the 1st R-R-R Dyad
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We will use the Point at the Trace-Point We can now add the 2nd R-R-R Dyad
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Question: Why a 3rd R-R-R Dyad? Answer: To drive the Piggy-Back Sliders from a position that is nearer to the drive of the 1st Dyad. Note the 'Bell Crank'
We can now add the 3rd R-R-R Dyad
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Now, the two Parts This makes it more convenient for cams and servomotors.
Please view the Video. |
![]() P = Parts; J = Joints, F = 3*(9-1) - 2*11 = 2 |
DEGREES-OF-FREEDOM The new design has:
GRUEBLER EQUATION: F = 3(P–1) – 2J : P = # Parts ; J = # Joints F = 3 * (9–1) – 2 * 11 F = 24 – 22 = 2 Degrees-of-Freedom = 2 MOBILITY Mobility = Degrees-of-Freedom – Number of Motion-Dimensions. Mobility = 2 – 2 = 0 |
We can 'drive' the Dyad Parts connected to the BasePart – Parts 7P and 8P in the image above.
We can use:
• | Servomotor Drives : We would need to save the motions of the driven Parts to a text file, and format it for the servo controller. |
• | Cams and Cam-Followers : Add the Cam-Follower 'Rollers' and Camshafts. See Tutorial 5. |
The video clip to the left shows the Piggyback Sliders driven by two 2D-Cams |
This is a more convenient configuration. Now two cams mounted to one cam-shaft. |