Step 11.3: Remove the Piggyback Sliders

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Step 11.3: Remove the Piggyback Sliders

The Piggyback Sliders specify the motion. However, the Piggyback Sliders are not always necessary in the 'physical' design.


Question 1: Why remove the Linear Sliders?

Answer Part 1a: Linear Slides are more expensive than rotary bearings.

Answer Part 1b: It is easier to seal rotary bearings than to seal Linear Slides. Often, it is important for food production machines in the FMCG industries.

Model with Sliders 'Virtually' Removed

In the model, we design the motions for the Piggyback Sliders and these move the Parts in the Dyads.

Can we configure Dyads to move a Part with a motion that is identical the Y-Slider of the Piggyback Sliders?

That is, can we find a Part that copies the XY-Path given to the Y-Slider.


Piggy-back Slider Motions - Reminder from STEP 11-1

X-Slider -Linear Translation - all XY positions on the X-Slider move parallel to the X-axis.

Y-Slider - Planar Translation - all XY positions on the Y-Slider move with the combined (superposition) motions of the of the X-axis and the Y-axis motions.

The Y-Slider is a Translating Part.


Dyad Motions

Not one Part of the 3 × R-R-R Dyads is a Translating-Part.

The three PartsRed-14-1 that are joined to the Base-Part (machine-frame) rotate.

The three PartsRed-14-2 that are joined to the Bell-Crank, the X-Slider, and Y-Slider rotate and translate.


Question 2: Can we add new R-R-R Dyads so that at least one Part does not rotate.

If we can, then we can remove the X-Sliders and Y-Sliders.

See below.


In the image above, we have added two more R-R-R Dyads.

The length of the Parts in the Dyads and the position of the Pin-Joints with the Base-Part are important.

The orange Part does not rotate – it 'translates'. Hence we can remove the Sliders in the real design.

Here, we use the Sliders only to specify the XY-Path of the Translating Part.


The Video shows the mechanism movement.

All the Points in the Translating Part move with the same 2D path. We do not use the Sliders in the physical machine. They only give a useful means to force the translating part to move with the XY-Path.


For completion, I have added two 2D-Cams and Cam-Followers to move the translating part with the 2D Planar Motion.

Add 2D-Cams to drive the Cam-Followers with the required motions.


MechDesigner derives the motions of the Cam-Followers.