We must model the motion of a point on the path of a Belt.
To do this, we design two motions for the Point: its X-axis and Y-axis motion components.
We give the each motion to a different Slider. We configure the two sliders as 'Piggyback Sliders'.
When we cycle, the Y-axis Slider moves in the Y-axis direction. The Y-axis Slider is being carried by the X-axis Slider. Thus, the Point also move in the X-axis direction.
If we design the motions correctly, the Point on the Y-axis Slider has the same motion as a Point on a Belt.
In this Tutorial Step, we add a set of Piggyback Sliders. We call the two Sliders a Slider Set.
We design the two motions for Slider-X and Slider-Y in Tutorial Step 15.2.
Note - From Release 11+, it is easier to use a sketch-loop and Motion-Path FB. See Tutorial 11.
However, we should learn how we go about the model the piggyback sliders, as it is an important modelling method.
What is a Piggyback? I am not sure if it is only an English term. When someone is off the ground and on the back of a standing person, and their hands are around the standing person's neck (to hold on, not to strangle!) and their legs around each side and help up the standing person's arms, then the person that is off the ground is being given a 'Piggyback'. The motion of the person on the back is a combination of their own motion and the motion of the person on the ground. Why Piggyback Sliders? We can design a motion for a Point to move along the X direction and a different motion to move along the Y direction. The total motion gives the motion of a Point on a Plane that moves (translates) on the XY Plane. The total motion relative to ground of the Slider(1), which moves relative to Slider(2), which moves relative to ground = Motion Slider 1 + Motion Slider 2. Why not Piggyback Rockers? Yes we can have Piggyback Rockers also - exactly like a SCARA robot - see below. However, it is almost impossible to predict exactly what the motion of the Point at the end of the second Rocker relative to ground will be if we give rotational motions to the Rockers only. We can also add a Slider to the Base-Part that moves along the Y-axis of the Base-Part. (Slider-Y). Add Slider-X to Slider-Y in the -Y-axis direction of the Slider-Y (in the horizontal direction of the Base-Part). A Point in Slider-X with coordinates (x,y) has coordinates (X+x, Y+y) in the Base-Part. |
We add the Piggyback Sliders as follows:
A Point, called Point-XY, is a child to the Slider-Y. The movement of the Piggyback Sliders and the Point XY, is as follows:
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Add the X-Slider The X-Slider will move along the X-axis of the Mechanism-Plane . It is the horizontal motion of the point on the belt. |
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To add the Line, drag from Left-to-Right. The positive direction of the Line will agree with the positive X-axis of the Base-Part.
Drag from Left-to-Right to add the Part. Add the Part adjacent to the Line. The positive direction of the Part agrees with the positive X-axis of the Base-Part.
The positive direction of the X-Slider and Motion-Dimension is to the right. Edit the Base-Value of the Motion-Dimension |
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Edit the X-Slider, Add a Vertical Line |
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Edit the Length of the CAD-Line to 100mm - my habit.
Drag from Bottom-to-Top to add the Line. The positive direction of the Line agrees with the positive Y-axis of the X-Slider Part.
The length of the Line is 50. The Origin of the Line is Coincident, not merged, with the Origin of the X-Slider.
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Add the Y-Slider The Y-Slider will move in the Y-axis of the XY-Plane. It is the vertical motion component of the point on the belt. |
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Drag from Bottom-to-Top to add the Part. The positive direction of the Part agrees with the positive Y-axis of the X-Slider Part.
The positive direction of the Y-Slider and Motion-Dimension is to the Top. The Base-Value of the Motion-Dimension is 100. You can specify the Base-Values . Edit the Base-Values to offset the 'belt' in the horizontal and vertical directions. |