Step 15.1: Piggyback Sliders and the Motion

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Step 15.1: Piggyback Sliders and the Motion

NOTE:

This Tutorial was written before the Motion-Path FB tool became available to you in the Kinematic FB toolbar.

In this Step, we introduce Piggyback Sliders. They are an important modeling technique.


What is a Piggyback? Is it only an English term?

When a person is off the ground and on the back of a standing person, their hands of the person off the ground are around the standing person's neck (to hold, not to strangle!), and their legs around each side and held by the standing person's arms, then the person that is off the ground is being given a Piggyback.

We can imagine in a circus act, that the person on the back can also climb up and down a ladder (that is also held by the person on the ground)! The motion of the person on the ladder is a combination of their own motion and the motion of the person on the ground.

Why Piggyback Sliders?

We can replace the each person with a Slider. The result is we can design a different motion for each Slider, say in the X-and Y directions, to give an X-Y planar motion.

Why not Piggyback Rockers?

Yes, you can add Piggyback Rockers - exactly like a SCARA robot.

However, it is almost impossible to predict the planar motion of the Point at the end of a SCARA robot when you design the motion for each Rocker. You will see that, even for a SCARA robot, we design the motion with Piggyback Sliders. We join the tip of the SCARA robot to the Piggyback Slider.


Piggyback Sliders and a Chain.

We add two Motion-Parts - Sliders - and assemble them as Piggyback Sliders.

We name the Sliders : Slider-X and Slider-Y

We design motions for Slider-X and Slider-Y such that a Point on Slider-Y follows the path of a Point on a chain.

The motions for Slider-X and Slider-Y are designed here.


How to add Piggyback Sliders

Basic Instructions: Add Piggyback Sliders

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Basic Instructions:

1.Add a Line to the Base-Part that is parallel to the X-axis of the Mechanism-Plane

2.Add the SliderRed-14-1b to the Line in the Base-Part - Slider-X

3.Edit the Slider-X to add a Line that is parallel to its Y-axis

4.Add aSliderRed-14-2 to the Line in Slider-X - this is Slider-Y

5.Design the motions for each Slider.

6.Add a Trace-PointRed-14-4 to a PointRed-14-3 on Slider-Y - this is Point-XY.

7.Run menu  > Cycle to watch the Piggyback Sliders.

Detailed Instructions: Add Piggyback Sliders

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Add the Slider-X

1.Edit the Base-Part

2.Part-Editor: Geometry toolbar > Add Line

3.Constraints toolbar > Add Horizontal to the Line ; Add Dimensions to locate the Line ; Close the Part-Editor

4.Mechanism-Editor: Add a Part; Add a Slide-Joint between the Part and the Line in the Base-Part

5.Add a Motion-Dimension FB to control the motion of the horizontal Slider

6.Add a Linear-Motion FB and a Motion FB to the graphic-area ;

7.Connect the FBs with wires.

8.Rename the Slider to SLIDER-X

 

GST-11-1-A-003

Edit the Slider-X, Add a Vertical Line

1.Mechanism-Editor: Edit the Part that now has the name: Slider-X

2.Part-Editor:  Edit its length to 100mm.

3.Part-Editor: Geometry toolbar > Add Line , Drag UPWARDS to add the Line : Constraints toolbar > Add Vertical to the Line;

4.Geometry toolbar > Add Dimension  - Line = 100mm

5.Part-Editor: Constraints toolbar > Coincident , Click start-Point of the Part's CAD-Line  , and the new vertical Line.

6.Close the Part-Editor

 

GST-11-1-A-004

Add the Slider-Y

1.Mechanism-Editor: Add a Part

2.Mechanism-Editor: Add Slide-Joint : Click CAD-Line in new Part and vertical Line in the Slider-X

3.Mechanism-Editor: Add a Motion-Dimension FB to control the Position of the Slider-Y

4.Mechanism-Editor: Add a Linear-Motion FB and a Motion FB to the graphic-area

5.Mechanism-Editor: Connect the FBs

6.Rename the new Slider to Slider-Y

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Get Motions for the Sliders - Example Motions

1.Mechanism-Editor: Edit the Motion FB connected to the Slider-X to open the Motion FB dialog

2.Mechanism-Editor: Select X-Motion in the drop-down box.

3.Close the Motion FB dialog

4.Mechanism-Editor: Edit the Motion FB connected to the Slider-Y to open the Motion FB dialog

5.Mechanism-Editor: Select the Y-Motion in the drop-down box for the Slider-Y

6.Close the Motion FB dialog

Show the Trace-Path:

7.Mechanism-Editor: Do Kinematic-element > Add Trace-Point , click a Point on the Slider-Y

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Run menu > Cycle (or ALT+C)


Example Motion - not the motion for the chain

X Motion -

A motion for the X-axis.

Use a Motion FB to link this motion to the Motion-Dimension FB to control the motion of the Slider-X.

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Y Motion

A different motion for the Y-axis.

Use a different Motion FB to link to the Motion-Dimension FB to control the motion of the Slider-Y.


These two example motions define the motion on the Mechanism-Plane

To show how the X and Y motions combine we can add a Trace-Point to the Slider that controls the Y-axis motion.


Design the Motion of the Chain.

We need to design the motions for a point that follows the path of a chain that moves around two sprockets

The motion of the Point is an oval shape. The oval has two equal arcs and two straight line segments between the arcs.

This tutorial does not consider the polygonal/chordal action of a chain as it moves around the sprockets.

Design decisions for the chain, that we have made for you:

The chain has twelve (12) chain-links

Each chain-link has a pitch of 100mm

Each sprocket has five teeth

From these parameters, we can also calculate:

oThe length of the chain is exactly 12 × 100mm = 1200mm

oPitch-Circle Circumference of each sprocket = 5 × 100 = 500mm

oPitch-Circle Radius of each sprocket = 500/2π = 79.577mm

oDistance between sprockets = (1200 – 500) / 2 = 350mm

tog_minusMotion Design Preparation and Calculations for the Piggyback Sliders
tog_minusPhase Parameter for the Sinusoid Segments
tog_minusComplete the Model in MechDesigner