Step 11.1: Piggyback Sliders as XY Table

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Step 11.1: Piggyback Sliders as XY Table

Piggyback Sliders

The Piggyback Slider configuration has two Sliders:

•Slider(A) : moves along the X-axis* of the Mechanism-Plane

•Slider(B) : moves relative to Slider(A), and parallel to the Y-axis of Slider(A)

* The two Sliders do not need to be parallel to the X-axis or the Y-axis, or even perpendicular to each other. We use the X and Y-axis directions for convenience only. They can be, for example, in the Radial and Tangential directions of a circle.

Mechanical Systems that have an XY Motion :

Piggyback Sliders E.g. Gantry Robot

The Piggyback Sliders are usually perpendicular (normal, 90º, orthogonal) to each other.

•A servo-motor that drives an axis has a linear relationship with the motion of each of the Piggyback Sliders.

•The servo-motor can drive different linear-technologies: Pulley & Belt, Ball-Screw & Nut, Rack & Pinion, Linear-Servomotor, ... .

Piggyback Sliders and Dyads

The Piggyback Sliders are usually perpendicular (normal, 90º, orthogonal) to each other.

•Connect a dyad from the machine-frame and each Piggyback-Slider.

•Add a cam or servo-motor to drive a Part in each dyad

•Inverse-kinematics calculates the motion of each follower or servo-motor from the motion designed for each Piggyback Sliders - See Step 11.2

Translating Beam (a Part that moves on the Mechanism-Plane but does not rotate)

The Piggyback Sliders are usually perpendicular (normal, 90º, orthogonal) to each other.

•In this case, the Sliders are not used in the physical machine. They are used to design the XY motion only.

•Design a mechanism with a translating-beam that is not physically connected to the machine-frame or the Piggyback Sliders.

•Look at this video to see the design.

Add Piggyback Sliders - Quick Instructions

GST-11-1-A-001

Quick Instructions:

1.Add Slider-XRed-14-1b to a horizontal Line in the Base-Part

2.Edit Slider-X. Add a Line that is parallel to the Y-axis

3.Add the Slider-YRed-14-2 to the Line that is parallel to the Y-axis of Slider-X.

4.Design the motions for each Slider.

5.Add a Trace-PointRed-14-4 to a PointRed-14-3 that moves with the Slider-Y.

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

Add Piggyback Sliders - Detailed Instructions

GST-11-1-A-002

Add Slider-X

1.Edit the Base-Part

2.Part-Editor: Geometry toolbar > Add Line , Constraints toolbar > Add Horizontal : Click the Line; Close the Part-Editor

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

4.Mechanism-Editor: Add a Motion-Dimension FB to control Slider - rename it to Slider-X

5.Edit the Motion-Dimension FB > Base-Value =50

6.Mechanism-Editor: Add a Linear-Motion FB and a Motion FB to the graphics-area Connect the FBs with wires.

7.Rename the Slider to Slider-X
GST-11-1-A-003

Edit Slider-X, Add a Vertical Line

1.Mechanism-Editor: Edit Slider-X : Part-Editor:  Edit length of the CAD-Line to 100mm

2.Part-Editor: Geometry toolbar > Add Line , Drag UPWARDS to add a new Line : Constraints toolbar > Add Vertical click the Line

3.Part-Editor: Geometry toolbar > Add Dimension : Edit the length of the Line to 100mm

4.Part-Editor: Constraints toolbar > Coincident , Click start-Point of the CAD-Line and the new Line

5.Close the Part-Editor
GST-11-1-A-004

Add the Slider-Y

1.Mechanism-Editor: Add a Part; Add a Slide-Joint between the new Part and the vertical Line in Slider-X

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

3.Edit the Motion-Dimension FB > Base-Value =50

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

5.Mechanism-Editor: Connect the FBs

6.Rename the new Slider to Slider-Y
GST-11-1-A-005

Get Motions for the Sliders

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

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

3.Close the Motion FB dialog

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

5.Mechanism-Editor: Select Motion-Y in the drop-down box for 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 Slider-Y
GST-11-1-A-007

Run menu > Cycle (or ALT+C)

Motion-X

Blend-Point #

X - Input

Y - Output

Y-Vel

Motion-Law

1

0

0

180/s

Const. Vel.

2

120

(60)

(180/s)

Flex-Poly

1

360 / 0

0

(180/s

Const-Vel.

Link Motion-X to a Motion FB to connect a wire to the Motion-Dimension FB to move Slider-X.
GST-11-1-A-008

Motion-Y

Blend-Point #

X - Input

Y - Output

Y-Vel

Motion-Law

1

0

0

0

Dwell

2

120

0

0

Poly 345

3

240

50

0

Poly 345

1

360 / 0

0

0

Dwell

Link Motion-Y to a different Motion FB and connect a wire to the Motion-Dimension FB to move Slider-Y.

Degrees-of-Freedom of Piggyback Sliders

GST-11-1-A-009

Degrees-of-Freedom and Mobility

Gruebler Equation

D = 3.(P-1) – 2.J  : P = Number of Parts (1 × Base-Part + 2 × Parts) ; J = Number of Joints ( 2 × Slide-Joints)

D = 3(3-1) – 2.2

D = 6 – 4 = 2

Mobility = # Degrees-of-Freedom(D) – # Motion-Dimensions = 2 – 2 = 0.

Kinematics Tree of Piggyback Sliders

GST-11-1-KT-PiggybackSliders

Kinematics-Tree for Piggyback Sliders.

One kinematic-chain

Two Sliders

Machines that use Piggyback Sliders

An XY-Gantry Robot

This Plotter moves a Pen along a slide, say the Y-axis slide. The X-axis carries the Y-axis slide.  The combined movement plots the drawing.

With this machine, there is an EXACT linear-equivalence between the XY-Path and the control positions of the slider motors. The system is Kinematically Linear.