<< Click to Display Table of Contents >> Navigation: Getting Started Tutorials - MechDesigner > Tutorial 11: Two Degrees-of-Freedom Planar Kinematic-Chains > Step 11.1: Piggyback Sliders as XY Table |
The Piggyback Slider configuration is 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 Piggyback Slider Configuration is only one way to model an XY-Path. You can also use a Motion-Path FB. See: Motion-Path and Blend-Curves. † The Sliders do not need to be in the X-axis and Y-axis directions or even at right-angles to each other. We describe them in these directions for convenience only. They can equally be in the Radial and Tangential directions of a circle. |
Piggyback Sliders, and a Drive
•Piggyback Sliders •The motion of each Slider has a linear relationship to the motion of the motor. •Each motor to rotate a Pulley to move a Belt, or a motor to rotate a Ball-Screw to move a Nut. |
Piggyback Sliders and a Dyad and a Drive.
•Piggyback Sliders •Connect dyads from the machine-frame to each Slider. •Add Cams or Servomotors to drive a Part in each dyad •Inverse-kinematics to calculate the motions for the cam-followers or servomotors to give the motions designed for the XY-Table- See Step 11.2 |
Translating Beam (a Part that moves on the Mechanism-Plane but does not rotate)
•Piggyback Sliders to define the XY-Motion •Design a mechanism with a translating-beam that is not physically connected to the machine-frame. •Look at this video. |
Terminology:
Rectilinear Translation: All points in a Part have the same translating and parallel motions. Curvilinear Translation: All points in a Part have the same, but not necessarily straight, motions. |
Quick Instructions:
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Add the X-Slider
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Edit the X-Slider, Add a Vertical Line
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Add the 'Y'-Slider
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Get Motions for the Sliders
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Run menu > Cycle (or ALT+C) X Motion This is a motion for the X-axis. Use a Motion FB to link this motion to the Motion-Dimension FB to move the X-Slider. |
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Y Motion This is a motion for the Y-axis. Use a different Motion FB to link to the Motion-Dimension FB to move the Y-Slider. These two example motions define the motion along the XY-path on the Mechanism-Plane We show the XY-path in the graphic-area with a Trace-Point. |
Degrees-of-Freedom and Mobility of Piggyback Sliders Gruebler Equation to find the number of Degrees-of-Freedom (F): F = 3(P-1) – 2J : P = Number of Parts (1 × Base-Part + 2 × Added-Parts) ; J = Number of Joints ( 2 × Slide-Joints) F = 3×(3-1) – 2×2 F = 6 – 4 = 2 Mobility = # Degrees-of-Freedom(F) – # Motion-Dimensions = 2 – 2 = 0. |
Kinematics-Tree for Piggyback Sliders. There is: •One kinematic-chain (Solved Mechanisms) The Solved Mechanism has: •Two Sliders |
Example machines include:
•Pen Plotters
•Water-Jet Cutters
•Laser Markers or Cutters
An XY-Gantry Robot Look at the video to the left. 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. This 'Plotter' moves a Pen with a slider along the X-axis. A different slider carries the X-axis slider, but along the Y-axis. The two movements of the slider plot the drawing. |