Two Degree of Freedom Planar Kinematic-Chains
Background: Properties of a Point that moves along an XY-Path
If a Point has a general motion on the , we can think of its:
| A. | Path on the Plane, and also its, |
| B. | Motion magnitude [velocity and acceleration] along the Path |
In MechDesigner, to define the motion for a Point on the Mechanism-Plane, you can use:
Piggyback Sliders : use a Slider to move in an axial direction; connect a Slider to the first Slider, to which it moves at right-angles.
Motion-Path FB : use a sketch to define the path for the Point, and use a motion to define the motion along the Path.
Some designs are easier to design with Piggyback Sliders and others with a Motion-Path FB.
This tutorial uses Piggyback Sliders.
See 'Tutorial 16 Motion-Path FB and Blend-Curves' for the other technique.
An example of a Piggyback slider application:
A tool (say a vacuum cup) must take a carton from a stationary magazine and insert it into a pocket on a moving conveyor.
To place the carton, you must move the tool along with the moving conveyor (say, the X-direction) and also move it down into the pocket (say, the Y-direction) at the same time. To make sure the carton does not touch the sides of the pocket, we must synchronize the motion of the tool in both the X and Y directions.
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 Two Degree-of-Freedom Kinematic-Chains
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Examples: Two Degree-of-Freedom Robots: XY-Path to give the letters 'MD'
2D Point Motion
Machines that move a point in the X- and Y-axis directions, include:
| • | Laser Markers or Cutters |
Each machine is a two degree-of-freedom (2 DOF) system.
Many kinematic-chains have two degrees-of-freedoms.
 Gantry Robot
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Imagine a 'Pen Plotter'. Look at the video to the left.
This 'Plotter' moves a Pen with a slide along the X-axis. Another slide carries the X-axis slide, but along the Y-axis. The combined movement of the slides plots the drawing.
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SCARA Robot
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See https://www.youtube.com/watch?v=v5eR0eHknZk
This SCARA robot, as another 'Plotter', is also a two degree-of-freedom system.
The two inputs rotate as an alternative to the two Sliders.
The motions we give to the two motors are not the same as those we give to sliders in the Gantry Robot.
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Parallel '5-bar' Robot
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Here is a different 'Plotter'. An example is shown here, https://www.youtube.com/watch?v=b2UkmcPLEOs
In this model, the motors are attached to the frame. It is potentially a much faster (more responsive, more accurate) system, because the one motor does not carry the mass of the other motor.
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2D Planar Motion
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In this model,
| • | we have fixed three 'motors', shown as black cylinders, to 'Ground'. |
| • | we have connected a Part (a Dark Green colour) to each motor. |
| • | we keep the tool platform at the same angle relative to the frame while the other two axes write the letters 'MD'. |
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