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 Mechanism-Plane, we can think of its:
A.Path on the Plane, or, 'Where it moves on the Plane'.
B.Motion along the Path, or, 'How it moves along the Path'.
In MechDesigner, to define the motion for a Point on the Mechanism-Plane, you can use:
1.Piggyback Sliders : Slider(A), to which we add Slider(B) that moves at right-angles to Slider(A). Design two motions: a motion for Slider(A) and Slider(B).
2.Motion-Path FB : sketch the Path for the Point. Design one motion for a Point 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 also: Tutorial 16 - Motion-Path FB and Blend-Curves
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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:
•Pen Plotters
•Water-Jet Cutters
•Laser Markers or Cutters
•Engravers
Each machine is a two degree-of-freedom (2 DOF) system.
Many kinematic-chains have two degrees-of-freedoms.
Imagine a 'Pen Plotter'. Look at the video to the left. 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. |
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 The motions we give to the two motors are not the same as those we give to sliders in the Gantry Robot. in fact they are much more complex. Their movements are solved with Inverse-Kinematics. |
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 The motions we give to the two motors are not the same as those we give to sliders in the Gantry Robot. in fact they are much more complex. Their movements are solved with Inverse-Kinematics. |
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 need to move the mass of the other motor. |
A Plane that is coplanar with a fixed-plane has 3 degrees-of-freedom.
However, if each Point on the Plane has the same general XY-motion - that is, the Plane moves, but does not rotate relative to the fixed-plane - then it has Curvilinear Motion.
Planar Guidance Click to Play Video |
In this model: •we have fixed three 'motors', shown as black cylinders, to 'Ground'. •we have connected a Part (a Dark Green color) 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'. •This can be used with DNA sequencing where multiple pipettes need to take sample or add an 'ingredient'. |