Two Degree of Freedom Kinematic-Chains
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. |
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, and its B.Motion along the Path In MechDesigner, to define a motion for a Point (on the Mechanism-Plane) you can use: 1.Piggyback Sliders : Slider(A) onto which we add Slider(B) Design two motions: a motion for Slider(A) and Slider(B). 2.Motion-Path FB : sketch the Path. Design one motion for the Motion-Point along the Path. There are designs that easier with Piggyback Sliders and others with a Motion-Path FB. This tutorial uses Piggyback Sliders. |
An example application of a Piggyback Slider: 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 at the same linear speed as 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. This design problem is usually easier with Piggyback Sliders. |
Two Degree-of-Freedom Kinematic-Chains
Examples: Two Degree-of-Freedom
Robots: XY-Path to give the letters 'MD'
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 motions 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. Their motions are solved with Inverse-Kinematics. |
Here is a different Plotter. An example is here also: 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 XY-motion - that is, the Plane does not rotate relative to the fixed frame - then it has Curvilinear Motion.
Planar Guidance Click to Play Video |
In this model: •There are three fixed motors, shown as black cylinders, to the frame. •There a Part (a Dark Green color) that is connected to each motor. •There is platform that does not rotate relative to the frame. •We can use this motion to do DNA sequencing. |