﻿ Two Degrees-of-Freedom Planar Kinematic-Chains

# Tutorial 11: Two Degrees-of-Freedom Planar Kinematic-Chains

## Two Degree of Freedom Planar Kinematic-Chains

#### Background: Properties of a Point that moves along an XY-Path

If we make a Point move with a general motion on the Mechanism-Plane, we can think of its:

 A. Path on the Plane
 B. Motion magnitude [velocity and acceleration] along the path

In MechDesigner, to define the motion of a Point on the Mechanism-Plane, you can use:

Piggyback Sliders : give each slider a different motion.

Motion-Path FB : pre-define a sketch-path and give a motion to a Point along the Path.

Some design problems are easier to design with Piggyback Sliders and others with a Motion-Path FB.

This tutorial uses the Piggyback Slider procedure. SeeMotion-Path FB and Blend-Curve 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.

## Two Degree-of-Freedom Kinematic-Chains

 ➢ Step 11.1: Introduce the Piggyback Sliders
 ➢ Step 11.3: Remove the XY Piggyback Sliders

### 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.

#### Gantry Robot

 Gantry Style Robot 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.

#### SCARA Robot

 Scara Style Robot This SCARA robot, as another 'Plotter', is also a two degree-of-freedom system. Instead of two sliders, 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.

#### Parallel '5-bar' Robot

 Five-Bar Parallel Robot 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.

### 2D Planar Motion

Planar Guidance

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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