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. See Tutorial 16 Motion-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.

AddMechanism1 Two Degree-of-Freedom Kinematic-Chains

'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

Each machine is a two degree-of-freedom (2 DOF) system.

Many kinematic-chains have two degrees-of-freedoms.

tog_minus        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.

tog_minus        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.

tog_minus        Parallel '5-bar' Robot

Five-Bar Parallel Robot

Here is a different 'Plotter'. An example is shown here,

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'.

Help Files for MechDesigner and MotionDesigner 11.1 + © Machine, Mechanism, Motion and Cam Design Software by PSMotion Ltd