A Comparative Analysis Between Probabilistic Roadmaps and Rapidly
Exploring Random Trees for Puma 560
Prasanth Murali, Himtanaya Bhadada, Robert Platt
Northeastern University
ABSTRACT
This work explores motion planning algorithms
for the puma 560 robot in a high dimensional
configuration space. We illustrate the two
popular sampling algorithms (Probabilistic
Roadmaps (PRM*) and Rapidly Exploring
Random Trees (RRT*) ) and present a
comparative analysis for convergence of the
algorithms in finding a collision free path from
start to end position in the workspace.
INTRODUCTION
Sampling-based planners create possible paths
by randomly adding points to a tree until some
solution is found or time expires instead of
evaluating all possible solutions. They are hence
probabilistic complete since a path will be found
if times goes to infinity.
RRTs can be thought of as creating a tree from a
robot’s starting point until one of its branches
reaches the goal. On the other hand,
probabilistic road-maps create a tree by
randomly sampling points in the configuration
space, keeping only those points that are
collision free, connecting them with nearby points
using paths that depend on the kinematics of a
robot, and then using graph shortest search
algorithms to find shortest paths on the resulting
tree.
Such probabilistic roadmaps have to be created
only once (assuming the environment is not
changing) and can then be used for multiple
queries. This is a particular advantage that the
PRM presents, over the RRT algorithm. In
contrast, RRT’s are known as single query
path-planning algorithms. Thus, for the same
workspace, running a RRT for the robot can lead
to different solutions each time while PRM is
more consistent in this way.
But, it should be noticed that there is no gold
standard or heuristic and even their
parameter-sets are highly problem-specific.
Figure 1: Workspace representing the Puma 560
robot and the obstacles
In this project, we are studying the application of
PRM and RRT to the puma 560 robot, provided
by Peter Corke’s Robotics Toolbox. The puma
560 is modeled as a Serial Link object having 6
DOF. The script creates the workspace variable
p560 which describes the kinematic and dynamic
attributes of a Unimation Puma 560 manipulator
using standard DH conventions.
The configuration space consists of five
spherical, four hemispherical and two cylindrical
obstacles as shown in Figure 1. The goal of the
robot is to traverse from the current joint