Design and Development of a Redundant Manipulator Arm
Aims and Objectives: The central idea is this project is to use a Redundant
Manipulator to work around obstacles. It is expected that the manipulator
would successfully demonstrate Path Planning and Obstacle
Avoidance in its way
towards the goal as shown in the following animated gif.
Plants which require maintenance and inspection of sites which are inhospitable to
human beings due to number of reasons like, high temperature, presence of toxic
or radioactive substances, demand such manipulators. Redundancy is required for
Obstacle Avoidance (A manipulator is said to have redundant links,
if it has degrees of freedom
more than required to reach a point. In the case of parallel plane and
serial manipulators, a manipulator is said to have redundant links if it has more than
2 degrees of freedom).
The situation is complicated as many of the inspection sites
are difficult to access manually (as the workspace may be very congested)
as well as by mobile robots (as the terrain may not be
even). In such a scenario, the inspection sites can be accessed in a
The present project is intended to meet such demands of a complicated
environment, by harnessing the potential of redundant manipulators to move in a
A robot manipulator having more degrees of freedom than essential for
accessing a point in space is called a redundant manipulator. Such redundancy helps in
obstacle avoidance, singularity avoidance, workspace enhancement, performance optimization
and improvement in reliability leading to safer operational situations. The redundancy
will be utilized for reaching and dexterous maneuvering at locations that are difficult
to reach, but nevertheless require periodic maintenance. Path Planning and Obstacle
Avoidance strategies are required. Subsequently various control schemes will be
designed for the system and comparatively evaluated in order to finalize the most suitable
strategy.This entire exercise is expected to lead to a systematic methodology to design a
redundant manipulator for any workcell that may involve inaccessible locations.
Path Planning and Obstacle Avoidance:
Intermediate pathpoints for the end effector is required for moving
from start to goal point; also the manipulator should avoid obstacles.
Initially we tried to test the traditional "Potential Field approach"
graphically in OpenGL. It is very difficult to find a potential function applicable
to all obstacles. We concluded that potential field approach is not at all practical,
as the manipulator tends to vibrate near the obstacles.
Next we have explored through another approach called: "Visibility
This along with Inverse Kinematics has proved to be quite feasible. Though Inverse
Kinematics for redundant manipulators is not easy to handle, one can simplify
the Inverse Kinematics for 4 DOF parallel plane, serial manipulators.
Finally we will also demonstrate Path Planning and Obstacle Avoidance
using Genetic Algorithm. This is an original contribution from our side towards
Path Planning and Obstacle Avoidance.
We have found by the use of Genetic Algorithm one can easily eliminate the problems
of Potential Field Approach and Inverse Kinematics and the manipulator can very easily
navigate through very narrow regions without getting stuck.
Manipulator/Workcell Design and Development:
In our four-link manipulator, links would be made of a light and sturdy composite
material called "perspex". The links would be driven by servomotors.
The following figure gives the overall look of our proposed design. Roller supports to
links are given to avoid sagging. The design is portable and can be easily moved
from one place to another.
To start with we try our manipulator in the workcell shown in first figure.
But our manipulator should work for any workcell. Every time a new workcell is
given,we would only change the description of obstacles in our Path Planning
program, rest will remain same.
Keeping the obstacles under consideration, redundancy
resolution schemes will be developed to maximize the dexterous
performance of the manipulator. We need to find the time behavior of the
force and torques to be delivered by the joint actuators so as to ensure the
execution of the desired trajectories. Control of end-effector motion
demands an accurate analysis of the characteristic of the mechanical
structure, actuators etc. Therefore manipulator control is ensured to the
closure of feedback loops, by computing the deviation between the reference
inputs and the data provided by the proprioceptive sensors. A feedback
control system is capable to satisfy accuracy requirements on the execution
of the prescribed trajectories. Servo and model-based control strategies will
be developed and experimentally evaluated with respect to their performance
and cost in order to finalize the most suitable control scheme. In fact much
of the challenge of the design and its efficient use focuses on this aspect.
The data generated by the path-planning program is fed to control software
called LABVIEW. This software converts the digital signal to analog using a
control card called FLEX MOTION PC1-6c. The specifications of this
control card are shown after few pages. The signal is fed to motor, which
drives the manipulator using the gear head. The encoder senses the position
of the joints at regular interval of time. This provides data for feedback
control in terms of velocity and position. It is converted to analog signal
using the same control card. Thus the feed back loop is completed and the
desired motion is obtained.
Calibration and Testing:
The project does not end with Controller design. Kinematic Calibration
is also required at the end, after the manipulator has been developed along with the
Path Planner and the controller.
Till now we have completed the theoretical aspects, like Path Planning and
Mechanical Designing. However graphical testing of the Path Planner is still
going on. Attempt to make it as general as possible, i.e. independent of
workspace, is going on. Manufacturing of the components has started. This project is
expected to complete by February end. If successfully completed we will go for its publication.
Meanwhile the page will be updated from time to time till the end of the project.
Home Page & Other Works