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Modular ApproachIn

Robotic Design(An Overview)



ABSTRACT

Long development times and high costs prevent robots from

being practical for use in many important fields of applications. Robotics is one

particular area attracting growing interest amongst a number of countries. Most of

their work is following along the conventional lines of designing specialized robots to

perform specific tasks. Such robots work tends not to be multi-purpose and their

performance suffers when forced to deal with different environments. This paper

proposes a more versatile solution: modular self-reconfigurable robot. Here a modular

design approach is proposed to produce a rapidly deployable Low cost field robotic

system. An inventory of components such as actuated joints, links, power supplies

and software modules are assembled to produce a field robotic system for a specified

task. This paper proposes using a multipurpose modular self-reconfigurable robot.

These are capable of adapting their very structure to match the tasks and environment

at hand. Their extreme modular construction enables easy in the – field diagnosis and

repair by untrained users.

The key benefits are flexibility, maintainability and robustness.

This paper includes the discussion about modular design and its optimization,

industrial modular manipulators and their design in detail .This paper also gives

information about reconfigurable modular robots with an example- Polybot.

In this paper a design approach based on modular components

for field robots is proposed. It has potential to all robotic systems to be rapidly and

cost effectively designed and fabricated.



MODULAR APPROACH IN ROBOTIC DESIGN

INTRODUCTION

The approach is based on the use of an inventory of physical roboticmodules such as actuated joints, links and power units that are assembled in different

configuration to perform different tasks. This approach also uses software action

modules that are assembled to produce an execution plan for a given robot assembly

and its task. Using pre-fabricated modules would greatly shorten development times.

Also substantial cist savings would be realized by using an inventory of reusable

‘standard’ modules that could be used for number of applications.

MODULAR SYSTEM LEVEL DESIGN

The key to our approach in the use of modular components for robotic

systems is to apply fundamental engineering principles to reduce the design space in a

series of structuring and tests.

The module inventory includes a set of modular components namely

• Body

• Link

• Rotary joint• Wheel

• Foot

• Linear joint & Gripper

Combining of these small set of modules in different ways permit

many topologically diverse

robots to be constructed.

Three sample robots

assemblies that can be

produced from this

inventory are shown.

Sample Robot

Assemblies



STEPS IN DESIGN AND SYNTHESIS

Manipulator is an electromechanical system consisting of two basic

building blocks: Links and Actuators.

Step1 : Choosing a kinematic configuration that has some desired characteristics such

as reach and dexterity.

Step 2 : Parametric modeling of Em actuator

It is performed allowing the designer to calculate the

Performance parameters such as weight, inertia and torque.

Design parameters such as material properties and dimensions.

Intermediate parameters are grouping of several design parameterssuch as gear reduction ratio.

Step 3 : Construction of global performance maps

Global performance maps are constructed via some designmeasures such as Inertia frobenius norm (IFN), end-effector acceleration, end-



effector static load which measures kinetic energy in system, ability to

acceleration, and ability to apply or resist static loads. The different designs

are achieved by changing the properties of actuators. Evaluating many designs

yield the global performance maps for IFN,acceleration capability,force

capability etc.,

Step 4 : Developing constraints

Constraint equations based on physical limitations on actuators such as motor

speed, gear teeth strength.

Step 5 : Optimisation techniques are employed to select the actuator parameters that

yield the best design for the given constraints.

Step 6 : System level configuration

OPTIMISATION OF MODULAR DESIGN

Due to typical symmetries in module design different assembly

configurations may lead to robotic structures which are kinematically identical. To

enumerate the non isomorphic assembly configurations of a modular robotic system

an Assembly Incidence

Matrix was introduced. Then

symmetries of module

geometry and graph

isomorphism can be used to

define an equivalence

relation on AIMs.

Equivalent AIMs represent

isomorphic robot assembly

configuration based on the

equivalence relation we

propose an algorithm to

generate non-isomorphic

assembly of n-link tree-link

robot with different joint and

link module types.

Modular Design Process



The genetic algorithm takes a number of robot assemblies

called a generation and combines some attributes from one assembly with those of

another, thus creating a new generation of robot. This process is called Crossover. The

algorithm also adds new characteristics that were not present in previous generation

called Mutation. The genetic algorithm uses assembly rules and filters to produce a

fitness value for a given robot configuration. This fitness value is used to compare one

assembly to another.

Assembly filters make estimates of system performance

measures such as power consumption, applicable forces, static stability and mobility.

Using the techniques of Crossover and Mutation a final robot configuration evolves

after multiple generations.

Genetic Algorithm Representation

ADVANTAGES OF MODULAR RECONFIGURABLE ROBOTS

Infact within certain reasonable constraints a well designed set

of modules can be used to construct a specialized robot for almost any purpose. A

huge number of radically different robots can be constructed with same set of

modules. This provides the potential for cost savings at the factory level: making each

of many different robots from just one or two components.

Flexibility: The properties of robot changes with its form, for one MRR might be

built so as to have six appendages which serves as legs for walking on rough terrain

(insect motion). Another MRR composed from the very same modules might instead

form a long thin snake capable of crawling through cracks and up pipes for access to

denied areas (snake motion). The modules can connect and disconnect under the

robot’s own control. By disconnecting and reconnecting all of its modules a MSRR is

capable of completely changing its fundamental structure.



Various structures of MSRR

An MSRR can change form enabling to perform multiple tasks. Such

changes also allow it to adapt for locomotion through, or work in a varied

environment.

Self repairable:

If one of the modules in a MSRR fails, then this can be internally

diagnosed. Upon recognizing, the system will simply reconfigure while physically

disconnecting the failed module. Through its ability to self reconfigure an MSRR can

perform a certain amount of running repairs on itself. To continue doing its

commanded job with less modules will require some adaptation such as shortening of

each leg perhaps(if a few modules are borrowed from each)something impossible

with a conventional robot. The combination of graceful degradation through adaptivecontrol, Self-repair ability, means that many independent failures within the robot can

be sustained without catastrophic failure of entire system.

Conceptual Reconfigurable Robotic Workcell

MODULAR ROBOTIC MANIPULATORS

ALPHA (Advanced Light Weight Prototype High performance Arm)

- It is a high payload, modular and extremely accurate, all revolute,

7DOF serial robotic manipulator.



- To achieve high precision under load ALPHA was designed to be

structurally very stiff.

- It was designed to perform Industrial applications such as precision operators

like die production, air frame assembly and fully integrated manufacturing cells.

POLY BOT

-There are three versions (started in 1998). The current version of

polybot consists of just two modules types

The segments are 5 x 5 x 5 cubes with a single degree of freedom and two inter

connect faces.

The nodes are slightly larger cubes stationary but have six interconnect faces.The communication layer has been augmented by MDCN

A diagram showing some aspects of the third generation

of polybot

R e f e r e n c e s :

1. Cole.j Rapid generation of motion plans for Modular Robotic systems



2. Design and Motion Planning of multi-limb Robotic systems by Madhani, A.

and Dubowsky,S.

3. Rutman, N. Automated design of Modular field robots.

4. A.Casal and M.Yim, Self reconfiguration planning for a class of modular

robots

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