27-08-2014, 01:04 PM
Multiconfigurable Inspection Robots for Low
Diameter Canalizations
Multiconfigurable.pdf (Size: 430.25 KB / Downloads: 20)
Abstract—
Pipe inspection is a very important issue in
construction. The inspection of low diameter canalizations is a
pending issue nowadays, however it would help to repair and
maintain a large amount of installations. In this article the lines
that are followed to build a robot that is capable to move inside
pipes of less than 26mm and negotiate bends while carrying a
camera are described, together with a walk through the state of
the art of the robots which are related to the research.
I. INTRODUCTION
NOWADAYS, the number of pipes around us is very
large, including sewer systems, gas pipelines,
hydroelectric and nuclear power stations, water, gas and
heating pipes in buildings… Among them, there are many low
diameter pipes which require to be inspected every year. The
cost to inspect such systems can be very high. There are
basically two techniques to inspect these pipes: passive and
active systems. Passive systems are usually intelligent pigs
driven by the pressure difference of fluid inside the pipelines,
which are not suitable for many applications (i.e. to be still or
go back in the pipe). Active systems are mainly based on
robots, which is our case.
Two main application can be found in robotic inspection of
pipes: in buildings already built it is a good way to check the
structure in case any modification must be done; and in
buildings under construction to make sure tasks has been done
properly, i.e. assembling, welding…etc.
II. DESCRIPTION OF MICROTUB.
The goal of the project MICROTUB is to build an
autonomous multiconfigurable microrobot for low diameter
pipes inspection and maintenance. It is being designed to
explore pipes with a camera to detect breakages, holes, leaks
and any kind of defects. This microrobot is to be composed of
different modules, each of them performing a different task.
Thus, multiconfigurability is an essential characteristic, so
these modules can be easily interchanged depending on the
task.
In first place, different drive modules are being developed
due to the different environments in which the microrobot is
going to perform the tasks. Two main investigation lines are
being followed: worm-like and wheel driven (helicoidal). The
other main module is the camera module, which is a two
degrees of freedom platform carrying the camera and leds.
There are also other modules under research: rotation,
batteries and communication. The modules that are already
developed are described in next section.
III. MODULES BUILT
A. Helicoidal drive module
This module (fig. 2) was design to be a fast drive module. It
is composed of two parts: the body and the rotating head. The
wheels in the rotating head are distributed along the crown
making a 15º angle with the vertical. When the head turns, it
goes forward in a helicoidal movement that pulls the body of
the microrobot. The wheels of the body help to keep the
module centered in the pipe.
The wheels, its axis and the support system have been
manufactured by micromachining, and the other parts (except
for the gears) have been made using stereolithography.
The fact that the head of the robot rotates around the robot
axis involves the necessity to design a channel for electrical
wires that goes through the entire robot to interconnect the
front and the rear part of the robot.
One of the main problems that this board has is the power
consumption. It operates at a range of 8 to 30 V, and requires
up to 5A. This is a huge power demand, so in next versions a
special control board is being design. Also, some similar
models but with miniaturized conventional motors are being
researched.
This module was tested in a 30 cm straight pipe with speeds
of up to 30mm/seg. The microrobot was able to go forward
even when the pipe was set to vertical position. The helicoidal
approach shows itself as a very interesting mean of
locomotion inside pipes.
B. Worm-like drive module based on servomotors
This module is composed of two kinds of submodules:
expansion module and support module (fig. 3), which allows
the microrobot to move as a worm [14]. The support module
is used to fix the microrobot to the pipe, so this module does
not move. And the expansion module is used to expand the
robot (make it go forward), and to turn to right and left (in the
next version of this model it will be able to move also up and
down). The drive unit is composed of two support modules
and one expansion module (fig. 3).
The sequence of movement is as follows (fig. 4):
1. The rear module (3) expands (making pressure against the
pipe) and the front one (1) releases.
2. The central module (2) expands straight or in angle.
3. The front module expands and the rear one releases.
4. The central module contracts.
All the modules use a microservomotor. It is a linear servo
which weights 3.0g, has a maximum deflection of 14mm in
0.15 sec and provides a maximum output force of 200g. The
support modules use one servo only and the expansion module
uses two.
The support module consists of three rubber bands
positioned around the module at 120º from each other, which
are bent when the servomotor is activated, exercising a force
against the walls of the pipe that allows the module to be still.
On the other hand, the expanding module consists of two arms
(each of them droved by a servo) that allows expansion
C. SMAs-based worm-like drive module
This module uses Shape Memory Alloys (SMA) to achieve
a snake-like system of locomotion, based on contraction and
expansion of the SMAs.
Each module is composed of a support board, a control
board (that acts as a support board that additionally holds the
electronics), SMAs wires to make the contraction and springs
to make the expansion when the SMAs releases (fig. 6). Each
module has three degrees of freedom.
The main advantages of this module are: very good relation
torque – dimensions (provide a good torque in a very small
space), simple electronic circuit, SMAs can act as “Smart
Actuators” (resistivity changes depending on the grade of
deformation) and great versatility (it can contract-expand and
rotate). The main disadvantages are: the power consumption is
too high, SMAs act in one direction but they need a ‘rest’ to
get back to the initial position (else a spring to get back to that
position), assembly requires a lot of precision and appropriate
tools, and SMAs have hysteresis.
Due to these disadvantages, we consider that SMAs are
better suitable for tasks that require small and discontinuous
movements, i.e. latching mechanisms or grippers.
D. Rotation module
The rotation module (fig. 8) is a two degrees of freedom
module that allows rotations in the horizontal and vertical
planes. Because of the low dimensions requirements (diameter
smaller than 26mm) no available commercial servos could be
used. Therefore it was built out of the components (axis,
gears…etc) of two commercial servomotors and some other
parts made by stereolithography.
The integration of the parts was very difficult due to the
small dimensions of the components, which required a great
precision in both the design and assembling.
The motivations of this module are three: in first place it
will allow turning around corners. In second place, it is
suitable to hold a camera and allow a two DOF movement of
the camera. And finally, a set of this modules put together will
allow a snake-like movement.
E. Support module II
This module is design to get fixed to the pipe through two
plates that can be expanded or contracted. It can be used as a
more robust alternative to the support module in the wormlike drive module (section B). It has a simple design, being its
main characteristics the robustness and small dimensions
(25mm diameter and 26mm long).
It is based on a commercial microservomotor of
characteristics: 4,4g, 1300g/cm, 0,12s/60º. Two racks are used
to transform the circular movement into a linear movement
(fig. 5)
IV. MAIN FEATURES COMPARED TO OTHER ROBOTS
In the following subsections the main characteristics of
MICROTUB are explained together with the improvements
that are being carried out in comparison to the state of the art
in pipe inspection robots.
A. Modularity and Reconfigurability
The advantages of modularity have been described in the
previous sections. Instead of designing a new and different
mechanical robot for each task, different copies of simple
modules are built. The modules can't do much by itself, but
when many of them are connected together, a system that can
do complicated things appears. In fact, a modular robot can
even be configured in different ways to meet the demands of
different tasks or different working environments.
Each module is virtually a robot in itself having a computer,
a motor, sensors and the ability to attach to other modules.
This is going to be the same in MICROTUB. It is very useful
in case any of the modules failed, i.e. selfreparation
B. Multiconfigurability vs self-reconfigurability
Reconfigurable robots present the ability to change its
configuration either manually or autonomously. If the
reconfiguration is done autonomously, it is called selfreconfiguration. On the other hand, if the reconfiguration has
to be done manually, we talk about multiconfiguration. There
is a lot of research in selfreconfiguration, but most of the
robots in this field have the same features. Two of the most
known robots are Polybot [3] and M-TRAN[4]. These robots
present several features that are very interesting: connection
mechanism between modules, sensors, power supply…etc.
Both PolyBot and M-TRAN are made up of many repeated
modules.
C. Homogeneous vs Heterogeneous modules
Depending on the number of modules that the robot is
compound of, the robot can be classified in homogeneous (all
the modules are the same) and heterogeneous (different
modules). MICROTUB could be defined as in [7] as a nmodular microrobot with n from 2 to 5. Polybot and M-TRAN
are homogeneous
The man advantage of homogeneous robots is that they are
easy to build. On the contrary they are limited to to movement
tasks. Heterogeneous robots are more versatile and can
perform as many tasks as modules have
D. Miniaturization
The term microrobot appears nowadays in many articles
referring to mini-robots, robots of very small dimensions
(millimeters). This is because we are still far from seeing a
real “micro” robot (µm). Thus, in this paper we say
microrobot when we talk about MICROTUB since for most of
the people it is accepted this meaning too.
Keeping in mind that for most of the researches it is not
possible to build a real microrobot, it is necessary to
miniaturize its components and to make the mechanical and
electronic design together to minimize the space
(mechatronics). This work is what we have carried out, and it
is what makes the design so expensive.
V. CONCLUSION
In this article the lines that have been followed to build an
autonomous multiconfigurable microrobot for low diameter
pipes inspection and maintenance have been stated. The main
characteristics of the microrobot have been explained together
with a walk through the state of the art of the robots which are
related to the research.
Several types of modules for pipe inspection microrobots
have been presented. The helicoidal and worm-like drive
modules have been tested and their results have been
described. The helicoidal model is faster and it could be used
when a long distance must be done. On the contrary, the
modular model provides more control and could be used when turns and rotation must be done. Also, the helicoidal module
has helped to prove the efficiency of this kind of movement
for in-pipe microrobots.
In addition, a camera module and a graphical user interface
have been presented. Some other modules (rotation, support)
have been presented and will be used in the future version of
MICROTUB.