Wireless indoor mobile robot with RFID navigation map and live video : a thesis in the partial fulfilment of the requirements for the degree of Masters of Engineering in Mechatronics, Massey University, Palmerston North, New Zealand
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Date
2011
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Massey University
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Abstract
A mobile robot was designed in order to move freely within a map built in an indoor
environment. The aim is for the robot to move between passive RFID (Radio Frequency
Identification) tags in an environment that has been previously mapped by the designed
software. Passive RFID tags are inexpensive, the same size and shape as a credit card and are
attached to other objects. They don’t require any power of their own but operate through an
RFID reader that induces a magnetic field in their antenna, which then creates power for the
tag. This makes the tags inexpensive, and easy to setup and maintain.
The robot is a three wheeled vehicle driven by two stepper motors and is controlled
wirelessly through a PC. It has a third omniwheel at the front for maintaining the balance of
the robot. Since the PC communicates continuously with the robot, all the major processing
and data management can be done on the computer making the microcontroller much simpler
and less expensive. Infrared distance sensors are placed around the robot to detect short range
obstacles and a sonar sensor at the front can detect obstacles further away. This data is used
so that the robot can avoid obstacles in its path between tags. An electronic compass is used
to provide absolute orientation of the robot at all times to correct for errors in estimating the
angle. A camera is attached to the front of the robot so that an operator can see the robot and
manually control it if necessary. This could also be used to a video a certain environment
from a robot’s perspective.
The sensors and the RFID tags are all inexpensive, making the mass reproduction of the robot
feasible and implementation practically possible for small firms. The RFID tags can be
quickly attached or detached from an environment leaving no trace of their prior existence. A
map can then be formed on a PC automatically by the robot through its detection of the tags.
This makes the entire system very flexible and quick to set up, something that is needed in
the present day as changes to buildings and factories become more common.
There are still many improvements needed to improve the stability of the compass’s signal in
the presence of magnetic fields, the stability of the wheels so that slippage is rare, and the
range of the wireless signal and camera.
A flexible, easily configurable moving robot could be used to serve fields such as the medical
field by transporting goods within a hospital, or in factories where goods need to be
transported between locations. Since the system is flexible, and maps can be formed quickly,
the robot can fit in with the changes to an industry’s environment and requirements.
However, since the robot can only move to approximately five metres from the computer
controlling it and the inaccuracy in sensor data, it is not currently ready for industrial use. For
example, the sensors are only placed at 6 orientations around the robot and so do not cover a
full span of the robots area. These sensors also only detect a two dimensional plane around
the robot so could not detect obscure objects that have a part sticking out at height higher
than the sensors. Therefore, further work is needed to be done to make the robot reliable,
safe, and fault-proof before it could be used in industry.
Since the movement of the robot with inexpensive sensors and motors is bound to have
problems in perfectly moving between RFID tags, due to small dead reckoning errors, simple
algorithms are shown in this research that moves the robot around its current location until it
finds a tag. These algorithms involve finding a path between two RFID tags that will make
use of any tags in between them to localise itself and moving in a spiral to search for a tag
when, due to odometry errors, it is not detected where it is expected to be.
The robot built has demonstrated being able to navigate between RFID tags within a small
lab environment. It has proven to be able to avoid obstacles with a size of 30 x 30 cm.
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Keywords
Mobile robots, Robot design, RFID, Radio frequency identification systems, Robot controllers, Robot sensors