Re: Location Detection

Self - calibration --- why not just place occasional RFID tag (extremely short range antenna) on the floor, 
and those can be used by the robot as a calibration point when it runs over it??

Regards, a.m.

On 7/9/05, Athanasios Anastasiou <thanos@xxxxxxxxxx> wrote:

Hello Jeremy

I also had the idea of using several ultrasound fixed beacons and
deriving the position from these BUT there is a much easier solution to
this which is used as an alternative navigational aid.

It is called Inertial Navigation and it breaks down to basic principles
of Kinematics.

You just mount an accelerometer on your robot and calibrate it before it
sets off moving around. The calibration is just setting the starting
point. Lets suppose that this is A(0,0). When the robot starts to move,
the accelerometer records the dx, dy and dz of the robot chassis and
updates the starting point. So after integrating the accelerations you
get a new point B(x,y).

Ofcourse there are a few caveats in this method, one of which is that if
your robot moves towards a direction, under the threshold of detection
of the accelerometer, its movement will not be recorded and its position
not updated. But this is not so serious in robots that have 4 wheels and
move in interior spaces (probably more of a problem for marine robots
using this method.).

The second problem is that you have to make sure that the accelerometer
is always vertical in respect to the chassis of the robot (otherwise you
need to correct the accelerations for the angle of movement). If you are
absolutely sure that the robot is not going to get tilted you can use a
single accelerometer...If not, you need an extra accelerometer just for
measuring the angles and thus adding three more degrees of freedom
(movement in three directions plus roll pitch and yaw angle).

STMicroelectronics sells some very interesting accelerometers that can
give you the three basic accelerations (dx,dy,dz) over serial or I2C
buses. In an application note i noticed that a single accelerometer can
also be used to provide angular position as well. I am not so sure about
that...

Could there be any other alternatives to correcting the values that an
accelerometer returns except mounting it on super slick gimbals and
gyroscopic mechanisms??????

I hope this helps

All the best
thanOS


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