Theory

We present an RF design which is a compromise between dead reckoning and mapping.

A remote base station broadcasts an unmodulated sine wave on a set channel. A receiver on the robot detects the signal and compares its' phase to a locally generated signal of identical frequency. The phase difference goes as a saw wave with respect to the distance of the robot from the transmitter (this is illustrated in the upper right hand corner of the summary poster). This phase difference determines the robot's position within one wavelength (similar to a local mapping). By counting the phase difference's transitions from +180 to -180 degrees (the vertical portion of the saw wave - called sharp transitions) one can determine how many wavelengths the robot has moved (similar to dead reckoning).

"Slip" can only occur if the robot moves so fast that one of the transitions can't be detected. Position can be triangulated if multiple base stations are used.

Summary:

x=x0+L*(n+d/360)

where:

x = position
x0 = initial position
L = wavelength
n = # of 180 to -180 transitions - # of -180 to 180 transitions
d = phase difference in degrees

© 2002 Peter Schmidt, All rights reserved.