Where am I? Sensors and Methods for Mobile Robot Positioning

142 Part II Systems and Methods for Mobile Robot Positioning
b actual
90( b nominal
90(
(5.13)
so that
b actual
90(
90( b nominal
(5.14)
where, per definition of Equation (5.2)
E b
90(
90( .
(5.15)
Once E b and E d are computed, it is straightforward to use their values as compensation factors
in the controller software [see Borenstein and Feng, 1995a; 1995b]. The result is a 10- to 20-fold
reduction in systematic errors.
Figure 5.10 shows the result of a typical calibration session. D Rand D Lare the effective wheel
diameters, and b is the effective wheelbase.
100
Y [mm]
50
-50 50 100 150 200 250
-50
-100
-150
-200
Center of gravity of cw runs,
after correction
Center of gravity of ccw runs,
after correction
Before correction, cw
Before correction, ccw
After correction, cw
X [mm]
After correction, ccw
-250
\book\deadre81.ds4, .wmf, 07/19/95
Figure 5.10: Position rrors after completion of the bidirectional square-path
experiment (4 x 4 m).
Before calibration: b = 340.00 mm, D R/D L = 1.00000.
After calibration: b = 336.17, D R/D L = 1.00084.