Where am I? Sensors and Methods for Mobile Robot Positioning

Chapter 2: Heading Sensors 53
A system block diagram is presented in Figure 2.21. The sensor consists of two orthogonal pickup
coils arranged around a toroidal excitation coil, driven in turn by a local oscillator. The outputs V x
and V y of amplifier channels A and B are applied across an air-core resolver to drive the display
indicator. The standard resolver equations [ILC Corporation, 1982] for these two voltages are
V = K sin sin(7t + a )
x x x
V = K cos sin(7t + a )
y y y
(2.12a)
(2.12b)
where
= the resolver shaft angle
7 = 2%f, where f is the excitation frequency.
K and K are ideally equal transfer-function constants, and a and a are ideally zero time-phase
x y x y
shifts.
Thus, for any static spatial angle , the equations reduce to
V = K sin
x
x
V = K cos
y
y
(2.13a)
(2.13b)
which can be combined to yield
V x
V Y
sin
cos tan .
(2.14)
The magnetic heading
therefore is simply the
arctangent of V xover V y.
Everett [1995] recounts
his experience with two models
of the Zemco fluxgate
compass on ROBART II as
follows:
Problems associated with
the use of this particular
fluxgate compass on
ROBART, however, included
a fairly high current consumption
(250 mA), and
stiction in the resolver reflecting
back as a load into
the drive circuitry, introducing
some error for minor
Fluxgate
sensor
Amplifier
Driver
Driver
Oscillator
Amplifier Driver
Figure 2.21: Block diagram of ZEMCO Model DE-700 fluxgate compass.
(Courtesy of ZEMCO, Inc.)
Air
core
resolver