Sensors and Methods for Mobile Robot Positioning

34 Part I Sensors for Mobile Robot Positioning
the vibrations are picked up by the two other transducers at equal intensity. When the prism is
rotated around its longitudinal axis, the resulting Coriolis force will cause a slight difference in the
intensity of vibration of the two measuring transducers. The resulting analog voltage difference is
an output that varies linearly with the measured rate of rotation.
Figure 2.4: The Murata Gyrostar ENV-05H is a piezoelectric
vibrating gyroscope. (Courtesy of [Murata]).
One popular piezoelectric vibrating gyroscope is the ENV-05 Gyrostar from [MURATA], shown
in Fig. 2.4. The Gyrostar is small, lightweight, and inexpensive: the model ENV-05H measures
47×40×22 mm (1.9×1.6×0.9 inches), weighs 42 grams (1.5 oz) and costs $300. The drift rate, as
quoted by the manufacturer, is very poor: 9(/s. However, we believe that this number is the worst
case value, representative for extreme temperature changes in the working environment of the
sensor. When we tested a Gyrostar Model ENV-05H at the University of Michigan, we measured
drift rates under typical room temperatures of 0.05(/s to 0.25(/s, which equates to 3 to 15(/min (see
[Borenstein and Feng, 1996]). Similar drift rates were reported by Barshan and Durrant-Whyte
[1995], who tested an earlier model: the Gyrostar ENV-05S (see Section 5.4.2.1 for more details on
this work). The scale factor, a measure for the useful sensitivity of the sensor, is quoted by the
manufacturer as 22.2 mV/deg/sec.
2.3 Optical Gyroscopes
Optical rotation sensors have now been under development as replacements for mechanical gyros
for over three decades. With little or no moving parts, such devices are virtually maintenance free
and display no gravitational sensitivities, eliminating the need for gimbals. Fueled by a large