Inertial Sensors and Their Applications - Signal Processing Systems - page 70

creates different requirements to inertial sensors in terms of accuracy, size, power
consumption, and cost. For example, the principal driving force for high-accuracy
inertial sensors development has been inertial navigation for aircraft and sub-
marines, precise aiming of telescopes, imaging systems, and antennas. For some
applications, improved accuracy is not necessarily the most important issue, but
meeting performance at reduced cost and size is. The major requirements to inertial
sensors in automotive industry are low cost, high reliability, and possibility of mass
production. In the following sections some examples of applications are given.

1.3.1 Navigation

INSs normally consist of three gyros and three accelerometers. The data from
inertial sensors are processed to calculate the position, velocity, and attitude of
the vehicle. High performance INSs require accurate sensors. Such systems are
expensive, weigh several kilos, and have significant power consumption. However,
not in every navigation application has a high-performance INS to be used.
For example, land vehicle navigation systems can significantly reduce INS error
growth by applying non-holonomic constraints 1 and using odometer measurements.
Therefore, in many land vehicle applications a lower cost tactical grade INS can
be used instead of a more expensive navigation grade INS. Pedestrian navigation
systems take advantage of biomechanics of walking. Recognizing that people
move one step at a time, the pedestrian mechanization restricts error growth by
propagating position estimates in a stride-wise fashion, rather than on a fixed time
interval. Inertial sensors are used to detect the occurrence of steps, and provide a
means of estimating the distance and direction in which the step was taken. For step
detection, accelerometers don't have to be of high accuracy. Pedestrian navigation
is addressed more profoundly in Sect. 3 .

1.3.2 Automotive

In modern cars, MEMS accelerometers are used in airbag deployment systems
to detect a rapid negative acceleration of the vehicle, determine if a collision
occurred, and estimate the severity of the collision. Another common automotive
use of MEMS gyros and accelerometers is in electronic stability control systems.
It compares the driver's intended direction which can be determined through the
measured steering wheel angle to the vehicle's actual direction determined through
measured lateral acceleration, vehicle yaw rotation, and individual wheel speeds.
Other automotive applications include monitoring of noise, vibration, harshness,
and conditions that cause discomfort for drivers and passengers and may also be
indicators of mechanical faults.

1 In short, non-holonomic constraints allow to neglect the lateral and vertical speeds of the vehicle.