ABSTRACT
These sensors provide reference outputs that are
processed to develop navigation data.
To illustrate the principle of inertial navigation,
consider the accelerometer device illustrated in
Figure 17.1; this is formed with a mass and two
springs within a housing. Newton’s second law of
motion states that a body at rest (or in motion)
tends to stay at rest (or in motion) unless acted
upon by an outside force. Moving the
accelerometer to the right causes a relative
movement of mass to the left. If the applied force
is maintained, the mass returns to the neutral
position. When the accelerometer is moved to the
left, or brought to rest, the relative movement of
the mass is to the right. The mass continues in its
existing state of rest or movement unless the
applied force changes; this is the property of
inertia. Attaching an electrical pick-up to the
accelerometer creates a transducer that can
measure the amount of relative movement of the
mass. This relative movement is in direct
proportion to the acceleration being applied to
the device, expressed in m/s2. If we take this
Figure 17.1 Accelerometer
electrical output and mathematically integrate
the value, we are effectively multiplying the
acceleration output by time; this can be expressed
as:
Time × acceleration = s × m/s2 = m/s = velocity
If we now take this velocity output and
mathematically integrate the value, we are once
again multiplying the output by time; this can be
expressed as:
Time × velocity = s × m/s= m = distance
In summary, we started by measuring
acceleration, and were able to derive velocity
and distance information by applying the
mathematical process of integration. To illustrate
this principle, consider a body accelerating at 5
m/s2, after ten seconds the velocity of the body
will be 50 m/s. If this body now travels at a
constant velocity of 50 m/s for ten seconds, it will
have changed position by 500 m.
