Gyroscopic Instruments |
Gyroscopic Instruments Principle of Operation
Gyroscopes
A gyroscope is a device used for measuring or maintaining orientation and angular velocity of aircraft. It is a spinning wheel or disc where the spin axis is unrestricted in its orientation choices. The orientation of this axis remains constant when the mounting rotates or tilts in accordance with the rule of conservation of angular momentum.
There are various gyroscopes
with different operating principles, including the MEMS gyroscopes packaged on
microchips that are used in electronic devices (also known as gyrometers),
solid-state ring lasers, fibre optic gyroscopes, and the incredibly sensitive
quantum gyroscope.
Gyroscopes are used in
inertial navigation systems, such as those found in submerged submarine hulls
or the Hubble Space Telescope. Gyroscopes are also employed in gyrotheodolites
to maintain orientation in underground mining because of their accuracy. Gyroscopes
can be used to make gyrocompasses, which can be added to or used in place of
magnetic compasses in ships, aeroplanes, and other types of vehicles. They can
also be used to help stabilise objects like bicycles, motorcycles, and ships,
or they can be incorporated into inertial guidance systems.
Description
Gyroscopes are devices
that allow a wheel to rotate around a single axis by mounting it into two or
three gimbals that act as pivot points. A wheel positioned on the innermost
gimbal may be able to maintain an orientation separate from the orientation of
its support by using a trio of gimbals, each mounted on the other with
orthogonal pivot axes.
The outer gimbal, which
is the gyroscope frame in the case of a gyroscope with two gimbals, is positioned
so that it can pivot about an axis in its own plane that is dictated by the
support. There is only one degree of rotational freedom in this outer gimbal,
and none in its axis. In order for the second gimbal, or inner gimbal, to pivot
about an axis in its own plane that is always perpendicular to the pivotal axis
of the gyroscope frame, it is positioned in the outer gimbal (outer gimbal).
There are two rotating degrees of freedom in this inner gimbal.
The spin axis is
determined by the axle of the rotating wheel (the rotor). The rotor must rotate
continuously about the axis of the inner gimbal, which is perpendicular to this
axis. Therefore, the rotor has three degrees of freedom during rotation, while
the axis has two. A response force supplied to the output axis causes the rotor
to react to a force applied to the input axis.
The front wheel of a
bicycle is the best analogy for understanding how a gyroscope behaves. The
forward rim of the wheel turns to the left when the wheel is leaned away from
vertical, causing the top of the wheel to move in that direction. In other
words, the third axis of the turning wheel rotates when the first axis of the
wheel is rotating.
Depending on whether the
output gimbals are in a free or fixed configuration, a gyroscope flywheel will
roll or resist about the output axis. The attitude control gyroscopes used to
sense or measure the pitch, roll, and yaw attitude angles in a spaceship or
aircraft are an example of certain free-output-gimbal devices.
The rotor's center of
gravity may be set in place. The rotor can oscillate about the two additional
axes while concurrently spinning about one axis, and it is free to rotate about
the fixed point in any direction (except for its inherent resistance caused by
rotor spin). Some gyroscopes replace one or more of the elements with
mechanical equivalents. Instead of being positioned in gimbals, the rotating
rotor may, for instance, be hung in a fluid. An example of a fixed-output
gimbal device used on spacecraft to keep or maintain a desired attitude angle
or pointing direction utilizing the gyroscopic resistance force is a control
moment gyroscope (CMG).
The outer gimbal (or its
equivalent) may be skipped in some unique circumstances, leaving the rotor with
only two degrees of freedom. Other times, the rotor's center of gravity may not
line up with its center of suspension because the rotor's center of gravity is
offset from its axis of oscillation.
Basic Gyro
Mechanical Gyros
Gyroscopes are used to
regulate three of the most popular flying instruments: the attitude indicator,
heading indicator, and turn needle of the turn-and-bank indicator. Gyroscopic
principles and instrument power systems must be understood in order to
comprehend how these instruments work.
A wheel or rotor with its
mass centered on its edge makes up a mechanical gyroscope, or gyro. The rotor
contains bearings that allow for rapid rotation.
The rotor assembly can
rotate about one or two axes perpendicular to its axis of spin thanks to
several mounting options for the rotor and axle. The axle is first installed in
a supporting ring before being used to hang the rotor for spinning. The
supporting ring and rotor can both move freely 360° if brackets are mounted 90°
around the supporting ring from where the spin axle attached. The gyro is
referred described as a captive gyro in this design. It can only spin around a
single axis that is perpendicular to the axis of spin.
Another option is to
install the supporting ring inside of an outer ring. The bearing points are 90
degrees around the supporting ring from where the spin axle was mounted, much
as the bracket I just described. This outer ring's attachment to a bracket enables
the rotor to spin while rotating in two planes. Both of these are orthogonal to
the rotor's spin axis. The rotor's rotational plane, which results from its
revolution around its axle, is not taken into account.
Because it may freely
rotate around two axes that are both perpendicular to the rotor's spin axis, a
gyroscope that has two rings and a mounting bracket is known to be a free gyro.
Because of this, the supporting ring with the affixed spinning gyro is able to
freely rotate 360 degrees inside the outer ring.
A gyro is just a wheel
that can be installed anywhere; it has no distinctive characteristics unless
the rotor is spinning. The gyro displays a few special traits when the rotor is
rotating at a high speed. Gyroscopic rigidity, or rigidity in space, is the
first. As a result, regardless of how the gyro's base is positioned, the rotor
of a free gyro always points in the same direction.
Gyro Horizon
Gyroscopic Rigidity
Gyroscopic rigidity is
influenced by various design aspects, including:
- Weight: A heavy mass is more resistant to disrupting forces than a light mass for a given size.
- Angular velocity: The stiffness or resistance to deflection increases with increasing rotational speed.
- Radius at which the weight is concentrated: A mass rotates most efficiently when its main weight is concentrated close to the rim.
- Bearing Friction: Low bearing friction maintains low deflecting forces.
Gyros are used in
attitude-indicating instruments and directional indicators because of their
ability to remain rigid in space.
Gyroscopic Precession
A second significant
point of gyroscopes is precession. A special phenomena happens when the gyro's
horizontal axis is forced. The exerted pressure is resisted. The gyro travels
about its vertical axis in reaction to the force rather than about its horizontal
axis. Or, to put it another way, the axis of the rotating gyro does not tilt
when a force is applied to it. Instead, the gyro reacts as though the force had
been applied 90 degrees in the opposite direction from the rotor's spin. Rather
than tilting, the gyro revolves. In a turn and bank instrument, a gyroscope's
predictable, regulated precession is used.
Solid State Gyros and Related Systems
In aviation, better
attitude and direction information is always the aim. Modern aircraft use
solid-state, mechanically inert attitude and directional systems that are
extremely accurate. As a result, there is extremely little maintenance and very
high reliability.
Ring Laser Gyros (RLG)
In commercial aviation,
the ring laser gyro (RLG) is frequently utilized. RLG operation is based on the
fact that light takes time to circle a stationary, nonrotating object. If the
path is rotating in the same direction as the light is travelling, it takes
more time for the light to reach its destination. Additionally, if the path is
rotating in the opposite direction from the light, it takes less time for the
light to complete the loop. In essence, the rotation of the path lengthens or
shortens it. The Sagnac effect is what is meant by this.
A laser is a device that
amplifies light by radiation stimulation. In order for a laser to work,
plasma's atoms must be stimulated to emit electromagnetic energy, or photons. A
ring laser gyro generates laser beams that circle a closed triangular chamber
in opposition to one another. Light passing through the loop has a constant
wavelength. The length or width of the lasers' required path changes as the
loop turns. As the loop's effective length varies, the light wavelengths either
shorten or lengthen to complete their journey around the loop. The frequencies
alter along with the wavelengths.
The rate of rotation of
the route can be determined by comparing the two counterrotating beams of
light's frequencies. To prevent output signal lock-in at slow rotating speeds,
the unit's piezoelectric dithering motor vibrates. When functioning, it makes
equipment installed on aircraft hum.
The cavity route revolves
around one of the axes of flight thanks to an RLG that is remotely placed. The
rate of the aircraft's rotation about that axis can be calculated from the
frequency phase change between the counterrotating lasers. For each axis of
flight of an aircraft, an RLG is placed. Systems for analogue instrumentation
and autopilot can use the output. Additionally, it may be adapted to work with
digital display and autopilot computers with ease.
Due to the fact that they
have no moving parts, RLGs are extremely durable and have a long service life.
They offer continuous output while measuring movement along an axis very
quickly. They are far more precise than mechanical gyroscopes and are often
preferred.
MEMS Gyro
Attitude and directional
systems based on Microelectromechanical technology
Microelectromechanical
systems (MEMS) components reduce weight and space in aeroplanes. The
reliability is improved by using solid-state MEMS devices, mainly because there
are no moving parts. ADCs are integrated with the development of MEMS
technology for application in aviation instrumentation. This most recent
technological advancement is inexpensive and is expected to spread throughout
all types of aviation.
Both larger commercial
aeroplanes and smaller general aviation aircraft use MEMS for gyroscopic
applications. Only a few millimetres in length and width, tiny vibration-based
devices with capacitance and resistance measuring pick-offs are accurate and dependable.
They are typically integrated into a whole micro-electronic solid-state chip
that is intended to produce an output after completing a number of conditioning
operations. The chips, which resemble miniature circuit boards, can be packaged
for installation within an aircraft module or special computer.
The movement of the
aircraft is observed and measured while a sizable mechanical gyroscope rotates
in the plane. Despite their small size, many MEMS gyroscopes operate on the
same principle. The spinning, weighted ring of the mechanical gyro is replaced
with a vibrating or oscillating piezoelectric device in the difference.
However, once in motion, any out-of-plane motion can be picked up by shifting
microvoltages or capacitances picked up by pickups that are placed
geometrically. Since piezoelectric materials have a link between movement and
electricity, a piezoelectric gyro can be placed in motion using microelectrical
stimulation, and the minute voltages generated by the piezo's movement can be
retrieved. They can be used as the inputs for the necessary variables when
calculating attitude or direction.
Other Attitude and Directional Systems
In contemporary
aeroplanes, the gyroscope and other individual instruments have been replaced
by attitude heading and reference systems (AHRS). GPS, solid state
magnetometers, solid state accelerometers, and digital air data signals are all
combined in an AHRS to calculate and output highly reliable information for
display on a cockpit screen, while MEMS devices provide some of the system's
attitude information.
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