A gyrometer is any device that measures angular speed. At present, there are many types of gyro, each functioning differently depending on their type. While gyroscopes were traditionally used for sailing ships through foggy conditions, their applications have since diversified and, today, high-tech gyros can be found in consumer goods such as cameras, drones and smartphones or in high-end applications such as military and aerospace.
- Providing stabilization around one axis – most commonly found in civilian cameras and security cameras
- Trajectory control of a moving device – most commonly found in RC helicopters, drones, but also in large-scale applications such as helicopters and planes
- Orientation with reference to the North – used in estimating the geographical North by measuring the Earth’s rotational speed
- System stabilization with a land reference – common in Altitude and Heading Reference Systems (AHRS)
- Navigation – used to measure position, speed and altitude autonomously with inertial measurements
Types of gyro technologies
This type of gyroscope performs flawlessly in terms of performance and is commonly used in high-end and strategic applications. It provides the stability needed for aerial reconnaissance and mapping operation, which require that cameras be fixed on the photographic target during the period of exposure. However, gyro-stabilized platforms are very expensive and their implementation is quite complex.
Ring laser gyros
Ring laser gyroscopes (RLGs) rely on the movement of a light source and a co-located color detector. The constant velocity of light waves from a moving platform will cause the beam to change phase. They operate on the principle of the Sagnac effect, which shifts the nulls of the internal standing wave pattern in response to angular rotation. When observed externally, the interference between the counter-propagating beams reflects shifts in the standing wave pattern, generating rotation.
Ring laser gyros have been in production for around 40 years and offer very good performance and reduced power consumption. However, aside from requiring high processing speeds, ring laser gyros are expensive and big, which makes them tricky to implement.
Fiber-optic gyroscopes (FOGs) rely on the interference of light to detect mechanical rotation. The way it works is that two laser beams are inserted into the same fiber, but in opposite directions. The beam that travels against the rotation experiences a slightly shorter path delay than the other beam due to the Sagnac effect. The sensor is comprised of a coil that can have as much as 5 km of optical fiber.
These types of gyros were invented during the early 1970s, when the telecommunication industry enabled the development of low-loss, single-mode optical fiber. Fiber-optic gyros are easier to assemble than RLGs and are more cost effective. However, high-quality FOGs still require high-grade fiber optics, which drives product prices upwards, making them quite expensive.
Dynamically tuned gyrometer (DTG)
A DTG is basically a rotor suspended by a universal joint with flexure pivots, with the flexure spring stiffness being independent of the spin rate. However, the dynamic inertia from the gimbal, a result of the gyroscopic reaction effect, provides negative spring stiffness proportional to the square of the spin speed. As a result, the two moments cancel each other once they reach a particular spin (often referred to as the ‘tuning speed’), freeing the rotor from torque, a necessary condition for an ideal gyroscope.
DTGs have the advantage of being small, which makes them quite useful in today’s application. However, their implementation involves complex techniques, which makes the whole process quite expensive.
MEMS gyroscopes operate on the same principle as a Foucault pendulum, the only difference being that they use MEMS as vibrating elements. They incorporate multi-axis silicon-based gyroscopes and accelerometers in order to achieve output that has six degrees of freedom. It’s important to mention that MEMS gyroscopes have no rotating parts that require bearings, which means that they can be easily miniaturized and fabricated in large batches using micromachining techniques.
Although MEMS gyroscopes provide a cost-effective solution, the limits in the vibrating mass induces limited performance, as well as some degree of noise and bias stability.