Gyro how does it work

Very important improvements have been done since the earliest solutions to date. In , the first air-core photonic-bandgap fiber gyroscope was reported [ 32 ].

Because the optical mode in the sensing coil largely travels through air having low Kerr, Faraday and thermal constants than silica , a lower power and magnetic field dependences were obtained. With a m fiber coil, a minimum detectable rotation rate of 2. In , a new open-loop configuration of an IFOG was presented. A single mode telecommunication optical fiber and an EDFA pumped with DFB laser were used as sensing coil and broadband source, respectively [ 33 ].

The Sagnac phase shift was extracted by a phase tracking circuit with an RC band pass filter, an amplifier and a modulator chip. It measured a bias stability of 1. The proposed structure can reduce the effect of the polarization crosstalk and improves production efficiency.

Through the application of all-digital closed-loop control and random modulation signal processing technology, the dead zone problem, typical of IFOG, caused by electronic cross-coupling, has been eliminated and the SNR of the gyro output has been improved. A zero-bias instability of 0.

In [ 35 ], it is shown that electro-optic polymers have been used in fabricating low loss phase modulators with low half-wave drive voltage for an Inertial Measurement Unit based on an IFOG. A novel technique was introduced for assessing the error caused by backscatter and an offset waveguide design was developed to suppress the interference of backscattered light. An average ARW of about 0.

In , Yahalom et al. The design was based on an innovative approach that enabled the production of a small and low-cost gyro with excellent noise and bandwidth characteristics. The goal was to develop an inexpensive sensor in less than 50 cm 3.

The head sensor was 6. They obtained a bias long-term stability of 0. In , it was demonstrated that, by driving an IFOG with a laser of relatively broad linewidth about 10 MHz , the noise would be reduced to 0.

Researchers used a m fiber coil, with a 3. Using a laser instead of a broadband light source, it offers increased scale factor arising from the frequency stability of the laser.

However, driving a FOG with a laser leads to large noise and drift, because of the coherent backscattering, the Kerr effect and polarization non-reciprocity. It was demonstrated that, carefully selecting the laser linewidth and using a symmetric phase modulation scheme, one can reduce these sources of error to a very low level. In , Wang et al. With a 2 km coil and an open-loop configuration, a bias instability of 0. In the era of miniaturization, the possibility of integrating optical waveguides leads to even smaller solutions.

Thus, RMOG is a promising candidate for applications requiring small, light and robust gyros. In RMOGs, clockwise and counter-clockwise waves are phase-modulated at different frequencies to reduce backscattering induced noise. The effectiveness of this technique, however, is determined by the carrier suppression level. In the experiment reported in [ 39 ], carrier suppression is applied onto both the CW and the CCW waves at the same time to achieve higher total suppression.

Ma et al. In , a 2. The proposed solution can detect a minimum rotation rate of 0. In the same year, Lei et al. The experimental results from the established RMOG setup demonstrate a bias stability of 2. MEMS gyroscopes generally use a vibrating mechanical element as a sensing element for detecting the angular velocity. They do not have rotating parts that require bearings and this allows an easy miniaturization and the use of the manufacturing techniques typical of MEMS devices.

All MEMS gyroscopes with vibrating element are based on the transfer of energy between two vibration modes caused by the acceleration of Coriolis. The Coriolis acceleration, proportional to the angular velocity, is an apparent acceleration that is observed in a rotating frame of reference. To better understand the concept, we can consider a particle of mass m moving in space with a velocity v See Figure 9 a. This is the key physical principle of the vibrating mass MEMS gyroscope, described like a mass-spring system see Figure 9 b.

The vibrating mass MEMS gyroscope has two orthogonal mechanical excitation modes along which the mass can move. If k y and k z are the elastic stiffness parameters proper of the frame, while c x and c y are the respective damping coefficients, the master equations result to be [ 42 ]:.

The primary mode is excited along y drive axis by applying a force F Drive see Equation 19 , while the secondary mode along x sense axis is excited by the Coriolis force F z see Equation Based on these physical principles, a brief panoramic of the research development of silicon MEMS gyroscope that were designed, prototyped and realized from the late s to the s. The following listed sensors are based on revealing Coriolis force and represent, someway, the milestone in the roadmap of MEMS gyro technology improvement.

The pioneering work to miniaturize inertial systems, made by Draper Laboratory expert in inertial guidance systems for military and space applications , led to the creation of MEMS gyros and accelerometers as we know today. In the late s, they developed a hand-assembled device to prove the feasibility of a silicon gyro. Until , in Draper Laboratory, other structures were designed to improve performance with an even simpler fabrication process.

A planar design of a gyro based on the tuning fork principle was then presented. It was equipped with the comb drive mechanism developed at UC Berkeley, which showed a rate capability of about 0.

Afterwards, they explored the fabrication advantages of the vibrating wheel on a gimbal-based gyro design capable of a better rate sensing [ 12 , 44 ].

Several researches, aimed to integrate part of control and signal processing on chip, to develop dual-axis gyroscope and to improve fabrication and performance with multi degree of freedom design, were made at UC Berkeley during next years. In , Clark, Howe, and Horowitz presented a z -axis vibratory rate gyroscope. This device integrated with a trans-resistance amplifier while the sense mode offers a differential measurement using interdigitated comb fingers.

After that, Juneau, Pisano and Smith reported a surface-micromachined dual-axis gyroscope based on a rotor disk that can equally sense rotation about two orthogonal axes. They characterized the two devices through laser meter equipment to observe displacements and the overall behavior, so they found that the gyroscope with independent beams had a resolution of 0. This performance resulted to be better than that related to the reference device, due to weak coupling between the two modes [ 48 ].

Further development followed since the late s, thanks to the fact that silicon technology became more mature, so it was possible to integrate control and processing electronic components into MEMS. Studies aiming at improving MEMS gyroscopes increased, being already known the main aspects of theory and operation; the availability of more sophisticate test equipment to characterize prototypes, more powerful design tools and industrial interest in other application fields at consumer level contributed to the progress of this technology.

It used an electrostatic comb drive to move the proof-masses in x -axis and a capacitive detecting in y -axis to sense rotation in z -axis. Drive and sense mode were electrostatically balanced to achieve perfect mode matching; this design improved sensitivity, bias stability and noise floor.

Sharma, through further research on the M2-TFG, designed the closed-loop circuit based on a transimpedance amplifier with a dynamic range of dB, capable to keep the matched-mode.

Experimental data showed a capacitive resolution of 0. Zaman in reported an improvement of the M2-TFG using two high-quality factor resonant modes. From to , Trusov et al.

These structures forced an anti-phase drive-mode and a linearly-coupled dynamically-balanced anti-phase sense-mode, that prioritizes sense-mode quality factor. The prototypes were characterized in a vacuum chamber, demonstrating a quality factor drive-mode of 67, and of , for the sense-mode [ 54 , 55 ].

In fact, Wang et al. Further measurements pointed out a rate resolution of 0. Other researches were performed towards enabling a wider bandwidth to expand flexibility and ease of use. Thus, in , Tsai et al. Finally, the report by Pyatishev et al.

In this section, five critical parameters for consumer grade gyros will be overviewed:. In the output of a gyro, there is always a broadband white noise element. Angle Random Walk describes the error resulting from this noise element and can be evaluated using the Allan Variance technique.

Active elements of the gyro are the major contributors to random noise laser diode and photo diode for optical gyroscopes and the vibrating beam and detection electronics for MEMS. Noise is one of the most important differences between optical and MEMS gyro performance, resulting in different precision and accuracy in measurements.

When input rotation is null, the output of the gyro could be nonzero. The equivalent input rotation detected is the Bias Offset Error. Fixed errors, such as Bias Offset Error, can be easily corrected. Bias Instability is the instability of the bias offset at any constant temperature and ideal environment.

It can be measured using the Allan Variance technique. Bias instability introduces errors that may not be easy to calibrate. Its influence is greater on longer measurement periods, so Bias Instability is one of the most critical factors in the gyro selection process for applications that requires excellent accuracy over long time.

Gyro performance changes over temperature. A characterization of parameters such as noise, bias offset and scale factor over temperature is necessary to verify that gyro performance meets system targets. Noise and Bias offset of gyros also degrade under vibration and shock input.

Vibration performance is critical in many military and industrial applications, because of the presence of numerous factors such as engines or gunfire. The evolution of modern gyros technology, performance and application could be understood through an overview of its history starting from midth century.

Originally, it was a full mechanical system that found its major use in navy and aviation applications, especially during WWI as a pilot system for ship steering and for self-guided missiles. The first improvement step consisted in developing several DTG versions equipped with electronics.

These kinds of systems are still used, even if their commercialization stopped some years after. Being very accurate but complex at the same time, large and expensive to manufacture, their main application consisted in replacing mechanical gyros components and systems in a wide variety of guidance, navigation and aeronautics applications, including man-portable and tripod target locator systems. In the last twenty years, a different technology, based on solid state integrated devices, appeared.

MEMS have achieved important improvements since first solutions to date. They have met the market request, in particular in consumer and industrial fields, allowing high robustness and sufficiently high performance for the corresponding grade.

In consumer market, a large number of devices are provided with an embedded MEMS gyroscope. Segway-like Human Transporter, drones, smartphones and IOT devices are examples of markets and applications. In industrial applications, the majority of systems where feedback control is needed, are equipped with a MEMS gyro, e. FOG-grade MEMS gyros are currently in an advanced stage of development, paving the way to the replacement of optical gyros in the next future.

Actually, we can classify gyro technology considering the bias stability as fundamental performance parameter as shown in Table 1. Fiber Optic Gyroscopes could be considered the low-cost version of Ring Laser Gyroscopes, being a mature technology with similar performance and sizes.

Thus, development in fiber technology can lead to the design of high-performance FOGs. At the same time, a similar process will involve FOGs and MEMS gyro technologies, because they show a few significant advantages, such as reduction of size, power and cost, and it seems to be almost mature to move on the next performance grade.

In [ 59 , 60 ], two comparison tables on commercial MEMS gyros by two different manufacturers are shown. They focus on the most important performance parameters of their available products.

The crucial point that influences the price of the product is the bias instability, which is one of the most important elements identifying the performance grade each gyro receives. All of the shown parameters especially the dynamic range are useful to choose the best gyro for the specific application. In [ 61 , 62 ], comparative tables on commercial FOGs are shown. In this section, with reference to the previous gyroscope technologies, we report in Table 2 the companies, divided for geographic area, that actually are the main players in the gyroscope market.

As discussed before, this market trend is related to the low cost of MEMS gyroscopes, allowing them to be employed for low-cost consumer electronics applications. North America is the geographic area where the gyroscope technologies are more developed and it is followed by Europe and Asia. In this review, we reported the currently more diffused gyroscope technologies. All authors have contributed in writing this review paper, discussing the main technology features and performance.

A DTG is a rotor suspended by a universal joint with flexure pivots. The flexure spring stiffness is independent of spin rate. But the dynamic inertia from the gyroscopic reaction effect from the gimbal lends a negative spring stiffness proportional to the square of the spin speed. So at a particular speed, the two moments cancel each other, freeing the rotor from torque, making it an ideal gyroscope.

A ring laser gyroscope uses the Sagnac effect to calculate rotation by measuring the shifting interference pattern of a beam split into two-halves, even as the two-halves move around the ring in opposite directions. In the Sagnac effect, a beam of light is split and the two beams are made to follow the same path but in opposite directions. On return to the point of entry the two light beams are allowed to exit the ring and undergo interference.

A fiber optic gyroscope uses the interference of light to detect mechanical rotation. How a gyroscope works in a ship. With steadicam : During the filming of the speeder bike chase scene in the movie Return of the Jedi, a steadicam - aka camera stabilizer - rig was used along with two gyroscopes for extra stabilization.

In Heading indicators : Gyroscopes are used in heading indicators, also known as directional gyros. The heading indicator has an axis of rotation that is set horizontally, pointing north. But unlike a magnetic compass, it does not seek north.

In an airliner, the heading indicator slowly drifts away from north and needs to be reoriented at regular intervals, using a magnetic compass as a reference. As gyrocompass : The directional gyro may not seek out north, but a gyrocompass does.

It does so by detecting the rotation of the earth about its axis and then seeking the true north, instead of the magnetic north. Usually, they have built-in damping to prevent overshoot when re-calibrating from sudden movement. With accelerometers : Gyroscopes are also used along with accelerometers, which are used to measure proper acceleration. While a simple accelerometer consists of a weight that can freely move horizontally, a more complicated design comprises a gyroscope with a weight on one of the axes.

For more information about accelerometers, check out our blog on accelerometers. This is this basis of inertial navigation systems INS. In an INS, sensors on the gimbals' axles detect when the platform rotates.

The INS uses those signals to understand the vehicle's rotations relative to the platform. If you add to the platform a set of three sensitive accelerometers , you can tell exactly where the vehicle is heading and how its motion is changing in all three directions.

With this information, an airplane's autopilot can keep the plane on course, and a rocket's guidance system can insert the rocket into a desired orbit!

Sign up for our Newsletter! Mobile Newsletter banner close. Mobile Newsletter chat close. Mobile Newsletter chat dots. Mobile Newsletter chat avatar. Mobile Newsletter chat subscribe. How Gyroscopes Work. Precession " ". Click here to download the second full-motion video showing precession at work. In figure 1, the gyroscope is spinning on its axis.

In figure 2, a force is applied to try to rotate the spin axis. There are various ways to make an accelerometer with most using either the piezoelectric effect or through sensing capacitance. The former tend to consist of microscopic crystal structures that become stressed by accelerative forces and generate a voltage in return.

The latter makes use of two microstructures placed next to one another. Each has a certain capacitance, and as accelerative forces move one of the structures, its capacitance will be changed.

By a dding some circuitry to convert from capacitance to voltage, and you will get a very useful little accelerometer. There are even more methods, including the use of the piezoresistive effect, hot air bubbles, and light, to name but a few. So, as you can see, accelerometers and gyroscopes are very different beasts indeed. In essence, the main difference between the two is that one can sense rotation, whereas the other cannot.

Since gyroscopes work through the principle of angular momentum, they are perfect for helping indicate an object's orientation in space. Accelerometers, on the other hand, are only able to measure linear acceleration based on vibration. However, there are some variations of accelerometer that do also incorporate a gyroscope. These devices consist of a gyroscope with a weight on one of its axes.

The device will react to a force generated by the weight when it is accelerated by integrating that force to produce velocity. Another form of the gyroscope is an optical gyroscope. This device has no moving parts and is commonly used in modern commercial jetliners, booster rockets, and orbiting satellites.

Taking advantage of something called the Sagnac effect , these devices use beams of light to provide a similar function to mechanical gyroscopes. The effect was first demonstrated in by Franz Harris, but it was French scientist Georges Sagnac who correctly identified the cause.

I f a beam of light is split and sent in two opposite directions around a closed path on a revolving platform with mirrors on its perimeter, and then the beams are recombined, they will exhibit interference effects. In , Sagnac concluded that light propagates at a speed independent of the speed of the source. He also discovered that despite the beams both being within a closed-loop, the beam traveling in the same direction of rotation arrived at its starting point slightly later than the other one.

To do this, take your right hand and make a right angle. Then you can stretch your fingers out along the radius of the wheel. If you curl the end of your fingers in the direction of the spin your thumb will be pointing in the direction of the angular momentum. Basically, the axle of the wheel will be the direction that the entire spinning wheel "wants" to move in. This video gives us a pretty simple explanation using a suspended bicycle wheel. The interesting properties of gyroscopes have provided scientists and engineers with some fascinating applications.

Their ability to maintain a particular orientation in space is fantastic for some applications. Slap on some sensors and you've got a recipe for usefulness.