How does Tactical Fiber Optic Gyroscope Work？

 

Fiber optic gyroscope industry market

With its unique advantages, fiber optic gyroscope has a broad development prospect in the field of precision physical quantity measurement. Therefore, exploring the influence of optical devices and physical environment on the performance of fiber optic gyros and suppressing the relative intensity noise have become the key technologies to realize the high precision fiber optic gyro. With the deepening of research, the integrated fiber gyroscope with high precision and miniaturization will be greatly developed and applied.

Fiber optic gyroscope is one of the mainstream devices in the field of inertia technology at present. With the improvement of technical level, the application scale of fiber optic gyro will continue to expand. As the core component of fiber optic gyros, the market demand will also grow. At present, China's high-end optical fiber ring still needs to be imported, and under the general trend of domestic substitution, the core competitiveness of China's optical fiber ring enterprises and independent research and development capabilities still need to be further enhanced.

At present, the optical fiber ring is mainly used in the military field, but with the expansion of the application of optical fiber gyroscope to the civilian field, the application proportion of optical fiber ring in the civilian field will be further improved.

According to the "2022-2027 China Fiber Optic Gyroscope industry Market Survey and Investment Advice Analysis Report" :

The fiber optic gyroscope is a sensitive element based on the optical fiber coil, and the light emitted by the laser diode propagates along the optical fiber in two directions. The difference of light propagation path determines the angular displacement of the sensitive element. Modern fiber optic gyro is an instrument that can accurately determine the orientation of moving objects. It is an inertial navigation instrument widely used in modern aviation, navigation, aerospace and national defense industries. Its development is of great strategic significance to a country's industry, national defense and other high-tech development.
Fiber optic gyro is a new all-solid-state fiber optic sensor based on Sagnac effect. Fiber optic gyro can be divided into interferometric fiber optic gyros (I-FOG), resonant fiber optic gyro (R-FOG) and stimulated Brillouin scattering fiber optic gyro (B-FOG) according to its working mode. According to its accuracy, fiber optic gyro can be divided into: low-end tactical level, high-end tactical level, navigation level and precision level. Fiber optic gyroscopes can be divided into military and civilian according to their openness. At present, most fiber optic gyros are used in military aspects: fighter and missile attitude, tank navigation, submarine heading measurement, infantry fighting vehicles and other fields. Civil use is mainly automobile and aircraft navigation, bridge surveying, oil drilling and other fields.
Depending on the accuracy of the fiber optic gyroscope, its applications range from strategic weapons and equipment to commercial grade civilian fields. Medium and high-precision fiber optic gyroscopes are mainly used in high-end weapons and equipment fields such as aerospace, while low-cost, low-precision fiber optic gyroscopes are mainly used in oil exploration, agricultural aircraft attitude control, robots and many other civilian fields with low precision requirements. With the development of advanced microelectronics and optoelectronics technologies, such as photoelectric integration and the development of special fiber optics for fiber optic gyros, the miniaturization and low-cost of fiber optic gyros have been accelerated.

Summary

Ericco's fiber optic gyro is mainly a medium precision tactical fiber optic gyro, compared with other manufacturers, low cost, long service life, the price is very dominant, and the application field is also very wide, including two very hot selling ER-FOG-851, ER-FOG-910, you can click the details page for more technical data,

Tactical Grade Fiber Optic Gyro Comparison

If you have any purchase needs, feel free to send the inquiry, or contact us directly: Phone: +86-13992884879
Email: info@ericcointernational.com.

What is a tactical grade fiber optic gyro?

 

Ericco fiber optic gyro are mainly divided into tactical and navigation levels, and the accuracy of tactical fiber optic gyroscopes is generally 0.x-xº/h. Our tactical fiber-optic gyroscope is ER-FOG-50, https://www.ericcointernational.com/.../single-axis-fog... its accuracy is 0.2~2.0º/h, its size is very small, only Φ50mm×38mm, tactical fiber-optic gyroscope is mainly used in optical pods, missile seeker, UAV, small IMU, inertial navigation system, etc., the measurement range is -500~+500º/s. Both in terms of price and longevity, it will be your choice. If you want to get more technical data, please feel free to contact us at: info@ericcointernational.com. Phone: +86-13992884879

Fiber Optic Gyroscopes for Inertial Navigation

 

1. What is inertial navigation

To understand what inertial navigation is, we first need to break the phrase into two parts, that is, navigation + inertia.
Navigation, in simple terms, solves the problem of getting from one place to another, indicating the direction, typically the compass.
Inertia, originally derived from Newtonian mechanics, refers to the property of an object that maintains its state of motion. It has the function of recording the motion state information of the object.
A simple example is used to illustrate inertial navigation. A child and a friend play a game at the entrance of a room covered with tiles, and walk on the tiles to the other side according to certain rules. One forward, three left, five front, two right... Each of his steps is the length of a floor tile, and people outside the room can get his complete motion trajectory by drawing the corresponding length and route on the paper. He doesn't need to see the room to know the child's position, speed, etc.
The basic principle of inertial navigation and some other types of navigation is pretty much like this: know your initial position, initial orientation (attitude), the direction and direction of movement at each moment, and push forward a little bit. Add these together (corresponding to the mathematical integration operation), and you can just get your orientation, position and other information.
So how to get the current orientation (attitude) and position information of the moving object? You need to use a lot of sensors, in inertial navigation is the use of inertial instruments: accelerometer + gyroscope.
Inertial navigation uses gyroscope and accelerometer to measure the angular velocity and acceleration of the carrier in the inertial reference frame, and integrates and calculates the time to obtain the velocity and relative position, and transforms it into the navigation coordinate system, so that the carrier's current position can be obtained by combining the initial position information.
Inertial navigation is an internal closed loop navigation system, and there is no external data input to correct the error during the carrier movement. Therefore, a single inertial navigation system can only be used for short periods of navigation. For the system running for a long time, it is necessary to periodically correct the internal accumulated error by means of satellite navigation.

2. Gyroscopes in inertial navigation

Inertial navigation technology is widely used in aerospace, navigation satellite, UAV and other fields because of its high concealment and complete autonomous ability to obtain motion information. Especially in the fields of micro-drones and autonomous driving, inertial navigation technology can provide accurate direction and speed information, and can play an irreplaceable role in complex conditions or when other external auxiliary navigation signals fail to play the advantages of autonomous navigation in the environment to achieve reliable attitude and position measurement. As an important component in inertial navigation system, fiber optic gyro plays a decisive role in its navigation ability. At present, there are mainly fiber optic gyroscopes and MEMS gyroscopes on the market. Although the precision of the fiber optic gyroscope is high, its entire system is composed of couplers,
Modulator, optical fiber ring and other discrete components, resulting in large volume, high cost, in the micro UAV, unmanned and other fields can not meet the requirements for its miniaturization and low cost, the application is greatly limited. Although MEMS gyro can achieve miniaturization, its accuracy is low. In addition, it has moving parts, poor resistance to shock and vibration, and is difficult to apply in harsh environments.

 

3 Summary

Ericco's fiber optic gyroscope ER-FOG-851 is specially designed according to the concept of traditional fiber optic gyroscopes, with a small size of 78.5*78.5*35mm; Light weight, less than or equal to 300g; Low power consumption, less than or equal to 4W; Start fast, start time is only 5s; This fiber optic gyroscope easy to operate and easy to use, and is widely used in INS, IMU, positioning system, north finding system, platform stability and other fields.
The accuracy of our ER-FOG-851 is between 0.05 and 0.1, and the 851 is divided into ER-FOG-851D and ER-FOG-851H. The biggest difference between these two fiber optic gyroscope is that the measurement range is different, of course, the accuracy is different, and the measurement range of ER-FOG-851D is wider. The application range is naturally wider than the ER-FOG-851H. Our fiber optic gyroscope can be used in inertial navigation, you can make a detailed choice according to the accuracy value and measurement range, you are welcome to consult us at any time and get more technical data.

 

Features of Fiber Optic Gyroscope

 

1.Characteristics of fiber optic gyro

Compared with electromechanical gyro or laser gyro, fiber optic gyro has the following characteristics:

(1) fewer parts, the instrument is firm and stable, and has a strong ability to resist impact and accelerate movement;
(2) The wound fiber is longer, so that the detection sensitivity and resolution are several orders of magnitude higher than that of the laser gyroscope;
(3) No mechanical transmission parts, no wear problems, so it has a long service life;
(4) Easy to use integrated optical path technology, signal stability, and can be directly digital output, and connected with the computer interface;
(5) By changing the length of the fiber or the number of times the light circulates in the coil, different accuracy can be achieved and a wide dynamic range can be achieved;
(6) The propagation time of the coherent beam is short, so in principle it can be started instantaneously without preheating;
(7) can be used with ring laser gyro to form sensors of various inertial navigation systems, especially sensors of strapdown inertial navigation systems;
(8) Simple structure, low price, small size, light weight.

2.Principle of fiber optic gyroscope

Fiber optic gyro is a fiber optic angular velocity sensor, which is the most promising one among all kinds of fiber optic sensors. Like ring laser gyro, fiber optic gyro has the advantages of no mechanical moving parts, no preheating time, insensitive acceleration, wide dynamic range, digital output and small size. In addition, fiber optic gyro also overcomes the fatal shortcomings of ring laser gyro such as high cost and blocking phenomenon. Therefore, fiber optic gyro has been paid attention to by many countries. Low precision civilian fiber optic gyro has been produced in small batch in Western Europe, it is estimated that in 1994, the sales of fiber optic gyro in the United States gyro market reached 49%, and the cable gyro fell to the second place (accounting for 35% of sales).

The working principle of fiber optic gyroscopes is based on the Sagnac effect. Sagnac effect is a general correlation effect of light propagated in a closed loop optical path rotating relative to inertial space, that is, two beams of light with equal characteristics emitted from the same light source in the same closed optical path propagate in opposite directions, and finally converge to the same detection point.

3.Application of fiber optic gyro

What if a car with a satellite navigation system is driving and suddenly can't receive GPS navigation signals? With the addition of a fiber optic gyroscope, it can form integrated navigation with GDS to achieve automatic driving.

Fiber optic gyro technology is based on mechanical gyro, MEMS gyro, laser gyro upgrade and development, with self-correcting, high sensitivity, long life, low temperature and high temperature resistance, no electromagnetic interference and many other advantages, is the best comprehensive performance of inertial sensors. Due to high cost, it is mainly used in military industry, aerospace and other fields.

Fiber optic gyro technology can be widely used in automotive navigation, high-speed rail track detection, Internet of Things components module, smart grid transmission, consumer electronics and many other fields, experts predict that the potential market size of domestic fiber optic gyro reached 100 billion, the next 5-10 years, most of China's traditional gyro market will be replaced by fiber optic gyro.

4.Summary

Ericco's fiber optic gyro is also a leading level in the world, ER-FOG-851 (≤0.05 ~ 0.1º/h), ER-FOG-910(0.02º/h) are a good choice, because they are medium precision, widely used, if you want to get more technical parameters, please feel free to contact us.

Application of Fiber Optic Gyroscope

 There are many ways to classify fiber optic gyroscopes. According to the working principle, it can be divided into three types: interference type, resonant type and stimulated Brillouin scattering fiber gyro. Among them, the interferometric fiber optic gyroscope is the first generation of fiber optic gyroscope, which uses multi-turn fiber coil to enhance the Sagnac effect. It is currently the most widely used; it can be divided into open-loop fiber gyroscope and closed loop according to different electric signal processing methods. Fiber optic gyroscopes, in general, closed-loop fiber optic gyroscopes have higher precision due to closed-loop control; they can be divided into single-axis fiber gyroscopes and multi-axis gyroscopes according to structure, among which three-axis fiber gyroscopes have volume Small, measurable spatial position and other advantages are an important development direction of fiber optic gyroscopes.

1.What is a fiber optic gyroscope? What are its applications in life?

A fiber optic gyroscope (FOG) is an angular velocity sensor based on the Sagnac effect, which detects angular velocity by measuring the phase difference of light traveling through an optical fiber. Compared with the traditional mechanical gyroscope, fiber optic gyroscope has the advantages of small size, light weight, high precision and good reliability, so it has been widely used in many fields.
In life, fiber optic gyro is mainly used in the field of navigation, such as car navigation, ship navigation, aircraft navigation and so on. Fiber optic gyroscopes can provide high-precision angular velocity measurements to help navigation systems more accurately determine the position and direction of a vehicle, boat or aircraft. In addition, fiber optic gyro can also be used in industrial control fields, such as robot attitude control, motion control of industrial machine tools, etc. In these applications, fiber optic gyroscopes can help achieve high-precision motion control and improve production efficiency and quality.
In addition, fiber optic gyro has also been widely used in the military field, such as missile guidance, spacecraft attitude control and so on. In these applications, the high accuracy and reliability of fiber optic gyroscopes are crucial. In general, the fiber optic gyro is a very important sensor, its application field is constantly expanding, for our life and work to bring a lot of convenience.

2.How does a fiber optic gyroscope work?

The working principle of a fiber optic gyroscope is based on the Sagnac effect. In simple terms, the Sagnac effect means that when light travels in a closed optical path, the phase of the light changes if there is an angular velocity of rotation.
In a fiber optic gyroscope, light from a light source passes through a coil of fiber and forms two beams of light in the fiber, which travel in opposite directions. When a fiber optic gyroscope spins, the phase of the two beams of light differs due to the Sagnac effect. By detecting this phase difference, the rotation angular speed of the fiber optic gyroscope can be calculated.
In order to detect phase differences, interferometers are usually used in fiber optic gyroscopes. The interferometer can convert the phase difference of two beams of light into the change of light intensity, so as to measure the rotational angular velocity. In practical applications, the fiber optic gyroscope also needs to carry out temperature compensation, polarization control and other measures to improve the measurement accuracy and stability.
The working principle of fiber optic gyroscope is relatively complicated, but its high precision and high reliability make it widely used in many fields. In the future, with the continuous development of technology, the performance of fiber optic gyro will continue to improve, bringing convenience to more fields.

3.What factors will affect the use of fiber optic gyroscopes? How to improve its measurement accuracy?

The measurement accuracy of fiber optic gyroscope will be affected by many factors during its use. Here are some common contributing factors:
Temperature: Changes in temperature can cause changes in the length and refractive index of the fiber, which affects the speed and phase of light propagation. Therefore, the fiber optic gyroscope needs temperature compensation to reduce the influence of temperature on the measurement accuracy.
Vibration: Vibration will change the optical path of the fiber optic gyroscope, which will affect the measurement of the phase difference. In order to reduce the impact of vibration, vibration reduction measures can be adopted, such as using shock absorbers, increasing the stiffness of the structure, etc.
Magnetic field: The magnetic field will change the polarization state of the light in the fiber, which will affect the output of the interferometer. In order to reduce the influence of magnetic fields, magnetic shielding technology can be used or diamagnetic fiber can be used.
Light source stability: the power fluctuation and wavelength drift of the light source will affect the measurement accuracy of the fiber optic gyroscope. Therefore, it is necessary to select a stable light source and control the temperature and power of the light source.
Fiber loss: The loss of the fiber will lead to the attenuation of the optical signal, which will affect the measurement accuracy. In order to reduce the impact of fiber loss, it is necessary to select low-loss fiber, and optimize the fiber connection and packaging.
In order to improve the measurement accuracy of the fiber optic gyroscope, the following measures can be taken:
Optimizing the design of the fiber optic gyroscope: the sensitivity and stability of the fiber optic gyroscope can be improved by reasonably designing the fiber winding structure and optical path layout.
The use of high-precision detection technology: for example, the use of high-resolution photodetectors, advanced signal processing algorithms, etc., can improve the measurement accuracy of phase difference.
Error compensation: According to the specific use of the environment and conditions, the temperature, vibration, magnetic field and other factors for error compensation to improve the measurement accuracy.
Multi-axis measurement: Using multiple fiber optic gyroscopes for multi-axis measurement can improve the measurement accuracy and reliability of the system.
Regular calibration and maintenance: Regularly calibrate and maintain the fiber optic gyro to ensure that it is in good working condition, thereby improving the measurement accuracy.
In addition, with the continuous progress of technology, new optical fiber materials, light sources and detection technologies can be used to further improve the measurement accuracy and performance of the fiber optic gyroscope. At the same time, in practical applications, it is also necessary to choose the right fiber optic gyroscope according to the specific needs and environment, and carry out reasonable installation and use to give full play to its advantages.

Ericco's fiber optic gyroscopes have long life and medium accuracy, such as ER-FOG-50, ER-FOG-60 is our very hot selling fiber optic gyroscopes, if you are interested in our products, please feel free to contact us.

Precision Analysis of Fiber Optic Gyro Engineering Structure Deformation Detection

 

1 Method of engineering structure deformation detection based on fiber optic gyroscope

The principle of the engineering structure deformation detection method based on fiber optic gyro is to fix the fiber optic gyro to the detection device, measure the angular velocity of the detection system when running on the measured surface of the engineering structure, measure the operating distance of the detection device, and calculate the operating trajectory of the detection device to realize the detection of engineering structure deformation. This method is referred to as the trajectory method in this paper. This method can be described as "two-dimensional plane navigation", that is, the position of the carrier is solved in the plumb surface of the measured structure surface, and the trajectory of the carrier along the measured structure surface is finally obtained.

According to the principle of trajectory method, its main error sources include reference error, distance measurement error and Angle measurement error. The reference error refers to the measurement error of the initial inclination Angle θ0, the distance measurement error refers to the measurement error of ΔLi, and the Angle measurement error refers to the measurement error of Δθi, which is mainly caused by the measurement error of the angular velocity of the fiber optic gyroscope. This paper does not consider the influence of reference error and distance measurement error on the deformation detection error, only the deformation detection error caused by the fiber optic gyroscope error is analyzed.

2 Analysis of deformation detection accuracy based on fiber optic gyroscope

2.1 Error modeling of fiber optic gyroscope in deformation detection applications

Fiber optic gyro is a sensor for measuring angular velocity based on Sagnac effect. After the light emitted by the light source passes through the Y-waveguide, two beams of light rotating in opposite directions in the fiber ring are formed. When the carrier rotates relative to the inertial space, there is an optical path difference between the two beams of light, and the optical interference signal related to the rotational angular speed can be detected at the detector end, so as to measure the diagonal speed.
The mathematical expression of the fiber optic gyro output signal is: F=Kw+B0+V. Where F is the gyro output, K is the scale factor, and ω is the gyro
The angular velocity input on the sensitive axis, B0 is the gyroscopic zero bias, υ is the integrated error term, including white noise and slowly varying components caused by various noises with long correlation time, υ can also be regarded as the error of zero bias.
The sources of measurement error of fiber optic gyroscope include scale factor error and zero deviation error. At present, the scale factor error of the fiber optic gyroscope applied in engineering is 10-5~10-6. In the application of deformation detection, the angular velocity input is small, and the measurement error caused by the scale factor error is much smaller than that caused by the zero deviation error, which can be ignored. The DC component of the zero-bias error is characterized by the zero-bias repeatability Br, which is the standard deviation of the zero-bias value in multiple tests. The AC component is characterized by zero bias stability Bs, which is the standard deviation of the gyroscope output value from its mean in one test, and its value is related to the sampling time of the gyroscope.

2.2 Calculation of deformation error based on fiber optic gyroscope

Taking the simple supported beam model as an example, the error of deformation detection is calculated, and the theoretical model of structural deformation is established. On this basis, the detection is set
Based on the operating speed and sampling time of the system, the theoretical angular velocity of the fiber optic gyro can be obtained. Then the angular velocity measurement error of the fiber optic gyro can be simulated according to the zero deviation error model of the fiber optic gyro established above.

2.3 Example simulation calculation

The simulation setting of running speed and sampling time adopts a range-varying mode, that is, the ΔLi passed by each sampling time is fixed, and the sampling time of the same line segment is changed by changing the running speed. For example, when the ΔLi is 1 mm, such as the running speed is 2 m/s, the sampling time is 0.5 ms. If the operating speed is 0.1 m/s, the sampling time is 10 ms.

3 Relationship between fiber optic gyroscope performance and deformation measurement error

Firstly, the effect of zero-bias repeatability error is analyzed. When there is no zero bias stability error, the angular velocity measurement error caused by zero bias error is fixed, such as the faster the motion speed, the shorter the total measurement time, the smaller the impact of zero bias error, the smaller the deformation measurement error. When the running speed is fast, the zero bias stability error is the main factor causing the system measurement error. When the running speed is low, the zero bias repeatability error becomes the main source of the system measurement error.
Using typical medium precision fiber optic gyro index, that is, zero bias stability is 0.5 °/h when sampling time is 1 s, Zero repeatability is 0.05 °/h. Compare the system measurement errors at the operating speed of 2 m/s, 1 m/s, 0.2 m/s, 0.1 m/s, 0.02 m/s, 0.01 m/s, 0.002 m/s and 0.001 m/s. When the operating speed is 2 m/s, The measurement error is 8.514μm (RMS), when the measurement speed is reduced to 0.2m /s, the measurement error is 34.089μm (RMS), when the measurement speed is reduced to 0.002m /s, the measurement error is 2246.222μm (RMS), as can be seen from the comparison results. The faster the running speed, the smaller the measuring error. Considering the convenience of engineering operation, the running speed of 2 m/s can achieve better than 10 μm measurement accuracy.

4 Summary

Based on the simulation analysis of the engineering structure deformation measurement based on fiber optic gyro, the error model of fiber optic gyro is established, and the relationship between the deformation measurement error and the performance of fiber optic gyro is obtained by using the simple supported beam model as an example. The simulation results show that the faster the system runs, that is, the shorter the sampling time of the fiber optic gyroscope, the higher the deformation measurement accuracy of the system when the sampling number is unchanged and the distance detection accuracy is guaranteed. With the typical medium precision fiber optic gyro index and the running speed of 2 m/s, the deformation measurement accuracy of better than 10 μm can be achieved.
Ericco's ER-FOG-851 has a diameter of 78.5mm and an accuracy of ≤0.05 ~ 0.1º/h. ER-FOG-910 precision 0.02º/h, belongs to the high tactical level of the fiber optic gyroscope, our company produced gyroscope with small size, light weight, low power consumption, fast start, simple operation, easy to use and other characteristics, widely used in INS, IMU, positioning system, north finding system, platform stability and other fields. If you are interested in our fiber optic gyro, please feel free to contact us.

Analysis of Main Performance Parameters of Fiber Optic Gyroscope

 

1.Fiber Optic Gyroscope

When measuring the rotation and direction of aircraft and other moving objects, the accuracy of fiber optic gyroscopes is inherently limited by using ordinary classical optical methods.
The phase difference measurement accuracy of fiber optic gyroscope determines the overall precision of rotation measurement. The accuracy of fiber optic gyro is limited by many noise sources, and the main influence factor is shot noise. The quantization of photons produces shot noise. When a single photon passes through a device, its discrete nature means that the flow is not perfectly smooth, resulting in white noise. While it is possible to reduce shot noise by increasing the power (the rate at which photons pass through), the greater the power, the greater the other noise, so there is a trade-off.
At present, due to the low power of the detectors used, the new fiber optic gyroscopes do not yet pose a threat to commercial (classical) fiber optic gyros. The researchers expect that as detector technology advances and photon source brightness increases, entangled photon fiber gyroscopes will be commercially available in the near future. Overall, physicists hope that the current results represent a first step toward pushing the ultimate limits of sensitivity in fiber-optic gyroscopes.
The realization of the fiber optic gyroscope is mainly based on the theory of Segnick: when the light beam travels in a circular channel, if the circular channel itself has a rotational speed, then the time required for the light to travel along the direction of rotation of the channel is more than the time required to travel along the opposite direction of the channel.

2. Main performance parameters of fiber optic gyroscope

Through the above introduction, we must have a preliminary understanding of the fiber optic gyro. In this part, we mainly understand some of the main performance parameters of fiber optic gyroscopes.

2.1 Zero bias and zero drift

Zero bias is the output of the gyroscope when the input angular velocity is zero (i.e. the gyroscope is at rest), expressed as the equivalent input angular velocity corresponding to the average output value measured within a specified time, ideally the component of the Earth's rotation angular velocity. Zero drift is zero bias stability, indicating the degree of dispersion of the gyroscope output around its zero bias mean when the input angular rate is zero, expressed by the equivalent input angular rate corresponding to the standard deviation of the output in a specified time. Zero drift is the most important and basic index to measure the accuracy of FOG(fiber optic gyro). The main factor of zero drift is the non-reciprocal phase shift error introduced in the fiber coil by the ambient temperature variation. In order to stabilize zero drift, temperature control or temperature compensation of IFOG is often required. In addition, polarization will also have a certain influence on zero drift. In IFOG, polarization filtering and polarization-maintaining fiber are often used to eliminate the influence of polarization on zero drift.

2.2 Scale factor

Scale factor is the ratio of the output of the gyroscope to the input angular rate, which can be expressed by a specific linear slope on the coordinate axis. It is an index reflecting the sensitivity of the gyroscope, and its stability and accuracy are an important index of the gyroscope, comprehensively reflecting the test and fitting accuracy of the fiber optic gyro. The stability of the scale factor is dimensionless and is usually expressed in parts per million (ppm). The error of the scale factor mainly comes from the temperature change and the instability of the polarization state of the fiber.

2.3 Random walk coefficient

A technical index to characterize the white noise of the angular velocity output in a fiber optic gyro, it reflects the uncertainty of the angular velocity integral of the fiber optic gyro output over time, so it can also be called an angular random walk. The random walk coefficient reflects the development level of the gyroscope, and also reflects the minimum detectable angular rate of the gyroscope. The error is mainly due to random spontaneous emission of photons, noise and mechanical jitter introduced by photodetector and digital circuit.

2.4 Threshold and resolution

The threshold indicates the minimum input rate that a fiber optic gyro can sense. Resolution represents the minimum input rate increment that a gyroscope can sense at a specified input angular rate. Both threshold and resolution characterize the sensitivity of a fiber optic gyroscope.

2.5 Maximum input angular speed

Represents the maximum input rate of the gyroscope in the positive and negative directions, and represents the dynamic range of the gyroscope, that is, the rate range of the fiber optic gyro can be induced.

3.Summary

When choosing a fiber optic gyros, we mainly look at its zero bias stability, zero bias repeatability, measurement range, etc., such as our Ericco fiber optic gyro ER-FOG-50, its measurement range is -500~500, zero bias stability is 0.2~2.0º/h, zero bias repeatability and zero bias stability are consistent. ER-FOG-60, its measuring range is -1000~+1000, zero bias stability is 0.06~0.5º/h, compared with the ER-FOG-60 measurement range is large, the accuracy is relatively high, of course, we have a variety of medium precision fiber optic gyro models, mainly according to your application scenario to decide. If you are interested in our fiber optic gyro, please feel free to contact us.

Ripple Free Minimum Beat Control of Closed-loop FOG Gyro

 The interferometric FOG gyro is a kind of angular velocity sensor based on Sagnac effect, which has the advantages of all-solid state, shock resistance, low cost, small size, etc., and has been widely used in aerospace, aviation, navigation, oil exploration well and other fields. Digital closed-loop IFOG carries out phase modulation according to the feedback signal, eliminates the phase shift caused by the speed, improves the dynamic range and scale factor linearity of IFOG, and is currently the mainstream scheme of medium-high precision IFOG. In the digital closed-loop fiber optic gyroscope, it is necessary to control according to the intrinsic frequency. The intrinsic frequency of different fiber optic gyroscopes is different, and the intrinsic frequency is usually generated by phase-locked loop technology. However, the system clock will have random fluctuations, and the frequency generated by the PLL will also fluctuate, which will lead to ripple interference in the output of the control system, and seriously affect the precision of the digital closed-loop fiber optic gyro.

In order to improve the reliability and adaptability of digital closed-loop IFOG, we established a theoretical model of digital closed-loop IFOG based on the principle of four-state square wave modulation and demodulation, analyzed the stable operating conditions and dynamic performance of digital closed-loop IFOG, and pointed out the shortcomings of the original IFOG digital closed-loop FOG gyro control system. An optimal control scheme of minimum beat without ripple is proposed. The performance of the digital closed-loop FOG gyro before and after optimization is compared by experiments. The results show that the zero bias stability and other performance indexes of the gyroscope after optimization are obviously improved.

1 Theoretical model

The digital closed-loop IFOG structure mainly includes light source, coupler, phase modulator (y-waveguide), optical fiber ring, photodetector, preamplifier, analog/digital converter (ADC), digital logic processor, digital/analog converter (DAC) and output buffer amplifier. The Sagnac interferometer consists of a light source, a coupler, a phase modulator and a fiber ring. When the fiber ring rotates, the phase difference generated by the two light waves traveling opposite each other in the loop is proportional to the rotation rate Ω.

2 Performance analysis and optimization

2.1 Control system performance analysis

The digital closed-loop IFOG frequency bandwidth increases with the increase of open-loop gain K, when the open-loop gain is greater than 0.2, in the high band, the gain is greater than 1. In order to obtain large bandwidth and stable control, 0.2 open loop gain is the best open loop gain.

2.2 Optimization of closed-loop control system

The performance analysis of the IFOG control system shows that the control system is a type I system with steady-state error under the input of angular acceleration. The sampler introduced in the design of integrator and step wave increases the overshoot and decreases the stability of the system. In order to improve the stability of the digital closed-loop FOG gyro, two samplers can be eliminated by output from the front stage of the cache during integral control and step wave generation. According to the control design method of second-order ripple free minimum beat system, the original IFOG controller is modified to eliminate the static error under the ramp input, and the optimized digital closed-loop IFOG ripple free minimum beat control system is obtained.

3. Experiment and result analysis

According to the block diagram of the digital closed-loop IFOG non-ripple minimum beat control system, the input-output relationship of the controller can be obtained as
Y (k) = y (k - 1) + [y (k - 1) - (k - 2)] y + x (k - 1) + [x (k - 1) - x (k - 2)], type: x (k) for k times the amount of error; y(k) is the output at time k. The above analysis shows that the output error and output can be delayed by two control cycles respectively through registers in FPGA, and the change of error and output can be obtained by subtracter and used for integral control, so as to realize the control of ripple free minimum beat system in FPGA.

According to the GJB2426A-2004 test method of FOG gyro, we evaluate the advantages and disadvantages of the non-ripple minimum beat control method by comparing the difference between the original control and non-ripple minimum beat control in the main indexes of FOG gyro, such as zero bias stability, Angle random walk and scale factor nonlinearity. The specific steps are as follows: the original control method and the non-ripple minimum beat control method are used to test the performance index of type 70 fiber optic gyro at room temperature respectively for 1 h. During the experiment, the length of the fiber ring in the fiber optic gyro is 800 m, the average diameter of the fiber ring is 70 mm, and the light source is the superradiation light-emitting diode. The optical wavelength is 1 310 nm, the ADC bit width is 12 bit, and the DAC bit width is 16 bit. The test results show that the output noise of the fiber optic gyro is obviously reduced under the control of the minimum beat without ripple, which indicates that the original control system results in a large output noise due to the influence of the control ripple. The analysis results show that the performance of fiber optic gyro is obviously improved under the control of non-ripple and minimum beat.

4 Summary

The theoretical model of IFOG digital closed loop under four-state square wave modulation is analyzed theoretically. It is pointed out that the original control system is a type I system, and the two-stage delay generated in the process of integral control and step wave generation reduces the reliability of the system, and the steady state error is proportional to the acceleration and inversely proportional to the open-loop control gain under the input of angular acceleration. In order to eliminate the influence of steady-state error, a digital closed-loop FOG gyro control system without ripple minimum beat is designed to eliminate the ripple error caused by the frequency of digital closed-loop IFOG in principle. The experimental results show that the ripple free minimum beat control can effectively improve the performance of digital closed-loop IFOG.

Ericco's ER-FOG-851, ER-FOG-910 stable performance, low power consumption, long life, is a very good choice, if you want to buy our fiber optic gyroscope, please feel free to contact us.

Do you Know What Digital Fiber Optic Gyro is?

 

1. What is Digital Fiber Optic Gyroscope (DFOG)?

DFOG, short for Digital FOG or Digital Fiber Optic Gyroscope, is a patent-pending technology that has been jointly developed by two research institutions for more than 25 years. DFOG was created to meet the need for a smaisller, more cost-effective FOG while improving reliability and accuracy.
This technological breakthrough opens up new opportunities for commercial and defense applications that require always-available, ultra-precision, orientation and navigation.

2. Next generation fiber optic gyroscope

Fiber optic gyroscopes set a high standard for inertial navigation. Their performance and accuracy have been recognized for decades, with each generation offering innovative improvements.
The first generation of FOG, introduced in 1976, used analog signals and analog signal processing. The second generation was developed in 1994 and is still in use today. It improves on the first generation with a hybrid approach, using analog signals in the coil and digital signal processing.
In 2021, FOG has evolved into digital FOG. The third-generation FOG stands out for its full digitalization, offering increased performance and reliability while reducing size, weight, power, and cost (SWaP-C) by 40%.

3. How does a digital fiber gyroscope work?

The innovations that make DFOG possible are three different but complementary technologies that have been developed to improve the capabilities of fiber optic gyroscopes.

3.1 Digital modulation technology

DFOG uses specially developed digital modulation technology to transmit spread spectrum signals through coils. The new digital modulation technology introduced in DFOG technology allows for variable errors in operation in the measurement coil and eliminates errors from the measurement. This makes DFOG more stable and reliable than traditional FOG. It also allows the use of smaller fiber optic gyroscopes with smaller coil lengths to achieve the accuracy of fiber optic gyroscopes with longer coils.

3.2 Revolutionary optical chip

By integrating five sensors into a single chip and removing all fiber connectors, size, weight and power consumption are greatly reduced, while reliability and performance are significantly improved.

3.3 Specially designed optical coils

DFOG uses a specially designed closed-loop optical coil designed to take full advantage of digital modulation technology. The design allows optimal sensing of variable coil errors in operation using new digital modulation techniques. It also provides a very high level of protection for optical components against shock and vibration.

4. What are the advantages of digital fiber optic gyro?

For the past two decades, fiber optic gyroscopes have been the gyroscopes of choice for high-performance inertial navigation systems (INS). But their high cost and large size make them unsuitable for many applications. DFOG alleviates these limitations while significantly improving accuracy and reliability.
DFOG makes high-precision inertial navigation affordable for a wide range of applications, including subsea, surveying, Marine, robotics, aerospace and space.

5. Summary

Ericco provides customers worldwide with high-performance, low-cost fiber optic gyroscopes (FOG) to measure angular rates. Quality and after-sales service are well guaranteed. We not only provide standard fiber optic gyroscopes, but also customize fiber optic gyroscopes according to customers' special requirements. Fiber optic gyroscopes (FOG) have many important applications in navigation and positioning systems, angular rate sensors, stabilizers, and, more recently, navigation backup systems for autonomous vehicles in areas not accessible by gps. Our FOG program has been awarded multiple patents, and fiber optic and MEMS gyroscopes set new benchmarks for accurate and economical guidance, navigation, and control in a variety of applications. ER-FOG-50, ER-FOG-60, ER-FOG-70 these are very popular models, if you have any needs, feel free to contact us.

What is an Inertial Measurement Unit?

 

An inertial Measurement Unit (IMU) is a device that typically consists of a gyroscope for measuring angular rate and an accelerometer for measuring linear speed. In this article, we'll delve into the inner workings of an inertial measurement unit to explore all the relevant specifications and information you need to choose the right IMU for your application.

1. What is IMU?

An Inertial Measurement Unit (IMU) is a device that can measure and report the specific gravity and angular rate of an object to which it is attached. Imus typically include:
Gyro: provides angular rate measurement
Accelerometer: Provides specific force/acceleration measurement
Magnetometer (optional) : Measures the magnetic field around the system
Adding magnetometers and filtering algorithms to determine directional information results in a device called the Attitude and Heading Reference System (AHRS).
Imus are available in a variety of performance levels. According to the specifications of accelerometers and gyroscopes, they are divided into one of four categories:
Consumer/Automotive grade
Industrial grade
Tactical level
Marine class
These performance categories are often defined in terms of the sensor's operational bias stability, which plays such an important role in determining inertial navigation performance. The following table summarizes the various levels of performance for these specifications.

Class	Cost	gyroscope operation bias stability	GNSS reject navigation time	applications
Consumer	< $10	--	--	Smartphone
Industrial grade	100$- 1000$	<10°/h	<1 minute	UAV
Tactical level	$5,000- $50,000	<1°/h	<10 minutes	smart ammunition
Navigation class	< $100,000	<0.1°/h	a few hours	military

Let's dive into the specific sensors used in IMUs, namely accelerometers and gyroscopes.

2. Accelerometers

Accelerometers are the primary sensors responsible for measuring changes in inertial acceleration or velocity over time, and there are many different types, including mechanical accelerometers, quartz accelerometers, and MEMS accelerometers. MEMS accelerometers are essentially mass blocks suspended by springs, as shown in Figure 2. This mass block is called the test mass, and the direction in which the mass block is allowed to move is called the sensitivity axis. When the accelerometer is subjected to linear acceleration along the sensitivity axis, the acceleration causes the mass block to move sideways, and the amount of deflection is proportional to the acceleration.

3. Gyroscope

A gyroscope is an inertial sensor that measures the angular rate of an object with respect to an inertial reference frame. There are many different types of gyroscopes on the market with varying levels of performance, including mechanical gyroscopes, fiber optic gyroscopes (FOG), ring laser gyroscopes (RLG), and quartz /MEMS gyroscopes. Quartz and MEMS gyroscopes are typically used in the consumer, industrial, and tactical markets, while fiber optic gyroscopes cover all four performance categories. Ring laser gyroscopes typically have in-operation bias stability and range from 1°/ hour to less than 0.001°/ hour, covering tactical and navigation levels. Mechanical gyroscopes are the highest performing gyroscopes on the market with bias stability of less than 0.0001°/ hour in operation.

4. Magnetometer

A magnetometer is a sensor that measures the strength and direction of a magnetic field. While there are many different types of magnetometers, most MEMS magnetometers rely on magnetoresistance to measure the surrounding magnetic field. Magnetoresistive magnetometers are composed of permalloy, and their resistance changes in response to changes in the magnetic field. Typically, MEMS magnetometers are used to measure a local magnetic field that is a combination of the Earth's magnetic field and any magnetic fields generated by nearby objects.

5. How does the Inertial Measurement Unit (IMU) work?

A single inertial sensor can only sense measurements along or around a single axis. To provide a three-dimensional solution, three separate inertial sensors must be mounted together to form an orthogonal cluster called a triplet. This set of inertial sensors installed in a triplet is often referred to as a triaxial inertial sensor because the sensor can provide a measurement along each of the three axes. Similarly, an inertial system consisting of a 3-axis accelerometer and a 3-axis gyroscope is called a 6-axis system because it provides two different measurements along each of the three axes for a total of six measurements.
The Inertial Measurement Unit (IMU) measures and reports the raw or filtered angular rate and specific force/acceleration experience of the object to which it is attached.
The data output of the IMU is typically body frame acceleration, angular rate, and (optionally) magnetic field measurements.
The user is then responsible for determining the pose by implementing an independent fusion algorithm, such as a Kalman filter.

6 Summary

Ericco's FOG Inertial Measurement Unit ER-FIMU-50, gyro bias stability is 0.5°-1°/h, ER-FIMU-60, gyro bias stability is 0.1°-0.5°/h, these two belong to the tactical class of fiber optic IMU. ER-FIMU-70 gyro bias stability is 0.05°-0.1°/h, it belongs to the navigation level of fiber optic inertial measurement unit, mainly used in the inertial navigation of surface-to-air missiles, air-to-air missiles and navigation missiles, space stability system, mapping system, attitude reference system and other fields.