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.

Why is it Called Fiber Optic Gyroscope?

 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.

Fiber optic gyro is a kind of optical fiber sensor used in inertial navigation.
Because it has no moving parts - high-speed rotor, called solid state gyroscope. This new all-solid gyroscope will become the leading product in the future and has a wide range of development prospects and application prospects.

1. Fiber optic gyro classification

According to the working principle, fiber optic gyroscope can be divided into interferometric fiber optic gyro (I-FOG), resonant fiber optic gyro (R-FOG) and stimulated Brillouin scattering fiber optic gyroscope (B-FOG). At present, the most mature fiber optic gyro is the interferometric fiber optic gyroscope (that is, the first generation of fiber optic gyroscope), which is the most widely used. It uses multi-turn optical fiber coil to enhance SAGNAC effect. A double-beam ring interferometer composed of multi-turn single-mode optical fiber coil can provide high accuracy, but also will inevitably make the overall structure more complicated.
Fiber optic gyros are divided into open ring fiber optic gyroscopes and closed loop fiber optic gyros according to the type of loop. Open-loop fiber optic gyro without feedback, directly detect the optical output, save many complex optical and circuit structure, has the advantages of simple structure, cheap price, high reliability, low power consumption, the disadvantage is the input-output linearity is poor, small dynamic range, mainly used as an Angle sensor. The basic structure of an open-loop interferometric fiber optic gyro is a ring dual-beam interferometer. It is mainly used for occasions where the accuracy is not high and the volume is small.

2. Status and future of fiber optic gyroscope

With the rapid development of fiber optic gyro, many large companies, especially military equipment companies, have invested huge financial resources to study it. The main research companies for the United States, Japan, Germany, France, Italy, Russia, low and medium precision gyroscope has completed the industrialization, and the United States has maintained a leading position in this area of research.
The development of fiber optic gyroscope is still at a relatively backward level in our country. According to the level of development, the gyro development is divided into three echelons: the first echelon is the United States, the United Kingdom, France, they have all the gyro and inertial navigation research and development capabilities; The second tier is mainly Japan, Germany, Russia; China is currently in the third tier. The research of fiber optic gyro in China started relatively late, but with the efforts of the majority of scientific researchers, it has gradually narrowed the gap between us and the developed countries.
At present, China's fiber optic gyro industry chain is complete, and manufacturers can be found upstream and downstream of the industry chain, and the development accuracy of fiber optic gyro has reached the requirements of middle and low accuracy of inertial navigation system. Although the performance is relatively poor, it will not bottleneck like the chip.
The future development of fiber optic gyro will focus on the following aspects:
(1) High precision. Higher precision is an inevitable requirement for fiber optic gyro to replace laser gyro in advanced navigation. At present, the high precision fiber optic gyro technology is not fully mature.
(2) High stability and anti-interference. Long-term high stability is also one of the development directions of fiber optic gyroscope, which can maintain navigation accuracy for a long time under harsh environment is the requirement of inertial navigation system for gyroscope. For example, in the case of high temperature, strong earthquake, strong magnetic field, etc., the fiber optic gyro must also have sufficient accuracy to meet the requirements of users.
(3) Product diversification. It is necessary to develop products with different precision and different needs. Different users have different requirements for navigation accuracy, and the structure of the fiber optic gyro is simple, and only the length and diameter of the coil need to be adjusted when changing the accuracy. In this respect, it has the advantage of surpassing mechanical gyro and laser gyro, and its different precision products are easier to achieve, which is the inevitable requirement of the practical application of fiber optic gyro.
(4) Production scale. The reduction of cost is also one of the preconditions for fiber optic gyro to be accepted by users. The production scale of various components can effectively promote the reduction of production costs, especially for middle and low precision fiber optic gyro.

3.Summary

The accuracy of the fiber optic gyroscope ER-FOG-50 is 0.2~2.0º/h, and the accuracy of the ER-FOG-60 is 0.06~0.5º/h. Their application fields are basically the same, and can be used in small IMU, INS, missile seeker servo tracking, photoelectric pod, UAV and other application fields. If you want more technical data, please feel free to contact us.

Do You Know Minimum FOG IMU?

 

ER-FIMU-50 FOG IMU is a minimum cost-effective inertial measurement device for navigation, control and dynamic measurement. The system adopts high reliability closed-loop

hashtagfiber optic gyroscope and hashtagaccelerometer, and ensures the measurement accuracy through multiple compensation techniques.

Applications

hashtagAHRS
Guidance control system
Vehicle and ship attitude measurement
Inertial/satellite hashtagintegrated hashtagnavigation hashtagsystem
Drilling system
Mobile mapping system
Satellite communication in motion

Measurement Error and Calibration of FOG IMU

 

1. What causes FOG IMU measurement errors?

Inertial measurement unit is the core component of navigation information and heading attitude reference system, which determines the accuracy and environmental adaptability of the system. Fiber optic gyro is a kind of photoelectric inertial sensor based on Sagnac effect. It has the advantages of high precision, strong resistance to vibration and shock, fast start, etc. It is an ideal angular velocity sensor for rotorcraft, high performance navigation information and heading attitude measurement system. FOG's adaptability to temperature environment is poor, and the dynamic temperature environment in the working process of rotorcraft is harsh, which leads to the measurement error of FOG inertial measurement unit. It is necessary to study the precise calibration compensation method of FOG inertial measurement unit error to improve its environmental adaptability and measurement accuracy.

2. Calibration method 

Traditional IMU calibration methods include static multi-position calibration under normal temperature environment, angular rate calibration and hybrid calibration, etc. Among them, static multi-position calibration method can calibrate the error coefficient of IMU acceleration channel with high precision, but due to the small Earth rotation rate, The precision of the small FOG used in the high performance navigation information and heading attitude measurement system of the rotorcraft is similar to the earth rotation rate, resulting in low calibration accuracy of the error coefficient of the angular velocity channel. The error coefficient of FOG IMU angular velocity channel can be accurately calibrated by the traditional simple angular velocity calibration method, but the error coefficient of acceleration channel cannot be accurately calibrated. How to further reduce the calibration workload and improve the calibration accuracy is the key technology to be solved by FOG inertial measurement unit. In addition, parameters calibrated at room temperature will reduce FOG inertial measurement unit measurement accuracy if applied at high or low temperatures. Methods such as least squares fitting are often used to compensate the zero-bias or scale-factor temperature errors of inertial devices. Among them, the high-order least squares fitting compensation method can improve the system accuracy, but significantly increase the calculation amount of real-time compensation. The one-time fitting method has a small calculation amount, but it cannot meet the actual compensation accuracy requirements. Therefore, it is another key problem for FOG inertial measurement unit, a high performance and reliable navigation information and heading attitude measurement system of rotorcraft, to study the compensation method with small amount of computation and high precision.
Based on the FOG inertial measurement unit integrated error modeling in the high performance navigation information and heading attitude measurement system of rotorcraft, we calibrate and compensate the temperature and dynamic errors of the small low-precision FOG inertial measurement unit system, and propose a FOG inertial measurement unit full temperature tripartite positive and negative rate/position calibration method and piecewise linear interpolation compensation method for temperature errors. A tripartite positive and negative speed/one position calibration scheme is designed at each constant temperature point, and piecewise linear interpolation method is used to compensate the zero deviation of angular velocity channel, zero deviation of acceleration channel and scale factor temperature errors. The vehicle-mounted experiments show that the method can improve the system's environmental adaptability and measurement precision significantly, which lays a foundation for the further development of a small and high-performance fiber optic gyro IMU aircraft navigation information and heading attitude reference system.

3.FOG IMU deterministic error modeling

3.1 Angular velocity channel error model

FOG inertial measurement unit in rotorcraft, high performance navigation information and heading attitude measurement system consists of three fiber optic gyroscopes and accelerometers, IMU structure and data acquisition and preprocessing module. Three domestic small low-precision 11-FA fiber optic gyroscope sensitive carrier external input angular velocity, three GJ-27 quartz flexible accelerometers sensitive carrier external linear acceleration. FOG is insensitive to g and g2 terms. Considering the installation error, scale factor error and zero bias error of FOG IMU, the angular velocity channel error model of FOG inertial measurement unit in northeast sky coordinate system is established as

Where, i is the output angular velocity of FOG inertial measurement unit i axial gyro, and i is the input angular velocity of i axial gyro. i is zero deviation of i axis gyroscope; Ki is the scale factor of i axial gyroscope; Eij is the installation error coefficient of the angular velocity channel, and i and j are collectively referred to as the coordinate axes X, Y and Z.

3.2 Acceleration channel error model

FOG IMU acceleration channel error model is:

Where, ai is the output of FOG inertial measurement unit i axial addition, ai is the input of i axial addition,  i is zero deviation of i axial addition, Kai is the scale factor of i axial addition, Mij is the installation error coefficient of acceleration channel.

3.3 Full temperature tripartite positive/negative speed/one position calibration

The precision of inertial devices in FOG IMU is mainly related to external environment mechanics and temperature excitation. The operating environment temperature of rotorcraft varies greatly with the different seasons and flight altitudes. Due to the large random dynamic disturbance caused by wind gust and turbulence during successive flights, the influence of different temperatures and dynamic environment on FOG inertial measurement unit accuracy is mainly studied. The calibration temperature range, temperature point distribution density and calibration dynamic range are set according to the actual working environment and accuracy requirements of the system.
According to the mathematical model of system error, a FOG inertial measurement unit tripartite positive and negative rate/one position error calibration method is designed based on a temperature-controlled single-axis speed turntable without pointing north and a high-precision hexahedron tool. As shown in Figure 1, the hexahedron tooling is turned three times at each calibrated temperature point to ensure that the X, Y, and Z axes of FOG inertial measurement unit and the ZT axis of the turntable are reconnected respectively. According to the dynamic environment of the system, set the turntable in each direction to calibrate the positive and negative speed, and ensure that the rotation is above 360° at the speed point.

4. Full temperature piecewise linear interpolation compensation

In order to solve the problem of using FOG IMU in the navigation information and heading attitude measurement system of rotorcraft with high performance and small amount of computation and high precision error compensation, we use the segmented low-order linear interpolation method, dividing the interpolation interval into several cells, and using linear interpolation polynomial on each cell. It can be seen that the FOG inertial measurement unit angular velocity channel and acceleration channel zero bias, scale factor temperature error piecework linear interpolation compensation algorithm of rotor aircraft operating environment are between -10℃ and 40℃, so the calibration temperature points are set as -10℃, 5℃, 20℃, 30℃ and 40℃ respectively. The FOG inertial measurement unit is installed in the center of the hexahedron tool, and the X, Y and Z axes of the inertial navigation system are respectively parallel to the datum normal of the hexahedron tool through the high-precision positioning table. Then the hexahedral tooling is fixed horizontally on the plane of the temperature controlled single-axis rate turntable. The three-bit positive and negative speed/one-position calibration as shown in Figure 1 was realized by flipping the hexahedron tooling. Then change the temperature setting value, according to the above method, carry out the calibration experiment at -10℃, 5℃, 20℃, 30 ℃, 40 ℃ in turn.

5. Summary

FOG IMU is the core component of the navigation information and heading attitude reference system of small rotorcraft. ericco's ER-FIMU-50 and ER-FIMU-70, we can use full-temperature three-way positive and negative rate/one position calibration and PLI compensation method. According to the error characteristics of fiber optic gyro and quartz flexible accelerometer, the FOG inertial measurement unit error model is established, and the three-bit positive and negative rate/one-position calibration scheme is designed at each constant temperature point. The PLI algorithm is used to compensate the zero bias and scale factor temperature errors of the system in real time, reducing the calibration workload and the calculation amount of the compensation algorithm, and improving the system dynamics, temperature environment adaptability and measurement accuracy.

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.

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.

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.